Patent ID: 7383932

Claim:
A clutch hub for use in a wet-type multiple disc clutch assembly that has a cylindrical clutch case with a female spline formed on an inner peripheral surface of the clutch case, the clutch hub having a sidewall and an opening at respective ends of a cylindrical portion, an outer peripheral surface of which is formed with a male spline radially opposed to the female spline, the clutch assembly having friction plates and separator plates alternately disposed to be slidable on the female spline and the male spline, the male spline of the clutch hub being formed by radially convex and concave portions defining crests and troughs, respectively, of spline teeth, the crests having oil passages therethrough, the clutch hub having oil dams formed as deformations of inner peripheral surfaces of the crests at a position between the opening and the sidewall of the clutch hub, the clutch hub being characterized by: first and second pairs of concave grooves that modify deformation of the spline teeth due to forming of the oil dams; the first pairs of concave grooves extending axially on outer peripheral surfaces of corresponding crests along opposite edge regions thereof; and the second pairs of concave grooves extending axially on outer peripheral surfaces of corresponding troughs along opposite edge regions thereof.