| 摘要 |
PROBLEM TO BE SOLVED: To provide a good shift timing by detecting by means of detecting means that it reaches an intersection point of relative curves between a motor output before speed changing and an output torque after a speed mechanism part is passed, and the motor output after speed change and the output torque after the speed change mechanism part is passed. SOLUTION: An intersection point of both curves is found out from a relative curve between a motor output PH before speed change and the motor output PL after speed change, and a tool output torque, and the intersection point is set to a speed change point CP from a high speed rotation low torque condition to a low speed rotation high torque condition. A tool output rotational speed NX in the speed change point CP is found out from a relative curve between the tool output rotational speed NH before speed change and a tool output torque, an electromagnetic driving part is operated at the time point when tool output rotational speed N measured by a rotational speed detecting means reaches a value NX, speed change is carried out at a timing capable of utilizing the maximum output of a motor preferentially. It is thus possible to balance a work amount and work speed with each other at a high level. |
