Crankshaft support device

Abstract

To provide a crankshaft support device capable of gripping a crankshaft with sufficient holding force, finishing quenching of the crankshaft by gripping the crankshaft once, and improving machining efficiency.SOLUTION: A crankshaft W to be quenched has a tapered shape in which at least the one end side of the crankshaft W is tapered toward a tip. The crankshaft support device rotates the crankshaft W by gripping at least the shaft on the tapered shape side by a work carry 60. The holding surfaces 44 and 45 of the work carry 60 for gripping the crankshaft W have a tapered shape to match the axis of the crankshaft W.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] The present invention relates to a crankshaft support device. [Background technology]

[0002] When hardening a crankshaft, at least one side of the crankshaft becomes thinner and tapered toward the tip. When hardening a crankshaft, it is necessary to attach a carrier jig to the tapered shaft portion and fix it with a fixing bolt. However, because the tip of the crankshaft is tapered, the carrier jig cannot completely hold the crankshaft between the fixing part and the gripping part, so when the crankshaft is rotated, it does not rotate concentrically, and vibration occurs in the rotation and position shift occurs. Therefore, in the past, a carrier was attached to the straight shaft portion. However, since the straight shaft portion to which the carrier is attached also requires hardening, the crankshaft is removed after hardening processing other than the straight shaft portion is completed, and the carrier is attached to the straight shaft portion where hardening is completed, and hardening processing is performed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 11-207576 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 relates to a shaft clamping device for supporting a crankshaft on the spindle head of a machine tool, and although it is not a hardening processing device, it is related in that it processes crankshafts having tapers on both ends of the crankshaft.

[0005] According to Patent Document 1, when grinding a crankshaft, a male thread that screws into a female thread formed on the end face of the crankshaft is moved in a direction away from the crankshaft, and a work center through which the male thread slidably passes is pressed into a tapered hole connected to the female thread, making it possible to firmly hold the axial end of the crankshaft without applying an axial force in the compressive direction to the crankshaft.

[0006] Furthermore, Patent Document 1 states that a drive carrier is engaged with the other axial end surface of the crankshaft, thereby enabling the crankshaft to be rotated with sufficient torque, but there is no mention of providing a tapered surface on the carrier.

[0007] To provide a crankshaft supporting device capable of clamping a crankshaft with sufficient holding force, enabling hardening of the crankshaft to be completed by clamping the crankshaft once, and improving processing efficiency. [Means for solving the problem]

[0008] An embodiment for solving the above-mentioned problems is a crankshaft support device for rotating a crankshaft by gripping at least the tapered side of the crankshaft, the shaft of which is tapered toward the tip at least on one end side of the crankshaft to be hardened, the holding surface of the crankshaft that grips the crankshaft being tapered to match the axis of the crankshaft.

[0009] According to this embodiment, the diameter of the crankshaft gripping portion of the carrier that grips the crankshaft becomes smaller as the crankshaft approaches the tip, so the gripping portion also has a gripping surface that grips the crankshaft, which is the opening of the carrier, and is a tapered surface that gradually reduces its inner diameter from the entry side of the crankshaft to the opposite side to match the outer diameter of the crankshaft. This allows the surface of the crankshaft to match the tapered surface of the carrier.

[0010] This embodiment is a crankshaft support device in which the taper ratio of the taper shape of the crankshaft is the same as the taper ratio of the supporting surface of the carrier.

[0011] In this embodiment, the taper ratio of the tapered shape of the crankshaft and the taper ratio of the holding surface of the carrier are the same, so when the crankshaft is inserted into the opening of the carrier, the tapered surface of the crankshaft and the holding surface of the carrier match.

[0012] This embodiment is a crankshaft support device in which the gripping surface of the carrier that grips the crankshaft has at least two tapered surfaces.

[0013] According to this embodiment, the gripping surface of the carrier that grips the crankshaft has at least two tapered surfaces, and similarly to the above, both tapered surfaces have gradually smaller inner diameters from the entry side of the crankshaft and on the opposite side, so that the surface of the crankshaft mates with the tapered surface of the carrier in two places.

[0014] This embodiment is a crankshaft support device in which a taper ratio of the tapered shape of the crankshaft is equal to a taper ratio of the first retaining surface and the second retaining surface.

[0015] In this embodiment, the taper ratio of the tapered shape of the crankshaft is the same as the taper ratio of the first retaining surface and the second retaining surface, so that when the crankshaft is inserted into the opening of the carrier, the tapered surface of the crankshaft matches the first retaining surface and the second retaining surface of the carrier.

[0016] In this embodiment, the crankshaft support device has a fixing member for fixing the crankshaft, and the pressing surface of the fixing member that contacts the crankshaft is tapered, and the taper ratio of the pressing surface is the same as the taper ratio of the tapered shape of the crankshaft.

[0017] According to this embodiment, the carrier has a fixing member for fixing the crankshaft, and the pressing surface of the fixing member that contacts the crankshaft is tapered, and the taper ratio of the pressing surface is the same as the taper ratio of the taper shape of the crankshaft. The crankshaft is pressed by the fixing member, and the pressing surface of the fixing member is arc-shaped, and the arc diameter of the pressing surface gradually decreases from the entry side of the crankshaft to the opposite side, forming a tapered shape. Furthermore, since the taper ratio of the pressing surface is the same as the taper ratio of the taper shape of the crankshaft, the pressing surface matches the surface of the crankshaft, and the crankshaft can be reliably pressed by the fixing member.

[0018] This embodiment is a crankshaft support device in which, when the crankshaft is fixed with the carrier, the first and second retaining surfaces of the carrier and the pressing surface of the fixing member are each positioned at equal intervals.

[0019] According to this embodiment, when the crankshaft is fixed with the carrier, the first and second retaining surfaces of the carrier and the pressing surface of the fixing member are each arranged at equal positions in the crankshaft support device, so that the crankshaft is gripped by three tapered surfaces and the retaining surfaces of the carrier and the pressing surfaces of the fixing member match up with the surfaces of the crankshaft, respectively, so that the crankshaft can be securely gripped by the carrier and the fixing member.

[0020] In this embodiment, the first retaining surface, the second retaining surface, and the pressing surface of the fixing member are disposed at positions spaced apart from each other by 120 degrees.

[0021] According to this embodiment, the crankshaft support device has the first retaining surface, the second retaining surface, and the pressing surface of the fixing member positioned 120 degrees apart from each other. Therefore, by holding the crankshaft at an even position, force is applied to the crankshaft evenly, and the crankshaft can be held more securely. Effect of the Invention

[0022] The crankshaft support device of this embodiment is capable of holding the crankshaft with sufficient holding force, and enables the crankshaft to be hardened by holding it once, thereby improving processing efficiency. [Brief description of the drawings]

[0023] [Figure 1] 1 is a perspective view of a suspension unit of an induction hardening apparatus using a crankshaft support device of the present invention; FIG. [Diagram 2] 1A is a side view of a crankshaft, in which the first pin part P1 and the fourth pin part P4 are at the top dead center position, and the second pin part P2 and the third pin part P3 are at the bottom dead center position, and FIG. 1B is a side view of a crankshaft, in which the first pin part P1 and the fourth pin part P4 are at the bottom dead center position, and the second pin part P2 and the third pin part P3 are at the top dead center position. [Diagram 3] 1 is a front view of a crankshaft and an induction hardening device using the crankshaft support device of the present invention. FIG. [Figure 4] FIG. 2 is a side view of the crankshaft support device of the present invention. [Diagram 5] FIG. 5 is an enlarged view of part B in FIG. [Figure 6] 1 is a perspective view of the crankshaft supported by a carrier in accordance with the present invention; FIG. [Figure 7] FIG. 7 is an enlarged view of part A in FIG. 6. [Figure 8] FIG. 2 is a perspective view of a carrier used in the crankshaft support device of the present invention. [Figure 9] FIG. 2 is a perspective view of a crankshaft, showing a taper axis of the crankshaft. [Figure 10] 1 is a schematic diagram for explaining the taper ratio of the first support surface and the second support surface of the carrier used in the crankshaft support device of the present invention. FIG. [Figure 11]2 is a perspective view showing a first holding surface, a second holding surface, and a fixing member of a carrier used in the crankshaft support device of the present invention. FIG. [Figure 12] 5 is a schematic diagram for explaining a taper ratio of a fixing member used in the crankshaft support device of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] The following description will be given with reference to the drawings. As shown in FIG. 1, a high-frequency hardening apparatus 50 (high-frequency heating apparatus) using the crankshaft supporting device of the present invention has a suspension unit 1, a transformer unit 4, and a high-frequency power source (not shown).

[0025] The high frequency power supply has a high frequency oscillator, converts AC power supplied from a commercial power supply into a high frequency power, and outputs the converted power to the transformer unit 4 side.

[0026] 1, the transformer unit 4 is formed by connecting and integrating a transformer 25 and an induction heating coil body 2. In general, the transformer 25 is called a disk transformer. The induction heating coil body 2 includes a heating coil 7, a spacer 8, side plates 9 and 10, and cooling jackets 11 and 12.

[0027] The heating coil 7 is made of a tubular wire member made of a good conductor such as copper or a copper alloy, and is connected to the secondary winding of the transformer. The heating coil 7 has a curved semi-open shape that can approach and face approximately half of the entire circumference of the pin parts P1 to P4 of the crankshaft W shown in FIG. 2, which is the object to be induction heated. In other words, the heating coil 7 can move toward and away from the pin parts P1 to P4 in the radial direction of the pin parts P1 to P4. The heating coil 7 is made of a hollow conductor, and during induction heating, a coolant is circulated and supplied into the heating coil 7 from a coolant supply source (not shown).

[0028] The side plates 9, 10 are made of a metal material that is not easily affected by electromagnetic induction, and are arranged on both sides of the heating coil 7 to sandwich and fix the heating coil 7. The side plates 9, 10 are provided with semicircular recesses 9a, 10a. The recesses 9a, 10a form a work placement area 13 between the side plates 9, 10 that can accommodate the pin portions P1 to P4.

[0029] The spacer 8 is made of a material such as ceramic that is not affected by electromagnetic induction, and is fixed to the side plates 9 and 10 with screws.

[0030] The cooling jackets 11, 12 have a large number of injection holes. The cooling jackets 11, 12 are disposed below the side plates 9, 10 and on both sides of the workpiece placement area 13. When cooling water is supplied to the cooling jackets 11, 12 from a cooling water supply source (not shown), the cooling water can be injected from the injection holes toward the workpiece placement area 13.

[0031] Next, the suspension unit 1 will be described. As shown in FIG. 1, the suspension unit 1 includes a receiving member 52 and a support arm 3 .

[0032] The support arm 3 is a long, thin plate-like member with its longitudinal direction oriented horizontally and its long side oriented vertically and its short side oriented horizontally. A first spherical bearing 17 is provided at one end (fixed end) of the support arm 3, and a second spherical bearing 18 is provided at the other end (free end).

[0033] As shown in FIG. 1, the receiving member 52 has a support 14, an upper overhanging portion 15a, and a lower overhanging portion 15b.

[0034] The support pillar 14 is fixed in a vertical position to a fixed member (not shown).

[0035] The upper protrusion 15a is a horizontally extending member connected to the upper part of the support column 14. One end of the upper protrusion 15a is connected to the support column 14, and a horizontal position is maintained by the reinforcing rib 16. A third spherical bearing 37 is provided on the other end (free end) of the upper protrusion 15a.

[0036] The lower overhang 15b is a horizontally extending member connected to the lower part of the support 14. The lower overhang 15b is disposed below the upper overhang 15a. As shown in FIG. 1, plate-shaped connecting members 31 and 32 that function as reinforcing ribs are provided at the connection between the lower overhang 15b and the support 14. The connecting members 31 and 32 are disposed in parallel with a predetermined distance apart. The connecting members 31 and 32 keep the lower overhang 15b in a horizontal position. The connecting members 31 and 32 are provided with holes 31a and 32a, respectively. The holes 31a and 32a have the same diameter and are disposed concentrically.

[0037] A seat 33 is disposed on the other end (free end) of the lower protrusion 15b. The seat 33 is disposed on the upper surface side of the lower protrusion 15b and has a V-shaped groove formed by two inclined surfaces. The V-shaped groove extends along the longitudinal direction of the lower protrusion 15b.

[0038] In addition, the lower end of a biasing member 38, which is a spiral spring, is connected to a connection portion 19 provided at the upper part of the longitudinal center of the support arm 3. Therefore, the support arm 3 is constantly biased upward by the biasing member 38.

[0039] Furthermore, the support arm 3 is disposed at the center of the connecting members 31, 32 of the receiving member 52. When the support arm 3 swings downward on a plane parallel to the connecting members 31, 32 around the first spherical bearing portion 17, the tapered lower portion 30 fits into the V-shaped groove of the seating portion 33. The inclined surface of the lower portion 30 coincides with the inclined surface of the V-shaped groove. In other words, even if the position of the support arm 3 is slightly misaligned with respect to the receiving member 52, the support arm 3 sits on the seating portion 33 along the V-shaped groove, and the position of the support arm 3 is corrected.

[0040] Next, a method for hardening the crankshaft W will be described with reference to FIG. As shown in Fig. 3, one end (drive side) of the crankshaft W is held by a carrier 60, and the other end (tail side) is supported by a center pin (not shown). The carrier 60 is connected to a drive device (not shown). That is, the crankshaft W is rotatably supported at both ends. The center pin supporting the other end of the crankshaft W can move in response to the expansion and contraction of the crankshaft W in the axial (longitudinal) direction. That is, the center pin has a moving device 34 (moving means) that moves it in the axial direction of the crankshaft W.

[0041] 3, the high-frequency hardening device for hardening each of the shaft portions w1 to w5 includes an induction heating coil body 2, a transformer 25, and a moving device 34. The high-frequency hardening device also includes a control device (not shown).

[0042] The transformer 25 (voltage transformer) is disposed between a high-frequency power source (not shown) and the induction heating coil body 2. Although not shown, the primary side of the transformer 25 is connected to the high-frequency power source, and a part of the secondary side is adjacent to the induction heating coil body 2. The transformer 25 and the induction heating coil body 2 each have a connection terminal, and are fixed together with their connection terminals connected to each other.

[0043] The moving device 34 has a fixed part 34a (ball screw), a movable part 34b (nut), and a servo motor (not shown). The fixed part 34a is fixed to an immovable member (not shown) and does not fluctuate in position, but is rotated and driven by the servo motor. The movable part 34b engages with the fixed part 34a, and is movable relative to the fixed part 34a when the fixed part 34a is rotated. The movable part 34b is capable of fine movement relative to the fixed part 34a, and is capable of reciprocating movement along the axial direction (longitudinal direction) of the crankshaft W.

[0044] The control device has a central processing unit (CPU) and has a function of controlling the operation of the moving device .

[0045] An induction heating coil body 2 is disposed adjacent to the shaft portions w1 to w5 of the crankshaft W. The distance between each heating coil and each shaft portion w1 to w5 is set within a predetermined range by a spacer fixed to the side plate. Furthermore, when the crankshaft W is rotationally driven by a drive device (not shown), preparation for hardening (induction heating process and cooling process) is completed.

[0046] Then, a high-frequency current is supplied from a high-frequency power source (not shown) to the heating coil to start hardening (induction heating process) of the crankshaft W. When the shaft portions w1 to w5 of the crankshaft W are heated, the crankshaft W expands in the axial direction, and the center pin moves. Therefore, the movable part approaches the fixed part of the displacement sensor, and the displacement sensor detects that the crankshaft W has expanded, detects the amount of expansion, and transmits a detection signal to a control device (not shown).

[0047] In the quenching, when the induction heating process is completed, a cooling process is immediately carried out. In the cooling process, cooling water is sprayed from a cooling jacket onto each of the shaft parts w1 to w5. Each of the shaft parts w1 to w5 is cooled by the cooling water, and the temperature quickly drops to the Ms point (martensitic transformation point).

[0048] At that time, the crankshaft W contracts, and the positions of the shaft portions w1 to w5 change. The displacement sensor detects the contraction of the crankshaft W and transmits a detection signal to the control device. The control device, having received the detection signal from the displacement sensor, drives each of the movement devices 34 to move each of the induction heating coil bodies 2a to 2e facing each of the shaft portions w1 to w5.

[0049] Next, a description will be given of the crankshaft support device 5 that grips and supports the crankshaft W when the crankshaft W is driven to rotate.

[0050] As shown in FIGS. 4 and 5, the crankshaft rotating means 20 for rotating the crankshaft W is a spindle unit 21, and the spindle unit 21 has an engagement means 22 for engaging with a carrier 60. In order to rotate the crankshaft W, centering is performed on both ends of the crankshaft W. At this time, the shaft 24 of the carrier 60 is hooked onto the rotating plate 23 of the spindle unit 21 that rotates the crankshaft W. Then, the carrier 60 is rotated together to rotate the crankshaft W.

[0051] As shown in Figures 6, 7 and 8, when the crankshaft W is hardened as described above, at least one end of the crankshaft W is tapered to become thinner toward the tip, forming a tapered shaft 43. The crankshaft support device 5 holds at least the tapered shaft 43 by the carrier opening 70 of the carrier 60, and rotates the crankshaft W. In the carrier opening 70, a first holding surface 44 and a second holding surface 45 for holding the crankshaft W are tapered to match the tapered shaft 43 of the crankshaft W. The carrier opening 70 also has a fixing member insertion opening 82 for inserting a fixing member 80 for fixing the crankshaft W.

[0052] Fig. 7 is an enlarged view of part A in Fig. 6. The holding surfaces for holding the tapered shaft 43 of the crankshaft W of the carrier 60 are at least the first holding surface 44 and the second holding surface 45. The first holding surface 44 and the second holding surface 45 have a tapered shape that matches the tapered shaft 43. The taper ratio of the tapered shaft 43 to the first holding surface 44 and the second holding surface 45 is all 1 / 10.

[0053] FIG. 9 is a diagram showing the tapered shaft 43 of the crankshaft W. The taper ratio of the tapered shaft 43 is expressed as (D1-D2) / L, which is 1 / 10. Here, D1 is the larger diameter of the tapered shaft 43, and D2 is the smaller diameter of the tapered shaft 43. Also, L is the length of the tapered shaft 43. FIG. 10 is a schematic diagram showing the first holding surface 44 and the second holding surface 45 of the carrier 60 that holds the tapered shaft 43. The taper ratio of the first holding surface 44 and the second holding surface 45 is expressed as (d1-d2) / l1×2, which is 1 / 10. Here, d1 is the larger radius of the first holding surface 44 and the second holding surface 45, and d2 is the smaller radius of the first holding surface 44 and the second holding surface 45. Also, l1 is the length of the first holding surface 44 and the second holding surface 45. Here, the taper ratio of the tapered shaft 43 and the taper ratio of the first holding surface 44 and the second holding surface 45 are equal to each other.

[0054] 11, the carrier 60 has a fixing member 80 for fixing the crankshaft W, and the surface of the fixing member 80 that comes into contact with the tapered shaft 43 of the crankshaft W is tapered. The fixing member 80 presses the tapered shaft 43 with a screw 62, and the pressing surface 61 of the fixing member 80 is arc-shaped, and the pressing surface 61 is tapered by gradually decreasing the arc diameter from the entry side of the crankshaft W to the opposite side, so that the pressing surface 61 fits with the tapered shaft 43.

[0055] 12, the taper ratio of the pressing surface 61 of the fixing member 80 is expressed as (d3-d4) / l2×2, which is 1 / 10. Here, d3 is the larger radius of the pressing surface 61, and d4 is the smaller radius of the pressing surface 61. Also, l2 is the length of the pressing surface 61. The taper ratio of the pressing surface 61 also coincides with the taper ratio of the taper shaft 43.

[0056] When the crankshaft W is fixed by the carrier 60, the first holding surface 44, the second holding surface 45, and the pressing surface 61, which are brought into contact with the carrier 60 and the tapered shaft 43, are disposed at equal positions. Therefore, the positions are divided into three equal parts of 360 degrees, that is, each surface is disposed at an interval of 120 degrees. By doing so, when the crankshaft W is held, the first holding surface 44, the second holding surface 45, and the tapered shaft 43 are in close contact with each other, and the tapered shaft 43 can be completely held by pressing it with the pressing surface 61 of the fixing member 80. Therefore, by holding the crankshaft W once, it is possible to complete the hardening of the crankshaft W, and there is an effect of improving the processing efficiency.

[0057] The first holding surface 44, the second holding surface 45 and the pressing surface 61 are machined by a known wire electric discharge machining. The carrier 60 or the fixed member 80 is set in a wire electric discharge machine (not shown) and filled with machining fluid. The machining tank is also equipped with a cooling device, which keeps the temperature of the machining fluid constant to suppress thermal expansion and deformation of the carrier 60. Then, current is passed through the wire electrode wire to perform machining. When the carrier 60 or the fixed member 80 and the wire electrode wire, which are insulated by the machining fluid, approach each other to a distance of about a discharge gap, and insulation breakdown occurs between the two. This insulation breakdown causes a pulse current to flow in instantly, generating a high-density discharge state called an arc column, which locally reaches a high temperature of 6000 to 7000 degrees, and melts the machining area of ​​the carrier 60 or the fixed member 80.

[0058] Furthermore, the temperature of the machining fluid around the arc column also rises, causing it to vaporize instantly and rapidly accumulate and expand. This causes a localized explosion, blowing away the molten metal on the surface of the carrier 60 or the fixed member 80 and the wire electrode. When the flow of the pulse current ends, machining fluid flows in by the amount of accumulated expansion. A flow of machining fluid also occurs around the electrode wire, at which time the molten metal is cooled and washed away as extremely small machining debris. Then, when the machining area becomes insulated again, it waits for the voltage supply until the next insulation breakdown occurs. This cycle of insulation breakdown, melting, removal, recovery, and insulation breakdown is repeated at very short intervals of several μs for each pulse voltage, thereby performing continuous electric discharge machining, and the first and second holding surfaces 44 and 45 of the carrier 60, as well as the pressing surface 61 of the fixed member 80, can be machined.

[0059] In order to confirm that the taper ratio of the first holding surface 44, the second holding surface 45, and the pressing surface 61 machined in this manner coincides with the taper ratio of the taper axis 43 of the crankshaft W, for example, a known 3D shape measuring machine can be used. A 3D scan is performed to measure the taper shapes of the first holding surface 44 and the second holding surface 45 with high accuracy. This makes it possible to measure the cross section without cutting the carrier 60 or the fixing member 80.

[0060] In this embodiment, the tapered holding surfaces are provided at two locations, but they may be provided at three locations or more, and the tapered shape may be formed over the entire circumference of the carrier opening 70 except for the pressing surface 61. In this case, the taper ratio of the holding surfaces or carrier opening is made to match the taper ratio of the tapered shaft 43, but the taper ratio is not particularly limited to 1 / 10, and may be made to match the taper ratio of the tapered shaft 43. [Explanation of symbols]

[0061] 1 Hanging unit 3 Support Arm 5 Crankshaft support device 25. Transformer 44 First holding surface 45 Second holding surface 50 Tapered section 60 Kelley 61 Pressing surface 80 Fixing member

Claims

1. A crankshaft support device for rotating a crankshaft to be hardened, wherein at least one end of the crankshaft has a tapered shape in which the axis becomes thinner as it approaches the tip, and wherein at least the tapered side of the axis is gripped by a carrier and the crankshaft is rotated, wherein the holding surface of the carrier that grips the crankshaft is tapered to match the axis of the crankshaft.

2. 2. The crankshaft support device according to claim 1, wherein a taper ratio of the taper shape of the crankshaft is equal to a taper ratio of the support surface of the carrier.

3. 3. The crankshaft support device according to claim 2, wherein the support surface of the carrier that grips the crankshaft has at least two tapered surfaces, the two tapered surfaces being a first support surface and a second support surface.

4. 4. The crankshaft support device according to claim 3, wherein a taper ratio of the tapered shape of the crankshaft is equal to a taper ratio of the first retaining surface and the second retaining surface.

5. 5. A crankshaft support device as described in claim 4, wherein the carrier has a fixing member for fixing the crankshaft, the pressing surface of the fixing member that contacts the crankshaft is tapered, and the taper ratio of the pressing surface is the same as the taper ratio of the tapered shape of the crankshaft.

6. 6. A crankshaft support device as described in claim 5, wherein when the crankshaft is fixed by the carrier, the first and second retaining surfaces of the carrier and the pressing surface of the fixing member are each disposed at equal positions.

7. 7. The crankshaft support device according to claim 6, wherein the first retaining surface, the second retaining surface, and the pressing surface of the fixing member are disposed at positions spaced apart from each other by 120 degrees.

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