Electronic Stability Control System

Basic Description

Electronic Stability Control (ESC), also called Vehicle Dynamic Control (VDC), Dynamic Stability Control (DSC) or an Electronic Stability Program (ESP), is one of the most significant active safety systems in modern automobiles. The main function of this system is to improve the handling performance of the vehicle and prevent possible accidents during severe driving maneuvers (e.g. fast cornering or lane changing with emergency braking). Generally, these systems stabilize the vehicle by applying the necessary yaw moment (generated by individual braking force on each wheel) and regulating the side slip angle of the vehicle based on a comparison between the vehicle state and the driver's demand. Some ESC systems also reduce the power from the engine during excessive steering.

The figure above shows the architecture of a typical stability control system, incorporating three fundamental elements: the driver, the vehicle and the environment. In the normal control loop, the driver detects the deviation of the vehicle from the current road trajectory and corrects it through the steering system. When the electronic stability control system senses that the driver is about to lose control of the vehicle, it generates the necessary yaw moment automatically based on the difference between the driver's demand and actual vehicle state and help him pull the vehicle back to the desired trajectory.

Sensors

Steering wheel angle sensor: detects the steering wheel position and provides a reference input for the ESC controller.
Yaw rate sensor: measures the actual yaw rate of the vehicle and can also estimate the yaw angle by integrating.
Lateral acceleration sensor: measures the lateral acceleration of the vehicle (also called a G-force sensor.
Wheel speed sensor: measures the spin speed of each wheel for individual braking control.

Actuators

The main actuator of the stability control system is a hydraulic modulator, similar to those used in ABS systems, which controls the braking pressure at each wheel individually according to ESC system commands. Electronic throttle, fuel injector and spark plugs may also be actuated in order to control the engine output.

Data Communications

The communications between the controllers, sensors and actuators are performed through high-speed CAN bus.

Manufacturers

Bendix, Bosch, Continental, TRW

For More Information

[1] Federal Motor Vehicle Safety Standards; Electronic Stability Control Systems, NHTSA website.

[2] Electronic Stability Control, Wikipedia.

[3] Safety and Performance Enhancement: The Bosch Electronic Stability Control (ESP), E. K. Liebemann; K. Meder; J. Schuh; G. Nenninger, Robert Bosch GmbH, Paper Number 05-0471, Germany.

[4] Simulated Comparison between vehicles with and without ESC systems (video), Clemson Vehicular Electronics Laboratory video. [wmv format]

[5] Electronic Stability Control, Freescale website.