JP3940862B2

JP3940862B2 - Exhaust gas recirculation control valve

Info

Publication number: JP3940862B2
Application number: JP33134497A
Authority: JP
Inventors: 一良渡壁; 徳朗柴田
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 1997-06-25
Filing date: 1997-12-02
Publication date: 2007-07-04
Anticipated expiration: 2017-12-02
Also published as: JPH1172166A

Description

【０００１】
【発明の属する技術分野】
本発明は、いわゆる複座弁による排気圧力相殺機構を備えた排気ガス還流制御弁に関するものである。
【０００２】
【従来の技術】
排気ガス還流装置（ＥＧＲ装置）を搭載した車両では、近年の排気ガス規制の強化に伴って、排気ガス還流量（ＥＧＲ量）を大流量で且つ制御良く制御する必要がある。しかし、ＥＧＲ量を大流量化すると、排気ガス還流制御弁（ＥＧＲ弁）の弁体に加わる排気圧力が非常に大きくなるため、この排気圧力に抗して弁体を開弁させるためには、相当に強力なリニアソレノイド等のアクチュエータが必要となり、アクチュエータの大型化・高コスト化を招いてしまう。
【０００３】
この対策として、いわゆる複座弁による排気圧力相殺機構を備えたＥＧＲ弁が提案されている。このものは、図１２に示すように、弁ハウジング１１内に２つの弁座１２，１３を対向させて配置し、両弁座１２，１３の中心に１本の弁シャフト１４を貫通させると共に、該弁シャフト１４に２つの弁体１５，１６を固定し、該弁シャフト１４をリニアソレノイド等のアクチュエータで駆動することで、各弁体１５，１６で各弁座１２，１３の開口を開閉するようにしている。
【０００４】
この場合、ＥＧＲ配管を流れる排気ガスは、図１２に矢印で示すように、弁ハウジング１１の流入ポート１７から弁体１５，１６間の空間に流入し、開弁時には、両弁座１２，１３の開口から弁ハウジング１１内に流れ、流出ポート１８から流出する。この構成では、両弁体１５，１６に加わる排気圧力Ｆ1 ，Ｆ2 が反対向きになるため、排気圧力Ｆ1 ，Ｆ2 が相殺され、排気圧力Ｆ1 ，Ｆ2 の影響を受けずに両弁体１５，１６を駆動することができる。
【０００５】
この構成では、両弁体１５，１６の間隔と両弁座１２，１３の間隔を正確に一致させる必要があるが、実際には、組立誤差により両者の間隔を正確に合わせることは困難である。また、仮に、組立時に両者の間隔を正確に合わせることができたとしても、ＥＧＲ弁は高温の排気ガス中で使用されるため、各部の熱膨張差により両者の間隔に誤差が生じてしまう。従って、上記構成では、組立誤差や熱膨張差により２つの弁体１５，１６を確実に２つの弁座１２，１３に着座させることは困難であり、弁漏れが発生しやすい。
【０００６】
この対策として、図１３に示すように、一方の弁体１５を弁シャフト１４に摺動可能に挿通支持させると共に、両弁体１５，１６間にスプリング１９を介在させ、閉弁時には、スプリング１９の弾発力により弁体１５を弁座１２に着座させるようにすることが考えられている。
【０００７】
【発明が解決しようとする課題】
しかし、上記構成のように、一方の弁体１５を弁シャフト１４に摺動可能にすると、排気圧力Ｆ1 ，Ｆ2 を相殺できない。すなわち、弁シャフト１４に固定されていない上方の弁体１５に加わる排気圧力Ｆ1 は、弁座１２で受け支えられ、弁シャフト１４には伝わらない。これに対し、弁シャフト１４に固定されている下方の弁体１６に加わる排気圧力Ｆ2 は弁シャフト１４に伝わるため、排気圧力Ｆ2 が弁シャフト１４を押し下げる方向に働く。更に、上方の弁体１５を付勢するスプリング１９の弾発力も下方の弁体１６を介して弁シャフト１４を押し下げる方向に働く。このため、弁シャフト１４を閉弁方向（上方）に付勢するスプリング２０のばね力を、排気圧力Ｆ2 とスプリング１９のばね力とに打ち勝つ大きさに増加させる必要がある。このため、開弁時にスプリング２０のばね力に抗して弁シャフト１４を押し下げるアクチュエータの駆動力を、排気圧力Ｆ2 とスプリング１９の弾発力との合力分だけ増加させる必要があり、相当に強力なアクチュエータが必要となる。従って、上記構成では、複座弁方式のＥＧＲ弁本来の目的であるアクチュエータの負荷軽減、小型化を達成できない。
【０００８】
本発明はこのような事情を考慮してなされたものであり、従ってその目的は、複座弁方式を採用しながら、組立誤差や熱膨張差による弁漏れを防止できると共に、複座弁方式の本来の目的であるアクチュエータの負荷軽減、小型化を達成できる排気ガス還流制御弁を提供することにある。
【０００９】
【課題を解決するための手段】
上記目的を達成するために、本発明の請求項１の排気ガス還流制御弁は、２つの弁体を備えた複座弁方式を採用し、一方の弁体の少なくとも一部を弾性変形可能に構成し、その弾性変形可能な弁体は、リーフスプリング状又は放射状に形成された板ばねを用い、この板ばねの開口部を変形容易な部材で閉鎖した構成としている。この構成によれば、組立誤差や熱膨張差による両弁体の間隔と両弁座の間隔との誤差を一方の弁体の弾性変形により吸収できて、２つの弁体を同時に２つの弁座に着座させることができ、弁漏れを防止できる。しかも、弾性変形可能な弁体は弁シャフトに固定されているため、弾性変形可能な弁体に加わる排気圧力が弁シャフトにも働く。これにより、２つの弁体を介して弁シャフトに働く排気圧力が相殺され、弁シャフトを駆動するアクチュエータの負荷を軽減でき、アクチュエータの小型化を実現できる。
【００１０】
この場合、請求項２のように、２つの弁座の間隔を保持する部材と弁シャフトとを同等の熱膨張係数を有する材料で形成しても良い。このようにすれば、両弁体の間隔と両弁座の間隔との熱膨張差が無くなり、より確実に弁漏れを防止できる。
【００１１】
ところで、排気ガス還流制御弁は高温の排気ガス中で使用されるため、弁体は耐熱性が要求され、その観点から、一般に金属製の弁体が用いられている。従って、弾性変形可能な弁体も、耐熱性の観点から金属弾性材で形成することが好ましい。しかし、弁体全体を厚い金属弾性板材で形成すると、弁体の弾性力が大きくなって、それがアクチュエータの負荷を増大させる要因となる。これを避けるために、弁体全体を薄く形成しすぎると、弁体の耐久性が低下し、弁体と弁座との衝突の繰り返しで弁体の着座面が摩耗した時に、弁体の着座面に穴が開いて弁漏れが発生しやすい。
【００１２】
この対策として、請求項１に係る発明では、弾性変形可能な弁体は、リーフスプリング状又は放射状に形成された板ばねを用い、この板ばねの開口部を変形容易な部材で閉鎖した構成としている。このようにすれば、弁体の着座面等、耐摩耗性や機械的強度が要求される部分に、適度な厚みの板ばねを延在させた適度な弾性力の弁体を形成でき、アクチュエータの負荷を軽減しながら、弁体の摩耗による弁体の穴開きを防止でき、負荷軽減と弁体の耐久性向上とを両立させることができる。
【００１８】
【発明の実施の形態】
以下、本発明に関連する参考例（１）を図１に基づいて説明する。排気ガス還流制御弁（ＥＧＲ弁）の弁ハウジング２１は例えばアルミダイカストにより形成され、その内部にＥＧＲガス通路２７が形成されている。このＥＧＲガス通路２７の入口側に形成された弁座収納部２１ａ内に、２つの弁座２２，２３が上下に対向するように組み付けられている。上方の弁座２２は、下方に延びる囲壁部２２ａを一体に有する箱型の弁座であり、その囲壁部２２ａの下端に下方の弁座２３が溶接等により固定されている。両弁座２２，２３で囲まれた空間がＥＧＲガス流入室２４となり、このＥＧＲガス流入室２４の側壁部に、ＥＧＲ配管を通して流れてくるＥＧＲガスが流入する流入ポート２５が形成されている。ＥＧＲガス通路２７の出口側には、開弁時に両弁座２２，２３の開口から流れ出るＥＧＲガスを吸気管（図示せず）側へ流出させる流出ポート２６が形成されている。
【００１９】
弁ハウジング２１には、ＥＧＲガス通路２７の上方にスプリング室２８が形成され、その上方にアクチュエータ室２９が形成され、このアクチュエータ室２９内にリニアソレノイド、ステップモータ等のアクチュエータ３０がプランジャ３１を下向きにして取り付けられている。このプランジャ３１の真下には、弁シャフト３２がスプリング室２８を貫通するように配置され、この弁シャフト３２の下部が２つの弁座２２，２３の中心を貫通している。この弁シャフト３２は、スプリング室２８の底部に固定された軸受３３に上下方向に摺動可能に支持され、該弁シャフト３２の上端に嵌着固定された皿状のスプリング受け部材３４とスプリング室２８の底壁部との間にスプリング３５が装着され、このスプリング３５の弾発力によって弁シャフト３２が上方（閉弁方向）に付勢され、該弁シャフト３２の上端がアクチュエータ３０のプランジャ３１の下端に当接している。
【００２０】
２つの弁座２２，２３に対応して、弁シャフト３２の下部には２つの弁体３６，３７が固定されている。下方の弁体３７は、従来と同じく、耐熱性・対摩耗性のある金属（ステンレス鋼等）で厚く形成されているが、上方の弁体３６は、薄いステンレス板等、耐熱性・対摩耗性のある弾性板材で弾性変形可能に形成されている。この場合、上方の弁体３６の弾性変形を容易にするために、上方の弁体３６には波形が同心状に形成されている。
【００２１】
また、両弁体３６，３７の間隔と両弁座２２，２３の間隔との熱膨張差を無くすために、２つの弁座２２，２３の間隔を保持する部材（弁座２２の囲壁部２２ａ）と弁シャフト３２とを、同等の熱膨張係数を有する材料（本参考例ではステンレス鋼）で形成している。また、２つの弁体３６，３７に作用する排気圧力Ｆ1 ，Ｆ2 の差圧を利用してセルフシール効果を持たせるために、上方の弁座２２の開口径Ｄ1 を下方の弁座２３の開口径Ｄ2 よりも若干大きく形成し、上方の弁体３６に働く上向きの排気圧力Ｆ1 が下方の弁体３７に働く下向きの排気圧力Ｆ2 より若干大きくなるようになっている。
【００２２】
以上のように構成したＥＧＲ弁では、アクチュエータ３０の通電時に、プランジャ３１が下方に突出して、弁シャフト３２をスプリング３５の弾発力に抗して押し下げることで、２つの弁体３６，３７を２つの弁座２２，２３から下方に離間させて両弁座２２，２３の開口を開放する。これにより、弁ハウジング２１の流入ポート２５からＥＧＲガス流入室２４内に流入するＥＧＲガスを、両弁座２２，２３の開口からＥＧＲガス通路２７内に流入させ、流出ポート２６から吸気管側へ流出させる。
【００２３】
一方、アクチュエータ３０の非通電時には、スプリング３５の弾発力によって弁シャフト３２を引き上げ、２つの弁体３６，３７を２つの弁座２２，２３に確実に着座させる。つまり、上方の弁体３６を弾性変形可能に形成しているので、仮に、組立誤差や熱膨張差によって両弁体３６，３７の間隔と両弁座２２，２３の間隔とが正確に一致しなくても、その誤差を上方の弁体３６の弾性変形により吸収でき、２つの弁体３６，３７を２つの弁座２２，２３に同時に着座させることができて、弁漏れを防止できる。
【００２４】
しかも、弾性変形可能な弁体３６は弁シャフト３２に固定されているため、弾性変形可能な弁体３６に加わる排気圧力Ｆ1 が弁シャフト３２にも働く。これにより、２つの弁体３６，３７を介して弁シャフト３２に働く排気圧力Ｆ1 ，Ｆ2 が相殺され、弁シャフト３２を駆動するアクチュエータ３０の負荷を軽減でき、アクチュエータ３０の小型化を実現できる。
【００２５】
この場合、２つの弁座２２，２３の開口径Ｄ1 ，Ｄ2 を同一に形成して、２つの弁体３６，３７に働く排気圧力Ｆ1 ，Ｆ2 を完全に相殺させるようにしても良いが、本参考例のように、上方の弁座２２の開口径Ｄ1 を下方の弁座２３の開口径Ｄ2 より若干大きく形成しても良い。このようにすれば、上方の弁体３６に働く上向きの排気圧力Ｆ1 が下方の弁体３７に働く下向きの排気圧力Ｆ2 より若干大きくなり、その排気圧力Ｆ1 ，Ｆ2 の差圧を利用してセルフシール効果を持たせることができる。
【００２６】
更に、２つの弁座２２，２３の間隔を保持する弁座２２の囲壁部２２ａと弁シャフト３２とを、同等の熱膨張係数を有する材料（本参考例ではステンレス鋼）で形成しているため、両弁体３６，３７の間隔と両弁座２２，２３の間隔との熱膨張差が無くなる。従って、本参考例では、両弁体３６，３７の間隔と両弁座２２，２３の間隔とがずれる要因は、組立誤差のみとなり、両者のずれが少なくなる。これにより、２つの弁体３６，３７の同時着座が一層確実なものとなり、弁漏れ防止性能を更に向上できる。
【００２７】
但し、本発明は、２つの弁座２２，２３の間隔を保持する部材（囲壁部２２ａ）と弁シャフト３２とを、熱膨張係数の異なる材料で形成しても良く、この場合でも、熱膨張差を上方の弁体３６の弾性変形により吸収できるので、２つの弁体３６，３７を同時に着座させることができる。
【００２８】
弾性変形可能な弁体３６は、図１に示す形状に限定されず、種々の形状が考えられる。
例えば、図２及び図３に示す参考例（２），（３）の弾性変形可能な弁体３８，３９は、共に薄いステンレス板で蛇腹状に形成され、その下端部のみが弁シャフト３２に固定され、蛇腹部分が上下方向に伸縮可能となっている。
【００２９】
図１乃至図３に示す弾性変形可能な弁体３６，３８，３９は、いずれも、弁体全体が同一の弾性板材で一体に形成されているが、弾性部材と非弾性部材とを組み合わせて１つの弾性変形可能な弁体を構成しても良い。
【００３０】
例えば、図４に示す参考例（４）の弾性変形可能な弁体４０は、薄いステンレス板等で形成した弾性変形可能な蛇腹部４１の上端に、弁座２２に着座するリング状の着座部材４２を溶接等で固着し、該蛇腹部４１の下端に円板状の支持部材４３を溶接等で固着し、この支持部材４３を弁シャフト３２に嵌着固定している。この場合、蛇腹部４１のみが弾性変形し、着座部材４２と支持部材４３は変形しない。このようにすれば、耐摩耗性や機械的強度が要求される部分（着座部材４２と支持部材４３）を耐摩耗性や機械的強度に優れた材料で形成でき、耐久性を向上できる。
【００３１】
ところで、弁体の弾性力は、アクチュエータ３０の負荷を増大させる要因となるため、弁体の弾性力は小さい方が好ましい。しかし、弁体の弾性力を小さくするために、弁体全体を薄く形成しすぎると、弁体の耐久性が低下し、弁体と弁座との衝突の繰り返しで弁体の着座面が摩耗した時に、弁体の着座面に穴が開いて弁漏れが発生しやすい。
【００３２】
この対策として、図５に示す本発明の実施形態（１）の弾性変形可能な弁体４５は、リーフスプリング状に形成された皿状の板ばね４６を用い、この板ばね４６の下面に変形容易な皿状の金属薄膜４７を貼り合わせることで、該板ばね４６の開口部４８を金属薄膜４７で塞いでいる。板ばね４６は、弁シャフトに嵌着される中央の嵌着部４６ａと外周の着座面部４６ｂとを共に円環状に形成し、嵌着部４６ａと着座面部４６ｂとの間に複数本のアーム部４６ｃを等ピッチで形成している。各アーム部４６ｃは、放射状（直線状）に形成しても良いが、図５に示すように曲線形状に形成して各アーム部４６ｃを長くすれば、各アーム部４６ｃが弾性変形しやすくなる。
【００３３】
このようにすれば、耐摩耗性や機械的強度が要求される部分である着座面部４６ｂと固定部４６ａに、適度な厚みの板ばねを延在させた適度な弾性力の弁体４５を形成でき、アクチュエータの負荷を軽減しながら、弁体４５の摩耗による弁体４５の穴開きを防止でき、負荷軽減と弁体４５の耐久性向上とを両立させることができる。
【００３４】
一方、図６に示す実施形態（２）の弾性変形可能な弁体４９は、放射状に形成された皿状の板ばね５０を用い、この板ばね５０の下面に変形容易な皿状の金属薄膜５１を貼り合わせることで、該板ばね５０のスリット５２（開口部）を金属薄膜５１で塞いでいる。このようにしても、アクチュエータの負荷軽減と弁体４９の耐久性向上とを両立させることができる。
【００３５】
上記実施形態（１），（２）の弁体４５，４９は、図１のＥＧＲ弁に用いても良く、また、図７に示す実施形態（３）のＥＧＲ弁に用いても良い（図７は図５の弁体４５を用いたＥＧＲ弁の構成例を示している）。
【００３６】
このＥＧＲ弁の弁ハウジング６０は、円筒状の吸気通路６１を有し、この吸気通路６１が内燃機関の吸気管（図示せず）の途中に連結され、該吸気管を流れる吸入空気が吸気通路６１を通ってスロットルバルブ（図示せず）側に流れる。弁ハウジング６０の吸気通路６１の下方には、ＥＧＲガス流入室６２が形成され、このＥＧＲガス流入室６２の側壁には、ＥＧＲ配管（図示せず）を通って流れてくるＥＧＲガスが流入する流入ポート６３が形成され、該ＥＧＲガス流入室６２の上面部と下面部には、それぞれ弁座６４，６５が上下に対向するように設けられている。
【００３７】
上方の弁座６４は、弁ハウジング６０に一体に形成され、下方の弁座６５は、ステンレス鋼等により形成され、ＥＧＲガス流入室６２の下面に固着されている。上方の弁座６４の開口は吸気通路６１に連通し、該弁座６４の上方部には、吸気通路６１内を流れる吸入空気の風圧が弁座６４の開口に作用するのを防ぐ防風フード部６６が形成されている。下方の弁座６５の開口は、弁ハウジング６０の下部に形成されたＥＧＲガス通路６７を介して吸気管のＥＧＲガス導入口（図示せず）につながっている。従って、２つの弁座６４，６５の開口を通ったＥＧＲガスは、共に吸気管内に流れ込む。
【００３８】
２つの弁座６４，６５を貫通する弁シャフト３２には、２つの弁体４５，３７が固定されている。弁シャフト３２の駆動系は、図１と同じ構成であり、図１と同一符号を付して説明を省略する。尚、上方の弾性変形可能な弁体４５は、前記各実施形態のいずれの弁体を用いても良い。
【００３９】
一方、図８に示す実施形態（４）は、弾性変形可能な弁体（以下「弾性弁体」という）７１を除いて、図７に示す実施形態（３）と同じ構造である。弾性弁体７１は、ステンレス薄板等の弾性薄板により形成された皿型の板ばね７２の中央部分を、例えば鉄板等の剛性板により形成された２枚の円形のセンタープレート７３で挟み付けて構成したものである。この弾性弁体７１は、弁シャフト３２に下方から挿通され、その下方に圧入されたスリーブ７４と弁シャフト３２の段部３２ａとの間に挟み付け固定されている。これにより、センタープレート７３は弁シャフト３２に固定され、“非弾性部”となる。一方、板ばね７２のうちセンタープレート７３から外側に突出した部分は、“非弾性部”で支持された“弾性部”となり、上下方向に弾性変形可能である。
【００４０】
この場合、弾性弁体７１の有効受圧面積であるセンタープレート７３の受圧面積（投影面積）は、弁シャフト３２の下端に固着された他方の弁体（以下「剛性弁体」という）３７の受圧面積と略同一に形成されている。センタープレート７３と剛性弁体３７の受圧面（弁座６５の開口部）が共に円形の場合には、両者の直径Ｄ１，Ｄ２を略同一に形成すれば良い。その他の構成は、図７に示す実施形態（３）と同じであるので、図７と同一符号を付して説明を省略する。
【００４１】
図８に示すように、２つの弁体７１，３７が弁座６４，６５に着座した状態では、各弁体７１，３７に次のような排気圧力による荷重が加わる。
弾性弁体７１側に加わる荷重は、弾性弁体７１の有効受圧面積であるセンタープレート７３の受圧面積×排気圧力となる。
一方、剛性弁体３７側に加わる荷重は、剛性弁体３７の受圧面積×排気圧力となる。
【００４２】
この場合、センタープレート７３の受圧面積が剛性弁体３７の受圧面積と略同一に形成されているので、弾性弁体７１側に加わる荷重と剛性弁体３７側に加わる荷重が略同一となり、両者が釣り合った状態となる。従って、排気圧力が高圧になった時でも、両弁体７３，３７から弁シャフト３２に加わる力の均衡を保つことができて、剛性弁体３７の浮き上がりによる弁漏れを少なくすることができる。しかも、弾性弁体７３の外周部の板ばね７２が弾性変形可能であるため、前記各実施形態と同じく、２つの弁体７３，３７の同時着座も容易である。
【００４３】
本発明者は、上記実施形態（４）で用いた弾性弁体７１の弁漏れ防止性能を評価する試験を行ったので、その試験結果を図９（ａ）に示す。この試験では、弾性弁体７１のセンタープレート７３の直径Ｄ１を１５ｍｍとすると共に、弁座６４の開口径Ｄ３を１８ｍｍとし、剛性弁体３７の受圧面の直径Ｄ２を１６ｍｍとした。この構造では、図９（ａ）に示すように、排気圧力を上限圧力である２ｋｇｆ／ｃｍ²に高めた時でも、弁漏れを目標値である８リットル／分以下に抑えることができた。
【００４４】
一方、図９（ｂ）に示す比較例では、スパイラル形状の板ばねに金属薄膜を貼り合わせて構成した弾性弁体を用いた。比較例でも、排気圧力が１．４ｋｇｆ／ｃｍ²以下の領域では、弁漏れが目標値である８リットル／分以下であったが、排気圧力が約１．４ｋｇｆ／ｃｍ²を越えると、弁漏れが急激に増大して目標値を満足できなかった。
【００４５】
以上の試験結果から、実施形態（４）の構造では、高圧時でも高い弁漏れ防止性能を維持できることが確認された。
尚、上記各実施形態では、上方の弁体を弾性変形可能に形成したが、下方の弁体を弾性変形可能に形成しても良い。
【００４６】
図１０及び図１１に示す実施形態（５）では、剛性弁体３７を上方に配置し、弾性弁体８１を下方に配置している。弾性弁体８１は、薄いステンレス板等、耐熱性・対摩耗性のある弾性板材で皿状に形成され、弁シャフト３２にスリーブ８２で固定されている。この弾性弁体８１が着座する円環状の弁座（以下「弾性弁座」という）８３は、薄いステンレス板等、耐熱性・対摩耗性のある弾性板材で弾性変形可能に形成されている。この弾性弁座８３の開口面積（開口径）は上方の弁座６４の開口面積（開口径）とほぼ同一に設定されている。その他の構成は図７に示す実施形態（３）と同じであるので、図７と同一符号を付して説明を省略する。
【００４７】
次に、本実施形態（５）のＥＧＲ弁の閉弁特性・開弁特性について説明する。閉弁状態の時に、高圧の排気圧力で弾性弁体８１が開弁方向（下方）に弾性変形したとしても、これに追従して弾性弁座８３も高圧の排気圧力で開弁方向に弾性変形して、弾性弁体８１と弾性弁座８３との密着状態が維持される。これにより、排気圧力が高圧になった時でも、弁漏れが有効に防止されて、閉弁性能が向上する。
【００４８】
閉弁状態の時に、弁シャフト３２（両弁体３７，８１）に加わる荷重には、次の３種類の荷重Ｆs ，Ｆv ，Ｆn がある。
（１）弁シャフト３２を閉弁方向（上方）に付勢するスプリング３５による閉弁方向の荷重Ｆs
（２）剛性弁体３７と弾性弁体８１の有効受圧面積の差と排気圧力とで発生する閉弁方向の荷重Ｆv （両弁体３７，８１に働く排気圧力による荷重の差）
（３）弾性弁座８３が排気圧力で開弁方向に弾性変形することで、弾性弁座８３から弾性弁体８３に働く開弁方向の荷重Ｆn
【００４９】
ここで、閉弁時の弁漏れを抑制するには、次の▲１▼式のように、閉弁方向の荷重（Ｆs ＋Ｆv ）が開弁方向の荷重Ｆn よりも大きくなるように設定する必要がある。
▲１▼ Ｆs ＋Ｆv ＞Ｆn （弁漏れを抑制するための条件）
【００５０】
仮に、下方の弁体８１の有効受圧面積が上方の剛性弁体３７の有効受圧面積よりも大きいとすると、上記(1) 式において、排気圧力による荷重Ｆv は負の値（つまり開弁方向の荷重）になるが、本実施形態（５）のように、下方の弁体８１を弾性弁体とし、両弁座６４，８３の開口面積（開口径）をほぼ同一に設定した場合には、弾性弁体８１の有効受圧面積が剛性弁体３７の有効受圧面積よりも小さくなり、排気圧力による荷重Ｆv は正の値（つまり閉弁方向の荷重）になる。
【００５１】
この場合、図１１に示すように、スプリング３５による閉弁方向の荷重Ｆs は排気圧力が変化しても一定であるが、排気圧力による閉弁方向の荷重Ｆv は、排気圧力が高くなるに従って大きくなり、それによって、閉弁方向の総荷重（Ｆs ＋Ｆv ）が大きくなる。もし、弁座８３を剛体構造とした場合には、開弁方向の荷重Ｆn が０であるため、排気圧力の上昇により閉弁方向の総荷重（Ｆs ＋Ｆv ）が大きくなると、閉弁状態から開弁する際に必要となるアクチュエータの駆動力が大きくなるため、開弁特性（駆動力と弁体リフト量との関係）が排気圧力の変化によって変化してしまい、安定した開弁特性が得られない。
【００５２】
これに対し、本実施形態（５）では、弾性弁体８１が着座する弁座として、弾性弁座８３を用いているため、弾性弁座８３が排気圧力で開弁方向に弾性変形することで、弾性弁座８３から弾性弁体８３に開弁方向の荷重Ｆn が働く。この開弁方向の荷重Ｆn は、図１１に示すように排気圧力が高くなるに従って大きくなるため、排気圧力による閉弁方向の荷重Ｆv の増大分が開弁方向の荷重Ｆn の増大分によってほぼ相殺され、次の(2)式が成立する。
【００５３】
▲２▼ Ｆv −Ｆn ＝Δｆ＝ほぼ一定（開弁特性向上のための条件）
この▲２▼式が成立すれば、排気圧力が変化しても、排気圧力による荷重の合計値（Ｆv −Ｆn ）がほぼ一定となって、閉弁状態から開弁する際に必要となる駆動力（Ｆs ＋Ｆv −Ｆn ）がほぼ一定となり、開弁特性（駆動力と弁体リフト量との関係）が排気圧力の変化に左右されず、安定した開弁特性が得られ、高精度なＥＧＲ制御が可能となる。
【００５４】
このように、本実施形態（５）では、上記(1) 式及び(2) 式の関係が同時に成立するため、排気圧力の全変動域（エンジンの全負荷域）で、閉弁時の弁漏れ抑制と開弁特性向上の双方を実現することができる。しかも、一方の弁体８１と弁座８３が共に弾性変形可能であるため、前記各実施形態と同じく、２つの弁体８１，３７の同時着座も容易である。
【図面の簡単な説明】
【図１】本発明に関連する参考例（１）のＥＧＲ弁を示す縦断面図
【図２】本発明に関連する参考例（２）の弁体と弁座の構造を示す縦断面図
【図３】本発明に関連する参考例（３）の弁体と弁座の構造を示す縦断面図
【図４】本発明に関連する参考例（４）の弁体と弁座の構造を示す縦断面図
【図５】本発明の実施形態（１）を示し、（ａ）は弾性変形可能な弁体の平面図、（ｂ）は（ａ）のＡ−Ａ断面図、（ｃ）は金属薄膜の平面図
【図６】本発明の実施形態（２）を示し、（ａ）は弾性変形可能な弁体の縦断面図、（ｂ）は放射状の板ばねの平面図、（ｃ）は（ｂ）のＥ−Ｅ断面図、（ｄ）は金属薄膜の平面図、（ｅ）は（ｄ）のＦ−Ｆ断面図
【図７】本発明の実施形態（３）のＥＧＲ弁を示す縦断面図
【図８】本発明の実施形態（４）のＥＧＲ弁の主要部の構造を示す縦断面図
【図９】（ａ）は実施形態（４）の弁漏れ特性を示す図、（ｂ）は比較例の弁漏れ特性を示す図
【図１０】本発明の実施形態（５）のＥＧＲ弁の主要部の構造を示す縦断面図
【図１１】弁シャフトに加わる荷重Ｆs ，Ｆv ，Ｆn と排気圧力との関係を示す図
【図１２】従来の複座弁型のＥＧＲ弁を示す縦断面図
【図１３】従来の改良された複座弁型のＥＧＲ弁を示す縦断面図
【符号の説明】
２１…弁ハウジング、２２，２３…弁座、２５…流入ポート、２６…流出ポート、２７…ＥＧＲガス通路、３０…アクチュエータ、３１…プランジャ、３２…弁シャフト、３３…軸受、３５…スプリング、３６〜４０，４１…蛇腹部、４２…着座部材、４５…弁体、４６…板ばね、４７…金属薄膜（変形容易な部材）、４８…開口部、４６ｂ…着座面部、４９…弁体、５０…板ばね、５１…金属薄膜（変形容易な部材）、５２…スリット（開口部）、６０…弁ハウジング、６１…吸気通路、６２…ＥＧＲガス流入室、６３…流入ポート、６４，６５…弁座、６７…ＥＧＲガス通路、７１…弾性弁体（弾性変形可能な弁体）、７２…板ばね、７３…センタープレート、８１…弾性弁体、８３…弾性弁座。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas recirculation control valve having an exhaust pressure canceling mechanism using a so-called double seat valve.
[0002]
[Prior art]
In a vehicle equipped with an exhaust gas recirculation device (EGR device), it is necessary to control the exhaust gas recirculation amount (EGR amount) with a large flow rate and with good control in accordance with recent tightening of exhaust gas regulations. However, if the EGR amount is increased, the exhaust pressure applied to the valve body of the exhaust gas recirculation control valve (EGR valve) becomes very large. In order to open the valve body against this exhaust pressure, A considerably strong actuator such as a linear solenoid is required, which leads to an increase in size and cost of the actuator.
[0003]
As a countermeasure, an EGR valve provided with an exhaust pressure canceling mechanism using a so-called double seat valve has been proposed. As shown in FIG. 12, two valve seats 12 and 13 are arranged in the valve housing 11 so as to oppose each other, and one valve shaft 14 is passed through the center of both valve seats 12 and 13, Two valve bodies 15 and 16 are fixed to the valve shaft 14, and the valve shaft 14 is driven by an actuator such as a linear solenoid, thereby opening and closing the openings of the valve seats 12 and 13 with the valve bodies 15 and 16. I am doing so.
[0004]
In this case, the exhaust gas flowing through the EGR pipe flows into the space between the valve bodies 15 and 16 from the inflow port 17 of the valve housing 11 as indicated by arrows in FIG. Into the valve housing 11 and out of the outflow port 18. In this configuration, the exhaust pressures F1 and F2 applied to the both valve bodies 15 and 16 are in opposite directions, so that the exhaust pressures F1 and F2 are canceled out, and the both valve bodies 15 and 16 are not affected by the exhaust pressures F1 and F2. Can be driven.
[0005]
In this configuration, the distance between the valve bodies 15 and 16 and the distance between the valve seats 12 and 13 need to be exactly matched, but in practice, it is difficult to accurately match the distance between the two due to assembly errors. . Even if the distance between the two can be accurately adjusted during assembly, since the EGR valve is used in high-temperature exhaust gas, an error occurs in the distance between the two due to the difference in thermal expansion of each part. Therefore, in the above configuration, it is difficult to reliably seat the two valve bodies 15 and 16 on the two valve seats 12 and 13 due to an assembly error or a thermal expansion difference, and valve leakage is likely to occur.
[0006]
As a countermeasure against this, as shown in FIG. 13, one valve body 15 is slidably inserted into and supported by the valve shaft 14, and a spring 19 is interposed between both valve bodies 15 and 16, and the spring 19 is closed when the valve is closed. It is considered that the valve body 15 is seated on the valve seat 12 by the elastic force of the above.
[0007]
[Problems to be solved by the invention]
However, if one of the valve bodies 15 is slidable on the valve shaft 14 as described above, the exhaust pressures F1 and F2 cannot be offset. That is, the exhaust pressure F1 applied to the upper valve body 15 that is not fixed to the valve shaft 14 is supported by the valve seat 12 and is not transmitted to the valve shaft 14. On the other hand, since the exhaust pressure F2 applied to the lower valve body 16 fixed to the valve shaft 14 is transmitted to the valve shaft 14, the exhaust pressure F2 acts in the direction of pushing down the valve shaft 14. Furthermore, the elastic force of the spring 19 that biases the upper valve body 15 also acts in the direction of pushing down the valve shaft 14 via the lower valve body 16. Therefore, it is necessary to increase the spring force of the spring 20 that urges the valve shaft 14 in the valve closing direction (upward) to overcome the exhaust pressure F2 and the spring force of the spring 19. For this reason, it is necessary to increase the driving force of the actuator that pushes down the valve shaft 14 against the spring force of the spring 20 when the valve is opened by the resultant force of the exhaust pressure F2 and the spring force of the spring 19, which is considerably strong. An actuator is required. Therefore, with the above-described configuration, it is impossible to reduce the load and reduce the size of the actuator, which is the original purpose of the double seat valve EGR valve.
[0008]
The present invention has been made in consideration of such circumstances. Accordingly, the object of the present invention is to prevent valve leakage due to assembly errors and thermal expansion differences while adopting the double seat valve system, and It is an object of the present invention to provide an exhaust gas recirculation control valve that can reduce the load on the actuator and reduce the size, which is the original purpose.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the exhaust gas recirculation control valve according to claim 1 of the present invention employs a double seat valve system having two valve bodies, and at least a part of one valve body can be elastically deformed. Configure The elastically deformable valve body uses a leaf spring formed in a leaf spring shape or a radial shape, and the opening of the leaf spring is closed with a member that can be easily deformed. According to this configuration, an error between an interval between both valve bodies and an interval between both valve seats due to an assembly error or a difference in thermal expansion can be absorbed by elastic deformation of one valve body. The valve can be prevented from leaking. In addition, since the elastically deformable valve element is fixed to the valve shaft, the exhaust pressure applied to the elastically deformable valve element also acts on the valve shaft. As a result, the exhaust pressure acting on the valve shaft via the two valve bodies is canceled out, the load on the actuator that drives the valve shaft can be reduced, and the actuator can be downsized.
[0010]
In this case, as in claim 2, the member that holds the interval between the two valve seats and the valve shaft may be formed of a material having an equivalent thermal expansion coefficient. In this way, there is no difference in thermal expansion between the distance between both valve bodies and the distance between both valve seats, and valve leakage can be prevented more reliably.
[0011]
By the way, since the exhaust gas recirculation control valve is used in high-temperature exhaust gas, the valve body is required to have heat resistance. From this point of view, a metal valve body is generally used. Therefore, the elastically deformable valve body is preferably formed of a metal elastic material from the viewpoint of heat resistance. However, if the entire valve body is formed of a thick metal elastic plate material, the elastic force of the valve body increases, which increases the actuator load. To avoid this, if the entire valve body is made too thin, the durability of the valve body will be reduced, and when the seating surface of the valve body is worn due to repeated collisions between the valve body and the valve seat, There is a hole in the surface and valve leakage is likely to occur.
[0012]
As a countermeasure, the claims In the invention according to 1, The elastically deformable valve body uses a leaf spring or a leaf spring formed in a radial shape, and the opening of the leaf spring is closed with an easily deformable member. ing . In this way, a valve body with a moderate elasticity can be formed by extending a leaf spring of a moderate thickness on a portion where wear resistance and mechanical strength are required, such as a seating surface of the valve body, and an actuator While reducing the load of the valve body, it is possible to prevent the valve body from being punctured due to wear of the valve body, and to achieve both reduction of the load and improvement of the durability of the valve body.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention Reference examples related to (1) will be described with reference to FIG. The valve housing 21 of the exhaust gas recirculation control valve (EGR valve) is formed by, for example, aluminum die casting, and an EGR gas passage 27 is formed therein. Two valve seats 22 and 23 are assembled in the valve seat storage portion 21a formed on the inlet side of the EGR gas passage 27 so as to face each other vertically. The upper valve seat 22 is a box-shaped valve seat integrally including a surrounding wall portion 22a extending downward, and a lower valve seat 23 is fixed to the lower end of the surrounding wall portion 22a by welding or the like. A space surrounded by both valve seats 22 and 23 becomes an EGR gas inflow chamber 24, and an inflow port 25 into which EGR gas flowing through the EGR pipe flows is formed in a side wall portion of the EGR gas inflow chamber 24. An outlet port 26 is formed on the outlet side of the EGR gas passage 27 to allow EGR gas flowing out from the openings of the valve seats 22 and 23 to flow out to the intake pipe (not shown) when the valve is opened.
[0019]
In the valve housing 21, a spring chamber 28 is formed above the EGR gas passage 27, and an actuator chamber 29 is formed above the spring chamber 28. In the actuator chamber 29, an actuator 30 such as a linear solenoid or a step motor faces the plunger 31 downward. It is attached. A valve shaft 32 is disposed directly below the plunger 31 so as to penetrate the spring chamber 28, and a lower portion of the valve shaft 32 penetrates the centers of the two valve seats 22 and 23. The valve shaft 32 is supported by a bearing 33 fixed to the bottom of the spring chamber 28 so as to be slidable in the vertical direction, and a plate-shaped spring receiving member 34 fitted and fixed to the upper end of the valve shaft 32 and the spring chamber. A spring 35 is mounted between the bottom wall 28 and the elastic force of the spring 35 urges the valve shaft 32 upward (in the valve closing direction). The upper end of the valve shaft 32 is the plunger 31 of the actuator 30. It is in contact with the lower end of.
[0020]
Corresponding to the two valve seats 22 and 23, two valve bodies 36 and 37 are fixed to the lower portion of the valve shaft 32. The lower valve body 37 is made of a heat-resistant and wear-resistant metal (stainless steel or the like) as in the prior art, but the upper valve body 36 is made of a thin stainless steel plate or the like. It is formed so as to be elastically deformable with a flexible elastic plate. In this case, in order to facilitate elastic deformation of the upper valve body 36, the upper valve body 36 is formed with a concentric waveform.
[0021]
Further, in order to eliminate the difference in thermal expansion between the distance between the valve bodies 36 and 37 and the distance between the valve seats 22 and 23, a member for holding the distance between the two valve seats 22 and 23 (the surrounding wall portion 22a of the valve seat 22). ) And the valve shaft 32 are made of a material having the same coefficient of thermal expansion (this Reference example In stainless steel). Further, in order to provide a self-sealing effect by utilizing the differential pressure between the exhaust pressures F1 and F2 acting on the two valve bodies 36 and 37, the opening diameter D1 of the upper valve seat 22 is set to open the lower valve seat 23. The upward exhaust pressure F1 acting on the upper valve body 36 is slightly larger than the downward exhaust pressure F2 acting on the lower valve body 37.
[0022]
In the EGR valve configured as described above, when the actuator 30 is energized, the plunger 31 protrudes downward, and the valve shaft 32 is pushed down against the elastic force of the spring 35, whereby the two valve bodies 36 and 37 are moved. The openings of both valve seats 22 and 23 are opened away from the two valve seats 22 and 23. As a result, the EGR gas flowing into the EGR gas inflow chamber 24 from the inflow port 25 of the valve housing 21 is caused to flow into the EGR gas passage 27 from the openings of the valve seats 22 and 23, and from the outflow port 26 to the intake pipe side. Spill.
[0023]
On the other hand, when the actuator 30 is not energized, the valve shaft 32 is pulled up by the elastic force of the spring 35, and the two valve bodies 36 and 37 are securely seated on the two valve seats 22 and 23. That is, since the upper valve body 36 is formed so as to be elastically deformable, it is assumed that the distance between both valve bodies 36 and 37 and the distance between both valve seats 22 and 23 are exactly the same due to an assembly error and a difference in thermal expansion. Even if not, the error can be absorbed by the elastic deformation of the upper valve body 36, and the two valve bodies 36 and 37 can be seated simultaneously on the two valve seats 22 and 23, thereby preventing valve leakage.
[0024]
Moreover, since the elastically deformable valve body 36 is fixed to the valve shaft 32, the exhaust pressure F1 applied to the elastically deformable valve body 36 also acts on the valve shaft 32. As a result, the exhaust pressures F1 and F2 acting on the valve shaft 32 via the two valve bodies 36 and 37 are offset, the load on the actuator 30 that drives the valve shaft 32 can be reduced, and the actuator 30 can be downsized.
[0025]
In this case, the opening diameters D1 and D2 of the two valve seats 22 and 23 may be formed to be the same so that the exhaust pressures F1 and F2 acting on the two valve bodies 36 and 37 can be completely canceled. Reference example As described above, the opening diameter D1 of the upper valve seat 22 may be slightly larger than the opening diameter D2 of the lower valve seat 23. In this way, the upward exhaust pressure F1 acting on the upper valve body 36 is slightly larger than the downward exhaust pressure F2 acting on the lower valve body 37, and the self pressure is utilized by utilizing the differential pressure between the exhaust pressures F1 and F2. A sealing effect can be provided.
[0026]
Furthermore, the surrounding wall portion 22a of the valve seat 22 that holds the interval between the two valve seats 22 and 23 and the valve shaft 32 are made of a material having the same thermal expansion coefficient (this book Reference example Therefore, the difference in thermal expansion between the distance between the valve bodies 36 and 37 and the distance between the valve seats 22 and 23 is eliminated. Therefore, the book Reference example Then, the cause of the gap between the valve bodies 36 and 37 and the gap between the valve seats 22 and 23 is only the assembly error, and the deviation between the two is reduced. Thereby, the simultaneous seating of the two valve bodies 36 and 37 becomes more reliable, and the valve leakage prevention performance can be further improved.
[0027]
However, in the present invention, the member (enclosure 22a) that holds the interval between the two valve seats 22 and 23 and the valve shaft 32 may be formed of materials having different thermal expansion coefficients. Since the difference can be absorbed by elastic deformation of the upper valve body 36, the two valve bodies 36 and 37 can be seated simultaneously.
[0028]
The elastically deformable valve body 36 is not limited to the shape shown in FIG. 1, and various shapes are conceivable.
For example, as shown in FIGS. Reference example The elastically deformable valve bodies 38 and 39 of (2) and (3) are both formed in a bellows shape with a thin stainless steel plate, only the lower end portion thereof is fixed to the valve shaft 32, and the bellows portion can be expanded and contracted in the vertical direction. It has become.
[0029]
The elastically deformable valve bodies 36, 38, and 39 shown in FIGS. 1 to 3 are all integrally formed of the same elastic plate material, but the elastic member and the non-elastic member are combined. One elastically deformable valve body may be configured.
[0030]
For example, as shown in FIG. Reference example In the elastically deformable valve body 40 of (4), a ring-shaped seating member 42 seated on the valve seat 22 is fixed to the upper end of an elastically deformable bellows portion 41 formed of a thin stainless plate or the like by welding or the like. A disc-shaped support member 43 is fixed to the lower end of the bellows portion 41 by welding or the like, and the support member 43 is fitted and fixed to the valve shaft 32. In this case, only the bellows portion 41 is elastically deformed, and the seating member 42 and the support member 43 are not deformed. In this way, the portions (the seating member 42 and the support member 43) that require wear resistance and mechanical strength can be formed of a material having excellent wear resistance and mechanical strength, and durability can be improved.
[0031]
By the way, since the elastic force of a valve body becomes a factor which increases the load of the actuator 30, it is preferable that the elastic force of a valve body is small. However, if the entire valve body is made too thin in order to reduce the elastic force of the valve body, the durability of the valve body will decrease, and the seating surface of the valve body will wear due to repeated collisions between the valve body and the valve seat. When this happens, a hole is made in the seating surface of the valve body and valve leakage is likely to occur.
[0032]
As a countermeasure, it is shown in FIG. Of the present invention Embodiment ( 1 The elastically deformable valve body 45 uses a plate-shaped plate spring 46 formed in a leaf spring shape, and a plate-shaped metal thin film 47 that can be easily deformed is bonded to the lower surface of the plate spring 46, thereby The opening 48 of the leaf spring 46 is closed with a metal thin film 47. The leaf spring 46 has a central fitting portion 46a fitted on the valve shaft and an outer peripheral seating surface portion 46b formed in an annular shape, and a plurality of arm portions between the fitting portion 46a and the seating surface portion 46b. 46c is formed at an equal pitch. Each arm portion 46c may be formed radially (straight), but if each arm portion 46c is elongated as shown in FIG. 5, each arm portion 46c is easily elastically deformed. .
[0033]
In this way, the valve body 45 having an appropriate elastic force is formed by extending a leaf spring having an appropriate thickness on the seating surface portion 46b and the fixing portion 46a, which are parts requiring wear resistance and mechanical strength. It is possible to prevent the opening of the valve body 45 due to wear of the valve body 45 while reducing the load on the actuator, and to achieve both reduction of the load and improvement of the durability of the valve body 45.
[0034]
On the other hand, the embodiment shown in FIG. 2 The elastically deformable valve body 49 uses a plate-shaped plate spring 50 formed radially, and a plate-shaped metal thin film 51 that is easily deformed is bonded to the lower surface of the plate spring 50, whereby the plate spring 50 slits 52 (openings) are closed with a metal thin film 51. Even in this case, it is possible to achieve both the reduction of the load on the actuator and the improvement of the durability of the valve body 49.
[0035]
The above embodiment ( 1 ), ( 2 ) May be used for the EGR valve of FIG. 1, and the embodiment shown in FIG. 3 (FIG. 7 shows a configuration example of an EGR valve using the valve body 45 of FIG. 5).
[0036]
The valve housing 60 of the EGR valve has a cylindrical intake passage 61, which is connected to an intake pipe (not shown) of the internal combustion engine, and intake air flowing through the intake pipe is taken into the intake passage. It flows through 61 to the throttle valve (not shown) side. An EGR gas inflow chamber 62 is formed below the intake passage 61 of the valve housing 60, and EGR gas flowing through an EGR pipe (not shown) flows into the side wall of the EGR gas inflow chamber 62. An inflow port 63 is formed, and valve seats 64 and 65 are provided on the upper surface and the lower surface of the EGR gas inflow chamber 62 so as to face each other vertically.
[0037]
The upper valve seat 64 is formed integrally with the valve housing 60, and the lower valve seat 65 is formed of stainless steel or the like, and is fixed to the lower surface of the EGR gas inflow chamber 62. An opening of the upper valve seat 64 communicates with the intake passage 61, and a windproof hood portion that prevents the wind pressure of the intake air flowing through the intake passage 61 from acting on the opening of the valve seat 64 is provided above the valve seat 64. 66 is formed. The opening of the lower valve seat 65 is connected to an EGR gas inlet (not shown) of the intake pipe via an EGR gas passage 67 formed in the lower part of the valve housing 60. Therefore, the EGR gas that has passed through the openings of the two valve seats 64 and 65 flows into the intake pipe.
[0038]
Two valve bodies 45 and 37 are fixed to the valve shaft 32 passing through the two valve seats 64 and 65. The drive system of the valve shaft 32 has the same configuration as that in FIG. 1, and the same reference numerals as those in FIG. The upper elastically deformable valve body 45 may be any valve body of the above-described embodiments.
[0039]
On the other hand, the embodiment shown in FIG. 4 ) Is an embodiment shown in FIG. 7 except for an elastically deformable valve body (hereinafter referred to as “elastic valve body”) 71. 3 ). The elastic valve body 71 is configured by sandwiching a central portion of a plate-shaped leaf spring 72 formed of an elastic thin plate such as a stainless thin plate with two circular center plates 73 formed of a rigid plate such as an iron plate. It is a thing. The elastic valve body 71 is inserted into the valve shaft 32 from below, and is clamped and fixed between a sleeve 74 press-fitted below and the stepped portion 32 a of the valve shaft 32. Thereby, the center plate 73 is fixed to the valve shaft 32 and becomes an “inelastic portion”. On the other hand, a portion of the leaf spring 72 that protrudes outward from the center plate 73 becomes an “elastic portion” supported by the “non-elastic portion” and can be elastically deformed in the vertical direction.
[0040]
In this case, the pressure receiving area (projected area) of the center plate 73, which is the effective pressure receiving area of the elastic valve element 71, is the pressure receiving pressure of the other valve element (hereinafter referred to as “rigid valve element”) 37 fixed to the lower end of the valve shaft 32. It is formed approximately the same as the area. When both the pressure receiving surface (opening portion of the valve seat 65) of the center plate 73 and the rigid valve element 37 are circular, the diameters D1 and D2 of both may be formed substantially the same. Other configurations are the same as those shown in FIG. 3 ), The same reference numerals as in FIG.
[0041]
As shown in FIG. 8, in the state where the two valve bodies 71 and 37 are seated on the valve seats 64 and 65, the following loads due to the exhaust pressure are applied to the valve bodies 71 and 37, respectively.
The load applied to the elastic valve element 71 side is the pressure receiving area of the center plate 73 which is the effective pressure receiving area of the elastic valve element 71 x the exhaust pressure.
On the other hand, the load applied to the rigid valve element 37 side is the pressure receiving area of the rigid valve element 37 x the exhaust pressure.
[0042]
In this case, since the pressure receiving area of the center plate 73 is formed substantially the same as the pressure receiving area of the rigid valve element 37, the load applied to the elastic valve element 71 side and the load applied to the rigid valve element 37 side are substantially the same. Will be in a balanced state. Therefore, even when the exhaust pressure becomes high, the balance of the force applied to the valve shaft 32 from both valve bodies 73 and 37 can be maintained, and the valve leakage due to the floating of the rigid valve body 37 can be reduced. In addition, since the leaf spring 72 on the outer peripheral portion of the elastic valve body 73 can be elastically deformed, the two valve bodies 73 and 37 can be seated simultaneously as in the above embodiments.
[0043]
The inventor described the above embodiment ( 4 Since the test which evaluates the valve-leakage prevention performance of the elastic valve body 71 used in) was performed, the test result is shown in FIG. In this test, the diameter D1 of the center plate 73 of the elastic valve body 71 was 15 mm, the opening diameter D3 of the valve seat 64 was 18 mm, and the diameter D2 of the pressure receiving surface of the rigid valve body 37 was 16 mm. In this structure, as shown in FIG. 9A, the exhaust pressure is 2 kgf / cm, which is the upper limit pressure. ² Even when the pressure was increased, the valve leakage could be suppressed to the target value of 8 liters / minute or less.
[0044]
On the other hand, in the comparative example shown in FIG. 9B, an elastic valve element constituted by bonding a metal thin film to a spiral leaf spring was used. Even in the comparative example, the exhaust pressure is 1.4 kgf / cm. ² In the following region, the valve leakage was the target value of 8 liters / minute or less, but the exhaust pressure was about 1.4 kgf / cm. ² Exceeding the value, the valve leakage increased rapidly and the target value could not be satisfied.
[0045]
From the above test results, the embodiment ( 4 ), It was confirmed that high valve leakage prevention performance can be maintained even at high pressure.
In the above embodiments, the upper valve body is formed to be elastically deformable, but the lower valve body may be formed to be elastically deformable.
[0046]
Embodiment shown in FIGS. 10 and 11 ( 5 ), The rigid valve element 37 is disposed above and the elastic valve element 81 is disposed below. The elastic valve body 81 is formed in a dish shape with an elastic plate material having heat resistance and wear resistance, such as a thin stainless steel plate, and is fixed to the valve shaft 32 with a sleeve 82. An annular valve seat (hereinafter referred to as “elastic valve seat”) 83 on which the elastic valve body 81 is seated is formed of an elastic plate material having heat resistance and wear resistance such as a thin stainless steel plate so as to be elastically deformable. The opening area (opening diameter) of the elastic valve seat 83 is set to be substantially the same as the opening area (opening diameter) of the upper valve seat 64. The other configuration is the embodiment shown in FIG. 3 ), The same reference numerals as in FIG.
[0047]
Next, this embodiment ( 5 The valve closing characteristics and valve opening characteristics of the EGR valve will be described. Even when the elastic valve element 81 is elastically deformed in the valve opening direction (downward) by the high exhaust pressure when the valve is closed, the elastic valve seat 83 is also elastically deformed in the valve opening direction by the high exhaust pressure. Thus, the contact state between the elastic valve body 81 and the elastic valve seat 83 is maintained. Thereby, even when the exhaust pressure becomes high, valve leakage is effectively prevented and the valve closing performance is improved.
[0048]
The loads applied to the valve shaft 32 (both valve bodies 37 and 81) in the closed state include the following three types of loads Fs, Fv and Fn.
(1) The load Fs in the valve closing direction by the spring 35 that biases the valve shaft 32 in the valve closing direction (upward).
(2) Load Fv in the valve closing direction generated by the difference in effective pressure receiving area between the rigid valve element 37 and the elastic valve element 81 and the exhaust pressure (difference in load due to the exhaust pressure acting on both valve elements 37 and 81)
(3) The valve opening direction load Fn acting on the elastic valve body 83 from the elastic valve seat 83 by elastically deforming the elastic valve seat 83 in the valve opening direction by the exhaust pressure.
[0049]
Here, in order to suppress valve leakage when the valve is closed, it is necessary to set the load in the valve closing direction (Fs + Fv) to be larger than the load Fn in the valve opening direction as shown in the following equation (1). There is.
(1) Fs + Fv> Fn (Conditions for suppressing valve leakage)
[0050]
Assuming that the effective pressure receiving area of the lower valve element 81 is larger than the effective pressure receiving area of the upper rigid valve element 37, the load Fv due to the exhaust pressure in the above equation (1) is a negative value (that is, in the valve opening direction). Load), but this embodiment ( 5 ), When the lower valve body 81 is an elastic valve body and the opening areas (opening diameters) of both valve seats 64 and 83 are set substantially the same, the effective pressure receiving area of the elastic valve body 81 is a rigid valve. The effective pressure receiving area of the body 37 becomes smaller, and the load Fv due to the exhaust pressure becomes a positive value (that is, the load in the valve closing direction).
[0051]
In this case, as shown in FIG. 11, the load Fs in the valve closing direction by the spring 35 is constant even when the exhaust pressure changes, but the load Fv in the valve closing direction by the exhaust pressure increases as the exhaust pressure increases. Thus, the total load (Fs + Fv) in the valve closing direction is increased. If the valve seat 83 has a rigid structure, the load Fn in the valve opening direction is zero. Therefore, if the total load (Fs + Fv) in the valve closing direction increases due to an increase in exhaust pressure, the valve seat 83 opens from the valve closed state. Since the driving force of the actuator required for valve operation increases, the valve opening characteristics (relationship between the driving force and the valve body lift amount) change due to changes in exhaust pressure, and stable valve opening characteristics are obtained. Absent.
[0052]
In contrast, this embodiment ( 5 ), Since the elastic valve seat 83 is used as the valve seat on which the elastic valve body 81 is seated, the elastic valve seat 83 is elastically deformed in the valve opening direction by the exhaust pressure. A load Fn in the valve opening direction acts on 83. Since the load Fn in the valve opening direction increases as the exhaust pressure increases as shown in FIG. 11, the increase in the load Fv in the valve closing direction due to the exhaust pressure is almost offset by the increase in the load Fn in the valve opening direction. Then, the following equation (2) is established.
[0053]
(2) Fv−Fn = Δf = almost constant (conditions for improving valve opening characteristics)
If equation (2) is satisfied, the total load value (Fv−Fn) due to the exhaust pressure becomes substantially constant even when the exhaust pressure changes, and the drive required for opening the valve from the closed state is required. The force (Fs + Fv-Fn) is almost constant, and the valve opening characteristics (relationship between the driving force and the valve lift) are not affected by changes in the exhaust pressure, and stable valve opening characteristics are obtained and highly accurate EGR. Control becomes possible.
[0054]
Thus, this embodiment ( 5 ), The relationship between the above formulas (1) and (2) is established at the same time. Therefore, both the suppression of valve leakage during valve closing and the improvement of the valve opening characteristics in the total exhaust pressure fluctuation range (full engine load range). Can be realized. In addition, since both the valve body 81 and the valve seat 83 can be elastically deformed, it is easy to seat the two valve bodies 81 and 37 at the same time as in the above embodiments.
[Brief description of the drawings]
FIG. 1 shows the present invention. Reference examples related to (1) Longitudinal sectional view showing the EGR valve
FIG. 2 Reference examples related to (2) Longitudinal sectional view showing the structure of valve body and valve seat
FIG. 3 Reference examples related to (3) Longitudinal sectional view showing the structure of valve body and valve seat
FIG. 4 The present invention Reference examples related to (4) Longitudinal sectional view showing the structure of valve body and valve seat
FIG. 5 shows an embodiment of the present invention ( 1 (A) is a plan view of an elastically deformable valve body, (b) is a cross-sectional view taken along line AA of (a), and (c) is a plan view of a metal thin film.
FIG. 6 shows an embodiment of the present invention ( 2 (A) is a longitudinal sectional view of an elastically deformable valve body, (b) is a plan view of a radial leaf spring, (c) is an EE sectional view of (b), and (d) is a metal Plan view of thin film, (e) is FF cross section of (d)
FIG. 7 shows an embodiment of the present invention ( 3 ) Longitudinal sectional view showing EGR valve
FIG. 8 shows an embodiment ( 4 ) Is a longitudinal sectional view showing the structure of the main part of the EGR valve
FIG. 9A is an embodiment ( 4 The figure which shows the valve leakage characteristic of (), (b) is the figure which shows the valve leakage characteristic of the comparative example
FIG. 10 shows an embodiment of the present invention ( 5 ) Is a longitudinal sectional view showing the structure of the main part of the EGR valve
FIG. 11 is a graph showing the relationship between loads Fs, Fv, Fn applied to the valve shaft and exhaust pressure.
FIG. 12 is a longitudinal sectional view showing a conventional double seat valve type EGR valve.
FIG. 13 is a longitudinal sectional view showing a conventional improved double seat valve type EGR valve.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 21 ... Valve housing, 22, 23 ... Valve seat, 25 ... Inflow port, 26 ... Outflow port, 27 ... EGR gas passage, 30 ... Actuator, 31 ... Plunger, 32 ... Valve shaft, 33 ... Bearing, 35 ... Spring, 36 -40, 41 ... bellows part, 42 ... seating member, 45 ... valve body, 46 ... leaf spring, 47 ... metal thin film (member that can be easily deformed), 48 ... opening, 46b ... seating surface part, 49 ... valve body, 50 ... Plate spring, 51 ... Metal thin film (easy deformable member), 52 ... Slit (opening), 60 ... Valve housing, 61 ... Intake passage, 62 ... EGR gas inflow chamber, 63 ... Inlet port, 64, 65 ... Valve Seat, 67 ... EGR gas passage, 71 ... Elastic valve element (elastically deformable valve element), 72 ... Plate Right, 73 ... Center play G 81: elastic valve body, 83: elastic valve seat.

Claims

Two valve seats are arranged facing each other in the valve housing, one valve shaft is passed through the center of both valve seats, two valve bodies are fixed to the valve shafts, and the valve shafts are arranged in the axial direction. In the exhaust gas recirculation control valve that seats or separates each valve body from each valve seat by
At least a part of one valve body is configured to be elastically deformable, and the elastically deformable valve body uses a leaf spring formed in a leaf spring shape or a radial shape, and an opening of the leaf spring is easily deformable. An exhaust gas recirculation control valve, characterized in that it is closed at the end.

2. The exhaust gas recirculation control valve according to claim 1, wherein a member that holds an interval between the two valve seats and the valve shaft are formed of a material having an equivalent thermal expansion coefficient.