Worm gear drives are widely employed to transmit power at high velocity ratios between shafts which do not intersect and which are usually at right angles. Such drives may be used as speed increasers but their usual use is as speed reducers in which the worm is the driver and the wheel is the driven member. Single-threaded or double-threaded worms are available and usually they are of straight cylindrical form. It is known however to configure a worm along a variable diameter locus corresponding to an arcuate locus of a radius equal to that of the pitch circle of the wheel with which it meshes, a so-called hour-glass worm.
It is always the case with worm wheel drives employing wheels with ordinary teeth that there is measurable friction between the wheel teeth and the worm groove as the two mesh together. The side surface of the worm groove inevitably slides across the face of the wheel tooth as they pass in contact. To reduce this friction designs have been proposed wherein the teeth of the wheel are replaced by rotatable members such as conical spindles, as shown for example in U.S. Pat. Nos. 1,262,932 and 1,463,687. Such spindles or conical rollers substantially eliminate skidding across the side of the worm groove during meshing. However they always present the same circumferential zone of engagement to the worm and thus they tend to flatten through wear along that zone, thus introducing slight but measurable skidding between the edge portions of the flattened zone and the worm.
It has been proposed to replace spindles with spheres such as is taught in U.S. Pat. No. 3,274,847. In that design the spheres transfer from races on the wheel to be captured between the worm and the wheel while they are in meshed engagement and transmitting torque. However, even though the spheres roll in the helical worm groove, they nonetheless are in sliding engagement with the wheel race while doing work. Sliding friction is still not eliminated. Another disadvantage of that design is that the wheel cannot be disassembled from the worm without allowing some of the spheres to fall out of the assembly because in the meshing sector of the wheel the spheres float freely and require the worm and the wheel to be together in order to stay in place.
It is a principal purpose of the present invention to provide a worm gear drive wherein spheres are utilized in place of rigid gear teeth or conical spindles but in a manner such that the spheres mesh in a helical worm groove in rolling engagement along a sphere track without any sliding engagement between the wheel and the worm or between the spheres and their wheel. The spheres are intended to present infinitely variable equators to roll on the track so that they wear uniformly and do not flatten. It is an object of the invention to achieve this effect by a cage design for each sphere which permits the sphere to mesh and roll in the worm groove while rolling freely in the cage. An additional purpose of the invention is to achieve these objects while always retaining the spheres captured in their cages so that they do not fall free from the wheel when the worm and wheel are disassembled.