A fixed axis for a wind turbine

Abstract

The application discloses a kind of fixed shaft of wind power fan, it is related to wind generator technical field, the device includes first locating section, shaft body section, second locating section, main shaft connecting section and cabin connecting section sequentially connected along the axis, form hollow cylinder;The circumferential surface of shaft body section is equipped with wiring hole and overhaul hole;Main shaft connecting section is equipped with connecting seat, connecting column and locating block;Multiple connecting seats are evenly distributed on the outer circumferential surface of main shaft connecting section, and the connecting seat is rectangular overhanging cantilever;Connecting column and locating block are arranged on connecting seat, and the inner hole of connecting column penetrates connecting seat;By setting wiring hole, the weight of shaft body section can be reduced, and the wire slot originally designed in the middle hole of fixed shaft is removed;And set connecting seat, the gap left between multiple connecting seats can reduce the weight of the connecting flange originally designed, simplify the structure of fixed shaft, so as to solve the problems that the existing fixed shaft has relatively complex structure, large casting and processing difficulty, low efficiency, and prone to stress concentration.

Description

Technical Field

[0001] This invention relates to the field of wind turbine technology, and in particular to a fixed shaft for a wind turbine. Background Technology

[0002] Many wind turbines operate on the same principle, and their structures mainly consist of blades, hub, main shaft, controller, gearbox, braking device, generator, cooling system, anemometer, wind vane, yaw system, etc.

[0003] The nacelle is primarily used to house the key equipment of the wind turbine, including the gearbox and generator. During maintenance, personnel can access the nacelle through the wind turbine tower. The wind turbine rotor consists of rotor blades and a shaft, and is located at one end of the nacelle. The rotor blades capture wind and transmit wind power to the rotor shaft. Each rotor blade is approximately 20 meters long, and to ensure high strength, high durability, and low weight, the blades are laminated and bonded using carbon fiber composite materials. The rotor shaft is attached to the low-speed shaft of the wind turbine to form a transmission connection, which connects the rotor shaft to the gearbox.

[0004] In current large mainstream wind turbines, the rotor speed is very slow, about 19 to 30 revolutions per minute; the gearbox connected to the rotor via the low-speed shaft can transmit the low speed and high torque of the rotor to the low-speed shaft, and then transfer it to the high-speed shaft to form high speed and low torque power. The speed of the high-speed shaft is 50 times that of the low-speed shaft. The high-speed shaft typically operates at 1500 revolutions per minute, transmitting power to the generator to drive its rotating components. It is also equipped with an emergency mechanical brake for use in case of aerodynamic brake failure or during maintenance of the wind turbine. The generator, usually called an induction motor or asynchronous generator, typically has a maximum power output of 500 to 1500 kilowatts in wind turbines. The wind turbine tower carries the nacelle, stator, stator shaft, main shaft, and rotor. Generally, taller towers are more advantageous because higher ground allows for higher wind speeds. The tower can be tubular or lattice-shaped. Tubular towers offer greater safety for maintenance personnel, who can access the top via an internal ladder. Grid-shaped towers are cheaper.

[0005] The bottom of the nacelle connects to the platform inside the tower, where the stator is located. One end of the stator shaft connects to the stator, and the main shaft passes through and connects to the stator shaft. One end of the main shaft connects to the rotor, thus completing the rear end fixation of the main shaft. The nacelle, stator shaft, base, and other shell-type components of the wind turbine are formed into an integral shape through casting, and then the connecting parts are precision machined. Therefore, the shape and structure of the stator shaft have a great influence on the difficulty of casting and subsequent processing, as well as the processing time. At the same time, a reasonable structure should increase the structural strength of the stator shaft. However, the existing stator shaft has a relatively complex structure due to the large number of additional connected parts. For large castings, the more complex the structure, the higher the casting difficulty, the longer the manufacturing time, and the lower the process efficiency. At the same time, there are more stresses between the various structural blocks of the casting, making it susceptible to static loads or impact loads during use, which reduces the durability of the stator shaft components in subsequent use.

[0006] In summary, the applicant has found that the prior art has at least the following technical problems:

[0007] Existing wind turbine shafts are complex in structure, difficult to cast and process, inefficient, and prone to stress concentration. Summary of the Invention

[0008] The purpose of this invention is to provide a fixed shaft for a wind turbine, in order to solve the problems of existing wind turbine fixed shafts, which have complex structures, are difficult to cast and process, have low efficiency, and are prone to stress concentration.

[0009] The preferred technical solutions among the many technical solutions provided by this invention can produce a variety of technical effects, which are described in detail below.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0011] This invention provides a fixed shaft for a wind turbine, comprising a first positioning section, a shaft body section, a second positioning section, a main shaft connecting section, and a nacelle connecting section connected sequentially along the axial direction to form a hollow column; the first positioning section is used to contact the inner annular surface of the main shaft; multiple component positioning ears are evenly distributed on the inner circumference of the first positioning section, and each component positioning ear is provided with a component through hole; the circumferential surface of the shaft body section is provided with wiring holes and inspection holes; in the vertical direction of the nacelle connecting section standing on the ground, the wiring holes and the inspection holes are arranged sequentially from top to bottom along the axial direction of the shaft body section, and the wiring holes and inspection holes are staggered; multiple inspection holes are respectively arranged between two wiring holes; the second... The positioning section is used to contact the inner annular surface of the spindle to be assembled; the spindle connecting section is provided with a connecting seat, a connecting column, and a positioning block; multiple connecting seats are evenly distributed on the outer circumferential surface of the spindle connecting section, and the connecting seat is a rectangular cantilever; the connecting column and the positioning block are provided on the connecting seat, and the inner hole of the connecting column penetrates the connecting seat; the positioning block is arranged adjacent to the connecting column, and the axis of the connecting column is located on the length centerline of the positioning block; the nacelle connecting section is provided with a positioning ring and a connecting hole; the positioning ring is stacked on the end face of the nacelle connecting section, and the diameter of the positioning ring is smaller than the diameter of the nacelle connecting section; the connecting hole is provided on the end face of the nacelle connecting section.

[0012] In one embodiment, the first positioning section, the shaft section, the second positioning section, the main shaft connecting section, and the cabin connecting section are integrally cast.

[0013] In one embodiment, the periphery of the wiring hole protrudes from the outer peripheral surface of the shaft section to the inner peripheral surface, and the outer peripheral surface of the shaft section and the edge of the wiring hole are provided with rounded corners, and the inner peripheral surface of the shaft section and the edge of the wiring hole are provided with rounded corners; there are three wiring holes.

[0014] In one embodiment, the inspection hole is provided with a boss on the edge of the hole on the outer peripheral surface of the shaft section, and the boss and the outer peripheral surface of the shaft section are provided with rounded corners; the periphery of the inspection hole rises from the outer peripheral surface of the shaft section to the inner peripheral surface, and the inner peripheral surface of the shaft section and the edge of the inspection hole are provided with rounded corners; there are three inspection holes.

[0015] In one embodiment, the connecting seat has a positioning groove on its surface facing the shaft section, the connecting post is disposed in the positioning groove, and the positioning block is arranged on the edge of the positioning groove; a plurality of mounting holes are arrayed on the side of the connecting seat adjacent to the positioning block; a rectangular groove is provided on the surface of the connecting seat facing the cabin connecting section, and the center line of the rectangular groove in the length direction coincides with the center line of the connecting seat and the positioning block connected in series; there are six connecting seats.

[0016] In one embodiment, the connecting column has a conical body, the larger diameter end of the connecting column engages with the positioning groove, and the connection between the larger diameter end of the connecting column and the positioning groove is provided with a rounded corner; the side of the positioning block away from the connecting column is rounded, the side of the connecting seat away from the main shaft connecting section is rounded, and the rounded side of the positioning block and the rounded side of the connecting seat are parallel.

[0017] In one embodiment, the first positioning segment is provided with a first shoulder for positioning; the cross-sectional shape of the first shoulder is trapezoidal, and the first shoulder is arranged adjacent to the shaft segment.

[0018] In one embodiment, the second positioning segment is provided with a second shoulder to improve the alignment of the shaft center; the second shoulder is a chamfered platform connecting the second positioning segment and the shaft body segment.

[0019] The beneficial effects of this invention are as follows:

[0020] The main structure of the fixed shaft of a wind turbine includes a first positioning section, a shaft body section, a second positioning section, a main shaft connecting section, and a nacelle connecting section connected sequentially along the axial direction, forming a hollow column. By dividing the fixed shaft into multiple functional sections connected along the axial direction, the mold can be divided into five sections during the casting of the fixed shaft. The structure of each section corresponds to the first positioning section, the shaft body section, the second positioning section, the main shaft connecting section, and the nacelle connecting section, respectively. Before casting begins, the entire fixed shaft casting mold can be assembled using a crane or overhead crane for hoisting and assembly. This makes it easier to disassemble the fixed shaft mold for maintenance of the mold's inner wall surface and to modify the internal structure of the mold. Furthermore, when the fixed shaft is not being cast, each mold section can be disassembled and placed in batches, avoiding the occupation of the factory's production area and making the use of the factory's work area more reasonable.

[0021] By providing wiring holes and inspection holes on the circumferential surface of the shaft section; in the vertical direction of the engine room connecting section standing on the ground, the wiring holes and inspection holes are arranged sequentially from top to bottom along the axial direction of the shaft section, and the wiring holes and inspection holes are staggered; multiple inspection holes are respectively arranged between two wiring holes; the setting of the wiring holes can reduce the weight of the shaft section, and unlike the existing fixed shaft structure, it eliminates the wire groove originally designed at the through hole in the middle of the fixed shaft, so that the transmission line can pass through the circumference of the shaft section, that is, in the wiring hole, simplifying the structure of the fixed shaft and reducing some of its weight, and the holes provided by the wiring holes and inspection holes can increase the structural strength of the shaft section; since the fixed shaft is a large casting, and the shaft section is relatively long in the structure of the fixed shaft, and the casting internal stress on the wall is large, the wiring holes and inspection holes can reduce the internal stress of the shaft section.

[0022] The main spindle connection section is equipped with a connecting seat, a connecting column, and a positioning block. Multiple connecting seats are evenly distributed along the outer circumferential surface of the main spindle connection section, and each connecting seat is a rectangular cantilever. The connecting column and the positioning block are mounted on the connecting seat, with the inner hole of the connecting column penetrating the connecting seat. The positioning block is arranged adjacent to the connecting column, and the axis of the connecting column is located on the length centerline of the positioning block. This design differs from the flange structure used in existing fixed-spindle and main-spindle connections. The gaps between the multiple connecting seats reduce the weight of the original connecting flange. Furthermore, by casting multiple connecting seats, which are relatively smaller than the connecting flange, the internal stress generated during casting is also relatively less. This achieves the goal of reducing the weight of the main spindle connection section while simultaneously improving the structural strength of the connecting components and reducing internal stress. This simplifies the structure of the fixed spindle, thus solving the problems of complex structures, difficult casting and machining, low efficiency, and the tendency for stress concentration in existing fixed spindles. Attached Figure Description

[0023] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is an isometric drawing of the fixed axis of the present invention;

[0025] Figure 2 This is a front view of the fixed-axis invention;

[0026] Figure 3 This is a side view of the fixed axis of the present invention;

[0027] Figure 4 This is a sectional view of the fixed axis of the present invention;

[0028] Figure 5 This is a top view of the fixed-axis invention.

[0029] The reference numerals in the attached figures are as follows:

[0030] 1. First positioning section; 11. Component positioning ear; 12. Component through hole; 13. First shoulder;

[0031] 2. Shaft section; 21. Wiring hole; 22. Inspection hole; 221. Boss;

[0032] 3. Second positioning section; 31. Second shoulder;

[0033] 4. Spindle connecting section; 41. Connecting seat; 42. Connecting column; 43. Positioning block; 44. Positioning groove; 45. Mounting hole; 46. Rectangular groove;

[0034] 5. Cabin connection section; 51. Positioning ring; 52. Connection hole;

[0035] 6. Rising. Detailed Implementation

[0036] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0037] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other implementations obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0038] The specific implementation provides a fixed shaft for a wind turbine, which effectively solves the problems of existing wind turbine fixed shafts, such as complex structure, high casting and processing difficulty, low efficiency, and easy occurrence of stress concentration.

[0039] Hereinafter, embodiments will be described with reference to the accompanying drawings. Furthermore, the entirety of the configurations illustrated in the following embodiments is not limited to those necessary for the solution of the invention as described in the claims.

[0040] An embodiment of a fixed axis wind turbine, for example Figures 1 to 5As shown, the structure includes a first positioning section 1, a shaft section 2, a second positioning section 3, a main shaft connecting section 4, and a nacelle connecting section 5 connected sequentially along the axial direction to form a hollow cylinder. The first positioning section 1 is used to contact the inner annular surface of the main shaft. Multiple component positioning ears 11 are evenly distributed on the inner circumference of the first stage, and each component positioning ear 11 is provided with a component through hole 12. The circumferential surface of the shaft section 2 is provided with a wiring hole 21 and a maintenance hole 22. In the vertical direction where the nacelle connecting section 5 stands on the ground, the wiring hole 21 and the maintenance hole 22 are arranged sequentially from top to bottom along the axial direction of the shaft section 2, and the wiring hole 21 and the maintenance hole 22 are staggered. Multiple maintenance holes 22 are respectively arranged between two wiring holes 21. The second positioning section 3 is used to connect... The spindle is to be assembled on its inner annular surface; the spindle connecting section 4 is provided with a connecting seat 41, a connecting column 42, and a positioning block 43; multiple connecting seats 41 are evenly distributed on the outer circumferential surface of the spindle connecting section 4, and the connecting seat 41 is a rectangular cantilever; the connecting column 42 and the positioning block 43 are provided on the connecting seat 41, and the inner hole of the connecting column 42 penetrates the connecting seat 41; the positioning block 43 is arranged adjacent to the connecting column 42, and the axis of the connecting column 42 is located on the length centerline of the positioning block 43; the nacelle connecting section 5 is provided with a positioning ring 51 and a connecting hole 52; the positioning ring 51 is stacked on the end face of the nacelle connecting section 5, and the diameter of the positioning ring 51 is smaller than the diameter of the nacelle connecting section 5; the connecting hole 52 is provided on the end face of the nacelle connecting section 5.

[0041] The main manufacturing method of the fixed shaft is that the first positioning section 1, the shaft body section 2, the second positioning section 3, the main shaft connecting section 4, and the engine compartment connecting section 5 are cast as a single piece.

[0042] Since the main structure of the fixed shaft of a wind turbine consists of a first positioning section 1, a shaft body section 2, a second positioning section 3, a main shaft connecting section 4, and a nacelle connecting section 5 connected sequentially along the axial direction, forming a hollow column, the mold can be divided into five sections during the casting of the fixed shaft. The structure of each section corresponds to the first positioning section 1, the shaft body section 2, the second positioning section 3, the main shaft connecting section 4, and the nacelle connecting section 5, respectively. The entire fixed shaft casting mold can be assembled by using a crane or overhead crane for hoisting and assembly before casting begins. This makes it more convenient to disassemble the mold for maintaining the inner wall of the mold and to modify the internal structure of the mold. Furthermore, when the fixed shaft is not being cast, each section of the mold can be disassembled and placed in batches, avoiding the occupation of the factory's production area and making the use of the factory's working area more reasonable.

[0043] By providing wiring holes 21 and inspection holes 22 on the circumferential surface of the shaft section 2; in the vertical direction where the nacelle connecting section 5 stands on the ground, the wiring holes 21 and inspection holes 22 are arranged sequentially from top to bottom along the axial direction of the shaft section 2, and the wiring holes 21 and inspection holes 22 are staggered; multiple inspection holes 22 are respectively arranged between two wiring holes 21; the setting of wiring holes 21 can reduce the weight of the shaft section 2, and unlike the existing fixed shaft structure, the wire groove originally designed at the through hole in the middle of the fixed shaft is removed, so that the transmission line can pass through the circumference of the shaft section 2, that is, in the wiring holes 21, which simplifies the structure of the fixed shaft and reduces some of its weight. In addition, the holes 21 and inspection holes 22 can increase the structural strength of the shaft section 2; since the fixed shaft is a large casting, and the shaft section 2 is relatively long in the structure of the fixed shaft, and the casting internal stress on the wall is large, the wiring holes 21 and inspection holes 22 can reduce the internal stress of the shaft section 2.

[0044] By providing a connecting seat 41, a connecting column 42, and a positioning block 43 in the main spindle connecting section 4; multiple connecting seats 41 are evenly distributed along the outer circumferential surface of the main spindle connecting section 4, and the connecting seat 41 is a rectangular cantilever; the connecting column 42 and the positioning block 43 are set on the connecting seat 41, and the inner hole of the connecting column 42 penetrates the connecting seat 41; the positioning block 43 is arranged adjacent to the connecting column 42, and the axis of the connecting column 42 is located on the length centerline of the positioning block 43; the design differs from the flange structure used in the existing connection between the fixed shaft and the main spindle. The gap left between the multiple connecting seats 41 can reduce the weight of the original connecting flange. In addition, by casting multiple connecting seats 41, the connecting seats 41 are relatively smaller than the connecting flange, and the internal stress generated by the connecting seats 41 during casting is also relatively less. This achieves the goal of reducing the weight of the main spindle connecting section 4 while improving the structural strength of the connecting components, reducing internal stress, and simplifying the structure of the fixed shaft. This solves the problems of the existing fixed shaft having a relatively complex structure, high casting and machining difficulty and low efficiency, and being prone to multiple stress concentrations.

[0045] As one of the alternative implementation methods,

[0046] Regarding the specific structure of the wiring hole 21 of the aforementioned shaft section 2, as follows: Figures 1 to 4 As shown, the periphery of the wiring hole 21 protrudes 6 from the outer peripheral surface of the shaft section 2 to the inner peripheral surface, and the outer peripheral surface of the shaft section 2 and the edge of the wiring hole 21 are provided with rounded corners, and the inner peripheral surface of the shaft section 2 and the edge of the wiring hole 21 are provided with rounded corners; there are three wiring holes 21.

[0047] Regarding the specific structure of the inspection hole 22 of the aforementioned shaft section 2, as follows: Figures 1 to 4As shown, the inspection hole 22 is provided with a boss 221 on the edge of the hole on the outer peripheral surface of the shaft section 2, and the boss 221 and the outer peripheral surface of the shaft section 2 are provided with rounded corners; the periphery of the inspection hole 22 protrudes 6 from the outer peripheral surface of the shaft section 2 to the inner peripheral surface, and the inner peripheral surface of the shaft section 2 and the edge of the inspection hole 22 are provided with rounded corners; there are three inspection holes 22.

[0048] Regarding the specific structure of the connecting seat 41 of the aforementioned main spindle connecting section 4, as follows: Figures 1 to 5 As shown, the connecting seat 41 has a positioning groove 44 on the surface facing the shaft section 2, the connecting post 42 is located in the positioning groove 44, and the positioning block 43 is arranged on the edge of the positioning groove 44; multiple mounting holes 45 are arrayed on the side of the connecting seat 41 adjacent to the positioning block 43; a rectangular groove 46 is provided on the surface of the connecting seat 41 facing the engine room connecting section 5, and the center line of the rectangular groove 46 in the length direction coincides with the center line of the connecting seat 41 and the positioning block 43 in series; there are six connecting seats 41.

[0049] Regarding the specific structure of the connecting post 42 and the positioning block 43 of the aforementioned main spindle connecting section 4, as follows: Figures 1 to 5 As shown, the body of the connecting column 42 is conical, the large diameter end of the connecting column 42 is engaged with the positioning groove 44, and the connection between the large diameter end of the connecting column 42 and the positioning groove 44 is provided with a rounded corner; the side of the positioning block 43 away from the connecting column 42 is rounded, the side of the connecting seat 41 away from the main shaft connecting section 4 is rounded, and the rounded side of the positioning block 43 and the rounded side of the connecting seat 41 are parallel.

[0050] Regarding the positioning structure of the first positioning segment 1 mentioned above, as follows: Figure 4 As shown, a first shoulder 13 is provided on the first positioning section 1 for positioning; the cross-sectional shape of the first shoulder 13 is trapezoidal, and the first shoulder 13 is arranged adjacent to the shaft section 2.

[0051] Regarding the positioning structure of the second positioning segment 3 mentioned above, as follows: Figure 4 As shown, the second positioning section 3 is provided with a second shoulder 31 to improve the alignment of the shaft center; the second shoulder 31 is a chamfered platform connecting the second positioning section 3 and the shaft body section 2.

[0052] When in use, three component positioning ears 11 are provided, and the three component positioning ears 11 are respectively arranged on the center of the three wiring holes 21.

[0053] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described.

[0054] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A fixed shaft for a wind turbine, characterized in that, The assembly comprises a first positioning section, a shaft section, a second positioning section, a main shaft connecting section, and a nacelle connecting section connected sequentially along the axial direction, forming a hollow cylinder. The first positioning section is used to contact the inner annular surface of the main shaft. Multiple component positioning ears are evenly distributed on the inner circumference of the first positioning section, and each component positioning ear has a component through hole. The shaft section has wiring holes and inspection holes on its circumferential surface. In the vertical direction of the nacelle connecting section, which is positioned on the ground, the wiring holes and inspection holes are arranged sequentially from top to bottom along the axial direction of the shaft section, and are staggered. Multiple inspection holes are respectively arranged between two wiring holes. The second positioning section is used to contact the assembly to be assembled. The spindle has an inner annular surface; the spindle connecting section is provided with a connecting seat, a connecting column, and a positioning block; multiple connecting seats are evenly distributed on the outer circumferential surface of the spindle connecting section, and the connecting seat is a rectangular cantilever; the connecting column and the positioning block are disposed on the connecting seat, and the inner hole of the connecting column penetrates the connecting seat; the positioning block is arranged adjacent to the connecting column, and the axis of the connecting column is located on the length centerline of the positioning block; the nacelle connecting section is provided with a positioning ring and a connecting hole; the positioning ring is stacked on the end face of the nacelle connecting section, and the diameter of the positioning ring is smaller than the diameter of the nacelle connecting section; the connecting hole is disposed on the end face of the nacelle connecting section; The connecting seat has a positioning groove on its surface facing the shaft section, the connecting column is disposed in the positioning groove, and the positioning block is arranged on the edge of the positioning groove; the connecting seat has a plurality of mounting holes arrayed on its edge adjacent to the positioning block; the connecting seat has a rectangular groove on its surface facing the nacelle connecting section, and the center line of the rectangular groove in the length direction coincides with the center line of the connecting seat and the positioning block connected in series; there are six connecting seats. The connecting column has a conical body, and the larger diameter end of the connecting column engages with the positioning groove. The connection between the larger diameter end of the connecting column and the positioning groove is provided with a rounded corner. The side of the positioning block away from the connecting column is rounded, and the side of the connecting seat away from the main shaft connecting section is rounded. The rounded side of the positioning block and the rounded side of the connecting seat are parallel. The first positioning section is provided with a first shoulder for positioning; the cross-sectional shape of the first shoulder is trapezoidal, and the first shoulder is arranged adjacent to the shaft section; The second positioning section is provided with a second shoulder to improve the alignment of the shaft center; the second shoulder is a chamfered platform connecting the second positioning section and the shaft body section.

2. The fixed axis according to claim 1, characterized in that, The first positioning section, the shaft section, the second positioning section, the main shaft connecting section, and the cabin connecting section are integrally cast.

3. The fixed axis according to claim 1, characterized in that, The periphery of the wiring hole protrudes from the outer peripheral surface of the shaft section to the inner peripheral surface, and the outer peripheral surface of the shaft section and the edge of the wiring hole are provided with rounded corners, and the inner peripheral surface of the shaft section and the edge of the wiring hole are provided with rounded corners. There are three wiring holes.

4. The fixed axis according to claim 3, characterized in that, The inspection hole is provided with a boss on the edge of the hole on the outer peripheral surface of the shaft section, and the boss and the outer peripheral surface of the shaft section are provided with rounded corners; the periphery of the inspection hole rises from the outer peripheral surface of the shaft section to the inner peripheral surface, and the inner peripheral surface of the shaft section and the edge of the inspection hole are provided with rounded corners. There are three inspection holes.

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