Abstract:
The invention relates to a high-speed impeller for delivering gaseous or liquid media, for example as a compressor wheel for an exhaust-gas turbocharger. The high-speed impeller has a reinforcing core structure and an outer functional section. The invention is distinguished by the fact that reinforcing sleeves are pushed concentrically over one another for producing the core structure, in which case the length of the respective reinforcing sleeves varies. Furthermore, the functional section is cast onto the core structure.

Description:
[0001]     This application claims the priority of 103 41 415.0, filed Sep. 5, 2003, the disclosure of which is expressly incorporated by reference herein.  
       BACKGROUND AND SUMMARY OF THE INVENTION  
       [0002]     The invention relates to a high-speed impeller for delivering gaseous or liquid media.  
         [0003]     DE 101 63 951 C1 describes a rotor disk which is made of a metal and has local fiber reinforcements. In this case, the fiber reinforcements consist of metal matrix composites (MMC). These inner MMC rings are pressed into the circumference of the rotor disk by means of a radial press fit.  
         [0004]     A rotor consisting of a composite material is described in WO 02/01311 A1, various rings of fiber-reinforced wound bodies being slipped concentrically over one another and thus forming a flat cylindrical rotor disk.  
         [0005]     Said examples show methods of reinforcing an impeller subjected to high centrifugal loading. However, the arrangements described have the disadvantage that complex impeller structures cannot be reproduced or the fiber reinforcements are not fully integrated in the impeller.  
         [0006]     An object of the invention includes providing a high-speed impeller which has an integrated reinforcement in a complex cross-sectional contour.  
         [0007]     A solution of this object includes a high-speed impeller in which a reinforcing core structure is surrounded by an outer functional section, and reinforcing sleeves are pushed concentrically over one another for producing the core structure. In this case, “pushed concentrically over one another” refers to the fact that the outside diameter of an inner reinforcing sleeve equals an inside diameter of an outer reinforcing sleeve to the extent that the outer reinforcing sleeve can be pushed with little play over the inner reinforcing sleeve.  
         [0008]     In this case, the length of the respective reinforcing sleeve varies in such a way that it can approximately reproduce a predetermined cross-sectional geometry of the core contour.  
         [0009]     Due to such a construction of the core structure, a reinforcement of the impeller can be produced which, in deviation from the cylindrical structure of the reinforcements which are mentioned in the prior art, is designed, for example, in hyperbolic shape or in a rising exponential manner. The reinforcement is therefore not only settled in a narrow cylindrical region, but it can also be adapted along a complex cross-sectional structure of the high-speed impeller.  
         [0010]     In many cases, the cross-sectional geometry of the high-speed impeller narrows with increasing diameter, for which reason it is expedient that, in a development of the invention, the length of the reinforcing sleeves is reduced with increasing outside diameter.  
         [0011]     A further aspect of the invention constitutes a high-speed impeller which, claim  3 . Such a high-speed impeller, like previously mentioned the high-speed impeller, has a reinforcing core structure which is surrounded by an outer functional section. However, this embodiment of the high-speed impeller is distinguished by the fact that, in order to produce the core structure, a plurality of reinforcing sleeves with in each case inner bores having the same diameter are aligned in such a way that the inner bores are aligned congruently. The expression “congruently” in this case refers to the fact that the inner bores are concentrically aligned on a common axis in such a way that a shaft can be pushed with little play through the aligned arrangement of the inner bores. However, the outside diameter of the aligned reinforcing sleeves varies in order to reproduce a predetermined cross-sectional geometry of the core structure. The functional section of the high-speed impeller is likewise cast onto the core structure.  
         [0012]     By the arrangement of the reinforcing sleeves being modified, the high-speed impeller according to this latter embodiment achieves the same advantages as are also described by the arrangement of the high-speed impeller as in the first-described embodiment.  
         [0013]     As described, the aligned arrangement of the reinforcing sleeves having the congruently superimposed inner bores can be pushed onto a shaft; however, it can also be pushed onto a reinforcing sleeve of the same kind. In this way, additional radial and axial strengthening is achieved.  
         [0014]     In an advantageous development of the invention, the reinforcing sleeves are produced from a fiberreinforced material. Any form of fiber-reinforced materials by means of which a marked increase in the tensile strength and thus a marked increase in the strength of the high-speed impeller is achieved is suitable in this case. In a further development, the reinforcing sleeves comprise long-fiber-reinforced wound bodies. Such wound bodies may either already be infiltrated with a metal before the integral casting of the functional section, or they may be infiltrated with the metal of the functional section during the integral acasting of the functional section.  
         [0015]     Furthermore, the reinforcing sleeves may consist of a metal-matrix composite material reinforced with short fibers. Furthermore, a porous ceramic infiltrated by metal may be used for the reinforcing sleeves. An increase in the tensile strength and in the modulus of elasticity is also achieved by such reinforcing sleeves.  
         [0016]     It may also be expedient to produce the reinforcing sleeves from non-fiber-reinforced, high-strength metal materials, for example from spray-compacted metal materials or from high-strength wrought alloys. As a rule, such materials can be produced more cost-effectively than fiber-reinforced materials and are used when there is little latitude in terms of the cost of the component.  
         [0017]     The use of the high-speed impeller according to the invention is in particular especially expedient in exhaust-gas turbochargers, in this case equally as a compressor wheel or a turbine wheel. The impellers may also be used in an expedient manner as gas turbine wheels or as water pump wheels.  
         [0018]     Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  shows a graphic illustration of a compressor impeller of an exhaust-gas turbocharger,  
         [0020]      FIG. 2  shows a schematic illustration of a core structure with reinforcing sleeves pushed over one another in accordance with an exemplary embodiment of the present invention.  
         [0021]      FIG. 3  shows a schematic illustration of a core structure with aligned reinforcing sleeves having a constant inside diameter, the aligned arrangement being pushed concentrically onto a reinforcing sleeve of the same kind,  
         [0022]      FIG. 4  shows a schematic illustration of a core structure with aligned reinforcing sleeves which each have an identical inside diameter,  
         [0023]      FIG. 5  shows a schematic illustration of a core structure with aligned reinforcing sleeves which each have an identical inside diameter.  
     
    
     DETAILED DESCRIPTION  
       [0024]     A schematic illustration of a high-speed impeller in the form of a compressor wheel  2  for an exhaust-gas turbocharger is shown in  FIG. 1 . This compressor wheel  2  has a functional section  6  which comprises, for example, compressor blades  7 . Furthermore, the compressor wheel  2  comprises a core structure  4  which, starting from a concentric region around a bore  9  in the center of the compressor wheel  2 , runs outward with increasing diameter and is designed as a support structure of the compressor blades  7 .  
         [0025]     For the sake of clarity, only a cross section of the core structure is shown in FIGS.  2  to  5 . The illustration of the functional section  6  having the compressor blades  7  is dispensed with.  
         [0026]     Shown in  FIG. 2  is a core structure  4  which is produced from a plurality of reinforcing sleeves  8  which are pushed over one another concentrically. For the sake of clarity, only two reinforcing sleeves  8  are provided with the corresponding reference numerals, corresponding designations being provided with the same reference numerals.  
         [0027]     The reinforcing sleeves  8  have an outside diameter  12  and an inside diameter  14 . In this case, the outside diameter  12  of each reinforcing sleeve  8  is configured in such a way that it corresponds to the inside diameter  14  of the following reinforcing sleeve  8  to the extent that the two reinforcing sleeves  8  can be pushed over one another with little play (cf.  FIG. 2 , right-hand side). In this case, in the example according to  FIG. 2 , the reinforcing sleeves  8  become shorter from the inside outward; that is to say the length  10  of the reinforcing sleeves  8  decreases from the inside outward. If need be, for reproducing the cross section of the core structure  4 , a wall thickness  13  may also vary from one reinforcing sleeve  8  to the next reinforcing sleeve  8 .  
         [0028]     The result of such a type of construction is shown schematically in  FIG. 2  on the left-hand side. Indicated by the dot-dash line, the cross-sectional geometry of the reinforcing structure  4  runs outward in a similar manner to an exponential curve until it reaches a maximum value in order to then fall away again roughly in a hyperbolic shape in the direction of a center axis  16 . In this case, a plan view of the core structure  4  is depicted in the top part of the lefthand sketch in  FIG. 2 , and a section through the core structure  4  is shown in the bottom part of the sketch.  
         [0029]     The core structure  4  from  FIG. 3  differs from the core structure  4  in  FIG. 2  in that reinforcing sleeves  20  which each have an inner bore  22  of identical diameter are provided. The reinforcing sleeves  20  are aligned in such a way that the inner bores  22  are congruently superimposed, a reinforcing sleeve  26  of the same kind being shown in such a way that its outside diameter  28  can be pushed with little play into the inner bores  22  of the reinforcing sleeves  20 . The reinforcing sleeves  20  are therefore aligned on the reinforcing sleeve  26  of the same kind. According to the example from  FIG. 3 , the reinforcing sleeves  20  likewise have a different length  10 . By means of this measure, the predetermined cross-sectional geometry of the core structure  4 , which is shown by the dot-dash line in  FIG. 3  in the sketch on the left-hand side, can be filled as fully as possible.  
         [0030]     An aligned arrangement of various sleeves  20 , with in each case a constant inner bore  22 , is shown in the example in  FIG. 4 , which is similar to the example from  FIG. 3 . The difference from  FIG. 3  consists in the fact that a reinforcing sleeve  26  of the same kind, onto which the aligned arrangement of the reinforcing sleeves  20  is pushed, is not used here. The aligned arrangement of reinforcing sleeves  20  in  FIG. 4  can be soldered, adhesively bonded or stitched, for example, depending on which materials are used for the reinforcing sleeves  20 . The aligned arrangement of reinforcing sleeves  20  can then be pulled onto a shaft.  
         [0031]     An aligned arrangement of reinforcing sleeves  20 , similar to the example from  FIG. 4 , is likewise shown in  FIG. 5 . This involves a simplified form, since the reinforcing sleeves  20  essentially have the same length. As can be seen in the sketch on the left-hand side of  FIG. 5 , the cross-sectional geometry of the reinforcing structure  4  is not filled to the optimum extent, as occurs, for example, by means of the exemplary embodiment in  FIG. 4 . However, such a simpler, cost-effective type of construction may be advantageous for simple compressor wheels which are not subjected to very high loading.  
         [0032]     The types of construction of the reinforcing structure  4  which are shown in FIGS.  2  to  5  involve comparatively complex arrangements. In practice, it may therefore often be expedient for reasons of cost for only two _einforcing sleeves  8  to be pushed concentrically over one another according to the example from  FIG. 2 . It may also be expedient, for example, in accordance with  FIG. 3 , for only two reinforcing sleeves  20  to be aligned and for said reinforcing sleeves  20  to be pulled onto a reinforcing sleeve  26  of the same kind or for them to be pushed directly onto a shaft (not shown here). In this case, the existing loading condition at the compressor wheel  2  and the cost framework are to be taken into account in each case.  
         [0033]     The materials which are used for producing the reinforcing sleeves  8  or  20  are likewise adapted to the mechanical stresses which act on the compressor wheel  2 . The production of the reinforcing sleeves from a fiber-reinforced material has been found to be expedient.  
         [0034]     A possible example for the production of a reinforcing sleeve  8  or  20  consists in producing a wound body of long-fiber material or of spun short-fiber material. In this case, the fibers are impregnated in a wax, resin or polymer. The impregnated material hardens after the wound body has been wound up, thereby resulting in “preforms” of the reinforcing sleeves  8 ,  20 . These preforms of the reinforcing sleeves  8 ,  20  can be cut into segments having the desired lengths  10 , in which case these segments, according to the mode of expression used here, may already be referred to as reinforcing sleeves  8 ,  20 . These reinforcing sleeves  8 ,  20  can be attached to one another or pushed over one another, for example, by adhesive bonding, pressing, stitching, stacking or hot melting. Thus preliminary fixing already exists and already represents the cross-sectional geometry of the core structure  4 .  
         [0035]     Organic material such as wax or polymer is then melted or the resin or the polymer or the wax is burnt out of the reinforcing sleeves  8 ,  20 . The reinforcing sleeves  8 ,  20 , which are thus free of organic bonding agents, are placed in a casting mold and are infiltrated during the pouring with the metal melt, which also subsequently forms the functional section  6 . In this case, a die-casting or a squeeze-casting process is expedient. If appropriate, the burning-out and the pouring of the metal melt can also be effected at the same time.  
         [0036]     In another variant of the method of producing the core structure  4 , fiber-reinforced wound bodies, which are inflitrated with polymers or resins or waxes, are produced in a similar manner to the preceding example and are assembled to form a core structure  4  similar to FIGS.  2  to  5 , the organic material—wax, resin or polymer—is removed, and the core structure  4  is infiltrated with a special metal in a corresponding casting process, for example a die-casting process. The core structure  4  infiltrated in this way is then encapsulated with the functional section  6  in the precision casting or in another low-pressure casting process.  
         [0037]     In the casting process described last, it may be expedient to provide the already pre-infiltrated core structure  4  with an adhesion layer so that the liquid metal adheres more effectively to the core structure during the integral casting of the functional section  6  and thus forms a firm bond.  
         [0038]     In the cases in which the fiber wound body is infiltrated with liquid metal, it may possibly be expedient to coat the fibers, so that, on the one hand, a reaction of the infiltration metal with the fiber is avoided and, on the other hand, better wetting and better infiltration is ensured.  
         [0039]     For reasons of cost, when less stringent mechanical demands are made on the compressor wheels  2  or in general on the high-speed impeller to be produced, the reinforcing sleeves may be produced, for example, from a wrought alloy, in particular an aluminum wrought alloy. The use of metal-matrix composites, which if appropriate are reinforced with short fibers, or the use of spray-compacted metallic materials may be expedient for the reinforcing sleeves  8 ,  20 .  
         [0040]     The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.