Spark plug for a hybrid engine and method of preventing cracking of an insulator

Abstract

The invention relates to a spark plug for a hybrid engine, comprising an insulator and a metal shell, a center electrode and a terminal screw, the insulator being connected with a spark coil sheath and having an axial hole formed in the insulator, the insulator having a large cylindrical part near the rear end side, the height of the large cylindrical part in the axial direction being greater than 30 mm, and the insulator further having a small cylindrical part kept inside the metal shell, the ratio of the diameter of the small cylindrical part to the diameter of the threaded part of the metal shell being greater than 0.62. By controlling the diameter ratio of the insulator of the spark plug to the metal shell and the volume ratio of the protruding insulator skirt outside the threaded part of the metal shell to the center electrode, the voltage resistance of the spark plug is improved and the straight line of the front end of the insulator skirt is prevented from cracking.

Description

Technical Field

[0001] This invention relates to a method for improving the overall performance of spark plugs, and more particularly to a method for improving the voltage resistance level and preventing cracking of the insulator skirt of a small spark plug with a diameter less than M12mm and used in high compression ratio operating environments, as well as the spark plug itself; it belongs to the field of spark plug manufacturing technology in engine parts. Background Technology

[0002] In recent years, with increasingly stringent emission standards, especially those for fuel consumption and nitrogen oxides, engines have increasingly adopted hybrid technology to achieve low fuel consumption, no longer pursuing so-called higher power output. These hybrid engines are characterized by ultra-high compression ratios, boost ratios, high exhaust gas recirculation (EGR) rates, and high-energy ignition. This brings challenges such as difficulty in engine ignition, further increases in spark plug discharge voltage, and reduced spark plug life. Existing spark plugs have encountered problems such as unreliable ignition, insulator breakdown, and poor durability in response to these changes. Furthermore, the high EGR rate of hybrid engines also brings high-intensity thermal shock, posing a risk of cracking to the spark plug insulators exposed inside the engine combustion chamber.

[0003] On the other hand, with the development of engine technology, especially the continuous improvement of new energy hybrid vehicles in recent years, hybrid engines are becoming smaller and smaller, which makes the installation position of the spark plug smaller and smaller, and thus the spark plug size is also getting smaller and smaller. Moreover, hybrid engines no longer pursue the so-called power output per unit area. The main characteristics of these engines are ultra-high compression ratio, boost ratio, high exhaust gas recirculation rate (EGR rate) and high-energy ignition. Therefore, the compression ratio is getting higher and higher, and the breakdown voltage of the air-fuel mixture is also increasing.

[0004] Considering the two factors mentioned above, the voltage withstand capability and mechanical strength of spark plug insulators have been greatly challenged, often resulting in problems such as insufficient voltage withstand capability of spark plugs or cracking of the straight protruding part of the insulator skirt; it is necessary to improve these aspects.

[0005] After searching, no relevant patent technology reports were found. The most similar patent documents are as follows:

[0006] 1. Chinese patent application CN201720523628.9 discloses a spark plug protective sleeve and a large-bore gas turbine engine, mainly relating to the field of engine technology. The spark plug protective sleeve includes a protective sleeve body, a first elastic mounting seat, an elastic element, and a fastening connector. The protective sleeve body includes a main body and a pre-combustion part, which are fixedly connected. The pre-combustion part has a pre-combustion cavity, and the main body has a receiving hole communicating with the pre-combustion cavity. The pre-combustion part has a first vent hole connecting the pre-combustion cavity to the outside. However, while the spark plug protective sleeve can significantly increase the engine compression ratio, it does not solve the aforementioned problems caused by the spark plug itself.

[0007] 2. Patent application CN201020219945.X, entitled "Protruding Precious Metal Spark Plug", discloses a protruding precious metal spark plug, including a terminal screw, an insulator, a shell, a center electrode and a side electrode. The ignition end of the center electrode has a layer of precious metal. The characteristic is that the side electrode, corresponding to the ignition end of the center electrode, has a circular protrusion. A platinum metal layer is welded on the protrusion. The precious metal is resistance welded and then directly melted onto the side electrode substrate by laser to form a metallurgical bonding layer. By stamping, the precious metal metallurgical bonding layer flows to the top of the protrusion to form the spark end face of the electrode, thus solving the problems of ignition performance and long life. While the spark plugs provided by this patent are low in cost, have no polarity effect, good flame extinguishing effect, low ignition voltage, are suitable for higher compression ratios, provide reliable ignition for turbocharged engines, have a wide range of engine air-fuel ratios, are suitable for lean combustion, have good cold start performance, reduce engine vibration, run more smoothly, and have extended lifespan, they do not take into account the aforementioned problems caused by the smaller size of the spark plugs due to the increased compression ratio.

[0008] 3. Patent CN201410790440.1, entitled "Spark Plug Structure with Protective Sleeve," discloses a spark plug structure with a protective sleeve, comprising a fixed sleeve, a connecting sleeve, and a guide sleeve connected in sequence. The center lines of the inner holes of the fixed sleeve, connecting sleeve, and guide sleeve are collinear. The inner hole of the guide sleeve is a flared opening, smaller inside and larger outside. The guide sleeve has an exhaust port penetrating its inner and outer walls. Using this structure, installing the spark plug on the cylinder head can reduce the impact of the flow field on ignition stability. The guide surface in the inner hole of the guide sleeve allows the in-cylinder flow field to develop in a reasonable direction, thereby guiding the flame towards an ideal direction. Simultaneously, the engine compression ratio can be further increased, the lean-burn coefficient can be improved, and power and efficiency can be significantly increased. However, this invention does not address the aforementioned problems caused by the spark plug itself.

[0009] As can be seen from the description of the above patents, although some people have proposed technical solutions to improve spark plug performance, most of them only consider how to increase the compression ratio and efficiency, but none of them address the problems existing in the spark plugs of current hybrid engines. Therefore, as hybrid engines become smaller and the compression ratio becomes higher, no effective solution has been proposed to solve the technical problem of insulator cracking in spark plugs. Thus, the aforementioned problems still exist and require further research. Summary of the Invention

[0010] This invention addresses a series of problems existing in spark plugs in hybrid engines, proposing a spark plug that can effectively improve the voltage resistance level of spark plugs and effectively prevent the spark plug insulator from cracking in hybrid engines. This spark plug not only has excellent ignition performance and high insulator strength, but also effectively overcomes the cracking of the straight part of the spark plug insulator skirt.

[0011] Another objective of this invention is to provide an insulator for spark plugs in a hybrid power engine that, even with a reduced diameter, can still effectively improve the voltage withstand level of the spark plug insulator and effectively prevent cracking of the spark plug insulator in the hybrid power engine.

[0012] Another objective of this invention is to propose a method for improving the voltage withstand level of the spark plug insulator in a hybrid engine, while effectively preventing cracking of the straight section of the insulator skirt, by utilizing the above-mentioned spark plug and insulator.

[0013] To achieve this objective, the present invention provides a spark plug for a hybrid power engine, comprising an insulator and a metal housing, a center electrode, a side electrode, and a connecting thread; wherein the insulator is installed inside the metal housing and sleeved outside the center electrode; the insulator has a large cylindrical portion near the rear end side, and has a shaft hole formed along the axis within the insulator body, in which the center electrode is installed; the axial height of the large cylindrical portion is 30 mm or more; the insulator also has a small cylindrical portion retained inside the metal housing, characterized in that: the ratio of the diameter (d1) of the small cylindrical portion of the insulator to the diameter (D1) of the threaded portion of the metal housing is 0.62 or more.

[0014] Preferably, the diameter (d1) of the small cylindrical portion is the average diameter.

[0015] Preferably, the insulator has a skirt (2C) below the small cylindrical part, and a straight part (2D) below the skirt (2C). The height of the straight part (2D) is H, and a portion of the straight part (2D) protrudes beyond the lower end face of the threaded part of the metal shell. Let the volume of the straight part (2D) at height H be volume 1 (v1), and the volume of the end of the center electrode at the corresponding height be volume 2 (v2), satisfying 0.155≤volume 2 / volume 1≤0.417.

[0016] Preferably, the front end of the central electrode has a boss portion, the height of the boss portion in the axial direction is L, and L is between 0.05 and 0.25 mm.

[0017] Preferably, the precious metal end is connected to the boss portion through the melting zone, the precious metal diameter d3 is 0.7-1.0 mm, and the axial height E is 0.3-0.4 mm.

[0018] Preferably, the ignition gap distance between the center electrode and the side electrode is G, which satisfies the ratio of G / E*d3*L between 8.25 and 52.75 mm.

[0019] Preferably, the ignition gap distance between the center electrode and the side electrode is G, which satisfies the ratio of G / E*d3*L between 15.1 and 35.5 mm.

[0020] Preferably, the ignition gap distance between the center electrode and the side electrode is set as G, and G is controlled between 0.7-1.1 mm.

[0021] A spark plug insulator for a hybrid power engine, the insulator having a large cylindrical portion near the rear end and a axial hole formed along the axis within the insulator body; the axial height of the large cylindrical portion is 30 mm or more; the insulator also has a small cylindrical portion retained inside a metal housing, characterized in that the ratio of the diameter (d1) of the small cylindrical portion of the insulator to the diameter (D1) of the threaded portion of the metal housing is 0.62 or more.

[0022] Preferably, the insulator has a skirt 2C below the small cylindrical part, and a straight part 2D below the skirt 2C. The height of the straight part 2D is H, and a portion of the straight part 2D protrudes beyond the lower end face of the threaded part of the metal shell. Let the volume of the straight part 2D at height H be volume 1 (v1), and the volume of the end of the center electrode at the corresponding height be volume 2 (v2), satisfying 0.155≤volume 2 / volume 1≤0.417.

[0023] Preferably, the insulator is made of α-alumina or silicon nitride material, and the high-temperature insulation performance of the insulator is ensured to have a voltage breakdown capability of more than 30 kV under the spark plug ignition temperature conditions.

[0024] A method for preventing cracking of spark plug insulators in hybrid engines improves the spark plug's voltage withstand capability and prevents cracking of the insulator skirt front end by controlling the diameter ratio of the spark plug insulator to the metal shell and the volume ratio of the straight section insulator to the center electrode.

[0025] Preferably, the ratio of the diameter of the control spark plug insulator to the diameter of the metal housing is set to 0.62 or higher.

[0026] Preferably, the volume ratio of the outer insulating skirt of the threaded portion of the control protruding metal shell to the central electrode is such that the volume of the straight portion 2D below the insulating skirt 2C at height H is volume 1 (v1), and the volume of the end of the central electrode at the corresponding height is set as volume 2 (v2), satisfying 0.155≤volume2 / volume1≤0.417.

[0027] The beneficial technical effects of this invention are:

[0028] The present invention controls the diameter ratio of the spark plug insulator to the metal shell, and the volume ratio of the outer insulator skirt protruding from the threaded portion of the metal shell to the center electrode, and has the following advantages:

[0029] 1. By limiting the diameter of the small cylindrical part of the insulator to a ratio of the diameter of the small cylindrical part to the diameter of the threaded part of the metal shell of 0.62 or higher, the voltage resistance level of the spark plug can be effectively improved.

[0030] 2. In this invention, the volume of the straight section 2D below the skirt 2C is set as volume 1, that is, the volume of the straight section 2D within the height H range is set as volume 1, and the volume of the center electrode corresponding to its height is set as volume 2. Under such circumstances, 0.155≤volume 2 / volume 1≤0.417 is satisfied, so that the straight section will not crack.

[0031] 3. The present invention uses α-alumina or silicon nitride materials to make the insulator, which can effectively improve the voltage withstand capability of the spark plug insulator and ensure that the high-temperature insulation performance of the insulator has a voltage breakdown capability of more than 30 kV under the spark plug ignition temperature conditions. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the overall structure of the spark plug of the present invention;

[0033] Figure 2 This is a partially enlarged schematic diagram of the small cylindrical portion of the insulator in this invention;

[0034] Figure 3This is a schematic diagram of the insulator and center electrode structure of the protruding metal shell threaded portion of the present invention;

[0035] Figure 4 This is a schematic diagram of the insulator structure of the present invention. Detailed Implementation

[0036] Researchers have discovered that with the miniaturization and high compression ratios of hybrid engines, the requirements for ignition and insulation performance of existing spark plugs are becoming increasingly stringent. This presents a growing challenge for spark plugs used in hybrid engines. On one hand, the decreasing size of engines necessitates further reduction in spark plug size; on the other hand, the increasing compression ratios demand even better ignition and insulation performance from the spark plugs. Currently, spark plugs used in hybrid engines are simply scaled-down versions of conventional spark plugs, leading to numerous compatibility issues. In particular, the insulation is prone to breakdown or cracking, significantly impacting the spark plug's performance and lifespan.

[0037] Researchers, through their study of these issues, discovered that this situation is largely related to the choice of structural dimensions between the spark plug insulator and the metal shell. Firstly, the small cylindrical portion of the insulator is spatially constrained by the shrinking diameter of the spark plug, resulting in an increasingly smaller diameter. Furthermore, because it is not exposed inside the combustion chamber, it is not protected from high pressure and is the part of the spark plug most susceptible to high-voltage penetration. Secondly, the skirt of the insulator is exposed to the engine combustion chamber. Due to the reduction in the spark plug's structural dimensions, the skirt of the insulator also shrinks accordingly. Since the most prominent straight section at the front end of the skirt is in a high-temperature environment, and the wall thickness of the skirt is correspondingly reduced, it is prone to cracking at the front end under high compression ratio impact.

[0038] Therefore, the present invention adopts strict control over the volume ratio between the end of the insulator skirt and the metal shell, as well as the ratio of the diameter of the small cylindrical part to the diameter of the threaded part of the metal shell, to prevent the small cylindrical part of the insulator skirt from being punctured or the insulator skirt from cracking, thereby effectively improving the overall performance of the insulator skirt, which is a direction worth studying.

[0039] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Example 1

[0040] A hybrid spark plug has a thread diameter of M12 and includes an insulator 2, a metal shell 6, a center electrode 9, and a connecting screw 1. The insulator 2 is made of α-alumina or silicon nitride, and can also be made of silicon nitride. The insulator's high-temperature insulation performance ensures that its voltage breakdown capability is above 30 kV under the spark plug ignition temperature conditions. The insulator 2 has a axial hole formed along its axis and a large cylindrical part 2A near the rear end. 2A is connected to the ignition coil sheath and its function is to isolate high voltage. Its axial height is above 30 mm, thereby preventing fly-through between the connecting screw 1 and the metal shell 6. The insulator 2 also has a small cylindrical part 2B that is retained inside the metal shell 6. The small cylindrical part 2B is spatially constrained by the small diameter of the hybrid spark plug, and its diameter is small. Since it is not exposed inside the combustion chamber and is not protected by high pressure, it is the part of the spark plug most susceptible to high voltage penetration.

[0041] In this invention, the ratio of the diameter d1 of the small cylindrical portion 2B to the diameter D1 of the threaded portion of the metal housing 6 is controlled to be above 0.62. Experiments have shown that by reasonably controlling the diameter ratio of the insulator to the metal housing, the spark plug's withstand voltage level can be effectively improved while simultaneously preventing insulation breakdown. It should be noted that this is not simply about increasing the insulator wall thickness. In practical applications, manufacturing issues must also be considered, as a thicker insulator diameter makes interference more likely when the insulator is joined to the metal housing. Therefore, a reasonable ratio must be controlled. Furthermore, the diameter of the small cylindrical portion referred to here is the average diameter.

[0042] The insulator 2 also has a front-side skirt 2C, which is exposed to the engine combustion chamber during operation, and a straight portion 2D closer to the front end than the front-side skirt 2C (see...). Figure 2The straight section 2D helps improve the spark plug's resistance to carbon buildup. When the diameter of the straight section 2D is smaller, its temperature rises rapidly to over 500°C, which can quickly remove carbon buildup adhering to its surface. However, in high-temperature areas, the temperature of the straight section 2D may be too high. When used in engines with high EGR rates, the straight section 2D is prone to cracking due to more severe thermal shocks. In this invention, to avoid cracking of the straight section 2D due to thermal shocks, the following technical solution is adopted: the volume of the straight section 2D below the skirt 2C is set as a solid. Volume 1 (V1), that is, the volume of the straight section 2D within the height range of H, is defined as volume 1 (V1), and the volume of the center electrode corresponding to its height is defined as volume 2 (V2). In this case, 0.155 ≤ volume 2 / volume 1 ≤ 0.417 is satisfied. Here, controlling the volume ratio is actually to balance the temperature of the straight section 2D of the insulator. In order to increase the spark plug's anti-carbon deposit performance, the straight section 2D is often set at the front end of the insulator skirt 2C, and a part of it extends out of the lower end face 61 of the threaded part of the metal shell. The total length of its straight section is H, see Appendix. Figure 3 As shown; this allows the front end of the insulator to heat up quickly, thus reaching the self-cleaning temperature faster when there is carbon buildup. However, in engines of vehicles with EGR, if the temperature is too high, the insulator is prone to cracking under thermal shock. By controlling the ratio of the volume of the insulator in the threaded part of the metal shell to the volume of the central electrode, the temperature of the straight part of the insulator can be controlled within a suitable range, so that the straight part can be present without cracking.

[0043] Furthermore, the center electrode 9 is roughly cylindrical and is located inside the insulator 2 and at the front end of the spark plug. One end of it protrudes from the front end of the insulator, forming an ignition gap with the side electrode. To cope with the high EGR rate (Exhaust Gas Recirculation) of the engine, the discharge gap is set to be above 0.8mm, which can improve the problem of high misfire rate in high EGR rate engines. The center electrode 9 can be made of nickel alloy. To increase thermal conductivity, a copper core can also be set inside the center electrode. Since the temperature of the center electrode is higher than that of the insulator in the thermal equilibrium state of the spark plug, the center electrode will radiate heat to the insulator, especially in the high speed range, where the temperature of the center electrode is even higher and it is easier to radiate heat to the insulator. In engines with EGR, the EGR rate is higher in the high speed range, so the insulator is more subjected to thermal shock in the high speed range, and the insulator is at risk of cracking. In the configuration of this invention, the volume 2 (V2) / volume 1 (V1) is controlled within the range of 0.155-0.412. Experiments have shown that this can effectively avoid the occurrence of insulator cracking.

[0044] The center electrode 9 has a boss at its front end with an axial height of E. The precious metal end 12 is connected to the boss through a molten zone. The diameter d3 of the precious metal is greater than 0.7 mm, and the axial height E is less than 0.35 mm. The ignition gap distance is set as G, and the height of the boss at the front end of the center electrode 9 is L. The ratio of G / E*d3*L is between 10 and 53, preferably between 15 and 25. This ensures excellent ignition performance and durability even in engines with high EGR rates and high-energy ignition.

[0045] The metal housing 6 is located on the outer periphery of the insulator and has a threaded portion for fastening to the engine cylinder head and fixing the spark plug to the engine. The metal housing 6 can be made of high-quality carbon steel suitable for cold heading, such as SWCH10A (Japanese grade) or SWCH18A. In addition, to increase its corrosion resistance, a zinc or nickel plating can be applied to its surface.

[0046] The side electrode 10 is fixed to the metal housing 6 by welding and forms a discharge gap G with the center electrode by bending. Alternatively, a noble metal 11 can be provided on the side electrode 10 to increase its durability. When the noble metal 11 is provided, the discharge gap is formed by the distance between the noble metal 12 on the center electrode 9 and the noble metal 11 on the side electrode 10. This gap can be obtained by plugging a needle or by projection detection.

[0047] The wiring screw 1 has a head 1A that protrudes from the insulator and a rod-shaped part 1B that is inserted into the insulator. The head 1A is electrically connected to the ignition coil, and the current is transmitted to the center electrode 9 through the rod-shaped part 1B. It is worth noting that in order to make the length of the rear end of the insulator more than 30mm, the length of the head 1A can be set to less than 8mm. In addition, in order to prevent bending during processing, the rod-shaped part 1B can also be set to a multi-segment structure. The wiring screw 1 can be made of high-quality carbon steel.

[0048] Resistor 7 is located between the connecting screw 1 and the center electrode 9. Its function is to absorb electromagnetic noise and provide a connection. 7A is generally made of conductive material, and 7B is generally made of semiconductor material.

[0049] Alternatively, talc powder 4 and steel wire rings 3 and 5 can be placed between the metal shell 6 and the insulator 2. This structure can improve the overall sealing performance of the spark plug.

[0050] Alternatively, a sealing ring 8 can be installed between the metal housing 6 and the insulator 2 to improve the overall sealing performance of the spark plug.

[0051] Alternatively, the spark plug can be a flat sealing type, in which case a sealing ring 13 can be set to achieve a seal between the engine cylinder head and the spark plug. Of course, the spark plug can also be a cone seat type.

[0052] To verify the above technical effects, the inventors manufactured 22 samples. The sample information and test results are as follows:

[0053]

[0054] During the test, a water spray test bench was used to heat and cool the linear section of the spark plug insulator. This test bench is equipped with a flame gun, spark plug holder, temperature detection device, control panel, and high-pressure water spray device. Using these devices, the linear section of the spark plug was heated to 850°C, held at that temperature for 1 minute, and then cooled to 200°C using water mist. This test was repeated cyclically, and the linear section was visually inspected for cracking after each cycle. Spark plugs that completed 10 or more cycles were considered excellent and marked with "◎"; those that completed 5 to 10 cycles were considered acceptable and marked with "○"; and those that completed less than 5 cycles were considered unacceptable and marked with "△".

[0055] The above experiments verified that by controlling the ratio of the insulator volume to the central electrode volume in the threaded part of the metal shell, the temperature of the straight part of the insulator can be controlled within a suitable range, thus achieving a straight part without cracking.

[0056] As can be seen from the above description of the embodiments, the present invention also relates to a method for improving the overall performance of spark plugs. By controlling the diameter ratio of the spark plug insulator to the metal shell and the volume ratio of the straight section insulator to the center electrode, the two parameters are controlled to improve the voltage resistance of the spark plug and prevent the straight front end of the insulator skirt from cracking.

[0057] The ratio of the diameter of the control spark plug insulator to the diameter of the metal shell is set to be 0.62 or higher.

[0058] The volume ratio of the outer insulating skirt of the threaded part of the control protruding metal shell to the central electrode is such that the volume of the insulating part of the threaded part of the control metal shell is set as volume 1 (V1), and the volume of the corresponding central electrode is set as volume 2 (V2), satisfying 0.155≤volume2 / volume1≤0.417.

[0059] It should be noted that the above-listed embodiments are merely a clear and complete description of the technical solution of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Furthermore, terms such as "upper," "lower," "front," "rear," and "middle" used in this specification are only for clarity of description and are not intended to limit the scope of the present invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of the present invention. Simultaneously, the structures, proportions, sizes, etc., depicted in the accompanying drawings are only used to complement the content disclosed in the specification for those skilled in the art to understand and read, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by the present invention, should still fall within the scope of the technical content disclosed in the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

Claims

1. A spark plug for a hybrid power engine, comprising an insulator and a metal housing, a center electrode, a side electrode, and a terminal screw; wherein, An insulator is installed inside a metal housing and located outside the central electrode. The insulator has a large cylindrical portion near the rear end and a shaft hole formed along the axis within the insulator body, in which the central electrode is installed. The axial height of the large cylindrical portion is 30 mm or more. The insulator also has a small cylindrical portion retained inside the metal housing. The characteristic is that the ratio of the diameter d1 of the small cylindrical portion of the insulator to the diameter D1 of the threaded portion of the metal housing is 0.62 or more. Below the small cylindrical portion of the insulator is a skirt 2C of the insulator, and below the skirt 2C is a straight portion 2D of the insulator. The height of the straight portion 2D is H, and a portion of the straight portion 2D protrudes beyond the lower end face of the threaded portion of the metal housing. Let the volume of the straight portion 2D of the insulator at height H be volume 1, and the volume of the end of the central electrode at the corresponding height be volume 2, satisfying 0.155 ≤ volume 2 / volume 1 ≤ 0.

417.

2. The spark plug for a hybrid engine as described in claim 1, characterized in that: The diameter d1 of the small cylindrical part is the average diameter.

3. The spark plug for a hybrid engine as described in claim 1, characterized in that: The central electrode has a boss at its front end, and the height of the boss in the axial direction is L, which is between 0.05mm and 0.25mm.

4. The spark plug for a hybrid engine as described in claim 3, characterized in that: The precious metal end is connected to the boss part through the molten zone. The diameter d3 of the precious metal is 0.7mm-1.0mm and the axial height E is 0.3mm-0.4mm.

5. The spark plug for a hybrid engine as described in claim 3 or 4, characterized in that: The ignition gap distance between the center electrode and the side electrode is G, which satisfies the ratio of G / E*d3*L between 8.25mm and 52.75mm.

6. The spark plug for a hybrid engine as described in claim 3, characterized in that: The ignition gap distance between the center electrode and the side electrode is G, which satisfies the ratio of G / E*d3*L between 15.1mm and 35.5mm.

7. The spark plug for a hybrid engine as described in claim 6, characterized in that: The ignition gap distance between the center electrode and the side electrode is set as G, and G is controlled between 0.7mm and 1.1mm.

8. A spark plug insulator for a hybrid power engine, the insulator having a large cylindrical portion near the rear end and a axial hole formed along the axis within the insulator body; the large cylindrical portion having an axial height of 30 mm or more; the insulator further having a small cylindrical portion retained within a metal housing, characterized in that: The ratio of the diameter d1 of the small cylindrical part of the insulator to the diameter D1 of the threaded part of the metal shell is greater than 0.62; the small cylindrical part of the insulator has a skirt 2C below it, and a straight part 2D of the insulator is below the skirt 2C. The height of the straight part 2D is H, and a portion of the straight part 2D protrudes beyond the lower end face of the threaded part of the metal shell; let the volume of the straight part 2D of the insulator at height H be volume 1, and let the volume of the end of the center electrode at the corresponding height be volume 2, satisfying 0.155≤volume 2 / volume 1≤0.

417.

9. The spark plug insulator for a hybrid engine as described in claim 8, characterized in that: The insulator is made of α-alumina or silicon nitride material, and the high-temperature insulation performance of the insulator is ensured to have a voltage breakdown capability of more than 30 kV under the spark plug ignition temperature conditions.

10. A method for preventing cracking of the spark plug insulator in a hybrid engine, comprising controlling the diameter ratio of the spark plug insulator to the metal shell and the volume ratio of the linear portion insulator to the center electrode, thereby improving the spark plug's voltage withstand capability and preventing cracking of the linear portion at the front end of the insulator skirt; characterized in that: The control ratio of the spark plug insulator diameter to the metal shell diameter is a ratio of the diameter d1 of the small cylindrical part of the insulator to the diameter D1 of the threaded part of the metal shell diameter of 0.62 or greater. The small cylindrical part of the insulator has a skirt 2C below it, and a straight part 2D of the insulator is below the skirt 2C. The height of the straight part 2D is H, and a portion of the straight part 2D protrudes beyond the lower end face of the threaded part of the metal shell. Let the volume of the straight part 2D of the insulator at height H be volume 1, and the volume of the end of the center electrode at the corresponding height be volume 2, satisfying 0.155 ≤ volume 2 / volume 1 ≤ 0.417.

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