JPH07119524A - Intake air flow rate detection device of internal combustion engine - Google Patents

Abstract

PURPOSE:To maintain the accuracy of flow rate detection by calculating an average flow rate of the intake air flow rate basing on the adopted detection value as well as by detecting the maximal point of the intake air flow rate variations and selecting the detected value of the intake air flow rate after comparing the maximal point occurring interval time with the standard time. CONSTITUTION:A temperature sensing type flow meter 1 is impressed with power supply voltage through an ignition switch 2. The output voltage of the temperature sensing type flow meter 1 is inputted into a microcomputer 4 through an A/D transducer 3. Further the detection signal of an engine speed sensor 5 is inputted into the microcomputer 4 which then controls the fuel supply quantity to the internal combustion engine in accordance with each input signal. At this time, the microcomputer 4 calculates an average flow rate of the intake air flow rate basing on the adopted detection value as well as detects the maximal point of the intake air flow rate variations and selects the detected value of the intake air flow rate by comparing the maximal point occurring interval time with the standard time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an intake air flow rate detecting device for an internal combustion engine, and more particularly to a device for detecting an engine intake air flow rate based on a temperature-sensitive resistance arranged in an intake passage of the internal combustion engine.

[0002]

2. Description of the Related Art An electronically controlled fuel injection system for an internal combustion engine is equipped with an air flow meter (air flow meter) for detecting an intake air flow rate Q of the engine, and the intake air flow rate Q detected by this air flow meter is It is known that the basic fuel injection amount Tp = K × Q / Ne (K is a constant) is calculated from the engine speed Ne and the air flow meter is disclosed in Japanese Utility Model Laid-Open No. 59-78926. A temperature sensitive flow meter as disclosed in U.S. Pat.

In the temperature-sensitive flow meter, a so-called hot wire type or hot film type temperature sensitive resistor is arranged in the intake passage, and a current is supplied to the temperature sensitive resistor to generate heat at a constant temperature (resistance value). The temperature decrease due to the intake air is compensated for by increasing the current, and the intake air flow rate is calculated from the current value. That is, the temperature-sensitive flowmeter 1 in FIG. 2 will be described as an example. In addition to the temperature-sensitive resistance R _H (hot wire or hot film), temperature compensation resistance R _K, reference resistance R _s, fixed resistance R _{1 ,} R ₂ and the bridge circuit B is constituted by them.

The temperature sensing resistor R of the bridge circuit B
_H and the reference resistance R _s are connected in series, the potential of the voltage dividing point (the terminal voltage of the reference resistance R _s ) and the temperature compensation resistance R
_K and the potential at the voltage dividing point on the side where the fixed resistors R _{1 and} R ₂ are connected in series (the terminal voltage of the fixed resistor R ₂ ) are input to the differential amplifier OP. The supply current to the bridge circuit B is corrected via the transistor Tr according to the output of the dynamic amplifier OP.

That is, when the intake air flow rate of the engine increases, for example, when the bridge circuit B is in equilibrium,
The temperature sensitive resistance R _H is further cooled by this air flow, its resistance value decreases, and the terminal voltage of the reference resistance R _s increases,
The bridge circuit B becomes unbalanced and the output of the differential amplifier OP increases. As a result, the supply current to the bridge circuit B controlled by the transistor Tr increases, the temperature-sensitive resistor R _H is heated, and its resistance value increases, whereby the balanced condition of the bridge circuit B is restored.

Here, when the temperature of the intake air decreases, for example, the temperature-sensitive resistor R _H is cooled and its resistance value decreases, but the temperature-compensating resistor R _{K in the} same atmosphere as the temperature-sensitive resistor R _H.
At the same time, the resistance value of the bridge circuit B is reduced and the resistance value of the bridge circuit B is reduced, so that the current value supplied to the bridge circuit B is prevented from changing due to the temperature change of the intake air. Therefore, the intake air flow rate Q of the engine and the current supplied to the bridge circuit B correspond independently of the intake air temperature, and the intake air flow rate Q is measured by detecting the terminal voltage of the reference resistance R _s. be able to.

[0007]

By the way, when the throttle valve opening is large and the engine speed is in the low speed region or the high speed region, the intake pulsation including the backflow component is applied to the temperature sensitive flowmeter from the cylinder side. It may reach the temperature-sensitive resistance R _H. At this time, since the temperature-sensitive flow meter cannot determine the flow direction, backflow is detected in the same way as in the forward direction (Fig.
As a result, there is a problem that a value larger than the true intake air flow rate (see FIG. 11) is detected as the average flow rate.

When the intake air flow rate of the engine is detected to be larger than the true value as described above, the extra fuel is injected and supplied by the electronic fuel injection control based on the detected value to make the air-fuel ratio overrich. I will end up. The present invention has been made in view of the above problems, and it is possible to maintain the accuracy of flow rate detection even when intake pulsation including a backflow component occurs, and thereby improve the accuracy of fuel injection control. To aim.

[0009]

Therefore, an intake air flow rate detecting device for an internal combustion engine according to the present invention is constructed as shown in FIG. In FIG. 1, the temperature-sensitive flow rate detecting means detects the intake air flow rate of the engine based on the resistance value change of the temperature-sensitive resistance arranged in the intake passage of the internal combustion engine according to the intake air flow rate.

Further, the maximum flow rate detecting means detects the maximum point of the change in the intake air flow rate detected by the temperature sensitive flow rate detecting means, and the detected value selecting means detects the maximum point detected by the maximum flow rate detecting means. The detection value of the intake air flow rate is selected based on the comparison between the occurrence interval time and the reference time. Then, the average flow rate calculation means calculates the average flow rate of the intake air flow rate based on the detection value adopted by the detection value selection means.

[0011]

When the intake pulsation including the backflow component is generated, as shown in FIG. 10, the temperature-sensitive flow rate detecting means also detects the backflow component as the positive direction, so that only the forward direction is detected. The generation cycle of the maximum point becomes shorter than that.
Therefore, if the maximum point of the change in the intake air flow rate detected by the temperature-sensitive flow rate detection means is detected and the generation cycle of the detected maximum point is shorter than the generation cycle when the backflow component is not included, Considering that the maximum point is due to the detection of the backflow component, the detection value of the backflow component detected is not adopted, and only the result of the detection of the forward flow is adopted. Then, the average flow rate is calculated by using the detected value only in the positive direction.

[0012]

EXAMPLES Examples of the present invention will be described below. FIG. 2 shows the hardware configuration of the embodiment. In FIG. 2, the power supply voltage (battery voltage) V _B is applied to the temperature-sensitive flow meter 1 as the temperature-sensitive flow rate detecting means via the ignition switch 2. The output voltage Us of the temperature-sensitive flow meter 1 is input to the microcomputer 4 via the A / D converter 3.

In addition to the above, a rotation speed sensor 5 for detecting the engine rotation speed Ne (rpm) is provided, and the detection signal of the rotation speed sensor 5 together with the output voltage Us of the temperature-sensitive flow meter 1 is supplied to the microcomputer 4. It is designed to be input to. Here, the microcomputer 4 determines the basic fuel injection amount Tp = K based on the engine intake air flow rate Q detected by the temperature-sensitive flow meter 1 and the engine rotation speed Ne detected by the rotation speed sensor 5. × Q / Ne (K is a constant) is calculated, the basic fuel injection amount Tp is appropriately corrected to calculate the final fuel injection amount Ti, and an injection pulse signal having a pulse width corresponding to the fuel injection amount Ti is calculated. Is output to an electromagnetic fuel injection valve (not shown) at a predetermined timing synchronized with the engine rotation, thereby electronically controlling the fuel supply to the internal combustion engine.

Since the structure and operation of the temperature-sensitive flow meter 1 have been described above, a detailed description of the temperature-sensitive flow meter 1 will be omitted here. Next, the microcomputer 4
The state of detection of the average intake air flow rate Qav of the engine performed by means of will be described with reference to the flowchart of FIG. still,
In the present embodiment, the functions of the maximum flow rate detecting means, the detected value selecting means, and the average flow rate calculating means are assumed to be provided in software by the microcomputer 4 as shown in the flow chart of FIG.

In the flowchart of FIG. 3, first, in step 1 (denoted as S1 in the figure, the same applies hereinafter),
The maximum point in the change of the intake air flow rate Q is detected based on the intake air flow rate Q obtained by converting the output voltage Us read through the A / D converter 3 by the conversion table. To detect the maximum point, the difference between the latest read intake air flow rate Q and the last read intake air flow rate Q ₋₁ is sequentially calculated, and the point where the sign of the difference is inverted from positive to negative,
The maximum point of the intake pulsation is determined (see FIG. 4).

When the maximum point is detected in step 1, in the next step 2, a predetermined number of intake air flow rate Q data read within a predetermined time from the maximum point, including the intake air flow rate Q data at the maximum point. Is stored as data for calculating the average flow rate (see FIG. 5). In a 4-cycle in-line internal combustion engine, assuming that the number of cylinders is Cyl, the intake stroke phase difference time, that is, the intake pulsation cycle that does not include the backflow component,
Since it is calculated as (60 × 2) / (Ne × Cyl), in order to avoid sampling the backflow component, the predetermined time for storing the intake air flow rate Q data from the maximum point is (60 × 2)
2) / (Ne × Cyl × 4), and the number of stored intake air flow rate Q data within the predetermined time is preferably 2 ⁿ (n = about 2 to 4).

The intake air flow rate data detected within a predetermined time before and after the detected maximum point may be stored for calculating the average flow rate. As described above, when the maximum point is detected and the intake air flow rate Q data within a predetermined time from the maximum point is stored, in the next step 3, the maximum point obtained this time and the flow in the positive direction last time are determined. The interval time between the corresponding maximum point and the maximum point
Inspiratory pulsation cycle that does not include the backflow component = (60 × 2) /
It is determined whether or not it substantially matches (Ne × Cyl).

Here, when the current maximum point is detected in a time period much shorter than the intake pulsation period = (60 × 2) / (Ne × Cyl) from the previous maximum point corresponding to the forward flow, It is considered that the maximum point this time is the result of detecting the backflow component, and the data of the intake air flow rate Q stored with the maximum point of this time as the starting point is not adopted in step 4, and then the process proceeds to step 1 again. A new maximum point is detected.

That is, when an intake pulsation containing a backflow component occurs, a pulsation peak as a result of detecting the backflow component appears between the pulsation peaks of the forward flow, as shown in FIG. The interval between the points is reduced to about half as compared with the case where the pulsation component is not included (see FIG. 6). Therefore, when the interval from the maximum point adopted as one corresponding to the flow in the positive direction to the detection of the next maximum point is extremely shorter than the pulsation cycle (predetermined time) of the positive flow, It is recognized that the maximum point this time corresponds to the backflow component. Then, when it is recognized that it is the maximum point corresponding to the backflow component, a plurality of flow rate data stored with the maximum point as the starting point is not used for the final average flow rate calculation, and the flow in the forward direction is dealt with. It is used to calculate the average flow rate by selecting and discarding only a plurality of flow rate data stored with the maximum point recognized as the starting point.

On the other hand, in step 3, the interval time between the maximum point that was previously adopted as the maximum point corresponding to the flow in the positive direction and the maximum point detected this time is the intake pulsation cycle that does not include the backflow component = (60 When it is determined that it substantially matches (× 2) / (Ne × Cyl) (see FIG. 7), the current maximum point is regarded as the maximum point as a result of detecting the flow in the positive direction. Then, in order to calculate the average flow rate using the plurality of intake air flow rate Q data stored with the current maximum point as the starting point, the process proceeds to step 5.

In step 5, the frequency analysis of the data of the plurality of intake air flow rates Q recognized as having detected the flow component in the positive direction as described above is performed by using the fast Fourier transform or the like (see FIG. 8). , In the next step 6, 0
By performing an inverse Fourier transform using only the frequency component (DC component) of Hz to restore the waveform on the time axis, the average flow rate Qav is obtained (see FIG. 9).

As described above, the average flow rate is calculated using only the intake air flow rate Q data detected in the region where it is recognized that the forward flow is detected without using the result of detecting the backflow component. Even if the intake pulsation including the backflow component occurs, it is possible to avoid that the average flow rate is calculated to be larger than the true intake air flowrate due to the backflow component.
As a result, the fuel control accuracy can be improved.

The output read cycle (A / D conversion cycle) of the temperature sensitive flow meter 1 may be a fixed value or may be changed to increase the engine speed Ne. . Further, the generation region of the intake pulsation including the backflow component can be substantially specified by the engine speed Ne and the throttle valve opening. Therefore, when the non-generation condition of the backflow is detected from the rotation speed Ne and the throttle valve opening, It is also possible to perform a simple smoothing process without selecting the intake air flow rate detection data based on the detection of the maximum point, or based on the engine speed Ne and the throttle valve opening. The sampling interval or sampling range of the intake air flow rate data used for calculating the average flow rate may be changed.

[0024]

As described above, according to the present invention, even if the intake pulsation including the backflow component occurs, a value corresponding to the true intake air flow rate can be obtained as an average value of the engine intake air flow rate. Thus, there is an effect that it can contribute to the improvement of the accuracy of fuel injection control.

[Brief description of drawings]

FIG. 1 is a block diagram showing the basic configuration of the present invention.

FIG. 2 is a system schematic diagram showing a hardware configuration of an embodiment of the present invention.

FIG. 3 is a flowchart showing how the average flow rate is detected in the embodiment.

FIG. 4 is a time chart showing how the maximum point of the intake air flow rate is detected.

FIG. 5 is a time chart showing storage control of detection data starting from a maximum point.

FIG. 6 is a time chart showing a state of intake pulsation including a backflow component.

FIG. 7 is a time chart showing how intake pulsation does not include a backflow component.

FIG. 8 is a time chart showing storage control of detection data starting from a maximum point.

FIG. 9 is a time chart showing a state of intake pulsation that does not include a backflow component.

FIG. 10 is a time chart showing the occurrence of an average flow rate error due to backflow component detection.

FIG. 11 is a time chart showing a true engine intake air flow rate when a backflow component is generated.

[Explanation of symbols]

1 Temperature-sensitive flow meter 2 Ignition switch 3 A / D converter 4 Microcomputer 5 Rotation speed sensor _RH Temperature-sensitive resistance _RH

Claims (1)

[Claims] 1. A temperature sensitive flow rate detecting means for detecting an intake air flow rate of an engine based on a resistance value change of a temperature sensitive resistance arranged in an intake passage of an internal combustion engine according to an intake air flow rate, and the temperature sensitive system. Intake based on a comparison between the maximum flow point detection means for detecting the maximum point of the change in the intake air flow rate detected by the flow rate detection means, and the time interval between the maximum points detected by the maximum flow point detection means and the reference time. A detection value selection means for selecting the detection value of the air flow rate, and an average flow rate calculation means for calculating the average flow rate of the intake air flow rate based on the detection value adopted by the detection value selection means. An intake air flow rate detection device for an internal combustion engine, comprising: