GF42.45-P-0001RT Electronic Stability Program (ESP), Function

GF42.45-P-0001RT Electronic stability program (ESP), function

Component Identification:

Advantages of Electronic Stability Program (ESP)
^ Improves moving-off and acceleration capabilities by increasing traction; especially useful on road surfaces with different levels of grip and when cornering.
^ Increases the level of active driving safety since only non-spinning wheels provide optimum traction without impairing side stability.
^ Automatically adapts the engine torque to the respective transmission opportunities of the wheels to the road, even if the driver accelerates too hard.
^ Reduces the risk of skidding under all driving conditions and road conditions by automatic stabilization.
^ Significantly improves the directional stability of the vehicle when cornering up to the limit range.
^ Reduces the brake distance.
^ A flashing warning lamp in the instrument signals antilock brake system (ABS) closed-loop operation or ESP [Electronic Stability Program] closed-loop operation to the driver and informs him that he has approached the physical limits of driving with his vehicle.
^ An ESP control and acceleration slip regulation (ASR) can be switched off via the ESP Off switch (N72/1s1). This can be recognized by the warning lamp in the instrument cluster lighting up permanently. Better traction can be achieved as a result in deep snow or when snow chains are fitted.

ESP
ESP [Electronic Stability Program] is an active safety system for improving vehicle stability under all driving situations. It monitors the driving characteristics with regard to longitudinal and lateral dynamics.

The specified value requirements initiated by the driver, such as steering wish, brake pressure, steering wheel position or drive torque are read in by the ESP control unit and processed further to stabilize the vehicle.

It operates by actuating the brakes individually on one or more wheels on the front or rear axle.

Follow the instructions for towing in the operator's manual.

Drive torque control
The ESP control unit communicates with the ME-SFI [ME] control unit for adjusting the drive torque. To calculate the ESP drive torque control the gear stage is also evaluated by the electric control unit (VGS).

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 Anti lock brake system prevents the wheels locking when braking and thus maintains the steerability and directional stability and road adhesion during vehicle deceleration.
ASR Acceleration slip regulation prevents the drive wheels spinning by adapting the drive torque. It also improves directional control with better traction across the entire speed range.
BAS Brake Assist assists the driving during panic braking.
EBV Electronic brake force distribution prevents the rear wheels being overbraked by appropriate brake force distribution between the front and rear axle.
ETS Electronic traction system achieves a locking effect by selective use of the brakes.
HSA Start-off assist delays the depressurization in the brake on a longitudinal incline (ascent).
EBR Engine braking regulation reduces wheel slip of the drive wheels in overrun mode and takes care of directional stability and road adhesion.
SPS Speed-sensitive power steering varies the power steering assistance corresponding to vehicle speed.
RDW By comparing the wheel speeds (FL and RR as well as FR and RL) tire pressure loss warning detects pressure loss in a tire before it can be damaged due to running flat.
^ Signal evaluation and monitoring of sensors
^ Safety circuits with shut-off strategy

The functions of the ESP control unit are divided into:
^ 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:
^ Calculation of vehicle speed/slip

- Signals from the 4 rpm sensors at the wheels

^ Calculation of lateral forces

- Steering angle sensor signal via CAN C
- micro mechanical 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 conditioned 4 wheel speed signals are constantly compared with each other and with specified engagement limits at the front and rear wheels depending on 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 driving direction or cornering is detected via the steering angle sensor signal and the different wheel speeds of the front wheels.

The steering angle sensor signal in combination with the vehicle speed provide the ESP control unit with the facility of recording the characteristics required by the driver.

Micromechanical yaw rate sensor AY pickup
The ESP control unit determines the lateral forces occurring when cornering and the yaw rate about the vertical axis from the sensor signal. The drive status regulator in the ESP control unit detects an over steering or under steering vehicle from the lateral acceleration signal, the yaw rate signal and the steering angle sensor signal.

CAN C information on engine torque
The ESP control unit is informed by the ME-SFI [ME] control unit about the engine torque delivered via CAN C. 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
The function logic section is continuously informed by the electric control unit (VGS) about the current gear via CAN C. Via the current gear and the engine torque signal from the ME-SFI [ME] control unit the drive torques acting on the drive wheels are calculated and used for drive torque control.

ESP Off switch signal
If a switch signal is applied, the drive torque control circuit is switched off and the ESP warning lamp (A1e41) is actuated permanently.

- ESP brake pressure sensor signal
The brake pressure is recorded by the sensor and used by the function logic section to calculate 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 for calculating the lateral stability (lateral forces).

Parking brake indicator switch signal
If a signal from this switch exists, then no engine drag torque 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 this 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)
From the vehicle speed available internally and the status signal the control unit calculates the specified current for actuating the SPS [PML] solenoid valve.

Brake Assist (BAS) sub-function
The conditioned input signals are processed in the function logic section and a BAS brake application introduced if necessary.

Wheel speeds and speed status signal outputs

^ Output of wheel rpm
Systems which require a wheel speed signal are provided with the current wheel speed from each wheel by the ESP control unit.

^ Output of rpm status signal
Systems which require information about the current vehicle status (vehicle stationary, vehicle moving, rpm sensor faulty) are provided with the speed status signal by the ESP control unit.

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. Together with the signals for the multifunction display, the ABS indicator lamp (A1e17) and the ESP warning lamp (A1e41) they are passed on to the instrument cluster via CAN C.

Function overview
All the 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 acting on one side, driving power or side forces. The ESP records the vehicle characteristics and for correction introduces specific brake forces at the individual wheels.

Example A: understeered vehicle (cornering left)
The vehicle pushes outwards over the front wheels.

A precisely calculated braking action is performed on the left rear wheel.

Example B: oversteered vehicle (cornering left)
The tail of the vehicle breaks away.

A precisely calculated braking action is performed on the right front wheel.

Component Identification:

Displays with various symbols for ESP are located in the instrument cluster.

Switching on ignition and starting engine
The warning lamps and indicator lamps in the instrument cluster (bulb check) light up when the ignition is switched on (Ignition/starter switch in position 2) 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 a 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 into 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 out, as long as ESP closed-loop operation is not active (no wheel has exceeded the adhesion limit).

ESP warning lamp flashes.
The ESP warning lamp flashes while ESP closed-loop operation is active (at least one wheel has exceeded the adhesion limit). The ESP warning lamp flashes if during a starting off process or during a brake application, one wheel has exceeded the adhesion limit.

ESP warning lamp lights up permanently.
The ESP warning lamp lights up permanently if the ESP is not available. This is the case when there is an ESP system error (e.g. fault in the ESP control unit).

The brake system continues to function normally.