What is ABS in a car. How does the ABS (anti-lock braking system abs) work?

Highly efficient vehicles can in some cases lead to road accidents. This is due to the fact that when braking suddenly, the wheels are completely blocked, and traction disappears. And the inexperienced driver is not always able to cope with the car and quickly reduce the speed. It is possible to prevent a slip into a skid and blocking of the wheels by intermittently pressing the brake. There is also an ABS system, which is designed to prevent dangerous situations while driving. It improves the quality of adhesion to the road surface and maintains controllability of the car, regardless of the type of surface.

Principle of operation

The mechanism of the system can be compared to the actions of an experienced driver. This is especially noticeable on ice, when the wheels are on the verge of blocking. In addition, it is worth noting the automated distribution of braking forces and the preservation of vehicle stability.

The operation of the device is based on the influence on the wheel mechanism. This contributes to the appearance of braking force at the point of contact between the road and the wheels. An increase in this effect occurs only up to a set moment, otherwise slip increases due to a stop of rotation.

This is what becomes a frequent reason for the loss of control of the car owner. The devices receive signals from the corresponding sensors, after which the pressure in the brake system decreases, while the degree of pressing the pedal does not matter.

What you need to know

The ABS system of a car has one distinctive feature, which is to determine the braking of each wheel separately. The normalization of fluid pressure occurs immediately after the movement becomes more stable. It should be noted that driving a car without ABS and equipped with this system has some differences. In the latter case, you can safely press the brake without worrying about the likelihood of a blockage. This is especially important for drivers who have little experience and are faced with such an add-on for the first time.

with ABS

Before starting work, you should pay attention to the thread of the union. If there are traces of rust on it, it is necessary to treat the surface with a special compound, this will prevent damage to the threads.

A transparent hose is put on the cylinder fitting, the other end of which is lowered into the container. The gear lever must be in neutral. The brake pedal is applied until resistance starts. In the process of holding the pedal, the union is unscrewed, after which it should come into contact with the floor. It can only be released after tightening the union. In the process of work, it is of particular importance to regularly add brake fluid, this will prevent air from entering the circuit.

Checking the quality of work

The ABS brakes are bleed on each wheel. At the same time, there should be no even the slightest bubbles in the brake fluid. The last step is to check the pedal free play and add fluid until the required level is reached. It is also worth making sure of the tightness and tightness of fastening of each of the parts.

Performance can be checked by pressing the brake pedal for 15 seconds with the engine running. At this time, the indicator should turn on for a few seconds, informing about the self-test. If nothing happens, this indicates that there is a malfunction in the ABS system. Driving with systematic braking will additionally assess the quality of work.

Design

The system consists of several main elements:

• hydraulic block;
• electronic control unit;
• wheel speed indicators.

As a rule, the sensors work on an electromagnetic principle. They consist of a coil with a special core. The magnetic current inside the sensor changes due to the movement of the grooves and teeth of the rim during the rotation of the wheel. The electronic control unit receives the incoming signals and determines the rotation speed. Using special tables, the ECU calculates the optimal braking algorithm, the maximum brake pressure and the quality of the road surface. In the control of the block there are modulators that determine the appropriate pressure level for the wheels. When a malfunction occurs, the malfunction indicator comes on, which informs the driver that an ABS diagnosis is required.

Dignity

The ABS system gained its distribution due to the presence of many advantages, which include the following:

• there is no need to study different methods of braking;
• the gas pedal does not require intensive control, which is especially important for novice drivers;
• implementation of maneuvers with simultaneous braking;
• the possibility of braking on any part of the turn.

disadvantages

Despite the ease of use, the car's anti-lock braking system is not able to become a panacea for all the troubles on the road associated with braking.

It is not devoid of negative aspects, which include the lack of the ability to use during maneuvers in extreme conditions. It is also worth noting the following:

• there is a likelihood of a delay in turning on the system, since its full operation is possible only after determining the coefficient of adhesion of the wheels and road surface and testing the quality of the web;
• the driver does not control the braking process, which makes the ABS anti-lock system unpredictable;
• the coefficient of adhesion can be calculated incorrectly if the uneven road surface is frequently changed, which leads to a decrease in efficiency;
• the ABS system does not work at a speed of less than 10 km / h, this is especially true for heavy or armored vehicles, since in this case, the likelihood of an accident increases significantly and there is a possibility of an accident;
• the complexity of operation on loose and loose soil due to the elimination of the slightest blocking of the wheels.

When using, it is necessary to take into account all the features and disadvantages. The ABS system is designed to provide full control of the vehicle during hard braking. Thus, the driver can confidently drive the vehicle and be able to maneuver during braking. The combination of these factors makes the system an effective assistant on the road and increases the safety of the driver and passengers. A car owner with sufficient experience can cope with difficult situations without the help of the system, but it is indispensable for inexperienced drivers.

Diagnostics

In the event of a malfunction, the car's ABS system instantly stops working, due to which the restrictions in the car disappear. The driver can be alerted to a problem by a warning light on the front panel. Diagnostics can be done in several ways, depending on the type of device and the year of manufacture. The most common cause is defective fuses.

First you need to inspect the block and make sure there is no damage. It is also worth paying attention to the condition of the conductors and connectors. They must be firmly attached and have a flat surface, free of scuffs and scratches that could cause a short circuit.

Axle suspension (support and additional joints) and bearings should be checked for play and workmanship. Particular attention is paid to the high pressure pump. It is necessary to disconnect the connector and apply a voltage from the battery to the pump for a short time. To do this, you can use two conductors of any type. If it starts working, you can proceed to further inspection.

Sensors

There should be no signs of damage and stains on the sensor of revolutions and their elements. It is worth noting the increasing popularity of touch sensitive sensors. This is due to the presence of many advantages that passive counterparts cannot boast of. They are distinguished by greater signal accuracy and the ability to determine the speed in two directions with maximum accuracy. Devices with similar measurement accuracy are used in various systems, including anti-theft devices and satellite navigation. Their indisputable advantage is their compact design.

Modern cars are equipped with a significant number of active safety systems, the task of which is to prevent the driver from losing control over the car in different traffic situations. These include the anti-lock braking system (ABS).

Note that the ABS is the first among the systems related to active safety, which began to be massively used on cars. At the same time, it also acts as a base for other systems.

The first working prototypes were used on cars more than 40 years ago. As technology developed, it was improved and refined. For example, the first systems included more than a hundred composite components, and the latest versions of the ABS system consist of only 18 elements.

Features of the system

The ABS is installed on the braking system and makes its own adjustments to its operation. As the name suggests, its task is to prevent the wheels from locking up during braking.

The peculiarity of car wheels is that the force of rolling friction is higher than sliding friction. That is, a wheel that is rolling adheres better to the road surface than a wheel that is sliding along the road, which occurs if it is completely blocked. As a result, the braking distance of the car increases.

Also, the sliding of the wheel does not always occur in a straight-line direction, since lateral forces can prevail over longitudinal ones, due to which the trajectory of movement of such a wheel changes. The result is unpredictable and uncontrolled movement of the machine.

But if you create a force on the brake mechanism that will slow down the rotation speed as much as possible, but without blocking it (keeps it on the edge), then the braking distance will be shortened and the car will not lose controllability.

In cars without this system, experienced drivers use the method of repeatedly pressing the pedal (intermittent braking) to obtain maximum effect during braking. To prevent the wheels from getting blocked, the driver, when braking, presses the pedal, then releases it and so repeats it many times.

The essence of this method is very simple - to catch the moment on the brakes when they slow down the wheels as much as possible without breaking them into blocking, but this is not always possible, especially if the wheels are moving on different surfaces.

Intermittent braking (pressed and released) does not allow the wheels to be completely locked, since the driver simply periodically looses the force on the brake mechanism. The same principle is used by the ABS.

The design and purpose of the constituent parts

The anti-lock braking system device consists of three main components:

1. Wheel Speed ​​Sensors
2. Control unit (module)
3. Executive device

Vehicle ABS elements

As noted, this system is often used as a base for others. In this case, the constituent parts of a number of other systems are only an addition to the ABS.

Speed ​​sensors are very important components, as the ABS system is based on their readings. Based on the impulses they give, the control module calculates the rotation speed of each of the wheels, and based on the calculations, the actuator is controlled.

Location of the speed sensor on the wheel hub

There are two types of sensors used in the ABS design. The first are called passive sensors. These elements are of an inductive type.

Their design includes the sensor itself, consisting of a winding, a core and a magnet, as well as a ring gear used as a master element. The ring gear is mounted on the hub, so it rotates with the wheel.

Inductive type sensor

The essence of the functioning of the passive element is very simple - the winding generates a magnetic field through which the ring gear passes. The available teeth affect the field as it travels through the field, which ensures that a voltage is excited in the sensor. The alternation of teeth with cavities provides the creation of voltage pulses, which allow calculating the speed of rotation of the wheel.

The negative quality of passive sensors is the lack of measurement accuracy when driving at low speeds, which can cause incorrect operation of the ABS system.

Now, due to the existing drawback, passive sensors in the anti-lock braking system are not used and they have been replaced by so-called active elements.

As in the first version, active sensors consist of two main components - the sensor itself and the target element. But sensors in active elements are built either on the magnetoresistive effect or on the Hall effect. Both options require power supply for operation (passive elements generated it themselves).

As for the master element, here the design uses a ring with magnetized sectors (multipole).

The device and principle of operation of an active speed sensor

The essence of the work of active elements is different. In the magnetoresistive version, a constantly changing field (from the driver ring) leads to changes in the resistance readings in the sensor. In a Hall element, this field changes the voltage itself. In both cases, an impulse is generated from which the rotational speed can be calculated.

Active type elements are widely used due to their high measurement accuracy at any speed.

Control block

The ABS control module, like other ECUs used in car systems, is needed to receive and process pulses transmitted from wheel sensors. It contains tabular data, on the basis of which it controls the executive mechanism. That is, after receiving a signal from each sensor, it compares it with the information entered in the table, and based on the results obtained, it will be determined what should be done.

In a car with a number of ABS-based systems, the control unit has additional modules that are responsible for the operation of their systems.

Actuating mechanism

The actuator (also called the valve body or the ABS module) is the most complex in design and consists of a number of elements:

• solenoid valves (inlet, outlet);
• pressure accumulators;
• return pump;
• shock-absorbing chamber.

ABS block device

In the classical scheme, only one line goes to the working mechanism of the brakes, through which fluid is supplied from the master cylinder. In the ABS, a return line is cut into it, but it only passes inside the module.

The inlet valve is the only element installed on the main supply line. Its task is to shut off the fluid supply under certain conditions, by default it is open.

The return line is tapped downstream of the inlet valve. An outlet valve is installed at the entrance to it, which in the normal position is closed.

If the volume of the accumulator is not enough to take all the liquid, the pump is switched on, which pumps the excess into the main line.

But the pumping process is accompanied by pulsation, and in order to extinguish the fluctuations of the liquid, it first enters the shock-absorbing chambers and only after that - into the pipeline.

Generations and types

The modern system installed on the car is four-channel. It includes two valves for each wheel, as well as one pressure accumulator and a shock-absorbing chamber per circuit (and there are two of them).

In general, this system has already been running for 5 generations. The first of them appeared in 1978, the second replaced it in 1980 and it was installed until 1995, after which the 2nd generation supplanted the 3rd. The modern 4th generation of the system appeared in 2003, and now the 5th generation is used, which continues to be used to this day.

In terms of design features, the four-channel system is the latest and most technologically advanced. But it was preceded by:

• single-channel system (it used only two valves, which regulated the pressure in all lines at the same time. It is noteworthy that in the single-channel type, the system usually made adjustments only in the mechanisms of the driving axle, that is, the ABS worked with only two wheels);
• two-channel (in this type of ABS, the brakes were divided along the sides, each of which has its own set of valves. That is, one channel combined the mechanisms of the front and rear wheels of one side);
• Three-channel (in it, one set of valves was provided for the wheels of the rear axle, and the front ones were each equipped with its own channel).

Now these three types of ABS systems are found only perhaps on old cars.

Modes of operation

The anti-lock braking system can operate in three modes:

• Injection. In this mode, the brakes operate in the usual way. After pressing the pedal, the liquid goes to the mechanisms, the wheel slows down the rotation. In this mode, the inlet valve is open, and the outlet valve is closed, that is, the liquid moves only along the supply line;
• Hold. If the unit calculates according to the signals that one of the wheels reduces rotation faster than the others, it will close the intake valve. As a result, the force of the mechanism will stop increasing, so the deceleration of the wheel stops at a certain level. On other mechanisms, the effort will continue to grow;
• Pressure relief. If, even after switching to the holding mode, the wheel still continues to decelerate, the control unit activates the outlet valve (inlet closes) and part of the fluid goes into the pressure accumulator, thereby reducing the pressure in the mechanism (the wheel is released and begins to increase speed). As stated above, one accumulator is dedicated to two brakes (included in the circuit). There are situations when pressure is released from these two mechanisms at once, so the volume of the accumulator may simply not be enough. And then the pump turns on, pumping the excess into the main line.

ABS system diagram

During braking, the system changes the operating mode many times, which ensures effective braking. At the same time, the driver does not need to "play" with the pedal himself in order to exclude wheel blocking, the system does everything by itself.

Advantages and disadvantages

Other advantages of this system also include:

• maintaining the trajectory of movement during braking when entering a turn;
• when braking, maneuvering is allowed;
• convenience for novice drivers.

But the ABS is not perfect. Under certain conditions, this system may not function correctly and make mistakes. This affects the braking efficiency and can disorient the driver a little.

These conditions are:

• road with problematic surface;
• sand;
• pavement with bumps, "comb".

In general, the ABS works perfectly only on a flat road with good grip. Otherwise, the ABS system can make mistakes.

For example, on a problem track with a frequently alternating surface (asphalt changes with gravel or other bulk material), the system will not be able to select the optimal force on the mechanisms, which is why the braking distance increases.

When leaving the road, the ABS is also not a "helper". Here, blocking is the best way to stop the car as quickly as possible.

The features of the anti-lock braking system also include some delay in switching on when driving at high speeds (over 130 km / h). It's just that the control unit under such conditions needs some time to make calculations and activate the valve body.

At low speeds (10-15 km / h), the system is completely turned off. If this is a stop on a flat surface, then disabling the ABS has no effect, but when braking on a descent, deactivating the system can have a negative effect.

Note that disabling the ABS is a conditional concept, since the system works constantly and it is impossible to turn it off. Here, deactivation should be understood as a transition to "standby mode". That is, it will be activated again and will begin to perform its function when the brake pedal is pressed again. The only thing when it will not turn on is braking when driving at low speeds.

Improvements and improvements

Engineers have brought the design of the ABS to a high level and there is practically nothing to improve. Only some of the constituent elements are subject to modifications. So, wheel sensors now not only measure the rotational speed, they additionally integrate G-sensors and accelerometers.

Also, improvements include an increase in the functionality of the electronic unit (the very use of ABS as a basis for other systems). For example, the ABS control unit is involved in traction control and brake force distribution.

How ABS works in a car

Today's new cars are equipped with a variety of systems that even novice drivers can handle with ease. One of the very first systems is the anti-lock braking system. The ABS system is installed even in basic vehicle configurations. It is an electromechanical unit that controls the braking of the vehicle in difficult road situations such as slippery, wet or icy roads. In fact, this is the right hand of a driver, especially a beginner.

Correct braking without ABS

Every driver should be aware that it is not enough just to use the brake pedal in time. Since if you press the brake sharply at high speed, the wheels of the car are blocked, as a result of which there will be no coupling of the wheels with the road surface. The road surface can be different, therefore, the sliding speed of the wheels will be different. As a result, the vehicle is no longer steerable and can easily skid. If the owner of the car is inexperienced, then controlling the direction of the car may not be able to him.

The most important thing in such braking is to prevent the wheels from locking rigidly, causing the vehicle to skid. In order to avoid such cases, it is recommended to use the intermittent braking technique. To implement such correct braking, it is necessary to periodically press and release the brake pedal at short intervals, and in no case should the brake pedal be kept pressed until it stops completely. With such a simple braking technique, it is possible to control the vehicle regardless of the quality of the road surface.

However, it is necessary to take into account a simple human factor - the driver in an unforeseen situation is able to get confused and all the braking rules can simply fly out of his head. To control the vehicle in such emergency situations, the anti-lock braking system was developed.

What is the secret of ABS work

It is important to know on what principle the ABS works, because it has a close connection with the control system, which means that, accordingly, with the safety level of the driver and passenger. So, the main idea of ​​the system is that when the driver presses the brake pedal, instant control occurs, and braking force is redistributed to the wheels. Thereby, the vehicle is steerable in all conditions, and a speed reduction effect is achieved. However, you cannot rely only on various additional systems because the driver has to master his own car - the length of the braking distance and the behavior in emergency situations. It is recommended to test the ability of the car on specialized race tracks, in order to prevent awkward situations on the road in the future.

There are still some features of the ABS. For example, when the driver decides to stop the movement of a car equipped with the ABS system, then when the brake pedal is pressed, a slight vibration is felt on the pedals, and an accompanying sound similar to a "ratchet" can be heard. Vibration and sound are a sign that the system is working. In the meantime, the sensors read the speed values ​​and the control unit monitors the pressure inside the brake cylinders. Thus, it does not allow wheel blocking, but slows down with quick jerks. Due to this, the speed of the car drops, and at the same time does not go into a skid, which allows you to drive the vehicle until the very stop. Even on slippery roads, with ABS, the driver only needs to keep the direction of the vehicle under control. This perfect and controlled braking is only possible thanks to the ABS system.

The following steps should be emphasized:

1. Release of pressure in the brake cylinder.
2. Maintain continuous cylinder pressure.
3. Increase the pressure to an appropriate level in the brake cylinder itself.

It is important to know that the valve body in the vehicle is mounted in the brake system in a row right after the main brake cylinder. As for the solenoid valve, this is a kind of valve that admits and blocks the flow of liquid substance to the brake cylinders themselves.

Monitoring, as well as the working processes of the vehicle braking system are carried out in accordance with the information that came to the ABS control unit from the speed sensors.

During the braking process, ABS decodes information from the wheel speed sensors, due to which the vehicle's speed decreases evenly. In the event of a stop of any wheel, the signal is instantly sent from the speed sensors to the control unit. Upon receipt of such a signal, the control module releases the blockage by activating the exhaust valve, which blocks the entry of liquid into the wheel brake cylinder. At this moment, the pump returns the liquid to the accumulator. When the wheel rpm increases to the permissible speed, the control unit will give the command to close the exhaust valve and open the intake valve. After that, the pump starts, which will build up pressure into the brake cylinder, as a result of which the wheel will continue to brake. These processes are carried out instantly, and last until the final stop of the vehicle.

The discussed essence of the ABS operation represents the newest four-channel system in which all wheels of the vehicle are monitored.

Other notable types

1. The single-channel consists of a sensor located on the rear axle, the task of which is to distribute the braking force synchronously to four wheels. This kind of system has only one pair of valves, due to which, the pressure is varied simultaneously throughout the entire circuit.
2. Two-channel - it carries out paired control of the wheels, which are located on one side.
3. The three-channel consists of three speed sensors: one is mounted on the rear axle, and the rest are mounted on the front wheels separately. In the mentioned type of system, there are three pairs of valves (inlet and outlet). The action of this type of ABS is to individually control the front wheels and a pair of rear wheels.

Comparing different types of ABS, we can conclude that their difference is manifested only in a different number of valves themselves and speed control sensors. However, the essence of the system in the vehicle, as well as the order of the ongoing processes, is identical for all types of systems.

System implementation history

Engineers from leading automotive companies worked diligently to develop ABS in the first half of the 70s. Even the very first systems were quite successful, and already in that decade, similar systems began to be installed in mass-produced cars.

Initially, mechanical sensors were mounted on cars only on one axle, which sent data to the control module about the change in pressure in the brake circuits. Developers from Germany took this area one step further and began to use sensors without contacts, and this, in turn, catalyzed the transfer of information to the logic block. In addition, the number of false alarms has been reduced, and due to the fact that rubbing surfaces have been eliminated, wear has disappeared. The modern system works according to the same principle that was used in the first anti-lock braking systems.

Anti-lock braking system components

Hypothetically, the structure of the ABS is absolutely simple, and consists of the following devices:

• valve body
• speed sensors
• electronic control unit

The latter plays the role of the "intelligence" of the system (computer), so it is not difficult to imagine what role it plays. As for the speed control sensors and valve body, a deeper analysis is needed.

How the speed sensor works

The sensors that control the speed work on the principle of electromagnetic induction. A coil with a magnetic core is rigidly fixed in the drive axle gearbox. Also, a gear ring is fixed in the hub, which rotates in parallel with the wheel. Then this rotation changes the parameters of the magnetic field, which in response causes the appearance of a current. The strength of the electric current will increase in direct proportion to the speed of rotation of the wheels. Based on this force, in turn, a signal is generated and transmitted to the electronic control unit. The pulses are transmitted from four speed sensors, which are of two types: active and passive, and also differ in design.

The active type of sensor operates with a magnetic sleeve. The transmission of a binary signal is carried out by reading its label. Thanks to the rotational speed, there are no errors and, as a result, accurate pulse data.

The passive type uses a specific comb in the hub block. Thanks to such signals, the sensor is able to determine the rotational speed. It is important to take into account one drawback of this design - at low speed, inaccuracy may result.

The valve body includes:

• a reservoir for storing brake fluid - a hydraulic accumulator;
• intake and exhaust solenoid valves, which regulate the pressure supplied to the brake cylinders of the vehicle. Each type of ABS differs in the number of valve pairs;
• thanks to the universal pump, the required pressure in the system is generated, as a result of which the brake fluid is supplied from the accumulator, and, when necessary, takes it back.

Some disadvantages of ABS

One of the biggest disadvantages of anti-lock braking systems is that their effectiveness depends on the quality and condition of the road surface. If the road surface is not good enough, the braking distance is much longer. This is due to the fact that from time to time the wheel loses contact or grip on the asphalt and stops rotating. ABS detects this kind of wheel stop as a blockage, and thus stops braking. At the moment of coupling the wheels to the asphalt, the programmed command does not agree with the one necessary in this case, and the system itself needs to rebuild again, which takes time and increases the braking distance. This effect can be minimized only by reducing the vehicle speed.

In the case of an uneven road surface, for example, snow - asphalt or ice - asphalt, getting on a wet or slippery road section, ABS evaluates the surface and adjusts the braking process for this road. At the same time, when the wheels hit the asphalt, the ABS is rebuilt again, due to which the length of the braking tupi again increases.

On unpaved roads, conventional braking systems perform much better and more reliably than anti-lock braking systems. Indeed, during normal braking, the locked wheel pushes the ground, creating a small hill, which does not allow the vehicle to move further. Thanks to this, the car stops very quickly.

Another flaw in the anti-lock braking system is that at low speeds, the system is completely disabled. In the case when the road is sloping and at the same time slippery, you need to remember that a reliable hand brake may be required for braking. Therefore, it must always be in working order.

Regular deactivation of the anti-lock braking system in cars is not provided. Sometimes drivers want to disable this system. To do this, pull the plug out of the block. It is also necessary to take into account that in new cars the redistribution of inter-axle braking forces depends on ABS. Therefore, by braking, the rear wheels are completely locked.

It is important to note that the ABS system is an excellent addition to the vehicle's braking system, thanks to which it is possible to control the vehicle in the most difficult and unusual situations. Despite this, it should not be forgotten that it is impossible to rely entirely on the machine. On the driver's side, too, you need to make great efforts to keep the situation under control.

K-075 ›Blog› Anti-lock braking system ABS. Principle of operation.

Oddly enough, many accidents occur precisely because of the high efficiency of the brakes. On slippery roads - wet or ice-covered - emergency braking to quickly stop the car or drastically reduce its speed usually leads to the exact opposite result. The wheels are blocked and lose grip on the road surface, and the car does not slow down in any way and, moreover, does not obey the steering wheel at all.

An experienced driver in such cases will brake intermittently, adjusting the effort on the brake pedal in such a way as to maintain maximum grip and prevent the car from skidding. However, not all drivers have sufficient experience to accurately assess the situation, and very few have the endurance and necessary skills to react to changing traffic conditions properly. Hence the accidents and the legitimate desire of engineers to put a "shepherd" on the brakes, absolutely impartial, capable of correcting the driver's mistakes and keeping him in control of the car in any driving conditions.

History of the creation of ABS

So, anti-lock braking systems owe their appearance to the work of designers to improve the active safety of the car. The first ABS variants were introduced back in the early 70s. They coped well with the assigned duties, but they were built on analog processors, and therefore turned out to be expensive to manufacture and unreliable in operation. Further, the production of prototypes did not progress, although, in any case, it was, of course, a step forward.

The ice was broken, and the next step of the designers was to replace the analog processor with more reliable and inexpensive digital electronic blocks based on integrated circuits. In 1978, the second generation ABS was released, and the first car to receive it (though not in the basic configuration, but on order for an additional fee) was the Mercedes-Benz 450 SEL. And today it is already difficult to calculate both the number of generations of ABS and the number of cars on which the anti-lock braking system is installed as standard.

General structure and principle of operation of ABS

The anti-lock braking system (see Mercedes W123 ABS diagram) consists of three main elements: an electronic control unit (4), a hydraulic unit (3) and wheel speed sensors (1, 2). ABS is brought into working condition after turning on the ignition and reaching a certain speed of the vehicle.

The wheel sensors are based on the principle of electromagnetic induction. When the wheel rotates, the teeth and cavities of a special rotor pass by the sensor and induce an electrical signal in the sensor winding, the frequency of which is proportional to the angular speed of the wheel and the number of teeth on the rotor.

During braking, as soon as the sensor detects that the wheel is starting to block, the electronic unit, which processes signals from all sensors, sends a control impulse to the solenoid valves of the hydraulic unit (see the principle diagram of ABS operation). The hydraulic unit is installed in the brake line immediately after the brake master cylinder, and its valves control the fluid pressure in the brake circuits. If the braked wheel begins to slide, the valve body valves reduce or temporarily cut off the fluid supply to the working brake cylinder. This may not be enough to unlock the wheel, and then the solenoid valve will direct the brake fluid into the return line, thereby reducing the pressure in the working brake cylinder. When the wheel starts to rotate again, when it reaches a certain angular velocity, the ABS electronic unit removes its command, the valves open, and the hydraulic pressure is again transmitted to the brake mechanism. Braking and wheel release will occur periodically (this process is called modulation, and the valve body is sometimes called a brake pressure modulator), and the driver feels the ABS work with frequent sharp jerks on the brake pedal until the threat of blocking disappears or until the vehicle comes to a complete stop.

When ABS is working, the vehicle deceleration efficiency, besides the fact that the control does not get out of the control of the driver, remains higher than during skid braking. Tests have shown that on slippery surfaces, the braking distance of a car equipped with ABS can be 15% shorter than that of a conventional car. In addition, the mileage of the tire tread when using ABS increases by 5-7%.

And yet ABS is not a panacea

At one time, US insurance companies conducted an analysis of road accidents, and it turned out that cars with ABS are more likely to be involved in accidents than cars with a conventional braking system. So, on a dry surface, an increase in road traffic accidents was noted by 42%, and on a wet surface - even by 65%. Agree, in light of what was said in the previous chapter, these numbers are discouraging. Experts believe that the presence of ABS in a car creates an illusion of safety for the driver, as a result of which he does not take into account that ABS does not create traction - this is the prerogative of the tread and the size of the tire contact patch. Yes, ABS will prevent the brakes from locking and allow you to maintain control over directional stability and steering, but it does not guarantee a reduction in braking distance. When it comes to dry and non-slip roads, it is quite the opposite - the braking distance is longer than that of a conventional car, but, unfortunately, this understanding comes too late.

Another question is whether ABS can always reliably recognize a situation? I remember that the World Off Road journalists simulated an unsuccessful entry to the hill during the tests of SUVs: loss of traction halfway up, pressing the brake pedal hard to keep the car on the slope, engaging reverse gear - and a soft descent from the mountain using engine braking.

Everything went well until it was the turn of the Ford Explorer, and then the Mitsubishi Pajero, equipped with ABS. Jeeps stubbornly rolled down the hill, despite the fact that the testers squeezed the brake pedal all the way: the system perceived a slight slide down on a loose slope and a sharp press on the brake at that moment as a command to unlock the wheels. As a result, both Ford and Mitsubishi could not stay on the slope without the use of a “handbrake”. It is not hard to imagine what such a situation is fraught with in real life, if the slope is long enough, the collision happened closer to the top, the driver was confused (or the parking brake does not work), and some car had already joined behind. In a word, no matter how good ABS is in terms of improving the active safety of the car, the main thing is still the driver, who is obliged to critically reflect on the road situation and the real capabilities of his “iron friend”.

ABS operation problems

Note that modern ABS have a fairly high reliability and can work for a long time without failing. ABS electronic units fail extremely rarely, since they are protected by special relays and fuses, and if such a malfunction does happen, then its cause is often associated with violations of the rules and recommendations, which we will mention below. The most vulnerable in the ABS scheme are wheel sensors located near the rotating parts of the hub or axle shafts.

The location of these sensors cannot be called safe: various contaminants or even too much play in the hub bearings can cause malfunctions in the sensors, which are most often the culprits of ABS malfunctions.

In addition, the performance of the ABS is influenced by the voltage between the battery terminals. When the voltage drops to 10.5 V and below, ABS can generally turn off on its own through the safety electronic unit.

The safety relay can also trip in the event of unacceptable fluctuations and surges in the vehicle network. To prevent this from happening, here are the promised recommendations: it is impossible to disconnect the electrical connectors when the ignition is on and the engine is running, it is not advisable to start the engine by “lighting” from an external battery, or to provide your own car as a “donor” for this purpose, and, in addition, you must strictly monitor the condition of the contact connections on the generator. What else? If the car requires repair using welding, then before starting work, disconnect the wiring from the ABS electronic control unit. In addition, it is not recommended to expose this unit to over 85 degrees Celsius for more than two hours. This is if the car is supposed to be painted and then hot dried in a special chamber.

The fact that ABS is defective is indicated by the illumination of the warning lamp on the instrument panel. You should not react too nervously to this, the car will not remain without brakes, but when braking it will behave like a car in which ABS is absent.

If the ABS control lamp comes on while driving, you must stop the car, turn off the engine and check the voltage between the battery terminals. If it turns out to be below 10.5 V, then you can continue driving, and charge the battery as soon as possible. If the ABS light periodically turns on and off, then, most likely, some contact in the ABS electrical circuit is junk. The car should be driven into the inspection ditch, check all the wires and strip the electrical contacts. If the cause of the flashing of the ABS lamp is not found, then further troubleshooting should be continued in a specialized car service.

There are a number of features associated with servicing or repairing an ABS braking system. For example, before changing the brake fluid, the pressure accumulator in the ABS valve body must be discharged. To do this, with the ignition off, you must press the brake pedal twenty times. It should be remembered that, by turning on the ignition, you are simultaneously connecting the electric pump in the ABS valve body. If the system is depressurized, then the liquid will simply be expelled from it. But the same technique can be used when pumping the system - the ignition is turned on exactly as much as air bubbles will come out of the transparent hose put on the pumping fitting.

What is ABS, and why it has become mandatory for the modern car

The abbreviation ABS, or ABS in the Russian version, has become absolutely familiar to the ear of every motorist. Some novice drivers know that their car is equipped with ABS, but sometimes they do not know what it is and how it works, until one day the brake pedal, when pressed, starts to “crunch”, vibrate and “shoot” in the leg. What is ABS, and why did it become unspoken, and in many countries a legally established standard piece of equipment for a modern car?

ABS, or ABS, is an anti-lock braking system that prevents the wheels from locking when braking. If, during braking, one or more of the car's wheels are blocked and begin to slide on the surface, the ABS will release the pressure in the corresponding brake line and the wheel will start rotating again. If the brake pedal is constantly and strongly depressed, this process of locking and unlocking the wheel will continue continuously until the end of braking and can be carried out several times per second.

Even many of those who know what ABS is, sometimes mistakenly or not fully understand the main purpose of this system. The main mistake in the presentation of the ABS functionality is the belief that the anti-lock braking system is needed to reduce the braking distance of the car. However, in fact, its main purpose is to retain the ability to drive a vehicle during braking, even emergency.

On a car without ABS, during emergency braking by an inexperienced driver, the steering wheels will be locked - which means that turning the steering wheel in any direction will not have any effect on the vehicle's trajectory: it will continue to move straight until the front grip is restored. control wheels with a surface. ABS, on the other hand, solves this problem: by continuously controlling the rotation of the wheels and unlocking them if necessary, it ensures their rotation and thus maintains the necessary grip on the road surface, allowing you to brake and maneuver at the same time.

Another fundamentally important function of the ABS, directly derived from the above, is to provide safe, uniform and linear braking on surfaces with uneven traction. For example, if one side of the car hits a wet surface, slippery lane markings or ice, and the other is moving on relatively clean asphalt, emergency braking without ABS will cause one side to brake more efficiently than the other - and the car will immediately turn around and spin out of control. skidding. This is especially dangerous when driving in a corner, when lateral force is already acting on the car: the difference in wheel braking efficiency in this case easily disturbs the balance.

However, the statement about the usefulness of ABS for reducing the braking distance of a car is also true, but only partially. On surfaces with uniform and sufficient grip of the coated wheels, skid braking with locked wheels will be less effective than braking without locking the wheels, and the braking distance in the former case will usually be longer. In this case, the use of ABS really reduces the braking distance, preventing the wheels from sliding on the surface. However, on loose surfaces such as gravel, snow or sand, when braking without ABS, the locked wheels burrow inward, creating an additional barrier in front of them to shorten the braking distance. The work of the ABS in this case forces the wheels to rotate, preventing them from burying and thereby lengthening the braking distance of the car.

The anti-lock braking system and braking on clean ice on studded tires "deteriorate": a blocked studded wheel "bites" into the ice, leaving furrows behind it, and works to its limit - and if ABS comes into play, the wheel rotates with short slippage, and efficiency such inhibition will be lower. This fact is used by many "experienced" and "knowledgeable" drivers, who consider ABS to be a technological surplus that prevents them from "controlling" the car. However, despite the increase in the braking distance, the ABS retains its main advantage on ice: it makes it possible to maneuver and control the car, and not just wait for the outcome by pressing the brake pedal.

Over the years of its existence, ABS has undergone a noticeable evolution, but the basic principle and functional elements have been developed long ago. A typical ABS includes wheel speed sensors, control valves in the hydraulic brake line, and an electronic unit that receives information from the sensors and controls the valve operation.

If a sensor installed on the wheel hub signals a sudden deceleration or complete stop, the control unit gives a command to open the valve for a short time in order to reduce the pressure in the brake line and make the wheel rotate. The process of polling the wheel sensors by the control unit and unlocking the wheels can be carried out several times per second - that is why the pedal “vibrates” when the ABS is activated. In addition to the three above-mentioned components, the ABS can include a pump, which is designed to quickly restore the pressure in the brake line after it has dropped due to the opening of the valve.

The ABS can have a different number of sensors and control valves: depending on their number, the so-called “four-channel”, “three-channel”, “two-channel” and “single-channel” ABS are distinguished. The number of "channels" is determined precisely by the number of control valves that can control the pressure in the brake line: if there are four of them, one individual for each of the wheels, then the system is four-channel, if three - one for each of the front wheels and one common for the rear the axis is three-channel, if there are two valves, one per axis is two-channel, and if there is one valve, then it is single-channel. Modern ABS, of course, are four-channel - the rest of the circuits are found on old cars.

It is worth noting that wheel rotation sensors react precisely to a sharp decrease in the speed of this rotation, and can also transmit information to the control unit about a large differential difference between the wheel rotation speeds on different axles or sides of the car. However, the work of the ABS takes into account the fact that the speed of rotation of the wheels on one axle can be uneven under normal conditions: for example, when turning, the wheels on the outside of the turn will rotate faster than on the inside.

Given the above, the answer to this question is now obvious: ABS significantly improves the vehicle's active safety. The modern driver is much less specific and professional than half a century ago: if once upon a time high demands were made on the driver, forcing him to be able to do a lot, now the car has become a household item, and its control is made as accessible as possible for everyone. Accordingly, a modern car should be as comfortable and safe to drive as possible, even for a novice driver with minimal qualifications.

Well, the ABS, in particular, solves the problem of loss of control during emergency braking. The sudden appearance of an obstacle on the road makes a person instinctively hit the brakes. In case he entered a corner at too high a speed, the solution would be the same. Hooked on the side of the road - also braking ... In general, the natural reaction of a person to the occurrence of a dangerous or just an abnormal situation is a sharp pressing on the brake pedal, and only then - perhaps an attempt to correct this situation by driving. The ABS in this case significantly reduces the cost of this error. Therefore, it is not surprising that, for example, in the European Union, equipping a car with ABS became mandatory by law back in 2004.

If your car is not equipped with ABS, its work can be imitated by a simple technique, which is called quite obviously - "intermittent braking". Actually, it is precisely the possession of it that characterizes drivers with some experience: such a driver, having felt the wheels are blocked, overrides the natural instinctive desire to continue to press on the pedal harder, and reduces the effort on it and begins to brake intermittently, pressing the pedal with jerks. Such braking can be compared to the operation of a primitive single-channel ABS - only even an experienced driver is not able to provide such a frequency of "jolts" as in electronics. However, intermittent braking still provides the desired effect by keeping the wheels spinning when decelerating.

Technology ›Why brakes anti-lock braking system (ABS)

The first production car to be fitted with ABS was the Mercedes model year. The system was offered as an option for a long time and only in 1992 it entered the list of standard equipment. At the beginning, ABS was available as an option on the BMW series.

Have you ever had to go around a sudden obstacle and brake at the same time? Surely yes. It would seem that this is difficult - pressed the brake, turned the steering wheel and corrected the trajectory. However, everything is relatively simple up to a certain point. If, during emergency braking, you press the brake pedal harder than necessary, the wheels may lock and ...

Further, there are two possible scenarios for the development of events. Both are due to the presence or absence of an anti-lock brake system (ABS - Anti-lock Brake System). If the car is archaic, has its pedigree from the mid-seventies of the last century, or rolled off the assembly line of one of the domestic car factories, then, no matter how diligently you turn the steering wheel, the vehicle will not change its trajectory. The fact is that the locked wheels, sliding, deprive the driver of the opportunity to maneuver - having fallen into a skid, the car will go stupidly in a straight line, as if the steering wheel was chopped off. Only an experienced pilot will be able to coolly unlock the wheels by momentarily releasing the brake pedal. And then, using impulse braking, regain control and dampen the speed. The second option is for a car equipped with ABS. The driver is only required to press the brake pedal harder and work calmly at the steering wheel. Do you feel the difference?

For 30 years, the system has undergone dramatic changes. The performance and the number of operating cycles per unit of time have increased tenfold. For example, the first control units for light vehicles weighed over 7 kg. Modern ones are much more compact and pull a kilogram and a half.

Blocking is also dangerous because it can cause the car to skid or skid to the side. This can happen when there is a dissimilar coating under the wheels, the axle load is greatly changed during the previous maneuver, or there are different tires (the latter sounds crazy, but in Russia, alas, it is not uncommon). In addition, when the wheels are locked, the vehicle can change its trajectory under the influence of any lateral force (road slope or collision). In this case, it is almost impossible to correct the trajectory.

The ABS uses induction and Hall-effect sensors to determine the rotational speed. Each new generation of wheel speed sensors is getting smaller, more accurate and more reliable. At first, only one sensor was installed, which was mounted on the rear axle gearbox or gearbox. Later, two more were added to it - on the front wheels. And only the latest versions of the ABS provide for the installation of sensors on each wheel, respectively, with individual modulators. By the way, the most ancient and primitive single-channel ABS acted on all braking mechanisms at once.

Another negative effect of blocking is an increase in stopping distance. The point here is that the static friction force is usually greater than the sliding friction force. Therefore, to stop the car as quickly as possible, it is necessary to generate such an amount of pressure in the brake lines so that the wheels rotate on the verge of blocking during braking. There is such an important indicator as relative slippage. Depending on the degree of braking of the wheel, it can vary from zero (the wheel rolls without slipping) to 100% (the wheel is completely locked). It has been experimentally established that the maximum braking efficiency is achieved with -percentage slippage - that is, in the case when the rotation speed of the braked wheel is% lower than the speed of the free-wheeling wheel at a constant speed of the machine. Looking ahead, let's say that the electronics maintains exactly this value during braking, periodically blocking and unlocking the wheels.

Almost any modern ABS system includes: an electronic control unit (1), a modulator (2) that changes the pressure in the hydraulic lines, wheel speed sensors (3) installed on the inner part of the wheel hub.

Progressive humanity finally realized the harm of locked wheels only in the last century. The pioneer in this area was Mercedes-Benz, which, together with Bosch, developed a system that was installed on Mercedes in 1979. The basic operating principle of the ABS was formed just then, and then it was only improved.

Modern electronics (ABS, traction control, ESP) take into account more than just the wheel speed in order to keep the vehicle's lateral and longitudinal dynamics under control. Controllable are the steering angle, the degree of body roll, acceleration ... The pressure in the brake circuits is generated from the totality of the received data, plus, in some cases, the engine thrust is forcedly changed.

The task of ABS is to regulate the speed of rotation of the wheels by changing the pressure in the lines of the brake system. To control the angular velocity, you need to know its magnitude and how it changes over time. Each wheel is equipped with a sensor that emits electrical impulses with a frequency proportional to the wheel speed. This information goes to the ABS control unit.

If, during braking, the angular speed of the wheel approaches zero, the electronic brain will immediately decide to “release” it. The hydraulic modulator, with the help of an electrovalve, will release the pressure from the line and redirect the "excess" portion of the brake fluid to the accumulator. The pressure will decrease until the wheel, again "grasping" the surface, spins up to a certain speed. Further, ABS will again sharply increase the pressure in the line and slow down the wheel. The cycle will continue until the car stops or the driver releases the pedal pressure to a position where ABS is not needed.

The systems available on the market are highly tuned and provide maximum braking performance.

Many will say: "Little wisdom!" You can intermittently brake yourself. And it's true: in many cases, this method of deceleration on vehicles not equipped with ABS allows you to bypass a sudden obstacle during emergency braking. When the wheels are locked - you brake, as soon as "released" - you get the opportunity to correct the direction of travel. Naturally, in this situation, the braking distance will increase significantly, but the driver will be able to bypass the obstacle and extinguish the skid with the preemptive action of the steering wheel.

Unfortunately, no award-winning racer is capable of delivering "portion" braking at the rate that ABS does. The system (depending on the version) manages to lock and unlock the wheels about 15 times per second. In addition, the driver simultaneously acts on all braking mechanisms (this is how the first ABS systems worked), while modern anti-lock braking systems monitor the speed of rotation and regulate the braking force for each wheel separately.

Hydraulic modulator combined with control unit (black).

In most modern cars, ABS works in conjunction with EBD (Electronic Brake Distribution), a brake force distribution system that doses the intensity of the braking to each wheel. With EBD, you can safely brake in the corner and on the "mixed". The electronics, by the difference in rotational speeds, will understand that the wheels have hit areas with a dissimilar surface, and will reduce the braking forces on the wheels, which have better grip. By the way, the intensity of deceleration in this case will decrease and will be determined by the friction force of the wheel (s), which has the worst grip.

It is worth noting that for maximum deceleration efficiency, the brake pedal on cars with ABS must be pressed into the floor as much as possible. However, the latter does not have to be done by those drivers whose cars are equipped with the Brake Assist system, which itself creates excess pressure in the brake line, "braking" for a weak or indecisive person. With standard decelerations, it does not interfere. However, a sharp pressing (blow) on the Brake Assist pedal is regarded as a signal for emergency braking and takes effect.

When braking on dissimilar surfaces, the electronics will do everything to resist skidding. But sometimes a car equipped with ABS and EBD can turn quite a lot. It all depends on how the system is configured.

But not everything is so smooth. ABS, like any other system, has disadvantages. For example, a simple "antiblock" can lose the usual brakes on snow, ice or sand, negate the advantages of studded rubber. Indeed, on ice, the spikes provide the greatest deceleration only with the maximum relative slippage, when they, like claws, dig into the ice and furrow it. The trick is that ABS, trying to release the wheels, does not allow the studs to work and thereby increases the braking distance. The same happens on unpaved roads (sand, gravel, clay) and snow-covered surfaces.

The presence of ABS is not a reason for abandoning studded rubber. During blocking, the studs will still cling to the ice and provide more reliable deceleration than non-studded tires.

Cars with ABS in this case have a longer braking distance, because the permanently unlocking wheels do not create a "plow effect". But it is precisely on such surfaces that the locked wheels have the maximum braking efficiency - what "rollers" of soil or snow rake in front of them. This is why you need to remember that on an icy, snowy or unpaved surface, the braking distance of a vehicle without ABS may be shorter.

Vehicles with ABS remain steerable during emergency braking.

The ABS can put a small pig on an uneven road. If, during braking, one wheel hovers for a moment in the air and is blocked, the deceived electronics will begin to save you from skidding and immediately reduce the pressure in the remaining lines. When cornering, the car will unpleasantly wag its "tail", and the braking distance will increase. In principle, no one is insured against such accidental breaks, but it must be remembered that a good suspension is the key to adequate ABS operation.

In case of any malfunction in the system, a warning lamp on the dashboard comes on. In this case, there is only one piece of advice - run to the service.

Progress gives birth to more and more advanced systems. Operating with a large number of indications, they are able to adapt to the type of road surface and brake according to one of the previously laid down effective algorithms. Of course, electronics cannot be perceived as a panacea for all ills, but statistics are stubborn things: a competently tuned ABS with all vehicle systems in good condition on dry and wet surfaces, on average, helps to save up to 20% of the braking distance and leaves the driver a chance to maneuver. Needless to say, life and health can depend on these precious meters?

Everything about ABS: the principle of operation, what it consists of, fault diagnosis

Serial production of cars with ABS (Anti-lock Brake System) started in the late 70s. It was a revolutionary new braking system that was designed to improve the safety of motorists in critical situations associated with emergency braking.

From now on, in any driving situation in the most critical conditions (wet or slippery asphalt), the wheels of the car were not blocked even during emergency braking.

The ABS system consists of:

• Hydraulic block;
• Control unit;
• Wheel brakes;
• Sensor speed sensors.

The brain of the ABS system, as you understand, is the control unit, it receives signals that come from sensor sensors in the form of the number of wheel revolutions. After that, the received data is processed and, based on them, the block concludes whether the wheel is sliding or not, slowing down or accelerating. The decision is made with lightning speed, after which a signal is sent in the form of a command to the magnetic valves of the hydraulic unit, which actually carry out these commands.

The hydraulic block is located between the caliper brake cylinders and the brake master cylinder (GTZ). The pressure that comes from the GTZ in the brake cylinders of the calipers is converted into a pushing force, due to which the brake pads are pressed against the brake discs. Regardless of how hard the driver presses on the brake pedal and in what situation, the pressure in the brake system will always be optimal.

The beauty of the ABS system is that it is able to analyze the condition of each wheel and individually select the optimal pressure to prevent wheel blocking. Braking to a standstill is controlled by ABS using the pressure in the brake drive system, so it is directed directly to the braking effect.

The pressure is regulated according to the following principle: the speed sensor sensors count the revolutions of not only the front wheels, but also the rear axle differential (in rear- and all-wheel drive models) and the rear wheels. The data is needed by the control unit in order to calculate the peripheral speed of the wheels. After completing the counting and determining that the wheel or wheels are locked or are on the verge of locking, a command is sent to the solenoid valves and the return pump of the corresponding wheel (s). Each of the calipers is pressurized to provide the wheel with maximum braking performance and no blocking effect. Rear-wheel drive and all-wheel drive cars, equipped with only one sensor of the number of revolutions on the differential of the rear axle, the possibility of locking the wheels is determined by the one most located to this wheel, after which the braking force for the entire row is determined. As a result, the wheel with the best adhesion coefficient receives slightly less braking, which cannot but increase the braking distance, but at the same time much better vehicle handling is maintained compared to a vehicle without ABS.

The device that controls the solenoid valves is capable of operating in three different positions:

• The first is to create pressure ... The GTZ is connected to the brake cylinder, which means that the exhaust valve is closed, and the intake valve is open, therefore the pressure can easily build up.
• The second is to hold pressure ... Interruption of communication between the GTZ and the brake caliper cylinder is a condition when the pressure in the brake drive system is constant. That is, a signal is sent to the intake valve, as a result of which the valve remains closed, thereby preventing an increase in pressure.
• The third is pressure reduction ... The pressure in the brake system is reduced because the exhaust valve is signaled to release pressure and then opens. At the same time, the pressure decreases due to the activation of the return pump, as a result of which the inlet valve closes.

Thanks to three different operating positions, the ABS system is able to increase or decrease the pressure in the braking system in a “stepwise” manner by stepping action on the solenoid valves. In a working system, these positions are capable of changing from 4 to 10 times per second, this largely depends on the type of road surface.

If a malfunction is detected in the system, it is deactivated at the same minute, at the same time the brake system continues to work in normal mode, but without the participation of ABS. The braking itself is significantly different and has a significantly lower efficiency. The driver will recognize that the ABS system is out of order by the emergency indicator located on the dashboard. The method of finding and determining the malfunction may differ, here the year of manufacture and the type of ABS play a greater role.

Diagnostics of malfunctions of the ABS system

Circuit breakers

1. Visual inspection of the fuse box makes it possible to rule out the first possible cause of the malfunction. Before disassembling all other components of the ABS system.
2. Inspect all connections and connectors for scuffs or poor contact. Such seemingly insignificant malfunctions can damage the entire system or cause it to malfunction. Make sure. that there are no traces of mech on the parts (speed sensors, sensor wheels). damage and check if everything is in order with the mass.

Unfortunately, it often happens that the ABS system fails due to incorrect tire selection.

To eliminate the likelihood of "cheating" sensors, check

1. Wheel bearing play.
2. The performance of the brake system, preferably on the bench, also check its tightness.

If, after carrying out the above checks, the malfunction could not be identified, you must continue the search.

Experience shows that most of the ABS faults are associated with a broken connector connection or wire breakage, in order to confirm or deny these faults, it is enough to have a tester or an oscilloscope.

Before starting testing, make sure that the car battery is fully charged so that during measurements you can track possible voltage surges on connectors or conductors.

Failures in the operation of ABS sometimes arise due to malfunction of the speed sensor sensors, which will be discussed below.

The speed sensors are located above the impulse rotor connected to the drive shaft or hub. A winding is located around the pole core, it is connected to a permanent magnet, due to which the magnetic field easily penetrates the inductor. The change in the magnetic flux through the winding and the core occurs due to the rotation of the impulse rotor and the associated change of teeth and interdental cavities. The magnetic field is constantly changing, inducing an alternating voltage in the winding, which can be measured. The amplitude and frequency of this voltage is equal to the number of revolutions of the wheel.

To check the speed sensor you need to measure the resistance and voltage in the system. The resistance should vary from 800 Ohm to 1200 Ohm (take the nameplate values ​​into account). If the resistance is 0 Ohm, we can safely talk about a short circuit, but if the value is equal to infinity, this is an open circuit.

In the event of a sensor malfunction, it must be replaced, the main selection criteria in this regard should be quality, so take this procedure seriously so that the money is not wasted. Remember that your safety and the safety of other road users depend on the serviceability and efficiency of the ABS and the entire braking system as a whole.

The structure and principle of operation of the ABS system

Anti-lock braking system (ABS) is an electro-hydraulic active safety system that allows you to maintain control and stability of the vehicle when braking by preventing the wheels from locking. ABS is especially effective on road surfaces with a low coefficient of adhesion, as well as in bad weather (snow, ice, rain). Deciphering the abbreviation ABS - Antilock Brake System, which literally translates as "anti-lock braking system". Consider the principle of the system, its main components, generations, as well as the pros and cons of using.

Device and main components of the system

The anti-lock braking system includes:

• Wheel speed sensors. The sensors work on the basis of the Hall effect and are mounted on the hub of each wheel. They determine the wheel speed and transmit a signal to the ABS control unit.
• Control block. The main function of the electronic control unit (ECU) is to ensure the operation of the braking system in the most effective and stable range, at which the braking force will be maximum, and the wheels of the car will not be blocked. For this, the control unit continuously calculates the change in wheel speed (deceleration). Based on these indicators, control signals are generated for the actuators: the pump and the electromagnetic valves of the hydraulic unit.
• Hydraulic block. This ABS component is an actuator. The hydraulic unit includes solenoid valves (inlet and outlet), hydraulic accumulators, a cam pump with an electric motor, damping chambers.

The solenoid valves control the braking process, each in its own circuit. For each working brake cylinder, a pair of valves is assumed (one inlet and one outlet). Hydraulic accumulators are designed to accelerate the release of pressure in the brake circuit. They are filled with brake fluid when the exhaust valves are opened. Next, a cam pump is switched on, which pumps the brake fluid back into the brake master cylinder. It is for this reason that when the ABS system is operating, the driver feels jolts on the brake pedal. Damping chambers dampen fluid vibrations during system operation. Since the car has two hydraulic circuits for the brake system, two pressure accumulators and two damping chambers are usually integrated into the hydraulic unit.

How the system works

The anti-lock braking system performs its work cyclically, with each cycle consisting of three phases:

1. Increased pressure (by the driver)... Braking occurs in normal mode, the pressure in the system is increased by pressing the brake pedal by the driver. The valve body inlet valves are open, the outlet valves are closed. If the speed of rotation of the wheel slows down too much and exceeds a certain value, then the ABS control unit moves the inlet valve to the "closed" position, the outlet is also closed. The system enters the next phase.
2. Hold pressure... At this stage, the ABS system, as it were, “cuts off” the main brake cylinder from the braking process, and constant pressure is maintained in the circuit “hydraulic block - working brake cylinder of the wheel”. Even if the driver presses the brake pedal further, the pressure will not increase. In this mode, braking occurs at the maximum braking force, that is, the most effective. The control unit continues to control the speed of rotation of the wheels, and if it decreases below the permissible threshold, that is, there is a threat of wheel blocking, a command will be sent to open the exhaust valve and release the pressure.
3. Pressure relief... In this phase, the outlet valve opens and the pressure drops sharply. First, the liquid enters the accumulator, then it is pumped out by the pump back to the GTZ. The inlet valve remains closed. After the speed of deceleration of the wheels returns to the permissible values, the exhaust valve closes. The inlet valve opens and the cycle starts over.

There is a fairly common misconception that ABS independently increases the pressure in the brake system. In fact, this is not the case when it comes to the ABS system in its purest form (without ESP). The pressure in it increases solely due to the actions of the driver.

This cycle of the vehicle's anti-lock braking system is repeated until braking is complete, and can be repeated about 6 times per second. Note that ABS is triggered during emergency (sharp) braking. It is impossible to turn off the ABS system without interfering with the design of the car, since the suspension of its operation can lead to tragic consequences (therefore, it is not provided for by the automakers).

Note that ABS is integrated into the vehicle's standard braking system without structurally changing it. If the vehicle's anti-lock braking system is defective, the corresponding indicator (warning lamp) on the instrument panel will light up.

Generations of anti-lock braking systems

It took a huge number of engineers 14 years to create the ABS system. ABS has been produced since 1978 by Bosch.

The first generation of the system (1970) was named ABS-1. This electromechanical product was not reliable and durable due to the thousands of analog components that were used in the ECU. Although the main function of ABS was fulfilled, the product was not suitable for mass production.

Second generation (1978). Bosch ABS-2 was first installed as an option in Mercedes-Benz S-class cars, and after a while in BMW 7-series limousines. The number of components was reduced to 140, and the mass of the hydraulic unit was 6.3 kg.

In subsequent generations of ABS, Bosch engineers focused on improving the system and reducing its size. So, in 1980, ABS-2E came out, in which the mass of the hydraulic unit was already 4.9 kg, and the number of components decreased to 40. In 1995, ABS 5.3 appeared with a hydraulic unit weighing 2.6 kg and 25 components. In 2003, ABS 8 comes out, in which 16 components, and the mass of the hydraulic unit has decreased to 1.6 kg. Since 2010, Bosch has been producing the 9th generation of the ABS system, which is distinguished by its compact dimensions and a hydraulic unit weighing only 1.1 kg.

Advantages and disadvantages of the system

Let's consider the main advantages of the ABS system:

• maintains controllability and stability of the vehicle during emergency braking, bad weather, etc .;
• in most cases, it reduces the length of the stopping distance;
• increases the efficiency of the braking process;
• provides better vehicle maneuverability on slippery road surfaces.

The anti-lock braking system also has disadvantages: its use increases the braking distance on soft soils (sand). On such surfaces, the wheels, on the contrary, must be blocked. In the latest generations of ABS, this defect has been practically eliminated: the system "learned" to determine the type of surface, and then implement a separate algorithm for a specific coating.

The principle of operation of the ABS. Anti-lock braking system ABS. What is ABS in a car?

What is ABS (anti-lock braking system), or rather, how this abbreviation is correctly deciphered, is now known to many drivers, but what exactly it blocks, and why it is done, only very curious people know. And this despite the fact that now such a system is installed on most vehicles, both imported and domestically produced.

The ABS is directly related to the vehicle's braking system, and therefore, to the safety of the driver, passengers, and all surrounding road users. Therefore, it will be useful for every driver to know how it functions. But first, in order to understand the principle of operation of the ABS, you need to figure out what "correct braking" means.

Correct braking principle

To stop the car, it is not enough just to press the brake pedal in good time. After all, if you brake sharply during fast driving, then the wheels of the car will be blocked, and they will no longer roll, but slide along the road. It may happen that under all tires the surface is not equally uniform, so their sliding speed will be different, and this is already dangerous. The car will cease to be controllable and will go into a skid, which, in the absence of the driver's skills, will be difficult to control. An uncontrollable car is a potential source of danger.

Therefore, the main thing in braking is not to allow the wheels to lock rigidly and go to uncontrolled sliding. There is a simple technique for this - intermittent braking. To perform it, you do not need to keep the brake pedal constantly pressed, but periodically release and press it again (as if shaking). Such a seemingly simple action will not allow the driver to lose control of the car, since it will not allow the tire tread to lose traction.

But there is also the notorious human factor - a driver in an extreme situation can simply get confused and forget about all the rules. For such cases, the ABS was invented, or in another way - the anti-lock braking system.

What is ABS (ABS)

In a simple explanation, the ABS system is an electromechanical unit that controls the braking process of the vehicle in difficult road conditions (ice, wet road, etc.).

ABS is a good helper for a driver, especially a beginner, but you need to understand that it only helps in driving a car, and does not control it, so you do not need to rely on the "antiblock" completely. The driver needs to study his car, its behavior on the road, in what cases and how the ABS brake works, what is the braking distance on various surfaces. Ideally, this should be checked at a specialized circuit in order to avoid further trouble on the real road.

The first mechanisms, the action of which resembled the principle of operation of the ABS, appeared at the beginning of the last century, only they were intended for aircraft landing gear. A similar, but already automobile system, was developed by Bosch, a patent for which they received in 1936. However, this technology was introduced into a really working device only by the 60s, when the first semiconductors and computers appeared. Moreover, in addition to Bosch, General Motors, General Electric, Lincoln, Chrysler and others also sought to create a prototype of the ABS on their own.

The first automotive ABS

• In the USA, what is ABS, or rather its close analogue, was learned in 1970 by the owners of Lincoln cars. A system was installed on the car, which the engineers of the "Ford" company began to develop back in 1954, and were able to "bring to mind" only by the 70th.
• An ABS-like mechanism in Britain was developed by General Electric in conjunction with Dunlop. We tried it on a Jenssen FF sports car, it happened in 1966.
• In Europe, the concept of "anti-lock braking system" was learned from Heinz Lieber, who started developing it in 1964 while working as an engineer at Teldix GmbH, and graduated in 1970, already working for Diamler-Benz. The ABS-1 he created was tested in close collaboration with Bosch. Bosch, in turn, has already built its own full-fledged ABS-2, which was first installed on a Mercedes W116 in 1978, and a few years later on a BMW-7. However, due to the high cost of the new braking system, it was used only as an option.

Full-scale serial production of cars with "antiblock" began in 1992. Some major car manufacturers began to install it on their products. And already in 2004, all cars coming off the conveyors of European factories began to be equipped with such a system.

Anti-lock braking system elements

In theory, the ABS design looks simple and includes the following elements:

• Electronic control unit.
• Speed ​​control sensors.
• Hydroblock.

The control unit (CU), in fact, is the "brain" of the system (computer), and what functions it performs is approximately clear, but we need to talk in more detail about the speed sensor and the valve body.

The principle of operation of the speed sensor

The operation of speed control sensors is based on the effect of electromagnetic induction. The coil with a magnetic core is fixedly mounted in the wheel hub (on some models - in the drive axle gearbox).

A toothed ring is installed in the hub, rotating with the wheel. The rotation of the crown changes the parameters of the magnetic field, which leads to the emergence of an electric current. The magnitude of the current, respectively, depends on the speed of rotation of the wheel. And already, depending on its value, a signal is generated, which is transmitted to the control unit.

The valve body includes:

• Solenoid valves, divided into inlet and outlet, designed to regulate the pressure created in the brake cylinders of the vehicle. The number of valve pairs depends on the type of ABS.
• The pump (with the possibility of a return flow) - pumps the required amount of pressure in the system, supplying the brake fluid from the accumulator, and, if necessary, taking it back.
• Accumulator - storage for brake fluid.

ABS system, principle of operation

There are three main phases of the ABS operation:

1. Release of pressure in the brake cylinder.
2. Maintaining constant pressure in the cylinder.
3. Increasing the pressure in the brake cylinder to the required level.

First of all, it should be noted that the valve body in the car is built into the brake system sequentially, immediately after the main brake cylinder. And the solenoid valves are a kind of valve that opens and closes the access of fluid to the brake cylinders of the wheels.

The operation and control of the vehicle's braking system is carried out in accordance with the data received by the ABS control unit from the speed sensors.

After the start of braking, the ABS reads the readings from the wheel sensors and gradually reduces the vehicle speed. If any of the wheels stopped (began to slide), the speed sensor instantly sends a signal to the control unit. Having received it, the control unit activates the outlet valve, which blocks the access of fluid to the wheel brake cylinder, and the pump immediately begins to withdraw it, returning it to the accumulator, thereby removing the blockage. After the rotation of the wheel exceeds the preset speed limit, the "antiblock", closing the outlet and opening the inlet valve, activates the pump, which starts to work in the opposite direction, pressurizing the brake cylinder, thereby braking the wheel. All processes take place instantly (4-10 repetitions / sec.), And continue until the machine stops completely.

The principle of operation of the ABS, considered above, refers to the most advanced - 4-channel system, which carries out separate control of each wheel of the car, but there are other types of "antiblocks".

Other types of ABS

Three-channel ABS - this type of system contains three speed sensors: two are installed on the front wheels, the third on the rear axle. Accordingly, the valve body also contains three pairs of valves. The principle of operation of this type of ABS is to separately control each of the front wheels, and in a pair of rear ones.

Two-channel ABS - in such a system, the wheels located on one side are monitored in pairs.

Single-channel ABS - the sensor is installed on the rear axle and distributes the braking force to all 4 wheels simultaneously. This system contains one pair of valves (intake and exhaust). The magnitude of the pressure changes equally throughout the circuit.

Comparing the types of "antiblocks", we can conclude that the difference between them lies in the number of speed control sensors and, accordingly, valves, but, in general, the principle of operation of the ABS on a car, the order of the processes occurring in it, is the same for all types of systems.

How does ABS work or perfect braking

Having decided to stop his car equipped with the ABS system, the driver, pressing the brake pedal, feels that it begins to vibrate slightly (vibration may be accompanied by a characteristic sound resembling the sound of a "ratchet"). This is a kind of report from the system that it has started working. Sensors read speed indicators. The control unit controls the pressure in the brake cylinders, preventing the wheels from locking rigidly, while braking them with quick "jerks". As a result, the car gradually slows down and does not skid, which means it remains controllable. Even if the road is slippery, the driver with such braking can only control the direction of the car until it comes to a complete stop. Thus, thanks to the ABS, ideal, and most importantly, controlled braking is obtained.

Of course, the anti-lock system makes life much easier for the driver, making the braking process easier and more efficient. However, it has a number of disadvantages that need to be known and taken into account in practice.

Disadvantages of ABS

The main disadvantage of ABS is that its efficiency directly depends on the condition of the road.

If the road surface is uneven, bumpy, the vehicle will have a longer braking distance than usual. The reason for this is that during braking, the wheel periodically loses grip (bounces) and stops spinning. The ABS regards such a stop of the wheel as blocking, and stops braking. But when contact with the road is restored, the specified braking program no longer corresponds to the optimal one, the system has to rebuild again, and this takes time, which increases the braking distance. This effect can be reduced by reducing the vehicle speed.

If the road surface is not uniform, with alternating sections, for example: snow is replaced by ice, ice is replaced by asphalt, then ice again, etc. on the asphalt, the "antiblock" again has to readjust, since the selected braking force for a slippery surface on the asphalt becomes ineffective, this leads to an increase in the braking distance.

ABS is also not “friendly” with loose soil, in this case the conventional braking system works much better, since a locked wheel burrows into the ground during braking, forming a hill on its way that prevents further movement and accelerates the car's stop.

At low speed, the "antiblock" is turned off altogether. Therefore, when driving on a slippery road going downhill, you need to be prepared for such an unpleasant moment, and keep the "handbrake" in good condition, which you can use if necessary.

In conclusion, I would like to note that ABS is definitely a good addition to the braking system, which allows you not to lose control of the car when braking. However, you should always remember that this system is not omnipotent, and in some situations it can do a disservice.

ABS (ABS) - anti-lock braking system

The ABS system (ABS) is an anti-lock braking system. An extremely useful option that prevents the wheels of the car from locking during emergency braking. This statement is known to almost all car owners, but how this system works, how to behave when it is triggered in different situations and how to identify problems with the ABS, we will tell you in our review article.

Modern cars are equipped with a wide variety of systems and sensors. Some improve comfort, others improve environmental performance and much more. But passive and active safety systems are especially useful. The ABS system is an active safety element, that is, it functions and brings its benefits even before the accident.

For reference: passive safety systems are seat belts, airbags, safety glasses, crossbars in doors and much more. All these elements perform one or another role directly at the moment of a collision in an accident.

Anti-lock braking system is installed on most vehicles as an option. There are models with standard ABS, that is, it is available on all trim levels. One of these models is Lada Vesta, in the simplest configuration it already has ABS + BAS (Anti-lock braking system with emergency braking booster).

How ABS works

ABS prevents the wheels from locking during hard braking, and as a result, prevents the car from falling into a skid. With the correct functioning of the system, the car effectively brakes and remains fully controllable.

Why is it so important to exclude blocking of even one wheel when braking? When sliding, the coefficient of friction is significantly lower than when at rest. When a wheel is blocked, it glides over the road surface - friction is reduced and braking is ineffective.

When the surface of the tire and the road are at rest, relative to each other, the coefficient of friction is as high as possible and braking is efficient.

An experienced driver himself can feel the moment the wheels are locked and slightly loosen the pressure on the brake pedal. In this case, the wheels begin to rotate again and the grip on the road surface becomes better. But the braking system of the car does not allow you to control the braking force on each wheel.

The modern ABS system controls the rotation of each wheel and is able to increase or decrease the braking force on each wheel separately from the others. As soon as one wheel is locked, the system reduces the braking pressure on it, allows it to spin and again increases the braking force to improve braking. And this happens with each wheel - effective intermittent braking is achieved while maintaining control of the car.

ABS device

The anti-lock braking system is simple. It consists of several main elements, which are partially integrated into the vehicle's standard braking system:

Wheel speed sensors, which are mounted directly on the wheel hubs;
The system of control valves, it is with their help that the braking pressure on each individual wheel increases or decreases;
All signals from the sensors come to the electronic control unit, which analyzes them and sends the necessary signals to the valves of specific wheels.

Modern four-channel ABS systems are able to analyze the speed of rotation of the wheels 15-20 times per second and send the appropriate commands to prevent wheel locking.

ABS performance

The main role of the ABS is to maintain control over the vehicle during emergency braking. If you brake smoothly, then the system does not participate in braking in any way, although it continues to constantly analyze the speed of rotation of the wheels.

During emergency braking "to the floor", the system comes to life and takes an active part in braking, adjusts the braking force and does not allow any wheel to lock. For the driver, the most important thing is that the car, with effective braking, remains fully controllable, that is, you can go around an obstacle, avoid a collision, or simply "refuel" the car into a turn at a higher speed.

The combination of effective braking and maintaining control is a major plus in terms of active vehicle safety.

Experienced drivers are able to simulate the operation of the ABS system, but the maximum that can be achieved is to weaken and increase the total braking pressure on all wheels at the same time. The very first single-channel ABS systems worked in a similar way - when one wheel was blocked, they weakened the braking pressure on all wheels. In modern ABS, one channel is responsible for one wheel, due to which the maximum efficiency of the system is achieved.

The system is especially useful for novice drivers who feel insecure while driving even in normal situations, and, if emergency braking is necessary, can quickly lock the wheels and lose control. ABS allows you to perform intuitive actions in emergency situations - to press the brake pedal "to the floor" and maneuver.

Depending on the type of road surface, the ABS system can be both an advantage and a disadvantage.

On loose surfaces (gravel, sand, snow) ABS increases the braking distance. This is explained by the fact that locked wheels on loose surfaces are buried in the surface, which has a good effect on the braking efficiency. It is important to note that the car still loses controllability.

On slippery and hard surfaces (ice, dry and wet asphalt) ABS is much more effective.

The anti-lock braking system on some cars is turned off or with functions of adjusting to the type of road surface. In some cars, the driver himself indicates the type of coverage, in others the system determines automatically using special sensors.

The driver is informed about the activation of the ABS by a special indicator on the instrument panel, but in most cases it is not needed. And all because when the ABS is working, a quiet characteristic crackling is heard, and slight and frequent jolts are felt on the brake pedal.

Tasks performed by the ABS:

• Provides safe braking;
• Reduces the braking distance on the most dangerous surfaces: slippery or wet road surfaces;
• Maintains control under heavy braking.

ABS video

The principle of operation of the modern ABS system is clearly shown in this video:

ABS malfunctions and how to fix them

ABS does not function

• We check for errors with ABS fault codes;
• We check the power lines of the electronic control unit;
• We check the power supply lines of the sensors and the sensors themselves for correct functioning (correct installation and connection, measure the speed sensor signal with a multimeter, check that there is no short circuit between the sensor terminals);
• We check the brake system for brake fluid leaks.

All these checks can be carried out independently, it is enough to have a multimeter, a device for reading errors on-board computer (if there is no standard one), as well as a general idea of ​​electrical circuits.

ABS works but is ineffective

• We carry out all the checks, as with a completely inoperative system;
• Additionally, we check the supply voltage of the ABS electronic control unit; it must correspond to the voltage of the on-board network.

A disabled or non-functioning ABS system allows the continuation of the movement. But please note that all malfunctions in the operation of the standard ABS system must be taken into account by the driver when driving: more accurately assess the road surface, observe the speed limit, keep a large distance from the car in front, etc.

The electric valve of the hydromodulator does not work

• We use standard programs for checking the hydromodulator.

If all components are working well, then most likely it will be necessary to change the electronic-hydraulic unit.

"And all because when the ABS is working, a quiet characteristic crackling is heard, and a slight and frequent jolt is felt on the brake pedal." Faint crackling sound? Have you heard how there is a crack in Vesta when working with Abs? No? Then don't write nonsense. The crackle is such that you think something will fall off in the car.

ABS system: what is it and how it works

Modern cars are equipped with active safety systems that help to avoid loss of control of the car in various traffic situations. Some models use more than ten of these systems. The first was anti-lock braking (ABS, ABS), which is now widespread, and it is used even on budget versions. ABS is also the basis for a number of other systems.

What is ABS for a car

ABS is needed to prevent complete blocking of the wheels during braking, which eliminates the likelihood of skidding and reduces the length of the braking distance. The theory of the anti-lock braking system is as follows - when braking between a locked wheel and the road surface, sliding friction occurs, the force of which is lower than rolling friction (when the wheel rotates). In addition, when sliding, lateral forces prevail on the longitudinal ones and it is easier for the wheel to "go" to the side than to maintain a given trajectory - a hard-to-control skid occurs. But if the wheel turns during braking, then the car will not break into a skid and will maintain its trajectory, and the braking system will work with maximum efficiency.

What does the anti-lock braking system consist of?

The ABS includes two components - an electronic and an executive module. The first one controls the speed of rotation of the wheels on the machine and, on the basis of this, sends signals to the module, which prevents complete blocking of the wheels.

Electronic component

The electronic component includes a control unit and follower devices, an abs sensor installed on the wheel hubs.

Sensors are the main element of the entire system, since the operation of the ABS depends on their readings. Previously, passive sensors were used on cars. In modern models, active sensors are used. Both versions consist of two elements - a follower, installed on the stationary part, and a master - located on the rotating part of the hub.

How ABS sensors work

In passive sensors, the tracking component creates a magnetic field. The setting element, passing through this field, leads to its changes. As a result, a pulse voltage is induced in the tracking component, which acts as a signal for the electronic unit.

In active sensors, the principle of operation is different. In them, the changing magnetic field is created by driving components (multipole rings). The tracking elements are supplied with voltage from a third-party source. The acting field leads to changes in the voltage parameters (resistance changes in magnetoresistive sensors, the voltage itself changes in the Hall elements). These changes are sent to the block, which calculates the speed of rotation of the wheels.

Video: ABS - the pros and cons of an anti-lock braking system

The electronic unit is a control element. Based on the signals received from the sensors, it determines the rotation speed of each wheel on the basis of the information received and sends signals to the executive module to make adjustments to the operation of the brake system.

Executive module

It is possible to act on the braking mechanisms by means of which the wheels slow down by changing the pressure in the brake system drive. Therefore, the executive module is cut into the brake drive and the lines coming from the master brake cylinder are connected to it, and the lines leading to the brake mechanisms come out of it.

The executive module includes:

• intake and exhaust valves;
• hydroaccumulator;
• return pump with electric motor;
• damper chamber.

Each brake mechanism has one set of valves (intake and exhaust). One damper chamber and one accumulator is used per circuit. As for the pump, it is one for the executive module. The elements are interconnected by pipelines.

The module makes a ringing of the drive line, which allows, if necessary, a part of the working fluid through the formed ring to be pumped from the module outlet to the inlet.

Principle of operation

The work of the executive module is cyclical and includes three phases:

1. Pressure build-up. When braking, the brake cylinder creates fluid pressure, and it moves freely along the highway to the mechanisms. The direct movement of the fluid gives an open inlet valve, while the outlet valve is closed. As a result, the pressure on the mechanisms builds up and the wheel slows down intensively.
2. Hold. If, according to the sensor readings, the control unit has detected a faster deceleration of one of the wheels, then it sends a signal to close the inlet valve of this wheel (the outlet is also closed). As a result, the pressure build-up on the mechanism stops, the wheel stops decelerating, since the friction force on the mechanism stops at the same level.
3. Reset. In the case when the block “noticed” that the wheel, on which the holding phase was applied, still slows down faster than the others, it gives a signal to open the outlet valve (the inlet valve remains closed) and the pressure in the line is released due to the overflow of a part of the liquid into the one created by the module ring - the brake mechanism is released.

When the outlet valve is opened, the liquid enters the hydraulic accumulator first (acts as a container for collecting excess). If a lot of liquid is discharged and the volume of the accumulator is not enough, the pump is switched on, which pumps the excess into the line at the module inlet.

Since the pulsation of the liquid is created during the operation of the pump, to eliminate this negative effect, after the pump, it is first fed into the damper chamber, where the pulsation is smoothed, and only then into the line.

The ABS functioning speed is very high. When the car brakes, the system is triggered up to several hundred times, changing phases in order to achieve deceleration of the car. The ABS works on the car all the time and cannot be turned off.

Conditions under which ABS is ineffective

ABS prevents skidding and maintains controllability of the car. But under certain conditions, the efficiency of its work drops dramatically, or it even has a negative impact.

ABS does not provide effective braking if the car is driving on poorly paved roads. The fact is that when the wheel moves over pits and bumps, the wheel breaks off the surface. Due to the fact that there is no resistance, even a slight impact of the pads on the disc or drum will block the wheel. And the system “notices” this and releases the wheel, although it is only necessary to increase the pressure of the pads in order for the car to stop.

ABS has a negative effect when driving on a loose surface (snow, sand). In such conditions, a locked wheel in front of it "rakes" a boulder, which acts as a wedge, which additionally slows down the car. Due to the operation of the system, the wheel turns during braking, which is why a wedge does not appear and the braking distance is lengthened.

Video: ABS: Pros and Cons

Any modern vehicle undergoes strict checks by the controlling services before entering the territory of the dealership. The most important criterion in the framework of the inspection is the safety of the driver and passengers. Inside the cabin, they have long been installed, firing at the moment of impact. But for the driver, many additional systems have been invented, by means of which the safety of driving a car is increased. One of these is ABS. In this article we will tell you what is the ABS system, we will analyze its key features, the principle of application and touch on other important issues.

What is it?

ABS is an auxiliary system, the purpose of which is to prevent the car wheels from locking when the brake pedal is depressed. In such a situation, the use of the system helps to reduce the distance from the moment when the driver applied the brake to the time of a complete stop. As a result, the controllability of the car increases during hard braking. It should be noted that the system is designed to eliminate the likelihood of a car getting into a skid when it encounters an uncontrolled slip.

At the moment, ABS is an auxiliary element of the stopping system, controlled by the electronic unit. It is characterized by a large number of complementary technologies. Traction control, ESC (Electric Stability Control) and Emergency Stop Assist can be added here.

Due to its proven high operating efficiency, ABS is installed almost everywhere these days. At first it was invented for light transport, then it was introduced into passenger buses and minibuses. In almost an identical period, ABS began to be used in trucks and light vehicles, in trailers, and also in motorcycles. To understand how efficiently ABS functions in transport, it can be noted that now it is present even on the retractable landing gear of large passenger or cargo airliners.

The structure and principle of operation of ABS

This includes such main components:

• deceleration or speed sensors installed on the machine hub;
• a set of control valves that act as auxiliaries for the pressure modulator. They are pressed into the line hoses where the brake fluid is located. Moreover, they are integrated into all contours;
• a control unit that receives and processes signals from sensors. Based on the information received, he independently controls the operation of the valves in real time.

During the movement of the vehicle, the wheels have a fixed contact patch relative to the roadbed. In other words, the wheel collides with frictional force at rest. Since it is larger when compared to the sliding frictional force, as wheels spinning at the same speed are decelerated, the stopping becomes faster when compared to the stopping of wheels that are slipping. In parallel, it should be noted that when one or more wheels on the machine fail to slip, there is an increased chance of loss of control.

As soon as braking begins, ABS starts constantly, while quite accurately fixing the speed of rotation of each wheel. Since the speedometer usually takes into account the intensity of operation of the wheelset that is not involved in acceleration, the ABS is not connected to it. After all, if the car is front-wheel drive, it is enough to press the handbrake to confuse all the sensors. It is for this reason that sensors are integrated into each wheel hub separately. If any wheel rotates at a much slower speed in comparison with others (which indicates a state close to blocking), the internal valves of the line reduce the amount of braking force on the selected wheel. After restoring the normal speed of its rotation, the system automatically resumes the optimal level of braking force.

The above procedure can be continued more than 20 times in one second. In the vast majority of cars, this behavior of sensors leads to the fact that the brake pedal begins to pulsate. Accordingly, the driver independently understands when exactly the anti-lock braking system is automatically triggered.

It is noteworthy that the transmission of braking force can be regulated in the brake system as a whole, or on one of the circuits. In modern vehicles a separate wheel is subject to monitoring. Based on this behavior, the system is usually divided into:

• single-channel - the entire trunk is analyzed;
• two-channel - one of the boards is analyzed;
• multichannel - each wheel is limited individually.

Single channel the system is characterized by a sufficiently effective level of deceleration, but provided that the grip of each wheel is at the same level. Multichannel the design is characterized by an increased level of complexity, so its cost is much higher. At the same time, the level of efficiency increases significantly if the car is operated on non-uniform surfaces. For example, when the car is driven on ice, roadside, or wet road.

In the current design of ABS, a self-diagnostic module was added in parallel, capable of automatically checking the health and accuracy of all system components for a number of physical characteristics. Self-diagnosis is also responsible for activating the ABS lamp in the instrument panel if it detects that the system has become faulty. The received information is additionally sent to the control unit in the form of a special combination, which is stored in the internal memory. After the fault is identified, the component will not function at all, or the entire system will become inactive. But this will not affect the serviceability of the brakes themselves.

Among modern cars, mechanisms powered by electrics can boast of great popularity. Their advantage lies in the following - the brake mechanism independently serves its wheel, not being dependent on the others. In such a situation, ABS is used as one of the safety elements controlled by the ECU. It is noteworthy that the anti-lock does not affect the handle or pedal.

Why do you need ABS?

In most situations, it helps to shorten the stopping distance when compared to a car without it. Also one of the basic tasks maintaining a high level of control over the machine during the emergency stop maneuver is considered. In other words, the driver has an increased ability to make a rather sharp maneuver right when stopping. These two factors, combined with each other, make ABS a very useful auxiliary element in terms of increasing the level of safety during vehicle operation.

For drivers with extensive experience, as practice shows, there is not much difference between the absence or presence of ABS in the transport, since they are perfectly able to feel the moment when the wheels break off on their own. A similar stopping technique is also used by motorcycle owners. When the force reaches the stop of rotation of the wheels, the motorist does not "sink" on the pedal even more, keeping it in the same position. The advantage of this technique is comparable to slowing down using a single channel system. In multichannel, the advantage lies in controlling the force of the individual wheels. Consequently, a high level of efficiency is achieved and the predictability of the response of the vehicle when it travels on a road with uneven grip is improved.

If the motorist does not have the required level of experience, the presence of ABS is preferable, regardless of how long he has been driving. The point is, an emergency stop becomes intuitively simple. You just need to press hard on the brake lever or pedal, while retaining the ability to perform maneuvers. At this time, the ABS will independently determine when the force transmitted to the caliper should be limited.

Sometimes ABS does increase the braking distance. On loose surfaces such as deep snow, gravel or sand, the locked wheels begin to bury themselves, thereby enhancing stopping efficiency. But an unlocked wheel in such a situation will behave differently, slowing down the car. Then the developers allow you to disable ABS.

Do not assume that manufacturers did not provide for such a moment - in some types of ABS there is a specialized algorithm developed for loose types of surfaces. Its essence boils down to the fact that blocking occurs in large quantities with a minimum time interval between each of them. This technique promotes effective deceleration while maintaining control, as is often the case with total blocking. The driver can independently select the type of surface. But for greater convenience, the software selects it automatically, analyzing the behavior, or by using sensors that determine the road surface.

conclusions

Based on the above, we can draw the following conclusions. The ABS system is an indispensable element of the safety of any vehicle. It contributes to more efficient stopping, and also prevents the vehicle from stalling into a skid. The principle of operation is that when stopped, the wheels are not blocked, but continue to scroll on the verge of a breakdown moment. The system can drive four wheels at once, two or each separately. For winter operation, there is a choice in favor of completely disabling the ABS operation, or using several coverage modes. The last car can switch independently, or entrust the choice to the driver.

Almost any modern car is automated to a fairly large extent, if not even computerized. Various electronic systems are designed not only to increase comfort while driving, but also to help the driver, eliminate certain dangers and negative phenomena that arise in various road situations. One of the most common automatic driver assistants is the ABS system (from the English Antilock Brake System). In this article we will try to explain in an accessible way what ABS is in a car, how it works and how it is useful.

ABS, or anti-lock braking system, helps to improve the braking efficiency of the car by eliminating wheel slip when the wheel is completely blocked by the brake pads. In other words, such a system prevents the wheel from completely blocking and thus optimizes the entire braking process.

In addition to shortening the stopping distance, the ABS system has other advantages. For example, it extends the life of car tires, which wear out when the wheels are locked. Also, the ABS allows the driver to maintain control over the car and to maneuver even during emergency braking, which certainly significantly increases the chances of avoiding an accident.

In general, we can safely say that in the braking competition, between a professional in a car without ABS and an ordinary amateur in a car equipped with such a system, it is the amateur who will win.

Well, in order to understand what makes the ABS so effective, you need to understand its structure and principle of operation.

How the ABS system works on a car

Schematic representation of the ABS system: 1 - control module, 2 - wheel speed sensor, 3 - pump and valves.

And so, the following components are included in the anti-lock braking system:

• wheel speed sensors;
• valves;
• pump;
• electronic control module;

Here are all the ABS components. The sensors register the rotation of the wheels and transmit the necessary information to the electronic control module. During braking, especially hard braking, the module compares the braking speed of the vehicle and the braking speed of the wheels. If the wheels are braking too actively, the ABS valves open and the pressure in the brake lines decreases slightly. Then the pump comes into play, which, if necessary, immediately restores the required pressure in the system. Thus, no matter how hard the driver presses the brake pedal, the car with ABS will brake in the most optimal way. In some cases, up to one and a half dozen cycles of pressure relief and restoration in the brake system occur per second. This means that the blocking force of the brake pads changes the same number of times. This can be felt by a person as a pulsation of the brake pedal, which is an echo of the operation of the anti-lock braking system.

As a result, the car brakes more efficiently, quickly and safely. Although, there is nothing particularly complicated in ABS itself, as well as in the principle of its operation. Of course, it is necessary to calculate the optimal algorithms for the control unit, to create sufficiently accurate sensors, but for the modern industry that produces automotive electronics, this task is quite feasible and not even particularly difficult. Each valve of the anti-lock braking system can have two positions - open and closed, and it can also have an intermediate position in which the pressure on the pad only decreases but does not completely disappear. Such modernization allows the system to work more efficiently, as it increases its variability.

Video about ABS work on a car

Types of anti-lock braking system

There are several types of ABS. They differ in the number of channels, both for wheel control and impact on them. The most efficient and reliable is the four-channel ABS. It has a sensor on each wheel, as well as a valve in the brake line to each wheel. This system provides effective braking of all wheels, but it is also the most expensive type of ABS.

The three-channel system monitors and controls both front wheels, as well as rear ones, but already in a pair. Accordingly, the effectiveness of such an ABS will be somewhat less.

And finally, the single-channel system works only with the rear wheels and is also paired. This is the cheapest but also the least efficient ABS option. However, even in this configuration, the anti-lock braking system allows the vehicle to be braked much more efficiently than if it were not.

How to brake on a car with ABS

Today, almost all cars are equipped with anti-lock braking systems, but many drivers still remember well the time when the absence of this system in the standard equipment of a car was a common practice. It was necessary to brake on such machines by intermittently pressing the brake pedal. So it was possible to avoid blocking the wheels.

While on cars equipped with ABS, such tricks are not required. You just need to confidently press the brake pedal, and the anti-lock braking system will deal with the problem with wheel locking. Moreover, intermittent pedal presses in the presence of ABS, on the contrary, reduce the braking efficiency, and therefore are harmful.

ABS is a system that prevents the wheels from locking when the vehicle is braking. In cars without this system, when the brake is applied, the wheels lock, which causes the vehicle to slide on the surface. And the ABS system is aimed at solving this problem, it relieves the pressure, thanks to which the wheels begin to rotate. Thus, even in a situation where the brake pedal is constantly depressed, the process of locking and unlocking the wheels will be continuously carried out, and may occur several times per second.

Today, ABS systems use the same principle as in the first developments. The foremost automotive company in this area was Mercedes. Their designs with mechanical sensors were changed, after numerous experiments and tests, proximity sensors came to replace them. This development made it possible to quickly transfer information to the control unit of the car, it is its principle that modern companies use.

Even motorists with a lot of driving experience and knowledge of cars sometimes make mistakes about what this system is intended for. Usually when talking about ABS, drivers are confident that it is necessary to reduce the braking distance, although in reality this system is needed so that the driver can control the vehicle during braking and in emergency situations. The ABS system is required for:

• Ensuring the rotation of the wheels in such a way that the driver has the ability to brake and make maneuvers. After all, the necessary adhesion to the road surface is maintained. In the case of a car without this system, turning the steering wheel in any direction will not give any result, and the car will move in a straight path until the front wheels regain traction;
• Safe straight braking distance when the vehicle hits an uneven grip surface. For example, if one wheel of a car hits the wet part of the road, and the other on clean asphalt. A car without this system can turn around during emergency braking, because one part will brake more efficiently than the other. And with the ABS system, wheel braking is regulated even when turning;
• Decrease in braking distance on flat surfaces when there is sufficient traction of the wheels with the surface;
• Preventing wheels from burying on loose surfaces such as snow, mud, sand. ABS makes the wheels spin, which prevents such situations;
• Improves vehicle braking on ice on studded tires. Thanks to locking and unlocking, the car brakes with a short slip, which ensures a timely stop.

The ABS system provides reliable safety in any weather and on different surfaces. This system allows the driver to feel control during any braking, which is very important in emergency situations.

The ABS system has noticeably evolved over all its years of existence, but the basic principle of operation has remained unchanged. The most common system has sensors that monitor the speed of the wheels. An electronic unit that performs the function of controlling the operation of the valves, based on the information received from the sensors. The ABS also includes valves that are controlled in the hydraulic brake line. Thus, when braking, the following occurs:

• The sensor, which is located on the wheel hub, sends a signal to slow down or stop to the control unit;
• The control unit, in order to reduce the pressure and make the wheels rotate, provokes the opening of the valve for a short time;
• The pump, which is part of the ABS, ensures that the pressure is restored after it has dropped due to the operation of the valve.

This locking and unlocking process can be performed several times per second, and the driver can feel the vibration of the brake pedal.

It is also worth noting that this system can be single-channel, two-channel, three-channel and four-channel. It depends on the number of control valves and sensors. Now a four-channel system is installed on cars, since it is more efficient and takes into account the speed of rotation of each wheel. By comparison, a single-channel system has the same effect on all 4 wheels and does not take into account which of the wheels are locked. The principle is that each of the sensors reacts to a sharp decrease in wheel rotation. They also transmit information about the large difference between the speeds of both wheel axles. But the ABS system also takes this fact into account, therefore, when the car is turning, if there is a difference in speed, the system does not block the wheels.

On average, this system can be activated about 20 times within one second. And this is a good result, given that a person cannot press the brake pedal so many times.

Despite the fact that now this system is used in cars of all classes, it has its advantages and disadvantages. The following advantages of ABS are distinguished:

• Improving the safety of the driver and his passengers;
• Affects the life of tires, increasing it due to the fact that with such braking, the wheels turn, reducing the pressure on the tires;
• reduction of braking distance on a flat surface;
• enables the driver to perform braking maneuvers.

Like any other system, ABS has its drawbacks:

• Cracking sound that is heard when the system is triggered;
• Ineffectiveness of system response on uneven surfaces
• The inability to brake on an icy road.

If you need to brake on ice, when the system does not work, you must use the hand brake. Thus, the rear wheels will be locked and the system will automatically shut down for a while.

Despite the presence of disadvantages, this system has long been used for production vehicles. It provides safety, which is very important at the present time, because now the drivers are not as experienced as they used to be. Investing a car has become a common thing for everyone, while few people know how to act in emergency situations, and thanks to the ABS, such situations have become much less.

What problems can there be with the ABS?

Usually, there are no problems with the ABS device, in the absence of mechanical influences, because the system is very simple and reliable in operation. However, even the fact that the electronic components are protected by a fuse does not save the device from damage. The reasons for the non-colorful operation of the device can be:

• Constant exposure to difficult environmental conditions;
• Vehicle battery charge status;
• Car wiring problems.

When the voltage drops to 10.5 V, the device switches itself off and remains inactive.

In order to prevent a spontaneous shutdown, the following recommendations must be followed:

• You should not light the battery from another car, and also use your own for the same purposes;
• When the ignition is running, do not disconnect the electrical connectors.

Proceeding from this, in order to save the operation of the device, you should monitor the condition of the car. And if you suspect that the ABS is distracting, you should contact a specialist who will help identify the cause

In the structure of the ABS, there are speed sensors, they work on the basis of the principle of electromagnetic induction. The coil with a special magnetic core is fixed in the gearbox located in the drive axle. The ring gear attached to the hub has the property of rotating parallel to the wheel. This rotation leads to a change in the parameters of the magnetic field, the response of which is the appearance of a current. The strength of this current increases in relation to the speed of rotation of the wheels. Thus, a signal is generated that is transmitted to the control system. One of the reasons for the malfunction may be a wire break. This can be checked using a special tester, pins and a soldering iron:

• Pins that are used for repairs must be connected to connectors;
• Then use a tester to measure the resistance of the speed sensor. The limit of the norm values ​​are indicated in the manual, their tendency to resistance to zero or infinity indicates the presence of a short circuit or an open circuit;
• After that, the wheel and resistance should be checked; in a working sensor, these indicators change.

If the sensor breaks down, you should find out how to remove it, and then take it to a specialist for diagnostics, after which it will be clear whether it can be repaired or whether you need to purchase a new one.

Not a single modern vehicle can do without the ABS system today. A feature of this device is its simple principle of operation and efficiency. Thanks to this, many drivers can control the braking of the car in the event of an emergency. Therefore, it is so important to monitor the state of the system and periodically check it with specialists.