Installation For The Support Of Pivotal Guide Blades

Abstract

An installation for the pivotal support of guide blades of turbo machines particularly gas turbines in which chambers or passages are provided in the bearing support through which flows the cooling air; the blade shaft constructed as adjusting shaft is provided with an annular groove in its center bearing area and with another annular groove at the blade end whereby the two annular grooves are connected with each other by a thread; the central annular groove is in communication with the chambers or passages while the other annular groove is in communication with the guide blade space of the machine.

Description

The present invention relates to an installation for the support of pivotal guide blades of turbo-machines, especially of gas turbines, whereby chambers or passages are provided in a bearing support, through which flows cooling air. Particular difficulties have to be overcome in the support of pivotal guide blades of gas turbines, by reason of the large temperature range in which a satisfactory operation must be assured at all times, which difficulties consist in that the bearing clearance necessary for the pivoting movement has to be maintained notwithstanding the considerable thermal expansions.

It is known to cool the bearing places with compressed air in order to avoid large thermal expansions and the danger connected therewith of a binding of the guide blades. The heretofore known arrangements, however, provide only cooling passages or chambers in the bearing housing whereby the cooling flow frequently cannot be conducted sufficiently close to the hottest and therewith the most endangered places of the bearing so that the desired cooling effect is completely absent or is attained only unsatisfactorily.

It is therefore the object of the present invention to provide a bearing support installation for guide blades, in which a cooling medium is conducted directly to the hottest places of the bearing and thus an effective cooling of the bearing is achieved.

As solution to the underlying problems, it is proposed in accordance with the present invention that a blade shaft constructed as adjusting or actuating shaft be provided with annular grooves in its central bearing portion and at the blade end, which are connected with each other by a thread with cylindrical external surfaces, whereby the central annular groove is in communication with the chambers or passages conducting the cooling air and the annular groove at the blade side is in communication with the guide blade space of the machine.

The cooling air, which can be derived, for example, from a suitable compressor stage or from a similar air supply, flows through the central bore into the central annular groove of the blade shaft and from there by way of the thread to the blade end of the shaft where it flows off into the guide blade space by way of the second bore. The particular advantage of this arrangement resides in that the bearing support is effectively cooled at its hottest place; namely, at the blade shaft itself.

A further advantage resides in that the blade shaft and bearing bore are kept by the cooling system approximately at the same operating temperature at their contact places whereby the bearing clearance which exists with a cold machine, remains approximately constant over the entire operating range (temperature range) of the machine.

Finally, an extradordinarily favorable sealing of the guide blade space with respect to the surrounding area is achieved simultaneously by the cooling air guide system of the present invention since the cooling air has simultaneously the effect of a sealing medium.

In an appropriate construction of the present invention, the blade shaft includes, starting from its central annular groove toward the outside, a labyrinth seal having cylindrical external surfaces and consisting of a large number of annular grooves. The labyrinth is advantageously formed by a number of annular grooves of rectangular cross-section. With this type of labyrinth, the cooling air flow from the shaft center in the outward direction is kept as small as possible since it is only of subordinate significance for a cooling effect within this area and the cooling medium mass flow, which represents a loss, should be kept as small as possible.

According to a further feature of the present invention, the blade shaft is constructed as hollow shaft which results in a relatively slight heat flow from the blade through the shaft so that the ratio of heat transferred to the bearing place to the heat removed by cooling can be kept small.

According to a further favorable construction of the bearing support installation according to the present invention, a bearing bush with good anti-friction properties is inserted between the bearing support and the blade shaft, which bush is provided with inlet and outlet bores or ports for the cooling air corresponding to the bores in the bearing support.

The use of a bearing bush between housing and adjusting shaft offers the advantage that a material can be selected for the bearing bush which, first of all, has good anti-friction properties that do not change or change only slightly over a certain temperature range, without requiring at the same time high strength properties as are required, for example, in connection with the housing material. The good anti-friction properties must be ensured by a suitable material combination since a reduction of the friction by a lubricant must be considered impractical. Thus, by the use of anti-friction bushes, a favorable low friction clearance conditioned on the material can be attained at the blade adjusting shaft which results correspondingly in slight adjusting forces (moments).

According to a further feature of the present invention, the bearing bush is provided at its blade end with an offset of reduced diametric dimension so that an inwardly open annular space results between the housing bore and bearing bush, through which the cooling air leaving the bearing bush is conducted into the main gas stream of the turbo-machine. Returning the cooling air into the guide blade space through such an annular space offers the advantage that any combustion residues which are deposited in the annular gap between the upper guide blade end and the housing bore, are constantly blown off by the inwardly directed air stream and are returned to the main gas stream.

According to a further development of the present invention, the blade shaft is provided at its blade end with an annular collar that abuts at the inner end face of the housing or of the bearing bush. An outwardly directed pressure force results at the annular collar from the gas pressure in the guide blade space which presses the annular collar against the end surface of the housing or bearing bush so that a good seal of the guide blade space with respect to the bearing place is realized.

In an advantageous manner according to a further feature of the present invention, a spring prestressed in the axial direction is provided which is supported on the outer side of the bearing support, on the one hand, and on the blade shaft, on the other. This spring pulls the blade shaft outwardly with its prestress so that it causes an abutment of the annular collar of the blade shaft at the inner end face of the bearing bush or housing also with a slight excess pressure in the guide blade space and thus assures a good sealing effect.

These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawing which shows, for purposes of illustration only, one embodiment in accordance with the present invention, and wherein;

The single FIGURE is a partial cross-sectional view through a guide blade adjusting mechanism of a gas turbine with a bearing bush in accordance with the present invention.

Referring now to the single FIGURE of the drawing, a bearing bush 3 is securely fitted into a bore 21 provided in a housing 2 forming a bearing support. A bore or port 5 is disposed approximately in the center of the bush 3 which is in communication by way of a further bore or port 25 in the housing 2 with a cooling air passage 4 of the housing. At the inner end of the housing, the bush 3 is provided with a reduced diametric portion forming an offset 23 so that an annular space 22 remains between the bore 21 and the bush 3 at this place. One or several radial bores 6 of the bush 3 terminate in this annular space 22. The shaft of the guide blade 9 constructed as actuating or adjusting shaft 7 is supported in the bush 3. The guide blade shaft 7 is provided at its blade end with an annular collar 8 and adjoining the same with an annular groove 18. The shaft 7 is provided in the central area thereof, at the place of the bore 5 of the bush 3, with an annular groove 16. This annular groove 16 is in communication with the annular groove 18 by way of several threads of trapezoidal cross-section such as ACME thread form. The support of the shaft 7 takes place at the cylindrical outer surfaces of the thread 17 within the bearing bush 3. Extending outwardly from the annular groove 16, the shaft surface is provided with a number of annular grooves 20 constructed as labyrinth seal. A pivot or actuating lever 13 is clampingly secured to the outer end 12 of the blade shaft 7. The pivoting of this adjusting lever 13 takes place by an adjusting or actuating ring 14 arranged at the housing 2. An axially prestressed disk or cup spring 10 is provided between the lever 13 and the outer end face of the bush 3, on which rests a closure disk or carrying washer 10a; the prestress force of the spring 10 is transmitted by way of the lever 13 to the blade shaft 7 so that the annular collar 8 of the shaft 7 is pressed against the end surface 3a of the bush 3, located at the inner side of the housing.

The compressed air supplied by an air source and flowing through one or several passages 15 into the space 4, flows through the bores 25 and 5 into the annular groove 16 between the bush 3 and the blade shaft 7.

From there, the cooling air flows inwardly and outwardly, following the pressure drop, and more particularly inwardly by way of the thread 17 whereby it cools in an effective manner the blade shaft 7 and the bush 3. After leaving the thread 17, the cooling air reaches the annular groove 18 from where it flows off by way of the bore 6 into the annular space 22 and from there into the main stream duct 1. A very small amount of compressed air flows from the annular groove 16 in the outward direction by way of the labyrinth seal 20 and exits into the atmosphere at the spring 10 by way of gaps.

While I have shown and described only one embodiment in accordance with the present invention, it is understood that the same is not limited thereto but is susceptible of numerous changes and modifications as known to those skilled in the art, and I therefore do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.

Claims

I claim:

1. An installation for supporting pivotal guide blades of turbo-machines in which at least one passage is provided in a bearing support through which flows cooling air, characterized in that a blade shaft constructed as an adjusting shaft is provided with annular grooves in its central bearing area and near the blade end thereof, which are in communication with each other by way of a thread, the central annular groove being in communication with the passage conducting the cooling air while the annular groove near the blade end is in communication with the guide blade space of the machine.

2. An installation according to claim 1, characterized in that said thread has substantially cylindrical external surfaces.

3. An installation according to claim 2, characterized in that the blade shaft, starting from the central annular groove in the outward direction, is provided with a labyrinth seal means consisting of a number of annular grooves.

4. An installation according to claim 3, characterized in that the labyrinth seal means has cylindrical outer surfaces.

5. An installation according to claim 4, characterized in that the blade shaft is constructed as a hollow shaft.

6. An installation according to claim 5, characterized in that a bearing bush means with good anti-friction properties is inserted between the bearing support and the blade shaft, said bush means being provided with inlet and discharge bores for the cooling air corresponding to the support means.

7. An installation according to claim 6, characterized in that the bearing bush means is provided near the blade end with a portion of reduced diametric dimension so that an inwardly open annular space results between the housing bore and the bearing bush means, and in that the cooling air leaving the bearing bush means is conducted through the inwardly open annular space into the main flow channel of the turbo-machine.

8. An installation according to claim 7, characterized in that the blade shaft is provided near the blade end thereof with an annular collar that abuts at the inner end face of one of the two parts consisting of housing and bearing bush means.

9. An installation according to claim 8, characterized in that an axially prestressed spring means is provided which is supported, on the one hand, on the outer side of the bearing support and, on the other, at the blade shaft.

10. An installation according to claim 1, characterized in that a bearing bush means with good anti-friction properties is inserted between the bearing support and the blade shaft, said bush means being provided with inlet and discharge bores for the cooling air corresponding to the support means.

11. An installation according to claim 10, characterized in that the bearing bush means is provided near the blade end with a portion of reduced diametric dimension so that an inwardly open annular space results between the housing bore and the bearing bush means, and in that the cooling air leaving the bearing bush means is conducted through the inwardly open annular space into the main flow channel of the turbo-machine.

12. An installation according to claim 1, characterized in that the blade shaft is provided near the blade end thereof with an annular collar that abuts at the inner end face of one of the two parts consisting of housing and bearing bush means.

13. An installation according to claim 12, characterized in that an axially prestressed spring means is provided which is supported, on the one hand, on the outer side of the bearing support and, on the other, at the blade shaft.

14. An installation according to claim 12, characterized in that the blade shaft, starting from the central annular groove in the outward direction, is provided with a labyrinth seal means consisting of a number of annular grooves.

15. An installation according to claim 1, characterized in that an axially prestressed spring means is provided which is supported, on the one hand, on the outer side of the bearing support and, on the other, at the blade shaft.

16. An installation according to claim 1, characterized in that the blade shaft, starting from the central annular groove in the outward direction, is provided with a labyrinth seal means consisting of a number of annular grooves.

17. An installation for supporting pivotal guide blades of turbo-machines, comprising a blade shaft formed as an adjusting shaft carrying a blade at one end thereof, a bearing support surrounding said shaft and having at least one passage for conducting cooling air, said shaft being provided with an annular groove in its central bearing area and an annular groove near the blade end thereof, the central annular groove being in communication with the passage conducting the cooling air while the annular groove near the blade end is in communication with the guide blade space of the machine, the portion of said blade shaft between the central and blade end grooves being provided with a helical thread for communication therebetween.

18. An installation according to claim 17, wherein the portion of said shaft extending from the central annular groove in the outward direction is provided with a labyrinth seal means in the form of a plurality of annular grooves for preventing the flow of cooling air.