Screw mechanism and an electric power steering apparatus equipped with a worm mechanism

摘要

Worm gear mechanism (44; 44A) is provided which includes a worm (47), a torque-transmitting worm wheel (48) and an auxiliary worm wheel (49). In order to secure a sufficient face width of the torque-transmitting worm wheel, a pitch diameter (D2) of the auxiliary worm wheel is set to be greater than a pitch diameter (D1) of the torque-transmitting worm wheel. Thus, undesired backlash can be eliminated by the auxiliary worm wheel meshing with the worm with a different meshing phase from the torque-transmitting worm wheel.