JPH07229776A - Air flow rate measuring device - Google Patents

Abstract

PURPOSE:To improve the measuring accuracy of air flow, by providing a humidity detecting device in an air passage or in an air cleaner, detecting the humidity of the flowing-in air so as to decide the correcting amount, and correcting the output signal of an air flow rate measuring device. CONSTITUTION:In the same air passage, a hygrometer, a heating resistor, and a heat sensitive resistor are provided, a heating resistor signal 5, a heat sensitive resistor signal 6, and humidity detecting device signal 7 are taken in to a CPU, and the air flow rate found from the heating resistor signal 5 and the heat sensitive resistor signal 6 lay applying an operation process is corrected by the humidity detecting device signal 7, and it is output as an output signal 4 after the humidity correction. Consequently, by adding the humidity which is an important parameter of the air together with the air pressure and the temperature, the measuring accuracy of the air flow rate, especially the measuring accuracy at the variation of the ambiance, can be improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air flow measuring device for measuring the amount of air taken into an internal combustion engine of an automobile.

[0002]

2. Description of the Related Art Generally, air can be considered as a mixed gas of dry air and water vapor, and the pressure, temperature, and humidity are constantly changing. Among these, as an output correction of the air flow rate measuring device with respect to a change in temperature, a specific example is disclosed in Japanese Patent Laid-Open No. 60-100218. However, there is no specific example of the humidity correction of the air flow measuring device, and the present invention was invented as a specific correction method.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a highly accurate air flow rate measuring device which does not impair the air flow rate measurement accuracy under any environmental conditions.

[0004]

In order to achieve the above object, a humidity detecting device is installed in an air passage, inside an air cleaner, or in an air cleaner duct, and a correction amount is determined based on a signal from the humidity detecting device. This is achieved by correcting the signal of the measuring device.

[0005]

The main point of the present invention is to add humidity correction to the output signal of the air flow meter and to correct the error component due to the environmental change contained in the output signal. Generally, air can be considered as a mixed gas of dry air and water vapor. However, pure dry air condition (humidity: 0% RH) and water vapor (humidity: 10%)
0% RH) is extremely rare, and most of the operating environment is in the state of the mixed gas of dry air and water vapor.

In the case of an air flow meter, the state of air is constantly changing depending on the parameters of atmospheric pressure, temperature and humidity. Of these, the atmospheric pressure has a negligible effect on the air flow rate measuring device and is negligible, so that it is not necessary to make any particular correction. The temperature correction can be dealt with by improving the drive circuit of the air flow meter. However, it is difficult to correct the humidity term by taking measures such as improving the arithmetic circuit. Humidity correction is essential to improve measurement accuracy. Therefore, by installing the humidity detecting device in the air passage and calculating the humidity correction value based on the humidity signal and correcting the output signal of the air flow meter, it is possible to measure the air flow rate with high accuracy in any environment. Become.

Particularly, in the case of a thermal type air flow meter, it is a flow meter for measuring the air flow rate by converting the amount of heat transfer to the air from a heating resistor heated to a certain temperature to measure the air flow rate. When the amount of heat transfer into the air changes depending on the state of the air, the measurement signal changes variously. That is, the measurement error of the air flow meter indicates the variation in the amount of heat transfer from the heating resistor to the air. Thermal conductivity and kinematic viscosity coefficient are items that determine the amount of heat transferred from the heating resistor to the air.
However, these coefficients vary with temperature, pressure, and humidity parameters. Therefore, when the humidity changes, the temperature,
Error correction for environmental changes is not complete just by correcting the pressure.

In the present invention, the air flow meter is attached to
Alternatively, the output signal of the air flow meter is corrected by the signal of a separately installed humidity detecting device.

[0009]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of the humidity correction of the present invention, FIG. 2 is an embodiment of the humidity correction shown in FIG. 1, and FIG. 3 is a sectional structural view of an air flow rate measuring device with a humidity correction function of the present invention.
FIG. 4 is a graph showing the humidity dependence of the air flow measuring device.

The present invention is means for performing humidity correction for the purpose of improving the accuracy of the air flow rate measuring device. An example will be described with reference to FIG. Signal 2 detected by the air flow rate detection device 1
In addition, the signal 2 detected by the air flow rate detecting device 1 is corrected based on the humidity signal detected by the separately installed humidity detecting device 3. The signal after this correction becomes the air flow rate output signal 4 after the humidity correction.

FIG. 2 shows, as an embodiment, an invention relating to a humidity correction method for a thermal type air flow meter. The same drive circuit that takes in the heating resistor signal 5, the temperature sensitive resistor signal 6 and the humidity detecting device signal 7 and corrects the air flow rate obtained by the heating resistor signal 5 and the temperature sensitive resistor signal 6 by the humidity detecting device signal 7 The output signal 4 is calculated inside and the humidity of the air flow meter is corrected. In this humidity correction, if the humidity detecting device 3 is installed in the same air passage as the heating resistor 8 and the temperature sensitive resistor 9, the humidity correction for the air flow rate signal in the same state can be simultaneously corrected, so that the humidity correction can be performed with high accuracy. It will be possible.

The structure and operating principle of the air flow rate measuring device will be described with reference to FIG. Reference numeral 8 is a heating resistor arranged in the center of the air passage. Reference numeral 9 is a temperature-sensitive resistor for temperature compensation, 10 is a small passage in which the heat-generating resistor 8 and the temperature-sensitive resistor 9 for temperature compensation are installed, 11 is a main passage for introducing intake air, 12 is a main air passage 11 Is a metal or resin body that forms the element, and 13 is an arithmetic circuit that electrically processes the signal detected by the heating resistor. The humidity detecting device 3 has a structure installed in the main passage 11 or the small passage 10.
The humidity detecting device 3 is installed not only in the passage of the air flow measuring device but also in the duct upstream of the air flow measuring device, inside the air cleaner, air introduction part of the air cleaner, in the duct downstream of the air flow measuring device, near the throttle chamber. Even if it becomes a structure which can exhibit the effect of this invention.

Particularly in the case of a thermal type air flow meter, it is a flow rate measuring device for measuring the air flow rate by converting the amount of heat transfer to the air from the heating resistor heated to a certain temperature to measure the air flow rate. When the amount of heat transfer into the air changes depending on the state of the air, the measurement signal changes variously. That is, the measurement error of the air flow meter indicates the variation in the amount of heat transfer from the heating resistor to the air. Thermal conductivity and kinematic viscosity coefficient are items that determine the amount of heat transferred from the heating resistor to the air. Since these coefficients change with parameters of temperature, pressure, and humidity, the amount of heat transfer from the heating resistor to the air changes, which causes an error in the air flow measuring device. Further, since the thermal air flow meter is a device for measuring the mass flow rate of air, if the specific weight of air changes, an error will occur as it is. The specific weight of moist air: γ is represented by the equation (1).

[0015]

[Equation 1]

T: Temperature (° C.) P: Absolute pressure (mmHg) ψ: Relative humidity h _s : Pressure of saturated steam at t (° C.) (mmHg) (Equation 1) Specific weight of humid air Is the temperature,
It has three parameters, pressure and humidity, and the specific weight of air changes due to changes in humidity, resulting in an error in measuring the air flow rate.

FIG. 4 shows the error rate of the air flow rate measuring device with respect to changes in humidity. For convenience, relative humidity 50 (% RH)
When the humidity is changed with reference to the output of the air flow rate measurement device in, the error of the air flow rate measurement device is 50 (% RH) of the standard.
It gets bigger as you move away from it. The automobile to which the present invention is mainly applied is used under all environments on the earth. Therefore, when comparing a tropical region with high humidity and a desert region with low humidity, the air flow measuring device outputs a completely different output signal. Here, by structuring the humidity correction function of the present invention in the air flow rate measurement device or systematizing the control unit, it is possible to perform environment correction without changing the output of the air flow rate measurement device under any environment, High accuracy of the air flow rate measuring device can be realized.

[0018]

According to the present invention, there is an effect that it is possible to provide an air flow rate measuring device capable of highly accurately measuring the air flow rate under any environment.

[Brief description of drawings]

FIG. 1 is a block diagram of humidity correction of an air flow measuring device of the present invention.

FIG. 2 is a block diagram of humidity correction of the air flow rate measuring device of the present invention.

FIG. 3 is a sectional structural view of an air flow rate measuring device of the present invention.

FIG. 4 is a diagram showing humidity dependence of an air flow measuring device.

[Explanation of symbols]

1 ... Air flow rate detecting device, 2 ... Output signal, 3 ... Humidity detecting device, 4 ... Humidity corrected output signal, 5 ... Heating resistor signal, 6
... temperature sensitive resistor signal, 7 ... humidity detection device signal, 8 ... heating resistor, 9 ... temperature sensitive resistor, 10 ... small passage, 11 ... main passage,
12 ... Body, 13 ... Arithmetic circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Ishikawa 2477 Kashima Yatsu Kashima, Katsuta City, Ibaraki Prefecture 3 Hitachi Automotive Engineering Co., Ltd.

Claims (2)

[Claims] 1. An air flow meter for detecting an air flow rate,
An air flow measuring device, characterized in that a humidity detecting device arranged in an air passage detects humidity and outputs a signal obtained by adding humidity correction to an output signal of the air flow meter as an output of the air flow meter. 2. An output signal of an air flow meter for detecting an air flow rate from a heating current value required for heating a heating resistor to a predetermined temperature, and a signal detected by a humidity detecting device. An air flow rate measuring device, wherein an air flow rate signal whose humidity is corrected by a humidity correction amount calculated by a calculation circuit is output from the air flow rate measuring device.