Details of anti-lock braking system and vehicle stability control system: 1 - bracket for mounting hydraulic units, 2 - vacuum pump for brake booster (only for petrol engines with automatic transmission), 3 - control device for anti-lock braking system with electronic differential lock (J104), 4 - hydraulic 6noK (N55), 5 - pressure sensor in the brake drive system, 6 - hydraulic control unit (J104 and N55), 7 - speed sensor rotor (front right), 8 - front right speed sensor (G45), 9 - contact of the signaling device for low level of brake fluid (F34), 10 - combined instrument, 11 - push button for adjusting the traction of the drive wheels (E132), 12 - steering angle sensor (G85) in the presence of a vehicle stability control system, 13 - lateral acceleration sensor (G200) and speed sensor (G202), 14 - switch for signaling device for turning on the parking brake system (F9), 15 - speed sensor rotor (rear right), 16 - rear right speed sensor (G44), 17 - rear left speed sensor (G46), 18 - speed sensor rotor (rear left), 19 - signaling device for traction control and vehicle stability control (K86), 20 - signaling device for anti-lock braking system (K47), 21 - control lamp (K118) «Brake system malfunction», 22 - brake light switch (F), 23 - speed sensor rotor (front left), 24 - front left speed sensor (G47).
Anti-lock braking system control device. This device is located in the engine compartment on the left. It constantly processes the speed data from the wheel sensors and compares it with programmed values. If the wheels begin to rotate at different speeds, which indicates the danger of blocking one or more wheels, then the control device activates the hydraulic unit and the pressure for the corresponding wheel is reduced until it starts to rotate freely again, after which the braking process can be renewed. Depending on the condition of the road during braking, these changes can occur with an interval of several milliseconds.
The control unit is also responsible for a number of systems to improve the vehicle's safety while driving. These systems include electronic brake force distribution, electronic differential lock and electronic vehicle stability control.
Electronic brake force distribution (EBV). A special program in the anti-lock brake control device regulates the brake pressure in such a way as to protect the rear wheels from exceeding the brake pressure. There is no need for a brake force regulator or pressure reducing valve.
Electronic differential lock (EDS). This device is used when starting off. When accelerating on a slippery road, it automatically brakes the slipping wheel. In this case, the drive torque is transmitted through the differential to the wheel that does not rotate. In front-wheel drive models, the differential lock regulates speeds up to 40 km/h, in all-wheel drive models up to 80 km/h. This device is complemented by an anti-slip system. The traction control system does not intervene in the regulation of braking, but in the management of the engine. If the speed sensors, which are part of the anti-lock braking system, receive data on wheel slip, then engine power is reduced. This regulation is carried out at any speed.
Electronic Vehicle Stability Control (ESP). This system automatically reduces the risk of skidding and thus improves vehicle safety in critical situations. The system is able to brake individual wheels, which helps to stabilize the car if it tends to skid. If, for example, the rear of the car begins to skid, then the anti-lock braking system slows down the front wheel, which is located on the outside of the turn. The electronic stability control system, which is available at an additional cost, requires an additional hydraulic pump, which, if necessary, creates the appropriate pressure in the brake actuator (see also technical vocabulary in chapter «Chassis»).
Hydraulic block. The main part of the anti-lock braking system. This unit is screwed to the control unit and can only be separated when dismantled. The block consists of an electric pump and a valve block with solenoid valves. If the anti-lock braking system starts to operate, the control device gives a command to reduce the pressure in the brake actuator. Brake fluid flows from the valve block directly into the expansion tank. If the pressure in the brake actuator rises again, then the brake fluid from the reservoir through the hydraulic pump is fed directly into the corresponding brake circuit. The operation of the pump can be seen on the brake pedal - the pedal begins to pulsate slightly.
The hydraulic block and the control device form one unit. Due to the direct connection, fault sources are eliminated. The screws connecting the individual parts of the hydraulic control unit must not be loosened. The block is not repaired, but replaced
Speed sensor. The sensor is mounted on each wheel at a small distance from the toothed disk (rotor), which is rigidly connected to the wheel hub. The rotor, together with its toothed protrusions, depending on the speed of rotation of the wheel, rotates past the sensor faster or slower. Each tooth of the encoder induces a voltage pulse. Due to this, an alternating voltage is produced in the sensor, the frequency of which changes in accordance with the speed of the wheel. Thus, the sensors measure the rotational speed of a particular wheel and transmit it in the form of an electrical signal to the control device.
Malfunctions of the anti-lock braking system. The anti-lock braking system warning light comes on when the ignition is turned on and goes out when the engine is running. This happens no later than after 2 seconds, and also if the speed exceeds 6 km/h. If the warning light comes on while driving, it means that either one of the wheels is spinning for more than 20 seconds, or there is a malfunction in the anti-lock system. Another reason could be a voltage drop below 10 volts. Even though the warning light comes on, you can continue to drive, but the brake system functions as if the car does not have any anti-lock system. In this case, be careful as the electronic brake force distribution does not work and the rear wheels may lock up.
To eliminate this defect, you should contact the workshop. In the workshop, using a special device, they will interrogate system fault codes that are stored in the memory of the control device.
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