Patent Description:
Gear pumps have been employed in a variety of industries and environments. In general, gear pumps include a housing with one or more plates that hold a set of intermeshing gears. As the gears turn, fluid moves between the gear teeth and the housing and is discharged from the pump due to the intermeshing of the gears. The gears are attached to shafts that run axially from the gear faces, and these shafts run on one or more bearing surfaces.

Lubrication of bearing surfaces in gear pumps is often provided by the fluid being conveyed through the pump. One problem with such an arrangement is that upon startup, an adequate lubricating film may not be present (or may not be immediately generated) and thus some bearing surfaces can be subject to wear resulting in damage or premature failure. For example, where an inadequate lubricating film exists between the side faces of the gears and the adjacent end plates, wear related damage to the gears and/or end plates can occur. This problem has previously been addressed by employing hydrodynamic slide bearings with variable depth, and/or through the use of gall-resistant materials aimed at withstanding harsh contact. Surface treatments or coatings of other wear resistant materials have also been applied to the plate surface to resist galling.

Problems with these approaches include difficulty in generating adequate thrust (using the aforementioned slide bearings) without adversely affecting the pumps overall efficiency. In addition, under adverse pumping conditions, gall-resistant materials are still subject to premature failure.

<CIT> discloses a gear pump with lubricating spiral grooves in the gears and thrust generating spiral grooves in a thrust washer, <CIT> discloses an internal gear pump with pressure generating spiral grooves in a bearing, <CIT> discloses a vane pump with pressure generating spiral grooves in a lateral wall of a housing.

Thus, there is a need for an improved design for reducing wear in gear pumps, particularly in gear and endplate bearing surfaces.

A gear pump is disclosed. A gear pump according to the invention is defined in independent claim <NUM>.

An end plate is disclosed for use in a gear pump. The end plate can include a central opening and a first opening for receiving shafts associated with first and second gears of the gear pump. A plurality of spiral grooves can be formed in a side surface of the end plate. The plurality of spiral grooves can include a first groove region positioned adjacent the central opening and a second groove region positioned adjacent the first opening.

An alternative gear pump according to the invention is defined in independent claim <NUM>.

By way of example, a specific embodiment of the disclosed device will now be described, with reference to the accompanying drawings:.

A gear pump is disclosed having features configured to reduce wear of bearing surfaces during pump startup and to provide efficient performance in operation. In one embodiment, spiral grooves are provided in the end-plates adjacent to the faces of the pump gears. These grooves are oriented in an inward-pumping orientation in order to generate a high pressure zone between the opposing faces and ensure separation between the gear and plate.

<FIG> show an exemplary gear pump <NUM> having first, second and third end plates <NUM>, <NUM>, <NUM>, first and second gear plates <NUM>, <NUM>, a plurality of intermeshing gears <NUM>, <NUM>, and a drive shaft <NUM>. The gear pump <NUM> also includes a packing assembly <NUM> including a packing housing <NUM>, a plurality of packing rings <NUM>, a packing gland <NUM>, a plurality of fasteners <NUM> and a thrust washer <NUM> seals against the first end plate <NUM> to prevent fluid leakage past the drive shaft <NUM>. A key <NUM> may be set into the drive shaft <NUM> to couple the drive shaft to a motor (not shown). The drive shaft <NUM> may be coupled to the drive gears <NUM>, while the driven gears <NUM> may be coupled to associated arbors <NUM> which themselves are rotatably supported in openings <NUM> in the first end plate <NUM>. The drive gears <NUM> and driven gears <NUM> may be received within openings <NUM> in the first and second gear plates <NUM>, <NUM>.

Inlet and outlet ports (not shown) may be formed in one or more of the end plates <NUM>, <NUM>, <NUM> for moving fluid through the pump <NUM>. These ports may be coupled to appropriate inlet and outlet piping or tubing (not shown) via an O-ring or other appropriate connection. The first, second and third end plates <NUM>, <NUM>, <NUM> and the first and second gear plates <NUM>, <NUM>, may be aligned using a series of dowels <NUM> positioned in associated openings in the respective plates, and the plates may be fixed in its assembled form via a plurality of fasteners <NUM>, which in the illustrated embodiment are socket head cap screws.

<FIG> shows the pump <NUM> in exploded form. As can be seen, the drive shaft <NUM> couples to first and second driving gears <NUM>, which in the illustrated embodiment are the center gears of two three-gear stages <NUM>, <NUM>. The first and second driving gears <NUM> intermesh with respective second and third driven gears <NUM> to power each of the three-gear stages. <FIG> is an end view of the pump <NUM> showing the drive shaft <NUM>, packing assembly <NUM> and end plate <NUM>.

<FIG> shows the internal inter-relation of components of the pump <NUM> when assembled. As can be seen, the first and third end plates <NUM>, <NUM> sandwich the first and second gear plates <NUM>, <NUM> and the second end plate <NUM> therebetween, along with the driving and driven gears <NUM>, <NUM> of the first and second three-gear stages <NUM>, <NUM>.

As can be seen, the drive gears <NUM> and driven gears <NUM> are positioned directly adjacent to the first, second and third end plates <NUM>, <NUM>, <NUM> such that side faces <NUM> of the drive gears <NUM> and the driven gears <NUM> can contact opposing side surfaces <NUM>, <NUM>, <NUM> of the first, second and third end plates, respectively. It will be appreciated that gaps can exist between the side faces <NUM> of the gears and the opposing side surfaces <NUM>, <NUM>, <NUM> of the end plates. As such, a quantity of the pumped fluid can be drawn into these gaps during operation of the pump <NUM> to lubricate the surfaces and to prevent or minimize direct contact between the surfaces.

Referring to <FIG>, the first end plate <NUM> is shown. Although this description will proceed with relation to the first end plate <NUM> it will be appreciated that the description will apply equally to the second and third end plates <NUM>, <NUM>. The side surface <NUM> of the first end plate <NUM> may be a substantially planar surface having a central opening <NUM> for receiving the drive shaft <NUM>, and first and second oppositely disposed openings <NUM> for receiving the arbor <NUM> therethrough. A first groove region <NUM> is disposed in the side surface <NUM> adjacent the central opening <NUM>, while a pair of second groove regions <NUM> is disposed in the side surface adjacent the first and second openings <NUM>.

The first groove region <NUM> comprises first and second sets of spiral grooves 56A, B formed in the side surface <NUM> of the first end plate <NUM>. Each of the first and second sets of spiral grooves 56A, B includes a plurality of individual spiral grooves <NUM> having first ends 58A positioned a first distance "D" from the central opening <NUM>, and second ends 58B fanning out in a direction away from the central opening. The first and second sets of spiral grooves 56A, B may be disposed on opposite sides of the central opening <NUM> such that first and second non-grooved regions <NUM>, <NUM> are formed adjacent the central opening <NUM>. These non-grooved regions <NUM>, <NUM> are positioned adjacent to the outlet ports "OP" of the first end plate <NUM>. These non-grooved regions <NUM>, <NUM> can be positioned to avoid creating a flow path between high and low pressure sides of the meshing gears.

The second groove region <NUM> associated with each of the first and second openings <NUM> each includes a single set of spiral grooves <NUM> formed in the side surface <NUM> of the first end plate <NUM>. The single set of spiral grooves <NUM> includes a plurality of individual spiral grooves <NUM> having first ends 66A positioned a first distance "D" from the respective first and second opening <NUM>, and second ends 66B fanning out in a direction away from the opening. The single set of spiral grooves <NUM> may be arranged such that a non-grooved region <NUM> is formed adjacent each of the first and second openings. The non-grooved region <NUM> may be positioned adjacent to the outlet ports "OP" of the first end plate <NUM>. The non-grooved region <NUM> can be positioned to avoid creating a flow path between high and low pressure sides of the meshing gears.

In some embodiments the spiral grooves <NUM>, <NUM> may have the shape of a logarithmic curve, and are disposed in the surface of the end-plates <NUM>, <NUM>, <NUM> adjacent to the running faces <NUM> of the gears <NUM>, <NUM>. As can be seen in <FIG>, which shows an exemplary view illustrating the disclosed spiral grooves <NUM> in the context of an exemplary gear <NUM>, the second ends 66B of the spiral grooves <NUM> begin immediately beyond the root diameter "RD" of the gear and terminate at the first ends 66A at a diameter that is larger than the ID of the opening <NUM> in the end-plate <NUM> leaving a specified dam region <NUM> that runs the circumference of the opening. The rotation of the gear <NUM> in relation to the grooves <NUM> drives the fluid along the length of the groove <NUM> in the direction of arrow "A" (i.e., from the second end 66B to the first end 66A) until it reaches the dam region <NUM>. This generates a low pressure zone in the grooves <NUM> at the gear root (adjacent the second ends 66B of the grooves <NUM>) and a high pressure zone located at the termination (i.e., the first ends 66A) of the grooves <NUM>. This high pressure causes an increase in the fluid film thickness between the gear <NUM> and end-plate <NUM>, and imparts an axial force between the gear and end plate, eliminating contact.

In some embodiments the grooves <NUM> are formed by a laser etching process, and have a uniform depth along their length. It will be appreciated that other techniques may be used to form the grooves. In addition, it is contemplated that in some instances the grooves may not be of uniform depth along their lengths.

In some embodiments, the groove-to-dam ratio is optimized for high load-carrying capacity or minimum take-off velocity (i.e., the speed at which separation between the gears and the end plate occurs). Groove depth may also be optimized for high load-carrying capacity. The grooves may have a depth of less than about <NUM> micrometers to optimize load carrying capacity and to minimize wear. In addition, if kept shallow the grooves may be used as wear indicators. That is, if the grooves begin to disappear such a condition can be observed during routine maintenance and/or cleaning.

According to the invention a width of the grooves adjacent to the root diameter "RD" of the associated gear <NUM>, <NUM> does not exceed a width of the gear tooth at the root diameter. It will be appreciated that if the groove were wider than the gear tooth the groove could connect two fluid pockets, thus reducing the pressure differential between the volumes and adversely affecting the overall pressure building capability of the pump.

In some embodiments groove spiral shape may be obtained using the formula: <MAT>.

Where r and ϕ are polar coordinates, r<NUM> is the radius at termination (i.e., at the first ends 58A, 66A of the grooves <NUM>, <NUM>) and α is the angle between the tangent line at any point on the log curve and the moving direction at that same point.

As previously noted, although a single set of grooves <NUM> have been described in relation to the first end plate <NUM>, it will be appreciated that the same description equally applies to the remaining groove sets and the second and third end plates <NUM>, <NUM>. It will also be appreciated that the second end plate <NUM> will have groove sets on both sides of the end plate to interact with the first and second gear sets <NUM>, <NUM>.

As such, the driving and driven gears <NUM>, <NUM> of each of the first and second gear sets <NUM> will oppose groove sets on both sides of the gears, providing a self-centering feature for the gears which centering thrust is applied to either side of the gears. This equal and opposite thrust load can serve to center the gears between their associated end plates. Thus, the disclosed arrangement provides a benefit during startup and well as operation.

Referring now to <FIG> and <FIG>, an alternative gear pump <NUM> is shown. The gear pump <NUM> includes a central gear plate <NUM>, front and rear plates <NUM>, <NUM>, a seal plate <NUM> and a drive shaft <NUM>. An inlet port (not shown) and an outlet port <NUM> may be formed in the central gear plate for moving fluid through the pump <NUM>. The inlet and outlet ports may be coupled to inlet and outlet piping or tubing via an o-ring connection. The pump <NUM> may be fixed in its assembled form via a plurality of fasteners, which in the illustrated embodiment are socket head cap screws <NUM>, <NUM>.

The drive shaft <NUM> includes a first gear <NUM> which intermeshes with a second gear <NUM> of a driven shaft <NUM>. First and second asymmetrical bearings <NUM>, <NUM> are positioned on opposite sides of the first and second gears <NUM>, <NUM> and receive the drive shaft <NUM> and driven shaft <NUM> via respective bores 128A, B, 130A, B. The first and second gears <NUM>, <NUM> and first and second asymmetrical bearings <NUM>, <NUM> are received within an asymmetrical opening <NUM> in the central gear plate <NUM>. In the illustrated embodiment, the asymmetrical opening <NUM> is shaped to correspond to the shape of the asymmetrical bearings <NUM>, <NUM>, which facilitates installation of the bearings and maintains their alignment during operation.

The seal plate <NUM> may fix a variety of sealing elements to the front plate <NUM> to prevent fluid leakage around the drive shaft <NUM>. The sealing elements may include an o-ring <NUM>, a lip seal <NUM> and a sealing sleeve <NUM>, all of which may be received in a suitably configured recess <NUM> in the front plate <NUM>.

<FIG> shows the second asymmetrical bearing <NUM>. Although this description will proceed with relation to the second asymmetrical bearing <NUM> it will be appreciated that the description equally applies to the first asymmetrical bearing <NUM>. The side surface <NUM> of the second asymmetrical bearing <NUM> may have a substantially planar surface with bores 130A and 130B. The side surface <NUM> will face the drive gear <NUM> and the driven gear <NUM> when the pump <NUM> is assembled. Groove regions <NUM> are disposed in the side surface <NUM> adjacent the bores 130A, 130B. The groove regions <NUM> each include a set of spiral grooves <NUM> formed in the side surface <NUM> of the second asymmetrical bearing <NUM>. The set of spiral grooves <NUM> includes a plurality of individual spiral grooves <NUM> having first ends 166A positioned a first distance "D" from the respective bores 130A, 130B, and second ends 166B fanning out in a direction away from the bores. The set of spiral grooves <NUM> may be arranged such that a non-grooved region <NUM> is formed adjacent each of the bores. The non-grooved region <NUM> may be positioned to avoid creating a flow path between high and low pressure sides of the meshing gears <NUM>, <NUM>.

In some embodiments the spiral grooves <NUM> may have the shape of a logarithmic curve, and are disposed in the surface of the asymmetrical bearings <NUM>, <NUM> adjacent to the running faces of the gears <NUM>, <NUM>. Thus, the grooves and groove arrangement of the embodiment of <FIG> and <FIG> can have any or all of the physical and/or operational features previously described in relation to the grooves of the embodiment of <FIG> and <FIG>.

In some embodiments not within the scope of the claims the spiral grooves can be provided on the side faces <NUM> of the drive and/or driven gears <NUM>, <NUM> in lieu of the first, second and third end plates <NUM>, <NUM>, <NUM> or the first and second asymmetrical bearings <NUM>, <NUM>. Such spiral grooves can have some or all of the features previously described in relation to <FIG> and <FIG>.

In pumps that are subject to significant axial load in one direction, the disclosed arrangement can be applied to only one plate in order to generate a counteracting axial force.

The disclosed arrangement can be incorporated into pumps that will have applications with high rates of gear face galling or low lubricity applications that impart high wear on the gear faces. This disclosed arrangement can also be utilized in low viscosity applications, making use of the side clearance equalization to reduce side clearance slip and therefore improve overall efficiency. The disclosed arrangement can also be used in applications having start-up face failure issues.

This disclosed spiral groove arrangement can be installed after all other manufacturing processes are completed, thus enabling better control of groove location and depth. As noted, this precise and symmetric spiral groove feature positioned adjacent to opposed gear face can create a desirable centering balance of forces. The presence of the disclosed fluid dam can ensure minimal negative impact on pumping efficiency. The disclosed arrangement can generate separation force in addition to acting as a fluid reservoir. The extension of the spiral groove feature beyond the root diameter of the gear can allow for more efficient filling of the groove and better pressure generation. At a threshold speed, the thrust load can cause the gear to run with more equal side clearances. The disclosed arrangement thus eliminates the need for exotic materials, coatings, or surface treatments to prevent wear.

The disclosed arrangement provides a less costly manufacturing solution, and is also more easily controlled as compared to pre-heat treatment processes or hard ground features as have been used previously. The disclosed arrangement can also improve pump efficiency, due to equalized side clearances between the gear side faces and the associated end plates. Equalized side clearances can also reduce asymmetrical wear of the pump end plates or bearing surfaces. The inward-pumping action caused by the spiral grooves can generate higher load-bearing capability as compared to other thrust generating designs such as sliding bearings.

Claim 1:
A gear pump (<NUM>), comprising:
a housing (<NUM>);
a drive gear (<NUM>) and a driven gear (<NUM>), the drive gear (<NUM>) and the driven gear (<NUM>) each having gear side surfaces (<NUM>); and
first and second end plates (<NUM>,<NUM>,<NUM>) having plate side surfaces (<NUM>,<NUM>,<NUM>), the plate side surfaces each including a plurality of spiral grooves (<NUM>,<NUM>) disposed opposite the gear side surfaces;
the first and second end plates further comprising:
a first opening (<NUM>) and a second opening (<NUM>) for receiving shafts (<NUM>,<NUM>) associated with the drive gear (<NUM>) and the driven gear (<NUM>); and
wherein the plurality of spiral grooves includes a first groove region (56A,56B) positioned adjacent the first opening (<NUM>) and a second groove region (66A) positioned adjacent the second opening (<NUM>);
wherein the plurality of spiral grooves are oriented such that rotation of the drive gear (<NUM>) and the driven gear (<NUM>) generates a low pressure zone in the plurality of spiral grooves adjacent a gear root of the drive gear and a gear root of the driven gear and generates a high pressure zone in the plurality of spiral grooves adjacent the first opening (<NUM>) and the second opening (<NUM>); and
wherein the plurality of spiral grooves of the first groove region (56A, 56B) have first ends positioned a first distance from the first opening (<NUM>), thereby forming a circumferential dam around the first opening; and wherein the plurality of spiral grooves of the second groove region (66A) have first ends positioned a first distance from the second opening (<NUM>), thereby forming a circumferential dam around the second opening; and
wherein the width of the plurality of spiral grooves adjacent a root diameter (RD) of the gear teeth of the drive gear (<NUM>) and driven gear (<NUM>) does not extend beyond a width of the gear teeth of the drive gear (<NUM>) and the driven gear (<NUM>) at the root diameter (RD) of the gear teeth.