A brake assist system is an automatic safety feature designed to reduce the stopping distance of a car in an emergency. It is currently offered by many manufacturers but, in some cases, the naming convention varies. Mercedes, for example, calls one of its set-ups 'Brake Assist System'. Volvo, on the other hand, dubs its offering 'Emergency Brake Assistance'.
How does an emergency brake assistance system work?
The system relies on monitoring the driver's brake pedal inputs. If the driver applies the brakes extremely quickly, suggesting that they're trying to carry out an emergency stop, then the brake assist steps in to apply all the stopping power that's available.
When this emergency braking mode is triggered, the anti-lock braking system will ensure that the wheels don't lock up - preventing a skid and allowing the driver to retain directional control of the car. When the driver removes their foot from the pedal, the brakes will be released and normal service will resume.
The pressure required to operate the brakes for the brake assist system is typically generated by the car's ABS pump. This pump, in conjunction with a series of electronically operated valves, is also used by the ABS to regulate the braking power at each wheel.
Other systems may rely on components inside the master cylinder's brake servo (which generates assistance to make the brake pedal lighter) to deliver this driver-independent brake assist function. Bosch, for example, produces a modern electromechanical unit called the 'iBooster'. The operation of this unit causes the brake servo to act on the master cylinder, as if the driver were stepping on the pedal, actuating the brakes when needed.
Why did manufacturers fit emergency brake assistance systems?
A driver is travelling down the road in their car when, suddenly, a car unexpectedly pulls out in front of them. It takes a moment for the driver to react, at which point they suddenly stab the brakes.
The driver, however, may not have much experience with emergency braking - and may not press the pedal hard enough. As a result, maximum braking power isn't delivered and the stopping distance of the car increases.
This trend of misjudging braking effort during emergencies was noticed by Mercedes during the early 1990s, following a series of simulator tests. Drivers were often quick to respond to hazards but, not being familiar with the braking force required, they didn't apply the brakes fully.
Mercedes subsequently developed its 'Brake Assist System' to deliver the required full-force braking automatically, removing the driver from the loop and greatly reducing the stopping distance of the vehicle. The benefits are considerable, with stopping distances in trials on dry surfaces being up to 45 percent shorter with BAS than those achieved without.
Consequently, the chance of a collision with another car is greatly reduced. The system also substantially improves pedestrian safety; if a person steps out into the road and a driver reacts by braking sharply but not fully, the BAS can step in and help avoid an accident - or, at least, significantly reduce the speed of the vehicle before an impact.
A brief history of emergency brake assistance
Mercedes-Benz first introduced its emergency braking system in December 1996, in the flagship S-Class and the SL-Class. It was deemed so significant that the company then made BAS standard in 1997.
The system's capabilities have since increased, primarily by using a radar input that lets the car deliver audible and visual warnings of a potential collision - as well as allowing it to prime the braking system to deliver maximum stopping power the moment the driver touches the pedal. As the electronics and hardware continue to advance, other automated features are also being made available.
Much like when Mercedes introduced mass-market ABS, other manufacturers promptly followed in deploying their own brake assist systems - including Honda, Volvo and Volkswagen.
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