Coupling device and improved fluid pressure system therefor

A coupling device including a rotatable housing defining a clutch cavity;

• a clutch assembly disposed in said clutch cavity and including a first clutch member fixed to rotate with said housing, and a second clutch member fixed to rotate with an output;
• said housing defining a pressure chamber, and a clutch apply member disposed in said pressure chamber and being operable to bias said first and second clutch members into torque-transmitting relationship in response to the presence of pressurized fluid in said pressure chamber;
• said coupling device including a source of said pressurized fluid, and a control valve assembly operable to vary the fluid pressure in said pressure chamber in response to variations in an input;
• said housing defining a hub portion defining an outer cylindrical surface, said housing defining a high pressure fluid passage providing fluid communication from said pressure chamber to a first port formed in said outer cylindrical surface;
• characterized by:
• (a) a stationary plenum member defining an inner cylindrical surface disposed in a surrounding relationship about said outer cylindrical surface defined by said hub portion;
• (b) said plenum member defining a high pressure fluid passage providing fluid communication from a second port formed in said inner cylindrical surface, in fluid communication with said first port formed in said outer cylindrical surface, to said control valve assembly;
• and
• (c) a first annular seal member disposed within said inner cylindrical surface adjacent said second port, to define an annular pressure region;
• and
• (d) said first annular seal member being disposed in a seal cavity and having a radial height H, greater than the radial dimension of said seal cavity, and an axial width W less than the axial width of said seal cavity, wherein said height H and said width W are selected such that said first seal member has a H/W ratio in the range of about 2.5:1 to about 5:1.