Patent ID: 8528687

Claim:
An electric power assisted steering system of the kind in which a motor is connected to a portion of a steering mechanism through a worm carried by a worm shaft and a wheel carried by an output shaft operatively coupled to the steering mechanism, the shaft being supported in at least one bearing assembly, in which the bearing assembly has some internal clearances supports the worm shaft in such a manner that it is free to pivot through an angle in planes which include its own axis due to a degree of axial free play of the bearing assembly, and further in which the bearing assembly comprises an inner race having a groove, an outer race having a groove, and a plurality of ball bearings located between the inner and outer races, and in which the inner race groove defines an inner ball bearing path which is round and the outer race groove defines an outer ball bearing path which is not round, wherein along a central axis of the bearing assembly and between the ball bearings and at least the outer race groove there is defined at least a first radial clearance and at least a second radial clearance which is greater than the first radial clearance for the ball bearings at different points around the bearing assembly such that the ball bearings permit a greater freedom of movement of the inner race relative to the outer race in a first radial direction than in a second radial direction that is orthogonal to the first direction.