Dog clutch and method for overdrive

A clutch adapted for engagement in a transmission having a fixed housing at least partially covering an electric power unit having a rotatable hub and sun gear, said clutch comprising:

• a clutch cavity defined by said fixed housing and said sun gear and having a fluid inlet and a spring;
• a piston slidably movable within said clutch cavity, said piston being in fluid flow communication with said fluid inlet for causing movement in one direction and in biased relationship with said spring for causing movement in the opposite direction;
• a plurality of first splines on said fixed housing and a plurality of second splines on said sun gear;
• a plurality of third splines on said piston for engaging with said plurality of second splines and not with said plurality of first splines when said piston has moved in said one direction and for engaging with both of said plurality of first splines and said plurality of second splines when said piston has moved in said opposite direction;
• wherein said spring biases said piston to engage the fixed housing with the sun gear when fluid pressure at said fluid inlet is insufficient to compress said spring;
• wherein sufficient fluid pressure at said fluid inlet forces said piston to disengage the sun gear from the fixed housing;
• and
• wherein when fluid pressure is decreased in said clutch cavity, said spring forces said piston to reengage the sun gear with the fixed housing.