Nozzle ring with stress reducing portion

Abstract

An axial turbine (100, 200) is described herein. The axial turbine has a turbine casing (160), a turbine wheel (180) arranged in the turbine casing (160) and mounted on a shaft, and a nozzle ring (110) arranged in the turbine casing (160) 5 and at least partially upstream of the turbine wheel (180). The nozzle ring (110) comprises an inner ring (114), a plurality of nozzle blades (113) arranged radially outward of the inner ring (114), and an outer ring (112) arranged radially outward of the nozzle blades (113). The nozzle ring (110) is releasably attached within the turbine casing (160). The nozzle ring (110) includes a circumferentially extending 10 stress-relief groove (116, 117) on the inner ring (114) and / or the outer ring (112).

Description

NOZZLE RING WITH STRESS REDUCING PORTIONTECHNICAL FIELD

[0001] Embodiments of the present disclosure relate to an axial turbine, in particular an axial turbine for an exhaust turbocharger.BACKGROUND

[0002] Axial turbines commonly include a nozzle ring with an outer and an inner ring as well as nozzle blades located between outer and inner ring. The nozzle blades are intended to redirect the gas, such as exhaust gas in case the application is an exhaust turbocharger, and guide it in a certain angle to the axial turbine.

[0003] Different concepts of mounting the nozzle ring within the axial turbine are known. For example, the nozzle ring may be attached within the turbine casing by means of a screw connection. The screw connection of the nozzle ring can be attached to an inner or outer surface of the nozzle ring. Alternatively, the nozzle ring can also be held in place by means of a clamp connection, for example between the gas inlet casing or a calotte and the turbine diffusor or the gas outlet casing.

[0004] Problems can arise during transient conditions due to thermal expansion or thermally induced deformation of any of the components which the nozzle ring is attached to or abuts with. This in turn can lead to substantial stress in the nozzle ring, in effect limiting the number of load cycles and an operating lifetime before maintenance is required or replacement of the nozzle ring is required.

[0005] There is a continuous demand for axial turbines with an increased operating lifetime and that require less maintenance. In particular, there is a need for axial turbines including components that allow for at least partially counteracting thermally induced stress to reduce degradation effects.SUMMARY

[0006] In light of the above, an axial turbine according to independent claim 1 is provided. Further aspects, advantages, and features are apparent from the dependent claims, the description, and the accompanying drawings.

[0007] According to an aspect of the present disclosure, an axial turbine, in particular for an exhaust turbocharger is provided. The axial turbine includes a turbine casing, and a turbine wheel arranged in the turbine casing and mounted on a shaft. The axial turbine further includes a nozzle ring arranged in the turbine casing and at least partially upstream of the turbine wheel. The nozzle ring includes an inner ring, a plurality of nozzle blades arranged radially outward of the inner ring, and an outer ring arranged radially outward of the nozzle blades. The nozzle ring is releasably attached within the turbine casing. The nozzle ring includes a circumferentially extending stress-relief groove on the inner ring and / or the outer ring. The stress-relief groove axially overlaps with the plurality of nozzle blades.

[0008] The axial direction, the radial direction and the circumferential direction are defined by the shaft of the axial turbine.

[0009] The “stress-relief groove axially overlaps with the plurality of nozzle blades” is to be understood such that the groove and the nozzle blades at least partially overlap in axial direction, but can also fully overlap in axial direction. “Circumferentially extending” is to be understood such that the stress-relief groove extends in a circumferential direction. As described further below, the stress-relief groove can extend along a portion of thecircumference of the inner / outer ring or along the entire circumference of the inner / outer ring.

[0010] The stress-relief groove of the present disclosure is configured to reduce mechanical stress on the nozzle ring, in particular the trailing edge of the nozzle blades, during transient and / or stationary conditions. Thermal expansion and / or thermally induced deformation of various components of the axial turbine can occur during transient and / or stationary conditions. Especially the components directly adjacent to the nozzle ring and components which abut with or that are mechanically connected to the nozzle ring can cause mechanical stress on the nozzle ring and induce deformation in the nozzle ring. Various embodiments relating to the attachment of the nozzle ring within the axial turbine are described in more detail below. Mechanical stress may be particularly caused by the turbine casing, such as a gas-outlet casing or a gas inlet casing of the turbine casing, a calotte, a cover ring or a turbine diffusor. Advantageously, the nozzle ring has a reduced thickness at the location of the stress-relief groove, which reduces the radial stiffness of the nozzle ring in the vicinity of the stress-relief groove. As a result of mechanical stress caused by the other components of the axial turbine during transient conditions, the nozzle ring can more flexibly deform, thereby reducing degradation of the nozzle ring and especially the nozzle blades.

[0011] Providing the stress-relief groove such that it axially overlaps with the nozzle blades allows to reduce the thickness of the outer or inner ring at a location where the influence of transient thermal deformation is the largest. This in turn ensures that mechanical stress induced during transient conditions is not or only to a lesser extent passed on to the nozzle blades. In other words, the nozzle blades may be decoupled from mechanical stress induced during transient and / or stationary conditions. The groove is preferably spaced apart from axial ends of the inner ring and / or the outer ring.

[0012] Thus, an axial turbine is advantageously provided, which enables a longer operating lifetime and requires less maintenance. Another advantage is that the stress-relief groove can be manufactured by means of simple machining on a surface of the nozzle ring.

[0013] Illustratively, the stress-relief groove of the present disclosure is not provided for the engagement of mechanical components with each other or the mechanical connection between two components. The nozzle ring or the axial turbine may additionally include a fixation groove or a fixation slot for fixing the nozzle ring with another component of the axial turbine. For example, the stress-relief groove is not provided for an interlocking connection, or for receiving another component (such as an O-ring). A cavity defined by the groove may be spaced apart from other components of the axial turbine and / or the cavity of the stress-relief groove may be unobstructed by or free of other components of the axial turbine. Stated differently, the groove is preferably empty.

[0014] In case the groove is arranged at the inner ring of the nozzle ring, the groove is preferably arranged on an inner surface of the inner ring. In case the groove is arranged at the outer ring of the nozzle ring, the groove is preferably arranged on an outer surface of the outer ring. This allows to ensure that a fluid flow within the turbine is not obstructed or impaired. The groove preferably does not extend through an entire radial depth of the inner ring or outer ring. Stated differently, the groove may not be a through-opening and / or has a radial depth which is less than a radial depth of the inner or outer ring. The groove is preferably not in fluid communication with a (main) fluid flow path of the axial turbine. A gas inlet passage of the nozzle ring may be arranged radially between the inner and outer ring.

[0015] According to an embodiment, the groove axially overlaps with a trailing edge of at least one of the nozzle blades of the plurality of nozzle blades. The groove may be axially aligned with the trailing edges of at leastone of the nozzle blades. In a preferred implantation thereof, the groove axially overlaps with the trailing edges of the plurality of nozzle blades. The trailing edge may also be referred to as downstream end of the nozzle blades. The inventors of the present disclosure have found that the influence of mechanical stress induced during transient conditions may be largest in the vicinity of the trailing edges of the nozzle blades.

[0016] According to an embodiment, the nozzle ring includes a circumferentially extending stress-relief groove on the inner ring and a circumferentially extending stress-relief groove on the outer ring. This allows for further improving the effect of stress-relief. By having grooves on the inner and outer ring, a groove depth can be reduced on both of the rings, thereby avoiding that the rings are weakened too substantially.

[0017] The outer ring, the inner ring and the nozzle blades, and in particular the nozzle ring, may be formed integrally.

[0018] A ratio between a radial depth of the groove and a radial depth of the inner ring and / or the outer ring may be at least 20%. Beneficially, a stiffness of the nozzle ring is substantially reduced or a flexibility increased when the ratio is at least 20%. Preferably, the ratio between the radial depth of the groove and the radial depth of the inner ring and / or the outer ring may be at least 40%, and more preferably at least 60%.

[0019] Additionally, or alternatively, the ratio between a radial depth of the groove and a radial depth of the inner ring and / or the outer ring may be no more than 80%, preferably no more than 75% and more preferably no more than 70%. This may ensure that the nozzle ring is not weakened too substantially in the vicinity of the groove, and may avoid fracturing of the nozzle ring during transient conditions.

[0020] A ratio between an axial thickness of the groove and an axial thickness of the inner ring and / or the outer ring may be at least 5%. Thegroove can axially extend only along a small portion of the nozzle ring in the vicinity of the nozzle blades or the trailing edge of the nozzle blades. Preferably, the ratio between the axial thickness of the groove and the axial thickness of the inner ring and / or the outer ring may be at least 7% and more preferably at least 10%.

[0021] Additionally, or alternatively, the ratio between the axial thickness of the groove and the axial thickness of the inner ring and / or the outer ring may be no more than 80%, preferably no more than 60% and more preferably no more than 40%. This may ensure that the nozzle ring is not weakened too substantially, and may avoid fracturing of the nozzle ring during transient conditions.

[0022] In an embodiment, the stress-relief groove extends substantially along the entire perimeter of the inner ring and / or the outer ring. This may allow to reduce the stiffness of the nozzle ring in the vicinity of each of the nozzle blades. Providing the groove along the entire perimeter also simplifies machining of the nozzle ring and thereby reduces the costs for manufacturing.

[0023] In an alternative embodiment, the groove extends along a portion of the perimeter of the inner ring and / or the outer ring. In other words, the groove extends only along a fraction of the entire circumference of the inner or outer ring. In a preferred embodiment, the nozzle ring may include several stressrelief grooves at the inner and / or outer ring. Each of the stress-relief grooves extends along a portion of the perimeter of the inner ring and / or the outer ring. Each stress-relief groove is preferably spaced apart from an adjacent stressrelief groove. In one illustrative example, the nozzle ring includes four stressrelief grooves at the outer ring. Each groove may be spaced apart by 90° from an adjacent groove. In another illustrative example, the nozzle ring includes four stress-relief grooves at the outer ring and four stress-relief grooves at the inner ring. A stress-relief groove which extends only along a fraction of the circumference of the inner or outer ring allows for providing the groove wheremechanical loading is most substantial. For example, in case the nozzle ring is connected to other components of the axial turbine at a connection point with fastening means (e.g. screws, bolts or the like), mechanical loading may be most substantial at the connection point. Providing the groove radially or axially adjacent to the connection point may reduce mechanical stress to the nozzle ring. Preferably, the groove circumferentially overlaps with the trailing edge of at least one nozzle blade.

[0024] In one implementation, a central angle of the groove is at least 15° and / or no more than 90°. Stated differently, the groove may extend at least 15° of the perimeter of the inner or outer ring. Preferably, the central angle of the groove is at least 25°, and more preferably at least 35° and / or preferably no more than 70°, and more preferably no more than 55°. A ratio between a circumferential length of the groove and an entire perimeter of the inner ring and / or the outer ring may be at least 4%, preferably at least 7%, more preferably at least 10% and / or no more than 25%, preferably no more than 20%, and more preferably no more than 15%.

[0025] The axial turbine may further include a calotte arranged at an upstream end portion of the nozzle ring.

[0026] In one illustrative embodiment, the calotte is fixed to or is integrally formed with the turbine casing. For example, the calotte may be fixed to or integrally formed with the gas inlet casing of the turbine casing. The calotte may be affixed to the gas inlet casing by means of one or more struts.

[0027] In another illustrative embodiment, the calotte is integrally formed with the nozzle ring. Typically, the calotte is integrally formed with the inner ring of the nozzle ring.

[0028] In a further alternative embodiment, the axial turbine does not include a calotte, and instead the gas inlet casing may include a lid or cover.

[0029] The axial turbine may further include a cover ring and / or a diffusor. The diffusor is arranged downstream of the nozzle ring and / or may be releasably attached within the turbine casing. The cover ring, if present, may be arranged downstream of the nozzle ring and / or upstream of the diffusor. The cover ring may be releasably attached within the turbine casing. For example, the cover ring may be releasably attached to the diffusor and / or the nozzle ring.

[0030] The nozzle ring may be releasably attached within the turbine casing in several different ways. For example, the nozzle ring may be attached via a clamping mechanism or via fastening means, such as screws.

[0031] According to an embodiment, the nozzle ring is clamped between the calotte and the cover ring or the diffusor. In this implementation, the calotte is preferably integrally formed with the gas inlet casing of the turbine casing. During transient and / or stationary conditions, the fixation of the nozzle ring to the turbine diffusor or the cover ring leads to substantial stress in the clamping portions of the nozzle ring. The stress-relief groove allows for decoupling the mechanical loading such that the trailing edge of the nozzle blades are not as heavily demanded.

[0032] According to a further embodiment, the axial turbine further comprises a fastening means. The fastening means may be a stud, in particular a stud with an internal thread, a bolt, in particular a bolt with an internal thread, or a screw. The fastening means may releasably attach the outer ring of the nozzle ring to the cover ring or the diffusor in the axial direction.

[0033] In an implementation, an upstream end portion of the cover ring is releasably connected to a downstream end portion of the nozzle ring via fastening means. Additionally, a downstream end portion of the cover ring may be releasably connected to an upstream end portion of the turbine diffuser via attachment elements. The attachment element may be a stud, in particular a stud with an internal thread, a bolt, in particular a bolt with aninternal thread, or a screw. The cover ring may be arranged within the gas outlet housing and in the vicinity of the turbine wheel. The cover ring may surround at least a section of the turbine wheel. The cover ring can enclose a portion of the turbine wheel radially on the outside and delimit a flow channel radially on the outside in the vicinity of the nozzle blades. The cover ring is typically not attached directly to the turbine housing.

[0034] In a further implementation, an upstream end portion of the turbine diffuser is releasably connected to a downstream end portion of the nozzle ring via fastening means. In this implementation, the cover ring may be omitted. This implementation may be utilised for applications in which the fluid flowing through the turbine is substantially free of abrasive particles.

[0035] In yet a further implementation, the turbine diffuser is integrally formed with the cover ring. The upstream end portion of the cover ring may be releasably connected to a downstream end portion of the nozzle ring via the fastening means.

[0036] In an embodiment, a downstream end portion of the outer ring has a radially outwardly projecting nozzle ring cam and an upstream end portion of the cover ring or the diffusor has a cam receptacle. The nozzle ring cam engages the cam receptacle. To attach the nozzle ring with the cover ring or the diffusor, the nozzle ring can be aligned (rotated) so that the nozzle ring cam can be sunk into the cam receptacle. The engagement of the cam in the cam receptacle creates a tangential contact surface. This allows the nozzle ring to be centred and its position to be fixed in the circumferential direction. Furthermore, the tangential contact surface between the nozzle ring cam and the cam receptacle enables a more secure torque transmission. The cam receptacle can have dimensions corresponding to those of the nozzle ring cam. For example, the cam receptacle can have slightly larger dimensions in the circumferential direction than the cam. This type of torque transmissionbetween the cam and cam receptacle allows for radial expansion of the nozzle ring during operation, thus improving thermo-mechanical fatigue behaviour.

[0037] The stress-relief groove may be arranged on the outer ring, and the groove may extend along a portion of the perimeter of the outer ring. Preferably, the stress-relief groove circumferentially overlaps with the nozzle ring cam of the outer ring. Due to the connection between the nozzle ring and the cover ring or the diffusor via the fastening means, the cam and the cam receptacle, the mechanical load may be largest in the vicinity of the nozzle ring cam during transient conditions. The stress-relief groove allows for decoupling the fixation force from the nozzle blades such that the trailing edge of the nozzle blades are not as heavily demanded.

[0038] The outer ring may further comprise a clamping segment. The fastening means may extend through an insertion opening in the clamping segment. Further, the fastening means may engage a thread in the cover ring or the diffusor.

[0039] Additionally, the cover ring or the diffusor may include a clamping projection for receiving the clamping segment. The fastening means, preferably together with the clamping segment (and, if present, the clamping segment extension), may allow for axial fixation of the nozzle ring and the cover ring. In this case, the fastening means enable the clamping segment to be pressed against the cover ring or the diffusor (optionally against the clamping projection) and the clamping segment can press the cam into the cam receptacle. In other words, axial fastening of the outer ring to the cover ring or the diffusor by means of the at least one fastening means enables the nozzle ring cam to be pressed into the cover ring cam receptacle. The combination of cam and cam receptacle on the one hand and fastening means and clamping segment on the other hand enable simultaneous centring and axial fastening of the nozzle ring.

[0040] According to a further aspect, a turbomachine is provided. Preferably, the turbomachine is an exhaust gas turbocharger. The turbomachine comprises an axial turbine according to one of the embodiments described herein and a compressor connected to the shaft. The turbomachine is not particularly limited, but may be a medium or low speed turbomachine.

[0041] Those skilled in the art will recognise additional features and advantages upon reading the following detailed description, and upon viewing the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The components in the Figures are not necessarily to scale, instead emphasis being placed upon illustrating the principles of the invention. Moreover, in the Figures, like reference signs designate corresponding parts. The accompanying drawings relate to embodiments of the disclosure and are described in the following:Fig. 1 shows a schematic view of an axial turbine according to embodiments described herein;Fig. 2 shows a close up view of a portion of the axial turbine of Figure 1;Fig. 3 shows a schematic exploded-view of an axial turbine according to embodiments described herein;Fig. 4 shows a schematic view of an axial turbine according to embodiments described herein;Fig. 5 shows a schematic view of an axial turbine according to embodiments described herein.DETAILED DESCRIPTION OF EMBODIMENTS

[0043] Reference will now be made in detail to the various embodiments, one or more examples of which are illustrated in each figure. Each example is provided by way of explanation and is not meant as a limitation. For example, features illustrated or described as part of one embodiment can be used on or in conjunction with any other embodiment to yield yet a further embodiment. It is intended that the present disclosure includes such modifications and variations.

[0044] Within the following description of the drawings, the same reference numbers refer to the same or to similar components. Generally, only the differences with respect to the individual embodiments are described. Unless specified otherwise, the description of a part or aspect in one embodiment can apply to a corresponding part or aspect in another embodiment as well.

[0045] With exemplary reference to Figure 1 an axial turbine 100 is described. The axial turbine 100 includes a turbine casing 160. The turbine casing includes 160 a gas-outlet casing 161 and a gas inlet casing 162.

[0046] Further, the axial turbine 100 includes a turbine wheel 180 (partially shown in Figure 1) arranged in the turbine casing 160. The turbine wheel 180 is mounted on a shaft. The shaft is not shown in Figure 1, but longitudinal axis 190 is included in Figure 1. The shaft defines longitudinal axis 190, and more generally defines the longitudinal or axial direction, the radial direction and the circumferential direction.

[0047] Axial turbine 100 further includes a nozzle ring 110 arranged in the turbine casing. The nozzle ring 110 is arranged at least partially upstream of the turbine wheel 180.

[0048] The nozzle ring 110 comprises an inner ring 114, a plurality of nozzle blades 113 arranged radially outward of the inner ring 114, and anouter ring 112 arranged radially outward of the nozzle blades 113. In the embodiment shown in Figure 1, the inner and outer ring 112, 114 as well as the blades 113 are integrally formed with each other.

[0049] Further, the nozzle ring 110 includes a calotte 111 at its upstream end. The calotte 111 is integrally formed with the inner ring 114. In other embodiments, the axial turbine 100 may not include a calotte, and in yet further embodiments the axial turbine 100 may include a calotte attached to the gas inlet casing 162, for example by means of struts.

[0050] The nozzle ring 110 is releasably attached within the turbine casing 160. The fixation mechanism is only partially visible in Figure 1. In the embodiment shown in Figure 1, the nozzle ring 110 is releasably attached to a turbine diffusor 130. The turbine diffusor includes a thread 131 for receiving a fastening means (not shown in Figure 1) to fasten the nozzle ring 110 to the diffusor 130. In other embodiments, the nozzle ring 110 may be releasably attached to a cover ring 220 as illustrated in Figure 3.

[0051] Further, the nozzle ring 110 includes a circumferentially extending stress-relief groove. In the embodiment shown in Figure 1, the nozzle ring 110 includes both a stress-relief groove 116 on the inner ring 114 as well as a stress-relief groove 117 on the outer ring 112. The vicinity of the grooves 116, 117 is highlighted with a dotted rectangle in Figure 1.

[0052] The stress-relief groove 116, 117 axially overlaps with the plurality of nozzle blades 113. In a preferred embodiment, the stress-relief groove 116, 117 axially overlaps with at least one trailing edge 115 of a nozzle blade 113.

[0053] In the embodiment shown in Figure 1, the stress-relief grooves 116, 117 extend along the entire circumference of the inner / outer ring 112, 114.

[0054] Figure 2 shows a close up view of a portion of the axial turbine of Figure 1 mainly illustrating the outer ring 112 of the nozzle ring 110.

[0055] A ratio between an axial thickness 124 of the groove and an axial thickness 123 of the outer ring may be at least 5%, preferably at least 7% and more preferably at least 10%, and / or no more than 80%, preferably no more than 60% and more preferably no more than 40%.

[0056] A ratio between a radial depth 126 of the groove and a radial depth 125 of the outer ring is at least 20%, preferably at least 40% and more preferably at least 60% and / or no more than 80%, preferably no more than 75% and more preferably no more than 70%.

[0057] With exemplary reference to Figure 3 an axial turbine 200 according to another embodiment is described. The embodiment illustrated in Figure 3 corresponds to that illustrated in Figure 1 unless stated to the contrary.

[0058] The axial turbine 200 includes nozzle ring 210 which is integrally formed of a calotte 211, an inner ring 214, a plurality of blades 213 and an outer ring 212. The axial turbine 200 further includes a cover ring 220 and a turbine diffusor 230. The nozzle ring 210 is releasably attached to the cover ring 220 and the cover ring 220 is releasably attached to the diffusor 230.

[0059] Axial turbine 200 includes fastening means 240 for releasably fixing nozzle ring 210 to cover ring 220 in the axial or longitudinal direction.

[0060] Nozzle ring 210 further includes a nozzle ring cam 215. Nozzle ring cam 215 is arranged at a downstream end portion or a downstream end of the outer ring 112. Nozzle ring cam 215 projects radially outward from the outer ring 112 and thereby defines a cam or a tab.

[0061] Cover ring 220 includes a cam receptacle 221. Cam receptacle 221 is arranged at an upstream end portion or an upstream end of the cover ring 220. The nozzle ring cam 215 engages the cam receptacle 221. The engagement of the cam 215 in the cam receptacle 221 creates a tangentialcontact surface. This allows the nozzle ring 210 to be centred and its position to be fixed in the circumferential direction.

[0062] The outer ring 212 further includes a clamping segment 216. The fastening means 240 extends through an insertion opening in the clamping segment 216 and engages a thread in the cover ring 220. The fastening means 240, together with the clamping segment 216 allow for axial fixation of the nozzle ring 210 and the cover ring 220. The cover ring 220 has a clamping projection 222 for receiving the clamping segment 216. The fastening means 240 enable the clamping segment 216 to be pressed against the cover ring 220 and the clamping segment 216 can press the cam 215 into the cam receptacle 221. Figure 4 illustrates a close-up view of the connection between cover ring 220 and nozzle 210.

[0063] Further, axial turbine 200 includes attachment elements 250 for releasably attaching cover ring 220 to diffusor 230. Attachment elements 250 extend through an insertion opening 225 in the cover ring 220 and engage with a thread 231 in diffusor 230.

[0064] With exemplary reference to Figure 5 an axial turbine 300 according to another embodiment is described. The embodiment illustrated in Figure 5 corresponds to that illustrated in Figure 3 unless stated to the contrary.

[0065] Nozzle ring 310 includes a plurality of stress-relief grooves 316. The particular embodiment illustrated in Figure 5 has four stress-relief grooves 316 arranged in the outer ring 312. Each of the grooves 316 is spaced apart from an adjacent groove by about 90°.

[0066] Each of the grooves 316 extends only along a portion of the perimeter of the outer ring 312. A central angle a of the groove 316 is at least 15°, preferably at least 25°, and more preferably at least 35° and / or no more than 90°, preferably no more than 70°, and more preferably no more than 55°.

[0067] A ratio between a circumferential length or arc length 319 of the groove 316 and an entire perimeter of the outer ring 312 may be at least 4%, preferably at least 7%, more preferably at least 10% and / or no more than 25%, preferably no more than 20%, and more preferably no more than 15%.

[0068] Nozzle ring 310 further includes one or more nozzle ring cams 315.The number of grooves 316 may correspond to the number of nozzle ring cams 315. Preferably, the groove 316 circumferentially overlaps with the nozzle ring cam 315 of the outer ring 312.

[0069] While the foregoing is directed to embodiments, other and further embodiments may be devised without departing from the basic scope, and the scope is determined by the claims that follow.REFERENCE NUMERALS100, 200, 300 axial turbine 110, 210, 310 nozzle ring111, 211, 311 calotte112, 212, 312 outer ring113. 213. 313 nozzle blades114. 214. 314 inner ring115 trailing edges of blades116, 316 groove in outer ring117 groove in inner ring123 axial thickness of outer ring124 axial thickness of groove125 radial depth of outer ring126 radial depth groove130, 230 turbine diffuser131, 231 thread in diffusor160 turbine casing161 gas-outlet casing162 gas inlet casing180 turbine wheel190 longitudinal axis215, 315 nozzle ring cam216 clamping segment220 cover ring221 cam receptacle222 clamping projection225 insertion opening in the cover ring240 fastening means250 attachment elements319 arc length a central angle

Claims

CLAIMS1. An axial turbine (100, 200), in particular for an exhaust turbocharger, comprising:- a turbine casing (160);- a turbine wheel (180) arranged in the turbine casing (160) and mounted on a shaft;- a nozzle ring (110) arranged in the turbine casing (160) and at least partially upstream of the turbine wheel (180), wherein the nozzle ring (110) comprises an inner ring (114), a plurality of nozzle blades (113) arranged radially outward of the inner ring (114), and an outer ring (112) arranged radially outward of the nozzle blades (113); wherein the nozzle ring (110) is releasably attached within the turbine casing (160); and wherein the nozzle ring (110) includes a circumferentially extending stress-relief groove (116, 117) on the inner ring (114) and / or the outer ring (112), wherein the stress-relief groove axially overlaps with the plurality of nozzle blades; and wherein the groove is arranged at an inner surface of the inner ring (114) and / or the groove is arranged at the outer surface of the outer ring (112).

2. The axial turbine of claim 1, wherein the groove (116, 117) axially overlaps with a trailing edge (115) of at least one of the nozzle blades (113), preferably with the trailing edges (115) of the plurality of nozzle blades (H3).

3. The axial turbine of any preceding claim, wherein a cavity defined by the groove is spaced apart from other components of the axial turbine (100).

4. The axial turbine of any preceding claim, wherein the stress-relief groove (116, 117) is unobstructed by other components of the axial turbine (100).

5. The axial turbine of any preceding claim, wherein the nozzle ring (110) further comprises a calotte (111, 211) which is arranged at an upstream end portion of the nozzle ring (110) and is integrally formed with the nozzle ring (110), in particular the inner ring (114) of the nozzle ring (110).

6. The axial turbine of any preceding claim, wherein the groove (116, 117) extends substantially along the entire perimeter of the inner ring (114) and / or the outer ring (112).

7. The axial turbine of any one of claims 1 to 5, wherein the groove (316) extends along a portion of the perimeter of the inner ring (314) and / or the outer ring (312); in particular wherein the wherein the nozzle ring (110) includes a plurality of grooves (316) each extending along a portion of the perimeter of the inner ring (314) and / or the outer ring (312).

8. The axial turbine of claim 7, wherein a central angle (a) of the groove (316) is at least 15°, preferably at least 25°, and more preferably at least 35° and / or no more than 90°, preferably no more than 70°, and more preferably no more than 55°.

9. The axial turbine of any preceding claim, wherein a ratio between a radial depth (126) of the groove and a radial depth (125) of the inner ring and / or the outer ring is at least 20%, preferably at least 40% and more preferably at least 60% and / or no more than 80%, preferably no more than 75% and more preferably no more than 70%.

10. The axial turbine of any preceding claim, wherein the nozzle ring is releasably attached to a cover ring (220) or a diffusor (130), in particular wherein the axial turbine further comprises a fastening means (240) releasably attaching the outer ring (112) to the cover ring (220) or the diffusor (130) in the axial direction.

11. The axial turbine of any preceding claim, wherein a downstream end portion of the outer ring (112) has a radially outwardly projecting nozzle ring cam (215) and an upstream end portion of the cover ring (220) or the diffusor (130) has a cam receptacle (221), and wherein the nozzle ring cam (215) engages in the cam receptacle (221).

12. The axial turbine of claim 11, wherein the groove (316) is arranged on the outer ring (312), and the groove (316) circumferentially overlaps with the nozzle ring cam (315) of the outer ring (312).

13. The axial turbine of any preceding claim, wherein the outer ring (212) comprises a clamping segment (216), wherein the fastening means (240) extends through an insertion opening in the clamping segment (216); and optionally wherein the fastening means (240) engages a thread (131) in the cover ring or the diffusor.

14. The axial turbine of claim 13, wherein the cover ring (220) or the diffusor (130) has a clamping projection (222) for receiving the clamping segment (216).

15. The axial turbine of any preceding claim, wherein: a) an upstream end portion of the cover ring (220) is releasably connected to a downstream end portion of the nozzle ring (210) via fastening means (240) and a downstream end portion of the cover ring (220) is releasably connected to an upstream end portion of the turbine diffuser (230) via attachment elements (250); or b) an upstream end portion of the turbine diffuser (130) is releasably connected to a downstream end portion of the nozzle ring (110) via fastening means; or c) wherein the turbine diffuser is integrally formed with the cover ring, and wherein an upstream end portion of the cover ring is releasably connected to a downstream end portion of the nozzle ring via the fastening means; or d) wherein the nozzle ring is clamped between a calotte integrally formed with a gas inlet casing of the turbine casing and the cover ring or the diffusor.21 / 22

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