JPH06101528A - Evaporated fuel treatment device for engine - Google Patents

Abstract

PURPOSE:To reduce error in an air-fuel ratio until first purge learning is carried out after starting an engine by performing battery-backup of a purge learning value, and topping a specified value to the learning value at the starting time of the engine. CONSTITUTION:When a purge-ON condition is judged receiving an operation condition signal, a purge valve is opened for introducing purge gas from a canistor to an intake pipe by means of a purge gas introduction device 32. A purge learning value stored in a memory 35 is renewed by means of a learning value renewal means so as to store an air-fuel feedback correction rate within a specified range based on fluctuation the value at the time of switching between purge-ON and OFF condition. The purge learning value is battery- backed up by means of a battery backup means 39. At the starting time, an addint means 41 adds a topped amount corresponding to an increase rate of adhesion in canistor during engine stop to the purge learning value which is battery-backed up.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved engine fuel vapor treatment system.

[0002]

2. Description of the Related Art In order to prevent the fuel evaporated from a fuel tank from diffusing into the atmosphere, the fuel vapor is adsorbed to an activated carbon canister, and the fuel accumulated in the activated carbon canister is purged into an intake pipe under predetermined operating conditions (by the atmosphere, It is burnt in the cylinder together with the fuel injected from the injector by ejecting it from the canister.

However, when a purge gas which is not measured by an air flow meter is added, it affects the control air-fuel ratio, so that there is a valve that opens the purge valve (purge control valve) during air-fuel ratio feedback control. Although the air-fuel ratio shifts to the rich side at the beginning of the purge valve opening, the air-fuel ratio feedback correction coefficient α shifts to the lean side from the control center (1.0) and eventually settles to a certain value (for example, 0.8). As a result, the air-fuel ratio can be kept within the catalyst window (a predetermined width around the theoretical air-fuel ratio) even during purging.

However, even if the accelerator pedal is depressed during the purging, the supplied fuel amount cannot be increased to the required value corresponding to the depression amount of the accelerator pedal at once, so-called breathing occurs and the drivability deteriorates. Since α has to start from the above value (0.8) deviating to the lean side and becomes large, and α increases only at a constant rate, the fuel amount cannot be rapidly increased.

Therefore, in Japanese Patent Application Laid-Open No. 2-19631, the difference between α when the value becomes equal to or less than a predetermined value after the start of purging and α immediately before the start of purging is calculated, and the operating condition is adjusted by the reduction correction amount according to this difference. While the basic injection amount corresponding to the above is subtracted, α is forcibly returned to the value immediately before the start of the purge from the time when α becomes equal to or less than the predetermined value.

When α is settled to a lean value by the purge and becomes equal to or less than a predetermined value (0.8), the fuel is supplied by correcting the fuel injection amount from the basic injection amount by the fuel increase amount by the purge. Since the amount of fuel is kept the same before and after purging, and when the accelerator pedal is depressed during purging, α is increased from the value before purging (usually 1.0) to increase α as soon as possible. is there.

[0007]

By the way, in the above apparatus, since the difference between α before and after the change is observed after the change of α is completed by the purge, the air-fuel ratio error (theoretical air gap) Deviation from the fuel ratio) is large,
There is room for improvement in exhaust performance and driving performance.

On the other hand, the poor response of α can be compensated by the so-called basic air-fuel ratio learning value αm.
However, the basic air-fuel ratio learning value αm does not originally take into consideration the air-fuel ratio error due to purging, but takes into consideration the steady-state error of the air-fuel ratio caused by the air flow meter or the injector due to aging. Therefore,
If the air-fuel ratio error during purging is also incorporated into the basic air-fuel ratio learning value αm, a learning error will occur. Therefore, learning is prohibited during purging even with the conventional device, and learning is restarted after α has settled down. . That is, the basic air-fuel ratio learning value cannot deal with the air-fuel ratio error during purging.

Therefore, there has been proposed an apparatus which starts updating the purge learning value WC introduced separately from the basic air-fuel ratio learning value αm at the time of switching the purge ON and OFF. As will be described later, rather than waiting for the change in α to be completed by turning ON and OFF the purge, the learning frequency is increased by starting the purge learning immediately after the switching, and the learning is rapidly advanced.

For example, if purge learning has never been performed, α (= ALPHA) when switching to purge ON.
Is shifted to the smaller side as shown in Fig. 36.
V (average value of α) is ALPST (average value of α before switching)
The purge learning value (corresponding to the fuel concentration of purge gas) WC is rewritten from the time point when it becomes smaller (point A). Thus, if the purge learning is started immediately after switching, the air-fuel ratio can be contained in the catalyst window from the beginning without depending on α unless the fuel concentration of the purge gas is significantly different from that of the previous purge during the next purge. Even if the fuel concentration has changed from the previous time, the purge learning value WC is updated at that time, and the air-fuel ratio is immediately contained in the catalyst window according to the updated value.

In this case, it is possible to hold the purge learning value WC by backing up the battery so that the purge learning value WC does not disappear when the key switch is turned off. As a result, if the adsorption amount of the canister at the present start is the same as that at the time when the key switch was turned off last time, the air-fuel ratio error does not have to occur during the first purge immediately after the start.

However, except when the engine is restarted immediately after it is stopped, it is considered that the adsorbed amount of the canister increases during the stop of the engine and that the fuel concentration of the purge gas is higher than that before the stop of the engine during the present operation. This is more natural, and the increase in the adsorbed amount of the canister while the engine is stopped causes a deviation from the battery-backed learned value WC. Due to this deviation, an air-fuel ratio error is likely to occur until the first purge learning is performed during the current operation, which affects each performance of exhaust and operation.
Therefore, the present invention reduces the air-fuel ratio error until the first purge learning is performed after the engine is started by backing up the purge learning value with a battery and by adding a predetermined value to the learned value at the engine start. The purpose is to do.

[0013]

As shown in FIG. 1, a first aspect of the present invention is a means 31 for determining a purge ON / OFF condition by receiving an operation condition signal, and a purge O based on the determination result.
In an evaporative fuel treatment system for an engine, which includes a device 32 that opens a purge valve under N conditions and introduces purge gas from a canister into an intake pipe, an air-fuel ratio sensor (for example, O2) so that the air-fuel ratio feedback correction amount α falls within a predetermined range. ₂ sensor) 33 for calculating an air-fuel ratio feedback correction amount α from the output of the sensor, and a purge learning value stored in the memory 35 under the purge ON condition based on the determination result, the feedback correction amount α, and the operating condition. A means 36 for calculating the fuel injection amount using the basic injection amount, a device 37 for supplying the fuel injection amount to the intake pipe, the purge ON,
At the time of switching to OFF, the air-fuel ratio feedback correction amount α
This air-fuel ratio feedback correction amount α
Means for updating the purge learning value stored in the memory 35 so as to be within the predetermined width, means 39 for backing up the purge learning value stored in the memory 35 by a battery, and whether or not at the time of starting. And a means 41 for adding the additional amount corresponding to the increase in the adsorbed amount of the canister when the engine is stopped to the purge backup value backed up by the battery at the time of starting.

As shown in FIG. 47, the second invention is a means 31 for judging an ON / OFF condition of purge by receiving an operating condition signal, and a purge valve is opened from the canister under the purge ON condition based on the judgment result. In an evaporative fuel treatment system for an engine, which comprises a device 32 for introducing a purge gas into an intake pipe, an air-fuel ratio feedback from an output of an air-fuel ratio sensor (for example, an O ₂ sensor) 33 so that an air-fuel ratio feedback correction amount α falls within a predetermined range. Means 3 for calculating the correction amount α
4, means 36 for calculating the fuel injection amount using the purge learning value stored in the memory 35 under the purge ON condition, the feedback correction amount α, and the basic injection amount according to the operating condition based on the determination result; A device 37 for supplying a fuel injection amount to the intake pipe, and the air-fuel ratio feedback correction amount α is set within the predetermined width based on the change of the air-fuel ratio feedback correction amount α when the purge is turned on and off. A means 38 for updating the purge learning value stored in the memory 35, a means 39 for backing up the purge learning value stored in the memory 35 by a battery, a means 40 for determining whether or not the engine is starting, and a means 40 for starting the engine. 51 for detecting the water temperature of the engine, a means 52 for predicting the outside air temperature from the data of the starting water temperature, and a starting time from the outside air temperature and the starting water temperature. A means 53 for predicting the amount placed, provided with means 54 for adding the predicted additional amount in the battery backed-up purge learning value at startup.

[0015]

When the canister adsorption amount is increasing during the period since the start is delayed, an error occurs between the purge gas fuel concentration predicted from the battery backup learned value and the first time after the start. An air-fuel ratio error is particularly likely to occur until purge learning is performed.

On the other hand, in the first aspect of the present invention, the learned value backed up by the battery is added by a predetermined value at the time of starting, so that the fuel concentration becomes rich due to the increase in the canister adsorption amount while the engine is stopped. It is regarded as a value. As a result, the air-fuel ratio error is reduced until the first purge learning is performed after the start, and the learning update amount at the first purge learning is reduced, so that the learning ends promptly.

By the way, the adsorbed amount of canister varies depending on the time when the engine is stopped and the difference in the outside air temperature, and increases as the outside air temperature before starting increases and as the engine stop time before starting increases, and is proportional to this. As a result, the concentration of purge gas fuel increases.

In this case, according to the second aspect of the invention, the additional amount at the time of starting is predicted from the water temperature at the time of starting and the predicted value of the outside temperature, the outside temperature before starting is high, or the engine stop time before starting is long and the canister is too long. When the adsorption amount is increasing, the addition amount is increased, and conversely, when the outside air temperature before starting is low or the engine stop time before starting is short and the adsorption amount of the canister has hardly increased, the addition amount is increased. The amount is reduced.

When the fuel concentration of the purge gas immediately after the start changes due to the difference in the engine stop time and the outside air temperature, the additional amount can be estimated according to the change amount of the fuel concentration, and thus the engine stop time before the start and the engine stop time can be estimated. Even if the outside air temperature before starting is different, the air-fuel ratio error can be kept small from the beginning of the first purge after starting.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 2, a control unit 2 comprising a microcomputer (for example, a 16-bit microcomputer) is provided for engine control.

The exhaust pipe 3 is provided with a three-way catalyst 4 for treating three harmful components such as CO, HC and NOx discharged from the engine. The three-way catalyst 4 can process the harmful three components at the same time only when the air-fuel ratio of the air-fuel mixture supplied to the engine is within a narrow range (catalyst window) centered on the theoretical air-fuel ratio. If the air-fuel ratio deviates from this catalyst window to the rich side, CO, H
When the amount of C emission increases and, on the contrary, it shifts to the lean side, a large amount of NOx is emitted.

Therefore, the control unit 2 feedback-controls the fuel injection amount based on the actual air-fuel ratio signal from the O ₂ sensor 5 so that the three-way catalyst 4 can fully exert its capacity.

The output of the O ₂ sensor 5 provided upstream of the three-way catalyst 4 changes abruptly at the stoichiometric air-fuel ratio (the output is approximately 1 V on the rich side and about 0 V on the lean side of the stoichiometric air-fuel ratio). Therefore, it is determined that the air-fuel ratio is on the rich side when the O ₂ sensor output is higher than the slice level (approximately 0.5 V), and is on the lean side when the O ₂ sensor output is lower than the slice level. If such a determination is made in synchronization with the engine rotation, it can be determined whether the air-fuel ratio has just changed to the rich side (or the lean side) or whether the air-fuel ratio is on the rich or lean side.

From these judgment results, the step amount P is subtracted from the air-fuel ratio feedback correction coefficient α immediately after the air-fuel ratio is reversed to the rich side, and the integral amount I is subtracted from α until just before the air-fuel ratio is next reversed to the lean side. (Conversely, P is added to α immediately after the actual air-fuel ratio is reversed to the lean side, and I is added until just before the actual air-fuel ratio is next reversed to the rich side). Immediately after the air-fuel ratio is reversed, a large value of P is given in a stepwise manner to change the response to the opposite side, and after the step change, a small value of I is used to slowly change the air-fuel ratio to the opposite side. It stabilizes the feedback control.

Even if the operating conditions of the engine are different,
Ratio of intake air amount measured by the air flow meter 7 located upstream of the throttle valve 6 and fuel amount supplied from the injector 8 toward the cylinder (that is, air-fuel ratio)
The control unit 2 determines the valve opening pulse width (injection pulse width) of the injector 8 that is intermittently opened in synchronization with the engine rotation so that the ratio becomes approximately the stoichiometric air-fuel ratio.

Reference numeral 9 denotes a signal corresponding to the engine speed and Re
The crank angle sensor 10 for outputting the f signal (crank angle reference position signal) is a throttle valve opening (T
A sensor for detecting VO), a water temperature sensor 11 and a vehicle speed sensor 12 are also input to the control unit 2.

By the way, if the injector 8 is clogged due to aging, the supplied fuel amount will be small even if the injector 8 is driven with the same pulse width. Therefore, each time the engine is started, the air-fuel ratio feedback control is started for a while. Has a leaner air-fuel ratio. To avoid this,
The control unit 2 performs basic air-fuel ratio learning.

After a while after entering the air-fuel ratio feedback control, the average value of α settles to a value larger than the control center (1.0) (α itself swings around this value), so this value is basically used. If the battery is backed up as the air-fuel ratio learning value αm, the air-fuel ratio can be kept in the catalyst window from the beginning of the feedback control by increasing the injection pulse width by the learning value αm from the next engine operation. Of.

On the other hand, the fuel evaporated from the fuel tank 15 when the engine is stopped and adsorbed by the activated carbon in the canister 16 is released from the activated carbon when the atmosphere is introduced from the outside of the canister 16 while the engine is operating, and contains the released fuel. Clean air (purge gas) is sucked into the intake passage.

A purge valve 21 is provided in a passage 18 which connects the activated carbon canister 16 and the collector portion 17a of the intake manifold 17 to adjust the inflow amount of the purge gas. The purge valve 21 is a valve driven by a linear solenoid, and is driven by a pulse signal having a constant cycle (for example, a cycle of 6.4 ms) from the control unit 2, and the valve opening increases as the ON duty (ON time ratio) increases. Increase.

If the purge valve 21 sticks in the fully opened state, the engine may stall (engine stall) or the idle speed may increase due to the purge. To prevent this, a VC negative pressure valve (diaphragm valve) is provided. 22 is provided in the passage 18 in series with the purge valve 21. The VC negative pressure is a negative pressure that rises with respect to the throttle opening TVO as shown in FIG. 6. If the accelerator pedal is released and the throttle valve 6 is closed, the VC negative pressure becomes close to the atmospheric pressure, and the VC negative pressure becomes VC. The negative pressure valve 22 is closed. As a result, the passage 18 is closed regardless of whether the purge valve 21 is opened or closed.

By the way, although the purging is performed during the air-fuel ratio feedback control, if the basic air-fuel ratio learning value αm is updated during the purging, an error occurs in the learning value αm. Therefore, the control unit 2 updates the learning value αm during the purging. It is prohibited.

However, if the variation of the air-fuel ratio due to the purge is dealt with only by chasing α, α changes only at a constant rate, so that the air-fuel ratio may shift to the rich side until the change of α ends. .

For this reason, the flow charts shown in FIGS. 5 to 22 are assembled.

In a nutshell, this control system is for absorbing the air-fuel ratio error due to the purge.
The concept of the control system will be briefly described using, and then it will be divided into terms and outlined. Since the present invention forms a part of this control system, it will be described in detail at the end.

Quantitatively looking at fuel and air using the symbols shown in FIG. 4, the purge valve flow rate (total of fuel flow rate and air flow rate) Qpv is calculated from the purge valve duty (EVAP) and the differential pressure across the purge valve. Qef = Qpv · WC ... [A] However, WC; the purge fuel flow rate Qef can be obtained by the fuel concentration of the purge gas.

On the other hand, the purge air flow rate Qea is Qea = Qpv-Qef.KFQ # ... [B] where KFQ # is a constant for converting the fuel flow rate into the air flow rate, so the purge gas inflow portion of the intake pipe is The air flow rate immediately downstream of the air flow rate is the sum of Qea and the air flow rate Qs measured by the air flow meter 7.

When the air amount (Qs + Qea) flowing at the upstream position away from the injector 8 is determined in this way, a known manifold-cylinder filling model can be applied, and Qc = (Qs + Qea) .Fload + Qc. (1-Fload) ... [C] However, the cylinder air amount (air amount flowing into the cylinder) Qc is obtained as a first-order lag of (Qs + Qea) by the Fload; weighting coefficient.

On the other hand, the fuel injection amount Qf from the injector 8 provided at the port is Qf = Qc.K # -Qefc ... [D] where K # is a constant for keeping the air-fuel ratio constant Qefc; The purged fuel amount (Qefc) is subtracted from the cylinder intake amount.

Note that Qefc is determined with respect to Qef in consideration of the fact that the fuel gas is propagated while being diffused and a simple time delay.

That is, if the fuel concentration of the purge gas is accurately obtained by learning, it becomes clear how much the air amount and the fuel amount should be corrected during purging. However, conventionally, the fuel concentration was not measured,
Only an appropriate value was adopted based on empirical values, and there was room for improvement in exhaust performance and operation performance when switching purge ON and OFF.

Next, the control system itemization will be described.
In the following, in principle, capital letters are used for symbols that indicate quantities, and sometimes the symbols and statements used for operators are diverted from those used in programming languages.

(1) Purge cut condition (1-1) When any of the following conditions <1> to <5> is satisfied, the purge valve duty (EVAP) is set to 0 to turn off the purge valve. Close in steps (cut immediately). Since the VC negative pressure valve 22 is closed under these conditions, the purge valve 21 is also closed stepwise in accordance therewith. On the contrary, when all of these conditions are cancelled, the valve is opened stepwise as in the case of canceling the conditions <6> to <11> described later.

<1> When the ignition switch is OFF (step 23 in FIG. 7). <2> At the time of engine stall determination (step 24 in FIG. 7). <3> When the starter switch is ON (step 25 in FIG. 7). <4> When the idle switch is ON (step 26 in FIG. 7). <5> When the vehicle speed (VSP) is lower than the predetermined value (VCPC #) (step 27 in FIG. 7).

These conditions are checked, and if either of them is satisfied, the zero cut flag = 1 and the cut flag = 1 are set (steps 23 to 27 in FIG. 7, step 30 in FIG. 8). The cut flag = 1 indicates that the purge cut is to be performed, and the zero cut flag = 1 indicates that the purge cut is to be performed stepwise. Therefore, the purge cut is performed stepwise by the zero cut flag = 1 and the cut flag = 1. .

However, since it is sufficient to set these flags once, in step 29 of FIG. 8, if the flag (# F1STGKZ) which has passed once is set to 1, it is judged that the flag was previously set, and the process proceeds to step 30. You are exiting the routine without proceeding. For the first time, the other two flags that passed once (# F1STGKP and # F1STGKY) =
0, continuous purge ON time counter value (PONREF) =
By setting it to 0, it is prepared for the next time (steps 30 and 28 in FIG. 8).

(1-2) When any of the following conditions <6> to <11> is satisfied, the purge valve is closed stepwise. This is because purging under these conditions adversely affects operating performance and exhaust performance. Therefore, when all of these conditions are released, the purge valve is opened stepwise.

<6> When the load is too small (step 33 in FIG. 7). For example, a cylinder air amount equivalent pulse width (described later) TP is compared with a purge lower limit allowable value (TPCPC), and if TP <TPCPC, it is determined that the load is too small (steps 32 and 33 in FIG. 7). TPCPC
With respect to, the table having the contents of FIG. 31 is looked up from the engine speed NE (with interpolation calculation).
Since all the table lookups have an interpolation calculation, they will be simply referred to as table lookups below.

<7> When the load is too large (step 34 in FIG. 7). For example, the air flow rate QH0 is compared with the purge upper limit allowable value (EVPCQH #), and QH0 ≧ EVPCQ
It is judged that the load is too large in H #. Note that QH0 is an air flow rate (volume flow rate) at the throttle valve portion, which will be described later, and is determined from the throttle opening TVO and the engine speed NE.

<8> When the air-fuel ratio feedback control is not in progress (step 35 in FIG. 7). This is because the air-fuel ratio cannot be contained in the catalyst window unless the air-fuel ratio feedback control is being performed. For example, the flag (#FCLS
Since 1) = 0, it is determined that feedback control is not in progress.

<9> During clamping (while air-fuel ratio feedback control is stopped), an artificial selection flag introduced corresponding to the following various clamps (provided as an option) =
When 0 (steps 37 to 44 in FIG. 7).

Temin clamp (flag is #FPG
TEM). O ₂ sensor initialization clamp (flag is #FPGCL
C). High load KMR clamp (flag is #FPGKM
R). KHOT clamp (flag is #FPGKH).

The clamping condition of is the effective pulse width T
When e (which is a value obtained by subtracting the invalid pulse width Ts from TI described later) is less than or equal to the minimum value, the clamp condition of is during initialization of the O ₂ sensor, the clamp condition of is in the high load range,
Clamping conditions are when the engine is overheated and the water temperature is high.

The artificial selection flag is used here because the purging speed demand varies depending on the vehicle type (fuel tank system), and the purging area is adjusted. This allows the developer to artificially select the value of the flag in order to be compatible with the inability to correct the error. Therefore, the value of the flag is determined by the specifications at the time of development.

FIG. 32 shows what happens to the purge area under the purge OFF conditions of <1> to <9> above.
When the condition of <6> is satisfied, the purge cut is performed in the area shown by the TP cut arrow in the figure. Similarly, when the condition of <7> is satisfied, in the region indicated by the arrow of QH0 cut in the figure,
When the condition of <9> is satisfied, purge cutting is performed in each of the regions shown by KMR cutting in the figure. Therefore, the remaining area is the area to be purged. However, it is shown that even in the purge region, purge cut may be performed by KHOT cut (heat resistant cut) or the like.

<10> When the cut flag for purge learning = 1. Purge learning (W in the figure
Cut flag (#FWCCU) for C learning
T) = 1 (step 60 in FIG. 9). The purge learning is learning for absorbing the air-fuel ratio error due to the purge and will be described later.

EONREF # ≠ FFFF (step 51 in FIG. 9). This is an EONREF # (described later) that allows you to select whether or not to perform a purge cut for purge learning artificially.
Artificial FFFF (maximum hexadecimal value) for ONREF #
By putting in, it is possible to prevent the purge cut for purge learning from being performed. Offset learning reservation flag (#FOFGKGO) = 1
If not (step 52 in FIG. 9). The offset learning is learning for absorbing variations in the purge valve and will be described later. When the purge learning permission flag (#FWCGKOK) is not 1 (step 54 in FIG. 9). If purge learning is enabled, PONREF (continuous purge ON time counter value)
= 0 (steps 54 and 61 in FIG. 9). This is to count the continuous purge ON time from the end of purge learning. When the continuous purge ON time counter value (PONREF) is greater than or equal to the predetermined value (#EONREF) (step 55 in FIG. 9). When the air-fuel ratio feedback control is in progress (# FCLS1 = 1) and the clamp is not in progress (# FCLMP1 = 0) (step 56 in FIG. 9). The basic duty (EVAP0) described below is the lower limit value (W
CGDTY #) or more (step 5 in FIG. 9)
7). When the load (QH0) is less than or equal to the upper limit value (WCGQH #) (step 58 in FIG. 9). When a certain delay time has passed after the conditions (1) to (3) have been satisfied (CONTWCJ ≧ WCGDLY #) (step 59 in FIG. 9).

In particular, the reason why the purge is cut when the condition is satisfied is that if the purge is performed for a long time, the amount of fuel desorbed from the activated carbon canister 16 is reduced, and the fuel concentration of the purge gas is lowered. This is because there is a gap between the purge learning value WC) and the purge learning value WC. Therefore, even under the purging conditions, the purge learning is performed while intermittently performing the purge cut.

<11> When the cut flag for offset learning = 1. When all of the following conditions are satisfied, the cut flag (#FOFCUT) for offset learning is set to 1 (step 67 in FIG. 9).

When the offset learning reservation flag = 1 (step 52 in FIG. 9). This reservation is reserved when the purge learning value is clamped and the purge learning is completed as described later. When the air-fuel ratio feedback control is being performed (# FCLS1 = 1) and the clamp is not being performed (# FCLMP1 = 0) (step 64 in FIG. 9). The basic duty (EVAP0) described later is the upper limit value (O
FGDTY #) or less (step 6 in FIG. 9)
5). When a certain delay time has passed after the conditions (1) to (3) have been satisfied (CONTOFJ ≧ OFGDLY #) (step 66 in FIG. 9).

When any of the above conditions <6> to <11> is satisfied, the cut flag = 1 and the slow flag = 1 are set (step 47 in FIG. 8). Since the slow flag = 1 indicates that the purge valve is opened and closed in stages, the purge valve is gradually closed by the slow flag = 1 and the cut flag = 1. On the other hand, <6>
~ When the conditions of <11> are all cleared, purge O
At the time of switching to N, the purge flag is opened stepwise, so that the cut flag = 0 and the slow flag = 1 are set (FIG. 8).
Step 49).

When the purge valve is opened and closed stepwise, it is sufficient to set the flag once and to clear the continuous purge ON time counter (PONREF). This is the same as 30, 28 (steps 46, 47, 45, steps 48, 49 in FIG. 8).

(2) Purge valve opening characteristic (2-1) Connection with purge cut condition When any of the above conditions <6> to <11> is satisfied, until (EVAP = EVPCUT #), (EVAP
The purge valve duty (EVAP) is reduced at a speed of (T-EVPCUT #) * SPECUT # (steps 91 to 95, steps 91 to 94, 96, 97 in FIG. 10).

When all of the above conditions <1> to <11> are released, once EVAP = EVPCUT # is set, and (EVAPT-
EVPCUT #) * SPEOON # at a speed of increasing the purge valve duty EVAP (step 91 in FIG. 10,
92, 98-100, steps 91, 92, 98, 9
9, 101, 102).

Here, EVPCUT # is the purge valve duty under the purge OFF condition, EVAPT is the purge valve target duty, SPECTUT # is the closing speed of the purge valve, SP
EON # is the opening speed of the purge valve.

FIG. 33 shows a control waveform of EVAP (purge valve duty) with a solid line. From purge OFF to purge O.
When switching to N, EVAP is once set to EVPCUT # and then gradually increased toward EVAPT,
By switching from purge ON to purge OFF, this time E
It is gradually reduced from VAPT to EVPCUT #. In FIG. 33, the switching to the immediate cut is also shown by overlapping with a broken line, and only in this case, the EVAP is set to 0 stepwise.

On the other hand, the value of EVAP is also given to the background job shown in FIG. 5 (steps 12 to 1).
7). This is 100m as shown in Fig. 10 in all cases.
If the value of EVAP is given by the job every sec, a response delay occurs in the change of EVAP at the time of transition (for example, a response delay occurs when it is desired to immediately cut immediately). To switch
The calculation is performed in the background job except when the opening and closing is performed stepwise at a cycle of 100 msec.

(2-2) Purge Valve Target Duty The target duty EVAPT of the purge valve is EVAPT = EVAP0 + OFSTPV + VBOFPV ... [1] where EVAP0: Basic duty of the purge valve OFSTPV; Learning value of the purge valve rising duty VBOFPV It is determined by the duty battery voltage correction rate (step 9 in FIG. 5). The calculated EVAPT is limited to the upper limit value (EVPMAX #) (steps 10 and 11 in FIG. 5).

Here, OFSTPV in the equation [1] is a learning value (simply referred to as an offset learning value) corresponding to the purge valve rising duty, which will be described later.

The basic duty EVAP0 of the equation [1] is
Basically, EVAP0 = constant * TQPV / (KPVQH * KPVVB) ... [a] However, TQPV; purge valve target flow rate KPVQH; purge valve flow rate negative pressure correction rate KPVVB; purge valve flow rate battery voltage correction rate, or The table having the characteristics shown in FIG. 27 is looked up to obtain.

Further, the purge valve target flow rate TQP of the formula [a] is used.
V is TQPV = Qs * PAGERT ... [b] where Qs is the intake air amount of the airflow meter section PAGERT is the target purge rate.

The target purge rate PAGERT in the equation [b] is
The purge learning value WC corresponding to the fuel concentration of the purge gas is looked up to obtain a table having the characteristics shown in FIG. 23 (step 3 in FIG. 5).

As shown in FIG. 23, PAGERT is reduced when WC is large, and PAGE is reduced when WC is reduced.
RT is increased. This is because the purge rate may be increased in order to prevent the fuel vapor of the purge gas from leaking to the outside of the vehicle, but in this case, if the fuel concentration is high, the error of the air-fuel ratio A / F becomes large. So WC
Is judged to be large (fuel concentration is high), A /
In order to prevent the error of F from becoming large, the target purge rate PAGERT is made small, while when it is judged that the WC is small (the fuel concentration has become thin), the purge is rapidly performed at a large target purge rate. Of.

PAGERT is the air flow meter flow rate Qs
As a general rule, even if WC changes, the characteristics are horizontal regardless of whether WC is large or small as shown in the upper part of FIG. 34 (shown by a solid line). However, since the flow rate of the purge valve becomes maximum when the purge valve is fully opened, the purge rate gradually decreases after the maximum flow rate of the purge valve.

If any of the sensors (O ₂ sensor, air flow meter, throttle sensor) is abnormal (indicated by NG in the figure), RAGERT = NGPGRT
# (Steps 1 and 2 in FIG. 5). NGPGRT
# Is the purge rate (constant rate) when the sensor is abnormal.

By the way, EV is expressed by the equations [a] and [b].
If the number of variables used to calculate AP0 increases (TQ
PV, KPVQH, KPVVB, Qs, and PAGERT), and the precision of EVAP0 depends on the precision of the number of bytes and table given to these variables.

Therefore, here, the purge valve target flow rate TQ is set.
PV is calculated by TQPV = (Qs * PAGERT * coefficient) / KPVQH ... [2] (step 7 in FIG. 5), and EVAP0 is obtained from EVAP0 = table value / KPVVB ... [3] (step 8 in FIG. 5). ). Since these methods have better correction accuracy than the above equations [a] and [b], they are used.

The table value of the equation [3] is a value obtained by looking up a table having the characteristics shown in FIG. 28 from the purge valve target flow rate TQPV.

The KPVQH in the equation [2] is a correction factor for changing the flow rate due to the differential pressure across the purge valve even if the flow passage area of the purge valve is constant, and a table having the characteristics of FIG. Up and ask (step 4 in FIG. 5). As the differential pressure across the flow decreases, it becomes more difficult to flow, so
When the front-rear differential pressure is small (when QHO is large), the target flow rate is corrected to be large.

Since the differential pressure is not actually detected,
Here, QHO is used as the differential pressure equivalent amount. QH
0 is a known volume flow rate of the throttle valve portion determined by the engine speed NE and the throttle opening TVO.

In terms of the transition phase, since the cylinder air amount equivalent pulse width TP is closer to the differential pressure across the purge valve than QH0, it is desirable to use TP, but TP is different in atmospheric pressure and intake temperature. Therefore, QHO is used here because the relationship with the differential pressure across the purge valve deviates. In addition,
TP is also publicly known, and in consideration of the fact that even if the air flow meter section measures the air amount as will be described later, it actually flows into the cylinder with a first-order lag, and the cylinder air amount that flows in with the first-order lag is considered. On the other hand, the fuel amount is given in a fixed proportional relationship.

KPVVB in the equation [3] is the battery voltage V
A table containing the characteristics of FIG. 25 is looked up from B (step 5 of FIG. 5), and the battery voltage correction factor VBOF of the purge valve rising duty of the formula [1] is calculated.
PV is obtained by looking up a table having the characteristics of FIG. 26 from the battery voltage VB (step 6 of FIG. 5).

In KPVVB, the correction ratio is such that the relationship between the basic duty EVAP0 of the purge valve and the flow rate of the purge valve varies depending on the voltage applied to the purge valve, and VBOFPV is also the purge valve duty when the flow path of the purge valve starts to open. The correction rate varies depending on the voltage applied to the valve, and the correction rate varies depending on the type of purge valve. 25 and 26 are examples when the purge valve is driven by a linear solenoid.

(2-3) Purge valve flow rate predicted value Purge valve flow rate predicted value QPV is QPV = EVAPQ * KPVQH ... [4] where EVAPQ: basic flow rate of purge valve KPVQH: negative pressure correction rate of purge valve flow rate (Step 19 in FIG. 6).

The EVAPQ in the equation [4] is (EVAP-O
FSTPV-VBOFPV) * KPVVB is searched to obtain a table having the characteristics of FIG. 29 (step 18 in FIG. 6). In FIG. 29, the horizontal axis is EV
Not purging AP0 * KPVVB is purge ON / OFF
This is because the value of EVAP-OFSTPV-VBOFPV (that is, the value at the time of transition) and the value of EVAP0 (the value at the time of equilibrium) do not match when switching to.

(3) Purge learning control In addition to the basic air-fuel ratio learning value αm, a purge learning value (also a learning value of the mixture ratio of purge gas) WC corresponding to the fuel concentration of the purge gas is introduced. αm is different from αm
Unlike the air-fuel ratio error that changes very slowly, which is the purpose of introducing m (due to variations in the characteristics of the air flow meter and the injector), the air-fuel ratio error due to purge gas changes relatively quickly, so the purge learning value WC Therefore, the control accuracy of the air-fuel ratio is increased by separating the basic air-fuel ratio learning value αm and the basic air-fuel ratio learning value αm.

The fuel concentration of the purge gas is the purge O
Prediction can be made from α that changes due to switching between N and OFF as follows.

If only the fuel concentration of the purge gas becomes darker than the previous time (assuming there is no air-fuel ratio error due to an air flow meter, etc.), the air-fuel ratio shifts to the rich side, so the value of α (or its average value) is It shifts to the side smaller than the control center (1.0). Therefore, when α is shifted to the smaller side, the purge learning value WC is updated to the larger side, and the updated WC corresponds to the fuel concentration that is higher than the previous time. On the contrary, when the fuel concentration is lower than the previous time, α and its average value deviate from the control center to the larger side. Therefore, if WC is updated to the smaller side at this time, the updated WC becomes thinner than the previous time. It corresponds to the fuel concentration.

By thus predicting the fuel concentration of the purge gas, the purge ON,
It is possible to prevent an air-fuel ratio error immediately after switching to OFF.

(3-1) Permitting Conditions for Purge Learning Since purge learning is permitted at the time of switching to purge ON or purge OFF, after the flag for instructing switching of purge ON and OFF is set, that is, step 30, FIG. It is performed following 47 or 49. In FIG. 8, if offset learning is not reserved, the WC learning permission flag (#FWC
GKOK) = 1 (steps 82 and 83 in FIG. 8).

The reason why learning is permitted at the time of switching to purge ON and OFF without waiting for the change of α to end is as follows.
This is to increase the frequency of learning.

(3-2) Purge learning interrupting condition Purge learning is interrupted when the following conditions are satisfied (FIG. 1).
2 steps 116-119, 113).

When the purge learning permission flag = 0 (see FIG.
2 step 116). This is because the purge learning is interrupted when the purge ON is switched to the purge OFF or vice versa while the purge learning condition is satisfied (steps 81 and 85 in FIG. 8). Under the conditions other than the condition that the air-fuel ratio feedback control is being performed and the clamping is not being performed (step 117 in FIG. 12). This is because the learning condition is a condition during the air-fuel ratio feedback control and not during the clamp. Basic duty (EVAP0) is a predetermined value (WCGDT)
Y #) smaller (step 118 in FIG. 12). This is because when the basic duty is small, it is confused with the air-fuel ratio error due to the variation in the purge valve rising duty, which is to be avoided. As shown in FIG. 34,
In terms of the purge valve flow rate, the high flow rate range is the purge learning condition and the low flow rate range is the offset learning condition. When the load (QH0) is too high above the predetermined value (WCGQH #) (step 119 in FIG. 12).

However, even if one of the conditions (1) to (4) is satisfied, if the cut flag for purge learning = 1,
Step 113 is skipped (step 12 in FIG. 12).
0,114). In this case, the purge learning permission flag is not set to 0. When the purge learning is interrupted by the purge cut for the purge learning, it is switched to the purge ON again, but the purge learning is not started at that time. This is because

If any of the sensors is abnormal, W
Since C = NGWC # and the purge learning is interrupted,
The purge learning permission flag is set to 0 (step 11 in FIG. 12).
1 to 113), and initialization and post-processing of RAM and flags for purge learning (step 11 in FIG. 12).
4).

In the learning when the purge is ON, the EVAP
Is the purge valve offset (for example, VBOFPV + D
Purge learning is kept waiting until LYWCG # (set to the delay time equivalent amount) is passed (step 12 in FIG. 12).
1, 122).

(3-3) Update of Purge Learning Value The average value ALPAV of the first air-fuel ratio feedback correction coefficient that has entered the purge learning is stored in ALPST of the memory (steps 131 to 133 in FIG. 13). The ALPAV at the start of learning (which is also the ALPAV before the purge ON / OFF switching) is stored in ALPST.

When the purge learning is permitted, the purge learning value WC is updated by WC = WC holding value + ΔWC (step 181 in FIG. 14). WC after update
Is limited between the upper limit value (WCMAX #) and the lower limit value (WCMIN #) (steps 183 to 18 in FIG. 14).
5).

ΔWC is the learning update amount, which is the air-fuel ratio feedback correction coefficient ALPHA (α
The difference between (1) and ALPST is large and the difference is small (± PWCH and ± IWCH when large, ± PWCL and ± IWCL when small), and ΔWC is given as shown in the table. Therefore, FIG. 14 and FIG. 15 are combined.

Here, instead of the description of FIGS. 14 and 15, by explaining how the learning update amount ΔWC is given with the waveform shown in FIG.

FIG. 36 shows the state when switching to purge ON.

When α is moved to the lean side by switching to purge ON (a long integration amount I is acting), α
When the average value of ALPAV (shown by the broken line) also moves to the lean side and ALPAV <ALPST (point A)
The learning value WC is stepwise by PWCL # (step amount)
Then, it is gradually increased by IWCL # (integration amount).

These learning update amounts (PWCL # and IWC)
L #) is not enough and α moves across the predetermined width (DALPH #) toward the lean side, and at this crossing point (point B), the learning value WC is larger than PWCL # above.
The WCH # (this is also the step amount) is increased stepwise, and thereafter the I value of the value larger than the IWCL # is used.
WCH # (integrated amount) is gradually increased. α is ALP
When the width of DALPH # based on ST is deviated, the learning speed is increased by giving a larger step amount PWCH #.

However, in order to avoid overshooting of the learning value WC, the addition (or subtraction) of the step amount PWCH # is performed only once during the purge learning permission.

As a result, the difference between α and ALPST is DALP.
If it falls within the width of H #, IWCL # from point D
And IWCH # are used, and ALPAV is ALPST.
From the point of time (point E) that exceeds, the PWCL # and IWCL # with small values for both the step amount and the integration amount are used.

(3-4) Clamp for purge learning EVAP = EVAPT or EVAP = EVPCUT #
Then, the average value of the peak values of the latest two learning values WC (that is, WC immediately before PWCL # addition / subtraction) is calculated, and thereafter, WC is clamped to this value to complete the purge learning.

Therefore, in FIG. 14, ΔWC is + PW.
Immediately before entering CL # (or -PWCL #), the value stored in OLDWC1 of the memory is changed to OLDWC of the memory.
2, the value stored in WC of the memory is set to the OLDW of the memory
If each is moved to C1 and the PWCL addition count counter value (CONTPWCL) is incremented by 1 (steps 155, 158 and 16 in FIG. 14).
4,166), CONTPWCL is a predetermined value NSWCGK
It is determined that the learning value has converged when # (for example, 3) or more, and the value of (OLDWC1 + OLDWC2) / 2 is reset to WC (steps 125 and 126 in FIG. 12),
The purge learning permission flag = 0 is set (step 128 in FIG. 12).

The reason for clamping the purge learning value is as follows. By separating the purge learning value WC from the basic air-fuel ratio learning value αm, the control accuracy of the air-fuel ratio is increased.
I want to finish the purge learning early. This is because if purge learning is performed forever, the amount of change in α due to changes in operating conditions will be included in the purge learning as an error. In other words, it is desirable to end the purge learning while the operating condition does not change and eliminate the air-fuel ratio error by the basic air-fuel ratio learning when the operating condition changes (except when the purge ON / OFF is switched).

The PWCL added at point Q in FIG.
# Indicates purging switching (slowly flag = 1)
Therefore, the PWCL addition count counter value (CONTPWC
L) is not counted (step 1 in FIG. 12).
24, 130).

(3-5) Air-fuel ratio feedback correction coefficient ALPAV is calculated by a known method often used in basic air-fuel ratio learning. For example, when ALPAV is added with the step amount P (steps 263 and 268 in FIG. 18), ALPAV = (ALPHA + ALPO) / 2, where ALPO; is obtained by α immediately before the addition of the previous P minutes (steps 263 and 2 in FIG. 18).
66).

However, when the feedback control is started during the clamp in the air-fuel ratio feedback control, the ALP is started from the first cycle of the control after the clamp is released as shown in FIG.
In order to calculate AV, the P addition counter value (CO
When (UNTP) is less than 3, ALPAV is 1.0 (steps 265 and 269 in FIG. 18). Of course, during clamping during air-fuel ratio feedback control, A
Both LPAV and ALPO are 1.0 (steps 261 and 262 in FIG. 21).

(4) Learning of Purge Valve Rising Duty When the purge valve 21 is driven by the linear solenoid, the purge valve rising duty (duty when the purge valve starts to open) is dependent on the temperature as shown in FIG.
However, due to this valve variation, the purge rate in the small flow rate range fluctuates greatly. Since the purge valve becomes harder to open as the temperature becomes higher, even if the same basic duty EVAP0 is given, the purge rate becomes substantially smaller at high temperature.

Therefore, a learning value (also referred to as an offset learning value) OFSTP corresponding to the purge valve rising duty is set.
V is introduced separately from the purge learning value WC.

If the linear flow rate characteristic of the purge valve is considered to move in parallel to the left and right according to the temperature as shown in FIG. 38 (that is, the change in the inclination of the straight line is ignored), target duty = basic duty The target duty may be given by the + purge valve rising duty.

If the purge valve temperature is higher than the previous time and the purge valve rising duty becomes large without changing other conditions (the air-fuel ratio error due to other causes is not considered), the opening of the purge valve is delayed. The purge valve flow rate decreases and the purge rate decreases. Due to the decrease in the purge rate, the air-fuel ratio shifts to the lean side, and the average value of α and α (ALPAV) deviates to the side larger than the control center (1.0) in order to return it to the rich side.

Therefore, when α deviates to the large side, the offset learning value OFSTPV can be updated to the large side to make the purge valve flow rate the same as before the temperature change, and the learned value after the update rises in temperature. This corresponds to the subsequent duty of the purge valve rising.

On the contrary, when the purge valve opens faster due to the decrease in the purge valve temperature, the flow rate of the purge valve increases and the air-fuel ratio becomes rich, so that α and ALPAV deviate from the control center to the smaller side. At this time, by updating the offset learning value OFSTPV to the smaller side, the updated learning value corresponds to the purge valve rising duty after the temperature decrease.

In this way, the concept of offset learning is exactly the same as that of purge learning, and the only difference is that the constants and variable names are different and the learning value is updated in the opposite direction. Therefore, only the differences will be briefly described.

(4-1) Condition for permitting offset learning Offset learning is also permitted when switching to purge ON or purge OFF, but offset learning is reserved after the purge learning value WC is clamped (step in FIG. 12). 126, 127). This is because the air-fuel ratio error (corrected by the learned value WC) caused by the purge and the air-fuel ratio error (learned value OFSTPV that occurs due to the variation in the purge valve).
It is to separate with).

This will be further explained with reference to FIG. 34. When the variation of the valve characteristic caused by the temperature characteristic is superimposed on the purge rate characteristic, the variation of the purge rate as shown by the broken line in the small flow rate region (the region with a small Qs). Expand rapidly. This is because, even if the purge valve has the same flow rate variation, when converted into the purge rate, the smaller the Qs, the larger the rate of the variation amount with respect to Qs.

An air-fuel ratio error occurs due to such valve variations and the purge itself. In other words, even though an air-fuel ratio error is a superposition of two air-fuel ratio errors,
By learning (purge learning) the large flow rate range that is not affected by valve variation as the purge learning condition, first eliminate the air-fuel ratio error caused by the purge, and then learn the small flow rate range where large valve variation occurs as the offset learning condition (offset learning). By performing the learning, the air-fuel ratio error due to the variation in the rising duty is eliminated.

(4-2) Interrupt Learning Condition for Offset Learning As can be seen by comparing step 118 of FIG. 12 and step 194 of FIG. 15, when the basic duty (EVAP0) is larger than the predetermined value (OFGDTY #) in offset learning. Stop learning (steps 194, 1 in FIG. 15).
96). The range where EVAP0 is small (small flow rate range) is the offset learning condition, and the range where EVAP0 is large (large flow rate range) is the purge learning condition.

(4-3) Update of Learning Value As can be seen by comparing FIG. 39 with FIG. 35, the method of giving the positive / negative of the learning update amount ΔOFSTPV is opposite to the case of ΔWC. Therefore, the change of the learning value OFSTPV at the time of switching to the purge ON is as shown in FIG. In addition,
In FIG. 40, OFSTPV is negative on the upper side and positive on the lower side.

(5) Basic air-fuel ratio learning (5-1) Learning prohibition condition When any of the following conditions is satisfied, the basic air-fuel ratio learning value αm is not updated (steps 281 to 28 in FIG. 18).
4, 285).

When the purge learning is not performed even once (step 281 in FIG. 18). Slowly flag = 1 (step 28 in FIG. 18)
2). That is, it is the time of switching to purge ON or purge OFF. When the purge learning permission flag = 1 (step 283 in FIG. 18). When the offset learning reservation flag = 1 or the offset learning permission flag = 1 (step 284 in FIG. 18).

The basic air-fuel ratio learning is prohibited not only during (during) the purge but also during the purge learning and the offset learning (during the,) because the air-fuel ratio error due to the purge gas that changes relatively quickly is prevented. , Αm is introduced for the purpose of preventing the influence of an air-fuel ratio error that changes very slowly (due to characteristic variations of the air flow meter and the injector).

The basic air-fuel ratio learning αm is αm = αm holding value + Δαm where Δαm is updated by the learning update amount, and the learning update amount Δαm is Δαm = (ALPAV-1.0) · GAIN where ALPAV; ALPHA It goes without saying that the average value GAIN is calculated by the update ratio (value of 1 or less).

(6) Characteristic Expression of Fuel Injection Pulse Width (6-1) Fuel Injection Pulse Width The fuel injection pulse width CTIn for each cylinder is CTIn = TI + CHOSn + ERACIn ... [5] where n; injector number TI; common to all cylinders Fuel injection pulse width CHOSn; cylinder-by-cylinder increase / decrease amount ERACIn; This formula itself is known.

Here, the fuel injection pulse width TI of the equation [5]
Is simultaneous injection: TI = (TP-TEFC + KATHOS) * TFBYA * (α + αm) + Ts ... [6] Sequential injection: TI = (TP-TEFC + KATHOS) * TFBYA * (α + αm) * 2 + Ts ... [7] However, TP; Cylinder air amount equivalent pulse width TEFC; Purge fuel equivalent pulse width KATHOS; Wall flow correction amount TFBYA; Target fuel air ratio α; Air fuel ratio feedback correction coefficient αm; Basic air fuel ratio learning value Ts; Invalid pulse width (Fig. 21) Step 322).

What is different from the conventional method is that TEFC is subtracted from TP in the equations [6] and [7]. This is because when the purge gas is introduced into the intake pipe, the fuel component (TEFC) of the purge gas is additionally added and flows into the cylinder, so that the same air-fuel ratio is maintained during purging as when not purging. In order to do so, the fuel amount obtained by subtracting this purge gas fuel amount may be supplied from the injector 8 for each cylinder.

Cylinder air amount equivalent pulse width TP
Is TP0 = Qs * KCONST # * KTRM / NE ... [8] TP = TP0 * FLOAD + TP * (1-FLOAD) ... [9] where TP0: Airflow meter air amount equivalent pulse width Qs; Airflow meter air amount KCONST #; Constant KTRM; Trimming coefficient used for correction of air amount error NE; Engine speed FLOAD;
12, 313). These expressions are also known and are for phase matching to correspond to the cylinder intake air amount.

(6-2) Purge fuel equivalent pulse width The purge fuel equivalent pulse width TEFC is TEFC = QEFC * KCONST # / NE ... [10] where QEFC; Purge fuel cylinder intake amount predicted value KCONST #; Constant NE; It is determined by the engine speed (step 311 in FIG. 21). The equation [10] is the same as the equation [8], and is a unit conversion of the predicted cylinder intake amount of purge fuel (QEFC) into the injection pulse width equivalent unit.

The purge fuel cylinder intake amount predicted value QEFC of the equation [10] is represented by two primary delays (weighted average) in series connection plus dead time with respect to the purge fuel flow rate (QEF). That is, QEF1 = QEF * EDMP1 # + QEF1 * (1-EDMP1 #) ... [11] QEF2 = QEF1 * EDMP2 # + QEF2 * (1-EDMP2 #) ... [12] However, QEF1; Purge fuel flow rate intermediate predicted value EDMP1 # ; Weighted average coefficient 1 QEF2; Purge fuel flow rate intermediate predicted value EDMP1 #; QEF2 is obtained by the weighted average coefficient 2, and a Ref signal of a predetermined number of times (QEFDLY #) for this QEF2 (180 ° for 4 cylinders)
For each CA, the value delayed by the number of 6 cylinders rises every 120 ° is set as QEFC (steps 293 to 295 in FIG. 19).

This has a dead time (simple time delay) before the purge fuel flow rate (only the fuel amount) QEF that has flowed out from the purge valve to the intake pipe reaches the cylinder, and the gaseous fuel is diffused. This is because the QEFC waveform can be expressed as shown in FIG. 41 because it is transmitted.

When the calculated QEF2 value is stored in the memory, if a certain number of memories are prepared and sequentially shifted to the adjacent memory, the value of QEFDLY # times before is selected from these memories. Be QEFC (step 295 in FIG. 19).

The purge fuel flow rate QEF in the equation [11] is obtained by QEF = WC * QPV * KQPV ... [13] where WC: purge learning value QPV: purge valve flow rate predicted value KQPV; purge valve flow rate correction rate (Fig. 6 step 21). By multiplying the purge valve flow rate estimated value QPV by the fuel concentration equivalent value (WC) of the purge gas, the QEF as the purge fuel amount can be obtained.

The flow rate correction factor KQPV of the equation [13] is obtained by looking up a table having the characteristics of FIG. 30 from the purge valve flow rate predicted value QPV (step 20 of FIG. 6).

(7) Intake air amount When purging, the air amount Q used for the injection amount calculation is Q = Qs + QEA ... [14] where Qs: air flow meter air amount QEA; purge air flow rate (fuel amount) Except).

Here, the artificial selection flag (FPQ
If A) = 1, the air amount is corrected by the purge air amount by the equation [14], and if FPQA = 0, it is not corrected (steps 302 and 303, steps 302 and 304 in FIG. 20).

The reason why the formula [14] is adopted during purging is as follows.
Since the amount of air leaking from the purge valve 21 to the intake pipe (intake manifold 17) is not measured by the upstream air flow meter 7, the leaked air due to the purge causes a lean error in the air-fuel ratio. Therefore, during the purging (including the case where the fuel is not adsorbed to the activated carbon canister 16 and only the air leaks), the lean error is prevented by using Q in the formula [14].

The air flow meter 7 also has a measurement delay, which can be dealt with by the method described in JP-A-3-222849.

The purge air flow rate QEA in the equation [14] is QEA = QPV-QEF * KFQ # ... [15] However, QPV; purge gas flow rate (air + fuel) QEF; purge fuel flow rate KFQ #; fuel flow rate → air flow rate transition Derived correction rate.

Since QEA is synchronized with the output of EVAP (purge valve duty) executed in the Ref signal job (step 291 in FIG. 19), the value of QEA obtained in the background job is stored in QEAB of the memory ( (Temporary storage) (Step 22 in FIG. 6), Ref
The signal job transfers the value of QEAB to QEA in the memory (step 292 in FIG. 19).

The KFQ # in the equation [15] corrects the difference because the flow rates of air and fuel vapor are different even in the same flow path.

(8) Wall flow correction amount For the purpose of correcting the low frequency component of the wall flow (the wall flow component that changes relatively slowly), the equilibrium adhesion amount (M
FH) is stored and a change in the equilibrium adhesion amount due to a transient is added as a total correction amount (KATHOS) to the cylinder air amount equivalent pulse width TP at a predetermined ratio for each fuel injection (subtraction during deceleration). (Japanese Patent Laid-Open No. 63-38656)
No. JP-A-63-38650). Furthermore, for the purpose of correcting the high frequency component of the wall flow (the wall flow component that changes relatively quickly), the wall flow rate (CHOS
In some cases, n: increase / decrease amount for each cylinder, INJSETn: interrupt injection amount for each cylinder, ERACIn; interrupt injection → synchronous injection transition pulse width) are introduced (see Japanese Patent Laid-Open No. 3-116139).

The wall flow correction amount KATHOS takes the fuel supply delay into consideration. Although the injection amount must be increased during acceleration, no matter how good the atomization characteristics of the injector are, a part of the fuel adheres to the intake manifold wall and flows as a liquid along the intake pipe wall (this flow Wall flow), flowing into the cylinder at a slower rate than the fuel carried in the air. That is, the air-fuel mixture sucked into the cylinder is temporarily thinned by the wall-flow fuel, so that the wall-flow correction amount KATHOS is accelerated at the time of acceleration in order to prevent the temporary lean mixture.
Just increase the amount. On the contrary, during deceleration when the manifold pressure suddenly becomes a high negative pressure, the fuel adhering to the manifold wall is vaporized all at once, so the mixture becomes temporarily too rich, and CO and HC increase. To do. Therefore, during deceleration, the vaporized wall flow is reduced.

However, since the gaseous fuel in the purge gas is a light component (a component that volatilizes at a low temperature such as butane) that evaporates from the fuel tank 15, even in the intake pipe, most of it vaporizes and forms a flow wall flow. Never. Therefore, when calculating the wall flow correction amount KATHOS, it is necessary to exclude the purge fuel amount (TEFC).

Therefore, when purging is performed, the equilibrium adhesion amount MFH is calculated as follows: MFH = MFHTVO * CYLINDR # * (TP-TEFC) ... [16] where MFHTVO: Adhesion ratio CYLINDR #; Pulse width TEFC; Purge fuel equivalent pulse width. That is, by subtracting TEFC, which is the fuel amount that does not form the wall flow, from TP, the wall flow correction amount KATH
The prediction accuracy of S is improved, and the air-fuel ratio during transition can be made more appropriate.

However, since some engines do not introduce the wall flow correction amount, an artificial selection flag (FPFHL) =
When the value is 1, the formula [16] is adopted (step 31 in FIG. 21).
5, 316), and when FPFHL = 0, MFH = MFHTVO * CYLINDR # * TP is used as in the conventional case (steps 315 to 31 in FIG. 21).
8), so that it can be applied to any type of engine.

Similarly, CHOSn, INJSET
Also for n and ERACIn, the artificial selection flag (F
When PFHS) = 1, TP-TEFC (= TPP) is used, and when FPFHS = 0, TP is used as before (steps 319 and 320, steps 319 and 321 in FIG. 21).

(9) Idle speed control When the purge air is drawn into the engine, the output (torque) increases. In other words, even if the accelerator opening is the same, the output fluctuates greatly when the load is low and the drivability deteriorates by switching the purge ON and OFF.

In this case, when a valve (auxiliary air valve) whose opening can be continuously changed according to the duty signal is provided in the passage bypassing the throttle valve 6, this auxiliary air valve is used to introduce purge air. If you squeeze according to, you can prevent the driving performance from getting worse.

Therefore, the artificial selection flag (F
When EVISC = 1, the control duty (ISCON) to the auxiliary air valve is ISCON = conventional ISCON-ISCEVP ... [17] where ISCEVP; is determined by the purge correction amount (steps 324 and 326 in FIG. 22), F
If EVISC = 0, ISCON = conventional ISCON is used (steps 324 and 32 in FIG. 22).
7).

Purge correction amount ISC EVP of equation [17]
42 looks up a table containing the characteristics of FIG. 42 from QEA / KPVQH (step 325 in FIG. 22).

The conventional ISCON of the formula [17] is
For example, ISCON = ISCi + ISCp + ISCtr + ISCat + ISCa + ISCrfn ... [18] However, ISCi: integral part of idle feedback control ISCp; differential part of idle feedback control ISCtr; air increase amount during deceleration (equivalent to dashpot) ISCat; N ← → D of A / T vehicle Range correction (large in D range) ISCa: Correction when the air conditioner is ON ISCrfn: Correction when the radiator fan is ON

This is the end of the description of the control system itemization.

The purge learning value WC is held even when the key switch is OFF by the battery backup. However, the purge gas fuel concentration predicted from the battery backup learned value WC is increased by the increase in the canister adsorption amount while the engine is stopped. There is a gap between

In order to eliminate this deviation, the battery-backed purge learning value WC is read out when the control unit 2 is energized, and is added to this at the time of start-up (W
The value added with CST #) is stored in the WC of the register (step 105 in FIG. 11).

Since there is no learning value WC to be held when the control unit 2 is energized for the first time, WC = IN
WC # (steps 101 and 10 in FIG. 11)
2). INWC # is an initial value of WC for the first energization.

The operation of this example will be described below.

If there is no time between the stop of the engine and the start of the engine this time, the air-fuel ratio error will not occur from the beginning of the purge after the start by using the battery backup learned value WC immediately after the start. However, when the canister adsorption amount increases during the period since the start is delayed, there is an error between the purge gas fuel concentration predicted from the battery-backed learned value WC, and after the start. An air-fuel ratio error occurs until the first purge learning is performed.

On the other hand, in this example, the learned value WC backed up by the battery is increased by a predetermined value (WCST #) when the control unit 2 is energized, so that the adsorbed amount of the canister increases while the engine is stopped. Is set to a value commensurate with the fuel concentration. As a result, the air-fuel ratio error can be made small until the first purge learning is performed after the start, and the learning update amount at the first purge learning becomes small, so that the learning is quickly terminated. It is possible.

By the way, when the adsorbed amount of the canister increases, the fuel concentration of the purge gas increases in proportion to the adsorbed amount of the canister, but the adsorbed amount of the canister varies depending on the time when the engine is stopped and the difference in the outside temperature. Regardless of these, if the additional amount at the time of starting is set to a constant value, an error will occur when the condition when the value is set and the condition largely deviated.

Therefore, in another embodiment shown in FIG. 43,
(1) Predict the outside temperature from the starting water temperature, and (2) predict the starting additional amount from the outside temperature predicted value and the starting water temperature.

FIG. 3 shows an initialization routine executed when the control unit is energized to start the engine. First, the registers and RAM are initialized, the cooling water temperature is A / D converted, and the result is put in the TW of the memory. As a result (steps 331 and 332 in FIG. 43), the starting water temperature is stored in the TW.

(1) Prediction of outside air temperature The minimum value of the water temperature at startup is held, and the held value is regarded as the outside air temperature.

By comparing the two memories (TW and TWMIN), the value of TW can be calculated as TWM when TW <TWMIN.
Move to IN (steps 339 and 340 in FIG. 43), TW
If ≧ TWMIN, by gradually increasing TWMIN by TWMIN = TWMIN + ΔTWST (steps 339 and 341 in FIG. 43), the minimum value of the starting water temperature can be held in TWMIN. If the engine is stopped for half a day, the water temperature will drop to the outside temperature,
The outside temperature can be predicted by TWMIN. In addition, TW
As shown in FIG. 46, MIN corresponds to a long-term average value of outside temperature.

(2) Calculation of additional amount at startup Here, the additional amount at startup (WCST) is not a constant value unlike the previous embodiment, and is calculated by the formula WCST = WCST1 × WCST2 (step 337 in FIG. 43). ).

Among them, WCST1 (amount of stop time correction of the additional amount) takes into consideration that the amount of adsorption of the canister changes depending on the length of the engine stop time. Therefore, the starting water temperature TW and the outside temperature predicted value TWMIN are Difference (TW-TWM
IN) to look up a table having the content of FIG. 44 as a characteristic (steps 333 and 33 in FIG. 43).
4).

As shown in FIG. 44, the reason why the value of WCST1 is increased in the range where (TW-TWMIN) is small is that if TW is close to TWMIN, it can be judged that the engine stop time is long, and therefore the adsorption amount of the canister increases. This is because it seems that the fuel concentration of the purge gas is high.

On the other hand, if TW ≧ 75 ° C., it can be determined that the engine has been restarted immediately after the engine was stopped (that is, the time has not elapsed since the engine was stopped). In this case, a small value (WCSTHT #) is selected. Then, this is put into WCST1 of the memory (steps 333 and 33 in FIG. 43).
5).

WCST2 (amount of outside air temperature correction of additional amount)
Is to consider that the adsorption amount of the canister changes depending on the level of the outside air temperature, and from the outside air temperature predicted value TWMIN shown in FIG.
It is found by looking up a table having the contents of 5 (step 336 in FIG. 43).

As shown in FIG. 45, the value of WCST2 is increased as TWMIN increases, because it can be determined that the evaporated fuel from the fuel tank 15 increases and the canister adsorption amount increases as the outside air temperature increases. .

[0174] The start-up additional amount WCST thus obtained
Is the purge learning value WC that is backed up by the battery
And store the result in the register (step 338 in FIG. 43).

In this example, the starting additional amount WCST is not a constant value, but is predicted from the starting water temperature and the outside air temperature predicted value. When the outside air temperature before starting is high, or when the canister adsorption amount is increasing due to a long engine stop time before starting, the additional amount (WCST) increases, and conversely, the outside air temperature before starting is low, Alternatively, if the engine stop time before starting is short and the canister adsorption amount hardly increases, the additional amount decreases. Since the fuel concentration of the purge gas immediately after the start changes depending on the time when the engine is stopped and the difference in the outside temperature, the additional amount is estimated according to the change amount of the fuel concentration.

As a result, the air-fuel ratio error can be reduced from the beginning of the first purge after the start even if the degree of increase in the adsorbed amount of the canister varies depending on the engine stop time before the start and the difference in the outside air temperature before the start. Can be suppressed to

In the embodiment, the linear solenoid driven purge valve has been described, but the present invention is not limited to this, and a rotary valve or a step motor driven valve may be used. However, in the step motor driven valve, unlike the purge valve and rotary valve driven by the linear solenoid, the flow rate characteristics are not affected by temperature (the purge valve rising duty is zero), so it is necessary to introduce the offset learning value. There is no.

[0178]

According to the first aspect of the present invention, the purge stored in the memory so that the air-fuel ratio feedback correction amount falls within a predetermined range based on the change in the air-fuel ratio feedback correction amount when the purge is turned on and off. While updating the learning value, the purge learning value stored in the memory is backed up by the battery, and the additional amount corresponding to the increase in the adsorption amount of the canister while the engine is stopped is added to the purge learning value backed up by the battery at the time of starting. With this configuration, the air-fuel ratio error until the first purge learning is performed after the start can be made small, and the learning update amount at the first purge learning is made small to end the learning promptly. be able to.

In the second aspect of the present invention, the start-up additional amount of the first aspect of the invention is configured to be predicted from the outside air temperature predicted value and the start-up water temperature. Therefore, in addition to the effects of the first aspect of the invention, Even if the adsorption amount of the canister changes variously depending on the stop time and the outside air temperature, the air-fuel ratio error can be suppressed to a small value from the beginning of the first purge after the start.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to a claim of the first invention.

FIG. 2 is a system diagram of an embodiment.

FIG. 3 is a characteristic diagram of a VC negative pressure and a VC negative pressure valve lift.

FIG. 4 is a characteristic diagram showing a manifold-cylinder filling model.

FIG. 5 is a flowchart for explaining calculation of the purge valve duty EVAP and setting of the purge valve duty EVAP at the transition time.

FIG. 6 is a flowchart for explaining calculation of a purge air amount QEA.

FIG. 7 is a flow chart for explaining determination of purge ON / OFF conditions.

FIG. 8 is a flow chart for explaining setting of a flag for instructing purge ON and OFF and learning permission (including reservation).

FIG. 9 is a flowchart for explaining determination of purge cut conditions for purge learning and offset learning.

FIG. 10 is a flow chart for explaining calculation of a purge valve duty EVAP during switching between purge ON and OFF.

FIG. 11 is a flowchart for explaining initialization of a learning value.

FIG. 12 is a flowchart for explaining determination of a purge learning interruption condition and clamping of the purge learning value WC.

FIG. 13: ALPAV before switching to purge ON / OFF
5 is a flowchart for explaining sampling and selection of a learning update amount ΔWC.

FIG. 14: Selection of learning update amount ΔWC and purge learning value WC
5 is a flowchart for explaining the update of the.

FIG. 15 is a flowchart for explaining determination of an interruption learning interruption condition and clamping of an offset learning value OFSTPV.

FIG. 16: ALPAV before switching to purge ON / OFF
5 is a flow chart for explaining sampling and selection of a learning update amount ΔOFSTPV.

FIG. 17 is a flowchart for explaining selection of a learning update amount ΔOFSTPV and updating of an offset learning value OFSTPV.

FIG. 18 is a flowchart for explaining calculation of an air-fuel ratio feedback correction coefficient α and determination of an update prohibition condition for basic air-fuel ratio learning.

FIG. 19 is a flowchart illustrating a Ref job.

FIG. 20 is a flowchart for explaining calculation of an air amount Q used for calculating a fuel injection amount.

FIG. 21 is a flowchart for explaining calculation of a fuel injection pulse width CTIn.

FIG. 22: ON-duty ISCO to auxiliary air control valve
6 is a flowchart for explaining calculation of N.

FIG. 23 is a characteristic diagram of a target purge rate PAGERT.

FIG. 24 is a characteristic diagram of a negative pressure correction factor KPVQH of a purge valve flow rate.

FIG. 25: Purge valve flow rate battery voltage correction factor KPVV
It is a characteristic view of B.

FIG. 26 is a characteristic diagram of a battery voltage correction factor VBOFPV of a purge valve rising duty.

FIG. 27 is a characteristic diagram of the basic duty EVAP0 of the purge valve.

FIG. 28 is a characteristic diagram of lookup values.

FIG. 29 is a characteristic diagram of the basic flow rate EVAPQ of the purge valve.

FIG. 30 is a characteristic diagram of a purge fuel flow rate correction rate KQPV.

FIG. 31 is a characteristic diagram of a load purge permission lower limit value TPCPC.

FIG. 32 is a characteristic diagram showing a purge region.

FIG. 33 is a characteristic diagram showing a switching waveform of the purge valve.

FIG. 34 is a characteristic diagram of purge valve flow rate and purge rate with respect to valve characteristics.

FIG. 35 is a table diagram for explaining selection of a learning update amount ΔWC.

FIG. 36 is a waveform diagram of a purge learning value WC when switching to purge ON.

FIG. 37 is a waveform diagram of α after unclamping.

FIG. 38 is a flow rate characteristic diagram of a purge valve driven by a linear solenoid.

FIG. 39 is a table diagram for explaining selection of the learning update amount ΔOFSPV.

FIG. 40: Offset learning value O when switching to purge ON
It is a waveform diagram of FSTPV.

FIG. 41: Purge fuel cylinder intake amount predicted value QEFC
It is a waveform diagram of.

FIG. 42 is a characteristic diagram of a purge correction amount ISCEVP when purge is ON.

FIG. 43 is a flowchart of another embodiment.

FIG. 44 is a characteristic diagram of a stop time correction amount WCST1 of an additional amount.

FIG. 45 is a characteristic diagram of an additional ambient temperature correction amount WCST2.

FIG. 46 is a waveform diagram for explaining an outside air temperature predicted value TWMIN.

FIG. 47 is a diagram corresponding to the claim of the second invention.

[Explanation of symbols]

2 control unit 3 exhaust pipe 4 three-way catalyst 5 O ₂ sensor (air-fuel ratio sensor) 6 throttle valve 7 air flow meter 8 injector (fuel supply device) 15 fuel tank 16 activated carbon canister 21 purge valve 31 purge condition determination means 32 purge gas introduction device 33 air-fuel ratio sensor 34 feedback correction amount calculation means 35 purge learning value memory 36 fuel injection amount calculation means 37 fuel supply device 38 purge learning value update means 39 battery backup means 40 start time determination means 41 start time addition means 51 start time water temperature detection Means 52 Outdoor temperature predicting means 53 Added amount predicting means 54 Starting time adding means

Claims (2)

[Claims] 1. A purge ON, OF in response to an operating condition signal
Means for judging the condition of F, and purging O from the judgment result
In an evaporative fuel processor for an engine equipped with a device for introducing a purge gas from a canister into an intake pipe by opening a purge valve under N conditions, an air-fuel ratio sensor output is used so that an air-fuel ratio feedback correction amount falls within a predetermined range. Means for calculating a feedback correction amount, and a purge learning value stored in the memory under the purge ON condition from the determination result,
Means for calculating the fuel injection amount using the feedback correction amount and the basic injection amount according to the operating condition, a device for supplying the fuel injection amount to the intake pipe, and the purge ON, O
Means for updating the purge learning value stored in the memory so that the air-fuel ratio feedback correction amount falls within the predetermined range based on the change in the air-fuel ratio feedback correction amount when switching to the FF, and the memory. A means for backing up the stored purge learning value with a battery,
A means for determining whether or not the engine is starting, and a means for adding an additional amount corresponding to an increase in the adsorbed amount of the canister while the engine is stopped to the purge backup value backed up by the battery when the engine is started are provided. Evaporative fuel processor. 2. Purging ON and OF in response to an operating condition signal
Means for judging the condition of F, and purging O from the judgment result
In an evaporative fuel processor for an engine equipped with a device for introducing a purge gas from a canister into an intake pipe by opening a purge valve under N conditions, an air-fuel ratio sensor output is used so that an air-fuel ratio feedback correction amount falls within a predetermined range. Means for calculating a feedback correction amount, and a purge learning value stored in the memory under the purge ON condition from the determination result,
Means for calculating the fuel injection amount using the feedback correction amount and the basic injection amount according to the operating condition, a device for supplying the fuel injection amount to the intake pipe, and the purge ON, O
Means for updating the purge learning value stored in the memory so that the air-fuel ratio feedback correction amount falls within the predetermined range based on the change in the air-fuel ratio feedback correction amount when switching to the FF, and the memory. A means for backing up the stored purge learning value with a battery,
Means for determining whether or not at the time of starting, means for detecting the water temperature at the time of starting, means for predicting the outside temperature from the data of the water temperature at the time of starting, and predicting the additional amount at the time of starting from this outside temperature and the water temperature at the time of starting And a means for adding the predicted additional amount to the purge backup value backed up by the battery at the time of start-up.