SURFACE FINISHES IN OIL PUMPS

Field of the Invention

The invention relates to the field of oil pumps, and in particular, to surfaces finishes for oil pumps and methods of providing surfaces finishes in oil pumps to reduce friction between portions of oil pumps that move relative to one another.

Background of the Invention

A primary consideration in designing fluid pumps is maximizing the total efficiency of the fluid pump. This is especially important in fluid pumps designed to transport high-viscosity fluids, such as oil. One of the primary efficiency losses in oil pumps is friction created between surfaces that move relative to one another. Accordingly, many previous designs have been directed toward reducing the surface area of such moving parts of an oil pump by employing pump geometries that limit the degree of contact between surfaces that move relative to one another.

Summary of the Invention

A pump according to the invention includes a housing and a pumping mechanism. A pumping chamber is defined in the housing. An inlet is formed in the housing and is in communication with the pumping chamber to provide a fluid to the pumping chamber. An outlet is formed in the housing and is in communication with the pumping chamber to receive the fluid from the pumping chamber. The pumping mechanism is disposed within the pumping chamber and moves with respect to the housing to pump the fluid from the inlet to the outlet. At least a first engaging surface is formed on the housing adjacent to the pumping chamber. At least a second engaging surface formed on the pumping mechanism. The second engaging surface frictionally engages the first engaging surface during movement of the pumping mechanism with respect to the housing. A surface finish is provided on at least one of the first engaging surface or the second engaging surface to create a plurality of recesses therein to reduce the surface area of the first and second engaging surfaces that is in factional engagement.

At least one of the first engaging surface or the second engaging surface can be fabricated from metal, wherein the surface finish is provided thereon by shot-peening. Alternatively, at least one of the first engaging surface or the second engaging surface can be fabricated from plastic, wherein the surface finish is molded thereon.

The housing can be fabricated from metal, wherein the surface finish is provided on the first engaging surface by shot peening. Furthermore, the pumping mechanism can be fabricated from metal, wherein the surface is finish is provided on the second engaging surface by shot peening.

The housing can be fabricated from plastic, wherein the surface finish is molded on the first engaging surface. Furthermore, the pumping mechanism can be fabricated from plastic, wherein the surface finish is molded on the second engaging surface.

The pumping mechanism can be a gear-type pumping mechanism. Alternatively, the pumping mechanism can be a roller vane pumping mechanism.

A method according to the invention comprises the steps of providing a housing having a pumping chamber defined therein, an inlet in communication with the pumping chamber to provide a fluid to the pumping chamber, an outlet in communication with the pumping chamber to receive the fluid from the pumping chamber and at least a first engaging surface formed on the housing adjacent to the pumping chamber, providing a pumping mechanism having at least a second engaging surface, and providing a surface finish on at least one of the first engaging surface or the second engaging surface to create a plurality of recesses therein. The method also includes the steps of assembling the housing and the pumping mechanism so that the pumping mechanism is disposed within the pumping chamber of the housing and the first engaging surface is adjacent to the second engaging surface, and applying a motive force to the pumping mechanism to move the pumping mechanism with respect to the housing and thereby pump fluid from the fluid inlet to the fluid outlet, wherein the first engaging surface frictionally engages the second engaging surface.

Brief Description of the Drawings

The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout several views and wherein:

FIG. 1 is a top view of a gear-type pump according to the invention;

FIG. 2 is a sectional view of a gear-type pump according to the invention;

FIG. 3 is a top view of a roller-vane pump according to the invention;

FIG. 4 is a sectional view of a roller-vane pump according to the invention;

FIG. 5 is an illustration showing a pair of engaging surfaces; and

FIG. 6 is a sectional view showing a mold that can be used to fabricate a pump according to the invention.

Detailed Description

Referring to FIGS. 1-5, the present invention will be seen to most generally pertain to fluid pumps having a low friction surface finish provided on at least one engaging surface of a pair of engaging surfaces and methods for making pumps having a low friction surface finish on at least one engaging surface of a pair of engaging surfaces, as will now be described in detail with reference to the disclosed embodiments.

FIGS. 1-2 show a gear-type pump 100 for pumping fluids according to the present invention. The pump 100 includes a housing 101 that is defined by a housing body 102 and a housing cover 104. The pump 100 further includes a pumping mechanism 105 that is defined by an inner rotor 106 and an outer rotor 107. The housing 101 and the pumping mechanism 105 can be fabricated from metals, such as aluminum or steel, or from plastics. As will be explained in detail herein, the housing 101 and the pumping mechanism 105 can be provided with surface finishes that reduce friction between surfaces that move relative to one another, by reducing the area of those surfaces that is in frictional engagement. The pump 100 is well suited for use in pumping relatively high viscosity fluids, such as oil., but it should be understood that the present invention is not limited to pumping high viscosity fluids, but rather, the pump 100 could be utilized to pump any type of fluid.

In order to direct fluid to and from the housing 101, an inlet 108 and an outlet 110 are formed in the housing body 102. The inlet 108 and the outlet 110 are in communication with a pumping chamber 111, in which the pumping mechanism 105 is disposed. An input shaft 112 extends through the housing cover 104 and is connected to the inner rotor 106. The input shaft 112 provides a rotational force to the inner rotor 106 and the outer rotor 107. The inner rotor 106 and the outer rotor 107 rotate with respect to the housing body 102 and engage one another to pump the fluid from the inlet 108 to the outlet 110.

The housing body 102 is further defined by having an internal axial wall 114 and an internal radial wall 116 that is formed at the periphery of the internal axial wall 114. The internal radial wall 116 extends substantially perpendicular to the internal axial wall 114. The internal axial wall 114 and the internal radial wall 116 cooperate to define a pumping chamber 111 in which the inner rotor 106 and the outer rotor 107 are received. The inlet 108 and the outlet 110 both extend through the internal axial wall 114 for fluid communication with the pumping chamber 111.

Rotation of the input shaft 112 causes rotation of the inner rotor 106 with the respect to the housing body 102, by having the inner rotor 106 connected to the input shaft 112. For example, the input shaft 112 can extend axially through the inner rotor 106 and engage the inner rotor 106 by a friction fit, a splined connection, or other suitable means, so that the input shaft 112 and the inner rotor 106 rotate in unison.

The inner rotor 106 is captured between the internal axial wall 114 of the housing body 102 and an internal surface 118 of the housing cover 104 that is opposite and parallel to the internal axial wall 114 of the housing body 102. In particular, the inner rotor 106 has a lower axial surface 120 that is parallel to and abuts the internal axial wall 114 of the housing body 102 so that the lower axial surface 120 of the inner rotor 106 frictionally engages the internal axial wall 114 of the housing body 102 during movement of the inner rotor 106 relative to the housing 101. The inner rotor also has an upper axial surface 122 that is parallel to and abuts the internal surface 118 of the housing cover 104 so that the upper axial surface 122 of the inner rotor 106 frictionally engages the internal surface 118 of the housing cover 104 during movement of the inner rotor 106 relative to the housing 101. The inner rotor 106 also includes an outer periphery 124 having a plurality of teeth or lobes 126 formed thereon for engagement with the outer rotor 107.

The outer rotor 107 is mounted for rotation with respect to the housing body 102 and is eccentrically mounted with respect to the inner rotor 106. In particular, rotation of the outer rotor 107 with respect to the housing body 102 may be constrained by engagement of an outer periphery 128 of the outer rotor 107 with the internal radial wall 116 of the housing body 102. The outer rotor 107 is captured between the housing body 102 and the housing cover 104. A lower axial surface 130 of the outer rotor 107 is parallel to and abuts the internal axial wall 114 so that the lower axial surface 130 of the outer rotor 107 frictionally engages the internal axial wall 114 of the housing body 102 during relative movement of the outer rotor 107 with respect to the housing 101. An upper axial surface 132 of the outer rotor 107 is parallel to and abuts the internal surface 118 of the housing cover 104 so that the upper axial surface 132 of the outer rotor 107 frictionally engages the internal surface 118 of the housing cover 104 during relative movement of the outer rotor 107 with respect to the housing 101. The outer rotor 107 has an inner periphery 134 having a plurality of teeth or lobes 136 formed thereon. The inner periphery 134 of the outer rotor 107 faces the outer periphery 124 of the inner rotor 106, so that the inner periphery 134 of the outer rotor 107 can meshingly engage the outer periphery 124 of the inner rotor 106 during meshing rotation of the inner rotor 106 and the outer rotor 107 with respect to one another, as will be explained herein.

The eccentric mounting of the inner rotor 106 with respect to the outer rotor 107 causes the lobes 126 of the inner rotor 106 to mesh and un-mesh with respect to the lobes 136 of the outer rotor 107 as the inner rotor 106 rotates with respect to housing body 102. This meshing and unmeshing of the lobes 126, 136 causes rotation of the outer rotor 107 relative to both the inner rotor 106 and the housing body 102. As the lobes 126 of the inner rotor 106 mesh and un-mesh with respect to the lobes 136 of the outer rotor 107, variable volume spaces 138 are defined between the lobes 126 of the inner rotor 106 and the lobes 136 of the outer rotor 107. The change in volume of the spaces 138 creates a change in pressure across the lobes 126, 136, thereby drawing in and pumping fluid from the inlet 108 to the outlet 110. In particular, the inlet 108 is positioned so that the spaces 138 are increasing in volume as they pass over the inlet 108 to thereby draw fluid from the inlet 108 into the spaces 138. The outlet 110 is positioned so that the spaces 138 are decreasing in volume as they pass over the outlet 110 to thereby expel fluid from the spaces 138 into the outlet 110.

FIGS. 3-4 show a roller- vane type pump 200 for pumping fluids according to the present invention. The pump 200 includes a housing 201 that is defined by a housing body 202 and a housing cover 204. The pump 200 further includes a pumping mechanism 205 defined by a carrier 206 and a plurality of roller vanes 207. The housing 201 and the pumping mechanism 205 can be fabricated from metals, such as aluminum or steel, or from plastics. As will be explained in detail herein, the housing 201 and the pumping mechanism 205 can be provided with surface finishes that reduce friction between surfaces that move relative to one another, by reducing the area of those surfaces that is in frictional engagement. The pump 200 is well suited for use in pumping relatively high viscosity fluids, such as oil, but it should be understood that the present invention is not limited to pumping high viscosity fluids, but rather, the pump 100 could be utilized to pump any type of fluid. To direct fluid to and from the housing 201, an inlet 208 and an outlet 210 are formed in the housing body 202. The inlet 208 and the outlet 210 are in communication with a pumping chamber 211, in which the pumping mechanism 205 is disposed. An input shaft 212 extends through the housing cover 204 and is connected to the carrier 206. The input shaft 212 provides a rotational force to the carrier 206 and the roller vanes 207. The inner rotor 206 and the outer rotor 207 rotate with respect to the housing body 202 and engage one another to pump the fluid from the inlet 208 to the outlet 210.

The housing body 202 includes an internal axial wall 214 and an internal radial wall 216 that is formed at the periphery of the internal axial wall 214. The internal radial wall 216 extends substantially perpendicular to the internal axial wall 214. The internal axial wall 214 and the internal radial wall 216 cooperate to define the pumping chamber 211 in which the carrier 206 and the roller vanes 207 are received. The inlet 208 and the outlet 210 both extend through the internal axial wall 214 for fluid communication with the pumping chamber 211.

Rotation of the input shaft 212 causes rotation of the carrier 206 with the respect to the housing body 202, by having the carrier 206 connected to the input shaft 212. For example, the input shaft 212 can extend axially through the carrier 206 and engage the carrier 206 by a friction fit, a splined connection, or other suitable means, so that the input shaft 212 and the carrier 206 rotate in unison.

The carrier 206 is captured between the internal axial wall 214 of the housing body 202 and an internal surface 218 of the housing cover 204 that is opposite and substantially parallel to the internal axial wall 214 of the housing body 202. A lower axial surface 220 of the carrier 206 is parallel to and abuts the internal axial wall 214 of the housing body 202 such that the lower axial surface 220 of the carrier 206 frictionally engages the internal axial wall 214 of the housing body 202 during movement of the carrier 206 relative to the housing 201. The carrier 206 also includes an upper axial surface 222 that is parallel to and abuts the internal surface 218 of the housing cover 204 such that the upper axial surface 222 of the carrier 206 frictionally engages the δ internal surface 218 of the housing cover 204 during movement of the carrier 206 relative to the housing 201. The carrier 206 also includes an outer periphery 224 that faces the internal radial wall 216 of the housing body 202. A portion of the outer periphery 224 of the carrier 206 may frictionally engage the internal radial wall 216 of the housing body 202 during rotation of the carrier 206 with respect to the housing 201.

In order to receive the roller vanes 207 on the carrier, a plurality of slots 226 are defined in the carrier 206 by slot walls 227 that extend radially inward from the outer periphery 224 of the carrier 206 in a substantially u-shaped configuration. The slots 226 are configured and arranged so that the roller vanes 207 may be received therein and move radially with respect to the carrier 206 during rotation of the carrier 206 and the roller vanes 207 with respect to the housing body 202.

The outer periphery 224 of the carrier 206 and the internal radial wall 216 of the housing body 202 are sized and configured relative to one another to allow radial motion of the roller vanes 207 at least partially out of the slots 226 of the carrier 206. For example, the outer periphery 224 of the carrier 206 and the internal radial wall 216 of the housing body 202 may both be circular, where the internal radial wall 216 of the housing body 202 is larger in diameter than the outer periphery 224 of the carrier 206, and the carrier 206 may be mounted eccentrically with respect to the center of the circle defined by the internal radial wall 216 of the housing body 202. Thus, as the carrier 206 rotates with respect to the housing body 202, a discrete point along the outer periphery 224 of the carrier 206 will continuously vary in distance from the internal radial wall 216 of the housing body 202 between a maximum distance at which the outer periphery 224 of the carrier 206 is spaced from the internal radial wall 216 of the housing body 202, and a minimum distance, where the carrier 206 may be frictionally engaged with the internal radial wall 216 of the housing body 202.

In order to provide rolling engagement of the roller vanes 207 with the internal radial wall 216 of the housing body 202, the roller vanes 207 are disc-like members, each having an outer periphery 228. Because the roller vanes 207 are disposed within respective slots 226 of the carrier 206, the outer peripheries 228 of the roller vanes 207 are frictionally engageable with the slot walls 227 as well as the internal radial wall 216 of the housing body 202. Each of the roller vanes 207 is captured between the housing body 202 and the housing cover 204. A lower axial surface 230 of each roller vane 207 is parallel to and abuts the internal axial wall 214 of the housing body 202 such that the lower axial surfaces 230 of the roller vanes 207 frictionally engage the internal axial wall 214 of the housing body 202 during movement of the carrier 206 relative to the housing 201. An upper axial surface 232 of each roller vane 207 is parallel to and abuts the internal surface 218 of the housing cover 204 such that the upper axial surfaces 232 of the roller vanes 207 frictionally engage the internal surface 218 of the housing cover 204 during movement of the carrier 206 relative to the housing 201.

As the roller vanes 207 rotate with respect to the housing body 202 in unison with the carrier 206, the radial position of the roller vanes 207 with respect to the carrier 206 is dictated by the variation in distance between the outer periphery 224 of the carrier 206 and the internal radial wall 216 of the housing body 202, and the effective volume of each slot 226 of the carrier 206 varies according to the degree to which the respective roller vane 207 is disposed within the slot. Where the carrier 206 is at its maximum distance from the internal radial wall 216 of the housing body 202, the volume of the adjacent slot 226 is maximized. Where the carrier 206 is at its minimum distance from the internal radial wall 216 of the housing body 202, the volume of the adjacent slot 226 is minimized. Thus, to pump fluid from the inlet 208 to the outlet 210, the inlet 208 is positioned so that the slots 226 are increasing in volume as they pass over the inlet 208, and the outlet 210 is positioned so that the slots 226 are decreasing in volume as they pass over the outlet 210.

Both the gear type pump 100 and the roller vane type pump 200 include a number of pairs of engaging surfaces that frictionally engage one another. Friction losses between these pairs of engaging surfaces decreases the total efficiency of the pump because additional torque must be supplied by the input shaft 112, 212 of the pump 100, 200 to pump the fluid. The efficiency losses caused by engagement of any of the pairs of engaging surfaces may be reduced by providing a surface finish 300 on at least one of a first engaging surface 302 and a second engaging surface 304, as shown in FIG. 5, wherein the first engaging surface 302 and the second engaging surface 304 are exemplary of any of the pairs of engaging surfaces of the gear type pump 100 and the roller vane type pump 200. In the gear-type pump 100, as seen in FIGS. 1-2, these pairs of engaging surface can include, but are not limited to, the lower axial surface 120 of the inner rotor 106 and the internal axial wall 114 of the housing body 102; the upper axial surface 122 of the inner rotor 106 and the internal surface 118 of the housing cover 104; the outer periphery 124 of the inner rotor 106 and the inner periphery 134 of the outer rotor 107; the outer periphery 128 of the outer rotor 107 and the internal radial wall 114 of the housing body 102; the lower axial surface 130 of the outer rotor 107 and the internal axial wall 114 of the housing body 102; and the upper axial surface 132 of the outer rotor 107 and the internal surface 118 of the housing cover 104. In the roller vane pump 200, as seen in FIGS. 3-4, these pairs of engaging surface can include, but are not limited to, the lower axial surface 220 of the carrier 206 and the internal axial wall 214 of the housing body 202; the upper axial surface 222 of the inner rotor 206 and the internal surface 218 of the housing cover 204; the outer periphery 224 of the carrier 206 and the internal radial wall 216 of the housing body 202; the lower axial surfaces 230 of the roller vanes 207 and the internal axial wall 214 of the housing body 202; the upper axial surfaces 232 of the roller vanes 207 and the internal surface 218 of the housing cover 204; the outer peripheries 228 of the roller vanes 207 and the slot walls 227 of the carrier 206; and the outer peripheries 228 of the roller vanes 207 and the internal radial wall 216 of the housing body 202.

In FIG. 5, the surface finish 300 is provided on the first engaging surface 302. Of course, the surface finish 300 could be provided on either or both of the first engaging surface 302 and the second engaging surface 304. The surface finish 300 provides a plurality of recesses 306 on the first engaging surface 302 to thereby reduce the surface area of the first engaging surface 302 that is in frictional engagement with the second engaging surface 304. Furthermore, lubricants may pool in the recesses 306 to further decrease friction losses during frictional engagement with the first engaging surface 302 and the second engaging surface 304.

The surface finish 300 may be provided on either or both of the first engaging surface 302 and the second engaging surface 304 by a controlled shot peening process, wherein shot particles, which are typically fabricated from metal, glass, or ceramic in round or cylindrical shapes, are propelled toward the first engaging surface 302 or the second engaging surface 304 with sufficient force to create plastic deformation of that surface. The shot peening process is applicable to portions of the gear type pump 100 and the roller vane type pump 200 that are fabricated from metals, such as aluminum or steel.

In cases where the first engaging surface 302 or the second engaging surface 304 is fabricated from plastic, the surface finish 300 may be molded onto the first engaging surface 302 or the second engaging surface 304. One way in which the surface finish 300 may be molded is by an injection molding process using a mold 400, as shown in FIG. 6, that includes a first mold portion 402 that cooperates with a second mold portion 404 to define a molding chamber 406, where plastic is pumped into the molding chamber 406 through an injection port 408. The mold 400 is used to fabricate the portion of the gear type pump 100 or the roller vane pump 200 having the first engaging surface 203 thereon and is provided with a negative-profile surface treatment 410 on an interior surface 412 of the mold 400 that corresponds to the first engaging surface 302. The negative profile surface treatment 410 may be provided on the interior surface 412 of the mold 400 by machining or by other suitable methods.

In operation, the gear type pump 100 or the roller vane pump type 200 according to the present invention is provided by forming a surface treatment on at least one of the first engaging surface 302 or the second engaging surface 304. The pump 100, 200 is then assembled and utilized to pump fluid from the inlet 108, 208 to the outlet 110, 210 thereof. While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiments, but to the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as is performed under the law.