GF42.45-P-0001VC Electronic Stability Program (ESP) Function
GF42.45-P-0001VC Electronic Stability Program (ESP) Function
-MODEL 203.08 /265 /28
- with CODE (472) Electronic Stability Program (ESP) up to Model Year 08 /modification year 07
The "Electronic Stability Program" (ESP) is an active safety system for improving the stability of the vehicle in all driving situations. It operates by means of individual brake control cycles at one or several wheels of the front or rear axle. ESP stabilizes the vehicle when cornering, while braking or when coasting without power and holds it safely on course.
ESP completes the familiar functions of the antilock brake system (ABS), the acceleration slip regulation (ASR) and engine braking regulation (MSR).
The function of the stability control overrides the ABS and ASR control systems. In addition to the active braking control of the ESP, it also influences the engine-transmission management.
The Electronic Stability Program (ESP) contains the following systems:
ABS prevents the wheels from locking up during braking and thus maintains the steerability and directional control of the vehicle during deceleration.
ASR/ETS prevents the spinning of all 4 drive wheels while driving. It also improves directional stability with better traction across the entire speed range. The effect of up to 3 differential locks can be simulated.
EBR reduces brake slip at the drive wheels during deceleration and ensures directional control.
ESP prevents the vehicle from breaking away when oversteering or understeering. In all situations it ensures that the vehicle does not deviate from the course specified by the driver (as part of the physical limits). Brake forces are produced selectively at the individual wheels to correct this.
System correlations
Motor electronics (ME) is used to adjust the drive torque. This system controls the engine by regulating the throttle valve and the firing point.
For computation of the ESP-drive torque control the gear stage is also evaluated by the electronic transmission control (EGS). The ABS and ASR and BAS functions are included in the ESP electronics of the brake control.
The ABS and ASR basic components are also combined in the ESP hydraulic unit.
The engine control unit includes the functions for the electronic accelerator (EA) and the cruise control (Tempomat).
Data are exchanged over the CAN data bus between the ESP control unit, the BAS control unit (integrated), the engine control unit and, if fitted, the transmission control unit.
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.
^ 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 capabilities of the wheels to the road when the driver opens the throttle too much.
^ Reduces the risk of skidding under all road conditions by automatic stabilization when braking, when accelerating or when driving along at constant speed.
^ Improves the lane stability of the vehicle significantly when cornering - up to the critical limits.
^ Shortens the stopping distance in corners or on slippery roads.
^ A flashing warning lamp in the speedometer signals ESP closed-loop operation to the driver and informs him that the vehicle is approaching its physical handling limits.
^ An ESP or ASR shutoff can take place via an ESP OFF switch. This is recognized by the warning lamp in the speedometer lighting up constantly. This can provide better traction (grinding effect) in deep snow or when snow chains are fitted.
Function overview
All the forces acting on a vehicle from outside always want to turn the vehicle about the center of gravity, irrespective of whether these are one-sided brake forces or drive forces or lateral forces.
The electronic stability program (ESP) detects the behavior of the vehicle and specifically controls the braking forces of the individual wheels as a corrective measure.
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.
a Desired direction of travel
b Braked wheel
c Vehicle correction torque produced
d Understeering vehicle movement
e Oversteering vehicle movement
ESP operates:
^ when cornering (vehicle understeering or oversteering)
^ when driving straight ahead (vehicle deviates from course on account of dissimilar 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 detect the driver's requirement
^ Steering angle sensor
^ Accelerator pedal position (throttle valve actuator)
2.) Sensors which measure the actual vehicle response
^ ESP rotational speed sensor
^ Lateral acceleration sensor
^ ESP brake pressure sensor
^ Wheel speed sensor
The wheel speeds, the steering angle the vehicle rotational speed, the lateral acceleration and the brake pressure are recorded and processed in the ESP control unit (N47-5).
The ESP control unit (N47-5) is connected to the control units of the engine/transmission management via a data bus. This digital line connection makes possible a rapid data exchange between the ESP, ME and ETC control units.
The ESP control unit (N47-5) is constantly 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 by the rotational speed 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 via the ESP control unit, (N47-5) the corresponding solenoid valves, as well as the high pressure/return flow pump are actuated in the hydraulic unit in order to regulate a defined brake pressure in one or more wheels.
Simultaneously commands are passed on to the ME and EGS control units via the CAN data bus. To reduce the drive torque, calculated values for the 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 torque reduction by the ESP ensure optimum vehicle stability.
The following processes are performed:
ESP brake moment 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 ESP hydraulic unit (A7/3) takes place by the control phases pressure buildup, pressure holding and pressure reduction via the solenoid valves.
ESP braking torque control circuit
ASR/ETS control
A spinning wheel is braked by a pressure system in the hydraulic unit which directs brake pressure into the appropriate brake caliper (pressure build-up).
This allows the other wheel to transmit the optimum drive force (differential lock effect).
Brake torque is regulated by pressure buildup, pressure holding and pressure reduction via solenoid valves in the ESP hydraulic unit (A7/3).
ESP drive moment control circuit
ASR control
In order to reduce a too large drive torque and therefore achieve optimum traction, a drive torque reduction takes place between the ESP and ME control units via the CAN data bus.
The throttle valve position is reduced by the actuator in contrast to the accelerator pedal position input by the driver, and the ignition timing point is reduced.
In the ESP control unit, it is constantly checked 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 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 control unit via the CAN data bus. On the basis of this information, wheel slip is reduced by defined opening of the throttle valve, and, as a result of this, the cornering stability of the vehicle is enhanced. This process takes place without informing the driver (ESP warning lamp).
ESP brake and drive moment 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 hydraulic unit. This braking action deliberately counteracts the undesirable vehicle motion.
A signal via the CAN data bus to the ME control unit means the drive torque reduction to suit the requirement is achieved by engine torque reduction.
