GF42.45-P-0001TX Electronic Stability Program (ESP) Function
GF42.45-P-0001TX Electronic stability program (ESP) function
MODEL 219.3 up to 31.5.06
except CODE (494) USA version
MODEL 219.3 up to 30.6.06
with CODE (494) USA version
TheElectronic Stability Program (ESP) is an active safety system for improving the vehicle stability in all driving situations. It works by individual intervention in the braking system at one or more wheels on the front or rear axle. ESP stabilizes the vehicle when cornering or when rolling without drive and keeps it safely on course.
With its function ESP takes priority over the control systems of the antilock brake system (ABS) and acceleration slip regulation (ASR). In addition to active ESP brake intervention there is also an influence on the engine/transmission management ESP comprises the following system connections.
The antilock brake system (ABS) prevents the wheels locking when braking and thus maintains steerability and directional stability and road adhesion then vehicle decelerates.
Acceleration slip regulation (ASR) prevents the drive wheels from spinning when driving. It also improves directional stability with better traction across the entire speed range.
Engine braking regulation (MSR) reduces drive wheel slip in overrun mode and takes care of directional stability and road adhesion.
ESP prevents the vehicle from breaking away during oversteer or understeer. In all situations 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 this.
System correlations
To adjust the drive torque the system intervenes in the engine control via the ME gasoline injection and ignition system (motor electronics) (ME) or via the Common-Rail Diesel Injection (CDI). On gasoline injection engines the throttle valve position and ignition timing is corrected accordingly and on diesel engines the injection quantity is corrected accordingly.
To calculate the ESP drive torque control the gear stage of the fully integrated transmission control (VGS) (series production) or of the electronic transmission control (ETC) (AMG only) is also evaluated.
The functions of ABS< ASR and MSR are contained in the electronics of the ESP braking torque control circuit.
The controls for ABS, ASR and ESP are carried out in the traction system hydraulic unit (A7/3).
The function for the of the electronic accelerator (EA) and for the speed control system (cruise control) is contained in the ME-SFI [ME] control unit (N3/10) (gasoline injection engine) or CDI control unit (N3/9) (diesel engine)).
Data is exchanged between the ESP control unit, the ME-SFI [ME] control unit (gasoline injection engine) or the CDI control unit (diesel engine) and the fully integrated transmission control (VGS) control unit (Y3/8n4) or the ETC [EGS] control unit (N15/3) (AMG) via the CAN engine compartment.
The ESP control unit communicates with the SBC control unit via the CAN-SBC (system's own CAN Bus) (A7/3n1).
Advantages of ESP system
^ Improves moving-off and acceleration capabilities by increasing traction; especially useful on road surfaces with different levels of grip and when cornering.
^ Increases the level of active driving safety since only non-spinning wheels provide optimum traction without impairing side stability.
^ Automatically adapts the engine torque to the respective transmission possibilities of the wheels to the road if the driver accelerates too hard.
^ Reduces the risk of skidding under all road conditions by stabilizing automatically when braking, accelerating, in overrun mode or when driving at a constant speed.
^ Significantly improves the directional stability of the vehicle when cornering up to the limit range.
^ Reduces the brake distance in curves, on a wet or icy road.
^ The flashing ESP and ABS warning lamp (A1e41) in the instrument cluster (A1) signals ABS or ESP closed-loop operation to the driver and informs him that he has got close to the physical driving limits with his vehicle.
^ Via the ESP Off switch an ESP and ASR-shutoff can take place which is detected by the ESP and ABS warning lamp which lights up permanently in the instrument cluster. This can provide better traction (grinding effect) in deep snow or when snow chains are fitted. The ABS function is retained in full.
Function overview
All the forces which act on the vehicle from outside always want to rotate the vehicle about its vertical axis, equally whether they are one-sided brake forces, drive forces or side forces.
ESP records the vehicle handling characteristics and, for correction, specifically introduces brake forces at the individual wheels.
Example A: Understeering vehicle (in left-hand curve)
The vehicle pushes outwards over the front wheels.
A precisely calculated braking action is performed on the left rear wheel.
Example B: Oversteering vehicle (in left-hand curve)
The tail of the vehicle breaks away.
A precisely calculated braking action is performed on the right front wheel.
ESP operates:
^ when cornering (vehicle understeering or oversteering)
^ when driving straight ahead (vehicle deviates off course due to uneven road conditions)
In order to be able to perform these control intervention functions, an expanded system of sensors is required compared with ASR.
A distinction is made between:
1.) Sensors which detect the driver's requirement
^ Steering angle sensor
^ Accelerator pedal sensor (B37)
2.) Sensors which measure the actual vehicle response
^ Yaw rate and lateral acceleration sensor
^ Brake pressure sensors in the traction system hydraulic unit
^ 4 wheel speed sensors
The wheel speeds, steering angle, vehicle yaw speed, the lateral acceleration and brake pressure of the individual wheels are recorded and processed in the ESP control unit.
The ESP and BAS control unit is connected to the control units of the engine/transmission management via the CAN engine compartment. This makes possible rapid data exchange between the ESP control unit, the ME-SFI [ME] control unit (gasoline injection engine) or CDI control unit (diesel engine) and the fully integrated transmission control (VGS) control unit.
The ESP control unit 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 detected via the yaw rate and lateral acceleration sensor.
The longitudinal and lateral forces acting on the wheels can be calculated based on the data listed above.
If these values exceed certain control thresholds, then the corresponding control valves are actuated by the ESP control unit via the SBC control unit in order to regulate a specific defined brake pressure at one or more wheels.
The ESP control unit is connected to the SBC control unit via the CAN SBC (system's own CAN connection).
Commands are passed on simultaneously to the engine control unit and transmission control unit via the CAN engine compartment. For drive torque reduction a drive torque requirement is given to the ME-SFI [ME] control unit (gasoline injection engine) or CDI control unit (diesel engine) as well as if necessary a downshift prevented by the fully integrated transmission control (VGS) control unit.
The precise and accurately proportioned intervention is completed within a few fractions of a second.
The active brake intervention and drive torque reduction by ESP take care of optimum vehicle stability.
The following processes are performed:
ESP braking torque control circuit
ABS control
If for example one wheel tends to lock, then the brake pressure in this wheel brake is regulated.
The control in the traction system hydraulic unit takes place via the control valves by the control phases of pressure buildup, pressure holding and depressurization (see ABS closed-loop operation, function).
ESP drive torque control circuit
ASR control
In order to reduce a too large drive torque and therefore to achieve optimum traction, data is exchanged between the ESP control unit and the ME-SFI [ME] control unit or the CDI control unit via the CAN engine compartment. The ME-SFI [ME] control unit or CDI control unit subsequently adjust a drive torque reduction. In the ESP control unit a check is constantly made as to whether, for example, the control functions can be canceled as a result of a sudden improvement in road adhesion so that the drive torque specified by the driver via the accelerator pedal can be permitted again as quickly as possible.
ESP braking torque control circuit
ASR control
If the drive torque reduction via the ME-SFI [ME] control unit (gasoline injection engine) or the CDI control unit (diesel engine) is not adequate then an ASR control intervention function takes place via the rear axle brake. To brake the spinning wheel via a pressure system in the traction system hydraulic unit the brake pressure is lead into the rear axle brake caliper (pressure buildup). This allows the other wheel to transmit the optimum drive force (differential lock effect).
Via control valves in the traction system hydraulic unit the braking torque is regulated by pressure buildup, pressure holding and depressurization (see ASR closed-loop operation, function).
ESP drive torque control circuit
EBR control
If when the throttle is released wheel slip occurs at the drive wheels, this is likewise detected in the ESP control unit. The signal is reported to the ME-SFI [ME] control unit or the CDI control unit via the CAN engine compartment.
Using this information by increasing the drive torque, wheel slip is reduced and as a result the side stability of the vehicle is increased. This process takes place without the driver being informed via the ESP and ABS warning lamp.
ESP brake torque and drive torque control circuit
ESP control
If oversteering or understeering is detected, then a calculated intervention in the braking system at the front and rear axle is performed via the ESP control unit and traction system hydraulic unit. This intervention in the braking system specifically counteracts unintentional handling characteristics This intervention is displayed to the driver by the ESP and ABS warning lamp flashing.
By a signal via the CAN-engine compartment to the ME-SFI [ME] control unit or to the CDI control unit simultaneously the drive torque reduction to suit requirements is achieved by the engine torque reduction.
Exhaust emission test/rolling mode
For vehicle test purposes the ESP can be set in the "exhaust gas test" mode if via the instrument cluster the corresponding workshop menu is activated and then the engine is started. ESP, ASR and MSR are then switched passive. The ESP and ABS warning lamp 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. The wheel speeds of the driven axle are reflected on the wheels of the non-driven axle.
