Internally supercharged axial piston pump

An axial piston fluid pump comprising:

• a housing having an inner wall surface surrounding a barrel chamber and a port surface at a first end of the barrel chamber, the port surface including a delivery port and an exhaust port circumferentially spaced apart in relation to a center axis of the barrel chamber;
• a barrel rotatably mounted within the barrel chamber in the housing and having a plurality of axially extending;
• circumferentially spaced piston bores therein, each piston bore having associated therewith a cylinder port in an end wall of the barrel located adjacent the port surface which cylinder port sequentially communicates with the delivery and exhaust ports during rotation of the barrel in the barrel chamber;
• a plurality of pistons disposed in the piston bores for reciprocation;
• and
• a drive shaft for rotatably driving the barrel in the barrel chamber;
• and wherein:
• the housing includes an inlet passage for delivering low pressure fluid to a second end of the barrel chamber opposite the port surface;
• the barrel has a radially outer surface radially inwardly spaced from the inner wall surface of the barrel chamber to form an impeller pump chamber;
• at least one impeller vane projects radially outwardly from the outer wall surface of the barrel and terminates at a radially outer vane edge adjacent the inner wall surface of the barrel chamber;
• and
• the impeller pump chamber has an inlet end in fluid communication with the second end of the barrel chamber and an outlet end in fluid communication with the delivery port, whereby upon rotation of the barrel in the barrel chamber, low pressure fluid from the second end of the barrel chamber is supercharged by the impeller vane prior to passage through the delivery port.