The car as a mechanism is sufficient simple, and reached the level when it is actually nothing to improve. But the battle for more comfortable and safe management of the vehicle does not stop, and engineers of the whole world create all sorts of additional devicesdesigned to facilitate the management process, help the driver in emergency situation Faster to make a decision, or vice versa, do not perform a fatal error.
Here you can attribute hydro and electric power steering, ABS, a system of course stability and other technical solutions, actively and passively involved in management. In this article, we will talk about such an option as a raising rear wheels.
What do you need twisting wheels
The inertia of the rectilinear movement of the rear wheels, especially on high speedslargely affects the car handling when entering turns. Simply put, they resist turn, seeking to stay on their former trajectory. Justice It is worth saying that the idea itself is not new, and the raising rear wheels have long been used on the loaders who are forced to maneuver in closed warehouse spaces. A pre-war Jeep Mercedes Kübelwagen G5 was also equipped with twisted wheels.
Today, many famous automakers have a similar system developed and implemented. All of them have their own name, differ constructively, but the essence remains unchanged - the rear wheels change their position when turning, reducing the trajectory and increasing stability.
Types of sweeping suspension
A pouring suspension can be active, or passive. If the first is working at the expense of electronics, then the second with the help of levers and thrust, as well as the laws of physics. Consider each separately.
Passive
By itself, the topic is quite large and complicated. AT general features The principle of operation of the passive pouring suspension can be described as follows. Mutually located levers and specially attached pillows and silent blocks have been added to the rear suspension. Under the influence of the car lateral forces and during the formation of a roll in turn, these elements ensure the effect of a small rotation of the wheel, even the indicator of several degrees significantly improves the entry of the car in turns.
For straight movement vehicle, rear wheels take a neutral position, the suspension continues to work only in the vertical direction. Various modifications Passively, the pussy suspension is present in such cars as Ford, Peugeot, Toyota with a number of others.
Active
More progressive and expensive is the active infringement system. In it, the rear wheels are answered by the actuators, the coherence and the clarity of which electronics are monitored. Here everything is arranged in such a way that all 4 wheels react to turning the steering wheel. The angle of rotation is calculated electronic block The control, which, in turn, is guided by the testimony of all sorts of sensors, and calculates the optimal angle.
In addition, such a suspension has several modes of operation. At low speeds, when the driver maneuverates in the parking lot and other bounded spaces, the rear wheels are turned into the opposite side from the front (grind the steering wheel to the right, the rear is twisted to the left). Due to this, the car becomes significantly maneuverable, the rotation radius is reduced by a quarter.
At high speeds, everything changes, and the system switches to the mode when the rear wheels rotate towards the rotation of the front wheels, providing optimal conditions for entering the turn.
Today active systems Renault (Active Drive), BMW (Integral Active Steering), Nissan, Infiniti boast.
Advantages and disadvantages
In completion, we note the advantages and cons of the twisted wheels:
- to positive sides It is possible to include an increase in maneuverability due to the smaller radius of rotation, improving the controllability of the vehicle;
- the most serious minus can be considered the complication of the suspension design, which leads to its declaration, and also increases repair costs.
The idea of \u200b\u200bmaking rear wheels managed is a well forgotten old. In fact, making controlled rear wheels originated during the times of wooden wagon (the so-called slaveless wagons). But the company in his new model 911 GT3 decided to remember the old idea and, using modern technologies, equip your novelty managed rear wheels.
Why in old times on carts made controlled rear wheels? As a rule, most of the carts were used in rural areas for agriculture, where the relevance of limited reversal or turning, as ever is very important. In a new unique sports car, the GT3 system of controlled rear wheels is a unique development of a German company.
Since the appearance of official information about a novelty, disputes did not subscribe how the company has implemented the rear wheel control system, since a detailed release of the system has not been represented. Today our offers you two detailed video Roller, from which you learn how to turn along with the front, rear wheels that help sports car Not only easily undergo turns, but also increase the dynamics when overclocking.
In general, the idea to equip the rear-controlled wheels is a great solution for a sports car. It would be stupid if a similar system would appear on traditional city cars. Of course, new technology It has a greater complexity in the design, which makes the risk of complex repair in the event of a breakdown, but for those who buy similar cars, we think that for them the mainly indescribable sensations that this powerful sports car can give than the technical complexity of the design.
Video
Help 1Gai.ru: Porsche rear axle wheel management system - this is an electromechanical system for regulating the rear wheels. This system allows the car to take turns of any complexity at different angles.
On ne. large speeds Rear wheels are adjusted not synchronously with the front to ensure the steady passage of turns. For high speedAs the front and rear wheels rotate synchronously. Due to the peculiar change in the short size of the wheelbase, the car equipped with this system is more dynamic and resistant on the road. During sports competition, the rear wheel control system allows you to bypass rivals on turns.
The fact that we ruls exactly the front wheels are perceived as a matter of course. However, any more or less experienced driver He knows that on the car it is more convenient to park with the ass, that is, when the controlled axis is behind relative to the direction of movement of the machine. So why do the automakers do not make passenger cars with controlled wheels from behind instead of adopted now everywhere "front-controlled" standard?
Actual autonews
Existing systems of tuning rear wheels installed on some modern passenger and large trucks, the answer to the question of interest will not be given. They are twisted, and not rule. The main role is still playing front wheels. At the same time, there is enough transport in the world, which is controlled exclusively by the rear wheels. For example, all sorts of loaders: from warehouse fork babes to career giants. Increased maneuverability due to the rear steering wheels, for them - the need. So what is worse in this sense of passenger transport?
One of the first explanations of such "injustice" from the number of other coming to mind is the strength of the tradition. As the "motorism proof" did the front axis of the managing, and goes. But it sounds, you see, weakly weak. How many years have been accustomed and traditional, for example, rear drive. But as soon as they came up with a more convenient front, the whole world immediately silently on the "tradition" and reoriented to the front-wheel drive type of passenger cars. The second version explaining the fact of the prevalence of the front controlled wheels is technological. The driver sits in the front of the car, so the Baranka is also in the front of it. In such conditions, "pull" the mechanism of drive controlled wheels to the rear axis is to complicate the structure for absolutely no obvious advantages.
In short, the heater is not worth it. This version appears quite viable. The main reason why controlled wheels in most machines - front, completely different. Tip here can serve precisely high maneuverability of the same loaders, turning the rear wheels capable of turning around almost in place. The fact is that the rotating rear wheels report vehicle Excess turning. At speeds 5-10 km / h, it is good, providing great maneuverability. But when it comes to shooting a little greater, each turn of the rear wheels will lead to the drift of the machine's feed.
Actual autonews
Imagine the same loader riding a city street with a typical "automotive" speed of 50-60 km / h. The car in such a speed will calmly fit into a smooth turn of the road. And our conditional loader, in best casewill unfold sideways and, most likely, will also turn over. Now imagine what will be with a car ruling "ass" at speeds about 100 km / h, and even in the rain, when the road is slippery. The slightest rebuilding - and it will spin the wolf. That is why, by the way, on all modern cars equipped with a twirling rear suspension, at high speeds rear wheels turn into the same direction as the front - so that the car is moving towards almost sideways, and did not turn across the general direction of movement.
When japanese cars They were considered the most advanced, legends came that in the country of the rising sun there are cars that turn all four wheels. Then in the bustle of the new things, those times were somehow forgotten. The rapid beginning of the nineties has passed, and only the most necessary of the technical solutions remained in mass production. But now interest in full chassis is growing again, though on another technical level, without additional steering shafts and with a noticeably simplified rear suspension.
Well, alone, only on Porsche 911 GT3 or Lamborghini Aventador - but after all, on the usual Renault Espace, also introduce rotating rear wheels. What is the meaning of such a technical solution, and for which the manufacturers went to such complexity? And why did you forget about technology until recently?
Why do you need controllability
The controllability configuration has always been considered a very difficult job, and the perfect balance machines fell into the number of the best. The chassis of modern cars, at first glance, has changed little in comparison with the eighties, but there is difference. And it manifests itself perfectly if you look at the speed-reaching speeds on the "Perestrovka" maneuver or on the racing track.
Modern family hatchback is able to beat most of the supercars of thirty years old on the road, and not least due to the fine tuning of the chassis and excellent "chassis". Of course, rubber, and the elasticity of the motors also play their role, but now first of all we will talk about geometry.
No, we are not at all about the school subject - I'm talking about the geometry of the chassis. This is a set of parameters describing changes in the position of the chassis elements when the load changes. The essence of the focus is that when turning turns, the car leans, and the road has its own profile. With the correct calculation of the geometry parameters, the tire chassis are always optimal for these conditions. Contact with expensive.
It is not about the maximum clamping force here, but about the ratio of the coefficient of clutch of the wheels of the front and rear axle, the right and left wheels, and the ability of the wheel at each moment to perceive the load in three directions.
The task to increase the area of \u200b\u200bcontact of the wheels with an expensive is not so simple, as it seems.
Of course, you can "clamp" suspensions and make moving less. This is useful from many points of view, and often do it, but it can be used for a good deal. For example, that the wheels in turn rotate themselves. If it is difficult to calculate movements, you can play a little by putting it, putting steering And on the back axis, creating a full-controlled car.
And you can set the movement using a complicated suspension - for example, a multi-dimensional, which allows you to adjust the wheels movement geometry in very wide limits and save these parameters when the elements wear for a long time.
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If you are not a racer, it does not mean that handling is not important for you. Simply in your case, this term means a completely different set of preferred parameters than the perfect accuracy and speed of reactions. Actually, active security Machines largely depends on its controllability, and therefore over these parameters, car constructors work a lot and productively. And what does this have to do with the geometry of the chassis?
How the car turns
It would seem that it's easier: turned the front wheels - and the car turned. But in practice everything is more difficult. To start even on standing Machine Not only the front wheels will turn. Since the front suspension has an angle of the caster, then the front wheels are raised, each on its height. As far as it depends on the width and hardness of rubber, suspension geometry, and so on.
The car will result in some roll, depending on the height of the center of the front and rear suspension and the position of the mass center at this moment. Rear wheels or even continuous rear axle Also turn - just because with any change in the position of the body of the wheel, do not just go up-down, but also a bit, but turn.
In the dynamics of this pile of parameters, a lathe point from the center of mass machine and rubber leads is added. Among all the parameters that need to be calculated, the instantaneous center of rotation and the radii of rotation of the front and rear axes and the center of mass will be most important for us. The instantaneous rotation center does not match the geometric, which is calculated according to the akkerman rule - a point in which the centers of rolling circumferences of all wheels are located. Moreover, in the dynamics of such a point simply does not exist due to slides. But in the figures for example, a simpler situation is considered not to bring confusion.
At first glance, if you print the rear wheels in the opposite from the front side, the rotation radius of the machine decreases. This is important in terms of ease of operation and maneuverability. The smaller the radius, the more convenient. But the cars ride not only at the speeds of loaders in the mall, so you have to take into account other factors.
And what if turning the wheels in the same direction as the front? At first glance, nonsense: the car "will go sideways" by a large radius if the rear wheels are rotated to a smaller angle than the front. By itself, the larger turning radius means that there will be less than the redistribution of loads between the right and left wheels, and therefore better clutch Wheels with expensive and comfort.
But it seems that you can achieve the same, just turning the steering wheel to a smaller corner? You can even do it automatically - good, steering mechanisms with a variable step are not uncommon now. But when turning the rear wheels towards turning, the angle of the rear axle is also reduced, which means that the tendency to excessive turning. If it is completely simple - the car becomes more resistant to the occurrence of drift. At high speeds it is extremely important.
Similar effect could be obtained by a simple increase in the wheelbase. But the size of the machines are limited - it is possible to get the desired, without increasing the dimensions by changing the angle of rotation of the rear wheels. And for a short-passage car, it is just a salvation: you can save a combination of sustainability on the road characteristic of large carswithout damaging good turning.
Not only control
For stability on the road, the rear wheel in turn should be rotated towards the turn of the front, and for the best maneuverability - in the opposite. If there are no special difficulties with maneuverability, then you can use for the rotation of the wheels features of the movement of the machine in the turn. For example, the presence of a roll. When compressing the suspension will be protected, and we get the desired.
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But there are two problems. First, the suspension reacts in the same way to change the load, and I would like the handling less dependent on the load and more from the roll and lateral efforts. Secondly, on rear-wheel drive cars, it is very seductive to tie a rotation of the wheels to the vector of thrust.
If you complicate the suspension, entering the levers that affect the corners of the wheels of the wheels at a certain load, then we will get a multi-dimensional suspension. Yes, the one that appeared on Mercedes W201 and is now applied on most C-class machines and higher. And not only on the rear axle, but also on the front.
It is a multi-dimensional suspension that made it possible to obtain the same effect as the forced turn of the rear axle, and refuse to apply complex coordination systems by a quarter of a century. The lever system in such a suspension sets a complex trajectory of the wheel movement depending on the longitudinal, transverse and vertical loads.
It can be quite accurate to adjust the geometry of the chassis, taking into account how the machine will behave when there is significant lateral forces, with a different ratio of vertical and transverse loads. For rear-wheel drive cars, it turned out to be a serious help in the struggle for better handling from the very beginning, and the front-wheel drives tried out such technology a little later, with an increase in mass, loads and requirements for their manageability.
First full-controlled lights
Machines with two controlled axes were not at all for excellent controllability. Such cars did not go along the highway at high speed, because these were all-terrain vehicles. For example, famous Unimog - Universal Chassis increased passibility It has all four controlled wheels. Of course, in order to better ride off the road and maneuver in a limited space.
Japanese cars of the beginning of the 80s, the complexity of the design near them left. On the Honda Prelde. 1987 was the rear steering Reika And the shaft connecting it with the steering wheel, and the system has worked depending on the angle of rotation of the wheels. At small angles turning the rear wheels turned into the same direction as the front, and at large - in the opposite. Even in this form, the effect turned out to be sufficient so that such technology also implemented other Japanese manufacturers.
Only on the next generations, the rear steering rack drive has become electrical, and the angle of rotation depended on the speed on which the maneuver was made. However, from the shafts and rails did not guess. The designs remained complex, massive, voluminous and expensive. As a result - cars with them did not discharge specially popularity and sold only in the inner Japanese market. In the rest of the world, unconditional leadership seized multi-dimensional suspensions.
Why again come full chassis
The most obvious answer to this question is to reduce the price of drive mechanisms and control electronics and the development of sustainability and safety systems. At the new technological level, they abandoned the rear steering trapezium and rails. Multi-dimensional suspensions Provide an adequate angle of trust of wheels to implement the desired effect. It remains to equip them instead of a lever that is responsible for the coating of the wheel, an active electrical or hydraulic drive.
Electronics is much more accurately determines what is happening at the moment with the machine, allows you to use big angles of delivery, and besides cheaper in the setting than a complex suspension. And as an additional factor is the most improved turning at low speeds. You can trust the wheels in the opposite direction and improve the maneuverability of the car on narrow streets.
Will not be surprised if such systems in the near future will be massively implemented on machines from C-class and higher, and in combination with simplified geometry rear suspension - For example, not with multi-dimensions, but with a twisted beam. Economic meaning in this definitely there is, because you can get handling like more expensive cars, at less cost. Yes, and another complex and expensive wear node will not be "superfluous". After all, car manufacturers seem to have committed to make a machine one-time.
When drivers are managed ordinary car, they turn steering wheel, and after this movement, the front wheels change their direction - while the rear wheels are constantly directed forward.
Such is the standard system called "two-wheeled taxi" or, abbreviated, 2 WS. However, some firms are currently producing four-wheeled cars (4 WS). 4 WS systems of different firms differ from each other, but in most of them the rear wheels turn into the same direction as the front, if the car makes a high speed. At low speeds, the direction of rotation of the rear wheels at 4 kr is the opposite direction of the turn of the front. Such a feature allows, in particular, to make sharp turns, which is useful when driving around the city or when parking in close places. Road tests of 4 WS systems have shown that such systems provide greater safety. Nevertheless, four-wheeled taxi did not receive even widespread. Due to the fact that the cost of 4 WS system, according to drivers, does not justify benefits from it.
Two wheels against four
In 2 kr cars (at the bottom left) only the front wheels are rotated. If the direction of movement is 4 cr of the car, then all four wheels can be rotated (right).
How 4 kr turn the wheels
Suppose two cars: 2 kr (blue) and 4 kr (yellow in the picture above) begin with one place (green) to do a slow steep turn. Thanks to the rotation of the rear wheels, the 4 Cr machine turns the cooler of the machine 2 kr and, it means that it needs less place to turn.
If these two machines will make a smooth wide turn (as shown on the right figure), then all the wheels of the machine 4 kr go, as they say, a rut of a rut, and thus ensures a more reliable clutch of wheels with a roadbed.
Change of traffic stripes
If the driver is rebuilt into another strip on the high-speed highway, then 2 kr of the car is manifested by the "Fish-tail effect": his back brings, because the rear wheels seek to go to the old direction. To correct this position, the driver has to turn the steering wheel twice before changing the strip and turn it twice after changing the strip. 4 kr car there is no fish tail effect.
Steering wheel and 4 WS system
sensitive sensors in the 4 kr system are watching how turned the steering wheel and, therefore, the front wheels at each moment of time (the red line is in the picture). When the angle of rotation of the steering wheel is small (the first two speakers), the 4 Cr system leaves the rear wheels directly or slightly turns along the direction of the front wheels. With more sharp turns - when the steering wheel makes more than one full turn (Fourth column) - System 4 Cr rotes the rear wheels in the opposite direction.
