Ignition coil device

An ignition coil device is mounted in a plug hole member forming a plug hole with forming internal space with the plug hole member. The ignition coil device includes a primary spool, a primary coil wire that is wound around an outer surface of the primary spool. At least a given portion of the outer surface of the primary spool is formed of crystalline resin. Here, the given portion fluidly communicates with the internal space of the plug hole.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is based on and incorporates herein by reference Japanese Patent Applications No. 2002-354113 filed on Dec. 5, 2002 and No. 2003-373496 filed on Oct. 31, 2003.

FIELD OF THE INVENTION

The present invention relates to an ignition coil device. Specifically, it relates to a stick-type ignition coil device, which is mounted in a plug hole of an engine, with having high environment resistance.

BACKGROUND OF THE INVENTION

U.S. Patent of U.S. Pat. No. 6,417,752 discloses a stick-type ignition coil device whose peripheral core is exposed to a plug hole.FIG. 4shows an exploded perspective view of the coil ignition device100. As shown inFIG. 4, the ignition coil device100includes a secondary spool101, a primary spool102, and a peripheral core103. The ignition coil device100is inserted in a plug hole (not shown). The secondary spool101is cylindrical. A secondary coil wire (not shown) is wound around an outer surface of the secondary spool101. The primary spool102is cylindrical. The primary spool102is disposed as surrounding the secondary coil wire. A primary coil wire (not shown) is wound around an outer surface of the primary spool102. The peripheral core103is cylindrical with having a slit104longitudinally extending. The peripheral core103is disposed as surrounding the primary coil wire with being exposed within the plug hole.

Non-crystalline resin such as PPE (Polyphenylene ether) sometimes develops cracks due to an even slight stress after contacting given gas, liquid, or solid. It is because developing of structure change such as breakage or cross bridging of molecular chains results in lowering strength. These phenomena are called ESC (environment stress crack). An instance of combinations of substances developing ESC is a combination of non-crystalline resin and blowby gas that is mixed gas including combustion gas, non-combustion gas, and atomized engine oil from an engine combustion chamber.

In the plug hole, the blowby gas flows from the engine combustion chamber through a plug insertion hole disposed in the bottom of the plug hole. In the ignition plug device100, the primary spool102is exposed to the blowby gas that flows in through the slit104of the peripheral core103and then space between turns of the primary coil wire.

The primary spool102is generally formed of non-crystalline resin that has high adhesiveness to epoxy resin (not shown) filled in the ignition coil device100. Furthermore, linear expansion coefficients of the primary spool102and members around the primary spool102are different. The primary spool102thereby suffers thermal stress due to heating/cooling cycles of an engine.

Thus, the primary spool102exposed to the blowby gas for a long time frame suffers the thermal stress, so that the primary spool102has possibility of developing the ESC. As a result, the ignition coil device100has poor environment resistance.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a ignition coil device having a primary spool that has high environment resistance.

In order to achieve the above and other objects, an ignition coil device is provided with the following. An ignition coil device is mounted in a plug hole member while forming internal space with the plug hole member. A primary spool and a primary coil wire are included. The primary coil wire is wound around an outer surface of the primary spool. At least a given portion of the outer surface of the primary spool is formed of crystalline resin. Here, the given portion fluidly communicates with the internal space.

The crystalline resin has superiority in heat resistance, chemical resistance, dimensional stability, mechanical strength in comparison with non-crystalline resin. Accordingly, even when thermal stress is applied after long hour exposure to blowby gas, i.e., under a condition where heat, blowby gas, and thermal stress work as composite, the crystalline resin that has superior characteristics can be relatively stable. The crystalline resin has thereby preferable blowby gas resistance. The ignition coil device has little possibility of developing environment stress cracks (ESC) due to the blowby gas and thermal stress. Accordingly, the ignition coil device that has the above structure has high environment resistance. This results in enhancing reliability of the ignition coil device itself.

In another aspect of the present invention, an ignition coil device mounted in a plug hole member is provided with the following. A secondary spool and a secondary coil wire are included. The secondary coil wire is wound around an outer surface of the secondary spool. A high voltage tower is included as being disposed closer, than the secondary spool, to a bottom of the plug hole member and as covering a bottom of the secondary spool. Here, a linear expansion coefficient of resin of which the secondary spool is formed is larger than that of the high voltage tower.

In this structure, the secondary spool thereby thermally expands more than the high voltage tower when the ignition coil device is heated up. The secondary spool that is disposed inside thereby contacts, under pressure, the high voltage tower that is disposed outside. This results in enhancing a sealing characteristic between the secondary spool and the high voltage tower. This also results in restricting development of ESC in members forming the ignition coil device. When a resin-made insulator such as epoxy is filled in, sealing to a secondary spool or other members can be enhanced.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A structure of an ignition coil device1according to a first embodiment will be described with reference toFIG. 1.FIG. 1shows an axial sectional view of the ignition coil device1. A so-called stick-type ignition coil device1is housed (or mounted) in a plug hole member forming a plug hole5that is formed in each cylinder at the top of an engine block53. Here, the ignition coil device1forms internal space with the plug hole member. Namely, the internal space being a subset of the plug hole5is space between the plug hole member and an outer surface of the ignition coil device1. As will be discussed below, the ignition coil device1is connected to an ignition plug6at a lower portion in the drawing.

A peripheral core20is cylindrical and formed of a single sheet of silicon steel with having a slit (not shown) extending longitudinally. The peripheral core20surrounds a central core21, a secondary spool22, a secondary coil wire23, a primary spool24, and a primary coil wire25.

The central core21is formed with compression molding where magnetic material particles inserted in a core mold is molded under given temperature and pressure. The central core21is formed like a round bar whose longitudinally centered portion has a broadened diameter.

The secondary spool22is formed of resin and is formed like a cylinder having a base. The secondary spool22is disposed as surrounding the central core21. The secondary spool22includes a secondary spool body220and a base221. The secondary spool body220is cylindrical. A lower portion from a longitudinal center to a longitudinal bottom end of the body220is shaped as being mating with a lower portion from a longitudinal center to a longitudinal bottom end of the central core21that the body220faces. The lower portion from the center of an outer surface of the central core21is thereby supported by contacting an inner surface of the secondary spool body220. The base221occludes a bottom opening of the secondary spool body220. The base221is shaped like a convexity. A bottom portion of the central core21is supported by the base221. A cylindrical space26is partitioned between an upper portion of the outer surface of the central core21and an upper portion of the inner surface of the secondary spool body220. The secondary coil wire23is wound around the outer surface of the secondary spool body220.

The primary spool24is a cylinder formed of PPS (polyphenylene sulfide). The primary spool24is disposed as surrounding the secondary coil wire23. The primary spool24is integrated with a high voltage tower241to be described later. Namely, the high voltage tower241is also formed of PPS. Around the outer surface of the primary spool24, an upper flange240aand a lower flange240bare disposed with mutually having an axially-directional distance. The primary coil wire25is wound around the outer surface of the primary spool24between the upper and lower flanges240a,240b.

The high voltage tower241covers the base221of the secondary spool22. A linear expansion coefficient of PPS of which the high voltage tower241is formed is designed as being lower than that of resin of which the base221is formed. The high voltage tower241is connected, around its center, with a high voltage terminal241. The high voltage terminal241is formed of metal and like a cup. The high voltage terminal241downwardly opens. The high voltage terminal242is electrically connected with the secondary coil wire23. A top end of a metal-made coil spring243is attached on a cup-bottom wall of the high voltage tower242. A top end of an ignition plug6is elastically attached on a lower end of the coil spring243. A rubber-made plug cap244covers an almost entire surface of the high voltage tower241. An upper portion of the ignition plug6is press-inserted into an inner surface of the plug cap244. A lower portion of the ignition plug6screws in a plug insertion hole52that is bored in the bottom of the plug hole5. A gap62of a lower end of the ignition plug6protrudes within a combustion chamber7.

A rubber-made seal ring30is inset at the top end of the peripheral core20. The seal ring30is elastically attached around an opening brim of the plug hole5. A connector section31is disposed over the seal ring30.

The connector section31includes a case310and plural connector pins311. The case310is resin-made and shaped like a center-hollow prism. An igniter32is disposed within the case310. The igniter32is formed by sealing a power transistor (not shown), a hybrid integrated circuit (not shown), and a heatsink (not shown) with molding resin. A cylindrical metal-made collar312is formed by being inserted around a side portion of the case312. A lower end of the collar312contacts an upper surface of a boss portion54that is disposed as protruding from an engine block53. A bolt supporting hole51is bored around a central part of the boss portion54. A metal-made bolt8screws in the bolt supporting hole51through the collar312. Namely, the bolt8fixes the ignition coil device1in the plug hole5.

The connector pins311are metal-made and shaped like strips. The connector pins311are molded by being inserted into the case310. The connector pins311penetrate through the case310between an inner side and an outer side. Inner-side ends of the connector pins311are electrically connected with the igniter32, the primary coil wire25, and the secondary coil wire23. By contrast, outer-side ends of the connector pins311are electrically connected with an ECU (engine control unit, not shown).

Within the ignition coil device1, two types of resin-made insulators40,41are used. The first insulator40is formed of epoxy resin and filled within the case310for supporting an upper end210of the central core21. The first insulator40occludes an upper portion of the space26. The second insulator41is filled between the outer surface of the secondary spool22and the inner surface of the primary spool24with penetrating between turns of the secondary coil wire23.

In the next place, operation of the ignition coil device1according to the first embodiment will be explained below. A control signal from the ECU is sent to the igniter32through the connector pins311. The igniter32turns on and off an electric current, so that given voltage is generated in the primary coil wire25due to self-induction. The generated voltage is amplified through mutual-induction between the primary coil wire25and the secondary coil wire23. The amplified high voltage is sent to the ignition plug6through the secondary coil wire23, the high voltage terminal242, and the coil spring243. The amplified high voltage thereby generates sparks in the gap62.

In the next place, an assembling method of the ignition coil device1according to the first embodiment will be explained below. Solid components are at first assembled. The solid components are as follows: the central core21, the secondary spool22where the secondary coil wire23is previously wound; the primary spool24and high voltage tower241where the primary coil wire25is previously wound; the connector section31; and the like. Thereafter, the second insulator41is filled between the outer surface of the secondary spool22and the inner surface of the primary spool24from an opening of the upper end of the case310. The first insulator40is then filled within the case310. Here, the first insulator has relatively high kinetic viscosity, so that the fluidity of the first insulator40is relatively low during the filling. The first insulator40therefore has little possibility of entering the space26. Thereafter, the ignition coil device1where the first and second insulators are already filled is heated under a given temperature for a given period to thermally harden the resin-made insulators40,41. Thus, the ignition coil device1is assembled.

In the next place, functions and effects of the ignition coil device1will be explained below. The blowby gas generated from the combustion chamber7flows in the plug hole5through space between an outer surface of a lower portion of the ignition plug6and an inner surface of the plug insertion hole52as shown in arrows90. The blowby gas then flows within the ignition coil device1through the slit of the peripheral core20. The blowby gas then flows to contact the primary spool24through space between turns of the primary coil wire25as shown in arrows91.

Furthermore, the blowby gas that flows within the ignition coil device1directly contacts the upper portion of the high voltage tower241as shown in arrows92along with the lower flange240bof the primary spool24.

Here, if the primary spool24and the high voltage tower241are formed of non-crystalline resin, the both have possibility of developing the ESC due to the blowby gas and thermal stress acting on the both. However, the both of the ignition coil device1according to the first embodiment of the present invention are formed of the crystalline resin of PPS, so that the both have little possibility of developing the ESC due to the blowby gas and thermal stress acting on the both. Accordingly, the primary spool24and the high voltage tower241according to the first embodiment of the present invention has high environment resistance, which results in enhancing reliability of the ignition coil device1itself.

In the above embodiment, the primary spool24and the high voltage tower241are entirely formed of PPS and are integrated with each other. In comparison with a device where the both are separately provided, the number of components of the ignition coil device1thereby is small. This results in reducing the number of processes for assembling. the ignition coil device1.

Furthermore, PPS has high insulation performance and high heat resistance, so that the ignition coil device1that uses PPS as the crystalline resin has little possibility of developing dielectric breakdown.

Incidentally, corona discharge sometimes occurs between the secondary coil wire23and the primary coil wire25. Here, the primary spool24is disposed between the secondary and primary coil wires23,25. The primary spool24is thereby attacked by the corona discharge. Electrons collision energy derived from the attack of the corona discharge cuts molecular chains of the resin of the primary spool24which the electrons collide with. In addition, the collision energy is converted to thermal energy in the collision region of the resin. The collision region of the resin is thereby heated. Furthermore, oxygen within air close to the collision region ionizes. Ozone is thereby generated to oxidize the resin forming the collision region. In this respect, PPS used for the primary spool24has relatively strong bonding of the molecular chains, high heat resistance due to a high melting point, and also high ozone resistance. PPS thereby has high damage resistance, i.e., corona discharge resistance. Damage, due to the corona discharge, of the primary spool24in the ignition coil device1according to the first embodiment can be restricted.

Furthermore, PPS has enough fluidity during the molding to have less warpage after molding. Therefore, if a primary spool is formed through potting, operability in the potting can be enhanced. Accuracy of molding is additionally improved. Furthermore, PPS is not so hydrolyzed. That is, PPS has high hydrolysis resistance. As a result, an ignition coil device1according to the embodiment has high durability to moisture within a plug hole5.

Furthermore, in the above embodiment, a linear expansion coefficient of the resin of which the base221of the secondary spool22is formed is larger than that of the resin of PPS of which the high voltage tower241is formed. The base221thereby thermally expands more than the high voltage tower241when the ignition coil device1is heated up. The secondary spool22that is disposed inside thereby contacts, under pressure, the high voltage tower241that is disposed outside. This results in enhancing a sealing characteristic between the base221and the high voltage tower241. This also results in restricting development of the ESC in members forming the ignition coil device1. When a resin-made insulator such as epoxy is filled in, sealing to a primary spool or a secondary spool can be enhanced.

Difference between the first embodiment and a second embodiment is that a primary spool and a high voltage tower are formed by potting and that no high voltage terminal is provided. Only the difference will be explained below.

FIG. 2is an axial sectional view of an ignition coil device1according to the second embodiment. Parts corresponding to that of the first embodiment use the same indicating numbers as in the first embodiment. A primary spool24and a high voltage tower241are formed by filling SPS (syndiotactic polystyrene) along an outer surface of a secondary spool22to harden it, i.e., by potting. In detail, a coil spring243, a central core21, and the secondary spool22where a second coil wire23is wound are disposed within dividable molds that mate with the primary spool24and the high voltage tower241. Here, the secondary coil wire23and the coil spring243are previously electrically connected with each other. Thereafter, SPS is filled within the dividable molds to be then heated under a given temperature for a given period. The dividable molds are then cooled down to be divided. A primary coil wire25, a plug cap244, a peripheral core20, a connector section31, and the like are assembled. At last, a first insulator40is filled in from an opening of the upper end of a case310.

In the above embodiment, the primary spool24and the high voltage tower241are entirely integrated with each other including a portion corresponding to the second insulator41shown inFIG. 1. The number of components of the ignition coil device1thereby becomes small. The high voltage terminal242shown inFIG. 1is not disposed, so that the secondary coil wire23is directly connected with the coil spring243. In this respect, the number of components is also reduced.

Furthermore, SPS used as the crystalline resin has high heat resistance, high dielectiric breakdown resistance, high tracking resistance. SPS also has high fluidity during the potting and small warpage posterior to molding. This results in increasing operability of the potting. Molding accuracy for the primary spool24and the high voltage tower241is high.

Difference between the first embodiment and a third embodiment is that a primary spool and a high voltage tower are provided as separated independent members and that the high voltage tower is not exposed to a plug hole. Only the difference will be explained below.

FIG. 3is an axial sectional view of an ignition coil device1according to the third embodiment. Parts corresponding to that of the first embodiment use the same indicating numbers as in the first embodiment. A primary spool24and a high voltage tower241are provided as separated independent members with being axially mated with each other. The primary spool24is formed of SPS (syndiotactic polystyrene), while the high voltage tower241is formed of PPE (polyphenylene ether). The primary spool24contacts the blowby gas as shown in arrows91inFIG. 3. The primary spool24is thereby formed of crystalline resin of SPS. By contrast, the high voltage tower241does not contact the blowby gas, so that it does not need to be formed of crystalline resin. The high voltage tower241is formed of PPE that is non-crystalline resin and much adherent to the second insulator41.

In the above embodiment, in comparison with a device where the primary spool24and the high voltage tower241are formed of SPS as being integrated with each other, expensive SPS can be decreased in production. The production cost of the ignition coil device1according to the third embodiment thereby becomes low. Since the high voltage tower241is formed of PPE that is much adherent to the second insulator41, the high voltage tower241and the second insulator41are seldom separated from each other.

Explanation regarding crystalline resin will be added below. The crystalline resin has crystalline region whose polymer chains are regularly arranged under the melting point. With having the more crystalline region, the crystalline resin has superiority in heat resistance, chemical resistance, dimensional stability, and mechanical strength in comparison with non-crystalline resin. Accordingly, even when thermal stress is applied after long hour exposure to the blowby gas, i.e., under a condition where heat, blowby gas, and thermal stress work as composite, the crystalline resin that has superior characteristics can be relatively stable. As a result, the crystalline resin has preferable blowby gas resistance. An ignition coil device1according to the embodiments has thereby less possibility of dielectric breakdown.

Here, a crystallinity degree of the crystalline resin is preferably set between 20% and 80%. With the crystallinity degree of less than 20%, the crystalline resin does not properly show superiority in heat resistance, chemical resistance, dimensional stability, or mechanical strength. With the crystallinity degree of more than 80%, the crystalline resin is too much hardened, which results in lowering workability. Furthermore, a crystallinity degree of the crystalline resin is more preferably set between 30% and 80% with regard to ESC resistance.

A crystallinity degree (X %) of the crystalline resin is obtain from a formula as follows.
X=((ΔHTm−ΔHTcc)/(ΔH0×W))×100

Here, ΔHTmis melting heat (J/g) at melting point Tm, ΔHTccis a peak value (J/g) at re-crystalline temperature Tcc, ΔH0is melting heat (J/g) at a crystallinity degree of 100% of a crystalline resin, and W is % by weight of a crystalline resin.

These parameters can be measured with a DSC (differential scanning calorimeter). In detail, ΔHTmis measured as dimensions of an endothermal reaction peak. ΔHTccis measured as dimensions of an exothermal reaction peak. ΔH0can be obtained from a reference. W is obtained by dividing crystalline resin weight as a measurement target within a specimen by entire specimen weight.

Although an ignition coil device of the present invention is explained above, it is not limited to the above embodiments.

For instance, in the third embodiment, although the primary spool24is entirely formed of SPS, the primary spool24can be structured as a spool body formed of non-crystalline resin and an SPS-made protection tape. The SPS-made protection tape can be wound, between an upper flange240aand a lower flange240b, around the spool body which the blowby gas contacts. The conventional spool formed of non-crystalline resin can be used in an embodiment of the present invention.

Similarly, the high voltage tower can be also structured as a high voltage tower body formed of non-crystalline resin and an SPS-made protection tape. The SPS-made protection tape can be wound, around a portion of the high voltage tower body which the blowby gas contacts. The conventional high voltage tower formed of non-crystalline resin can be also used in an embodiment of the present invention.

Crystalline resin such as SPS can be used not only as a tape but also a film. Furthermore, crystalline resin can be applied as an embrocation on a spool body or a high voltage tower body.

As the crystalline resin, not only PPS or SPS, but also PBT (polybutylene terephthalate) or PET (polyethylene terephthalate) can be used. Here, PBT or PET is relatively low in price. Furthermore, a primary spool and a high voltage tower can be formed of different crystalline resin types, respectively.