Method for balancing a turbine wheel of an exhaust gas turbine and balanced turbine wheel

Abstract

A method for balancing an exhaust gas turbine turbine wheel (10) and a balanced turbine wheel (10) are described. The exhaust gas turbine turbine wheel has a hub rear wall (15) facing away from a fluid flow region and has a recess (13) formed by material removal and a marking bead (16).

Description

[Technical Field]

[0001] The present disclosure relates to a method for balancing a turbine wheel of an exhaust gas turbine by forming a mass removal area of ​​defined shape and position on the rear hub wall of the turbine wheel of the exhaust gas turbine, and a balanced turbine wheel for an exhaust gas turbine. [Background technology]

[0002] Exhaust gas turbines are used to utilize the energy contained in exhaust gases. To extract energy from the exhaust gas flow, a turbine wheel of the exhaust gas turbine is used, which is arranged in the exhaust gas flow and has a hydro-mechanically optimized shape. Here, the turbine wheel is arranged on a shaft and is mounted so that it can rotate around the axis of rotation.

[0003] Due to the high rotational speed of the turbine wheel of an exhaust gas turbine and its position in the exhaust gas flow path, the turbine wheel is a component of the exhaust gas turbine that is subjected to high thermal and mechanical loads. In particular, the mechanical loads in the turbine wheel of an exhaust gas turbine are large, and are largely due to the high rotational speed and the associated centrifugal forces. Deviations in the mass distribution on the periphery of the turbine wheel play a key role here, as they can disrupt the turbine wheel's out-of-roundness and potentially generate additional loads. Therefore, mass unevenly distributed on the periphery, known as imbalance, is actively addressed by both structural measures and subsequent machining of the turbine wheel of an exhaust gas turbine.

[0004] In the prior art, in order to reduce imbalance of the turbine wheel of an exhaust gas turbine, a balancing rim is usually provided on the rear wall of the hub. The balancing rim takes the form of a convex bead extending in the circumferential direction of the rear wall of the hub. During the balancing process, the balancing rim can be removed in a defined manner, so that an even distribution of the mass in the circumferential direction of the turbine wheel of the exhaust gas turbine is achieved. It is known to remove the balancing rim using a surface grinding process.

[0005] However, balancing rims provided for the balancing process have many drawbacks, including, but not limited to, providing, designing, and calculating additional components (and therefore mass) on the exhaust gas turbine turbine wheel, additional machining processes required in the manufacturing process, and adverse effects on the internal load distribution and stress of the exhaust gas turbine turbine wheel. Adding mass to the exhaust gas turbine turbine wheel, which rotates at high speeds, creates additional centrifugal forces and adverse characteristics of the balancing rim, which are detrimental to the mechanical stresses within the exhaust gas turbine turbine wheel. Therefore, balancing rims also have an adverse effect on cycle capability, particularly with respect to low cycle fatigue, also referred to herein as low cycle capability.

[0006] In view of the above, there is a need for a method for balancing a turbine wheel of an exhaust gas turbine, and a corresponding balanced turbine wheel, which can at least partially reduce the above-mentioned drawbacks. U.S. Patent Application Publication No. 2020 / 392848 describes an exhaust gas turbocharger wheel having a hub with lugs, a rear disc with a shaft connection, a rotation axis, and blades extending from the hub to define an exhaust gas flow path. U.S. Patent Application Publication No. 8,936,439 also describes a turbine wheel having a rear side disposed around a shaft and having a separator disposed thereon, an inner undercut disposed between the separator and the shaft, and an outer periphery allocated to the rear side. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Patent Application Publication No. 2020 / 392848 [Patent Document 2] U.S. Patent No. 8,936,439 Summary of the Invention [Means for solving the problem]

[0008] This object is achieved by a method for balancing a turbine wheel according to claim 1. This object is further achieved by a turbine wheel according to claim 8 and an exhaust gas turbine according to claim 12. Further embodiments, modifications and improvements arise from the following description and the appended claims.

[0009] According to one aspect of the present invention, there is provided a method for balancing a turbine wheel for an exhaust gas turbine. The turbine wheel is rotatable about an axis of rotation and has a hub and a plurality of turbine blades attached to the hub and disposed in a fluid flow region. The hub has a rear wall facing away from the fluid flow region and including a marking bead extending concentrically about the axis of rotation. The method includes: moving an elliptical-shaped material removal tool relative to the turbine wheel at a mass removal location adjacent the marking bead; creating a mass-removal recess in the hub rear wall that is asymmetric with respect to the axis of rotation for balancing the turbine wheel by removing hub material in the hub rear wall adjacent the marking bead with a material removal tool and leaving the marking bead intact; Includes:

[0010] According to one aspect of the present invention, a turbine wheel for an exhaust gas turbine is provided, the turbine wheel being rotatable about a rotation axis and including a hub and a plurality of turbine blades attached to the hub and disposed in a fluid flow region, the hub having a hub rear wall facing away from the fluid flow region. A mass removal recess asymmetrical with respect to the rotation axis is provided in the hub rear wall for balancing the turbine wheel. The mass removal recess is configured as a concave recess in the hub rear wall having a cross-sectional profile in the form of an elliptical segment, the cross-sectional profile being defined in a cross-sectional plane ZZ that includes the rotation axis. The hub rear wall further includes a marking bead extending concentrically with the rotation axis, the marking bead and the mass removal recess being adjacent to each other without radial overlap.

[0011] According to a preferred embodiment of the present invention, the mass removal recess is configured as a concave recess in the rear wall of the hub, eliminating the need for a balancing rim on the rear wall of the hub. In particular, after balancing, the rear wall of the hub can be free of rotationally asymmetric convex protrusions. This reduces the rotational mass and inertia of the hub. This reduction in inertia can contribute to improving the acceleration behavior of the rotor. The cross-sectional profile of the mass removal recess is an elliptical segment, further reducing stresses in the hub and avoiding additional loads.

[0012] The invention is explained in more detail below with reference to non-limiting embodiments, the scope of protection being defined by the claims.

[0013] The accompanying drawings illustrate embodiments and, together with the description, serve to explain the principles of the invention. Elements in the drawings are relative to each other and are not necessarily to scale. Like reference numerals indicate like elements. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a top view of a hub rear wall (15) of a turbine wheel (10) of an exhaust gas turbine according to one embodiment. [Figure 2] 2 shows a radial cross section of the turbine wheel (10) of FIG. 1 along the cross section plane ZZ. [Figure 3] A radial cross section similar to that of FIG. 2 is shown with the geometric dimensions of the individual (sub)components. [Figure 4] 3 shows a detailed view of the cross section of FIG. 2. [Figure 5] 1 shows a radial cross section of a turbine wheel (10) along a cross section plane ZZ during the execution of a method according to one embodiment of the invention. DETAILED DESCRIPTION OF THE INVENTION

[0015] A turbine wheel (10) of an exhaust gas turbine according to one embodiment will now be described with reference to Figures 1 to 4. The turbine wheel (10) is rotatable about its axis of rotation (11).

[0016] 1 shows a schematic top view of a hub back wall (15) of an exhaust gas turbine turbine wheel (10) according to one embodiment. The turbine wheel (10) has been balanced using the method described herein. The drawing shows a hub back wall (15) design with a scallop (undulating edge) on the radially outer edge of the hub back wall (15) of the exhaust gas turbine turbine wheel (10). The scalloped design is not strictly necessary; alternatively, the hub back wall could be, for example, rounded.

[0017] The drawing shows schematically a plurality of turbine blades mounted to the hub (12) radially outwardly of the hub (12) and positioned in a fluid flow region (14).

[0018] The hub rear wall 15 further has a marking bead 16 that is rotationally symmetrical about the rotation axis 11 and arranged concentrically with the rotation axis 11. The marking bead 16 can be arranged at any radial position on the hub rear wall 15, preferably in the radially outer half of the hub rear wall 15, and particularly preferably in the radially outer one-third of the hub rear wall 15. Here, the marking bead forms a protrusion on the base surface of the hub rear wall 15 and can therefore protrude axially beyond the base surface.

[0019] Furthermore, the hub rear wall (15) is provided with a mass removal recess (13). The mass removal recess (13) is configured as a circular arc extending around the rotation axis (11). The mass removal recess (13) therefore extends concentrically with the marking bead (16) that serves as a visual reference. The mass removal recess (13) is not rotationally symmetrical but is angled circumferentially, covering only a portion of the hub rear wall, an angular area of ​​up to 180°, i.e., up to half of the hub rear wall (15). The mass removal recess (13) serves to balance the turbine wheel (10), and its dimensions are set according to the determined imbalance.

[0020] The mass relief recess (13) extends radially outward of and immediately adjacent to the marking bead (16). The mass relief recess (13) extends across the radially outer half, preferably the radially outer one-third, of the hub rear wall (15). The marking bead (16) may be radially spaced from the mass relief recess (13).

[0021] Figures 2 and 3 are cross-sectional views of the turbine wheel (10) of Figure 1, with cross-sectional plane ZZ including the axis of rotation (11). The drawings show the turbine wheel (10) rotatable about the axis of rotation (11) with a hub (12). Forward of the hub (12) is the fluid flow region (14) of the turbine wheel (10); the turbine blades disposed on the hub (12) in the fluid flow region (14) are not shown. The cross-sectional contours of the mass-removal recesses (13) and the marking beads (16) can be seen on the rear wall (15) of the hub.

[0022] Figure 3 shows the same cross-sectional view as Figure 2, with geometric dimensions. F denotes the diameter of the rear wall of the turbine wheel (10). The diameter F of the turbine wheel (10) of an exhaust gas turbine is defined as the smallest diameter through the axis, i.e., the diameter relative to the radially innermost extent of the hub rear wall, in the case of a non-circular rear wall. In the case of scallops, as shown in Figure 1, the diameter F refers to the radially innermost (smallest) diameter of the hub (12). In the embodiment of Figure 1, this is the radius in the cross-sectional plane ZZ. In another embodiment (not shown), there are no scallops, and the hub rear wall is circular with a constant diameter F.

[0023] FIG. 3 also shows the geometric dimensions and relationships of the elements of the hub rear wall 15, particularly the mass relief recesses 13 therein. The mass relief recesses 13 are designed in cross section as elliptical segments, with H representing the semi-major axis of the ellipse and B representing the semi-minor axis of the ellipse. The penetration depth C of the mass relief recesses 13 is the penetration depth of the ellipse into the hub rear wall 15. Here, C is more precisely defined as the deepest penetration depth relative to the contour of the hub rear wall 15 without the mass relief recesses 13. This contour without the mass relief recesses 13 is evident from a cross section of a portion of the hub rear wall 15 without the mass relief recesses, for example, a cross section of the side of the hub rear wall 15 opposite the cross-sectional plane ZZ, i.e., a mirror image of the axis 11 in FIG. 1.

[0024] Additionally, FIG. 3 shows a marking bead (16). Unless otherwise specified, all position data relating to the marking bead (16) refers to the apex of the marking bead (16). The marking bead apex diameter G is defined, for example, as the diameter of the apex of the marking bead (16). The marking bead (16), or more precisely its apex, is radially spaced from the mass removal indentation (13), with D indicating the radial distance between the apex of the marking bead (16) and the nearest (here, radially inner) boundary of the mass removal indentation (13). The radial distance between the apex of the marking bead (16) and the farthest (here, radially outer) boundary of the mass removal indentation (13) is designated E. The mass removal indentation (13) has a radial extent A from the radially inner boundary to the radially outer boundary. The ellipse-like mass removal recess (13) is defined by an ellipse, which has a semi-major axis H and a semi-minor axis B. The penetration depth of the mass removal recess (13) is designated C. Furthermore, F denotes the diameter of the rear wall of the turbine wheel (10) of the exhaust gas turbine.

[0025] Figure 4 is a detailed view of Figures 2 and 3, including a close-up of the marking bead (16) and the nearest (radially inner) boundary of the mass removal indentation (13) with distance D. The radii of curvature K, L, and M geometrically define the marking bead (16). K denotes the concave radius of curvature of the transition between the apex of the marking bead (16) and the radially inner boundary of the mass removal indentation (13), L denotes the convex radius of curvature of the transition from the apex of the marking bead (16) to the region of the hub rear wall (15) located radially inward of the marking bead (16). The radius of curvature L can also be 0, corresponding to an acute angle.

[0026] Furthermore, FIG. 4 shows that the marking bead (16) is created as a convex protrusion within and relative to the hub rear wall (15), the marking bead (16) being geometrically defined by radii of curvature K, L, and M.

[0027] As shown in Figure 1, all elements of the hub rear wall shown in Figures 2 and 3, except for the mass relief recess (13), extend around the axis of rotation (11) in the figures.

[0028] Figure 5 shows a method for balancing a turbine wheel (10) for or of an exhaust gas turbine. The starting point of the method is the turbine wheel (10) of Figures 1 to 4 without the mass removal recesses (13). According to the method, the unbalance is first determined in a known manner, for example by assessing the unbalance of the rotating turbine wheel (10).

[0029] A material removal profile of the mass removal depressions (13) is determined in response to the determined imbalance of the turbine wheel (10). The material removal profile indicates how material should be removed and is parameterized, for example, by the angular extent (start and end angles) and penetration depth of the mass removal depressions (13) created. The material removal profile and resulting mass removal depressions (13) are asymmetric with respect to the axis of rotation (11) to compensate for the imbalance.

[0030] A mass removal recess (13) is then created in the hub rear wall according to a material removal profile by an elliptical mass removal tool (20) shown in Figure 5. The mass is removed at the mass removal location by relative movement of the tool (20) and the hub rear wall (15), i.e., by moving the tool (20) relative to the stationary hub rear wall (15). The shape and movement of the elliptical material removal tool (20) define the shape of the mass removal recess (13).

[0031] The movement of the tool 20, and therefore the position of the mass-removal indentation 13, is now oriented relative to the marking bead 16, i.e., adjacent to and along the marking bead 16, leaving the marking bead 16 intact. This allows for precise orientation to create the mass-removal indentation 13 at a defined location on the hub rear wall 15. This ensures that the radially inner area of ​​the hub rear wall 15 (radially inward of the marking bead 16), which is subject to the greatest mechanical loads or stresses, is not adversely affected during this process. Additionally, visual inspection is possible after balancing. Balancing in an area radially smaller than the marking bead 16 could potentially lead to mechanical limitations with regard to low-cycle fatigue of the turbine wheel 10. Preferably, the radial distance of the tool 20 from the marking bead 16 does not change during movement.

[0032] The elliptical material removal tool (20) is depicted here schematically as a grinding tool with an elliptical grinding head, which rotates, for example, about a radially extending axis. In alternative embodiments, other, possibly inclined, rotation axes are also possible. In the case of spherical material removal tools, such as spherical grinding heads, the rotation axis is freely variable.

[0033] The method may optionally include at least one further determination of the (remaining) imbalance and fitting or adding to the mass removal recess (13) according to the steps described above.

[0034] Further details, possible variations and description of general aspects Possible variations and general optional aspects of the invention are described below, where, unless excluded, any aspect can be combined with any other aspect of the invention, and the aspects are shown as embodiments and are indicated in part by reference characters referring to elements shown in the figures described above, but are not in any further respect limited to the embodiments shown therein.

[0035] First, an embodiment of a method for balancing a turbine wheel 10 of an exhaust gas turbine will be described below. The turbine wheel 10 of the exhaust gas turbine is rotatably mounted and rotates about its rotation axis 11. The turbine wheel 10 has a hub 12 and a plurality of turbine blades mounted on the hub 12 and arranged in a fluid flow area 14. The fluid flow area 14 is an area where fluid, specifically exhaust gas, flows over the turbine blades, resulting in work. The hub 12 also has a hub rear wall 15 facing away from the fluid flow area 14. Therefore, the hub rear wall 15 is located on the side of the hub 12 facing away from the fluid flow area 14, i.e., on the opposite side. However, this does not exclude the possibility that fluid may also cover the hub rear wall 15. The hub rear wall (15) is preferably free of turbine blades and / or may preferably extend radially (e.g., at an angular displacement of up to 40° from the radial plane). The hub rear wall (15) has a marking bead (16) extending concentrically around the rotation axis (11).

[0036] According to a general aspect, a mass is removed by an elliptical material removal tool at a mass removal location adjacent a marking bead (16) on a hub rear wall (15) of a turbine wheel (10) of an exhaust gas turbine.

[0037] In this mass removal position, the mass is removed by relative movement between the elliptical material removal tool and the hub rear wall 15. The elliptical material removal tool can move while the hub rear wall 15 remains stationary, the hub rear wall 15 can move while the elliptical material removal tool remains stationary, the elliptical material removal tool and the hub wall 15 can move simultaneously, or some combination thereof. Preferably, the elliptical material removal tool is moved at least in the depth direction. The marking bead 16 is particularly advantageous when the elliptical material removal tool is a freely movable tool, for example, held and guided by a human hand.

[0038] For any type and combination of relative movement between the elliptical material removal tool and the hub rear wall (15), the (relative) movement of the material removal tool is directed by a marking bead (16) located on the hub rear wall (15) of the turbine wheel (10).

[0039] The mass is removed by an elliptical material removal tool at a mass removal location on the hub rear wall (15) to balance the turbine wheel (10) of an exhaust gas turbine by forming a mass removal depression (13) that is asymmetric about the rotation axis (11). The location of the mass removal depression (13) is oriented relatively adjacent to the marking bead (16), leaving the marking bead (16) intact. Thus, the most protruding portion of the marking bead (16), including the apex of the marking bead, remains untouched and unmachined.

[0040] An ellipsoid-like material removal tool has a tool machining geometry configured in the shape of an ellipsoid. Accordingly, the tool has an ellipsoid-like shaped material removal tool head for removing material from the hub rear wall in elliptical segments. The ellipsoid describing the tool machining geometry is defined by three semiaxes H, B, and Y. H and B represent the semiaxes shown in FIG. 3 of the cross-sectional profile of the resulting mass removal recess (13), and Y is a further semiaxis extending perpendicular to these two semiaxes (and thus the drawing plane of FIG. 5 ) of the ellipsoid representing the tool machining geometry. For rotating tool heads, the two semiaxes extending perpendicular to the rotation axis R are preferably equal, i.e., for axially rotating tool heads, Y=H, and for radially rotating tool heads, Y=B.

[0041] In one embodiment of the ellipse-like material removal tool, the ellipsoid representing the tool machining geometry has a configuration in which at least two of the three semi-axes H, B, Y have the same longitudinal extent (German: Laengenausdehnung). In a further embodiment of the ellipse-like material removal tool, the ellipsoid representing the tool machining geometry has a configuration in which all three semi-axes H, B, Y have the same longitudinal extent. According to one aspect, the tool can have a rotating tool head having an elliptical shape corresponding to the tool machining geometry. If the tool head rotates, the axis of rotation is preferably one of the semi-axes, and at least the other two semi-axes are the same.

[0042] When all three semi-axes H, B, Y have the same longitudinal extent, the tool machining geometry is a ball, i.e., a spherical material removal tool (e.g., a tool with a spherical head). Such spherical material removal tools have the advantage that the angular orientation of the tool relative to the hub rear wall is not important, at least within a certain angular range, which makes the tool easier to handle (especially for freely movable tools).

[0043] The elliptical material removal tool can be any tool capable of machining by material removal, typically including, but not limited to, a turning tool, a drilling tool, a chamfering tool, a friction tool, a milling tool, a planing tool, a grooving tool, a broaching tool, a sawing tool, a filing tool, a sanding tool, a brush grinding tool, a scraping tool, a chiseling tool, a grinding tool (with or without a rotary tool), a belt grinding tool, a honing tool, a lapping tool, or a slide machining tool.

[0044] In one embodiment, the elliptical material removal tool is a grinding tool having an elliptical grinding head, for example a spherical grinding tool having a spherical grinding head.

[0045] According to one embodiment, the mass removal recess (13) is created by an elliptical-like material removal tool in the hub rear wall (15) of a turbine wheel of an exhaust gas turbine. According to one embodiment, the machining is performed circumferentially along a circular area of ​​the hub rear wall (15) and along an arc around the axis (11). Preferably, the machining is performed in annular or circular segments along the arc. According to a further embodiment, the machining can be performed along any one-dimensional contour on the hub rear wall (15) of the turbine wheel (10).

[0046] According to one embodiment, the mass removal indentations (13) can be provided as continuous circular segments, as shown, for example, in Figure 1. More generally, the mass removal indentations (13) can be provided as continuous, segmental, intermittent, or discrete spot machining along a circular arc along which the relative movement of the elliptical material removal tool and the hub rear wall (15) occurs is oriented relative to the marking bead (16) on the hub rear wall (15) such that the arc extends adjacent to the marking bead (16) on the hub rear wall (15).

[0047] According to one aspect, the method includes first determining an imbalance of the turbine wheel (10). A material removal profile for the mass removal indentation (13) is generated in response to the determined imbalance of the turbine wheel (10). The material removal profile may be a one-dimensional profile along a circular segment of the hub rear wall (15) and may extend along an arc to the marking bead (16) on the hub rear wall (15). The material removal profile indicates how material should be removed. Possible embodiments include continuous, segmented, intermittent, and / or discrete spot material removal profiles. Profiles with any (continuous or discontinuous) angle-dependent penetration depth may be used. According to one aspect, the profile is limited by a maximum angle range and / or a maximum penetration depth. According to a further aspect, the material removal profile for the mass removal indentation (13) may also be generated without a prior determination of the imbalance of the turbine wheel (10).

[0048] According to one embodiment, the material removal profile can include, for example, an (annular) intermediate position on the hub rear wall (15), an angular region along the arc, a longitudinal extent along the arc of the mass removal indentation (13), and / or a (constant or angle-dependent) material removal depth C. In particular, a material removal depth C that varies over each angular region can be set for the mass removal indentation (13) and thus, for example, for the runout that is generated. Similarly, material removal profiles for multiple mass removal indentations (13) can be provided in this manner.

[0049] Using the provided material removal profile, a mass removal recess (13) is created in a hub rear wall (15) of a turbine wheel of an exhaust gas turbine. According to one embodiment, creating the mass removal recess (13) reduces turbine wheel imbalance.

[0050] In order to optimally create the mass removal recesses 13, according to one embodiment, a no-removal hub test geometry is defined, which is a configuration of the hub 12, and in particular the hub rear wall 15, in which there is no material removal from the hub rear wall 15.

[0051] According to a further aspect (e.g., as a further hub test geometry), a maximum removal hub test geometry can be defined as a hub test geometry for maximum allowable material removal at the hub rear wall 15. The maximum allowable material removal at the hub rear wall 15 is predetermined from considerations such as, for example, typically required removal, minimum allowable remaining hub wall thickness at the material removal location, manufacturing process and manufacturability at the material removal location, and / or structural-mechanical requirements at the material removal location.

[0052] According to one embodiment, the first hub quality parameter is calculated from a maximum removal hub test geometry, i.e., taking into account the maximum allowable material removal at the hub rear wall 15. Preferably, the hub geometry is optimized by optimizing the hub optimization variables determined using the first hub quality parameter.

[0053] According to one embodiment, the second hub quality parameter is calculated from the no-removal hub test geometry, i.e., without taking into account the maximum allowable material removal at the hub rear wall 15. Preferably, the hub optimization variables are then further determined using the second hub quality parameter, for example by summation of the respective summands determined using the first or second hub quality parameter.

[0054] The (first or second) hub quality parameter may include at least one parameter selected from the following list: mechanical stress, mechanical principal stress, mechanical normal stress, mechanical shear stress, mechanical cycle optimization variable, in particular cycle fatigue coefficient (e.g., simulated cycle capacity for fatigue at low cycles), notch bar impact coefficient, shape factor, number of supports (German: Stuetzziffer), force flow, geometric design of the mass removal recesses (13), deviation from a predetermined target total removal. The hub optimization variable may, for example, include the norm (German: Norm) of such parameter (e.g., L2 norm, i.e., squared) or possibly a weighted sum of such norms for multiple parameters. In particular, the hub optimization variable may result in a penalty for an increase in simulated cycle capacity for low cycle fatigue relative to a hub test geometry without removal and / or with maximum removal.

[0055] The optimization is preferably performed iteratively, preferably by iteratively varying the parameters defining the hub test geometry to arrive at optimal values ​​for the hub optimization variables.

[0056] According to one embodiment, the shape of the maximum allowable material removal can be optimized when parameters defining the maximum allowable material removal are iteratively varied, where the hub optimization variables may also include terms that ensure a sufficiently large maximum allowable material removal or terms that penalize deviations from a predefined total target removal.

[0057] The hub rear wall geometry is optimized using at least one parameter designated as a hub quality parameter.

[0058] Preferably, the optimization of the hub geometry is a multi-factorial optimization in which multiple hub quality parameters are used. Preferably, the hub geometry is optimized by optimizing hub optimization variables determined using the multiple hub quality parameters. Preferably, the optimization is performed iteratively. Preferably, material removal from the hub test geometry is iteratively varied, and the resulting multiple hub quality parameters are calculated and compared with existing similar hub quality parameters. The comparison and optimization of the hub quality parameters can be performed by any form of mathematical optimization procedure suitable therefor. The iterative variation of material removal from the hub test geometry is limited by a hub test geometry with no material removal and a hub test geometry with maximum allowable material removal.

[0059] Further aspects of a turbine wheel (10) for or of an exhaust gas turbine manufactured using the described method are described below. The turbine wheel (10) is rotatably mounted and rotates about its rotation axis (11). The turbine wheel (10) has a hub (12) and a plurality of turbine blades attached to the hub (12) and disposed in a fluid flow region (14). The hub (12) also has a hub rear wall (15) facing away from the fluid flow region (14). The hub rear wall (15) includes a mass removal recess (13) that is asymmetric with respect to the rotation axis (11) for balancing the turbine wheel (10). The mass removal recess (13) is formed as a concave recess in the hub rear wall (15), and the cross-sectional profile of the mass removal recess (13) is in the shape of an elliptical segment. The cross-sectional profile of the mass removal recess (13) is defined by a cross-sectional plane ZZ that includes the rotation axis (11). The hub rear wall 15 also has a marking bead 16 extending concentrically around the rotation axis 11, and the marking bead 16 and the mass removal indentation 13 are adjacent but do not overlap in the radial direction. In other words, the mass removal indentation 13 does not overlap with the apex of the marking bead 16, and therefore the apex extends continuously around the hub rear wall in the circumferential direction.

[0060] The mass-removal recess (13) according to one embodiment has a cross-sectional profile in a cross-sectional plane ZZ that includes the axis of rotation (11). The cross-sectional profile is ellipse-like, i.e., formed by an ellipse segment. The ellipse representing this ellipse segment is defined by a first (e.g., long) semi-axis H and a second (e.g., short) semi-axis B of the ellipse. The first semi-axis H may extend in a radial direction, and the second semi-axis B of the ellipse may extend in an axial direction. Preferably, the first semi-axis H and the second semi-axis B of the ellipse have the same longitudinal extent, so that the cross-sectional profile in the cross-sectional plane ZZ that includes the axis of rotation (11) has the geometric form of a circular segment.

[0061] Preferably, the definitions given herein for cross-sectional profile apply to multiple cross-sectional planes ZZ that include the axis of rotation 11 and a portion of the mass relief indentation 13, and particularly preferably to any such cross-sectional planes in at least a continuous angular area that covers at least half, or even at least 80%, of the total angular area of ​​the mass relief indentation 13. In the case of multiple mass relief indentations 13, the definitions given herein preferably apply to all of the mass relief indentations 13.

[0062] The cross-sectional profile of the mass removal recess (13) according to one embodiment has a minimum radius of curvature Kr min The minimum radius of curvature of the base ellipse is the ratio Ke min = ((B*B) / H), where H is the long (here first) semi-axis of the ellipse and B is the short (here second) semi-axis of the ellipse. The radius of curvature is typically min / F≧0.03 and / or Ke min The ratio R / F ≥ 0.03 should be satisfied, where F is the diameter of the turbine wheel (10). If the semimajor axis H and semiminor axis B of the ellipse have the same length and therefore have a circular (i.e., circular segment-shaped) cross-sectional profile, then the ratio R / F ≥ 0.03, where R is the radius of the circular cross-sectional profile. If the semimajor axis H and semiminor axis B of the ellipse have the same length, then the semimajor axis H and semiminor axis B correspond to each other and also correspond to the radius R of the circular cross-sectional profile.

[0063] According to one embodiment, the mass removal recess (13) has a penetration depth C of C>0 and / or C<0.6*B, preferably C<0.5*B, particularly preferably C<0.4*B, where B is the second (axial and / or short) semi-axis of the ellipse.

[0064] The mass removal recess 13 is located within the hub rear wall 15 of the turbine wheel 10 and adjacent to a marking bead 16 also present within the hub rear wall 15. In one embodiment, the mass removal recess 13 and / or marking bead 16 may be located at any circumferential and radial position on the hub rear wall 15, where they stand side by side with no additional functional surface features between them.

[0065] Preferably, the mass removal indentations 13 and / or the marking beads 16 are formed in the radially outer half (relative to the diameter F) of the hub rear wall 15, preferably at least partially in the radially outer third. Preferably, the mass removal indentations 13 are arranged (completely) radially outside the marking beads 16. According to one embodiment, the area of ​​the hub rear wall 15 within the marking beads 16 is free of mass removal indentations 13 and / or is completely rotationally symmetrical. According to one embodiment, the marking beads 16 enable marking of areas reserved for the mass removal indentations 13 (i.e., for example, radially outside the marking beads 16) and / or ensure marking of areas not reserved for the mass removal indentations 13 (i.e., for example, radially inside the marking beads 16). Due to the marking bead 16, it is possible to ensure and easily verify that the mass removal recesses 13 are only made in the provided area and not outside this area, which is particularly useful when the geometry of the hub rear wall is optimized for the mass removal recesses 13 provided therein.

[0066] To create the mass-removal recesses (13), according to one embodiment, any tool capable of removing material can be used, typically including, but not limited to, a turning tool, a drilling tool, a chamfering tool, a friction tool, a milling tool, a planing tool, a grooving tool, a broaching tool, a sawing tool, a filing tool, a sanding tool, a brush grinding tool, a scraping tool, a chiseling tool, a grinding tool (with or without a rotary tool), a belt grinding tool, a honing tool, a lapping tool, or a slide machining tool.

[0067] Preferably, the material removal tool is a grinding tool with an elliptical grinding head. Typically, the grinding tool has a spherical grinding head, resulting in a spherical grinding tool with a spherical grinding head. The material removal tool with an elliptical grinding head can also be formed such that only the portion of the material removal tool that contacts the turbine wheel (10) during the creation of the mass removal recesses (13) has an elliptical shape.

[0068] According to one embodiment, mass removal recesses (13) for balancing an exhaust gas turbine turbine wheel (10) are created along a circumferential arc within a circular area of ​​the hub rear wall (15) of the exhaust gas turbine turbine wheel (10). Preferably, the machining is performed in annular or circular segments along the arc. Examples include, but are not limited to, continuous, segmental, intermittent, or discrete spot machining along the arc.

[0069] The hub rear wall (15) of the turbine wheel (10) of the exhaust gas turbine has a marking bead (16), which is rotationally symmetrical with respect to the rotation axis (11) and extends concentrically around the rotation axis (11).

[0070] According to one aspect, the marking bead (16) of the hub rear wall (15) has a cross-sectional profile that lies in a cross-sectional plane Z-Z containing the axis of rotation (11). The cross-sectional profile of the marking bead (16) is convex and raised with respect to the hub rear wall (15).

[0071] According to one aspect, the marking bead (16) is also radially spaced from the mass removal recess (13) contained in the hub rear wall (15) of the turbine wheel (10) of the exhaust gas turbine by a distance D. Preferably, E = A + D and E ≤ (F - G) / 2 and G / F ≥ 0.5, where A is the radial extent of the mass removal recess (13) (the radial distance between the inner radial boundary of the mass removal recess (13) and the outer radial boundary of the mass removal recess (13)), D is the radial distance between the marking bead (16) and the closer (here, inner radial) boundary of the mass removal recess (13), E is the radial extent between the marking bead (16) and the farther (here, outer radial) boundary of the mass removal recess (13), F is the diameter of the rear wall of the turbine wheel (10) of the exhaust gas turbine, and G is the diameter of the marking bead (16), i.e., the diameter of the circle defined by the circumferential marking bead (16) on the hub rear wall (15). Here, unless otherwise specified, the radial position of the marking bead is always defined by its apex. In the case of multiple mass removal recesses (13), the individual radial distances D from the marking bead (16) can be determined and applied to each mass removal recess (13). Typically, the same radial distance D is selected and applied to all mass removal recesses (13). The minimum radial distance D between the mass removal recess (13) and the marking bead (16) is preferably 0 < D < 0.05*F, particularly preferably 0 < D < 0.025*F.

[0072] According to one embodiment, the cross-sectional profile (preferably rotationally symmetrical) of the marking bead (16) has an apex, a flank (German: Flanke) radially inward relative to the apex, and a flank radially outward relative to the apex. The radially inward flank has a concave radius of curvature M, the radially outward flank has a concave radius of curvature K, and the apex has a convex radius of curvature L. If the radii of curvature are not constant, these variables represent the minimum radii of curvature, respectively. In other words, K denotes the (minimum) radius of curvature of the transition between the apex of the marking bead (16) and the radially inner boundary of the mass-removal recess (13), L denotes the (minimum) radius of curvature at the apex of the marking bead (16), and M denotes the (minimum) radius of curvature of the transition from the apex of the marking bead (16) to the region of the hub rear wall (15) located radially inward of the marking bead (16). According to one embodiment, K>0, L≧0, and / or M>0. Furthermore, preferably, K / F<0.07, M / F<0.07, L / K<0.15, and / or L / M<0.1.

[0073] According to one embodiment, the surface of the hub rear wall (15) in the entire radial area, at least from the radius of the marking bead (16) to the outermost radius of the mass removal recess (13), is a machined surface, i.e., has a higher smoothness and precision than a surface obtained directly by, for example, casting.

[0074] The marking bead (16) on the hub rear wall (15) of the turbine wheel (10) of the exhaust gas turbine can be made at any radial position. Preferably, the marking bead (16) is located radially inward of the mass removal recess (13).

[0075] According to one embodiment, the unbalance of the turbine wheel is less than the unbalance of a corresponding (theoretical) turbine wheel having a rotationally symmetric hub without the mass removal indentations 13. According to one embodiment, the low cycle fatigue capacity of the turbine wheel is no less than, or at most 2% less than, the cycle capacity of a corresponding (theoretical) turbine wheel having a rotationally symmetric hub without the mass removal indentations 13.

[0076] All of the above aspects of the turbine wheel 10 for an exhaust gas turbine relate to any design of exhaust gas turbine, preferably a radial exhaust gas turbine or a mixed flow exhaust gas turbine (also called a mixed flow exhaust gas turbine). In a radial exhaust gas turbine, the turbine wheel 10 is configured as a radial turbine wheel. In a mixed flow exhaust gas turbine, the turbine wheel 10 is configured as a mixed flow (mixed flow) exhaust gas turbine wheel, i.e., with a hub front wall extending diagonally, whose inlet tangent has both axial and radial components.

[0077] According to one embodiment, the exhaust gas turbine is configured to be driven by exhaust gas from an internal combustion engine. According to one embodiment, the exhaust gas turbine is provided in a turbocharger. In the turbocharger, the exhaust gas turbine drives a compressor wheel arranged on a common shaft to increase the pressure, density, and enthalpy of the aspirated fluid, thereby increasing the charging pressure and generally increasing the efficiency of the internal combustion engine. Alternatively or additionally, the exhaust gas turbine can drive other energy users, such as a generator and / or a drive shaft. According to one embodiment, an internal combustion engine is provided, wherein the exhaust gas turbine is driven by exhaust gas from the internal combustion engine, and the turbocharger includes the exhaust gas turbine.

[0078] In a further aspect of the invention, an exhaust gas turbine comprises a turbine wheel (10) satisfying any of the features of the second aspect of the invention. The exhaust gas turbine can be driven by any type of exhaust gas. Furthermore, all designs of the exhaust gas turbine can be considered, such as radial exhaust gas turbines or mixed flow exhaust gas turbines. Also, all possible consumers on the exhaust gas turbine shaft can be considered, such as compressor wheels, generators, drive shafts, etc. Preferably, the exhaust gas turbine is an exhaust gas turbocharger. [Explanation of symbols]

[0079] 10 Turbine wheel of exhaust gas turbine 11 Rotating shaft of the turbine wheel of the exhaust gas turbine 12. Hub of turbine wheel of exhaust gas turbine 13 Mass removal recess 14 Fluid flow area of ​​the turbine wheel of an exhaust gas turbine 15 Rear wall of the hub of the turbine wheel of an exhaust gas turbine 16 Marking bead 20 Ellipse-like material removal tool A the radial extent of the ellipse-like mass removal indentation from the radially inner boundary of the ellipse-like mass removal indentation to the radially outer boundary of the ellipse-like mass removal indentation B Second (short) semi-axis of the elliptical mass-removal depression C Material removal depth D Radial distance from the marking bead to the radially inner boundary of the elliptical mass-removal depression E Radial distance from the marking bead to the radially outer boundary of the elliptical mass-removal depression F diameter of the rear wall of the turbine wheel of the exhaust gas turbine G Marking bead diameter H First (long) semi-axis of the elliptical mass-removal depression K is the radius of curvature of the transition between the apex of the marking bead and the radially inner boundary of the mass-removal recess L Radius of curvature at the apex of the marking bead M Radius of curvature of the transition from the apex of the marking bead to the rear wall of the hub radially inward of the marking bead Detail of Figure 2, enlarged view of X marking bead Y is the third semi-axis of the ellipse that defines the tool machining head ZZ Cross section of the turbine wheel of an exhaust gas turbine including the rotating shaft

Claims

1. 1. A method for balancing a turbine wheel (10) of an exhaust gas turbine, the turbine wheel (10) being rotatable about a rotation axis (11) and having a hub (12) and a plurality of turbine blades attached to the hub (12) and arranged in a fluid flow region (14), the hub having a rear hub wall (15) facing away from the fluid flow region (14) and provided with a marking bead (16) extending concentrically around the rotation axis (11), the marking bead (16) being rotationally symmetrical with respect to the rotation axis (11); moving an elliptical material removal tool relative to the turbine wheel (10) at a mass removal location adjacent the marking bead (16); removing hub material from the hub rear wall (15) adjacent to the marking bead (16) with the material removal tool, leaving the marking bead (16) intact, thereby creating a mass removal recess (13) in the hub rear wall (15) that is asymmetric with respect to the rotation axis (11) for balancing the turbine wheel (10); A method comprising:

2. 2. The method for creating a turbine wheel (10) for an exhaust gas turbine according to claim 1, wherein the material removal tool is a grinding tool with an oval-like grinding head.

3. 2. The method for creating a turbine wheel (10) for an exhaust gas turbine according to claim 1, wherein the material removal tool is a spherical grinding tool with a spherical grinding head.

4. 4. The method according to any one of claims 1 to 3, wherein the mass removal recesses (13) are made along circumferential annular segments around the axis of rotation (11).

5. determining an imbalance of the turbine wheel; setting a material removal profile of the mass removal recess (13) in response to the determined imbalance; creating said mass removal recesses (13) with said set material removal profile; The method of any one of claims 1 to 3, further comprising:

6. defining a no-removal hub test geometry; calculating a first hub quality parameter using the defined no-removal hub test geometry minus a maximum amount of removal from the hub rear wall of the no-removal hub test geometry; further comprising 4. The method of claim 1, wherein the removal of hub material at the rear hub wall (15) is limited by the maximum removal amount.

7. 7. The method of claim 6, further comprising optimizing the hub geometry by optimizing hub optimization variables calculated using the first hub quality parameter by iteratively varying the hub test geometry between the no removal hub test geometry and the maximum removal hub test geometry.

8. The method of claim 6 , wherein the hub quality parameters include at least one parameter selected from mechanical stress, mechanical cycle optimization variables, and cycle fatigue index.

9. 7. The method of claim 6, further comprising calculating a second hub quality parameter using the defined hub test geometry without removing hub backwall material from the hub test geometry.

10. 10. The method of claim 9, further comprising optimizing the hub geometry by optimizing hub optimization variables calculated using the first and second hub quality parameters by iteratively varying the hub test geometry between a no removal hub test geometry and a maximum removal hub test geometry.

11. A turbine wheel (10) for an exhaust gas turbine, said turbine wheel (10) being rotatable about an axis of rotation (11), a hub (12); a plurality of turbine blades attached to the hub (12) and positioned in a fluid flow area (14), the hub having a rear hub wall (15) facing away from the fluid flow area (14); and a mass removal recess (13) in the rear hub wall (15) that is asymmetric with respect to the rotation axis (11) and that is created by a material removal tool to balance the turbine wheel (10); the mass-removal recess (13) is configured as a concave recess in the hub rear wall (15) having a cross-sectional profile in the form of an elliptical segment; the cross-sectional profile of the mass-removal recess (13) is defined in a cross-sectional plane (Z-Z) containing the axis of rotation (11); The hub rear wall (15) further has a marking bead (16) extending concentrically with respect to the rotation axis (11), the marking bead (16) being rotationally symmetrical with respect to the rotation axis (11); A turbine wheel (10) for an exhaust gas turbine, wherein the marking bead (16) and the mass removal recess (13) are adjacent to each other without overlapping in the radial direction.

12. The mass removal recess (13) (a) the cross-sectional profile of the mass-relief recess (13) has the shape of a circular segment; (b) the cross-sectional profile of the mass-removal recess (13) has a minimum radius of curvature greater than 0.03*F, where F is the diameter of the rear wall of the turbine wheel (10); (c) the cross-sectional profile of the mass removal indentation (13) satisfies the condition ((B*B) / H) / F≧0.03, where H is the semi-major axis of the elliptical cross-sectional profile of the mass removal indentation (13), B is the semi-minor axis of the elliptical cross-sectional profile of the mass removal indentation (13), and F is the diameter of the rear wall of the turbine wheel (10); (d) the mass-relief recess (13) is at least partially disposed in the radially outer half of the hub rear wall (15); (e) the mass-relief recess (13) extends along an annular segment extending circumferentially about the axis of rotation; (f) the mass removal depressions (13) extend as a continuous line, as parts of a series of continuous lines, or as a series of individual spot depressions; 12. The turbine wheel of claim 11, having at least one of the following characteristics:

13. The marking bead (16) is (i) the marking bead (16) is raised and convex in the cross-sectional plane; (ii) the marking bead (16) is arranged according to the inequality E≦(F−G) / 2 and / or G / F>0.5, wherein A is the radial extent of the mass removal indentation (13) from the radially inner end of the mass removal indentation (13) to the radially outer end of the mass removal indentation (13), D is the radial distance of the apex of the marking bead (16) from the mass removal indentation (13), E=A+D is the radial distance of the apex of the marking bead (16) from the radially outer boundary of the mass removal indentation (13), F is the diameter of the turbine wheel (10), and G is the diameter of the circle defined by the apex of the marking bead (16). (iii) the marking bead (16) is disposed radially inward of the mass-removal recess (13); The turbine wheel (10) of claim 11, having at least one of the following characteristics:

14. 12. The turbine wheel (10) of claim 11, wherein the turbine wheel is a radial turbine wheel for a radial exhaust gas turbine or a mixed flow turbine wheel for a mixed flow exhaust gas turbine.

15. An exhaust gas turbine comprising a turbine wheel (10) according to any one of claims 11 to 14.

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