ESP Brake Torque Control Loop Function
Terminology
- ESP Electronic Stability Program
- ETC Electronic Transmission Control
- BAS Brake Assist System
- MIL Malfunction Indicator Lamp
- ABS Anti-lock Brake System
- ASR Acceleration Slip Regulation
- MSR Engine Braking Regulation
- CAN Controller Area Network
- DTR Distronic Function
- ME-SFI Engine Control Module
- EA Electronic Accelerator
- EBR Engine Braking Regulation
- SPS Speed-sensitive Power Steering
General
The corresponding functions of the brake moment control circuit are controlled by the electrical/electronic components.
The voltage is supplied to the ESP control module (N47-5) via the fuse and relay module (K40/2).
The ESP control module (N47-5) receives input signals from the following components:
- 4 wheel speed sensors
- Steering angle sensor
- Lateral acceleration sensor
- Yaw rate sensor
- ESP brake pressure sensors
- Stop lamp switch
- Parking brake switch
- Engine control module (ME-SFI) via CAN data bus
- ETC control module via CAN data bus
- ESP OFF switch
- BAS release switch
- BAS diaphragm travel sensor
In the ESP control module the input signals are processed into output signals for the following components:
- BAS solenoid valve
- Solenoid valves in the hydraulic unit
- High pressure/return pump
- Stop lamp suppression relay
- Engine control module via CAN data bus
- ETC control module via CAN data bus
- ESP warning lamp via CAN data bus
- ABS malfunction indicator lamp via CAN data bus
- BAS/ESP malfunction indicator lamp via CAN data bus
Based on the input signals, the ESP control module (N47-5) decides which of the following 7 operating modes should be switched on:
- Normal mode
- ABS control mode
- ASR control mode
- EBR control mode
- ESP control mode
- ESP off mode
- BAS mode.
Normal Mode
In normal mode there is no vehicle driving condition which requires a control mode. All the solenoid valves in the ESP hydraulic unit (A7/3) are in the initial position, i.e. switched deenergized. The system is ready for operation.
This operating mode exists even if there is a fault in the ESP,BAS or ABS. Drive moment control is not activated.
ABS Control Mode
From the wheel speed signals the ESP control module (N47-5) recognizes that the criteria for ABS control exist and the appropriate solenoid valves are actuated in the hydraulic unit. The solenoid valves for the front and rear axle in the ESP hydraulic unit (A7/3) are actuated separately (4 channel control).
ASR control Mode
As soon as a drive wheel has a tendency to slip, the ESP control module (N47-5) actuates the high-pressure and return pump (A7/3m1) the rear axle switchover solenoid valve, the rear axle inlet solenoid valve and the solenoid valves for the rear axle. The solenoid valves for the left or right of the rear axle are actuated separately.
ESP control Mode
In the ESP control module (N47-5) the signals for wheel speeds, steering angle, vehicle yaw rate and lateral acceleration as well as the brake pressures of the front and rear axle circuit are recorded and processed by a vehicle condition controller. Once the input signals are evaluated, the BAS solenoid valve (A7/7y1), inlet solenoid valves, switchover valves, high pressure,return pump (A7/3m1) as well as the solenoid valves required are actuated to regulate the brake pressure in the individual wheel brakes.
ESP Off Mode (ESP OFF)
When the ESP OFF switch (S76/6) is pressed the ASR drive moment control is switched off and in addition the ESP stability function Is cancelled when accelerating and freewheeling. The ESP stability function is retained when braking. The EBR control is switched off.
In this switch position, a brake intervention takes place via the brake moment control circuit up to 40km/h when one drive wheel is spinning. If other intervention conditions are at hand the brake intervention is maintained up to a maximum of 60 km/h. The brake moment is continually reduced however.
BAS Mode
The ESP control module (N47-5) recognizes that emergency braking is taking place from the rate at which the brake pedal is operated and initiates BAS mode, (refer to BAS function).