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HAST Drive uses a meshing clutch to change speeds, reducing power transmission losses. The motor connected to the transmission has three functions: Gear control, engine power assist and electricity generation.
The structure of a HAST Drive
The engine stops when the train is at rest, to reduce noise at stations. The train is driven by the motor when it starts moving. The engine starts when the train reaches a certain speed, and motor-assisted drive, powered by the engine and the motor, is used for acceleration. The battery is charged when the train is coasting. After repeated acceleration and coasting, the brake acts to stop the train at the station. At that stage, the battery is charged with power from the wheels. Braking energy, which was previously dispersed as heat etc., is recovered as electricity and put to effective use.