Patent Description:
Stationary or floating bearings are used to support gears in a gear pump. Wear damage on the surface of the gear or bearing can result from contact between the gear and the bearing. These surfaces can mechanically wear over time and are sensitive to friction or contact. Mechanical efficiency, pump operating life, operating pressures, and speeds are all limited by preventing gear and bearing wear and the materials usable for the gear and bearing. Accordingly, there remains a need to reduce friction and prevent metal-to-metal contact by controlling a fluid film thickness between the gear and bearing during operation.

<CIT> describes a gear pump with end plates or bearings having spiral grooves. <CIT> describes a hydraulic geared machine. <CIT> describes a vane pump.

A fuel pump assembly for a gas turbine engine is described herein and defined in claim <NUM>.

A method of operating a pair of gear and bearing assemblies is described herein and defined in claim <NUM>.

While the above-identified figures set forth one or more embodiments of the present invention, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents embodiments by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope of the invention as defined by the appended claims. The figures may not be drawn to scale, and applications and embodiments of the present invention may include features and components not specifically shown in the drawings.

Gear pumps utilize gears to transfer fluids through the gear pump from an inlet to an outlet. The circumferential rotation of the gears deliver the fluid from the inlet to the outlet through each gear tooth. Gear pumps typically utilize two gears that have meshing teeth and are well suited for pumping low and high viscosity fluids. The gears in gear pumps are supported by bearings for handling axial load.

A gear and bearing assembly for a gear pump is disclosed herein that includes a drive shaft, a gear set, and bearings. The drive gear is connected to and coaxial with the shaft. The shaft transmits rotational motion to the gear and the gear rotates about the same axis as the shaft. The bearings support the gear and handle axial loads during shaft rotation. The gear or bearings have a plurality of indents in a wear surface to create a fluid film thickness with a fluid between the gear and bearing. The indents create a separation force on the fluid film, causing turbulent fluid flow between the gear and bearing. This separation force generates an appropriate fluid film thickness for tribology lubrication that assists in counteracting the axial load pushing the gear and bearing closer to each other. The fluid film thickness reduces or prevents solid surface contact between the gear and bearing and acts as a lubricant.

<FIG> shows a perspective view of first gear and bearing assembly <NUM> and second gear and bearing assembly <NUM>, which can be a portion of a gear pump that includes two gears along two separate shafts with the two gears having teeth that mesh with each other to pump the fluid. First gear and bearing assembly <NUM> includes axial centerline <NUM>, shaft <NUM>, first bearing <NUM>, first gear <NUM>, and second bearing <NUM>. Shaft <NUM> extends along axial centerline <NUM>. First gear <NUM> is connected to and coaxial with shaft <NUM>. First bearing <NUM> is coaxial with shaft <NUM> and is on one axial side of first gear <NUM>. First bearing <NUM> is configured to support first gear <NUM>. Second bearing <NUM> is coaxial with shaft <NUM> and is on an opposite axial side of first gear <NUM> from first bearing <NUM>. Second bearing <NUM> is configured to support first gear <NUM>. First bearing <NUM>, first gear <NUM>, and second bearing <NUM> are arranged sequentially along axial centerline <NUM>. First gear and bearing assembly <NUM> can include other components not expressly shown in <FIG>. For example, first gear and bearing assembly <NUM> can include a housing or casing, seal, inlet port, outlet port, and safety valve. First gear and bearing assembly <NUM> can be a portion of an internal gear pump assembly or an external gear pump assembly. First gear and bearing assembly <NUM> can include a different number of gears or bearings from what is shown in <FIG>.

Second gear and bearing assembly <NUM> can be similar in components and configuration to first gear and bearing assembly <NUM> and can mirror first gear and bearing assembly <NUM>. Second gear and bearing assembly <NUM> includes third bearing <NUM>, second gear <NUM>, and fourth bearing <NUM>. Second gear <NUM> is connected to and coaxial with a second shaft (not shown). Third bearing <NUM> is coaxial with the second shaft and is on one axial side of second gear <NUM>. Third bearing <NUM> is configured to support second gear <NUM>. Fourth bearing <NUM> is coaxial with the second shaft and is on an opposite axial side of second gear <NUM> from third bearing <NUM>. Fourth bearing <NUM> is configured to support second gear <NUM>. Third bearing <NUM>, second gear <NUM>, and fourth bearing <NUM> can be arranged sequentially along a separate axial centerline than axial centerline <NUM>. Second gear and bearing assembly <NUM> can include other components not expressly shown in <FIG>. For example, second gear and bearing assembly <NUM> can include a housing or casing, seal, inlet port, outlet port, and safety valve. Second gear and bearing assembly <NUM> can be a portion of an internal gear pump assembly or an external gear pump assembly. Second gear and bearing assembly <NUM> can include a different number of gears or bearings from what is shown in <FIG> and can be oriented differently with respect to first gear and bearing assembly <NUM>.

Second gear and bearing assembly <NUM> can have similar features, components, characteristics, and/or configurations to that of first gear and bearing assembly <NUM>. For example, second gear and bearing assembly <NUM> can include gaps, indents, and wear surfaces like first gear and bearing assembly <NUM>. Third bearing <NUM> and fourth bearing <NUM> can have wear surfaces like first wear surface <NUM> and second wear surface <NUM> with indents similar to indents <NUM>. Second gear and bearing assembly <NUM> can have a fluid film thickness to prevent metal-to-metal or surface contact like that of first gear and bearing assembly <NUM>.

During operation, shaft <NUM> rotates about axial centerline <NUM> and transmits rotational motion to first gear <NUM>. First bearing <NUM> and second bearing <NUM> support first gear <NUM> directly by handling axial loads (i.e., by preventing substantial axial movement of first gear <NUM>) and indirectly by handling radial loads (i.e., by preventing radial movement of shaft <NUM>). Fluid is pumped with first gear and bearing assembly <NUM> when first gear <NUM> is rotated. First gear and bearing assembly <NUM> increases the pressure of the fluid (i.e., pumps the fluid). First bearing <NUM> and second bearing <NUM> are configured to support the axial loads imparted on first bearing <NUM> and second bearing <NUM> by first gear <NUM> during rotation. First bearing <NUM> and second bearing <NUM> can be stationary or floating bearings such that bearings <NUM> and <NUM> are stationary relative to shaft <NUM> and first gear <NUM>, rotate at a slower or faster speed relative to shaft <NUM> and first gear <NUM>, or rotate in an opposite direction relative to shaft <NUM> and first gear <NUM>. Shaft <NUM> can be a drive shaft and first gear <NUM> can be a drive gear. For example, shaft <NUM> can transmit rotational motion to first gear <NUM> causing second gear <NUM> to rotate. First gear <NUM> and second gear <NUM> have teeth that mesh causing first gear <NUM> and second gear <NUM> to rotate together to pump a fluid. In another example, second gear and bearing assembly <NUM> can have a drift shaft and a drive gear. For example, second gear <NUM> could be a drive gear causing first gear <NUM> to rotate. Third bearing <NUM> and fourth bearing <NUM> are configured to support the axial loads imparted on third bearing <NUM> and fourth bearing <NUM> by second gear <NUM> during rotation. Third bearing <NUM> and fourth bearing <NUM> can be stationary relative to second gear <NUM>, rotate at a slower or faster speed relative to second gear <NUM>, or rotate in an opposite direction relative to second gear <NUM>.

<FIG> shows a side view of first gear and bearing assembly <NUM> and includes axial centerline <NUM>, shaft <NUM>, first bearing <NUM>, second wear surface <NUM>, first gear <NUM>, first wear surface <NUM>, third wear surface <NUM>, second bearing <NUM>, fourth wear surface <NUM>, first axial side <NUM>, second axial side <NUM>, gap 40A, and gap 40B.

Shaft <NUM> extends along axial centerline <NUM>. In one example, shaft <NUM> can have a circular cross-sectional shape or can be other cross-sectional shapes, such as rectangle, triangle, pentagon, or hexagon. Shaft <NUM> can be within a gas turbine engine and can be a main shaft, a secondary shaft, or another component for transmitting rotational energy. Shaft <NUM> can transmit motion to other components and can rotate about axial centerline <NUM>. Shaft <NUM> can be made from a variety of different materials.

First gear <NUM> is connected to and coaxial with shaft <NUM> and contains first wear surface <NUM> on first axial side <NUM> and third wear surface <NUM> on second axial side <NUM>. First gear <NUM> can be annular in shape with teeth extending radially outward along the entire circumference of first gear <NUM>. First gear <NUM> can be made of various materials. In one example, first gear <NUM> is made of a single material. In another example, first gear <NUM> is made of multiple materials or pieces fastened together. First gear <NUM> can be built with shaft <NUM> as a single piece or can be two separate pieces welded, attached, or otherwise fastened together. First wear surface <NUM> and third wear surface <NUM> can be the same material as first gear <NUM> or different materials from first gear <NUM> and fastened to first gear <NUM>. First wear surface <NUM> and third wear surface <NUM> can be two different materials. In one example, first gear <NUM> has teeth for meshing with another gear to pump a fluid through a gear pump. First wear surface <NUM> and third wear surface <NUM> can be on any portion of the axial ends of first gear <NUM>, including the radially outermost portion of the axial ends of first gear <NUM> that include teeth.

First bearing <NUM> is coaxial with shaft <NUM> and is on first axial side <NUM> of first gear <NUM>. First axial side <NUM> includes a portion of shaft <NUM>, first bearing <NUM>, first wear surface <NUM>, second wear surface <NUM>, and gap 40A. In one example, first bearing <NUM> has an annular shape. In another example, first bearing <NUM> can be stationary or floating. First bearing <NUM> supports first gear <NUM>. First bearing <NUM> allows first gear <NUM> to rotate for pumping fluid and ensures first gear <NUM> does not move too much in the axial direction. First bearing <NUM> can also indirectly support first gear <NUM> in the radial direction. Second wear surface <NUM> is on first bearing <NUM> and is positioned to interact with first wear surface <NUM> on first gear <NUM>. First bearing <NUM> can be made from a variety of different materials. First bearing <NUM> can be the same or different material as second wear surface <NUM>. If second wear surface <NUM> is a different material, first bearing <NUM> can be attached to second wear surface <NUM>. Indents <NUM> (as shown in <FIG>, <FIG>, and <FIG>) are distributed in first wear surface <NUM> or second wear surface <NUM>. Indents <NUM> can be on any portion of first wear surface <NUM> or second wear surface <NUM>, including the portion of teeth on first wear surface <NUM> of first gear <NUM>.

Gap 40A is positioned between first wear surface <NUM> and second wear surface <NUM>. Gap 40A is a gap between first wear surface <NUM> and second wear surface <NUM> for the fluid film to enter and/or flow. The size of gap 40A (distance between first wear surface <NUM> and second wear surface <NUM>) can vary depending on, but not limited to, fluid type, first gear <NUM> rotation speed, environmental conditions, thermal energy, separation forces, friction, and fluid film interaction with indents <NUM>. In one example, the fluid film can consist of a fuel. In another example, the fluid film can consist of jet fuel. As discussed below, indents <NUM> on either first wear surface <NUM> or second wear surface <NUM> create turbulent flow of the fluid therebetween, which causes a separation force to push first wear surface <NUM> away from second wear surface <NUM> to control/increase gap 40A.

Second bearing <NUM> is coaxial with shaft <NUM> and is on second axial side <NUM> of first gear <NUM>. Second bearing <NUM> can be similar to first bearing <NUM>, but second bearing <NUM> is on an opposite side of first gear <NUM>. Second axial side <NUM> includes a portion of shaft <NUM>, second bearing <NUM>, third wear surface <NUM>, fourth wear surface <NUM>, and gap 40B. In one example, second bearing <NUM> has an annular shape. Second bearing <NUM> can be stationary or floating. Second bearing <NUM> allows first gear <NUM> to rotate and ensures first gear <NUM> does not move too much in the axial direction. Second bearing <NUM> can also indirectly support first gear <NUM> in the radial direction.

Fourth wear surface <NUM> is on second bearing <NUM> and is positioned to interact with third wear surface <NUM> on first gear <NUM>, which is on an opposite side of first wear surface <NUM> of first gear <NUM>. Second bearing <NUM> can be made from a variety of different materials. Second bearing <NUM> can be the same or different material as fourth wear surface <NUM>. If fourth wear surface <NUM> is a different material, second bearing <NUM> can be attached to fourth wear surface <NUM>. Indents <NUM> are distributed in third wear surface <NUM> or fourth wear surface <NUM>. Indents <NUM> can be on any portion of the third wear surface <NUM> or the fourth wear surface <NUM>, including the portion of teeth on third wear surface <NUM> of first gear <NUM>.

Gap 40B is positioned between third wear surface <NUM> and fourth wear surface <NUM>. Gap 40B is a gap between the third wear surface <NUM> and fourth wear surface <NUM> for the fluid film to enter and/or flow. The size of gap 40B (distance between third wear surface <NUM> and fourth wear surface <NUM>) can vary depending on, but not limited to, fluid type, first gear <NUM> rotation speed, environmental conditions, thermal energy, separation forces, friction, and the fluid film interaction with indents <NUM>. As discussed below, indents <NUM> of either third wear surface <NUM> and fourth wear surface <NUM> create turbulent flow of the fluid therebetween, which causes a separation force to push third wear surface <NUM> away from fourth wear surface <NUM> to control/increase gap 40B.

During operation, fluid is pumped by first gear and bearing assembly <NUM> when first gear <NUM> is rotated. First gear <NUM> rotation allows fluid to enter gap 40A between first wear surface <NUM> and second wear surface <NUM> and gap 40B between third wear surface <NUM> and fourth wear surface <NUM>. Indents <NUM> create a separation force on the fluid film to produce a certain fluid film thickness. This separation force during rotation increases the width of gaps 40A and 40B to reduce or prevent contact between first gear <NUM> and first bearing <NUM> and first gear <NUM> and second bearing <NUM> because the separation force ensures gaps 40A and 40B are sufficiently large enough. While the surfaces are described as "wear surfaces" herein, gaps 40A and 40B can be sufficient to prevent any wear altogether by preventing contact between the wear surfaces. Due to indents <NUM>, fluid film can have a turbulent movement during first gear <NUM> rotation. The fluid film can support first gear <NUM> during rotation because of indent <NUM> separation force. The fluid film generation prevents or reduces contact damage to first gear <NUM>, first bearing <NUM>, and second bearing <NUM>. Thus, less waste heat is created allowing for a variety of different materials to be used that could not previously be used due to temperature limitations.

Indents <NUM> can reduce rotating friction by improving the fluid film thickness between both first gear <NUM> and first bearing <NUM> and first gear <NUM> and second bearing <NUM>. Indents <NUM> form a sufficiently thick fluid film to prevent or reduce contact. The fluid between first gear <NUM> and first bearing <NUM> and first gear <NUM> and second bearing <NUM> has more of a turbulent flow or movement because of indents <NUM> on the surface of first wear surface <NUM>, second wear surface <NUM>, third wear surface <NUM> and/or fourth wear surface <NUM>. Gear fuel pump friction reduction will improve pump mechanical efficiency, which translates to extended pump operating life and cavitation erosion reduction. Different first gear and bearing assembly <NUM> materials could be utilized that have lower coefficients of thermal conductivity and the disclosed first gear and bearing assembly <NUM> can have an extended operating life as compared to existing gear pumps due to better fluid film generation and less mechanical wear. The disclosed first gear and bearing assembly <NUM> can be operated at higher pressure and speed conditions as compared to existing gear pumps without inducing first bearing <NUM> and second bearing <NUM> face wear. Without indents <NUM> on the surface of first wear surface <NUM>, second wear surface <NUM>, third wear surface <NUM> and/or fourth wear surface <NUM>, first gear <NUM> and first bearing <NUM> and first gear <NUM> and second bearing <NUM> can damage each other with contact.

In one example, first gear and bearing assembly <NUM> is part of a fuel pump assembly. In another example, first gear and bearing assembly <NUM> is part of a fuel pump assembly for a gas turbine engine. Indents <NUM> can be especially important in making a fluid film thickness to reduce or prevent bearing and/or gear wear for a gas turbine engine due to extreme operating conditions such as high temperatures. When temperature rises, the viscosity of jet fuel drops and makes separation of the gear and bearing more difficult. Indents <NUM> solve this problem by creating the separation force to maintain or increase the fluid film thickness.

<FIG> are cross-sectional views of various indent <NUM> shapes. Indents <NUM> can be distributed in first wear surface <NUM>, second wear surface <NUM>, third wear surface <NUM>, and fourth wear surface <NUM>.

<FIG> shows a cross-sectional view of indent 44A with a cylindrical indent shape with a depth "D" and width at the surface "W. " For example, indent 44A depth can be the same distance as the width at the surface (such as a semi-circle). Indent 44A depth can also be longer or shorter than the width at the surface.

<FIG> shows a cross-sectional view of indent 44B with a rectangular indent shape. For example, indent 44B depth can be the same distance as the width at the surface (such as a square). Indent 44B depth can also be longer or shorter than the width at the surface for a deeper or shallower indent 44B, respectively (such as a rectangle).

<FIG> shows a cross-sectional view of indent 44C with a triangular indent shape. For example, the triangular shape could be that of an equilateral triangle, isosceles triangle, or scalene triangle. The depth of indent 44C can be the same, shorter, or longer than the width at the surface.

<FIG> shows a cross-sectional view of indent 44D with a wedge indent shape. Indent 44D can have various angles with a steeper wall and a flatter wall. The steeper wall or flatter wall can be on the first side in the direction of fluid flow. The depth of indent 44D can be the same, shorter, or longer than the width at the surface.

<FIG> shows a cross-sectional view of indent 44E with a semi-ellipse indent shape. The depth of indent 44E can be the same, shorter, or longer than the width at the surface. <FIG> are non-limiting examples of cross-sectional views of indent <NUM> shapes. Any side or wall of indents 44A-44E can be rotated towards the direction of fluid flow.

In one example, each of the indents <NUM> has a depth that the indents <NUM> extend into the first wear surface <NUM>, second wear surface <NUM>, third wear surface <NUM> or fourth wear surface <NUM>. The ratio of surface area of one of the indents <NUM> to the depth of one of the indents <NUM> in this example is <NUM>. According to the invention, the indents <NUM> have a ratio of surface area to depth of between <NUM> and <NUM>.

In one example, the depth of each indent <NUM> can range from <NUM> micrometer to <NUM> micrometers. In another example, the depth of each indent <NUM> is approximately <NUM> micrometers.

During first gear <NUM> rotation, indents <NUM> create a separation force on the fluid film to produce a certain fluid film thickness. Different indent <NUM> cross-sectional shapes (44A-44E) create different fluid film thicknesses depending on gear rotation speed because the separation force applied to the fluid is different depending on indent <NUM> cross-sectional shapes (44A-44E). The fluid interacts differently with various cross-sectional shapes because of the edges or curves of the cross-sectional shapes and because different amounts of fluid can interact with the shape. Various cross-sectional shapes of indents <NUM> may be chosen based off operating conditions or desired fluid film thickness. For example, the hydrodynamic lifting forces can change based on indent <NUM> cross-sectional shapes (44A-44E). Multiple different indent <NUM> cross-sectional shapes can be on the same wear surface. The cross-sectional shapes (44A-44E) are shown as non-limiting examples of possible indent <NUM> cross-sectional shapes.

Indents <NUM> creating a sufficiently thick fluid film thickness allows for use of other first gear and bearing assembly <NUM> materials that may have different properties optimized for cavitation, heat, sliding, operating life, or operating conditions such as pressure or velocity. Higher temperatures and operating speeds may be utilized because less waste heat is created with a sufficiently thick fluid film in first gear and bearing assembly <NUM>. Thus, higher operating temperatures can be maintained because of this fluid film thickness. First gear and bearing assembly <NUM> surfaces such as first wear surface <NUM>, second wear surface <NUM>, third wear surface <NUM> and/or fourth wear surface <NUM> with indents <NUM> can be made using micro-laser etching or laser ablation. For example, femtosecond laser ablation machines can create indents <NUM> in first wear surface <NUM>, second wear surface <NUM>, third wear surface <NUM> and fourth wear surface <NUM>. Laser ablation works well for the depths of indents <NUM> that are desired. Other surface modification techniques can also be used to create indents <NUM>.

<FIG> are plan views of various indent <NUM> surface shapes. A surface shape is the shape of indent <NUM> when looking straight down on first wear surface <NUM>, second wear surface <NUM>, third wear surface <NUM> or fourth wear surface <NUM>. <FIG> shows a plan view of indent 44F with a rectangle surface shape with side length "L" and width "W. " Indent 44F has a length of a side and a width (the distance of the top and bottom). Indent 44F can have equal lengths and widths to be a square. Indent 44F can also be a rectangle with unequal lengths and widths. Any side can be the leading side towards the direction of fluid flow.

<FIG> shows a plan view of indent <NUM> with a circle surface shape. Indent <NUM> can have an equal radius at all points. The radius can be changed for various indents <NUM> so as to have a mixture of different sized indent <NUM> on a surface.

<FIG> shows a plan view of indent <NUM> with a triangle surface shape. Indent <NUM> can be any triangular shape, such as an equilateral triangle, isosceles triangle, or scalene triangle. Any side can be the leading side towards fluid flow. In another example, one of the points of the triangle could be pointed towards the direction of fluid flow.

<FIG> shows a plan view of indent 44I with an ellipse surface shape. Indent 44I can have a longer and shorter axis where the longer and shorter axis lengths can vary in length.

<FIG> shows a plan view of indent 44J with an oval surface shape. Indent 44J can be such that the oval surface shape has only one axis of symmetry (egg shaped).

<FIG> shows a plan view of indent <NUM> with a stadium surface shape. Indent <NUM> straight sides can be shorter or longer. Indent <NUM> rounded corners can be more or less rounded. Indent <NUM> can be oriented in any direction and with any side or edge towards fluid flow. <FIG> are non-limiting examples of possible indent <NUM> surface shapes (44F-<NUM>). Any of indents 44F-<NUM> along with other surface shapes can be rotated in any direction to have any part of the shape facing towards the fluid flow direction.

In one example, the length of indent 44F can be from <NUM> micrometer to <NUM> micrometers. In another example, the length of indent 44F can be approximately <NUM> micrometers. In one example, the width of indent 44F can be <NUM> micrometer to <NUM> micrometers. In another example, the width of indent 44F is approximately <NUM> micrometers. These lengths and widths can be used for any indent <NUM> surface shapes (44F-<NUM>) or other surface shapes.

These indent <NUM> surface shapes can be on the surfaces of first wear surface <NUM>, second wear surface <NUM>, third wear surface <NUM>, and fourth wear surface <NUM>. Different indent <NUM> surface shapes can create different magnitudes of separation force creating a different fluid film thickness. Depending on the application and operating conditions, the surface shape can be changed to create a lesser or greater fluid film thickness. The surface shapes may have different edges or curves on the surface causing different interactions with the fluid. The fluid interaction with indent <NUM> surface shapes can increase the turbulent movement of the fluid.

<FIG> are plan views of various indent <NUM> configurations. Indents <NUM> are shown on a surface, for example, on first wear surface <NUM>, second wear surface <NUM>, third wear surface <NUM>, or fourth wear surface <NUM>. Each indent <NUM> has a surface shape midpoint <NUM>. The radial direction is shown as "R" and the circumferential direction as "C. " Surface shape midpoint <NUM> is the midpoint of the surface shape of indent <NUM> in circumferential direction C. Indents <NUM> also have a surface shape midpoint <NUM> in the radial direction.

<FIG> is a plan view of an indent configuration where surface shape midpoints <NUM> of indents <NUM> are aligned in both the radial direction and the circumferential direction. <FIG> shows first column <NUM>, second column <NUM>, third column <NUM>, first row <NUM>, second row <NUM>, third row <NUM>, and fourth row <NUM>. Indents <NUM> are aligned with indents <NUM> in adjacent columns and rows.

<FIG> is a plan view of an indent configuration where surface shape midpoints <NUM> of indents <NUM> are aligned in the radial direction. For example, <FIG> shows indents <NUM> with first column <NUM>, second column <NUM>, and third column <NUM>. The indents <NUM> are offset so there are no rows of indents <NUM> like that of <FIG>.

<FIG> is a plan view of an indent configuration where surface shape midpoints <NUM> of indents <NUM> are aligned in the circumferential direction. For example, <FIG> shows indent <NUM> with first row <NUM>, second row <NUM>, and third row <NUM>. The indents <NUM> are offset so there are no columns of indents <NUM>.

<FIG> is a plan view of an indent configuration where surface shape midpoints <NUM> of indents <NUM> are not aligned in either the radial direction or the circumferential direction but are arranged diagonally when looking in the radial direction.

<FIG> is a plan view of an indent configuration where surface shape midpoints <NUM> of indents <NUM> are not aligned in either the radial direction or the circumferential direction. <FIG> of various indent <NUM> configurations are non-limiting examples of indent <NUM> configurations.

<FIG> show examples of indent configurations that can extend circumferentially around the entirety of the first wear surface <NUM>, second wear surface <NUM>, third wear surface <NUM>, and fourth wear surface <NUM>. Indents <NUM> can also be distributed in certain circumferential portions of the previously mentioned wear surfaces while other circumferential sections of the wear surfaces may have no indents. In one example, the total surface area of all the indents <NUM> occupies between <NUM> percent and <NUM> percent of a total surface area of the first wear surface <NUM>, second wear surface <NUM>, third wear surface <NUM> or fourth wear surface <NUM>. This percentage of a total surface area on a wear surface can be advantageous to fully support first gear <NUM> while creating enough separation to prevent any wear. In another example, the indents <NUM> have a gap between each other <NUM> degrees in the radial direction.

Indents <NUM> as shown in <FIG> are shown with indent 44F rectangular surface shape as an example. Indents <NUM> in <FIG> can have other surface shapes such as <NUM>-<NUM>. Indents <NUM> can also have any cross-sectional shape such as indents 44A-44E. In one example of an indent <NUM>, the cross-sectional shape could be that of 44A, the surface shape could be that of 44F, and the orientation on the surface could be that of <FIG>. In another example of an indent <NUM>, the cross-sectional shape could be that of 44B, the surface shape could be that of 44F, and the orientation on the surface could be that of <FIG>.

Different indent <NUM> configurations can cause the fluid film thickness to be different depending on the operating conditions. This is due to the different spacing between indents <NUM> and the way the fluid interacts with indents <NUM> during rotation of first gear <NUM>. Different separation forces creating different fluid film thicknesses can be advantageous because different operating conditions may require more or less separation force. Indent <NUM> configurations can change how turbulent the movement of the fluid is between first gear <NUM> and the first bearing <NUM> and second bearing <NUM> and can increase the separation force. The turbulence of the fluid help to maintain the fluid film thickness.

A fuel pump assembly for a gas turbine engine, among other possible options, includes a shaft, a gear, a first wear surface, a first bearing, a second wear surface, and a plurality of indents. The shaft transmits motion. The gear is connected to and coaxial with the shaft and the gear has a first wear surface. The first bearing is coaxial with the shaft and the first bearing is configured to support the gear. The first bearing has a second wear surface positioned to interact with the first wear surface. The plurality of indents is distributed in the first wear surface or the second wear surface and at least two of the plurality of indents are partially aligned in a radial direction. Each of the indents has a depth that the indents extend into the first wear surface or the second wear surface and a ratio of a surface area of one of the indents to the depth of one of the indents is between <NUM> and <NUM>.

The fuel pump assembly of the preceding paragraph can optionally any one or more of the following features, configurations and/or additional components.

In the fuel pump assembly, the first bearing can be on a first axial side of the gear. The assembly can comprise a third wear surface on the gear and a second bearing, wherein the third wear surface is on a second axial side of the gear that is opposite the first wear surface. The second bearing is coaxial with the shaft, the second bearing being configured to support the gear, wherein the second bearing has a fourth wear surface positioned to interact with the third wear surface, wherein the indents are distributed in the third wear surface or the fourth wear surface.

A total surface area of all the indents can occupy between <NUM> percent and <NUM> percent of a total surface area of the first wear surface or the second wear surface.

At least one of the indents can have a cross-sectional shape selected from the group consisting of a rectangle, triangle, wedge, semicircle, and semi-ellipse.

At least one of the indents can have a surface shape selected from the group consisting of a rectangle, circle, triangle, ellipse, oval, and stadium.

Each of the indents has a surface shape midpoint in a circumferential direction, and the midpoints of at least two of the indents can be aligned in a radial direction.

Each of the indents has a surface shape midpoint in a circumferential direction, and the midpoints of at least two of the indents can be aligned in the circumferential direction.

The fuel pump assembly can include a fuel between the first wear surface and the second wear surface when the fuel pump assembly is in operation, wherein the indents control a film thickness of the fuel.

In the assembly, the first bearing can be on a first axial side of the gear. The assembly can include a third wear surface, a second axial side of the gear, a second bearing, and a fourth wear surface. The third wear surface is on the gear, wherein the third wear surface is on a second axial side of the gear that is opposite the first wear surface. The second bearing is coaxial with the shaft, the second bearing being configured to support the gear, wherein the second bearing has the fourth wear surface positioned to interact with the third wear surface, wherein the indents are distributed in the third wear surface or the fourth wear surface.

A method of operating a gear and bearing assembly, among other possible options, includes rotating a gear adjacent a bearing configured to support the gear, the gear having a first wear surface positioned to interact with a second wear surface of the bearing, wherein one of the first wear surface and the second wear surface includes a plurality of indents with at least two of the plurality of indents being partially aligned in a radial direction. The method also includes generating a fluid film thickness with a fluid between the first wear surface and the second wear surface, wherein during said gear rotation the plurality of indents creates a separation force on the fluid to produce the fluid film thickness. Each of the indents has a depth that the indents extend into the first wear surface or the second wear surface and a ratio of a surface area of one of the indents to the depth of one of the indents is between <NUM> and <NUM>.

The method of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following steps, features, configurations, steps, and/or additional components.

The fluid can be a fuel and the method further can include pumping the fuel through the assembly by rotating the gear.

A total surface area of all of the indents can occupy between <NUM> percent and <NUM> percent of a total surface area of the first wear surface or the second wear surface.

Claim 1:
A fuel pump assembly for a gas turbine engine, the fuel pump assembly comprising:
a shaft (<NUM>) for transmitting motion;
a gear connected to and coaxial with the shaft (<NUM>), the gear having a first wear surface;
a first bearing (<NUM>) coaxial with the shaft (<NUM>), the first bearing (<NUM>) being configured to support the gear, wherein the first bearing (<NUM>) has a second wear surface positioned to interact with the first wear surface; and
a plurality of indents (<NUM>), wherein the indents (<NUM>) are distributed in the first wear surface or the second wear surface and at least two of the plurality of indents (<NUM>) are partially aligned in a radial direction, and characterized in that each of the indents (<NUM>) has a depth that the indents (<NUM>) extend into the first wear surface or the second wear surface and a ratio of a surface area of one of the indents (<NUM>) to the depth of one of the indents (<NUM>) is between <NUM> and <NUM>