JP2898468B2 - Evaporative purge control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an evaporative purge control method for an evaporative emission purge system mainly applied to automobiles.

[0002]

2. Description of the Related Art Conventionally, as an evaporative purge control method of this kind, for example, a gasoline vapor (evaporative emission) from a fuel tank described in Japanese Patent Application Laid-Open No. 2-245461 is purged into an intake system when the internal combustion engine is idling. Like a purge control device, for example, a duty VSV is provided in a passage communicating the charcoal canister and the intake system, and the duty VSV is opened and closed with a variable duty to purge gasoline vapor attached to the charcoal canister. There is known an apparatus that varies a valve opening speed of a duty VSV according to the concentration of gasoline vapor.

Further, an evaporation reduction correction coefficient for correcting the gasoline vapor amount to be reduced so that the purged gasoline vapor does not affect the learning of the A / F learning correction coefficient is set. In some cases, the air-fuel ratio is controlled to be maintained near the stoichiometric air-fuel ratio.

[0004]

In the above configuration, the opening of the duty VSV is varied according to the concentration of gasoline vapor, but when the concentration is high, the air-fuel ratio tends to become rich. In such a case, the gasoline vapor amount is reduced by the evaporation reduction correction coefficient KPG. However, if the fuel injection amount is determined by changing the evaporation reduction correction coefficient KPG at a constant value regardless of the concentration, the gasoline concentration is reduced. If the concentration is high, there is no problem, but if the concentration is high, the change in the evaporation reduction correction coefficient KPG does not follow the gasoline vapor amount. To compensate for this, feedback correction using the A / F feedback correction coefficient FAF is performed. However, as shown in FIG. 5, when the purge is stopped while the reduction correction is being performed by the feedback correction, the average value FA of the A / F feedback correction coefficient FAF is determined.
Since the FAV does not instantaneously return to the basic value of 1.0 following the closing of the duty VSV, NOx increases and emission deteriorates.

[0005] An object of the present invention is to solve such a problem.

[0006]

In order to achieve the above object, the present invention takes the following measures. That is, the evaporation purge control method according to the present invention includes:
At least the air-fuel ratio is adjusted by the feedback correction coefficient.
In addition to the feedback control , the gasoline vapor adsorbed by the gasoline vapor adsorbing means is discharged with the passage of time based on the purge duty ratio when idling operation is performed.
When purging the intake system by gradually increasing the opening of the valve, a reduction correction coefficient for correcting the fuel amount in accordance with the purged amount of gasoline vapor is set, and the reduction correction coefficient and An evaporative purge control method in which an air-fuel ratio is controlled by performing addition and subtraction with a predetermined value to perform a purge, wherein the predetermined value is different from at least a subtraction tendency.
Set a large set value and a set value with a small subtraction tendency ,
Feedback supplementation of the gasoline vapor concentration during purging
Determined on the basis of the positive coefficients, the determined concentration of the concentration determination
If it is less than the switching judgment value for the
Selected setting value, and the determined density is equal to or greater than the switching determination value.
And if it is equal to or greater than the basic value that is greater than the switching determination value,
It is characterized in that a set value with a small subtraction tendency is selected, and the set value is switched in accordance with the level of the determined density to perform addition and subtraction with the weight loss correction coefficient.

[0007]

With such a configuration, the reduction correction coefficient is varied according to the concentration of gasoline vapor during the purge. That is, the determined density is used for the density determination.
Is smaller than the switching determination value of
Add or subtract the weight loss correction coefficient according to the set value, and determine the density
Is greater than or equal to the switching judgment value and larger than the switching judgment value
In the above case, the value is reduced by the small set value of the subtraction tendency.
Addition and subtraction with the amount correction coefficient. Therefore, the air-fuel ratio can always be controlled near the theoretical value, and the gasoline vapor purge
The feedback correction coefficient suddenly increases when
In addition, the emission does not deteriorate.

[0008]

An embodiment of the present invention will be described below with reference to the drawings.

An engine 100 schematically shown in FIG. 1 is for an automobile, and its intake system 1 is provided with a throttle valve 2 which opens and closes in response to an accelerator pedal (not shown). A tank 3 is provided.
Intake manifold 4 of intake system 1 communicating with surge tank 3
A fuel injection valve 5 is further provided near one end of the fuel injection valve 5, and the fuel injection valve 5 is controlled by an electronic control device 6. Further, an O ₂ sensor 21 for measuring the oxygen concentration in the exhaust gas is attached to the exhaust system 20 at a position upstream of a three-way catalyst 22 provided in a pipe leading to a muffler (not shown). I have. This O ₂ sensor 21
Outputs a voltage signal h corresponding to the oxygen concentration.
Reference numeral 23 denotes a charcoal canister as gasoline vapor adsorbing means for adsorbing gasoline vapor retained in the fuel tank 24. The atmosphere is introduced from the lower part of the charcoal canister 23, and opens and closes a duty VSV 26 provided in the charcoal canister 23 and a pipe 25 communicating with a pipe line between the throttle valve 2 and the surge tank 3. The duty VSV 26 is controlled to open and close by the ratio, that is, the purge duty ratio described below, so that the purge amount of the gasoline vapor adsorbed by the charcoal canister 23 is controlled.

The electronic control unit 6 includes a central processing unit 7
, Storage device 8, input interface 9, A / D
The microcomputer mainly comprises a converter 10 and an output interface 11. The input interface 9 has an intake pressure from an intake pressure sensor 13 for detecting a pressure in the surge tank 3. A signal a, a rotation speed signal b from a rotation speed sensor 14 for detecting an engine rotation speed NE, a vehicle speed signal c from a vehicle speed sensor 15 for detecting a vehicle speed, and an idle for detecting an open / closed state of the throttle valve 2. Switch 1
LL signal d from 6, water temperature signal e from the water temperature sensor 17 for detecting a cooling water temperature of the engine, such as a voltage signal h from the O ₂ sensor 21 as described above are input. On the other hand, from the output interface 11, a fuel injection signal f for the fuel injection valve 5, an ignition pulse g for the spark plug 18, and an evaporative purge duty signal j for turning on and off at a predetermined purge duty ratio EPDUTY for the duty VSV26. , Respectively. The A / D converter 10 converts an analog signal such as a voltage signal output from the O ₂ sensor 21 input from the input interface 11 into a digital signal, and outputs the A / D converted signal to the central processing unit 7. I do.

The electronic control unit 6 uses the intake pressure signal a output from the intake pressure sensor 13 and the rotational speed signal b output from the rotational speed sensor 14 as main information, and various types of information determined according to the engine conditions. Based on the correction coefficient and the voltage signal h from the O ₂ sensor 21, the A / F feedback correction coefficient F
The basic injection time TP is corrected by AF or an A / F learning correction coefficient KG learned under predetermined operating conditions to determine the fuel injection valve opening time, that is, the injector final energization time T,
A program for feedback control for controlling the fuel injection valve 5 based on the determined energization time T and injecting fuel corresponding to the engine load from the fuel injection valve 5 to the intake system 1 is incorporated. Further, in this program, when the idling operation is performed, the gasoline vapor adsorbed by the charcoal canister 23 is gradually decomposed over time based on the purge duty ratio EPDUTY.
When purging the intake system 1 by increasing the opening of the utility VSV 26, an evaporation reduction correction coefficient KPG for correcting the fuel amount in accordance with the purged amount of gasoline vapor is set, and the evaporation reduction is performed. performs purge control the air-fuel ratio by adding or subtracting a correction coefficient KPG with a predetermined value, sizes of different subtraction tendency value as the predetermined value
The set value, ie , the set value KEPMI2 for the high concentration of the evaporator, is reduced.
The set value with a small calculation tendency, that is, the set value KE for evaporative normal use
PMI1 is set, the concentration of the gasoline vapor being purged is determined based on the A / F feedback correction coefficient FAF, and the determined concentration is a switching determination value K for the concentration determination.
If the value is lower than PGCHG, the set value for high evaporation concentration KE
PMI2 is selected, and the determined density is the switching determination value KPG
CHG or more and larger than the switching determination value KPGCHG
If the value is equal to or more than the basic value, the evaporative normal setting value KEPMI1
Select, by switching the set value according to the level of the determined concentrations are programmed to subtract evaporative loss correction coefficient KPG and pressure. In this embodiment, the calculation of the effective injection time TAU is performed by the following arithmetic expression.

TAU = TP * FAF * KPG * α (where α represents another correction coefficient) FIGS. 2 and 3 show the outline of the evaporative purge control program.
It is as shown in.

In step 51, it is determined whether or not the purge duty ratio EPDUTY is zero, in other words, whether or not the duty VSV 26 is closed (opening = 0). The process proceeds to step 61 if not. In step 52, it is determined whether or not the evaporation reduction correction coefficient PKG is less than 1.0, which is the basic value. In step 53, the value of the A / D converted signal of the voltage signal output from the _{O 2} sensor 21 A / D value OXAD setting value LV
It is determined whether or not the value is equal to or greater than EPOX.
Proceed to. In step 54, the evaporation reduction correction coefficient KPG
Then, the addition value KPGINC at the time of the return to the evaporative reduction is added to the above-mentioned value, and the routine proceeds to step 55. In step 55, step 54
It is determined whether or not the evaporation reduction correction coefficient KPG calculated in the step is larger than 1.0. If the coefficient is larger than 1.0, the routine proceeds to step 56, and if it is smaller than 1.0, the learning routine GR
Proceed to. In step 56, the evaporative reduction correction coefficient KPG exceeding 1.0 is set to 1.0, and the learning routine GR
Proceed to.

The learning routine GR may perform learning of the A / F learning correction coefficient KG by a method widely known in the art. That is, for example, for each skip of the A / F feedback correction coefficient FAF, an arithmetic mean of the immediately preceding skip value and the immediately preceding skip value is obtained, and it is detected which learning zone the engine operating condition corresponds to, Each time the air-fuel ratio feedback correction coefficient FAF is skipped, the value of the A / F learning correction coefficient KG in the learning zone is updated according to the magnitude of the arithmetic mean, and the A / F learning correction coefficient KG updated by the learning is used as the fuel injection amount. This is done by reflecting the above. The learning zone is defined by the engine speed NE and the intake pressure PM over substantially the entire operating range of the engine. When such learning is performed, it is detected whether or not the vehicle is in an operating condition that satisfies the learning condition. Specifically, for example, a cooling water temperature as an engine temperature is measured by a water temperature signal e from the water temperature sensor 17, and the measured cooling water temperature is a predetermined temperature α, for example, 70 ° C.
It is determined whether the temperature is equal to or higher than the predetermined value. If it is determined that the cooling water temperature is equal to or higher than the predetermined temperature α, the transient air-fuel ratio correction coefficient FA
It is programmed to determine whether or not EW is zero. If it is zero, it is determined whether or not the operating condition is within the learning zone. If it is within the learning zone, learning is performed. These determinations determine whether or not the operating state of the engine at the time of idling satisfies a predetermined learning condition. The determination that the engine is not warming up from the cooling water temperature by the transient air-fuel ratio correction coefficient F
Since the AEW is zero, it is determined that the operation is not in the transient state, and that the operation condition is in the learning zone. When at least the above three conditions are not satisfied, the process proceeds to a subroutine without learning as a driving situation that cannot be learned.

In FIG. 3, at step 61, the A / F
It is determined whether or not the average value FAFAV of the feedback correction coefficient FAF is less than a switching determination value KPGCHG of the evaporation reduction correction coefficient KPG.
If so, the process proceeds to step 71. That is, in step 61, the concentration of gasoline vapor is determined based on the value of the average value FAFAV, and the switching determination value KPGCH
If it is less than G, it is determined that the gasoline vapor concentration during the purge is high. When the density determination is completed,
In step 62, the evaporative high concentration set value KEPMI2 is determined as the evaporative decrease correction value KEPMI.
Proceed to 3. In the initial state, the evaporation reduction amount correction value KEPMI is set to an evaporation normal setting value KEPMI1 which is smaller than the evaporation high concentration setting value KEPMI2. In this embodiment, as the evaporation reduction correction value KEPMI which is a predetermined value to be added to or subtracted from the evaporation reduction correction coefficient KPG, an evaporation normal setting value KEPMI1 and an evaporation high concentration setting value KEPMI2 having different values are set. On the other hand, in step 71, it is determined whether or not the average value FAFAV is equal to or greater than 1.0, which is the basic value. If it is, the process proceeds to step 72; Step 7
In step 2, an evaporative normal set value KEPMI1 is determined as the evaporative decrease correction value KEPMI, and the routine proceeds to step 63. In step 63, the A / F feedback correction coefficient FAF
Is the average value FAFAV of the lower evaporative weight loss calculation value lower limit KPGLO
It is determined whether or not it is smaller. If smaller, the process proceeds to step 64; otherwise, the process proceeds to step 81. In step 64, the evaporation reduction correction value KEPMI is subtracted from the evaporation reduction correction coefficient KPG, and the routine proceeds to step 65. In step 65, the calculated evaporation reduction coefficient KPG is calculated.
Is within the set upper limit KPGHI and lower limit KPGLO, the evaporative reduction correction is performed using the evaporative reduction correction coefficient KPG, and the upper limit K of the evaporative reducer is calculated.
If it exceeds the PGHI or the lower limit KPGLO, the evaporative reduction calculation is performed by the upper limit KPGHI or the lower limit KPGLO, respectively. In step 81, the A / F
It is determined whether or not the average value FAFAV of the feedback correction coefficient FAF is larger than the calculated upper limit KPGHI of the evaporative loss reduction. If it is, the process proceeds to step 82; In step 82, the evaporation reduction correction value KEPMI is added to the evaporation reduction correction coefficient KPG, and the routine proceeds to step 65. Note that idling may be detected by determining that the LL signal d from the idle switch 16 is on.

In the above configuration, as shown in FIG.
The opening of the duty VSV 26 is gradually increased over time.
When the gasoline vapor purge is started so that the gasoline vapor concentration is neither excessively high nor low, the opening degree of the duty VSV 26 is positive, so the control is performed. Step 51 → 61 → 71
Go to → 63 → 64 → 65. After such control, the average value FA of the A / F feedback correction coefficient FAF is obtained.
FAV is the switching determination value KPG of the evaporation reduction correction coefficient KPG.
When it is less than CHG, that is, when the concentration of gasoline vapor increases,
The control proceeds in steps 61 → 62 → 63. in this case,
Since it is determined that the concentration of the gasoline vapor during the purge is high, the evaporation reduction correction value KEPMI is switched to the evaporation high concentration setting value KEPMI2, and thereafter the control proceeds to set the average value FAFAV to the basic value of 1.0. When the approximate values are obtained, the process proceeds to steps 61 → 71 → 63, and the evaporation reduction correction value KEPMI is fixed to the switched value, and the control is continued. In steps 61, 62, 71, and 72, as shown in FIG. 4, the evaporation reduction correction value KEPMI is switched according to the gasoline concentration, and the average value FAFAV of the A / F feedback correction coefficient FAF is always 1.0. Is controlled as follows. Thereafter, when the average value FAFAV of the A / F feedback correction coefficient FAF becomes smaller than the lower limit value KPGLO of the calculated evaporative reduction amount, step 64 →
The control proceeds to step 65, where the evaporation reduction correction coefficient KPG
Is gradually reduced, and the air-fuel ratio A / F is controlled so as to be maintained near the stoichiometric air-fuel ratio. This step 63, 64, 6
5, 81, 82, the air-fuel ratio feedback correction coefficient F
The average value FAFAV of AF is the upper limit KPG
If the value exceeds the HI and the lower limit KPGLO, the evaporation reduction correction value KEPMI is added or subtracted to correct the evaporation reduction correction coefficient KPG with the width of the evaporation reduction correction value KEPMI, and the air-fuel ratio A / F is set to the stoichiometric air-fuel ratio. It is controlled to keep it near.

Next, when the purging of gasoline vapor is stopped,
The control proceeds from step 51 to step 52, and if the evaporation reduction correction coefficient KPG at that time is less than 1.0, step 53 is executed. O ₂ when is the output A / D value OXAD sensor 21 is the set value LVEPOX above, and thereafter step 54 is executed, evaporative decreasing correction coefficient KPG it from evaporative loss during return sum of running the purge It will be asymptotic to the basic value of 1.0 by KPGINC. Conversely, this step 5
The third determination, the output of the _{O 2} sensor 21 is set value LVE
When it is detected that the value is less than POX, the control proceeds to step 56, where the evaporation reduction correction coefficient KPG is returned to the basic value of 1.0, and the engine 100 is controlled. At the time of correction of the evaporation reduction correction coefficient KPG by the addition value KPGINC at the time of the evaporation reduction return, it is determined in step 55 whether or not the evaporation reduction correction coefficient KPG exceeds 1.0. If so, the control proceeds from step 56 to the learning routine GR, and if it is 1.0 or less, the flow shifts to the learning routine.

That is, if the evaporation reduction correction coefficient KPG is different from 1.0 when the gasoline vapor purge is stopped, the control proceeds to steps 51 → 52 → 53 → 54 → 55 →
56 → The learning routine GR is repeated, and if the A / D value OXAD becomes smaller than the set value LVEPOX during the control, the control proceeds to steps 51 → 52 → 53 → 56 and the evaporative reduction correction coefficient KPG is immediately set. The basic value is returned to 1.0, and when the evaporation reduction correction coefficient KPG exceeds 1.0, the process proceeds to steps 54 → 55 → 56 → learning routine GR.

As described above, during the purge, the concentration of the gasoline vapor is determined from the fluctuation state of the average value FAFAV of the A / F feedback correction coefficient FAF, and the average value FAFAV is constantly set to the basic value 1.0. The correction values for the correction of the evaporation reduction correction coefficient KPG are defined as an evaporation normal setting value KEPMI1 and an evaporation high concentration setting value KEPM.
Since the switching to I2 is performed, the evaporation reduction correction coefficient KPG can be corrected according to the concentration of gasoline vapor, and deterioration of emission can be prevented.

Further, after the purge is stopped, the evaporation reduction coefficient KPG is made to gradually approach 1.0, so that even if gasoline vapor remains in the surge tank 3, the residual amount is reduced by the evaporation reduction correction coefficient KPG. , The air-fuel ratio does not become rich, and deterioration of emission is prevented. Further, as described above, the evaporation loss correction coefficient KP
In operating conditions that modify the G, it detects the moment when the actual air-fuel ratio from the output of the O ₂ sensor 21 eliminates the gasoline vapor becomes lean, so immediately the evaporative weight loss correction factor KPG to 1.0, empty Fuel ratio becomes lean and NO
It is possible to prevent x from increasing and the emission from becoming worse. Under such circumstances, the A / F learning correction coefficient KG
Learning is performed, so that it is not affected by the purged gasoline vapor.

The present invention is not limited to the embodiment described above. For example, in the above embodiment, the calculation of the effective injection time is performed by multiplying each correction coefficient. However, the effective injection time may be calculated by adding each correction coefficient. In this case, the basic value of the weight loss correction coefficient is 0, and when the correction coefficient is negative, various constants may be added to the weight loss correction coefficient at that time to correct it.

The output of the gasoline O ₂ sensor 21 is A
The A / D value OXAD after the A / D conversion may be used after a certain delay time after the A / D conversion in order to confirm the stability of the value. A set value LVEPOX for determining such an A / D value OXAD
As, in response to the use of A / D conversion value, can be set by a numerical, air-fuel ratio or to approximate the O ₂ sensor 21 output when close to the rich, or in the case close to the lean The timing at which the evaporation amount reduction correction coefficient KPG is set to the basic value may be adjusted to the characteristics of the engine by approximating the setting.

In addition, the configuration of each section is not limited to the illustrated example, and various modifications can be made without departing from the spirit of the present invention.

[0024]

According to the present invention, as described in detail above, the reduction correction coefficient can be varied according to the concentration of gasoline vapor being purged by at least two set values. can be controlled at all times air-fuel ratio to the theoretical value near when discontinued purged gasoline vapor, off
To prevent the feedback correction coefficient from suddenly increasing.
Therefore , deterioration of emission can be prevented.

[Brief description of the drawings]

FIG. 1 is a schematic configuration explanatory view showing one embodiment of the present invention.

FIG. 2 is a flowchart showing a control procedure of the embodiment.

FIG. 3 is a flowchart showing a control procedure of the embodiment.

FIG. 4 is an operation explanatory view of the embodiment.

FIG. 5 is an operation explanatory view of a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Intake system 7 ... Central processing unit 8 ... Storage device 9 ... Input interface 11 ... Output interface 23 ... Charcoal canister EPDUTY ... Purge duty ratio KEPM ... Evaporation reduction correction value KEPMI1 ... Evaporation normal setting value KEPMI2 ... Evaporation high concentration Set value KPG: Evaporation reduction correction coefficient KPGCHG: Switching judgment value

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F02M 25/08 F02D 41/00-41/40

Claims (1)

(57) [Claims] At least a feedback correction coefficient
In addition to the feedback control of the air-fuel ratio , the gasoline vapor adsorbed by the gasoline vapor adsorbing means is used for the time based on the purge duty ratio when idling operation .
When purging the intake system by gradually increasing the opening of the valve as time passes, a reduction correction coefficient for correcting the fuel amount in accordance with the purged amount of gasoline vapor is set. An evaporative purge control method in which air-fuel ratio is controlled and purged by adding or subtracting the decrease correction coefficient and a predetermined value, wherein the predetermined value differs from at least a set value having a large tendency to be subtracted. Setting values with small trends
Set the door, Fi concentration of the gasoline vapor in the purge
It determined based on the readback correction coefficient was determined concentration
Is smaller than the switching judgment value for density judgment,
Select a setting value with a large calculation tendency and switch the determined concentration
Not less than the judgment value and not less than the basic value larger than the switching judgment value
In this case, an evaporative purge control method is characterized by selecting a set value having a small subtraction tendency, switching the set value according to the level of the determined density, and performing addition and subtraction with a weight reduction correction coefficient.