Clutch assembly and improved low pressure control therefor

A clutch assembly (35) is disclosed of the type which can retard rotation of an output member (27) relative to an input member (33). The clutch assembly includes discs (59, 61) fixed for rotation with the input and output members, respectively. Also included is a clutch apply piston (63) which defines a high pressure chamber (67), the apply piston being responsive to pressure in the high pressure chamber to apply a biasing force to the clutch discs. A low pressure piston (69) defines a low pressure chamber (79), the low pressure piston having a transverse area (A) and also including a secondary piston portion (71) extending axially into the high pressure chamber and having a transverse area (B) the volume of the high pressure chamber (67) is maintained substantially constant by a chamber piston (65) and a one-way clutch assembly (93). Changes in pressure in the low pressure chamber (79) result in amplified changes in pressure in the high pressure chamber (67) in a ratio approximately equal to the ratio of the transverse area (A) to the transverse area (B).