Linear motion shaft for steering device, steering device, and method of manufacturing these

A method for manufacturing a linear motion shaft for a steering device,

• the linear motion shaft comprising:
• a first shaft portion having a first input section on an outer peripheral surface thereof to which a driving force for making linear motion in an axial direction is input, a second shaft portion, and a joint between the first shaft portion and the second shaft portion,
• the manufacturing method comprising:
• a process of manufacturing the first shaft portion, and
• a process of connecting the first shaft portion and the second shaft portion by friction welding,
• the process of manufacturing the first shaft portion including a process of forming the first input section in a material for the first shaft portion and a process of forming a gripped section for centering on an outer peripheral surface of an end portion in the axial direction of the first shaft portion on a side connected to the second shaft portion based on the first input section after forming the first input section, and
• the friction welding is performed by abutting an end portion in the axial direction of the first shaft portion and an end portion in the axial direction of the second shaft portion in a state where the gripped section of the first shaft portion is gripped by a first gripping tool for centering and the second shaft portion is gripped by a second gripping tool for centering,
• wherein the friction welding is performed while relatively rotating the first shaft portion and the second shaft portion by rotationally driving at least one of the first gripping tool and the second gripping tool, and
• wherein the friction welding is performed while rotating the first shaft portion by rotationally driving the first gripping tool and holding the second shaft portion without rotating.

A linear motion shaft for a steering device, comprising:

• a first shaft portion having a first input section on an outer peripheral surface thereof to which a driving force for making linear motion in an axial direction is input,
• a second shaft portion,
• a joint between the first shaft portion and the second shaft portion, and
• a gripped section for centering which is provided on an outer peripheral surface of an end portion in the axial direction on a joint side of the first shaft portion and is coaxial with a portion having the first input section.