Anti-Lock Control - Stability Assist

1-----Yaw rate sensor and accelerometer

2-----Steering wheel rotation sensor

3-----Hydraulic control unit (HCU) and stability assist module assembly

The stability assist module adds a further function known as electronic stability program (ESP) to the anti-lock brake system (ABS) and includes a traction control function. Whereas the ABS prevented wheel lock up during braking, the traction control function controls wheel slip during acceleration (longitudinal dynamics) and the ESP stabilizes the vehicle about its vertical axis.
Sensors measure the position of the steering wheel, the pressure in the brake master cylinder, the yaw velocity (yaw rate) and the acceleration transverse to the vehicle (lateral acceleration). This makes it possible to compare the driver's intention with the momentary vehicle behaviour so that in the event of the vehicle becoming unstable, ESP can initiate the appropriate corrective action.
The ESP recognizes critical driving conditions, such as panic reactions in dangerous situations, and stabilizes the vehicle, within the physical limits, by individually braking each wheel and giving engine control intervention without need for the driver to actuate the brake or the accelerator pedal.
Stability assist components
The ESP uses the same components as the ABS program with the addition of the following:
* Stability assist module: This is attached to the HCU and is fitted instead of the ABS module. The stability assist module carries out the same function as the ABS module.
* Yaw rate sensor and accelerometer: This sensor cluster combines the yaw rate and the lateral acceleration sensors in a single component. The sensor is attached the floor crossmember.

NOTE: Since September 16, 2010 the yaw rate sensor and accelerometer function is part of the restraints control module (RCM)

* Steering wheel rotation sensor: This sensor measures the rotation of the steering wheel. It is attached to the clockspring and is located on the steering column.