Patent Application
20210249846
The present invention relates to a spark plug.
A spark plug that is used for an internal combustion engine (engine), such as a spark plug disclosed in PTL 1, typically includes a cylindrical insulator having an axial hole extending in an axial direction, a cylindrical metal shell provided on the outer periphery of the insulator, and a rod-shaped center electrode extending in the axial direction. In the spark plug disclosed in PTL 1, the center electrode is disposed on a front end side in the axial hole formed in the insulator, and a ground electrode is provided on a front end side of the metal shell, so that a spark discharge is generated between the center electrode and the ground electrode.
In the spark plug of this type, a large-diameter portion having an outside diameter that is larger than that of the other portion is provided in a predetermined region of the center electrode in the axial direction. In addition, the axial hole of the insulator has a rear facing surface. The center electrode disposed in the axial hole is positioned such that the large-diameter portion is retained at the rear facing surface.
PTL 1: Japanese Patent Application Laid-open No. 2019-3721
In recent years, an engine with increased supercharging, increased compression, and so forth, is suggested to improve fuel economy and to respond to environmental regulation. When this type of engine is used, the pressure in a combustion chamber is increased during operation of the engine, and hence the spark discharge voltage for generating a spark discharge is required to be increased. However, when the spark discharge voltage is increased, a spark that penetrates through the insulator (spark penetration) is more likely to occur between the large-diameter portion of the center electrode and the metal shell, possibly disrupting a normal spark discharge.
A method of suppressing such spark penetration may be increasing the thickness of the insulator to improve voltage resistance performance of the insulator. However, merely increasing the thickness of the insulator causes an increase in the diameter of the metal shell by the amount of the increase in the thickness of the insulator, consequently leading to an increase in the entire size of the plug.
The present invention is made to address at least one of the above-described problems, and an object of the invention is to provide a spark plug capable of further suppressing a spark that penetrates through an insulator while an increase in the diameter of a metal shell is suppressed.
A spark plug according to an aspect of the present invention includes
a cylindrical insulator having an axial hole extending in an axial direction and a rear facing surface formed in the axial hole;
a cylindrical metal shell disposed on an outer periphery of the insulator; and
a center electrode disposed on a front end side in the axial hole,
the center electrode having a large-diameter portion having an outside diameter that is the largest in the center electrode, the large-diameter portion being retained at the rear facing surface, and
the metal shell having a diameter increased portion on a rear end side with respect to the center electrode, the diameter increased portion having an inside diameter that is increased toward the rear end side, in which
the insulator has a first portion that is a portion of the insulator in a region from a rear end of the rear facing surface to a front end of the diameter increased portion,
the first portion has a thickness that is the largest in the region, and is disposed at least on an outer periphery of the large-diameter portion,
the insulator is retained at the metal shell via a packing, on the front end side with respect to the first portion, and
the insulator has a second portion on the rear end side with respect to the first portion in the region, the second portion having an outside diameter that is smaller than an outside diameter of the first portion.
In the spark plug, the first portion is disposed on a side close to the packing (a component that positions the insulator while being supported by the metal shell), and the second portion is disposed on a side farther from the packing than the first portion. Moreover, the first portion is disposed on the outer periphery of the large-diameter portion of the center electrode and has a larger thickness than that of the second portion.
With such a configuration, an effect of suppressing spark penetration can be increased in the vicinity of the large-diameter portion where a countermeasure for spark penetration is more required.
In addition, the side close to the packing has a feature that “the insulator is more stably held and the position thereof is hardly shifted relative to the metal shell”. Thus, disposing the first portion on the side close to the packing can use this feature effectively. That is, on the side close to the packing, although the first portion having a relatively large outside diameter is disposed and hence the gap between the outer peripheral surface of the insulator (the outer peripheral surface of the first portion) and the inner peripheral surface of the metal shell is relatively small, the positional shift of the insulator is suppressed, and hence the insulator hardly comes into contact with the metal shell. Hence, on the side close to the packing, by using both the structure in which the position of the insulator is hardly shifted and the first portion together, prevention of the contact and suppression of spark penetration can be both provided.
In contrast, on the side far from the packing, the second portion having a relatively small outside diameter is disposed, and hence a larger gap is ensured between the outer peripheral surface of the insulator (the outer peripheral surface of the second portion) and the inner peripheral surface of the metal shell. That is, on the side far from the packing, the allowance for the positional shift of the insulator is larger, so that the insulator is less likely to come into contact with the metal shell even when the position of the insulator is shifted to some extent. Thus, the effect of preventing the contact can be increased.
In the spark plug, the first portion may be disposed at least on an outer periphery of a whole range in the axial direction of the center electrode in the region.
With the spark plug configured as described above, the whole range in the axial direction of a portion of the center electrode disposed in the region (the region from the rear end of the rear facing surface to the front end of the diameter increased portion) can be surrounded by the first portion. Thus, in the above-described portion where spark penetration possibly occurs, spark penetration can be further effectively suppressed, and voltage resistance performance can be further enhanced.
In the spark plug, an inside diameter of the insulator may be the smallest in the first portion in the region.
In the spark plug, the inside diameter of the insulator is the smallest in the first portion. Thus, the distance between the metal shell and the center electrode can be largely ensured while the thickness of the first portion is largely obtained, thereby suppressing the electrostatic capacity in the vicinity of the first portion. As a result, wear of the center electrode and the ground electrode can be suppressed.
In the spark plug, the metal shell may have an inside-diameter portion that is a portion of the metal shell in the region. The inside-diameter portion may have an inside diameter that is the largest in the region, and may be disposed at least on an outer periphery of the first portion.
With the spark plug, the portion of the metal shell disposed in the region (the region from the rear end of the rear facing surface to the front end of the diameter increased portion) and having the largest inside diameter (inside-diameter portion) is disposed at least on the outer periphery of the first portion. Thus, in the vicinity of the first portion, the distance between the metal shell and the center electrode is further largely ensured because of the presence of the inside-diameter portion, thereby further suppressing electrostatic capacity. Accordingly, wear of the center electrode and the ground electrode can be further suppressed. The inside-diameter portion (the portion having the largest inside diameter) is provided not in the entirety of the region (the region from the rear end of the rear facing surface to the front end of the diameter increased portion), but is selectively provided only in a portion of the region. Hence, a decrease in the strength of the metal shell is suppressed compared with a configuration in which the inside-diameter portion is provided in the whole range of the region.
In the spark plug, a portion in the axial hole, on the rear end side with respect to the rear facing surface, may be filled with a front seal member that is in contact with an inner peripheral surface of the insulator and the center electrode and that contains an electrically conductive material. The first portion may be disposed at least in a region from the rear end of the rear facing surface to a rear end of the front seal member.
In a spark plug in which the gap between an insulator and a center electrode is filled with an electrically conductive front seal member, since the front seal member is electrically conductive, the front seal member transmits a spark from the center electrode, and the spark reaches the insulator. When the energy of the spark is high, the spark may penetrate through the insulator and a discharge may occur. However, in the above-described spark plug, since the thickness of the insulator is increased in the vicinity of the center electrode and the front seal member, occurrence of spark penetration can be suppressed.
According to the present invention, a spark plug capable of further suppressing a spark that penetrates through an insulator while an increase in the diameter of a metal shell is suppressed can be provided.
A spark plug 1 according to a first embodiment illustrated in
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A portion of the insulator 10 surrounding the center electrode 50 has a step portion 13 (
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The metal shell 30 is formed of an electrically conductive metal material (for example, low-carbon steel). The metal shell 30 is a metal part for fixing the spark plug 1 to an engine head of the internal combustion engine. The metal shell 30 has a cylindrical shape having the through hole 31 extending therethrough in the axial direction. The metal shell 30 is disposed on the outer periphery of the insulator 10, and is fixed to the insulator 10 by crimping.
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The insulator 10 is pressed toward the front end side in the through hole 31 via the seal members 41 and the talc due to compression deformation of the compression deformation portion 38 of the metal shell 30. The packing 45 is in close contact with a slanted surface (projecting-portion slanted surface) 35A of the projecting portion 35 facing the rear end side and a slanted surface (step-portion slanted surface) 13A of the step portion 13 facing the front end side, and is sandwiched between the slanted surfaces 35A and 13A. With the configuration in which the packing 45 is thus sandwiched, the gas in the combustion chamber is prevented from leaking to the rear end side through a gap between the metal shell 30 and the insulator 10.
The ground electrode 42 is joined to the front end of the metal shell 30, for example, by resistance welding. A spark gap which is a gap for generating a spark is formed between the ground electrode 42 and the center electrode 50.
The center electrode 50 is formed by using a metal having high corrosion resistance and high heat resistance, for example, nickel (Ni) or an alloy containing nickel as the major component. The center electrode 50 has a rod shape extending in the axial direction, and is disposed on the front end side in the axial hole 20 of the insulator 10. The front end of the center electrode 50 projects to the front end side with respect to the front end of the insulator 10. The rear end of the center electrode 50 is located in the front trunk portion 14.
The center electrode 50 includes a leg portion 51, a large-diameter portion 52, and a head portion 53 in this order from the front end side in the axial direction. The outside diameter of the large-diameter portion 52 is larger than the outside diameter of the leg portion 51 and the outside diameter of the head portion 53. The large-diameter portion 52 is a portion having an outside diameter that is the largest in the center electrode 50, and is retained at the rear facing surface 22A of the insulator 10. The large-diameter portion 52 has a columnar portion 54 having an outside diameter (the diameter of the outer peripheral surface) that is constant in a predetermined range in the axial direction, and a tapered portion 56 having an outside diameter that is gradually decreased toward the front end side. The outside diameter of the columnar portion 54 is the largest in the center electrode 50. The rear end of the columnar portion 54 is a rear end 55 of the large-diameter portion 52. The rear end 55 is located at the same position as the position of the front end of the head portion 53 in the axial direction. The tapered portion 56 is a portion that is in contact with and supported by the rear facing surface 22A, and is a portion continuous from the front end of the columnar portion 54 toward the front end side.
The metal terminal 60 is formed of an electrically conductive metal material (for example, low-carbon steel). The metal terminal 60 is a rod-shaped member extending in the axial direction, and is disposed on the rear end side in the axial hole 20 of the insulator 10. A rear end portion of the metal terminal 60 projects to the rear end side with respect to the insulator 10. A high voltage for generating a spark discharge is applied to the metal terminal 60 from a power supply member.
The resistor 61 is disposed in the axial hole 20, between the center electrode 50 and the metal terminal 60. The resistor 61 is formed of a composition containing, for example, an electrically conductive material, glass particles, and ceramic particles other than the glass particles.
In the axial hole 20, the gap between the resistor 61 and the center electrode 50 is filled with the front seal member 62 containing an electrically conductive material. The filling with the front seal member 62 is provided in the axial hole 20 on the rear end side with respect to the rear facing surface 22A. The front seal member 62 is in contact with the inner peripheral surface of the insulator 10, the center electrode 50, and the resistor 61. The front seal member 62 separates the center electrode 50 and the resistor 61 from each other. The front seal member 62 is a member that seals and fixes the insulator 10 and the center electrode 50.
In the axial hole 20, the gap between the resistor 61 and the metal terminal 60 is filled with the rear seal member 63 which is electrically conductive. The rear seal member 63 is in contact with the metal terminal 60 and the resistor 61 and separates the metal terminal 60 and the resistor 61 from each other. The rear seal member 63 is a member that seals and fixes the insulator 10 and the metal terminal 60. The front seal member 62 and the rear seal member 63 electrically and physically connect the center electrode 50 and the metal terminal 60 to each other via the resistor 61. The front seal member 62 and the rear seal member 63 are formed of an electrically conductive material, for example, a composition containing glass particles and metal particles.
The specific configurations of the insulator and other components are described below in detail.
In the insulator 10, the front trunk portion 14 has a feature configuration. The front trunk portion 14 is a portion disposed so as to continue from the rear end position of the step portion 13 to the front end position of the flange portion 15 in the axial direction. At least a portion of the front trunk portion 14 is disposed inside the screw portion 34 of the metal shell 30. The front trunk portion 14 includes a first portion 70 having an outer peripheral surface that constitutes a first structure, and a second portion 80 having an outer peripheral surface that constitutes a second structure.
The first portion 70 is a portion of the insulator 10 in a region AR from the rear end of the rear facing surface 22A to the front end of the diameter increased portion 36. The first portion 70 has a thickness that is the largest in the region AR, and is disposed at least on the outer periphery of the large-diameter portion 52. Specifically, the first portion 70 is disposed on the outer periphery of the whole range in the axial direction of the center electrode 50 in the region AR. In the axial direction, the rear end of the first portion 70 is located on the rear end side with respect to the rear end 55 of the large-diameter portion 52 and is located on the rear end side with respect to the rear end of the center electrode 50. The front end of the first portion 70 is located on the front end side with respect to the front end of the large-diameter portion 52 and is located on the front end side with respect to the rear end of the rear facing surface 22A. The first portion 70 is disposed at least in a region from the rear end of the rear facing surface 22A to the rear end of the front seal member 62.
A length M of the first portion 70 in the axial direction is larger than a length N from the rear end of the step portion 13 to the rear end of the front seal member 62 in the axial direction, and is larger than a length L from the rear end of the step portion 13 to the rear end of the center electrode 50 in the axial direction. The rear end of the front seal member 62 is located on the rear end side with respect to the rear end of the center electrode 50. The rear end of the first portion 70 is located on the rear end side with respect to the rear end of the front seal member 62. The front end of the first portion 70 is located on the front end side with respect to the front end of the front seal member 62.
The first portion 70 is disposed on the rear end side with respect to the packing 45. That is, the insulator 10 is retained at the metal shell 30 via the packing 45, on the front end side with respect to the first portion 70.
In the region AR, the inside diameter of the insulator 10 is constant in the axial direction. The bore of the insulator 10 is a cylindrical surface centered on the axial line X in the whole range of the region AR in the axial direction, and the inside diameter of the insulator 10 is constant in the whole range of the region AR. Thus, in the region AR, the inside diameter of the insulator 10 is the smallest in the first portion 70.
The second portion 80 is a portion of the insulator 10 disposed on the rear end side with respect to the first portion 70 in the region AR, and is a portion having an outside diameter B that is smaller than an outside diameter A of the first portion 70.
In the axial direction, the position of the rear end of the first portion 70 is the same as the position of the front end of the second portion 80, and the position of the front end of the first portion 70 is the same as the position of the rear end of the step portion 13 (the position of the rear end of the slanted surface 13A). In the axial direction, the position of the rear end of the second portion 80 is the same as the position of the front end of the flange portion 15 (the position of the front end of the slanted surface provided on the front end side of the flange portion 15), and the position of the front end of the second portion 80 is the same as the position of the rear end of the first portion 70.
The outside diameter A (the diameter of the outer peripheral surface) of the first portion 70 is larger than the outside diameter B (the diameter of the outer peripheral surface) of the second portion 80. The outer peripheral surface of the first portion 70 is a cylindrical surface centered on the axial line X. The outer peripheral surface of the second portion 80 is a cylindrical surface centered on the axial line X. The outside diameter A of the first portion 70 and the outside diameter B of the second portion 80 are larger than the outside diameter (the diameter of the outer peripheral surface) of the leg portion 12. The outside diameter A of the first portion 70 is constant from the rear end of the step portion 13 to the front end of the second portion 80 in the axial direction. At any position in the axial direction, a cut section of the first portion 70 cut in a direction orthogonal to the axial line X has a circular external shape centered on the axial line X with the predetermined diameter A (the same diameter). The outside diameter B of the second portion 80 is constant from the rear end of the first portion 70 to the front end of the flange portion 15 in the axial direction. At any position in the axial direction, a cut section of the second portion 80 cut in a direction orthogonal to the axial line X has a circular external shape centered on the axial line X with the predetermined diameter B (the same diameter).
In the spark plug 1, the first portion 70 is disposed on a side close to the packing 45 (a component that positions the insulator 10 while being supported by the metal shell 30), and the second portion 80 is disposed on a side farther from the packing 45 than the first portion 70. Moreover, a thickness X1 of the first portion 70 in the radial direction is larger than a thickness Y1 of the second portion 80 in the radial direction. The first portion 70 is disposed on the outer periphery of the large-diameter portion 52 and has a larger thickness than that of the second portion 80.
With such a configuration, an effect of suppressing spark penetration can be increased in the vicinity of the large-diameter portion 52 where a countermeasure for spark penetration is more required.
In addition, the side close to the packing 45 has a feature that “the insulator 10 is more stably held and the position thereof is hardly shifted relative to the metal shell 30”. Thus, disposing the first portion 70 on the side close to the packing 45 can use this feature effectively. That is, on the side close to the packing 45, although the first portion 70 having a relatively large outside diameter is disposed and hence the gap between the outer peripheral surface of the insulator 10 (the outer peripheral surface of the first portion 70) and the inner peripheral surface of the metal shell 30 is relatively small, the insulator 10 hardly comes into contact with the metal shell 30. Hence, on the side close to the packing 45, by using the structure in which the position of the insulator 10 is hardly shifted and the first portion 70 both together, prevention of contact and suppression of spark penetration can be both provided.
In contrast, on the side far from the packing 45, the second portion 80 having a relatively small outside diameter is disposed, and hence a larger gap is ensured between the outer peripheral surface of the insulator 10 (the outer peripheral surface of the second portion 80) and the inner peripheral surface of the metal shell 30. That is, on the side far from the packing 45, the allowance for the positional shift of the insulator 10 is larger, so that the insulator 10 is less likely to come into contact with the metal shell 30 even when the position of the insulator 10 is shifted to some extent. Thus, the effect of preventing the contact can be increased.
With such a configuration, when a vibration or the like is applied during use of the spark plug 1, a situation in which the insulator 10 comes into contact with the metal shell 30 is less likely to occur in the vicinity of either of the first portion 70 and the second portion 80.
In the spark plug 1, the first portion 70 is disposed at least on the outer periphery of the whole range in the axial direction of the center electrode 50 in the region AR. In the spark plug 1, the whole range in the axial direction of “a portion of the center electrode 50 disposed in the region AR” can be surrounded by the first portion 70. Thus, in the above-described portion where spark penetration possibly occurs, spark penetration can be further effectively suppressed, and voltage resistance performance can be further enhanced.
Specifically, the first portion 70 is disposed outside of edge portions 57A, 57B, 57C, and 57D to surround all the edge portions 57A, 57B, 57C, and 57D at which spark penetration is likely to start. Thus, spark penetration can be further effectively suppressed. The edge portion 57A is an outer peripheral edge at the rear end of the center electrode 50 (the rear end of the head portion 53). The edge portion 57B is an outer peripheral edge at the front end of the head portion 53. The edge portion 57C is an outer peripheral edge at the rear end of the large-diameter portion 52. The edge portion 57D is an outer peripheral edge at the front end of the columnar portion 54 of the large-diameter portion 52.
In the spark plug 1, since the inside diameter of the insulator 10 is the smallest in the first portion 70, the distance between the metal shell 30 and the center electrode 50 can be largely ensured while the thickness of the first portion 70 is largely obtained, thereby suppressing the electrostatic capacity in the vicinity of the first portion 70. As a result, wear of the center electrode 50 and the ground electrode 42 can be suppressed.
In the spark plug 1, the portion in the axial hole 20 on the rear end side with respect to the rear facing surface 22A is filled with the front seal member 62 containing an electrically conductive material. The front seal member 62 is in contact with the inner peripheral surface of the insulator 10, and the center electrode 50. The first portion 70 is disposed in a region from the rear end of the rear facing surface 22A to the rear end of the front seal member 62. Ina spark plug in which the gap between an insulator and a center electrode is filled with an electrically conductive front seal member, since the front seal member is electrically conductive, the front seal member transmits a spark from the center electrode, and the spark reaches the insulator. When the energy of the spark is high, the spark may penetrate through the insulator and a discharge may occur. However, in the spark plug 1, since the thickness of the insulator 10 is increased in the vicinity of the center electrode 50 and the front seal member 62, occurrence of spark penetration can be suppressed.
A spark plug 201 according to a second embodiment is described next mainly with reference to
The spark plug 201 according to the present embodiment illustrated in
The spark plug 201 illustrated in
In the spark plug 201 illustrated in
The spark plug 201 configured as described above also attains an advantageous effect similar to that of the spark plug 1 (
Furthermore, in the spark plug 201, the inside diameter of the insulator 210 in the region AR is the smallest in the first portion 270. Specifically, a portion of the first portion 270 having the inside diameter D that is smaller than the inside diameter C of a second portion 280 is provided in the region AR. Thus, the thickness of the first portion 270 can be further sufficiently ensured, and the electrostatic capacity in the vicinity of the first portion 270 can be further suppressed.
A spark plug 301 according to a third embodiment is described next mainly with reference to
The spark plug 301 according to the present embodiment illustrated in
The metal shell 330 of the spark plug 301 illustrated in
As illustrated in
The inner peripheral surface of the first inside-diameter portion 331A is a cylindrical surface having the constant inside diameter F centered on the axial line X on the rear end side with respect to the step portion 13. The inner peripheral surface of the second inside-diameter portion 331B is a cylindrical surface having the constant inside diameter E centered on the axial line X on the rear end side with respect to the first inside-diameter portion 331A. Either of the inside diameter F and the inside diameter E is larger than either of the outside diameter A and the outside diameter B. The inside diameter F is larger than the inside diameter E. It is desirable that the rear end of the first inside-diameter portion 331A is disposed at a position on the rear end side with respect to the rear end of the first portion 70 at a predetermined distance in the axial direction. Moreover, it is desirable that the front end of the first inside-diameter portion 331A is disposed at a position on the front end side with respect to the front end of the first portion 70 at a predetermined distance in the axial direction.
The spark plug 301 configured as described above also attains an advantageous effect similar to that of the spark plug 1 (
In the spark plug 301, the first inside-diameter portion 331A is “an inside-diameter portion having an inside diameter that is the largest in a portion of the metal shell 330 disposed in the region AR (
The resent invention is not limited to aspects and modifications of the embodiments of the specification, and can be implemented by various configurations within the scope not departing from the gist of the present invention. For example, the technical features in the embodiments, examples, and modifications corresponding to the technical features in the aspects described in the section of Summary of Invention can be exchanged or combined if needed to address part or the entirety of the above-described problems or to attain part or the entirety of the above-described advantageous effects. In particular, the various technical features according to the above-described embodiments or embodiments which will be described later can be combined in a desirable way within a range involving no contradiction. When the technical features are not described as being essential in the specification, the technical features can be omitted if needed. The modifications include, for example, the following modifications.
In the above-described embodiments, the front end or the rear end of the outer peripheral surface of the first portion, or the front end of the outer peripheral surface of the second portion is constituted as an angular corner portion (edge portion). However, such a corner portion may be chamfered to be round, for example, like a spark plug 401 illustrated in
In the above-described embodiments, the rear end of the first portion is located on the rear end side with respect to the rear end of the front seal member 62 (the front end of the resistor 61). However, it is sufficient that the first portion is disposed on the outer periphery of the large-diameter portion 52. For example, the rear end of the first portion may be located in the range of the head portion in the axial direction.
According to the second and third embodiments and so forth, the step is formed at the boundary between the inner peripheral surface of the first portion 270 and the inner peripheral surface of the second portion 80. However, like a spark plug 501 illustrated in
According to the third embodiment and so forth, the step is formed at the boundary between the inner peripheral surface of the first inside-diameter portion and the inner peripheral surface of the second inside-diameter portion of the metal shell. However, like a spark plug 601 illustrated in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-056440 | Mar 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/012264 | 3/19/2020 | WO | 00 |
