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Co-Co is the
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 ...
for
diesel Diesel may refer to: * Diesel engine, an internal combustion engine where ignition is caused by compression * Diesel fuel, a liquid fuel used in diesel engines * Diesel locomotive, a railway locomotive in which the prime mover is a diesel engin ...
or
electric Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described by ...
locomotives with two six-wheeled
bogie A bogie ( ) (in some senses called a truck in North American English) is a chassis or framework that carries a wheelset, attached to a vehicle—a modular subassembly of wheels and axles. Bogies take various forms in various modes of transp ...
s with all axles powered, with a separate
traction motor A traction motor is an electric motor used for propulsion of a vehicle, such as locomotives, electric vehicle, electric or hydrogen vehicles, elevators or electric multiple unit. Traction motors are used in electrically powered rail vehicles (ele ...
per axle. The equivalent
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'', Cre ...
(Europe) for this arrangement is Co′Co′, or C-C for AAR (North America).


Use

Co-Cos are most suited to
freight Cargo consists of bulk goods conveyed by water, air, or land. In economics, freight is cargo that is transported at a freight rate for commercial gain. ''Cargo'' was originally a shipload but now covers all types of freight, including transp ...
work as the extra wheels give them good traction. They are also popular because the greater number of axles results in a lower
axle load An axle or axletree is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to the vehicle, with the wheels rotating around the axle. In the former case, bearing ...
to the track.


History

The first mainline diesel-electric locomotives were of
Bo-Bo B-B and Bo-Bo are the Association of American Railroads (AAR) and British classifications of wheel arrangement for railway locomotives with four axles in two individual bogies. They are equivalent to the B′B′ and Bo′Bo′ classifications in ...
arrangement. As they grew in power and weight, from 1937 the
EMD E-unit EMD E-units were a line of passenger train streamliner diesel locomotives built by the General Motors Electro-Motive Division (EMD) and its predecessor the Electro-Motive Corporation (EMC). Final assembly for all E-units was in La Grange, Illino ...
s used an
A1A-A1A The AAR wheel arrangement system is a method of classifying locomotive (or unit) wheel arrangements that was developed by the Association of American Railroads. Essentially a simplification of the European UIC classification, it is widely used in ...
layout with six axles to reduce axle load, but only four of them were powered. After WWII, the British LMS ordered two prototype locomotives with some of the first Co-Co arrangements. The first C-C design recorded was a narrow-gauge Hornsby
opposed-piston An opposed-piston engine is a piston engine in which each cylinder has a piston at both ends, and no cylinder head. Petrol and diesel opposed-piston engines have been used mostly in large-scale applications such as ships, military tanks, and f ...
Hornsby-Akroyd-engined locomotive of 1903 for the
Chattenden and Upnor Railway The Chattenden and Upnor Railway (also known as the Lodge Hill and Upnor Railway) was a narrow gauge railway serving the military barracks and depot at Upnor, Kent and associated munitions and training depots. It was preceded in the early 1870 ...
. There was a two-speed mechanical transmission with drive shafts to the bogies and the axles on each bogie were linked by
coupling rod A coupling rod or side rod connects the driving wheels of a locomotive. Steam locomotives in particular usually have them, but some diesel and electric locomotives, especially older ones and shunters, also have them. The coupling rods transfer t ...
s.


Variants


Electric locomotives

There were initially few
electric locomotive An electric locomotive is a locomotive powered by electricity from overhead lines, a third rail or on-board energy storage such as a battery or a supercapacitor. Locomotives with on-board fuelled prime movers, such as diesel engines or gas ...
s with this wheel arrangement, as they are usually lighter than diesel-electrics of similar power and so could manage a similar axle loading with a simpler
Bo-Bo B-B and Bo-Bo are the Association of American Railroads (AAR) and British classifications of wheel arrangement for railway locomotives with four axles in two individual bogies. They are equivalent to the B′B′ and Bo′Bo′ classifications in ...
arrangement. Some of the few early examples were the French CC 7100 of 1949 and the British Railways EM2 of 1953. As high-speed electric locomotives in the 1980s began to achieve powers in the 6,000 hp range, new Co-Co designs appeared, as more axles were needed to distribute this high power. The BR class 92 was a predominantly freight locomotive of this arrangement for the
Channel Tunnel The Channel Tunnel (french: Tunnel sous la Manche), also known as the Chunnel, is a railway tunnel that connects Folkestone (Kent, England, UK) with Coquelles ( Hauts-de-France, France) beneath the English Channel at the Strait of Dover. ...
, although the passenger
Eurotunnel Class 9 The Eurotunnel Class 9 or Class 9000 are six-axle high-power Bo′Bo′Bo′ single-ended electric locomotives built by the ''Euroshuttle Locomotive Consortium'' (ESCL) of Brush Traction and ABB. The class was designed for and is used exclusive ...
instead use a
Bo-Bo-Bo A Bo-Bo-Bo or Bo′Bo′Bo′ (UIC classification) is a locomotive with three independent two-axle bogies with all axles powered by separate traction motors. In the AAR system, this is simplified to B-B-B. The Bo-Bo-Bo configuration is of ...
arrangement. This provides the same number of axles for traction, although with shorter bogie wheelbases and so gives a smoother ride.


C-C

In C-C (Commonwealth) or C′C′ (UIC) arrangements, the axles of each bogie are coupled together. This may be for either a
diesel-hydraulic A diesel locomotive is a type of railway locomotive in which the prime mover 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 wheels ...
transmission with a mechanical
drive shaft A drive shaft, driveshaft, driving shaft, tailshaft (Australian English), propeller shaft (prop shaft), or Cardan shaft (after Girolamo Cardano) is a component for transmitting mechanical power (physics), power and torque and rotation, usually ...
to the bogie and
final drive A drivetrain (also frequently spelled as drive train or sometimes drive-train) is the group of components that deliver mechanical power from the prime mover to the driven components. In automotive engineering, the drivetrain is the components o ...
s to each axle. Otherwise a
monomotor bogie A monomotor bogie (french: bogie monomoteur) is a form of traction bogie (railway), bogie used for an electric locomotive or diesel-electric locomotive. It is distinguished by having a single traction motor on each bogie. Development The first el ...
with a single traction motor. These are used for both electrics and diesel-electrics. In AAR notation, the notation is the same for both variants and cannot distinguish them. However hydraulic transmissions are almost unknown in the US, the
Krauss-Maffei ML 4000 The Krauss-Maffei ML 4000 is a road switcher diesel-hydraulic locomotive, built between 1961 and 1969 by German manufacturer Krauss-Maffei in Munich, Germany. It generated from two Maybach V16 engines. 37 examples were built for two North Americ ...
and the ALCO DH643 being the only C′C′ examples.


Co+Co

Co+Co is the code for a similar wheel arrangement but with an articulated connection between the bogies. The buffer and drawbar forces are taken between the bogies rather than through the frame. These were mostly popular in South Africa.


1Co-Co1

The 1Co-Co1 wheel arrangement is an alternative to the Co-Co arrangement which has been used where it was desired to reduce axle load. Each "Co" bogie has an additional non-powered axle in an integral
pony truck A Bissell or Bissel truck (also Bissel bogie or Pony truck) is a single-axle bogie which pivots towards the centre of a steam locomotive to enable it to negotiate curves more easily. Invented in 1857 by and usually then known as a ''pony truck' ...
to spread the load. As the pony truck is articulated within the bogie, the arrangement is (1′Co)(Co1′) in
UIC notation 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'', Cre ...
. This rare arrangement was used primarily in Britain; on the Southern Railways' first three prototype mainline diesel-electric designs, 10201–10203, and then on production vehicles in British Rail's Class 40 and "Peaks" (BR classes 44, 45, and 46).


1Co+Co1

1Co+Co1 Under the British and Imperial classification scheme of locomotive axle arrangements, which is related to the UIC classification, 1Co+Co1 is a classification code for a locomotive wheel arrangement of two eight-wheeled bogies with an articulated ...
, like Co+Co, is an articulated variant where the drawbar forces are taken between the bogies rather than through the frame. These were used in South Africa, for lighter loadings on the lightly-laid . A number of Japanese electrics from the 1930s, also on Cape gauge, such as the EF10 also used this arrangement.


2Co-Co2

The New Zealand DF class were built in the mid-1950s by English Electric in Britain, as the first diesels for the New Zealand railways. They were derived from the earlier English Electric 1Co-Co1 bogie design, but to provide increased flexibility for the long wheelbase bogie they used a four-wheeled bogie with more sideplay, rather than a pony truck.


See also

*
Co-Bo Co-Bo or Co′Bo′ is a wheel arrangement in the UIC classification system for railway locomotives. It features two uncoupled bogies. The "Co" bogie has three driven axles and the "Bo" bogie has two. The arrangement has been used to even out ax ...
, which has two uncoupled
bogie A bogie ( ) (in some senses called a truck in North American English) is a chassis or framework that carries a wheelset, attached to a vehicle—a modular subassembly of wheels and axles. Bogies take various forms in various modes of transp ...
s


References

{{Locostyles Co-Co CC,Co-Co