Patent Application
20200025195
The subject invention is directed to fuel pumps, and more particularly, to a gear driven fuel pump used in aerospace applications.
Aircraft gas turbine engines typically receive pressurized fuel from a gear driven fuel pump. A gear driven pump utilizes rotating gears to pump fluid from an inlet to an outlet. In use, a rotating drive gear turns a driven gear at a location where their respective teeth mesh together. Fluid enters the pump inlet and travels between the teeth of the drive gear and a housing, and then between the teeth of the driven gear and the housing. As the gears turn, fluid is pulled through the pump and pushed from the outlet due to a pressure differential between the inlet and outlet.
Both the drive gear and the driven gear are supported within the pump on respective gear shafts. Each gear shaft is supported by a pressure loaded journal bearing and a stationary journal bearing, both of which react to a gear shaft load. The gear shaft load is carried through a fluid film pressure in each journal bearing, between a surface of the gear shaft and a surface of the journal bearing. Bearings such as these, which support their loads on a fluid layer, are known as hydrodynamic bearings.
A common problem with traditional gear pumps operating at high rotational speeds, such as those used in aircraft gas turbine engines, is cavitation erosion of surfaces of the gear teeth and journal bearings. Cavitation is the result of a sudden drop in fluid pressure during operation, which causes dissolved gas bubbles to collapse and implode on a surface with forces up to 1000 Mpa. Cavitation can cause pitting and/or material loss on surfaces of the gear teeth and journal bearings, which may eventually result in degraded volumetric pump capacity, and even premature pump failure due to the forces exerted on the bearings and gear teeth.
It would be beneficial therefore, to design a gear driven pump with cavitation resistant components, such as the gear teeth and journal bearings, so as to reduce the risk of pump failure. The subject invention provides such a solution through the use of cavitation resistant materials and coatings.
The subject invention is directed to a new and useful gear driven pump for an aircraft gas turbine engine, that includes a first gear having a plurality of gear teeth supported for rotation on a gear shaft relative to a second gear, wherein the gear teeth are formed from a steel base material and surfaces of the gear teeth are coated with a cavitation resistant coating material, and a journal bearing for carrying a gear shaft load through a fluid film pressure between a surface of the gear shaft and a surface of the journal bearing, wherein at least a portion of the journal bearing is formed from a cavitation resistant base material.
In an embodiment of the subject invention, the cavitation resistant base material from which at least a portion of the journal bearing is formed is an aluminum (Al) bronze material. In another embodiment of the subject invention, the cavitation resistant base material from which at least a portion of the journal bearing is formed is nickel aluminum (NiAl) bronze material.
In accordance with the subject invention, the gear teeth are coated with a vapor-deposited cavitation resistant coating selected from the group consisting of titanium nitride (TiN), titanium aluminum nitride (TiAlN), titanium aluminum silicon nitride (TiAlSiN), titanium aluminum carbonitride (TiAlCN), chromium nitride (CrN), aluminum chromium nitride (AlCrN), and chromium aluminum carbonitride (CrAlCN).
Preferably, the gear teeth are made from CPM10V steel coated with a vapor-deposited cavitation resistant coating of TiAlN. It is envisioned that the gear teeth can be coated by way of physical vapor deposition (PVD), chemical vapor deposition (CVD), or by way of atomic layer deposition (ALD).
These and other features of the cavitation resistant gear driven pump of the subject invention will become more readily apparent to those having ordinary skill in the art to which the subject invention appertains from the detailed description of the preferred embodiments taken in conjunction with the following brief description of the drawings.
So that those having ordinary skill in the art will readily understand how to make and use the cavitation resistant gear driven pump of the subject invention without undue experimentation, preferred embodiments thereof will be described in detail herein below with reference to the figures wherein:
Referring now to the drawings wherein like reference numerals identify similar structural elements or features of the subject invention, there is illustrated in
Gear driven pump 10 includes an exterior housing 12 that receives an input shaft 14 and defines a fluid inlet 16 and a fluid outlet 18. Input shaft 14 functions to drive an intermeshed pair of gears (shown in
Referring now to
The first stage 20 includes first and second gears 24 and 26. The first gear 24 is supported for rotation on a first gear shaft 28 about the first rotation axis A. The second gear 26 is supported for rotation on a second gear shaft 30 about rotation axis B. The first and second gears 24 and 26 are rotatably supported is parallel such that the teeth of the first gear 24 are intermeshed with teeth of second gear 26. Furthermore, the load of the first gear shaft 28 is carried by a first set of journal bearings 32 and 34, and the load of the second gear shaft 30 is carried by a second set of journal bearings 36 and 38.
Input shaft 14 is mechanically coupled to the first gear shaft 28 for rotating the second gear shaft 30. More particularly, rotation of first gear shaft 28 rotates the first gear 24 (i.e., the driven gear). As the first gear 24 rotates, the teeth of the first gear 24 intermesh and rotate with the teeth of the second gear 26. This action pumps fluid disposed between the teeth of second gear 26 so that it is subsequently provided at the fluid outlet 18 of the pump 10.
Referring now to
It is known in the art that cavitation can occur when the local fluid pressure falls below the true vapor pressure of a fluid, allowing fluid bubbles to form and violently collapse back into solution. When cavitation occurs on or near a solid surface, the high intensity collapse force or cavitation damage power, similar to a shockwave, can cause high surface stresses and lead to local deterioration of a bearing surface, potentially damaging the surface, such as through pitting and/or material loss through erosion.
In the case of a journal bearing in a gear driven pump, such as the bearing 34 shown in
It is known to fabricate the journal bearings in a gear driven pump from leaded bronze (e.g. 30% leaded bronze) with a MoS2 solid lubricant coating. Leaded bronze is a material that tends to prevent galling and seizing, but it is relatively soft and therefore susceptible to cavitation induced pitting. In an effort to combat the impact of cavitation on the surfaces of journal bearings formed from leaded bronze, testing has been done to select a more durable bearing material that can effectively resist wear and erosion caused by cavitation. A particular material of distinction in this regard, which exhibits improved cavitation and wear resistance as compared to leaded bronze, while having a similar coefficient of friction, is an aluminum (Al) bronze material, and in particular, a nickel aluminum (NiAl) bronze material.
Referring to
For these reasons, in accordance with a preferred embodiment of the subject invention, at least portions of the first set of journal bearings 32 and 34, and at least portions of the second set of journal bearings 36 and 38, are formed from an aluminum (Al) bronze material or a nickel aluminum (NiAl) bronze material. Those skilled in the art will readily appreciate that aluminum (Al) bronze is easier to machine than nickel aluminum (NiAl) bronze, so it may be the more preferable bearing material from a manufacturing standpoint, even though nickel aluminum (NiAl) bronze is a more cavitation resistant material.
For example, as shown in
It is envisioned that the aluminum (Al) bronze material can be cladded to the leaded bronze substrate, such as through a laser cladding process or the like. The selected nickel aluminum (NiAl) bronze material has a similar dry coefficient of friction on steel to leaded bronze, while providing improved mechanical stress resistance, rendering the area of the bridge 54 and its surrounding surfaces more resistant to cavitation damage and/or erosion and material loss from cavitation.
It is envisioned, and wholly within the scope of the subject disclosure, that the entirety of each of the journal bearings within the first and second stages of the gear driven pump 10 could be formed from an aluminum (Al) bronze material, to combat or otherwise resist cavitation. This will reduce deterioration of the journal bearings and other system components, thus maintaining pump and system performance and increasing component operating life.
Referring now to
In an effort to combat the impact of cavitation on the surfaces of the gear teeth, testing has been done to select a durable coating material that can effectively resist wear and erosion caused by cavitation. A particular material of distinction in this regard, which exhibits improved wear resistance as compared to an uncoated CPM10V steel base material, is a vapor-deposited cavitation resistant coating of titanium aluminum nitride (TiAlN).
Referring now to
For these reasons, in accordance with a preferred embodiment of the subject invention, the leading and trailing edge surfaces 62 and 66 of the gear teeth 60 of gears 24 and 26 are coated with a vapor-deposited cavitation resistant coating of titanium aluminum nitride (TiAlN). Alternatively, surfaces of the gear teeth 60 may be coated with a vapor-deposited cavitation resistant coating selected from the group consisting of titanium nitride (TiN), titanium aluminum silicon nitride (TiAlSiN), titanium aluminum carbonitride (TiAlCN), chromium nitride (CrN), aluminum chromium nitride (AlCrN), and chromium aluminum carbonitride (CrAlCN).
It is envisioned that the gear teeth 60 can be coated by way of physical vapor deposition (PVD), chemical vapor deposition (CVD), or by way of atomic layer deposition (ALD). The use and application of these cavitation resistant coatings extends part life, which leads to lower overhaul and replacement costs. Moreover, the gear teeth 60 can be recoated, to avoid having to replace the entire gear.
In sum, the use of an aluminum (Al) bronze material for fabricating at least portions of the journal bearings of a gear pump and a vapor-deposited coating of titanium aluminum nitride (TiAlN) on the teeth of the driving and driven gears of the pump, can reduce or otherwise prevent cavitation induced pitting and/or material loss on critical surfaces of the journal bearings and gear teeth, thereby preventing any degradation in the volumetric capacity of the pump, or premature pump failure due to the cavitation induced forces exerted on the bearings and gear teeth.
While the subject disclosure has been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that changes and/or modifications may be made thereto without departing from the scope of the subject disclosure.
