JP3883921B2 - Intake flow rate detection device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an intake flow rate detection device for an internal combustion engine using a hot-wire air flow meter.
[0002]
[Prior art]
A hot wire type air flow meter is provided with a hot wire element (hot wire) as a heat generating part, and the energization amount is controlled so that the temperature of the hot wire element is maintained at a predetermined temperature difference with respect to a reference temperature (cold wire temperature). Yes. The energization amount is measured as a voltage to detect the intake flow rate.
[0003]
In such a hot-wire air flow meter, when the power is turned on,
(1) Due to the heat capacity of the heat ray element, excessive current flows as a surge current until the heat ray element reaches a predetermined temperature. (2) Since heat conduction from the heat ray element to the lead occurs, the current for the lead heating is also excessive. Therefore, the heat balance of the hot wire element is delayed, and the intake flow rate is excessively detected until the final equilibrium temperature is reached.
[0004]
In order to solve this problem, conventionally, as shown in Japanese Patent Laid-Open No. 5-149185, a map using the output voltage of the hot-wire air flow meter and the elapsed time since the power supply to the hot-wire air flow meter as parameters is used. Is used to determine the intake air flow rate, or the intake air flow rate detected based on the output voltage of the hot-wire air flow meter is corrected by a correction coefficient set in accordance with the elapsed time from power-on.
[0005]
[Problems to be solved by the invention]
However, in the above conventional technique (Japanese Patent Laid-Open No. 5-149185), a map or a table with the elapsed time from power-on to the hot-wire air flow meter as a parameter must be used, and the ROM capacity increases. Since there are many conforming items, there was a problem that man-hours increased when adapting each engine.
[0006]
In addition, with the configuration that corrects the intake air flow rate, it is not possible to separate the influence of flow rate variation (blowback, inertial supercharging, etc.) due to the difference in the intake system layout for each vehicle and the error inherent in the air flow meter itself at the time of adaptation. .
For this reason, the method of error generation due to the power-on characteristics of the air flow meter does not match the method of correction, and as a result, it is necessary to review the conformity for each engine, increasing the workload (using the same air flow meter) Have to be adapted separately).
[0007]
An object of the present invention is to solve such conventional problems.
[0008]
[Means for Solving the Problems]
For this reason, in the present invention, the detection error calculation means obtains the detection error of the intake air flow rate for the lead heating due to heat conduction from the heat ray element to the lead as the detection error of the air flow meter output voltage , and further, the detection error correction means Correction is performed with a correction factor corresponding to the intake flow rate. Then, the air flow meter output voltage is corrected by the detection error of the air flow meter output voltage corrected by the detection error correction means, and used for detecting the intake air flow rate. The correction rate according to the intake flow rate used by the detection error correction unit is a voltage ratio between the air flow meter output voltage at the representative flow rate and the actual corrected air flow meter output voltage.
[0009]
【The invention's effect】
According to the present invention, the correction value for the air flow meter output voltage (the detection error of the output voltage) is determined instead of the correction value for the intake air flow rate, so that the air flow meter is not affected by the difference in the intake system layout for each vehicle. Only its own error can be corrected. In addition, since it is possible to adapt the correction with a desktop setting (air flow meter alone), it is not necessary to review the adaptation for each engine, and the adaptation can be simplified.
In addition, by providing a detection error correction means that corrects the detection error of the air flow meter output voltage with a correction rate according to the intake flow rate, an appropriate detection error for the lead heating can be obtained according to the intake flow rate. Can be corrected accurately.
The correction rate according to the intake flow rate is the voltage ratio between the air flow meter output voltage at the representative flow rate and the actual corrected air flow meter output voltage, which eliminates the need for a map or table for each flow rate and reduces the ROM capacity. An increase in the number of conforming man-hours can be suppressed.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a system diagram of an electronically controlled fuel injection device for an internal combustion engine equipped with a hot-wire air flow meter (hereinafter referred to as AFM).
An electronically controlled fuel injection device for an internal combustion engine includes a hot-wire AFM 1, and a power supply voltage VB is applied via an ignition switch 2 to generate an output voltage corresponding to the intake flow rate of the engine.
[0011]
The output voltage of the AFM 1 is input to the microcomputer 4 via the A / D converter 3.
In the microcomputer 4, from the intake flow rate Q detected based on the output voltage US of the AFM 1 and the engine speed N detected from the crank angle sensor 5 based on the crank angle signal generated in synchronization with the engine rotation, The basic fuel injection amount Tp = K × Q / N (K is a constant) is calculated. Then, various corrections are performed to obtain a final fuel injection amount, and a fuel injection pulse signal having a pulse width corresponding to the final fuel injection amount is output to the fuel injection valve 6 to control the fuel injection amount to the engine.
[0012]
The hot wire type AFM 1 will be described in more detail.
The hot wire type AFM 1 supports a hot wire element (hot wire) which is a temperature sensitive resistor by means of leads on both ends and is arranged in the intake passage (see FIG. 2), supplies current to generate heat to a constant temperature (resistance value), The temperature drop due to the intake air flow is compensated for by increasing the current, and the intake air flow rate is obtained from the current value.
[0013]
That is, in addition to the heat ray element (temperature sensitive resistor) RH, a temperature compensation resistor RK, a reference resistor RS, and fixed resistors R1 and R2 are provided, and a bridge circuit is configured by these.
The potential of the voltage dividing point (terminal voltage of the reference resistor RS) on the side of the bridge circuit where the temperature sensitive resistor RH and the reference resistor RS are connected in series, the temperature compensation resistor RK, and the fixed resistors R1 and R2 are connected in series. The voltage at the voltage dividing point connected to the terminal (terminal voltage of the fixed resistor R2) is input to the differential amplifier OP, and the transistor Tr is passed through in accordance with the output of the differential amplifier OP. Thus, the supply current to the bridge circuit is corrected.
[0014]
That is, when the intake flow rate of the engine increases, for example, in a state where the bridge circuit is balanced, the temperature-sensitive resistance RH is further cooled by the intake flow and the resistance value decreases, and the terminal voltage of the reference resistance RS increases. As a result, the bridge circuit becomes unbalanced and the output of the differential amplifier OP increases. As a result, the supply current to the bridge circuit controlled by the transistor Tr is increased, and the temperature sensing resistor RH is heated to increase its resistance value, thereby restoring the equilibrium condition of the bridge circuit.
[0015]
Here, when the intake air temperature is lowered, for example, the temperature sensing resistor RH is cooled and its resistance value is decreased, but the temperature compensation resistor RK in the same atmosphere as the temperature sensing resistor RH is also simultaneously cooled and its resistance value is decreased. Thus, the change in the value of the current supplied to the bridge circuit due to the change in the intake air temperature is suppressed.
Therefore, the intake air flow rate of the engine and the supply current to the bridge circuit correspond to each other regardless of the intake air temperature, and the intake air flow rate can be detected by detecting the terminal voltage of the reference resistor RS. Therefore, the terminal voltage (US) of the reference resistor RS is input to the microcomputer 4 via the A / D converter 3 as the output voltage of the AFM 1.
[0016]
FIG. 3 is a flowchart of intake flow rate Q detection performed by the microcomputer 4.
In S1, after the ignition switch is turned on, it is determined whether or not it is the first calculation, and the process proceeds to S2 in the first time and to S3 in the second and subsequent times.
In S2, since it is the first case, the detection error (hereinafter referred to as AFM output error) VERR of the AFM output voltage is set to a predetermined error initial value VERRINI # (VERR = VERRINI #).
[0017]
In S3, since the second and subsequent cases, as shown in the following equation, the previous AFM output error VERRz is multiplied by a predetermined attenuation coefficient RELR # (for example, 0.9), and the AFM output is reduced so as to decrease with a first-order lag. The error VERR is calculated.
VERR = VERRz × RELR #
The thin line in FIG. 4 shows a representative flow rate (the intake air flow rate at idle immediately after engine startup, for example, 14 kg / h) at the time of immediate application to the AFM output voltage at the time of waiting (when started after turning on the power to the AFM) ( (1) is an error for surge current, and (2) is an error for lead heating.
[0018]
Here, the initial value VERRINI # and the attenuation coefficient RELR # are set so as to ride on the error curve (shown in bold) after the end of the surge current in FIG.
In S4, the flow rate correction factor A is calculated by the following equation.
A = US14 # / (USBz + USOFS #)
The flow rate correction is performed to correct the difference in heat conduction to the lead portion depending on the intake flow rate as shown in FIG. 2 and the flow rate error (ΔQ / Q) depending on the intake flow rate as shown in FIG.
[0019]
Here, the flow rate correction factor A is an AFM output voltage US14 # at a representative flow rate (an intake flow rate at idle immediately after engine startup, for example, 14 kg / h), and an actual corrected AFM output voltage obtained in S10 described later. The voltage ratio with respect to the previous value USBz is given with a predetermined offset value USOF #.
In S5, the AFM output error VERR is corrected by the flow rate correction factor A. That is, the corrected AFM output error VERR ′ is obtained by multiplying the AFM output error VERR by the flow rate correction factor A as shown in the following equation.
[0020]
VERR '= VERR × A
In S6, it is determined whether or not a predetermined time has elapsed since the first calculation after the ignition switch is turned on. If the predetermined time has elapsed, the process proceeds to S8 to set the corrected AFM output error VERR ′ to 0 (VERR ′). = 0). This is to prevent the AFM output error from being overcorrected after the heat ray element is in a temperature equilibrium state by setting the AFM output error to 0 when the time at which the AFM output error is near 0 is reached.
[0021]
In S7, it is determined whether or not there is a forced reset. In other words, when the microcomputer is forcibly reset due to a noise or battery voltage drop other than when the power is first turned on, there is a reset by means of forced reset judgment (determined because the number of revolutions is high at the time of reset). In S8, the corrected AFM output error VERR ′ is set to 0 (VERR ′ = 0). This initializes the calculation when it is forcibly reset during driving, etc., but the heat rays are in a temperature equilibrium state, so if an unnecessary correction is made accidentally, the intake air flow rate will be detected incorrectly. It is for preventing.
[0022]
In S9, the actual AFM output voltage US is A / D converted and read.
In S10, the AFM output voltage US is corrected by the corrected AFM output error VERR ′. That is, the corrected AFM output voltage USB is obtained by subtracting the corrected AFM output error VERR ′ from the AFM output voltage US as shown in the following equation.
USB = US-VERR '
In S11, the corrected AFM output voltage USB is converted into the intake flow rate Q with reference to a predetermined voltage-flow rate table. Using this, the basic fuel injection pulse width Tp can be accurately calculated.
[0023]
Through the processing as described above, the detection error of the AFM can be corrected more easily than before, and the ROM capacity and the adaptation man-hour can be reduced. Further, since the AFM response characteristic does not depend on the time until the final equilibrium temperature of the heat ray is reached, an error in the AFM response characteristic at the time of immediate application and waiting due to the time difference from the ignition switch ON can be eliminated. Variations in the fuel injection amount calculated based on the output voltage are reduced, and variations in air-fuel ratio control can be reduced.
[0024]
According to the present embodiment, the correction of the AFM output voltage is performed by subtracting the detection error of the AFM output voltage at that time from the AFM output voltage at that time (S10) every predetermined time. Corresponding to the error decreasing with time, appropriate correction can be made.
In addition, according to the present embodiment, the detection error calculation means (S1 to S3) uses the error initial value VERRINI # and the attenuation coefficient RELR #, and sets the error initial value by decreasing it with a first-order lag over time. It is only necessary to set VERRINI # and attenuation coefficient RELR #, the ROM capacity is small, and the conforming items and the conforming man-hours can be decreased.
[0025]
Also, according to the present embodiment, the initial error value VERRINI # and the attenuation coefficient RELR # are set so as to be on the error curve after the end of the surge current, so that the influence of the surge period can be avoided and the surge Error correction after completion can be performed accurately.
In addition, according to the present embodiment, by providing the detection error correction means (S4, S5) for correcting the AFM output error VERR by the correction rate A corresponding to the intake flow rate, an appropriate lead heating component can be obtained according to the intake flow rate. Detection error can be obtained, and the error can be corrected accurately.
[0026]
Further, according to the present embodiment, the correction rate A according to the intake flow rate is set to a voltage ratio between the AFM output voltage US14 # at the representative flow rate and the actual corrected AFM output voltage USB, so that a map for each flow rate is obtained. Alternatively, a table is not required, and an increase in ROM capacity and an increase in man-hours can be suppressed.
Further, according to the present embodiment, the following effects can be obtained by using the idle intake flow rate immediately after engine startup as the representative flow rate. The detection error of the lead heating may not be completely proportional to the flow rate ratio, and includes a possibility of causing a slight error depending on the flow rate. In order to reduce this error, emphasis is placed on the correction at the time of starting, and the correction variation due to the flow rate can be reduced by using the air flow rate immediately after the engine start as the representative flow rate.
[0027]
Further, according to the present embodiment, when calculating the voltage ratio, the offset value USOFS # is added to either the AFM output voltage US14 # at the representative flow rate or the actual corrected AFM output voltage USB. Thus, the following effects can be obtained. Since the AFM output voltage (US14V #) at the representative flow rate is set to a steady state output voltage, there may be a deviation from the actual output voltage at the start. Therefore, this deviation can be corrected by providing an offset.
[0028]
In addition, according to the present embodiment, when the elapsed time from the start of calculation by the detection error calculation means becomes a predetermined time or more, the detection error of the AFM output voltage is set to 0 (S6 → S8), so that It is possible to prevent overcorrection after the temperature equilibrium state is reached.
In addition, according to the present embodiment, when the microcomputer constituting the detection error calculation means is forcibly reset, the detection error of the AFM output voltage is set to 0 (S7 → S8), and unnecessary correction is made at the time of the forced reset. It is possible to prevent erroneous detection of the intake air flow rate.
[Brief description of the drawings]
FIG. 1 is a system diagram showing an embodiment of the present invention. FIG. 2 is a diagram showing a heat ray element structure. FIG. 3 is a flow chart of intake flow rate detection. FIG. 4 is a voltage error characteristic diagram. [Explanation of symbols]
1 Hot wire AFM
2 Ignition switch 3 A / D converter 4 Microcomputer

Claims (8)

In an intake air flow detection device for an internal combustion engine that detects an intake air flow based on an output voltage of a hot-wire air flow meter,
A detection error calculating means for obtaining a detection error of the intake flow rate for the lead heating due to heat conduction from the hot wire element to the lead as a detection error of the air flow meter output voltage ;
Detection error correction means for correcting the detection error of the air flow meter output voltage obtained by the detection error calculation means with a correction rate according to the intake flow rate ,
The air flow meter output voltage is corrected by the detection error of the air flow meter output voltage corrected by the detection error correction means and used to detect the intake flow rate. The correction rate corresponding to the intake flow rate used by the detection error correction means is a representative flow rate. An intake flow rate detection device for an internal combustion engine, characterized in that a voltage ratio between the air flow meter output voltage and the actual corrected air flow meter output voltage is used.   2. The internal combustion engine according to claim 1, wherein the correction of the air flow meter output voltage is performed by subtracting a detection error of the current air flow meter output voltage from the current air flow meter output voltage every predetermined time. Intake flow rate detection device.   The intake air of the internal combustion engine according to claim 1 or 2, wherein the detection error calculation means uses an initial error value and an attenuation coefficient, and sets the initial error value by decreasing with a first-order lag with time. Flow rate detection device.   4. The intake flow rate detection device for an internal combustion engine according to claim 3, wherein the error initial value and the attenuation coefficient are set so as to be on an error curve after the end of a surge current. The intake flow rate detection device for an internal combustion engine according to any one of claims 1 to 4 , wherein an intake flow rate at idle immediately after engine startup is used as the representative flow rate. When calculating the voltage ratio, either one of the air flow meter output voltage or actual corrected air flow meter output voltage representative flow rate of claims 1 to 5, characterized in adding the offset value The intake flow rate detection device for an internal combustion engine according to any one of the above. 7. A device according to claim 1, further comprising a means for setting an air flow meter output voltage detection error to zero when an elapsed time from the start of calculation by the detection error calculation means exceeds a predetermined time. An intake flow rate detection device for an internal combustion engine according to any one of the above. 8. The apparatus according to claim 1 , further comprising means for setting a detection error of an air flow meter output voltage to zero when a microcomputer constituting the detection error calculation means is forcibly reset. An intake flow rate detection device for an internal combustion engine according to claim 1.

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