JPH11107864A - Control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the occurrence of displacement in an air-fuel ratio due to uncontrollability due to purge to an intake passage for evaporated fuel and to suppress the occurrence of unevenness in an air-fuel ratio due to defective purge distribution between cylinders. SOLUTION: In an engine wherein feedback control of an air-fuel ratio is effected based on the output of an O2 and a control of purge to an intake passage for evaporated fuel, a purge factor is corrected by a high density correction value considering the surging limit of a vehicle and a purge decrease amount correction value considering the limit of feedback control of an air-fuel ratio. In this case, based on a ratio tratio between of an actual fuel injection amount to a demand fuel injection amount corresponding to a target air-fuel ratio, the limit of feedback control of an air-fuel ratio to a demand fuel injection amount corresponding to a target air-fuel ratio, the limit of feedback control of an air-fuel ratio is decided, and when reaching a threshold, a flag xpgaf is erected and a purge reduction amount correction value pgaf is gradually increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for an engine that performs feedback control of an air-fuel ratio and controls purging of fuel vapor generated in a fuel tank into an intake passage.

[0002]

BACKGROUND ART In an engine of a fuel injection quantity feedback correction to control feedback of the air-fuel ratio of the engine to the target air-fuel ratio based on the output of the O ₂ sensor provided in the engine exhaust system, the evaporative fuel generated in the fuel tank When the purge to the intake passage is performed, in an operation region in which the purge gas has a high concentration and the required fuel injection amount is small, the ratio of the fuel including the evaporated fuel becomes too large, and the correction value of the air-fuel ratio feedback correction becomes lean ( Air-fuel ratio lean side)
There is a case where the feedback control of the air-fuel ratio becomes impossible because further correction cannot be performed. Therefore, it has been conventionally performed to detect that the feedback correction value of the air-fuel ratio control sticks to the lean side, close the purge valve, and reduce or stop the purge of the evaporated fuel.
The one described in Japanese Utility Model Laid-Open No. 58-191361 is an example of such a control device.

[0003]

As described above, when the correction value of the air-fuel ratio feedback correction is stuck on the lean side due to purging, the air-fuel ratio cannot be controlled as described above, and there is one limitation of the purge amount. However, the limit of the purge amount is not limited to this.In addition, if the fuel injection amount is smaller than the minimum injection pulse width derived from the characteristics of the fuel injection valve, the air-fuel ratio cannot be controlled. There is a limit, and when this limit is reached, a purge reduction is still required. Further, when the amount of fuel in the purge gas exceeds the limit of the fuel injection amount from the fuel injection valve, the distribution of the purge gas to each cylinder is deteriorated, and therefore, the variation of the air-fuel ratio between the cylinders is increased. As a result, emission and traveling performance deteriorate (surging of the vehicle occurs). Therefore, it is necessary to perform a purge correction so as not to cause a purge distribution failure.

It is desired that purge control effectively meet all of these various requirements. However, if the amount of purge is reduced or stopped only after the feedback correction value of the air-fuel ratio sticks to the lean side as in the above-described conventional control, the desired purpose is to end the state in which the air-fuel ratio cannot be controlled in a short time. In some cases, the purpose cannot be sufficiently achieved, and purge control with a high degree of freedom that can effectively respond to various requirements including the minimum injection pulse width and purge distribution cannot be performed.

Therefore, an engine capable of reducing the deviation of the air-fuel ratio due to the inability to control the air-fuel ratio feedback due to the purge of the evaporated fuel into the intake passage, and suppressing the variation in the air-fuel ratio among the cylinders due to poor purge distribution. The problem is to provide a control device of the type described above.

[0006]

The engine control apparatus of the present invention In order to achieve the above object, according to the fuel injection amount feedback correction target air-fuel ratio of the engine from the fuel injection valve based on the output of the O ₂ sensor in the engine exhaust system A purge passage for purging evaporated fuel generated in the fuel tank to the intake passage of the engine, a purge valve for opening and closing the purge passage, and performing a purge in a predetermined operation region. In addition, in the control device of the engine including the purge control means for controlling the purge valve so as to adjust the purge amount, the fuel injection amount from the fuel injection valve is corrected in consideration of the air-fuel ratio deviation due to the execution of the purge when the purge is executed. A fuel injection amount purge correction unit that corrects according to the value and a value corresponding to the target air-fuel ratio when the purge amount is not considered. It is provided with a purge amount correction means for correcting the purge amount based on the ratio of the actual fuel injection amount from the fuel injection valve during purging execution to the fuel injection amount.

[0007] According to this control device, feedback correction of the fuel injection amount is performed based on the output of the O ₂ sensor, whereby the air-fuel ratio of the engine is feedback-controlled to the target air-fuel ratio. Further, a correction value is set in consideration of a deviation of the air-fuel ratio due to the execution of the purge, and when the purge is executed, the fuel injection amount is corrected based on the correction value. Then, the purge amount of the evaporated fuel is corrected by the ratio of the actual fuel injection amount from the fuel injection valve during the purge to the required fuel injection amount corresponding to the target air-fuel ratio when the purge amount is not considered. If the ratio of the actual fuel injection amount from the fuel injection valve at the time of performing the purge to the required fuel injection amount corresponding to the target air-fuel ratio when the purge amount is not considered is small, the amount of fuel due to the purge is large. The correction allows the purge amount to be controlled. Then, before the feedback correction value of the air-fuel ratio sticks to the lean side, the purge reduction is started, so that the state in which the air-fuel ratio cannot be controlled can be ended in a short time. In addition, since the purge amount can be reduced in accordance with the purge limit at an arbitrary level regardless of whether the feedback correction value of the air-fuel ratio is stuck to the lean side, a purge having a large degree of freedom that can effectively cope with various demands. It is possible to control the air-fuel ratio due to the inability to control the air-fuel ratio feedback caused by the purge, and to suppress the inter-cylinder variation in the air-fuel ratio due to poor purge distribution.

[0008] The purge amount correcting means prevents the purge amount from exceeding the predetermined purge amount when the ratio of the actual fuel injection amount from the fuel injector during the purge to the required fuel injection amount is smaller than 1 and smaller than a predetermined value. The purge amount can be corrected to decrease. The fact that the ratio of the actual fuel injection amount from the fuel injection valve at the time of purging to the required fuel injection amount is smaller than 1 means that the fuel in the purge gas is equal to or greater than a predetermined amount. When the value reaches the above-mentioned predetermined value corresponding to a limit value for suppressing air-fuel ratio feedback uncontrollability or poor purge distribution, the purge amount is reduced so that the purge amount does not exceed the predetermined amount. Thus, the state in which the air-fuel ratio feedback cannot be controlled due to the sticking of the feedback correction value can be ended in a short time. In addition, by setting the above-mentioned predetermined value, it is also possible to realize, for example, suppression of the inter-cylinder variation of the air-fuel ratio due to the poor purge distribution.

[0009] The purge amount correction means may be configured to determine whether the ratio of the actual fuel injection amount from the fuel injector during the purge to the required fuel injection amount is greater than 1 and equal to or greater than a predetermined value.
The purge amount can be reduced. The fact that the ratio of the actual fuel injection amount from the fuel injection valve at the time of purging to the required fuel injection amount is greater than 1 means that the fuel concentration of the purge gas is low, and a large amount of air may enter and the air-fuel ratio may shift. Therefore, in this case, when the ratio becomes equal to or more than the predetermined value, the purge amount is corrected to the decreasing side, so that the deviation of the air-fuel ratio can be prevented.

[0010]

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

FIG. 1 shows a schematic structure of an engine to which the present invention is applied. In this figure, reference numeral 1 denotes an engine body having a cylinder, and an intake port 3 opened and closed by an intake valve and an exhaust port 4 opened and closed by an exhaust valve are opened in a combustion chamber 2 of the cylinder.
An intake passage 5 is connected to the intake port 3, and an exhaust passage 13 is connected to the exhaust port 4.

In the intake passage 5, an air cleaner 6, an air flow sensor 7, and a throttle valve 8 are arranged in this order from the upstream side.
And a surge tank 9, and an injector (fuel injection valve) 10 for injecting fuel is provided near the intake port 5. Further, an ISC passage 11 that bypasses the throttle valve 8 is provided.
The C passage 11 is provided with an ISC valve 12 for adjusting the air flow rate in the passage 11 for controlling the idle speed. On the other hand, an O ₂ sensor 14, a catalyst device 15, and the like are provided in the exhaust passage 13. An idle switch 16 and an engine speed sensor 17 are provided in the intake passage 5 and the engine body 1, respectively.

A fuel system for supplying fuel to the injector 10 includes a fuel tank 20, a fuel pump 21, a fuel supply passage 22, and a return passage 23. The fuel pump 21 allows the fuel from the fuel tank 20 to pass through the fuel supply passage 22. Fuel is sent to the injector 10. The fuel filter 2 is provided in the fuel supply passage 22.
4 are interposed. The return passage 23 is provided with a pressure regulator 25 for adjusting the fuel pressure in accordance with the intake pressure.

An evaporative fuel supply system is provided for supplying the evaporative fuel generated in the fuel tank 20 to the intake side. The evaporative fuel supply system includes a purge passage 30. The purge passage 30 has an upstream end at the fuel tank 20.
And a downstream end thereof is connected to the surge tank 9 of the intake passage 5. A canister 31 for adsorbing the evaporated fuel is provided in the middle of the purge passage 30.
2 are connected.

In the purge passage 30 between the fuel tank 20 and the canister 31, an open / close valve (hereinafter, referred to as a TPCV valve) 34 composed of a solenoid valve is provided in parallel with the check valve 33. The air release passage 32 has an air filter 35 and a check valve 3.
6 and an opening / closing valve (hereinafter, referred to as a CDCV valve) 37 composed of a solenoid valve. TPCV valve 34 and CDCV valve 37
Constitutes a passage opening / closing means which enables opening / closing of the purge passage 30 and opening / closing of the atmosphere opening portion between the fuel tank 20 and the intake passage 5 respectively.

The purge passage 30 between the canister 31 and the surge tank 9 is provided with a purge valve 38 composed of a duty solenoid valve for adjusting a supply amount (purge amount) of a purge gas containing evaporated fuel. Further, the fuel vapor supply system is provided with a fuel tank pressure sensor (hereinafter referred to as an FTP sensor) 39 as pressure detecting means for detecting the pressure of the purge passage 30 on the fuel tank 20 side.

The purge valve 38 and the TPCV valve 3
4 and the CDCV valve 37 are connected to an engine control unit (ECU) 40 as a control unit. The engine control unit 40, the air flow meter 7, O ₂ sensor 14, the idle switch 16, the rotational speed sensor 17, FT
Upon receiving a signal from the P sensor 39 or the like, the injector 10
, The ISC valve 12, and the like, and the purge valve 38, the TPCV valve 34, and the CDCV valve 37.

The engine control unit 40 performs feedback correction of the fuel injection amount from the injector 10 based on the output of the O ₂ sensor 14 in a predetermined operation range (O ₂ feedback range) to control the air-fuel ratio of the engine to a target air-fuel ratio. At the same time, when the fuel vapor is supplied (when the purge is executed), the fuel injection amount correction corresponding to the learning is performed, and the feedback control of the ISC valve 12 is performed and the learning is performed during the idling operation.

The engine control unit 40 adsorbs the canister 31 in the low / medium load region where the intake pipe pressure becomes negative and the purge gas is sucked into the intake passage 5 (surge tank 9), and in the O ₂ feedback region. The duty of the purge valve 38 is controlled such that the evaporated fuel is introduced (purged) into the intake passage 5 at a predetermined purge rate. This purge control will be described in detail below.

In the purge control, the ratio of the purge amount to the total gas amount including the intake air of the engine and the purge gas, that is, the target value of the purge rate (target purge rate) is calculated as follows:
It is set in advance as a map value. Then, high concentration correction is performed in consideration of the surging limit of the vehicle, and further, barge reduction correction is performed in consideration of the control limit of the air-fuel ratio feedback, and the final purge valve opening (duty ratio) is calculated. Control.

FIG. 2 is a flowchart showing the flow of the entire purge control. This flow corresponds to step S101.
Then, the target purge rate is searched from the map of the engine speed and the load. Then, in step S102, the high density correction is performed, and the high density correction value pgaf is added to the target purge rate.
Multiply by 2 divided by 100 (pgaf2 / 100). Then, in step S103, the target mass flow rate of the purge gas is calculated based on the target purge rate after the high concentration correction,
Next, in step S104, the purge reduction correction is performed by subtracting the purge reduction correction value pgaf from 1 (1).
-Pgaf) is multiplied by the target mass flow rate. In step S105, the purge target mass flow rate is converted to calculate a target volume flow rate, and in step S106, a purge valve opening (duty ratio) required to flow the target volume flow rate is calculated.

The purge reduction correction is based on a variable called ratio, which is a ratio of the actual fuel injection amount (actual injection pulse width) to the required fuel injection amount (required injection pulse width) with respect to the target air-fuel ratio without considering the purge amount. Do. That is, the control limit of the air-fuel ratio feedback is determined based on the value of the ratio, and the purge reduction correction value pgaf is set by feedback using the limit value based on the ratio as a threshold. FIG. 3 is a time chart thereof. FIG. 4 is a flowchart showing the flow of the purge decrease correction value calculation.

In the flow of FIG. 4, at step S201, t
Calculate the value of ratio. Then, step S202
Then, it is determined whether the value of ratio is equal to or greater than an upper limit value (a purge reduction start threshold value where the ratio is greater than 1) or less than or equal to a lower limit value (a purge reduction start threshold value where the ratio is smaller than 1). In the time chart of FIG. 3, ratio = 1 indicates a line where the purge amount is zero. Cevln is a negative value corresponding to the learned value of the fuel injection amount correction at the time of performing the purge, and
A ratio smaller than tio = 1 by | cevln | + | KPTRMN (negative value) | corresponds to the above lower limit. The upper limit is cevln from ratio = 1.
The value is set to a value larger by + KPTRMX (positive value).
Here, KPTRMN and KPTRMX are respectively set in consideration of the control limit of the air-fuel ratio feedback.

If the ratio is equal to or lower than the lower limit value, the air-fuel ratio is shifted to the rich side due to the purge, and the feedback control becomes impossible.
gaf = 1). Then, in step S204, x
Checking whether pgaf = 1, if xpgaf = 1, in step S205, the purge decrease correction value pgaf is gradually increased (I value is added). Then, the process returns, and steps S201 to S205 are repeated, and
While tio is equal to or smaller than the lower limit, p is set in step S205.
gaf is gradually increased until the guard value is reached. Then, when the ratio becomes larger than the lower limit, it is further determined in step S206 that hysteresis is added. And the flag xpgaf is lowered (xp
gaf = 0). In step S207, the flag xp
When the gaf is lowered, the flag xp is again set in step S204.
gaf is determined, and the determination at this time is NO (xpg
af = 0), and in this case, the purge reduction correction value pgaf is gradually reduced to the original value in step S208 (I value is reduced).

If the ratio is equal to or higher than the upper limit in step S202, a large amount of air enters due to the purging and the air-fuel ratio shifts.
Proceed to 3 and set xpgaf = 1. Then, in step S204, it is determined whether or not xpgaf = 1, and
If f = 1, in step S205, the purge decrease correction value pgaf is increased (I value is added). Then, the process returns and repeats steps S201 to S205,
While the ratio is equal to or more than the upper limit, step S20
In step 5, pgaf is gradually increased until the guard value is reached. When the ratio becomes smaller than the upper limit, it is further determined in step S206 that hysteresis has been added. The program proceeds to xpgaf = 0, and the flag xpgaf is determined again in step S204.
Since this determination is NO (xpgaf = 0), the process proceeds to step S208, and the purge reduction correction value pgaf is gradually reduced to the original value (I value is reduced).

In the high concentration correction, the actual fuel injection amount (actual injection pulse width) with respect to the required fuel injection amount (required injection pulse width) corresponding to the target air-fuel ratio when the purge amount is not considered.
The ratio is determined based on a ratio variable, and the value of the ratio determines the limit of the occurrence of surging. Then, feedback is performed so that this ratio does not exceed the surging limit value, and the high density correction value p
gaf2 is set. FIG. 5 is a time chart thereof. FIG. 6 is a flowchart showing the flow of the high density correction value calculation.

The flow of FIG.
Atio value is calculated, and in step S302, trat
It is determined whether or not the value of io is equal to or less than a threshold value (surging limit value). If the ratio is equal to or less than the threshold, in step S303, the high density correction flag x
Set pgaf2 (set xpgaf2 = 1). Then, in step S304, it is determined whether or not xpgaf2 = 1, and if xpgaf2 = 1, the process proceeds to step S305.
Then, the high density correction value pgaf2 is gradually reduced (I value is reduced). Then, the process returns to steps S301 to S301.
By repeating 305, pgaf2 is gradually reduced while the ratio is equal to or smaller than the threshold. Where pga
f2 is a positive value, and reducing the value means increasing the correction toward the decrease side.

When the ratio becomes larger than the threshold value, it is further determined in step S306 that a hysteresis is added. When the ratio becomes larger than the return threshold value set by the threshold value + the hysteresis, the process proceeds to a step S307. Proceed to. Then, the flag xpgaf2 is lowered (xpgaf2 = 0).

When the flag xpgaf2 is lowered in step S307, the flag xpgaf2 is again set in step S304.
Is determined, the determination at this time is NO (xpgaf2
= 0), and in this case, the high-density correction value pgaf2 is gradually increased to the original value in step S308 (I value is added).

The calculation of the ratio of step S201 in the flow of FIG. 4 and the calculation of the ratio of step S301 in the flow of FIG. 6 are performed according to the flowchart shown in FIG.

In the flow of FIG. 7, in step S401, a required fuel injection amount (required injection pulse width) of the engine for burning at the target air-fuel ratio is calculated. Here, the required fuel injection amount is calculated by multiplying the basic injection amount based on the intake air charging efficiency by various correction coefficients, and is a value that does not consider the purge amount.

Then, in step S402, the actual fuel injection amount (actual injection pulse width) is calculated. The actual fuel injection amount is calculated by correcting the required fuel injection amount by a learning value of a deviation due to the amount of the purge gas, and corresponds to the fuel actually injected from the injector 10.

Then, in step S403, the ratio of the actual fuel injection amount to the required fuel injection amount is determined, and the value is tr
atio.

[0034]

According to the present invention, a state in which air-fuel ratio control is impossible due to a limit of air-fuel ratio feedback correction due to purging of fuel vapor into an intake passage and a limit of a minimum injection pulse width is terminated in a short time. Of the air-fuel ratio between cylinders due to poor purge distribution when the purge amount is large can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an engine to which the present invention is applied.

FIG. 2 is a flowchart of the entire purge control in the embodiment.

FIG. 3 is a time chart of purge reduction correction in the embodiment.

FIG. 4 is a flowchart of a purge reduction correction value calculation in the embodiment.

FIG. 5 is a time chart of high density correction in the embodiment.

FIG. 6 is a flowchart of a high density correction value calculation in the embodiment.

FIG. 7 is a flowchart of a ratio operation in the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine main body 5 Intake passage 9 Surge tank 10 Injector (fuel injection valve) 20 Fuel tank 30 Purge passage 31 Canister 38 Purge valve 40 Engine control unit

Claims (3)

[Claims] An air-fuel ratio feedback control means for feedback-correcting a fuel injection amount from a fuel injection valve based on an output of an O ₂ sensor of an engine exhaust system and controlling an air-fuel ratio of an engine to a target air-fuel ratio. A purge passage for purging evaporative fuel generated in the tank into an intake passage of the engine, a purge valve for opening and closing the purge passage, and controlling the purge valve to execute a purge in a predetermined operation region and adjust the purge amount. A fuel injection amount purge correction unit that corrects a fuel injection amount from the fuel injection valve at the time of purging with a correction value in consideration of a deviation of an air-fuel ratio due to execution of a purge. The fuel injection valve at the time of purging the required fuel injection amount corresponding to the target air-fuel ratio when the amount is not considered Engine control apparatus wherein in that a purge amount correction means for correcting the purge amount based on the ratio of the actual fuel injection amount. 2. The purge amount correction means according to claim 1, wherein the ratio of the actual fuel injection amount from the fuel injection valve during the purge to the required fuel injection amount is smaller than 1 and equal to or smaller than a predetermined value. 2. The engine control apparatus according to claim 1, wherein the purge amount is corrected so as not to be as described above. 3. The purge amount correction means, when the ratio of the actual fuel injection amount from the fuel injector during the purge execution to the required fuel injection amount is greater than 1 and equal to or more than a predetermined value, adjusts the purge amount. 3. The engine control device according to claim 1, wherein the control is performed for weight reduction.