ABSTRACT

Brake assist senses emergency braking by detecting the speed at which the driver

presses the brake pedal and immediately applying all available power boosts. Brake

Assist can potentially reduce overall stopping distance by eliminating the delay caused by

a common human tendency of not braking hard enough or soon enough. Of course, in

actual driving situations, braking effectiveness also depends on proper brake system

maintenance and tire and road conditions.

The system developed by Mercedes-Benz to shorten emergency stopping

distances takes over if a driver applies the brakes quickly but too gently in a critical

situation. The system automatically develops maximum brake boost with split-second

speed, so reducing the stopping distance by a significant margin.

Tests provide impressive proof of the effectiveness of Brake Assist: on a dry road,

most drivers need up to 73 meters for an emergency stop at 100 km/h, since they apply

the brakes too gently. With Brake Assist, the car can be brought to a standstill after just

40 meters, a reduction of 45 per cent.

BRAKE ASSIST HISTORY

Mercedes originally invented the brake assist system in the 1990’s. Their tests

showed that although many drivers, especially women, reacted quickly in emergency

situations, they did not apply enough pressure to the brake pedal to be completely

effective. Their results also showed that drivers tend to apply the brake with less force in

the initial stages of a potentially dangerous situation, and then increase the pressure as

they moved further into that situation. The time spent in making the decision to apply the

brakes with full force, even if it was only a delay of a split-second, meant that the car was

not able to stop as soon as it would have if full pressure had been applied to the brake

pedal immediately. Other studies also made engineers believe that the pulsing

experienced when antilock brakes were engaged was mistakenly interpreted as a problem

by inexperienced drivers, who then reduced the pressure on the brake pedal too early and

inadvertently increased their risk of an accident. Mercedes theorized that if the car could

sense when a driver was applying the brakes in a panic stop situation and automatically

go to full force, regardless of how hard the driver pushed the pedal, stopping distances

could be greatly reduced and many accidents avoided as a result.

Brake Assist

Brake Assist (BA) is a new technology that ensures that the maximum pressure is

applied by the brakes to stop a vehicle in an emergency situation. Some manufacturers

also refer to the same system as Emergency Brake Assist (EBA).

Working and its advantages

When a driver makes an emergency stop the brake pedal has to be pressed, the

more pressure applied to the brake pedal, the greater the pressure through the braking

system, which is amplified and provided to the brake.

In some cases a driver might fail to respond to a hazard up ahead as well as

possible and fail to depress the brake pedal fully, meaning that the full pressure of the

braking system is not being applied to the wheels. Brake Assist detects how quickly the

pedal is depressed to judge whether the driver wanted to perform an emergency-braking

man oeuvre. If it concludes that the situation is an emergency and the pedal isn’t

depressed fully then it will increase the hydraulic pressure in the braking system to make

up the gap. If the driver successfully avoids the danger and removes or reduces the force

on the pedal then the system will also reduce its involvement.

Brake Assist in a vehicle

The system will not reduce the stopping distance of the car, but it will make sure that the

car is stopped in the shortest distance that it potentially could by compensating for any

hesitancy in applying the brakes hard in an emergency situation.

Brake Assist is based on the ABS technology of a vehicle and will not be found on a

vehicle without ABS. It should not change how drivers respond to an emergency – you

should still brake as hard as possible. Like all braking systems on a vehicle, it is safest

to never get into an emergency situation where you need to use them. The best way of

doing this is to ensure there is at least a two second gap between yourself and the vehicle

in-front, and to drive at a speed suitable for the conditions.

Working of Brake assist using diagram

1. Driver does not step forcefully enough on the brake in an emergency. As a

result, only a small amount of brake force is generated.

2. The pedal effort of this type of driver might weaken as time passes, causing a

reduction of braking force.

3. Based on how quickly the brake pedal is depressed, brake assist assesses the

intention of the driver to apply emergency braking and increases the brake

force.

4. After the brake assist operation, if the driver intentionally releases the brake

pedal, the assist operation reduces the amount of force simultaneously.

Basically, a brake assist system monitors the driver’s use of the brake pedal,

automatically sensing an attempt to stop the car as a result of panic. It then generates

very high braking power, even when the driver is only pressing lightly on the brake

pedal. When this is used together with anti-lock braking systems, it results in faster and

safer braking. Depending on the driver, statistics for emergency stops in cars using this

technology range from a 20% - 45% reduction in stopping distances, a potentially

significant difference in critical situations. Some road tests show that a driver needs up to

240 feet (73 meters) to stop a car going approximately 60 mph (100 km/h). In the same

scenario, cars with brake assist were able to come to a complete stop in as little as 130

feet (40 meters). Since it only takes one-fifth of a second to travel a car length at highway

speeds, the superior speed with which the brake assist is able to react also accounts for its

improved safety results over traditional braking systems.

ABS and Brake Assist

Active Safety Systems that ensure vehicle movement stability under extreme

circumstances This is a brake system that prevents slippage due to tire lock when

applying the brake under conditions like sudden braking and slippery road surfaces,

ensuring stable vehicle orientation and obstacle avoidance with steering wheel inputs.

ABS is standard equipment on all our regular-sized and small-sized passenger vehicles.

ABS is optional on all our mini-sized vehicle models. Plans to provide ABS as standard

equipment on all vehicles are in place.

ABS Effectiveness(Illustration)

[Vehicles not Equipped with ABS]Tires lock under sudden braking, vehicle body orientation becomes unstable, and steering wheel inputs cannot control the vehicle.[Vehicles Equipped with ABS]Tires do not lock under sudden braking, vehicle body orientation is as stable as possible, and steering wheel inputs can help avoid an obstacle.

Cars having Brake Assist system

Brake assist systems were originally only found on high-end luxury cars. However, as

the technology has become a little older, it is now more widely available. Once only

offered on cars from manufacturers such as Mercedes, Lexus, and Audi, brake assist is

now available from more accessible makes such as Citroen, Honda, Toyota, and Ford.

Cars that come standard with antilock brake systems will now typically also include

brake assist systems. The list of cars equipped with the system grows by the day

In Europe, even the little Nissan Micra comes with brake assist standard. The even

smaller Daihatsu Cuore -one of the cheapest cars on market- offers brake assist as an

option. The safety ratings on many cars include information about whether brake assist is

an option for that model, so you can check their availability when making purchasing

decisions.

Brake Assist Systems

Brake assist systems are an important aid in emergency braking situations - such

as when the driver applies the brake fast, but not with sufficient pressure, which leads to

dangerously long braking distances. The brake assist recognizes the brake application

speed to detect this type of panic situation and activates the brake booster or the EBS

hydraulic unit, so that even with moderate pedal forces maximum deceleration is

achieved. We offer different technologies for this purpose

Types of Brake assists

Electronic Brake Assist

Mechanical Brake Assist

Hydraulic Brake Assist

Electronic Brake Assist BAVacuum brake booster with electronic brake assist function and standard ABS-TMc interface. This type of active brake booster is also used to increase the response dynamics of ESC* systems (Electronic Stability Control) and to realize the comfortable electronically controlled application of the brakes for an Adaptive Cruise Control system (ACC).

Mechanical Brake Assist MBA The MBA replaces the sensor required in the electronically controlled system to detect pedal velocity utilizing the inertial effect of an intelligent mechanism. At high pedal speeds, this mechanism triggers the BA function.

Hydraulic Brake Assist HBAThis latest solution is based on existing components in the Electronic Stability Control (ESC)*. The BA function is triggered through extension of the ESC software and requires inputs e.g. from the pressure sensor in the tandem master cylinder.

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Brake Assist PLUS: Radar sensors for early accident detection

Situation-related braking assistance when an accident threatens

Accident rate reduced from 44 to 11 percent in simulator tests

It was in 1992 that Mercedes 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 optimizes the brake pressure. This meets one of

the major conditions for preventing rear-ends 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: 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 meters

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 meters.

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 percent 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 kilometers 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 percent of accidents involving

fatalities or injuries in Germany. Statistics compiled by the road safety authority NHTSA

in the USA show that around 31 percent 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.

In the field of vehicle safety, Mercedes-Benz is redoubling its commitment to

accident prevention with the introduction of Brake Assist PLUS. This system registers

vehicles ahead by radar and gives a warning if the gap is too small or the closing speed is

too high. If a collision threatens, Brake Assist PLUS calculates the ideal braking

assistance in fractions of a second and makes this available immediately - even if the

driver applies too little pressure to the brake pedal. This significantly reduces the

incidence of rear-end collisions. The adaptive brake light, which warns following traffic

by flashing during emergency braking, also makes a major contribution.

Mercedes-Benz combines Brake Assist PLUS with the equally unique occupant

protection system PRE-SAFE®, which offers even more safety functions on board the

new S-Class. PRE-SAFE® recognizes potential accident situations as they arise: if

deceleration exceeds a certain level or a skid is imminent, the system tensions the front

seat belts as a precaution and inflates air cushions in the multi-contour seats to envelop

and support the driver, front passenger and rear seat occupants. For the first time

Mercedes-Benz has also integrated the side windows into this preventive protection

system; they are automatically closed when an accident threatens.

This combination of the new Brake Assist PLUS system and PRE-SAFE® is a further

enhancement to occupant protection. Mercedes-Benz is the world’s first and only vehicle

brand with a comprehensive safety system of this kind, which already goes into action

before an impending accident.

Electronic Stability Program (ESP)

ESP was invented which controls the car's sideways motion by pulsing individual

wheel brakes. Several sensors are used: It shares the wheel speed sensors with a four

channel ABS system and in addition employs a steering angle, yaw rate, brake pressure

and sideways acceleration sensor. From these inputs two variables are calculated and

internally compared to expected values, derived from a bicycle model: the yaw rate and

the side slip angle. Controlling the yaw rate alone was found to be insufficient. Whenever

a discrepancy is detected, individual wheel slip controllers are actuated, also known as

disk brakes, to bring the wheel back to its desired ratio, and the vehicle back onto its

intended track.

ESP works in all regimes like: acceleration, coasting, light braking, hard braking,

engine drag and load shift and enhances vehicle stability even during extreme steering

maneuvers (panic reactions).In general when over steering - fishtailing - the outside

wheel or wheels will be braked. When under steering - plowing - the rear inside wheel

will be braked preferably. But other combinations are possible. ESP is flexible. It also

depends on the version of the system.

Find a large flat surface, like an empty parking lot or frozen lake. Then drive the

car close to the critical speed with ESP OFF and ON. Listed some speeds for a 300 foot

diameter circle:

surface adhesion

coefficient critical speed

black ice 0.1 15 MPH

packed snow, gravel 0.2 20 MPH

wet asphalt 0.5 30 MPH

dry asphalt 0.8 40 MPH

Black ice is also called "surface ice", a thin ice layer on the road, bridges etc.

Low traction surfaces are preferred for two reasons, to keep the speed low, and drifts are

much easier to control, particularly on packed snow. The closer one gets to the critical

speed, the more difficult it is to keep the car under control without ESP. Once ESP is on,

it's pretty easy to drive right at the physical limit, and it follows the drivers intention

within limits (steering wheel, acceleration, braking). In this regime ESP is using side-slip

control which means it tries to steer via individual wheel braking into the direction to

which the driver points the front wheels via the steering wheel.

Here's the skidpad experiment again, donuts in a parking lot. In a 300 ft circle on

packed snow the critical speed is about 20 MPH. The ML with ESP ON or OFF behaves

the same until about 19.5 MPH. With ESP ON at 19.5 MPH the warning triangle may

flash and individual wheels are braked to keep the side slip to a minimum, and ESP may

refuse more throttles to keep the ML inside the stable regime.

Now, with ESP switched OFF, one can increase the speed a bit further and the

triangle may not flash until close to 20 MPH. Demands for steering inputs increase

drastically, the driver sweats. It's a lot of work to keep the car on the pad at the limit,

while the guy with ESP just cruises by, smiling. If the limit is exceeded, the rear breaks

away; one must counter steer or spin out and leave.

ESP works at any vehicle speed and is only limited by the response of the system,

which is rather fast. In the ML it can activate 150 times per second. And braking latency

is much lower than either engine or drive train latency, which makes the brakes the best,

maybe the only method to handle fast dynamics.

ESP works quite nicely during braking. But what happens during full force

braking inside the ABS regime when no additional force can be applied without

saturation? ESP will then invert, and momentarily reduce the brake force on the other

three wheels, just enough to produce a realigning momentum.

It disables the engine-torque-reduction capability and thus reduces the computers'

intervention capabilities to about 20%.

The center triangle in the speedometer flashes when ESP intervenes. Flashing at

low speeds is usually caused by 4ETS, but flashing above the 4ETS limit speeds is

caused by ESP. For example, on a 1'20" dry and wet concrete slalom track, with an initial

entry velocity of 100 MPH, the minimum speeds through a series of S turns were

between 35 to 40 MPH, mostly higher. ESP was switched off, the warning triangle light

solid on. It flashed off about 2 to 10 times per run, with 1 to 16 flashes each, depending

on the smoothness of the driver. The speedometer was taped to record speed and flashing.

Under these conditions only ESP flashes the light.

ESP together with 4ETS all wheel drive is called 4ESP, presently the most

advanced traction control system offered by Mercedes-Benz. 4ESP is standard on the

1999 M-Class and an option in E320 models. The hydraulic modulator can be found in

the engine compartment with 4ESP stamped on it. The master control unit right next to it

is labeled 4ESP MCU and is interfaced to the traction controller in the sturdy vented E-

box.

Anton Theodor van Zanten at Bosch, who worked on ESP already at Cornell

(1973) and Armin Mueller at Daimler-Benz were the project leaders. Teams of about 40

engineers moved into a common building. The inventors received the Society of

Automotive Engineer's Henry Ford award and more recently the "Professor Ferdinand

Porsche Preis" from Porsche and the TU Wien. Wendelin Wiedeking commented: "With

their invention, the price winners made a significant contribution to the general safety of

road traffic." ESP world premiered in 1995 on the 12 cylinder Mercedes CL600 coupe

S600 sedan as standard and was optional for $1200 to $1500 in other W140 S-Class

models, the S420 and S500.

Mercedes accidents declined 42% when ESP was introduced. Serious accidents

declined even faster by 66%. Similar numbers were found in Japan and Sweden. NHTSA

studied accidents in five states and found passenger cars with ESP (many of them

Mercedes) single car accidents dropped by 35% while fatal accidents dropped 30%. They

also studied SUVs: ML320, ML430, ML350, ML500, G500, G55 AMG. Single vehicle

accidents declined by 67% and fatal crashes by 63%. The IIHS studied ESP and found it

reduced all accidents by 7% and all fatal accidents by 34%. Single vehicle accidents were

reduced by 41% and fatal single vehicle accidents by 56%. ESP is thus as important as

other Mercedes safety innovations like seat belts and probably more important than

airbags

ESP in action

ESP holds cars on a steady course: During under steering (left) the front wheels turn

outward; ESP automatically applies the brake to the left rear wheel. When the rear end

breaks away during over steering (right), ESP brakes the right front wheel.

CONCLUSION

Tests provide impressive proof of the effectiveness of Brake Assist: on a dry road,

most drivers need up to 73 meters for an emergency stop at 100 km/h, since they apply

the brakes too gently. With Brake Assist, the car can be brought to a standstill after just

40 meters, a reduction of 45 per cent.

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.