Patent ID: 7806016

Claim:
A worm gear mechanism, comprising: a worm on a drive side, the worm having a screw thread; a torque-transmitting worm wheel having first teeth for meshing with the screw thread of the worm to transmit a torque from the worm to a load side, said torque-transmitting worm wheel having an outer peripheral surface; and an auxiliary worm wheel disposed concentrically with the torque-transmitting worm wheel and having second teeth for meshing with the screw thread of the worm, said second teeth of the auxiliary worm wheel surrounding the outer peripheral surface of the torque-transmitting worm wheel and lying over the torque-transmitting worm wheel; wherein said screw thread of the worm has a length which is approximately equal to an actual meshing length in which the screw thread actually meshes with the first teeth of the torque-transmitting worm wheel, and further said screw thread actually meshes with the second teeth of the auxiliary worm wheel also only within the length which is approximately equal to said actual meshing length, the first teeth of the torque-transmitting worm wheel mesh at a first meshing portion of the screw thread of the worm, the second teeth of the auxiliary worm wheel mesh at a second portion of the screw thread of the worm, the second meshing portion is provided not to be in a plane extending from the first meshing portion in a direction of tooth width of the torque-transmitting worm wheel, and the second meshing portion is positioned radially outwardly of the first meshing portion.