JP3701184B2 - Thermal flow measuring device and resistor element used therefor - Google Patents

Description

表１に示すように生材の状態に比較して、１０００℃の加熱工程を経たＰｔＩｒ１０％リードの強度は、その引っ張り強度が約５５％低下することが判明している。
【００２４】
本発明では、この種の抵抗素子１において、例えば上記したＰｔＩｒ１０％のように優れた耐食性を生かしつつ、機械的強度を損なわないリードを次のようにして提案する。
【００２５】
基本的な考えは、リード５に再結晶温度以上の熱履歴が加わらないようにすることである。例えば、ＰｔＩｒ１０％リードでは、再結晶温度は４５０℃以上であるので、熱履歴はそれ以下にする必要がある。すなわち、リードは、ほぼ生材の状態の機械的性能を維持したままの熱履歴により、抵抗体素子１のリード５とするものである。
【００２６】
例えば、ＰｔＩｒ１０％リード表面には、再結晶温度（４５０℃）以下の加熱工程を経たならば、結晶粒界８を確認することはできない〔図１（ｂ）に示すＳＥＭ写真の如く〕。
【００２７】
本実施例では、リード５に結晶粒界を生じさせないために、構造的にはガラス接着剤による接着を止め、金属薄膜抵抗体３の形成後に、リード５をキャップ６を介してセラミック基体２の両端に取り付けるようにした。リード５はセラミック基体２に取り付ける前に予めキャップ６にスポット溶接により取付けられており、このリード付きキャップ６は、リード表面に結晶粒界を生成させない熱履歴によりセラミック基体２に圧入により被着されている。
【００２８】
すなわち、セラミック基体２に白金薄膜抵抗体３を形成した後に、リード付きキャップ６をセラミック基体２の両端に圧入した。リード付きキャップ６の被着を白金薄膜抵抗体３の形成後にしたのは、白金薄膜抵抗体３の焼成工程（約６５０〜８００℃）の熱履歴をリード５に与えないためである。ちなみに、白金薄膜抵抗体３は、セラミック基体２の全外周にスパッタリングにより形成される。
【００２９】
なお、キャップを介してリードを取り付ける抵抗体素子は、熱式流量測定装置以外の一般の回路抵抗に使用されているが、本実施例は、これとは次の点が異なる。すなわち、熱式流量測定装置対応となるように、リード５を白金或いは白金を含む合金とすること、リード５に結晶粒界を焼成させない熱履歴を与える手段が存在している点であり、この相違点は、今までに例のないことである。
【００３０】
ところで、熱式流量測定装置の感温抵抗体に用いる抵抗体素子は、一般的には保護膜もガラスでコートしている例が多いが、保護膜に用いるガラス（例えばシリカガラス、ホウケイ酸鉛ガラス、結晶化ガラス等）は、５００℃以上の加熱温度により焼成している例が多い。したがって、このようなガラス保護膜を採用すると、例えば、ＰｔＩｒ１０％リードを使用した場合には、上記のようにリード付きキャップ６を金属薄膜抵抗体３の形成後に取り付けたとしても、再結晶温度以上の熱履歴により結晶の再整列が開始され結晶粒が発生することになる。
【００３１】
そこで、本実施例では、保護膜７も、リード５の再結晶温度以下で焼成できかつ化学的に安定なコート材料を用いることにした。例えば、２００℃以上の高温連続環境に耐えるコート材料として、ガラスの代わりにポリイミドを使用する。
【００３２】
このポリイミドの焼成温度は約３００〜４００℃であるため、ＰｔＩｒ１０％リードの再結晶温度以下となり、ほぼ生材と同等の機械的強度を得ることが可能となる。
【００３３】
表２はＰｔＩｒ１０％リードを、３５０℃で焼成した後の引張り強度測定結果であるが、引張り強度は表１に示した生材の引張り強度とほぼ同等の強度を保持していることが判る。
【００３４】
【表２】

図１（ｂ）は、このようにして形成した抵抗体素子１のリード５（３５０℃の熱履歴を加えた後のＰｔＩｒ１０％リード）の表面状態を撮影したセム写真の模式図であり、その表面状態には、図２に確認できるような結晶粒界８は存在せず、ＰｔＩｒ１０％リードの生材の表面状態と同等の表面状態が得られた。
【００３５】
したがって、本実施例によれば、耐食性を有する白金などの貴金属をリードとして用いた熱式流量測定用の抵抗体素子の機械的強度を向上させ、信頼性の高い抵抗体素子を提供できる。さらに、キャップ式抵抗体素子１は、外観は、一般の市販抵抗器と同一であるので、製造上は、何等問題点はなく、逆に汎用設備を使用できるミリットがあるため歩留まりの良いコスト的にも安価な抵抗体素子１を製作できる。
【００３６】
上記実施例では、リード５表面に結晶粒界８が確認できない抵抗体素子１を提案したが、このようなリード５を機械的特性の観点より特徴をとらえると、リード５は、引張り強度と弾性限度（或いは０．２％耐力）との比が０．９以上の部材により構成することが可能であると定義できる。ここで、引っ張り強度と弾性限度について説明する。
【００３７】
図３（ａ）は、ＰｔＩｒ１０％リードを１０００℃で焼成したものについて、縦軸に荷重（引っ張り強度）、横軸に伸びを取った関係をプロットした線図である。同じように、図３（ｂ）には生材（ＰｔＩｒ１０％）における荷重−伸び特性の線図を、図３（ｃ）には３５０℃で焼成したリード５（ＰｔＩｒ１０％）における荷重−伸び特性の線図を示す。図３（ａ）〜（ｃ）において、符号の９は引っ張り強度特性線であり、図３（ａ）にみられる符号１０は、弾性限度である。
【００３８】
一般的に鉄以外の金属部材（合金部材を含む）の場合、熱履歴の加わらない生材の状態では、図３（ｂ）に示すように弾性限度１０が確認できない場合が多く、上記ＰｔＩｒ１０％リードの場合には、生材のほかに３５０℃の熱履歴を施したリード５においても、図３（ｃ）に示すように弾性限度１０が確認できず、降伏状態に達した後破断する。
【００３９】
しかしながら、その破断強度は約１ｋｇｆを超え、実用に耐えうる強度を有する。更に、弾性状態のまま延性し、そのまま破断する特徴を持っている。つまりリードの破断荷重と永久歪みを発生する降伏荷重が同等の荷重であることにより、熱履歴を受けたリードより耐久信頼性が高いことことが判る。
【００４０】
これに対し１０００℃の熱履歴を施したリードは一旦降伏点を迎え、更に延性したのち破断する傾向にある。伸びが大きいだけリード５破断に対する余裕はあるものの弾性限度１０が低いため、永久歪みは発生し易く、その信頼性には改善の余地がある。
【００４１】
リード５の引張り強度９（破断強度）と弾性限度１０との比を０．９以上とすることで、機械的強度が強く信頼性の高いリード５を提供することができる。なお、本実施例において、ＰｔＩｒ１０％リードにおいて生材と３５０℃の熱履歴が加わったリードについては、弾性限度が確認できないため、これに代わる０．２％耐力を以って引っ張り強度９との比とした。
【００４２】
図６は、上記実施例の応用例を示すものであり、本発明に係る抵抗体素子１を自動車の熱式空気流量測定装置１１に適用した例である。
【００４３】
熱式空気流量測定装置の吸気ボディ１５は、エンジンの吸入空気通路の一部を構成し、そのボディ１５には、吸気の一部が流れる副通路１６及びそれと一体のセンサハウジング１８が導入されている。
【００４４】
副通路１６には、空気流量を測定するための発熱抵抗体１２と温度補償抵抗体１３と吸気温度測定抵抗体（吸気温度センサ）１７とが配置されている。センサハウジング１８には、上記発熱抵抗体１２に流れる加熱電流を制御し、かつ上記各抵抗体１２，１３，１７に流れる電流を電気信号として検出し信号処理する制御回路１４が内装されている。
【００４５】
すでに周知のように、発熱抵抗体１２と温度補償抵抗体１３は、ゲージ回路（図示せず）を構成するブリッジに組み込まれ、発熱抵抗体１２に流れる加熱電流は、発熱抵抗体１２の温度と吸入空気温度（温度補償抵抗体）との温度差（抵抗値差）が常に一定に保たれるように、制御回路１４により制御される。
【００４６】
発熱抵抗体１２は、空気流の中に設置されるため、その表面部分が放熱面、つまり熱伝達面となる。この熱伝達で空気流に奪われた熱量を電気的信号に変換し（換言すれば発熱抵抗体に流れる加熱電流の電気信号）、空気流量を計測するものである。吸入空気温度測定センサ１７は、エンジン制御などの種々の用途に使用される。
【００４７】
これら抵抗体素子と制御回路１４は、ハウジング１８に埋設された導電性部材（ターミナル）を介し電気的に接続されている。
【００４８】
本実施例では、温度補償抵抗体（感温抵抗体）１３に既述した実施例の抵抗体素子１、すなわち結晶粒界のないリードを有する抵抗体素子を用いている。
【００４９】
一方、発熱抵抗体（感温抵抗体）１２には、そのリード表面に結晶粒界８（図２参照）が発生している抵抗体素子を用いている。このような発熱抵抗体１２と温度補償抵抗体１３とを組み合わせることにより、以下に述べる理由により、熱式空気流量測定装置１１の性能の改善、特に温度変化時の出力誤差の低減を図り、流量計の高精度化に貢献することができる。
【００５０】
これは、以下に説明する現象による。一般的に金属部材は、生材と熱履歴を施した部材とでは、熱履歴を施した部材の方が抵抗率が小さくなる傾向にある。この現象は熱履歴を施すことにより金属原子の再結晶を迎えた後、金属原子群は規則正しく再配列するために金属原子の最外殻の自由電子が活性となるためである。この現象は、熱的見地より捕らえると、熱履歴を施した部材の熱伝導率が生材に比較して高くなることを意味している。
【００５１】
本実施例では、発熱抵抗体１２のリードの表面には結晶粒界８が存在し、抵抗体１３のリード５の表面には結晶粒界８が存在しないといった組み合わせを行なうことにより、温度補償抵抗体１３のリード５は周囲の温度影響が受け難く、より正確に流体の温度計測を行なうことが可能となり得る。逆に発熱抵抗体１２においては熱伝導率が抵抗体１３より大きいリードを用いることになるので、そのリードは、ボディ１５やターミナル１９等周囲の温度影響を受けることにより発熱抵抗体１２の加熱電流が減少する傾向となる。つまり、発熱抵抗体１２と温度補償抵抗体１３についてそれぞれのリードの熱バランスを変化させることにより、温度変化時もにおいても、定常状態と何等変わりない出力を得ることが可能となる。従って、本発明の実施例による熱式空気流量測定装置１１によれば、吸気温度などの周囲の温度変化時においても誤差の少ないしかも省電力の熱式空気流量測定装置を実現することができる。
【００５２】
以上、本発明の実施例を説明したが、本発明の基本的要旨は、そのような実施例の記載によって、何等の制約をも受けるものではないことは言うまでもない。
【００５３】
【発明の効果】
以上のように、本発明によれば、熱式流量測定装置用に用いられる抵抗体素子について、耐食性の優れた貴金属リードを使用した場合でも、その機械的強度を向上させ、さらには抵抗体素子ひいては熱式流量測定装置の信頼性を向上させることができる。さらに、精度の高い熱式流量測定装置を提供することができる。
【図面の簡単な説明】
【図１】（ａ）は本発明の特徴を示す抵抗体素子の構造図、（ｂ）はそのリード部の表面部を撮影したＳＥＭ写真を模式的に描画した図。
【図２】１０００℃で焼成した白金合金リードの表面を撮影したＳＥＭ写真を模式的に描画した図。
【図３】（ａ）は１０００℃で焼成した白金合金リードの荷重と伸びの関係を示す線図、（ｂ）は白金合金リードの生材における荷重と伸びの関係を示す線図、（ｃ）は３５０℃で焼成した白金合金リードの荷重と伸びの関係図。
【図４】本発明の一実施例に係る熱式流量測定装置の断面図。
【符号の説明】
１…抵抗体素子、２…セラミック基体、３…白金薄膜抵抗、５…リード、６…キャップ、７…ポリイミドコート、８…結晶粒界、１１…熱式空気流量測定装置、１２…発熱抵抗体、１３…温度補償抵抗体、１６…副通路。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thermal flow measuring device and a resistor element used therefor. The resistor element relates to a resistor element (temperature-sensitive resistor) whose electric resistance value is temperature-dependent, for example, a resistor element suitable for a thermal flow measuring device that detects an air flow rate or a flow velocity in an internal combustion engine or the like. .
[0002]
[Prior art]
As this type of resistor element, an element in which a resistance of a metal thin film is formed on a cylindrical or plate-like substrate or a resistance of a thin metal wire is wound is known.
[0003]
For example, in the resistance element described in Japanese Patent Application Laid-Open No. 1-45009, platinum or platinum having an outer diameter of about 0.15 to 0.2 mm at both ends of a ceramic pipe (alumina or the like) having an outer diameter of about 0.5 mm. After a lead made of an alloy containing is inserted and fixed with a glass adhesive, a platinum wire of about φ20 μm is spirally wound around the outer surface of the ceramic pipe so as to have a predetermined resistance value. It is a line. Further, a protective film made of glass is formed on the resistor forming portion.
[0004]
In the resistance element described in Japanese Patent Laid-Open No. 5-52626, a platinum thin film is patterned on the outer surface of a ceramic pipe having an outer diameter of about φ0.5 mm so as to have a predetermined resistance value. At both ends of the ceramic pipe, lead of about φ0.2mm is inserted (plated with platinum on the outer surface of an iron-nickel alloy wire), and it is bonded and fixed using platinum paste as an adhesive ing. Further, the platinum thin film and the lead are electrically connected at both ends of the ceramic pipe.
[0005]
As described above, various types of temperature sensitive resistors have been proposed. Of these, when the leads inserted at both ends of the ceramic pipe are bonded and fixed with a glass adhesive, the bonding is performed. The lead is fired at a temperature of 800 ° C. or higher required for the above. When platinum or an alloy containing platinum is used for the lead, a crystal grain boundary is generated on the surface of the lead by the firing. This crystal grain boundary becomes an element that decreases the mechanical strength (tensile strength) of the lead, and the lead after firing has a lower tensile strength than the annealed raw material.
[0006]
Known examples of such measures for reducing the mechanical strength include, for example, an average value of crystal grain sizes in the direction perpendicular to the axial direction of the lead of 10 μm or less as described in JP-A-6-231903. The technology to make is proposed. In this known example, an iron-nickel alloy lead base material (core wire) is covered with platinum clad, and the wire is subjected to an annealing temperature of, for example, about 650 ° C. and subjected to a heat treatment for about 1 hour. The diameter is 10 μm or less.
[0007]
When platinum is clad on a core wire such as an alloy of iron and nickel, the mechanical strength of the lead can be maintained high because it depends mostly on the base material of iron and nickel, but the lead is cut or welded to other members In this case, the degree of scattering of the platinum clad increases in the vicinity of the cut portion and the weld portion.
[0008]
[Problems to be solved by the invention]
The present invention has been made in view of the above points, and its purpose is to improve the mechanical strength of a platinum lead having excellent corrosion resistance or an alloy lead containing platinum for a resistor element used for a thermal flow rate measuring device, The object is to improve the reliability of the resistor element and thus the thermal flow rate measuring device.
[0009]
[Means for Solving the Problems]
The resistor element according to the present invention basically has the following characteristics.
[0010]
A temperature-dependent resistor is provided on the surface of the ceramic base, and caps with leads are attached to both ends of the ceramic base. The lead is made of a noble metal or an alloy containing a noble metal, and the cap with lead is a lead surface. It is deposited on the ceramic substrate by a thermal history that does not generate crystal grain boundaries.
[0011]
Furthermore, as an application device of the above invention, in the thermal air flow measurement device in which a heating resistor for measuring the air flow rate and a temperature compensation resistor are arranged in the intake passage of the internal combustion engine, the heating resistor includes crystal grains. Proposed is a flow rate measuring device comprising a temperature sensitive resistor having a lead in which a boundary is generated, and the temperature compensating resistor is a temperature sensitive resistor having a lead in which no crystal grain boundary is generated.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings.
[0013]
The resistor element 1 in FIG. 1A is used in a thermal flow measuring device, and the ceramic substrate 2 is a solid alumina bobbin having an outer diameter of about φ0.5 to φ2 mm and a length of about 2 to 4 mm. .
[0014]
A platinum thin film 3 (thickness: about 0.5 μm to 1 μm) serving as a temperature sensitive resistor is formed on the outer surface of the ceramic substrate 2 by sputtering. The platinum thin film 3 is provided with a spiral cut groove 4 by laser trimming to form a thin film resistor having a resistance value of about 400Ω.
[0015]
Leads 5 made of platinum or an alloy containing platinum are disposed through caps 6 at both ends of the ceramic substrate 2 after the thin film resistor is formed.
[0016]
The lead 5 has an outer diameter of about φ0.15 to φ0.2 mm, and is joined to the outer end of a cap 6 formed by drawing a stainless steel plate by spot welding.
[0017]
The cap 6 is attached to both ends of the ceramic base 2 on which the resistor 3 is formed by fitting or press fitting. Further, the protective film 7 is coated on the entire circumference of the resistor element 1. The protective film 7 is a member such as polyimide having excellent heat resistance, for example.
[0018]
Here, although the lead 5 is made of platinum or an alloy containing platinum, the lead 5 (hereinafter referred to as PtIr10%) obtained by adding 10 wt% of iridium to 90 wt% of platinum is generally used in many cases. In addition, platinum-based noble metal alloys containing 5 to 30 wt% of platinum group elements such as iridium, palladium, ruthenium, rhodium and osmium, noble metal alloys of platinum group elements other than platinum, or platinum-based tungsten, nickel An alloy or the like to which 5 to 30 wt% of a transition metal group such as titanium and iron is added is considered as a lead material. This lead 5 is configured so that no crystal grain boundary is generated for the following reason.
[0019]
In many cases, the lead 5 of the resistor element 1 used in the thermal flow rate measuring device is formed of platinum or an alloy containing platinum in order to improve the corrosion resistance. A field was created, and the structure was unable to prevent it. Improvement of the grain boundary is also desired in order to improve the reliability because the mechanical strength decreases.
[0020]
Normally, it is ideal that the lead 5 be as thin as possible in order to improve the thermal response of the resistor element 1, but in reality, the lead 5 is about φ0.15 to φ0.2 mm considering the balance with the mechanical strength. There are many examples that are used with an outer diameter of.
[0021]
However, in the case of a PtIr 10% lead, if the lead is inserted into both ends of the ceramic substrate 2 and fixed with a glass adhesive (silica glass, crystallized glass, etc.) as in the conventional method described above, 800 required for the bonding process is required. The lead is baked at a temperature of not lower than ° C., and crystal grain boundaries 8 are generated on the surface of the lead 5 as shown in FIG. The crystal grain boundary 8 reduces the mechanical strength of the lead. The mechanism is due to the grain boundary slip, but further, since a groove is formed between the crystal grain boundaries, the lead cross-sectional area is partially reduced. This is also a decline factor.
[0022]
The data shown in Table 1 is the measurement result of the tensile strength of the raw material in the annealed state in the PtIr 10% lead and the lead that has undergone the heating process (firing conditions) at 1000 ° C.
[0023]
[Table 1]

As shown in Table 1, it has been found that the tensile strength of the PtIr 10% lead subjected to the heating process at 1000 ° C. is reduced by about 55% as compared with the state of the raw material.
[0024]
In the present invention, in this type of resistance element 1, a lead that does not impair mechanical strength while utilizing excellent corrosion resistance such as PtIr10% described above is proposed as follows.
[0025]
The basic idea is to prevent the lead 5 from being subjected to a thermal history higher than the recrystallization temperature. For example, with a PtIr10% lead, the recrystallization temperature is 450 ° C. or higher, so the thermal history needs to be lower. In other words, the lead is the lead 5 of the resistor element 1 due to the thermal history while maintaining the mechanical performance of the raw material state.
[0026]
For example, if a PtIr 10% lead surface is subjected to a heating step below the recrystallization temperature (450 ° C.), the grain boundary 8 cannot be confirmed (as shown in the SEM photograph shown in FIG. 1B).
[0027]
In this embodiment, in order not to generate crystal grain boundaries in the lead 5, structurally, the adhesion by the glass adhesive is stopped, and after the metal thin film resistor 3 is formed, the lead 5 is connected to the ceramic substrate 2 via the cap 6. Attach to both ends. The lead 5 is attached to the cap 6 in advance by spot welding before being attached to the ceramic base 2, and the cap 6 with lead is attached to the ceramic base 2 by press fitting by a thermal history that does not generate crystal grain boundaries on the lead surface. ing.
[0028]
That is, after the platinum thin film resistor 3 was formed on the ceramic base 2, the cap 6 with leads was press-fitted into both ends of the ceramic base 2. The reason why the lead cap 6 is attached after the platinum thin film resistor 3 is formed is that the thermal history of the baking process (about 650 to 800 ° C.) of the platinum thin film resistor 3 is not given to the lead 5. Incidentally, the platinum thin film resistor 3 is formed on the entire outer periphery of the ceramic substrate 2 by sputtering.
[0029]
In addition, although the resistor element which attaches a lead via a cap is used for general circuit resistances other than a thermal type flow measuring device, this example differs in the following points. That is, the lead 5 is made of platinum or an alloy containing platinum so as to be compatible with a thermal flow measuring device, and there is a means for giving a thermal history that does not cause the grain boundaries to be fired on the lead 5. The difference is unprecedented.
[0030]
By the way, as for the resistor element used for the temperature sensitive resistor of the thermal type flow measuring device, there are many examples in which the protective film is generally coated with glass, but glass used for the protective film (for example, silica glass, lead borosilicate) Glass, crystallized glass, and the like) are often fired at a heating temperature of 500 ° C. or higher. Therefore, when such a glass protective film is employed, for example, when a PtIr 10% lead is used, even if the cap 6 with lead is attached after the formation of the metal thin film resistor 3 as described above, the recrystallization temperature or higher is reached. Re-alignment of crystals is started by the thermal history of and crystal grains are generated.
[0031]
Therefore, in this embodiment, the protective film 7 is also made of a coating material that can be fired at a temperature lower than the recrystallization temperature of the lead 5 and is chemically stable. For example, polyimide is used instead of glass as a coating material that can withstand a high temperature continuous environment of 200 ° C. or higher.
[0032]
Since the firing temperature of this polyimide is about 300-400 ° C., it becomes below the recrystallization temperature of the PtIr 10% lead, and it becomes possible to obtain mechanical strength substantially equivalent to that of the raw material.
[0033]
Table 2 shows the tensile strength measurement results after firing the PtIr 10% lead at 350 ° C., and it can be seen that the tensile strength is almost equal to the tensile strength of the raw material shown in Table 1.
[0034]
[Table 2]

FIG. 1B is a schematic diagram of a semi-photograph of the surface state of the lead 5 of the resistor element 1 thus formed (PtIr 10% lead after applying a thermal history at 350 ° C.). In the surface state, there was no crystal grain boundary 8 as can be confirmed in FIG. 2, and a surface state equivalent to the surface state of the raw material of PtIr 10% lead was obtained.
[0035]
Therefore, according to the present embodiment, it is possible to improve the mechanical strength of the resistance element for thermal flow rate measurement using a noble metal such as platinum having corrosion resistance as a lead, and provide a highly reliable resistance element. Furthermore, since the external appearance of the cap-type resistor element 1 is the same as that of a general commercially available resistor, there is no problem in manufacturing, and conversely, there is a mirit that can use general-purpose equipment, so that the yield is high and the cost is high. In addition, an inexpensive resistor element 1 can be manufactured.
[0036]
In the above embodiment, the resistor element 1 in which the crystal grain boundary 8 cannot be confirmed on the surface of the lead 5 has been proposed. However, if such a lead 5 is characterized from the viewpoint of mechanical properties, the lead 5 has a tensile strength and elasticity. It can be defined that a member having a ratio with the limit (or 0.2% yield strength) of 0.9 or more can be used. Here, the tensile strength and the elastic limit will be described.
[0037]
FIG. 3A is a diagram in which the relationship between the PtIr 10% lead fired at 1000 ° C. is plotted with the load (tensile strength) on the vertical axis and the elongation on the horizontal axis. Similarly, FIG. 3B is a diagram of load-elongation characteristics of raw material (PtIr 10%), and FIG. 3C is a load-elongation characteristic of lead 5 (PtIr 10%) fired at 350 ° C. The diagram is shown. In FIGS. 3A to 3C, reference numeral 9 denotes a tensile strength characteristic line, and reference numeral 10 shown in FIG. 3A denotes an elastic limit.
[0038]
In general, in the case of a metal member other than iron (including an alloy member), in the state of raw material to which no thermal history is applied, the elastic limit 10 is often not confirmed as shown in FIG. In the case of the lead, in addition to the raw material, the lead 5 having a heat history of 350 ° C. cannot be confirmed as shown in FIG. 3C, and breaks after reaching the yield state.
[0039]
However, the breaking strength exceeds about 1 kgf, and has a strength that can withstand practical use. Furthermore, it has the characteristics that it is ductile while still in an elastic state and breaks as is. In other words, it can be seen that the durability reliability is higher than the lead subjected to the thermal history because the breaking load of the lead and the yield load generating permanent distortion are equivalent loads.
[0040]
On the other hand, a lead subjected to a thermal history of 1000 ° C. once reaches the yield point and tends to break after further ductility. Although there is a margin for breaking the lead 5 as long as the elongation is large, the elastic limit 10 is low, so permanent set is likely to occur, and there is room for improvement in its reliability.
[0041]
By setting the ratio of the tensile strength 9 (breaking strength) and the elastic limit 10 of the lead 5 to 0.9 or more, the lead 5 having high mechanical strength and high reliability can be provided. In this example, since the elastic limit cannot be confirmed for the PtIr 10% lead with the raw material and the heat history of 350 ° C. added, the tensile strength of 9 with 0.2% proof stress is substituted. Ratio.
[0042]
FIG. 6 shows an application example of the above embodiment, and is an example in which the resistor element 1 according to the present invention is applied to a thermal air flow measuring device 11 of an automobile.
[0043]
The intake air body 15 of the thermal air flow measuring device constitutes a part of an intake air passage of the engine, and a sub-passage 16 through which a part of the intake air flows and a sensor housing 18 integrated therewith are introduced into the body 15. Yes.
[0044]
In the auxiliary passage 16, a heating resistor 12, a temperature compensation resistor 13, and an intake air temperature measurement resistor (intake air temperature sensor) 17 for measuring the air flow rate are arranged. The sensor housing 18 includes a control circuit 14 that controls the heating current flowing through the heating resistor 12 and detects and processes the current flowing through the resistors 12, 13, and 17 as an electrical signal.
[0045]
As already known, the heating resistor 12 and the temperature compensation resistor 13 are incorporated in a bridge constituting a gauge circuit (not shown), and the heating current flowing through the heating resistor 12 is the same as the temperature of the heating resistor 12. Control is performed by the control circuit 14 so that the temperature difference (resistance value difference) from the intake air temperature (temperature compensation resistor) is always kept constant.
[0046]
Since the heating resistor 12 is installed in the air flow, the surface portion thereof becomes a heat radiating surface, that is, a heat transfer surface. The amount of heat taken by the air flow by this heat transfer is converted into an electrical signal (in other words, an electrical signal of the heating current flowing through the heating resistor), and the air flow rate is measured. The intake air temperature measurement sensor 17 is used for various applications such as engine control.
[0047]
These resistor elements and the control circuit 14 are electrically connected via a conductive member (terminal) embedded in the housing 18.
[0048]
In this embodiment, the resistor element 1 of the above-described embodiment, that is, a resistor element having a lead having no crystal grain boundary, is used as the temperature compensation resistor (temperature sensitive resistor) 13.
[0049]
On the other hand, a resistor element in which a crystal grain boundary 8 (see FIG. 2) is generated on the lead surface is used for the heating resistor (temperature sensitive resistor) 12. The combination of the heating resistor 12 and the temperature compensation resistor 13 improves the performance of the thermal air flow measuring device 11 for the reason described below, particularly reducing the output error when the temperature changes. It can contribute to high accuracy of the meter.
[0050]
This is due to the phenomenon described below. In general, a metal member tends to have a lower resistivity than a raw material and a member subjected to a thermal history when the member is subjected to a thermal history. This phenomenon is because the metal atom group is regularly rearranged after the recrystallization of the metal atoms by applying a thermal history, and the free electrons in the outermost shell of the metal atoms become active. This phenomenon means that the thermal conductivity of the member subjected to the thermal history is higher than that of the raw material when captured from a thermal standpoint.
[0051]
In this embodiment, the temperature compensation resistance is obtained by performing a combination in which the crystal grain boundary 8 exists on the surface of the lead of the heating resistor 12 and the crystal grain boundary 8 does not exist on the surface of the lead 5 of the resistor 13. The lead 5 of the body 13 is not easily affected by the ambient temperature, and it can be possible to measure the temperature of the fluid more accurately. On the contrary, in the heating resistor 12, a lead having a higher thermal conductivity than that of the resistor 13 is used. Therefore, the lead is affected by the ambient temperature of the body 15 and the terminal 19 and thereby the heating current of the heating resistor 12 is increased. Tend to decrease. That is, by changing the thermal balance of each lead for the heating resistor 12 and the temperature compensation resistor 13, it is possible to obtain an output that is not different from the steady state even when the temperature changes. Therefore, according to the thermal air flow rate measuring device 11 according to the embodiment of the present invention, it is possible to realize a thermal air flow rate measuring device with less error and power saving even when the ambient temperature such as the intake air temperature changes.
[0052]
As mentioned above, although the Example of this invention was described, it cannot be overemphasized that the basic gist of this invention does not receive any restrictions by description of such an Example.
[0053]
【The invention's effect】
As described above, according to the present invention, even when a noble metal lead having excellent corrosion resistance is used for a resistor element used for a thermal flow measuring device, its mechanical strength is improved, and further, a resistor element As a result, the reliability of the thermal flow rate measuring device can be improved. Furthermore, it is possible to provide a highly accurate thermal flow measuring device.
[Brief description of the drawings]
FIG. 1A is a structural diagram of a resistor element showing the features of the present invention, and FIG. 1B is a schematic drawing of an SEM photograph taken of the surface of a lead portion.
FIG. 2 is a schematic drawing of an SEM photograph taken of the surface of a platinum alloy lead fired at 1000 ° C.
3A is a diagram showing the relationship between the load and elongation of a platinum alloy lead fired at 1000 ° C., FIG. 3B is a diagram showing the relationship between the load and elongation of a raw material of the platinum alloy lead, FIG. ) Is a graph showing the relationship between the load and elongation of a platinum alloy lead fired at 350 ° C.
FIG. 4 is a cross-sectional view of a thermal flow rate measuring device according to one embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Resistor element, 2 ... Ceramic base | substrate, 3 ... Platinum thin film resistance, 5 ... Lead, 6 ... Cap, 7 ... Polyimide coat, 8 ... Crystal grain boundary, 11 ... Thermal air flow measuring device, 12 ... Heating resistor , 13 ... temperature compensation resistor, 16 ... sub-passage.

Claims (7)

A resistance having temperature dependency is provided on the surface of the ceramic base, and caps with leads are attached to both ends of the ceramic base. The leads are made of platinum or an alloy containing platinum. And a protective film is formed on the surface of the resistor at a temperature lower than the recrystallization temperature of the lead. Resistor element for use in thermal flow measurement devices. A resistance having temperature dependency is provided on the surface of the ceramic base, and caps with leads are attached to both ends of the ceramic base. The leads are made of platinum or an alloy containing platinum. The lead is applied to the ceramic base by a thermal history that does not generate crystal grain boundaries , and the lead is manufactured at a thermal history of 450 ° C. to 600 ° C. or less. Resistor element. The thermal flow rate according to claim 2 , wherein the resistor formed on the surface of the ceramic substrate is a platinum thin film resistor having a thermal history of firing, and the lead cap is attached after the platinum thin film resistor is formed. Resistor element used in measuring equipment. A ceramic substrate, a resistor arranged on the ceramic substrate, and a lead made of an alloy member containing a noble metal or noble metal, and said lead is made Li Cheng by conductive member joined cap, said ceramic substrate The cap is attached to both ends of the substrate, and a protective film is coated on the entire circumference of the ceramic substrate on which the resistor is formed.
A resistor element used in a thermal flow rate measuring apparatus, wherein the lead has a ratio of tensile strength to elastic limit or 0.2% proof stress of 0.9 or more. The thermal type air flow rate measuring device for measuring using a temperature sensitive resistor for intake air flow of an internal combustion engine, the resistor element according at least one of claims 1 to any one of 4 of the temperature sensitive resistor A thermal flow rate measuring device characterized by In a thermal air flow measurement device in which a heating resistor and a temperature compensation resistor used for air flow measurement are arranged in an intake passage of an internal combustion engine,
The heating resistor is a temperature-sensitive resistor having a lead in which a crystal grain boundary is generated, and the temperature compensation resistor is a temperature-sensitive resistor having a lead in which a crystal grain boundary is not generated. A featured thermal air flow measurement device. The lead of the heating resistor and the temperature compensation resistor is made of the same noble metal or an alloy containing a noble metal, and the presence or absence of generation of the crystal grain boundary is set by changing the thermal history of each lead. Item 7. The thermal air flow rate measuring device according to Item 6 .

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