JPH05231211A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To accurately control air fuel ratio even during transitional driving period which regard to a fuel injection control device of an internal combustion engine provided with a variable valve timing unit (VVT) attached thereto by finding a forecasted quantity of intake air conforming to the actual intake air quantity irrespective of the valve timing. CONSTITUTION:The most suitable VVT target spark advance value 'd' for the operation condition of an internal combustion engine at the present point of time is found and an actual spark advance value C is calculated by taking into consideration the response delay of the VVT due to the viscosity of the working oil. (Step 102 to step 110). Respective GNTA maps are provided for the maximum spark advance time and the maximum spark delay time of the VVT, and GNTA values a, b for respective cases are calculated based on the data of an engine speed NE and a throttle aperture TA at the present point of time. (Steps 112 and 114). Furthermore, a GNTAf corresponding to the VVT actual spark advance value c is calculated on the basis of a, b through an interpolation process (Step 116). A forecast intake air quantity GNFWD is calculated from this GNTAf. (Step 122).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel injection control device for an internal combustion engine, and more particularly to a fuel injection control device for an internal combustion engine which has a variable valve timing device and which predicts an intake air amount to control the fuel injection amount. ..

[0002]

2. Description of the Related Art As for the intake air amount that determines the fuel injection amount of an internal combustion engine, it is generally known that the sensor value detected by a sensor such as an intake pipe pressure sensor or an air flow meter is used as it is. .. However, according to this method, the sensor value itself deviates from the actual value due to sensor detection delay during transient operation such as when the throttle is suddenly opened by depressing the accelerator, so that the air-fuel ratio during transient operation can be accurately controlled. It was difficult to do. Therefore, in order to solve the above problems, in recent years, the throttle opening TA
A technique for predicting the intake air amount based on the engine speed NE and the engine speed NE has been developed and is well known. This predicted intake air amount GNF
Although the calculation method of WD will be described in detail later, GNTA (intake air amount at steady time determined by TA and NE) is calculated from a two-dimensional map using the throttle opening TA and the engine speed NE as parameters, and this GNTA is calculated. It is basically to obtain GNFWD by performing a predetermined calculation with respect to. According to this GNFWD, the actually taken intake air amount is always accurately obtained without delay, so that the air-fuel ratio can be accurately controlled even during the transient operation.

[0003]

In an internal combustion engine equipped with a variable valve timing device (hereinafter referred to as VVT) that changes the valve timing of an intake valve, the throttle opening TA and the engine speed NE are the same condition. However, the actual intake air amount changes due to the change in the valve timing of the intake valve. On the other hand, the predicted intake air amount G
Since NFWD is uniquely calculated from the values of TA and NE via GNTA as described above, only one predicted intake air amount GNFWD is calculated when TA and NE are under the same condition. Therefore, in the case of the internal combustion engine with VVT, the predicted intake air amount GNFWD deviates from the actual intake air amount except for the specific valve timing.
Even if the predicted intake air amount GNFWD is adopted, there is a problem that the air-fuel ratio cannot be accurately controlled during the transient operation.

Therefore, the present invention has been made in view of the above problems. In an internal combustion engine with VVT, the air-fuel ratio is accurately controlled even during transient operation by always obtaining an accurate intake air amount regardless of valve timing. An object of the present invention is to provide a fuel injection control device for an internal combustion engine.

[0005]

FIG. 1 is a block diagram showing the principle of the present invention for achieving the above object. As shown in the figure, the present invention is predicted from the variable valve timing device 3 that changes the valve timing of the intake valve 2 according to the operating conditions of the internal combustion engine 1, and the rotational speed and throttle opening of the internal combustion engine 1. In a fuel injection control device for an internal combustion engine, which comprises a control means 4 for controlling a fuel injection amount of the internal combustion engine 1 based on a predicted intake air amount, the control means 4 includes a rotation speed of the internal combustion engine 1 and a throttle. At least two maps 5 for obtaining the predicted intake air amount from the opening are provided corresponding to different valve timings, and based on the values of the reference predicted intake air amounts respectively obtained from the plurality of maps 5, Calculating means 6 for calculating a predicted intake air amount corresponding to an arbitrary valve timing of the intake valve 2 which is changed by the variable valve timing device 3. It is the only configuration.

[0006]

In the present invention, even when the valve timing of the intake valve 2 is changed to a portion other than the valve timing which is the reference of the map 5, the calculating means 6 is
The predicted intake air amount corresponding to the valve timing changed based on the plurality of reference predicted intake air amount values respectively calculated from the plurality of maps 5. That is, the calculation means 6 uses the intake valve 2 that the variable valve timing device 3 changes.
The accurate intake air amount that matches the actual intake air amount is predicted for any valve timing of. Therefore, the control means 4 controls the fuel injection amount of the internal combustion engine 1 to an optimum value at any valve timing of the intake valve 2.

[0007]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 2 shows an embodiment of an internal combustion engine (engine) and its peripheral devices to which the present invention is applied. This embodiment is an example in which the internal combustion engine 1 is applied to a 4-cylinder 4-cycle spark ignition type internal combustion engine, and FIG. 2 shows a structural sectional view of an arbitrary 1-cylinder. Each part of this internal combustion engine (engine) is controlled by a microcomputer described later.

In FIG. 2, reference numeral 10 denotes an engine body, and an engine block 22 accommodates a piston 23 that reciprocates in the vertical direction in the figure. A combustion chamber 24 formed in the upper portion of the piston 23 is connected to an intake manifold 25 through an intake valve 26 (corresponding to the intake valve 2).
On the other hand, the exhaust manifold 27 communicates with the exhaust manifold 28. In addition, the combustion chamber 24
An ignition plug 29 is provided so that the plug gap protrudes.

An upstream side of the intake manifold 25 is connected to an intake pipe 31 via a surge tank 30 for all four cylinders. Inside this intake pipe 31, the throttle valve 3
3. A hot-wire type air flow meter 32 is provided respectively. The opening of the throttle valve 33 is adjusted in conjunction with the accelerator pedal, and the opening is detected by the throttle position sensor 34. The hot wire type air flow meter 32 is a hot wire 32a.
Is a signal of the flow rate of the intake air, that is, the intake air amount, with a current value necessary for maintaining a constant temperature. An intake air temperature sensor 35 that measures the intake air temperature is provided downstream of the hot wire air flow meter 32.

A bypass passage 36 that bypasses the throttle valve 33 and connects the upstream side and the downstream side of the throttle valve 33 is provided, and the bypass passage 36 is provided.
Idle speed control valve (ISCV) 37 whose valve opening is controlled by a solenoid in the middle of
Is installed.

A fuel injection valve 38 injects fuel into the air flow passing through the intake manifold 25 in accordance with an instruction from the microcomputer 21, which will be described later. Further, the oxygen concentration detection sensor (O ₂ sensor) 39 is an exhaust manifold 2
It is provided so as to partially penetrate 8 and detects the oxygen concentration in the exhaust gas before entering the catalyst device. A water temperature sensor 40 is provided so as to penetrate the engine block 22 and partially project into the water jacket, and detects the water temperature of the engine cooling water. An igniter 41 opens and closes a primary current of an ignition coil (not shown).
Further, 42 is a distributor, which has a cylinder discrimination sensor 43 for generating a reference position detection signal of the engine crankshaft, and a rotation angle sensor 44 for generating an engine speed signal every 30 ° C., for example.

Further, reference numeral 46 is a hydraulically driven valve operating mechanism for changing the valve timing of the intake valve 26 and the exhaust valve 27, and a hydraulic pressure for controlling the hydraulic pressure supplied to the valve operating mechanism 46 in response to a signal from the microcomputer 21. A variable valve timing device 47 (VVT) corresponding to the variable valve timing device 3 is configured together with a control solenoid valve (hereinafter, simply referred to as a solenoid valve) 45. Lubricating oil for the engine 10 having a predetermined hydraulic pressure is supplied to the solenoid valve 45 as hydraulic oil. Reference numeral 48 is an oil temperature sensor for detecting the temperature of the lubricating oil of the engine 10 as hydraulic oil, the output value of which is used for the control of the present invention as described later. VVT
Reference numeral 47 has a known structure for changing the opening / closing timing of the intake valve 26 or the exhaust valve 27 in accordance with the hydraulic pressure of the working oil.

The microcomputer 21 for controlling the operation of each unit having such a configuration has a hardware configuration as shown in FIG. 2, those parts which are the same as those corresponding parts in FIG. 2 are designated by the same reference numerals, and a description thereof will be omitted. In FIG. 3, a microcomputer 21 is a central processing unit (CPU) 5
0, a read-only memory (ROM) 51 storing a processing program, a random memory used as a work area
An access memory (RAM) 52, a backup RAM 53 that retains data even after the engine is stopped, an input interface circuit 54, an A / D converter 56 with a multiplexer, an input / output interface circuit 55, and the like, which are connected via a bus 57. Are connected to each other.

The A / D converter 56 receives an intake air amount detection signal from the hot wire type air flow meter 32 and an intake air temperature sensor 3
5, an intake air temperature detection signal, a throttle position sensor 34 throttle opening detection signal, a water temperature sensor 40 water temperature detection signal, an O ₂ sensor 39 oxygen concentration detection signal, an oil temperature sensor 48 oil temperature detection hand. The signals are sequentially switched and captured through the input interface circuit 54,
It is converted from analog to digital and sent to the bus 57 sequentially.

The input / output interface circuit 55 receives a detection signal from the throttle position sensor 34 and a rotation speed signal corresponding to the engine rotation speed (NE) from the rotation angle sensor 44, respectively, and outputs them via the bus 57 to the CPU.
Enter 50.

The CPU 50 also receives the input / output interface circuit 55 and the A / D converter 56 from the bus 57.
Various arithmetic processes are executed based on each data input through the ISCV 37, the fuel injection valve 3 through the bus 57 and the input / output interface circuit 55.
8, the igniter 41 and the hydraulic control solenoid valve 45 are appropriately selected and output to control the opening of the ISCV 37 to control the idle speed to the target speed, or the fuel injection time by the fuel injection valve 38, that is, per unit time. The fuel injection amount and injection timing are controlled, the ignition timing is controlled by the igniter 41, and the solenoid valve 4
5 is driven to control the valve timing by the valve mechanism 46.

Next, the valve timing control by the VVT 47 will be described.

The intake valve 26 is shown in each of FIGS.
5 is a timing chart showing the valve timing of the case of the most advanced angle (x = 60 ° CA) and the case of the most retarded angle (x = 0 ° CA). Comparing FIGS. 4A and 4B, the intake valve 26 is closed at the VVT most retarded angle (I.
C) The timing is the valve closing (I.
C) It is behind the timing (β '> β). Generally, in a high engine speed region, the flow velocity of the intake air entering the cylinder is high. Therefore, by delaying the closing of the intake valve 26, it is possible to expect an inertia supercharging effect due to the inertial force of the intake air, thereby improving the charging efficiency. It is possible to improve and increase the output torque. On the contrary, since the flow velocity of the intake air is slow and the inertial force of the intake air is small in the low rotation speed region, the intake valve 26 is closed earlier,
It is possible to prevent the intake air in the cylinder from being pushed back into the intake port as the piston rises. In this way, the valve timing of the intake valve 26 is basically such that the higher the engine speed is, the later the intake valve is closed (retarded), and the lower the engine speed is, the earlier the valve is closed (advanced). Side), the optimum valve timing is controlled between the most advanced angle and the most retarded angle.

FIG. 5 is a diagram showing changes in pressure in the intake port during the intake stroke under both conditions of the most advanced VVT angle and the most retarded VVT angle. In the figure, the pressure change at the most advanced angle shown by the solid line becomes a large positive pressure in the vicinity of the intake TDC, then becomes a large negative pressure in accordance with the downward movement of the piston 23, and the intake valve 26 closes after passing the BDC. Be spoken. Further, the pressure change at the most retarded angle shown by the dotted line temporarily becomes positive pressure at the intake TDC when the intake valve 26 is opened, then becomes a large negative pressure, and the piston 23 moves upward after passing BDC. Is pushed back to positive pressure again, and the intake valve 26 is closed. In FIG. 5, the positive pressure in the intake TDC portion is an effect due to the residual pressure of the exhaust gas and is not taken into consideration. In the case of the most retarded angle, the intake air is pushed back by the positive pressure after BDC and the most advanced angle. The amount of intake air is reduced compared to the case. However, in the high rotation region, since the intake air having inertia as described above is supplied into the cylinder even at the positive pressure after BDC, the intake air amount becomes larger on the retard side. As described above, although it varies depending on the engine speed, it is clear from the figure that the intake port pressure in the intake stroke changes by changing the valve timing of the intake valve 26, and the intake air amount changes accordingly. ..

Therefore, as described above, the conventional problem arises that the predicted intake air amount uniquely obtained from the engine speed and the throttle opening deviates from the actual intake air amount which changes according to the valve timing. .. Therefore, the present embodiment aims to accurately obtain the intake air amount for an arbitrary valve timing of the intake valve 26 and thereby accurately control the air-fuel ratio.

Therefore, the microcomputer 21 in this embodiment executes the processing of the flowchart described below according to the program stored in the ROM 51,
The above-mentioned control means 4 (including the map 5 and the calculation means 6) according to the present invention is realized by software processing. Next, VVT control / prediction is performed as a control program which constitutes a main part of an embodiment of the present invention device. The intake air amount GNFWD calculation routine will be described. FIG. 6 shows a flow chart of the VVT control / predicted intake air amount GNFWD calculation routine. This routine is a subroutine that is activated each time the main routine goes around. When this VVT control / predicted intake air amount GNFWD calculation routine is started, first, at step 102, the engine speed NE and the throttle opening degree at the present time are determined from the detection signal from the rotation angle sensor 44 and the detection signal from the throttle position sensor 34. T
Read the data of A. Each read data is NE
₁ and TA ₁ . In the next step 104, various data of the engine at the present time is read from the detection signals of the above-mentioned sensors, and together with NE ₁ and TA ₁ obtained in step 102, the VVT target advance value d, that is, the current engine operating state. The optimum valve timing of the intake valve 26 according to the above is calculated. In the next step 106,
The control output is performed from the microcomputer 21 to the VVT 47 so that the valve timing of the intake valve 26 becomes the VVT target advance value d calculated in step 104. In the VVT 47, a hydraulic pressure corresponding to the VVT target advance value d is created by the solenoid valve 45 in response to a signal from the microcomputer 21, and this hydraulic pressure acts on the intake valve 26 side of the valve mechanism 46. The timing changes to the target advance value d.

Here, at low temperature where the viscosity of the hydraulic oil is high,
Since the movement of the VVT 47 becomes slow, a time difference occurs after the microcomputer 21 outputs the control output to the VVT 47 as described above and before the valve timing of the intake valve 26 actually reaches the target advance value d. That is, VV
A response delay occurs at T47. Then, the change in the actual intake air amount when the valve timing changes also gradually changes over a certain time due to this response delay. Steps 108 and 110 to be described next are processes for making the predicted intake air amount when the valve timing changes close to the above-described change of the actual intake air amount. In step 108, the smoothing coefficient n is calculated from the map of the smoothing coefficient n shown in FIG. And step 1
In 10, the VVT actual advance angle value c in consideration of the response delay of the VVT 47 is calculated by the following equation.

C (i) = c (i−1) + {d−c (i−1)} / n (1) From the above equation (1), the actual VVT advance value c when the current routine is passed (I) is the actual advance value c (i-1) obtained by dividing the difference between the target advance value d and the actual advance value c (i-1) at the time of the previous routine passage by the smoothing coefficient n. Calculated by adding.
According to the above equation (1), by repeating the routine, the VVT actual advance value c gradually approaches the target advance value d from the advance value before the start of change over time. Also,
As shown in FIG. 7, the smoothing coefficient n is the oil temperature sensor 48.
Since the VVT actual advance value c reaches the target advance value d, the speed becomes slower as THO is smaller (the smoothing coefficient n is larger), because it changes depending on the oil temperature THO of the hydraulic oil that is the detection signal of The larger THO is, the faster the speed is (the smoothing coefficient n is small). At the steady-state oil temperature THO ₁ when the warm-up is completely completed, n = 1.0, and in this case, the actual advance value c immediately becomes the target advance value d. That is, in the steady state, VV
This means that there is almost no delay in response at T47.

As described above, according to the map shown in FIG. 7 and the above equation (1), the response delay of the VVT 47 due to the viscosity of the hydraulic oil is considered, and the actual VVT advance value c corresponding to the actual valve timing change is taken into consideration. Can be asked. In this embodiment, the smoothing coefficient n is calculated from the oil temperature THO by the oil temperature sensor 48, but the cooling water temperature THW by the water temperature sensor 40 also changes in the same manner as the oil temperature THO, and the VVT 47 as in the oil temperature THO. Since it can be a value representative of the viscosity of the hydraulic oil in Fig. 7, even if the smoothing coefficient n is obtained from the cooling water temperature THW as shown in Fig. 7, the same effect as above can be obtained. The equipment of the temperature sensor 48 can be omitted.

In the next step 112, the above step 1
02, the engine speed NE ₁ , the throttle opening TA ₁ at the present time, and the VV shown in FIG.
GNTA map 1 for T most advanced angle (corresponding to map 5 above)
From this, GNTA at the most advanced angle is calculated. The calculated data is defined as a. In the next step 114, the GNTA at the most retarded angle is calculated from the values of NE ₁ and TA ₁ and the GNTA map 2 for VVT most retarded angle (corresponding to the map 5) shown in FIG. 8B. Then, the calculated data is b
And Here, GNTA is the intake air amount in a steady state determined by the engine speed NE and the throttle opening TA. However, in the VVT internal combustion engine, the intake air amount changes depending on the valve timing of the intake valve as described above. Therefore, in this embodiment, the VVT shown in FIG.
GNT shown in FIG. 8A is obtained by previously measuring the intake air amount when NE and TA are changed at the valve timing at the most advanced angle.
A map 1 is created, and the intake air amount when NE and TA are changed in the same manner as above at the valve timing when the VVT is most retarded as shown in FIG. The GNTA map 2 shown in FIG. As described above, in this embodiment, two GNTA maps for the most advanced VVT and the most retarded VVT are provided.

Next, the routine proceeds to step 116, where GNT, which is the GNTA value corresponding to the VVT actual advance value c, is calculated by the following equation.
Calculate Af.

GNTAf = (ab) × c / 60 + b (2) The meaning of the above equation (2) is that the GNTA value corresponding to the VVT actual advance value c is set to the maximum value as shown in FIG. Interpolation is performed from a which is GNTA at the time of angle and b which is GNTA at the time of the most retarded angle. VV of each valve timing displacement is about 60 ° CA
In the case of T, since the intake air amount changes almost linearly according to the displacement of VVT, G corresponding to the actual advance value c without causing a large error in the primary interpolation as in the above equation (2).
NTAf can be determined.

Since the calculation of GNTAf is performed every time the routine is passed, the change in valve timing due to NE, TA and VVT 47 is dealt with momentarily.

In the next steps 118 to 122, a predetermined calculation is performed on the GNTAf corresponding to the VVT actual advance value c obtained in step 116 to obtain the predicted inhalation corresponding to the VVT actual advance value c. This is a process of calculating the air amount GNFWD. Therefore, steps 112 to 12 above
The calculation means 6 described above is realized by the processing contents up to 2. Then, the control means 4 is realized together with the two GNTA maps shown in FIG.

Next, step 1 of the routine shown in FIG.
The processing contents of 18 to 122, that is, a method of obtaining the predicted intake air amount GNFWD from GNTAf will be described. still,
In the following description, for convenience of description, the GNTAf will be simply referred to as GNTA.

The present embodiment is applied to an internal combustion engine that controls the fuel injection amount based on the intake air amount and the engine speed. However, since the intake pipe pressure per revolution corresponds to the intake air amount, It is well known that the fuel injection amount may be controlled based on the intake pipe pressure per one revolution and the engine speed. In the latter device, although not shown in the figure, a diaphragm type pressure sensor is attached to the surge tank downstream of the throttle valve, and the intake pipe pressure is detected by this pressure sensor.

However, as described above, the change in the intake pipe pressure detection value is delayed due to the response delay of the pressure sensor with respect to the actual change in the intake pipe pressure during the transient operation. Therefore, the applicant calculates the intake pipe pressure in the steady state from the throttle opening and the engine speed without time delay, and performs the first-order delay processing on the calculated intake pipe pressure in the steady state so that there is no time delay. In addition to calculating the intake pipe pressure at the present time, predicting the intake pipe pressure at the time of closing the intake valve where the intake air amount into the engine combustion chamber is determined, and further calculating the difference between the calculated intake pipe pressure at the present time and the predicted time, There has been proposed an intake air amount predicting device that calculates the predicted value PMFWD by adding this difference to the measured intake pipe pressure at present (Japanese Patent Laid-Open No. 42160/1990).

That is, according to this proposed apparatus, first, the intake pipe pressure PMTA during steady running determined by the throttle opening TA and the engine speed NE is calculated. Therefore, the intake pipe pressure PMTA changes as shown in FIG. 10 in response to the change in the throttle opening during acceleration without any time delay. on the other hand,
Since the actual intake pipe pressure changes with respect to the throttle opening change through the first-order lag system of the intake pipe pressure PMTA during steady running, PMTA is calculated by first-order lag processing of PMTA. ..

Subsequently, the PMCRT is once again subjected to the first-order delay processing as a value having the same response as the pressure sensor value PM, and the value shown in FIG.
An averaging value indicated by PMCRT4 at 0 is calculated in a half cycle of the calculation cycle of PMCRT. Assuming that the leak air amount of the throttle valve, the opening degree of the idle speed control valve, and the atmospheric pressure have not changed, the smoothed value PMCRT4 and the sensor value PM are the same.

Assuming that the time from the present moment until the intake valve is closed is T, T is the calculated value PM of the intake pipe pressure.
The expression of tA _i = tA _i-1 + TIM × (PMTA-tA _i-1 ) is repeatedly calculated by the number of times divided by the calculation cycle Δt of the CRT, and finally the predicted value tPMVLV is obtained.
To calculate. However, the initial value tA ₀ is PMCRT.

If PM and PMCRT4 are equal, tPM
Although VLV may be used as the predicted value, since there is a deviation in practice, the difference (tpMVL) between the calculated intake pipe pressure tPMVLV at the predicted time point and the calculated intake pipe pressure PMCRT4 at the current time point (tpMVL).
The predicted intake pipe pressure PMFWD when the intake valve is closed is obtained by adding the current sensor measured intake pipe pressure PM to V-PMCRT4).

By the way, in the internal combustion engine which controls the fuel injection amount based on the intake air amount and the engine speed as in the present embodiment, the air flow meter 32 is located upstream of the throttle valve 33, so that the pressure sensor described above is used. The measured value (intake pipe pressure) PM is a value advanced in phase. Therefore, by delaying the measured intake air amount GN of the air flow meter 32 per revolution to create a value GNSM corresponding to the measured intake pipe pressure value PM, the above-described logic is also applied to the present embodiment to predict the intake air amount. The quantity GNFWD can be obtained.

FIG. 11 shows the above predicted intake air amount GNFWD.
9 is a flowchart of an embodiment of the main part of the present invention for calculating This GNFWD calculation routine is started by the microcomputer 21 every 8 msec, for example. When this routine is started, first in step 202,
From the intake air amount Q measured by the air flow meter 32 and the engine speed NE measured by the rotation angle sensor 44, the intake air amount GN per one engine speed is calculated.

Next, at step 204, VV shown in FIG.
G corresponding to the VVT actual advance value c obtained in step 116 of the T control / predicted intake air amount GNFWD calculation routine
Read NTA.

In the next steps 206 to 220,
First-order lag processing is performed on the intake air amount GNTA during steady running. That is, in step 206, the engine speed N
The map of the time constant TIMCA of the first-order delay determined based on E and the intake air amount GNTA during steady running is stored in the ROM 51.
And the time constant TIMCA of the first-order delay is calculated. Then, in step 208, a primary delay processing value GNCRT corresponding to the primary delay processing value PMCRT is calculated based on the following equation.

GNCRT _i = GNCRT _i-1 + (GNTA-GNCRT _i-1 ) × TIMCA (3) However, in the above formula (3), GNCRT _i-1 is the first-order lag processing value of the previous intake air amount. Is. In the next step 210, GN is determined as a value having the same response as the smoothed value GNSM of the detected intake air amount of the air flow meter 32 during transient operation.
The CRT is further subjected to first-order delay processing according to the following equation, and the smoothed value GN
Calculate CRT4.

GNCRT4 _i = GNCRT4 _i-1 + (GNCRT-GNCRT4 _i-1 ) × K (4) However, in the above formula (4), GNCRT4 _i-1 is the previous smoothed value GNCRT4, and K is a constant, which is a coefficient for correcting the amount of response delay that the air flow meter 32 is on the upstream side of the throttle valve 33.

Next, at step 212, the engine speed N
After the one-dimensional map in the ROM 51 is searched according to E to calculate the time constant TIMC, at step 214, the intake air amount smoothing value GNSM corresponding to the measured intake pipe pressure PM is calculated by the following equation.

GNSM _i = GNSM _i-1 + (GN-GNSM _i-1 ) × TIMC (5) In the above equation (5), the intake air amount smoothing value GNSM _i is determined by the time constant TIMC according to the engine speed NE. It has been corrected to have excellent responsiveness. Note that GNSM _i-1 is the previous smoothed value GNSM.

Next, at step 216, the time T from the present time to the intake air amount prediction time point (that is, the closing time point of the intake valve 26 at which the intake air amount into the engine combustion chamber is determined) is calculated. Then, in step 218, this GNF
The execution cycle of the WD calculation routine is Δt (8 _{msec in} this case)
Then, the calculation of the following equation is repeatedly executed the number of times of calculation represented by T / Δt.

TA _i = tA _i-1 + TIMCA × (GNTA-tA _i-1 ) (6) However, in the above formula (6), tA _i-1 is the previous smoothed value tA.
Is. The initial value tA ₀ is GNCRT. Then, in step 218, the smoothed value tA _i calculated after T / Δt times is used, and in step 220, the predicted intake air amount GNFWD when the intake valve 26 is closed is calculated by the following equation, and the RAM 62 is calculated. After storing in, the routine ends.

GNFWD = GNSM + (tA _i −GNCRT4) (7) This predicted intake air amount GNFWD is the predicted intake pipe pressure P.
Predicted value similar to MFWD, intake air amount G during steady running
It is a value obtained by first-order lag processing of NTA.

In the GNFWD calculation routine shown in FIG. 11, since GNFWD is obtained by using GNTA corresponding to the VVT actual advance value c obtained in the routine shown in FIG. 6, the finally obtained GNFWD is , VVT 47 when the valve timing is changed, the change in the actual intake air amount that changes momentarily in response to the change in the valve timing is accurately represented without delay.

In this embodiment, the value of GNFWD is multiplied by the fuel injection amount conversion coefficient tKINJ, and various correction values are multiplied or added to calculate the fuel injection amount TAU. Therefore, the calculated fuel injection amount TAU is always a value that causes the theoretical air-fuel ratio without causing a response delay with respect to the actual intake air amount obtained as the predicted intake air amount GNFWD as described above. Therefore, according to the fuel injection control device of the present embodiment, even in the internal combustion engine provided with the VVT 47, the predicted intake air amount GNFWD matches the actual intake air amount for any valve timing of the intake valve 26 to be controlled. Since the intake air amount is shown, the air-fuel ratio can be accurately controlled even during transient operation such as acceleration. As a result, in an internal combustion engine with VVT, it is possible to improve exhaust emission, fuel efficiency, and drivability.

The present invention is not limited to the above-described embodiment, but is provided with an on / off type VVT that selectively uses either the advance side or the retard side as the valve timing of the intake valve. It can also be applied to an internal combustion engine. In this case, in the flowchart shown in FIG. 6, the part where the VVT target advance value d is switched to either the most advanced angle (x = 60 ° CA) or the most retarded angle (x = 0 ° CA) is described above. Although different from the embodiment, the other parts are exactly the same as the above embodiment. Even in this case, the oil temperature TH
When O is low, the valve timing is switched, and the response delay described above accompanies the change in the intake air amount, so that the GNTAf and GN in step 116 are changed.
By obtaining the GNFWD by TAf for each routine passage, the GNFWD can be accurately adapted to the actual change in the intake air amount at the time of switching the valve timing.

Further, in the above embodiment, the VVT actual advance value with a response delay was estimated in the processing of steps 108 and 110 of the flow chart shown in FIG. 6, but this sensor is provided separately. The VVT actual advance value may be obtained from the value, and in this case, the value of GNFWD becomes closer to the actual intake air amount, so that the above effect can be made more effective.

[0053]

As described above, according to the present invention, in the internal combustion engine equipped with the variable valve timing device, the calculating means matches the actual intake air amount for any valve timing of the controlled intake valve. Since the accurate intake air amount is predicted, the air-fuel ratio can always be accurately controlled not only during steady operation but also during transient operation such as acceleration. As a result, in an internal combustion engine equipped with a variable valve timing device, it is possible to improve exhaust emission, fuel efficiency, and drivability.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is a system configuration diagram showing an embodiment of an internal combustion engine and its peripheral devices to which the present invention is applied.

FIG. 3 is a hardware configuration diagram of the microcomputer in FIG.

FIG. 4 is a timing chart showing the valve timing of the intake valve in the case of the most advanced angle and the case of the most retarded angle.

FIG. 5 shows the change in pressure in the intake port during the intake stroke as V
It is a figure showing both conditions at the time of VT most advanced angle and VVT most retarded angle.

FIG. 6 is a flowchart of a VVT control / predicted intake air amount GNFWD calculation routine according to an embodiment of a main part of the present invention.

FIG. 7 is a map explanatory view of a moderating coefficient n used in the flowchart of FIG.

FIG. 8: GNTA used in the flow chart of FIG.
It is a map explanatory view of.

9 is a diagram illustrating a method of calculating GNTAf in the flowchart of FIG.

FIG. 10 is a principle explanatory diagram of a method for calculating a predicted intake pipe pressure previously proposed by the applicant.

FIG. 11 is a flowchart showing a GNFWD calculation routine according to an embodiment of the main part of the present invention.

[Explanation of symbols]

1 Internal Combustion Engine 2,26 Intake Valve 3,47 Variable Valve Timing Device (VVT) 4 Control Means 5 Map 6 Calculating Means 10 Engine Main Body 21 Microcomputer 25 Intake Manifold 28 Exhaust Manifold 30 Surge Tank 32 Heat Wire Air Flow Meter 33 Throttle Valve 34 Throttle position sensor 39 Oxygen concentration (O ₂ ) sensor 40 Water temperature sensor 42 Distributor 44 Rotation angle sensor 45 Hydraulic control solenoid valve 46 Valve mechanism 50 Central processing unit (CPU)

Claims (1)

[Claims] 1. A variable valve timing device for changing the valve timing of an intake valve according to operating conditions of an internal combustion engine; and a variable intake valve based on a predicted intake air amount predicted from a rotational speed of the internal combustion engine and a throttle opening. In a fuel injection control device for an internal combustion engine, which comprises a control means for controlling the fuel injection amount of the internal combustion engine, the control means is a map for obtaining the predicted intake air amount from the rotational speed and the throttle opening of the internal combustion engine, At least two or more corresponding to different valve timings are provided, and any one of the intake valves is changed by the variable valve timing device based on the value of the reference predicted intake air amount obtained from each of the plurality of maps. An internal combustion engine characterized in that it is provided with a calculating means for obtaining a predicted intake air amount corresponding to valve timing. Fuel injection control device.