GF42.45-P-0001MK Electronic Stability Program (ESP), Function
GF42.45-P-0001MK Electronic stability program (ESP), function
Function overview
All the forces which act on a vehicle from outside always want to rotate the vehicle about the center of gravity irrespective of whether they are braking or drive forces acting on one side or side forces. The Electronic Stability Program (ESP) measures the vehicle characteristics and introduces brake forces selectively at the individual wheels for correction
The Electronic Stability Program (ESP) is an active safety system for improving vehicle stability 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. The Electronic Stability Program (ESP) supplements the familiar functions of the antilock brake system (ABS), acceleration slip regulation (ASR) and engine braking regulation (MSR). The function of the stability control overrides the ABS and ASR control systems. As well as actively intervening with the brakes, ESP also has an influence on engine/transmission management.
System overview
The antilock brake system (ABS) prevents the wheels from locking up when braking and as a result maintains the steerability and directional stability and road adhesion during vehicle deceleration. The acceleration slip regulation (ASR) prevents the drive wheels from spinning while driving. In addition they result in improved directional stability and road adhesion for increased traction potential over the entire vehicle speed range. Engine braking regulation (MSR) reduces the wheel slip of the drive wheels in overrun mode and ensures directional stability and road adhesion. The Electronic Stability Program (ESP) prevents breakaway when the vehicle oversteers or understeers. In all situations it ensure 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. The tire pressure loss warning (RDW) prevents run-flat damage to the tire. It detects pressure loss via a comparison of wheel rpm and shows it in the multifunction display (A1p13). Tire pressure loss warning (RDW) is a pure software constituent of the ESP and BAS control unit (N47-5) (model 203) with CODE (477) tire pressure loss warning.
System correlations
The motor electronics are used to adjust the drive torque. This system controls the engine by regulating the throttle valve and the firing point. The gear stage of the electronic transmission control (EGS) is also evaluated for calculating ESP drive torque control. 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 module includes the functions for the electronic accelerator (EA) and the cruise control (Tempomat).
Via the engine compartment CAN (CAN-C) data is exchanged between the ESP and BAS control unit (N47-5), the engine control unit and if necessary with 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.
^ Shortens the stopping distance in corners or on slippery roads.
^ Improves active dynamic safety, since only a wheel which is not spinning can provide optimum traction with no loss of lateral stability.
^ Adapts the engine torque automatically to the respective transmission potential of the wheels on the road (if the driver accelerates too hard).
^ Reduces the risk of skidding under all road conditions by stabilizing automatically when braking, when accelerating or when driving at a constant speed.
^ Improves the course stability when cornering.
^ The flashing ESP warning lamp (A1e41) in the instrument cluster (A1) signals ESP [Electronic Stability Program] closed-loop operation and informs him that he has approached the physical limit with his vehicle.
^ Via an ESP OFF switch (N72/1s1) an ESP or ASR cutout can occur which is recognized by the ESP warning lamp (A1e41) lighting up continuously. This can provide better traction (grinding effect) in deep snow or when snow chains are fitted.
ESP operates:
^ when cornering (vehicle under steering or over steering)
^ 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 detect the driver's wishes:
^ Steering angle sensor (N49)
^ Accelerator pedal position (throttle valve actuator)
Sensors which measure the effective vehicle characteristics:
^ ESP yaw rate sensor (N64)
^ ESP lateral acceleration sensor (B24/2)
^ ESP brake pressure sensor (B34)
^ Wheel speed sensor
The wheel rpm, steering angle, the vehicle yaw rate, lateral acceleration and brake pressure of the front axle are recorded and processed in the ESP and BAS control unit (N47-5). The ESP and BAS control unit (N47-5) is connected to the control units of the engine/transmission management via the engine compartment CAN (CAN-C).
This digital line connection makes possible rapid data exchange between ESP and BAS control unit (N47-5), motor electronics control unit (N3/10) or CDI control unit (N3/9) and the ETC [EGS] control unit (N15/3).
The ESP and BAS control unit (N47-5) is continuously supplied with the current data on engine torque, accelerator pedal position and transmission ratio.
Via the ESP yaw rate sensor (N64) and ESP lateral acceleration sensor ESP (B24/2) the forces which want to rotate the vehicle about its center of gravity are detected.
The longitudinal and lateral forces acting on the wheels can be calculated by means of the data acquisition described. If these values exceed certain control thresholds, then via the ESP and BAS control unit (N47-5) the corresponding solenoid valves, as well as the high pressure- and return flow pump (A7/3m1) in the hydraulic unit are actuated, in order to introduce a defined brake pressure selectively at one or more wheels. Simultaneously via the engine compartment CAN (CAN-C) commands are passed on to the motor electronics control unit (N3/10) or CDI control unit (N3/9) and ETC [EGS] control unit (N15/3).
To reduce the drive torque, calculated values for the throttle valve position and ignition timing are specified and a downshift prevented if necessary. Active brake intervention and drive torque reduction by the ESP ensure optimum vehicle stability.
The following processes are performed:
^ ESP drive moment control circuit (ASR control)
In order to reduce an excessive drive torque and thus achieve optimal traction, a drive moment reduction takes place between the ESP and BAS control unit (N47-5) and motor electronics control unit (N3/10) or CDI control unit (N3/9) via the engine compartment CAN (CAN C). In the ESP and BAS control unit (N47-5) it is constantly checked whether, for example, the control functions can be canceled as a result of a sudden improvement in road adhesion, in order to permit again as soon as possible the drive torque again specified by the driver via the accelerator pedal.
^ ESP [Electronic Stability Program] drive moment control circuit (MSR [engine braking regulation] control) (not on engines with fuel cutoff)
If wheel slip occurs at the drive wheels when the driver reduces the throttle opening, this is likewise detected in the ESP and BAS control unit (N47-5). The signal is sent to the motor electronics control unit (N3/10) or CDI control unit (N3/9). With this information wheel slip is reduced by increasing drive torque and as a result the lateral control of the vehicle is increased. This process takes place without informing the driver (ESP warning lamp (A1e41)).
^ ESP braking torque control circuit (ASR control)
To brake the spinning wheel, brake pressure is lead into the rear axle brake caliper (pressure buildup) via a pressure system in the traction system hydraulic unit (A7/3). This allows the other wheel to transmit the optimum drive force (differential lock effect). The braking torque is regulated by pressure buildup, pressure holding and pressure reduction via solenoid valves in the traction system hydraulic unit (A7/3).
^ ESP braking and drive torque control circuit (ESP control)
If oversteer or understeer is detected, a calculated brake intervention is carried out at the front and rear axle via the ESP and BAS control unit (N47-5) and traction system hydraulic unit (A7/3). This braking action deliberately counteracts the undesirable vehicle motion. Through a signal via the engine compartment CAN (CAN-C) to the motor electronics control unit (N3/10) or CDI control unit (N3/9) the drive torque reduction to suit the requirements is achieved by an engine torque reduction.
^ ESP braking torque control circuit (ABS control)
If a wheel tends to lock, for example, the brake pressure in this wheel brake is regulated. The regulation in the traction system hydraulic unit (A7/3) takes place via the solenoid valves through the control phases pressure buildup, pressure holding and pressure reduction.
