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B-B and Bo-Bo are the Association of American Railroads (AAR) and British classifications of wheel arrangement for
railway locomotive A locomotive or engine is a rail transport vehicle that provides the motive power for a train. If a locomotive is capable of carrying a payload, it is usually rather referred to as a multiple unit, motor coach, railcar or power car; the us ...
s with four axles in two individual bogies. They are equivalent to the B′B′ and Bo′Bo′ classifications in the UIC system. The arrangement of two, two-axled, bogies is a common wheel arrangement for modern electric and
diesel locomotive 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 whee ...
s.


Bo-Bo

Bo-Bo is the UIC indication of a wheel arrangement for railway vehicles with four axles in two individual bogies, all driven by their own
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 ...
s. It is a common wheel arrangement for modern electric and diesel-electric locomotives, as well as power cars in
electric multiple unit An electric multiple unit or EMU is a multiple-unit train consisting of self-propelled carriages using electricity as the motive power. An EMU requires no separate locomotive, as electric traction motors are incorporated within one or a numbe ...
s. Most early electric locomotives shared commonalities with the steam engines of their time. These features included side rods and frame mounted driving axles with leading and trailing axles. The long rigid wheelbase and the leading and trailing axles reduced cornering stability and increased weight. The Bo-Bo configuration allowed for higher cornering speeds due to the smaller rigid wheelbase. Furthermore, it allowed better
adhesion Adhesion is the tendency of dissimilar particles or surfaces to cling to one another ( cohesion refers to the tendency of similar or identical particles/surfaces to cling to one another). The forces that cause adhesion and cohesion can be ...
because all the wheels were now powered. Due to the absence of frame mounted wheels no leading or trailing axles were necessary to aid cornering, reducing weight and maintenance requirements. Due to the advent of modern motors and electronics more power can be brought to the rail with only a few axles. Modern electric locomotives can deliver up to 6400 kW on only four axles. For very heavy loads, especially in transportation of bulk goods, a single unit with this wheel arrangement tends to have too little adhesive weight to accelerate the train sufficiently fast without wheelslip.


Bo-1-Bo

Eighteen of the Japanese narrow-gauge Bo-Bo electric were rebuilt in the late 1970s to form the Class ED62. An additional carrying axle was added between the bogies to give a B-1-B (AAR) or Bo′1Bo′ (UIC) arrangement. The intention was to give a lighter axle loading for the Iida Line.


Bo-2-Bo

Another rare arrangement was the Bo-2-Bo used for two gauge Japanese diesel-electric classes, the ED76 and ED78. These used
flexicoil Flexicoil suspension is a type of secondary suspension for railway vehicles, typically having steel coil springs between the bogie trucks and chassis/frame of a passenger coach, goods freight wagon, or locomotive. Suspension systems using ste ...
outer bogies which permitted the bogies some lateral movement, as well as swivelling.


Bo′Bo′+Bo′Bo′

These are a pair of Bo′Bo′ locomotives semi-permanently coupled as a single unit. They are each constructed with a single cab, giving a cab at each end. This layout includes the Alstom Prima II, one of the most powerful electric locomotives in production (). Versions include the China Railways HXD2 and the Indian WAG-12.


B′B′

The B′B′ or B-B arrangement is similar, but usually applies to diesel-hydraulic locomotives rather than diesel-electrics. The axles on each bogie are coupled together mechanically, rather than being driven by individual traction motors. Diesel-hydraulics have their engine mounted on the main frame of the locomotive, together with a hydraulic transmission. Power is then transmitted to the bogies by
cardan 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 and torque and rotation, usually used to connect ...
s and a short driveshaft between axles. A common example of this is the German V200 design and its many international derivatives. The need to arrange the bogie suspension around the drive shafts led to an unusual bogie design with radius arms rather than hornblocks and so prominently visible wheels and rims. In some rare examples, such as the
SNCF Class BB 71000 The SNCF Class BB 71000 is a class of 30 centre-cab Bo-Bo diesel shunting locomotives. They were the last locomotives in service with SNCF to feature side rods. The class was withdrawn from traffic between 1998 and 1999. A number were sold on for ...
and the narrow-gauge , the bogie axles have been linked by coupling rods. Having only a single final-drive per bogie allows more room for the bogie pivots on this narrow-gauge design. With high power full-size locomotives, splitting the drive directly to two axles is preferred, as it only requires a less powerful final drive gearbox. In AAR notation a Bo-Bo is regarded as a B-B because the AAR system does not take traction motors into consideration, only powered axles. An AAR-like notation is used in France too, making it hard to tell the B-B and Bo-Bo engines apart, both of which are common there.


1A-A1 (or A1-1A)

Railcar A railcar (not to be confused with a railway car) is a self-propelled railway vehicle designed to transport passengers. The term "railcar" is usually used in reference to a train consisting of a single coach (carriage, car), with a drive ...
s and
multiple unit A multiple-unit train or simply multiple unit (MU) is a self-propelled train composed of one or more carriages joined together, which when coupled to another multiple unit can be controlled by a single driver, with multiple-unit train contr ...
s use similar two-axle powered bogies and many of them use similar hydraulic or mechanical transmissions, rather than traction motors. However railcars are also lightweight and do not require all axles to be powered in order to gain adequate adhesion. They thus use a wheel arrangement of 1A-A1 (UIC: (1A)(A1) ) (or A1-1A (UIC: (A1)(1A) ) ) rather than B-B. A common arrangement is for each power car to have two independent engines and transmissions, each driving a single axle of each bogie. The difference between 1A-A1 and A1-1A is that 1A-A1 has the powered axles being the axles furthest from the ends, whilst A1-1A has the powered axles closest to the ends.


2-B

The 2'Bo' (AAR:2-B) arrangement has been used similarly, but rarely, for lightweight railcars that only needed two powered axles. Only one example is recorded, the diesel-electric four-car ''
Rebel A rebel is a participant in a rebellion. Rebel or rebels may also refer to: People * Rebel (given name) * Rebel (surname) * Patriot (American Revolution), during the American Revolution * American Southerners, as a form of self-identification; s ...
'' railcars of 1935. Three powercars were built, with a 600 bhp engine and two traction motors on a single bogie. Half of the powercar was used as a baggage car, supported by a conventional coaching stock unpowered bogie.


Gallery


See also

* :Bo-Bo locomotives * Co-Co *
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 ...


References

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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 ...