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Dodge Durango
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Brakes » Four wheel antilock brakes » Description and operation
Antilock brake system

DESCRIPTION

The antilock brake system (ABS) is an electronically operated, all wheel brake control system.

The system is designed to prevent wheel lockup and maintain steering control during periods of high wheel slip when braking. Preventing lockup is accomplished by modulating fluid pressure to the wheel brake units.

The hydraulic system is a three channel design.

The front wheel brakes are controlled individually and the rear wheel brakes in tandem (Fig. 1). The ABS electrical system is separate from other electrical circuits in the vehicle. A specially programmed controller antilock brake unit operates the system components.

ABS system major components include:

  • Controller Antilock Brakes (CAB)
  • Hydraulic Control Unit (HCU)
  • Wheel Speed Sensors (WSS)
  • ABS Warning Light

OPERATION

Battery voltage is supplied to the CAB ignition terminal when the ignition switch is turned to Run position.

The CAB performs a system initialization procedure at this point. Initialization consists of a static and dynamic self check of system electrical components.

The static and dynamic checks occurs at ignition start up. During the dynamic check, the CAB briefly cycles the pump and solenoids to verify operation. An audible noise may be heard during this self check.

This noise should be considered normal.

Fig. 1 Antilock Brake System Fig. 1 Antilock Brake System

1 - MASTER CYLINDER AND RESERVOIR

2 - POWER BRAKE BOOSTER

3 - WIRES TO WHEEL SPEED SENSORS

4 - RIGHT REAR WHEEL

5 - LEFT REAR WHEEL

6 - HYDRAULIC BRAKE LINES TO WHEELS

7 - COMBINATION VALVE

8 - HARNESS

9 - RIGHT FRONT WHEEL

10 - LEFT FRONT WHEEL

11 - CAB/HCU

If an ABS component exhibits a fault during initialization, the CAB illuminates the amber warning light and registers a fault code in the microprocessor memory.

The CAB monitors wheel speed sensor inputs continuously while the vehicle is in motion. However, the CAB will not activate any ABS components as long as sensor inputs indicate normal braking.

During normal braking, the master cylinder, power booster and wheel brake units all function as they would in a vehicle without ABS. The HCU components are not activated.

The purpose of the antilock system is to prevent wheel lockup during periods of high wheel slip. Preventing lockup helps maintain vehicle braking action and steering control.

The antilock CAB activates the system whenever sensor signals indicate periods of high wheel slip.

High wheel slip can be described as the point where wheel rotation begins approaching 20 to 30 percent of actual vehicle speed during braking. Periods of high wheel slip occur when brake stops involve high pedal pressure and rate of vehicle deceleration.

The antilock system prevents lockup during high slip conditions by modulating fluid apply pressure to the wheel brake units.

Brake fluid apply pressure is modulated according to wheel speed, degree of slip and rate of deceleration.

Sensors at each front wheel convert wheel speed into electrical signals. These signals are transmitted to the CAB for processing and determination of wheel slip and deceleration rate.

The ABS system has three fluid pressure control channels. The front brakes are controlled separately and the rear brakes in tandem. A speed sensor input signal indicating a high slip condition activates the CAB antilock program.

Two solenoid valves are used in each antilock control channel. The valves are all located within the HCU valve body and work in pairs to either increase, hold, or decrease apply pressure as needed in the individual control channels.

The solenoid valves are not static during antilock braking. They are cycled continuously to modulate pressure. Solenoid cycle time in antilock mode can be measured in milliseconds.

    More about «Description and operation»:

    Antilock brake system

    Controller antilock brakes

    Hydraulic control unit

    Wheel speed sensor

    Abs warning lamp

    Dodge Durango Service Manual / Brakes / Four wheel antilock brakes / Description and operation / Antilock brake system

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