Anti-lock braking system

from Wikipedia, the free encyclopedia

The anti-lock braking system ( ABS ) is a technical system for more driving safety and less wear and tear on the tire treads . In the German and also Swiss StVZO it is called Automatic Blocking Preventer (ABV), in Austria ( Motor Vehicle Act 1967 ) it is an anti- blocking device . It is mainly used in motor vehicles , but also in railways and aircraft landing gears .

When braking the motor vehicle, ABS counteracts any possible locking of the wheels by reducing the brake pressure. As a result, when braking road vehicles and airplanes, it makes it possible to maintain steerability and directional stability. In addition, the system can reduce the braking distance on wet roads by regulating the wheel slip . On a dry road or loose surface - for example gravel or snow - the braking distance can be longer. The system called “ anti-skid ” by railways is intended to prevent the formation of flat spots on the wheels, which lead to a characteristic beating noise while driving.

ABS symbol
ABS symbol in the cockpit

history

In 1903 the Frenchman Paul Hallot applied for a patent for a brake force regulator for rail vehicles. In 1928 Karl Wessel received a patent (No. 492799) for a brake force regulator for motor vehicles. In 1940 Fritz Ostwald proposed an electromechanical brake controller, which was tested in trials. The first use of a blocking preventer has been in the United States of Vincent Hugo Bendix in the aviation tested. The aircraft should stay on track when braking from high speed after landing. From 1952 various military and commercial aircraft were equipped with the Maxaret anti-skid developed by Dunlop Rubber .

principle

The main objective of ABS in road vehicles is to prevent the tires from locking continuously in order to keep the vehicle steerable even during emergency braking. If the tires block, no transmission of lateral forces is possible because the vehicle slides over the entire contact surface of the tires; a steering angle then does not change direction.

Depending on the condition of the road surface, the condition of the tires and the quality of the ABS system, this can lead to both a shortening and an extension of the braking distance compared to a vehicle without ABS. The safety gain by maintaining the steerability almost always outweighs a possibly somewhat longer braking distance.

The maximum braking deceleration is achieved at around 8-25% slip, depending on the condition of the road surface and tires. 20% brake slip means that in the same period in which the vehicle covers a distance of one meter, the wheels only roll 0.8 meters. After reaching the maximum braking force - that is, the slip value at which the greatest deceleration is achieved - the slip continues to increase as the braking force decreases, until the wheel finally locks (= 100% brake slip). In the blocked state, only sliding friction is used to brake.

In addition, at the wheel when blocked by selective abrasion a so-called brake plates arise.

Structure and mode of operation

4-channel ABS in a 1995 Fiat Punto .
The distinguishing features are the four brake lines routed individually to the wheels and the electronic control on the right under the cover labeled "ABS".

The first ABS systems were 3-channel systems, i.e. H. the brake pressure could be controlled individually for the two front wheels, but only jointly for both rear wheels. In the meantime, only 4-channel ABS are used in newly registered cars, which control all wheels individually.

An ABS system follows a different principle than the previously standardized dual-circuit brake systems , in which two of the four wheel brake cylinders were actuated by the tandem master cylinder for safety reasons ( redundancy ) . Double master cylinders are no longer necessary due to the high reliability of today's systems. With a 4-channel ABS, the pressure can be reduced individually in each of the four wheel brake cylinders.

ABS sensors as passive induction sensors.

Each wheel has a perforated or toothed washer that is scanned by an induction sensor or, in newer vehicles, a Hall sensor . This measures the wheel speed . With a constant braking force, it decreases proportionally to the time that has passed. The speed of a wheel drops sharply when it can no longer transfer the braking force to the road, as it has to absorb the braking torque itself. The control unit detects this jump in speed and reduces the brake pressure on this wheel. In the hydraulic part of the ABS, which is conventionally designed, two solenoid valves are attached to the pressure line leading to each wheel. First, the first valve blocks the line to the master brake cylinder. If the speed continues to decrease, the second valve, which is closed in the idle state, drains brake fluid, the brake pressure dropping. This liquid is pumped back into the space and to the pressure level between the master brake cylinder and the first solenoid valve using an electric pump that starts up at the same time. Otherwise there would be no fluid there and the brake pedal would continue to be depressed when the first solenoid valve opens again after the speed increase, the brake pedal would soon be fully depressed and braking would no longer be possible. When the wheel speed has risen again, the drain valve closes and the pressure valve opens. This work cycle is repeated about 10 times per second, with motorcycles 15 times per second. The increase in pressure as a result of pumping back is perceived as vibrating on the pedal with the foot. The vehicle jerks and rattles due to the automatic, rapid stuttering of the brakes. According to the basic concept of hydraulic separation into two circuits, there are two pumps (but often driven by only one electric motor).

In the event of moderate braking during normal driving and if the ABS fails, the braking system acts like a normal two-circuit system. The brake pressure from the master cylinder acts unabated on the wheel cylinders via the open lines. The two valves (eight per four-wheeled vehicle) are kept open (first valve) or closed (second valve) in the idle state with spring force. The brake also works in the event of a power failure.

The signals from the speed sensors are processed by a central control unit. The ABS is switched off below a minimum speed (approx. 6 km / h). When the ignition is switched on and when the ABS is switched on after the minimum speed has been exceeded, the system tests itself. Detected errors are written to an electronic memory in order to facilitate troubleshooting in the event of defects.

In trucks with compressed air braking systems, the ABS works on the same principle. Since an air compressor works permanently, there are no return pumps for the discharged air. The additional valves are located directly on the wheel brake cylinders, because changes in air pressure from a central point over long lines would arrive too late at the wheels. Changes in pressure in hydraulic systems have significantly shorter running times. (Higher speed of sound in liquids)

Additional functions

Brake force distribution

Newer versions of the ABS also take over the brake force distribution ( electronic brake force distribution - EBV) between the front and rear axles (4-channel systems) and thus replace the mechanical regulators (brake force distributors) that used to be common, some of which are still installed in trucks. This has several advantages:

  • Optimal use of the coefficient of adhesion on both axles - including diagonal wheel loads, which could not be optimally represented with mechanical controllers.
  • Even with light braking, the rear axle is braked and a known problem is eliminated: With the mechanical brake force distribution, it could happen that the brake discs on the rear axle were cleaned too seldom by braking and so corrosion on the surface or dirt reduced the braking effect.

Newer systems also include emergency wheel recognition. Emergency bicycles have a smaller rolling circumference and turn faster, so that the ABS can correctly process the feedback from its speed sensor in the event of an emergency stop.

Since 2014, it has been mandatory in the EU that an ESC (vehicle dynamics control) is installed in addition to ABS .

Yaw moment weakening

-Split

If the vehicle is on a roadway with different coefficients of friction between the right and left side (for example snow or wet leaves on the edge of the road), a sudden emergency braking without ABS would cause a moment around the yaw axis to the side with the higher static friction (yaw moment) because the side of the vehicle is braked more strongly on the non-slip surface than the side on the smooth surface. When tuning the ABS in the vehicle, the manufacturers ensure that the braking pressure of the wheel does not increase as quickly as it would be physically possible on a non-slip surface. This gives the driver additional reaction time to react by counter-steering. The time that the ABS needs to achieve full braking performance on a non-slip surface depends on the manufacturer's philosophy. It is usually shorter in sporty vehicles than in sedans. The slower build-up of the braking force also increases the braking distance. However, this is accepted in view of the advantages in terms of vehicle control.

In the meantime, there are also systems that replace the yaw moment reduction with automatic intervention in the steering . In the case of active counter-steering by means of superimposed steering ( active steering ), the braking distance is not lengthened due to the yaw moment weakening.

Off-road ABS

Offroad ABS is an additional function offered primarily in off-road vehicles , which largely eliminates the previous system-related extension of the braking distance on loose surfaces. Intermittent locking of one or more wheels utilizes the braking effect of the wedge that forms in front of the wheel when braking. The system works like a conventional ABS on other road surfaces. The additional function was introduced in 2006 in the VW Touareg under the name ABSplus and is now also available from other manufacturers. The modified brake control can also be activated manually with some manufacturers.

Vehicle installation

Passenger cars

The first car with ABS was the Jensen FF with mechanical Dunlop -Maxaret ABS from 1966. In 1969 Ford equipped the Lincoln Continental Mark III with an ABS system called Sure-Track Brake System , which only affects the rear wheels ; likewise the Ford Thunderbird . In 1969 the first generation of an ABS (electronically controlled anti-lock braking system) was presented at the International Motor Show by the American company ITT Automotive ( Alfred Teves until 1967 ). 1970 Citroën was about to launch the Teldix -ABS ( Teldix for Tel efunken - Ben dix ), which ultimately failed due to financial problems at the automobile manufacturer and the first oil crisis .

In 1971, the Nissan President introduced the Electro Anti-lock System, an electronic anti-lock braking system.

From 1971 to 1973, the Chrysler Group offered its luxury model Imperial for an additional charge with an electronic anti-lock braking system from Bendix called Sure Brake , which included front and rear wheels.

In 1978 Bosch launched its electronic ABS on the market; at the same time, the term ABS was legally protected by Bosch. Other manufacturers sometimes refer to their systems as ABV (automatic blocking preventer). ABS was initially available for the S-Class W 116 from Mercedes-Benz , then for the BMW 7 Series of the E23 series . In 1985 the Ford Scorpio was the first mass-produced car with ABS as standard. From 1987 the VW Golf II , Passat III and the Transporter T3 were also available with the system at high surcharges (Golf: 1800 DM, Passat: 2200 DM, Transporter: 3720 DM, prices 1989). At the end of 2003, around 90 percent of new vehicles registered in Germany had ABS. As a result of a voluntary commitment by the European automotive industry ( ACEA ), all vehicles with a gross vehicle weight of less than 2.5 t have been equipped with ABS as standard since July 1, 2004. The Japanese automobile associations have made identical commitments.

Trucks

Mercedes-Benz has been offering the ABS for air brakes since 1981, developed together with WABCO . All coaches have been equipped with ABS since 1987 and all trucks since 1991. Since January 1991, trucks with a gross vehicle weight of over 3.5 t and buses with more than eight seats can only be registered with ABS.

motorcycles

ABS front wheel sensor of a BMW K 1100 LT

In 1985 Lucas Girling introduced the first ABS for motorcycles . The first series manufacturer was FTE automotive , based in Ebern / Lower Franconia (at that time still a division of FAG Kugelfischer ). Its ABS was first introduced as an option in the BMW K models in 1988 and at that time cost DM 1980  surcharge.

Since January 1, 2016, a standard anti-lock braking system has been stipulated for new types of motorcycles over 125 cm³ and over 11 kW output by EU regulation 168/2013 / EU. Exceptions apply to competition enduros and trial machines. For the first registration, the new regulations came into force on January 1, 2017. However, light motorcycles can also be equipped with a combination brake.

Studies from 2009 projected that 160 fewer motorcyclists would have been killed per year and up to 6900 motorcycle accidents with injuries could have been prevented if the motorcycles had ABS. At the time, the ADAC criticized the inadequate dissemination of ABS on motorcycles.

The motorcycle ABS is designed to maintain driving stability in straight ahead emergency braking. Newer systems are considered to be suitable for curves to a limited extent, systems that are fully suitable for curves are already well advanced. The systems vary depending on the manufacturer. The pressure modulation is carried out either via electronically controlled solenoid valves (e.g. BMW, Ducati, Kawasaki, KTM, Suzuki, Yamaha), plunger system (old BMW, Honda) or magnet system (Honda). The control frequencies are also different. The first systems (ABS I) had a maximum of 7 control processes per second, the latest systems achieve 15 control processes per second. The system is switched off below 4 km / h (BMW, Honda etc.) or 10 km / h (Honda SH 300). Manufacturers of ABS include a. Bosch , Nissin Kogyo , Continental-Teves and Brembo .

Cycles

Mechanism of a 1-4-2 safety brake

In 2004 Biria introduced an anti-lock braking system for bicycles, the 1-4-2 Safety Brake . Here, the torque support of the coaster brake acts on the front brake via a mechanism with a cable, in addition to the hand brake lever. If the front wheel overbrakes, the rear wheel loses contact with the ground, whereupon the braking torque on the rear wheel is lost and the front wheel brake loosens. The advantage of this process is that without actuating the brake, no additional driving resistance occurs and the coaster brake acts on both brakes. The associated patent describes “ a certain ABS effect ”.

In 1995, the Italian company Brovedani offered a cantilever- style ABS brake . The principle is to continuously change its distance to the rim by means of rollers running on the rim, which are coupled to the brake shoe via an unbalance lever, and thus to achieve an ABS effect that is independent of acceleration.

An electronically controlled hydraulic system has been on the market since 2018. However, it is only available for e-bikes .

Railways

Systems known as " anti-skid " have been in use on rail vehicles for several decades , which are intended, among other things, to prevent the wheels from locking when braking. However, this is primarily not because of a better braking effect, but to protect the rail and above all the wheels from uneven wear due to blocking.

Advantages and disadvantages

With a firm road surface and the usual material pairings (rubber with asphalt / concrete), the shortest possible braking distance results when the wheel is still rolling. Under certain conditions (wedge formation on snow or loose sand), the shortest possible braking distance is achieved with the wheels locking, but steering ability is lost. As a braking aid, ABS offers a compromise here: Although ABS can lengthen the braking distance, blocking with its disadvantageous consequences is avoided.

A similar effect as ABS was previously achieved by the so-called stutter brake , especially on slippery roads. The brake pedal was pressed and relieved in quick succession. This made it possible to achieve a compromise between braking effect and steerability. In contrast to modern ABS, the braking effect could not be dosed differently for each wheel. This driving technique does not apply to vehicles with ABS.

Advantages (especially when operating on solid ground)
  • The vehicle remains steerable even when the brakes are fully applied so that the obstacle can be avoided.
  • On wet roads, the vehicle has better braking behavior and sometimes shorter braking distances.
  • Protection of the tires, as tire wear is evenly distributed over the circumference. In contrast to this, if the tire is locked, the tire can be severely worn at one point, resulting in brake plates . This tire damage leads, among other things, to uneven running and increased noise development.
  • Better steerability on road surfaces with different levels of grip thanks to the reduction in yaw moments .
  • The braking force can be optimally controlled for each individual wheel
disadvantage
  • On road surfaces with loose ground, such as If, for example, sand, gravel or snow is not used, if the wheels are locked, a wedge will form in front of the wheel. This wedge can reduce the braking distance. If this brake wedge is not installed, the braking distance usually increases.

literature

  • Karl-Heinz Dietsche, Thomas Jäger, Robert Bosch GmbH: Automotive pocket book. 25th edition, Friedr. Vieweg & Sohn Verlag, Wiesbaden, 2003, ISBN 3-528-23876-3 .
  • Robert Bosch (Ed.): Autoelectronics Autoelectronics. 5th completely revised and expanded edition. Vieweg & Sohn Verlag, Wiesbaden 2007, ISBN 978-3-528-23872-8 .
  • Bert Breuer, Karlheinz H. Bill: Brake manual: Fundamentals, components, systems, driving dynamics. 3rd completely revised and expanded edition. Vieweg & Sohn Verlag, Wiesbaden 2006, ISBN 978-3-8348-0064-0 .
  • Hans-Rolf Reichel: Electronic brake systems. From ABS to brake-by-wire . Expert Verlag, 2001, ISBN 3-8169-2010-1 .

Individual evidence

  1. ↑ bosch-automotive.com Guardian angel for the car (as of February 21, 2017)
  2. ↑ Hans-Rolf Reichel: Electronic brake systems. P. 43.
  3. ↑ U.S. Patent 845633
  4. ↑ Hans-Rolf Reichel: Electronic brake systems. P. 44.
  5. ↑ Hans-Rolf Reichel: Electronic brake systems. P. 49.
  6. ↑ www.aviationancestry.com . Dunlop Maxaret Anti-Skid. Retrieved November 26, 2009.
  7. ^ B. Breuer, K. Bill: Brake manual , 2006, p. 21.
  8. ^ B. Breuer, K. Bill: Brake manual, 2006, p. 111.
  9. ↑ Scheme of an anti-lock braking system automotive technology, interesting facts, simulation, questions, tasks
  10. ↑ https://www.kfz-tech.de/Biblio/Hydraulische_Bremse/ABSRegelung.htm
  11. ↑ B. Heissing: Fahrwerkhandbuch, 2007, p. 515.
  12. ↑ B. Heissing: Fahrwerk Handbuch, 2007, p. 504.
  13. ↑ H. Winner: Handbook Driver Assistance Systems, 2009, p. 430.
  14. ↑ To the point: Mondial de l'Automobile 2006. Volkswagen AG, September 28, 2006, archived from the original on October 17, 2006 ; Retrieved January 26, 2014 .
  15. ↑ https://www.thetruthaboutcars.com/2018/03/rare-rides-1979-nissan-president-executive-luxury-brougham/
  16. ↑ Description of the Imperial Sure Brake System dealer catalog on ImperialClub.org
  17. ↑ Chrysler press release dated August 27, 1970 ImperialClub.org
  18. ↑ motorradonline from September 4, 2009 ( Memento from July 26, 2010 in the Internet Archive ) ABS special (part 5) The story
  19. ↑ Regulation (EU) No. 168/2013 of the European Parliament and of the Council on the approval and market surveillance of two-, three-wheel and four-wheel vehicles , accessed on December 14, 2015
  20. ↑ MOTORRAD No. 23 of October 29, 2010, page 10
  21. ↑ europarl.europa.eu More safety for motorcycles thanks to new provisions for type approvals , plenary session on transport / consumers on November 20, 2012 (accessed on June 10, 2013)
  22. ↑ motorradonline.de of April 7, 2010 ( Memento of July 2, 2010 in the Internet Archive ) ADAC Accident Research: Motorcycle ABS saves lives
  23. ↑ The Integral ABS from BMW Motorrad ( Memento from November 1, 2007 in the Internet Archive )
  24. ↑ motorradonline.de from November 18, 2009 ( Memento from May 7, 2010 in the Internet Archive ) Basics (Part 7) Conclusion
  25. ↑ Huber Verlag: Technology - ABS curves for everyone! Retrieved February 26, 2020 .
  26. ↑ motorradonline.de from September 4, 2006 ( Memento from July 26, 2010 in the Internet Archive ) ABS special (part 4) The technology
  27. ↑ Jürgen Stoffregen: Motorcycle technology. 7th edition 2010. Page 378 ff
  28. ↑ See utility model DE20309375U1 : Combination brake system . Published on August 14, 2003 , inventor: Mahdi Biria (page 1 below). ‌
  29. ↑ Jo Beckendorff: Five selected e-bike brands make their debut with Bosch ABS. March 22, 2018, accessed February 26, 2020 .
  30. ↑ bosch-kraftfahrzeugtechnik.de Important questions and answers (accessed on April 3, 2013)

Web links

Wiktionary: Anti-lock braking system  - explanations of meanings, word origins, synonyms, translations
Commons : Anti-lock Braking Systems  - Collection of pictures, videos and audio files