TABLE OF CONTENTS
What are Brakes? : History of Brakes
Today’s Brakes And Their Histories
Power Assisted Brakes
Brake Energy Conversion
What Are X-By-Wire Systems?
X-by-Wire in Automotive Systems
Introduction to SBC
Development and Working
Brake pedal: Electronics Instead of a Vacuum
Control unit: Pressure Modulators for Each Wheel
Emergency braking: Stopping Distance Reduced by up to Three per cent
Driving stability: Precise Braking Impulses for Perfect ESP® Performance
Braking in Corners: Greater Safety Thanks to Variable Brake Force Distribution
Comfort: No Pedal Vibrations During ABS Operation
SBC add-on functions: Support systems to reduce driver strain
SBC Traffic Assist
SBC Soft Stop
The Failure of SBC
Current Research in Braking
Future Scope In Braking Technology
Sensotronic Brake Control (SBC) is an electronic system which Mercedes-Benz introduced in October 2001, and has been fitting on passenger car models since. Following the ideas like ABS ASR, ESP and Brake Assist, this system is regarded as another important milestone to enhance driving safety. Also, the system offers features to reduce the driver’s workload. These featured include:
Traffic Jam Assist, which breaks the vehicle automatically in the bumper-to-bumper traffic once the driver takes his or her foot off the accelerator.
The Soft-Stop function, which allows soft and smooth stopping in town traffic.
Thus, SBC transforms the conventional hydraulic brake into a more powerful mechatronic system. In the old brake system, when drivers hit the brake pedal, their foot moves a piston rod which is linked to the brake booster and the master brake cylinder. Depending on the pedal force, the master brake cylinder builds up the appropriate amount of pressure in the brake lines which in turn presses the brake pads against the brake discs via the wheel cylinders. By contrast, in the Mercedes-Benz Sensotronic Brake Control, a large number of mechanical components are simply replaced by electronics. The brake booster will not be needed in future either. Instead sensors gauge the pressure inside the master brake cylinder as well as the speed with which the brake pedal is operated, and pass these data to the Sensotronic Brake Control computer in the form of electric impulses. To provide the driver with the familiar brake feel, the engineers have developed a special simulator which is linked to the following master cylinder and which moves the pedal using spring force and hydraulics. In other words: during braking, the actuation unit is completely disconnected from the rest of the system and serves the sole purpose of recording any brake command.
What Are Brakes?: History of Brakes
Car brakes are based on the law of conversion of energy: mainly, conversion of kinetic energy into heat energy/ frictional energy which in-turn opposes the motion of the wheel, ultimately stopping the vehicle.
Prior to the introduction of pneumatic rubber tires in 1895 the rims of car wheels were initially made of iron and, from the mid 1800s, either steel rimmed or lined with solid rubber. The first solid rubber tires were manufactured in 1846. On iron or steel rimmed vehicles the driver typically pulled a lever to apply a block of wood to the wheel’s rim. This type of brake is called a “Shoe Brake”. It was reasonably effective up to 10-20 mph.The 1885 Benz Patent-Motorwagen was fitted with solid rubber tires. The upgraded 1887 chassis included a manual leather shoe brake on the rear wheels.
In 1895 the first pneumatic car tires were fitted to a Peugeot “L’Eclair” motor car. The pneumatic tire however that could not be used with wooden shoe block brakes and a new method of braking was required. The first “external contracting brake” devices attempted to apply force by means of a steel strap or cable directly to the axle, to a drum fitted onto the axle or to the transmission shaft. A method that became known as a contracting “Band Brake” (sometimes referred to as an external drum brake) was employed during the late 1890sand early 1900s. The band tightened around the drum to slow or stop the car when the driver depressed a foot pedal or operated a lever. Metal bands lined with lead, leather, cotton and camel hair were also tried.
The disadvantages of these early band brake systems were:
No protection from the elements and they suffered from a build up of dirt.
Excessive wear to both the drum and the band. Maintenance was required every 300-400 km.
Herbert Frood (British) is credited with inventing the first brake lining material in 1897 and founded the Ferodo Company. Frood’s original brake lining material was made from laminated hair and bitumen.
On an 1897 Roberts electric car (USA) leather-lined brakes were installed inside the housings of the two 2hp motors.
In 1898, Elmer Ambrose Sperry (American) designed an electric car that had electromagnet front-wheel disc brakes.
In 1899 Gottlieb Daimler (German) wrapped a cable around a drum and anchored it to the chassis. The forward motion of the car tightened the cable, making it easier for the driver to pull the brake lever. It was the first, if basic application, of servo assisted braking.
In 1901 Wilhelm Maybach (German) designed the first internal drum brake. Maybach’s brake drum used rollers to press a ring of friction material against the inside of a drum fitted on the rear axle. A water sprinkling system cooled the hot zones of both brake systems when the brakes were applied.
Finally, in 1902 Louis Renault (French) designed an internal drum brake that the modern version is based upon. Renault’s drum brake used two curved shoes (pads) fixed to a back plate with each pivoted at one end. The other ends rested on a cam. When the brake pedal was pressed, the cam forced the shoes apart and against the inside of the drum.On 1 December 1902 Frederick Lanchester (British) submitted an application for a patent for non-electric calliper-type automobile spot disc brake system. The brake pads were made of copper and the intense noise created by the metal-to-metal contact when the brakes were applied was a major problem. The copper brake pads also wore out much too quickly. In 1907 Herbert Frood (British) solved the noise problem when he lined the brake pads with asbestos that was woven into a loose fabric and impregnated with high melting point resin and varnish, which were more durable, and achieved up to 15000 km.
At the turn of the 2oth century roads were very crude and dirty and “internal” drum brakes kept out water and materials that could damage disc brakes. More importantly “internal” drum brakes required drivers to apply less pressure on the pedal compared to the early disc brakes. This was especially relevant prior to the introduction of hydraulic and power brake systems. In 1910 Giustino Cattaneo of an Italian Company designed a four wheel brake system. A pedal operated the rear wheel brakes, with a hand lever actuating via a cable the brakes on the front wheels.
At the January 1923 New York Automobile Show only two manufacturers, Duesenburg (hydraulic brakes) and Rickenbacker (mechanical brakes) offered cars with four-wheel brakes.
A report published in 1929 stated: “70% of British, US and Continental cars in Britain in 1924 were rear-braked only. By 1929 that figure had reduced to 1%”.
Malcolm Lougheed (American) designed a hydraulic braking system for cars, receiving 7 patents for his idea between Dec 1917 and July 1923.
Cylinders and tubes were used to transmit fluid pressure against brake shoes that were then pressed against the outside of a brake drum. In 1921 Lougheed’s hydraulic brake system was fitted to all four wheels of a Model A Duesenberg car. The system was however beset with leakage problems.
Lougheed used rawhide cup seals to prevent hydraulic fluid leakage when the brakes were applied but these seals quickly dried out and shrank under heavy brake usage.
Engineers of the Maxwell Motor Corporation (of which Walter P Chrysler was chairman) produced seals in the form of rubber cups that solved the problem.
For $75 the improved Lougheed four-wheel hydraulic brakes were offered as an optional extra on Maxwell-Chalmers car from October 1923.
In 1924 the American Chrysler Six Phaeton B-70 and the British Triumph 13/35 models were the next two production cars to be equipped with the improved, four-wheel, Lougheed hydraulic brakes.
Fig 3.1: (Hydraulic Brake System)
The 1926 Adler Standard model was the first German car to be fitted with (ATE-Lougheed) hydraulic brakes.
In 1926, Stutz used a system called Hydrostatic Brakes; using water instead of hydraulic fluid. “Each wheel used one bladder and six brake pads”.
The brakes hydrostatic system leaving the factory filled with a 50/50 solution of alcohol and water to prevent freezing.
The system was only used for one year. In 1927 Stutz switched to Lougheed hydraulic brakes, the company producing kits to convert the 1926 models.
By 1931 various US manufacturer’s, including Chrysler, Dodge, Desoto, Dodge, Franklin, Graham, Plymouth, Reo and Graham produced cars with hydraulic brakes.
During the 1930s hydraulic braking systems became standard fit on most cars.
In 1931 Lincoln introduced the Model K which was fitted with cable-operated Bendix Duo-Servo brakes.
Two years later, in 1933, the Lincoln KB model featured four-wheel vacuum servo-assisted mechanical drum brakes.
Other early models to use servo assisted hydraulic brakes include; in 1934 the Hispano-Suiza T6ORL, Chrysler Airflow, Mercedes 500K and LaSalle Series 50, and in 1936 the Cadillac Twelve and the Hotchkiss 486 (the latter for one year only before returning to mechanical brakes).
In 1967 it became a requirement that all cars sold in the USA had to have two separate hydraulic circuits.
3.2 Power Assisted Brakes:
Fig 3.2: (Power Assisted brake)
Power assisted brakes were first employed in 1903 when air brakes were fitted to a car called the Tincher that was developed by Thomas L Tincher (American).
The pressure required to apply the foot operated four wheel drum brakes on the 1919 Hispano-Suiza H6 model was enhanced by a mechanical servo system that was driven by a special shaft from the transmission.
On 19 October 1920 John Godfrey Thomas (British) submitted and on 9 January 1923 was granted US patent #1,441,545 for an invention which “enables the brake to be applied or the clutch to be engaged by power”.
“A convenient source of (vacuum) power for the purpose is the suction pipe of the internal combustion engine”.
On 2 February 1926 the patent was assigned to the General Motor Corporation.
In 1928 a vacuum power booster braking system designed by Bragg-Kliesrath (USA) was fitted to a Pierce-Arrow car.
In 1985 some cars produced by General Motors use an electrically driven brake booster.
3.3 Disc Brakes:
In 1949 Crosley Motors became the first American manufacturer to fit disc brakes.
They were fitted to Crosley’s Hotshot model but discontinued the following year.
Fig 3.3: (Disk Brake Diagram)
Between 1949 and 1953 Chrysler fitted a type of disc brake to their fourth generation Imperial models.
Disc brakes were further developed by Dunlop in Great Britain in the early1950s and fitted to a Jaguar C-Type racing car in 1953.
In 1954 an Austin Healey 100S became the first British production car to be fitted with disc brakes on all four wheels.
Powered inboard front disc brakes were fitted to the 1955 Citroen DS model.
In 1956 the front brakes on the Triumph TR3 model were changed from drum to disc.
During the 1960s numerous manufacturers around the world started to replace drum brakes with disc brakes. Some of the first companies to do so in the 1960s were:
1961 (Germany): The Mercedes-Benz 220Se model was the first German production car with disc brakes.
1962 (France): The Renault R8 model was supplied with four-wheel disc brakes.
1963 (USA): Bendix produced caliper-type disc brakes supplied as standard fit on Studebaker Advant model and as optional extras on their Hawk and V8 Lark models.
1965 (Japan): Nissan fitted disc brakes to their Datsun Silva model.
1966 (Sweden): The Volvo 144 was supplied with four wheel disc brakes.
1967 (Japan): The Toyota 2000GT was the first Japanese car fitted with four-wheel disc brakes.
3.4 Self Adjusting Brakes
In 1925 Cole and Jowett models are believed to be the first cars to be equipped with self-adjusting brakes.
The self-adjusting disc brakes were supplied as standard fit on the Series 890 Cole model.
Jewett’s self-adjusting brakes were fitted to all four wheels “at extra cost to the owner” on their Touring, Brougham, and Sedan models.
For their 1947 model Studebaker replaced Lockheed brakes with ones produced by the Wagner Electric Co. which had a self adjusting feature.
3.5 Anti-Lock Braking (ABS)
In 1936 Bosch filed a patent application in Germany for an “Apparatus for preventing lock-braking of the wheels of a motor vehicle”.
ABS is derived from the German “Anti blocker system”, the name given to it by its inventors at Bosch.
In 1978 Bosch introduced an electronic 4-wheel multi-channel ABS system.
It was initially installed in the Mercedes-Benz S-Class model and shortly after in the BMW 7-Series.
In 1952 the British Road Research Laboratory (RRL) adapted an aircraft anti-skidding devise called Maxaret and carried out trials using a 1950 Morris 6 car fitted with drum brakes.
By 1958 RRL and Dunlop had developed a practical mechanical anti-lock braking system for a car and tested it on a Jaguar Mark VII fitted with disc brakes.
It wasn’t until 1966 that the system was first fitted to a production model four-wheel drive Jensen FF sports sedan car.
Ford offered an anti-skid system as an option on the 1954 Lincoln Continental Mk ll. It weighed and cost too much and was soon withdrawn.
In April 1968 Ford introduced “Sure Track”, an analogue anti lock brake system it developed jointly with Kelsey-Haynes. It operated only on the rear wheels.
It was initially offered as an option on the Thunderbird and Lincoln Continental Mark III, becoming standard fit on the Mark III in 1970.
Fig 3.4: (ABS)
The 1964 Austin 1800 model was fitted with a limited form of ABS, utilizing a valve which could adjust front to rear brake force distribution when a wheel locked.
Chrysler fitted their new four-wheel “Sure Brake” ABS system into some of their 1966 models but it “did not perform up to expectations”.
Chrysler entered into a joint venture with Bendix and developed a computerized, three-channel, four-sensor all-wheel ABS version of “Sure Brake”.
It was fitted to Chrysler’s 1971 Imperial model. The system functioned on demand when the car was travelling over 5 mph.
In the same year Nissan offered a Kelsey Hayes Electro Anti-lock (EAL) system as an option on its President model.
In 1984 Tevis in Germany commenced production of their new generation, microprocessor controlled, Mark II ABS System.
It was initially fitted to the Lincoln Mark VII and in Europe to the Ford Scorpio.
During the 1980s it was also fitted to the Pontiac 6000, Ford’s 89 Thunderbird Super Coupe and Buick’s 1988 Riviera and Reatta models.
It was also installed in various SAAB, Mercedes-Benz, Jaguar, Alfa-Romero, Buick, Ford and Porsche models.
In 1998 Tevis became part of Continental AG of Germany.
Features added over the years to the Tevis ABS system include a Traction Control System, an Electronic Stability Program and in 1999 a Sidewall Torsion Sensor system that was designed and developed by Continental AG.
3.6 Brake Energy Conversion
Car brakes are based on the conversion of kinetic (motion) energy into other forms of energy, usually heat. Other, more recent methods include:
Regenerative braking which converts much of the braking energy into stored electrical energy.
Hybrid and electric vehicles using this technique to extend the range of the battery pack include the Toyota Prius, Honda Insight and the Chevrolet Volt.
Another method converts the kinetic energy into potential energy; stored as pressurised air or pressurised oil.
Another method transfers the braking energy to a rotating flywheel.
4.1 What Are X-By-Wire Systems?
Mechanical systems are being replaced with “X-by-Wire” systems. These determine the driver’s commands via sensors process the information electronically and pass on the commands to the actuators. A current example system is “Drive by Wire”, the electronic throttle. Bosch has also worked intensively on electronic systems in the areas of braking and steering. “Steer by Wire” and “Brake by Wire” are prerequisites for new safety and comfort enhancing functions, which can only be created by the interaction of several vehicle systems.
Brake-by-Wire separates the mechanical hydraulic connection between brake pedal and wheel brake. Sensors determine the driver’s braking command and transmit this information to an electronic control unit. Using the corresponding actuators, the control unit creates the required brake effect on the wheels. At the moment, the best concept for brake-by-wire is the electro-hydraulic brake SBC (Sensotronic Brake Control).
Bosch has developed the electro hydraulic brake SBC together with DaimlerChrysler, or Mercedes and has started production of the system with the SL-Class.
4.2 X-by-Wire in Automotive Systems:
In automotive environment the ”X” stands for the commanded action such as accelerating, braking and steering. A lot of modern cars are equipped with drive-by-wire systems and a combined mechanical backup. In the future mechanical backup systems will be replaced by pure electronic solutions. Reasons for this development are manifoldly. Because hydraulic systems will no longer be necessary in the future and the electronic devices are shrunk more and more, the packaging density can be higher. The producer hope to reduce production costs using new devices. Another main reason for developing new solutions is that many new functions could be integrated. For example the adaptive cruise control (ACC), which accelerates and brakes the car autonomously for holding a safety distance to the car in front, is still inbuilt in cars of the upper price class. Particularly such systems can be found in safety relevant ﬁelds, a high reliability is absolutely essential. A basis for legal requirements gives the international standard IEC 61508 , adopted in the European standard EN 61511 and supervised by the TUV in Germany .
In evolution of vehicles the braking system is a basic module for driving safety. This system is subjected to a permanent development. Started with mechanic brakes, today hydraulic systems, assisted by inventions such as ABS, are the standard in cars and lorries. Nowadays development departments of all manufacturers are working on new brake-by-wire systems. First versions are still included in a lot of modern cars. The idea is that wires replace the hydraulic systems and commands are transmitted electronically through the wire. The built-in devices are electrohydraulic brakes (EHB), where hydraulic and electronic components have been combined. A future solution will be the electro-mechanical brake (EMB). It totally forswears hydraulic components
Introduction To SBC (Sensotronic Brake Control)
Mechatronics – a new term is gaining popularity within the automotive industry and is rapidly developing thus bringing about technological revolution. Mechatronics brings together two disciplines viz. mechanics and electronics.
Because of mechatronics, automobile functions which worked purely mechanically and partly with hydraulic assistance earlier, are now being controlled by high-performance microcomputers and electronically controllable actuators. These either replace the conventional mechanical components or else enhance their function. The mechatronic interface therefore opens up to unexplored possibilities which further raise the safety and comfort levels of modern passenger cars. For example: it was only because of mechatronics that an electronically controlled suspension system which instantly adapts to prevailing conditions when driving off, braking or cornering became a reality. This suspension gave a completely new experience. In 1999 Mercedes-Benz launched this system under the name Active Body Control (ABC) in the flagship CL coupé, thereby signalling the advent of a new era of suspension technology.
This electronically controlled suspension system was followed by an electronic brake system. Mercedes-Benz and Bosch teamed up on the development project which later came forth under the name Sensotronic Brake Control (or SBC).
Fig 5.1: (Diagram Of the Complete Working Of SBC)
In addition to the data relating to the brake pedal actuation, the SBC computer also receives the sensor signals from the other electronic assistance systems. For example, the anti-lock braking system (ABS) provides information about wheel speed, while Electronic Stability Program (ESP®) makes available the data from its steering angle, turning rate and transverse acceleration sensors. The transmission control unit finally uses the data highway to communicate the current driving range. The result of these highly complex calculations is rapid brake commands which ensure optimum deceleration and driving stability as appropriate to the particular driving scenario. What makes the system even more sophisticated is the fact that Sensotronic Brake Control System calculates the brake force separately for each wheel.
Fig 5.2: (Setup of SBC in a Car)
Following on from the Mercedes innovations ABS, ASR, ESP® and Brake Assist, this system is regarded as yet another important milestone to enhance driving safety. With Sensotronic Brake Control electric impulses are used to pass the driver’s braking commands onto a microcomputer which processes various sensor signals simultaneously and, depending on the particular driving situation, calculates the optimum brake pressure for each wheel. As a result, SBC offers even greater active safety than conventional brake systems when braking in a corner or on a slippery surface. A high-pressure reservoir and electronically controllable valves ensure that maximum brake pressure is available much sooner. Moreover, the system offers innovative additional functions to reduce the driver’s workload. These include Traffic Jam Assist, Soft-Stop.
Development And Working
6.1 Brake pedal: Electronics Instead of a Vacuum
In the conventional brakes, when the pedal is pressed, it moves a piston rod which is linked to the brake booster and the master brake cylinder. Depending on the pedal force, the brake cylinder builds up the required amount of pressure in the brake lines which then presses the brake pads against the brake discs via the wheel cylinders.
By contrast, in the Mercedes-Benz Sensotronic Brake Control, a large number of mechanical components are simply replaced by electronics. The brake booster will not be needed in future either. Instead sensors gauge the pressure inside the master brake cylinder as well as the speed with which the brake pedal is operated, and pass these data to the SBC computer in the form of electric impulses. In other words: during braking, the actuation unit is completely disconnected from the rest of the system and serves the sole purpose of recording any given brake command.
Only in the event of a major fault or power failure does SBC automatically use the services of the tandem master cylinder and instantly establishes a direct hydraulic link between the brake pedal and the front wheel brakes in order to decelerate the car safely.
_ Sensor to Measure Pedal Travel
Fig 6.1: (Picture of the mechanism linked to the accelerator pedal)
To provide the driver with the familiar brake feel engineers have developed a special simulator which is linked to the tandem master cylinder and which moves the pedal using spring force and hydraulics.
6.2 Control unit: Pressure Modulators for Each Wheel
The central control unit under the bonnet is the centrepiece of the electro hydraulic brake. This is where the interdisciplinary interaction of mechanics and electronics provides its greatest benefits – the microcomputer, software, sensors, valves and electric pump work together and allow totally novel, highly dynamic brake management.
In addition to the data relating to the brake pedal actuation, the SBC computer also receives the sensor signals from the other electronic assistance systems. For example, the anti-lock braking system (ABS) provides information about wheel speed, while ESP® makes available the data from its steering angle, turning rate and transverse acceleration sensors. The transmission control unit finally uses the data highway to communicate the current driving range. The result of these highly complex calculations is rapid brake commands which ensure optimum deceleration and driving stability as appropriate to the particular driving scenario. What makes the system even more sophisticated is the fact that SBC calculates the brake force separately for each wheel.
_ The ECU
Fig 6.2: (Location of the ECU under the Hood)
The high-pressure reservoir contains the brake fluid which enters the system at a pressure between 140 and 160 bars. The SBC computer regulates this pressure and also controls the electric pump which is connected to the reservoir. This ensures much shorter response times than on conventional brake systems. Yet another advantage: full braking power is available even when the engine is switched off. The hydraulic unit mainly comprises four so-called wheel pressure modulators. They mete out the brake pressure as required and pass it onto the brakes. In this way it is possible to meet the microcomputer’s stipulations while each wheel is slowed down separately in the interests of driving stability and optimum deceleration. These processes are monitored by pressure sensors inside the wheel pressure modulators.
6.3 Emergency braking: Stopping Distance Reduced by up to Three per cent
The main performance characteristics of Sensotronic Brake Control include the extremely high dynamics during pressure build-up and the exact monitoring of driver and vehicle behaviour using sophisticated sensors. Mercedes-Benz is thus moving into new dimensions of driving safety. Take the example of the emergency brake: SBC already recognises the driver’s rapid movement from the accelerator onto the brake pedal as a clue to an imminent emergency stop and responds automatically: with the aid of the high-pressure reservoir, the system increases the pressure inside the brake lines and instantly presses the pads onto the brake discs so that they can get a tight grip the moment the driver steps onto the brake pedal. As a result of this so-called pre filling of the brake system, the stopping distance of an SBC-equipped sports car from a speed of 120 km/h is cut by around three per cent compared to a car featuring conventional braking technology.
Fig 6.3: (Stopping Distance Reduced By Up To 3%)
Thanks to electro hydraulic back-up, the performance of Brake Assist is also improved further. If this system issues the command for an automatic emergency stop, the quick pressure build-up and the automatic pre filling of the wheel brakes leads to a shorter braking distance.
It turns the conventional hydraulic brake into an even more powerful mechatronic system. Its microcomputer is integrated into the car’s data network and processes information from various electronic control units. In this way, electric impulses and sensor signals can be instantly converted into braking commands, providing a marked safety and comfort gain for drivers.
6.4 Driving stability: Precise Braking Impulses for Perfect ESP® Performance
It is not just in emergency braking that Sensotronic Brake Control proves its worth, but also in other critical situations – for example, when there is a risk of swerving. Under such conditions, the system interacts with the Electronic Stability Program (ESP®) which keeps the vehicle safely on course through precise braking impulses at all wheels and/or by reducing engine speed. SBC once again offers the benefits of greater dynamics and precision: thanks to the even faster and more accurate braking impulses from the SBC high-pressure reservoir, ESP® is able to stabilise early and comfortably a vehicle which is about to break away.
This is evident, for example, from the results of the VDA lane-change test which suspension engineers use to simulate a quick obstacle-avoidance manoeuvre and to demonstrate the high capabilities of the Electronic Stability Program. In conjunction with SBC, ESP® works even more effectively and significantly reduces vehicle swerving through quick and precise braking impulses.
Fig 6.4: (Reduction in Accidents after EBC)
At the same time the driver’s steering effort is reduced. Thanks to SBC and ESP® he or she will have even less difficulty keeping the car on course.
Mercedes Passenger Cars Get Into Fewer Accidents:
• Accident rate dropped by 15 percent especially due to standard ESP
• Share in driving accidents with serious consequences declining greatly since 2000
• Stability program makes important contribution to accident prevention
• ESP standard in all Mercedes passenger cars since summer 1999
Fig 6.5: (Function of ESP)
The number of Mercedes passenger cars with road traffic accidents has declined sharply since the series production/standard employment of the Electronic Stability Program ESP. This is shown by a representative random sample analysis of the accident data* of the Federal Statistics Office, which Mercedes-Benz published today. Accordingly, the accident rate of Mercedes Models first licensed in 2000/2001 compared with 1999/2000 has dropped by 15 percent, and thus dropped by 4 percentage points more than the average of other automobile manufacturers. Mercedes-Benz analyzed a total of over 1.5 million traffic accidents.
As the first automobile brand, Mercedes-Benz put the Electronic Stability Program ESP into all of its passenger car models, starting in the summer of 1999, as standard equipment, which reduces the danger of spinning in curves, in avoidance manoeuvres or during braking, and supports the driver in better controlling critical situations. “The current analysis of the accident statistics shows, that ESP makes an important contribution to accident prevention, and is therefore as significant for traffic safety as ABS, seat belt and airbag,” says Dr. Hans-Joachim Schöpf, head of passenger car development at Mercedes-Benz.
6.5 Braking in Corners: Greater Safety Thanks to Variable Brake Force Distribution
Even when braking in corners, SBC also offers more safety than a conventional brake system. This is where the variable and targeted brake force distribution is of particular advantage to actively influence the car’s compliance steer.
While conventional brake systems always mete out the brake pressure equally to the inner and outer wheels, SBC offers the possibility of assigning brake forces in a way appropriate to the situation. Hence the system will automatically increase the brake pressure at the outer wheels because the higher vertical forces also allow them to transfer greater brake forces. At the same time the brake forces at the inner wheels are reduced to provide the higher cornering forces needed to stay on course. The result is a more stable braking behaviour along with optimum deceleration values.
With the innovative Sensotronic Brake Control Mercedes engineers still stick to the proven principle of a variable brake force control for the front and rear axles. They program the system in such a way that, when slowing down from a high speed, the larger part of the brake force continues to act on the front axle. This prevents a potentially hazardous over braking of the rear axle. Again SBC is capable of adapting to the prevailing situation. At low speeds or during partial braking, the system automatically increases the brake force share at the rear axle to improve brake system response and achieve even wear and tear of the brake pads.
Fig 6.5: (Greater Safety When Braking in Corners)
6.6 Comfort: No Pedal Vibrations during ABS Operation
Both the separation of the SBC pedal from the rest of the brake system and the proportional pressure control using mechatronics serve to increase brake comfort – particularly during sharp deceleration or when the anti-lock braking system is operational. The usual vibration of the brake pedal when ABS sets in does not occur, which, Mercedes engineers have found, is not only a comfort feature of the new system but also offers measurable safety benefits. Their research in DaimlerChrysler’s Berlin driving simulator has revealed that almost two thirds of all drivers are startled when ABS pulsation sets in: they do not increase the brake force further and are even prone to taking their foot off the brake pedal for a short while, thereby lengthening the stopping distance of their vehicle – in the driving simulator by an average of 2.10 metres – 7 feet – during ABS braking from 60 km/h – 37 MPH – on a snow-covered road surface.
SBC add-on functions: support systems to reduce driver strain
7.1 SBC Traffic Assist
The system offers several additional functions besides a new braking behaviour, due to its electronic brain: In stop-and-go traffic the vehicle brakes automatically, when the foot is lifted off the accelerator pedal (“Traffic Jam Assist”). It can be engaged under 10 MPH, using the cruise control lever and switches off automatically at higher speeds. It remains active under 40 MPH. When engaged the instrument cluster indicates “SBC S”. One can also activate it on downhill slopes via cruise control, so the car won’t speed over the set limit. It was deleted starting with MY 2005.
7.2 SBC Soft Stop
Though is not yet released, though few people are aware of it since Mercedes advertises it already. It might be released later on. In city traffic soft-stop supposedly allows soft, jerk less stopping. Not sure if it’s needed since SBC brakes can be modulated well, with good feel.
7.3 SBC Hold
A “drive-away assistant” prevents the vehicle from rolling backwards or forward when starting on a hill or steep incline. A firm push onto the brake pedal, and the car remains stopped, even when taking the foot off the brake pedal, until the driver accelerates and the vehicle begins to roll. When it is set, the instrument cluster indicates “SBC Hold”. I like using this function and miss it when switching back to other cars. As far as I know it was first introduced in the spring of 2003 in the 04 E-class Estate and later on in the 2004 SLs.
7.4 DRY Brake
And finally there is the dry brake function. It is always activated when the windshield wipers run. The system then knows, that it rains and, with short brake pulses unnoticed by the driver, keeps the brake discs always dry and fully functional.
The Failure of SBC
Mercedes decided to discontinue its Sensotronic Brake Control system following a number of problems with the brake-by-wire technology. Failures related to the system have lead to two significant recalls involving over 2 million vehicles. There have been no accidents as a result of these defects, but Mercedes reportedly decided to quit using the system in an effort to improve its reputation for build quality.
Problems with SBC include the system prematurely switching to the hydraulic emergency backup due to a problem with wiring. According to Mercedes, vibration from the Sensotronic hydraulic braking unit could affect the electrical contacts within the connector plug. The emergency mode still provides “safe” braking, but not what the driver is accustomed to.
Brake-by-wire means there is no mechanical connection between the car’s brakes and the brake pedal. Rather, small electric motors near the wheels generate brake pressure. They are governed by electronic control units connected to the brake pedal i.e. during braking the actuation unit is completely disconnected from the rest of the system and serves the sole purpose of recording any given brake command.
The system is offered on E-Class, SL-Class and CLS-Class vehicles.
Gothenburg / Borås (Sweden), June 21, 2011. The steady growth of road transportation is an increasing issue in today’s traffic stream. The more trucks and busses there are on the open road the more important and critical are their braking performance to avoid crashes and blocked motorways. Over the years, new brake system technologies on commercial vehicles have been developed and introduced.
The HAVEit Brake-by-Wire demonstrator truck is a perfect example of the HAVEit technology partnership between an OEM like Volvo, a supplier like Haldex, a scientific institution like the University of Stuttgart (Germany) and a specialist company like (Explinovo). “Research work aiming at improving safety, such as the progress within brake technology, is of great importance to Volvo and the ambition to reach our zero accident vision,” says Carl Johan Almqvist, Volvo Trucks.
The vehicle is equipped with a full Brake-by-Wire system which replaces the current technology based on a pneumatic system. The now fully electromechanical brake system enables increased braking performance for actuation and advanced slip control resulting in an improved stability control and reduced stopping distance by about 15 percent compared to state-of-the art brake systems. The system uses the principle of self-enforcement for generating brake force. This means very low energy consumption compared to alternative systems. Apart from these advantages the driver has a better pedal feeling. The truck itself profits from an improved brake balance and therefore improved vehicle stability.
The demonstrator truck is equipped with an electromechanical brake system developed by Haldex and uses a redundant system architecture to ensure safety and to comply with the brake regulations. In the system controllers for the system a redundancy management, developed by the Faculty of Aerospace Engineering at the University of Stuttgart (ILS) is used and in order to secure FlexRay/CAN communication between the brake system and the overall system a gateway was developed by Explinovo.
On the HAVEit Final Event various driving scenarios will be demonstrated showing both braking performance and system redundancy. This includes braking on a low friction area and simulation of system failures.
The EU funded R&D project HAVEit („Highly Automated Vehicles for Intelligent Transport“) is set to develop research concepts and technologies for highly automated driving.
Haldex, headquartered in Landskrona, Sweden, develops and provides reliable and innovative solutions with focus on brake and air suspension products to the global commercial vehicle industry.
About Volvo Technology
Volvo Technology is the centre of research and innovation within the Volvo Group and responsible for long term technological development as well as both basic and applied research & development. Volvo Technology is a wholly owned subsidiary of the Volvo Group.
Future Scope In Braking Technology:
The advent of electronics in brake technology opens up new and promising opportunities to Mercedes engineers – and not only in the disciplines of safety and comfort. By means of SBC they have also moved a considerable way closer to the realisation of their long-term objective, namely to be able to automatically guide the cars of the future along the roads with the aid of video cameras, proximity radar and advanced telematics. For such autonomous vehicle guidance, the experts need a computer-controlled brake system which automatically acts on the instructions of an electronic autopilot and stops the car safely.
In the area of wheel brakes, Continental is responding to this challenge with the new, very light FS fixed-type calliper brake. In comparison to fist-calliper brakes, the FS design has two major advantages: first, it is lighter; because of the smaller clearance possible with this design it responds very quickly, which increases its safety potential. In addition, Continental has been able to equip this brake type with drawn brake pads, which optimizes the acoustics of the brake.
In the new MK C1 generation, the braking function, the brake booster and the brake pressure control module (ABS, ESC) are combined into a compact, weight-saving braking unit. This is made possible because the system is completely electro-hydraulic, and it is no longer dependent on the relatively low energy density provided by the vacuum. Furthermore, the MK C1 fulfils the increased pressure dynamics requirements for advanced driver assistance systems – preventing accidents and protecting pedestrians – significantly better than the previous braking systems. Thus the braking distance for an electronically initiated emergency braking action was significantly shorter in tests with the MK C1. This reduces the likelihood of serious injuries in the event of an accident. The high pressure dynamics also create ideal conditions for other driving safety systems. For instance, a short braking distance reduces the time-slot in which active and passive safety systems can be coordinated and optimized in terms of timing. Since an increasing number of vehicles will be equipped with “vehicle surrounding sensor systems” in the future, dangerous situations and potential accidents can be detected even earlier. One of the main factors influencing such a risk analysis is always the braking system.
A hydraulic-by-wire system like the MK C1 provides the ideal conditions for determining every conceivable contribution to driving safety provided by the braking system, in a sustainable and calculable way. The “power on demand” principle of braking also reduces energy requirements for the braking system, and a pulsation-free linear pump means a much lower noise emission level than in conventional solutions with ESC multi-piston pumps and the electric vacuum pumps that are often required. Drivers of electric vehicles will also appreciate the quiet braking system because of the lack of “noise cancellation” from a combustion engine – especially if the system is also more dynamic. This level is scheduled for availability starting in 2015, as a “Premium Compact” braking system.
Ultimately, however, these additional options always rely on the basic braking system, which must therefore provide uncompromising quality, stability and longevity.
The conventional braking systems have the disadvantage of causing excessive fatigue to the driver under extreme braking conditions. With the help of sensotronic braking systems the above disadvantage is being efficiently overcome with the help of sensors.
The Sensotronic braking systems can be considered as the basis of development of future brakes for all automobiles due to its efficiency and reliability.