【発明の詳細な説明】[Detailed description of the invention]
（産業上の利用分野）
この発明は火花ギヤツプを形成する中心電極、
外側電極の火花放電部に特定配合のPt合金より
なる貴金属小片を配設してなるスパークプラグに
関する。
（従来の技術）
従来、スパークプラグの電極消耗を少なく耐久
性を向上する方法として、ニツケル合金等の卑金
属からなる電極に代え、火花放電部に耐熱性、耐
酸化性の優れた貴金属小片電極を用いることは知
られており、そのためにPt−Ir合金を少量使用し
たスパークプラグが提案されているが、このスパ
ークプラグは1000〜1100℃以上の熱サイクル負荷
下での貴金属小片の剥離性、長時間使用に伴う火
花消耗性について問題があり、又剥離安定性と火
花消耗を満足するためにクラツド構造とすること
も提案されているが、材料コスト、生産性の点で
高価なものとなつた。
（発明が解決しようとする問題点）
そこで、これら問題を改善する観点から特願昭
58−100316で電極の火花放電部にPt−Pd合金を
使用することを提案したが、冷熱サイクル時に結
晶粒成長に伴う粒界割れが生じる問題が起つた。
（問題点を解決するための手段）
本発明はPt−Pd合金における冷熱サイクル時
の結晶粒成長に伴う粒界割れの問題を解決しよう
とするものであつて、電極の火花放電部の貴金属
小片の材質がPd15〜60重量％、結晶粒成長抑制
のためNi，Ｙ，Ru，Rh，Moの少なくとも１種
２〜20重量％と残部Ptからなる合金で合成した
ことにより耐久性に優れ、プラグの長寿命化をよ
り低コストでなしたスパークプラグを提供しよう
とするものである。
（実施例）
以下、本発明ほ具体的に説明する。
第１図は本発明スパークプラグの発火部の要部
断面図であり、図中１は機関取付ねじを具えた主
体金具、２は前記主体金具１の内腔内に封入固定
されたアルミナ磁器等からなる絶縁体、３は前記
絶縁体２の軸孔内にその先端面より突出して封着
された内部に銅芯を配したニツケル合金からなる
中心電極、４は前記中心電極３の火花放電部３ａ
に接合された貴金属小片電極、５は主体金具１の
端面１ａより突設されたニツケル合金等からなる
外側電極、６は前記外側電極の火花放電部５ａに
形成された貴金属小片であり、上記中心電極３の
貴金属小片４の先端面との間に火花ギヤツプ７を
形成したスパークプラグである。
火花放電部に配設する本発明の貴金属小片４及
び６の材質は、Pdが15〜60重量％と残部Ptより
なるPt−Pd合金に第三元素としてNi，Ｙ，Ru，
Rh，Moの少なくとも１種を２〜20重量％の範囲
内で添加することにより、高温時の結晶粒成長抑
制効果、耐火花消耗性に有効であることを見出し
たものである。
即ち、実施例ではPt−30Pd（30重量％添加した
Pd）合金に種々の第三元素を配合した表１に示
すNo.２〜９の合金を用い、これをニツケル合金
（２％Si，２％Cr，２％Alと残Ni合金）の中心電
極母材３の凹部３ｂにそれぞれ0.4mmの貴金属小
片を電気抵抗溶接にて接合したもので性能を比較
した。なお性能評価のうち、結晶粒成長抑制効果
としては大気中1000℃×10Hr熱処理後の結晶粒
度No（オーステナイド粒度）と、バーナーによる
1100℃×３分と放冷３分×500∞の冷熱サイクル
後の粒界亀裂によつて比較した。
(Industrial Application Field) This invention provides a center electrode that forms a spark gap;
This invention relates to a spark plug in which precious metal pieces made of a Pt alloy with a specific composition are arranged in the spark discharge part of an outer electrode. (Prior art) Conventionally, as a method to reduce electrode wear and improve durability of spark plugs, instead of electrodes made of base metals such as nickel alloys, small pieces of precious metal electrodes with excellent heat resistance and oxidation resistance were used in the spark discharge area. For this purpose, a spark plug using a small amount of Pt-Ir alloy has been proposed. There is a problem with spark consumption over time, and a clad structure has been proposed to satisfy peeling stability and spark consumption, but it is expensive in terms of material cost and productivity. . (Problems to be solved by the invention) Therefore, from the perspective of improving these problems, the patent application
58-100316 proposed the use of a Pt-Pd alloy for the spark discharge part of the electrode, but a problem occurred in which intergranular cracking occurred due to grain growth during cooling and heating cycles. (Means for Solving the Problems) The present invention aims to solve the problem of grain boundary cracking caused by crystal grain growth during cooling and heating cycles in Pt-Pd alloys. The material of the plug is composed of an alloy consisting of 15 to 60% by weight of Pd, 2 to 20% by weight of at least one of Ni, Y, Ru, Rh, Mo to suppress grain growth, and the balance Pt, resulting in excellent durability. The aim is to provide a spark plug that has a longer service life at a lower cost. (Example) The present invention will be described in detail below. FIG. 1 is a cross-sectional view of the main parts of the ignition part of the spark plug of the present invention, in which 1 is a metal shell equipped with engine mounting screws, and 2 is alumina porcelain etc. sealed and fixed in the inner cavity of the metal shell 1. 3 is a center electrode made of a nickel alloy with a copper core arranged inside the shaft hole of the insulator 2 and sealed to protrude from its tip surface; 4 is a spark discharge portion of the center electrode 3; 3a
5 is an outer electrode made of a nickel alloy or the like that protrudes from the end surface 1a of the metal shell 1; 6 is a small precious metal piece formed in the spark discharge portion 5a of the outer electrode; This is a spark plug in which a spark gap 7 is formed between an electrode 3 and the tip end surface of a small precious metal piece 4. The material of the precious metal pieces 4 and 6 of the present invention disposed in the spark discharge part is a Pt-Pd alloy consisting of 15 to 60% by weight of Pd and the balance being Pt, and Ni, Y, Ru, and Ni as third elements.
It has been found that adding at least one of Rh and Mo in an amount of 2 to 20% by weight is effective in suppressing crystal grain growth at high temperatures and in improving spark wear resistance. That is, in the example, Pt-30Pd (30% by weight added) was used.
Using alloys No. 2 to 9 shown in Table 1, which are Pd) alloys mixed with various third elements, this was used as the center electrode of a nickel alloy (2% Si, 2% Cr, 2% Al and balance Ni alloy). The performance was compared using pieces of precious metal each having a diameter of 0.4 mm joined to the concave portion 3b of the base material 3 by electric resistance welding. In the performance evaluation, the effect of suppressing grain growth was determined by the grain size No. (austenide grain size) after heat treatment at 1000℃ x 10 hours in the atmosphere and by the burner.
A comparison was made based on grain boundary cracks after cooling/heating cycles of 1100°C x 3 minutes and air cooling for 3 minutes x 500∞.
【表】
このテスト結果は、No.１のPt−30Pd合金が高
温時の結晶粒成長が早くて粒度が大きく、冷熱サ
イクル繰返しにおいては剥離はしないが境界で亀
裂が認められた。これに対して、本発明の合金材
料No.２〜No.９のものはいずれもNo.１のものより結
晶粒成長が遅く粒度が小さく、冷熱サイクル繰返
しにおいても亀裂は僅少であつて良好な接着性を
もつものである。
次に耐火花消耗性については、CDI電源を用い
て火花回数100PPS（毎秒当りのパルス）の条件下
で同一材質の貴金属棒材を対向させて配設して行
つたもので、その時のギヤツプ増加量を第２図に
示した。本発明の合金材料No.２，３，６，９は
Pt−30Pdよりは若干劣るが、比較的耐消耗性が
良好とされたPt−20Irよりもギヤツプ増加量が少
なく、耐久性がよいことが確められた。
なお、本発明の第三元素のNi，Ｙ，Ru，Rh，
Moの添加量は２〜20重量％の範囲内であり、２
重量％以下では結晶粒成長抑制効果が得られず20
重量％以上では耐消耗性が実用範囲を越えるため
好ましくない。又Pdの添加量を15〜60重量％と
する理由は前記添加範囲を外れると耐消耗性及び
溶接良好な接合範囲の硬度（ブリネル160以上）
が得られなくなるためである。
又本発明スパークプラグは第１図では中心電
極、外側電極の両者の火花放電部に貴金属小片を
配設したが、この実施例だけに限定されず、機関
の性能、電源極性に応じていずれか一方の電極に
本発明の合金材料を、又他方の電極に本発明合金
材料以外の貴金属合金例えばPt−Ni，Pt−IrPt
−Pd等を必要特性に合わせて用いることができ
る。更に実施例の如く火花ギヤツプが中心電極の
先端面に対向した外側電極との間に形成するスパ
ークプラグだけでなく、中心電極の先端部側面又
は先端周縁との間に形成するスパークプラグにも
適用することができる。
（発明の効果）
以上の如く、本発明のスパークプラグは火花放
電部にPt−Pd合金に第三元素としてNi，Ｙ，
Ru，Rh，Moの少なくとも１種を添加した合金
材料を用いることにより、耐火花消耗性が良好で
あるだけでなく、高温時の結晶粒成長抑制効果を
著しく高めることによつてニツケル合金電極母材
との接着性を向上し、耐久性の優れたスパークプ
ラグが得られ、かつPd材料費が比較的安く、プ
ラグ長寿命化をより低コストに達成できる顕著な
効果をもつものである。[Table] The test results show that the No. 1 Pt-30Pd alloy has fast grain growth and large grain size at high temperatures, and although it does not peel off during repeated cooling and heating cycles, cracks are observed at the boundaries. On the other hand, alloy materials No. 2 to No. 9 of the present invention all have slower grain growth and smaller grain size than No. 1, and show good performance with few cracks even after repeated heating and cooling cycles. It has adhesive properties. Next, regarding the spark wear resistance, we used a CDI power supply and placed precious metal rods of the same material facing each other under the condition of 100 PPS (pulses per second) of sparks, and the gap increase at that time. The amounts are shown in Figure 2. Alloy materials No. 2, 3, 6, and 9 of the present invention are
Although slightly inferior to Pt-30Pd, it was confirmed that the gap increase was smaller than that of Pt-20Ir, which was said to have relatively good wear resistance, and its durability was good. Note that the third elements of the present invention are Ni, Y, Ru, Rh,
The amount of Mo added is within the range of 2 to 20% by weight, and 2
If it is less than 20% by weight, the effect of suppressing grain growth cannot be obtained.
If it exceeds % by weight, the abrasion resistance exceeds the practical range, which is not preferable. Also, the reason why the amount of Pd added is 15 to 60% by weight is that outside the above addition range, the wear resistance and the hardness in the welding range where welding is good (Brinell 160 or higher)
This is because it becomes impossible to obtain. Furthermore, although the spark plug of the present invention has small pieces of precious metal arranged in the spark discharge parts of both the center electrode and the outer electrode in FIG. 1, the present invention is not limited to this embodiment. One electrode is made of the alloy material of the present invention, and the other electrode is made of a noble metal other than the alloy material of the present invention, such as Pt-Ni, Pt-IrPt.
-Pd etc. can be used depending on the required characteristics. Furthermore, the present invention is applicable not only to spark plugs in which the spark gap is formed between the tip surface of the center electrode and the opposing outer electrode as in the embodiment, but also to spark plugs in which the spark gap is formed between the side surface of the tip or the periphery of the tip of the center electrode. can do. (Effects of the Invention) As described above, the spark plug of the present invention has a Pt-Pd alloy with Ni, Y, and Ni as the third element in the spark discharge part.
By using an alloy material containing at least one of Ru, Rh, and Mo, it not only has good spark abrasion resistance, but also significantly increases the effect of suppressing grain growth at high temperatures, making it possible to improve the nickel alloy electrode matrix. This has the remarkable effect of improving the adhesion to the material, producing a spark plug with excellent durability, and the Pd material cost being relatively low, making it possible to extend the life of the plug at a lower cost.
【図面の簡単な説明】[Brief explanation of the drawing]
第１図は本発明スパークプラグの一実施例を示
す発火部の要部断面図であり、第２図は本発明合
金材料と比較合金材料の耐火花消耗性を示す特性
図である。
３……中心電極、３ａ，５ａ……火花放電部、
５……外側電極、４，６……貴金属小片。
FIG. 1 is a cross-sectional view of a main part of the ignition part of an embodiment of the spark plug of the present invention, and FIG. 2 is a characteristic diagram showing the spark wear resistance of the alloy material of the present invention and a comparative alloy material. 3... Center electrode, 3a, 5a... Spark discharge part,
5... Outer electrode, 4, 6... Precious metal piece.