Patent Application
20180375298
The present invention relates to a spark plug.
A spark plug used for an internal combustion engine generally includes: a tubular metal shell; a tubular insulator disposed in an inner hole of the metal shell; a center electrode inserted in an axial hole of the insulator so as to protrude from a front end of the insulator to the outside; a metal terminal inserted in the axial hole of the insulator so as to protrude from a rear end of the insulator to the outside; and a ground electrode having one end joined to the front side of the metal shell and having the other end opposed to the center electrode with a spark discharge gap interposed therebetween. The center electrode and the metal terminal are electrically connected to each other by a conductive seal portion provided in the axial hole of the insulator.
In recent years, as output of an internal combustion engine comes to be higher, it is required to increase spark discharge voltage of a spark plug. There is a concern that an increase in spark discharge voltage of a spark plug results in an increase in high frequency noise that occurs at the time of discharge, and an electronic control device of a vehicle is adversely affected. Therefore, it has been desired to reduce the high frequency noise of the spark plug.
Conventionally, various techniques have been proposed in order to reduce high frequency noise that occurs at the time of discharge performed by the spark plug. For example, in Japanese Patent Application Laid-Open (kokai) No. 2004-259605, a configuration is proposed in which a noise-suppressing resistor is provided at a position, in an axial hole of an insulator, above an upper end of a metal shell.
However, in the above-described conventional technique, there is a problem that the insulator has a high risk of being damaged by vibrations of the resistor, and impact resistance and airtightness are difficult to be ensured. Therefore, a technique for reducing high frequency noise of a spark plug by means that is different from the conventional means, has been desired.
The present invention has been conceived of in order to address the above-described problem, and can be embodied in the following modes.
(1) According to a first aspect of the present invention, there is provided a spark plug which includes: an insulator having an axial hole extending in a direction of an axis; a center electrode inserted in the axial hole so as to protrude from a front end of the insulator to an outside; a metal terminal inserted in the axial hole so as to protrude from a rear end of the insulator to the outside; a conductive seal portion disposed in the axial hole so as to electrically connect the center electrode and the metal terminal to each other; and a metal shell accommodating the insulator. The metal terminal has a terminal flange portion which is in contact with the rear end of the insulator. In the spark plug, a Fe-containing oxide layer is formed on a surface of a beneath-flange rod-shaped portion, of the metal terminal, between the terminal flange portion and a rear end of the metal shell, and a surface area of the Fe-containing oxide layer is not less than 10% of a surface area of the beneath-flange rod-shaped portion. In a portion, of a generally used spark plug, on the rear side relative to the rear end of the metal shell (i.e., a portion above an upper end of the metal shell), no high frequency current flows via the insulator, and thus, noise reduction effect of a Fe-containing oxide is likely to be obtained. According to the above-described spark plug, since the Fe-containing oxide layer is provided on the surface of the beneath-flange rod-shaped portion between the terminal flange portion and the rear end of the metal shell so as to coat not less than 10% of the surface area of the beneath-flange rod-shaped portion, sufficiently high noise reduction effect can be obtained.
(2) In accordance with a second aspect of the present invention, there is provided a spark plug as described above, wherein a plating layer is formed from one or more metals selected from among Ni, Cu, Cr, Zn, and Fe may be formed on the surface of the beneath-flange rod-shaped portion, and the Fe-containing oxide layer may be formed on the plating layer. By coating the surface of the beneath-flange rod-shaped portion with the plating layer, when the conductive seal portion is subjected to heat treatment, a reactional phase is formed between the plating layer and the Fe-containing oxide layer, whereby adhesion therebetween becomes satisfactory. As a result, the Fe-containing oxide layer is less likely to peel off from the beneath-flange rod-shaped portion, whereby the noise reduction effect of the Fe-containing oxide layer can be further improved.
(3) In accordance with a third aspect of the present invention, there is provided a spark plug as described above, wherein an average thickness of the Fe-containing oxide layer is not smaller than 10 μm and is not larger than 200 μm. If the average thickness of the Fe-containing oxide layer is smaller than 10 μm, the noise attenuation effect tends to be reduced to some extent. In addition, if the average thickness is larger than 200 μm, there is a possibility that the Fe-containing oxide layer peels off owing to the difference in thermal expansion coefficient between the beneath-flange rod-shaped portion and the Fe-containing oxide layer, and the noise reduction effect is reduced.
(4) In accordance with a fourth aspect of the present invention, there is provided a spark plug as described above, wherein the surface area of the Fe-containing oxide layer is not less than 50% of the surface area of the beneath-flange rod-shaped portion. The larger the surface area of the Fe-containing oxide layer is, the higher the noise reduction effect becomes. By setting the surface area of the Fe-containing oxide layer to be not less than 50% of the surface area of the beneath-flange rod-shaped portion, the highest noise reduction effect can be obtained.
(5) In accordance with a fifth aspect of the present invention, there is provided a spark plug as described above, wherein the conductive seal portion has a magnetic composite phase formed from a Fe-containing oxide, conductive particles, and a glass component. By providing such a magnetic composite phase to the conductive seal portion, the noise reduction effect can be further improved.
The present invention can be embodied in various modes such as modes of a spark plug and a spark plug manufacturing method.
The metal shell 7 has a substantially cylindrical shape, and is formed so as to accommodate and hold the insulator 3. A screw portion 9 is formed on an outer circumferential surface, in the frontward direction, of the metal shell 7. With use of the screw portion 9, the spark plug 1 is mounted to a cylinder head of an internal combustion engine that is not shown.
The insulator 3 is held by an inner circumference portion of the metal shell 7 via a talc 10 and a packing 11. The axial hole 2 of the insulator 3 includes: a small-diameter portion 12 holding the center electrode 4 on the front side of the axis O; and an intermediate-diameter portion 14 accommodating the conductive seal portion 60 and having a larger inner diameter than the small-diameter portion 12. The axial hole 2 further includes, between the small-diameter portion 12 and the intermediate-diameter portion 14, a tapered first stepped portion 13 having a diameter increasing toward the rear side. The insulator 3 is fixed to the metal shell 7 in a state where the front end thereof protrudes from the front end surface of the metal shell 7. It is desirable that the insulator 3 is formed from a material having mechanical strength, thermal strength, electrical strength, and the like. Examples of such a material include a ceramic sintered body containing alumina as a main ingredient.
The center electrode 4 is accommodated in the small-diameter portion 12 of the insulator 3, and is held so as to be insulated from the metal shell 7 in a state where a flange portion 17 provided at a rear end of the center electrode 4 and having a large diameter is locked by the first stepped portion 13 of the insulator 3 and where a front end of the center electrode 4 protrudes from a front end surface of the insulator 3. It is desirable that the center electrode 4 is formed from a material having thermal conductivity, mechanical strength, and the like. The center electrode 4 is formed from, for example, a Ni-based alloy such as INCONEL (trademark). An axial portion of the center electrode 4 may be formed from a metal material, such as Cu or Ag, that has excellent thermal conductivity.
The ground electrode 8 is formed such that: one end thereof is joined to the front end surface of the metal shell 7; an intermediate portion thereof is bent to be substantially L-shaped; and the other end is opposed to the front end of the center electrode 4 with a gap interposed therebetween. The ground electrode 8 is formed from a material similar to the material from which the center electrode 4 is formed.
Noble metal tips 29, 30 formed from a platinum alloy, an iridium alloy, or the like are provided at portions, which are opposed to each other, of the center electrode 4 and the ground electrode 8. A spark discharge gap g is formed between the noble metal tips 29, 30. Either or both of the noble metal tips of the center electrode 4 and the ground electrode 8 may be omitted.
The metal terminal 5 is a terminal for externally applying, to the center electrode 4, a voltage for causing spark discharge between the center electrode 4 and the ground electrode 8. An uneven portion 54 of which the outer circumferential surface is unevenly shaped by knurling or the like is preferably provided on the front side of the metal terminal 5. By providing such an uneven portion 54, adhesion between the metal terminal 5 and the conductive seal portion 60 becomes satisfactory, and the metal terminal 5 and the insulator 3 are firmly fixed to each other. A terminal flange portion 50 is provided on the rear side of the metal terminal 5 so as to be in contact with the rear end 3t of the insulator 3. The metal terminal 5 is formed from a metal material such as low-carbon steel.
A portion, of the metal terminal 5, between the terminal flange portion 50 and a rear end 7t of the metal shell 7 is referred to as “beneath-flange rod-shaped portion 52”. A Fe-containing oxide layer described below is formed on the surface of the beneath-flange rod-shaped portion 52. As an underlayer for the Fe-containing oxide layer, a plating layer formed from one or more metals selected from among Ni, Cu, Cr, Zn, and Fe is preferably formed. These features will be further described below.
The conductive seal portion 60 is disposed between the center electrode 4 and the metal terminal 5 in the axial hole 2 so as to electrically connect the center electrode 4 and the metal terminal 5 with each other. The conductive seal portion 60 has a magnetic composite phase 63 formed from a Fe-containing oxide, conductive particles, and a glass component, has a first seal phase 61 between the magnetic composite phase 63 and the center electrode 4, and has a second seal phase 62 between the magnetic composite phase 63 and the metal terminal 5. The first seal phase 61 and the second seal phase 62 fix the insulator 3 and the center electrode 4 to each other, and the insulator 3 and the metal terminal 5 to each other, respectively, in a sealed state. The first seal phase 61 and the second seal phase 62 can be each formed by sintering a seal powder that contains glass powder of borosilicate soda glass or the like and metal powder of Cu, Fe, or the like.
As the Fe-containing oxide of the magnetic composite phase 63, an iron oxide (FeO, Fe2O3, Fe3O4, or the like) or various kinds of ferrite may be used, for example. As the conductive particles of the magnetic composite phase 63, Ni powder, C powder, or the like may be used, for example. By providing such a magnetic composite phase 63 to the conductive seal portion 60, the noise reduction effect can be further improved. However, the magnetic composite phase 63 may be omitted.
As the Fe-containing oxide forming the Fe-containing oxide layer 56, one or more of the following Fe-containing oxides may be used.
Iron oxide: FeO, Fe2O3, Fe3O4; spinel ferrite: (Ni, Zn) Fe2O4, Ni2Fe2O4, (Mn, Zn) Fe2O4, CuFe2O4, NiFe2O4; hexagonal crystal ferrite: BaFe12O19, SrFe12O19, Ba2Mg2Fe12O22, Ba2Ni2Fe12O22, Ba2CO2Fe12O22; and garnet ferrite: YFe5O12
The surface area of the Fe-containing oxide layer 56 is preferably not less than 10% of the surface area of the beneath-flange rod-shaped portion 52. In a portion, of the spark plug 1, that is closer to the terminal flange portion 50 than the rear end 7t of the metal shell 7, no high frequency current flows via the insulator 3, and thus, the noise reduction effect of the Fe-containing oxide is likely to be obtained. By providing the Fe-containing oxide layer 56 on the surface of the beneath-flange rod-shaped portion 52 so as to coat not less than 10% of the surface area thereof, sufficiently high noise reduction effect can be obtained. In addition, since the Fe-containing oxide layer 56 is a thin layer that is adhered to the surface of the beneath-flange rod-shaped portion 52, the Fe-containing oxide layer 56 is unlikely to peel off by vibrations of the spark plug 1, and a problem regarding impact resistance and airtightness hardly arises. The surface area of the Fe-containing oxide layer 56 is further preferably not less than 50% of the surface area of the beneath-flange rod-shaped portion 52. The larger the surface area of the Fe-containing oxide layer 56 is, the higher the noise reduction effect becomes. By setting the surface area of the Fe-containing oxide layer 56 to be not less than 50% of the surface area of the beneath-flange rod-shaped portion 52, the highest noise reduction effect can be obtained.
In step T120, a region of the Fe-containing oxide layer 56 is identified with use of a composition analysis. For the composition analysis, an X-ray photoelectron spectroscopic device (XPS) may be used, for example.
In step T130, a three-dimensional image of the metal terminal 5 is captured with use of a three-dimensional scanner, and the surface area of the Fe-containing oxide layer 56 is measured from the three-dimensional image. This surface area is a surface area in a state of being expanded as in
In step T140, the Fe-containing oxide layer 56 and the second seal phase 62 (if adhered) are removed from the metal terminal 5. The reason why these components are removed is because the surface area of the beneath-flange rod-shaped portion 52 cannot be accurately measured in a state where the Fe-containing oxide layer 56 and the second seal phase 62 are adhered to the surface of the beneath-flange rod-shaped portion 52.
In step T150, a three-dimensional image of the resultant metal terminal 5 is captured again with use of the three-dimensional scanner, and the surface area of the beneath-flange rod-shaped portion 52 is measured from the three-dimensional image. In a case where a part of the uneven portion 54 is included in the beneath-flange rod-shaped portion 52, the surface area of the beneath-flange rod-shaped portion 52 is calculated while portions corresponding to grooves and roots in the uneven portion 54 are ignored. Specifically, the surface area is calculated on the premise that the uneven portion 54 has a columnar shape of which the outer shape is a portion corresponding to a projection (crest) thereof.
In step T160, the proportion of the surface area of the Fe-containing oxide layer 56 to the surface area of the beneath-flange rod-shaped portion 52 is calculated.
By obtaining the surface areas of the beneath-flange rod-shaped portion 52 and the Fe-containing oxide layer 56 with use of the three-dimensional images, the surface areas can be measured with high accuracy even if the beneath-flange rod-shaped portion 52 is bent to some extent.
The average thickness of the Fe-containing oxide layer 56 is preferably not smaller than 10 μm and not larger than 200 μm. If the average thickness of the Fe-containing oxide layer 56 is smaller than 10 μm, there is a possibility that the noise attenuation effect is not sufficiently obtained. If the average thickness is larger than 200 μm, there is a possibility that the Fe-containing oxide layer 56 peels off owing to the difference in thermal expansion coefficient between the Fe-containing oxide layer 56 and the beneath-flange rod-shaped portion 52, and the noise reduction effect is reduced.
The average thickness of the Fe-containing oxide layer 56 is measured by the following method. First, in a vertical cross section (
On the right side of
From the test results shown in
(1) In each of samples S01 to S21 of the examples, the coating percentage of the surface, of the beneath-flange rod-shaped portion 52, coated with the Fe-containing oxide layer 56 is not lower than 10%. More specifically, the coating percentages in samples S01 to S21 are within a range of not lower than 10% and not higher than 92%. Meanwhile, in each of samples S31 to S35 of the comparative examples, the coating percentage is lower than 10%. In each of samples S01 to S21 of the examples, as compared with samples S31 to S35 of the comparative examples, noise at any of the frequencies is small, and satisfactory noise reduction effect is obtained.
(2) Each of samples S06 to S21 is different from samples S01 to S05 in that the plating layer 58 formed from metal such as Ni, Cu, Cr, Zn, and/or Fe was formed on the surface of the beneath-flange rod-shaped portion 52, and the Fe-containing oxide layer 56 was formed on the plating layer 58. These samples S06 to S21 are preferable in that the noise reduction effect is higher to some extent than in samples S01 to S05 including no plating layer 58. However, it is assumed that a major effect of the plating layer 58 is that the Fe-containing oxide layer 56 and the plating layer 58 are firmly adhered to each other so that the Fe-containing oxide layer 56 is less likely to peel off. It is highly probable that also the increase in the noise reduction effect obtained in
(3) Each of samples S11 to S21 is different from samples S01 to S10 in that the average thickness of the Fe-containing oxide layer 56 is not smaller than 10 μm and not larger than 200 μm. These samples S11 to S21 are preferable in that the noise reduction effect is further higher than in samples S01 to S10 in each of which the average thickness of the Fe-containing oxide layer 56 is not within this range. If the average thickness of the Fe-containing oxide layer 56 is smaller than 10 μm, the noise attenuation effect tends to be reduced to some extent. It is assumed that the reason why the noise reduction effect is low in samples S03 and S08 in each of which the average thickness of the Fe-containing oxide layer 56 is larger than 200 μm is because a part of the Fe-containing oxide layer 56 peeled off owing to the difference in thermal expansion coefficient between the beneath-flange rod-shaped portion 52 and the Fe-containing oxide layer 56, and the noise reduction effect was reduced.
(4) Each of samples S15 to S21 is different from samples S01 to S14 in that the coating percentage of the surface, of the beneath-flange rod-shaped portion 52, coated with the Fe-containing oxide layer 56 is not lower than 50%. These samples S15 to S21 are preferable in that the noise reduction effect is further higher than in samples S01 to S14 in each of which the coating percentage is lower than 50%. No significant improvement in the noise reduction effect is observed after the coating percentage exceeds 50%. Therefore, the coating percentage is further preferably not lower than 50% and not higher than 60%.
(5) Each of samples S19 to S21 is different from samples S01 to S18 in that the conductive seal portion 60 includes the magnetic composite phase 63. These samples S19 to S21 are preferable in that the noise reduction effect is further higher than in samples S01 to S18 including no magnetic composite phase 63.
The present invention is not limited to the above-described embodiments and modes, but may be embodied in various other forms without departing from the scope of the invention.
As the spark plug, spark plugs having various configurations other than that shown in
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-251395 | Dec 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/004262 | 9/19/2016 | WO | 00 |
