JP2551396B2 - Fuel injection amount control method for internal combustion engine - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection amount control method for an internal combustion engine, and more specifically, it calculates a basic fuel injection time based on a measured value of an intake pipe pressure and calculates the calculated basic fuel injection time. The present invention relates to a fuel injection amount control method for an internal combustion engine that injects fuel based on the above.

[0002]

2. Description of the Related Art Conventionally, a basic fuel injection time is calculated based on an intake pipe pressure, that is, a measured value of the intake pipe pressure and a measured value of an engine speed at predetermined time intervals, and the basic fuel injection time is absorbed. 2. Description of the Related Art There is known an internal combustion engine in which a fuel injection time is obtained by correcting the temperature and the engine cooling water temperature, and a fuel injection valve is opened for a time corresponding to the fuel injection time to inject fuel. Further, in such an internal combustion engine, in order to improve the responsiveness during acceleration, the rate of change of the measured value of the intake pipe pressure is detected, and the time basic fuel injection time proportional to this rate of change is corrected to increase the amount of fuel. I am trying to increase the acceleration.

In an internal combustion engine that calculates the basic fuel injection time based on the intake pipe pressure as described above, a pressure sensor that measures the intake pipe pressure (absolute pressure) is attached to the intake pipe, and the measured intake pipe pressure is used. The basic fuel injection time is calculated by using the
Due to this variation, there is a possibility that the basic fuel injection time will change and accurate fuel injection amount control will not be performed. Therefore, conventionally, as shown in Japanese Patent Laid-Open No. 59-201938, two filters having different time constants are used to relax the pressure sensor output to completely remove the pulsating component from the pressure sensor output. The filter output having a large time constant is subtracted from the filter output having a small time constant to provide an overshoot characteristic, and the acceleration amount is increased according to the difference. However, in the method using two filters as described above, the degree of relaxing the pressure sensor output is increased by using the filter having a relatively large time constant in order to remove the pulsating component, and therefore the actual intake pipe pressure Responsiveness of changes in filter output to changes,
In some cases, the followability becomes poor, the amount of acceleration increase is delayed, the fuel injection amount becomes insufficient at the initial stage of acceleration to cause a lean spike, and at the end of acceleration, a latch spike occurs due to the overshoot characteristic.

For this reason, recently, a pressure sensor output is processed using a CR filter having a relatively small time constant such that a pulsating component composed of a resistor and a capacitor can be removed, and the CR filter output is processed every predetermined time. It has been proposed to use a measured value that is converted into a digital value and has better responsiveness and followability than the case where two filters are used. in this case,
Since the pulsation component cannot be completely removed by the CR filter, the digital value is used to reduce the degree of relaxation 2
One weighted average value is calculated, and the acceleration increase value is determined based on the difference obtained by subtracting the weighted average value with a large degree of relaxation from the weighted average value with a small degree of relaxation.

[0005]

However, in any of the above methods, since a large degree of relaxation is used to obtain the acceleration increase value, the response and the followability deteriorate, and the acceleration / deceleration is repeated. In the running pattern, there is a problem that a phase delay of the acceleration increase occurs, the fuel injection amount does not match the increase request of the engine, and the exhaust emission and the driver ability deteriorate. To solve this problem, the pressure sensor output is relaxed to such an extent that the engine pulsation component can be removed, and only a relaxation value with a small degree of relaxation is obtained, and the fuel injection amount including the acceleration increase is calculated based on this relaxation value. However, it takes a certain amount of time for the injected fuel to reach the combustion chamber after the fuel injection time is calculated, depending on the calculation time and the flight time of the fuel. Since there is a difference between the intake pipe pressure (relaxation value) and the intake pipe pressure corresponding to the actual intake air amount, the air-fuel ratio required by the engine cannot be controlled.

The above will be described in more detail with reference to FIG. FIG. 2 shows the calculated basic fuel injection time TP and the intake pipe pressure P during acceleration of a four-cylinder, four-cycle internal combustion engine that injects 1/2 of the required fuel amount in one intake stroke per engine revolution.
It is a figure which shows the change with M. In this example, the fuel is injected once per revolution of the engine, that is, twice per cycle (points c and b in the figure), and the amount of fuel contributing to one combustion can be understood from the figure. Thus, the amount corresponds to TPc + TPb. However, the intake pipe pressure that represents the actual intake air amount is at the end of the intake stroke (intake bottom dead center) shown by a in the figure.
It is the intake pipe pressure at. As described above, since there is a delay of time t _D between the intake pipe pressure at the time of calculating the fuel injection time and the intake pipe pressure representing the actual intake air amount, it is possible to inject fuel according to the actual intake air amount. It becomes impossible to control the air-fuel ratio required by the engine. On the other hand, even if the calculation time is shortened to make the delay time t _D small enough to be ignored, an internal combustion engine that injects fuel once per engine revolution requires a fuel amount corresponding to 2TPb at point b. In contrast, TPc + TPb
Since only the fuel corresponding to the
The fuel amount for b-TPc (= ΔTP) is insufficient.

On the other hand, the pulsation of the intake pipe pressure becomes particularly large at full load, and in the case of a four-cylinder four-cycle internal combustion engine, there are four explosive strokes in two revolutions of the engine, so 180 ° CA
It appears in the cycle of. Further, when the CR filter is used, the pulsation component cannot be completely removed because the response is good, and the CR filter output changes as shown in FIG. 4 (1). Furthermore, since the CR filter output is converted into a digital value every predetermined time and a weighted average value with a small degree of relaxation is also calculated, the cycle of digital conversion becomes 90 ° CA and the peaks and valleys of the CR filter output. And may be digitally converted alternately. In this case, the weighted average value also changes as shown in FIG. 4A according to the fluctuation of the intake pipe pressure.
Therefore, considering the case where the basic fuel injection time is calculated once per engine revolution based on the weighted average value and the acceleration is increased by correcting the difference in the weighted average value, the calculation timing is as shown in FIG. 4 in the case of the points X ₁ and X ₂ in FIG.
As shown in (2), since there is no change in the weighted average value, the basic fuel injection time does not fluctuate and the acceleration amount is not increased, but the basic fuel injection time is calculated using the weighted average value corresponding to the peak of the CR filter output. Is calculated, the basic fuel injection time becomes larger than the average value at full load, and the air-fuel ratio shifts to the latch side. Further, when the calculation timing X ₂ is deviated to X ₂ ′ due to rotation fluctuation or the like, not only the basic fuel injection time fluctuates but also the difference between the weighted average values becomes negative as shown in FIG. 4 (2). Will be decelerated and reduced. Therefore, when a CR filter is used, there is a problem that the air-fuel ratio fluctuates at the time of full load and the exhaust emission and driver bilities deteriorate.

The present invention has been made to solve the above problems, and provides a fuel injection amount control method for an internal combustion engine in which the air-fuel ratio does not change during transient operation and the exhaust emission and driver variability are improved. The purpose is to do.

[0009]

To achieve the above object, the invention according to claim 1 detects the relaxation value of the intake pipe pressure by relaxing the change in the signal output from the pressure sensor for measuring the intake pipe pressure. In a fuel injection amount control method for an internal combustion engine, a basic fuel injection time is calculated in a predetermined cycle based on the relaxation value, and a fuel injection amount is controlled based on the calculated current basic fuel injection time. From less than value to more than specified value
After a predetermined time has elapsed from the time when the change occurs, the change in the signal is largely alleviated.

According to a second aspect of the present invention, in the first aspect of the invention, the calculation is performed one cycle before the current basic fuel injection time.
Difference between the basic fuel injection time or the current relaxation value and 1
Depending on the difference between the relaxation value detected before the cycle and the engine speed,
And the current basic fuel injection based on
I am trying to correct the time .

The invention according to claim 3 is claim 1 or claim
In the invention of item 2, the relaxation value is calculated in the past.
The weighted average value weighted is calculated in the past.
Weighted average value and signal output from the pressure sensor
And the current weighted mean value calculated with
doing.

[0012]

According to the first aspect of the invention, the relaxation value of the intake pipe pressure is detected by relaxing the change in the signal output from the pressure sensor for measuring the intake pipe pressure, and the predetermined period is determined based on the relaxation value. The basic fuel injection time is calculated at, and the fuel injection amount is controlled based on the calculated current basic fuel injection time .

Here, when the engine load is above a predetermined value,
Greater reduction of the signal than when the engine load is less than the specified value
By doing so, once the engine load reaches a certain value or more,
The pulsation of the intake pipe pressure that is remarkable at the time of high load including
It is possible to prevent erroneous increase and decrease of fuel injection amount due to
It

However, if the engine load exceeds a predetermined value,
When the engine load is less than the specified value
If alleviated, the operating condition will be moderate immediately after entering the high engine load range.
The sum value cannot change following the change in engine load,
Transiently lower than intake pipe pressure. Therefore, the air-fuel ratio is
Exhaust emission deteriorates with leanness.

Therefore, in the present invention, a change in the air-fuel ratio during transition is prevented by greatly mitigating a change in the signal after a lapse of a predetermined time from the time when the engine load changes from less than a predetermined value to a predetermined value or more. I have to.

According to a second aspect of the present invention, in the first aspect of the invention, the difference between the current basic fuel injection time and the basic fuel injection time calculated one cycle before or the current relaxation value and 1
The current basic fuel injection time is corrected based on the difference between the relaxation value detected before the cycle and the coefficient changed according to the engine rotation speed.

The invention as set forth in claim 3 will be described in more detail with reference to a four-cylinder, four-cycle internal combustion engine in which fuel is injected once per revolution of the engine.
If the delay time t _D from the fuel injection time calculation is ignored,
The basic fuel injection time TP corresponding to the actual intake air amount is expressed by the following equation (1).

[0018]

## EQU1 ## TP = TPb + ΔTP (1) On the other hand, as shown in FIG. 3, assuming that the acceleration is performed at equal acceleration, the difference ΔT in basic fuel injection time between points b and c is ΔT.
Since the difference ΔTP ′ of the basic fuel injection time between the points P, b and b ′ is equal, the basic fuel injection time TPb ′ at the point b ′ is
The basic fuel injection time TPb at the point b and the above ΔTP (= ΔT
P ′) and can be expressed as in the following equation (2).

[0019]

TP ′ = TPb + ΔTP (2) Here, assuming that the calculation of the basic fuel injection time is performed every 360 ° CA, as understood from the above equation (2), b This means that the basic fuel injection time 360 ° CA ahead of the point is predicted.

Therefore, generally, assuming that the calculation of the basic fuel injection time is performed every CY ° CA, the delay time t _D between points a and b in FIG. 2 is calculated as the crank angle CA. _If converted to _D and the correction amount W corresponding to this crank angle CAD is obtained, the following equation (3) is obtained, and the predetermined crank angle C is calculated from point b.
It is possible to predict the basic fuel injection time A _D ahead.

[0021]

(Equation 3)

Therefore, considering the correction when the point c changes to the point b in FIG. 2, the basic fuel injection time TP corresponding to the actual intake air amount when the basic fuel injection time is calculated for each CY ° CA. Is expressed by the following equation (4) using the immediately preceding basic fuel injection time TP ₀ .

[0023]

TP = TP ₀ + K · ΔTP (4) where K is a value represented by the following equation (5), and ΔT
P is a difference obtained by subtracting the basic fuel injection time calculated before CY ° CA from the current basic fuel injection time, and this difference is positive for acceleration and negative for deceleration.

[0024]

(Equation 5)

Here, the delay time t _D is often maintained at a constant crank angle for control purposes, but considering the flight time of the injected fuel, this flight time is substantially constant regardless of the engine speed. Therefore, at high engine speed, the fuel injected immediately before the intake stroke cannot reach the combustion chamber due to the delay due to the flight time, and the fuel is sucked for the first time in the second intake stroke. Thus, the crank angle CA _D to be predicted fuel injection time is larger as the engine speed increases.

On the other hand, when the CR filter is used, the CR filter output has a good response to the change of the actual intake pipe pressure, and therefore it is considered that the CR filter output shows substantially the actual intake pipe pressure. The weighted average value (relaxation value) for calculation is slightly behind the actual intake pipe pressure, as shown in FIG. This delay (control delay t _D ') is the detection delay of the pressure sensor, the signal transmission delay of the input circuit, the calculation timing delay due to these delays, the calculation time delay, C
This occurs due to a delay caused by relaxing the R filter output. Therefore, the control delay t _D ′ from the PMb ′ for calculating the fuel injection amount at point b in FIG.
It is necessary to predict the actual intake pipe pressure PMb in consideration of A _D '), calculate the basic fuel injection time based on this predicted value, and further perform the prediction in consideration of the delay time t _D described above. .

Therefore, the control delay t _D '(=
If the correction of CA _D ') is also added, it is expressed by the following equation (6).

[0028]

[Equation 6] TP = TP ₀ + K · ΔTP (6) where K is a value represented by the following equation (7).

[0029]

(Equation 7)

Further, the intake pipe pressure PM and the engine speed NE
When calculating the basic fuel injection time TP with and, TP∝PM
Therefore, the above equation (6) is calculated by using the difference in the relaxation value of the intake pipe pressure (the value obtained by subtracting the relaxation value for calculating the basic fuel injection time before CY ° CA from the current relaxation value for calculating the basic fuel injection) ΔPM. It is expressed by the following equation (8).

[0031]

TP = TP ₀ + K · ΔPM · C (8) where C is a proportional constant for converting the intake pipe pressure into the basic fuel injection time.

Here, the control delay time t _D 'can be regarded as substantially constant due to the phenomenon of the time period, and therefore, the crank angle CA _D ' is increased as the engine speed increases.

The values of the crank angles CA _D and CA _D 'at each rotational speed can be calculated, and the K value at each rotational speed can be obtained without considering the manufacturing error of the engine under test. . Further, although an example in which the basic fuel injection time is calculated for each predetermined crank angle (CY ° CA) has been described above, the present invention can also be applied to a case where the basic fuel injection time is calculated for each predetermined time. In this case CA
_The correction of the engine speed is not necessary for _D ', but the delay due to the flight time of the injected fuel is affected by the engine speed, and therefore the correction of the engine speed is necessary for K as a whole. Furthermore, in the above, one revolution per engine
The example of injecting the fuel twice has been described, but even in the independent injection, when the engine rotation speed becomes high, the basic fuel injection time becomes long and there is a region where unsucked fuel remains. Therefore, it is desirable to predict the intake pipe pressure (a value near the intake bottom dead center) that represents the actual intake air amount when the basic fuel injection time is calculated one time before the current basic fuel injection time is calculated. Can also be applied to independent injection.

As described above, in the invention described in claim 2, in the invention described in claim 1, the difference between the current basic fuel injection time and the basic fuel injection time calculated one cycle before or the current relaxation value and 1 By correcting the current basic fuel injection time based on the difference between the relaxation value detected before the cycle and the coefficient changed according to the engine speed, the delay due to the flight time of the fuel, the control delay, Alternatively, the delay due to the flight time of fuel and the control delay are corrected so that the air-fuel ratio does not change during a transition.

As described above, according to the present invention, since it is possible to predict and inject the basic fuel injection time corresponding to the actual intake air amount, it is possible to prevent a change in the air-fuel ratio during the transition and to prevent the exhaust emission and the exhaust emission. The effect that the driver's ability can be improved is obtained.

The invention according to claim 3 is claim 1 or claim
In the invention of item 2, the weighted average value calculated in the past by weighting the relaxation value and the weighted average value calculated in the past and the current level of the signal output from the pressure sensor are used. as computed current weighted average value
I have. That is, the weighted average value PMN _i calculated according to the following equation (9) may be used as the relaxation value.

[0037]

[Equation 9]

However, PMN _i-1 is a weighted average value calculated in the past, N is a weight, PMAD is the current level of the signal output from the pressure sensor, and the signal output from the pressure sensor is directly digitalized. It is possible to adopt a value converted into the value of or a value obtained by converting the pressure sensor output processed by the CR filter into a digital value.

[0039]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 6 schematically shows an internal combustion engine (engine) equipped with a fuel injection amount control device to which the present invention can be applied.

This engine is controlled by an electronic control circuit such as a micro computer, and a throttle valve 8 is arranged downstream of an air cleaner (not shown). The throttle valve 8 has a throttle opening. Power switch 10 that turns on at a predetermined value (for example, 50 °) or more
And a surge tank 12 is provided on the downstream side of the throttle valve 8. Instead of the power switch, a linear throttle sensor that outputs a voltage proportional to the throttle opening may be used to detect whether or not the throttle opening is equal to or larger than a predetermined value. A diaphragm type pressure sensor 6 is attached to the surge tank 12. The pressure sensor 6 is connected to a filter (FIG. 7) composed of a CR filter or the like having a small time constant (for example, 3 to 5 msec) for removing the pulsating component of the intake pipe pressure and having good responsiveness. . This filter may be built in the pressure sensor. Further, a bypass passage 14 is provided so as to bypass the throttle valve 8 and connect the upstream side of the throttle valve and the surge tank 12 on the downstream side of the throttle valve. The bypass path 14 is an IS whose opening is adjusted by a pulse motor 16A having a 4-pole stator.
A C (idle speed control) valve 16B is attached. The surge tank 12 is connected to the engine 20 via the intake manifold 18 and the intake port 22.
Is connected to the combustion chamber. Then, the fuel injection valve 2 is provided for each cylinder so as to project into the intake manifold 18.
4 is attached.

The combustion chamber of the engine 20 has an exhaust port 26
And an exhaust manifold 28 to communicate with a catalyst device (not shown) filled with a three-way catalyst. An O ₂ sensor 30 that outputs a signal inverted at the stoichiometric air-fuel ratio is attached to the exhaust manifold 28. A cooling water temperature sensor 34 is attached to the engine block 32 so as to penetrate the engine block 32 and project into the water jacket. The cooling water temperature sensor 34 detects the engine cooling water temperature and outputs a water temperature signal, and the water temperature signal represents the engine temperature. The engine oil temperature may be detected to represent the engine temperature.

The spark plug 3 is provided for each cylinder so as to penetrate the cylinder head 36 of the engine 20 and project into the combustion chamber.
8 are attached. The ignition plug 38 is connected via a distributor 40 and an igniter 42 to an electronic control circuit 44 composed of a microcomputer or the like. Inside the distributor 40, a cylinder discriminating sensor 46 and a rotation angle sensor 48, each of which is composed of a signal rotor fixed to the distributor shaft and a pick-up fixed to the distributor housing, are mounted. The cylinder discrimination sensor 46 outputs a cylinder discrimination signal, for example, every 720 ° CA, and the rotation angle sensor 48 outputs an engine rotation number signal, for example, every 30 ° CA.

As shown in FIG. 7, the electronic control circuit 44 includes a micro processing unit (MPU) 60, a lead
Only memory (ROM) 62, random access
Memory (RAM) 64, Back-up Plum (BU-RA
M) 66, an input / output port 68, an input port 70, output ports 72, 74 and 76, and a bus 75 such as a data bus or a control bus connecting these. The input / output port 68 has an analog-digital (A /
D) The converter 78 and the multiplexer 80 are connected in order. To the multiplexer 80, the pressure sensor 6 is connected via a filter 7 and a buffer 82 each composed of a resistor R and a capacitor C, and the cooling water temperature sensor 34 is connected via a buffer 84. Further, the power switch 10 is connected to the multiplexer 80.
The MPU 60 includes a multiplexer 80 and an A / D converter 7
8 is controlled to sequentially convert the output of the pressure sensor 6, the output of the power switch 10 and the output of the cooling water temperature sensor 34, which are input via the filter 7, into digital signals and store them in the RAM 64. Therefore, the multiplexer 80, the A / D converter 78, the MPU 60, and the like act as sampling means for sampling the pressure sensor output at predetermined time intervals.
The input port 70 has a comparator 88 and a buffer 8
An O ₂ sensor 30 is connected via 6 and a cylinder discrimination sensor 46 and a rotation angle sensor 48 are connected via a waveform shaping circuit 90. The output port 72 is a drive circuit 92
To the igniter 42, the output port 74 to the fuel injection valve 24 via a drive circuit 94 with a down counter, and the output port 76 to the drive circuit 9
6 is connected to the pulse motor 16A of the ISC valve. Note that 98 is a clock and 99 is a timer. The ROM 62 stores in advance programs and the like for control routines described below.

Next, the control routine of the first embodiment of the present invention when the present invention is applied to the above engine and the relaxation value is detected by the weighted average value by calculation will be described. In the following, numerical values that do not hinder the present invention will be used for description, but the present invention is not limited to these numerical values.

FIG. 8 shows an A / D conversion rule executed every 4 msec.
The pressure sensor in step 100.
The signal output from the server 6 is the CR filter 7 and the buffer 8
2 and the multiplexer 80 to the A / D converter 78
Intake pipe pressure PM input and converted by the A / D converter 78
Is taken in as a digital value PMAD. Next step 1
In 02, digital value PMAD of intake pipe pressure and 4 msec before
Weighted average value PMN of intake pipe pressure calculated in_i-1When
Let N be the weight N in the above equation (9) using
As a result, the weight of the current intake pipe pressure is calculated according to equation (9).
With average value PM _iIs calculated.

Then, in step 104, the weighted average value PMN _i of the current intake pipe pressure is calculated in order to calculate the weighted average value of the next intake pipe pressure PMN _i- Store as ₁ in the register.

FIG. 1 shows a fuel injection amount calculation routine executed at every fuel injection amount calculation timing (every 360 ° CA in the case of a 4-cylinder 4-cycle engine).
At 06, the coefficient K is calculated. This coefficient K is determined by the engine speed N in step 122 as shown in FIG.
It is obtained by taking in E and calculating the coefficient K corresponding to the current engine speed from the map shown in FIG. 10 in step 124. The coefficient K is calculated in advance and stored in the ROM as a map.
As the engine speed increases, as shown in 1.
It is represented as an increasing function increasing from zero.

In step 108 of FIG. 1, the weighted average value of the current intake pipe pressure is fetched as PMN. In step 104 of FIG. 8, since the weighted average value PMN _i of the current intake pipe pressure is stored in the register as PMN _i-1 ,
By reading the value of this register, the weighted average value of the current intake pipe pressure can be taken in as PMN. In the next step 110, the basic fuel injection time TP is calculated in the same manner as in the conventional method from the current weighted average value PMN of the intake pipe pressure and the engine speed NE fetched in step 122. In the next step 112, the weighted average value PMN ₀ of the past intake pipe pressure used to calculate the basic fuel injection time before 360 ° CA is subtracted from the weighted average value PMN ₀ of the current intake pipe pressure. Then, the difference ΔPM between the weighted average values of the intake pipe pressure is calculated.

At step 114, the difference K between the coefficient K calculated at step 124, the weighted average value of the intake pipe pressure calculated at step 112, and the constant C for converting the intake pipe pressure into the basic fuel injection time. By multiplying the correction value TPACC (corresponding to the second term on the right side of the equation (8)) by multiplying the correction value TPACC by adding the correction value TPACC to the current basic fuel injection time TP in step 116. Correct the injection time TP. Note that the correction value T
The PACC may be calculated based on the above equations (4) and (6). Then, in step 118, the current weighted average value PMN of the intake pipe pressure is stored in the register as the weighted average value PMN ₀ of the intake pipe pressure before 360 ° CA, and in step 120, the basic fuel injection time TP is set to the intake temperature or the intake air temperature. The fuel injection time TAU is calculated by making corrections according to the engine cooling water temperature and the like. Then, in a fuel injection amount control routine (not shown), fuel is injected once per engine revolution.

The basic fuel injection time TP used for calculating the fuel injection time TAU in step 120.
Is corrected according to the equation (8) described above in step 114, the control delay and the delay due to the flight time of the fuel are prevented, and the value is corrected to a value corresponding to the actual intake air amount. It is possible to prevent fluctuations in the air-fuel ratio.

Next, a second embodiment of the present invention will be described. FIG.
Reference numeral 1 denotes an A / D conversion processing routine executed every 4 msec. In step 130, it is determined whether or not the pressure sensor output input via the CR filter is A / D conversion, and in step 132, a power switch. It is determined whether the output is A / D converted. When it is determined in step 132 that the power switch output is A / D converted, it is determined in step 144 based on the A / D converted value whether the power switch is on. When it is determined that the power switch is off,
That is, when the engine load is less than the predetermined value, the count value CPSW is reset in step 146.

When it is determined that the pressure sensor output is A / D converted, the output of the A / D converter is taken in as a digital value PMAD of the current intake pipe pressure in step 134, and the count value CPSW is set to a predetermined value (eg, a predetermined value) in step 136. , 32) or more. This count value CPSW is counted in the routine executed every 32 msec shown in FIG.
At 8, it is determined whether the count value CPSW is the maximum value, and if it is not the maximum value, at step 150 the count value CPSW is incremented. Count value CP
Since SW is incremented every 32 msec, 32 in step 136 corresponds to approximately 1 second.

At step 136, the count value CPS
When W is determined to be 32 or more, since the power switch is turned on for the predetermined time, the weighted average of the current intake pipe pressure is set with the weight N of the above equation (9) as m (for example, 32). By calculating the value PMN _i , the relaxation value in which the change in the intake pipe pressure is greatly eased is calculated. On the other hand, in step 136, the count value CPSW is 32.
If it is determined that the value is less than the above, in step 138, the weight N of the equation (9) is set to n (for example, 4) to calculate the current weighted average value that is less than the degree of relaxation.

As a result of the above, the weighted average value PMN _i of the current intake pipe pressure is increased and the degree of relaxation is increased after a lapse of a predetermined time after the power switch is turned on.

FIG. 13 shows the fuel injection time calculation routine of this embodiment. Since it is almost the same as the fuel injection time routine explained in FIG. 1, corresponding parts are designated by the same reference numerals and described. Is omitted. The correction value TPACC in step 114 may be obtained in the same manner as in the first embodiment, and the correction value TPACC may be calculated according to the weight of the weighted average value of the intake pipe pressure set at the time of calculation of the correction value TPACC. The K value shown in 1 may be variable.

Next, when the weighted average value of the intake pipe pressure is calculated with the weight N set to m when the power switch is turned on, and when the weight N is set to m and the intake pipe pressure is set to a predetermined time after the power switch is turned on. The change of the weighted average value of the intake pipe pressure will be described in comparison with the case of calculating the weighted average value of. FIG. 14 shows a change in the weighted average value when the weighted average value is calculated by increasing the weight when the power switch is turned on. Since the intake pipe pressure transiently changes, the weighted average value is However, there is a large difference between the intake pipe pressure and the weighted average value. On the other hand, when a weighted average value with a large weight is calculated a predetermined time after the power switch is turned on as in the present embodiment, a transient change in intake pipe pressure as shown in FIG. Since the weighted average value is calculated after the end, the weighted average value is relaxed to the extent that the pulsating component of the intake pipe pressure can be removed.

Although an example in which the coefficient K is changed according to the engine speed has been described above, the amount of fuel adhering to the inner wall of the intake manifold increases when the engine cooling water temperature is low and the engine cooling is low. More fuel needs to be added than when the water temperature is high. Therefore,
The coefficient K may be expressed as a function of the engine speed and the engine cooling water temperature, and the coefficient K may be increased as the engine speed increases and may be decreased as the engine cooling water temperature increases.

[0058]

As described above, the present invention is suitable for the engine load.
Is a predetermined time from when the value of the
Increase the change in the signal output from the pressure sensor after the passage of time.
As the engine load is reduced, the engine load will be below the specified value and below the specified value.
The air-fuel ratio becomes lean immediately after it goes above the exhaust air.
It has the effect of preventing the mission from deteriorating .

[Brief description of drawings]

FIG. 1 is a flow chart showing a fuel injection time calculation routine of a first embodiment of the present invention.

FIG. 2 is a diagram for explaining a delay in a fuel injection amount when fuel is injected once per engine revolution.

FIG. 3 is a diagram showing changes in intake pipe pressure and basic fuel injection time in a constant acceleration state.

FIG. 4 is a diagram showing a change between a CR filter output and a weighted average value of the CR filter output under a high load.

FIG. 5 is a diagram for explaining a shortage of fuel amount due to a control delay.

FIG. 6 is a schematic diagram showing an engine including a fuel injection amount control device to which the present invention is applicable.

7 is a block diagram showing details of the control circuit of FIG.

FIG. 8 is a flowchart showing an A / D conversion routine of the first embodiment of the present invention.

FIG. 9 is a flowchart showing a calculation routine of a coefficient K of the above embodiment.

FIG. 10 is a diagram showing a map of a coefficient K.

FIG. 11 is a flow chart showing an A / D conversion processing routine of a second embodiment of the present invention.

FIG. 12 is a flowchart showing a routine executed every 32 msec in the above embodiment.

FIG. 13 is a flow chart showing a fuel injection time calculation routine of the above embodiment.

FIG. 14 is a diagram showing a change in weighted average value when the weighted average value is calculated when the power switch is turned on.

FIG. 15 is a diagram showing a change in the weighted average value when the weighted average value is calculated after a predetermined time has elapsed since the power switch was turned on.

[Explanation of symbols]

 6 Pressure sensor 7 CR filter 10 Power switch 24 Fuel injection valve 48 Rotation angle sensor

Claims (3)

(57) [Claims] 1. A relaxation value of the intake pipe pressure is detected by relaxing a change in a signal output from a pressure sensor for measuring the intake pipe pressure, and a basic fuel injection time is calculated at a predetermined cycle based on the relaxation value. In a fuel injection amount control method for an internal combustion engine that controls the fuel injection amount based on the calculated current basic fuel injection time, the engine load is changed from less than a predetermined value to more than a predetermined value.
The method for controlling the fuel injection amount of an internal combustion engine is characterized in that the change in the signal is largely mitigated after a lapse of a predetermined time from the point of time . 2. A difference between a current basic fuel injection time and a basic fuel injection time calculated one cycle before or a difference between a current relaxation value and a relaxation value detected one cycle before and an engine speed. The fuel injection amount control method for an internal combustion engine according to claim 1, wherein the current basic fuel injection time is corrected based on the coefficient that is changed according to the coefficient. 3. The relaxation value is a weighted average value calculated in the past by weighting a weighted average value calculated in the past, and a current level of a signal output from the pressure sensor. The fuel injection amount control method for an internal combustion engine according to claim 1 or 2, wherein the calculated current weighted average value is used.