Induction heating device and method for heating a stabilizer

Abstract

To provide an induction heating apparatus capable of heating a part to be heated of a bar-shaped workpiece into a temperature distribution close to uniform one.SOLUTION: An induction heating apparatus 20 includes a first coil part 30 and a second coil part 40. A bar-shaped workpiece is disposed between the first coil part 30 and the second coil part 40. The first coil part 30 includes a pair of small pitch parts 71, 72 formed at both ends, large pitch parts 73, 74 formed between the small pitch parts 71, 72, and a middle pitch part 75 formed at the center. The second coil part 40 includes a pair of small pitch parts 111, 112 formed at both ends, large pitch parts 113, 114 formed between the small pitch parts 111, 112, and a middle pitch part 115 formed at the center.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an induction heating device for heating a rod-shaped workpiece such as a metal rod or a steel pipe by a high-frequency induction coil, and a method for heating a stabilizer.

Background Art

[0002] A stabilizer device disposed in a suspension mechanism portion of a vehicle includes a stabilizer made of a steel bar or a hollow member, and a support portion for supporting the stabilizer on the vehicle body. The stabilizer has a torsion portion extending in the vehicle width direction, and a pair of arm portions connected to both ends of the torsion portion via bent portions. An example of the support portion is a pair of bush units provided with rubber bushes, and the stabilizer is supported on the vehicle body via the bush units. Further, the tip of the arm is connected to a suspension member or the like via a connecting member.

[0003] In order to fix the rubber bush to the stabilizer, for example, a thermosetting adhesive may be used. In that case, a part (bush mounting portion) in the length direction of the stabilizer is heated. The rubber bush coated with the adhesive is overlapped with the heated stabilizer, and the adhesive is cured under a pressurized state.

[0004] In order to heat a part in the length direction of a rod-shaped workpiece, a high-frequency induction heating device may be used. For example, the high-frequency induction heating device described in Patent Document 1 has a pair of induction heating coils. Generally, an induction heating coil is made of a conductor wound at the same pitch.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] We have found that when a portion of a rod-shaped workpiece along its length is uniformly heated by a conventional induction heating coil, the following problems occur.

[0007] When a rod-shaped workpiece is heated by a conventional induction heating coil (a coil with a constant pitch), the heated area is heated with a generally uniform heat density within the coil width. However, immediately after heating begins, some of the heat escapes to the surrounding area due to heat transfer. As a result, the temperature near both ends of the heated area is lower than the temperature near the center of the heated area.

[0008] To attach a rubber bushing to a heated stabilizer, the stabilizer must be transported to the rubber bushing attachment stage. During this transport, a decrease in the temperature of the bushing attachment area (the heated area) is unavoidable, particularly near both ends of the bushing attachment area. Therefore, temperature control during heating is necessary to ensure that the temperature of the bushing attachment area is maintained at the curing temperature of the adhesive.

[0009] Furthermore, the stabilizer has compressive residual stress generated by shot peening to enhance its durability. If the stabilizer is heated above the permissible temperature, the compressive residual stress will disappear. Therefore, it is necessary to control the temperature so that the temperature of the heated part does not exceed the permissible value, and in addition, the temperature at which the adhesive hardens must be maintained when bonding the rubber bushing. Due to these circumstances, temperature control is difficult, and there was room for improvement.

[0010] Therefore, the object of the present invention is to provide an induction heating device capable of heating the heated portion of a rod-shaped workpiece, such as a stabilizer, to a nearly uniform temperature. [Means for solving the problem]

[0011] One embodiment is an induction heating device for heating a portion of a rod-shaped workpiece such as a stabilizer, and comprises a first coil and a second coil. The first coil includes a first coil portion consisting of a plurality of windings and has a first axis passing through the center of the first coil portion. The second coil includes a second coil portion consisting of a plurality of windings and has a second axis passing through the center of the second coil portion. The first coil portion and the second coil portion may each have an even number of turns or an odd number of turns. A workpiece placement portion is formed between the first coil portion and the second coil portion.

[0012] The first coil has a pair of first small-pitch sections formed at both ends of the first coil section, and a first large-pitch section formed between the pair of first small-pitch sections, with a pitch larger than that of the first small-pitch sections. The second coil also has a pair of second small-pitch sections formed at both ends of the second coil section, and a second large-pitch section formed between the pair of second small-pitch sections, with a pitch larger than that of the second small-pitch sections.

[0013] In the induction heating device of this embodiment, there may be a first medium-pitch portion formed in the center of the first coil portion and a second medium-pitch portion formed in the center of the second coil portion. The pitch of the first medium-pitch portion is greater than that of the first small-pitch portion and smaller than that of the first large-pitch portion. The pitch of the second medium-pitch portion is greater than that of the second small-pitch portion and smaller than that of the second large-pitch portion.

[0014] Each winding portion of the first coil may include a first side facing the workpiece placement portion, a second side opposite to the workpiece placement portion, an upper third side, and a lower fourth side. When viewed from the side of the first coil, the first sides may be parallel to each other and extend in a direction perpendicular to the first axis. The first coil may be inclined with respect to the workpiece placement portion. Each winding portion of the second coil may include a fifth side facing the workpiece placement portion, a sixth side opposite to the workpiece placement portion, an upper seventh side, and a lower eighth side. When viewed from the side of the second coil, the fifth sides may be parallel to each other and extend in a direction perpendicular to the second axis. The second coil may be inclined with respect to the workpiece placement portion.

[0015] In one example of the first coil section, when viewed from above, the third side portion may extend parallel to each other and perpendicular to the first axis, and the fourth side portion may extend parallel to each other and perpendicular to the first axis. When viewed from the side of the first coil section, the second side portion has a pitch angle corresponding to the first small pitch section and the first large pitch section. The third side portion or the fourth side portion may also have the pitch angle. In one example of the second coil section, when viewed from above, the seventh side portion may extend parallel to each other and perpendicular to the second axis, and the eighth side portion may extend parallel to each other and perpendicular to the second axis. When viewed from the side of the second coil section, the sixth side portion has a pitch angle corresponding to the second small pitch section and the second large pitch section. The seventh side portion or the eighth side portion may have the pitch angle.

[0016] The induction heating device according to one embodiment further includes a frame structure made of an electrically insulating material, and a first positioning member is provided on each winding portion of the first coil portion, and a second positioning member may be provided on each winding portion of the second coil portion. The first positioning member and the second positioning member are fixed to the frame structure.

[0017] The induction heating device may include a power supply conductor that conducts with the first coil portion, a connection conductor that electrically connects the first coil portion and the second coil portion to each other, and a conductor adjacent portion where the power supply conductor and the connection conductor are adjacent to each other and extend in the same direction. The power supply conductor and the connection conductor are arranged in the conductor adjacent portion such that the direction of the current flowing through the power supply conductor and the direction of the current flowing through the connection conductor are opposite to each other.

Advantages of the Invention

[0018] According to the induction heating device according to the present embodiment, for example, a part in the longitudinal direction of a bar-shaped workpiece such as a vehicle stabilizer can be heated to a temperature range that is uniformly close.

Brief Description of the Drawings

[0019] [Figure 1] A perspective view schematically showing a part of a vehicle and a stabilizer. [Figure 2] A perspective view of a part of the stabilizer and a rubber bush shown in FIG. 1. [Figure 3] A perspective view of a part of the induction heating device according to the first embodiment. [Figure 4] A plan view of the induction heating device shown in FIG. 3. [Figure 5] A front view of the induction heating device shown in FIG. 3. [Figure 6] A side view of the first coil along the line F6-F6 in FIG. [Figure 7] A side view of the second coil along the line F7-F7 in FIG. [Figure 8] A perspective view of the state where the induction heating device shown in FIG. 3 is assembled to the frame structure. [Figure 9] A diagram showing the relationship between the position of a heated portion heated by an induction heating device and the heat generation density. [Figure 10] A diagram showing the relationship between the position of a heated portion and the temperature after the heating by the induction heating device has stopped. [Figure 11] A plan view of a part of an induction heating device according to a second embodiment. [Figure 12] A diagram showing the relationship between the position of a heated portion heated by the induction heating device shown in FIG. 11 and the heat generation density. [Figure 13] A diagram showing the relationship between the position of a heated portion and the temperature after the heating by the induction heating device shown in FIG. 11 has stopped.

Embodiments for Carrying Out the Invention

[0020] Hereinafter, an induction heating device according to a first embodiment will be described with reference to FIGS. 1 to 10. FIG. 1 shows a part of a vehicle 2 equipped with a stabilizer device 1. The stabilizer device 1 includes a solid or hollow stabilizer 4 made of steel and a support portion 5 that supports the stabilizer 4 on the vehicle body 3. The stabilizer 4 extends in the width direction of the vehicle body 3 (the direction indicated by arrow Y). An example of the support portion 5 includes a pair of rubber bushes 6, 7. The stabilizer 4 is an example of a bar-shaped workpiece.

[0021] The stabilizer 4 includes a torsion portion 10 that extends in the width direction of the vehicle body 3 and a pair of arm portions 11, 12. The torsion portion 10 is supported on, for example, a part of the vehicle body 3 via the rubber bushes 6, 7. The arm portions 11, 12 are connected to a suspension mechanism via connecting members 13, 14. Compressive residual stress is applied to the stabilizer 4 by shot peening to enhance its durability. Also, a resin-based paint film is provided on the surface of the stabilizer 4.

[0022] The pair of rubber bushings 6 and 7 have a common configuration. One of the rubber bushings 6 is shown representatively in Figure 2. The rubber bushing 6 is bonded to a portion of the stabilizer 4 along its length (the bushing mounting portion) with a thermosetting adhesive 15. An example of the rubber bushing 6 shown in Figure 2 consists of a pair of divided first bushing pieces 6a and second bushing pieces 6b.

[0023] When attaching the rubber bushing 6 to the stabilizer 4, the bushing attachment area of ​​the stabilizer 4 is heated by an induction heating device 20 (shown in Figures 3 to 8). A thermosetting adhesive is pre-applied to the inner surfaces of the first bushing piece 6a and the second bushing piece 6b. The first bushing piece 6a and the second bushing piece 6b are placed on top of the bushing attachment area heated to a predetermined temperature, and the adhesive 15 hardens under pressure.

[0024] Figures 3 to 8 show an induction heating device 20 according to the first embodiment. Figure 3 is a perspective view of a part of the induction heating device 20, Figure 4 is a plan view of the induction heating device 20, and Figure 5 is a front view of the induction heating device 20.

[0025] The induction heating device 20 comprises a first coil C1 and a second coil C2. The first coil C1 includes a first coil section 30 having a plurality (e.g., six) of winding sections 31, 32, 33, 34, 35, and 36. The first coil section 30 has a first axis X1 (shown in Figures 3 and 4) passing through the centers of the winding sections 31, 32, 33, 34, 35, and 36. When the first coil section 30 is viewed from the front, as shown in Figure 5, each of the winding sections 31-36 has a similar shape (a rounded square).

[0026] The second coil C2 includes a second coil section 40 having a plurality (e.g., six) of winding sections 41, 42, 43, 44, 45, and 46. The second coil section 40 has a second axis X2 (shown in Figures 3 and 4) passing through the centers of the winding sections 41, 42, 43, 44, 45, and 46. When the second coil section 40 is viewed from the front, as shown in Figure 5, each of the winding sections 41-46 has a similar shape (a rounded square).

[0027] Figure 6 is a side view of the first coil C1 as seen from the direction of arrow F6 in Figure 5. Figure 7 is a side view of the second coil C2 as seen from the direction of arrow F7 in Figure 5. Figure 8 is a perspective view of the induction heating device 20 assembled to the frame structure 50. The frame structure 50 is made of an electrically insulating material such as fiber-reinforced plastic (FRP).

[0028] The first coil C1 and the second coil C2 are each formed by winding a conductor 51 made of solid or hollow copper with a circular cross-section, for example, in a left-handed (counterclockwise) direction. The cross-section of the conductor 51 is constant along its length. The cross-section of the conductor 51 may be other than circular (for example, square). The surface of the conductor 51 is covered with an insulating coating 52 made of an electrical insulating material such as glass fiber (partially shown in Figures 5 and 8).

[0029] As shown in Figure 4, the first coil section 30 and the second coil section 40 are 180° rotationally symmetrical when viewed from above, with respect to a virtual point Z1. That is, the shape obtained by rotating the first coil section 30 180° around the virtual point Z1 is substantially the same as the shape of the second coil section 40. Alternatively, the first coil section 30 and the second coil section 40 may be lineally symmetrical with respect to the central axis of the workpiece (stabilizer 4). The first coil section 30 and the second coil section 40 are arranged such that their respective axes X1 and X2 (shown in Figures 3 and 4) are parallel to each other. Between the first coil section 30 and the second coil section 40, a workpiece placement section 55 is formed into which a stabilizer 4, as an example of a rod-shaped workpiece, is inserted. A part of the stabilizer 4 (bush mounting section) is positioned in the workpiece placement section 55 along axes X1 and X2.

[0030] A specific example of the configuration of the first coil C1 will be described below with reference to Figures 3 to 6. As shown in Figures 3 and 4, the first coil section 30, which is the main component of the first coil C1, includes multiple (e.g., six) winding sections 31, 32, 33, 34, 35, and 36. These winding sections 31 to 36 have a common shape when viewed from the front of the first coil section 30, as shown in Figure 5.

[0031] Each of the winding sections 31 to 36 includes, respectively, a first side section 61 facing the workpiece placement section 55, a second side section 62 located on the opposite side of the workpiece placement section 55, an upper third side section 63, a lower fourth side section 64, a first corner section 65, a second corner section 66, a third corner section 67, and a fourth corner section 68.

[0032] The first side portion 61, the second side portion 62, the third side portion 63, and the fourth side portion 64 are all substantially straight or nearly straight in shape. The lengths of these side portions 61, 62, 63, and 64 are approximately the same. As a result, the first coil portion 30, when viewed from the front, has a shape similar to a rounded square, as shown in Figure 5. However, the first coil portion 30 may also be cylindrical.

[0033] The first corner portion 65 is formed between the first side portion 61 and the third side portion 63. The second corner portion 66 is formed between the second side portion 62 and the third side portion 63. The third corner portion 67 is formed between the second side portion 62 and the fourth side portion 64. The fourth corner portion 68 is formed between the first side portion 61 and the fourth side portion 64. All corner portions 65 to 68 are arc-shaped. However, corner portions 65 to 68 may have shapes other than arcs (for example, shapes that bend at an angle close to a right angle).

[0034] G The windings 31 to 36 of the first coil section 30 are formed to have predetermined pitches P1 to P5 (shown in Figure 4) in a direction along the first axis X1. Specifically, a narrow pitch P1 is formed at one end of the first coil section 30 in the axial direction by the first winding section 31 and the second winding section 32. A narrow pitch P5 is formed at the other end of the first coil section 30 in the axial direction by the fifth winding section 35 and the sixth winding section 36. Pitches P1 and P5 are equivalent to each other.

[0035] Furthermore, a moderate pitch P3 is formed in the axial center of the first coil section 30 by the third winding section 33 and the fourth winding section 34. The central pitch P3 is greater than or equal to the pitches P1 and P5 at both ends. Preferably, the central pitch P3 is greater than the pitches P1 and P5 at both ends.

[0036] The second winding section 32 and the third winding section 33 form a large pitch P2. Furthermore, the fourth winding section 34 and the fifth winding section 35 form a large pitch P4. Pitches P2 and P4 are equivalent to each other. Moreover, pitches P2 and P4 are larger than the medium pitch P3.

[0037] In this way, first small-pitch sections 71 and 72 having the smallest pitches P1 and P5 are formed at both ends of the first coil section 30. A first medium-pitch section 75 having a medium pitch P3 is formed in the center of the first coil section 30. A first large-pitch section 73 with a pitch P2 is formed between one small-pitch section 71 and the medium-pitch section 75. A first large-pitch section 74 with a pitch P4 is formed between the other small-pitch section 72 and the medium-pitch section 75.

[0038] As shown in Figures 3 and 4, the first sides 61 of each winding section 31-36 of the first coil section 30 are substantially parallel to each other. The third sides 63 of each winding section 31-36 are also substantially parallel to each other. The fourth sides 64 of each winding section 31-36 are also substantially parallel to each other. In this specification, "substantially parallel" includes parallelism in a strictly geometric sense, but also includes tolerances for errors that occur during the manufacturing and assembly of coils C1 and C2.

[0039] When the first coil section 30 is viewed from the side, the first side portion 61 extends in a direction approximately perpendicular to the first axis X1. Therefore, the pitch angle of the first side portion 61 is approximately zero. Also, as shown in Figure 4, when the first coil section 30 is viewed from above, the third side portion 63 and the fourth side portion 64 each extend in a direction approximately perpendicular to the first axis X1. Therefore, the pitch angles of the third side portion 63 and the fourth side portion 64 are also approximately zero.

[0040] In contrast, the second side portion 62, located on the opposite side of the workpiece placement portion 55, has a shape in which the pitch angle θ1 (partially shown in Figure 6) changes according to the pitch P1 to P5 of the winding portions 31 to 36. In other words, the pitch angle θ1 is given only to the second side portion 62. Moreover, the pitch angle θ1 is larger in areas with a larger pitch compared to areas with a smaller pitch.

[0041] A first positioning member 80 is attached to the winding portions 31-36 of the first coil section 30. The first positioning member 80 is formed, for example, by brazing a bolt to the conductor 51. By inserting the first positioning member 80 into a hole formed in the frame structure 50 (shown in Figure 8) and fixing it to the frame structure 50 with a fixing means such as a nut, the pitch P1-P5 of the first coil section 30 can be accurately maintained.

[0042] One end 30a of the first coil section 30 is connected to the first electrode member 82 (shown in Figure 4) via the first power supply conductor 81. The other end 30b of the first coil section 30 is connected to one end 40a of the second coil section 40 via the connecting conductor 83. The other end 40b of the second coil section 40 is connected to the second electrode member 85 (shown in Figures 4 and 5) via the second power supply conductor 84. The first electrode member 82 and the second electrode member 85 are connected to an AC power supply 86 for applying a high-frequency voltage to the first coil C1 and the second coil C2.

[0043] The second coil C2 is described below. As shown in Figures 3 and 4, the second coil section 40, which is the main component of the second coil C2, includes multiple (e.g., six) winding sections 41, 42, 43, 44, 45, and 46. These winding sections 41 to 46 have a common shape when viewed from the front of the second coil section 40, as shown in Figure 5. As shown in Figure 4, the winding sections 41 to 46 of the second coil section 40 are opposite the winding sections 31 to 36 of the first coil section 30.

[0044] Each of the winding sections 41 to 46 includes, respectively, a fifth side section 101 facing the workpiece placement section 55, a sixth side section 102 located on the opposite side of the workpiece placement section 55, an upper seventh side section 103, a lower eighth side section 104, a fifth corner section 105, a sixth corner section 106, a seventh corner section 107, and an eighth corner section 108.

[0045] The fifth side portion 101, the sixth side portion 102, the seventh side portion 103, and the eighth side portion 104 are all substantially straight or nearly straight. The lengths of these side portions 101, 102, 103, and 104 are approximately the same. As a result, the second coil portion 40, when viewed from the front, has a shape resembling a rounded square, as shown in Figure 5. However, the second coil portion 40 may also be cylindrical.

[0046] The fifth corner portion 105 is formed between the fifth side portion 101 and the seventh side portion 103. The sixth corner portion 106 is formed between the sixth side portion 102 and the seventh side portion 103. The seventh corner portion 107 is formed between the sixth side portion 102 and the eighth side portion 104. The eighth corner portion 108 is formed between the fifth side portion 101 and the eighth side portion 104. Corner portions 105 to 108 are all arc-shaped. However, corner portions 105 to 108 may have shapes other than arcs (for example, shapes that bend at an angle close to a right angle).

[0047] The windings 41-46 of the second coil section 40 are formed to have a predetermined pitch P6-P10 (shown in Figure 4) in the direction along the second axis X2. Specifically, a narrow pitch P6 is formed at one end of the second coil section 40 in the axial direction by the first winding section 41 and the second winding section 42. A narrow pitch P10 is formed at the other end of the second coil section 40 in the axial direction by the fifth winding section 45 and the sixth winding section 46. Pitches P6 and P10 are equivalent to each other.

[0048] Furthermore, a moderate pitch P8 is formed in the axial center of the second coil section 40 by the third winding section 43 and the fourth winding section 44. The central pitch P8 is larger than the pitches P6 and P10 at both ends. The central pitch P8 is greater than or equal to the pitches P6 and P10 at both ends. Preferably, the central pitch P8 is larger than the pitches P6 and P10 at both ends.

[0049] The second winding section 42 and the third winding section 43 form a large pitch P7. The fourth winding section 44 and the fifth winding section 45 form a large pitch P9. Pitches P7 and P9 are equivalent to each other. Moreover, pitches P7 and P9 are larger than the medium pitch P8.

[0050] In this way, second small-pitch sections 111 and 112 having the minimum pitches P6 and P10 are formed at both ends of the second coil section 40. A second medium-pitch section 115 having a medium pitch P8 is formed in the center of the second coil section 40. A second large-pitch section 113 with a pitch P7 is formed between one small-pitch section 111 and the medium-pitch section 115. A second large-pitch section 114 with a pitch P9 is formed between the other small-pitch section 112 and the medium-pitch section 115.

[0051] As shown in Figures 3 and 4, the fifth side portions 101 of each winding portion 41-46 of the second coil portion 40 are substantially parallel to each other. The seventh side portions 103 of each winding portion 41-46 are also substantially parallel to each other. The eighth side portions 104 of each winding portion 41-46 are also substantially parallel to each other.

[0052] When the second coil section 40 is viewed from the side, the fifth side section 101 extends in a direction approximately perpendicular to the second axis X2. Therefore, the pitch angle of the fifth side section 101 is approximately zero. Also, as shown in Figure 4, when the second coil section 40 is viewed from above, the seventh side section 103 and the eighth side section 104 each extend in a direction approximately perpendicular to the second axis X2. Therefore, the pitch angles of the seventh side section 103 and the eighth side section 104 are approximately zero.

[0053] In contrast, the sixth side portion 102, located on the opposite side of the workpiece placement portion 55, has a shape in which the pitch angle θ2 (partially shown in Figure 7) changes according to the pitch P6 to P10 of the winding portions 41 to 46. In other words, the pitch angle θ2 is given only to the sixth side portion 102. Moreover, the pitch angle θ2 is larger in areas with a larger pitch compared to areas with a smaller pitch.

[0054] A second positioning member 120 is attached to the winding portions 41-46 of the second coil section 40. The second positioning member 120 is formed, for example, by brazing a bolt to the conductor 51. By inserting the second positioning member 120 into a hole formed in the frame structure 50 (shown in Figure 8) and fixing it to the frame structure 50 with a fixing means such as a nut, the pitch P6-P10 of the second coil section 40 can be accurately maintained.

[0055] As shown in Figure 5, the ends of the first coil C1 and the ends of the second coil C2 may be electrically and mechanically connected to each other by a connecting portion 88. In this way, the first coil C1 and the second coil C2 can be molded separately and then connected at the connecting portion 88 by brazing or the like.

[0056] Figures 3 and 8 show the adjacent conductor section 90. In the adjacent conductor section 90, the power supply conductor 81, which is in conductivity with the first coil section 30, and the connecting conductor 83, which is in conductivity with the second coil section 40, are arranged substantially parallel to each other. In this specification, "substantially parallel" includes parallelism in a strictly geometric sense, but also includes the shape variations that inevitably occur when manufacturing the coil sections 30 and 40, and the tolerances that are permissible in the product specifications. In the adjacent conductor section 90, currents flow in opposite directions (indicated by arrows A1 and A2 in Figure 3) through the power supply conductor 81 and the connecting conductor 83. As a result, the magnetic flux generated in the power supply conductor 81 and the magnetic flux generated in the connecting conductor 83 cancel each other out. Thus, it is avoided that the magnetic flux generated in the power supply conductor 81 and the connecting conductor 83 adversely affects the magnetic fields of the coil sections 30 and 40.

[0057] The solid line L1 in Figure 9 shows the relationship between the position of the heated portion in the longitudinal direction and the heat generation density when the heated portion of a rod-shaped workpiece is heated using the induction heating device 20 of this embodiment. The induction heating device 20 of this embodiment has small pitch portions 71 and 72 at both ends of the first coil portion 30, a medium pitch portion 75 in the center, and large pitch portions 73 and 74 on both sides of the medium pitch portion 75. The second coil portion 40 has small pitch portions 111 and 112 at both ends, a medium pitch portion 115 in the center, and large pitch portions 113 and 114 on both sides of the medium pitch portion 115. Therefore, the heat generation density from the coil portions 30 and 40 is greatest near both ends of the coil width W1 (shown in Figures 4 and 9), and the heat generation density is second greatest in the center of the coil width W1.

[0058] The dashed line L2 in Figure 9 shows the temperature distribution of the heated portion when a rod-shaped workpiece is heated using a conventional induction heating device (with a constant coil pitch). When heated by a coil with a constant pitch, the entire width of the coil is heated fairly evenly.

[0059] The solid line L3 in Figure 10 shows the temperature distribution at the moment when heating by the induction heating device 20 of this embodiment is stopped. When heating stops, some of the heat near both ends of the heated part escapes from the heated part. However, as shown in Figure 9, during heating, the heat generation density is maximum near both ends of the coil width W1, and the temperature in the center is also somewhat high. Therefore, as shown by the solid line L3 in Figure 10, the temperature of the heated part after heating stops is equalized, and the heated part can be maintained within a predetermined temperature range T1.

[0060] The dashed line L4 in Figure 10 shows the temperature distribution at the moment when heating by the conventional coil is stopped. As shown by the dashed line L4, heat escapes to the surroundings near both ends of the heated area, so the temperature near the ends of the heated area becomes considerably lower than the central part. For this reason, it was difficult to maintain the entire heated area within the predetermined temperature range T1.

[0061] Figure 11 is a plan view of an induction heating device 20A according to a second embodiment. In this induction heating device 20A, the first coil section 30A has a pitch P11, P12 at one end that is smaller than the pitch P13 at the center. Also, the pitch P14, P15 at the other end is smaller than the pitch P13 at the center. That is, first small-pitch sections 71A, 72A are formed at both ends of the first coil section 30A, and a first large-pitch section 73A is formed between the small-pitch sections 71A, 72A.

[0062] Similarly, in the second coil section 40A, the pitches P16 and P17 at one end are smaller than the pitch P18 in the center. Also, the pitches P19 and P20 at the other end are smaller than the pitch P18 in the center. That is, second small-pitch sections 111A and 112A are formed at both ends of the second coil section 40A, and a second large-pitch section 113A is formed between the small-pitch sections 111A and 112A. As for the other configurations and operations, the induction heating device 20A of the second embodiment is the same as the induction heating device 20 of the first embodiment (Figures 3 to 8), so the same reference numerals as the first embodiment are used and their explanation is omitted.

[0063] Figure 12 shows the relationship between the longitudinal position of the heat-generating part heated by the induction heating device 20A and the heat generation density. As shown in Figure 12, when heated by the induction heating device 20A, the heat generation density at both ends of the coil width W2 (shown in Figures 11 and 12) is greater than the heat generation density in the center.

[0064] Figure 13 shows the temperature distribution of the heated area after heating by the induction heating device 20A has stopped and several tens of seconds have elapsed. When heating stops, some of the heat near both ends of the heated area escapes. However, as shown in Figure 12, the heat generation density is high near both ends of the coil width W2 during heating. Therefore, as shown in Figure 13, the temperature of the heated area after heating stopped could be maintained within the predetermined temperature range T1.

[0065] In implementing the present invention, the number of windings in the first coil section and the second coil section may be other than six. Furthermore, the number of intermediate pitch sections may be multiple as needed. The rod-shaped workpiece is not limited to vehicle stabilizers; in short, the induction heating device of the present invention can be applied to any rod-shaped workpiece that requires heating in a portion of its length. [Explanation of Symbols]

[0066] 4…Stabilizer (rod-shaped workpiece), 20,20A…Induction heating device, C1…First coil, C2…Second coil, 30,30A…First coil section, X1…First axis, 31~36…Winding section, 40,40A…Second coil section, X2…Second axis, 41~46…Winding section, 50…Frame structure, 51…Conductor, 55…Workpiece placement section, 61…First side section, 62…Second side section, 63…Third side section, 64…Fourth side section, 71,71A,72,72A…Small pitch section, 73 73A,74...Large pitch section, 75...Medium pitch section, 80...First positioning member, 81...Power supply conductor, 82...First electrode member, 83...Connecting conductor, 84...Power supply conductor, 85...Second electrode member, 90...Conductor adjacent section, 101...Fifth side section, 102...Sixth side section, 103...Seventh side section, 104...Eighth side section, 111,111A,112,112A...Small pitch section, 113,113A,114...Large pitch section, 115...Medium pitch section, 120...Second positioning member.

Claims

1. An induction heating device for heating the part of a rod-shaped workpiece to be heated, A first coil having a first coil section consisting of multiple winding sections and a first axis passing through the center of the first coil section, A second coil is positioned opposite the first coil and has a second coil section consisting of multiple windings and a second axis passing through the center of the second coil section. A workpiece placement section is formed between the first coil section and the second coil section, into which the rod-shaped workpiece is inserted, A pair of first small-pitch portions formed at both ends of the first coil portion, Two first large pitch sections are formed between the pair of first small pitch sections, and the pitch of these two large pitch sections is greater than that of the first small pitch sections. A first medium pitch portion is formed between the pair of first small pitch portions and located in the center of the first coil portion, and has a pitch that is larger than the first small pitch portion and smaller than the first large pitch portion, A pair of second small-pitch portions formed at both ends of the second coil portion, Two second large pitch sections are formed between the pair of second small pitch sections, and the pitch of these second large pitch sections is greater than that of the second small pitch sections. A second medium-pitch portion is formed between the pair of second small-pitch portions and is located in the center of the second coil portion, with a pitch that is larger than the second small-pitch portion and smaller than the second large-pitch portion. An induction heating device characterized by being equipped with the following.

2. In the induction heating apparatus according to claim 1, An induction heating device characterized in that the first medium-pitch portion and the second medium-pitch portion have a shape that is symmetrical with respect to the central axis of the workpiece.

3. In the induction heating apparatus according to claim 1, Each winding portion of the first coil section includes a first side facing the workpiece placement section, a second side opposite to the workpiece placement section, an upper third side, and a lower fourth side. When the first coil portion is viewed from the side, the first sides are parallel to each other and extend in a direction perpendicular to the first axis, Each winding portion of the second coil section includes a fifth side facing the workpiece placement section, a sixth side opposite to the workpiece placement section, an upper seventh side, and a lower eighth side, An induction heating device characterized in that, when the second coil portion is viewed from the side, the fifth side portions are parallel to each other and extend in a direction perpendicular to the second axis.

4. In the induction heating apparatus according to claim 3, When the first coil portion is viewed from above, the third side portions extend parallel to each other and perpendicular to the first axis, and the fourth side portions extend parallel to each other and perpendicular to the first axis. When the first coil portion is viewed from the side, the second side portion has a pitch angle corresponding to the first small pitch portion and the first large pitch portion. When the second coil portion is viewed from above, the seventh side portion extends parallel to each other and perpendicular to the second axis, and the eighth side portion extends parallel to each other and perpendicular to the second axis, An induction heating device characterized in that, when the second coil portion is viewed from the side, the sixth side portion has a pitch angle corresponding to the second small pitch portion and the second large pitch portion.

5. In the induction heating apparatus according to claim 1, It further comprises a frame structure made of an electrically insulating material, A first positioning member is provided on each of the winding portions of the first coil portion, and the first positioning member is fixed to the frame structure. An induction heating device characterized in that a second positioning member is provided on each of the winding portions of the second coil portion, and the second positioning member is fixed to the frame structure.

6. In the induction heating apparatus according to claim 1, A power supply conductor that is in electrical contact with the first coil section, A connecting conductor electrically connects the first coil portion and the second coil portion to each other, A conductor adjoining portion is provided in which the power supply conductor and the connecting conductor are adjacent to each other and extend in the same direction, and the direction of the current flowing through the power supply conductor and the direction of the current flowing through the connecting conductor are opposite to each other, An induction heating device characterized by having

7. A heating method comprising placing the part to be heated of a stabilizer between a first coil and a second coil, and inductively heating the part to be heated by applying a high-frequency voltage to the first coil and the second coil, The first coil has a pair of first small-pitch sections provided on a first coil section consisting of a plurality of winding sections, two first large-pitch sections formed between the pair of first small-pitch sections, and a first medium-pitch section formed between the pair of first small-pitch sections and located in the center of the first coil section, with a pitch that is larger than the first small-pitch sections and smaller than the first large-pitch sections. The second coil has a pair of second small-pitch sections provided on a second coil section consisting of a plurality of winding sections, two second large-pitch sections formed between the pair of second small-pitch sections, and a second medium-pitch section formed between the pair of second small-pitch sections and located in the center of the second coil section, with a pitch larger than that of the second small-pitch sections and smaller than that of the second large-pitch sections. The high-frequency voltage is applied to the first coil and the second coil, The first small-pitch section and the second small-pitch section induce heating of both ends of the part to be heated, and the first large-pitch section and the second large-pitch section and the first medium-pitch section and the second medium-pitch section induce heating of the middle part of the part to be heated, The heat generation density at both ends of the heated portion is made greater than the heat generation density at the intermediate portion. A method for heating a stabilizer, characterized in that induction heating is stopped when the heat generation density at both ends is greater than the heat generation density at the intermediate part.

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