Power steering pump

This invention relates to a power steering pump for an automotive vehicle, and, more particularly, to a cover that includes an annular contact for engaging an adjacent pressure plate and a central recess for creating a hydraulic sump.

A power steering system of an automotive vehicle comprises a pump for supplying hydraulic fluid under pressure to a power steering gear assembly. U.S. patent application Ser. No. 10/443,320, filed May 22, 2003, describes a power steering pump that includes a cam plate that defines a cam chamber, and a vaned rotor within the cam chamber for pumping fluid. The cam plate is interposed between pressure plates within a canister housing. The cam plate and the pressure plates are retained by a cover that is secured by a retainer ring. In common practice, the retainer ring is a snap ring that fits in a groove in the inner surface of the can housing. Insertion of the retainer ring is accommodated by clearance between the several elements within the housing. This clearance increases stress on, and wear of, seals between the elements. Also, under the high pressures created during operation, even slight spacing increases noise and vibration.

Therefore, a need exists for a power steering pump wherein the cam plate and the pressure plates are secured within the can housing with reduced clearance, thereby improving sealing and reducing vibration and noise resulting from high pressure operation.

This invention provides a power steering pump for an automotive vehicle that includes a can housing that defines a compartment having an axis and includes an open end. A cam plate and an upper pressure plate are disposed within the compartment, such that the upper pressure plate is adjacent the open end. A cover is threadingly secured in the open end to enclose the cam plate and the upper pressure plate. The interior side of the cover includes an annular pressure plate contact that engages the upper pressure plate axially opposite the cam plate and a central recess within the annular pressure plate contact that cooperates with the upper pressure plate to define a hydraulic fluid sump that generally axially overlies the cam chamber of the cam plate spaced apart by the upper pressure plate. During manufacture, when the cover is threaded into the open end of the can housing, the annular pressure plate contact is urged against the pressure plate to provide a tight fit between the upper pressure plate and the cam plate, as well as other components within the compartment of the cam housing. This reduces axial clearance between the components within the compartment to enhance sealing and minimize noise and vibration during operation.

This invention will be further described with reference to the drawings wherein:

FIG. 1 is a cross-sectional view of a power steering pump in accordance with a preferred embodiment of this invention;

FIG. 2 is a cross-sectional view of the power steering pump in FIG. 1 , taken along line 2 — 2 in the direction of the arrows;

FIG. 3 is a cross-sectional view of the power steering pump in FIG. 1 , taken along line 3 — 3 in the direction of the arrows; and

FIG. 4 is a cross-sectional view of a portion of the power steering pump in FIGS. 1 and 2 , taken along line 4 — 4 in FIG. 2 in the direction of the arrows.

In accordance with a preferred embodiment of this invention, referring to the Figs., a power steering pump 10 is adapted for use in a power steering system of an automotive vehicle for providing pressurized fluid to a power steering gear assembly. Pump 10 comprises a can housing 12 that defines a compartment surrounded by an inner wall 14 generally cylindrical about an axis 16 . Housing 12 includes a closed end 18 and an open end 20 axially spaced from end 18 and including an inner threaded rim 22 .

Received within the compartment perpendicular to axis 16 is a cam plate 24 interposed between a lower pressure plate 26 and an upper pressure plate 28 . Cam plate 24 defines a cam chamber 30 . A rotor 32 is disposed within cam chamber 30 and mounted on a shaft 34 that extends axially through closed end 18 . Shaft 34 is adapted to be driven by a vehicle motor through a belt and pulley arrangement and rotates rotor 32 about axis 16 . Rotor 32 includes radially slidable vanes 35 that engage the surface of the cam chamber 30 to pump fluid as rotor 32 is rotated.

The several elements of pump 10 cooperate to define suction passages 36 for conveying relatively low pressure fluid to cam chamber 30 and discharge passages 38 for conveying pressurized fluid from cam chamber 30 . It would be appreciated that only a portion of the porting that defines the suction passages and discharge passages are depicted in the figures, and that additional passages are provided for conveying the fluid from the pump inlet and to the pump outlet. In the depicted embodiment, suction passages 36 include axial channels 37 in inner wall 14 of housing 12 and communicate with cutaway slots 43 in upper pressure plate 28 that overlie a portion of the cam chamber 30 to inlets 44 for supplying low pressure hydraulic fluid to the cam chamber. Outlets (not shown) for discharging pressurized fluid from the cam chamber are formed through openings in the lower pressure plate 28 . In addition, upper pressure plate 28 includes a conduit 40 that communicates with the cam chamber opposite the outlets for distributing high pressure fluid to undervane porting 42 in rotor 32 for urging the vanes against the surface of the cam chamber. O-ring seals 48 and 49 between low pressure plate 26 and end 18 of can housing 12 separate the suction passages from the discharge passages at closed end 18 .

U.S. patent application Ser. No. 10/443,320, filed May 22, 2003, provides further description, particularly with respect to the inlets and outlets to the cam chamber, and the pumping operation of the rotor 32 , and is incorporated herein by reference.

In accordance with this invention, housing 12 further comprises a cover 50 for enclosing cam plate 24 and pressure plates 26 and 28 within the compartment in can housing 12 . More particularly, cover 50 is mounted within open end 20 of housing 12 and includes outer threads that engage the threaded lip 22 . Notches 52 in the outer side of cover 50 are provided for purposes of engaging a tool to screw cover 50 into position. The inner side of cover 50 includes an annular pressure plate contact 54 for engaging the adjacent surface 56 of upper pressure plate 28 . In addition, annular contact 54 defines a central recess 57 within cover 50 that cooperates with the adjacent surface of pressure plate 28 to form a hydraulic sump 55 . Sump 55 communicates with slots 43 to provide a reservoir for supplying hydraulic fluid to inlets 44 and equalizes pressures between the inlets to provide more uniform pressure in the pumped fluid.

During assembly, cover 50 is threaded into open end 20 to seal the compartment within housing 12 and to secure cam plate 24 , lower pressure plate 26 and upper pressure plate 28 in position. Annular contact 54 is strategically located to engage plate 28 axially opposite from cam plate 24 and thereby urge plate 28 into intimate contact with plate 24 , and plate 24 into intimate contact with lower pressure plate 26 . This produces a tight fit of the several elements within the compartment in marked contrast to the clearance that results with a snap ring to secure the cover. As a result of the tight fit, the stress and wear are reduced thereby extending the durability and useful life of the pump. The tight fit also reduces vibration among the elements that might otherwise lead to damage or produce noise during operation. This is accomplished while providing a sump to enhance distribution of low pressure hydraulic fluid to the inlets to the cam chamber.

In the described embodiment, a single lock cover is utilized to seal and secure the several elements, including the cam plate and the pressure plates, within the pump compartment. The use of a single cover threadingly mounted into the open end of the canister housing reduces the part count, particularly in comparison to a cover and snap ring design, thereby reducing cost and complexity of the pump. In an alternate embodiment, the pump cover may be designed without outer threads to slide into position against the upper pressure plate and secured by a retainer ring threaded into the open end of the canister housing.

While this invention has been described in terms of certain embodiments thereof, it is not intended to be so limited, but rather only to the extent set forth in the claims that follow.