Patent Application
20100316507
1. Field of the Invention
The subject invention is directed to rotary vane pumps, and more particularly, to a balanced split discharge vane pump that provides a first discharge flow for high fluid demand conditions and a second discharge flow for low fluid demand conditions, and to a system for metering fluid flow from a split discharge vane pump depending upon fluid demand conditions.
2. Description of Related Art
Rotary hydraulic vane pumps are well known in the art, as disclosed for example in U.S. Pat. No. 4,274,817 to Sakamaki et al. and U.S. Pat. No. 5,064,363 to Hansen. A typical rotary vane pump includes a circular rotor mounted for rotation within a larger circular pumping chamber. The centers of these two circles are typically offset, causing eccentricity. Vanes are mounted to slide in and out of the rotor to create a plurality of volume chambers or vane buckets that perform the pumping work. On the intake side of the pump, the vane buckets increase in volume. These increasing volume vane buckets are filled with fluid that is forced into the pumping chamber by an inlet pressure. On the discharge side of the pump, the vane buckets decrease in volume, forcing pressurized fluid out of the pumping chamber.
It is desirable to match the fluid displacement of a vane pump to the operating characteristics of the system with which the pump is to be associated. For example, the maximum displacement of a fuel pump should be coordinated with the maximum fuel requirements of the associated engine application. However, system requirements typically vary with operating conditions, so that a fixed displacement fuel pump that is designed as a function of the most demanding engine operating conditions may function with less than desired efficiency under other operating conditions.
In the case of a fuel pump associated with a gas turbine engine of an aircraft, fuel flow requirements, as quantified by pump displacement per rotational speed, under engine starting conditions greatly exceed fuel flow requirements during other less demanding engine operating conditions, such as cruise, idle, decent and taxi. Various attempts have been made to improve fuel pump efficiency over the operating envelope of a gas turbine engine, by utilizing different valving arrangements at the pump outlet to meter a portion of the pump discharge to the engine as a function of engine demand, while recirculating the remainder of the flow back into the pump. However, these prior art arrangements are typically complex and thus add cost to the pumping system. In other implementations, variable displacement pumps have been utilized to match pump output flow to system demand. However, these implementations are at the expense of pump size/weight and reliability because of an increase in pump radial/axial loading and incorporation of additional moving parts.
It would be beneficial therefore to provide a positive displacement vane pump that is adapted and configured to more closely match the operating characteristics of the system with which it is associated, as well as a valving arrangement for effectively managing the flow of fluid from the pump depending upon the fluid demand conditions of the system with which it is associated. This is achieved by retaining the simple features of fixed displacement pumps and hence preserving their weight and reliability advantages.
The subject invention is directed to a new and useful rotary hydraulic pump, which is well adapted for use as a fuel pump for engine applications, such as, for example, aircraft gas turbine engines. More particularly, the subject invention is directed to a positive displacement rotary vane pump that includes a pump body having an interior pumping chamber with a central axis and a continuous peripheral cam surface. The cam surface includes four quadrantal cam segments, wherein diametrically opposed cam segments have identical cam profiles, and each cam segment defines an inlet arc, a discharge arc and two seal arcs.
A cylindrical rotor is mounted for axial rotation within the pumping chamber and a plurality of circumferentially spaced apart radially extending vanes are mounted for radial movement within the rotor. The vanes define an equal number of circumferentially spaced apart volume chambers or buckets which extend between an outer periphery of the rotor and the cam surface for carrying pressurized fluid.
Preferably, a seal arc separates the inlet arc and discharge arc in each cam segment, and a seal arc separates the inlet arc in one segment from the discharge are in a circumferentially adjacent segment. The discharge arcs of diametrically opposed cam segments are equally sized, whereas the discharge arcs of circumferentially adjacent cam segments are not of equal size. Preferably, there are sixteen circumferentially spaced apart radially extending vanes and an equal number of circumferentially spaced apart volume chambers or buckets for carrying pressurized fluid.
The pump body includes inlet port means communicating with the inlet arc of each cam segment and outlet port means communicating with the discharge arc of each cam segment. In addition, the rotor includes a plurality of circumferentially spaced apart radially extending vane slots for accommodating the plurality of vanes. The pump further includes laterally opposed side plates for enclosing the pumping chamber. Each vane slot has an undervane pocket for receiving pressurized fluid and each side plate includes means for feeding fluid into the undervane pocket of each vane slot based on an angular position of the rotor.
In accordance with an embodiment of the invention, the pressurized fluid in the rotor undervane while it is located in the inlet arc of a cam segment is relatively low pressure fluid associated with an inlet arc of a cam segment, and is equal to pump inlet pressure. Conversely, the pressurized fluid in the rotor undervane while it is located in the discharge arc of a cam segment is relatively high pressure fluid associated with a discharge arc of a cam segment, and is equal to pump discharge pressure. In contrast, the pressurized fluid in the rotor undervane while it is located in a seal arc of a cam segment is relatively high pressure fluid associated with a discharge arc of a cam segment, and is equal to pump discharge pressure.
The split discharge vane pump of the subject invention further includes a fluid metering system for extracting fluid flow from the discharge arcs of the four cam segments. The fluid metering system has a first operating condition in which fluid is extracted from the discharge arcs of all four cam segments and combined for delivery to a source of fluid demand. The fluid metering system has a second operating condition wherein fluid is extracted from a first pair of diametrically opposed discharge arcs for delivery to a source of fluid demand and fluid from a second pair of diametrically opposed discharge arcs bypasses the source of fluid demand and returns to inlet side of the pumping chamber.
The subject invention is also directed to a fluid metering system that includes a balanced positive displacement vane pump having primary and secondary pairs of discharge arcs, wherein the primary pair of discharge arcs is adapted and configured to discharge pressurized fluid from the pump at a first volumetric flow rate and the secondary pair of discharge arcs is adapted and configured to discharge pressurized fluid from the pump at a second volumetric flow rate. The system further includes means for extracting pressurized fluid flow from the primary and secondary pairs of discharge arcs for combined delivery to a source of fluid demand so as to satisfy a first demanded fluid condition, and for extracting pressurized fluid from the primary pair of discharge arcs for delivery to the source of fluid demand while at the same time directing pressurized fluid from the secondary pair of discharge arcs to bypass the source of fluid demand so as to satisfy a second demanded fluid condition. It is envisioned and well within the scope subject disclosure that any fluid demand condition can be satisfied by an appropriate combination of the primary and secondary flows, since each can be modulated by the subject fluid metering system.
The means includes a regulator valve for controlling the extraction of pressurized fluid from one or both pairs of discharge arcs depending upon the demanded fluid condition. The means further includes a bypass valve, the opening of which is controlled by the regulator valve, for causing fluid from the secondary pair of discharge arcs to bypass the source of fluid demand and return to the inlet side of the pump in response to the second demanded fluid condition. The means further includes a check valve in communication with the source of fluid demand and having a normally closed position corresponding to the second demanded fluid condition wherein fluid from the primary pair of discharge arcs is permitted to flow to the source of fluid demand and an open position corresponding to the first demanded fluid condition wherein fluid from the primary and secondary pairs of discharge arcs is permitted to flow to the source of fluid demand.
The fluid metering system further comprises external control means for controlling the regulator valve. The external control means can take the form of a dual channel torque motor, an electro-hydraulic servo valve or a similar control device known in the art. The external controller would be in communication with and receive commands from a Full-Authority Digital Controller (FADEC).
In another embodiment of the subject invention, the split discharge vane pump is operatively associated with separate fluid metering systems that function independently to extract fluid flow from the respective discharge arcs of the four cam segments. The system has an alternative operating condition (with alternative control schema) in which high pressure fluid is extracted from the discharge arcs of each pair of diametrically opposed cam segments and ported to separate loads (i.e., the flow is not combined). Each pump pair is controlled and plumbed independently at different operating pressures. Alternatively, fluid flow from one or both pairs of diametrically opposed cam segments is bypassed to inlet pressure.
These and other features of the split discharge vane pump and fuel metering system of the subject invention will become more readily apparent to those having ordinary skill in the art from the following detailed description of the invention taken in conjunction with the several drawings described below.
So that those skilled in the art to which the subject invention appertains will readily understand how to make and use the split discharge vane pump of the subject invention without undue experimentation, preferred embodiments thereof will be described in detail below with reference to certain figures, wherein:
Referring now to the drawings wherein like reference numerals identify similar structural features or elements of the subject invention, there is illustrated in
Vane pump 10 is preferably associated with a fluid metering or distribution system that is adapted and configured to control or otherwise regulate the flow of fluid discharged from the pump during operation. In accordance with one embodiment of the subject invention, this fluid metering system has a first operating condition in which fluid from the primary and secondary discharge arc pairs is conveyed to a source of fluid demand at a combined volumetric flow rate (e.g., 65 gpm). The fluid metering system has a second operating condition in which fluid from the primary pair of discharge arcs is conveyed to the source of fluid demand, while fluid discharged from the secondary pair of discharge arcs is caused to bypass the source of fluid demand and return to the pump. Bypassing a portion of the pump's discharge capacity back to the inlet side of the pump serves to reduce the input power consumption of the and thereby improve overall system thermal efficiency.
It is envisioned that the vane pump of the subject invention can be employed as a positive displacement fuel pump and the fluid metering system can be configured as a fuel metering system associated with an aircraft gas turbine engine. In such a configuration, the first system operating condition would correspond to high fuel flow conditions such as engine start-up and the second system operating condition would correspond to low fuel flow conditions such as idle, cruise, decent or taxi. Thus, the discharge arc pairs of the vane pump 10 of the subject invention can be sized to a specific mission profile for an aircraft so as to optimize thermal efficiency across an entire engine operating envelope.
Referring now to
Referring to
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As explained in more detail below with respect to
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Referring to
The pump body 14 further includes a group of discharge portals for directing relatively high pressure fluid from the pumping chamber 20 to a source of fluid demand, such as a gas turbine engine. One pair of discharge portals 74a, 74b is illustrated in
Referring to
With continuing reference to
It is envisioned that the symmetric face plates 16 and 18 of vane pump 10 can be machined, cast or formed by laminating plural plate layers to one another to form the undervane fluid feed passages, ports and slots formed therein. Furthermore, the direct undervane porting through the symmetric fluid conduits of the front and rear face plates 16 and 18 serves to improve vane tracking, reduce the possibility of undervane cavitation that can reduce pump efficiency, and eliminate the parasitic flow losses associated with communicating an intermediate fluid pressure to the undervane pockets, as is often the case in prior art vane pumps employing undervane porting.
Referring now to
In addition, each of the four cam segments A-D defines an inlet arc section 122 in which low pressure fluid is received with a pumping bucket 30, a discharge arc section 124 in which fluid is discharged from a pumping bucket 30 at a relatively higher pressure, and two seal arcs sections 126, 128 which fluidly isolate the pumping buckets 30 as they translate from an inlet arc to a discharge arc. Thus, cam segment A includes inlet arc section 122a, discharge arc section 124a and seal arc sections 126a, 128a; cam segment B includes inlet arc section 122b, discharge arc section 124b and seal arc sections 126b, 128b; cam segment C includes inlet arc section 122c, discharge arc section 124c and seal arc sections 126c, 128c; and cam segment D includes inlet arc section 122d, discharge arc section 124d and seal arc sections 126d, 128d.
In accordance with the subject invention, a seal arc 126 separates the inlet arc 122 and discharge arc 124 in each cam segment A-D. A seal arc 128 also separates the inlet arc 122 in one segment from the discharge arc 124 in a circumferentially adjacent segment. Furthermore, the discharge arcs 122a and 122c of diametrically opposed cam segments A and C are equally sized, while the discharge arcs 122a and 122b of circumferentially adjacent cam segments A and B are unequal in size. For example, in an embodiment of the subject invention, diametrically opposed discharge arcs 122a and 122c may be sized and configured as primary discharge arcs that discharge fluid from the pump at a volumetric rate of 35 gpm, whereas diametrically opposed discharge arcs 122b and 122d may be sized and configured as secondary discharge arcs that discharge fluid from the pump at a relatively lower volumetric rate of 30 gpm.
Referring now to
As this pumping action is taking place, the undervane pockets 28a of vane slots 28 receive low pressure fluid the low pressure feed ports 104a-104d in face plates 16 and 18, and the undervane pockets 28a of vane slots 28 receive high pressure fluid from arcuate feed slots 114a-114d in face plates 16 and 18, depending upon an angular position of the rotor 24. More particularly, the pressurized fluid in the rotor undervane pockets 28a while they are located in the inlet arc sections 122a-122d of cam segments A-D is relatively low pressure fluid associated with an inlet arc of a cam segment and is equal to pump inlet pressure. Conversely, the pressurized fluid in the rotor undervane pockets 28a while they are located in the discharge arc section 124a-124d of cam segments A-D is relatively high pressure fluid associated with a discharge arc of a cam segment, and is equal to pump discharge pressure. In contrast, the pressurized fluid in the rotor undervane pockets 28a while they are in a seal arc section 126a-126d or 128a-128 of cam segments A-D is relatively high pressure fluid associated with a discharge arc of a cam segment, and is also equal to pump discharge pressure. This undervane porting provides a balancing pressure below the vanes 26 to improve vane tip tracking along cam surface 22.
Turning now to
Vane pump 10 receives fluid from a low pressure source at pump inlet pressure PB. Vane pump discharges fluid from the primary pair or discharge arcs 122a, 122c at a primary discharge pressure PF, and it discharges fluid from the secondary pair of discharge arcs 122b, 122d at a secondary discharge pressure P2.
Fluid metering system 200 further includes a regulator valve 210 in the form of a spool valve or the like which is adapted and configured to control the extraction of pressurized fluid from one or both pairs discharge arcs depending upon the demanded fluid flow condition. More particularly, regulator valve 210 is configured to extract high pressure discharge flow from both the primary pair of discharge arcs 122a, 122c and from the secondary pairs of discharge arcs 122b, 122d under a first demanded fluid flow condition (e.g., at engine start-up) and it is configured to extract high pressure discharge flow from only the primary pair of discharge arcs 122a, 122c under a second demanded fluid flow condition (e.g., at engine idle).
Fluid metering system 200 also includes a bypass valve 220 which causes high pressure discharge flow from the secondary pair of discharge arcs 122b, 122d to bypass the source of fluid demand (e.g., a gas turbine engine) and return to the inlet or low pressure side of the pump when regulator valve 210 is operating under the second demanded fluid flow condition. Bypass valve 220 and regulator valve 210 communicate with one another through a sensing line that reports the bypass head pressure PBH acting on the valve.
Fluid metering system 200 also includes a check valve 230 in communication with the source of fluid demand. Check valve 230 has a normally closed position that corresponds to the second demanded fluid flow condition wherein fluid from the primary pair of discharge arcs 122a, 122c is permitted to flow to the source of fluid demand. Conversely, check valve 230 has open or actuated position that corresponds to the first demanded fluid flow condition wherein fluid from the primary pair of discharge arcs 122a, 122c and the secondary pair of discharge arcs 122b, 122d is permitted to flow to the source of fluid demand in an additive or cumulative manner.
Referring to
Fluid metering system 300 differs from fluid metering system 200 in that it includes an external controller 340 for controlling the pressure differential across the regulator valve 310. It is envisioned that the external controller 340 could take the form of a dual channel torque motor or an electro-hydraulic servo valve (EHSV) or a similar device known in the art. The external controller 340 would be in communication with and receive commands from a Full-Authority Digital Controller (FADEC).
While the subject invention has been shown and described with reference to preferred embodiments, those skilled in the art will readily appreciate that various changes and/or modifications may be made thereto without departing from the spirit and/or scope of the subject disclosure.
