JPH07166978A - Evaporative fuel treatment system of engine - Google Patents

Abstract

PURPOSE:To enhance the frequency of learning by renewing learned values to such an extent that no great mistakes in learning occur during purging under stoichiometric operation. CONSTITUTION:A renewal inhibit means 40 inhibits renewal of learned values by a learned value renewal means 37 prior to purging under stoichiometric operation. If a start means 41 opens a purge valve 38 to start purging while renewal of the learned values is inhibited, a calculation means 43 calculates a purge gas concentration lambdap according to an air-to-fuel ratio lambda'a immediately after the start of the purging and an air-to-fuel ratio lambdaa prior to the purging. A control means 44 controls the opening of the purge valve 38 according to the purge gas concentration lambdap and an inhibit canceling/continuing means 46 cancels the inhibit of renewal by the learned value renewal inhibit means 40 when the judgment result of a judgment means 45 shows that the purge gas concentration lambdap is not more than a predetermined value lambdap1; when the purge gas concentration lambdap is in excess of the predetermined value lambdap1 the means 46 continues the inhibit of renewal.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art In order to eliminate the deviation of the base air-fuel ratio from the theoretical air-fuel ratio due to the deterioration and variations of components such as air flow meters and injectors, and the non-linearity of the injector pulse width-flow rate characteristics, stoichiometric operation ( During the operation in which the stoichiometric air-fuel ratio is made the target air-fuel ratio), the air-fuel ratio learning control is performed.

On the other hand, the fuel vapor generated in the fuel tank is adsorbed on the activated carbon of the canister, generally after a predetermined time has elapsed after the engine has been started, the cooling water temperature is at or above a predetermined water temperature, and the vehicle speed is at or above a set value. That there is
When all the conditions that the throttle valve is opened are satisfied, the purge valve is opened, and the fuel vapor separated from the activated carbon by the fresh air becomes the purge gas together with the fresh air and is introduced into the intake pipe.

When the air-fuel ratio feedback condition is satisfied, the introduction of the purge gas causes the air-fuel ratio feedback correction coefficient α to move to the lean side (α <1.0), and when a certain learning condition is satisfied, the air-fuel ratio learning correction is performed based on this α. The coefficient (hereinafter referred to as the learning value) αm is updated to the lean side so that the exhaust air-fuel ratio returns to the stoichiometric air-fuel ratio (αm <1.0), but it is easy to vaporize under hot weather where a large amount of fuel vapor is generated. When gasoline is used or when traveling at high altitudes, high-concentration purge gas is introduced, and when the learning value is continuously updated accordingly, the learning value αm becomes a value on the over lean side.
If the learned value αm that has become the value on the over lean side is used immediately after the purge is cut from this state, the air-fuel ratio becomes over lean, the engine becomes unstable, and the running performance and exhaust performance deteriorate.

Therefore, in order to prevent the learning value from becoming an over lean value due to the introduction of the rich purge gas,
In the device disclosed in Japanese Patent Laid-Open No. 2-67441, updating of the learning value αm is prohibited during purging. Since the learning value during purging is prohibited, the learning value αm is maintained at the value immediately before purging even during purging, and this value will be used immediately after shifting to purge cutting, and the air-fuel ratio becomes over lean immediately after purging cutting. There is nothing.

[0006]

However, if the learning value update is prohibited during purging as in the above apparatus, the chances of updating the learning value are significantly reduced (or even eliminated) depending on operating conditions. )Sometimes. For example, when starting and stopping repeatedly under high temperature conditions such as traffic congestion under hot weather, the fuel vapor is repeatedly charged to the canister while the vehicle is stopped, so if you try to purge as much as possible while driving, There is no opportunity to update the learning value. On the other hand, if the opportunity for purging is limited in order to increase the chances of updating the learning value, the purging becomes insufficient when the vehicle is running in a traffic jam under hot weather as described above.

For this reason, if the learned value has not converged before the congested operation in hot weather and the learned value is on the over lean side, the exhaust performance and drivability associated with over lean continue to deteriorate. Will end up. Even if the feedback correction of the air-fuel ratio is performed, the control accuracy of the air-fuel ratio deteriorates until the average value of the correction coefficient α converges.

Further, there is a device such as the device disclosed in Japanese Patent Laid-Open No. 63-131843 which uses different learning values during purging and during purge cutting. The backup RAM has a large capacity, which increases the cost.

Therefore, an object of the present invention is to increase the learning frequency by updating the learning value to the extent that a large erroneous learning does not occur during purging during stoichiometric operation.

[0010]

As shown in FIG. 1, a first invention is a memory 31 for storing a learning value .alpha.m and a means 32 for reading the learning value .alpha.m according to a driving condition signal.
And means 3 for calculating the fuel injection amount by correcting the basic injection amount TP according to the operating condition signal with the read learning value αm.
3 and a device 34 for supplying this injection amount of fuel to the intake pipe
And a sensor for detecting the oxygen concentration in the exhaust gas (for example, O
₂ sensor or wide range air-fuel ratio sensor) 35, means 36 for calculating the air-fuel ratio feedback correction amount α so that the exhaust air-fuel ratio falls within the vicinity of the theoretical air-fuel ratio based on the sensor detection value, and this air-fuel ratio feedback correction amount α Based on the above, means 37 for updating the learning value αm, a purge valve 38 for opening and closing a passage for introducing the fuel adsorbed in the canister together with fresh air into the intake pipe as a purge gas, and the air-fuel ratio λa before purging Means 3 for calculating
9, and means 40 for prohibiting the learning value updating means 37 from updating the learning value before purging during stoichiometric operation,
A means 41 for opening the purge valve 38 to start the purge in a state where the update of the learning value is prohibited, and an air-fuel ratio immediately after the start of the purge (for example, a minimum air-fuel ratio value λ ′ within a predetermined time T1 from the purge start timing). a), a means 43 for calculating the purge gas concentration λp based on the air-fuel ratio λ'a immediately after the start of the purge and the pre-purge air-fuel ratio λa, and the purge valve 38 according to the purge gas concentration λp. 44 for controlling the valve opening of the
And a means 45 for determining whether the purge gas concentration λp is less than or equal to a predetermined value λp1, and based on the determination result, the update inhibition by the learning value update inhibiting means 40 is released when the purge gas concentration λp is less than or equal to the predetermined value λp1. Further, there is provided a means 46 for continuing the update prohibition when the purge gas concentration λp exceeds the predetermined value λp1.

The second aspect of the present invention, as shown in FIG. 24, is a means 51 for determining whether the engine is in a lean operating condition, and when the operating condition is lean based on the result of the determination, a value on the lean side of the theoretical air-fuel ratio is targeted. Means 52 for calculating the stoichiometric air-fuel ratio as the target air-fuel ratio as the air-fuel ratio and during stoichiometric operation that is not the lean operating condition, the memory 31 for storing the learning value αm, and the learning value αm according to the operating condition signal. Means 32 for reading, means 53 for calculating the fuel injection amount by correcting the basic injection amount TP according to the operating condition signal with the read learning value αm and the target air-fuel ratio, and the fuel of this injection amount for the intake pipe and supplying device 34, a sensor (e.g., O ₂ sensor or wide-range air-fuel ratio sensor) 35 for detecting the oxygen concentration in the exhaust gas, the stoichiometric operation based on the sensor detection value Only, means 36 for calculating the air-fuel ratio feedback correction amount α so that the exhaust air-fuel ratio is close to the stoichiometric air-fuel ratio, means 37 for updating the learning value αm based on this air-fuel ratio feedback correction amount α, and adsorption to the canister A purge valve 38 that opens and closes a passage for introducing the fuel thus made into the intake pipe together with fresh air as a purge gas according to a drive signal, a means 39 for calculating an air-fuel ratio λa before purging during the stoichiometric operation, and a purge during the stoichiometric operation. Means 40 for prohibiting the learning value update means 37 from updating the learning value, means 41 for opening the purge valve 38 in the state where the learning value update is prohibited and starting the purge, and starting the purge. A means 42 for calculating an air-fuel ratio immediately after (for example, an air-fuel ratio minimum value λ'a within a predetermined time T1 from the timing of starting purge), The means 43 for calculating a purge gas concentration λp on the basis of the purge start the air-fuel ratio λ'a immediately and the purge air fuel ratio [lambda] a, the a predetermined air-fuel ratio variation allowable width D ₁ of the lean operation the purge air fuel Means 54 for calculating the enrichment error learning allowable limit air-fuel ratio λ ″ a from the fuel ratio λa, and the enrichment error learning allowable limit air-fuel ratio based on the enrichment error learning allowable limit air-fuel ratio λ ″ a and the purge gas concentration λp. A means 55 for calculating a purge rate that gives a fuel ratio λ ″ a as a target purge rate Rp, a means 56 for opening the purge valve 38 during the stoichiometric operation at a valve opening PVO _T according to the target purge rate Rp, and the purge gas. Means 45 for determining whether the concentration λp is less than or equal to the predetermined value λp1 and the learning value update prohibition when the purge gas concentration λp is less than or equal to the predetermined value λp1 based on the determination result. Releases the update prohibition by means 42, also the purge gas concentration λp is provided with means 46 to continue the update prohibition when exceeding a predetermined value [lambda] p1.

A third aspect of the present invention is the same as the first aspect of FIG.
As shown in FIG. 5, during the valve opening control by the valve opening control means 44, the air-fuel ratio feedback correction amount α
Means 61 for calculating the change amount δα _AVE of the average value from the above, and the change amount δα per predetermined time.
_AVE is the determining means 62 whether equal to or less than a predetermined value .delta..alpha _AVE 1, the determination result from the variation .delta..alpha _AVE per predetermined time by a predetermined time T2 is when it becomes less than a predetermined value .delta..alpha _AVE 1 wherein the purge valve 38 After the valve is fully closed, the valve opening (eg, PVO1) that is larger than the valve opening (eg, PVO1) at the start of the previous purge is set.
And a means 63 for restarting the purge at a value obtained by adding VO1).

According to a fourth aspect of the present invention, in any one of the first to third aspects of the invention, the purge gas concentration calculating means 43 calculates the purge gas concentration λp using a theoretical formula.

In a fifth invention, in any one of the first to third inventions, the purge gas concentration calculating means 43 subtracts the air-fuel ratio immediately after the start of the purge from the pre-purge air-fuel ratio λa. The purge gas concentration λp is obtained by referring to a map using the value and the suction negative pressure ΔP as parameters.

[0015]

In the first aspect of the invention, the purge valve is opened and the purge is started in a state where the update of the learning value αm is prohibited before performing the purge during the stoichiometric operation, and the pre-purge air-fuel ratio λa and the air-fuel ratio immediately after the start of the purge are set. Based on the purge gas concentration λp
Is required. While the valve opening of the purge valve 38 is controlled according to the purge gas concentration λp, the learning value update prohibition is released when the purge gas concentration λp is less than or equal to the predetermined value λp1, and when λp> λp1. Since the update prohibition continues, even if the learning value is updated during purging during stoichiometric operation, there is no large mis-learning, and the learning value is updated even during purging, so there is no The learning frequency is higher than when the learning value update is prohibited.

In the second aspect of the invention, the enrichment error learning permissible limit air-fuel ratio λ ″ a is determined from the purge gas concentration λp and the air-fuel ratio variation permissible range D ₁ during lean operation. The purge rate that gives ″ a is the target purge rate R
When the purge valve is opened at the valve opening PVO _T according to the target purge rate Rp, the learning value update prohibition is released, and false learning is started.
The learning value converges to 1-D ₁ .

Therefore, the air-fuel ratio error when the learned value obtained by this erroneous learning is used as it is during lean operation is within D ₁ , and in addition to the effect of the first invention, it is obtained during stoichiometric operation. When the learned value is used as it is during lean operation, the stability of the engine during lean operation is not deteriorated.

In the third aspect of the invention, when the change amount δα _AVE of the average value of the air-fuel ratio feedback correction amount per predetermined time becomes less than the predetermined value δα _AVE 1 during the control of the purge valve opening according to the purge gas concentration λp. After the purge valve is fully closed for the predetermined time T2, when the purge is restarted at a valve opening larger than the valve opening at the start of the previous purge, in addition to the action of the first invention, the purge gas concentration is increased. λp
Even if the value becomes low, the calculation accuracy of the purge gas concentration λp does not decrease and the flow rate of the purge gas increases.

When the purge gas concentration λp is calculated using a theoretical formula in the fourth invention, in addition to the action of any one of the first to third inventions, the characteristics of the device such as the purge valve and If the specifications of the engine are decided, it is possible to adapt it on the desk.

In the fifth aspect of the present invention, the purge gas concentration λp is obtained by referring to a map having the intake negative pressure and the value obtained by subtracting the air-fuel ratio immediately after the start of the purge from the pre-purge air-fuel ratio λa as a parameter. In addition to the operation of any one of the inventions to the third invention, the procedure for calculating the purge gas concentration λp is simple and the processing speed is increased.

[0021]

In FIG. 2, the air sucked from the air cleaner 3 is temporarily stored in a collector portion 2a having a constant volume and then flows into each cylinder through a branch pipe. An injector 4 is provided at the intake port 2b of each cylinder, and fuel is intermittently injected from the injector 4 in synchronization with the engine rotation. The air-fuel mixture formed from the injected fuel and air is compressed by the piston in the combustion chamber and burns with the help of sparks emitted from the spark plug.

The longer the injection time from the injector 4, the larger the injection amount, and the shorter the injection time, the smaller the injection amount. The richness of the air-fuel mixture, that is, the air-fuel ratio, shifts to the rich side when the fuel injection amount for a fixed amount of intake air increases, and shifts to the lean side when the fuel injection amount decreases. Therefore, if the control unit 11 including a microcomputer determines the basic injection flow rate of fuel so that the ratio to the intake air flow rate becomes a constant value, the same air-fuel ratio can be obtained even under different operating conditions. Fuel injection is engine 1
When the rotation is performed once, the basic injection pulse width TP is obtained from the intake air flow rate and the engine speed at that time with respect to the air amount sucked in one rotation. Usually, the air-fuel ratio determined by Tp (called the base air-fuel ratio) is close to the theoretical air-fuel ratio.

In the exhaust pipe 5, CO discharged from the combustion chamber,
A catalyst (three-way catalyst) 6 for treating three harmful components such as HC and NOx is provided. The catalyst 6 can efficiently treat harmful three components simultaneously only when the exhaust air-fuel ratio is in a narrow range centered on the stoichiometric air-fuel ratio. In order to keep the air-fuel ratio within this range, the control unit 11 feedback-corrects the fuel injection amount from the injector 4 based on the output of the O ₂ sensor 7 provided upstream of the catalyst 6.

When the cause of the air-fuel ratio is deviated during stoichiometric operation due to variations in the flow characteristics of the air flow meter or injector that greatly deviate from the specified values due to variations or changes over time, feedback correction works. It takes some time to return to an air-fuel ratio close to the stoichiometric air-fuel ratio, and the unstable state continues during that time. After that, the normal state is maintained until the engine is stopped, but when the air-fuel ratio feedback correction condition after restart is reached, the O ₂ sensor 7 detects an abnormality again → The microcomputer adjusts the injection amount ... Repeat the feedback cycle. That is, each time the engine is restarted, an unstable state occurs for a while. In addition, the optimum air-fuel ratio may not be obtained under operating conditions in which the air-fuel ratio feedback correction is stopped, such as at start-up, when the cooling water temperature is low, or when the load is high.

Therefore, in order to improve the response of the air-fuel ratio correction during the stoichiometric operation, the control unit 11 performs learning control. In this learning function, if the correction amount necessary for learning control (that is, the learning value αm) is obtained by observing feedback correction, the learning value αm will be remembered even if the engine is stopped unless the backup power supply of the microcomputer is stopped. Therefore, even at the time of restart, appropriate increase (decrease) correction is performed from the beginning with this learning value αm.

On the other hand, under the condition that the lean operation is possible,
In order to improve fuel efficiency, the control unit 11 operates by changing the target value of the air-fuel ratio from the theoretical air-fuel ratio to a value leaner than the theoretical air-fuel ratio.

Looking at the air-fuel ratio control in the control unit 11 up to this point in a flow chart, FIG. 3 is a flow chart showing the calculation of the fuel injection pulse width Ti given to the injector 4, which is executed at a constant cycle (for example, 10 msec).

In step 1, the target fuel-air ratio equivalent amount TFBY
A is TFBYA = KMR + KAS + KTW (1) However, KMR; fuel-air ratio correction coefficient KAS; post-start increase correction coefficient KTW; water temperature increase correction coefficient, and in step 2, the basic injection pulse width TP is TP = (Qa / NE) × K (2) where Qa is the intake air flow rate NE is the engine speed K is a constant that determines the base air-fuel ratio.

From the start of the engine to immediately after that, the air-fuel ratio feedback correction is not performed, but the amount of fuel is increased by the water temperature increase correction coefficient KTW and the post-start increase correction coefficient KAS in equation (1) to improve the combustion state and the exhaust temperature. Is increased to accelerate the warm-up of the catalyst 6, and after the engine is warmed up such that KAS = KTW = 0, the fuel-air ratio correction coefficient KMR of the equation (1) is calculated.
The air-fuel ratio is controlled by.

In step 3, the learning value αm of the learning area to which NE and TP belong is obtained from the engine speed NE and the basic injection pulse width (engine load equivalent amount) TP with reference to the map of FIG. A large number of areas are provided on the map of the learning value αm as shown in FIG. 4, and the learning value is different for each divided area. This learning value αm
Is read and used during stoichiometric operation and lean operation.

In step 4, the fuel injection pulse width Ti given to the injector is Ti = TP × TFBYA × (α + αm) + TS (3) where TP; basic injection pulse width TFBYA; target fuel-air ratio equivalent amount α; air-fuel ratio feedback The correction coefficient αm; learning value TS; invalid pulse width is obtained by the equation, and this is transferred to the output register in step 5.

FIG. 5 shows a background job, which is also executed at regular intervals. In step 11, it is determined whether or not the lean operation condition is satisfied. This will be described in the subroutine of FIG. 6 described later.

At step 12, the value of the flag FLEAN is checked, and if FLEAN = 1, it is judged that the lean operation condition is satisfied, and the routine proceeds to step 13, where the lean operation map MKMRL of FIG. In step 14, the stoichiometric operation map MKMRS of FIG. 8 is selected. Two maps, one for stoichiometric operation and one for lean operation, are switched depending on the operating conditions.

At step 15, the engine speed NE and the basic injection pulse width TP are read, and at step 16, the value of the flag FLEAN is checked again. If FLEAN = 1, then at step 17, the lean operation map having the contents of FIG. 7 is read. Referring to MKMRL and if FLEAN = 0,
In step 19, the stoichiometric operation map MKMRS of FIG.
Is entered into the variable TKMR representing the map value of the target fuel-air ratio equivalent amount. As shown in FIGS. 7 and 8, the map value 1.0 is the theoretical air-fuel ratio equivalent amount,
If the value is smaller than 1.0, the lean side air-fuel ratio is obtained.

In step 18, the value obtained by subtracting the fuel-air ratio transition step amount ΔKMR from the previous value of KMR (that is, KMR-ΔKMR) is compared with the value of the variable TKMR, and in step 20, KMR + ΔKM is calculated.
R is compared with the value of the variable TKMR and the smaller one is KMR
The value of this time. As shown in FIG. 9, the transition period from the stoichiometric operation to the lean operation and the transition period from the lean operation to the stoichiometric operation are from the map value before the transition to the map value after the transition by the step amount ΔKMR. This is to make the change in the air-fuel ratio smooth when the air-fuel ratio is switched by shifting.

FIG. 6 is a subroutine of step 11 of FIG. 5, which is executed at a constant cycle independently of the control cycle of FIG.

Regarding the idle switch, the cooling water temperature TW, the basic injection pulse width TP, and the engine speed NE, the following conditions <1> The idle switch is not ON (step 2).
2), <2> TW ≧ predetermined value TWLL (step 24), <3> predetermined value TPLL ≦ TP <predetermined value TPL
H (step 26), <4> predetermined value NELL
≦ NE <predetermined value NELH (step 28),
If all the conditions are satisfied, the routine proceeds to step 29, where the lean operation permission flag FL is
If EAN is set to "1" and even one condition is not satisfied, the flag FLEAN is set to "0" in step 30.

FIG. 10 is a flow chart showing the update of the learning value αm, which is executed in synchronization with the crank angle reference signal Ref.

In step 41, the value of the flag FLEAN is checked, and if the lean operation is performed from FLEAN = 1, the learning value αm is not updated. This is because the O ₂ sensor 7 cannot detect the air-fuel ratio during lean operation, and therefore cannot perform air-fuel ratio feedback correction during lean operation.

If it is in stoichiometric operation since FLEAN = 0, the routine proceeds to step 61, where the update permission flag FKYO
Look at KA. Although this flag will be described later, it is assumed that FKYOKA = 1 now, and the routine proceeds to step 42.

In step 42, the engine speed NE and the basic injection pulse width TP are read, and step 4
In 3, the learning area pointer PL is calculated. As the learning area pointer, as shown in FIG. 11, it may be considered that a different value is put in each area in association with the map of learning values. At present, the engine speed NE and the basic injection pulse width TP are NE1 ≦ NE <NE2 and TP1 ≦ T, respectively.
If P <TP2 (where NE1 and NE2 are rotation speeds for dividing the area, and TP1 and TP2 are basic injection pulse widths for dividing the area), the learning area pointer PL is PL = 5. The learning area pointer PL is used to check whether the driving conditions are in the same learning area.

At steps 44, 45, 46, 47 and 49, it is determined whether the following conditions are satisfied.

<11> PL = PL Be OLD.
PL OLD is the previous learning area pointer, PL = P
L If it is OLD, the driving condition is in the same learning area again.

<12> TW ≧ learning start water temperature TWLRC. <13> Air-fuel ratio feedback correction is being performed.

<14> (VO ₂ OLD-SLO2)
(SLO2-VO _2)> it is 0. Here, VO ₂ is the output of the O ₂ sensor of this time (approximately 1.0 V when the exhaust air-fuel ratio is on the rich side, and almost 0 when it is on the lean side.
V), VO ₂ OLD is the previous O ₂ sensor output, SLO
2 is the slice level (set to about 0.5V),
When the condition of <14> is satisfied means VO ₂ OLD-SLO2
<0 and either when the SLO2-VO ₂ <0 (when this time is the last time in the lean of the rich), or VO ₂ OLD-S
LO2> 0 and when the SLO2-VO _2> 0 (the last time this time in the rich when the lean) is. That is, <14>
When the condition of is satisfied, it means a reversal from the lean side to the rich side and vice versa.

<15> CJRC ≧ NJRC.
CJRC is a count value that increases by 1 from the time when the three conditions <12>, <13>, and <14> are satisfied, and NJRC is a predetermined value (for example, a value of 2 or more). The condition <15> is to see whether or not a certain time has elapsed after all the conditions <11> to <14> were satisfied.

When any of the above conditions <11> to <13> is not satisfied, the count value CJ is determined in step 53.
Put an initial value of 0 in RC.

When all the conditions <11> to <15> are satisfied, it is judged that the learning condition is satisfied, and the half-cycle minimum value of the air-fuel ratio feedback correction coefficient α and the half-cycle maximum value of α are set to the past values. Using the data stored a predetermined number of times over the NLRC, the minimum value a and the maximum value b thereof are a = Min (α ₁ , α ₂ , ..., α _NLRC ) (4) b = Max in step 50. (Α ₁ , α ₂ , ..., α _NLRC ) (5) For example, as shown in FIG. 12, when the half-period minimum value and the half-period maximum value are alternately turned, the minimum value a is the smallest of α ₁ , α ₃ , ..., α _i , α _NLRC. The value and the maximum value b are the largest values of α ₂ , α ₄ , ..., α _{i + 1} . Note that FIG. 12 exaggerates the slice level SLO2 in which hysteresis is provided as a countermeasure against noise, and actually there is no step difference as in FIG. Although it is written that the output of the O ₂ sensor also changes obliquely, in reality, the waveform changes more rapidly.

The predetermined number of times NLRC is the predetermined value N
Must be set below JRC.

In step 50, the average value ALP _AVE of the air-fuel ratio feedback correction coefficient α is further calculated by using the minimum value a and the maximum value b of the above equations (4) and (5): ALP _AVE = (a + b) / 2 ( 6), and in step 51, the learning value αm is calculated based on the deviation between the average value ALP _AVE and the learning center value 1.0, αm = αm + G1 · (ALP _AVE −1.0) (7) However, G1 is updated by the formula of positive proportional constant. Αm on the right side of the equation (7) is a learning value in the learning area indicated by the learning area pointer PL,
The value of αm on the left side of the equation (7) is stored in the same learning area.

For example, when the average value ALP _AVE is smaller than 1.0 (the air-fuel ratio average value is on the rich side), the learning value α
When m is corrected to a value smaller than the present value, the amount of fuel injection is corrected according to the equation (3) so that the air-fuel ratio is returned to the rich side. As the learning progresses, the air-fuel ratio approaches the stoichiometric air-fuel ratio, the deviation between the average value ALP _AVE and the learning center value 1.0 also decreases, and the learning value αm converges to a certain value. The learned value is backed up by a battery so that it does not disappear even after the engine is stopped.

In step 52, as a post-processing, the learning area pointer PL and the O ₂ sensor output VO ₂ are respectively set as a variable PL representing the previous value. Transfer to OLD and VO ₂ OLD.

On the other hand, returning to FIG. 2, the fuel evaporated in the fuel tank 21 is guided to the canister 23 through the passage 22 while the engine is stopped, and is adsorbed by the activated carbon in the canister 23. Reference numeral 24 is a check valve that prevents a backflow from the canister 23 to the fuel tank 21.

The canister 23 includes the throttle valve 2
The intake pipe 2 downstream of 5 is communicated with a passage 26, and a normally closed purge valve 27 driven by a step motor is provided in the passage 26. A linear solenoid type purge valve may be used.

When the purge valve 27 is opened in response to a signal from the control unit 11 under a certain condition, the suction negative pressure developing downstream of the throttle valve 25 causes a new air to be introduced from the fresh air introduction passage 23a provided under the canister 23. Qi is guided into the canister 23. The vaporized fuel separated from the activated carbon by this fresh air is purged into the intake pipe 2 together with the fresh air and burned in the combustion chamber.

The reason why the normally-closed diaphragm actuator 28 is provided in series with the purge valve 27 is for fail-safe in case of failure of the purge valve 27. When the purge valve 27 is opened due to a failure, the purge gas is introduced even while the engine is warming up, and the mixture becomes rich. Therefore, when purging is not performed, the normally closed diaphragm actuator 28
By shutting off the passage 26 in step 2, the purge gas is prevented from being introduced into the intake pipe 2 under conditions other than the purging conditions.

When the purge cut valve 29 is simultaneously opened under the condition of purging and the suction negative pressure downstream of the throttle valve 25 is guided to the diaphragm actuator 28 (the negative pressure operating chamber thereof) via the passage 30, this negative pressure is used. The diaphragm is pulled against the return spring and the passage 26 is opened.

If the learning value is continuously updated even during purging, the learning value is updated to the value on the over lean side when gasoline that is easily vaporized under the hot sun where a large amount of fuel vapor is generated is used. If the value is used immediately after the purge cut, the air-fuel ratio becomes over lean,
The instability of the engine deteriorates driving performance and exhaust performance.

On the other hand, if the updating of the learning value is prohibited during the purging, a large amount of fuel vapor charged in the canister during a stop due to traffic congestion in the hot sun,
When trying to perform purging as much as possible during traveling, there is almost no opportunity to update the learning value, and if the learning value does not converge before the traffic jam operation, exhaust performance and drivability deteriorate.

In order to deal with this, in the control unit 11, when the purge is performed during the stoichiometric operation, the purge valve 27 is first opened with the learning value update prohibited and the purge is started. The purge gas concentration λp is obtained based on the air-fuel ratio of the purge gas concentration λp, the purge valve 27 is controlled by the valve opening degree according to the purge gas concentration λp, and the purge gas concentration λp
Is less than or equal to the predetermined value λp1, the learning value update prohibition is released, and when λp> λp1, the learning value update prohibition is continued.

The sensors required for this control are the same as the sensors required for normal air-fuel ratio control, and include an O ₂ sensor 7, a crank angle sensor 12, an air flow meter 13 that outputs according to the intake air flow rate, and a cooling. The signal from the sensor 14 that detects the water temperature Tw is input to the control unit 11 together with the signal from the sensor 15 that detects the throttle valve opening.

FIG. 13 is a flow chart showing the purging process, which is executed at regular intervals. Note that the air-fuel ratio feedback correction during stoichiometric operation must be in progress as a premise for starting the purge process.

At step 71, processing for prohibiting the update of the learning value is performed. For example, by setting the learning permission flag FKYOKA to "0", while adding step 61 to the learning value update flow of FIG. 10, FKYOKA
When = 0, the learning value is not updated after step 42. The fuel injection pulse width T
When i is obtained, the learning value is used regardless of prohibition of updating the learning value.

In step 72, the purge valve is opened at a predetermined opening degree to start the purge, and the purge gas concentration λp, based on the air-fuel ratio before the purge and the minimum air-fuel ratio λ'a within the predetermined time T1 immediately after the start of the purge, The purge gas flow rate Qp and the target purge rate Rp are obtained, and the purge gas concentration λp and the rich side limit value λp1 of the purge gas concentration are compared in step 73. As a result of the comparison, the process proceeds to step 74 only when λp ≦ λp1 to release the prohibition of updating the learning value αm (set the flag FKYOKA = 1). The details of step 72 will be described later in the subroutine of FIG.

On the other hand, when λp> λp1, step 74 is skipped and the learning value update prohibition is not released. As a result, it is possible to prevent erroneous learning when the air-fuel ratio is greatly enriched even if the purge gas concentration λp is high and the purge valve opening is reduced.

In step 75, the purge valve 27 is controlled so that the valve opening degree is set according to the target purge rate Rp. Details of this step 75 will be described later in the subroutine of FIG.

At step 76, the average value α _AVE of the air-fuel ratio feedback correction coefficient is controlled during the control of the purge valve opening.
Α _AVE = (α _j-1 + α _j ) / 2 (8) where α _j ; α α _j-1 immediately before adding the step amount; α just before adding the step amount. For example, when _{obtaining the} average value α _AVE at the timing when the air-fuel ratio is reversed to the rich side, as shown in FIG. 14, α _j and α _{j-1 in the} equation (8) are the half values that have risen in the past from that timing. The average value α _AVE is the center value of the fluctuation of α, since it becomes the maximum value of the period and the minimum value of the half period.

In step 77, the change amount δα of the average value α _AVE per predetermined time (for example, the control cycle in FIG. 13).
_AVE is calculated by the formula of α _AVE = α _AVE OLD-α _AVE (9) where α _AVE OLD; previous value of α _AVE . Step 7 for the next calculation of δα _AVE
In 8, the value of the average value α _{AVE is} the variable α _AVE OL representing the previous value.
Move to D.

At steps 79 and 80, it is checked whether the following conditions are satisfied. <21> PL = PL Be OLD. That is, the driving conditions are in the same learning area. This is a condition because when the operating condition is changed, an error occurs in the determination of whether or not the purge gas concentration falls below a predetermined value under the condition of <22> described below.

<22> δα _AVE ≦ predetermined value δα _AVE 1. The case where δα _AVE ≦ δα _AVE 1 is when the purge gas concentration becomes lower than a predetermined value. As shown in FIG. 15, the purge gas concentration decreases with a first-order delay from the start of purging (the average value α _AVE also decreases with a first-order delay corresponding to the purge gas concentration), so the change amount δα _AVE
Is equivalent to the slope (Δy / Δx) of the curve shown in FIG. That is, the amount of change in the purge gas concentration is captured by the amount of change Δα _AVE .

If either of the conditions <21> and <22> is not satisfied, the process returns to step 75 to continue the purging.

On the other hand, if both conditions are satisfied, it is judged that the purge gas concentration has fallen below a predetermined value, and step 81
To the variable PVO indicating the purge valve opening and the maximum controllable purge valve opening PVO. Compared with MAX, PVO <PVO If it is MAX, step 8
After the purge valve 27 is fully closed for a predetermined time T2 at 2 to stabilize the air-fuel ratio, the process returns to step 71 of FIG. 13, the purge valve is opened with the valve opening increased from the previous time, and the purge gas concentration λp and the purge gas flow rate Qp, The target purge rate Rp is obtained, and the purge valve is controlled to the purge valve opening corresponding to the new target purge rate Rp. When the purge gas concentration falls below a predetermined value, the purge valve is closed once, and the purge valve is opened again with the valve opening increased from the previous time, so that the purge gas flow rate can be increased while improving the purge gas concentration calculation accuracy. . The details of step 82 will be described later with reference to the subroutine of FIG.

On the other hand, PVO ≧ PVO In the case of MAX, the purge valve opening cannot be increased next time within the controllable range even if the purge valve is closed once.
The flow of 3 ends.

In step 81, PVO ≧ PVO M
The fact that the flow of FIG. 13 is terminated from AX does not mean that the purge valve remains open. FIG. 13 is only a flow chart for determining the target opening of the purge valve, and the actual opening control of the purge valve is executed according to another flow not shown. For example, when the engine is idling or fuel is cut after the flow of FIG. 13 is completed, the purge valve is returned to the fully closed position.

FIG. 16 is a subroutine of step 72 of FIG. 13, which is executed at a constant cycle independently of the control cycle of FIG.

In step 91, the throttle valve opening TV
O, engine speed NE, intake air flow rate Qa, and air-fuel ratio λa before purging are read.

Here, the pre-purging air-fuel ratio λa is expressed by the following formula: λa = [target air-fuel ratio] · αm · α _AVE 0 (10) where α _AVE 0; average value of air-fuel ratio feedback correction coefficient before purging Looking for. The reason why the pre-purge air-fuel ratio λa is calculated using the above formula is that the pre-purging air-fuel ratio is in the lean operation, the air-fuel ratio in the lean operation cannot be calculated from the O ₂ sensor output.

The [target air-fuel ratio] of the equation (10) is [target air-fuel ratio] = [theoretical air-fuel ratio (≈14.7)] / TFBYA (11) where TFBYA is the target fuel-air ratio equivalent amount. Since the target fuel-air ratio equivalent amount TFBYA is a relative value in which the reciprocal of the theoretical air-fuel ratio is 1, the reciprocal of TFBYA is the theoretical air-fuel ratio of 14.7 in order to convert it to the target air-fuel ratio.
It is necessary to spend time.

In step 92, the purge valve is opened to the predetermined opening P.
Open at VO1 to start purge, and in step 93, the air-fuel ratio is continuously calculated for a predetermined time T1 from the purge start timing, and the minimum air-fuel ratio (air-fuel ratio immediately after purge) λ'a Pick up.

An appropriate value is set in advance for the predetermined opening degree PVO1 by a confirmation experiment or the like. When the maximum fuel charge to the canister is assumed to be the maximum value, the purge valve opening is made lean enough to prevent the air-fuel ratio from becoming overrich enough to affect the drivability due to the purge and to detect the air-fuel ratio difference before and after the purge. The degree is PVO1.

The details of step 93 will be described later in the subroutine of FIG. Further, in order to open the purge valve at the predetermined opening PVO1, the initial value stored in the variable PVO1 is referred to and converted into the number of steps STEP given to the step motor, which is stored in the output register. Just transfer it.

At step 94, the throttle valve opening T
Intake negative pressure by referring to the map from VO and engine speed NE (intake pipe negative pressure downstream of throttle valve 25)
Calculate ΔP [Pa]. All the values of the suction negative pressure ΔP are given as positive values, so that the larger the value of ΔP, the closer the value to the atmospheric pressure. The reason why the intake negative pressure ΔP is obtained by referring to the map is that no intake negative pressure sensor is provided downstream of the throttle valve. The cost can be reduced by reducing the suction negative pressure sensor.

In step 95, the purge gas concentration λp and the purge gas flow rate Qp are obtained using the suction negative pressure ΔP and the theoretical formula. Details of step 95 will be described later with reference to FIG.

In step 96, the enrichment error learning permissible limit air-fuel ratio λ ″ a is set to λ ″ a = (from the pre-purge air-fuel ratio λa and the air-fuel ratio variation allowable range D ₁ (0 <D ₁ <1) during lean operation. 1-D ₁ ) · λa (12), and this enrichment error learning allowable limit air-fuel ratio λ ″ a
Rp = (λpp · (λa−λ ″ a)) / (λa · (λ ″ a−λpp)), where λpp is the purge gas air-fuel ratio (13) Ask.

Even with respect to a temporary disturbance such as a purge to the air-fuel ratio, if the basic injection pulse width TP is corrected so that the air-fuel ratio becomes the stoichiometric air-fuel ratio by updating the learning value αm, the purge gas When the air-fuel ratio of is extremely rich, the learning value αm becomes small, and the fuel injection amount is corrected to be smaller. On the other hand, the learning value αm is originally
Since the purpose is to correct the base air-fuel ratio in order to improve the accuracy of the air-fuel ratio during open control and speed up the convergence of the air-fuel ratio feedback correction coefficient α, the fuel injection pulse width Ti It is used to calculate. For this reason, in the lean burn system using the O ₂ sensor, the air-fuel ratio is open control during lean operation. Therefore, by using the learning value obtained during stoichiometric operation during lean operation, control accuracy of the air-fuel ratio is required. It can be secured to a certain degree.

On the other hand, on the other hand, during stoichiometric operation, the operation shifts to lean operation while continuing purging, and the fuel charge amount of the canister becomes almost empty with the air-fuel ratio kept open control (the rich portion due to purging has disappeared).
At this time, since the learning value is used, the air-fuel ratio becomes rather lean, and if the degree of leaning is large, the engine tends to become unstable due to the lean operation.

In this case, assuming that the air-fuel ratio becomes lean to the engine stability limit (the allowable range of the air-fuel ratio variation at this time is D ₁ ), the learning value αm at that time is 1-D ₁ . The air-fuel ratio when the learning value αm becomes 1-D ₁ (that is, the enrichment error learning allowable limit air-fuel ratio λ ″ a) is given by the equation (12).

The learning value αm when the air-fuel ratio becomes lean to the allowable limit of engine stability during lean operation is 1−D ₁
The reason is as follows. The target air-fuel ratio before purging during the stoichiometric operation is Λa, the air-fuel ratio when the purge gas is introduced and the air-fuel ratio learning control is not performed is Λ ″ a, and the relationship between them is Λ ″ a = k · Λa = (1 -D ₀ ) Λa However, if k; constant D ₀ ; constant (0 <D ₀ <1), the air-fuel ratio becomes (1-D ₀ ) times (thickens) when the purge gas is introduced. In order to return the air-fuel ratio from Λ ″ a to Λa, the basic injection pulse width TP needs to be (1-D ₀ ) times (decreased). Therefore, the fuel injection amount is corrected by the air-fuel ratio learning control. Considering this, the learning value αm when the learning is sufficiently advanced should be αm = 1−D ₀ .

Here, Λ ″ a is Λ ″ a = (Qa + Qp) / (Qa / Λa + Qp / λpp), where Qa: intake air flow rate not including purge gas Qp; purge gas flow rate λpp; purge gas air-fuel ratio Can be represented. In the formula, Qa /
Λa is the fuel flow rate supplied from the injector, Qp /
λpp is the fuel flow rate in the purge gas.

The air-fuel ratio when the learning value converges is Λ
Since it is a, Λa = (Qa + Qp) / (αm · Qa / Λa + Qp / λpp).

In the above, the learned value remains the above 1-D ₀ and does not change and only the purge proceeds (the learned value is not updated because the air-fuel ratio feedback correction cannot be made during lean operation, and only the purge proceeds). Assuming that the purge gas air-fuel ratio becomes infinite (that is, Qp / λpp≈0), the air-fuel ratio Λat at that time can be calculated from the equation as follows: · (1 + Qp / Qa) = (Λa / (1-D ₀ )) · (1 + Qp / Qa) ...

In the equation, normally D ₀ << 1, Qp << Q
Since it is a, Λat≈Λa / (1−D ₀ ) ≈ (1 + D ₀ ) · Aa, and it can be seen that the target air-fuel ratio Λa is leaned by D ₀ .

Therefore, if the allowable range D ₁ of air-fuel ratio variation during lean operation is given as D ₀ , the learning value αm when the variation range of air-fuel ratio D ₁ during lean operation becomes 1-D _{1 according to the} equation.
It becomes.

The allowable range of air-fuel ratio variation D ₁ here is a constant, and is determined in advance by experiments or the like within a range that does not significantly deteriorate drivability.

The above equation (13) is derived as follows. Considering the amount of fuel contained, (Qa + Qp) / λ = Qa / λa + Qp / λpp (14) where Qa: intake air flow rate (excluding purge gas) Qp: purge gas flow rate λ: intake air including purge gas Of the total air-fuel ratio λa; pre-purge air-fuel ratio λpp; purge gas air-fuel ratio.

Formula (14) is summarized for the total air-fuel ratio λ. λ = λaλpp (Qa + Qp) / (λaQp + λppQa) = λaλpp (1 + Qp / Qa) / (λa · Qp / Qa + λpp) (15)

Here, since it is desired to set the target purge rate Rp to the purge rate that gives the enrichment error learning allowable limit air-fuel ratio λ ″ a as a result of introducing the purge gas, the total air-fuel ratio λ is the enrichment error learning allowable limit air-fuel ratio λ. The purge rate (that is, Qp / Qa) when equal to "a" becomes the target purge rate Rp.

Therefore, in equation (15), λ = λ ″
When a and Qp / Qa = Rp are set, λ ″ a = λaλpp (1 + Rp) / (λa · Rp + λpp) (16), and when the equation (16) is rearranged with respect to the target purge rate Rp, the above (13) is obtained. You can get the formula.

At step 97, a value obtained by adding the constant value ΔPVO1 to the value of the variable PVO1 is newly put into the variable PVO1. As a result, when the purge valve is once closed due to the decrease of the purge gas concentration and then the process proceeds to step 92 to restart the purge, the valve opening degree at the restart of the purge becomes larger than that at the start of the previous purge. In this way, the purge valve opening at the time of restarting the purge is increased because the calculation accuracy of the purge gas concentration λp deteriorates when the purge gas concentration λp decreases as the purge progresses. This is to increase the calculation accuracy of λp and to increase the purge rate.

FIG. 18 is a subroutine of step 93 of FIG. 16, which is executed at a constant cycle. Here, the minimum value of the average value α _AVE of the air-fuel ratio feedback correction coefficient per predetermined time T1 is calculated, and the air-fuel ratio for this minimum value is calculated as the minimum air-fuel ratio value λ'a.

In step 101, the timer value TMT1 is set to a predetermined time (fixed value) T1.

At step 102 (VO ₂ OLD-SL
O2) · (SLO2-VO ₂ ) value, see (VO ₂ O
If LD-SLO2) · (SLO2-VO ₂ )> 0, it is determined that reversal is occurring and the routine proceeds to step 103, where the average value α _AVE of the air-fuel ratio feedback correction coefficient is set to (8) above.
Same as the formula, α _AVE = (α _j-1 + α _j ) / 2 (17) is calculated, and in step 104, the average value α _AVE and the value of the variable α _AVE min are compared, and the smaller of the two is calculated. To the variable α _AVE min.

(VO ₂ OLD-SLO2) ・ (SLO
When 2-VO ₂ ) ≦ 0, it is not inversion, so steps 103 and 104 are skipped, and in step 105, the timer value TM is irrespective of whether it is inversion or not.
T1 is TMT1 = TMT1−Δt (18) where Δt is decremented by the formula of control cycle in FIG.

When the timer value TMT1 decremented in step 106 is compared with 0 and steps 102 to 105 are repeated while TMT1> 0, the value in the variable α _AVE min is averaged when TMT1 ≦ 0. Since the value α _AVE becomes the minimum value per predetermined time T1,
When TMT1 ≦ 0, the routine proceeds to step 107, where the minimum air-fuel ratio value λ′a is set to λ′a = λa · α _AVE min / α _AVE 0 (19) where λa; air-fuel ratio before purge α _AVE 0 ; Obtained by the formula of average value of air-fuel ratio feedback correction coefficient before purging.

FIG. 19 is a subroutine of step 95 of FIG. 16, which is executed at a constant cycle.

The purge gas flow rate Qp is the purge gas concentration λp.
The purge gas flow rate Qp is required to obtain the purge gas concentration λp. Therefore, the initial value (fixed value) λp ₀ 1 is substituted for the variable λp ₀ representing the temporary purge gas concentration, the purge gas flow rate Qp is determined from this, and the purge gas concentration λp is determined from this purge gas flow rate Qp. The purge gas concentration λp is substituted into the variable λp ₀ until the difference between the purge gas concentration λp and the variable λp ₀ falls within a predetermined value,
It is possible to obtain the purge gas concentration λp and the purge gas flow rate Qp by cyclically repeating the calculation of the purge gas flow rate Qp from the purge gas concentration λp ₀ and the calculation of ...

First, in step 111, an initial value λp ₀ 1 is put into the variable λp ₀ representing the temporary purge gas concentration, and step 1
12 using the value of the variable .lambda.p ₀ purge gas density [rho [g /
litre] ρ = (28.95 × λp ₀ +68.0) × {273.15 / (273.15 + t)} / {22.4 × (λp ₀ +1)} (20) However, 28.95; Molecular weight of air 68.0; average molecular weight of gasoline gas 22.4; volume of gas in a standard state of 1 mol [litr
e] 273.15; absolute zero [K] t; gasoline gas temperature (≈40) [° C.], and from this purge gas density ρ, step 113
And the purge gas flow rate Qp [litre / min] is Qp = A · Cq · ε · (2ΔP / ρ) ^1/2 · 60 × 10 ⁻³ (21) where A: purge valve opening area [mm ² ] Cq; orifice Flow coefficient (≈0.7) ΔP; suction negative pressure [Pa] 60 × 10 ⁻³ ; conversion value to litre

Ε in the equation (21) is ε = 1- (3 / (4 × κ)) · (ΔP / P ₀ ) ... (22) where κ; specific heat ratio (= 1.4) P ₀ ; large Atmospheric pressure [Pa]. The purge valve opening area A of the equation (21) is obtained from the variable PVO1 by referring to the table, as in step 123 of FIG. 20 described later.

In step 114, the purge gas concentration λp is determined from the purge gas flow rate Qp by the following equation: λp = λaλ'aQp / (λa (Qa + Qp) -λ'aQa) (23) The equation (23) can be obtained by modifying the equation in which the pre-purge air-fuel ratio λ′a is substituted for the total air-fuel ratio λ of the equation (14).

At step 115, the absolute value of the difference between the purge gas concentration λp obtained by the equation (23) and the variable λp ₀ | λp-λp ₀
| And a predetermined value Δλp1 are compared, and | λp−λp ₀ |> Δ
If λp1, it is determined that the purge gas concentration λp obtained this time is not yet close to the true value, the routine proceeds to step 116, where the purge gas concentration λp of the equation (23) is put into the variable λp ₀ , and steps 112 to 114 are repeated, │λp-λp ₀ │ ≦ Δ
Purge gas concentration λ obtained this time when λp1 is reached
It is determined that p has reached an allowable level from the true value, and the calculation of the purge gas concentration λp and the purge gas flow rate Qp ends.

FIG. 20 is a subroutine of step 75 of FIG. 13, which is executed at a constant cycle.

[0112] In the formula of the target purge flow rate Qp _T a Qp _T = Qa × Rp from the target purge rate Rp at step 121 ... (24) Step 1 from the target purge gas flow rate Qp _T
At 22, the target purge valve opening area A _T [mm ² ] is calculated as follows: A _T = Qp _T / (Cq · ε · (2ΔP / ρ) ^1/2 · 60 × 10 ⁻³ ) ... (25) From the opening area _AT , referring to the table in step 123, the target purge valve opening P
Determine the VO _T.

In step 124, the purge valve opening is adjusted to the target purge valve opening PVO _T. For example, the target purge valve opening PVO _T may be converted into the step number STEP by referring to the table having the contents of FIG. 17, and this may be transferred to the output register.

FIG. 21 is a subroutine of step 82 of FIG.

In step 131, the timer value TMT2 is set to the predetermined time T2. After the purge valve is fully closed in step 132, the timer value TMT2 is TMT2 = TMT2-Δt (26) in step 133, where Δt is decremented by the control cycle formula in FIG. This decremented timer value TMT2 and 0 are compared in step 133, and TMT1>
While it is 0, the decrement of step 133 is repeated and the process ends when TMT2 ≦ 0.

The above-mentioned predetermined time T2 is the time period until the air-fuel ratio becomes stable when the purge is cut from the purging state when the canister charge amount is the maximum at the assumed maximum purge rate. Determine an appropriate value (fixed value) in advance through confirmation experiments.

The operation of this example will now be described with reference to FIG. 22. The scale of the time axis (horizontal axis) t in FIG. 22 is about 10 times larger than the scale of the time axis t in FIG. The upper part shows the purge valve opening, and the lower part shows the change of the average value α _AVE of the air-fuel ratio feedback correction coefficient.

[0118] In this example, first purge valve while prohibiting update of the learning value is purged opened to a predetermined degree PVO1 is started (timing of time t ₁₎ when performing the purge process to stoichiometric operation, purge air fuel The purge gas concentration λp is obtained based on the fuel ratio λa and the minimum air-fuel ratio value λ'a within the predetermined time T1 from the purge start timing. While the purge valve 27 is controlled by the purge valve opening degree according to the purge gas concentration λp, the learning value update prohibition is released when the purge gas concentration λp is equal to or less than the predetermined value λp1, and when λp> λp1, the learning value is changed. Since the update prohibition continues, even if the learning value is updated during purging during stoichiometric operation, there is no large mis-learning, and there is an opportunity to update the learning value during purging, The learning frequency is higher than when the learning value update is prohibited at all.

Further, from the purge gas concentration λp and the air-fuel ratio variation allowable range D ₁ during lean operation, the enrichment error learning allowable limit air-fuel ratio λ ″ a further gives this enrichment error learning allowable limit air-fuel ratio λ ″ a. The purge rate is calculated as the target purge rate Rp, and the valve opening P corresponding to the target purge rate Rp
When the purge valve is opened at VO _T (timing at time t ₂ ), erroneous learning is started and the learning value converges to 1-D ₁ when the learning value update prohibition is released.

Therefore, the air-fuel ratio error when the learned value that was erroneously learned is used as it is during lean operation is within D ₁ , and when the learned value obtained during stoichiometric operation is used as it is during lean operation. Moreover, the stability of the engine during lean operation is not deteriorated.

Further, when it is determined that the purge gas concentration has decreased by comparing the variation amount δα _AVE of the average value of the air-fuel ratio feedback correction coefficient per predetermined time and the predetermined value δα _AVE 1 during the purge during the stoichiometric operation (time t ₃ timing), the purge valve for a predetermined time T2 is fully closed, the timing after a lapse of T2 (timing of time t ₄₎
When the purge valve opening is increased by a constant value ΔPVO1 from the previous time and the purging is restarted, the calculation accuracy of the purge gas concentration λp does not decrease even if the purge gas concentration λp becomes low, and the purge gas flow rate can be increased. .

In this way, the learning value is updated so as not to cause a large erroneous learning during the purge during the stoichiometric operation to increase the learning frequency, and the purge valve opening degree is appropriately controlled according to the purge gas concentration λp. By doing so, the purge flow rate can be increased as much as possible while reducing the influence on the air-fuel ratio.

Further, since the purge gas concentration λp and the purge gas flow rate Qp required for this calculation are calculated by the theoretically derived method as described with reference to FIG.
If the characteristics of the device such as the purge valve and the specifications of the engine are decided, it is possible to adapt it on a desk.

FIG. 23 shows another embodiment, which is shown in FIG. 1 of the previous embodiment.
Corresponds to 9. In this example, the purge gas concentration λp is obtained not by a theoretically derived method but by a map reference.

For example, the pre-purging air-fuel ratio λa and the minimum air-fuel ratio λ'a within a predetermined time T1 from the purge start timing.
The purge gas concentration λp is obtained by referring to a map using the difference (λa-λ'a) and the suction negative pressure ΔP as parameters (step 141).

In this case, if the suction negative pressure ΔP is constant, the value of the purge gas concentration λp increases as the difference (λa-λ'a) increases (the purge gas concentration increases), and the difference (λa-λ) increases. If'a) is constant, suction negative pressure ΔP
Becomes larger (that is, the suction negative pressure approaches the atmospheric pressure).

After obtaining the purge gas concentration λp, the purge gas concentration ρ [g / litre] is set to ρ = (28.95 × λp + 68.0) × {273. 15 / (273.15 + t)} / {22.4 × (λp + 1)} (31), and the purge gas flow rate Qp [litre / min] is calculated from the purge gas density ρ by the equation (21).

In this example, since the purge gas concentration λp is obtained by referring to the map, it is necessary to adapt it to an actual engine, but the procedure for calculating the purge gas concentration λp is simpler than that in the previous embodiment. The processing speed can be increased.

[0129]

According to the first aspect of the invention, a memory for storing a learned value, a means for reading the learned value according to an operating condition signal, and a basic injection amount according to the operating condition signal are corrected by the read learned value. To calculate the fuel injection amount, a device that supplies the fuel of this injection amount to the intake pipe, a sensor that detects the oxygen concentration in the exhaust gas, and the exhaust air-fuel ratio based on the sensor detection value Means for calculating the air-fuel ratio feedback correction amount so as to be in the vicinity, means for updating the learning value based on this air-fuel ratio feedback correction amount, and the fuel adsorbed in the canister is introduced into the intake pipe as purge gas together with fresh air. The purge valve that opens and closes the passage according to the drive signal, a means for calculating the air-fuel ratio before purging, and the learning value updating means before purging during stoichiometric operation A means for prohibiting the update of the learned value, a means for opening the purge valve in the state where the update of the learned value is prohibited, a means for starting the purge, a means for calculating the air-fuel ratio immediately after the start of the purge, and a means for immediately after the start of the purge. Means for calculating the purge gas concentration based on the air-fuel ratio and the pre-purging air-fuel ratio, means for controlling the valve opening of the purge valve according to this purge gas concentration, and whether the purge gas concentration is below a predetermined value. Means for determining
From the result of this determination, when the purge gas concentration is less than or equal to a predetermined value, the update prohibition by the learning value update prohibiting means is released,
Further, since the means for continuing the update prohibition when the purge gas concentration exceeds the predetermined value is provided, it is possible to increase the frequency of learning within a range that does not largely mislearn during purging during stoichiometric operation.

A second aspect of the present invention is a means for determining whether or not the engine is in a lean operating condition, and when a lean operating condition is obtained from the result of this determination, a value on the lean side of the theoretical air-fuel ratio is set as a target air-fuel ratio, and is not a lean operating condition. During stoichiometric operation, means for calculating the theoretical air-fuel ratio as the target air-fuel ratio, memory for storing the learned value, means for reading this learned value according to the operating condition signal, this read-out learned value and the target air-fuel ratio A means for calculating the fuel injection amount by correcting the basic injection amount according to the operating condition signal with the fuel ratio, a device for supplying this injection amount of fuel to the intake pipe, a sensor for detecting the oxygen concentration in the exhaust gas, A means for calculating the air-fuel ratio feedback correction amount so that the exhaust air-fuel ratio falls within the vicinity of the stoichiometric air-fuel ratio only during the stoichiometric operation based on this sensor detection value, and this air-fuel ratio feed Means for updating the learning value based on the correction amount, a purge valve for opening and closing a passage for introducing the fuel adsorbed in the canister together with the fresh air into the intake pipe as a purge gas, and the stoichiometric operation Means for calculating the air-fuel ratio before purging, means for prohibiting the update of the learned value by the learned value updating means before purging during the stoichiometric operation, and the purge valve with the update of the learned value prohibited A means for opening and starting the purge, a means for calculating the air-fuel ratio immediately after the start of the purge, a means for calculating the purge gas concentration based on the air-fuel ratio immediately after the start of the purge and the pre-purging air-fuel ratio,
Based on the means for calculating the enrichment error learning allowable limit air-fuel ratio from the predetermined air-fuel ratio variation allowable range during the lean operation and the pre-purge air-fuel ratio, and the enrichment error learning allowable limit air-fuel ratio and the purge gas concentration. Means for calculating a purge rate that gives an enrichment error learning allowable limit air-fuel ratio as a target purge rate, a means for opening the purge valve during the stoichiometric operation at a valve opening degree according to the target purge rate, and the purge gas concentration A means for determining whether or not it is less than or equal to a predetermined value, and if the purge gas concentration is less than or equal to a predetermined value from this determination result, the update prohibition by the learning value update prohibiting means is released, and if the purge gas concentration exceeds the predetermined value, Since a means for continuing the update prohibition is provided, when the learning value that was erroneously learned by releasing the update prohibition of the learning value is used as it is during lean operation. The air-fuel ratio error falls within the predetermined allowable range of air-fuel ratio variation, and in addition to the effect of the first invention, when the learned value obtained during stoichiometric operation is used as it is during lean operation, It does not deteriorate the stability of the engine.

In a third aspect based on the first aspect, means for calculating a variation amount of the average value per predetermined time from the air-fuel ratio feedback correction amount during valve opening control by the valve opening control means. , Means for determining whether or not the amount of change per predetermined time period is below a predetermined value,
If the change amount per predetermined time is less than or equal to the predetermined value as a result of this determination, the purge valve is fully closed for a predetermined time, and then the purge is performed at a valve opening that is larger than the valve opening at the time of the start of the previous purge. Since the means for restarting is provided, in addition to the effect of the first invention, even if the purge gas concentration becomes low, the purge gas flow rate can be increased without lowering the calculation accuracy of the purge gas concentration.

In the fourth invention, in any one of the first invention to the third invention, the purge gas concentration calculating means calculates the purge gas concentration by using a theoretical formula. In addition to the effect of any one of the inventions up to the third invention, if the characteristics of the device such as the purge valve and the specifications of the engine are determined, it is possible to adapt it on a desk.

In a fifth aspect of the invention, in any one of the first to third aspects of the invention, the purge gas concentration calculating means has a value obtained by subtracting the air-fuel ratio immediately after the start of the purge from the air-fuel ratio before the purge. Since the purge gas concentration is obtained by referring to the map using the suction negative pressure as a parameter,
In addition to the effect of any one of the inventions 1 to 3, the purge gas concentration calculation procedure is simple and the processing can be speeded up.

[Brief description of drawings]

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

FIG. 2 is a control system diagram of an embodiment.

FIG. 3 is a flow chart for explaining calculation of a fuel injection pulse width Ti.

FIG. 4 is a region diagram for explaining a learning area.

FIG. 5 is a flowchart for explaining calculation of a fuel-air ratio correction coefficient KMR.

FIG. 6 is a flow chart for explaining lean operation permission determination.

FIG. 7 is a characteristic diagram of a lean operation map.

FIG. 8 is a characteristic diagram of a stoichiometric operation map.

FIG. 9 is a change waveform diagram of a fuel-air ratio correction coefficient KMR when the target air-fuel ratio is switched.

FIG. 10 is a flowchart for explaining updating of a learning value αm.

FIG. 11 is an area diagram for explaining a learning area pointer.

FIG. 12 is a waveform diagram for explaining updating of the learning value αm.

FIG. 13 is a flowchart for explaining calculation of a target opening degree of a purge valve.

FIG. 14 is an average value α of the air-fuel ratio feedback correction coefficient α
It is a waveform diagram for explaining the calculation of _AVE .

FIG. 15 is a change waveform diagram of purge gas concentration.

FIG. 16 is a purge gas concentration λp, a purge gas flow rate Qp,
6 is a flowchart for explaining calculation of a target purge rate Rp.

FIG. 17 shows the number of steps STE with respect to the purge valve opening.
It is a characteristic view of P.

FIG. 18 is a flow chart for explaining calculation of the minimum air-fuel ratio value λ′a within a predetermined time T1 from the purge start timing.

FIG. 19 is a flowchart for explaining theoretical calculation of the purge gas concentration λp and the purge gas flow rate Qp.

FIG. 20 is a flowchart for explaining control of a purge valve opening.

FIG. 21 is a flowchart for explaining temporary full closing of the purge valve.

FIG. 22 is a waveform chart for explaining the operation of the embodiment.

FIG. 23 is a flow chart for explaining calculation of a purge gas concentration λp and a purge gas flow rate Qp according to another embodiment.

FIG. 24 is a diagram corresponding to claims of the second invention.

FIG. 25 is a diagram corresponding to the claim of the third invention.

[Explanation of symbols]

4 injector (fuel supply device) 6 catalyst 7 O ₂ sensor (oxygen concentration sensor) 11 control unit 12 crank angle sensor 13 air flow meter 23 canister 27 purge valve 31 learning value memory 32 learning value reading means 33 fuel injection amount calculating means 34 fuel supply Device 35 Oxygen concentration sensor 36 Air-fuel ratio feedback correction amount calculation means 37 Learning value update means 38 Purge valve 39 Pre-purge air-fuel ratio calculation means 40 Update prohibition means 41 Purge start means 42 Immediately after purge air-fuel ratio calculation means 43 Purge gas concentration calculation means 44 Valve open Degree control means 45 determination means 46 prohibition release / continuation means 51 lean operation condition determination means 52 target air-fuel ratio calculation means 53 fuel injection amount calculation means 54 enrichment error learning permissible limit air-fuel ratio calculation means 55 target parameters Di calculating means 56 opening means 61 change amount calculating unit 62 determination unit 63 fully closed and resumption means

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display area F02D 45/00 340 D 364 K

Claims (5)

[Claims] 1. A memory for storing a learned value, a means for reading the learned value according to an operating condition signal, and a fuel injection amount by correcting the basic injection amount according to the operating condition signal with the read learned value. A means for calculating, a device for supplying this injection amount of fuel to the intake pipe, a sensor for detecting the oxygen concentration in the exhaust gas, and an air-fuel ratio so that the exhaust air-fuel ratio falls near the stoichiometric air-fuel ratio based on this sensor detection value. A means for calculating the fuel ratio feedback correction amount, a means for updating the learning value based on this air-fuel ratio feedback correction amount, and a passage for introducing the fuel adsorbed in the canister together with fresh air into the intake pipe as a purge gas as a drive signal. A purge valve that opens and closes according to the above, a means for calculating the air-fuel ratio before purging, and a learning value update means for updating the learning value before purging during stoichiometric operation. Means for opening the purge valve in a state where the learning value update is prohibited, means for calculating the air-fuel ratio immediately after the start of the purge, and an air-fuel ratio immediately after the start of the purge. Means for calculating the purge gas concentration based on the pre-purging air-fuel ratio, means for controlling the valve opening of the purge valve according to the purge gas concentration, and means for determining whether the purge gas concentration is below a predetermined value According to this determination result, when the purge gas concentration is equal to or lower than the predetermined value, the update prohibition by the learning value update prohibiting means is released,
An evaporated fuel processing apparatus for an engine, further comprising means for continuing prohibition of renewal when the purge gas concentration exceeds a predetermined value. 2. A means for determining whether or not the engine is in a lean operating condition, and based on the result of the determination, when the lean operating condition is reached, a value on the lean side of the stoichiometric air-fuel ratio is used as a target air-fuel ratio, and in a stoichiometric operation which is not the lean operating condition. In this case, means for calculating the stoichiometric air-fuel ratio as the target air-fuel ratio, memory for storing the learned value, means for reading this learned value according to the operating condition signal, and operation with this read learned value and the target air-fuel ratio A means for calculating the fuel injection amount by correcting the basic injection amount according to the condition signal, a device for supplying this injection amount of fuel to the intake pipe, a sensor for detecting the oxygen concentration in the exhaust gas, and this sensor detection value Based on this, means for calculating the air-fuel ratio feedback correction amount so that the exhaust air-fuel ratio falls within the vicinity of the stoichiometric air-fuel ratio only during the stoichiometric operation, and this air-fuel ratio feedback compensation A means for updating the learned value based on the amount, a purge valve for opening and closing a passage for introducing the fuel adsorbed in the canister as purge gas into the intake pipe together with fresh air, and a purge valve before purging during the stoichiometric operation. Means for calculating the air-fuel ratio, means for prohibiting update of the learned value by the learned value updating means before purging during the stoichiometric operation, and opening of the purge valve while the update of the learned value is prohibited Means for calculating the air-fuel ratio immediately after the start of the purge, a means for calculating the purge gas concentration based on the air-fuel ratio immediately after the start of the purge and the air-fuel ratio before the purge, and a predetermined value for the lean operation. Means for calculating the enriched erroneous learning allowable limit air-fuel ratio from the air-fuel ratio fluctuation allowable range and the pre-purge air-fuel ratio, and the enriched erroneous learned allowable limit Means for calculating a purge rate that gives an enrichment error learning allowable limit air-fuel ratio based on the air-fuel ratio and the purge gas concentration as a target purge rate, and the purge valve at the time of the stoichiometric operation at a valve opening degree according to this target purge rate. Means for opening, means for determining whether or not the purge gas concentration is less than or equal to a predetermined value, and if the purge gas concentration is less than or equal to a predetermined value from this determination result, the update prohibition by the learning value update prohibiting means is released,
An evaporated fuel processing apparatus for an engine, further comprising means for continuing prohibition of renewal when the purge gas concentration exceeds a predetermined value. 3. A means for calculating a variation amount of the average value per predetermined time from the air-fuel ratio feedback correction amount during the valve opening control by the valve opening control means, and a variation amount per predetermined time is predetermined. Means for determining whether or not the value is less than or equal to a value, and if the result of this determination shows that the amount of change per predetermined time is less than or equal to a predetermined value, the purge valve is fully closed for a predetermined time and then the valve at the start of the previous purge The evaporated fuel processing apparatus for an engine according to claim 1, further comprising: a means for restarting purging at a valve opening that is larger than the opening. 4. The evaporative fuel treatment apparatus for an engine according to claim 1, wherein the purge gas concentration calculating means calculates the purge gas concentration using a theoretical formula. 5. The purge gas concentration calculating means obtains the purge gas concentration by referring to a map having a parameter obtained by subtracting the air-fuel ratio immediately after the start of the purge from the air-fuel ratio before the purge and the suction negative pressure. The evaporated fuel processing device for an engine according to any one of claims 1 to 3.