Combined braking system

A combined braking system (CBS), also called linked braking system (LBS), is a system for linking front and rear brakes on a motorcycle or scooter.[1] In this system, the rider's action of depressing one of the brake levers applies both front and rear brakes. The amount of each brake applied may be determined by a proportional control valve. This is distinct from integrated brakes, where applying pressure to brake pedal only includes application of some front brake. [2]

Legal issues

In many countries, including the United States, the law requires a motorcycle to have two separate braking systems.[3] Invariably, the handlebar lever operates the front brake, and the foot pedal operates the rear. Any bike with CBS must still have two separate inputs for braking, even if (as on the Honda VFR1200) each control independently operates both front and rear brakes. By contrast, a car is required to have only one braking system for dynamic braking (i.e. braking when moving), plus a separate parking brake.

The justification for two separate braking systems is that, compared to cars, a motorcycle has, proportionately, a higher centre of gravity, a shorter wheelbase, a higher power-to-weight ratio, and a smaller tyre contact patch area. All these factors lead to a much greater weight transfer to the front wheel on braking, and a greater risk of skidding.[4] A rider needs to be able to use each brake independently to maintain control, and a CBS system seeks to further reduce any skid risk.

Examples of CBS

BMW Motorrad uses a system called Integral ABS, in which the front brake lever operates both the front and rear brakes, while the brake pedal operates only the rear brake.[5] In the inverse, Honda's system that features both combined brakes and anti-lock brakes is dubbed Combined ABS. In this system, the rear brake pedal operates both front and rear brake, and the front brake lever operates the front calipers, which in turn activates a secondary master cylinder to engage the rear brake. ABS modulators are installed on both the front and rear wheel.[6]

Honda’s first street motorcycle with a combined braking system (then called Unified Braking) was the 1983 GL1100. This system was derived from a 1970s RCB1000 world endurance race bike.[7][8] Honda made several variations of the LBS system with differing levels of complexity and integration.[9] The Honda CBR1000F and CBR1100XX and VFR800 featured what Honda called LBS II (now called Dual CBS), a system where both levers would activate both brakes through a system of secondary pistons and proportioning/delay valves.[10] One front brake caliper was connected to a secondary master cylinder, and the caliper was allowed to rotate slightly to apply pressure to the piston in that secondary master cylinder. Braking force was translated into pressure that was sent to the rear brake cylinder. Only the two outer pistons in the front brake calipers were directly activated by the brake lever; the center piston received pressure from the rear pedal via the proportioning and delay valve.

From 2009 the Honda CBR1000RR and CBR600RR sport bikes are optionally equipped with an integrated Dual CBS and ABS system which uses an electronic control unit to distribute hydraulic pressure between front and rear brakes.[11] The combined anti-lock braking system is called C-ABS.[12]

Moto Guzzi has CBS braking on models such as the 750 cc Strada.

References

  1. ↑ Effectiveness of Antilock Braking Systems in Reducing Fatal Motorcycle Crashes (PDF), Insurance Institute for Highway Safety, March 2009, p. 2, retrieved 2009-11-11
  2. ↑ Motorcycle Safety Foundation, Basic Rider Course Manual 7.1, page 37
  3. ↑ http://www.law.cornell.edu/cfr/text/49/571.122
  4. ↑ http://genjac.com/BoomerBiker/Braking.htm
  5. ↑ "BMW ABS and Automatic Stability Control". webBikeWorld. Retrieved 31 January 2010.
  6. ↑ "Two types of combined ABS combining CBS and ABS". Honda Worldwide. Honda Motor Co. Retrieved 22 February 2014.
  7. ↑ "Advanced brake introduced for motorcycles by Honda ahead of others". Honda Worldwide. Honda Motor Co. Retrieved 22 February 2014.
  8. ↑ "Combined Braking System (CBS)". Honda Powersports. American Honda Motor Co. 9 December 2013. Retrieved 22 February 2014.
  9. ↑ "Two types of CBS, Combi Brake (Single CBS) and dual CBS". Honda Worldwide. Honda Motor Co. Retrieved 22 February 2014.
  10. ↑ "Dual CBS for large sports tourers". Honda Worldwide. Honda Motor Co. Retrieved 22 February 2014.
  11. ↑ Wasef, Basem (26 March 2012). "Honda Motorcycles Combined ABS". Popular Mechanics. Hearst Communication. Retrieved 22 February 2014. The bike's uprated stoppers (a $1,000 option) are a combined system-- ie, they operate the front and rear brakes independently depending on stopping needs-- and involve a complex sequence of events involving valve units, ECUs, and a motor-driven hydraulic setup that avoids the pulsing sensation in circulating type ABS systems.
  12. ↑ Canet, Don (1 May 2009). "Braking New Ground". Cycle World. Bonnier Corp. Retrieved 22 February 2014. After years of riding bikes with anti-lock brakes, we’ve come to expect compromises in the feel and function during high-performance braking. Honda has made us rethink our position; to do so with a pure sporting platform makes this doubly astonishing.
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