GF42.45-P-0001GM Electronic Stability Program (ESP) Function
GF42.45-P-0001GM Electronic stability program (ESP) function
Function requirements, general
^ Circuit 61 ON
Electronic Stability Program (Electronic Stability Program) (ESP), general information
The ESP system supports the driver in critical driving situations through interventions by the brake system and influencing the engine control. The ESP system is controlled by the ESP control unit (N47-5).
To determine the driving situation at any given time, the ESP control unit evaluates the signals from the following components:
- micro mechanical turn rate sensor AY pickup (B24/15)
- Left front rpm sensor (L6/1)
- Right front rpm sensor (L6/2)
- Left rear rpm sensor (L6/3)
- Right rear rpm sensor (L6/4)
- Steering angle sensor (N49)
- BAS diaphragm travel sensor (A7/7b1)
- BAS release switch (A7/7s1)
- BAS solenoid valve (A7/7y1)
- ESP brake pressure sensor (B34)
- Accelerator pedal sensor (B37)
The ESP system is comprised of the following partial functions:
^ Function sequence, ESP
^ Function sequence for roller dynamometer mode
^ Anti lock brake system (ABS) function sequence
^ Acceleration Slip Regulation (ASR) and Electronic Traction System (ETS) function sequence
^ Engine braking regulation (EBR [MSR]) function sequence Electronic brake force distribution (EBD) function sequence
^ Brake Assist System (BAS) function sequence
^ Trailer stabilization (Trailer Stability Assist) (TSA) function sequence (with code (550) Trailer hitch)
^ Hill Start Assist function sequence
^ Function sequence for downhill speed regulation (with model 164)
^ Function sequence for off-road mode (with model 164 with code (430) Off-road package)
^ Passive ASR and ESP switching function sequence
^ Fault handling function sequence
^ System fault display function sequence
Additional function requirements, ESP
^ ESP active
Function sequence, ESP
ESP prevents breakaway when the vehicle oversteers or understeers. It ensures that the vehicle does not deviate from the course specified by the driver (within physical limits). Brake forces are produced selectively at the individual wheels to correct any deviations. Furthermore, reduction of the drive torque takes place in order to increase directional stability and road adhesion.
The ESP control unit processes the following measured quantities to determine the vehicle behavior:
^ Yaw velocity
^ Steering wheel angle
^ Brake pressure
^ Engine torque
^ Transmission stage
^ Lateral acceleration
The side-slip angle (angle between vehicle longitudinal axis and direction of movement of the vehicle's center of gravity) is calculated using the yaw rate (speed of vehicle rotation about vertical axis). The yaw rate, the lateral acceleration and the turning angle of the front wheels (calculated from the steering wheel angle) can be used to determine the lateral forces on the wheels. The longitudinal forces on the wheels are calculated using the engine torque, transmission stage and brake pressure at each wheel.
If the yaw angle velocity measured does not match the specified value or if the determined side-slip angle is too large, the ESP control unit generates a signal for brake force build-up or reduction for the relevant wheel. The resulting forces stabilize the vehicle.
A distinction is made between under steering and over steering vehicle behavior.
Intervention in the case of oversteer:
If the vehicle begins to oversteer, brake pressure is built up at the outer front wheel. The resulting reduction in lateral force at the outer front wheel generates a yawing moment which counteracts the tendency of the vehicle to rotate inward. The vehicle speed decreases as a result of the brake force at the front wheel, which also enhances stability.
Intervention in the case of understeer:
If the vehicle understeers, the maximum possible lateral force at the front axle has been exceeded. This means that the vehicle pushes itself over the front axle and toward the outer edge of the corner. If at this point the driver depresses the accelerator pedal, the drive torque is first of all reduced.
If this is not enough or the accelerator pedal is not depressed, any starting instability can be prevented through brake application at up to three wheels:
Stage 1: Brake pressure reduction at inner rear wheel
Stage 2: Stage 1 plus brake pressure buildup at outer rear wheel
Stage 3: Stage 2 plus brake pressure buildup at inner front wheel
Depending on the brake force, a torque is generated which causes the vehicle to rotate inward with a simultaneous reduction in speed. This has a stabilizing effect.
The ESP control unit sends a reduce drive torque signal over the engine compartment CAN to the CDI control unit (N3/9) (with diesel engine) or to the ME-SFI [ME] control unit (N3/10) (with gasoline engine), which then reduces the engine performance accordingly.
A pending shift operation is suppressed for the duration of control intervention.
For this purpose, the ESP control unit transmits a signal over the engine compartment CAN to the CDI control unit or ME-SFI [ME] control unit, which transmits the information to the fully integrated transmission control unit (VGS) (Y3/8n4) over the engine compartment CAN. The fully integrated transmission control unit suppresses the shift operation.
Function sequence for roller dynamometer mode
The ESP, ABS and ASR can be switched into passive mode to enable the vehicle to be tested (roller dynamometer mode).
To do so, the Workshop menu in the instrument cluster (A1) has to be activated and the engine started.
The ESP warning lamp (A1e41) and the ABS indicator lamp (A1e17) light up in the instrument cluster. In addition, a message is displayed in the multifunction display (A1p13) of the instrument cluster.
Roller dynamometer mode can also be activated via diagnosis.
ABS function sequence
ABS prevents the wheels from locking up when braking and as a result maintains the steerability and directional stability and road adhesion during vehicle deceleration.
If a locking wheel is detected by the ESP control unit on the basis of the signals from the rpm sensors, the brake pressure is reduced at the appropriate brake cylinder until the wheel begins to turn again.
ASR/ETS function sequence
ASR/ETS prevents the driven wheels from spinning when the vehicle is being driven. In addition it causes an improved directional stability and road adhesion with an increased traction potential over the entire vehicle speed range. The ESP control unit records the spinning of the drive wheels via the signals from the rpm sensors. Wheel spinning is countered by reduction of the drive torque.
For this purpose, the ESP control unit sends a signal requesting a reduction in drive torque via the engine compartment CAN to the CDI control unit or ME-SFI [ME] control unit, which then reduces the engine output.
The drive torque is transmitted to the opposite, stable drive wheel by means of intervention by the brake system on the spinning wheel.
The system constantly checks whether the drive torque specified by the driver via the accelerator pedal sensor (B37) can be allowed again e.g. due to improved road adhesion.
EBR [MSR] function sequence
EBR [MSR] reduces brake slip at the drive wheels during deceleration and ensures directional control. If slip occurs at the drive wheels when the accelerator pedal is released, this is detected by the ESP control unit. The signal is sent via the engine compartment CAN to the CDI control unit or ME-SFI [ME] control unit.
Wheel slip is reduced by increasing drive torque and as a result the lateral stability of the vehicle is improved.
EBD function sequence
EBD allows the vehicle brake system to be configured according to requirements. Corresponding brake force distribution of the front axle to the rear axle helps to prevent over braking of the rear wheels.
If the rear wheel/front wheel slip ratio exceeds a specified limit value during a brake application, the ESP control unit prevents any further increase in brake pressure at the rear wheel.
BAS function sequence
BAS detects emergency braking situations from rapid actuation of the brake pedal and, if necessary, increases the brake pressure in order to achieve maximum possible deceleration. The ESP control unit evaluates the increase in pressure in the brake system and initiates an emergency stop if a certain triggering threshold is exceeded.
Function sequence for trailer stabilization
The trailer stabilization detects pendular swinging motion in a tractor/trailer combination based on the yawing vibrations caused in the tractor vehicle by the trailer.
The yawing vibrations are recorded by the ESP control unit through the yaw rate sensor for lateral and longitudinal acceleration.
Alternate brake application requests at the front axle help to stabilize the vehicle combination. If this is unable to be achieved, all the wheels are braked and the drive torque is reduced.
No additional sensors are used on the trailer or trailer hitch.
Information about a recognized trailer is sent by the rear SAM control unit (N10/8) over the interior CAN to the central gateway control unit (N93). This routes the information over the engine compartment CAN to the ESP control unit.
Additional function requirements for the Hill Start Assist
^ Vehicle not secured with parking brake
^ Incline detected with vehicle at standstill
Hill Start Assist function sequence
Hill Start Assist helps to prevent the vehicle rolling back when starting off in a forward gear range as the foot moves from the brake pedal to the accelerator pedal.
The function is triggered automatically when the yaw rate, lateral and longitudinal acceleration sensor detects an incline with the vehicle at a standstill which would cause the vehicle to roll contrary to the gear range engaged.
This information is transmitted to the ESP control unit via the vehicle dynamics CAN. The ESP control unit also reads the BAS release switch discretely and thus detects the status of the brake pedal.
The status of the parking brake is detected via the parking brake indicator switch (S12). This switch is read in discretely via the front SAM control unit (N10) and its status is sent to the central gateway control unit via the interior CAN.
The central gateway control unit routes the information on the engine compartment CAN. This is read by the ESP control unit. The brake pressure applied by the driver is maintained in the brake calipers by the traction system hydraulic unit (A7/3).
Once the brake pedal is released, the brake pressure is modulated based on the balance of torques (downward torque due to slope, braking torque and drive torque).
When the torque is sufficient to move off, the Hill Start Assist function is deactivated and the vehicle drives off.
However, if the driver does not press the accelerator pedal, the pressure in the brake calipers is reduced to zero after t = 0.8 to 1.5 s.
Hill Start Assist does not assume any "HOLD" functions.
Additional function requirements for speed control during downhill driving
^ v < 30 km/h
Function sequence for speed control during downhill driving
The downhill speed regulation serves to provide greater safety when driving on steep terrain.
The vehicle speed is then maintained in accordance with the speed setting (this is shown on the multifunction display of the instrument cluster).
During downhill driving the setting speed can be varied using the CC [TPM] button (S40) (with code (494) USA version) or the CC [TPM] button (S40/4) (without code (494) USA version).
On model 164.8 and model 164.1 with code (430) Off-road package,
The corresponding menu in the instrument cluster can be used to set the relevant setting speed for the downhill speed regulation function, in a range of v = 4 km/h up to v = 18 km/h in increments of 2 km/h.
The system is activated as follows:
^ On model 164.1 without code (430) Off-road package:
- Over the Downhill Speed Regulation switch (N72/1s24) in the upper control panel control unit (N72/1)
^ On model 164.8 and on model 164.1 with code (430) Off-road package:
- Via the Downhill Speed Regulation switch (N72s30) in the lower control panel control unit (N72)
The activation is indicated by a light-emitting diode in the Downhill Speed Regulation switch.
the request to activate the downhill speed regulation is read-in by the lower control panel control unit and transmitted to the upper control panel control unit via the instrument panel LIN.
On model 164.1 without code (430) Off-road package, the request to activate the downhill speed regulation is read-in directly by the upper control panel control unit.
In both cases, the upper control panel control unit places the signal on the interior CAN. The instrument cluster receives the signal and places this information along with the current speed setting on the engine compartment CAN.
The ESP control unit receives the signals and adjusts the vehicle speed to comply with the setting by means of brake interventions and appropriate requests to the engine control and transmission control systems. If the driver accelerates the vehicle by pressing the accelerator pedal while the function is active, the downhill speed regulation switches to passive mode.
If the vehicle speed is v > 35 km/h when the accelerator pedal is not pressed, it is actively regulated to the configured setting speed.
If the driver accelerates the vehicle to a speed of v > 35 km/h using the accelerator pedal while the function is active, the downhill speed regulation switches off automatically and the LED in the Downhill Speed Regulation switch goes out. A message also appears on the multifunction display of the instrument cluster and warning tone sounds. If the downhill speed regulation is switched off manually using the Downhill Speed Regulation switch, a message also appears on the instrument cluster's multifunction display. A warning tone does not sound in this case.
Additional function requirements for off-road mode
^ Circuit 61 ON
^ Gear range "N" active
^ v < 40 km/h
Function sequence for off-road mode
The off-road mode function sequence comprises the following component functions:
^ Function sequence for activating the off-road mode
^ Function sequence for adaptation of the threshold values
^ Function sequence for engine torque support (model 164.8 and model 164.1 with code (430) Off-road package)
^ Function sequence for locking influence (model 164.8 and model 164.1 with code (430) Off-road package)
Function sequence for activating off-road mode
Model 164.1 without Code (430) Off-road package:
Off-road mode is activated using the off-road program switch (N72/1s25) in the upper control panel control unit.
Activation is indicated by an illuminated light emitting diode in the off-road program switch. The off-road symbol also appears on the multifunction display of the instrument cluster.
Off-road mode is deactivated by pressing the off-road program switch again. The light-emitting diode in the off-road program switch goes out and the display in the multifunction display goes off.
Model 164.8 and model 164.1 with code (430) Off-road package
Off-road mode is activated using the Low Range switch (N72s31) in the lower control panel control unit.
The light emitting diode in the Low Range switch flashes during the shift operation. The off-road symbol also appears on the multifunction display of the instrument cluster.
The light emitting diode in the Low Range switch lights up to indicate that the shift operation is complete and off-road mode is activated.
The shift operation can be aborted while the light emitting diode in the Low Range switch is flashing by pressing the Low Range switch again.
Function requirements for deactivation of off-road mode:
^ Circuit 61 ON
^ Gear range "N" active
^ v < 70 km/h
Off-road mode is deactivated by pressing the Low Range switch again.
The light emitting diode in the Low Range switch flashes during the shift operation.
Once the shift operation is complete, the light emitting diode in the Low Range switch goes out and the indicator on the multifunction display of the instrument cluster goes out.
The shift operation can be aborted while the light emitting diode in the Low Range switch is flashing by pressing the Low Range switch again.
Adjustment of threshold values function sequence
By activating off-road mode:
- The thresholds for potential ESP intervention are widened i.e. ESP intervention only occurs under high vehicle dynamics.
- The ABS lockup phases are extended. For example, during a poor stretch of road the wheels are allowed to lock to reduce the braking distance (a loose surface supports a braking effect through a corresponding buildup of material in front of the front wheels).
- Ground with a low friction value is detected during ASR control. The ASR activation thresholds are varied depending on the tire characteristics to improve traction.
The above-specified changes with respect to ESP, ABS and ASR are dependent on speed.
This means that the threshold values when off-road mode is active match those of on-road mode as of a speed of approx. v = 50 km/h.
If the vehicle decelerates to below a speed of approx. v = 50 km/h, the thresholds return to the off-road values.
Function sequence for engine torque support
If braking torque can no longer be applied for at least one wheel (wheel is stationary because there is no load on it) with the downhill speed regulation activated, off-road mode activated and differential locks disengaged, brake pressure is built up actively at the wheels with traction using the ESP control unit.
Engine torque support is active up to a speed of v =18 km/h, coming from a lower speed.
Function sequence for locking influence
In the following driving situations the activated locks are immediately released:
- ESP intervention
- ABS control at a speed of v < 15 km/h
- Brake application by driver at a speed of v > 15 km/h
The actuation to disengage the locks is performed by the ESP control unit, which transmits a corresponding signal to the transfer case control unit (N15/7) via the engine compartment CAN. The transfer case control unit disengages the activated lock between front and rear axle.
The transfer case control unit (lock master) transmits the signal on to the rear axle differential lock control unit (N15/9) via the engine compartment CAN, which disengages the activated rear axle lock.
Passive ASR and ESP switching function sequence
The ASR and ESP functions can be switched passive via the ESP OFF button (N72/1s1) in the upper control panel control unit. The upper control panel control unit transmits the signal to the ESP control unit.
If the system is switched to passive, the ESP warning lamp lights up in the instrument cluster. The control thresholds are raised in the case of passive activation. ABS cannot be deactivated. ESP is always active during a brake application.
Fault handling function sequence
The range of functions can vary depending on the received signals.
The following table represents the function shutdown due to component failure or defect.
System fault display function
The driver is informed of the system status and any faults by means of the following:
^ ABS indicator lamp
^ ESP warning lamp
^ Message in instrument cluster
In the event of a failure of the ESP control unit a basic brake function without ABS is always available.
The status of the brake fluid check switch (S11) is read-in by the front SAM control unit and transmitted over the interior CAN to the instrument cluster.
