Electronic Stability Program (ESP)

ELECTRONIC STABILITY PROGRAM

DESCRIPTION

ESP (R) (Electronic Stability Program), which includes a Brake Assist feature, is standard on some models and optional on others. ESP aids the driver in maintaining vehicle directional stability ESP will do whatever can be done, within the limits of available traction, to keep the car on course.

ESP uses the ABS with Traction Control along with the following components to operate:
^ Active Brake Booster
^ Brake Pressure Switch
^ Dynamics Sensor
^ Travel Sensor
^ Steering Angle Sensor (SAS)

The Active Brake Booster is part of the Power Brake Booster. The Brake Pressure Switch is mounted to the bottom of the Master Cylinder. The Dynamics Sensor that is mounted under the center console, which is near the center of gravity of the car for effective sensing. The Travel Sensor is mounted in the Power Brake Booster. The Steering Angle Sensor is located in the steering column.

OPERATION

To determine whether the car is responding properly to cornering commands, ESP uses steering wheel angle, yaw (turning) rate and lateral acceleration sensors (combined into Dynamics Sensor). Using signals from these sensors, in addition to individual wheel speed sensor signals, the system determines appropriate brake and throttle actions. Once initiated, ESP operates much like All-Speed Traction Control, except that the goal is directional stability. If the vehicle yaw response, or rate of turning, is inconsistent with the steering angle and vehicle speed indications, the ESP system applies the brakes and, if necessary closes the throttle, to restore control. This occurs whether the vehicle is turning too rapidly (oversteering) or not rapidly enough (understeering).

ESP notifies the active brake booster electronically of the need for maximum output. A solenoid opens a valve in the booster that immediately applies maximum boost to the master cylinder. A travel sensor in the booster detects the rate and travel of the brake pedal. Above the threshold of an extreme brake application, ESP activates the solenoid, thus applying maximum available hydraulic pressure to the brakes. In this type of situation, stopping distance is determined by the ABS system based on available traction, rather than the amount of force that the driver can exert on the brake pedal. This becomes the deciding factor in how quickly the vehicle will stop.