spark plug

Abstract

Spark plug (100, 200, 300, 400, 500), exhibiting: a central electrode (10); a ground electrode (13) which includes a section (13A) facing a front end section (11) of the center electrode (10) and forms a discharge gap (SG) between the facing section (13A) of the ground electrode (13) 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 metal housing (40) containing the insulator (20); and a cover part (50, 250, 350, 450, 550) 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 (100, 200, 300, 400, 500) to form a pre-chamber (51), wherein the cover part (50, 250, 350, 450, 550) includes an injection port (55) which is a through-hole, wherein with respect to a cross-sectional area of ​​a region surrounded by an inner wall surface (53) of the cover part (50, 250, 350, 450, 550), in a cross-section along a plane perpendicular to an axial line (CX) of the spark plug (100, 200, 300, 400, 500), The cover part (50, 250, 350, 450, 550) contains: a narrow section (60, 260) which is arranged at the front end face with respect to the ground electrode (13) in a direction of the axial line (CX) and is narrowed in such a way that the cross-sectional area is at its smallest, and a cover front section (70, 470) which is arranged at a front end side of the narrow section (60, 260) and has a cross-sectional area which is larger than the cross-sectional area of ​​the narrow section (60, 260), and which is largest at a front end of the cover front section (70, 470), wherein the cover front section (70, 470) has a first area (73) obtained by projecting an area of ​​the narrow section (60, 260) surrounded by the inner wall surface (53, 353) onto a front-end surface (53A, 453A) of the inner wall surface (53, 353) in the direction of the axial line (CX), and a second area (75) arranged in the inner wall surface such that it surrounds the first area (73), and where only the second area (75) contains the injection port (55).

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] Japanese utility model JP 2 545 621 Y2 discloses a spark plug with a capsule forming an ignition chamber. The spark plug is configured such that the ignition chamber has a narrowest section in or near an electrode gap, and that the diameter of the ignition chamber decreases downwards from a first plane located below the narrowest section. The capsule forming the ignition chamber has four lateral openings and one bottom opening.

[0003] When a spark is generated in the electrode gap of the spark plug, it ignites a flammable air-fuel mixture in the ignition chamber. The ignited air-fuel mixture expands and injects the flame through the side and bottom openings. These flame jets ignite a flammable air-fuel mixture in a main combustion chamber. SUMMARY OF THE INVENTION

[0004] According to the technology disclosed in the registered Japanese utility model JP 2 545 621 Y2, even if the effect of increasing the temperature of a combustion gas in a pre-chamber is achieved by narrowing a section of the ignition chamber, the diameter of the ignition chamber is reduced below the narrowest section, thus creating the possibility of a pressure drop in the section with the reduced diameter. Additionally, according to the technology disclosed in Japanese utility model JP 2 545 621 Y2, because the capsule contains a bottom opening, the length of the flame injected from the side openings may decrease. Consequently, there is a possibility that the high-temperature flame will not reach the end of the combustion chamber and that the combustion rate of an engine may decrease, which poses a problem.

[0005] The present invention was developed taking into account the above-mentioned circumstances, and one object of the present invention is the increase of the combustion speed of an engine. The present invention can be implemented in the following embodiments.

[0006] A spark plug according to one embodiment of the present invention comprises: a central electrode; a ground electrode having a facing section which is oriented towards 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 that accommodates the central electrode, wherein the front end section of the central electrode is exposed from a front end of the insulator; a metal housing that contains the insulator; and a cover part which, extending 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 pre-chamber, wherein the cover part has an injection port which is a through-hole.

[0007] With respect to a cross-sectional area of ​​a region surrounded by an inner wall surface of the cover part, in cross-section along a plane perpendicular to an axial line of the spark plug, The cover part contains: a narrow section, which is arranged at the front end face in relation to the ground electrode in one direction of the axial line and is narrowed in such a way that the cross-sectional area is at its smallest, and a cover front section which is located at a front end side of the narrow section and has a cross-sectional area which is larger than the cross-sectional area of ​​the narrow section and which is largest at a front end of the cover front section.

[0008] The front cover section has a first area, which is obtained by projecting an area of ​​the narrow section surrounded by the inner wall surface onto a front-end surface of the inner wall surface in the direction of the axial line, and a second area, which is positioned in the inner wall surface such that it surrounds the first area.

[0009] Only the second area contains the injection port.

[0010] Because the cover section has a narrow passage, this configuration makes it possible to increase the temperature of the combustion gas in the pre-chamber. Since the injection port is located not in the first area but in the second area of ​​the front section of the cover, it is also possible to inject the flame, whose velocity increases as it passes through the narrow passage, radially outwards from the injection port formed in the second area, towards the spark plug. In this way, a high-temperature flame easily reaches the lateral end of the combustion chamber, thus increasing the combustion velocity of the engine.

[0011] According to one embodiment of the aforementioned spark plug, the cover part on the front end side has a cover rear section in relation to the ground electrode, which is arranged at a rear end side of the narrow section.

[0012] If the largest cross-sectional area of ​​the rear cover section is designated by a first cross-sectional area S1 and the cross-sectional area of ​​the narrow section by a second cross-sectional area S2, the second cross-sectional area S2 can be 0.05 times or more and 0.15 times or less than the first cross-sectional area S1.

[0013] Since the second cross-sectional area S2 is 0.15 times or less than the first cross-sectional area S1, this configuration makes it possible to effectively increase the temperature of the combustion gas in the prechamber. Furthermore, since the second cross-sectional area S2 is 0.05 times or more than the first cross-sectional area S1, it is possible to suppress any pressure drop that might be caused by the narrow section. Consequently, both the temperature increase of the combustion gas in the prechamber and the suppression of pressure drop can be achieved, thus effectively increasing the combustion rate of the engine.

[0014] According to one embodiment of the above-mentioned spark plug, the cover part may further include a cover rear section on the front end side with respect to the ground electrode, which is arranged at a rear end side of the narrow section.

[0015] The rear cover section may contain a first conically tapered section which has a shape in which its diameter continuously decreases towards the narrow section.

[0016] According to this configuration, it is possible to suppress a pressure loss that may be caused by the provision of the narrow section.

[0017] According to one embodiment of the aforementioned spark plug, the rear cover section between the first conically tapered section and the narrow section can have a second conically tapered section which has a shape in which a diameter of this section decreases continuously towards the narrow section.

[0018] An angle formed by the inner wall surface of the second tapered section and the axial line can be smaller than an angle formed by the inner wall surface of the first tapered section and the axial line.

[0019] Since the tapered shape of the rear cover section is a shape whose diameter gradually decreases, it is possible with this configuration to further reduce any pressure loss that may be caused by the provision of the narrow section.

[0020] According to one embodiment of the aforementioned spark plug, the front cover section can contain a third conically tapered section at a position on the rear end side in relation to the injection opening, with a shape in which the diameter of this section increases continuously from the narrow section to the front end side.

[0021] According to this configuration, the flame that has passed through the narrow section spreads easily along the third conical section towards the injection port, making it possible to inject the flame from the injection port outwards in a radial direction towards the spark plug.

[0022] According to one embodiment of the aforementioned spark plug, at least one of the sections in the inner wall surface of the cover part, in which an inner diameter changes, can be a section in which the inner diameter changes gradually.

[0023] According to this configuration, it is possible to suppress a pressure loss at the section where the inner diameter changes in the inner wall surface of the cover part.

[0024] According to one embodiment of the aforementioned spark plug, the front end surface of the inner wall surface of the cover front section can have a convex shape that rises towards the narrow section.

[0025] According to this configuration, the flame that has passed through the narrow section can be caused to move along the front end surface of the inner wall surface of the cover front section towards the injection port, and it is thus possible to inject the flame outwards from the injection port in a radial direction towards the spark plug.

[0026] According to one embodiment of the aforementioned spark plug, the cover part may contain: a first part, which at least forms the narrow section, and a second part that forms at least one section of the front cover section.

[0027] With this configuration, the narrow section and the front cover section can each be easily formed in the first part and the second part, respectively, which facilitates the manufacture of the cover part. BRIEF DESCRIPTION OF THE FIGURES

[0028] In the following, embodiments of the invention are described with reference to the drawings, without being limited thereto. Fig. Figure 1 is a sectional view showing a configuration of a spark plug according to a first embodiment. Fig. Figure 2 is a partially enlarged cross-sectional view of the spark plug. Fig. 3 is a section along line III-III from Fig. 2, illustrating a first area and a second area of ​​a cover front section. Fig. Figure 4 is a cross-sectional image showing a state in which the spark plug is arranged in an internal combustion engine. Fig. Figure 5 is a diagram showing a relationship between the ratio (S2 / S1) of S2 to S1 and the combustion rate of the engine. Fig. Figure 6 is a partially enlarged cross-sectional view of a spark plug according to a second embodiment. Fig. Figure 7 is a partially enlarged cross-sectional view of a spark plug according to a third embodiment. Fig. Figure 8 is a partially enlarged cross-sectional view of a spark plug according to a fourth embodiment. Fig. Figure 9 is a partially enlarged cross-sectional view of a spark plug according to a fifth embodiment. DESCRIPTION OF PREFERRED EXECUTION FORMS<Erste Ausführungsform>

[0029] A first embodiment of a spark plug 100 is described in detail below with reference to the drawings. The following description focuses on the lower side of Fig. 1 the front end (front side) of the spark plug 100 and the upper side of Fig. 1 is its rear end.

[0030] Fig. Figure 1 is a sectional view showing an outline of the configuration of the spark plug 100 in the first embodiment.

[0031] In Fig. 1 is a central axial line CX of the spark plug 100 (an axial line of the spark plug) marked by a single-dot dashed line. In Fig. 4 are a ceiling surface 105A and a side wall surface 105B of a combustion chamber 105 when the spark plug 100 is mounted on an internal combustion engine, characterized by two-dot-dash lines. In Fig. Figure 4 shows a piston 107 located at top dead center in the combustion chamber 105.

[0032] The spark plug 100 is mounted on an internal combustion engine and serves to ignite the engine. When mounted on the internal combustion engine, the front end of the spark plug 100 (lower side) is... Fig. 1) within the combustion chamber 105 of the internal combustion engine and the rear end (upper side in Fig. 1) arranged outside the combustion chamber 105. As in Fig. As shown in Figure 1, the spark plug 100 contains a center electrode 10, a ground electrode 13, an insulator 20, a terminal electrode 30 and a metal housing 40.

[0033] The center electrode 10 is formed from a shaft-shaped electrode element and is arranged such that its central axis 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 is positioned in 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 side.

[0034] The ground electrode 13 is a rod-shaped electrode extending towards the front end section 11 of the center electrode 10. Within the front-end opening section 40A of the metal housing 40, the ground electrode 13 extends from an inner circumferential surface to the inside. The ground electrode 13 extends to the front face of the front end section 11 of the center electrode 10. The ground electrode 13 includes a facing section 13A that faces the front end section 11 of the center electrode 10. A discharge gap SG is formed between the facing section 13A of the ground electrode 13 and the front end section 11 of the center electrode 10.

[0035] The insulator 20 is a cylindrical element containing 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 the front end section 11 exposed. The terminal electrode 30, which is a shaft-shaped electrode element, is held at the rear of the axial hole 21. A rear end section 31 of the terminal electrode 30 projects from a rear end opening section 22 of the insulator 20 for connection 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.

[0036] The metal housing 40 is an essentially cylindrical metal element containing a cylindrical hole 41 in its center, in which the insulator 20 is housed. The metal housing 40 is, for example, made 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 mounted in the front-end opening section 40A of the metal housing 40.

[0037] As in Fig. As shown in Figure 2, the spark plug 100 has a cover part 50. The cover part 50 has a cylindrical shape towards the bottom and includes a lower wall section and a side wall section. The rear end of the cover part 50 is attached to the front end of the metal housing 40. From its front end, the cover part 50 covers the front end section 11 of the center electrode 10 and the adjacent section 13A of the ground electrode 13 to form a pre-chamber 51. In other words, the pre-chamber 51 is a space enclosed by an inner wall surface 53 of the cover part 50 and the inner circumferential surface of the metal housing 40. The cover part 50 includes injection openings 55 in the form of through holes.

[0038] The cover part 50 comprises a narrow section 60, a front cover section 70 located at the front end of the narrow section 60, and a rear cover section 80 located at the rear end of the narrow section 60. Within the cover part 50, the rear cover section 80, the narrow section 60, and the front cover section 70 are arranged at the front end, relative to the ground electrode 13, in that order. The cover part 50 has a configuration in which one of its inner diameters changes towards the front end. This configuration is described using relationships between a first plane P1 and a fourth plane P4, which are virtual planes perpendicular to the central axial line CX.At the front end of the ground electrode 13, the cover part 50 has an inner diameter that is constant up to the first level P1, and the inner diameter decreases from the first level P1 to the second level P2. The section up to the second level P2 is the rear cover section 80. The inner diameter of the cover part 50 is constant from the second level P2 to the third level P3. The section from the second level P2 to the third level P3 is the narrow section 60. The inner diameter of the cover part 50 increases from the third level P3 to the fourth level P4, and the inner diameter is constant from the fourth level P4 to a front end surface (hereinafter also referred to as the front end surface) 53A of the inner wall surface 53. The section from the third level P3 to the front end surface 53A is the front cover section 70.The cover part 50 has an outer diameter that is constant from the ground electrode 13 to the front end surface 53A and has a circular, columnar outer shape. In the following description, when a cross-sectional area is simply referred to in the description of the narrow section 60, the cover front section 70, and the cover rear section 80, it refers to the cross-sectional area of ​​a region enclosed by the inner wall surface 53 of the cover part 50 in a cross-section along a plane perpendicular to the central axial line CX. The cross-sectional area can be confirmed by observing a cross-section of the spark plug 100 and, alternatively, by observing a cross-sectional image acquired with an X-ray CT (computed tomography) scanner or similar device.

[0039] The cover part 50 comprises a first part 57 and a second part 59. The first part 57 is an element that forms at least the narrow section 60. Specifically, the first part 57 is an element that forms a section on the back of the cover part 50 with respect to the fourth plane P4. Since a circular, columnar component is machined from both the front and the back, the first part 57 takes the form of the rear cover section 80, the narrow section 60, and a front tapered section 71 of the front cover section 70. The second part 59 is an element that forms a section on the front of the cover part 50 with respect to the fourth plane P4. Since a circular, column-shaped component is machined from the rear, the second part 59 is provided in the form of a section of the cover front section 70, which differs from the front conically tapered section 71.The first part 57 and the second part 59 are, for example, integrally connected to each other by welding or similar means and form the cover part 50.

[0040] The rear cover section 80 has a larger cross-sectional area than the narrow section 60. The rear cover section 80 is formed from a section with a cross-sectional area that is constant in the direction of the central axial line CX and a section with a cross-sectional area that decreases towards the front end. The rear cover section 80 includes a rear tapered section (first tapered section) 81 with a shape whose diameter decreases continuously in the direction of the narrow section 60. In particular, in the rear cover section 80, a region surrounded by the inner wall surface 53 has a circular cross-section. The rear cover section 80 contains, up to the first level P1, a circular columnar interior with the central axial line CX as its axis, and from the first level P1 to the second level P2, a frustoconical interior with the central axial line CX as its axis.

[0041] The narrow section 60 is located at the front end face relative to the ground electrode 13 in the direction of the central axial line CX and is thus constricted to have a minimum cross-sectional area. In particular, within the narrow section 60, a region surrounded by the inner wall surface 53 has a circular cross-section. The narrow section 60 contains a circular, columnar interior space with the central axial line CX as its axis. The interior space of the narrow section 60 and the interior spaces of the rear cover section 80 are coaxial and interconnected. The narrow section 60 is thicker in a direction orthogonal to the central axial line CX than the rear cover section 80 and the front cover section 70. In other words, the narrow section 60 is a thick section within the cover section 50, which has a high heat capacity and is not easily cooled. The cross-sectional area of ​​the narrow section 60 will be described later.

[0042] The front cover section 70 has a cross-sectional area larger than that of the narrow section 60, and this area is greatest at the front end of the front cover section 70. The largest cross-sectional area of ​​the front cover section 70 corresponds to the largest cross-sectional area of ​​the rear cover section 80. The front cover section 70 is formed from a section with a cross-sectional area that increases towards the front end and a section with a cross-sectional area that is constant in the direction of the central axial line CX. The front cover section 70 includes, at a position on the rear end relative to the injection ports 55, the front tapered section (third tapered section) 71, the shape of which has a diameter that increases continuously from the narrow section 60 towards the front end. In particular, a region in the front cover section 70, surrounded by the inner wall surface 53, has a circular cross-section.The front cover section 70 contains, from the third level P3 to the fourth level P4, a frustoconical space whose axis is the central axial line CX, and from the fourth level P4 to the front end surface 53A, a circular, columnar space whose axis is the central axial line CX. The front cover section 70 is closed at its front end by a disc-shaped lower wall section. The inner wall surface of the lower wall section forms the front end surface 53A.

[0043] As in Fig. 2 and Fig. As shown in Figure 3, the front cover section 70 has a first region 73, obtained by projecting a region of the narrow section 60, surrounded by the inner wall surface 53, onto the front end surface 53A in the direction of the central axial line CX, and a second region 75, positioned in the inner wall surface 53 to surround the first region 73. The first region 73 is a circular region located at the center of the front end surface 53A. The first region 73 is positioned in the inner wall surface 53 at the front face where the flame has passed through the narrow section 60. The second region 75 comprises the entire area of ​​the front cover section 70, excluding the first region 73, and includes both the inner surface of the lower wall section and the inner surface of the side wall section.

[0044] In the cover part 50, only the second region 75 has the injection openings 55. In the present embodiment, the injection openings 55 are formed in the second region 75, near corner sections between the lower wall section and the side wall section. A plurality (for example, four to eight) of injection openings 55 are formed. The plurality of injection openings 55 is located on a virtual circumference centered on the axial centerline CX of the spark plug 100. The injection openings 55 are arranged at equal intervals on the virtual circumference. Each of the injection openings 55 is a through-hole with a circular cross-section. The injection openings 55 are connected to the pre-chamber 51 (ignition chamber), which is a space covered by the cover part 50, and the

[0045] Combustion chamber 105. In a state where the spark plug 100 is inserted in the combustion chamber 105, the injection openings 55 are designed to allow the spark plug 100 to penetrate towards the side of the combustion chamber 105. In particular, the injection openings 55 extend outwards in the radial direction of the spark plug 100 and are inclined such that the direction of penetration decreases outwards in the radial direction of the spark plug 100.

[0046] Next, the cross-sectional area of ​​the narrow section 60 is described. Using the largest cross-sectional area of ​​the rear cover section 80, designated by a first cross-sectional area S1, and the cross-sectional area of ​​the narrow section 60, designated by a second cross-sectional area S2, a simulation was performed to determine the relationship between the ratio (S2 / S1) of S2 to S1 and the combustion rate of an engine. The combustion rate of the engine was evaluated in terms of MFB (Mass Fraction Burnt), which is the rate at which fuel is burned. A crank angle at which the MFB is 10% to 90% (MFB 10-90 crank angle [degrees]) was used as the evaluation index. A small value of MFB 10-90 crank angle [degrees] indicates a high combustion rate. The results of the simulation are shown in Table 1 and the graph in [Figure 1]. Fig. 5 shown. When a similar simulation was performed for a cover part that does not have the narrow section 60 and whose cross-sectional area across the entire area of ​​the cover part is equal to the first cross-sectional area S1, the MFB 10-90 crank angle [degrees] was 12.2 (in the graph in Fig. 5 (represented by a dashed line). Table 1 S2 / S1 0,019 0,043 0,077 0,121 0,174 0,309 MFB 10-90Kurbelwinkel [Grad] 13,1 12,6 12,1 12,1 12,3 12,5

[0047] The simulation results show that the cross-sectional area of ​​the narrow section 60 preferably lies within the following ranges. The second cross-sectional area S2 is preferably 0.05 times or more and 0.15 times or less than the first cross-sectional area S1. The second cross-sectional area S2 is even more preferably 0.07 times or more than the first cross-sectional area S1. The second cross-sectional area S2 is even more preferably 0.13 times or less than the first cross-sectional area S1. If the second cross-sectional area S2 has a value greater than or equal to the lower limit of the aforementioned ranges, it is possible to ensure gas passage in the pre-chamber 51 and reduce the pressure drop. If the second cross-sectional area S2 has a value less than or equal to the upper limit of the aforementioned ranges, it is possible to increase the temperature of a combustion gas in the pre-chamber 51 around the narrow section 60.The simulation results show that, compared to a spark plug without the narrow section 60, the spark plug 100 can achieve a maximum improvement in combustion speed of 1.3%.

[0048] The effects of the present embodiment will be described next. Since the cover part 50 contains the narrow section 60, it is possible, according to the present embodiment, to increase the temperature of a combustion gas in the prechamber 51. In particular, since the narrow section 60 is designed to project into the prechamber 51, the heat stored in the narrow section 60 prevents the temperature of the combustion gas near the discharge gap SG in the prechamber 51 from falling to a predetermined temperature or below. Furthermore, since the injection ports 55 are formed not in the first region 73 of the front cover section 70, but in the second region 75, it is possible to inject a flame outwards from the injection ports 55 formed in the second region 75 in a radial direction towards the spark plug 100 at a velocity increased by the passage through the narrow section 60.If the injection ports are formed only in the first region 73, the flame that has passed through the narrow section 60 is injected from the injection ports towards the front end. In this case, the flame is injected towards the piston 107 and the like, and cannot reach the vicinity of the side wall surface 105B of the combustion chamber 105. In contrast, in the present embodiment, the injection ports 55 are formed only in the second region 75, so that the flame that has passed through the narrow section 60 is injected from the injection ports 55 towards the side wall surface 105B of the combustion chamber 105.Since the injection ports 55 are not formed in the first region 73, it is possible at this point to increase the length of the flame injected from the injection ports 55, compared to a configuration in which the injection ports 55 are formed in both the first region 73 and the second region 75. As a result, the high-temperature flame easily reaches the lateral end section of the combustion chamber 105, as shown by the dotted line in Figure 1. Fig. 4 is displayed, and it is therefore possible to increase the combustion speed of the engine.

[0049] In the present embodiment, if the largest cross-sectional area of ​​the rear cover section 80 is designated as the first cross-sectional area S1 and the cross-sectional area of ​​the narrow section 60 as the second cross-sectional area S2, the second cross-sectional area S2 is 0.05 times or more and 0.15 times or less than the first cross-sectional area S1. Since the second cross-sectional area S2 is 0.15 times or less than the first cross-sectional area S1, it is possible to effectively increase the temperature of the combustion gas in the pre-chamber 51. Furthermore, since the second cross-sectional area S2 is 0.05 times or more than the first cross-sectional area S1, it is possible to suppress any pressure loss that may be caused by the narrow section 60.This allows both the effect of improving the temperature of a combustion gas in the pre-chamber 51 and the effect of suppressing a pressure loss to be exerted, and it is thus possible to effectively increase the combustion speed of the engine.

[0050] In the present embodiment, the rear cover section 80 has a rear conically tapered section 81, the shape of which causes the diameter of this section to decrease continuously towards the narrow section 60. According to this configuration, it is possible to suppress any pressure loss that may be caused by the narrow section 60.

[0051] In the present embodiment, the front cover section 70 includes, at a point on its rear end face relative to the injection ports 55, the front conically tapered section 71, the shape of which increases continuously from the narrow section 60 to the front end face. According to this configuration, the flame, having passed through the narrow section 60, spreads easily along the front conically tapered section 71 to the injection ports 55, thus enabling the flame to be sprayed outwards from the injection ports 55 in a radial direction towards the spark plug 100.

[0052] In the present embodiment, the cover part 50 comprises the first part 57, which forms at least the narrow section 60, and the second part 59, which forms at least part of the cover front section 70. According to this configuration, the narrow section 60 and the cover front section 70 can each be easily formed in the first part 57 and the second part 59, respectively, which simplifies the manufacture of the cover part 50. <Zweite Ausführungsform>

[0053] Next, a spark plug 200 according to a second embodiment is selected with reference to Fig. 6 described. The spark plug 200 of the second embodiment differs from the spark plug 100 according to the first embodiment by the configuration of a cover rear section 280 and a narrow section 260 of a cover part 250. The other configurations are essentially the same as in the spark plug 100 of the first embodiment. Components that have essentially the same configurations are thus given identical reference numerals, and the description of their structures, actions, and effects is omitted.

[0054] At the front end of the ground electrode 13, the cover part 250 has a constant inner diameter up to the first level P1, and the inner diameter decreases from the first level P1 to the second level P2. The inner diameter then decreases more gently from the second level P2 to the third level P3. The section from the ground electrode 13 to the third level P3 is the rear cover section 280. The cover part 250 has its smallest inner diameter at the third level P3. The section located at the third level P3 is the narrow section 260. In the cover part 250, the configuration of a section at the front end with respect to the third level P3 is the same as in the first embodiment, so its description is omitted. In other words, in the cover part 250 of the present embodiment, an interior space of the narrow section 260 is not configured to extend in the direction of the central axial line CX.Only the front end of the narrow section 60 of the first embodiment corresponds to the narrow section 260 of the present embodiment, and a section on the rear side in relation to the front end of the narrow section 60 of the first embodiment forms a second tapered section 283 of the rear cover section 280 of the present embodiment.

[0055] The rear cover section 280 contains, between the rear tapered section (first tapered section) 81 and the narrow section 260, the second tapered section 283, the latter having a shape in which its diameter decreases continuously towards the narrow section 260. The angle formed by the inner wall surface 53 of the second tapered section 283 and the central axial line CX is smaller than the angle formed by the inner wall surface 53 of the rear tapered section 81 and the central axial line CX. The angles formed by the inner wall surface 53 and the central axial line CX are compared at their respective acute angles.In other words, the angle of inclination of the second tapered section 283 is smaller than the angle of inclination of the rear tapered section 81, and the second tapered section 283 has a gentler angle of inclination than the rear tapered section 81. A configuration in which the angle of inclination of the second tapered section is 0° corresponds to the configuration of the narrow section 60 of the first embodiment. The angle (acute angle) formed by the inner wall surface 53 of the second tapered section 283 and the central axial line CX is smaller than the angle (acute angle) formed by the front tapered section 71 and the central axial line CX.

[0056] Since the conical shape of the rear cover section 280 in the present embodiment is a shape in which its diameter gradually decreases, it is possible to further reduce the pressure loss that may be caused by the provision of the narrow section 260. <Dritte Ausführungsform>

[0057] Next, a spark plug 300 according to a third embodiment is described with reference to Fig. 7 described. The spark plug 300 of the third embodiment differs from the spark plug 100 according to the first embodiment in the shape of an inner wall surface 353 of a cover part 350. The other configurations are essentially the same as those of the spark plug 100 according to the first embodiment. Components that have essentially the same configurations are thus given identical reference numerals, and the description of their structures, actions, and effects is omitted.

[0058] In the inner wall surface 353 of the cover part 350, at least one of the sections 54A, 54B, 54C, and 54D, in which the inner diameter changes, is a section in which the inner diameter changes gradually. Specifically, in the cover part 350, the sections positioned on the first level P1 to the fourth level P4 are sections 54A, 54B, 54C, and 54D, in which the inner diameter changes. In the cover part 350, these sections 54A, 54B, 54C, and 54D form an R-shape. In other words, sections 54A and 54B have such a shape, which is obtained by chamfering corner sections on both sides of the rear tapered section 81 in the direction of the central axial line CX, and sections 54C and 54D have such a shape, which is obtained by chamfering corner sections on both sides of the front tapered section 71 in the direction of the central axial line CX.

[0059] According to the present embodiment, it is possible to suppress a pressure loss at the sections in which the inner diameter in the inner wall surface 353 of the cover part 350 changes. <Vierte Ausführungsform>

[0060] Next, a spark plug 400 according to a fourth embodiment is described with reference to Fig. 8 described. The spark plug 400 of the fourth embodiment differs from the spark plug 100 according to the first embodiment in the shape of a front end surface 453A of a cover front section 470 of a cover part 450. The other configurations are essentially the same as those of the spark plug 100 according to the first embodiment. Components that have essentially the same configurations are thus given identical reference numerals, and the description of their structures, actions, and effects is omitted.

[0061] The front end surface 453A of the cover front section 470 has a convex shape that rises towards the narrow section 60. In particular, the front end surface 453A has such a shape that its circumferential edge is continuous with the inner circumferential surfaces of the injection ports 55 and is slightly inclined along the penetration direction of the injection ports 55. The front end surface 453A has an upper section located in the first region 73 and is designed as a gently curved surface such that the position of the upper section does not extend beyond the positions of the upper sections of the injection ports 55. The shape of the front end surface 453A can, if necessary, be modified in accordance with the position and direction of passage of the injection ports 55 to guide the flame, which has passed through the narrow section 60, to the injection ports 55.

[0062] According to the present embodiment, the flame that has passed through the narrow section 60 can be moved along the front end surface 453A of the cover front section 470 in the direction of the injection openings 55, and it is thus possible to direct the flame from the injection openings 55 outwards in a radial direction towards the spark plug 400. <Fünfte Ausführungsform>

[0063] Next, a spark plug 500 according to a fifth embodiment is described with reference to Fig.9 described. The spark plug 500 of the fifth embodiment differs from the spark plug 100 according to the first embodiment in the configuration of a first part 557 and a second part 559 of a cover part 550. The other configurations are essentially the same as those of the spark plug 100 according to the first embodiment. Components that have essentially the same configurations are thus given identical reference numerals, and the description of their structures, actions, and effects is omitted.

[0064] The cover part 550 comprises the first part 557 and the second part 559. The first part 557 is an element that forms at least the narrow section 60. In particular, the first part 557 is an element that, in the cover part 550, forms the inner circumferential side of a rear section with respect to the positions of the injection ports 55. Since a circular, columnar component, slightly smaller than the cover part 550, is machined from both the front and rear, the first part 557 is provided with the shape of the rear cover section 80, the narrow section 60, and the front tapered section 71 of the front cover section 70. The second part 559 is an element that forms in the cover part 550 the outer circumferential side of a section on the rear side with respect to the positions of the injection ports 55, and of a section on the front side containing the positions of the injection ports 55.As a result of machining a downwardly cylindrical component from the rear, the second part 559 is provided in the shape of a front-end section of the cover front section 70. The first part 557 and the second part 559 are, for example, welded together to be integrated after the first part 557 has been pressed and inserted into an inner section of the second part 559, thereby forming the cover part 550.

[0065] According to the present embodiment, the narrow section 60 and the cover front section 70 can be easily formed in the first part 557 and the second part 559, respectively, which facilitates the manufacture of the cover part 50. Furthermore, the second part 559 is connected in such a way that it surrounds the outer circumference of the first part 557, which is preferable with regard to improving the connection strength between the two parts 557 and 559. <Verschiedene Ausführungsformen (Modifikation)>

[0066] The present invention is not limited to the embodiments mentioned above and can be embodied in various forms within the core of these embodiments.

[0067] (1) As an alternative to the aforementioned embodiments, the configuration of the narrow section may be modified as necessary. In the first embodiment, a configuration is shown as an example in which a section of the cover part from the second level to the third level is the narrow section; however, the narrow section may, for example, be a predetermined section from the second level to the third level. In the aforementioned embodiments, a configuration is shown as an example in which the thickness of the narrow section is greater than the thickness of the other sections; however, the thickness of the narrow section may be equal to the thickness of the other sections. As an alternative to the aforementioned embodiments, the cross-sectional area of ​​the narrow section may be designed as required.

[0068] (2) As an alternative to the aforementioned embodiments, the configurations of the rear cover section and the front cover section may be modified. For example, the rear cover section is not limited to including the rear tapered section. The entire rear cover section may have a tapered shape, with its diameter decreasing continuously towards the narrow section. The front cover section is not limited to including the front tapered section. The entire front cover section may have a tapered shape, with its diameter increasing continuously from the narrow section towards the front end.

[0069] (3) As an alternative to the aforementioned embodiments, the number and positions of the injection ports, the direction in which the injection ports pass through the cover, and the like may be modified as required. For example, the injection ports may be provided at an opening point in the front end face in the second region. The direction of passage of the injection ports may, if necessary, be modified according to the shape and the like of a combustion chamber into which the spark plug is inserted.

[0070] (4) In the third embodiment, a configuration is shown as an example in which, in the inner wall surface of the cover part, all sections in which the inner diameter changes are sections in which the inner diameter changes gradually; however, the configuration is not limited to this. A configuration in which at least one of the sections in which the inner diameter changes is a section in which the inner diameter changes gradually may be used.

[0071] (5) In the embodiment described above, an example configuration is shown in which the cover part contains the first part and the second part; however, the configuration is not limited to this. For example, the cover part can be formed by only a single element. As an alternative to the first embodiment and the fifth embodiment, the configurations of the first part and the second part can be modified as required.

Claims

[1] Spark plug (100, 200, 300, 400, 500), comprising: a central electrode (10); a ground electrode (13) which includes a section (13A) facing a front end section (11) of the center electrode (10) and forms a discharge gap (SG) between the facing section (13A) of the ground electrode (13) 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 metal housing (40) containing the insulator (20); and a cover part (50, 250, 350, 450, 550) 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 (100, 200, 300, 400, 500) to form a pre-chamber (51), wherein the cover part (50, 250, 350, 450, 550) includes an injection port (55) which is a through-hole, wherein with respect to a cross-sectional area of ​​a region surrounded by an inner wall surface (53) of the cover part (50, 250, 350, 450, 550), in a cross-section along a plane perpendicular to an axial line (CX) of the spark plug (100, 200, 300, 400, 500), The cover part (50, 250, 350, 450, 550) contains: a narrow section (60, 260) which is arranged at the front end face with respect to the ground electrode (13) in a direction of the axial line (CX) and is narrowed in such a way that the cross-sectional area is at its smallest, and a cover front section (70, 470) which is arranged at a front end side of the narrow section (60, 260) and has a cross-sectional area which is larger than the cross-sectional area of ​​the narrow section (60, 260), and which is largest at a front end of the cover front section (70, 470), wherein the cover front section (70, 470) has a first area (73) obtained by projecting an area of ​​the narrow section (60, 260) surrounded by the inner wall surface (53, 353) onto a front-end surface (53A, 453A) of the inner wall surface (53, 353) in the direction of the axial line (CX), and a second area (75) arranged in the inner wall surface such that it surrounds the first area (73), and where only the second area (75) contains the injection port (55). [2] Spark plug (100, 200, 300, 400, 500) according to claim 1, wherein the cover part (50) further comprises, on the front end side with respect to the ground electrode (13), a cover rear section (80, 280) which is arranged on a rear end side of the narrow section (60, 260), and where, if the largest cross-sectional area of ​​the rear cover section (80, 280) is designated by a first cross-sectional area S1, and if the cross-sectional area of ​​the narrow section (60, 260) is designated by a second cross-sectional area S2, the second cross-sectional area S2 is 0.05 times or more and 0.15 times or less than the first cross-sectional area S1. [3] Spark plug (100, 200, 300, 400, 500) according to claim 2, wherein the cover rear section (80, 280) has a first conically tapered section (81) having a shape in which a diameter of this section decreases continuously towards the narrow section (60, 260). [4] Spark plug (100, 200, 300, 400, 500) according to claim 1, wherein the cover part (50, 250, 350, 450, 550) further comprises, on the front end side with respect to the ground electrode (13), a cover rear section (80, 280) which is arranged on a rear end side of the narrow section (60, 260), and wherein the cover rear section (80, 280) has a first conically tapered section (81) which has a shape in which a diameter of this decreases continuously towards the narrow section (60, 260). [5] Spark plug (200) according to claim 3 or 4, wherein the cover rear section (280), between the first tapered section (81) and the narrow section (260), has a second tapered section (283) which has a shape in which a diameter of this decreases continuously towards the narrow section (260), and wherein an angle formed by the inner wall surface (53) of the second conically tapered section (283) and the axial line (CX) is smaller than an angle formed by the inner wall surface (53) of the first conically tapered section (81) and the axial line (CX). [6] Spark plug (100, 200, 300, 400, 500) according to any one of claims 1 to 5, wherein the cover front section (50, 250, 350, 450, 550) has a third conically tapered section (71) at a position on the rear end side in relation to the injection opening (55), which has a shape in which a diameter thereof increases continuously from the narrow section (60, 260) towards the front end side. [7] Spark plug (300) according to one of claims 1 to 6, wherein in the inner wall surface (53) of the cover part (350) at least one of the sections in which an inner diameter changes is a section (54A, 54B, 54C, 54D) in which the inner diameter changes gradually. [8] Spark plug (400) according to any one of claims 1 to 7, wherein the front end surface (453A) of the inner wall surface of the cover front section (470) has a convex shape which rises towards the narrow section (60). [9] Spark plug (100, 200, 300, 400, 500) according to any one of claims 1 to 8, wherein the cover part comprises (50, 250, 350, 450, 550) a first part (57, 557), which at least forms the narrow section (60, 260), and a second part (59, 559) that forms at least one section of the front cover section (70, 470).

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