Spark plug electrode and spark plug

A spark plug electrode is provided, in which an electrode member in which a total of 0.3 to 7.5 wt % of at least one of Ta and Nb is added to an IrRh alloy is provided at a discharge part.

BACKGROUND

1. Technical Field

The present disclosure relates to an electrode to be used for a spark plug of an internal combustion engine.

2. Related Art

There is a spark plug electrode in which an IrRh alloy in which 3 to 30 wt % of Rh (rhodium) is added to Ir (iridium) is used as an electrode member for a discharge part.

SUMMARY

The present disclosure provides a spark plug electrode. As an aspect of the present disclosure, a spark plug electrode is provided, in which an electrode member in which a total of 0.3 to 7.5 wt % of at least one of Ta and Nb is added to an IrRh alloy is provided at a discharge part.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Conventionally, among spark plug electrodes, there is a spark plug electrode in which an IrRh alloy in which 3 to 30 wt % of Rh (rhodium) is added to Ir (iridium) is used as an electrode member for a discharge part. According to the spark plug electrode disclosed in Japanese Patent No. 2877035 (JP 2877035 B), excellent high-temperature heat resistance is provided, while wear resistance can be improved.

In recent years, in an internal combustion engine, to realize higher output and improve fuel efficiency, a current and a voltage of a spark plug are made increasingly higher. It is therefore desired to further improve wear resistance for a spark plug electrode.

The present disclosure has been made to solve the above-described problem, and is mainly directed to providing a spark plug electrode which can realize further improved wear resistance.

A first aspect of the disclosure for solving the above-described problem is a spark plug electrode, in which an electrode member in which a total of 0.3 to 7.5 wt % of at least one of Ta and Nb is added to an IrRh alloy is provided at a discharge part.

According to the above-described configuration, the electrode member is provided at the discharge part of the spark plug electrode. Therefore, discharging of the spark plug is performed at the electrode member. The electrode member is an IrRh alloy, preferably an IrRh alloy contains 5 to 50 wt % of Rh, and more preferably an IrRh alloy contains 5 to 30 wt % of Rh. Therefore, it is possible to suppress volatilization and consumption of Ir due to generation of an oxide at high temperatures, with Rh which is less likely to volatilize at high temperatures.

Further, in the electrode member, a total of 0.3 to 7.5 wt %, preferably a total of 0.3 to 6 wt % of at least one of Ta (tantalum) and Nb (niobium) is added to the above-described IrRh alloy. It has been confirmed by the discloser of the present application that wear resistance is improved by a total of equal to or greater than 0.3 wt % of at least one of Ta and Nb being added to the IrRh alloy. Because melting points of Ta and Nb are higher than that of Rh, it is estimated that melting and scattering of the electrode member upon spark discharge can be suppressed. However, it has been confirmed by the discloser of the present application that, if a total additive amount of Ta and/or Nb exceeds 6 wt % and becomes equal to or greater than 8 wt %, wear resistance is lowered. It is believed that wear resistance is lowered due to grain boundaries becoming brittle as a result of Ta and/or Nb segregating at the grain boundary. Concerning this point, according to the above-described configuration, it is possible to further improve wear resistance of the spark plug electrode. Further, in the electrode member, it is also possible to add 0.3 to 7.5 wt %, preferably 0.3 to 6 wt % of Ta to the above-described IrRh alloy without adding Nb.

In a second aspect of the disclosure, a total of 1 to 5 wt % of at least one of Ta and Nb is added to the electrode member. It has been confirmed by the discloser of the present application that wear resistance is further improved by a total of 1 to 5 wt % of at least one of Ta and Nb being added to the IrRh alloy. Therefore, according to the above-described configuration, it is possible to further improve wear resistance of the spark plug electrode. Further, it is also possible to add 1 to 5 wt % of Ta to the electrode member without adding Nb.

In a third aspect of the disclosure, a total of 0.3 to 3 wt % of at least one of Ni (nickel) and Co (cobalt) is added to the electrode member. It has been confirmed by the discloser of the present application that wear resistance is improved by a total of equal to or greater than 0.3 wt % of at least one of Ni and Co being added to a material in which a total of 0.3 to 7.5 wt %, preferably a total of 0.3 to 6 wt % of at least one of Ta and Nb is added to the IrRh alloy. It is estimated that volatilization and consumption of Ir due to generation of an oxide can be suppressed by at least one of Ni and Co being added. However, it has been confirmed by the discloser of the present application that, if a total additive amount of Ni and/or Co exceeds 3 wt %, wear resistance is lowered. It is believed that this is because melting points of Ni and Co are lower than those of Ir and Rh, so that melting and scattering of the electrode member upon spark discharge increase. Concerning this point, according to the above-described configuration, it is possible to further improve wear resistance of the spark plug electrode. Further, it is also possible to add a total of 0.3 to 3 wt % of at least one of Ni and Co to a material in which 0.3 to 7.5 wt %, preferably 0.3 to 6 wt % of Ta is added to the IrRh alloy, without Nb being added.

In a fourth aspect of the disclosure, a total of 0.5 to 1.5 wt % of at least one of Ni and Co is added to the electrode member. It has been confirmed by the discloser of the present application that wear resistance is further improved by a total of 0.5 to 1.5 wt % of at least one of Ni and Co being added to a material in which a total of 0.3 to 7.5 wt %, preferably a total of 0.3 to 6 wt % of at least one of Ta and Nb is added to the IrRh alloy. Therefore, according to the above-described configuration, it is possible to further improve wear resistance of the spark plug electrode. Further, it is also possible to add a total of 0.5 to 1.5 wt % of at least one of Ni and Co to a material in which 0.3 to 7.5 wt %, preferably 0.3 to 6 wt % of Ta is added to the IrRh alloy without Nb being added.

A fifth aspect of the disclosure is a spark plug including the spark plug electrode according to any one of the first to the fourth aspects.

The above and other objects, features and advantages of the present disclosure will become more clear from the following detailed description with reference to the accompanying drawings.

An embodiment embodied in a spark plug to be used at an internal combustion engine will be described below with reference to the drawings.

As illustrated inFIG. 1, a spark plug10includes a cylindrical housing11formed of a metal material such as iron. A screw portion11ais formed around an outer periphery at a lower portion of the housing11.

Inside the housing11, a lower end portion of cylindrical insulating glass12is coaxially inserted. The insulating glass12is formed of an insulating material such as alumina. The housing11and the insulating glass12are integrally coupled by an upper end portion11bof the housing11being pressed against the insulating glass12. Then, a center electrode13is inserted into a through-hole12a(hollow portion) and held at a lower portion (one end portion) of the insulating glass12.

The center electrode13(spark plug electrode) is formed in a columnar shape using a Ni alloy which excels in heat resistance, or the like, as a base material. Specifically, an inner material (core material) of the center electrode13is formed of copper, and an outer material (skin material) is formed of a Ni (nickel)-based alloy. A tip portion13aof the center electrode13is exposed from a lower end (one end) of the insulating glass12.

At a position facing the tip portion13aof the center electrode13, a ground electrode14which integrally curves and extends from a lower end face (one end face) of the housing11is disposed. The ground electrode14(spark plug electrode) is also formed of a Ni-based alloy.

As illustrated inFIG. 2, a discharge part of the spark plug10is constituted by the tip portion13aof the center electrode13and a tip portion14aof the ground electrode14, which faces the tip portion13a. Noble metal chips15and16are respectively attached to the tip portion13aof the center electrode13and the tip portion14aof the ground electrode14. The noble metal chips15and16(electrode members) are respectively joined to the tip portions13a,14athrough joining processing such as laser welding and resistance welding. A spark gap17is formed between the noble metal chip15and the noble metal chip16. That is, a spark is formed by discharge being performed between the noble metal chip15and the noble metal chip16.

The noble metal chips15and16are both formed in a columnar shape. For example, an outer diameter A of the noble metal chip15is 1.0 mm, and a height B is 1.5 mm. An outer diameter C of the noble metal chip16is 1.0 mm, and a height D is 0.5 mm.

Returning toFIG. 1, as is known, a central axis18and a terminal portion19are electrically connected at an upper portion of the center electrode13. An external circuit which applies a high voltage for spark generation is connected to the terminal portion19. Further, a gasket20to be used for attachment to the internal combustion engine is provided at an upper end portion of the screw portion11aof the housing11.

The noble metal chips15and16are formed of an IrRh alloy containing Rh (rhodium) using Ir (iridium) which has a high melting point and which excels in wear resistance as a base, to suppress high-temperature volatility of Ir. The IrRh alloy can suppress oxidation and volatilization of Ir from a crystal grain boundary in a high-temperature gas or in an oxidizing atmosphere. Preferably an IrRh alloy containing 5 to 50 wt % of Rh, more preferably an IrRh alloy containing 5 to 30 wt % of Rh can suppress oxidization and volatilization of Ir from a crystal grain boundary in a high-temperature gas or in an oxidizing atmosphere. The discloser of the present application has found that wear resistance is improved by Ta being added to the IrRh alloy. Note that, in the above-described IrRh alloy, a component except Rh and Ta is Ir.

FIG. 3is a graph indicating a result of a wear resistance test of the noble metal chip15of the IrRh alloy to which Ta is added. In the wear resistance test, ignition (spark discharge) to a fuel is performed for 50 hours at 5,600 rpm with the spark plug10fitted to the internal combustion engine.FIG. 3indicates a ratio of a consumed amount of the noble metal chip15for which an additive amount of Ta is changed while a consumed amount (volume decrease amount) of the noble metal chip15in a first comparison example in which Ta is not added is set as 1.FIG. 3indicates cases where a contained amount of Rh is respectively 5 wt %, 10 wt %, 30 wt % and 50 wt %.

As illustrated inFIG. 3, in all cases where the contained amount of Rh is 5 wt %, 10 wt %, 30 wt % and 50 wt %, the consumed amount of the noble metal chip15decreases in a range where the additive amount of Ta is between 0.3 and 7.5 wt %, preferably in a range where the additive amount of Ta is between 0.3 and 6 wt %. Particularly, in a range where the additive amount of Ta is between 1.0 and 5.0 wt %, the consumed amount of the noble metal chip15prominently decreases. Because a melting point (3027° C.) of Ta is higher than a melting point (1960° C.) of Rh, it is estimated that melting and scattering of the noble metal chip15upon spark discharge can be suppressed.

Note that, if the additive amount of Ta exceeds 6 wt % and becomes equal to or greater than 8 wt %, the consumed amount of the noble metal chip15is greater than that in the first comparison example (consumption rate=1). It is believed that this is because wear resistance is lowered due to grain boundaries becoming brittle as a result of Ta segregating at the grain boundary.

FIG. 4is a graph indicating a result of a wear resistance test of the noble metal chip15of the IrRh alloy to which Ta and Ni are added. In the wear resistance test, ignition of a fuel is performed for 50 hours at 5,600 rpm with the spark plug10fitted to the internal combustion engine.FIG. 4indicates a ratio of a consumed amount of the noble metal chip15for which an additive amount of Ni (nickel) is changed while a consumed amount of the noble metal chip15in a second comparative example in which the contained amount of Rh is 10 wt % and Ta is added is set as 1.FIG. 4indicates cases where the additive amount of Ta is respectively 0.3 wt %, 3.0 wt %, and 8.0 wt %. Note that, in the above-described IrRh alloy, a component except Rh, Ta and Ni is Ir.

As illustrated inFIG. 4, in all cases where the additive amount of Ta is 0.3 wt %, 3.0 wt % and 8.0 wt %, the consumed amount of the noble metal chip15decreases in a range where the additive amount of Ni is between 0.3 and 3 wt %. Particularly, in a range where the additive amount of Ni is between 0.5 and 1.5 wt %, the consumed amount of the noble metal chip15prominently decreases. It is estimated that volatilization and consumption of Ir due to generation of an oxide can be suppressed by Ni whose melting point of an oxide is high being added.

Note that, if the additive amount of Ni becomes equal to or greater than 4 wt % (exceeds 3 wt %), the consumed amount of the noble metal chip15becomes greater than that in the second comparative example. It is believed that this is because melting and scattering of the noble metal chip15upon spark discharge increases because the melting point (1450° C.) of Ni is lower than a melting point (2454° C.) of Ir and a melting point (1960° C.) of Rh.

Therefore, in the noble metal chips15and16in the present embodiment, 0.3 to 7.5 wt % of Ta, preferably 0.3 to 6 wt % of Ta, more preferably 1 to 5 wt % of Ta is added to the IrRh alloy, and preferably the IrRh alloy contains 5 to 50 wt % of Rh, more preferably the IrRh alloy contains 5 to 30 wt % of Rh. Further, in the noble metal chips15and16, 0.3 to 3 wt % of Ni, preferably 0.5 to 1.5 wt % of Ni is added.

The present embodiment which has been described in detail above has the following advantages.

The noble metal chips15and16are an IrRh alloy, preferably an IrRh alloy contains 5 to 50 wt % of Rh, and more preferably an IrRh alloy contains 5 to 30 wt % of Rh. Therefore, it is possible to further suppress volatilization and consumption of Ir due to generation of an oxide at high temperatures, with Rh which is less likely to volatilize at high temperatures.

In the noble metal chips15and16, 0.3 to 7.5 wt % of Ta, preferably 0.3 to 6 wt % of Ta is added to the above-described IrRh alloy. By equal to or greater than 0.3 wt % of Ta being added to the IrRh alloy, wear resistance is improved. However, if the additive amount of Ta exceeds 6 wt % and becomes equal to or greater than 8 wt %, wear resistance is lowered. Concerning this point, according to the above-described configuration, it is possible to further improve wear resistance of the noble metal chips15and16(the center electrode13and the ground electrode14).

In the noble metal chips15and16, 1 to 5 wt % of Ta is added. By 1 to 5 wt % of Ta being added to the IrRh alloy, wear resistance is further improved. Therefore, it is possible to further improve wear resistance of the noble metal chips15and16.

In the noble metal chips15and16, 0.3 to 3 wt % of Ni is added. By equal to or greater than 0.3 wt % of Ni being added to a material in which 0.3 to 8 wt % of Ta is added to the IrRh alloy, wear resistance is improved. However, if the additive amount of Ni exceeds 3 wt %, wear resistance is lowered. Concerning this point, according to the above-described configuration, it is possible to further improve wear resistance of the noble metal chips15and16.

In the noble metal chips15and16, 0.5 to 1.5 wt % of Ni is added. By 0.5 to 1.5 wt % of Ni being added to a material in which 0.3 to 8 wt % of Ta is added to the IrRh alloy, wear resistance is further improved. Therefore, it is possible to further improve wear resistance of the noble metal chips15and16.

Note that the above-described embodiment can be changed and implemented as follows. The same reference numerals will be assigned to portions which are the same as those in the above-described embodiment, and description will be omitted.

FIG. 3indicates a consumed amount of the noble metal chip15in which Ta is added to the IrRh alloy. In contrast, it is also possible to provide similar effects even if Nb (niobium) which belongs to the same group5element is added in place of Ta. In short, by a total of 0.3 to 7.5 wt %, preferably a total of 0.3 to 6 wt %, more preferably a total of 1 to 5 wt % of at least one of Ta and Nb being added to the IrRh alloy, it is possible to further improve wear resistance of the noble metal chips15and16. Note that, in the above-described IrRh alloy, a component except Rh, Ta and Nb is Ir.

FIG. 4indicates the consumed amount of the noble metal chip15in which Ni is added to a material in which the contained amount of Rh is 10 wt % and Ta is added. In contrast, it is possible to provide similar effects even if Co (cobalt) which has similar chemical properties is added in place of Ni. In short, by a total of 0.3 to 3 wt %, preferably a total of 0.5 to 1.5 wt % of at least one of Ni and Co being added to a material in which a total of 0.3 to 7.5 wt %, preferably a total of 0.3 to 6 wt % of at least one of Ta and Nb is added to the IrRh alloy, it is possible to further improve wear resistance of the noble metal chips15and16. Note that, in the above-described IrRh alloy, a component except Rh, Ta, Nb, Ni and Co is Ir. Further, it is estimated that volatilization and consumption of Ir due to generation of an oxide can be suppressed also by Cr (chrome) and Re (rhenium) being added. Therefore, by a total of 0.3 to 3 wt %, preferably a total of 0.5 to 1.5 wt % of at least one of Ni, Co and Cr being added to a material in which a total of 0.3 to 7.5 wt %, preferably a total of 0.3 to 6 wt % of at least one of Ta, Nb and Re is added to the IrRh alloy, it is possible to further improve wear resistance of the noble metal chips15and16. Note that, in the above-described IrRh alloy, a component except Rh, Ta, Nb, Re, Ni, Co and Cr is Ir.

It is also possible to form the whole of the tip portion13a(electrode member) of the center electrode13with a material which is the same as that of the noble metal chip15.

It is also possible to form the whole of the tip portion14a(electrode member) of the ground electrode14with a material which is the same as that of the noble metal chip16.

It is also possible to provide an electrode member corresponding to the noble metal chips15and16at one of the tip portion13a(discharge part) of the center electrode13and the tip portion14a(discharge part) of the ground electrode14.

While the present disclosure has been described with reference to the examples, it is understood that the present disclosure is not limited to the examples and structures. The present disclosure incorporates various modified examples and modifications within an equivalent range. In addition, various combinations, forms, and other combinations and forms including only one element or more or less elements fall within the scope and the scope of mind of the present disclosure.