ESP braking moment control circuit, function

CAN data bus

ESP control module
(N47)

CR control module or engine control unit with integrated throttle valve positioner

VSS control module (N15/7)

Left front wheel speed sensor (L6/1)

Right front wheel speed sensor (L6/2)

Left rear wheel speed sensor (L6/3)

Right rear wheel speed sensor (L6/4)

Stop lamp switch (S9/1)

Parking brake switch (S12)

ASR OFF switch (S6/2s8)

ESP brake pressure sensors (B34/1-2)

Steering angle sensor (N49)

Voltage supply, term. 30, 31, 87

Traction system
hydraulic unit (A7/3)

High-pressure/return-flow

pump (A7/3m1)

Solenoid valves

(A7/3y6 to A7/3y27)

High-pressure/
return-flow pump relay (K20/1)

Instrument cluster (A1)

ESP warning lamp (A1e41)

ABS malfunction indicator lamp (A1e17)

BAS/ESP malfunction indicator lamp (A1e47)

Test connector for diagnosis X11/4

Rotational speed and lateral acceleration sensor (B24/15)

The functions of the braking moment control circuit are controlled using the components of the electric/electronic system.

The ESP control module (N47) is supplied with power via the fuse and relay box (F1).

The ESP control module (N47) receives input signals from the following components:

 Four wheel speed sensors

 Steering angle sensor

 Sensor for rotational speed and lateral acceleration

 ESP brake pressure sensors

 Stop lamp switch

 Parking brake switch

 Engine control unit via CAN data line

 VSS control module via CAN data line

 ASR OFF switch

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The input signals are processed in the ESP control module ESP to form output signals for the following components:

 Solenoid valves in the hydraulic unit

 High-pressure/ return-flow pump (via relay)

 Engine control unit via CAN data line

 VSS control module via CAN data line

 ESP warning lamp over CAN data line

 ABS malfunction indicator lamp over CAN data line

 BAS/ESP malfunction indicator lamp over CAN data line

On the basis of the input signals, the ESP control module (N47) decides which of the 7 operating modes

 Normal mode

 ABS control mode

 ASR control mode

 EBR control mode

 ESP control mode

 ASR OFF mode

 BAS mode

must be activated.

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Normal mode

This is the case when the driving state requires no control mode. All solenoid valves in the traction system hydraulic unit (A7/3) are in the basic position, i.e. de-energized. The system is ready for braking.

This mode also exists when there is a malfunction in the ESP, BAS or ABS system. Drive torque control is not activated.

ABS control mode

The ESP control module (N47) uses the wheel speed signals to determine whether the criteria for ABS control exist. The appropriate solenoids in the hydraulic unit are then actuated.

The solenoids for front and rear axle in the traction system hydraulic unit (A7/3) are actuated individually (4-channel control).

ASR control mode

As soon as a driving wheel shows a tendency to spin, the ESP control module (N47) actuates the high-pressure/return-flow pump (A7/3m1), the appropriate switchover solenoid and charging solenoid, and the solenoids for the drive axle. The solenoids for the left and right-hand side of the rear axle are actuated separately.

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ESP control mode

A status controller in the ESP control module (N47) receives and processes the signals for the wheel speeds, the steering angle, the yaw rate of the vehicle, the lateral acceleration and the brake pressure in the front and rear axles. After evaluating the input signals, the inlet solenoid valves, the switchover valves, the high-pressure/return-flow pump (A7/3m1) and the necessary solenoid valves are actuated to regulate the brake pressure in the individual wheel brakes.

ASR OFF mode

If the ASR OFF switch is pressed (S6/2s8), the ASR drive torque control function is deactivated. The ESP stability function remains operational. EBR control is deactivated.

With the switch in this position, braking force is applied to one spinning drive wheel via the braking moment control circuit.

If, when the switch is pressed, the vehicle speed is >10 km/h and the lateral acceleration is >2.5 m/s2, the driver's request is recognized by the system, but does not become effective until the vehicle speed and/or lateral acceleration drops below the respective activation threshold.

If the vehicle exceeds a speed of 60 km/h, the ASR OFF mode is canceled again.

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BAS mode

From the speed of the brake pedal the ESP control module (N47) recognizes that emergency braking is in progress and initiates BAS mode (see Brake Assist (BAS), function).