Patent ID: 8511186

Claim:
An engine starter, comprising: a motor that includes a motor shaft that rotates in response to a motor driving force; a reduction mechanism to engage with the motor shaft and transmit a driving force to a drive shaft; a unidirectional rotation clutch system that is helical-splined to the drive shaft, the clutch system being movable from an inactive position on a base end side of the drive shaft to an active position on a tip end side of the drive shaft when relative rotation occurs in a predetermined rotating direction from a side of the drive shaft, and further being structured such that the motor driving force can be transmitted while an engine driving force cannot be transmitted when an engine starts; and a pinion gear that connects with the clutch system and engages with a ring gear on a side of the engine, wherein: the clutch system comprises: a clutch inner; a clutch outer; a clutch roller that is interposed between the clutch outer and the clutch inner; and a spring that urges the clutch roller, the clutch roller slips while engaging with the clutch inner when a torque impacts the drive shaft from the side of the engine, the clutch roller is made of bearing steel, and a gas soft nitriding treatment is applied to a surface of the clutch roller such that an external phase and an internal phase are formed on the surface of the bearing steel, wherein the gas soft nitriding treatment is not applied to a surface of the clutch inner and the gas soft nitriding treatment is not applied to a surface of the clutch outer, so that a nitride phase is formed, where a mixed phase of Fe 2+3 N and Fe 3 C is formed on the surface as the external phase and a diffused phase of Fe 4 N is formed inside the external phase as the internal phase.