Let's be more specific about what power steering? If you have not yet experienced its effects on your front-wheel drive, then your car does not have very much 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 of different torque output to each of the shafts in geometry, in suspension tolerance deviations, in unequal tractive effort caused by the difference in grip with the road surface, as well as due to uneven wear tires and other differences used in drives, for example, in their different diameters.
Thus, such a power steering can also manifest itself over time due to worn suspension bushings or tires, and the poor-quality roadway itself also negatively affects. The same list can include engine tuning, which significantly raised it, well, and many other specific factors.
Over the years, automakers have been looking for and developing solutions to reduce or complete elimination this phenomenon on front wheel drive models with high power. Dear readers, we will consider today the most progressive methods of dealing with this phenomenon and explain the technology as well as various technical solutions, which are used nowadays by most automakers, which make their car models pleasant to drive.
Drive shafts of equal length.
Since transversely mounted engines tend to suffer from power steering, one of the first solutions developed by automakers was to install drives on the car equal length. To implement this solution, it was necessary to install the engine 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 an intermediate shaft instead of a longer drive shaft, which was attached to the gearbox on one side and another shaft of equal and the same length on its other side. Some companies produced and marketed for secondary market shafts of even longer lengths, which were offered as an option by manufacturers. The results in this case could be very different, and only in the worst side. Since the manufacturing precision of these tuned shafts had to be very high in order to ensure reliability and further safety.
Other solutions included the installation of a short hollow drive shaft and a one piece solid shaft. But not all of these solutions worked, as their performance could be limited in corners, or in case high power and great torque.
Revo Knuckle (special design steering knuckle from Ford).
This system the suspension was used on the Mk 2 auto. Its development enabled the automaker to provide customers with high-performance front-wheel drive hot hatches that did not suffer from loss of control due to the vehicle pulling to the side. Those lucky people who managed to ride this car will tell you the following, that the Mk 2 Ford Focus The RS did not completely get rid of the annoying "bug", during intensive acceleration the steering wheel still behaved not quite naturally, a 100% modified suspension and self-locking did not help in solving this problem. However, this impact was minimal.
An interesting fact about the development of the suspension strut was that it (the strut) was originally designed for model range Mondeo car, who suffered most from power steering in his powerful diesel versions. Ford designed their suspension system to handle the extra torque without the need for a limited slip differential. Although in the Focus RS car, as we have already said, an LSD differential was additionally installed due to even more torque.
How it works? Let's consider. The idea of this witty 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 to allow the steering wheel to move and separate it from the suspension arms.
"Toyota" back in the late 1990s was the first to release cars with a similar suspension system, called "Super Struts", but later systems from the companies "" and "" have become more widespread. The modern car has similar installation, which was developed specifically by the Japanese automaker. The company calls it Dual Axis Strut Front Suspension and it is used in the front suspension with two kingpins and electronically adjustable shock absorbers.
To improve the performance of the car, a limited slip differential was also put on it. Engineers have calculated that power steering is reduced by about 55% when compared to conventional suspension.
Suspension HiPer Strut.
Company " General Motors just as Ford developed their special front suspension that would allow front-wheel drive vehicles to experience less torque. As we have seen above, this system worked by separating the steering from the suspension at the front axle, by adding improved struts.
This system works wonderfully, it does not change the steering properties and eliminates the "torque steer" effect, since it allows to reduce the change in camber when the vehicle is driven in an arc, thereby ensuring that the tires of the car are constantly perpendicular to road when cornering.
Of course, such a "Super Strut" type suspension adds weight and cost to the car, it complicates the system. front wheel drive car, but to achieve high-quality work, you always have to sacrifice something and, as usual, overpay. Along with powerful versions Opel/Vauxhall Astra and the Insignia in Europe, GM also used the HiPer Strut system on their Buick LaCross CXS and Buick Regal GS models.
Electronically controlled differentials.
The ever-increasing popularity of "hot hatchbacks" that need to handle well enough to deliver the right amount of power and torque has led automakers to look for torque management solutions. One of the solutions they saw was the use of electronically controlled differentials in the system.
Concern "Volkswagen" also uses similar system. The Germans call it XDS XDS Electronic Differential Lock. Some time ago they used a feature called EDL on the machines, and now the XDS system has become its evolutionary continuation. This system turned out to be more advanced, since it acts ahead of the curve, that is, it does not “wait” until the wheel is inside turn will begin to slip, thereby simulating a self-locking differential for this.
The basis 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 valve, steering angle and natural transmission. All parameters are compared in real time with the values loaded into the computer and when electronic system determines (according to the driving parameters) that steering steering may occur, it immediately activates the XDS function.
This XDS works and activates brake system inner wheel in a turn. As the concern "Volkswagen" explains, the pressure level in the system ranges from 5 to 15 bar. The system works adequately and accurately in most of these cases, feeling 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 well as the same mechanical LSD in high-performance versions of cars.
Self-locking differential.
The last reason we gave is the main reason why this system is used in many sports hatches already sold around the world, as it helps to increase cornering speed in a sporty manner. These latest limited slip differential technologies allow more control for each wheel and improve stability and traction itself when cornering as well as when driving in a straight line. The point of this system is to brake a wheel that tends to lose traction, similar to those electronically controlled solutions.
As we have seen from the example ford car Focus RS, that experience of building a powerful, drivable, front-wheel-drive car doesn't 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 the operation of the HiPer Strut system.
Ford Focus RS Mk 2 Revo Knuckle system.
When we turn the steering wheel, the front wheels of the car also turn according to the direction we have chosen. And the rears move in parallel. It seems to be obvious! But it happens otherwise. There are car models in which the rear wheels turn together / simultaneously with the front wheels when turning. These are buckets with the so-called rear wheel thrusters or, as they are also called, cars with a rear thruster suspension, fully controlled, or cars with a 4 Wheel Steer system (abbreviated as 4WS, translated as “4 steerable wheels", this name is more often applied to Japanese models). Moreover, the rear wheels at speeds up to about 35-40 km / h (for different models different speed indicators) turn in the direction opposite to the front wheels, and above this indicator - in the same direction.
Here's what it looks like:
1 - at high speed 4WS-auto
2 - regular car
3 - 4WS-auto when parking or turning on high speed
Why is this needed?
Steering wheels have been developed to improve the car's handling, especially in turns (better sensitivity), as well as when turning in narrow streets (after all, when quiet ride on city alleys it is better to have a "sharp" steering rather than turning the steering wheel while maneuvering) and for easier parking. In general, such a system improves the response of the car to steering, stabilizes body roll at high speed, which means it increases directional stability.
In fact, the angle of deflection of the rear wheels of a 4WS car is not large. 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 ones is different - the range from 30 km / h to 60 km / h, sometimes even higher.
To service the 4WS system and, for example, toe-in, special stands are required.
How it works?
On the rear subframe is a 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 or 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
The use of thruster rear wheels is especially common for trucks, construction, military equipment, long buses etc. In principle, the technology was just developed for special equipment operating in small spaces of factory warehouses, then migrated to serial cars. On special equipment, the angle of rotation is greater, up to 15 degrees.
For passenger control all-wheel drive was especially popular in the 1990s and into the early 2000s. A booming full-time rule Japanese manufacturers. Now, these wheels are not particularly indulged. 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), Porsche 991 GT3 and Porsche 991 Turbo (since 2014 th), etc.
Kinds
The rear thruster suspension can be active or passive. In the first case, all four wheels turn simultaneously, in response to the movement of the steering wheel. 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 by up to 25%.
And at speed, the active steering suspension behaves like this: the rear wheels are steered in the same direction as the front ones, but at a smaller angle. Responsible for angle accuracy the electronic unit control, 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 meet Bavarians with a rear wheel steering system called BMW Integral Active Steering.
The passive option is now more popular. And this is, as it were, a simplified system of steering wheels. In such cars, the rear suspension is built according to a special geometry and most often using Watt's movable traction. What happens: when making a turn at high speed, the rear wheels tend to steer in the same direction as the front wheels due to the redistribution of forces in the suspension. And it makes the car more stable. An example of a car with such rear rollers - Ford Focus first generations.
Why are there so few cars with this technology now? Manufacturers note that developments in the field of 4WS are underway, but are no longer focused on improving the maneuverability of the car, but on its stability.
Have you come across such rear wheels? What can you name the pros and cons?
- , 20 Aug 2014
The modern car steering system 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 that further simplify the driving process.
To devices that facilitate management and help to cope with extreme situations on the road, include: steering electric and hydraulic boosters, a mechanism exchange rate stability, ABS, thruster rear suspension and other equipment.
Steering wheels - purpose
Straightness of movement rear discs at various speeds, it greatly affects the entire controllability of the machine as a whole, especially when making maneuvers. The thruster suspension is designed to reduce the resistance of the rear wheels, which always tend to maintain their original trajectory.
Such mechanisms are not a great innovation in the automotive industry, they have long been used in the manufacture of equipment, loaders.
Thruster suspension types
The device is made 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 thruster rear suspension
Such a system is considered more modern and efficient. Accordingly, the cost of the active steering mechanism is also higher. It is equipped with actuators, electronically controlled. The components provide agility to the rear wheels. When the unit is operating, the reaction 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 thruster suspension
Such a device has a rather complex design. In simple words, levers, pillows and silent blocks are attached to the rear suspension. Their location is in a special order. This arrangement allows the elements to respond to lateral forces and roll in a turn, thereby improving wheel entry into the turn. When the car is pointing straight ahead, rear discs are in the neutral state, and the suspension operates only in a vertical position.
Pros and cons of steering wheels
Among the advantages of the system, experts note the increase in maneuverability and efficiency of transport management. The disadvantages include the cost of completing and the need for additional repair car in the event of a breakdown.
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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 overall volume or method of repair.
Rear multi-link independent suspension It is designed to provide comfort and accuracy of taxiing at any speed and any surface. There are so many components in it that it is even impossible to place it schematically in one figure.
And like any movable structure, it has its own resource.
Cars of this platform have been driving for a long time to collect statistics on the most frequently replaced components. These can be safely attributed to the so-called thrusters and silent blocks in the rear lower wishbones. But in fact, in the rest of the levers, the silent blocks are almost the same diameter. And that means they have about the same resource. But diagnosing their condition visually is almost impossible. And it turns out that hands reach them only when the collapse / convergence cannot be moved at the stand 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 reach
Therefore, in this article we will consider the bulkheading of all elements rear suspension, with beam removal.
While everything is firmly screwed to the body, it makes sense to "stroke" all the nuts and bolts, which then need to be unscrewed
-disconnect the handbrake cable from the calipers. To do this, the "whiskers" on the cable jacket must be compressed
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
In order not to depressurize the brake system, you need to disconnect the pipes from the beam. To do this, remove the clamps
Now you can bring both the tube and the hose to the side through the slot
The tube going to the right caliper along the beam is snapped off from the clamps
Unscrews the body position sensor from the lever (for those versions who have it)
Let's start dismantling. We put an emphasis under the rear lever and create an emphasis. Unscrew the bolt securing the lever to knuckle
We lower the rack, lower the lever, take out the spring
Loosen the lower shock absorber bolt.
On the left side, remove the muffler mounting rubber
Disconnect connectors from ABS sensors
Installing the hydraulic rack under the beam
We unscrew the bolts of the trailing arms
Unscrew the 4 bolts securing the beam to the body
The beam can be removed
Now let's start parsing.
Unscrew the outer bolts of the upper arms
Let's move on to the inside.
And if it is not very difficult to unscrew the nut, then the bolt itself most often turns out to be sour inside the bushing of the silent block. By the way: even in this position, it is almost impossible to determine the state of the silent block itself.
We pick up the "grinder" and cut the bolt
We take out the lower bolts of the thruster rods to the steering knuckle
We are trying to unscrew rear rack stabilizer from the lever
Most likely it won't work.
Then we take the "Bulgarian" in our hands again
We split the unscrewed parts so as not to get confused during assembly
We unscrew the bolts securing the trailing arms to the steering knuckles
Turn the beam over and unscrew the bottom rear arms. And again, there is a chance that the nuts will unscrew, but the bolts will not.
We take in our hands (in chorus!) “Bulgarian ...
Loosen the stabilizer bolts
We unscrew the last levers, those same thrusters.
Suspension disassembled
And here is a set of new parts, waiting for installation
do not rush to copy the numbers from the boxes. This article does not discuss manufacturers and the method of repair (replacement of silent blocks or the entire lever)
Install the thrusters first. Don't confuse left with right! (for some models from a certain year they may be symmetrical)
-before pressing 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 need to be combined with the protrusions of the lever
To avoid displacement, you can mark with a marker
And you also need to consider that the bushing of the silent block is narrower than the lever itself
And this is where the marker comes in handy.
We press in
However, you can use a more accurate measuring tool.
We install the levers in the beam, insert new bolts and new eccentric washers
We fasten the stabilizer in place, already with new racks
We turn over the beam, we take the upper levers
Please note that the silent blocks are almost identical in appearance, differ only in the internal 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 that certain dimensions must be adhered to during installation and pressing,
I do this: before unscrewing the central bolt, I measure the distance between the lever and the body
Then you can unscrew the central bolt
Before removing the old silent block, it is convenient to make a mark on which to orient the new silent block
By the way, the separation of this silent block can be considered only after dismantling
Already familiar extraction procedure
we clamp the lever in a vise, install the body, bait the central bolt. We set the required distance, tighten it first, then clamp the body itself into a vise, 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 the spot
I will share little secret: the clip of these silent blocks is plastic, and for easier removal, you can use an industrial hair dryer or even a compact gas burner. Jumping 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 whole procedure, but it is worth paying attention to a few points:
- there are several washers in the bolt-nut connection.
They are placed like this:
screwing trailing arm to the steering knuckle, do not tighten them immediately, as you must first insert the stabilizer strut bolt.
And in general, you can not tighten any of the fasteners up to a certain point, only bait and twist.
To make it more convenient to insert the beam into place, you can cut off the heads of a pair of old bolts and use them as guides
This will make it easier to line up the holes.
Springs must be installed in a strictly defined position. This can be helped by a protrusion on the rubber sole, which must be inserted into the reciprocal hole of the lever
A jack or hydraulic rack is placed under the lever.
Align the holes, insert the bolt, screw on 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 it is necessary to tighten all the bolts and nuts.
Insert brake pipe into retainers
Connect connectors to ABS sensors
After that, you can fasten the wheels and go straight to the camber / convergence stand.
For your own peace of mind, you can re-tighten all the bolts and nuts securing the levers when the car is on wheels.
In the usual sense, the direction of movement of the car changes when the steering wheel is turned, which transmits force to the front wheels through a simple mechanism, thereby turning them either to the left or to the right. Well rear wheels, of course, move exclusively in parallel, but what else? They don't make any turns, do they? Yes, for the most part this is true, as it applies to the vast majority of cars. But for some modern cars established special devices, which actuate the mechanism of a kind of steering rear wheels. So why did they invent such an innovation and on what principle does it work? We will tell you about this and much more later in this article.
Thruster suspension - the history of creation
There is no limit to perfection, and therefore today a priority factor in the creation of new automotive systems is improved handling. Although modern existing systems car controls perform their functions well enough, restless developers all compete in the pursuit of creating additional devices positively affecting steering. Current and all acquaintances include traction control systems and systems.
But even before the full introduction of all kinds of gadgets and microprocessors into vehicle control systems, there were other developments that were not so technically complex, but useful in terms of improving handling. These include the rear wheel steering system.
Examples of ground mobile units with installed system taxiing rear axle could have been seen hundreds of years ago. This principle has long been successfully applied in forklifts that operate in tight spaces. warehouses, in factories and other places. Such a system was used back in the late thirties on agricultural machinery and SUVs, for example, in the pre-war “rogue” Mercedes Kübelwagen G5.
Types of thruster suspension on modern cars
In the first rear wheel steering systems, the steering angle was impressive and amounted to about 15 degrees. When the rate of produced Vehicle began to increase significantly, such large angles had to be cut. In modern cars, the steering angle reaches a maximum of 8 degrees. The rear thruster suspension is divided into two types: active and passive. More on this later.
Active
In a car equipped with an active rear wheel steering system, all four wheels turn at once with the movement of the steering wheel by the driver. IN modern machines transmission of force through steering wheel carried out not through mechanics - a lever system, but through the command of the computer and retractor relays, which are also called actuators. They move the rear tie 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, when the front wheels turn in one direction, the rear wheels turn in the opposite direction. Due to this, the turning radius is reduced by 20-25%.
On high speeds working scheme changes. When turning the front wheels, the rear ones steer, but with a smaller angle. At what angle to turn the rear wheels, the electronic control unit controls, guided by the readings of the angular acceleration sensor, as well as the speed sensor and others. Based on the readings, an optimal algorithm for passing a turn is formed.
Most known systems rear suspension steering from Japanese manufacturers. For example, Honda introduced steering option rear axle back in 1987 on sports coupe Prelude models. A year later, Mazda introduced 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 placed on Suburban SUVs and Yukon and Silverado pickup.
At Nissan the steering system was called HICAS. At the beginning of production, it was powered by a hydraulic mechanism and was combined with a power steering. She was placed on Nissan models and Infiniti rear wheel drive. But in the mid-nineties, such a system was abandoned, since it was complex and did not differ high reliability, and switched to actuators.
In 2008, Renault-Nissan introduced Renault Laguna With new system steer the Active Drive rear suspension. The Europeans also did not stand aside. For example, BMW company introduced a steering system called Integral Active Steering to 7 series and 6 series Gran coupes.
Passive
Many modern cars are equipped with a simplified rear wheel steering system. Elements with certain characteristics are built into the rear suspension. physical properties, counteracting the inertia of rectilinear motion. This type of steering is called passive. In such cars, the rear suspension is designed according to a special geometry using Watt's movable rod.
The system is built in such a way that when you gain enough 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 by the installation of silent blocks of a certain elasticity and shape. This design has a positive effect on the stabilization of the car when cornering. Such a system was equipped with the 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, engineers have taken into account the thruster properties. But some manufacturers, such as Ford, have given Special attention these properties and singled out the design into one special system.
Advantages and disadvantages
And in conclusion, we will discuss the main pros and cons of the thruster rear suspension. TO positive aspects This includes an increase in maneuverability due to a smaller turning radius and an improvement in 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 the cost of repairs.
