ESP braking moment control circuit, function

CAN data bus

ESP/BAS control module

(N47-5)

Control unit: ME (N3/10), EGS (N15/3), transfer case (N78)

L6/1 Left front wheelspeed sensor

L6/2Right front wheelspeed sensor

L6/3Left rear wheelspeed sensor

L6/4Right rear wheelspeed sensor

Stop lamp switch (S9/1)

Parking brake monitor switch (S12)

ESP OFF switch (S76/6)

ESP yaw rate sensor (B45)

Brake pressure sensors:

ESP Pressure sensor 1 (B34/1)

ESP pressure sensor 2 (B34/2)

Lateral acceleration sensor (B43)

Steering angle sensor (N49)

Power supply, terminal 15

ESP brake light supression relay (F1k6)

Hydraulic unit for traction-control systems (A7/3)

High-pressure and return pump (A7/3m1)

Solenoid valves

(A7/3y6 to A7/3y13 and

A7/3y24 to A7/3y27)

High-pressure/return pump relay (F1k25)

Instrument cluster (A1)

ABS indicator lamp (A1e17)

ETS indicator lamp (A1e35)

ESP warning lamp (A1e41)

BAS/ESP indicator lamp (A1e47)

Diagnostic data link connectorX11/4

Power supply Terminal 30, 31

Brake booster
BAS (A7/7)

BAS solenoid valve (A7/7y1)

BAS release switch (A7/7s1)

BAS diaphragm travel sensor (A7/7b1)

The functions of the braking moment control circuit are controlled using the components of the electric/electronic system. This process employs selective application of specifically modulated fluid-pressure levels within the wheel cylinders for precise deceleration of individual wheels.

The ESP control module (N47-5) receives its electrical power from the fuse and relay module (F1).

To provide closed-loop control of all functions based on braking intervention, the ESP control unit (N47-5) relies on signals from the following components:

 4 Wheelspeed sensors (L6/1, L6/2, L6/3 and L6/4)

 Steering angle sensor (N49)

 Lateral acceleration sensor (B43)

 ESP yaw rate sensor B45

 ESP brake pressure sensor 1 (B34/1)

 ESP brake pressure sensor 2 (B34/2)

 Stop lamp switch (S9/1)

 Parking brake monitor switch (S12)

 Engine-management control unit (ME, N3/10) via CAN data wire

 EGS control unit (N15/3) via CAN data wire

 ESP OFF switch (S76/6)

 BAS release switch (A7/7s1)

 BAS diaphragm travel sensor (A7/7b1)

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The incoming signals monitored by the ESP control unit (N47-5) are processed to generate output signals for transmission to the following components:

 BAS solenoid valve (A7/7y1)

 Solenoid valves (A7/3y6 to A7/3y13 and A7/3y24 to A7/3y27) in the hydraulic unit (A7/3)

 High-pressure/return pump relay (F1k25) for control of high-pressure/return pump (A7/3m1)

 ESP stop lamp suppression relay (F1k6)

 Engine-management control unit (ME, N3/10) via CAN data wire

 EGS control unit (N15/3) via CAN data wire

 Warning and indicator lamps in instrument cluster (A1) via CAN data wire:

ABS malfunction indicator lamp (A1e17)

 ETS indicator lamp (A1e35)

 ESP warning lamp (A1e41)

 BAS/ESP indicator lamp (A1e47)

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The ESP control unit (N47-5) determines which of the 7 operational modes to activate based on the input signals:

 Normal operation

 ABS control mode

 ETS/ASR closed-loop control activated

 EBR control mode (see drive moment control circuit)

 ESP control mode

 BAS mode

 Electronic brake force distribution

 ESP OFF mode

Normal operation

No control intervention is required during normal vehicle operation. All of the solenoid valves in the ESP hydraulic unit (A7/3) are in their no-current, passive state. The system is ready for braking. Drive torque control is not activated.

The system also assumes this operational status in response to malfunctions in the BAS, ABS or ESP.

ABS control mode

The ESP control unit (N47-5) recognizes the presence of the criteria that render closed-loop ABS intervention necessary based on the signals from the wheelspeed sensors. It responds by triggering selected solenoid valves in the hydraulic unit.

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

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Closed-loop ETS/ASR control intervention

The ESP control unit (N47-5) responds to incipient wheel slip at a drive wheel by activating the high-pressure and return pump (A7/3m1) along with selected solenoid valves in the traction-control systems hydraulic unit (A7/3). The solenoids for front and rear wheels in the ESP hydraulic unit (A7/3) are actuated individually.

ESP control mode

The ESP control unit's (N47-5) integrated operation status controller monitors and processes data on vehicle wheelspeeds, steering angle, yaw rate and lateral acceleration as well as the braking pressure on the control rod and hydraulic piston sides of the brake ciruit.

After processing the monitored signals the unit triggers the BAS solenoid valve (A7/7y1), the high-pressure and return pump (A7/3m1) and selected valves in the traction-control systems hydraulic unit (A7/3) to modulate the braking pressure at the individual wheel brakes.

BAS mode

The ESP control unit (N47-5) monitors the rate at which the brake pedal is depressed to recognize panic stops, to which it responds by activating the BAS mode (refer to BAS function).

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Electronic brake force distribution

During every brake application the wheelspeed is used for precise monitoring of rear-wheel slip rates. Specific solenoid valves within the hydraulic unit are triggered to prevent the acceptable rear-wheel slip rates from being exceeded.

ESP OFF mode

Activation of the ESP OFF switch (S76/6) deactivates the drive torque control and the engine darg torque (MSR) control.

This also deactivates the ESP stability-maintenance function during acceleration and coasting. ESP continues to enhance stability when the driver initiates braking maneuvers.