Electronic Stability Program (ESP)
Task
Execute all brake control functions of Antilock Brake System (ABS), Acceleration Slip Regulation (ASR) and Electronic Stability Program (ESP). For ASR and ESP data is exchanged with the control modules of the engine/transmission control via a Controller Area Network (CAN) data bus. Influence the engine/transmission management in the event of a control.
Incorporates the complete Brake Assist (BAS) control module function.
The ESP control module also incorporates the necessary electronics and control logic for Speed-Sensitive Power Steering (SPS).
Supplies other systems with the vehicle speed signal and wheel speed status signal (direct or via CAN).
Supplies the instrument cluster with the signals for the multifunction display (A1p13) for the following displays via CAN. "ESP EL. STAG. PROGRAM - FIND A WORKSHOP! "BAS BRAKE ASSIST - FIND A WORKSHOP! "RELEASE PARKING BRAKE!".
Supplies the instrument cluster with the signal for the ABS MIL (A1e17) via CAN.
Sends the stop lamp signal to the rear SAM control module to continue actuating the stop lamps or suppresses this when ESP control is active.
Function
The Functions of the ESP control module are divided up as follows:
^ Signal conditioning
^ Function logic section
^ Safety circuit
^ Additional Functions
Signal Conditioning
The following input signals are processed by the function logic section for calculation or as information:
^ Calculation Of Vehicle Speed/Slip
- Speed sensor signals
^ Calculation Of Lateral Forces
- Steering angle sensor signal
- Lateral acceleration sensor signal
- Yaw rate sensor signal
^ Calculation Of Longitudinal Forces
- CAN information, engine torque
- CAN information. current transmission gear
- Brake pressure sensor signal
^ Information Signals (Operation)
- Stop lamp switch signal
- Parking brake switch signal
- ESP OFF switch signal
- BAS release switch signal
- BAS diaphragm travel sensor signal
Function Logic Section
The conditioned input signals are processed in the logic section and converted into output signals.
^ Speed Sensor Signals
The conditioned 4 wheel speed signals are constantly compared with each other and with specified slip thresholds at the front and rear wheels, depending on vehicle speed.
The following values or control variables are determined by this comparison process.
- Vehicle Speed
- Acceleration/Deceleration
- Brake Slip (ABS)
- Drive Slip (ASR)
- Overrun Slip (EBR)
^ Steering Angle Sensor (N49) Signal:
The change in the direction of travel or cornering is recognized via the steering angle sensor signal and different wheel speeds of the front wheels. These two recognition variables in conjunction with vehicle speed provide the ESP control module with the driver's desired handling of the vehicle.
^ Lateral Acceleration Sensor (B24/2) Signal:
The ESP control module recognizes the lateral forces occurring when cornering from the lateral acceleration sensor signal. The vehicle status controller in the ESP control module recognizes an oversteering vehicle from the lateral acceleration signal together with the yaw rate signal.
^ ESP Yaw Rate Sensor (N64) Signal.
The movements (yaw rate) which want to turn the vehicle about its perpendicular axis as occur when a vehicle skids are registered by the yaw rate sensor in the ESP control module. The ESP control module recognizes the actual handling of the vehicle using the lateral acceleration sensor signals and yaw rate sensor signals.
^ CAN Information. Engine Torque
The ESP control module is informed about the engine torque delivered by the ME-SFI control module via the CAN data bus. In ESP control mode the Function logic section of the ME-SFI control module requests the adjustment of the reduced engine torque and a brief reduction of the ignition advance angle.
^ CAN Information. Current Transmission Gear
The Function logic section (ESP) is constantly informed about the current transmission gear by the ETC control module via the CAN data bus. The drive forces acting on the drive wheels are calculated via the current transmission gear and used for drive moment con' Sol (ESP).
^ Brake Pressure Sensor (B34) Signal.
The brake pressure is registered by the brake pressure sensor and used by the logic sect on to calculate the wheel brake forces (longitudinal forces). If ESP control is required during a braking process, the existing wheel brake forces (!longitudinal forces) are also included for calculating the lateral control forces (lateral forces).
^ Stop Lamp Switch (S9/1) Signal:
When the brake is operated signals of the double contact switch (Normally Open contact and Normally Closed contact) are recognized and evaluated by the ESP logic section. If there is an ASR control node. for example, this process is terminated immediately. During ESP control these information signals are processed in addition to the brake pressure sensor signal.
^ Parking Brake Switch (S12) Signal:
No EBR control mode is permitted if there is a signal from the parking brake switch.
^ ESP OFF Switch (S76/5) Signal.
The drive moment control circuit is switched off and the ESP warning lamp is activated permanently if there is a signal from the ESP OFF switch.
^ BAS Release Switch Signal
The stop lamp suppression relay is actuated when the BAS release switch is not operated and the BAS solenoid value is active at the same time. This prevents the stop lamps coming on when the brake pedal is not operated.
^ BAS Diaphragm Travel Sensor Signal
The rate at which the brake pedal is operated. which is required for the BAS operation. is calculated using the BAS diaphragm travel sensor signal.
Safety Circuit
The Task of the safety circuit is to recognize faulty sensor signals, faults in the control module and the electrical cable system. The actuation of the charging pump and the high-pressure/ return pump is monitored during the control process. The solenoid valves are monitored constantly. If a fault is recognized the system is switched off and this is indicated to the driver by the BAS/ESP malfunction indicator lamp (A1e47) coming on. A fault code is also stored in the control module.
The safety circuit also constantly monitors the battery voltage. if the voltage drops below 10.5 V or exceeds 17.5 V, the system is also switched off until the voltage is in the specified range again.
Additional Functions
Partial Function Speed-Sensitive Power Steering
The control module calculates the specified current to actuate the SPS P-valve (Y10) from the internal vehicle speed and status signal.
Partial Function Brake Assist (BAS)
The conditioned input signals are processed in the logic section and BAS braking initiated if necessary (refer to BAS control module Function).
Wheel Speed Outputs And Speed Status Signal Outputs
^ Wheel Speed Output: The ESP control module supplies the current wheel speed of each wheel for systems which need a wheel speed signal.
^ Speed Status Signal Output: The ESP control module supplies the speed status signal for systems which need information on the current vehicle condition (vehicle stationary, vehicle moving, speed sensor defective).
Indicator Lamp Actuation
The signals from the brake pad wear contacts and the parking brake are registered by the ESP control module. They are transmitted to the instrument cluster via a serial data bus together with the signals for the ABS and ESP MIL and warning lamps and on vehicles with CAN connection on the instrument cluster via a CAN data-bus