ESP braking moment control circuit, function

CAN data bus

ESP control module
(N47-5)

Engine control module

Transmission control module

Left front wheelspeed sensor (L6/1)

Right front wheelspeed sensor (L6/2)

Left rear wheelspeed sensor (L6/3)

Right rear wheelspeed sensor (L6/4)

Parking brake switch (S12)

ESP OFF switch (S76/6)

Yaw rate and lateral acceleration sensor (B24/15)

ESP brake pressure sensor (B34)

Steering angle sensor (N49)

Voltage supply term.30, 31, 87

ESP hydraulic unit (A7/3)

High pressure and return pump (A7/3m1)

Solenoid valves (A7/3y6 through A7/3y23)

Instrument cluster (A1)

ESP warning lamp (A1e41)

ABS indicator lamp (A1e17)

multifunction display (A1p13)

Diagnostic data link connectorX11/4

BAS brake booster
(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.

The ESP control module (N47-5) is supplied with power via the fuse and relay module (K40/2).

The ESP control module (N47-5) receives input signals from the following components:

 4 wheel speed sensors

 Steering angle sensor

 Yaw rate and
lateral acceleration sensor via CAN data line

 ESP brake pressure sensor

 Parking brake switch

 ME-SFI control module over CAN data line

 ETC control module over CAN data line

 ESP OFF switch

 BAS release switch

 BAS diaphragm travel sensor

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

 BAS solenoid valve

 Solenoid valves in the hydraulic unit

 High pressure and return pump

 Engine control module over CAN data line

 ETC control module over CAN data line

 ESP warning lamp over CAN data line

 ABS indicator lamp over CAN data line

 BAS/ESP indicator lamp over CAN data line

On the basis of the input signals, the ESP control module (N47-5) decides which of the 7 operating modes

 Normal operation

 ABS control mode

 ETS/ASR closed-loop control activated

 EBR control mode

 ESP control mode

 ESP OFF mode

 BAS mode

must be activated.

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Normal operation

This is the case when the driving state requires no control mode. All solenoid valves in the ESP hydraulic unit (A7/3) are in their passive, no-current state. 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 (N47-5) 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 ESP hydraulic unit (A7/3) are actuated individually (4-channel control).

ETS/ASR closed-loop control activated

The ABS control module (N47-2) registers and processes the rotation rates of all wheels. These data serve as the basis for calculating a vehicle reference velocity.

When the wheelspeed signals indicate to the ESP control unit (N47-5) that one or several drive wheels are about to start slipping, the system assumes active ETS/ASR closed-loop control status. At extremely low traction coefficients simultaneous brake-system pressurization at all four wheels is possible.

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The drive wheel(s) displaying a tendency to slip is (are) braked by the appropriate wheelbrake(s) until the calculated drive slip (approximately 5 kph above the reference velocity) has been reached. The system allows only the limited amount of slip required to obtain optimal traction at each wheel.

Spinning wheels are decelerated by a pressurization system in the hydraulic unit which supplies pressurized brake fluid to the brake caliper (pressurization phase).

Solenoid valves within the ESP hydraulic unit (A7/3) furnish closed-loop control of braking force with selective activation of three operating modes: pressurization, maintenance and pressure discharge.

With activation conditions present, this ETS control status is available only within a speed range extending from 0-60 kph.

If the activation conditions remain present during acceleration to speeds above the 60 kph threshold, closed-loop ETS/ASR control is active to approximately 80 kph.

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ESP control mode

A status controller in the ESP control module (N47-5) receives and processes the signals for the wheel speeds, the steer angle, the yaw rate of the vehicle, the lateral acceleration and the brake pressure in the front and rear axle circuit. After assessing the monitored signal data the system triggers the BAS solenoid valve (A7/7y1), the solenoid supply valves, circuit-selection valves, high-pressure and return pump (A7/3m1) and selected solenoid valves to modulate braking pressure at the individual wheel brakes..

ESP OFF mode

The ESP OFF switch (S76/6) deactivates the ASR Acceleration Slip Regulation along with the ESP system's functions for enhancing stability during acceleration and coasting. The ESP stability function remains operational during braking. MSR control is deactivated.

With the switch in this position, braking force is applied to one spinning drive wheel via the braking moment control circuit at vehicle speeds of up to 40 km/h. If activation conditions continue to exist, brake intervention continues up to max. 60 km/h. The braking torque is, however, reduced continuously.

BAS mode

From the speed of the brake pedal the ESP control module (N47-5) recognizes that emergency braking is in progress and initiates BAS mode (see Brake Assist (BAS), function).