Dual circuit braking system

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Dual circuit brake system (HT distribution)

In vehicle construction, a dual-circuit brake system is a brake system whose service brakes are operated via two independent circuit lines. They occur both as hydraulic brakes in passenger vehicles - with a master brake cylinder - and as compressed air brakes or combined hydraulic / compressed air systems in trucks or large machines. The two independent circuits make it possible to bring the vehicle to a standstill with the service brake in the event of a brake circuit failure without using the parking brake .

Beginnings and legal regulations

Malcolm Loughead received a patent for a hydraulic brake (wheel and master cylinder) in 1917 . The first car model with this hydraulic brake system - acting on all four wheels - was the Duesenberg model A (1921), and the Chrysler B-70 model (1924) in larger numbers . Alfred Teves received the marketing rights for Germany in 1926 , and the Adler Standard 6 was equipped with them in the same year . With a few exceptions, all manufacturers introduced the oil pressure brake by the end of the 1930s: Maybach (passenger cars) had mechanical four-wheel brakes until production was discontinued in 1941 and the VW Beetle (standard) had cable brakes until March 1962.

A patent in favor of Vincent Hugo Bendix for a tandem master cylinder was registered on January 2, 1934. ATE introduced the tandem master cylinder in 1937. The Bugatti Type 57 (1938) is the first car model with a tandem master brake cylinder . The Simca-Fiat 11 CV (1934 to 1938) had two pressure cylinders . The Jaguar C-Type (1953) and Aston Martin DB3 S (1955) cars , like the Simca-Fiat 11 CV, had a black and white layout (front and rear wheels separated). The diagonal separation was first used on Saab 95 and Saab 96 (1963).

In the Federal Republic of Germany , the dual-circuit braking system was made mandatory by law on July 1, 1963 for buses and coaches . For motor vehicles and their trailers , regulation 71/320 / EEC of July 30, 1971 stipulated the dual-circuit brake, which had to be implemented in the countries of the EC on January 30, 1973. The corresponding US regulation ( FMVSS ) came into force on January 1, 1976.

Five systems

TT division (black and white division)

The wheels on an axle are each controlled by a circle. If a circle fails, the brakes on the wheels of an axle are available. Since the brakes on the front axle provide the greater part of the braking power during braking, the braking distance can be longer if they fail. There is a risk of breaking away in curves. When braking, however, there is no yaw moment around the vertical axis of the vehicle, so that a negative scrub radius does not necessarily have to be used. The TT division has proven to be useful for commercial vehicles. This type is used in racing vehicles because it allows the braking forces on the front and rear axles to be adjusted in a simple manner; in Formula 1 it is mandatory.

K distribution (diagonal dual circuit brake)

With the diagonal division (also X division), one of the diagonally opposite wheels on the front and rear axles is supplied by a circle. In the event of a circuit failure, a wheel is always available on the front axle. However, when braking with only one brake circuit, a yaw moment arises around the vertical axis of the vehicle, because one of the braked front wheels transmits significantly higher braking forces than the braked rear wheel on the other side of the vehicle. In order to ensure sufficient driving stability, a negative scrub radius is therefore almost inevitable. Another disadvantage is that if the thermal load on the brakes on the front axle is too high, both brake circuits can fail at the same time.

This design is mainly used in front-wheel drive vehicles because, due to the low rear axle load, they require at least one braked front wheel in order to be able to meet the legal requirements for the minimum deceleration in the event of a brake circuit failure.

LL split

One circuit supplies both wheels on the front axle and one wheel on the rear axle. The disc brakes on the front axle have double brake pistons that are controlled independently of each other. If one circuit fails, 80 percent of the braking power is still available, as both front wheels and one wheel on the rear axle are still braked. The Swedish car manufacturer Volvo used the system for the first time in 1966 in the Volvo 140 .

HT split

One circle brakes all wheels, the second circle only controls the front axle. In the event of a circuit failure, at least the front axle brake is available. First used in the NSU Ro 80 (1967).

HH division

Each brake circuit supplies all wheels. All brakes have double brake cylinders that are controlled independently of each other. If one circuit fails, the full braking power is still available.

Effects of system failure

The regulations for the introduction of dual-circuit brakes have been issued due to the failure safety. Modern car braking systems achieve a failure safety of 96 percent after millions of kilometers. If a system circuit fails in the K or LL division, an angular pulse is generated when braking.

  • K-distribution
    When braking with only one front wheel brake, an angular momentum arises (here: braking effect on the right front wheel - angular momentum clockwise)

  • LL distribution
    When braking with only one rear wheel brake, an angular momentum arises. (Here: braking effect left rear wheel - angular momentum counterclockwise)

literature

  • Bert Breuer, Karlheinz H. Bill: Brake manual. Basics, components, systems, driving dynamics. Verlag Friedrich Vieweg and Son, Wiesbaden, 2nd edition 2004, ISBN 3-528-13952-8 .
  • Olaf von Fersen : A Century of Automotive Technology . Passenger cars. VDI-Verlag, Düsseldorf 1986, ISBN 3-18-400620-4 .

References and comments

  1. ↑ U.S. Patent 1249143
  2. ↑ Olaf von Fersen : A Century of Automobile Technology, p. 31.
  3. ↑ Hugo Mayer from Rudolfstadt (DRP 84748) patented a fluid brake as early as 1895. See Olaf von Fersen, p. 405.
  4. ^ LJK Setright: The Guinness Book of Motorcycling . Facts and Feats. 1982, ISBN 0-85112-255-8 , p. 257.
  5. ↑ See [1] , [2]
  6. ↑ See [3]
  7. ^ Hugh Conway: Bugatti - le pursang des automobiles. JH Haynes, Yeovil Sommerset, 3rd edition 1974, ISBN 0-85429-158-X , p. 267.
  8. ↑ While Matschinsky (cf. Radführung der Straßenfahrzeuge. 2007, p. 320) speaks of a two-circuit brake, Conway (cf. Bugatti. P. 267) does not mention this.
  9. ^ Fiat Ardita
  10. ↑ The Fiat dual-circuit brake system can be seen in Notice d'entretien N. 02161 - VIII - 1936 - XIV - 1000. The publication does not state whether the system was installed from 1934 or from 1936.
  11. ↑ Olaf von Fersen : Ein Jahrhundert Automobiltechnik, p. 419.
  12. ↑ See § 72 and § 41 Paragraph 16 StVZO
  13. ↑ 71/320 / EEC
  14. ↑ Official Journal 71/320 / EEC (PDF)
  15. ↑ Standard No. 105
  16. ↑ Breuer, Bill, p. 128.
  17. ↑ Michael Trzesniowski: racing car technology . 2nd Edition. Vieweg and Teubner Verlag, Wiesbaden 2010, ISBN 978-3-8348-0857-8 , p. 407.
  18. ↑ Olaf von Fersen, p. 420.
  19. ↑ Bert Breuer, Karlheinz H. Bill: Brake manual , p. 15.