JP3282591B2 - Fuel supply control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fuel supply control device for an internal combustion engine.

[0002]

2. Description of the Related Art A purge passage is provided for supplying evaporated fuel generated in a fuel tank into an engine intake passage, and a purge control valve for controlling a purge amount of purge gas is disposed in the purge passage. 2. Description of the Related Art An internal combustion engine is known in which the amount of purge gas purged into an engine intake passage is controlled by controlling a duty ratio of a control pulse of a control valve (see Japanese Patent Publication No. 63-39787).

In an internal combustion engine equipped with such a purge control valve, when the purge operation is to be started and the purge control valve is fully opened at a stretch, evaporated fuel is supplied to the engine intake passage at a stretch, resulting in a large air-fuel ratio. Will fluctuate. Therefore, in the above-described internal combustion engine, when the purge action is started in order to prevent the air-fuel ratio from fluctuating, the duty ratio of the control pulse of the purge control valve is gradually increased at a constant rate, that is, the purge control valve is opened. When the amount should be changed, the opening amount of the purge control valve is gradually changed at a constant rate.

[0004]

However, even if the opening amount of the purge control valve is gradually increased at a constant rate as described above, if the engine load changes, for example, when the acceleration operation is performed, the air-fuel ratio becomes large. There is a problem that fluctuates. That is, when the throttle valve is opened to accelerate, the negative pressure in the intake passage decreases and the intake air amount increases. When the negative pressure in the intake passage decreases, the amount of purge gas decreases, and at this time, the amount of intake air increases. Therefore, the concentration of purge fuel in the intake air sharply decreases. Will fluctuate.

[0005]

According to a first aspect of the present invention, as shown in the block diagram of the invention of FIG. 1, evaporated fuel generated in a fuel tank is removed from an engine intake passage. In an internal combustion engine provided with a purge control valve 17 for controlling a purge amount of a purge gas in a purge passage for supplying the purge gas to the engine, the ratio of the purge amount to the intake air amount, and the same purge control valve opening degree, Reference purge rate calculation means A for calculating a reference purge rate determined by an operation state, target purge rate setting means B for setting a target purge rate, and opening of a purge control valve according to a ratio of the target purge rate to the reference purge rate. A purge control valve opening control means C for controlling the amount is provided, and when the target purge rate is to be changed, the target purge rate is gradually changed. According to a second aspect, in the first aspect, the target purge rate is gradually increased from zero when the purge action is started.

[0006] In the third invention, in the first invention,
A fuel injection amount calculating means for calculating a fuel injection amount, an air-fuel ratio sensor disposed in an engine exhaust passage for detecting an air-fuel ratio, and a target air-fuel ratio based on an output signal of the air-fuel ratio sensor. A first injection amount correction means for correcting the fuel injection amount by a feedback correction coefficient so as to obtain a purge vapor concentration calculation means for calculating a purge vapor concentration based on a deviation of the feedback correction coefficient generated when purging is performed; And a second injection amount correcting means for correcting the fuel injection amount based on the purge vapor concentration when performing the above. In the fourth invention, in the first invention,
A fuel injection amount calculating means for calculating a fuel injection amount, an air-fuel ratio sensor arranged in an engine exhaust passage for detecting an air-fuel ratio, and a target air-fuel ratio based on an output signal of the air-fuel ratio sensor. A first injection amount correction means for correcting the fuel injection amount with a feedback correction coefficient so as to obtain a purge vapor concentration per unit target purge rate based on a deviation of the feedback correction coefficient generated when purging is performed. There is provided a concentration calculating means and a second injection amount correcting means for correcting the fuel injection amount based on the product of the purge vapor concentration and the target purge rate when purging is performed.

According to a fifth aspect of the present invention, there is provided an internal combustion engine provided with a purge control valve for controlling a purge gas purge amount in a purge passage for supplying evaporated fuel generated in a fuel tank into an engine intake passage. Target purge rate setting means for setting the rate, and purge control valve opening control means for controlling the opening of the purge control valve so that the ratio between the purge amount and the intake air amount becomes the target purge rate in accordance with the intake air amount When the target purge rate is to be changed, the target purge rate is gradually changed. In a sixth aspect based on the fifth aspect, the target purge rate is gradually increased from zero when the purge action is started.

[0008]

According to the first aspect of the invention, when the opening amount of the purge control valve is controlled in accordance with the ratio of the target purge rate to the reference purge rate, the purge fuel concentration in the intake air is reduced regardless of the operating state of the engine. The concentration is proportional to. That is, as long as the target purge rate is the same, the purge fuel concentration in the intake air is not affected by the operating state of the engine, and therefore the air-fuel ratio does not change. In the fifth aspect, the opening degree of the purge control valve is controlled so that the ratio between the purge amount and the intake air amount becomes the target purge rate. Therefore, regardless of the operating state of the engine, the purge fuel concentration in the intake air is reduced to the target purge rate. It is proportional to the rate and therefore the air-fuel ratio does not fluctuate.

[0009]

Referring to FIG. 2, reference numeral 1 denotes an engine main body, 2 denotes an intake branch pipe, 3 denotes an exhaust manifold, and 4 denotes a fuel injection valve attached to each intake branch pipe 2 respectively. Each intake branch pipe 2 is connected to a common surge tank 5, and this surge tank 5 is connected to an air cleaner 8 via an intake duct 6 and an air flow meter 7. A throttle valve 9 is arranged in the intake duct 6. Further, as shown in FIG. 2, the internal combustion engine includes a canister 11 in which the activated carbon 10 is built. The canister 11 has a fuel vapor chamber 12 on each side of the activated carbon 10.
And an atmosphere chamber 13. The fuel vapor chamber 12 is connected on the one hand to a fuel tank 15 via a conduit 14 and on the other hand to the surge tank 5 via a conduit 16. Conduit 1
A purge control valve 17 controlled by an output signal of the electronic control unit 20 is arranged in the inside of the apparatus. The fuel vapor generated in the fuel tank 15 is sent into the canister 11 through the conduit 14 and is adsorbed on the activated carbon 10. When the purge control valve 17 is opened, air is sent from the atmosphere chamber 13 through the activated carbon 10 and into the conduit 16. When the air passes through the activated carbon 10, the fuel vapor adsorbed on the activated carbon 10 is desorbed from the activated carbon 10, so that the air containing the fuel vapor, that is, the purge gas is discharged through the conduit 16 through the surge tank 5.
Purged inside.

The electronic control unit 20 is composed of a digital computer, and a ROM (read only memory) 22, a RAM (random access memory) 23, a CPU (microprocessor) 24, and an input port 25 interconnected by a bidirectional bus 21. And an output port 26. The air flow meter 7 generates an output voltage proportional to the amount of intake air, and the output voltage is input to the input port 25 via the AD converter 27. A throttle switch 28 that is turned on when the throttle valve 9 is at the idling opening is attached to the throttle valve 9, and an output signal of the throttle switch 28 is input to an input port 25.
A water temperature sensor 29 for generating an output voltage proportional to the engine cooling water temperature is attached to the engine body 1.
Is input to the input port 25 via the AD converter 30. An air-fuel ratio sensor 31 is attached to the exhaust manifold 3, and an output signal of the air-fuel ratio sensor 31 is input to an input port 25 via an AD converter 32. Further, the input port 25 is connected to a crank angle sensor 33 that generates an output pulse every time the crankshaft rotates, for example, 30 degrees. The CPU 24 calculates the engine speed based on the output pulse. On the other hand, the output port 26 is connected to the fuel injection valve 4 and the purge control valve 17 via the corresponding drive circuits 34 and 35.

In the internal combustion engine shown in FIG. 2, the fuel injection time TAU is basically calculated based on the following equation. TAU = TP ｛{1 + K + (FAF-1) + FPG} Here, each coefficient represents the following. TP: Basic fuel injection time K: Correction coefficient FAF: Feedback correction coefficient FPG: Purge A / F correction coefficient The basic fuel injection time TP is an injection time obtained by a necessary experiment for setting an air-fuel ratio to a target air-fuel ratio. The basic fuel injection time TP is stored in advance in the ROM 2 as a function of the engine load Q / N (intake air amount Q / engine speed N) and the engine speed N.
2 is stored.

The correction coefficient K represents the warm-up increase coefficient and the acceleration increase coefficient collectively. When no increase correction is required, K = 0. Purge A / F correction coefficient FPG
Is used to correct the injection amount when the purge is performed. Therefore, when the purge is not performed, FPG =
It becomes 0. The feedback correction coefficient FAF is for controlling the air-fuel ratio to the target air-fuel ratio based on the output signal of the air-fuel ratio sensor 31. Although any air-fuel ratio may be used as the target air-fuel ratio, in the embodiment shown in FIG. 2, the target air-fuel ratio is set to the stoichiometric air-fuel ratio. Therefore, a case where the target air-fuel ratio is set to the stoichiometric air-fuel ratio will be described below. . When the target air-fuel ratio is the stoichiometric air-fuel ratio, a sensor whose output voltage changes according to the oxygen concentration in the exhaust gas is used as the air-fuel ratio sensor 31. Therefore, the air-fuel ratio sensor 31 is hereinafter referred to as an O ₂ sensor. The O ₂ sensor 31 generates an output voltage of about 0.9 (V) when the air-fuel ratio is rich, that is, when the air-fuel ratio is rich, and 0.1 when the air-fuel ratio is lean, that is, when the air-fuel ratio is lean, that is, when the air-fuel ratio is lean.
(V) output voltage is generated. First, this O ₂
The control of the feedback correction coefficient FAF performed based on the output signal of the sensor 31 will be described.

FIG. 3 shows a routine for calculating the feedback correction coefficient FAF. This routine is executed, for example, in a main routine. Referring to FIG. 3, first, at step 40, it is determined whether or not the output voltage V of the O ₂ sensor 31 is higher than 0.45 (V), that is, whether or not it is rich. When V ≧ 0.45 (V), that is, when rich, the routine proceeds to step 41, where it is determined whether or not the engine was lean during the previous processing cycle. When the process is lean in the previous processing cycle, that is, when the state changes from lean to rich, the routine proceeds to step 42, where the feedback correction coefficient FAF is set to FAFL, and the routine proceeds to step 43. In step 43, the skip value S is subtracted from the feedback correction coefficient FAF. Therefore, the feedback correction coefficient FAF is rapidly reduced by the skip value S as shown in FIG. Next, at step 44, the FAF
An average value FAFAV of L and FAFR is calculated. on the other hand,
If it is determined in step 41 that the air conditioner was rich in the previous processing cycle, the process proceeds to step 45 where the integral value K (K≪S) is subtracted from the feedback correction coefficient FAF. Therefore, as shown in FIG. 4, the feedback correction coefficient FAF is gradually reduced.

On the other hand, in step 40, V <0.45
When it is determined that (V), that is, when it is lean, the routine proceeds to step 46, where it is determined whether or not it was rich in the previous processing cycle. When rich in the previous processing cycle, that is, when the state changes from rich to lean, the routine proceeds to step 47, where the feedback correction coefficient FAF is set to FAFR, and the routine proceeds to step 48. In step 48, the skip value S is added to the feedback correction coefficient FAF. Therefore, the feedback correction coefficient FAF is rapidly increased by the skip value S as shown in FIG.
Next, at step 44, the average value F of FAFL and FAFR
AFAV is calculated. On the other hand, if it is determined in step 46 that the engine was lean in the previous processing cycle, the process proceeds to step 49, where the feedback correction coefficient FA
The integral value K is added to F. Therefore, as shown in FIG. 4, the feedback correction coefficient FAF is gradually increased.

When the fuel becomes rich and the FAF becomes smaller, the fuel injection time TAU becomes shorter, and when the fuel becomes lean and the FAF becomes larger, the fuel injection time TAU becomes longer, so that the air-fuel ratio is maintained at the stoichiometric air-fuel ratio. When the purge operation is not performed, the feedback correction coefficient FAF fluctuates around 1.0 as shown in FIG.
Also, as can be seen from FIG. 4, the average value FAFAV calculated in step 44 is the feedback correction coefficient FAFAV.
The average value of F is shown.

As can be seen from FIG. 4, the feedback correction coefficient FAF is changed relatively slowly by the integration constant K, so that a large amount of purge vapor is rapidly purged into the surge tank 5 and the air-fuel ratio is suddenly changed. The fuel ratio cannot be maintained at the stoichiometric air-fuel ratio,
Thus, the air-fuel ratio fluctuates. Therefore, in the embodiment shown in FIG. 2, when purging is performed in order to prevent the air-fuel ratio from fluctuating, the purge amount is gradually increased. When the purge amount is gradually increased in this manner, the feedback correction coefficient FAF is increased even when the purge amount is increasing.
The air-fuel ratio is maintained at the stoichiometric air-fuel ratio by the feedback control according to the above, and thus the fluctuation of the air-fuel ratio can be prevented.

However, for example, when an acceleration operation is performed, the concentration of the purge vapor in the intake air fluctuates greatly, and accordingly, the air-fuel ratio of the air-fuel mixture supplied into the engine cylinder fluctuates greatly. That is, assuming that the opening degree of the purge control valve 17 is constant, the purge amount decreases as the negative pressure of the surge tank 5 decreases, so that the purge vapor concentration in the intake air decreases, and as the intake air amount increases, the purge air concentration increases. Purge gas concentration decreases. Therefore, as in the case of acceleration operation, the surge tank 5
When the negative pressure in the chamber becomes small and the amount of intake air increases, the concentration of purge vapor in the intake air greatly decreases. As described above, since the air-fuel ratio fluctuates greatly during the transient operation, the air-fuel ratio fluctuates even if the purge amount is simply gradually increased. Therefore, in order to prevent such a change in the air-fuel ratio during the transient operation, in the embodiment according to the present invention, the reference purge rate determined by the engine operating state,
For example, the purge amount is controlled using the maximum purge rate. Next, a method of controlling the purge amount will be described.

The maximum purge rate MAXPG is determined by the purge control valve 1
7 shows the ratio between the purge amount and the intake air amount when the valve 7 is fully opened. An example of the maximum purge rate MAXPG is shown in Table 1 below.

[0019]

[Table 1] As can be seen from Table 1, the maximum purge rate MAXPG is a function of the engine load Q / N and the engine speed N. The maximum purge rate MAXPG increases as the engine load Q / N decreases, and the engine speed N increases. The lower the value, the larger. When purging, first, the target purge rate TGTPG
Is gradually increased at a constant rate, and when the target purge rate reaches a constant value, the target purge rate is kept constant, and the valve opening rate of the purge control valve 17 is adjusted according to the ratio of the target purge rate TGTPG to the maximum purge rate MAXPG. Is controlled. In the embodiment shown in FIG. 2, the duty ratio of the opening time of the purge control valve 17 is controlled. In this case, the purge control valve 17 is controlled according to the ratio of the target purge rate TGTPG to the maximum purge rate MAXPG. The duty ratio of the valve opening time is controlled.

That is, since the amount of evaporated fuel in the purge gas is not known, it is not known what the concentration of the purge vapor in the intake air will be when the purge control valve 17 is fully opened.
However, when the amount of fuel vapor adsorbed on the activated carbon 10 by the canister 11 is the same, the concentration of the purge vapor in the intake air is proportional to the maximum purge rate MAXPG. Therefore, in order to keep the purge vapor concentration in the intake air constant, it is necessary to increase the opening of the purge control valve 17 and increase the purge amount as the maximum purge rate MAXPG decreases. In other words, when the target purge rate TGTPG is kept constant, if the opening ratio of the purge control valve 17 is controlled according to the ratio of the target purge rate TGTPG to the maximum purge rate MAXPG, that is, the maximum purge rate MAXPG becomes If the opening degree of the purge control valve 17 is increased as it becomes smaller, the concentration of the purge vapor in the intake air becomes constant irrespective of the operating state of the engine, so that the air-fuel ratio does not fluctuate even during the transient operation. On the other hand, while the target purge rate TGTPG is gradually increased, the purge vapor concentration in the intake air increases in proportion to the target purge rate TGTPG,
At this time, even if the transient operation is performed, the purge vapor concentration in the intake air is proportional to the target purge rate TGTPG. That is, if the target purge rate TGTPG is the same, the purge vapor concentration is not affected at all by the operating state of the engine. Therefore, even if the acceleration operation is performed while the target purge rate TGTPG is increased, the air-fuel ratio does not fluctuate, and the air-fuel ratio is maintained at the stoichiometric air-fuel ratio by the feedback control using the feedback correction coefficient FAF.

In the time chart shown in FIG. 5, 0 second indicates the time when the purge action is started. As shown in FIG. 5, when the purge action is started, the actual purge rate PRG, which normally increases together with the target purge rate TGTPG, is gradually increased. Next, as shown in FIG. 5A, when the acceleration operation is performed and the intake air amount Q increases, the maximum purge rate MAXPG decreases, and therefore the duty ratio PGD for the purge control valve 17 as shown in FIG.
UTY is increased. As a result, as described above, the purge vapor concentration in the intake air increases in proportion to the increase in the purge rate PRG, and thus the air-fuel ratio does not fluctuate.

On the other hand, when the purge operation is started, the feedback correction coefficient FAF is set to maintain the air-fuel ratio at the stoichiometric air-fuel ratio.
Therefore, as shown in FIG. 5, the average value FAFAV of the feedback correction coefficient FAF gradually decreases when the purge operation is started. In this case, the higher the concentration of the purge vapor in the intake air, the greater the decrease in the feedback correction coefficient FAF. At this time, the decrease in the feedback correction coefficient FAF is proportional to the concentration of the purge vapor in the intake air. From this, the concentration of the purge vapor in the intake air can be determined.
In this case, as described above, the purge vapor concentration is not affected by the transient operation, and even during the transient operation, the purge vapor concentration is proportional to the target purge rate TGTPG, and the difference between the purge vapor concentration per unit target purge rate and the target purge rate is determined. The product is proportional to the target purge rate TGTPG even if the transient operation is performed. Therefore, if the fuel injection amount is corrected based on the purge vapor concentration or the product of the purge vapor concentration per unit purge rate and the target purge rate when the feedback correction coefficient FAF decreases, the air-fuel ratio can be theoretically determined whether or not the transient operation is performed. The air-fuel ratio can be maintained. This is the basic concept of the purge control employed in the embodiment of the present invention.

Next, the correction of the injection amount based on the purge vapor concentration will be described in more detail. When the purge is performed, the feedback correction coefficient FAF decreases to a value corresponding to the concentration of the purge vapor in the intake air. However, the feedback correction coefficient FAF also decreases due to other causes, for example, a measurement error caused by the air flow meter 7. Therefore, it is necessary to determine whether the fluctuation of the feedback correction coefficient FAF is caused by the purge. However, the amount of decrease in the feedback correction coefficient FAF due to the purge is greater than the amount of decrease in the feedback correction coefficient FAF due to other causes. However, the feedback correction coefficient FAF
Considering open-loop control in which is fixed at 1.0, the feedback correction coefficient FAF cannot be greatly reduced. Therefore, in the embodiment according to the present invention, as shown in FIG. 5, when the average value FAFAV of the feedback correction coefficient FAF decreases to some extent, the feedback correction coefficient FAF
F is suppressed from decreasing, and the feedback correction coefficient FA
After the decrease in F is suppressed, the purge vapor concentration is obtained using a coefficient FPGA representing the purge vapor concentration per unit target purge rate. Next this coefficient FPGA
6 in which section a in FIG. 5 is enlarged for FIG.
This will be described with reference to FIG.

FIG. 6A shows changes in the feedback correction coefficient FAF and the purge vapor concentration coefficient FPGA per unit target purge rate when the purge action is started at 0 second. In the example shown in FIG. 6A, the feedback correction coefficient FAF is prevented from decreasing as much as possible from the lower limit threshold value (FBA-X). As can be seen from FIG. 6A, when the feedback correction coefficient FAF is smaller than the lower limit threshold value (FBA-X) and rich, the purge vapor concentration coefficient FPG per unit target purge rate is used.
A is increased. The above-mentioned purge A / F correction coefficient FPG is expressed in the form of a negative value (FPG = -FPGA.PRG) of a product of a purge vapor concentration coefficient FPGA per unit target purge rate and a purge rate PRG corresponding to the target purge rate TGTPG. Therefore, when the purge vapor concentration coefficient FPGA per unit target purge rate increases, the fuel injection amount is reduced as can be seen from the above-described equation for calculating the fuel injection time TAU. In other words, when the purge vapor concentration coefficient FPGA per unit target purge rate is increased, the fuel injection amount is reduced, so that the effect of decreasing the feedback correction coefficient FAF is suppressed.

Next, when the feedback correction coefficient FAF is smaller than the lower limit threshold value (FBA-X) and rich, the purge vapor concentration coefficient F per unit target purge rate is used.
The reason for increasing PGA will be described. FIG. 6 (B)
Shows a comparative example in which when the feedback correction coefficient FAF becomes smaller than the lower threshold value (FBA-X), the FPGA is increased irrespective of whether it is rich or lean. Before the purge is started, a large amount of fuel vapor not adsorbed to the activated carbon 10 is present in the canister 11, and when the purge is started, the fuel vapor not adsorbed to the activated carbon 10 and the fuel vapor are adsorbed to the activated carbon 10. Both fuel vapors are purged into the surge tank 5.
Therefore, even if the target purge rate TGTPG at the start of the purge is reduced, the mixture becomes rich until the purge of the fuel vapor not adsorbed on the activated carbon 10 is completed. Therefore, as shown in FIGS. 6A and 6B, when the purge is started at 0 second, the feedback correction coefficient FAF is started.
Decreases beyond the lower threshold (FBA-X). When the feedback correction coefficient FAF is equal to the lower threshold (FBA-
When X) is exceeded, the FPGA is increased, so that the fuel injection amount gradually decreases, and then, when the mixture becomes lean, the feedback correction coefficient FAF starts to increase.

By the way, when the feedback correction coefficient FAF is smaller than the lower limit threshold value (FBA-X), the FPGA is increased regardless of whether it is rich or lean, as shown in FIG. Even if the feedback correction coefficient FAF starts to increase, the FPGA continues to increase. However, as the FPGA continues to increase, the feedback correction coefficient FAF increases to increase the fuel injection amount. However, the fuel injection amount is reduced by the increase in the FPGA, so that the air-fuel mixture does not easily become rich. After a while after the coefficient FAF becomes larger than the lower threshold value (FBA-X) and the increasing action of the FPGA is stopped, the air-fuel mixture becomes rich. That is, the air-fuel mixture becomes lean for a considerable period of time, and during this time the air-fuel ratio becomes very lean, so that not only the air-fuel ratio fluctuates, but also the output torque of the engine temporarily drops, causing discomfort to the driver. Will give.

On the other hand, as in the present invention, the feedback correction coefficient FAF is set to the lower limit threshold value (FBA-X).
When the FPGA is increased when the amount of fuel injection is reduced and becomes rich, the feedback correction coefficient FAF increases and the amount of fuel injection by the FPGA is maintained at a constant value when the amount of fuel injection is being increased. Is not performed, and the mixture changes quickly from lean to rich as shown in FIG. 6 (A). In other words, the air-fuel ratio is quickly controlled to the stoichiometric air-fuel ratio. Therefore, it is possible to prevent the air-fuel ratio from fluctuating immediately after the start of the purge action. Thereafter, the feedback correction coefficient FAF gradually increases as a whole while the air-fuel ratio is maintained at the stoichiometric air-fuel ratio. After a while, the minimum value of the feedback correction coefficient FAF has a lower limit as shown by f in FIG. Threshold (FBA-X)
And continue to fluctuate. At this time, the FPGA is kept at a constant value.

As described above, the feedback correction coefficient F
The amount of decrease in AF is proportional to the concentration of the purge vapor in the intake air, and the FPGA increases by the amount by which the feedback correction coefficient FAF should be reduced. Therefore, the concentration of the purge vapor in the intake air becomes the feedback correction coefficient F indicated by f in FIG.
The sum of the decrease in AF and the FPGA indicated by g in FIG. 6, that is, the decrease in the feedback correction coefficient FAF indicated by f in FIG. 6 and the target purge rate in the FPGA indicated by g in FIG. It is represented by the sum of the multiplied values.

As shown in FIG. 5, the purge rate PR corresponding to the target purge rate takes about 30 seconds after the purge is started.
When G was maximized, the purge vapor concentration per unit purge rate settled to a substantially constant value in about 15 seconds after the start of purging, and the purge vapor concentration per unit purge rate was kept substantially constant for several minutes or more. It gradually decreases later. Therefore, the FPGA is maintained at a substantially constant value if left as it is for a while after 15 seconds have elapsed since the start of the purge.

As described above, the feedback correction coefficient F
AF is preferably maintained at 1.0. Therefore, as shown in FIG. 5, the average value FAFAV of the feedback correction coefficient FAF is forcibly set to 1.0 every 15 seconds.
Approached. As described above, the purge vapor concentration in the intake air is determined by the amount of decrease in the feedback correction coefficient FAF and F
Since it is expressed by the sum of the value obtained by multiplying the PGA by the target purge rate, when the feedback correction coefficient FAF is forcibly increased, the FPGA is increased by an amount corresponding to the increase of the feedback correction coefficient FAF. Therefore, when the feedback correction coefficient FAF is returned to 1.0, FP
GA will accurately represent the concentration of purge vapor per unit purge rate. In addition, as shown in FIG.
The reason why FAFAV gradually decreases between 5 seconds and 30 seconds is that the purge rate PRG corresponding to the target purge rate is increased during this time.

The purge A / F correction coefficient FP shown in FIG.
G is expressed in the form of the negative of the product of the FPGA and the purge rate PRG (−FPGA · PRG) as described above. Here, the product of the purge vapor concentration coefficient FPGA and the PRG per unit target purge rate represents the purge vapor concentration, so that the decrease amount of the purge A / F correction coefficient FPG represents the purge vapor concentration. As can be seen from FIG. 5, the purge rate PRG increases from 0 to 15 seconds, and the purge vapor concentration coefficient FPGA increases, so that the purge vapor concentration increases relatively rapidly. On the other hand, at 15 seconds, the purge vapor concentration coefficient FPGA is forcibly increased, so that the purge vapor concentration is also forcibly increased.

From 15 seconds to 30 seconds, the purge vapor concentration coefficient FPGA becomes constant, but the purge rate PRG is increased, so that the purge vapor concentration is also increased. Next, every time the purge vapor concentration coefficient FPGA is increased every 15 seconds, the purge vapor concentration is also increased.
The purge vapor concentration and the feedback correction coefficient FAF
The sum with the decrease amount indicates the purge vapor concentration in the intake air. Therefore, as shown in the above-described equation for calculating the fuel injection time TAU, the decrease amount (1-FAF) of the feedback correction coefficient FAF and the purge A / F correction If the basic fuel injection time TP is corrected by the sum of the coefficients FPG, the air-fuel ratio will be maintained at the stoichiometric air-fuel ratio. When the feedback correction coefficient FAF becomes 1.0, the purge vapor concentration represented by FPG accurately represents the purge vapor concentration in the intake air. 90 after the purge is started
After about seconds, the FAFAV becomes almost 1.0, and it is understood that the purge A / F correction coefficient FPG represents the purge vapor concentration in the intake air at this time.

As shown by B in FIG. 5, even when the acceleration operation is performed and the amount of intake air increases when the purge rate PRG is at the maximum, basically as shown by the broken line in FIG. Since the duty ratio PGUDUTY is increased while the purge rate PRG is kept constant, the air-fuel ratio does not change. However, before the acceleration operation indicated by B is performed, as shown in FIG.
If the UTY is close to 100%, the duty ratio PGDUTY reaches 100% when the acceleration indicated by B is performed. However, in this case, even if the target purge rate is kept constant, the actual purge rate PRG is reduced as shown in FIG. 5, and the purge A / F correction coefficient FPG is increased accordingly. Can be At this time, the purge vapor concentration in the intake air decreases, but the purge A / F correction coefficient FPG is increased by an amount corresponding to the decrease amount of the purge vapor concentration, so that the stoichiometric air-fuel ratio is maintained without fluctuation. become.

In the internal combustion engine shown in FIG. 2, fuel injection from the fuel injection valve 4 is stopped during engine deceleration operation. If the fuel vapor is purged when the fuel injection is stopped, the fuel vapor is discharged into the exhaust manifold 3 without burning.
Therefore, when the fuel injection is stopped, the purging operation must be stopped. When the fuel injection is to be stopped, a cut flag is set, and when the cut flag is set, the purging operation is stopped. The processing routine of this cut flag will be described next with reference to FIG.

The cut flag processing routine shown in FIG. 7 is executed, for example, in a main routine. Referring to FIG. 7, first, at step 50, it is determined whether or not the cut flag is set. When the cut flag has not been set, the routine proceeds to step 51, where it is determined whether or not the throttle switch 28 is on, that is, whether the throttle valve 9
Is the idling opening degree. When the throttle valve 9 is at the idling opening, step 5
2 and the engine speed N becomes a constant value, for example, 1200 r.p.
m is determined. N ≧ 1200r.pm
If so, the routine proceeds to step 53, where the cut flag is set. That is, when the throttle valve 9 has an idling opening degree and N ≧ 1200 rpm, it is determined that deceleration operation is being performed, and the cut flag is set.

Step 5 when the cut flag is set
From 0, the routine proceeds to step 54, where it is determined whether or not the throttle switch 28 is on, that is, whether or not the throttle valve 9 is at the idling opening. When the throttle valve 9 is at the idling opening, the routine proceeds to step 56, where it is determined whether or not the engine speed N is lower than 1000 rpm. When N ≦ 1000 rpm, the routine proceeds to step 57, where the cut flag is reset. On the other hand, N> 1000
If the throttle valve 9 is opened even at rpm, the control jumps from step 54 to step 57 to reset the cut flag. When the cut flag is set, the fuel injection is stopped.

Next, the purge control method will be described in detail with reference to FIGS. 8 to 12 while referring to FIGS. 5 and 6. FIG. FIG. 8 shows a purge control initialization processing routine executed when an ignition switch (not shown) is turned on. Referring to FIG. 8, first, at step 60, the purge count value PGC is cleared, and then at step 61, the timer count value TGC is cleared.
Is cleared. Next, at step 62, the drive duty ratio PGDUTY for the purge control valve 17 is made zero, and then at step 63, the purge rate PRG is made zero. Next, at step 64, the purge vapor concentration coefficient FP
GA is set to zero. Next, at step 65, the purge control valve 17 is closed, and then the processing cycle is completed.

FIGS. 9 to 12 show a purge control routine, which is executed by interruption every 1 msec. Referring to FIG. 9, first of all, step 70 is executed.
, The timer count value T is incremented by one. Next, at step 71, the timer count value T is 1
It is determined whether it is 00 or not. When T = 100, the process proceeds to step 72. Therefore, in step 72, 100 ms
It will advance every ec. At step 72, the timer count value T is cleared, and then the routine proceeds to step 73. In step 73, it is determined whether the purge count value PGC is greater than one. When the routine proceeds to step 73 for the first time after the ignition is turned on, the purge count value PGC is zero, so the routine proceeds to step 74 shown in FIG.

In step 74, it is determined whether or not a condition for starting the purge control is satisfied. Engine cooling water temperature 70
° C, the feedback control of the air-fuel ratio has been started, and the skip processing of the feedback correction coefficient FAF (S in FIG. 4) has been performed five times or more, it is determined that the condition for starting the purge control has been satisfied. You. When the condition for starting the purge control is not satisfied, the processing cycle is completed. On the other hand, when the condition for starting the purge control is satisfied, the routine proceeds to step 75, where the purge count value P
GC is set to 1. Next, at step 76, the feedback correction coefficient F calculated in the routine shown in FIG.
The average value FAFAV of AF is set as FBA. Therefore FB
A indicates the average value FAFAV of the feedback correction coefficient FAF when the condition for starting the purge control is satisfied. Then the processing cycle is completed.

When it is determined that the condition for starting the purge control is satisfied, it is determined in step 73 in FIG. 9 that the purge count value PGC ≧ 1. At step 77, it is determined whether or not the cut flag is set, that is, whether or not the fuel injection is stopped. If the cut flag has not been set, the routine proceeds to step 78, where the purge count value PGC is incremented by 1, and then at step 79, it is determined whether the purge count value PGC is greater than 6. Step 8 when the purge count value PGC <6
Proceeding to 0, the purge rate PRG is made zero. Next, at step 81, the purge control valve 17 is closed.
At this time, since the purge control valve 17 has already been closed, the purge control valve 17 is kept closed. On the other hand, if it is determined in step 79 that the purge count value PGC ≧ 6, that is, if 500 msec has elapsed after the conditions for starting the purge control have been satisfied, step 8 in FIG.
Proceed to 2. Steps 82 to 91 are for calculating the purge vapor concentration, which will be described later. In the following step 92, the engine load Q / N and the engine speed N are stored based on the above-mentioned Table 1 stored in the ROM 22.
Is calculated according to the maximum purge rate MAXPG. Next, at step 93, the target purge rate TGTPG is calculated by adding a predetermined constant purge change rate PGA to the purge rate PRG. Therefore, the target purge rate TG
TPG is increased by PGA every 100 msec.
Next, the routine proceeds to step 94 in FIG.

In step 94, the target purge rate TGTPG
Is greater than 0.04, ie, greater than 4%. If TGTPG <0.04, the routine jumps to step 96, and if TGTPG ≧ 0.04, the routine proceeds to step 95, where TGTPG is set to 0.04 and then step 95
Proceed to. That is, if the target purge rate TGTPG becomes too large and the purge amount becomes too large, it becomes difficult to maintain the air-fuel ratio at the stoichiometric air-fuel ratio. Therefore, the target purge rate TGT
PG should not be higher than 4%.

Next, at step 96, the drive duty ratio PGDUTY of the purge control valve 17 is calculated based on the following equation. Duty ratio PGDUTY = (Target purge rate TGTP
G / maximum purge rate MAXPG) · 100 Next, at step 98, it is determined whether the duty ratio PGUDUTY is 100 or more, that is, 100% or more. P
If GDUTY <100, the process jumps to step 99. If PDUTY ≧ 100, the process proceeds to step 98, where the duty ratio PGUDUTY is set to 100, and then to step 99. In step 99, the timer count value Ta when closing the purge control valve 17 is set to the duty ratio PGDUTY. Next, at step 100, the actual purge rate PRG is calculated based on the following equation.

Actual purge rate PRG = (maximum purge rate M
AXTG / duty ratio PGDUTY) .100 That is, the duty ratio PGDUT in step 96
In the calculation of Y, when the maximum purge rate MAXPG becomes smaller (TGTPG / MAXPG) · 100 exceeds 100, the duty ratio PGUDUTY is fixed at 100. In this case, the actual purge rate PRG is smaller than the target purge rate TGTPG. Become smaller. That is, the purge control valve 17
When the maximum purge rate MAXPG is reduced when is in the fully open state, the actual purge rate PRG is accordingly reduced. Note that (TGTPG / MAXPG) · 10
As long as 0 does not exceed 100, the actual purge rate PRG matches the target purge rate TGTPG.

Next, at step 101, it is determined whether or not the duty ratio PGDUTY is larger than 1. P
When GDUTY <1, the routine proceeds to step 102, where the purge control valve 17 is closed, and then the processing cycle is completed. On the other hand, if PGDUTY ≧ 1, the routine proceeds to step 103, where the purge control valve 17 is opened, and then the processing cycle is completed.

In the next processing cycle, step 71 in FIG.
Then, the routine proceeds to step 104, where it is determined whether or not the cut flag is set. If the cut flag has not been set, the routine proceeds to step 105, where it is determined whether the purge count value PGC is larger than 6. At this time, since PGC = 6, the routine proceeds to step 106, where it is determined whether or not the timer count value T is larger than Ta. When T <Ta, the processing cycle is completed, and T ≧ T
When it becomes a, the routine proceeds to step 81, where the purge control valve 17 is closed. Therefore, when PGC becomes larger than 6, that is, when 500 msec has elapsed since the start of the purge control, the purge control valve 17 is opened and the supply of the purge gas is started. Matches PGDUTY. Next, as the purge count value PGC increases, the target purge rate TGTP
As G increases, the duty ratio PGD
UTY increases, and thus the purge vapor amount is gradually increased. During this time, when the intake air amount Q increases as shown by A in FIG. 5, the duty ratio PGDUTY is increased as described above, and the actual purge rate PRG
Is increased at a constant rate.

Next, FIG. 11 shows steps 82 to 9
1 will be described. In step 82, it is determined whether or not the purge count value PGC is 156. When the process proceeds to step 82 for the first time after the purge control is started, the process proceeds to step 83 because PGC = 6. In step 83, it is determined whether or not the feedback correction coefficient FAF is larger than the upper threshold (FBA + X). Here, FBX is the average value FAFAV of the feedback correction coefficient FAF at the start of the purge control as described above, and X is a small constant value. FAF <(FBA + X)
If so, go to step 86.

In step 86, the feedback correction coefficient FAF is set to the lower threshold (FBA-X) shown in FIG.
It is determined whether it is smaller than. FAF> (FBA-
In the case of X), the process proceeds to step 92. In contrast, FA
If F ≦ (FBA-X), the routine proceeds to step 87, where O ₂
It is determined whether or not the output voltage V of the sensor 31 is higher than 0.45 (V), that is, whether or not the sensor 31 is rich. If it is lean, the process proceeds to step 92. On the other hand, if rich, the routine proceeds to step 88, where the purge vapor concentration coefficient FPGA
, And then proceeds to step 92. Accordingly, as shown in FIG. 6A, when FAF ≦ (FBA-X) and the air-fuel ratio is rich, the purge vapor concentration coefficient FP
GA will be increased by a constant value Y.

On the other hand, in step 83, FAF ≧ (F
If (BA + X), the routine proceeds to step 84, where the O ₂ sensor 3
1 is determined whether the output voltage V is lower than 0.45 (V), that is, whether the output voltage V is lean. If it is rich, go to step 92. On the other hand, when the engine is lean, the routine proceeds to step 85, where the constant value Y is subtracted from the purge vapor concentration coefficient FPGA, and the routine proceeds to step 92. Therefore, the feedback correction coefficient FAF is set to the upper threshold (FBA +
When the value is larger than X) and lean, the purge vapor concentration coefficient FPGA is decreased by a constant value Y. In this way, the air-fuel ratio does not change after the FAF exceeds the upper threshold (FBA + X).

On the other hand, in step 82, PGC = 15
If it is determined to be 6, that is, if 15 seconds have passed after the process first proceeds to step 82, the process proceeds to step 89, where the purge vapor concentration coefficient FPGA is calculated based on the following equation. FPGA = FPGA− (FAFAV−FBA) / (purge rate PRG · 2) That is, half of the deviation per unit purge rate PRG between the current feedback correction coefficient average value FAFAV and the feedback correction coefficient average value FBA at the start of purge is purge gas. It is subtracted from the density coefficient FPGA. In other words, half of the amount of change in FAF per unit purge rate PRG is subtracted from the FPGA. When FAFAV becomes smaller than FBA as shown in FIG. 5, the purge vapor concentration coefficient FPGA is increased as shown in FIG. Then step 9
At 0, the purge count PGC is set to 6. Therefore 15
It can be seen that the process proceeds to step 89 every second. Next, at step 91, a calculation flag indicating that the calculation of the FPGA at step 89 has been completed is set, and the routine proceeds to step 92.

On the other hand, step 77 or step 1 in FIG.
When it is determined in 04 that the cut flag has been set, the routine proceeds to step 107, where the purge count PGC is set to 1. Next, at step 80, the purge rate PR
G is made zero, and then in step 81, the purge control valve 17 is closed. That is, when the cut flag is set, the purging operation is stopped, and after the PGC becomes 6, the purging operation is started again.

FIG. 13 shows a routine for calculating the fuel injection time. This routine is executed by interruption every fixed crank angle. Referring to FIG. 13, first, in step 200, it is determined whether or not the calculation flag is set. If the calculation flag is not set, the process jumps to step 204. When the calculation flag is set, the routine proceeds to step 201, where half of the difference between the current feedback correction coefficient average value FAFAV and the feedback correction coefficient average value FBA at the start of the purge control is subtracted from the feedback correction coefficient FAF. Since the calculation flag is set every 15 seconds, this process is executed every 15 seconds. As shown in FIG.
When V becomes smaller than FBA, as shown in FIG.
Is increased. That is, as shown in FIG.
Is increased by half of the decrease amount of the FAF every 15 seconds. At this time, the purge vapor concentration coefficient FPGA is increased by an amount corresponding to the increase amount of the FAF.

Next, at step 202, (FAFAV-FBA) / 2 is subtracted from FAFAV in order to change FAFAV by an amount corresponding to the change in FAF. Next, at step 203, the calculation flag is reset, and the routine proceeds to step 204. In step 204, the purge A / F correction coefficient FPG is calculated based on the following equation. Purge A / F Correction Coefficient FPG = − (Purge Vapor Concentration Coefficient FPGA · Purge Rate PRG) FIG. 5 shows how the purge A / F correction coefficient FPG changes. Next, at step 205, the basic fuel injection time TP is calculated, and then at step 206, the correction coefficient K is calculated. Next, at step 207, the fuel injection time TAU is calculated based on the following equation.

TAU = TP · {1 + K + (FAF−1) + FPG} Fuel is injected from the fuel injection valve 4 based on the fuel injection time TAU.

[0054]

According to the present invention, it is possible to prevent the air-fuel ratio from fluctuating during purging.

[Brief description of the drawings]

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

FIG. 2 is an overall view of an internal combustion engine.

FIG. 3 is a flowchart for calculating a feedback correction coefficient.

FIG. 4 is a diagram showing a change in a feedback correction coefficient.

FIG. 5 is a time chart during a purge control.

FIG. 6 is a time chart at the start of purging.

FIG. 7 is a flowchart for controlling a cut flag.

FIG. 8 is a flowchart for performing a purge control initialization process.

FIG. 9 is a flowchart for performing purge control.

FIG. 10 is a flowchart for performing purge control.

FIG. 11 is a flowchart for performing purge control.

FIG. 12 is a flowchart for performing purge control.

FIG. 13 is a flowchart for calculating a fuel injection time.

[Explanation of symbols]

 4 fuel injection valve 9 throttle valve 11 canister 17 purge control valve 31 air-fuel ratio sensor

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Tohru Kisokoro 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Co., Ltd. (56) References JP-A-57-52663 (JP, A) 131047 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) F02M 25/08 301 F02M 25/08 F02D 41/02 330 F02D 41/14 310 F02D 41/14 330

Claims (6)

(57) [Claims] In an internal combustion engine provided with a purge control valve for controlling a purge amount of a purge gas in a purge passage for supplying evaporated fuel generated in a fuel tank into an engine intake passage, a purge amount and an intake air amount. Reference purge rate calculating means for calculating a reference purge rate determined by the operating state of the engine for the same purge control valve opening degree, target purge rate setting means for setting a target purge rate, and a reference purge rate. Purge control valve opening control means for controlling the opening amount of the purge control valve according to the ratio of the target purge rate to
A fuel supply control device for an internal combustion engine, wherein the target purge rate is gradually changed when the target purge rate is to be changed. 2. The fuel supply control device for an internal combustion engine according to claim 1, wherein the target purge rate is gradually increased from zero when the purging operation is started. 3. A fuel injection amount calculating means for calculating a fuel injection amount, an air-fuel ratio sensor disposed in an engine exhaust passage for detecting an air-fuel ratio, and an air-fuel ratio sensor based on an output signal of the air-fuel ratio sensor. First injection amount correction means for correcting the fuel injection amount with a feedback correction coefficient so that the fuel ratio becomes a target air-fuel ratio, and purge vapor concentration for calculating a purge vapor concentration based on a deviation of the feedback correction coefficient generated when purging is performed. 2. The fuel supply control device for an internal combustion engine according to claim 1, further comprising: a calculation unit; and a second injection amount correction unit that corrects a fuel injection amount based on a purge vapor concentration when purging is performed. 4. A fuel injection amount calculating means for calculating a fuel injection amount, an air-fuel ratio sensor disposed in an engine exhaust passage for detecting an air-fuel ratio, and an air-fuel ratio sensor based on an output signal of the air-fuel ratio sensor. First injection amount correction means for correcting the fuel injection amount by a feedback correction coefficient so that the fuel ratio becomes a target air-fuel ratio; and purge vapor per unit target purge rate based on a deviation of the feedback correction coefficient generated when purging is performed. 2. A purge vapor concentration calculating means for calculating a concentration, and a second injection amount correcting means for correcting a fuel injection amount based on a product of a purge vapor concentration and a target purge rate when purging is performed. Fuel control device for an internal combustion engine. 5. A target purge rate is set in an internal combustion engine provided with a purge control valve for controlling a purge gas purge amount in a purge passage for supplying evaporated fuel generated in a fuel tank into an engine intake passage. Target purge rate setting means, and purge control valve opening degree control means for controlling the opening degree of the purge control valve so that the ratio between the purge amount and the intake air amount becomes the target purge rate in accordance with the intake air amount. A fuel supply control device for an internal combustion engine, wherein the target purge rate is gradually changed when the target purge rate is to be changed. 6. The fuel supply control device for an internal combustion engine according to claim 5, wherein the target purge rate is gradually increased from zero when the purging operation is started.