JP5120289B2 - Air flow measurement device - Google Patents

Air flow measurement device Download PDF

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JP5120289B2
JP5120289B2 JP2009035076A JP2009035076A JP5120289B2 JP 5120289 B2 JP5120289 B2 JP 5120289B2 JP 2009035076 A JP2009035076 A JP 2009035076A JP 2009035076 A JP2009035076 A JP 2009035076A JP 5120289 B2 JP5120289 B2 JP 5120289B2
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air
flow
flow rate
flow direction
frequency value
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JP2010190715A (en
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彰利 水谷
隆央 伴
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Denso Corp
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Denso Corp
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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
    • G01F1/696—Circuits therefor, e.g. constant-current flow meters
    • G01F1/698—Feedback or rebalancing circuits, e.g. self heated constant temperature flowmeters
    • G01F1/699—Feedback or rebalancing circuits, e.g. self heated constant temperature flowmeters by control of a separate heating or cooling element
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
    • G01F1/684—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
    • G01F1/6842—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow with means for influencing the fluid flow
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
    • G01F1/684—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
    • G01F1/6845—Micromachined devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
    • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
    • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
    • G01F1/684—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
    • G01F1/688—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow using a particular type of heating, cooling or sensing element
    • G01F1/69—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow using a particular type of heating, cooling or sensing element of resistive type
    • G01F1/692—Thin-film arrangements

Description

本発明は、空気通路に配置される発熱抵抗体の発熱により生じる温度分布を基に、空気通路を流れる空気の流量および流れ方向を測定できる空気流量測定装置に関する。   The present invention relates to an air flow rate measuring apparatus capable of measuring a flow rate and a flow direction of air flowing through an air passage based on a temperature distribution generated by heat generation of a heating resistor disposed in the air passage.

従来、自動車等に搭載される内燃機関の吸気量に関わる情報をアナログ電圧として検出し、そのアナログ電圧を周波数値に変換して出力する周波数出力（時間出力）方式のエアフロメータが公知である（特許文献１参照）。
この周波数出力方式のエアフロメータは、例えば、空気量が０〜１０ｇ／ｓ程度の低流量側を１ＫＨｚ（１ｍｓ）、高流量側を１０ＫＨｚ（０．１ｍｓ）というように、低流量側の出力値に低周波数（長い周期）を割り付けている。この理由は、エアフロメータの出力値をＥＣＵ（エンジン制御を行う電子制御装置）でデジタル値に変換して処理する場合に、例えば、１ｍｓを１２ビットでＡＤ変換すると、分解能１ＬＳＢは、１ｍｓ／２12＝０．２４μｓとなる。ここで、１ＬＳＢ誤差が発生した場合、１ＫＨｚ（１ｍｓ）で０．２４μｓずれた場合と、１０ＫＨｚ（０．１ｍｓ）で０．２４μｓずれた場合とでは、前者の方が１ＬＳＢ誤差による影響度は小さい。特に、自動車用のエアフロメータは、低流量側の精度誤差を小さくする必要があるため、１ＬＳＢ誤差の影響度が小さくなる低周波数（長い周期）を低流量側に割り付けている。 2. Description of the Related Art Conventionally, a frequency output (time output) type air flow meter that detects information related to an intake air amount of an internal combustion engine mounted on an automobile or the like as an analog voltage, converts the analog voltage into a frequency value, and outputs the same is known ( Patent Document 1).
This frequency output type air flow meter has an output value on the low flow rate side such as 1 KHz (1 ms) on the low flow rate side and 10 KHz (0.1 ms) on the high flow rate side where the air amount is about 0 to 10 g / s. Is assigned a low frequency (long period). This is because when the output value of the air flow meter is converted into a digital value by an ECU (electronic control unit that performs engine control), for example, if 1 ms is AD-converted with 12 bits, the resolution 1LSB is 1 ms / 2. 12 = 0.24 μs. Here, when a 1LSB error occurs, the influence of the 1LSB error is smaller in the former when the deviation is 0.24 μs at 1 KHz (1 ms) and when the deviation is 0.24 μs at 10 KHz (0.1 ms). . In particular, since an airflow meter for automobiles needs to reduce the accuracy error on the low flow rate side, a low frequency (long cycle) in which the influence of 1LSB error is reduced is assigned to the low flow rate side.

特開平０１−０３５２１８号公報JP-A-01-035218

ところが、特許文献１に記載された従来技術は、吸気通路を順流方向（エンジンに空気が吸入される方向）に流れる空気流量を計測するだけであるため、例えば、流量０ｇ／ｓ時を１ＫＨｚに割り当てることができたが、吸気通路を逆流する空気量も測定できるエアフロメータの場合には、例えば、流量−５０ｇ／ｓ時に１ＫＨｚを割り当てると、流量−５０ｇ／ｓ〜０ｇ／ｓ間の周波数分だけ出力特性がオフセットされる。その結果、低流量側（０〜１０ｇ／ｓ）に割り当てる出力周波数値が比較的高周波になってしまうため、１ＬＳＢ誤差の影響が従来に比べて大きくなるという問題が発生する。
本発明は、上記事情に基づいて成されたもので、その目的は、空気通路を流れる空気の流量と流れ方向とを測定でき、且つ、順流方向における低流量域（例えば０〜１０ｇ／ｓ）の精度誤差を小さくできる空気流量測定装置を提供することにある。 However, since the conventional technique described in Patent Document 1 only measures the flow rate of air flowing in the forward flow direction (the direction in which air is sucked into the engine) in the intake passage, for example, the flow rate at 0 g / s is set to 1 KHz. In the case of an air flow meter that can measure the amount of air flowing back through the intake passage, for example, if 1 KHz is assigned when the flow rate is −50 g / s, the frequency component between the flow rate −50 g / s and 0 g / s can be obtained. Only the output characteristics are offset. As a result, since the output frequency value assigned to the low flow rate side (0 to 10 g / s) becomes a relatively high frequency, there arises a problem that the influence of the 1LSB error becomes larger than the conventional one.
The present invention has been made based on the above circumstances, and its object is to measure the flow rate and flow direction of the air flowing through the air passage, and to achieve a low flow rate range (for example, 0 to 10 g / s) in the forward flow direction. It is an object of the present invention to provide an air flow rate measuring device that can reduce the accuracy error.

（請求項１の発明）
本発明は、空気通路に配置され、且つ、通電により発熱する発熱抵抗体を有し、この発熱抵抗体の発熱により生じる温度分布を基に、空気通路を流れる空気の流量と流れ方向とに応じたアナログ電圧を出力するセンサ部と、このセンサ部より出力されるアナログ電圧をデジタル値に変換するＡ／Ｄ変換器を内蔵し、このＡ／Ｄ変換器でデジタル変換された電圧値を周波数値に変換して出力する信号処理回路部とを有する空気流量測定装置において、空気通路を一方から他方に向かって空気が流れる方向を順流方向と呼び、空気通路を他方向から一方に向かって空気が流れる方向を逆流方向と呼ぶ時に、信号処理回路部は、Ａ／Ｄ変換器でデジタル変換されたデジタル値を周波数値に直線変換する際の傾きが、順流方向に空気が流れる時よりも、逆流方向に空気が流れる時のほうが小さく設定されていることを特徴とする。 (Invention of Claim 1)
The present invention has a heating resistor that is disposed in the air passage and generates heat when energized. Based on the temperature distribution generated by the heat generation of this heating resistor, the flow rate depends on the flow rate and flow direction of the air flowing through the air passage. A sensor unit that outputs an analog voltage and an A / D converter that converts the analog voltage output from the sensor unit into a digital value are built in, and the voltage value digitally converted by the A / D converter is a frequency value. In the air flow rate measuring device having a signal processing circuit unit that converts and outputs the air passage, the direction in which the air flows from one side to the other is called the forward flow direction, and the air passage moves from the other direction to the one side. when the flow direction is referred to as a reverse flow direction, the signal processing circuit section, the inclination at the time of linear converting digital converted digital value by the a / D converter into frequency values, than when the air flows in the forward flow direction Wherein the better when the backflow direction air flow is set smaller.

本発明では、デジタル変換されたデジタル値（センサ電圧と呼ぶ）を周波数値に直線変換する際に、言い換えると、流量０ｇ／ｓ相当時（空気通路に空気の流れが生じていない時）のセンサ電圧を境に、逆流方向に空気が流れる時は、センサ電圧を周波数値に直線変換する際の傾きが小さく、順流方向に空気が流れる時は、センサ電圧を周波数値に直線変換する際の傾きが大きく設定される。
これにより、流量０ｇ／ｓ相当時のセンサ電圧を境に順流方向と逆流方向とでセンサ電圧を周波数値に一律に直線変換する場合、つまり、順流方向と逆流方向とでセンサ電圧を周波数値に直線変換する時の傾きが同じ場合と比較して、流量０ｇ／ｓ時の周波数値を下げることができる。その結果、順流方向における低流量側（例えば０〜１０ｇ／ｓ）の出力値に低周波数（長い周期）を割り付けることができるので、順流方向における低流量域の精度誤差（１ＬＳＢ誤差による影響度）を小さくできる。 In the present invention, when the linear transformed digital converted digital value (referred to as sensor voltage) to a frequency value, In other words, the flow rate 0 g / s equivalent-time (when the air passage does not occur airflow) When air flows in the reverse flow direction with the sensor voltage as a boundary, the gradient when converting the sensor voltage to a frequency value is small, and when air flows in the forward flow direction, the air pressure when converting the sensor voltage to a frequency value is small. The inclination is set large.
As a result, when the sensor voltage is linearly converted into a frequency value uniformly in the forward direction and the backward direction with the sensor voltage at a flow rate equivalent to 0 g / s as a boundary, that is, the sensor voltage is converted into the frequency value in the forward direction and the backward direction. The frequency value at the flow rate of 0 g / s can be lowered as compared with the case where the gradient at the time of linear conversion is the same. As a result, a low frequency (long cycle) can be assigned to the output value on the low flow rate side (for example, 0 to 10 g / s) in the forward flow direction, so that the accuracy error in the low flow rate region in the forward flow direction (influence by 1LSB error) Can be reduced.

また、流量０ｇ／ｓ相当時のセンサ電圧に対する周波数値を下げることにより、順流方向の周波数ダイナミックレンジを広く取れるため、逆流方向より相対的に高精度を要する順流方向の分解能を向上させることができる。
さらに、本発明では、センサ部より出力されるアナログ電圧をデジタル値に変換しているので、温度補正を行う際に、デジタル多点補正が可能であり、簡易な回路構成で温度特性のばらつきを精度良く補正することが可能である。 Moreover, since the frequency dynamic range in the forward flow direction can be widened by lowering the frequency value with respect to the sensor voltage at the flow rate of 0 g / s, the resolution in the forward flow direction that requires relatively higher accuracy than the reverse flow direction can be improved. .
Furthermore, in the present invention, since the analog voltage output from the sensor unit is converted into a digital value, digital multipoint correction is possible when performing temperature correction, and variations in temperature characteristics can be achieved with a simple circuit configuration. It is possible to correct with high accuracy.

（請求項２の発明）
本発明は、空気通路に配置され、且つ、通電により発熱する発熱抵抗体を有し、この発熱抵抗体の発熱により生じる温度分布を基に、空気通路を流れる空気の流量と流れ方向とに応じたアナログ電圧を出力するセンサ部と、このセンサ部より出力されるアナログ電圧を周波数値に変換して出力する信号処理回路部とを有する空気流量測定装置において、空気通路を一方から他方に向かって空気が流れる方向を順流方向と呼び、空気通路を他方向から一方に向かって空気が流れる方向を逆流方向と呼ぶ時に、信号処理回路部は、センサ部より出力されるアナログ電圧を周波数値に直線変換する際の傾きが、順流方向に空気が流れる時よりも、逆流方向に空気が流れる時のほうが小さく設定されていることを特徴とする。 (Invention of Claim 2)
The present invention has a heating resistor that is disposed in the air passage and generates heat when energized. Based on the temperature distribution generated by the heat generation of this heating resistor, the flow rate depends on the flow rate and flow direction of the air flowing through the air passage. In an air flow rate measuring apparatus having a sensor unit that outputs an analog voltage and a signal processing circuit unit that converts the analog voltage output from the sensor unit into a frequency value and outputs the frequency value, the air passage is directed from one to the other. When the direction in which air flows is called the forward flow direction, and the direction in which the air passage flows from one direction to the other is called the reverse flow direction, the signal processing circuit section uses the analog voltage output from the sensor section as a straight line to the frequency value. The inclination at the time of conversion is set to be smaller when air flows in the reverse flow direction than when air flows in the forward flow direction .

本発明では、センサ部より出力されるアナログ電圧（センサ電圧と呼ぶ）を周波数値に直線変換する際に、言い換えると、流量０ｇ／ｓ相当時（空気通路に空気の流れが生じていない時）のセンサ電圧を境に、逆流方向に空気が流れる時は、センサ電圧を周波数値に直線変換する際の傾きが小さく、順流方向に空気が流れる時は、センサ電圧を周波数値に直線変換する際の傾きが大きく設定される。
これにより、流量０ｇ／ｓ相当時のセンサ電圧を境に順流方向と逆流方向とでセンサ電圧を周波数値に一律に直線変換する場合、つまり、順流方向と逆流方向とでセンサ電圧を周波数値に直線変換する時の傾きが同じ場合と比較して、流量０ｇ／ｓ時の周波数値を下げることができる。その結果、順流方向における低流量側（例えば０〜１０ｇ／ｓ）の出力値に低周波数（長い周期）を割り付けることができるので、順流方向における低流量域の精度誤差（１ＬＳＢ誤差による影響度）を小さくできる。
また、流量０ｇ／ｓ時の周波数値を下げることにより、順流方向の周波数ダイナミックレンジを広く取れるため、逆流方向より相対的に高精度を要する順流方向の分解能を向上させることができる。 When the present invention, (referred to as sensor voltage) analog voltage output from the sensor unit when a straight line into a frequency value, In other words, the flow rate 0 g / s equivalent time (not cause air flow into the air passage ) When the air flows in the reverse flow direction with the sensor voltage as the boundary, the gradient when converting the sensor voltage into a linear value is small, and when the air flows in the forward direction, the sensor voltage is converted into a frequency value. The tilt is set large.
As a result, when the sensor voltage is linearly converted into a frequency value uniformly in the forward direction and the backward direction with the sensor voltage at a flow rate equivalent to 0 g / s as a boundary, that is, the sensor voltage is converted into the frequency value in the forward direction and the backward direction. The frequency value at the flow rate of 0 g / s can be lowered as compared with the case where the gradient at the time of linear conversion is the same. As a result, a low frequency (long cycle) can be assigned to the output value on the low flow rate side (for example, 0 to 10 g / s) in the forward flow direction, so that the accuracy error in the low flow rate region in the forward flow direction (influence by 1LSB error) Can be reduced.
Moreover, since the frequency dynamic range in the forward flow direction can be widened by lowering the frequency value at a flow rate of 0 g / s, the resolution in the forward flow direction requiring relatively higher accuracy than the reverse flow direction can be improved.

（請求項３の発明）
請求項１または２に記載した空気流量測定装置において、空気通路は、内燃機関の吸気ポートに接続される吸気通路であり、この吸気通路を内燃機関に向かって空気が流れる方向を順流方向と呼び、吸気通路を内燃機関と反対方向へ空気が流れる方向を逆流方向と呼ぶことを特徴とする。
本発明の空気流量測定装置は、内燃機関の吸入空気量を測定するエアフロメータに用いることができる。内燃機関では、例えば、低回転且つ高負荷の時に吸気脈動が大きくなり、吸気弁と排気弁との開弁期間が重なると、ピストン上昇時に吸気弁から吸気が逆流する、つまり、空気通路を逆流方向に空気が流れることがある。これに対し、本発明の空気流量測定装置は、発熱抵抗体の発熱により生じる温度分布を基に、空気の流量だけでなく、流れ方向も検出できるので、順流方向に流れる空気（内燃機関に吸入される吸入空気量）を精度良く検出できる。 (Invention of Claim 3)
3. The air flow rate measuring apparatus according to claim 1, wherein the air passage is an intake passage connected to an intake port of the internal combustion engine, and a direction in which air flows toward the internal combustion engine is referred to as a forward flow direction. The direction in which air flows in the intake passage in the opposite direction to the internal combustion engine is referred to as a reverse flow direction.
The air flow rate measuring device of the present invention can be used in an air flow meter that measures the intake air amount of an internal combustion engine. In an internal combustion engine, for example, when intake pulsation becomes large at low rotation and high load, and the valve opening periods of the intake valve and exhaust valve overlap, intake air flows backward from the intake valve when the piston rises. Air may flow in the direction. On the other hand, the air flow rate measuring device of the present invention can detect not only the air flow rate but also the flow direction based on the temperature distribution generated by the heat generation of the heating resistor, so that the air flowing in the forward direction (intake into the internal combustion engine) Can be detected with high accuracy.

実施例１に係るエアフロメータの回路構成図である。1 is a circuit configuration diagram of an air flow meter according to Embodiment 1. FIG. （ａ）センサ部により空気の流量と流れ方向とを測定するための原理を説明する温度分布図、（ｂ）センサ部の構造を簡略的に示す断面図である。(A) Temperature distribution diagram for explaining the principle for measuring the flow rate and flow direction of air by the sensor unit, (b) a sectional view schematically showing the structure of the sensor unit. エアフロメータを吸気ダクトに取り付けた状態を示す断面図である。It is sectional drawing which shows the state which attached the air flow meter to the intake duct. （ａ）センサ電圧と周波数との相関を示す特性グラフ、（ｂ）周波数と流量との相関を示す特性グラフである。(A) The characteristic graph which shows the correlation with a sensor voltage and a frequency, (b) The characteristic graph which shows the correlation with a frequency and flow volume. 実施例２に係るエアフロメータの回路構成図である。6 is a circuit configuration diagram of an air flow meter according to Embodiment 2. FIG.

本発明を実施するための最良の形態を以下の実施例により詳細に説明する。   The best mode for carrying out the present invention will be described in detail with reference to the following examples.

この実施例１は、例えば、自動車用エンジンの吸入空気量を測定するエアフロメータに本発明の空気流量測定装置を適用した一例を説明する。
図１は実施例１に係るエアフロメータ１の回路構成図、図２（ａ）はエアフロメータ１のセンサ部２により空気の流量と流れ方向とを測定するための原理を説明する温度分布図、同図（ｂ）はセンサ部２の構造を簡略的に示す断面図、図３はエアフロメータ１を吸気ダクト３に取り付けた状態を示す断面図である。
本実施例のエアフロメータ１は、以下に説明するセンサボディ４、センサ部２、回路モジュール５等により構成される。 In the first embodiment, for example, an example in which the air flow measuring device of the present invention is applied to an air flow meter that measures the intake air amount of an automobile engine will be described.
FIG. 1 is a circuit configuration diagram of the air flow meter 1 according to the first embodiment, and FIG. 2A is a temperature distribution diagram for explaining the principle for measuring the flow rate and flow direction of air by the sensor unit 2 of the air flow meter 1. FIG. 3B is a cross-sectional view schematically showing the structure of the sensor unit 2, and FIG. 3 is a cross-sectional view showing a state where the air flow meter 1 is attached to the intake duct 3.
The air flow meter 1 according to the present embodiment includes a sensor body 4, a sensor unit 2, a circuit module 5, and the like described below.

センサボディ４は、図３に示す様に、吸気ダクト３に開けられた取付け孔より吸気ダクト３の内部に着脱可能に挿入され、取付け孔との間がＯリング６によって気密にシールされている。なお、吸気ダクト３は、エンジンの吸気ポート（図示せず）に接続される吸気通路の一部を形成するもので、例えば、吸気通路の最上流に配置されるエアクリーナの出口パイプ、あるいは、この出口パイプの下流側に接続される吸気管等である。
センサボディ４には、図３に示される吸気ダクト３の内部を図示左側（エアクリーナ側）から右側（エンジン側）に向かって流れる空気、つまり、エンジンに吸入される空気の一部を取り込むバイパス通路（図示せず）が形成され、このバイパス通路の途中にセンサ部２が配置される。 As shown in FIG. 3, the sensor body 4 is detachably inserted into the intake duct 3 through an attachment hole formed in the intake duct 3, and is hermetically sealed with an O-ring 6 between the attachment hole. . The intake duct 3 forms a part of an intake passage connected to an intake port (not shown) of the engine. For example, an outlet pipe of an air cleaner arranged at the uppermost stream of the intake passage, or this An intake pipe connected to the downstream side of the outlet pipe.
In the sensor body 4, a bypass passage that takes in the air that flows from the left side (air cleaner side) to the right side (engine side) in the intake duct 3 shown in FIG. (Not shown) is formed, and the sensor unit 2 is disposed in the middle of the bypass passage.

センサ部２は、図１に示す様に、通電により発熱する発熱抵抗体７を有し、この発熱抵抗体７の温度を所定の基準温度に制御する発熱温度制御部２ａと、発熱抵抗体７の発熱により生じる温度分布を基に、空気の流量と流れ方向に応じたアナログ電圧を出力するセンサ電圧出力部２ｂとを有する。
発熱温度制御部２ａは、図１に示す様に、上記の発熱抵抗体７と、この発熱抵抗体７の傍らに近接設置され、発熱抵抗体７の温度を受熱する傍熱抵抗体８と、バイパス通路を流れる空気の温度（吸気温度と呼ぶ）を検出する吸気温度検出抵抗体９と、抵抗値が固定された第１抵抗体１０および第２抵抗体１１とを有し、傍熱抵抗体８と、吸気温度検出抵抗体９、第１抵抗体１０、および第２抵抗体１１とでブリッジ回路を構成している。このブリッジ回路は、二つの中点がオペアンプ１２の入力端子に接続され、オペアンプ１２の出力端子がトランジスタ１３に接続されている。 As shown in FIG. 1, the sensor unit 2 includes a heating resistor 7 that generates heat when energized, a heating temperature control unit 2 a that controls the temperature of the heating resistor 7 to a predetermined reference temperature, and a heating resistor 7. And a sensor voltage output unit 2b for outputting an analog voltage corresponding to the flow rate and flow direction of air based on the temperature distribution generated by the heat generation.
As shown in FIG. 1, the heating temperature control unit 2 a is installed in the vicinity of the heating resistor 7 and the side heating resistor 8 that receives the temperature of the heating resistor 7. It has an intake air temperature detection resistor 9 for detecting the temperature of air flowing through the bypass passage (referred to as intake air temperature), a first resistor 10 and a second resistor 11 having fixed resistance values, and a side heat resistor. 8, the intake air temperature detection resistor 9, the first resistor 10, and the second resistor 11 constitute a bridge circuit. In this bridge circuit, two middle points are connected to the input terminal of the operational amplifier 12, and the output terminal of the operational amplifier 12 is connected to the transistor 13.

この発熱温度制御部２ａは、傍熱抵抗体８で検出される温度（発熱抵抗体７の温度）が基準温度より低くなると、傍熱抵抗体８の抵抗値が低下して、ブリッジ回路の中点間に電位差が生じるため、オペアンプ１２の出力によりトランジスタ１３がオンになり、発熱抵抗体７に電流が流れて、発熱抵抗体７の温度が上昇する。この発熱抵抗体７の温度上昇により、傍熱抵抗体８で検出される温度が基準温度に達して傍熱抵抗体８の抵抗値が上昇すると、オペアンプ１２の出力によりトランジスタ１３がオフになり、発熱抵抗体７への電流供給が遮断される。この作動により、傍熱抵抗体８が検出する発熱抵抗体７の温度は、吸気温度検出抵抗体９が検出する吸気温度よりも一定温度高い基準温度に制御される。   When the temperature detected by the indirectly heated resistor 8 (temperature of the exothermic resistor 7) becomes lower than the reference temperature, the exothermic temperature control unit 2a decreases the resistance value of the indirectly heated resistor 8 and causes the bridge circuit to Since a potential difference is generated between the points, the transistor 13 is turned on by the output of the operational amplifier 12, current flows through the heating resistor 7, and the temperature of the heating resistor 7 rises. When the temperature detected by the indirectly heated resistor 8 reaches the reference temperature and the resistance value of the indirectly heated resistor 8 increases due to the temperature rise of the heating resistor 7, the transistor 13 is turned off by the output of the operational amplifier 12. The current supply to the heating resistor 7 is interrupted. By this operation, the temperature of the heating resistor 7 detected by the indirectly heated resistor 8 is controlled to a reference temperature that is higher than the intake air temperature detected by the intake air temperature detecting resistor 9 by a certain temperature.

センサ電圧出力部２ｂは、空気の流れ方向において、発熱抵抗体７の上流側に近接して配置される２個の側温抵抗体ＲＵ１、ＲＵ２と、発熱抵抗体７の下流側に近接して配置される２個の側温抵抗体ＲＤ１、ＲＤ２とで構成され、この４個の側温抵抗体ＲＵ１、ＲＵ２、ＲＤ１、ＲＤ２でブリッジ回路を構成している。
この４個の側温抵抗体ＲＵ１、ＲＵ２、ＲＤ１、ＲＤ２は、発熱抵抗体７と共に、例えば、図２（ｂ）に示す様に、シリコン基板１４に設けられるダイヤフラム１５の表面上に形成されている。ダイヤフラム１５は、シリコン基板１４の表面にスパッタ法あるいはＣＶＤ法等により形成される絶縁膜であり、シリコン基板１４の裏側から絶縁膜との境界面までシリコン基板１４の一部を除去してシリコン基板１４に空洞部を形成することにより設けられる。
なお、図２（ｂ）には示されていないが、上記の傍熱抵抗体８、および、吸気温度検出抵抗体９も絶縁膜上に形成されている。但し、吸気温度検出抵抗体９は、発熱抵抗体７の熱が温度検出に影響を及ぼさないように、発熱抵抗体７から離れた位置に配置される。 The sensor voltage output unit 2b is adjacent to the two side temperature resistors RU1 and RU2 disposed close to the upstream side of the heating resistor 7 and the downstream side of the heating resistor 7 in the air flow direction. The four side temperature resistors RU1, RU2, RD1, and RD2 form a bridge circuit. The two side temperature resistors RD1 and RD2 are arranged.
The four side temperature resistors RU1, RU2, RD1, and RD2 are formed on the surface of a diaphragm 15 provided on the silicon substrate 14 together with the heating resistor 7, for example, as shown in FIG. Yes. The diaphragm 15 is an insulating film formed on the surface of the silicon substrate 14 by a sputtering method, a CVD method, or the like. A part of the silicon substrate 14 is removed from the back side of the silicon substrate 14 to the boundary surface with the insulating film. 14 is formed by forming a cavity.
Although not shown in FIG. 2B, the indirectly heated resistor 8 and the intake air temperature detecting resistor 9 are also formed on the insulating film. However, the intake air temperature detection resistor 9 is arranged at a position away from the heating resistor 7 so that the heat of the heating resistor 7 does not affect the temperature detection.

上記のセンサ電圧出力部２ｂの働きについて図２を基に説明する。
発熱抵抗体７が基準温度に通電制御されると、発熱抵抗体７の発熱による温度分布が生じる。バイパス通路に空気の流れが発生していない時は、図２（ａ）に実線グラフで示す様に、発熱抵抗体７の位置を中心として上流側と下流側とで温度分布が左右対称となるため、発熱抵抗体７より上流側に配置される側温抵抗体ＲＵ１、ＲＵ２の検出温度と、発熱抵抗体７より下流側に配置される側温抵抗体ＲＤ１、ＲＤ２の検出温度とが等しくなる。 バイパス通路に順流方向の流れが生じると、図２（ａ）に破線グラフで示す様に、温度分布の中心点（最高温度を示す位置）が下流側（図示右側）へ片寄るため、発熱抵抗体７より上流側に配置される側温抵抗体ＲＵ１、ＲＵ２で検出される温度と、発熱抵抗体７より下流側に配置される側温抵抗体ＲＤ１、ＲＤ２で検出される温度との間に温度差ΔＴが生じる。 The operation of the sensor voltage output unit 2b will be described with reference to FIG.
When the heating resistor 7 is energized and controlled to the reference temperature, a temperature distribution due to heat generated by the heating resistor 7 occurs. When there is no air flow in the bypass passage, the temperature distribution is symmetrical between the upstream side and the downstream side with respect to the position of the heating resistor 7 as shown by the solid line graph in FIG. Therefore, the detected temperatures of the side temperature resistors RU1 and RU2 arranged on the upstream side of the heating resistor 7 are equal to the detected temperatures of the side temperature resistors RD1 and RD2 arranged on the downstream side of the heating resistor 7. . When a flow in the forward flow direction is generated in the bypass passage, the center point of the temperature distribution (the position indicating the maximum temperature) is shifted to the downstream side (the right side in the figure) as shown by the broken line graph in FIG. 7 between the temperature detected by the side temperature resistors RU1 and RU2 arranged upstream of 7 and the temperature detected by the side temperature resistors RD1 and RD2 arranged downstream of the heating resistor 7. A difference ΔT occurs.

この温度差ΔＴにより、上流側の側温抵抗体ＲＵ１、ＲＵ２と下流側の側温抵抗体ＲＤ１、ＲＤ２とで、それぞれ抵抗値が変化して、ブリッジ回路の二つの中点間に電位差が生じる。この電位差が増幅アンプ１６により増幅されて、回路モジュール５に内蔵されるデジタル部５Ａ（図１参照）へ出力される。
一方、バイパス通路を逆流方向に空気の流れが生じる場合は、温度分布の中心点が上流側へ片寄る、つまり、順流方向に空気が流れる場合と温度分布の変化が反転するため、ブリッジ回路の二つの中点間に生じる電位差が逆転して、逆流方向の空気流量を検出できる。これにより、エンジンに吸入される吸入空気量だけでなく、吸気脈動等によって生じる逆流方向の空気流量も検出できる。 Due to this temperature difference ΔT, the resistance values change between the upstream side temperature resistors RU1, RU2 and the downstream side temperature resistors RD1, RD2, respectively, and a potential difference is generated between the two middle points of the bridge circuit. . This potential difference is amplified by the amplification amplifier 16 and output to the digital unit 5A (see FIG. 1) built in the circuit module 5.
On the other hand, when air flows in the reverse direction in the bypass passage, the center point of the temperature distribution is shifted to the upstream side, that is, the change in temperature distribution is reversed when the air flows in the forward direction. The potential difference generated between the two midpoints is reversed, and the air flow rate in the reverse flow direction can be detected. Thereby, not only the amount of intake air sucked into the engine but also the air flow rate in the reverse flow direction caused by intake pulsation or the like can be detected.

回路モジュール５は、本発明の請求項１に記載した信号処理回路部を構成するデジタル部５Ａを備えている。このデジタル部５Ａは、図１に示す様に、増幅アンプ１６によって増幅されたアナログ電圧をデジタル変換するＡ／Ｄ変換器１７と、温度補正に関するデータを組み込んだ補正マップを記憶するＥＥＰＲＯＭ１８と、このＥＥＰＲＯＭ１８に記憶された補正マップを基に、デジタル変換された電圧値（以下、センサ電圧と呼ぶ）に対する温度特性のずれを補正する演算部１９と、温度補正されたセンサ電圧を周波数値に変換してＥＣＵ（図示せず）へ出力するＦ／Ｖ出力変換部２０などを備える。   The circuit module 5 includes a digital unit 5A constituting the signal processing circuit unit described in claim 1 of the present invention. As shown in FIG. 1, the digital unit 5A includes an A / D converter 17 that digitally converts the analog voltage amplified by the amplification amplifier 16, an EEPROM 18 that stores a correction map incorporating data related to temperature correction, Based on the correction map stored in the EEPROM 18, an arithmetic unit 19 that corrects a deviation in temperature characteristics with respect to a digitally converted voltage value (hereinafter referred to as a sensor voltage), and converts the temperature-corrected sensor voltage into a frequency value. F / V output conversion unit 20 that outputs to an ECU (not shown).

ここで、Ｆ／Ｖ出力変換部２０は、デジタル値に変換されたセンサ電圧と周波数値との相関を示す周波数変換テーブルを有し、この周波数変換テーブルを基に、センサ電圧を周波数値に変換する。但し、周波数変換テーブルは、図４（ａ）に示す様に、センサ電圧の変化に対する周波数値の変動率を、逆流方向に空気が流れる時は小さく、順流方向に空気が流れる時は大きく設定している。つまり、センサ電圧を周波数値に直線変換する際に、図４（ａ）に実線で示す特性グラフの様に、流量０ｇ／ｓ相当時（バイパス通路に空気の流れが生じていない時）のセンサ電圧を境に、逆流方向に空気が流れる逆流側では、直線変換を示す特性グラフの傾きが小さく、順流方向に空気が流れる順流側では、直線変換を示す特性グラフの傾きが大きく設定されている。   Here, the F / V output conversion unit 20 has a frequency conversion table indicating the correlation between the sensor voltage converted into a digital value and the frequency value, and converts the sensor voltage into a frequency value based on the frequency conversion table. To do. However, in the frequency conversion table, as shown in FIG. 4A, the fluctuation rate of the frequency value with respect to the change in the sensor voltage is set small when air flows in the reverse flow direction and large when air flows in the forward flow direction. ing. That is, when the sensor voltage is linearly converted to a frequency value, as shown in the characteristic graph shown by the solid line in FIG. 4A, the sensor at a flow rate equivalent to 0 g / s (when no air flows in the bypass passage). The slope of the characteristic graph indicating linear transformation is small on the reverse flow side where air flows in the reverse flow direction from the voltage, and the slope of the characteristic graph indicating linear conversion is set large on the forward flow side where air flows in the forward direction. .

（実施例１の効果）
実施例１に記載したエアフロメータ１は、上述の様に、発熱抵抗体７の発熱により生じる温度分布を基に、バイパス通路を流れる流量の測定だけでなく、空気の流れ方向も検出できる。また、回路モジュール５に内蔵されたＦ／Ｖ出力変換部２０では、センサ電圧を周波数値に変換する際に、逆流側と順流側とでセンサ電圧の変化に対する周波数値の変動率を変えている。具体的には、逆流側では、センサ電圧を周波数値に直線変換する際の傾きが小さく、順流側では、センサ電圧を周波数値に直線変換する際の傾きが大きく設定される。これにより、逆流側と順流側とでセンサ電圧の変化に対する周波数値の変動率を一定にする場合、つまり、図４（ａ）に破線で示す特性グラフの様に、逆流側と順流側とでセンサ電圧を周波数値に一律に直線変換する場合と比較すると、図４（ｂ）に示す様に、流量０ｇ／ｓ時の周波数値を図示矢印で示す様に下げることができる。 (Effect of Example 1)
As described above, the air flow meter 1 described in the first embodiment can detect not only the flow rate flowing through the bypass passage but also the air flow direction based on the temperature distribution generated by the heat generation of the heating resistor 7. Further, in the F / V output conversion unit 20 built in the circuit module 5, when the sensor voltage is converted into the frequency value, the fluctuation rate of the frequency value with respect to the change in the sensor voltage is changed between the reverse flow side and the forward flow side. . Specifically, on the reverse flow side, the gradient when converting the sensor voltage into a frequency value is small, and on the forward flow side, the gradient when converting the sensor voltage into a frequency value is set large. As a result, when the fluctuation rate of the frequency value with respect to the change of the sensor voltage is constant on the reverse flow side and the forward flow side, that is, on the reverse flow side and the forward flow side as in the characteristic graph shown by the broken line in FIG. Compared with the case where the sensor voltage is linearly converted to a frequency value uniformly, as shown in FIG. 4B, the frequency value at a flow rate of 0 g / s can be lowered as shown by the arrow in the figure.

上記の結果、順流方向における低流量側の出力値に低周波数（長い周期）を割り付けることができるので、特に、０〜１０ｇ／ｓの低流量域の精度誤差（１ＬＳＢ誤差による影響度）を小さくできる。
また、逆流側と順流側とでセンサ電圧を周波数値に一律に直線変換する場合と比較して、流量０ｇ／ｓ時の周波数値を下げることにより、逆流側に比べ、順流側の周波数ダイナミックレンジを広く取れるため、逆流側より相対的に高精度を要する順流側の分解能を向上させることができる。
さらに、本実施例のエアフロメータ１は、センサ部２より出力されるアナログ電圧をデジタル値に変換しているので、演算部１９で温度補正を行う際に、デジタル多点補正が可能であり、簡易な回路構成で温度特性のばらつきを精度良く補正することが可能である。 As a result, a low frequency (long cycle) can be assigned to the output value on the low flow rate side in the forward flow direction, and in particular, the accuracy error in the low flow rate region of 0 to 10 g / s (the degree of influence due to the 1LSB error) is reduced. it can.
In addition, the frequency dynamic range on the forward flow side compared to the reverse flow side is reduced by lowering the frequency value at a flow rate of 0 g / s as compared with the case where the sensor voltage is linearly converted into frequency values uniformly on the reverse flow side and the forward flow side. Therefore, it is possible to improve the resolution on the forward flow side that requires higher accuracy than the reverse flow side.
Furthermore, since the airflow meter 1 of the present embodiment converts the analog voltage output from the sensor unit 2 into a digital value, digital multipoint correction is possible when performing temperature correction in the calculation unit 19, It is possible to accurately correct variations in temperature characteristics with a simple circuit configuration.

図５は実施例２に係るエアフロメータ１の回路構成図である。
実施例１では、センサ部２より出力されるアナログ電圧をデジタル値に変換してから周波数値に変換する一例を説明したが、この実施例２に記載するエアフロメータ１は、図５に示す様に、センサ部２より出力されるアナログ電圧を周波数値に変換する構成である。つまり、増幅アンプ１６で増幅されたアナログ電圧がデジタル変換されることなく、そのままＦ／Ｖ出力変換部２０で周波数値に変換されてＥＣＵへ出力される。なお、センサ部２の構成は、実施例１と同じである。 FIG. 5 is a circuit configuration diagram of the air flow meter 1 according to the second embodiment.
In the first embodiment, an example in which the analog voltage output from the sensor unit 2 is converted into a digital value after being converted into a digital value has been described. However, the air flow meter 1 described in the second embodiment has a configuration as shown in FIG. In addition, the analog voltage output from the sensor unit 2 is converted into a frequency value. That is, the analog voltage amplified by the amplification amplifier 16 is converted into a frequency value by the F / V output conversion unit 20 as it is without being digitally converted and output to the ECU. The configuration of the sensor unit 2 is the same as that of the first embodiment.

但し、Ｆ／Ｖ出力変換部２０は、実施例１と同様に、センサ電圧（アナログ電圧）を周波数値に変換する際に、逆流側では、センサ電圧を周波数値に直線変換する際の傾きが小さく、順流側では、センサ電圧を周波数値に直線変換する際の傾きが大きく設定される。 これにより、実施例１の場合と同じく、順流方向における低流量側の出力値に低周波数（長い周期）を割り付けることができるので、特に、０〜１０ｇ／ｓの低流量域の精度誤差（１ＬＳＢ誤差による影響度）を小さくできる。また、逆流側に比べ、順流側の周波数ダイナミックレンジを広く取れるため、逆流側より相対的に高精度を要する順流側の分解能を向上させることができる。   However, when the F / V output conversion unit 20 converts the sensor voltage (analog voltage) to a frequency value, as in the first embodiment, the gradient when the sensor voltage is linearly converted to the frequency value on the reverse flow side is as follows. On the small forward side, a large gradient is set when the sensor voltage is linearly converted to a frequency value. As a result, as in the case of the first embodiment, a low frequency (long cycle) can be assigned to the output value on the low flow rate side in the forward flow direction. (Influence degree due to error) can be reduced. Further, since the frequency dynamic range on the forward flow side can be widened compared to the reverse flow side, it is possible to improve the resolution on the forward flow side that requires relatively higher accuracy than the reverse flow side.

なお、実施例１および２において、センサ電圧を周波数値に直線変換する際に、流量０ｇ／ｓ相当時（バイパス通路に空気の流れが生じていない時）のセンサ電圧を境に、逆流方向に空気が流れる逆流側では、直線変換を示す特性グラフの傾きが小さく、順流方向に空気が流れる順流側では、直線変換を示す特性グラフの傾きが大きく設定されると述べたが、特性グラフの傾きの境界点は、電圧−流量特性の製品毎の固体ばらつきを考慮して、必ずしも流量０ｇ／ｓ点ではなく、流量０ｇ／ｓ点付近の順流側、逆流側どちらかの流量点に設定しても良い。   In Examples 1 and 2, when the sensor voltage is linearly converted to a frequency value, the sensor voltage at the time of a flow rate of 0 g / s (when no air flows in the bypass passage) is used as a boundary in the reverse flow direction. It has been stated that the slope of the characteristic graph showing linear transformation is small on the reverse flow side where air flows, and that the slope of the characteristic graph showing linear transformation is set large on the forward flow side where air flows in the forward flow direction. The boundary point is set at either the forward flow side or the reverse flow side near the flow rate 0 g / s point, not necessarily at the flow rate 0 g / s point, in consideration of the individual variation of the voltage-flow characteristics for each product. Also good.

１ エアフロメータ（空気流量測定装置）
２ センサ部
５Ａ デジタル部（実施例１に係る信号処理回路部）
７ 発熱抵抗体
１７ Ａ／Ｄ変換器（実施例１に係る信号処理回路部）
２０ Ｆ／Ｖ出力変換部（実施例１および実施例２に係る信号処理回路部） 1 Air flow meter (air flow measuring device)
2 sensor unit 5A digital unit (signal processing circuit unit according to the first embodiment)
7 Heating Resistor 17 A / D Converter (Signal Processing Circuit Unit According to Embodiment 1)
20 F / V output conversion unit (signal processing circuit unit according to the first and second embodiments)

Claims (3)

空気通路に配置され、且つ、通電により発熱する発熱抵抗体を有し、この発熱抵抗体の発熱により生じる温度分布を基に、前記空気通路を流れる空気の流量と流れ方向とに応じたアナログ電圧を出力するセンサ部と、
このセンサ部より出力されるアナログ電圧をデジタル値に変換するＡ／Ｄ変換器を内蔵し、このＡ／Ｄ変換器でデジタル変換された電圧値を周波数値に変換して出力する信号処理回路部とを有する空気流量測定装置において、
前記空気通路を一方から他方に向かって空気が流れる方向を順流方向と呼び、前記空気通路を他方向から一方に向かって空気が流れる方向を逆流方向と呼ぶ時に、
前記信号処理回路部は、前記Ａ／Ｄ変換器でデジタル変換されたデジタル値を周波数値に直線変換する際の傾きが、前記順流方向に空気が流れる時よりも、前記逆流方向に空気が流れる時のほうが小さく設定されていることを特徴とする空気流量測定装置。 An analog voltage corresponding to the flow rate and flow direction of the air flowing through the air passage, based on the temperature distribution generated by the heat generation of the heating resistor, having a heating resistor that is disposed in the air passage and generates heat when energized. A sensor unit that outputs
A signal processing circuit unit that includes an A / D converter that converts an analog voltage output from the sensor unit into a digital value, and that converts the voltage value digitally converted by the A / D converter into a frequency value and outputs the frequency value. In an air flow measuring device having
When the direction of air flow from one direction to the other is called the forward flow direction, and the direction of air flow from the other direction to the one direction is called the reverse flow direction,
In the signal processing circuit unit, when the digital value digitally converted by the A / D converter is linearly converted into a frequency value, the air flows in the reverse flow direction rather than when the air flows in the forward flow direction. An air flow rate measuring device characterized in that the hour is set smaller . 空気通路に配置され、且つ、通電により発熱する発熱抵抗体を有し、この発熱抵抗体の発熱により生じる温度分布を基に、前記空気通路を流れる空気の流量と流れ方向とに応じたアナログ電圧を出力するセンサ部と、
このセンサ部より出力されるアナログ電圧を周波数値に変換して出力する信号処理回路部とを有する空気流量測定装置において、
前記空気通路を一方から他方に向かって空気が流れる方向を順流方向と呼び、前記空気通路を他方向から一方に向かって空気が流れる方向を逆流方向と呼ぶ時に、
前記信号処理回路部は、前記センサ部より出力されるアナログ電圧を周波数値に直線変換する際の傾きが、前記順流方向に空気が流れる時よりも、前記逆流方向に空気が流れる時のほうが小さく設定されていることを特徴とする空気流量測定装置。 An analog voltage corresponding to the flow rate and flow direction of the air flowing through the air passage, based on the temperature distribution generated by the heat generation of the heating resistor, having a heating resistor that is disposed in the air passage and generates heat when energized. A sensor unit that outputs
In the air flow rate measuring device having the signal processing circuit unit that converts the analog voltage output from the sensor unit into a frequency value and outputs the frequency value,
When the direction of air flow from one direction to the other is called the forward flow direction, and the direction of air flow from the other direction to the one direction is called the reverse flow direction,
The signal processing circuit unit has a smaller slope when the analog voltage output from the sensor unit is linearly converted to a frequency value when air flows in the reverse flow direction than when air flows in the forward flow direction. An air flow rate measuring device that is set . 請求項１または２に記載した空気流量測定装置において、
前記空気通路は、内燃機関の吸気ポートに接続される吸気通路であり、この吸気通路を前記内燃機関に向かって空気が流れる方向を前記順流方向と呼び、前記吸気通路を前記内燃機関と反対方向へ空気が流れる方向を前記逆流方向と呼ぶことを特徴とする空気流量測定装置。
In the air flow rate measuring device according to claim 1 or 2,
The air passage is an intake passage connected to an intake port of an internal combustion engine. The direction of air flow toward the internal combustion engine is referred to as the forward flow direction, and the intake passage is opposite to the internal combustion engine. A direction in which air flows is referred to as the reverse flow direction.
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