ESP braking moment control circuit, function - GF42.45-P-2000E

MODEL 163 up to 31.8.02 with CODE (472a) Electronic Stability Program (ESP) 

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)

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 (F1 k25) 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)

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).

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 circuit.

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).

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 drag 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.

	ABS closed-loop operation function		GF42.45-P-3000C
	ASC control mode, function		GF42.45-P-3500C
	ESP control mode, function		GF42.45-P-3700C
	Electronic brake pressure distribution, function		GF42.35-P-3600A
	BAS function		GF42.31-P-0001A