Antilock Brake System Description

SYSTEM DESCRIPTION AND FUNCTIONAL OPERATION

ABS

The Controller Antilock Brake (CAB) is used to monitor wheel speeds and modulates (controls) hydraulic pressure in each brake channel. The modulated hydraulic pressure is used to prevent wheel lock up during braking and maintain vehicle stability. The CAB also provides a vehicle speed signal (VSS) to the Electronic Control Module (ECM). During a non-ABS stop, the system functions as a standard braking system. The CAB uses special software that monitors the wheel speed(s) and when certain criteria are met, the software will enable the HCU to perform the brake fluid management control as the combination/proportioning valves.

The Bosch 5.7 system uses Electronic Brake Distribution (EBD). The HCU replaces the conventional proportioning valve as a means of balancing the front-to-rear braking effort under normal braking conditions. EBD makes the rear brakes more effective when the truck is lightly loaded, balancing front-to-rear lining wear and minimizing instances of rear wheel antilock action. As with a proportioning valve, EBD uses the rear axle speed sensor to determine how much, if any, to reduce the rear brake hydraulic pressure based on the deceleration of the rear wheels. EBD automatically adapts to variations in the vehicle loading and road surface, where as a proportioning valve is fixed.

The Bosch 5.7 uses the CAB/HCU/Pump Motor to make an integral electronic/hydraulic unit which shares data with other electronic modules on the vehicle via the CAN C Bus network. To access DTCs from the CAB, the DRBIII uses the K - ABS line located in the Data Link Connector (DLC).