Electronic stability program (ESP), function - GF42.45-P-0001A
MODEL 140 with CODE (472a) Electronic Stability Program (ESP)
MODEL 129 with ENGINE 104, 119, 120 with CODE (472a) Electronic Stability Program (ESP)
MODEL 210 with ENGINE 119 with CODE (472a) Electronic Stability Program (ESP)
The "E lectronic S tability P rogram" (ESP) is an active safety system for improving vehicle stability in all driving situations.
It works through individual brake intervention at one or several wheels on the front or rear axle. ESP stabilizes the vehicle when cornering, braking or when rolling without drive and it keeps it safely on course.
ESP complements the familiar functions of the anti-lock brake system (ABS), acceleration slip regulation (ASR) and engine braking regulation (EBR).
The function of stability control overrides the ABS and ASR control systems. In addition to the active brake intervention of the ESP it also has an influence on engine/transmission management.
The "Electronic Stability Program" (ESP) is made up of the following system correlations.
ABS prevents the wheels locking when braking, maintaining steerability and vehicle stability when the vehicle decelerates.
ASR prevents the drive wheels spinning when driving. It also improves vehicle stability with better traction throughout the entire speed range.
EBR reduces brake slip at the drive wheels on overrun and ensures vehicle stability.
ESP prevents the vehicle breaking away when oversteering or understeering. It ensures that the vehicle does not deviate from the course specified by the driver (within the bounds of physical limits) in all situations. Brake forces are produced selectively at the individual wheels to correct this.
System correlations
Motor electronics (ME-SFI) are used to adjust the drive torque. Using this system, the engine is controlled by the throttle valve and ignition timing.
The gear stage is also evaluated by the electronic transmission control (ETC) to calculate the ESP drive moment control.
The ABS and ASR functions are included in the ESP electronics of the brake control circuit. The Brake Assist (BAS) function is also included on model 168 and on vehicles with engine 112, 113 (model 210 also engine 606, 611).
The ABS and ASR basic components are also combined in the traction systems hydraulic unit.
The functions for the electronic accelerator (EA) and cruise control system (Tempomat) are included in the engine control module.
Via a CAN data bus data can be exchanged between the ESP control module and the engine control module and, if necessary, with the transmission control module and BAS control module.
Advantages
- Improves the starting off and acceleration capacity due to increased traction; particularly beneficial on road surfaces with different levels of adhesion and when cornering.
- Increases active dynamic safety, since only a wheel which is not skidding can provide optimum propulsion without any loss of lateral control.
- Automatically adapts the engine torque to the ability of the wheels to transmit this to the road when the driver applies too much throttle.
- Reduces the risk of skidding under all road conditions by automatic stabilization when braking, accelerating or rolling away evenly.
- Significantly improves the directional stability of the vehicle when cornering - up to the limit range.
- Reduces the stopping distance at corners or on roads with a slippery surface.
- A flashing warning lamp in the speedometer signals ESP control mode to the driver and informs him that he has approached the physical limit with his vehicle.
- ESP or ASR can be shut off using the ESP OFF switch (ASR OFF, on model 168) which is recognized by the warning lamp in the speedometer illuminating permanently. Better traction (milling effect) can therefore be achieved in deep snow or when snow chains are fitted.
Basically all forces, which act on a vehicle externally, turn the vehicle about the center of gravity irrespective of whether they are brake or drive forces acting on one side or whether they are side forces.
The electronic stability program (ESP) records the vehicle characteristics and controls the braking forces of the individual wheels selectively for the purposes of correction.
Example A: Understeering 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: Oversteering vehicle (cornering left)
The tail of the vehicle breaks away.
A precisely calculated braking action is performed on the right front wheel .
ESP controls:
- when cornering (vehicle oversteers or understeers)
- when driving straight ahead (vehicle deviates off course due to uneven road conditions)
To be able to perform these extremely precise control interventions, an expanded system of sensors is required compared with ASR.
A distinction is made between:
- Sensors which recognize the driver requirement
- Steering angle sensor
- Accelerator pedal position (throttle valve actuator)
- Sensors which measure the actual vehicle characteristics
- ESP yaw rate sensor
- Lateral acceleration sensor
- ESP brake pressure sensor
- Wheel speed sensor
The wheel speeds, steering angle, yaw rate of vehicle, lateral acceleration and brake pressures on the front axle are recorded and processed in the ESP control module (N47-5).
The ESP control module (N47-5) is connected to the control modules of the engine transmission management system via a CAN data bus. This digital line connection enables rapid exchange of data between the ESP, ME-SFI and ETC control modules. The ESP, SPS and BAS control module (N47-5) is continuously supplied with current data on engine torque, accelerator pedal position and transmission ratio.
The forces which want to turn the vehicle about the center of gravity are recognized via the turn rate and lateral acceleration sensor.
The longitudinal and lateral forces at the wheels can be calculated by means of the value acquisition which is carried out.
If these values exceed certain control thresholds, the appropriate solenoid valves and the high pressure and return pump in the hydraulic unit are actuated via the ESP, SPS and BAS control module (N47-5) in order to control a defined brake pressure selectively at one or several wheels.
At the same time commands are passed on to the ME-SFI and ETC control modules via the CAN data bus. To reduce the drive moment, calculated values for throttle valve position and ignition timing are specified and a downshift prevented if necessary.
The precise and accurately proportioned intervention is completed within a few fractions of a second.
Active brake intervention and drive moment reduction by the ESP ensure optimum vehicle stability.
The following processes are performed:
ESP brake moment control circuit
ABS control
If a wheel is about to lock up, for example, then the brake pressure in this wheel brake is regulated. The pressure in the ESP hydraulic unit (A7/3) is regulated via the solenoid valves by the pressure build-up, hold pressure and pressure reduction control phases.
ESP brake moment control circuit
ASR control
A spinning wheel is braked by a pressure system in the hydraulic unit which directs brake pressure into the brake caliper on the rear axle (pressure build-up).
This allows the other wheel to transmit optimum drive force (differential lock effect).
Solenoid valves in the ESP hydraulic unit (A7/3) regulate the brake moment by pressure build-up, hold pressure and pressure reduction.
ESP drive moment control circuit
ASR control
In order to reduce an excessive drive moment and thereby obtain optimum traction, the drive moment is reduced over he CAN data bus between the ESP control module and the engine control module.
The ESP control module constantly checks whether the control functions can be canceled, e.g. due to a sudden improvement in road grip, so as to allow the drive moment specified by the driver on the accelerator pedal at the earliest possible opportunity.
ESP drive moment control circuit
EBR control (except engines with fuel shutoff)
The ESP control module also detects if brake slip occurs at the drive wheels when the accelerator is released. The signal is sent to the engine control module over the CAN data bus. With this information the brake slip is reduced by increasing the drive moment, thus increasing the lateral stability of the vehicle. This process occurs without notifying the driver (ESP warning lamp).
ESP brake and drive moment control circuit
ESP control
If oversteer or understeer is detected, a calculated braking action is performed at the front or rear axle via the ESP control module and the hydraulic unit. This braking action deliberately counteracts the undesirable vehicle motion.
A signal over the CAN data bus to the engine control module reduces the drive moment as required by reducing the engine torque.
| Notes on towing | AH42.00-P-0001-05B | ||
| Notes on testing electronic components and systems for damage | AH42.00-P-0001-06B | ||
| Electronic stability program (ESP), location of electrical components | Model 129 with engines 104, 119, 120 | GF42.45-P-0001-03A | |
| Model 140 | GF42.45-P-0001-03B | ||
| Model 210 with engine 119 | GF42.45-P-0001-03C | ||
| Electronic stability program (ESP), driver information | GF42.45-P-0001-04A | ||
| Electronic stability program (ESP), location of hydraulic components | Model 129 with engines 104, 119, 120 | GF42.45-P-0001-02A | |
| Model 140 Model 210 with engine 119 |
GF42.45-P-0001-02B | ||
| ESP brake moment control circuit, function | GF42.45-P-2000A | ||
| ASR drive moment control circuit, function | GF42.40-P-2100A |