1. Field of the Invention
The present invention relates to an ignition coil for an internal combustion engine adapted to supply high voltage to an ignition plug of the engine for generating spark discharge. In particular, the invention relates to an ignition coil, for an internal combustion engine, of a type having a main core portion (also called a main yoke portion) to which a coil is attached, and an auxiliary core portion (also called an auxiliary yoke portion) or a side core portion (also called a side yoke portion), the auxiliary core portion or the side core portion being combined with the main core portion to form a closed magnetic path.
2. Description of the Related Art
The ignition coil for an internal combustion engine as described above is configured as below. A coil is attached to a main core portion (some are provided with an auxiliary core portion), and a side core portion is assembled to the main core portion (an auxiliary core portion and the side core portion are assembled to the main core portion not provided with the auxiliary core portion). The main core portion and the side core portion are set up inside a casing. The coil is connected at its winding-start-end to a terminal of an external-connection connector attached to the casing. In addition, the coil is connected at its winding-terminal-end to a terminal of the plug. Thereafter, an insulating resin is poured into the casing for resin molding.
However, the divided core portions (or including a permanent magnet if the permanent magnet is attached) likely deviate from each other due to external force, molding pressure resulting from the flow of molding resin, or molding strain during hardening, until the resin molding will be finished. Thus, there is a problem in that variations in the performance of ignition coils are increased.
To solve such a problem, an ignition coil disclosed in e.g. JP-2007-194364-A is such that a core holder is installed to hold the positional relationship among three members until the whole will be molded with resin.
JP-8-17657-A discloses an ignition coil as below. A main core portion and an auxiliary core portion are formed integrally with each other. A coil is attached to the main core portion. Thereafter, a side core portion and the auxiliary core portion are engaged and united with each other by press fitting. In addition, JP-8-17657-A describes the fact that the circumferences of core portions are covered by an elastic material to prevent the occurrence of cracking during the molding of mold resin.
Since the core holder is provided in JP-2007-194364-A, it has a problem in that assembly man-hours are increased and the cost is increased.
In the configuration of JP-8-17657-A, the core portions are held by the press-fitting engaging portion; therefore, the possibility of the positional deviation is low until the resin-molding. However, the coil portion attached to the main core portion is floating before the resin molding using an insulating resin and during the resin molding. Therefore, there is a possibility that the core portions and the coil may deviate due to the action of gravity force, or external force such as the flow-pressure occurring during the pouring of molding resin or molding-strain during the hardening of the resin. Thus, variations in the performance of ignition coils are increased and because of the positional deviation of the coil, excessive force is exerted on a connecting portion between the winding of the coil and the terminal portion of the case to disconnect the winding or the connecting portion.
It is an object of the present invention to provide an ignition coil in which a coil is hard to deviate until the finish of resin molding with a simple configuration. If a coil bobbin is simply directly sandwiched between core portions made of stacked steel plates, the coil bobbin may possibly be damaged. Thus, it is another object of the present invention to provide an ignition coil for an internal combustion engine that aims to prevent excessive force from being exerted on a coil bobbin when a coil attached to a main core portion is held between an auxiliary core portion and a side core portion and that is consequently suitable for automated assembly.
To achieve the above object of the present invention, a covering layer made of an elastic body is formed at least on an inner circumferential surface of a main core portion or an auxiliary core portion facing an end face of a coil bobbin, when a coil being attached to the main core portion, and being sandwiched between and held by the auxiliary core portion and a side core portion.
Preferably, the covering layer is formed on the full circumferences of the main core portion and the auxiliary core portion except a fitting-engaging portion of the auxiliary core portion with the side core portion.
The covering layer may be formed also on an inner circumferential surface, of the side core portion, facing the coil bobbin.
The inner and outer full circumferences of the iron core portion, except the engaging portion of the core portions, may be covered by the elastic body.
A magnet member is sandwiched between the auxiliary core portion and the main core portion.
The magnet member may be a magnetized or non-magnetized magnet member.
The auxiliary core portion and the main core portion are formed as a continuous integral one by punching out a steel plate and stacking the steel plates.
A fitting-engaging portion of the auxiliary core portion with the side core portion may be formed between an end portion outer circumferential surface of the auxiliary core portion and an end portion inner circumferential surface of the side core portion or between the end portion inner circumferential surface of the auxiliary core portion and an end portion outer circumferential surface of the side core portion.
According to the present invention, the coil bobbin is put between and held by the auxiliary core portion and the side core portion. The clearance between the core portion and the end portion of the coil bobbin can be reduced by the elastic covering layer installed between the core portion and the end portion of the coil bobbin. Therefore, the positional deviation of the coil bobbin is small. In addition, the covering layer prevents the coil bobbin and the core portion from being brought into direct pressure contact with each other. Thus, the coil bobbin is unlikely to be damaged.
Incidentally, if the core portion is divided into a plurality of portions, the auxiliary core portion and the main core portion (three members if the magnet member is sandwiched therebetween) are covered by the elastic covering layer. Consequently, they can be handled as one component. Thus, because of satisfactory assembly performance, the ignition coil for an internal combustion engine suitable for automated assembly can be provided.
Preferred embodiments of the present invention will hereinafter be described with reference to the drawings.
An ignition coil for an internal combustion engine according to a first embodiment of the present invention is shown in
Referring to
The coil case 7 is molded integrally with a connector portion 8B and an attachment flange 1B. The connector portion 8B is used for connection with an external connector. The attachment flange 1B is used to attach the ignition coil 1 on a wall surface of an engine. The attachment flange 1B is formed with a hole 10 adapted to receive an attachment screw inserted thereinto. A front surface of an insulating resin 10 for insulating the inside of the coil case is seen on the upper surface of the coil case 7.
Referring to
The ignition coil 1 according to the first embodiment has an iron core assembly 6 composed of a main core portion 6a, a side core portion 6b and an auxiliary core portion 6c. The main core portion 6a, the side core portion 6b and the auxiliary core portion 6c constitute a magnetic path indicated by an arrow Q in
In the iron core assembly 6, the main core portion 6a, the side core portion 6b and the auxiliary core portion 6c are each formed as a core portion by punching a silicon steel plate with a thickness of 0.2 to 0.7 mm into a respective shape, stacking a plurality of the silicon steel plates and press-forming the stacked silicon steel plates.
As shown in
A secondary coil bobbin 4 of rectangular cross-section is concentrically disposed around the primary coil bobbin 2 with a clearance defined therebetween. The secondary coil bobbin 4 is formed of a thermoplastic synthetic resin similarly to the primary coil bobbin 2. A plurality of winding grooves are formed on the outer circumference of the secondary coil bobbin 4 in the longitudinal direction. An enamel wire having a diameter of approximately 0.03 to 0.1 mm is wound around the outer circumference of the secondary coil bobbin 4 at several ten layers to several hundred layers per each groove, and five thousand to thirty thousand times in total.
The primary coil bobbin 2 is inserted into the inside of the secondary coil bobbin 4. A magnet member 11 is mounted so as to be sandwiched between an auxiliary core portion side end of the main core portion 6a and the auxiliary core portion 6c. The magnet member 11 is magnetized in the direction opposite to the direction of the magnetic flux generated in the main core portion 6a when the primary coil 3 is energized. A primary coil portion C1, a secondary coil portion C2 and the iron core assembly 6 are housed in the coil case 7. The primary coil portion C1 is composed of the primary coil bobbin 2 and the primary coil 3 wound around the primary coil bobbin 2. The secondary coil portion C2 is composed of the secondary coil bobbin 4 and the secondary coil 5 wound around the secondary coil bobbin 4.
The coil case 7 is resin-molded integrally with a connector portion 8B. An electric connection terminal 8A is insert-molded integrally with a resinous compact of the coil case 7 in the connector portion 8B. The electric connection terminal 8A is used to electrically connect the primary coil 3 to the outside. A projecting portion 2C is formed at the auxiliary core portion 6c side end portion of the primary coil bobbin 2 of the primary coil 3 so as to extend to a stacking-directional upper surface of the auxiliary core portion 6c. An input terminal 8C is insert-molded in the projecting portion 2C. The input terminal 8C and the electric connection terminal 8A of the connector portion 8B are electrically interconnected inside the coil case 7 via a line 8D. An electric current to be supplied to the primary coil 3 is supplied thereto via the electric connection terminal 8A. Although not shown, an external connector is inserted into the connector portion 8B for connection and the electric connection terminal 8A is connected to a power terminal of the external connector.
On the other hand, a high-voltage terminal 9 is integrally insert-molded by a resin mold on a plug hole insertion portion 9A side of the coil case 7. An output end 5A of a winding of the secondary coil 5 is connected to the high-voltage terminal 9. An electric current applied to the primary coil 3 is cut by a semiconductor switching element not shown to induce high voltage in the secondary coil 5. The high voltage induced in the secondary coil 5 is supplied to an ignition plug (not shown) via the high-voltage terminal 9 resin-molded integrally with the coil case 7. Thus, the ignition plug generates spark discharge.
The output terminal 5A of the winding of the secondary coil 5 is connected to the high-voltage terminal 9 and the input terminal 8C of the winding of the primary coil is connected to the electric connection terminal 8A of the connector portion 8B. In this state, the iron core assembly 6, the primary coil portion C1 and secondary coil portion C2 are housed and set up in the coil case 7. A thermo-setting resin (specifically, an epoxy resin) as an insulating resin 10 is filled in the coil case 7. The insulating resin 10 is filled in the entire inside of the coil case 7: clearances between the windings of the primary coil 3 wound around the primary coil bobbin 2 and between the windings of the secondary coil 5 wound around the secondary coil bobbin 4; the circumferences of the primary coil portion C1, the secondary coil portion C2 and the iron core assembly 6 and the clearances therebetween; the circumference of the connecting portion between the input end 8C of the primary coil 3 and the connecting terminal 8A of the connector portion 8B; and the circumference of the connecting portion between the high-pressure terminal 9 and the output end 5A of the secondary coil 5. In this way, these components are insulated from one another and united with one another in the coil case 7.
As shown in
In the present embodiment, the non-magnetized magnet member 11 is sandwiched between flange portions 6a3 formed at end portions of the main core portion 6a and the auxiliary core portion 6c and is set up in a mold. A mold material (a thermoplastic resin, elastomer or rubber such as silicon rubber) is poured into the mold to cover the circumferential surfaces of the main core portion 6a, the magnet member 11 and the auxiliary core portion 6c. In this way, these three components are configured as a single molded assembly component.
In this case, the main core portion 6a, the magnet member 11 and the auxiliary core portion 6c are tightly pressed so as to prevent the mold material from pouring in the joint surface between the main core portion and the magnet member 11 and the joint surface between the magnet member 11 and the auxiliary core portion 6c. The joint surface (both sides) 6c1 of the auxiliary core portion 6c with the side core portion 6b and the contact surface 6a1 of the main core portion 6a with the side core portion 6b are brought into tight contact with the front surface of the mold so as to prevent the molding material from extending over the joint surface and the contact surface mentioned above. Then, the main core portion 6a and the auxiliary core portion 6c are molded. A tape capable of being removed later may be applied to the joint surface (both sides) 6c1 of the auxiliary core portion 6c with the side core portion 6b and to the contact surface 6a1 of the main core portion 6a with the side core portion 6b. Then, the main core portion 6a and the auxiliary core portion 6c are molded. After the molding, the tape may be removed to expose the joint surface and the contact surface.
As shown in
With this configuration, the respective assembly positions of the auxiliary core portion 6c, the magnet member 11 and the main core portion 6a are determined in the mold. Therefore, their positions will not be misaligned after the molding of such components. The circumferential surface of an outside portion 11E of the magnet member 11 sandwiched between the main core portion 6a and the auxiliary core portion 6c is covered and protected by the film of a core mold 12a4. Therefore, an edge portion of the magnet member 11 is hard to be damaged by shocks during the assembly. Even if the edge portion of the magnet member 11 is damaged, then broken pieces of the permanent magnet will not fly apart. Therefore, the broken pieces of the magnet member will not drop in a production line.
As shown in
Further, the core mold 12a has a covering layer 12a5 covering an longitudinal outer surface of the main core portion 6a, a covering layer 12a3 covering an outer surface portion of the flange portion 6a3, and a covering layer 12a4 covering the circumference of the outer side surface 11E of the magnet member 11. The primary coil bobbin 2 is inserted through above the covering layer of the core mold 12a5 of the main core portion 6a. Therefore, the primary coil bobbin 2 is not rubbed by the edge of the main core portion 6a so that it will not chip off.
With this configuration, although the magnet member 11 is assembled in the non-magnetized state, the main core portion 6a, the magnet member 11 and the auxiliary core portion 6c are positioned by being set up in the mold. Therefore, an assembly error for each product is small. After the molding, the main core portion 6a, the magnet member 11 and the auxiliary core portion 6c can be handled as one component; therefore, assembly performance is enhanced. This configuration is particularly advantageous to automated assembly. Incidentally, if the core mold 12a is applied in the non-magnetized state, then magnetization is performed in a subsequent process.
As shown in
In this way, the joint surfaces 6a1, 6b2 between the main core portion 6a and the side core portion 6b and the joint surface portions 6b1, 6c1 between the side core portion 6b (both sides) and the side core portion 6c are in magnetically tight contact with each other to form an appropriate magnetic path.
As shown in
The configuration described above is useful to firmly hold the mutual positional relationship among the iron core assembly 6 and the coil portions C1, C2 until they are set up in the coil case 7 and the molding is finished.
The core mold 12b covering the circumference of the side core portion 6b has a covering layer 12b1 covering an upper end portion (the upper end portion in
As shown in
Incidentally, the primary and secondary coil portions C1, C2 are temporarily mounted by engaging means not shown so as not to be relatively displaced in the longitudinal direction. Therefore, if the side core portion 6b and the auxiliary core portion 6c are mating-engaged with each other in the state where the primary and secondary coil portions C1, C2 are attached to the main core portion 6a, the primary coil bobbin 2 is held between the side core portion 6b and the auxiliary core portion 6c mostly without play.
The primary and secondary coil portions C1, C2, along with the iron core assembly 6, are set up in the coil case 7 and the insulating resin 10 is poured into the coil case.
In this case, the flow of the insulating resin 10 reaches the clearance of 0 to 0.2 mm (millimeter) between both the end portions of the primary coil bobbin 2 and the core molds 12a1, 12a2, 12a3; 12b1, 12b2, 12b5 facing both the end portions of the primary bobbin 2. However, the clearance is originally small; therefore, the primary coil bobbin 2 is not relatively displaced by the flow-pressure of the insulating resin. The primary coil bobbin 2 has both end faces firmly held between the core molds 12a1, 12a2, 12a3 and 12b1, 12b2, 12b5. Therefore, the winding is not disconnected and the joint portion between the winding and the connecting terminal does not come off. The molding resin becomes hardened which flows into the clearances of 0 to 0.2 mm (millimeter) between both the end faces of the primary coil bobbin 2 and the core molds 12a1, 12a2, 12a3 and 12b1, 12b2, 12b5. Molding strain occurring due to this hardening is absorbed by the core molds 12a, 12b or elastic bodies. Thus, the molding strain will not deform the primary coil bobbin 2 and will not break the magnet member 11.
As described above, the core molds 12a, 12b of the iron core assembly 6 are each formed thicker at the upper surface portion and the lower surface portion, in the stacking direction, of the iron core assembly 6 than at the other portion corresponding to the direction perpendicular to the stacking direction of the iron core assembly 6. In addition, the core molds 12a, 12b are each formed thicker at the inner surface portion of the iron core assembly 6 than at the outer surface portion. This intends to prevent cracking of the insulating resin 10 covering the circumference of the core mold 12, as below. When the ignition coil 1 undergoes heat stress, the insulating resin 10 may be subjected to stress concentration by the corner of the iron core and cracked. Specifically, if the corner portion of the core mold 12 is rounded, the insulating resin 10 is hard to be cracked. However, the rounded portion having a larger radius is more effective. If the rounded portion is increased in radius, since the inner wall of the coil case is located in the outer circumferential direction of the iron core assembly, the core mold 12 is formed thick at the upper surface portion and lower surface portion, in the stacking direction, of the iron core assembly 6. If the core mold 12 is formed thick at a portion corresponding to the direction perpendicular to the stacking direction of the iron cores, i.e., to the coil case 7 side, the ignition coil 1 grows in size. Because of this, the core mold 12 is formed thick in the stacking direction of iron cores; therefore, the corner portion of the core mold 12 can be made to have a large radius without the enlargement of the size of the ignition coil 1. Since the core mold 12 is provided with the thick portions, the flowing performance of resin is enhanced during the molding. Specifically, as shown in
As shown in
The iron core assembly 6 has a complicated shape and many edge portions on the inner circumferential surface side thereof. This inner circumferential surface side has enlarged clearances serving as mold-material flow passages formed between the iron core assembly 6 and the mold. This makes it easy for the mold material to flow. Consequently, the covering layers of the mold material are thick at large clearances (see the core molds 12a4, 12a6, 12b3).
As shown in
A second embodiment is hereinafter described with reference to
In the second embodiment, a main core portion 6a and an auxiliary core portion 6c are punched out as an integral thin steel plate and the integral thin plates are stacked one on another. Therefore, a magnet member is not installed between the main core portion 6a and the auxiliary core portion 6c.
The coil case 7 is shared by the first embodiment and the second embodiment; therefore, an iron core assembly 6 has the same external dimensions as those of the first embodiment. The second embodiment uses the same coil assembly as that of the first embodiment.
A core mold 12a8 between an end portion of a primary coil bobbin 2 and the auxiliary core portion 6c is increased in thickness by the thickness of the magnet member 11. In addition, the core mold 12a8 has an outer shape formed to conform to the shape of a projecting portion of the primary coil bobbin 2.
The main core portion 6a has a side core portion 6b side end portion covered by a core mold 12a9. Consequently, a magnetic gap corresponding to the thickness of the core mold 12a9 is defined between the side core portion 6b and the end portion of the main core portion 6a. Thus, magnetic saturation of a magnetic path is suppressed at this portion.
In this way, the auxiliary core portion and main core portion covered by the core molds 12a7, 12a8, 12a3, 12a9 according to the second embodiment are formed to have the same external shape as that according to the first embodiment.
Thus, the auxiliary core portion and the main core portion can be handled as one component during assembly regardless of the absence or presence of the magnet member. As described above, the auxiliary core portion and the main core portion are covered by the core molds; therefore, ignition coils can be assembled in the same production line regardless of the absence or presence of the magnet member. This leads to the reduced cost of installation.
Incidentally, to prevent erroneous assembly in the same production line by distinguishing between the absence and presence of the magnet assembly, it is preferable to make it possible to visually confirm the absence and presence of the magnet member by forming a concavo-convex portion on the core mold on the iron-core-stacking-directional surfaces as shown in
As shown in
A fourth embodiment is described with reference to
Referring to
In the embodiments described above, the material of the iron core assembly 6 is the stacked silicon steel plates. However, also iron cores formed by compressing iron-based powder and covered by a resinous cover, an elastomer film or a rubber film can produce the same function and effect as above.
Number | Date | Country | Kind |
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2011-118609 | May 2011 | JP | national |