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Cut-away Bowden cable view. From left to right: Protective plastic coating, steel structure, inner sleeve to reduce friction, inner cable.
Bowden cables controlling an automobile throttle.

A bowden cable is a type of flexible cable used to transmit mechanical force or energy by the movement of an inner cable (most commonly of steel or stainless steel) relative to a hollow outer cable housing. The housing is generally of composite construction, consisting of a helical steel wire, often coated with plastic, and with a plastic outer sheath.

The linear movement of the inner cable is generally used to transmit a pulling force, although for very light applications over shorter distances (such as the remote shutter release cables on mechanical film cameras) a push may also be used. Usually provision is made for adjusting the cable tension using an inline hollow bolt (often called a "barrel adjuster"), which lengthens or shortens the cable housing relative to a fixed anchor point. Lengthening the housing (turning the barrel adjuster out) tightens the cable; shortening the housing (turning the barrel adjuster in) loosens the cable.

History

The origin and invention of the Bowden Cable is open to some dispute, confusion and popular myth.

The invention of the Bowden cable has been popularly attributed to Sir Frank Bowden, founder and owner of the Raleigh Bicycle Company who, circa 1902, was reputed to have started replacing the rigid rods used for brakes with a flexible wound cable. There appears to be no current definitive reference for this.

The Bowden mechanism was invented by Irishman Ernest Monnington Bowden (1860 to April 3rd 1904[1]) of 35 Bedford Place, London, W.C[1]. The first patent was granted in 1896. (English Patent 25,325 and U.S. Pat. No. 609,570)[2]. The device did not work particularly effectively and was never used on bicycles. It is reported that "on 12th January 1900 E. M. Bowden granted a license to The Raleigh Cycle Company of Nottingham", whose directors were Frank Bowden and Edward Harlow. At this signing they became members of 'E. M. Bowden's Patent Syndicate Limited'. The syndicate included, among others, R. H. Lea & Graham I. Francis of Lea & Francis Ltd, and William Riley of the Riley Cycle Company.

According to the British National Archives[3] a flexible cable brake for cycles was separately 'invented' by George Frederick Larkin, a skilled automobile and motorcycle engineer, who patented his design in 1902. He was subsequently recruited by, and worked for E.M. Bowden until 1917 as General Works Manager.

George Larkin is known for his invention of the flexible cable brake for cycles, which was patented in 1902. The original patent for a similar invention known as the 'Bowden mechanism' was granted to Ernest Monnington Bowden in 1896. The following year E.M. Bowden's Patents Syndicate Ltd. was formed to market the device but initially the project was a failure because all the company could offer was a flimsy mechanism capable of transmitting comparatively enormous power. The Bowden Mechanism was not developed in connection with a cycle brake as there is no record of the cable having been associated with the cycle industry until 1902, when George Larkin's invention was patented.[3]

During Larkin's employment with Bassett Motor Syndicate his duties included the assembly of motor cars and motor cycles, and a major difficulty was the assembly of the braking systems which at that time comprised steel rods, not easily adaptable to the contour of the chassis. He designed a flexible cable brake and approached S.J. Withers, Patent Agent, to have the design patented. Withers noticed the similarity of Larkin's idea to the Bowden Mechanism and introduced him to the Bowden Syndicate, who agreed to manufacture and market the invention with the proviso that it should be patented jointly in the names of the inventor and themselves. Within a few months, Larkin, then aged 23, was engaged as Motor Department Manager with E.M. Bowden's Patents Syndicate, and he was appointed General Works Manager on 1 May 1904.[3]

Variations

Bowden cable with a barrel adjuster controlling a bicycle rear derailleur.
Bowden cable with a barrel adjuster and locking nut in a BMX rear brake detangler.

Housing

The original, standard Bowden cable housing consists of a close-wound helix of round or square steel wire. This makes a flexible housing but causes the length to change as the housing flexes. Because on the inside of the bend the turns of a close-wound helix can't get any closer together, the bending causes the turns to separate on the outside of the bend, and so at the centerline of the housing, there must also be an increase of length with increasing bend.

In order to support indexed shifting, Shimano developed a type of housing that does not change length as it is flexed. This housing has several wire strands running in a multiple helix, with a pitch short enough that bends in the cable are shared by all strands, but long enough that the housing's flexibility comes by bending the individual strands rather than twisting them. Another consequence of the long pitch of the helix is that the essentially parallel strands are only bound together by the plastic jacket, and so this type of housing cannot withstand high tension in the inner cable which causes high compression in the housing and can result in failure by buckling of the housing strands. This type of housing should not be used for brake cables.[4]

Inner wire

Some applications such as lawn mower throttles, automobile manual chokes, and some bicycle shifting systems require significant pushing ability and so use a cable with a solid inner wire. These cables are usually less flexible than ones with stranded inner wires.

Ends

One end of the inner cable may have a small shaped piece of metal, known (somewhat confusingly) as a nipple (as can be seen in the BMX rear brake detangler picture) that fits into a shifter or brake lever mechanism. The other end is usually clamped (as can be seen in the rear derailleur picture) to the part of the brake or shifter that needs to be moved. A small ferrule (as can also be seen in the rear derailleur picture) may be crimped on to prevent stranded cable from fraying. Traditionally, shifter cables have a small cylindrical nipple concentric to the cable, while brake cables have a larger, flatter cylindrical nipple whose center axis is perpendicular to the cable axis.

Some replacement cables come with both styles, one on each end. The unneeded end is to be cut off and discarded upon installation.

Nipples are also available separately from the cable, for purposes of repair or custom cable construction. They are fitted to the cable by soldering. Nipples that clamp to the cable by means of a grubscrew are also available for emergency field repair purposes.

If the inner wire is solid, as in automotive and lawnmower throttle and choke applications, it may simply have a bend at one or both ends to engage what ever it pushes or pulls.

Uses

References

  1. ^ a b Irish Genealogy, Dublin Evening Telegraph; Ireland; Wednesday, 6 Apr 1904 - Deaths
  2. ^ "Patent Storm: Mechanical cable system having a bellows seal". http://www.patentstorm.us/patents/5765447-description.html. Retrieved on 2008-02-07. 
  3. ^ a b c National Archives, National Motor Museum, George Larkin Collection
  4. ^ Brown, Sheldon. "Sheldon Brown: Cables". Sheldon Brown. http://www.sheldonbrown.com/cables.html. Retrieved on 2007-10-19. 

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