Patent Application
20140186171
This application claims priority to German Patent Application No. 10 2012 219 355.3 filed Oct. 23, 2012, which is hereby incorporated by reference in its entirety.
The present invention relates to a guide blade arrangement, in particular for an exhaust gas turbocharger, and to an exhaust gas turbocharger having such a guide blade arrangement. The invention furthermore relates to a motor vehicle having such an exhaust gas turbocharger.
As is known, exhaust gas turbochargers for internal combustion engines consist of two continuous-flow machines: on the one hand of a turbine, on the other hand of a compressor. The turbine utilises the energy contained in the exhaust gas for driving the compressor, which draws in fresh air and introduces compressed air into the cylinders of the internal combustion engine. Because of the usually very high rotational speed range of the internal combustion engine, regulating the exhaust gas turbocharger is required so that as constant as possible a charge pressure in as large as possible a rotational speed range of the internal combustion engine can be ensured. To this end, solutions are known according to which a part of the exhaust gas flow is guided about the turbine by means of a bypass channel. An energetically more favourable solution however is made possible by the so-called variable turbine geometry, in which the accumulation behaviour of the turbine is continuously changed and thus the entire exhaust gas can be utilised in each case. Such a variable turbine geometry is realised in the conventional manner by means of adjustable guide blades, by means of which the desired exhaust gas flow flowing through an exhaust gas turbocharger can be variably adjusted.
For adjusting the guide blades, different adjusting mechanisms are known. Usually, the guide blades are mounted on a guide blade carrier ring via a respective blade bearing. Spaced from the guide blade carrier ring, a cover disc is arranged, so that the guide blades are arranged between this cover disc and the guide blade carrier ring. The cover disc can be produced from a ceramic material.
DE 10 2008 039 508 A1 describes a charging device of an exhaust gas turbocharger with a variable turbine geometry. The charging device comprises a blade bearing ring with guide blades rotatably mounted thereon. On a side of the guide blades located opposite the blade bearing ring, an annular disc for covering the guide blades is provided. The annular disc comprises a heat-insulating and friction-reducing material.
It is an object of the present invention to state an improved embodiment for a guide blade arrangement.
This object is solved through the subject of the independent claims. Preferred embodiments are subject of the dependent claims.
The invention is based on the general idea of using a ceramic material for the cover disc of the guide blade arrangement, which has a high thermal conductivity. In this way, heat occurring in the guide blade arrangement can be quickly and effectively discharged, so that the temperature loading of a turbine housing, in which the guide blade arrangement according to the invention can be employed, can be significantly reduced.
Ceramics with a high thermal conductivity are largely objects which are shaped from anorganic, fine-grained raw materials with the addition of water at room temperature and which are dried thereafter, which in a subsequent burning process above 900° C. are sintered into hard, durable objects. Ceramic materials can have a very high thermal conductivity, as a result of which they are particularly predestined for the use of a cover disc of a guide blade arrangement of an exhaust gas turbocharger according to the invention. In addition, ceramic materials are also able to withstand high temperatures, such as occur in such an exhaust gas turbocharger, over long periods of time. Ceramic materials or coatings can be produced cost-effectively and in almost any embodiment, as a result of which an economical industrial use is possible.
In particular, by using ceramic materials with high thermal conductivity, a thermally-induced expansion of individual components of the guide blade arrangement or of the exhaust gas turbocharger using the guide blade arrangement can be avoided. This in turn allows reducing a gap width between the guide blades and the cover disc in size, since through the use of a cover disc with high thermal conductivity according to the invention it is ensured that a heat-induced, undesirable thermal expansion of the guide blades is avoided, so that no thermally-induced friction effects between the guide blades and the cover disc (up to a jamming of the guide blades) can occur.
Since the cover disc according to the invention thus makes possible a minimal gap width between the guide blades and the cover disc, a bypass flow through such a gap which lowers the efficiency of the guide blade arrangement or of the exhaust gas turbocharger using this guide blade arrangement can be reduced or even completely eliminated, which significantly improves the efficiency of the guide blade arrangement or of the exhaust gas turbocharger.
In an advantageous further development of the solution according to the invention, the ceramic material can have a thermal conductivity of at least 120 W/mK. By using a ceramic material with such a high thermal conductivity, (waste) heat can be discharged out of the guide blade arrangement in a particularly favourable manner.
In a particularly preferred embodiment, the ceramic material can be silicon nitride or silicon carbide. Silicon carbide is a ceramic compound of silicon and carbon belonging to the group of carbides. Since silicon carbide has a high mechanical hardness and on the other hand a very high thermal conductivity (pure silicon carbide: approx. 350 W/mK, technical silicon carbide: up to 140 W/mK), it is particularly well suited as ceramic material for the cover disc of the guide blade arrangement according to the invention.
Similar is true for silicon nitride, which in addition to its high strength is also characterized by a very low thermal expansion coefficient and a small modulus of elasticity. Ceramics of silicon nitride can be employed at temperatures of up to approximately 1,300° C. and are therefore particularly well suited for use in exhaust gas turbochargers.
In a furthering embodiment, the guide blade carrier ring or/and the guide blades or/and the blade bearing pins can be produced of a metal having a lower thermal conductivity than the thermal conductivity of the ceramic material. In this way, the cover disc of the ceramic material with high thermal conductivity according to the invention can be combined with the further components of the guide blade arrangement such as for example the guide blade carrier ring, the guide blades and the blade bearing pin, which are usually produced from a metal.
In a particularly preferred embodiment, the metal can have a maximum thermal conductivity of 20 W/mK. Combined with a cover disc of the ceramic material with high thermal conductivity, which usually has at least 120 W/mK, heat can be particularly effectively discharged out of the guide blade arrangement and the turbine housing of an exhaust gas turbocharger using this guide blade arrangement.
In a particularly preferred embodiment, the metal can be a steel.
In order to ensure a particularly effective heat transport through the cover disc of the guide blade arrangement, this can be completely produced from the ceramic material in a further embodiment.
In an embodiment that is alternative or furthering thereto, the cover disc however can also comprise a cover disc of the ceramic material. This means that the actual cover disc need not be formed of the ceramic material with high thermal conductivity according to the invention. This makes possible a particularly cost-effective production of the cover disc, which for example can be produced of a metal, in particular steel, so that the material system of the cover disc and that of the remaining components of the guide blade arrangement (guide blade carrier ring etc.) can be identical. An advantage of such a design of the cover disc consists in that all substantial components of the guide blade arrangement are then constructed from the same material system and thus also have a substantially identical thermal expansion coefficient.
In order to ensure a mechanically stable construction of the guide blade arrangement, in particular when used in a turbine housing of an exhaust gas turbocharger, the guide blade arrangement in a particularly preferred embodiment can comprise at least one spacer element, which is arranged coaxially to the blade bearing pin, holding the guide blade carrier ring spaced from the cover disc.
The invention also relates to an exhaust gas turbocharger, in particular for a motor vehicle, having a guide blade arrangement with one or a plurality of the features explained above and having a turbine housing with a housing wall facing the guide blade arrangement, on which the cover disc of the guide blade arrangement is arranged. The exhaust gas turbocharger furthermore comprises a bearing housing and a spring element supporting itself on the bearing housing, by means of which in the axial direction via the guide blade carrier ring a pressure force is exerted onto the at least one spacer element, so that the latter pushes the cover disc against the turbine housing for the axial fixing.
The invention furthermore relates to a motor vehicle having an internal combustion engine and to an exhaust gas turbocharger with the features explained above which is operationally connected to this internal combustion engine for increasing its the power.
Further important features and advantages of the invention are obtained from the subclaims, from the drawing and from the associated FIGURE description by means of the drawing.
It is to be understood that the features mentioned above and still to be explained in the following cannot only be used in the respective combination stated but also in other combinations or by themselves without leaving the scope of the present invention.
A preferred exemplary embodiment of the invention is shown in the drawing and is explained in more detail in the following description.
In the representation of
The guide blade carrier ring 2 can be produced from a metal or another suitable material, which has a lower thermal conductivity than the thermal conductivity of the ceramic material. Similar applies to the guide blades or/and the blade bearing pins. For example, these components of the guide blade arrangement can be produced from a metal (e.g. steel), which has a maximum thermal conductivity of 20 W/mK.
In a first variant, the cover disc 4 can be designed entirely of the ceramic material with high thermal conductivity, which makes possible a particularly effective discharge of heat via the cover disc 4. Alternatively to this, the cover disc 4 however can also be formed of another material system with lower thermal conductivity than the ceramic material with high thermal conductivity and comprise a covering layer of the ceramic material with high thermal conductivity. This makes possible a particularly cost-effective production of the guide blade arrangement 1.
For example, the cover disc 4 in this case can be produced from the same material, for example metal or steel, as the further components of the guide blade arrangement 1, such as for example the guide blade carrier ring 2 or the guide blades 3. In this case, all components will then have substantially identical physical properties. In particular, the thermal expansion coefficient of cover disc and the remaining components is the same in this case.
The guide blade arrangement can comprise at least one spacer element 5, which is arranged coaxially to the blade bearing pin and which holds the guide blade carrier ring 2 spaced from the cover disc 4. The guide blade arrangement 1 can be part of an exhaust gas turbocharger. Such an exhaust gas turbocharger can comprise a turbine housing 6, which in
The exhaust gas turbocharger can furthermore comprise a bearing housing 8 which is likewise only partially shown. On the bearing housing 8, a spring element 9 can support itself, by means of which in the axial direction A via the guide blade carrier ring 2 a pressure force (see arrow D) can be exerted on the at least one spacer element 5, so that the latter pushes the cover disc 4 against the turbine housing 6 for the axial fixing.
The exhaust gas turbocharger can be employed together with an internal combustion engine in a motor vehicle, wherein the exhaust gas turbocharger can be operationally connected to the internal combustion engine to increase its power.
| Number | Date | Country | Kind |
|---|---|---|---|
| 102012219355.3 | Oct 2012 | DE | national |
