Variable displacement pump having rotating cam ring
Vane pump mechanical losses are reduced by removing vane friction losses and replacing them with lower magnitude journal bearing fluid film viscous drag losses. A freely rotating cam ring is supported by a journal bearing. A relatively low sliding velocity is imposed between the cam ring and the vanes). This permits the use of less expensive and less brittle materials in the pump by allowing the pump to operate at much higher speeds without concern for exceeding vane tip velocity limits.
1. A pump comprising:
a housing having a cavity, at least a portion of the cavity forming a pump chamber;
a shaft;
a rotor received in the pump chamber and operatively driven by the shaft for rotation relative to the housing;
at least one vane extending radially outward from the rotor;
an annular cam ring received around the rotor and mounted for rotation relative to the housing, and relative to the rotor;
a cam sleeve received around the cam ring;
an actuator assembly including first and second piston actuators operatively engaging the cam sleeve and selectively moving a centerpoint of the cam sleeve relative to the housing to alter the displacement of the pump; and
a journal bearing formed by a passage between the cam ring and the cam sleeve for receiving associated pump fluid therebetween and without any structural component interconnecting the cam ring and the cam sleeve.
2. The pump of claim 1 wherein the first and second piston actuators are disposed in opposing relation.
3. The pump of claim 2 wherein the first and second piston actuators engage first and second lobes, respectively, extending from the cam sleeve.
4. The pump of claim 3 wherein the first and second lobes extend from a peripheral region of the cam sleeve and the piston actuators move along a tangential region relative to the cam sleeve.
5. The pump of claim 4 wherein the cam sleeve is secured against rotation relative to the housing by a pin located at a region diametrically opposite the tangential region.
6. The pump of claim 5 further comprising a spacer ring interposed between the cam sleeve and the housing, the cam sleeve secured to the spacer ring with the pin for selective pivoting movement relative thereto.
7. The pump of claim 1 wherein the at least one vane includes multiple circumferentially spaced vanes.
8. The pump of claim 7 wherein the multiple vanes are received in corresponding radially extending grooves.
9. A method of forming a variable pump comprising:
providing a housing with a cavity, at least a portion of the cavity forming a pump chamber;
inserting a shaft and a rotor in the pump chamber so that the shaft operatively drives the rotor for rotation relative to the housing;
including an annular cam ring around the rotor and mounted for rotation relative to the housing and relative to the rotor;
positioning a cam sleeve around the cam ring;
mounting an actuator assembly on the housing, the actuator assembly including first and second piston actuators arranged to operatively engage the cam sleeve and selectively move a centerpoint of the cam sleeve relative to the housing to alter the displacement of the pump; and
forming a passage between the cam ring and the cam sleeve dimensioned to receive associated pump fluid to form a journal bearing therebetween without any structural component interconnecting the cam ring and the cam sleeve.