Patent ID: 7566287

Claim:
A clutch device for an automatic transmission, comprising: (a) a clutch drum supporting frictional coupling elements on an inner circumferential surface thereof, (b) a clutch piston disposed radially outwardly of the clutch drum, and (c) a rotary speed sensor disposed radially outwardly of the clutch piston and operable to detect a rotating speed of the clutch piston, wherein: said clutch piston has an inner spline for engagement with an outer spline of said clutch drum to prevent relative rotation between said clutch piston and said clutch drum; and said clutch piston further has a plurality of recesses formed in an outer circumferential surface thereof and corresponding to respective teeth of said inner spline, and a plurality of oil holes formed therethrough at an axial position of the clutch device at which said rotary speed sensor is located, said recesses and said oil holes being equally spaced apart from each other in a circumferential direction of said clutch piston, and cooperating to provide a sensed portion to be sensed by said rotary speed sensor.