| It was in 1992 that Mercedes-Benz engineers conducting tests in the driving simulator found that while the majority of male and female drivers operate the brake pedal rapidly in an emergency situation, they often do not do so with sufficient force. The braking performance is therefore not used to the full, and the braking distance is considerably increased. These findings led to the development of Brake Assist, which first entered series production in 1996 and has been standard equipment in all Mercedes cars since 1997.
The technology interprets a certain speed with which the brake pedal is depressed as an emergency braking situation, and builds up the maximum braking assistance within fractions of a second. This significantly shortens the vehicle’s braking distance – by up to 45 percent at 100 km/h on a dry road surface, for example.
Brake Assist has proven its worth millions of times since its invention. It not only helps to prevent rear-end collisions, but also contributes greatly to pedestrian protection. This was demonstrated by a Mercedes-Benz study in the driving simulator: 55 male and female drivers were asked to drive through a town, and a child suddenly ran into the road. An accident could only be avoided by emergency braking. The result was that drivers with the benefit of Brake Assist had significantly fewer accidents than those without the system. The accident rate was reduced by 26 percentage points with Brake Assist.
Brake Assist PLUS: two radar systems looking ahead
In the new S-Class, Mercedes-Benz has expanded Brake Assist into a preventive system which assists the driver even more effectively than before in critical situations. The system is based on radar technology: it registers the distance from vehicles ahead, warns the driver if the gap is too small and calculates the necessary brake force assistance if a rear-end collision threatens. If traffic tails back and the driver is obliged to operate the brake pedal, the new Brake Assist PLUS instantly builds up the braking pressure required to manage the situation.
While reflex-like operation of the brake pedal is necessary with a conventional Brake Assist system, the new system already detects the driver’s braking intention when the pedal is depressed and automatically optimises the brake pressure. This meets one of the major conditions for preventing rear-end collisions, namely the best possible deceleration for the situation in hand.
Preventive Brake Assist PLUS uses two radar systems to monitor the traffic situation ahead of the vehicle: a newly developed close-range radar based on 24-Gigahertz technology works together with the 77-Gigahertz radar of the DISTRONIC PLUS proximity control system. These systems complement each other: while the DISTRONIC radar is configured to monitor three lanes of a motorway to a range of up to 150 metres with a spread of nine degrees, the new 24-Gigahertz radar registers the situation immediately ahead of the vehicle with a spread of 80 degrees and a range of 30 metres.
Testing: successful trials with about 300 drivers
Mercedes-Benz has intensively tested the effectiveness of this innovative technology in the driving simulator and in practical trials:
• 100 male and female drivers took part in a series of tests in the driving simulator. They each completed a 40-minute journey with several critical situations on motorways and country roads. It was only possible to avoid accidents by hard braking. Thanks to the new Brake Assist PLUS system, the accident rate during this test series fell by three quarters compared to the average of 44 per cent with conventional brake technology.
The new technology demonstrated its advantages particularly well when driving in a line of traffic at 80 km/h on a country road: when the vehicle ahead was suddenly braked, the radar-based Brake Assist system prevented an accident in 93 percent of cases – while more than one in two test drives ended in a rear-end collision without the system. Even in situations where a collision was unavoidable owing to a late response by the driver, the new system helped to reduce the severity of the impact. This was confirmed by the measured impact speed, which was reduced from an average of 47 to 26 km/h thanks to Brake Assist PLUS.
• More than 200 male and female drivers took part in practical trials in Europe and the USA, covering a total of more than 450,000 kilometres in 24 test cars. These journeys were recorded with the help of the latest measuring and video technology. Evaluation of the data and video sequences showed that Brake Assist PLUS also makes a major contribution to safety under real conditions.
Accident research: focus of attention on rear-end collisions
With Brake Assist PLUS Mercedes-Benz has once again confirmed its role as the trendsetter in the field of road safety. As in the case of the airbag, belt tensioner, ESP and other pioneering safety systems, the development focus for the preventive Brake Assist system was on the real accident situation, or more precisely the high number of rear-end collisions, which account for more than 17 per cent of accidents involving fatalities or injuries in Germany.
Statistics compiled by the road safety authority NHTSA in the USA show that around 31 per cent of all accidents with fatalities or injuries are rear-end collisions.
The future: from Brake Assist PLUS to the PRE-SAFE braking system
Brake Assist PLUS has the potential to achieve further milestones in safety technology: on the basis of radar sensors, Mercedes engineers are working on a system which monitors the traffic situation ahead of the car very precisely. If the driver fails to respond even after a warning that an accident is impending, the technology automatically initiates braking action and activates the PRE-SAFE functions in the interior after a certain level of deceleration. This autonomous braking intervention with a deceleration of up to about 0.4 g prompts the driver to act, i.e. to brake hard or take evasive action. The PRE-SAFE braking system then assists as the situation requires, with the aim of preventing the imminent collision or reducing the impact energy if a collision is unavoidable.
In the future this innovative technology could also be developed into an autonomous braking system which is automatically activated when danger threatens and initiates emergency braking action – a further step on the way to the "vision of accident-free driving", the long-term goal of safety developers at Mercedes-Benz.
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