KR100985367B1 - Spark plug designed to minimize drop in insulation resistance - Google Patents

Abstract

Spark plugs for internal combustion engines include metal shells, porcelain insulators, center electrodes, and ground electrodes. The center electrode is formed in the magnetic insulator to form a spark gap between the center electrode itself and the ground electrode. The magnetic insulator has a nose composed of an upright portion and a tapered portion extending from the upright portion to an upper end of the magnetic insulator. The tapered portion is shaped to decrease in diameter toward the top of the magnetic insulator. The upstanding portion has an outer wall extending substantially parallel to the inner wall of the metal shell, thereby inducing side spark formation between the tapered portion and the metal shell before the insulation resistance between the center electrode and the metal shell drops. In this way, the driver can be signaled to indicate such an event.

Spark Plugs, Magnetic Insulators, Center Electrode, Metal Shell, Spark Gap, Annular Shoulder, Insulator Nose

Description

Spark plugs designed to minimize drop in insulation resistance {SPARK PLUG DESIGNED TO MINIMIZE DROP IN INSULATION RESISTANCE}

The present invention claims the benefit of Japanese Patent Application No. 2006-331749, filed December 8, 2006, and Japanese Patent Application No. 2007-194666, filed July 26, 2007, all of which are incorporated herein by reference in their entirety. .

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to spark plugs for internal combustion engines that can be used in auto propulsion vehicles, cogeneration systems, or gas supply pumps, and more particularly to spark plugs designed to ensure the stability of insulation resistance.

13 and 14 show a spark plug 9 as a typical example used in an internal combustion engine. The spark plug 9 includes a metal shell 94 having an external plug mounting screw 941, a magnetic insulator 92 held in the metal shell 94, and a center electrode disposed in the magnetic insulator 92. 93, and a ground electrode 95 welded to the metal shell 94 to form a spark gap 911 between the ground electrode 95 itself and the center electrode 93.

Normally, low speed running of the engine can cause the engine to burn, so that combustion of the air-fuel mixture produces carbon that adheres to the nose 922 surface of the magnetic insulator 92. The increase in carbon deposits forms a conductive connection between the center electrode 93 and the metal shell 94, thereby significantly reducing the dielectric resistance therebetween. This in turn disables spark discharge in the spark gap 911. This is particularly prone to occur in high temperature range spark plugs, ie spark plugs having a short insulator nose.

The phenomenon found in the spark plug 9 will be analyzed below with reference to FIG.

Carbon particles C are continuously deposited from the tip to the base of the insulator nose 922 disposed inside the metal shell 94.

The insulator nose 922 of the spark plug 9 is gradually from the outer annular shoulder 921 disposed in conjunction with the inner annular shoulder 942 of the metal shell 94 to its tip, as can be seen in FIG. It is a shape having a decreasing diameter. In other words, the insulator nose 922 is so designed that the air gap between the insulator itself and the inner wall of the metal shell 94 is reduced from its tip towards the outer annular shoulder 942. As such, an increase in the deposition of carbon particles (C) on the insulator nose (922) results in a reduction in the spacing between the layer surface of the carbon particles (C) and the inner wall of the metal shell (94). When such spacing reaches a value, a spark (also called side spark) forms between the outer surface of the insulator nose 922 and the metal shell 94.

Further increase in the deposit of carbon particles C on the insulator nose 922 results in the formation of an electrical connection between the center electrode 93 and the metal shell 94, thus insulating resistance therebetween. Will be greatly reduced.

The drop in insulation resistance between the center electrode 93 and the metal shell 94 resulting from soot of the engine causes the temperature in the combustion chamber to burn off the carbon particles C condensed on the surface of the magnetic insulator 92. It can be mitigated by increasing the engine speed to raise it. The formation time of the side sparks can be seen as an indication of a suitable time for the carbon deposit to burn off. In particular, the formation of side sparks indicates the fact that a large amount of carbon deposit has condensed on the insulator nose 922, which also shows the appropriate time for any action to be taken to burn off the carbon deposit. The formation of side sparks represents the occurrence of so-called tracking (i.e., the formation of conductive paths through which the side sparks travel) in the engine that the vehicle driver usually perceives as mechanical vibration of the engine.

However, the structure of the spark plug 9 is such that the spacing between the insulator nose 922 and the metal shell 94 decreases at a constant rate from the tip of the insulator nose 922 to the outer annular shoulder 921 and thus the side sparks. Is formed and after a short time a short circuit is formed between the metal shell 94 and the center electrode 93, which takes measures to burn off carbon deposits on the spark plug 9 after the vehicle driver recognizes the occurrence of tracking. It has a problem that makes it difficult to take. In addition, when the vehicle driver perceives tracking and stops the engine, the center electrode 93 and the metal shell 94 (ie, ground electrode 95) are consequently due to deposits of carbon particles C on the insulator nose 922. Another problem is that the engine cannot be restarted due to a large decrease in insulation resistance between)).

The shape of the insulator nose 922 having a diameter that gradually decreases from the outer annular shoulder 921, which is disposed in engagement with the inner annular shoulder 942 of the metal shell 94, to its tip, results in heat being insulated nose 922. Making it difficult to convey or dissipate towards the base. As such, a rapid rise in temperature of the engine combustion chamber resulting from, for example, sudden vehicle acceleration can exert a large pressure on the insulator nose 922.

Poor heat transfer from the insulator nose 922 results in an increase in the temperature of the insulator nose 922. Thus, when the insulator nose 922 to which fuel is bonded is rapidly cooled, the insulator nose 922 will be subjected to a great pressure, which may be broken.

The above-mentioned drop in insulation resistance between the center electrode 93 and the metal shell 94 or breakdown of the insulator nose 922 due to carbon deposition on the insulator nose 922 is a particularly high-power engine mounted in tuned up cars. Tends to occur in

Japanese Patent No. 2953227 describes a spark plug designed such that the base of the insulator nose 922 facing the inner annular shoulder 942 of the metal shell 94 has a width large enough to improve its dielectric strength. . However, this structure is not configured to rapidly form side sparks due to carbon deposition.

Therefore, the main object of the present invention is to avoid the problems of the prior art.

Another object of the invention is a spark plug for an internal combustion engine designed to induce the formation of rapid side sparks that signal the drop in insulation resistance between the center electrode of the spark plug and the metal shell and minimize thermal pressure on the magnetic insulator. To provide an improved structure.

According to one aspect of the present invention, there is provided a spark plug for an internal combustion engine, comprising: (a) a hollow metal shell having an inner shoulder formed on an inner wall thereof; (b) a magnetic insulator having an outer shoulder formed on its outer wall, wherein said outer shoulder is disposed inside said metal shell in a joined state with an inner shoulder of said metal shell so as to extend longitudinally of said spark plug; Magnetic insulators; (c) a center electrode disposed inside the magnetic insulator; (d) a ground electrode, said ground electrode coupled to said metal shell to form a spark gap between said ground electrode itself and said center electrode; And (e) an insulator nose that is part of a magnetic insulator and continues from an outer shoulder to the top of the magnetic insulator. The insulator nose includes an upright portion and a tapered portion extending from the upright portion to an upper end of the magnetic insulator. The upstanding portion has an outer circumferential surface extending substantially parallel to the longitudinal center line of the spark plug. The tapered portion is shaped to decrease in diameter from the upright portion toward the upper end of the magnetic insulator. The tapered portion has an outer circumferential surface having a contour extending in a straight line on one plane and curved outwardly, as installed through the longitudinal center line of the spark plug.

Normally, low speed running of the engine can burn the engine, so combustion of the performance mixture produces carbon particles. The carbon particles are continuously deposited from the top to the base of the insulator nose because the taper portion faces the combustion chamber (ie, spark gap).

The insulator nose is shaped such that its diameter gradually decreases from the outer shoulder to its upper end. In other words, the insulator nose is so designed that the air gap between itself and the inner wall of the metal shell decreases from the top towards the outer shoulder. As such, increasing the deposit of carbon particles on the insulator nose results in a decrease in the spacing between the surface of the carbon particle layer and the inner wall of the metal shell. When such spacing reaches a constant value, a spark (so-called side spark) is formed between the outer surface of the insulator nose and the metal shell.

As the deposition amount of carbon particles increases, it will begin to stick to the outer periphery of the upright portion. However, the upright portion extends in a straight line parallel to the longitudinal center line (ie, the central axis) of the spark plug. In other words, the peripheral surface of the upstanding portion does not face the top of the spark plug, thereby increasing the difficulty of depositing carbon particles entering the gap between the top of the upstanding portion and the inner wall of the metal shell on the peripheral surface of the upstanding portion.

The upstanding portion has a constant diameter, so that the gap between itself and the inner wall of the metal shell is kept constant in the longitudinal direction of the magnetic insulator. As such, even when a deposit of carbon particles grows continuously deep into the gap between the upright and the inner wall of the metal shell, the gap between the carbon-deposited region of the upright and the inner wall of the metal shell is sufficient to induce side sparks. It will take a lot of time until it decreases, thus consuming enough time before the insulation resistance between the center electrode and the metal shell drops undesirably.

 Thus, the construction of the magnetic insulator sufficiently generates side sparks before the insulation resistance between the center electrode and the metal shell drops, thus ensuring a large amount of time between the start of the formation of the side sparks and the drop in insulation resistance. The operator of the vehicle will be able to recognize the tracking that causes mechanical vibration of the engine (ie, the formation of a conductive path between the magnetic insulator and the metal shell, from which the side spark will move) and take measures to remove the soot of the engine. You can take it.

In particular, after recognizing the tracking, the driver may accelerate the engine to raise the temperature in the combustion chamber to burn off carbon deposits on the surface of the magnetic insulator, and the driver may recognize the tracking and stop the engine after stopping the engine. You can restart it. This is because, when tracking occurs, the required degree of insulation resistance is still ensured between the center electrode and the metal shell.

The insulator nose has an upright portion with a constant diameter and not tapered, thereby facilitating the transfer of heat that the upper end of the tapered portion reaches to the upright portion, thus relieving thermal pressure that acts on the insulator nose and causes it to break. Let's do it.

The tapered portion is designed to have a straight or curved outline extending on a plane including the longitudinal centerline of the spark plug, thereby facilitating heat transfer to the base of the tapered portion, and also the tapered and upright portions By reducing the concentration of pressure on the boundary between them, it is possible to minimize breakage of the insulator nose.

In a preferred embodiment of the present invention, the upright portion may have a length of 1.5 mm to 6 mm. The length of the upright portion is selected to lie in the range of 7% to 40% of the total length, which is the sum of the lengths of the outer shoulder and the insulator nose. This ensures an increase in time between the drop in insulation resistance between the center electrode and the metal shell and the formation of side sparks.

The size (Gm) of the spark gap and the distance (Gs) between the outer periphery of the boundary between the tapered and upright portions of the magnetic insulator and the inner wall of the metal shell are selected such that a relationship of Gm ≧ Gs ≧ 0.4Gm is established, This results in the rapid formation of side sparks, a signal that indicates the likelihood of insulation resistance between the center electrode and the metal shell.

The upright portion of the insulator nose is continuous to the outer surface of the tapered portion through a rounded surface whose shape is curved on a plane including the longitudinal centerline of the spark plug, thereby between the upright portion and the tapered portion. Relieve the pressure concentration into the interface phase.

The center electrode may have a noble metal chip connected to an upper end thereof facing the spark gap. The precious metal chip has a diameter of 0.7 mm or less, preferably 0.45 mm or less, thereby reducing the voltage required for the spark plug to generate a series of sparks. The precious metal chip may be made of an iridium alloy to improve the durability of the spark plug.

The total length, which is the sum of the lengths of the outer shoulder of the magnetic insulator and the insulator nose, is 11 mm or less, thereby facilitating heat transfer from the insulator nose to the metal shell. This allows the spark plug to be designed in a high temperature range.

The metal shell has an inner circumferential surface extending from an inner shoulder to an upper end thereof facing the spark gap parallel to the longitudinal centerline of the spark plug. Therefore, the inner circumferential surface of the upright portion of the magnetic insulator extends parallel to the inner circumferential surface of the metal shell. Additionally, the gap between the tapered portion of the magnetic insulator and the inner circumferential surface of the metal shell widens toward the top of the magnetic insulator, thereby minimizing carbon adhesion to the outer surface of the upstanding portion, while on the magnetic insulator In the early stages of carbon deposition it is possible to ensure a gap between the carbon-adhesive region of the magnetic insulator and the inner periphery of the metal shell.

The metal shell forms a protrusion on an upper end thereof facing the spark gap. The protrusion extends inside the metal shell, thereby reducing the amount of carbon entering the air pocket between the magnetic insulator and the metal shell.

The distance Gp between the inner end surface of the protrusion and the outer wall of the magnetic insulator and the size Gm of the spark gap are selected such that a relationship of Gm ≦ Gp ≦ 1.8Gm is established. This forms a series of reliable sparks between the center electrode and the ground electrode and ensures that the carbon ingress into the air pocket between the metal shell and the magnetic insulator can be minimized.

The invention will be more fully understood from the detailed description of the invention and from the accompanying drawings of the preferred embodiments, but it is given for the purpose of explanation and understanding rather than to limit the invention to the specific embodiments.

Referring to the drawings, like elements are referred to by the same reference numerals in the various figures, and in particular with respect to FIGS. 1 to 4, there is shown a spark plug 1 for use in an internal combustion engine according to a first embodiment of the invention. .

As illustrated in FIGS. 1 and 2, the spark plug 1 comprises a hollow cylindrical metal shell 4, a magnetic insulator 2, a center electrode 3 and a ground electrode 5. The metal shell 4 is formed on the outer periphery of the plug-mounting screw 41 for installation of the spark plug 1 in the internal combustion engine. The magnetic insulator 2 is held in the metal shell 4. The center electrode 3 is fixed within the magnetic insulator 2 and exposed outside the top of the magnetic insulator 2 to form a spark gap 11 between the magnetic insulator 2 itself and the ground electrode 5. It has a tip 31.

The magnetic insulator 2 is directed from the outer annular shoulder 21 and the outer annular shoulder 21 disposed in contact with the inner annular shoulder 42 of the metal shell 4 toward the top of the spark plug 1. And an extended nose 22.

The insulator nose 22 is continuous from the outer annular shoulder 21 and consists of an upright portion 221 and a tapered portion 222. The upright portion 221 has an outer peripheral wall extending substantially parallel to the central axis M of the spark plug 1 (ie, the longitudinal center line of the magnetic insulator 2). The taper portion 222 is reduced in diameter from the upright portion 221 to the top surface of the insulator nose 22.

The tapered portion 222 has an outer surface that extends evenly, but may alternatively be shaped to have an outer surface that is convex (ie, curved) to the outside.

The upright portion 221 has a length A of 1.5 mm to 6 mm, as formed in the longitudinal direction of the spark plug 1. The length A is also chosen to lie in the range of 7% to 40% of the total length B of the upper end of the magnetic insulator 21 which is the sum of the lengths of the outer annular shoulder 21 and the insulator nose 22. do. The length B is selected to be 11 mm or less.

The metal shell 4 is formed in an axial aperture 40 through which the magnetic insulator 2 extends. The axial aperture 40 has an inner annular shoulder 42 formed in its inner wall. The axial aperture 40 also extends from the inner annular shoulder 42 to the upper end 44 of the metal shell 4 parallel to the central axis M of the spark plug 1. ) Thus, the front inner peripheral wall 43 has a constant inner diameter along its length.

The front inner circumferential wall 43 of the metal shell 4 is arranged to face the outer circumference of the insulator nose 22 in the radial direction of the spark plug 1, whereby a cylindrical air pocket 12 therebetween. ). The air pocket 12 opens at the upper end 44 of the metal shell 4.

The outer annular shoulder 21 of the magnetic insulator 2 is disposed on the inner annular shoulder 42 of the metal shell 42 via the gasket 13.

The size or length Gm of the spark gap 11, as formed along the central axis M of the spark plug 1, and the inner wall of the metal shell 4 and the uprights 221 of the magnetic insulator 2. The distance Gs between the outer wall (ie, at least the outer periphery of the boundary between the upright portion 221 and the tapered portion 222) is selected to satisfy a relationship of Gm ≧ Gs ≧ 0.4Gm.

The outer surface of the upright portion 221 is connected to the surface of the tapered portion 222 through the rounded surface 223, as is clearly illustrated in FIG. 3. As formed on the plane extending through the central axis M of the spark plug 1, the radius of curvature of the contour of the rounded surface 223 is selected to about 2 mm.

The center electrode 3 has a precious metal chip 31 made of an Ir (iridium) alloy. The precious metal chip 31 has a diameter d of 0.7 mm or less and preferably 0.45 mm or less.

The center electrode 3 has a cylindrical base 30 fitted to a magnetic insulator 2. The base 30 has a tapered head to which the precious metal 31 is welded. The diameter D of the base 30 is 2mm to 3mm.

The advantages of the spark plug 1 will be described below.

The insulator nose 22 is comprised from the upright part 221 and the taper part 222 as mentioned above. This structure causes the carbon particles to coalesce in the tapered portion 222 gradually from the top to the base, as shown in FIG. The tapered portion 222 is shaped such that its diameter increases toward the upright portion 221, so that the gap between the tapered portion itself and the inner wall of the metal shell 4 gradually decreases toward the upright portion 221. do. In other words, the peripheral surface of the tapered portion 222 faces the top of the spark plug 1. This facilitates the deposition of carbon particles C on the tapered portion 222, so that the amount increases with time, and thus the carbon-deposited region of the insulator nose 22 and the metal shell 4 Decreases the distance between the inner walls of the If such a distance reaches a constant value, it will form a side spark S between the magnetic insulator 2 and the metal shell 4. As the deposition amount of carbon particles (C) increases, they will also begin to adhere to the outer periphery of the upright portion 221. However, the upright portion 221 extends in a straight line parallel to the central axis (M) of the spark plug (1). In other words, the peripheral surface of the upright 221 does not face the top of the spark plug 1, and thus the carbon particles introduced into the gap between the top of the upright 221 and the inner wall of the metal shell 4. Difficulty in depositing the field C on the peripheral surface of the upright portion 221 is increased.

The upright portion 221 has a constant diameter, so that the distance between itself and the inner wall of the metal shell 4 is kept constant in the longitudinal direction of the magnetic insulator 2. Therefore, even when the deposition of the carbon particles (C) grows continuously deep into the gap between the upright portion 221 and the inner wall of the metal shell 4, the carbon-deposited region of the upright portion 221 and the Much time will be spent until the distance between the inner walls of the metal shell 4 decreases, so that much time will be spent until the insulation resistance between the center electrode 3 and the metal shell 4 undesirably drops. will be.

Thus, the structure of the magnetic insulator 2 ensures a large amount of time between the start of the side spark formation and the drop in the insulation resistance between the center electrode 3 and the metal shell 4, whereby the vehicle driver generally As a result, it is possible to recognize tracking which causes the formation of side sparks that generate mechanical vibrations of the engine, and to take measures to eliminate soot of the engine. In particular, after recognizing tracking, the vehicle driver can accelerate the engine to raise the temperature in the combustion chamber to burn off carbon deposits on the surface of the magnetic insulator 2, and the vehicle driver also recognizes the tracking and Allow the engine to restart after stopping. This is because, when tracking occurs, the required degree of insulation resistance is still secured between the center electrode 3 and the metal shell 4.

The insulator nose 22 has an upright portion 221 having a constant diameter without tapering its end, thereby facilitating the movement of heat in which the upper end of the tapered portion 222 extends to the upright portion 221, Thus, it acts on the insulator nose 22 to relieve thermal pressure which usually causes it to break.

The tapered portion 222 is designed to have a straight or curved outline extending on a plane including the central axis M of the spark plug 1, thereby transferring heat to the base of the tapered portion 222. It is possible to easily promote and also to reduce the pressure concentration on the boundary between the tapered portion 222 and the upright portion 221 to minimize the breakage of the insulator nose (22).

The upright portion 22 has a length A of 1.5 mm to 6 mm, whereby a lot of time between the start of the formation of the side sparks and the drop in insulation between the center electrode 3 and the metal shell 4. This can be secured.

The length A of the upright portion 221 is also between 7% and 40% of the total length B of the upper end of the magnetic insulator 21, which is the sum of the lengths of the outer annular shoulder 21 and the insulator nose 22. It is selected to lie in range, thereby ensuring an increase in time between the start of side spark formation and the drop in insulation between the center electrode 3 and the metal shell 4.

The size Gm of the spark gap 11 and the distance Gs between the outer wall of the upright portion 221 of the magnetic insulator 2 and the inner wall of the metal shell 4 have a relationship of Gm ≧ Gs ≧ 0.4Gm. It is chosen to satisfy, thereby facilitating the rapid induction of the side spark, which represents a drop in the insulation resistance between the center electrode and the metal shell 4.

The outer surface of the upright portion 221 leads to the outer surface of the tapered portion 222 through the rounded surface 223, thereby creating pressure concentration on the boundary between the upright portion 221 and the tapered portion 222. Significantly reduced, it ensures the durability of the magnetic insulator 2.

The center electrode 3 has a precious metal chip 31 having a diameter of 0.7 mm or less and made of an Ir alloy, thereby reducing the voltage required for the spark plug to generate sparks, and improving the durability of the spark plug 1. Will be improved.

The length B, which is the sum of the lengths of the outer annular shoulder 21 and the insulator nose 22, is selected to be 11 mm or less, thereby increasing the heating range of the spark plug 1, ie from the insulator nose 22. This will promote heat transfer up to the metal shell 4, which ensures the durability of the spark plug 1 against use under severe conditions where the combustion chamber of the engine is subjected to strong heat.

Usually, high temperature range spark plugs tend to burn the fuel mixture, but the structure of the spark plug 1 facilitates the easy taking of steps to remove such burns, and thus, of the spark plug 1 Ensures an increased service life.

We ran a test to evaluate the anti-soot characteristics of the spark plug 1 with respect to the insulation resistance between the center electrode 3 and the metal shell 4.

We prepared four plug samples having the same structure as the spark plug 1 of FIG. 1 and four comparison plug samples having the same structure as any of FIGS. 13 and 14, and the upright portion 221 in FIG. A magnetic insulator with a tapered nose without uprights was prepared.

We installed each of the plug samples in an internal combustion engine mounted in the test car and ran the test car under the conditions as described above. 60 seconds after the magnetic insulator was covered with carbon to allow tracking, we stopped the engine. We measured the insulation resistance between the center electrode and the metal shell before and after each test.

The engine mounted on the test car was an 223cc 1-cylinder 4-cycle engine. We ran the test car at a constant speed of 40 km / h on a flat road. The temperature of the engine coolant was 30 ° C.

A series of sparkles as monitored by each of the plug samples in the form of electrical waveforms were monitored. The engine running was continued for 60 seconds after the waveform indicative of tracking inducing side sparks was detected and the engine was then stopped.

The dimensions of each of the plug samples are listed in Table 1 below. Values following "±" or "+" indicate tolerances.

Invention sample Comparison sample Gm 0.7 + 0.1 0.7 + 0.1 Gs 0.4 ± 0.1     - A 3.0 ± 0.5     - B  11 ± 0.2  11 ± 0.2 d 0.4 ± 0.05 0.4 ± 0.05 D 2.65 ± 0.10 2.1 ± 0.1

Unit: mm

The values of the insulation resistance between the center electrode and the metal shell of each of the plug samples as measured before and after each test are shown in the graphs of FIGS. 5 and 6. 5 shows the measured values of the insulation resistance in the plug sample having the same structure as the spark plug 1 (which will be referred to as the inventive plug sample below). 6 shows measurements of insulation resistance in a comparative plug sample.

The graphs of FIGS. 5 and 6 show that the insulation resistance of the plug sample of the present invention hardly drops but has a value of 500 MΩ or more, while the insulation resistance of the comparative plug sample greatly drops when measured after the test. Therefore, if the tracking is stopped within 60 seconds after the occurrence of tracking, the engine can be restarted by using the spark plug 1 and soot or incomplete combustion of the engine can be alleviated, so that the engine speed within 60 seconds after the occurrence of tracking By increasing the temperature in the combustion chamber to, for example, about 800 ° C., it is possible to ensure reliable running of the engine, while the comparative plug samples have already greatly reduced the insulation resistance upon the occurrence of tracking, It can be seen that failure occurs when driving the engine or restarting the engine which raises the temperature in the chamber.

We also conducted a heat resistance test on the magnetic insulator 2 of the spark plug 1.

We prepared inventive plug samples and comparative plug samples. As illustrated in FIG. 7, the inventive plug samples were the same as the samples used in the first test, with the metal shell 4 removed. Similarly, the comparative plug samples were the same as the samples used in the first test, with the metal shells removed.

As described below, a test was run on each of the plug samples under conditions severer than those described above by JIS (Japanese Industrial Standard) B8031.

In particular, a hot bath 61 filled with tin (Sn) was prepared and initially the insulator nose 22 of each of the plug samples at ambient temperature was immersed into a bath 618 mm deep from the top for 30 seconds.

Comparative plug samples were immersed four in each bath at 800 ° C., 850 ° C., and 900 ° C., while inventive plug samples were immersed four in each bath at 850 ° C., 900 ° C., and 950 ° C.

After the test, it was observed whether the magnetic insulator of each of the plug samples was cracked. The observations are shown in Table 2. The denominator of each fraction represents the total number of plug samples used in each test. The molecule represents the total number of cracked plug samples.

High temperature bath Invention sample Comparison sample 950 ℃ 4/4  - 900 ℃ 0/4 4/4 850 ℃ 0/4 1/4 800 ℃  - 0/4

Table 2 shows that some of the comparative plug samples cracked at 850 ° C. and all of them completely cracked at 900 ° C., while the plug samples of the present invention did not crack at all even at 900 ° C.

We also conducted a quench durability test on the magnetic insulator 2 of the spark plug 1.

We prepared inventive plug samples and comparative plug samples. The inventive plug samples were the same as the samples used in the first test, as shown in FIG. Likewise, the comparative plug samples were the same as the samples used in the first test.

The test was run on each of the plug samples under more severe conditions than those described by JIS (Japanese Industrial Standard) B8031.

In particular, we heated the plug sample for 30 minutes at 240 ° C. or higher in a hot furnace, and then insulated nose 22 was cooled to room temperature water 62 (eg, Immersion to a depth of 5 mm from its top for 5 minutes).

Comparative plug samples were immersed four in water 62 of 240 ° C., 260 ° C., 280 ° C., and 300 ° C., respectively. Similarly, inventive plug samples were immersed four in water 62 each of 240 ° C, 260 ° C, 280 ° C, and 300 ° C.

After the test, it was observed whether the magnetic insulator of each of the plug samples was cracked. The observations are shown in Table 3. The denominator of each fraction represents the total number of plug samples used in each test. The molecule represents the total number of cracked plug samples.

Furnace temperature Invention sample Comparison sample 300 ° C 4/4 4/4 280 ℃ 0/4 4/4 260 ℃ 0/4 0/4 240 ℃ 0/4 0/4

Table 3 shows that the comparative plug samples cracked when quenched at 280 ° C., while the plug samples of the present invention did not crack when quenched at 280 ° C.

From the second and third tests, it is evident that the structure of the magnetic insulator 2 of the spark plug 1 is improved in heat resistance and quench durability, and can be used under severe conditions such as a high temperature combustion chamber of an internal combustion engine.

We also conducted endurance tests on the spark plug 1 under severe conditions.

In particular, we prepared eight inventive plug samples and eight comparative plug samples. The inventive plug samples were the same as the samples used in the first test. Likewise, the comparative plug samples were the same as the samples used in the first test.

We installed each of the plug samples in a typical two-cycle two-cylinder motorcycle engine, a steady state drive where the motorcycle travels at 40 km / h on a smooth road and a high speed at which the engine runs at an increased speed of up to 8900 rpm. The engine was run for five cycles, each consisting of a run, leading to a series of self-ignition events on the engine. Steady running was maintained for 60 seconds in each cycle. The high speed run was maintained for 15-20 seconds in each cycle.

After the test, we observed whether the insulator nose of each of the plug samples cracked and found that all of the comparative plug samples cracked while the inventive plug samples did not crack at all.

9 to 11 illustrate a spark plug 1 according to a second embodiment of the invention.

The metal shell 4 has an annular projection 45 formed in the inner wall 43 of its upper end 44. The annular protrusion 45 extends inside the metal shell 4.

The distance between the protrusion 45 and the outer wall of the insulator nose 222 or the air gap Gp and the size Gm of the spark gap 11 are selected such that a relationship of Gm ≦ Gp ≦ 1.8Gm is established. This is the height or distance between the inner top surface of the protrusion 45 and the inner wall 43 of the metal shell 4 is 0.2 mm to 2.4 mm.

As is evident in FIG. 10, the projections 45 extend over the entire periphery of the inner wall 43 of the metal shell 4, but as shown in FIG. 11, a plurality of arcs spaced apart from each other at regular intervals. It may also consist of mold parts.

Other arrangements are the same as in the first embodiment, and detailed description thereof will be omitted here.

The annular protrusion 45 operates to minimize carbon inflow into the air pocket 12 between the metal shell 4 and the magnetic insulator 2, whereby the center electrode 3 and the metal shell 4 are minimized. Decreases the drop in insulation resistance, and as a result it increases the time between the occurrence of tracking and the drop in insulation resistance.

The air gap Gp between the protrusion 45 and the outer wall of the insulator nose 222 is selected such that a relationship of Gm ≤ Gp ≤ 1.8 Gm is established, whereby between the center electrode 3 and the ground electrode 5 The formation of a series of reliable sparks is ensured and also it is possible to minimize the carbon ingress into the air pocket 12 between the metal shell 4 and the magnetic insulator 2.

As is evident in FIG. 10, the projections 45 formed to extend over the entirety around the inner wall 43 of the metal shell 4 serve to enhance carbon penetration into the packet 12. As shown in FIG.

As illustrated in Fig. 11, the projection 45 composed of arc-shaped portions has a plurality of inner edges which function as sub-ground electrodes when the magnetic insulator 2 is covered with carbon, thereby making the magnetic insulator ( A series of sparks is formed between the protrusion 45 and the magnetic insulator 2 to burn off the carbon on 2). This rapidly removes the soot state of the spark plug 1.

We also conducted anti-soot tests to evaluate the anti-soot characteristics of the spark plug 1 of the second embodiment.

The tests were performed in the same manner as in the first test described above. The plug samples of the invention used in the test have substantially the same dimensions as the sample used in the first test. The height of the protrusion 45 between the inner top surface of the protrusion 45 and the inner wall 43 of the metal shell 4 was 0.3 ± 0.1 mm. The air gap Gp between the protrusion 45 and the outer wall of the insulator nose 222 of the magnetic insulator was 1.1 ± 0.2 mm.

We measured the insulation resistance between the center electrode 3 and the metal shell 4 after each test. The result of the measurement is shown in the graph of FIG.

The graph shows that all of the plug samples of the present invention have better anti-soot characteristics than the structure of the spark plug 1 of the first embodiment without the drop in insulation resistance between the center electrode 3 and the metal shell 4. It shows the appearance. We have found that when the spark plug 1 of the second embodiment is used, the insulation resistance drop can be avoided within 60 seconds after the occurrence of tracking.

While the invention has been described in terms of preferred embodiments in order to facilitate understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principles of the invention. As such, it is to be understood that the present invention includes all possible embodiments and modifications to the described embodiments that can be embodied without departing from the principles of the invention as set forth in the appended claims.

1 is a partial longitudinal sectional view showing an upper end portion of a spark plug according to a first embodiment of the present invention;

2 is a side view showing a spark plug according to a first embodiment of the present invention;

3 is a partial longitudinal sectional view showing the surface of the insulator nose of the spark plug of FIG.

4 is a partial longitudinal cross-sectional view illustrating the process of carbon coalescence to the insulator nose as shown in FIG.

Fig. 5 is a graph showing experimental results showing a change in insulation resistance between the magnetic insulator and the metal shell of the samples of the spark plug according to the first embodiment.

Fig. 6 is a graph showing experimental results showing the change in insulation resistance between the magnetic insulator and the metal shell of the comparative spark plugs.

7 is a side view showing a method of testing the heat resistance of plug samples.

8 is a side view illustrating a method of testing the quenching durability of plug samples.

9 is a partial longitudinal sectional view showing the upper end of the spark plug according to the second embodiment of the present invention;

FIG. 10 is a cross sectional view as taken along the line C-C in FIG. 9; FIG.

Fig. 11 is a cross sectional view showing a modification of the magnetic insulator of the spark plaque of Fig. 9;

FIG. 12 is a graph showing experimental results showing a change in insulation resistance between a magnetic insulator and a metal shell of samples of a spark plug in a second embodiment. FIG.

Fig. 13 is a partial longitudinal sectional view showing the upper end of a conventional spark plug.

FIG. 14 is a side view of the entirety of a conventional spark plug as shown in FIG.

FIG. 15 is a partial longitudinal cross-sectional view illustrating the process of coalescence of carbon to the insulator nose of a conventional spark plug as shown in FIGS. 13 and 14;

<Explanation of symbols for the main parts of the drawings>

1: spark plug

2: magnetic insulator

3: center electrode

4: hollow cylindrical metal shell

5: electrode

11: spark gap

21: outer annular shoulder

22: insulator nose

42: inner annular shoulder

221: upright part

222: tapered portion

Claims (12)

Spark plugs for internal combustion engines, A metal shell, comprising: a hollow metal shell having an inner shoulder formed on an inner wall thereof; A magnetic insulator having an outer shoulder formed on its outer wall, the magnetic insulator disposed inside the metal shell with the outer shoulder joined to the inner shoulder of the metal shell so as to extend in the longitudinal direction of the spark plug; , A center electrode disposed inside the magnetic insulator; A ground electrode, comprising: a ground electrode connected to the metal shell to form a spark gap between the ground electrode itself and the center electrode; A portion of the magnetic insulator and comprising an insulator nose continuous from an external shoulder to an upper end of the magnetic insulator, The insulator nose includes an upright portion and a tapered portion extending from the upright portion to an upper end of a magnetic insulator, the upright portion having an outer circumferential surface extending parallel to a longitudinal centerline of the spark plug and between the outer circumferential surface and the inner wall of the metal shell. The distance is kept constant in the longitudinal direction of the magnetic insulator, wherein the tapered portion is shaped to decrease in diameter from the upright portion toward the upper end of the magnetic insulator, and the tapered portion is straight on a plane including the longitudinal center line of the spark plug. A spark plug having an outer circumferential surface of a shape having a contour extending outwardly or convex outwardly. The spark plug of claim 1 wherein the upstanding portion has a length of 1.5 mm to 6 mm. The spark plug of claim 1 wherein the upstanding portion has a length selected to lie within a range of 7% to 40% of a total length that is the sum of the lengths of the outer shoulder and insulator nose. The method of claim 1, wherein the size of the spark gap Gm and the distance Gs between the outer periphery of the boundary between the tapered and upright portions of the magnetic insulator and the inner wall of the metal shell satisfy a relationship of Gm ≥ Gs ≥ 0.4 Gm. Spark plugs for internal combustion engines selected. The spark plug for an internal combustion engine according to claim 1, wherein the upright portion of the insulator nose has an outer surface continuous to the outer surface of the tapered portion through a rounded surface having a curved contour on a plane including a longitudinal centerline of the spark plug. . The spark plug for an internal combustion engine according to claim 1, wherein the center electrode has a noble metal chip bonded to an upper end thereof facing the spark gap. The spark plug for an internal combustion engine according to claim 6, wherein the precious metal chip has a diameter of 0.7 mm or less. The spark plug of claim 6, wherein the precious metal chip is made of an iridium alloy. 2. The spark plug of an internal combustion engine as set forth in claim 1, wherein a total length of the sum of the lengths of the outer shoulder of the magnetic insulator and the insulator nose is 11 mm or less. The spark plug of claim 1, wherein the metal shell has an inner circumferential surface extending parallel to a longitudinal centerline of the spark plug from the inner shoulder to an upper end thereof facing the spark plug. The spark plug of claim 1, wherein a protrusion is formed on an upper end of the metal shell facing the spark gap, the protrusion extending into the interior of the metal shell. 12. The spark plug according to claim 11, wherein the distance Gp between the inner end face of the protrusion and the outer wall of the magnetic insulator and the size Gm of the spark gap are selected to satisfy a relationship of Gm &lt; Gp &lt; 1.8Gm.

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