Abstract: An apparatus for use in turning steerable vehicle wheels includes a rotatable shaft that is rotatable relative to the vehicle to effect turning movement of the steerable vehicle wheels. A ball nut assembly is connected with an externally threaded portion of the rotatable shaft. The ball nut assembly moves axially relative to the rotatable shaft upon rotation of the rotatable shaft relative to the ball nut assembly. A steering member is connected to the ball nut assembly and at least one steerable vehicle wheel. The steering member moves with the ball nut assembly relative to the shaft. An electrical motor is connected with the rotatable shaft. The motor is operable to effect rotation of the rotatable shaft relative to the ball nut assembly to turn the steerable vehicle wheels.

Abstract: A power steering gear assembly 10 which is used to turn steerable vehicle wheels 50, 52 includes a piston 20 disposed in a motor cylinder 16. A series 44 of rack teeth are connected with the piston 20. A first tooth space 94 is formed between first and second teeth 80, 76 in the series 44 of rack teeth. The first tooth space 94 has a root portion 126 which includes first and second fillets 132, 136. The first fillet 132 has a larger radius of curvature 130 than the second fillet 136. The first and second fillets 132, 136 have centers of curvature which are both disposed between a central axis 104 of the first tooth space 94 and the second rack tooth 76. The center pinion gear tooth 190 has side surfaces 200 and 202 with intermediate portions 216 and 230 which are offset from continuously curving spatial envelopes 212 and 228 containing tip end portions 208 and 222 and root end portions 210 and 224 of the center pinion gear tooth.