Patent Application
20080010986
The text which follows provides a more detailed explanation of the process according to the invention and the subject matter of the invention on the basis of a preferred exemplary embodiment, which is illustrated in the accompanying drawings, in which:
The FIGURE shows, in section along the machine axis, an excerpt from a turbocharger having a compressor according to the invention.
The reference designations used in the drawing and the meaning of these designations are summarized in the list of references. The embodiments described are examples of the subject matter of the invention and do not have any restricting action.
In the text which follows, the invention is explained on the basis of the example of a turbocharger, comprising a compressor 1 with a compressor wheel 3 and a gas inlet housing 2.
The FIGURE shows, in section along the machine axis of a turbocharger, a compressor-side excerpt from a turbocharger having a compressor 1. The compressor 1 has a gas inlet housing 2, a compressor wheel 3 which is mounted on a shaft (not shown in the FIGURE) and has rotor blades 31 and a hub 32, and a diffusor 4. A turbine wheel is likewise mounted on the shaft (not shown in the FIGURE). The gas inlet housing 2 has a housing inner side 21, which faces the medium that is to be compressed and along which the medium that is to be compressed flows. On the outside, a flow channel 5 is delimited by the housing inner side 21 of the gas inlet housing 2, and on the inside it is delimited by the hub 32 of the compressor wheel 3. The direction of flow of the medium 6 that is to be compressed runs along the flow channel 5 from the opening of the gas inlet housing toward a diffusor 4 (illustrated by arrows in
In the compressor 1 according to the invention, flow-guiding parts are at least partially provided with a catalytic coating. Examples of flow-guiding parts are the parts which delimit the flow channel 5 or are arranged in the flow channel, in particular the housing inner side 21, the compressor wheel 3, diffusor walls 41 or diffusor guide vanes 42. In the FIGURE, the compressor 1 has a catalytic coating 7 (illustrated by a dashed line) on the housing inner side 21 of the gas inlet housing 2 and on the diffusor walls 41 and diffusor guide vanes 42. A catalytic coating 7, 7′ can be applied to any other flow-guiding part at which, when the compressor is operating, the temperatures generated are so high that a catalytic effect can take place. The compressor is typically operated at 180 to 300° C. These temperatures are sufficient to produce a catalytic effect in the coating 7, 7′.
The coating 7, 7′ comprises at least one oxide of a transition metal or an oxide of a mixture of transition metals, i.e. an oxide of at least one transition metal. Transition metals are the elements of groups I B (in particular Cu, Ag, Ag), II B (in particular Zn, Cd, Hg), III B (in particular Sc, Y), IV B (in particular Ti, Zr, Hf), V B (in particular V, Nb, Ta), VI B (in particular Cr, Mo, W), VII B (in particular Mn, Tc, Re) and/or VIII B (in particular Fe, Ru, Os, Co, Rh, Ir, Ni, Pd, Pt). In a preferred embodiment, the coating comprises at least one oxide or an oxide of a mixture of elements of in each case these groups of the fourth period (Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn) and/or the fifth period (Y, Zr, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd), preferably the fourth period.
In addition, the coating may also comprise at least one metal oxide, preferably Al oxide, or the coating comprises an oxide of a mixture of at least one transition metal and of at least one metal, preferably Al and/or semimetal, preferably Si. Particularly suitable materials for the coating 7, 7′ are oxides of an alloy of TiZrNi, TiCrSi, AlFeCrCo and/or AlFeCuCr.
One suitable example is a coating of an oxide of a mixture of Al in a range from 57 to 85 at %, preferably in a range from 64 to 78 at %, preferably in a range from 64.5 at % to 74.5 at % and in particular 71 at %, Fe in a range from 6.9 to 10.4 at %, preferably in a range from 7.8 to 9.6 at %, preferably in a range from 8.3 to 9.1 at % and in particular 8.7 at %, Cr in a range from 8.5 to 12.7 at %, preferably in a range from 9.5 to 11.7 at %, preferably in a range from 10.1 to 11.1 at % and in particular 10.6 at % and Cu in a range from 7.8 to 11.6 at %, preferably in a range from 8.7 to 10.7 at %, preferably in a range from 9.2 to 10.2 at % and in particular 9.7 at %. The fractions indicated in the mixture should be understood in such a way that the fractions of the metals/transition metals together amount to 100%, in which context the mixture may also comprise further metals/transition metals, i.e. the range details given relate only to the relative ratio of Al, Fe, Cr and Cu to one another; however, it is also possible for further metals/transition metals to be present. A mixture of this type is obtainable, for example, from Saint Gobain under trade name Cristome Al with a composition of 71% Al, 8.7% Fe, 10.6% Cr and 9.7% Cu.
Another suitable coating is an oxide of a mixture of Al in a range from 57 to 85 at %, preferably in a range from 64 to 78 at %, preferably in a range from 64.5 at % to 74.5 at % and in particular 71.3 at %, Fe in a range from 6.5 to 9.7 at %, preferably in a range from 7.3 to 8.9 at %, preferably in a range from 7.7 to 8.5 at % and in particular 8.1 at %, Co in a range from 10.2 to 15.4 at %, preferably in a range from 11.5 to 14.1 at %, preferably in a range from 12.2 to 13.4 at % and in particular 12.8 at %, and Cr in a range from 6.2 to 9.4 at %, preferably in a range from 7.0 to 8.6 at %, preferably in a range from 7.4 to 8.2 at % and in particular 7.8 at %. The fractions given for the mixture are to be understood in such a way that the fractions of the metals/transition metals together add up to 100%, in which context the mixture may also comprise further metals/transition metals, i.e. the range details given relate only to the relative ratio of Al, Fe, Co and Cr to one another; however, it is also possible for further metals/transition metals to be present. A mixture of this type is available for example from Saint Gobain under the trade name Cristome BT1 with a composition of 71.3 at % Al, 8.1 at % Fe, 12.8 at % Co and 7.8 at % Cr.
The catalytic coating 7, 7′ has a long-term heat resistance at the temperatures produced during operation of the turbocharger.
To produce a turbocharger according to the invention, the catalytic coating 7 can be applied to the housing inner side 21 of the gas inlet housing 2 by thermal spraying. Thermal spray-coating processes are described for example in the document “Moderne Beschichtungsverfahren” [Modern coating processes] by F.-W. Bach et al., Wiley-VCH Verlag, 2000.
In the case of a compressor with diffusor 4, it is also conceivable for a catalytic coating 7′ to be applied to the diffusor walls 41. Typical thermal spraying processes include flame spraying, high-velocity flame spraying, arc spraying and plasma spraying. It is advantageous to select a process which produces surfaces of low porosity and/or low roughness. Typically, a transition metal or an alloy of transition metals is applied to the housing inner side 21 of the gas inlet housing 2, in particular by thermal spraying and oxidation of the transition metal or the alloy of the transition metals takes place during the application step, in particular during the thermal spraying.
After the spraying operation, the surface of the catalytic coating 7, 7′ can be treated further until the surface has the desired roughness. On the one hand, a smooth surface is advantageous for operation of the compressor, since such a surface produces little air flow turbulence close to the surface, but on the other hand the catalytic action increases if the surface area is increased, since in this case a larger area of catalytic coating contributes to the catalytic effect.
As a surface treatment for producing the desired roughness, the surface can be smoothed by a suitable process, such as grinding, drag finishing or by means of glass beads. Then, grooves or striations can be deliberately produced again in the surface, for example by sand-blasting, so as to form depressions which increase the surface area of the catalytic coating compared to a smooth surface but which produce scarcely any turbulence, since depressions of this type have only a small influence on the air flow.
The maximum surface roughness should typically not exceed 40 μm (corresponding to an N9 roughness class).
Depending on the particular use and/or depending on the production process, the maximum surface roughness may also be 25 μm (corresponding to an N8 roughness class), 16 μm (corresponding to an N7 roughness class) or even 6.4 μm (corresponding to an N6 roughness class). The roughness average is typically less than 6.3 μm. Depending on the particular application and/or the production process, the roughness average may also be less than 3.2, 1.6 or even 0.8 μm.
| Number | Date | Country | Kind |
|---|---|---|---|
| 06405306.9 | Jul 2006 | EP | regional |
