- Brake assist systems increase brake pressure and shorten braking distance during emergency braking
- EU Commission recommends brake assist systems as standard feature from 2009
- ESP® vehicles almost always equipped with brake assist
If a driver wants to come to a stop as quickly as possible in a critical situation, he usually steps on the brake quickly, but often not firmly enough – and therefore wastes valuable braking distance. A brake assist system provides support here. During emergency braking, it builds up the maximum braking force within fractions of a second, so that the vehicle stops sooner. According to the EU Commission, if all vehicles were equipped with these kinds of systems, up to 1,100 fatal accidents involving pedestrians could be avoided in the EU every year. It therefore recently recommended mandating the installation of brake assist systems in all passenger cars registered in the EU from 2009 on. Bosch offers automakers various technical solutions that allow this function to be integrated cost-effectively.
Evaluations of the accidents stored in the GIDAS (German in Depth Accident Study) database show that drivers failed to brake with sufficient force in just under half of all accidents. According to studies, a brake assist allows an average driver traveling at a speed of 100 kph (about 60 mph) to reduce braking distance by an average of 7.6 meters (24.9 feet). If he is traveling at 50 kph (30 mph), braking distance can be reduced by a further 0.7 meters (2.3 feet). In other words, where a vehicle equipped with a brake assist function has already stopped, a car without this safety system is still traveling at a speed of 45 kph and 10 kph (28 mph and 6 mph) respectively. If a driver brakes more timidly than the average, the gain in safety can even be considerably greater. What this ultimately means is shown by an evaluation of official accident statistics: on the basis of a representative random analysis of the German Federal Statistics Office’s accident figures, Mercedes-Benz calculated the share of serious collisions with pedestrians for every 10,000 newly registered vehicles. The analysis showed that if the brake assistant were standard equipment, the number of serious pedestrian accidents could be reduced by 13 percent.
If a vehicle is equipped with the Electronic Stability Program, the brake assist does not require any additional components. Emergency braking is detected through the very fast actuation of the brake. The hydraulic pump of the ESP® unit then builds up the maximum brake pressure as quickly as possible. With a corresponding software adjustment, this so-called hydraulic braking assistant (HBA) can also be individually adapted to the actual driving situation, i.e. it becomes intelligent. For example, the triggering threshold of the brake assist can be lowered if radar data tell the ACC system to classify the situation ahead the vehicle as potentially critical. "Vehicles with ESP® therefore offer twice the safety,” said Werner Struth, president of Bosch Chassis Systems Control. "On the one hand, ESP® supports the driver in all critical situations and, on the other hand, the integrated brake assist considerably reduces the danger to pedestrians.”
For vehicles without ESP®, Bosch offers a mechanical solution integrated in the brake booster. If the speed at which the brake pedal is pressed exceeds a certain value, an inertia-controlled valve of the so called Emergency Valve Assist (EVA) opens immediately, allowing ambient air to enter the working chamber of the brake booster. This instantly boosts the braking force until the ABS kicks in. If the driver lifts his foot from the brake pedal, the additional boost is immediately canceled again.
