Gerotor pump having axial fluid transfer passages through the lobes

A gerotor pump comprising a casing having an internal chamber;

• an externally lobed rotor member rotatably accommodated within said chamber;
• an internally lobed annulus member rotatably accommodated within said casing, said rotor member being accommodated within and in mesh with said annulus member, said annulus member having one lobe more than said rotor member, each lobe of said rotor member contacting said annulus member at circumferentially spaced points to provide a series of circumferentially spaced working chambers;
• means for rotating said rotor member about an axis;
• a fluid inlet in said casing and in communication with said rotor member at one axial side thereof to admit fluid to each of said working chambers in response to rotation of said rotor member;
• a fluid outlet in said casing circumferentially spaced from said inlet, the spacing between said inlet and said outlet being such that each of said chamber is exposed in turn to said inlet and said outlet in response to rotation of said rotor member;
• an axial fluid transfer passage extending through each of the lobes of at least one of said members and being so located that each of said passages is exposed in succession to said inlet and outlet in response to rotation of said rotor member;
• and fluid transfer cavities in said casing at the opposite axial side of said rotor member from each of said fluid inlet and fluid outlet, said fluid transfer cavities enabling the passages that are exposed to said inlet and outlet in succession to be in communication with the working chambers at both axial sides of the members at the same time.