AIR BEARING ARRANGEMENT FOR FUEL CELL COMPRESSORS HAVING AN EXPANDER

Abstract

A turbomachine, in particular for a fuel cell system of a vehicle, such as a utility vehicle, has a rotor shaft, an expander wheel fastened on the rotor shaft, and an air bearing arrangement, which is configured to support the rotor shaft rotatably about a rotor axis, wherein a flow path is formed between the expander wheel and the air bearing arrangement. A flow generator is arranged in the flow path between the air bearing arrangement and the expander wheel and configured to generate, depending on a rotation of the rotor shaft, an air flow directed toward the expander wheel, for the purpose of building up a blocking pressure.

Claims

1. A turbomachine comprising: a rotor shaft; an expander wheel fastened on said rotor shaft; an air bearing arrangement configured to support said rotor shaft rotatably about a rotor axis; wherein a flow path is formed between said expander wheel and said air bearing arrangement; and, a flow generator arranged in said flow path between said air bearing arrangement and said expander wheel and configured to generate, depending on a rotation of said rotor shaft, an air flow directed toward said expander wheel.

2. The turbomachine of claim 1, wherein: said expander wheel is arranged in an expander chamber into which a cathode exhaust gas of a fuel cell is conveyed at a predetermined hydrostatic inlet pressure; and, said flow generator is configured to build up a blocking pressure on a pressure side facing said expander wheel, wherein said blocking pressure is equal to or greater than said predetermined hydrostatic inlet pressure of said expander chamber.

3. The turbomachine of claim 2, wherein said blocking pressure exceeds the inlet pressure by 0.5 bara or more when said rotor shaft reaches or exceeds a predetermined rotational speed.

4. The turbomachine of claim 1, wherein said flow generator has a number of at least one of recesses and projections, which are formed on said rotor shaft.

5. The turbomachine of claim 4, wherein said at least one of recesses and projections are aligned parallel to the rotor axis or at an angle relative to the rotor axis.

6. The turbomachine of claim 5, wherein the turbomachine is configured to rotate said rotor shaft in a preferred direction of rotation, wherein the angle of said at least one of recesses and projections has a pitch opposed to the preferred direction of rotation.

7. The turbomachine of claim 5, wherein said angle lies in a range of 10 to 80 with respect to the rotor axis.

8. The turbomachine of claim 4, wherein said at least one of recesses and projections are formed relative to a surface of said rotor shaft and have a radial extent relative to the surface in a range of up to 20 m.

9. The turbomachine of claim 1, wherein said flow generator is assigned an air supply line, which is provided separately from said air bearing arrangement.

10. The turbomachine of claim 1, wherein said flow generator and said air bearing arrangement are arranged in a direction of the rotor axis adjacent to each other or spaced apart from each other by a distance, said flow generator being arranged on a side of said air bearing arrangement facing said expander wheel.

11. The turbomachine of claim 1, wherein said flow generator is a first flow generator; the turbomachine comprises a second flow generator arranged relative to said first flow generator opposite said air bearing arrangement relative to said first flow generator; and, said second flow generator is configured to generate, depending on a rotation of said rotor shaft, an air flow directed away from said air bearing arrangement.

12. The turbomachine of claim 11, wherein said second flow generator has a number of at least one of second recesses and second projections, which are formed on said rotor shaft.

13. The turbomachine of claim 12, wherein said first flow generator has a number of at least one of first recesses and first projections, which are formed on said rotor shaft; said at least one of first recesses and first projections are aligned parallel to the rotor axis or at a first angle relative to the rotor axis; and, said at least one of second recesses and second projections are aligned parallel to the rotor axis or relative to the rotor axis at a second angle which is aligned in an opposite direction to said first angle of said first flow generator.

14. The turbomachine of claim 13, wherein second angle of said second flow generator is equal to said first angle of said first flow generator.

15. The turbomachine of claim 13, wherein said at least one of second recesses and second projections of said second flow generator have a smaller radial extent than said at least one of first recesses and second projections of said first flow generator.

16. The turbomachine of claim 1, wherein the turbomachine is for a fuel cell system of a vehicle.

17. The turbomachine of claim 16, wherein the vehicle is a utility vehicle.

18. The turbomachine of claim 2, wherein said blocking pressure exceeds the inlet pressure by 1.0 bara or more when said rotor shaft reaches or exceeds a predetermined rotational speed.

19. The turbomachine of claim 2, wherein said blocking pressure exceeds the inlet pressure by 1.0 bara to 2.0 bara when said rotor shaft reaches or exceeds a predetermined rotational speed.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0030] The invention will now be described with reference to the drawings wherein:

[0031] FIG. 1 shows a schematic illustration of a turbomachine according to a preferred embodiment; and,

[0032] FIG. 2 shows a detailed view of the turbomachine according to FIG. 1.

DETAILED DESCRIPTION

[0033] FIG. 1 shows a turbomachine 1, which is part of a fuel cell system 100 of a vehicle 200, preferably a utility vehicle. The turbomachine 1 has a compressor wheel 3, which is arranged in a compressor chamber 5.

[0034] The compressor chamber 5 has an inlet 7, which is configured to supply the compressor chamber 5, for example via an intake tract (not shown), with air at an inlet pressure p.sub.1, which is then compressed in the compressor chamber 5 by rotation of the compressor wheel 3 to an outlet pressure p.sub.2 and discharged via an outlet 9 of the compressor chamber 5.

[0035] The turbomachine 1 is fluid-conductively connected to a fuel cell 101 of the fuel cell system 100 and configured to use the air compressed by the compressor wheel in a fuel cell reaction in a generally known manner. The air constitutes the cathode-side reactant.

[0036] The compressed air is fed to the fuel cell 101 at the pressure p.sub.2.

[0037] After passage through the fuel cell 101, an air/water mixture is discharged from the fuel cell 101 as what is referred to as cathode exhaust gas with a hydrostatic pressure p.sub.3, which is lower than p.sub.2. The fuel cell 101 is fluid-conductively connected to an expander chamber 11 of the turbomachine 1, more precisely to an inlet 13 of the expander chamber 11. The expander chamber 11 is assigned to the turbomachine 1 and has an expander wheel 15 in its interior. As a result of the cathode exhaust gas entering with the pressure p.sub.3 as the inlet pressure, the flow is incident on the expander wheel 15 and the cathode exhaust gas is expanded here in a generally known manner such that the cathode exhaust gas leaves the expander chamber 11 through an outlet 17 at a pressure p.sub.4 which is approximately or equal to the ambient pressure p.sub.U. The pressure of the cathode exhaust gas p.sub.3 is indeed lower than the pressure p.sub.2 after passage through the compressor chamber 5. However, it is still above the suction pressure p.sub.1, which would be equal to or higher than the ambient pressure p.sub.U.

[0038] The compressor wheel 3 and the expander wheel 15 are connected via a rotor shaft 19 and are each fastened to the rotor shaft 19 for rotation therewith. The rotor shaft 19 is driven rotatably about a rotor axis X, clockwise in the present embodiment according to FIG. 1, in a generally known manner by an electric machine 21.

[0039] The rotor shaft 19 is rotatably mounted in a compressor housing 23 via an air bearing arrangement 21, which is preferably also assigned the expander chamber 11 and the compressor chamber 5.

[0040] The air bearing arrangement 21 has at least one first air bearing 21a, which may be a radial air bearing, and a second air bearing 21b, which may likewise be a radial air bearing. Preferably, the air bearing arrangement 21 additionally has one or more axial air bearings (not shown), which also support the rotor shaft 19 and the parts rotating therewith relative to the axis X in the axial direction. For understanding of the air bearing arrangement 21, only the radial air bearings 21a, 21b are shown here.

[0041] The air bearing arrangement 21 is fluid-conductively connected for aerostatic support via an air bearing flow path 25 preferably to a compressed air source, which is configured to support the blowing of compressed air at a pressure p into the air bearing arrangement 21, in order to support the load-bearing capacity of the air bearing 21, as long as the rotor shaft 19 has not yet reached its required lift-off rotational speed to form an air cushion of sufficiently load-bearing capacity.

[0042] A first flow path 27 is formed between the air bearing 21 and the expander wheel 15 or the expander chamber 11, the flow path being configured as an annular gap between the compressor housing 23 and the rotor shaft 19. This first flow path 27 is ultimately established because of the aim of a contact-free movement of the rotor shaft 19 relative to the compressor housing 23.

[0043] The flow path 27 is thus a potential gateway for water and possibly solid-state particles that could penetrate in the direction of the air bearing arrangement 21 because of the positive pressure as a result of the inlet pressure p.sub.3 within the expander chamber 11 and/or as a result of capillary action.

[0044] In order to prevent this, a first flow generator 29 is arranged between the air bearing arrangement 21 and the expander chamber 11 or the expander wheel 15, the first flow generator being configured in a manner described further below to build up a blocking pressure p.sub.S on its side facing the expander wheel 15 within the flow path 27, depending on the rotational speed of the rotor shaft 19. The flow generator 29 is configured to build up the blocking pressure p.sub.S (cf. FIG. 2) at a level of p.sub.S>p.sub.3 in order to prevent water droplets and/or particles from being able to move through the flow path 27 as far as the air bearing arrangement 21. Thus, the first flow generator 29 creates a contact-free fluid and particle seal on the basis of the generation of a local positive pressure in the flow path 27 on the side facing from the flow generator 29 to the expander wheel 15.

[0045] The first flow generator 29 is furthermore fluid-conductively connected via an air supply line 31. Via the air supply line 31, air can be guided on the suction side of the first flow generator 29, that is, on the side facing the air bearing arrangement 21, as seen from the first flow generator 29, for example from the environment with ambient pressure p.sub.U. This effectively prevents bearing air being cannibalized from the air bearing arrangement 21 via the first flow generator 29 by rotation of the rotor shaft 19, and therefore the first flow generator 29 does not impair the load-bearing capacity of the air bearing arrangement 21.

[0046] The first flow generator 29 has a number, preferably a plurality, of recesses and/or projections 33, which are provided on the rotor shaft 19 and rotate with the rotor shaft 19 at its rotational speed about the axis X. In the embodiment shown, the recesses and/or projections 33 are configured as grooves which have a predetermined radial extent t.sub.1, namely a depth defining the grooves, and are arranged at an angle .sub.1 with respect to the rotor axis X. The angle .sub.1 is aligned rising to the left in relation to the rotor axis X, that is, in the opposite direction to the movement direction of the rotor shaft 19, so that the blocking pressure p.sub.S (cf. FIG. 2) is generated on the correct side of the flow generator 29.

[0047] The turbomachine 1 furthermore, in addition to the first flow generator 29, has a second flow generator 35, which is arranged acting between the air bearing arrangement 21 and the compressor wheel 3, or the compressor chamber 5 in a second flow path 37. The second flow path 37 is likewise configured as an annular gap between the compressor housing 23 and the rotor shaft 19, for the same structural configuration reasons as the first flow path 27.

[0048] In basically the same mode of operation as the first flow generator 29, the second flow generator 35 also has a number of projections and/or recesses 39, which are arranged on the rotor shaft 19. The projections and/or recesses 39 are preferably configured as grooves. The projections/recesses 39 have a radial extent t.sub.2, in the case of grooves thus likewise a measure of the groove depth, which is preferably smaller than the radial extent t.sub.1 of the recesses/projections of the first flow generator 29. By differentiating between the radial extents t.sub.1, t.sub.2, a partial compensation of the axial forces generated by the flow generators is achieved, which can also be matched to the axial forces emanating from the compressor wheel 3 or expander wheel 15 in the direction of the axis X.

[0049] The alignment of the projections or recesses 39 is carried out in FIG. 1 at an angle .sub.2, which is aligned in the opposite direction to the angle .sub.1 of the first flow generator 29, in the case of a right-rotating rotor shaft 19, that is, also rising to the right. Accordingly, the second flow generator 35 generates its blocking pressure on the other side relative to the first flow generator 39, that is, on the side of the flow path 37 facing the compressor wheel 3, or the compressor chamber 5, in order at least to minimize entry of undesired particles also from this side into the flow path 37, and especially also to ensure the abovementioned at least partial compensation of axial force.

[0050] In FIG. 2, the right side of the turbomachine 1 according to FIG. 1 is shown on a larger scale. The invention is explained in more detail with respect to the first flow generator 29, wherein the technical functions can be analogously also transferred to the second flow generator 35, the separate illustration of which is omitted here for the sake of clarity.

[0051] When the shaft 19 rotates about the axis X in the right-hand direction of rotation, the oppositely directed alignment of the projections or recesses 33 about the angle .sub.1 on the flank side trailing in the direction of rotation, that is, on the right-hand side in FIG. 2, causes a blocking pressure p.sub.S to be built up as a result of the air turbulence in the flow path 27, which blocking pressure, under unobstructed flow conditions, would cause an air flow in the direction of the expander chamber 11. At least, however, the dynamic or blocking pressure p.sub.S is generated which, at a sufficiently high rotational speed of the rotor shaft 19, is higher than the hydrostatic inlet pressure p.sub.3 in the expander chamber 11. The blocking pressure p.sub.S is preferably 1.0 bar or more higher than the hydrostatic pressure p.sub.3 in the expander chamber 11.

[0052] For tracking and/or at least relieving the suction side of the flow generator 29 of load, that side of the flow generator 29 which faces away from the expander wheel 15 is preferably assigned to one or more partially encircling grooves 41, which are fluid-conductively connected to the air supply line 31, in order, via air tracking, to compensate for the locally arising suction negative pressure p.sub.A. Preferably, this is carried out with air being sucked in from the environment.

[0053] The first flow generator 29 is spaced apart from the air bearing 21 by a distance .sub.1 in the direction of axis X. This distance .sub.1 to a certain extent creates a neutral zone, in which there are no structural elements on the rotor shaft 19, and preferably also not on the part of the compressor housing 23, in order to minimize mutual interference of the flow generator 29 and the air bearing arrangement 21 as far as possible. Also, a possibly disadvantageous effect of the flow generator 29 or the air turbulence generated by the latter on the air bearing arrangement 21, which could be constructed, for example, as a spiral groove bearing or as a foil bearing, is thus minimized.

[0054] Similarly, the second flow generator is preferably spaced apart axially from the air bearing arrangement 21 by a distance .sub.2 in the direction of the axis X, see FIG. 1.

[0055] It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.

REFERENCE SIGNS (PART OF THE DESCRIPTION)

[0056] 1 Turbomachine [0057] 5 Compressor chamber [0058] 7 Inlet [0059] 9 Outlet [0060] 11 Expander chamber [0061] 15 Expander wheel [0062] 17 Outlet [0063] 19 Rotor shaft [0064] 21 Air bearing [0065] 21a, b Air bearing arrangement [0066] 23 Compressor housing [0067] 25 Air bearing flow path [0068] 27 Flow path, on expander side [0069] 29 First flow generator [0070] 31 Air supply line [0071] 33 Projections/recesses, first flow generator [0072] 35 Second flow generator [0073] 37 Flow path, on compressor side [0074] 39 Projections/recesses, second flow generator [0075] 100 Fuel cell system [0076] 101 Fuel cell [0077] 200 Vehicle [0078] X Axis [0079] p.sub.1 Pressure, inlet compressor [0080] p.sub.2 Pressure, outlet compressor [0081] p.sub.3 Inlet pressure expander, cathode exhaust gas [0082] p.sub.4 Outlet pressure expander, cathode exhaust gas [0083] p.sub.S Blocking pressure, flow generator [0084] P.sub.A Suction pressure, flow generator [0085] p.sub.U Ambient pressure [0086] .sub.1 Angle, first flow generator [0087] .sub.2 Angle, second flow generator [0088] .sub.1 Distance, first flow generator [0089] .sub.2 Distance, second flow generator