Oil seal and power transmission apparatus

A power transmission apparatus comprising:

• a hollow rotary shaft;
• an oil seal for sealing the hollow rotary shaft, the hollow rotary shaft formed with an internal flow passage through which oil flows and also with an oil discharge port from which the oil flies out as the hollow rotary shaft rotates, comprising:
• a fixed portion that is fixedly attached to a case of the power transmission apparatus;
• a seal portion that seals the rotary shaft at a position that is axially offset from the fixed portion and allows the rotary shaft to rotate;
• and
• a radiator portion that is disposed so as to overlap with the oil discharge port in an axial direction of the rotary shaft, is formed from a metallic material between the fixed portion and the seal portion, is formed in a substantially tapered shape such that a diameter of a tapered portion decreases steadily towards the seal portion, receives the oil that flies out as the rotary shaft rotates, and dissipates heat generated by the seal portion by exchanging heat with the oil,
• wherein the oil discharge port is an opening formed on an outer circumferential surface of the hollow rotary shaft, and
• wherein the hollow rotary shaft comprises a first shaft portion and a second shaft portion, an outer surface of the first shaft portion being disposed within an inner hollow part of the second shaft portion, and the opening of the discharge port is formed by an outer circumferential surface of the first shaft portion and an end of the second shaft portion.