Rack and pinion steering. Purpose and steering device

Steering is one of the main systems of a car, which is a set of units and mechanisms designed to synchronize the position of the steering wheel (steering wheel) and the angle of rotation of the steered wheels (in most car models, these are the front wheels). The main purpose of steering for any vehicle is to provide a turn and maintain the direction of travel set by the driver.

Steering system design

Steering diagram

Structurally, the steering system consists of the following elements:

• Steering wheel (steering wheel) - designed to control the driver to indicate the direction of the vehicle. IN modern models it is additionally equipped with control buttons multimedia system... also in wheel the driver's front airbag is integrated.
• - performs the transfer of power from the steering wheel to the steering mechanism. It is a shaft with articulated joints. For security and protection against theft, the column can be equipped with electric or mechanical systems folding and locking. Additionally, an ignition lock, lighting controls and a wiper are installed on the steering column windscreen car.
• - performs the transformation of the effort created by the driver through the turn of the steering wheel and transfers it to the wheel drive. Structurally, it is a gearbox with a certain gear ratio. The mechanism itself connects to the steering column cardan shaft steering control.
• - consists of steering rods, tips and levers that transfer power from the steering mechanism to steering knuckles driving wheels.
• Power Steering - Increases the effort that is transferred from the steering wheel to the drive.
• Additional elements (steering damper or "damper", electronic systems).

It is also worth noting that the vehicle's suspension and steering are closely related. The stiffness and height of the former determine the degree of response of the car to the rotation of the steering wheel.

Steering types

Depending on the type of gearbox of the system, the steering mechanism (steering system) can be of the following types:

• Rack is the most common type used in passenger cars... This type of steering gear has simple design and has a high efficiency. The disadvantages are that this type of mechanism is sensitive to the arising shock loads during operation in difficult road conditions.
• Worm gear - provides good maneuverability of the car and a sufficiently large angle of rotation of the wheels. This type of mechanism is less susceptible to shock loading, but more expensive to manufacture.
• Screw - the principle of operation is similar to worm gearhowever, it has a higher efficiency and allows more effort.

Depending on the type of amplifier, which provides for the steering device, systems are distinguished:

• FROM . Its main advantage is its compactness and simplicity of design. Hydraulic steering is one of the most common among modern vehicles. The disadvantage of such a system is the need for level control working fluid.
• FROM . This power steering system is considered the most advanced. It provides easy adjustment of control settings, high operational reliability, economical fuel consumption and the ability to drive without driver intervention.
• FROM . The principle of operation of this system is similar to the system with a hydraulic booster. The main difference is that the amplifier pump is driven by an electric motor, not an internal combustion engine.

The steering of a modern car can be supplemented with the following systems:

• - the system changes the value of the gear ratio depending on the current speed. It allows you to adjust the angle of rotation of the wheels and provides a safer and more stable ride on slippery surfaces.
• Dynamic steering - works similarly active system, however, in this case, an electric motor is used instead of a planetary gear.
• Adaptive steering for vehicles - main feature is the lack of a rigid connection between the steering wheel of the car and its wheels.

Vehicle Steering Requirements

According to the standard, the following basic requirements apply to steering:

• Providing a given trajectory of movement with the necessary parameters of turnability, steering and stability.
• The effort on the steering wheel for maneuvering should not exceed the normalized value.
• The total number of turns of the steering wheel from the middle position to each of the extreme ones should not exceed the set value.
• If the amplifier fails, it must be possible to drive the vehicle.

There is one more standard parameterwhich determines the normal functioning of the steering is the total play. This parameter is the value of the steering angle before the steering wheel starts turning.

The value of the permissible total backlash in the steering must be within:

• 10 ° for cars and minibuses;
• 20 ° for buses and similar vehicles;
• 25 ° for trucks.

Features of right-hand and left-hand drive

Left hand drive and right hand drive

IN modern cars right-hand or left-hand steering can be provided, which depends on the type vehicle and the legislation of individual countries. Depending on this, the steering wheel can be located on the right (with left-hand traffic) or left (with right-hand traffic).

In most countries, left-hand drive (or right-hand drive). The main difference between the mechanisms is not only in the steering position, but also in the steering gear, which is adapted to different connection sides. On the other hand, it is still possible to convert right-hand drive to left-hand drive.

In some types of special equipment, for example, in tractors, hydrostatic steering is provided, which ensures the independence of the steering position from the layout of other elements. There is no mechanical connection between the drive and the steering wheel in this system. Hydrostatic steering includes a power cylinder that is controlled by a metering pump to perform wheel steering.

The main advantages that hydrostatic steering for vehicles has in comparison with the classic hydraulic power steering: the need to apply less effort to perform a turn, no backlash, and the possibility of arbitrary arrangement of system components.

The basis of the steering of any car is the steering mechanism. It is designed to convert rotational movements of the steering wheel into reciprocating movements of the steering gear. In other words, this device turns the steering wheel movements into the desired rods and steering wheel movements. The main parameter of the mechanism is gear ratio... And the device itself, in fact, is a gearbox, i.e. mechanical transmission.

Mechanism functions

Steering rack

The main functions of the device are:

• conversion of effort from the steering wheel (steering wheel);
• transfer of the received effort to the steering gear.

Types of steering mechanisms

The design of the steering mechanism differs depending on the way the torque is converted. According to this parameter, worm and rack types of mechanisms are distinguished. There is also a screw type, the principle of operation of which is similar to a worm gear, but it has greater efficiency and implements more force.

Worm steering gear: device, principle of operation, advantages and disadvantages

This steering gear is one of the "outdated" devices. Almost all models of domestic "classics" are equipped with it. The mechanism is used on vehicles with increased cross-country ability with dependent suspension of steered wheels, as well as in light trucks and buses.

Worm gear diagram

Structurally, the device consists of the following elements:

• steering shaft;
• transfer "worm-roller";
• crankcase;
• steering bipod.

The worm-roller pair is in constant engagement. The globoid worm is the lower part of the steering shaft, and the roller is attached to the bipod shaft. When the steering wheel rotates, the roller moves along the teeth of the worm, due to which the steering arm shaft also turns. The result of this interaction is the transmission of translational movements to the drive and wheels.

Steering gear worm-type has the following advantages:

• the ability to turn the wheels to a greater angle;
• damping shocks from road irregularities;
• transfer of great efforts;
• ensuring better maneuverability of the machine.

Manufacturing the structure is rather complicated and expensive - this is its main disadvantage. Steering with such a mechanism consists of many connections, periodic adjustment of which is simply necessary. Otherwise, damaged elements will have to be replaced.

Rack and pinion steering gear: device, principle of operation, advantages and disadvantages

Gear-rack mechanism

The rack and pinion steering mechanism is considered more modern and convenient. Unlike the previous unit, this device is applicable to vehicles with independent suspension steered wheels.

The rack and pinion steering gear includes the following elements:

• mechanism body;
• gear-rack transmission.

The gear is mounted on the steering shaft and is in constant engagement with the rack. During the rotation of the steering wheel, the rack moves in the horizontal plane. As a result, the steering rods connected to it also move and drive the steered wheels.

The gear-rack mechanism is distinguished by its simplicity of design and high efficiency. Its advantages also include:

• fewer hinges and rods;
• compactness and low price;
• reliability and simplicity of design.

On the other hand, this type of gearbox is sensitive to shocks from bumps in the road - any shock from the wheels will be transmitted to the steering wheel.

Helical gear

Device helical gear

A special feature of this mechanism is the connection by means of screw and nut balls. Due to this, there is less friction and wear of the elements. The mechanism consists of the following elements:

• steering wheel shaft with screw
• screw-driven nut
• toothed rack cut on a nut
• toothed sector with which the rack is connected
• steering bipod

The helical steering gear is used in buses, heavy trucks and some passenger cars. executive class.

Device adjustment

Steering gear adjustment is used to compensate for gaps in the worm-roller and gear-rack mechanisms. During operation, play may appear in these mechanisms, which can lead to rapid wear of the elements. It is only necessary to adjust the steering mechanism in accordance with the manufacturer's recommendations and at specialized service stations. Excessive "clamping" of the mechanism can lead to its jamming when turning the steering wheel to extreme positions, which is fraught with loss of control of the vehicle with the corresponding consequences.

It allows steering wheels to be steered with little steering effort. This can be achieved by increasing the steering gear ratio. However, the gear ratio is limited by the number of turns of the steering wheel. If you choose a gear ratio with the number of turns of the steering wheel more than 2-3, then the time required to turn the car significantly increases, and this is unacceptable due to driving conditions. Therefore, the gear ratio in the steering mechanisms is limited to 20-30, and to reduce the effort on the steering wheel, an amplifier is built into the steering mechanism or drive.

The limitation of the gear ratio of the steering mechanism is also associated with the property of reversibility, i.e. the ability to transfer reverse rotation through the mechanism to the steering wheel. With large gear ratios, the friction in the engagement of the mechanism increases, the reversibility property disappears and self-return of the steered wheels after turning into a straight-line position is impossible.

Steering mechanisms, depending on the type of steering gear, are divided into:

worm,

screw,

gear.

The steering gear with a worm-type transmission - the roller has a worm as a driving link, fixed on the steering shaft, and the roller is mounted on a roller bearing on the same shaft with the bipod. To make full engagement at a large angle of rotation of the worm, the worm is cut along an arc of a circle - a globoid. Such a worm is called globoid.

In the screw mechanism, the rotation of the screw connected to the steering shaft is transferred to the nut, which ends with a rack meshed with the toothed sector, and the sector is installed on the same shaft with the bipod. Such a steering mechanism is formed by a screw-nut-sector steering gear.

In gear steering mechanisms, the steering gear is formed by cylindrical or bevel gears, which also include a gear-rack transmission. In the latter, the cylindrical gear is connected to the steering shaft, and the rack, meshed with the gear teeth, acts as a lateral thrust. Rack and pinion gears and worm-roller type gears are mainly used on passenger cars, since they provide a relatively small gear ratio. For trucks, steering gears of the worm-sector and screw-nut-sector type are used, equipped with either amplifiers built into the mechanism, or amplifiers placed in the steering gear.

3.2. Steering drive.

The design of the steering gear differs in the arrangement of the levers and rods that make up the steering linkage in relation to the front axle. If the steering linkage is in front of the front axle, then this design of the steering drive is called the front steering linkage, with the rear positioning - the rear linkage. The design of the front wheel suspension has a great influence on the design and layout of the steering linkage.

With dependent suspension (Fig. 2. (a)), the steering drive has a simpler design, since it consists of a minimum of parts. Transverse tie Rod in this case, it is made in one piece, and the bipod swings in a plane parallel to the longitudinal axis of the vehicle. You can make a drive with a bipod swinging in a plane parallel to front axle... Then the longitudinal thrust will be absent, and the force from the bipod is transmitted directly to the two lateral rods associated with the wheel journals.

With independent suspension of the front wheels (Fig. 2. (b)), the steering drive circuit is structurally more complicated. In this case, additional drive parts appear, which are not in the scheme with dependent wheel suspension. The design of the tie rod is changed. It is splitted, consisting of three parts: the main transverse link and two side links - left and right. The main link is supported by a pendulum arm, which in shape and size corresponds to the bipod. The connection of the lateral transverse rods with the pivot levers of the pins and with the main transverse rod is made using hinges that allow independent movement of the wheels in the vertical plane. The considered steering drive scheme is used mainly on passenger cars.

The steering drive, being a part of the vehicle's steering, provides not only the ability to turn the steered wheels, but also allows the wheels to oscillate when they hit the bumps in the road. In this case, the drive parts receive relative displacements in the vertical and horizontal planes and, when turning, transmit the forces that turn the wheels. The connection of parts for any drive scheme is carried out using ball or cylindrical hinges.

Many would agree that the engine is the foundation of a car. And indeed it is. However, it is also difficult to imagine a car without steering. This is an important and necessary element in every car. The task of the steering is to ensure the movement of the vehicle in a given direction. This unit consists of several components. These are the steering wheel, column, drive and steering gear. We will talk about the latter today.

Functions

The steering mechanism has several main tasks:

• Transfer of forces to the drive.
• An increase in the effort that the driver applies to the steering wheel.
• Automatic return of the steering wheel to neutral position when removing the load.

Varieties

This element can be of several types. The following types of steering mechanisms are found today:

• Rack.
• Worm.
• Screw.

What are each of them? We will consider all these types of mechanisms separately.

Rack

At the moment, it is one of the most common. Mainly installed on passenger cars and crossovers. The rack and pinion steering mechanism requires the following parts:

The first was installed on the steering shaft. The pinion is in constant engagement with the rack. Works this mechanism pretty simple. When you turn the steering wheel, the rack moves to the right or left. In this case, the rods that are attached to the drive turn the steered wheels at a given angle.

Among the advantages of such a mechanism, it is worth noting the simplicity of the design, high efficiency and high rigidity. However, at the same time, such a mechanism is highly sensitive to irregularities on the road, which is why it quickly wears out. Often, owners of used cars were faced with the problem of knocking rail. This is a consequence of the wear of the steering mechanism. Therefore, the element is installed only on certain types of vehicles. These are mainly front-wheel drive cars with independent front suspension. If we talk about VAZ, then the rail is found on all models, starting with the "eight". A slightly different steering mechanism is installed on the "classic".

Worm

It is this type that is used on domestic Zhiguli, as well as on some buses and light trucks. This node consists of:

• Globoid worm with variable diameter.
• The steering shaft with which the worm is connected.
• Roller.

The bipod is located outside the steering gear. This is a special lever that is associated with the drive rods. The steering mechanism on the GAZ-3302 is arranged in the same way.

Among the advantages of such a unit, it is worth noting less sensitivity to shock loads. Therefore, this steering mechanism, installed on the VAZ-2107, is practically eternal. Owners rarely experience knocking and vibration on the steering wheel. However, this design has more connections. Therefore, the mechanism needs to be adjusted periodically.

Screw

This is a more complex unit in the device. Its design includes:

• Screw. Located on the steering wheel shaft.
• Nut. It moves to the previous item.
• Rack.
• Serrated selector. It is connected to the rail.
• Steering bipod. Located on the selector shaft.

The key feature of this mechanism is the way the nut and screw are connected. Fastening is carried out using balls. Thus, less wear and friction of the pair is achieved.

The principle of operation of the screw element is similar to the worm. The steering wheel is turned by turning the screw, which moves the nut. The latter moves the toothed sector with the help of a rack, and with it and steering bipod.

Where is the screw mechanism used? It is often used on heavy commercial vehicles such as trucks and buses. If we talk about passenger cars, then these are only models of the executive class. The mechanism is more complex and expensive, therefore it significantly increases the cost of the car itself.

Amplifier

Now almost all cars use power steering. It serves to reduce the effort required to turn the front wheels. This element allows for high accuracy and speed of steering. At the moment, there are several types of amplifiers:

• Hydraulic.
• Electric.

The first type is more popular. Fits both on cars and trucks. The booster device has a pump that creates a certain pressure in the hydraulic system. Depending on the steering side, this fluid presses on the first or second contour of the rack. Thus, the force required to turn is reduced. Among the advantages hydraulic system high reliability should be noted. The amplifier rarely fails. However, since the pump mechanism is driven by the crankshaft, some of the power is taken from the internal combustion engine. Although on modern engines it is completely imperceptible.

Electric amplifier consists of a separate motor. The torque from it is transmitted to the steering wheel shaft itself. The design is used only on passenger cars, as it is not designed for great efforts.

The EUR is equipped with separate electronics, which controls this engine. Sometimes the amplifier is supplemented with adaptive systems that are aimed at increasing safety when driving on the lane.

Among the innovative solutions, it is worth noting the dynamic control system from Audi. Here the gear ratio changes depending on the current vehicle speed. Thus, on high speeds the steering wheel is hard and knocked down, and when parking it becomes light. The gear ratio is changed by a dual planetary gearbox, which is added to the shaft. Its body can rotate depending on the speed of the vehicle.

Conclusion

So, we found out what this mechanism is. This is a very important steering unit. Regardless of the type, it should be checked periodically. After all, losing control at speed is the most dangerous thing that can happen to a driver.

The following requirements are imposed on the steering gear:
- the optimal gear ratio, which determines the ratio between the required angle of rotation of the steering wheel and the effort on it; - insignificant energy losses during operation (high efficiency);
- the possibility of spontaneous return of the steering wheel to the neutral position after the driver has ceased to hold the steering wheel in the turned position;
- slight clearances in movable joints to ensure low backlash or freewheel steering wheel;
- high reliability.

Rack and pinion steering mechanisms are most widely used in passenger cars today.

Rack and pinion steering gear without hydraulic booster:
1 - cover;
2 - insert;
3 - spring;
4 - ball pin;
5 - ball joint;
6 - emphasis;
7 - steering rack;
8 - gear

The design of such a mechanism includes a gear mounted on the steering wheel shaft and a gear rack associated with it. When the steering wheel rotates, the rack moves to the right or left and through the steering rods attached to it turns the steered wheels.
The reasons for the widespread use of just such a mechanism in passenger cars are: simplicity of design, low weight and manufacturing cost, high efficiency, a small number of rods and hinges. In addition, the rack and pinion steering housing located across the vehicle leaves sufficient space in the engine compartment to accommodate the engine, transmission and other vehicle units. Rack and pinion steering is highly rigid for more precise steering during harsh maneuvers.
At the same time, the rack and pinion steering mechanism has a number of disadvantages: increased sensitivity to shocks from road irregularities and the transmission of these shocks to the steering wheel; a tendency to vibroactivity of the steering, increased loading of parts, the complexity of installing such a steering mechanism on cars with dependent suspension of steered wheels. This limited the scope of application of this type of steering mechanisms only to passenger cars (with a vertical steering axle load of up to 24 kN) vehicles with independent steering wheel suspension.

Rack and pinion steering gear with hydraulic booster:
1 - high pressure liquid;
2 - piston;
3 - liquid under low pressure;
4 - gear wheel;
5 - steering rack;
6 - hydraulic booster distributor;
7 - steering column;
8 - power steering pump;
9 - reservoir for liquid;
10 - suspension element

Steering gear of the "globoidal worm-roller" type without power steering:
1 - roller;
2 - worm

Cars with dependent suspension of steering wheels, light trucks and buses, cars high cross-country ability are equipped, as a rule, with steering mechanisms of the "globoidal worm-roller" type. Previously, such mechanisms were also used on passenger cars with independent suspension (for example, the VAZ-2105, -2107 family), but now they are practically supplanted by rack and pinion steering mechanisms.
Mechanism type "Globoidal worm-roller" is a type of worm gear and consists of a globoidal worm (a worm with variable diameter) connected to the steering shaft and a roller mounted on the shaft. A lever (bipod) is installed on the same shaft outside the steering gear housing, with which the steering linkages are connected. The rotation of the steering wheel ensures that the roller rolls over the worm, the bipod sways and the steering wheels turn.
In comparison with rack and pinion steering mechanisms, worm gears are less sensitive to the transmission of shocks from road irregularities, provide greater maximum angles turning the steered wheels (better vehicle maneuverability), are well combined with dependent suspension, allow the transfer of large forces. Sometimes worm gears are used on cars. high class and a large unladen weight with independent suspension of steered wheels, but in this case, the design of the steering gear becomes more complicated - an additional steering rod and a pendulum arm are added. In addition, the worm gear requires adjustment and is expensive to manufacture.

Steering gear of the type "screw-ball nut-rack-toothed sector" without power steering (a):
1 - crankcase;
2 - screw with a ball nut;
3 - shaft-sector;
4 - filler plug;
5 - shims;
6 - shaft;
7 - steering shaft seal;
8 - bipod;
9 - cover;
10 - shaft-sector seal;
11 - outer ring of the shaft-sector bearing;
12 - retaining ring;
13 - a sealing ring;
14 - side cover;
15 - cork;
with built-in hydraulic booster (b):
1 - adjusting nut;
2 - bearing;
3 - a sealing ring;
4 - screw;
5 - crankcase;
6 - piston rack;
7 - hydraulic distributor;
8 - cuff;
9 - sealant;
10 - input shaft;
11 - shaft-sector;
12 - protective cover;
13 - retaining ring;
14 - sealing ring;
15 - outer ring of the shaft-sector bearing;
16 - side cover;
17 - nut;
18 - bolt

The most common steering gear for heavy-duty trucks and buses is the screw-ball-nut-rack-toothed sector. Sometimes steering mechanisms of this type can be found on large and expensive passenger cars (Mercedes, Range rover and etc.).
When the steering wheel is turned, the shaft of the mechanism with a helical groove rotates and the nut put on it moves. In this case, the nut having on outside toothed rack, turns the toothed sector of the bipod shaft. To reduce friction in a screw-nut pair, the transfer of forces in it occurs by means of balls circulating in a screw groove. This steering mechanism has the same advantages as the worm gear discussed above, but it has a high efficiency, allows you to effectively transfer large forces and is well combined with a hydraulic power steering.
Previously, other types of steering mechanisms could be found on trucks, for example, "worm-side sector", "screw-crank", "screw-nut-connecting rod-lever". On modern cars, such mechanisms are practically not used due to their complexity, the need for adjustment and low efficiency.