GF42.45-P-0001B Electronic Stability Program (ESP) Function
GF42.45-P-0001B Electronic Stability Program (ESP) Function
-MODEL 129 with ENGINES 112, 113
- with CODE (472a) Electronic Stability Program (ESP)
-MODEL 170, 202, 203 up to 31.7.01, 208, 215, 220 / (except, 220.08 /18)
- with CODE (472a) Electronic Stability Program (ESP)
-MODEL 210 with ENGINE 111, 112, 113, 605, 606, 611, 612, 613
- with CODE (472a) Electronic Stability Program (ESP)
-MODEL 210 / (except 210.08 /28)
- with CODE (472a) Electronic Stability Program (ESP)
The "Electronic Stability Program" (ESP) is an active safety system which improves vehicle stability in all driving situations.
It operates by actuating the brakes individually on one or more wheels on the front or rear axle. ESP stabilizes the vehicle when cornering, when braking or when coasting without power and holds it reliably in track.
ESP complements the familiar functions of the anti-lock brake system (ABS), acceleration slip regulation (ASR) and engine braking regulation (EBR).
The stability regulation function is superordinate to the ABS and ASR control systems. As well as actively intervening with the brakes, ESP also has an influence on engine / transmission management.
The Electronic Stability Program (ESP) includes the following system interplay.
ABS prevents the wheels from locking up during braking and thus maintains the steerability and directional control of the vehicle during deceleration.
ASR prevents the drive wheels from spinning while driving. It also improves directional control with better traction across the entire speed range.
EBR reduces brake slip at the drive wheels during deceleration and ensures directional control.
ESP prevents the vehicle from breaking away when it is oversteered or understeered. In all situations it ensures that the vehicle does not deviate from the course specified by the driver (within the bounds of physical limits). Brake forces are produced selectively at the individual wheels to correct this.
System interplay
The engine electronics (ME) is used to adjust the drive torque. This system controls the engine by regulating the throttle valve and the firing point.
The gear setting is also evaluated by the electronic transmission control (EATC) to calculate the ESP drive torque control.
The ABS and ASR functions are integrated in the ESP electronics of the brake control loop. In the following vehicles it also includes the BAS function (as of 2/02):
^ Model 129 with engine 112, 113
^ Model 202 with engine 111, 112, 113, 605, 611
^ Model 210 with engine 112, 113, 605, 606, 611, 612, 613
^ Model 210 with engine 111 as of 08/99
^ Model 170, 203, 208, 215, 220
The ESP hydraulic unit also houses the main components of the ABS and ASR.
The engine control module includes the functions for the electronic accelerator (EA) and the cruise control (Tempomat).
Data is exchanged between the ESP control module, the engine control unit and (if fitted) with the transmission control module and BAS control module via a CAN data line.
Advantages of ESP
^ Improves moving-off and acceleration capabilities by increasing traction; especially useful on road surfaces with different levels of grip and when cornering.
^ Improves active dynamic safety, since only a wheel which is not spinning can provide optimum traction with no loss of lateral stability.
^ Automatically adapts the engine torque to the respective wheel-to-road-surface traction possibilities if the driver accelerates too heavily.
^ Reduces the risk of skidding under all road conditions by automatically stabilizing the vehicle when braking, accelerating or coasting smoothly.
^ Significantly improves the directional stability of the vehicle when cornering - up to the limit range.
^ Shortens the stopping distance in corners or on slippery roads.
^ A flashing warning lamp in the speedometer notifies the driver of ESP control and informs him that his vehicle is approaching the physical limits.
^ ESP or ASR can be shut down using the ESP OFF switch, which is indicated by the warning lamp in the speedometer shining constantly. This can provide better traction (grinding effect) in deep snow or when snow chains are fitted.
Function overview
Essentially, all the forces acting on a vehicle from outside attempt to rotate the vehicle about its center of gravity, regardless of whether these are one-sided braking or drive forces or lateral forces.
The Electronic Stability Program (ESP) analyzes the vehicle behavior and applies specific braking force to individual wheels to correct any instability.
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.
a Desired travel direction
b Braked wheel
c Corrective moment produced in vehicle
d Understeering vehicle motion
e Oversteering vehicle motion
ESP operates:
^ when cornering (vehicle understeering or oversteering)
^ 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:
1.) Sensors which recognize the driver requirement
^ Steering angle sensor
^ Accelerator pedal position (throttle valve actuator)
2.) Sensors which measure the actual vehicle behavior
^ Yaw rate sensor
^ Lateral acceleration sensor
^ Brake pressure sensor
^ Wheel speed sensor
The ESP control module (N47-5) records and processes the wheel speeds, the steering angle, the yaw rate of the vehicle, the lateral acceleration and the brake pressure at the front axle.
The ESP control module (N47-5) is linked to the control modules of the engine/transmission management system over a CAN data bus.
This digital link permits fast data exchange between the ESP control module, engine control module, and transmission control module.
The ESP control module (N47-5) is continuously supplied with current data on engine torque, accelerator pedal position and transmission ratio.
The forces attempting to rotate the vehicle about its center of gravity are detected via the yaw rate and lateral acceleration sensors.
The longitudinal and lateral forces acting on the wheels can be calculated by this data acquisition.
If these values exceed certain control thresholds, the appropriate solenoids as well as the high-pressure/return-flow pump in the hydraulic unit are actuated via the ESP control module (N47-5) in order to apply precisely defined brake pressure to one or more wheels.
At the same time, commands are sent to the engine and transmission control module via the CAN data bus. Calculated values for throttle valve position and ignition timing are predefined and downshifting is suppressed in order to reduce driving torque.
The precise and accurately proportioned intervention is completed within a few fractions of a second.
Active brake intervention and drive torque reduction by the ESP ensure optimum vehicle stability.
The following processes are performed:
ESP brake moment control circuit
ABS control
If, for example, a wheel has a tendency to lock, 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 buildup, pressure hold and pressure reduction control phases.
ESP braking torque control circuit
ASR control
To brake the spinning wheel, the brake pressure is fed to the rear brake caliper via a pressure system in the hydraulic unit (pressure build-up).
This allows the other wheel to transmit the optimum drive force (differential lock effect).
Solenoid valves in the ESP hydraulic unit (A7/3) regulate the braking torque with pressure build-up, pressure hold and pressure reduction phases.
ESP drive torque control circuit
ASR control
In order to reduce an excessive drive torque and thereby obtain optimum traction, the drive torque is reduced over the CAN data bus between the ESP control module and the engine control module.
The ESP control module continuously checks whether the control functions can be canceled owing to, for example, a sudden improvement in road grip so that the drive torque requested by the driver via the gas pedal can then be made available again.
ESP drive torque 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 pedal is released. The signal is sent to the engine control module over the CAN data bus. On the basis of this information, the wheel slip is reduced by increasing the drive torque, and the side stability of the vehicle is thus increased. This process occurs without notifying the driver (ESP warning lamp).
ESP braking and drive torque control circuit
ESP control
If over-or understeering is detected, calculated braking force is applied to the front or rear axle via the ESP control module and the hydraulic unit. This brake intervention counteracts the undesired driving behavior.
A signal over the CAN data bus to the engine control module reduces the drive torque as required by reducing the engine torque.
