US3712756A

US3712756A - Centrifugally controlled flow modulating valve

Info

Publication number: US3712756A
Authority: US
Inventors: I Kalikow; E Sterling; W Anderson
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1971-07-22
Filing date: 1971-07-22
Publication date: 1973-01-23
Anticipated expiration: 1990-01-23
Also published as: IT950837B; DE2218705A1; FR2146715A5; BE780106A

Abstract

A centrifugally controlled valve assembly for modulating the rate of flow of a fluid includes a hollow annular housing having an inlet and outlet, together with a Bellville washer modified by a plurality of weights attached thereto and disposed within the annular housing for rotation therewith. Increased rotational speed operates to distort the geometry of the washer thereby changing the degree of obstruction which the washer presents to the rate of flow through the housing.

Description

United States Patent 91 Kalikow et al.

[ 1 Jan. 23, 1973 CENTRIFUGALLY CONTROLLED FLOW MODULATING VALVE [75] Inventors: Irving Kalikow, Swampscott', Eliot Morton Sterling, Needham; William Paul Anderson, Wenham, all of Mass.

[73] Assignee: General Electric Company 22 Filed: July 22,1971

211 App1.No.: 165,168

[52] US. Cl. ..415/l75, 137/56, 416/97 [51] Int. Cl ..F0ld 5/08, 005d 13/10 [58] Field otSearch...;.l37/56;415/175,115,173 A;

[56] References Cited UNITED STATES PATENTS 2,787,960 4/1957 Wightman ..415/173 A 2,936,715 5/1960 Southam et al 3,028,181 4/1962 Thompson et a1. 3,366,068 1/1968 Rye ..4l5/173 A Primary ExaminerI-Ienry F. Raduazo Attorney-Edward S. Roman et a1.

[57] ABSTRACT 8 Clair 11s, 6 Drawing Figures 2,478,649 8/1949 Wightman ..4l5/173 A w" 7 g 2.4 M a PATENTEDJAH 23 1915 PPM PATENTEDJMI 23 I975 SHEET 2 OF 2 4.9 I I I INVENTOR5.

5 Mme M my um W 4 (5P m a r N m 4 wmm CENTRIFUGALLY CONTROLLED FLOW MODULATING VALVE BACKGROUND OF THE INVENTION In general, this invention relates to a centrifugally controlled, flow modulating valve and more particularly to a centrifugally controlled valve for modulating the rate of-flow of cooling fluid to the turbine disc and blades of a gas turbine engine.

The power output and thermal efficiency of a gas turbine engine can be increased by increasing the temperature of the combustion gases supplied to the turbine blades. In general, however, any such increase is limited by the maximum permissible operating temperature of the turbine rotor and its blades. It is known to the art to use a portion of the compressor air for cooling the turbine rotor and/or its blades. However, any use of the compressor air for turbine cooling decreases the amount of compressor air available for the combustion chamber of the gas turbine, thereby decreasing the thermal efficiency of the engine. Thermal efficiency could be substantially improved in certain operating regimes if the flow of cooling fluid to the turbine rotor and blades could be scheduled to coincide with increases in engine operating temperatures. In general, increased engine operating temperatures coincide with increased engine rotational speed making centrifugally operated valves an attractive means for scheduling cooling flow to the turbine.

However, conventional spring type centrifugally operated valves have proved entirely inadequate for modulating the rate of turbine cooling flow within gas turbine engines. Known gas turbine shafts may rotate at speeds up to 45,000 rpm, generating high centrifugal force fields in the order of 50,000 to 80,000 Gs. Suitable means for scheduling the flow of cooling fluid to the turbines of a gas turbine engine must be capable of modulating the flow even under these high rotational speeds. Known spring-type centrifugal valves, however, become fully opened at substantially lower rotational speeds, and therefore are inadequate for modulating cooling flow in high speed gas turbine engines.

Conventional turbines and gas generators are designed to operate at high temperatures whereas available cooling flow is normally at the substantially lower compressor discharge temperature. Therefore, a cooling flow modulating valve must be capable of operation within a large temperature differential including temperatures up to l,000F.

Therefore, it is an object of this invention to provide a centrifugally controlled valve for effectively modulating the rate of cooling flow to the turbine of a gas turbine engine. 7

It is also an object of this invention to provide a centrifugally controlled valve which operates at substantially higher rotational speeds and temperatures than heretofore possible.

It is a further object of this invention to provide a centrifugally controlled valve which is made both simple and reliable by a one piece construction.

SUMMARY OF THE INVENTION A valve assembly is included within a gas turbine engine for modulating the rate of flow of cooling fluid to a turbine as a function of rotational speed. The valve assembly includes a valve housing disposed for rotation with the engine shaft. The walls of the housing define an annular plenum chamber therein, and include an inlet port and an outlet port therethrough. A modified Belleville washer is disposed within the plenum chamber for rotation therewith. The modified Belleville washer has an inner and outer frustoconical surface, together with a plurality of weights disposed on the inner frustoconical surface. Increased engine rotational speed operates to modulate the rate of cooling flow through the housing by forcing the frustoconical surfaces of the washer to move toward a radial direction, after which further increased rotational speed causes the inner and outer frustoconical surfaces to invert themselves into outer and inner frustoconical surfaces respectively. This distortion of the washer changes the degree of obstruction which the washer presents to the rate of flow through the housing.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a gas turbine engine which includes the valve assembly of this inven- DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. I, a gas turbine engine is shown at 10 as comprising a cylindrical housing 12 having an axial flow compressor 14 journaled within the housing adjacent to its forward end. The compressor 14 receives air through an annular air inlet 16 and delivers compressed air to a combustion chamber 18. Within the combustion chamber 18, air is burned with fuel and the resulting combustion gases are directed by a nozzle or guide vane structure 20 to the rotor blades 22 of a turbine rotor 24 for driving the rotor. A shaft 26 drivably connects the turbine rotor 24 with the compressor 14. From the turbine blades 22, the exhaust gases discharge rearwardly into the surrounding atmosphere through an exhaust nozzle 28 whereby the gas turbine engine is provided with forward propulsive thrust. The gas turbine structure so far described is conventional.

In order to cool the turbine rotor, air is bled off from the compressor and supplied to the turbine 24 through an annular conduit 30 which is in direct flow communication with the compressor discharge. The cooling flow modulating valve assembly of this invention is shown generally M31 and provides modulation of cooling flow to the turbine rotor '24 and turbine blades 22 as a function of engine rotational speed.

Referring now to FIG. 2, the cooling flow modulating valve assembly 31 is shown in substantial detail as including a housing 32 which is either formed integral with, or attached to, a shaft 26 for rotation therewith.

Housing 32 defines an annular plenum chamber 34, through which compressor cooling air is directed. Cooling air is directed to the valve housing 32 through an annular conduit 30 which remains in fixed position relative to the rotating housing. Cooling air flow enters the valve housing from conduit 30 through an annular inlet port 40. Sealing between the conduit 30 and valve housing 32 is provided by means of two axially spaced

labyrinth seals

70, 72. Cooling air flow exits from the valve housing through an annular conduit 44, whereupon it is directed radially outwardly over the turbine rotor disc 24 and thence through openings 45 into the turbine rotor blades and out through suitable openings in the blades (not shown). It should be noted that the invention is in no way limited to any specific turbine rotor structure for utilizing the cooling air supplied to the turbine rotor. The annular plenum chamber 34 includes an inner concentric surface 36 having a circumferential groove 42 in the surface thereof, and two axially spaced, outer concentric surfaces 38, 48 between which the annular inlet port 40 is disposed.

The valve assembly 31 also includes a Belleville washer 50, the details of which may be better understood by referring to FIGS. 3d and 3b in conjunction with FIG. 2. The Belleville washer 50 includes opposing inner and outer

frustoconical surfaces

52, 54, together with an inner concentric edge 56 and an outer concentric edge 58. The inner frustoconical surface 52 of the Belleville washer is preferably modified by inclusion of a plurality of circumferentially spaced weights 60 thereon, which may be characterized as integral radially extending fins. The inner concentric edge 56 of the modified Belleville washer is preferably radiused for seating engagement within the groove 42. The minimum axial width of the outer concentric edge 58 of the modified Belleville washer is determined by the axial width of the inlet port 40. The outer concentric surface 38 of the plenum chamber 34 is of sufficient radius to clear the outer concentric edge 58 of the modified Belleville washer. The washer is preloaded so as to force the frustoconical surfaces radially outward by abutting engagement of the inner frustoconical surface 52 of the washer with the circumferential edge of the outer concentric surface 48 of the plenum chamber. Pressure on either side of the modified Belleville washer is maintained equal by means of passages or undercuts shown generally at 49 which establish flow communication between both sides of the washer. At least one axially extending drive pin 62 interconnects the wall of the valve housing 32 to the modified Belleville washer 50 to insure rotation of both the housing and washer without circumferential slippage therebetween. The drive pin 62 is free to axially slide within its engaging slot so as not to constrain axial movement of the modified Belleville washer within the housing.

At low engine rotational speed the modified Belleville washer occupies the position shown by solid lines in FIG. 2. As can be seen from the drawing, the outer concentric edge 58 of the modified Belleville washer obstructs compressor cooling air flow through the annular inlet port 40. As engine rotational speed is accelerated, increased centrifugal force acting on the Belleville washer and its associated weights gradually generates an overturning moment which forces the inner and outer

frustoconical surfaces

52, 54 toward substantial radial alignment with the center axis. A further increase in engine rotational speed results in the frustoconical surfaces of the Belleville washer inverting themselves as shown by the phantom lines wherein surface 52 becomes the outer frustoconical surface of the Belleville washer and surface 54 becomes the inner frustoconical surface of the Belleville washer. Engagement of the inner concentric edge 56 with the annual groove 42 maintains the axial position of the inner concentric edge during engine rotation. The outer concentric edge 58 moves out of obstructing alignment with the inlet port 40, thereby allowing increased cooling air flow through the plenum chamber 34 and hence to the rotor disc and blades. in order to meet requisite temperature capability, the modified Belleville washer may be made of a spring steel alloy such as is sold under the trade name of lnconel. Spring steel also provides for return of the washer back to its original configuration upon decreased engine rotational speed.

Referring now to the graphs of FIG. 4, there are shown three curves representing washer deflection, plotted as functions of engine rotational speed. The curves are non-linear due to the combination of hoop and bending stresses within the modified Belleville washers. However, as may be readily observed from the graphs, different washers provide more or less nonlinear curves. Curve B characterizes a Belleville washer wherein the deflection is a function of the engine RPM. A modulating valve having this washer therefore would allow a gradual increase of compressor cooling air flow to the turbine disc and blades for increased engine rotational speed. However, it is generally desirable to have a modulating valve that fully opens for a relatively small change in engine RPM. Such a valve would include a modified Belleville washer characterized by curve C, wherein the area of steep slope represents an area of rapidly changing washer deflection for small changes in engine rotational speed. It has been found that changing the geometry of the sides of the modified Belleville washer by axially thinning the washer results in the steeper sloped curve C. Also, reducing the thickness of the weights 60 has been found to delay the start of the steep portion of the curve. There may also be engine applications where it becomes desirable to have the modulating valve open at a different engine rotational speed from that which the valve closes. The deflection of such a washer is shown graphically by curve A, wherein the hysteresis is the result of an even further axial thinning of the washer. Preloading the washer in the previously described manner eliminates the slight gradual deflection of the washer at low engine rotational speeds, thereby narrowing the differential speed within which substantially all washer deflection occurs. The variety of curves shown graphically in FIG. 4 are indicative of the increased accuracy and flexibility with which turbine cooling flow may be modulated by the valve of this invention.

IN order to increase cooling air flow through the valve and to provide an added margin of safety in the unlikely event that one washer should seize, two modified Belleville washers may be placed back to back for opening two annular ports as shown in FIG. 5 where like numerals designate previously described elements. The modulating valve housing is shown generally at 32' and is either formed integral with or attached to the shaft 26 for rotation therewith. Housing 32' also defines an annular plenum chamber 34' through which compressor cooling air is directed. The annular plenum chamber 34' includes an inner concentric surface 36 having a pair of axially spaced, circumferential grooves 42, 42' in the surface thereof. A pair of axially spaced, annular inlet ports 40, 40' direct cooling air through the outer concentric surface of the plenum chamber.

The plenum chamber 34 includes two back to back modified Belleville washers 50, 50' wherein washer 50' may be identical with washer 50. The washers 50, 50' include inner

concentric edges

56, 56 radiused for seating engagement with the

grooves

42, 42 respectively. The inlet ports 40, 40' are axially divided by an annular rib 80 which is maintained in fixed relation to the valve housing by means of a plurality of circumferentially spaced apart, axial ribs 82. An inner concentric surface 84 of the annular rib 80 is of sufficient radius to clear the outer

concentric edges

58, 58 of the modified Belleville washers 50, 50'. The circumferential edges of the outer concentric surfaces 48, 48' of the plenum chamber 34' are of sufficiently small radius to abut the frustoconical surfaces 52, 52' respectively of the modified Belleville washers thereby preloading the washers. Cooling air flow through inlet port 40 is directed to outlet conduit 44 by means of interconnecting passages 49'.

At low engine RPM the modified Belleville washers occupy the positions shown in solid lines and the outer concentric edges 58, 58' obstruct compressor cooling air flow through the annular inlet ports 40, 40' respectively. As engine rotational speed is accelerated, increased centrifugal force acting on the modified Belleville washers gradually forces the frustoconical surfaces of the washers to invert themselves in the manner previously described, thereby allowing increased cooling air flow through the plenum chamber and thence to the turbine rotor or blades.

In addition to engine rotational speed modulation, it is possible also to combine a degree of temperature modulation by including a bimetallic Belleville washer within the valve assembly. The inner frustoconical layer may be of a metal having a higher coefficient of thermal expansion than the outer frustoconical layer, such that an increased temperature causes a nonuniform expansion of the Belleville washer, causing it to actuate at a lower engine rotational speed.

Also, it is to be understood that the intended scope of invention is by no means limited to Belleville washers having weights of the integral radial fin type and that the weights may be formed in shapes other than radial fins without departing from the scope of the invention.

in fact, although not preferred, it is possible to eliminate the weights entirely from the Belleville washer, in which case total washer deflection would likely be reduced so as not to distort beyond a radial plane.

Having above described preferred embodiments of the invention, though not exhaustive of all possible equivalents, what is desired to be secured by letters patent is claimed below:

What is claimed is: 1. A valve assembly for modulating the flow of fluid therethrough as a function of rotational speed comprises:

a valve housing disposed for rotation about a central axis wherein the walls of the housing define an annular plenum chamber therein and include an inlet port and outlet port therethrough; and

at least one Belleville washer having an inner and outer frustoconical surface, wherein the washer is disposed within the plenum chamber for rotation therewith, such that increased rotational speed and centrifugal force operate to modulate the rate of fluid flow through the housing by forcing the frustoconical surfaces of the washer to move toward a radial direction, after which continued increased centrifugal force causes the inner and outer frustoconical surfaces to invert themselves into outer and inner frustoconical surfaces respectively, thereby changing the degree of obstruction which the washer presents to the rate of flow through the housing.

2. The valve assembly of claim 1 wherein the Belleville washer is modified to include a plurality of weights disposed on the inner surface thereof.

3. The valve assembly of claim 2 as include in a gas turbine engine wherein the valve modulates cooling flow to a turbine.

4. The valve assembly of claim 2 wherein the inlet port is an annular opening through the outer radial wall of the housing and the outer concentric edge of the washer substantially obstructs the flow of fluid through the inlet port such that increased rotational speed and centrifugal force operate to modulate the rate of fluid flow by forcing the outer concentric edge of the washer away from the inlet port.

5. The valve assembly of claim 4 wherein the inner concentric edge of the washer is restrained from axial translation upon increased rotational speed and centrifugal force by engagement within an annular groove in the inner concentric surface of the annular plenum and circumferential slippage between the washer and housing is restrained by an axially extending pin, the opposing ends of which engage a weight of the washer and wall of the housing respectively.

6. The valve assembly of claim 2 wherein the weights I are radially extending fins which project from the inner frustoconical surface of the washer.

7. The valve assembly of claim 2 wherein temperature modulation is included by forming the modified Belleville washer of two layers having different coefficients of thermal expansion.

8. The valve assembly of claim 2 including a second annular opening axially spaced apart from the first opening and a second modified Belleville washer in back to back relationship with the first washer so that the outer concentric edge of the second washer substantially obstructs the flow of fluid through the second annular opening, wherein increased rotational speed and centrifugal force operate to modulate the rate of fluid flow by moving the outer concentric edges of the washers away from the respective annular inlet openings.

Claims

1. A valve assembly for modulating the flow of fluid therethrough as a function of rotational speed comprises: a valve housing disposed for rotation about a central axis wherein the walls of the housing define an annular plenum chamber therein and include an inlet port and outlet port therethrough; and at least one Belleville washer having an inner and outer frustoconical surface, wherein the washer is disposed within the plenum chamber for rotation therewith, such that increased rotational speed and centrifugal force operate to modulate the rate of fluid flow through the housing by forcing the frustoconical surfaces of the washer to move toward a radial direction, after which continued increased centrifugal force causes the inner and outer frustoconical surfaces to invert themselves into outer and inner frustoconical surfaces respectively, thereby changing the degree of obstruction which the washer presents to the rate of flow through the housing.

6. The valve assembly of claim 2 wherein the weights are radially extending finS which project from the inner frustoconical surface of the washer.