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Home >> Mercedes Benz Truck >> 2003 >> G 55 AMG (463.246) V8-5.5L (113.982) >> Repair and Diagnosis >> Brakes and Traction Control >> Description and Operation >> GF42.35-P-2000F ETS Braking Torque Control Circuit, Function

GF42.35-P-2000F ETS Braking Torque Control Circuit, Function




GF42.35-P-2000F ETS Braking Torque Control Circuit, Function
MODEL 463.243 /244 /246 /247 /249 /250 /254 ## as of 127357 as of 1.9.01 up to 31.5.12, 463.270 /271 up to 31.5.12, 463.309 /322 /323 /332 /333 ## as of 127357 as of 1.9.01 up to 31.5.12
- with CODE (BB3) Electronic Stability Program (ESP)
MODEL 463.248 ## as of 127357 as of 1.9.01 up to 31.5.12
- with CODE (BB3) Electronic Stability Program (ESP)
- except CODE (979) Special protection version





"Pressure build-up" function
Shown on right front wheel brake

4 BAS brake booster
5a Right front wheel brake
A7/3 Traction systems hydraulic unit
A7/3p1 Front axle high pressure and return pump
A7/3y6 Left front solenoid valve, hold pressure
A7/3y7 Left front solenoid valve, reduce pressure
A7/3y8 Right front solenoid valve, hold pressure
A7/3y9 Right front solenoid valve, reduce pressure
A7/3y18 Front axle switchover valve
A7/3y22 Front axle inlet solenoid valve

a Suction pressure
f High pressure





"Hold pressure" function
Shown on right front wheel brake with calculated brake pressure of 60 bar

4 BAS brake booster
5a Right front wheel brake
A7/3 Traction system hydraulic unit
A7/3p1 Front axle high pressure and return pump
A7/3y6 Left front solenoid valve, hold pressure
A7/3y7 Left front solenoid valve, reduce pressure
A7/3y8 Right front solenoid valve, hold pressure
A7/3y9 Right front solenoid valve, reduce pressure
A7/3y18 Front axle switchover valve
A7/3y22 Front axle inlet solenoid valve

a Suction pressure
b Brake pressure
e Reduced pressure
f High pressure





"Pressure reduction" function
Shown on right front wheel brake with calculated brake pressure of 60 bar

4 BAS brake booster
5a Right front wheel brake
A7/3 Traction systems hydraulic unit
A7/3p1 Front axle high pressure and return pump
A7/3y6 Left front solenoid valve, hold pressure
A7/3y7 Left front solenoid valve, reduce pressure
A7/3y8 Right front solenoid valve, hold pressure
A7/3y9 Right front solenoid valve, reduce pressure
A7/3y18 Front axle switchover valve
A7/3y22 Front axle inlet solenoid valve
a Suction pressure
e Reduced pressure
f High pressure

1 Capture and process sensor signals and status of switches
The ESP and BAS control module (N47-5) reads in and evaluates the electric signals from the following system components:
1.1 Wheel rpm sensors (L6/1 to L6/4)
The conditioned wheel rpm signals are constantly compared both with each other and with the specified slip thresholds on the front and rear wheels in relation to the speed of the vehicle. Calculate the values for vehicle speed, acceleration, deceleration, drive slip.
1.2 Stop lamp switch (S9/1)
Detect and evaluate the position of the dual contact switch (NO contact and NC contact) when the driver applies the brake.
2 Activation of ETS braking torque control
The ESP and BAS control module (N47-5) uses the information it has read in to check that all the conditions for activation of the ETS braking torque control are fulfilled before it is activated.
Conditions for activation:
- After successful self-diagnosis after starting the engine, there are no faults and the system is enabled.
- The vehicle speed is not greater than 60 km/h.
- One or more wheels begin to spin, i.e. the number of revolutions increases per unit of time, which does not correspond to the wheel speed during normal slip.
3 Deactivation of ETS braking torque control
The ESP and BAS control module (N47-5) uses the information it has read in to check that at least one of the conditions for deactivation of the ETS braking torque control is fulfilled before deactivating it.
Conditions for deactivation:
- Driver presses the brake pedal.
- Brake pad temperature too high.
- Vehicle speed exceeds 60 km/h.
- Normal slip is achieved.
4 Calculating the brake pressures and actuating the traction system hydraulic unit (A7/3)
The ESP and BAS control module (N47-5)
- calculates the brake pressures for the wheel brakes (variables of the braking torque control) for each control interval in line with the relevant reference variables (specified values for the wheel slip)
- and uses electric output signals to actuate both the solenoid valves and the high pressure and return pumps of the traction system hydraulic unit (A7/3), which functions as an electromechanical actuator in the braking torque control circuit.
5 Brake pressure build-up
The solenoid valves of the traction system hydraulic unit (A7/3) are controlled differently during the three control phases (pressure build-up, hold pressure and pressure reduction) according to the brake pressure calculated by the ESP and BAS control module (N47-5).
5.1 Pressure build-up
During the "pressure build-up" control phase, the brake pressure is increased until the calculated brake pressure is achieved.
5.2 Hold pressure
The "hold pressure" control phase begins when the pressure build-up phase has been completed provided that the brake pressure does not need to be increased further.
This control phase remains active unless deviating values for the brake pressure are calculated.
5.3 Pressure reduction
If the brake pressure available during the "hold pressure" phase is too high, the "pressure reduction" control phase begins.
6 Actuation of the traction system hydraulic unit (A7/3) solenoid valves
The following example describes the actuation of the traction system hydraulic unit (A7/3) solenoid valves during the three control phases at the right front axle brake (5a).
The relevant solenoid valves of the front and rear axle brake circuit would be actuated in the same way at the other wheel brakes.
In the example, the braking torque control does not intervene at the rear wheel brakes and so the status in the rear wheel brake circuit set during the pressure build-up phase remains the same during the entire control interval.
6.1 Front axle inlet solenoid valve (A7/3y22)
Same function as rear axle inlet solenoid valve (A7/3y23).
^ Pressure build-up
--> Actuated, switches to flow position.
^ Hold pressure, reduce pressure
Case 1: Calculated brake pressure in right front axle brake (5a) less than or equal to 60 bar (see illustration).
--> No longer actuated after successful pressure build-up and switches back to lock position (basic position).
Case 2: Calculated brake pressure in right front axle brake (5a) > 60 bar.
--> Continues to be actuated and remains in the flow position during the entire control interval.
6.2 Front axle switchover solenoid valve (A7/3y18)
Same function as rear axle switchover solenoid valve (A7/3y19).
^ Pressure build-up, hold pressure
--> Actuated, switches to lock position and therefore uncouples the front axle brake circuit from the master brake cylinder. The integrated pressure limiting valve (approx. 170 bar) limits the high pressure.
^ Pressure reduction
Case 1: Calculated brake pressure in right front axle brake (5a) less than or equal to 60 bar (see illustration).
--> Is no longer actuated, switches to the flow position and therefore initiates the pressure reduction phase.
Case 2: Calculated brake pressure in right front axle brake (5a) > 60 bar.
--> Remains in the lock position after the pressure holding phase. The integrated pressure limiting valve (approx. 170 bar) limits the high pressure.
6.3 Front axle high pressure / return pump (A7/3p1)
Same function as rear axle high pressure / return pump (A7/3p2).
^ Pressure build-up
--> Actuated, draws brake fluid out of the reservoir via the open front axle inlet solenoid valve (A7/3y22) via the master brake cylinder and increases the high pressure in the system for the front axle brake circuit.
^ Hold pressure
Case 1: Calculated brake pressure in right front axle brake (5a) less than or equal to 60 bar.
--> Still in operation after the pressure build-up phase but can no longer draw brake fluid out of the reservoir via the master brake cylinder when the inlet solenoid valve (A7/3y22) is closed and therefore cannot increase the brake pressure any further.
Case 2: Calculated brake pressure in right front axle brake (5a) > 60 bar.
--> Continues to draw brake fluid from the reservoir via the open front axle inlet solenoid valve (A7/3y22) via the master brake cylinder and increases the pressure in the system for the front axle brake circuit.
^ Pressure reduction
Case 1: Calculated brake pressure in right front axle brake (5a) less than or equal to 60 bar.
--> Remains in operation after the pressure holding phase. The brake fluid flows back to the reservoir via the open front right solenoid valve, hold pressure (A7/3y8), the front axle switchover solenoid valve (A7/3y18), which is also open, and via the master brake cylinder.
Case 2: Calculated brake pressure in right front axle brake (5a) > 60 bar.
--> Remains in operation after the pressure holding phase. The brake fluid flows back to the reservoir via the open right front solenoid valve, reduce pressure (A7/3y9), via the open front axle inlet solenoid valve (A7/3y22), partially via the pressure limiting valve integrated in the front axle switchover solenoid valve (A7/3y18), and via the master brake cylinder.
6.4 Left front solenoid valve, hold pressure (A7/3y6)
Same function as:
Right front solenoid valve, hold pressure (A7/3y8)
- Left rear solenoid valve, hold pressure (A7/3y10)
- Right rear solenoid valve, hold pressure (A7/3y12)
^ Pressure build-up, hold pressure
--> Actuated and switches to lock position. The same pressure is applied as at the front right solenoid valve, hold pressure (A7/3y8) of the right front wheel brake (5a).
^ Pressure reduction
--> Remains in the lock position after the pressure holding phase. The same reduced pressure is applied as at the right front wheel brake (5a).
6.5 Right front solenoid valve, hold pressure (A7/3y8)
Same function as:
Left front solenoid valve, hold pressure (A7/3y6)
- Left rear solenoid valve, hold pressure (A7/3y10)
- Right rear solenoid valve, hold pressure (A7/3y12)
^ Pressure build-up
--> Not actuated, remains in flow position and therefore allows pressure build-up in the right front wheel brake (5a).
^ Hold pressure, reduce pressure
Case 1: Calculated brake pressure in right front axle brake (5a) less than or equal to 60 bar (see illustration).
--> Remains in flow position after successful pressure build- up, the check valves in the brake circuit prevent pressure reduction.
Case 2: Calculated brake pressure in right front axle brake (5a) > 60 bar.
--> Actuated after successful pressure build-up, switches to and remains in lock position.
6.6 Right front solenoid valve, reduce pressure (A7/3y9)
Same function as:
- Left front solenoid valve, reduce pressure (A7/3y7)
Left rear solenoid valve, reduce pressure (A7/3y11)
- Right rear solenoid valve, reduce pressure (A7/3y13)
^ Pressure build-up
--> Not actuated and remains in lock position, high pressure is applied and prevents pressure reduction in the right front wheel brake (5a).
^ Hold pressure
--> Remains in the lock position after pressure build-up, brake pressure is applied and pressure reduction in the right front wheel brake (5a) is still not possible, i.e. the brake pressure level remains unchanged.
^ Pressure reduction
Case 1: Calculated brake pressure in right front axle brake (5a) less than or equal to 60 bar (see illustration).
--> Remains in the lock position after the pressure holding phase.
Case 2: Calculated brake pressure in right front axle brake (5a) > 60 bar.
--> Actuated and switches to the flow position, the pressure reduction in the right front wheel brake (5a) is therefore initiated when the right front solenoid valve, hold pressure (A7/3y8) is closed.




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