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Traction Control / Brake Assist System - BAS Brake Assist System (BAS)
    - Tech Info


Mercedes-Benz Brake Assist System can Stop 45 percent Shorter!

Mercedes-Benz is the first automaker to introduce an electronic brake-assist system which can recognize emergency braking and automatically apply full-power brake force for shorter stopping distances.

The system, which is activated only in emergency braking situations and doesn’t affect normal brake operation, made its' debut on many 1998 Mercedes-Benz models.

Why was the BAS Developed?
Many Drivers Don’t Apply Full Braking in Emergencies.   In tests on their driving
simulator and on the test track, Mercedes-Benz safety researchers discovered that even experienced drivers may not apply full braking force in emergency situations.

Although the reasons for this are unclear, the solution is relatively simple: use technology to design a system which can recognize emergency braking (whenever the pedal is being depressed very quickly), then react with split-second electronic speed to apply full brake force automatically.

Tests showed that 99 percent of drivers were slow in applying the brakes or only applied full brake pressure when it was too late. Mercedes-Benz researchers found that the new brake assist system can provide 45 percent shorter stopping distances for many drivers, and even skilled drivers find about a 15 percent improvement.

Most drivers took 239 feet to stop a car from 100 kilometers per hour (or 62 mph), while cars equipped with the new Mercedes-Benz brake assist system came to a halt in just 131 feet. Even when drivers applied the brakes very late in an emergency, stopping distance was reduced by nearly 20 feet more than a car length.

The new Mercedes-Benz brake assist system provide the critical difference between an accident and a close call because the electronic system can react far faster than any human.

How It Works

Brake assist is a driver-adaptive system which learns each driver’s braking habits by using electronic sensors to monitor every movement of the brake pedal and feed information to a mini-computer.

As a result, the system can instantly recognize when the driver pushes the brake pedal quicker than normal.

If it ever reads pedal speed signals which clearly mean an emergency, the computer instantly applies an electronic valve on the brake booster system for full braking. The wheels do not lock because of the presence of the standard ABS anti-lock brakes, so that the new Mercedes-Benz brake assist system takes advantage of the safety benefits of ABS.
As soon as the driver eases up on the brake pedal, normal brake control resumes.

To exchange important data at lightening speeds, the Mercedes-Benz brake assist system networks withother in-car micro-computers for ABS brakes, ASR traction control or ESP stability control, and the engine/transmission electronics.

The system even processes information about the amount of brake wear and vehicle speed.

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Mercedes-Benz is the first manufacturer in the world to offer a Brake Assist System (BAS).


Braking in Normal Mode

The BAS brake booster (A7/7) is continuously supplied via the vacuum pipe with intake pipe vacuum or pump vacuum on the diesel. When the brake pedal is not operated the same vacuum prevails on both sides of the diaphragms. The compression spring holds the diaphragm plate in its initial position.

When braking, outside air is lead to the back of the diaphragms via a port. As braking takes place, increasing pressure difference occurs between the front and back chamber of the booster which acts in the direction of the master brake cylinder and thus boosts the force applied by the driver's foot.

BAS pressure increase

The conditions for switching on BAS braking are met, the BAS solenoid valve (y1) is open. Atmospheric pressure acts on the back of the rolling diaphragm. The pressure difference between the back and front side of the diaphragm causes maximum brake boost.

BAS pressure reduction

The BAS release switch (s1) is switched passive. The solenoid valve (y1) is switched off and therefore only the amount of brake pressure which corresponds to the position of the brake pedal is generated.


BAS Components

1Tandem master brake cylinder vacuum connection
A7/7 BAS brake booster A7/7b1 BAS diaphragm travel sensor
A7/7s1 BAS release switch
A7/7y1 BAS solenoid valve N48 BAS control module (integrated in the ESP control module N47-5 on all vehicles with engine 112, 113 and ESP. Integrated in the ESP control module N47-5 on model 210 with engine 606 and ESP). Y61 Master brake cylinder switchover valve (model
129.067 with ESP, 129.076,140.04/05/06/07)


BAS Control Module: Function

A7/ BAS brake booster

b1BAS diaphragm travel sensor

N48 BAS control module (integrated in the ESP control module N47-5 on all vehicles with engine 112, 113 and ESP. Integrated in the ESP control module N47-5 on model 210 with engine 606 and ESP).

Y61 Master brake cylinder switchover valve (model 129.067 with ESP, 129.076, 140.04/05/06/07)

1 Tandem master brake cylinder

Location: Under the tandem master brake cylinder or integrated in the ESP control module (N47-5)

Purpose: Perform all BAS brake control functions

Supplies the instrument cluster with the signal for the BAS, BAS/ETS, BAS/ASR or BAS/ESP malfunction indicator lamps.


BAS Diaphragm Travel Sensor

A7/1 BAS Brake Booster

b1BAS diaphragm travel sensor

Location: on the BAS brake booster.

Purpose: Supplies a signal to the control module about the position of the diaphragm plate in the brake booster.

Function: Analog resistance potentiometer with feeler bar to diaphragm plate. A different voltage is effective in the potentiometer depending on the travel of the probe.

BAS Release Switch

A7/7 BAS brake booster

s1BAS release switch

Location: in the BAS brake booster

Purpose: Supplies a signal to the control module when the brake is released.

Function: When the force applied by the driver's foot to the brake pedal reduces to almost 0, movement takes place in the control valve of the BAS brake booster. This is sampled by the release switch and signalled to the BAS control module.