Abstract: A rack-and-pinion steering system includes a pinion shaft having pinion teeth, a rack shaft on which rack teeth are formed which mesh with the pinion teeth; and a rack bush which supports the rack shaft slidably in an axial direction thereof. An outer circumferential surface of the rack shaft includes a first area which is a concave formed on an outer circumferential surface of the rack shaft and extending in the axial direction and a second area which is an area of the outer circumferential surface excluding the first area and lies adjacent to an end portion of the first area in the axial direction. The rack teeth are formed in the first area. A chamfered portion or a rounded portion is provided on a boundary between the end portion of the first area and the second area to chamfer or round a corner portion on the boundary.

Abstract: A rack bush for supporting a rack shaft in a rack-and-pinion steering system so that the rack shaft slides in an axial direction thereof includes a teeth side support portion and a back side support portion. Rack teeth are formed in a first area of an outer circumferential surface of the rack shaft. The teeth side support portion contacts a second area of the outer circumferential surface to support the rack shaft from a teeth side where the rack teeth are formed. The second area lies adjacent to the first area in the axial direction. The back side support portion contacts a third area of the outer circumferential surface to support the rack shaft from a back side other than the teeth side. The third area is positioned out of the first area in a circumferential direction around an axis of the rack shaft.

Abstract: A rack bush for supporting a rack shaft in a rack-and-pinion steering system so that the rack shaft slides in an axial direction thereof includes a teeth side support portion and a back side support portion. Rack teeth are formed in a first area of an outer circumferential surface of the rack shaft. The teeth side support portion contacts a second area of the outer circumferential surface to support the rack shaft from a teeth side where the rack teeth are formed. The second area lies adjacent to the first area in the axial direction. The back side support portion contacts a third area of the outer circumferential surface to support the rack shaft from a back side other than the teeth side. The third area is positioned out of the first area in a circumferential direction around an axis of the rack shaft.

Abstract: A rack-and-pinion steering system includes a pinion shaft having pinion teeth, a rack shaft on which rack teeth are formed which mesh with the pinion teeth; and a rack bush which supports the rack shaft slidably in an axial direction thereof. An outer circumferential surface of the rack shaft includes a first area which is a concave formed on an outer circumferential surface of the rack shaft and extending in the axial direction and a second area which is an area of the outer circumferential surface excluding the first area and lies adjacent to an end portion of the first area in the axial direction. The rack teeth are formed in the first area. A chamfered portion or a rounded portion is provided on a boundary between the end portion of the first area and the second area to chamfer or round a corner portion on the boundary.

Abstract: A pinion shaft (7) formed using a non-refined steel as a material comprises a shaft section (71, 72) and a pinion teeth forming section (70) connecting with the shaft section (71, 72). The pinion teeth forming section (70) comprises pinion teeth (7a) and a tooth bottom (7b). The pinion teeth forming section (70) and the shaft section (71, 72) are provided with a hardened layer (80) that has been subjected to induction hardening and tempering. The steel contains 0.45 to 0.55% by mass of C, 0.10 to 0.50% by mass of Si, 0.15 to 0.25% by mass of Mo, and 0.0005 to 0.005% by mass of B. The surface hardnesses of the pinion teeth forming section (70) and the shaft section (71, 72) are 650 to 760 HV in terms of Vickers hardness.