6.1.6. Anti-blocking system of brakes (ABS)
Braking is most effective, when coupling of the tire with a road surface the maximum. In the course of braking the tire slides on a surface, and district speed of a wheel becomes less speed of the car.
The anti-blocking system limits the pressure created in a hydraulic drive of brakes so that the size of sliding was optimum. Action of this system should be separate for each wheel. The system should answer immediately each change of a surface (factor of coupling) and load of the car.
The anti-blocking system interferes with blocking of wheels at sharp braking thanks to what the brake way decreases. Force of adhesion between wheels and the road in this case is more, if when braking wheels continue to rotate. Even at complete braking the car remains operated. Sensors of frequency of rotation, on one on each wheel, measure frequency of rotation of a wheel. On signals of sensors the electronic control unit calculates the average speed approximately corresponding to speed of movement of the car. Comparing speed of rotation of each separate wheel with the average calculated speed, the electronic block defines a condition of a proskalzyvaniye of a separate wheel and by that, establishes which wheel is in a preblocking condition.
When one of four sensors of speed of wheels transmits a signal about blocking of the corresponding wheel, the electronic actuation device immediately gives out a signal of closing to the corresponding inlet electromagnetic valve which blocks supply of brake liquid via the pipeline to a wheel brake. Thus force of braking remains to a constant. If sliding proceeds, the final valve and pressure in hydraulic system of this brake opens decreases. The wheel does not brake, surpluses of brake liquid come back to a tank. As soon as the wheel again will start to rotate, the inlet valve opens, and final – is closed. Pressure increases in a contour, and the wheel again brakes.
Change of cycles of braking and free rotation of a wheel occurs very quickly (several times in a second) and proceeds to a stop of the car or to an otpuskaniye of a pedal of a brake.
Process repeats at sharp braking separately for each wheel until the brake pedal will be released.
The emergency system provides ABS shutdown at any malfunction or a low voltage in an onboard network of the car (below 10 In). Malfunction of ABS does not influence work of brakes.
The hydraulic drive consists of the hydraulic block, supports of brakes and brake tubes. The electric pump creating pressure, and electromagnetic valves enter into the hydraulic block.