Patent Application
20120207626
1. Field of the Invention
The subject invention is directed generally to fuel delivery systems for gas turbine engines, and more particularly, to a thermally efficient multiple stage fixed displacement gear pump for use in aerospace engine applications.
2. Background of the Related Art
Single stage fixed displacement gear pumps are well known in the art and are often used in low horsepower aerospace applications for delivering fuel to a fuel metering unit of a gas turbine engine. These pumps are used to create pressure through the meshing of gear teeth, which forces fluid around the gears to the outlet side of the pump. In a gear pump, a drive mechanism delivers power to a driving gear. The driving gear then transmits the power to a meshing driven gear to perform work and move fluid through the pump.
Low energy consumption pumping systems are being developed in the aerospace industry as an alternative to traditional single stage fixed displacement gear pumps. One way of doing this is to divide the single pumping stage into multiple pumping stages that can be switched on and off at different operating regimes, depending upon the demand for fluid. These systems improve pump performance by reducing excess heat generated by the pumping gears of a single stage pump. However, each stage typically includes a separate set of gears and bearings, thus increasing the cost and weight of such a pumping system.
Because low cost and weight are critical factors in designing hardware for aerospace applications, it would be beneficial to provide a thermally efficient multiple stage fixed displacement gear pump that utilizes fewer component parts. The pumping system of the subject invention achieves this goal by sharing various mechanical components between pumping stages.
The subject invention is directed to a new and useful. low cost, light weight thermally efficient multiple stage gear pump for delivering fuel to a gas turbine engine used for aerospace applications. The multiple stage gear pump includes a pump housing, a boost stage having an impeller assembly operable at engine start to draw fuel into the pump housing through a fuel inlet at a boost stage pressure. A first set of pumping gears is operable upon engine start for receiving fuel from the boost stage and delivering the fuel from the pump housing to a fuel metering unit. A second set of pumping gears is operable upon engine start and during engine cruise operation for receiving fuel from the boost stage and delivering the fuel from the pump housing to the fuel metering unit.
The gear pump further includes a hydraulically actuated valve in fluid communication with the first and second sets of pumping gears, and configured to control fuel flow through the first set of pumping gears when the boost stage pressure rises to a predetermined level. The valve is also in fluid communication with the boost stage and it includes a spring biased valve element that motively reacts to fluid pressure changes generated at the boost stage. The valve prevents discharge flow from the first pumping stage when the boost stage pressure rises to a predetermined level. At such a time, the valve switches the first pumping stage to a low pressure recirculating fuel circuit within the pump housing.
The first set of pumping gears includes a driving start gear and a driven start gear, while the second set of pumping gears includes a driving cruise gear and a driven cruise gear. The pump further includes a main drive shaft that is operatively connected to the driving cruise gear. The driving start gear is piloted on a journal of the driven cruise gear. In addition, the driving start gear is threadably connected to a journal of the driven cruise gear.
The impeller assembly of the boost stage is mounted for axial rotation on a shaft operatively associated with a journal of the driving cruise gear. Preferably, a floating bearing set is shared between both sets of pumping gears and a fixed bearing set is associated with the second set of pumping gears.
These and other aspects of the multiple stage gear pumping system of the subject invention will become more readily apparent from the following detailed description of the preferred embodiments taken in conjunction with the drawings.
So that those having ordinary skill in the art to which the subject invention pertains will more readily understand how to make and use the multiple stage gear pump assembly of the subject invention, preferred embodiments thereof will be described in detail hereinbelow with reference to the drawings, wherein:
Referring now to the drawings wherein like reference numerals identify similar structural elements or features, there is schematically illustrated in
Referring to
It is envisioned that alternative devices can be employed to control the flow of fluid through the secondary pump stage 16 in dependence upon changing conditions at the boost stage. For example, a solenoid valve could be employed in conjunction with a speed sensor. The speed sensor would monitor changes in the pump shaft speed at the boost stage and communicate with the solenoid valve when the pump shaft speed reaches a predetermined value.
In operation, at engine start-up, the boost stage 12 receives fuel at an inlet pressure “PIN” which is essentially zero at the start condition. Fuel is delivered from the boost stage 12 to the primary and secondary pumping stages 12, 14 at a boosted pressure “PB” through main delivery conduit 20. More particularly, fuel at a boosted pressure “PB” is delivered from boost stage 12 to the primary gear pump stage 14 through fuel conduit 22, and fuel is delivered from boost stage 12 at boosted pressure “PB” to the secondary gear pump stage 14 through fuel conduit 24. Pressurized fuel is discharged from the primary gear pump stage 14 to the fuel metering unit at a pressure “PF” through outlet conduit 28. Pressurized fuel is discharged from the secondary gear pump stage 16 at a pressure “PS” through outlet conduit 26. Outlet conduit 26 is bifurcated into to outlet passages 26a, 26b that feed into the shuttle valve 18. During engine start-up, when the spring biased valve member 25 of shuttle valve 18 is in the open position shown in
Shuttle valve 18 is in direct fluid communication with the boost stage 12 through intermediate fuel conduit 30. Pumping system 10 further includes a high pressure relief valve 40, which communicates with the low pressure side of the primary gear pump stage 14 through conduit 32 and with the high pressure side of primary gear pump stage 14 through a conduit 34.
Referring to
Referring now to
The primary gear set 14 (the engine cruise pumping gears) includes an upper primary gear 120 and a lower primary gear 122. The upper primary gear 120 is the driven gear, while the lower primary gear 122 is the driving gear. The secondary gear set 16 (the engine start pumping gears) includes an upper secondary gear 130 and a lower secondary gear 132. The upper secondary gear 130 is the driving gear, while the lower secondary gear 132 is the driven gear of the set.
As best seen in
The interior pumping chamber 112 also houses two bearing sets. These include a fixed bearing set consisting of an upper fixed bearing 140 and a lower fixed bearing 142, and a floating bearing set consisting of an upper floating bearing 150 and a lower floating bearing 152. The upper fixed bearing 140 supports the front journal 124a of the upper primary gear 120, while the lower fixed bearing 142 supports the front journal 126a of the lower primary gear 122. The upper floating bearing 150 supports the rear journal 124b of the upper primary gear 120, while the lower floating bearing 152 supports the rear journal 126b of the lower primary gear 122. The floating bearings 150, 152 are loaded into the pump housing 110, between the primary and secondary gear sets to minimize leakage across the two stages. The floating bearing set 150, 152 is advantageously shared by the primary and secondary pump gear sets (14, 16), thereby reducing the overall number of component parts in gear pump 100.
Gear pump 100 further includes an impeller assembly 160 defining boost stage 12, which is contained within a boost housing 162 attached to the inlet side of pump housing 110 by threaded fasteners (e.g., fastener 163). Boost housing 162 is enclosed by a boost cover 164 attached by threaded fasteners 167. The boost cover 164 defines an inlet passage 166, while the boost housing 162 defines a boost chamber 165. Impeller assembly 160 includes an axial screw portion 170, an annular disk portion 172 and an elongated drive shaft 174. The screw portion 170 extends into the inlet passage 166 of boost cover 164 for drawing fuel into pump 100 through the inlet port 166. The impeller disk 172 is disposed within the impeller cavity 165 of boost housing 162 and has a plurality of circumferentially spaced impeller blades 176 thereon for imparting angular momentum to the fuel drawn into the pump 100. The drive shaft 174 of impeller assembly 160 is engaged within the central bore 127 of the lower primary gear 122 by brazing or other known joining techniques.
The impeller assembly 160 is adapted and configured to draw low pressure fuel into inlet passage 166, through the impeller cavity 165, and into the interior chamber 112 of pump housing 110, as illustrated schematically in
The pump 100 further includes an end plate 175 that is attached to pump housing 110 by threaded fasteners 177. An input shaft 180 is rotatably supported by the end plate 175 for driving the pumping gears. A shaft seal 190 is disposed between the end plate 175 and the pump housing 110 to prevent fuel leakage from the pumping chamber 112 relative to the input shaft 180. The input shaft 180 has opposed proximal and distal end portion 182 and 184. The proximal end portion 182 extends from the pump housing 110 and includes gear teeth for engaging a drive system associated with the engine (not shown). The distal end portion 184 is mechanically connected to the central bore 127 of the lower primary gear 122. Consequently, the input shaft 180 and the impeller drive shaft 174 are axially aligned with one another. Moreover, the input shaft 180 and the impeller assembly 160 rotate in unison during engine operation.
While the subject invention has been described with respect to preferred and exemplary embodiments, an in particular, with respect to a two-stage gear pump, those skilled in the art will readily appreciate that various changes and/or modifications can be made to the invention without departing from the spirit or scope of the invention as described herein, including for example, providing additional pump stages for different operating regimes.
