Even a short brake pedal may cause wheel lock the vehicle, even on dry roads. Locked wheels cannot react accordingly to lateral forces and the vehicle cannot turn while braking. ABS recognizes one or more wheels tend to lock and keep constant or reduce brake pressure and thus the wheels do not lock. The vehicle remains steerable during braking and the driver can choose the desired trajectory.
The main components in the ABS system are:
- Aggregate ABS Hydraulic consisting of hydraulic unit that intervenes with braking forces and a microprocessor control unit;
- The speed transducer which monitors the rotational speed of each wheel;
When the brake is applied, the master cylinder and servo amplifier creates brake pressure required. The control unit that continuously monitors the situation braking system and sensor rotation intervene if detects a tendency to lock one or more wheels, adjusting the pressure to each wheel independently.
The operating principle is simple and effective. Each sensor monitors a wheel and when that it is no longer revolves send signal to the computer, which weakens the tightening exercised brake pads on the disc or drum allowing the wheel to spin, and thus to retain grip after that it notices again moving pads gather again on disc or drum braking the wheel. If the sensor detects wheel lock again resumes the process. As seen is the pulse and the time intervals are irregular pulses.
Each caliper brake is hydraulically through a separate pipeline that comes from the central control unit. With one transducer at each wheel and each wheel is controlled separately, then any wheel is controlled individually and can have different behavior. The system works as follows: the brake pedal is operated directly on the brake caliper and starts the process.
Depending on the information received from the transducer, solenoid locks the brake pipes and do not allow liquid to flow to the caliper bracket in this way is no longer under pressure and unlocking system. With the supply conduit blocking the stirrup, unlocks a fluid return line. Everything happens at the central unit and is controlled automatically by computer according to: pressure on the brake pedal, how long it kept the pedal and information from transducers or other car systems.
On newer systems an important parameter that takes into account the ABS computer is the speed with which the brake pedal is pressed. Thus he notifies emergency and when the speed pedal is great computer maintains and increases the pressure in the brake system for a period even if you took your foot off the brake. This is BAS (Brake Assist System) – translation system Emergency Brake Assist.
Operation: braking pressure pump made by central servo vacuum inlet valve is transmitted by the wheel braking mechanism. The speed of rotation is reduced until the control unit to the ABS system recognizes the tendency of locking the wheel using the wheel speed sensor. If the wheel has the tendency to lock to prevent further increase in brake pressure, the inlet valve coil is energized, it is closed (the outlet valve is still closed) and the brake pressure remains constant. If the wheel speed drops below (wheel still has a tendency to lock) is fed coil valve outlet and it opens.
Brake pressure is reduced through the hydraulic accumulator. The hydraulic pump begins to work and pumping the brake fluid from the hydraulic pump central battery and the brake pedal to move slightly upward. Tended wheel lock is released, increasing its speed and blocking disappears.
For optimum braking is required another increase brake pressure at a certain speed of the wheel. To this end, coil inlet valve will not be fed (inlet valve opens), the hydraulic pump is still working, it absorbs fluid from hydraulic accumulator and discharges it into the brake circuit, brake pressure increases, and the wheel will be braking again. These phases are repeated up to 5 … .6 times per second and can recognize the pulsating movement of the brake pedal.