US Patent 7350631 Automatic transmission

An automatic transmission includes a clutch drum formed, by press forming, with splines including recessed portions and raised portions, and engaging with clutch plates; and a rotational speed measuring device configured to measure a rotational speed of the clutch drum, and including a surface sensing device disposed outside an outer surface of the clutch drum, and configured to sense movement of the recessed portions and the raised portions of the splines. The clutch drum includes first openings each formed in one of the recessed portions recessed radially inwards, and each confronting the clutch plates radially.