Patent ID: 7637100

Claim:
An automatic transmission comprising: a transmission case, a speed change apparatus enclosed in the transmission case, a torque converter having a pump impeller that is connected to and rotated by a drive source and a turbine runner that is connected to an input shaft of the speed change apparatus and rotated in accompaniment with the rotation of the pump impeller, and an oil pump that is driven to rotate by the drive source via the torque converter so as to discharge oil, wherein: a drive gear of the oil pump is connected to the pump impeller and fitted into a notch formed in an end portion of an impeller hub that extends toward the speed change apparatus in an axial direction thereof; the impeller hub is supported rotatably on an oil pump wall which is fixed to the transmission case and encloses the drive gear; an oil seal comprising a lip portion fitted to the impeller hub is mounted between an inner peripheral surface of the oil pump wall and an outer peripheral surface of the impeller hub; the impeller hub is inserted into the oil seal from the lip portion side thereof with an end portion in which the notch is formed leading and such that the lip portion has a tightening margin relative to the impeller hub; the impeller hub has a first chamfer portion formed in a bottom portion outer peripheral edge portion of the notch as an inclined surface that decreases radially in an axial direction of the impeller hub toward an end portion of the impeller hub; a width of the first chamfer portion in the axial direction increases from sides of the notch circumferentially toward a central portion of the notch; and wherein the first chamfer portion has a recessed curved surface.