Torque rotor and method for its manufacture

Abstract

Torque rotor (300), which includes the following: a magnet (320) with alternating repeated north poles and south poles for generating a magnetic force; a yoke (310) that is inserted into an inner peripheral surface of the magnet (320); and a tube (330) inserted into an inner peripheral surface of the yoke (310), wherein the magnet (320) and the yoke (310) comprise a fastening element to prevent the magnet (320) and the yoke (310) from rotating during idling rotation, wherein the fastening part comprises at least one pair of a projection (333) and a groove (317) formed on the inner peripheral surface of the magnet (320) and an outer peripheral surface of the yoke (310), such that the yoke (310) is inserted into the magnet (320) in a central shaft direction and thus joined together, and the magnet (320) and the yoke (310) are supported in a circumferential direction, wherein the yoke (310) and the tube (330) comprise the fastening part to prevent the yoke (310) and the tube (330) from rotating during idling rotation, wherein the fastening part comprises at least one pair of a projection part and a recess part formed on the inner peripheral surface of the yoke (310) and an outer peripheral surface of the tube (330), such that the yoke (310) is inserted into the tube (330) in a central shaft direction and thus joined together to support the yoke (310) and the tube (330) in a circumferential direction.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention

[0001] The present invention relates to a torque rotor. More particularly, the present invention relates to a torque rotor and a method for manufacturing the torque rotor, which can prevent the inflow of plastic between a yoke and a magnet during a conventional plastic injection molding process for forming a mounting structure after joining between the yoke and the magnet, thereby preventing deterioration of the roundness of the magnet or damage to the magnet due to the difference between the thermal expansion coefficients, and preventing idle rotation of the yoke and the magnet relative to each other. 2. Description of the state of the art

[0002] A vehicle generally uses a power steering device, or power assisted steering device, which serves as a means for reducing steering force of a steering wheel and ensuring stability of a steering state. In this regard, a conventional hydraulic power steering system (EPS) that utilizes hydraulic pressure has been widely used for the vehicle's HPS. However, in contrast to the conventional scheme of using hydraulic pressure, an electronic power steering system (EPS) that facilitates a driver's steering performance by utilizing the rotational force of an engine and is environmentally friendly has recently been widely installed in vehicles.

[0003] Such an EPS drives a motor with the aid of an electronic control unit according to a vehicle's driving condition detected by a vehicle speed sensor, steering angle sensor, steering torque sensor, or the like, thus providing a light and comfortable steering feel during low-speed driving, a heavy steering feel and satisfactory directional stability during high-speed driving, and a restoring force for promptly returning the steering wheel according to a steering wheel rotation angle. Therefore, the EPS enables prompt steering in an emergency, thus providing the driver with an optimal steering condition.

[0004] Meanwhile, in the EPS, the motor is installed on an outer side of a steering column which is located between the steering wheel and a gearbox to transfer the rotational force of the driver's steering wheel downward so that it rotates a steering spindle inside the steering column, thereby complementing the driver's steering force according to the steering of the steering wheel.

[0005] The prior art includes the documents DE 27 13 037 A1, DE 693 15 586 T2, JP H06- 78 481 A, JP H07- 222 385 A, JP H09- 56 092 A, DE 103 07 231 A1, JP 2004- 274 860 A, DE 10 2004 015 041 A1, DE 10 2005 013 674 A1 and US 2006 / 0 284 506 A1.

[0006] Fig. 1 is a view schematically illustrating a conventional electronic power steering apparatus. As shown in Fig. 1, the electronic power steering apparatus 100 includes a steering system 130 extending from a steering wheel 102 to the wheels 126 on both sides, and an assist mechanism 140 for providing a steering assist force to the steering system 130.

[0007] The steering system 130 includes a steering shaft 106, one side of which is connected to the steering wheel 102 for rotation with the steering wheel 102, and the other side of which is connected to a pinion shaft 108 through a pair of universal joints 104. Furthermore, the pinion shaft 108 is connected to a rack bar 112 through a rack and pinion mechanism member 110, and both ends of the rack bar 112 are connected to the wheels 126 of a vehicle through a tie rod 112 and a tie rod arm 124.

[0008] The assist mechanism 140 includes a torque sensor 142 for detecting the torque applied by the driver to the steering wheel 102 and outputting an electrical signal proportional to the detected torque, an electrical control unit (ESU) 144 for generating a control signal based on the electrical signal transmitted from the torque sensor 142, a motor 146 for generating an assist power based on the control signal transmitted from the electrical control unit 144, and a reducer 150 including a worm gear 152 and a worm wheel gear 156 for transmitting the assist power generated in the motor 146 to the steering shaft 106.

[0009] Fig. Figure 2 is an exploded perspective view illustrating the conventional torque sensor.

[0010] As in Fig. 2, the conventional torque sensor 142 includes a torque rotor 220, a position rotor 230, a magnetic charge sensing unit 204, the electrical control unit, and a housing 255.

[0011] The torque sensor 142 measures the torque of an input shaft 180 and an output shaft 140 of the steering shaft and sends the measured torque to the electric control unit. The electric control unit then actuates a drive motor and provides steering assist force. Recently, a non-contact torque sensor that measures a variation in the magnetic field to measure torque fluctuation has been widely used.

[0012] The torque rotor 220 includes a rotor body 224 having a magnet 225 provided along an outer peripheral surface of the rotor body 224, an input shaft insertion hole 221 formed in a center of the rotor body 224, a plurality of compression pieces 222 protruding along an edge of the input shaft insertion hole 221, and a compression ring 223 fitted into the compression piece 222.

[0013] The rotor body 224 is generally manufactured by injection molding a plastic into a yoke (not shown) having a ring shape and includes the magnet 225 on the outer peripheral surface thereof, the magnet 225 having north poles and south poles alternately repeated along one edge of the peripheral surface of the rotor body 224.

[0014] Here the north poles and the south poles are repeated alternately 6 times, 8 times or the like.

[0015] The position rotor 230 includes a torque rotor insertion part 239 into which the torque rotor 220 is inserted, and an output shaft fitting part 237 into which one end of the output shaft 140 is fitted at a center thereof. An upper magnetic body 236 connected to an upper stator 231 and a lower magnetic body 235 connected to a lower stator 232 are alternately arranged along a circumference of the torque rotor insertion part 239.

[0016] Here, the upper stator 231 and the upper magnetic body 236 connected to the upper stator 213 are steel sheets magnetized as a north pole, and the lower stator 232 and the lower magnetic body 235 connected to the lower stator 213 are steel sheets magnetized as a south pole. Here, a position of the north pole and the south pole can be switched.

[0017] The magnetic charge detection unit 240 is fixed to one side of an outer peripheral surface of the positioning rotor 230 and includes a concentrator 242 provided vertically between the upper stator 231 and the lower stator 232 of the positioning rotor 230. The magnetic charge detection unit 240 is rotatable relative to the positioning rotor 230.

[0018] The electric control unit receives the variation amount of the magnetic flux detected in the magnetic charge detection unit and controls a drive motor based on the received variation amount of the magnetic flux to complement the driver's steering force.

[0019] The housing 255 is divided into an upper housing 210 and a lower housing 250, which encloses the position rotor 230 and the magnetic charge detection unit 240.

[0020] A torsion bar 205 is press-fitted and secured into the input shaft 180 and the output shaft 140, and then secured with a pin. When the driver turns the steering wheel, the input shaft 180, which is connected to the steering wheel, rotates, and the output shaft 140, which is connected to the input shaft 180 by the torsion bar 205, rotates in conjunction with the input shaft 180.

[0021] At this time, when torsion is generated between the input shaft 180 and the output shaft 140, a difference of a rotation angle is generated between the position rotor 230, which is press-fitted and fitted into the output shaft 140 to be fixed, and the input shaft 180.

[0022] As described above, when the rotation angle difference is generated, the magnetic field formed between the upper magnetic body 236 and the lower magnetic body 235, which are alternately repeated along the circumference of the positioning rotor 230, and the magnet 225 fluctuates. Therefore, the torque can be measured by a quantity of magnetic flux collected in the concentrator 242 of the torque sensor passing through two hole IC chips 243 and 245 installed on a substrate 241.

[0023] However, in the conventional torque rotor, a plastic injection molding process is required to create a structure for mounting the input shaft after the yoke and magnet are assembled. At this time, the plastic is injected into the yoke and magnet, deteriorating the roundness of the magnet, causing a problem of magnetic field declination between the magnet and the position rotor.

[0024] Furthermore, the joining of the yoke and the magnet is not stable, so that the yoke and the magnet become idling relative to each other due to a shock or a difference in a coefficient of thermal expansion, which causes a serious problem of generating an error of a torque measurement value or breaking the magnet. SUMMARY OF THE INVENTION

[0025] Accordingly, the present invention has been created to solve the above-mentioned problems encountered in the prior art, and the present invention provides a torque rotor and a method for manufacturing the torque rotor, which can prevent the inflow of plastic between a yoke and a magnet during a conventional plastic injection molding process for forming a mounting structure after joining between the yoke and the magnet, thereby preventing deterioration of roundness of the magnet or damage to the magnet due to the difference between the thermal expansion coefficients, and preventing idle rotation of the yoke and the magnet relative to each other.

[0026] In accordance with one aspect of the present invention, there is provided a torque rotor comprising: a magnet having alternately repeated north poles and south poles for generating a magnetic force, a yoke inserted into an inner peripheral surface of the magnet; and a tube inserted into an inner peripheral surface of the yoke, wherein the magnet and the yoke include a fixing member for preventing the magnet and the yoke from idling during rotation.

[0027] In accordance with another aspect of the present invention, there is provided a method of manufacturing a torque rotor, the method comprising the steps of: applying an adhesive to an inner peripheral surface of a magnet and an outer peripheral surface of a yoke; assembling the magnet to the yoke by inserting a projection or groove of the magnet into a corresponding groove or projection of the yoke, and placing one end of the magnet on a stopper flange formed at one end of the yoke; and assembling the yoke to a tube by inserting the tube into an inner surface of the yoke, and placing one end of the yoke on a coupling flange formed at one end of the tube.

[0028] Consequently, the torque rotor and the method for manufacturing the torque rotor of the present invention have an effect of preventing inflow of plastic between a yoke and a magnet during a conventional plastic injection molding process for forming a mounting structure after joining between the yoke and the magnet, thereby preventing deterioration of roundness of the magnet or damage to the magnet due to the difference between the thermal expansion coefficients, and preventing idle rotation of the yoke and the magnet relative to each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings in which: Fig. 1 is a view schematically illustrating a conventional electronic power steering apparatus; Fig. 2 is an exploded perspective view illustrating a conventional torque sensor; Fig. 3 is an exploded perspective view illustrating a torque rotor in accordance with an exemplary embodiment of the present invention; Fig. 4 is a perspective view illustrating an assembly state of a torque rotor in accordance with an exemplary embodiment of the present invention; and Fig. 5 is a flow chart illustrating a method of manufacturing the torque rotor in accordance with the present invention. DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0030] Preferred embodiments of the present invention will be described below with reference to the accompanying drawings. In the following description, the same elements will be denoted by the same reference numerals even though they are shown in different drawings. In the following description, detailed explanation of known related functions and constitutions may be omitted to avoid unnecessarily obscuring the subject matter of the present invention.

[0031] Furthermore, the terms "first," "second," "A," "B," (a), (b), and the like may be used to describe a structural element of the present invention. Such a term merely serves to distinguish the respective structural element from another structural element, but does not limit a nature, sequence, or order of the respective structural element. When a structural element is described as being "coupled," "joined," or "connected" to another structural element, the structural element may be directly coupled or connected to another structural element, but it will also be understood that another structural element may be further "coupled," "joined," or "connected" between each of the structural elements.

[0032] Fig. 3 is an exploded perspective view illustrating a torque rotor in accordance with an exemplary embodiment of the present invention, Fig. 4 is a perspective view illustrating an assembly state of a torque rotor in accordance with an exemplary embodiment, and Fig. 5 is a flowchart illustrating a method of manufacturing the torque rotor in accordance with the present invention.

[0033] With reference to the Fig. 3 to 5, a torque rotor 300 according to an exemplary embodiment of the present invention includes a magnet 320 for generating a magnetic force in which the north poles and the south poles are alternately repeated, a yoke 310 inserted into an inner peripheral surface of the magnet 320, and a tube 330 inserted into an inner peripheral surface of the yoke 310. The magnet 320 and the yoke 310 include a fixing member that prevents the magnet 320 and the yoke 310 from rotating idle during rotation.

[0034] The torque rotor 300 in accordance with an exemplary embodiment of the present invention basically includes the magnet 320, the yoke 310, and the tube 330, which include a mounting structure including a protrusion 313, a groove 317, an adhesive / glue, and a caulking 333, which serve as the fastening part or fastening means for preventing failure caused by separation and idle movement of the magnet 320, the yoke 310, and the tube 330 relative to each other.

[0035] The magnet 320 is shaped like a ring having a predetermined width and is easily broken due to a property of a material, so the magnet 320 is assembled with and supported by the yoke 310 for protection. The magnet 320 has the north poles and the south poles alternately repeated on a circumferential edge.

[0036] Here, the magnetism of the magnet 320 is constructed in a manner that the north poles and the south poles are alternately repeated 6 times, 8 times, or the like, but is not limited thereto.

[0037] Meanwhile, the magnet 320 and the yoke 310 include the fixing part for preventing the magnet 320 and the yoke 310 from rotating idle during rotation. The fixing part includes at least a pair of a protrusion and a groove.

[0038] That is, the magnet 320 includes at least one projection 313 projecting inward from the inner peripheral surface of the magnet 320 or at least one groove 317 recessed outward from the inner peripheral surface of the magnet 320 to prevent the magnet 320 from rotating separately with respect to the yoke 310, which may cause an error in the torque measurement value necessary for a driver's operation of a steering wheel.

[0039] The yoke 310, which is fitted to the magnet 320, has a ring shape so as to prevent the magnet 320 from breaking when the yoke 310 is in contact with the ring-shaped magnet 320. An outer peripheral surface of the yoke 310, which is fitted into the inner peripheral surface of the magnet 320, includes at least one groove 317 or a projection (not shown) that respectively fit and fit the projection 313 and the groove 317 formed in the inner peripheral surface of the magnet 320.

[0040] That is, when the magnet 320 includes the protrusion 313, the yoke 310 has the groove 317 that matches and mates with the protrusion 313 of the magnet 320, and when the magnet 320 has the groove 317, the yoke 310 has the protrusion (not shown) that matches and mates with the groove 317 of the magnet 320.

[0041] If the protrusion 313 or the groove 317 formed in the magnet 320 and the yoke 310 can prevent the magnet 320 and the yoke 310 from rotating separately relative to each other when the magnet 320 is mated with the yoke 310, then the magnet 320 and the yoke 310 may each include at least one protrusion 313 and one groove 317. However, in some cases, the magnet 320 may include both the protrusion 313 and the groove 317, and the yoke 310 then includes the groove 317 and the protrusion 313, which respectively match the protrusion 313 and the groove 317 of the magnet 320.

[0042] Further, the yoke 310 includes a stopper flange 315 extending outwardly from the external peripheral surface at one side end of the yoke 310 so as to seat one side end of the magnet 320 on the stopper flange 315 and prevent the magnet 320 from becoming eccentric with respect to the central axis.

[0043] A tube 330, which is joined to an inner side of the yoke 10, includes a large-diameter portion 331 and a small-diameter portion 337 having a predetermined diameter, and an inclined portion 339 formed by joining the large-diameter portion 331 and the small-diameter portion 337. The large-diameter portion 331 is in contact with the inner peripheral surface of the yoke 310, and the small-diameter portion 337 is joined to the input shaft 180 connected to the steering shaft.

[0044] Furthermore, one end of the large-diameter portion 331 includes a coupling flange 335 on which the other side end of the magnet 320, which is seated on the stopper flange 315 of the yoke 310, is disposed, so that it is possible to prevent the magnet 320 from deviating from the axial direction. Furthermore, the yoke 310 is firmly bonded to the tube 330 by applying an adhesive to a coupling surface of the yoke 310 and the tube 330, so that it is possible to prevent an error in the torque measurement value caused by the idle movement of the yoke 310 and the tube 330 relative to each other.

[0045] Furthermore, the yoke 310 and the tube 330 include the fixing part for preventing the yoke 310 and the tube 330 from rotating idle, which is caused by the omission of an adhesive process or the deterioration of the adhesive property of the adhesive due to a change in temperature or environment. The fixing part includes at least a pair of a protrusion and a groove.

[0046] That is, the yoke 310 includes at least one protrusion (not shown) protruding inward from the inner peripheral surface of the yoke 310, or at least one groove 317 recessed outward from the inner peripheral surface of the yoke 310. The tube 330 includes at least one groove (not shown) or one protrusion 313, which respectively fit and fit the protrusion (not shown) or the groove 317 formed on the yoke 310. Therefore, the protrusion 313 is inserted into the groove 317 and fitted thereto.

[0047] In addition, a contact surface between the stopper flange 315 of the yoke 310 and an external side of the large diameter portion 331 of the pipe 330 is caulked 333 in a state where the yoke 310 is joined to the pipe 330, so that it is possible to join the yoke 310 and the pipe 330 more firmly and stably.

[0048] Therefore, by the caulking 333, it is possible to achieve a double complementary structure that can prevent the magnet 320 and the yoke 310 and the yoke 310 and the tube 330 from rotating idle, and the magnet 320, the yoke 310 and the tube 330 from becoming eccentric with respect to the central axis when the torque rotor 300 rotates while being arranged at a center of the position rotor 230.

[0049] Meanwhile, according to a method of manufacturing the torque rotor 300 of the present invention as shown in Fig.5, an adhesive is first applied to the inner peripheral surface of the magnet 320 and the outer peripheral surface of the yoke 310 in step S510. The projection 313 of the magnet 320 or the groove 317 is respectively inserted into the corresponding groove (not shown) or projection 313 of the yoke 310, and the end of the magnet 320 is fitted onto the stopper flange 315 formed at the end of the yoke 310, so that the magnet 320 is joined to the yoke 310 in step S520. Next, the tube 330 is inserted into the inner side of the yoke 310, and the end of the yoke 310 is fitted onto the coupling flange 335 formed on the end of the tube 330, so that the yoke 310 is joined to the tube 330 in step S530.

[0050] First, the adhesive is applied to the inner peripheral surface of the magnet 320 and the outer peripheral surface of the yoke 310 to prevent the magnet 320 and the yoke 310 from rotating freely when joined together. The projection 313 or the groove 317 of the magnet 320 is inserted into the corresponding groove (not shown) or projection 313 of the yoke 310, so that the end of the magnet 320 is seated on the stopper flange 315 of the yoke 310.

[0051] When the magnet 320 is assembled with the yoke 310 as described above, the end of the yoke 310 is placed on the coupling flange 335 formed on the end of the tube 330 to join them together.

[0052] Here, in the step of joining the yoke 310 to the tube 330, the yoke 310 is bonded to the tube 330 by applying an adhesive to the inner peripheral surface of the yoke 310 and the outer peripheral surface of the tube 330. In a state where the adhesive is applied thereto, the projection 313 or the groove 317 of the yoke 310 is respectively inserted into the corresponding groove 317 or the corresponding projection 313 of the tube 330, and the end of the yoke 310 is fitted onto the coupling flange 335 formed at the end of the tube 330, so that the yoke 310 is joined to the tube 330.

[0053] In addition, after the yoke 310 is joined to the pipe 330, a step of caulking 333 the space between the stopper flange 315 of the yoke 310 and the external side of the large diameter portion 331 of the pipe 330 may be additionally included for the joining.

[0054] Therefore, by the caulking step 333, it is possible to form a double complementary structure that can prevent the magnet 320 and the yoke 310 and the yoke 310 and the tube 330 from rotating idly and the magnet 320, the yoke 310 and the tube 330 from becoming eccentric with respect to the central axis when the torque rotor 300 rotates while being located at the center of the position rotor 230 to rotate.

[0055] Accordingly, the present invention described above has an effect of preventing deterioration of the roundness of the magnet caused by inflow of resin between a yoke and a magnet by a conventional resin injection molding for forming a mounting structure after the yoke and the magnet are joined, or preventing damage to the magnet due to a difference in a thermal expansion coefficient, and preventing the yoke and the magnet from idlingly rotating relative to each other.

[0056] Although the above description describes that each structural element in the embodiment of the present invention is actuated by joining together, the present description is not necessarily limited to the embodiment. That is, at least one structural element can be selectively joined together for actuation within a range of the object of the present invention.

[0057] Furthermore, the terms "comprising," "constructing," or "having" used in the above description have a meaning that includes the corresponding design element, unless there is a specific description to the contrary. Therefore, this should be interpreted to further include another design element, but not to exclude any other design element. Any term that includes a technical or scientific term has an identical meaning that is generally understood by those skilled in the art, unless otherwise defined.The general terms, such as a term defined in the dictionary, should be interpreted as the meaning it has according to a contextual meaning of the related technology, and should not be interpreted as an ideal or overly formal meaning unless they are obviously defined in the present invention.

[0058] Although an exemplary embodiment of the present invention has been described for illustrative purposes, it will be apparent to those skilled in the art that various modifications, additions, and substitutions are possible without departing from the scope and spirit of the invention as disclosed in the appended claims. Although the present invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined in the appended claims.Therefore, an exemplary embodiment of the present invention has been described for non-limiting purposes, and the scope and spirit of the invention should not be limited by the exemplary embodiment thereof. Accordingly, the scope of the invention should not be limited by the above-mentioned embodiments, but rather by the claims and their equivalents.

Claims

[1] Torque rotor (300) comprising: a magnet (320) having alternately repeated north poles and south poles for generating a magnetic force; a yoke (310) inserted into an inner peripheral surface of the magnet (320); and a tube (330) inserted into an inner peripheral surface of the yoke (310), wherein the magnet (320) and the yoke (310) comprise a fixing member for preventing the magnet (320) and the yoke (310) from rotating during idle rotation, wherein the fixing member comprises at least one pair of a projection (333) and a groove (317) formed on the inner peripheral surface of the magnet (320) and an outer peripheral surface of the yoke (310), so that the yoke (310) is inserted into and fitted to the magnet (320) in a central shaft direction, and the magnet (320) and the yoke (310) are supported in a circumferential direction, wherein the yoke (310) and the tube (330) comprise the fastening part for preventing the yoke (310) and the tube (330) from rotating during idle rotation, wherein the fixing part comprises at least a pair of a projection part and a recess part formed on the inner peripheral surface of the yoke (310) and an outer peripheral surface of the tube (330) such that the yoke (310) is inserted into and fitted to the tube (330) in a center shaft direction to support the yoke (310) and the tube (330) in a circumferential direction. [2] The torque rotor (300) according to claim 1, wherein the yoke (310) comprises a stopper flange (315) provided at one side end of the yoke (310) on which one side end of the magnet (320) is disposed to prevent the yoke (310) and the magnet (320) from becoming eccentric with respect to a central axis. [3] The torque rotor (300) according to claim 2, wherein the tube (330) includes a large-diameter portion (331) inserted into the inner peripheral surface of the yoke (310), a small-diameter portion (337) into which an input shaft is inserted, and an inclined portion (339) formed by connecting the large-diameter portion (331) to the small-diameter portion (337) having a smaller diameter than the large-diameter portion (331), the large-diameter portion including a coupling flange (335) on which another side end of the magnet (320) is disposed to prevent the magnet (320) from becoming eccentric with respect to the central axis, the coupling flange (335) being provided at one end of the large-diameter portion (331). [4] The torque rotor (300) according to claim 2, wherein the yoke (310) and the tube (330) are joined by caulking a contact surface between the stopper flange (315) and the large diameter portion after the tube (330) is inserted into the yoke (310). [5] A method of manufacturing a torque rotor (300), the method comprising the following steps: Applying (S510) an adhesive to an inner peripheral surface of a magnet (320) and an outer peripheral surface of a yoke (310); Assembling (S520) the magnet (320) with the yoke (310), wherein a projection (333) or a groove (317) of the magnet (320) is inserted into a corresponding groove (317) or a corresponding projection (333) of the yoke (310) and one end of the magnet (320) is arranged on a stop flange (315) formed at one end of the yoke (310); and Joining (S530) the yoke (310) to a tube (330), wherein the tube (330) is inserted into an inner surface of the yoke (310) and one end of the yoke (310) is arranged on a coupling flange (335) formed at one end of the tube (330), wherein in the step of joining (S530) the yoke (310) to the tube (330), the projection (333) or the groove (317) of the yoke (310) is inserted into a corresponding groove (317) or a corresponding projection (333) of the tube (330) and one end of the yoke (310) is arranged on the coupling flange (335) formed on the end of the tube (330). [6] The method according to claim 5, wherein in the step of joining (S530) the yoke (310) to the tube (330), the yoke (310) is firmly bonded to the tube (330) by applying an adhesive to an inner peripheral surface of the yoke (310) and an outer peripheral surface of the tube (330) by bonding. [7] The method according to claim 5, further comprising a step of caulking a space between the stopper flange (315) of the yoke (310) and an outer side of a large diameter portion (331) of the pipe (330) after the yoke (310) is joined to the pipe (330).

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