Power transmission shaft and method for manufacturing the same

A method for manufacturing a propeller shaft provided between a drive source and a drive wheel of a vehicle and configured to transmit a rotational force of the drive source to the drive wheel,

• the propeller shaft including
• an outer cylinder member, the outer cylinder member including an outer cylinder member main body portion and a female spline portion,
• the outer cylinder member main body portion having a cylindrical shape,
• the outer cylinder member main body portion including an outer cylinder member first end portion and an outer cylinder member second end portion as a pair of end portions thereof, the female spline portion being provided on an inner peripheral side of the outer cylinder member main body portion in a predetermined range including the outer cylinder member first end portion of these end portions,
• the female spline portion including a female spline first end portion and a female spline second end portion as a pair of end portions of the female spline portion in a direction of a rotational axis of the outer cylinder member,
• the female spline first end portion being provided at a position closer to the outer cylinder member first end portion than the female spline second end portion is,
• the propeller shaft further including
• an inner cylinder member, the inner cylinder member including an inner cylinder member main body portion and a male spline portion,
• the inner cylinder member main body portion having a cylindrical shape,
• the inner cylinder member main body portion including an inner cylinder member first end portion and an inner cylinder member second end portion as a pair of end portions thereof, the male spline portion being provided on an outer peripheral side of the outer cylinder member main body portion in a predetermined range including the inner cylinder member first end portion of these end portions, the male spline portion being able to be meshed with the female spline portion,
• the male spline portion including a male spline first end portion and a male spline second end portion as a pair of end portions of the male spline portion in a direction of a rotational axis of the inner cylinder member,
• the male spline first end portion being provided at a position closer to the inner cylinder member first end portion than the male spline second end portion is,
• wherein a tooth of the male spline portion is brought into pressure contact with a tooth of the female spline portion circumferentially adjacent thereto to generate a predetermined frictional force, by which the axial position between the outer cylinder member and the inner cylinder member is maintained,
• when one and the other of the outer cylinder member and the inner cylinder member are a first shaft member and a second shaft member, respectively,
• the first shaft member including a first spline portion that is one of the female spline portion and the male spline portion,
• the first spline portion including a first spline first end portion and a first spline second end portion as a pair of end portions of the first spline portion,
• the first spline first end portion corresponding to one of the female spline first end portion and the male spline first end portion,
• the first spline second end portion corresponding to the other of the female spline second end portion and the male spline second end portion,
• the second shaft member including a second spline portion that is the other of the female spline portion and the male spline portion,
• the second spline portion including a second spline first end portion and a second spline second end portion as a pair of end portions of the second spline portion,
• the second spline first end portion corresponding to one of the female spline first end portion and the male spline first end portion,
• the second spline second end portion corresponding to the other of the female spline second end portion and the male spline second end portion, and
• the second spline portion including a second spline tooth tip surface, a second spline tooth root surface, and a crowning portion,
• the method for manufacturing the propeller shaft comprising:
• a crowning portion formation step of forming the crowning portion in such a manner that a tooth thickness of the second spline tooth tip surface gradually increases from the second spline first end portion toward an intermediate portion of the second spline portion in the direction of the rotational axis of the second shaft member in a predetermined range including the second spline first end portion in the direction of the rotational axis of the second shaft member;
• and
• a press-fitting step of inserting the inner cylinder member first end portion of the inner cylinder member from the outer cylinder member first end portion of the outer cylinder member, and press-fitting the inner cylinder member into the outer cylinder member until the female spline portion and the male spline portion are meshed with each other.