JPS59190623A - Heat type air flowmeter - Google Patents

Abstract

PURPOSE:To improve response of the titled device, by providing heating resistor bodies for measuring the flow rate of air and for correcting air temperature in a bypass, into which part of the air flow is divided, so that the longitudinal direction is set at a specified angle with respect to the flowing direction of the air. CONSTITUTION:A hot wire 1 of a heating resistor body, which detects the amount of intake air, and a cold wire 2 of a resistor body, which detects the temperature of the intake air, are formed as follows: platinum wire 102 is wound around an alumina bobbin 101; both ends of the wire are welded to a lead 103; and thereafter a thin glass coating 104 is applied to the surface thereof. Said heating resistor bodies are provided in a bypass 106 of a body 107 at a slant angle theta with respect to the bypass air flow. The length of the hot wire 1 can be made sufficiently large without increasing the diameter of the bypass. Therefore, a hot-wire type air flowmeter having excellent response can be provided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a thermal air flow meter, and more particularly to a thermal air flow meter for detecting the intake air flow rate of an internal combustion engine.

[Background of the invention]

Since the amount of fuel supplied to the engine is determined according to the measured intake air flow rate, the thermal air flow meter must respond quickly to sudden changes in the intake air flow rate, such as when the engine suddenly accelerates or decelerates. It is.

It is desirable for an air flow meter for an internal combustion engine to be less affected by intake pulsation and blowback caused by opening and closing of an intake valve of the engine, and to output an average value of the intake air flow rate. To deal with this, a method has been adopted in which a heating resistor is installed in a bypass passage that diverts a part of the airflow (for example, Japanese Patent Laid-Open No. 56-18721
number, etc.).

In this system in which a heat generating resistor is installed in the bypass passage, if the ratio of the amount of air flowing through the bypass passage to the total amount of air is increased, the ventilation resistance of the entire air flow meter increases and the intake air loss of the engine increases. This will cause a decrease in output, so the smaller the proportion of air flowing through the bypass passage, the better.

On the other hand, in an air flow meter for an internal combustion engine, it is necessary to quickly respond to sudden changes in the intake air flow rate, such as when the engine suddenly accelerates or decelerates.

This response speed is affected by the dimensions of the heating resistor, and
In a cylindrical heating resistor as shown in the figure, the ratio t/d of the outer diameter d to the length t changes significantly. Figure 2 and 1
The table shows experimental results regarding the relationship between response speed and t/d.

FIG. 2 shows how the output of the hot wire air flow meter changes when the air flow rate is abruptly changed from O to 200/h to 9/h. The output when air flow rate Q = OKg/h is V
Table 1 shows the results of measuring the time TR until the amount of change in output reaches 90% of the total amount of change when the output at Q=200Kg/h is set to V2O0.

Table 1 The response speed, that is, the rise time TR varies greatly depending on t/d, and the larger t/d is, the smaller TR is. The response speed is fast, making it desirable as an air flow meter for internal combustion engines.

However, the outer diameter d of the heating resistor has a lower limit due to manufacturing constraints such as strength, and it is necessary to increase the length t. If the length t is increased, the diameter of the bypass passage becomes smaller, which has disadvantages such as an increase in ventilation resistance and an increase in the size of the air flow meter as a whole, as described above.

[Purpose of the invention]

An object of the present invention is to provide a thermal air flow meter with good responsiveness.

[Summary of the invention]

The present invention aims to improve responsiveness by installing the heating resistor at a certain angle in the longitudinal direction with respect to the air flow in the bypass passage.

[Embodiments of the invention]

Examples of the present invention will be described below.

The hot wire 1 of the heating resistor for sensing the amount of intake air and the cold wire 2 for the resistor for sensing the intake air temperature are both made by winding a platinum wire 102 around an alumina bobbin 101, as shown in FIG. is welded to a lead 103, and then a thin glass coating 104 is applied to the surface. As shown in FIG. 3, this heating resistor is installed in a bypass passage 106 of a body 107, which has a main passage 105 through which most of the intake air passes and a bypass passage 106 through which a portion of the intake air flows. It is installed at an angle θ.

As shown in FIG. 4, the hot wire 1 and the cold wire 2 described above are connected to bins 110 and 1 which are integrally formed with a case 108 of a module that houses a lead 103 and a drive circuit.
It is welded to 11.

FIG. 5 shows a drive circuit for a hot wire air flowmeter.

In the figure, the drive circuit includes a hot wire l, a hot wire drive section 3 including a cold wire 2, an output stage amplification section 4, and a constant voltage section 5.

The power supply terminal 6 is connected to the battery (G), the output terminal 7 is connected to the input terminal of a microcomputer that controls the engine using the output signal of this air flow meter, and the ground terminal 8 is connected to the battery (→ and The ground end of the microcomputer mentioned above is connected.

A power transistor 9 supplies current to the hot wire 1, heats the hot wire 1, and maintains the temperature of the hot wire 1 at a constant temperature higher than the intake air temperature. At this time, since only a minute current is allowed to flow through the cold wire 2 so that heat generation is negligible, the cold wire 2 is kept at the same temperature as the intake air temperature, and the intake air temperature is corrected.

When the airflow hits the hot wire 1, the temperature difference between the temperature of the hot wire 1 and the intake air temperature is controlled to be constant by the operation of the hot wire drive unit described above. This operation reduces the potential difference between the two ends of the hot wire 1 to the resistor 10 and 1
Feedback is applied so that the voltage divided by 1 and the voltage obtained by amplifying the voltage drop across the resistor 12 caused by the current flowing through the hot wire 1 by an operational amplifier are always equal.

The relationship between the air flow rate Q and the current I flowing through the hot wire 1 is (
1) It is expressed by the formula.

I”・Rio (1+αTi)=(Ct+C+V
'Q)・(THTC)・・・・・・・・・・・・α) Rio: Resistance value of hot wire 1 of QC α: Resistance temperature coefficient of hot wire 1 TR: Temperature of hot wire 1 (heating state ) Tc: Temperature of the cold wire 2 (i.e., air temperature) C,, C,: Constant Here, if (TH-Tc) is proportional to (1+αT■), the current ■ flowing through the hot wire will be limited to the air flow rate Q only. Dependent. This circuit realizes this, and by measuring the current of the hot wire 1, the air flow rate is measured without being affected by the air temperature (as a voltage drop across the resistor 12).

Therefore, according to this embodiment, since the axial direction of the hot wire 1 is set at an oblique angle θ with respect to the air flow in the bypass passage 106, that is, with respect to the direction of the bypass passage, there is no need to increase the diameter of the bypass passage. Length t of hot wire 1
can be made sufficiently large, and the ratio t/d to the outer diameter d can be made large, making it possible to provide a hot wire air flow meter with good responsiveness.

If the axial direction of the hot wire 1 is made to completely match the air flow, the air flow will not hit the entire outer diameter of the cylindrical portion of the hot wire 1, so the angle θ shown in FIG. 3 is required to a certain extent.

Furthermore, according to this embodiment, by arranging the cold wire 2 in parallel with the hot wire 1 with respect to the air flow, the air heated by the hot wire 1 does not hit the cold wire 2, and the intake air temperature is accurately measured. There is also the effect of

Furthermore, according to this example, the cold wire 2 is used to measure the intake air temperature, and it is desirable that the cold wire 2 is not affected by the temperature of the body 107 or the case 108 of the drive circuit. For this purpose, it is necessary to reduce the influence of heat exchange between the case 108 and the body 107 through the bins 110° 112, and increasing the t/d of the cold wire 2 has this effect.

Further, according to this embodiment, the length of the cold wire 2 can be easily increased by installing the cold wire 2 in the axial direction of the bypass passage, similar to the hot wire, and the length of the cold wire 2 can be easily increased. This has the effect of reducing the influence of temperature on the air and allowing accurate measurement of intake air temperature.

〔Effect of the invention〕

As explained above, according to the present invention, responsiveness can be improved.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of a resistor of a hot wire flowmeter, Fig. 2 is a diagram showing the response speed, Fig. 3 is a diagram showing an embodiment of the present invention, and Fig. 4 is a diagram showing an example of the present invention.
The figure is a plan view of FIG. 3, and FIG. 5 is a drive circuit diagram of the hot wire flowmeter. Dormitory 1 flash 20th 3rd flash 4th η Dormitory! l;

Claims (1)

[Scope of Claims] 1. A thermal air flowmeter in which heating resistors for measuring air flow rate and for correcting air temperature are installed in a binox passage that divides a part of the air flow. A thermal air flowmeter characterized in that the longitudinal direction of the resistor is installed at a predetermined angle with respect to the air flow direction. 2. The thermal air flow meter according to claim 1, wherein the predetermined angle is smaller than 90°.