Overview
This document contains information on:
General
Function requirements
Function
General
The Electronic Stability Program (ESP®) counteracts oversteering or understeering of the vehicle. The ESP® ensures, within the 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 combustion engine 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.
Additional base function | |||
Basic function for trailer stabilization | Model all (CAR) | ||
Control units | |||
Combustion engine control unit, basic function | Model all (CAR) | ||
Electronic Stability Program control unit, basic function | Model all (CAR) | ||
Components | |||
Fully integrated transmission control electrohydraulic controller unit, basic function | Transmission 724.033/044/045/103/114/115/120 | ||
Wheel speed sensors, basic function | Model all (CAR) |