JP3569146B2 - Flow detector - Google Patents

Description

【００４７】
【数３】

【００４８】
【数４】

【００４９】
ここで、第１の所定周波数ｆ１ は、感温抵抗体７，８等の熱時定数τによって決定され、流量検出信号Ｖ４ が減衰し始める周波数を示している。即ち、第１の所定周波数ｆ１ は、感温抵抗体７，８等の熱容量によって流量検出信号Ｖ４ に対して低域通過フィルタとして作用するときに、この低域通過フィルタのカットオフ周波数を示すものである。また、第２の所定周波数ｆ２ は、利得の補償が必要となる流量検出信号Ｖ４ の最高の周波数を示すものである。
【００５０】
そして、信号出力回路２１は、以下の数５に示すように、第１，第２の所定周波数ｆ１ ，ｆ２ 間の周波数ｆで脈動する流量に対しては、ほぼ周波数ｆに比例して利得Ｇ１ ，Ｇ３ 間の値となって利得Ｇ２ で、流量検出信号Ｖ４ を増幅するものである（図４中の特性線２６参照）。
【００５１】
【数５】

【００５２】
このため、流量検出信号Ｖ４ が周波数の上昇に応じて減少するときには信号出力回路２１の利得が増加するから、信号出力回路２１は、流量検出信号Ｖ４ を周波数に関係なく流量に応じた出力信号Ｖ５ を出力するものである。
【００５３】
本実施の形態による流量検出装置は上述の如き構成を有するもので、次に吸入空気の流量検出動作について説明する。
【００５４】
まず、吸入空気が矢示Ａ方向に向けて流れるときには、シリコン基板４上の上流側に位置した第１の感温抵抗体７がこの空気の流れによって冷やされ、下流側に位置した第２の感温抵抗体８はヒータ６からの熱を受ける。この結果、第１，第２の感温抵抗体７，８の抵抗値ＲＴ１，ＲＴ２が変化するから、第１，第２の流量検出回路１１，１３からの流量電圧Ｖ１ ，Ｖ２ に電位差が生じる。このため、差動増幅回路１５はこの電位差（Ｖ１ −Ｖ２ ）に応じた差動信号Ｖ３ を出力し、非反転増幅回路１６は差動信号Ｖ３ を増幅した流量検出信号Ｖ４ を出力する。
【００５５】
ここで、流量検出信号Ｖ4 が立ち上がり状態になく、矢示Ａ方向に流れる吸入空気の流量がほぼ一定値となっているときには、流量検出信号Ｖ4 はほとんど変化せず一定値に保持される。このとき、立ち上がり判定回路１８の演算増幅器１９は、利得補償回路１７においてバッファとして作用し、トランジスタ２０はＯＮ状態となるから、流量検出信号Ｖ4 は、以下の数６に示すように出力信号Ｖ5 、接続点ｅの電圧である接続点電圧信号Ｖe とほぼ同じ値となる。
【００５６】
【数６】
Ｖ４ ＝Ｖ５ ＝Ｖｅ
【００５７】
また、流量検出信号Ｖ4 が立ち上がり状態になく、矢示Ａ方向に流れる吸入空気の流量が減少するときには、流量検出信号Ｖ4 も、図５中に実線で示す特性線２７のように流量の減少に従って徐々に低下する。このとき、信号出力回路２１の演算増幅器２２の出力信号Ｖ5 も、図５中に点線で示す特性線２８のように流量検出信号Ｖ4 に従って低下する。このため、立ち上がり判定回路１８の演算増幅器１９の出力電圧も低下するから、トランジスタ２０はＯＮ状態に保持される。この結果、コンデンサ２５はトランジスタ２０を通じて充電が行なわれ、接続点ｅの接続点電圧信号Ｖe は、図５中に実線で示す特性線２７のように、流量検出信号Ｖ4 、出力信号Ｖ5 に追従して低下する。これにより、流量検出信号Ｖ4 、出力信号Ｖ5 、接続点電圧信号Ｖe は、数６の関係に保たれる。
【００５８】
一方、矢示Ａ方向に流れる吸入空気の流量が増加するとき、即ち流量検出信号Ｖ４ が立ち上がり状態にあるときには、流量検出信号Ｖ４ と出力信号Ｖ５ とは、徐々に増加することになる。このとき、流量検出信号Ｖ４ は、図５中に実線で示す特性線２７のように第１，第２の感温抵抗体７，８の熱容量と流量に対する非線形応答性によって、流量の増加に対応できず、低下する傾向がある。
【００５９】
しかし、立ち上がり判定回路１８の演算増幅器１９の出力電圧も増加するから、トランジスタ２０はＯＦＦ状態となり、コンデンサ２５への充電ができなくなる。このため、コンデンサ２５に充電された電荷は、利得設定用抵抗２３、負帰還抵抗２４を介して放電される。この結果、トランジスタ２０のエミッタ側電圧である接続点ｅの接続点電圧信号Ｖｅ は、図５中に一点鎖線で示す特性線２９のように、流量検出信号Ｖ４ よりも低くなる。即ち、接続点電圧信号Ｖｅ は、コンデンサ２５の容量Ｃと利得設定用抵抗２３の抵抗値Ｒ１ との積（時定数）によって流量検出信号Ｖ４ に対してその応答が遅れるから、流量検出信号Ｖ４ よりも低下する。これにより、出力信号Ｖ５ は、接続点電圧信号Ｖｅ 、流量検出信号Ｖ４と以下の数７に示す関係により、図５中の特性線２８に示すように時間変化する。
【００６０】
【数７】

【００６１】
かくして、本実施の形態によれば、利得補償回路１７を、立ち上がり判定回路１８と信号出力回路２１とによって構成したから、利得補償回路１７は、流量検出信号Ｖ４ が流量の対応して変化しない立ち上がり状態のときのみ流量検出信号Ｖ４ を増幅し、常に出力信号Ｖ５ を流量に対応して変化させることができる。これにより、流量をほぼ正確に検出することができる。
【００６２】
また、立ち上がり状態における流量検出信号Ｖ４ の低下は、感温抵抗体７，８等の熱時定数τによってその量が決まるため、流量が脈動する周波数ｆ、即ち流量検出信号Ｖ４ の周波数ｆに応じて変化する。このため、流量検出信号Ｖ４ は、高い周波数ｆほど低下量が大きく、低い周波数ｆほど低下量が小さくなる。
【００６３】
しかし、信号出力回路２１は、図４に示すように熱時定数τによって決まる第１の所定周波数ｆ１ よりも低い周波数ｆでは流量検出信号Ｖ４ と出力信号Ｖ５ とがほぼ同じ値となるように利得Ｇ１ が１程度に設定し、第１，第２の所定周波数ｆ１ ，ｆ２ 間の周波数ｆではほぼ周波数ｆに比例した増加する利得Ｇ２ に設定し、第２の所定周波数ｆ２ よりも高い周波数ｆではほぼ利得Ｇ３ となるように設定している。
【００６４】
これにより、流量が所定周波数ｆ１ よりも低い周波数ｆをもって脈動するときには、流量検出信号Ｖ４ は、立ち上がり状態であっても流量の脈動にほぼ比例した値となる。このとき、信号出力回路２１は、ほぼ１程度の利得Ｇ１ で流量検出信号Ｖ４ を増幅するから、信号出力回路２１は、流量の脈動にほぼ比例した出力信号Ｖ５ を出力する。
【００６５】
また、流量が第１の所定周波数ｆ１ よりも高く第２の所定周波数ｆ２ よりも低い周波数ｆの範囲で脈動するときには、信号出力回路２１は、周波数ｆにほぼ比例した利得Ｇ２ で流量検出信号Ｖ４ を増幅するから、周波数ｆが高くなるほど減衰する流量検出信号Ｖ４ の利得を補償することができる。このため、信号出力回路２１は周波数ｆに関係なく常に流量に対応した出力信号Ｖ５ を出力することができる。
【００６６】
さらに、信号出力回路２１は、高周波数側の所定周波数ｆ２ よりも高い周波数ｆをもった流量検出信号Ｖ４ はほぼ一定の利得Ｇ３ で増幅する構成としたから、流量の検出にほとんど影響を与えない高周波数側の流量検出信号Ｖ４ を必要以上に増幅することがなくなる。このため、高周波数側の流量検出信号Ｖ４ による誤差等をなくし、流量の検出精度を高めることができる。
【００６７】
次に、図６に本発明による第２の実施の形態を示すに、本実施の形態の特徴は、立ち上がり判定手段をダイオードによって構成したことにある。なお、前述した第１の実施の形態と同一の構成要素の同一の符号を付し、その説明を省略するものとする。
【００６８】
３１は本実施の形態による利得補償回路で、該利得補償回路３１は、後述するダイオード３２と信号出力回路３３とによって構成している。
【００６９】
３２は立ち上がり判定手段としてのダイオードで、該ダイオード３２は、後述する信号出力回路３３の演算増幅器３４の出力端子と反転入力端子との間に接続され、反転入力端子から出力端子に向けて電流が流れるのを許し、出力端子から反転入力端子に向けて電流が流れるのを阻止するものである。
【００７０】
３３は信号出力手段としての信号出力回路で、該信号出力回路３３は演算増幅器３４、利得設定用抵抗３５、負帰還抵抗３６、コンデンサ３７によって構成されている。
【００７１】
ここで、演算増幅器３４の非反転入力端子は、非反転増幅回路１６の出力端子に接続され、流量検出信号Ｖ４ が入力される。また、演算増幅器３４の反転入力端子は、抵抗値Ｒ１ を有する利得設定用抵抗３５、容量Ｃを有するコンデンサ３７を介してアースに接続されている。さらに、演算増幅器３４の出力端子と反転入力端子との間には抵抗値Ｒ２ を有する負帰還抵抗３６が接続されると共に、該、負帰還抵抗３６にはダイオード３２が並列接続されている。
【００７２】
本実施の形態による流量検出装置は上述の如き構成を有するもので、次に利得補償回路３１の作動について説明する。
【００７３】
そして、流量検出信号Ｖ４ が立ち上がり状態のときには、流量検出信号Ｖ４ よりも演算増幅器３４の出力端子の電圧である出力信号Ｖ５ は大きくなる。このとき、演算増幅器３４の反転入力端子の電圧は、流量検出信号Ｖ４ とほぼ同じ値となっているから、ダイオード３２には電流が流れることはなく、ダイオード３２は絶縁体として作用する。このため、利得補償回路３１は、ダイオード３２を省いた増幅回路として作用する。
【００７４】
一方、流量検出信号Ｖ4 が立ち上がり状態にないときには、出力信号Ｖ5 は流量検出信号Ｖ4 よりも大きくなることはなく、ほぼ同じ程度の値となる。また、出力信号Ｖ5 が流量検出信号Ｖ4 よりも小さくなったときには、ダイオード３２に電流が流れるから、ダイオード３２は導体として作用する。このため、利得補償回路３１は、流量検出信号Ｖ4 とほぼ同じ出力信号Ｖ5 を出力する。
【００７５】
かくして、このように構成される本実施の形態の流量検出装置においても、前記第１の実施の形態と同様の作用効果を得ることができるが、立ち上がり判定手段をダイオードによって構成したから、演算増幅器３４を１個だけ用いればよく、第１の実施の形態と同様の作用効果をもった利得補償回路３１を簡易に構成することができる。
【００７６】
次に、図７および図８に本発明による第３の実施の形態を示すに、本実施の形態の特徴は、利得補償回路は吸入空気の逆流を検出する逆流判定回路を手段を備え、信号出力回路は該逆流判定回路の判定結果に基づき正流時、逆流時の流量検出信号を増幅する構成したことにある。
【００７７】
なお、前述した第１の実施の形態と同一の構成要素の同一の符号を付し、その説明を省略するものとする。また、本実施の形態では図１、図２中の矢示Ｂ方向に向けて吸入空気が逆流したときには、流量検出信号Ｖ４ が逆流判定電圧Ｅ０ である１Ｖよりも低下するものとする。
【００７８】
図７において、４１は本実施の形態による利得補償回路で、該利得補償回路４１は、後述する逆流判定回路４２、立ち上がり判定回路４７、信号出力回路５１によって構成している。
【００７９】
４２は逆流判定手段としての逆流判定回路で、該逆流判定回路４２はコンパレータ４３、インバータ４４、リレー４５，４６によって構成されている。
【００８０】
そして、コンパレータ４３は、その反転入力端子が非反転増幅回路１６の出力端子に接続され、流量検出信号Ｖ４ が入力されている。一方、コンパレータ４３の非反転入力端子は、例えば１Ｖ程度の逆流判定電圧Ｅ０ に接続されている。また、コンパレータ４３の出力端子は、リレー４５に接続されると共に、インバータ４４を介してリレー４６に接続されている。
【００８１】
このため、流量検出信号Ｖ４ が逆流判定電圧Ｅ０ よりも大きいときには、コンパレータ４３は、ほぼ０Ｖ程度の電圧を出力する。これにより、リレー４５は開成すると共に、リレー４６にはインバータ４４によって例えば５Ｖ程度の電圧が印加されるから、リレー４６は閉成する。
【００８２】
また、流量検出信号Ｖ４ が逆流判定電圧Ｅ０ よりも小さいときには、コンパレータ４３は、例えば５Ｖ程度の電圧を出力する。これにより、リレー４５は閉成すると共に、リレー４６にはインバータ４４によって例えば０Ｖ程度の電圧が印加されるから、リレー４６は開成する。
【００８３】
４７は非反転増幅回路１６から出力される流量検出信号Ｖ４ が立ち上がり状態か否かを判定する立ち上がり判定回路で、該立ち上がり判定回路４７は、演算増幅器４８、ＮＰＮ形のトランジスタ４９、ＰＮＰ形のトランジスタ５０によって構成されている。
【００８４】
そして、演算増幅器４８の反転入力端子は、非反転増幅回路１６の出力端子に接続されている。また、演算増幅器４８の非反転入力端子は、信号出力回路５１の出力端子に接続され、演算増幅器４８の出力端子は、リレー４５を介してトランジスタ４９のベース側に接続されると共に、リレー４６を介してトランジスタ５０のベース側に接続されている。
【００８５】
また、トランジスタ４９は、そのコレクタ側がバッテリ電圧Ｅｂ に接続され、エミッタ側がトランジスタ５０のコレクタ側に接続されている。一方、トランジスタ５０は、そのエミッタ側がトランジスタ４９のエミッタ側に接続され、コレクタ側がアースに接続されている。
【００８６】
このため、トランジスタ４９，５０は、バッテリ電圧Ｅｂ とアースとの間に直列接続され、トランジスタ４９のエミッタ側とトランジスタ５０のエミッタ側との間には接続点ｅ′が設けられている。
【００８７】
５１は信号出力手段としての信号出力回路で、該信号出力回路５１は演算増幅器５２、利得設定用抵抗５３、負帰還抵抗５４、コンデンサ５５によって構成されている。
【００８８】
ここで、演算増幅器５２の非反転入力端子は、非反転増幅回路１６の出力端子に接続され、流量検出信号Ｖ４ が入力される。また、演算増幅器５２の反転入力端子は、抵抗値Ｒ１ を有する利得設定用抵抗５３、容量Ｃを有するコンデンサ５５を介してアースに接続されている。さらに、演算増幅器５２の出力端子と反転入力端子との間には抵抗値Ｒ２ を有する負帰還抵抗５４が接続されている。
【００８９】
本実施の形態による流量検出装置は上述の如き構成を有するもので、次に利得補償回路４１の作動について説明する。
【００９０】
まず、吸入空気が図１中の矢示Ａ方向に向かい正流しているときには、流量検出信号Ｖ4 は図８中に実線で示す特性線５５Ａのように逆流判定電圧Ｅ0 よりも大きいから、コンパレータ４３はほぼ０Ｖの電圧を出力し、リレー４５は開成し、リレー４６は閉成する。このとき、トランジスタ４９は作動せず、トランジスタ５０のみ作動する。そして、トランジスタ５０は、第１の実施の形態によるトランジスタ２０とほぼ同様に矢示Ａ方向に向かう流量が増加した立ち上がり状態でＯＦＦ状態となり、矢示Ａ方向に向かう流量が減少した立ち上がり状態にないときにＯＮ状態となる。
【００９１】
このため、吸入空気が正流状態で流量検出信号Ｖ4 が立ち上がり状態となっているときには、演算増幅器５２から出力される出力信号Ｖ5 は、図８中に点線で示す特性線５６Ａのように流量検出信号Ｖ4 よりも振幅が大きくなり、接続点ｅ′の接続点電圧Ｖe ′は、図８中に一点鎖線で示す特性線５７Ａのように流量検出信号Ｖ4 よりも振幅が小さくなる。一方、吸入空気が正流状態で流量検出信号Ｖ4 が立ち上がり状態にないときには、出力信号Ｖ5 、接続点電圧Ｖe ′は、流量検出信号Ｖ4 とほぼ同じ値となる。
【００９２】
次に、吸入空気が図１中の矢示Ｂ方向に向かい逆流しているときには、流量検出信号Ｖ4 は図８中に実線で示す特性線５５Ｂのように逆流判定電圧Ｅ0 よりも小さいから、コンパレータ４３はほぼ５Ｖの電圧を出力し、リレー４５は閉成し、リレー４６は開成する。このとき、トランジスタ５０は作動せず、トランジスタ４９のみ作動する。そして、トランジスタ４９は、矢示Ｂ方向に向かう流量が増加した立ち上がり状態でＯＦＦ状態となり、矢示Ｂ方向に向かう流量が減少した立ち上がり状態にないときにＯＮ状態となる。
【００９３】
このため、吸入空気が逆流状態で流量検出信号Ｖ4 が立ち上がり状態となっているときには、出力信号Ｖ5 は、図８中に点線で示す特性線５６Ｂのように流量検出信号Ｖ4 よりも振幅が大きくなり、接続点ｅ′の接続点電圧Ｖe ′は、図８中に一点鎖線で示す特性線５７Ｂのように流量検出信号Ｖ4 よりも振幅が小さくなる。一方、吸入空気が逆流状態で流量検出信号Ｖ4 が立ち上がり状態にないときには、出力信号Ｖ5 、接続点電圧Ｖe ′は、流量検出信号Ｖ4 とほぼ同じ値となる。
【００９４】
かくして、このように構成される本実施の形態の流量検出装置においても、前記第１の実施の形態と同様の作用効果を得ることができるが、特に本実施の形態は逆流判定回路４２を設けたから、吸入空気が逆流状態になると共に、逆流方向の流量が増加するときに感温抵抗体７，８等の熱時定数τによって流量検出信号の振幅が低下しても、逆流判定回路４２、立ち上がり判定回路４７、信号出力回路５１からなる利得補償回路４１によって、この低下した利得を補償することができる。このため、吸入空気が逆流状態となるときであっても流量を正確に検出することができる。
【００９５】
なお、前記各実施の形態では、２個の感温抵抗体を用いて流量検出手段を構成するものとしたが、例えば特開平８−８６６７７号公報に記載されているように１個の発熱性をもつ感温抵抗体によってブリッジ回路を構成し、このブリッジ回路に一定電流を流すことによって、感温抵抗体の抵抗値に応じた流量検出信号を出力する構成としてもよい。
【００９６】
【発明の効果】
以上詳述した如く請求項１に記載の発明によれば、利得補償手段を、立ち上がり判定手段と信号出力手段とによって構成したから、信号出力手段は、流量検出信号が立ち上がり状態にあるときに流量検出信号を増幅した出力信号を出力し、立ち上がり状態にないときには流量検出信号とほぼ同じ出力信号を出力する。これにより、感温抵抗体の熱時定数によって流量検出信号の立ち上がりが遅れ、流量検出信号が低下した場合であっても、信号出力手段は、この低下した利得を補償し、流量の変化に対応した出力信号を出力することができ、正確な流量を検出することができる。
【００９７】
また、請求項２の発明によれば、信号出力手段を、流量検出信号が立ち上がり状態のときには、感温抵抗体の熱時定数によって決まる所定周波数よりも低い周波数をもった流量検出信号はほぼ一定の利得で増幅し、当該所定周波数よりも高い周波数をもった流量検出信号は周波数に対応した利得で増幅する構成としたから、流量が所定周波数よりも低い周波数をもって脈動するときには、流量検出信号は、流量の脈動にほぼ比例した値となり、信号出力手段は一定の利得で流量検出信号を増幅する。一方、流量が所定周波数よりも高い周波数をもって脈動するときには、流量検出信号は、感温抵抗体等の熱容量によってその値が低下し、信号出力手段は、周波数に対応した利得で流量検出信号を増幅する。このため、信号出力手段は、周波数が高くなるほど減衰する流量検出信号の利得を補償することができ、周波数に関係なく常に流量に応じた出力信号を出力すると共に、正確な流量を検出することができる。
【００９８】
また、請求項３の発明によれば、信号出力手段を、流量検出信号が立ち上がり状態のときには、感温抵抗体の熱時定数によって決まる第１の所定周波数に比較して高い第２の所定周波数よりも高い所定周波数をもった流量検出信号はほぼ一定の利得で増幅する構成としたから、流量の検出にほとんど影響を与えない高周波数側の流量検出信号を必要以上に増幅することがなくなる。このため、高周波数側の流量検出信号による誤差等をなくし、流量の検出精度を高めることができる。
【００９９】
また、請求項４の発明によれば、信号出力手段による第１の所定周波数を流量検出信号が減衰し始める周波数に設定し、第２の所定周波数を利得の補償が必要となる流量検出信号の最高の周波数に設定したから、信号出力手段は流量検出信号が減衰し始める周波数よりも高い周波数で流量が脈動するときには、流量検出信号を周波数に対応した利得で増幅することができる。また、第２の所定周波数を利得の補償が必要となる流量検出信号の最高の周波数に設定したから、利得の補償が必要となる流量検出信号を確実に増幅することができる。
【０１００】
また、請求項５の発明によれば、立ち上がり判定手段を、逆流検出手段によって被測流体が逆流状態にあると判定したときには被測流体が逆流方向に向かう流量が増加したときを立ち上がり状態として判定し、被測流体が正流状態にあると判定したときには被測流体が正流方向に向かう流量が増加したときを立ち上がり状態として判定する構成としたから、被測流体が逆流し、このときの流量検出信号が感温抵抗体等の熱時定数によって減少したときであっても、立ち上がり状態判定手段は、逆流時の立ち上がり状態を判定することができる。このため、信号出力手段は、逆流時の立ち上がり状態にある流量検出信号を増幅するから、逆流する被測流体の流量を正確に検出することができる。
【図面の簡単な説明】
【図１】第１の実施の形態による流量検出装置を吸気管に取付けた状態を示す縦断面図である。
【図２】シリコン基板上に形成されたヒータ、第１の感温抵抗体、第２の感温抵抗体を示す斜視図である。
【図３】第１の実施の形態による流量検出装置の流量演算回路、利得補償回路等を示す回路図である。
【図４】利得補償回路の利得と周波数との関係を示す特性線図である。
【図５】第１の実施の形態による流量検出信号、出力信号、接続点電圧信号と時間との関係を示す特性線図である。
【図６】第２の実施の形態による流量検出装置の利得補償回路等を示す回路図である。
【図７】第３の実施の形態による流量検出装置の利得補償回路等を示す回路図である。
【図８】第３の実施の形態による流量検出信号、出力信号、接続点電圧信号と時間との関係を示す特性線図である。
【符号の説明】
７，８ 感温抵抗体
１０ 流量演算回路（流量演算手段）
１７，３１，４１ 利得補償回路（利得補償手段）
１８，４７ 立ち上がり判定回路（立ち上がり判定手段）
２１，３３，５１ 信号出力回路（信号出力手段）
３２ ダイオード（立ち上がり判定手段）
４２ 逆流判定回路（逆流判定手段）[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a thermal type flow rate detection device suitably used for detecting an intake air flow rate of, for example, an automobile engine.
[0002]
[Prior art]
Generally, an automobile engine or the like burns a mixture of fuel and intake air in a combustion chamber of an engine body, and obtains a rotational output of the engine from the combustion pressure. Detecting the intake air flow rate is an important factor. For this reason, a thermal type flow detecting device is known as a flow detecting device for detecting an intake air amount of an engine (Japanese Patent Application Laid-Open No. 57-22563).
[0003]
Such a flow rate detecting device according to the prior art is constituted by a bridge circuit or the like including a temperature-sensitive resistor, and a flow rate calculating means for calculating a flow rate detection signal according to the flow rate of the fluid to be measured based on the resistance value of the temperature-sensitive resistor. And a gain compensating means for amplifying the flow rate detection signal by the flow rate calculating means and compensating for the gain lowered by the thermal time constant of the temperature sensitive resistor.
[0004]
In the flow rate detecting device according to the related art, the temperature of the temperature-sensitive resistor in the bridge circuit rises and falls according to the amount of intake air, and the resistance value of the temperature-sensitive resistor rises and falls according to the temperature. . At this time, the resistance value of the temperature sensitive resistor is output as, for example, a voltage signal, and a flow rate detection signal corresponding to the flow rate is calculated using the voltage signal.
[0005]
Further, in such a flow rate detecting device according to the prior art, since the temperature-sensitive resistor or the like has a heat capacity, this heat capacity acts as a first-order lag element. As a result, the response of the flow rate detection device to the change in the intake air flow rate is delayed, and the flow rate detection signal may be lower than the intake air flow rate. For this reason, in the conventional flow rate detecting device, the decrease in the flow rate detection signal is compensated by the gain compensating means.
[0006]
[Problems to be solved by the invention]
By the way, in the above-mentioned prior art, the gain compensating means compensates for a decrease in the flow rate detection signal due to the thermal time constant of the temperature sensitive resistor or the like. Here, in the thermal type flow rate detection device, since the heat capacity of the temperature-sensitive resistor or the like acts as a first-order lag element, that is, a low-pass filter, the flow rate detection signal tends to decrease as the flow rate pulsates at a higher frequency. There is. On the other hand, the flow rate detecting device according to the prior art compensates for a decrease in the flow rate detection signal by increasing only the falling portion of the flow rate detection signal. As a result, since the flow rate detection signal is converted into a signal of a lower frequency, there is a problem that the flow rate when pulsating at a high frequency cannot be accurately detected.
[0007]
The present invention has been made in view of the above-described problems of the related art, and the present invention can accurately detect an intake air flow rate even when a high-frequency pulsation occurs, and can improve the flow rate detection accuracy. It is intended to provide a flow rate detection device.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problem, the present invention has a temperature-sensitive resistor provided in a fluid to be measured, and outputs a flow rate detection signal corresponding to a flow rate of the fluid to be measured by a resistance value of the temperature-sensitive resistor. The present invention is applied to a flow rate detecting device comprising a flow rate calculating means for calculating and a gain compensating means for amplifying a flow rate detection signal by the flow rate calculating means and compensating for a gain reduced by a thermal time constant of the temperature sensitive resistor.
[0009]
The first aspect of the present invention is characterized in that the gain compensating means includes a rising determining means for determining whether or not the flow detection signal is in a rising state; Outputs an amplified signal of the flow rate detection signal when it is determined that the Up In a biting state Absent And a signal output means for outputting an output signal substantially the same as the flow rate detection signal when it is determined.
[0010]
With such a configuration, the signal output unit outputs an output signal obtained by amplifying the flow rate detection signal when the flow rate detection signal is in a rising state. Therefore, even if the rise of the flow detection signal is delayed due to the thermal time constant of the temperature sensitive resistor and the flow detection signal is reduced, the signal output means compensates for the reduced gain and responds to the change in the flow. Output signal can be output. On the other hand, the signal output means generates a flow detection signal. Up In a biting state Absent Flow rate detection signal When Outputs almost the same output signal. At this time, the flow detection signal changes substantially corresponding to the change in the flow. For this reason, the flow detection signal rises. Up In a biting state Absent Even at this time, the signal output means can output an output signal corresponding to the change in the flow rate.
[0011]
Further, the invention according to claim 2 is characterized in that, when the rise determination means determines that the flow rate detection signal is in a rising state, the signal output means has a frequency lower than a predetermined frequency determined by a thermal time constant of the temperature sensitive resistor. The flow detection signal having the frequency is amplified at a substantially constant gain, and the flow detection signal having a frequency higher than the predetermined frequency is output as an output signal amplified at a gain corresponding to the frequency.
[0012]
Accordingly, when the flow rate pulsates at a frequency lower than the predetermined frequency, the flow rate detection signal output from the flow rate calculating means has a value substantially corresponding to the flow rate pulsation. At this time, the signal output unit amplifies the flow rate detection signal with a predetermined constant gain. On the other hand, when the flow rate pulsates at a frequency higher than the predetermined frequency, the flow rate detection signal output from the flow rate calculation means decreases due to the heat capacity of the temperature-sensitive resistor. At this time, the signal output unit amplifies the flow rate detection signal with a gain corresponding to the frequency.
[0013]
Further, the invention according to claim 3 is characterized in that when the rise determination means determines that the flow rate detection signal is in a rising state, the signal output means sets the signal output means to a first predetermined frequency determined by a thermal time constant of the temperature sensitive resistor. The flow detection signal having a lower frequency is amplified with a substantially constant first gain, and the flow detection signal having a frequency higher than the first predetermined frequency and lower than a predetermined second predetermined frequency is a frequency. And a flow rate detection signal having a frequency higher than the second predetermined frequency outputs an output signal amplified by a third gain which is larger than the second gain and substantially constant. Configuration.
[0014]
Thus, when the flow rate pulsates at a frequency lower than the first predetermined frequency, the flow rate detection signal has a value substantially corresponding to the flow rate pulsation. At this time, the signal output unit amplifies the flow rate detection signal with a constant first gain. Further, when the flow rate pulsates in a frequency range higher than the first predetermined frequency and lower than the predetermined second predetermined frequency, the flow rate detection signal decreases due to the heat capacity of the temperature-sensitive resistor. At this time, the signal output unit amplifies the flow rate detection signal with the second gain corresponding to the frequency. Further, when the flow rate pulsates at a frequency higher than the second predetermined frequency, the signal output unit amplifies the flow rate detection signal with a third gain which is larger than the second gain and is substantially constant.
[0015]
The invention according to claim 4 is characterized in that the signal output means sets the first predetermined frequency to a frequency at which the flow detection signal starts to attenuate, and sets the second predetermined frequency to the flow detection signal for which gain compensation is required. I set it to the highest frequency.
[0016]
Thus, when the flow rate pulsates at a frequency higher than the frequency at which the detection signal starts to attenuate, the signal output means can amplify the flow rate detection signal with a gain corresponding to the frequency. Further, since the second predetermined frequency is set to the highest frequency of the flow rate detection signal requiring the gain compensation, the flow rate detection signal requiring the gain compensation can be surely amplified.
[0017]
Further, in the invention according to claim 5, the gain compensating means includes a backflow judging means for judging whether or not the fluid to be measured is flowing backward, and the rising judging means comprises a means for detecting the backflow of the fluid to be measured by the backflow detecting means. When it is determined that the fluid to be measured is in the reverse flow direction, it is determined that the flow rate of the fluid to be measured in the backward flow direction is determined to be a rising state. Is determined to be a rising state when the value increases.
[0018]
Thereby, the backflow judging means judges whether the measured fluid is in a normal flow state or a backflow state, and the rise judging means is a rising state at the time of normal flow and a rising state at the time of reverse flow based on the judgment result of the backflow judging means. Is determined. Thereby, even when the measured fluid flows backward and the flow rate detection signal at this time decreases due to the thermal time constant, the rising state determination means determines the rising state at the time of reverse flow where the flow rate detection signal decreases at the time of reverse flow. The flow rate of the measured fluid flowing backward can be accurately detected.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a flow detection device according to an embodiment of the present invention will be described in detail with reference to FIGS.
[0020]
First, a first embodiment according to the present invention will be described with reference to FIGS. Reference numeral 1 denotes a cylinder serving as a flow path through which a fluid to be measured such as air flows. The cylinder 1 is connected in the middle of an intake pipe (not shown) of the engine. During operation of the engine, intake air drawn into the combustion chamber of the engine body from the outside through the intake pipe flows in the cylinder 1 in the direction of arrow A.
[0021]
Reference numeral 2 denotes a casing which forms the outer shape of the flow rate detecting device. The casing 2 is composed of a flange-shaped connector 2A attached to the cylindrical body 1 and a housing 2B extending from the connector 2A into the cylindrical body 1. ing. The casing 2 houses a flow rate detection element 3 and a detection circuit 9 described later.
[0022]
Reference numeral 3 denotes a flow rate detecting element. The flow rate detecting element 3 includes a silicon substrate 4 having a trapezoidal concave portion 4A formed on the back side as shown in FIG. And a heater 6 formed at a position corresponding to the concave portion 4A on the silicon substrate 4 via the insulating film 5, and a heater 6 formed near the heater 6. It comprises first and second temperature-sensitive resistors 7 and 8 formed in the same manner as the heater 6. The heater 6 and the first and second temperature-sensitive resistors 7, 8 are provided with electrode portions 6A, 7A, 8A for connecting to reference resistors 12, 14, which will be described later.
[0023]
Here, the heater 6 is formed by depositing a platinum film with a thickness of, for example, about 0.2 μm on the silicon substrate 4 using a means such as print printing or sputtering. The current value of the heater 6 is controlled by a current control transistor (not shown), and the heater 6 generates heat so as to keep the temperature at a constant temperature (for example, about 240 ° C.).
[0024]
On the other hand, the first temperature-sensitive resistor 7 is located on the upstream side of the heater 6 and is formed so as to have a resistance value RT1, and the second temperature-sensitive resistor 8 is located on the downstream side of the heater 6. Is formed so as to have a resistance value RT2.
[0025]
When the air flows in the direction indicated by the arrow A, the flow detection element 3 detects the flow using the change in the resistance value of the temperature-sensitive resistors 7 and 8 cooled by the air flow.
[0026]
Reference numeral 9 denotes a detection circuit housed in the housing portion 2B of the casing 2. The detection circuit 9 includes a heater control circuit (not shown) mounted on an insulating substrate made of, for example, a ceramic material, and a flow rate calculation circuit described later. 10, a gain compensation circuit 17 and the like. Then, the heater control circuit always keeps the heater 6 at a constant temperature (for example, 240 ° C.).
[0027]
Reference numeral 10 denotes a flow rate calculation circuit as flow rate calculation means. The flow rate calculation circuit 10 includes first and second flow rate detection circuits 11 and 13 which are bridge circuits to be described later, and the first and second flow rate detection circuits. It comprises a differential amplifier circuit 15 for differentially amplifying the first and second flow voltages V1 and V2 output from 11 and 13, and a non-inverting amplifier circuit 16. Then, the flow rate calculation circuit 10 outputs a flow rate detection signal V4 corresponding to the flow rate.
[0028]
Reference numeral 11 denotes a first flow detection circuit. The first flow detection circuit 11 is configured by connecting a first temperature-sensitive resistor 7 having a resistance value RT1 and a reference resistor 12 in series. The first flow rate detection circuit 11 is connected between the battery voltage Eb set to a voltage of, for example, about 5 V and the ground, and is connected to the battery voltage Eb side connection point a and the ground side connection point b. 2 is connected in parallel to the second flow rate detection circuit 13. For this reason, the first and second flow detection circuits 11 and 13 constitute a bridge circuit in which the resistance values of the opposing sides are equal.
[0029]
Further, a connection point c between the first temperature-sensitive resistor 7 and the reference resistor 12 is connected to a non-inverting input terminal of a differential amplifier 15 described later. Then, the first flow detection circuit 11 outputs a change in the resistance value RT1 of the first temperature sensitive resistor 7 as a first flow voltage V1.
[0030]
Reference numeral 13 denotes a second flow rate detection circuit. The second flow rate detection circuit 13 includes a second temperature-sensitive resistor 8 having a resistance value RT2 and a reference resistor 14 in substantially the same manner as the first flow rate detection circuit 11. The first flow rate detection circuit 11 and the first flow rate detection circuit 11 constitute a bridge circuit.
[0031]
Further, the second flow rate detection circuit 13 is connected between the battery voltage Eb and the ground, and a connection point d between the second temperature sensitive resistor 8 and the reference resistor 14 is connected to the differential amplifier circuit 15. Connected to inverting input terminal. Then, the second flow detection circuit 13 outputs a change in the resistance value RT2 of the second temperature-sensitive resistor 8 as a second flow voltage V2.
[0032]
Reference numeral 15 denotes a differential amplifying circuit. The input side of the differential amplifying circuit 15 is connected to connection points c and d of the first and second flow rate detection circuits 11 and 13, and the output side of the differential amplifying circuit 15 is connected to a gain compensator (described later). Circuit 17 is connected. Then, the differential amplifier circuit 15 calculates a difference between the first and second flow voltage V1 and V2, and outputs a differential signal V3 according to the difference.
[0033]
Reference numeral 16 denotes a non-inverting amplifier. The non-inverting amplifier 16 includes an operational amplifier 16A, a resistor 16B connected between an inverting input terminal of the operational amplifier 16A and a reference voltage Es, and an output terminal of the operational amplifier 16A. , And a negative feedback resistor 16C connected between the inverting input terminal. The output terminal of the differential amplifier circuit 15 is connected to the non-inverting input terminal of the operational amplifier 16A. Then, the non-inverting amplifier circuit 16 outputs a flow rate detection signal V4 obtained by amplifying the differential signal V3 output from the differential amplifier circuit 15 as a signal indicating the flow rate of the intake air.
[0034]
Reference numeral 17 denotes a gain compensating circuit as a gain compensating means. The gain compensating circuit 17 includes a rising judgment circuit 18 and a signal output circuit 21 which will be described later.
[0035]
Reference numeral 18 denotes a rising judgment circuit for judging whether or not the flow rate detection signal V4 output from the non-inverting amplifier circuit 16 is in a rising state. The rising judgment circuit 18 includes an operational amplifier 19 and a PNP transistor 20. I have.
[0036]
The inverting input terminal of the operational amplifier 19 is connected to the output terminal of the non-inverting amplifier circuit 16. The non-inverting input terminal of the operational amplifier 19 is connected to the output terminal of the signal output circuit 21, and the output terminal of the operational amplifier 19 is connected to the base of the transistor 20.
[0037]
On the other hand, the transistor 20 has a base connected to the output terminal of the operational amplifier 19, an emitter connected to the battery voltage Eb via the capacitor 25, and a collector connected to the ground. Further, a connection point e is provided between the emitter side of the transistor 20 and the capacitor 25.
[0038]
When the flow rate of the air flowing in the direction indicated by the arrow A in FIG. 1 increases and the flow rate detection signal V4 increases, the output voltage of the operational amplifier 19 increases. It becomes. Thus, the rise determination circuit 18 determines that the flow rate detection signal V4 is in a rising state.
[0039]
On the other hand, when the flow rate of the air flowing in the direction indicated by the arrow A in FIG. 1 decreases and the flow detection signal V4 decreases, the output voltage of the operational amplifier 19 decreases. It becomes. Thus, the rise determination circuit 18 determines that the flow rate detection signal V4 is not in the rising state, that is, in the falling state.
[0040]
Reference numeral 21 denotes a signal output circuit as signal output means. The signal output circuit 21 includes an operational amplifier 22, a gain setting resistor 23, a negative feedback resistor 24, and a capacitor 25.
[0041]
Here, the non-inverting input terminal of the operational amplifier 22 is connected to the output terminal of the non-inverting amplifier circuit 16, and the output terminal of the operational amplifier 22 is connected to the non-inverting input terminal of the operational amplifier 22 of the rise determination circuit 18. I have. The inverting input terminal of the operational amplifier 22 is connected to a connection point e between the capacitor 25 and the emitter of the transistor 20 via a gain setting resistor 23 having a resistance value R1. Further, a negative feedback resistor 24 having a resistance value R2 is connected between the output terminal and the inverting input terminal of the operational amplifier 19.
[0042]
The resistance value R2 of the negative feedback resistor 24 is set to a value (R2≫R1) sufficiently larger than that of the gain setting resistor 23. The gain setting resistor 23 and the negative feedback resistor 24 set the gain to be compensated by the gain compensating circuit 17, and the negative feedback resistor 24 and the capacitor 25 set the first predetermined frequency f1, and set the gain for the gain setting. The resistor 23 and the capacitor 25 set the second predetermined frequency f2.
[0043]
That is, the product of the resistance value R2 of the negative feedback resistor 24 and the capacitance C of the capacitor 25 is set so as to be substantially equal to the thermal time constant τ of the temperature sensitive resistors 7 and 8 as shown in the following Expression 1. I have.
[0044]
(Equation 1)
τ = CR2
[0045]
Then, as shown by a characteristic line 26A in FIG. 4, the signal output circuit 21 becomes substantially 1 for a flow rate pulsating at a frequency f lower than the first predetermined frequency f1 shown in the following Expression 2. The gain G1 is set to 1. Further, as shown by a characteristic line 26B in FIG. 4, the signal output circuit 21 outputs the flow rate pulsating at a frequency f higher than the first predetermined frequency f1 and lower than the second predetermined frequency f2 shown in the following Expression 3. Is set to be a second gain G2 which is substantially proportional to the frequency f. Further, as shown by the characteristic line 26C in FIG. 4, the signal output circuit 21 has a constant third gain substantially as shown in Expression 4 for a flow rate pulsating at a frequency f higher than the second predetermined frequency f2. G3 is set.
[0046]
(Equation 2)

[0047]
(Equation 3)

[0048]
(Equation 4)

[0049]
Here, the first predetermined frequency f1 is determined by the thermal time constant τ of the temperature-sensitive resistors 7, 8 and the like, and indicates a frequency at which the flow rate detection signal V4 starts to attenuate. That is, the first predetermined frequency f1 indicates a cutoff frequency of the low-pass filter when acting as a low-pass filter on the flow rate detection signal V4 due to the heat capacity of the temperature-sensitive resistors 7, 8, etc. It is. The second predetermined frequency f2 indicates the highest frequency of the flow rate detection signal V4 for which gain compensation is required.
[0050]
The signal output circuit 21 provides a gain G1 substantially proportional to the frequency f for a flow rate pulsating at the frequency f between the first and second predetermined frequencies f1 and f2, as shown in Expression 5 below. , G3 to amplify the flow rate detection signal V4 with the gain G2 (see the characteristic line 26 in FIG. 4).
[0051]
(Equation 5)

[0052]
Therefore, when the flow rate detection signal V4 decreases as the frequency increases, the gain of the signal output circuit 21 increases. Therefore, the signal output circuit 21 converts the flow rate detection signal V4 into an output signal V5 corresponding to the flow rate regardless of the frequency. Is output.
[0053]
The flow rate detection device according to the present embodiment has the above-described configuration. Next, an operation of detecting the flow rate of intake air will be described.
[0054]
First, when the intake air flows in the direction of arrow A, the first temperature-sensitive resistor 7 located on the upstream side of the silicon substrate 4 is cooled by the flow of the air, and the second temperature-sensitive resistor 7 located on the downstream side is cooled. The temperature-sensitive resistor 8 receives heat from the heater 6. As a result, the resistance values RT1 and RT2 of the first and second temperature-sensitive resistors 7 and 8 change, so that a potential difference occurs between the flow voltages V1 and V2 from the first and second flow detection circuits 11 and 13. . Therefore, the differential amplifier circuit 15 outputs a differential signal V3 corresponding to the potential difference (V1−V2), and the non-inverting amplifier circuit 16 outputs a flow detection signal V4 obtained by amplifying the differential signal V3.
[0055]
Here, the flow detection signal V4 rises. Up Biting condition In When the flow rate of the intake air flowing in the direction indicated by the arrow A is substantially constant, the flow rate detection signal V4 hardly changes and is maintained at a constant value. At this time, the operational amplifier 19 of the rise determination circuit 18 acts as a buffer in the gain compensation circuit 17, and the transistor 20 is turned on. Therefore, the flow rate detection signal V4 becomes the output signal V5, as shown in the following Expression 6. The value is substantially the same as the connection point voltage signal Ve which is the voltage of the connection point e.
[0056]
(Equation 6)
V4 = V5 = Ve
[0057]
Also, the flow detection signal V4 rises. Up Biting condition In When the flow rate of the intake air flowing in the direction indicated by the arrow A decreases, the flow rate detection signal V4 also gradually decreases as the flow rate decreases, as indicated by a characteristic line 27 shown by a solid line in FIG. At this time, the output signal V5 of the operational amplifier 22 of the signal output circuit 21 also decreases in accordance with the flow rate detection signal V4, as indicated by a dotted line in FIG. Therefore, the output voltage of the operational amplifier 19 of the rise determination circuit 18 also decreases, so that the transistor 20 is kept in the ON state. As a result, the capacitor 25 is charged through the transistor 20, and the connection point voltage signal Ve of the connection point e follows the flow rate detection signal V4 and the output signal V5 as indicated by the solid line 27 in FIG. Low Down. As a result, the flow rate detection signal V4, the output signal V5, and the connection point voltage signal Ve are maintained in the relationship represented by Expression 6.
[0058]
On the other hand, when the flow rate of the intake air flowing in the direction of arrow A increases, that is, when the flow rate detection signal V4 is in the rising state, the flow rate detection signal V4 and the output signal V5 gradually increase. At this time, the flow rate detection signal V4 corresponds to the increase in the flow rate due to the non-linear responsiveness to the heat capacity and the flow rate of the first and second temperature sensitive resistors 7, 8 as indicated by a characteristic line 27 shown by a solid line in FIG. No, tend to decrease.
[0059]
However, since the output voltage of the operational amplifier 19 of the rise determination circuit 18 also increases, the transistor 20 is turned off, and the capacitor 25 cannot be charged. Therefore, the charge charged in the capacitor 25 is discharged through the gain setting resistor 23 and the negative feedback resistor 24. As a result, the connection point voltage signal Ve at the connection point e, which is the emitter-side voltage of the transistor 20, becomes lower than the flow rate detection signal V4, as indicated by the characteristic line 29 indicated by the dashed line in FIG. That is, the response of the connection point voltage signal Ve to the flow rate detection signal V4 is delayed by the product (time constant) of the capacitance C of the capacitor 25 and the resistance value R1 of the gain setting resistor 23. Also decrease. As a result, the output signal V5 changes with time as shown by the characteristic line 28 in FIG. 5 according to the relationship shown in the following Expression 7 with the connection point voltage signal Ve and the flow rate detection signal V4.
[0060]
(Equation 7)

[0061]
Thus, according to the present embodiment, the gain compensation circuit 17 is constituted by the rise determination circuit 18 and the signal output circuit 21. Only in the state, the flow detection signal V4 can be amplified, and the output signal V5 can always be changed according to the flow. As a result, the flow rate can be detected almost accurately.
[0062]
Further, the amount of decrease in the flow rate detection signal V4 in the rising state is determined by the thermal time constant τ of the temperature-sensitive resistors 7, 8, etc. Change. For this reason, the flow rate detection signal V4 has a larger amount of decrease as the frequency f increases, and decreases as the frequency f decreases.
[0063]
However, as shown in FIG. 4, the signal output circuit 21 has a gain such that the flow rate detection signal V4 and the output signal V5 have substantially the same value at a frequency f lower than the first predetermined frequency f1 determined by the thermal time constant τ. G1 is set to about 1, and at a frequency f between the first and second predetermined frequencies f1 and f2, the gain G2 is set to increase so as to be substantially proportional to the frequency f. At a frequency f higher than the second predetermined frequency f2, The gain is set to be approximately G3.
[0064]
Thus, when the flow rate pulsates at a frequency f lower than the predetermined frequency f1, the flow rate detection signal V4 has a value substantially proportional to the flow rate pulsation even in the rising state. At this time, since the signal output circuit 21 amplifies the flow rate detection signal V4 with a gain G1 of about 1, the signal output circuit 21 outputs an output signal V5 substantially proportional to the pulsation of the flow rate.
[0065]
When the flow rate pulsates in a range of a frequency f higher than the first predetermined frequency f1 and lower than the second predetermined frequency f2, the signal output circuit 21 outputs the flow rate detection signal V4 with a gain G2 substantially proportional to the frequency f. Therefore, the gain of the flow rate detection signal V4, which attenuates as the frequency f increases, can be compensated. For this reason, the signal output circuit 21 can always output the output signal V5 corresponding to the flow rate regardless of the frequency f.
[0066]
Further, since the signal output circuit 21 is configured to amplify the flow rate detection signal V4 having a frequency f higher than the predetermined frequency f2 on the high frequency side with a substantially constant gain G3, it hardly affects the flow rate detection. It is not necessary to amplify the flow rate detection signal V4 on the high frequency side more than necessary. Therefore, errors due to the flow rate detection signal V4 on the high frequency side can be eliminated, and the flow rate detection accuracy can be improved.
[0067]
Next, FIG. 6 shows a second embodiment according to the present invention. The feature of the present embodiment lies in that the rising judgment means is constituted by a diode. The same components as those in the above-described first embodiment are denoted by the same reference numerals, and description thereof will be omitted.
[0068]
Reference numeral 31 denotes a gain compensation circuit according to the present embodiment. The gain compensation circuit 31 includes a diode 32 and a signal output circuit 33 described later.
[0069]
Reference numeral 32 denotes a diode serving as a rise determination means. The diode 32 is connected between an output terminal of an operational amplifier 34 of a signal output circuit 33 described later and an inverting input terminal, and a current flows from the inverting input terminal to the output terminal. This allows the current to flow, and prevents the current from flowing from the output terminal to the inverting input terminal.
[0070]
Reference numeral 33 denotes a signal output circuit as signal output means. The signal output circuit 33 includes an operational amplifier 34, a gain setting resistor 35, a negative feedback resistor 36, and a capacitor 37.
[0071]
Here, the non-inverting input terminal of the operational amplifier 34 is connected to the output terminal of the non-inverting amplifier circuit 16 and receives the flow rate detection signal V4. The inverting input terminal of the operational amplifier 34 is connected to the ground via a gain setting resistor 35 having a resistance value R1 and a capacitor 37 having a capacitance C. Further, a negative feedback resistor 36 having a resistance value R2 is connected between the output terminal and the inverting input terminal of the operational amplifier 34, and the diode 32 is connected in parallel to the negative feedback resistor 36.
[0072]
The flow rate detection device according to the present embodiment has the above-described configuration. Next, the operation of the gain compensation circuit 31 will be described.
[0073]
When the flow rate detection signal V4 is in the rising state, the output signal V5, which is the voltage at the output terminal of the operational amplifier 34, is larger than the flow rate detection signal V4. At this time, since the voltage at the inverting input terminal of the operational amplifier 34 has substantially the same value as the flow rate detection signal V4, no current flows through the diode 32, and the diode 32 functions as an insulator. For this reason, the gain compensation circuit 31 functions as an amplifier circuit without the diode 32.
[0074]
On the other hand, the flow detection signal V4 rises. Up Biting condition Not in In some cases, the output signal V5 does not become larger than the flow rate detection signal V4, and has almost the same value. When the output signal V5 becomes smaller than the flow rate detection signal V4, a current flows through the diode 32, so that the diode 32 functions as a conductor. Therefore, the gain compensation circuit 31 outputs an output signal V5 substantially the same as the flow rate detection signal V4.
[0075]
Thus, in the flow rate detecting device of the present embodiment configured as described above, the same operation and effect as those of the first embodiment can be obtained. Only one 34 needs to be used, and the gain compensation circuit 31 having the same operation and effect as the first embodiment can be easily configured.
[0076]
Next, FIGS. 7 and 8 show a third embodiment according to the present invention. The feature of this embodiment is that the gain compensation circuit includes a backflow determination circuit for detecting a backflow of intake air, The output circuit is configured to amplify the flow rate detection signal at the time of normal flow and at the time of reverse flow based on the determination result of the reverse flow determination circuit.
[0077]
The same components as those in the above-described first embodiment are denoted by the same reference numerals, and description thereof will be omitted. Further, in the present embodiment, when the intake air flows backward in the direction of arrow B in FIGS. 1 and 2, the flow rate detection signal V4 becomes lower than 1 V which is the backflow determination voltage E0.
[0078]
In FIG. 7, reference numeral 41 denotes a gain compensation circuit according to the present embodiment. The gain compensation circuit 41 includes a backflow determination circuit 42, a rise determination circuit 47, and a signal output circuit 51, which will be described later.
[0079]
Reference numeral 42 denotes a backflow judging circuit as backflow judging means. The backflow judging circuit 42 includes a comparator 43, an inverter 44, and relays 45 and 46.
[0080]
The comparator 43 has its inverting input terminal connected to the output terminal of the non-inverting amplifying circuit 16, and receives the flow rate detection signal V4. On the other hand, the non-inverting input terminal of the comparator 43 is connected to a backflow determination voltage E0 of, for example, about 1V. The output terminal of the comparator 43 is connected to the relay 45 and also to the relay 46 via the inverter 44.
[0081]
Therefore, when the flow rate detection signal V4 is higher than the backflow determination voltage E0, the comparator 43 outputs a voltage of about 0V. As a result, the relay 45 is opened and a voltage of, for example, about 5 V is applied to the relay 46 by the inverter 44, so that the relay 46 is closed.
[0082]
When the flow rate detection signal V4 is smaller than the backflow determination voltage E0, the comparator 43 outputs a voltage of, for example, about 5V. As a result, the relay 45 is closed, and a voltage of, for example, about 0 V is applied to the relay 46 by the inverter 44. Therefore, the relay 46 is opened.
[0083]
A rising determination circuit 47 determines whether the flow rate detection signal V4 output from the non-inverting amplifier circuit 16 is in a rising state. The rising determination circuit 47 includes an operational amplifier 48, an NPN transistor 49, and a PNP transistor. 50.
[0084]
The inverting input terminal of the operational amplifier 48 is connected to the output terminal of the non-inverting amplifier circuit 16. The non-inverting input terminal of the operational amplifier 48 is connected to the output terminal of the signal output circuit 51, and the output terminal of the operational amplifier 48 is connected to the base of the transistor 49 via the relay 45. The transistor 50 is connected to the base side of the transistor 50.
[0085]
The transistor 49 has a collector connected to the battery voltage Eb and an emitter connected to the collector of the transistor 50. On the other hand, the transistor 50 has an emitter connected to the emitter of the transistor 49 and a collector connected to the ground.
[0086]
Therefore, transistors 49 and 50 are connected in series between battery voltage Eb and ground, and a connection point e 'is provided between the emitter side of transistor 49 and the emitter side of transistor 50.
[0087]
Reference numeral 51 denotes a signal output circuit as signal output means. The signal output circuit 51 includes an operational amplifier 52, a gain setting resistor 53, a negative feedback resistor 54, and a capacitor 55.
[0088]
Here, the non-inverting input terminal of the operational amplifier 52 is connected to the output terminal of the non-inverting amplifier circuit 16, and receives the flow rate detection signal V4. The inverting input terminal of the operational amplifier 52 is connected to ground via a gain setting resistor 53 having a resistance value R1 and a capacitor 55 having a capacitance C. Further, a negative feedback resistor 54 having a resistance value R2 is connected between the output terminal and the inverting input terminal of the operational amplifier 52.
[0089]
The flow detection device according to the present embodiment has the above-described configuration, and the operation of the gain compensation circuit 41 will be described next.
[0090]
First, when the intake air is flowing forward in the direction of arrow A in FIG. 1, the flow rate detection signal V4 is larger than the backflow determination voltage E0 as indicated by the characteristic line 55A shown by the solid line in FIG. Outputs a voltage of approximately 0 V, the relay 45 is opened, and the relay 46 is closed. At this time, the transistor 49 does not operate, and only the transistor 50 operates. The transistor 50 is turned off in the rising state in which the flow rate in the direction indicated by the arrow A increases in substantially the same manner as the transistor 20 according to the first embodiment, and the transistor 50 decreases when the flow rate in the direction indicated by the arrow A decreases. Up Biting condition When not in It turns on.
[0091]
For this reason, when the flow rate detection signal V4 is in a rising state while the intake air is in a normal flow state, the output signal V5 output from the operational amplifier 52 is output as indicated by a characteristic line 56A indicated by a dotted line in FIG. The amplitude is larger than the signal V4, and the connection point voltage Ve 'at the connection point e' is smaller in amplitude than the flow rate detection signal V4, as indicated by a characteristic line 57A indicated by a dashed line in FIG. On the other hand, the flow rate detection signal V4 rises when the intake air is in the normal flow state. Up Biting condition Not in In some cases, the output signal V5 and the connection point voltage Ve 'have substantially the same value as the flow rate detection signal V4.
[0092]
Next, when the intake air is flowing backward in the direction of arrow B in FIG. 1, the flow rate detection signal V4 is smaller than the reverse flow determination voltage E0 as indicated by the characteristic line 55B shown by the solid line in FIG. 43 outputs a voltage of approximately 5 V, relay 45 closes, and relay 46 opens. At this time, the transistor 50 does not operate, and only the transistor 49 operates. Then, the transistor 49 is turned off in the rising state in which the flow rate in the arrow B direction is increased, and the transistor 49 is in the rising state in which the flow rate in the arrow B direction is reduced. Up Biting condition When not in It turns on.
[0093]
For this reason, when the flow rate detection signal V4 is in a rising state while the intake air is flowing backward, the amplitude of the output signal V5 becomes larger than that of the flow rate detection signal V4 as shown by a characteristic line 56B shown by a dotted line in FIG. The amplitude of the connection point voltage Ve 'at the connection point e' is smaller than the flow rate detection signal V4, as indicated by the characteristic line 57B shown by the dashed line in FIG. On the other hand, when the intake air flows backward, the flow detection signal V4 rises. Up Biting condition Not in In some cases, the output signal V5 and the connection point voltage Ve 'have substantially the same value as the flow rate detection signal V4.
[0094]
Thus, in the flow rate detecting device of the present embodiment configured as described above, the same operation and effect as those of the first embodiment can be obtained. In the present embodiment, particularly, the backflow determination circuit 42 is provided. Therefore, even if the intake air enters a backflow state and the amplitude of the flow rate detection signal decreases due to the thermal time constant τ of the temperature-sensitive resistors 7 and 8 when the flow rate in the backflow direction increases, the backflow determination circuit 42 The reduced gain can be compensated for by the gain compensation circuit 41 including the rise determination circuit 47 and the signal output circuit 51. Therefore, the flow rate can be accurately detected even when the intake air is in the reverse flow state.
[0095]
In each of the above embodiments, the flow rate detecting means is constituted by using two temperature-sensitive resistors. However, as described in Japanese Patent Application Laid-Open No. 8-86677, one heat-generating element is used. A bridge circuit may be configured by a temperature-sensitive resistor having a constant current, and a flow rate detection signal corresponding to the resistance value of the temperature-sensitive resistor may be output by supplying a constant current to the bridge circuit.
[0096]
【The invention's effect】
According to the first aspect of the present invention, as described in detail above, the gain compensating means is constituted by the rise determination means and the signal output means. Outputs an output signal that amplifies the detection signal and Up In a biting state Absent At times, the output signal is substantially the same as the flow rate detection signal. Thus, even when the rise of the flow detection signal is delayed due to the thermal time constant of the temperature-sensitive resistor and the flow detection signal decreases, the signal output means compensates for the reduced gain and responds to the change in the flow. The output signal thus output can be output, and an accurate flow rate can be detected.
[0097]
According to the second aspect of the present invention, when the flow rate detection signal is in a rising state, the flow rate detection signal having a frequency lower than a predetermined frequency determined by the thermal time constant of the temperature-sensitive resistor is substantially constant. Since the configuration is such that the flow rate detection signal having a frequency higher than the predetermined frequency is amplified with the gain corresponding to the frequency, when the flow rate pulsates at a frequency lower than the predetermined frequency, the flow rate detection signal is , The signal output means amplifies the flow rate detection signal with a constant gain. On the other hand, when the flow rate pulsates at a frequency higher than the predetermined frequency, the value of the flow rate detection signal decreases due to the heat capacity of the temperature sensitive resistor or the like, and the signal output unit amplifies the flow rate detection signal with a gain corresponding to the frequency. I do. For this reason, the signal output means can compensate for the gain of the flow rate detection signal, which attenuates as the frequency increases, and always outputs an output signal corresponding to the flow rate regardless of the frequency, and can detect an accurate flow rate. it can.
[0098]
According to the third aspect of the present invention, when the flow rate detection signal is in the rising state, the signal output means outputs the second predetermined frequency higher than the first predetermined frequency determined by the thermal time constant of the temperature sensitive resistor. Since the flow rate detection signal having a higher predetermined frequency is amplified with a substantially constant gain, the flow rate detection signal on the high frequency side, which hardly affects the flow rate detection, is not unnecessarily amplified. For this reason, errors due to the flow rate detection signal on the high frequency side can be eliminated, and the flow rate detection accuracy can be improved.
[0099]
According to the invention of claim 4, the first predetermined frequency by the signal output means is set to the frequency at which the flow detection signal starts to attenuate, and the second predetermined frequency is set to the frequency of the flow detection signal which requires gain compensation. Since the highest frequency is set, the signal output means can amplify the flow detection signal with a gain corresponding to the frequency when the flow pulsates at a higher frequency than the frequency at which the flow detection signal starts to attenuate. Further, since the second predetermined frequency is set to the highest frequency of the flow rate detection signal requiring the gain compensation, the flow rate detection signal requiring the gain compensation can be surely amplified.
[0100]
According to the fifth aspect of the present invention, the rise determination means determines the rising state when the flow rate of the measured fluid in the reverse flow direction increases when the backflow detection means determines that the fluid to be measured is in the backward flow state. Then, when it is determined that the measured fluid is in the normal flow state, since the measured fluid is determined to be in the rising state when the flow rate of the measured fluid in the normal flow direction increases, the measured fluid flows in the reverse direction. Even when the flow rate detection signal decreases due to the thermal time constant of the temperature-sensitive resistor or the like, the rising state determination means can determine the rising state at the time of backflow. Therefore, the signal output unit amplifies the flow rate detection signal in the rising state at the time of the backflow, so that the flow rate of the measured fluid flowing back can be accurately detected.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a state in which a flow detecting device according to a first embodiment is attached to an intake pipe.
FIG. 2 is a perspective view showing a heater, a first temperature-sensitive resistor, and a second temperature-sensitive resistor formed on a silicon substrate.
FIG. 3 is a circuit diagram illustrating a flow calculation circuit, a gain compensation circuit, and the like of the flow detection device according to the first embodiment.
FIG. 4 is a characteristic diagram showing a relationship between gain and frequency of a gain compensation circuit.
FIG. 5 is a characteristic diagram showing a relationship between a flow rate detection signal, an output signal, a connection point voltage signal, and time according to the first embodiment.
FIG. 6 is a circuit diagram illustrating a gain compensation circuit and the like of a flow rate detection device according to a second embodiment.
FIG. 7 is a circuit diagram illustrating a gain compensation circuit and the like of a flow rate detection device according to a third embodiment.
FIG. 8 is a characteristic diagram illustrating a relationship between a flow rate detection signal, an output signal, a connection point voltage signal, and time according to the third embodiment.
[Explanation of symbols]
7,8 Temperature-sensitive resistor
10 Flow rate calculation circuit (flow rate calculation means)
17, 31, 41 Gain compensation circuit (gain compensation means)
18, 47 Rising judgment circuit (rising judgment means)
21, 33, 51 signal output circuit (signal output means)
32 diode (rise judgment means)
42 Backflow determination circuit (backflow determination means)

Claims (5)

A flow rate calculating means having a temperature-sensitive resistor provided in the fluid to be measured, and calculating a flow rate detection signal corresponding to a flow rate of the fluid to be measured by a resistance value of the temperature-sensitive resistor; In a flow rate detecting device comprising a gain compensating means for amplifying a detection signal and compensating for a gain reduced by a thermal time constant of the temperature sensitive resistor,
The gain compensating means includes a rising determination means for determining whether the flow detection signal is in a rising state, and an output obtained by amplifying the flow detection signal when the rising determination means determines that the flow detection signal is in a rising state. outputs a signal, the flow rate detection signal flow rate detecting device, wherein a configured by the signal output means for outputting the substantially same output signals as the flow rate detection signal when it is determined that there is no in the rising state. The signal output unit is configured such that when the rise determination unit determines that the flow detection signal is in a rising state, the flow detection signal having a frequency lower than a predetermined frequency determined by a thermal time constant of the temperature-sensitive resistor is substantially constant. 2. The flow rate detection device according to claim 1, wherein the flow rate detection signal amplified by a gain of the predetermined frequency and having a frequency higher than the predetermined frequency outputs an output signal amplified by a gain corresponding to the frequency. The signal output means, when the rise determination means determines that the flow detection signal is in a rising state, the flow detection signal having a frequency lower than a first predetermined frequency determined by a thermal time constant of the temperature sensitive resistor is substantially The flow rate detection signal which is amplified with a constant first gain and is in a frequency range higher than the first predetermined frequency and lower than a predetermined second predetermined frequency is amplified with a second gain corresponding to the frequency. 2. The flow rate detection signal according to claim 1, wherein the flow rate detection signal having a frequency higher than the second predetermined frequency outputs an output signal amplified with a substantially constant third gain larger than the second gain. Flow detector. The signal output means sets the first predetermined frequency to a frequency at which the flow detection signal starts to attenuate, and sets the second predetermined frequency to the highest frequency of the flow detection signal requiring gain compensation. Item 4. A flow rate detecting device according to item 3. The gain compensating means includes a backflow judging means for judging whether or not the fluid to be measured is flowing backward, and the rise judging means measures the flow rate when the backflow detecting means determines that the fluid to be measured is in a backflow state. A rising state is determined when the flow rate of the fluid flowing in the reverse flow direction increases, and a rising state is determined when the flow rate of the measured fluid increases in the normal flow direction when the measured fluid is determined to be in the normal flow state. The flow rate detecting device according to claim 1, 2, 3, or 4, wherein

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