Turbine wheel

A turbine wheel is provided with a groove having a bottom surface and a pair of side wall surfaces. The turbine wheel includes: a balance weight that is arranged in the groove, is insertable from any circumferential position of the opening of the groove, and has a through-hole opened toward one of the pair of side wall surfaces; and a retaining member that contacts the one of the pair of side wall surfaces in a state of being inserted in the through-hole of the balance weight, to thereby cause the balance weight to abut against the other one of the pair of side wall surfaces and be retained in the groove. The groove has engagement recesses provided at intervals in a circumferential direction at the bottom surface or an engagement protrusion fitted to one of fitting recesses provided at intervals in the circumferential direction at the bottom surface and protruding from the bottom surface. The balance weight has an engagement protrusion or an engagement groove that engages with one of the engagement recesses or the engagement protrusion of the groove, to thereby restrict a circumferential shift of the balance weight in the groove.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a turbine wheel of a gas turbine, and in particular relates to a turbine wheel including a balance weight.

2. Description of the Related Art

A gas turbine generally includes: a compressor that compresses air to generate compressed air; a combustor that mixes the compressed air from the compressor with fuel, and combusts the mixture to generate a combustion gas; and a turbine that obtains shaft power by the combustion gas from the combustor. The turbine includes a turbine rotor that converts the kinetic energy of the combustion gas into rotational power. In the turbine, it is necessary to adjust the balance of the turbine rotor in order to reduce vibrations during its rotation. Examples of the method of adjusting the balance of the turbine rotor include a method in which a portion of a component of the turbine rotor is machined, and a method in which a balance weight is attached to a component of the turbine rotor.

In the technology of adjusting the balance of the turbine rotor by attaching the balance weight, typically, at least one balance weight is arranged at an appropriate position, in the circumferential direction, in an annular dovetail groove provided at the wall surface of the turbine wheel (see JP 48-064601 U1 (1971), for example). JP 48-64601 U1 discloses that a balance weight attachment for turbine wheels is formed such that it can be inserted in any position in a dovetail-shaped annular groove formed on a turbine wheel without providing an access slot. The balance weight is retained in the annular groove of the turbine wheel with a projection of one side of its body portion abutted against one side of the annular groove when fastening means is inserted in an oblique passageway that is opened on the other side of the body portion and loads against the other side of the annular groove.

Meanwhile, since a gas turbine obtains shaft power of a turbine rotor from a high-temperature and high-pressure combustion gas, it is necessary to cool each part of the turbine rotor such as turbine wheels or turbine rotor blades by cooling air, and to suppress a temperature increase of each part. In the gas turbine, typically, compressed air bled from a compressor is used as the cooling air. In this case, increasing the flow rate of the cooling air means increasing the flow rate of the compressed air bled from the compressor. Accordingly, if the flow rate of the cooling air is increased, the flow rate of the combustion gas to drive the turbine rotor decreases by a corresponding amount, and thus the overall efficiency of the gas turbine deteriorates.

One of the effective means for attaining high efficiency of a gas turbine is to reduce cooling air used to cool each part of a turbine rotor. In this case, the ambient temperature in a wheel space formed in front and rear of the turbine wheel in the axial direction increases. In view of this, it has been proposed to change the material of a turbine wheel to a Ni based alloy that is more heat-resistant than conventionally used 12Cr steel materials. It should be noted however that there is a concern that cracks due to the residual tensile stress occur if parts formed of a Ni based alloy material are used in a high temperature environment in a state in which they are receiving a residual tensile stress.

In the technology described in JP 48-064601 U1, the balance weight is retained in the annular groove of the turbine wheel with the projection of the balance weight abutted against the one side of the annular groove when the fastening means is inserted in the oblique passageway of the balance weight and loads against the other side of the annular groove. In the technology of retaining the balance weight in the annular groove in this manner, an opening edge portion of the annular groove of the turbine wheel is crimped in some cases in order to inhibit a circumferential shift of the balance weight along the annular groove. In this case, a residual tensile stress is generated in and around the crimped portion of the turbine wheel.

In a case where not a 12Cr steel material, but a Ni based alloy material is applied to a turbine wheel for which a method, like the one mentioned above, of inhibiting the shift of a balance weight by crimping a portion of the turbine wheel is employed, there is a concern over occurrences of cracks in the turbine wheel due to a residual tensile stress generated by the crimping.

The present invention has been made in order to solve the problems described above, and an object of the present invention is to provide a turbine wheel that can suppress a residual tensile stress caused in a turbine wheel by fixing a balance weight.

SUMMARY OF THE INVENTION

The present application includes a plurality of means for solving the problems described above, and one example thereof is a turbine wheel provided with a groove having a bottom surface extending circumferentially and a pair of side wall surfaces forming an opening. The turbine wheel including: a balance weight that is arranged in the groove, is configured to be insertable from any circumferential position of the opening of the groove, and has a through-hole opened toward one of the pair of side wall surfaces of the groove; and a retaining member that contacts a portion of the one of the pair of side wall surfaces of the groove in a state of being inserted in the through-hole of the balance weight, to thereby cause the balance weight to abut against other one of the pair of side wall surfaces of the groove and be retained in the groove. The groove has a plurality of engagement recesses provided at intervals in a circumferential direction at the bottom surface; or an engagement protrusion fitted to one of a plurality of fitting recesses provided at intervals in the circumferential direction at the bottom surface and protruding from the bottom surface. The balance weight has an engagement protrusion that engages with one of the engagement recesses of the groove to restrict a circumferential shift of the balance weight in the groove or an engagement groove that engages with the engagement protrusion of the groove to restrict a circumferential shift of the balance weight in the groove.

According to the present invention, since the engagement protrusion or the engagement groove of the balance weight engages with the engagement recess or the engagement protrusion in the groove of the turbine wheel, the circumferential shift of the balance weight within the groove is restricted, and thus it becomes unnecessary to crimp the turbine wheel in order to fix the balance weight. Accordingly, it is possible to suppress a residual tensile stress caused in the turbine wheel by fixing the balance weight.

Problems, configurations and effects other than those described above become apparent from the following explanation of embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of a turbine wheel according to the present invention are explained by using the drawings.

First Embodiment

First, the configuration of a gas turbine including a turbine wheel according to a first embodiment of the present invention is explained by usingFIG. 1andFIG. 2.FIG. 1is a cross-sectional diagram illustrating the gas turbine including the turbine wheel according to the first embodiment of the present invention in a state in which a lower half section is omitted therefrom.FIG. 2is an enlarged cross-sectional diagram illustrating a portion of a turbine rotor including the turbine wheel according to the first embodiment of the present invention illustrated inFIG. 1.

InFIG. 1, the gas turbine includes a compressor1, a combustor2and a turbine3. The compressor1compresses air taken in to generate compressed air. The combustor2mixes the compressed air generated by the compressor1with fuel from a fuel system (not illustrated), and combusts the mixture to generate a combustion gas. The gas turbine has a multi-can type combustor, for example, and in the multi-can type, a plurality of combustors2are annularly arranged at intervals. The turbine3is rotation-driven by the high temperature and high-pressure combustion gas generated at the combustor2to drive the compressor1and a load (a driven device such as a generator, a pump, and a process compressor) which is not illustrated. The turbine3is supplied with compressed air bled from the compressor1as cooling air to cool components of the turbine3.

The compressor1includes: a compressor rotor10that is rotation-driven by the turbine3; and a compressor casing15that houses the compressor rotor10such that compressor rotor10can rotate therein. The compressor1is an axial compressor, for example. The compressor rotor10includes: a plurality of disc-like compressor wheels11stacked in the axial direction; and a plurality of compressor rotor blades12that are coupled to an outer circumferential edge portion of each compressor wheel11. In the compressor rotor10, the plurality of compressor rotor blades12arrayed annularly at the outer circumferential edge portion of each compressor wheel11form one compressor rotor blade row.

A plurality of compressor stator blades16are arrayed annularly downstream side of a working fluid from each compressor rotor blade row. The plurality of compressor stator blades16arrayed annularly form one compressor stator blade row. The compressor stator blade rows are fixed inside the compressor casing15. In the compressor1, each compressor rotor blade row, and each compressor stator blade row located immediately downstream of the compressor rotor blade row form one stage.

The turbine3includes: a turbine rotor30that is rotation-driven by the combustion gas from the combustor2; and a turbine casing35that houses the turbine rotor30such that the turbine rotor30can rotate therein. The turbine3is an axial turbine. A flow passage P through which the combustion gas flows is formed between the turbine rotor30and the turbine casing35.

As illustrated inFIG. 1andFIG. 2, the turbine rotor30is built by alternately stacking, in the axial direction, a plurality of disc-like turbine wheels40having a plurality of turbine rotor blades31coupled thereto circumferentially at an outer circumferential edge portion, and a plurality of disc-like spacers32. The stacked turbine wheels40and spacers32are fixed by stacking bolts33. In the turbine rotor30, a plurality of turbine rotor blades31arrayed annularly at an outer circumferential edge portion of each turbine wheel40form one turbine rotor blade row. Each turbine rotor blade row is disposed in the flow passage P.

A plurality of turbine stator blades36are arrayed annularly upstream of the working fluid from each turbine rotor blade row. The plurality of turbine stator blades36arrayed annularly form one turbine stator blade row. The turbine stator blade rows are fixed inside the turbine casing35, and are disposed in the flow passage P. In the turbine3, each turbine stator blade row, and each turbine rotor blade row located immediately downstream of the turbine stator blade row form one stage.

The turbine rotor30is connected to the compressor rotor10via an intermediate shaft38. The turbine casing35is connected to the compressor casing15.

Next, the configuration and structure of the turbine wheel according to the first embodiment of the present invention are explained by usingFIG. 2toFIG. 8.FIG. 3is an enlarged view of an attachment structure of a balance weight of the turbine wheel according to the first embodiment of the present invention as seen in the axial direction.FIG. 4is a cross-sectional diagram illustrating the fixed state of the balance weight in a groove of the turbine wheel according to the first embodiment of the present invention illustrated inFIG. 3as seen in the direction of arrows IV-IV.FIG. 5is a cross-sectional diagram of the groove of the turbine wheel according to the first embodiment of the present invention illustrated inFIG. 3as seen in the direction of arrows V-V.FIG. 6is a cross-sectional diagram of the balance weight of the turbine wheel according to the first embodiment of the present invention.FIG. 7is a diagram of the balance weight of the turbine wheel according to the first embodiment of the present invention illustrated inFIG. 6as seen in the direction of an arrow VII.FIG. 8is a front view illustrating a retaining member of the turbine wheel according to the first embodiment of the present invention.

InFIG. 2andFIG. 3, the turbine wheels40are formed with a Ni based alloy as their base material. An annular thicker portion41at an intermediate section in a radial direction R of a turbine wheel40is provided with bolt holes43that penetrates the thicker portion41in an axial direction A (the thickness direction of the turbine wheel40). The bolt holes43are provided at predetermined intervals in a circumferential direction C. A stacking bolt33is inserted into each bolt hole43.

In addition, as illustrated inFIG. 3, on the end surface of the thicker portion41of the turbine wheel40in the axial direction A, a groove50is formed such that it extends in the circumferential direction C of the turbine wheel40. The groove50intermittently extends over the entire circumference of the turbine wheel40such that the bolt holes43are sandwiched between parts of the groove50, for example. A balance weight60is arranged in the groove50for the balance adjustment of the turbine rotor30(seeFIG. 2). A plurality of balance weights60are arranged in the groove50as necessary in some cases. The balance weight60is retained in the groove50by a retaining screw member80as a retaining member.

As illustrated inFIG. 4andFIG. 5, the groove50is formed such that the width (the length in the upward/downward direction or the radial direction R inFIG. 4andFIG. 5) of a bottom surface51is larger than the width (the length in the upward/downward direction or the radial direction R inFIG. 4andFIG. 5) of an opening58, and is formed like a dovetail groove, for example. The groove50is formed such that the width of the bottom surface51and the width of the opening58are each approximately the same in the circumferential direction C, for example.

The groove50has the flat bottom surface51that is approximately parallel to the end surface, in the axial direction A, of the thicker portion41of the turbine wheel40, and a first side wall surface52and a second side wall surface53as a pair of side wall surfaces that form the opening58and is closer to each other on a direction away from the bottom surface51(leftward direction inFIG. 4andFIG. 5). The first side wall surface52is inclined such that it is gradually positioned radially outward Ro as it comes from the side where the bottom surface51is located toward the side where the opening58is located. On the other hand, the second side wall surface53is inclined such that it is gradually positioned radially inward Ri as it comes from the side where the bottom surface51is located toward the side where the opening58is located, and is positioned radially outward Ro relative to the first side wall surface52.

A first corner portion54between the first side wall surface52and the bottom surface51is formed as a concave curved surface. The concave curved surface of the first corner portion54has a predetermined radius of curvature in its cross-sectional shape, for example. Similarly to the first corner portion54, a second corner portion55between the second side wall surface53and the bottom surface51is formed as a concave curved surface having a predetermined radius of curvature in its cross-sectional shape.

As illustrated inFIG. 3toFIG. 5, a plurality of engagement recesses56are provided at intervals in the circumferential direction C on the bottom surface51of the groove50. The engagement recesses56are configured to engage with engagement protrusion71, which is mentioned below, of the balance weight60, and have the function of restricting the shift of the balance weight60in the groove50in the circumferential direction C (the extending direction of the groove50). The engagement recesses56are formed as grooves (engagement grooves) that extend in the groove widthwise direction of the groove50(in the upward/downward direction or the radial direction R inFIG. 4andFIG. 5), for example. As illustrated inFIG. 5, in a meridional cross-section of the turbine wheel40including an engagement recess56, a length Lg from an opening edge58b, which is on a side where the second side wall surface53is located, of the opening58of the groove50to an end section59a, which is on a side where a first side wall surface52is located, of an opening edge59of the engagement recess56in the groove50is set to a predetermined length.

InFIG. 3andFIG. 4, the balance weight60is formed such that it is insertable from any position, in the circumferential direction C, of the opening58of the groove50of the turbine wheel40. In addition, the balance weight60is formed such that it abuts against the second side wall surface53of the groove50, and engages with the engagement recess56of the groove50.

Specifically, as illustrated inFIG. 4, the balance weight60includes a body section61to be arranged between the first side wall surface52and second side wall surface53of the groove50, and an engagement protrusion71formed integrally with the body section61. The body section61is a portion to abut against the second side wall surface53of the groove50, and has the function of restricting the shift of the balance weight60in the groove50in the radial direction R (the groove widthwise direction of the groove50). The engagement protrusion71is a portion to engage with any one of the engagement recesses56of the groove50, and has the function of restricting the shift of the balance weight60in the groove50in the circumferential direction C (the extending direction of the groove50).

A side portion of the body section61on a side where the second side wall surface53of the groove50is located is formed in a shape that is approximately complementary to the groove shape of the groove50, and has a shape that can make surface contact with (abut against) the second side wall surface53of the groove50. In addition, the side portion on the second side wall surface53side of the body section61is shaped such that a portion corresponding to a corner portion on a side where the second corner portion55of the groove50is located is cut out, and has a shape that does not inhibit the insertion of the balance weight60through the opening58of the groove50. In addition, a side portion of the body section61on a side where the first side wall surface52is located is formed not in a shape complementary to the groove shape of the groove50, but in a shape that creates a gap between itself and the first side wall surface52, and is shaped such that a portion corresponding to a corner portion on a side where the first corner portion54of the groove50is located is cut out. That is, the side portion on the first side wall surface52side of the body section61has a shape that does not inhibit the insertion of the balance weight60through the opening58of the groove50.

More specifically, as illustrated for example inFIGS. 4, 6 and 7, the body section61has a rear surface62that faces the bottom surface51of the groove50, a front surface63that is positioned on the side opposite to the rear surface62and faces the opening58of the groove50, a first side surface64that is connected to the rear surface62and the front surface63and faces the first side wall surface52of the groove50, a second side surface65that is connected to the rear surface62and the front surface63, positioned on the side opposite to the first side surface64, and faces the second side wall surface53of the groove50, and a pair of circumferential side surfaces66that are connected to the rear surface62and the front surface63, are connected to the first side surface64and the second side surface65, and face the circumferential direction C of the groove50.

The front surface63and the rear surface62are formed such that they become approximately parallel to each other. As illustrated inFIG. 4, a length Lw1(seeFIG. 6) from a ridge E1, which is on a side where the first side surface64is located, of the front surface63to a ridge, which is on a side where the second side surface65is located, of the front surface63is set such that it is slightly shorter than the width of the opening58of the groove50.

As illustrated inFIG. 4andFIG. 6, the first side surface64includes: a perpendicular surface64athat is substantially perpendicularly connected to the front surface63; and a first inclined surface64bthat extends from the perpendicular surface64aand is connected to the rear surface62while being inclined in a direction toward the second side surface65. This configuration of the first side surface64allows the balance weight60to be inserted into the groove50without making the first side surface64contact an opening edge on the first side wall surface52side of the groove50.

The second side surface65includes: an abutting surface65athat extends from the front surface63toward the rear surface62while being inclined in a direction away from the first side surface64; and a second inclined surface65bthat extends from the abutting surface65aand is connected to the rear surface62while being inclined in a direction toward the first side surface64. The abutting surface65ais formed such that its angle of inclination is approximately the same as the angle of inclination of the second side wall surface53of the groove50, and it is possible for the abutting surface65ato make surface contact with the second side wall surface53.

As illustrated inFIG. 7, the pair of circumferential side surfaces66are formed such that they are substantially perpendicular to the bottom surface62and the front surface63, and are approximately parallel to each other. For example, the pair of circumferential side surfaces66are portions to serve as a portion to be gripped by an operator when the operator inserts the balance weight60into the groove50.

As illustrated inFIGS. 4, 6, and 7, the engagement protrusion71of the balance weight60is formed such that it protrudes from the rear surface62of the body section61, and forms a shape that is generally complementary to the engagement recess56of the groove50. The engagement protrusion71is formed as a projecting section that extends in a direction (the groove widthwise direction of the groove50) connecting the side where the first side surface64is located and the side where the second side surface65is located, for example.

The balance weight60is provided with a through-hole68that penetrates the body section61, and that is opened toward the first side wall surface52of the groove50. The through-hole68is opened at the front surface63of the body section61and at the first inclined surface64bof the first side surface64, for example. The through-hole68is provided with a female thread portion, for example. As illustrated inFIG. 4, the retaining screw member80as the retaining member is disposed in a screwed (inserted) state in the through-hole68having the female thread portion.

In addition, the balance weight60is formed such that a length Lw2(seeFIG. 6) from the ridge E1, which is located between the front surface63and the second side surface65, of the body section61to an end portion E2, which is on a side where the first side surface64is located, of a tip surface71aof the engagement protrusion71is shorter than the length Lg (seeFIG. 5) from the opening edge58bon the second side wall surface53side of the opening58of the groove50to the end portion59aon the first side wall surface52side of the opening edge59of the engagement recess56(seeFIG. 9mentioned below also). This allows the balance weight60to be inserted into the groove50without making the engagement protrusion71contact the opening edge59of the engagement recess56of the groove50.

Note that, for example, the length between the pair of circumferential side surfaces66of the balance weight60may vary. In this case, it is possible to ensure balance weights having different weights.

As illustrated inFIG. 4, the retaining screw member80contacts the first corner portion54of the first side wall surface52of the groove50in a state of being inserted in the through-hole68of the balance weight60, thereby causing the second side surface65(the abutting surface65a) of the body section61of the balance weight60to abut against the second side wall surface53of the groove50and the balance weight60to be retained in the groove50. As illustrated inFIGS. 4 and 8, the retaining screw member80includes: a body section81having a male thread portion; and a tip section82that is formed integrally on one side of the body section81and has a curved surface. The tip section82is formed such that it makes line contact with a part of the concave curved surface of the first corner portion54of the groove50. For example, a shape profile of the tip section82in a meridional plane cross-section has a convex curved shape having a radius of curvature approximately the same as the radius of curvature of the cross-sectional shape of the concave curved surface of the first corner portion54.

Next, an example of the procedure of attachment of the balance weight into the groove in the turbine wheel according to the first embodiment of the present invention is explained by usingFIGS. 4 and 9.FIG. 9is an explanatory diagram illustrating an example of the method of insertion of the balance weight into the groove in the turbine wheel according to the first embodiment of the present invention.

First, as illustrated inFIG. 9, the ridge E1between the front surface63and the second side surface65of the body section61of the balance weight60is caused to contact on the opening edge58bon the second side wall surface53side of the opening58of the groove50. In this state, the balance weight60is turned about the ridge E1as the turning axis toward the bottom surface51of the groove50. At this time, the engagement protrusion71of the balance weight60relatively shifts along the engagement recess56of the groove50. Thereby, the body section61of the balance weight60is arranged between the first side wall surface52and second side wall surface53of the groove50, and the engagement protrusion71of the balance weight60is arranged in the engagement recess56of the groove50.

In the present embodiment, the length Lw2of the balance weight60from the ridge E1to the end portion E2on the first side surface64side of the tip surface71aof the engagement protrusion71is set shorter than the length Lg of the groove50from the opening edge58bon the second side wall surface53side of the opening58to the end portion59aon the first side wall surface52side of the opening edge59of the engagement recess56. Accordingly, it is possible to insert the balance weight60into the groove50without making the engagement protrusion71of the balance weight60contact the opening edge59of the engagement recess56of the groove50.

Next, as illustrated inFIG. 4, the retaining screw member80is screwed (inserted) into the through-hole68of the balance weight60in which the female thread portion is formed, and the tip section82of the retaining screw member80is pressed against the concave curved surface of the first corner portion54of the groove50. By further screwing the retaining screw member80into the through-hole68, the balance weight60shifts toward the second side wall surface53of the groove50along the retaining screw member80. Eventually, the abutting surface65aof the second side surface65of the balance weight60makes surface contact with the second side wall surface53of the groove50.

In this manner, in the present embodiment, the retaining screw member80contacts the first corner portion54on the first side wall surface52side of the groove50in a state of being inserted in the through-hole68of the balance weight60, thereby causing the abutting surface65aof the balance weight60to make surface contact with (abut against) the second side wall surface53of the groove50. As a result, the shift of the balance weight60in the radial direction R (in the groove widthwise direction of the groove50) within the groove50is restricted, and the balance weight60is retained in the groove50. In addition, the engagement protrusion71of the balance weight60engages with the engagement recess56of the groove50, thereby restricting the shift of the balance weight60within the groove50in the circumferential direction C (in the extending direction of the groove50). Accordingly, it is possible to fix the balance weight60in the groove50of the turbine wheel40without crimping the turbine wheel40.

As mentioned above, according to the first embodiment of the turbine wheel according to the present invention, the engagement protrusion71of the balance weight60engages with the engagement recess56of the groove50of the turbine wheel40, thereby restricting the shift of the balance weight60in the circumferential direction C within the groove50. In this way, the shift of the balance weight60is restricted also by the engagement protrusion71in addition to fixation by the retaining screw member80, and therefore the balance weight60can be firmly fixed. Thus, it becomes unnecessary to crimp the turbine wheel40in order to fix the balance weight60. Accordingly, it is possible to suppress a residual tensile stress caused in the turbine wheel40by fixing the balance weight60.

In addition, according to the present embodiment, the length Lw2from the ridge E1, which is located between the front surface63and the second side surface65, of the body section61to the end portion E2, which is closer to the first side surface64, of the tip surface71aof the engagement protrusion71in the balance weight60is set shorter than the length Lg from the opening edge58b, which is closer to the second side wall surface53, of the opening58to the end portion59a, which is closer to the first side wall surface52, of the opening edge59of the engagement recess56in the groove50, and thus it is possible to insert the balance weight60into the groove50from any position, in the circumferential direction C, of the opening58of the groove50of the turbine wheel40.

Furthermore, according to the present embodiment, the body section61and engagement protrusion71of the balance weight60are formed integrally, and thus the attachment of the balance weight60in the groove50is easy as compared with a configuration in which a body section and an engagement protrusion of a balance weight are separate members. That is, the integral structure of the body section61and engagement protrusion71of the balance weight60does not require assembly work of the balance weight60itself. As a result, the integral structure can avoid the falling of an engagement protrusion71from a body section61, which may occur in a case where a body section61and an engagement protrusion71are separate members.

In addition, according to the present embodiment, the first corner portion54of the groove50is formed as a concave curved surface, and the tip section82of the retaining screw member80is formed such that it makes line contact with a portion of the concave curved surface of the first corner portion54of the groove50. Accordingly, it is possible to suppress a residual tensile stress caused in the portion of the first corner portion54of the groove50with which the retaining screw member80makes contact.

Second Embodiment

Next, a turbine wheel of a second embodiment according to the present invention is explained by usingFIGS. 10 and 11.FIG. 10is a cross-sectional diagram illustrating a balance weight of the turbine wheel according to the second embodiment of the present invention.FIG. 11is a diagram of the balance weight of the turbine wheel according to the second embodiment of the present invention illustrated inFIG. 10as seen in the direction of an arrow XI. Note that since the reference characters inFIGS. 10 and 11that are the same as reference characters illustrated inFIGS. 1 to 9denote similar portions, detailed explanations thereof are omitted.

While the body section61and engagement protrusion71of the balance weight60in the first embodiment are formed integrally (seeFIG. 6), the turbine wheel according to the second embodiment of the present invention illustrated inFIGS. 10 and 11has a configuration including a body section61A and an engagement protrusion72of a balance weight60A as separate members.

Specifically, the balance weight60A includes: the body section61A having the through-hole68and a fitting recess69; and a pin72attached to the fitting recess69of the body section61A by being fit thereto. Similarly to the body section61of the balance weight60of the first embodiment, the body section61A has the rear surface62, the front surface63, the first side surface64, the second side surface65and the pair of circumferential side surfaces66. Similarly to the first embodiment, the first side surface64includes the perpendicular surface64aand the first inclined surface64b. Similarly to the first embodiment, the second side surface65includes the abutting surface65aand the second inclined surface65b. The fitting recess69is provided in an approximately middle portion of the rear surface62. The fitting recess69has a circular cross-section shape, for example. The pin72is a member separate from the body section61A, and functions as an engagement protrusion to engage with any one of the engagement recesses56of the groove50. The pin72has a circular transverse cross-section shape, for example.

The balance weight60A is formed such that a length Lw3from the ridge E1, which is located between the front surface63and the second side surface65, of the body section61A to an end portion E3, which is on a side where the first side surface64is located, of the tip surface72aof the pin72as the engagement protrusion is shorter than the length Lg (seeFIG. 5) from the opening edge58bon the second side wall surface53side of the opening58of the groove50to the end portion59aon the first side wall surface52side of the opening edge59of the engagement recess56. This allows the balance weight60A to be inserted into the groove50without making the pin72as the engagement protrusion contact the opening edge59of the engagement recess56of the groove50.

According to the second embodiment of the turbine wheel according to the present invention mentioned above, similarly to the first embodiment mentioned before, the pin72as the engagement protrusion of the balance weight60A engages with the engagement recess56of the groove50of the turbine wheel40, thereby restricting the shift of the balance weight60A in the circumferential direction C within the groove50. As a result, it becomes unnecessary to crimp the turbine wheel40in order to fix the balance weight60A. Accordingly, it is possible to suppress a residual tensile stress caused in the turbine wheel40by fixing the balance weight60A.

Third Embodiment

Next, the configuration and structure of a turbine wheel according to a third embodiment of the present invention are explained by usingFIGS. 12 to 14.FIG. 12is a cross-sectional diagram illustrating a groove of the turbine wheel according to the third embodiment of the present invention.FIG. 13is a cross-sectional diagram illustrating a balance weight of the turbine wheel according to the third embodiment of the present invention.FIG. 14is a diagram of the balance weight of the turbine wheel according to the third embodiment of the present invention illustrated inFIG. 13as seen in the direction of an arrow XIV. Note that since the reference characters inFIGS. 12 to 14that are the same as reference characters illustrated inFIGS. 1 to 11denote similar portions, detailed explanations thereof are omitted.

A difference of the third embodiment of the turbine wheel according to the present invention illustrated inFIGS. 12 to 14from the first embodiment is that the recessed shape and the projecting shape in engagement between the groove and the balance weight in the turbine wheel40are interchanged. That is, in the first embodiment, the engagement protrusion71of the balance weight60engages with the engagement recess56of the groove50of the turbine wheel40, thereby restricting the shift of the balance weight60in the circumferential direction C within the groove50(seeFIG. 4). On the other hand, in the third embodiment, an engagement groove69B of a balance weight60B engages with a pin57as an engagement protrusion of a groove50B, thereby restricting the shift of the balance weight60B in the circumferential direction C within the groove50B.

Specifically, as illustrated inFIG. 12, the bottom surface51of the groove50B is provided with a plurality of fitting recesses56B at intervals in the circumferential direction C. A pin57can be fit to and fixed to each fitting recess56B. The pin57protrudes from the bottom surface51of the groove50B, engages with the engagement groove69B of the balance weight60B, and functions as an engagement protrusion that restricts the shift of the balance weight60B in the circumferential direction C within the groove50B. The pin57may be fit only to a fitting recess56B corresponding to the attachment position of the balance weight60B among the plurality of fitting recesses56B of the groove50B.

As illustrated inFIGS. 13 and 14, in the balance weight60B, the rear surface62of a body section61B is provided with the engagement groove69B. The engagement groove69B extends toward the first side surface64from the end edge closer to the second side surface65to the position of a middle portion, and is opened at the rear surface62and the second side surface65. The engagement groove69B engages with the pin57fitted to the fitting recess56B of the groove50B, and has the function of restricting the shift of the balance weight60B in the circumferential direction C within the groove50B.

Next, an example of the procedure of attachment of the balance weight into the groove in the turbine wheel according to the third embodiment of the present invention is explained by usingFIG. 15.FIG. 15is an explanatory diagram illustrating an example of the method of insertion of the balance weight into the groove in the turbine wheel according to the third embodiment of the present invention.

As illustrated inFIG. 15, the ridge E1of the body section61B of the balance weight60B, which is located between the front surface63and the second side surface65, is caused to contact on the opening edge58b, closer to the second side wall surface53, of the opening58of the groove50B. In this state, the balance weight60B is turned toward the bottom surface51of the groove50B about the ridge E1as the turning axis.

In the present embodiment, the pin57fitted to the fitting recess56B of the groove50B relatively shifts along the engagement groove69B of the body section61B of the balance weight60B. Thereby, the balance weight60B is inserted into the groove50B without making the second side surface65and rear surface62of the balance weight60B contact the pin57as the engagement protrusion of the groove50B.

Similarly to the first embodiment, in the present embodiment also, the retaining screw member80(seeFIG. 4) contacts the first corner portion54of the groove50B closer to the first side wall surface52in a state of being inserted in the through-hole68of the balance weight60B, thereby causing the abutting surface65aof the balance weight60B to make surface contact with the second side wall surface53of the groove50B. As a result, the shift of the balance weight60B in the radial direction R (in the groove widthwise direction of the groove50) within the groove50B is restricted, and the balance weight60B is retained in the groove50B. In addition, the engagement groove69B of the balance weight60B engages with the pin57fitted to the fitting recess56B of the groove50B, thereby restricting the shift of the balance weight60B in the circumferential direction C (in the extending direction of the groove50B) within the groove50B. Accordingly, it is possible to fix the balance weight60B in the groove50B without crimping the turbine wheel40.

According to the third embodiment of the turbine wheel according to the present invention mentioned above, since the engagement groove69B of the balance weight60B engages with the pin57as the engagement protrusion of the groove50B of the turbine wheel40, the shift of the balance weight60B in the circumferential direction C within the groove50B is restricted, and thus it becomes unnecessary to crimp the turbine wheel40in order to fix the balance weight60B. Accordingly, it is possible to suppress a residual tensile stress caused in the turbine wheel40by fixing the balance weight60B.

Other Embodiments

Note that the present invention is not limited to the first to third embodiments mentioned above, but includes various modification examples. The embodiments described above are explained in detail in order to explain the present invention in an easy-to-understand manner, and the present invention is not necessarily limited to embodiments including all the configurations explained. For example, some of the configurations of an embodiment can be replaced with configurations of another embodiment, and configurations of an embodiment can also be added to the configurations of another embodiment. In addition, some of the configurations of individual embodiments can have other additional configurations, or can be removed or replaced with other configurations.

For example, in the first embodiment mentioned above, the engagement protrusion71of the balance weight60is formed as a projecting section that extends in the direction connecting the side where the first side surface64is located and the side where the second side surface65is located (in the groove widthwise direction of the groove50). However, the engagement protrusion71may have any shape as long as the engagement protrusion71engages with the engagement recess56of the groove50of the turbine wheel40, and thereby restricts the shift of the balance weight60in the circumferential direction C. It is also possible to form the cross-sectional shape of the engagement protrusion71in a circular, rectangular or polygonal shape, for example.

In addition, in the first and second embodiments mentioned above, the engagement recess56is formed as a groove (engagement groove) that extends in the groove widthwise direction of the groove50. However, the engagement recess56may have any shape as long as the engagement recess56engages with the engagement protrusion71of the balance weight60or the pin72of the balance weight60A, and thereby can restrict the shift of the balance weights60and60A in the circumferential direction C.