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Bowden cable

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File:Bowden.jpg
File:Bowden cable throttle.jpg

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 lined 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.

HistoryEdit

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 3 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 licence 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]

Parts and variationsEdit

File:Bowden cable.JPG
File:Bowden cable with barrel adjuster.jpg

HousingEdit

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]

A third type of housing consists of short hollow rigid aluminum or carbon fiber cylinders slid over a flexible liner. Claimed benefits over steel wire housing include less weight, tighter curves, and less compression under load.[5][6]

Inner wireEdit

Inner wire ropes for push applications have an additional winding that runs in the opposite direction to the wind of the actual inner wire. The wind may be like that of a spring or a wind with a flat strip; these are called spring wrap and spiral wrap respectively.[citation needed]

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.[7] These cables are usually less flexible than ones with stranded inner wires.

EndsEdit

One end of the inner cable may have a small shaped piece of metal, known (from the pear-shaped soldered terminations used in some cases) 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 often clamped (as can be seen in the rear derailleur picture) to the part of the brake or shifter that needs to be moved, or as is most common with motorcycle control cables, fitted with another nipple.

Traditionally, in bicycle applications, shifter cables have a small cylindrical nipple concentric with the cable, while brake cables have a larger, barrel (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. Where free rotation of nipples, relative to the cable axis is required, the cable end may be finished with a brass ferrule or "trumpet" soldered to the cable. The barrel nipple will be a sliding fit over the brass ferrule, and can thus rotate, to ensure alignment of the nipples at each end of the cable, and avoidance of twisting of the inner cable. Applying heat to the inner cable for soldering may weaken the steel, and although soft soldering is less strong than silver solder, a lower temperature is required to form the joint, and there is less likelihood of the inner cable being damaged as a result. Silver soldering may require additional heat treatment of the wire to preserve the temper of it in order to prevent it from becoming too soft or too brittle[citation needed]

Nipples that clamp to the cable by means of a screw also are available for emergency repair purposes, or where removal is required for maintenance.

A small ferrule (as can also be seen in the rear derailleur picture) may be crimped on, and so also called a crimp, to prevent stranded cable from fraying.[8]

Other methods to prevent fraying include soft or silver soldering the wire ends, or ideally by flash cutting the wires.

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.

DonutsEdit

Small rubber tori, called donuts, can be threaded onto a bare run of the inner cable to prevent it from striking the bicycle frame causing rattles or abrasion.[9]

UsesEdit

ReferencesEdit

Template:CarDesign navcs:Bowden de:Bowdenzug es:Chicote fr:Câble Bowden nl:Bowdenkabel sk:Bovden it:Guaina (meccanica)

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