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

The ESP control module is divided up functionally 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

Function logic section 

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

• Speed sensor signals:

  The 4 conditioned 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 controlled variables are determined by this comparison process:

  • Vehicle speed
  • Acceleration/deceleration
  • Brake slip (ABS)
  • Drive slip (ASR)
  • Overrun slip (MSR)
• 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 transmits the recording of the driver's required handling of the vehicle to the ESP control module.

• Lateral acceleration sensor (B24/2) signal:

  The ESP control module recognizes the lateral forces occurring when cornering through the lateral acceleration signal. The vehicle condition controller in the ESP control module recognizes an oversteering vehicle through 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 recorded by the yaw rate sensor in the ESP control module. The ESP control module records 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.

  With ESP control mode the function logic section of the ME-SFI control module the requests the adjustment of the reduced engine torque and a brief reduction of 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 control (ESP). With ESP control mode the current transmission gear is taken into account by the vehicle condition controller.

• Brake pressure sensor (B34) signal:

  The brake pressure is recorded by the brake pressure sensor 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) are also included in calculating the lateral control forces (lateral forces).

• Stop lamp switch (S9/1) signal:

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

• Parking brake switch (S12) signal:

  No MSR 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 actuated permanently if there is a signal from the ESP OFF switch.

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 displayed to the driver by the illumination of the ESP MIL or BAS/ESP malfunction indicator lamp (A1e42 or A1e47). 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 of speed-sensitive power steering (models 140, 210) 

The control module calculates the specified current to actuate the SPS P-valve (Y10) from the internal vehicle speed and status signal.

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.
• 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 driving, speed sensor defective).

Indicator lamp actuation 

The signals from the brake pad wear contacts and the parking brake are recorded by the ESP control module. They are transmitted to the instrument cluster via a serial data bus together with signals for the ABS and ESP MIL and warning lamps and on vehicles with CAN connection on the instrument cluster via a data bus.