Electronic Stability Control (ESC) recognises critical driving situations, such as risk of skidding, and systematically prevents the car from doing so.
For the ESC to respond to critical situations, the system must constantly receive information.
For instance, the system needs to know which way the driver is steering and where the car is moving. The system receives the steering direction from the steering angle sensor and the ABS wheel speed sensors on the wheels. From these two pieces of information, the controller calculates the desired steering direction and the intended driving behaviour of the car. Other important data are the yaw rate and lateral acceleration of the vehicle. Using this information, the control unit calculates the current state of the vehicle.
ESC prevents instability of the car when cornering. Instability can occur either while driving at an inappropriate speed, as a result of an unpredictable change in the road surface (wetness, slickness, dirt), or due to an emergency evasive action (the "Elk test"). In this case, it does not matter whether the instability manifests itself by means of understeering (i.e. when the car moves to the outer edge of the bend despite steering at full lock) or by means of oversteering (the rear end breaks away).
The computer unit of the ESC detects the type of instability based on the data provided by the sensor technology. It corrects the instability by intervening in the braking system and engine management.
In the event of understeering, the ESC decelerates the inside rear wheel. At the same time, the ESC reduces the engine power until the car has stabilised again. ESC prevents oversteering by selectively activating the front brake on the outside of the bend and intervening in the engine and transmission management.