a Insufficient brake application b Hesitant brake application c BAS brake application Tests with normal drivers in a driving simulator and on the test track have shown that, in emergency braking situations, most drivers actually operate the brake pedal quickly enough but with insufficient force, above all in the initial phase of brake application. Differentiation is made between: Hesitant brake application - the driver applies too little pedal force in the initial phase and increases it too slowly. Insufficient brake application - the driver applies too little pedal force during the entire brake application. To improve these situations, Brake Assist has been developed.
		P42.31-0210-11

Task "Brake Assist" BAS is an active safety system. It becomes active when the driver brakes very quickly in an emergency situation. The 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, a solenoid valve opens in the brake servo and activates the full servo power. If the driver releases the brake, this is detected and the solenoid valve closes again.

Advantages Optimum deceleration reduces the risk of an accident in danger situations and thus provides vital support to the driver. Supports the ABS by providing the greatest possible servo action. ABS maintains full steerability even during BAS intervention. Considerably reduces the braking distance in the case of hesitant or insufficient brake application.

Function overview The normal brake servo amplifies the force of the driver's foot proportionally. If braking is not taking place, a vacuum created by the engine or by a vacuum pump exists in both chambers. A mechanical control valve in the brake servo operated by the force of the driver's foot allows air at atmospheric pressure to flow into the rear chamber when braking. The pressure difference existing between the two chambers and the amplification force created is therefore proportional to the force applied by the driver's foot. Amplification of the force of the foot takes place up to the point at which full atmospheric pressure exists in the rear chamber. With the BAS brake servo, the basic version is expanded with the following parts: BAS diaphragm travel sensor for measuring the brake pedal travel. BAS solenoid valve for active implementation of braking force support. BAS release switch to detect the end of the brake application. BAS control module to measure the values and to control the BAS braking intervention.

In vehicles with engines 111, 112, 113, 605, 606, 611, 612, 613 and ESP, the BAS function is integrated in the ESP control module. In models 163, 168, 203, 215, 220, the BAS function is integrated in the ESP control module. After the engine is started, a vehicle identification and self-check of the system takes place. The BAS is ready to function if no fault is present and the vehicle has exceeded a speed of 8 km/h after driving off. Following this, BAS can be activated down to a speed of 3 km/h. The actuating speed of the brake pedal and the vehicle speed are measured in the BAS control module (N48) / ESP (N47-5). If the pedal speed is greater than the threshold value specified for the particular vehicle speed, a solenoid valve in the brake servo is activated and full servo force is achieved. In the case of a defect, the BAS is not brought into use (indication by malfunction indicator lamp or multi-function display in the instrument cluster). The normal function of the brake servo is not affected by this.

	Notes on testing electronic components and system for damage resulting from an accident		AH42.00-P-0001-06A
	Brake Assist (BAS) driver information	Models 129, 140, 163, 168, 170, 202, 208, 210	GF42.31-P-0001-01A
		Model 203, 215, 220	GF42.31-P-0001-01B
	Brake Assist (BAS), arrangement of components		GF42.31-P-0001-02A
	BAS brake application function		GF42.31-P-2000A

GF42.31-P-0001-01A

Brake Assist (BAS): Driver Information

A system indicator lamp is provided for the BAS in the instrument cluster. In the case of vehicles with ETS, ASC, or ESP, the BAS indicator lamp is combined with the indicator lamp for the respective traction system. A1 Instrument cluster A1e17 ABS indicator lamp A1e39 BAS indicator lamp A1e47 BAS / ESP indicator lamp A1e48 BAS / ASC indicator lamp A1e49 BAS/ETS indicator lamp
		P42.31-0200-01

Turning on ignition and starting engine When the ignition is switched on (ignition/starter switch position "2"), the indicator lamp in the instrument cluster lights up (bulb check) and goes out when the engine is running. If the BAS indicator lamp lights up while the engine is running, there is a fault in the BAS. The system is no longer functional, but the full braking effect with ABS is retained. In the case of the combined indicator lamp (BAS/ETS, BAS/ASC, BAS/ESP), the fault may be located in the BAS and/or the traction system. If the fault is located in the BAS, the ETS, ASC or ESP system remains functional. If the fault is located in the traction system, the BAS remains functional.

In the case of vehicles with BAS integrated in the ESP, the ESP no longer functions if there is a fault in the BAS. When driving System faults which occur while the vehicle is being driven also cause the BAS indicator lamp to light up permanently. The BAS indicator lamp may light up when the vehicle is being driven and then go out again after a while. This is caused by battery undervoltage.

GF42.31-P-0001-02A

Brake Assist (BAS), arrangement of components

1 Tandem master brake cylinder 2 Vacuum connection A1e17 ABS malfunction indicator lamp A1e39 EA [EFP] warning lamp A1e47 BAS/ESP malfunction indicator lamp A1e48 BAS / ASR malfunction indicator lamp A1e49 BAS/ETS malfunction indicator lamp A7/7 BAS brake servo A7/7b1 BAS diaphragm travel sensor A7/7s1 BAS release switch A7/7y1 BAS solenoid valve N48 BAS control module (all vehicles with engines 111, 112, 113, 605, 606, 611, 612, 613 and ESP integrated in ESP control module N47-5. Models 163, 168, 203, 215, 220, ESP integrated in ESP control module N47-5) Y61 Master brake cylinder changeover valve (model 129.067 with ESP, 129.076, 140.04/05/06/07)
		P42.31-0201-06

Models 203, 215, 220 have a multifunction display (A1p13) in the instrument cluster instead of the malfunction indicator lamp.

The functions of the BAS brake servo (A7/7) are controlled using the components of the electric/electronic system. In model 168, the voltage supply for the BAS control module (N48) is via the fuse and relay box (F1). In models 129 and 140 via the base module (N16/1). In models 163, 170, 202, 208, 210, 215, 220 via the relay module (K40). In model 203 via the SAM control module (N10/1). In all vehicles with engines 112, 113, 605, 606, 611, 612, 613 and ESP, the BAS control module function is integrated in the ESP control module (N47-5). In models 163, 168, 203, 215, 220, the BAS control module function is integrated in the ESP control module (N47-5). The BAS control module receives input signals from the following components: ME control module (via CAN data line) Traction system control module (via CAN data line) BAS diaphragm travel sensor BAS release switch

In the BAS control module, the input signals are converted into output signals for the following components: BAS solenoid valve BAS/ESP malfunction indicator lamp (via CAN data line) On the basis of the input signals, the BAS (N48) or ESP (N47-5) control module decides which of the 3 operating modes Normal operation BAS pressure increase BAS pressure reduction is to be activated. Normal operation In this case, the brake application is not at the higher pedal speed (that requires activation of BAS). The solenoid valve in the BAS brake servo (A7/7) is de-energized in the basic position. The system is ready for braking. Service brake and ABS function normally. This mode is also set if there is a fault in the BAS.

BAS pressure increase From the speed of the brake pedal, the BAS control module (N48) recognizes that the preconditions exist for activation of BAS. The BAS solenoid valve (A7/7y1) is activated by the BAS control module (N48) and the brake servo produces the maximum brake assistance power. BAS is activated when the following conditions exist simultaneously: Speed >8 km/h + BAS release switch is operated + no fault is currently detected + the system is enabled (after self-test) + the activation threshold of the pedal speed has been exceeded

BAS pressure reduction The BAS control module (N48) receives information from the BAS release switch (A7/7s1) that the emergency brake application has terminated. The BAS solenoid valve (A7/7y1) is no longer activated and the maximum braking assistance force is switched off. The normal braking assistance force remains unchanged. BAS is switched off when one of the following conditions exists: BAS release switch is not actuated Speed <3 km/h Duration of activation >20 s If no signal from the stop light switch is present after activation of BAS A fault is detected that causes the BAS malfunction indicator lamp to be activated

Brake application in normal operation The BAS brake servo (A7/7) is supplied continuously via the vacuum line with inlet manifold vacuum or pump vacuum on diesel models. If the brake is not actuated, equal vacuum exists on both sides of the diaphragms. The compression spring holds the vacuum piston in its starting position. On brake application, atmospheric air is fed to the back of the diaphragms via a duct. A pressure difference that increases with the braking is created between the front and rear chambers of the servo and the resulting force acts in the direction of the master brake cylinder and supplements foot pressure. Illustration: Partial braking a Atmospheric pressure b Reduced vacuum c Vacuum
		P42.31-0212-76

BAS pressure increase The activation conditions for a BAS brake application are fulfilled, the BAS solenoid valve (y1) is opened. Atmospheric pressure is applied to the back of the power diaphragm. The pressure difference between the front and back of the diaphragm provides maximum brake power assistance. Illustration: BAS brake application A7/7 BAS brake servo y1 BAS solenoid valve (control valve) a Atmospheric pressure c Vacuum
		P42.31-0213-76

BAS pressure reduction The BAS release switch (s1) is switched passively. Solenoid valve (y1) is switched off and only creates sufficient brake pressure to correspond to the position of the brake pedal. Illustration: release position A7/7 BAS brake servo S1 BAS release switch y1 BAS solenoid valve (control valve) a Atmospheric pressure c Vacuum
		P42.31-0214-76