Co-Bo or Co′Bo′ is a

wheel arrangement In rail transport, a wheel arrangement or wheel configuration is a system of classifying the way in which wheels are distributed under a locomotive. Several notations exist to describe the wheel assemblies of a locomotive by type, position, and c ...

in the

UIC classification The UIC classification of locomotive axle arrangements, sometimes known as the German classification''The Railway Data File''. Leicester: Silverdale, 2000. p. 52. . or German system,Kalla-Bishop P.M. & Greggio, Luciano, ''Steam Locomotives'', Cr ...

system for railway

locomotive A locomotive is a rail transport, rail vehicle that provides the motive power for a train. Traditionally, locomotives pulled trains from the front. However, Push–pull train, push–pull operation has become common, and in the pursuit for ...

s. It features two uncoupled

bogie A bogie ( ) (or truck in North American English) comprises two or more Wheelset (rail transport), wheelsets (two Railroad wheel, wheels on an axle), in a frame, attached under a vehicle by a pivot. Bogies take various forms in various modes ...

s. The capital letter indicates the number of axles on the bogie, the 'o' indicates that they are driven, so the "Co" bogie has three driven axles and the "Bo" bogie has two. The arrangement has been used to even out axle loading. The weight distribution of the locomotive depends on the

power unit In electricity generation, a generator, also called an ''electric generator'', ''electrical generator'', and ''electromagnetic generator'' is an electromechanical device that converts mechanical energy to electrical energy for use in an externa ...

, the engine and generator. If these are not placed symmetrically, the weight distribution is also biased to one end. Placing three axles beneath the engine end and just two beneath the other, with the lighter ancillaries, gives more even loading per-axle. Leyland railway Metro-Vickers Co-Bo cropped

Leyland railway Metro-Vickers Co-Bo cropped

Examples

Diesel

The British Railways Class 28 is the first (and only) diesel locomotive with a Co-Bo wheel arrangement, where the wheels are independently driven.

C'B'

DE10-1081 in Ajikawaguchi IMG 6709 20130811

A similar wheel arrangement, with five axles across two bogies, is also used in Japan for the Class DE10, DE11, and DE15 locomotives. As these are

diesel-hydraulic locomotive A diesel locomotive is a type of railway locomotive in which the power source is a diesel engine. Several types of diesel locomotives have been developed, differing mainly in the means by which mechanical power is conveyed to the driving whee ...

s, they are of C-B arrangement, not Co-Bo. A hydrodynamic transmission on the locomotive frame is driven by the

prime mover Prime mover may refer to: Philosophy *Unmoved mover, a concept in Aristotle's writings Engineering * Prime mover (engine or motor), a machine that converts various other forms of energy (chemical, electrical, fluid pressure/flow, etc.) into ener ...

, then drive to each bogie is taken by

cardan shaft Cardan may refer to: * Gerolamo Cardano or Jerome Cardan (1501–1576), Renaissance mathematician, physician, astrologer, and gambler * Cornelius Castoriadis (1922–1997), Greek-French philosopher who used the pseudonym Paul Cardan * Cardan, Giro ...

s. The axles of each bogie are all driven, and all geared together, rather than having separate traction motors.

Steam

Some Engerth

steam locomotives A steam locomotive is a locomotive that provides the force to move itself and other vehicles by means of the expansion of steam. It is fuelled by burning combustible material (usually coal, oil or, rarely, wood) to heat water in the locomot ...

were built to the Fink system, with the four trailing wheels driven by a crankshaft and connecting rods, thus making them 0-6-4-0Ts instead of 0-6-4Ts.

Electric

The also used a Co'Bo' wheel arrangement with three-phase slip-ring motors driving each axle.

In fiction

BoCo is a fictional Co-Bo locomotive, a

British Rail Class 28 The British Rail Class 28 ( Metro-Vick Type 2) diesel-electric locomotives, known variously as 'Metrovicks', 'Crossleys' or 'Co-Bos', were built under the Pilot Scheme for diesel locomotives as part of the British Railways 1955 Modernisation P ...

. The locomotive appeared in the

Railway Series ''The Railway Series'' is a series of British books about a railway known as the North Western Railway, located on the fictional Sodor (fictional island), Island of Sodor. There are 42 books in the series, the first published in May 1945 by Wi ...

book ''Main Line Engines'' and the

Thomas & Friends ''Thomas & Friends'' is a British children's television series which aired from 9 October 1984 to 20 January 2021. Based on ''The Railway Series'' books by Wilbert Awdry and his son Christopher Awdry, Christopher, the series was developed for ...

television series.

References

* CB,0C00B0,Co-Bo {{Loco-stub