Rotating body, turbocharger, and rotating body manufacturing method

Provided is a rotating body, including: a shaft; and a compressor impeller including: a main body having an insertion hole, which extends from one end to another end side and is configured to receive the shaft inserted therethrough; a boss portion formed at one end side of the main body; and a joint portion, which is formed on an inner peripheral surface of the insertion hole at the boss portion and is welded to the shaft.

BACKGROUND ART

Technical Field

The present disclosure relates to a rotating body including a compressor impeller and a shaft, a turbocharger including the rotating body, and to a manufacturing method for a rotating body.

Related Art

Hitherto, there has been known a turbocharger in which a shaft is axially supported in a bearing housing so as to be freely rotatable. A turbine wheel is provided at one end of the shaft, and a compressor impeller is provided at another end of the shaft. The turbocharger is connected to an engine. In the turbocharger, the turbine wheel is rotated by exhaust gas discharged from the engine. The rotation of the turbine wheel causes the compressor impeller to rotate via the shaft. The turbocharger is configured to compress air in association with the rotation of the compressor impeller and send the compressed air to the engine.

For example, a compressor impeller disclosed in Patent Literature 1 has an insertion hole. A shaft is inserted through the insertion hole of the compressor impeller. The shaft has a step portion. The compressor impeller is held in abutment against the step portion of the shaft. A part of the shaft which projects from the insertion hole has a thread. The compressor impeller is sandwiched between a nut, which is threadedly engaged with the thread, and the step portion of the shaft. The compressor impeller is fixed to the shaft by an axial force applied by the nut.

CITATION LIST

Patent Literature

SUMMARY

Technical Problem

With the above-mentioned configuration described in Patent Literature 1, it is difficult to manage the axial force. Therefore, there has been a demand for development of a rotating body which can be easily manufactured, a turbocharger, and a manufacturing method for a rotating body.

The present disclosure has an object to provide a rotating body which can be easily manufactured, a turbocharger, and a manufacturing method for a rotating body.

Solution to Problem

In order to solve the problem described above, according to one embodiment of the present disclosure, there is provided a rotating body, including: a shaft; and a compressor impeller including: a main body having an insertion hole, the insertion hole extending from one end to another end side and being configured to receive the shaft inserted therethrough; a boss portion formed at one end side of the main body; and a joint portion, which is formed on an inner peripheral surface of the insertion hole at the boss portion, and is welded to the shaft.

The insertion hole includes: a small-inner-diameter portion formed on the another end side with respect to the boss portion; and a radially expanded portion, which is located between the small-inner-diameter portion and the joint portion, and has an inner diameter larger than an inner diameter of the small-inner-diameter portion.

The compressor impeller includes: blades which are provided at the another end side with respect to the boss portion on an outer periphery of the main body; and an extending portion, which is located between the blades and the boss portion, and has a thickness in the radial direction larger than that of the boss portion.

The shaft includes: a small-diameter portion welded to the joint portion; a large-diameter portion, which is formed on the another end side with respect to the small-diameter portion, and has a diameter larger than that of the small-diameter portion; and a step portion extending from the small-diameter portion to the large-diameter portion.

The boss portion is divided into a plurality of segments in the circumferential direction.

In order to solve the problem described above, according to one embodiment of the present disclosure, a turbocharger includes a rotating body.

In order to solve the problem described above, according to one embodiment of the present disclosure, there is provided a manufacturing method for a rotating body, including: inserting a shaft through an insertion hole extending from one end to another end side of a main body of a compressor impeller; and joining a boss portion, which is formed at one end of the main body, and the shaft by electromagnetic forming.

Effects of Disclosure

According to the present disclosure, a rotating body can be easily manufactured.

DESCRIPTION OF EMBODIMENT

Now, with reference to the attached drawings, an embodiment of the present disclosure is described in detail. The dimensions, materials, and other specific numerical values represented in the embodiment are merely examples used for facilitating the understanding of the present disclosure, and do not limit the present disclosure otherwise particularly noted. Elements having substantially the same functions and configurations herein and in the drawings are denoted by the same reference symbols to omit redundant description thereof. Further, illustration of elements with no direct relationship to the present disclosure is omitted.

FIG.1is a schematic sectional view of a turbocharger C. In the following, a direction indicated by the arrow L illustrated inFIG.1is described as a left side of the turbocharger C. A direction indicated by the arrow R illustrated inFIG.1is described as a right side of the turbocharger C. As illustrated inFIG.1, the turbocharger C includes a turbocharger main body1. The turbocharger main body1includes a bearing housing2. A turbine housing4is coupled to the left side of the bearing housing2by a fastening bolt3. A compressor housing6is coupled to the right side of the bearing housing2by a fastening bolt5.

The bearing housing2has a bearing hole2a. The bearing hole2apasses through the turbocharger C in the right-and-left direction. Radial bearings7are provided in the bearing hole2a. InFIG.1, illustration is given of full-floating bearings as one example of the radial bearings7. However, the radial bearings7may be other radial bearings such as semi-floating bearings or rolling bearings. The shaft8is axially supported by the radial bearings7so as to be freely rotatable. A turbine wheel9is provided at a left end portion of the shaft8. The turbine wheel9is accommodated in the turbine housing4so as to be freely rotatable. Moreover, a compressor impeller10is provided at a right end portion of the shaft8. The compressor impeller10is accommodated in the compressor housing6so as to be freely rotatable.

The compressor housing6has a suction port11. The suction port11is opened on the right side of the turbocharger C. The suction port11is connected to an air cleaner (not shown). A diffuser flow passage12is defined on a radially outer side of the suction port11. The diffuser flow passage12is defined by opposed surfaces of the bearing housing2and the compressor housing6. The diffuser flow passage12is configured to increase the pressure of the air. The diffuser flow passage12is defined so as to have an annular shape extending from an inner side toward an outer side in the radial direction of the shaft8. The diffuser flow passage12communicates to the suction port11through intermediation of the compressor impeller10.

The compressor housing6has a compressor scroll flow passage13. The compressor scroll flow passage13is defined so as to have an annular shape. For example, the compressor scroll flow passage13is located on an outer side in the radial direction of the shaft8with respect to the diffuser flow passage12. The compressor scroll flow passage13communicates to a suction port of an engine (not shown). The compressor scroll flow passage13communicates also to the diffuser flow passage12. When the compressor impeller10rotates, air is breathed into the compressor housing6through the suction port11. The air having been breathed is pressurized and accelerated by an action of a centrifugal force in a course of flowing through blades of the compressor impeller10. The air having been pressurized and accelerated is increased in pressure in the diffuser flow passage12and the compressor scroll flow passage13. The air having been increased in pressure is guided to the suction port of the engine.

The turbine housing4has a discharge port14. The discharge port14is opened on the left side of the turbocharger C. The discharge port14is connected to an exhaust gas purification device (not shown). The turbine housing4has a flow passage15and a turbine scroll flow passage16. The turbine scroll flow passage16is defined so as to have an annular shape. For example, the turbine scroll flow passage16is located on the radially outer side of the turbine wheel9with respect to the flow passage15. The turbine scroll flow passage16communicates to a gas inflow port (not shown). Exhaust gas discharged through a discharge manifold of the engine (not shown) is guided to the gas inflow port. The exhaust gas having been guided to the turbine scroll flow passage16through the gas inflow port is guided to the discharge port14through the flow passage15and the turbine wheel9.

The turbine wheel9rotates in a course of flow of the exhaust gas from the flow passage15to the discharge port14. A rotational force of the turbine wheel9is transmitted to the compressor impeller10via the shaft8. The rotational force of the compressor impeller10causes the air having been increased in pressure to be guided to the suction port of the engine.

A turbine-side bearing17and a compressor-side bearing18are provided in the bearing housing2. The turbine-side bearing17has a through hole configured to receive the shaft8inserted therethrough. The compressor-side bearing18has a through hole configured to receive the shaft8inserted therethrough. The turbine-side bearing17is provided at an opening of the bearing hole2a. The compressor-side bearing18is provided on the compressor impeller10side with respect to the turbine-side bearing17. The compressor-side bearing18is separated apart from the turbine-side bearing17in the axial direction of the shaft8(hereinafter simply referred to as “axial direction”). A seal plate19is provided between the compressor-side bearing18and the compressor impeller10. The seal plate19is mounted to the bearing housing2.

FIG.2is a partial enlarged view of the rotating body A. InFIG.2, illustration is given of the rotating body A, the radial bearing7, the turbine-side bearing17, and the compressor-side bearing18. The rotating body A includes at least the shaft8and the compressor impeller10of, for example, a radial type. The shaft8has an abutment surface8a. In the shaft8, an outer diameter thereof on the compressor impeller10side is smaller than an outer diameter thereof on the turbine wheel9side over the abutment surface8aas a boundary. That is, the abutment surface8ais formed by an outer diameter difference of the shaft8.

The abutment surface8ais an annular flat surface facing the compressor impeller10side. A collar8bprovided to the shaft8is held in abutment against the abutment surface8a. The collar8bis held in abutment against the abutment surface8afrom the compressor impeller10side. The collar8bis located between the turbine-side bearing17and the compressor-side bearing18. The collar8brotates integrally with the shaft8. The collar8bis opposed to the turbine-side bearing17and the compressor-side bearing18in the axial direction. Lubricating oil is supplied to a gap between the collar8band the turbine-side bearing17. Lubricating oil is supplied to a gap between the collar8band the compressor-side bearing18. When the rotating body A moves in the axial direction, a thrust load acts on the turbine-side bearing17or the compressor-side bearing18via the collar8b. That is, the turbine-side bearing17and the compressor-side bearing18function as thrust bearings.

An oil thrower member8chaving a cylindrical shape is provided between the collar8band the compressor impeller10. The shaft8is inserted through the oil thrower member8c. The oil thrower member8chas one end in contact with the compressor impeller10and has another end in contact with the collar8b. In the oil thrower member8c, an outer diameter thereof on the collar8bside is smaller than an inner diameter of a through hole of the compressor-side bearing18. The collar8bside of the oil thrower member8cis inserted through the through hole of the compressor-side bearing18. In the oil thrower member8c, an outer diameter thereof on the compressor impeller10side is larger than an inner diameter of the through hole of the compressor-side bearing18. The oil thrower member8ccauses the lubricating oil, which flows from the through hole of the compressor-side bearing18toward the compressor impeller10, is caused to scatter radially outward with a centrifugal force.

The compressor impeller10includes a main body20. The main body20has such a shape of being radially expanded from the right side toward the left side inFIG.2in the axial direction. In the main body20, an outer peripheral surface20afaces one side in the axial direction (right side inFIG.2), and a back surface20bfaces another side in the axial direction (left side inFIG.2).

The outer peripheral surface20aof the main body20is gradually increased in outer diameter toward the another side in the axial direction. For example, the back surface20bof the main body20is gradually increased in outer diameter toward the one side in the axial direction. The outer peripheral surface20aincludes a plurality of blades21which are separated apart from each other in a rotation direction of the shaft8(hereinafter simply referred to as “rotation direction” or “circumferential direction”). The blades21project in the radial direction from the outer peripheral surface20aof the main body20. The blades21include long blades21aand short blades21b. The long blades21aextend longer than the short blades21bin the axial direction. In other words, the long blades21aproject toward one side (right side inFIG.2) with respect to the short blades21b. The long blades21aand the short blades21bare provided alternately in the rotation direction.

The main body20of the compressor impeller10has an insertion hole22. The insertion hole22is formed (extends) from one end (end portion on the right side inFIG.2) of the main body20toward another end side (end portion side on the left side inFIG.2). The insertion hole22passes through the main body20from the one end to the another end. The shaft8is inserted through the insertion hole22.

A boss portion23is formed on one end side (right side inFIG.2) of the main body20. The boss portion23is a part of the main body20, which projects toward one side in the axial direction with respect to the blades21(long blades21a). In other words, the blades21are provided on the another end side with respect to the boss portion23on an outer periphery of the main body20. The boss portion23is separated apart from the blades21in the axial direction. The main body20includes an extending portion24. The extending portion24is a part located between the blades21(long blades21a) and the boss portion23. The extending portion24has a thickness in the radial direction larger than that of the boss portion23. In other words, the boss portion23has a thickness in the radial direction smaller than that of the extending portion24.

The outer peripheral surface20aof the main body20is gradually reduced in diameter toward one side in the axial direction (right side inFIG.2). In the extending portion24, a diameter of the outer peripheral surface20ais approximately constant or is gently reduced toward one side in the axial direction (right side inFIG.2). In the outer peripheral surface20aat the boss portion23, an outer diameter on one end side of the main body20(right side inFIG.2) is smaller than an outer diameter on another end side (left side inFIG.2). For example, the boss portion23is tapered off toward the one end side (right side inFIG.2) of the main body20. A joint portion25is formed on an inner peripheral surface of the insertion hole22at the boss portion23. The joint portion25is a part at which the main body20(boss portion23) and the shaft8are welded to each other. That is, the joint portion25is formed over both the main body20(boss portion23) and the shaft8.

The insertion hole22includes a small-inner-diameter portion26and a radially expanded portion27on another end side of the main body20(left side inFIG.2) with respect to the joint portion25described above. The small-inner-diameter portion26is formed on another end side (left side inFIG.2) of the main body20with respect to the boss portion23. That is, the small-inner-diameter portion26is located on a radially inner side of the blades21and the extending portion24. The radially expanded portion27is located between the small-inner-diameter portion26and the joint portion25. The radially expanded portion27extends from the small-inner-diameter portion26to the joint portion25. The radially expanded portion27has an inner diameter larger than that of the small-inner-diameter portion26. The radially expanded portion27has a maximum inner diameter on the small-inner-diameter portion26side, and the inner diameter is gradually reduced toward the joint portion25side. The radially expanded portion27has a tapered shape, which is gradually reduced in inner diameter on the joint portion25side.

A step surface28extending in the radial direction is formed in the insertion hole22. The step surface28is located at a boundary portion between the boss portion23and the extending portion24. In other words, the boss portion23and the extending portion24have a boundary therebetween at the step surface28. The step surface28is formed by an inner diameter difference between the small-inner-diameter portion26and an end portion of the radially expanded portion27on the small-inner-diameter portion26side. A difference in thickness in the radial direction between the boss portion23and the extending portion24is approximately equal to an inner radius difference between the small-inner-diameter portion26and the end portion of the radially expanded portion27on the small-inner-diameter portion26side. That is, a difference between the boss portion23and the extending portion24in thickness in the radial direction is approximately equal to a width of the step surface28in the radial direction. With the radially expanded portion27, a space S is defined inside the boss portion23.

Next, description is made of a method of assembling the rotating body A described above.FIG.3Ais an illustration of the shaft8and the compressor impeller10before being joined to each other.FIG.3Bis an illustration of the shaft8and the compressor impeller10after being joined to each other.FIG.3Cis a partial enlarged view of a joint surface between the shaft8and the compressor impeller10. InFIG.3C, illustration of the joint surface between the shaft8and the compressor impeller10is simplified. As illustrated inFIG.3A, in a state before the shaft8and the compressor impeller10are joined to each other, the boss portion23is separated apart from the shaft8in the radial direction. That is, an inner diameter of the insertion hole22at the boss portion23is equal to an outer diameter of the step surface28, and is approximately constant from one side to another side in the axial direction. The boss portion23has a bottomed cylindrical shape with the step surface28as a bottom part. The boss portion23has the space S opened on one end side of the main body20.

In an assembling step, the radial bearing7, the shaft8, the collar8b, the oil thrower member8c, the turbine wheel9, the compressor-side bearing18, and the seal plate19are assembled to the bearing housing2by a predetermined procedure. After that, the shaft8is inserted through the insertion hole22of the compressor impeller10.

The collar8bis held in abutment against the abutment surface8a. The oil thrower member8cis in contact with the collar8b. Another end of the compressor impeller10is in contact with the oil thrower member8c. That is, the collar8band the oil thrower member8care sandwiched between the abutment surface8aand the compressor impeller10. At this time, the compressor impeller10is pressed toward the oil thrower member8cside with a jig (not shown). Moreover, on this occasion, one end of the shaft8is pulled with a jig (not shown).

In this state, as illustrated inFIG.3B, the boss portion23is inserted into a coil30. When a large current flows through the coil30, a magnetic flux and an eddy current flow to the boss portion23by electromagnetic induction. Electromagnetic forces repel each other between the coil30and the boss portion23so that the electromagnetic force imparted radially inward to the boss portion23(indicated by outlined arrows inFIG.3B) act. The boss portion23is radially contracted at high speed in a sequential manner from the one end side of the shaft8(right side inFIG.3B) toward the another end side of the shaft8(left side inFIG.3B). An inner peripheral surface of the insertion hole22at the boss portion23collides with an outer peripheral surface of the shaft8at high speed. As a result, the boss portion23is deformed with viscoplasticity of a material thereof, thereby being welded (joined) in the radial direction of the shaft8. The joint portion25is formed on the inner peripheral surface of the insertion hole22at the boss portion23. In this case, the joint surface of the welded portion (outer peripheral surfaces of the joint portion25and the shaft8) is formed into, for example, a corrugated shape due to a behavior of the viscoplasticity as illustrated inFIG.3C.

As described above, in the assembling step for the rotating body A, the shaft8is inserted through the insertion hole22formed in the compressor impeller10. Then, the boss portion23, which is formed at one end of the main body20, and the shaft8are welded (joined) to each other by electromagnetic forming. In the related art, the compressor impeller10is fastened to the shaft8by a nut. In the assembling step having hitherto been employed, it is required that the axial force be strictly managed. When the compressor impeller10is to be welded to the shaft8, in the assembling step, it is only required that an axial force which prevents rotation of the collar8band the oil thrower member8cbe applied. Management of the axial force becomes extremely easier. As a result, the rotating body A and the turbocharger C can easily be manufactured. Moreover, in the assembling step having hitherto been employed, the axial force for holding the compressor impeller10with respect to the shaft8significantly varies, with the result that the rotation number is limited. With the rotating body A according to the embodiment, the variation of the axial force for holding the compressor impeller10with respect to the shaft8is small, thereby being capable of meeting the demand for increase in speed. Moreover, when the boss portion23and the shaft8are welded (joined) to each other in the radial direction, as compared to the case in which the boss portion23and the shaft8are welded (joined) in the axial direction, a high degree of freedom in design, such as increase in a welding (joining) area in an easy manner, can be secured. Moreover, when the boss portion23and the shaft8are welded (joined) to each other in the radial direction, as compared to the case in which the boss portion23and the shaft8are welded (joined) to each other in the axial direction, a space for arranging a jig at the time of welding (joining) can easily be secured. Therefore, operability is improved.

In this case, the extending portion24is formed between the blades21and the boss portion23. In general, in the turbocharger C, balance adjustment is performed after assembly of the rotating body A. In the related-art configuration in which the compressor impeller10is fastened to the shaft8with a nut, the balance adjustment is performed by grinding the nut. The extending portion24has a thickness larger than that of the boss portion23. Therefore, in the rotating body A, the extending portion24can be used for the balance adjustment. However, the extending portion24is not essentially required.

Herein, as one example, description is made of the case in which the joint portion25is formed by the electromagnetic forming. However, the joint portion25may be formed by other joining processing such as explosive bonding. Moreover, for example, at the time of assembling the compressor impeller10to the shaft8, the electromagnetic bonding described above and shrink fitting may be used in combination. In this case, it is preferred that the range of shrink fitting be set at a part of the small-inner-diameter portion26on the oil thrower member8cside. In the small-inner-diameter portion26, the part on the oil thrower member8cside and a part of the shaft8which is opposed to the part of the small-inner-diameter portion26(part of the small-inner-diameter portion26on the oil thrower member8cside) in the radial direction have a dimensional relationship achieving interference fitting. That is, an outer diameter of the part of the shaft8on the oil thrower member8cis larger than an inner diameter of the insertion hole22opposed to the part of the shaft8(part of the shaft8on the oil thrower member8cside) in the radial direction. The shaft8is inserted into the insertion hole22of the compressor impeller10with the main body20having been warmed, and one end side of the shaft8is pulled. When the main body20is cooled, the insertion hole22is radially contracted, and hence the compressor impeller10is brought into pressure contact with the shaft8. After that, in a manner similar to that described above, the boss portion23is joined to the shaft8by the electromagnetic forming. With the combination of the electromagnetic forming and the shrink fitting, the compressor impeller10can be more rigidly assembled to the shaft8.

FIG.4is an extraction view for illustrating a part corresponding toFIG.3Bin a first modification example. In the first modification example, a rotating body A1is provided in place of the rotating body A according to the embodiment described above. Configurations other than the rotating body A1are the same as those described above. Configurations which are the same as those described above are denoted by the same reference symbols, and detailed description is omitted. The rotating body A1includes a shaft8A. The shaft8A has an annular groove31formed in an outer peripheral surface on one end side. The annular groove31is a groove extending in the circumferential direction.

The annular groove31is located on a radially inner side of the boss portion23. In an assembling step for the rotating body A1, for example, the electromagnetic forming is performed in a manner similar to that described above. In this case, a joint portion25A is formed on an inner peripheral surface of the insertion hole22at the boss portion23. The joint portion25A bites into the annular groove31of the shaft8A. That is, the boss portion23is caulked with respect to the shaft8A at the joint portion25A.

In the first modification example, description is made of the case in which the annular groove31is formed. However, on the outer peripheral surface of the shaft8A, there may be formed, in place of the annular groove31, an annular projection extending in the circumferential direction. Moreover, there may be formed, in place of the annular groove31, a spline-shaped groove extending in the axial direction. In the outer peripheral surface of the shaft8A, there may be formed grid-shaped grooves formed of a plurality of grooves intersecting one another. Moreover, on the outer peripheral surface of the shaft8A, the annular groove31and the annular projection may be omitted, and the inner peripheral surface of the insertion hole22at the boss portion23may be press-joined to the outer peripheral surface of the shaft8A. In any of those cases, for example, when the boss portion23extends over the circumferential direction, a press-joining force is likely to be generated. On the inner peripheral surface of the insertion hole22at the boss portion23, there is formed the joint portion25A. The joint portion25A may be welded or not welded to the shaft8A.

FIG.5is an extraction view for illustrating a part corresponding toFIG.3Bin a second modification example. In the second modification example, a rotating body A2is provided in place of the rotating body A according to the embodiment described above. Configurations other than the rotating body A2are the same as those described above. Configurations which are the same as those described above are denoted by the same reference symbols, and detailed description is omitted. The compressor impeller10of the rotating body A2includes a main body20A. The main body20A has a boss portion23A formed at one end. The extending portion24is formed on another end side of the boss portion23A. An abutting surface32is formed between the outer peripheral surface of the boss portion23A and the outer peripheral surface of the extending portion24. The abutting surface32is an annular flat surface extending in the radial direction and the circumferential direction. An outer diameter of the boss portion23A is, for example, smaller than an outer diameter of the extending portion24by a thickness of the abutting surface32in the radial direction. The abutting surface32is formed at a base end of the boss portion23A.

When the main body20A and the shaft8are to be joined to each other, one end of the shaft8is pulled toward one side in the axial direction (right side inFIG.5) with a jig (not shown). In this state, the jig is pressed against the abutting surface32, and the main body20A is pressed toward another side in the axial direction (left side inFIG.5). With the main body20A being pressed, the abutment surface8a, the collar8b, and the oil thrower member8cof the shaft8as well as the compressor impeller10are brought into contact with one another in the axial direction. In this state, the joint portion25is formed by, for example, the electromagnetic forming, and the boss portion23A is joined (welded) to the shaft8. With the abutting surface32formed at the base end of the boss portion23A, the boss portion23A is appropriately held at the time of joining, thereby improving accuracy in joining.

FIG.6is an extraction view for illustrating a part corresponding toFIG.3Bin a third modification example. In the third modification example, a rotating body A3is provided in place of the rotating body A according to the embodiment described above. Configurations other than the rotating body A3are the same as those described above. Configurations which are the same as those described above are denoted by the same reference symbols, and detailed description is omitted. The compressor impeller10of the rotating body A3includes a main body20B. The main body20B has a boss portion23B formed at one end. The extending portion24is formed on another end side of the boss portion23B. The boss portion23B and the extending portion24have thicknesses in the radial direction which are approximately equal to each other.

The rotating body A3includes a shaft8B. The shaft8B includes a small-diameter portion33at one end thereof. The shaft8B includes a large-diameter portion34on another end side with respect to the small-diameter portion33. The large-diameter portion34has a diameter larger than that of the small-diameter portion33. A step portion35is formed between the small-diameter portion33and the large-diameter portion34. The step portion35extends from the small-diameter portion33to the large-diameter portion34. The step portion35is an annular flat surface extending in the radial direction and the circumferential direction.

In the rotating body A3, the boss portion23B of the main body20B is joined to the shaft8B. Before the boss portion23B and the shaft8B are joined to each other, an inner diameter of the insertion hole22is approximately equal from one end side to another end side. An inner diameter of the insertion hole22is approximately equal to a diameter of the large-diameter portion34of the shaft8B, or is slightly larger than a diameter of the large-diameter portion34. Thus, a space S is defined between the inner peripheral surface of the insertion hole22at the boss portion23B and the outer peripheral surface of the small-diameter portion33. In a manner similar to that described above, when the electromagnetic forming is performed on the boss portion23B, the joint portion25is formed on the inner peripheral surface of the insertion hole22at the boss portion23B. Under a state in which the boss portion23B and the shaft8B are joined to each other, an inner diameter of the insertion hole22is smaller on a side closer to the joint portion25.

The rotating body A of the embodiment described above has a step in the insertion hole22of the main body20. Also in a case in which the step is formed in the shaft8B as in the case of the rotating body A3of the third modification example, an action similar to that of the embodiment described above is achieved.

FIG.7Ais a sectional view of a boss portion23C in a fourth modification example. In the fourth modification example, the boss portion23C is different from the boss portion23of the embodiment described above. Similarly to the description above, the boss portion23C is joined to the shaft8. InFIG.7A, there is illustrated a state before the boss portion23C and the shaft8are joined to each other. The boss portion23C of the fourth modification example has two slits36. The slits36passes from the inner peripheral surface of the insertion hole22to the outer peripheral surface of the boss portion23C. The slits36extend in the axial direction. However, a length and a width of the slits36are not particularly limited. For example, the slits36may be formed within a range of the boss portion23C, or may extend to the extending portion24. In the fourth modification example, the two slits26are arranged opposed to each other at positions shifted by 180 degrees in the circumferential direction.

FIG.7Bis a sectional view of a boss portion23D in a fifth modification example. Similarly to the description above, the boss portion23D is joined to the shaft8. InFIG.7B, illustration is given of a state before the boss portion23D and the shaft8are joined to each other. The boss portion23D of the fifth modification example has two more slits36as compared to the boss portion23C of the fourth modification example. The boss portion23D has four slits36which are formed at positions shifted by 90 degrees in the circumferential direction. Also in the fifth modification example, a length and a width of the slits36in the axial direction are not particularly limited.

FIG.7Cis a sectional view of a boss portion23E in a sixth modification example. Similarly to the description above, the boss portion23E is joined to the shaft8. InFIG.7C, illustration is given of a state before the boss portion23E and the shaft8are joined to each other. The boss portion23E of the sixth modification example has a rectangular sectional shape as compared to the boss portion23D of the fifth modification example. That is, the boss portion23E is partially different in thickness in the radial direction. The boss portion23E is divided by the slits36into four segments in the circumferential direction. The four divided segments of the boss portion23E are each increased in thickness in the radial direction as extending from both end sides toward a center side in the circumferential direction.

According to the fourth to sixth modification examples described above, the joint portion25to be joined to the shaft8is formed on the boss portion23C,23D,23E. The boss portion23C,23D,23E having the joint portion25is divided by the slits36into a plurality of segments in the circumferential direction. When the main body20C,20D,20E and the shaft8are to be joined to each other, one end of the shaft8is pulled toward one side in the axial direction (close side on the drawing sheets inFIG.7A,FIG.7B, andFIG.7C) with a jig (not shown). In this state, a jig (not shown) is pressed against a bottom surface36aof the slit36on another side in the axial direction (far side on the drawing sheets inFIG.7A,FIG.7B, andFIG.7C), and the main body20C,20D,20E is pressed toward another side in the axial direction. The boss portion23C,23D,23E is appropriately held at the time of joining, thereby improving accuracy in joining. Moreover, the boss portion23C,23D,23E is divided in the circumferential direction, and hence is likely to be radially contracted at the time of performing the electromagnetic forming. Thus, the rotating body A can easily be assembled and manufactured.

The embodiment of the present disclosure has been described above with reference to the attached drawings, but, needless to say, the present disclosure is not limited to the embodiment. It is apparent that those skilled in the art may arrive at various alternations and modifications within the scope of claims, and those examples are construed as naturally falling within the technical scope of the present disclosure.

For example, configurations of the embodiment and modification examples described above may be combined.

Moreover, in the embodiment and modification examples described above, description is made of the case in which the blades21include the long blades21aand the short blades21b. However, the blades21may have one kind of length in the axial direction.

INDUSTRIAL APPLICABILITY

The present disclosure is applicable to a rotating body including a compressor impeller and a shaft, to a turbocharger including the rotating body, and to a manufacturing method for a rotating body.