Monomotor bogie
A monomotor bogie (French: bogie monomoteur) is a form of traction bogie used for an electric locomotive or diesel-electric locomotive. It is distinguished by having a single traction motor on each bogie.
The first electric locomotives used large diameter electric motors, mounted rigidly on their frames and using jackshaft drives and coupling rods to carry their torque to the driving wheels. This increased their unsprung weight and limited their maximum speed, despite the greater power of electric locomotives.
To achieve a higher speed, locomotives began using wheel arrangements such as 2'Do2' (AAR: 2-Do-2), with the SNCF Class 2D2 5500 This used leading (and trailing) pony trucks or bogies to provide stability at high speed, with individual traction motors for each axle, avoiding the weight of the coupling rods. Suspension travel for each axle was achieved with a Buchli drive on each axle. Unlike the original Swiss practice with a Buchli drive on one end of the axle, the French locomotives used a double-ended drive. This was later given as a reason for the low wear rates experienced with them. These locomotives first appeared during the 1930s with the 2D2 5500, and later during the post-war push for electrification the SNCF Class 2D2 9100 (1950).
Shortly after the 9100 class, the French absorbed another new Swiss idea, that of the high-speed double-bogie locomotive. Previous French Bo-Bo locomotives had been considered suitable only for medium speeds, with the pony truck and rigid frame used for express passenger service. The Swiss Re4/4I of 1946 achieved speeds of up to 125 kilometres per hour (78 mph), owing to the advanced design of its bogies.
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