Electronic stability program (ESP) function - GF42.45-P-0001GZ
MODEL 164 up to Model Year 08
Shown on model designation 164.1
Shown on model designation 164.1
Advantages of Electronic Stability Program (ESP)
- Improves the starting off and acceleration capacity by increased traction; particularly advantageous on a road surface with different adhesion and in curves
- Increases the active driving dynamics safety as only a wheel which is not spinning makes possible optimum traction without loss of lateral support
- Automatically adapts the engine torque to the respective transmission possibilities of the wheels to the road, even if the driver accelerates too hard
- Reduces the danger of skidding under all driving and road conditions by automatic stabilization
- Improves the on-course stability significantly when cornering up to the critical limits
- Reduces the brake distance
- A flashing warning lamp in the instrument cluster signals antilock brake system (ABS) or ESP closed-loop operation to the driver and informs him that he has got close to the physical limits with his vehicle
- Via the ESP Off switch (N72/1s1) an ESP and acceleration slip regulation (ASR) shutoff can take place which is recognized by the warning lamp in the instrument cluster lighting up permanently. As a result better traction can be achieved in deep snow or when snow chains are fitted
ESP
ESP is an active safety system for improving the vehicle stability under all driving situations. It monitors the driving characteristics with the longitudinal and transverse dynamics.
The specified value requirements starting from the driver, such as steering requirements, brake pressure, steering wheel position or drive torque are read in by the ESP control unit and processed further for vehicle stabilization.
It operates by means of individual brake control cycles at one or several wheels of the front or rear axle.
The instructions on towing in the operator's manual must be observed.
Drive torque control
The ESP control unit communicates with the ME-SFI [ME] control unit to adjust the drive torque. The gear stage is also evaluated by the Electric control unit (VGS) to calculate the ESP drive moment control.
Data is exchanged between the electric control unit (VGS), the ME-SFI [ME] control unit and the ESP control unit via the Controller Area Network bus class C (engine compartment) (CAN-C).
The following system functions are integrated in the ESP control unit:
ABS antilock brake system prevents the wheels locking when braking and thus maintains the steerability and directional stability and road adhesion when the vehicle decelerates.
ASR acceleration slip regulation prevents the drive wheels spinning by adapting the drive torque. It also improves directional stability with better traction across the entire speed range.
BAS Brake Assist supports the driver during panic braking.
EBV Electronic brake force distribution prevents overbraking of the rear wheels by corresponding brake force distribution between the front and rear axle.
ETS electronic traction system achieves a locking effect by specific brake application.
EBR engine braking regulation prevents brake slip of the drive wheels in overrun mode and take care of directional stability and road adhesion.
PML speed-sensitive power steering varies the steering assistance corresponding to the vehicle speed.
RDW By comparing the wheel speeds (FL and RR as well as FR and RL) tire pressure loss warning detects the pressure loss at a tire before flat tire damage can occur.
- Signal evaluation and monitoring of sensors
- Safety circuits with shutoff strategy
The ESP control unit is divided up functionally as follows:
- Signal conditioning
- Function logic component
- Safety circuit
- Additional functions
Signal conditioning
The following input signals are processed by the function logic component for calculations or as information:
- Computation of vehicle speed/slip
- Signals of the four rpm sensors at the wheels
- Calculation of lateral forces
- Steering angle sensor signal via CAN-C
- Micromechanical yaw rate sensor AY pickup signal
- BAS diaphragm travel sensor signal (A7/7b1)
- Calculation of longitudinal forces
- CAN C information on engine torque
- CAN C information on current gear
- ESP brake pressure sensor signal (B34)
- Information signals (operation)
- ESP brake pressure sensor signal
- Parking brake indicator switch signal via CAN-C
- ESP Off switch signal
- BAS release switch signal (A7/7s1)
- BAS diaphragm travel sensor signal
Function logic component
The conditioned input signals are processed in the logic section and converted into output signals. The processed four wheel speed signals are constantly compared amongst each other and with specified slip thresholds at the front and rear wheels, depending on the vehicle speed.
The following values and controlled variables are determined:
- Vehicle speed
- Acceleration/deceleration
- Wheel slip (ABS)
- Drive slip (ASR)
- Decel slip (MSR)
Steering angle sensor
The change in the direction of travel or cornering is detected via the signal from the steering angle sensor and different wheel speeds of the front wheels.
The signal from the steering angle sensor in combination with the vehicle speed enable the ESP control unit to record the driver's personal preferences.
Micromechanical yaw rate sensor AY pickup
From the sensor signal the ESP control unit determines the lateral forces when cornering and the rotational speed about the vertical axis. The drive status regulator in the ESP control unit detects an oversteering or understeering vehicle from the lateral acceleration signal, the yaw rate signal and the signal from the steering angle sensor.
CAN C information on engine torque
Via CAN C the ESP control unit is informed by the ME-SFI [ME] control unit about the engine torque delivered. In ESP control mode the function logic component requests the engine control unit to set a reduced engine torque.
CAN C information on the current gear
Via CAN C the function logic section is constantly informed by the electric control unit (VGS) about the current gear. The drive torques acting on the drive wheels are calculated via the current gear and the engine torque signal from the ME-SFI [ME] control unit and are used for drive torque control.
ESP Off switch signal
If a signal from the switch is applied, then the drive moment control circuit is switched off and the ESP warning lamp (A1e41) actuated continuously.
ESP brake pressure sensor signal
The brake pressure is recorded by the sensor and used by the function logic section for calculating the wheel brake forces (longitudinal forces). Actuation of the brake is also registered by the driver.
If an ESP control is necessary, the existing wheel brake forces (longitudinal forces) are also included as well for calculating the lateral stability (lateral forces).
Parking brake indicator switch signal
If there is a signal from this switch, no engine braking regulation is permitted.
BAS diaphragm travel sensor signal
Using this the brake pedal speed is calculated which is needed for the use of BAS.
Safety circuit
The safety circuit detects faulty signals from sensors, faults in the control unit and in the electric line system. The actuation of the high pressure and return pump (A7/3m1) is monitored during the control process. The solenoid valves are monitored permanently.
If a fault is detected, the system is switched off and this is displayed to the driver by the multifunction display (A1p13). In addition, a fault code is stored in the control unit. The safety circuit also constantly monitors the battery voltage. If the voltage drops below 10.5 V or rises above 17.5 V, the system is again shut down until the voltage returns to the specified range.
Speed-sensitive power steering subfunction (SPS)
The control unit calculates the specified current for actuating the SPS [PML} solenoid valve from the internal vehicle speed and the status signal (Y10).
Brake Assist (BAS) sub-function
The conditioned input signals are processed in the function logic section and a Brake Assist System brake application is introduced if necessary.
Wheel speeds and speed status signal outputs
- Output of wheel rpm
For systems which need a wheel speed signal the ESP control unit supplies the current wheel speed from each wheel.
- Output of rpm status signal
The ESP control unit supplies the rotational speed status signal for systems which need information on the current vehicle condition (vehicle stationary, vehicle being driven, rpm sensor defective).
Indicator lamp actuation
The ESP control unit records the signals from the parking brake indicator switch and the signals from the brake lining wear contacts. They are passed on via CAN C to the instrument cluster together with the signals for the multifunction display, the ABS indicator lamp (A1e17) and ESP warning lamp (A1e41).
Function overview
All forces which act on a vehicle outside the center of gravity always want to turn the vehicle about this center of gravity, irrespective of whether they are brake forces, driving forces or side forces acting on one side. The ESP records the vehicle behavior and specifically introduces brake forces for correction at the individual wheels.
Example A: Understeering vehicle (in left-hand curve)
The vehicle pushes outwards over the front wheels.
A precisely calculated braking action is performed on the left rear wheel .
Example B: Oversteering vehicle (in left-hand curve)
The tail of the vehicle breaks away.
A precisely calculated braking action is performed on the right front wheel .
For the ESP, displays with various symbols are located in the instrument cluster.
Turning on the ignition and starting the engine
When the ignition is switched on (ignition/starter switch in position 2) the warning lamps and indicator lamps light up in the instrument cluster (bulb check) and go out when the engine is running and the systems are operational.
Function of ABS indicator lamp
The ABS indicator lamp in the instrument cluster lights up when the key is turned into position "circuit 15 ON". The ABS indicator lamp goes out once the engine has started. This indicates that the ABS is operational.
ABS indicator lamp lights up permanently
The ABS indicator lamp lights up permanently if the ABS/ESP/BAS is not available due to a fault, CAN communication with the instrument cluster is faulty, or ESP is on the diagnosis test or exhaust emission test.
Function of ESP warning lamp
The ESP warning lamp in the instrument cluster lights up if the key is turned to position "circuit 15 ON". The ESP warning lamp goes out once the engine has started. This indicates that the ESP is operational.
Function of ESP warning lamp in driving mode
Once the ESP warning lamp has gone out, it remains off, as long as the ESP closed-loop operation is not active (no wheel has exceeded the adhesion limit).
ESP warning lamp flashes
The ESP warning lamp flashes whilst the ESP closed-loop operation is active (at least one wheel has exceeded the adhesion limit). The ESP warning lamp flashes if one wheel has exceeded the adhesion limit during a starting off process or during a brake application.
ESP warning lamp lights up permanently
The ESP warning lamp lights up permanently if the Electronic Stability Program [ESP] is not available. This is the case if there is an ESP system fault (e.g. fault in the ESP control unit).
The brake system continues to function normally.
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| ESP braking moment control circuit, function | GF42.45-P-2000GZ | ||
| Steering angle sensor, component description | GF42.45-P-5107GZ | ||
| Description of components in ESP control unit | GF42.45-P-5118GZ | ||
| Yaw rate and lateral acceleration sensor, component description | GF42.45-P-5120GZ | ||
| ESP Off switch, component description | GF42.45-P-5121GZ | ||
| Wheel rpm sensor, component description | GF42.45-P-5134GZ | ||
| Traction system hydraulic unit, component description | GF42.50-P-4001GZ |