Stub shaft, power transmission shaft, and method for manufacturing a stub shaft

A propeller shaft comprising:

• a pipe portion connected to a rotational shaft configured to transmit a driving force of a vehicle;
• and
• a stub shaft, the stub shaft including
• a flange portion welded to the pipe portion and including a tubular portion and a bottom portion,
• the tubular portion being hollowly formed, the tubular portion having a first end portion and a second end portion, which are both end portions in an axial direction, assuming that the axial direction is a direction along a rotational axis of the rotational shaft, the first end portion of the two end portions being welded to the pipe portion,
• the bottom portion being provided on the second end portion side, the bottom portion serving as a bottom of the tubular portion,
• a shaft portion connected to the flange portion and having an intermediate portion and a thin shaft portion,
• the intermediate portion being connected to the bottom portion, the intermediate portion being formed so as to have a diameter smaller than the flange portion in a radial direction with respect to the rotational axis,
• the thin shaft portion being connected to the intermediate portion, the thin shaft portion being formed so as to have a diameter smaller than the intermediate portion in the radial direction, and
• a heat hardening treatment portion provided on a surface of the shaft portion, the heat hardening treatment portion being provided on the shaft portion side with respect to a boundary portion in the axial direction, assuming that the boundary portion is a portion where an imaginary line forming an angle of 45 degrees with the rotational axis is connected to a surface between the flange portion and the shaft portion in a cross-section passing through the rotational axis.

A method for manufacturing a stub shaft,

• the stub shaft including
• a flange portion including a tubular portion and a bottom portion,
• the tubular portion being hollowly formed, the tubular portion having a first end portion and a second end portion, which are both end portions in an axial direction, assuming that the axial direction is a direction along a rotational axis of the rotational shaft, the first end portion of the two end portions being welded to a pipe portion connected to the rotational shaft configured to transmit a driving force of a vehicle,
• the bottom portion being provided on the second end portion side, the bottom portion serving as a bottom of the tubular portion,
• a shaft portion connected to the flange portion and having a first outer diameter portion and a second outer diameter portion,
• the first outer diameter portion being connected to the bottom portion, the first outer diameter portion being formed so as to have a diameter smaller than the flange portion in a radial direction with respect to the rotational axis,
• the second outer diameter portion being connected to the first outer diameter portion, the second outer diameter portion being formed so as to have a diameter smaller than the first outer diameter portion in the radial direction, and
• a heat hardening treatment portion provided on a surface of the shaft portion, the heat hardening treatment portion being provided on the shaft portion side with respect to a boundary portion in the axial direction, assuming that the boundary portion is a portion where an imaginary line forming an angle of 45 degrees with the rotational axis overlaps a surface between the flange portion and the shaft portion in a cross-section passing through the rotational axis,
• the method for manufacturing the stub shaft comprising:
• a placement step of placing the second outer diameter portion of the shaft portion inside an annular coil used in a heat hardening treatment;
• and
• a high-frequency quenching step of forming the heat hardening treatment portion by moving the coil from an end portion of the second outer diameter portion to a position just before the boundary portion in the axial direction.