Spark plug

Abstract

To provide a spark plug having excellent load life performance.SOLUTION: A spark plug 1 includes a resistor 5 between a center electrode 3 and a terminal fitting 6. The resistor 5 includes phase-separated borosilicate glass and a conductive material. The proportion of the phase separation in the borosilicate glass is 10% or less. The borosilicate glass preferably contains Ca and / or Ba. The ratio of the phase separation in the borosilicate glass is preferably calculated from an area ratio of the binarized image by extracting the binarized image of Ca or Ba detached from the borosilicate glass from the element map image of Ca or Ba of the borosilicate glass by the electron probe microanalyzer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Spark plugs are used as ignition means in internal combustion engines such as automobile engines. Spark plugs have a resistor between a center electrode and a metal terminal.

[0003] For example, Patent Document 1 discloses a spark plug having a resistor between a center electrode and a terminal metal fitting, the resistor containing glass, ceramic powder, conductive material, and metal powder. According to Patent Document 1, the reducing action of the metal powder suppresses oxidation of conductive material such as carbon, thereby improving the load life performance of the spark plug. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5087136 Summary of the Invention [Problem to be solved by the invention]

[0005] The reducing effect of the metal powder is lost when it is oxidized. In other words, once the metal powder is oxidized, the oxidation of conductive materials such as carbon is inevitable. As a result, the electrical resistance of the resistor increases, causing spark plug ignition failure.

[0006] In recent years, high-efficiency engine systems that comply with environmental regulations have inevitably increased the voltage required of spark plugs, which in turn increases the load on resistors. As a result, the time until the resistor's electrical resistance rises and misfires occur (i.e., its load life) becomes increasingly shorter.

[0007] The present invention has been made in view of the above-mentioned problems, and aims to provide a spark plug having excellent load life performance. [Means for solving the problem]

[0008] One aspect of the present invention is a spark plug (1) having a resistor (5) between a center electrode (3) and a terminal fitting (6), The resistor includes a phase-separated borosilicate glass (50, 51) and a conductive material (53), The spark plug is characterized in that the borosilicate glass has a phase separation rate of 10% or less. [Effects of the Invention]

[0009] In the spark plug, the resistor contains phase-separated borosilicate glass, and the phase separation ratio is 10% or less. Therefore, even if the load voltage applied to the resistor increases, the electrical resistance value of the resistor is unlikely to increase, and the spark plug is unlikely to experience ignition failure. In other words, the spark plug has an excellent load life against high voltages.

[0010] As described above, according to the above aspect, a spark plug having excellent load life performance can be provided. In addition, the symbols in parentheses in the claims and the means for solving the problems indicate the correspondence with the specific means described in the embodiments described below, and do not limit the technical scope of the present invention. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a vertical cross-sectional view showing the overall structure of a spark plug according to a first embodiment. [Figure 2] FIG. 2 is a scanning electron microscope image of a cross section of the resistor in the first embodiment. [Figure 3] FIG. 3 is a schematic cross-sectional view of the resistor in the first embodiment. [Figure 4] FIG. 4 is an explanatory diagram showing the observation position of the resistor with the EPMA in Experimental Example 1. [Figure 5] Figure 5(a) is an SEM image of borosilicate glass with a phase separation rate of 20.1% in Experimental Example 1, Figure 5(b) is a Ca map of the borosilicate glass with a phase separation rate of 20.1% in Experimental Example 1, taken by EPMA, and Figure 5(c) is a binarized image of the Ca map in (b). [Figure 6] Figure 6(a) is an SEM image of borosilicate glass with a phase separation rate of 3.47% in Experimental Example 1, Figure 6(b) is a Ca map of the borosilicate glass with a phase separation rate of 3.47% in Experimental Example 1, taken by EPMA, and Figure 6(c) is a binarized image of the Ca map in (b). [Figure 7] FIG. 7 is a diagram showing the relationship between the phase separation rate and the load life time of each test specimen in Experimental Example 1. [Figure 8] FIG. 8 is a diagram showing the relationship between the elapsed time in the loaded life test in Experimental Example 1 and the rate of change in resistance value. DETAILED DESCRIPTION OF THE INVENTION

[0012] [Embodiment 1] An embodiment of a spark plug will be described with reference to Figures 1 to 3. As illustrated in Figure 1, a spark plug 1 of this embodiment has a resistor 5 between a center electrode 3 and a terminal fitting 6. This will be described in detail below.

[0013] In the spark plug 1, as illustrated in Figures 2 and 3, the resistor 5 contains borosilicate glass 50, 51. Figures 2 and 3 show an example in which the borosilicate glass 50, 51 is composed of glass particles 51 and portions 50 in which the glass particles 51 have melted and solidified. The borosilicate glass composed of the partially solidified portions 50 can serve as a binder.

[0014] The borosilicate glass 50, 51 preferably contains Ca and / or Ba, which has the effect of lowering the melting point of the borosilicate glass of the resistor 5 and improving the bonding strength.

[0015] The resistor 5 contains phase-separated borosilicate glasses 50, 51. Phase separation is a phenomenon in which glass is separated into a Si-rich phase and a Si-lean phase when heated. In a spark plug, for example, heating during assembly of the resistor 5 causes phase separation in the borosilicate glasses 50, 51, forming a Si-rich phase and a Si-lean phase in the glasses 50, 51. Si is concentrated in the Si-rich phase, and Si is released from the Si-lean phase, so that components other than Si are relatively concentrated. The components other than Si are specifically B, Ca, Ba, etc. The electrical resistance of the Si-rich phase is high, and the electrical resistance of the Si-rich phase is low. If the electrical resistance of both is, for example, 10 16 Since the difference is more than 100 times, the presence of a Si-lean phase with a significantly reduced electrical resistance due to phase separation makes it easier for discharge to occur through the glass. The heat generated by the discharge then dissipates the conductive material 53, increasing the electrical resistance of the resistor 5.

[0016] In the spark plug of the present disclosure, the phase separation ratio of the borosilicate glasses 50, 51 in the resistor 5 is 10% or less (including 0). By setting the phase separation ratio to 10% or less, the formation of Si-rich phases or Si-lean phases due to phase separation is suppressed. This makes discharge less likely to occur, and the electrical resistance of the glass itself is lowered. As a result, even if a high voltage of, for example, 35 V or more is applied to the spark plug and the load on the resistor 5 increases, the electrical resistance of the resistor 5 is less likely to increase, improving the load life performance. From the viewpoint of achieving a more significant improvement in the load life performance, the phase separation ratio of the borosilicate glasses 50, 51 is preferably 5.5% or less, and more preferably 1.7% or less.

[0017] The phase separation is quantified by quantifying the elements of the Si-rich phase and / or the Si-lean phase based on, for example, an elemental map image obtained by EPMA. Since the main component elements of the borosilicate glass 50, 51 of the resistor 5 are generally Si or B, Si and B are expected to be the elements to be quantified. However, because the content of these elements in the glass is too high, it is difficult to obtain a clear shading in, for example, an elemental map obtained by EPMA, and they may be unsuitable as elements to be quantified.

[0018] When borosilicate glass 50, 51 contains Ca and / or Ba, it is preferable to quantify Ca and / or Ba in the EPMA element map. In this case, the EPMA element map can be used to more accurately quantify the Si-lean phase and, ultimately, the phase separation. Ca and / or Ba are elements used to modify the properties of borosilicate glass, and their content is generally smaller than that of Si or Ba, so that shading is likely to occur in the EPMA element map. The Ca content in borosilicate glass, calculated as oxide (CaO), is approximately 10% by mass or less, and the Ba content, calculated as oxide (BaO), is approximately 10% by mass or less.

[0019] Specifically, a binary image of the portion where Ca and / or Ba have been desorbed from the borosilicate glass 50, 51 is extracted from an elemental map image of Ca and / or Ba of the borosilicate glass 50, 51 obtained by an electron probe microanalyzer (i.e., EPMA), and the proportion of phase separation in the borosilicate glass 50, 51 can be calculated from the area ratio of the binary image. This is because the desorption of Ca and / or Ba due to phase separation indicates the formation of a Si-rich phase. In this specification, the area ratio of the portion where Ca and / or Ba have been desorbed is referred to as the phase separation ratio. The phase separation ratio can be indirectly determined by this phase separation ratio. From the viewpoint of ease of determination using an EPMA elemental map, it is preferable to determine the proportion of phase separation by the phase separation ratio.

[0020] In the assembly process of the resistor 5, the borosilicate glasses 50, 51 are generally softened by heating and then fused and sealed to the metal terminal and insulator. The thermal history at this time can cause phase separation in the borosilicate glasses 50, 51 of the resistor 5. The rate of phase separation can be controlled by changing the composition of the borosilicate glasses 50, 51 or by changing the thermal history (specifically, the heating temperature, heating time, etc.) during assembly of the resistor 5 to the spark plug 1. For example, the rate of phase separation tends to increase by increasing the heating temperature or lengthening the heating time during assembly. On the other hand, the rate of phase separation tends to decrease by decreasing the heating temperature or shortening the heating time.

[0021] The resistor 5 may further contain a zirconia-based material as the dispersion material 52. Specifically, the zirconia-based material is composed of zirconia and / or stabilized zirconia. In this specification, the term "stabilized zirconia" is used to refer not only to stabilized zirconia in the narrow sense, in which the crystal structure is stabilized by a stabilizer, but also to a concept that includes partially stabilized zirconia in which a stabilized portion and an unstable portion are mixed.

[0022] The resistor 5 includes a conductive material 53 such as carbon. As shown in Figures 2 and 3, the conductive material 53 is dispersed, for example, between particles of the borosilicate glass 51, between particles of the dispersion material 52, and between particles of the borosilicate glass 51 and particles of the dispersion material 52.

[0023] As long as the spark plug 1 has the resistor 5 described above between the center electrode 3 and the metal terminal 6, known configurations can be appropriately applied to the other components. An example of the overall configuration of the spark plug 1 will be shown below, but the spark plug 1 is not limited to this.

[0024] The spark plug 1 shown in Fig. 1 has an elongated shape. The spark plug 1 is for use in an internal combustion engine. The internal combustion engine is, for example, an automobile engine, and the spark plug 1 is attached to a mounting hole in a cylinder head (not shown) facing the engine combustion chamber by a mounting bracket 11 (described later).

[0025] The side of the spark plug 1 that protrudes into the combustion chamber in the axial direction D is called the tip side D1, and the opposite side is called the base side D2. In other words, the lower side in Figure 1 is the tip side D1, and the upper side is the base side D2.

[0026] The spark plug 1 includes a mounting metal fitting 11, an insulator 2, a center electrode 3, conductive glass seals 4, 48, the resistor 5 described above, a terminal fitting 6, and a ground electrode 7. The conductive glass seals 4, 48 include a first conductive glass seal 4 provided between the base end side D2 of the center electrode 3 and the tip end side D1 of the resistor 5, and a second conductive glass seal 48 provided between the base end side D2 of the resistor 5 and the tip end side D1 of the terminal fitting 6.

[0027] The cylindrical mounting fitting 11 holds the insulator 2 inside. The insulator 2 holds the center electrode 3 on the tip side D1 within the axial hole 210, and holds the shank 61 of the terminal fitting 6 on the base side within the axial hole 210. The first conductive glass seal 4 fixes the base side D2 of the center electrode 3 within the axial hole 210 of the insulator 2. The second conductive glass seal 48 fixes the tip side D1 of the terminal fitting 6 within the axial hole 210 of the insulator 2.

[0028] The ground electrode 7 faces the center electrode 3 at the tip end side D1 of the axial hole 210 of the insulator 2. The resistor 5 is disposed between the center electrode 3 and the metal terminal 6 within the axial hole 210 of the insulator 2. In the spark plug 1, the insulator 2 and the center electrode 3 are disposed coaxially. Each component of the spark plug 1 will be described in detail below.

[0029] The mounting bracket 11 is cylindrical and holds the insulator 2 inside. The mounting bracket 11 has a mounting thread portion 12 on the outer periphery of the tip side D1 in the axial direction D, and has a large diameter portion 13 with an outer diameter larger than that of the mounting thread portion 12 on the base end side D2.

[0030] A large diameter portion 22 provided in the middle of the insulator 2 is housed and held inside the large diameter portion 13 of the mounting bracket 11, and a base end edge 24 of the large diameter portion 22 is crimped to provide an airtight seal. The mounting bracket 11 is made of an iron-based alloy material such as carbon steel, for example.

[0031] The insulator 2 is held inside the cylindrical mounting bracket 11. The insulator 2 has an axial hole 210 that passes through in the axial direction D. A center electrode 3 is held inside the axial hole 210 of the insulator 2. A tip portion 23 of the insulator 2 protrudes to the tip side D1 beyond a tip opening 111 of the mounting bracket 11. The insulator 2 is made of insulating ceramics such as alumina.

[0032] The center electrode 3 has an elongated shape extending in the axial direction D of the spark plug 1. The center electrode 3 is held on a tip side D1 within the axial hole 210 of the insulator 2. The center electrode 3 has a large-diameter base end 32, which is supported on a tapered stepped surface 211 provided on the inner periphery of the axial hole 210 of the insulator 2. On the other hand, the center electrode 3 has a tapered tip end 311, which protrudes further toward the tip side D1 than the tip end 23 of the insulator 2.

[0033] The ground electrode 7 is a plate-like body whose entire cross section is bent into an L-shape (specifically, an inverted L-shape in FIG. 1 ), and its base end D2 is joined and fixed to the tip surface of the mounting bracket 11. The ground electrode 7 extends in the axial direction D beside the center electrode 3, and its tip end 71 is bent radially inward to face the tip end 311 of the center electrode 3. As a result, a spark discharge gap G is formed between the tip end 311 of the center electrode 3 and the tip end 71 of the ground electrode 7.

[0034] The center electrode 3 and the ground electrode 7 are formed of a base material made of a metal material such as a Ni-based alloy containing Ni (nickel) as a main component. The electrodes may each have a core material made of a metal with excellent thermal conductivity, such as Cu (copper) or a Cu alloy. A cylindrical noble metal tip is joined by welding or the like to the opposing surfaces of the front end portion 311 of the center electrode 3 and the front end portion 71 of the ground electrode 7. Examples of noble metal materials include Pt (platinum), Ir (iridium), and Rh (rhodium). A noble metal or noble metal alloy containing at least one selected from these noble metals as a main component can be used.

[0035] The terminal fitting 6 includes a large-diameter terminal portion 62 and a smaller-diameter shaft portion 61. The shaft portion 61 is made up of a base end portion 611 on the terminal portion 62 side and a main shaft portion 612 on the tip side D1. The main shaft portion 612 has an outer circumferential groove portion 613 formed by threading or grooving the outer periphery of the tip side D1. The outer circumferential groove portion 613 improves the adhesive strength between the conductive glass seal portion 48 and the resistor 5.

[0036] In FIG. 1, the small-diameter shank 61 of the terminal fitting 6 is housed in the axial hole 210 of the insulator 2, and applies pressure to the resistor 5 via the conductive glass seal 48 when assembled to the insulator 2. The large-diameter terminal portion 62 of the terminal fitting 6 protrudes toward the base end D2 beyond the base end opening of the axial hole 210 of the insulator 2 and is connected to a high-voltage source (not shown). The high-voltage source is, for example, an ignition coil connected to an on-board battery to generate a high voltage for ignition, and is connected to a control device (not shown). The terminal fitting 6 is also sometimes referred to as a stem.

[0037] Within the axial hole 210 of the insulator 2, a resistor 5 is provided between the axial portion 61 of the terminal fitting 6 and the center electrode 3 via the conductive glass seals 4, 48. The resistor 5 is a cylindrical member, and is adjusted to a desired electrical resistance value. The resistor 5 electrically connects the center electrode 3 and the terminal fitting 6, and also has the function of absorbing radio noise.

[0038] A first conductive glass seal 4 is provided between the resistor 5 and the center electrode 3. A second conductive glass seal 48 is provided between the resistor 5 and the terminal fitting 6.

[0039] The first conductive glass seal 4 and the second conductive glass seal 48 are made of conductive bonding glass, which may be copper glass made by mixing copper powder into glass. This forms a conductive path from an external high-voltage source through the terminal fitting 6, the second conductive glass seal 48, the resistor 5, and the first conductive glass seal 4 to the center electrode 3, and a high voltage is applied between the center electrode 3 and the ground electrode 7, causing a spark discharge.

[0040] In the spark plug 1, the resistor contains phase-separated borosilicate glass, and the phase separation rate is 10% or less. Therefore, even if the load voltage applied to the resistor increases, the electrical resistance value of the resistor is unlikely to increase, and the spark plug is unlikely to experience ignition failure. In other words, the spark plug has an excellent load life against high voltages.

[0041] [Experimental Example 1] In this example, a number of spark plugs were produced, each containing a resistor made of borosilicate glass with different phase separation ratios (specifically, phase separation rates), and the lifespan until ignition failure occurred was examined.

[0042] -Preparing resistor materials- The resistor material was prepared by thoroughly kneading 50 parts by mass of glass powder made of borosilicate glass as the welding material, 48 parts by mass of a zirconia-based material as the dispersing material, and 2 parts by mass of carbon black as the conductive material to a homogeneous state. The borosilicate glass used had a CaO content of 7% by mass.

[0043] -Preparation of test specimen- After inserting a center electrode into the axial hole of the insulator, a conductive glass seal material was filled and pre-compressed. Next, a predetermined resistor material and a conductive glass seal material were filled into the axial hole in the same order and pre-compressed. Next, a terminal fitting was inserted into the axial hole. Next, this was heated in a furnace at a predetermined temperature for a certain period of time, and then the terminal fitting was pressed in and welded. This resulted in a test specimen. In this example, multiple test specimens with different phase separation ratios of the borosilicate glass in the resistor were produced by changing the heating temperature and heating time in the furnace.

[0044] -Calculation of phase separation ratio- For each specimen, the phase separation ratio (specifically, the phase separation rate) of the borosilicate glass resistor was calculated as follows. The resistor in each specimen was divided into five equal parts along the axial direction, and the observation area was the most proximal region. Scanning electron microscope (SEM) observation and quantitative analysis of Ca elements were performed using EPMA. The observation area is area A shown in Figure 4. The Shimadzu EPMA-8050G analyzer was used, and the measurement conditions were a magnification of 50x and a Ca map count of 5 to 50. In the Ca map obtained by EPMA, Ca desorption areas were extracted by binarization, and the area ratio of the desorption areas was used as the phase separation rate. The software Winroof 2018 was used for binarization, and the threshold condition was set to 40. The Ca desorption areas are represented by white areas after binarization (see Figures 5(c) and 6(c)). As representative examples of calculated phase separation data, images of borosilicate glass with a phase separation rate of 20.1% are shown in Figures 5(a) to 5(c), and images of borosilicate glass with a phase separation rate of 3.47% are shown in Figures 5(a) and 6(a). Figures 5(a) and 6(a) show SEM photographs, Figures 5(b) and 6(b) show EPMA Ca maps, and Figures 5(c) and 6(c) show binarized images of the Ca maps.

[0045] -Evaluation of test specimen- For each test piece, a load life test was carried out under the spark plug load life test conditions specified in JIS B8031 (hereinafter referred to as "JIS conditions"), as well as under more stringent conditions based on these conditions (hereinafter referred to as "JIS-based accelerated conditions"). The JIS conditions are: number of ignitions: 1.3 x 10 7 The JIS-based acceleration conditions were: number of ignitions, frequency: not specified, discharge voltage: 20±5 kV, temperature: not specified, and standard: resistance change rate ±30% or less. In contrast, the number of ignitions under the JIS-based acceleration conditions was determined based on the JIS standard requirement of "resistance change rate ±30% or less," and was defined as the time required to reach a resistance change rate of ±30%. The conditions were: frequency: 100 Hz, discharge voltage: 35 kV, 40 kV, 45 kV, temperature: room temperature (specifically, 20°C), and standard: resistance change rate ±30% or less. The JIS-based acceleration conditions were stricter than the JIS conditions in terms of discharge voltage and temperature, anticipating future increases in engine ignition discharge voltage. In this experimental example, resistance was measured every two hours, and the load life was defined as two hours before the resistance change rate exceeded 30%. Figure 8 illustrates the relationship between elapsed time and resistance change rate during the load life test. In the example shown in Figure 8, the resistance change rate exceeded 30% and was within ±30% after 52 hours, failing the standard. In this experiment, the load life is the time immediately before failure, i.e., the time elapsed until the last time compliance with the standard was confirmed. Figure 7 shows the relationship between the phase separation ratio and the load life for each specimen. The specimen with a phase separation rate of 13% in Fig. 7 was obtained at a furnace heating temperature of 900°C for 30 minutes. For example, by lowering the heating temperature from this specimen, the phase separation rate tends to decrease, and the specimen with a phase separation rate of 10% was obtained at a heating temperature of 860°C for 30 minutes.

[0046] As shown in Figure 7, the load life at high voltage tends to improve as the phase separation ratio (specifically, the phase separation rate) of borosilicate glass decreases. As can be seen from Figure 7, when the phase separation rate is 10% or less, the load life at high voltage of the resistor is significantly improved, and the test specimens exhibit excellent load life performance. Furthermore, the load life performance is further improved when the phase separation rate is 5.5% or less, and even more improved when the phase separation rate is 1.7% or less.

[0047] The present invention is not limited to the above-described embodiments and experimental examples, and can be applied to various embodiments without departing from the spirit of the present invention. In experimental example 1, borosilicate glass containing Ca was used, and the phase separation ratio was calculated from a Ca map obtained by EPMA. However, when borosilicate glass containing Ba is used, the phase separation ratio can be calculated from a Ba map obtained by EPMA. [Explanation of symbols]

[0048] 1 spark plug 3 Center electrode 5 Resistors 50, 51 Borosilicate glass 52 Dispersion material 53 Conductive materials 6 Terminal fittings

Claims

1. A spark plug (1) having a resistor (5) between a center electrode (3) and a terminal metal fitting (6), The resistor includes a phase-separated borosilicate glass (50, 51) and a conductive material (53), A spark plug, wherein the borosilicate glass has a phase separation rate of 10% or less.

2. the borosilicate glass contains Ca and / or Ba, 2. The spark plug according to claim 1, wherein the ratio of phase separation in the borosilicate glass is calculated from an area ratio of a binary image of a portion where Ca and / or Ba have been desorbed from the borosilicate glass, extracted from an element map image of Ca and / or Ba of the borosilicate glass obtained by an electron probe microanalyzer.

3. 3. The spark plug according to claim 1, wherein the borosilicate glass has a phase separation rate of 5.5% or less.

4. 3. The spark plug according to claim 1, wherein the borosilicate glass has a phase separation rate of 1.7% or less.

Images