JP7277298B2 - Spark plug - Google Patents

Description

The present invention relates to spark plugs.

Spark plugs are used as ignition means in internal combustion engines such as vehicle engines and cogeneration systems. Patent Literature 1 discloses a spark plug in which a spark gap that generates spark discharge is covered with a plug cover, and an auxiliary combustion chamber is formed inside the plug cover.

In such a spark plug, the air-fuel mixture in the combustion chamber of the internal combustion engine is introduced into the sub-combustion chamber through the injection hole formed in the plug cover, and the air-fuel mixture is ignited by performing spark discharge in the discharge gap. A flame is generated in the combustion chamber. Then, a flame jet is ejected from the injection hole into the combustion chamber outside the sub-combustion chamber, and the flame spreads over the entire combustion chamber. As a result, an internal combustion engine with a high combustion speed can be obtained.

Here, in the spark plug described in Patent Document 1, the plug cover is composed of an inner layer, an outer layer, and a core layer having a higher thermal conductivity than these layers. Thus, the spark plug of Patent Document 1 is intended to improve the heat dissipation of the plug cover.

JP 2012-199236 A

However, in the spark plug disclosed in Patent Document 1, when the flame grows in the sub-combustion chamber, the plug cover may take heat from the flame and hinder the growth of the flame. Therefore, the spark plug described in Patent Document 1 has room for improvement from the viewpoint of improving ignitability.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems, and an object of the present invention is to provide a spark plug capable of improving ignitability.

One aspect of the present invention is a tubular housing (2),
a cylindrical insulator (3) held inside the housing;
a center electrode (4) held inside the insulator;
a ground electrode (5) forming a discharge gap (G) with the center electrode;
a plug cover (6) that constitutes, together with the housing, a sub-combustion chamber (7) in which the discharge gap is disposed, and that has an injection hole (611) penetrating inside and outside;
A spark plug (1) comprising: a low thermal conductivity member (8) disposed opposite to the inner surface (60) of the plug cover and having a lower thermal conductivity than the plug cover ,
The low thermal conductivity member is formed along the entire circumference of the spark plug in the circumferential direction,
The low thermal conductivity member is arranged at least in a region where the discharge gap is formed in the axial direction (Z) of the spark plug,
The low thermal conductivity member is formed in a tubular shape having openings on both sides in the axial direction,
In a cross section including the central axis (C) of the spark plug, a straight line connecting the central portion (GC) of the discharge gap and the tip of the low heat conductive member is defined as a first imaginary straight line (VL1), and the center of the discharge gap When a straight line connecting the portion and the base end of the low thermal conductive member is defined as a second virtual straight line (VL2), the acute angle (θ1) formed by the first virtual straight line and the central axis is 75° or less. and wherein an acute angle (θ2) formed by the second imaginary straight line and the central axis is 75° or less .

The spark plug of the aspect described above is provided with a low thermal conductive member having a thermal conductivity lower than that of the plug cover and arranged opposite to the inner surface of the plug cover. Therefore, it is easy to suppress the heat of the flame generated in the sub-combustion chamber from being taken away by the plug cover. This makes it easier to improve the ignitability of the spark plug.

As described above, according to the aspect, it is possible to provide a spark plug capable of improving ignitability.
It should be noted that the symbols in parentheses described in the claims and the means for solving the problems indicate the corresponding relationship with the specific means described in the embodiments described later, and limit the technical scope of the present invention. not a thing

FIG. 2 is a partially cross-sectional front view of a spark plug in Reference Embodiment 1 ; FIG. 1 is a cross-sectional view taken along line II-II. FIG. 4 is a partially cross-sectional front view of a spark plug for explaining how flame grows in the sub-combustion chamber according to Reference Embodiment 1 ; 2 is a partially cross-sectional front view of the spark plug in Embodiment 1. FIG . FIG. 4 is a partially cross-sectional front view of a spark plug in Embodiment 2 ; FIG. 10 is a schematic view of the engine head with the spark plug attached, viewed from the combustion chamber side in Experimental Example 1, and is a schematic diagram for explaining the flame reaching distance. 4 is a graph showing the relationship between the time from ignition and the flame reaching distance in Experimental Example 1. FIG. 10 is a graph showing A/F limits of a comparative sample without a low thermal conductivity member and a sample 1 with a low thermal conductivity member in Experimental Example 2; FIG. 11 is a partially cross-sectional front view of a spark plug in Experimental Example 3; 10 is a graph showing the relationship between the angle θ and the flame reaching distance 9 ms after ignition in Experimental Example 3. FIG.

( Reference form 1 )
A reference form of the spark plug will be described with reference to FIGS. 1 to 3. FIG.
A spark plug 1 of this embodiment comprises a housing 2, an insulator 3, a center electrode 4, a ground electrode 5, a plug cover 6, and a low thermal conductive member 8, as shown in FIG.

The housing 2 has a tubular shape. The insulator 3 is held inside the housing 2 and has a tubular shape. A center electrode 4 is held inside the insulator 3 . The ground electrode 5 forms a discharge gap G with the center electrode 4 .

The plug cover 6 forms, together with the housing 2, an auxiliary combustion chamber 7 in which the discharge gap G is arranged. Further, the plug cover 6 is provided with injection holes 611 penetrating inside and outside thereof. The low thermal conductivity member 8 is arranged to face the inner surface 60 of the plug cover 6 . The low thermal conductivity member 8 has lower thermal conductivity than the plug cover 6 .
Hereinafter, this embodiment will be described in detail.

Hereinafter, the center axis of the spark plug 1 will be referred to as a plug center axis C. As shown in FIG. Further, the direction in which the plug central axis C extends is referred to as an axial direction Z. As shown in FIG. The side of the spark plug 1 on which the sub-combustion chamber 7 of the spark plug 1 is located in the axial direction Z is called the tip end side, and the opposite side is called the base end side. In addition, the term “radial direction” simply means the radial direction of the spark plug 1 . The term “circumferential direction” simply means the circumferential direction of the spark plug 1 .

The spark plug 1 can be used, for example, as ignition means in internal combustion engines such as automobiles and cogeneration systems. A base end portion of the spark plug 1 is connected to an ignition coil (not shown), and a distal end portion of the spark plug 1 is arranged in a combustion chamber of an internal combustion engine.

The housing 2 is made of a heat-resistant metal material such as iron, nickel, iron-nickel alloy, stainless steel, etc., and formed into a cylindrical shape. A mounting screw portion 21 is formed on the outer peripheral portion of the housing 2 . The spark plug 1 is attached to the cylinder head by screwing the attachment screw portion 21 into a female screw hole provided in a cylinder head (not shown). When the spark plug 1 is attached to the cylinder head, a portion of the spark plug 1 on the tip side of the attachment screw portion 21 is exposed to the combustion chamber.

A housing front end portion 22 to which the plug cover 6 is attached is formed on the front end side of the mounting screw portion 21 in the housing 2 . The outer peripheral surface of the housing tip portion 22 has a housing concave portion 221 . The housing recessed surface portion 221 is formed to be recessed more toward the inner peripheral side than the portion adjacent to the proximal end side, and the distal end side is open. A plug cover 6 is attached so as to be inserted into the housing concave portion 221 of the housing tip portion 22 .

The plug cover 6 has a cup shape with an open proximal end. Further, the plug cover 6 has a shape of a body of revolution with the central axis C of the plug as a rotation axis. The plug cover 6 includes a cover bottom wall 61 and a cover peripheral wall 62 extending from the entire peripheral edge of the cover bottom wall 61 toward the base end side. As shown in FIGS. 1 and 2, the cover bottom wall 61 is formed in a disc shape. The cover peripheral wall 62 is formed in a cylindrical shape. As shown in FIG. 1, the cover peripheral wall 62 is joined to the housing concave portion 221 of the housing distal end portion 22 along the entire periphery of the base end portion thereof. A secondary combustion chamber 7 is formed by the plug cover 6 and the housing 2 .

A plurality of injection holes 611 are formed in the cover bottom wall 61 so as to penetrate the cover bottom wall 61 and communicate the auxiliary combustion chamber 7 with the space outside the spark plug 1 . The plurality of injection holes 611 are arranged on the outer peripheral side of the plug center axis C in the radial direction. The plurality of injection holes 611 are formed at regular intervals in the circumferential direction. Each injection hole 611 is formed so as to incline toward the outer peripheral side in the radial direction as it goes toward the tip side in the axial direction Z. As shown in FIG. It should be noted that the number, shape, location, etc. of the injection holes 611 are appropriately determined according to a request. A low thermal conductivity member 8 is arranged so as to face the inner surface 60 of the plug cover 6 .

The low thermal conductivity member 8 is made of a material having a thermal conductivity lower than that of the plug cover 6 . For example, the plug cover 6 can be made of a heat-resistant metal material such as iron, nickel, an iron-nickel alloy, or stainless steel, and the low heat-conducting member 8 can be made of ceramic whose thermal conductivity is lower than that of the plug cover 6. The low thermal conductivity member 8 is fixed to the plug cover 6 by welding, for example. The low thermal conductivity member 8 is formed to be thinner than the plug cover 6 .

The low thermal conductivity member 8 is formed along substantially the entire portion of the inner surface 60 of the plug cover 6 facing the sub-combustion chamber 7 . That is, like the plug cover 6, the low thermal conductivity member 8 is formed in a cup shape with an open base end. The low heat conductive member 8 includes a member bottom wall 81 facing the cover bottom wall 61 and a member peripheral wall 82 facing the cover peripheral wall 62 .

The member bottom wall 81 is formed like a disk like the cover bottom wall 61 . A communication hole 811 communicating with the injection hole 611 is formed through the member bottom wall 81 . That is, a plurality of communication holes 811 are formed in the member bottom wall 81 so as to be connected to the proximal end of each injection hole 611 .

The member peripheral wall 82 extends from the entire peripheral edge of the member bottom wall 81 toward the base end side, and has a cylindrical shape. Thereby, the low heat conductive member 8 is formed on the entire circumference in the circumferential direction, as shown in FIG. As shown in FIG. 1, the member peripheral wall 82 is formed so as to cover the discharge gap G from the outer peripheral side. That is, the member peripheral wall 82 is formed at least in the entire region where the discharge gap G in the axial direction Z is formed. The proximal end of the member peripheral wall 82 is formed up to the distal end surface of the housing distal end portion 22, and is closely opposed to the distal end surface.

An electrode arrangement hole H is formed through the cover bottom wall 61 and the member bottom wall 81 in the axial direction Z at the center when viewed from the axial direction Z. As shown in FIG. A ground electrode 5 is inserted into the electrode arrangement hole H. As shown in FIG.

The ground electrode 5 is formed so that its central axis coincides with the central axis C of the plug. The ground electrode 5 is formed in a substantially columnar shape. The ground electrode 5 is arranged so as to protrude from the electrode arrangement hole H toward the base end side. The end face of the ground electrode 5 on the base end side faces the tip end face of the center electrode 4 in the axial direction Z, and forms a discharge gap G between the end face of the center electrode 4 and the tip end face of the center electrode 4 .

The center electrode 4 is formed so that its center axis coincides with the center axis C of the plug. It is inserted and held inside the insulator 3 , and has its tip protruded from the insulator 3 .

The insulator 3 is formed by forming alumina or the like into a cylindrical shape. The insulator 3 is held inside the housing 2 . The tip portion of the insulator 3 protrudes further to the tip side than the tip surface of the housing tip portion 22 .

Next, the effects of this embodiment will be described.
The spark plug 1 of this embodiment is provided with a low thermal conductive member 8 that is arranged to face the inner surface 60 of the plug cover 6 and has a lower thermal conductivity than the plug cover 6 . Therefore, it is easy to suppress the heat of the flame generated in the auxiliary combustion chamber 7 from being taken away by the plug cover 6 . As a result, the ignitability of the spark plug 1 can be easily improved.

Further, the low thermal conductivity member 8 is formed all around the spark plug 1 in the circumferential direction. Therefore, it is possible to suppress the heat of the flame generated in the sub-combustion chamber 7 from being taken away by the plug cover 6 along the entire circumference.

Further, the low thermal conductive member 8 is arranged at least in the region where the discharge gap G in the axial direction Z is formed. As a result, the flame growth in the sub-combustion chamber 7 can be further facilitated. This will be explained below.

As shown in FIG. 3, the spark discharge S in the discharge gap G ignites the air-fuel mixture introduced into the sub-combustion chamber 7 through the nozzle hole 611, and the flame F is generated in the sub-combustion chamber 7. As shown in FIG. Such flame spreads in a substantially concentric shape. Therefore, by arranging the low thermal conductivity member 8 in the region where the discharge gap G is formed in the axial direction Z, it is possible to prevent the flame from colliding with the plug cover 6 at an early stage. As a result, it is possible to prevent the heat of the flame from being taken away by the plug cover 6 at an early stage and hinder the growth of the flame. In FIG. 3, the states of flame growth are represented by symbols F1 to F5. Symbols F1 to F5 indicate flame outline positions by time, and time progresses in the order of symbols F1 to F5. In addition, in FIG. 3, the outline of the flame F is schematically shown by a line, but in reality, as the flame propagates, the air-fuel mixture around the flame is compressed, so the temperature of the air-fuel mixture that the flame has not yet reached rises. do.

As described above, according to the present embodiment, it is possible to provide a spark plug capable of improving ignitability.

( Embodiment 1 )
As shown in FIG. 4, the present embodiment is an embodiment in which the configuration of the low thermal conductive member 8 is changed with respect to the reference embodiment 1. As shown in FIG.

In this embodiment, the low thermal conductivity member 8 is formed in a tubular shape having openings on both sides in the axial direction Z. As shown in FIG. That is, the low heat conductive member 8 is composed only of the member peripheral wall 82 covering the inner surface of the cover peripheral wall 62 and does not include the member bottom wall (see reference numeral 81 in FIG. 1) that covers the inner surface of the cover bottom wall 61 . Also in this embodiment, the low heat conductive member 8 is arranged at least in the region in which the discharge gap G is formed in the axial direction Z, and surrounds the entire discharge gap G on the entire circumference.

As shown in FIG. 4, in the cross section of the spark plug 1 including the plug central axis C, a straight line connecting the central portion GC of the discharge gap G and the tip of the low thermal conductive member 8 is defined as a first imaginary straight line VL1. In the cross section, a straight line connecting the central portion GC of the discharge gap G and the base end of the low thermal conductive member 8 is defined as a second imaginary straight line VL2. A central portion GC of the discharge gap G is a central portion between the tip of the center electrode 4 and the ground electrode 5 on the central axis C of the plug.

At this time, the acute angle θ1 formed between the first virtual straight line VL1 and the plug central axis C is 75° or less, and the acute angle θ2 formed between the second virtual straight line VL2 and the plug central axis C is , 75° or less. In this embodiment, the center of the low thermal conductive member 8 in the axial direction Z is arranged eccentrically so as to be located closer to the proximal side than the central portion GC of the discharge gap G, and the angle θ2 is smaller than the angle θ1. ing.

Others are the same as those of the first embodiment .
Among the reference numerals used in Embodiment 1 and subsequent embodiments, the same reference numerals as those used in the reference embodiments and embodiments described above are the same components as those in the reference embodiments and embodiments described above unless otherwise indicated. represents

In this embodiment, the low thermal conductivity member 8 is formed in a tubular shape having openings on both sides in the axial direction Z. As shown in FIG. Therefore, it is easy to insert the low thermal conductivity member 8 into the plug cover 6 . Further, there is no need to form a hole communicating with the injection hole 611 of the plug cover 6 or a hole for arranging the ground electrode 5, so that the productivity of the spark plug 1 can be easily improved.

Furthermore, in a cross section including the plug central axis C, the angle θ1 is 75° or less and the angle θ2 is 75° or less. As a result, even when the low heat conduction member 8 is formed in a cylindrical shape that opens on both sides in the axial direction Z, the low heat conduction member 8 can be arranged so as to widely cover the discharge gap G, and the auxiliary combustion chamber 7 It is possible to prevent the inner flame from being deprived of heat by the plug cover 6 and inhibiting its growth. As a result, it is easy to inject flame from the injection hole 611 toward the combustion chamber, and it is easy to improve the ignitability of the air-fuel mixture in the combustion chamber. This numerical value is supported by the experimental examples described later.
In addition, it has the same effects as those of the reference form 1 .

( Embodiment 2 )
As shown in FIG. 5, this embodiment has the same basic structure as that of the first embodiment , but has a plug cover 6 formed with a recess 600 for disposing a low thermal conductive member 8 therein.

The low thermal conductive member 8 is formed at least in the region where the discharge gap G is formed in the axial direction Z, and surrounds the entire discharge gap G from the outer peripheral side. In this embodiment, the length of the low thermal conductivity member 8 in the axial direction Z is half or less than the length of the cover peripheral wall 62 in the axial direction Z. As shown in FIG. Further, in this embodiment, the center of the low thermal conductive member 8 in the axial direction Z is at the same position as the central portion GC of the discharge gap G. As shown in FIG. Accordingly, the angles θ1 and θ2 are the same.

A surface of the plug cover 6 facing the low thermal conductive member 8 is formed with a recess 600 that is recessed toward the outer periphery from the periphery. The radial depth of the recess 600 is equivalent to the thickness of the low thermal conductive member 8 . A low thermal conductive member 8 is arranged in the concave portion 600 . The inner diameter φ1 of the low thermal conductive member 8 is equivalent to the inner diameter φ2 of the portion of the plug cover 6 adjacent to the recess 600 . As a result, the inner surface 80 of the low heat conductive member 8 and the inner surface 60 of the plug cover 6 are flush with each other.
Others are the same as those of the first embodiment .

In this embodiment, the plug cover 6 has a recess 600 in which the low thermal conductivity member 8 is arranged. Therefore, formation of a step between the low thermal conductive member 8 and the plug cover 6 can be easily prevented. As a result, the surface area of the wall surface surrounding the auxiliary combustion chamber 7 increases due to the formation of the step, which makes it easier for the heat of the flame in the combustion chamber to be lost, and unburned air-fuel mixture remains around the step. can be prevented.
In addition, it has the same effects as those of the first embodiment .

(Experimental example 1)
This example is an example of measuring the relationship between the time from ignition of the spark plug and the flame reaching distance described later, for a spark plug with a low heat conductive member and a spark plug without a low heat conductive member.

In this example, a sample 1, which is a spark plug having the same basic structure as that of reference 1 , and a comparative sample, which is a spark plug in which the low thermal conductivity member is removed from the spark plug of reference 1, were prepared. In Sample 1, the low thermal conductive member was made of ceramic with a thermal conductivity of 1.6 [W/mK]. The thickness of the low thermal conductive member of Sample 1 was set to 500 μm. Also, in each sample, the thermal conductivity of the plug cover was set to 90 [W/mK].

Then, each sample was attached to an internal combustion engine, the air-fuel ratio (A/F) of the combustion chamber was set to 20, and the flame reaching distance was measured by time from the ignition of the spark plug. As shown in FIG. 6, the flame arrival distance D is the linear distance from the nozzle hole 611 to the tip of the flame when the spark plug 1 attached to the cylinder head 11 of the internal combustion engine is viewed from the tip side in the axial direction.

The results are shown in FIG. In FIG. 7, the time on the horizontal axis means the time from ignition. That is, 0 [ms] on the horizontal axis is the time of ignition. In addition, in FIG. 7, the results of Sample 1 are plotted with square symbols "□", and the results of the comparative samples are plotted with diamond symbols "◇".

From FIG. 7, it can be seen that the sample 1 with the low heat conductive member tends to have earlier timing at which the flame blows out from the injection hole than the comparative sample without the low heat conductive member. It is considered that this is because Sample 1 is less likely to hinder the growth of the flame in the sub-combustion chamber due to the provision of the low heat conductive member compared to the Comparative Sample. By shortening the time from the ignition of the spark plug until the flame blows out from the nozzle hole, the spark plug provided with the low heat conductive member can move from the nozzle hole to the combustion chamber at a crank angle closer to TDC (that is, top dead center). can shoot flames. As a result, the spark plug provided with the low heat-conducting member can inject flame into the combustion chamber at a crank angle close to TDC and the cylinder temperature is high, thereby improving ignitability and improving each cycle. It is easy to realize combustion with little fluctuation in

In addition, it can be seen from FIG. 7 that the sample 1 including the low thermal conductive member has a larger slope of the plot than the comparative sample. In other words, it can be seen that the spark plug including the low heat-conducting member has a higher velocity of the flame ejected from the injection hole than the comparative sample. As a result, the spark plug including the low heat conductive member increases the fluidity of the airflow in the combustion chamber (that is, increases the turbulence of the airflow), and tends to increase the combustion speed. As a result, the spark plug provided with the low heat-conducting member is more effective in introducing EGR, stabilizing combustion in lean operating conditions, and suppressing knock under high loads than the comparative sample.

(Experimental example 2)
In this example, as shown in FIG. 8, the ignitability of a spark plug with a low heat conductive member and a spark plug without a low heat conductive member were evaluated. The ignitability of each spark plug was examined by measuring the A/F limit value. Here, the A/F limit is the limit air-fuel ratio for normal combustion, and it can be said that the larger the value of the A/F limit, the better the combustion performance. In this example, normal combustion means that the combustion variation rate is 3% or less. The combustion fluctuation rate is indicated by (standard deviation/average)×100% of the indicated mean effective pressure Pmi.

In this example, the same spark plug as the sample 1 shown in Experimental Example 1 was used as the spark plug provided with the low thermal conductive member, and the same spark plug as the comparative sample shown in Experimental Example 1 was used as the spark plug without the low thermal conductive member. used something.

In this example, while changing the A/F value, the combustion variation rate was measured from the output of the combustion pressure sensor, and the value of the A/F limit was examined. The combustion conditions for each cycle in each sample were the same. That is, the test was conducted under the conditions that the intake air amount, the fuel injection amount, and the opening/closing timing of the intake and exhaust valves were constant in each cycle, the engine speed was 2000 rpm, and the indicated mean effective pressure Pmi was 600 kPa. Results are shown in FIG.

As can be seen from FIG. 8, the sample 1 provided with the low heat conductive member has a higher A/F limit than the comparative sample without the low heat conductive member, indicating that the ignitability is improved.

(Experimental example 3)
In this example, as shown in FIG. 9, in a spark plug 1 having a basic structure similar to that of the first embodiment , an acute angle θ1 formed between a first imaginary straight line VL1 and the plug central axis C and a second imaginary straight line VL2 This is an example of measuring the flame reaching distance 9 ms after ignition when variously changing the angle θ2 on the acute angle side formed by the C and the plug central axis C. FIG.

In this example, the length of the low heat conduction member 8 in the axial direction Z can be varied while the center position of the low heat conduction member 8 in the axial direction Z is aligned with the central portion GC of the discharge gap G in the axial direction Z. , the angles θ1 and θ2 are changed. In this case, since the angles θ1 and θ2 are geometrically equivalent, they are hereinafter collectively referred to as the angle θ.

In this example, each sample was attached to an internal combustion engine and operated under the conditions that the engine speed was 2000 rpm and the indicated mean effective pressure Pmi was 600 kPa, and the flame reaching distance was measured 9 [ms] after ignition. . The results are shown in FIG.

As can be seen from FIG. 10, by setting the angle θ to 75° or less, the flame reaching distance becomes longer after 9 ms of ignition. That is, by setting the angle θ to 75° or less, it is easy to spread the flame in the combustion chamber early after ignition, and it is easy to strengthen the flame injection. Moreover, it can be understood from FIG. 10 that such an effect can be obtained more easily when the angle θ is set to 65° or less.

The present invention is not limited to the embodiments described above, and can be applied to various embodiments without departing from the scope of the invention. For example, an example in which the low thermal conductivity member is ceramic has been shown, but the present invention is not limited to this, and various other materials can be employed as long as the thermal conductivity is lower than that of the plug cover.

REFERENCE SIGNS LIST 1 spark plug 2 housing 3 insulator 4 center electrode 5 ground electrode 6 plug cover 60 inner surface of plug cover 611 injection hole 7 auxiliary combustion chamber 8 low heat conductive member

Claims (2)

a cylindrical housing (2);
a cylindrical insulator (3) held inside the housing;
a center electrode (4) held inside the insulator;
a ground electrode (5) forming a discharge gap (G) with the center electrode;
a plug cover (6) that constitutes, together with the housing, a sub-combustion chamber (7) in which the discharge gap is disposed, and that has an injection hole (611) penetrating inside and outside;
A spark plug (1) comprising: a low thermal conductivity member (8) disposed opposite to the inner surface (60) of the plug cover and having a lower thermal conductivity than the plug cover ,
The low thermal conductivity member is formed along the entire circumference of the spark plug in the circumferential direction,
The low thermal conductivity member is arranged at least in a region where the discharge gap is formed in the axial direction (Z) of the spark plug,
The low thermal conductivity member is formed in a tubular shape having openings on both sides in the axial direction,
In a cross section including the central axis (C) of the spark plug, a straight line connecting the central portion (GC) of the discharge gap and the tip of the low heat conductive member is defined as a first imaginary straight line (VL1), and the center of the discharge gap When a straight line connecting the portion and the base end of the low heat conductive member is defined as a second virtual straight line (VL2), the acute angle (θ1) formed by the first virtual straight line and the central axis is 75° or less. and an acute angle (θ2) formed by the second imaginary straight line and the central axis is 75° or less . The spark plug of claim 1, wherein said plug cover has a recess (600) in which said low thermal conductivity member is located.

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