Whether it was necessary to you to go round suddenly arisen obstacle and simultaneously to brake? For certain yes. It would Seem that in it difficult — has pressed a brake, has turned a wheel and has corrected a trajectory. However all is rather simple till the certain moment. If at emergency braking to press a pedal of a brake is stronger, than it is necessary, wheels can be blocked and …
Two variants of succession of events Further are possible. Both are caused by presence or ABS — Anti-lock Brake System. If the car archaic, conducts the family tree from the middle of the seventieth last century or has descended from the conveyor of one of domestic car factories, that, is as though assiduous you twisted “steering-wheel”, the vehicle of a trajectory will not change. The matter is that the blocked wheels, sliding, deprive of the driver of possibility to maneuver — having broken on skid, the car it will be stupid to go on a straight line as if at it have chopped off a wheel. Only skilled pilot will manage to unblock coolly wheels, for an instant having released a brake pedal. And then, using pulse braking, to return the control and to reduce speed. The second variant — for the car equipped ABS. From the driver it is required to press more feasibly only a pedal of a brake and easy to work as a wheel. Feel a difference? For 30 years the system has undergone strong changes. In tens times speed and quantity of cycles of operation for a time unit have increased. So, for example, the first blocks of management for cars weighed more than 7 kg. Modern much more compactly also pull kg on ones and a half.
Blocking is dangerous also that is capable to become the reason of drift or car withdrawal aside. Occur it can, when under wheels a diverse covering, loading on axes is strongly changed during the previous maneuver or there are different tyres (the last sounds wildly, but in Russia, alas, not a rarity). Besides, at the blocked wheels the car can change a trajectory under the influence of any lateral force (a bias of road or collision). To correct a trajectory in this case it is almost impossible. In ABS for definition of speed of rotation induction gauges of frequency and the gauges working on effect of the Hall are used. Each new generation of wheel gauges of frequency of rotation becomes less, more precisely and more reliably. At first one sensor control which was mounted on a reducer of the back bridge or a check point was established only. Later to it two were added more — on forward wheels. And only in last versions ABS installation of gauges on each wheel, accordingly, with individual modulators is provided. By the way, the most ancient and primitive single-channel ABS influenced at once all brake mechanisms. One more negative effect of blocking — increase in a brake way. Here all the matter is that force of a friction of rest usually is more than force of a sliding friction. Hence, for as much as possible fast stop of the car it is necessary to generate such size of pressure in brake highways that wheels at braking rotated on the verge of blocking. There is such important indicator, as relative slip. It depending on degree of block of a wheel can vary from zero (the wheel slides without slip to 100 % (the wheel is completely blocked). It is experimentally established that peak efficiency of braking is reached at 15–20-% slip — that is in that case, when speed of rotation of the braked wheel on 15–20 % below speed free-rotary wheels at constant speed of movement of the car. Running forward, say, that electronics at braking supports this size, periodically blocking and deploy wheels.
Into structure of almost any modern system ABS enter: the electronic block of management (1), the modulator (2) changing pressure in hydraulic highways, gauges of angular speeds of rotation of the wheels (3), the naves of a wheel established on an internal part. The progressive mankind has definitively realised harm of the blocked wheels only in 70 last centuries. The pioneer in the field became Mercedes-Benz, together with company Bosch developed system which in 1979 began to be established on S-class Mercedes. The main principle of work ABS has been generated then, and then only was improved. Modern electronics (ABS, the system, ESP) to keep control of cross-section and longitudinal dynamics of the car, considers not only frequency of rotation of wheels. The wheel angle of rotation, degree of a list of a body, acceleration … Pressure in brake contours are under control is generated on set of the received data, plus in certain cases compulsorily changes draught of the engine. Problem ABS — to regulate speed of rotation of wheels by change of pressure in highways of brake system. To supervise angular speed, it is necessary to know its size and how it varies in due course. Each wheel is supplied by the gauge which gives out electric impulses with the frequency proportional to speed of rotation of a wheel. This information arrives in the block of management ABS.
If during braking angular speed of a wheel has come nearer to zero, the artificial intelligence there and then will make its decision. The hydraulic modulator by means of the electrovalve will pit pressure from a highway and will redirect “a superfluous” portion of a brake liquid to the hydroaccumulator. Pressure will decrease until a wheel, again “having grasped” a covering, will not be untwisted till certain speed. Further ABS again will sharply increase pressure in a highway and will brake a wheel. The cycle will proceed until the car will not stop or the driver will not weaken pressure upon a pedal before position when ABS it is not necessary. Systems existing in the market differ rather exact adjustment and provide peak efficiency of braking. Many will tell: «the knowledge Is insignificant!» Falteringly it is possible to brake also most. And the truth: in many cases such way of delay on the cars which have been not equipped ABS, allows to go round suddenly arisen obstacle during emergency braking. When wheels are blocked — you brake, as soon as “are released” — have an opportunity to correct a movement direction. Naturally, in this situation the brake way considerably will increase, but the driver will have an opportunity to go round an obstacle and anticipatory action of a wheel to extinguish drift. But, unfortunately, any titled racer is not capable to provide «ration» braking with frequency from which it does ABS. The system (depending on an execution variant) for a second has time to block-unblock wheels about 15 times. Besides the driver simultaneously influences all brake mechanisms (so the first systems ABS worked) while modern 4-channel antiblocking systems watch speed of rotation and regulate brake effort for each wheel separately.
In the majority of modern cars ABS works together with EBD (Electronic Brake Distribution) — system of distribution of brake efforts which doses out intensity of braking for each wheel. C EBD it is possible to brake safely in turn and on . Electronics on a difference of frequencies of rotation will understand that wheels have got on sites with a diverse covering, and will reduce brake forces on wheels which have the best coupling with road. By the way, intensity of delay in this case will decrease and will be defined by force of a friction of the wheel (wheels) having the worst coupling with road. It is not out of place to notice that for peak efficiency of delay the brake pedal on cars with ABS should be pressed into a floor that there are forces. However, the last to do to not necessarily those drivers, whose cars are equipped by system Brake Assist, which itself creates superfluous pressure in a brake highway, for the weak or irresolute person. At regular delays it does not interfere. However sharp pressing (blow) pedal Brake Assist regards as a signal to emergency braking and comes into effect. At braking on diverse coverings electronics will make everything to resist to drift. But sometimes the car equipped ABS and EBD, can develop strongly enough. Here all depends on how the system is adjusted.