Patent ID: 7780172

Claim:
A rotation shaft seal provided with a rubber lip portion disposed between a housing and a rotation shaft to slide on the rotation shaft and a supporting member to receive the lip portion from a back face on a low-pressure side comprising a construction in which a cross-sectional configuration of the lip portion in free state is having a maximum thickness portion in an area received by the supporting member and provided with a diminishing lip end portion gradually reducing the thickness from the maximum thickness portion to a tip end of the lip, when a back face inclination angle of a back face of the lip end portion to an axis of the rotation shaft is expressed as α and an inclination angle on pressure-receiving side of an inclining face of the lip end portion on the high-pressure side is expressed as β, relational express ons 15°≦α≦30° and 1.7≦β/α≦3.5 are fulfilled, and a distribution curve of contact pressure under pressure-receiving state in which the lip end portion contacts the rotation shaft is hill-shaped and a peak is on the low-pressure side to a center in axis direction, wherein the tip end of the lip is composed of a ring end face, ring-shaped when observed in the axis direction of the rotation shaft and inclined at an angle so that the tip end increases in diameter parallel to the axis of the rotation shaft toward the high-pressure side, and, when an end face inclination angle of the ring end face to the axis of the rotation shaft is expressed as γ, a relational expression 60°≦γ≦90° is fulfilled; a width dimension of the ring end face is set to be 0.5 mm to 1.5 mm; and the maximum thickness portion of the lip portion exists on a position of a corner portion where the inclining face on the high-pressure side, of which cross section in free state is straight, and a straight portion of cylindrical external configuration parallel to the axis are crossing, and the position of the corner portion is disposed on the high-pressure side to a tip end on the high-pressure side of the supporting member.