Bo+Bo

Baltimore and Ohio LE-1steeple cabin 1899

ABo+Bowheel arrangement is anelectric locomotive,with two four-wheeled chassis orbogieswith an articulated connection between them, with the drawbar forces taken through these bogies, and with all axles powered by individualtraction motors.

This is in contrast to the more commonBo-Boarrangement where the two bogies are mounted beneath a shared frame, and the forces are taken through that frame.

Partial sectioned drawing of a small boxcabBaltimore and Ohio LE-2of 1903, showing the connection between bogies and drawbar

The type was important for early electric locomotives such as the firstBaltimore and Ohio LE-1in 1899or the ItalianE.430of 1901. These had two separate chassis and half-cabs, linked by a pin connector. A canvas dodger joined the gap between the cabs.

Later designs resembled the Bo-Bo layout, where a single largeboxcabspanned the two bogies and was pivoted upon them. As these pivots did not carry the tractive force, they could be of simple design.

LNER 6000, the prototype of theBritish Railways class 76,while on hire to theDutch national railwaysin 1947

Typical mid-century Bo+Bo locomotives include theSouth African Class 1EandClass 2Eor theJapanese National RailwaysJNR ED17.Railways usingCape gaugesuch as the South African or Japanese narrow gauge systems with long locomotives found Bo+Bo advantageous over Bo-Bo as there was less overhang of the couplers and so less sideways misalignment on tight curves.

(Bo′Bo′)(Bo′Bo′)

ChME5and the four-axled articulated bogie

In the 1980s an extension of the Bo+Bo concept was used byČKD PrahainCzechoslovakiafor theChME5,a small class of a dozen largeswitching locomotivesfor theDonets Railway.Although of modest power, 2,000 hp (1,500 kW), they were heavy and also geared for a high tractive effort at low speeds; so they required good traction. Rather than more conventional three-axled bogies for a Co-Co arrangement, a four-axled bogie was required. This would have been an excessively long wheelbase and so hard on track curves. A solution was to articulate the bogie itself, making each bogie a Bo+Bo chassis.

The earlier SovietТЭМ7and the high-speedTEP80had already used a (Bo′Bo′)(Bo′Bo′) layout with sub-bogies. The ChME5 repeated this, and retained the largespan bolstersandflexicoil-stylesecondary suspensionof the ТЭМ7. For the ChME5 though, the vertical forces were taken through the over-bogie frames, but the tractive effort were taken by coupling the sub-bogies as a Bo+Bo.