JPH09218064A - Flow rate measuring apparatus - Google Patents
Flow rate measuring apparatusInfo
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- JPH09218064A JPH09218064A JP8022342A JP2234296A JPH09218064A JP H09218064 A JPH09218064 A JP H09218064A JP 8022342 A JP8022342 A JP 8022342A JP 2234296 A JP2234296 A JP 2234296A JP H09218064 A JPH09218064 A JP H09218064A
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- Prior art keywords
- flow rate
- vibrating body
- heating element
- substrate
- change
- Prior art date
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Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、例えば電子制御燃
料噴射装置を備えた自動車用エンジンにおいて吸入空気
量の計測装置として用いるのに好適な流量測定装置に関
する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flow rate measuring device suitable for use as a device for measuring an intake air amount in an automobile engine equipped with an electronically controlled fuel injection device.
【０００２】[0002]
【従来の技術】従来、エンジン制御用の吸入空気量の計
測装置に用いられるエアフローセンサとして、加熱した
抵抗体を空気流にさらし、空気流の冷却効果による抵抗
体の温度変化を抵抗変化として測定して空気流量を検出
するものが知られている。2. Description of the Related Art Conventionally, as an air flow sensor used in an intake air amount measuring device for engine control, a heated resistor is exposed to an air flow, and a temperature change of the resistor due to a cooling effect of the air flow is measured as a resistance change. It is known to detect the air flow rate.
【０００３】これら熱式エアフローセンサには、加熱抵
抗体として白金細線を用いるホットワイヤ式および白金
等の薄膜抵抗を用いるホットフィルム式等があり、シリ
コン基板をエッチング等の微細加工によって薄膜化し、
その上に白金等の薄膜抵抗を配置した半導体ホットフィ
ルム式エアフローセンサも提案されている（特開平７−
１５９２１５号参照）。These thermal air flow sensors include a hot wire type using a platinum thin wire as a heating resistor and a hot film type using a thin film resistor such as platinum, and the like, and a silicon substrate is thinned by fine processing such as etching,
A semiconductor hot film type air flow sensor, in which a thin film resistor such as platinum is arranged, is also proposed (Japanese Patent Laid-Open No. 7-
159215).
【０００４】[0004]
【発明が解決しようとする課題】近時、環境汚染の低減
および省燃費を実現するリーンバーンエンジン等におい
て、排気浄化用触媒容量の低減と、燃費と走りとを高次
元でバランスさせたエンジン制御とを目指して、制御用
センサの高機能化が重要な問題となっている。特に、精
密な空燃比制御に要求される吸入空気量の高感度、高精
度計測、および逆流検出の実現と、高過給エンジンに要
求される空気流量計測のダイナミックレンジの拡大等の
ニーズが顕在化している。Recently, in a lean burn engine or the like which realizes reduction of environmental pollution and fuel efficiency, engine control in which exhaust gas purifying catalyst capacity is reduced and fuel efficiency and running are balanced at a high level. With the aim of achieving the above, the sophistication of control sensors has become an important issue. In particular, there is a clear need for high sensitivity, high precision measurement of intake air volume required for precise air-fuel ratio control, and detection of backflow, and expansion of the dynamic range of air flow rate measurement required for a highly supercharged engine. It has become.
【０００５】しかしながら、従来の熱式エアフローセン
サは、検出部の熱容量を極力小さくした半導体ホットフ
ィルム式のものにおいても、そのダイナミックレンジは
十分とは言えないものであった。そのため、発熱体（ホ
ットワイヤ、ホットフィルム）を２００℃以上の高温に
することにより辛うじてクリアしているが、その場合、
発熱体が高温になるためにその耐久性や信頼性の悪化が
問題になっている。However, the conventional thermal air flow sensor, even the semiconductor hot film type in which the heat capacity of the detecting portion is made as small as possible, cannot be said to have a sufficient dynamic range. Therefore, it is barely cleared by heating the heating element (hot wire, hot film) to a high temperature of 200 ° C or higher, but in that case,
Since the heating element becomes high in temperature, deterioration of its durability and reliability has become a problem.
【０００６】また、従来の熱式エアフローセンサでは、
空気流の冷却効果による抵抗体の温度変化を抵抗変化と
して検出しているために、高感度とは言いがたく、抵抗
体の大きな温度変化を必要とするという問題もある。Further, in the conventional thermal air flow sensor,
Since the temperature change of the resistor due to the cooling effect of the air flow is detected as the resistance change, it cannot be said that the sensitivity is high, and there is also a problem that a large temperature change of the resistor is required.
【０００７】さらに、センサ出力が、抵抗変化を電圧で
読み取るアナログ信号であるため、エンジン制御用コン
ピュータへ入力する際に、Ａ／Ｄコンバータを介在させ
なければならない。ところが、必要な計測領域を全域満
たすような計測精度を得るには大きな分解ビット数を有
するＡ／Ｄコンバータを必要とすることから、センサの
計測レンジおよび精度が、Ａ／Ｄコンバータの性能によ
り制限を受けるという不都合がある。Further, since the sensor output is an analog signal for reading the resistance change by voltage, an A / D converter must be interposed when inputting to the engine control computer. However, since an A / D converter having a large number of decomposition bits is required to obtain the measurement accuracy that satisfies the required measurement area, the measurement range and accuracy of the sensor are limited by the performance of the A / D converter. There is an inconvenience of receiving.
【０００８】さらに、自動車のエンジン付近等の電気的
な悪環境では、アナログ信号である出力信号が、電磁ノ
イズやグラウンドノイズ等により常に影響を受けるた
め、高精度の計測は望めなかった。Further, in an electrically bad environment such as in the vicinity of the engine of an automobile, the output signal, which is an analog signal, is always affected by electromagnetic noise, ground noise, etc., so that highly accurate measurement cannot be expected.
【０００９】上述の事情に鑑み、本発明は、極めて高感
度でありながら、信頼性、耐久性に富み、かつＡ／Ｄコ
ンバータを必要としない流量測定装置を提供することを
目的とする。In view of the above-mentioned circumstances, it is an object of the present invention to provide a flow rate measuring device which has extremely high sensitivity, is highly reliable and durable, and does not require an A / D converter.
【００１０】[0010]
【課題を解決するための手段】本発明による流量測定装
置は、基板上に発熱体と両持ち梁を近接させて配設し、
発熱体の熱によって両持ち梁に発生している熱応力が、
流体の質量流量に応じた冷却効果による発熱体の温度変
化によって変化するのを両持ち梁の機械的変化として検
出するように構成されていることを特徴とするものであ
る。In a flow rate measuring device according to the present invention, a heating element and a doubly supported beam are arranged close to each other on a substrate,
The thermal stress generated in the doubly supported beam due to the heat of the heating element,
It is characterized in that it is configured to detect a change due to a temperature change of a heating element due to a cooling effect according to a mass flow rate of a fluid, as a mechanical change of a doubly supported beam.
【００１１】この場合、上記両持ち梁がシリコン単結晶
基板から一体に削出され、両端を支持端として上記シリ
コン単結晶基板に支持された構成とすることが好まし
い。In this case, it is preferable that the both-supported beams are integrally cut from the silicon single crystal substrate and are supported by the silicon single crystal substrate with both ends as supporting ends.
【００１２】また、上記両持ち梁が、両持ち梁構造を有
する振動体よりなり、上記両持ち梁の、それに加わる熱
応力変化に起因する機械的変化を測定する手段が、上記
振動体の共振周波数の変化を測定する手段よりなること
が好ましい。The doubly supported beam is composed of a vibrating body having a doubly supported beam structure, and the means for measuring a mechanical change of the doubly supported beam due to a change in thermal stress applied thereto causes resonance of the vibrating body. It preferably comprises means for measuring changes in frequency.
【００１３】上記振動体の厚さｈおよび長さＬと、該振
動体に予め内在する長手方向の応力による歪みε0 と、
上記発熱体の熱によって生じる圧縮歪みεheatとは、次
式で表される関係にあることが好ましい。The thickness h and the length L of the vibrating body, and the strain ε 0 due to the longitudinal stress existing in the vibrating body in advance,
The compressive strain ε heat generated by the heat of the heating element preferably has a relationship represented by the following equation.
【００１４】ε0 ＋εheat＞（−π2 ／３）ｈ2 ／Ｌ2 さらに、本発明による流量測定装置は、流体の冷却効果
による発熱体の温度低下を補う手段を備え、該手段によ
り、発熱体の温度がほぼ一定に保たれるように構成する
こともできる。[0014] ε 0 + ε heat> (- π 2/3) h 2 / L 2 Additionally, the flow rate measuring device according to the invention comprises means to compensate for the temperature drop of the heating element due to the cooling effect of the fluid, the said means, It can also be configured such that the temperature of the heating element is kept substantially constant.
【００１５】その場合、発熱体近傍の基板温度の２次元
分布が流体流量によって変化する基板上の位置に上記振
動体が配置され、基板温度の２次元分布の変化に起因す
る振動体の共振周波数の変化の測定に基づいて流体の流
量測定がなされる。In this case, the vibrating body is arranged at a position on the substrate where the two-dimensional distribution of the substrate temperature near the heating element changes depending on the fluid flow rate, and the resonance frequency of the vibrating body caused by the change in the two-dimensional distribution of the substrate temperature. The flow rate of the fluid is measured based on the measurement of the change in
【００１６】また、上記基板上に振動体の複数が上記流
体の流れの方向に沿って配設され、これら複数の振動体
間の共振周波数変化の差異に基づいて流体の流量および
流れの方向の測定がなされるように構成することができ
る。A plurality of vibrators are arranged on the substrate along the flow direction of the fluid, and the flow rate of the fluid and the flow direction of the fluid are determined based on the difference in resonance frequency change between the plurality of vibrators. It can be configured so that measurements are made.
【００１７】[0017]
【発明の効果】理論的に発熱体から奪われる熱量Ｑと質
量流量Ｇとの関係は次式のようになる。The relationship between the heat quantity Q and the mass flow rate G theoretically taken from the heating element is as follows.
【００１８】Ｑ＝Ｋ√Ｇ （ Ｋは定数） したがって、両持ち梁に作用する温度変化ΔＴも次式の
ようになる。Q = K√G (K is a constant) Therefore, the temperature change ΔT acting on the doubly supported beam is also given by the following equation.
【００１９】ΔＴ＝Ｋ√Ｇ 両持ち梁に作用する熱応力は両持ち梁付近とそれ以外の
基板部分の温度差によって発生する。その発生機構の概
略を図１および図２に示す。図１は動かない壁に両端を
固定された剛体棒を加熱すると、熱膨脹により棒が伸び
ようとするために、棒に圧縮応力が発生した状態を示
す。また、図２は両持ち梁構造を有する振動体における
加熱による応力発生状態を示し、図２（ａ）は振動子を
直接的に加熱するタイプであり、図２（ｂ）は振動子を
間接的に加熱するタイプである。ΔT = K√G The thermal stress acting on the doubly supported beam is generated by the temperature difference between the vicinity of the doubly supported beam and the other substrate portion. The outline of the generation mechanism is shown in FIGS. 1 and 2. FIG. 1 shows a state in which when a rigid rod whose both ends are fixed to a stationary wall is heated, the rod tends to expand due to thermal expansion, so that compressive stress is generated in the rod. Further, FIG. 2 shows a stress generation state due to heating in a vibrating body having a doubly supported beam structure. FIG. 2 (a) is a type in which a vibrator is directly heated, and FIG. It is a type of heating.
【００２０】上記両持ち梁が、その両端の支持部を含め
てシリコン単結晶基板からエッチング等により一体に削
出された場合は、その内部応力はほとんどゼロとなり、
この両持ち梁を振動体として用いた場合、センサ特性を
容易に制御することができる。またシリコン単結晶は、
半導体集積回路の基板材料として、極めて純度の高いも
のが容易に得られるから、機械的特性の揃ったかつ安定
なものが得られ、振動体の共振特性の安定化に寄与する
ことができる。When the above-mentioned doubly supported beam is integrally cut out from the silicon single crystal substrate including the supporting portions at both ends by etching or the like, the internal stress becomes almost zero,
When this double-supported beam is used as the vibrator, the sensor characteristics can be easily controlled. In addition, silicon single crystal is
As a substrate material for a semiconductor integrated circuit, a material having extremely high purity can be easily obtained, so that a material having uniform mechanical characteristics and stable characteristics can be obtained, which can contribute to stabilization of the resonance characteristics of the vibrating body.
【００２１】振動体を構成する材料の熱膨脹係数をαと
して、振動体と基板部分との温度差をＴとすると、発生
する応力σは次式のようになる。When the coefficient of thermal expansion of the material forming the vibrating body is α and the temperature difference between the vibrating body and the substrate portion is T, the generated stress σ is as follows.
【００２２】 σ＝εＥ＝αＴＥ （Ｅ：ヤング率，ε：発生歪み） したがって、冷却効果による温度変化ΔＴと熱応力変化
σとの関係は次式のようになる。Σ = εE = αTE (E: Young's modulus, ε: generated strain) Therefore, the relationship between the temperature change ΔT due to the cooling effect and the thermal stress change σ is as follows.
【００２３】εheat＝Ｋα√Ｇ 一方、発生歪みに対する振動体の共振周波数変化は次式
で理論的に表される。Ε heat = Kα√G On the other hand, the resonance frequency change of the vibrating body with respect to the generated strain is theoretically expressed by the following equation.
【００２４】[0024]
【数１】 [Equation 1]
【００２５】ここで、 αn ，γn ：振動の態様（モード）で決まる定数 Ｌ，ｈ：振動体の長さ、厚さ Ｅe ：実効ヤング率＝Ｅ／（１−ν2 ）、νはポアソン
比 Ｉ：振動体の断面２次モーメント ρ：振動体材料の密度 Ａ：振動体の断面積 また振動体に加わる歪みεは、振動体に予め残留してい
る歪みε0 と熱応力εheatの和で表される。Here, α n , γ n : constants determined by the mode (mode) of vibration L, h: length and thickness of the vibrating body E e : effective Young's modulus = E / (1-ν 2 ), ν Is the Poisson's ratio I: Second moment of area of the vibrating body ρ: Density of the vibrating body material A: Cross-sectional area of the vibrating body The strain ε applied to the vibrating body is the strain ε 0 and the thermal stress ε remaining in the vibrating body in advance. Expressed as the sum of heat .
【００２６】ε＝ε0 ＋εheat＝ε0 ＋Ｋα√Ｇ したがって、質量流量Ｇによる熱応力の変化分を考慮し
た振動体の共振周波数ｆ0 は次式で表される。Ε = ε 0 + ε heat = ε 0 + Kα√G Therefore, the resonance frequency f 0 of the vibrating body in consideration of the change in thermal stress due to the mass flow rate G is expressed by the following equation.
【００２７】[0027]
【数２】 [Equation 2]
【００２８】このように、計測する質量流量Ｇと振動体
の共振周波数ｆ0 との関係は１／４乗特性となる。この
特性は、微小流量域では高感度（出力の傾きが大きい）
で、大流量になるに伴って出力の傾きが低下して行くよ
うなダイナミックレンジの広い理想に近い出力特性が得
られることになる。As described above, the relationship between the mass flow rate G to be measured and the resonance frequency f 0 of the vibrating body has a 1/4 power characteristic. This characteristic has high sensitivity in the minute flow rate range (large output slope)
Thus, it is possible to obtain an output characteristic close to an ideal with a wide dynamic range in which the output slope decreases as the flow rate increases.
【００２９】振動体に加わる応力に対する共振周波数の
特性は、図３に示すような１／２乗特性となる。図３に
おいて、振動体の初期状態として、残留応力がゼロの点
を発熱体（ヒータ）の無加熱ポイントとする。振動体を
センサとして作動させるため、予め発熱体により振動体
を加熱しておくと、周囲の冷たい基板との温度差により
振動体にはこれを圧縮するように応力が加わり、共振周
波数ｆ0 が低下する。The characteristic of the resonance frequency with respect to the stress applied to the vibrating body is a 1/2 power characteristic as shown in FIG. In FIG. 3, as an initial state of the vibrating body, a point where the residual stress is zero is set as a non-heating point of the heating element (heater). In order to operate the vibrating body as a sensor, if the vibrating body is previously heated by the heating element, stress is applied to the vibrating body due to the temperature difference between the vibrating body and the surrounding cold substrate, and the resonance frequency f 0 is increased. descend.
【００３０】すなわち、所定の温度に加熱した振動体の
共振周波数が、流量ゼロのときのセンサ出力となる。そ
して、これに空気流による冷却効果が加わると、振動体
の温度が低下するため、圧縮応力が減少し、空気流量に
応じて共振周波数が上昇する。That is, the resonance frequency of the vibrating body heated to a predetermined temperature becomes the sensor output when the flow rate is zero. Then, when the cooling effect by the air flow is added to this, the temperature of the vibrating body is lowered, the compressive stress is reduced, and the resonance frequency is increased according to the air flow rate.
【００３１】図３から明らかなように、圧縮応力が増大
すると、振動体の共振周波数がゼロになる点がある。こ
の点を構造力学的に座屈点と言い、このときの応力を座
屈応力と言う。フローセンサとして計測のダイナミック
レンジの拡大と感度の向上のためには、座屈点により近
い領域における応力対周波数特性を用いるのがよいが、
加熱による圧縮応力が座屈点を越えると、振動体として
機能しない。As is apparent from FIG. 3, when the compressive stress increases, the resonance frequency of the vibrating body becomes zero. This point is called a buckling point in structural mechanics, and the stress at this time is called a buckling stress. In order to expand the dynamic range of measurement and improve sensitivity as a flow sensor, it is better to use stress versus frequency characteristics in a region closer to the buckling point,
If the compressive stress due to heating exceeds the buckling point, it will not function as a vibrator.
【００３２】したがって、振動体をフローセンサとして
機能させるための発熱体による加熱は、座屈点を越えな
い範囲で、かつ所望の感度およびダイナミックレンジが
得られるように、なるべく圧縮応力の大きい側に設定す
る必要がある。Therefore, the heating by the heating element for causing the vibrating body to function as a flow sensor is applied to the side where the compressive stress is as large as possible so that the buckling point is not exceeded and the desired sensitivity and dynamic range are obtained. Must be set.
【００３３】振動体の座屈点はその振動体の寸法で決定
されることが知られており（オイラーの座屈点）、これ
を座屈歪みεb で表すと、次式のようになる（ｈ：振動
体の厚さ、Ｌ：振動体の長さ）。It is known that the buckling point of the vibrating body is determined by the size of the vibrating body (Euler's buckling point). When this is expressed by buckling strain ε b , the following equation is obtained. (H: thickness of the vibrating body, L: length of the vibrating body).
【００３４】εb ＝（−π2 ／３）ｈ2 ／Ｌ2 したがって、振動体の厚さｈおよび長さＬと、振動体に
予め残留する歪みε０と、発熱体の熱によって生じる圧
縮歪みεｈｅａｔとが以下のような関係を満足するよう
な設定となる。The ε b = (- π 2/ 3) h 2 / L 2 Therefore, the thickness h and the length L of the vibrating body, the strain epsilon 0 to advance remaining in the vibration member caused by the heat of the heating element compression The strain ε heat is set so as to satisfy the following relationship.
【００３５】ε0 ＋εheat＞（−π2 ／３）ｈ2 ／Ｌ2 また、εheatを発熱体の加熱温度Ｔとの関係に直すと εb ＋αＴ＞（−π2 ／３）ｈ2 ／Ｌ2 すなわち、本発明では、発熱体の加熱温度Ｔ、振動体の
残留応力ε0 および振動体の寸法（ｈ，Ｌ）が上式を満
足させる関係にあることも特徴となっている。The ε 0 + ε heat> (- π 2/3) h 2 / L 2 Further, when fix epsilon heat on the relationship between the heating temperature T of the heating element ε b + αT> (- π 2/3) h 2 / L 2, that is, the present invention is also characterized in that the heating temperature T of the heating element, the residual stress ε 0 of the vibrating body, and the dimension (h, L) of the vibrating body satisfy the above equation.
【００３６】また、フローセンサとして振動体を用いた
場合、出力が周波数出力となり、Ａ／Ｄコンバータが不
要となるから、センサの計測レンジおよび精度がＡ／Ｄ
コンバータの性能により制限を受けるという従来技術の
問題点が解決される。そしてこの場合、センサ出力をエ
ンジン制御用コンピュータのタイマカウンタポートに直
接入力することができ、コンピュータの時間計測が高精
度なこと相俟って、空気流量の高精度、高分解能計測が
可能になる。また、センサ出力が周波数変調信号である
ため、電磁ノイズやグラウンドノイズ等に影響されず、
誤差の少ない信号伝送が実現できる。When a vibrating body is used as the flow sensor, the output is a frequency output and the A / D converter is not required, so that the measurement range and accuracy of the sensor are A / D.
The prior art problem of being limited by converter performance is solved. In this case, the sensor output can be directly input to the timer counter port of the engine control computer, and the time measurement of the computer is highly accurate, which enables highly accurate and high resolution measurement of the air flow rate. . Also, since the sensor output is a frequency modulated signal, it is not affected by electromagnetic noise, ground noise, etc.
Signal transmission with less error can be realized.
【００３７】発熱体の近傍に配設された両持ち梁に加わ
る熱応力変化の計測は、必ずしも上記両持ち梁が振動体
でなくても可能ではあるが、振動体は応力に対する検出
感度が極めて高く、微妙な温度変化に対しても十分検出
できるほどの周波数変化をもたらす。したがって、従来
技術のように発熱体の温度を高温にしておく必要がな
く、信頼性および耐久性が著しく向上する。The change in thermal stress applied to the both-supported beams arranged near the heating element can be measured even if the above-mentioned both-supported beams are not the vibrating body. However, the vibrating body has extremely high detection sensitivity to stress. The frequency change is high enough to be detected even with a slight temperature change. Therefore, unlike the prior art, it is not necessary to keep the temperature of the heating element at a high temperature, and the reliability and durability are significantly improved.
【００３８】また、振動体は、上述のように温度変化に
敏感であるため、発熱体自身の空気流による直接の冷却
効果だけでなく、振動体付近の熱分布の変化にも敏感に
反応する。Further, since the vibrating body is sensitive to the temperature change as described above, it is sensitive not only to the direct cooling effect of the air flow of the heating element itself but also to the change of the heat distribution near the vibrating body. .
【００３９】ところで、発熱体を有するセンサ構造体上
における発熱体の周囲の２次元温度分布を温度等高線で
表すと、図４（ａ）に示すように、発熱体を中心に左右
対称になるが、発熱体の表面上を空気流が流れると、空
気流の流量とともに流れの方向によって２次元温度分布
が変化する。そこで、空気流による発熱体の温度低下を
フィードバック制御によって補って、発熱体の温度を常
に一定に保った状態にしておくと、図４（ｂ）に示すよ
うに、発熱体の上流と下流とで熱分布に差異を生じる。By the way, when the two-dimensional temperature distribution around the heating element on the sensor structure having the heating element is represented by a temperature contour line, it is symmetrical with respect to the heating element as shown in FIG. 4 (a). When an air flow flows over the surface of the heating element, the two-dimensional temperature distribution changes depending on the flow direction and the flow direction of the air flow. Therefore, when the temperature drop of the heating element due to the air flow is compensated by the feedback control so that the temperature of the heating element is always kept constant, as shown in FIG. Causes a difference in heat distribution.
【００４０】したがって、このような熱分布が変化する
部分に、温度変化を検出する振動体を配置することによ
り、発熱体と振動体とを配設したセンサ基板上における
２次元的な熱分布の空気流による変化も検出できるエア
フローセンサが実現できる。特に熱分布の変化は、質量
流量のみでなく、流れの方向成分の情報を含んでいるか
ら、流れの方向により温度に差異の発生する複数位置に
それぞれ振動体を配設することにより、流れの方向も検
出可能なエアフローセンサが実現できる。図４（ｂ）に
おいては、発熱体に対し、空気流の上流側と下流側とに
振動体を対称的に配設し、各振動体の出力周波数信号の
差分を算出することにより、逆流も検出可能なエアフロ
ーセンサが実現され、自動車エンジンの高精度空燃比制
御に貢献することができる。Therefore, by disposing a vibrating body for detecting a temperature change in such a portion where the heat distribution changes, a two-dimensional heat distribution of the two-dimensional heat distribution on the sensor substrate on which the heat generating body and the vibrating body are arranged is provided. An air flow sensor that can detect changes due to air flow can be realized. In particular, the change in the heat distribution includes not only the mass flow rate but also the information on the direction component of the flow. Therefore, by disposing vibrators at multiple positions where temperature differences occur depending on the flow direction, An air flow sensor that can detect the direction can be realized. In FIG. 4 (b), the vibrating body is symmetrically arranged on the upstream side and the downstream side of the air flow with respect to the heating element, and the difference in the output frequency signal of each vibrating body is calculated, so that the back flow can be prevented. A detectable airflow sensor is realized, which can contribute to high-precision air-fuel ratio control of an automobile engine.
【００４１】[0041]
【発明の実施の形態】以下、本発明の実施の形態につい
て、図面を参照して説明する。BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.
【００４２】図５は本発明による流量測定装置の第１の
実施の形態を示す振動式エアフローセンサの斜視図、図
６はその要部の拡大斜視図、図７は図６の VII−VII 線
に沿った拡大断面図、図８は振動体の拡大断面図であ
る。FIG. 5 is a perspective view of a vibration type air flow sensor showing a first embodiment of a flow rate measuring device according to the present invention, FIG. 6 is an enlarged perspective view of the main part thereof, and FIG. 7 is a VII-VII line of FIG. 8 is an enlarged cross-sectional view of the vibrating body.
【００４３】図５において、２０はシリコン単結晶基板
１からなるセンサ構造体で、基板１の上面１ａは、例え
ば図７に示すように、シリコン単結晶のミラー指数で表
される（１００）面となっている。２はこのシリコン単
結晶基板１からエッチング加工により一体に削出された
両持ち梁構造を有する三角柱からなる振動体である。In FIG. 5, reference numeral 20 denotes a sensor structure composed of a silicon single crystal substrate 1. The upper surface 1a of the substrate 1 is, for example, as shown in FIG. 7, a (100) plane represented by the Miller index of the silicon single crystal. Has become. Reference numeral 2 is a vibrating body composed of a triangular prism having a doubly supported beam structure, which is integrally cut out from the silicon single crystal substrate 1 by etching.
【００４４】この振動体２の断面形状は、基板面１ａで
ある（１００）面が二等辺三角形の底面になり、二等辺
の部分はともに（１１１）面になっている。上記底面と
二等辺とのなす角度は、結晶面から見て（１００）面と
（１１１）面との交わる角度である５４．７度となって
おり、振動体２の長手方向は、基板面１ａ内での＜１１
０＞方向に平行であり、振動体２はその両端を固定端と
してシリコン単結晶基板１に支持され、両持ち梁構造を
構成している。一例として、振動体２の寸法を以下に記
す（図８参照）。Regarding the cross-sectional shape of the vibrating body 2, the (100) plane, which is the substrate surface 1a, is the bottom surface of an isosceles triangle, and the isosceles parts are both (111) planes. The angle between the bottom face and the isosceles is 54.7 degrees, which is the angle at which the (100) face and the (111) face intersect with each other when viewed from the crystal face, and the longitudinal direction of the vibrating body 2 is the substrate face. <11 within 1a
The vibrating body 2 is parallel to the 0> direction, and the vibrating body 2 is supported by the silicon single crystal substrate 1 with both ends thereof as fixed ends to form a doubly supported beam structure. As an example, the dimensions of the vibrating body 2 are described below (see FIG. 8).
【００４５】 振動体長さＬ： １．６mm 振動体高さｈ： ２０μｍ 振動体幅ｂ ： ２８．３μｍ 基板面１ａ上には、白金の薄膜により形成された発熱体
３，３が振動体２の各固定端近傍にそれぞれ配設されて
おり、さらに、図６に示すように、振動体２の一方の固
定端から振動体２の面上に延びる駆動用抵抗４と、振動
体２の他方の固定端から振動体２の面上に延びる振動検
出用抵抗（ピエゾ抵抗）５とが拡散抵抗により形成され
ている。Vibrating body length L: 1.6 mm Vibrating body height h: 20 μm Vibrating body width b: 28.3 μm On the substrate surface 1 a, heating elements 3 and 3 formed of a platinum thin film are provided on each vibrating body 2. As shown in FIG. 6, a driving resistor 4 is provided near each fixed end and extends from one fixed end of the vibrating body 2 onto the surface of the vibrating body 2, and another vibrating body 2 is fixed. A vibration detecting resistance (piezo resistance) 5 extending from the end to the surface of the vibrating body 2 is formed by a diffusion resistance.
【００４６】シリコン単結晶基板１は、裏面からエッチ
ング加工等によって深く掘られ、発熱体３，３や振動体
２が配設されている部分はダイアフラム構造を有してい
る。これは、少ない電力で発熱体の温度を上昇させるた
めと、センサの感度と応答性を向上させるために、熱容
量を下げる必要があるからである。The silicon single crystal substrate 1 is deeply dug from the back surface by etching or the like, and the portion where the heating elements 3 and 3 and the vibrating body 2 are arranged has a diaphragm structure. This is because it is necessary to lower the heat capacity in order to raise the temperature of the heating element with a small amount of electric power and to improve the sensitivity and responsiveness of the sensor.
【００４７】図９は、振動体２に振動を励起させ、かつ
その振動を検出する回路の一例を示す概略図である。図
６に示すように、振動体２上には駆動用抵抗４が拡散に
より形成されており、この駆動用抵抗４に交番電流を供
給して交番的に発熱させることによって、振動体２に交
番応力をかけ振動を励起させる。振動体２上には検出用
ピエゾ抵抗５が拡散により形成されているので、このピ
エゾ抵抗５が振動体２が振動により曲がることにより発
生する応力を検出用抵抗５の抵抗変化ととして読み出せ
ばよい。FIG. 9 is a schematic diagram showing an example of a circuit for exciting the vibration of the vibrating body 2 and detecting the vibration. As shown in FIG. 6, a driving resistor 4 is formed on the vibrating body 2 by diffusion, and an alternating current is supplied to the driving resistor 4 to cause the vibrating body 2 to generate heat in an alternating manner. Apply stress to excite vibration. Since the detecting piezoresistor 5 is formed on the vibrating body 2 by diffusion, if the piezoresistor 5 reads the stress generated when the vibrating body 2 bends due to the vibration as the resistance change of the detecting resistor 5. Good.
【００４８】振動体２の自励発振は、振動の検出信号を
駆動用抵抗４に正帰還させることにより発生させる。図
９においては、検出用抵抗５を含むブリッジ回路６で検
出した検出出力をプリアンプ７で増幅して得られた周波
数出力を駆動用抵抗４に帰還させる正帰還ループに、増
幅率を制御して駆動用抵抗４に供給される電力を一定に
コントロールするＡＧＣアンプ８を介在させて、正帰還
による無限大発振を防止している。The self-excited oscillation of the vibrating body 2 is generated by positively feeding back the vibration detection signal to the driving resistor 4. In FIG. 9, the amplification factor is controlled in the positive feedback loop that feeds back the frequency output obtained by amplifying the detection output detected by the bridge circuit 6 including the detection resistor 5 by the preamplifier 7 to the driving resistor 4. An AGC amplifier 8 that constantly controls the electric power supplied to the driving resistor 4 is interposed to prevent infinite oscillation due to positive feedback.
【００４９】図１０は、空気流の流量が０〜１５０g/se
c の範囲において発熱体３，３の温度が約５０℃変化す
ると仮定した場合の空気流の質量流量と振動体２の共振
周波数特性を示すグラフである。図１０から明らかなよ
うに、０〜１５０g/sec の流量範囲で共振周波数の変化
範囲は２３．３kHz 〜３９．９kHz となる。この場合、
エンジン制御用コンピュータ内のカウンタ／タイマ機能
を用いて、１MHz の基準クロックと１msecの時間で周波
数計測を行なう場合において、１．０g/sec の微小流領
域から１５０g/sec まで±３％の精度分解能をもって計
測することができる。このように、本実施の形態によれ
ば、１５０倍のダイナミックレンジの領域を精度良く計
測することが可能な高感度流量測定装置を得ることがで
きる。FIG. 10 shows that the flow rate of the air flow is 0 to 150 g / se.
6 is a graph showing the mass flow rate of the air flow and the resonance frequency characteristic of the vibrating body 2 when it is assumed that the temperature of the heating elements 3, 3 changes by about 50 ° C. in the range of c. As is clear from FIG. 10, the change range of the resonance frequency is 23.3 kHz to 39.9 kHz in the flow rate range of 0 to 150 g / sec. in this case,
When the counter / timer function in the engine control computer is used to measure the frequency with a reference clock of 1 MHz and a time of 1 msec, a precision resolution of ± 3% from a minute flow area of 1.0 g / sec to 150 g / sec. Can be measured with. As described above, according to the present embodiment, it is possible to obtain a high-sensitivity flow rate measuring device capable of accurately measuring a region having a dynamic range of 150 times.
【００５０】図１１は、図５〜図８に示す振動体２の製
造方法の一例を説明する工程図である。FIG. 11 is a process chart for explaining an example of a method of manufacturing the vibrating body 2 shown in FIGS.
【００５１】工程１：先ず基板面が（１００）面である
シリコンウエハ（シリコン単結晶基板）１０を用意す
る。Step 1: First, a silicon wafer (silicon single crystal substrate) 10 whose substrate surface is a (100) surface is prepared.
【００５２】工程２：エッチングマスクにするためのシ
リコン酸化膜１１をシリコンウエハ１０の表面に付け
る。ここでは、通常の半導体集積回路の製造工程で用い
られる熱酸化による方法あるいはＣＶＤによる膜形成法
等を適用すればよい。なお、このエッチングマスクは、
酸化膜に限定されるものでなく、窒化膜その他、強アル
カリ溶液による後工程でのエッチングに対し十分な耐性
を有する膜材料であればよい。Step 2: A silicon oxide film 11 serving as an etching mask is attached to the surface of the silicon wafer 10. Here, a method using thermal oxidation or a film forming method using CVD, which is used in a normal semiconductor integrated circuit manufacturing process, may be applied. This etching mask is
The material is not limited to the oxide film, and may be a nitride film or any other film material having sufficient resistance to etching in a post-process using a strong alkaline solution.
【００５３】工程３：振動体２の形状を決定するため、
酸化膜１１のパターニングを行なって、作成すべき振動
体２の幅に等しい間隔を隔てて＜１１０＞方向に延びる
互いに平行でかつ作成すべき振動体２の長さに等しい長
さを有する一対の開口１２，１２を備えた酸化膜マスク
１３をシリコンウエハ１０の表面に形成する。このパタ
ーニングは、フォトレジスト等を用いたフォトリソグラ
フィ工程の後、エッチング液としてフッ酸水溶液等を用
いて行なう。Step 3: To determine the shape of the vibrator 2,
By patterning the oxide film 11, a pair of parallel to each other extending in the <110> direction at intervals equal to the width of the vibrator 2 to be created and having lengths equal to the length of the vibrator 2 to be created. An oxide film mask 13 having openings 12 and 12 is formed on the surface of the silicon wafer 10. This patterning is performed using a hydrofluoric acid aqueous solution or the like as an etching solution after a photolithography process using a photoresist or the like.
【００５４】工程４：酸化膜マスク１３をエッチングマ
スクとして、シリコン基板に対して開口１２，１２を通
じてエッチングを行なって、基板面に対してほぼ垂直な
壁面を備えた互いに平行な一対の凹溝１４，１４を形成
する。この場合のエッチングは、フッ素系のガスを用い
たＲＩＥ（リアクティブ イオンエッチング）法を用い
て行なう。Step 4: Using the oxide film mask 13 as an etching mask, the silicon substrate is etched through the openings 12 and 12 to form a pair of mutually parallel concave grooves 14 having wall surfaces substantially perpendicular to the substrate surface. , 14 are formed. The etching in this case is performed by the RIE (reactive ion etching) method using a fluorine-based gas.
【００５５】工程５：同じ酸化膜マスク１３をエッチン
グマスクとして、凹溝１４，１４に対してＫＯＨやＴＭ
ＡＨ（テトラメチルアンモニウムハイドロオキサイド）
等の強アルカリ溶液によってエッチングを行なう。Step 5: Using the same oxide film mask 13 as an etching mask, KOH or TM is applied to the grooves 14, 14.
AH (tetramethylammonium hydroxide)
Etching is performed with a strong alkaline solution such as.
【００５６】このように、シリコン単結晶材料を上記の
ような特定の強アルカリ溶液によってエッチングを行な
うと、シリコン単結晶の特定の結晶面によってエッチン
グ速度が著しく異なる性質がある。例えばシリコン単結
晶の（１００）面や（１１０）面に対して（１１１）面
のエッチングされる速度は非常に遅く、速度比で約１０
０：１程度になる。このような性質から、この工程での
エッチングは、エッチング速度の速い（１１０）面を進
行面としてその両端部に（１１１）面が残る状態で結晶
異方性エッチングが進行して行く。As described above, when the silicon single crystal material is etched by the above-mentioned specific strong alkaline solution, the etching rate remarkably varies depending on the specific crystal plane of the silicon single crystal. For example, the etching rate of the (111) plane is very slow with respect to the (100) plane and the (110) plane of silicon single crystal, and the etching rate is about 10
It will be about 0: 1. Due to such properties, in the etching in this step, the crystal anisotropic etching proceeds with the (110) plane having a high etching rate as the progress plane and the (111) planes remaining at both ends thereof.
【００５７】工程６：最終的には振動体２となる部分の
両側から（１１０）面を進行面として横方向にエッチン
グが進行して行き、両凹溝１４，１４間がそれらの底部
において互いに連通し、振動体２となる部分の下方に空
間１５が形成されることによって、残った２つの（１１
１）面と１つの（１００）面とによって囲まれた三角柱
からなる梁を得る。最終的に梁の上面を覆う酸化膜マス
ク１３をエッチング等で除去すればよい。Step 6: Etching proceeds laterally from both sides of the portion which will finally become the vibrating body 2 with the (110) plane as the traveling plane, and the two concave grooves 14 and 14 are mutually at their bottoms. A space 15 is formed below the portion which is in communication and becomes the vibrating body 2, so that the remaining two (11
A beam consisting of a triangular prism surrounded by 1) plane and one (100) plane is obtained. Finally, the oxide film mask 13 covering the upper surface of the beam may be removed by etching or the like.
【００５８】このような結晶異方性エッチングを実施す
れば、エッチング後の形状がエッチング条件（温度や撹
拌等）によらず高い精度で予測でき、加工が容易とな
る。If such crystal anisotropic etching is carried out, the shape after etching can be predicted with high accuracy regardless of etching conditions (temperature, stirring, etc.), and processing becomes easy.
【００５９】このような製造工程によって得られた、１
つの（１００）面と、極めてエッチング速度が遅い２つ
の（１１１）面とで構成された三角柱からなる振動体２
は、結晶面上の幾何学的特性から、その形状がほぼ決定
される。すなわち、振動体２の幅ｂが酸化膜マスク１３
上のパターニングで決定されれば、三角柱断面における
高さｈは一義的に決まってしまう。1 obtained by such a manufacturing process
A vibrating body 2 composed of a triangular prism composed of two (100) planes and two (111) planes having an extremely low etching rate.
The shape is almost determined from the geometrical characteristics on the crystal plane. That is, the width b of the vibrating body 2 is set to the oxide film mask 13
If determined by the above patterning, the height h in the triangular prism cross section is uniquely determined.
【００６０】ｈ＝tan(５４．７°）・ｂ／２ このことは、振動体２の幅ｂの加工精度を高めておけ
ば、高さｈの寸法精度が自動的に向上することを意味す
る。H = tan (54.7 °) · b / 2 This means that if the processing accuracy of the width b of the vibrating body 2 is increased, the dimensional accuracy of the height h is automatically improved. To do.
【００６１】一般に、エッチングによって深さ方向の加
工を行なう場合、その加工精度はエッチングの終点を判
断するのが困難なためその寸法精度は悪い。たとえばＲ
ＩＥ等でシリコンのエッチングを行なう場合でも、深さ
寸法の加工の絶対値で±５％程度のばらつきが生じた
り、加工の均一性においてもウエハ面内で±５％いない
の精度を得るのに極めて複雑なエッチング装置を用いな
ければならない。一方、フォトリソグラフィによるパタ
ーニングで代表される面上での加工精度は、半導体集積
回路の製造工程の進歩に見られるように極めて高精度な
加工（絶対、相対加工精度で±１％以下）が比較的容易
に得られる。In general, when etching is performed in the depth direction, it is difficult to determine the end point of etching, so that the dimensional accuracy is low. For example R
Even when the silicon is etched by IE or the like, the absolute value of the processing of the depth dimension may have a variation of about ± 5%, and the uniformity of the processing can be obtained within the accuracy of ± 5% within the wafer surface. Very complex etching equipment must be used. On the other hand, the processing accuracy on the surface typified by patterning by photolithography is very high as compared with the advanced manufacturing process of semiconductor integrated circuits (absolute and relative processing accuracy is less than ± 1%). Easily obtained.
【００６２】したがって、上述した製造方法によれば、
その製造工程と得られる構造体の構造的特徴とから、深
さ方向の加工精度（ここでは三角断面の高さｈ）につい
ても面内のパターニング精度と同程度の精度が容易に実
現できる。Therefore, according to the manufacturing method described above,
Due to the manufacturing process and the structural characteristics of the obtained structure, the processing accuracy in the depth direction (here, the height h of the triangular cross section) can be easily achieved with the same accuracy as the in-plane patterning accuracy.
【００６３】上記工程４においては、ＲＩＥによるエッ
チング加工を施しているが、この工程でのエッチング加
工は、振動体２の下部の中空になる部分が貫通できるだ
けの深さがあればよく、次式に示すようにその下限より
深くエッチングすれば事足りることになる（エッチング
壁面が基板面に対して９０°をなす場合）。In step 4 above, etching processing by RIE is performed. The etching processing in this step should have a depth such that the hollow portion in the lower portion of the vibrating body 2 can penetrate, and the following formula is used. It is sufficient to etch deeper than the lower limit as shown in (1) (when the etching wall surface forms 90 ° with respect to the substrate surface).
【００６４】エッチング深さｄ＞ｂtan(５４．７°） 次に、図１２は本発明による流量測定装置の第２の実施
の形態を示す振動式エアフローセンサの斜視図である。Etching Depth d> btan (54.7 °) Next, FIG. 12 is a perspective view of a vibration type air flow sensor showing a second embodiment of the flow rate measuring device according to the present invention.
【００６５】本実施の形態のエアフローセンサの特徴
は、空気流の流量のみでなく流れの方向をも検出可能な
点にある。The feature of the air flow sensor of the present embodiment is that not only the flow rate of the air flow but also the flow direction can be detected.
【００６６】図１２に示すセンサ構造体３０は、図５と
同様のシリコン単結晶基板３１上に特性の一致した２つ
の振動体２，２を、計測する空気流に対して中央の発熱
体３３を挾んで上流側と下流側に配置してある。センサ
構造体３０は、図５に示す第１の実施の形態と同様のダ
イアフラム構造を有し、また振動体２，２の構造および
それらの自励振動の機構と動作も第１の実施の形態と同
様である。The sensor structure 30 shown in FIG. 12 has two vibrators 2 and 2 having the same characteristics on a silicon single crystal substrate 31 similar to that shown in FIG. It is located on the upstream side and the downstream side. The sensor structure 30 has a diaphragm structure similar to that of the first embodiment shown in FIG. 5, and the structures of the vibrators 2 and 2 and the mechanism and operation of their self-excited vibration are the same as those of the first embodiment. Is the same as.
【００６７】空気流量の測定には、いずれか一方の振動
体２の共振周波数を測定することにより達成できる。ま
た、発熱体３３の下流側よりも上流側の方が温度低下が
大きいことから、空気流の方向の検出は、２つの振動体
２，２の共振周波数の差を求め、その正負を判定するこ
とにより達成できる。すなわち、振動体２，２の共振周
波数のうち、上流側をｆup、下流側をｆdownとすると、
ｆup−ｆdown＜０で順流、ｆup−ｆdown＞０で逆流とな
る。The air flow rate can be measured by measuring the resonance frequency of either one of the vibrators 2. Further, since the temperature drop is larger on the upstream side than on the downstream side of the heating element 33, the direction of the air flow is detected by obtaining the difference between the resonance frequencies of the two vibrating bodies 2 and 2 and determining the positive / negative thereof. Can be achieved by That is, of the resonance frequencies of the vibrators 2 and 2, if the upstream side is f up and the downstream side is f down ,
When f up −f down <0, the flow is forward flow, and when f up −f down > 0, the flow is back flow.
【００６８】発熱体３３の駆動には、空気流の冷却効果
による温度低下を補うべく、温度検出用抵抗と、外部回
路とを用いて、発熱体３３の温度を一定に保つようにし
ている。すなわち、発熱体３３は、図１３に示すよう
に、発熱用抵抗ＲH と発熱温度をモニタする温度検出用
抵抗ＲHTからなり、さらに基準温度（ここでは空気温）
を測定するための抵抗ＲT を図１４に示す外部回路に設
けてあり、抵抗ＲHT，ＲT と定抵抗Ｒ1 ，Ｒ2 とによっ
てブリッジ回路を構成している。そして冷却により発熱
体３３の温度が低下するとブリッジ回路のバランスが崩
れ、ブリッジ出力に電位差が発生する。この電位差を演
算増幅器３４を通じて増幅して、その出力により、発熱
用抵抗ＲHTに対する供給電流を増加させて、発熱体３３
を加熱するように構成されている。このようなフィード
バック回路を用いることにより、発熱体３３の温度が基
準温度（空気温）に対して所定の温度差を有する温度の
制御される。In order to drive the heating element 33, the temperature of the heating element 33 is kept constant by using a temperature detecting resistor and an external circuit in order to compensate for the temperature drop due to the cooling effect of the air flow. That is, as shown in FIG. 13, the heating element 33 includes a heating resistor R H and a temperature detecting resistor R HT for monitoring the heating temperature, and further has a reference temperature (air temperature here).
The the R T resistor for measuring is provided with an external circuit shown in FIG. 14, the resistance R HT, constitute a bridge circuit by the R T and constant resistance R 1, R 2. When the temperature of the heating element 33 decreases due to cooling, the balance of the bridge circuit is lost and a potential difference occurs in the bridge output. This potential difference is amplified through the operational amplifier 34, and the output thereof increases the supply current to the heating resistor R HT , and the heating element 33.
Is configured to be heated. By using such a feedback circuit, the temperature of the heating element 33 is controlled to a temperature having a predetermined temperature difference from the reference temperature (air temperature).
【００６９】図１５は本発明による流量測定装置の第３
の実施の形態を示す振動式エアフローセンサの斜視図、
図１６はその要部の拡大断面図である。FIG. 15 shows a third example of the flow rate measuring device according to the present invention.
A perspective view of a vibration type air flow sensor showing an embodiment of
FIG. 16 is an enlarged cross-sectional view of the main part thereof.
【００７０】本実施の形態におけるエアフローセンサの
センサ構造体４０は、シリコン単結晶基板４１上に２つ
の振動体２，２を、計測する空気流に対して中央の発熱
体３３を挾んで上流側と下流側に配置してある点、およ
び空気流の流量のみでなく流れの方向をも検出可能な点
で、図１２に示す第２の実施の形態と同様であるが、本
実施の形態においては、センサ構造体４０の発熱体３３
および振動体２，２が配設されているダイヤフラム構造
部が、図１６に示すように、このダイヤフラム構造部と
の間に所定の間隙４４を形成したガラスキャップ４５で
封止された構成を有する。この封止された間隙４４は１
０〜３Torr程度の真空に保たれていることにより、振動
体２，２の空気粘性による振動の減衰効果が減少し、極
めて安定で高純度の共振振動が得られる。上記ガラスキ
ャップ４５は、陽極接合法等により、基板４１の上面に
気密に接合されている。The sensor structure 40 of the air flow sensor according to the present embodiment has two vibrating bodies 2 and 2 on a silicon single crystal substrate 41, and an upstream side with respect to the air flow to be measured with the central heating element 33 interposed therebetween. Is similar to that of the second embodiment shown in FIG. 12 in that it is located on the downstream side and that the flow direction as well as the flow rate of the air flow can be detected. Is the heating element 33 of the sensor structure 40.
As shown in FIG. 16, the diaphragm structure portion in which the vibrating bodies 2 and 2 are disposed is sealed with a glass cap 45 having a predetermined gap 44 formed between the diaphragm structure portion and the diaphragm structure portion. . This sealed gap 44 is 1
By maintaining a vacuum of about 0 to 3 Torr, the damping effect of vibration due to the air viscosity of the vibrating bodies 2 and 2 is reduced, and extremely stable and highly pure resonance vibration is obtained. The glass cap 45 is hermetically bonded to the upper surface of the substrate 41 by an anodic bonding method or the like.
【００７１】このように、上面を封止された構造の場
合、空気流はダイヤフラム構造部の裏面に沿って流れる
ように構成される。そのため、基板４１の側面がエッチ
ング加工等により削られた形状になっており、また、ダ
イヤフラム構造部は、発熱体３３の熱が裏面に十分に作
用するような厚さに設定されている。Thus, in the case of the structure in which the upper surface is sealed, the air flow is configured to flow along the back surface of the diaphragm structure portion. Therefore, the side surface of the substrate 41 is shaped by etching or the like, and the diaphragm structure is set to a thickness such that the heat of the heating element 33 sufficiently acts on the back surface.
【００７２】また、本実施の形態においては、振動体２
に振動を励起させるために、駆動用抵抗に代えて、基板
４１の上面とガラスキャップ４５の下面との間に形成さ
れた間隙４４を利用した駆動用静電電極を用いている。
すなわち、図１６に示すように、振動体２の上面に下部
電極４６が設けられ、この下部電極４６に対向する上部
電極４７がガラスキャップ４５の下面に設けられてい
る。そして、両電極４６，４７間に交番電圧を印加する
ことにより、静電気力によって振動体２が振動せしめら
れる。振動体２の振動は、前述の実施の形態と同様に、
振動体２の一方の固定端付近に設けられたピエゾ抵抗４
８によってその抵抗変化として検出される。Further, in the present embodiment, the vibrating body 2
In order to excite the vibration, instead of the driving resistance, a driving electrostatic electrode utilizing a gap 44 formed between the upper surface of the substrate 41 and the lower surface of the glass cap 45 is used.
That is, as shown in FIG. 16, the lower electrode 46 is provided on the upper surface of the vibrating body 2, and the upper electrode 47 facing the lower electrode 46 is provided on the lower surface of the glass cap 45. Then, by applying an alternating voltage between the electrodes 46 and 47, the vibrating body 2 is vibrated by the electrostatic force. The vibration of the vibrating body 2 is similar to that of the above-described embodiment.
Piezoresistor 4 provided near one fixed end of the vibrating body 2
It is detected by 8 as the resistance change.
【００７３】図１７は、振動体２に振動を励起させ、か
つその振動を検出する回路の一例を示す概略図である。FIG. 17 is a schematic diagram showing an example of a circuit for exciting the vibration of the vibrating body 2 and detecting the vibration.
【００７４】振動体２の自励発振は、駆動用電極４６，
４７に正帰還させることにより発生させる。図９と同様
に、検出用ピエゾ抵抗４８を含むブリッジ回路４９で検
出した検出出力をプリアンプ５０で増幅して得られた周
波数出力を駆動用電極４６，４７に帰還させる正帰還ル
ープに、増幅率を制御して駆動用電極４６，４７に供給
される電力を一定にコントロールするＡＧＣアンプ５１
を介在させて、正帰還による無限大発振を防止してい
る。Self-excited oscillation of the vibrating body 2 is caused by the drive electrodes 46,
It is generated by positively feeding back to 47. Similar to FIG. 9, the amplification factor is added to the positive feedback loop that feeds back the frequency output obtained by amplifying the detection output detected by the bridge circuit 49 including the detection piezoresistor 48 by the preamplifier 50 to the drive electrodes 46 and 47. AGC amplifier 51 for controlling the electric power supplied to the driving electrodes 46 and 47 by controlling
To prevent infinite oscillation due to positive feedback.
【００７５】以上の実施の形態においては、空気流の冷
却効果による発熱体３，３３の温度変化に基づく両持ち
梁の熱応力変化をすべて両持ち梁構造を有する振動体２
の共振周波数の変化として検出しているが、これは前述
したように、振動体２が極めて検出感度が良いからであ
る。しかしながら、本発明は、両持ち梁の熱応力変化を
直接ピエゾ抵抗等を用いて検出する形式の流量測定装置
をも含むことは言うまでもない。In the above embodiment, all the changes in the thermal stress of the doubly supported beam due to the temperature change of the heating elements 3 and 33 due to the cooling effect of the air flow have the doubly supported beam structure.
Is detected as a change in the resonance frequency, because, as described above, the vibrating body 2 has extremely high detection sensitivity. However, it goes without saying that the present invention also includes a flow rate measuring device of a type that directly detects a thermal stress change of the both-supported beam by using piezo resistance or the like.
【図１】両端を固定した剛体棒を加熱することにより剛
体棒に応力が発生する機構を説明する図FIG. 1 is a diagram illustrating a mechanism in which stress is generated in a rigid rod by heating a rigid rod having both ends fixed.
【図２】両持ち梁構造を有する振動体を加熱することに
より振動体に応力が発生する機構を説明する図FIG. 2 is a diagram illustrating a mechanism in which stress is generated in a vibrating body by heating the vibrating body having a doubly supported beam structure.
【図３】両持ち梁構造を有する振動体に加わる応力に対
する共振周波数の変化を示す特性図FIG. 3 is a characteristic diagram showing changes in resonance frequency with respect to stress applied to a vibrator having a doubly supported beam structure.
【図４】センサ構造体上における発熱体近傍の２次元温
度分布を示す図FIG. 4 is a diagram showing a two-dimensional temperature distribution near a heating element on a sensor structure.
【図５】本発明による流量測定装置の第１の実施の形態
を示す振動式エアフローセンサの斜視図FIG. 5 is a perspective view of a vibration type air flow sensor showing a first embodiment of a flow rate measuring device according to the present invention.
【図６】図５の要部拡大斜視図FIG. 6 is an enlarged perspective view of an essential part of FIG.
【図７】図６の VII−VII 線に沿った拡大断面図FIG. 7 is an enlarged sectional view taken along line VII-VII of FIG. 6;
【図８】振動体の拡大断面図FIG. 8 is an enlarged sectional view of a vibrating body.
【図９】振動検出回路の一例を示す概略図FIG. 9 is a schematic diagram showing an example of a vibration detection circuit.
【図１０】空気流の質量流量に対すると振動体の共振周
波数特性を示すグラフFIG. 10 is a graph showing the resonance frequency characteristic of the vibrating body with respect to the mass flow rate of the air flow.
【図１１】振動体の製造方法を説明する工程図FIG. 11 is a process diagram illustrating a method for manufacturing a vibrator.
【図１２】本発明による流量測定装置の第２の実施の形
態を示す振動式エアフローセンサの斜視図FIG. 12 is a perspective view of a vibration type air flow sensor showing a second embodiment of the flow rate measuring device according to the present invention.
【図１３】同 要部の概略的平面図FIG. 13 is a schematic plan view of the same part.
【図１４】同 発熱体の温度を一定に保つ装置の回路図FIG. 14 is a circuit diagram of a device for keeping the temperature of the heating element constant.
【図１５】本発明による流量測定装置の第３の実施の形
態を示す振動式エアフローセンサの斜視図FIG. 15 is a perspective view of a vibration type air flow sensor showing a third embodiment of the flow rate measuring device according to the present invention.
【図１６】同 要部の拡大断面図FIG. 16 is an enlarged cross-sectional view of the same part.
【図１７】同 振動検出回路の概略図FIG. 17 is a schematic diagram of the vibration detection circuit.
１，３１，４１ シリコン単結晶基板 ２ 振動体 ３，３３ 発熱体 ４ 駆動用抵抗 ５，４８ 振動検出用抵抗 ８，５１ ＡＧＣアンプ ２０，３０，４０ センサ構造体 ４４ 間隙 ４５ ガラスキャップ ４６，４７ 電極 1,31,41 Silicon single crystal substrate 2 Vibrating body 3,33 Heating element 4 Driving resistor 5,48 Vibration detecting resistor 8,51 AGC amplifier 20,30,40 Sensor structure 44 Gap 45 Glass cap 46,47 Electrode
Claims (7)
発熱体あるいはその近傍の基板の温度変化に基づく上記
両持ち梁の、それに加わる熱応力変化に起因する機械的
変化を測定する手段とを備え、 該手段による上記両持ち梁の機械的変化の測定に基づい
て上記流体の流量の測定がなされることを特徴とする流
量測定装置。1. A heating element disposed on a substrate, a cantilever beam disposed near the heating element, and the heating element or its vicinity due to a cooling effect of a fluid flowing along the surface of the substrate. Means for measuring a mechanical change in the both-end supported beam caused by a change in thermal stress applied to the both-end supported beam based on the temperature change in the substrate, and the fluid based on the measurement of the mechanical change in the both-end supported beam by the means. The flow rate measuring device is characterized in that the flow rate is measured.
一体に削出され、両端を支持端として上記シリコン単結
晶基板に支持されてなることを特徴とする請求項１記載
の流量測定装置。2. The flow rate measuring device according to claim 1, wherein the both-end supported beam is integrally cut out from the silicon single crystal substrate and is supported by the silicon single crystal substrate with both ends as supporting ends.
動体よりなり、上記両持ち梁の、それに加わる熱応力変
化に起因する機械的変化を測定する手段が、上記振動体
の共振周波数の変化を測定する手段よりなることを特徴
とする請求項１または２記載の流量測定装置。3. The double-supported beam comprises a vibrator having a double-supported beam structure, and the means for measuring a mechanical change of the double-supported beam due to a change in thermal stress applied thereto has a resonance frequency of the vibrator. The flow rate measuring device according to claim 1 or 2, further comprising means for measuring a change in
振動体に予め内在する長手方向の応力による歪みε
0 と、上記発熱体の熱によって生じる圧縮歪みεheatと
が、次式で表される関係にあることを特徴とする請求項
３記載の流量測定装置。 ε0 ＋εheat＞（−π2 ／３）ｈ2 ／Ｌ2 4. The thickness h and the length L of the vibrating body, and the strain ε due to the stress in the longitudinal direction pre-existing in the vibrating body.
The flow rate measuring device according to claim 3, wherein 0 and the compressive strain ε heat generated by the heat of the heating element have a relationship represented by the following equation. ε 0 + ε heat> (- π 2/3) h 2 / L 2
温度低下を補う手段を備え、該手段により、上記発熱体
の温度がほぼ一定に保たれることを特徴とする請求項３
記載の流量測定装置。5. A means for compensating for the temperature decrease of the heating element due to the cooling effect of the fluid, the temperature of the heating element being kept substantially constant by the means.
The flow measurement device described.
が流体流量によって変化する基板上の位置に上記振動体
が配置され、上記基板温度の２次元分布の変化に起因す
る上記振動体の共振周波数の変化の測定に基づいて上記
流体の流量の測定がなされることを特徴とする請求項５
記載の流量測定装置。6. The vibrating body is arranged at a position on the substrate where the two-dimensional distribution of the substrate temperature near the heating element changes depending on the fluid flow rate, and the vibrating body is caused by the change in the two-dimensional distribution of the substrate temperature. The flow rate of the fluid is measured based on a change in resonance frequency.
The flow measurement device described.
体の流れの方向に沿って配設され、該複数の振動体間の
共振周波数変化の差異に基づいて上記流体の流量および
流れの方向の測定がなされることを特徴とする請求項６
記載の流量測定装置。7. A plurality of the vibrating bodies are arranged on the substrate along a flow direction of the fluid, and the flow rate and the flow of the fluid are determined based on a difference in resonance frequency change between the plurality of vibrating bodies. 7. A directional measurement is made.
The flow measurement device described.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP02234296A JP3603447B2 (en) | 1996-02-08 | 1996-02-08 | Flow measurement device |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP02234296A JP3603447B2 (en) | 1996-02-08 | 1996-02-08 | Flow measurement device |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH09218064A true JPH09218064A (en) | 1997-08-19 |
| JP3603447B2 JP3603447B2 (en) | 2004-12-22 |
Family
ID=12080019
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP02234296A Expired - Fee Related JP3603447B2 (en) | 1996-02-08 | 1996-02-08 | Flow measurement device |
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| Country | Link |
|---|---|
| JP (1) | JP3603447B2 (en) |
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2004053186A1 (en) * | 2002-12-04 | 2004-06-24 | The Board Of Trustees Of The University Of Illinois | Sensor for monitoring material deposition and method of monitoring material deposition |
| RU177514U1 (en) * | 2017-12-20 | 2018-02-28 | Федеральное государственное автономное образовательное учреждение высшего образования "Национальный исследовательский университет "Московский институт электронной техники" | THERMOANEMOMETRIC FLOW AND GAS FLOW SENSOR |
| CN111474381A (en) * | 2020-04-27 | 2020-07-31 | 吉林大学 | Air flow velocity sensing device containing bionic cross beam sensor and preparation method thereof |
-
1996
- 1996-02-08 JP JP02234296A patent/JP3603447B2/en not_active Expired - Fee Related
Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2004053186A1 (en) * | 2002-12-04 | 2004-06-24 | The Board Of Trustees Of The University Of Illinois | Sensor for monitoring material deposition and method of monitoring material deposition |
| US6884458B2 (en) * | 2002-12-04 | 2005-04-26 | The Board Of Trustees Of The University Of Illinois | Sensor for monitoring material deposition and method of monitoring material deposition |
| US7445675B2 (en) | 2002-12-04 | 2008-11-04 | The Board Of Trustees Of The University Of Illinois | Sensor for monitoring material deposition |
| RU177514U1 (en) * | 2017-12-20 | 2018-02-28 | Федеральное государственное автономное образовательное учреждение высшего образования "Национальный исследовательский университет "Московский институт электронной техники" | THERMOANEMOMETRIC FLOW AND GAS FLOW SENSOR |
| CN111474381A (en) * | 2020-04-27 | 2020-07-31 | 吉林大学 | Air flow velocity sensing device containing bionic cross beam sensor and preparation method thereof |
| CN111474381B (en) * | 2020-04-27 | 2021-06-01 | 吉林大学 | Air flow velocity sensing device containing bionic cross beam sensor and preparation method thereof |
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