JP2005353606A - Spark plug - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve wear-out resistance of noble metal tips, in a spark plug fixing the noble metal tips to opposing faces of a center electrode and a ground electrode separated by a discharge gap. <P>SOLUTION: This spark plug is provided with the center electrode (30) and the ground electrode (40) facing the center electrode (30) via the discharge gap (50), and the noble metal tips (35, 45) are fixed to the facing faces (32, 43) of the center electrode (30) and the ground electrode (40), respectively. With regard to the noble metal tip (45) of the ground electrode (40), the cross section A is ≥0.1 mm<SP>2</SP>and ≤1.15 mm<SP>2</SP>, and the amount of protrusion t from the facing face of the ground electrode (40) is ≥0.3 mm and ≤1.5 mm. The noble metal tip (45) of the ground electrode (40) possesses superior oxidation resistance volatile resistance, compared with the noble metallic tip (35) of the center electrode (30). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a spark plug, and in particular, it has improved high wear resistance by joining a thin noble metal tip to a center electrode and a ground electrode, and further improves the wear resistance of the noble metal tip, so The present invention relates to a spark plug for an internal combustion engine that can be adapted to an engine with severe load.

  Conventionally, as described in Patent Document 1, in order to obtain a spark plug having high ignitability, it has been proposed to project both the center electrode and the ground electrode from the electrode support portion and to form a thin electrode. Yes.

Further, in order to ensure the wear resistance of the electrode, as a configuration of the thin electrode, for example, a noble metal tip made of Pt, Pd, Au or the like or an alloy thereof is fixed to the opposing surface with a discharge gap between the center electrode and the ground electrode. What has been proposed.
JP 52-36237 A

  However, due to recent trends in engines such as high output, low fuel consumption, and low exhaust gas, the combustion atmosphere is higher than that of conventional engines, and the electrode temperature of the spark plug becomes very high.

  Furthermore, in the ground electrode, when a noble metal tip having a narrow shape is projected, the noble metal tip becomes a heat spot and is consumed at an accelerated rate, and the problem that the lifetime is reached in a short time has become apparent. .

  In view of the above problems, an object of the present invention is to improve the wear resistance of a noble metal tip in a spark plug in which a noble metal tip is fixed to the opposing surfaces of a center electrode and a ground electrode with a discharge gap therebetween.

  In order to achieve the above object, intensive studies were conducted. The consumption of the noble metal tip is the total of the spark consumption consumed by melting due to the discharge energy and the oxidation volatilization consumed due to oxidation volatilization due to high temperature. There is a large difference in the ratio. Here, it is presumed that the oxidation volatilization is consumed when an oxide film is formed on the chip surface at a high temperature and the oxide film is dropped.

  In general, since the noble metal tip in the center electrode has a negative polarity, the rate of spark consumption is high and the oxidation and volatilization is low. On the other hand, the precious metal tip in the ground electrode has a higher temperature than the center electrode, so the rate of oxidative volatilization consumption is high. However, since it is a positive polarity, there is little spark consumption.

  In view of the above findings, the inventors have focused on making the noble metal tip of the center electrode and the noble metal tip of the ground electrode have material compositions adapted to the respective consumption forms, and as a result of experimental studies, the present invention has been created.

In other words, the invention according to claim 1 includes a center electrode (30) and a ground electrode (40) opposed to the center electrode via a discharge gap (50), and the opposed surfaces of the center electrode and the ground electrode. In (32, 43), in the spark plug in which the noble metal tip (35, 45) is fixed, the noble metal tip (45) in the ground electrode has a cross-sectional area A of 0.1 mm ² or more and 1.15 mm ^2. The protrusion t from the opposing surface of the ground electrode is 0.3 mm or more and 1.5 mm or less, and the oxidation volatility is superior to the noble metal tip (35) in the center electrode. And

  According to the study of the present inventor, when the noble metal tip on the ground electrode is protruded from the facing surface of the ground electrode in order to improve the ignitability, the noble metal in the ground electrode is projected when the protrusion amount t is 0.3 mm or more. It was found that the chip consumption mode has a higher rate of oxidative volatilization consumption than spark consumption (see FIGS. 3 and 4).

  Therefore, when the protruding amount t is 0.3 mm or more as in the present invention, the noble metal tip in the ground electrode is more excellent in oxidation volatility than the noble metal tip in the center electrode. The wear resistance of the noble metal tip can be improved.

Further, the sectional area A of the noble metal tip (45) of the ground electrode (40) is at 0.1 mm ² or more 1.15 mm ² or less, if the protrusion amount t is 1.5mm or less, wear resistance improvement and high It is advantageous for achieving both ignitability.

Incidentally, if the cross-sectional area A is less than 0.1 mm ² , the amount of chip consumption tends to increase significantly (see FIG. 7), and if it exceeds 1.15 mm ^2, it is difficult to ensure high ignitability. Further, if the protruding amount t is larger than 1.5 mm, the chip consumption amount is likely to increase significantly (see FIG. 8).

  In the invention according to claim 2, the noble metal tip (35, 45) in the center electrode (30) and the ground electrode (40) is allowed to stand at 1100 ° C. for 30 hours in the atmosphere for 30 hours. ) Where the ratio Lmax2 / Lmax1 of the maximum oxidation volatilization width Lmax2 of the noble metal tip (45) at the ground electrode with respect to the maximum oxidation volatilization width Lmax1 is X ≦ 0.8.

  When the oxidation volatilization ratio X is smaller than 1, it can be said that the noble metal tip at the ground electrode is substantially superior in oxidation volatility than the noble metal tip at the center electrode. Therefore, if the oxidation volatilization ratio X is 0.8 or less, the oxidation volatilization consumption of the noble metal tip at the ground electrode can be greatly reduced (see FIG. 6).

  In addition, in order to improve the wear resistance due to oxidative volatilization and consumption of the noble metal tip at the ground electrode, the present inventor adds an additive that easily oxidizes itself to the noble metal constituting the noble metal tip, and oxidizes by this additive. I thought it would be good to form a film to form a kind of protective film.

  In view of this, a study was conducted to examine wear resistance by changing the content ratio of the above additives in a noble metal tip using an Ir alloy which is a high melting point material. The invention described in claim 3 has been made based on the results of this study.

  That is, in the invention according to claim 3, both the noble metal tips in the center electrode and the ground electrode are made of an Ir alloy containing at least one additive in Ir exceeding 50% by weight, and are contained in the noble metal tips in the ground electrode. The total amount of additives to be added is 15% by weight or more.

  According to this, both the noble metal tips in the center electrode and the ground electrode are made of an Ir alloy containing at least one additive in 50% by weight or more of Ir, so that it has a high melting point and excellent heat resistance. Chip characteristics can be secured.

  Further, the total amount of additives contained in the noble metal tip in the ground electrode is not less than 15% by weight and not more than 50%, whereby the wear resistance of the noble metal tip is greatly improved. Here, if the total amount of the additives is less than 15% by weight, it is difficult to suppress oxidative volatilization and consumption increases, and if it exceeds 50% by weight, the melting point decreases and the consumption is reduced. Will increase (see FIG. 9).

  For these reasons, also in the spark plug of the present invention, the wear resistance of the noble metal tip can be improved.

  Further, as a result of investigations to obtain a more preferable range of the total weight% of additives contained in the noble metal tip in the ground electrode, the invention according to claim 4 has been obtained.

  That is, in the invention according to claim 4, the total of the weight% of the additive contained in the noble metal tip (45) in the ground electrode (40) is contained in the noble metal tip (35) in the center electrode (30). It is characterized by being 1.5 times or more of the total of the weight% of additives.

  Regardless of the amount of additive contained in the noble metal tip in the center electrode, the total amount of the additive contained in the noble metal tip in the center electrode is the sum of the weight percentage of the additive contained in the noble metal tip in the ground electrode. If the total weight% is 1.5 times or more, the noble metal tip in the ground electrode is also advantageous for suppressing the oxidation and volatilization and extending the life of the spark plug (see FIG. 10).

  In the invention according to claim 5, the noble metal tip (35) in the center electrode is made of an Ir alloy containing at least one additive in Ir exceeding 50% by weight, and the noble metal tip in the ground electrode is 50% by weight. It is characterized by comprising a Pt alloy containing at least one additive in Pt exceeding wt%.

  According to this, Ir alloy, which is a high melting point material, is used for the noble metal tip in the center electrode having a high spark consumption rate, and a Pt alloy having excellent oxidation volatility is used for the noble metal tip in the ground electrode having a high rate of oxidation volatilization consumption. Therefore, the wear resistance of the noble metal tip can be improved.

Further, in the spark plug according to claim 3 to claim 5, the additive contained in the noble metal tip (35, 45) in the center electrode (30) and the ground electrode (40) is Ir, Pt, Rh, It is preferably at least one of Ni, W, Pd, Ru, Os, Al, Y, Y ₂ O ₃ and Re. Of course, two or more of these additives may be used, or different additives may be used for the center electrode and the ground electrode.

  Further, in the spark plug according to claim 5, as in the invention according to claim 7, only an additive contained in the noble metal tip (45) in the ground electrode (40) has a melting point higher than that of Pt. And at least one such additive is preferably contained.

  In consideration of wear resistance, the noble metal tip in the ground electrode may be only Pt, that is, no additive, but Pt alone has a weak strength and has problems such as cracking and breakage at high temperatures. Therefore, Pt contains at least one additive to ensure the strength of the chip.

  At this time, by making the additive only one having a melting point higher than that of Pt, it is possible to realize a noble metal tip that has no practical problem of wear resistance even when compared with a noble metal tip of 100% Pt (FIG. 11).

  In the invention according to claim 8, in the spark plug according to claim 5 or 7, the additive contained in the noble metal tip (45) in the ground electrode (40) has a linear expansion coefficient higher than that of Pt. Is small and contains at least one kind, and the noble metal tip in the ground electrode is fixed by laser welding.

  Accordingly, in the noble metal tip in the ground electrode, it is preferable in order to achieve both spark consumption and bonding reliability.

  In particular, when the additive contained in the noble metal tip in the ground electrode is composed only of a material having a melting point higher than that of Pt as in the spark plug according to claim 7, such an additive has a linear expansion more than that of Pt. In many cases, the coefficient is small. At that time, if the noble metal tip on the ground electrode is fixed by laser welding, the joining reliability can be easily secured (see FIG. 12).

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments shown in the drawings will be described below. FIG. 1 is a half sectional view showing an overall configuration of a spark plug S1 for an internal combustion engine according to an embodiment of the present invention. This spark plug S1 is applied to a spark plug of an automobile engine, and is inserted and fixed in a screw hole provided in an engine head (not shown) that defines a combustion chamber of the engine. It is like that.

The spark plug S1 has a cylindrical housing (mounting bracket) 10 made of a conductive steel material (for example, low carbon steel or the like), and the housing 10 is mounted for fixing to an engine block (not shown). A screw portion 11 is provided. An insulator (insulator) 20 made of alumina ceramic (Al ₂ O ₃ ) or the like is fixed inside the housing 10, and one end 21 of the insulator 20 is exposed from one end 12 of the housing 10. It is provided as follows.

  A center electrode 30 is fixed to the shaft hole 22 of the insulator 20, and the center electrode 30 is insulated and held with respect to the housing 10. The center electrode 30 is, for example, a cylindrical body made of a metal material having excellent heat conductivity such as Cu as an inner material and a metal material having excellent heat resistance and corrosion resistance such as a Ni-based alloy as shown in FIG. As described above, the one end portion 31 is provided so as to be exposed from the one end portion 21 of the insulator 20.

  On the other hand, the ground electrode 40 has a columnar shape such as a prism made of Ni-based alloy or the like, and its one end 41 faces the one end 31 of the center electrode 30 via the discharge gap 50 and is bent in the middle. The other end 42 is fixed to the one end 12 of the housing 10 by resistance welding.

  Here, FIG. 2 is an explanatory view showing, in an enlarged manner, the vicinity of the discharge gap 50 in the spark plug S1. As shown in FIG. 2, the end surface 32 of the one end portion 31 of the center electrode 30 and the side surface 43 of the one end portion 41 of the ground electrode 40 are arranged to face each other via the discharge gap 50 as described above. The surfaces 32 and 43 are configured as opposing surfaces 32 and 43 of the center electrode 30 and the ground electrode 40 with the discharge gap 50 therebetween.

  And the noble metal tips 35 and 45 are joined and fixed to both the opposing surfaces 32 and 43 by resistance welding, laser welding, etc., respectively. In this example, both the tips 35 and 45 are cylindrical, and both the tips 35 and 45 are joined and fixed to the opposing surfaces 32 and 43 by resistance welding.

  Here, the noble metal tip 35 in the center electrode 30 is hereinafter referred to as a center electrode side tip 35, and the noble metal tip 45 in the ground electrode 40 is hereinafter referred to as a ground electrode side tip 45.

  On the ground electrode 40 side, the ground electrode side tip 45 protrudes from the opposing surface 43 of the ground electrode 40 by the protrusion amount t in order to reduce the diameter of the discharge part and realize high ignitability. ing. The shortest distance G between both the chips 35 and 45 is formed as a discharge gap 50, and the size G of the discharge gap 50 is, for example, about 1 mm.

  In such a spark plug S1, discharge occurs in the discharge gap 50 formed between the tips 35 and 45 of both electrodes 30 and 40, and the air-fuel mixture in the combustion chamber is ignited. After ignition, the flame kernel formed in the spark gap 50 grows and is combusted in the combustion chamber.

  The spark plug S1 employs a unique configuration as described below.

  [First Configuration] First, as a first characteristic configuration, the ground electrode side chip 45 has a protruding amount t of 0.3 mm or more from the facing surface 43 of the ground electrode 40, and is mainly oxidation volatile. It is superior to the electrode side tip 35 (first configuration). The grounds for adopting the first configuration will be described with reference to FIGS.

  FIG. 3 is a diagram showing the results of an engine durability evaluation, and examining the influence of the protrusion amount t (unit: mm) of the ground electrode side tip 45 on the life of the spark plug as a gap expansion amount (unit: mm). .

  The engine durability was evaluated for 800 hours with a high-speed simulation pattern in which idling (900 rpm) to throttle full open (5000 rpm) was combined. This is equivalent to about 100,000 km in terms of travel distance.

  The gap enlargement amount is an enlargement amount of the discharge gap 50 from the initial gap. In FIG. 3, in each protrusion amount t, the portion indicated by hatching is the gap enlargement due to wear of the center electrode side tip 35, and the portion indicated by hatching is the gap enlargement due to wear of the ground electrode side tip 45, The sum of both of these gap enlargements is the gap enlargement amount of the discharge gap 50.

  For example, when the protruding amount t is 1.5 mm, the gap enlargement due to the consumption of the center electrode side tip 35 is 0.2 mm, and the gap enlargement due to the consumption of the ground electrode side tip 45 is 0.45 mm. The gap enlargement amount is 0.65 mm.

The example shown in Figure 3, the noble metal tip 35 and 45 used in the evaluation, the center side, cross-sectional area (chip cross-sectional area) to the ground both A is 0.1mm ² Ir-10Rh (Ir90 wt%, RH10 weight % Alloy). This is a fairly severe condition for wear. The cross-sectional area A of the chip is the area of the cross section in the direction orthogonal to the protruding direction.

  Further, the projecting amount t of 0 is a conventional spark plug in which the ground electrode side chip 45 is embedded in the facing surface 43 of the ground electrode 40. Conventionally, when the ground electrode side chip 45 protrudes, the chip becomes a heat spot and is consumed at an accelerated rate, so that it is not actually realized as a product.

  From FIG. 3, in the conventional spark plug shape (projection amount t = 0), the center electrode side tip 35 is consumed more than the ground electrode side tip 45. In the illustrated example, the consumed amount of the center electrode side chip: the consumed amount of the ground electrode side chip = 4: 1. This is because the center electrode 30 having a negative polarity consumes more sparks than the ground electrode 40, and this consumption form is common in spark plugs.

  On the other hand, in the shape in which the ground electrode side tip 45 is protruded from the facing surface 43 of the ground electrode 40, the larger the protrusion amount t, the more the ground electrode side tip 45 is consumed, and the life of the spark plug is increased. It will be shortened. This is because, as described above, when the ground electrode side chip 45 is protruded, it becomes a heat spot, the chip temperature rises, and the oxidative volatilization consumption due to the high temperature increases.

  FIG. 4 is a diagram showing a result of calculating a consumption volume ratio of only the ground electrode side tip 45 in the engine durability evaluation for the spark plug in which the protruding amount t (unit: mm) of the ground electrode side tip 45 is changed. is there.

In FIG. 4, the black circle plot shows the case where the ground electrode side tip 45 and the center electrode side tip 35 are made of the same composition material (same material: Ir-10Rh) as in FIG. Also, the white circle plot shows a case where a material (oxidation volatility improvement material: Ir-30Rh) having better oxidation volatility than the center electrode side tip 35 is used for the ground electrode side tip 45. Further, the cross-sectional area A of each of the chips 35 and 45 is 0.1 mm ² , which is a condition that is considerably severe with respect to wear.

  In FIG. 4, the consumption volume of the ground electrode side tip 45 is normalized to 1 in the case of the same material with the protrusion amount t being 0. For example, in the case of the same material with a protruding amount t of 1.5 mm, the consumption volume of the ground electrode side tip 45 is about nine times larger than that of the same material with a protruding amount t of 0. Is shown.

  From FIG. 4, when the same material as the center electrode side tip 35 is used for the ground electrode side tip 45, the ground electrode side tip becomes larger if the protruding amount t is larger than 0.3 mm because of the above-mentioned heat spot. It can be seen that the amount of wear of 45 increases significantly.

  On the other hand, when the oxidation volatilization improving material is used for the ground electrode side tip 45, if the protrusion amount t is smaller than 0.3 mm, the consumption amount slightly increases, but the protrusion amount t is 0.3 mm. From the above, it can be seen that the amount of consumption can be greatly reduced.

  This is due to the following reason. When the protrusion amount t is smaller than 0.3 mm, that is, when the ground electrode side chip 45 does not become a heat spot and the chip temperature does not become so high, the ground electrode side chip 45 also has a rate of spark consumption rather than oxidation volatilization consumption. Becomes higher. Therefore, in the ground electrode side chip 45 using the oxidation volatile resistance improving material, the melting point is low and the spark consumption is deteriorated.

  In order to improve the oxidation volatility resistance, an additive that easily oxidizes itself is added to the noble metal constituting the noble metal tip, and an oxide film is formed by this additive to form a kind of protective film. It is done. Therefore, as the oxidation volatility improver, it is preferable to use a material in which the amount of additive element is increased as compared with the center electrode tip 35.

  In this example, an oxidation volatility improving material in which the additive element Rh is increased to 30 wt% with respect to Ir-10Rh of the center electrode side tip 35 is used for the ground electrode side tip 45. However, in general, when the amount of additive element is increased, the melting point is lowered. Therefore, when the protruding amount t is smaller than 0.3 mm and the ratio of spark consumption is high, the case where the oxidation volatilization improving material is used is better. Increases consumption.

  On the other hand, when the protrusion amount t is 0.3 mm or more, that is, when the ground electrode side chip 45 becomes a heat spot and the chip temperature becomes extremely high, the rate of oxidative volatilization consumption becomes higher than the spark consumption. Therefore, when the oxidation volatilization resistance improving material is used, the consumption amount can be greatly reduced with respect to the same material.

  From the examination results shown in FIG. 3 and FIG. 4, in the present embodiment, the ground electrode side tip 45 has a protrusion amount t of 0.3 mm or more and is more resistant to oxidation than the center electrode side tip 35. The first configuration is excellent. As a result, the wear resistance of the ground electrode side tip 45 can be improved, the amount of tip wear can be greatly reduced, and the life of the spark plug S1 can be greatly extended.

  In the example shown in FIG. 4, Ir-10Rh is used for the center electrode side chip 35 and Ir-30Rh is used for the ground electrode side chip 45. However, this is an example, and the present invention is not limited thereto. That is, the same effect can be obtained if a chip having better oxidation resistance and volatility than the center electrode side chip 35 is used for the ground electrode side chip 45 regardless of the type of the main component and additive of the chip.

  In the first configuration, the ground electrode with respect to the maximum oxidation volatilization width Lmax1 of the center electrode side chip 35 after leaving both the center electrode side and ground electrode side chips 35 and 45 in the atmosphere at 1100 ° C. for 30 hours. When the ratio Lmax2 / Lmax1 of the maximum oxidation volatilization width Lmax2 of the side chip 45 is the oxidation volatilization ratio X, it is preferable that X ≦ 0.8.

  This is based on the results of a more specific evaluation of the oxidation volatilization resistance of the ground electrode side chip 45 and the examination of the effect thereof. An example of the examination result will be described with reference to FIGS.

  FIG. 5 is an explanatory diagram showing a method for evaluating oxidation volatility. In this method, the center electrode side chip 35 and the ground electrode side chip 45 are evaluated by the respective maximum oxidation volatilization widths after being left in the atmosphere at a high temperature of 1100 ° C. for 30 hours.

  The cross-sectional shape before the test of each chip 35, 45, that is, the initial shape, is indicated by a broken line in FIG. After being left at the high temperature, the chips 35 and 45 are volatilized and consumed from the outer peripheral side, and are composed of a healthy portion K1 made of the original material and an oxide layer K2 formed on the surface of the healthy portion K1. .

  As shown in FIG. 5, each of the maximum oxidation volatilization widths Lmax1 and Lmax2 is the maximum width of the volatile part K3 that has been volatilized away from the initial shape. The ratio Lmax2 / Lmax1 of the maximum oxidation volatilization width Lmax2 of the ground electrode side chip 45 to the maximum oxidation volatilization width Lmax1 of the center electrode side chip 35 is defined as an oxidation volatilization ratio X.

  FIG. 6 is a diagram showing a result of calculating the consumption volume ratio of the ground electrode side tip 45 by performing the engine durability evaluation on the spark plug having an oxidation volatilization ratio X of 0.2 to 1.2.

In FIG. 6, the consumption volume of the ground electrode side chip 45 is normalized to 1 when the oxidation volatilization ratio X is 0.2. Note that the tip used for the evaluation is a condition that is considerably severe with respect to wear, with the ground electrode side tip 45 having a cross-sectional area A = 0.1 mm ² and a protruding amount t = 1.5 mm. The material composition is all the same.

  As can be seen from FIG. 6, when the oxidation volatilization ratio X exceeds 0.8, the consumption volume of the ground electrode side chip 45 is greatly increased. Therefore, in order to significantly reduce the oxidation volatilization consumption of the ground electrode side chip 45, the oxidation volatilization ratio X is preferably 0.8 or less.

Further, in the first configuration, the cross-sectional area A of the ground electrode tip 45 is at 0.1 mm ² or more 1.15 mm ² or less, the amount of protrusion t is preferably at 1.5mm or less. The basis for this is shown in FIGS.

FIG. 7 is a diagram showing the results of examining the relationship between the cross-sectional area A (unit: mm ² ) of the ground electrode side tip 45 and the consumption volume ratio in the engine durability evaluation described above.

In FIG. 7, the consumption volume of the ground electrode side chip 45 is normalized to 1 when the cross-sectional area A of the ground electrode side chip 45 is 0.1 mm ² . Note that the ground electrode side tip 45 used for the evaluation has a protruding amount t = 1.5 mm and an oxidation volatilization ratio X = 0.8, which is a condition that is considerably severe with respect to wear.

As shown in FIG. 7, when the chip cross-sectional area A is smaller than 0.1 mm ² , the consumption amount of the ground electrode side chip 45 is greatly increased. This is because if the chip cross-sectional area A is too small, the chip temperature rises at an accelerated rate, making it difficult to suppress oxidative volatilization.

Although not shown in the figure, according to the study conducted by the present inventors, when the chip cross-sectional area A is larger than 1.15 mm ² , it is difficult to ensure high ignition performance in the spark plug.

  Further, FIG. 8 is a diagram showing the results of examining the relationship between the protruding amount t (unit: mm) of the ground electrode side tip 45 and the consumption volume ratio in the engine durability evaluation described above.

In FIG. 8, the ground electrode side chip 45 used for the evaluation has a cross-sectional area A = 0.1 mm ² and an oxidation volatilization ratio X = 0.2, 0.8. The cross-sectional area condition is fairly severe against wear. The consumption volume of the ground electrode side tip 45 when the protrusion amount t is 0.3 mm is normalized to 1.

  As shown in FIG. 8, regardless of the oxidation volatilization ratio X, if the tip protrusion amount t is larger than 1.5 mm, the consumption amount of the ground electrode side tip 45 is greatly increased. This is because if the tip protrusion amount t is too large, the tip temperature rises at an accelerated rate, making it difficult to suppress oxidative volatilization.

From the results shown in FIGS. 7 and 8, the cross-sectional area A of the ground electrode side tip 45 is 0.1 mm ² or more and 1.15 mm ² or less in order to ensure high ignitability and suppress oxidation volatilization. It is preferable that the tip protrusion amount t is 1.5 mm or less.

  [Second Configuration] In the spark plug S1 of the present embodiment, in order to improve the wear resistance of the noble metal tips 35, 45 when the protruding amount t of the ground electrode side tip 45 is 0.3 mm or more. May adopt the following second configuration.

  That is, both the center side and ground side chips 35 and 45 are made of an Ir alloy containing at least one additive in Ir exceeding 50 wt%, and the additive contained in the ground electrode side chip 45. The total is 15% by weight or more. The grounds for adopting this second configuration will be described next.

  First, both the tips 35 and 45 in the center electrode and the ground electrode are made of an Ir alloy containing at least one additive in 50% by weight or more of Ir, so that it has a high melting point and excellent heat resistance. Chip characteristics can be secured. Further, the total amount of additives contained in the ground electrode side chip 45 is 15% by weight or more and 50% by weight or less, and this is based on the result shown in FIG.

  FIG. 9 is a diagram showing the results of examining the relationship between the total amount (unit: wt%) of additives contained in the ground electrode side tip 45 and the consumption volume ratio of the ground electrode side tip 45 by engine durability evaluation.

In FIG. 9, Rh, Rh-Pt, and Pt were used as additives contained in Ir that is a base material of the ground electrode side chip 45. The consumption volume of the ground electrode side chip 45 is normalized to 1 when the additive is Rh and the amount is 15% by weight. The ground electrode-side tip 45 used for the evaluation has a protruding amount t = 1.5 mm and a cross-sectional area A = 0.1 mm ² , which is a condition that is considerably severe with respect to wear.

  As shown in FIG. 9, regardless of the type and number of additives added to Ir, if the total amount of additives is less than 15% by weight, it becomes difficult to suppress oxidative volatilization, and the ground electrode side tip The amount of wear of 45 will increase. Further, if the total amount of the additives is larger than 50% by weight, the melting point is lowered, and the consumption amount of the ground electrode side tip 45 is increased.

  Therefore, in order to suppress the consumption amount in the spark plug in which the protruding amount t of the ground electrode side tip 45 is 0.3 mm or more, Ir as a high melting point material is a main component (more than 50% by weight), and at least 1 It is preferable to use a tip made of an Ir alloy containing seed additives, the total of which is 15 wt% or more for the ground electrode side tip 45.

FIG. 9 shows an example in which Rh, Rh—Pt, and Pt are used as additives, but besides these, Ni, W, Pd, Ru, Os, Al, Y, Y ₂ O ₃ , Re Similar results were obtained for the chips to which selenium was added and chips containing three or more of these additives.

  As described above, the spark plug S1 adopting the second configuration instead of the first configuration also results in oxidation volatile resistance when the protruding amount t of the ground electrode side tip 45 is 0.3 mm or more. Since the ground electrode side tip 45 having higher performance than the center electrode side tip 35 can be realized, the wear resistance of the noble metal tip can be improved.

  In the second configuration, the total weight% of additives contained in the ground electrode side tip 45 is 1.5 times or more of the total weight% of additives contained in the center electrode side chip 35. It is preferable that The basis for this is shown in FIG.

  FIG. 10 shows a ratio T2 / T1 where T2 is the total weight% of the additives contained in the ground electrode side tip 45 and T1 is the total weight% of the additives contained in the center electrode side chip 35. It is a figure which shows the result of having investigated about the relationship between a certain addition amount ratio (grounding side chip | tip / center side chip | tip) and the consumption ratio ((DELTA) GAP) which is a gap expansion amount.

  Here, the black circle plot in FIG. 10 shows the result of the engine durability evaluation described above using Ir-10Rh as the center electrode side chip 35. The white circle plot is a result of carrying out engine durability evaluation more severe than the above engine durability evaluation using Ir-15Rh for the center electrode side chip 35.

  In the engine durability evaluation described above, the temperature of the one end portion 41 of the ground electrode 40, that is, the tip temperature is about 950 ° C., whereas in the more severe engine durability evaluation, the tip temperature is set to 1000 by changing the ignition timing. It was as high as ℃. In short, the influence on the gap expansion amount of the spark plug when the addition amount of the center electrode side tip 35 is adapted to the use environment of the spark plug was examined with respect to the total addition amount ratio.

In FIG. 10, the ground electrode side tip 45 is also made of an Ir—Rh alloy, and the weight percentage of Rh in the ground electrode side tip 45 and the weight percentage of Rh in the center electrode side tip 35 is the total addition amount ratio. . The ground electrode-side tip 45 used for the evaluation has a protruding amount t = 1.5 mm and a cross-sectional area A = 0.1 mm ² , which is a condition that is considerably severe with respect to wear.

  In addition, the wear ratio is normalized to 1 when the center electrode tip 35 is Ir-10Rh and the total addition ratio is 1.5. As shown in the case of the protrusion amount t = 1.5 mm in FIG. 3, the gap expansion amount greatly contributes to the consumption of the ground electrode side tip 45.

  From FIG. 10, in order to suppress the oxidation volatilization consumption of the ground electrode side tip 45 and extend the life of the spark plug, the total addition ratio is 1.5 or more regardless of the addition amount of the center electrode side tip 35. Preferably there is.

In FIG. 10, Rh is shown as an additive as an example, but the additive is not limited. In addition, similar results were obtained for Ni, Pt, W, Pd, Ru, Os, Al, Y, and Y ₂ O ₃ . Similar results were also obtained for chips containing two or more of these additives, and for those having different types of additives between the center electrode side chip 35 and the ground electrode side chip 45.

  [Third Configuration] Also, in the spark plug S1 of the present embodiment, in order to improve the wear resistance of the noble metal tips 35, 45 when the protruding amount t of the ground electrode side tip 45 is 0.3 mm or more. May adopt the following third configuration.

  That is, the center electrode side tip 35 is made of an Ir alloy containing Ir as a main component (with Ir exceeding 50% by weight) and containing at least one additive, and the ground electrode side tip 45 is made of Pt as a main component. (Pt exceeding 50% by weight) is made of a Pt alloy containing at least one additive.

  According to the third configuration, an Ir alloy that is a high melting point material is used for the center electrode side tip 35 with a high spark consumption rate, and the ground electrode side tip 45 with a high rate of oxidation and volatilization has excellent oxidation volatility. Pt alloy is used. Therefore, the spark plug S1 adopting the third configuration instead of the first or second configuration can also improve the wear resistance of the noble metal tip, and can greatly extend the life of the spark plug. it can.

Furthermore, in the third configuration, the effect can be further improved by adding the additive in the chips 35 and 45 to Ir, Pt, Rh, Ni, W, Pd, Ru, Os, Al, Y, and Y ₂ O _3. In addition to increasing the chip strength, chip cracks and cracks due to high temperatures can be prevented.

  Here, in the third configuration, the additive contained in the noble metal tip in the ground electrode 40, that is, the ground electrode side tip 45, consists only of those having a melting point higher than Pt, and such an additive is at least It is preferable that 1 type is contained.

  Further, in the third configuration, the additive contained in the ground electrode side chip 45 is composed only of an additive having a smaller linear expansion coefficient than Pt, and contains at least one such additive. The ground electrode side tip 45 is preferably fixed to the ground electrode 40 by laser welding. The basis of the preferable form in these 3rd structures is as follows.

When the ground electrode side chip 45 is made of a Pt alloy containing Pt as a main component and containing at least one additive, the additive includes Ir, Rh, Ni, W, Pd, Ru, Os, al, Y ₂ O _3, Re, and the like. Here, the melting point (° C.) and the linear expansion coefficient (× 106 / ° C.) of Pt are 1769 and 9.0.

On the other hand, the melting point (° C.) and the linear expansion coefficient (× 106 / ° C.) of these additives are Ir 2443, 6.8, Rh 1966, 8.5, Ni 1453, 13.3, W 3400. 4.5, Pd 1552, 11.0, Ru 2250, 9.6, Os 3030, 4.6, Al 660, 23.5, Y ₂ O ₃ 4300, 7.2, Re 3180, 6.6.

  Then, the relationship between the kind of additive contained in the ground electrode side chip 45 and the spark consumption was examined by experiments. An example of the result is shown in FIG.

  FIG. 11 shows the relationship between the composition of the ground electrode side tip 45 and the consumption volume ratio as spark consumption, and the consumption volume ratio is 100 Pt when the composition of the ground electrode side chip 45 is Pt. The consumption volume in the case of consisting of only (no additive) is normalized to 1.

  In FIG. 11, Rh, Ir, Pd, Ni, Ir—Rh, and Ir—Ni are used as the additive contained in the main component Pt in the ground electrode side chip 45. In addition, the evaluation method is such that a spark bench durability test at room temperature is conducted for 700 hours in order to exclude the influence of oxidative volatilization consumption due to high temperature, and the consumption volume ratio after the test is performed is observed.

  As shown in FIG. 11, 100 Pt is the most excellent in spark erosion, but 100 Pt is extremely impractical, and thus has problems such as chip cracking and cracking due to high temperature, and is not practical. Therefore, although the strength is improved by the above-mentioned additive, the amount of spark consumption is increased as shown in FIG. In particular, when even one kind of additive such as Pd or Ni having a melting point lower than that of Pt is contained, the amount of consumption is greatly increased.

  Therefore, in order to suppress the increase in the amount of spark consumption of the ground electrode side tip 45 to the minimum and to improve the strength, as shown in FIG. 11, only an additive having a melting point higher than that of Pt is included. preferable.

  In FIG. 11, Rh, Ir, Pd, Ni, Ir—Rh, and Ir—Ni are used as additives, but other additives and ground electrode side tips 45 containing two or more of these additives are used. The same tendency as in FIG. 11 was obtained.

For these reasons, it is preferable that the additive contained in the ground electrode-side chip 45 consists only of those having a melting point higher than that of Pt, and at least one such additive is contained. Examples of such additives include Ir, Rh, W, Ru, Os, Y ₂ O ₃ , and Re.

  Also, FIG. 12 shows the bonding reliability when the ground electrode side tip 45 of each composition used in FIG. 11 is fixed to the ground electrode 40 by resistance welding and when it is fixed to the ground electrode 40 by laser welding. It is a graph which shows the result of having investigated.

  As a joining reliability test, a spark plug was mounted on the engine and a durability test was conducted. The endurance test was conducted with a 6-cylinder 2000cc engine, and the operating condition was that the engine was kept idle for 1 minute and the throttle fully opened at 6000 rpm for 1 minute for 100 hours.

  The bonding reliability was evaluated by the peeling rate shown in FIG. FIGS. 13A and 13B are cross-sectional views showing the joining form of the ground electrode side tip 45, where FIG. 13A shows the case of resistance welding, and FIG. 13B shows the case of laser welding. In the case of laser welding, a melted portion 47 is formed at the joint between the ground electrode side tip 45 and the ground electrode 40.

  13 (a) and 13 (b), the length of the part that is originally bonded at the interface between the chip 45 and the ground electrode 40 or the interface between the chip 45 and the melted portion 47 (that is, the bonding length) is a, The length of the part which peeled among these joining lengths (namely, peeling length) is shown by b1, b2. Each of these lengths and cut surface shapes can be known by observing the cut surfaces with a metal microscope or the like.

  And the peeling rate in the case of resistance welding shown in FIG. 13A is obtained by {(b1 + b2) / a} × 100 (%), and peeling in the case of laser welding shown in FIG. 13B. The rate is obtained by {(b1 + b2) / (a1 + a2)} × 100 (%).

  Here, after the bonding reliability test, these peeling rates are obtained. In FIG. 12, when these peeling rates are 0 to 25%, “◯”, and when 25 to 50%, “Δ”, 50 When it was% or more, it was shown as “×”.

  From the results shown in FIG. 12, when only an additive having a linear expansion coefficient smaller than Pt such as Rh and Ir is contained, it is difficult to ensure the bonding reliability by resistance welding. Further, in the above-described chip composition having excellent spark depletion in FIG. 11, the bonding reliability tends to be low.

  In addition, as shown in the example of the melting point and linear expansion coefficient data for the additive described above, an additive having a higher melting point than Pt often has a smaller linear expansion coefficient than Pt.

  In this regard, as shown in FIG. 12, it can be seen that laser welding can ensure bonding reliability regardless of the composition of the ground electrode tip. In FIG. 12, Rh, Ir, Pd, Ni, Ir—Rh, and Ir—Ni are used as additives, but other additives and ground electrode side chip 45 containing two or more of these additives are used. The same tendency as in FIG. 12 was obtained.

  Therefore, in the ground electrode side chip 45, in order to achieve both the spark consumption and the bonding reliability, the additive contained in the ground electrode side chip 45 is only one having a smaller linear expansion coefficient than Pt. It is preferable that at least one kind is contained and the ground electrode side tip 45 is fixed by laser welding.

Also in the second and third configurations, the cross-sectional area A of the ground electrode side tip 45, which is a Pt alloy tip, is 0.1 mm ² or more in order to ensure high ignitability and suppress oxidative volatilization. It is preferable that the tip protrusion amount t is 1.15 mm ² or less and 1.5 mm or less. This is the same reason as described above.

  As described above, in the spark plug S1 of the present embodiment, by providing any one of the first, second and third configurations described above, the wear resistance of the noble metal tip can be improved, and the life of the spark plug can be increased. It can be greatly enlarged.

  (Other Embodiments) The noble metal tips 35 and 45 are in any shape such as a cylindrical shape (including an ellipse), a prismatic shape, a conical shape, a rivet shape, etc. on both the center electrode side and the ground electrode side. However, the above-described effects are also exhibited.

  Further, as shown in FIGS. 14A to 14D, the welding of the center electrode 30 and the ground electrode 40 to the noble metal tips 35 and 45 is performed by any welding method such as laser welding, arc welding, resistance welding, or the like. There may be. In FIG. 14, the joint in which the melted portions 37 and 47 are illustrated is laser welding or arc welding, and the joint not illustrated is resistance welding.

As shown in FIG. 15, the ground electrode 40 may house a core material 48 made of, for example, Cu, Cu + Ni clad or the like, which has better thermal conductivity than the base material 49. According to this, the temperature of the front-end | tip part, ie, the one end part 41, of the ground electrode 40 can be reduced, and as a result, the oxidation volatilization consumption of the ground electrode side chip 45 can be further reduced, which is preferable.
In FIG. 15, (a) has a core material 48 made of a Cu material as a good heat conducting material inside, and a ground electrode 40 formed by covering the core material 48 with a base material 49 made of a Ni-based alloy. (B) is a ground electrode 40 in which the core material 48 has a two-layer structure in which a Ni material 48 a is covered with a Cu material 48 b and this is covered with a base material 49.
Further, as shown in FIG. 16, the ground electrode 40 may be disposed obliquely. As a result, the ground electrode 40 can be shortened and the temperature at the tip thereof can be reduced. As a result, the oxidation and volatilization consumption of the ground electrode side chip 45 can be further reduced, which is preferable.

1 is a half sectional view showing an overall configuration of a spark plug for an internal combustion engine according to an embodiment of the present invention. FIG. 2 is an enlarged explanatory view in the vicinity of a discharge gap in the spark plug in FIG. 1. It is a figure which shows the relationship between the protrusion amount t of the ground electrode side chip | tip, and the gap expansion amount by engine durability evaluation. It is a figure which shows the relationship between the protrusion amount t of the ground electrode side chip | tip, and the consumption volume ratio of the ground electrode side chip | tip by engine durability evaluation. It is explanatory drawing which shows the evaluation method of oxidation volatility. It is a figure which shows the relationship between the oxidation volatilization ratio X and the consumption volume ratio of the ground electrode side chip | tip by engine durability evaluation. It is a figure which shows the relationship between the cross-sectional area A of a ground electrode side chip | tip, and the consumption volume ratio of the ground electrode side chip | tip by engine durability evaluation. It is a figure which shows the relationship between the protrusion amount t of the ground electrode side chip | tip, and the consumption volume ratio of the ground electrode side chip | tip by engine durability evaluation. It is a figure which shows the relationship between the sum total of the additive contained in a ground electrode side chip | tip, and the consumption volume ratio of the ground electrode side chip | tip 45 by engine durability evaluation. A total additive amount ratio that is a ratio of a sum of weight percent of additives contained in the ground electrode side tip and a sum of weight percent of additives contained in the center electrode side tip, and a wear ratio that is an amount of gap enlargement. It is a figure which shows the relationship. It is a figure which shows an example of the result of having investigated the relationship between a ground electrode side chip | tip composition and spark consumption. It is a figure which shows an example of the result of having investigated the relationship between a ground electrode side chip composition and joining reliability. It is a figure which shows the evaluation method of the peeling rate as joining reliability shown in FIG. It is a figure which shows the various examples of the welding form of the noble metal tip in this invention. It is a figure which shows the other example of the material of the ground electrode used for this invention. It is a figure which shows the other example of the shape of the ground electrode used for this invention.

Explanation of symbols

30 Center electrode 32 Opposite surface at center electrode 35 Noble metal tip at center electrode (tip at center electrode side)
40 Ground electrode 43 Opposite surface of ground electrode 45 Noble metal tip on ground electrode (ground electrode side tip)
50 Discharge gap

Claims (8)

A center electrode (30);
The center electrode and a ground electrode (40) opposed via the discharge gap (50),
In the spark plug in which the noble metal tip (35, 45) is fixed to the mutually facing surfaces (32, 43) of the center electrode and the ground electrode,
The noble metal tip (45) in the ground electrode is:
Cross-sectional area A is at 0.1 mm ² or more 1.15 mm ² or less,
The protruding amount t from the facing surface of the ground electrode is 0.3 mm or more and 1.5 mm or less,
A spark plug characterized in that oxidation volatility is superior to the noble metal tip (35) in the center electrode. Maximum oxidation volatilization width of the noble metal tip (35) in the center electrode after leaving the noble metal tip (35, 45) in the center electrode (30) and the ground electrode (40) in the atmosphere at 1100 ° C. for 30 hours 2. The relation according to claim 1, wherein when the ratio Lmax2 / Lmax1 of the maximum oxidation volatilization width Lmax2 of the noble metal tip (45) in the ground electrode with respect to Lmax1 is an oxidation volatilization ratio X, X ≦ 0.8. Spark plug. Both the noble metal tips in the center electrode and the ground electrode are made of an Ir alloy containing at least one additive in Ir exceeding 50 wt%,
The spark plug according to claim 1, wherein the total amount of additives contained in the noble metal tip in the ground electrode is 15 wt% or more. The sum of the weight percent of the additive contained in the noble metal tip (45) in the ground electrode (40) is the sum of the weight percent of the additive contained in the noble metal tip (35) in the center electrode (30). The spark plug according to claim 3, wherein the spark plug is 1.5 times or more. The noble metal tip (35) in the center electrode is made of an Ir alloy containing at least one additive in Ir exceeding 50% by weight;
The spark plug according to claim 1, wherein the noble metal tip in the ground electrode is made of a Pt alloy containing at least one additive in Pt exceeding 50 wt%. Additives contained in the noble metal tips (35, 45) in the center electrode (30) and the ground electrode (40) are Ir, Pt, Rh, Ni, W, Pd, Ru, Os, Al, Y, Y ₂ O _3, Re spark plug according to any one of claims 3 to 5, characterized in that at least one. The additive contained in the noble metal tip (45) in the ground electrode (40) is only one having a melting point higher than that of Pt and at least one additive. Spark plug as described in. The additive contained in the noble metal tip (45) in the ground electrode (40) is only one having a linear expansion coefficient smaller than that of Pt and at least one additive, and the additive in the ground electrode The spark plug according to claim 5 or 7, wherein the noble metal tip is fixed by laser welding.

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