ESP hydraulic system
N47-5
Sensor signal reception, sensor monitoring and calibration, CAN monitoring
Status controller
1. Detects driver's desired behavior with respect to actual vehicle behavior (lateral acceleration, yaw rate)
2. Determines friction-factor-dependent specification values as well as drive slip of rear wheels
3. Calculates increase and reduction in specified wheel slip
Brake-slip control and engine braking regulation (ABS and EBR)
1. For ABS braking: Calculates braking slip specifications
2. Calculates wheel brake pressure specifications (ABS) as well as (EBR)
Acceleration slip regulation (ASR)
Computes wheel brake pressure specifications and for EBR
Conversion of pressure specifications into valve control times
Monitoring control module, operating conditions and control signals
Fault identification, cutout, type of fault, diagnosis entry
Engine and transmission data via CAN
Steering angle
Yaw rate
Brake pressure in pressure circuit 1
Wheel speeds
Lateral acceleration
Output stages
Data link connector
Wheel speed signals, speed status signal
CAN data on engine, transmission and instrument cluster lamp actuation
Stop lamp suppression relay
Brake pressure in pressure circuit 2
Brake Assist (BAS)
Calculates the pedal speed and cut-in threshold
The functions of the ESP control module are divided as follows:
Signal conditioning
Function logic component
Safety circuit
Auxiliary functions
Signal conditioning
The following input signals are processed by the function logic component for calculations or as information:
Calculation of vehicle speed/slip
- Signals from wheel speed sensors
Calculation of lateral forces
- Signal from steering angle sensor
- Signal from lateral acceleration sensor
- Signal from yaw rate sensor
Calculation of longitudinal forces
- CAN data on engine torque
- CAN data on current gear
- Signals from brake pressure sensors
Information signals (control)
- Signal from stop lamp switch
- Signal from parking brake switch
- Signal from ASR OFF switch
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Function logic component
The conditioned input signals are processed in the logic component and converted into output signals.
Signals from wheel speed sensors:
The 4 conditioned wheel speed signals are constantly compared with each other and with specified slip thresholds on the front and rear wheels in relation to the speed of the vehicle.
This comparison is used to determine the following values and control variables:
- Vehicle speed
- Acceleration/deceleration
- Brake slip (ABS)
- Acceleration slip (ASR)
- Deceleration slip (EBR)
Signal from steering angle sensor
If the vehicle changes direction or is being driven on a curve, this is detected using the signal from the steering angle sensor and on the basis of the different rotational speeds of the front wheels. These two variables in conjunction with the ground speed informs the ESP control module of the vehicle handling characteristics desired by the driver.
Signal from lateral acceleration sensor
The ESP control module uses the signal from the lateral acceleration sensor to determine the lateral forces occurring during cornering. The status controller in the ESP control module can detect whether the vehicle is oversteering from the lateral acceleration signal together with the yaw rate signal.
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Signal from yaw rate sensor:
The ESP control module uses the yaw rate sensor to detect the movements (yaw rate) that the vehicle attempts to make about the vertical axis (e.g. when the vehicle is accelerated). Using the signals from the lateral acceleration sensor and yaw rate sensor, the ESP control module determines the actual handling characteristics of the vehicle.
CAN data on engine torque
The ESP control module is informed about the engine torque output by the engine control module via the CAN data bus.
In the case of ESP control mode, the function logic component tells the engine control unit to set a reduced engine torque.
CAN data on currently engaged gear (automatic transmission only)
Via the CAN data bus the function logic component (ESP) is constantly informed about the currently engaged gear by the gear detection module. The current gear is used to calculate the drive forces acting on the drive wheels and for drive torque control.
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Signal from brake pressure sensors (B34/1, B34/2):
The brake pressure sensors detect the brake pressure which is used by the logic component to calculate the wheel brake forces (longitudinal forces). If ESP control becomes necessary, the existing wheel-brake forces (longitudinal forces) are taken into consideration when the cornering forces (lateral forces) are calculated.
The brake pressure build-up speed is used to calculate the brake pedal speed for the BAS function.
Signal from stop lamp switch (S9/1):
When the brake is actuated, signals from the dual contact switch (NO and NC contact) are registered and evaluated by the ESP logic component. This process is terminated immediately if, for example, ASR control becomes active. In the case of ESP control, these information signals are processed in addition to the signal from the brake pressure sensor.
Signal from parking brake switch:
If a signal is issued from the parking brake switch, EBR control mode is not permitted.
Signal from ASR OFF switch (S6/2s8):
If a signal is received from the ASR OFF switch, the drive torque control circuit is deactivated and the ESP warning lamp is actuated to shine constantly.
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Safety circuit
The safety circuit detects faulty signals from sensors, faults in the control module and in the electric line system. Actuation of the high-pressure and return-flow pump is monitored during the control process. The solenoid valves are monitored permanently. If a fault is detected, the system is shut down and the driver is alerted by the lighting of the BAS/ESP indicator lamp (A1e47). In addition, a fault code is stored in the control module.
Moreover, the safety circuit continuously monitors the battery voltage. If the voltage falls below 10.5 V or exceeds 17.5 V, the system is switched off until the voltage returns to the specified range.
Auxiliary functions
Brake Assist (BAS), subfunction
The conditioned input signals are processed in the logic component and a BAS braking sequence is initiated if required (see BAS, function).
Wheel speeds and speed status signal outputs
Wheel speed output: Systems which require a wheel speed signal are provided with the current wheel speed from each wheel by the ESP control module.
Speed status signal output: Systems which require information on the current status of the vehicle (vehicle stationary, vehicle in motion, rpm sensor defective) are provided with the speed status signal by the ESP control module.
Indicator lamp actuation
The ESP control module receives the signals from the brake lining wear contacts and the parking brake. These signals, together with the signals for the ABS and ESP indicator and warning lamps, are passed on to the instrument cluster via a serial data line.