Fluid pressure operated pump or motor with secondary valve means for minimum and maximum volume chambers

A rotary fluid pressure device comprising:

• (a) housing means defining fluid inlet means and fluid outlet means;
• (b) an internal gear set associated with said housing means and including an internally-toothed member, and an externally-toothed member eccentrically disposed within said externally-toothed member for relative movement therebetween, the teeth of said members interengaging to define expanding and contracting volume chambers during said relative movement, one of said members having rotational movement about its own axis and one of said members having orbital movement about the axis of the other of said members;
• (c) first and second relatively movable valve elements having respective first and second slidably engaging valve surfaces, one of said valve elements being movable in synchronism with one of said movements of one of said toothed members, said first valve element defining a plurality N of fluid passages in fluid communication with said expanding and contracting volume chambers and having passage openings in said first valve surface arranged circumferentially relative to the axis thereof, said second valve element defining a plurality of valve ports having openings in said second valve surface arranged circumferentially relative to the axis thereof, said plurality of valve ports including a first group of valve ports having constant fluid communication with said fluid inlet means, and a second group of valve ports having constant fluid communication with said fluid outlet means, at least a portion of said first valve element passage openings being in fluid communication with at least a portion of said second valve element port openings during said relative movement to direct fluid from said fluid inlet means to said expanding volume chambers, and to direct fluid from said contracting volume chambers to said fluid outlet means;
• and
• (d) secondary valve means associated with at least one of said first and second valve elements and being operable to permit fluid communication between each of said volume chambers and a source of relatively lower pressure fluid, said permitted communication occurring as each volume chamber is at approximately its minimum volume position and fluid communication is blocked between the respective first valve element passage opening and both of the adjacent second valve element port openings.