Dynamic Model of the Roller Float Condition in One-Way Clutch (OWC) Applied to Motorcycle Engine Starters

In motorcycle engine starter the rotation of an electric motor (starter motor) is transmitted to the crankshaft to allow engine start up; as the engine starts, the rotation of the crankshaft should not be transmitted to the electric motor armature to avoid system failure due to the high rotational speed of the internal combustion engine. In order to obtain this function the starter system has a one-way clutch (OWC) assembled between the crankshaft and the driven gear that is rotated by the starter motor. The OWC assembly is held in position by the armature shaft of the electric starter motor. Considering the OWC dynamic performance, the study of the roller float condition can improve product durability by avoiding excessive contact between roller and race, the components responsible for the torque transmission. Assuming that "roller float" condition happens because the OWC in motorcycle starters is permanently engaged to the engine crankshaft, this can lead to a potential failure mode due to the premature wear; hence this is an important design aspect to be considered during OWC development for motorcycle starters systems. To perform this study a lumped parameter model based on a single roller analysis was developed. The model represents the behavior of the roller when the outer cam is increasing its angular velocity. It comprehends the centrifugal force generated by the rotational speed, the elastic contact that is the focus of the investigation and the roller and cam spring data. All those variables were determined to influence the roller float condition. By changing design variables in the model the angular velocity in which roller float occurs can be modified. Experimental validation has confirmed the simulation results and the potential application of the dynamic model to improve roller clutch performance in the early phases of the Product Development Process.