Blade wheel, in particular compressor wheel or turbine wheel, with blades having a root fillet

Description

[0001] The invention relates to a blade wheel, in particular a compressor wheel or a turbine wheel, preferably for a gas compressor, turbocharger, in particular an exhaust gas turbocharger.

[0002] The impeller according to the invention has a base body which has a flow side and a rear side opposite the flow side, wherein a flow surface is formed on the flow side, wherein blades protrude from the flow surface, wherein the blades are integrally connected to the flow surface via a connecting section, wherein a rotational axis of the impeller extends between the flow side and the rear side, wherein a flow channel with a channel bottom is formed between at least two adjacent blades, wherein the blades each have a pressure side and a suction side opposite the pressure side, wherein one of the adjacent blades delimits the flow channel with its pressure side and the other of the adjacent blades delimits the flow channel with its suction side,and wherein the connecting section forms a throat-shaped surface contour extending along the connecting section in the transition from the channel bottom to the pressure side of one blade and / or in the transition from the channel bottom to the suction side of the adjacent blade.

[0003] Compressor wheels have blades with a pressure side facing in the direction of rotation and a suction side facing opposite to the direction of rotation.

[0004] Turbine wheels have blades with a suction side pointing in the direction of rotation and a pressure side pointing opposite to the direction of rotation.

[0005] Ever-increasing speeds of impellers in gas compressors, especially in turbochargers, lead to ever-increasing stresses on all rotating components due to the resulting increase in centrifugal force. In compressor wheels, these stresses occur primarily in various areas of the connecting section, i.e., the transition between the flow surface and the blade.

[0006] In turbochargers, it is common practice to form the connecting section in the form of a groove for the blade connection, the geometry of which is created by the rolling of an imaginary sphere between the pressure or suction side and the channel bottom.

[0007] If the connecting sections dimensioned with a specific geometry no longer meet the strength requirements, a new surface contour of the connecting section is designed, whereby at least locally a different, usually larger, sphere diameter of the imaginary sphere is selected.

[0008] One problem here is that, for example, a structural increase in the suction-side blade connection radius leads to a local improvement, i.e., a local reduction in the stress level, but this also means additional mass over a large diameter. In the case of blades that overlap in some areas in the circumferential direction, this additional mass, in turn, leads to increased stress on the blade connection on the pressure side of the adjacent blade, which forms the flow channel with the first blade.

[0009] This results in an optimization problem in which the designer attempts to achieve a suitable ratio between the stresses on the pressure and suction sides by varying the blade connection radius. If the stresses on the pressure and suction sides reach a ratio that results in the same service life at both locations, the designer has very limited flexibility in designing the blade connection, and often has to resort to other means, such as using a higher-quality, but more expensive, material.

[0010] The problems of compressor wheels can essentially be applied analogously to turbine wheels. In turbine wheels, increased stress often occurs at the narrowest point of the flow channel between the blades. Here, the stresses often cannot be sufficiently reduced using conventional methods for dimensioning the connecting section because the space between the blades is insufficient to increase the radius of the surface contour of the connecting section. Therefore, even in high-performance turbine wheels, there is a need to improve the connections between the blades and the flow surface.

[0011] Another problem with the service life of compressor wheels arises from the application of a coating, e.g., in the form of a conversion layer. Material defects in the surface of the coating, such as micro-notches, porosities, etc., can significantly reduce the service life of the compressor wheel. In other words, the stresses on the coating are crucial for the service life of the compressor wheel. The service life of a coated impeller can therefore be significantly improved if the stresses on the coated impeller, and thus on the coating, can be reduced.

[0012] Compressor wheels, such as those used in turbochargers, are typically manufactured with ball-end mills. These are oriented to create the blade connection so that the spherical cutter tip contacts the blade and the hub simultaneously. This creates the rolling ball geometry described above. This is a quick and cost-effective solution.

[0013] Circular blade connections, defined using the rolling ball method described above, are a cost-effective and sufficient solution for most compressor and turbine wheels. However, when the loads are very high, the disadvantages of this blade connection become apparent. The strong increase in cross-section when approaching the theoretical joint line from the pressure or suction side to the channel floor leads to a stress concentration in blade connections with a radius at the outlet of the rounding area, typically, but not always, at the outlet to the channel floor. This problem can be counteracted to some extent by a rolling ball diameter that can be varied along the length of the joint line. However, the general problem remains.In the case of turbine wheels, the blades are often so close together that increasing the blade connection radius is not possible. The only options are to radially enlarge the hub or to remove a blade to make room for an enlarged blade connection. JP 2006 226199 A discloses a blade connection that has the greatest curvature of the throat-shaped surface contour in the area of its apex and whose curvature decreases continuously from there towards the blade and the channel floor. This creates a curvature-continuous transition at these transitions. This type of blade connection is therefore a good solution for reducing stress peaks. However, the geometry of the surface contour used is a freeform surface tailored to the individual application, which is complex to manufacture.

[0014] US 2015 316 073 A1 discloses another known compressor wheel. The type of blade connection is not specified in detail here.

[0015] US 8,721,287 B2 discloses a blade connection in which the surface contour of the connecting section has an elliptical shape. It is proposed to arrange the long axis of the ellipse parallel to the blade or perpendicular to it. While this achieves a smoother transition from the channel floor to the blade, it also results in a material thickening, i.e., a mass concentration, which has a negative impact on other areas of the compressor wheel located in the radial direction of this reinforcement.

[0016] US 2010 / 284815 A1 and US 2011 / 064583 A1 disclose further prior art.

[0017] It is an object of the invention to provide a blade wheel of the type mentioned at the outset, which provides a highly resilient blade connection to the flow surface.

[0018] This object is achieved with the features of claim 1. According to the invention, it can therefore be provided that in a cross-section through at least one of the blades transverse to the longitudinal extent of the blade, the surface contour in the cross-sectional plane is designed such that it transitions continuously and differently into the suction side and the channel floor at connecting points and / or that the surface contour in the cross-sectional plane is designed such that it transitions continuously and differently into the pressure side and the channel floor at connecting points, that two tangents running through the connecting points in this cross-sectional plane form an intersection point, that a virtual connecting line is formed between the connecting points, that the surface contour forms a vertex between the connecting points, that a first distance line formed perpendicular to the virtual connecting line and running through the vertex,a first distance measure is formed between the vertex and the virtual connecting line; a second distance line formed perpendicular to the virtual connecting line and passing through the intersection of the tangents forms a second distance measure between the intersection and the virtual connecting line; and a geometric parameter determined by the ratio of the first distance measure to the second distance measure is selected in the range from 0.3 to 0.7. The vertex is the point on the surface contour in the cross-sectional plane at which it has the greatest curvature or intersects an axis of symmetry.

[0019] By means of the tangential transitions, the connecting section according to the invention enables the design of a stress-optimized cross-sectional profile. In particular, notch stresses in these areas can be reduced or prevented.

[0020] Furthermore, the inventive geometry parameter creates a surface contour that is highly resilient, yet requires only a small cross-sectional area. This also reduces the mass required in the connecting section. This reduces the mass moment of inertia compared to existing solutions.

[0021] The reduction in mass not only has a beneficial effect on the immediate vicinity of the connecting section, but also on the far region of the connecting section, which is influenced by centrifugal forces. In particular, the stresses in rapidly rotating impellers can be significantly reduced due to the lower mass in the radially outer region of the impeller. For example, a significant reduction in centrifugal forces can be achieved in areas that lie in the same radial grain as the connecting section. Surprisingly, it has been shown that the effects are so great that they often make the use of an alternative material with greater strength unnecessary.

[0022] If the impeller has a bore forming the axis of rotation, this bore is subject to significant stress in rapidly rotating impellers. Since the invention saves mass, the load on the bore can also be reduced, thus increasing its service life.

[0023] Due to the significantly increased strength of the connecting section, higher speeds can be achieved. Furthermore, blade geometries with particularly effective shapes can be used, which cannot be reliably connected with conventional connecting sections in high-speed impellers. With the connecting section designed according to the invention, these highly effective impellers can now be used, thus significantly increasing the overall performance in terms of efficiency, pressure build-up, and throughput of the impeller.

[0024] The innovative surface contour requires a smaller cross-sectional area for the connecting section while maintaining higher load capacity. This simultaneously increases the free cross-sectional area in the flow channel and thus the throughput compared to known solutions with conventionally designed surface contours.

[0025] Overall, the invention allows impellers to be designed with a smaller moment of inertia and / or better thermodynamic properties.

[0026] According to the invention, it can be the case that, in a section defined by two intersecting straight lines, one of which is perpendicular to the pressure side or the suction side of the blade through the first connection point and the other perpendicular to the channel floor through the second connection point, the surface contour in this cross-sectional plane is designed such that, at the connection points, it transitions continuously and differently into the suction side or the pressure side or the channel floor. In other words, a cross-sectional plane perpendicular to an intersection curve is formed by two intersecting surfaces, the first surface being formed by an offset of the pressure side or the suction side of the blade at a constant distance from the pressure side or suction side of the blade, and the second surface being formed by an offset of the channel floor at a constant distance from the channel floor, and the offset taking place into the flow channel, i.e.not into the material, but out of it.

[0027] According to a preferred embodiment of the invention, the geometric parameter, which is determined by the ratio of the first distance to the second distance, can be selected in the range of 0.4 to 0.6. This achieves a particularly stress-optimized design.

[0028] According to the invention, it is further provided that the surface contour has, at least in part, the shape of a conic section or, at least in part, the shape of a linear combination of conic sections. If the surface contour is formed by a single conic section, i.e., an ellipse, a parabola, or a hyperbola, the surface contour can be manufactured relatively easily; the same often applies to linear combinations of conic sections. In principle, it is also conceivable that sections of conic sections or sections of linear combinations of conic sections are combined to form an overall contour. These contours can also be produced relatively easily by machining.

[0029] According to a particularly preferred variant of the invention, it is provided that the ellipse generating the surface contour has the shape of a highly elongated ellipse, with a ratio of the major semi-axis to the minor semi-axis: semi-major axis / semi-minor axis greater than or equal to 5, preferably greater than or equal to 10.

[0030] Such a design is particularly suitable for compressor wheels for gas compression, especially for use in turbochargers. This design is particularly suitable for compressor wheels, which typically use tilted blades that are angled between 30 and 60° from the vertical (parallel to the rotation axis) in the area of the outlet edge of the flow channel.

[0031] It is also conceivable for the surface contour to have the shape of a hyperbola, preferably a moderate hyperbola. Hyperbolas, and especially moderate hyperbolas, achieve a good balance between a stress-optimized result and a small cross-section of the joint section.

[0032] It is also conceivable for the surface contour to have a parabolic shape. Such a geometry leads to a very good compromise in terms of stress-optimized design, especially if a surface contour according to the invention is designed on the suction and pressure sides.

[0033] According to the invention, the surface contour forms a continuous surface that has the geometric parameter at least in partial areas. In particular, a corresponding geometric parameter can be designed in the highly stressed connecting areas along the longitudinal extension of the blades.

[0034] If it is intended that the channel bottom and the suction side and / or the channel bottom and the pressure side enclose a (suction-side or pressure-side) connection angle with one another in the area of the surface contour and that the surface contour is formed symmetrically to the bisector of this connection angle at least in a partial area, or that the connection points are the same distance from the intersection point, then the surface contour can be manufactured relatively easily and none of the boundaries (blade or channel bottom) is preferred in the load distribution.

[0035] However, it is also conceivable that the duct floor and the suction side and / or the duct floor and the pressure side enclose a suction-side or pressure-side connection angle with each other in the area of the surface contour, and that the surface contour is, at least in a partial area, symmetrical to an axis of symmetry that is not the bisector of this connection angle, or that the connection points are at different distances from the intersection point. In this way, the stresses of the blades and the area forming the duct floor are not treated equally, but one side is given priority over the other. In other words, the stresses can then be partially shifted to another area, thus reducing their maxima. This can be particularly useful when there are very different stresses on the blade and the duct floor.

[0036] It can also be provided that the axis of symmetry of the surface contour is tilted relative to the bisector of the connection angle.

[0037] In particular, it can be provided that the apex of the surface contour is located between the angle bisector of the connection angle and the channel floor. Thus, the cross-sectional area of the transition area between the surface contour and the blade is reinforced.

[0038] Alternatively, the apex of the surface contour can be arranged between the angle bisector of the connecting angle and a blade. This reinforces the cross-section of the transition area between the surface contour and the channel floor.

[0039] Preferably, the axis of symmetry not formed by the angle bisector should lie within an angular range corresponding to ±40%, preferably ±15%, of the enclosed connection angle between the blade and the channel bottom and measured from the angle bisector between the blade and the channel bottom. In this way, either the transition area between the surface contour and the blade side on the pressure or suction side or the transition area between the surface contour and the channel bottom can be effectively reinforced, depending on how the axis of symmetry is tilted relative to the angle bisector or whether the vertex of the surface contour is located between the angle bisector of the connection angle and the channel bottom or between the angle bisector of the connection angle and a blade.

[0040] A particularly effective impeller can be designed such that the channel bottom of the flow surface is concave, at least in a partial region, in the direction of the longitudinal extension of the blades adjoining the channel bottom. Particularly preferably, the channel bottom can be trumpet-shaped.

[0041] An alternative blade connection of a blade wheel according to the invention can be designed such that the surface contour in the areas adjoining the connection points is elliptical, parabolic or hyperbolic, and that the surface contour in the area passing through the apex has a geometrically different shape, in particular a contour that follows a circular segment.

[0042] A further alternative blade connection of a blade wheel according to the invention can be designed such that the surface contour is elliptical, parabolic, or hyperbolic in a first region adjoining one of the two connection points, and that the surface contour has a geometrically different shape in a second region adjoining the other of the two connection points, in particular a contour that follows a circular segment, and that the first and second regions are separated from one another by the angle bisector of the connection angle. Particularly preferably, the surface contour can have a continuous, in particular a tangent-continuous transition from the first to the second region.

[0043] Particularly high performance, especially in compressor wheels, can be achieved if the projections of at least two adjacent blades in a plane perpendicular to the rotation axis overlap at least partially, especially if the connection areas of two adjacent blades overlap in the radial direction. In other words, a radial plane through the rotation axis intersects at least the blade connections of two adjacent blades.

[0044] Furthermore, a blade wheel according to the invention can be designed such that at least two adjacent blades have a different length of blade length in the longitudinal direction of the flow channel. The longitudinal direction of the flow channel is the direction in which the flow channel is flowed through during operation.

[0045] In particular, effective radial or diagonal paddle wheels can be designed as paddle wheels within the scope of the invention.

[0046] The invention is explained in more detail below with reference to exemplary embodiments illustrated in the drawings. They show: Figure 1 : a sectional view of an exhaust gas turbocharger, Figure 2 : a compressor wheel of the exhaust gas turbocharger according to Figure 1 in perspective view, Figure 3 : the compressor wheel according to Figure 2 in rear view, Figure 4 : a schematic representation of a blade connection according to the invention in its cross-sectional plane, Figures 5A to 5C : alternative designs of the Figure 4 shown area of the compressor wheel in schematic representation, Figure 6 : the compressor wheel according to the previous illustrations in front view, Figure 7 : the compressor wheel according to the previous illustrations in a perspective side view, Figure 8 : a schematic representation of possible surface contours of the blade connection on the compressor wheel according to the Figures 1 to 7 and Figure 9 : a schematic representation of a surface contour tilted relative to the angle bisector.

[0047] Figure 1shows an exhaust gas turbocharger in side view and in section, wherein the compressor housing surrounding the compressor wheel 30 and the turbine housing surrounding the turbine wheel 20 are not shown. The exhaust gas turbocharger has a rotor 10 with a rotor shaft 11. The compressor wheel 30 is connected in a rotationally fixed manner to the turbine wheel 20 via the rotor shaft 11. The turbine wheel 20, driven by exhaust gas, thus transfers energy to the compressor wheel 30 for compressing air. The compressor wheel 30 sucks in the air to be compressed axially along the direction R and discharges the compressed air in the radial direction (perpendicular to R) into the compressor housing (not shown). The rotor shaft 11 has a central section which can have a taper. At its end facing the compressor, the central section has a stop 13. Accordingly, a circumferential collar 12 can be formed between the stop 13 and the taper of the central section.The stop 13 can preferably be designed as a shaft shoulder with a radially oriented surface that runs annularly around it. Adjacent to the collar 12, the rotor shaft 11 has a support section 14 on the compressor side. This support section can be designed in the form of a machined circumferential surface. The support section 14 transitions into a shaft section 15 for receiving the compressor wheel 30, which then terminates in a threaded section 16.

[0048] A bearing section 17 can preferably be provided on the side of the rotor shaft 11 opposite the threaded section 16. The bearing section 17 can be formed by machining the rotor shaft 11. The bearing section 17 of the rotor shaft 11 has a circumferential bearing contour.

[0049] Adjacent to the bearing section 17, the rotor shaft 11 can have a deflector 18 in the form of an oil slinger, for example, in the form of a diameter enlargement. In the present embodiment, the diameter enlargement is designed in the form of a circumferential collar. However, the deflector 18 can also have another suitable contour that effectively prevents or at least reduces oil leakage through the shaft passage in the bearing housing.

[0050] The rotor shaft 11 can also have a seal receptacle 19. In the present exemplary embodiment, two seal receptacles 19, for example in the form of piston ring grooves, are used, which are arranged axially spaced from one another. Piston rings are inserted into the seal receptacles 19. A turbine wheel 20 is arranged at the end of the rotor shaft 11 opposite the compressor wheel 30. The turbine wheel 20 can be integrally connected to the rotor shaft 11.

[0051] On the side facing away from the turbine wheel 20, the rotor 10 has a rotor part 40. This rotor part 40 has a base part 41. The base part 41 can, for example, have at least one circumferential seal receptacle 42 in the form of a piston ring groove. In the present embodiment, two circumferential seal receptacles 42 are used. Annular sealing elements 43 in the form of piston rings are inserted into the seal receptacle 42.

[0052] The rotor part 40 may have a bearing section 44 adjacent to the base part 41. The bearing section 44 forms a circumferential bearing contour, which may be similar or identical in construction to the bearing contour 17.

[0053] At its end facing the collar 12, the rotor part 40 can have a shoulder 45. The end face of the shoulder 45 is radially aligned. In this way, the shoulder 45 rests flat against the stop 13 of the collar 12. To ensure flat contact, the shoulder 45 is chamfered all the way around its inside. For this purpose, an undercut is machined into the rotor shaft 11 adjacent to the collar 12.

[0054] The base part 41 has Fig. 1 on the left has an annular and radially extending contact surface 48. This contact surface 48 is therefore parallel to the end face of the projection 45, which rests against the collar 12.

[0055] A compressor wheel 30 is pushed onto the rotor shaft 11 in the area of the shaft section 15. The compressor wheel 30 rests with a radially extending contact surface against the contact surface 48 of the rotor part 40. To fix the rotor part 40 and the compressor wheel 30, a nut 31 is screwed onto the threaded section 16. The nut 31 thus clamps the compressor wheel 30 against the rotor part 40 and the rotor part 40 against the stop 13. In this way, both the compressor wheel 30 and the rotor part 40 are axially fixed on the rotor shaft 11 and held there non-rotatably in the circumferential direction.

[0056] How Figure 1As can be seen, the exhaust gas turbocharger has a counter-bearing part 50, which is inserted into a bearing housing 60 of the exhaust gas turbocharger. The counter-bearing part has a central part 51. Lugs 53 adjoin the central part 51 on both sides. The two lugs 53 each have a circumferential bearing contour. This circumferential bearing contour is complementary to the bearing contour formed by the rotor part 40 or the bearing section 17 of the rotor shaft 11.

[0057] To Figure 1A fixing element 70 is used to fix the counter-bearing part 50 in the predetermined position shown in the drawing. The fixing element 70 has a holding section 72. This holding section 72 engages in a fixing receptacle 52 of the counter-bearing part 50. To install the fixing element 70, it can be inserted through a lubricant guide channel 61 of the bearing housing 60. To keep the fixing element 70 captive, it can be screwed, pressed, or secured with a holding element in the bearing housing 60.

[0058] Figure 2 shows the compressor wheel 30 in an enlarged view. As can be seen from this drawing, the compressor wheel 30 has a base body 32, which forms a hub. The base body 32 has a rear side 32.1, which can be designed as a curved, in particular concave, surface, as shown in FIG. Figure 1illustrated in more detail. Opposite the rear side 32.1, the compressor wheel 30 has a flow side 32.3. On the circumferential side, the base body 32 is circumferentially delimited by a circumferential edge U with a circular shape. The circumferential edge U can preferably merge into the rear side 32.1 by means of a rounded or beveled edge section 32.2 (see Figure 3 ).

[0059] Preferably, the flow surface 33 extends on the flow side 32.3 from a nose section 38 to the peripheral edge U. The nose section 38 can, as in the present embodiment, be designed as a hollow cylinder that is integrally connected to the base body 32. A chamfer can be provided in the transition between the nose section 38 and the flow surface 33.

[0060] As the Figure 2 and 3show, the base body 32 is penetrated by an opening 37, which is preferably designed as a bore. The opening 37 forms a central rotation axis R (see Figure 3 ), which runs from the rear side 32.1 to the flow side 32.3 of the nose section 38.

[0061] The nose section 38 forms a pressure surface 38.1, which runs annularly around the opening 37 and serves to support the nut 31. As Figure 1 shows, the compressor wheel 30 rests with a contact section 39 of the rear side 32.1 on the contact surface 48 of the rotor part 40.

[0062] A plurality of blades 35 are arranged on the flow surface 33 and protrude beyond the flow surface 33. The blades 35 are each integrally connected to the flow surface 33 and thus to the base body 32 via a connecting section 36.

[0063] How Figure 2As illustrated, two types of blades 35 can be used on a compressor wheel 30. For example, blades 35 of different lengths can be arranged alternately on the flow surface 33. In principle, however, more than two types of blades on a compressor wheel are also conceivable.

[0064] The blades 35 preferably extend from the nose section 38 in the direction of the circumferential edge U. At least some of the blades 35 preferably extend in a spiral manner, so that these blades 35 extend in the circumferential direction on the flow surface 33.

[0065] The blades 35 have a pressure side 35.3, which is "red" in the direction of rotation (see Figure 2 ) is oriented. Opposite the pressure side 35.3, the blades 35 have a suction side 35.2. This suction side 35.2 is oriented opposite to the direction of rotation "red".

[0066] Opposite the connecting section 36, the blades 35 terminate with an edge that forms a radial end region 35.1 of the blades 35. In the radially outer edge region of the base body 32, the blades 35 have a trailing edge 35.4 that circumferentially delimits the flow surface 33 and a (front) leading edge 35.5 in the end region facing the nose section 38.

[0067] For example, the trailing edges 35.4 of the blades 35 may merge flush with the peripheral edge U of the base body 32. However, it is also conceivable that the trailing edges 35.4 of the blades 35 extend at least partially beyond the peripheral edge U of the base body 32, thus forming a so-called "extended tip."

[0068] Flow channels 34 are formed between two adjacent blades 35. The flow channel 34 has a channel bottom 34.1 formed by the flow surface 33. On its longitudinal sides, the flow channel 34 is delimited by the associated sides of the blades 35. Accordingly, a pressure side 35.3 of a first blade 35 and a suction side 35.2 of an adjacent second blade 35, together with the channel bottom 34.1, delimit the flow channel 34. On the side opposite the channel bottom, the flow channel 34 is formed by a contour of the compressor housing surrounding the compressor wheel 30 in the region of the radial end region 35.1.

[0069] In the present compressor wheel 30, air is conveyed via an inlet 34.3 located radially inward or facing the nose section 38 to a radially outer outlet 34.2 of the flow channels 34.

[0070] At the Figure 2In the design shown, in which blades 35 of different lengths are used, a flow channel 34 is divided into two flow channel sections 34a and 34b. Downstream of the inlet 34.3 of the flow channel 34 and upstream of the leading edge 35.5 of the short blades 35, a first flow channel section 34a is formed, which is delimited in the circumferential direction by two long blades 35. Downstream of the leading edge 35.5 of the short blades 35, the flow channel 34 branches into two flow channel sections 34b separated from one another by a short blade 35, which are each delimited in the circumferential direction by a short blade 35 and a long blade 35. Between adjacent blades 35, a channel base 34.1 is provided, which is delimited by a pressure side 35.3 of a first blade 35 and a suction side 35.2 of a second blade 35.

[0071] The Figure 2 and 3The hatched areas show the main load areas in which the greatest stresses are to be expected in the compressor wheel 30 during operation: the rear side 32.1, the connecting sections 36 and the blades 35 in the area of the trailing edges 35.4.

[0072] In Figure 4 the design of the connecting section 36, with which the blades 35 are connected in one piece to the base body 32, is detailed in more detail.

[0073] Figure 4 shows a section through one of the blades 35, with a section path in a cross-sectional plane perpendicular to a center line of a rolling ball rolling on the blade 35 and the channel bottom 34.1. As the illustration illustrates, the suction side 35.2 and the pressure side 35.3 merge into the channel bottom 34.1 of the adjoining flow channels 34. At least one of these transitions, preferably both transitions, are formed by a surface contour 36.1 according to the invention.

[0074] Accordingly, the surface contour 36.1 is designed such that it transitions continuously into the suction side 35.2 and the duct floor 34.1 at connecting points P and Q. Respectively, the surface contour 36.1 is designed such that it transitions continuously into the pressure side 35.3 and the adjoining duct floor 34.1 at connecting points P and Q.

[0075] In the following, the transition between the pressure side 35.3 and the adjoining channel bottom 34.1 is described using the Figure 4 explained in more detail. Analogous explanations also apply to the transition from the suction side 35.2 to the channel bottom 34.1 of the adjacent flow channel 34.

[0076] How Figure 4 shows, two tangents T1, T2 can be applied to the connecting points P, Q. These two tangents T1, T2 form an intersection point D in the area of the connecting section 36. A virtual connecting line V can be formed between the connecting points P, Q.

[0077] The connecting section 36 has a groove-shaped surface contour that is concave. Accordingly, the surface contour 36.1 forms a vertex S between the connecting points P, Q.

[0078] Figure 4 illustrates that a first distance line formed perpendicular to the virtual connecting line V, which runs through the vertex S, forms a first distance VS between the vertex S and the virtual connecting line V. A second distance line formed perpendicular to the virtual connecting line V, which runs through the intersection point D of the tangents T1, T2, forms a second distance VD between the intersection point D and the virtual connecting line V. According to the invention, the surface contour 36.1 is designed such that a geometric parameter GP, which is determined by the ratio of the first distance VS to the second distance VD: VS : VD in the range from 0.3 to 0.7. Preferably, the surface contour 36.1 forms a continuous and continuously differentiable curve. This curve is particularly preferably configured as a parabola, hyperbola, or ellipse, wherein, in the case of an ellipse, the ratio of the major semi-axis to the minor semi-axis is preferably selected in the range greater than or equal to 5, preferably in the range greater than or equal to 10.

[0079] For gas compressors, in particular exhaust gas turbochargers, a design has proven particularly suitable in which the surface contour 36.1 is designed with a geometry parameter GP in the range between 0.4 and 0.6.

[0080] In the Figures 5A to 5C various possible surface contours 36.1 according to the invention are illustrated. Figure 5a shows a surface contour 36.1 formed by an ellipse. Figure 5bshows an embodiment in which the surface contour 36.1 is formed by a parabola. Figure 5c shows an embodiment in which the surface contour 36.1 is formed by a hyperbola.

[0081] With the curve design according to the invention, the surface contour 36.1 preferably extends over the entire length of the pressure side 35.3 and / or the suction side 35.2. However, it is also conceivable that this surface contour 36.1 according to the invention is used only over a partial region of the longitudinal extent of the connecting section 36. Furthermore, it is conceivable that the surface contour 36.1 according to the invention changes geometrically along the longitudinal extent of the blade 35.

[0082] In principle, the permissible stresses in the connecting sections 36 must not be exceeded. The greatest stress arises due to centrifugal forces, typically in a radially outer region of the connecting sections 36 in the area of the trailing edges 35.4. If the connecting section 36 is reinforced, e.g., by a larger transition radius between the channel bottom 34.1 and the pressure side 35.3 and / or the suction side 35.2 according to a surface contour 36.1 from the prior art, this has a detrimental effect on a connecting section 36 of an adjacent blade located further inward in a radial direction, where the stress limit can then be exceeded. Accordingly, in compressor wheels of the type shown, the main load with regard to the connecting sections 36 arises at the pressure-side blade connection of a first blade 35 (see Figure 6). It occurs approximately where a straight line or plane drawn radially through the rotation axis R through the center of the blade connection of the trailing edge 35.4, in particular through the center of the suction-side surface contour 36.1 in the area of the trailing edge 35.4, of the neighboring blade 35 located in the direction of rotation "red" in front of the first blade 35, intersects the pressure-side blade connection of the first blade 35. Accordingly, in Figure 6 This area is marked with a dashed oval.

[0083] By means of a connecting section 36 according to the invention, at least in the radially outer section of a connecting section 36 of a neighboring blade 35, the stresses in the (pressure-side) connecting section 36 of the first blade 35 can be reduced if the connecting section 36 of the first blade 35 lies in the region of a radial fiber through the radially outer section of a connecting section 36 of the neighboring blade 35. In Figure 6 The course of such a radial fiber is indicated by an arrow along the radial direction to the rotation axis. A section of the connecting section 36 of the adjacent blade 35, which influences a connecting section 36 of a first blade 35 (indicated by a dashed oval), is shown as an example. Figure 7A region of the pressure-side connecting section 36 of a first blade 35 is shown in sharp focus, which is influenced along a radial fiber by a radially outwardly located, inventive surface contour 36.1 of the connecting section 36 of an adjacent blade 35. In other words, a surface contour 36.1 according to the invention reduces both the stresses in the connecting section 36 of the associated blade 35 and the stresses on connecting sections 36 of adjacent blades 35 located further inward along a radial direction.

[0084] How Figure 6shows, the position of this highly stressed area can vary depending on the angular extension of the blade 35, i.e., the extension of the blade 35 in the circumferential direction, the connection angle between the blade 35 and the channel bottom 34.1, and the specific design of the flow channels 34. In the area of the trailing edge 35.4 of the blades 35, it does not have to be exactly in the direction of a radial fiber through the center of the blade connection of the trailing edge 35.4. In common compressor wheels for turbochargers of the type shown in the drawings, this highly stressed area varies by ±15° in the circumferential direction around the described intersection point. This highly stressed area is usually shifted against the "red" direction of rotation to the radial fiber by the trailing edge 35.4.

[0085] In Figure 7This area, which varies by ±15°, is indicated by hatching. Preferably, the surface contour 36.1 according to the invention extends at least over a radially outer portion of the connecting portion 36, so that the connecting portions 36 do not exceed the permissible stresses.

[0086] In Figure 8 Possible surface contours 36.1 are illustrated and compared with a surface contour K, which results from the rolling process described above, in which a circular rounding surface is selected.

[0087] The dash-dotted surface contours 36.1 are formed by hyperbolas. The long-dashed surface contour 36.1 is formed by a parabola. The two short-dashed surface contours 36.1, which adjoin the circular surface contour K, are formed by ellipses.

[0088] The illustration clearly illustrates that with the designs according to the invention, connecting sections 36 can be designed that have a significantly smaller cross-section than connecting sections 36 that have a circular surface contour K. It is the case that with the surface contours 36.1 according to the invention, even though less material is used, a higher load-bearing capacity can be achieved than with the circular surface contour K.

[0089] Since a lower mass is required for the connecting section 36, the overall mass of the compressor wheel 30 is also reduced. However, since the connection according to the invention now offers a higher load-bearing capacity than that achieved by a surface contour K with a circular shape, a greater load on the blades 35 is also possible. In particular, higher rotational speeds for the compressor wheel 30 are then possible. More effectively designed blade geometries can also be used, which would not be sufficiently load-bearing or able to be connected to the base body 32 in a robust manner with a circular surface contour K. This would also not be possible if the radius of the circular surface contour K were reduced, but is attributable exclusively to the shape of the surface contour 36.1 according to the invention.

[0090] Figure 8clearly illustrates that due to the smaller space requirement of the connecting section 36, the free surface in the flow channel 34 is also increased in favor of improved performance.

[0091] A symmetrical surface contour 36 can be constructed according to the invention as follows: As with the blade connection with a circular cross-section, a sphere rolls along the blade surface and the adjacent hub surface, creating two lines of contact. A cross-sectional plane is introduced perpendicular to the center curve of the rolling sphere. The cross-sectional plane intersects the contact lines of the rolling sphere, and the resulting points P and Q are connected with a virtual connecting line V. On the cross-sectional plane, tangents T1 and T2 are drawn through points P and Q to the respective body surface (pressure side 35.3 or suction side 35.2 or channel bottom 34.1). The intersection point of tangents T1 and T2 is point D. The connection of P, Q, and D results in a triangle. A coordinate system with origin O is placed on the straight line PQ. The abscissa axis corresponds to the direction vector of the straight line QP and the ordinate axis runs perpendicular to it through the intersection point D of the two tangents T1 and T2.The boundary line of the blade connection results from a conic section or a linear combination of conic sections, which contains or contains the points P and Q and is or are tangent to the body surfaces at these points, with a geometry parameter GP. .

[0092] The geometry parameter GP is defined as the quotient of the lengths (OS) and (OD): GP = OS ¯ OD ¯

[0093] The range of GP, which is particularly relevant for turbomachinery, ranges from approximately 0.3 to 0.7, where in the case of conic sections: Values less than 0.5 describe ellipses, the value 0.5 describes a parabola and values greater than 0.5 describe hyperbolas.

[0094] In most cases, values between 0.4 and 0.6 lead to the best results in terms of stress optimization, i.e. in the case of conic sections the transition area from ellipses to hyperbolas.

[0095] For example, in compressor wheels with a pressure-side connection angle of 70° and a surface contour 36.1 aligned symmetrically to the angle bisector 36.2, it has been shown that a geometry parameter GP of at least 0.47 or an ellipse ratio of at least 2.5 leads to a significantly improved stress distribution.

[0096] For compressor wheels with a pressure-side connection angle of 45° and a surface contour 36.1 aligned symmetrically to the angle bisector 36.2, a geometry parameter GP of at least 0.4 or an ellipse ratio of at least 2.25 leads to a significantly improved stress distribution.

[0097] For compressor wheels with a pressure-side connection angle of 40° and a surface contour 36.1 aligned symmetrically to the angle bisector 36.2, a geometry parameter GP of at least 0.47 or an ellipse ratio of at least 5.9 leads to a significantly improved stress distribution.

[0098] For the blade tilts typically used on compressor wheels at the trailing edge (trailing edge 35.4) of 30° to 60° relative to the vertical (parallel to the rotational axis R), ellipse ratios (ratio of the major to the minor semi-axis) of 1.5 and greater, preferably 5 and greater, particularly preferably 10 and greater, have proven effective. Ellipse ratios of 5 and greater, preferably 10 and greater, have proven particularly advantageous for blade tilts at the trailing edge (trailing edge 35.4) of 45° to 60° relative to the vertical (parallel to the rotational axis R).

[0099] With a clever choice of the rolling ball diameter (and thus the beginning of the blade connection), a value of 0.5 (parabola) often results in the best possible compromise between the stress on the pressure side and the stress on the suction side of the blade connection. A further advantage of a value of 0.5 for the geometry parameter GP is that machining the surface contour 36.1 is generally more economical with smaller geometry parameters, while larger geometry parameters can offer advantages in terms of load distribution.

[0100] A possible (but not exclusive) mathematical description of a curve symmetrical to the angle bisector is as follows: F 0 x y = y = 0 F 1 x y = y − ax + b = 0 Geradengleichung Tangente QD in allg . Form F 2 x y = y + ax + b = 0 Geradengleichung Tangente PD in allg . Form G x y μ = 1 − μ * F 1 x y * F 2 x y − μ * F 0 x y ∧ 2 = 0

[0101] By solving G for y, one obtains the equation of the boundary line as a function of x and µ.

[0102] For µ < 0.5, hyperbolas result (cf. Fig.5 c) .

[0103] For µ > 0.5 ellipses result (cf. Fig. 5 a) , where the ellipse degenerates into a circle for a value of µ=(a 2< +1) / (a 2< +2), thus defining the limiting case for the orientation of the semi-major axis, e.g., along the angle bisector 36.2 or perpendicular to it. This clearly shows that the elliptical region, or the transition to a circle, depends on the choice of parameter a, i.e., the inclination of the blade 35. Parabolas result between µ < 0.5 and µ > 0.5.

[0104] Alternatively, instead of a single rolling ball, different rolling balls can be used to determine P and Q, which corresponds to the selection of arbitrary points P and Q on the pressure side 35.3 and / or the suction side 35.2 or the channel floor 34.1. This allows the creation of ellipses, parabolas, or hyperbolas that are tilted relative to the previously described shape, i.e., their axis of symmetry 36.3 no longer runs along the angle bisector 36.2. The resulting surface contour 36.1 is therefore only symmetrical in certain areas. Preferably, the axis of symmetry 36.3 should lie in an angular range which corresponds to + / - 40%, preferably + / - 15% of the connection angle enclosed by the pressure side 35.3 or the suction side 35.2 and the channel bottom 34.1 (pressure-side or suction-side) and is measured from the angle bisector 36.2 between the pressure side 35.3 or the suction side 35.2 and the channel bottom 34.1.As a result, the stresses on blade 35 and base body 32 are not treated equally, but rather one side is given priority over the other. The stresses are thus shifted to one area or the other. This can be useful if the stresses on blade 35 and base body 32 differ significantly.

[0105] Figure 9schematically illustrates, using a blade connection of a compressor wheel 30, a tilting of the axis of symmetry 36.3 of a surface contour 36.1 formed by a parabola with respect to the angle bisector 36.2. In the example shown, the parabola is rotated with respect to a parabola (shown in dashed lines) that is aligned symmetrically to the angle bisector 36.2 and serves as a reference, such that the connection point P on the pressure side 35.3 of the blade 35 moves away from the intersection point D along the tangent T1, while the connection point Q on the duct floor 34.1 moves towards the intersection point D along the tangent T2. The distance of the connection point P from the intersection point D is therefore greater than the distance of the connection point Q from the intersection point D. The vertex S of the parabola then lies between the angle bisector 36.2 of the connection angle and the duct floor 34.1. The transition region of the surface contour 36.1 to the blade 35 reinforced in cross-section.

[0106] Likewise, the connecting section 36 can be reinforced in the area of the channel bottom 34.1 if the distance of the connecting point Q from the intersection point D is greater than the distance of the connecting point P from the intersection point D. The vertex S of the parabola then lies between the angle bisector 36.2 of the connection angle and the pressure side 35.3 of the blade 35. Thus, the transition area of the surface contour 26.1 to the channel bottom 34.1 is reinforced in terms of cross section.

[0107] It is understood that a cross-sectional reinforcement of the transition area of the surface contour 36.1 to the blade 35 or of the transition area of the surface contour 36.1 to the channel bottom 34.1 can be achieved not only for a parabola, but also in a corresponding manner for an ellipse or a hyperbola.

[0108] A surface contour 36.1 according to the invention is relatively complex to produce with a ball-end milling cutter, since a very small milling cutter tip radius would be required in this area to create a corresponding non-circular geometry. By using a suitable form milling cutter, the milling operations in the area of the connecting section 36 can be significantly reduced. However, if the connection angle of the blade 35 relative to the base body 32 changes over the length of the blade 35, it is difficult to create the surface contour 36.1 with a form milling cutter using one milling path. However, with a symmetrical surface contour 36.1, it is conceivable to design the form milling cutter in such a way that it creates a good approximation of the blade-side half and the channel-bottom-side half over the length of the surface contour 36.1, so that the surface contour 36.1 can be produced, for example, with just two milling operations.It is particularly advantageous to produce the impeller according to the invention by primary molding, for example, by a casting process or an additive process (e.g., by 3D printing). With an impeller according to the invention produced by a casting process, the effort required to machine the surface contour 36.1 only occurs once during mold production. With an additively manufactured impeller according to the invention, the surface contour 36.1 according to the invention does not result in any additional effort, but rather even results in a slight saving due to the reduced material consumption and the resulting shortened construction time.

[0109] Typically, the material properties of cast materials do not match those of wrought alloys, which is why in many cases the significantly more expensive process of milling compressor wheels 30 from forged or semi-finished bar stock must be chosen. With the surface contour 36.1 according to the invention, the maximum stress level of the compressor wheels 30 can be reduced sufficiently in some cases that they can be manufactured using a casting process and thus produced significantly more cost-effectively.

[0110] For certain applications, it is necessary to coat a blade wheel. The service life of coated blade wheels is largely determined by the properties of the coating, while the base material has a subordinate influence on the service life. To improve the service life of the blade wheel, it may therefore be necessary to reduce the stress level in the coating. By means of a blade connection 36 according to the invention, the stress level of the blade wheel, and thus also the stress level in its coating, can be reduced, which leads to an improvement in the service life. In other words, the use of a blade connection 36 according to the invention allows a coating of blade wheels that would otherwise not meet the service life requirements of certain applications due to this very coating.Other measures, such as the introduction of residual stresses, are partly no longer required by using the blade connection 36 according to the invention. Another major advantage is that a blade connection 36 according to the invention can lead to an increase in service life even when other measures have already been exhausted.

[0111] The invention thus also includes impellers that are provided with a coating on at least a portion of the blades 35 or have a conversion layer on their surface. A layer of Al2O3 or nickel-phosphorus can be used as the coating or conversion layer.

Claims

1. Blade wheel, in particular compressor wheel (30) or turbine wheel (20), preferably for a gas compressor or turbocharger, with a base body (32) that has a flow side (32.3) and a rear side (32.1) opposite the flow side (32.3), wherein a flow surface (33) is formed on the flow side (32.3), wherein blades (35) project from the flow surface (33), wherein the blades (35) are connected integrally to the flow surface (33) via a connecting section (36), wherein an axis of rotation (R) of the blade wheel extends between the flow side and the rear side (32.3, 32.1), wherein a flow channel (34) with a channel bottom (34.1) is formed between at least two neighboring blades (35), wherein the blades (35) extend longitudinally in the direction of the flow channel longitudinal direction and each have a pressure side (35.3) and a suction side (35.2) opposite the pressure side, wherein one of the neighboring blades (35) delimits the flow channel (34) with its pressure side (35.3) and the other of the neighboring blades (35) delimits the flow channel (34) with its suction side (35.2), and wherein the connecting section (36) forms a throat-shaped surface contour (36.1) extending along the connecting section (36) in the transition from the channel bottom (34.1) to the pressure side (35.3) of the one blade (35) and / or in the transition from the channel bottom (34.1) to the suction side (35.2) of the neighboring blade (35), wherein, in a cross section through at least one of the blades (35) transverse to the longitudinal extension of the blade (35), the surface contour (36.1), in the cross-sectional plane, is designed such that it merges into the suction side (35.2) and the channel bottom (34.1) at connection points (P, Q) into the suction side (35.2) and the channel bottom (34.1) continuously differentiably and / or wherein the surface contour (36.1) is designed, in the cross-sectional plane, such that it merges into the pressure side (35.3) and the channel bottom (34.1) at connection points (P, Q) continuously differentiable, wherein the surface contour (36.1), in the cross-sectional plane, has, at least in some areas, the shape of a conical section or, at least in some areas, the shape of a linear combination of conical sections, wherein the surface contour (36.1) forms a continuous surface, which has, at least in some areas, an ellipse, a parabola or a hyperbola, wherein two tangents (T1, T2) passing through the connection points (P, Q) in this cross-sectional plane form an intersection point (D), characterized in that the surface contour (36.1) forms an apex (S) between the connection points (P, Q), that a virtual connecting line (V) is formed between the connection points (P, Q), that a first distance line formed perpendicular to the virtual connecting line (V) and passing through the apex (S) forms a first distance value (VS) between the apex (S) and the virtual connecting line (V), that a second distance line formed perpendicular to the virtual connecting line (V) and passing through the intersection point (D) of the tangents (T1, T2) forms a second distance value (VD) between the intersection point (D) and the virtual connecting line (V), and that a geometry parameter (GP), which is determined by the ratio of the first distance value (VS) to the second distance value (VD) VS / VD is selected in the range from 0.3 to 0.7.

2. Blade wheel according to claim 1, characterized in that the geometry parameter (GP), which is determined by the ratio of the first distance value (VS) to the second distance value (VD), is selected in the range from 0.4 to 0.6, particularly preferably = 0.5.

3. Blade wheel according to claim 1 or 2, characterized in that that the surface contour (36.1) is elliptical, parabolic or hyperbolic in the areas adjacent to the connection points (P, Q), and that the surface contour (36.1) has a geometrically different shape in the area passing through the apex (S), in particular a contour that follows a circular segment.

4. Blade wheel according to one of claims 1 to 3, characterized in that the surface contour (36.1) has the shape of an ellipse with a ratio of the major semi-axis to the minor semi-axis: major semi − axis / minor semi − axis greater than or equal to 1.5, preferably greater than or equal to 5, particularly preferably greater than or equal to 10, or that the surface contour (36.1) has the shape of a hyperbola, or that the surface contour (36.1) has the shape of a parabola.

5. Blade wheel according to one of claims 1 to 4, characterized that the channel bottom (34.1) and the suction side (35.2) and / or the channel bottom (34.1) and the pressure side (35.3) enclose a connection angle with one another in the region of the surface contour (36.1) and that the surface contour (36.1) is formed symmetrically with respect to the bisector (36.2) of this connection angle at least in a partial region, or that the connection points (P, Q) are equidistant from the intersection point (D).

6. Blade wheel according to one of claims 1 to 5, characterized that the channel bottom (34.1) and the suction side (35.2) and / or channel bottom (34.1) and the pressure side (35.3) enclose a connection angle with one another in the region of the surface contour (36.1) and that the apex of the surface contour (36.1) is arranged between the bisector (36.2) of the connection angle and the channel bottom (43.1) or that the apex of the surface contour (36.1) is arranged between the bisector (36.2) of the connection angle and the blade (35).

7. Blade wheel according to claim 6, characterized in that the surface contour (36.1) is formed, at least in a partial region, symmetrically with respect to an axis of symmetry (36.3) which is not the bisector (36.2) of this connection angle, and that the axis of symmetry of the surface contour (36.1) is tilted relative to the bisector (36.2) of the connection angle, or that the connection points (P, Q) are at different distances from the intersection point (D).

8. Blade wheel according to claim 7, characterized that the axis of symmetry (36.3) forms an angle with the bisector (36.2) of the connection angle, which is preferably in a range between 15% of the connection angle and 40% of the connection angle, measured from the bisector (36.2) of the connection angle.

9. Blade wheel according to one of claims 1 to 8, characterized in that the channel bottom (34.1) of the flow surface (33) is designed concave at least in a partial region in the direction of the longitudinal extension of the flow channel.

10. Blade wheel according to one of claims 1 to 9, characterized in that the projections of at least two neighboring blades (35) overlap in a plane perpendicular to the axis of rotation, at least in some areas.

11. Blade wheel according to one of claims 1 to 10, characterized in that at least two neighboring blades (35) have a different longitudinal extension in the direction of the longitudinal extension of the flow channel.

12. Blade wheel according to one of claims 1 to 11, characterized in that it is a radial or diagonal blade wheel.

13. Blade wheel according to one of claims 1 to 12, characterized in that the blade wheel is integrally formed, in particular as a metal casting or as a plastic casting, and / or in that the blade wheel has at least one surface coating, and / or in that the blade wheel has a conversion layer on its surface.

14. Gas compressor, in particular turbocharger with a blade wheel according to one of claims 1 to 13.