Gear shifting power tool

A rotatably-driven, torque-responsive, gear shift device comprising:

• a drive spindle having a first end, a second end, a first hole, a second hole, and a partially hollow interior volume;
• a plunger having a first tapered end and a second tapered end, the plunger positioned within the partially hollow interior volume of the drive spindle;
• a reset biasing means coupled to the second tapered end of the plunger and positioned in the partially hollow interior volume of the drive spindle;
• a first ball movably positioned within the first hole of the drive spindle and contacting the plunger near the first tapered end;
• a second ball movably positioned within the second hole of the drive spindle and contacting the plunger near the second tapered end;
• an inertial device coupled to the drive spindle near the first hole and in contact with the first ball;
• a drive clutch member drivably engaged to the drive spindle and having an inner axial groove for receiving a portion of the second ball;
• and
• a biasing means between the drive spindle and the drive clutch member.

A gear shifting power tool comprising:

• a casing;
• a motor disposed within the casing;
• a rotatably-driven, torque-responsive, gear shift device having a first end and a second end, rotatably coupled to the motor at the first end, the gear shift device including:
• a drive spindle having a first end, a second end, a first hole, a second hole, and a partially hollow interior volume;
• a plunger having a first tapered end and a second tapered end, the plunger positioned within the partially hollow interior volume of the drive spindle;
• a reset biasing means coupled to the second tapered end of the plunger and positioned in the partially hollow interior volume of the drive spindle;
• a first ball movably positioned within the first hole of the drive spindle and contacting the plunger near the first tapered end;
• a second ball movably positioned within the second hole of the drive spindle and contacting the plunger near the second tapered end;
• an inertial device coupled to the drive spindle near the first hole and in contact with the first ball;
• a drive clutch member drivably engaged to the drive spindle and having an inner axial groove for receiving a portion of the second ball;
• and
• a biasing means for applying a force between the drive spindle and the drive clutch member;
• a driven clutch member having a ring gear;
• and
• a gear set drivably engaged with the ring gear of the driven clutch member.

A method for shifting gears, in response to an applied resistive torque, from an output rotational motion having relative high speed and low torque to an output rotational motion having relative low speed and high torque, the method comprising the steps of:

• engaging a drive clutch member to a driven clutch member where the drive clutch member has an inner axial groove and is drivably engaged to a drive spindle having a partially hollow interior volume, a first hole, a second hole, a first end, and a second end;
• biasing a plunger longitudinally away from the second end of the drive spindle where the plunger is positioned in the partially hollow interior volume of the drive spindle and contains a first tapered end and a second tapered end;
• rotating the drive spindle with a motor;
• applying a radially inward force to a first ball tending to force the first ball radially inward through the first hole towards plunger to provide a longitudinal force on the plunger opposite the biasing applied to the plunger in the step of biasing a plunger longitudinally;
• applying a torque to the drive spindle that resists the rotation of the drive spindle produced by the motor;
• disengaging the drive clutch member from the driven clutch member in response to the step of applying a torque to the drive spindle that resists the rotation of the drive spindle by compressing a spring between the drive clutch member and the drive spindle so that the drive clutch member moves longitudinally away from the driven clutch member and the inner axial groove positions over the second hole in the drive spindle;
• moving the plunger longitudinally towards the second end of the drive spindle in response to the step of applying a radially inward force on the first ball and the step of disengaging the drive clutch member from the driven clutch member;
• and
• forcing a second ball radially outward through the second hole of the drive spindle and into the inner axial groove of the drive clutch member in response to moving the plunger longitudinally towards the second end of the drive spindle.