Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Access opening through portion of casing or cover
Reexamination Certificate
1999-11-01
2001-11-20
Ryznic, John E. (Department: 3745)
Rotary kinetic fluid motors or pumps
Working fluid passage or distributing means associated with...
Access opening through portion of casing or cover
C415S209400, C416S235000
Reexamination Certificate
active
06318961
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an axial-flow turbine.
2. Description of the Related Art
The essential components of the axial-flow turbines of fluid-flow machines are the rotor with the moving blades, the nozzle ring and the cover for the moving blades. Slight discontinuities, which result in a reduction in the efficiency, occur in the flow duct of such axial-flow turbines due to unavoidable production and assembly tolerances.
An axial-flow turbine of an exhaust-gas turbocharger has been disclosed by EP 806 547 A1, this axial-flow turbine being subjected to relatively high temperatures during operation of the internal combustion engine connected to it. High thermal stresses thus occur in the turbine-side components, such as, for example, the gas-inlet casing, the nozzle ring, the cover and the gas-outlet casing. Since each of these components is at a different distance from the internal combustion engine and since, in addition, different materials are used, the component temperatures accordingly differ. The result is different thermal expansions with relative movements between the individual components, which may lead to screw fractures, gas leakages and component cracks. The design and arrangement of the separating locations of gas-inlet casing, gas-outlet casing, nozzle ring and cover are therefore of considerable importance for the operability of the axial-flow turbine and thus of the exhaust-gas turbocharger.
Especially critical with regard to thermal expansions is the nozzle ring, which is usually cast and is arranged between the fixed casing parts and the rotating moving blades of an axial turbine. EP 806 548 A1 discloses a solution for the simple and reliable fastening of the nozzle ring. To this end, the nozzle ring bears with its outer ring against the cover and with its inner ring against the gas-inlet casing. An axial expansion gap is formed between the outer ring and the gas-inlet casing, and a radial expansion gap is formed between the outer ring and the gas-outlet casing.
However, it has been found that, in particular also in the case of discontinuities in the transition region between the outer ring of the nozzle ring and the cover, which are also caused by thermal expansions in addition to the production and assembly tolerances already described above, a corresponding decrease in the efficiency can be expected.
In addition, Dejc & Trojanovskij “Untersuchung und Berechnung axialer Turbinenstufen” [Investigation and design of axial turbine stages], VEB Verlag Technik, Berlin, 1973, page 452 (FIG. 7.32: II) discloses a device for the reduction of the gap losses caused by the radial clearance of the turbine blades. To this end, the moving blades are arranged to be stepped relative to the guide blades combined in the nozzle ring and have a positive overlap, i.e. the inner contour of the cover is arranged radially further to the outside in the region of the moving blades than in the region of the guide blades.
During dismantling, however, such a configuration has the disadvantage that the axial-flow turbine can only be displaced in the opposite direction to the nozzle ring and not in both directions.
SUMMARY OF THE INVENTION
The object of the invention, in attempting to avoid all of these disadvantages, is to provide an axial-flow turbine having an improved efficiency. In addition, the assembly and dismantling possibilities are to be extended.
According to the invention, this is achieved in a device according to the preamble of claim
1
in that the parting seam between the outer ring of the nozzle ring and the cover is arranged on the moving-blade side of an imaginary plane passing through the center of the gap width of the axial gap.
As a result, the outer ring of the nozzle ring is extended in the direction of the moving blades, so that the flow duct has no discontinuities at all over most of the gap width of the axial gap. An improvement in the flow conditions and in the efficiency of the axial-flow turbine can thus be achieved.
In an especially advantageous manner, the parting seam between outer ring and cover is arranged directly upstream of the moving blades. In this case, virtually the entire gap width of the axial gap is formed without discontinuities, as a result of which a further increase in the efficiency of the axial-flow turbine is made possible.
It is especially expedient if the inner contour of the cover is additionally arranged radially outside the inner contour of the outer ring. Obtained in this case is a step having a so-called positive blade overlap, which reduces flow over the moving blades in their upstream region and, in combination with the markedly reduced discontinuity, can lead to a disproportionate increase in the efficiency.
As a result of the arrangement of the parting seam between outer ring and cover directly upstream of the moving blades, no overlap of the moving blades by the cover radially to the inside is necessary in the region of the guide blades. This overlap and thus the production of the requisite step is now taken over by the outer ring of the nozzle ring, which in turn projects radially inward beyond the inner contour of the cover of the moving blades. Despite the use of such an advantageous blade overlap, the axial-flow turbine, after removal of the nozzle ring, can therefore be dismantled on both sides, which was not possible hitherto.
Furthermore, it is advantageous if the blade profile, provided with a pressure side, a suction side and a blade tip, of each moving blade is designed in such a way that a bracket projecting beyond the blade profile at least on the pressure side is arranged on the blade tip. The flow over the blade tip, which flow is detrimental to the efficiency, can be markedly reduced by the vortex forming in the region of the bracket.
Finally, a web projecting beyond the bracket in the direction of the cover is advantageously arranged on the blade tip. This web reduces the gap losses in the radial gap formed between the moving blades and the cover.
REFERENCES:
patent: 2980396 (1961-04-01), Movsesian
patent: 3067983 (1962-12-01), Koziura
patent: 3817655 (1974-06-01), Huesgen et al.
patent: 3985465 (1976-10-01), Sheldon et al.
patent: 4063845 (1977-12-01), Allen
patent: 4684320 (1987-08-01), Kunz
patent: 5618161 (1997-04-01), Papageorgiou et al.
patent: 2445705C2 (1975-04-01), None
patent: 2405050 (1975-08-01), None
patent: 0806548A1 (1997-11-01), None
patent: 0806547A1 (1997-11-01), None
Untersuchung und Berechnung axialer Turbinenstufen, Dejc, et al., 1973, p. 452.
Asea Brown Boveri AG
Burns Doane Swecker & Mathis L.L.P.
Ryznic John E.
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