Clutch mechanism and power tool having same

A power-driven tool, comprising:

• a motor;
• an output shaft;
• a transmission configured to transmit a torque generated by the motor to the output shaft;
• and
• a clutch configured to selectively disengage torque transfer from the transmission to the output shaft when an output torque exceeds a threshold torque value, the clutch including:
• a clutch selector actuatable to select the threshold torque value;
• a retaining ring moveably coupled to the clutch selector to move relative to the transmission in response to selection of the threshold torque value by actuation of the clutch selector;
• a clutch engagement member selectively engageable with a component of the transmission to interrupt torque transfer from the transmission to the output shaft;
• and
• a biasing mechanism coupled between the retaining ring and the clutch engagement member, the biasing mechanism including at least one spring member having a variable spring rate,
• wherein a biasing force applied to the clutch engagement member by the biasing mechanism corresponds to the selected threshold torque value and can be varied in a non-linear manner in accordance with movement of the retaining ring that adjusts the biasing force in accordance with the variable spring rate.