JP2007285950A

JP2007285950A - Heating resistor type air flowmeter

Info

Publication number: JP2007285950A
Application number: JP2006115136A
Authority: JP
Inventors: Chihiro Kobayashi; 千尋小林; Shinya Igarashi; 信弥五十嵐; Yukio Kato; 幸夫加藤; Kiyotomo Ide; 聖智井手; Takeshi Morino; 毅森野; Hiroki Okamoto; 裕樹岡本
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 2006-04-19
Filing date: 2006-04-19
Publication date: 2007-11-01

Abstract

<P>PROBLEM TO BE SOLVED: To minimize a property change of a heating resistor type air flowmeter, by reducing adhesion of oil components generated, especially by PCV, EGR, etc. aimed at securing measurement accuracy of the flowmeter and reducing the characteristic changes due to dust adhesion. <P>SOLUTION: The heating temperature of a heating resistor for suction air is set at 230-290°C. Thus, even when oil is dispersed, the oil evaporates in short time. It is also possible to guarantee long-term accuracy, in terms of the reliability of an ON/OFF repeating test or the like. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は自動車用の内燃機関に吸入される空気流量を測定するために用いられる発熱抵抗体式空気流量測定装置に関し、特にディーゼル車において吸気管内に空気と一緒に吸入される塵等による空気流量計測誤差の低減に関する発明である。 BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating resistor type air flow rate measuring device used for measuring an air flow rate sucked into an internal combustion engine for automobiles, and more particularly to measuring an air flow rate by dust or the like sucked together with air into an intake pipe in a diesel vehicle. This invention relates to error reduction.

内燃機関用の流量測定技術としては発熱抵抗体式空気流量測定装置が知られている。これは発熱抵抗体の奪われる熱量が流入流量に対し相関関係があることを利用したものであり、エンジンの燃焼制御で必要となる質量流量を直接測定出来るため特に自動車の空燃比制御用の流量計として広く使われている。 A heating resistor type air flow rate measuring device is known as a flow rate measuring technique for an internal combustion engine. This is based on the fact that the amount of heat taken away by the heating resistor has a correlation with the inflow flow rate, and it is possible to directly measure the mass flow rate required for engine combustion control. Widely used as a total.

塵による特性変化を抑えるための手法として特許文献１では、発熱抵抗体の上流側に迂回部を設け、遠心力により塵と空気を分離させる通路が公知技術として知られている。 As a technique for suppressing characteristic changes due to dust, Patent Document 1 discloses a known technique in which a bypass is provided on the upstream side of the heating resistor and dust and air are separated by centrifugal force.

また、本発明の構成に近い公知技術として特許文献２がある。これは、発熱抵抗体の表面に接触した液滴が膜沸騰で蒸発消滅する温度かそれ以上の温度に設定するものであり、具体的な発熱抵抗体の加熱温度として３００℃以上との記載がある。 Moreover, there is Patent Document 2 as a known technique close to the configuration of the present invention. This is set to a temperature at which the droplet contacting the surface of the heating resistor evaporates or disappears due to film boiling or higher, and a specific heating temperature of 300 ° C. is described as the heating temperature of the heating resistor. is there.

特開２００４−３７１３１号公報JP 2004-37131 A 特開２００３−３３７０５６号公報JP 2003-337056 A

発熱抵抗体式空気流量測定装置は車輌の吸気ダクトの一部に装着され、吸入空気流量を測定する役割を持つ。車輌の吸気ダクトは通常、アクセルペダルに連動して吸入空気流量が増減し、アクセルの踏み込み量が増加するとダクト内へ吸入される空気流量も増加する。吸入空気量が増加すると空気だけでなく、空気中に浮遊するダストや、前を走行する車輌のタイヤでまき上げられた塵等も空気と一緒にエンジンに吸入されてしまう。発熱抵抗体は加熱されているため、一般的には塵は付着し難いとされているが、塵の種類と飛来量によっては経年的には少しずつではあるが塵が付着してしまう。発熱抵抗体式空気流量測定装置の流量検出部である発熱抵抗体部に塵が付着すると、塵がコーティング状態となり、発熱抵抗体からの空気への放熱量が初期状態と比べて変化してしまう。この放熱量の変化量が発熱抵抗体式空気流量測定装置の計測誤差となってしまう。 The heating resistor type air flow measuring device is attached to a part of the intake duct of the vehicle and has a role of measuring the intake air flow rate. In the intake duct of a vehicle, the intake air flow rate usually increases or decreases in conjunction with the accelerator pedal, and when the accelerator depression amount increases, the air flow rate sucked into the duct also increases. When the amount of intake air increases, not only air but also dust floating in the air, dust blown up by the tire of the vehicle traveling ahead, and the like are sucked into the engine together with the air. Since the heating resistor is heated, it is generally considered that dust does not easily adhere to it. However, depending on the type of dust and the amount of flying dust, dust adheres little by little over time. When dust adheres to the heating resistor part, which is a flow rate detection unit of the heating resistor type air flow measuring device, the dust enters a coating state, and the heat radiation from the heating resistor to the air changes compared to the initial state. The amount of change in the heat dissipation amount becomes a measurement error of the heating resistor type air flow rate measuring device.

塵等はエアクリーナ内のエアフィルタで捕獲する事は可能であるが、塵の大きさによってはエアフィルタを通過してエンジン内へ入り込んでしまう。エアフィルタで捕獲できる塵の粒子径は一般的には約１０μｍ程度であるとされており、それ以下の粒子径では容易にエアフィルタを通過してしまう。また、エアクリーナの外気以外にも特にディーゼルエンジンにおいては燃焼時に発生するカーボン等も発熱抵抗体への付着部質の一つである。更に、エンジンの吸気ダクト内には吸入空気だけでなくＰＣＶ（Positive Crankcase
Ventilation：ブローバイガス還流装置）や、ＥＧＲ（Exhaust Gas Recirculation：排出ガス再循環システム）等から排出されるオイル成分も存在する。このオイル成分が存在するとオイル成分が粘着成分となり、前記した塵やカーボン等を付着し易くさせてしまう。 Dust and the like can be captured by the air filter in the air cleaner, but depending on the size of the dust, the dust passes through the air filter and enters the engine. The particle size of the dust that can be captured by the air filter is generally about 10 μm, and if the particle size is smaller than that, it easily passes through the air filter. In addition to the outside air of the air cleaner, especially in diesel engines, carbon generated during combustion is one of the adhesion parts to the heating resistor. Furthermore, not only the intake air but also PCV (Positive Crankcase) is placed in the intake duct of the engine.
There are also oil components discharged from Ventilation (blow-by gas recirculation device), EGR (Exhaust Gas Recirculation) and the like. When this oil component is present, the oil component becomes an adhesive component, which makes it easy to attach the dust, carbon, and the like.

特に今後、排ガス規制の進むディーゼル車においては、燃焼を最適に制御するために空気流量の高精度計測が必須となってきている。このため、発熱抵抗体式空気流量測定装置の塵付着による計測誤差低減のために、発熱抵抗体へのオイル成分の付着を防止する必要性がある。 In particular, in the future, in diesel vehicles that are subject to exhaust gas regulations, high-precision measurement of the air flow rate is indispensable in order to optimally control combustion. For this reason, it is necessary to prevent the oil component from adhering to the heating resistor in order to reduce measurement errors due to dust adhesion in the heating resistor type air flow measuring device.

本課題に対応するため、本発明では発熱抵抗体の加熱温度に着目した。つまり、オイルが発熱抵抗体に付着し難い温度に設定する事が解決方法の一つとなる。加熱温度が低いとオイルは発熱抵抗体に残ったままとなり、そこへ塵が飛来するとオイルが塵を簡単にトラップさせてしまい発熱抵抗体の計測誤差を助長させてしまう。そのため、発熱抵抗体を高温に加熱させてオイルが飛来した際に瞬時に蒸発させて発熱抵抗体への付着を防止すれば発熱抵抗体への塵の付着を大幅に抑える事が可能である。 In order to address this problem, the present invention focuses on the heating temperature of the heating resistor. That is, one solution is to set the temperature at which oil does not easily adhere to the heating resistor. If the heating temperature is low, the oil remains in the heating resistor, and if dust comes into it, the oil easily traps the dust, which promotes the measurement error of the heating resistor. For this reason, if the heating resistor is heated to a high temperature and oil is instantly evaporated to prevent the oil from adhering to the heating resistor, adhesion of dust to the heating resistor can be greatly suppressed.

但し、発熱抵抗体をむやみに高温に加熱する事は発熱抵抗体の信頼性を低くする可能性が高く、充分な検討が必要となる。例えば薄膜抵抗体を使った発熱抵抗体では薄膜の基体への密着力や、薄膜同士の密着力の信頼性は温度により大きく左右される。つまり、加熱温度が低いと充分な密着力が得られるが、加熱温度が高くなると短時間で密着力が弱まり、抵抗値が変化してしまう。このため、長期間に渡り使用する際の薄膜の発熱抵抗体では加熱温度は１００℃〜１５０℃が限界でありそれ以上の加熱温度では抵抗値が短時間に経時変化してしまうのである。 However, excessively heating the heating resistor to a high temperature has a high possibility of reducing the reliability of the heating resistor, and sufficient study is required. For example, in a heating resistor using a thin film resistor, the adhesion strength of the thin film to the substrate and the reliability of the adhesion strength between the thin films are greatly affected by temperature. That is, when the heating temperature is low, sufficient adhesion can be obtained, but when the heating temperature is increased, the adhesion decreases in a short time and the resistance value changes. For this reason, the heating temperature is limited to 100 ° C. to 150 ° C. for a thin film heating resistor when used for a long period of time, and the resistance value changes with time in a short time at higher heating temperatures.

これに対して、例えばアルミナ等により造られたボビン状の基体に白金線を巻線し、更に腐食防止のためにガラス材等により白金線をコートした発熱抵抗体では加熱温度を薄膜と比べ容易に上げる事が可能である。これは、白金線では前記したような密着力の低下が無いためであり、かなりの温度まで抵抗体の温度を上げる事が可能となる。 In contrast, a heating resistor with a platinum wire wound around a bobbin-shaped substrate made of alumina or the like and coated with a platinum wire with a glass material to prevent corrosion is easier than a thin film. Can be raised. This is because the platinum wire does not have a decrease in adhesion as described above, and the temperature of the resistor can be increased to a considerable temperature.

しかし、発熱抵抗体の放熱量の変化は抵抗値だけの変化では無い。一例をあげれば前記したガラス材等のコートの劣化も発熱抵抗体の放熱量の経時劣化の原因となる。例えば、発熱抵抗体への電源通電のＯＮ／ＯＦＦを繰り返すと、ガラスは膨張／収縮を繰り返し、ガラス表面に亀裂等を生じさせる原因となる。このようなガラス表面の亀裂は発熱抵抗体の放熱表面積を変えてしまうため、このような場合も発熱抵抗体の放熱量は変化してしまい、その結果、出力特性が経時劣化をしてしまうのである。一般的には自動車用の空気流量計の場合には、自動車の車両としての寿命で考えるとＯＮ／ＯＦＦ回数は数万回の耐久性が必要となる。 However, the change in the heat radiation amount of the heating resistor is not only a change in the resistance value. As an example, the deterioration of the coating of the above-described glass material or the like also causes deterioration with time of the heat radiation amount of the heating resistor. For example, when ON / OFF of power supply to the heating resistor is repeated, the glass repeatedly expands / contracts, causing a crack or the like on the glass surface. Since such a glass surface crack changes the heat dissipation surface area of the heating resistor, the heat dissipation amount of the heating resistor also changes in this case, and as a result, the output characteristics deteriorate over time. is there. In general, in the case of an air flow meter for an automobile, the durability of the ON / OFF times of tens of thousands of times is required in view of the life of the automobile.

よって、発熱抵抗体式空気流量測定装置の経時劣化防止のためには、上記したような、アルミナ等により造られたボビン状の基体に白金線を巻線し、更に腐食防止のためにガラス材等により白金線をコートした発熱抵抗体の加熱温度を信頼性に影響を及ぼさない程度まで高温にする事が必要となる。 Therefore, in order to prevent deterioration over time of the heating resistor type air flow measuring device, a platinum wire is wound around a bobbin-shaped substrate made of alumina or the like as described above, and further glass material is used to prevent corrosion. Therefore, it is necessary to raise the heating temperature of the heating resistor coated with the platinum wire to such an extent that the reliability is not affected.

現在、地球温暖化等、世界的に環境に関して目が向けられている。特に、低燃費ではあるが排ガスの面で敬遠されているディーゼルエンジンで排ガス規制に対応するためには、高精度な空気流量計測を長期間に渡って保つことが必須な技術課題である。前記の構成により、発熱抵抗体へのオイル成分の付着を大幅に低減する事が可能となり、発熱抵抗体式空気流量測定装置の経年による特性変化量を低減する事が可能となる。これにより、長期間に渡り吸入空気量計測の高精度が可能となり、低燃費でありながら且つ、排出ガスのクリーンなエンジン制御システムを有するディーゼル車を市場に送り込むことが可能となる。 At present, attention is focused on the global environment such as global warming. In particular, maintaining a highly accurate air flow measurement over a long period of time is an essential technical issue in order to comply with exhaust gas regulations in a diesel engine that has low fuel consumption but is avoided in terms of exhaust gas. With the above configuration, it is possible to significantly reduce the adhesion of oil components to the heating resistor, and it is possible to reduce the amount of change in characteristics over time of the heating resistor type air flow measuring device. This makes it possible to measure the intake air amount over a long period of time, and to send a diesel vehicle having a low engine fuel consumption and a clean engine control system to the market.

本発明は自動車用であり、特にディーゼル車に用いられエンジンに吸入される空気流量を測定するために用いられる発熱抵抗体式空気流量測定装置において、長期間に渡り吸入空気量を高精度に保つ発熱抵抗体式空気流量計測方法として考案したものである。 The present invention is for automobiles, and particularly in a heating resistor type air flow measuring device used for measuring the flow rate of air sucked into an engine used in a diesel vehicle, heat generation for maintaining the intake air amount with high accuracy over a long period of time. It was devised as a resistor type air flow measurement method.

本発明の実施例を以下の図面に従い詳細に説明する。 Embodiments of the present invention will be described in detail with reference to the following drawings.

まず、最初に発熱抵抗体式空気流量測定装置の動作原理について説明する。図２は発熱抵抗体式空気流量測定装置の概略構成回路図である。発熱抵抗体式空気流量測定装置の駆動回路１は大きく分けてブリッジ回路とフィードバック回路から成り立っている。吸入空気流量測定を行うための発熱抵抗体３ＲＨ，吸入空気温度を補償するための感温抵抗体
４ＲＣ及びＲ１０，Ｒ１１でブリッジ回路を組み、オペアンプＯＰ１を使いフィードバックをかけながら発熱抵抗体３ＲＨと感温抵抗体４ＲＣの間に一定温度差を保つように発熱抵抗体３ＲＨに加熱電流Ｉｈを流して空気流量に応じた出力信号Ｖ２を出力する。つまり流速の速い場合には発熱抵抗体３ＲＨから奪われる熱量が多いため加熱電流Ｉｈを多く流す。これに対して流速の遅い場合には発熱抵抗体Ｒｈから奪われる熱量が少ないため加熱電流も少なくてすむのである。 First, the operation principle of the heating resistor type air flow measuring device will be described. FIG. 2 is a schematic circuit diagram of a heating resistor type air flow rate measuring device. The drive circuit 1 of the heating resistor type air flow measuring device is roughly divided into a bridge circuit and a feedback circuit. The heating resistor 3RH for measuring the intake air flow rate and the temperature sensitive resistors 4RC, R10, and R11 for compensating the intake air temperature are combined to form a bridge circuit, and the feedback is made using the operational amplifier OP1 to feel the heating resistor 3RH. A heating current Ih is supplied to the heating resistor 3RH so as to maintain a constant temperature difference between the temperature resistors 4RC, and an output signal V2 corresponding to the air flow rate is output. That is, when the flow rate is high, a large amount of heat is taken from the heating resistor 3RH, so that a large amount of heating current Ih flows. On the other hand, when the flow rate is low, the amount of heat taken away from the heating resistor Rh is small, so that the heating current can be reduced.

図８は発熱抵抗式空気流量計の一例を示す横断面であり、図９はその上流（左側）から見た外観図である。 FIG. 8 is a cross-sectional view showing an example of a heating resistance type air flow meter, and FIG. 9 is an external view as viewed from the upstream side (left side).

発熱抵抗体式空気流量測定装置の構成部品としては駆動回路を構成する回路基板２を内蔵するハウジング部材１及び非導電性部材により形成される副空気通路構成部材１０等があり、副空気通路構成部材１０の中には空気流量検出のための発熱抵抗体３，吸入空気温度を補償するための感温抵抗体４が導電性部材により構成された支持体５を介して回路基板２と電気的に接続されるように配置され、ハウジング，回路基板，副空気通路，発熱抵抗体，感温抵抗体等、これらを発熱抵抗体式空気流量測定装置の一体のモジュールとして構成されている。また、吸気管路を構成する主空気構成部材２０の壁面には穴２５があけられており、この穴２５より前記発熱抵抗体式空気流量測定装置の副空気通路部分を外部より挿入して副空気通路構成部材の壁面とハウジング部材１とをネジ７等で機械的強度を保つように固定されている。また、副空気通路構成部材１０と主空気通路構成部材の間にシール材６を取り付けて、吸気管内外との気密性を保っている。 Components of the heating resistor type air flow rate measuring device include a housing member 1 containing a circuit board 2 constituting a driving circuit, a sub air passage constituent member 10 formed by a non-conductive member, and the like. 10, a heating resistor 3 for detecting the air flow rate 3 and a temperature sensitive resistor 4 for compensating the intake air temperature are electrically connected to the circuit board 2 via a support 5 made of a conductive member. The housing, the circuit board, the auxiliary air passage, the heating resistor, the temperature sensing resistor, and the like are arranged as an integrated module of the heating resistor type air flow measuring device. Also, a hole 25 is formed in the wall surface of the main air constituting member 20 constituting the intake pipe, and a sub air passage portion of the heating resistor type air flow measuring device is inserted from the hole 25 from the outside to obtain a sub air. The wall surface of the passage constituting member and the housing member 1 are fixed with screws 7 or the like so as to maintain mechanical strength. Moreover, the sealing material 6 is attached between the auxiliary air passage constituting member 10 and the main air passage constituting member, and the airtightness between the inside and outside of the intake pipe is maintained.

副空気通路内に設置される発熱抵抗体３ＲＨは例えば図３のような形状であり、アルミナ等の耐熱絶縁材で構成された筒状のボビンに白金線等を巻線したり、或いは白金膜を蒸着し、両端を導電性部材により構成されるリード材と支持材を介して、電気的導通を取ると同時に機械的な固定を行う。また、白金線等の上にはガラス材等によりコーティングを施し、耐腐食性の向上を図ると同時に、表面の凹凸を無くして塵等の異物の付着を最小限に抑える工夫が取られている。 The heating resistor 3RH installed in the auxiliary air passage has a shape as shown in FIG. 3, for example, a platinum bobbin wound around a cylindrical bobbin made of a heat-resistant insulating material such as alumina, or a platinum film. Is vapor-deposited, and both ends are electrically connected through a lead material and a support material composed of a conductive member, and at the same time, mechanical fixing is performed. In addition, the platinum wire is coated with a glass material, etc. to improve the corrosion resistance, and at the same time, the surface unevenness is eliminated to minimize the adhesion of foreign matters such as dust. .

次に発熱抵抗体の汚損時の特性変化について説明する。図３に示したようなボビン状の発熱抵抗体の場合には、空気の当たる正面が最も発熱が促進され、特に高流速時にはこの正面での発熱が支配的となる。一方で図４に示すＡ点では空気の流れがよどんでしまうため、空気の流れによるせん断力が最も弱い位置であり、塵が付着し易い場所でもある。つまり、吸入空気中に塵等が入り込み、図示Ａ点に付着するとＡ点を基点としてその周囲にも塵が積もり最終的には三角状の山形に塵が付着してしまう。このため、最も発熱量が多い部分が塵で覆われてしまうため、発熱量が減少してしまい特性変化量としてはマイナスの特性変化を示すのである。これを横軸を流速として、縦軸を特性変化量とすると図１に示すように高流速ほどマイナスとなる右下がりの特性変化を示し、実際の空気量に対して少ない空気量であると検出するのである。このため、内燃機関でこの現象が生じると、実際の空気量に対して、少ない燃料を噴射する事となり空燃比が薄くなり、燃焼温度が高くなって最悪の場合にはエンジンの焼付け等の不具合を起こしてしまうのである。 Next, a change in characteristics when the heating resistor is soiled will be described. In the case of a bobbin-like heating resistor as shown in FIG. 3, heat generation is most promoted on the front surface where the air hits, and heat generation on this front surface becomes dominant particularly at a high flow rate. On the other hand, at point A shown in FIG. 4, since the air flow is stagnant, the shearing force due to the air flow is the weakest position, and it is also a place where dust easily adheres. That is, when dust or the like enters the intake air and adheres to the point A in the figure, dust accumulates around the point A as a base point, and eventually adheres to a triangular mountain shape. For this reason, since the part with the largest amount of heat generation is covered with dust, the amount of heat generation decreases, and the characteristic change amount shows a negative characteristic change. If the horizontal axis is the flow velocity and the vertical axis is the characteristic change amount, as shown in FIG. To do. For this reason, when this phenomenon occurs in an internal combustion engine, less fuel is injected than the actual amount of air, the air-fuel ratio becomes thin, the combustion temperature rises, and in the worst case, problems such as engine burning It will cause.

次に、発熱抵抗体にオイルが付着した際の蒸発時間について図５を使い説明する。図５の横軸は発熱抵抗体の加熱温度、縦軸は発熱抵抗体にオイルを付着させた時の蒸発するまでに要する時間を表したグラフである。オイルは３種類のエンジンオイルを使用して実験を行った。蒸発に要する時間は、発熱抵抗体にオイルを一滴垂らして、発熱抵抗体表面からオイルが蒸発してオイル分が完全に無くなるまでの時間を表している。実際の内燃機関ではオイルは細かなミスト状に飛散してくるため、一滴という量は実際にはかなり多い量ではあるが、今回は蒸発時間の比較のため一滴分のデータを表している。本評価結果より、オイルは低温では蒸発量は非常に少なく、２００℃でも２分以上の時間を要してしまう。これに対して、発熱抵抗体の加熱温度を２５０℃にすると急激に蒸発時間は短くなりオイルはほぼ瞬時に蒸発してしまい、２００℃の時と比べ、１／１０以下の時間で蒸発してしまう。更に、加熱温度を３００℃とすると蒸発時間は更に短くはなるが２００℃→250℃の時ほど急激に蒸発時間が短くなるということはない。本実験結果より発熱抵抗体の加熱温度はおおよそ２３０℃以上であれば蒸発時間に大きな差は無くオイルの付着している時間を大幅に短くする事が可能となるのである。 Next, the evaporation time when oil adheres to the heating resistor will be described with reference to FIG. The horizontal axis of FIG. 5 is a graph showing the heating temperature of the heating resistor, and the vertical axis is the time required to evaporate when oil is attached to the heating resistor. The oil was tested using three types of engine oil. The time required for evaporation represents the time from when one drop of oil is dropped on the heating resistor until the oil evaporates from the surface of the heating resistor and the oil component is completely eliminated. In an actual internal combustion engine, the oil scatters in a fine mist, so the amount of one drop is actually quite large, but this time represents data for one drop for comparison of evaporation times. From this evaluation result, the amount of evaporation of oil is very small at low temperatures, and it takes 2 minutes or more even at 200 ° C. On the other hand, when the heating temperature of the heating resistor is 250 ° C., the evaporation time is abruptly shortened, and the oil is evaporated almost instantaneously, evaporating in 1/10 or less time compared to 200 ° C. End up. Furthermore, when the heating temperature is 300 ° C., the evaporation time is further shortened, but the evaporation time is not shortened as rapidly as 200 ° C. → 250 ° C. From the results of this experiment, if the heating temperature of the heating resistor is about 230 ° C. or higher, there is no significant difference in the evaporation time, and the time during which the oil is attached can be greatly shortened.

このオイルの付着時間を短くする事は発熱抵抗体式空気流量測定装置の汚損に対して非常に有利になる。つまり、オイルは粘着性があるためオイル成分が発熱抵抗体の表面にオイル成分が残ると、塵やカーボン等の汚損物が付着し易くなってしまう。一度付着物が着いてしまうと、オイル成分が蒸発しても、付着物はそのまま残ってしまうため、前記したような発熱抵抗体の汚損による特性変化が生じ易くなってしまうのである。よって、前記した発熱抵抗体の加熱温度を２３０℃以上に設定する事は発熱抵抗体式空気流量測定装置の汚損性に対して非常に優位に働く事になる。 Shortening the oil adhesion time is very advantageous for the fouling of the heating resistor type air flow measuring device. In other words, since the oil is sticky, if the oil component remains on the surface of the heating resistor, a fouling substance such as dust or carbon is likely to adhere. Once the adhering material has adhered, the adhering material remains as it is even if the oil component evaporates, so that the characteristic change due to the fouling of the heating resistor is likely to occur. Therefore, setting the heating temperature of the heating resistor to 230 ° C. or more works very favorably on the fouling property of the heating resistor type air flow measuring device.

次に、発熱抵抗体への通電ＯＮ／ＯＦＦを繰り返し与えた時の発熱抵抗体の特性変化について説明する。自動車用の発熱抵抗体式空気流量測定装置は自動車の寿命に応じた製品寿命を必要とされ、１５年程度の製品寿命を要求される。よって、例えばエンジンのＯＮ／ＯＦＦを２０回／日程度行うと仮定すると、２０回／日×３６５日／年×１５年＝
１０９５００回となり、約１１万回ＯＮ／ＯＦＦが繰り返される事になる。発熱抵抗体は前記したとおり、ボビン状の基体に白金を巻線し、それをガラス等でコートしている。このため、発熱抵抗体への通電を繰り返すと、発熱抵抗体が加熱と冷却を繰り返すため、その結果、発熱抵抗体が膨張／収縮を繰り返す事になる。この膨張／収縮は発熱抵抗体の構造体の耐久性の悪化要因となる。特にコート材として使うガラスへダメージを大きく与えてしまい、場合によってはガラスに亀裂等が生じてしまう事がある。このガラスへ亀裂が生じてしまうと亀裂により発熱抵抗体の放熱表面積が変化してしまい、発熱抵抗体式空気流量測定装置の特性変化の原因となってしまうのである。この膨張／収縮は発熱抵抗体の加熱温度が高いほどこの膨張と収縮の差は大きくなり、加熱温度を高くする際にはこの
ＯＮ／ＯＦＦ繰り返しによる特性変化に注意が必要となる。 Next, the characteristic change of the heating resistor when the energization ON / OFF is repeatedly applied to the heating resistor will be described. The heating resistor type air flow measuring device for automobiles requires a product life corresponding to the life of the automobile, and a product life of about 15 years is required. Therefore, for example, assuming that the engine is turned ON / OFF about 20 times / day, 20 times / day × 365 days / year × 15 years =
109500 times, and ON / OFF is repeated about 110,000 times. As described above, the heating resistor is formed by winding platinum around a bobbin-like substrate and coating it with glass or the like. For this reason, when energization to the heating resistor is repeated, the heating resistor repeats heating and cooling. As a result, the heating resistor repeats expansion / contraction. This expansion / contraction causes deterioration of the durability of the heating resistor structure. In particular, the glass used as the coating material is greatly damaged, and in some cases, the glass may be cracked. If a crack occurs in this glass, the heat dissipation surface area of the heating resistor changes due to the crack, which causes a change in the characteristics of the heating resistor type air flow measuring device. In this expansion / contraction, the difference between the expansion and the contraction increases as the heating temperature of the heating resistor increases. When the heating temperature is increased, it is necessary to pay attention to the characteristic change due to repeated ON / OFF.

図６に示したグラフは、横軸に発熱抵抗体式空気流量測定装置への通電のＯＮ／ＯＦＦを繰り返した回数であり、縦軸は初期値を基準とした発熱抵抗体式空気流量測定装置の特性変化量を表したグラフである。加熱温度を２００℃，２５０℃，３００℃の３つで評価を行った。結果として、発熱抵抗体の加熱温度を高くすると、繰り返し回数に応じた特性変化量が大きくなる事を確認した。また、発熱抵抗体式空気流量測定装置の耐久性を考慮した特性変化の許容値（約３％程度）と、前記した発熱抵抗体式空気流量測定装置として必要なＯＮ／ＯＦＦである１１万回を比べてみると、加熱温度２００℃と、２５０℃ではＯＮ／ＯＦＦ回数が１１万回でも特性変化量は、許容値の範囲内に収まる。これに対し、加熱温度を３００℃にすると、１１万回より少ない回数で特性変化の許容値を超えてしまう。つまり、加熱温度を３００℃とすると発熱抵抗体式空気流量測定装置としての製品寿命の間の特性変化を許容値内に収める事が困難であり、耐久性に課題を残す事となるのである。更に、図６に示した検討結果を横軸に加熱温度、縦軸にＯＮ／ＯＦＦ回数１１万回での特性変化量で表したグラフを図７に示す。本結果より、発熱抵抗体式空気流量測定装置としての許容特性変化量の３％を越える加熱温度は約２９０℃である。このため、ＯＮ／ＯＦＦ繰り返し耐久より発熱抵抗体の加熱温度は２９０℃以下である事が必要となる。 In the graph shown in FIG. 6, the horizontal axis represents the number of times the energization of the heating resistor type air flow measuring device was repeatedly turned ON / OFF, and the vertical axis represents the characteristics of the heating resistor type air flow measuring device based on the initial value. It is a graph showing the amount of change. Evaluation was performed at three heating temperatures of 200 ° C., 250 ° C., and 300 ° C. As a result, it was confirmed that when the heating temperature of the heating resistor is increased, the characteristic change amount corresponding to the number of repetitions increases. Moreover, the allowable value (about 3%) of the characteristic change considering the durability of the heating resistor type air flow measuring device is compared with 110,000 times that is ON / OFF necessary as the heating resistor type air flow measuring device. As a result, at the heating temperature of 200 ° C. and 250 ° C., the characteristic change amount is within the allowable range even if the ON / OFF frequency is 110,000 times. On the other hand, when the heating temperature is set to 300 ° C., the allowable value of the characteristic change is exceeded in less than 110,000 times. That is, when the heating temperature is 300 ° C., it is difficult to keep the characteristic change during the product life as the heating resistor type air flow measuring device within the allowable value, and there is a problem in durability. Further, FIG. 7 is a graph in which the examination results shown in FIG. 6 are represented by the heating temperature on the horizontal axis and the characteristic change amount at 110,000 ON / OFF times on the vertical axis. From this result, the heating temperature exceeding 3% of the allowable characteristic change amount as the heating resistor type air flow measuring device is about 290 ° C. For this reason, it is necessary for the heating temperature of the heating resistor to be 290 ° C. or less because of repeated ON / OFF durability.

よって、図５に示したオイル蒸発時間と、図６に示したＯＮ／ＯＦＦ繰り返し試験による特性変化を考慮すると、発熱抵抗体の加熱温度は約２３０〜２９０℃程度が望ましい結果といえる。 Therefore, considering the oil evaporation time shown in FIG. 5 and the characteristic change due to the ON / OFF repeated test shown in FIG. 6, the heating temperature of the heating resistor is preferably about 230 to 290 ° C.

次に本発明の具体的な副空気通路と発熱抵抗体の設置位置について図１１を使い説明する。主空気通路構成部材１００にて構成される主空気通路１０１内に配置された副空気通路１２０は副空気通路構成部材１０２により形成され、副空気通路入口１２１，曲り通路１２２，曲り下流直線部１２３，副空気通路出口１２４から構成される。また、曲り通路１２２は主空気通路下流側から上流側へほぼ１８０°迂回する形となっており、迂回部では最も下流側となる場所が曲り通路の頂点１２５となる。流量計測部である発熱抵抗体
１１０は曲り通路の曲り終端または、曲り下流直線部１２３の始点近傍の位置に設置されており、リード材１１１と一体で支持材１０３を介して駆動回路（図示せず）と電気的に接続されている。本来であれば駆動回路の一部を構成する感温抵抗体も図示すべきであるが、今回の発明には感温抵抗体の位置には特に重要視しないため、発熱抵抗体近傍に有れば良いとして今回の図示には省略した。オイル付着に関しては前記したとおり加熱温度を約２５０℃とする事でオイルの付着量を大幅に低減できる。しかし、塵やカーボン等の付着物を低減するためには、通路による工夫が必要となる。このため、図１０に示したような発熱抵抗体の上流側に迂回する通路構造を設け、付着物を遠心力を使い遠心分離する事が望ましい構造である。よって、遠心分離構造の副空気通路内に約２５０℃に加熱した発熱抵抗体を設置する事が発熱抵抗体式空気流量測定装置の耐汚損性の向上に最も有利な構成になる。 Next, specific installation positions of the auxiliary air passage and the heating resistor of the present invention will be described with reference to FIG. The sub air passage 120 disposed in the main air passage 101 constituted by the main air passage constituting member 100 is formed by the sub air passage constituting member 102, and the sub air passage inlet 121, the curved passage 122, and the curved downstream straight portion 123 are formed. , The auxiliary air passage outlet 124. Further, the curved passage 122 has a shape that makes a detour of about 180 ° from the downstream side to the upstream side of the main air passage, and the most downstream side of the bypass portion becomes the apex 125 of the curved passage. The heating resistor 110 serving as a flow rate measuring unit is installed at the end of the bent passage or near the starting point of the bent downstream straight portion 123, and is integrated with the lead material 111 via the support member 103 to drive a circuit (not shown). Are electrically connected. Although the temperature sensitive resistor that constitutes a part of the drive circuit should be illustrated in the original, the position of the temperature sensitive resistor is not particularly important in the present invention. It is omitted in this illustration as it should be. Regarding oil adhesion, the amount of oil adhesion can be greatly reduced by setting the heating temperature to about 250 ° C. as described above. However, in order to reduce deposits such as dust and carbon, it is necessary to devise a passage. For this reason, it is desirable to provide a bypass structure on the upstream side of the heating resistor as shown in FIG. 10 and to centrifuge the deposit using centrifugal force. Therefore, installing a heating resistor heated to about 250 ° C. in the sub-air passage of the centrifugal separation structure is the most advantageous configuration for improving the fouling resistance of the heating resistor type air flow measuring device.

最後に、図１０を使いディーゼル車における電子燃料噴射方式に本発明品を適用した一実施例を示す。エアクリーナから吸入された吸入空気は、発熱抵抗式空気流量測定装置が設置されるダクト，ターボ，インタークーラを経由してエンジンに吸入される。発熱抵抗体式空気流量測定装置とエンジンの間にはエンジンのシリンダ内で発生するブローバイガスを吸気管に戻すためのＰＣＶ（ブローバイガス還流装置）と、排気に含まれるＮｏｘ
（窒素酸化物）の低減のために排気の一部を吸気管に戻すＥＧＲ（排ガス還流装置）が接続されている。エンジンで燃焼した排ガスはターボ，ＤＰＦ(ディーゼル微粒子除去装置)，触媒を介して大気に排出される。 Finally, FIG. 10 is used to show an embodiment in which the product of the present invention is applied to an electronic fuel injection system in a diesel vehicle. The intake air drawn from the air cleaner is drawn into the engine via a duct, a turbo, and an intercooler in which a heating resistance type air flow measuring device is installed. Between the heating resistor type air flow measuring device and the engine, PCV (blowby gas recirculation device) for returning blowby gas generated in the cylinder of the engine to the intake pipe, and Nox included in the exhaust gas
In order to reduce (nitrogen oxide), an EGR (exhaust gas recirculation device) that returns a part of the exhaust gas to the intake pipe is connected. The exhaust gas combusted by the engine is discharged to the atmosphere through a turbo, DPF (diesel particulate removal device), and catalyst.

発熱抵抗式空気流量測定装置から出力される空気流量信号，温度センサからの吸入空気温度信号，アクセル開度センサから出力されるアクセル開度信号，エンジン回転速度計から出力されるエンジン回転速度信号等、これらを入力するコントロールユニット、これらの信号を逐次演算して最適な燃料噴射量を求め、その値を使ってインジェクタでの燃料噴射量を制御する。 Air flow signal output from the heating resistance air flow measurement device, intake air temperature signal from the temperature sensor, accelerator opening signal output from the accelerator opening sensor, engine rotation speed signal output from the engine tachometer, etc. The control unit for inputting these values calculates the optimum fuel injection amount by sequentially calculating these signals, and uses this value to control the fuel injection amount at the injector.

自動車用としてのエンジン制御が主な使用用途になるが、船舶や発電機等のディーゼルエンジンを使った制御に対しても同様に利用が可能となる。 Engine control for automobiles is the main application, but it can be used for control using diesel engines such as ships and generators as well.

発熱抵抗体に汚損物が付着した際の特性変化を示すグラフ。The graph which shows the characteristic change at the time of fouling material adhering to a heating resistor. 発熱抵抗体式空気流量測定装置の駆動回路略図。The drive circuit schematic diagram of a heating resistor type air flow measuring device. 発熱抵抗体の構造を示す。The structure of a heating resistor is shown. 発熱抵抗体への塵堆積を示す図。The figure which shows the dust accumulation on a heating resistor. 発熱抵抗体の加熱温度とオイルの蒸発時間。Heating temperature of heating resistor and oil evaporation time. 発熱抵抗体式空気流量測定装置のＯＮ／ＯＦＦ繰り返し回数と特性変化。The number of ON / OFF repetitions and changes in characteristics of the heating resistor air flow measurement device. ＯＮ／ＯＦＦ繰り返し回数１１万回における各加熱温度の特性変化量。Characteristic change amount of each heating temperature at 110,000 ON / OFF repetitions. 代表的な発熱抵抗体式空気流量測定装置横断面図。1 is a cross-sectional view of a typical heating resistor type air flow measuring device. 図８を上流側から見た図。The figure which looked at FIG. 8 from the upstream. 発熱抵抗体式空気流量測定装置を使ったディーゼルエンジンのシステム概略図。The system schematic diagram of the diesel engine using the heating resistor type air flow measuring device. 本発明の一実施例を示す発熱抵抗体式空気流量測定装置の副空気通路構成。The sub-air channel | path structure of the heating resistor type air flow measuring device which shows one Example of this invention.

符号の説明Explanation of symbols

１…ハウジング構成部材、２…回路基板、３…第一の発熱抵抗体、４…感温抵抗体、５…導電性支持体、６…シール材、７…ネジ部材、１０，１０２…副空気通路構成部材、
１４，１２０…副空気通路、２０，１００…主空気通路構成部材、２２，１０１…主空気通路、２５…副空気通路挿入穴、１０３…支持材、１１０…発熱抵抗体、１１１…リード材、１２１…副空気通路入口、１２２…曲り通路、１２３…直管通路、１２４…副空気通路出口、１２５…曲り部頂点。 DESCRIPTION OF SYMBOLS 1 ... Housing structural member, 2 ... Circuit board, 3 ... 1st heating resistor, 4 ... Temperature sensitive resistor, 5 ... Conductive support body, 6 ... Sealing material, 7 ... Screw member, 10,102 ... Sub air Passage components,
DESCRIPTION OF SYMBOLS 14,120 ... Sub air passage, 20, 100 ... Main air passage component, 22, 101 ... Main air passage, 25 ... Sub air passage insertion hole, 103 ... Support material, 110 ... Heating resistor, 111 ... Lead material, 121 ... Sub-air passage inlet, 122 ... Bent passage, 123 ... Straight pipe passage, 124 ... Sub-air passage outlet, 125 ... Bend portion apex.

Claims

抵抗体に電流を流して発熱させ、空気流量を測定する発熱抵抗体式空気流量測定装置において、
抵抗体の加熱温度を略２３０〜２９０℃の範囲内に制御することを特徴とする発熱抵抗体式空気流量測定装置。 In a heating resistor type air flow measurement device that measures the air flow rate by causing a current to flow through the resistor,
A heating resistor type air flow rate measuring device, wherein the heating temperature of the resistor is controlled within a range of about 230 to 290 ° C.

請求項１に記載の前記抵抗体は円柱状の基体に白金線を巻線して構成されていることを特徴とする発熱抵抗体式空気流量測定装置。 2. The heating resistor type air flow measuring device according to claim 1, wherein the resistor is formed by winding a platinum wire around a cylindrical base.

請求項１に記載の発熱抵抗体式空気流量測定装置において、副空気通路には少なくとも一つの曲り部を有しており、曲り部の頂点より下流に前記抵抗体を設置することを特徴とする発熱抵抗体式空気流量測定装置。 2. The heating resistor type air flow measuring device according to claim 1, wherein the auxiliary air passage has at least one bent portion, and the resistor is installed downstream from the apex of the bent portion. Resistor type air flow measuring device.

請求項１から請求項３に記載のいずれかの発熱抵抗体式空気流量測定装置を用いたことを特徴とする内燃機関の燃料噴射システム。 A fuel injection system for an internal combustion engine using the heating resistor type air flow measuring device according to any one of claims 1 to 3.

請求項１から請求項３に記載のいずれかの発熱抵抗体式空気流量測定装置を用いたことを特徴とするディーゼル車における燃料噴射システム。
A fuel injection system for a diesel vehicle using the heating resistor type air flow measuring device according to any one of claims 1 to 3.