US 3635602 A
A pumping system has a centrifugal pump and a tip seal-type positive displacement pump which includes a seal block. Means are provided to move the seal block away from the gears of the tip seal pump at a predetermined centrifugal pump discharge pressure.
Description (OCR text may contain errors)
States Patent [151 3 65 6 r: Grennari et air.  1 n W7 LliFTliNG TIP SEAL PUMP  Meierences Cited  Inventors: Charles W. Grennan, Newington; Evert UNITED STATES PATENTS ltk f e 0rd both 1,927,799 9/1933 Mann ..417/203  Assignee: Chandler Evans lnc., West Hartford, 3,026,929 3/1962 Burns 417/201 X Conn.
. Primary Examiner-Robert M. Walker  plied 1970 Attorney-Radford W. Luther  Appl.N0.: 73,378
 AIBS'KCT [S21 H.813! ..417/20l, 417/205, 417/216 A pump ng sys em has a cent fugal pump and a up seal-type ml lnmfl .JlMh 23/14,FO4b 23/08,F04b 49/00 po i e d place ent pump which includes a seal block. 58] i'lauiniswrch ..417/201,202, 203, 205,216; M ns r pro i d t move he seal lock away from the 4l8/24, 25, 26 gears of the tip seal pump at a predetermined centrifugal pump discharge pressure.
8 Claims, 3 Drawing Figures 72 V e k l Ii -ss i 62 1O 4 i 24 I 30 5O 5 I 36 W, To 1: I T 56 PUMP f X BEARINGS Q Li l8 8 52 PUMP OUTLET PATENTEDJmwmz SHEET 1 [1F 3 E 250 QZDA INVENTORS CHARLES w GRENNAN EVERT VON MOLTKE BY Raw MM H 325mm H :25 oh mo n I 2-I2 I I:
PATENTED JAN? 8 1972 3.635602 sum 2 0F 3 urrmo TIP SEAL PUMP BACKGROUND OF THE INVENTION pumps) are unable to prime themselves at low speeds.
Moreover, if a hydrodynamic pump is to avoid supplying excess pressure at maximum turbine engine speeds, it will not alone be capable of generating pressures needed to supply fuel to the engine at low speeds.
In general, aircraft gas turbine engines require fuel pumps which can furnish dry lift and high output pressure necessary to fulfill engine startup and low-speed requirements. Positive displacement pumps, notable of the gear type, have been employed in previous fuel control systems to meet these dry lift and high pressure starting requirements. However, recent development of high-speed auxiliary equipment (such as fuel controls) for modern high efficiency engines precludes, of at least makes highly undesirable, the use of positive displacement pumps throughout the entire range of engine operation because such use results in large power losses and temperature rises caused by high bypass flows associated with positive displacement pumps and by the fluid and mechanical friction inherent in high-speed machinery.
A solution to the aforementioned difficulties is presented in U.S. Pat. application No. 767,293, entitled FLUID PUMP AND DELIVERY SYSTEM, filed on Oct. 14, 1968, in the names of C. W. Grennan et al., now U.S. Pat. No. 3,547,557 granted Dec. 15, 1970. This patent application discloses a unitized pump which incorporates interrelated pumping circuits to meet engine fuel delivery requirements over the entire range of engine operation. The disclosed pump employs one circuit having a positive displacement pump for startup and low-speed operations, a second circuit for normal operation incorporating a centrifugal pump and a third circuit for high altitude cruise operation incorporating a vapor core centrifugal pump. In disclosed pump, the positive displacement pump ceases to supply fuel to the engine after the centrifugal pump supplies the necessary fuel pressure. Basically, this pump provides a means whereby the positive displacement pump can be unloaded when the centrifugal pump is capable of supplying the needed fuel at pressure to the engine, thereby eliminating the high bypass flows normally associated with positive displacement pumps.
SUMMARY OF THE INVENTION The instant invention combines a hydrodynamic pump with a tip seal-type positive displacement pump, whereby the tip seal pump generates the pressure at low speeds and the hydrodynamic pump supplies the pressure at high speeds. Thus, the instant invention is conceptually similar to the pump disclosed in the aforementioned application.
In the instant invention, there is provided a centrifugal pump and a tip seal-type positive displacement gear pump in series flow relationship in a single-pumping circuit. When pressure generation by the tip seal pump is not required, an actuating means causes the sealing block of the tip seal pump to be displaced from the peripheries of the gears. In contrast to the pump of the aforementioned application, only a singlepumping circuit is employed. Moreover, a unique arrangement is provided to remove the sealing block from the gears peripheries when pressure generation by the tip seal pump is no longer required.
Accordingly, it is a primary object of the invention to provide a pumping system for a gas turbine engine which obviates high bypass flows, thereby alleviating the difiiculties as sociated therewith.
It is another object to provide a pumping system incorporating a centrifugal pump and a tip seal-type positive displacement gear pump in series flow relationship, wherein means are provided to unload the tip seal pump.
It is another object to provide a unique means of unloading a tip seal pump.
These and other objects will become more readily apparent from the following detail description taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a schematic diagram of a pump embodying a form of the present invention.
FIG. 2 is a schematic diagram of a pump embodying another form of the present invention.
FIG. 3 is a schematic diagram of a pump embodying yet another form of the present invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to the drawings, wherein like reference characters are used throughout to designate like elements, there is shown in FIG. 1 a pump generally designated at 10. The pump 10 is designed primarily for use in a fuel control system for a gas turbine engine and may be incorporated as part of the fuel control itself. It will, however, be understood that the invention is not limited to pumps embodied in fuel controls, but applies to pumps in general. Pump comprises an inlet 12 and an outlet 14. Flow proceeds from the inlet 12 to the outlet 14 via a main conduit 16 formed by a first conduit or segment 18 and a second conduit or segment 21. Mounted within the segment 18 of main conduit 16 is a hydrodynamic pump 20, shown in the form of a centrifugal inducer pump, which receives fluid from a suitable supply source under low pressure P, via inlet 12. Flow emerges from the outlet of the centrifugal inducer pump 20 at a pressure P and proceeds through segment 18 to a cavity 22, in which is mounted a tip seal-type positive displacement gear pump 24. Flow proceeds from the outlet 26 of pump 24 at a pressure P through seg ment 21 to outlet 14. A wash flow filter 27 is positioned in segment 21 for supplying a clean flow of fluid to the pump bearings and clean servo flow. The flow from the wash flow filter may also be used to wash the valves in a fuel control with which it is associated.
A pressure relief conduit 28 fluidly interconnects the outlet 26 of positive displacement gear pump 24 with segment 18. A check valve 30 is mounted within conduit 28 and is set to crack open to permit a flow from outlet 26 to segment 11% when the pressure difference (P -P between the outlet and the inlet of the positive displacement gear pump 24 exceeds a predetermined value, thereby bypassing excess flow during gear pump operation. The valve 30 :is essentially a safety device and will not open during normal operation.
The pump 24 has two intermeshing gears 32 and 34 respectively mounted upon shafts 36 and 38 by means well known to those skilled in the art. The shaft 38 and the inducer pump 20 are drivingly interconnected to a drive spline 40 adapted to be connected to the gearbox of a gas turbine engine. It will be understood that the shafts 36 and 38 are journaled in appropriate bearings with a close running tolerance, so that the axes of rotation of the shafts 36 and 38 are substantially parallel. Thus, an inlet region 42 is formed to the left of the area of intermesh of gears 32 and 34 and an outlet region 44 is formed to the right of this area of intermesh. Fluid is carried from the inlet region 42 to the outlet region 44 in pockets defined between the adjacent teeth of each gear and is expelled from these pockets in the discharge region at the area of intermesh.
A sealing block 46 engages the periphery of each gear adjacent the outlet region 44 along arcuate peripheral sealing surfaces 48 and 50. The sealing surfaces 48 and 50 are urged into engagement with at least two teeth of each gear by means of a compression spring 52 and the pressure behind or to the right of the sealing block 46 in variable volume chamber 54. The lateral or upper and lower portions of the sealing block 46 are structurally interconnected by means of a web 56 which embodies a passageway or orifice 58 to communicate discharge pressure to variable volume chamber 54. As will be recognized by those skilled in the art, the construction of the sealing block 46, per se, is conventional.
A vent conduit 60 communicates with the right portion of pumping cavity 22 and hence variable volume chamber 54 to control the pressure in variable volume chamber 54. The venting of the pressure in the variable volume chamber 54 is controlled by a gear to centrifugal pump changeover valve, generally designated at 62.
The changeover valve 62 includes a housing 64 having two chambers 66 and 68. An orifice 70 is mounted within chamber 66 to allow a flow from conduit 60 to proceed to the inlet side of pump through a conduit 72, the conduit serving to fluidly interconnect orifice 70 and the inlet side of pump 20 at a location depicted at 73. A cylindrical spool 74 having a flange or disc 76 thereupon is slideably disposed in a bore which interconnects chambers 66 and 68. The left lateral surface of spool 74 is adapted to cover orifice 70, thereby preventing a flow from conduit 60 to location 73. An evacuated spring-loaded bellows 78 is secured to the periphery of the flange 76 to render the position of the spool 74 a function of the pressure in chamber 68. A conduit 80 interconnects the chamber 68 and the annular volume 81 surrounding the wash flow filter 26 to port the pressure therein to chamber 68. The pressure in the annular volume 81 surrounding the wash flow filter 26 is the discharge pressure (P from the gear pump 24 minus the head loss across the filter.
During startup, the spring urging in the bellows 78 urges spool 74 into covering engagement with orifice 70, but when the pressure in chamber 68 is sufficient to overcome the spring force exerted on the flange 76 by the bellows 78, the spool 74 is shifted to the right, thereby uncovering orifice 70. It should be noted that the pressure in variable volume chamber 54 is equal to pump discharge pressure P when the spool 74 covers the orifice 70, the discharge pressure being communicated from the discharge region 44 of pump 24 to chamber 54 through interconnecting passageway 58 in web 56. Thus, when the orifice 70 is closed, the under or right surface of the sealing block 46 is subjected to a discharge pressure responsive force which supplements that provided by spring 52. The total spring and pressure forces acting on the right face of sealing block 46 act to urge the arcuate sealing surfaces 48 and 50 into engagement with the respective peripheries of the gears 34 and 32. When centrifugal pump 20 and gear pump 24 attain a sufficient speed, the pressure in chamber 68 acting on the left face of flange 76 is sufficient to overcome the spring force exerted thereon by bellows 78 and the spool 74 is thereby shifted to the right, uncovering orifice 70 and engendering a flow from chamber 54 to the inlet side of pump 20 via conduits 60, orifice 70 and conduit 72. This flow acts to relieve the force exerted on the right face of sealing block 46 (because of the pressure drop across orifice 58), thereby permitting the pressure forces exerted on the left side of the web 56 and the arcuate sealing surfaces to move the sealing block 46 to the right against the bias of spring 52. When the sealing block 46 is shifted to the right so as to move the arcuate sealing surfaces out of engagement with the teeth of the gears, pump 24 is removed as a pressure generating source from the pumping circuit, but of course continues to deliver fluid from the inlet region 42 to the outlet region 44. This condition will prevail as long as the centrifugal pump 20 develops sufficient pressure to fulfill the system requirements. Tests have shown that when the gear pump is unloaded, the pressure P drops to a value slightly below that of P,,. This is because the flow path then defined between the gear teeth and the displaced arcuate sealing surfaces acts as a restriction. The particular output pressure at which the pump 24 is unloaded should, of course, be determined with a view toward the application for which the pump is selected. For example, if the pump is associated with a fuel control for a gas turbine engine, unloading should normally occur near the idling speed of the engine.
The manner of operation of the pump of FIG. 1 is as follows:
During startup the drive spline 40 rotates, thereby driving pump 24 and pump 20, pumps 24 and 20 being drivingly interconnected by a suitable means (not shown) such as a shaft. The sealing block 46 is initially urged into contact with the peripheries of the gears by the spring 52. Subsequently, as the speed of pump 24 increases, the pressure in variable volume chamber 54 supplements the force exerted on the sealing block 46 by spring 52 to provide a greater force, urging the sealing block 46 into engagement with the gears 32 and 34. After the speed of the pumps increases sufficiently such that pump 20 is capable of supplying the needed fluid at the prescribed pressure, the pressure in chamber 68 overcomes the spring force exerted by the diaphragm 78 on the spool 74, thereby uncovering orifice 70. As the orifice 70 is uncovered, flow proceeds from variable volume chamber 54 to the inlet side of the centrifugal pump 20, thereby relieving the pressure in variable volume chamber 54. The pressure forces acting on the sealing faces of the sealing block 46 and the web 56 then cause the sealing block 46 to shift to the right, which action removes the gear pump 24 as a pressure generating source. Stated another way, when the spool 74 uncovers orifice 70, the flow through orifice 70 is greater than the flow through passageway 58 which results in a pressure differential between variable volume chamber 54 and the discharge region 44. Since the sealing faces of sealing block 46 are only in contact with the peripheries of the gears during low-speed operation, the life of a gear pump 24 will accordingly be prolonged.
The embodiment of FIG. 2 operates in a manner similar to that of FIG. 1 but employs a slightly different sealing block structure and actuating arrangement therefor. The right or bottom side of sealing block has two converging inclined surfaces 102 and 104 fashioned thereon which are respectively slidingly engaged by wedge-shaped structures 106 and 108, shaped as right triangles. The hypotenuse of each of the wedge-shaped structures slidingly contacts its associated inclined surface on the sealing block 100 to urge the arcuate sealing surfaces 50 and 48 towards the peripheries of the gears 32 and 34. Depending from the respective bases of wedge structures 106 and 108 are shafts 110 and 112 which function as pistons, as is explained hereinafter. Compression springs 114 and 116 are interposed between the periphery of the chamber and the bases of the wedge structures 106 and 108, respectively. During starting, these springs urge the wedges towards the sealing block 100, thereby urging the sealing faces 48 and 50 into contact with the peripheries of the gears 34 and 32.
A conduit 1 18, having an orifice 120 disposed therein, communicates with another conduit 122 to direct filtered fluid, substantially at discharge pressure (P to the bases of the shafts 110 and 112. Another conduit 124 joins conduit 122 to place conduit 122, and hence the bases of shafts 110 and 112 in fluid communication with chamber 66.
When spool 74 covers orifice 70 discharge pressure is exerted behind shafts 110 and 112, thereby urging the wedgeshaped members 106 and 108 towards the sealing block, supplementing the force provided by springs 114 and 116. When the discharge pressure from the pump 24 attains a sufficient value, spool 74 is shifted to the right in the manner heretofore explained, thereby uncovering orifice 70. The uncovering of orifice 70 effects a reduced pressure behind shafts 110 and 112, (due to the pressure drop across restriction 120) thereby allowing the pressure forces exerted on the sealing block 100 to shift the sealing block to the right against the bias of springs 114 and 1 16. Movement of the sealing block to the right engenders a sliding contact between the inclined surfaces 102 and 104 and the respective hypotenuses of the wedge-shaped members 106 and 108. If desired, the entire face of the sealing block may be shaped to provide an inclined surface for a single-wedge member extending therealong.
The embodiment of FIG. 3 illustrates still another method for implementing the present invention. The sealing block 200 is somewhat T-shaped and the lower or right portion has a passage 202 which communicates with the chamber 47 and has an orifice 204 disposed therein. It should be noted that passage 202 does not pass completely through the right extremity or base surface of the sealing block 200, but terminates adjacent thereto. Lateral passages 206 and 20%, formed in the sealing block 200, communicate with passage 202 intermediate its point of termination adjacent the base of sealing block 200 and orifice 204. Hollow pistons 210 and 212 are respectively slidingly disposed within the lateral passages 206 and 200 and project outwardly therefrom. A compression spring 214 is received within the hollow portions of the pistons and extends laterally therebetween across passage 202. The outboard tips of pistons 210 and 212 contact the sides of struts 216 and 218 to urge them against the sealing block 200. The lower or right surfaces of the struts 216 and 218 are beveled to match the inclined contour of the housing and are adapted to slide therealong. The tips of the struts 216 and 218 respectively slidingly contact the intermediate lateral surfaces 220 and 222 of sealing block 200. The passage 202 is in communication with a vent port 224 in the housing 17 downstream of orifice 204. The vent port 224, in turn, communicates with chamber 66 of the changeover valve 62 via a conduit 226.
Therefore, during low-speed operation of the gear pump 24 of FIG. 3, the high pressure in passage 202 downstream of the orifice 204 supplements the spring force acting on the hollowed pistons 210 and 212 to contribute to the outward force which they exert on the struts 216 and 218. It should be clear from FIG. 3 that the pushing or urging of the pistons against these struts will cause the struts to slide along the inclined surfaces of the housing 17, thereby urging the sealing block into firm contact with the peripheries of the gears. When orifice 70 is uncovered, in the manner heretofore described, the pressure downstream of the orifice 204 decreases, thereby allowing the pressure forces acting on the sealing block to displace it to the right. A rightward displacement of sealing block 200 will result in the struts sliding along the housing and a consequential inward displacement of the pistons 210 and 206. This action produces an unloading of the gear pump as in the previously described embodiments.
It will be understood, of course, that the pumps shown herein may be provided with sideplates. Sideplates suitable for inclusion in the disclosed pump are those shown, for example, in U.S. Pat. Nos. 2,420,622, 2,742,862, 2,996,999, 3,292,550 and 3,427,985.
While certain specific embodiments have been described, it is obvious that numerous changes may be made without departing from the general principles and scope of the invention as defined by the subjoined claims.
1. A pump having an inlet and an outlet comprising in combination:
a housing having a pumping cavity therein, the cavity having an inlet and an outlet;
a pair of intermeshing gears mounted for rotation within the cavity;
a sealing block having a discharge chamber movably mounted within the cavity, the sealing block having two arcuate sealing surfaces for contacting the respective peripheries of the gears, the sealing block being adapted to be urged by a fluid pressure into firm contact with peripheries of the gears;
a first conduit fluidly interconnecting the pump inlet with the cavity inlet;
a hydrodynamic pump mounted within the first conduit in series flow relationship with the gears for increasing the pressure of fluid flowing thereto;
a second conduit fluidly interconnecting the cavity outlet with the pump outlet;
a positionable valve operatively connected to the housing for varying the fluid pressure urging the sealing block toward the gears;
means at least partially located in the cavity and subjected to the fluid pressure to urge the sealing block into engagement with the gears and to allow fluid pressure forces actmg directly on the sealing block to move the sealing block away from the gears; and
a third conduit fluidly interconnecting the valve to the urging means to vent the fluid pressure to which the urging means is subjected and thereby allow the fluid pressure forces acting directly on the sealing block to move the sealing block away from the gears.
2. A pump as defined in claim 1 wherein the urging means comprises:
a web integral with the sealing block, the web having a passageway extending therethrough, the web serving to define a variable volume chamber within the cavity, and the third conduit communicating with the chamber.
3. A pump as defined in claim 1 wherein the urging means comprises:
a wedge-shaped member;
a shaft depending from the wedge-shaped member slideably positioned in the third conduit;
and wherein the base of the sealing block has a beveled surface thereupon;
and wherein the wedge-shaped member slidingly contacts the beveled surface.
4. A pump as defined in claim 3 further including:
conduit means to fluidly interconnect the second conduit with the third conduit; and
orifice means positioned in the conduit means.
5. A pump as defined in claim 1 wherein the urging means comprises:
a piston slideably mounted in the sealing block for lateral movement relative to the sealing block;
and wherein the sealing block comprises a passage in communication with the discharge chamber having an orifice therein, the piston being mounted downstream of the orifice in communication with the passage;
and wherein the sealing block has a laterally extending surface and the cavity has an inclined surface;
and wherein a movable strut in contact with the piston con tacts and extends between the laterally extending and inclined surfaces.
6. A pump as defined in claim ll wherein the valve comprises:
a housing having first and second chambers therein;
an orifice mounted in the first chamber, the first chamber communicating with the third conduit;
pressure sensitive means mounted in the second chamber;
a member extending between the chambers slideably mounted in the valve housing, the member being integral with the pressure sensitive device and positionable thereby to open and close the orifice.
7. A pump as defined in claim 6 further including:
conduit means fluidly interconnecting the first chamber and the first conduit; and
conduit means fluidly interconnecting the second chamber and the second conduit.
0. A pump as defined in claim 7 wherein the pressure sensitive means comprises:
an evacuated bellows secured to he wall of the second chamber.