BAS brake application, function - GF42.31-P-2000F

MODEL 463.243 /244 /246 /247 /249 /250 /254 ## as of 127357 as of 1.9.01, 463.270 /271, 463.309 /322 /323 /332 /333 ## as of 127357 as of 1.9.01 with CODE (BB3) Electronic stability program (ESP) 

MODEL 463.248 ## as of 127357 as of 1.9.01 with CODE (BB3) Electronic stability program (ESP) except CODE (979) Special protected version 

Fig 1: Identifying Brake Assist Characteristics Graph

Courtesy of MERCEDES-BENZ USA

The adjacent diagram shows the "BAS brake application" function of the "Brake Assist (BAS)" as a graphic.

The maximum level of braking deceleration is reached considerably quicker when the BAS system is active and this deceleration level is maintained for as long as the BAS control mode is active.

1. The ESP and BAS control module (N47-5) reads in and evaluates the electric signals from the following system components:
   • Wheel rpm sensors (L6/1 to L6/4)

     Electrical signal for determining the vehicle speed.

   • BAS diaphragm travel sensor (A7/7b1)

     Electrical signal for determining the pedal speed of the brake pedal.

   • BAS release switch (A7/7s1)

     Electrical signal for determining the foot pressure the driver applies to the brake pedal.

   • Stop lamp switch (S9/1)

     Electrical signal for determining the status of the brake pedal.

2. Activating the Brake Assist (BAS) 

   The ESP and BAS control module (N47-5) uses the information it has read in to check that all the conditions for Brake Assist (BAS) activation are fulfilled before activating the BAS. Conditions for activation:

   • After successful self-diagnosis after starting the engine, there are no faults and the system is enabled.
   • The vehicle speed after moving off is greater than 8 km/h.
   • The BAS release switch (A7/7s1) is actuated.
   • The differential locks are not activated.
   • When the driver presses the brake pedal, the pedal speed is greater than the specified threshold value for the corresponding vehicle speed.
3. Deactivating the Brake Assist (BAS) 

   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 Brake Assist (BAS) deactivation is fulfilled before deactivating the BAS. Conditions for deactivation:

   • The vehicle speed is less than 3 km/h.
   • The Brake Assist (BAS) has been in operation for at least 20 s.
   • No signal from the stop lamp switch (S9/1)
   • There is an operational problem with the BAS.
   • The BAS release switch (A7/7s1) is not actuated.
   • The driver is no longer pressing the brake pedal.
   • The differential locks were activated.
4. Brake application when Brake Assist (BAS) is activated 
   • The ESP and BAS control module (N47-5) actuates the BAS solenoid valve (A7/7y1) with an electric control signal so that the solenoid valve is activated.
   • The opened BAS solenoid valve (A7/7y1) controls the air at atmospheric pressure inside the BAS brake booster (A7/7) so that the maximum brake force is achieved.
   • The ESP and BAS control module (N47-5) controls the stop lamp supression relay (K55) for as long as the Brake Assist (BAS) is activated so that the stop lamps cannot light up when the driver is not pressing the brake pedal.
   • When the driver releases the brake pedal, i.e. the foot pressure on the brake pedal is reduced to almost zero, movement is triggered in the BAS solenoid valve (A7/7y1) which is detected by the BAS release switch (A7/7s1). The release switch is now no longer actuated and passes an electrical signal to the ESP and BAS control module (N47-5).
   • The BAS solenoid valve (A7/7y1) is no longer controlled by the ESP and BAS control module (N47-5) and the valve closes. The maximum brake servo assistance is therefore deactivated. The normal brake servo assistance corresponding to the position of the brake pedal is maintained.
5. Brake application when Brake Assist (BAS) is not activated 
   • The BAS solenoid valve (A7/7y1) is de-energized when the Brake Assist (BAS) is not activated.
   • The braking force is increased in the conventional way, i.e. the brake booster (A7/7) proportionally increases the pedal force applied by the driver.