Hydraulic Control Assembly - Antilock Brakes: Description and Operation
ICU (INTEGRATED CONTROL UNIT) DESCRIPTIONIntegrated Control Unit (ICU):
The Hydraulic control unit (HCU) and the Controller Antilock Brake (CAB) used with this antilock brake system are combined (integrated) into one unit, which is called the Integrated Control Unit (ICU). The ICU is located in front of the driver's side front tire, behind the inner fender splash shield.
Two different ICU's (HCU and CAB) are used on this vehicle depending on whether or not the vehicle is equipped with traction control. The HCU on a vehicle equipped with traction control has a valve block that is approximately one inch longer than a HCU on a vehicle that is equipped with ABS only.
The ABS-only ICU consists of the following components: the CAB, eight (build/decay) solenoid valves (four inlet valves and four outlet valves), valve block, fluid accumulators, a pump, and an electric motor.
The ABS-with traction control ICU consists of the following components: the CAB, eight (build/decay) solenoid valves (four inlet valves and four outlet valves), two traction control (ASR) valves, two hydraulic shuttle valves, valve block, fluid accumulators, a pump, and an electric motor.
he replaceable components of the ICU are the HCU and the CAB. No attempt should be made to service any individual components of the HCU or CAB.
OPERATION
For information of the ICU, refer to these individual components of the ICU:
- CONTROLLER ANTILOCK BRAKE (CAB)
- HYDRAULIC CONTROL UNIT (HCU)
For information on the ICU's hydraulic circuits, refer to HYDRAULIC CIRCUITS AND VALVE OPERATION.
HYDRAULIC CONTROL UNIT
Teves Mark 20 ICU:
DESCRIPTION
The Hydraulic Control Unit (HCU) is mounted to the CAB as part of the ICU. The ICU is located in front of the driver's side front tire, behind the inner fender splash shield. The HCU controls the flow of brake fluid to the brakes using a series of valves and accumulators. A pump/motor is mounted on the HCU to supply build pressure to the brakes during an ABS stop.
The HCU on a vehicle equipped with traction control has a valve block that is approximately one inch longer than a HCU on a vehicle that is equipped with ABS only in order to incorporate the additional valves.
For more information, see INTEGRATED CONTROL UNIT.
BRAKE FLUID ACCUMULATORS
Teves Mark 20 ICU:
There are two fluid accumulators in the HCU-one for the primary hydraulic circuit and one for the secondary hydraulic circuit. Each hydraulic circuit uses a 5 cc accumulator.
The fluid accumulators temporarily store brake fluid that is removed from the wheel brakes during an ABS cycle. This stored fluid is used by the pump/ motor to provide build pressure for the brake hydraulic system. When the antilock stop is complete, the accumulators are drained by the pump/motor.