| 摘要 |
A worm gear mechanism (44) includes a worm (47), a torque-transmitting worm wheel (48) meshing with the worm, and an auxiliary worm wheel (49) disposed concentrically with the torque-transmitting worm wheel. The auxiliary worm wheel has a pitch circle diameter (D2) set to be greater than a pitch circle diameter (D1) of the torque-transmitting worm wheel and hence meshes with the worm in a meshing phase different from that of the torque-transmitting worm wheel. A screw thread (131) provided on the worm actually meshes with teeth of the torque-transmitting worm wheel along a length defined as an actual meshing length (L2). The screw thread has an effective length (L1) reduced to be approximately equal to the actual meshing length. A further embodiment discloses a first threaded part (L2, fig 12) meshing with the torque-transmitting wheel and a second part (Pib or Pic, fig 12) having a different pitch and not meshing with the torque-transmitting wheel. |
