JP5590979B2 - Spark plug electrode material with excellent spark wear resistance - Google Patents

Description

  The present invention relates to a material constituting a center electrode and a ground electrode of a spark plug, and provides a material having excellent durability, particularly durability against spark consumption and excellent discharge characteristics.

  An ignition plug for an internal combustion engine is required to have excellent wear resistance so that it can be used for a long time even in a harsh environment in a combustion chamber. In order to satisfy such required characteristics, materials composed of Ir, Pt, Ni, and alloys thereof are used as constituent materials of the center electrode and the ground electrode, which are the main members (Patent Document 1). These materials are known as excellent plug electrode materials that have a high melting point and are not easily oxidized and consumed even in a high-temperature, high-oxidation combustion chamber.

JP 2009-295427 A

  By the way, the development of materials for plug electrodes is often focused on improving the durability as described above, but as long as it is used for electrodes (discharge electrodes), its discharge characteristics are also important. I can say that. Particularly in recent automobile engines, the internal temperature has been increased and precise electronic control has progressed, and although discharge characteristics can be an important index for material selection, there have been few such studies.

  In addition, as described above, many examples of studies on the durability of conventional plug electrode materials have been focused on the development of a material having a high melting point and low consumption due to oxidation even in a highly oxidizing atmosphere. However, the consumption of the plug electrode includes not only oxidation consumption but also spark consumption due to sparks constantly generated during use. Therefore, although there is no mistake in the conventional policy itself, it can be said that it is necessary to clearly add a viewpoint regarding resistance to spark consumption.

  Therefore, the present invention provides a material for a plug electrode that is excellent not only in oxidation resistance but also in spark consumption, and further considering discharge characteristics during use.

  The present invention that solves the above-mentioned problems is a plug electrode material, comprising 5% by mass to 30% by mass of Cu, 0.1% by mass to less than 10% by mass of Rh, and comprising the balance Pt. It is.

  The plug electrode material according to the present invention is a ternary alloy obtained by adding Cu (copper) to platinum and further adding Rh (rhodium) which is a noble metal. Thus, the composite of the two kinds of metals Cu and Rh can reduce the discharge voltage and improve the durability against spark consumption. This means that the object of the present invention cannot be achieved by adding only Cu or Rh. That is, when only Cu is added, the effect of improving the spark erosion is thin, whereas an alloy containing only Rh (corresponding to the prior art) cannot be expected to reduce the discharge voltage.

  In the present invention, the amount of each alloy metal added is limited. According to the present inventors, when the amount of each metal added is outside the proper range, the spark consumption and discharge characteristics are deteriorated and the oxidation consumption is increased. That is, it is necessary to limit the amount of each alloy metal added in order to achieve a good balance of spark consumption, discharge characteristics, and oxidation consumption.

  Hereinafter, the configuration of the Pt alloy according to the present invention will be described in more detail. Cu mainly has the effect of reducing the discharge voltage of the alloy material. The amount of addition is set to 5 to 30% by mass, when the amount is less than 5% by mass, the discharge voltage is less likely to decrease. Moreover, 8 mass% or more is preferable and, as for content of Cu, 10 mass% or more is especially preferable. This is because the discharge voltage is particularly low.

  The Pt alloy of the present invention contains 0.1% by mass or more and less than 10% by mass of Rh in addition to the above Cu content. By including a small amount of Rh, the discharge voltage is further reduced, and the consumption of the electrode due to spark discharge is reduced. Specifically, the consumption area after spark discharge is reduced to about 40% compared to a Pt alloy containing only Cu. In addition, variations in discharge voltage are reduced, and voltage stability is improved. The present invention is characterized in that even if the Rh content is small as described above, the plug material has high wear resistance and excellent discharge characteristics. This is because when the content of Rh is high, it is difficult to dissolve at the time of manufacturing the alloy, and the manufactured alloy tends to be difficult to process.

  The content of Rh is 0.1% by mass or more and less than 10% by mass. If the content is less than 0.1% by mass, it is difficult to obtain the effect of suppressing the consumption due to spark discharge. This is because it tends to vary. Rh is preferably 0.3% by mass to 9.5% by mass and particularly preferably 0.7% by mass to 8.5% by mass. The discharge voltage tends to be particularly low.

  The Pt alloy of the present invention described above can be manufactured by mixing constituent metals, melting and casting, and using the obtained Pt alloy as a plate or wire and then cutting it to a desired length It can be used as a spark plug by processing it into a noble metal tip.

  The Pt alloy of the present invention is a plug material that has both high temperature oxidation resistance and spark resistance consumption. In addition, the material has less variation in discharge voltage and improved stability.

The evaluation result of the wear resistance with respect to Rh content of a Pt-Cu-Rh alloy (Cu concentration 10 mass%).

  Hereinafter, preferred embodiments of the present invention will be described. First, as a preliminary test, characteristics of a Pt—Cu alloy were evaluated in order to confirm the influence on the discharge characteristics due to the addition of Cu to Pt.

  As raw materials, small pieces (dimensions: 2 to 10 mm) of Pt and alloy metal (Cu) were prepared and loaded into a water-cooled copper mold so as to have a predetermined alloy composition. And it melt | dissolved and casted in the inert gas by the high frequency induction heating method (floating dissolution method). The melting conditions were an output of 40 kW and a frequency of 250 kHz, and the entire alloy was melted to obtain a uniform composition. After the alloy was melted, the output was controlled, and the alloy was gradually cooled at a cooling rate of 200 ° C./min to discharge the residual gas, thereby producing a marble ingot (diameter 15 mm, thickness 8 mm) having no voids. Next, the manufactured marble ingots were arranged in contact with each other on a water-cooled copper mold, and the contact portions were irradiated with an argon arc to be melted and joined.

  After the marble ingot was integrated, it was hot forged and formed into a 12 mm square ingot. Then, groove rolling, swaging, and die drawing were performed to obtain a wire having a diameter of 0.6 mm. In these processing steps, heat treatment at 1000 ° C. to 1200 ° C. was performed at the stage of reducing the cross-sectional area from 20% to 50%. A noble metal tip having a length of 0.8 mm was cut out from this wire. In the process of the above processing, there was no noticeable crack or disconnection in the work material. Further, when the metal structure of the processed wire was observed, it was a homogeneous material with a uniform crystal grain size. About the obtained noble metal chip | tip, the residual rate after high temperature oxidation and the discharge characteristic were evaluated as follows.

[High temperature oxidation resistance]
The manufactured high temperature oxidation resistance of the precious metal tip was evaluated. The chip was heated in the atmosphere at 1200 ° C. for 50 hours, and the residual ratio was calculated by measuring the weight before and after the test.

[Discharge characteristics]
The discharge voltage was measured using a φ0.6 mm noble metal wire. The noble metal wire is a center electrode and a ground electrode, and the gap between them is 1.0 mm. Discharge for 140 hours in a nitrogen atmosphere (6 atm) and measure voltage for about 2 minutes at 28-minute intervals. The maximum voltage and average voltage in each measurement section were obtained, and the maximum value of the entire maximum voltage, the average value of the average voltage, and the standard deviation of each were calculated.

  The amount of consumption due to spark consumption was also evaluated. The spark consumption was evaluated by measuring the size of the tip of the noble metal tip before and after the discharge characteristics and measuring the consumption area.

  From Table 1, it was found that the Pt alloy is effective in reducing the average voltage by containing Cu. On the other hand, an increase in the Cu content tends to lower the residual rate due to high-temperature oxidation of the Pt alloy. For this reason, the present invention takes into consideration the balance between a decrease in discharge voltage and consumption due to high-temperature oxidation, with a discharge voltage of 10 kV or less and a high-temperature oxidation residual ratio of 85% or more as references. Mass%.

  Next, a noble metal tip made of a Pt—Cu—Rh alloy was prepared, and the remaining rate after high-temperature oxidation and discharge characteristics were evaluated. The precious metal tip was manufactured in the same manner as in the preliminary test, and the remaining rate after high-temperature oxidation, the discharge characteristics, and the evaluation of the amount of spark consumption thereafter were also the same.

  The evaluation results are shown in Table 2. Table 2 shows the evaluation results of noble metal tips made of Pt—Cu alloy (Cu 10%) as a comparison. FIG. 1 shows the evaluation results for an alloy in which the Cu concentration is fixed (10% by mass) and the Rh concentration is changed.

  From Table 2 and FIG. 1, it has confirmed that the reduction of a spark consumption area was seen by further adding Rh to a Pt-Cu alloy. Further, regarding the discharge characteristics, it has been found that in addition to the decrease in the average voltage, the effect of decreasing the maximum voltage also occurs, and the variation (standard deviation) thereof also decreases. However, if Rh is added in excess of 10% by mass, the effect of improving the discharge characteristics is diminished, so Rh should be in a range not exceeding 10% by mass.

  The present invention is a plug electrode material that has high wear resistance and can be used for a long period of time. In addition, there is little variation in the discharge voltage, and stability when using the plug is improved.

Claims (1)

In plug electrode materials,
Plug electrode material comprising Cu of 5% by mass to 30% by mass, Rh of 0.7% by mass to 8.5% by mass, and the balance being Pt

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