Balanced vane type oil pumps

An oil pump comprising:

• a pump body having a rotary shaft;
• a single rotor mounted to said rotary shaft for rotation therewith, said single rotor having a plurality of radially movable vanes;
• a cam ring coaxially mounted with said single rotor and rotatably containing said single rotor to define a pair of pump chambers, each of said pump chambers comprising:
• an inlet passage;
• a first discharge passage spaced a predetermined distance in a direction of rotation of said single rotor from said inlet passage;
• and
• a second discharge passage spaced a predetermined distance in a direction of rotation of said single rotor from said first discharge passage;
• a first valve bore extending in a direction substantially perpendicular to said rotary shaft;
• a second valve bore spaced a predetermined distance from said first valve bore and further being parallel thereto;
• first and second spool valve means, said second spool valve means mounted in said second valve bore, said second spool valve means operative to selectively connect and disconnect said second discharge passage of each one of said pair of pump chambers to one of said inlet passages of said pump, said second spool valve means further operative to selectively connect said second discharge passages of said pump chambers to said first discharge passages of said pump chambers;
• and
• said first spool valve means mounted in said first valve bore, said first spool valve means selectively operative to connect said first and second discharge passages of said pair of pump chambers to the other of said inlet passages.