Spark plug

Abstract

To provide a spark plug capable of attaining prolongation of lifetime.SOLUTION: A spark plug 1 is used for an internal combustion engine which uses a hydrogen gas as a fuel. The spark plug 1 comprises a cylindrical insulator 2, a center electrode 3, a first conductive seal layer 41, and a resistor 5. The center electrode 3 is disposed while being inserted into a shaft hole 21 of the insulator 2. The first conductive seal layer 41 is disposed within the shaft hole 21 on a proximal end side Z2 of the center electrode 3. The resistor 5 is disposed within the shaft hole 21 on the proximal end side Z2 of the first conductive seal layer 41 and includes carbons. A length L1 from a proximal end of the center electrode 3 to a distal end of the resistor 5 in a plug axis direction Z is 2 mm or more.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a spark plug.

Background Art

[0002] A spark plug is used as an ignition means in an internal combustion engine such as a vehicle engine. The spark plug described in Patent Document 1 has a function of absorbing radio wave noise generated at the time of discharge spark in the axial hole of an insulator, and includes a resistor containing glass, zirconia, and carbon. And the spark plug described in Patent Document 1 tries to prevent an increase in the resistance value of the resistor due to oxidation and disappearance of carbon by setting the carbon content rate in the resistor and the mass ratio of zirconia to carbon to predetermined values, aiming for a longer service life.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, when a spark plug is installed in an internal combustion engine using hydrogen gas as fuel, even when the mass ratio of zirconia to carbon or the like is set to a predetermined value as in the spark plug described in Patent Document 1, there is a possibility that an increase in the resistance value of the resistor cannot be sufficiently prevented. That is, the fuel hydrogen gas becomes ions and moves to the resistor disposed in the axial hole of the insulator, and may act on the carbon contained in the resistor, thereby reducing the conduction path in the resistor. As a result, there is a possibility that the resistance value of the resistor increases. Therefore, it can be said that the spark plug described in Patent Document 1 has room for further improvement from the viewpoint of preventing an increase in the resistance value of the resistor and achieving a longer service life of the spark plug.

[0005] The present invention has been made in view of such problems, and aims to provide a spark plug that can achieve a longer service life.

Means for Solving the Problems

[0006] One aspect of the present invention is a spark plug (1) used in an internal combustion engine that uses hydrogen gas as fuel, a cylindrical insulator (2), a center electrode (3) inserted and disposed in the axial hole (21) of the insulator, a first conductive seal layer (41) disposed on the base end side (Z2) of the center electrode in the axial hole, and a resistor (5) containing carbon, which is disposed on the base end side of the first conductive seal layer in the axial hole, In the spark plug, the length (L1) from the base end of the center electrode to the tip of the resistor in the plug axis direction (Z) is 2 mm or more.

Advantages of the Invention

[0007] In the above spark plug, the length from the base end of the center electrode to the tip of the resistor in the plug axis direction is 2 mm or more. Therefore, even if the fuel hydrogen gas becomes ions and diffuses into the first conductive seal layer, the period until the hydrogen ions reach the resistor can be lengthened. As a result, an increase in the resistance value of the resistor can be prevented, and the service life of the spark plug can be extended.

[0008] As described above, according to the above aspect, a spark plug that can achieve a longer service life can be provided. Note that the reference numerals in parentheses described in the claims and the means for solving the problems indicate the correspondence with the specific means described in the embodiments described later, and do not limit the technical scope of the present invention.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Mode for Carrying Out the Invention

[0010] (Embodiment 1) An embodiment of the spark plug will be described with reference to FIGS. 1 to 3. The spark plug 1 of this embodiment is used in an internal combustion engine that uses hydrogen gas as fuel. As shown in FIGS. 1 and 2, the spark plug 1 has a cylindrical insulator 2, a center electrode 3, a first conductive seal layer 41, and a resistor 5. The center electrode 3 is inserted and disposed in the axial hole 21 of the insulator 2. The first conductive seal layer 41 is disposed on the base end side Z2 of the center electrode 3 within the axial hole 21. The resistor 5 is disposed on the base end side Z2 of the first conductive seal layer 41 within the axial hole 21 and contains carbon. As shown in FIG. 2, the length L1 from the base end of the center electrode 3 to the tip of the resistor 5 in the plug axis direction Z is 2 mm or more. Further, the length L1 is preferably 4 mm or more.

[0011] The spark plug 1 of this embodiment can be used as an ignition means in an internal combustion engine such as an automobile that uses hydrogen gas as fuel. As shown in FIG. 1, the spark plug 1 includes a cylindrical housing 7 that holds an insulator 2 inside and has a threaded portion 71 on a part of the outer peripheral side. The spark plug 1 is attached to the internal combustion engine by screwing the threaded portion 71 of the housing 7 into the female threaded portion of the plug hole of the cylinder head (not shown). One end of the spark plug 1 in the axial direction Z is disposed in the combustion chamber (not shown) of the internal combustion engine. In the axial direction Z of the spark plug 1, the side exposed to the combustion chamber is referred to as the tip side Z1, and the opposite side is referred to as the base end side Z2. Also, the axial direction Z of the spark plug 1 is also appropriately referred to as the plug axial direction Z. Note that the plug central axis C means the central axis of the spark plug 1. Also, the plug radial direction means the radial direction of a circle centered on the plug central axis C on a plane orthogonal to the plug central axis C. Further, in this embodiment, the plug central axis C is also the central axis of the center electrode 3 and the central axis of the insulator 2.

[0012] A ground electrode 11 that forms a discharge gap G1 with the center electrode 3 is joined to the tip of the housing 7. The center electrode 3 is held on the inner peripheral side of the insulator 2 and exposed from the insulator 2 to the tip side Z1. A center chip 34 is joined to the tip of the center electrode 3, and a ground chip 111 is joined to the ground electrode 11 at a position facing the center chip 34 in the plug axial direction Z. The discharge gap G1 is formed by the center chip 34 and the ground chip 111 facing each other in the plug axial direction Z. The center chip 34 and the ground chip 111 can be made of, for example, a noble metal such as iridium or platinum, or an alloy mainly composed of these.

[0013] Also, a leg portion 22 that tapers toward the tip side Z1 is formed at the tip of the insulator 2. The tip of the center electrode 3 projects from the leg portion 22 to the tip side Z1. The insulator 2 can be made of, for example, insulating ceramics such as alumina.

[0014] The shaft hole 21 of the insulator 2 has a small-diameter hole 211 that opens to the tip side Z1, and a large-diameter hole 212 that has a larger diameter than the small-diameter hole 211 and opens to the base end side Z2. In this embodiment, both the small-diameter hole 211 and the large-diameter hole 212 of the shaft hole 21 are cylindrical spaces. Further, as shown in FIGS. 1 and 2, the shaft hole 21 of the insulator 2 has a tapered locking step portion 213 for locking the center electrode 3 between the small-diameter hole 211 and the large-diameter hole 212 in the plug axis direction Z. The locking step portion 213 is formed so as to increase in diameter from the base end of the small-diameter hole 211 toward the tip of the large-diameter hole 212. In FIG. 2, the illustration of the housing is omitted.

[0015] The center electrode 3 has a cylindrical electrode main body portion 31, a head portion 32, and a center tapered portion 33. The electrode main body portion 31 is inserted into the small-diameter hole 211 of the insulator 2. The head portion 32 has an outer diameter larger than that of the electrode main body portion 31 and is formed on the base end side Z2 with respect to the electrode main body portion 31. The outer diameter of the head portion 32 is larger than the outer diameter of the electrode main body portion 31 throughout the plug axis direction Z. Further, the outer diameter of the head portion 32 is larger than the inner diameter of the small-diameter hole 211. The center tapered portion 33 connects the electrode main body portion 31 and the head portion 32 to each other and is formed so as to increase in diameter toward the base end side Z2.

[0016] The center tapered portion 33 is supported by the locking step portion 213 of the insulator 2 from the tip side Z1. Further, in this embodiment, the head portion 32 of the center electrode 3 is disposed inside the large-diameter hole 212, and the resistor 5 and the first conductive seal layer 41 are also disposed inside the large-diameter hole 212.

[0017] The resistor 5 is a member containing a conductive material and is adjusted to a desired resistance value. The resistor 5 electrically connects the central electrode 3 and a stem 6 (to be described later) and has a function of absorbing radio frequency noise. The resistor 5 can be, for example, an aggregate in which a conductive material containing carbon is dispersed in a base material including a glass material such as borosilicate glass and an aggregate. Specifically, the resistor 5 can be obtained by heat-treating a mixed powder material containing a powder of a conductive material, a glass powder, and an aggregate powder. The mixed powder material before this heat treatment corresponds to a resistor material 50 (to be described later). For example, a ceramic powder such as zirconia powder is used as the aggregate powder. The powder of the conductive material can be added, for example, as a carbon-glass mixed powder mainly composed of glass mixed with carbon powder.

[0018] In this embodiment, the outer diameter D3 of the resistor 5 shown in FIG. 2 is the same size as the outer diameter of the first conductive seal layer 41 and the outer diameter of a second conductive seal layer 42 (to be described later). In this embodiment, the outer diameter D3 of the resistor 5 is 1.8 to 3.2 mm.

[0019] Further, the spark plug 1 has a second conductive seal layer 42 disposed on the proximal end side Z2 of the resistor 5 in the axial hole 21, and a stem 6 that is disposed on the proximal end side Z2 of the second conductive seal layer 42 and closes the proximal end portion of the axial hole 21. The second conductive seal layer 42 is disposed inside the large-diameter hole 212.

[0020] The first conductive seal layer 41 and the second conductive seal layer 42 have conductivity and seal the axial hole 21. The first conductive seal layer 41 electrically connects the resistor 5 and the central electrode 3. The second conductive seal layer 42 electrically connects the stem 6 and the resistor 5.

[0021] The first conductive seal layer 41 and the second conductive seal layer 42 can be made of, for example, conductive bonding glass. The bonding glass can be made of, for example, copper glass formed by mixing copper powder into glass. In this embodiment, the first conductive seal layer 41 and the second conductive seal layer 42 are obtained by heat-treating copper glass powder. The copper glass powder before this heat treatment corresponds to the first conductive glass material 410 and the second conductive glass material 420 described later. Also, the first conductive glass material 410 and the second conductive glass material 420 can contain oxides such as Na2O (that is, sodium oxide) in order to control physical property values such as the glass transition point.

[0022] Also, as shown in FIG. 2, a gap G2 is formed over the entire circumference between the outer peripheral surface of the head 32 and the inner peripheral surface of the shaft hole 21. A part of the first conductive seal layer 41 is filled in the gap G2.

[0023] Also, as shown in FIG. 1, the stem 6 includes a large-diameter terminal portion 62 and a shaft portion 61 having a smaller diameter than this. In the stem 6, the shaft portion 61 is inserted into the large-diameter hole 212 of the shaft hole 21, and the terminal portion 62 protrudes toward the base end side Z2 of the insulator 2. The spark plug 1 is electrically connected to an ignition coil (not shown) at the terminal portion 62.

[0024] Next, a method for manufacturing the spark plug 1 of this embodiment will be described. First, as shown in FIG. 3(a), the center electrode 3 is inserted and arranged in the shaft hole 21 of the insulator 2. Next, as shown in FIG. 3(b), the first conductive glass material 410 is arranged on the base end side Z2 of the center electrode 3 in the shaft hole 21. Then, as shown by the arrow P in FIG. 3(b), the first conductive glass material 410 arranged in the shaft hole 21 is pressed toward the tip side Z1 by a rod-shaped pressing jig 19. Thereby, the first conductive glass material 410 is compressed at the base end side Z2 of the center electrode 3.

[0025] Next, as shown in FIG. 3(c), the resistor material 50 is disposed on the proximal end side Z2 of the first conductive glass material 410 within the shaft hole 21. After the resistor material 50 is disposed within the shaft hole 21, as indicated by the arrow P in FIG. 3(c), the resistor material 50 is pressed toward the distal end side Z1 by the pressing jig 19.

[0026] Next, as shown in FIG. 3(d), the second conductive glass material 420 is disposed on the proximal end side Z2 of the resistor material 50 within the shaft hole 21. Then, as indicated by the arrow P in FIG. 3(d), the second conductive glass material 420 disposed within the shaft hole 21 is pressed toward the distal end side Z1 by the pressing jig 19. As a result, the second conductive glass material 420 is compressed at the proximal end side Z2 of the resistor material 50. Further, due to the pressing at this time, not only is the second conductive glass material 420 compressed, but also the resistor material 50 and the first conductive glass material 410 disposed on its distal end side Z1 are compressed.

[0027] Next, as shown in FIG. 3(e), the stem 6 is inserted and disposed on the proximal end side Z2 of the second conductive glass material 420 within the shaft hole 21. At this stage, a part of the shaft portion 61 of the stem 6 is exposed at the proximal end side Z2 of the shaft hole 21.

[0028] Next, while heating and softening the first conductive glass material 410, the resistor material 50, and the second conductive glass material 420, the stem 6 is pressed toward the distal end side Z1 in the plug axis direction Z as indicated by the arrow P in FIG. 3(e).

[0029] That is, the first conductive glass material 410, the resistor material 50, and the second conductive glass material 420 are heated to about 800 to 900 °C, for example. As a result, at least a part of the glass components of the first conductive glass material 410, the resistor material 50, and the second conductive glass material 420 are in a softened state. In this way, by heating, the first conductive glass material 410, the resistor material 50, and the second conductive glass material 420 melt and soften, so that the voids existing between the powder particles are gradually filled. Also, as the heating progresses, the stem 6 is pushed into the tip side Z1, so that the filling region of the first conductive glass material 410, the resistor material 50, and the second conductive glass material 420 in the shaft hole 21 is compressed in the plug axis direction Z. As a result, as shown in Fig. 3(f), the entire shaft portion 61 of the stem 6 is inserted into the shaft hole 21, and the tip of the terminal portion 62 abuts against the base end of the insulator 2.

[0030] Thereafter, the first conductive glass material 410, the resistor material 50, and the second conductive glass material 420 are cooled and solidified. Next, by inserting and fixing the insulator 2 inside the housing 7, the spark plug 1 shown in Fig. 1 is obtained.

[0031] Next, the operation and effects of this embodiment will be described. In the spark plug 1, the length L1 (see Fig. 2) is 2 mm or more. Therefore, even if the hydrogen gas of the fuel becomes ions and diffuses into the first conductive seal layer 41, the period until the hydrogen ions reach the resistor 5 can be lengthened. As a result, an increase in the resistance value of the resistor 5 can be prevented, and the long life of the spark plug 1 can be achieved. Also, the length L1 is preferably 4 mm or more. In this case, the period until the hydrogen ions reach the resistor 5 can be further lengthened. Therefore, an increase in the resistance value of the resistor 5 can be further prevented.

[0032] As a path for the hydrogen gas of the fuel to move to the resistor, the following paths can be considered. First, hydrogen gas penetrates into the gap between the inner peripheral surface of the small-diameter hole of the insulator and the outer peripheral surface of the electrode body portion of the center electrode. Next, the hydrogen gas enters and diffuses into the first conductive seal layer filled between the inner peripheral surface of the large-diameter hole of the insulator and the outer peripheral surface of the head of the center electrode in the state of H + ions. Here, SiO2 (that is, silicon dioxide) contained in the first conductive seal layer is considered to have a network structure based on SiO4 tetrahedrons. And the first conductive seal layer is considered to have an amplified irregularity in its network structure and a portion with a large interatomic distance due to an oxide such as Na2O added to control physical property values such as the glass transition point. Therefore, the first conductive seal layer is considered to have a structure in which other atoms etc. can easily move at the portion with a large interatomic distance. Therefore, the H + ions that have penetrated into the first conductive seal layer are considered to diffuse within the first conductive seal layer and move to the resistor. The H + ions that have reached the resistor are considered to increase the resistance value of the resistor by breaking the connection of the carbon powder added as a conductive medium and reducing the cross-sectional area of the conductive path by carbon. In this way, in a spark plug used in an internal combustion engine that uses hydrogen gas with a very small molecular size as fuel compared to gasoline and natural gas generally used as fuel for internal combustion engines, there is a possibility that the resistance value of the resistor as described above will increase. Therefore, the spark plug 1 of the present embodiment has a length L1 of 2 mm or more. That is, in the present embodiment, the length L1 that is not considered as a means for suppressing an increase in resistance value in a spark plug used in a gasoline engine or a natural gas engine is considered as a means for suppressing an increase in resistance value. Thereby, even if hydrogen gas of the fuel penetrates into the first conductive seal layer 41 as H + ions, the period until the H + ions reach the resistor 5 through the first conductive seal layer 41 can be lengthened. That is, the longer the length L1 is, the H +The period until the ions reach the resistor 5 can be lengthened. Therefore, an increase in the resistance value of the resistor 5 can be prevented, and discharge can be generated in the discharge gap G1 for a relatively long period. As a result, the long life of the spark plug 1 can be achieved.

[0033] Also, even if a slight gap is formed at the interface between the center electrode 3 made of metal and the first conductive seal layer 41 made mainly of glass due to the difference in the linear expansion coefficients of the center electrode 3 and the first conductive seal layer 41, H + The period until the ions reach the resistor 5 can be lengthened. That is, if the hydrogen gas of the fuel is, H + Assume a case where, as ions, not only do they enter from the first conductive seal layer 41 filled in the gap G2 (see FIG. 2), but also they move through a slight gap formed at the interface between the center electrode 3 and the first conductive seal layer 41 in the state of hydrogen gas. In this case, the hydrogen gas is, H + As ions, when compared with when they enter from the first conductive seal layer 41 filled in the gap G2, they are likely to move immediately to the position of the tip of the center electrode 3 in the plug axis direction Z. Even in such a case, since the length L1 is sufficiently ensured, the period until the hydrogen ions reach the resistor 5 through the first conductive seal layer 41 can be made sufficiently long. As a result, an increase in the resistance value of the resistor 5 can be prevented.

[0034] The spark plug 1 of this embodiment will be described while comparing it with the spark plug 9 of the comparative embodiment shown in FIGS. 4 and 5. In the spark plug 9 of the comparative embodiment, the head 32 of the center electrode 3 has a head main body portion 38 having an outer diameter larger than that of the electrode main body portion 31, and a constriction portion 39 protruding from the head main body portion 38 toward the base end side Z2. The constriction portion 39 has a width smaller than that of the head main body portion 38 in the plug diameter direction, and has a shape branched into three branches when viewed from the plug axis direction Z as shown in FIG. 5. Further, as shown in FIG. 4, in the spark plug 9 of the comparative embodiment, the length L91 from the base end of the head main body portion 38 to the tip of the resistor 5 in the plug axis direction Z is 2 mm or more. Further, in the spark plug 9 of the comparative embodiment, the length L92 from the base end of the center electrode 3 to the tip of the resistor 5 in the plug axis direction Z is about 1 mm, which is smaller than 2 mm.

[0035] As described above, although the length L91 of the spark plug 9 is 2 mm or more, the length L92 is about 1 mm, which is smaller than 2 mm. Here, assume a case where a gap is formed at the interface between the center electrode 3 and the first conductive seal layer 41 due to the difference in the linear expansion coefficients of the center electrode 3 and the first conductive seal layer 41. In this case, the hydrogen gas of the fuel moves to the position of the base end of the constriction portion 39, and from the position of the base end of the constriction portion 39, there is a risk of invading the first conductive seal layer 41 as H + ions. Then, compared with the spark plug 1 of this embodiment, the spark plug 9 of the comparative embodiment has a shorter distance from the base end of the center electrode 3 to the resistor 5, so H +The period until the ions reach the resistor 5 tends to be short. As a result, there is a risk that sufficient extension of the service life cannot be achieved. On the other hand, as described above, the spark plug 1 of the present embodiment has a length L1 of 2 mm or more. Therefore, a sufficient distance can be ensured from the base end of the center electrode 3 to the resistor 5. As a result, an increase in the resistance value of the resistor 5 can be sufficiently prevented, and the service life of the spark plug 1 can be extended. Further, the spark plug 1 of the present embodiment does not have a throttle portion as in the comparative embodiment. Therefore, even when the length L1 is 2 mm or more, for the conductor including the center electrode 3 disposed on the tip side Z1 with respect to the tip of the resistor 5, the volume can be easily reduced and the capacitance can be easily reduced. Therefore, when a spark discharge is generated in the discharge gap G1, the current amount of the capacitive discharge, which is the first formed discharge, can be reduced. Therefore, it is possible to reduce the consumption of the center chip 34 and the ground chip 111 due to the discharge. As a result, the service life of the spark plug 1 can be further extended.

[0036] As described above, according to the present embodiment, it is possible to provide the spark plug 1 capable of extending the service life.

[0037] (Experimental Example) In this example, as shown in the graph of FIG. 6, while the basic structure was the same as that of the first embodiment, a durability test was conducted to obtain the relationship between the length L1 and the resistance value change rate using a plurality of spark plugs having different values of the length L1. The resistance value change rate is the change rate from the initial resistance value in the resistance value of the resistor. In this example, durability tests were conducted using samples with length L1 values of 1.0 mm, 1.5 mm, 2.0 mm, 4.0 mm, and 6.0 mm, respectively. Also, in this example, four samples each having a different length L1 were used, and the average value of the four samples was plotted on the graph of FIG. 6. Further, the graph of FIG. 6 shows an approximate curve in the plot of the experimental results.

[0038] As the specifications of the spark plug used in this example, the length L2 (see Fig. 2) from the tip of the resistor 5 to the tip of the second conductive seal layer 42 in the plug axis direction Z is set to 6 mm, and the length L3 (see Fig. 2) from the tip of the second conductive seal layer 42 to the tip of the stem 6 in the plug axis direction Z is set to 4.2 mm. Also, the outer diameter D3 of the resistor 5 (see Fig. 2) is 2 mm, the outer diameter D2 of the electrode body portion 31 disposed inside the small-diameter hole 211 (see Fig. 1) is 1.2 mm, the length L4 of the leg portion 22 of the insulator 2 in the plug axis direction Z (see Fig. 1) is 5 mm, the length L5 from the tip of the housing 7 to the tip of the center electrode 3 in the plug axis direction Z (see Fig. 1) is 2.5 mm, the length L6 of the discharge gap G1 in the plug axis direction Z (see Fig. 1) is 0.5 mm, and the nominal diameter of the screw portion 71 of the housing 7 is M12. Further, the initial resistance value of the resistor is set to 5.0 kΩ, and the discharge energy by an ignition coil (not shown) is set to 60 mJ.

[0039] Also, in this example, a discharge bench (not shown), which is equipment for performing a durability test of the spark plug, was used. The discharge bench is provided with a plug hole having a female screw. Then, by screwing the screw portion of the housing into this plug hole, each spark plug was attached to the discharge bench, and a durability test was performed. Also, the ambient temperature around the tip of the screwed portion between the screw portion of the housing and the plug hole was maintained at 300 °C, and the pressure due to hydrogen gas applied to the tip of this screwed portion and the tip of the spark plug was set to 13 MPa. The ambient temperature around the tip of the screwed portion is a temperature corresponding to the actually measured operating temperature in the internal combustion engine in which the spark plug is installed. Also, regarding the experimental conditions of the number of discharges of the spark plug, referring to JIS B8031, 13 million discharges, which is the number of discharges corresponding to a vehicle driving distance of 120,000 km, were continuously applied. Also, the discharge voltage was set to 20 ± 5 kV. Also, in this example, as shown in Fig. 6, in any of the samples, as the number of ignition times increased, the resistance value of the resistor increased.

[0040] As shown in the graph of FIG. 6, when comparing the results of each sample at the position of the same number of ignition times, it can be seen that the larger the value of the length L1, the lower the resistance change rate of the resistor. In particular, in the case of samples with a length L1 of 2.0 mm or more, it can be seen that the resistance change rate of the resistor is significantly lower compared to samples with a length L1 of 1.5 mm or less. That is, it was confirmed that by setting the value of the length L1 to 2 mm or more, the effect of extending the life of the spark plug can be obtained with a significant difference. From this, it can be said that the spark plug of Embodiment 1 with a length L1 of 2.0 mm or more can prevent the increase in the resistance value of the resistor and achieve a longer life. Further, samples with a length L1 of 4.0 mm or more have a lower resistance change rate compared to samples with a length L1 of 2 mm, and furthermore, even after performing 13 million discharges corresponding to a vehicle driving distance of 120,000 km, the resistance change rate is within 30%. From this, it can be said that when the length L1 is 4.0 mm or more, the increase in the resistance value of the resistor can be further prevented. Also, from the results shown in the graph of FIG. 6, it can be said that when the length L1 is 6.0 mm or more, the increase in the resistance value of the resistor can be further prevented.

[0041] (Embodiment 2) In this embodiment, as shown in FIGS. 7 and 8, the shape of the first conductive seal layer 41 is changed with respect to Embodiment 1. In FIGS. 7 and 8, the illustration of the housing is omitted.

[0042] In this embodiment, the outer diameter D3 of the resistor 5 shown in FIG. 8 is 1.8 to 3.2 mm. Also, as shown in FIGS. 7 and 8, the first conductive seal layer 41 has a small diameter portion 411, a large diameter portion 412, and a seal layer tapered portion 413. The large diameter portion 412 is provided on the base end side Z2 rather than the small diameter portion 411 and has a larger outer diameter than the small diameter portion 411. The seal layer tapered portion 413 connects the small diameter portion 411 and the large diameter portion 412 and expands in diameter toward the base end side Z2. The outer diameter D11 of the large diameter portion 412 and the outer diameter D3 of the resistor 5 are of the same size. Also, the outer diameter D3 and the outer diameter D4 of the second conductive seal layer 42 are of the same size.

[0043] As shown in FIG. 7, the length L11 from the tip of the large-diameter portion 412 to the tip of the resistor 5 in the plug axis direction Z is longer than the length L10 from the base end of the center electrode 3 to the base end of the small-diameter portion 411 in the plug axis direction Z. That is, the length from the boundary between the large-diameter portion 412 and the seal layer taper portion 413 to the tip of the resistor 5 in the plug axis direction Z is longer than the length from the base end of the center electrode 3 to the boundary between the small-diameter portion 411 and the seal layer taper portion 413 in the plug axis direction Z.

[0044] Also, the outer diameter D10 of the small-diameter portion 411 shown in FIG. 8 is smaller than the outer diameter D11. Further, the outer diameter D12 of the electrode main body portion 31 shown in FIG. 7 is smaller than the outer diameter D10.

[0045] The shaft hole 21 has a base-end side step portion 215 that expands in diameter toward the base-end side Z2 on the base-end side Z2 of the center electrode 3. Also, the shaft hole 21 has a middle-diameter hole 214 between the small-diameter hole 211 and the large-diameter hole 212, the inner diameter of which is larger than that of the small-diameter hole 211 and smaller than that of the large-diameter hole 212. A locking step portion 213 is formed between the small-diameter hole 211 and the middle-diameter hole 214, and a base-end side step portion 215 is formed between the middle-diameter hole 214 and the large-diameter hole 212. The outer peripheral surface of the small-diameter portion 411 and the inner peripheral surface of the middle-diameter hole 214 are in contact with each other, and the outer peripheral surface of the seal layer taper portion 413 and the inner peripheral surface of the base-end side step portion 215 are in contact with each other. Also, the outer peripheral surface of the large-diameter portion 412 and the inner peripheral surface of the large-diameter hole 212 are in contact with each other. Further, the head 32 of the center electrode 3 is disposed on the tip side Z1 of the large-diameter hole 212 and is disposed inside the middle-diameter hole 214. The rest is the same as in Embodiment 1. Among the reference numerals used in Embodiment 2 and later, those the same as the reference numerals used in the previous embodiments represent the same components and the like as those in the previous embodiments unless otherwise specified.

[0046] The outer diameter D3 of the resistor 5 is 1.8 to 3.2 mm. The first conductive seal layer 41 has a small-diameter portion 411, a large-diameter portion 412, and a seal layer taper portion 413. Also, the outer diameter D11 of the large-diameter portion 412 and the outer diameter D3 of the resistor 5 are of the same size. Therefore, H +The period until the ions reach the resistor 5 can be further lengthened. As a result, an increase in the resistance value of the resistor 5 can be prevented, and the long life of the spark plug 1 can be further achieved. That is, since the first conductive seal layer 41 has the small-diameter portion 411, it is easy to reduce the gap between the outer peripheral surface of the center electrode 3 and the inner peripheral surface of the insulator 2. Specifically, in particular, since it is easy to reduce the cross-sectional area orthogonal to the plug axis direction Z of the gap G2 (see FIG. 7), the amount of hydrogen gas invading the first conductive seal layer 41 can be reduced. Further, by having the large-diameter portion 412, even if the fuel hydrogen gas enters the first conductive seal layer 41 as H + ions, even if the fuel hydrogen gas enters the first conductive seal layer 41 as H + ions, the ions are likely to diffuse so that the concentration becomes low in the large-diameter portion 412, and it is easy to reduce the H + ion concentration in the large-diameter portion 412. That is, since the outer diameter of the large-diameter portion 412 is larger than that of the small-diameter portion 411, the volume is likely to be large. Therefore, due to the diffusion of H + ions in the large-diameter portion 412, the concentration of H + ions in the large-diameter portion 412 is likely to become low. Therefore, it can be expected that the period until H + ions reach the resistor 5 becomes long, and it is easy to suppress the amount of H + ions invading the resistor 5. Therefore, an increase in the resistance value of the resistor 5 can be further prevented. Further, since it has the seal layer tapered portion 413, damage to the insulator 2 can be sufficiently suppressed during the manufacture of the spark plug 1. That is, the shaft hole 21 has a base-end side stepped portion 215 having a tapered shape that contacts the seal layer tapered portion 413 and expands in diameter toward the base-end side Z2. Therefore, compared with the case where the surface connecting the inner peripheral surface of the medium-diameter hole and the inner peripheral surface of the large-diameter hole in the shaft hole is formed to be orthogonal to the plug axis direction, the load applied to the insulator 2 during manufacture can be suppressed. Specifically, during manufacture, after filling the shaft hole 21 with the first conductive glass material 410, the load applied to the insulator 2 can be sufficiently suppressed when the first conductive glass material 410 is compressed by the pressurizing jig 19 or the like. As a result, damage to the insulator 2 can be sufficiently suppressed.

[0047] Also, as described above, the outer diameter D11 and the outer diameter D3 are of the same size. Therefore, it is easy to increase the outer diameter D3. Therefore, it is easy to increase the amount of carbon contained in the resistor 5. As a result, it is even easier to further suppress the increase in the resistance value of the resistor 5.

[0048] The outer diameter D12 is smaller than the outer diameter D10. Therefore, as shown in FIG. 7, even if a slight gap G3 is formed between the outer peripheral surface of the electrode main body portion 31 and the inner peripheral surface of the small-diameter hole 211 of the insulator 2, it is easy to reduce the cross-sectional area orthogonal to the plug axis direction Z of the gap G3. As a result, the amount of hydrogen gas of the fuel invading the first conductive seal layer 41 as H + ions can be reduced.

[0049] The length L11 is longer than the length L10. Therefore, the volume of the large-diameter portion 412 is more likely to become larger. Therefore, H + ions are more likely to diffuse so that the concentration becomes lower in the large-diameter portion 412, and the H + ion concentration in the large-diameter portion 412 is more likely to be further reduced. Therefore, H + it can be further expected that the period until H ions invade the resistor 5 becomes longer, and the amount of H + ions invading the resistor 5 is more likely to be suppressed. As a result, an increase in the resistance value of the resistor 5 can be further prevented. In addition, it has the same operational effects as those of the first embodiment.

[0050] The present invention is not limited to the above-described embodiments, and can be applied to various embodiments without departing from the gist thereof.

Explanation of Reference Numerals

[0051] 1... Spark plug, 2... Insulator, 3... Central electrode, 5... Resistor, 21... Axial hole, 41... First conductive seal layer, Z... Plug axis direction, Z2... Base end side

Claims

1. A spark plug (1) used in an internal combustion engine that uses hydrogen gas as fuel, comprising: a cylindrical insulator (2); a center electrode (3) inserted and disposed in the axial hole (21) of the insulator; a first conductive seal layer (41) disposed on the proximal end side (Z2) of the center electrode in the axial hole; a resistor (5) containing carbon, disposed on the proximal end side of the first conductive seal layer in the axial hole; and a spark plug, wherein a length (L1) from the proximal end of the center electrode to the distal end of the resistor in the plug axial direction (Z) is 2 mm or more.

2. The spark plug according to claim 1, wherein a length from the proximal end of the center electrode to the distal end of the resistor in the plug axial direction is 4 mm or more.

3. an outer diameter (D3) of the resistor is 1.8 to 3.2 mm; the first conductive seal layer has a small-diameter portion (411), a large-diameter portion (412) provided on the proximal end side of the small-diameter portion and having an outer diameter larger than that of the small-diameter portion, and a seal layer taper portion (413) connecting the small-diameter portion and the large-diameter portion and having a diameter increasing toward the proximal end side; and an outer diameter (D11) of the large-diameter portion is equal to the outer diameter of the resistor; the spark plug according to claim 1 or 2.

4. The spark plug according to claim 3, wherein a length (L11) from the distal end of the large-diameter portion to the distal end of the resistor in the plug axial direction is longer than a length (L10) from the proximal end of the center electrode to the proximal end of the small-diameter portion in the plug axial direction.

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