JP2008218204A - Multi-point ignition plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a breakdown voltage in a multi-point ignition plug having a plurality of ignition gaps. <P>SOLUTION: At least the ignition gap 13a formed between a plus electrode 6 and an intermediate electrode 7a, and the ignition gap 13d formed between the intermediate electrode 7c and an earth electrode 8 are electrically connected in series via a plus electrode 6, the intermediate electrodes 17a to 17d, and the earth electrode 8, and since a part retained by an insulating part 4 of the intermediate electrodes 7a to 7c is opposed to the main body fitting 5 by pinching one part of the insulating part 4, a capacitor C is formed between the intermediate electrodes 7a to 7c and the main body fitting 5. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

The present invention relates to a multipoint spark plug having a plurality of spark gaps.

  In an ultra-high speed engine that requires a high combustion rate, or a lean burn engine that has a slow spark propagation speed in addition to unstable ignition, it is essential to ensure ignition and increase the initial flame propagation speed.

  In this regard, Japanese Patent Laid-Open No. 2006-140072 discloses an ignition plug in which a plurality of ignition electrodes are arranged at the tip, and the plurality of ignition electrodes are electrically connected in series with an ignition gap therebetween. If this spark plug is used, the air-fuel mixture can be simultaneously ignited from a plurality of ignition gaps to improve the ignitability and realize high-speed combustion.

JP 2006-140072

  However, since the spark plug having the above-described configuration is configured to discharge simultaneously from a plurality of ignition gaps, there is a problem that an ignition coil having a high breakdown voltage and a large capacity is required.

  The present invention has been made in view of such a technical problem, and an object of the present invention is to lower a breakdown voltage in a multipoint ignition plug having a plurality of ignition gaps.

  A multipoint spark plug according to the present invention includes a terminal, a main conductor electrically connected to the terminal, a lever portion that holds the main conductor inside, and a main body that is externally fitted to a tip portion of the lever portion. A metal fitting, a positive electrode that is electrically connected to the main conductor and exposed from the tip of the lever portion, a part is held inside the lever portion, and the remaining portion is exposed from the tip of the lever portion One or two or more intermediate electrodes, and a ground electrode connected to the main body metal fitting and exposed from the tip of the insulator part.

  An ignition gap formed between at least the positive electrode and the intermediate electrode and an ignition gap formed between the intermediate electrode and the ground electrode are electrically connected via the positive electrode, the intermediate electrode, and the ground electrode. Are connected in series, and a portion of the intermediate electrode held by the insulator portion is opposed to the body metal fitting with a part of the insulator portion interposed therebetween, thereby forming a capacitor between the intermediate electrode and the body metal fitting. Is done.

  In the multi-point spark plug according to the present invention, discharge occurs in all ignition gaps by one energization, but the breakdown voltage causes discharge from a single ignition gap equal to the sum of the gaps of each ignition gap. The voltage is lower than that required for

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  1A is a partial cross-sectional view of a spark plug 1 according to the present invention, FIG. 1B is a bottom view showing the tip surface of the spark plug 1, and FIG. 2 is a view taken in the direction of the arrow X in FIG. .

  The spark plug 1 has a terminal 2, main conductors 3 a and 3 b electrically connected to the terminal 2 and extending in the plug axis direction, and a hole having substantially the same diameter as the main conductors 3 a and 3 b. A lever part 4 that holds 3b, a body fitting 5 that is externally fitted to the lower half of the lever part 4, a positive electrode 6 and three intermediate electrodes 7a to 7c that are held by the lever part 4, and A ground electrode 8 connected to the lower end and a gasket 9 fitted to the body fitting 5 are provided. An electric resistor 10 of about 5 kΩ is interposed between the main conductors 3a and 3b. The electric resistor 10 is for suppressing radio noise generated when the spark plug 1 is discharged.

  A hexagonal portion 5 a and a screw portion 5 b are formed on the outer periphery of the main body metal 5. The spark plug 1 is attached to the cylinder head by attaching a plug wrench to the hexagonal portion 5a and screwing it into a plug hole formed in the cylinder head. FIG. 3 shows a case where the spark plug 1 is attached to a four-valve engine provided with two intake valves 11 and two exhaust valves 12 per combustion chamber. As shown in this figure, it is advantageous to arrange the spark plug 1 at the center of the combustion chamber as much as possible in order to reduce the propagation distance of the flame to the periphery of the combustion chamber.

  From the tip of the spark plug 1, a plus electrode 6, three intermediate electrodes 7 a to 7 c and a ground electrode 8 protrude. Between the positive electrode 6 and the intermediate electrode 7a closest to the positive electrode 6, between the intermediate electrodes 7a to 7c, and between the intermediate electrode 7c closest to the ground electrode 8 and the ground electrode 8, ignition gaps 13a to 13d are respectively provided. It is formed. The electrodes are electrically connected in series via the ignition gaps 13a to 13d, and the ignition gaps 13a to 13d are arranged at equal intervals on the same circumference with the central axis of the spark plug 1 as the center.

  The interval between the respective ignition gaps 13a to 13d is preferably set to be larger as the downstream ignition gap closer to the ground electrode 8. Thereby, it becomes easy to discharge from the plus electrode 6 to the intermediate electrode 7a closest to the plus electrode 6, and the discharge (leakage) from the plus electrode 6 to the body fitting 5 and the ground electrode 8 can be suppressed.

  In this example, the entire lower ends of the plus electrode 6, the intermediate electrodes 7a to 7c and the ground electrode 8 are exposed. However, it is not necessary to expose the entire lower end of each electrode. It suffices that only the part to be exposed is exposed.

  Further, a depression 14 for adjusting the heat value is formed at the center of the front end surface 1a of the spark plug 1. If the depth of the recess 14 is reduced, the heat of the spark plug 1 is improved, and the heat value of the spark plug 1 can be increased, that is, a cold type can be obtained. Conversely, if the depth of the recess 14 is increased, the area exposed to the combustion gas is increased, the heat value is lowered, and a burn-up type in which carbon is difficult to accumulate in the ignition gaps 13a to 13d can be obtained.

  The insulator part 4 and the main body metal fitting 5 are joined by caulking the upper edge part 5c of the main body metal fitting 5. Between the main body metal fitting 5 and the insulator part 4, cushioning seal members 16 a to 16 c and a spacer 17 are interposed to prevent the combustion gas from leaking outside through the gap in the spark plug 1.

  Between the hexagonal part 5a and the screw part 5b of the main body metal fitting 5, the curved part 5d which curved the outer peripheral surface of the main body metal fitting 5 in the plug axial direction is provided. The curved portion 5d is for adjusting the axial length of the metal shell 5, but when the caulking force of the upper edge portion 5c is too strong, the caulking force of the upper edge portion 5c is increased by caulking the curved portion 5d. Can be relaxed.

  The lever portion 4 is configured by combining a main body lever 4a shown in FIG. 4 and a cylindrical lever 4b whose upper and lower sides are opened as shown in FIG. The main body insulator 4a includes a body part 41a, a head part 41b connected to the body part 41a, and a leg part 41c connected to the body part 41a. A corrugation 43 is formed on the head 41b to prevent discharge that occurs along the surface of the insulator 4 (see FIG. 1). The leg portion 41 c has a smaller diameter than the body portion 41 a and has a round bar shape having the same diameter as the inner diameter of the cylindrical insulator 42. When the leg portion 41c is inserted inside the cylindrical insulator 42 and the main body insulator 41 and the cylindrical insulator 42 are combined, the lower surface of the leg portion 41c is exposed from the lower opening of the cylindrical insulator 42, and the tip surface of the spark plug 1 1a is constituted.

  Four electrode holding grooves 44, 45a to 45c extending in the axial direction from the distal end side are formed at equal intervals on the outer peripheral surface of the leg portion 41c. The electrode holding groove 44 is longer than the other electrode holding grooves 45a to 45c, extends to the center in the axial direction of the leg portion 41c, and is connected to a lateral hole 46 formed in the center in the axial direction of the leg portion 41c and extending in the radial direction. The lateral hole 46 is connected to the hole 47 for holding the main conductors 3a and 3b extending in the axial direction at the center of the main body insulator 41. The remaining three electrode holding grooves 45a to 45c extend from the bottom of the leg portion 41c to a position about ¼ and are connected to a circular recess 48 formed on the outer peripheral surface in the middle of the leg portion 41c.

  As shown in FIG. 6, the plus electrode 6 includes an electrode main body 61 extending in the plug axis direction, and a locking portion 62 extending from the upper end of the electrode main body 61 in a direction perpendicular to the electrode main body. The locking part 62 has a semicircular cross section whose upper side is flat. The plus electrode 6 is made of a heat-resistant alloy containing a large amount of nickel, and platinum or iridium is welded to the tip 63 of the electrode body 61 serving as a discharge part. The tip portion 63 is bent laterally with respect to the electrode body 61, and the shortest distance between the plus electrode 6 and the ground electrode 8 is made larger than the sum of the intervals of all the ignition gaps 13 a to 13 d, thereby The ground electrode 8 is prevented from leaking (discharging).

  The positive electrode 6 is attached to the leg portion 41c by inserting the locking portion 62 having a semicircular cross section into the lateral hole 46 of the leg portion 41c and by fitting the electrode body 61 into the electrode holding groove 44 of the leg portion 41c. . At this time, the surface of the electrode main body 61 is curved with the same radius of curvature as the outer peripheral surface of the leg portion 41c, and the electrode main body 61 has a thickness equal to the depth of the electrode holding groove 44. It is stored without.

  As shown in FIG. 7, the intermediate electrodes 7 a to 7 c include an inverted T-shaped electrode body 71 and a circular locking portion 72 connected to the upper end of the electrode body 71. Similarly to the plus electrode 6, the intermediate electrodes 7a to 7c are made of a heat-resistant alloy containing a large amount of nickel, and platinum and iridium are welded to both sides 74a and 74b of the distal end portion 73 of the electrode body serving as a discharge portion.

  The electrode body 71 has a facing surface 75 that curves in the circumferential direction of the plug facing the body fitting 5. The area (width, length) of the facing surface 75 is made as large as possible within a range in which insulation can be ensured between adjacent electrodes, and the capacitance of the capacitor C formed between the intermediate electrodes 7a to 7c and the body fitting 5 is increased. Secure enough.

  The intermediate electrodes 7a to 7c accommodate the circular engaging portion 72 in the circular concave portion 48 of the leg portion 41c, and also accommodate the electrode main body 71 in the electrode holding grooves 45a to 45c of the leg portion 41c. It is attached to. Since the surface of the electrode body 71 is curved with the same radius of curvature as the outer peripheral surface of the leg portion 41c, and the electrode body 71 has a thickness equal to the depth of the electrode holding grooves 45a to 45c, the intermediate electrodes 7a to 7c are formed on the leg portion 41c. It is stored without gaps.

  The leg portion 41 c on which the plus electrode 6 and the intermediate electrodes 7 a to 7 c are mounted is inserted into the cylindrical insulator 42. Thus, the plus electrode 6 and the intermediate electrodes 7 a to 7 c are sandwiched between the main body insulator 41 and the cylindrical insulator 42, and the plus electrode 6 and the intermediate electrodes 7 a to 7 c are fixed to the insulator portion 4. In addition, the fixing method of the plus electrode 6 and the intermediate electrodes 7a to 7c is not limited thereto, and an insulating and heat resistant adhesive such as water glass may be used.

  Next, the operation at the time of discharging of the spark plug 1 having the above configuration will be described.

  An ignition coil is connected to the terminal 2 via a plug cord (not shown). When a voltage is applied from the ignition coil to the terminal 2, a voltage is applied to the plus electrode 6 through the main conductors 3 a and 3 b, and discharge is sequentially generated from an ignition gap close to the plus electrode 6.

  Discharge occurs in all the ignition gaps 13a to 13d by one energization, but the voltage (breakdown voltage) required at this time is from a single ignition gap equal to the sum of the gaps of the respective ignition gaps 13a to 13d. The voltage is about 70% to 80% lower than the voltage required to cause discharge. This is presumably because a capacitor C is formed between the intermediate electrodes 7a to 7c and the body fitting 5 (see FIG. 1), and this capacitor C contributes to discharge in the downstream ignition gap.

  That is, when a discharge occurs in the upstream ignition gap and a charge flows into the capacitor located downstream, the potential difference between the ignition gaps located further downstream increases and a discharge occurs also in the ignition gap located downstream. Since the discharge of the adjacent ignition gap occurs with a slight time difference corresponding to the time required for charging the capacitor, as a result, the breakdown voltage can be greatly reduced compared to the case where the discharge is simultaneously performed from the entire ignition gap. It can be done.

  FIG. 8 shows how a flame spreads in the combustion chamber when the air-fuel mixture in the combustion chamber is ignited using the ignition plug 1 having the above-described configuration.

  At the beginning of ignition, each of the four ignition gaps 13a to 13d generates a flame in a circular shape (spherical when viewed in three dimensions). For this reason, the front end surface of the entire flame at the beginning of ignition becomes a quadrangular shape with rounded corners as indicated by F1, but as the flame spreads, the front end surface of the entire flame is centered on the spark plug 1 as indicated by F2 and F3. It approaches a circular shape and eventually becomes a circular flame, and the flame spreads toward the peripheral edge of the combustion chamber at a substantially uniform speed Y.

  This is because the front end of the flame is positively charged at the portion where the fuel is ionized and violently oxidized while emitting light, and the front end surface of the flame from the adjacent ignition gap passes between the two ignition gaps L1, L2. It is considered that when the collision occurs, the flames are pressed against each other and a velocity Z toward the outside in the radial direction of the combustion chamber is generated, so that all the flames spread in the radial direction.

  Therefore, according to the ignition plug 1 having the above-described configuration, the number of initial flame nuclei can be increased by multi-point ignition and the energy injected from the ignition plug 1 into the air-fuel mixture can be increased, thereby improving ignitability and flame propagation speed. It is possible to realize high-speed combustion due to the increase of.

  The high-speed engine has a small piston stroke so that the piston speed does not exceed the limit speed, while a large cylinder diameter is set to ensure the displacement, thereby improving the radial flame propagation speed. However, according to the spark plug 1 having the above-described configuration, high-speed combustion can be realized, and it is possible to meet such a requirement. In addition, it is possible to obtain a stable ignitability even with an ultra-lean mixture having an excess air ratio of about 2, which has been difficult to stably ignite with a conventional spark plug having only a single ignition gap. If the spark plug 1 is used for a lean burn engine, the lean limit can be expanded. Needless to say, the engine to which the spark plug 1 having the above-described configuration can be applied is not limited to a high-speed engine and a lean burn engine, but can be widely applied to a spark ignition engine.

  As mentioned above, although embodiment of this invention was described, the said structure has shown one of the application examples of this invention, and is not the meaning which limits the technical scope of this invention to the said structure. As described below, the configuration of the above embodiment can be variously modified without departing from the spirit of the present invention.

  For example, in the above embodiment, the three ignition electrodes 13a to 13d are formed by arranging the three intermediate electrodes 7a to 7c between the plus electrode 6 and the ground electrode 8, but the number of intermediate electrodes is increased or decreased. Thus, an arbitrary number of ignition gaps of 2 or more can be formed.

  FIG. 9 shows a modification in which a spring 81 is interposed between the main conductor 13 b and the plus electrode 6. According to this configuration, since the spring 81 is pressed against the engaging portion 62 of the main conductor 13b and the plus electrode 6, the main conductor 13b and the plus electrode 6 can be reliably connected. It is possible to replace the spring 81 with the electric resistor 10.

  Further, as shown in FIG. 10, the exposure amount (projection height) of the positive electrode 6, the intermediate electrodes 7a to 7c, and the ground electrode 8 from the plug tip surface 1a is small, or the lower end of each electrode is connected to the tip surface 1a. The discharges at the ignition gaps 13a to 13d may be creeping discharges along the plug tip surface 1a. According to this configuration, the holding strength of each electrode is increased, and the ignition gaps 13a to 13d are strong against fouling, so that stable ignitability can be obtained.

  Further, as shown in FIG. 11, the main conductor 13b is extended to penetrate the insulator portion 4, the plus electrode 6 is connected to the lower end of the extension portion 1c exposed from the center of the tip surface 1a, and the tip of the plus electrode 6 is You may make it extend to the side of the intermediate electrode 7a. According to this configuration, it is not necessary to form the horizontal hole 46 in the main body insulator 41, and the shape of the positive electrode 6 is also simple, so that the manufacturing cost of the spark plug 1 is reduced and the strength of the insulator portion 4 is improved. be able to.

  However, in the configuration shown in FIG. 11, the depression 14 for adjusting the heat value cannot be formed in the center of the front end surface 1 a of the spark plug 1. A recess 82 is formed between them, and the heat value of the spark plug 1 is adjusted by adjusting the width and depth of the recess 82. At this time, the depth of the recess 82 is made shorter than the length of the portion held by the insulator portion 4 of the intermediate electrodes 7a to 7c. This is because, when the depth of the recess 82 is larger than the length of the portion held by the insulator 4 of the intermediate electrodes 7a to 7c, no capacitor is formed between the intermediate electrodes 7a to 7c and the body fitting 5, and the breakdown is thereby reduced. This is because the voltage cannot be lowered.

The spark plug which concerns on this invention is shown, (a) is a fragmentary sectional view of a spark plug, (b) is a bottom view of a spark plug. FIG. 2 is a view taken in the direction of an arrow X in FIG. It is the figure which looked at the combustion chamber upper surface from the combustion chamber side. A main body insulator is shown, (a) is a front view of the main body insulator, (b) is a side view thereof, and (c) is a bottom view thereof. It is a front view of a cylindrical insulator. A positive electrode is shown, (a) is a front view, (b) is a side view, (c) is a bottom view, and (d) is a VId-VId cross section of (a). An intermediate electrode is shown, (a) is a front view, (b) is a bottom view, and (c) is a VIIc-VIIc cross section of (a). It is the figure which showed a mode that a flame propagated in a combustion chamber. It is a figure which shows the partial modification of this invention. It is a figure which shows the partial modification of this invention similarly. It is a figure which similarly shows the some modification of this invention, (a) is XIa-XIa sectional drawing of (b), (b) is a bottom view of a spark plug.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Spark plug 2 Terminal 3a, 3b Main conductor 4 Insulator part 5 Body metal fitting 6 Positive electrode 7a-7c Intermediate electrode 8 Ground electrode C Capacitor 13a-13d Ignition gap 14 Indentation 41 Main body insulator 42 Cylindrical insulator 82 Indentation

Claims (7)

Terminal,
A main conductor electrically connected to the terminal;
An insulator for holding the main conductor inside;
A body fitting that is externally fitted to the distal end of the lever part;
A positive electrode electrically connected to the main conductor and exposed from the tip of the insulator,
One or more intermediate electrodes, part of which is held inside the insulator part and the remaining part is exposed from the tip of the insulator part;
A ground electrode that is connected to the body fitting and exposed from the tip of the insulator,
An ignition gap formed between at least the positive electrode and the intermediate electrode and an ignition gap formed between the intermediate electrode and the ground electrode through the positive electrode, the intermediate electrode, and the ground electrode. A capacitor is formed between the intermediate electrode and the main body metal part by being electrically connected in series and a portion held by the insulator part of the intermediate electrode facing the main body metal part with a part of the insulator part in between. A multipoint spark plug characterized by being made.   The multi-point spark plug according to claim 1, wherein the intermediate electrode has an inverted T shape, and discharge portions are formed on both sides of a lower end.   3. The multipoint ignition plug according to claim 1, wherein the ignition gap is disposed on the same circumference around a central axis of the ignition plug.   The insulator portion is composed of a cylindrical insulator and a main body insulator that is at least partially inserted into the cylindrical insulator, and an outer periphery of a portion of the main body insulator that is inserted into the cylindrical insulator is provided on the outer periphery of the spark plug. The multipoint ignition plug according to any one of claims 1 to 3, wherein an electrode holding groove extending in an axial direction is formed, and the intermediate electrode is held in the electrode holding groove.   The multipoint ignition plug according to any one of claims 1 to 4, wherein a hole for adjusting a heat value is formed at a center of a front end surface of the insulator portion.   The said main conductor is exposed from the center of the front end surface of the said insulator part, The said plus electrode is connected to the exposed part of the said main conductor, and is extended to the side of the said intermediate electrode. The multi-point spark plug according to any one of 1 to 4.   The exposure amount from the front end surface of the plus electrode, the intermediate electrode, and the ground electrode is set to an exposure amount at which discharge in each ignition gap becomes creeping discharge that travels through the front end surface. The multipoint spark plug according to any one of 1 to 6.

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