GF42.45-P-0001SK Electronic Stability Program (ESP), Function
GF42.45-P-0001SK Electronic stability program (ESP), function
Example A
A vehicle understeers on a left curve. The vehicle pushes outwards over the front wheels. Precisely calculated braking force is applied to the left rear wheel.
Example B
A vehicle oversteers in a left curve. In the process the rear of the vehicle breaks away. A precisely calculated braking action is performed on the right front wheel.
The Electronic Stability Program (Electronic-Stability-Program) (ESP) is an active safety system for improving the vehicle stability under all driving situations. It operates by individual brake intervention at one or more wheels on the front or rear axle. ESP stabilizes the vehicle while cornering, when braking or when rolling without drive and keeps it safely on course. It supplements the familiar functions of the antilock brake system (ABS), the acceleration slip regulation (ASR) and the engine braking regulation (MSR). The function of the stability control overrides the ABS and ASR control systems.
In addition to active ESP brake intervention there is also an influence on the engine/transmission management
The ESP controls under the following driving conditions:
^ when cornering (vehicle under steering or over steering)
^ when driving straight ahead (vehicle deviates off course due to uneven road conditions)
Advantages:
^ Improvement in the starting-off and acceleration capability due to increased traction, particularly on a road with different adhesion and on curves
^ Automatic adaptation of the engine torque depending on the traction condition of the wheels
^ Reduces the risk of skidding under all driving conditions due to automatic stabilization when braking, when accelerating or rolling
^ Improvement in the lane stability of the vehicle when cornering, also up to the critical limits
^ Shortening of brake distance in curves or on roads with a smooth surface
^ Increase in active driving dynamics safety, as only one wheel which is not spinning permits the optimum traction without loss of lateral stability
^ Via the ESP OFF switch (N72/1s1) an ESP and ASR cutout can occur which is detected by the ESP warning lamp (A1e41) lighting up permanently in the instrument cluster (A1). This can provide better traction (grinding effect) in deep snow or when snow chains are fitted.
The ESP comprises the following system relationships:
^ Anti lock brake system (ABS) closed-loop operation Prevents individual wheels locking by means of brake pressure control at the wheel brakes of the wheels affected
^ Acceleration slip regulation (ASR) closed-loop operation Prevents a too high slip of the driven wheels when starting off and accelerating by intervening in the engine management
^ Engine braking regulation (MSR) closed-loop operation Reduction in wheel slip at the drive wheels and better directional stability and road adhesion as a result
^ Tire pressure loss warner
The tire pressure loss warner detects the pressure loss in a tire before rolling-flat damage to tire occurs.
^ System correlations
The motor electronics are used to adjust the drive torque.
Via this system an engine control is performed by the throttle valve and ignition timing. To calculate the ESP drive torque control the gear stage is evaluated by the control unit (ETC) (N15/3) or by the electronic selector lever module control unit (N15/5) The ABS, ASR and MSR functions are included in the ESP electronics of the brake control circuit. The function for the electronic accelerator pedal and for the speed control system (cruise control) is included in the motor electronics control unit (N3/10).
The ESP and BAS control unit (N47-5) is connected to the motor electronics control unit (N3/10), the ETC [EGS] control unit (N15/3) and the electronic selector lever module control unit (N15/5) via the Controller Area Network bus class C (engine compartment) (CAN C). This digital line connection makes possible a rapid exchange of data.
Function overview
Brake forces, drive forces and side forces acting on one side and which act on a vehicle from the outside try to rotate the vehicle about its own center of gravity. The ESP detects the vehicle handling and selectively brakes individual wheels for correction. It regulates when cornering (vehicle understeers or oversteers) and when driving straight ahead (vehicle deviates from course due to dissimilar road conditions).
In order to be able to perform these control interventions, an expanded system of sensors is required compared with ASR.
A distinction is made between sensors which detect the driver's wish (steering angle sensor, throttle valve actuator (M16/6)) and sensors which measure the effective vehicle characteristics. These include:
^ Yaw rate sensor
^ Lateral acceleration sensor
^ Brake pressure sensors
^ Wheel speed sensor
The ESP and BAS control unit (N47-5) is constantly supplied with current data about engine torque, accelerator pedal position and transmission ratio.
Via the yaw rate sensor and lateral acceleration sensor the brake forces, drive forces and side forces which want to turn the vehicle about its center of gravity are detected. The longitudinal forces and lateral forces at the wheels can be calculated from the information listed. If these values exceed certain control thresholds, the corresponding control valves are actuated by the ESP and BAS control unit (N47-5) in order to selectively regulate the brake pressure at one or several wheels.
Simultaneously commands are passed on via CAN-C to the motor electronics control unit (N3/10), the ETC [EGS] control unit (N15/3) or electronic selector lever module control unit (N15/5). A torque requirement is made on the motor electronics control unit (N3/10) for reducing drive torque. If necessary, a downshift is prevented by the ETC [EGS] control unit (N15/3) or by the electronic selector lever module control unit (N15/5). The selective and accurately modulated intervention takes place in 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 braking torque control circuit
^ ABS control
ESP braking torque control circuit
ABS control
If a wheel tends to lock, the brake pressure in this wheel brake is regulated. The control in the traction system hydraulic unit (A7/3) in the ESP and BAS control unit (N47-5) takes place via the control valves by the control phases pressure buildup, pressure holding and depressurization.
ESP braking torque control circuit
ASR control
To brake the spinning wheel the brake pressure is led into the rear axle brake caliper (pressure build-up) via a pressure system in the traction system hydraulic unit (A7/3). As a result the other wheel can transmit the optimum drive force (locking differential effect).
ESP drive torque control circuit
ASR control
In order to reduce a too high drive torque and to achieve optimum traction as a result, the drive torque is reduced via CAN-C between the ESP and BAS control unit (N47-5) and motor electronics control unit (N3/10). 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 surface adhesion. So the drive torque specified by the driver via the accelerator pedal can be permitted again in good time. Via control valves in the traction system hydraulic unit (A7/3) the braking torque is regulated by pressure buildup, pressure holding and depressurization.
ESP drive torque control circuit
EBR control
If slip occurs at the drive wheels when the throttle is released, this is detected by the ESP and BAS control unit (N47-5). The signal is reported to the motor electronics control unit (N3/10) via CAN-C. 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 and drive torque control circuit
ESP control
If oversteer or understeer is detected, a calculated braking intervention is applied to the front or rear axle via the ESP and BAS (N47-5)control unit and the traction system hydraulic unit(A7/3) This braking action deliberately counteracts the undesirable vehicle motion. The drive torque reduction to suit the requirements is achieved by a decrease in engine torque by means of a signal via CAN-C to the motor electronics control unit (N3/10).
Brake Assist (BAS) operation
From the pedal speed of the brake pedal the ESP and BAS control unit (N47-5) detects that an emergency case braking exists and introduces BAS-mode.
ESP OFF mode
When the ESP OFF switch (N72/1s1) in the upper control panel control unit (N72/1) is pressed the ESP drive torque regulation is switched off and in addition the ESP stability function is canceled when accelerating and coasting. The ESP stability function remains operational during braking. EBR control is deactivated. In this switch position a brake intervention takes place via the braking torque control circuit up to 40 km/h when a drive wheel is spinning. In addition if cut-in conditions are present, brake intervention is retained up to a maximum of 60 km/h. The braking torque, however, is gradually reduced.
Due to the discontinuation of a separate stop lamp switch, pressing the brake pedal is detected as a signal via the release switch in the brake booster and is used for further processing. If the release switch is defective, the signal from the brake pressure and pedal travel is used.
The signal flow from the stop lamp goes from the ESP and BAS control unit (N47-5) (via CAN-C) to the central gateway control unit (N93) and via the Controller Area Network bus class B (interior) (CAN-B) to the rear SAM control unit with fuse and relay module (N10/2) which then actuates the stop lamps. The feedback goes to the electronic ignition switch control unit (N73) and is placed on CAN-C.
In the event of intervention by the brake system information is likewise transmitted by ESP and BAS control unit (N47-5), which then has stop lamp actuation suppressed.
