ESP function: Notes

ESP is a stability system that helps to keep the vehicle on the right course when cornering, taking evasive action, braking and accelerating. The stabilizing effect of the ESP system is based on calculations made by the control module, which evaluates information sent from the various system sensors:

• Wheel speed sensors
• Steering wheel angle sensor
• Yaw rate sensor
• Lateral acceleration sensor
• Brake pressure sensor (integrated)

Data from these sensors informs the control module of the driver's intentions, e.g. in which direction the driver wishes to drive, if the driver is braking, etc. The ESP control module, integrated in the hydraulic unit, continuously calculates the direction of the vehicle, the actual value, and compares this with desired direction indicated by the steering wheel, the desired value.

• If the car starts to understeer (when the front tends to continue straight ahead in a bend) the yaw rate sensor measures a lower value than that calculated. The system applies the brakes on the inside rear wheel until the measured and calculated yaw rates agree.
• If the car starts to oversteer (the rear tends to drift out) the measured yaw rate will be greater than that calculated. The system will apply the brakes on the outside wheels until the measured and the calculated yaw rates correspond.

When the system is activated, it can counteract a skid by braking one or two of the wheels without the driver needing to touch the brake pedal. The system reduces engine torque after an engine torque request to the engine control module and applies the brakes on the wheels individually.

The ESP system comprises three different functions: ABS, TCS and ESP. ABS and TCS have the same function as earlier.

The wheel brake is the fastest and most powerful method of braking a spinning wheel, while engine torque limitation is the smoothest and most comfortable method. These two methods are often employed simultaneously while some cases demand brake application.

If the car starts to understeer (1) the yaw rate sensor measures a lower value than that calculated. The system applies the brakes on the inside rear wheel until the measured and calculated yaw rates agree.