Spark plug for an internal combustion engine

Abstract

Spark plug for an internal combustion engine, including: a housing (11) having a cylindrical shape; an insulator (12) having a cylindrical shape and being held on an inside of the housing (11); a central electrode (2) which is held against an inner side of the insulator (12); a ground electrode (3) which forms a discharge gap (G) with the center electrode (2); and a candle cover (4) which, together with the housing (11), configures an auxiliary combustion chamber (5) in which the discharge gap (G) is arranged and which has a spray opening (41) that communicates between an inside and an outside of the candle cover (4), wherein the ground electrode (3) is connected to a plurality of locations on an auxiliary chamber inner wall surface (6) comprising the surfaces of the housing (11) and the spark plug cover (4) which are exposed to the auxiliary combustion chamber (5) configured by the housing (11) and the spark plug cover (4), wherein a section of the ground electrode (3) is connected to a position on the auxiliary chamber inner wall surface (6) which is opposite a distal end face (221) of the center electrode (2) in an axial direction (Z).

Description

BACKGROUND[Technical Area]

[0001] The present disclosure relates to a spark plug for an internal combustion engine. [State of the art]

[0002] US 3 896 322 A discloses a spark plug with a flow regulating device for regulating the flow direction of a fuel-air mixture so that it traverses a spark gap which is prepared so as to extend substantially along the flow direction, the gap being provided with a constricted portion between two oppositely arranged electrodes in an upstream region of the flow of the fuel-air mixture, whereby an arc is always ignited at the constricted portion of the gap region and carried down the gap by the flow of the mixture while maintaining a steady state for a period of time sufficient to complete the ignition.

[0003] DE 10 2011 006 597 A1 discloses a spark plug mounted in an indirect-injection internal combustion engine. The spark plug contains a center electrode and a ground electrode (16b) within an ignition chamber in such a way that they oppose each other. A spark plug cover has a plurality of communication holes that facilitate communication between the ignition chamber and a combustion chamber. When a distance from a small-diameter end portion of the center electrode to an intersection of the communication holes is Z and a diameter of a virtual circle connecting the centers of the communication holes is L, a relationship of 0.3 < Z / L' < 0.7 is realized.

[0004] DE 102012 102 731 A1 discloses a pre-chamber spark plug having a shell. Furthermore, the pre-chamber spark plug has an insulator arranged within the shell. In a specific embodiment, a center electrode has a first portion surrounded by the insulator and a second portion extending from the insulator into a pre-chamber. The pre-chamber is defined by the shell. In a further embodiment, a ground electrode is attached to the insulator. In specific embodiments, the ground electrode is tubular in shape and has an inner spark surface ring arranged in a position surrounding and spaced from the center electrode to create a spark gap, an outer ring attached to the shell, and a plurality of rounded spokes connecting the inner and outer rings.In a special embodiment, the ground and center electrodes allow the application of precious metal alloys to increase the service life of the electrode surface. In another embodiment, the ground electrode and the insulator are connected to the center electrode.

[0005] A spark plug is used as an ignition device in an internal combustion engine, such as automotive engines and combined heat and power plants. JP 2018 006 304 A discloses a spark plug in which a discharge gap is covered by a spark plug cover. An auxiliary combustion chamber is formed on an inner side of the spark plug cover.

[0006] In the aforementioned spark plug, an air-fuel mixture located in a combustion chamber of the internal combustion engine is introduced into the auxiliary combustion chamber via a spray orifice formed in the plug cover. Furthermore, the air-fuel mixture is ignited by a spark discharge in the discharge gap, thereby generating a flame in the auxiliary combustion chamber. Subsequently, a flame jet is shot from the spray orifice into the combustion chamber outside the auxiliary combustion chamber, and the flame is distributed throughout the combustion chamber. This makes it possible to achieve an internal combustion engine with a high combustion rate.

[0007] Here, according to the spark plug described in JP 2018 006 304 A, a ground electrode is connected to the plug cover. An end portion of the ground electrode on a side opposite a connecting portion connected to the plug cover forms the discharge gap with a distal end surface of a center electrode.

[0008] In the spark plug described in JP 2018 006 304 A, the heat from the ground electrode is dissipated primarily through the metallic plug cover into a housing. However, the heat transfer distance to the housing at the portion of the ground electrode on the side (i.e., the discharge gap side) opposite the side connected to the plug cover is long. Heat dissipation is poor. Therefore, this portion becomes too hot. This is believed to cause preignition and knocking in the internal combustion engine. SUMMARY

[0009] It is therefore an object of the present invention to provide a spark plug for an internal combustion engine which is capable of improving the heat dissipation of a ground electrode.

[0010] The object is achieved by the spark plug having the features of claim 1. Further advantageous developments and embodiments of the invention are the subject of the subsequent claims.

[0011] An exemplary embodiment of the present disclosure provides a spark plug for an internal combustion engine, including: a shell having a cylindrical shape; an insulator having a cylindrical shape and supported on an inner side of the shell; a center electrode supported on an inner side of the insulator; a ground electrode forming a discharge gap with the center electrode; and a plug cover that, together with the shell, configures an auxiliary combustion chamber in which the discharge gap is disposed, and includes a spray opening communicating between the inner side and the outer side of the plug cover. The ground electrode is connected to a plurality of locations on an auxiliary chamber inner wall surface, including surfaces of the shell and the plug cover exposed to the auxiliary combustion chamber.

[0012] In the spark plug for an internal combustion engine according to the exemplary embodiment described above, the ground electrode is connected to a plurality of locations on the inner wall surface of the auxiliary chamber. Therefore, the heat in the ground electrode is distributed toward the plurality of locations connected to the inner wall surface of the auxiliary chamber and released. This can improve heat dissipation of the ground electrode.

[0013] As described above, according to the exemplary embodiment described above, a spark plug for an internal combustion engine can be provided which can improve heat dissipation of a ground electrode.

[0014] The reference numerals in the parentheses of the claims indicate corresponding relationships to specific means according to the embodiments described below and do not limit the technical scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWING

[0015] The attached figures show the following: Fig. 1 is a cross-sectional view according to a first embodiment, in which the cross section passes through a central axis of a spark plug and is parallel to an axial direction; Fig. 2 is a cross-sectional view along the line II-II in Fig. 1; Fig. 3 is a cross-sectional view according to a second embodiment, in which the cross section passes through the central axis of the spark plug and is parallel to the axial direction; Fig. 4 is a cross-sectional view according to a third embodiment, in which the cross section passes through the center axis of the spark plug and is parallel to the axial direction; Fig. 5 is a cross-sectional view according to a fourth embodiment, in which the cross section passes through the center axis of the spark plug and is parallel to the axial direction; Fig. 6 is a cross-sectional view according to a fifth embodiment, in which the cross section passes through the center axis of the spark plug and is parallel to the axial direction; Fig. 7 is a cross-sectional view along the line VII-VII in Fig. 6; Fig. 8 is a cross-sectional view according to a sixth embodiment, in which the cross section passes through the center axis of the spark plug and is parallel to the axial direction; Fig. 9 is a cross-sectional view along the line IX-IX in Fig. 8; Fig. 10 is a cross-sectional view according to a seventh embodiment, in which the cross section is perpendicular to the axial direction and passes through a portion of a ground electrode on a proximal end side; Fig. 11 is a cross-sectional view according to an eighth embodiment, in which the cross section passes through the center axis of the spark plug and is parallel to the axial direction; and Fig. 12 is a cross-sectional view taken along the line XII-XII in Fig. 11. DESCRIPTION OF THE EMBODIMENTS (First Embodiment)

[0016] A spark plug for an internal combustion engine according to a first embodiment is described with reference to Fig. 1 and Fig. 2 described.

[0017] As in Fig. 1, a spark plug 1 for an internal combustion engine according to the present embodiment includes a housing 11, an insulator 12, a center electrode 2, and a ground electrode 3. The housing 11 has a cylindrical shape. The insulator 12 is held in the housing 11. Furthermore, the insulator 12 has a cylindrical shape. The center electrode 2 is held inside the insulator 12. The ground electrode 3 forms a discharge gap G with the center electrode 2. A plug cover 4, together with the housing 11, configures an auxiliary combustion chamber 5 in which the discharge gap G is arranged. In addition, the plug cover 4 includes a spray opening 41 that communicates between the inside and the outside of the plug cover 4. The ground electrode 3 is connected to a plurality of locations on an auxiliary chamber inner wall surface 6.The auxiliary chamber inner wall surface 6 includes the surfaces of the casing 11 and the plug cover 4 exposed to the auxiliary combustion chamber 5. A detailed description according to the present embodiment will be given below.

[0018] In this specification, a direction in which a central axis of the spark plug 1 extends is referred to as the axial direction Z. Furthermore, a side of the spark plug 1 in the axial direction Z on which the auxiliary combustion chamber 5 is formed is referred to as the distal end side (tip end side). A side of the spark plug 1 opposite to the distal end side is referred to as a proximal end side (base end side).

[0019] Furthermore, a circumferential direction of the spark plug 1 is simply referred to as a circumferential direction. Furthermore, a radial direction of the spark plug 1 is simply referred to as a radial direction.

[0020] For example, the spark plug 1 can be used as an ignition means in an internal combustion engine for an automobile, in combined heat and power systems (combined heat and power plants), and the like. A proximal end portion of the spark plug 1 is connected to an ignition coil (not shown). A distal end portion of the spark plug 1 is arranged in a combustion chamber of the internal combustion engine.

[0021] As in Fig. 1, a fastening screw portion 111 is formed in an outer peripheral portion of the housing 11. The spark plug 1 is screwed into a screw hole provided in a cylinder head (not shown) through the fastening screw portion 111. The spark plug 1 is thereby fixed to the cylinder head. In the state where the spark plug 1 is fixed to the cylinder head, a part of the spark plug 1 located further toward the distal end side than the fastening screw portion 111 is exposed to the combustion chamber.

[0022] As in Fig. 1, a circular cylindrical cover fixing portion 112 is provided on the distal end side of the fixing screw portion 111 of the housing 11. The cover fixing portion 112 protrudes toward the distal end side. An outer peripheral surface of the cover fixing portion 112 faces further toward an inner peripheral side than the fixing screw portion 111. In addition, the plug cover 4 is fixed to the cover fixing portion 112. That is, according to the present embodiment, the housing 11 and the plug cover 4 are separate components.

[0023] The plug cover 4 has an approximately hemispherical dome shape. The plug cover 4 is in the shape of a rotating body whose central axis of the spark plug is a rotation axis. The plug cover 4 is fixed to the cover fixing portion 112 of the housing 11 in a state where an open end thereof is directed toward the proximal end side. The plug cover 4 is arranged such that a proximal end portion 42 thereof covers the cover fixing portion 112 from the outer circumference. In the proximal end portion 42 of the plug cover 4, an inner peripheral surface has wider recesses toward the outer peripheral side than the distal end side portion. In addition, the proximal end portion 42 of the plug cover 4 is mounted on the cover fixing portion 112 such that the cover fixing portion 112 is inserted into the recess.In addition, the proximal end portion 42 of the candle cover 4 is welded to the cover fixing portion 112 over the entire circumference.

[0024] The plug cover 4 includes a plurality of spray holes 41, or a plurality of spray openings 41, communicating between the inside and outside of the plug cover 4. The plurality of spray holes 41 are formed at the distal end portion of the plug cover 4. Moreover, the plurality of spray holes 41 are formed further toward the outer peripheral side in the radial direction than the center axis of the spark plug 1. The plurality of spray holes 41 are formed at a uniform interval in the circumferential direction. Each spray hole 41 is formed further toward the outer peripheral side in the radial direction and toward the distal end side in the axial direction Z. The number, shape, arrangement, and the like of the spray holes 41 are determined as needed.

[0025] A space surrounded by both the casing 11 and the plug cover 4 is the auxiliary combustion chamber 5. Moreover, the surfaces of the casing 11 and the plug cover 4 exposed to the auxiliary combustion chamber 5 are the auxiliary chamber inner wall surface 6. The ground electrode 3 is connected to a plurality of locations on the mutually separated inner wall surfaces 6 of the auxiliary chamber.

[0026] As in Fig. 1 and Fig. 2, the ground electrode 3 has a circular columnar shape that is straight. For example, the ground electrode 3 comprises a Ni-based alloy whose main component is Ni (ie, nickel). As shown in Fig. 1, according to the present embodiment, a diameter of the ground electrode 3 is larger than a thickness of the plug cover 4. According to the present embodiment, the ground electrode 3 is connected only to the plug cover 4, the housing 11 and the plug cover 4, which configure the auxiliary chamber inner wall surface 6.

[0027] The ground electrode 3 is connected to a plurality of locations on the auxiliary chamber inner wall surface 6, the positions of which differ from each other in the axial direction Z. In the axial direction Z, a portion of the ground electrode 3 is connected to a region of the auxiliary chamber inner wall surface 6 that is further toward the distal end side than a distal end surface 221 of the center electrode 2. Another portion of the ground electrode 3 is connected to a region of the auxiliary chamber inner wall surface 6 that is further toward the proximal end side than the distal end surface 221 of the center electrode 2.

[0028] A distal end portion 31, i.e., one end of the ground electrode 3, is connected to a position on the auxiliary chamber inner wall surface 6 that overlaps the distal end surface 221 of the center electrode 2 in the axial direction Z. The distal end portion 31 is positioned on the distal end side of the distal end surface 221 of the center electrode 2. The distal end portion 31 is connected to a portion of the plug cover 4 where a heat transfer distance to the connecting portion connected to the housing 11 (i.e., the proximal end portion 42) is the furthest or at the periphery of this portion. In the cross-sectional view in Fig. 1, an outer shape position of the distal end face 221 of the center electrode 2 in a direction perpendicular to the axial direction Z is represented by one-dot chain lines.

[0029] Furthermore, a proximal end portion 32, which is an end portion of the ground electrode 3 on the side opposite to the distal end portion 31, is connected to a portion of the auxiliary chamber inner wall surface 6 adjacent to the proximal end portion 42 of the plug cover 4 on the distal end side. The proximal end portion 32 of the ground electrode 3 is formed at a position on the auxiliary chamber inner wall surface 6 adjacent to the distal end surface of the cover fixing portion 112 of the housing 11 on the distal end side. Here, to improve the attachability of the plug cover 4 to the housing 11, a space is preferably formed between the proximal end portion 32 of the ground electrode 3 and the distal end surface of the cover fixing portion 112.At least a part of the proximal end portion 32 of the ground electrode 3 is positioned further toward the proximal end side in the axial direction Z than the distal end surface 221 of the center electrode 2. Furthermore, a portion of the ground electrode 3 between the distal end portion 31 and the proximal end portion 32 is exposed over an entire circumference of the auxiliary combustion chamber 5. This can suppress the ground electrode 3, which prevents the propagation of a flame generated in the auxiliary combustion chamber 5.

[0030] The ground electrode 3 is connected to the spark plug cover 4 at both ends by welding. The ground electrode 3 forms the discharge gap G with the distal end surface 221 of the center electrode 2 in a longitudinal center portion. The longitudinal center portion of the ground electrode 3 is closest to the distal end surface 221 of the center electrode 2 in a direction perpendicular to the longitudinal direction of the ground electrode 3. Between this center portion and the distal end surface 221 of the center electrode 2, the discharge gap G is formed, in which a spark discharge is generated.

[0031] The housing 11, the spark plug cover 4, and the ground electrode 3 contain materials with electrical and thermal conductivity. Furthermore, the housing 11, the spark plug cover 4, and the ground electrode 3 are thermally and electrically connected to each other.

[0032] The insulator 12 is held in the housing 11. A distal end portion of the insulator 12 protrudes toward the distal end side of the fixing screw portion 111 of the housing 11. A proximal end portion of the insulator 12 protrudes toward the proximal end side of the housing 11. The center electrode 2 is inserted and held in a distal end portion on the inside of the insulator 12.

[0033] A distal end portion of the center electrode 2 is exposed from the insulator 12 on the distal end side. The center electrode 2 includes a center electrode element 21 and a center electrode chip 22 fixed to a distal end of the center electrode element 21. For example, the center electrode element 21 includes a Ni-based alloy. Furthermore, the center electrode chip 22 includes, for example, Pt (i.e., platinum) and is formed into a circular columnar shape. Furthermore, a distal end surface 221 of the center electrode chip 22 forms the discharge gap G with the ground electrode 3.

[0034] Next, the effects according to the present embodiment will be described.

[0035] In the spark plug 1 for an internal combustion engine according to the present embodiment, the ground electrode 3 is connected to a plurality of locations on the inner wall surface 6 of the auxiliary chamber. Therefore, the heat in the ground electrode 3 is distributed toward the plurality of locations connected to the inner wall surface 6 of the auxiliary chamber and released. This can improve the heat dissipation of the ground electrode 3.

[0036] Furthermore, the ground electrode 3 is connected to a plurality of locations on the auxiliary chamber inner wall surface 6, the positions of which are different from each other in the axial direction Z. This can facilitate the uniformity of temperature distribution in the plug cover 4. That is, the distal end side of the plug cover 4 is located near a central portion of the combustion chamber. Moreover, the heat transfer distance to the housing 11 at the distal end side of the plug cover 4 is wide. Therefore, the plug cover 4 tends to reach a higher temperature toward the distal end side. Thus, by connecting the ground electrode 3 to a plurality of locations on the auxiliary chamber inner wall surface 6, the positions of which are different from each other in the axial direction Z, heat in the portion of the plug cover 4 on the distal end side is efficiently dissipated through the ground electrode 3.This can easily prevent the temperature level of the distal end side portion of the plug cover 4 from becoming locally high.

[0037] Furthermore, the ground electrode 3 is connected to a position on the auxiliary chamber inner wall surface 6 that overlaps the distal end surface 221 of the center electrode 2 in the axial direction Z. Here, the heat transfer distance to the housing 11 is particularly wide in the portion of the auxiliary chamber inner wall surface 6 that overlaps the distal end surface 221 of the center electrode 2 in the axial direction Z. Therefore, this portion, in particular, tends to have a high temperature. Thus, by connecting the ground electrode 3 to the position on the auxiliary chamber inner wall surface 6 that overlaps the distal end surface 221 of the center electrode 2 in the axial direction Z, heat can be efficiently dissipated through the ground electrode 3 in the periphery of the portion of the plug cover 4 that overlaps the distal end surface 221 of the center electrode 2 in the axial direction Z.

[0038] Furthermore, in the axial direction Z, a part of the ground electrode 3 is connected to a portion of the auxiliary chamber inner wall surface 6 that is further toward the distal end side than the distal end surface 221 of the center electrode 2. Another portion is connected to a portion of the auxiliary chamber inner wall surface 6 that is further toward the proximal end portion than the distal end surface 221 of the center electrode 2. Therefore, the heat in the distal end side portion of the plug cover 4 can be easily dissipated to the case 11 side through the ground electrode 3. This can prevent the plug cover 4 from becoming too high in temperature locally. The uniformity of the temperature distribution in the plug cover 4 can be enabled.

[0039] Furthermore, the housing 11 and the plug cover 4 are separate components. The ground electrode 3 is only connected to the plug cover 4, the housing 11, and the plug cover 4, which configure the auxiliary chamber inner wall surface 6. Therefore, in the manufacturing of the spark plug 1, the ground electrode 3 is first connected to the plug cover 4. Then, the plug cover 4 is attached to the housing 11. This allows the spark plug 1 to be manufactured easily.

[0040] As described above, according to the present embodiment, a spark plug for an internal combustion engine is provided which can improve heat dissipation of a ground electrode. (Second embodiment)

[0041] According to a second embodiment, as shown in Fig. 3, the shape of the ground electrode 3 is changed from that of the first embodiment.

[0042] According to the present embodiment, the ground electrode 3 includes a ground electrode base material 33 and a ground electrode chip 34. The ground electrode base material 33 forms a base material of the ground electrode 3. The ground electrode chip 34 is bonded to the ground electrode base material 33. For example, the ground electrode base material 33 includes a Ni-based alloy. For example, the ground electrode chip 34 includes Pt. Moreover, in the ground electrode 3, the ground electrode chip 34 forms the discharge gap G. That is, the ground electrode 3 is closest to the distal end surface 221 of the center electrode on the ground electrode chip 34.

[0043] The ground electrode base material 33 has a circular columnar shape formed in a straight line. A diameter of the ground electrode base material 33 is equal to or smaller than the thickness of the plug cover 4. The proximal end portion 32 of the ground electrode base material 33 is connected to a position on the auxiliary chamber inner wall surface 6 that is far from the distal end surface of the cover fixing portion 112 of the housing 11 toward the distal end side. Other connecting portions of the ground electrode base material 33 to the plug cover 4 are similar to the connecting portions of the ground electrode 3 to the auxiliary chamber inner wall surface 6 according to the first embodiment.

[0044] The ground electrode chip 34 is bonded to a surface in a central portion of the ground electrode base material 33 on a side facing the distal end surface 221 of the center electrode 2. The ground electrode chip 34 is formed into a circular columnar shape having a height in a direction in which the ground electrode chip 34 and the distal end surface 221 of the center electrode 2 are aligned. Here, the ground electrode chip 34 may have other shapes, such as a prismatic shape.

[0045] Other configurations are similar to those of the first embodiment.

[0046] Here, of the reference numerals used according to the second and subsequent embodiments, the reference numerals identical to those of a previous embodiment indicate constituent elements and the like similar to those of the previous embodiment unless otherwise specified.

[0047] According to the present embodiment, the ground electrode 3 includes the ground electrode base material 33 and the ground electrode chip 34 bonded to the ground electrode base material 33. The ground electrode chip 34 forms the discharge gap G. Thus, for example, by using the ground electrode chip 34 with a highly wear-resistant material and the ground electrode base material 33 with a material with high thermal conductivity, heat dissipation of the ground electrode 3 can be more easily ensured. Furthermore, by using the ground electrode chip 34 with a material with high wear resistance, the service life of the ground electrode 3 can be improved.

[0048] Other working effects are similar to the first embodiment. (Third embodiment)

[0049] According to a third embodiment, as shown in Fig. 4, the shape of the ground electrode base material 33 is changed from that of the second embodiment.

[0050] According to the present embodiment, the ground electrode 3 is curved to protrude toward the discharge gap G side. Specifically, the ground electrode base material 33 is shaped to extend toward the discharge gap G side and toward the center in the longitudinal direction. Therefore, the entire ground electrode 3 has a curved shape that protrudes toward the discharge gap G side.

[0051] Other configurations are similar to those of the second embodiment.

[0052] According to the present embodiment, the ground electrode 3 is curved to protrude toward the discharge gap G side. Therefore, portions of the ground electrode 3 other than the portion (the ground electrode chip 34 according to the present embodiment) forming the discharge gap G can be arranged away from the distal end surface 221 of the center electrode 2. Thus, the occurrence of a discharge with an unexpected part of the ground electrode 3 serving as its origin point can be prevented.

[0053] Other working effects are similar to the second embodiment. (Fourth embodiment)

[0054] According to a fourth embodiment not belonging to the invention, which nevertheless contributes to the understanding of the present disclosure, as in Fig. 5, the positions where the ground electrode 3 is connected to the auxiliary chamber inner wall surface 6 are changed from those of the third embodiment.

[0055] According to the present embodiment, both end portions of the ground electrode base material 33 are bonded to positions on the auxiliary chamber inner wall surface 6 located on opposite sides with the center axis of the spark plug 1 therebetween. Both end portions of the ground electrode base material 33 are bonded to positions on the auxiliary chamber inner wall surface 6 that are different in the axial direction Z. Here, the ground electrode base material 33 is not bonded to a portion of the auxiliary chamber inner wall surface 6 that overlaps the distal end surface 221 of the center electrode 2 in the axial direction Z.

[0056] Other configurations are similar to those of the third embodiment.

[0057] Also according to the present embodiment, similar working effects as those according to the third embodiment are achieved. (Fifth embodiment)

[0058] According to a fifth embodiment, as shown in Fig. 6 and Fig. As shown in Figure 7, the spark plug 1 contains two ground electrodes 3. In Fig. 7, a projected contour in which the outer shape of the distal end surface 221 of the center electrode 2 is projected onto the candle cover 4 in the axial direction Z is represented by two-dot chain lines.

[0059] According to the present embodiment, the two ground electrodes 3 have identical or equivalent shapes. However, the two ground electrodes 3 are arranged in different attitudes or postures. Each ground electrode 3 has a similar shape to the ground electrode 3 according to the third embodiment. The distal end portion 31 of each ground electrode 3 is connected to a position on the auxiliary chamber inner wall surface 6 that overlaps the distal end surface 221 of the center electrode 2 in the axial direction Z. Meanwhile, as shown in Fig. 7, the proximal end portions 32 of the two ground electrodes 3 are connected to positions on the auxiliary chamber inner wall surface 6 that are shifted by 90 degrees in the circumferential direction. The spray holes or spray openings are in Fig. 7 not shown.

[0060] Other configurations are similar to those of the third embodiment.

[0061] According to the present embodiment, heat in the distal end portion of the plug cover 4 is dissipated through the plurality of ground electrodes 3. Therefore, the heat release path for the heat in the distal end portion of the plug cover 4 can be increased. The uniformity of the temperature distribution in the plug cover 4 can be further improved. Furthermore, by providing a plurality of ground electrodes 3, the total heat capacity of the housing 11, the plug cover 4, and the ground electrode 3 can also be increased.

[0062] Other working effects are similar to the third embodiment. (Sixth Embodiment)

[0063] According to a sixth embodiment, as in Fig. 8 and Fig. As shown in Figure 9, the spark plug 1 contains three ground electrodes 3.

[0064] According to the present embodiment, the three ground electrodes 3 have identical shapes. However, the three ground electrodes 3 are arranged in different postures. Each ground electrode 3 has a similar shape to the ground electrode 3 according to the third embodiment. The distal end portion 31 of each ground electrode 3 is connected to a position on the auxiliary chamber inner wall surface 6 that overlaps the distal end surface 221 of the center electrode 2 in the axial direction Z. Meanwhile, the proximal end portions 32 of the three ground electrodes 3 are connected to positions on the auxiliary chamber inner wall surface 6 that are shifted from each other by 90 degrees in the circumferential direction.

[0065] Other configurations are similar to those of the fifth embodiment.

[0066] Even according to the present embodiment, working effects similar to those of the fifth embodiment are achieved. (Seventh Embodiment)

[0067] According to a present embodiment, as shown in Fig. As shown in Figure 10, the spark plug 1 contains four ground electrodes 3.

[0068] According to the present embodiment, the four ground electrodes 3 have identical shapes. However, the four ground electrodes 3 are arranged in different postures. Each ground electrode 3 has a similar shape to the ground electrode 3 according to the third embodiment. The distal end portion 31 of each ground electrode 3 is connected to a position on the auxiliary chamber inner wall surface 6 that overlaps the distal end surface 221 of the center electrode 2 in the axial direction Z. Meanwhile, the proximal end portions 32 of the four ground electrodes 3 are connected to positions on the auxiliary chamber inner wall surface 6 that are shifted from each other by 90 degrees in the circumferential direction.

[0069] Other configurations are similar to those of the fifth embodiment.

[0070] Even according to the present embodiment, working effects similar to those of the fifth embodiment are achieved. (Eighth Embodiment)

[0071] According to an eighth embodiment, as shown in Fig. 11 and Fig. 12, a bypass element 7 is further provided, which is connected to a plurality of locations on the auxiliary chamber inner wall surface 6.

[0072] According to the present embodiment, a basic structure is similar to that of the third embodiment. In addition, as shown in Fig. 12, one end of the bypass member 7 is connected to a position adjacent to the distal end portion 31 of the ground electrode in the longitudinal direction of the ground electrode 3 when viewed from the axial direction Z. The ground electrode 3 and the bypass member 7 are arranged linearly when viewed in the axial direction Z.

[0073] The bypass member 7 has a circular columnar shape that is straight. The bypass member 7 is connected to a plurality of locations on the auxiliary chamber inner wall surface 6, the positions of which are different from each other in the axial direction Z. A distal end end portion 71 of the bypass member 7 is connected to a region of the auxiliary chamber inner wall surface 6 that is further toward the distal end side than the distal end surface 221 of the center electrode 2. A proximal end end portion 72 of the bypass member 7 is connected to a region of the auxiliary chamber inner wall surface 6 that is further toward the proximal end side than the distal end surface 221 of the center electrode 2. The distal end end portion 71 of the bypass member 7 is connected to a position on the auxiliary chamber inner wall surface 6 that overlaps the distal end surface 221 of the center electrode 2 in the axial direction Z.

[0074] The proximal end portion 72 of the bypass member 7 is connected to a position on the auxiliary chamber inner wall surface 6 that is shifted by 180 degrees in the circumferential direction from the portion to which the proximal end portion 32 of the ground electrode 3 is connected. The proximal end portion 72 of the bypass member 7 is connected to a position on the auxiliary chamber inner wall surface 6 that is distant from the proximal end portion 42 of the plug cover 4 toward the distal end side. At least a portion of the proximal end portion 72 of the bypass member 7 is located farther toward the proximal end side in the axial direction Z than the distal end surface 221 of the center electrode 2. The bypass member 7 is connected to the plug cover 4 at both end portions by welding.

[0075] The shortest distance between the bypass element 7 and the distal end surface 221 of the center electrode 2 is greater than the discharge gap G. The shortest distance between the bypass element 7 and the distal end surface 221 of the center electrode 2 can be determined from the shortest distance (ie, the length of the discharge gap G) between the ground electrode 3 and the distal end surface 221 of the center electrode 2. That is, the shortest distance between the bypass element 7 and the center electrode 2 is such that the bypass element 7 and the center electrode 2 are separated enough that the discharge occurs in the discharge gap G and no discharge occurs between the bypass element 7 and the distal end surface 221 of the center electrode 2.

[0076] Other configurations are similar to those of the third embodiment.

[0077] According to the present embodiment, the bypass element 7, which is connected to a plurality of locations on the inner wall surface 6 of the auxiliary chamber, is further provided. This allows the heat dissipation path for heat in the distal end portion of the plug cover 4 to be increased. The uniformity of the temperature distribution in the plug cover 4 can be further improved. Furthermore, the total heat capacity of the housing 11, the plug cover 4, the ground electrode 3, and the bypass element 7 can also be increased.

[0078] Other working effects are similar to the third embodiment.

[0079] The present disclosure is not limited to the above-described embodiments. For example, according to the above-described embodiments, the ground electrode 3 is connected only to the plug cover 4. However, the present disclosure is not limited thereto. A part of the ground electrode 3 may be connected to the housing 11. Furthermore, a portion of the bypass element 7 according to the eighth embodiment may be connected to the housing 11 in a similar manner.

Claims

[1] Spark plug for an internal combustion engine, comprising: a housing (11) having a cylindrical shape; an insulator (12) having a cylindrical shape and held on an inner side of the housing (11); a center electrode (2) held on an inner side of the insulator (12); a ground electrode (3) which forms a discharge gap (G) with the center electrode (2); and a candle cover (4) which, together with the housing (11), configures an auxiliary combustion chamber (5) in which the discharge gap (G) is arranged, and which has a spray opening (41) communicating between an inside and an outside of the candle cover (4), wherein the ground electrode (3) is connected to a plurality of locations on an auxiliary chamber inner wall surface (6) comprising surfaces of the housing (11) and the plug cover (4) exposed to the auxiliary combustion chamber (5) configured by the housing (11) and the plug cover (4), wherein a portion of the ground electrode (3) is connected to a position on the auxiliary chamber inner wall surface (6) opposite to a distal end surface (221) of the center electrode (2) in an axial direction (Z). [2] Spark plug for an internal combustion engine according to claim 1, wherein: in an axial direction (Z), a portion of the ground electrode (3) is connected to a region on the auxiliary chamber inner wall surface (6) which is further toward a distal end side than a distal end face (221) of the center electrode (2), and another portion is connected to a region of the auxiliary chamber inner wall surface (6) which is further toward a proximal end side than the distal end face of the center electrode (2). [3] Spark plug for an internal combustion engine according to claim 1, wherein: the ground electrode (3) is connected to a plurality of locations on the auxiliary chamber inner wall surface (6), the positions of which differ from one another in an axial direction (Z). [4] Spark plug for an internal combustion engine according to claim 3, wherein: in an axial direction (Z), a portion of the ground electrode (3) is connected to a region on the auxiliary chamber inner wall surface (6) which is further toward a distal end side than a distal end face (221) of the center electrode (2), and another portion is connected to a region of the auxiliary chamber inner wall surface which is further toward a proximal end side than the distal end face of the center electrode (2). [5] Spark plug for an internal combustion engine according to one of claims 3 or 4, wherein: the ground electrode (3) is curved so that it protrudes towards the discharge gap side. [6] Spark plug for an internal combustion engine according to one of claims 1 to 5, wherein: the ground electrode (3) comprises a plurality of ground electrodes. [7] Spark plug for an internal combustion engine according to any one of claims 1 to 6, further comprising: a bypass element (7) connected to a plurality of locations on the auxiliary chamber inner wall surface (6). [8] Spark plug for an internal combustion engine according to one of claims 1 to 7, wherein: the housing (11) and the spark plug cover (4) are separate components; and the ground electrode (3) is only connected to the housing (11) and the spark plug cover (4) which configure the auxiliary chamber inner wall surface (6). [9] Spark plug for an internal combustion engine according to any one of claims 1 to 8, wherein: the ground electrode (3) includes a ground electrode base material (33) and a ground electrode chip (34) connected to the ground electrode base material (33), in which the ground electrode chip (34) forms the discharge gap (G).

Images