Power Transmission & Drives

'Drive' is the arrangement that transmits the torque produced by the traction motor to the axle/wheel. Indian Railways locomotives use five distinct real drive types, each tied to specific loco classes.

Single Reduction Gear Drive

The most widely used drive on Indian Railways (used across the largest number of loco classes, from the WAM/4 era right through WAP/5 and WAP/7). A pinion mounted directly on the traction motor shaft drives the main gear, which is mounted on the axle — torque from the motor pinion is transmitted straight through the main gear to the axle.

Jacquemin Drive — Real Torque Path & Gear-Tooth Counts

Real torque path: traction motor pinion → elastic gear → intermediate pinion → intermediate gear wheel → main gear. The main gear mounts on a bearing supported by the gear case, and is mechanically connected to a cardan shaft (hollow shaft); torque from the main gear transmits to the cardan shaft and cardan ring, which is mechanically coupled to the wheel through a resilient (silent-block/elastic rubber bush) arrangement on the opposite side of the main gear. This design lets power transmit from the cog wheel (main gear) to the axle regardless of the axle's vertical up-and-down movement from bogie springing — and one motor drives two wheels in this arrangement. In Bo-Bo Jacquemin drives specifically, the chain is: traction motor pinion → intermediate gear → main gear/main cog wheel → cardan ring/driving ring → hollow shaft → driving ring at the hollow shaft's other end → wheel. Jacquemin transmission is designed for a tractive effort of 15 tonnes per bogie.

Quill Drive

Used on WAG/2. Consists of the traction motor pinion, an intermediate gear, and the main gear. The main gear wheel mounts on two taper roller bearings and couples flexibly to a hollow shaft surrounding the axle through ten pieces of cylindrical quill rubber — this arrangement absorbs the relative motion between the axle and the gear wheel.

WN Coupling Drive — Real Misalignment Tolerances

Used on WAM/6B and YAM. WN (Westinghouse Nippon) coupling consists of two hubs/pinions with external gear teeth engaging ring gears with internal teeth, inside each section of a two-piece sleeve housing bolted together as a single unit. The external teeth are crowned (rounded) on their sides and top; the internal teeth are straight-sided, without crown. The whole assembly is fully enclosed with lubricated rubber seals. The driving pinion in the gear box mounts on roller bearings and drives the main gear wheel.

Rotor Hollow Shaft Drive — Real Component List

Used on WAG/6A. The drive/transmission consists of a torsion shaft passing through the centre of a hollow rotor; one end of the torsion shaft connects to the hollow rotor shaft via a gear coupling. The couplings in the transmission absorb the various relative movements between motor and gear unit caused by bogie-spring action and by axle movement over track irregularities. The gear coupling's axial clearance lets the locomotive axle move laterally relative to the motor; the torsional resilience of the shaft and rubber coupling compensates for rotor-torque pulsation. Tooth coupling for the hollow-rotor-design motor permits large axial movements and angular displacements; the rubber coupling absorbs both angular and axial movements while simultaneously damping torque pulsation.

Advantages — Real Summary by Drive Type