Patent Description:
Aircraft gas turbine engines receive pressurized fuel from different kinds of fuel pumps including gear-type fuel pumps. The gear pump typically performs over a wide operational speed range while providing needed fuel flows and pressures for various engine performance functions.

Gear pumps often comprise two coupled gears of similar configuration and size that mesh with each other inside an enclosed gear housing. A drive gear may be connected rigidly to a drive shaft. As the drive gear rotates, it meshes with a driven gear thus rotating the driven gear. As the gears rotate within the housing, fluid is transferred from an inlet to an outlet of the gear pump. Typically, the drive gear carries the full load of the gear pump drive or input shaft. The two gears may operate at high loads and high pressures, which may stress the gear teeth.

For given gear sizes the volume of fluid pumped through the gear pump may partially depend on the geometry of the tooth (e.g., depth, profile, etc.), the tooth count, and the width of the gear. Most gear pumps have gears with about ten to sixteen teeth. As the gears rotate, individual parcels of fluid are released between the teeth to the outlet. A common problem with more traditional gear pumps operating at high rotational speeds is cavitation erosion of the surfaces of the gear teeth and bearings. Cavitation erosion results in pitting of surfaces of the gear teeth that may eventually result in degraded pump volumetric capacity and affect pump operability and durability.

<CIT> relates to a gear pump. <CIT> relates to a positive-displacement pump. <CIT> relates to a precision liquid pump. <CIT> relates to a cutting tool using a sintered body. <CIT> relates to a piston pump for injecting gasoline.

According to one embodiment, a fluid gear pump that includes a first gear constructed and arranged to rotate about a first axis is disclosed as claimed in claim <NUM>. The first gear includes a concentrically disposed first hub portion and a plurality of first teeth radially projecting and circumferentially spaced about the first hub portion, the first hub portion being formed of a ceramic material. The pump also includes a second gear operably coupled to the first gear for rotation about a second axis, the second gear including a concentrically disposed second hub portion and a plurality of second teeth radially projecting and circumferentially spaced about the second hub portion, wherein at a time in operation the plurality of first teeth and the plurality of second teeth contact at first contact point and a second contact point to create a backlash volume interposed between the first contact point and the second contact point. The pump further includes a first bearing abutting and coaxial to the first hub portion and a second bearing abutting and coaxial to the second hub portion.

The first gear is formed of a silicon-aluminum-oxygen-nitrogen (SiAlON) ceramic.

In a pump of any prior embodiment, the second gear is formed of a SiAlON ceramic.

The first gear is formed of partially stabilized zirconia.

In a pump of any prior embodiment, wherein, when the first gear is partially stabilized zirconia, it is doped with yttrium.

In a pump of any prior embodiment, the pump also includes a first shaft on which the first gear is carried, a second shaft on which the second gear is carried and the second gear is formed of a ceramic material.

In a pump of any prior embodiment, the pump also includes a third gear carried on the second shaft.

In a pump of any prior embodiment, one or more of the first, second and third gear are formed of a SiAlON ceramic.

In a pump of any prior embodiment, one or more of the first, second and third gears are formed of partially stabilized zirconia.

In one embodiment, a method of reducing cavitation damage during fluid gear pump operation is disclosed as claimed in claim <NUM>. The method includes: rotating a first gear around first axis, the first gear including a concentrically disposed first hub portion and a plurality of first teeth radially projecting and circumferentially spaced about the first hub portion, wherein the first teeth are formed of a ceramic material; rotating a second gear coupled to the first gear about a second axis, the second gear including a concentrically disposed second hub portion and a plurality of second teeth radially projecting and circumferentially spaced about the second hub portion, wherein the plurality of first teeth engage the plurality of second teeth; and transferring fluid from a low pressure side to a high pressure side when the first gear is rotating and the second gear is rotating.

In a method of any prior embodiment, the second gear is formed of a SiAlON ceramic.

In a method of any prior embodiment, the partially stabilized zirconia is doped with yttrium.

In one embodiment a fluid gear pump gear arranged to rotate about a first axis is disclosed. The fluid gear pump gear includes a concentrically disposed first hub portion and a plurality of first teeth radially projecting and circumferentially spaced about the first hub portion, the first hub portion and the first teeth being formed of a ceramic material, and a first shaft on which the first hub portion is carried.

In a fluid gear pump gear of any prior embodiment, the first gear is formed of a silicon-aluminum-oxygen-nitrogen (SiAlON) ceramic.

In a fluid gear pump gear of any prior embodiment, the first gear is formed of partially stabilized zirconia.

In a fluid gear pump gear of any prior embodiment, partially stabilized zirconia is doped with yttrium.

In a fluid gear pump gear of any prior embodiment, the gear also includes a second gear carried on the first shaft.

Various embodiments of the present disclosure are related to the reduction of fluid cavitation within gear pumps. Aircraft engine high pressure fuel pumps typically use a pair of involute gears to generate fuel pressure for the burner injectors. These gears are enclosed in a housing within which they are supported by bearings. In the vicinity of the gear meshing region these bearings form a bridgeland that separates the high and low pressure regions and maintains high pump efficiency. A pump of this description experiences significant pressure oscillations that may lead to the formation and subsequent collapse of cavitation bubbles that may cause material damage. The gears may be especially susceptible to cavitation damage and that results in a deterioration of pump performance and can significantly reduce the useable life of these components. To address these issues a gear shaft that includes gear teeth formed of a ceramic material. Utilization of a ceramic for the gears generally and gear teeth in particular may have the technical effect of reducing cavitation on the gear teeth. Two non-limiting examples of such ceramic materials include, but are not limited to, partially stabilized zirconia and silicon-aluminum-oxygen-nitrogen (SiAlON) ceramics. In one embodiment the stabilized zirconia may be doped with yttrium. In some embodiments, only a portion of gear tooth may be formed of a ceramic and the rest formed of another material, such as stainless steel. In one embodiment, the gear teeth are formed of solid pieces of ceramic.

Referring to <FIG>, one embodiment of a fuel system <NUM> of the present disclosure is illustrated. The fuel system <NUM> may be an aircraft fuel system and may include a fuel supply line <NUM> that may flow liquid fuel from a fuel tank <NUM> to fuel nozzles <NUM> of an engine (not shown). A fuel bypass line <NUM> may be arranged to divert fuel from the supply line <NUM> and back to the fuel tank <NUM>. Various fuel system components may interpose the fuel supply line <NUM> and may include a low pressure fuel pump <NUM>, a heat exchanger <NUM>, a fuel filter <NUM>, a high pressure fuel pump <NUM>, a metering valve <NUM>, a high pressure fuel shutoff valve <NUM>, a screen <NUM>, a fuel flow sensor <NUM>, and a fuel tank shutoff valve <NUM>. The low pressure fuel pump <NUM> may be located downstream of the fuel tank <NUM>. The heat exchanger <NUM> may be located downstream of the low pressure fuel pump <NUM>. The fuel filter <NUM> may be located downstream of the heat exchanger <NUM>. The high pressure fuel pump <NUM> may be located downstream of the fuel filter <NUM> and upstream of the fuel bypass line <NUM>. The metering valve <NUM> may be located downstream from the bypass line <NUM>. The high pressure fuel shutoff valve <NUM> may be located downstream from the bypass line <NUM>. The screen <NUM> may be located downstream from the high pressure fuel shutoff valve <NUM>, and the fuel flow sensor <NUM> may be located downstream from the screen <NUM>. It is further contemplated and understood that other component configurations of a fuel system are applicable and may further include additional sensors, valves and other components.

The heat exchanger <NUM> may be adapted to use the flowing fuel as a heat sink to cool other liquids flowing from any variety of auxiliary systems of an aircraft and/or the engine. For example, the heat exchanger <NUM> may transfer heat from an oil and to the fuel. The oil may be used to lubricate any variety of auxiliary components including, for example, a gear box (not shown) of the engine. Such a transfer of heat may elevate the temperature of the fuel which may make the high pressure fuel pump <NUM> more prone to cavitation.

Referring to <FIG> and <FIG>, one non-limiting example of the high pressure fuel pump <NUM> is illustrated as a gear pump with a housing removed to show internal detail. The housing is shown, generally, by dashed line <NUM>.

The gear pump <NUM> may be a dual stage pump and may include a fuel centrifugal boost pump housing <NUM>, an input drive shaft <NUM> constructed for rotation about a first axis <NUM>, a coupling shaft <NUM> constructed for rotation about a second axis <NUM>, a drive gear <NUM> with associated bearings <NUM>, a driven gear <NUM> with associated bearings <NUM>, a motive drive gear <NUM> and a motive driven gear <NUM> configured for rotation about a third axis <NUM>. The axis <NUM>, <NUM>, <NUM> may be substantially parallel to one-another. The drive shaft <NUM> may attach to an engine gear box (not shown). The drive gear <NUM> is engaged and concentrically disposed about the drive shaft <NUM>. The driven gear <NUM> and motive drive gear <NUM> are engaged and concentrically disposed about the coupling shaft <NUM>.

The drive and driven gears <NUM>, <NUM> are rotationally coupled to one another for the pumping (i.e., displacement) of fuel as a first stage, and the motive drive gear <NUM> and motive driven gear <NUM> are rotationally coupled to one another for the continued pumping of the fuel as a second stage.

In one embodiment, some or all of at least one of the drive gear <NUM> and the driven gear <NUM> is formed of a ceramic material. In one embodiment, all of the one or both of the drive or driven gears <NUM>, <NUM> are formed of a ceramic material. In another, only the teeth are formed of ceramic and in yet another, only a portion of one or more of the teeth is formed of a ceramic. As discussed above, examples of suitable ceramics includes SiAlON ceramics and stabilized zirconia that may be doped with yttrium. The same may also apply to the motive drive and motive driven gears <NUM>, <NUM>.

It is further contemplated and understood that many other types of gear pumps may be applicable to the present disclosure. For example, the gear pump may be a single stage gear pump, and/or the drive shaft <NUM> may be attached to any other device capable of rotating the drive shaft <NUM> (e.g., electric motor).

The bearings <NUM>, <NUM> may be inserted into a common carrier <NUM> that generally resembles a figure eight. A gear bearing face geometry, known in the art as a bridgeland <NUM> may be sculpted to minimize cavitation and pressure ripple that may deteriorate the integrity of the pump components, discussed further below. The bridgeland <NUM> separates a low pressure side and a high pressure side of the pump.

In operation, the gear pump <NUM> is capable of providing fuel at a wide range of fuel volume/quantity and pressures for various engine performance functions. The engine gearbox provides rotational power to the drive shaft <NUM> which, in-turn, rotates the connected drive gear <NUM>. The drive gear <NUM> then drives (i.e., rotates) the driven gear <NUM> that rotates the coupling shaft <NUM>. Rotation of the coupling shaft <NUM> rotates the motive drive gear <NUM> that, in-turn, rotates the motive driven gear <NUM>.

<FIG> shows a perspective view of a gear. The gear can be any of the drive gear <NUM>, the driven gear <NUM>, the motive drive gear <NUM> and the motive driven gear <NUM>. Referring to <FIG>, each of the gears <NUM>, <NUM>, <NUM>, <NUM> may include a hub portion <NUM> and a plurality of teeth <NUM> that may both span axially between two opposite facing sidewalls <NUM>, <NUM>. Each sidewall <NUM>, <NUM> may lay within respective imaginary planes that are substantially parallel to one-another. The hub portion <NUM> may be disc-like and projects radially outward from the respective shafts <NUM>, <NUM> and/or axis <NUM>, <NUM>, <NUM> to a circumferentially continuous face <NUM> generally carried by the hub portion <NUM>. The face <NUM> may generally be cylindrical. The plurality of teeth <NUM> project radially outward from the face <NUM> of the hub portion <NUM> and are circumferentially spaced about the hub portion <NUM>. The gears <NUM>, <NUM>, <NUM>, <NUM> may be spur gears, helical gears or other types of gears with meshing teeth, and/or combinations thereof.

The hub portion <NUM> can be formed of a ceramic material in one embodiment. In such an embodiment, the spaces between the teeth <NUM> (shown by reference numeral <NUM>) may be formed of ceramic. The ceramic can include any of the ceramics disclosed herein or other suitable ceramics. In another embodiment, the hub portion <NUM> is formed of metal, such as steel or stainless steel and the teeth <NUM> are formed of ceramic either attached to the hub portion <NUM> or that pass at least partially through the hub portion <NUM>.

<FIG> shows a perspective view of another embodiment of a gear. The gear can be any of the drive gear <NUM>, the driven gear <NUM>, the motive drive gear <NUM> and the motive driven gear <NUM>. Each of the gears <NUM>, <NUM>, <NUM>, <NUM> may include a hub portion <NUM> and a plurality of teeth <NUM> that may both span axially between two opposite facing sidewalls <NUM>, <NUM>. The hub portion <NUM> may be disc-like and projects radially outward from the respective shafts <NUM>, <NUM> and/or axis <NUM>, <NUM>, <NUM> to a circumferentially continuous face <NUM> generally carried by the hub portion <NUM>. The face <NUM> may generally be cylindrical. The plurality of teeth <NUM> project radially outward from the face <NUM> of the hub portion <NUM> and are circumferentially spaced about the hub portion <NUM>. As in prior embodiments, the gears <NUM>, <NUM>, <NUM>, <NUM> may be spur gears, helical gears or other types of gears with meshing teeth, and/or combinations thereof.

In one embodiment, the hub portion <NUM> is formed of metal, such as steel or stainless steel and a portion of the teeth <NUM> are also formed of a metal. A portion of the teeth <NUM>/hub can be formed of ceramic as indicated by way of example in regions <NUM>.

In such an example, the hub can include two portions (72a/72b) separated by a ring shaped in the same manner and having teeth formed of ceramic and sandwiched between the two portions. Construction of such an assembly can be achieved by gluing the pieces together or by any other effective construction method.

Claim 1:
A fluid gear pump comprising:
a first gear constructed and arranged to rotate about a first axis (<NUM>), the first gear including a concentrically disposed first hub portion (<NUM>) and a plurality of first teeth (<NUM>) radially projecting and circumferentially spaced about the first hub portion (<NUM>), the first hub portion being formed of a ceramic material;
a second gear operably coupled to the first gear for rotation about a second axis (<NUM>), the second gear including a concentrically disposed second hub portion and a plurality of second teeth radially projecting and circumferentially spaced about the second hub portion, wherein at a time in operation the plurality of first teeth and the plurality of second teeth contact at first contact point and a second contact point to create a backlash volume interposed between the first contact point and the second contact point;
a first bearing abutting and coaxial to the first hub portion (<NUM>); and
a second bearing abutting and coaxial to the second hub portion (<NUM>);
wherein the first teeth of the first gear include a portion formed of metal and a portion formed of a silicon-aluminum-oxygen-nitrogen (SiAlON) ceramic or of partially stabilized zirconia.