JP2012169466A - Reactor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurence of cracks in a dust core.SOLUTION: A reactor 10 includes a pillar shaped center core 12, a coil 14 inserted into the center core 12 along a direction of a center axis C of the center core 12, and a dust core 16 filling surrounding areas of the center core 12 and the coil 14 and made of a magnetic powder mixed resin. At least one of a rib 26 protruding in a radius direction R of the center core 12 and a groove 36 recessed in the radius direction R of the center core 12 is formed on a fastened surface 24 of the center core 12 to which the dust core 16 is fastened.

Description

  The present invention relates to a reactor.

  Conventionally, a reactor in which a coil is embedded in a so-called dust core in which magnetic powder is kneaded in an insulating resin is known. In addition to the coil, a cooling member called a core may be embedded in the dust core. For example, in Patent Document 1, as shown in FIG. 10, a center core 114 is provided at the center of the housing 112, a coil 116 is disposed around the center core 114, and the dust core 110 is filled in the housing 112, and then the dust core is placed. Reactor 100 is formed by heat curing 110.

  The core 114 is made of a material having high thermal conductivity such as aluminum, and functions as a cooling member that releases the heat of the dust core 110 to the outside. The dust core 110 is fixed to the center core 114. When an alternating current is passed through the coil 116 and a magnetic flux passes through the dust core 110 along with it, the coil 116 and the dust core 110 generate heat due to Joule heat. The heat of the dust core 110 is transmitted from the adherend surface 120 of the center core 114 to the center core 114, and further released from the center core 114 to the outside.

  In addition, reactor 100 vibrates when an alternating current flows through coil 116. If the excitation frequency at this time and the natural frequency of the reactor 100 coincide, the reactor 100 resonates and so-called NV characteristics (noise / vibration characteristics) deteriorate. Therefore, the conventional reactor 100 has a structure in which the natural frequency takes a value different from the excitation frequency. For example, the natural frequency of the reactor 100 is shifted from the harmonic component of the alternating current by adjusting the shape of the core 114 and the filling amount of the dust core 110.

JP 2008-182151 A

  By the way, the dust core contracts or expands as the temperature of the dust core changes, and as a result, cracks (cracks) may occur in the dust core. When cracks occur, the rigidity of the entire reactor decreases. Since the natural frequency changes according to the rigidity, the natural frequency of the reactor changes due to the occurrence of a crack. As a result, the natural frequency of the reactor may coincide with the excitation frequency. Then, an object of this invention is to provide the reactor which suppresses generation | occurrence | production of the crack in a dust core.

  The present invention relates to a reactor. The reactor includes a columnar core, a coil inserted into the core along the axial direction of the core, and a dust core made of a magnetic powder mixed resin filled around the core and the coil. Yes. At least one of a rib projecting in the radial direction of the central core and a groove portion recessed in the radial direction of the central core is formed on the fixed surface of the central core to which the dust core is fixed.

  Moreover, in the said invention, it is suitable that the rib or groove part is formed in the both ends of the axial direction in a to-be-adhered surface.

  Moreover, in the said invention, it is suitable for the length L of the axial direction of a center core to form the rib in the area | region of L / 3 from the axial direction both ends of a to-be-adhered surface.

  According to the present invention, the occurrence of cracks in the dust core can be suppressed as compared with the prior art.

It is a figure which illustrates the reactor which concerns on this embodiment. It is sectional drawing of the reactor which concerns on this embodiment. It is an enlarged view of the reactor which concerns on this embodiment. It is a figure explaining the principle of generation | occurrence | production of a crack. It is a figure explaining the force which acts on a dust core at the time of a temperature fall. It is sectional drawing of the reactor which concerns on this embodiment. It is a figure which shows the result of the thermal shock test of the reactor which concerns on this embodiment. It is a figure which shows the result of the thermal shock test of the reactor which concerns on this embodiment. It is a figure which illustrates the reactor which concerns on another embodiment. It is a figure which illustrates the conventional reactor.

  FIG. 1 shows a reactor according to the present embodiment. The reactor 10 includes a core 12, a coil 14 disposed around the core 12, and a dust core 16 filled around the core 12 and the coil 14. The reactor 10 is provided as a passive element that stores / discharges electrical energy in a power conversion circuit such as a DC / DC converter.

  The center core 12 is a substantially cylindrical member and is fixed to the housing 18. As the fixing means, for example, as shown in FIG. 2, a screw hole 20 that is penetrated along the central axis C of the core 12 and has a thread groove is provided at the center of the core 12.

  The core 12 is made of a material having higher thermal conductivity than the dust core 16, for example, a material such as aluminum. Thereby, the core 12 functions as a cooling member that releases the heat of the coil 14 and the dust core 16 to the outside. Specifically, the heat of the dust core 16 is transmitted from the adherend surface 24 of the core 12 to which the dust core 16 is fixed, and then the heat is released to the outside of the core 12.

  Returning to FIG. 1, ribs 26 that protrude in the radial direction R of the core 12 are formed on the fixed surface 24 of the core 12. The ribs 26 are formed so that the cross-sectional shape of the adherend surface 24 is uneven in a cross section parallel to the central axis C. For example, the ribs 26 are configured as annular projecting members. The ribs 26 may be formed integrally with the core 12 or may be attached to the core 12 as a separate member from the core 12. The ribs 26 are made of a material such as aluminum having a higher thermal conductivity than the dust core 16, as with the core 12. The ribs 26 are formed at both ends of the center core 12 in the direction of the central axis C. For example, when the length of the center core 12 in the axial direction is L, the ribs 26 extend from the both ends of the core 12 to a region of L / 3. Is formed. In FIG. 1 and FIG. 2, two ribs 26 are provided at both ends, but it is sufficient that at least one rib 26 is provided at each end.

  As will be described later, the ribs 26 are provided in order to disperse the shearing force generated on the fixing surface 27 of the dust core 16. Therefore, the rib 26 is formed to have a protruding height and thickness that can disperse the shearing force. FIG. 3 shows an enlarged view around the rib 26. The ribs 26 are preferably formed in a thin annular shape so that the shearing force can be dispersed. For example, the thickness W of the ribs 26 is preferably 1 to 3 mm. The overhang height H of the rib 26 is preferably 1 to 3 mm. Here, the overhang height H represents the height from the fixed surface 24 where the ribs 26 are not formed to the maximum height point of the ribs 26. Further, when a plurality of ribs 26 are formed, the distance D between the ribs 26 is preferably 3 to 5 mm.

  Returning to FIG. 1, a coil 14 is provided around the core 12. The coil 14 is shaped into a predetermined shape so as to surround the core 12 such as a cylindrical shape. Further, the length of the coil 14 in the axial direction C is formed to be shorter than the height of the side wall 29 of the housing 18. Specifically, when the coil 14 is spaced apart from the bottom surface of the housing 18 in the direction of the central axis C by a predetermined distance and further filled with the dust core 16 to the height of the side wall of the housing 18, the coil 14 The length of the coil 13 in the axial direction C is determined so as to be embedded in the coil 16. The end portion 28 of the coil 14 is connected to a switching element and a power source (not shown), and an alternating current shaped by the switching element is caused to flow through the coil 14. Here, the coil 14 vibrates when an alternating current flows. The excitation frequency at this time corresponds to the alternating current flowing through the coil 14. For example, when the switching element is ON / OFF controlled by PWM control, a frequency component of a carrier (carrier wave) serving as a reference for ON / OFF control of the switching element is superimposed on the alternating current flowing through the coil 14. At this time, the frequency of the alternating current, the harmonic component thereof, and the frequency of the carrier become the excitation frequency to the coil 14.

  Further, the housing 18 that accommodates the core 12 and the coil 14 is formed of a material such as aluminum having a higher thermal conductivity than the dust core 16, as in the case of the core 12, so that the heat of the coil 14 and the dust core 16 can be transferred to the outside. It functions as a cooling member to escape. Further, as shown in FIG. 2, a projection 30 is formed at the center of the housing 18 so as to protrude in the direction of the central axis C. The protrusion 30 is formed with a screw hole 32 having a thread groove in the axial direction C.

  The dust core 16 is made of a resin in which magnetic powder is dispersed and mixed. For example, ferrite powder, iron powder, silicon alloy powder, or the like is used as the magnetic powder, and thermosetting resin such as epoxy resin is used as the resin.

  Next, an assembly process of the reactor 10 according to this embodiment will be described. After aligning the screw hole 32 of the housing 18 and the screw hole 20 of the core 12, the screw 22 is inserted (screwed) to fix the core 12 to the housing 18. Further, the coil 14 is inserted into the core 12 along the axis C direction of the core 12. At this time, the coil 14 is positioned so that the central axis of the coil 14 and the central axis C of the center coincide. Further, the coil 14 is held by a holding member (not shown) so that the coil 14 is separated from the bottom surface of the housing 18 by a predetermined distance, and then the dust core 16 is filled in the housing 18. The dust core 16 is filled to the height of the side wall of the housing 18, for example. Thereafter, the dust core 16 is heated and cured. The dust core 16 adheres to the inner wall surface of the housing 18 and the center core 12 with heating.

  Next, cracks occurring in the dust core 16 will be described. As shown in FIG. 4, the present inventors have concentrated cracks on the fixing surface 124 of the dust core 110 fixed to the conventional core 114, particularly on both ends of the fixing surface 124 in the direction of the central axis C of the core 114. 34 was found to occur. The generation principle of the crack 34 will be described with reference to FIG. FIG. 5 shows a state when the temperature of the reactor is decreasing. As the temperature decreases, the dust core 110 and the core 114 shrink. Here, the dust core 110 having a resin as a main component has a higher coefficient of thermal expansion than the core 114 having a metal as a main component, and thus the shrinkage ratio of the dust core 110 is higher than that of the core 114. At this time, a force acts on the adherend surface 120 of the core 114 in a direction that prevents the dust core 110 from contracting in order to maintain the adhesion to the dust core 110. The force that the dust core 110 tends to contract and the force that prevents the dust core 110 act in the direction along the adherend surface 120 at both ends of the center core 114. As a result, a shearing force acts on the fixing surfaces 124 of the dust core 16 fixed to both ends of the surface to be fixed 120. The present inventors consider that this shearing force is the cause of the crack 34 generated in the dust core 110, and the ribs 26 for dispersing the shearing force are provided on the core 12 as shown in the reactor 10 according to the present embodiment.

  A schematic diagram of the distribution of shear force around the ribs 26 is shown in FIG. The shearing force is generated along the shape of the rib 26 and acts in different directions along the uneven shape of the rib 26. Force components in different directions cancel each other, and when viewed macroscopically, the shearing force acting on both ends of the core 12 is reduced compared to the case where the ribs 26 are not provided. By reducing the shear force, the occurrence of cracks is suppressed.

  7 and 8 show the results of a thermal shock test performed on the reactor 10 according to this embodiment in which the conventional reactor without the ribs 26 and the ribs 26 are provided. In the thermal shock test, the natural frequency (FIG. 7) and NV characteristics of the reactor 10 after 300 cycles of the thermal shock cycle in which the reactor 10 is heated from −40 ° to 90 ° and then cooled to −40 ° are performed. Fig. 8) is measured. Further, the conventional reactor and the reactor 10 according to the present embodiment are formed so that the natural frequency before the thermal shock test becomes a predetermined value separated from the carrier frequency. Moreover, in both FIG. 7, FIG. 8, the conventional reactor is represented by the white rhombus plot, and the reactor 10 which concerns on this embodiment is represented by the solid rhombus plot.

  As apparent from FIG. 7, in the conventional reactor, the natural frequency decreases after the thermal shock test and approaches the carrier frequency, whereas the reactor 10 according to the present embodiment is sufficient from the carrier frequency even after the thermal shock test. The natural frequency far away is maintained. As described above, the reactor 10 according to the present embodiment can maintain the natural frequency sufficiently separated from the carrier frequency, so that resonance can be avoided even if an alternating current is supplied. Since resonance can be avoided, noise generated by vibration can also be suppressed. As apparent from FIG. 8, in the conventional reactor, the NV characteristic deteriorates after the thermal shock test and more than half exceeds the target value, whereas the NV characteristic of the reactor 10 according to the present embodiment shows the thermal shock. Even after the test, the NV characteristics are kept below the target value.

  In the embodiment described above, the ribs 26 are formed at both ends of the core 12, but the present invention is not limited to this embodiment. That is, since it is only necessary to disperse the shearing force at both ends of the core 12, grooves 36 that are recessed in the diameter R direction of the core 12 may be formed instead of the ribs 26 as shown in FIG. 9. In this case, like the rib 26, the groove 36 is formed to have a groove depth and width that can disperse the shearing force. Specifically, the groove depth from the adherend surface 24 where the groove 36 is not formed to the deepest portion of the groove 36 is preferably 1 to 3 mm. The width of the groove 36 is preferably 1 to 3 mm. Further, when a plurality of grooves 36 are formed, the distance between adjacent grooves 36 is preferably 3 to 5 mm.

10 reactors, 12 cores, 14 coils, 16 dust cores, 18 housings, 20 core screw holes, 22 screws, 24 fixed surfaces, 26 ribs, 27 fixing surfaces, 28 coil ends, 30 protrusions, 32 housings Screw hole, 36 grooves.

Claims (3)

The core of the column,
A coil inserted into the core along the axial direction of the core;
A dust core made of a magnetic powder mixed resin filled around the core and the coil;
With
At least one of a rib projecting in the radial direction of the core and a groove portion recessed in the radial direction of the core is formed on the fixed surface of the core to which the dust core is fixed. Reactor. The reactor according to claim 1,
The reactor is characterized in that the ribs or grooves are formed at both ends in the axial direction of the fixed surface. The reactor according to claim 2,
The reactor is characterized in that the rib is formed in a region of L / 3 from both axial ends of the fixed surface with respect to the axial length L of the core.