Abstract:
In an ignition device for an internal combustion engine, comprising a spark plug made to carry out an electric discharge between an center electrode and an earth electrode and an ignition coil having a primary winding and a secondary winding for supplying a high voltage to the spark plug, notch portions are made in a ceramic spool on which one of the primary and secondary windings is wound and projecting portion are made in an insulating-resin-made holding member into which connector terminals are incorporated, with the projecting portions being engaged with the notch portions. The engagement of the projecting portions and the notch portions prevents the connector terminals from moving with respect to the ceramic spool in circumferential directions of the ceramic spool during terminal connection work. This solves the problems in that, in the case of the employment of a ceramic spool, because difficulty is encountered in insert-molding the connector terminals in the ceramic spool, the connector terminals can move with respect to the ceramic spool during terminal connection work for the connection of the winding to the connector terminals to cause poor terminal connection workability.

Description:
BACKGROUND OF THE INVENTION 
     1) Field of the Invention 
     The present invention relates to an ignition device for use in an internal combustion engine, which has an integral construction of an ignition plug and an ignition coil. 
     2) Description of the Related Art 
     So far, as ignition devices for use in internal combustion engines, there have been proposed various types (see Japanese Patent Laid-Open Nos. 2000-252040 and 2000-277232 and European Patent Laid-Open No. 0907019). In such types of ignition devices, each of primary and secondary windings is wound around a resin-made spool and a connector terminal, to which connected is an end portion (terminal) of the winding, is insert-molded in a resin-made spool. 
     Meanwhile, the present inventors have studied the replacement of one of the two spools with a ceramic spool and an integral construction of a plug side tube section, internally including a center electrode and a stem, and the ceramic spool for the purpose of the cost reduction based on the structural simplification. However, this has indicated the following problems. 
     That is, in the case of a conventional resin-made spool, a connector terminal is insert-molded in the spool to inhibit motions of the connector terminal with respect to the spool, which can facilitate the terminal connection work for the connection between an end portion of a winding and the connector terminal. 
     However, for a spool to be of a ceramics-made type, difficulty is experienced in insert-molding a connector terminal in a spool, which leads to arbitrary motions of the connector terminal with respect to the spool during the terminal connection work, thereby creating a problem in the impairment of workability of terminal connection. 
     SUMMARY OF THE INVENTION 
     The present invention has been developed with a view to eliminating the above-mentioned problem, and it is therefore an object of the invention to eliminate problems occurring in the case of the employment of a ceramic spool in an ignition device for an internal combustion engine in which a spark plug and an ignition coil are integrated with each other and is mounted in a cylinder head. 
     For this purpose, in accordance with the present invention, there is provided an ignition device for an internal combustion engine, which is equipped with a spark plug ( 2 ) made to carry out an electric discharge between an center electrode ( 22 ) and an earth electrode ( 23 ) and an ignition coil ( 3 ) having a primary winding ( 31 ) and a secondary winding ( 32 ) for supplying a high voltage to the spark plug ( 2 ), with the spark plug ( 2 ) and the ignition coil ( 3 ) being mounted in a cylinder head of the internal combustion engine in an integrated condition, the ignition device comprising a tube-like ceramic spool ( 52 ) on which one of the primary winding ( 31 ) and the secondary winding ( 32 ) is wound, two conductive connector terminals ( 61 ) located at an axial end portion of the spool ( 52 ) and connected to both end portions ( 31   a ) of the winding ( 31 ) wound on the spool ( 52 ), an insulating-resin-made holding member ( 9 ) into which the two connector terminals ( 61 ) are incorporated, and positioning means ( 55 ,  92 ) for inhibiting a relative motion of the connector terminals ( 61 ) and the holding member ( 9 ) with respect to the spool ( 52 ) in circumferential directions of the spool ( 52 ). 
     This inhibits the motion or movement of the connector terminals with respect to the ceramic spool in the circumferential directions of the spool during the terminal connection work for establishing the connection between the windings and the connector terminals, thus improving the workability or work efficiency of the terminal connections. 
     In addition, according to the present invention, it is also appropriate that the positioning means ( 55 ,  92 ) comprises a notch portion made in the spool ( 52 ) and a projecting portion ( 92 ) made in the holding member ( 9 ) to engage with the notch portion ( 55 ). This contributes to the facilitation of the construction of the ignition device according to the present invention. 
     Still additionally, according to the present invention, it is also appropriate that the spool ( 52 ) is integrated with a ceramics-made plug side tube section ( 51 ) internally accommodating the center electrode ( 22 ). This contributes to the facilitation of the construction of the ignition device according to the present invention, thereby achieving the cost reduction. 
     The reference numerals in parentheses attached to the respective means or members signify the corresponding relation with respect to the concrete means in an embodiment which will be described later. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and features of the present invention will become more readily apparent from the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings in which: 
     FIG. 1 is a front-elevational cross-sectional view showing an ignition device for an internal combustion engine according to an embodiment of the present invention; 
     FIG. 2 is a perspective view showing an insulator on which a primary winding shown in FIG. 1 is wound; 
     FIG. 3 is an exploded perspective view useful for explaining an incorporation process for an ignition coil section shown in FIG. 1; 
     FIG. 4 is an exploded perspective view useful for explaining an incorporation process for the ignition device shown in FIG. 1; 
     FIG. 5 is a plan view showing connector terminals for a primary winding and a holding plate shown in FIG. 1; and 
     FIG. 6 is a perspective view showing an essential part of an ignition device according to another embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1 to  5  are illustrations of an ignition device for use in an internal combustion engine according to an embodiment of the present invention. FIG. 1 is a cross-sectional view showing the entire construction of the ignition device, FIG. 2 is a perspective view showing an insulator  5  on which a primary winding  31  is put in a wound condition, FIG. 3 is an exploded perspective view useful for explaining an incorporation process for an ignition coil  3  section, FIG. 4 is an exploded perspective view useful for explaining an incorporation process for the ignition device, and FIG. 5 is a plan view showing connector terminals  61  for the primary winding  31  and a holding plate  9 . 
     In FIG. 1, the ignition device is designed such that a cylindrical case  1  accommodates a spark plug  2 , an ignition coil  3  and a pressure detecting element  4 , and is mounted in a plug hole of a cylinder head so that both electrodes of the spark plug  2  (which will be mentioned in detail later) are exposed to a combustion chamber of an internal combustion engine for a motor vehicle. 
     The case  1  is made of a magnetic and conductive metallic material, more concretely, is made of a steel material such as a carbon steel, and in an outer circumferential surface of the case  1 , a male screw portion  11  is made on the combustion chamber side while a tightening nut portion  12  is made on a side opposite to the combustion chamber side. The case  1  is rotated through the use of the nut portion  12  so that the male screw portion  11  engages with a female screw portion (not shown) of the cylinder head, thus fixedly securing the ignition device to the cylinder head. 
     In the case  1 , there is accommodated a cylindrical insulator  5  made of ceramics such as alumina having a sufficient electrical insulating property. This insulator  5  is equipped with a plug side tube section  51  positioned on the combustion chamber side and a coil side tube section  52  extending from the plug side tube section  51  to the side opposite to the combustion chamber side. 
     On an inner circumferential surface of the case  1 , a stepped receiving surface  13  is formed in the vicinity of the combustion chamber side, and on an outer circumferential surface of the plug side tube section  51  of the insulator  5 , a stepped working (contacting) surface  53  is formed to come into contact with the receiving surface  13 . Moreover, in a state where the receiving surface  13  and the working surface  53  are brought into contact with each other, the case  1  and the insulator  5  are positioned in an axial direction and the leakage of the combustion gas from a portion between the case  1  and the insulator  5  is preventable. 
     The spark plug  2  is composed of a stem  21  made of a conductive metal, a center electrode  22  made of a conductive metal, an earth electrode  23  made of a conductive metal, and others. The stem  21  and the center electrode  22  are inserted into a central hole of the plug side tube section  51  of the insulator  5 , and one end portion of the center electrode  22  is exposed to the combustion chamber. Moreover, the earth electrode  23  is integrated with the case  1  by means of welding or the like, and this earth electrode  23  is positioned to be in opposed relation to the one end portion of the center electrode  22 . 
     The ignition coil  3  is composed of a primary winding  31 , a secondary winding  32 , a cylindrical center core  33  made of a magnetic material, a secondary spool  34  made of an electrical insulating resin and formed into a blind-end type cylindrical configuration, and others. 
     The primary winding  31  is directly wound around a recess portion  54  of the coil side tube section  52  of the insulator  5 . This coil side tube section  52  corresponds to a tubular ceramic spool (made of ceramics) on which a winding is wound. Moreover, both end portions (terminals) of the primary winding  31  are connected to two primary winding connector terminals  61  of a connector  6  for connection by means of soldering or fusing and, hence, a current is supplied from an igniter (not shown) to the primary winding  31 . The terminal connection work will be mentioned later. 
     In the case  1 , a section surrounding the center core  33  functions as an outer circumferential core in which a magnetic flux flows, and a magnetic flux generated in the primary winding  31  flows through the center core  33  and the case  1 . 
     In addition, in the case  1 , the section surrounding the center core  33  has a slit  15  (see FIG. 4) formed to extend in an axial direction of the center core  33  for the purpose of preventing a loss stemming from a ring current developing due to a magnetic flux variation. 
     The secondary spool  34  is equipped with a winding tube section  34   a  on which the secondary winding  32  is wound and a protruding tube section  34   b  protruding from the winding tube section  34   a  toward the side opposite to the combustion chamber side. The secondary winding  32  is wound on an outer circumference of the winding tube section  34   b  and the center core  33  is inserted into a central hole of the secondary spool  34 . A core pressing cover  35  made of an elastic material such as a rubber or sponge is inserted into an opening of the central hole of the secondary spool  34  to fill up the central hole of the secondary spool  34 . 
     A high-voltage end portion of the secondary winding  32  is electrically connected through the stem  21  of the spark plug  2  to the center electrode  22 . On the other hand, a low-voltage end portion of the secondary winding  32  is electrically connected through parts, i.e., a ground terminal  36  (see FIG.  3 ), a ground plate  37  and a bolt  8 , placed in the interior of the case  1 , to the case  1 , and is further electrically connected through the case  1  to the earth electrode  23 . In other words, the low-voltage end portion of the secondary winding  32  is electrically connected to the earth electrode  23  without being connected through the internal combustion engine. 
     The ground terminal  36  is made of a conductive metal and formed into a plate-like or bar-like configuration, with one end portion thereof being connected to the low-voltage end portion of the secondary winding  32 . The ground plate  37  is made of a conductive metal and includes a sheet ring portion and an insert portion protruding inwardly from the ring portion, and the ring portion is located between the pressure detecting element  4  and the bolt  8  and the ground terminal  36  is inserted into a hole of the insert portion. 
     The pressure detecting element  4  shows a fluctuation of electric potential in accordance with a variation of a load applied thereto, and is made of, for example, lead titanate and is formed into a sheet ring-like configuration. Moreover, the pressure detecting element  4  is located at an end portion of the coil side tube section  52 , with one end portion of the pressure detecting element  4  being electrically connected through the ground plate  37 , the bolt  8  and the case  1  to the cylinder head. 
     In addition, a combustion pressure signal terminal  7  formed into a sheet ring-like configuration is located between the pressure detecting element  4  and the coil side tube section  52 . This combustion pressure signal terminal  7  is integrated with a combustion pressure signal connector terminal  71  (see FIG.  4 ). Thus, an output signal of the pressure detecting element  4  is fed to a control unit (not shown). 
     In this connection, for allowing the pressure detecting element  4  to be located at the end portion of the coil side tube section  52 , the end portion of the coil side tube section  52  is made to extend upwardly with respect to the primary winding  31  and the secondary winding  32  on the paper surface of FIG.  1 . In other words, the end portion of the coil side tube section  52  is made to protrude toward the side opposite to the combustion chamber with respect to the primary winding  31  and the secondary winding  32 . 
     The bolt  8  is made of a conductive metal and formed into a tube-like configuration. The bolt  8  is screw-engaged with the female screw portion  14  made in the case  1  on the side opposite to the combustion chamber so that the ground plate  37 , the pressure detecting element  4  and the combustion pressure signal terminal  7  are held between the end portion of the coil side tube section  52  and the bolt  8 . 
     In addition, by tightening the bolt  8 , a compression preload is applied to the pressure detecting element  4 , and a packing (not shown) is put in a contact portion between the receiving surface  13  of the case  1  and the working surface  53  of the insulator  5  to prevent the leakage of the combustion gas from between the case  1  and the insulator  5 . 
     After the bolt  8  is screw-engaged with the female screw portion  14 , a resin-made case  62  of the connector  6  is inserted into a hollow of the bolt  8 . 
     Secondly, a description will be given hereinbelow of a positioning construction for the secondary spool  34 , the primary winding connector terminal  61  and others with respect to the insulator  5 , a method of assembling these members and a terminal connection work for the primary winding  31 . 
     As FIG. 2 shows, in the coil side tube section  52 , three notch portions  55  are made in its end portion opposite to the combustion chamber side, and these notch portions  55  are arranged at an equal interval along a circumferential direction of the coil side tube section  52 . Moreover, both the end portions  31   a  of the primary winding  31  are drawn out toward the end portion of the coil side tube section  52  opposite to the combustion chamber side and are temporarily fixed at a predetermined position in the circumferential direction of the coil side tube section  52  through the use of a tape or the like. 
     As FIG. 3 shows, in the secondary spool  34 , three projecting portions  34   c  are made in its end portion opposite to the combustion chamber side to engage with the notch portions  55  of the coil side tube section  52 . In two of the three projecting portions  34   c , through holes (not shown) are made to accommodate the end portions  31   a , respectively. 
     In addition, as shown in FIGS. 3 and 5, the two primary winding connector terminals  61 , made of a conductive metal, are insert-molded in a disc portion  91  of the holding plate  9  made of an insulating resin so that the two primary winding connector terminals  61  and the holding plate  9  are formed into an integrated construction. Still additionally, in an outer circumference of the disc portion  91 , three projecting portions  92  are made to engage with the notch portions  55  of the coil side tube section  52 . Yet additionally, through holes  93 , which accommodate the end portions  31   a  of the primary winding  31 , are made in two of the three projecting portions  92 , and a through hole  94 , which accommodates the ground terminal  36 , is made in the disc portion  91 . 
     The holding plate  9  corresponding to a holding member, and the notch portions  55  of the coil side tube section  52  and the projecting portions  92  of the holding plate  9  correspond to positioning means. 
     In assembling, as shown in FIG. 3, the secondary spool  34  in which the secondary winding  32 , the center core  33  and the core pressing cover  35  are built is first inserted halfway into the central hole of the insulator  5  and the end portions  31   a  are then inserted into the through holes of the projecting portions  34   c  of the secondary spool  34 . Subsequently, as shown in FIG. 4, the secondary spool  34  is further pushed into the central hole of the insulator  5  so that the projecting portions  34   c  engage with the notch portions  55  of the coil side tube section  52 . 
     Following this, the end portions  31   a  are inserted into the through holes  93  of the holding plate  9  and the projecting portions  92  of the holding plate  9  are then engaged with the notch portions  55  of the coil side tube section  52  as shown in FIG.  4 . This engagement between the projecting portions  92  and the notch portions  55  inhibits or limits the relative movement between the coil side tube section  52  and the primary winding connectors  61  and/or the holding plate  9  in circumferential directions of the coil side tube section  52 . 
     Moreover, the terminal connection work is done in a state where the relative movement is inhibited in this way. That is, the end portions  31   a  are connected to the primary winding connector terminals  61  by means of soldering or fusing. 
     Thereafter, the insulator  5 , together with the combustion pressure signal terminal  7 , the pressure detecting element  4  and the ground plate  37  built in the insulator  5 , is inserted into the case  1  and after the insertion thereof into the case  1 , the bolt  8  is tightened with respect to the female screw portion  14 . Moreover, after the bolt  8  is screw-coupled with the female screw portion  14 , the resin-made case  62  of the connector  6  is inserted into the hollow of the bolt  8 , thus completing the assembling. 
     In the ignition device constructed as mentioned above, in response to the supply of a current from an igniter, the ignition coil  3  develops a high voltage, and the spark plug  2  discharges the high voltage in a spark gap to ignite an air-fuel mixture in the interior of the combustion chamber. Moreover, the pressure variation produced by the combustion in the combustion chamber is transmitted through the insulator  5  to the pressure detecting element  4  so that the pressure detecting element  4  undergoes a load variation. Still moreover, the pressure detecting element  4  outputs a voltage signal corresponding to this load variation. 
     In this embodiment, since the engagement between the projecting portions  92  of the holding plate  9  and the notch portions  55  of the coil side tube section  52  inhibits the relative movements between the coil side tube section  52  and the primary winding connector terminals  61  and/or the holding plate  9  in the circumferential directions of the coil side tube section  52 , during the terminal connection work, the primary winding connector terminals  61  do not move with respect to the coil side tube section  52  in the circumferential directions of the coil side tube section  52 , thus improving the workability of the terminal connection. 
     In addition, since the low-voltage side of the secondary winding  32  and the earth electrode  23  of the spark plug  2  are electrically connected to each other through the case  1 , it is possible to eliminate the need for connector terminals and wire harnesses for the low-voltage side of the secondary winding  32  to be electrically connected to the internal combustion engine. This enables the size reduction of the connector  6  and can eliminate the need for the laying of the wire harnesses for making an electrical connection of the low-voltage side of the secondary winding  32  to the internal combustion engine, thus enhancing the reliability of the device. 
     Still additionally, this shortens the distance between the low-voltage side of the secondary winding  32  and the earth electrode  23  of the spark plug  2  and reduces the number of connection places, thereby reducing the resistance loss of the discharge circuit and enabling efficient ignition. 
     Yet additionally, one end portion of the pressure detecting element  4  is electrically connected through the case  1  to the internal combustion engine, which eliminates the need for connector terminals and wire harnesses for the one end portion of the pressure detecting element  4  to be electrically connected to the internal combustion engine. 
     Moreover, since the end portion of the coil side tube section  52  is made to further protrude toward the side opposite to the combustion chamber with respect to the primary winding  31  and the secondary winding  32  and the pressure detecting element  4  is located at the end portion of the coil side tube section  52 , signals lines of the pressure detecting element  4  can be derived from the case  1  to the external without being required to pass by the ignition coil  3 . Accordingly, there is no need to increase the diameter of the case  1 , and the output signal of the pressure detecting element  4  is unsusceptible to the influence of discharge noises from the ignition coil  3 , and even the processing such as the laying of the signal lines becomes unnecessary or easy. 
     Still moreover, since a compression preload is applied to the pressure detecting element  4  by tightening the bolt  8 , the output thereof corresponding to the pressure variation in the combustion chamber is attainable with high accuracy. 
     Yet moreover, since the working surface  53  of the insulator  5  is pressed against the receiving surface  13  of the case  1  by tightening the bolt  8 , the contact portion between the receiving surface  13  and the working surface  53  can prevent the combustion gas from leaking between the case  1  and the insulator  5 . 
     Furthermore, since the case  1  and the section accommodating the ignition coil components are formed in an integrated fashion, the heat radiation property of the ignition coil components becomes further improvable, as compared with a type in which the ignition coil components are put in a resin-made case. 
     Still furthermore, since the case  1  itself has a function as an outer circumferential core of the ignition coil, unlike the conventional art there is no need to place an outer circumferential core separately, which achieves the reduction of the diameter of the ignition device and the cost reduction. 
     Moreover, since the slit  15  is provided in a section surrounding the center core  33  in the case  1 , the loss stemming from a ring current developing due to a magnetic flux variation is avoidable. 
     Still moreover, since the windings  31 ,  32  and others of the ignition coil  3  are covered with the metal-made case  1  connected through the cylinder head to the ground, the ignition noises generated in the interior of the ignition coil  3  are shielded by the case  1 , thus resulting in less leakage thereof to the external. 
     (Another Embodiment) 
     Although in the above-described embodiment the earth electrode  23  is provided as a member distinct from the case  1 , it is also appropriate that, without constructing the earth electrode  23  as the member distinct from the case  1 , the case  1  itself is used as an earth electrode to make discharge between a combustion chamber side end portion  16  of the case  1  and the center electrode  22 . 
     In addition, although in the above-described embodiment the secondary winding  32  is located on the inner circumferential side and the primary winding  31  is located on the outer circumferential side, the present invention is not limited to this, but it is also acceptable that the secondary winding  32  is put on the outer circumferential side and the primary winding  1  is put on the inner circumferential side. 
     Still additionally, although in the above-described embodiment a preload is applied to the pressure detecting element  4  by tightening the bolt  8 , it is also possible that a pressing member having no screw structure is used in place of the bolt  8  so that the pressing member is put in the case  1  under pressure, or the case  1  is caulked after the pressing member is inserted thereinto, for applying a preload to the pressure detecting element  4 . Yet additionally, it is also acceptable that, after the pressing member is inserted into the case  1 , the pressing member is welded with the case  1  in a state where a preload is given to the pressure detecting element  4 . 
     It should be understood that the present invention is not limited to the above-described embodiments, and that it is intended to cover all changes and modifications of the embodiments of the invention herein which do not constitute departures from the spirit and scope of the invention.