JP2616150B2 - Thermal air flow meter - Google Patents
Thermal air flow meterInfo
- Publication number
- JP2616150B2 JP2616150B2 JP2154436A JP15443690A JP2616150B2 JP 2616150 B2 JP2616150 B2 JP 2616150B2 JP 2154436 A JP2154436 A JP 2154436A JP 15443690 A JP15443690 A JP 15443690A JP 2616150 B2 JP2616150 B2 JP 2616150B2
- Authority
- JP
- Japan
- Prior art keywords
- resistor
- temperature
- output voltage
- heating
- air flow
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Description
【発明の詳細な説明】 ［産業上の利用分野］ この発明は、例えば自動車用エンジンに吸入される空
気の流量を測定する熱式空気流量計に関するものであ
る。Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal air flow meter that measures a flow rate of air taken into an automobile engine, for example.
［従来の技術］ 第２図は例えば特開昭55−50121号公報に示された従
来の熱式空気流量計の構成を示す回路図である。図にお
いて、（１）は流体の通路、（２）は発熱低抗体、
（３）は出力電圧検出用抵抗、（４）は温度補償用抵
抗、（５）は第１抵抗、（６）は第２抵抗、（７）は第
１抵抗（５）と第２抵抗（６）の分圧電圧と、発熱抵抗
体（２）と出力電圧検出用抵抗（３）の分圧電圧との電
位差を増幅する作動増幅器、（８）は作動増幅器（７）
の出力に応じて動作するパワートランジスタ、（９）は
出力端子である。[Prior Art] FIG. 2 is a circuit diagram showing a configuration of a conventional thermal air flow meter disclosed in, for example, JP-A-55-50121. In the figure, (1) is a fluid passage, (2) is a low heat generating antibody,
(3) is an output voltage detection resistor, (4) is a temperature compensation resistor, (5) is a first resistor, (6) is a second resistor, and (7) is a first resistor (5) and a second resistor ( An operational amplifier for amplifying the potential difference between the divided voltage of 6) and the divided voltage of the heating resistor (2) and the output voltage detecting resistor (3), and (8) an operational amplifier (7)
(9) is an output terminal.
このように構成された装置の動作について説明する。
発熱抵抗体（２）の抵抗値をＲH、発熱抵抗体（２）を
流れる電流をＩとすると、発熱抵抗体（２）への供給電
力Ｗは、 Ｗ＝ＲH・I2 ・・・（１） で表される。また、発熱抵抗体（２）と通路（１）を流
れる空気との間の熱伝達率をｈ、発熱抵抗体（２）の表
面積をＳ、発熱抵抗体（２）と空気との温度差を△Ｔと
すると、発熱抵抗体（２）と空気の間の伝熱量Ｈは Ｈ＝ｈ・Ｓ・△Ｔ ・・・（２） と表される。熱平衡状態においてはＷ＝Ｈが成立するの
で ＲH・I2＝ｈ・Ｓ・△Ｔ ・・・（３） となる。一般に熱伝達率ｈはA,Bを定数とすると ｈ＝Ａ＋Ｂ・Qn ・・・（４） なる実験公式で表されるので、温度差△Ｔを一定に保っ
て加熱電流Ｉを測定することにより、空気流量Ｑが得ら
れる。加熱電流Ｉは出力電圧検出用抵抗（３）の両端の
電圧として出力端子（９）より検出される。出力電圧検
出用抵抗（３）には温度による抵抗値変化の影響を小さ
くするため、抵抗温度係数の小さい精密抵抗を使用して
いる。The operation of the thus configured device will be described.
Assuming that the resistance value of the heating resistor (2) is RH and the current flowing through the heating resistor (2) is I, the power W supplied to the heating resistor (2) is: W = RH · I 2 (1) ). Further, the heat transfer coefficient between the heating resistor (2) and the air flowing through the passage (1) is h, the surface area of the heating resistor (2) is S, and the temperature difference between the heating resistor (2) and the air is h. If ΔT, the heat transfer amount H between the heating resistor (2) and the air is represented as H = h · S · ΔT (2). In the thermal equilibrium state, W = H holds, so that RH · I 2 = h · S · ΔT (3) Since generally the heat transfer coefficient h is A, h = A + B · Q n ··· (4) made experiments represented the official is when B is referred to as constant, to measure the heating current I while maintaining the temperature difference △ T constant As a result, an air flow rate Q is obtained. The heating current I is detected from the output terminal (9) as a voltage across the output voltage detection resistor (3). A precision resistor having a small temperature coefficient of resistance is used for the output voltage detection resistor (3) in order to reduce the influence of a change in resistance value due to temperature.
△Ｔを一定に保つために作動増幅器（７）によりフィ
ードバックをかけ加熱電流Ｉを制御している。しかし、
実際には熱伝達率ｈを表す定数A,Bが温度による依存性
を持つため△Ｔに適度な温度係数を持たせてその補償を
行っている。前記出力電圧検出用抵抗（３）の抵抗値を
ＲM、第１、第２抵抗の抵抗値をそれぞれR1、R2とする
と、ブリッジ回路の平衡条件より ＲH・R2＝ＲM（ＲK＋R1） ・・・（５） が成り立つ。また、発熱抵抗体（２）の抵抗温度係数を
αＨ、温度をＴH、温度補償用抵抗（４）の抵抗温度係
数をαＫ、温度をＴKとすると、それぞれの抵抗値ＲH、
ＲKは ＲH＝ＲHO（１＋αＨ・ＴH） ・・・（６） ＲK＝ＲKO（１＋αＫ・ＴK） ・・・（７） と表される。ここでＲHO、ＲKOはそれぞれ発熱抵抗体
（２）、温度補償用抵抗（４）の温度０℃の時の抵抗値
である。温度補償用抵抗の温度ＴKは吸入空気温度Taに
等しいので、上記（６）、（７）式を（５）式に代入し
て変形すると △Ｔ＝ＴH−Ta ＝（αＫ・ＲM・ＲKO／αＨ・R2・ＲHO−１）Ta ＋ＲM（ＲKO＋R1）／αＨ・R2・ＲHO−1/αＨ ・・・（８） となる。従って、R1とR2の値を変えることによって△Ｔ
の値及び温度係数を調整することができる。（３）、
（４）式より加熱電流Ｉは Ｉ＝（ｈ・Ｓ・△T/RH）1/2 ＝｛（Ａ＋Ｂ・Qn）・Ｓ・△T/RH｝1/2 ・・・（９） と表せるので、△T/RHの温度係数がA,Bの温度計数を相
殺するようなR1,R2を選ぶことより温度補償できる。
（９）式中のA,B,RHいずれも正の温度係数を持ち、A,B
の温度係数よりＲHの温度係数の方が大きいので、△Ｔ
にも正の温度係数を持たせることになる。In order to keep ΔT constant, feedback is applied by the operational amplifier (7) to control the heating current I. But,
Actually, since the constants A and B representing the heat transfer coefficient h have a temperature dependency, ΔT is given an appropriate temperature coefficient to compensate for it. Assuming that the resistance value of the output voltage detection resistor (3) is RM, and the resistance values of the first and second resistors are R1 and R2, respectively, RH · R2 = RM (RK + R1)... 5) holds. Assuming that the resistance temperature coefficient of the heating resistor (2) is αH, the temperature is TH, the resistance temperature coefficient of the temperature compensation resistor (4) is αK, and the temperature is TK, the respective resistance values RH,
RK is expressed as RH = RHO (1 + αH · TH) (6) RK = RKO (1 + αK · TK) (7) Here, RHO and RKO are resistance values of the heating resistor (2) and the temperature compensation resistor (4) at a temperature of 0 ° C., respectively. Since the temperature TK of the temperature compensation resistor is equal to the intake air temperature Ta, when the above equations (6) and (7) are substituted into the equation (5) and deformed, ΔT = TH−Ta = (αK · RM · RKO / αH · R2 · RHO-1) Ta + RM (RKO + R1) / αH · R2 · RHO−1 / αH (8) Therefore, by changing the values of R1 and R2, ΔT
And the temperature coefficient can be adjusted. (3),
From equation (4), the heating current I is given by I = (hｈS △ T / RH) 1/2 = ｛(A + B ・ Q n ) ・ S △ {T / RH} 1/2 (9) Since it can be expressed, temperature compensation can be performed by selecting R1 and R2 such that the temperature coefficient of ΔT / RH cancels the temperature coefficient of A and B.
(9) All of A, B, and RH in the equation have positive temperature coefficients, and A, B
Since the temperature coefficient of RH is larger than the temperature coefficient of
Also have a positive temperature coefficient.
［発明が解決しようとする課題］ しかしながら、前記（４）式の熱伝達率ｈは空気の対
流による熱伝達率であり、熱放射による熱伝達率は含ん
でいない。熱放射による熱伝達率を含んだ形で表すと ｈ＝（Ａ＋Ｂ・Qn）＋（Ｋε△T3） ・・・（10） となる。ここではＫは定数、εは発熱抵抗体（２）の放
射率である。上記（10）式から分かるように、流量Ｑが
小さくなると右辺第２頂で表される熱放射による熱伝達
率の影響が無視できなくなるが、同項中の△Ｔに温度係
数を持たせているため、全体の熱伝達率の温度係数は
（４）式で表される空気の対流のみの熱伝達率のそれよ
りも大きくなる。よって従来の温度補償の方法では小流
量域において空気温度の変化による誤差が生じることに
なる。[Problem to be Solved by the Invention] However, the heat transfer coefficient h in the equation (4) is a heat transfer coefficient due to convection of air, and does not include a heat transfer coefficient due to heat radiation. When expressed in a form including the heat transfer coefficient due to heat radiation, h = (A + B · Q n ) + (Kε △ T 3 ) (10) Here, K is a constant, and ε is the emissivity of the heating resistor (2). As can be seen from the above equation (10), when the flow rate Q becomes small, the influence of the heat transfer coefficient due to the heat radiation expressed by the second peak on the right side cannot be ignored, but ΔT in the same term has a temperature coefficient. Therefore, the temperature coefficient of the overall heat transfer coefficient becomes larger than that of the heat transfer coefficient of only the convection of the air represented by the equation (4). Therefore, in the conventional temperature compensation method, an error occurs due to a change in the air temperature in a small flow rate region.
また、空気の温度が高くなるにつれて温度差△Ｔも大
きくなるので加熱電流Ｉも大きくなる。加熱電流Ｉの最
大値は電源電圧とブリッジ回路の抵抗によって決まって
いるので、空気の温度が高いときには加熱電流Ｉが最大
値に達するときの流量Ｑは空気の温度が低いときに比べ
て小さくなる。つまり、空気の温度が高いときには測定
可能な流量範囲が小さくなることになる。Further, as the temperature of the air increases, the temperature difference ΔT increases, so that the heating current I also increases. Since the maximum value of the heating current I is determined by the power supply voltage and the resistance of the bridge circuit, when the air temperature is high, the flow rate Q when the heating current I reaches the maximum value is smaller than when the air temperature is low. . That is, when the air temperature is high, the measurable flow rate range becomes small.
この発明は上記のような問題点を解決するためになさ
れたもので、吸入空気の温度変化による流量誤差を低減
し、小流量域においてもより正確な流量計測ができる熱
式空気流量計を得ることを目的とする。SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a thermal air flow meter capable of reducing a flow rate error due to a change in intake air temperature and performing more accurate flow rate measurement even in a small flow rate range. The purpose is to:
［課題を解決するための手段］ この発明に係る熱式空気流量式は、発熱抵抗体と空気
との温度差を常に一定に保つと共に、上記発熱抵抗体の
一部とこの発熱低抗体と直列に接続された出力電圧検出
用抵抗とを合わせた抵抗の両端の電圧を出力電圧として
検出するものである。[Means for Solving the Problems] The thermal air flow type according to the present invention keeps the temperature difference between the heating resistor and the air always constant, and connects a part of the heating resistor and the heating low antibody in series. And a voltage across the resistor including the output voltage detecting resistor connected to the output voltage detecting circuit.
［作用］ 上記のように構成された熱式空気流量計では、前記
（10）式における△Ｔが定数となるので、同式右辺第２
項で表される熱放射による熱伝達率の温度依存性の影響
が除去され、全体の熱伝達率の温度係数は同式右辺第１
項で表される空気の対流による熱伝達率の温度係数のみ
となる。△Ｔを一定としたために従来の温度補償法は使
えず、前記（９）式の加熱電流Ｉは負の温度係数を持つ
ことになるが、出力端子を発熱低抗体（２）の一部より
引き出して、出力電圧検出用抵抗（３）と発熱抵抗体
（２）の一部の合わせた抵抗の両端の電圧を出力電圧と
して検出することにより、正の温度係数を持つ発熱低抗
体（２）の作用で加熱電流Ｉの温度依存性が相殺され
る。[Operation] In the thermal air flow meter configured as described above, ΔT in the above equation (10) is a constant, so that
The effect of the temperature dependence of the heat transfer coefficient due to the heat radiation represented by the term is eliminated, and the temperature coefficient of the overall heat transfer coefficient
Only the temperature coefficient of the heat transfer coefficient due to the convection of the air represented by the term. The conventional temperature compensation method cannot be used because ΔT is constant, and the heating current I in the above equation (9) has a negative temperature coefficient. By extracting the output voltage and detecting the voltage between both ends of the combined resistor of the output voltage detection resistor (3) and a part of the heating resistor (2) as an output voltage, a heat-generating low antibody (2) having a positive temperature coefficient , The temperature dependence of the heating current I is offset.
また、温度差△Ｔを一定としたため、空気温度の上昇
による加熱電流Ｉの増大が抑制され、高温時における測
定可能流量範囲が拡大される。Further, since the temperature difference ΔT is fixed, an increase in the heating current I due to an increase in the air temperature is suppressed, and the measurable flow rate range at a high temperature is expanded.
［実施例］ 第１図はこの発明の一実施例による熱式空気流量計の
構成を示す回路図である。図において、（１）〜（９）
は第２図に示した従来例の（１）〜（９）と相当部分を
示す。発熱抵抗体（２）と空気との温度差△Ｔを一定に
するために、この実施例では第２抵抗（６）に下記（1
1）式で与えられる抵抗値を持つものを使用している。FIG. 1 is a circuit diagram showing a configuration of a thermal air flow meter according to an embodiment of the present invention. In the figure, (1) to (9)
Indicates parts corresponding to (1) to (9) of the conventional example shown in FIG. In order to keep the temperature difference ΔT between the heating resistor (2) and the air constant, in this embodiment, the second resistor (6) has the following (1).
1) A resistor with the resistance given by the equation is used.
R2＝αＫ・ＲM・ＲKO／αＨ・ＲHO ・・・（11） このような抵抗値を持つ第２抵抗（６）を使用するこ
とにより前記（８）式の右辺第１項は０となり、△Ｔは
（12）式で与えられるような一定の値になる。R2 = αK · RM · RKO / αH · RHO (11) By using the second resistor (6) having such a resistance value, the first term on the right side of the equation (8) becomes 0, and △ T is a constant value as given by equation (12).
△Ｔ＝R1/αＫ・ＲKO−1/αＨ＋1/αＫ ・・・（12） またこの実施例では、出力端子（９）を発熱抵抗体
（２）の一部より取り出している。こうすることにより
出力電圧Ｖは Ｖ＝Ｉ（ＲM＋ｋ・ＲH） （ｋ＜１） ・・・（13） となり係数ｋを調節することにより加熱電流Ｉの温度係
数とｋ・ＲHの温度係数をうまく相殺させることがで
き、温度補償された出力電圧Ｖが得られる。ΔT = R1 / αK · RKO−1 / αH + 1 / αK (12) In this embodiment, the output terminal (9) is extracted from a part of the heating resistor (2). By doing so, the output voltage V becomes as follows: V = I (RM + k.RH) (k <1) (13) By adjusting the coefficient k, the temperature coefficient of the heating current I and the temperature coefficient of k.RH can be improved. The output voltage V can be canceled out and temperature compensated.
［発明の効果］ 以上のようにこの発明によれば、発熱抵抗体と空気と
の温度差を常に一定に保つと共に、上記発熱抵抗体の一
部とこの発熱抵抗体と直列に接続された出力電圧検出用
抵抗とを合わせた抵抗の両端の電圧を出力電圧として検
出するので、熱放射熱伝達率の温度係数による影響がな
くなり、空気温度の変化による誤差を低減でき、さら
に、高温時において従来より広い流量範囲の測定が可能
となる。[Effects of the Invention] As described above, according to the present invention, the temperature difference between the heating resistor and the air is always kept constant, and a part of the heating resistor and the output connected in series with the heating resistor are connected. Since the voltage at both ends of the resistor combined with the voltage detection resistor is detected as the output voltage, the effect of the temperature coefficient of the heat radiation heat transfer coefficient is eliminated, errors due to changes in air temperature can be reduced, and the conventional technology can be used at high temperatures. A wider flow range can be measured.
第１図はこの発明の一実施例による熱式空気流量計の構
成を示す回路図、第２図は従来の熱式空気流量計の構成
を示す回路図である。 図において、（１）は流体通路、（２）は発熱低抗体、
（３）は出力電圧検出用抵抗、（４）は温度補償用抵
抗、（５）は第１抵抗、（６）は第２抵抗、（９）は出
力端子である。 なお、各図中同一符号は同一または相当部分を示す。FIG. 1 is a circuit diagram showing a configuration of a thermal air flow meter according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a configuration of a conventional thermal air flow meter. In the figure, (1) is a fluid passage, (2) is a low heat-generating antibody,
(3) is an output voltage detection resistor, (4) is a temperature compensation resistor, (5) is a first resistor, (6) is a second resistor, and (9) is an output terminal. In the drawings, the same reference numerals indicate the same or corresponding parts.
Claims (1)
る発熱抵抗体と、上記流体通路中に配置され流体の温度
を検出する温度補償用抵抗及びこの温度補償用抵抗と直
列に接続された第１抵抗と、上記発熱低抗体と直列に接
続された出力電圧検出用抵抗と、上記第１抵抗と直列に
接続された第２抵抗とをそれぞれブリッジ回路の４辺と
して持つ熱式空気流量計において、上記発熱抵抗体と空
気との温度差を常に一定に保つと共に、上記発熱抵抗体
の一部と上記出力電圧検出用抵抗とを合わせた抵抗の両
端の電圧を出力電圧として検出することを特徴とする熱
式空気流量計。1. A heating resistor disposed in a fluid passage for detecting a flow rate of a fluid, a temperature compensating resistor disposed in the fluid passage for detecting a temperature of the fluid, and connected in series with the temperature compensating resistor. Thermal air flow having a first resistor, an output voltage detecting resistor connected in series with the heat-generating low antibody, and a second resistor connected in series with the first resistor as four sides of a bridge circuit, respectively. A temperature difference between the heating resistor and the air is always kept constant, and a voltage between both ends of a resistor obtained by combining a part of the heating resistor and the output voltage detection resistor is detected as an output voltage. A thermal air flow meter characterized by the following.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2154436A JP2616150B2 (en) | 1990-06-13 | 1990-06-13 | Thermal air flow meter |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2154436A JP2616150B2 (en) | 1990-06-13 | 1990-06-13 | Thermal air flow meter |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH0450621A JPH0450621A (en) | 1992-02-19 |
| JP2616150B2 true JP2616150B2 (en) | 1997-06-04 |
Family
ID=15584153
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2154436A Expired - Fee Related JP2616150B2 (en) | 1990-06-13 | 1990-06-13 | Thermal air flow meter |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2616150B2 (en) |
-
1990
- 1990-06-13 JP JP2154436A patent/JP2616150B2/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0450621A (en) | 1992-02-19 |
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| Date | Code | Title | Description |
|---|---|---|---|
| LAPS | Cancellation because of no payment of annual fees |