TIAGO TIGOR CNG - SERVICE MANUAL

BRAKES 16 C. BRAKING WITH ABS INTO OPERATION: In the case of braking where the ABS ECU detects a significant difference in the wheel speed information from the individual wheels. The electronic control unit instructs the hydraulic modulator to modulate the brake pressure being applied at the affected wheel(s). There are three stages to this control. 1. Pressure increase Phase: As the ECU detects that the speed of the controlled wheel has increased to the vehicle reference speed and hence the % slip reduced. It will sequentially deactivate the outlet and inlet valves switching them to their normal positions. With the outlet valve closed further pressure reduction is prevented and the inlet valve can be opened to allow brake fluid from the TMC to enter the wheel brake increasing the brake pressure once again. If the driver releases the brake at any time during ABS control the inlet valves will be deactivated and fluid can return to the TMC via the inlet valve and the one way valve. Solenoid valve Electricity status Valve open Open- close channel close INLET OFF OPEN Master cylinder Wheel cylinder OUTLET OFF CLOSE Wheel cylinder Reservoir 2. Pressure Maintaining (Hold) Phase: When the braking forces being applied are higher than can be transmitted to the road surface for a specific wheel the ECU will detects that wheel as tending towards lock (Slip relative to other wheels and a calculated vehicle reference speed). It will activate the relevant Inlet valve within the hydraulic modulator, switching it from its normally open position to closed, hence preventing further pressure being transmitted from the TMC to the affected wheel brake. As the outlet valve is also closed in this phase the pressure at the wheel is maintained. If the driver reduces the brake pedal effort during ABS control brake fluid can return to the TMC through the one way valve located within the modulator in parallel to the Inlet valve.