| 摘要 |
A portable electric impact drill, wrench or an analogous power tool wherein the motor shaft drives the intermediate shaft of a two-speed transmission which rotates the tool spindle. The transmission has a first gear rigid with the intermediate shaft and meshing with a second gear which is rotatable on the tool spindle but can drive the spindle by way of an overrunning clutch when the spindle is to rotate at the lower of two speeds. A third gear which is rigid with the spindle meshes with a fourth gear which is rotatable and axially movable on the intermediate shaft. The latter has a transverse bore for two balls which are biased apart by a helical spring to bear against the internal surface of the fourth gear. This fourth gear has an axial bore including a larger-diameter portion which receives portions of the balls in one axial position of the fourth gear whereby the intermediate shaft can rotate relative to the fourth gear to drive the spindle by way of the first and second gears and the overrunning clutch. A smaller-diameter portion of the axial bore in the fourth gear communicates with two axially parallel grooves which receive portions of the balls in a second axial position of the fourth gear whereby the latter drives the spindle by way of the third gear. The overrunning clutch then enables the spindle to rotate relative to the second gear. |
