JP3109301B2 - Method of forming a capacitor for detecting ignition voltage in a spark plug cap - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming an ignition voltage detecting capacitor on a spark plug cap for detecting misfire during operation of a spark ignition type internal combustion engine such as a gasoline engine. It is.

[0002]

2. Description of the Related Art As is well known, in a spark ignition type internal combustion engine such as a gasoline engine, a high voltage generated by an ignition coil (ignition coil) is applied to a spark plug of each cylinder, and a spark between electrodes of the spark plug is generated. The discharge ignites the fuel mixture sucked into the combustion chamber of each cylinder,
Burning occurs. In the ignition / combustion process of such an internal combustion engine, a phenomenon in which combustion of the fuel mixture is not performed normally, that is, misfire may occur for some reason. The causes of such misfires are broadly classified into those caused by the fuel system and those caused by the ignition system. The misfire caused by the fuel system is caused by a lean or rich fuel mixture, and is a phenomenon in which spark discharge occurs between the electrodes of the ignition plug but is not ignited by the fuel mixture. On the other hand, the latter type of misfire caused by the ignition system is a phenomenon in which normal spark discharge does not occur due to fogging of an electrode of a spark plug or abnormality of an ignition circuit.

If a misfire occurs during the operation of the internal combustion engine, not only does the operating performance deteriorate, but also the fuel consumption deteriorates, and further, the afterburning of the unburned gas in the exhaust system adversely affects the exhaust gas purifying device and the like. And other problems occur. In addition, once misfire has occurred, it means that inconvenience such as improper adjustment or failure has occurred in the fuel system or the ignition system. Therefore, it is necessary to avoid leaving the misfire occurring. Therefore, recently, there is a strong demand for the development of a device for immediately detecting a misfire when it has occurred.

[0004] As one type of a misfire detection device proposed in the past, there is a mis-spark detection device disclosed in Japanese Patent Application Laid-Open No. 52-118135. This Miss Spark Detector
As shown in FIG. 7, a conductor 51 is wound around the outer periphery of the high voltage cord 50 of the engine ignition system to form a detection capacitor (a kind of capacitance probe) 52 using the insulating coating 50A of the high voltage cord 50 as a dielectric. A voltage dividing capacitor 53 is connected between the detecting capacitor 52 and the ground, and the detecting voltage is applied to the conductive core 50B of the high-voltage cord 50 (secondary voltage of the ignition coil). A voltage is induced between both electrodes of the detection capacitor 52 by the capacitance of the capacitor 52, and the induced voltage is electrostatically divided by the detection capacitor 52 and the voltage dividing capacitor 53, so that a voltage between both ends of the voltage dividing capacitor 53 is obtained. (Divided voltage) is sent to the electronic circuit 54 for signal processing and determination as a detection voltage, and the ignition voltage waveform becomes a normal spark discharge. If time and spark discharge does not occur using a different out with (miss during spark) is to determine the occurrence of mistakes spark. Therefore, the above-described proposed device detects a misfire among the misfire phenomena particularly when no spark discharge occurs due to the ignition system.

On the other hand, the present applicant has already filed Japanese Patent Application No. 3-326.
No. 509 proposes a misfire detection device for an internal combustion engine. This misfire detection device detects the ignition voltage from the high voltage cord of the ignition system or the like based on the electrostatic partial pressure in the same manner as described above, and when the spark discharge is performed by the spark plug, the ignition voltage waveform is normal combustion and normal combustion. The misfire caused by the fuel system is determined and detected by utilizing the difference from the case where no misfire has occurred.

As described above, in the conventional misfire detecting device, as a means for detecting the ignition voltage, a strip-shaped or plate-shaped conductor is wound around the outer periphery of the high-voltage cord of the ignition system, and the conductor and the high-voltage cord are connected. In general, a so-called capacitance probe in which a detection capacitor having an insulating coating of a high-voltage cord as a dielectric is formed between the core wire and the core wire is used. However, high-pressure cords generally have flexibility and elasticity and are easily vibrated, and are susceptible to changes in surrounding humidity and water, oily dirt, dust, and the like. When the detection capacitor is formed by winding the above conductor, the capacitance is apt to change due to such misalignment due to mechanical vibration, change in humidity, wetness of water, or oil or dust. A slight change in capacitance is not a problem if it is merely to confirm the ignition voltage.However, when determining misfire, it is generally necessary to accurately detect even the voltage waveform. If a change in capacitance occurs, the detected voltage waveform deteriorates, and there is a possibility that misfire cannot be reliably determined.

Further, it is actually quite troublesome to securely mount and fix the conductor to form the detection capacitor on the insulating coating of the flexible and elastic high-voltage cord, and the maintenance thereof is difficult. However, there are also problems that require considerable effort.

On the other hand, the insulating coating of the high-voltage cord is generally made of synthetic rubber, but the rubber is liable to be deteriorated by heat, oil stains, etc. Therefore, when a conductor is wound around the outer periphery of the high-voltage cord to form a detection capacitor. In addition, not only does the capacitance change over time due to the deterioration of the insulation coating, but also the electrical insulation tends to decrease, in which case a high leakage voltage constitutes the detection capacitor. In addition to the conductor, the leak voltage may be led to the electronic circuit portion of the misfire detection device, which may cause a failure or malfunction of the electronic circuit portion. To more accurately detect the ignition voltage waveform by the detection capacitor, the conductor forming the detection capacitor should be as close as possible to the conductive core of the high-voltage cord, and the capacitance of the detection capacitor However, the insulation of the high-pressure cord made of synthetic rubber is inferior in insulation properties, and the insulation is easily deteriorated by corona discharge. Therefore, it is not sufficient to improve the detection accuracy of the ignition voltage waveform.

In order to solve the above-mentioned problems, the present inventors have already disclosed in Japanese Patent Application No. 4-56395.
It has been proposed to provide a conductor for forming a capacitor for detecting an ignition voltage in a spark plug cap inserted in a secondary circuit of an ignition system. Specifically, the above proposal is for a spark plug cap fixed to cover a terminal portion of a spark plug of an internal combustion engine, and a conductive material for high voltage conduction for guiding a high voltage for spark discharge to the terminal portion. A spark plug cap in which a high-voltage conductive conductor is surrounded by an insulator, at a position on the outer peripheral side of the high-voltage conductive conductor,
A conductor for ignition voltage detection is disposed at a predetermined distance from the surface of the high-voltage conductive conductor, and is integrated with the insulator. The gist is that a detection capacitor for detecting an ignition voltage is formed between the conductor and the conductor.

[0010] According to the above proposed structure, the detecting conductor constituting the detecting capacitor for detecting the ignition voltage for detecting the misfire in the spark ignition type internal combustion engine has a structurally stable spark plug cap. In addition to its excellent structural durability, it is detected by mechanical vibration as in the conventional case where a conductor for detection is provided on the high voltage cord of the ignition system. The detection conductor is not displaced or affected by humidity, water, oil, or dust, so that the capacitance of the detection capacitor will not change due to these. The ignition voltage can always be accurately detected up to its waveform, so that the presence or absence of a misfire can be accurately determined. Vinegar effects such as that becomes unnecessary can be obtained.

[0011]

In the structure in which the ignition voltage detecting capacitor is integrally formed in the spark plug cap as described above, various structures are required in comparison with the conventional structure in which the detecting capacitor is formed in a high-voltage cord. Although it has an excellent merit, there are the following problems when this structure is actually applied to a spark plug cap in consideration of mass productivity.

That is, the simplest method for producing a spark plug cap having the structure described above is as follows.
When an insulator (body) surrounding the outer periphery of the high-voltage conductor is molded with an insulating resin, a method of embedding the detection conductor at the same time in the resin is conceivable. However, in this case, it is necessary to float the detection conductor in the space in the mold for molding, and the molding is performed. In the actual mass production process, such molding is extremely difficult.

The present invention has been made in view of the above circumstances, and a method for easily forming a capacitor for detecting an ignition voltage without impairing mass productivity in a process of manufacturing a spark plug cap on an actual mass production scale. The purpose is to provide.

[0014]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, according to the present invention, basically, after forming an insulator body surrounding a high-voltage conductive conductor in a spark plug cap, The detection conductor is formed by winding a conductive plate material.

Specifically, the method according to the first aspect of the present invention surrounds a high-voltage conductive conductor for guiding a high voltage from an ignition coil to a spark plug, and surrounds the high-voltage conductive conductor. A spark plug cap having an insulator body;
In forming the ignition voltage detection capacitor, a circumferentially continuous concave portion is formed in advance on the outer periphery of the insulator body at a position corresponding to the high-voltage conductive member, and the concave portion is formed on the bottom surface of the concave portion. A detection plate is formed by winding a continuous plate-shaped conductive plate along the circumferential direction, and thereafter, an insulating material is arranged in the recess so as to cover the outer periphery of the detection conductor, A detection capacitor is formed between the detection conductor and the high-voltage conductor.

According to a second aspect of the present invention, in the method according to the first aspect of the present invention, when the insulating material is disposed in the recess, the insulating material is filled into the recess by molding. Things.

The method according to the third aspect of the present invention provides the method according to the first aspect.
In the method according to the invention, before disposing the insulating material in the concave portion, a pair of semi-annular halves made of an insulating material are prepared in advance, and the pair of halves are fitted from both sides of the concave portion. It is characterized in that

According to a fourth aspect of the present invention, in the method of the first aspect of the present invention, when the insulating material is disposed in the recess, the insulating material is shielded so as to surround the conductor for detection. It is characterized by providing a member.

[0019]

According to the method of the present invention, a continuous recess in the circumferential direction is previously formed on the outer periphery of a body (insulator body) made of an insulating material surrounding the periphery of the conductor for high voltage conduction. This recess may be formed at the same time as the molding of the insulator body, or may be formed by cutting after molding.

A continuous plate-shaped conductive plate is wound along the circumferential direction on the bottom surface of the concave portion on the outer periphery of the insulator body, and the wound conductive plate is used as a detection conductor. . Thereafter, an insulating material is disposed in the recess so as to cover the outer periphery of the wound conductive plate material, that is, the detection conductor.

As described above, the detecting conductor formed by winding the conductive plate material surrounds the outside of the high-voltage conducting conductor in the spark plug cap in a ring through a part of the insulator body. Will be. Therefore, a detection capacitor is formed between the high-voltage conductor and the detection conductor.

In the spark plug cap having the ignition voltage detecting capacitor formed as described above, the high voltage current for spark discharge introduced from the ignition coil causes the high voltage conductive material in the spark plug cap to be discharged. If it flows, a high voltage is induced in the detection conductor by the capacitance between the high-voltage conductor and the detection conductor. Therefore, the voltage is taken out as a detection voltage by electrostatic partial pressure or the like, subjected to signal processing as appropriate, and compared with a reference signal (usually a signal corresponding to a detection voltage waveform during normal combustion) to determine the ignition state. It can be determined whether or not there is.

Here, the insulator body surrounding the conductor for high-voltage conduction can be easily and easily formed by molding without applying a special molding method. In addition, the operation of forming a conductor for detection by winding a conductive plate material around the inner surface of the concave portion on the outer periphery of the insulator body can be performed very easily and easily, and furthermore, it is possible to cover the outer periphery of the conductor for detection. The work of providing an insulating material on the substrate can be easily performed by, for example, molding or fitting an insulating material molded body. Therefore, the ignition voltage detecting capacitor can be simply and easily formed on the ignition plug cap. In particular, in the case of the method according to the second aspect of the present invention, when the insulating material is disposed in the concave portion of the insulator body so as to cover the outer periphery of the wound conductive plate material, that is, the detection conductor, the insulating material is molded. Therefore, the insulating material portion in the concave portion can be easily formed by a normal molding method.

In the case of the method according to the third aspect of the present invention, a pair of half-rings made of an insulating material formed in a half-ring shape in advance are simply fitted from both sides of the recess, so that the insulation in the recess is easily formed. Material portions can be formed.

In the method according to the fourth aspect of the present invention, the detection conductor is electrically shielded from the outside. In other words, the detection capacitor consisting of the detection conductor and the high-voltage conductor in the spark plug cap is electrically shielded. Therefore, in this case, even if another conductive member is present near the spark plug cap, the capacitance of the detection capacitor changes due to a change in the distance between the conductive member and the conductive member. It is possible to effectively prevent the detection capacitor from picking up noise from the conductive member and adversely affecting the detection accuracy of the ignition voltage waveform, thus further improving the detection accuracy of the ignition voltage waveform. Can be planned.

[0026]

1 and 2 show a first embodiment of the present invention. In this embodiment, an ignition coil is provided in a one-to-one correspondence with the ignition plug of each cylinder of the engine, and the secondary voltage of the ignition coil is supplied directly to the ignition plug without passing through a distributor. An example is shown in which the present invention is applied to an ignition coil integral coupling type spark plug cap which is applied to an ignition system called (distributorless ignition type) or DI type (direct ignition type).

FIG. 1 shows an ignition plug cap 1 in a state before a detection capacitor is formed, together with an ignition coil portion 2 and an ignition plug 3, and also shows a conductive plate 10. In FIG. 1, an ignition coil section 2 is fixed to an upper end of a spark plug cap 1. The spark plug cap 1 is integrally formed of a hard resin having excellent heat resistance and electrical insulation such as polybutylene terephthalate (PBT) so as to form a hollow cylinder as a whole. The integrally formed hard resin will be described later. The insulator body 4 is formed. The upper part of the hollow part along the axial direction of the spark plug cap 1 is an upper insertion chamber 1A into which the secondary output terminal shaft 2A of the ignition coil part 2 is inserted. In the center of the hollow part, 2
A shaft-shaped high-voltage conductive conductor 6 that is in electrical and mechanical contact with the secondary output terminal shaft 2A via a conductive spring 5 is inserted. Further, a lower portion of the hollow portion serves as a cap chamber 1B which covers and is fixed to the upper terminal portion 3A of the ignition plug 3. The lower end of the conductor 6 for high voltage conduction is in contact with the terminal portion 3A of the ignition plug 3. Accordingly, the high-voltage conductive conductor 6 applies a high voltage for spark discharge to the secondary output terminal shaft 2A of the ignition coil unit 2.
, And guides it to the terminal portion 3A of the ignition plug 3. The periphery of the high-voltage conductor 6 is surrounded by the insulator body 4 made of the above-described hard resin.

Further, a concave portion 8 which is continuous in the circumferential direction is formed on the outer periphery of a portion of the insulator body 4 where the conductor 6 for high voltage conduction is located inside. The recess 8 is formed such that its inner surface has a U-shaped cross section. In the insulator body 4, a signal conductor 9 made of a copper wire, a copper strip or the like having a tip 9 </ b> A exposed at the bottom of the corner of the recess 8 is embedded at a position above the recess 8. .

The entire insulator body 4 of the ignition plug 1 as described above can be integrally formed by molding, and the formation of the concave portion 8 and the embedding of the signal conductor 9 are also performed by the molding process. Can be done simultaneously.

On the other hand, the conductive plate material 10 is wound around the outer peripheral surface of the concave portion 8 of the insulator body 4 as described above, and is made of a good conductive thin plate or foil such as copper or aluminum. The length L of the conductive plate 10 is substantially equal to the circumference of the inner surface of the recess 8, and the width W is determined to be equal to or slightly smaller than the width of the recess 8. A cutout 11 is formed at the edge of the conductive plate 10 in the width direction to fit with the exposed front end 9A of the signal conductor 9.

The conductive plate material 10 as described above is wound around the bottom surface of the concave portion 8 of the insulator body 4, and furthermore, an insulating material 12 such as a resin such as epoxy resin or rubber or the like is further applied thereon.
Is molded. FIG. 2 shows a state after the conductive plate material 10 is wound and the insulating material 12 is molded.

As shown in FIG. 2, by winding a conductive plate material 10 on the bottom surface of the recess 8, a portion of the insulator body 4 is used to surround the high voltage conductive conductor 6 in the spark plug cap 1. An annular (or notched annular) detection conductor 13 is formed to surround the detection conductor 13. And the high voltage conductive material 6
A capacitor 14 for detecting an ignition voltage is formed between the capacitor 14 and the detection conductor 13. Further, the notch 11 of the conductive plate 10 constituting the detection conductor 13
(Refer to FIG. 1), the exposed end portion 9A of the signal conductor 9 is provided.
Are brought into close contact with each other, and electrical continuity between the distal end portion 9A and the conductive plate material 10 constituting the detection conductor 13 is performed.
Therefore, the voltage (detection voltage) induced in the detection conductor 13 can be guided to an external signal processing circuit or the like by the signal conductor 9.

The insulating material 12 is essentially composed of the conductive plate material 10.
What is necessary is just to fill in the recessed part 8 so that it may cover and electrically insulate the detection conductor 13 made of. It is preferable that the outer peripheral surface of the insulating material 12 is usually set to the same surface position as the outer peripheral surface of the insulator body 4.

FIGS. 3 to 6 show a second embodiment of the present invention.
That is, the insulating material 12 arranged in the concave portion 8 of the insulator body 4 is constituted by a pair of half bodies 12A and 12B, and the shielding member 15 is provided inside the insulating material 12.
An embodiment in which A and 15B are provided will be described.

FIG. 3 shows a main part of a spark plug cap 1 used in the second embodiment together with a conductive plate 10. In FIG. 3, a concave portion 8 is formed on the outer periphery of the insulator body 4.
1 and the tip 9A of the signal conductor 9 embedded in the insulator body 4 is exposed in the recess 8 as in the case of FIG. In the case of this embodiment, similarly to the signal conductor 9 described above, the conductor 16 for ground potential made of a copper wire, a copper strip, or the like is placed on the side of the insulator body 4 symmetrical to the signal conductor 9. Embedded. Further, the tip 16A of the ground potential conductor 16 is also slightly exposed in the recess 8. On the other hand, in the conductive plate material 10, in addition to the notch 11 similar to the case of FIG. 2, a size larger than the size of the tip 16 A is formed at a position corresponding to the exposed tip 16 A of the ground potential conductor 16. Cut-out part 17
A and 17B are formed.

FIGS. 4 and 5 show a pair of half bodies 12A, which are fitted into the recesses 8 of the insulator body 4 in the second embodiment.
12B, and the halves 12A and 12B
B has a semi-annular (semi-cylindrical) shape, and the inner diameter (curvature diameter of the concave curved surface) is substantially equal to the outer diameter of the conductive plate material 10 wound around the concave portion 8. The diameter (the radius of curvature of the convex curved surface) is made substantially equal to the diameter of the outer peripheral portion of the insulator body 4. Each half body 12A, 1
2B is a semi-circular (semi-cylindrical) made of a good conductive material such as copper or aluminum in an insulating material 12 made of the same hard resin (for example, PBT) or another resin as the material of the insulator body 4 or rubber. Shield members 15A, 15B
Are molded integrally with each other. One end of each of the semi-annular shield members 15A, 15B has an insulating material 1
Projection portions 18A and 18B slightly projecting from the end surface position of the insulating material 12 are formed, and small recesses 19A and 19B slightly drawn from the end surface position of the insulating material 12 are formed at the other end portion. The protruding portions 18A and 18B are configured to fit into the small recesses 19A and 19B on the other end side, respectively. In the insulating material 12 of one half body 12B of the pair of half bodies 12A and 12B, a cut portion 20 is formed at a position corresponding to the exposed front end portion 16A of the ground potential conductor 16 described above. A part of the semi-annular shield member 15B is exposed at the cut portion 20. In each end face of each half body 12A, 12B, a portion of the insulating material 12 is extended outward in the radial direction to form ribs 21A, 21B; 22A, 22B. The ribs 21A, 22A at one end of the bodies 12A, 12B are provided with locking claws 23A, 23B.
In the ribs 21B, 22B on the other end side of each half body 12A, 12B, engagement holes 24A, 24B with which the locking claws 23A, 23B are engaged are formed. I have.

The pair of half bodies 12A and 12B having the above-described structure and shape are used as the semi-annular shield members 15A and 15A.
5B is formed by integrally molding the insulating material 12 with the insulating material 12.

In assembling the structure of the present invention using the above-described conductive plate material 10 and the half bodies 12A and 12B, first, the conductive plate material 10 is wound around the bottom surface of the concave portion 8 of the insulator body 4, The detection conductor 13 is formed, and then a pair of half bodies 12A and 12B are fitted from both sides of the concave portion 8. FIG. 6 shows a state after the conductive plate member 10 is wound and the half bodies 12A and 12B are fitted.

When fitting the pair of half bodies 12A and 12B from both sides of the concave portion 8, the locking claws 23A and 23B are engaged with the engagement holes 24A and 24B, and the left and right half bodies 12A and 23B are engaged.
A and 12B are connected. At this time, the semi-annular shield members 15 of the left and right half bodies 12A and 12B are also provided.
A and 15B are also protrusions 18A and 1 on one end side, respectively.
8B is fitted into the small recesses 19A, 19B on the other end side, and the two are electrically connected to each other. These semi-annular shield members 15A, 15B surround the detection conductor 13 as a whole. This constitutes the shield member 25. Further, the exposed end portion 16A of the conductor 16 for the ground potential is fitted into the cut portion 20 of one half body 12B,
The ground potential conductor tip 16A and the semi-annular shield member 15A of the half body 12B are electrically connected. Therefore, the semi-annular shield members 15A and 15B are kept at the ground potential from the outside via the ground potential conductor 16, thereby electrically connecting the detection capacitor 14 composed of the detection conductor 13 and the high-voltage conductor 6 to the detection capacitor 14. Can be shielded. The exposed end portion 16A of the ground potential conductor 16
Are located inside the cutouts 17A and 17B of the conductive plate 10 constituting the detection conductor 13, and are set so that they do not contact each other.

As shown in FIG. 6, when the detecting capacitor 14 is shielded, as described above, even if another conductive member exists close to the vicinity of the spark plug cap. , The capacitance of the detection capacitor changes due to a change in the distance between the conductive member and
It is possible to effectively prevent the detection capacitor from picking up noise from the conductive member and adversely affecting the detection accuracy of the ignition voltage waveform, thereby further improving the detection accuracy of the ignition voltage waveform. Can be.

In the example shown in FIGS. 3 to 6, the left and right half bodies 12A and 12B are connected and held by the engagement between the locking claws 23A and 23B and the engagement holes 24A and 24B as described above. However, in some cases, the half-body 12
A and 12B may be joined to the outer peripheral surface of the conductive plate 10 constituting the conductor 13 for detection by an adhesive or the like.

On the contrary, when the pair of half bodies 12A, 12B can be fixed and held sufficiently by an adhesive or pressure welding, the locking claws 23A, 23B and the engaging holes 24A, 24B are omitted. Can also.

Further, the present invention can of course be applied to a spark plug cap used in an ignition system having a distributor, that is, a spark plug cap in which an ignition coil is not integrally connected.

[0044]

According to the method of forming a capacitor for detecting an ignition voltage in a spark plug cap according to the present invention, a recess is previously formed on the outer periphery of an insulator body of a spark plug, and a conductive plate is wound around the recess. By simply placing an insulating material on the outer periphery of the ignition plug, a detection capacitor for detecting the ignition voltage can be formed. Therefore, the detection capacitor can be easily and easily formed on the ignition plug cap, and mass production is possible. Even in the production of a spark plug cap on a suitable scale, a detection capacitor can be formed with high productivity without particularly impairing mass productivity.

According to the method of the second aspect of the present invention, a general molding method can be applied to disposing the insulating material in the concave portion, so that the insulating material portion in the concave portion is extremely formed. Simple and easy.

According to the method of the third aspect of the present invention, the insulating material portion in the concave portion can be formed only by fitting a pair of half members made of the insulating material. The formation of the part is simple and easy.

Further, according to the method of the present invention, a structure in which the periphery of the detection capacitor is shielded can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a vertical sectional front view showing an ignition plug cap used in a method according to a first embodiment of the present invention, together with an ignition coil portion, an ignition plug, and a conductive plate material before winding.

FIG. 2 is a longitudinal sectional front view showing a state in which a detection capacitor is formed on the spark plug cap shown in FIG. 1 together with an ignition coil unit and a spark plug according to the first embodiment of the present invention.

FIG. 3 is an enlarged vertical sectional front view showing a main part of a spark plug cap used in a method according to a second embodiment of the present invention, together with a conductive plate material before winding.

FIG. 4 is an enlarged vertical sectional front view of a pair of halves used in the method according to the second embodiment of the present invention.

FIG. 5 is a cross-sectional plan view showing a pair of halves used in the method according to the second embodiment of the present invention, cut along line VV in FIG. 4;

FIG. 6 is an enlarged vertical sectional front view showing a state where a detection capacitor is formed on the spark plug cap shown in FIG. 3 according to a second embodiment of the present invention.

FIG. 7 is a schematic diagram showing an example of a conventional misfire detection device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ignition plug cap 2 Ignition coil part 3 Ignition plug 4 Insulator body 6 High voltage conductor 8 Depression 10 Conductive plate material 12 Insulating material 12A, 12B Half body 14 Ignition voltage detection capacitor 15A, 15B Semi-annular shield member

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Takashi Hisagi 1-4-1 Chuo, Wako-shi, Saitama Prefecture Honda R & D Co., Ltd. (56) References JP-A-3-264776 (JP, A) JP-A Heisei 4-314969 (JP, A) Jikai Sho 49-127645 (JP, U) JP-B 48-26688 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) F02P 17/12 F02P 13/00 303 F02P 15/00 302

Claims (4)

(57) [Claims] 1. A spark plug cap comprising: a high-voltage conductive conductor for guiding a high voltage from an ignition coil to a spark plug; and an insulator body surrounding the high-voltage conductive conductor. In forming the ignition voltage detecting capacitor, a circumferentially continuous concave portion is formed in advance on the outer periphery of the insulator body at a position corresponding to the high-voltage conductive member. A conductive plate in the form of a continuous plate is wound around the bottom surface along the circumferential direction to form a conductor for detection, and thereafter, an insulating material is disposed in the recess so as to cover the outer periphery of the conductor for detection. Forming a capacitor for detecting an ignition voltage in a spark plug cap, wherein a capacitor for detection is formed between the conductor for detection and the conductor for high voltage conduction. 2. The ignition voltage detecting capacitor for an ignition plug cap according to claim 1, wherein the insulating material is filled in the concave portion by molding when the insulating material is disposed in the concave portion. Forming method. 3. When arranging the insulating material in the recess, a pair of half-rings made of an insulating material are prepared in advance, and the pair of halves are fitted from both sides of the recess. 2. The method for forming an ignition voltage detecting capacitor in an ignition plug cap according to claim 1, wherein: 4. The spark plug cap according to claim 1, wherein when arranging the insulating material in the recess, a shield member is provided so as to surround the detection conductor in the insulating material. Of forming an ignition voltage detecting capacitor in the present invention.