US2966332A

US2966332A - Overspeed control for turbine rotor

Info

Publication number: US2966332A
Application number: US666937A
Authority: US
Inventors: Horace L Gardner
Original assignee: Fairchild Engine and Airplane Corp
Current assignee: Fairchild Engine and Airplane Corp
Priority date: 1957-06-20
Filing date: 1957-06-20
Publication date: 1960-12-27
Anticipated expiration: 1977-12-27

Description

Dec. 27, 1960 H. GARDNER OVERSPEED CONTROL FOR TURBINE ROTOR 2 Sheets-Sheet 1 Filed June 20, 1.957

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INVENTOR HORACE L.GARDNER IS ATTORNEYS Dec. 27, 1960 H. GARDNER OVERSPEED CONTROL FOR TURBINE ROTOR 2 Sheets-Sheet 2 Filed June 20. 1957 FIG.6.

INVENTOR HORACE L.GARDNER HISATTORNEYS United States Patent OVERSPEED CONTROL FOR TURBINE ROTOR Horace L. Gardner, Islip, N.Y., assignor to Fairchild Engine and Airplane Corporation, Hagerstown, Md., a corporation of Maryland Filed June 20, 1957, Ser. No. 666,937

3 Claims. (Cl. 253-59) This invention relates to an overspeed control for a turbine rotor in which, in the event of overspeed operation of the turbine rotor, the effective area of the inlet passage or passages through which the impelling fluid is directed toward the turbine rotor is substantially reduced, thereby substantially reducing the rotor speed.

It is well known that runaway turbines are highly dangerous due to the possibility of failure of the turbine rotor. Because of the extremely high rotational speeds at which turbine failures occur, it is not unusual for large fragments of the rotor to be projected with sufficient force to penetrate the housing within which the rotor is situated. It is apparent that such failures present an extreme hazard to both personnel and equipment.

In many conventional turbines the impelling fluid is directed against the turbine rotor through passages formed between a plurality of stator vanes. The stator vanes are ordinarily arranged in a circular array, either laterally offset from the impeller blades carried by the turbine rotor or around the outer periphery of the turbine blades carried by the rotor. In either case their function is to direct the impelling fluid in the desired direction against the impeller blades of the turbine rotor.

In the overspeed control of the present invention, the stator vanes are split into upstream and downstream portions, and the upstream and downstream portions are so mounted that they can be moved relatively to each other to decrease the effective area of the passages through which the impelling fluid is directed against the turbine rotor. This decrease in area, in turn, reduces the energy which the impelling fluid transmits to the turbine rotor, and so has the effect of slowing down the turbine rotor.

For a complete understanding of the present invention, reference may be had to the detailed description which follows and to the accompanying drawings in which:

Figure 1 is a fragmentary cross-sectional view of a portion of a turbine embodying the present invention;

Figure 2 is a cross-sectional view, taken along the line 2-2 of Figure 1, looking in the direction of the arrows;

Figure 3 is a view similar to Figure 2 but illustrating the relative displacement between the upstream and downstream portions of the stator vanes in the event of overspeed operation of the turbine rotor;

Figures 4 and 5 are fragmentary views, partly in crosssection, taken along the lines 4-4 and 55, respectively, of Figure 1, looking in the direction of the arrows; and

Figure 6 is a view similar to Figure 1, but illustrating another embodiment of the invention.

Referring to the drawings, a turbine rotor 10 is mounted on a rotatable shaft 11 within a turbine housing 12. The turbine illustrated in the drawings is an axial flow type wherein an impelling fluid is directed under pressure through a passage 13 toward the impeller blades 14 affixed to the outer periphery of the rotor 10. The annular passage 13 is defined between the inner surface of the housing 12 and the outer surface of a cylindrical support member 15 mounted centrally within the upstream end of the housing 12. As shown in Figure 5, the end of the 2,966,332 Patented Dec. 27, 1960 support member serves as a bearing for the rotatable shaft 11. A plurality of stator vanes, generally designated 16, are mounted within the annular passage 13 to direct the impelling fluid in the desired direction against the impeller blades 14 of the turbine rotor.

In accordance with the present invention, the stator vanes 16 are each split so as to form an upstream component 16a and a downstream component 16b. The upstream components 16a of the stator vanes are mounted around the outer periphery of a common annular support member 18 which is affixed to the end of the support member 15 by means of screws 19. The downstream components 16b of the stator vanes are aflixed to the outer periphery of a common annular support member 20 which is rotatably mounted with respect to the support member 18 from the position illustrated in Figure 2 to the position illustrated in Figure 3. More specifically, the support member 20 is held by a plurality of screws 21 to the adjacent face of the support member 18. The screws 21 pass through arcuate slots 23 in the support member 20, permitting limited rotational movement of the support member 20 relative to the support member 18. The screws 21 carry compressed springs 24 thereon which exert pressure against a face of the support member 20, urging the opposite face thereof against the adjacent face of the support member 18. The pressure exerted by the springs can be adjusted by tightening or loosening the screws, and in this way the frictional resistance of the support member 20 to rotate relatively to the support member 18 can be regulated. The opposed faces of the

support members

18 and 20 are aligned with respect to each other by a tongue and slot engagement. More specifically, referring to Figure 1, the lateral face of the support member 20 is provided with a curved tongue 25 which is accommodated within a curved slot 26 formed in the opposite face of the support member 18.

In the normal operation of the turbine rotor, the downstream components 16b of the stator vanes are registered with respect to the upstream components 16a thereof, as shown in Figure 2, so that the passages a intermediate adjacent downstream components 16b are substantially continuous with the passages b intermediate the upstream components 16a of the stator vanes. In the event of overspeed operation of the turbine rotor, however, the support member 20 is adapted to be rotated relatively to the support member 18 to a position in which the downstream components 16b are offset with respect to the upstream components 16a of the stator vanes. In the position illustrated in Figure 3, the downstream components 16b of the stator blades are moved into substantial registry with the passages b between upstream components of the stator vanes, and the upstream components 16a are in substantial registry with the passages a between the downstream components of the stator vanes. This represents a displacement of the support member 20 equal to one-half of the spacing between the upstream components of the stator vanes. As a result, the effective cross-sectional area of the passages intermediate the stator vanes is substantially reduced along the plane formed by the abutting faces of the

support members

18 and 20. This reduction in effective cross-sectional area acts as a valve to reduce the flow of impelling fluid against the impeller blades 14 of the turbine rotor and, hence, substantially reduces the speed at which the turbine rotor is driven by the impelling fluid.

Provision is made in the present invention for automatically displacing the

support members

18 and 20 relative to each other in the event of an overspeed operation of the turbine rotor. To accomplish this a plurality of trip flanges or projections 28 are mounted in circular array to the face of the turbine rotor 10 adjacent the support member 20, and a plurality of radial pins 29 are mounted to the support member 20 in circular array just outboard of the outer periphery of the projections 28. In the event of an overspeed operation of the turbine rotor, centrifugal force will deflect the trip projections outwardly, so that the outer surface of one or more of the trip projections will frictionally engage the inner end of one or more of the pins 29. This frictional engagement between the projections 28 and the pins 29 will rotatably displace the support member 20 relatively to the support member 18, at least to the extent permitted by the length of the arcuate slots 23 in the support member 20, thereby moving the support member 20 to the position illustrated in Figure 3. The resulting decrease in the cross-sectional area of the passages between the stator blades results in a decrease in the speed of rotation of the turbine rotor.

The trip projections 28 are illustrated in Figure 4 as elongated projections of arcuate curvature, but shorter or longer trip projections may be used. Preferably, however, the length of the trip projections 28 is designed to exceed the space between adjacent pins 29. In this way, the outer surface of the trip projection 28 will engage the inner end of a pin 29 and displace the support member 20 without damage to either the projection or the pin. n the other hand, the trip projections may be made shorter in length, in which case they will be more readily deflected outwardly by centrifugal force. If so designed, the leading edge of a trip projection may serve to engage one of the pins 29 and so displace the support member 20 from the position shown in Figure 2 to the position shown in Figure 3. Of course, in this case either the projection or pin will be sheared off. The slight damage caused by shearing off the pin or trip projection, however, is incidental in comparison with the very severe damage which is possible if the speed of the turbine rotor is not checked.

A modified form of the invention is illustrated in Figure 6 of the drawings. In this embodiment, the turbine rotor 30 carrying impeller blades 31 around the outer periphery thereof is mounted within a turbine housing 32. As in the form of the invention described above, the impelling fluid flowing through the passage 33 is guided by split stator vanes, generally designated 34, against the impeller blades 31, thereby driving the turbine rotor 30. The upstream components 34a of the split stator vanes are mounted around the outer periphery of an annular support member 35, and the downstream components 34b of the stator blades are mounted around the outer periphery of an annular support member 36. The annular support member 35, as in the form of the invention illustrated in Figures 1 to of the invention, is anchored by screws 37 to the frame structure 32a. The support member 36, in turn, is affixed to the support member 35 by screws 38 which pass through arcuate slots 39 in the support member 36 to permit displacement of the member 36 relative to the support member 35 in the event of overspeed operation of the turbine rotor. Spring washers 40 carried by the screws 38 serve the function of the compression springs 24 in the form of the invention described above.

In this form of the invention, the shear pins 42 interposed in aligned holes of the support members 35 and 36 determine the registered position of the blade components 34a and 34b. In the event of an overspeed operation of the turbine rotor, the pins 42 are readily sheared, permittin the displacement of the downstream components 34b of the stator blades relative to the upstream components 341: thereof.

In this modification, an extended shroud 45 encircles both the downstream components 34b of the stator vanes and the turbine rotor. The annular shroud 45 is attached to the outer peripheries of the downstream components 34b of the statorvanes, but there is a small clearance provided between the outer edges of the impeller blades 31 and the inner periphery of the annular shroud 45.

It is a well known phenomenon that turbine rotors rotating at high speeds expand in diameter, principally due to the effect of centrifugal force. The expansion of the turbine rotor at high speeds is utilized in this modification of the invention to displace the downstream stator components 34b relatively to the upstream components 34b thereof in the event of overspeed operation of the turbine rotor. More specifically, in the event of overspeed rotation of the turbine rotor, the outer edges of the impeller blades 41 will contact the inner surface of the annular shroud 45, and the frictional engagement therebetween will shear the pins 42 and displace the stator components 341) relatively to the components 34a to the extent permitted by the length of the arcuate slot 39. This permits the stator components 34b to rotate a distance equal to one-half the spacing between the upstream components 34a of the stator vanes, thereby appreciably reducing the effective area of the passage 33 to the impeller blades 31.

The invention has been shown and described in pre ferred forms and by way of example only, and obviously many modifications and variations may be made in the invention without departing from the spirit thereof. The invention, therefore, is not to be limited to any specified form or embodiment, except in so far as such limitations are set forth in the claims.

I claim:

1. An overspeed control for a turbine rotor which carries a plurality of impeller blades mounted in a circular array comprising a housing, passage in the housing for conducting an impel-ling fluid to the impeller blades of the turbine rotor, a plurality of stator vanes arranged in the passage immediately upstream of the impeller blades for deflecting the impelling fluid and directing it against the faces of the impeller blades, said stator vanes being split into upstream and downstream components, the downstream components of the stator blades constituting one group and the upstream components of the stator vanes constituting another group, a common movable support for the components of one of the groups, an independent support for the components of the other of said groups, means for limiting the relative displacement between the supports from one extreme position in which the upstream and downstream components of the stator vanes are aligned in complementary fashion to another extreme position in which the upstream and downstream components of the stator vanes are out of alignment so as to cut down the rate of flow of the impelling fluid to the impeller blades, means for yieldingly locking the supports irrespective of which of said extreme relative positions the two supports are positioned, the two supports being arranged so as to position the upstream and downstream components of the stator vanes in alignment at all speeds below a predetermined speed within the safe range, an inner deflectible element carried by the turbine rotor, an outer cooperating element carried by the movable support, the deflectible element carried by the turbine rotor being translated thereby at safe speeds of operation below the predetermined speed in a circular path closer to the axis of rotation of the rotor than the outer cooperating element and out of contact therewith, the centrifugal force at higher speeds causing the deflectible element to move outwardly from the axis of rotation of the rotor and into engagement with the cooperating element carried by the movable support, the engagement therebetween imparting rotation to the movable support to shift the movable support from the extreme position of alignment between the upstream and downstream components of the stator vanes to the other extreme position of misalignment therebetween.

2. An overspeed control for a turbine rotor as set forth in claim 1 in which the means for yieldingly locking the supports comprises a compressed spring which acts against one face of the movable support and including spring retaining means connected to the independent support for maintaining the compressed spring in position to exert a force against the said movable support in order to yieldingly lock the two supports in either of said extreme relative positions.

3. An overspeed control for a turbine as set forth in claim 2 in which the movable support and the independent support are in face-to-face relationship and including means defining an aperture in the movable support to accommodate the spring retaining element, whereby the spring acts to yieldingly lock the supports by increasing the frictional contact therebetween.

References Cited in the file of this patent UNITED STATES PATENTS Pollard et al. Ian. 10, Entz Dec. 31, Graham et al. Jan. 18, Millns Oct. 2, Teague Oct. 7, Volk Sept. 8, Iaquith Jan. 19,

FOREIGN PATENTS Canada Mar. 8, France June 22,