JP2795092B2 - Evaporative fuel processor for engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

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

However, if a purge gas which is not measured by an air flow meter is added, the control air-fuel ratio is affected, so that a purge valve (purge control valve) is opened during the air-fuel ratio feedback control (JP-A-2-1963).
No. 1).

According to this method, although the air-fuel ratio initially shifts to the rich side when the purge valve is opened, the air-fuel ratio feedback correction coefficient α shifts toward the lean side from the control center (1.0), and eventually. By settling to a value (for example, 0.8), the air-fuel ratio can be kept within the catalyst window (a predetermined width centered on the stoichiometric air-fuel ratio) even during the purge.

[0005]

By the way, in order to stabilize idling, feedback control of the idling speed is performed. When the cooling water temperature is low or when operating an air conditioner, set the target rotation speed according to the cooling water temperature or the operating condition of the air conditioner so that the first idle state is achieved, and set the actual rotation speed to the target rotation speed. If it is not enough, the opening of the auxiliary air valve provided in the auxiliary air passage bypassing the throttle valve is increased. Conversely, if the target rotation speed is exceeded, the opening of the auxiliary air valve is corrected to decrease.

On the other hand, when the state shifts from the idle state to the non-idle state, the feedback control of the idle speed is released. However, at the time of the shift, the auxiliary air valve is not held at the fully closed position, but is opened during the feedback control. Some are designed to keep the degree. In this case, the auxiliary air valve is opened even in the non-idle state, and the auxiliary air flows through the auxiliary air passage.

When purging is performed downstream of the throttle valve with the auxiliary air valve being opened, the torque increases by an amount corresponding to the increase in the flow rate of purge air accompanying the purging, so that a torque step occurs before and after purging. , Driving performance is deteriorated.

Therefore, the present invention reduces the opening of the auxiliary air valve by an opening corresponding to the amount of air generated by the purge when purging is performed in a state where the auxiliary air valve is opened when the auxiliary air valve is not idling. An object of the present invention is to prevent operability and driving feeling from being deteriorated before and after purging.

[0009]

As shown in FIG. 1, according to the present invention, there is provided a means 41 for judging a purge ON / OFF condition in response to an operation condition signal, and purging ON according to the judgment result.
A device 42 for opening the purge valve under conditions to introduce purge gas from the canister into the intake manifold downstream of the throttle valve, an auxiliary air valve 43 for adjusting the amount of auxiliary air bypassing the throttle valve, and an auxiliary air valve 43
Means 4 for setting the opening to a predetermined opening in a non-idle state
And a means 46 for detecting or predicting the fuel concentration of the purge gas, and a means 46 for detecting or predicting the fuel concentration of the purge gas. Means 47 for calculating the flow rate in response to the operating condition signal, means 48 for calculating the fuel flow rate of the purge valve flow rate based on the purge valve flow rate and the fuel concentration, and subtracting the fuel flow rate from the purge valve flow rate Means 49 for calculating the air flow rate of the purge valve flow rate, means 50 for calculating the degree of opening reduction of the auxiliary air valve 43 corresponding to this air flow rate, and turning on the purge under the specific operating conditions. Means 51 is provided for subtracting the opening reduction amount from the predetermined value set under a specific operating condition when the condition is satisfied.

[0010]

When the purge ON condition is satisfied while the auxiliary air valve is kept at a predetermined opening in the non-idle state, the opening of the auxiliary air valve is reduced. Due to the decrease in the opening degree of the auxiliary air valve, the flow rate of the auxiliary air that bypasses the throttle valve decreases, and the decrease in the flow rate absorbs the increase in the intake air amount accompanying the purge. That is, if purging is performed while the auxiliary air valve is opened, the torque increases by an amount corresponding to the increase in the purge air flow rate accompanying the purge, and the opening degree of the auxiliary air valve is reduced so as to absorb the increase in torque. The amount is determined.

As a result, the torque step at the time of switching the purge ON and OFF is suppressed, and the same operation feeling can be obtained before and after the purge.

[0012]

FIG. 2 shows a control unit 2 comprising a microcomputer (for example, a 16-bit microcomputer) for controlling the engine.

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 simultaneously treat the harmful three components only when the air-fuel ratio of the air-fuel mixture supplied to the engine is within a narrow range (catalyst window) around the stoichiometric air-fuel ratio. If the air-fuel ratio deviates slightly to the rich side from this catalyst window, CO, H
When the discharge amount of C increases and shifts to the lean side, a large amount of NOx is discharged.

For this reason, the control unit 2 performs feedback control of 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 sufficiently exhibit its ability.

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

Based on these determination results, immediately after the air-fuel ratio is inverted to the rich side, the step amount P is subtracted from the air-fuel ratio feedback correction coefficient α, and the integrated amount I is subtracted from α immediately before the air-fuel ratio is next inverted to the lean side. (Conversely, P is added to α immediately after the actual air-fuel ratio is inverted to the lean side, and I is added until immediately before the actual air-fuel ratio is next inverted to the rich side.) Immediately after the inversion of the air-fuel ratio, a large value of P is applied stepwise to change to the opposite side with good response, and after the step change, the air-fuel ratio is slowly changed to the opposite side with a small value of I. It stabilizes the feedback control.

Even if the operating conditions of the engine are different,
The ratio of the amount of intake air measured by the air flow meter 7 located upstream of the throttle valve 6 to the amount of fuel supplied from the injector 8 to the cylinder (that is, the 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 air-fuel ratio becomes substantially the stoichiometric air-fuel ratio.

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

If the injector 8 is clogged due to aging, the amount of fuel supplied is reduced even if the injector 8 is driven with the same pulse width. Depends on the air-fuel ratio on the lean side. To avoid this,
The control unit 2 performs basic air-fuel ratio learning.

After a while after the air-fuel ratio feedback control, the average value of α is settled to a value larger than the control center (1.0) (α itself fluctuates around this value). If the battery is backed up as the air-fuel ratio learning value αm, the air-fuel ratio can be stored 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. It is.

On the other hand, when the engine is stopped, the fuel evaporated from the fuel tank 15 and adsorbed by the activated carbon in the canister 16 is separated from the activated carbon when the atmosphere is introduced from outside the canister 16 during operation of the engine, and the separated fuel is contained. Air (purge gas) is sucked into the intake passage.

A purge valve 21 is provided in a passage 18 that connects the activated carbon canister 16 and the collector 17a of the intake manifold 17 in order to adjust the flow rate of the purge gas. The purge valve 21 is a valve driven by a linear solenoid. The purge valve 21 is driven by a pulse signal of a constant period (for example, a period of 6.4 ms) from the control unit 2, and the valve opening increases as the ON duty (ON time ratio) increases. Will 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 used. 22 is provided in the passage 18 in series with the purge valve 21. The VC negative pressure is a negative pressure that rises as shown in FIG. 3 with respect to the throttle opening TVO. As long as the accelerator pedal is released and the throttle valve 6 is closed, the VC negative pressure approaches the atmospheric pressure and the VC negative pressure becomes VC. The negative pressure valve 22 is closed. As a result, the passage 18 is blocked regardless of whether the purge valve 21 is opened or closed.

The purge is performed during the air-fuel ratio feedback control. However, if the basic air-fuel ratio learning value αm is updated during the purge, an error occurs in the learning value αm. Therefore, the control unit 2 updates the learning value αm during the purge. Prohibition.

However, if the change in the air-fuel ratio due to the purging is handled only by the following of 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 is completed. .

For this reason, the flowcharts shown in FIGS. 5 to 22 are set up.

In short, this control system is for absorbing an air-fuel ratio error caused by purging.
The concept of the control system will be briefly described using, and then the section will be outlined. Since the present invention forms a part of the control system, it will be described in detail at the end.

When the fuel and air are quantitatively examined using the symbols shown in FIG. 4, the purge valve flow rate (sum of the fuel flow rate and the air flow rate) Qpv is obtained from the purge valve duty (EVAP) and the differential pressure across the purge valve. Qef = Qpv · WC [A] where WC; the purge fuel flow rate Qef can be obtained from 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 to the air flow rate. Is the sum of Qea and the air flow rate Qs measured by the air flow meter 7.

When the amount of air (Qs + Qea) flowing upstream from the injector 8 is determined, a known manifold-cylinder filling model can be applied. Qc = (Qs + Qea) · Fload + Qc · (1-Fload) [C] Here, the cylinder air amount (air amount flowing into the cylinder) Qc is obtained as a first-order lag of (Qs + Qea) by Fload;

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

The Qefc is determined in consideration of the diffusion of the fuel gas while diffusing the Qef and a simple time delay.

That is, if the fuel concentration of the purge gas (hereinafter referred to as the purge fuel concentration) is accurately obtained by learning, it becomes clear how much correction should be performed on the air amount and the fuel amount during the purge. . However, conventionally, the purge fuel concentration has not been measured, and only an appropriate value based on empirical values has been adopted.
There was room for improvement in exhaust performance and driving performance when switching to F.

Next, a description of the control system will be given.
In the following, the symbols indicating the quantities use uppercase letters in principle, and sometimes use the symbols used in operators and statements used in programming languages.

(1) Purge cut conditions (1-1) When any of the following conditions <1> to <5> is satisfied, the purge valve duty (EVAP) is set to 0 to set the purge valve to zero. Close step by step (immediate cut). Under these conditions, the VC negative pressure valve 22 is closed, and accordingly, the purge valve 21 is also closed stepwise. Conversely, when all of these conditions are cancelled, the valve is opened in a stepwise manner as in the condition cancellation of <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) falls below a predetermined value (VCPC #) (step 27 in FIG. 7).

The conditions are checked, and if any of them is satisfied, the zero cut flag = 1 and the cut flag = 1 are set (steps 23 to 27 in FIG. 7 and step 30 in FIG. 8). Since 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, 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, if it is determined in step 29 in FIG. 8 that the flag passed once (# F1STGKZ) = 1, it is determined that the flag was set last time, and the process proceeds to step 30. The routine has been exited without proceeding. In the first time, the other two passed flags (# 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 the operation performance and the 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, the pulse width TP (described later) corresponding to the cylinder air amount 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
Is obtained by looking up a table having contents shown in FIG. 31 from the engine speed NE (with interpolation calculation).
Since all table lookups are provided with interpolation calculations, they are simply described 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 a purge upper limit allowable value (EVPCQH #), and QH0 ≧ EVPCQ
It is determined that the load is too large in H #. Note that QH0 is an air flow rate (volume flow rate) at the throttle valve section as 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 being performed (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
1) It is determined that feedback control is not being performed from = 0.

<9> During the clamping (while the air-fuel ratio feedback control is stopped), an artificial selection flag introduced corresponding to the following various clamps (optionally provided) =
When it is 0 (steps 37 to 44 in FIG. 7). Temin clamp (flag is #FPGTEM). O ₂ sensor initialization clamp (flag is #FPGCL
C). High load range KMR clamp (flag is #FPGKM
R). KHOT clamp (flag is #FPGKH).

The clamping condition is that the effective pulse width T
When e (a value obtained by subtracting the invalid pulse width Ts from TI described later) is equal to or smaller than the minimum value, the clamp condition is to initialize the O ₂ sensor.
The clamping condition is at a high water temperature when the engine tends to overheat.

The reason why the artificial selection flag is used is that it is desired to adjust the purge area because the purge speed requirement varies depending on the type of vehicle (fuel tank system). In order to be compatible with the inability to correct the error, the developer can artificially select the value of the flag. Therefore, the value of the flag is determined by the specification at the time of development.

FIG. 32 shows what happens to the purge area depending on the purge OFF conditions <1> to <9>.
When the condition of <6> is satisfied, the purge cut is performed in the region indicated by the TP cut arrow shown in the figure. Similarly, when the condition of <7> is satisfied, in the region indicated by the arrow of the QH0 cut shown in the drawing,
When the condition of <9> is satisfied, the purge cut is performed in the region indicated by the illustrated KMR cut. Therefore, the remaining area is the area to be purged. However, this also indicates that the purge area may be purge-cut by a KHOT cut (heat-resistant cut) or the like.

<10> When the cut flag for purge learning = 1. When all of the following conditions are satisfied, purge learning (in the figure, W
Cut flag (#FWCCU) for C learning
T) = 1 (step 60 in FIG. 9). The purge learning is learning for absorbing an air-fuel ratio error due to the purge, and will be described later. EONREF # ≠ FFFF (step 51 in FIG. 9). This allows the user to select whether or not to perform purge cut for purge learning artificially by EONREF # (described later), and artificially insert FFFF (maximum value of hexadecimal number) in EONREF #. By doing so, it is possible to prevent the purge cut for the purge learning from being performed. Offset learning reservation flag (#FOFGKGO) = 1
If not (step 52 in FIG. 9). The offset learning refers to learning for absorbing variations in the purge valve, which will be described later. When the purge learning permission flag (#FWCGKOK) is not 1 (step 54 in FIG. 9). If purge learning is permitted, 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 the purge learning. When the continuous purge ON time counter value (PONREF) is equal to or greater than a predetermined value (#EONREF) (step 55 in FIG. 9). When the air-fuel ratio feedback control is being performed (# FCLS1 = 1) and not being clamped (# FCLMP1 = 0) (step 56 in FIG. 9). The basic duty (EVAP0) to be described later is lower than the lower limit (W
CGDTY #) or more (Step 5 in FIG. 9)
7). When the load (QH0) is equal to or less than the upper limit (WCGQH #) (Step 58 in FIG. 9). When a certain delay time has passed after the condition (1) is satisfied (CONTWCJ ≧ WCGDLY #) (step 59 in FIG. 9).

In particular, the reason why the purge cut is performed when the condition (1) is satisfied is that if the purge is performed for a long time, the amount of fuel removed from the activated carbon canister 16 decreases, the purge fuel concentration decreases, and the purge fuel concentration used for calculation (described later) This is because there is a difference between the purge learning value WC and the purge learning value WC). Therefore, even under the condition of performing the purge, the purge learning is performed while performing the intermittent 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 is 1 (step 52 in FIG. 9). This reservation is reserved when the purge learning value is clamped and the purge learning ends, as described later. When the air-fuel ratio feedback control is being performed (# FCLS1 = 1) and not being clamped (# FCLMP1 = 0) (step 64 in FIG. 9). The basic duty (EVAP0) described later is set to the upper limit (O
FGDTY #) or less (Step 6 in FIG. 9)
5). When a certain delay time has passed after the condition (1) is satisfied (CONTOFJ ≧ OFGDLY #) (step 66 in FIG. 9).

When any one 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 stepwise, the purge valve is gradually closed by the slow flag = 1 and the cut flag = 1. On the other hand, <6>
When all of the conditions <11> to <11> are canceled, the purge O
N, the cut flag is set to 0 and the cut flag is set to 1 slowly to open the purge valve in stages (FIG. 8).
Step 49).

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

(2) Purge Valve Opening Characteristics (2-1) Connection with Purge Cut Conditions When any of the above conditions <6> to <11> is satisfied, (EVAP) is set until EVAP = EVPCUT #.
T-EVPCUT #) * The purge valve duty (EVAP) is reduced at the speed of SPECUT # (steps 91 to 95, 91 to 94, 96, and 97 in FIG. 10).

When all of the above conditions <1> to <11> are cancelled, EVAP = EVPCUT # is set once, and (EVAPT-EVPCT) is set until EVAP = EVAPT.
EVPCUT #) * The purge valve duty EVAP is increased at the speed of SPEON # (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, SPECUT # is the purge valve closing speed, SP
EON # is the opening speed of the purge valve.

FIG. 33 shows the control waveform of the EVAP (purge valve duty) by a solid line.
At the time of 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 #. FIG. 33 also shows the time of switching to the immediate cut by a broken line, and only at this time, the EVAP is set to 0 in a stepwise manner.

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

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

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

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

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

The target purge rate PAGERT in equation [b] is
From the purge learning value WC corresponding to the purge fuel concentration, FIG.
(See step 3 in FIG. 5).

As shown in FIG. 23, PAGERT is decreased where WC is large, and PAGE is decreased when WC is decreased.
RT is increased. In order to prevent the fuel vapor of the purge gas from leaking out of the vehicle, the purge rate may be increased. In this case, if the fuel concentration is high, the error in the air-fuel ratio A / F increases. So, WC
Is large (ie, the purge fuel concentration is high), the target purge rate PAGERT is made small while the WC is small (the purge fuel concentration becomes low) in order to prevent the A / F error from becoming large. ), The purging is rapidly performed at a large target purge rate.

PAGERT is an air flow meter section flow rate Qs
34, the horizontal characteristic is obtained when the WC is large or small as shown in the upper part of FIG. 34 (shown by a solid line). However, since the purge valve flow rate becomes maximum when the purge valve is fully opened, the purge rate gradually decreases after the purge flow rate becomes maximum.

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 a purge rate (constant rate) when the sensor is abnormal.

By the way, as shown in equations [a] and [b], EV
When the number of variables used for obtaining AP0 increases (TQ
PV, KPVQH, KPVVB, Qs, PAGERT), the precision of EVAP0 depends on the precision of the number of bytes and the table given to these variables.

Therefore, here, the purge valve target flow rate TQ
PV is obtained from 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 both of the equations [a] and [b], they are adopted.

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 of the equation [2] is a correction rate for changing the flow rate due to the differential pressure across the purge valve even when the flow path area of the purge valve section is constant, and looks up a table containing the characteristics of FIG. 24 from the flow rate QH0. It is obtained by raising (step 4 in FIG. 5). As the pressure difference becomes smaller and smaller,
When the pressure difference between front and rear is small (when QH0 is large), the correction is made so that the target flow rate becomes large.

Since the differential pressure is not actually detected,
Here, QH0 is adopted as the differential pressure equivalent amount. QH
0 is a well-known volume flow rate of the throttle valve portion determined from the engine speed NE and the throttle opening TVO.

When looking at the phase at the transition, the pulse width TP corresponding to the cylinder air amount is closer to the differential pressure across the purge valve than to QH0. Therefore, it is desirable to use TP. Therefore, QH0 is used here. In addition,
The TP is also known, and this means that even if the air flow rate is measured by the air flow meter section as described later, in consideration of the fact that the air actually flows into the cylinder with a first-order lag, the cylinder air amount flowing with the first-order lag is considered. On the other hand, the fuel amount is given in a constant proportional relationship.

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

KPVVB is a correction factor for the relationship between the basic duty EVAP0 of the purge valve and the flow rate of the purge valve depending on the voltage applied to the purge valve, and VBOFPV is the purge valve duty when the flow path of the purge valve starts opening. The correction rate differs depending on the applied voltage of the valve, and each of the correction rates differs depending on the type of the purge valve. FIGS. 25 and 26 show an example in which the purge valve is driven by a linear solenoid.

(2-3) Predicted value of the flow rate of the purge valve The predicted value of the flow rate of the purge valve QPV is QPV = EVAPQ * KPVQH... [4] where EVAPQ; the basic flow rate of the purge valve KPVQH; (Step 19 in FIG. 6).

The EVAPQ of the equation [4] is (EVAP-O
A table containing the characteristics shown in FIG. 32 is looked up from FSTPV-VBOFPV) * KPVVB to obtain (step 18 in FIG. 6). In FIG. 29, the horizontal axis represents EV
AP0 * KPVVB is not purge ON, OFF
This is because the value of EVAP-OFSTPV-VBOFPV (that is, the value at the time of transition) does not match the value of EVAP0 (the value at the time of equilibrium) when switching to.

(3) Purge learning control In addition to the basic air-fuel ratio learning value αm, a purge learning value WC (also a learning value of the mixture ratio of purge gas) WC corresponding to the purge fuel concentration is introduced. Unlike the purpose of introducing αm, the purpose of introducing αm is that the air-fuel ratio error due to purge gas is relatively time-varying, unlike the air-fuel ratio error, which changes very slowly (due to variations in the characteristics of air flow meters and injectors, etc.). Therefore, the control accuracy of the air-fuel ratio is improved by separating the learning value into the purge learning value WC and the basic air-fuel ratio learning value αm.

Now, the purge fuel concentration is set to purge ON, OF
It can be predicted as follows from α that changes by switching to F.

At this point, if only the purge fuel concentration is higher than the previous one (assuming that there is no air-fuel ratio error due to an air flow meter or the like), the air-fuel ratio shifts to the rich side, and α is set to return to the lean side. The value (or its average value) shifts to a side where it becomes smaller than the control center (1.0). Therefore, when α shifts to the smaller side, the purge learning value WC is updated to the larger side, and the updated WC corresponds to the purge fuel concentration that is higher than the previous time. Conversely, when the purge fuel concentration is lower than the previous time, α deviates from the control center to a larger value. Therefore, in this case, if the WC is updated to a smaller value, the updated WC becomes lower than the previous time. Is equivalent to

By predicting the purge fuel concentration in this manner, the purge ON and OFF can be performed without providing a sensor.
That is, it is possible to prevent an air-fuel ratio error immediately after switching to the mode.

(3-1) Battery Backup Although the purge learning value WC is a battery battery, WC = INWC # when the control unit 2 is first energized (steps 101 and 102 in FIG. 11). INWC # is an initial value of WC for the first energization.

Otherwise, when power is supplied to the control unit 2, WC = WC holding value + WCST #, where WCST # is an added value of WC at the time of starting (steps 101 and 105 in FIG. 11). WCST
# Takes into account the increase in fuel stored in the activated carbon canister during a stop. If there is not enough time between the previous engine stop and the current engine start, WC
Although the air-fuel ratio error does not occur during the purge during the current operation due to the retained value, if there is a time interval, the evaporated fuel accumulates in the activated carbon canister, and this amount will be the air-fuel ratio error during the current engine start Appears as.
Therefore, this amount (that is, the amount of fuel increase during stopping) is
It is estimated by T #.

(3-2) Conditions for Permitting Purge Learning Since purge learning is permitted at the time of switching to purge ON or purge OFF, after a flag for instructing switching of purge ON and OFF is set, that is, at step 30 in FIG. 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 for permitting learning when switching between purge ON and OFF without waiting for the change of α to end is as follows.
This is to increase the frequency of learning.

(3-3) Purge Learning Interruption Conditions Purge learning is interrupted when the following conditions are satisfied (FIG. 1).
2 steps 116 to 119, 113). When the purge learning permission flag = 0 (Step 116 in FIG. 12). This is because the purge learning is interrupted when the purge is switched from the purge ON to the purge OFF or vice versa while the purge learning condition is satisfied (steps 81 and 8 in FIG. 8).
5). When the condition is other than the condition that the air-fuel ratio feedback control is being performed and the clamp is not being performed (step 117 in FIG. 12). This is because the condition during the air-fuel ratio feedback control and not during the clamping is set as the learning condition. When the basic duty (EVAP0) is a predetermined value (WCCGDT)
Y #) (step 118 in FIG. 12). When the basic duty is small, it is confused with an air-fuel ratio error due to the variation of the purge valve rising duty, so that this is avoided. As shown in FIG.
In terms of the purge valve flow rate, the high flow rate range is set as the purge learning condition, and the low flow rate range is set as the offset learning condition. When the load (QH0) is too high beyond a predetermined value (WCGQH #) (step 119 in FIG. 12).

However, even if one of the conditions (1) to (5) 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 reason why the purge learning permission flag is not set to 0 is that if the purge learning is interrupted by the purge cut for the purge learning, the purge learning is switched back on, but the purge learning is not started at that time. To do that.

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) Further, initialization and post-processing of a RAM and a flag for purge learning are performed (step 11 in FIG. 12).
4).

In the learning when the purge is ON, the EVAP
Is the offset of the purge valve (for example, VBOFPV + D
The purge learning is made to wait until after LYWCG # (which is equivalent to the delay time) (step 12 in FIG. 12).
1, 122).

(3-4) Updating of Purge Learning Value The first average value ALPAV of the air-fuel ratio feedback correction coefficient that 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 (also the ALPAV before the purge ON / OFF switching) is stored in the ALPST.

When 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 restricted between the upper limit (WCMAX #) and the lower limit (WCMIN #) (steps 183 to 18 in FIG. 14).
5).

ΔWC is a learning update amount, which is an air-fuel ratio feedback correction coefficient ALPHA (α) as shown in FIG.
) And ALPST are given different values when the difference is large and small (± PWCH and ± IWCH if large, ± PWCL and ± IWCL if small), and ΔWC as shown in the table Therefore, FIGS. 14 and 15 are assembled.

Here, how the learning update amount ΔWC is given will be described with reference to the waveform shown in FIG. 36, so that the description in FIGS. 14 and 15 is replaced.

FIG. 36 shows the state at the time of switching to purge ON.

When α is moved toward the lean side by the switching to the purge ON state (a long integral amount I is acting), α
ALPAV (indicated by a broken line), which is the average value of, also moves to the lean side, and when ALPAV <ALPST is satisfied (point A)
The learning value WC is stepwise PWCL # (step amount)
And then gradually increased by IWCL # (integral amount).

The learning update amounts (PWCL # and IWC
When L moves to the lean side across the predetermined width (DALPH #), the learning value WC becomes larger at this crossing point (point B) than PWCL #.
The value is further increased stepwise by WCH # (also a step amount), and after that, ICH having a value larger than IWCL #
It is gradually increased by WCH # (integral amount). 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 an overshoot of the learning value WC, the addition (or subtraction) of the step amount PWCH # is performed only once while the purge learning is permitted.

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

(3-5) Purge learning clamp EVAP = EVAPT or EVAP = EVPCUT #
At this time, the average value of the peak values of the latest two learning values WC (that is, the WC immediately before PWCL # addition / subtraction) is obtained, and after that, WC is clamped to this value and the purge learning is completed.

Therefore, in FIG. 14, ΔP is increased by + PW
Immediately before entering CL # (or -PWCL #), the value stored in the memory OLDWC1 is replaced with the memory OLDWC1.
2, the value stored in the memory WC is stored in the memory OLDW.
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 is reached, and the value of (OLDWC1 + OLDWC2) / 2 is reset to WC (steps 125 and 126 in FIG. 12).
The purge learning permission flag is set to 0 (step 128 in FIG. 12).

The reason why the purge learning value is clamped is as follows. By making the purge learning value WC different from the basic air-fuel ratio learning value αm, the control accuracy of the air-fuel ratio is increased.
I want to finish purge learning early. This is because if the purge learning is performed forever, a change in α due to a change in the operating conditions will be mixed into the purge learning as an error. In other words, it is desirable to end the purge learning before the operating conditions change, and eliminate the air-fuel ratio error by the basic air-fuel ratio learning when the operating conditions change (except when the purge is switched between ON and OFF).

The PWCL added at point Q in FIG.
# Indicates that the PWCL addition frequency counter value (CONTP
WCL) is not counted (steps 124 and 130 in FIG. 12).

(3-6) 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 to the step amount P (steps 263 and 268 in FIG. 18), ALPAV = (ALPHA + ALPO) / 2 where ALPO is obtained by α immediately before the previous P component addition (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, as shown in FIG. 37, the ALP starts from the first cycle of the control after the clamp is released.
In order to calculate AV, the addition counter value of P (CO
If (UNTP) is less than 3, ALPAV = 1.0 (steps 265 and 269 in FIG. 18). Of course, during clamping in the air-fuel ratio feedback control, A
Both LPAV and ALPO are 1.0 (steps 261 and 262 in FIG. 18).

(4) Learning of Purge Valve Rise Duty When the purge valve 21 is driven by a linear solenoid, the purge valve rise duty (duty when the purge valve starts opening) depends on the temperature as shown in FIG.
And the flow rate of the purge valve fluctuates especially in the low flow rate range. Since the purge valve becomes more difficult to open as the temperature rises, the purge valve flow rate substantially decreases at the time of high temperature even if the same basic duty EVAP0 is given.

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

Assuming that the linear flow characteristic of the purge valve moves parallel to the left and right in accordance with the temperature as shown in FIG. 38 (that is, the change in the inclination of the straight line is ignored), the target duty is equal to the basic duty. The target duty may be given by the + purge valve rise duty.

If the rise duty of the purge valve becomes larger than the previous one due to the rise in the temperature of the purge valve (see FIG. 38), the purge rate (the ratio of the flow rate of the purge valve to the intake air amount) decreases due to the delay in valve opening. Leans toward the lean side and returns α and AL to return to the rich side
PAV is shifted to a side where it is larger than ALPST.

At this time, if the offset learning value (corresponding to the rising duty) OFSTPV is updated to a larger value, the updated learning value corresponds to the rising duty with respect to the purge valve temperature at that time. Raise the duty EVAP0 (add a value obtained by adding the learning value to the basic duty EVAP0 to the target duty E
VAPT), the flow rate of the purge valve can be made the same as before the temperature rise.

Conversely, if the valve opening is accelerated due to a decrease in the temperature of the purge valve, the flow rate of the purge valve increases and the air-fuel ratio leans to the rich side, so that α and ALPAV deviate from ALPST to the smaller one this time. By updating the offset learning value OFSTPV to a smaller value, the updated learning value corresponds to the rising duty with respect to the purge valve temperature at that time.

As described above, the concept of the offset learning is exactly the same as that of the purge learning, and the only difference is that the constants and variable names are different and the direction of updating the learning value is reversed. Therefore, only the differences will be briefly described.

(4-1) Conditions for Permitting Offset Learning Offset learning is permitted when switching to purge ON or purge OFF. 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 learning value WC) caused by the purge and the air-fuel ratio error (learned value OFSTPV) caused by the purge valve variation.
This is for the purpose of separating

This will be further described with reference to FIG. 34. When the variation in the valve characteristic caused by the temperature characteristic is superimposed on the purge rate characteristic, the variation in the purge rate in the small flow rate region (region where Qs is small) is indicated by the broken line. Expands rapidly. This is because, even if the purge valve has the same flow rate variation, if the value is converted into the purge rate, the smaller the Qs, the larger the ratio of the variation amount to the Qs.

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

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

(4-3) Updating of Learning Value As can be seen by comparing FIG. 39 with FIG. 35, the way of giving the positive / negative amount of the learning update amount ΔOFSTPV is opposite to that when 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 has not been performed even once (step 281 in FIG. 18). When the flag is slowly set to 1 (step 28 in FIG. 18)
2). That is, it is at 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 during the purge learning and the offset learning (at the time of,) in addition to during the purge (at the time of), because the air-fuel ratio error due to the purge gas whose change with time is relatively quick is relatively large. , Αm is introduced to prevent the air-fuel ratio error from changing very slowly (due to variations in the characteristics of the air flow meter and the injector).

Note that the basic air-fuel ratio learning αm is updated by αm = αm holding value + Δαm, where Δαm is the learning update amount, and the learning update amount Δαm is Δαm = (ALPAV-1.0) · GAIN where ALPAV; Average value GAIN: Needless to say, it is calculated based on the update rate (a 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 The fuel injection pulse width of CHOSn; the amount of increase / decrease of each cylinder ERACIn; is calculated by the transition pulse width from interrupt injection to synchronous injection (step 323 in FIG. 21). This equation itself is known.

Here, the fuel injection pulse width TI in equation [5]
Is at the time of simultaneous injection: TI = (TP−TEFC + KATHOS) * TFBYA * (α + αm) + Ts [6] At the time of sequential injection: TI = (TP−TEFC + KATHOS) * TFBYA * (α + αm) * 2 + Ts ... [7] where 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).

The difference from the prior art is that TEFC is subtracted from TP in equations [6] and [7]. This is because when the purge gas is introduced into the intake pipe, an extra amount of fuel (TEFC) of the purge gas is added and flows into the cylinder, so that the same air-fuel ratio is maintained during the purge as when the purge is not performed. For this purpose, the fuel amount obtained by subtracting the purge gas fuel amount may be supplied from the injector 8 for each cylinder.

The cylinder air amount equivalent pulse width TP
TP0 = Qs * KCONST # * KTRM / NE ... [8] TP = TP0 * FLOAD + TP * (1-FLOAD) ... [9] Here, TP0: pulse width equivalent to air flow meter section air quantity Qs: air flow meter section air quantity KCONST #; constant KTRM; trimming coefficient used to correct an air amount error NE; engine speed FLOAD; weighted average coefficient, which is conventionally obtained (step 3 in FIG. 21).
12, 313). These formulas are also known, and are used for phase adjustment corresponding to the cylinder intake air amount.

(6-2) Pulse Width Equivalent to Purge Fuel The pulse width TEFC equivalent to purge fuel is as follows: TEFC = QEFC * KCONST # / NE ... [10] where QEFC: Predicted cylinder intake amount of purge fuel KCONST #; Constant NE; It is determined by the engine speed (step 311 in FIG. 21). The expression [10] is similar to the expression [8], and is obtained by converting the predicted value of the cylinder intake amount (QEFC) of the purge fuel into a unit equivalent to the injection pulse width.

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

The reason is that the purge fuel flow rate (this is only the fuel amount) QEF flowing out of the purge valve to the intake pipe has a dead time (simple time delay) before reaching the cylinder, and the gaseous fuel is diffused. This is because the waveform of the QEFC can be represented as shown in FIG.

When storing the calculated value of QEF2 in the memory, a fixed number of memories are prepared and sequentially shifted to the next memory, so that the value of QEFDLY # times before May be QEFC (step 295 in FIG. 19).

The purge fuel flow rate QEF of the formula [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 factor 6 Step 21). By multiplying the purge valve flow rate predicted value QPV by the fuel concentration equivalent value (WC) of the purge gas, QEF as the purge fuel component is obtained.

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

(7) Intake air amount When purging is performed, the air amount Q used for the injection amount calculation is Q = Qs + QEA ... [14] where Qs is the air flow meter section air amount QEA; Calculate by flow rate (excluding fuel).

Here, an artificial selection flag (FPQ
If A) = 1, the air amount is corrected by the amount of the purge air by equation [14], and if FPQA = 0, no correction is made (steps 302, 303, 302, 304 in FIG. 20).

The purge air flow rate QEA in the equation [14] is as follows: QEA = QPV−QEF * KFQ #... [15] Where, QPV; purge gas flow rate (air + fuel) QEF; purge fuel flow rate KFQ #; Calculate the conversion rate.

(8) Wall Flow Correction Aiming at the correction of the low frequency portion of the wall flow (the wall flow that changes relatively slowly), the equilibrium adhesion amount (M
FH) is stored, and a change in the equilibrium adhesion amount due to the transition is added to the pulse width TP corresponding to the cylinder air amount by a predetermined ratio for each fuel injection (subtracted during deceleration) as a total correction amount (KATHOS). (JP-A-63-38656)
And JP-A-63-38650. Further, with the aim of correcting the high-frequency portion of the wall flow (the wall flow that changes relatively quickly), the wall flow (CHOS
In some cases, n: increase / decrease amount for each cylinder, INJSETn: interrupt injection amount for each cylinder, ERACIn; interrupt injection → pulse width for transition to synchronous injection (see Japanese Patent Application Laid-Open No. Hei 3-11139).

The wall flow correction amount KATHOS takes into account a fuel supply delay. When accelerating, the injection amount must be increased.However, even though the injector has good atomization characteristics, part of the fuel adheres to the intake manifold wall and flows in a liquid form along the intake pipe wall. Wall flow), which flows into the cylinder at a slower rate than the airborne fuel. That is, since the air-fuel mixture sucked into the cylinder by the wall-flow fuel is temporarily thinned, the wall-flow correction amount KATHOS is set during acceleration in order to prevent the temporary air-fuel mixture from being lean.
Only increase the amount. Conversely, 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 that the air-fuel mixture becomes temporarily too rich, and CO and HC increase. I do. Therefore, during deceleration, the amount of the vaporized wall flow is reduced.

However, since the gaseous fuel in the purge gas is a light component evaporating from the fuel tank 15 (a component that evaporates at a low temperature such as butane), the gaseous fuel forms a flow wall flow while being mostly vaporized even in the intake pipe. Nothing. Therefore, when calculating the wall flow correction amount KATHOS, it is necessary to exclude the purge fuel component (TEFC).

Therefore, when purging, the equilibrium adhesion amount MFH is determined by the following expression: MFH = MFHTVO * CYLINDR # * (TP-TEFC) (16) where MFHTVO; adhesion ratio CYLINDR #; number of cylinders TP; Pulse width TEFC: Calculated by pulse width equivalent to purge fuel. In other words, by subtracting TEFC, which is the fuel component that does not form a wall flow, from TP, the wall flow correction amount KATHO
The prediction accuracy of S is improved, and the air-fuel ratio at the time of transition can be made more appropriate.

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

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

The description of the classification of the control system has been completed.

In this example, as shown in FIG.
Auxiliary air passage 25 bypassing throttle valve 6
Is provided with an auxiliary air valve 26 which is driven by a pulse signal of a fixed period (for example, a period of 32 ms) from the control unit 2, and which determines the opening degree of the auxiliary air valve 26.
The duty ISCON is calculated as: ISCON = ISCi + ISCp + ISCtr + ISCat +
ISCa + ISCrfn ... [18] Where, ISCi; integral of idle feedback control ISCp; differential of idle feedback control ISCtr; correction value during deceleration (equivalent to dashpot) ISCat; gear position correction value of A / T vehicle ISCa; air conditioner load correction Value ISCrfn: Radiator fan load correction value (valve opening increases as ON duty increases).

At the time of idling when the engine rotation is unstable,
The feedback control is performed by increasing or decreasing ISCi and ISCp so that the target rotation speed (which is basically set in accordance with the cooling water temperature TW) (If the actual rotation speed is lower than the target rotation speed, ISCON is reduced). To be bigger,
Conversely, if the rotational speed is higher than the target rotational speed, the correction is made so that ISCON becomes smaller), and the idle rotation is stabilized.

Therefore, as shown in FIG. 42, signals from the throttle valve switch (turned on when the throttle valve reaches the idle contact) 31, the crank angle sensor 9, and the water temperature sensor 11 are transmitted to the vehicle speed sensor 12, the neutral switch 32, Signals from the air conditioner switch 33 and the radiator fan switch 34 are input to the control unit 2.

On the other hand, when the state changes from the idle state to the non-idle state, the feedback control of the idle speed until then is released, and the valve opening during the feedback control is maintained as it is. ISCON (= ISCi + ISCp) at the timing of shifting to the non-idle state continues to be output to the actuator of the auxiliary air valve 26, and auxiliary air corresponding to this valve opening degree flows through the auxiliary air passage 25.

In this case, if the operating condition is shifted to the purge region and the purging is performed, the torque increases due to the intake air amount increased by the decrease of the intake manifold negative pressure, so that a torque step occurs before and after the purge. , Driving performance is deteriorated.

To deal with this, the control unit 2 uses ISCON (ON duty to the auxiliary air valve).
When the purge is ON, ISCON = ISCON-ISCEVP... [17] where ISCEVP; purge correction value.

Since the purge air flow rate (air flow rate of the purge valve flow rate) QEA is applied downstream of the throttle valve 6, the purge correction value (opening reduction amount) ISCEVP corresponding to this purge air flow rate is calculated by the equation [18]. By re-calculating the value obtained by subtracting the value from ISCON into ISCON, the increase in the purge air flow rate is offset.

However, there is an engine to which the deceleration correction value ISCtr is not introduced or a vehicle to which the gear position correction value ISCat is not introduced, so that the artificial selection flag (FEVISC)
When = 1, ISCON is obtained by the equation [17] (steps 324 and 326 in FIG. 22). When FEVISC = 0, the ISCON obtained by the equation [18] is used as it is (step 324 in FIG. 22). 327). ISC
FEVISC = 1 only when one or both of tr and ISCat are introduced.

The purge correction value ISCEVP of the equation [17]
Is obtained by looking up a table containing the characteristics of FIG. 44 from the quotient of QEA and KPVQH (QEA / KPVQH) (step 325 in FIG. 22). Since the amount corresponding to the purge air flow rate QEA is reduced by the auxiliary air valve 26, the value of ISCEVP is increased in proportion to the purge air flow rate QEA.

It should be noted that KPVQH (the negative pressure correction rate of the purge valve flow rate) is, as described above in the equation [2], the value before and after the purge valve even when the flow passage area of the purge valve section is constant when the purge valve target flow rate TQPV is obtained. This is introduced as a correction factor corresponding to a change in the flow rate due to the differential pressure. In FIG. 44, the horizontal axis is QEA / KPVQH for the same reason. On the other hand, the purge air flow rate QEA is obtained as follows.

When the purge fuel concentration is predicted based on the purge learning value WC (FIGS. 12 to 14), and when the predicted purge valve flow rate QPV is determined according to the operating conditions (step 19 in FIG. 6), the purge fuel flow rate (step 19 in FIG. 6) is determined. The fuel flow rate QEF of the purge valve flow rate) is obtained by QEF = WC * QPV * KQPV [13] (step 21 in FIG. 6). [13]
KQPV in the equation is a flow rate correction factor, and it is not necessary to consider whether or not the flow rate of fuel from the canister 16 is the same whether the flow rate of the purge valve is large or small.

Since the purge valve flow rate QPV is the sum of the purge fuel flow rate QEF and the purge air flow rate QEA, the purge air flow rate QEA can be obtained by the following equation: QEA = QPV−QEF * KFQ #.

However, the KFQ # (the correction rate for shifting from the fuel flow rate to the air flow rate) in [15] is used to correct the difference because the flow rates of air and fuel vapor are different even in the same flow path. It is.

The QEA synchronizes the EVAP (purge valve duty) output (step 291 in FIG. 19) executed in the Ref signal job with the value on the right side of the equation [15] obtained in the background job. QEAB
(Temporary storage) (step 2 in FIG. 6).
2) In the Ref signal job, the value of QEAB is transferred to QEA in the memory (step 292 in FIG. 19).

Here, the operation of this example will be described with reference to FIG. 44. FIG. 44 shows the state when the accelerator pedal is depressed from the idle state.

At the time of transition from the idle state to the non-idle state, the feedback control of the idle speed is released.
When CON is continuously output, auxiliary air flows through the auxiliary air valve 26 held at the valve opening corresponding to the ISCON.

On the other hand, when the throttle valve 6 is opened in conjunction with the accelerator pedal, the TP (pulse width corresponding to the cylinder air amount) increases, and the TP cut region (purge OFF) as shown in FIG. When the purge range is entered from the condition (3), the target purge rate PAGERT is set from the purge learning value WC at that time, and the purge valve target duty E is set.
The opening of the purge valve 21 is controlled so as to be VAPT (FIG. 44 (D)).

However, if the purge valve 21 is opened while the auxiliary air valve 26 is open, the purge air flow rate Q
The manifold negative pressure decreases by the increase in EA (FIG. 44).
(F) (dashed line), a torque step occurs before and after purging.

On the other hand, when the purge valve 21 is opened in this example, the opening of the auxiliary air valve 26 is reduced by the opening reduction corresponding to the purge correction value ISCEVP (FIG. 4).
4 (C) dashed line). When the flow rate of the auxiliary air that bypasses the throttle valve 6 decreases due to the decrease in the opening degree of the auxiliary air valve 26, the purge air flow rate QEA
The increase in the amount of intake air due to the addition of is absorbed. To cancel the purge air flow (increase in the amount of intake air due to purge), ISCONVP to ISCEVP when purge is ON
By subtracting only this value (ISCON-ISCEVP) as the correction value during the purge, the waveform of the manifold negative pressure becomes the same as when there is no purge as shown by the two-dot chain line in FIG. is there.

As a result, the torque difference at the time of switching the purge ON and OFF is absorbed, and the same operation feeling can be obtained before and after the purge.

In the embodiment, the purge valve driven by the linear solenoid has been described. However, the present invention is not limited to this, and a rotary valve or a valve driven by a step motor may be used. The purge fuel concentration is not limited to the case where the purge fuel concentration is predicted by the purge learning value WC, but may be detected using a sensor.

[0157]

According to the present invention, the purge valve is opened under the purge ON condition, the purge gas from the canister is introduced into the intake manifold downstream of the throttle valve, and the auxiliary air valve provided in the bypass passage of the throttle valve is set in the non-idle state. While opening to a predetermined opening degree, the purge air flow rate is calculated by subtracting the purge fuel flow rate from the purge valve flow rate, and the opening degree reduction amount of the auxiliary air valve is calculated in accordance with the purge air flow rate. Purge O in idle state
Since the auxiliary air valve is closed by the opening reduction amount from the predetermined opening set in the non-idle state when the pressure becomes N, the torque step at the time of switching to the purge ON / OFF is suppressed, The same operation feeling can be obtained before and after the purge.

[Brief description of the drawings]

FIG. 1 is a diagram corresponding to claims of the present invention.

FIG. 2 is a system diagram of one embodiment.

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

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

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

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

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

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

FIG. 9 is a flowchart illustrating a purge cut condition determination for purge learning and offset learning.

FIG. 10 is a flowchart for explaining calculation of a purge valve duty EVAP during switching to 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 condition for suspending purge learning and clamping of a purge learning value WC.

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

FIG. 14 shows selection of learning update amount ΔWC and purge learning value WC.
9 is a flow chart for explaining updating of a.

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
3 is a flowchart for explaining sampling of the learning 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 the calculation of the air-fuel ratio feedback correction coefficient α and the determination of the update prohibition condition of the 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
9 is a flowchart for explaining the 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 rate KPVQH of a purge valve flow rate.

FIG. 25: Battery voltage correction rate KPVV of purge valve flow rate
6 is a characteristic diagram of B. FIG.

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

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

FIG. 28 is a characteristic diagram of a lookup value.

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

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

FIG. 31 is a characteristic diagram of the 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 a purge valve.

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

FIG. 35 is a table 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 the clamp is released.

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

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

FIG. 40: Offset learned value O when switching to purge ON
It is a wave form diagram of FSTPV.

FIG. 41 is a predicted cylinder intake amount QEFC of purge fuel.
FIG.

FIG. 42 is a control system diagram of an auxiliary air valve.

FIG. 43 is a characteristic diagram of a purge correction amount ISCEVP.

FIG. 44 is a waveform diagram illustrating an operation when the accelerator pedal is depressed from an idle state.

[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) 9 Crank angle sensor 11 Water temperature sensor 15 Fuel tank 16 Activated carbon canister 21 Purge valve 25 Auxiliary Air passage 26 Auxiliary air valve 31 Throttle valve switch 41 Purge condition determination means 42 Purge gas introduction device 43 Auxiliary air valve 44 Auxiliary air valve opening setting means 45 Auxiliary air valve driving means 46 Purge fuel concentration detection / prediction means 47 Purge valve flow rate calculation Means 48 Purge fuel flow rate calculation means 49 Purge air flow rate calculation means 50 Opening degree decrease amount calculation means 51 Subtraction means

Claims (1)

(57) [Claims] 1. A purge ON, OF, receiving an operation condition signal
Means for determining the condition of F, and purging O based on the determination result.
A device for opening a purge valve under N conditions to introduce purge gas from a canister into an intake manifold downstream of a throttle valve, an auxiliary air valve for adjusting an amount of auxiliary air bypassing the throttle valve, and an opening degree of the auxiliary air valve. Detecting or predicting the fuel concentration of the purge gas in an evaporative fuel processing apparatus for an engine comprising: means for setting a predetermined opening degree in a non-idle state; and means for driving an auxiliary air valve so as to have a predetermined opening degree. Means for calculating the flow rate of the purge valve in response to an operating condition signal; means for calculating the fuel flow rate of the purge valve flow rate based on the purge valve flow rate and the fuel concentration; and Means for calculating the air flow rate of the purge valve flow rate by subtracting the fuel flow rate from Means for calculating a reduction amount, and means for subtracting the opening reduction amount from the predetermined value set under a specific operation condition when the purge is turned on under the specific operation condition. Evaporative fuel treatment system for engines.