JP3577902B2 - Thermal flow sensor - Google Patents

Thermal flow sensor Download PDF

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JP3577902B2
JP3577902B2 JP21507697A JP21507697A JP3577902B2 JP 3577902 B2 JP3577902 B2 JP 3577902B2 JP 21507697 A JP21507697 A JP 21507697A JP 21507697 A JP21507697 A JP 21507697A JP 3577902 B2 JP3577902 B2 JP 3577902B2
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temperature
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downstream
heat generating
temperature detecting
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JPH1151954A (en
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雄二 有吉
考司 谷本
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Mitsubishi Electric Corp
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Mitsubishi Electric Corp
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Description

【０００１】
【発明の属する技術分野】
本発明は、例えば自動車のエンジン制御や空調機器など、空気等流体の流速計測が必要な場所に使用される流速センサに関し、特にその検出感度向上および測定可能流速範囲の拡大に関するものである。
【０００２】
【従来の技術】
図２７は例えば特公平５−７６５９号公報に示された従来の熱式流速センサ（従来例１）の要部断面図であり、図２８はその上面図である。図において、１はシリコン基板、２はこのシリコン基板１にエッチングにより形成された空気スペース、３，４はこの空気スペース２上に架橋された薄膜部材すなわち薄肉部、５はヒーター、６，７はそれぞれ上流側および下流側熱感知センサ、８は周囲の空気の温度をモニタする比較抵抗である。上流側および下流側熱感知センサ６，７はヒーター５を挟んで対称な位置に配されている。ヒーター５および熱感知センサ６，７は、例えば窒化シリコンからなる薄膜の絶縁層９，１０により包まれて薄肉部３，４を形成している。
【０００３】
この従来の熱式流速センサの基本的な動作について説明する。図２８において、ヒーター５はシリコン基板１の温度より２００℃高くなる温度に加熱されている。シリコン基板１の温度は周囲の空気の温度とほとんど同じであり、比較抵抗８により測定される。空気の流れがないときには、熱感知センサ６，７は、ヒーター５の熱により、平均で約１４０℃に熱せられる。すなわち、熱感知センサ６，７はヒーター５に対して正確に対称に配置されているので、空気の流速が０のときにはこの２つのセンサの温度は同一になり、熱感知センサ６，７の抵抗値に差は生じない。従って、この２つの熱感知センサ６，７に微小測定電流を流しても電圧の差は発生しない。
【０００４】
空気の流れがあるときには、上流側に位置する熱感知センサ６はヒーター５へ向かう空気の流れにより熱が運び去られるため冷やされ、一方、下流側に位置する熱感知センサ７はヒーター５からの空気の流れによって熱せられることになる。図２９に熱感知センサ６，７の温度の流速依存性を示す。流速が速くなるにつれて、上流側の熱感知センサ６の温度は低下し、下流側の熱感知センサ７の温度は上昇している。これによって生ずる熱感知センサ６，７の間の抵抗値の差が電圧値の差をもたらし、この電位差から流速が測定される。この２つの熱感知センサの温度差を縦軸にとったグラフを図３０に示す。流速（横軸）と温度差（縦軸）が一対一に対応しており、流速センサとして利用できることが判る。
【０００５】
図３１および図３２にこれらの機能を実現するための回路例を示す。図３１に示された回路はヒーター５の温度を制御するためのものであり、図３２に示された回路は熱感知センサ６，７の間の抵抗値の差に比例する電圧信号を得るためのものである。
【０００６】
図３１に示される温度制御回路は、ヒーター５の温度を、比較抵抗８によって検出される周囲温度よりも一定温度高く保つためのホイストンブリッジ回路４６により構成される。ホイストンブリッジ回路４６はヒーター５と抵抗４５により一辺を、比較抵抗８と抵抗４７，４８により他辺を構成している。アンプ４９，５０からなる積分回路は出力の電位を変化させることでブリッジ回路４６がバランスするように動作し、ヒーター５によって消費される電力を一定に保つようにする。
【０００７】
図３２に示す回路はヒーター５の上流側に位置する熱感知センサ６と下流側に位置する熱感知センサ７との間の差を検出するためのものである。この回路は、アンプ７２からなる定電流電源部５２と、アンプ６６，６８，７０からなる差動増幅部５４から構成される。定電流電源部５２は、一辺に高インピーダンス抵抗５６，５８と、他辺に零調用可変抵抗６０および熱感知センサ６，７を有するホイストンブリッジ回路を駆動する。差動増幅部５４の利得は可変抵抗６２により調整される。出力端６４は熱感知センサ６，７の間の抵抗値の差に比例する出力電圧を出力する。
【０００８】
【発明が解決しようとする課題】
このタイプの熱式流速センサを、測定可能流速範囲が広く感度の良いものにするためには、熱感知センサ６，７の温度が、広い流速範囲にわたって大きく変化することが望ましい。しかし、従来の熱式流速センサでは、流速が０の時に下流側の熱感知センサ７がすでにヒーター５の温度の６〜７割近くまで熱せられているため、ヒーター５から空気を介して伝達される熱量は少なく、しかも比較的低い流速で飽和温度に達する。図２９を見ると、実際に下流側感温抵抗体７の温度変化は小さく、５ｍ／ｓ以上ではすでに飽和傾向にあることが判る。
【０００９】
図３３にヒーター５および感温抵抗体６，７における熱の移動を表した模式図を示す。図において、Ｑ１はヒーター５から空気への熱伝達量、Ｑ２はヒーター５から薄膜部材を介して上流側熱感知センサ６へ伝わる熱伝導量、Ｑ３はヒーター５から薄膜部材を介して下流側熱感知センサ７へ伝わる熱伝導量、Ｑ４は上流側熱感知センサ６から空気への熱伝達量、Ｑ５は空気から下流側熱感知センサ７への熱伝達量である。
【００１０】
下流側熱感知センサ７について見ると、Ｑ３とＱ５の２つの熱流入が起こっている。このうちＱ３は流速には依存せず、流速依存性を持つのはＱ５のみである。Ｑ５は熱感知センサ７の上を通過する空気と熱感知センサ７自身との温度差に比例する。流速０のときの熱流入の大半はＱ３によると考えてよいが、図２９に示したように、この時すでに熱感知センサ７は１４０℃まで加熱されている。このため、熱感知センサ７と空気との温度差が小さくなり、この温度差に比例するＱ５も大きくできない。よって、流れが存在する状態でも熱感知センサ７の温度上昇は小さい。しかも、多少なりとも温度上昇が起これば、空気との温度差はさらに縮小され、飽和状態により近づくことになる。その結果、図３０に示したように、流速が増大するとともに上流と下流の熱感知センサ６，７の温度差の変化は小さくなり、感度は低下していく。
【００１１】
また、上流側熱感知センサ６について言えば、ヒーター５から伝わった熱量Ｑ２の一部がＱ４となって空気に伝わる。Ｑ２は空気の流速には依存しないが、Ｑ４は流速が速くなるにつれて増大するので、熱感知センサ６の温度は流速の増大とともに降下する。この場合、Ｑ２の値が大きいほどＱ４の変化幅が広くとれ、感度の向上、および測定可能流速範囲の拡大には有利である。図２９を見ても、上流側熱感知センサ６の温度は大きな傾きを持って変化している。しかし、例えば自動車のエンジン制御などに使用する場合は、図２９に示されている流速範囲（０〜２０００ｆｔ／ｍｉｎ＝０〜１０ｍ／ｓｅｃ）では不十分で、少なくとも０〜５０ｍ／ｓｅｃの測定範囲は必要である。図２９の上流側熱感知センサ６の温度変化の勾配を（−４０℃）／（１０ｍ／ｓｅｃ）と考えれば、流速が５０ｍ／ｓｅｃに達するまでに、この温度変化の勾配が徐々に減少していくことは明らかである。その結果、流速が増大するとともに上流側と下流側の熱感知センサ６，７の温度差の変化は小さくなり、感度は低下していく。
【００１２】
さらに、Ｆ．Ｍａｙｅｒらの研究（Ｆ．Ｍａｙｅｒ ｅｔ ａｌ ： Ｔｒａｎｓｄｕｃｅｒｓ■９５ Ｅｕｒｏｓｅｎｓｏｒｓ ＩＸ １３２−Ｃ２ ｐｐ．５２８−５３１）によれば、流速が速くなると下流側の熱感知センサ７の温度が低下することが報告されている。この現象は本願発明者の行った実験によっても確認されている（図３４）。また、Ｌｉ Ｑｕｉらの研究（Ｌｉ Ｑｕｉ ｅｔ ａｌ ： Ｔｒａｎｓｄｕｃｅｒｓ■９５ Ｅｕｒｏｓｅｎｓｏｒｓ ＩＸ １３０−Ｃ２ ｐｐ．５２０−５２３）によれば、ある流速以上で上下流の熱感知センサ６，７の温度差が低下することが報告されている。これらの報告は、流速が増大すると、出力の２値化（一つの出力に対応する流速ポイントが２つ存在すること）が起こり得ることを示している。これにより、測定可能流速範囲の拡大が制限される。
【００１３】
このように、従来の温度差を用いた熱式流速センサにおいては、流速が増大するとともに感度が低下し、測定可能流速範囲も大きく取れないという問題点があった。
【００１４】
本発明は、上記のような課題を解決するためになされたもので、感度を向上できるとともに測定可能流速範囲を拡大できる熱式流速センサを得ることを目的とする。
【００１５】
【課題を解決するための手段】
本発明の第１の構成による熱式流速センサは、薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部と、前記発熱部の極めて近傍に設けられた第３の温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に前記上流側温度検出部、下流側温度検出部、および第３の温度検出部との間に生じる温度差から流速を検出するようにしたものである。
【００１６】
本発明の第２の構成による熱式流速センサは、薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部と、発熱部の上流側近傍に設けられた第４の温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に生じる前記上流側温度検出部と下流側温度検出部との温度差から得られる信号により空気流速を検出する熱式流速センサにおいて、前記温度差信号に増幅を施す際に、その利得を前記第４の温度検出部の抵抗値によって変化させるようにしたものである。
【００１７】
本発明の第３の構成による熱式流速センサは、薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部と、発熱部の上流側近傍に設けられた第４の温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に生じる前記上流側温度検出部と下流側温度検出部との温度差から得られる信号により空気流速を検出する熱式流速センサにおいて、前記上流側、および下流側温度検出部の温度を検出するために流す電流値を前記第４の温度検出部の抵抗値によって変化させるようにしたものである。
【００１８】
本発明の第４の構成による熱式流速センサは、薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部と、発熱部の上流側近傍に設けられた第４の温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に生じる前記上流側温度検出部と下流側温度検出部との温度差から得られる信号により空気流速を検出する熱式流速センサにおいて、前記温度差信号に加えるバイアス信号を前記第４の温度検出部の抵抗値によって変化させるようにしたものである。
【００１９】
本発明の第５の構成による熱式流速センサは、薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部と、発熱部の上流側および下流側にそれぞれ設けられた第４および第５の温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に生じる前記上流側温度検出部と下流側温度検出部との温度差から得られる信号により空気流速を検出する熱式流速センサにおいて、前記第４，第５の温度検出部の抵抗値を用いて流速以外の原因による請求項２から４に記載の利得、電流、バイアス信号の変動を相殺するようにしたものである。
【００２０】
本発明の第６の構成による熱式流速センサは、薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に生じる前記上流側温度検出部と下流側温度検出部との温度差から得られる信号により空気流速を検出する熱式流速センサにおいて、前記発熱部と温度検出部を前記薄肉部上の空気の流れに対して下流側に偏った位置に配置するようにしたものである。
【００２１】
【発明の実施の形態】
実施の形態１．
以下、本発明の実施の形態を図について説明する。図１は本発明の実施の形態１を示す上面図、図２は図１のＡ−Ａ´線断面図である。ただし、図２の断面図は図１の上面図を多少拡大して示しており、これは、以降の同様のＡ−Ａ´線断面図においても同じである。図において、１はシリコン基板、２はシリコン基板１を裏からエッチングして形成した空気スペース、３は空気スペース２上に設けられたダイヤフラム型薄肉部である。５は発熱部すなわち発熱抵抗体、６，７は発熱抵抗体５の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部すなわち上流側および下流側感温抵抗体、８は上流側感温抵抗体６より上流側に配置され流体の温度を測定する流体温度検出部すなわち流体温度検出用感温抵抗体、９，１０は絶縁層、１１は発熱抵抗体５のごく近傍に配置された発熱抵抗体温度検出部、すなわち発熱抵抗体温度検出用感温抵抗体、１２は発熱抵抗体５、上流側および下流側感温抵抗体６，７、流体温度検出用感温抵抗体８、並びに発熱抵抗体温度検出用感温抵抗体１１の両端をそれぞれボンディングパッド１３に接続する配線である。薄肉部３は絶縁層９，１０、並びに絶縁層９，１０に挟まれた発熱抵抗体５、及び感温抵抗体６，７，１１から構成されている。
【００２２】
発熱抵抗体５、感温抵抗体６，７、流体温度検出用感温抵抗体８は、スパッタ、あるいは蒸着などの成膜技術により薄膜形成した後、エッチングにより所望の抵抗値になるようにパターニングしている。抵抗材料としては、信頼性の高い白金などを使用することが望ましい。
【００２３】
発熱抵抗体５は、流体温度検出用感温抵抗体８によって測定される空気の温度よりも常に一定温度だけ高くなるように定温度差駆動されている。図３は基本的な定温度差駆動回路の簡略回路図であり、発熱抵抗体５、流体温度検出用感温抵抗体８、及び固定抵抗１４，１５によりブリッジ回路を構成している。空気の流速の変動により発熱抵抗体５の温度が変化したり、空気の温度が変化して流体温度検出用感温抵抗体８の温度が変化したりして、ブリッジ回路のバランスが崩れると、差動増幅器１６、及び、トランジスタ１７が発熱抵抗体５に流れる加熱電流を制御し、元のバランス状態に戻すように働く。この結果、発熱抵抗体５と流体温度検出用感温抵抗体８との温度差が常に一定に保たれる。１８は電源である。
【００２４】
図４は基本的な温度差検出回路の簡略図であり、詳しくは、上流側感温抵抗体６と下流側感温抵抗体７の温度差を検出するための温度差検出回路の簡略図を示す。定電流源１９により上流側感温抵抗体６（Ｒｕ）と下流側感温抵抗体７（Ｒｄ）に一定電流Ｉｓを流し、両者の両端電圧の差を取って、増幅回路部２０により増幅し、出力端２１から出力電圧Ｖｏｕｔとして出力する。この場合の出力電圧Ｖｏｕｔは以下の式で表される。
Ｖｏｕｔ＝Ｖｒｅｆ＋Ｇ・Ｒｓ０・αｓ・Ｉｓ・（Ｔｄ−Ｔｕ） …（１）
ここで、Ｒｓ０は上流側、および下流側感温抵抗体６，７の０℃の時の抵抗値、αｓは上流側、及び下流側感温抵抗体６，７の抵抗温度係数である。また、Ｖｒｅｆ（３８）は（Ｔｄ−Ｔｕ）が負になった場合、つまり空気の流れが逆流の場合でも正の出力が得られるようにするために加えているバイアス電圧で定電圧源を用いている。上流側、および下流側感温抵抗体６，７を同じ材質で同じパターンに形成することにより、両者のＲｓ０とαｓ はほぼ同一の値が得られる。また、Ｔｄ，Ｔｓはそれぞれ上流側、及び下流側感温抵抗体６，７の温度である。Ｇは増幅回路部により決定されるゲインであり、次式で表される。
Ｇ＝１＋（Ｒ２ ／Ｒ１ ） …（２）
ただし、Ｒ２ ／Ｒ１ ＝Ｒ４ ／Ｒ３
また、上流側感温抵抗体６と下流側感温抵抗体７の温度差（Ｔｄ−Ｔｕ）は近似的に以下のように表せる。
Ｔｄ−Ｔｕ＝ＡＵｎΔＴ …（３）
ここで、Ｕは空気の流速、△Ｔは図３の定温度差駆動回路により一定に保たれる空気と発熱抵抗体５との温度差、Ａは係数である。式（１）と（３）を組み合わせると出力電圧Ｖｏｕｔが流速Ｕに依存することが判る。
Ｖｏｕｔ＝Ｖｒｅｆ＋Ｇ・Ｒｓ０・αｓ・Ｉｓ・ＡＵｎ・ΔＴ …（４）
【００２５】
前述したように、図３に示す定温度差駆動回路により、式（４）中の△Ｔは一定に保たれるはずである。しかし、実際には、発熱抵抗体５の発する熱が流体温度検出用感温抵抗体８にも伝わるため、流体温度検出用感温抵抗体８の温度は空気の温度よりも高くなっている。この流体温度検出用感温抵抗体８の温度上昇は空気の流速が小さいほど大きく、流速が速くなるにつれて流体温度検出用感温抵抗体８は冷却され、空気の温度に近づいていく。発熱抵抗体５の温度はこの流体温度検出用感温抵抗体８よりも一定温度高くなるように制御されるため、発熱抵抗体５の温度も空気の流速が大きくなるとともに低下することになる。従って、式（４）の△Ｔは実際は一定ではなく、流速が増すにつれて小さくなる。この△Ｔの負の流速依存性により、出力電圧Ｖｏｕｔの流速依存性が抑えられ、感度や測定可能流速範囲が低下する。
【００２６】
本実施の形態では、前述の△Ｔの流速による変動を、発熱抵抗体温度検出用感温抵抗体１１により検出し、この発熱抵抗体温度検出用感温抵抗体１１と上流側感温抵抗体６と下流側感温抵抗体７の３つの感温抵抗体の温度変化から出力電圧を導出するため、△Ｔの持つ負の流速依存性をキャンセルできる。
【００２７】
図５は本発明の実施の形態１に係わる温度差検出用回路の簡略図である。この例ではまず、差動増幅器２５により、下流側感温抵抗体７の温度に依存する電圧から発熱抵抗体温度検出用感温抵抗体１１の温度に依存する電圧を引き算し、その後差動増幅器２６によりさらに上流側感温抵抗体の温度に依存する電圧を引き算して出力電圧としている。こうすることにより、発熱抵抗体温度検出用感温抵抗体１１の温度低下分が加味された出力電圧が発生するのでセンサの感度や測定可能流量範囲を向上できる。もちろん、図４に示すような増幅回路部を通した後の電圧を出力電圧としても良い。
【００２８】
図５に示す３つの感温抵抗体６，７，１１の＋端側の電圧の流速による変化の様子を図６に示す。上流側感温抵抗体６の電圧２７（Ｖｕ）と発熱抵抗体温度検出用感温抵抗体１１の電圧２９（Ｖｓｈ）は流速が増すにつれて低下し、下流側感温抵抗体７の電圧２８（Ｖｄ）は流速が増すにつれて上昇する。固定抵抗２２，２３，２４を調節することにより、流速が零の時の３つの電圧を Ｖｄ＝Ｖｕ＋Ｖｓｈ となるようにすることができる。図６においてＶｄ―Ｖｓｈを計算すると、流速が零の時にＶｕと一致し、傾きがＶｄよりも大きい曲線３０が得られる。この曲線３０からさらにＶｕ曲線２７を引き算すれば、単にＶｄ−Ｖｕを計算した曲線より傾きが大きい曲線が得られ、この電圧を出力とすることにより、センサの感度を向上させることが出来る。
【００２９】
上記の効果は図５に示した回路だけではなく、図７および図８に示したような回路によっても実現することが出来る。図７はまず上流側感温抵抗体６の電圧２７（Ｖｕ）と発熱抵抗体温度検出用感温抵抗体１１の電圧（Ｖｓｈ）を加算回路３１により足し算し、その結果得られた電圧を下流側感温抵抗体７の電圧２８（Ｖｄ）から引算して出力電圧を得る回路、図８はまず上流側感温抵抗体６の電圧２７（Ｖｕ）から下流側感温抵抗体７の電圧２８（Ｖｄ）を引き算し、その後、発熱抵抗体温度検出用感温抵抗体１１の電圧（Ｖｓｈ）を引き算して出力電圧を得る回路である。図５、図７、図８の回路を簡単に式で表すと以下のようになる。
図５：（Ｖｄ−Ｖｓｈ）−Ｖｕ
図７：Ｖｄ−（Ｖｕ＋Ｖｓｈ）
図８：（Ｖｄ−Ｖｕ）−Ｖｓｈ
【００３０】
また、図９に示すような定電圧源３２と定電流源１９を併用した回路でも同様の効果を得ることが出来る。図９の回路において電圧Ｖｄは下式で表される。
Ｖｄ＝Ｒｄ・Ｖｃ／（Ｒｄ＋Ｒｓｈ）＝１・Ｖｃ／｛１＋（Ｒｓｈ／Ｒｄ）｝ …（５）
式（５）から判るようにＲｓｈが低下するとＶｄは大きくなる。このＶｄからＶｕを引き算すれば、発熱抵抗体温度検出用感温抵抗体１１の温度低下分を加味した出力電圧Ｖｏｕｔが得られる。
【００３１】
さらに、図１０に示すように、上流側感温抵抗体６と発熱抵抗体温度検出用感温抵抗体１１を直列に接続して定電流を流し、その最上段の電圧Ｖｕと下流側感温抵抗体７の電圧Ｖｄとの差を取ることによっても、発熱抵抗体温度検出用感温抵抗体１１の温度低下分を加味した出力電圧Ｖｏｕｔが得られる。
【００３２】
実施の形態２．
図１１は本発明の実施の形態２を示す上面図、図１２は図１１のＡ−Ａ´線断面図である。図において、シリコン基板１の薄肉部３に、発熱抵抗体５と発熱抵抗体５の上流側に感温抵抗体６，３３ａ，３３ｂ、および下流側に感温抵抗体７がそれぞれ形成されている。２個の上流側感温抵抗体３３ａ，３３ｂは同じ材質で同じパーターンに形成されているため、同じ抵抗温度特性を持つ。また、同じ温度になるようにごく近接した位置に形成されている。
【００３３】
この実施の形態においても、前述の実施の形態１と同様に、発熱抵抗体５、上流側感温抵抗体６、下流側感温抵抗体７、流体温度検出用感温抵抗体８を用いて温度差検出タイプの空気流速センサが構成される。このタイプのセンサの出力電圧Ｖｏｕｔは前述した式（４）で表される。ここで増幅回路部のゲインＧは図４の回路を用いると、前述した式２と同様に表される。
【００３４】
図４のＲ１〜Ｒ４は全て固定抵抗を用いていたが、この実施形態では図１３に示すように、Ｒ１に図１１の感温抵抗体３３ａを使用し、Ｒ３には感温抵抗体３３ｂを使用している。この感温抵抗体３３ａと３３ｂの抵抗値をＲ３３とおくと、増幅回路部のゲインＧは次式のようになる。
Ｇ＝１＋Ｒ２／Ｒ３３ …（６）
感温抵抗体３３ａと３３ｂはともに発熱抵抗体５の上流側に位置しているため、流速が増大するとともにその温度は低下し、抵抗値も低下する。このため式（６）で表されるゲインＧは逆に流速が増大するとともに大きくなる。よって式（４）で表される出力電圧Ｖｏｕｔは、流速が増大すると、このゲインＧの増大効果も含んだ形で大きくなり、ゲインＧが固定されている場合に比べ、出力電圧Ｖｏｕｔの流量依存性は大きくなり、センサの感度も向上し、測定可能流速範囲も拡大する。
【００３５】
実施の形態３．
図１４は本発明の実施の形態３に係わる定電流供給回路の簡略図である。図において、３２は定電圧源、３５，３６は固定抵抗である。図４で示した回路では定電流源１９を用いていたが、この図１４に示す回路はこの定電流源１９に代わって感度と測定範囲を改善する働きをする定電流回路である。図のように回路を構成すると、次式で表される定電流Ｉｓが端子ＡＢ間に流れる。
Ｉｓ＝Ｖｉ／Ｒ３３＝Ｒ３６・Ｖｃ／｛（Ｒ３５＋Ｒ３６）・Ｒ３３｝＝Ｖｃ／｛１＋（Ｒ３５／Ｒ３６）・Ｒ３３｝…（７）
式（７）のＲ３３を固定すると一定電流Ｉｓを得ることが出来る。しかし、本実施形態３においては図１３に示すように、このＲ３３に上流側感温抵抗体３３ａを用いることを特徴とする。上流側感温抵抗体３３ａは空気の流速が増大すると冷却され、抵抗値が下がるため、式（７）で表される電流Ｉｓは逆に流速の増大とともに大きくなる。よって式（４）で表される出力電圧Ｖｏｕｔは、流速が増大すると、この電流Ｉｓの増大効果も含んだ形で大きくなり、電流Ｉｓが固定されている場合に比べ、出力電圧Ｖｏｕｔの流量依存性は大きくなり、センサの感度も向上し、測定可能流速範囲も拡大する。
【００３６】
実施の形態４．
図１５は本発明の実施の形態４に係わる定電流供給回路の簡略図である。この回路を用いると電流Ｉｓは次式のように表される。
Ｉｓ＝Ｖｉ／Ｒ３５＝Ｒ３６・Ｖｃ／｛（Ｒ３３＋Ｒ３６）・Ｒ３５｝＝Ｖｃ／｛１＋（Ｒ３３／Ｒ３６）・Ｒ３５｝…（８）
上流側感温抵抗体３３ａは空気の流速が増大すると冷却され、抵抗値（Ｒ３３）が下がるため、式（８）で表される電流Ｉｓは逆に流速の増大とともに大きくなる。よって式（４）で表される出力電圧Ｖｏｕｔは、流速が増大すると、この電流Ｉｓの増大効果も含んだ形で大きくなり、電流Ｉｓが固定されている場合に比べ、出力電圧Ｖｏｕｔの流量依存性は大きくなり、センサの感度も向上し、測定可能流速範囲も拡大する。もちろん、２つの上流側感温抵抗体３３ａ，３３ｂを用いて実施の形態３と４を組み合わせ効果を倍増させても良い。
【００３７】
実施の形態５．
図１６は本発明の実施の形態５に係わるバイアス電圧供給回路の簡略図である。図において、３２は定電圧源、３７は固定抵抗である。図４で示した回路では、バイアス電圧Ｖｒｅｆ （３８）に定電圧源を用いていたが、本実施形態４においては、図１６に示すように定電圧源の電圧を分圧して出力する定電圧回路を用いてバイアス電圧Ｖｒｅｆ を印加している。しかも、Ｒ３３に図１１に示した上流側感温抵抗体３３ａを用いている。図１６の回路における出力端Ｃの電圧（Ｖｒｅｆ）は次式で表される。
Ｖｒｅｆ＝Ｒ３７・Ｖｃ／（Ｒ３７＋Ｒ３３）＝１・Ｖｃ／｛１＋（Ｒ３３／Ｒ３７）｝ …（９）
【００３８】
上流側感温抵抗体３３ａは空気の流速が増大すると冷却され、抵抗値（Ｒ３３）が下がるため、式（８）で表される電圧Ｖｒｅｆ は逆に流速の増大とともに大きくなる。よって式（４）で表される出力電圧Ｖｏｕｔは、流速が増大すると、このバイアス電圧Ｖｒｅｆ の増大効果も含んだ形で大きくなり、バイアス電圧Ｖｒｅｆ が固定されている場合に比べ、出力電圧Ｖｏｕｔの流量依存性は大きくなり、センサの感度も向上し、測定可能流速範囲も拡大する。
【００３９】
実施の形態６．
図１７は本発明の実施の形態６を示す上面図、図１８は図１７のＡ−Ａ´線断面図である。図において、シリコン基板１の薄肉部３に、発熱抵抗体５と発熱抵抗体５の上流側に感温抵抗体６，３３ａ，３３ｂ、および下流側に感温抵抗体７，３４ａ，３４ｂがそれぞれ形成されている。４個の上流側感温抵抗体３３ａ，３３ｂ、及び３４ａ，３４ｂは同じ材質で同じ形成方法により形成されている。また、上流側感温抵抗体３３ａと３３ｂ、及び、下流側感温抵抗体３４ａと３４ｂはそれぞれ同じ温度になるようにごく近接した位置に形成されている。
【００４０】
この実施の形態においても、前述の実施の形態２と同様に、発熱抵抗体５、上流側感温抵抗体６、下流側感温抵抗体７、流体温度検出用感温抵抗体８を用いて温度差検出タイプの空気流速センサが構成される。実施の形態２では、増幅回路部２０のゲインＧに上流側感温抵抗体３３ａによって流速依存性を持たせてセンサの感度を向上させており、ゲインＧは式（６）でＧ＝１＋Ｒ２ ／Ｒ３３）として表された。
【００４１】
しかし、上流側感温抵抗体３３ａの抵抗値Ｒ３３は空気の温度や湿度など流速以外の空気の状態によっても変化する。このため、流速が一定でも空気の温度等が変化すればゲインＧも変化することになり、空気の温度などが変化するような場合には正確な流速検知は出来ない。そこで、本実施の形態６では、図１９に示す回路図のように、増幅回路部２０の固定抵抗Ｒ２，Ｒ４の代わりに、下流側感温抵抗体３４ａと３４ｂを用いる。このときゲインＧは次式で表される。
Ｇ＝１＋Ｒ３４ａ／Ｒ３３ａ …（１０）
【００４２】
上流側感温抵抗体３３ａと３３ｂは、流速が増大するとともにその温度は低下し、抵抗値も低下する。また、下流側感温抵抗体３４ａと３４ｂは、流速が増大するとともにその温度は若干上昇し、抵抗値も上昇する。このため式（１０）で表されるゲインＧは流速が増大するとともに大きくなる。よって式（４）で表される出力電圧Ｖｏｕｔは、流速が増大すると、このゲインＧの増大効果も含んだ形で大きくなり、ゲインＧが固定されている場合に比べ、出力電圧Ｖｏｕｔの流量依存性は大きくなり、センサの感度も向上し、測定可能流速範囲も拡大する。
【００４３】
さらに、流速以外の条件によりＲ３３が変化した場合、同じ材質で同じ方法により形成されたＲ３４も同様に変化するため、ゲインＧは変化しない。例えば、空気の温度が上昇して上流側感温抵抗体３３ａと３３ｂの抵抗値が１０％増加したとすれば、下流側感温抵抗体３４ａと３４ｂの抵抗値も１０％増加するため、両者の変化はキャンセルされ、ゲインＧは一定に保たれる。このように、本実施の形態６によれば、ゲインＧを流速によってのみ変化させ、空気の温度などその他の因子には依存しないようにでき、空気の温度などが変化する場合にも使用できる。
【００４４】
実施の形態７．
本実施の形態７に係わるセンサの上面図と断面図は実施の形態６で示した図１７，図１８と同じである。この実施の形態においても、前述の実施の形態４と同様に、発熱抵抗体５、上流側感温抵抗体６、下流側感温抵抗体７、流体温度検出用感温抵抗体８を用いて温度差検出タイプの空気流速センサが構成される。実施の形態４では、上流、及び下流側感温抵抗体６，７に流す電流値Ｉｓを上流側感温抵抗体３３ａを用いて変化させてセンサの感度を向上させており、この電流値Ｉｓは式（８）で表された。
【００４５】
しかし、上流側感温抵抗体３３ａの抵抗値Ｒ３３は空気の温度や湿度など流速以外の空気の状態によっても変化する。このため、流速が一定でも空気の温度等が変化すれば電流値Ｉｓも変化することになり、空気の温度などが変化するような場合には正確な流速検知は出来ない。そこで、本実施形態７では、図２０に示す回路図のように、固定抵抗Ｒ３６の代わりに、下流側感温抵抗体３４ａを用いる。このとき電流値Ｉｓは次式で表される。

Figure 0003577902
【００４６】
上流側感温抵抗体３３ａは、流速が増大するとともにその温度は低下し、抵抗値Ｒ３３ａも低下する。また、下流側感温抵抗体３４ａは、流速が増大するとともにその温度は若干上昇し、抵抗値Ｒ３４ａも上昇する。このため式（１１）で表される電流値Ｉｓは流速が増大するとともに大きくなる。よって式（４）で表される出力電圧Ｖｏｕｔは、流速が増大すると、この電流値Ｉｓの増大効果も含んだ形で大きくなり、電流値Ｉｓが固定されている場合に比べ、出力電圧Ｖｏｕｔの流量依存性は大きくなり、センサの感度も向上し、測定可能流速範囲も拡大する。
【００４７】
さらに、流速以外の条件によりＲ３３ａが変化した場合、同じ材質で同じ方法により形成されたＲ３４ａも同様に変化するため、電流値Ｉｓは変化しない。例えば、空気の温度が上昇して上流側感温抵抗体３３ａの抵抗値が１０％増加したとすれば、下流側感温抵抗体３４ａの抵抗値も１０％増加するため、両者の変化はキャンセルされ、電流値Ｉｓは一定に保たれる。このように、本実施の形態７によれば、電流値Ｉｓを流速によってのみ変化させ、空気の温度などその他の因子には依存しないようにでき、空気の温度などが変化する場合にも使用できる。
【００４８】
実施の形態８．
本実施の形態８に係わるセンサの上面図と断面図は実施の形態６で示した図１７，図１８と同じである。この実施の形態においても、前述の実施の形態５と同様に、発熱抵抗体５、上流側感温抵抗体６、下流側感温抵抗体７、流体温度検出用感温抵抗体８を用いて温度差検出タイプの空気流速センサが構成される。実施の形態５では、バイアス電圧Ｖｒｅｆを上流側感温抵抗体３３ａを用いて変化させてセンサの感度を向上させており、この場合のバイアス電圧Ｖｒｅｆは式（９）で表された。
【００４９】
しかし、上流側感温抵抗体３３ａの抵抗値Ｒ３３は空気の温度や湿度など流速以外の空気の状態によっても変化する。このため、流速が一定でも空気の温度等が変化すればバイアス電圧Ｖｒｅｆも変化することになり、空気の温度などが変化するような場合には正確な流速検知は出来ない。そこで、本実施形態８では、図２１に示す回路図のように、固定抵抗Ｒ３７の代わりに、下流側感温抵抗体３４ａを用いる。このときバイアス電圧Ｖｒｅｆは次式で表される。
Ｖｒｅｆ＝Ｒ３４ａ・Ｖｃ／（Ｒ３４ａ＋Ｒ３３ａ）＝１・Ｖｃ／｛１＋（Ｒ３３ａ／Ｒ３４ａ）｝ …（９）
【００５０】
上流側感温抵抗体３３ａは、流速が増大するとともにその温度は低下し、抵抗値Ｒ３３ａも低下する。また、下流側感温抵抗体３４ａは、流速が増大するとともにその温度は若干上昇し、抵抗値Ｒ３４ａも上昇する。このため式（１２）で表されるバイアス電圧Ｖｒｅｆは流速が増大するとともに大きくなる。よって式（４）で表される出力電圧Ｖｏｕｔは、流速が増大すると、このバイアス電圧Ｖｒｅｆの増大効果も含んだ形で大きくなり、バイアス電圧Ｖｒｅｆが固定されている場合に比べ、出力電圧Ｖｏｕｔの流量依存性は大きくなり、センサの感度も向上し、測定可能流速範囲も拡大する。
【００５１】
さらに、流速以外の条件によりＲ３３ａが変化した場合、同じ材質で同じ方法により形成されたＲ３４ａも同様に変化するため、バイアス電圧Ｖｒｅｆは変化しない。例えば、空気の温度が上昇して上流側感温抵抗体３３ａの抵抗値が１０％増加したとすれば、下流側感温抵抗体３４ａの抵抗値も１０％増加するため、両者の変化はキャンセルされ、バイアス電圧Ｖｒｅｆは一定に保たれる。このように、本実施の形態８によれば、バイアス電圧Ｖｒｅｆを流速によってのみ変化させ、空気の温度などその他の因子には依存しないようにでき、空気の温度などが変化する場合にも使用できる。
【００５２】
実施の形態９．
図２２は本発明の実施の形態９を示す上面図、図２３は図２２のＡ−Ａ´線断面図である。図において、シリコン基板１の薄肉部３に、発熱抵抗体５、その上流側に感温抵抗体６、および下流側に感温抵抗体７がそれぞれ形成されている。抵抗体５，６，７は薄肉部３の下流側に偏った位置に形成されているため、上流側感温抵抗体６から薄肉部３の上流側エッジ部までの距離は、下流側感温抵抗体７から薄肉部３の下流側エッジ部までの距離よりも大きくなっている。
【００５３】
このように、抵抗体５，６，７を薄肉部３の下流側に偏った位置に形成することにより、上流側感温抵抗体６の流速増大による温度降下を大きくでき、また下流側感温抵抗体７の流速増大による温度上昇も大きくできる。
【００５４】
このことを裏付ける実験結果を図２４，２５，２６に示す。この実験は、図２４に示すような薄肉部３の幅の異なる２種類の流速センサに実際に空気の流れを与え、上流側、及び、下流側感温抵抗体６，７の温度の流速による変化を調べたものである。その結果が図２５と図２６で、図２５は２つのセンサの上流側感温抵抗体６の流速による温度変化を比較したグラフ、図２６は２つのセンサの下流側感温抵抗体７の流速による温度変化を比較したグラフである。
【００５５】
図２５を見ると、薄肉部３の幅が大きい方が上流側感温抵抗体６の温度変化が大きいことが判る。つまり、上流側感温抵抗体６の温度変化を大きくするには薄肉部３の幅が大きい方が有利である。また、図２６を見ると、薄肉部３の幅が小さい方が下流側感温抵抗体７の温度変化が大きいことが判る。つまり、下流側感温抵抗体７の温度変化を大きくするには薄肉部３の幅が小さい方が有利である。
【００５６】
以上の実験結果から、図２２のように薄肉部３の下流側に偏った位置に抵抗体５，６，７を形成することにより、上流側感温抵抗体６と下流側感温抵抗体７の温度変化を、抵抗体５，６，７が薄肉部の中央にあるときよりも大きくすることができ、両者の温度差もより大きな値が得られる。その結果、センサの感度を向上させ、測定可能流速範囲を拡大することが出来る。
【００５７】
【発明の効果】
本発明の第１の構成である熱式流速センサによれば、薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部と、前記発熱部の極めて近傍に設けられた第３の温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に前記上流側温度検出部、下流側温度検出部、および第３の温度検出部との間に生じる温度差から流速を検出するようにしたので、流体温度検出部の温度低下による発熱部の温度低下分が出力に加味され、センサの感度向上と測定可能流速範囲の拡大が実現できる。
【００５８】
また、本発明の第２の構成である熱式流速センサによれば、薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部と、発熱部の上流側近傍に設けられた第４の温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に生じる前記上流側温度検出部と下流側温度検出部との温度差から得られる信号により空気流速を検出する熱式流速センサにおいて、前記温度差信号に増幅を施す際に、その利得を前記第４の温度検出部の抵抗値によって変化させるようにしたので、利得の持つ流量依存性の分だけセンサの感度を向上させることができ、測定可能流速範囲も拡大できる。
【００５９】
また、本発明の第３の構成である熱式流速センサによれば、薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部と、発熱部の上流側近傍に設けられた第４の温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に生じる前記上流側温度検出部と下流側温度検出部との温度差から得られる信号により空気流速を検出する熱式流速センサにおいて、前記上流側、および下流側温度検出部の温度を検出するために流す電流値を前記第４の温度検出部の抵抗値によって変化させるようにしたので、電流の持つ流量依存性の分だけセンサの感度を向上させることができ、測定可能流速範囲も拡大できる。
【００６０】
また、本発明の第４の構成である熱式流速センサによれば、薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部と、発熱部の上流側近傍に設けられた第４の温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に生じる前記上流側温度検出部と下流側温度検出部との温度差から得られる信号により空気流速を検出する熱式流速センサにおいて、前記温度差信号に加えるバイアス信号を前記第４の温度検出部の抵抗値によって変化させるようにしたので、バイアス信号の持つ流量依存性の分だけセンサの感度を向上させることができ、測定可能流速範囲も拡大できる。
【００６１】
また、本発明の第５の構成である熱式流速センサによれば、薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部と、発熱部の上流側および下流側にそれぞれ設けられた第４および第５の温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に生じる前記上流側温度検出部と下流側温度検出部との温度差から得られる信号により空気流速を検出する熱式流速センサにおいて、前記第４，第５の温度検出部の抵抗値を用いて流速以外の原因による請求項２から４に記載の利得、電流、バイアス信号の変動を相殺するようにしたので、空気の流速以外の条件が変化する場合でも正確な流速検知ができる。
【００６２】
また、本発明の第６の構成である熱式流速センサによれば、薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に生じる前記上流側温度検出部と下流側温度検出部との温度差から得られる信号により空気流速を検出する熱式流速センサにおいて、前記発熱部と温度検出部を前記薄肉部上の空気の流れに対して下流側に偏った位置に配置するようにしたので、上流側温度検出部と下流側温度検出部の温度変化をより大きくすることができ、両者の温度差もより大きな値が得られ、センサの感度を向上させ、測定可能流速範囲を拡大することができる。
【図面の簡単な説明】
【図１】本発明の実施の形態１を示す上面図である。
【図２】図１のＡ−Ａ′線断面図である。
【図３】基本的な定温度差駆動回路の簡略図である。
【図４】基本的な温度差検出回路の簡略図である。
【図５】本発明の実施の形態１に係わる温度差検出用回路の簡略図である。
【図６】本発明の実施の形態１に係わる流速による各抵抗の電圧変化を表したグラフである。
【図７】本発明の実施の形態１に係わる温度差検出用回路の簡略図である。
【図８】本発明の実施の形態１に係わる温度差検出用回路の簡略図である。
【図９】本発明の実施の形態１に係わる温度差検出用回路の簡略図である。
【図１０】本発明の実施の形態１に係わる温度差検出用回路の簡略図である。
【図１１】本発明の実施の形態２，３を示す上面図である。
【図１２】図１１のＡ−Ａ′線断面図である。
【図１３】本発明の実施の形態２に係わる温度差検出用回路の簡略図である。
【図１４】本発明の実施の形態３に係わる定電流供給回路の簡略図である。
【図１５】本発明の実施の形態４に係わる定電流供給回路の簡略図である。
【図１６】本発明の実施の形態５に係わるバイアス電圧供給回路の簡略図である。
【図１７】本発明の実施の形態６を示す上面図である。
【図１８】図１７のＡ−Ａ′線断面図である。
【図１９】本発明の実施の形態６に利用される温度差検出回路の簡略図である。
【図２０】本発明の実施の形態７に係わる定電流供給回路の簡略図である。
【図２１】本発明の実施の形態８に係わるバイアス電圧供給回路の簡略図である。
【図２２】本発明の実施の形態９に係わる上面図である。
【図２３】本発明の実施の形態９に係わる断面図である。
【図２４】本発明の実施の形態９を裏付ける実験結果を示す図である。
【図２５】本発明の実施の形態９を裏付ける実験結果を示す図である。
【図２６】本発明の実施の形態９を裏付ける実験結果を示す図である。
【図２７】従来例を示す断面図である。
【図２８】図２７の上面図である。
【図２９】従来例に係わる感温抵抗体温度の流速依存性を示す図である。
【図３０】従来例に係わる感温抵抗体の温度差の流速依存性を示す図である。
【図３１】従来例に係わるヒーター温度制御回路図である。
【図３２】従来例に係わる温度差検出回路図である。
【図３３】従来例に係わる薄肉部の熱伝達模式図である。
【図３４】別の従来例に係わる感温抵抗体温度の流速依存性である。
【符号の説明】
１ シリコン基板、２ 空気スペース、３ 薄肉部、５ 発熱抵抗体、６ 上流側感温抵抗体、７ 下流側感温抵抗体、８ 流体温度検出用感温抵抗体、１１発熱抵抗体温度検出用感温抵抗体、３３ａ，ｂ 上流側感温抵抗体、３４ａ，ｂ 下流側感温抵抗体。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a flow rate sensor used in a place where a flow rate measurement of a fluid such as air is required, for example, an engine control of an automobile or an air conditioner, and more particularly to an improvement in detection sensitivity and an expansion of a measurable flow rate range.
[0002]
[Prior art]
FIG. 27 is a sectional view of a main part of a conventional thermal flow velocity sensor (conventional example 1) disclosed in Japanese Patent Publication No. 5-7659, for example, and FIG. 28 is a top view thereof. In the figure, 1 is a silicon substrate, 2 is an air space formed on the silicon substrate 1 by etching, 3 and 4 are thin-film members or thin portions cross-linked on the air space 2, 5 is a heater, and 6, 7 are The upstream and downstream heat sensing sensors 8, respectively, are comparative resistors that monitor the temperature of the surrounding air. The upstream and downstream heat sensing sensors 6 and 7 are arranged symmetrically with the heater 5 interposed therebetween. The heater 5 and the heat sensing sensors 6 and 7 are surrounded by thin-film insulating layers 9 and 10 made of, for example, silicon nitride to form thin portions 3 and 4.
[0003]
The basic operation of this conventional thermal flow sensor will be described. In FIG. 28, the heater 5 is heated to a temperature 200 ° C. higher than the temperature of the silicon substrate 1. The temperature of the silicon substrate 1 is almost the same as the temperature of the surrounding air, and is measured by the comparative resistor 8. When there is no air flow, the heat sensing sensors 6 and 7 are heated to an average of about 140 ° C. by the heat of the heater 5. That is, since the heat sensing sensors 6 and 7 are arranged exactly symmetrically with respect to the heater 5, when the flow rate of the air is 0, the temperatures of the two sensors become the same, and the resistance of the heat sensing sensors 6 and 7 becomes higher. There is no difference in the values. Therefore, even if a minute measurement current is applied to the two heat sensing sensors 6 and 7, no voltage difference occurs.
[0004]
When there is an air flow, the heat sensing sensor 6 located on the upstream side is cooled because heat is carried away by the flow of air toward the heater 5, while the heat sensing sensor 7 located on the downstream side is cooled by the heater 5. It will be heated by the flow of air. FIG. 29 shows the flow rate dependency of the temperature of the heat sensing sensors 6 and 7. As the flow velocity increases, the temperature of the upstream heat sensing sensor 6 decreases, and the temperature of the downstream heat sensing sensor 7 increases. The resulting difference in resistance between the heat sensing sensors 6, 7 results in a difference in voltage, from which the flow rate is measured. FIG. 30 is a graph in which the vertical axis represents the temperature difference between the two heat sensing sensors. The flow velocity (horizontal axis) and the temperature difference (vertical axis) correspond one-to-one, indicating that it can be used as a flow velocity sensor.
[0005]
FIG. 31 and FIG. 32 show circuit examples for realizing these functions. The circuit shown in FIG. 31 is for controlling the temperature of the heater 5, and the circuit shown in FIG. 32 is for obtaining a voltage signal proportional to the difference in resistance between the heat sensing sensors 6 and 7. belongs to.
[0006]
The temperature control circuit shown in FIG. 31 is configured by a Whiston bridge circuit 46 for keeping the temperature of the heater 5 higher than the ambient temperature detected by the comparison resistor 8 by a certain temperature. In the Whiston bridge circuit 46, one side is constituted by the heater 5 and the resistor 45, and the other side is constituted by the comparative resistor 8 and the resistors 47 and 48. The integration circuit including the amplifiers 49 and 50 operates so as to balance the bridge circuit 46 by changing the potential of the output, and keeps the power consumed by the heater 5 constant.
[0007]
The circuit shown in FIG. 32 is for detecting a difference between the heat sensor 6 located on the upstream side of the heater 5 and the heat sensor 7 located on the downstream side. This circuit includes a constant current power supply unit 52 including an amplifier 72 and a differential amplifier unit 54 including amplifiers 66, 68, and 70. The constant current power supply unit 52 drives a Whiston bridge circuit having high impedance resistors 56 and 58 on one side and a zero-adjustment variable resistor 60 and heat sensing sensors 6 and 7 on the other side. The gain of the differential amplifier 54 is adjusted by the variable resistor 62. The output terminal 64 outputs an output voltage proportional to the difference in resistance between the heat sensing sensors 6 and 7.
[0008]
[Problems to be solved by the invention]
In order to make this type of thermal flow sensor have a wide range of measurable flow speeds and high sensitivity, it is desirable that the temperature of the heat sensing sensors 6 and 7 greatly change over a wide flow speed range. However, in the conventional thermal type flow velocity sensor, when the flow velocity is 0, the heat detection sensor 7 on the downstream side is already heated to about 60 to 70% of the temperature of the heater 5, so that the heat is transmitted from the heater 5 via air. The heat content is low and the saturation temperature is reached at a relatively low flow rate. Referring to FIG. 29, it can be seen that the temperature change of the downstream temperature-sensitive resistor 7 is actually small, and the saturation is already observed at 5 m / s or more.
[0009]
FIG. 33 is a schematic diagram showing heat transfer in the heater 5 and the temperature-sensitive resistors 6 and 7. In the figure, Q1 is the amount of heat transferred from the heater 5 to the air, Q2 is the amount of heat transferred from the heater 5 to the upstream heat sensor 6 via the thin film member, and Q3 is the downstream heat from the heater 5 via the thin film member. Q4 is the amount of heat transfer from the upstream heat sensor 6 to the air, and Q5 is the amount of heat transfer from the air to the downstream heat sensor 7.
[0010]
Looking at the downstream heat sensing sensor 7, two heat inflows Q3 and Q5 occur. Of these, Q3 does not depend on the flow velocity, and only Q5 has flow velocity dependence. Q5 is proportional to the temperature difference between the air passing over the heat sensor 7 and the heat sensor 7 itself. Most of the heat inflow at the flow velocity 0 may be considered to be due to Q3, but as shown in FIG. 29, the heat sensing sensor 7 has already been heated to 140 ° C. at this time. Therefore, the temperature difference between the heat sensing sensor 7 and the air becomes small, and Q5 proportional to this temperature difference cannot be made large. Therefore, even when there is a flow, the temperature rise of the heat sensing sensor 7 is small. Moreover, if the temperature rises to some extent, the temperature difference from the air will be further reduced, and the temperature will be closer to the saturated state. As a result, as shown in FIG. 30, as the flow velocity increases, the change in the temperature difference between the upstream and downstream heat sensing sensors 6 and 7 decreases, and the sensitivity decreases.
[0011]
As for the upstream heat sensor 6, a part of the heat quantity Q2 transmitted from the heater 5 is transmitted to the air as Q4. Although Q2 does not depend on the flow rate of air, Q4 increases as the flow rate increases, so that the temperature of the heat sensing sensor 6 decreases as the flow rate increases. In this case, the larger the value of Q2, the wider the range of change of Q4, which is advantageous for improving sensitivity and expanding the measurable flow speed range. Referring to FIG. 29 as well, the temperature of the upstream heat sensing sensor 6 changes with a large inclination. However, for example, when used for controlling the engine of a car, the flow velocity range (0 to 2000 ft / min = 0 to 10 m / sec) shown in FIG. 29 is not sufficient, and the measurement range is at least 0 to 50 m / sec. Is necessary. Assuming that the gradient of the temperature change of the upstream heat sensing sensor 6 in FIG. 29 is (−40 ° C.) / (10 m / sec), the gradient of the temperature change gradually decreases until the flow velocity reaches 50 m / sec. It is clear that it will go. As a result, as the flow velocity increases, the change in the temperature difference between the upstream and downstream heat sensing sensors 6 and 7 decreases, and the sensitivity decreases.
[0012]
Further, F.I. According to a study by Mayer et al. (F. Mayer et al: Transducers @ 95 Eurosensors IX 132-C2 pp. 528-531), it is reported that the temperature of the downstream heat sensing sensor 7 decreases as the flow rate increases. I have. This phenomenon has been confirmed by an experiment conducted by the present inventors (FIG. 34). According to the study by Li Qui et al. (Li Qui et al: Transducers @ 95 Eurosensors IX130-C2 pp. 520-523), the temperature difference between the upstream and downstream heat sensing sensors 6 and 7 decreases at a certain flow rate or more. It has been reported. These reports show that as the flow velocity increases, output binarization (there are two flow velocity points corresponding to one output) can occur. This limits the expansion of the measurable flow velocity range.
[0013]
As described above, the conventional thermal flow rate sensor using the temperature difference has a problem that the sensitivity decreases as the flow rate increases, and the measurable flow rate range cannot be widened.
[0014]
The present invention has been made to solve the above-described problems, and has as its object to provide a thermal flow sensor capable of improving sensitivity and expanding a measurable flow speed range.
[0015]
[Means for Solving the Problems]
The thermal type flow sensor according to the first configuration of the present invention has a semiconductor substrate on which a thin portion is formed, a heat generating portion formed on the thin portion, and an upstream and downstream side of the heat generating portion which are also formed on the thin portion. And a third temperature detecting section provided very close to the heat generating section, and a fluid temperature detecting section located upstream of the upstream temperature detecting section. And when the heat generating unit is driven at a constant temperature difference with respect to the fluid temperature detected by the fluid temperature detecting unit, between the upstream temperature detecting unit, the downstream temperature detecting unit, and the third temperature detecting unit. The flow velocity is detected from the temperature difference generated at the time.
[0016]
The thermal type flow sensor according to the second configuration of the present invention has a semiconductor substrate on which a thin portion is formed, a heat generating portion formed on the thin portion, and an upstream and downstream side of the heat generating portion which are also formed on the thin portion. And a fourth temperature detection unit provided near the upstream side of the heating unit, and a fluid temperature detection unit located upstream of the upstream temperature detection unit. And air generated by a signal obtained from a temperature difference between the upstream temperature detection unit and the downstream temperature detection unit that is generated when the heating unit is driven at a constant temperature difference with respect to the fluid temperature detected by the fluid temperature detection unit. In the thermal type flow rate sensor for detecting a flow rate, when amplifying the temperature difference signal, the gain is changed by the resistance value of the fourth temperature detecting section.
[0017]
The thermal type flow sensor according to the third configuration of the present invention is a semiconductor substrate having a thin portion, a heat generating portion formed in the thin portion, and a heat generating portion formed in the same thin portion, and an upstream side and a downstream side of the heat generating portion. And a fourth temperature detection unit provided near the upstream side of the heating unit, and a fluid temperature detection unit located upstream of the upstream temperature detection unit. And air generated by a signal obtained from a temperature difference between the upstream temperature detection unit and the downstream temperature detection unit that is generated when the heating unit is driven at a constant temperature difference with respect to the fluid temperature detected by the fluid temperature detection unit. In the thermal type flow rate sensor for detecting a flow rate, the value of a current flowing for detecting the temperatures of the upstream and downstream temperature detecting sections is changed by the resistance value of the fourth temperature detecting section. .
[0018]
The thermal flow sensor according to the fourth configuration of the present invention is a semiconductor substrate having a thin portion, a heat generating portion formed in the thin portion, and a heat generating portion formed in the thin portion, and an upstream side and a downstream side of the heat generating portion. And a fourth temperature detection unit provided near the upstream side of the heating unit, and a fluid temperature detection unit located upstream of the upstream temperature detection unit. And air generated by a signal obtained from a temperature difference between the upstream temperature detection unit and the downstream temperature detection unit that is generated when the heating unit is driven at a constant temperature difference with respect to the fluid temperature detected by the fluid temperature detection unit. In a thermal type flow rate sensor for detecting a flow rate, a bias signal to be added to the temperature difference signal is changed by a resistance value of the fourth temperature detection section.
[0019]
A thermal flow sensor according to a fifth aspect of the present invention is a semiconductor substrate having a thin-walled portion, a heating portion formed in the thin-walled portion, and a heating portion formed in the thin-walled portion. And a fourth and a fifth temperature detector provided respectively on the upstream side and the downstream side of the heat generating part, and an upstream side and a downstream side of the upstream side temperature detector. A temperature difference between the upstream temperature detection unit and the downstream temperature detection unit that occurs when the heating unit is driven by a constant temperature difference with respect to the fluid temperature detected by the fluid temperature detection unit. 5. The gain, current, and bias according to claim 2, wherein the thermal flow velocity sensor detects an air flow velocity based on a signal obtained from a temperature, and uses a resistance value of the fourth and fifth temperature detectors for a cause other than the flow velocity. Signal It is obtained so as to offset the motion.
[0020]
A thermal flow sensor according to a sixth aspect of the present invention is a thermal flow sensor having a thin-walled portion, a heat-generating portion formed on the thin-walled portion, and a heat-generating portion formed on the thin-walled portion. And an upstream side and a downstream side temperature detecting unit disposed respectively on the sides, and a fluid temperature detecting unit provided upstream from the upstream side temperature detecting unit, and the heat generating unit detects the fluid temperature detected by the fluid temperature detecting unit. In a thermal type flow rate sensor that detects an air flow rate based on a signal obtained from a temperature difference between the upstream side temperature detection section and the downstream side temperature detection section that is generated when a constant temperature difference drive is performed, the heating section and the temperature detection section are It is arranged at a position deviated downstream with respect to the flow of air on the thin portion.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1 FIG.
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a top view showing the first embodiment of the present invention, and FIG. 2 is a sectional view taken along line AA ′ of FIG. However, the cross-sectional view of FIG. 2 is a slightly enlarged view of the top view of FIG. 1, and this is the same in the following similar cross-sectional views along the line AA ′. In the figure, 1 is a silicon substrate, 2 is an air space formed by etching the silicon substrate 1 from the back, and 3 is a diaphragm type thin portion provided on the air space 2. Reference numeral 5 denotes a heat generating portion, that is, a heat generating resistor, and reference numerals 6 and 7 denote upstream and downstream temperature detecting portions, that is, upstream and downstream temperature sensing resistors, which are disposed on the upstream and downstream sides of the heat generating resistor 5, respectively. A fluid temperature detecting portion disposed upstream of the side temperature sensitive resistor 6 for measuring the temperature of the fluid, that is, a temperature sensitive resistor for fluid temperature detection, 9 and 10 are insulating layers, and 11 is located very close to the heating resistor 5. The heat generating resistor temperature detecting section, that is, the temperature detecting resistor for detecting the temperature of the heat generating resistor, 12 is the heat generating resistor 5, the upstream and downstream temperature sensitive resistors 6, 7 and the temperature sensing resistor 8 for detecting the fluid temperature. And wires for connecting both ends of the heating resistor temperature detecting temperature sensitive resistor 11 to the bonding pads 13 respectively. The thin portion 3 includes insulating layers 9 and 10, a heating resistor 5 sandwiched between the insulating layers 9 and 10, and temperature-sensitive resistors 6, 7 and 11.
[0022]
The heating resistor 5, the temperature-sensitive resistors 6 and 7, and the fluid-temperature detecting temperature-sensitive resistor 8 are formed into thin films by a film forming technique such as sputtering or vapor deposition, and then patterned by etching to obtain a desired resistance value. are doing. It is desirable to use highly reliable platinum or the like as the resistance material.
[0023]
The heating resistor 5 is driven at a constant temperature difference so as to always be higher by a certain temperature than the temperature of the air measured by the temperature sensing resistor 8 for detecting fluid temperature. FIG. 3 is a simplified circuit diagram of a basic constant temperature difference drive circuit. A bridge circuit is constituted by the heating resistor 5, the temperature sensing resistor 8 for detecting fluid temperature, and the fixed resistors 14 and 15. If the temperature of the heating resistor 5 changes due to the fluctuation of the flow velocity of air, or the temperature of the air temperature changes and the temperature of the temperature-sensitive resistor 8 for detecting fluid temperature changes, the balance of the bridge circuit is lost. The differential amplifier 16 and the transistor 17 function to control the heating current flowing through the heating resistor 5 to return to the original balance state. As a result, the temperature difference between the heating resistor 5 and the temperature sensing resistor 8 for detecting fluid temperature is always kept constant. 18 is a power supply.
[0024]
FIG. 4 is a simplified diagram of a basic temperature difference detection circuit. More specifically, FIG. 4 is a simplified diagram of a temperature difference detection circuit for detecting a temperature difference between the upstream temperature sensing resistor 6 and the downstream temperature sensing resistor 7. Show. The constant current source 19 allows a constant current Is to flow through the upstream temperature-sensitive resistor 6 (Ru) and the downstream temperature-sensitive resistor 7 (Rd). , From the output terminal 21 as an output voltage Vout. The output voltage Vout in this case is expressed by the following equation.
Vout = Vref + G · Rs0 · αs · Is · (Td−Tu) (1)
Here, Rs0 is the resistance value of the upstream and downstream temperature sensitive resistors 6, 7 at 0 ° C., and αs is the resistance temperature coefficient of the upstream and downstream temperature sensitive resistors 6, 7. Vref (38) uses a constant voltage source with a bias voltage added to obtain a positive output even when (Td-Tu) becomes negative, that is, even when the air flow is reverse. ing. By forming the upstream and downstream temperature-sensitive resistors 6 and 7 from the same material in the same pattern, Rs0 and αs of the two can be almost the same value. Td and Ts are the temperatures of the upstream and downstream temperature sensitive resistors 6 and 7, respectively. G is a gain determined by the amplifier circuit, and is represented by the following equation.
G = 1 + (R2 / R1) (2)
Where R2 / R1 = R4 / R3
The temperature difference (Td-Tu) between the upstream temperature sensing resistor 6 and the downstream temperature sensing resistor 7 can be approximately expressed as follows.
Td-Tu = AU n ΔT (3)
Here, U is the flow velocity of air, ΔT is the temperature difference between the air and the heating resistor 5 kept constant by the constant temperature difference drive circuit of FIG. 3, and A is a coefficient. It can be seen from the combination of equations (1) and (3) that the output voltage Vout depends on the flow velocity U.
Vout = Vref + G · Rs0 · αs · Is · AU n ・ ΔT (4)
[0025]
As described above, ΔT in equation (4) should be kept constant by the constant temperature difference drive circuit shown in FIG. However, in practice, the heat generated by the heat generating resistor 5 is also transmitted to the fluid temperature detecting temperature sensitive resistor 8, so that the temperature of the fluid temperature detecting temperature sensitive resistor 8 is higher than the air temperature. The temperature rise of the fluid temperature detecting temperature-sensitive resistor 8 increases as the flow velocity of the air decreases, and as the flow rate increases, the fluid temperature-detecting temperature sensitive resistor 8 is cooled and approaches the temperature of the air. Since the temperature of the heating resistor 5 is controlled so as to be higher than the temperature sensing resistor 8 for detecting fluid temperature by a fixed temperature, the temperature of the heating resistor 5 also decreases as the flow rate of air increases. Therefore, ΔT in equation (4) is not actually constant, but decreases as the flow velocity increases. Due to the negative flow velocity dependence of ΔT, the flow velocity dependence of the output voltage Vout is suppressed, and the sensitivity and the measurable flow velocity range are reduced.
[0026]
In the present embodiment, the above-described fluctuation due to the flow rate of ΔT is detected by the heating resistor temperature detecting temperature sensing resistor 11, and the heating resistor temperature sensing temperature sensing resistor 11 and the upstream temperature sensing resistor are detected. Since the output voltage is derived from the temperature changes of the three temperature sensing resistors 6 and 7, the negative flow rate dependency of ΔT can be canceled.
[0027]
FIG. 5 is a simplified diagram of a temperature difference detection circuit according to Embodiment 1 of the present invention. In this example, first, the voltage dependent on the temperature of the heating resistor temperature detecting temperature sensitive resistor 11 is subtracted from the voltage dependent on the temperature of the downstream temperature sensitive resistor 7 by the differential amplifier 25, and then the differential amplifier 25 is subtracted. The voltage depending on the temperature of the upstream temperature sensing resistor is further subtracted by 26 to obtain an output voltage. By doing so, an output voltage is generated in which the temperature drop of the temperature sensing resistor 11 for detecting the temperature of the heating resistor is added, so that the sensor sensitivity and the measurable flow rate range can be improved. Of course, the voltage after passing through the amplifier circuit section as shown in FIG. 4 may be used as the output voltage.
[0028]
FIG. 6 shows how the voltages at the positive ends of the three temperature-sensitive resistors 6, 7, and 11 shown in FIG. The voltage 27 (Vu) of the upstream temperature sensing resistor 6 and the voltage 29 (Vsh) of the heating resistor temperature detecting temperature sensing resistor 11 decrease as the flow rate increases, and the voltage 28 (Vsh) of the downstream temperature sensing resistor 7 decreases. Vd) increases as the flow rate increases. By adjusting the fixed resistances 22, 23, and 24, the three voltages when the flow velocity is zero can be set to Vd = Vu + Vsh. When Vd-Vsh is calculated in FIG. 6, a curve 30 that matches Vu when the flow velocity is zero and has a slope larger than Vd is obtained. If the Vu curve 27 is further subtracted from the curve 30, a curve having a larger slope than the curve obtained by simply calculating Vd-Vu is obtained. By using this voltage as an output, the sensitivity of the sensor can be improved.
[0029]
The above effects can be realized not only by the circuit shown in FIG. 5 but also by the circuits shown in FIGS. FIG. 7 shows that the voltage 27 (Vu) of the upstream temperature sensing resistor 6 and the voltage (Vsh) of the temperature sensing resistor 11 for detecting the temperature of the heating resistor are added by an adding circuit 31, and the resulting voltage is added downstream. A circuit for obtaining an output voltage by subtracting from the voltage 28 (Vd) of the side temperature sensing resistor 7, and FIG. 8 first shows the voltage of the downstream temperature sensing resistor 7 from the voltage 27 (Vu) of the upstream temperature sensing resistor 6. 28 (Vd), and then subtracts the voltage (Vsh) of the heating resistor temperature detecting temperature sensitive resistor 11 to obtain an output voltage. The circuits of FIGS. 5, 7 and 8 are simply expressed by the following equations.
Figure 5: (Vd-Vsh) -Vu
Figure 7: Vd- (Vu + Vsh)
Figure 8: (Vd-Vu) -Vsh
[0030]
The same effect can be obtained by a circuit using both the constant voltage source 32 and the constant current source 19 as shown in FIG. In the circuit of FIG. 9, the voltage Vd is represented by the following equation.
Vd = Rd · Vc / (Rd + Rsh) = 1 · Vc / {1+ (Rsh / Rd)} (5)
As can be seen from equation (5), when Rsh decreases, Vd increases. By subtracting Vu from this Vd, an output voltage Vout that takes into account the temperature drop of the heating resistor temperature detecting temperature sensitive resistor 11 is obtained.
[0031]
Further, as shown in FIG. 10, the upstream temperature sensing resistor 6 and the heating resistor temperature detecting temperature sensing resistor 11 are connected in series to flow a constant current, and the uppermost voltage Vu and the downstream temperature sensing resistor are connected. By taking the difference from the voltage Vd of the resistor 7, an output voltage Vout that takes into account the temperature drop of the heating resistor temperature detecting temperature sensitive resistor 11 is also obtained.
[0032]
Embodiment 2 FIG.
FIG. 11 is a top view showing the second embodiment of the present invention, and FIG. 12 is a sectional view taken along line AA ′ of FIG. In the figure, a heating resistor 5 is formed on a thin portion 3 of a silicon substrate 1, and temperature-sensitive resistors 6, 33 a, 33 b are formed upstream of the heating resistor 5, and a temperature-sensitive resistor 7 is formed on a downstream side thereof. . Since the two upstream temperature sensing resistors 33a and 33b are formed of the same material and in the same pattern, they have the same resistance temperature characteristics. Further, they are formed at positions very close to each other so as to have the same temperature.
[0033]
Also in this embodiment, similarly to the first embodiment, the heating resistor 5, the upstream temperature sensing resistor 6, the downstream temperature sensing resistor 7, and the fluid temperature detecting temperature sensing resistor 8 are used. An air flow rate sensor of a temperature difference detection type is configured. The output voltage Vout of this type of sensor is expressed by the above-described equation (4). Here, the gain G of the amplifier circuit unit is expressed in the same manner as in the above-described Expression 2 using the circuit of FIG.
[0034]
Although R1 to R4 in FIG. 4 all use fixed resistors, in this embodiment, as shown in FIG. 13, the temperature sensitive resistor 33a of FIG. 11 is used for R1, and the temperature sensitive resistor 33b is used for R3. I'm using Assuming that the resistance values of the temperature-sensitive resistors 33a and 33b are R33, the gain G of the amplifier circuit section is as follows.
G = 1 + R2 / R33 (6)
Since the temperature-sensitive resistors 33a and 33b are both located on the upstream side of the heating resistor 5, the flow rate increases, the temperature decreases, and the resistance value also decreases. Therefore, the gain G expressed by the equation (6) increases as the flow velocity increases. Therefore, the output voltage Vout expressed by the equation (4) increases as the flow velocity increases, including the effect of increasing the gain G, and the output voltage Vout depends on the flow rate of the output voltage Vout as compared with the case where the gain G is fixed. Performance, sensor sensitivity is improved, and the measurable flow velocity range is expanded.
[0035]
Embodiment 3 FIG.
FIG. 14 is a simplified diagram of a constant current supply circuit according to Embodiment 3 of the present invention. In the figure, 32 is a constant voltage source, and 35 and 36 are fixed resistors. Although the constant current source 19 is used in the circuit shown in FIG. 4, the circuit shown in FIG. 14 is a constant current circuit that functions to improve the sensitivity and the measurement range in place of the constant current source 19. When the circuit is configured as shown in the figure, a constant current Is expressed by the following equation flows between the terminals AB.
Is = Vi / R33 = R36.Vc / {(R35 + R36) .R33} = Vc / {1+ (R35 / R36) .R33} (7)
When R33 in the equation (7) is fixed, a constant current Is can be obtained. However, the third embodiment is characterized in that an upstream temperature-sensitive resistor 33a is used for this R33 as shown in FIG. The upstream temperature-sensitive resistor 33a is cooled when the flow velocity of the air increases, and the resistance value decreases. Therefore, the current Is expressed by the equation (7) increases with the flow velocity. Therefore, the output voltage Vout expressed by the equation (4) increases as the flow velocity increases, including the effect of increasing the current Is, and the output voltage Vout depends on the flow rate of the output voltage Vout as compared with the case where the current Is is fixed. Performance, sensor sensitivity is improved, and the measurable flow velocity range is expanded.
[0036]
Embodiment 4 FIG.
FIG. 15 is a simplified diagram of a constant current supply circuit according to Embodiment 4 of the present invention. Using this circuit, the current Is is represented by the following equation.
Is = Vi / R35 = R36.Vc / {(R33 + R36) .R35} = Vc / {1+ (R33 / R36) .R35} (8)
The upstream temperature-sensitive resistor 33a is cooled when the flow rate of the air increases, and the resistance value (R33) decreases. Therefore, the current Is represented by the equation (8) increases with the flow rate. Therefore, the output voltage Vout expressed by the equation (4) increases as the flow velocity increases, including the effect of increasing the current Is, and the output voltage Vout depends on the flow rate of the output voltage Vout as compared with the case where the current Is is fixed. Performance, sensor sensitivity is improved, and the measurable flow velocity range is expanded. Of course, the effects may be doubled by combining the third and fourth embodiments using two upstream temperature-sensitive resistors 33a and 33b.
[0037]
Embodiment 5 FIG.
FIG. 16 is a simplified diagram of a bias voltage supply circuit according to Embodiment 5 of the present invention. In the figure, 32 is a constant voltage source, and 37 is a fixed resistor. In the circuit shown in FIG. 4, a constant voltage source is used for the bias voltage Vref (38). However, in the fourth embodiment, as shown in FIG. The bias voltage Vref is applied using a circuit. Moreover, the upstream temperature sensing resistor 33a shown in FIG. 11 is used for R33. The voltage (Vref) at the output terminal C in the circuit of FIG. 16 is expressed by the following equation.
Vref = R37 · Vc / (R37 + R33) = 1 · Vc / {1+ (R33 / R37)} (9)
[0038]
The upstream temperature-sensitive resistor 33a is cooled when the flow velocity of the air increases, and the resistance value (R33) decreases. Therefore, the voltage Vref expressed by the equation (8) increases with the increase of the flow velocity. Therefore, the output voltage Vout expressed by the equation (4) increases as the flow velocity increases, including the effect of increasing the bias voltage Vref, and the output voltage Vout of the output voltage Vout is smaller than when the bias voltage Vref is fixed. The flow rate dependency increases, the sensitivity of the sensor improves, and the measurable flow velocity range is expanded.
[0039]
Embodiment 6 FIG.
FIG. 17 is a top view showing the sixth embodiment of the present invention, and FIG. 18 is a sectional view taken along line AA ′ of FIG. In the figure, a heating resistor 5 and temperature-sensitive resistors 6, 33a, 33b upstream of the heating resistor 5 and temperature-sensitive resistors 7, 34a, 34b downstream are provided in the thin portion 3 of the silicon substrate 1, respectively. Is formed. The four upstream temperature-sensitive resistors 33a, 33b and 34a, 34b are formed of the same material by the same forming method. The upstream temperature-sensitive resistors 33a and 33b and the downstream temperature-sensitive resistors 34a and 34b are formed at positions very close to each other so as to have the same temperature.
[0040]
Also in this embodiment, similarly to the above-described second embodiment, the heating resistor 5, the upstream temperature sensing resistor 6, the downstream temperature sensing resistor 7, and the fluid temperature detecting temperature sensing resistor 8 are used. An air flow rate sensor of a temperature difference detection type is configured. In the second embodiment, the sensitivity of the sensor is improved by giving the flow rate dependency to the gain G of the amplifier circuit section 20 by the upstream temperature-sensitive resistor 33a, and the gain G is given by G = 1 + R2 // in equation (6). R33).
[0041]
However, the resistance value R33 of the upstream temperature-sensitive resistor 33a also changes depending on the state of the air other than the flow speed, such as the temperature and humidity of the air. For this reason, even if the flow velocity is constant, if the temperature of the air changes, the gain G also changes. If the temperature of the air changes, the flow velocity cannot be accurately detected. Therefore, in the sixth embodiment, as shown in the circuit diagram of FIG. 19, the downstream temperature-sensitive resistors 34a and 34b are used instead of the fixed resistors R2 and R4 of the amplifier circuit unit 20. At this time, the gain G is expressed by the following equation.
G = 1 + R34a / R33a (10)
[0042]
The temperature of the upstream temperature-sensitive resistors 33a and 33b decreases as the flow velocity increases, and the resistance value also decreases. Further, the temperature of the downstream-side temperature-sensitive resistors 34a and 34b increases slightly as the flow velocity increases, and the resistance value also increases. Therefore, the gain G represented by the equation (10) increases as the flow velocity increases. Therefore, the output voltage Vout expressed by the equation (4) increases as the flow velocity increases, including the effect of increasing the gain G, and the output voltage Vout depends on the flow rate of the output voltage Vout as compared with the case where the gain G is fixed. Performance, sensor sensitivity is improved, and the measurable flow velocity range is expanded.
[0043]
Further, when R33 changes due to conditions other than the flow velocity, the gain G does not change because R34 formed of the same material by the same method also changes. For example, if the temperature of the air rises and the resistance values of the upstream temperature sensing resistors 33a and 33b increase by 10%, the resistance values of the downstream temperature sensing resistors 34a and 34b also increase by 10%. Is canceled and the gain G is kept constant. As described above, according to the sixth embodiment, the gain G can be changed only by the flow velocity, and can be made independent of other factors such as the temperature of the air, and can be used even when the temperature of the air changes.
[0044]
Embodiment 7 FIG.
The top view and the cross-sectional view of the sensor according to the seventh embodiment are the same as FIGS. 17 and 18 shown in the sixth embodiment. Also in this embodiment, similarly to the above-described fourth embodiment, the heating resistor 5, the upstream temperature sensing resistor 6, the downstream temperature sensing resistor 7, and the fluid temperature detecting temperature sensing resistor 8 are used. An air flow rate sensor of a temperature difference detection type is configured. In the fourth embodiment, the sensitivity of the sensor is improved by changing the current value Is flowing through the upstream and downstream temperature sensing resistors 6 and 7 using the upstream temperature sensing resistor 33a. Was represented by equation (8).
[0045]
However, the resistance value R33 of the upstream temperature-sensitive resistor 33a also changes depending on the state of the air other than the flow velocity, such as the temperature and humidity of the air. For this reason, even if the flow velocity is constant, if the temperature of the air changes, the current value Is also changes. If the temperature of the air changes, the flow velocity cannot be accurately detected. Therefore, in the seventh embodiment, as shown in the circuit diagram of FIG. 20, the downstream temperature-sensitive resistor 34a is used instead of the fixed resistor R36. At this time, the current value Is is expressed by the following equation.
Figure 0003577902
[0046]
The temperature of the upstream temperature-sensitive resistor 33a decreases as the flow velocity increases, and the resistance value R33a also decreases. Further, the temperature of the downstream temperature-sensitive resistor 34a increases slightly as the flow velocity increases, and the resistance value R34a also increases. Therefore, the current value Is expressed by the equation (11) increases as the flow velocity increases. Therefore, the output voltage Vout represented by the equation (4) increases as the flow velocity increases, including the effect of increasing the current value Is, as compared with the case where the current value Is is fixed. The flow rate dependency increases, the sensitivity of the sensor improves, and the measurable flow velocity range is expanded.
[0047]
Further, when R33a changes due to conditions other than the flow velocity, R34a formed of the same material by the same method also changes, so that the current value Is does not change. For example, if the temperature of the air rises and the resistance value of the upstream temperature-sensitive resistor 33a increases by 10%, the resistance value of the downstream temperature-sensitive resistor 34a also increases by 10%, so that the change of both is canceled. The current value Is is kept constant. As described above, according to the seventh embodiment, the current value Is can be changed only by the flow velocity and can be made independent of other factors such as the temperature of the air, and can be used even when the temperature of the air changes. .
[0048]
Embodiment 8 FIG.
The top view and cross-sectional view of the sensor according to the eighth embodiment are the same as FIGS. 17 and 18 shown in the sixth embodiment. In this embodiment, similarly to the above-described fifth embodiment, the heating resistor 5, the upstream-side temperature sensing resistor 6, the downstream-side temperature sensing resistor 7, and the fluid temperature detecting temperature sensing resistor 8 are used. An air flow rate sensor of a temperature difference detection type is configured. In the fifth embodiment, the sensitivity of the sensor is improved by changing the bias voltage Vref using the upstream-side temperature sensing resistor 33a, and the bias voltage Vref in this case is expressed by Expression (9).
[0049]
However, the resistance value R33 of the upstream temperature-sensitive resistor 33a also changes depending on the state of the air other than the flow velocity, such as the temperature and humidity of the air. For this reason, even if the flow velocity is constant, if the air temperature or the like changes, the bias voltage Vref also changes. If the air temperature or the like changes, accurate flow velocity detection cannot be performed. Therefore, in the eighth embodiment, as shown in the circuit diagram of FIG. 21, the downstream-side temperature sensing resistor 34a is used instead of the fixed resistor R37. At this time, the bias voltage Vref is expressed by the following equation.
Vref = R34a · Vc / (R34a + R33a) = 1 · Vc / {1+ (R33a / R34a)} (9)
[0050]
The temperature of the upstream temperature-sensitive resistor 33a decreases as the flow velocity increases, and the resistance value R33a also decreases. Further, the temperature of the downstream temperature-sensitive resistor 34a increases slightly as the flow velocity increases, and the resistance value R34a also increases. Therefore, the bias voltage Vref expressed by the equation (12) increases as the flow velocity increases. Therefore, the output voltage Vout expressed by the equation (4) increases as the flow velocity increases, including the effect of increasing the bias voltage Vref, and the output voltage Vout of the output voltage Vout is smaller than when the bias voltage Vref is fixed. The flow rate dependency increases, the sensitivity of the sensor improves, and the measurable flow velocity range is expanded.
[0051]
Further, when R33a changes due to conditions other than the flow velocity, the bias voltage Vref does not change because R34a formed of the same material and by the same method changes similarly. For example, if the temperature of the air rises and the resistance value of the upstream temperature-sensitive resistor 33a increases by 10%, the resistance value of the downstream temperature-sensitive resistor 34a also increases by 10%, so that the change of both is canceled. And the bias voltage Vref is kept constant. As described above, according to the eighth embodiment, the bias voltage Vref can be changed only by the flow velocity, and can be made independent of other factors such as the temperature of the air, and can be used even when the temperature of the air changes. .
[0052]
Embodiment 9 FIG.
FIG. 22 is a top view showing the ninth embodiment of the present invention, and FIG. 23 is a sectional view taken along line AA ′ of FIG. In the drawing, a heating resistor 5 is formed on a thin portion 3 of a silicon substrate 1, a temperature-sensitive resistor 6 is formed on an upstream side thereof, and a temperature-sensitive resistor 7 is formed on a downstream side thereof. Since the resistors 5, 6, and 7 are formed at positions deviated to the downstream side of the thin portion 3, the distance from the upstream temperature-sensitive resistor 6 to the upstream edge portion of the thin portion 3 is determined by the downstream temperature-sensing. The distance is larger than the distance from the resistor 7 to the downstream edge of the thin portion 3.
[0053]
As described above, by forming the resistors 5, 6, and 7 at positions deviated to the downstream side of the thin portion 3, the temperature drop due to the increase in the flow velocity of the upstream temperature-sensitive resistor 6 can be increased, and The temperature rise due to the increase in the flow velocity of the resistor 7 can be increased.
[0054]
Experimental results supporting this fact are shown in FIGS. In this experiment, the flow of air was actually given to two types of flow rate sensors having different widths of the thin portion 3 as shown in FIG. 24, and the flow rate of the temperature of the upstream and downstream temperature sensing resistors 6 and 7 was changed. It examines the change. FIGS. 25 and 26 show the results, and FIG. 25 is a graph comparing the temperature change due to the flow rate of the upstream temperature sensitive resistor 6 of the two sensors, and FIG. 26 is the flow rate of the downstream temperature sensitive resistor 7 of the two sensors. 5 is a graph comparing the temperature change due to.
[0055]
25, it can be seen that the larger the width of the thin portion 3 is, the larger the temperature change of the upstream temperature-sensitive resistor 6 is. That is, in order to increase the temperature change of the upstream temperature-sensitive resistor 6, it is advantageous that the width of the thin portion 3 is large. 26, it can be seen that the smaller the width of the thin portion 3 is, the larger the temperature change of the downstream temperature-sensitive resistor 7 is. That is, in order to increase the temperature change of the downstream temperature-sensitive resistor 7, it is advantageous that the width of the thin portion 3 is small.
[0056]
From the above experimental results, by forming the resistors 5, 6, 7 at positions deviated to the downstream side of the thin portion 3 as shown in FIG. 22, the upstream temperature sensing resistor 6 and the downstream temperature sensing resistor 7 are formed. Can be made larger than when the resistors 5, 6, 7 are at the center of the thin portion, and a larger value of the temperature difference between the two can be obtained. As a result, the sensitivity of the sensor can be improved, and the measurable flow velocity range can be expanded.
[0057]
【The invention's effect】
According to the thermal type flow velocity sensor of the first configuration of the present invention, the semiconductor substrate having the thin portion, the heat generating portion formed in the thin portion, and the heat generating portion also formed in the thin portion, and the upstream of the heat generating portion An upstream side and a downstream side temperature detecting section disposed on the side and the downstream side, respectively, and a third temperature detecting section provided very close to the heat generating section, and a fluid is provided upstream of the upstream side temperature detecting section. A temperature detecting unit, wherein when the heating unit is driven at a constant temperature difference with respect to the fluid temperature detected by the fluid temperature detecting unit, the upstream temperature detecting unit, the downstream temperature detecting unit, and the third temperature detecting unit The flow rate is detected from the temperature difference that occurs between the sensor and the sensor, so the temperature drop of the heat generating part due to the temperature drop of the fluid temperature detector is added to the output, improving the sensor sensitivity and expanding the measurable flow rate range. it can.
[0058]
Further, according to the thermal type flow rate sensor of the second configuration of the present invention, the semiconductor substrate having the thin portion formed therein, the heat generating portion formed in the thin portion, and the heat generating portion formed in the thin portion also, Upstream and downstream temperature detectors respectively disposed on the upstream side and the downstream side, and a fourth temperature detector provided in the vicinity of the upstream side of the heat generating unit, and an upstream side from the upstream temperature detector. A fluid temperature detection unit, and the temperature difference between the upstream temperature detection unit and the downstream temperature detection unit that occurs when the heating unit is driven at a constant temperature difference with respect to the fluid temperature detected by the fluid temperature detection unit. In the thermal flow velocity sensor that detects the air flow velocity based on the obtained signal, when amplifying the temperature difference signal, the gain is changed by the resistance value of the fourth temperature detection unit. Flow rate dependence Min can be only improve the sensitivity of the sensor, the measurable flow rate range can be enlarged.
[0059]
Further, according to the thermal flow rate sensor having the third configuration of the present invention, the semiconductor substrate having the thin portion, the heat generating portion formed in the thin portion, and the heat generating portion also formed in the thin portion, Upstream and downstream temperature detectors respectively disposed on the upstream side and the downstream side, and a fourth temperature detector provided in the vicinity of the upstream side of the heat generating unit, and an upstream side from the upstream temperature detector. A fluid temperature detection unit, and the temperature difference between the upstream temperature detection unit and the downstream temperature detection unit that occurs when the heating unit is driven at a constant temperature difference with respect to the fluid temperature detected by the fluid temperature detection unit. In a thermal type flow velocity sensor that detects an air flow velocity based on an obtained signal, a current value flowing for detecting the temperatures of the upstream and downstream temperature detection sections is changed by a resistance value of the fourth temperature detection section. Made In, it is possible to improve the amount corresponding sensitivity of the sensor of the flow rate dependency with the current, the measurable flow rate range can be enlarged.
[0060]
Further, according to the thermal flow rate sensor having the fourth configuration of the present invention, the semiconductor substrate having the thin portion formed therein, the heat generating portion formed in the thin portion, and the heat generating portion also formed in the thin portion, Upstream and downstream temperature detectors respectively disposed on the upstream side and the downstream side, and a fourth temperature detector provided in the vicinity of the upstream side of the heat generating unit, and an upstream side from the upstream temperature detector. A fluid temperature detection unit, and the temperature difference between the upstream temperature detection unit and the downstream temperature detection unit that occurs when the heating unit is driven at a constant temperature difference with respect to the fluid temperature detected by the fluid temperature detection unit. In the thermal type flow velocity sensor that detects the air velocity based on the obtained signal, the bias signal to be added to the temperature difference signal is changed by the resistance value of the fourth temperature detection unit. Minute can be only improve the sensitivity of the sensor, the measurable flow rate range can be enlarged.
[0061]
Further, according to the thermal flow rate sensor having the fifth configuration of the present invention, the semiconductor substrate having the thin portion formed therein, the heat generating portion formed in the thin portion, and the heat generating portion also formed in the thin portion, Upstream and downstream temperature detectors respectively disposed on the upstream side and the downstream side, and fourth and fifth temperature detectors respectively provided on the upstream side and the downstream side of the heat generating unit. A fluid temperature detection unit provided upstream of the temperature detection unit, wherein the heating unit is driven by a constant temperature difference with respect to the fluid temperature detected by the fluid temperature detection unit, and the upstream temperature detection unit and the downstream temperature detection are generated. 5. A thermal flow sensor for detecting an air flow velocity based on a signal obtained from a temperature difference between the first and second temperature detectors, wherein the resistance value of the fourth and fifth temperature detectors is used to cause a cause other than the flow velocity. Gain, current, and Since so as to offset the variation of the astigmatism signal may correct the flow rate detection even when conditions other than the flow velocity of the air is changed.
[0062]
Further, according to the thermal flow rate sensor having the sixth configuration of the present invention, the semiconductor substrate having the thin portion, the heat generating portion formed in the thin portion, and the heat generating portion also formed in the thin portion, An upstream side and a downstream side temperature detector are respectively arranged on the upstream side and the downstream side, and a fluid temperature detector is provided on the upstream side of the upstream side temperature detector, and the heat generating part is provided by the fluid temperature detector. In the thermal type flow rate sensor for detecting an air flow rate by a signal obtained from a temperature difference between the upstream temperature detection section and the downstream temperature detection section which is generated when a constant temperature difference driving is performed with respect to the detected fluid temperature, the heat generation section And the temperature detector are arranged at a position deviated downstream with respect to the flow of air on the thin portion, so that the temperature change between the upstream temperature detector and the downstream temperature detector can be further increased. Yes, both Temperature difference also obtained a larger value, the sensitivity of the sensor is improved, it is possible to expand the measurable flow rate range.
[Brief description of the drawings]
FIG. 1 is a top view showing a first embodiment of the present invention.
FIG. 2 is a sectional view taken along line AA ′ of FIG.
FIG. 3 is a simplified diagram of a basic constant temperature difference drive circuit.
FIG. 4 is a simplified diagram of a basic temperature difference detection circuit.
FIG. 5 is a simplified diagram of a circuit for detecting a temperature difference according to the first embodiment of the present invention.
FIG. 6 is a graph showing a voltage change of each resistor according to a flow rate according to the first embodiment of the present invention.
FIG. 7 is a simplified diagram of a circuit for detecting a temperature difference according to the first embodiment of the present invention.
FIG. 8 is a simplified diagram of a circuit for detecting a temperature difference according to the first embodiment of the present invention.
FIG. 9 is a simplified diagram of a circuit for detecting a temperature difference according to the first embodiment of the present invention.
FIG. 10 is a simplified diagram of a circuit for detecting a temperature difference according to the first embodiment of the present invention.
FIG. 11 is a top view showing Embodiments 2 and 3 of the present invention.
FIG. 12 is a sectional view taken along line AA ′ of FIG. 11;
FIG. 13 is a simplified diagram of a temperature difference detection circuit according to a second embodiment of the present invention.
FIG. 14 is a simplified diagram of a constant current supply circuit according to a third embodiment of the present invention.
FIG. 15 is a simplified diagram of a constant current supply circuit according to a fourth embodiment of the present invention.
FIG. 16 is a simplified diagram of a bias voltage supply circuit according to a fifth embodiment of the present invention.
FIG. 17 is a top view showing the sixth embodiment of the present invention.
18 is a sectional view taken along line AA 'of FIG.
FIG. 19 is a simplified diagram of a temperature difference detection circuit used in Embodiment 6 of the present invention.
FIG. 20 is a simplified diagram of a constant current supply circuit according to a seventh embodiment of the present invention.
FIG. 21 is a simplified diagram of a bias voltage supply circuit according to an eighth embodiment of the present invention.
FIG. 22 is a top view according to the ninth embodiment of the present invention.
FIG. 23 is a sectional view according to a ninth embodiment of the present invention.
FIG. 24 is a diagram showing experimental results supporting the ninth embodiment of the present invention.
FIG. 25 is a diagram showing experimental results supporting the ninth embodiment of the present invention.
FIG. 26 is a diagram showing experimental results supporting the ninth embodiment of the present invention.
FIG. 27 is a sectional view showing a conventional example.
FIG. 28 is a top view of FIG. 27.
FIG. 29 is a diagram showing the flow velocity dependence of the temperature of a temperature-sensitive resistor according to a conventional example.
FIG. 30 is a diagram showing the flow rate dependence of the temperature difference of the temperature-sensitive resistor according to the conventional example.
FIG. 31 is a heater temperature control circuit diagram according to a conventional example.
FIG. 32 is a circuit diagram of a temperature difference detection circuit according to a conventional example.
FIG. 33 is a schematic diagram of heat transfer of a thin portion according to a conventional example.
FIG. 34 is a flow rate dependence of the temperature of a temperature sensitive resistor according to another conventional example.
[Explanation of symbols]
Reference Signs List 1 silicon substrate, 2 air space, 3 thin section, 5 heating resistor, 6 upstream temperature sensing resistor, 7 downstream temperature sensing resistor, 8 fluid temperature sensing temperature sensing resistor, 11 heating resistor temperature sensing Temperature sensing resistors, 33a, b Upstream temperature sensing resistors, 34a, b Downstream temperature sensing resistors.

Claims (6)

薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部と、前記発熱部の極めて近傍に設けられた第３の温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に前記上流側温度検出部、下流側温度検出部、および第３の温度検出部との間に生じる温度差から流速を検出するようにしたことを特徴とする熱式流速センサ。A semiconductor substrate on which a thin portion is formed, a heat generating portion formed on the thin portion, and an upstream and downstream temperature detecting portion also formed on the thin portion and disposed on the upstream and downstream sides of the heat generating portion, respectively. And a third temperature detecting unit provided very close to the heat generating unit, a fluid temperature detecting unit provided upstream of the upstream temperature detecting unit, and the heat generating unit detected by the fluid temperature detecting unit. The flow rate is detected from a temperature difference generated between the upstream temperature detection unit, the downstream temperature detection unit, and the third temperature detection unit when the constant temperature difference driving is performed with respect to the fluid temperature. Characteristic thermal flow sensor. 薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部と、発熱部の上流側近傍に設けられた第４の温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に生じる前記上流側温度検出部と下流側温度検出部との温度差から得られる信号により空気流速を検出する熱式流速センサにおいて、前記温度差信号に増幅を施す際に、その利得を前記第４の温度検出部の抵抗値によって変化させることを特徴とする熱式流速センサ。A semiconductor substrate on which a thin portion is formed, a heat generating portion formed on the thin portion, and an upstream and downstream temperature detecting portion also formed on the thin portion and disposed on the upstream and downstream sides of the heat generating portion, respectively. And a fourth temperature detecting unit provided near the upstream side of the heat generating unit, and a fluid temperature detecting unit upstream of the upstream temperature detecting unit, and the heat generating unit is detected by the fluid temperature detecting unit. A thermal flow rate sensor that detects an air flow rate by a signal obtained from a temperature difference between the upstream temperature detection section and the downstream temperature detection section that occurs when a constant temperature difference driving is performed with respect to the fluid temperature. Wherein the gain is changed by the resistance value of the fourth temperature detecting section when amplifying the thermal flow sensor. 薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部と、発熱部の上流側近傍に設けられた第４の温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に生じる前記上流側温度検出部と下流側温度検出部との温度差から得られる信号により空気流速を検出する熱式流速センサにおいて、前記上流側、および下流側温度検出部の温度を検出するために流す電流値を前記第４の温度検出部の抵抗値によって変化させることを特徴とする熱式流速センサ。A semiconductor substrate on which a thin portion is formed, a heat generating portion formed on the thin portion, and an upstream and downstream temperature detecting portion also formed on the thin portion and disposed on the upstream and downstream sides of the heat generating portion, respectively. And a fourth temperature detecting unit provided near the upstream side of the heat generating unit, and a fluid temperature detecting unit upstream of the upstream temperature detecting unit, and the heat generating unit is detected by the fluid temperature detecting unit. In a thermal flow sensor that detects an air flow velocity by a signal obtained from a temperature difference between the upstream temperature detection unit and the downstream temperature detection unit that occurs when a constant temperature difference drive is performed for the fluid temperature, the upstream side, And a current value for detecting a temperature of the downstream temperature detecting section is changed by a resistance value of the fourth temperature detecting section. 薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部と、発熱部の上流側近傍に設けられた第４の温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に生じる前記上流側温度検出部と下流側温度検出部との温度差から得られる信号により空気流速を検出する熱式流速センサにおいて、前記温度差信号に加えるバイアス信号を前記第４の温度検出部の抵抗値によって変化させることを特徴とする熱式流速センサ。A semiconductor substrate on which a thin portion is formed, a heat generating portion formed on the thin portion, and an upstream and downstream temperature detecting portion also formed on the thin portion and disposed on the upstream and downstream sides of the heat generating portion, respectively. And a fourth temperature detecting unit provided near the upstream side of the heat generating unit, and a fluid temperature detecting unit upstream of the upstream temperature detecting unit, and the heat generating unit is detected by the fluid temperature detecting unit. A thermal flow rate sensor that detects an air flow rate by a signal obtained from a temperature difference between the upstream temperature detection section and the downstream temperature detection section that occurs when a constant temperature difference driving is performed with respect to the fluid temperature. Wherein the bias signal applied to the temperature sensor is changed according to the resistance value of the fourth temperature detector. 薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部と、発熱部の上流側および下流側にそれぞれ設けられた第４および第５の温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に生じる前記上流側温度検出部と下流側温度検出部との温度差から得られる信号により空気流速を検出する熱式流速センサにおいて、前記第４，第５の温度検出部の抵抗値を用いて流速以外の原因による請求項２から４に記載の利得、電流、バイアス信号の変動を相殺することを特徴とする熱式流速センサ。A semiconductor substrate on which a thin portion is formed, a heat generating portion formed on the thin portion, and an upstream and downstream temperature detecting portion also formed on the thin portion and disposed on the upstream and downstream sides of the heat generating portion, respectively. And a fourth and a fifth temperature detector provided respectively on the upstream side and the downstream side of the heat generating unit, and a fluid temperature detector on the upstream side of the upstream temperature detector. A thermal flow sensor that detects an air flow rate based on a signal obtained from a temperature difference between the upstream temperature detection section and the downstream temperature detection section that is generated when a constant temperature difference driving is performed with respect to the fluid temperature detected by the fluid temperature detection section. 5. The thermal flow velocity according to claim 2, wherein the fluctuations of the gain, current, and bias signals due to factors other than the flow velocity are offset by using the resistance values of the fourth and fifth temperature detection units. Sen . 薄肉部が形成された半導体基板と、この薄肉部に形成された発熱部と、同じく薄肉部に形成され、前記発熱部の上流側および下流側にそれぞれ配置された上流側および下流側温度検出部を備えるとともに、前記上流側温度検出部より上流側に流体温度検出部を備え、前記発熱部を前記流体温度検出部により検出された流体温度に対して定温度差駆動した時に生じる前記上流側温度検出部と下流側温度検出部との温度差から得られる信号により空気流速を検出する熱式流速センサにおいて、前記発熱部と温度検出部を前記薄肉部上の空気の流れに対して下流側に偏った位置に配置することを特徴とする熱式流速センサ。A semiconductor substrate on which a thin portion is formed, a heat generating portion formed on the thin portion, and an upstream and downstream temperature detecting portion also formed on the thin portion and disposed on the upstream and downstream sides of the heat generating portion, respectively. And a fluid temperature detecting section upstream of the upstream temperature detecting section, wherein the upstream side temperature generated when the heating section is driven at a constant temperature difference with respect to the fluid temperature detected by the fluid temperature detecting section. In a thermal type flow velocity sensor for detecting an air flow velocity based on a signal obtained from a temperature difference between a detection section and a downstream temperature detection section, the heating section and the temperature detection section are arranged on the downstream side with respect to the flow of air on the thin section. A thermal type flow sensor which is arranged at a deviated position.
JP21507697A 1997-08-08 1997-08-08 Thermal flow sensor Expired - Lifetime JP3577902B2 (en)

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JPH1151954A JPH1151954A (en) 1999-02-26
JP3577902B2 true JP3577902B2 (en) 2004-10-20

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DE10000496A1 (en) * 2000-01-08 2001-07-12 Bosch Gmbh Robert Gas flow determination method and device
WO2003012376A1 (en) 2000-05-15 2003-02-13 Hitachi, Ltd. Thermal air flow rate measuring apparatus and its flowmeter and internal combustion engine and thermal air flow rate measuring method using it

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