Patent ID: 7188557

Claim:
A tightening tool, comprising: a motor, a driven shaft driven by the motor a tool bit driven by the driven shaft and a clutch mechanism disposed between the motor and the driven shaft, the clutch mechanism including: a driving-side clutch element driven by the motor, a driven-side clutch element mounted on the driven shaft to rotate together with the driven shaft, wherein the driven-side clutch element transmits torque of the motor to the driven shaft by moving toward the driving-side clutch element together with the driven shaft and engaging with the driving-side clutch element, while the driven-side clutch element stops transmitting the torque of the motor to the driven shaft by moving away from the driving-side clutch element and disengaging from the driving-side clutch element and an engagement speedup mechanism that speeds up engagement between the driving-side clutch element and the driven-side clutch element, wherein the engagement speedup mechanism causes the driven-side clutch element to move at higher speed than the driven shaft when the driven-side clutch element moves toward the driving-side clutch element together with the driven shaft so as to engage with the driving-side clutch element.