Basic principle

In a nutshell, the basic principle of the ESC system is as follows: by
braking individual wheels it is possible to influence the direction in
which a vehicle travels.

The front right wheel on the vehicle shown here is braked while travelling in a straight line. The brake force F acting on this wheel is at a distance s from the vehicle’s vertical axis. As a result, the brake force produces a torque Md about the vehicle’s vertical axis.

This can best be observed using a tracked vehicle as an example. This behaviour is specifically utilised to steer the vehicle.

Torque = force x leverage
Md = F x s
If no corrective steering inputs are made by the driver, this torqueproduces a change in the driving direction (the vehicle turns inwards to the right).

Configuration overview

Compared to ABS with EDL, a hydraulic unit with a modified configuration is used. The ESC control software and the other control systems are located centrally in a control unit. Apart from the wheel speed sensors, other sensors which monitor the movements of the vehicle are required to implement the ESC function. In
current Audi models, the sensors for monitoring the movements of the vehicle are located in a central unit, or in the ABS/ESC control unit (Audi A1, A3), or in the electro-mechanical parking brake control unit (Audi Q3). In addition to ABS with EDL, a steering angle sensor is also

Function

As the name indicates, the function of ESC is to stabilise the vehicle in dynamically critical driving situations. The system uses three different control strategies for this purpose:
• Active brake pressure build-up at certain wheels
• Intervention in the engine management system in order to
reduce power
• Intervention in the gearbox control unit in order to suppress
gearshifts

In vehicles with dynamic steering, the ESC also makes stabilising steering angle corrections, if necessary.

The main focus is on braking intervention. A reduction in power is achieved by using the same measures as the TCS function.

An ESC control process with braking intervention is shown below using an evasive manoeuvre as an example:

The driver spots a stationary vehicle in his/her lane. The driver steers the vehicle into the neighbouring lane by performing a quick steering movement. Due to adverse road conditions, the vehicle is prone to oversteer and the rear end has the tendency to break away
abruptly. Without controlled intervention, the vehicle would spin round sideways. Even a countersteering input by the driver will not be sufficient to stabilise the vehicle.

ESC reacts by actively building up brake pressure at the front left wheel. The torque produced in this way counteracts the fishtailing of the vehicle rear end and, thus, stabilises the vehicle. The ESC system makes these corrective adjustments within a matter of milliseconds. The aforementioned “brake pressure build-up”, “brake pressure holding” and “brake pressure reduction” functions are employed. required to monitor the steering wheel angle. Warning lamps and displays notify the driver of the system’s status. Depending on model, the driver can shut down and change over certain systems using a switch (button).