US Patent 7736264 Eight speed automatic transmission with dual area clutch piston

A transmission includes four planetary gearsets and five torque transmitting devices operative to provide eight forward speed ratios. At least one of the torque transmitting devices is engaged during two different speed ratios. The torque transmitting device includes a piston partially defining two separate and independently pressurizable chambers. Accordingly, the transmission enables both chambers to be pressurized for speed ratios in which a high torque capacity is required of the torque transmitting device, and only one of the chambers to be pressurized for speed ratios in which a low torque capacity is required of the torque transmitting device.