TECHNICAL FIELD

The present invention relates to a vane pump to serve as hydraulic fluid pressure source, particularly for a power steering system of a motor vehicle.

BACKGROUND ART

Generally, a power steering system in automobiles utilizes pressurized fluid discharged from a vane pump, enabling easy handle control.

A vain pump comprises a rotor with plurality of radial vanes disposed slidably, a cam ring receiving said rotor within its inner contour, a housing, a cover plate closing an open side of the housing. Two—piece structure with one end of the housing open which is closed by a cover plate, and three—piece structure with cam ring separately formed from a housing are used.

United States patent No. 4,408,964 is a prior art on vane pump. In this prior art, a high pressure chamber is formed either in a pump housing or in a cover plate by casting using a core. An end of the pump housing or of the cover plate defines a slide surface with which a rotor and vanes are slidably and directly engaged, thus being formed with delivery ports or suction ports. This prior art precludes the need for a side plate, a spring for biasing the side plate against the rotor. However, because the cam ring is not placed within the housing, there is a limit to reducing the size of the vane pump, and a seal to prevent leakage must be provided between the housing and the cam ring.

Another example of prior art on vane pump is shown in the Korean utility model application with publication

No.93—3890. This prior art comprises a one end open housing 1, a rotor 6 with plurality of radially slidable vanes attached, a cam ring receiving the rotor 6, a pin fixing a cam ring 7 to the housing 1, a cover plate 2 closing the open end of the housing 1, and a seal plate 3 covering the pin. The seal plate 3 which is essentially symmetric also provides an effective sealing between the housing 1 and the cover plate 2. In this prior art, however, a separately formed side plate 8 is used, increasing parts necessary for the vane pump and demanding additional manufacturing processes. Also, pressure formed in the pressure chamber 5 is applied on a whole side area of the side plate 8, hindering the stable rotation of the rotor 6. In particular, the pressure applied on the side plate 8 exerts strong force on the cover plate 2 or a housing cover which may cause distortion that can lead to unsteady operation or fracture that can be fatal. Also, the strong force demands a strong counter force to hold the cover plate 2 or the housing cover in place, which will increase the size or number of fastening means.

DISCLOSURE OF INVENTION

Therefore, objects of the present invention are to provide a vane pump which requires fewer parts and to provide a vane pump with a structure which alleviates force exerted on the cover plate, reducing the possibility of unstable operation or fracture.

A vane pump according to the present invention comprises a cam ring, a rotor, a housing, a cover plate, a fastening means and a locking means .

In the present invention, at least one partly open pressure chamber integrated to the housing, and the same number of discharge passage communicating fluid between the rotor and a pressure chamber are provided. An opening of the pressure chamber is connected to an outlet and another opening is connected to a discharge passage. Since force

exerted on the cover plate is determined by the cross section of the discharge passage and the pressure of fluid in the pressure chamber, decrease in the area of the cross section and the pressure decreases force exerted on the cover plate, which means less fastening force is required for maintaining the same level of discharge pressure.

The cam ring has a cylindrical outer surface and an oval or circular inner surface wherein a rotor is displaceable. The rotor has plurality of radial grooves placed substantially equidistance along the circumference of the rotor, each groove provided with a vane control groove at its inner radial end. The vanes slidably placed in each radial groove maintain slidable engagement with the inner surface of the cam ring. The rotor is locked onto a shaft means for driving the rotor for rotation.

The housing comprises an inlet, an outlet, at least one integrated pressure chamber, an inner annular groove to receive said cam ring therein, a slide surface engaged with a surface of the cam ring and corresponding surface of the rotor, and the discharge passage communicating fluid between the pressure chamber and the slide surface. Said housing rotatably supports said shaft means, and said slide surface comprises an annular recess at a location corresponding to the vane control groove.

The cover plate comprises a slide surface engaged with another surface of the cam ring and the rotor. The cover plate supports the cam ring and the rotor against the slide surface of the housing with predetermined force. The fastening means fastens the cover plate to the housing and the locking means locks the cam ring onto the inner annular groove of the housing. Any engagement parts, such as bolts or snap rings can be used as the fastening means, while such parts as keys and spline, can be used as the locking means. A cylinder bolt is particularly suitable as the fastening means, because it can exert uniform fastening pressure with less deformation than stud bolts.

Preferably, the cover plate should have at least one cavity formed on the circumference, the face of the cavity facing the cam ring, to allow fluid into the rotor inlet.

Grooves can be provided at the slide surface of the cover plate to help the discharge of the fluid.

The inner diameter of the inner annular groove formed in the housing should preferably be larger than the outer diameter of the cam ring, and the width of the annular diameter should be also larger than that of the cam ring, so that the fluid from the inlet passage can be provided to the rotor inlet via the inner annular groove and the cavity formed on the cover plate. Because the fluid is provided via the cover plate, not the slide surface of the housing, the housing structure can be simplified. The cavity is formed only on the circumference of the cover plate corresponding to the inlet part of the rotor, so that discharged fluid is not affected.

If necessary, spring means, such as a spring washer can be provided between the fastening means and the cover plate to exert predetermined force on the cover plate. The predetermined force can be exerted on the cam ring toward the slide surface of the housing to maintain the assembly liquid-tight, particularly at the start of operation of the pump. A prior art on excess fluid return mechanism can be provided between the inlet and the outlet to return fluid when excessive pressure forms at the outlet region.

Means to seal the cover plate and the housing, such as 0—ring can be provided between the cover plate and the housing to prevent fluid leaking.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the present invention will be more clearly understood by those skilled in the art with reference to the accompanying drawings in which:

FIG.l is a longitudinal _, sectional view of a prior art

vane pump;

FIG.2 is a perspective view of the vane pump according to the present invention;

FIG.3 is an exploded view of the vane pump according to the present invention;

FIG.4 is a longitudinal sectional view of the vane pump according to the present invention;

FIG.5 is a sectional view of the present invention cut along the line A-B-C-D-E-F of Fig.4; FIG.6 is a perspective view of the cover plate of the present invention;

FIG.7 shows the placement of the cover plate, the cylinder bolt and the spring washer; and

FIG.8 is a sectional view of the vane pump in operation.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will now be described in detail referring to the accompanying drawings.

Fig.2 shows the vane pump 100 according to the present invention where the housing 110 is connected to the reservoir(not shown) via inlet 170. The outlet 180 provides pressurized fluid to a hydraulic system(not shown). A pulley 101 is also illustrated, which drives a shaft connected to the rotor in the housing 110. A cylinder bolt 160 is placed at the open side of the housing to exert predetermined force on the cover plate 150 and serves as a seal against fluid leakage. Fig.3 shows components of the vane pump according to the present invention. The pulley 101 is locked onto the shaft 102 by a spline engagement, while the other end of the spline 102 is also locked onto the rotor 130 by another spline engagement. A nut 105 can be provided at the end of shaft 102 to prevent relative axial movement between the shaft 102 and the pulley 101. The shaft 102 is inserted into the housing supported by bearing 103 with seal 104 to

prevent fluid leakage. The housing comprises the inlet passage 171 connected to the inlet 170, the discharge passages 181 connected to the outlet 180 via the pressure chamber 185, at least one pressure chamber 185 connected to the discharge passage 181, the inner annular groove 111 to hold the cam ring 120 which is designed to hold the rotor 130 inside, the vanes 140 slidably engaged with the inner surface of the cam ring 122, an excess fluid return passage (not shown) to send fluid back to the inlet passage when excessive pressure results near the outlet region, a slide surface 183 with the annular recess 112 and a screw thread to engage the cylinder bolt 160 to the housing. The annular recess 112 is connected to the pressure chamber 185 via pressure passage 187. Force to push the vanes 140 to the inner surface 122 of the cam ring 120 is increased by pressure formed in the vane control grooves, as a result of the formation of pressure in the pressure chamber 185. The pressure of the vane grooves is delivered from the pressure chamber 185 via the annular recess 112 and the pressure passage 187. The vanes 140 are placed along the circumference of the rotor 130 substantially equidistance from each other. Vane control valves 131 are provided at the radial ends of the grooves that hold the vanes 140. The cylinder bolt 160 is provided to fasten the cam ring 120 and the rotor 130 within the housing 110. Predetermined force can be exerted to the cam ring 120 and the rotor 130 by controlling the fastening force of the cylinder bolt 160. A spring washer 161 is provided between the cylinder bolt 160 and the cover plate 150, which will exert additional force to prevent leaking during the start of the rotor rotation. An 0-ring seal 151 is provided in the housing 110 to prevent leaking at a location where the cover plate 150 will be placed.

Fig.4 shows said parts assembled. The slide surface 183 and the corresponding surface of the rotor 130 and the cam ring 120 are maintained liquid-tight by the force exerted by the cover plate 150. As can be seen, the width

of the inner annular groove 111 is bigger than that of the cam ring 120, with a part of the cover plate 150 placed in the inner annular groove 111. The inlet fluid flows to the inlet part of the rotor to the inlet passage 171 via the cavity 155 formed on the cover plate 150. The O-ring 110 provides a seal preventing the leaking of the fluid. The diameter of the inner annular groove 111 is larger than outer diameter of the cam ring 120, so that the cam ring 120 does not block the inlet passage 171. Fig.5 is a sectional view of the present invention cut along the line A—B-C-D-E-F. The section of discharge passage 181 connected to the outlet 180 is shown. The section of the inlet passage 171 that is connected to the inlet 170 is also shown. Fig.6 shows the cavities 155, grooves 157, annular recess 152 formed on the cover plate 150. The cavity 155 provides a passage to the inlet part of the rotor 130. The grooves 157 have the cross section same as that of the discharge passage 181 and is located at a location corresponding to the discharge passage 181. The annular recess 152 provides a passage for the pressurized fluid to form same pressure in each vane control groove 131. The annular recess 112 formed in the housing 110 has the same function as the annular recess 152 formed on the cover plate 150.

Fig.7 shows the relative position of the cover plate 150, the spring washer 161 and the cylinder bolt 160. As mentioned above, the spring washer 161 exerts predetermined force on the cover plate 150, consequently on the rotor 130 and the cam ring 120.

Fig.8 is a sectional view of the present invention showing the operation of the rotor 130. As can be seen, the contour of the inner surface 122 is oval. The spaces between the cam ring 120 and the rotor 130 are shown as blank areas. As the rotor 130 rotates, the fluid flows to the inlet part of the rotor 130, which has the largest area between the vanes 140, then the fluid is gradually

compressed as the vanes 140 rotate with the rotor 130. Then the compressed fluid is discharged through the discharge passage 181. While the rotation, slide contact between the vanes 140 and the inner surface 122 of the cam ring 120 is maintained. At the beginning of the rotor rotation, centrifugal force pushes the vanes 140 to the inner surface 122 of the cam ring 120. As pressure develops in the pressure chamber 185, the pressure in the vane control valve 131 increases the force pushing the vanes 140 radially outward.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teaching. It is therefore to be understood that the invention may be practiced otherwise than as specifically described herein.