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Brakes
For vehicles used by the service braking system with hydraulic drive.
The system operates as follows:
- The brake pedal is connected to the master cylinder;
- When the pedal is depressed, the pressurized fluid from the master cylinder by the metal tube and the flexible hose is transmitted to the front and rear brakes;
- The wheel cylinders are hydraulic modulators that convert the fluid pressure generated in the master cylinder to the brake moving element;
- Front and rear brake caliper pistons move, and by the friction of the brake discs and drums provide the required vehicle deceleration;
- When the brake pedal is released, the pressure in the system decreases. Brake pads and the pistons return to a neutral or home position and deceleration stops.
By reducing the brake fluid level, liquid level sensor in the master cylinder includes a warning lamp in the instrument cluster. If the warning lamp lights up, first check that the parking brake is released, as the lamp is indicating a reduced level of the liquid and apply the parking brake.
The braking system on the car
1 - the brake pipe;
2 - the brake pedal;
3 - the master cylinder;
4 - the vacuum brake booster;
5 - front disc brakes;
6 - a support; | 7 - Rear drum brakes (CBS);
8 - the parking brake;
9 - the parking brake cable;
10 - the parking brake lever;
11 - line pipe high pressure braking system;
12 - rear disc brakes (ABS) |
Anti-lock brakes (ABS)
Anti-lock braking system is designed to eliminate wheel lock under heavy braking.
The main function of ABS:
- Reducing the stopping distance by eliminating the wheels from locking under heavy braking;
- Improve the steering stability during braking.
Anti-lock brake system operates on the basis of information from four sensors transmit unit ABS. The system controls each wheel individually and reduces the fluid pressure in the wheel brake, the wheel is starting to be blocked.
Location of anti-lock brakes (ABS) on the car
1 - hydraulic control unit (HCU);
2 - a rotor of the wheel speed sensor; | 3 - wheel speed sensor;
4 - union pipelines |
Under normal conditions, the standard braking system provides braking torque to the wheels blocking, the detected block of management ABS. During normal braking the inlet valves are normally open and the exhaust valves are normally closed.
When the ABS control unit detects wheel lock, it controls each valve to increase or decrease the pressure.
ABS control unit determines the speed and rate of deceleration of each wheel on the basis of information from the wheel speed sensor. When braking wheel speed decreases, and the ABS unit determines a difference between the vehicle speed and wheel speed. If the deceleration of some of the wheels exceeds the expected value, ABS unit determines the beginning of the lock and opens the corresponding solenoid valves to reduce the pressure of the brake fluid.
| At this wheel speed increases and the solenoid pressure relief valve is closed and there is an increase of the brake pressure in the wheel cylinders of the corresponding wheels. |
ABS control unit
ABS control unit performs the following functions:
- Controls the ABS;
- Calculates the speed of the car;
- Carries out a self-test of the system: a self-diagnostic fault codes, and safety functions shall be stored in two separated microprocessors.
ABS control unit continuously checks the blocking of each wheel, and controls each valve to regulate the pressure of the brake fluid, if necessary. ABS control unit also checks that the components are operating properly, and turns off the ABS, in case of failures. Then the brake system works like a standard braking system.
RPM Sensor
| The speed sensor detects the rotation of the wheel and comprises a permanent magnet and coil. The sensors of the front wheels receive information from the toothed rotor disposed on the drive shafts. |
| When passing near the sensor rotor teeth, changing the magnetic field sensor, whereby the generated voltage pulse. This voltage is proportional to the wheel speed and can be measured. |
ABS warning lamp
ABS warning lamp located in the instrument cluster comes on for 2 seconds after ignition.
| If the ABS warning lamp does not go out 2 seconds after the ignition is switched on, or lights up periodically, so in ABS there are infringements.
If there is violation of the brake system works like a standard braking system. |
Hydraulic control unit (HCU)
Hydraulic control unit (HCU) consists of a pump with an electric motor and the valve block to control the pressure ABS.
The sensor is located in the motor and pump unit transmits the output signal ABS, which defines the performance of the pump.
| The diameter of the front opening of the pipe supplying the brake fluid:
The front left and rear right brake: 12 mm
Front right and rear left brake: 10 mm |
The pump with two circuits provide the required pressure and flow valves distribute the pressure transmitted to the wheel brake.
ABS self-diagnosis
ABS control unit begins to perform self-diagnostic function after switching on the ignition. ABS control unit detects a fault for each circuit and a component by comparing the state of the system with a limited set of conditions in the block of management ABS. ABS control unit stores a fault code and then displays a diagnostic tool in the form of code, referred to four digits.
Check self-diagnosis codes
| PERFORMANCE ORDER | | 1. Turn the ignition key to the OFF position and connect the scan tool to the diagnostic socket. | | 2. Turn the ignition switch to the ON position and set the device to your car model and model diagnostic tool. | | 3. Select the parameters to be checked after the initialization block. |  | 4. Click the check codes ?��1 and find out whether the problem is recorded. | |
A warning  Fault code - a four-digit number that appears continually until the DTC does not wiped off the diagnostic tool.
| | 5. In the list of fault codes, identify the faulty item and restore its performance. | | 6. After erasing fault codes from the memory control unit for ABS, select inspection post ?��4. |
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Precautions before repair
1. To prevent damage to the braking system before repair or diagnose the following conditions hold:
- Switch off the ignition and disconnect each component of the braking system;
- Components that are not repairable, replace the node;
- When using electric welding disconnect each component of the brake system.
2. The brake liquid dissolves a paint, plastic and wire insulation, so if you accidentally hit fluid on the paintwork of a vehicle or its components, rinse with plenty of water.
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