Synthetic resin-made thrust sliding bearing

A synthetic resin-made thrust sliding bearing comprising:

• a synthetic resin-made upper casing which includes an upper annular plate-like portion, an outer cylindrical portion formed integrally on an outer annular end portion of the upper annular plate-like portion at an upper annular end portion thereof and suspended downwardly from the outer annular end portion, and an inner cylindrical portion formed integrally on an inner annular end portion of the upper annular plate-like portion at an upper annular end portion thereof and suspended downwardly from the inner annular end portion;
• a synthetic resin-made lower casing which is superposed on said upper casing so as to be rotatable about an axis of said upper casing and includes a lower annular plate-like portion and a cylindrical portion formed integrally on an annular upper surface of the lower annular plate-like portion and erected uprightly from the annular upper surface;
• a synthetic resin-made thrust sliding bearing piece which is interposed between said upper casing and said lower casing and includes an annular plate-like portion in contact with an annular lower surface of the upper annular plate-like portion at an annular upper surface thereof so as to be rotatable about the axis of said upper casing and in contact with the annular upper surface of the cylindrical portion of said lower casing at an annular lower surface thereof and a cylindrical portion formed integrally on an inner annular end portion of the annular plate-like portion at an upper annular end portion thereof and suspended downwardly from the inner annular end portion;
• an outer elastic seal member which is in contact with an outer surface of the cylindrical portion of said lower casing at an inner elastically deformable lip portion thereof formed integrally on a cylindrical inner surface thereof in such a manner as to project diagonally inwardly and upwardly from the cylindrical inner surface and which is in contact with an inner surface of the outer cylindrical portion of said upper casing at an outer elastically deformable lip portion thereof formed integrally on a cylindrical outer surface thereof in such a manner as to project diagonally outwardly and downwardly from the cylindrical outer surface;
• and
• an inner elastic seal member which is in contact with an inner surface of the cylindrical portion of said lower casing at an outer elastically deformable lip portion thereof formed integrally on a cylindrical outer surface thereof in such a manner as to project diagonally outwardly and upwardly from the cylindrical outer surface and which is in contact with an outer surface of the inner cylindrical portion of said upper casing at an inner elastically deformable lip portion thereof formed integrally on a cylindrical inner surface thereof in such a manner as to project diagonally inwardly and downwardly from the cylindrical inner surface,
• wherein an annular lower end surface of the outer cylindrical portion of said upper casing opposes the annular upper surface of the lower annular plate-like portion of said lower casing with a gap therebetween,
• the inner surface of the outer cylindrical portion of said upper casing has a truncated cone-shaped inner surface which is continuously connected to the lower surface of the upper annular plate-like portion and with which the outer elastically deformable lip portion of said outer elastic seal member is in contact,
• the outer surface of the cylindrical portion of said lower casing has a small-diameter cylindrical outer surface with which the inner elastically deformable lip portion of said outer elastic seal member is in contact, a large-diameter cylindrical outer surface having a larger diameter than the small-diameter cylindrical outer surface, and an annular stepped surface which is disposed between the small-diameter cylindrical outer surface and the large-diameter cylindrical outer surface and with which an annular lower surface of said outer elastic seal member is in contact,
• the outer surface of the inner cylindrical portion of said upper casing has a large-diameter cylindrical outer surface which is continuously connected to the lower surface of the upper annular plate-like portion and a small-diameter cylindrical outer surface which is continuously connected to the large-diameter cylindrical outer surface and has a smaller diameter than the large-diameter cylindrical outer surface, and with which the inner elastically deformable lip portion of said inner elastic seal member is in contact,
• the inner surface of the cylindrical portion of said lower casing has a small-diameter cylindrical inner surface continuously connected to an annular inner surface of the lower annular plate-like portion of said lower casing, a large-diameter cylindrical inner surface having a larger diameter than the small-diameter cylindrical inner surface and continuously connected to the annular upper surface of the cylindrical portion of said lower casing, an intermediate cylindrical inner surface having a larger diameter than the small-diameter cylindrical inner surface but having a smaller diameter than the large-diameter cylindrical inner surface and with which the outer elastically deformable lip portion of said inner elastic seal member is in contact, a lower annular stepped surface which is disposed between the small-diameter cylindrical inner surface and the intermediate cylindrical inner surface and with which an annular lower surface of said inner elastic seal member is in contact, and an upper annular stepped surface disposed between the intermediate cylindrical inner surface and the large-diameter cylindrical inner surface,
• the annular lower end surface of the inner cylindrical portion of said upper casing, which is continuously connected to the small-diameter cylindrical outer surface of the inner cylindrical portion of said upper casing, opposes the lower annular stepped surface of the cylindrical portion of said lower casing with a gap therebetween, and
• the cylindrical portion of said thrust sliding bearing piece is disposed between the large-diameter cylindrical outer surface of the outer surface of the inner cylindrical portion of said upper casing and the large-diameter cylindrical inner surface of the inner surface of the cylindrical portion of said lower casing.