Patent ID: 7004871

Claim:
An automatic transmission apparatus comprising: a clutch drum rotating integrally with an input shaft and including a first cylindrical portion having an inner spline at an inner peripheral surface thereof; a hub including a second cylindrical portion having an outer spline for engaging with the inner spline of the clutch drum and an inwardly directed depressed portion located between two adjacent regions where the inner and outer splines engage one another; and a clearance which establishes a communication between an inner portion surrounded by the hub and an outer portion outside the clutch drum, the clearance being formed between an outer surface of the depressed portion of the hub and the inner peripheral surface of the clutch drum, the clearance possessing a radial dimension greater than a radial dimension between an inner surface of the inner spline and an outer surface of the outer spline in the two adjacent regions where the inner and outer splines engage one another.