Electronic stability program (ESP) function - GF42.45-P-0001G
MODEL 463.306 /336 /346 up to 31.5.12 as of Model Year 2011 / YoM 10
MODEL 463.202 /222 /237 up to 31.5.12 as of Model Year 2009 / YoM 08
MODEL 463.236 up to 31.5.12 except CODE (ZS6) Special protection version FB6 except CODE (ZS7) Special protection version FB7 as of Model Year 2009 / YoM 08
MODEL 463.270 /271 /303 /340 /341 up to 31.5.12 as of Model Year 2007
Function requirements:
- Circuit 61 ON
General information
The Electronic Stability Program (ESP®) is a control system for improving the handling characteristics which intervenes in the brake system and in the drive train. As an overall system ESP® prevents the vehicle from "skidding" when steering or becoming unstable and breaking out to the side as long as the physical limits are not exceeded.
For this purpose the ESP control unit evaluates the data from the following components:
- Rpm sensor
- Steering angle sensor
- Turn rate sensor
- Accelerator pedal sensor
- ESP OFF switch
- Stop lamp switch
- Parking brake indicator switch
The ESP® includes the following partial functions:
- ESP®
- Antilock brake system (ABS)
- Acceleration Slip Regulation (ASR)
- Engine braking regulation (MSR [EBR])
- Brake Assist System
- Switch ESP® passive
- Indicator/warning messages
- Hill Start Assist (HSA)
If a differential lock is activated using the differential lock switch group, the ESP control unit switches off all traction functions (ESP®, ABS, ASR, MSR) except the electrical brake force distribution. After deactivating the differential lock, all traction controllers are activated again by the ESP control unit.
ESP® function
Task
The ESP® prevents breaking away when the vehicle oversteers or understeers. Within physical limits it ensures that the vehicle does not deviate from the course specified by the driver.
Detection
A distinction is made between sensors which detect the driver's requirement:
- Steering angle from steering angle sensor
- Accelerator pedal position from accelerator pedal sensor
which determine the actual vehicle characteristics:
- Rotational speed from turn rate sensor
- Wheel speeds from the rpm sensors
Control
The ESP control unit records and processes wheel speeds via the rpm sensors, the steering angle via the steering angle sensor, the vehicle turn speed and the lateral acceleration via the turn rate sensor and the brake pressure of the individual wheels.
If these values exceed certain control thresholds then the appropriate control valves are actuated by the ESP control unit in order to regulate defined brake pressure selectively in one or several wheels.
At the same time, commands are sent over the drive train CAN to the CDI control unit or the ME-SFI [ME] control unit and forwarded to the fully integrated transmission control unit.
For drive torque reduction a drive torque reduction is specified to the CDI control unit or the ME-SFI [ME] control unit.
An imminent shift operation is prevented by the fully integrated transmission-control control unit.
A distinction is made between understeering and oversteering vehicle behavior.
Intervention in the case of oversteer:
When the vehicle starts to oversteer (the rear end breaks away) a brake pressure is built up at the front wheel on the outside of the curve.
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, the incipient instability is prevented by 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 arises which leads to the vehicle turning in with a simultaneous speed reduction, leading to a considerable stabilizing effect.
ABS function
Task
ABS prevents the wheels locking when braking and thus maintains the steerability and directional stability and road adhesion during vehicle deceleration.
Control
If a locking wheel is detected by the ESP control unit via the rpm sensors, then the brake pressure at the corresponding brake cylinder is reduced until the wheel turns freely again.
Function of ASR
Task
ASR prevents the drive wheels from spinning while driving. In addition it causes an improved directional stability and road adhesion with an increased traction potential over the entire vehicle speed range.
Control
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 over the drive train CAN to the CDI control unit or ME-SFI [ME] control unit, which then reduces the engine output.
The system constantly checks whether the drive torque specified by the driver via the accelerator pedal sensor can be allowed again e.g. due to improved road adhesion. The drive torque is transmitted to the opposite, stable drive wheel by means of intervention by the brake system on the spinning wheel.
Function of MSR [engine braking regulation]
Task
MSR prevents wheel slip occurring at the drive wheels when the accelerator pedal is released.
Control
If a blocking wheel is detected by the ESP control unit in deceleration mode through the rpm sensors, then brake slip is reduced by increasing the drive torque through the CDI control unit or the ME-SFI [ME] control unit, thereby improving the side stability of the vehicle.
Function of Brake Assist
Task
Brake Assist is a system for assisting the driver's braking requirements during hazard braking and emergency stops.
Control
Hazard braking and an emergency stop is detected by evaluating the rate of pressure rise and the operating speed when the brake pedal is operated.
Brake Assist reduces the brake distance due to a pressure boost in the brake system in order to achieve the full braking effect of the vehicle as soon as possible. Pressure is built up during a braking application via a hydraulic brake force boost through the hydraulic unit.
Switch ESP® to passive function
Task
It is advantageous to switch to ESP passive in particular situations (road glaze, soft road surfaces etc.).
Control
When the ESP Off switch in the upper control panel control unit is operated
- ESP® drive torque control is switched off and the
- ESP® stability function is also canceled when accelerating.
Only the ESP® stability function continues to function under braking. The MSR control is switched off.
With a vehicle speed v > 60 km/h the ESP® is activated again.
If ESP® is deactivated an intervention in the brakes takes place via the braking torque control circuit up to v = 40 km/h when a drive wheel is spinning.
If switch-on conditions continue to exist, then intervention in the brakes is retained up to max. v = 60 km/h. However the braking torque is continuously reduced.
Function of indicator/warning messages
ESP warning lamp (A1e41) (up to 31.8.10) or
ESP OFF indicator lamp (A1e30) (as of 1.9.10)
The ESP warning lamp or ESP OFF indicator lamp flashes for:
- Active intervention by the brake system in drive and deceleration mode
- An ASR or ESP® control intervention
- there is a reduction in engine torque
The ESP warning lamp or ESP OFF indicator lamp lights up for:
- A passive ESP®
- When differential locks are active
ABS indicator lamp (A1e17)
The ABS indicator lamp serves to display the operating condition of the ESP control unit.
- The ABS indicator lamp lights up:
- With ABS shutoff
- During diagnosis with STAR DIAGNOSIS
- When differential locks are active
brake fluid, parking brake and brake distribution warning lamp (A1e7)
The warning lamp lights up:
- When the parking brake indicator switch is operated
- If the minimum brake fluid level is reached
- In the event of failure of the electronic brake force distribution
Additional function requirements for HSA
- Transmission not in position "N"
- Vehicle not secured with parking brake
- Incline detected with vehicle at standstill
HSA function
HSA prevents the vehicle from rolling back contrary to the direction of the gear range engaged when starting off during the time it takes for the driver to move his foot from the brake pedal to the accelerator pedal.
The function is automatically triggered 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. The turn rate sensor transmits the corresponding data to the ESP control unit over drive train CAN.
The ESP control unit also reads in the status of the brake light switch thereby detecting the brake pedal status. The status of the parking brake is recorded by the parking brake inspection switch. The front signal acquisition and actuation module (SAM) reads in the status of the parking brake inspection switch and sends this to the interior CAN. The EZS control unit forwards the status of the parking brake inspection switch over the drive train CAN to 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 HSA function deactivated and the vehicle starts off.
However, if the driver does not actuate the accelerator pedal, the pressure in the brake calipers is reduced to zero after t = 1 s.
| Electronic stability program (ESP), location of electronic components | GF42.45-P-0001-03GA | ||
| Electronic Stability Program (ESP) block diagram | GF42.45-P-0001-06G | ||
| Turn rate sensor, component description | B24/9 | GF42.45-P-5135G | |
| Component description for front SAM control unit with fuse and relay module | N10/1 | GF54.21-P-6070G | |
| Component description for ESP control unit | N30/4 | GF42.45-P-5118G | |
| Upper control panel control unit, component description | N72/1 | GF54.21-P-6040G | |
| Electronic ignition/starter switch control unit (EZS), component description | N73 | GF80.57-P-6000G | |
| Component description for steering column tube module | N80 | GF54.21-P-6050G | |
| Accelerator pedal sensor, component description | B37 | GF30.20-P-2010G | |
| Wheel rpm sensor, component description | L6/1, L6/2, L6/3, L6/4 | GF42.45-P-5134G | |
| Steering angle sensor, component description | N49 | GF42.45-P-5107G | |
| Brake light switch, component description | S9/1 | GF42.10-P-2010G | |
| Parking brake indicator switch, component description | S12 | GF42.20-P-5002G | |
| Differential locks switch group, component description | S76 | GF54.25-P-4311G |