Antilock Brake System: Overview GMC Acadia I рестайлинг

Circuit/System Description

The wheel speed sensor receives ignition voltage from the electronic brake control module (EBCM) and provides a DC square wave signal back to the module. As the wheel spins, the EBCM uses the frequency of the square wave signal to calculate the wheel speed.

The pump motor is an integral part of the brake pressure modulator valve, while the pump motor relay is integral to the electronic brake control module (EBCM). The pump motor relay is not engaged during normal system operation. When the ABS, the traction control system or the stability control operation is required the EBCM activates the pump motor relay and turns the pump motor ON.

The electronic brake control module uses input from the brake pressure sensor for vehicle stability enhancement system functions. The brake pressure sensor is internal to the brake pressure modulator valve.

The electronic brake control module (EBCM) monitors the brake pressure sensor voltage, vehicle speed and a serial data message from the body control module (BCM) that the brake pedal is either Applied or Released. When the vehicle is stopping the EBCM detects the brake pressure sensor voltage increases and correlates the readings to the serial data message from the BCM that the brake pedal is applied and the vehicle is slowing down or when the vehicle is accelerating, the brake pedal is Released and brake pressure sensor voltage returns to 0 volts.

The yaw rate, lateral acceleration and longitudinal acceleration sensors are combined into one yaw/lateral/longitudinal accelerometer sensor, external to the electronic brake control module. The electronic brake control module supplies a 12 V reference and a low reference to the accelerometer sensor. The accelerometer sensor communicates with the electronic brake control module via serial data. The module activates the stability control and the hill start assist function depending on the information received from the accelerometer sensor.

The electronic brake control module controls (EBCM) it's internal valve relay to command the valve solenoids ON or OFF.

The electronic brake control module (EBCM) and the engine control module (ECM) simultaneously control the traction control. The EBCM sends a serial data message to the ECM requesting torque reduction. When certain ECM DTCs are set, the ECM will not be able to perform the torque reduction for traction control. A serial data message is sent to the EBCM indicating that traction control is not allowed.

The wheel speed sensor receives ignition voltage from the electronic brake control module (EBCM) and provides an output signal back to the EBCM. As the wheel spins the sensor sends a DC square wave signal to the EBCM. The EBCM uses the frequency of this signal to calculate the wheel speed.

The electronic brake control module (EBCM) controls the vehicle stability enhancement system (VSES) by monitoring the inputs of the yaw rate/lateral accelerometer sensor and steering wheel angle sensor. The readings are compared to an internal calibrated value so it knows if the vehicle is having an instability condition to activate the VSES. When the readings indicate a VSES event is occurring longer than 10 seconds is not possible under normal conditions. The yaw/lateral sensor is a combination sensor in one component.

The electronic brake control module (EBCM) receives serial data messages from the steering wheel position sensor identifying the position and direction of the steering wheel rotation.

The electronic brake control module (EBCM) receives serial data messages from the body control module (BCM), engine control module (ECM), instrument panel cluster and the transmission control module (TCM) which are needed to perform ABS, vehicle stability enhancement system or traction control system functions.

The electronic brake module (EBCM) receives a serial data message from each of the network modules. Each module contains its own unique identification (ID) code that must be programmed into a new the EBCM.

The electronic brake control module (EBCM) supplies ignition voltage to the steering wheel speed position sensor and the yaw/lateral accelerometer sensor. The EBCM receives serial data messages from both the steering wheel speed position sensor and the yaw/lateral accelerometer sensor. The steering wheel speed position sensor is an input to the EBCM and provides the position of the steering wheel.

The steering wheel speed position sensor measures the steering wheel degree of rotation. The EBCM utilizes this signal to calculate the driver intended driving direction. The electronic brake control module (EBCM) receives serial data inputs from the steering wheel speed position sensor identifying the position and direction of the steering wheel rotation.

The instrument panel cluster (IPC) momentarily illuminates the antilock brake system (ABS) indicator during the bulb check when the ignition is cycled ON. When the electronic brake control module (EBCM) detects a fault requiring ABS indicator ON, it sends a serial data message to the IPC to illuminate the ABS indicator.

ABS Description and Operation

This vehicle is equipped with a Bosch ABS/EBD/TCS/VSES brake system. The electronic brake control module (EBCM) and the brake pressure modulator valve is serviced separately. The brake pressure modulator valve uses a four circuit configuration to control hydraulic pressure to each wheel independently.

The following vehicle performance enhancement systems are provided.

1. Antilock Brake System (ABS)
2. Electronic Brake Distribution (EBD)
3. Hill Start Assist
4. Power Brake Booster Solenoid Vacuum Supply
5. Traction Control System (TCS)
6. Vehicle Stability Enhancement System (VSES)

Scheme 4

The following components are involved in the operation of the above systems.

1. ABS pump motor - The ABS pump motor is part of the brake pressure modulator valve. The ABS pump motor is active during ABS, VSES and base brake power assist functions. System relays - There are two system relays internal to the EBCM. The solenoid relay is energized when the ignition is ON. The ABS pump motor relay supplies a ground path to the ABS pump motor when the EBCM commands the ABS pump motor on. The system relays are non serviceable. Solenoids - The solenoids are commanded ON and OFF by the EBCM to operate the appropriate valves in the brake pressure modulator valve (BPMV).
2. Brake booster vacuum sensor - The Brake Booster Vacuum Sensor is a input to EBCM and operates the ABS pump motor to precharge the brake system.
3. Brake pressure modulator valve (BPMV) - The BPMV uses a 4-circuit configuration to control hydraulic pressure to each wheel independently. The BPMV contains the following components: ABS pump motor and pump Four inlet valves Four outlet valves Two TC isolation valves Two TC supply valves A master cylinder pressure sensor A front low-pressure accumulator A rear low-pressure accumulator
4. Master cylinder pressure sensor - The master cylinder pressure sensor is located within the brake pressure modulator valve. The master cylinder pressure sensor uses a 5-volt reference and generates an output signal proportionate to the hydraulic fluid pressure which is present in the front brake circuit at the master cylinder.
5. Steering wheel speed position sensor - The EBCM receives several inputs from the steering wheel position sensor. Three digital square wave signal inputs and one analog signal input are wired directly to the EBCM harness connector. The EBCM uses the signals A and B for determining position movement and uses the analog and index signals to determine absolute center. All signals are monitored for plausibility to each other. The sensor is provided ground and 5-volt power directly from the EBCM.
6. Traction control switch - The vehicle stability enhancement system and the engine torque reduction function of traction control system are manually disabled or enabled by pressing the traction control switch.
7. Wheel speed sensors (WSS) - EBCM sends a 12-volt reference voltage signal to each wheel speed sensor. As the wheel spins, the wheel speed sensor produces a square wave DC signal voltage. The wheel speed sensor increases the signal frequency as the wheel speed increases, but does not increase the signal amplitude.
8. Yaw/lateral accelerometer sensor - The yaw rate, lateral acceleration and longitudinal acceleration sensors are combined into one yaw/lateral accelerometer sensor, external to the EBCM. The EBCM receives serial data message inputs from the yaw rate, lateral acceleration and longitudinal acceleration sensor and activates stability control and hill start assist function depending on multi-axis acceleration sensor input

When wheel slip is detected during a brake application, an ABS event occurs. During anti-lock braking, hydraulic pressure in the individual wheel circuits is controlled to prevent any wheel from slipping. A separate hydraulic line and specific solenoid valves are provided for each wheel. The ABS can decrease, hold or increase hydraulic pressure to each wheel. The ABS does not, however, increase hydraulic pressure above the amount which is transmitted by the master cylinder during braking.

During anti-lock braking, a series of rapid pulsations is felt in the brake pedal. These pulsations are caused by the rapid changes in position of the individual solenoid valves as the electronic brake control module (EBCM) responds to wheel speed sensor inputs and attempts to prevent wheel slip. These pedal pulsations are present only during antilock braking and stop when normal braking is resumed or when the vehicle comes to a stop. A ticking or popping noise may also be heard as the solenoid valves cycle rapidly. During anti-lock braking on dry pavement, intermittent chirping noises may be heard as the tires approach slipping. These noises and pedal pulsations are considered normal during anti-lock operation.

Vehicles equipped with ABS may be stopped by applying normal force to the brake pedal. Brake pedal operation during normal braking is no different than that of previous non-ABS systems. Maintaining a constant force on the brake pedal provides the shortest stopping distance while maintaining vehicle stability. The typical ABS activation sequence is as follows.

Pressure Hold

The EBCM closes the isolation valve and keeps the dump valve closed in order to isolate the slipping wheel when wheel slip occurs. This holds the pressure steady on the brake so that the hydraulic pressure does not increase or decrease.

Pressure Decrease

If a pressure hold does not correct the wheel slip condition, a pressure decrease occurs. The EBCM decreases the pressure to individual wheels during deceleration when wheel slip occurs. The isolation valve is closed and the dump valve is opened. The excess fluid is stored in the accumulator until the pump can return the fluid to the master cylinder or fluid reservoir.

Pressure Increase

After the wheel slip is corrected, a pressure increase occurs. The EBCM increases the pressure to individual wheels during deceleration in order to reduce the speed of the wheel. The isolation valve is opened and the dump valve is closed. The increased pressure is delivered from the master cylinder.