SPARK PLUG

Abstract

Spark plug, showing: a central electrode (10); a ground electrode (13) having a facing section (13A) which is facing a front end section (11) of the center electrode (10) and forms a discharge gap (SG) between the facing section (13A) and the front end section (11) of the center electrode (10); a cylindrical insulator (20) which receives the central electrode (10) therein, wherein the front end section (11) of the central electrode (10) is exposed from a front end of the insulator (20); a cylindrical metal housing (40) that accommodates the insulator (20) therein; and a cover part (50) which covers the front end section (11) of the center electrode (10) and the facing section (13A) of the ground electrode (13) from a front end side of the spark plug to form a pre-chamber (63), wherein the cover part (50) is connected to a front end of the metal housing (40) and has an injection opening (61) which is a through-hole, where a metal housing volume A (specified in mm²) 3 ) of a section of the metal housing (40) on the front end side with respect to a rear end (65) of the pre-chamber (63) and a thermal conductivity B (specified in W / mK) of the metal housing (40) at a normal temperature satisfy the relationship (1): 3.6 < A / B < 98.0 where the metal housing volume A (specified in mm²) 3 ) and a pre-chamber volume C (specified in mm³) 3 ) the antechamber (63) fulfill the relationship (2): 0.18 < C / A < 1.20

Description

BACKGROUND OF THE INVENTION 1. Field of the invention

[0001] The present invention relates to a spark plug. 2. Description of the state of the art

[0002] Spark plugs with an ignition chamber have been developed. For example, a pre-chamber spark plug, according to the Japanese unexamined patent application with publication number JP 2012-199236A, contains a cylindrical metal housing and an ignition chamber cap that surrounds a center electrode and a ground electrode to form an ignition chamber. The ignition chamber cap has several openings through which an air-fuel mixture can flow from a combustion chamber into the ignition chamber. This spark plug ignites in the ignition chamber and sprays burner-shaped flames through the openings into the combustion chamber to combust the air-fuel mixture. SUMMARY OF THE INVENTION

[0003] The spark plug disclosed in the aforementioned JP 2012-199236A has a structure in which the ignition chamber is closed except for the openings. Therefore, the temperature inside the ignition chamber tends to rise during ignition, which can lead to pre-ignition. Conversely, if the temperature inside the ignition chamber drops too low, pressure and heat loss during combustion within the chamber increase, thus reducing the pressure and heat of the injection into the main combustion chamber, which can lead to misfires. Therefore, a configuration was desired that could suppress pre-ignition and misfires by adjusting the thermal conductivity and volume of a housing and ignition chamber cap to suitable values ​​that significantly influence heat conduction within the ignition chamber.

[0004] The present invention was developed in light of the circumstances described above and aims to suppress the occurrence of pre-ignition and misfires in a spark plug with a cover part that forms a pre-chamber. The present invention can be implemented in the following embodiments.

[0005] (1) A spark plug comprises a center electrode, a ground electrode having a facing section which is connected to a front end section of the center electrode and which forms a discharge gap between the facing section and the front end section of the center electrode, a cylindrical insulator in which the center electrode is housed, the front end section of the center electrode being exposed from a front end of the insulator, a cylindrical metal housing which receives the insulator therein, and a cover which, from a front end of the spark plug, covers the front end section of the center electrode and the facing section of the ground electrode to form a prechamber, the cover being connected to a front end of the metal housing and comprising an injection port which is a through-hole. A metal housing volume A (specified in mm³) 3) of a section of the metal housing on the front end with respect to a rear end of the pre-chamber and a thermal conductivity B (specified in W / mK) of the metal housing at a normal temperature satisfy relationship (1): 3.6

[0006] The metal case volume A (specified in mm³) 3 ) and a pre-chamber volume C (specified in mm³) 3 ) the antechamber fulfill the relationship (2): 0.18 <C / A<1,20

[0007] In the case of a spark plug according to one aspect of the present invention, the larger the metal housing volume A (specified in mm²) 3 ​The greater the temperature difference (λ) between a section of the metal housing at the front end and the rear end of the pre-chamber, the more heat is expected to be stored in the pre-chamber. Conversely, the higher the thermal conductivity (λ, expressed in W / mK) of the metal housing at normal temperature, the more heat is expected to be dissipated from the pre-chamber to the outside. Therefore, if the ratio between the metal housing volume (λ, expressed in mm³) 3The relationship between the front end of a section of the metal casing and the rear end of the pre-chamber, and the thermal conductivity B (expressed in W / mK) of the metal casing at normal temperature, as defined by the above relationship (1), improves the balance between the element that allows heat storage in the pre-chamber and the element that allows heat dissipation from the pre-chamber to the outside. In this way, the temperature in the pre-chamber can be adequately maintained, thus preventing pre-ignition and misfires. Normal temperature means 20 °C.

[0008] The larger the pre-chamber volume C (specified in mm³) 3 The larger the volume of the pre-chamber in the spark plug, the more heat is expected to be dissipated from the pre-chamber to the outside. Therefore, if the ratio between the metal casing volume A (specified in mm²) is 3) of a section of the metal housing at the front end in relation to the rear end of the prechamber and the prechamber volume C (specified in mm²) 3 Since the pre-chamber is defined by the above relationship (2), the balance between the element that enables heat storage in the pre-chamber and the element that enables heat dissipation from the pre-chamber to the outside is improved. In this way, the temperature in the pre-chamber can be adequately maintained, thus preventing pre-ignition and misfires.

[0009] (2) In the spark plug described above in (1), the metal casing volume A (specified in mm²) fulfills 3 ) and the pre-chamber volume C (specified in mm³) 3 ) the relationship (3): 0.36 <C / A<0,58

[0010] The spark plug according to one aspect of the present invention, using relationship (3), further improves the balance between the element that enables heat storage in the pre-chamber and the element that enables heat dissipation from the pre-chamber to the outside. In this way, the temperature within the pre-chamber can be maintained more effectively, thus further preventing pre-ignition and misfires.

[0011] (3) In the spark plug described above under (1) or (2), the metal casing volume A (mm³) 3 ) and the thermal conductivity B (W / mK) the relationship (4): 9.8

[0012] ​The spark plug according to one aspect of the present invention, using relationship (4), further improves the balance between the element that facilitates heat storage in the pre-chamber and the element that facilitates heat dissipation from the pre-chamber to the outside. In this way, the temperature in the pre-chamber can be maintained more effectively, thus further preventing pre-ignition and misfires. BRIEF DESCRIPTION OF THE FIGURES

[0013] Embodiments of the invention are described below in conjunction with the drawings, without being limited thereto. Fig. Figure 1 is a cross-sectional view of the structure of a spark plug according to a first embodiment. Fig. Figure 2 is a partially enlarged cross-sectional view of the spark plug according to a first embodiment. DESCRIPTION OF PREFERRED EXECUTION FORMS<Erste Ausführungsform>

[0014] The following describes in detail a first embodiment of a spark plug 100 with reference to the drawings. The following description focuses on the lower side. Fig. 1 as the front end (front side) of the spark plug 100 and the upper side in Fig. 1 is designated as the rear end of the spark plug 100.

[0015] Fig. Figure 1 is a cross-sectional view of a schematic assembly of the spark plug 100 according to the first embodiment. Fig. 1 is a central axial line CX of the spark plug 100 (an axial line of the spark plug) drawn with a dot-and-dash line.

[0016] The spark plug 100 is mounted on an internal combustion engine and serves to ignite an air-fuel mixture in a combustion chamber. When mounted on the internal combustion engine, the front end of the spark plug 100 (bottom side in the drawing) is located inside the combustion chamber of the engine, and the rear end (top side in the drawing) is located outside the combustion chamber. The spark plug 100 comprises a center electrode 10, a ground electrode 13, an insulator 20, a terminal electrode 30, and a metal housing 40.

[0017] The center electrode 10 is formed by a shaft-shaped electrode element and is arranged such that a central axis A of it coincides with the central axial line CX of the spark plug 100. The center electrode 10 is held by the metal housing 40 with the insulator 20 arranged between them, such that a front end section 11 on the rear end (top side in the drawing) is positioned with respect to a front-end opening section 40A of the metal housing 40. The center electrode 10 is electrically connected to an external power source via the terminal electrode 30 located on the rear end.

[0018] The ground electrode 13 is a rod-shaped electrode extending from a position slightly towards the rear end (top side in the drawing) with respect to the front-end opening section 40A of the metal housing 40 to a position slightly towards the front end (bottom side in the drawing) with respect to the front end section 11 of the center electrode 10. Specifically, the ground electrode 13 is connected to the metal housing 40 at a position slightly towards the rear end (top side in the drawing) with respect to the front-end opening section 40A. The ground electrode 13 extends to the front of the front end section 11 of the center electrode 10. As shown in Fig.As shown in Figure 2, the ground electrode 13 contains an adjacent section 13A, which faces the front end section 11 of the center electrode 10. A discharge gap SG is formed between the adjacent section 13A of the ground electrode 13 and the front end section 11 of the center electrode 10.

[0019] The insulator 20 is a cylindrical element with an axial hole 21 passing through its center. The insulator 20 is formed, for example, from a ceramic sintered body made of aluminum oxide or aluminum nitride. The center electrode 10 is located at the front end of the axial hole 21 of the insulator 20, with its front end section 11 exposed. The terminal electrode 30, which is a shaft-shaped electrode element, is held at the rear end of the axial hole 21. A rear end section 31 of the terminal electrode 30 projects from a rear opening section 22 of the insulator 20 to connect to the external power source. The center electrode 10 and the terminal electrode 30 are electrically connected to each other via a resistor 35, which is held between glass sealing materials to suppress the generation of radio interference noise when a spark discharge occurs.The central axis of the insulator 20 coincides with the central axial line CX of the spark plug 100.

[0020] The metal housing 40 is an essentially cylindrical metal element with a cylindrical hole 41 in its center. The metal housing 40 is made, for example, of carbon steel. The central axis of the metal housing 40 coincides with the central axial line CX of the spark plug 100. As described above, the ground electrode 13 is located near the front-end opening section 40A of the metal housing 40. A seal 43 is arranged between a diameter-reduced section within the metal housing 40 and the insulator 20. The seal 43 is made, for example, of a metallic material that is softer than the metallic material from which the metal housing 40 is formed.

[0021] The spark plug 100 includes a cover part 50. The cover part 50 is dome-shaped. The cover part 50 is made, for example, of stainless steel, a nickel-based alloy, or a copper-based alloy. The cover part 50 is connected annularly to the front end of the metal housing 40 (specifically to the front-end opening section 40A). The cover part 50 covers the front end section 11 of the center electrode 10 and the facing section 13A of the ground electrode 13 from the front. The space enclosed by the cover part 50 is a prechamber space 63. A rear end 65 of the prechamber space 63 is a section in which the inner diameter of the metal housing 40 is reduced (a section through which a dashed line L is drawn). Fig.2 extends, defined by a rear end of a tapered section of the metal housing 40 (to reduce the inner diameter of the metal housing 40). In particular, the rear end 65 is a section in which the insulator 20 and the metal housing 40 are close together at the rear end face of the front end section 11 of the center electrode 10. The thickness of the cover portion 50 gradually decreases from the rear end face to a tip 51A.

[0022] As in Fig.As shown in Figure 2, the cover part 50 has several injection ports 61 at the rear end of the tip 51A. The cover part 50 has, for example, four injection ports 61. Each of the injection ports 61 is an essentially cylindrical through-hole. The multiple injection ports 61 are located on a virtual circumference centered on the central axial line CX of the spark plug 100. The multiple injection ports 61 are arranged at equal intervals on the virtual circumference. The pre-chamber chamber 63, which is a space covered by the cover part 50, functions as an ignition chamber and is connected to the combustion chamber via the injection ports 61.

[0023] In the spark plug 100 according to the first embodiment, a metal housing volume A (specified in mm²) fulfills 3) of a section of the metal housing 40 at the front end with respect to the rear end 65 of the pre-chamber space 63 (at the front end with respect to the dashed line L) and a thermal conductivity B (given in W / mK) of the metal housing 40 at normal temperature the relationships (1), (5) and (6): 3.6 716≤A≤2191 13≤B≤372

[0024] Furthermore, the metal housing volume A (specified in mm²) meets the requirements. 3 ) a section of the metal housing 40 at the front end in relation to the rear end 65 of the prechamber space 63 and a chamber volume (prechamber volume) C (specified in mm²) 3 ) of the antechamber space 63 the relations (2) and (7): 0.18 <C / A<1,20 259≤C≤887

[0025] ​The volume C of the pre-chamber chamber 63, whose volume C extends only to the rear end 65 and not beyond, is a space surrounded by the cover part 50, which is assumed to have no injection port 61 (the cover part 50 is assumed to have a smoothly continuous inner surface with blocked injection ports 61), the metal housing 40, the center electrode 10, the ground electrode 13 and the insulator 20.

[0026] In the spark plug 100, the larger the metal housing volume A (specified in mm²) 3The greater the distance between the front end and the rear end 65 of the pre-chamber chamber 63, the more heat is expected to be stored in the pre-chamber chamber 63. Conversely, the greater the thermal conductivity B (specified in W / mK) of the metal casing 40 at normal temperature, the more heat is expected to be dissipated from the pre-chamber chamber 63 to the outside. Therefore, by using a structure that satisfies 3.6 < A / B < 98.0, the balance between the element that allows heat storage in the pre-chamber chamber 63 and the element that allows heat dissipation from the pre-chamber chamber 63 to the outside is improved. This allows the temperature in the pre-chamber chamber 63 to be maintained appropriately, thus preventing pre-ignition and misfires.

[0027] Furthermore, with the spark plug 100, the larger the pre-chamber volume C (specified in mm²) 3The larger the temperature of the pre-chamber chamber 63, the more heat is dissipated from the pre-chamber chamber 63 to the outside. Therefore, by using a structure that satisfies 0.18 < C / A < 1.20, the balance between the element that allows heat storage in the pre-chamber chamber 63 and the element that allows heat dissipation from the pre-chamber chamber 63 to the outside is improved. This allows the temperature in the pre-chamber chamber 63 to be maintained appropriately, thus preventing pre-ignition and misfires.

[0028] In the case of the spark plug 100 according to the first embodiment, the metal housing volume A (specified in mm²) fulfills 3 ) a section of the metal housing 40 at the front end in relation to the rear end 65 of the pre-chamber space 63 and the chamber volume C (specified in mm²) 3 ) of the antechamber space 63 the following relationship (3): 0.36 <C / A<0,58

[0029] The spark plug 100, using a structure that meets the requirements of 0.36 < C / A < 0.58, further improves the balance between the element that enables heat storage in the pre-chamber chamber 63 and the element that enables heat dissipation from the pre-chamber chamber 63 to the outside. In this way, the temperature in the pre-chamber chamber 63 can be maintained even more effectively, thus further preventing pre-ignition and misfires.

[0030] In the spark plug 100 according to the first embodiment, the metal housing volume A (specified in mm²) fulfills 3 ) of a section of the metal housing 40 on the front end section in relation to the rear end 65 of the pre-chamber space 63 and the thermal conductivity B (specified in W / mK) of the metal housing 40 at normal temperature the relationship (4) below: 9.8

[0031] ​The spark plug 100, using a structure that meets the conditions 9.8 < A / B < 42.5, further improves the balance between the element that enables heat storage in the pre-chamber chamber 63 and the element that enables heat dissipation from the pre-chamber chamber 63 to the outside. In this way, the temperature in the pre-chamber chamber 63 can be maintained even more effectively, thus further preventing pre-ignition and misfires. [Examples]

[0032] The present invention will now be described in more detail using examples. 1. Experiment (Experiment corresponding to the first embodiment)(1) Method of the experiment(1.1) Examples

[0033] Samples of the in Fig. 1 and Fig.The spark plug 100 shown in Figure 2 is used. Table 1, below, shows the detailed conditions. The spark plug 100 meets the requirements of the first embodiment. In Table 1, each experimental example is designated with "No." Nos. 1, 4, 7, 13, 14, 16 to 21, 23 to 26, 28 to 33, 35, 36, 42, 45, and 48 in Table 1 are examples. (1.2) Comparative examples

[0034] This section used examples of spark plugs that have a different design than those described in the... Fig. 1 and Fig. The spark plug shown in Figure 2 has 100. Table 1, below, shows the detailed conditions. This spark plug does not meet the requirements of the first embodiment. Numbers marked with an asterisk “*”, such as “1*” in Table 1, indicate that they are comparative examples. In particular, numbers 2, 3, 5, 6, 8 to 12, 15, 22, 27, 34, 37 to 41, 43, 44, 46 and 47 in Table 1 are comparative examples. (2) Method for evaluation (2.1) Measurement of the metal casing volume A (mm³) 3 ) and the volume C (mm³) 3 )

[0035] Each sample was scanned using an X-ray computed tomography (CT) scanner under conditions of a tube voltage of 200 kV and a tube current of 120 µA. A three-dimensional image was generated from the scan result for each sample, and the metal casing volume A (specified in mm³) was determined. 3 ) of a section of the metal housing 40 on the front end side in relation to the rear end of the pre-chamber space and the chamber volume C (specified in mm²) 3 ) of the anterior chamber were measured. (2.2) Test for evaluating pre-ignition resistance

[0036] Each sample was subjected to a pre-ignition resistance test. The summary of the pre-ignition resistance test is as follows. Each sample was mounted on a 1.3 L naturally aspirated inline four-cylinder engine, and the engine was run for 1000 cycles of a series of processes at full throttle (6000 rpm) and at an ignition timing (crankshaft angle) with a predetermined initial value. During engine operation, it was checked whether pre-ignition occurred. If pre-ignition occurred, the ignition timing at that time was recorded as the pre-ignition timing. If no pre-ignition occurred, the ignition timing was advanced by one degree, and the engine was again started at full throttle to check for pre-ignition. This process was repeated until pre-ignition occurred to specify the pre-ignition timing for each sample.Similarly, the advance angle of a reference spark plug (a real spark plug installed in a test engine) was specified. Then, the difference between the advance angle of the reference spark plug and the advance angle of each sample was calculated. If the advance angle is further forward relative to the reference spark plug, the spark plug is rated as having higher advance resistance. The advance angle of each sample relative to that of the reference spark plug was evaluated based on the following scales, and each sample received a rating. The results are listed in the "Advance Resistance" column in Table 1. <Bewertung des Vorzündungswiderstands>

[0037] Each sample was rated using the following three grades. Higher grades indicate greater pre-ignition resistance. Rating grades: 3: Improved by 5° CA (crankshaft angle) or more compared to the reference spark plug 1: Improved by 2° CA or more and less than 5° CA compared to the reference spark plug 0: Improved or delayed by less than 2° CA compared to the reference spark plug (2.3) Misfire resistance test

[0038] Each sample was subjected to a misfire resistance test. The summary of the misfire resistance test is as follows. Each sample was mounted on a 1.6 L turbocharged, direct-injection, inline four-cylinder engine, and the engine was run for 1000 cycles at 2000 rpm and 1000 kPa intake pressure to measure the misfire rate. Spark plugs with a low misfire rate are rated as having higher misfire resistance (ignitability). The misfire rate of each sample was evaluated based on the following scales, and each sample received an evaluation score. The results are listed in the "Misfire Resistance" column in Table 1. <Bewertung des Fehlzündungswiderstands>

[0039] Each sample was rated using the following three scores. Higher scores indicate greater resistance to misfires. Rating grades: 3: Misfire rate of less than 1%. 1: Misfire rate of 1% or more and less than 3% 0: Misfire rate of 3% or higher (2.4) Overall evaluation

[0040] Based on the combined scores for pre-ignition resistance and misfire resistance, an overall rating was assigned to each sample. Higher overall scores for both pre-ignition and misfire resistance are considered more advantageous. A sample with an overall score of 6 is designated "Excellent," a sample with a score of 4 or 2 is designated "Good," and a sample with a score of 3, 1, or 0 is designated "Poor." The results are listed in the "Overall Rating" column in Table 1. Table 1 Nr. A: Bulky metal housing on the other front end (mm) 3 ) B: Thermal conductivity of the metal casing (W / mK) C: Prechamber volume (mm 3 ) AWAY C / A Pre-ignition resistor Misfire resistance Overall rating 1 716 13 259 55,1 0,36 1 3 4 Good 2 * 1312 13 259 100,9 0,20 0 1 1 Deficient 3 * 2191 13 259 168,5 0,12 0 0 0 Deficient 4 716 13 450 55,1 0,63 1 1 2 Good 5 * 1312 13 450 100,9 0,34 0 1 1 Deficient 6 * 2191 13 450 168,5 0,21 0 1 1 Deficient 7 716 13 683 55,1 0,95 1 1 2 Good 8 * 1312 13 683 100,9 0,52 0 3 3 Deficient 9 * 2191 13 683 168,5 0,31 0 1 1 Deficient 10 * 716 13 887 55,1 1,24 1 0 1 Deficient 11 * 1312 13 887 100,9 0,68 0 1 1 Deficient 12 * 2191 13 887 168,5 0,40 0 3 3 Deficient 13 716 53 259 13,5 0,36 3 3 6 Excellent 14 1312 53 259 24,8 0,20 3 1 4 Good 15 * 2191 53 259 41,3 0,12 3 0 3 Deficient 16 716 53 450 13,5 0,63 3 1 4 Good 17 1312 53 450 24,8 0,34 3 1 4 Good 18 2191 53 450 41,3 0,21 3 1 4 Good 19 716 53 683 13,5 0,95 3 1 4 Good 20 1312 53 683 24,8 0,52 3 3 6 Excellent 21 2191 53 683 41,3 0,31 3 1 4 Good 22 * 716 53 887 13,5 1,24 0 3 3 Deficient 23 1312 53 887 24,8 0,68 3 1 4 Good 24 2191 53 887 41,3 0,40 3 3 6 Excellent 25 716 130 259 5,5 0,36 3 3 6 Excellent 26 1312 130 259 10,1 0,20 3 1 4 Good 27 * 2191 130 259 16,9 0,12 3 0 3 Deficient 28 716 130 450 5,5 0,63 3 1 4 Good 29 1312 130 450 10,1 0,34 3 1 4 Good 30 2191 130 450 16,9 0,21 3 1 4 Good 31 716 130 683 5,5 0,95 3 1 4 Good 32 1312 130 683 10,1 0,52 3 3 6 Excellent 33 2191 130 683 16,9 0,31 3 1 4 Good 34 * 716 130 887 5,5 1,24 0 1 1 Deficient 35 1312 130 887 10,1 0,68 3 1 4 Good 36 2191 130 887 16,9 0,40 3 3 6 Excellent 37 * 716 372 259 1,9 0,36 0 3 3 Deficient 38 * 1312 372 259 3,5 0,20 0 1 1 Deficient 39 * 2191 372 259 5,9 0,12 1 0 1 Deficient 40 * 716 372 450 1,9 0,63 0 1 1 Deficient 41 * 1312 372 450 3,5 0,34 0 1 1 Deficient 42 2191 372 450 5,9 0,21 1 1 2 Good 43 * 716 372 683 1,9 0,95 0 1 1 Deficient 44 * 1312 372 683 3,5 0,52 0 3 3 Deficient 45 2191 372 683 5,9 0,31 1 1 2 Good 46 * 716 372 887 1,9 1,24 0 0 0 Deficient 47 * 1312 372 887 3,5 0,68 0 1 1 Deficient 48 2191 372 887 5,9 0,40 1 3 4 Good (3) Evaluation results (3.1) Pre-ignition resistance

[0041] Test examples 2, 3, 5, 6, 8, 9, 11, 12, 37, 38, 40, 41, 43, 44, 46, and 47 (comparative examples), in which the A / B ratio does not satisfy relationship (1) (3.6 < A / B < 98.0), were rated 0 in the evaluation scores for "pre-ignition resistance". The A / B ratio is a ratio of the metal housing volume A (specified in mm²). 3 The thermal conductivity B (specified in W / mK) of a section of the metal housing 40 at the front end relative to the rear end 65 of the pre-chamber space 63 was compared to the thermal conductivity B (given in W / mK) of the metal housing 40 at normal temperature. On the other hand, test examples 1, 4, 7, 10, 13 to 36, 39, 42, 45 and 48 (Examples), in which the ratio A / B each satisfied relationship (1) (3.6 < A / B < 98.0), were rated 1 or 3 for the "pre-ignition resistance". Thus, the examples that satisfied relationship (1) (3.6 < A / B < 98.0) suppressed pre-ignition compared to the comparison examples.

[0042] Experimental examples 1, 4, 7, 10, 25, 28, 31, 34, 39, 42, 45, and 48 (Examples), in which the A / B ratio did not satisfy relationship (4) (9.8 < A / B < 42.5), were rated 1 for "pre-ignition resistance." In contrast, experimental examples 13 to 24, 26, 27, 29, 30, 32, 33, 35, and 36 (Examples), in which the A / B ratio satisfied relationship (4) (9.8 < A / B < 42.5), were rated 3 for "pre-ignition resistance." Thus, the examples that satisfied relationship (4) (9.8 < A / B < 42.5) further suppressed pre-ignition. (3.2) Misfire resistance

[0043] Test examples 3, 10, 15, 22, 27, 34, 39, and 46 (comparative examples), in which the C / A ratio does not satisfy relationship (2) (0.18 < C / A < 1.20), were rated 0 in the evaluation scores for "misfire resistance". The C / A ratio is a ratio of the metal casing volume A (given in mm³). 3 ) of a section of the metal housing 40 at the front end in relation to the rear end 65 of the pre-chamber space 63 to the chamber volume C (specified in mm²) 3 ) of the pre-chamber chamber 63. On the other hand, test examples 1, 2, 4 to 9, 11 to 14, 16 to 21, 23 to 26, 28 to 33, 35 to 38, 40 to 45, 47 and 48 (examples), in which the C / A ratio each satisfied relationship (2) (0.18 < C / A < 1.20), were rated with 1 or 3 in the evaluation scores for "misfire resistance". Thus, the examples that satisfied relationship (2) (0.18 < C / A < 1.20) suppressed misfires.

[0044] Experimental examples 2, 4 to 7, 9, 11, 14, 16 to 19, 21, 23, 26, 28 to 31, 33, 35, 38, 40 to 43, 45 and 47 (Examples), in which the C / A ratio does not satisfy relationship (3) (0.36 < C / A < 0.58), were rated 1 in the "Misfire Resistance" assessment. Conversely, experimental examples 1, 8, 12, 13, 20, 24, 25, 32, 36, 37, 44 and 48 (Examples), in which the C / A ratio satisfies relationship (3) (0.36 < C / A < 0.58), were rated 3 in the "Misfire Resistance" assessment. Thus, the examples that satisfied relationship (3) (0.36 < C / A < 0.58) further suppressed misfires. (3.3) Overall rating

[0045] Experimental examples 1, 4, 7, 13, 14, 16 to 21, 23 to 26, 28 to 33, 35, 36, 42, 45, and 48 (Examples) received scores of 1 or higher for both "pre-ignition resistance" and "misfire resistance." Therefore, these experimental examples suppressed both pre-ignition and misfires. In particular, experimental examples 13, 20, 24, 25, 32, and 36 (Examples) received a total score of 6 and effectively suppressed both pre-ignition and misfires. <Andere Ausführungsformen (Modifikationen)>

[0046] The present invention is not limited to the embodiments mentioned above and can be implemented in various forms within the scope which does not deviate from the core of the invention.

[0047] (1) In the above embodiments, the cover part has a specific shape, but the shape can be changed as required. For example, the cover part can have a circular cylindrical shape, a rectangular box shape, or a conical shape.

[0048] (2) In the embodiments described above, a spark plug with a specific number of injection ports is described as an example, but the number of injection ports is not limited to a specific number and can be changed as required. The arrangement of the injection ports and the direction of penetration of the injection port can also be changed as required.

Claims

[1] Spark plug, comprising: a central electrode (10); a ground electrode (13) having a facing section (13A) which is facing a front end section (11) of the center electrode (10) and forms a discharge gap (SG) between the facing section (13A) and the front end section (11) of the center electrode (10); a cylindrical insulator (20) which receives the central electrode (10) therein, wherein the front end section (11) of the central electrode (10) is exposed from a front end of the insulator (20); a cylindrical metal housing (40) that accommodates the insulator (20) therein; and a cover part (50) which covers the front end section (11) of the center electrode (10) and the facing section (13A) of the ground electrode (13) from a front end side of the spark plug to form a pre-chamber (63), wherein the cover part (50) is connected to a front end of the metal housing (40) and has an injection opening (61) which is a through-hole, where a metal housing volume A (specified in mm²) 3 ) of a section of the metal housing (40) on the front end side with respect to a rear end (65) of the pre-chamber (63) and a thermal conductivity B (specified in W / mK) of the metal housing (40) at a normal temperature satisfy the relationship (1): 3.6 where the metal housing volume A (specified in mm²) 3 ) and a pre-chamber volume C (specified in mm³) 3 ) the antechamber (63) fulfill the relationship (2): 0.18 <C / A<1,20 ​[2] Spark plug according to claim 1, wherein the metal housing volume A (specified in mm²) 3 ) and the pre-chamber volume C (specified in mm³) 3 ) fulfill the relationship (3): 0.36 <C / A<0,58 [3] Spark plug according to claim 1 or 2, wherein the metal housing volume A (specified in mm²) 3 ) and the thermal conductivity B (given in W / mK) satisfy relationship (4): 9.8

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