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

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


Schematic representation












A Understeering vehicle
B Oversteering vehicle

a Desired direction of travel
b Braked wheel
c Correction moment of the vehicle produced
d Understeering vehicle movement
e Oversteering vehicle movement

Example of understeering vehicle (A)
A vehicle understeers on a left curve. The vehicle pushes outwards over the front wheels. Precisely calculated braking force is applied at the left rear wheel.

Example of oversteering vehicle (B)
A vehicle oversteers in a left curve. In the process the rear of the vehicle breaks away. Precisely calculated braking force is applied at the right front wheel.

General
The Electronic Stability Program (ESP) is an active safety system for improving vehicle stability in all driving situations. It operates individually at one or more wheels on the front or rear axle. The ESP stabilizes the vehicle, if when cornering, when braking or when rolling without drive, forces acting from outside on one side have an effect on the vehicle and keep it safely on course.

It supplements the familiar functions of the antilock brake system (ABS), acceleration slip regulation (ASR), engine braking regulation (EBR) and electronic brake force distribution (EBD).
ESP regulates when:
^ cornering (vehicle understeers or oversteers)
^ driving straight ahead (vehicle deviates from its course on account of uneven road conditions)

The function of the ESP control system overrides the ABS and ASR control systems.
Apart from active intervention by the brake system through the ESP there is also an effect on the engine/transmission management.

Advantages of ESP:
^ Improvement in the starting-off and acceleration capability due to increased traction, particularly on a road with different adhesion and on curves
^ Reduction in the risk of skidding under all road surface conditions by automatic stabilization when braking, accelerating or rolling
^ Automatic adaptation of the engine torque depending on the traction condition of the wheels
^ Improvement in the lane stability of the vehicle when cornering, also up to the critical limits
^ Increase in active driving dynamics safety, as only one wheel which is not spinning permits the optimum traction without loss of lateral stability

The ESP contains the following systems:
^ Antilock brake system (ABS)
Prevents blocking of the individual wheels by reducing the brake pressure at the wheels affected
^ Acceleration slip regulation (ASR)
Prevents a too high slip of the drive wheels when starting off and accelerating by torque reduction
^ Electronic brake force distribution (EBV)
Assists the driver in the partial braking range. It prevents overbraking of the rear axle and when braking in the curve increases the vehicle stability, whilst if necessary the pressure at the rear wheel on the inside of the curve reduces or is increased at the front wheel on the outside of the curve
^ Engine braking regulation (MSR)
Reduces the wheel slip of the drive wheels in deceleration mode by slightly increasing the torque and as a result improved driving stability
The clutch can be disengaged as additional assistance.







1 ESP/ABS/ASR status display
2 Transmission control intervention
3 Wheel speeds
4 Steering angle
5 Steering speed
6 Lateral acceleration
7 Rotational speed
8 Engine torque control
A1 Instrument cluster
A1e17 ABS indicator lamp
A1e41 ESP warning lamp
B24/15 Yaw rate, lateral and longitudinal acceleration sensor
L6/1 Left front rpm sensor
L6/2 Right front rpm sensor
L6/3 Left rear rpm sensor
L6/4 Right rear rpm sensor
N3/10 ME-SFI [ME] control unit
N15/6 Automated manual transmission control unit
N47-5 ESP control unit
N49 Steering angle sensor
CAN Controller Area Network (data bus/CAN bus) (CAN)

Function overview
Brake forces, drive forces and side forces acting on one side, which act on the vehicle from outside endeavor to turn the vehicle about its vertical axis. The ESP acquires the vehicle characteristics and for correction selectively brakes individual wheels. It regulates when cornering (vehicle understeers or oversteers) and when driving straight ahead (vehicle deviates from course due to dissimilar road conditions).

Sensor system
A distinction is made between sensors which detect the driver's requirement (e.g. the steering angle sensor), and sensors which record the actual vehicle characteristics. These include:
^ Yaw rate, lateral and longitudinal acceleration sensor
^ Rpm sensor

The ESP control unit is constantly supplied with the current data on engine torque and rotational speed by the motor electronics control unit via CAN.
Via the turn rate, lateral and longitudinal acceleration sensor the brake forces, drive forces and side forces are recorded which want to turn the vehicle about the vertical axis (yaw rate). This information is transferred to the ESP control unit via CAN. The torque acting on the vehicle is calculated based on this information. If this torque exceeds defined thresholds then the corresponding wheels are braked by the ESP control unit to neutralize the torque which is acting.
Simultaneously requests for drive torque reduction are passed on to the motor electronics control unit via CAN.

Active brake intervention and drive torque reduction by the ESP ensure optimum vehicle stability. The following processes are performed:
^ ESP braking torque control circuit
- ABS control
- EBD control
- ASR control
^ ESP drive torque control circuit
- ASR control
- MSR control

ESP braking torque control circuit ABS control
If one wheel tends to lock the brake pressure at this wheel is reduced. The brake pressure is controlled via the ESP control unit. The various wheel speeds are transmitted to the ESP control unit by the rpm sensors. The ESP control unit compares the speeds against each other and reduces the brake pressure at the wheel which is tending to lock up.

Visual status indication:
Information on the status of the ABS control system is provided by the ABS indicator lamp.
Actuation possibilities:
^ ABS indicator lamp permanently on
- ABS has a malfunction

EBD control
The mass of the vehicle shifts during each brake application. The wheels are subjected to different loads depending on the direction of travel (straight-ahead driving or cornering).
To achieve optimal braking effect, the brake pressure is increased at the wheels subjected to heavier loads and reduced at the wheels subjected to lesser loads. The ESP control unit computes the required brake interventions based on the information from the yaw rate and lateral acceleration sensor.
This also has the simultaneous effect of preventing the wheels subjected to lesser loads from locking up.

ASR control
To brake the spinning wheel the brake pressure at the spinning wheel is increased via the ESP control unit.

ESP drive torque control circuit ASR control
In order to reduce a too large drive torque and thus achieve optimum traction, a drive torque reduction takes place between the ESP control unit and the motor electronics control unit via CAN. The ESP control unit constantly checks whether the control functions can be canceled, e.g. as a result of improved road adhesion. So the drive torque specified by the driver via the accelerator pedal can be permitted again in good time.

EBR control
If slip occurs at the drive wheels in overrun mode, this is detected by the ESP control unit. The signal is reported to the motor electronics control unit via CAN. With this information, wheel slip is reduced by increasing drive torque and as a result the lateral stability of the vehicle is increased. This process occurs without feedback from the ESP warning lamp.

ESP brake torque and drive torque control circuit ESP control
If oversteering or understeering is detected, a calculated intervention by the brake system is caused by the ESP control unit at the corresponding wheel. This intervention by the brake system counteracts undesired handling characteristics . Simultaneously requests for drive torque reduction are passed on to the motor electronics control unit via CAN.

Visual status indication:
Information on the status of the ESP is provided by the ESP warning lamp.

Actuation possibilities:
^ ESP warning lamp flashes
- ESP intervention
^ ESP warning lamp permanently on
- ESP is switched off
- ESP has a malfunction