An Investigation on Cranking Torque Reduction for Four-Stroke Motorcycle Engine

This study focuses on developing a cranking torque reduction strategy for a motorcycle with idling-stop system. At first, experiments are done to measure the electric current consumption of starting motor which is then converted into cranking torque by the motor torque constant. The experimental results also indicate that the piston position, after the engine is stopped, always remains at the bottom dead center of compression stroke. This will further increase the cranking torque for the next engine start due to static friction and compression pressure. This paper, therefore, proposes to retrofit the original generator of motorcycle as a motor/generator with the same operation power. The motor/generator could be worked in motor mode to assist the starting motor to crank the engine, and hence the instantaneous power provided by the starting motor could be reduced to extend its life time. Using motor/generator, this paper also proposes a piston positioning strategy that could avoid the piston position from remaining at bottom dead center of compression stroke after the engine is stopped.