Patent Publication Number: US-6982622-B2

Title: Ignition coil device

Description:
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. 4  shows an exploded perspective view of the coil ignition device  100 . As shown in  FIG. 4 , the ignition coil device  100  includes a secondary spool  101 , a primary spool  102 , and a peripheral core  103 . The ignition coil device  100  is inserted in a plug hole (not shown). The secondary spool  101  is cylindrical. A secondary coil wire (not shown) is wound around an outer surface of the secondary spool  101 . The primary spool  102  is cylindrical. The primary spool  102  is disposed as surrounding the secondary coil wire. A primary coil wire (not shown) is wound around an outer surface of the primary spool  102 . The peripheral core  103  is cylindrical with having a slit  104  longitudinally extending. The peripheral core  103  is 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 device  100 , the primary spool  102  is exposed to the blowby gas that flows in through the slit  104  of the peripheral core  103  and then space between turns of the primary coil wire. 
   The primary spool  102  is generally formed of non-crystalline resin that has high adhesiveness to epoxy resin (not shown) filled in the ignition coil device  100 . Furthermore, linear expansion coefficients of the primary spool  102  and members around the primary spool  102  are different. The primary spool  102  thereby suffers thermal stress due to heating/cooling cycles of an engine. 
   Thus, the primary spool  102  exposed to the blowby gas for a long time frame suffers the thermal stress, so that the primary spool  102  has possibility of developing the ESC. As a result, the ignition coil device  100  has 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. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above and other objects, features, and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: 
       FIG. 1  is an axial sectional view of an ignition coil device according to a first embodiment of the present invention; 
       FIG. 2  is an axial sectional view of an ignition coil device according to a second embodiment of the present invention; 
       FIG. 3  is an axial sectional view of an ignition coil device according to a third embodiment of the present invention; and 
       FIG. 4  is an exploded perspective view of an ignition coil device of a related art. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   (First Embodiment) 
   A structure of an ignition coil device  1  according to a first embodiment will be described with reference to  FIG. 1 .  FIG. 1  shows an axial sectional view of the ignition coil device  1 . A so-called stick-type ignition coil device  1  is housed (or mounted) in a plug hole member forming a plug hole  5  that is formed in each cylinder at the top of an engine block  53 . Here, the ignition coil device  1  forms internal space with the plug hole member. Namely, the internal space being a subset of the plug hole  5  is space between the plug hole member and an outer surface of the ignition coil device  1 . As will be discussed below, the ignition coil device  1  is connected to an ignition plug  6  at a lower portion in the drawing. 
   A peripheral core  20  is cylindrical and formed of a single sheet of silicon steel with having a slit (not shown) extending longitudinally. The peripheral core  20  surrounds a central core  21 , a secondary spool  22 , a secondary coil wire  23 , a primary spool  24 , and a primary coil wire  25 . 
   The central core  21  is formed with compression molding where magnetic material particles inserted in a core mold is molded under given temperature and pressure. The central core  21  is formed like a round bar whose longitudinally centered portion has a broadened diameter. 
   The secondary spool  22  is formed of resin and is formed like a cylinder having a base. The secondary spool  22  is disposed as surrounding the central core  21 . The secondary spool  22  includes a secondary spool body  220  and a base  221 . The secondary spool body  220  is cylindrical. A lower portion from a longitudinal center to a longitudinal bottom end of the body  220  is shaped as being mating with a lower portion from a longitudinal center to a longitudinal bottom end of the central core  21  that the body  220  faces. The lower portion from the center of an outer surface of the central core  21  is thereby supported by contacting an inner surface of the secondary spool body  220 . The base  221  occludes a bottom opening of the secondary spool body  220 . The base  221  is shaped like a convexity. A bottom portion of the central core  21  is supported by the base  221 . A cylindrical space  26  is partitioned between an upper portion of the outer surface of the central core  21  and an upper portion of the inner surface of the secondary spool body  220 . The secondary coil wire  23  is wound around the outer surface of the secondary spool body  220 . 
   The primary spool  24  is a cylinder formed of PPS (polyphenylene sulfide). The primary spool  24  is disposed as surrounding the secondary coil wire  23 . The primary spool  24  is integrated with a high voltage tower  241  to be described later. Namely, the high voltage tower  241  is also formed of PPS. Around the outer surface of the primary spool  24 , an upper flange  240   a  and a lower flange  240   b  are disposed with mutually having an axially-directional distance. The primary coil wire  25  is wound around the outer surface of the primary spool  24  between the upper and lower flanges  240   a ,  240   b.    
   The high voltage tower  241  covers the base  221  of the secondary spool  22 . A linear expansion coefficient of PPS of which the high voltage tower  241  is formed is designed as being lower than that of resin of which the base  221  is formed. The high voltage tower  241  is connected, around its center, with a high voltage terminal  241 . The high voltage terminal  241  is formed of metal and like a cup. The high voltage terminal  241  downwardly opens. The high voltage terminal  242  is electrically connected with the secondary coil wire  23 . A top end of a metal-made coil spring  243  is attached on a cup-bottom wall of the high voltage tower  242 . A top end of an ignition plug  6  is elastically attached on a lower end of the coil spring  243 . A rubber-made plug cap  244  covers an almost entire surface of the high voltage tower  241 . An upper portion of the ignition plug  6  is press-inserted into an inner surface of the plug cap  244 . A lower portion of the ignition plug  6  screws in a plug insertion hole  52  that is bored in the bottom of the plug hole  5 . A gap  62  of a lower end of the ignition plug  6  protrudes within a combustion chamber  7 . 
   A rubber-made seal ring  30  is inset at the top end of the peripheral core  20 . The seal ring  30  is elastically attached around an opening brim of the plug hole  5 . A connector section  31  is disposed over the seal ring  30 . 
   The connector section  31  includes a case  310  and plural connector pins  311 . The case  310  is resin-made and shaped like a center-hollow prism. An igniter  32  is disposed within the case  310 . The igniter  32  is 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 collar  312  is formed by being inserted around a side portion of the case  312 . A lower end of the collar  312  contacts an upper surface of a boss portion  54  that is disposed as protruding from an engine block  53 . A bolt supporting hole  51  is bored around a central part of the boss portion  54 . A metal-made bolt  8  screws in the bolt supporting hole  51  through the collar  312 . Namely, the bolt  8  fixes the ignition coil device  1  in the plug hole  5 . 
   The connector pins  311  are metal-made and shaped like strips. The connector pins  311  are molded by being inserted into the case  310 . The connector pins  311  penetrate through the case  310  between an inner side and an outer side. Inner-side ends of the connector pins  311  are electrically connected with the igniter  32 , the primary coil wire  25 , and the secondary coil wire  23 . By contrast, outer-side ends of the connector pins  311  are electrically connected with an ECU (engine control unit, not shown). 
   Within the ignition coil device  1 , two types of resin-made insulators  40 ,  41  are used. The first insulator  40  is formed of epoxy resin and filled within the case  310  for supporting an upper end  210  of the central core  21 . The first insulator  40  occludes an upper portion of the space  26 . The second insulator  41  is filled between the outer surface of the secondary spool  22  and the inner surface of the primary spool  24  with penetrating between turns of the secondary coil wire  23 . 
   In the next place, operation of the ignition coil device  1  according to the first embodiment will be explained below. A control signal from the ECU is sent to the igniter  32  through the connector pins  311 . The igniter  32  turns on and off an electric current, so that given voltage is generated in the primary coil wire  25  due to self-induction. The generated voltage is amplified through mutual-induction between the primary coil wire  25  and the secondary coil wire  23 . The amplified high voltage is sent to the ignition plug  6  through the secondary coil wire  23 , the high voltage terminal  242 , and the coil spring  243 . The amplified high voltage thereby generates sparks in the gap  62 . 
   In the next place, an assembling method of the ignition coil device  1  according to the first embodiment will be explained below. Solid components are at first assembled. The solid components are as follows: the central core  21 , the secondary spool  22  where the secondary coil wire  23  is previously wound; the primary spool  24  and high voltage tower  241  where the primary coil wire  25  is previously wound; the connector section  31 ; and the like. Thereafter, the second insulator  41  is filled between the outer surface of the secondary spool  22  and the inner surface of the primary spool  24  from an opening of the upper end of the case  310 . The first insulator  40  is then filled within the case  310 . Here, the first insulator has relatively high kinetic viscosity, so that the fluidity of the first insulator  40  is relatively low during the filling. The first insulator  40  therefore has little possibility of entering the space  26 . Thereafter, the ignition coil device  1  where the first and second insulators are already filled is heated under a given temperature for a given period to thermally harden the resin-made insulators  40 ,  41 . Thus, the ignition coil device  1  is assembled. 
   In the next place, functions and effects of the ignition coil device  1  will be explained below. The blowby gas generated from the combustion chamber  7  flows in the plug hole  5  through space between an outer surface of a lower portion of the ignition plug  6  and an inner surface of the plug insertion hole  52  as shown in arrows  90 . The blowby gas then flows within the ignition coil device  1  through the slit of the peripheral core  20 . The blowby gas then flows to contact the primary spool  24  through space between turns of the primary coil wire  25  as shown in arrows  91 . 
   Furthermore, the blowby gas that flows within the ignition coil device  1  directly contacts the upper portion of the high voltage tower  241  as shown in arrows  92  along with the lower flange  240   b  of the primary spool  24 . 
   Here, if the primary spool  24  and the high voltage tower  241  are 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 device  1  according 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 spool  24  and the high voltage tower  241  according to the first embodiment of the present invention has high environment resistance, which results in enhancing reliability of the ignition coil device  1  itself. 
   In the above embodiment, the primary spool  24  and the high voltage tower  241  are 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 device  1  thereby is small. This results in reducing the number of processes for assembling. the ignition coil device  1 . 
   Furthermore, PPS has high insulation performance and high heat resistance, so that the ignition coil device  1  that uses PPS as the crystalline resin has little possibility of developing dielectric breakdown. 
   Incidentally, corona discharge sometimes occurs between the secondary coil wire  23  and the primary coil wire  25 . Here, the primary spool  24  is disposed between the secondary and primary coil wires  23 ,  25 . The primary spool  24  is 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 spool  24  which 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 spool  24  has 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 spool  24  in the ignition coil device  1  according 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 device  1  according to the embodiment has high durability to moisture within a plug hole  5 . 
   Furthermore, in the above embodiment, a linear expansion coefficient of the resin of which the base  221  of the secondary spool  22  is formed is larger than that of the resin of PPS of which the high voltage tower  241  is formed. The base  221  thereby thermally expands more than the high voltage tower  241  when the ignition coil device  1  is heated up. The secondary spool  22  that is disposed inside thereby contacts, under pressure, the high voltage tower  241  that is disposed outside. This results in enhancing a sealing characteristic between the base  221  and the high voltage tower  241 . This also results in restricting development of the ESC in members forming the ignition coil device  1 . When a resin-made insulator such as epoxy is filled in, sealing to a primary spool or a secondary spool can be enhanced. 
   (Second Embodiment) 
   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. 2  is an axial sectional view of an ignition coil device  1  according to the second embodiment. Parts corresponding to that of the first embodiment use the same indicating numbers as in the first embodiment. A primary spool  24  and a high voltage tower  241  are formed by filling SPS (syndiotactic polystyrene) along an outer surface of a secondary spool  22  to harden it, i.e., by potting. In detail, a coil spring  243 , a central core  21 , and the secondary spool  22  where a second coil wire  23  is wound are disposed within dividable molds that mate with the primary spool  24  and the high voltage tower  241 . Here, the secondary coil wire  23  and the coil spring  243  are 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 wire  25 , a plug cap  244 , a peripheral core  20 , a connector section  31 , and the like are assembled. At last, a first insulator  40  is filled in from an opening of the upper end of a case  310 . 
   In the above embodiment, the primary spool  24  and the high voltage tower  241  are entirely integrated with each other including a portion corresponding to the second insulator  41  shown in  FIG. 1 . The number of components of the ignition coil device  1  thereby becomes small. The high voltage terminal  242  shown in  FIG. 1  is not disposed, so that the secondary coil wire  23  is directly connected with the coil spring  243 . 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 spool  24  and the high voltage tower  241  is high. 
   (Third Embodiment) 
   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. 3  is an axial sectional view of an ignition coil device  1  according to the third embodiment. Parts corresponding to that of the first embodiment use the same indicating numbers as in the first embodiment. A primary spool  24  and a high voltage tower  241  are provided as separated independent members with being axially mated with each other. The primary spool  24  is formed of SPS (syndiotactic polystyrene), while the high voltage tower  241  is formed of PPE (polyphenylene ether). The primary spool  24  contacts the blowby gas as shown in arrows  91  in  FIG. 3 . The primary spool  24  is thereby formed of crystalline resin of SPS. By contrast, the high voltage tower  241  does not contact the blowby gas, so that it does not need to be formed of crystalline resin. The high voltage tower  241  is formed of PPE that is non-crystalline resin and much adherent to the second insulator  41 . 
   In the above embodiment, in comparison with a device where the primary spool  24  and the high voltage tower  241  are formed of SPS as being integrated with each other, expensive SPS can be decreased in production. The production cost of the ignition coil device  1  according to the third embodiment thereby becomes low. Since the high voltage tower  241  is formed of PPE that is much adherent to the second insulator  41 , the high voltage tower  241  and the second insulator  41  are seldom separated from each other. 
   (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 device  1  according 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 =((Δ H   Tm   −ΔH   Tcc )/(Δ H   0   ×W ))×100
 
   Here, ΔH Tm  is melting heat (J/g) at melting point Tm, ΔH Tcc  is a peak value (J/g) at re-crystalline temperature Tcc, ΔH 0  is 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, ΔH Tm  is measured as dimensions of an endothermal reaction peak. ΔH Tcc  is measured as dimensions of an exothermal reaction peak. ΔH 0  can be obtained from a reference. W is obtained by dividing crystalline resin weight as a measurement target within a specimen by entire specimen weight. 
   (Modification) 
   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 spool  24  is entirely formed of SPS, the primary spool  24  can 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 flange  240   a  and a lower flange  240   b , 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. 
   It will be obvious to those skilled in the art that various changes may be made in the above-described embodiments of the present invention. However, the scope of the present invention should be determined by the following claims.