Press-fit structure and determination method of press-fit quality thereof

Abstract

To provide a press-fit structure capable of determining whether the press-fit is good or bad, and a determining method thereof.SOLUTION: A press-fit structure includes a support member having an insertion hole and a shaft member to be press-fitted into the insertion hole, in which the support member includes a fitting completion position where the fitting between the support member and the shaft member is completed, and a boring portion where the diameter of the support member is larger than the diameter of the shaft member is formed over a predetermined range in the press-fit direction at the fitting completion position.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a press-fitting structure and a method for determining the quality of press-fitting.

Background Art

[0002] Patent Document 1 discloses a structure in which a shaft is press-fitted into a support portion (a support portion having a recess) formed in a partition wall of a pump case in a water pump.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When performing press-fitting, press-fitting defects may occur. In the water pump described in Patent Document 1 above, the shaft is press-fitted into the support portion having a recess, but the inner diameter of the support portion is constant. Therefore, for example, when the contact pressure between the outer peripheral surface of the shaft and the inner peripheral surface of the support portion locally increases during press-fitting, so-called plastic flow may occur. When such plastic flow occurs, foreign matter (scraped chips) is generated, such as when the shaft scrapes the inner peripheral surface of the support portion, resulting in a press-fitting defect. However, since the inner diameter of the support portion is constant, it is difficult to determine whether a press-fitting defect has occurred because there is no space or gap for discharging the foreign matter.

[0005] The present invention has been made in view of the above problems, and an object thereof is to provide a press-fitting structure capable of determining the quality of press-fitting and a method for determining the same.

Means for Solving the Problems

[0006] In order to achieve the above object, a press-fitting structure includes a support member having an insertion hole and a shaft member press-fitted into the insertion hole. The support member includes a fitting completion position where the fitting between the support member and the shaft member is completed. At the fitting completion position, a counterbore portion is formed in which the diameter of the support member is larger than the diameter of the shaft member over a predetermined range in the press-fitting direction.

[0007] Further, there is provided a press-fitting structure including a support member having an insertion hole and a shaft member press-fitted into the insertion hole. The support member includes a fitting completion position where the fitting between the support member and the shaft member is completed. At the fitting completion position, a counterbore portion is formed in which the diameter of the support member is larger than the diameter of the shaft member over a predetermined range in the press-fitting direction. A method for determining the quality of press-fitting when the support member is press-fitted is provided. In the method, a press-fitting load is calculated during the press-fitting process. When the continuously increasing press-fitting load decreases, it is determined that the quality of the press-fitting is abnormal.

[0008] That is, in this press-fitting structure and the method for determining the quality of press-fitting, a counterbore portion is formed at the fitting completion position where the fitting between the support member and the shaft member is completed, and the diameter of the support member is larger than the diameter of the shaft member over a predetermined range in the press-fitting direction. Therefore, when the outer peripheral surface of the shaft member scrapes the inner peripheral surface of the support member during press-fitting, foreign matter (scrapings) is discharged into the counterbore portion, and the press-fitting load corresponding to the amount of scraping decreases. Therefore, it can be determined that a press-fitting defect has occurred due to the decrease in the press-fitting load. And by being able to determine that a press-fitting defect has occurred, for example, the possibility that the fastening force of the shaft member becomes insufficient (that is, the fitting becomes insufficient) due to the support member being scraped can be reduced.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0010] Here, embodiments of the present invention will be described in the following order. (1) Press-fitting structure: (2) Method for determining the quality of press-fitting: (3) Other embodiments, etc.:

[0011] (1) Press-fitting structure: Regarding the press-fitting structure in this embodiment, it will be described using the configuration of an electric pump. In this embodiment, the electric pump 1 is an electric water pump (hereinafter simply referred to as "electric pump") that circulates cooling water (an example of a refrigerant) for cooling an engine, a motor, or an inverter, etc. mounted on a vehicle. Note that the electric pump 1 can be used in any posture. In the example shown in FIG. 1, with the rotation axis X (the vertical direction of the paper surface) as a reference, the impeller 9 is arranged on the upper side of the paper surface, and the circuit board 6 is arranged on the lower side of the paper surface (that is, on the side opposite to the impeller 9). Also, in this specification, the direction along the rotation axis X is referred to as the "axial direction", and the direction perpendicular to the rotation axis X is referred to as the "radial direction".

[0012] FIG. 1 shows a cross-sectional view of the electric pump 1 according to this embodiment. The electric pump 1 includes a motor 4 having a rotor 2 that rotates around the rotation axis X and a stator 3 arranged opposite to the rotor 2, a motor housing 5 that is a metallic housing for housing the motor 4, a circuit board 6 for driving the motor 4, a shaft 7 whose end is fixed to the motor housing 5, a cylindrical bush 8 inserted outside the shaft 7 and rotating integrally with the rotor 2, and an impeller 9 that rotates by the driving force of the motor 4 and pumps the cooling water.

[0013] The electric pump 1 includes a resin cover member 10 that houses the circuit board 6 and a metal (e.g., aluminum) impeller housing 11 that houses the impeller 9. These cover member 10 and impeller housing 11 are fixed to the motor housing 5 by bolts, welding, or the like. This electric pump 1 is configured such that the impeller 9 sucks or discharges cooling water when the rotor 2 rotates by the driving force of the motor 4. For example, cooling water is made to flow through the motor 4 and an inverter (not shown), or cooling water is circulated between the engine and the radiator (both not shown).

[0014] The rotor 2 is made of, for example, PPS (polyphenylene sulfide) as a resin material for insert molding the bush 8. The rotor 2 includes a back yoke and a plurality of permanent magnets 12. The stator 3 includes a stator core formed by laminating a plurality of thin electromagnetic steel sheets, and a stator coil 13 is wound around the stator core. The motor 4 is configured as a three-phase brushless motor that generates a rotating magnetic field in the rotor 2 by energizing the stator 3.

[0015] The motor housing 5 is a metal housing as described above, for example, made of aluminum die-cast. The stator 3 is in contact with and fixed to the motor housing 5. Specifically, on the outer side in the radial direction (the side away from the rotation axis X in the radial direction), the stator 3 is in contact with and fixed to the motor housing 5. In the present embodiment, the stator 3 is fixed to the motor housing 5 by, for example, press-fitting or shrink-fitting. In this way, by fixing the stator 3 to the metallic motor housing 5 such as an aluminum die-cast, the heat generated in the stator 3 can be transferred (i.e., dissipated) to the motor housing 5.

[0016] And in the example shown in FIG. 1, a support portion 14 for supporting the shaft 7 is formed at the bottom portion 5a of the motor housing 5 in the axial direction, and the tip 7a of the shaft 7 is press-fitted and fixed to the support portion 14 from the impeller 9 side toward the circuit board 6 side. The fitting completion position where the fitting between the shaft 7 and the support portion 14 is completed by the press-fitting is a predetermined position such as a position where the shaft 7 does not come out in the support portion 14. Note that the fitting completion position may be within a predetermined range of the support portion 14 in the press-fitting direction (i.e., the axial direction). That is, as long as the shaft 7 does not come out and the fitted state can be maintained, the fitting completion position is not limited to a specific position, and may be provided over a predetermined range. In the example shown in FIG. 1, in the axial direction, the fitting completion position is provided over a predetermined range from the bottom portion 14a of the support portion 14 toward the impeller 9 side, and the fitting completion position is indicated by the symbol F. In the present embodiment, the shaft 7 corresponds to the "axial member", and the motor housing 5 (specifically, the support portion 14 formed at the bottom portion 5a) corresponds to the "support member".

[0017] Also, in the present embodiment, a counterbore portion 24 in which the inner diameter of the support portion 14 is larger than the inner diameter of the shaft 7 is formed over a predetermined range in the press-fitting direction at the fitting completion position F described above. Specifically, as shown in FIG. 2, with respect to the support portion 14 in which an insertion hole for inserting the shaft 7 is formed, a part of the insertion hole is further cut from the inside to increase the diameter (counterboring process). In the present embodiment, the counterboring process is performed at the fitting completion position F. By performing such a counterboring process to increase the diameter, a slight gap or space is generated between the outer peripheral surface of the shaft 7 and the inner peripheral surface of the support portion 14 at the fitting completion position F. In the example shown in FIG. 2, for convenience of explanation, the gap is shown enlarged.

[0018] Here, the reason for providing the counterbore portion 24 will be described. When press-fitting the shaft 7 into the support portion 14, the outer peripheral surface of the shaft 7 and the inner peripheral surface of the support portion 14 are press-fitted while being in contact with each other. At this time, if the contact pressure between the outer peripheral surface of the shaft 7 and the inner peripheral surface of the support portion 14 locally increases, so-called plastic flow may occur. When such plastic flow occurs, foreign matter (scrapings) may be generated by scraping the inner peripheral surface of the support portion 14, which may result in poor press-fitting. On the other hand, when a counterbore portion is not formed in the support portion as in the above-mentioned Patent Document 1, since no space for discharging foreign matter is formed, the foreign matter cannot be discharged, and there is a possibility that the quality of the press-fitting cannot be determined. Therefore, in the present embodiment, a space for discharging foreign matter is provided, and in the support portion 14, a counterbore portion 24 having a diameter larger than the diameter of the shaft 7 is provided so that it is possible to determine the quality of the press-fitting including poor press-fitting. By providing the counterbore portion 24 in this way, if the inner side of the support portion 14 is scraped by the shaft 7, for example, the scrapings scraped into the gap or space formed in the counterbore portion 24 will be discharged, and it can be determined that poor press-fitting has occurred in relation to the press-fitting load described later.

[0019] Regarding the method for determining the quality of the press-fitting, although it will be described later, the press-fitting device for the shaft 7 (not shown) is provided with a sensor (for example, an encoder) capable of detecting the press-fitting stroke amount indicating the press-fitting amount, and a sensor (for example, a load cell) capable of detecting the press-fitting load of the shaft 7 on the support portion 14. Based on the detection values of these sensors, the quality of the press-fitting is determined.

[0020] Returning to FIG. 1, the description will be continued. In the present embodiment, as described above, by fixing the stator 3 to the motor housing 5 by press-fitting, shrink-fitting, or the like, a space is formed on the circuit board 6 side. That is, a space is generated below the stator 3 in FIG. 1. In the present embodiment, a substantially L-shaped bus bar 15 is disposed in this space. One end of the bus bar 15 is attached to the stator coil 13 wound around the stator 3, and the other end is connected to a terminal provided on the circuit board 6 (more specifically, a terminal in the electronic component 19), and the circuit board 6 and the motor 4 are electrically connected via the terminal. Note that the bus bar 15 is provided in the number corresponding to the number of phases of the motor 4 (here, three phases of U-phase, V-phase, and W-phase).

[0021] Furthermore, as described above, the cover member 10 is attached to the motor housing 5, and the circuit board 6 for controlling (i.e., driving) the motor 4 is housed in the housing space 16 formed between the cover member 10 and the motor housing 5. A heat dissipation member 17 is provided between the circuit board 6 and the motor housing 5. That is, the circuit board 6 is in contact with the motor housing 5 via the heat dissipation member 17. As the heat dissipation member 17, for example, heat dissipation grease, heat dissipation adhesive, heat dissipation pad, heat dissipation sheet, etc. are assumed, but in order to dissipate the heat generated by the circuit board 6, it is preferable that the heat dissipation member 17 is a member with low thermal resistance. Therefore, in the present embodiment, for example, heat dissipation grease or heat dissipation adhesive with relatively low thermal resistance is used.

[0022] The circuit board 6 is arranged axially on the side opposite to the impeller 9 with respect to the motor 4 (corresponding to the other side of the rotation axis X with respect to the motor 4). Electronic components 19 such as an inverter circuit, a coil, and a capacitor that are driven by receiving power supply from the power terminal 18 are mounted on this circuit board 6. In the example shown in FIG. 1, the electronic components 19 are provided on the cover member 10 side axially with respect to the circuit board 6. Terminals (not shown) are electrically connected to the electronic components 19. And, through holes (not shown) that function as connection parts to which the terminals are electrically connected are formed in the circuit board 6. That is, in the present embodiment, the terminals are inserted into the through holes and soldered using pads (or lands) existing around the through holes, thereby being electrically connected to the circuit board 6. Also, a plurality of wirings are formed on both sides of the circuit board 6 with copper or the like. The wirings formed on both sides of the circuit board 6 are electrically connected through through holes formed at a plurality of positions on the circuit board 6. Therefore, the heat generated in the electronic components 19 mounted on one side of the circuit board 6 is also transmitted to the surface of the circuit board 6 on the side opposite to the surface on which the electronic components 19 are mounted through the plurality of wirings. Therefore, the heat generated in the electronic components 19 is also transmitted to the contact surface side between the circuit board 6 and the motor housing 5. Incidentally, as shown in FIG. 1, the power terminal 18 is provided in the vicinity of the circuit board 6 and outside the motor housing 5. And the circuit board 6 is fastened to the motor housing 5 with screws or the like. That is, in the present embodiment, the circuit board 6 and the motor housing 5 are arranged in the order of the heat dissipation member 17, the wiring, and the circuit board 6 when viewed from the motor housing 5 side. In other words, the motor housing 5 is in contact with and fastened to the circuit board 6 through the heat dissipation member 17 and the wiring in order.

[0023] Since the bush 8 slides on the shaft 7, a material with high wear resistance and heat resistance is used. For example, it is composed of a carbon bearing such as carbon fiber. The bush 8 is not particularly limited as long as it is a material with high wear resistance and heat resistance, and may be composed of a metal such as aluminum or a resin, for example.

[0024] The impeller 9 is arranged axially on the side opposite to the circuit board 6 with respect to the motor 4 (corresponding to one side of the rotation axis X with respect to the motor 4). This impeller 9 has a plurality of blade members 21 curved inside the shroud 20 and is covered with an impeller housing 11. These blade members 21 are welded (for example, vibration welding) to one end 2a of the rotor 2 on the impeller 9 side. In the example shown in FIG. 1, among the plurality of blade members 21, two representative blade members are labeled. The electric pump 1 is configured such that the current to the stator coil 13 wound around the stator 3 is controlled via the circuit board 6 by an ECU of a vehicle (not shown), so that the permanent magnet 12 in the rotor 2 receives a magnetic field and the bush 8 and the rotor 2 rotate integrally. When the bush 8 and the rotor 2 rotate integrally, the impeller 9 fixed to one end 2a of the rotor 2 also rotates.

[0025] Note that the impeller housing 11 has a suction port 11a for sucking cooling water into the pump chamber and a discharge port (not shown) for discharging the cooling water from the pump chamber. Also, a water chamber 22 is formed between the impeller housing 11 and the motor housing 5. As the impeller 9 rotates in the water chamber 22 as the rotor 2 rotates, the cooling water flows spirally from the suction port 11a to the outer peripheral side of the impeller 9. At this time, most of the cooling water is sent out to the outside from the discharge port, but a part of the cooling water flows out from the outer peripheral side of the impeller 9, circulates inside the motor housing 5, and is discharged from the discharge port. In this way, when a part of the cooling water circulates inside the motor housing 5, the rotor 2, the stator 3, etc. are cooled and foreign matters mixed in the cooling water are discharged. As shown in FIG. 1, seal members (for example, O-rings) 23 for preventing the leakage of the cooling water are provided at each part in contact with the motor housing 5. In the example shown in FIG. 1, there are a plurality of seal members 23, and two representative seal members are labeled.

[0026] (2) Method for judging the quality of press-fitting: Next, a method for determining the quality of press-fitting when press-fitting the shaft 7 into the above-described support portion 14 will be described. In the present embodiment, the quality of press-fitting is determined based on the change in the press-fitting load when press-fitting the shaft 7 into the support portion 14 in which the above-described reaming portion 24 is formed. FIGS. 3A to 3E are diagrams for explaining the process (press-fitting method) of press-fitting the shaft 7 into the support portion 14, and FIG. 4 is a diagram showing the change in the press-fitting load according to the stroke amount of the press-fitting. In addition, the downward arrow in FIGS. 3A to 3E indicates the press-fitting direction.

[0027] First, the state of FIG. 3A shows a state in which the shaft 7 and the support portion 14 are aligned. That is, the shape of the tip 7a of the shaft 7 is a tapered shape, and similarly, the shape of the end portion of the support portion 14 into which the shaft is inserted is also a tapered shape. Further, the diameter of the end portion of the support portion 14 is slightly larger than the diameter of the shaft 7 in order to align the shaft 7 and the support portion 14. By making the shapes of the tip 7a of the shaft 7 and the end portion of the support portion 14 tapered in this way, alignment becomes easy and press-fitting can be started smoothly. When the shaft 7 and the support portion 14 are aligned in the state of FIG. 3A, the state transitions to the state of FIG. 3B.

[0028] The state of FIG. 3B shows a state in which press-fitting of the shaft 7 and the support portion 14 is started. That is, the shaft 7 is inserted until the diameters of the shaft 7 and the support portion 14 become substantially the same. Up to the state of FIG. 3B (that is, the states of FIGS. 3A and 3B), the press-fitting load shown in FIG. 4 is "0".

[0029] When press-fitting is started, as shown in FIG. 3C, the shaft 7 and the support portion 14 start to fit (initial biting), and the contact area between the shaft 7 and the support portion 14 increases. Along with this, the press-fitting load shown in FIG. 4 starts to increase. Further, when the shaft 7 is press-fitted, as shown in FIG. 3D, the contact area between the shaft 7 and the support portion 14 increases, and accordingly, the press-fitting load shown in FIG. 4 also increases.

[0030] Then, when the shaft 7 is further press-fitted, as shown in FIG. 3E, the shaft 7 reaches the fitting completion position F at a predetermined depth. In the present embodiment, as described above, at this fitting completion position F, the counterbore portion 24 is formed in the support portion 14. Therefore, for example, when there is no abnormality such as the inside of the support portion 14 being scraped by the shaft 7 by more than a predetermined amount, the contact area between the shaft 7 and the support portion 14, which has been continuously increasing, becomes substantially constant. Along with this, the press-fitting load shown in FIG. 4 also becomes substantially constant as shown by the solid line. Here, "substantially constant" means that when the shaft 7 is press-fitted up to the fitting completion position F, the contact area between the shaft 7 and the support portion 14 does not change significantly, and accordingly, the press-fitting load does not change significantly either. However, it may change by a predetermined amount on the plus side or the minus side due to slight sliding or the like. Therefore, it is defined as "substantially constant" to include such a change in the predetermined amount.

[0031] On the other hand, if there is an abnormality such as the inside of the support portion 14 being scraped by the shaft 7 by more than a predetermined amount, the scrap scraped by the tip 7a of the shaft 7 is discharged into the gaps or spaces formed in the counterbore portion 24. In that case, the force for pushing out the scrap from the press-fitting load, which is the frictional force corresponding to the sliding between the outer peripheral surface of the shaft 7 and the inner peripheral surface of the support portion 14, is removed. That is, the press-fitting load is reduced by the amount of the force for pushing out the scrap. Therefore, as shown by the broken line in FIG. 4, the press-fitting load will decrease. Thereby, it can be determined that a press-fitting defect has occurred. The dashed-dotted line shown in FIG. 4 shows an example where no counterbore portion is provided (a conventional example such as Patent Document 1 cited above). In that case, even if scrap is generated by scraping the inside of the support portion 14 with the tip 7a of the shaft 7, since there is no space or gap for discharging the scrap, the press-fitting load will continue to increase. Therefore, in the conventional example, even when a press-fitting defect occurs, there is a possibility that it cannot be determined that a press-fitting defect has occurred.

[0032] Thus, in this embodiment, by forming the counterbore 24 at the fitting completion position F, it becomes possible to determine the quality of press-fitting. That is, when the tip 7a of the shaft 7 reaches the counterbore 24, if no abnormality such as gouging the inside of the shaft 7 described above has occurred, the contact area between the shaft 7 and the support portion 14, which has been continuously increasing during the press-fitting process, becomes substantially constant, so that the press-fitting load also becomes substantially constant, and it can be determined that the press-fitting has been completed normally. Further, if an abnormality such as gouging the inside of the shaft 7 occurs when the tip 7a of the shaft 7 reaches the counterbore 24, the gouged chips are discharged into the counterbore 24, reducing the press-fitting load corresponding to the amount of gouging. That is, the press-fitting load that has been continuously increasing decreases. Therefore, it can be determined that a press-fitting defect has occurred.

[0033] Also, by being able to grasp that a press-fitting defect has occurred as described above, for example, the possibility that the fastening force of the shaft 7 becomes insufficient (that is, the fitting between the shaft 7 and the support portion 14 becomes insufficient) due to the support portion 14 being gouged can be reduced.

[0034] (2) Other embodiments, etc.: The above embodiments are examples for implementing the present invention and are not limited thereto, and various other embodiments can be adopted. For example, the above-described counterbore 24 may have any shape and size as long as a space or gap for discharging foreign matter (gouged chips) when the inside of the support portion 14 is gouged by the shaft 7 is formed while ensuring the fastening force of the shaft 7.

[0035] Also, in the above-described embodiment, an example in which the counterbore portion 24 is formed at the fitting completion position F has been described. However, when only determining a poor press fit, the position where the counterbore portion 24 is formed may be formed at a location other than the fitting completion position in the support portion 14. Note that when determining not only a poor press fit but also whether the quality of the press fit is normal, the counterbore portion 24 is preferably formed at the above-described fitting completion position F. This is because if the counterbore portion 24 is formed at a location other than the fitting completion position, the press fit load becomes substantially constant at the position where the counterbore portion 24 is formed (in other words, the position where the fitting is not completed), and it becomes impossible to determine that the press fit has been completed normally.

[0036] Also, in the above-described embodiment, the motor housing 5 has been described as an example of a metallic housing made of aluminum die-cast, but it is not limited to this as long as it is metallic. For example, instead of being made of aluminum die-cast, it may be made of the above-described zinc die-cast. Zinc die-cast is advantageous in terms of, for example, higher workability compared to aluminum die-cast or the like.

[0037] The heat dissipation member 17 may be any member interposed between the motor housing 5 and the circuit board 6. That is, the circuit board 6 is fixed to the motor housing 5 with the heat dissipation member 17 present between the circuit board 6 and the motor housing 5. In the above-described embodiment, an example in which a heat dissipation grease or a heat dissipation adhesive is used as the heat dissipation member 17 has been described from the viewpoint of thermal resistance. However, for example, when the shape of the circuit board 6 is complex, a heat dissipation sheet or the like having a more stable shape than the heat dissipation grease or the heat dissipation adhesive may be used. Also, the shape, size, etc. of the heat dissipation member 17 are not limited. For example, if the heat dissipation member 17 is a heat dissipation grease, it is applied to cover the entire surface of the circuit board 6.

[0038] The circuit board 6 only needs to be provided with a drive circuit for the electronic component 19. That is, the electronic component 19 is driven by a drive circuit on the board. The connection part on the circuit board 6 is a part where a terminal is connected in order to electrically connect the drive circuit on the board and the electronic component via the terminal. In addition to through-holes, various connectors, etc. may be used, or it may be a part where the terminal is soldered, and it may have various configurations.

Explanation of Reference Numerals

[0039] 1…Electric pump, 2…Rotor, 2a…One end of the rotor, 3…Stator, 4…Motor, 5…Motor housing, 5a…Bottom (of the motor housing), 6…Circuit board, 7…Shaft, 7a…Tip (of the shaft), 8…Bush, 9…Impeller (pump part), 10…Cover member, 11…Impeller housing, 11a…Suction port, 12…Permanent magnet, 13…Stator coil, 14…Support part, 14a…Bottom (of the support part) 15…Bus bar, 16…Accommodation space, 17…Heat dissipation member, 18…Power supply terminal, 19…Electronic component, 20…Shroud, 21…Blade member, 22…Water chamber, 23…Sealing member, 24…Counterbore, F…Fitting completion position.

Claims

1. A press-fitting structure comprising a support member having an insertion hole and a shaft member press-fitted into the insertion hole, wherein the support member includes a fitting completion position at which the fitting between the support member and the shaft member is completed, and a counterbore portion is formed at the fitting completion position, the diameter of the support member being larger than the diameter of the shaft member over a predetermined range in the press-fitting direction. Press-fitting structure.

2. A press-fitting structure comprising a support member having an insertion hole and a shaft member press-fitted into the insertion hole, wherein the support member includes a fitting completion position at which the fitting between the support member and the shaft member is completed, and in the press-fitting structure in which a counterbore portion is formed at the fitting completion position, the diameter of the support member being larger than the diameter of the shaft member over a predetermined range in the press-fitting direction, a method for determining the quality of press-fitting when the support member is press-fitted, wherein a press-fitting load is calculated during the press-fitting process, and when the continuously increasing press-fitting load decreases, it is determined that the quality of the press-fitting is abnormal. Method for determining the quality of press-fitting.

3. When the continuously increasing press-fitting load becomes substantially constant, it is determined that the quality of the press-fitting is normal. The method for determining the quality of press-fitting according to Claim 2.

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