Hydraulic Control Assembly - Antilock Brakes: Description and Operation: Overview

CONTROL MODULE COMPONENTS
The ABS CM is located beneath the modulator valve block and is secured by two screws. The CM houses the solenoids which operate the inlet and outlet valves of the modulator valve block. When fitted, the valve stems locate in the CM mounted solenoids. The only electrical connection between the CM and the modulator valve block is to the hydraulic pump.

FUNCTIONS OF CM
- Providing control signals for the operation of ABS control solenoid valves
- Calculating wheel speed from voltage signals transmitted by the wheel speed sensors
- Monitoring of all electrical components
- On Board Diagnostics (OBD): storage of possible failures in a non-volatile memory.

Signals From The Wheel Speed Sensors - are independently processed by the ABS CM, calculating numerical values which correspond directly to the wheel speed. These values are converted into control signals for pressure modulation during ABS control.

The ABS Is Continuously Monitored- while the ignition is on, for possible faults and interruptions. If a fault is detected, the module de-activates the ABS and indicates this by lighting the ABS warning lamp. In a fault condition, conventional braking is unaffected. The module stores fault codes in a non-volatile memory which can be read via the OBD link.





PURPOSE
The hydraulic pump (1) is a reciprocating two-circuit pump in which one brake circuit is assigned to each pump circuit. The pump supplies adequate pressure and volume supply to the brake circuits under anti-lock braking conditions. The pump is driven by an electric motor (2). The pump housing incorporates two low pressure accumulators and damping chambers for each brake circuit.

MODULATOR VALVE BLOCK
A modulator valve block (3) incorporates the ABS CM or ABS/TC CM (4). Vehicles with traction control are fitted with a throttle position actuator (5), which is an electrical device controlled by the ABS/TC CM.





Valve blocks on vehicles without traction control comprise six solenoid valves, three normally open (NO) inlet valves and three normally closed (NC) outlet valves. These valve blocks have three outlet ports. Valve blocks on vehicles with traction control comprise nine solenoid valves, four NO inlet valves, four NC outlet valves and one special isolating valve. The image shows a hydraulic module for vehicles with traction control. The valve block (2) has four outlet ports (Individual control of the driven wheels).