GB2108243A

GB2108243A - Thermal insulation of blade wheel of turbo-machine

Info

Publication number: GB2108243A
Application number: GB08229060A
Authority: GB
Inventors: Georg Wahl
Original assignee: Voith Turbo GmbH and Co KG
Current assignee: Voith Turbo GmbH and Co KG
Priority date: 1981-10-28
Filing date: 1982-10-12
Publication date: 1983-05-11
Also published as: IT8236073V0; JPS5884232A; FR2515252A1; IT8249283A0; IT1149107B

Abstract

A blade wheel 11 of a turbo- machine, especially a hydrodynamic coupling or brake, comprises a ring of blades 13 and a flange 14 located radially within the latter. This flange 14 serves for fastening the blade wheel 11 to a shaft 19, hub or the like. Such a blade wheel 11 rotates at very high speeds under certain circumstances; it is also occasionally subjected to a high heat load. In order to reduce the high material stresses resulting from this in the transitional region between the ring of blades 13 and the flange 14, a thermal insulation layer 16 is provided between the flange 14 and a flange 15 located on the shaft 19. <IMAGE>

Description

SPECIFICATION Turbo-machine The invention relates to turbo-machines, and is concerned particularly although not exclusively with blade wheels of hydrodynamic couplings, brakes and torque converters.

Hydrodyanamic couplings are known, for example from German Patent Specifications 883987 and 1 600 974. Although the blade wheels of such hydrody namic couplings rotate at very high speeds under certain circumstances and are therefore stressed severely, these couplings have proved to be of great value for decades. An essential advantage of a hydrodynamic coupling is that, when it is used to transmit force from a prime moverto a working machine, very gentle starting can be achieved even when heavy masses are to be accelerated. At the same time, the prime mover can, at first, run up with only a slight load, after which the hydrodynamic coupling accelerates the working machine at an essentially constant torque.

Consequently, in such a starting operation, the hydrodynamic coupling initially works with a high slip. This means that for a certain period of time there is an energy loss which becomes noticeable in heating the working fluid of the hydrodynamic coupling.

Similar conditions prevail in a hydrodynamic brake, although, as is known, this operates constant lywitha 100% slip.

To eliminate the heat due to energy loss, it is known, for example, to provide an external cooling circuit for the working fluid. That is to say, some of the working fluid is constantly extracted from the coupling or brake and re-cycled via a cooling device.

In many cases, however, especially as regards hydrodynamic couplings, the outlay for an external cooling circuit is unreasonably high. Many known hydrodynamic couplings are therefore operated without an external cooling circuit. But, in this case, operation with a high clutch slip must be kept within limits so as to prevent an excessive incidence of heat. At the same time, for safety purposes, there may be an automatic emptying device which, when a specific temperature is exceeded, causes the working fluid to flow off outwards. However, this means an interruption of operation, which is in many cases undesirable.

Afurther problem arising in the operation of hydrodynamic couplings (or brakes) is that it is customary for the blade wheel to have a fastening flange in the radially inner region. Investigations have shown that, in the transitional region between this flange and the ring of blades around it, such high stresses on the material arise under certain conditions that the permissible values are exceeded.

Attempts have been made to solve this problem by improved shaping or by the use of materials with a higher loading capacity, but not with the desired success.

An object of preferred embodiments of the invention is to reduce such undue material stresses in the transitional region between the flange and the ring of blades with as low an outlay as possible.

According to the present invention, there is pro vided a turbo-machine having a blade wheel mounted on another part of the machine, with insulation interposed between the blade wheel and said part.

The invention is based on the foliowing finding, which is explained by way of example, with refer ence to a hydrodynamic coupling, having two rings of blades which afford a very large surface against which working fluid flows. During a starting operation, the working fluid which heats up rapidly flows at a high velocity along the surfaces of the blade wheel. Thus, the mass of the blade wheel is heated very quickly. In contrast to this, the mass of the shaft (or hub) to which the blade wheel is fastened, by means of a flange, is heated very much more slowly because the surface of the shaft (or hub) against which the working fluid flows amounts to only a small fraction (for example, approximately 1/30) of the corresponding surface of the ring of blades.The result of this is, apparently, that the shaft (or the hub) extracts heat from the flange of the blade wheel, so that a substantially lower temperature is established in the flange than in the ring of blades. This would seem to lead, in the transitional region between the flange and ring of blades, to high thermal stresses which are added to the purely mechanical operating stresses. The unduly high material stresses mentioned above arise in this way.

The thermal insulation provided, according to the invention, between, for example, the flange of the blade wheel and, for example, the shaft (or the hub) on which the blade wheel 1 is mounted acts in such a way that when the blade wheel is heated much less heat is extracted from the flange than hitherto. That is to say, the flange assumes essentially the same temperature as the ring of blades. Thus, the occurence of thermal stress in the transitional region between the flange and the ring of blades may be at least substantially prevented and the danger of excessive stress on the material may be overcome.

For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawing, the single Figure of which shows a hydrodynamic coupling in partial longitudinal section.

The essential parts of the hydraulic coupling illustrated are a drive shaft 9, an impeller blade wheel 10 fastened to the latter, a coupling housing 12 rotating with the impeller blade wheel 10, and also a driven shaft 19 on which a turbine blade wheel 11 is mounted. The turbine blade wheel 11 comprises in the conventional way a ring of blades 13 and a fastening flange 14. A corresponding flange 15 is provided on the driven shaft 19. The two flanges 14 and 15 are connected to one another by bolts 8. A thermally insulating disc 16, the effect of which has been described above, is provided between the two flanges 14 and 15.

The inside diameter of the blade wheel flange 14 forms in a conventional way a cylindrical centering surface by means of which the blade wheel rests on the shaft 19. Theoretically, a thermally insulating ring could also be arranged here. It has been shown, however, that such an additional measure is not always essential. It may be appropriate, nevertheless, to make the axial length of the centering surface smaller than the thickness of the flange 14, in order thereby to reduce even further the transfer of heat to the shaft 19. The same purpose could also be served by inserting between the heads of the bolts 8 and the flange 14 washers which are made of a thermally insulating material.

In the coupling design illustrated, it is generally sufficient to provide a thermally insulating disc 16 on the one inner blade wheel 11 only. If required, however, the same measure can also be taken on the other blade wheel, as, for example, in the case of a design according to German Patent Specification 1 600 974.

Claims

1. Aturbo-machine having a blade wheel mounted on another part of the machine, with thermal insulating interposed between the blade wheel and said part.

2. Aturbo-machine according to Claim 1,wherein in the blade wheel has a radially inner flange by means of which it is secured to said part.

3. Aturbo-machine according to Claim 1 or 2, wherein said part is a shaft.

4. A turbo-machine according to Claims 2 and 3, wherein the shaft is provided with a flange to one side of which the flange of the blade wheel is secured.

5. Aturbo-machine according to Claim 4, wherein said thermal insulation comprises a disc interposed axially between said flanged.

6. Aturbo-machine according to Claim 3,4 or 5, wherein said thermal insulation is interposed radially between the blade wheel and the shaft.

7. A turbo-machine according to Claim 3,4 or 5, wherein the blade wheel has a radially inner surface of reduced cross-section, which is mounted on the shaft.

8. Aturbo-machine according to any preceding claim, wherein said thermal insulation insulated all surfaces of the blade wheel adjacent said part.

9. Aturbo-machine according to any preceding claim, being a hydrodynamic coupling, brake, or torque converter.

10. Aturbo-machine substantially as hereinbefore described with reference to the accompanying drawing.