The Electronic Stability Program (ESP) is a driving safety system, which has been developed to stabilise the vehicle during critical driving conditions, such as, uneven braking force, braking on bends, cornering too fast, driving on slippery roads.
ESP operates by monitoring and comparing information from various sensors.
- 1. The Steering Angle Sensor measures the steering angle as an indication of the direction the driver intends to take.
- 2. The Yaw Rate Sensor (Acceleration) is the heart of the ESP. It measures the rotation about the vertical axis (oversteer/understeer) and the lateral drift of the vehicle. The sum of these is the actual direction of the vehicle.
- 3. The Wheel Speed Sensors register the vehicle velocity.
- 4. The Pressure Sensor (incorporated within the ABS Hydraulic Unit with Control Unit), measures the braking pressure.
From the information received from the sensors, the ESP control unit continuously compares the actual behaviour of the vehicle with the intended behaviour of the vehicle. This comparison is made up to 25 times per second. The moment the vehicle deviates from the intended direction, the control unit causes the system to intervene with split-second speed, bringing the vehicle back towards the intended direction. This is done in two ways: by precise controlled braking on individual wheels and/or by reducing the engine power.
- 1. Intended direction
- 2. Braking force
- 3. Compensating moment
- 4. Actual direction
- 5. Actual direction
- 6. Compensating moment
- 7. Braking force
- 8. Intended direction
A – ESP Effect on Understeer
In the case of understeer, the front of the vehicle will pull towards the outside of the curve. The ESP will intervene and apply the brakes to the relevant wheel, in order to stabilise the vehicle and restore it to its intended direction.
B – ESP Effect on Oversteer
In the case of oversteer, the front of the vehicle will pull towards the inside of the curve. The ESP will intervene and apply the brakes to the relevant wheel, in order to stabilise the vehicle and restore it to its intended direction.
ESP intervention is shown by the illumination of the indicator lamp (1).
If a fault occurs with the ESP, the warning lamp (2) illuminates simultaneously with the indicator lamp (1)