Abstract: Lubricating oil supply holes are drilled into a first member that is fitted to a plurality of first annular plates by a spline. Of splines to which each lubricating oil supply hole corresponds, lubricating oil grooves provided in the plurality of first annular plates do not overlap the splines on at least one of the front and rear surfaces of the first annular plates, and therefore lubricating oil flowing out of the lubricating oil supply holes is dispersed in a circumferential direction and flows from the inner periphery to the outer periphery of the first annular plates, rather than gathering in each lubricating oil groove and flowing in an outer peripheral direction. As a result, a force generated by an axial lubricating oil flow, which acts in a direction for causing the second annular plates to contact friction materials on the first annular plates, is suppressed, leading to a reduction in drag torque.

Abstract: Lubricating oil supply holes are drilled into a first member that is fitted to a plurality of first annular plates by a spline. Of splines to which each lubricating oil supply hole corresponds, lubricating oil grooves provided in the plurality of first annular plates do not overlap the splines on at least one of the front and rear surfaces of the first annular plates, and therefore lubricating oil flowing out of the lubricating oil supply holes is dispersed in a circumferential direction and flows from the inner periphery to the outer periphery of the first annular plates, rather than gathering in each lubricating oil groove and flowing in an outer peripheral direction. As a result, a force generated by an axial lubricating oil flow, which acts in a direction for causing the second annular plates to contact friction materials on the first annular plates, is suppressed, leading to a reduction in drag torque.

Abstract: A friction material has a resin amount distribution that is the largest at a portion near a non-friction surface, that becomes lower toward an inside and that is the lowest at a portion near a friction surface. For example, such friction material is manufacture as follows. First, two friction materials are overlapped while the friction surfaces faced with each other. Then, the friction materials are dried at a room temperature. At this time, the resin has such a characteristic as to move while dragged by a solvent that dries from the non-friction surface located outside. Using such characteristic, the resin amount at the portion near the friction surface is lessened. Then, a temperature at the friction surface is made low and a temperature at the non-friction surface is made high in a drying step of the fiction material. Thereby, the resin amount at the portion near the friction surface is lessened.

Abstract: In a segment-type wet friction material, an inner peripheral left corner of one segment piece and an inner peripheral right corner of another segment piece are respectively cut off at a fixed angle to a center line of an oil groove. The oil grooves have first oil grooves and second oil grooves. The second oil groove has nearly a uniform width. The first oil groove has an inner peripheral corner portion that is broadened to the center line of the oil groove from a fixed height. In case of being assembled in an automatic transmission, when the segment-type friction material rotates in one direction, an automatic transmission fluid supplied from an inner circumference bumps and touches the portion that is broadened at the fixed angle at a rear side in the rotating direction. Thus, the automatic transmission fluid is positively supplied to a friction surface of the segment piece so as to restrain a contact between a separator plate and the friction surface.