Patent ID: 12247617

DETAILED DESCRIPTION

To illustrate one environment in which the disclosed journal bearings are used,FIG.1shows a gear driven fuel pump10configured for use in an aircraft gas turbine engine, such as an aircraft main engine or auxiliary power unit. A person of ordinary skill will recognize that this illustration in non-limiting in that the journal bearings of the present disclosure are useful in any high pressure-velocity (PV) bearing environment.

Gear driven fuel pump10includes an exterior housing12that receives an input shaft14and defines a fluid inlet16and a fluid outlet18. Input shaft14drives an intermeshed pair of gears (seeFIG.2) disposed within exterior housing12, such that fluid entering fluid inlet16is pressurized and provided at the fluid outlet18.

FIG.2shows the interior of gear driven fuel pump10with exterior housing12removed. Gear driven fuel pump10includes first stage20and second stage22, which are serially arranged in relation to one another along rotation axis A and rotation axis B, respectively. First stage20includes first gear24and second gear26. First gear shaft28supports first gear24for rotation on about rotation axis A. Second gear shaft30supports second gear26for rotation on about rotation axis B. First gear24and second gear26are rotatably supported in parallel such that the teeth of first gear24are intermeshed with teeth of second gear26. A first set of journal bearings32and34carriers the load of first gear shaft28. A second set of journal bearings36and38carries the load of second gear shaft30.

Input shaft14is mechanically coupled to first gear shaft28for rotating second gear shaft30. Rotation of first gear shaft28rotates first gear24(i.e., the driven gear). As first gear24rotates, the teeth of first gear24intermesh and rotate with the teeth of second gear26. This action pumps fluid disposed between the teeth of second gear26so that the fluid is subsequently provided at the fluid outlet18of the gear driven fuel pump10.

FIG.3shows an exemplary configuration of first gear24on first gear shaft28with the first set of journal bearings32and34. First gear shaft28includes load surface29awhich is configured to slidably engage with journal bearing32when the gear shaft28and bearing32arc assembled as shown inFIG.2. First gear shaft28also includes load surface29bwhich is configured to slidably engage with journal bearing34when the gear shaft28and bearing34are assembled as shown inFIG.2. Second gear26, second gear shaft30, and the second set of journal bearings36and38are similarly configured but are not shown.

FIG.4is a perspective view of one bearing32of the first set of journal bearings32and34. Journal bearing32includes a bearing body42having a bearing body circular opening44that forms a cylindrical shaped bearing surface46along a length of bearing body42. The bearing body circular opening44and bearing surface46are sized to received gear shaft28and to form a hydrodynamic fluid film between load surface29aof gear shaft28and bearing surface46when the gear driven fuel pump10is in operation. Bearing body42can be formed as a single, unitary piece made from a single material. Alternately, bearing body42can be formed from more than one material—for example with a bearing surface46made from a lubricating bearing material such leaded bronze (e.g. 30% leaded bronze) and portions of the bearing body42other than the bearing surface46are made from a structural bearing material such as an aluminum or titanium alloy. Such a configuration could result in a lighter weight journal bearing compared one made entirely from a lubricating bearing material such leaded bronze.

Bearing surface46is sized to accommodate first gear shaft28when the gear shaft28and bearing32are assembled as shown inFIG.2. When the gear shaft28and bearing32are assembled as shown inFIG.2and gear driven fuel pump10is in operation, a hydrodynamic fluid film forms between load surface29aof gear shaft28and bearing surface46of journal bearing32to carrying a gear shaft load on gear shaft28that is created by operation of gear driven fuel pump10.

Bearing32further includes face plate48adjacent to bearing body circular opening44and bearing surface46. Face plate48includes a face plate circular opening49of the same size or larger size as bearing body circular opening44such that face plate48has a generally circular shape. The face plate circular opening49is sized to permit gear shaft28to be received by the bearing body circular opening44and bearing surface46. When the gear shaft28and bearing32are assembled as shown inFIG.2and gear driven fuel pump10is in operation face plate48faces first gear24. Face plate48includes bridge50(which can also be described as a “bridge land,” “face cut,” “pin,” or “hook”) that separates fluid inlet channel52from fluid outlet channel54. As first gear24rotates in operation, fluid is drawn from inlet channel52at a first pressure and into outlet channel54at a second pressure, where the second pressure is higher than the first pressure. In the example shown inFIG.4, face plate48is formed as an integral part of bearing body42and bearing surface46is a separate piece attached to bearing body42by means know in the art. In another example, face plate48could be formed as a separate component from the remainder of bearing body42and could be attached to bearing body42adjacent to bearing surface46by means know in the art (SeeFIG.5which shows face plate48formed from a different material than bearing surface46and bearing body42as further discussed below). A person of ordinary skill will recognize that other configurations are also feasible.

Cavitation can occur when the local fluid pressure, such as the pressure at face plate48, falls below the vapor pressure of the pumped fluid, allowing fluid bubbles to form and vigorously collapse back into solution. When cavitation occurs on or near a solid surface, such as face plate48, cavitation can cause high surface stresses and lead to local deterioration of a bearing surface, such as face plate48, potentially damaging the surface through pitting and/or erosion-caused material loss. With regard to exemplary journal bearing32as shown inFIG.4, cumulative pitting can erode the surface contours of the bridge50that separates the inlet channel52from the outlet channel54, especially in recessed area56of outlet channel54adjacent to bridge50. This erosion can have an adverse impact on fluid handling, diminishing the overall performance of the gear driven fuel pump10.

Previously, journal bearings for gear driven pumps have been made from lubricating bearing materials. Exemplary lubricating bearing materials include leaded bronze alloys (e.g. 30% leaded bronze) and similarly soft bronze alloys, which are available from a number of providers to a variety of specifications. Leaded bronze is a material that tends to prevent galling and seizing, but it is relatively soft and therefore susceptible to cavitation induced pitting, particularly at the face plate48of bearing32shown inFIG.4.

We propose making face plate48from a cavitation resistant base material. One such cavitation resistant base material is a copper-nickel alloy. For example, a nominal Cu-15 Ni-8 Sn alloy is useful as a cavitation resistant base material. We found that a particular copper-nickel alloy known by the designation C72900, which is available form a number of providers, is well suited to use in journal bearings for gear driven pumps. Table 1 shows the chemical composition of C72900 copper-nickel alloy.

TABLE 1Chemical Composition of C72900 Copper-Nickel alloyMinimum ContentMaximum ContentElement(weight %)(weight %)Nickel, Ni(4)14.515.5Tin, Sn7.58.5Iron, Fe00.50Zinc, Zn00.50Manganese, Mn00.30Magnesium, Mg00.15Niobium, Nb00.10Lead, Pb(3)00.02Copper, Cu(1, 2)BalanceBalance(1)Cu + sum of named elements = 99.7% minimum(2)Cu value includes Ag(3)0.005% Pb maximum for hot rolling(4)Ni value includes Co

FIG.6shows comparative data illustrating relative amounts of material weight loss over a period of time for different two bearing substrate materials tested in accordance with ASTM G32 Standard Test Method for Cavitation Erosion Using Vibratory Apparatus. In particular,FIG.6compares the current baseline material for journal bearings for gear driven pumps, which is a 30% leaded bronze alloy, with C72900 copper-nickel alloy, both in contact with Jet A fuel.FIG.6shows that C72900 copper-nickel alloy exhibits a rate of material loss that is 1%-2% that of the 30% leaded bronze baseline material based on the ASTM G32 test.

FIG.7shows comparative data illustrating pressure-velocity (PV) limits for candidate bearing substrate materials tested in conjunction with CPM 10V® steel (Registered Trademark of Crucible Industries LLC of Solvay, New York) in accordance with ASTM D3702-94 Standard Test Method for Wear Rate and Coefficient of Friction of Materials in Self-Lubricated Rubbing Contact Using a Thrust Washer Testing Machine. The tested bearing substrate materials were: 30% leaded bronze alloy, C26000 copper-zinc alloy (also known as “cartridge brass”), C48500 copper-zinc-lead alloy (also known as “high leaded naval brass”), and C72900 copper-nickel alloy.FIG.7shows that the C72900 copper-nickel alloy had an average load at failure of 300 lbs compared with an average load at failure of ˜250 lbs for the leaded bronze material based on the ASTM D3702-94 test.

Together, the data depicted inFIGS.6and7show that C72900 copper-nickel alloy has superior cavitation resistance compared with the leaded bronze baseline material. Accordingly, the disclosed face plate48of bearing32is fabricated from C72900 copper-nickel alloy instead of the leaded bronze material that has been used in the past.

During operation of gear driven fuel pump10there can be bearing touchdowns between load surface29aof gear shaft28and bearing surface46of journal bearing32. As a result, it is desirable to retain a lubricating bearing material, such as a leaded bronze alloy (e.g., 30% leaded bronze), for the bearing surface46of journal bearing32because the lead in leaded bronze acts as a lubricant to reduce friction and galling. Once such suitable material is C94310 leaded bronze alloy. Therefore, the disclosed cavitation resistant journal bearing32combines a leaded bronze bearing surface46along the gear shaft28and a C72900 copper-nickel alloy face plate48at the face of gear24.

FIG.5is a cross section of journal bearing32ofFIG.4that shows face plate48formed from a cavitation resistant base material, including the bridge50that separates the inlet channel52from the outlet channel54, especially in recessed area56of outlet channel54adjacent to bridge50. At least bearing surface46of journal bearing32, which are not typically subjected to cavitation induced pitting or material loss, is formed from a lubricating bearing material. As discussed above, the remaining portions of the bearing body42may be formed of a lubricating bearing material or a structural bearing material as deemed appropriate for a particular application.

Discussion of Possible Embodiments

The following are non-exclusive descriptions of possible embodiments of the present invention.

A gear driven pump includes a first gear having a plurality of gear teeth supported for rotation on a gear shaft relative to a second gear. The gear driven pump also includes a journal bearing for carrying a gear shaft load through a hydrodynamic fluid film between a load surface of the gear shaft and a bearing surface of the journal bearing. The journal bearing includes a bearing body having a bearing body circular opening that forms the bearing surface along a length of the bearing body and face plate adjacent to the bearing surface. The face plate is configured to interface with the first gear. The bearing body circular opening and bearing surface are sized to receive the gear shaft and to form a hydrodynamic fluid film between load surface and bearing surface when the gear driven pump is in operation. The face plate includes a face plate circular opening sized to permit the gear shaft to be received by the bearing body circular opening and bearing surface. The bearing surface is formed from a lubricating bearing material and the face plate is formed from a cavitation resistant base material.

The gear driven pump of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:

A further embodiment of the foregoing gear driven pump, wherein the face plate includes a bridge that separates a fluid inlet channel from a fluid outlet channel, where the face plate is configured such that in operation a fluid is drawn from the inlet channel at a first pressure and into the outlet channel at a second pressure, where the second pressure is higher than the first pressure and the face plate is formed as a separate component from the bearing body.

A further embodiment of any of the foregoing gear driven pumps, wherein the cavitation resistant base material is a copper-nickel alloy and the lubricating bearing material is a leaded bronze alloy.

A further embodiment of the foregoing gear driven pump, wherein the copper-nickel alloy is a nominal Cu-15 Ni-8 Sn alloy.

A further embodiment of any of the foregoing gear driven pumps, wherein portions of the bearing body other than the bearing surface are made from a structural bearing material.

A further embodiment of the foregoing gear driven pump, wherein the structural bearing material is an aluminum or titanium alloy.

A journal bearing for a gear driven pump includes a bearing body having a bearing body circular opening that defines a bearing surface along a length of the bearing body and a face plate adjacent to the bearing surface. The bearing surface is configured to carry a gear shaft load through a hydrodynamic fluid film pressure between a load surface of a gear shaft and the bearing surface. The bearing body circular opening and bearing surface are sized to receive the gear shaft and to form a hydrodynamic fluid film between load surface and bearing surface when the gear driven pump is in operation. The face plate is configured to interface with a gear on the gear shaft. The face plate includes a face plate circular opening sized to permit the gear shaft to be received by the bearing body circular opening and bearing surface. The bearing surface is formed from a leaded bronze material and the face plate is formed from a copper-nickel alloy.

The journal bearing of the preceding paragraph can optionally include, additionally and/or alternatively, any one or more of the following features, configurations and/or additional components:

A further embodiment of the foregoing journal bearing, wherein the face plate includes a bridge that separates a fluid inlet channel from a fluid outlet channel. The face plate is configured such that in operation a fluid is drawn from the inlet channel at a first pressure and into the outlet channel at a second pressure. The second pressure is higher than the first pressure. The face plate is formed as a separate component from the bearing body.

A further embodiment of the foregoing journal bearing, wherein the copper-nickel alloy is a nominal Cu-15 Ni-8 Sn alloy.

A further embodiment of any of the foregoing journal bearing, wherein portions of the bearing body other than the bearing surface are made from a structural bearing material.

A further embodiment of the foregoing journal bearing, wherein the structural bearing material is an aluminum or titanium alloy.

A method of making a journal bearing for a gear driven pump includes forming a bearing body having a bearing body circular opening that defines a bearing surface along a length of the bearing body. The bearing surface is configured to carry a gear shaft load through a hydrodynamic fluid film pressure between a load surface of a gear shaft and the bearing surface. The bearing body circular opening and bearing surface are sized to receive the gear shaft and to form a hydrodynamic fluid film between load surface and bearing surface when the gear driven pump is in operation. The method further includes forming a face plate adjacent to the bearing surface. The face plate is configured to interface with a gear on the gear shaft and includes a face plate circular opening sized to permit the gear shaft to be received by the bearing body circular opening and bearing surface. The bearing surface is formed from a leaded bronze material and the face plate is formed from a copper-nickel alloy.

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

A further embodiment of the foregoing method, wherein the face plate includes a bridge that separates a fluid inlet channel from a fluid outlet channel. The face plate is configured such that in operation a fluid is drawn from the inlet channel at a first pressure and into the outlet channel at a second pressure. The second pressure is higher than the first pressure. The face plate is formed as a separate component from the bearing body.

A further embodiment of the foregoing method, wherein the copper-nickel alloy is a nominal Cu-15 Ni-8 Sn alloy.

A further embodiment of any of the foregoing method, wherein portions of the bearing body other than the bearing surface are made from a structural bearing material.

A further embodiment of the foregoing method, wherein the structural bearing material is an aluminum or titanium alloy.

While the invention has been described with reference to an exemplary embodiment(s), it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment(s) disclosed, but that the invention will include all embodiments falling within the scope of the appended claims.