A spark plug

Abstract

The application discloses a spark plug, which comprises an insulator, a center electrode, a metal shell and a side electrode; an opening part is arranged at the front end of the side electrode; the projection of the center electrode ignition end face on the vertical plane Z of the center electrode axis is completely in the projection S1 of the opening part on the vertical plane Z of the center electrode axis, so that the center electrode ignition end face is not shielded, the opening part divides the front end of the side electrode into two small end parts, the ignition end of the center electrode is thin, oil is not easy to adhere to the center electrode ignition end face and the opening part of the side electrode, the ability of the spark plug to resist oil drop accumulation is enhanced, the side electrode is rapidly heated, the ignition performance of the spark plug is improved, and the width of the side electrode guarantees the heat dissipation capacity and service life of the spark plug.

Description

TECHNICAL FIELD

[0001] The present application relates to a spark plug, in particular to a spark plug assembled in an internal combustion engine for igniting an air-fuel mixture. BACKGROUND

[0002] With the continuous progress of engine technology, especially the continuous popularization and application of high compression ratio, high EGR rate, supercharged direct injection, lean burn and other technologies, the engine has higher and higher requirements for the ignition quality of the spark plug. The spark plug is an important electrical device in the ignition system of a gasoline engine. The spark plug is used to ignite the compressed gasoline mixture in the cylinder, so that the engine starts to work. With the in-depth development of new energy vehicles, hybrid power has become the mainstream. When the hybrid engine is used at low temperature, especially in winter, the engine frequently starts and stops at low temperature. Because the fuel atomization is poor under low temperature working condition, fuel droplets are easily attached to the surface of each part of the combustion chamber, especially when the engine fails to start for the first time. The oil droplets sprayed will be attached to the surface of the center electrode and the side electrode of the spark plug. At this time, a large amount of oil droplets is easily deposited at the spark plug jump fire gap, causing the jump fire gap to be invalid due to oil droplet accumulation (as shown in Figure 1 and Figure 2 which affects the ignition between the center electrode and the side electrode, and reduces the ignition performance of the spark plug.

[0003] Through retrieval, the patents related to the present application mainly include the following patents:

[0004] For example, the patent with the authorization announcement number CN2512137Y and the authorization announcement date of September 18, 2002 relates to a spark plug for gasoline and gas engine ignition, and specifically relates to a tooth side electrode spark plug, which includes a center electrode and a tooth side electrode. The tooth side electrode has a tooth tip at the upper end, and the lower end of the tooth side electrode is welded with the shell to achieve electrical communication. The tooth tip is higher than the end surface of the center electrode and does not cover the end surface of the center electrode. There is a certain gap between the axial projection of the tooth side electrode and the cylindrical surface of the center electrode. The tooth side electrode is single or uniformly distributed in two. The tooth side electrode and the outer edge of the end part of the center electrode form a sharp angle, which promotes the complete combustion of the mixture, reduces pollution, achieves reliable ignition, rapid start, fuel saving and power increase, and the effect is more obvious for the use of gas engine.

[0005] However, the area of the front end of the side electrode in the above-mentioned document is still large, so that more oil will be attached to the side electrode, which will affect the ignition. At the same time, the distance between the front end of the side electrode and the outer edge of the ignition end part of the center electrode away from the rear end part of the side electrode is far, which requires higher pulse ignition voltage, thereby causing poor spark plug ignition.

[0006] Therefore, how to design a spark plug which can reduce the oil attached to the side electrode and shorten the distance between the front end of the side electrode and the outer edge of the center electrode ignition end on the side away from the rear end of the side electrode, thereby greatly enhancing the oil-drop accumulation resistance of the spark plug is a technical problem to be solved. SUMMARY

[0007] The technical problem to be solved by the present application is to provide a spark plug with an open portion of a side electrode which can reduce the oil attached to the side electrode and shorten the distance between the front end of the side electrode and the outer edge of the center electrode ignition end on the side away from the rear end of the side electrode, thereby greatly enhancing the oil-drop accumulation resistance of the spark plug.

[0008] To solve the above technical problem, the technical solution adopted by the present application is as follows: a spark plug comprises a rod-shaped center electrode extending along an axial direction AL; an insulator having an axial hole extending along the axial direction and retaining the center electrode in the axial hole, the center electrode being arranged on the front end side of the insulator; a metal shell surrounding and retaining the insulator in the circumferential direction, the rear end of the insulator extending out of the metal shell along the axial direction; and a side electrode, the front end of the side electrode being arranged in the horizontal direction, the rear end of the side electrode being arranged along the center electrode axial direction AL, the rear end of the side electrode being welded to the front end surface of the metal shell, and the front end of the side electrode being provided with an open portion, the center electrode axial line being set as line P, the vertical plane of the center electrode axial line P being set as Z plane, and the ignition end surface of the center electrode being set as Z1 plane; the open portion of the side electrode is projected on the Z plane along the center electrode axial direction AL, the projection plane of the open portion of the side electrode on the Z plane being set as S1 plane, and the ignition end surface Z1 plane of the center electrode is projected on the Z plane along the center electrode axial direction AL, the projection plane of the ignition end surface Z1 plane of the center electrode on the Z plane being set as S2 plane; and S2 plane is completely within S1 plane.

[0009] Further, the center line of the front end of the side electrode is set as L in the horizontal direction, the center line L is consistent with the opening direction of the open portion of the side electrode, the perpendicular line passing through the bottom of the open portion of the side electrode is set as M, and the perpendicular line passing through the top of the open portion of the side electrode is set as N; the front end of the side electrode is projected on the Z plane along the center electrode axial direction AL, the projection plane of the front end of the side electrode on the Z plane being set as S plane; and the corresponding projection lines of the perpendicular line M and the perpendicular line N on the Z plane are set as M' and N' along the center electrode axial direction AL.

[0010] The area of S plane between the projection line M' and the projection line N' is set as A1, the area of the projection plane S1 between the projection line M' and the projection line N' is set as A2, and the relationship between A1 and A2 is 0.06≤A2 / (A1+A2)≤0.4.

[0011] Further, a radius of the Z1 plane is set as R, and the R satisfies: 0.2mm≤R≤0.8mm.

[0012] Further, the opening part is V-shaped, U-shaped, frustum-shaped, cube-shaped, cuboid-shaped, etc.

[0013] Further, an angle of the V-shaped opening part is set as θ, and the angle θ satisfies: 10°≤θ≤80°.

[0014] Further, a projection line of the center line L on the Z plane is set as L' along the center electrode axis direction AL, two tangent lines M1 and N1 of the S2 plane are drawn, the line M1 and the line N1 are both perpendicular to the projection line L', and the line M1 is close to the opening bottom side.

[0015] An area of the S plane between the tangent line M1 and the tangent line N1 is set as B1, an area of the S1 plane between the tangent line M1 and the tangent line N1 is set as B2, and a relationship between B1 and B2 is: 0.1≤B2 / B1≤2.

[0016] Further, a width of the side electrode is set as D, and the D satisfies: 2mm≤D≤3.2mm.

[0017] Further, a distance between the line N' and the line N1 is set as C, and the C satisfies: 0mm≤C≤0.8mm.

[0018] The beneficial effects of the present application are that: the present application is provided with an opening part at the front end of the side electrode, and the projection of the center electrode ignition end face Z1 on the vertical plane Z of the center electrode axis is completely within the projection S1 of the opening part on the vertical plane Z of the center electrode axis, so that the center electrode ignition end face is not blocked, and the opening part forms two sharp end parts at the front end of the side electrode, which can not only reduce the oil attached to the side electrode, but also shorten the distance between the front end of the side electrode and the outer edge of the center electrode ignition end part away from the side electrode rear end part, thereby greatly enhancing the oil droplet accumulation resistance of the spark plug jumping gap; the ignition end of the center electrode is thin and the radius of the center electrode ignition end face is further limited, so that the oil is more difficult to adhere to the center electrode ignition end face and the sharp end part of the opening of the side electrode, thereby solving the oil accumulation problem between the two electrodes of the spark plug, greatly enhancing the oil droplet accumulation resistance of the spark plug jumping gap, improving the ignition performance of the spark plug, and further making the fuel burn more fully, and the fuel will not adhere to the electrodes, and greatly improving the anti-carbon deposition capacity of the spark plug; by further limiting the angle of the opening part of the side electrode, the ignition performance of the spark plug is good and the electrodes can be quickly heated at low temperature; by setting the width of the side electrode, the side electrode can also be quickly cooled at high temperature, thereby ensuring the service life of the spark plug; and the ignition performance of the spark plug is greatly improved. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 It is an axial sectional structure schematic view of the prior art spark plug;

[0020] Figure 2 It is Figure 1 an enlarged structure schematic view of part A;

[0021] Figure 3 It is an axial sectional structure schematic view of the spark plug in the embodiment of the present application;

[0022] Figure 4 It is a front view structure schematic view of the spark plug in the embodiment of the present application;

[0023] Figure 5 It is a three-dimensional structure schematic view of the spark plug when it is inclined at a certain angle in the embodiment of the present application;

[0024] Figure 6 It is Figure 5 a local enlarged structure schematic view of part B;

[0025] Figure 7 It is a three-dimensional structure schematic view of the side electrode in the embodiment of the present application, which embodies the positional relationship between the two parallel lines of the top end of the opening part and the bottom of the opening part and the center line of the side electrode;

[0026] Figure 8Schematic diagram of a plan view of the corresponding positions of the front end portion of the side electrode along the axis of the center electrode, the opening portion thereof, and the projection of the ignition end face of the center electrode on a plane perpendicular to the axis of the center electrode in a spark plug according to an embodiment of the present invention;

[0027] Figure 9 In the spark plug of the embodiment of the present invention, along the axis direction of the central electrode Figure 5 A schematic plan view of the projection of the middle front end portion onto a plane perpendicular to the axis of the central electrode;

[0028] Figure 10 1 is a characteristic plan view of the front end portion of the side electrode in the spark plug according to an embodiment of the present invention;

[0029] Figure 11 for Figure 8 Plane diagram of two tangent lines to the mid-circle;

[0030] Figure 12 for Figure 10 Schematic diagram of the plan view of the closed area formed by the two tangent lines, the side electrode projection and the opening projection.

[0031] In the figure: 1. insulator, 2. metal shell, 3. center electrode, 31. ignition end face, 4. side electrode, 41. front end, 411. opening, 5. oil. DETAILED DESCRIPTION

[0032] To make the purpose, technical solutions and advantages of the embodiments of the invention clearer, the following will be combined with the appended drawings of the embodiments of the invention. Figures 3-12 , clearly and completely describing the technical solutions of the embodiments of the invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the described embodiments of the present invention, all other embodiments derived by ordinary technicians in this field fall within the scope of protection of the present invention.

[0033] It should be noted that all directional indications (such as up, down, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship of components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0034] In addition, the description of the shape in the present invention may include rectangular parallelepiped, cube, V-shape, U-shape, polygon and other irregular shapes, all of which fall within the scope of protection of the present invention.

[0035] Example:

[0036] like Figure 3As shown, a spark plug includes a rod-shaped center electrode 3, which extends along the axial direction AL; an insulator 1, which has an axial hole extending along the axial direction and holds the above-mentioned center electrode 3 in the axial hole, and the center electrode 3 is arranged on the front end side of the insulator 1 (the AL arrow direction in the figure is the front end); a metal shell 2, which surrounds and holds the insulator 1 in the circumferential direction, and the rear end of the insulator 1 extends out of the metal shell 2 along the axial direction; and a side electrode 4, the front end portion of the side electrode 4 is arranged in the horizontal direction, and the rear end portion of the side electrode 4 is arranged along the axial direction AL of the center electrode 3, and the rear end portion of the side electrode 4 is welded to the front end surface of the above-mentioned metal shell 2.

[0037] like Figure 5 and Figure 6 As shown, an opening 411 is provided at the front end portion 41 of the side electrode 4. Figure 4 and Figure 6 As shown, the axis of the center electrode 3 is now set as line P, the plane perpendicular to the axis P of the center electrode 3 is set as Z plane, and the ignition end face 31 of the center electrode 3 is set as Z1 plane; when projected along the axis direction AL of the center electrode 3, the projection plane of the opening 411 of the side electrode 4 on the Z plane is set as S1 plane, and when projected along the axis direction AL of the center electrode 3, the projection plane of the ignition end face 31 of the center electrode 3 on the Z plane is set as S2 plane; Figure 8 As shown, surface S2 falls completely within surface S1. This allows the ignition front end surface 31 of the center electrode 3 to be completely unobstructed by the side electrode 4, further reducing the remaining area of ​​the front end portion 41 of the side electrode 4, excluding the opening 411. This further reduces the amount of oil 5 adhering to the side electrode 4. Furthermore, the front end portion 41 of the side electrode 4 is closer to the ignition front end surface 31 of the center electrode 3, shortening the distance between the front end of the side electrode 4 and the outer edge of the ignition end of the center electrode 3, which is located away from the rear end of the side electrode 4. This shortens the spark gap and improves ignition performance.

[0038] like Figure 7 and Figure 9 As shown, the center line of the front end portion 41 of the side electrode 4 is set to L in the horizontal direction, and this center line L is consistent with the opening direction of the opening portion 411 of the front end portion 41 of the side electrode 4; the perpendicular line perpendicular to the center line L and passing through the bottom of the opening portion 411 of the side electrode 4 is set to M, and the perpendicular line perpendicular to the center line L and passing through the top of the opening portion 411 of the side electrode 4 is set to N; when projected along the axial direction AL of the center electrode 3, the projection surface of the front end portion 41 of the side electrode 4 on the Z plane is set to S plane; when the perpendicular line M and the perpendicular line N are projected along the axial direction AL of the center electrode 3, the corresponding projection lines of the perpendicular line M and the perpendicular line N on the Z plane are set to M′ and N′; the area of ​​the S plane between the projection line M′ and the projection line N′ is now set to A1, and the area of ​​the projection surface S1 between the projection line M′ and the projection line N′ is set to A2.

[0039] In order to better determine the influence of the opening part 411 of the side electrode 4 on the performance of the side electrode 4, the following will take several spark plugs and divide them into 9 groups, each group of the opening part 411 of the front end of the side electrode 4 corresponds to a specific size of the opening, then the area A2 of the opening part 411 of the front end part 41 of the side electrode 4 projected along the central electrode 3 axis between the projection line M' and the projection line N', and the area A1 of the side electrode 4 projected along the central electrode 3 axis direction AL between the projection line M' and the projection line N' correspond to 9 groups of different ratios of A2 and (A1+A2), under the same conditions, the heat capacity of the front end part 41 of the side electrode 4 of the 9 groups of spark plugs (that is, the ability of the side electrode to quickly heat up at low temperature), the anti-overheating ability of the front end part 41 of the side electrode 4 (that is, the ability of the side electrode to resist high temperature and heat dissipation), and the anti-oil immersion ability of the side electrode 4 (the ability to resist oil sticking and accumulation on the side electrode) are tested, and the test results are shown in the following figure (where "●" represents excellent, " " represents good, " " represents medium, " " represents qualified, and "○" represents poor):

[0040]

[0041] From the above test results, it can be seen that as the A2 / (A1+A2) ratio increases, the heat capacity and anti-oil immersion ability of the end part of the side electrode 4 gradually change from poor to excellent, while the anti-overheating ability of the front end of the side electrode 4 is just the opposite; while increasing the anti-oil accumulation ability of the side electrode 4, the volume of the front end part 41 of the side electrode 4 will not affect the high temperature resistance and heat dissipation performance of the side electrode 4, so the area ratio range of A2 / (A1+A2) is preferably 0.06-0.4.

[0042] In addition, the ignition end of the central electrode 3 of the prior art spark plug is generally thick, and when the engine starts, the oil 5 sprayed is easy to stick to the central electrode due to the greater tension on the flat surface, and when the oil 5 sprayed covers the ignition end of the central electrode 3, it will still affect the anti-oil accumulation performance of the spark plug jump gap and affect the ignition performance of the spark plug. Therefore, as Figure 10 shown, the applicant also improves the ignition end surface 31 of the central electrode 3, that is, the ignition end surface 31 of the central electrode 3 is set to different values of radius R: the area of the ignition end surface 31 of the central electrode 3 is reduced, so that the ignition end surface 31 of the central electrode 3 is not easy to stick to oil.

[0043] Through experiments, it can be determined (the data in the specific experiment is not shown) that when the range of R is 0.2mm-0.8mm, the ignition end of the center electrode 3 is relatively thin, the middle electrode 3 ignition end is not easy to adhere to the oil 5, and the spark plug is easy to ignite when R is preferably 0.20mm, 0.25mm, 0.30mm, 0.35mm, 0.4mm, and the ignition effect of the spark plug is better.

[0044] The opening part 411 of the front end part 41 of the side electrode 4 can be V-shaped, U-shaped, frustum-shaped, cubic-shaped, and cuboid-shaped, but in order to more clearly show the technical solution, the opening part is preferably V-shaped (as shown in Figure 7

[0045] As shown in Figure 10 , the angle θ of the V-shaped opening part 411, through the exploration of the angle θ of the V-shaped opening part 411, if the angle θ is too large, the front end part 41 of the side electrode 4 will be too small in volume, which will reduce the heat dissipation capacity of the side electrode 4 and affect the service life of the side electrode 4; if the angle is too small, the side electrode 4 will block the ignition end surface 31 of the center electrode 3, which is easy to accumulate oil in the spark plug gap, thereby affecting the ignition performance; when the angle θ is 10°-80°, the service life of the spark plug and the oil resistance of the front end of the side electrode 4 are guaranteed.

[0046] As shown in Figure 11 and Figure 12 , along the axis direction AL of the center electrode 3, the projection line of the center line L on the Z plane is set as L', the two tangent lines M1 and N1 of the S2 surface are introduced, the line M1 and the line N1 are both perpendicular to the projection line L', and the line M1 is close to the opening bottom side; the area of the S surface between the tangent line M1 and the tangent line N1 is set as B1, and the area of the S1 surface between the tangent line M1 and the tangent line N1 is set as B2.

[0047] In order to further determine the influence of the opening part 411 of the front end of the side electrode 4 on the oil resistance of the spark plug gap, the service life of the side electrode 4 and the ignition performance of the spark plug, the side electrode of the above-mentioned 9 groups of spark plugs is further limited, and the applicant carries out tests on the oil resistance of the spark plug gap, the service life of the side electrode 4 and the ignition performance of the spark plug for the 9 groups of spark plugs with different ratios of B2 to B1. The test results are shown in the following figure (wherein "●" represents excellent, " " represents good, " " represents medium, " " represents qualified, and "○" represents poor):

[0048]

[0049] ​From the above test results, it can be seen that: with the continuous increase of the B2 / B1 ratio, the anti-oil immersion ability at the spark plug gap gradually changes from poor to excellent, the service life of the side electrode 4 gradually changes from excellent to poor, and the spark plug ignition performance first changes from poor to excellent and then changes again. This shows that the larger the opening part 411 of the side electrode 4 is, the less oil is accumulated at the front end part 41 of the side electrode 4, but the larger the opening is, the smaller the volume of the front end part 41 of the side electrode 4 is, the worse the heat dissipation and high temperature resistance are, and the side electrode 4 is more likely to be burned, which affects the service life and ignition performance of the spark plug.

[0050] Through the test results, when the B2 / B1 range is preferably 0.1-2, the side electrode 4 increases the anti-oil droplet accumulation ability while ensuring the high temperature resistance and heat dissipation performance of the side electrode 4, thereby ensuring the ignition performance and service life of the side electrode 4.

[0051] The rear end part of the side electrode 4 is welded together with the metal shell 2 of the spark plug, and the heat dissipation of the spark plug side electrode 4 is through the rear end part of the side electrode 4 to transfer heat to the metal shell 2 for heat dissipation, so the width D (as shown in Figure 10 ) of the side electrode 4 directly affects the heat dissipation ability of the side electrode 4, thereby affecting the service life of the spark plug side electrode, but if the width D of the side electrode 4 is too wide, it will increase the production cost, and through test comparison, when the width of the spark plug side electrode 4 is in the range of 2mm-3.2mm, the heat dissipation ability of the side electrode 4 with the opening part 411 is good, which ensures the service life of the spark plug side electrode 4.

[0052] As shown in Figure 7 , Figure 9 , Figure 11 , the vertical line N perpendicular to the center line L of the front end part 41 of the side electrode 4 and passing through the top of the opening part 411 of the side electrode 4 is set as N, the corresponding projection line N' of the vertical line N on the Z plane, the straight line N perpendicular to the projection line L' and tangent to the S plane, when the distance C between the line N' and the line N1 is in the range of 0mm-0.8mm, that is, the most front end of the side electrode projects beyond the projection of the center electrode 3, so that the front end of the side electrode 4 and the ignition end surface 31 of the center electrode 3 are in a good ignition distance, which is easy to ignite the spark plug.

[0053] In summary, the application is provided with an opening part 411 at the front end part 41 of the side electrode 4, and the projection of the center electrode ignition end face Z1 in the center electrode axis direction AL is such that the projection face S2 of the center electrode ignition end face Z1 on the vertical plane Z of the center electrode axis falls completely within the projection face S1 of the opening part 411 on the vertical plane Z of the center electrode 3 axis, so that the center electrode 3 ignition end face is not blocked, and the opening part 411 forms two relatively sharp end parts of the front end part 41 of the side electrode 4, which can not only reduce the oil 5 attached to the side electrode 4, but also shorten the distance between the front end of the side electrode 4 and the outer edge of the ignition end part of the center electrode 3 away from the rear end part of the side electrode, thereby greatly enhancing the oil droplet accumulation resistance of the spark plug jumping gap; the ignition end of the center electrode 3 is relatively thin and the radius of the center electrode ignition end face is further limited, so that the oil is more difficult to adhere to the center electrode 3 ignition end face and the relatively sharp end part of the opening of the side electrode 4, thereby solving the problem of oil accumulation between the two electrodes of the spark plug, greatly enhancing the oil droplet accumulation resistance of the spark plug jumping gap, improving the ignition performance of the spark plug, and further making the fuel burn more fully, and the fuel is not attached between the electrodes, which greatly improves the anti-carbon deposition capacity of the spark plug; by further limiting the angle of the opening part 411 of the side electrode 4, the ignition performance of the spark plug is good and the electrode can be quickly heated at low temperature; by setting the width of the side electrode 4, the side electrode 4 can also be quickly cooled at high temperature, thereby ensuring the service life of the spark plug; and the ignition performance of the spark plug is greatly improved.

[0054] The above examples are only for illustrating the application, not limiting the application, and those skilled in the art can make various changes or modifications without departing from the spirit and scope of the application, therefore all equivalent technical solutions should belong to the protection scope of the application, and the protection scope of the application should be defined by the claims.

Claims

1. A spark plug comprising a rod-shaped center electrode extending in an axial direction AL, an insulator having a shaft hole extending in the axial direction and holding the center electrode in the shaft hole, the center electrode being disposed at a front end side of the insulator, a metal shell surrounding and holding the insulator in a circumferential direction, a rear end of the insulator extending out of the metal shell in the axial direction, and a side electrode, a front end portion of the side electrode being disposed in a horizontal direction, a rear end portion of the side electrode being disposed in the axial direction AL of the center electrode, the rear end portion of the side electrode being welded to a front end face of the metal shell, characterized in that: The front end of the side electrode is provided with an opening part, the center electrode axis is set as line P, the vertical plane of the center electrode axis P is set as Z plane, the ignition end surface of the center electrode is set as Z1 plane; the projection of the opening part of the side electrode on the Z plane is set as S1 plane along the center electrode axis direction AL, the projection of the ignition end surface Z1 plane of the center electrode on the Z plane is set as S2 plane along the center electrode axis direction AL; then S2 plane is completely in S1 plane; The center line of the front end of the side electrode is set as L along the horizontal direction, the center line L is consistent with the opening direction of the opening part of the side electrode; the perpendicular line perpendicular to the center line L and passing through the opening bottom of the side electrode is set as M, the perpendicular line perpendicular to the center line L and passing through the opening top of the side electrode is set as N; the projection plane of the front end of the side electrode on the Z plane is set as S plane along the center electrode axis direction AL; the corresponding projection lines of the perpendicular line M and the perpendicular line N on the Z plane are set as M' and N' along the center electrode axis direction AL; The area of S plane between the projection line M' and the projection line N' is set as A1, the area of the projection plane S1 between the projection line M' and the projection line N' is set as A2, then the relationship between A1 and A2 satisfies: 0.06≤A2 / (A1+A2)≤0.

4.

2. A spark plug according to claim 1, characterized in that: The radius of the Z1 plane is set as R, and the R satisfies: 0.2mm≤R≤0.8mm.

3. A spark plug according to either of claims 1 or 2, characterised in that The opening part is V-shaped, U-shaped, frustum-shaped, square-shaped or cuboid-shaped.

4. A spark plug according to claim 3, characterized in that The angle of the V-shaped opening part is set as θ, and the angle θ satisfies: 10°≤θ≤80°.

5. The spark plug of claim 1 wherein: The projection line of the center line L on the Z plane is set as L' along the center electrode axis direction AL, and the two tangent lines M1 and N1 of the S2 plane are drawn, the line M1 and the line N1 are both perpendicular to the projection line L', and the line M1 is close to the opening bottom side; The area of S plane between the tangent line M1 and the tangent line N1 is set as B1, and the area of S1 plane between the tangent line M1 and the tangent line N1 is set as B2, then the relationship between B1 and B2 satisfies: 0.1≤B2 / B1≤2.

6. The spark plug of claim 1, wherein: The width of the side electrode is set as D, and the D satisfies: 2mm≤D≤3.2mm.

7. A spark plug according to claim 5 wherein: The distance between the line N' and the line N1 is set as C, and the C satisfies: 0mm≤C≤0.8mm.

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