New Mercedes-Benz S-Class Thinking ahead

Mercedes-Benz Brake Assist PLUS

Setting the pace

April 12, 2005 8:07 PM
Filed Under: German, Mercedes-Benz

Press Release

New Mercedes S-Class Unveiled - UPDATED June 20, 2005

Short story

The trend-setting S-Class: Mercedes top of the range model will have Brake Assist PLUS and second-generation PRE-SAFE®

The PRE-SAFE® preventive occupant protection system is becoming even more effective. In the future S-Class, which will celebrate its world premiere in autumn of 2005, Mercedes-Benz is combining PRE-SAFE® with the new anticipatory Brake Assist PLUS, which uses radar to detect vehicles up ahead on the road and issues a warning when the vehicles come too close. When there is the risk of an accident, the system calculates in the blink of an eye the required braking power, which is immediately supplied when the driver applies the brakes. In critical braking situations, the front seatbelts are also tightened as a preventive measure, while the inflatable seat cushions are pumped up and the seats are brought into a position that provides the vehicle's occupants with maximum protection in the event of a collision, in keeping with the PRE-SAFE® concept.

Thanks to the anticipatory Brake Assist PLUS, the number of dangerous rear-end collisions can be significantly reduced. In tests conducted with 100 drivers in DaimlerChrysler Research's driving simulator, the new system made it possible to reduce the number of accidents in typical situations from 44 per cent to 11 per cent on average. What's more, the combination of the new Brake Assist PLUS and PRE-SAFE® made possible a higher level of occupant protection. Mercedes-Benz is the first and only automaker in the world to offer such a comprehensive safety system, which goes into action before a threatening accident has a chance to happen.

The anticipatory Brake Assist PLUS (BAS PLUS) uses two radar systems to scan the traffic in front of the vehicle: The DISTRONIC radar (77 GHz) is supplemented by a newly developed short-range radar (24 GHz), which monitors the immediate area in front of the vehicle at an angle of 80 degrees. The radar beams have a range of 150 metres, which means that vehicles up ahead can be detected in time. If a safe distance is no longer maintained, the system uses the radar data to calculate the braking power needed in each driving situation to prevent a possible accident. By applying the brake pedal, drivers can immediately summon this braking force, thus ensuring an optimal braking effect when there is a risk of an accident.

PRE-SAFE®: Inflatable seat cushions for an even higher level of occupant safety

The preventive PRE-SAFE® occupant protection system, which also has been enhanced by Mercedes-Benz, automatically switches on if the braking deceleration exceeds a certain level. In addition to tried-and-tested PRE-SAFE® functions such as seatbelt tightening and seat repositioning, the future S-Class will also be equipped with new multi-contour seats with cushions and backrests that automatically inflate if an accident threatens. These cushions envelop the occupants and support them, increasing the distance from the interior door panels during an accident. This enables the sidebag to provide even greater protection. Additionally, the individual rear seats are equipped with inflatable PRE-SAFE® support cushions in the backrests.

What's more, Mercedes-Benz is also integrating side windows into the preventive protection system. The windows automatically close in the event of a possible accident, to ensure optimal support for the windowbag during a side collision or rollover. The closed side windows also reduce the risk of occupants being thrown from the vehicle or objects flying into the car from outside.

Test results: Number of accidents reduced by 75 per cent

Mercedes-Benz has thoroughly tested the effectiveness of the anticipatory Brake Assist PLUS. The practical tests, conducted in Europe and the U.S., involved more than 200 drivers who drove 24 test vehicles over a total distance of more than 400,000 kilometres. Recording the tests with data recorders and video cameras made it possible to precisely analyse BAS functions. The new system greatly improved driving safety.

Mercedes-Benz also conducted several months of testing at DaimlerChrysler Research's driving simulator in Berlin. Each of the 100 drivers who took part completed a 40 minute drive and were confronted with a number of critical situations on motorways and rural roads, whereby intense emergency braking manoeuvres were the only way to prevent an accident.

Thanks to the new Brake Assist PLUS, the accident rate in these tests was reduced by 75 per cent � from 44 per cent to 11 per cent. The new technology was especially impressive during a drive in heavy traffic at 80 km/h on a rural road. In instances where the car in front braked suddenly, there were no accidents in 93 per cent of all cases in which the radar-supported Brake Assist was used; without this system, rear-end collisions occurred in around half of all tests.

"PRO-SAFE": the 5P concept for the highest level of automotive safety

With the anticipatory Brake Assist and the second-generation PRE-SAFE®, Mercedes-Benz is highlighting its role as the pacesetter in the field of passenger car safety while demonstrating once again that the brand sees safety as a holistic task � ranging from electronic assistance systems for accident prevention to occupant protection that's tuned to an accident's severity and measures serving to ensure the fastest possible rescue of occupants following a collision.

"PRO-SAFE" is the overarching term for this tried-and-tested principle for passenger car safety, which is geared toward actual driving situations. It is based on the Mercedes-Benz brand's many years of successful commitment to greater driving safety and is carrying on this tradition in four phases:

PRE-SAFE® and Brake Assist PLUS: Milestones in passenger car safety - now even more effective through new technology

Seven prizes and awards in just three years; praise from all quarters - these are the elements of the success story of the PRE-SAFE® precautionary occupant protection system to date. Mercedes-Benz first presented the system to the public in 2002, and since then PRE-SAFE® has proven its effectiveness in more than 140,000 S-Class saloons.

PRE-SAFE® recognizes a potential accident situation in its early stages, after which it prepares the vehicle and its occupants for the expected impact. If, for example, the vehicle is in danger of skidding, or the driver is forced to brake hard, PRE-SAFE® will tighten the front seatbelts as a precautionary measure and also adjust the passenger seat into the most favourable position. If necessary, it will even close the vehicle’s sunroof. The system also adjusts the electronically controlled individual seats in the rear of the vehicle. Such precautionary measures ensure that seatbelts and airbags offer the best possible protection in the event of an impact. If the driver is able to avoid the accident, PRE-SAFE® will loosen up the seatbelts again and passengers can return their seats and the sunroof to their original positions. The system is then ready to go into action again if necessary.

The PRE-SAFE® early warning system for accidents is based on a unique combination of active and passive safety elements. PRE-SAFE® is networked with standard-equipment safety systems such as Brake Assist (BAS) and the Electronic Stability Program (ESP®), whose sensors are able to recognize potentially dangerous driving manoeuvres. The relevant data is sent to an electronic control unit that implements the precautionary safety measures if certain values are exceeded.

Three years after the world premiere of this pioneering invention, with which Mercedes-Benz launched a new era in passenger car safety, the second generation of PRE-SAFE® is set to go into series production. Engineers at the Stuttgart-based premium brand have succeeded in further perfecting the interaction between active and passive safety systems. As a result, a refined Brake Assist PLUS and additional PRE-SAFE® features will offer even more possibilities for preventing accidents and protecting passengers in the new Mercedes-Benz S-Class in the future.

Brake Assist: Effectiveness in preventing accidents proved a million times over

Back in 1992, Mercedes engineers conducting tests with a driving simulator discovered that although most drivers react quickly in dangerous situations, they often fail to apply sufficient pressure to the brake pedal. This means that the braking system’s capability is not fully exploited, something which significantly increases the braking distance. The engineers’ discovery led to the development of Brake Assist, which went into series production in 1996 and has been standard equipment in all Mercedes-Benz passenger cars since 1997.

The system can interpret a certain speed at which the brake pedal is depressed as indicating an emergency situation, in which case it generates maximum braking power within fractions of a second. This leads to a significant reduction in braking distance � up to 45 per cent, for example, when the vehicle is travelling on a dry road at a speed of 100 km/h.

Brake Assist has proven itself more than a million times over since its inception. It not only helps prevent rear-end collisions but also makes an effective contribution to protecting pedestrians, as revealed in a study conducted by Mercedes-Benz with a driving simulator, in which 55 men and women took a simulated drive through a town at a speed of 50 km/h, during which a child suddenly ran into the street. The only way to avoid hitting the child was to initiate an emergency braking manoeuvre. The test showed that drivers supported by Brake Assist had far fewer accidents than those drivers who did not have the system; the overall accident rate was reduced by 26 percentage points through the use of Brake Assist.

Brake Assist PLUS: Two radar systems for monitoring the road ahead

Mercedes-Benz will expand Brake Assist’s features in the future to create a predictive system that provides even more effective support for drivers in dangerous situations. Radar technology will be used to determine the distance to vehicles ahead, warn drivers when they get too close, and provide the necessary braking power if it appears that a collision is unavoidable. In those situations where drivers are forced to brake, the new Brake Assist PLUS system will calculate and generate the braking force needed for a given situation within fractions of a second.

While the conventional Brake Assist requires a reflex activation of the brake pedal, the new system recognises the driver’s intention to brake when he or she puts clear pressure on the pedal, after which it automatically optimises the braking pressure. One of the key preconditions for preventing rear-end collisions is thus fulfilled: the best possible braking deceleration for each situation.

Mercedes-Benz has conducted extensive tests with the new technology, in both a driving simulator and under real conditions:

Radar technology: Large angle of coverage over short radius

The predictive Brake Assist uses two radar systems to monitor the traffic situation in front of the vehicle, whereby a newly developed close-proximity radar based on 24-Gigahertz technology works in tandem with the tried and proven 77-Gigahertz radar employed in the DISTRONIC proximity cruise control system. The two systems complement each other well: Whereas the DISTRONIC radar is designed to be able to track three motorway lanes over a distance of up to 150 metres with an angle of nine degrees, the new 24-Gigahertz radar uses an angle of 80 degrees to monitor the immediate area (30 metres) in front of the vehicle.

Accident types: Engineers focusing on rear-end collisions

With Brake Assist PLUS, which will be ready to go into series production in just a few months, Mercedes-Benz is once again underscoring its role as a trendsetter for road safety. As was the case with the airbag, seatbelt tensioner, ESP® and other pioneering safety systems, development of the predictive Brake Assist system also focused on the types of accidents that commonly occur under real conditions. More specifically, the researchers took into consideration the high number of rear-end collisions, which account for 17 percent of all traffic accidents that result in fatalities and injuries in Germany.

In the U.S., rear-end collisions account for 31 per cent of all accidents that result in deaths and injuries, according to statistics from the National Highway Traffic Safety Administration (NHTSA).

Precautionary occupant protection: BAS PLUS and PRE-SAFE® in tandem

Networking Brake Assist PLUS with PRE-SAFE® has opened up new dimensions in passenger car safety: Radar-based sensors make it possible to recognize potentially dangerous situations before they actually occur and then implement precautionary protection measures for vehicle occupants more quickly than was previously the case.

The system in use today engages during emergency braking manoeuvres (i.e. a reflexive reaction on the part of the driver). In the future, however, it will also be possible for PRE-SAFE® to go into action when Brake Assist PLUS has determined through its calculations that a rear-end collision is imminent - and that the driver’s braking manoeuvre has resulted in a certain deceleration value being exceeded.

The system will then tighten the front seatbelts and adjust the front and rear passenger seats as precautionary measures, thereby preparing occupants for a possible impact in such a way that seatbelts and airbags can provide the best possible protection.

PRE-SAFE®: Inflatable support upholstery in vehicle seats

In the future, Mercedes-Benz will supplement the proven PRE-SAFE® features with additional precautionary measures. These will prepare occupants for potential accidents even more extensively � always with the overall objective of ensuring that seatbelts, seatbelt tensioners, belt force limiters and airbags will all work perfectly in the event of a crash.

For example, a newly developed multi-contour seat makes it possible to more effectively fix the position of the driver, front passenger and rear occupants, and thus significantly restrict dangerous movements of the upper body in a crash. When the PRE-SAFE® control unit recognizes a critical driving situation, it will activate within seconds air cushions in the seats (front) and backrests (front and rear), which envelop and support vehicle occupants.

Rear-end collision tests conducted at the Mercedes-Benz Technology Center show that this new PRE-SAFE® feature and the precautionary tightening of seatbelts increase the distance of the occupants’ shoulders to the door trim by up to 40 millimetres at a lateral acceleration of 0.6 g. This enables the sidebag to provide even more protection.

Mercedes engineers will also be further improving the brand’s standard windowbags in the future by incorporating an additional precautionary feature: If the car is in danger of skidding and an accident thus appears likely, PRE-SAFE® will automatically close the side windows, which hold up the windowbags that inflate in the event of a side impact or rollover. This new PRE-SAFE® features also reduces the risk of occupants being thrown from the vehicle or objects flying into the car from outside.

Overview of all current and future PRE-SAFE® features:

  Longitudinal dynamics
- Emergency braking
- Powerful braking with the help of BAS PLUS		 Lateral dynamics
- Oversteering or understeering
- Critical steering manoeuvres
Fixing occupant position - Automatic seatbelt tensioning for driver and front passenger*

- Inflation of air cushions in seat upholstery...
            - in the front seats and their backrests*
            - in the backrests of the individual rear seats*
Position adjustment - Adjustment of seat lateral position and height as well as the incline of the front passenger seat and backrest

- Adjustment of the incline of the seats and backrests in the individual rear seats

- Adjustment of rear headrests in preparation for impact
Conditioning   - Closing of windows

- Closing of sunroof

* Reversible: If the anticipated accident does not occur, the systems will automatically return the components to their original positions.

Outlook: PRE-SAFE® support upholstery for the front passenger; autonomous braking systems

Mercedes-Benz will continue to refine its precautionary occupant protection systems over the next few years. Future PRE-SAFE® concepts for better preparing vehicle occupants for impending accidents will, for example, include a knee-protection system that automatically folds out from under the dashboard, providing support to the front passenger and reducing stress on the legs in the event of a collision. Like the PRE-SAFE® seatbelt tensioner, the knee protection system is also completely reversible, folding back in underneath the dashboard if the accident is avoided. In a similar vein, it might be possible to design door trim panels that move in towards occupants before a crash occurs, thus keeping them further away from parts of the vehicle body that could be forced into the interior in the event of a side impact. Fold-out trim panels on the inside of the B-pillar could also perform this type of support function.

When PRE-SAFE® developers look towards the future, they also imagine a protective system that can adapt to the individual parameters of vehicle occupants. For example, it might be possible for drivers and passengers to enter into the vehicle’s onboard computer personal data such as height, weight, gender, age, and any illnesses they may have. The system could then use this data to customize for each vehicle occupant elements such as volume flows in airbag inflation, level of seatbelt tensioning, or the functioning of the belt-tension limiter. Other PRE-SAFE® functions � for example, automatic seat repositioning prior to a crash � could also be regulated according to an occupant’s size.

There’s great potential for the further development of Brake Assist PLUS as well: Mercedes engineers are using radar sensors as the basis for developing a system that will precisely monitor both the traffic situation in front of the vehicle and the vehicle drivers themselves. If, for example, the driver fails to react when there’s danger of a rear-end collision (and a warning to this effect has also been issued), the new system would autonomously engage a partial braking manoeuvre and simultaneously activate the PRE-SAFE® features for the vehicle’s interior. This autonomous braking with up to 0.4 g deceleration would force the driver to act � in other words, to brake hard. After that, Brake Assist PLUS would provide the necessary braking support with the aim of preventing the accident, or at least reducing impact energy if the accident becomes unavoidable.

This new type of technology could also be used to develop an autonomous braking system that would automatically engage if an accident appeared imminent, at first initiating an emergency stop. Such a system would go a long way towards the “Vision of Accident-Free Driving� � the long-term goal of Mercedes-Benz safety engineers.

Brake Assist PLUS in test operations: Over 400,000 kilometres on the road, and 14 months on test rigs and in a driving simulator

There’s no substitute for reality � and recognition of this fact played a key role in the test operations conducted for the new Brake Assist (BAS) PLUS system. In order to test the radar-based system under tough everyday conditions, Mercedes engineers installed sensors in two dozen test vehicles that were driven more than 380,000 kilometres in Europe and the U.S. The new radar technology also underwent an additional series of tests for one year in a taxi in the German city of Stuttgart: The vehicle equipped with the system drove in congested urban traffic for a distance of approximately 40,000 kilometres, and a video camera in the S-Class saloon’s radiator grill recorded every kilometre travelled.

The tests focused on traffic situations in which the new radar technology had to differentiate between tight conditions (e.g. travelling through narrow streets with cars parked on the sides) and those situations actually more likely to lead to an accident.

The system’s measuring device and video camera recorded in parallel traffic data and images in each critical situation. Engineers used this information to directly compare the video images with the data recorded by the radar technology, thereby enabling them to make an objective assessment as to whether the close-proximity radar judged the traffic situation correctly, and actually sent the right control signals to the Brake Assist PLUS system.

The data collected under tough everyday conditions was also used to continually optimize the control unit’s software, and was incorporated into the computer simulation tests conducted in parallel as well.

Test rig: Combining the benefits of practical testing and simulation

“Hardware in the loop� is the name of a new procedure that combines the benefits of practical testing and computer simulation. In the case of Brake Assist PLUS, the procedure went beyond simply recreating critical driving situations on a computer; instead, it also incorporated the proposed BAS control unit into the testing process. Powerful computers fed the unit sensor data from simulated traffic situations and then monitored and recorded the control commands issued by the unit in response. The advantage of this procedure was that it enabled engineers to confront the Brake Assist PLUS control electronics with thousands of real traffic situations, which it had to react to correctly in an extremely short period of time.

Many of these testing runs involved an extensive catalogue of manoeuvres, including driving too close to the vehicle ahead or braking too late in heavy traffic. The radar technology in Brake Assist PLUS was forced to deal with moving and stationary obstacles and prepare for potential accidents � always with the goal of reliably recognizing objects in front of the vehicle and reacting to them appropriately. The test engineers also continually expanded the selection of critical traffic situations to include data gained from practical tests conducted in parallel with those undertaken with the test rig.

As was the case with the real-life tests, the simulations were marked by a certain “lack of clarity� so as to ensure that no one situation was completely like another. The engineers also supplied the unit with faulty data or data from false sources � i.e. "�electronic noise,� incorrect sensor data and simulated partial breakdowns of the system. All of these measures were designed to ensure that the system functions properly in all situations.

A network of computers operating in parallel spent well over a year recording the tests in real time. Weekends were particularly busy, as this was when the control unit was presented with approximately 1,400 critical situations that it had to reliably recognize, evaluate, and react to by issuing the correct commands to the PRE-SAFE® system in the virtual vehicle.

Driving simulator: Brake Assist PLUS significantly reduced accident rate

On its way to series production, the new Brake Assist PLUS system was also put through an unprecedented test program on the driving simulator operated by DaimlerChrysler Research in Berlin. In this series of tests, 100 men and women conducted 40-minute drives on virtual motorways and rural roads, during which time they had to deal with typical traffic situations in which accidents could be avoided only through emergency braking manoeuvres. The test subjects faced these situations both with and without Brake Assist PLUS in their virtual vehicles.

The new radar-sensor technology enabled the predictive system to recognize dangerous situations at an early stage and then support drivers with their braking manoeuvres. As such, the virtual vehicles with Brake Assist PLUS had considerably fewer accidents than those not equipped with the new system. The average accident rate fell from 44 to 11 per cent.

Moreover, the system helped mitigate the severity of the accidents that occurred in those cases where a collision could no longer be avoided because of the driver reacting too late. The braking-power support provided in line with the given situation also reduced impact speed by an average 21 km/h to 26 km/h.

Adaptive brake light: Effective warning of imminent rear-end collisions

Along with Brake Assist PLUS, Mercedes engineers have developed another system to help reduce the high number of dangerous rear-end collisions that occur on the road. This new technology more effectively warns drivers travelling behind of the danger of a rear-end collision by causing the front vehicle’s brake lights to blink in critical situations.

Studies conducted by experts in Sindelfingen, Germany show that drivers’ braking reaction time can be shortened by up to 0.2 seconds on average if a blinking red warning light is substituted for a conventional brake light in emergency braking situations. As a result, the braking distance can be reduced by approximately 4.4 metres at a speed of 80 km/h, and by as much as around 5.5 metres at 100 km/h. As such, blinking brake lights are an effective and easily implemented measure for helping to prevent rear-end collisions. A key positive aspect of the new system is that it makes driving safer even for those motorists who do not own a Mercedes-Benz.

EU authorities approved the technology in February 2005; the current Mercedes-Benz S-Class model is the first vehicle to be equipped with the new adaptive brake light. Mercedes-Benz will also begin fitting CL-Class coupes with the system in just a few weeks.

The Mercedes experts tested various types of hazard lights for their study. Brake lights that blink four times as rapidly as yellow hazard lights proved to be particularly effective in warning drivers of a possible rear-end collision. The Mercedes study also revealed that activating the hazard lights in dangerous situations had only a minor effect on drivers’ reaction times.

Berlin driving simulator: Virtual extreme driving situations

Driving simulators are playing an ever-greater role in the development of modern safety and assistance systems. The unit operated by DaimlerChrysler Research in Berlin, which is one of the most powerful driving simulators in the global automotive industry, has therefore been continually improved over the last few years. In 2004 alone, DaimlerChrysler invested approximately € 3 million in the facility, installing state-of-the-art technology that enables a realistic depiction of highly dynamic driving manoeuvres.

The improvements in quality are not only due to the simulator’s new, extremely stable hydraulic system; the newly installed computer system also allows much more rapid and precise driving dynamics models to be created than was previously the case. The system’s computing speed has more than doubled since 2002, with the computer now able to calculate the vehicle’s dynamics � and issue commands to the hydraulic system � at a rate of up to 1,000 times per second. The computer also moves the 18-ton simulator at a maximum speed of four metres per second (roughly 15 km/h) over a distance of up to seven metres to the side, which corresponds to a real lane change on a motorway.

Finally, a state-of-the-art imaging system ensures that traffic situations are depicted and experienced even more realistically than ever before. The push of a button is all it takes to get the system to project complete traffic scenes (cars up ahead, oncoming vehicles, pedestrians, houses and road signs) in realistic quality. The new 270-degree projection system also creates an all-round effect. The simulator can depict more than 250 moving objects.

The perfect illusion of driving is created because drivers sit in an actual Mercedes model and can also feel the resistance force on the steering wheel in any given situation. They can even hear the tyres squeal when the vehicle is taken into a curve. Dangerous segments of road � such as those with black ice � and strong side winds can also be simulated, as can the vehicle’s reaction to such phenomena.

Tests in extreme driving situations

The “real-life� simulations make the Berlin facility not only a research laboratory but also a multi-functional test rig on which systems and components for future Mercedes models can be tested and optimized as early as initial development stages. After being fed extensive vehicle data, characteristics and program maps from Passenger Car Development (e.g. mass, inertia, vehicle geometry, axle kinematics, suspension and shock absorber characteristics, tyre properties and drive-system characteristics), a driving dynamics program calculates the reactions of the vehicle type in question in real time. This makes it possible to test control, safety and assistance systems in extreme driving situations � without any danger to the test subjects.

Studies of driver acceptance

Many of the studies conducted in the driving simulator are used to test the acceptance of technical innovations among drivers, or determine the need for new systems. One example here is the Brake Assist system: During customer tests on the driving simulator, engineers discovered that although the majority of drivers react quickly in dangerous situations, they often fail to apply sufficient pressure to the brake pedal. The engineers’ discovery led to the development of the Brake Assist system, which went into series production for the first time at Mercedes-Benz and is now standard equipment in all Mercedes passenger cars. The effectiveness of the Brake Assist system in preventing accidents was initially proven through studies conducted with test subjects in the driving simulator � and later in practical road testing.

Mercedes-Benz also analysed the functioning and acceptance of the Electronic Stability Program (ESP®), the Active Body Control (ABC) system, DISTRONIC proximity cruise control, and the predictive PRE-SAFE® occupant protection system by conducting tests with the Berlin driving simulator before these systems were put through extensive practical road tests.

Researching to improve driving safety

The driving simulator has played a key role in more than 200 research projects as well. These not only included internal analyses but also a whole series of tests conducted by renowned research institutes such as the U.S. National Highway Traffic Safety Administration and Germany’s Federal Highway Research Institute. Some of these research projects led to new insights regarding issues such as drinking and taking medication while driving; because of the high risk involved, such information never could have been obtained through practical testing on real roads.