JPH0843159A - Air flowmeter - Google Patents

Abstract

PURPOSE:To measure an average air flow rate accurately by disposing two heating resistors in an air suction channel and subtracting the reverse flow rate automatically from a forward flow rate in case of a pulsating flow accompanied with reverse flow using the heat generated from the heating resistors. CONSTITUTION:Two heating resistors 2, 3 are disposed in a suction channel while being separated by 0.1-1.5mm and heated by means of hot wire circuits 1a, 1b. A signal from the upstream side resistor 2 is detected as a flow rate signal for forward flow. In case of reverse flow, the air heated by the downstream side resistor 3 covers the upstream side resistor 2 and the flow rate signal is decreased. At the initial stage of a subsequent forward flow, air heated by the resistors 2, 3 comes back to cover the upstream side resistor 2 thus decreasing the flow rate signal. In other words, the flow rate signal decrease two times and the reverse flow rate is subtracted automatically thus realizing accurate detection of the average flow rate of pulsating air flow containing a reverse flow.

Description

【発明の詳細な説明】Detailed Description of the Invention

【０００１】[0001]

【産業上の利用分野】内燃機関の吸入空気流量を測定す
る空気流量計に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air flow meter for measuring the intake air flow rate of an internal combustion engine.

【０００２】[0002]

【従来の技術】自動車の電子制御燃料噴射装置の空気流
量計として、熱線式流速計の原理を用いた流量計は、小
形で応答性が良く、かつ、質量流量が、直接測定できる
ので広く用いられている。しかし、熱線式空気流量計は
流れの方向を検出できない欠点があり、しぼり弁全開時
のように、空気流が逆流を伴った脈動流である場合に大
きな誤差を生じる課題がある。この課題に対して、従来
は特公昭62−14705 号公報に示すように、熱線式空気流
量計の信号に補正係数をかける方法を用いていた。ま
た、特開平1−185416 号公報には１枚の電気絶縁体上に
２ケの発熱抵抗体を設けて、該２ケの発熱抵抗体を用い
た熱線式空気流量計の信号の差から空気流の方向を検知
する方法を用いていた。2. Description of the Related Art As an air flow meter for an electronically controlled fuel injection system for automobiles, a flow meter using the principle of a hot-wire anemometer is widely used because it is small and has good responsiveness and the mass flow rate can be directly measured. Has been. However, the hot-wire air flow meter has a drawback that the flow direction cannot be detected, and there is a problem that a large error occurs when the air flow is a pulsating flow accompanied by backflow, such as when the restriction valve is fully opened. To solve this problem, conventionally, as shown in Japanese Patent Publication No. 62-14705, a method of applying a correction coefficient to the signal of the hot wire type air flow meter has been used. Further, in Japanese Patent Application Laid-Open No. 1-185416, two heating resistors are provided on one sheet of an electric insulator, and the air flow rate meter uses the two heating resistors to detect the difference in signal from the air. The method of detecting the flow direction was used.

【０００３】[0003]

【発明が解決しようとする課題】しかしながら、この方
法は、対症療法的で精度が悪くかつ補正係数を実験によ
り求めるのでシステムの開発に時間がかかる欠点があ
り、特に、しぼり弁全開時のように、空気流が逆流を伴
った脈動流である場合には十分な精度を確保することは
できなかった。However, this method has a drawback that it takes time to develop the system because it is symptomatic and inaccurate, and the correction coefficient is obtained by an experiment, and especially when the restriction valve is fully opened. However, when the air flow is a pulsating flow accompanied by backflow, sufficient accuracy could not be ensured.

【０００４】本発明の目的は、空気流が逆流を伴った脈
動流であるにも平均空気流量を高精度に測定することが
できる空気流量計を提供することにある。An object of the present invention is to provide an air flow meter capable of measuring the average air flow rate with high accuracy even if the air flow is a pulsating flow accompanied by backflow.

【０００５】[0005]

【課題を解決するための手段】本発明は、しぼり弁全開
時のように空気流が逆流を伴った脈動流である場合に、
発熱抵抗体の発生熱で逆流流量を順流流量から自動的に
減算する方法である。吸気通路内の空気流中に２ケの発
熱抵抗体を近接して配置した熱式空気流量計を設けて、
該２ケの発熱抵抗体のうち上流側の発熱抵抗体からの信
号を機関の吸入空気流量信号として、デジタルコンピュ
ータに入力する。該コンピュータ内で該流量信号を空気
流量に換算して、吸気工程の間、加算し平均空気流量を
求める。DISCLOSURE OF THE INVENTION The present invention, in the case where the air flow is a pulsating flow accompanied by backflow, such as when the restriction valve is fully opened,
This is a method of automatically subtracting the backward flow rate from the forward flow rate by the heat generated by the heating resistor. By providing a thermal air flow meter in which two heating resistors are arranged close to each other in the air flow in the intake passage,
The signal from the upstream heating resistor of the two heating resistors is input to the digital computer as an intake air flow rate signal of the engine. The flow rate signal is converted into an air flow rate in the computer and added during the intake stroke to obtain an average air flow rate.

【０００６】[0006]

【作用】２ケの発熱抵抗体を０.１から１.５mm程度離し
て並べ、両発熱抵抗体を熱線回路で発熱させておき、上
流側の発熱抵抗体の信号を流量信号とする。この構成に
よると、逆流時は、下流側の発熱抵抗体で加熱された空
気が、上流側の発熱抵抗体をおおい、流量信号が小さく
なる。さらに、続いて起こる順流の初期に、下流側と上
流側の発熱抵抗体で加熱された空気が戻ってきて、再
び、上流側の発熱抵抗体をおおうので、信号が低下す
る。この２回の信号低下が、逆流流量を自動的に減算す
ることになり、逆流を含む脈動流の平均流量を得ること
ができる。Operation: Two heating resistors are arranged at a distance of about 0.1 to 1.5 mm, both heating resistors are caused to generate heat by the hot wire circuit, and the signal of the upstream heating resistor is used as the flow rate signal. According to this configuration, during backflow, the air heated by the heating resistor on the downstream side covers the heating resistor on the upstream side, and the flow rate signal becomes small. Furthermore, the air heated by the heating resistors on the downstream side and the upstream side returns at the beginning of the subsequent forward flow, and covers the heating resistors on the upstream side again, so that the signal decreases. These two signal decreases automatically subtract the backflow rate, and the average flow rate of the pulsating flow including backflow can be obtained.

【０００７】[0007]

【実施例】図１は本発明の実施例である。２ケの発熱抵
抗体２，３を０.１から１.５mm程度離して並べ、両発熱
抵抗体をそれぞれ熱線回路１ａ，１ｂで発熱させてお
き、上流側の発熱抵抗体２の信号を流量信号とする。逆
流時は、下流側の発熱抵抗体３で加熱された空気が、上
流側の発熱抵抗体２をおおうので、流量信号は小さくな
る。さらに、続いて起きる順流の初期は、下流側と上流
側の発熱抵抗体３，２で加熱された空気が戻ってきて、
再び、上流側の発熱抵抗体２をおおうので、流量信号が
低下する。この２回の流量信号の低下が、逆流流量を自
動的に減算することになり、逆流を含む脈動流の平均流
量を得ることができる。なお、定常順流時には、上流側
の発熱抵抗体２は、下流側の発熱抵抗体３による加熱空
気の影響を全く受けないので、順流方向の空気流量も正
確に測ることができる。FIG. 1 shows an embodiment of the present invention. The two heating resistors 2 and 3 are arranged at a distance of 0.1 to 1.5 mm, both heating resistors are heated by the heating wire circuits 1a and 1b, respectively, and the signal of the upstream heating resistor 2 is flowed. Signal. During reverse flow, the air heated by the heating resistor 3 on the downstream side covers the heating resistor 2 on the upstream side, so that the flow rate signal becomes small. Furthermore, at the beginning of the subsequent forward flow, the air heated by the heating resistors 3 and 2 on the downstream side and the upstream side returns,
Since the heating resistor 2 on the upstream side is covered again, the flow rate signal is lowered. These two decreases in the flow rate signal automatically subtract the backflow rate, and the average flow rate of the pulsating flow including backflow can be obtained. During steady steady flow, the heating resistor 2 on the upstream side is not affected by the heating air by the heating resistor 3 on the downstream side, so that the air flow rate in the forward flow direction can be accurately measured.

【０００８】図２は発熱抵抗体２，３の詳細である。発
熱抵抗体２，３は特開昭56−106159号公報あるいは米国
特許明細書第4,517,837 号に開示された構造で、円筒型
のアルミナボビンの外周に細い白金線を巻くか、あるい
は白金薄膜を形成しその上をガラス被覆したものであ
る。発熱抵抗体２，３は０.１から１.５mm程度離して該
空気流に直角にかつその空気流に対して上下流の関係に
なるように、支柱６，７を用いて固定壁８に支持固定さ
れている。なお、支柱６は、支柱７に比べ細くすること
により、発熱抵抗体から固定壁への熱伝導量を小さくし
て空気流量の測定精度の改善を図っている。FIG. 2 shows details of the heating resistors 2 and 3. The heating resistors 2 and 3 have the structure disclosed in JP-A-56-106159 or US Pat. No. 4,517,837. A thin platinum wire is wound around the outer circumference of a cylindrical alumina bobbin or a platinum thin film is formed. The glass is coated on it. The heating resistors 2 and 3 are attached to the fixed wall 8 by using columns 6 and 7 so that they are separated from 0.1 to 1.5 mm at a right angle to the air flow and in an upstream / downstream relationship with respect to the air flow. Supported and fixed. In addition, by making the strut 6 thinner than the strut 7, the amount of heat conduction from the heating resistor to the fixed wall is reduced to improve the measurement accuracy of the air flow rate.

【０００９】図３は図２の変形例である。１枚の電気絶
縁板（セラミックス，プラスチック，シリコン等）９上
に２ケの発熱抵抗体２，３を設け、該２ケの発熱抵抗体
２，３の間にスリット１０を設けて発熱抵抗体２，３間
の熱伝導を遮断する構造である。電気絶縁板９は、熱容
量と機械的強度の両立の点から厚さは０.０３ から０.
０５mm が最適であり、セラミックス板１１にガラス等
で接着される。セラミックス板１１上には、熱線回路１
ａ，１ｂもあり、発熱抵抗体２，３と熱線回路１ａ，１
ｂとの接続はアルミ線等を用いたワイヤボンデングによ
る。この構造は、図２に比べ、空気流に対して発熱抵抗
体２と３の位置関係がばらつきにくい効果がある。FIG. 3 is a modification of FIG. Two heating resistors 2 and 3 are provided on one electric insulating plate (ceramics, plastic, silicon, etc.) 9, and a slit 10 is provided between the two heating resistors 2 and 3 to provide the heating resistor. It is a structure that blocks heat conduction between the second and third parts. The electrical insulating plate 9 has a thickness of 0.03 to 0.02 in terms of both heat capacity and mechanical strength.
The optimum length is 05 mm, which is adhered to the ceramic plate 11 with glass or the like. On the ceramic plate 11, the heat wire circuit 1
There are also a and 1b, and the heating resistors 2 and 3 and the heat wire circuits 1a and 1
Connection with b is by wire bonding using aluminum wire or the like. This structure has an effect that the positional relationship between the heating resistors 2 and 3 is less likely to vary with respect to the air flow, as compared with FIG.

【００１０】図４は熱線回路１ａ，１ｂの詳細である。
図３と同じ番号を付けた部分は同じ機能を持つ。１枚の
電気絶縁板９上に２ケの発熱抵抗体２，３を設けた流量
検出部、さらに他の１枚の電気絶縁板１１上に２ケの測
温抵抗体４，５を設けた空気温度検出部がある。熱線回
路１ａは該発熱抵抗体２，測温抵抗体４，抵抗１２，１
３，１６を含むホイートストンブリッジ，トランジスタ
２０，差動増幅器１９で構成される。熱線回路１ｂは発
熱抵抗体３，測温抵抗体５，抵抗１４，１５，１７を含
むホイートストンブリッジ，トランジスタ２１，差動増
幅器１８で構成される。その２ケの熱線回路のうち、吸
気通路の上流側に位置する発熱抵抗体２のホイートスト
ンブリッジ中点の電位を流量信号として、ゼロスパン調
整回路２２で空気流量と信号の関係を所望の値に調整さ
れ、デジタルコンピュータ２３に入力して必要燃料流量
を求める。FIG. 4 shows details of the hot wire circuits 1a and 1b.
The parts with the same numbers as in FIG. 3 have the same functions. A flow rate detection unit having two heating resistors 2 and 3 provided on one electric insulating plate 9, and two temperature measuring resistors 4 and 5 provided on another electric insulating plate 11. There is an air temperature detector. The heating wire circuit 1a includes the heating resistor 2, the temperature measuring resistor 4, the resistors 12, 1
It comprises a Wheatstone bridge including transistors 3 and 16, a transistor 20 and a differential amplifier 19. The hot wire circuit 1b is composed of a heating resistor 3, a temperature measuring resistor 5, a Wheatstone bridge including resistors 14, 15, and 17, a transistor 21, and a differential amplifier 18. Of the two heat wire circuits, the potential at the midpoint of the Wheatstone bridge of the heating resistor 2 located on the upstream side of the intake passage is used as the flow rate signal, and the zero span adjustment circuit 22 adjusts the relationship between the air flow rate and the signal to a desired value. Then, it is input to the digital computer 23 to obtain the required fuel flow rate.

【００１１】図５は図４の変形例で，ホイートストンブ
リッジを１ケにして電子回路を簡単化したものである。
図４と同じ番号を付した部分は同一の機能を持つ。空気
流に対して上流側の発熱抵抗体２，下流側の発熱抵抗体
３をホイートストンブリッジの１辺に組込み，温度補償
のための測温抵抗体４，抵抗１２，１３，１６，トラン
ジスタ２０，差動増幅器１９で、発熱抵抗体２と３の抵
抗値の和が一定値になるように供給電流を増減する。発
熱抵抗体２と３の中点の電位信号を流量信号としてゼロ
スパン調整回路２２で空気流量と信号の関係を所望の値
に調整して、デジタルコンピュータ２３に入力する。ま
た、図５には、空気流に対する発熱抵抗体２と３の位置
関係を示し、順流時に発熱抵抗体２が発熱抵抗体３に対
して上流に位置することを示している。FIG. 5 is a modification of FIG. 4, in which the Wheatstone bridge is one and the electronic circuit is simplified.
The parts with the same numbers as in FIG. 4 have the same functions. The upstream heating resistor 2 and the downstream heating resistor 3 with respect to the air flow are incorporated into one side of the Wheatstone bridge, and the temperature measuring resistor 4, the resistors 12, 13, 16 and the transistor 20, for temperature compensation are incorporated. The differential amplifier 19 increases or decreases the supply current so that the sum of the resistance values of the heating resistors 2 and 3 becomes a constant value. The zero-span adjusting circuit 22 adjusts the relationship between the air flow rate and the signal to a desired value by using the potential signal at the midpoint of the heating resistors 2 and 3 as a flow rate signal, and inputs the signal to the digital computer 23. Further, FIG. 5 shows the positional relationship between the heat generating resistors 2 and 3 with respect to the air flow, and shows that the heat generating resistor 2 is located upstream of the heat generating resistor 3 during forward flow.

【００１２】この構成によると、逆流時は、下流側の発
熱抵抗体３で加熱された空気が、上流側の発熱抵抗体２
をおおい、一方両発熱抵抗体の抵抗値の和は一定値に制
御されているので、上流側の発熱抵抗体２の抵抗値は下
流側の発熱抵抗体３の抵抗値より大となり、両発熱抵抗
体２，３の中点の電位が低下する。さらに、続いて起こ
る順流の始めは、下流側と上流側の発熱抵抗体で加熱さ
れた空気が戻ってきて、再び、上流側の発熱抵抗体２を
おおうので、該中点電位が低下する。この２回の信号低
下が、逆流流量を自動的に減算することになり、逆流を
含む脈動流の平均流量を近似的に得ることができる。According to this structure, during reverse flow, the air heated by the heating resistor 3 on the downstream side is heated by the heating resistor 2 on the upstream side.
On the other hand, since the sum of the resistance values of both heating resistors is controlled to a constant value, the resistance value of the heating resistor 2 on the upstream side becomes larger than the resistance value of the heating resistor 3 on the downstream side. The potential at the midpoint of the resistors 2 and 3 decreases. Further, at the beginning of the subsequent forward flow, the air heated by the heating resistors on the downstream side and the upstream side returns and covers the heating resistor 2 on the upstream side again, so that the midpoint potential decreases. These two signal decreases automatically subtract the backflow rate, and the average flow rate of the pulsating flow including backflow can be approximately obtained.

【００１３】図６は図４の変形例で、図５と同様にホイ
ートストンブリッジを１ケにして電子回路を簡単化した
ものである。図４と同じ番号を付した部分は同一の機能
を持つ。空気流に対して上流側の発熱抵抗体２，下流側
の発熱抵抗体３，温度補償のための測温抵抗体４，抵抗
１２，２４，２５，２６，トランジスタ２０，差動増幅
器１９からなり、両発熱抵抗体２，３の下端の電位の平
均値と抵抗１２，２６の中点の電位が等しくなるよう
に、即ち、ほぼ発熱抵抗体２と３の抵抗値の和が一定値
になるように供給電流が増減される。上流側の発熱抵抗
体２の下端の電位を流量信号としてゼロスパン調整回路
２２で空気流量と信号の関係を所望の値に調整して、デ
ジタルコンピュータ２３に入力する。FIG. 6 is a modification of FIG. 4, in which the Wheatstone bridge is set to one and the electronic circuit is simplified as in the case of FIG. The parts with the same numbers as in FIG. 4 have the same functions. It consists of a heating resistor 2 on the upstream side with respect to the air flow, a heating resistor 3 on the downstream side, a temperature measuring resistor 4 for temperature compensation 4, resistors 12, 24, 25, 26, a transistor 20, and a differential amplifier 19. , So that the average value of the potentials at the lower ends of both heating resistors 2 and 3 becomes equal to the potential at the midpoint of resistors 12 and 26, that is, the sum of the resistance values of heating resistors 2 and 3 becomes a constant value. Thus, the supply current is increased or decreased. The potential of the lower end of the heating resistor 2 on the upstream side is used as a flow rate signal, and the zero span adjusting circuit 22 adjusts the relationship between the air flow rate and the signal to a desired value and inputs it to the digital computer 23.

【００１４】この構成によると、図５と同様に、逆流時
は、下流側の発熱抵抗体３で加熱された空気が、上流側
の発熱抵抗体２をおおい、上流側の発熱抵抗体２の抵抗
値は下流側の発熱抵抗体３の抵抗値より大となり、上流
側の発熱抵抗体２の下端の電位即ち流量信号が低下す
る。さらに、続いて起こる順流の初期は、下流側と上流
側の発熱抵抗体２，３で加熱された空気が戻ってきて、
再び、上流側の発熱抵抗体２をおおうので、その流量信
号が低下する。この２回の信号低下が、逆流流量を自動
的に減算することになり、逆流を含む脈動流の平均流量
を近似的に得ることができる。According to this structure, as in the case of FIG. 5, the air heated by the heating resistor 3 on the downstream side covers the heating resistor 2 on the upstream side and the heating resistor 2 on the upstream side during reverse flow. The resistance value becomes larger than the resistance value of the heating resistor 3 on the downstream side, and the potential at the lower end of the heating resistor 2 on the upstream side, that is, the flow rate signal decreases. Further, in the initial stage of the subsequent forward flow, the air heated by the heating resistors 2 and 3 on the downstream side and the upstream side returns,
Again, since the heating resistor 2 on the upstream side is covered, the flow rate signal is lowered. These two signal decreases automatically subtract the backflow rate, and the average flow rate of the pulsating flow including backflow can be approximately obtained.

【００１５】[0015]

【発明の効果】本発明によれば、しぼり弁全開時のよう
に、空気流が逆流を伴った脈動流である場合にも、自動
的にその平均空気流量を求めることができる。その結果
として、エンジンの空燃比の高精度制御が可能となり低
燃費，低排気のエンジンを提供できる。According to the present invention, even when the air flow is a pulsating flow accompanied by a back flow, such as when the throttle valve is fully opened, the average air flow rate can be automatically obtained. As a result, it is possible to control the air-fuel ratio of the engine with high accuracy and to provide an engine with low fuel consumption and low exhaust.

【図面の簡単な説明】[Brief description of drawings]

【図１】本発明の実施例を説明する図である。FIG. 1 is a diagram illustrating an example of the present invention.

【図２】発熱抵抗体２，３の詳細図である。FIG. 2 is a detailed view of heating resistors 2 and 3.

【図３】図２の変形例を示す図である。FIG. 3 is a diagram showing a modification of FIG. 2;

【図４】熱線回路１ａ，１ｂの詳細図である。FIG. 4 is a detailed view of the heating wire circuits 1a and 1b.

【図５】図４の変形例を示す図である。FIG. 5 is a diagram showing a modification of FIG.

【図６】図４の変形例である。FIG. 6 is a modification of FIG.

【符号の説明】[Explanation of symbols]

１…熱線回路、２，３…発熱抵抗体、４，５…測温抵抗
体、９，１１…電気絶縁板、１０…スリット、１８，１
９…差動増幅器、２０，２１…トランジスタ、２２…ゼ
ロスパン調整回路、２３…デジタルコンピュータ、１２
〜１７，２４〜２６…抵抗。DESCRIPTION OF SYMBOLS 1 ... Hot wire circuit, 2, 3 ... Heating resistor, 4,5 ... Temperature measuring resistor, 9, 11 ... Electrical insulating plate, 10 ... Slit, 18, 1
9 ... Differential amplifier, 20, 21 ... Transistor, 22 ... Zero span adjustment circuit, 23 ... Digital computer, 12
~ 17, 24-26 ... Resistance.

Claims (2)

【特許請求の範囲】[Claims] 【請求項１】機関の吸気通路内に設置され空気流の上流
と下流に２ケの発熱抵抗体を用いて空気流量を計測する
空気流量計において、該２ケの発熱抵抗体は、上流側の
発熱抵抗体により加熱された空気流のために下流側の発
熱抵抗体の放熱量が影響させられる位置関係に配置した
ことを特徴とする空気流量計。1. An air flow meter installed in an intake passage of an engine for measuring an air flow rate by using two heating resistors upstream and downstream of an air flow, wherein the two heating resistors are upstream. The air flow meter is arranged in such a positional relationship that the heat radiation amount of the downstream heating resistor is affected by the air flow heated by the above heating resistor. 【請求項２】請求項１の空気流量計において、該２ケの
発熱抵抗体をホイートストンブリッジの１辺に設け、該
２ケの発熱抵抗体の中点の電位を流量信号として取り出
すことを特徴とする空気流量計。2. The air flowmeter according to claim 1, wherein the two heating resistors are provided on one side of the Wheatstone bridge, and the potential at the midpoint of the two heating resistors is taken out as a flow rate signal. And an air flow meter.