Modern system steering control of a car is a complex and at the same time simple mechanism that has reached a perfect level of design. Despite this, manufacturers are trying to create various options to further simplify the driving experience.
Devices that facilitate control and help to cope with extreme situations on the road include: electric and hydraulic power steering, directional stability mechanism, ABS, steering rear suspension and other equipment.
Steering wheels - purpose
Compliance with straightness of movement rear discs at various speeds greatly affects the overall handling of the machine as a whole, especially when making maneuvers. The steering suspension is designed to reduce the resistance of the rear wheels, which always strive to maintain their original trajectory.
Such mechanisms are not a big innovation in the automotive industry, they have long been used in the production of equipment, forklifts.
Thrusters types
The device is manufactured in two versions - active and passive. In the first case, the operation of the device is provided by electronics, while in the second - the process proceeds due to the mechanical efforts of the levers and traction elements. Let's take a closer look at each of these types.
Active steering rear suspension
Such a system is considered more modern and efficient. Accordingly, the cost of an active steering mechanism is also higher. It is equipped with electronically controlled actuators. Components provide the rear wheels with agility. When the unit is operating, the response to the steering wheel rotation occurs simultaneously with all wheels.
This type of suspension has several modes, which greatly facilitates driving and increases its stability.
Passive steering suspension
Such a device has a rather complex design. In simple words, levers, pillows and silent blocks are attached to the rear suspension. Their arrangement is in a special order. This design allows the elements to respond to lateral forces and roll when cornering, thereby improving wheel engagement. When the machine is pointing straight ahead, the rear discs are in neutral and the suspension only works in an upright position.
Pros and cons of steering wheels
Among the advantages of the system, experts note - an increase in the maneuverability and efficiency of transport management. The disadvantages include the cost of equipment and the need for additional repairs to the car in case of breakdown.
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In the usual sense, the direction of movement of the car changes when the steering wheel is turned, which transfers the force to the front wheels through a simple mechanism, thereby turning them either to the left or to the right. Well, the rear wheels, of course, move exclusively in parallel, but what else? They do not perform any turns, do they? Yes, for the most part this is true, as it applies to the vast majority of cars. But some modern cars are installed special devices, which activate the mechanism of a kind of steering of the rear wheels. So why was such an innovation invented and on what principle does it work? We will tell you about this and much more later in this material.
Steering suspension - history of creation
There is no limit to perfection, and therefore today the priority factor in the creation of new automotive systems is improved handling. Although modern existing systems car controls perform their functions quite well, restless developers are all competing in the pursuit of creating additional devicespositively affecting steering... The current and all acquaintances include traction control systems and systems.
But even before the full introduction of all kinds of gadgets and microprocessors in vehicle control systems, there were other developments, technically not so complex, but useful in terms of improving handling. These include the rear wheel steering system.
Examples of ground mobile units with installed system rear axle steering could be found a hundred years ago. This principle has long and successfully been used in forklifts that work in close warehouses, in the shops of factories and other places. This system was used in the late thirties on agricultural machinery and off-road vehicles, for example, in the pre-war "rogue" Mercedes Kübelwagen G5.
Types of steering suspension on modern cars
In the first systems for steering the rear wheels, the angle of rotation was impressive and amounted to about 15 degrees. When the speed of the produced vehicles began to increase significantly, such large corners had to be cut. In modern cars, the steering angle reaches a maximum of 8 degrees. The rear steering suspension is divided into two types: active and passive. More on this later.
Active
In a car equipped with a system of active rear-wheel steering, all four wheels turn at once with the movement of the steering wheel by the driver. IN modern machines power transmission through wheel is carried out not by means of mechanics - a lever system, but through a command from the ECU and retractor relays, which are also called actuators. They move the rear steering rods similar to those used in the main steering system.
The active suspension operates in two steering modes. For example, when leaving a parking lot or garage, at the moments of turning the front in one direction rear wheels turn in the opposite direction. This reduces the turning radius by 20-25%.
At high speeds working scheme changes. When turning the front wheels, the rear wheels steer, but with a smaller angle. Control over which angle to turn the rear wheels the electronic unit control, guided by the indications of the angular acceleration sensor, as well as the speed sensor and others. Based on the readings, an optimal cornering algorithm is formed.
The most famous rear suspension steering systems from Japanese manufacturers. For example, Honda has introduced a steer option rear axle back in 1987 on sports coupe Prelude models. A year later, Mazda adopted this option on its 626 and MX6 models.
The Americans at General Motors also experimented with this system, it was called Quadrasteer. It was optionally put on suburban SUVs and a Yukon and a Silverado pickup.
Have nissan the steering system was called HICAS. At the beginning of production, it was driven by a hydraulic mechanism and was combined with a power steering. She was put on nissan models and Infiniti with rear wheel drive... But in the mid-nineties, such a system was abandoned, since it was complex and not highly reliable, and switched to actuators.
In 2008, the Renault-Nissan concern presented the Renault Laguna with new system steering the rear suspension Active Drive. The Europeans also did not stay on the safe side. For instance, bMW company introduced a steering system called Integral Active Steering on 7 series and 6 series Gran coupe vehicles.
Passive
Many modern cars are equipped with a simplified rear-wheel steering system. Elements are built into the rear suspension, which have certain physical properties that counteract inertia straight motion... This type of steering is called passive. In such vehicles, the rear suspension is designed with a special geometry using Watt's movable rod.
The system is designed in such a way that when you gain sufficient speed and enter a turn, the rear wheels steer in the same direction as the front ones, due to the redistribution of forces in the suspension. In addition to the unusual geometry, the effect is enhanced due to the installation of silent blocks of a certain elasticity and shape. This design has a positive effect on the stabilization of the vehicle when cornering. Such a system was equipped with Ford focus in the first generation.
In fact, this principle is not some kind of innovative technological solution, since over the past couple of decades, thrusters have been taken into account by engineers. But some manufacturers, such as Ford, have paid particular attention to these properties and singled out the design into one special system.
Advantages and disadvantages
And in conclusion, let's discuss the main pros and cons of the steering rear suspension. TO positive sides refers to increased maneuverability due to a smaller turning radius and improved vehicle handling. The most serious disadvantage is the more complex design of the rear suspension system, which affects the cost of the car and increases repair costs.
this article was written while working with a car Skoda Octavia, front-wheel drive. There may be some differences on other models, but they do not affect the total volume or the method of repair.
Rear multi-link independent suspension designed to provide comfort and steering precision at all speeds and on all surfaces. There are so many components in it that even schematically it is impossible to place in one drawing
And like any movable structure, it has its own resource.
Cars of this platform have been running long enough to collect statistics on the most frequently replaced components. These include the so-called thrusters and silent blocks in the rear lower wishbones... But in fact, in the rest of the levers, silent blocks of almost the same diameter. This means that their resource is about the same. But it is almost impossible to diagnose their condition visually. And it turns out that their hands reach them only when the camber / convergence at the stand cannot be touched adjusting bolts... By the way, there are 4 of them.
And if the lower ones still have a chance to stir up or even cut off with a grinder, then the upper ones are very difficult to access
Therefore, in this article we will consider the bulkhead of all elements of the rear suspension, with the removal of the beam.
While everything is firmly screwed to the body, it makes sense to "remove" all the nuts and bolts, which then need to be unscrewed
-disconnect the parking brake cable from the calipers. For this, the "mustache" on the cable jacket must be squeezed
We take out the cable from the guides attached to the levers
Now you can unscrew the calipers themselves, and hang them on the locker using wire hooks, for example
That would not depressurize braking system you need to disconnect the tubes from the beam. To do this, take out the clips
Now you can bring both the tube and the hose to the side through the slot
We snap the tube going to the right caliper along the beam from the clips
Unscrews the body position sensor from the lever (for those versions that have it)
We start dismantling. Place a stop under the rear arm and create a stop. Unscrew the bolt securing the lever to the steering knuckle
Lower the rack, lower the lever, remove the spring
Unscrew the lower shock absorber mounting bolt
On the left side, remove the muffler mounting rubber
Disconnect the connectors from the ABS sensors
We install the hydraulic rack under the beam
We unscrew the bolts securing the trailing arms
Unscrew the 4 bolts securing the beam to the body
The beam can be removed
Now let's start parsing.
We unscrew the outer bolts of the upper levers
Let's move on to the internal ones.
And if the nut is not very difficult to unscrew, then the bolt itself most often turns out to be soured inside the bushing of the silent block. By the way: even in this position, it is almost impossible to determine the state of the silentblock itself
We take the "grinder" in our hands and cut off the bolt
We take out the lower bolts attaching the steering rods to the steering knuckle
Trying to unscrew the rear stabilizer post from the lever
Most likely it will not work.
Then we take the "grinder" in our hands again
We split the unscrewed parts so that they do not get confused during assembly
We unscrew the bolts attaching the trailing arms to the steering knuckles
We turn the beam over and unscrew the lower rear levers. And again, there is a possibility that the nuts will be unscrewed, but the bolts will not.
We pick up (in unison!) “Grinder ...
Unscrew the stabilizer mounting bolts
We unscrew the last levers, the very thrusters.
Suspension disassembled
And here is a set of new spare parts, awaiting installation
do not rush to copy numbers from boxes. This article does not discuss the manufacturers and the repair method (replacing the silent blocks or the entire lever)
Install the thrusters first. Do not confuse left with right! (for some models, from a certain year, they may be symmetrical)
-Before pressing in new silent blocks, it is necessary to clean the seat
The silent block itself must be correctly oriented relative to the lever. It has two protruding stripes
They must be aligned with the protrusions of the lever
To avoid displacement, you can apply a mark with a marker
And you also need to take into account that the silent block clip is narrower than the lever itself
And here the marker will help
Press in
However, a more accurate measuring instrument can also be used.
We install the levers into the beam, insert new bolts and new eccentric washers
We fasten the stabilizer in place, already with new struts
We turn the beam over, take the upper levers
Please note that the silent blocks are almost identical in appearance, differ only in their inner diameter.
We repress in the same way, only the head will need a different diameter
We fasten the levers to the beam, also using new bolts and washers
Now we take on the trailing arms. ELSA prescribes to adhere to certain dimensions during assembly and pressing,
i do this: before unscrewing the central bolt, I measure the distance between the lever and the body
Then you can already unscrew the central bolt
Before removing the old silentblock, it is convenient to make a mark on which to orient the new silentblock
By the way, the separation of this silent block can only be considered after dismantling
The already familiar extraction procedure
we clamp the lever in a vice, install the body, bait the central bolt. We set the required distance, tighten it in advance, then clamp the case itself in a vice, and make the final tightening with a torque wrench.
There were silent blocks in the steering knuckles themselves. To replace them with a press, you need to unscrew the caliper bracket, remove brake disk, wheel bearing, and unscrew the boot. But with a small number of mandrels and a long screw, everything can be done on site
I will share a little secret: the clip of these silent blocks is plastic, and to facilitate removal, you can use an industrial hair dryer or even a compact gas burner. Pop out "with a bang"
The reverse process is much easier.
All silent blocks have been replaced, you can proceed to reassembly... It makes no sense to describe the entire procedure, but it is worth paying attention to a few points:
- there are several washers in the bolt-nut bundle.
They are placed like this:
When screwing the trailing arm to the steering knuckle, do not tighten them immediately, as you must first insert the stabilizer bolt.
And in general, you can not tighten any fasteners to a certain point, just make money and tighten.
To make it more convenient to insert the beam into place, you can cut off the caps of a pair of old bolts, and use them as guides
This will make it easier to align the holes.
The springs must be installed in a strictly defined position. This can be helped by a protrusion on a rubber sole, which must be inserted into the mating hole of the lever.
A jack or hydraulic stand is placed under the lever.
Align the holes, insert the bolt, tighten the nut.
Jack up the lever until the weight rests on the spring
You can help determine this moment by the stop, a gap should appear between it and the body
And it is at this moment that all the bolts and nuts must be tightened.
Paste brake pipe in retainers
Put the connectors on the ABS sensors
After that, you can screw on the wheels and go straight to the camber / toe stand.
For your own peace of mind, you can re-tighten all the bolts and nuts that secure the levers when the machine is on its wheels.
Let's be more specific, what is power steering? If you have not tested on your front wheel drive its impact, it means that your car does not have a very large torque. For this to happen, technical tricks must be applied to solve the problem.
Why is this happening? The main reasons for power steering lie in the technical component of the car. More precisely, due to the asymmetric angles of the drive shafts, different torque outputting to each of the shafts in the geometry, in the deviations of the suspension tolerances, in the unequal traction forces caused by the difference in traction with the road surface, as well as due to uneven tire wear and other differences used in drives, for example in their various diameters.
Thus, such power steering can manifest itself over time also due to worn suspension bushings or due to tires, and also the poor-quality road surface itself negatively affects. Engine tuning, which significantly raised it, and many other specific factors, can also be included in this list.
Over the years, automakers have sought and developed solutions to reduce or eliminate this phenomenon on high power front wheel drive models. Dear readers, we will consider today the most progressive methods of combating this phenomenon and explain the technology as well as various technical solutions that are used in our time by most automakers, which make their car models pleasant to drive.
Drive shafts of equal length.
Since transverse engines usually suffer from power steering, one of the first solutions developed by automakers was the installation of drives of equal length on the car. To implement this solution, the engine had to be installed in a non-standard position, which further led to the effect of understeer.
But nevertheless, with this approach to the issue, there were other innovative solutions. For example using intermediate shaft instead of a longer drive shaft, which was attached to the gearbox on one side and another shaft of equal and equal length on the other side. Some companies produced and marketed for secondary market even longer shafts, which were offered by manufacturers as an option. The results in this case could be very different and only for the worse. Because the precision of these tuned shafts had to be very high to ensure reliability and further safety.
Other solutions included the installation of a short hollow drive shaft and a one-piece monolithic shaft. But not all of these solutions worked, as their performance could be limited in corners, or in the case of high power and high torque.
Revo Knuckle (custom design steering knuckle from Ford).
This suspension system was used on the Mk 2. Its development enabled the automaker to provide customers with front-wheel drive hot hatches of high power, which did not suffer from loss of control due to the car drifting to the side. Those lucky ones who managed to ride this car will tell you the following that the Mk 2 Ford Focus RS still did not get rid of the annoying "bug", during intensive acceleration the steering wheel still behaved not quite naturally, 100% changed suspension and self-locking did not help in solving this problem. However, this impact was minimal.
An interesting fact in the development of the suspension strut was the following, that it (strut) was originally developed for the lineup car mondeowho suffered the most from the power steering in his powerful diesel versions... Ford developed its suspension system to handle the extra torque without the need for a limited slip differential. Although in the Focus RS car, as we already said, an LSD differential was additionally installed due to even more torque.
How it works? Let's consider. The idea behind this ingenious one was to decouple the steering and suspension functions of the front axle. Ford's solution was to install a "knuckle" on each of the front wheels in order to allow movement of the steering wheel and separate it from the suspension arms.
In the late 1990s, Toyota was the first to produce cars with a similar suspension system, called Super Struts, but later systems from the and and companies became more widespread. Modern car has a similar installation, which was developed specifically by a Japanese automaker. The company calls it Dual Axis Strut Front Suspension and is used in a front suspension with two pivots and electronically controlled dampers.
To improve the performance of the car, a limited-slip differential was also installed on it. Engineers estimate that power steering is reduced by about 55% when compared to a conventional suspension.
Suspension HiPer Strut.
General Motors, like Ford, has developed a special front suspension that would allow front-wheel drive vehicles to experience less torque. As we discussed above, this system worked by separating the steering from the suspension on the front axle by adding improved struts.
This system performs its functions wonderfully, it does not change the steering properties and eliminates the "torque steer" effect, since it allows you to reduce the camber change when vehicle is driven in an arc, thereby ensuring that the tires of the car are always perpendicular to the road when cornering.
Of course, such a suspension of the "Super Strut" type adds weight and, of course, cost to the car, it complicates the system of a front-wheel drive car, but to achieve high-quality work, you always have to sacrifice something and, as usual, overpay. Along with the powerful versions of the Opel / Vauxhall Astra and the Insignia in Europe, GM also used the system HiPer Strut on their auto models Buick LaCross CXS and Buick Regal GS.
Electronic controlled differentials.
The ever-increasing popularity of "hot hatchbacks" that need to handle reasonably well and deliver the right amount of power and torque have led automakers to look for torque control solutions. They saw the use of electronically controlled differentials in the system as one of the solutions.
Concern "Volkswagen" also uses a similar system. The Germans call it XDS XDS Electronic Differential Lock. Some time ago they used a feature called EDL on machines, and now XDS has become its evolutionary continuation. This system turned out to be more advanced, since it acts ahead of schedule, that is, it does not "wait" until the wheel is located with inside cornering will begin to slip, thereby imitating a limited-slip differential.
The foundation electronic differential - these are its sensors, they control the speed of each wheel separately, as well as the speed of the car, the position itself throttle, steering angle and transmission of course. All parameters are compared in real time with the values \u200b\u200bloaded into the computer and when electronic system determines (according to the driving parameters) that steering can occur, then it immediately activates the XDS function.
This XDS works and activates the inner wheel braking system when cornering. As explained in the Volkswagen concern, the pressure level in the system ranges from 5 to 15 bar. The system responds adequately and accurately in most such cases, it feels almost like a "light" version of a mechanical limited slip differential. However, in the future, this causes additional wear on the front brakes, so the system cannot perform its task as efficiently as the same mechanical LSD in high-performance car variants.
Self-locking differential.
The last reason we have given is a major factor in the fact that this system is used in many sports hatches already sold around the world, as it helps to increase the speed of cornering in a sporty manner. Recently, these limited slip differential technologies allow for greater control for each wheel and improve stability and traction when cornering, as well as when driving in a straight line. The idea behind this system is wheel braking, which tends to lose traction, similar to those electronically controlled solutions.
As we have already found out with an example car ford For the Focus RS, this experience in creating a powerful, manageable front-wheel drive car does not always achieve its absolute goal, even with the same good suspension and the same mechanical limited slip differential. Nevertheless, we can say that these results are still very high.
Explanation of how the HiPer Strut system works.
Ford Focus RS Mk 2 Revo Knuckle system.
When we turn the steering wheel, the front wheels of the car also turn in accordance with the direction we have chosen. And the rear ones move in parallel. It seems obvious! But it also happens otherwise. There are car models in which the rear wheels turn together / simultaneously with the front wheels when turning. These are buckets with so-called thrusters rear wheels or, as they are also called, a car with a rear steering suspension, fully steered, or cars with a 4 Wheel Steer system (abbreviated 4WS, in translation - "4 steered wheels", this name is often applied to japanese models). Moreover, the rear wheels at a speed of about 35-40 km / h (at different models different speed indicators) turn in the opposite direction to the front wheels, and above this indicator - in the same direction.
This is how it looks:
1 - on high speed 4WS-auto
2 - regular car
3 - 4WS-cars when parking or turning on high speed
Why is this needed?
The steering wheels have been developed to improve the vehicle's handling, especially when cornering (improved sensitivity), as well as when turning on narrow streets (after all, when driving quietly along city lanes, it is better to have "sharp" steering, and not to turn the steering wheel, maneuvering) and for easier parking. In general, such a system improves the response of the car to steering, stabilizes body roll at high speed, and therefore increases directional stability.
In fact, the angle of deflection of the rear wheels of a 4WS car is not great. Maximum three degrees. And this is enough to reduce the turning angle of the car by 60–80 cm. Different automakers adjust the turning angles in different ways, in their own way. And the speed at which the rear wheels turn in the same direction as the front wheels is different - the range from 30 km / h to 60 km / h can be even higher.
For maintenance of the 4WS system and, for example, for camber-convergence, special stands are required.
How it works?
On the rear subframe 4WS-auto electric motor. It receives signals from the control unit. And through the steering rods, the electric motor drives the rear wheel hubs.
In turn, the power supply receives information from the vehicle wheel speed sensors, steering wheel position and accelerometers, which have the ability to distinguish between oversteer and understeer of the car. Here, in the block, all this is "digested", processed, and if necessary, a signal is sent to the electric motor, and the rear wheels begin to execute the necessary commands.
Examples of
The use of thrusters rear wheels is especially common for cargo, construction, military equipment, long buses and so on. In principle, the technology was just developed for special equipment operating in small spaces of factory warehouses, then migrated to serial cars. On special vehicles, the angle of rotation is larger, up to 15 degrees.
For cars, all-wheel steering was especially popular in the 1990s and until the early 2000s. The boom of the fully-run was ruled by Japanese manufacturers. Nowadays, they don't really indulge in such wheels. You can find, for example, on the BMW 7-Series (since 2009, such rear wheels are part of the sports package), Lexus GS (since 2013, it is listed as an option Lexus Dynamic Handling), on the Porsche 991 GT3 and Porsche 991 Turbo (since 2014 th), etc.
Views
The rear thrusters can be active or passive. In the first case, all four wheels are turned simultaneously in response to the steering wheel movement. In low speed mode, if the front wheels are turned to the right, the rear wheels will turn to the left, and vice versa. This reduces the turning radius to 25%.
And at speed, the active steering suspension behaves like this: the rear wheels steer in the same direction as the front ones, but at a smaller angle. The electronic control unit is responsible for the angle accuracy, taking into account the readings of the angular acceleration sensor, speed sensor and other parameters.
An example of a car with such a suspension - Honda prelude (since 1987).
And if you take something more modern, you can find Bavarians with a steering system of the rear wheels called BMW Integral Active Steering.
The passive option is now more popular. And it's like a simplified steering wheel system. In such cars, the rear suspension is built according to a special geometry and most often using Watt's movable rod. What happens: when making a turn at high speed, the rear wheels, due to the redistribution of forces in the suspension, tend to steer in the same direction as the front ones. And this makes the car more stable. An example of a car with such rear rollers is the first generation Ford Focus.
Why are there so few cars with such technology now? Manufacturers note that developments in the field of 4WS are underway, but they are no longer focused on increasing the maneuverability of the car, but on its stability.
Have you encountered rear wheels like this? What are the pros and cons?
- , 20 Aug 2014
