Throttle valve device and method for manufacturing throttle valve device

A method for manufacturing a throttle valve device having a valve that opens and closes a cylindrical passage, the manufacturing method comprising:

• forming a round end hole on one lateral side of a shaft in at least one end part of the shaft;
• forming a slit passing through the shaft on a central axis of the shaft, the forming the slit including moving a cutter having a disk shape from another lateral side of the shaft to the one lateral side of the shaft while rotating the cutter such that a cutting blade of the cutter moves in a direction from the one end part toward another end part of the shaft, a diameter of the cutter being larger than a diameter of the valve by 10% to 40% of the diameter of the valve;
• attaching a pair of bearings and the shaft to a body defining the cylindrical passage such that the shaft is orthogonal to the cylindrical passage, the pair of bearings rotatably support the shaft on both sides of the cylindrical passage, and at least a part of the round end hole is covered by the body;
• and
• inserting the valve into the slit such that the valve is rotatable together with the shaft, the valve having a circular plate shape with a thickness substantially the same as a width of the slit, wherein
• the forming the round end hole and the forming the slit are performed such that a diameter of the round end hole becomes equal to the width of the slit or larger than the width of the slit by 30% of the width of the slit or less, a depth of the round end hole from the one lateral side of the shaft in a radial direction of the shaft becomes deeper than a depth at which the round end hole contacts the slit, and an angle between an inner surface of an end of the slit and the round end hole becomes a predetermined angle.