Function of ESP control module - GF42.45-P-4500-01C

Model 163 

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:

• Calculation of vehicle speed/slip
  • Speed sensor signals (L6/1, L6/2, L6/3 and L6/4)
• Calculation of lateral forces
  • Steering angle sensor (N49) signal
  • Lateral acceleration sensor (B43) signal
  • ESP yaw rate sensor (B45) signal
• Calculation of longitudinal forces
  • CAN information, engine torque
  • CAN information, current transmission gear
  • Brake pressure sensor signal
• Information signals (operation)
  • Stop lamp switch (S9/1) signal
  • Parking brake switch (S12) signal
  • ESP OFF switch (S76/6) signal
  • BAS release switch (A7/7s1) signal
  • BAS diaphragm travel sensor (A7/7b1) signal

Function logic section 

The conditioned input signals are processed in the logic section and converted into output signals.

• Speed sensor signals:

  The 4 wheel speed signals conditioned 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 controlled 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 (cornering) is recognized via the steering angle sensor signal and the different wheel speeds of the front wheels. These two recognition variables in conjunction with vehicle speed signal the driver's desired handling of the vehicle to the ESP, SPS and BAS control module (N47-5).

• Lateral acceleration sensor (B43) signal:

  The ESP control module recognizes the lateral forces occurring when cornering from the lateral acceleration sensor signal. The vehicle condition 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 (B45) signal:

  The yaw rate at which the vehicle turns about the perpendicular axis (e.g. vehicle skidding) is recorded in the ESP control module by the yaw rate sensor. The ESP control module recognizes the actual handling of the vehicle using the signals from the lateral acceleration sensor and yaw rate sensor.

• CAN information, engine torque

  The ESP control module is informed of the engine torque delivered by the engine control module (ME-SFI) (N3/10) via the CAN data bus. In ESP control mode the function logic section of the engine control module calls for a reduced engine torque and a brief reduction in the ignition advance angle to be set.

• CAN information, current transmission gear (on automatic transmission only)

The function logic section (ESP) is constantly informed of 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 control.

• Brake pressure sensor (B34) signal:

  The brake pressure is recorded by the brake pressure sensors and used by the logic section to calculate the wheel brake forces (longitudinal forces). If an ESP control is required during a braking process, the wheel brake forces (longitudinal forces) measured are also included in calculating the lateral control forces (lateral forces).

• Stop lamp switch (S9/1) signal:

  When the brake is operated the signals of the stop lamp switch (NO contact and NC contact) are recognized and evaluated by the ESP logic section. If there is an ASR control mode, for example, this process is terminated immediately when the brake is operated. With an ESP control these information signals are processed in addition to the brake pressure sensor signals.

• 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 (A1 e41) is actuated permanently if there is a signal from the ESP OFF switch.

• BAS release switch (A7/7s1) signal

  The stop lamp suppression relay is actuated when the BAS release switch is not operated and the BAS solenoid valve is active at the same time. This prevents the stop lamps coming on when the brake pedal is not operated.

• BAS diaphragm travel sensor (A7/7b1) signal

The rate at which the brake pedal is operated by the driver is calculated using the BAS diaphragm travel sensor signal. The BAS function is effective if a defined pedal speed is exceeded.

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 high pressure and return pump is monitored during the control process. The solenoid valves are monitored constantly. If a fault is recognized the system is then 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 returns to the specified range.

Additional functions 

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 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.
• Wheel 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 parking brake are recorded by the ESP control module. They are transmitted to the instrument cluster (A1) via CAN data buses together with the signals for the ABS, ETS and ESP indicator and malfunction indicator lamps.