Brief description, ESP
ESP stands for Electronic Stability Program. This system regulates engine torque and braking to help the driver in unexpected situations that would otherwise be difficult to handle.
The ESP system comprises anti-lock brakes, traction control and stability program. In the event of an error in the traction control or stability program, both functions are switched off. The functionality of the anti-lock brakes is retained so long as the fault does not affect the braking function.
When the system is activated, it can counteract a skid, for example, by braking one or two of the wheels without the driver needing to touch the brake pedal. The system can also reduce engine torque with an engine torque request from the ESP control module to the engine control module, to reduce wheel spin.
Using the information on wheel speeds, lateral acceleration and vehicle rotation about the vertical axis, the system calculates how the vehicle is moving (actual value). This actual value is compared with information about the direction in which the driver wishes to steer (desired value). If the actual and desired values do not agree, the system takes corrective action by braking one or several wheels and/or limiting the engine torque.
- In the event of understeer, the brakes are applied on the rear inside wheel.
- In the event of oversteer, the brakes are applied on the outside wheel or wheels until the measured and calculated yaw rates are the same.
It is important to point out that the system requires sufficient friction between the tires and road surface. The driver must actively turn the steering wheel, and consequently the wheels, in the desired direction for the system to provide the correct modulation.