TECHNICAL FIELD
The present invention relates to a cellular wheel made of metal, comprising a cylindrical outer sleeve located symmetrically to a rotational axis and a cylindrical inner sleeve located concentrically to the outer sleeve, wherein the space between the outer sleeve and the inner sleeve is divided into a multiplicity of rotation-symmetrically arranged cells by cell wall parts delimited by cell edges oriented parallel to the rotational axis, which cell edges lie with rotation-symmetrically arranged axial planes on lines of intersection of cylinder shell surfaces arranged concentrically to the rotational axis. A method suitable for producing the cellular wheel also lies within the scope of the invention.
PRIOR ART
For some years, the process of downsizing has been one of the key issues in the design of new, supercharged engines. With downsizing, the fuel consumption and thus the exhaust emissions of a vehicle can be reduced. These aims are nowadays becoming increasingly important, since the high energy consumption by fossil fuels contributes strongly to air pollution and increasingly strict legislative measures are forcing automobile manufacturers to take action. By downsizing, the substitution of a high-volume engine by a reduced-capacity engine is understood. In this way, the engine power should be maintained at a constant rate by charging the engine. The aim is to achieve the same output values with low-volume engines as with equally powerful naturally aspirated engines. New insights in the field of downsizing have shown that, particularly in very small Otto engines with a cubic capacity of 1 liter or less, the best results can be obtained with pressure wave supercharging.
In a pressure wave supercharger, the rotor is configured as a cellular wheel and is enclosed by an air and exhaust housing having a common casing. The development of modern pressure wave superchargers for supercharging small engines leads to cellular wheels having a diameter in the order of magnitude of 100 mm or less. In order to obtain a maximum cell volume and also reduce the weight, cell wall thicknesses of 0.2 mm or less are aimed for. Given the high exhaust inlet temperatures of around 1000° C., virtually only high-temperature steels can be considered as materials for the cellular wheel. The production of dimensionally stable and high-precision cellular wheels with low cellular wall thickness is today barely possible, or else is associated with considerable additional costs.
It has already been proposed to form the chambers of a cellular wheel from aligned and partially overlapping, Z-shaped profiles. The production of such a cellular wheel is associated, however, with high time expenditure. Added to this is the fact that the alignment and positionally accurate fixing of Z-profiles is barely practicable with a precision sufficient to meet the required tolerances.
It has already been proposed to produce a cellular wheel from a solid body by erosion of the individual cells. With this method, it is not possible, however, to achieve cell wall thicknesses of 0.2 mm. A further fundamental drawback of the erosion method is constituted by the high material and machining costs associated therewith.
From EP-A-1 375 859, a cellular wheel of the type stated in the introduction is known. The cellular wheel comprises an outer sleeve, an inner sleeve located concentrically to the outer sleeve and an intermediate sleeve arranged between the outer sleeve and the inner sleeve concentrically to these same. Between the outer sleeve and the intermediate sleeve and between the intermediate sleeve and the inner sleeve are arranged blades oriented radially to the rotational axis. The individual cells are delimited by two adjacent blades and adjacent sleeves. In load tests under practical conditions, it has been shown that, particularly with cell wall thicknesses of 0.5. mm or less, a torsion of the sleeves and a vibration of the blades occur. This unstable behavior leads after a short while to failure of the cellular wheel.
REPRESENTATION OF THE INVENTION
The object of the invention is to provide a cellular wheel of the type stated in the introduction, which has a higher rigidity than cellular wheels according to the prior art, given comparable cell wall thickness. Moreover, the cellular wheel is designed to be able to be produced in a simple and cost-effective manner with the required precision, while avoiding the drawbacks of the prior art. A further aim of the invention is to provide a dimensionally stable, lightweight cellular wheel for use in a pressure wave supercharger for supercharging internal combustion engines, in particular for supercharging small Otto engines having a cubic capacity in the order of magnitude of 1 liter or less. A still further aim of the invention is to provide a method for the cost-effective production of dimensionally stable and high-precision cellular wheels having a cell wall thickness of 0.4 mm or less.
In a cellular wheel of the type stated in the introduction, the inventive solution of the object is achieved by the fact that the outer sleeve and the inner sleeve delimit a cell structure constructed from a network formed in cross section in mesh-like arrangement from connected cell wall parts, in which cell structure cell edges, which in pairs respectively delimit a cell wall part, lie simultaneously on adjacent cylinder shell surfaces and on adjacent axial planes, wherein each cell edge on a cylinder shell surface, with each of the cell edges lying on two adjacent axial planes of an adjacent cylinder shell surface, respectively delimits two cell wall parts.
By virtue of the cell structure which is used according to the invention, the cellular wheel has a substantially higher rigidity than the known cellular wheels. Moreover, the absence of intermediate sleeves leads, in addition to a considerable weight reduction, to a strongly increased passage cross section.
The cell structure preferably comprises three or four cylinder shell surfaces, though cellular wheels having more than four cylinder shell surfaces are also conceivable.
In a particularly preferred, cost-effective method for producing the cellular wheel according to the invention, the cell structure is formed, based on the industrial production of honeycomb structures, by stretching of blade assemblies made up of blades connected locally at different points.
The method is distinguished by the following steps to be executed in sequence:
- (a) provision of a predefined number of blades having a length corresponding to the length of the cellular wheel and a width appropriately tailored to the predefined thickness of the annular space between the outer sleeve and the inner sleeve;
- (b) paired welding together of the blades in the longitudinal direction at predefined points to form a blade assembly, with the formation of the cell edges;
- (c) stretching of the blade assembly in a direction perpendicular to the plane of the blades and of the stretched blade assembly to form the annular cell structure;
- (d) connection of the two terminal blades of the stretched and bent blade assembly along corresponding cell edges;
- (e) sliding of the inner sleeve into the annular cell structure and sliding of the outer sleeve onto the annular cell structure;
- (f) connection of the outer sleeve and inner sleeve to the blade edges.
The connection of the two terminal blades of the stretched and bent blade assembly along corresponding cell edges, and the connection of the outer sleeve and inner sleeve to the blade edges, is preferably carried out by welding together the parts by means of a laser beam or electron beam.
A further preferred method for producing the cellular wheel according to the invention is distinguished by the following steps to be executed in sequence:
- (a) provision of a predefined number of blades having a length corresponding to the length of the cellular wheel and a width appropriately tailored to the predefined thickness of the annular space between the outer sleeve and the inner sleeve;
- (b) shaping of the blades in accordance with their definitive shape predefined by the annular cell structure and, if necessary, connection of blade pairs to form individual cells;
- (c) placement of the shaped blades or the cells at predefined points in a predefined number on the outer side of the inner sleeve, and connection of the blades or the cells one to another to form the annular cell structure, and to the inner sleeve;
- (d) sliding of the outer sleeve onto the annular cell structure;
- (f) connection of the outer sleeve and inner sleeve to the blade edges.
The connection of the blade pairs to form individual cells, and the connection of the blades or the cells one to another to form the annular cell structure, and to the inner sleeve, is preferably carried out by welding together the parts by means of a laser beam or electron beam.
The cellular wheel produced with the method according to the invention is preferably used in a pressure wave supercharger for supercharging internal combustion engines, in particular Otto engines having a cubic capacity of 1 liter or less.
BRIEF DESCRIPTION OF THE DRAWING
Further advantages, features and details of the invention emerge from the following description of preferred illustrative embodiments and with reference to the drawing, which serves merely for illustrative purposes and should not be construed restrictively. The drawing shows schematically in
FIG. 1 a side view of a cellular wheel for a pressure wave supercharger;
FIG. 2 an oblique view of the front face of the cellular wheel of FIG. 1;
FIG. 3 a section perpendicular to the rotational axis of the cellular wheel of FIG. 1 along the line I-I;
FIG. 4 a side view of a variant of the cellular wheel of FIG. 1;
FIG. 5 an oblique view of the front face of the cellular wheel of FIG. 4;
FIG. 6 a section perpendicular to the rotational axis of the cellular wheel of FIG. 4 along the line II-II;
FIG. 7 a top view of a welded-together blade assembly for the production of the cellular wheel of FIG. 3;
FIG. 8 a cross section through the blade assembly of FIG. 7 along the line III-III;
FIG. 9 a detail from the blade assembly of FIG. 8 following stretching and bending into the cell structure, welded to the outer and inner sleeve;
FIG. 10 a welding variant of the blade assembly of FIG. 7;
FIG. 11 an oblique view of a cellular wheel produced from the blade assembly of FIG. 7;
FIG. 12 the blade assembly of FIG. 13 having the dimensions of the blade assembly of FIG. 8 following stretching and bending into the cell structure, welded to the outer and inner sleeve;
FIG. 13 a top view of a welded-together blade assembly for the production of the cellular wheel of FIG. 6;
FIG. 14 a cross section through the blade assembly of FIG. 13 along the line IV-IV;
FIG. 15 a detail from the blade assembly of FIG. 13 following stretching and bending into the cell structure, welded to the outer and inner sleeve;
FIG. 16 an oblique view of a cellular wheel produced from the blade assembly of FIG. 13;
FIG. 17 an oblique view of an inner sleeve of a cellular wheel in accordance with FIG. 3, with a part comprising mounted and joined blades;
FIG. 18 a section through a sub-region of the arrangement of FIG. 17 at right angles to the cellular wheel axis, in enlarged representation;
FIG. 19 a longitudinal section through the arrangement of FIG. 17 with inserted tool and slid-on outer sleeve;
FIG. 20 a cross section through a part of the arrangement of FIG. 19 along the line B-B, in enlarged representation;
FIG. 21 an oblique view of the arrangement of FIG. 19;
FIG. 22 a section through the arrangement of FIG. 21 at right angles to the cellular wheel axis;
FIG. 23 an enlarged detail of the region X of FIG. 22;
FIG. 24 an oblique view of an inner sleeve of a cellular wheel in accordance with FIG. 6, with a part comprising placed and joined blades;
FIG. 25 a section through a sub-region of the arrangement of FIG. 24 at right angles to the cellular wheel axis, in enlarged representation;
FIG. 26 a longitudinal section through the arrangement of FIG. 24 with inserted tool and slid-on outer sleeve;
FIG. 27 a cross section through a part of the arrangement of FIG. 26 along the line B-B, in enlarged representation;
FIG. 28 an oblique view of the arrangement of FIG. 26;
FIG. 29 a section through the arrangement of FIG. 28 at right angles to the cellular wheel axis;
FIG. 30 an enlarged detail of the region Y of FIG. 29.
DESCRIPTION OF PREFERRED EMBODIMENTS
A cellular wheel 10, shown in FIGS. 1 to 3 and 4 to 6, of a pressure wave supercharger (not represented in the drawing) consists of a cylindrical outer sleeve 12 located symmetrically to a rotational axis y of the cellular wheel 10 and a cylindrical inner sleeve 14 located concentrically to the outer sleeve 12. The outer sleeve 12 and the inner sleeve 14 delimit a cell structure 17 consisting of a network formed in cross section in mesh-like arrangement from connected cell wall parts 19. The annular space between the outer sleeve 12 and the inner sleeve 14 is divided into a multiplicity of rotation-symmetrically arranged cells 22, 22′, 22″, 22a, 22b by cell wall parts 19 delimited by cell edges 20 oriented parallel to the rotational axis y. The cell edges 20 lie on lines of intersection of cylinder shell surfaces 18a, 18b, 18b1, 18b2, 18c, arranged concentrically to the rotational axis y, with rotation-symmetrically arranged axial planes 21. The cell edges 20, which respectively delimit a cell wall part 19, lie simultaneously on adjacent cylinder shell surfaces 18a, 18b, 18b1, 18b2, 18c and on adjacent axial planes 21. Each cell edge 20 on a cylinder shell surface 18a, 18b, 18b1, 18b2, 18c delimits, with each of the cell edges 20 lying on two adjacent axial planes of an adjacent cylinder shell surface 18a, 18b, 18b1, 18b2, 18c, respectively two further cell wall parts 19. Half of the lines of intersection of the cylinder shell surfaces 18a, 18b, 18b1, 18b2, 18c with the axial planes 21 are occupied by cell edges 20, an unoccupied interface being respectively located between adjacent cell edges 20 on the cylinder shell surfaces 18a, 18b, 18b1, 18b2, 18c and between adjacent cell edges 20 on the axial planes 21. This arrangement of the cell edges 20 and the aforementioned condition that the cell edges 20, which in pairs respectively delimit a cell wall part 19, lie simultaneously on adjacent cylinder shell surfaces 18a, 18b, 18b1, 18b2, 18c and on adjacent axial planes 21, produces in the cross section of the cellular wheel 10 an extensive pattern of deltoids, which form the cross section of the individual cells 22, 22a, 22b. In the finished cellular wheel, the annular cell structure 17 is delimited by the inner sleeve 14 and the outer sleeve 12. In this way, the intermediate spaces of adjacent cells of deltoid cross section and the outer and inner sleeves 12, 14 give rise to further cells 22′, 22″ of triangular cross section.
In the cellular wheel 10 shown in FIGS. 1 to 3, the cell edges of the annular cell structure lie on points of intersection of 72 rotationally symmetric axial planes 21 with 3 cylinder shell surfaces 18a, 18b, 18c, wherein, in the finished cellular wheel 10, the outer and the inner cylinder shell surface 18a, 18c coincide with the inner wall of the outer sleeve 12 or of the inner sleeve 14. 36 cells 22 of deltoid cross section and 2×36 cells 22′, 22″ of triangular cross section are thus obtained. The cell structure 17 has a rotational symmetry with respect to the rotational or cellular wheel axis y with an angle of rotation of 360°/36=10°.
In the cellular wheel 10 shown in FIGS. 4 to 6, the cell edges of the annular cell structure lie on points of intersection of 72 rotationally symmetric axial planes 21 with 4 cylinder shell surfaces 18a, 18b1, 18b2, 18c, wherein in the finished cellular wheel 10 the outer and the inner cylinder shell surface 18a, 18c coincide with the inner wall of the outer sleeve 12 or the inner sleeve 14. 2×36 cells 22a, 22b of deltoid cross section and 2×36 cells 22′, 22″ of triangular cross section are thus obtained. The cell structure 17 has a rotational symmetry with respect to the rotational or cellular wheel axis y with an angle of rotation of 360°/36=10°.
The cellular wheel 10 represented by way of example in FIGS. 1 to 3 and 4 to 6 and having a diameter D and a length L of, for example, in each case 100 mm, has respectively 108 and 144 cells in total. The outer sleeve 12, the inner sleeve 14 and the cell wall parts have a standard wall thickness of, for example, 0.4 mm and consist of a highly heat resistant metallic material, for example Inconel 2.4856. The said parts have in the direction of the rotational axis y a same length L commensurate with the length of the cellular wheel 10 and extend between two front faces of the cellular wheel 10 which stand perpendicular to the rotational axis y. In the region of the two front faces are arranged profiles 24 of a labyrinth seal, which profiles encircle the outer sleeve 12. The counter profiles to the profiles 24, which counter profiles are necessary to the formation of the labyrinth seal, are found on the inner wall of a cellular wheel housing (not represented in the drawing) provided to accommodate the cellular wheel 10.
The production of a cellular wheel is explained in greater detail in the following description of illustrative embodiments.
As can be seen from FIGS. 7 to 11, in a first production method rectangular blades 16 of a length l and a width b are placed individually one after the other congruently one upon the other, wherein, prior to each mounting of a further blade 16, respectively the two topmost blades 16 are welded together at predetermined points by means of a laser beam guided parallel to the longitudinal direction of the blades 16.
The blades 16 are lamellar, flat sheet-metal parts and are usually cut to the predefined length from a sheet-metal strip which is present in roll form.
The length 1 of the blades corresponds to the length L of the cellular wheel 10. The width b of the blades 16 or of the blade assembly 26 is greater than the width or thickness B of the annular space or of the annular cell structure 17 between the outer sleeve 12 and the inner sleeve 14 and allows for the decrease in width b of the blade assembly 26 which occurs when the blade assembly 26 is subsequently stretched and bent into the cell structure 17.
For the formation of the cell structure 17 represented in FIG. 3, 72 blades 16 in total are alternately welded together in the region of the two longitudinal edges 16k and in the longitudinal middle 16m over the total length 1, so that finally an assembly 26 of 72 welded-together blades 16 is formed. The assembly 26 of welded-together blades 16 is then stretched in a direction z perpendicular to the plane of the blades 16 and bent into the annular cell structure 17 until the first and the last blade 16 of the assembly 26 touch. In this position, the two terminal blades 16 of the assembly are welded together along their longitudinal middles 16m.
In a next step, the outer sleeve 12 and the inner sleeve 14 in the form of tubular sleeves are slid on or in from a front face. Prior to the performance of the welding operation, the cell walls of the annularly bent cell structure 17 are fixed in the predefined angular position in a positionally accurate manner by means of frontally inserted tools. Following the positioning of the outer sleeve 12 and the inner sleeve 14, the longitudinal edges 16k of the welded-together blade pairs 16 are welded to the outer sleeve 12 or the inner sleeve 14 through the outer sleeve 12 or the inner sleeve 14 by means of a laser beam guided along each longitudinal edge 16k (FIG. 9 and FIGS. 19 to 23).
For the formation of the cell structure 17 represented in FIG. 6, 72 blades 16 in total are alternately welded together in the region of a first longitudinal edge 16k, as well as between the longitudinal middle and the second longitudinal edge 16k and in the region of the second longitudinal edge 16k, as well as between the longitudinal middle and the first longitudinal edge 16k over the total length l, so that finally an assembly 26 of 72 welded-together blades 16 is formed. The assembly 26 of the welded-together blades 16 is then stretched in a direction z perpendicular to the plane of the blades 16 and bent into the annular cell structure 17 until the first and the last blade 16 of the assembly 26 touch. In this position, the two terminal blades 16 of the assembly are welded together along corresponding edges.
In a next step, the outer sleeve 12 and the inner sleeve 14 in the form of tubular sleeves are slid on or in from a front face. Prior to the performance of the welding operation, the cell walls of the annularly bent cell structure 17 are fixed in the predefined angular position in a positionally accurate manner by means of frontally inserted tools 34. Following the positioning of the outer sleeve 12 and the inner sleeve 14, the longitudinal edges 16k of the welded-together blade pairs 16 are welded to the outer sleeve 12 or the inner sleeve 14 through the outer sleeve 12 or the inner sleeve 14 by means of a laser beam guided along each longitudinal edge 16k (FIG. 15 and FIGS. 26 to 30).
A comparison of FIGS. 9 and 12 shows that cell structures of different cell number according to FIGS. 3 and 6 can be installed in an annular space of predefined dimensions between the outer and inner sleeve.
In the paired welding of the blades 16 to form the blade assembly 26, all weld seams can be made with a laser beam guided perpendicular to the plane of the blades 16 (FIG. 8 and FIG. 13). In a variant shown in FIG. 10, the longitudinal edges 16k are welded in pairs with a laser beam guided laterally parallel to the plane of the blades 16.
FIGS. 17 and 18 and FIGS. 24 and 25 show, as a variant of the above-described production of a cellular wheel 10 according to FIG. 3 or FIG. 6, the furnishing of a prefabricated inner sleeve 14 or flanged sleeve 15 with individual blades 16 which have been preformed into their definitive shape predefined by the annular cell structure 17, or with such blades which have been welded in pairs to form cells 22 or 22a, 22b. The fundamental difference to the previously described production type lies in the fact that a previously produced inner sleeve 14 is suitably equipped. The joining of the individual blades 16 or cells 22 or 22a, 22b one to another is effected from outside by means of a laser beam 30 guided perpendicular to the rotational axis y along the butt edge. The welding of the individual blades 16 or cells 22 or 22a, 22b to the inner sleeve 14 can be effected from outside by means of a laser beam 30′ guided at an angle to the corresponding axial plane 21 along the butt edge, with the formation of a fillet weld, or from within the inner sleeve 14 by means of a laser beam 30″ guided perpendicular to the rotational axis y along the butt edge, with the formation of a blind weld. The welding of the last cell to the inner sleeve is in any event effected, however, from within the inner sleeve 14. The inner sleeve 14 can be a seamless sleeve, or a sheet-metal strip which has been bent into a tubular sleeve and has been welded along a butt edge, with the formation of a longitudinal weld seam.
As can be seen from FIG. 17 or 24, the inner sleeve 14 which is equipped with blades 16 welded in pairs to form cells 22 or 22a, 22b is directly connected to a drive shaft 13, i.e. a flanged sleeve can here be dispensed with, or the inner sleeve 14 is slid onto a flanged sleeve 15 already prior to being equipped with blades.
The connection of the inner sleeve 14 to the flanged sleeve 15 can be effected, for instance, by welding together the end edges of the inner sleeve 14 and the flanged sleeve 15 by means of laser beams 30 (not represented in the drawing).
As shown in FIGS. 19 to 23 for the production of a cellular wheel according to FIG. 3 and in FIGS. 26 to 30 for the production of a cellular wheel according to FIG. 6, the blades 16 or cells 22 already welded to the inner sleeve 14 are fixed in a predefined angular position by means of frontally inserted tools 34. After the outer sleeve 12 has been slid on, it is welded by means of laser beams 30, via a blind weld, to the free end edges of the underlying blades 16 or cells 22 or 22a, 22b (FIGS. 22 and 23 or FIGS. 29 and 30).
REFERENCE SYMBOL LIST
10 cellular wheel
12 outer sleeve
13 drive shaft
14 inner sleeve
15 flanged sleeve
16 blades
17 cell structure
18
a,18b,18c cylinder shell surface
19 cell wall part
20 cell edges
21 axial plane
22,22a,22b,22′,22″ cells
24 labyrinth cell part
26 blade assembly
30,30′,30″ laser beam
34 tool
y rotational axis
Patent Application
20120057994
