Improvement of Feeling of Motorcycle Acceleration by Altering the Crankpin Phase Angle

We attempt to improve the feeling of acceleration by considering the change in instantaneous torque when the throttle is opened in motorcycles equipped with parallel two cylinder engines. Feeling of acceleration and vibrations for motorcycles with five types of 400cc engines, including 3 types of engines with different crankpin phase angles varying by 90° each along with two variations in the firing interval were assessed by sensory evaluation and instruments. As the result, it was found that there is a correlation between the feeling of acceleration and the change in instantaneous torque caused by alteration of the crankpin phase angle. It was therefore determined that the feeling of acceleration could be improved by using a crankpin phase angle of 270° relative to crankpin phase angle of 180 or 360° conventionally used in parallel two cylinder engines.