JPH0718355B2 - Fuel injection amount control method for internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a fuel injection amount control method for an internal combustion engine, and in particular, 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 in which fuel is injected based on a fuel injection time.

[Conventional technology]

Conventionally, the basic fuel injection time is calculated 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 at predetermined time intervals, and the basic fuel injection time is used as the intake temperature or the engine cooling water temperature. There is known an internal combustion engine in which the fuel injection time is obtained by correcting the fuel injection time by the above, and the fuel injection valve is opened for a time corresponding to the fuel injection time to inject the 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 basic fuel is measured based on the measured intake pipe pressure. Although the injection time is calculated, the measured value fluctuates due to engine pulsation, and this fluctuation may change the basic fuel injection time, which may prevent accurate fuel injection amount control, and the intake pipe during acceleration. Since the pressure rapidly rises and the amount of evaporated fuel decreases, the injected fuel may adhere to the inner wall of the intake manifold and the fuel supply amount may become insufficient. 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 integrated value of this difference is attenuated to correct the fuel adhesion amount on the inner wall of the intake manifold. That is, as shown in FIG. 2, the integrated value is determined by the engine cooling water temperature at the levels L _C (when the engine is cold) and L _H (when the engine is warm).
When it is larger than the above, the damping speed is fast, and when it is smaller than the levels L _C and L _H , the damping speed is slow. 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 The responsiveness and followability of the change in the filter output to the change deteriorates, the increase in acceleration is delayed, the fuel injection amount is insufficient at the beginning of acceleration, and a lean spike occurs.At the end of acceleration, a latch spike occurs due to the overshoot characteristic. In some cases. Also, the decay speed of the integrated value can be switched in two steps, but since the decay speed is the same between engine warm and engine cold, it is possible to obtain the optimum damping curve according to each transient operating state. However, the air-fuel ratio fluctuated especially during transient operation during cold.

For this reason, recently, the pressure sensor output is processed using a CR filter with 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 digitally displayed every predetermined time. It has been proposed to use a measurement value that is more responsive and more trackable than when using two filters. In this case, since the pulsation component cannot be completely removed by the CR filter, two digital weighted average values with different degrees of relaxation are calculated using the digital value, and the first weighted average value with a small degree of relaxation is calculated. The acceleration increase value is determined based on the difference obtained by subtracting the second weighted average value having a large degree of relaxation, and the acceleration increase value is corrected by the engine cooling water temperature to determine the increase coefficient as shown in FIG. The basic fuel injection time is corrected.

[Problems to be solved by the invention]

However, in any of the above methods, since a value with a large degree of relaxation is used to obtain the increase coefficient, responsiveness and followability deteriorate, and in a traveling pattern in which acceleration / deceleration is repeated, there is a phase delay in acceleration increase. There is a problem in that the fuel injection amount may not match the increase request of the engine, and the exhaust emission and the driver's 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. 4 shows 1/1 / the amount of fuel required for one intake stroke per engine revolution.
FIG. 6 is a diagram showing changes in the 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. 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. Therefore, it is the amount corresponding to TPc + TPb. 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) shown by a in the figure. 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 and the delay time t _D is small enough to be ignored, an internal combustion engine that injects fuel once per revolution of the engine requires a fuel amount corresponding to 2TPb at point b. On the other hand, since only fuel corresponding to TPc + TPb is supplied, the fuel amount corresponding to TPb−TPc (= ΔTP) is insufficient during acceleration.

Further, in the method using the CR filter, the difference obtained by subtracting the second weighted average value having a large degree of relaxation from the first weighted average value having 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 a poor responsiveness to the fluctuation of the intake pipe pressure, and therefore, the transient operating states. There is a problem that an optimum attenuation curve cannot be obtained according to the above. In other words, in any of the above methods, it is not possible to obtain the optimum damping curve according to each transient operating state, and especially when the engine is cold when the fluctuation of the amount of fuel adhering to the inner wall of the intake manifold is large, the optimum acceleration amount increase Could not be achieved, leading to deterioration of exhaust emission and driver viability.

The present invention has been made to solve the above problems, and corrects the delay between the intake pipe pressure corresponding to the actual intake air amount and the relaxation value for calculating the basic fuel injection time and the amount of fuel adhered to the inner wall of the intake manifold. By doing so, the air-fuel ratio during transient operation does not change regardless of whether it is cold or warm,
An object of the present invention is to provide a fuel injection amount control method for an internal combustion engine, which has improved exhaust emission and driver ability.

[Means for solving problems]

To achieve the above object, the present invention relaxes a change in a signal output from a pressure sensor that measures an intake pipe pressure to detect a relaxation value of the intake pipe pressure, and based on the relaxation value, a basic value is determined in a predetermined cycle. In a fuel injection amount control method for an internal combustion engine, which calculates a fuel injection time and controls a fuel injection amount based on the calculated current basic fuel injection time, a current basic fuel injection time and a basic operation calculated one cycle before. The product of the amount of change represented by the difference between the fuel injection time or the difference between the current relaxation value and the relaxation value detected one cycle before and the first coefficient changed according to the engine speed, and the variation amount. It 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 and the second coefficient.

[Action]

Next, the principle of the present invention will be described. In the following description, a four-cylinder, four-cycle internal combustion engine that injects fuel once per engine revolution will be described as an example.

As described with reference to FIG. 4, the basic fuel injection time TP corresponding to the actual intake air amount is represented by the following equation, ignoring the delay time t _D from the fuel injection time calculation.

TP = TPb + ΔTP (1) On the other hand, as shown in FIG. 5, if acceleration is performed at uniform acceleration, the difference Δ in basic fuel injection time between points b and c is Δ.
Since TP is equal to the difference ΔTP ′ between the basic fuel injection times at points b and b ′, 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 + ΔTP (2) If the basic fuel injection time is calculated every 360 ° CA, 360 ° CA ahead of point b, as can be understood from the above equation (2). The basic fuel injection time of is predicted.

Therefore, generally, assuming that the calculation of the basic fuel injection time is performed for each CY ° CA, the delay time t _D between points a and b in FIG. 4 is set to the crank angle CA _D. converted, by obtaining the correction amount corresponding to the crank angle CA _D, Next, it is possible to predict the basic fuel injection time of a predetermined crank angle CA _D away from point b. Therefore, considering the correction when changing from the point c to the point b in FIG. 4, the basic fuel injection time TP corresponding to the actual intake air amount when calculating the basic fuel injection time for each CY ° CA is immediately before. Basic fuel injection time TP ₀
Is expressed as follows.

TP = TP ₀ + K ₁ · ΔTP (4) where K ₁ is ΔTP 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.

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, 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 first sucked in the intake stroke two times ahead. Therefore, the crank angle CA _{D at} which the fuel injection time should be predicted
Becomes larger as the engine speed increases.

On the other hand, when a CR filter is used, the CR filter output has a good response to the change in the actual intake pipe pressure, so it is considered that it shows almost the actual intake pipe pressure. The weighted average value (relaxation value) lags the actual intake pipe pressure as shown in FIG. This delay (control delay t _D ′) is caused by detection delay of pressure sensor, delay of signal transmission of input circuit, delay of calculation timing due to these delays, delay due to calculation time, delay due to relaxation of CR filter output, etc. It occurs as a cause. Therefore, the sixth
(Crank angle CA _D ')' control delay t _D from 'PMb for fuel injection quantity calculation taking into consideration the predicted actual intake pipe pressure PMb at point b in FIG., The basic fuel injection based on the predicted value It is necessary to calculate the time and further make a prediction in consideration of the delay time t _D described above.

Therefore, if the correction of the control delay t _D ′ (= CA _D ′) is also added to the above equation (4), it can be expressed as follows.

TP = TP ₀ + K ₁ · ΔTP (5) Is.

In addition, when calculating the basic fuel injection time TP from the intake pipe pressure PM and the engine speed NE, TP∝PM, so (5) above
Expressing the expression 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, the following (6) It becomes like a formula.

TP = TP ₀ + K ₁ · ΔPM · C (6) where C is a proportional constant for converting the intake pipe pressure into the basic fuel injection time.

Here, since the control delay time t _D ′ can be regarded as substantially constant due to the phenomenon of the time period, the crank angle CA _D ′ increases as the engine speed increases.

The values of the crank angles CA _D and CA _D ′ at each rotation speed can be calculated, and the K ₁ value at each rotation speed can be obtained without considering the manufacturing error of the test engine. 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 _D ′ does not need to be corrected by the engine speed, but the delay due to the flight time of the injected fuel is affected by the engine speed, so K _{1 as a} whole needs to be corrected by the engine speed. Becomes Further, although the example in which the fuel is injected once per one revolution of the engine has been described above, even in the independent injection, when the engine rotation speed increases, the basic fuel injection time becomes longer and a region where unsucked fuel occurs may occur. 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.

Further, according to the present invention, the basic fuel injection time is corrected by the following formula.

_{K 2 · DLPMI i · C ...} (7) however, K ₂ is the second coefficient, the engine rotational speed can be varied according to the engine coolant temperature or the intake pipe pressure and the like, also DLPMI _i following It is an integrated value of the attenuation values of the difference between the current relaxation value represented by the formula and the relaxation value detected one cycle before.

DLPMI _i = ΔPM + K ₃ · DLPMI _i-1 (8) Here, K ₃ is a positive damping coefficient less than 1, and DLPMI _i-1 is a previously calculated integrated value.

Assuming that the initial value of the integrated value is 0 in the equation (8) and the difference ΔPM changes to ΔPM ₁ , ΔPM ₂ , ... ΔPM _i during the calculation i times, the i-th DLPMI _i is as follows. Represented by.

DLPMI _i = ΔPM _i + K ₃・ ΔPM _i-1 + K ₃ ²・ ΔPM _i-2 + ・ ・ ・ + K ₃ ^{i-2
_{· ΔPM 2 + K 3 i-}} 1 · ΔPM 1 ... (9) Therefore, the integrated value gradually increases from the start acceleration, taking between certain values until after the end of acceleration also approaches zero by the attenuation coefficient K _3.

When the correction for predicting the basic fuel injection time corresponding to the actual intake air amount and the correction of the above equation (7) are performed at the same time, the basic fuel injection time TP is calculated by the following equation (10) or (11). Like

_{TP = TP 0 + K 1 ·} ΔPM · C + K 2 · DLPMI i · C ... (10) TP = TP 0 + K 1 · ΔTP + K 2 · DLPMI i ... (11) However, the above (11) DLPMI _i of formula below It 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

DLPMI _i = ΔTP + K ₃ · DLPMI _i-1 (12) Note that K ₁ , K ₂ , and K ₃ used in the above equations (10) and (11) are engine rotations so as to cover a wide range of transient operating conditions. It may be set according to parameters such as speed, engine cooling water temperature, intake pipe absolute pressure, etc., but the coefficient that the required value of fuel injection amount hardly changes in transient operating state even if each parameter is changed is defined as a constant value. do it.

When the basic fuel injection time was corrected as described above when the engine was cold, the changes in the acceleration increase value and the air-fuel ratio were adjusted to the value of K ₁ during warm time when the current basic fuel injection time TP ₀ was not corrected. When the value K _H is used, the experimental results will be described in comparison with the case where the value K _C (> K _H ) that is suitable for the cold state is used as the value of K ₁ . As shown in FIG. 7, if the fuel is injected only at the current basic fuel injection time TP ₀ in the acceleration operation state where the intake pipe pressure PM during engine cold changes from PM ₁ to PM ₂ , the increase value is 0. Then, the air-fuel ratio changes as shown in FIG. 7 (3), and a large lean spike occurs, resulting in exhaust emission and poor driver viability. Correcting this basic fuel injection time TP ₀ , TP ₀ + K _H・ ΔP
When the fuel is injected based on M / C, the lean spike is halved, but the change in the air-fuel ratio is still large. It is considered that this is because the amount of fuel adhering to the inner wall of the intake manifold changes greatly when cold. In addition, by increasing the value of K ₁ and using the value K _C that is suitable for cold conditions, TP ₀ + K _C
When fuel is injected based on C, the lean spike in the early stage of acceleration can be almost eliminated as shown in FIG. 7 (3), but the lean spike remains at the latter stage of acceleration and at the end of acceleration. this is,
It is considered that the intake pipe pressure increases and the fuel evaporation amount decreases at the latter stage of acceleration or the end of acceleration, so that the amount of injected fuel adhering to the inner wall of the intake manifold increases.

In consideration of the above phenomenon, the present invention provides a difference between the current basic fuel injection time and the basic fuel injection time calculated one cycle before or the current relaxation, as shown in the equations (10) and (11). The product of the amount of change represented by the difference between the value and the relaxation value detected one cycle before and the first coefficient changed according to the engine speed, and the integrated value of the attenuation value of the amount of change and the second coefficient. The present basic fuel injection time is corrected based on the product of the coefficient and the coefficient. Since the integrated value of the above damping value has 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 correcting the basic fuel injection time with K ₁ as K _C is used. By preventing it, the air-fuel ratio can be made substantially constant during a transition such as acceleration as shown by the solid line in FIG. 7 (3).

〔effect〕

As described above, according to the present invention, it is possible to supply the fuel corresponding to the actual intake air amount at the time of transition, and perform the correction due to the change in the fuel amount adhering to the inner wall of the intake manifold to warm or cool the engine. Since the air-fuel ratio can be made substantially constant regardless of the time period, it is possible to prevent deterioration of exhaust emission and driver viability during the entire transient operation.

[Description of mode]

Next, an aspect of the present invention will be described. The present invention can take the following aspects in carrying out the invention.

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. This is the current weighted average value. That is, the weighted average value PMN _i calculated according to the following equation is used as the relaxation value.

However, PMN _i-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 was directly converted to a digital value. The value or the value obtained by converting the pressure sensor output processed by the CR filter into a digital value can be adopted.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.
FIG. 8 shows an outline of an internal combustion engine (engine) provided 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 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 for outputting the above is attached, and a surge tank 12 is provided on the downstream side of the throttle valve 8. A diaphragm type pressure sensor 6 is attached to the surge tank 12. The pressure sensor 6 has a small time constant for removing the pulsating component of the intake pipe pressure (for example, 3 to
5 msec) and a responsive filter (Fig. 9) composed of a CR filter or the like is connected. The filter may be built in the pressure sensor. 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. An ISC (idle speed control) valve 16B whose opening is adjusted by a pulse motor 16A having a 4-pole stator is attached to the bypass passage 14. The surge tank 12 is in communication with the combustion chamber of the engine 20 via the intake manifold 18 and the intake port 22. Then, the fuel injection valve for each cylinder is projected so as to project into the intake manifold 18.
24 is installed.

The combustion chamber of the engine 20 is connected via an exhaust port 26 and an exhaust manifold 28 to 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. Engine block
A cooling water temperature sensor 34 is attached to the 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.

A spark plug 38 is attached to each cylinder so as to penetrate the cylinder head 36 of the engine 20 and project into the combustion chamber. 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 speed signal, for example, every 30 ° CA.

As shown in FIG. 9, the electronic control circuit 44 includes a micro processing unit (MPU) 60, a read only memory (R
OM) 62, Random Access Memory (RAM) 64, Back-up Plum (BU-RAM) 66, I / O Port 68, Input Port 70, Output Ports 72, 74, 76, and the data bus and control bus connecting them. Etc., and is configured to include a bus 75. The input / output port 68 has analog-digital (A /
D) The converter 78 and the multiplexer 80 are connected in sequence. To the multiplexer 80, the pressure sensor 6 is connected 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 connected via a buffer 84. Further, the linear slot sensor 10 is connected to the multiplexer 80. MPU60
Controls the multiplexer 80 and A / D converter 78 to
The pressure sensor 6 output, the linear throttle sensor 10 output, and the cooling water temperature sensor 34 output, which are input via the filter 7, are sequentially converted into digital signals and stored 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 O ₂ sensor 30 is connected to the input port 70 via the comparator 88 and the buffer 86, and the cylinder discrimination sensor 46 and the rotation angle sensor 48 are connected to the input port 70 via the waveform shaping circuit 90. The output port 72 is connected to the igniter 42 via a drive circuit 92, and the output port 74 is connected to a fuel injection valve via a drive circuit 94 equipped with a down counter.
24, and the output port 76 is connected via drive circuit 96 to the pulse motor 16A of the ISC valve. Note that 98 is a clock and 99 is a timer. Programs and the like for the control routines described below are stored in advance in the ROM 62.

Next, the control routine of the 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. It should be noted that the following description will be given using numerical values that do not hinder the present invention, but the present invention is not limited to these numerical values.

FIG. 10 shows an A / D conversion routine executed every 4 msec. In step 100, the signal output from the pressure sensor 6 is sent to the CR filter 7, buffer 82 and multiplexer.
The intake pipe pressure PM input to the A / D converter 78 via 80 and digitally converted by the A / D converter 78 is taken in as a digital value PMAD. In the next step 102, the weight N of the equation (13) is set to n (for example, 4 by using the digital value PMAD of the intake pipe pressure and the weighted average value PMN _{i-1 of} the intake pipe pressure calculated 4 msec before). ), The weighted average value PM _i of the current intake pipe pressure is calculated according to the equation (13).

Then, in step 104, in order to calculate the weighted average value of the next intake pipe pressure, the weighted average value PMN _i of the present intake pipe pressure is set to the weighted average value PMN _i of the intake pipe pressure 4 msec before.
Store it as _i-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).
Calculates ₁ , K ₂ , and K ₃ . This coefficient K ₁ is the weighted average value PM of intake pipe pressure at step 128 as shown in FIG.
It is determined by taking in parameters such as N, engine speed NE, engine cooling water temperature THW, etc., and calculating a coefficient K ₁ corresponding to the current engine speed NE from the map shown in FIG. 12 at step 130. The coefficient K ₁ is calculated in advance and stored in the ROM as a map, but as the engine speed NE becomes higher as shown in FIG. 12, 1.
It is represented as an increasing function that increases from zero.

The next step 132 is the map or 14 shown in FIG.
The map shown in the figure corresponds to the current engine speed NE.
Calculate the coefficient K ₂ corresponding to K ₂ or the current engine cooling water temperature THW. This coefficient K ₂ may be determined by a function f (NE, THW) of the engine speed NE and the engine cooling water temperature, and the weighted average value P
MN function f (PMN), engine speed NE, engine cooling water temperature THW
And the weighted average value PMN function f (NE, THW, PMN).

Here, as the engine speed NE becomes higher, the intake flow velocity becomes faster, and the amount of fuel adhering to the inner wall of the intake manifold decreases, and most of the fuel is considered to be supplied to the combustion chamber.
The coefficient K ₂ is set to decrease as the engine speed increases. Further, as the engine cooling water temperature rises, the amount of fuel that adheres to the inner wall of the intake manifold increases, and the amount of fuel that adheres to the inner wall of the intake manifold decreases, so the coefficient K ₂ decreases as the engine cooling water temperature increases. Determined. Then, as the intake pipe pressure increases, the amount of fuel evaporation decreases and the amount of fuel that adheres to the intake manifold inner wall increases.Therefore, the coefficient K ₂ is set to increase as the weighted average value of the intake pipe pressure increases. To be

In the next step 134, the damping coefficient K ₃ is calculated. The damping coefficient K ₃ is a positive value less than 1, and a constant value may be used. However, like the coefficient K ₂ , the engine speed NE, the weighted average value PMN of the intake pipe pressure, the engine cooling water temperature, etc. You may set according to THW etc. If the coefficient K ₃ is changed, the damping speed is slowed down by increasing the coefficient K ₃ in the transient operation state where the amount of fuel adhering to the inner wall of the intake manifold increases, as in the above case, and the fuel adhering to the inner wall of the intake manifold is reduced. In the transient operation state where the amount decreases, the coefficient K ₃ is reduced 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, since the weighted average value PMN _i of the current intake pipe pressure is stored in the register as PMN _i-1 , the weighted average value of the current intake pipe pressure is read by reading the value of this register. PM
Can be taken as N. In the next step 110, the current basic fuel injection time TP ₀ is calculated by the method similar to the conventional method from the weighted average value PMN of the current intake pipe pressure and the engine rotational speed NE fetched in step 128. At the next step 112, the value obtained by multiplying the integrated value DLPMI stored in the RAM by the damping coefficient K ₃ is stored in the register R, and the step 114 is performed.
At the current intake pipe pressure weighted mean value PMN of 3
The difference ΔPM between the weighted average values of the intake pipe pressure is calculated by subtracting the weighted average value PMN ₀ of the past intake pipe pressure used to calculate the basic fuel injection time before 60 ° CA. At step 116, the present integrated value DLPMI (= ΔPM + K ₃ · DLPMI _i-1 ) is calculated by adding the difference ΔPM of the weighted average value of the intake pipe pressure and the value stored in the register R. In step 118, the coefficient calculated in step 130
The coefficient K calculated in step 132 is multiplied by the product of K ₁ and the difference ΔPM between the weighted average values 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. ₂ and the integrated value DLPMI calculated in step 116 are multiplied by a constant C, and the product is added to obtain the increase value TPAC.
C (corresponding to the second and third terms on the right side of the equation (10)) is calculated, and at step 120, the current basic fuel injection time T
The current basic fuel injection time TP ₀ is corrected by adding the increase value TPACC to P ₀ . The increase amount TPACC may be calculated based on the above equation (11). And step
At 122, the weighted average value PMN of the present intake pipe pressure is set to 36
The weighted average value PMN ₀ of the intake pipe pressure before 0 ° CA is stored in the register, and at step 124, the basic fuel injection time T
The fuel injection time TAU is calculated by correcting P by the intake air temperature, engine cooling water temperature, and the like. Then, in a fuel injection amount control routine (not shown), fuel is injected once per engine revolution.

Since the basic fuel injection time TP used to calculate the fuel injection time TAU in the above step 124 is corrected according to the equation (10) or the equation (11) explained above in the step 120, the control delay and the fuel The delay due to the flight time is prevented, the influence of the amount of fuel adhering to the inner wall of the intake manifold is prevented, and the value is corrected to a value corresponding to the actual intake air amount, so fluctuations in the air-fuel ratio during transients can be prevented. .

In the above, the example in which the coefficient K ₁ is changed according to the engine rotation speed has been described, but when the engine cooling water temperature is low, the amount of fuel adhering to the inner wall of the intake manifold increases and the engine cooling water temperature increases. It is necessary to increase the amount of fuel more than when it is high. Therefore, even if the smaller the coefficient K ₁ according to the engine coolant temperature as well as increasing the coefficient K ₁ in accordance with the engine rotational speed represents the coefficient K ₁ as a function of the engine speed and the engine coolant temperature is high is high good.

[Brief description of drawings]

FIG. 1 is a flow chart showing a fuel injection time calculation routine according to the first embodiment of the present invention, FIGS. 2 and 3 are diagrams showing changes in an increase coefficient during conventional acceleration, and FIG. 4 is one engine revolution. FIG. 5 is a diagram for explaining the delay of the fuel injection amount when the fuel is injected once, FIG. 5 is a diagram showing changes in intake pipe pressure and basic fuel injection time in a constant acceleration state, and FIG. 6 is A diagram showing a change between the CR filter output and a weighted average value of the CR filter output at a high load, and FIGS. 7 (1) to (3) illustrate the increase value and the change of the air-fuel ratio 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 is applicable, FIG. 9 is a block showing the details of the control circuit of FIG. 8, and FIG. FIG. 11 is a flowchart showing the A / D conversion routine of the first embodiment of the invention, and FIG. 11 shows the coefficients K ₁ and K of the above embodiment.
₂ , a flow chart showing a calculation routine of K ₃ , FIG. 12 is a diagram showing a map of the coefficient K ₁ , and FIGS. 13 and 14 are diagrams showing a map of the coefficient K ₂ . 6 ... Pressure sensor, 7 ... CR filter, 10 ... Power switch, 24 ... Fuel injection valve, 48 ... Rotation angle sensor.

Claims (2)

[Claims] 1. A relaxation value of an intake pipe pressure is detected by relaxing a change in a signal output from a pressure sensor for measuring an 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 a fuel injection amount based on a calculated current basic fuel injection time, a difference between a current basic fuel injection time and a basic fuel injection time calculated one cycle before. Alternatively, the product of the amount of change represented by the difference between the current relaxation value and the relaxation value detected one cycle before and the first coefficient changed according to the engine rotation speed, and the integrated value of the attenuation values of the change amount. And a second coefficient, the present basic fuel injection time is corrected. A fuel injection amount control method for an internal combustion engine, comprising: 2. 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), which is the calculated current weighted average value.