The anti -lock brake system (ABS) prevents wheels lock by modulating braking pressure. These systems play an important role in improving the safety of modern vehicles. Braking is difficult, especially on ice or wet road, which can cause one or more wheels to block. This can lead to a longer stop or even to loss of controllability. The ABS system controls the speed of the wheel in real time and automatically adjusts the braking pressure to prevent wheel locks and improve the driver’s control over the vehicle. Currently, they are often combined with other systems such as electronic brake force distribution (EBD), electronic stabilization system (ESC) and traction control to further increase the handling of the driver and security of the driver. The main components of these systems are the regulatory parts of the brake system (for example, the brake pedal, hydraulic cylinders and lines), wheel rotation sensors, as well as a hydraulic modulator with an electronic control unit. ABS architecture (including a hydraulic modulator) is shown in the figure below.
Architecture ABS
When working in normal conditions, the exhaust valve (C) of the hydraulic modulator closes, and the inlet valve (a) remains open until the pressure reaches the required value. Whereas intake and exhaust valves remain closed to keep this pressure and provide a sufficient brake moment for the wheel brake cylinders. After the control unit detects any excessive wheel slippage, the corresponding exhaust valve opens to dump the pressure into the battery (D) and prevents the possible blocking of the wheel. Excess of the brake fluid is returned to the main brake cylinder through the reverse pump (E). After the rolling of the wheels is returned to the normal state, the valve solenoids are de -energized and the hydraulic modulator resumes the regular process of braking.
Antibular brake systems can be classified on the basis of the number of channels, and the number of sensors used.
Four channels, four ABS sensors — this type of ABS uses a speed sensor and separate valves for each of the four wheels. The maximum braking force is achieved with this type.
Three channels, three ABS sensors — the front wheels have a sensor and a valve. There is one valve and one sensor for both rear wheels.
One channel, one ABS sensor — one valve and speed sensor located on the rear axle control both rear wheels. This type of ABS is usually observed in pickups.
Sliding coefficient.
Sliding coefficient is a means of calculating and expressing the locking position of the wheel. This is the ratio of the difference between the speed of the vehicle and the speed of the wheel to the speed of the car. For example, when the vehicle operates in normal mode on the perfect surface of the road, the sliding coefficient is 0; When the wheels are blocked, the sliding coefficient is 1. During braking, the sliding coefficient increases, the ABS system supports the perfect sliding coefficient from 0, 10 to 0, 30 based on the characteristics of the road-shine. Thus, the vehicle supports maximum braking without a complete loss of steering ability.
ABS systems are required on vehicles sold in Europe. They are also required on trucks and buses sold in the United States. Although ABS systems are not clearly required on cars sold in the United States, they are on almost every new car due to the fact that the United States requires electronic system control (ESC). ESC cars have computer braking control for each wheel, so the introduction of ABS by car with ESC is relatively easy and inexpensive.
Sensors: The wheel frequency sensor Executive mechanisms: hydraulic modulator, main cylinder, brake cylinders of the wheel, signal lamp. Data transfer: High -speed CAN Tire. Manufacturers: Bendix, Bosch, Continental, Haldex, Kawasaki, Mitsubishi, Trw, Wabco