spark plug
The spark plug design addresses pre-ignition by controlling heat transfer through precise geometric relationships, reducing overheating and ignition risks.
Patent Information
- Application Number
- DE102025124138
- Authority / Receiving Office
- DE · DE
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2025-06-23
- Publication Date
- 2025-12-31
AI Technical Summary
Existing spark plugs are prone to pre-ignition due to overheating of the insulator, which acts as an ignition source, and there is a need to reduce this occurrence.
A spark plug design with specific geometric constraints, including a stepped insulator, a metal housing with a threaded section, and a retaining section, where the volume of the space at the front end and the relationship between the outer diameter of the threaded section and the distance from the front end to the seat surface satisfy the condition V/(R²·L) ≤ 0.0170, and the contact area between the metal casing and the space meets 1.90 ≤ S/V, to manage heat transfer effectively.
The design effectively reduces the occurrence of pre-ignition by managing heat absorption and transfer, ensuring efficient heat dissipation and minimizing the likelihood of ignition.
Smart Images
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Abstract
Description
BACKGROUND OF THE INVENTION 1. Field of the invention
[0001] The present invention relates to a spark plug. 2. Description of the related technology
[0002] A known spark plug comprises an insulator containing a central electrode and a metal casing arranged around an outer periphery of the insulator. Japanese unexamined patent application JP 2013-55022A describes a technology for preventing pre-ignition, which occurs when the insulator overheats and acts as an ignition source, by defining the volume of the space between an inner circumferential surface of the metal casing and an outer circumferential surface of the insulator within a predetermined area. SUMMARY OF THE INVENTION
[0003] There is a need for a technology to reduce the occurrence of pre-ignitions, as known in related technology.
[0004] The present invention was made to meet this demand, and one objective of the present invention is to provide a spark plug that can reduce the occurrence of pre-ignition.
[0005] To achieve the goal described above, a spark plug, according to a first aspect, has an insulator with an axial hole extending from the front end to the rear end along an axial line. The insulator has a stepped section whose outer diameter decreases from the rear end to the front end; a center electrode located in the axial hole; and a cylindrical metal housing, the metal housing being arranged around an outer periphery of the insulator and having an inner circumferential surface. The metal housing comprises a threaded section with an external thread; a seat section with a seating surface provided at the rear end of the threaded section; and a retaining section provided at the inner circumferential surface, the retaining section holding the stepped section. The spark plug satisfies the condition V / (R). 2 ·L) ≤ 0.0170, where V (mm 3) is the volume of a space located on the front end of the retaining section and within the inner circumferential surface including the retaining section, excluding the center electrode and the insulator, R (mm) is the outside diameter of the threaded section, and L (mm) is the distance from a front end of the metal housing to the seat surface.
[0006] According to a second aspect, based on the first, the insulator, in a cross-section including the axial line, has no protruding section on any outer circumferential surface of the insulator in a region located between an external corner at the front end of the insulator and an adjacent internal corner located on the front end face of the step section and facing the inner circumferential surface of the metal casing. The protruding section is a rounded external corner with a radius of 1 mm or less.
[0007] According to a third aspect, which builds upon the first or second aspect, the spark plug further contains a ground electrode connected to the metal housing. The ground electrode contains nickel or platinum as its main component.
[0008] According to a fourth aspect, which is based on one of the first to third aspects, the spark plug fulfills the condition 1.90 ≤ S / V, where S (mm 2 ) is an area where the metal casing is in contact with the room.
[0009] According to the present invention, the volume V (mm²) 3 ) of the space located on the front end of the retaining section and within the inner circumferential surface of the metal housing including the retaining section, excluding the center electrode and the insulator, the outer diameter R (mm) of the threaded section and the distance L (mm) from the front end of the metal housing to the seat surface, the condition V / (R 2·L) ≤ 0.0170. By focusing on the relationship between the volume of the space into which the combustion gas enters and the volume of a section that transfers the heat of the combustion gas to the engine, one can correctly determine the relationship between the heat absorbed by the spark plug from the combustion gas and the heat released by the spark plug. This can reduce the occurrence of pre-ignition. BRIEF DESCRIPTION OF THE FIGURES
[0010] The invention will be described below with reference to the drawings, without being limited thereto. Fig. 1 is a half-section view of a spark plug according to a first embodiment; Fig. Figure 2 is an enlarged cross-sectional view of part of the spark plug; Fig. 3 is a half-section view of a spark plug according to a second embodiment; Fig. Figure 4 is an enlarged cross-sectional view of part of the spark plug; Fig. 5 is a half-section view of a spark plug according to a third embodiment; Fig. Figure 6 is an enlarged cross-sectional view of part of the spark plug; Fig. 7 is a half-section view of a spark plug according to a fourth embodiment; and Fig. Figure 8 is an enlarged cross-sectional view of part of the spark plug. DESCRIPTION OF PREFERRED EXECUTION FORMS
[0011] Preferred embodiments of the present invention will now be described with reference to the accompanying drawings. Fig. Figure 1 is a half-section view of a spark plug 10 according to a first embodiment with an axial line X at the boundary. The lower part of Fig. 1 is referred to as the front end of spark plug 10, and the upper part of Fig. 1 is referred to as the rear end of the spark plug 10 (this also applies to the Fig. 2, Fig. 3, Fig. 4, Fig. 5 to Fig. 6). The spark plug 10 contains an insulator 11, a center electrode 14 and a metal housing 16.
[0012] The insulator 11 is an essentially cylindrical element made of ceramic, for example aluminum oxide, which exhibits good mechanical properties and insulating properties at high temperatures. The insulator 11 has an axial hole 12 extending along the axial line X and includes a stepped section 13 whose outer diameter decreases from the rear end to the front end.
[0013] The central electrode 14 is located in a front region of the axial hole 12 in the insulator 11. The central electrode 14 is a rod-shaped conductor containing a highly thermally conductive core material embedded in a base material. The base material can be, for example, a metal such as a nickel-based alloy or nickel. The core material can be, for example, copper or an alloy containing copper as the main component. The core material can also be omitted. The central electrode 14 can be provided with a tip located at its front end, primarily made of a noble metal such as platinum, iridium, or rubric. The tip can also be omitted.
[0014] The central electrode 14 is electrically connected to a metal terminal 15 in the axial hole 12. The metal terminal 15 is a rod-shaped element intended for connection to an ignition system (not shown) and is made of a conductive metal material (e.g., low-carbon steel).
[0015] The metal housing 16 is an essentially cylindrical element made of a conductive metal material (e.g., low-carbon steel). The metal housing 16 includes a threaded section 17 that engages an internal thread in a spark plug hole in an engine (not shown), and a seat section 18 provided at the rear end of the threaded section 17, which has a seating surface 19. A seal 23 is arranged between the threaded section 17 and the seat section 18.
[0016] The threaded section 17 has an external thread. When the threaded section 17 is screwed into the spark plug hole and the seat surface 19 with the interposed seal 23 is pressed against the engine, an axial stress is exerted on the threaded section 17. The metal housing 16 has an inner circumferential surface 20 that includes a retaining section 21 located at the front end of the stepped section 13 of the insulator 11 to hold the stepped section 13. The distance from a front end 22 of the metal housing 16 to the seat surface 19 is L (mm).
[0017] A ground electrode 24 is a rod-shaped conductor connected to the metal housing 16. The ground electrode 24 contains a highly thermally conductive core material embedded in a base material. The base material can, for example, be made of a nickel-based alloy. The core material can, for example, be made of copper or an alloy containing copper as the main component. The main component (element with the highest concentration) of the base material of the ground electrode 24 is nickel. The core material can be omitted. The ground electrode 24 is provided with a tip located at one end of the ground electrode 24, which is mainly made of a noble metal such as platinum, iridium, or rubble. The tip can be omitted. An ignition gap is provided between the ground electrode 24 and the center electrode 14.
[0018] Fig. Figure 2 is an enlarged sectional view of part of the spark plug 10, which contains the axial line X. Fig. Figure 2 shows an area on one side of the axial line X, while an area on the other side is omitted (this also applies to the Fig. 4, Fig. 6 and Fig. 8) An inner seal 25 is arranged between the stepped section 13 of the insulator 11 and the metal housing 16 to prevent gas from escaping into a combustion chamber of the engine (not shown). The inner seal 25 is part of the retaining section 21. The inner seal 25 is an annular plate element. The material of the inner seal 25 can be, for example, a metal such as iron or steel, which is softer than the metal material of the metal housing 16.
[0019] The insulator 11 has a front end 26 located at the front end 22 of the metal housing 16. The central electrode 14 projects from the front end 26 of the insulator 11 toward the front end. A cylindrical space 27 is formed within the inner circumferential surface 20 of the metal housing 16. The space 27 is defined by the insulator 11 and the inner seal 25. The space 27 has a volume V (mm³). 3 ), which corresponds to the volume of a solid of revolution created by rotating a surface (mm²) 2 ) of the space 27 around the axial line X is obtained, wherein the area has a outline defined by the inner circumferential surface 20 of the metal housing 16 (including an inner circumferential surface of the inner seal 25), an outer circumferential surface of the insulator 11 and the perpendicular from the front end 22 of the metal housing 16 to the axial line X in the cross-section containing the axial line X.
[0020] The outer circumferential surface of the insulator 11 comprises a projecting section 29a in a region located between an outer corner 28 at the front end 26 of the insulator 11 and an inner corner 29 adjacent to and on the front end face of the step section 13, and facing the inner circumferential surface 20 of the metal housing 16. In the present embodiment, the outer corner 28 and the inner corner 29 are rounded, but this is not the only possible configuration. The outer corner 28 and the inner corner 29 can, of course, also be formed without chamfer or rounding. Likewise, the projecting section 29a can be rounded or chamfered.
[0021] The preceding section 29a is a rounded external corner with a radius of 1 mm or less. If the preceding section 29a forms an angled corner surface created by chamfering, the preceding section 29a is an external corner for which an imaginary arc smoothly connecting the ends of the angled corner surface has a radius of 1 mm or less. The radius of the external corner of the preceding section 29a in the cross-section of the insulator 11 containing the axial line X can be measured with an image measuring device or a projector.
[0022] The spark plug 10 ignites the fuel supplied to the combustion chamber of the engine (not shown), and some of the high-temperature combustion gas produced by the combustion of the fuel enters the chamber 27. The combustion gas entering the chamber 27 heats the insulator 11, the metal housing 16, and the inner seal 25. As the volume V of the chamber 27 increases, so does the volume of combustion gas entering the chamber 27, resulting in an increased amount of heat transferred from the combustion gas to the insulator 11, the metal housing 16, and the inner seal 25.
[0023] The outside diameter (diameter) of the threaded section 17 is R (mm). The outside diameter R is the nominal diameter specified in JIS B 0205-4:2001. The outside diameter R (mm) of the threaded section 17, the distance L (mm) between the front end 22 of the metal housing 16 and the seat surface 19 (see Fig. ) and the volume V (mm³) 3) of space 27 satisfy the condition V / (R 2 ·L) ≤ 0.0170. Here, R is 2 ·L is proportional to the volume of a section that transfers the heat of the combustion gas to the engine. By focusing on the ratio between the volume V of the space 27 into which the combustion gas enters and the volume of the section that transfers the heat of the combustion gas to the engine, the heat absorbed by the spark plug 10 from the combustion gas can be transferred from the spark plug 10 to the engine via the threaded section 17, thus reducing the occurrence of pre-ignition with the insulator 11, the metal housing 16 and other components that serve as an ignition source.
[0024] The volume V (mm 3 ), the outer diameter R (mm) and the distance L (mm) preferably satisfy the condition 0.0010 ≤ V / (R 2·L). This is because a minimum size of room 27 ensures sufficient purging performance and leaves fewer superheated particles in room 27, thus reducing the likelihood of pre-ignition by unburned residues.
[0025] If the area where the metal housing 16 is in contact with the space 27 is S (mm 2 If the S / V value is 1.90, the spark plug 10 preferably meets the S / V ratio. This is because, with increasing surface area S of the metal housing 16, the combustion gas entering the space 27 is more easily cooled by the metal housing 16, thus reducing the heat accumulated in the spark plug 10 and further reducing the occurrence of pre-ignition.
[0026] The area S corresponds to the area of a cylindrical surface obtained by rotating, about the axial line X, the distance over which the inner circumferential surface 20 of the metal housing 16 extends between the front end of the inner seal 25 and the front end 22 of the metal housing 16. The area S can be increased by increasing the diameter of a section of the inner circumferential surface 20 of the metal housing 16 that is in contact with the space 27. The volume V can be prevented from increasing excessively by increasing the thickness of a section of the insulator 11 that is in contact with the space 27, corresponding to an increase in the diameter of the inner circumferential surface 20. Thus, both V / (R) 2 ·L) ≤ 0.0170 as well as 1.90 ≤ S / V are fulfilled.
[0027] A second embodiment is described with reference to the Fig. 3 and Fig. 4 described. In the spark plug 10 of the first embodiment described above, the front end 26 of the insulator 11 is located on the front end of the front end 22 of the metal housing 16. In contrast, in a spark plug 30 of the second embodiment described below, a front end 35 of an insulator 31 is located on the rear end of a front end 33 of a metal housing 32. In the second embodiment, elements identical to those of the first embodiment are designated with the same reference numerals, and the following description is partially omitted.
[0028] Fig. Figure 3 is a half-section view of the spark plug 30 according to the second embodiment. The spark plug 30 includes the insulator 31, the center electrode 14, and the metal housing 32. The distance from the front end 33 of the metal housing 32 to the seat 19 is L (mm). An ignition gap is provided between a rod-shaped ground electrode 34 connected to the metal housing 32 and the center electrode 14. The main component of the ground electrode 34 is platinum.
[0029] Fig. Figure 4 is an enlarged sectional view of a portion of the spark plug 30, including the axial line X. The front end 35 of the insulator 31 is located on the rear end face of the front end 33 of the metal housing 32. The center electrode 14 projects from the front end 33 of the metal housing 32 toward the front end face. A space 36, located within the inner circumferential surface 20 of the metal housing 32, excluding the center electrode 14 and the insulator 31, and defined by the inner seal 25, has a volume V (mm³). 3 The volume V (mm³) 3 ), the outer diameter R (mm) of the threaded section 17 and the distance L (mm) satisfy the condition V / (R 2 ·L) ≤ 0.0170. This can reduce the occurrence of pre-ignition.
[0030] The spark plug 30 is structured such that a section of the ground electrode 34 is located in the space 36. The volume of the section of the ground electrode 34 in the space 36 is subtracted from the volume V of the space 36. The volume V of the space 36 corresponds to the volume resulting from the subtraction of an overlapping volume of the ground electrode 34 from the volume of a solid of revolution generated by rotating about the axial line X of a surface (mm²). 2The area 36 is obtained, the outline of which is defined by the inner circumferential surface 20 of the metal housing 32 (including an inner circumferential surface of the inner seal 25), an outer circumferential surface and the front end 35 of the insulator 31, the central electrode 14, and the perpendicular from the front end 33 of the metal housing 32 to the axial line X. The volume of the ground electrode 34 in the space 36 (overlapping volume of the ground electrode 34) is determined by multiplying the area of a region (triangular region) in which the ground electrode 34 and the space 36 overlap in cross-section, containing the axial line X, by the width of the ground electrode 34 (volume of a triangular prism).
[0031] The outer circumferential surface of the insulator 31 has no projecting section with a rounded corner having a radius of 1 mm or less in a region 39 located between an outer corner 37 at the front end 35 of the insulator 31 and an inner corner 38 adjacent to and on the front end face of the step section 13, and facing the inner circumferential surface 20 of the metal housing 32. Since the region 39 has a substantially constant electric field strength, the occurrence of a discharge (side spark) between the region 39 and the metal housing 32 can be reduced. Although the region 39, in the present embodiment, runs parallel to the axial line X, it is not limited to this. The region 39 can, of course, also run at an angle to the axial line X or be curved.
[0032] Spark plug 30 preferably also meets 0.0010 ≤ V / (R 2·L). If, in addition, the area in which the metal housing 32 is in contact with the space 36 is S (mm 2 If the S / V is ) the spark plug 30 preferably meets the requirements of 1.90 ≤ S / V. This is because the occurrence of pre-ignition can be further reduced.
[0033] A third embodiment is described with reference to the Fig. 5 and Fig. 6 described. In the spark plug 30 of the second embodiment described above, the center electrode 14 projects from the front end 33 of the metal housing 32 towards the front end. In contrast, in a spark plug 40 of the third embodiment described below, the center electrode 14 is located on the rear end of a front end 43 of a metal housing 42. In the third embodiment, elements identical to those of the first embodiment are marked with the same reference numerals, and the following description is partially omitted.
[0034] Fig. Figure 5 is a half-section view of the spark plug 40 according to the third embodiment. The spark plug 40 comprises an insulator 41, the center electrode 14, and the metal housing 42. The distance from the front end 43 of the metal housing 42 to the seat 19 is L (mm). An ignition gap is provided between a rod-shaped ground electrode 44 connected to the metal housing 42 and the center electrode 14. The main component of the ground electrode 44 is platinum.
[0035] Fig. Figure 6 is an enlarged sectional view of a portion of the spark plug 40, including the axial line X. A front end 45 of the insulator 41 and the center electrode 14 are located on the rear end of the front end 43 of the metal housing 42. A space 46, located within the inner circumferential surface 20 of the metal housing 42, excluding the center electrode 14 and the insulator 41, and defined by the inner seal 25, has a volume V (mm³). 3 The volume V (mm³)3 ), the outer diameter R (mm) of the threaded section 17 and the distance L (mm) satisfy the condition V / (R 2 ·L) ≤ 0.0170. This can reduce the occurrence of pre-ignition.
[0036] The spark plug 40 is structured such that a section of the ground electrode 44 is located in the space 46. The volume of the section of the ground electrode 44 in the space 46 is subtracted from the volume V of the space 46. The volume V of the space 46 corresponds to the volume determined by subtracting an overlapping volume of the ground electrode 44 from the volume of a solid of revolution obtained by rotating about the axial line X of a surface (mm²). 2The outline of the space 46 is obtained by the inner circumferential surface 20 of the metal housing 42 (including an inner circumferential surface of the inner seal 25), an outer circumferential surface and the front end 45 of the insulator 41, the central electrode 14, the axial line X, and the perpendicular from the front end 43 of the metal housing 42 to the axial line X. The volume of the ground electrode 44 in the space 46 (overlapping volume of the ground electrode 44) is determined by multiplying the area of a region (quadrilateral region) in which the ground electrode 44 and the space 46 overlap in cross-section, containing the axial line X, by the width of the ground electrode 44 (volume of a quadrilateral prism).
[0037] The outer circumferential surface of the insulator 41 has no protruding section with a rounded corner having a radius of 1 mm or less in a region 49 located between an outer corner 47 at the front end 45 of the insulator 41 and an inner corner 48 adjacent to and on the front end face of the step section 13, and facing the inner circumferential surface 20 of the metal housing 42. Since the region 49 has a substantially constant electric field strength, the occurrence of side sparks between the region 49 and the metal housing 42 can be reduced. Although the region 49 in the present embodiment is parallel to the axial line X, it is not limited to this. The region 49 can, of course, also be at an angle to the axial line X or be curved.
[0038] Spark plug 40 preferably also meets the requirements of 0.0010 ≤ V / (R). 2·L). If, in addition, the area in which the metal housing 42 is in contact with the space 46 is S (mm 2 If the S / V is ) the spark plug 40 preferably meets the requirements of 1.90 ≤ S / V. This is because the occurrence of pre-ignition can be further reduced.
[0039] A fourth embodiment is described with reference to the Fig. 7 and Fig. 8 described. In the first embodiment of the spark plug 10 described above, the insulator 11 has the aforementioned section 29a in the area between the outer corner 28 at the front end 26 and the inner corner 29. In contrast, an insulator 51 in a spark plug 50 of the fourth embodiment does not have an outer corner in the area between an outer corner 55 at the front end 26 and an inner corner 56. In the fourth embodiment, elements identical to those of the first embodiment are identified by the same reference numerals, and the following description is partially omitted.
[0040] Fig. Figure 7 is a half-section view of the spark plug 50 according to the fourth embodiment. The spark plug 50 comprises the insulator 51, the center electrode 14, and a metal housing 52. The distance from a front end 53 of the metal housing 52 to the seat surface 19 is L (mm). An ignition gap is provided between a rod-shaped ground electrode 24 connected to the metal housing 52 and the center electrode 14.
[0041] Fig. Figure 8 is an enlarged sectional view of a portion of the spark plug 50, containing the axial line X. The front end 26 of the insulator 51 and the center electrode 14 are located on the front end face of the front end 53 of the metal housing 52. A space 54, located within the inner circumferential surface 20 of the metal housing 52, excluding the center electrode 14 and the insulator 51, and defined by the inner seal 25, has a volume V (mm³). 3 The volume V (mm³) 3), the outer diameter R (mm) of the threaded section 17 and the distance L (mm) satisfy the condition V / (R 2 ·L) ≤ 0.0170 to reduce the occurrence of pre-ignition. The volume V (mm³) 3 ) of space 54 corresponds to the volume of a solid of revolution formed by rotating a surface (mm²) 2 ) of the space 54 around the axial line X is obtained, wherein the outline of the area is defined by the inner circumferential surface 20 of the metal housing 52 (including an inner circumferential surface of the inner seal 25), an outer circumferential surface of the insulator 51 and the perpendicular from the front end 53 of the metal housing 52 to the axial line X in cross-section, which contains the axial line X.
[0042] The outer circumferential surface of the insulator 51 has no projecting section with a rounded corner having a radius of 1 mm or less in a region 57 located between the outer corner 55 at the front end 26 of the insulator 51 and the inner corner 56 adjacent to and on the front end face of the step section 13, and facing the inner circumferential surface 20 of the metal casing 52. Since the region 57 has a substantially constant electric field strength, the occurrence of side sparks between the region 57 and the metal casing 52 can be reduced. Although the region 57 is at an angle to the axial line X in the present embodiment, it is not limited to this. The region 57 can, of course, be parallel to the axial line X or curved.
[0043] Spark plug 50 preferably also meets the requirements of 0.0010 ≤ V / (R). 2·L). If, in addition, the area in which the metal housing 52 is in contact with the space 54, S (mm 2 If the S / V is ) the spark plug 50 preferably meets 1.90 ≤ S / V. This is because the occurrence of pre-ignition can be further reduced. Example
[0044] The present invention will now be described in more detail using an example. However, the present invention is not limited to this example.
[0045] Samples No. 1 to 13 of the spark plug 10 according to the first embodiment were prepared by the tester. The samples differed in volume V (mm³). 3 ) of space 27, the outer diameter (nominal diameter) R (mm) of the thread section 17, the distance L (mm) and the area S (mm) 2The tester attached the prepared samples to a 1.3-liter naturally aspirated inline four-cylinder engine and conducted a test by running the engine for one minute at 6000 rpm with the throttle fully open and determining the ignition advance based on the waveform of the ion current. If no advance occurred within one minute, the ignition timing (crankshaft angle) was advanced by 1° and the test was performed similarly. The test was repeated until the ignition timing that caused advance was determined.
[0046] The samples were rated A if the ignition timing was advanced by 4° or more compared to the regular ignition timing of an OES (Original Equipment Supplier) spark plug for the engine used in the test at the first occurrence of pre-ignition, B if the ignition timing was advanced by 2° or more and less than 4°, and C if the ignition timing was advanced by less than 2°.
[0047] The distance L (mm) of each sample was measured after the test. The distance L was determined by rounding the digit to the second decimal place. An image of the sample's cross-section after the test, including the axial line X, was taken, and the area of the space 27, whose outline is defined by the inner circumferential surface 20 of the metal housing 16, the inner circumferential surface of the inner seal 25, the outer circumferential surface of the insulator 11, and the perpendicular from the front end 22 of the metal housing 16 to the axial line X, was determined by image processing. Subsequently, the area was integrated to determine the volume (capacity V) of the solid of revolution obtained by rotating the area around the axial line X. The volume V was determined by rounding the digit to the second decimal place.Additionally, in the cross-section of the sample after the test, including the axial line X, the distance over which the inner circumferential surface 20 of the metal housing 16 extended between the front end of the inner seal 25 and the front end 22 of the metal housing 16 was measured, and this was integrated to determine the area S of the cylindrical surface obtained by rotation about the axial line X. The area S was determined by rounding the digit to the second decimal place.
[0048] Table 1 shows the volume V (mm³). 3 ) of space 27, the outer diameter R (mm) of the threaded section 17, the distance L (mm), the area S (mm) 2 ), V / (R 2 ·L), S / V and the quality of each of samples Nos. 1 to 13. The outside diameter R is not a value obtained by measuring the outside diameter of thread section 17, but the nominal diameter specified in a standard such as JIS. Here, V / (R) was used. 2·L) is determined by rounding the digit at the fifth decimal place and S / V by rounding the digit at the third decimal place. Table 1 Nr. V(mm 3 ) R(mm) L(mm) S(mm 2 ) V / (R 2 ·L) S / V Güte 1 12,8 12 26,5 72,3 0,0034 5,65 A 2 22,0 10 26,5 41,8 0,0083 1,90 A 3 22,0 12 12,7 41,8 0,0120 1,90 A 4 37,5 12 19,0 72,3 0,0137 1,93 A 5 54,0 12 26,5 142,4 0,0142 2,64 A 6 37,5 10 26,5 78,9 0,0142 2,10 A 7 37,5 10 26,5 68,0 0,0142 1,81 B 8 45,0 10 26,5 68,0 0,0170 1,51 B 9 22,0 10 12,7 35,2 0,0173 1,60 C 10 36,8 10 19,0 85,2 0,0194 2,32 C 11 37,5 10 19,0 72,3 0,0197 1,93 C 12 75,5 12 26,5 143,5 0,0198 1,90 C 13 122,5 14 26,5 152,3 0,0236 1,24 C
[0049] As can be seen from Table 1, samples No. 1 to 8, for which V / (R 2 ·L) ≤ 0.0170 applies, rated with A or B, while samples No. 9 to 13, for which V / (R 2 ·L) > 0.0170, were rated with C. For samples No. 1 to 8, for which V / (R 2 . L) ≤ 0.0170 applies, a large amount of the heat absorbed by the spark plug 10 from the combustion gas was probably transferred from the spark plug 10 to the engine via the threaded section 17, so that pre-ignition did not easily occur.
[0050] Among samples 1 to 8, samples 1 to 6, for which S / V was 1.90 ≤ 1.90, were rated A, while samples 7 and 8, for which S / V was < 1.90, were rated B. In samples 1 to 6, the combustion gas that entered chamber 27 was probably slightly cooled by the metal housing 16, thus reducing the heat stored in the spark plug 10 and making pre-ignition less likely.
[0051] The example shows that the occurrence of pre-ignition can be reduced if V / (R 2 ·L) ≤ 0.0170 is fulfilled. Furthermore, it also became clear that the occurrence of pre-ignition can be further reduced if 1.90 ≤ S / V is fulfilled.
[0052] Although the present invention is based on the embodiments described above, it is in no way limited to the embodiments described above, and it is easily understood that various improvements and modifications are possible without deviating from the core of the present invention.
[0053] Although the ground electrode 24, 34, 44 is connected to the metal housing 16, 32, 42, 52 in the spark plug 10, 30, 40, 50 according to the embodiments, this does not entail any limitation. The ground electrode 24, 34, 44 can of course also be omitted, so that the discharge takes place between the center electrode 14 and the metal housing 16, 32, 42, 52.
[0054] Although the inner seal 25 is arranged between the stepped section 13 of the insulator 11, 31, 41, 51 and the metal housing 16, 32, 42, 52, i.e., the inner seal 25 is part of the retaining section 21 in the embodiments, this does not imply any limitation. The inner seal 25 can, of course, be omitted so that the stepped section 13 is in direct contact with the retaining section 21. In this case, a portion of the retaining section 21 that is in direct contact with the stepped section 13 defines the space 27, 36, 46, 54.
[0055] Although the seal 23 is positioned between the threaded section 17 and the seat section 18 in the embodiments, this does not imply any limitation. The seal 23 can, of course, also be omitted. Furthermore, the seat surface 19 can be a conical surface (a conical shape) whose diameter decreases towards the front end, corresponding to the shape of the spark plug hole in the engine (tapered seat). In this case, the distance L between the front end of the metal housing and the seat surface corresponds to dimension A specified in JIS B 8031:2006. DESCRIPTION OF REFERENCE MARKS 10, 30, 40, 50 spark plug 11, 31, 41, 51 Insulator 12 axial holes 13th stage section 14 Center electrode 16, 32, 42, 52 metal housing 17 Thread section 18 Seating section 19 seats 20 inner circumferential area 21 Stop section 22, 33, 43, 53 Front end of the metal casing 24, 34, 44 Ground electrode 26, 35, 45 Front end of the insulator Rooms 27, 36, 46, and 54 37, 47, 55 outside corner 38, 48, 56 Inside corner 39, 49, 57 area X Axial line QUOTES INCLUDED IN THE DESCRIPTION
[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature
[0000] JP 2013 - 55022 A
[0002]
Claims
[1] Spark plug (30), comprising: an insulator (31) with an axial hole (12) extending from a front end to a rear end along an axial line (X), wherein the insulator (31) has a step section (13) with an outer diameter that decreases from the rear end to the front end; a central electrode (14) arranged in the axial hole (12); and a metal housing (32) having a cylindrical shape, wherein the metal housing (32) is arranged around an outer periphery of the insulator (31) and includes an inner circumferential surface (20), wherein the metal housing (32) comprises a threaded section (17) with an external thread, a seat section (18) with a seat surface (19) which is provided at the rear end side of the threaded section (17), and a holding section (21) which is provided on the inner circumferential surface (20), wherein the holding section (21) holds the step section (13), and where the spark plug (30) satisfies the condition V / (R 2 ·L) ≤ 0.0170 is satisfied, where V (mm 3 ) is a volume of a space (36) located at the front end of the retaining section (21) and within the inner circumferential surface (20) including the retaining section (21) and excluding the central electrode (14) and the insulator (31), R (mm) is an outer diameter of the threaded section (17) and L (mm) is a distance from a front end (33) of the metal housing (32) to the seat surface (19). [2] Spark plug (30) according to claim 1, wherein in a cross-section containing the axial line (X), the insulator (31) does not have a projecting section on an outer circumferential surface of the insulator (31) in a region (39) which is located between an outer corner (37) at a front end (35) of the insulator (31) and an inner corner (38) adjacent to and on the front end side of the step section (13) and which faces the inner circumferential surface (20) of the metal housing (32). [3] Spark plug (30) according to claim 1 or 2, further comprising: a ground electrode (34) connected to the metal housing (32), wherein the ground electrode (34) has Ni or Pt as its main component. [4] Spark plug (30) according to any one of claims 1 to 3, wherein the spark plug (30) satisfies 1.90 ≤ S / V, where S (mm 2 ) is a surface in which the metal housing (32) is in contact with the space (36).