BAS brake application, function

Studies in the driving simulator and on the test track have shown that most drivers in emergency driving situations, above all in the initial phase of brake application, in fact press the brake pedal quickly but not hard enough.

A distinction is made between:

 The hesitant brake application, e.g. the driver applies too little pedal force in the initial phase and increases it too slowly.

 Inadequate braking, e.g. the driver applies too little pedal force throughout the entire brake application.

The Brake Assist (BAS) system has been developed in order to improve these situations.

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Advantages:

 The BAS system reduces the accident risk in dangerous situations by optimum braking deceleration.

 The BAS system significantly reduces the brake distance during hesitant or inadequate braking.

The BAS system is part of the active safety system. It is active when the driver brakes very quickly in an emergency situation. The BAS system detects whether an emergency braking situation exists on the basis of the speed at which the brake pedal is depressed. If this is the case, the high-pressure charging pump in the traction system hydraulic unit (A7/3) is activated and consequently the full braking force is reached.

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If the driver releases the brake pedal, then the release of the brake pedal is detected and the BAS system is deactivated again.

A brake application with BAS functions exactly as with a normal brake application, only the pressure is built up more quickly corresponding to the pedal speed. From the operating speed of the brake pedal and the vehicle speed the ESP control unit (N30/4) detects that the conditions for a BAS cut-in exist.

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Using the speed of the pressure rise of the pilot pressure sensor and the signal of the pedal value sensor (B37/3) the ESP control unit (N30/4) calculates the operating speed of the brake pedal. The BAS system is fully integrated in the Electronic Stability Program) (ESP) system with the ESP control unit (N30/4).

The pressure reservoir in the traction system hydraulic unit (A7/3) is used to generate pressure. Once the engine has started, a vehicle identification and system self-diagnosis takes place.

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The electronic stability progam ESP (N30/4) reads in the electrical signals from the following system components and evaluates them:

 Left front rpm sensor (L6/1) for determining the current wheel speed

 Right front rpm sensor (L6/2) for determining the current wheel speed.

 Left rear rpm sensor (L6/3) for determining the current wheel speed.

 Right rear rpm sensor (L6/4) for determining the current wheel speed.

 ESP brake pressure sensor (B34) for determining the brake pressure

 "ASR OFF" switch (N72/1s5) for determining the driver requirement

 The yaw rate and lateral acceleration sensor (B24/15) for determining the rotational speed of the vehicle about the vertical axis

 The left front brake pad contact sensor (S10/1) for determining the wear of the brake linings.

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 The right front brake pad contact sensor (S10/2) for determining the wear of the brake linings.

 The left rear brake pad contact sensor (S10/3) for determining the wear of the brake linings

 The right rear brake pad contact sensor (S10/4) for determining the wear of the brake linings

 The steering angle sensor (B24/8) for determining the steering wheel rotary movements

 The CDI control unit (N3/9) (with engine 646), for determining the engine torque and the accelerator pedal position via the pedal value sensor (B37/3)

 The ME control unit (N3/10) (with engine 112) for determining the engine torque and the accelerator pedal position via the pedal value sensor (B37/3)

 The ETC [EGS] control unit (N15/3) (with transmission 722.6), for determining the gear currently engaged

 The electronic selector lever module control unit (N15/5) (with transmission 722.6) for determining the selector lever position.

 The stop lamp switch (S9/1) for determining the operating condition of the brake pedal

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The following functions are controlled in the ESP control unit (N30/4):

 The function of the ESP system

 The functions of the antilock brake system (ABS)

 The functions of the Electronic traction system (ETS)

 The functions of the BAS system

 The functions of the acceleration slip regulation (ASR) system

 The functions of the electronic brake force distribution (EBV) system

The BAS system cuts in when the following conditions apply:

 Once the engine has started "circuit 61 ON" and if no fault is present after self-diagnosis is complete, the BAS system is enabled

 The speed of the vehicle after starting off is > 8 km/h.

 When the brake pedal is operated the pedal speed is greater than the specified threshold value for the associated vehicle speed.

The BAS system is switched off when one of the following conditions applies:

 The vehicle speed is < 3 km/h.

 The duty cycle of the BAS system is more than t = 20 s.

 The signal from the stop lamp switch (S9/1) remains deactivated.

 There is a BAS system malfunction.

 The brake pedal pressure is reduced by the driver to such an extent that emergency braking is no longer required.