Spark plugs for internal combustion engines

Abstract

To provide a spark plug for an internal combustion engine capable of suppressing overheat of a ground electrode.SOLUTION: In a spark plug 1, a plug cover 5 is fixed to a front-end part of a housing 2 so as to cover a sub-combustion chamber 50 where a discharge gap G is arranged. The front-end part of the housing 2 has a housing fixing part 21 and an opposed surface 22. The housing fixing part 21 is opposed to a cover base end part 52 of the plug cover 5 in a diameter direction of a plug. The opposed surface 22 is opposed to a base end surface 53 of the plug cover 5 at a base end side from the housing fixing part 21 in a plug axis direction Z. The housing fixing part 21 and the cover base end part 52 are fixed to each other. The base end surface 53 of the plug cover 5 is arranged at a position apart from the opposed surface 22 in the plug axis direction Z. A ground electrode 6 and an inner wall surface 54 of the plug cover 5 abut on each other in the plug axis direction Z.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a spark plug for an internal combustion engine. [Background technology]

[0002] For example, as disclosed in Patent Document 1, a spark plug for an internal combustion engine having a pre-combustion chamber at its tip is known. In this spark plug, the plug cover covering the pre-combustion chamber has a thin tip. This is intended to reduce the amount of heat received by the tip, and to prevent the air-fuel mixture from igniting before the spark plug generates a discharge (i.e., pre-ignition). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2020-009747 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the spark plug described in Patent Document 1 takes into consideration overheating of the plug cover but does not take into consideration overheating of the ground electrode, which raises concerns about pre-ignition originating from the ground electrode, and thus leaves room for further improvement.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to provide a spark plug for an internal combustion engine that is capable of suppressing overheating of the ground electrode. [Means for solving the problem]

[0006] One aspect of the present invention is a cylindrical insulator (3), a center electrode (4) held on the inner circumferential side of the insulator and exposed from the insulator to the tip side; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between itself and the center electrode; a plug cover (5) fixed to the tip end of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, The ground electrode protrudes into the auxiliary combustion chamber from a fixed end (61) fixed to the housing, The plug cover is formed with a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, a front end portion of the housing has a housing fixing portion (21) facing a cover base end portion (52) of the plug cover in a plug radial direction, and an opposing surface (22) facing a base end surface (53) of the plug cover in a plug axial direction (Z) on the base end side of the housing fixing portion, The housing fixing portion and the cover base end portion are fixed to each other, the base end surface of the plug cover is disposed at a position spaced apart from the opposing surface in the plug axial direction, The ground electrode and the inner wall surface (54) of the plug cover are in contact with each other in the plug axial direction. Cage , The plug cover has a protrusion (55) formed by a part of the inner wall surface protruding toward the base end, and the protrusion and the ground electrode abut against each other in the plug axial direction. In a spark plug (1) for an internal combustion engine. Effect of the Invention

[0007] In the above spark plug, the ground electrode and the inner wall surface of the plug cover are in contact with each other in the axial direction of the plug, so that heat from the ground electrode is easily dissipated to the outside through the plug cover, thereby preventing overheating of the ground electrode.

[0008] As described above, according to the above aspect, it is possible to provide a spark plug for an internal combustion engine that is capable of suppressing overheating of the ground electrode. In addition, the symbols in parentheses described in the claims and the means for solving the problems indicate a correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief description of the drawings]

[0009] [Figure 1] 2 is a cross-sectional view taken along line II in FIG. 2, showing a portion near the tip end of the spark plug according to the first embodiment, taken along an axial direction of the plug; [Diagram 2] FIG. 2 is a cross-sectional view taken along line II-II in FIG. [Diagram 3] FIG. 4 is a cross-sectional view illustrating the direction of a swirl flow formed in an auxiliary combustion chamber in the first embodiment. [Figure 4] 4 is a cross-sectional view showing a state in which the ground electrode and the plug cover are brought into contact with each other in the first embodiment. FIG. [Diagram 5] 1 is a cross-sectional view of an internal combustion engine in which a spark plug is installed according to a first embodiment. [Figure 6] FIG. 4 is a cross-sectional view taken along the axial direction of a spark plug in the vicinity of a tip portion of the spark plug in a comparative embodiment 1. [Figure 7] 4 is a graph showing the relationship between the crank angle and the temperature of each portion in Experimental Example 1. [Figure 8] FIG. 11 is a cross-sectional view taken along the axial direction of a spark plug in a vicinity of a tip portion of a spark plug according to a second embodiment. [Figure 9] FIG. 11 is a cross-sectional view taken along the axial direction of a spark plug in a vicinity of a tip portion of a spark plug according to a third embodiment. [Figure 10] FIG. 11 is a cross-sectional view taken along the axial direction of a spark plug in a vicinity of a tip portion of the spark plug according to a fourth embodiment. [Figure 11] FIG. 11 is a cross-sectional view taken along the axial direction of a spark plug in a vicinity of a tip portion of the spark plug according to a fifth embodiment. [Figure 12] 12 is a cross-sectional view taken along line XII-XII in FIG. 13 , showing a portion near the tip end of a spark plug according to a sixth embodiment, taken along an axial direction of the plug. [Figure 13] 13 is a cross-sectional view taken along line XIII-XIII in FIG. 12 . [Figure 14] FIG. 13 is a cross-sectional view taken along the axial direction of a spark plug in a vicinity of a tip portion of the spark plug according to a seventh embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] (Embodiment 1) An embodiment of a spark plug for an internal combustion engine will be described with reference to Figs. In this embodiment, a spark plug 1 for an internal combustion engine has a cylindrical insulator 3, a center electrode 4, a cylindrical housing 2, a ground electrode 6, and a plug cover 5, as shown in Figures 1 and 2. The center electrode 4 is held on the inner periphery of the insulator 3 and is exposed from the insulator 3 to the tip side. The housing 2 holds the insulator 3 on the inner periphery. The ground electrode 6 forms a discharge gap G between itself and the center electrode 4. The plug cover 5 is fixed to the tip of the housing 2 so as to cover the auxiliary combustion chamber 50 in which the discharge gap G is located.

[0011] The ground electrode 6 protrudes into the auxiliary combustion chamber 50 from a fixed end portion 61 fixed to the housing 2. In addition, the plug cover 5 is formed with an injection hole 51 that connects the auxiliary combustion chamber 50 to the outside.

[0012] Further, the tip end of the housing 2 has a housing fixing portion 21 and an opposing surface 22. The housing fixing portion 21 faces a cover base end portion 52 of the plug cover 5 in the plug radial direction. The opposing surface 22 faces a base end surface 53 of the plug cover 5 in the plug axial direction Z on the base end side of the housing fixing portion 21. The housing fixing portion 21 and the cover base end portion 52 are fixed to each other. The base end surface 53 of the plug cover 5 is located at a position away from the opposing surface 22 in the plug axial direction Z.

[0013] Further, the ground electrode 6 and the inner wall surface 54 of the plug cover 5 abut against each other in the axial direction Z of the plug.

[0014] The spark plug 1 of this embodiment can be used, for example, as an ignition means in an internal combustion engine of an automobile, etc. As shown in Fig. 5, the threaded portion 23 of the housing 2 is screwed into the female threaded portion of a plug hole 711 of a cylinder head 71, so that the spark plug 1 is attached to the internal combustion engine 10. The housing 2 is in thermal contact with the cylinder head 71.

[0015] The internal combustion engine 10 includes a piston 74 that reciprocates within a cylinder 70. The volume of the main combustion chamber 101 changes due to the reciprocating motion of the piston 74. The internal combustion engine 10 is formed with an intake port 721 and an exhaust port 731, and is provided with an intake valve 72 and an exhaust valve 73, respectively.

[0016] One end of the spark plug 1 in the axial direction Z is disposed in the main combustion chamber 101 of the internal combustion engine 10. In the axial direction Z of the spark plug 1, the side exposed to the main combustion chamber 101 is referred to as the tip side, and the opposite side is referred to as the base side. The axial direction Z of the spark plug 1 is also referred to as the plug axial direction Z or simply as the Z direction, as appropriate. The plug central axis C refers to the central axis C of the spark plug 1. The plug radial direction refers to the radial direction of a circle centered on the plug central axis C on a plane perpendicular to the plug central axis C. The plug circumferential direction refers to the direction along the circumference centered on the plug central axis C. In this embodiment, the plug central axis C is also the central axis of the center electrode 4.

[0017] When the spark plug 1 is attached to the internal combustion engine 10, the plug cover 5 faces the main combustion chamber 101 and separates the auxiliary combustion chamber 50 from the main combustion chamber 101. The injection hole 51 communicates the auxiliary combustion chamber 50 with the main combustion chamber 101.

[0018] In this embodiment, the plug cover 5 has a peripheral wall portion 56, a bottom wall portion 57, and a corner portion 58, as shown in Fig. 1. The peripheral wall portion 56 is a generally cylindrical portion that covers part of the outer periphery of the auxiliary combustion chamber 50. The bottom wall portion 57 is a portion that covers the tip side of the auxiliary combustion chamber 50. The corner portion 58 is a portion that connects the tip of the peripheral wall portion 56 and the outer periphery of the bottom wall portion 57 in a curved shape.

[0019] The peripheral wall portion 56 has a cover base end portion 52 and a base end surface 53. In this embodiment, the bottom wall portion 57 is formed so that the inner wall surface 54 is substantially perpendicular to the Z direction. In addition, a plurality of injection holes 51 are formed in a corner portion 58.

[0020] The injection hole 51 opens at an incline with respect to the Z direction so as to move outward in the plug radial direction toward the tip side. As shown in Fig. 2, when viewed from the Z direction, the injection hole 51 is formed such that an injection hole axis 51L is inclined at an acute angle with respect to an imaginary line VL that extends in the plug radial direction and passes through the injection hole 51 and the plug central axis C. The inclination direction of the injection hole axis 51L of each of the multiple injection holes 51 with respect to the imaginary line VL is on the same side in the plug circumferential direction.

[0021] Due to such a formation mode of the injection hole 51, a swirl flow (see dashed arrow SF in FIG. 3) is formed in the auxiliary combustion chamber 50 by the airflow introduced into the auxiliary combustion chamber 50 through the injection hole 51. In this embodiment, the swirl flow SF is generated in a counterclockwise spiral shape in FIG. 3 around the plug central axis C.

[0022] Moreover, the plug cover 5 is fixed to the housing 2 by welding. Specifically, the cover base end 52 and the housing fixing part 21 are fixed to each other by welding. The cover base end 52 is in thermal contact with the housing fixing part 21.

[0023] 1, the tip end of the housing 2 is stepped by forming a housing fixing part 21 and an opposing surface 22. In addition, a cover base end part 52 is fixed to the outer periphery of the housing fixing part 21.

[0024] In addition, the base end surface 53 of the plug cover 5 is located on the tip side of the opposing surface 22. The opposing surface 22 and the base end surface 53 face each other in the Z direction without abutting each other. In other words, a gap g1 is formed between the opposing surface 22 and the base end surface 53.

[0025] In this embodiment, the ground electrode 6 is joined to the tip surface of the housing 2 by welding or the like. As shown in Fig. 2, when viewed from the Z direction, the ground electrode 6 is provided along the plug radial direction and protrudes toward the plug central axis C. The ground electrode 6 is in thermal contact with the housing 2.

[0026] In this embodiment, the ground electrode 6 has a standing portion 63, a bent portion 64, and an extended portion 65, as shown in Fig. 1. The standing portion 63 has a fixed end portion 61, and stands from the front end surface of the housing 2 toward the front end along the plug axial direction Z. The bent portion 64 is bent from the front end of the standing portion 63 toward the inside in the plug radial direction. The extended portion 65 is extended from the bent portion 64 toward the plug central axis C. The extended portion 65 forms a discharge gap G with the center electrode 4. In this embodiment, the extended portion 65 and the front end of the center electrode 4 face each other in the Z direction, thereby forming the discharge gap G.

[0027] The extension portion 65 is inclined in the Z direction so as to be more toward the tip side as it approaches the protruding end 62. In addition, a tip side surface 651 of the extension portion 65 is inclined in the Z direction so as to be more toward the tip side as it approaches the protruding end 62.

[0028] In this embodiment, the protruding end 62 forms the tip of the ground electrode 6. The protruding end 62 and the inner wall surface 54 of the plug cover 5 abut against each other in the plug axial direction Z. Specifically, the protruding end 62 and the inner wall surface 54 of the bottom wall portion 57 abut against each other in the Z direction. The ground electrode 6 is in thermal contact with the plug cover 5 via the abutment portion between the protruding end 62 and the bottom wall portion 57.

[0029] 4, the distance D1 in the Z direction from the opposing surface 22 to the tip of the ground electrode 6 is greater than the distance D2 in the Z direction from the base end surface 53 of the plug cover 5 to the inner wall surface 54 of the bottom wall portion 57. Since the distance D1 is greater than the distance D2, a gap g1 is formed between the opposing surface 22 and the base end surface 53 of the plug cover 5 when the protruding end 62 is brought into contact with the inner wall surface 54 of the bottom wall portion 57 in the contact step described below, as shown in FIG. In this embodiment, the distance in the Z direction from the base end surface 53 of the plug cover 5 to the tip of the auxiliary combustion chamber 50 is substantially the same as the distance D2.

[0030] In addition, the tip surface of the center electrode 4 is located further forward than the tip of the housing 2. In other words, the discharge gap G is formed further forward than the tip of the housing 2.

[0031] Next, a method for manufacturing the spark plug 1 of this embodiment will be described. In manufacturing the spark plug 1, a preparation step, a contact step, and a joining step are performed. In the preparation step, the housing 2 to which the ground electrode 6, the insulator 3, and the center electrode 4 are assembled, and the plug cover 5 are prepared. In the contact step, after the preparation step, the plug cover 5 is moved toward the base end side with respect to the housing 2 as shown by the arrow M in FIG. 4, so that the protruding end 62 and the inner wall surface 54 of the bottom wall portion 57 are contacted with each other in the Z direction as shown in FIG. 1. In the contact step, the housing fixing portion 21 and the cover base end portion 52 are overlapped in the plug radial direction, and the protruding end 62 and the inner wall surface 54 of the bottom wall portion 57 are contacted with each other in the Z direction. In this embodiment, the protruding end 62 and the inner wall surface 54 of the bottom wall portion 57 are contacted with each other in the Z direction with the plug cover 5 fitted to the housing 2. In the joining step, after the abutting step, the housing fixing portion 21 and the cover base end portion 52 are joined to each other. More specifically, in the joining step, the cover base end portion 52 is joined to the outer periphery of the housing fixing portion 21 by welding while maintaining the protruding end portion 62 and the inner wall surface 54 of the bottom wall portion 57 in abutting contact with each other in the Z direction. This makes it possible to manufacture the spark plug 1 of this embodiment as shown in Figs. 1 and 2.

[0032] Further, the outer peripheral surface of the housing fixing portion 21 and the inner wall surface 54 of the cover base end 52 are each formed to extend along the Z direction. In the abutting step, when the protruding end 62 and the inner wall surface 54 of the bottom wall portion 57 are abutted against each other in the Z direction, the outer peripheral surface of the housing fixing portion 21 and the inner wall surface 54 of the cover base end 52 are in a state of abutting against each other in the plug radial direction. However, a slight clearance may be provided between the outer peripheral surface of the housing fixing portion 21 and the inner wall surface 54 of the cover base end 52 to allow smooth sliding between them.

[0033] Next, the effects of this embodiment will be described. In the above-described spark plug 1, the ground electrode 6 and the inner wall surface 54 of the plug cover 5 abut against each other in the plug axial direction Z. Therefore, heat from the ground electrode 6 is easily dissipated to the outside via the plug cover 5. As a result, overheating of the ground electrode 6 can be suppressed.

[0034] Furthermore, the protruding end 62 has a longer heat dissipation path to the housing 2 than the other parts of the ground electrode 6, and therefore the temperature of the protruding end 62 is likely to become high. Therefore, in the spark plug 1 of this embodiment, the protruding end 62 of the ground electrode 6 and the inner wall surface 54 of the plug cover 5 abut against each other in the plug axial direction Z. Therefore, the heat of the ground electrode 6 can be effectively dissipated to the outside via the plug cover 5. Therefore, overheating of the ground electrode 6 can be further suppressed. Therefore, pre-ignition can be further suppressed during high load periods when the operating efficiency of the internal combustion engine is high. As a result, the output and fuel efficiency of the internal combustion engine can be further improved.

[0035] In addition, the protruding end 62 forms the tip of the ground electrode 6. This makes it easy to reliably bring the protruding end 62 into contact with the inner wall surface 54 of the plug cover. This makes it possible to reliably and effectively dissipate heat from the ground electrode 6. As a result, overheating of the ground electrode 6 can be reliably prevented.

[0036] The cover base end 52 is fixed to the outer periphery of the housing fixing portion 21. Therefore, the ground electrode 6 can be fixed to the tip surface of the housing 2. Therefore, it is easy to shorten the length from the fixed end 61 to the protruding end 62 of the ground electrode 6. Therefore, it is easy to shorten the heat dissipation path from the ground electrode 6 to the housing 2 and the heat dissipation path to the plug cover 5. Therefore, it is even easier to dissipate heat from the ground electrode 6 to the outside. As a result, overheating of the ground electrode 6 can be further suppressed.

[0037] In addition, since the cover base end portion 52 is fixed to the outer periphery of the housing fixing portion 21, the volume of the auxiliary combustion chamber 50 tends to be large. Therefore, the force of the flame ejected from the auxiliary combustion chamber 50 to the main combustion chamber through the injection hole 51 can be strengthened. As a result, the ignition performance can be improved.

[0038] The spark plug 1 of the present embodiment can be manufactured by performing a preparation step, a contact step, and a joining step. Therefore, the spark plug 1 can be manufactured efficiently. As a result, the productivity of the spark plug 1 can be improved.

[0039] Also, distance D1 is greater than distance D2 (see FIG. 4). Therefore, in the contacting step, the ground electrode 6 can be reliably contacted with the inner wall surface 54 of the bottom wall portion 57. That is, the ground electrode 6 can be contacted with the inner wall surface 54 of the bottom wall portion 57 without contacting the base end surface 53 of the plug cover 5 with the opposing surface 22. As a result, the spark plug 1 capable of suppressing overheating of the ground electrode 6 can be manufactured reliably and efficiently.

[0040] The nozzle hole 51 is formed so that the airflow introduced into the auxiliary combustion chamber 50 through the nozzle hole 51 generates a swirl flow SF in the auxiliary combustion chamber 50. Therefore, the initial flame formed by the discharge generated in the discharge gap G is likely to spread into the auxiliary combustion chamber 50 by the swirl flow SF. Therefore, combustion in the auxiliary combustion chamber 50 is likely to be promoted. As a result, the ignition ability of the auxiliary combustion chamber 50 can be improved.

[0041] The discharge gap G is formed on the tip side of the tip of the housing 2. Therefore, it is easy to check the discharge gap G formed between the ground electrode 6 and the center electrode 4 fixed to the housing 2 before fixing the plug cover 5 to the housing 2. This makes it easy to adjust the discharge gap G. As a result, the spark plug 1 can be manufactured efficiently.

[0042] As described above, according to this embodiment, it is possible to provide the spark plug 1 for an internal combustion engine, which is capable of suppressing overheating of the ground electrode 6.

[0043] (Comparative form 1) In this embodiment, as shown in FIG. 6, the ground electrode 6 and the plug cover 5 do not abut against each other in the Z direction.

[0044] In the spark plug 9 of this embodiment, the tip of the ground electrode 6 is located on the base end side of the inner wall surface 54 of the bottom wall portion 57, as shown in Fig. 6. In other words, the protruding end portion 62 and the inner wall surface 54 of the bottom wall portion 57 do not abut against each other. The rest is the same as in embodiment 1. Note that, among the reference characters used in Fig. 6, the same reference characters used in embodiment 1 represent the same components, etc. as in embodiment 1, unless otherwise specified.

[0045] (Experimental Example 1) In this example, as shown in the graph of Fig. 7, a spark plug having the same basic structure as that of Comparative Example 1 was used to analyze the relationship between the crank angle and the temperature of each part. The test conditions were: the rotation speed of the internal combustion engine in which the spark plug was installed was 4000 rpm, the equivalence ratio was 1.013, the EGR rate (i.e., exhaust gas recirculation rate) was 0%, the ignition timing by the spark plug was ATDC (abbreviation of after top dead center of compression) 3° CA (abbreviation of crank angle), and the ignition energy was 60 mJ. In this example, the temperature of the protruding end of the ground electrode and the temperature of the inner wall surface of the bottom wall of the plug cover were also analyzed.

[0046] From the graph in Figure 7, it can be seen that after ignition by the spark plug, the temperatures of both the protruding end and the inner wall surface of the bottom wall rise, and the temperature of the inner wall surface of the bottom wall is significantly lower than the temperature of the protruding end.

[0047] From the above results, it is presumed that when the ground electrode is in contact with the plug cover, the heat of the ground electrode can be efficiently dissipated to the outside via the plug cover. Therefore, it is considered that by abutting the ground electrode against the plug cover as in the spark plug of the first embodiment, overheating of the ground electrode can be suppressed. It is also considered that by abutting the protruding end, which is particularly prone to becoming hot, against the plug cover, overheating of the ground electrode can be further suppressed.

[0048] (Embodiment 2) As shown in FIG. 8, this embodiment is an embodiment in which the shape of the plug cover 5 is modified from that of the first embodiment.

[0049] 8, the plug cover 5 has a protrusion 55 formed by a part of the inner wall surface 54 protruding toward the base end side. The protrusion 55 and the ground electrode 6 abut against each other in the plug axial direction Z. More specifically, the protrusion 55 and the protruding end portion 62 abut against each other in the Z direction. In this embodiment, the protrusion 55 is formed integrally with other portions of the plug cover 5.

[0050] The protrusion 55 is formed on the bottom wall portion 57. A central axis 55L of the protrusion 55 is eccentric to the plug radially outward with respect to the plug central axis C. That is, the base end of the protrusion 55 is located on the plug radially outward with respect to the plug central axis C. When viewed from the Z direction (not shown), the central axis 55L is on the opposite side to the fixed end portion 61 across the plug central axis C in the protruding direction of the ground electrode 6.

[0051] Further, the extension portion 65 is inclined so as to be more inclined toward the base end side as it approaches the protruding end portion 62. The inclination angle θ1 of the extension portion 65 with respect to the Z direction is less than 90°. The rest is the same as in embodiment 1. Note that, among the symbols used in embodiment 2 and onwards, the same symbols used in the previous embodiments represent the same components, etc. as in the previous embodiments, unless otherwise specified.

[0052] The convex portion 55 and the ground electrode 6 abut against each other in the plug axial direction Z. Therefore, even if the inclination angle θ1 is less than 90°, the protruding end 62 can be reliably abutted against the plug cover 5. In other words, even if the protruding end 62 is located closer to the base end than the bent portion 64, the protruding end 62 can be reliably abutted against the plug cover 5. As a result, heat from the ground electrode 6 can be reliably and effectively dissipated.

[0053] The central axis 55L of the protrusion 55 is eccentric outward in the plug radial direction with respect to the plug central axis C. Therefore, by adjusting the position of the protrusion 55 in the plug circumferential direction with respect to the ground electrode 6, the protruding end 62 can be more reliably brought into contact with the plug cover 5 even if the inclination angle θ1 is less than 90°.

[0054] When viewed from the Z direction, the central axis 55L is on the opposite side to the fixed end 61 across the plug central axis C in the protruding direction of the ground electrode 6. Therefore, even if the inclination angle θ1 is less than 90°, the protruding end 62 can be more reliably brought into contact with the plug cover 5. As a result, the heat of the ground electrode 6 can be more reliably and effectively dissipated. In particular, when the heat dissipation path from the protruding end 62 to the housing 2 is long, the heat of the ground electrode 6 can be more effectively dissipated. In addition, the same effects as those of the first embodiment are achieved.

[0055] (Embodiment 3) As shown in FIG. 9, this embodiment is an embodiment in which the position of the protrusion 55 is changed from that of the second embodiment.

[0056] In this embodiment, as shown in FIG. 9, the protrusion 55 is formed so that the central axis 55L of the protrusion 55 substantially overlaps with the plug central axis C. The other configurations and effects are the same as those of the second embodiment.

[0057] (Embodiment 4) As shown in FIG. 10, this embodiment is an embodiment in which the shape of the ground electrode 6 is modified from that of the first embodiment.

[0058] In this embodiment, the ground electrode 6 protrudes from the fixed end 61 into the auxiliary combustion chamber 50 without bending, as shown in Fig. 10. In other words, the ground electrode 6 is formed in a rod shape. Also, the ground electrode 6 is inclined toward the tip side as it approaches the protruding end 62.

[0059] A flat ground contact surface 66 is formed on the tip side of the protruding end portion 62. The ground contact surface 66 is formed so as to be substantially perpendicular to the Z direction. The ground contact surface 66 is formed so as to be along the inner wall surface 54 of the bottom wall portion 57. The ground contact surface 66 is in surface contact with the inner wall surface 54 of the bottom wall portion 57. The rest is the same as in the first embodiment.

[0060] The protruding end 62 has a ground contact surface 66. Therefore, the protruding end 62 can be brought into surface contact with the inner wall surface 54 of the bottom wall portion 57. This makes it easier for heat from the ground electrode 6 to be dissipated to the outside via the plug cover 5. As a result, overheating of the ground electrode 6 can be further suppressed.

[0061] Furthermore, the ground electrode 6 protrudes from the fixed end 61 into the auxiliary combustion chamber 50 without being bent. This makes it easy to shorten the length of the ground electrode 6 from the fixed end 61 to the protruding end 62. This makes it easy to shorten the heat dissipation path of the ground electrode 6 to the housing 2 and the heat dissipation path to the plug cover 5. As a result, it is even easier to dissipate heat from the ground electrode 6 to the outside. In addition, the same effects as those of the first embodiment are achieved.

[0062] (Embodiment 5) In this embodiment, as shown in FIG. 11, a cover base end portion 52 is fixed to the inner periphery side of a housing fixing portion 21. As shown in FIG.

[0063] In this embodiment, the abutting step and the joining step are performed in a state in which the inner peripheral surface of the housing fixing portion 21 and the outer peripheral surface of the cover base end portion 52 are in contact with each other in the plug radial direction.

[0064] As shown in FIG. 11, the ground electrode 6 protrudes from the inner circumferential surface of the housing 2 into the auxiliary combustion chamber 50 . The other configurations and effects are the same as those of the first embodiment.

[0065] (Embodiment 6) In this embodiment, as shown in Figs. 12 and 13, a center electrode 4 and a ground electrode 6 are opposed to each other in the plug radial direction, thereby forming a discharge gap G.

[0066] As shown in Figs. 12 and 13, the discharge gap G is formed by the center-facing side surface 41 of the center electrode 4 and the ground-facing side surface 67 of the ground electrode 6 facing each other in the plug radial direction.

[0067] The ground electrode 6 is formed in a rod shape. Specifically, the ground electrode 6 is in the shape of a substantially rectangular prism. That is, the ground electrode 6 has four flat side surfaces, one of which is a ground-facing side surface 67. The ground-facing side surface 67 is formed in a continuous flat surface shape from the fixed end portion 61 to the protruding end portion 62. The ground electrode 6 is inclined toward the tip side as it approaches the protruding end portion 62. The rest is the same as in the first embodiment.

[0068] The ground electrode 6 has a ground-facing side surface 67. Therefore, the swirl flow formed in the auxiliary combustion chamber 50 is guided by the ground-facing side surface 67 and easily passes through the discharge gap G. Therefore, the discharge formed in the discharge gap G is easily extended. As a result, the ignition performance can be improved. In addition, the same effects as those of the first embodiment are achieved.

[0069] (Embodiment 7) In this embodiment, as shown in FIG. 14, a plug cover 5 is fixed to a housing 2 by screwing.

[0070] 14, the housing fixing portion 21 and the cover base end portion 52 form a threaded portion that is fixed to each other by threading the male thread portion 11 and the female thread portion 12. Specifically, the plug cover 5 is fixed to the housing 2 by threading the female thread portion 12 formed on the cover base end portion 52 and the male thread portion 11 formed on the housing fixing portion 21.

[0071] Next, a method for manufacturing the spark plug 1 of this embodiment will be described. In the abutting step, with the male threaded portion 11 and the female threaded portion 12 screwed together, the plug cover 5 is rotated in one circumferential direction of the plug relative to the housing 2. As a result, the plug cover 5 is moved toward the base end relative to the housing 2 until the protruding end portion 62 and the inner wall surface 54 of the bottom wall portion 57 abut against each other, as shown in FIG. The other configurations and effects are the same as those of the first embodiment.

[0072] In the above-mentioned embodiments 1 to 7, the nozzle hole 51 is formed so that the nozzle hole axis 51L is inclined with respect to the imaginary straight line VL when viewed from the Z direction. However, the nozzle hole can also be formed so that the nozzle hole axis is aligned along the plug radial direction when viewed from the Z direction.

[0073] In addition, in the above-mentioned embodiments 1 to 7, the ground electrode 6 is provided so that the ground electrode 6 and the injection hole 51 do not overlap each other when viewed from the Z direction. However, the ground electrode can also be provided so that the ground electrode and the injection hole overlap each other when viewed from the Z direction.

[0074] In the above-mentioned first to seventh embodiments, the spark plug 1 has one ground electrode 6. However, the spark plug may have two or more ground electrodes. When the spark plug has a plurality of ground electrodes, at least one of the ground electrodes may be configured to abut against the inner wall surface of the plug cover in the Z direction.

[0075] In the above-mentioned second and third embodiments, the protrusion 55 is formed integrally with other portions of the plug cover 5. However, the protrusion can also be formed by joining a separate member to the plug cover.

[0076] Also, the contact portion where the ground electrode and the plug cover contact each other in the Z direction can be joined by welding. Specifically, for example, after the joining process, the contact portion between the protruding end portion and the bottom wall portion can be joined by laser welding from the outside of the plug cover. This makes it possible to further dissipate heat from the ground electrode to the outside via the plug cover. As a result, overheating of the ground electrode can be further suppressed.

[0077] Also, a tip can be joined to each of the tip of the center electrode and the ground electrode that form the discharge gap. That is, a discharge gap can be formed between the tip joined to the tip of the center electrode and the tip joined to the ground electrode. The tip can be made of a precious metal such as iridium or platinum, or an alloy containing these as a main component.

[0078] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the gist of the present invention. [Explanation of symbols]

[0079] 1...spark plug, 2...housing, 21...housing fixing portion, 22...opposing surface, 3...insulator, 4...center electrode, 5...plug cover, 50...auxiliary combustion chamber, 51...nozzle hole, 52...cover base end, 53...base end surface, 54...inner wall surface, 6...ground electrode, 61...fixed end, G...discharge gap, Z...plug axial direction

Claims

1. A cylindrical insulator (3); a center electrode (4) held on the inner circumferential side of the insulator and exposed on the tip side from the insulator; a cylindrical housing (2) that holds the insulator on its inner periphery; a ground electrode (6) forming a discharge gap (G) between itself and the center electrode; a plug cover (5) fixed to the tip of the housing so as to cover a sub-combustion chamber (50) in which the discharge gap is disposed, The ground electrode protrudes into the auxiliary combustion chamber from a fixed end (61) fixed to the housing, The plug cover is formed with a nozzle hole (51) that communicates the auxiliary combustion chamber with the outside, the front end portion of the housing has a housing fixing portion (21) facing a cover base end portion (52) of the plug cover in the plug radial direction, and an opposing surface (22) facing a base end surface (53) of the plug cover in the plug axial direction (Z) on the base end side of the housing fixing portion, The housing fixing portion and the cover base end portion are fixed to each other, the base end surface of the plug cover is disposed at a position spaced apart from the opposing surface in the plug axial direction, The ground electrode and the inner wall surface (54) of the plug cover abut against each other in the plug axial direction, the plug cover has a protrusion (55) formed by a portion of the inner wall surface protruding toward the base end, and the protrusion and the ground electrode abut against each other in the plug axial direction.

2. 2. The spark plug for an internal combustion engine according to claim 1, wherein the projecting end portion (62) of said ground electrode and said inner wall surface of said plug cover abut against each other in the plug axial direction.

3. 3. A spark plug for an internal combustion engine as set forth in claim 2, wherein said projecting end portion forms a tip of said ground electrode.

4. 4. The spark plug for an internal combustion engine according to claim 1, wherein the base end portion of the cover is fixed to an outer circumferential side of the housing fixing portion.

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