Electronic Stability Program, Basic Function - GF42.45-P-1002A
Model All (4xWD, CAR)
Overview
This document contains information on:
- General
- Function requirements
- Function
- ESP® evaluation criteria
- Vehicle oversteers
- Vehicle understeers
General
The Electronic Stability Program (ESP®) counteracts any oversteering or understeering of the vehicle. ESP® ensures, within physical limits, that the vehicle follows the course specified by the driver.
If the ESP® detects that movement of the vehicle is deviating from the desired course, specific individual or multiple wheels are braked to stabilize the vehicle. In order to increase the driving stability, the drive torque is also reduced.
Function requirements
- Engine in operation
- ESP® ON
- Brake and traction system functional
Function
ESP® evaluation criteria
In order to monitor the vehicle characteristics, the ESP® processes the following evaluation criteria:
- Yaw velocity
- Steering wheel angle
- Brake pressure
- Engine torque
- Transmission stage
- Lateral acceleration
- Wheel speed
The type of intervention by the ESP® differs as follows:
- Vehicle oversteers
- Vehicle understeers
Vehicle oversteers
If the vehicle oversteers, then the maximum possible lateral stability of the wheels on the rear axle has been exceeded. The rear end breaks out toward the outside edge of the curve.
If the vehicle begins to oversteer, brake pressure is built up at the outer front wheel. Braking generates a counterforce that turns the vehicle about the vertical axis back into the curve. In addition, the vehicle speed is reduced, which stabilizes the vehicle further.
Vehicle understeers
If the vehicle understeers, then the maximum possible lateral stability of the wheels on the front axle has been exceeded. The vehicle pushes over the front axle toward the outer edge of the curve.
In order to counteract the resulting instability, the drive torque is reduced and the following brake interventions are performed at up to 3 wheels:
- Stage 1: Brake pressure buildup at inside rear wheel
- Stage 2: Stage 1 plus brake pressure buildup at outside rear wheel
- Stage 3: Stage 2 plus brake pressure buildup at inside front wheel
Depending on the brake force, a torque is generated which causes the vehicle to rotate inward with a simultaneous reduction in speed. This has a stabilizing
effect. To reduce the engine output, the ESP® sends a signal to the drivetrain control unit.
With automatic transmission:
During regulation by the ESP®, shift operations are suppressed. For this purpose, the ESP® control unit sends a signal to the fully integrated transmission control unit.
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