JPS63131840A - Control method for fuel injection amount of internal combustion engine - Google Patents

Abstract

PURPOSE:To increase accuracy of the air-to-fuel ratio at transient by computing the fundamental fuel injection amount on the basis of the relief value of suction pipe pressure, and correcting it with the product obtained by multiplying No.1 factor by the change amount of the suction pipe pressure from the previous value of relief value and the product of No.2 factor by the damping value of the change amount. CONSTITUTION:Into an electronic control circuit 44, a pressure sensor 6 of diaphragm type installed at a surge tank 12 is fed through a CR filter with small time constant and good response, and this circuit 44 computes weighted mean value of the suction pipe pressure. The fundamental fuel injection amount is computed on the basis of said weighted mean value of suction pipe pressure and the number of revolutions from a crank angle sensor 48. This fundamental fuel injection amount undergoes a correction with the product obtained from the difference in said weighted mean value between the previous and current values multiplied by No.1 factor due to the coolant temp. and number of revolutions and the product obtained from the cumulative products of weighted mean value and damping factor with a No.2 factor due to the coolant temp. and number of revolutions.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a fuel injection amount control method for an internal combustion engine, and in particular calculates a basic fuel injection time based on a measured value of intake pipe pressure, and The present invention relates to a fuel injection amount control method for an internal combustion engine that injects fuel based on fuel injection time.

[Conventional technology]

Conventionally, the basic fuel injection time is calculated at predetermined intervals based on the intake pipe pressure, that is, the measured value of the intake pipe pressure and the measured value of the engine rotation speed, and this basic fuel injection time is calculated based on the intake air temperature and the engine cooling water temperature. An internal combustion engine is known in which a fuel injection time is determined by correcting the fuel injection time, etc., and the fuel injection valve is opened for a time corresponding to the fuel injection time to inject fuel. In addition, in such an internal combustion engine, in order to improve responsiveness during acceleration, the rate of change in the measured value of intake pipe pressure is detected, and the amount of fuel is increased by correcting the basic fuel injection time by a time proportional to this rate of change. I am trying to increase the amount at an accelerated pace.

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 basic fuel injection time is calculated based on the measured intake pipe pressure. Although the injection time is calculated, the measured value fluctuates due to engine pulsation, and this fluctuation causes the basic fuel injection time to change and there is a risk that accurate fuel injection amount control cannot be performed. Since the pressure rapidly increases and the amount of fuel evaporated decreases, there is a risk that the injected fuel will adhere to the inner wall of the intake manifold, resulting in insufficient fuel supply.

For this reason, conventionally, as shown in Japanese Unexamined Patent Publication No. 59-201938, two filters with different time constants are used,
The pulsating component is completely removed from the pressure sensor output by relaxing the pressure sensor output, and overshoot characteristics are created by subtracting the filter output with a large time constant from the filter output with a small time constant, and this difference is integrated. The value was attenuated to compensate for fuel adhering to the inner wall of the intake manifold. That is, as shown in Fig. 2, when the integrated value is larger than the level Lc (when the engine is cold) or LH (when the engine is warm) determined by the engine cooling water temperature, the damping speed is fast, and when it is smaller than the level Lc-LII, the damping speed is low. It was corrected by multiplying the basic fuel injection time by the slow increase coefficient. However, in this method of using two filters, in order to remove pulsation components, a filter with a relatively large time constant is used to increase the degree of relaxation of the pressure sensor output, so the actual intake pipe pressure The responsiveness and followability of changes in filter output to changes is poor (this results in a delay in increasing the amount of acceleration, resulting in insufficient fuel injection at the beginning of acceleration and a lean spike, and at the end of acceleration due to overshoot characteristics, a rich spike occurs). In addition, the attenuation speed of the integrated value can be switched between two stages, but since the attenuation speed is the same when the engine is warm and when the engine is cold, the It was not possible to obtain an optimal damping curve, and the air-fuel ratio fluctuated, especially during cold transient operation.

For this reason, in recent years, CRs with relatively small time constants that can remove pulsating components and are made up of resistors and capacitors have been developed.
It has been proposed to process the pressure sensor output using a filter, convert the CR filter output into a digital value at predetermined intervals, and use a measured value with better responsiveness and followability than when two filters are used. . In this case, since the pulsating component cannot be completely removed by the CR filter, two weighted average values with different degrees of relaxation are calculated using the digital values, and the first weighted average value with a smaller degree of relaxation is calculated. The acceleration increase value is determined based on the difference obtained by subtracting the second weighted average value, which has a greater degree of relaxation, and this acceleration increase value is corrected by the prefectural cooling water temperature to determine the increase coefficient as shown in Figure 3. The basic fuel injection time is corrected.

[Problem that the invention seeks to solve]

However, in both of the above methods, a value with a large degree of relaxation is used to find the increase coefficient, resulting in poor responsiveness and followability, and in a driving pattern that repeats acceleration and deceleration, the phase delay of acceleration increase This causes a problem in that the fuel injection amount does not match the engine's increase request, and exhaust emissions and drivability deteriorate. In order to solve this problem, only a relaxation value with a small degree of relaxation, which relaxes the pressure sensor output to the extent that the engine pulsation component can be removed, is found, and the fuel injection amount including the acceleration increase is calculated based on this relaxation value. However, a certain amount of time is required from when calculating the fuel injection time until the injected fuel reaches the combustion chamber, depending on the calculation time and the flight time of the fuel, and the intake pipe pressure changes during acceleration. Since there is a difference between the used intake pipe pressure (relaxation value) and the intake pipe pressure corresponding to the actual intake air amount, it becomes impossible to control the air-fuel ratio to the level required by the engine.

The above will be explained in more detail with reference to FIG. Figure 4 shows the amount of fuel required for one intake stroke per engine revolution.
FIG. 2 is a diagram showing changes in calculated basic fuel injection time TP and intake pipe pressure PM during acceleration of a 4-cylinder, 4-cycle internal combustion engine that injects 2/2 fuel.

In this example, fuel is injected once per engine revolution, that is, twice per cycle (c, b in the figure).
point), the amount of fuel contributing to one combustion is an amount corresponding to TP C + TP b, as can be understood from the figure. However, the intake pipe pressure representing the actual intake air amount is the intake pipe pressure at the end of the intake stroke (intake bottom dead center), which is indicated by a in the figure.

In this way, since there is a delay of time t between the intake pipe pressure when calculating the fuel injection time and the intake pipe pressure representing the actual intake air amount, it is not possible to inject fuel according to the actual intake air amount. It becomes impossible to control the air-fuel ratio to the engine's required air-fuel ratio. On the other hand, even if the calculation time etc. is shortened and the delay time t is made negligible, in an internal combustion engine that injects fuel once per engine revolution, a fuel amount corresponding to 2TPb is required at point b. However, since only the fuel corresponding to TP c + TP b is supplied, TPb - TP'c (-
ΔTP) amount is insufficient.

In addition, in the method using a CR filter, the difference obtained by subtracting the second weighted average value, which has a large degree of relaxation, from the first weighted average value, which has a small degree of relaxation, is only corrected by the engine cooling water temperature. Therefore, as shown in Fig. 3, the rate at which the acceleration increase is attenuated is uniquely determined by the second weighted average value, which has poor responsiveness to fluctuations in intake pipe pressure. There is a problem in that it is not possible to obtain an optimal attenuation curve depending on the situation. In other words, in any of the above methods, it is not possible to obtain an optimal damping curve according to each transient operating state, and it is necessary to perform an optimal acceleration increase when the engine is cold, especially when the fluctuation in the amount of fuel adhering to the inner wall of the intake manifold is large. This resulted in deterioration of exhaust emissions and drivability.

The present invention was made to solve the above-mentioned problems, and corrects the delay between the intake pipe pressure corresponding to the actual intake air amount and the relaxation value for basic fuel injection time calculation, and the amount of fuel adhering to the inner wall of the intake manifold. This prevents the air-fuel ratio from changing during transient operation, whether cold or warm.
An object of the present invention is to provide a fuel injection amount control method for an internal combustion engine that improves exhaust emissions and drivability.

[Means for solving problems]

In order to achieve the above object, the present invention detects a relaxation value of the intake pipe pressure by relaxing changes in a signal output from a pressure sensor that measures the intake pipe pressure, and then detects a relaxation value of the intake pipe pressure at a predetermined period based on the relaxation value. In a fuel injection amount control method for an internal combustion engine that calculates a fuel injection time and controls the fuel injection amount based on the calculated current basic fuel injection time, the current basic fuel injection time and the basic calculated one cycle before are used. The product of the amount of change expressed by the difference between the fuel injection time or the difference between the current relaxation value and the relaxation value detected one cycle ago and the first coefficient that changes depending on the engine rotation speed, and the change The present invention is characterized in that the current basic fuel injection time is corrected based on the product of the integrated value of the attenuation value of the amount and the second coefficient.

[Effect]

Next, the principle of the present invention will be explained. Note that the following description will be made by taking as an example a 4-cylinder 4-cycle internal combustion engine in which fuel is injected once per engine revolution.

As explained in FIG. 4, if the delay time t from the calculation of the fuel injection time is ignored, the basic fuel injection time TP corresponding to the actual intake air amount is expressed by the following equation.

TP-TPb+ΔTP...(1) On the other hand, if the acceleration is uniform as shown in FIG.
Difference ΔTP in basic fuel injection time between point b and point 0 and point b and b
Since the difference ΔTP' in the basic fuel injection time from point ' is equal, the basic fuel injection time TPb' at point b is equal to the basic fuel injection time TPb at point b and the above ΔTP (=ΔTP')
It can be expressed as follows using

TP' - TPb + ΔT P ・+21 Here, if the calculation of the basic fuel injection time is performed every 360" CA, as understood from the above equation (2), 360 @ CA ahead from point b This means that the basic fuel injection time has been predicted.

Therefore, in general, the calculation of the basic fuel injection time is
If it was performed for each CA, points a and b in Figure 4
If we convert the delay time tゎ from point b to crank angle CA and find the correction amount corresponding to this crank angle CA, we get Can be predicted. Therefore, if we consider the correction when changing from point 0 to point b in Figure 4, CY ”
When calculating the basic fuel injection time for each CA, the basic fuel injection time TP corresponding to the actual intake air amount is expressed as follows using the immediately preceding basic fuel injection time TP.

TP=TPe+KI・ΔTP...(4) is the 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. becomes.

Here, the delay time t is often kept at a constant crank angle for control purposes, but considering the flight time of the injected fuel, this flight time is approximately constant regardless of the engine rotation speed. When the engine speeds up to high speeds, the fuel injected just before the intake stroke cannot reach the combustion chamber due to the delay due to the flight time, and the fuel is drawn in for the first time during the intake stroke, which is two ports ahead. Therefore, the crank angle C at which the fuel injection time should be predicted
Al1 increases as the engine rotation speed increases.

On the other hand, when a CR filter is used, the CR filter output has good responsiveness to changes in the actual intake pipe pressure, so it is considered to approximately indicate the actual intake pipe pressure. As shown in FIG. 6, the weighted average value (relaxation value) lags behind the actual intake pipe pressure. This delay (control delay t6°) is caused by pressure sensor detection delay, input circuit signal transmission delay, calculation timing delay due to these delays, calculation time delay, delay due to relaxing CR filter output, etc. This occurs. Therefore, PMb' for calculating the fuel injection amount at point b in FIG.
The actual intake pipe pressure PMb is predicted by considering the control delay t, ゛ (CAo' in crank angle), the basic fuel injection time is calculated based on this predicted value, and the delay time 1D explained above is calculated. It is necessary to make predictions that take this into account.

Therefore, the control delay t n'(-CAD'
) can be expressed as follows.

T P = T P e + K +・ΔTP...(
5).

In addition, when calculating the basic fuel injection time TP using the intake pipe pressure PM and the engine speed NE, TPO+:PM is obtained, so the above equation (5) can be used to calculate the difference in the relaxation value of the intake pipe pressure (current basic fuel injection The value obtained by subtracting the basic fuel injection time calculation relaxation value before cY''CA from the calculation relaxation value) can be expressed using ΔPM as shown in the following equation (6).

T P ”” T P o + K + 'ΔP M
-C-.-(6) However, C is a proportionality constant for converting the intake pipe pressure into the basic fuel injection time.

Here, since the control delay time tDl is a time period phenomenon and can be considered to be substantially constant, in terms of the crank angle CA D', it increases as the engine rotational speed increases.

Note that the values of the crank angles CAs and CAt' at each rotational speed can be calculated by calculation, and the value of 1 at each rotational speed can be obtained without considering manufacturing errors of the test engine. In addition, in the above, the predetermined crank angle (CY
Although we have described an example in which the basic fuel injection time is calculated for each predetermined period of time (CA), it can also be applied to the case where the basic fuel injection time is calculated for each predetermined time period.In this case, CA,'
Although it is not necessary to correct for engine speed,
Since the delay due to the flight time of the injected fuel is affected by the engine speed, K1 as a whole needs to be corrected based on the engine speed. Further, although an example in which fuel is injected once per engine revolution has been described above, even in independent injection, as the engine rotational speed increases, the basic fuel injection time becomes longer and a region where fuel remains unsucked occurs. For this reason, it is desirable to predict the intake pipe pressure (value near intake bottom dead center) that represents the actual intake air amount when calculating the basic fuel injection time one time before the current basic fuel injection time calculation.
The invention can also be applied to independent injection.

Further, the present invention corrects the basic fuel injection time using the following equation.

K, ・D L P M r I-C... (7) However, K2 is the second coefficient, which can change depending on the engine rotation speed, engine cooling water temperature, intake pipe pressure, etc. DLPMIi is an integrated value of the attenuation value of the difference between the current relaxation value and the relaxation value detected one cycle ago, which is expressed by the following equation.

DLPMl, proverb ΔP M + K s−D L P M
I Direct-5 (8) Here, K is a positive attenuation coefficient less than 1, and DLPM r +-+ is an integrated value calculated last time.

In the above equation (8), the initial value of the integrated value is set to 0, and during one calculation, the difference ΔPM becomes ΔPMI, ΔPM,...ΔP
M, then the i-th D L P M
I t is expressed as follows.

D L P M I 1-ΔPMi+!・ΔP Mt
−+ 10Ks”・ΔPMi−,+ ・ ・ ・
Ten K? −: ・ΔPM”+K,”−1・Δ
PM, ... (9) Therefore, the integrated value gradually increases from the start of acceleration, and even after acceleration ends, it takes a certain value until it approaches 0 due to the damping coefficient.

If the correction for predicting the basic fuel injection time corresponding to the actual intake air amount and the correction in (7) 2 above are performed at the same time, the basic fuel injection time TP becomes as shown in the following 0 [formula or 00 formula] .

T P ” T P o + K I・ΔPM−C+,・D L P M I !−C・・・α・T P ”
T P o + K + 'ΔTP+,・DLPM
Ii...αυ However, D L P M I + in the above formula 00 is the integrated value of the attenuation value of the difference between the current basic fuel injection time and the basic fuel injection time one cycle before, which is expressed by the following formula: .

3・DLPMIi to D L P M I +−ΔTP+
-,...0 In addition, Kl used in the above a[,00 formula,
Kg and K can be determined according to parameters such as engine speed, engine cooling water temperature, or intake pipe absolute pressure to cover a wide range of transient operating conditions, but even if each parameter is changed, transient operating conditions will not be affected. The coefficients for which the required value of the fuel injection amount hardly changes may be defined as constant values.

If the current basic fuel injection time T P o is not corrected, the change in acceleration increase value and air-fuel ratio when the basic fuel injection time is corrected as above when the engine is cold is used as the value of K, which is suitable for when the engine is warm. The experimental results will be described in comparison with the case where A is used as the value of K, and the case where KC (>K), which is suitable for the cold state, is used as the value of K.

As shown in Fig. 7, the intake pipe pressure PM when the engine is cold is P
If fuel is injected only at the current basic fuel injection interval TP e in an accelerated driving state changing from M + to pMt, the increase value becomes O and the air-fuel ratio changes as shown in Figure 7 (3). A large lean spike occurs, resulting in poor exhaust emissions and drivability. By correcting this basic fuel injection time TP0, 'rpo +KM ・
Although the lean spike is halved when fuel is injected based on ΔPM-C, there is still a large change in the air-fuel ratio.
This is thought to be due to the large change in the amount of fuel adhering to the inner wall of the intake manifold when the engine is cold. In addition, the value of K is further increased to a value suitable for cold conditions, and 'rp
o When fuel is injected based on +KC・ΔPM−C,
As shown in FIG. 7(3), although the lean spike in the early stage of acceleration can be almost eliminated, the lean spike remains in the latter stage of acceleration and at the end of acceleration. This is considered to be because the intake pipe pressure increases during the 2&nd period of acceleration and at the end of acceleration, and the amount of fuel evaporation decreases, so that a large amount of the injected fuel adheres to the inner wall of the intake manifold.

In consideration of the above phenomenon, the present invention calculates the difference between the current basic fuel injection time and the basic fuel injection time calculated one cycle ago, or the current relaxation value and 1 The product of the amount of change represented by the difference from the relaxation value detected before the cycle and the first coefficient that changes depending on the engine rotation speed, and the product of the cumulative value of the attenuation value of the amount of change and the second coefficient. The current basic fuel injection time is corrected based on the product. Since the integrated value of the above-mentioned damping value takes a certain value even at the end of acceleration and after the end of acceleration, the lean spike at the end of acceleration and at the end of acceleration that occurred when the basic fuel injection time was corrected by setting K to By preventing this, it is possible to keep the air-fuel ratio substantially constant during transients such as during acceleration, as shown by the solid line in FIG. 7(3).

〔effect〕

As explained above, according to the present invention, it is possible to supply fuel corresponding to the actual intake air amount during a transient period, and also to make corrections based on changes in the amount of fuel adhering to the inner wall of the intake manifold, so that the engine can be heated or cooled. Since the air-fuel ratio can be kept substantially constant regardless of the time, it is possible to prevent deterioration of exhaust emissions and drivability during all transient operations.

[Explanation of aspects]

Next, the embodiments of the present invention will be described. The present invention may take the following embodiments when carried out.

In this aspect, the relaxation value in the present invention is calculated by multiplying the weight of the weighted average value calculated in the past by the weighted average value calculated in the past and the current level of the signal output from the pressure sensor. The calculated current weighted average value is used as the relaxation value. That is, the weighted average value PMN calculated according to the following formula is used as the relaxation value.

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

〔Example〕 Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 8 schematically shows an internal combustion engine 9 (engine) equipped with a fuel injection amount control device to which the present invention is applicable.

This engine is controlled by an electronic control circuit such as a microcomputer, and a throttle valve 8 is arranged downstream of an air cleaner (not shown), and a voltage corresponding to the throttle opening is applied to the throttle valve 8. A linear throttle sensor 10 is attached that outputs , and a surge tank 12 is provided downstream of the throttle valve 8 .

A diaphragm type pressure sensor 6 is attached to this surge tank 12. This pressure sensor 6 is connected to a filter (Fig. 9) composed of a CR filter or the like that has a small time constant (for example, 3 to 5 m5ec) and good responsiveness to remove the pulsating component of the intake pipe pressure. ing.

Note that this filter may be built into the pressure sensor, or it may bypass the throttle valve 8 and be installed in the surge tank 12 on the upstream side of the throttle valve and the downstream side of the throttle valve.
A bypass path 14 is provided to communicate with the.

An I5O (idle speed control) valve 16B whose opening degree is adjusted by a pulse motor 16A having a four-pole stator is attached to the bypass path 14. The surge tank 12 is connected to the intake manifold 18
and is communicated with the combustion chamber of the engine 20 via an intake boat 22.

A fuel injection valve 24 is attached to each cylinder so as to protrude into the intake manifold 18.

The combustion chamber of the engine 20 is communicated via an exhaust port 26 and an exhaust manifold 28 to a catalyst device (not shown) filled with a three-way catalyst. A 0□ sensor 30 is attached to the exhaust manifold 28 and outputs a signal that is inverted at the stoichiometric air-fuel ratio. A cooling water temperature sensor 34 is attached to the engine block 32 so as to penetrate through the engine block 32 and protrude into the water jacket. This 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. Note that the engine oil temperature may be detected to represent the engine temperature.

A spark plug 38 is attached to each cylinder so as to penetrate the cylinder head 36 of the engine 20 and protrude into the combustion chamber. The spark 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 discrimination sensor 46 and a rotation angle sensor 48 are installed, each of which is composed of a signal rotor fixed to the distributor shaft and a pickup fixed to the distributor housing. The cylinder discrimination sensor 46 is, for example, 720"
A cylinder discrimination signal is output every CA, and the rotation angle sensor 48 outputs an engine rotation speed signal every 30'CA, for example.

As shown in FIG. 9, the electronic control circuit 44 includes a microprocessing unit (MPU) 60, a read-only memory (ROM) 62, and a random access memory (
RAM) 64, backup RAM (BU-RAM) 66
, input/output capotro 8, input port door 0, output port door 2
．． 74, 76 and a bus 75 such as a data bus or a control bus that connects them. An analog-to-digital (A/D) converter 78 and a multiplexer 80 are connected in sequence to the input/output capotro 8.

The pressure sensor 6 is connected to the multiplexer 80 via a CR filter 7 and a buffer 82 which are composed of a resistor R and a capacitor C, and the cooling water temperature sensor 34 is also connected via a buffer 84 . Further, a linear throttle sensor 10 is connected to the multiplexer 80.

The MPU 60 includes a multiplexer 80 and an A/D converter 7
8 to sequentially convert the pressure sensor 6 output, linear throttle sensor 10 output, and cooling water temperature sensor 34 output input through the CR filter 7 into digital signals.
Store it in AM64.

Therefore, multiplexer 80, A/D converter 78 and M
The PU 60 and the like act as sampling means that samples the pressure sensor output at predetermined time intervals. The 0□ sensor 30 is connected to the input port door 0 via a comparator 88 and a buffer 86, and the trachea discrimination sensor 46 and the rotation angle sensor 48 are also connected via a waveform shaping circuit 90. The output port door 2 is connected to the igniter 42 via a drive circuit 92, the output port door 4 is connected to the fuel injection valve 24 via a drive circuit 94 with a down counter, and the output port door 6 is connected to the fuel injection valve 24 via a drive circuit 96. It is connected to the pulse motor 16A of the ISO valve.

Note that 98 is a clock and 99 is a timer. The above RO
The M62 stores in advance a control B routine program, etc., which will be explained below.

Next, a control routine according to an embodiment of the present invention will be described when the present invention is applied to the above engine and the relaxation value is detected by a weighted average value calculated. In addition, although the present invention will be described below using numerical values that do not hinder the present invention, the present invention is not limited to these numerical values.

FIG. 10 shows an A/D conversion routine that is executed every 4 a+sec.
In the next step 102, the intake pipe pressure PM is inputted to the A/D converter 78 via the A/D converter 2 and the multiplexer 80, and is digitally converted by the A/D converter 78 as a digital value PMAD. Digital value PMA
By using D and the weighted average value PM N i −+ of the intake pipe pressure calculated 4 m5ec ago and setting the weight N of the α1 formula to n (for example, 4), the current intake pipe pressure is calculated according to the 01 formula. The weighted average value PM of is calculated.

Then, in step 104, in order to calculate the next weighted average value of the intake pipe pressure, the current weighted average value PMN of the intake pipe pressure is converted to the weighted average value PMN of the intake pipe pressure 4 m5ec ago. Store it in the register as +.

FIG. 1 shows a fuel injection amount calculation routine that is executed at each fuel injection amount calculation timing (every 360" CA in the case of a 4-cylinder 4-cycle engine). In step 106, +, Kg, and Ks are calculated as coefficients. .1 to this coefficient
As shown in FIG. 11, in step 128, the weighted average value PMN of the intake pipe pressure, the engine rotation speed N
Incorporating parameters such as E and engine cooling water ITHW,
In step 130, the coefficient corresponding to the current engine rotational speed NE is calculated from the map shown in FIG. The coefficient KI is calculated in advance and stored in the ROM as a map, and as shown in FIG. 12, it is expressed as an increasing function that increases from 1.0 as the engine speed NE increases.

In the next step 132, a coefficient of 2 corresponding to the current engine rotational speed NE or a coefficient of 2 corresponding to the current engine cooling water temperature THW is calculated from the map shown in FIG. 13 or the map shown in FIG. To this coefficient! is the engine rotation speed N
It may be determined by the function f (NE, THW) of E and the engine cooling water temperature, or the function f (PM
N), engine rotational speed NE, engine cooling water temperature THW and weighted average (!' P M N function f (NEST
HW, PMN).

Here, as the engine speed NE increases, the intake flow speed increases, the amount of fuel that adheres to the inner wall of the intake manifold decreases, and most of it is thought to be supplied to the combustion chamber, so a coefficient of 2 means that the engine speed increases. It is determined that the size will decrease accordingly. In addition, when the engine cooling water temperature is high (the amount of fuel adhering to the inner wall of the intake manifold evaporates increases, and the amount of fuel adhering to the inner wall of the intake manifold decreases, the coefficient becomes smaller as the engine cooling water temperature increases). stipulated in

And, as the intake pipe pressure increases, the amount of fuel evaporation decreases, and the amount of fuel that adheres to the inner wall of the intake manifold increases, so it becomes a coefficient! is determined to increase as the weighted average value of the intake pipe pressure increases.

In the next step 134, the damping coefficient is calculated. 3 is a positive value less than 1 for this damping coefficient, and a constant value may be used, but as with 2 for the above coefficient, the engine rotation speed NE,
Weighted average value PMN of intake pipe pressure, engine cooling water temperature TH
When changing the coefficient Ks, which may be determined according to W, etc., the damping speed can be slowed down by increasing the coefficient Ks in transient operating conditions where the amount of fuel adhering to the inner wall of the intake manifold increases, as described above. In a transient operating state where the amount of fuel adhering to the inner wall of the intake manifold decreases, the coefficient , is made smaller to increase the damping speed.

In step 108 of FIG. 1, the weighted average value of the current intake pipe pressure is taken in as PMN.

In step 104 of FIG. 10, the weighted average value P M N of the current intake pipe pressure is stored in the register as PMNt-+, so by reading the value of this register, the weighted average value of the current intake pipe pressure is stored. In the zero-order step 110, the current basic fuel injection time T P is calculated using the weighted average value PMN of the current intake pipe pressure and the engine rotation speed NE, which were taken in step 128, in a manner similar to the conventional method. In the zero-order step 112 of calculating o, the value obtained by multiplying the integrated value DLPMI stored in the RAM by the damping coefficient is stored in the register R, and in step 114, the weighted average value of the current intake pipe pressure is stored. Weighted average value PMN of past intake pipe pressures used to calculate basic fuel injection time 360@CA before PMN.

The difference ΔPM between the weighted average values of intake pipe pressure is calculated by subtracting ΔPM. In step 116, the difference ΔPM between the weighted average values of the intake pipe pressure and the value stored in the register R are added to create the current integrated value DLPMI(-Δ
PM+Ks ・DLPMI+-+) is calculated. In step 118, the coefficient calculated in step 130 is
The coefficient calculated in step 132 is the product of the difference ΔPM between the weighted average value of the intake pipe pressure calculated in step 114 and the constant C for converting the intake pipe pressure into the basic fuel injection time. By adding the product of the integrated value DLPMI calculated in step 116 and the constant C, the increase value TPACC (corresponding to the second and third terms on the right side of equation 11) is calculated, and step At step 120, the current basic fuel injection time TPACC is corrected by adding the increase value TPACC to the current basic fuel injection time TPe.The increase value TPACC may be calculated based on the above formula 011. Then, in step 122, the current weighted average value PMN of the intake pipe pressure is stored in a register as the weighted average value PMN of the intake pipe pressure 360°CA before, and in step 124, the basic fuel injection time TP is stored in the register. The fuel injection time TAU is calculated by correcting it based on the air temperature, engine cooling water temperature, etc. Then, in a fuel injection amount control routine (not shown), fuel is injected once per engine revolution.

The basic fuel injection time TP used to calculate the fuel injection time TAU in step 124 is
20 is corrected according to formula 01 or formula 00 explained above, thereby preventing control delays and delays due to fuel flight time, as well as preventing the influence of the amount of fuel adhering to the inner wall of the intake manifold, thereby reducing the actual intake air amount. Since the air-fuel ratio is corrected to a value corresponding to the air-fuel ratio, fluctuations in the air-fuel ratio during transient periods can be prevented.

In the above, an example was explained in which the coefficient is set to 1 and is changed according to the engine rotation speed, but when the engine cooling water temperature is low, such as when the engine is cold, the amount of fuel adhering to the inner wall of the intake manifold is large (because the engine cooling water temperature It is necessary to increase the amount of fuel when The coefficient K increases as it increases.

may be made smaller.

[Brief explanation of the drawing]

Fig. 1 is a flowchart showing the fuel injection time calculation routine of the first embodiment of the present invention, Figs. 2 and 3 are conventional diagrams showing changes in the increase coefficient during acceleration, and Fig. 4 is a diagram showing the change in the increase coefficient during one revolution of the engine. Figure 5 is a diagram showing the change in intake pipe pressure and basic fuel injection time in a constant acceleration state, Figure 6 is a diagram to explain the delay in fuel injection amount when fuel is injected once in A diagram showing the changes in the CR filter output and the weighted average value of the CR filter output under high load, and Figures 7 (1) to (3) explain the increase value and changes in the air-fuel ratio, etc. of the present invention. FIG. 8 is a schematic diagram showing an engine equipped with a fuel injection amount control device to which the present invention can be applied, FIG. 9 is a block diagram showing details of the control circuit in FIG. 8, and FIG. A of the first embodiment of the invention
/D conversion routine; FIG. 11 is a flowchart showing the calculation routine for the coefficients Kl, Kt, K of the above embodiment;
FIG. 12 is a diagram showing a map of 2 to a coefficient, and FIGS. 13 and 14 are diagrams showing a map of 2 to a coefficient. 6... Pressure sensor, 7... CR filter, 10... Power switch, 24... Fuel injection valve, 48... Rotation angle sensor.

Claims (2)

[Claims] (1) Detect the relaxation value of the intake pipe pressure by relaxing the change in the signal output from the pressure sensor that measures the intake pipe pressure, and calculate the basic fuel injection time at a predetermined period based on the relaxation value. In a fuel injection amount control method for an internal combustion engine in which the fuel injection amount is controlled based on the current basic fuel injection time that has been calculated, the difference between the current basic fuel injection time and the basic fuel injection time calculated one cycle ago or the current The product of the amount of change represented by the difference between the relaxation value and the relaxation value detected one cycle ago and the first coefficient that changes depending on the engine rotation speed, the integrated value of the attenuation value of the amount of change, and the first coefficient 1. A fuel injection amount control method for an internal combustion engine, characterized in that the current basic fuel injection time is corrected based on the product of 2 and a coefficient of 2. (2) The relaxation value is calculated by increasing the weight of the weighted average value calculated in the past and using the weighted average value calculated in the past and the current level of the signal output from the pressure sensor. The fuel injection amount control method for an internal combustion engine according to claim 1, wherein the current weighted average value is the current weighted average value.