In case of emergency braking of the vehicle, one or more wheels may be blocked. In this case, the entire margin of the grip of the wheel with the road is used in the longitudinal direction. A blocked wheel ceases to perceive the lateral forces that hold the car on a given path and slides along the road surface. The car loses control, and the slightest lateral force leads it to skid.rnThe anti-lock braking system (ABS, ABS, Antilock Brake System) is designed to prevent the wheels from locking during braking and to keep the car manageable. Anti-lock braking system increases braking efficiency, reduces the braking distance on dry and wet surfaces, provides better maneuverability on slippery roads, controllability during emergency braking. In the asset of the system, less and even tire wear can be recorded.rnHowever, the ABS system is not without a drawback. On a loose surface (sand, gravel, snow), the use of an anti-lock system increases the braking distance. On such a coating the smallest braking distance is provided just when the wheels are locked. At the same time, a wedge of soil is formed in front of each wheel, which leads to a reduction in the stopping distance. In modern ABS designs, this drawback is almost eliminated - the system automatically determines the nature of the surface and for each implements its own braking algorithm.rnThe anti-lock brake system has been available since 1978. Over the past period, the system has undergone significant changes. Based on the ABS system, a brake force distribution system is built. Since 1985, the system has been integrated with traction control. Since 2004, all cars manufactured in Europe have been equipped with anti-lock brakes.rnThe leading manufacturer of anti-lock braking systems is Bosch. Since 2010, the company has been producing the 9th generation ABS system, which is distinguished by the smallest weight and overall dimensions. So, the hydraulic unit of the system weighs only 1.1 kg. The ABS system is installed in the standard brake system of the car without changing its design.rnThe most effective is the anti-lock brake system with individual wheel slip control, the so-called four-channel system . Individual regulation allows you to get the optimal braking torque on each wheel in accordance with road conditions and, as a result, the minimum braking distance.rnThe design of the anti-lock system includes wheel speed sensors , a pressure sensor in the brake system, a control unit and a hydraulic unit as an actuator.
rnA speed sensor is mounted on each wheel. It captures the current value of the wheel speed and converts it into an electrical signal.rnBased on the sensor signals, the control unit detects a wheel lock situation. In accordance with the installed software, the unit generates control actions on the actuators - electromagnetic valves and the electric motor of the return pump of the hydraulic unit of the system.rnThe hydraulic unit combines the inlet and outlet solenoid valves, pressure accumulators, a reverse feed pump with an electric motor, damping chambers.rnIn the hydraulic unit, each brake cylinder of the wheel corresponds to one inlet and one exhaust valve, which control the braking within its circuit.rnThe pressure accumulator is designed to receive brake fluid when depressurizing the brake circuit. The reverse feed pump is connected when the pressure accumulator tanks are insufficient. It increases the pressure relief rate. Damping chambers receive brake fluid from the return pump and dampen its vibrations.rnTwo pressure accumulators and two damping chambers are installed in the hydraulic unit according to the number of hydraulic brake circuits.rnThe control lamp on the instrument panel indicates a system malfunction.rnThe principle of operation of the anti-lock brake systemrnThe operation of the anti-lock braking system is cyclical. The system operation cycle includes three phases:rn1. pressure retention;rn2. pressure relief;rn3. increase in pressure.rnBased on the electrical signals from the angular velocity sensors, the ABS control unit compares the angular velocity of the wheels. If there is a danger of blocking one of the wheels, the control unit closes the corresponding intake valve. The exhaust valve is also closed. There is a retention of pressure in the circuit of the brake cylinder of the wheel. Further pressing the brake pedal does not increase the pressure in the brake cylinder of the wheel.rnIf the wheel lock continues, the control unit opens the corresponding exhaust valve. The inlet valve remains closed. Brake fluid is transferred to the pressure accumulator. There is a pressure relief in the circuit, while the speed of rotation of the wheel increases. In case of insufficient pressure accumulator capacity, the ABS control unit connects the return pump to operation.
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