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 due to the system only taking powered axles into consideration, not traction axles.
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The Bo-Bo-Bo configuration is often used to lower axle weight while keeping lateral forces low compared to a locomotive with two three-axle bogies, thus allowing the locomotive to use lightly laid track, in particular narrow-gauge railways.
The State Rail Authority of New South Wales, Australia built the last of its 86 Class electric locomotives (8650) in the Bo-Bo-Bo arrangement (called locally a Tri-Bo), but this did not prove successful and it spent long periods out of traffic undergoing repair.
The first Italian six-axle electric locomotives, such as the E.626, used a Bo′BoBo′ layout, where the two centre axles were mounted on a rigid frame and only the outer pairs on bogies.
This wheel arrangement requires either an articulated frame (becoming a Bo+Bo+Bo arrangement) or else significant side play on the center bogie. The Italian locomotives and New Zealand EW class are articulated, whereas the Eurotunnel and New Zealand EF and DJ class locomotives' central bogies have a lot of sideplay.
B′B′B′ locomotives
A similar arrangement, but without separate traction motors for each axle, would be a B′B′B′ arrangement as UIC, indistinguishably B-B-B in AAR.
This arrangement has been used for electric locos with three monomotor bogies, such as the Italian FS Class E.632 of 1982.
Bo′Bo′Bo′+Bo′Bo′Bo′ locomotives
These are a pair of Bo′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 Russian freight electric locomotives VL15, VL85, VL86f and the experimental gas turbine electric locomotiveGT1h-001, which was converted from an electric locomotive VL15.
This article uses material from the Wikipedia article Bo-Bo-Bo, and is written by contributors.
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