Vane pump with rotating cam ring and increased under vane pressure

A vane pump comprising:

• a shaft driving a rotor, said rotor having a plurality of vane grooves, with a vane received in each of said plurality of vane grooves, and an under vane passage for communicating a pressurized fluid into said grooves to bias said vanes radially outwardly of said rotor;
• a cam ring positioned radially outwardly of said rotor, and said cam ring being free to rotate with said rotor through friction from said vanes as said rotor rotates;
• an inlet for delivering a fluid to be pumped into an inlet chamber, and a main outlet for receiving the fluid pumped by the vane pump;
• an under vane outlet for the fluid in said grooves, said under vane outlet communicating to said main outlet through a passage including a valve to increase the pressure of the fluid in the grooves;
• said vane pump including a pivoting housing structure for changing the displacement of the vane pump;
• said valve being positioned at an intersection of a first and second passage, and the fluid returning from the grooves must open the valve against a spring bias to pass from the first passage into the second passage;
• and
• the grooves that communicate to the under vane outlet to have the increased pressure being limited to only a portion of said plurality of vane grooves, the vanes that receive the increased pressure being those associated with the beginning of a discharge arc.