JP3601080B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly to a technique for increasing the accuracy of air-fuel ratio control when performing a purge process.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a measure for preventing the expansion of air pollution due to the release of evaporated fuel generated in a fuel supply system such as a fuel tank into the atmosphere, the evaporated fuel is temporarily adsorbed by an adsorbing means called a canister, and the adsorbed fuel is absorbed. 2. Description of the Related Art An evaporative fuel processing apparatus is known in which a purge is performed and the purged fuel is introduced into an intake air as an air-fuel mixture (purge gas) for processing. For example, as described in JP-A-63-186955. There is something.
[0003]
This is a purging apparatus of a type that connects / disconnects (ON / OFF) communication of a canister to an engine intake system.
In this apparatus, purging is performed by a constant purge orifice that constantly purges the canister and a purge opening / closing valve that purges a predetermined amount of gas when the throttle valve is opened.
[0004]
Here, there is a method using only a purge opening / closing valve without using a constant purge orifice.
In this method, for example, as shown in FIG. 17, an intake negative pressure introducing hole 2 is provided in the vicinity of the throttle valve 1, and a negative pressure introduced from the introducing hole 2 is used for opening / closing operation integrally formed with a purge opening / closing valve 3. To operate the purge opening / closing valve 3. In this case, when the throttle valve 1 is opened by a small angle, the negative pressure introducing hole 2 which has been located relatively upstream with respect to the throttle valve 1 is changed by the change in the angle of the throttle valve 1. 1 and is located downstream relative to 1 so that suction negative pressure is introduced into the canister 5.
[0005]
Therefore, when the throttle valve 1 is operated to start the vehicle from the idling state, the adsorbed fuel of the canister 5 is purged and flows into the intake pipe 6, and the pre-purging condition (that is, the canister 5) If the purge gas is extremely rich (or lean) due to the degree of adsorption of the evaporated fuel of No. 5), the air-fuel ratio of the air-fuel mixture after this gas flows in becomes rich (or lean), which affects drivability and exhaust emissions. There is a problem that gives.
[0006]
Therefore, as disclosed in Japanese Patent Application Laid-Open No. 63-85249, an electronically controlled purge valve is used in place of the purge on-off valve 3, and setting of operating conditions for opening the purge valve and the opening of the purge valve are performed. Many attempts have been made to perform fine control.
However, in this case, the throttle valve, the engine load, and the engine speed as the operating conditions may cause the purge valve to open greatly under the condition that the intake air flow rate of the engine is not sufficiently obtained. As described above, if the purge gas is extremely rich (or lean) depending on the conditions before the purge, the influence on the engine operability and the like is great.
[0007]
As a method for reducing such a possibility, the electronically controlled purge valve is used, and the purge rate (ie, the purge rate [purge amount / intake air flow rate]) becomes a predetermined value so that the purge amount is proportional to the intake air flow rate. As described above, a technique for controlling the purge amount is disclosed in, for example, JP-A-61-19962.
In this method, when the air-fuel ratio of the air-fuel mixture is made rich (or lean) by the purge gas, a predetermined oxygen sensor is used to detect the air-fuel ratio of the engine intake air-fuel mixture by detecting the oxygen concentration in the exhaust gas. The air-fuel ratio control amount (for example, the fuel injection amount) is feedback-controlled through the air-fuel ratio correction amount so as to obtain the air-fuel ratio. There is a large difference in the air-fuel ratio correction amount in the middle (hereinafter, also referred to as purge OFF), and a large air-fuel ratio step occurs when the purge is switched between ON and OFF. Could not.
[0008]
For this reason, for example, as disclosed in Japanese Patent Application Laid-Open No. 2-245442, the opening amount of a control valve for purging the fuel vapor adsorbed in the canister into the intake system of the engine is adjusted to the engine load and the engine speed. The control accuracy of the air-fuel ratio is improved by adjusting a learning value for adjusting the air-fuel ratio correction amount according to the valve opening amount, or disclosed in, for example, Japanese Patent Application Laid-Open No. 3-260351. In the non-purge region, the target air-fuel ratio is corrected by the non-purge region learning value, and in the purge region, the target air-fuel ratio is corrected by the purge region learning value, so that optimal learning control can be performed in each region. There is something.
[0009]
However, in these cases, the air-fuel ratio learning value during the purge control is stored in a memory provided by a table or map divided for each engine operating condition, similarly to the air-fuel ratio learning value during the non-purge control. Therefore, for example, the amount of adsorbed fuel in the canister is large (the air-fuel ratio of the purge gas tends to be rich), and the learning value in the operating condition during the purge control is updated (updated in a direction to prevent the enrichment). When the purge in the canister proceeds without passing through the learning region and then passes through the learning region, the request is completely different from the previously updated learning value (that is, when the air-fuel ratio of the purge gas becomes lean, If the learning value updated last time is used as it is, the air-fuel ratio is greatly disturbed, and exhaust emission and drivability are deteriorated.
[0010]
[Problems to be solved by the invention]
In order to solve such a problem, the present applicant discloses in Japanese Patent Application No. 6-49485 that the learning value of the air-fuel ratio correction amount is determined when the effect of the purge is large (corresponding to the air-fuel ratio of the purge gas regardless of the engine operating conditions). The purge control and the non-purge control are divided into two types: a learned value obtained when the purge is performed and the effect on the air-fuel ratio by the purge is small (a learned value stored in a table divided for each engine operating condition). A technique for improving the accuracy of the air-fuel ratio control at the time of switching between the two was proposed.
[0011]
However, even in the above Japanese Patent Application No. 6-49485, for example, immediately after switching from the purge control to the non-purge control, purge gas remains in the intake system, and depending on the air-fuel ratio of the residual purge gas, ( In many cases, the air-fuel ratio is rich or lean with respect to the target air-fuel ratio), an air-fuel ratio step occurs, and exhaust emission and drivability may deteriorate.
[0012]
Here, the problem will be described in more detail.
That is,
Japanese Patent Application No. 6-49485 has two learning maps according to when the degree of influence of the purge gas on the air-fuel ratio of the engine intake air-fuel mixture is large and when it is small, and each learning value is set to Lα1. , Lα2.
[0013]
When the degree of influence of the purge gas on the air-fuel ratio of the engine intake air-fuel mixture is large, a value Lα12 (= Lα1 + Lα2-1) obtained by subtracting 1 from the sum of Lα1 and Lα2 is used as a learning value. Lα2 is used as the learning value.
As described above, when the degree of influence of the purge gas on the air-fuel ratio of the engine intake air-fuel mixture is large, Lα12 is used. In this case, the influence of the purge gas on the air-fuel ratio is large. Lα1 corresponds to the air-fuel ratio of the purge gas that changes from moment to moment, while Lα2 learned according to the temporal change of the fuel injection valve, air flow meter, oxygen sensor, etc., responds to the deviation of the base air-fuel ratio. This is to improve the control accuracy of the air-fuel ratio control. When the degree of influence of the purge gas on the air-fuel ratio of the engine intake air-fuel mixture is large, Lα2 is not updated.
[0014]
By the way, since Lα1 is a learning value corresponding to the concentration of the purge gas that changes every moment, one value is sequentially updated irrespective of the engine operating conditions (for example, load and rotation speed), while Lα2 is changed over time. In order to correct the deviation of the base air-fuel ratio due to the above, there is a map that is classified according to the operating conditions of the engine.
Here, the time chart of FIG. 18 will be described. It should be noted that when the effect of the purge gas on the air-fuel ratio of the engine intake air-fuel mixture is large and when the effect is small, the typical cases are the purge control when the air-fuel ratio of the purge gas is rich and the non-purge control (when the purge cut is performed). ).
[0015]
At the time of such purge control, the feedback correction coefficient α is stabilized by the learning value Lα12, but immediately after the purge cut, the learning value is switched to Lα2. Since Lα2 is a learned value during purge cut (normal operation) in which rich purge gas is not sucked, it is learned to a large value (fuel increase direction) with respect to Lα12. Since the correction is made to the rich side, exhaust emissions such as HC deteriorate. At the time of the purge cut, the throttle valve is usually closed, so that the intake air flow rate is reduced and the air-fuel ratio of the air-fuel mixture actually sucked into the engine is reduced by the residual purge gas remaining in the intake manifold. Is rich, and the rich correction is performed by the aforementioned Lα2. Therefore, there is a problem that the final air-fuel ratio of the engine intake air-fuel mixture becomes extremely rich, and the deterioration of exhaust emissions such as HC becomes more remarkable. .
[0016]
Further, in order to recover this rich tendency, the learning value Lα2 is updated to a small value (fuel reduction direction). At this time, since the residual purge gas has already been consumed, this time the engine intake air-fuel mixture The air-fuel ratio becomes lean, and the drivability deteriorates and NOx increases.
The problem of the air-fuel ratio step is not limited to the purge cut. The learning value Lα1 (that is, Lα12) when the degree of influence of the purge gas on the air-fuel ratio of the engine intake air-fuel mixture is great, and the learning value Lα1 of the engine gas-fuel mixture of the purge gas. If there is a deviation between the learning value Lα2 when the degree of influence on the air-fuel ratio is small, the deviation occurs at the time of switching.
[0017]
SUMMARY OF THE INVENTION The present invention has been made in view of such a conventional problem. The present invention has been made in consideration of a case in which a purge gas has two learning values corresponding to when the degree of influence of the purge gas on the air-fuel ratio of the engine intake air-fuel mixture is large and when it is small. It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine, which can optimize air-fuel ratio control when the degree of influence on the air-fuel ratio of the engine intake air-fuel mixture changes from a large state to a small state. I do. It is also an object of the present invention to increase the accuracy and simplify the control.
[0018]
[Means for Solving the Problems]
For this reason, in the air-fuel ratio control device for an internal combustion engine according to the first aspect of the present invention, as shown in FIG.
After adsorbing the evaporated fuel generated in the fuel supply system, the apparatus further includes an evaporated fuel purging device A for purging the evaporated fuel together with air into an intake system such as an intake passage.
Operating condition detecting means B for detecting engine operating conditions;
Air-fuel ratio detecting means C for detecting the air-fuel ratio of the engine intake air-fuel mixture;
Air-fuel ratio basic control value setting means D for setting an air-fuel ratio basic control value based on engine operating conditions detected by the operating condition detecting means B;
Air-fuel ratio feedback correction value setting means E for setting an air-fuel ratio feedback correction value for increasing or decreasing the basic control value of the air-fuel ratio so that the air-fuel ratio detected by the air-fuel ratio detection means C approaches a target value;
Determining means F for determining whether the effect of the fuel vapor purge from the fuel vapor purge device A on the air-fuel ratio is large or small;
When the influence on the air-fuel ratio is determined to be small by the determination means F, the first learning value is updated for each operation region so as to reduce the deviation of the air-fuel ratio feedback correction value from the reference value. 1 learning value setting updating means G;
When the determining means F determines that the influence on the air-fuel ratio is large, the setting and updating of the first learning value by the first learning value setting and updating means G are prohibited, and the reference value of the air-fuel ratio feedback correction value is determined. Learning value setting updating means H for setting and updating a second learning value corresponding to the degree of influence of the evaporated fuel purge on the air-fuel ratio so as to reduce the deviation of
When the influence on the air-fuel ratio is determined to be small by the determination means F, the final value is determined based on at least the basic control value of the air-fuel ratio, the air-fuel ratio feedback correction value, and the first learning value. When the determination means F determines that the influence on the air-fuel ratio is large, a value based on the second learning value is used instead of the first learning value. Air-fuel ratio control value setting means I for setting a final air-fuel ratio control value using
In an air-fuel ratio control device for an internal combustion engine configured to include
The state in which the influence on the air-fuel ratio due to the vaporized fuel purge from the vaporized fuel purge device A changes from a large state to a small state, and in the air-fuel ratio control value setting means I, the value based on the second learning value is When switching to the first learning value,
A switching learning value equivalent value that sets a switching learning value equivalent value based on the value based on the second learning value and the first learning value so as to suppress a change in the air-fuel ratio due to the residual purge gas during the switching. Setting means J;
A switching air-fuel ratio control value for setting a final air-fuel ratio control value during switching based on the set switching learning value equivalent value, the air-fuel ratio basic control value, and the air-fuel ratio feedback correction value. Setting means K;
Was provided.
[0019]
In the invention according to claim 2, the value based on the second learning value is a value based on the second learning value and the first learning value.
According to the third aspect of the present invention, the switching-time learning value equivalent value setting means J is configured to set a value proportional to a deviation between the first learning value and the value based on the second learning value within a predetermined time after the switching instruction. Means for setting a value obtained by subtracting a value from a value based on the second learning value as a switching learning value equivalent value;
The switching-time air-fuel ratio control value setting means K is a means for setting a final air-fuel ratio control value at the time of switching using a value corresponding to the set switching learning value within a predetermined time after a switching instruction. ,
After a predetermined time has passed after the switching instruction, the air-fuel ratio control value setting means I sets the final control value of the air-fuel ratio using the first learning value.
[0020]
In the invention described in claim 4, the switching time is a purge cut time.
In the invention described in claim 5, the switching is performed on condition that the throttle valve is closed so that the opening of the throttle valve becomes equal to or less than a predetermined value.
[0021]
[Action]
The invention according to claim 1 having the above configuration switches from a state in which the degree of influence of the purge gas on the air-fuel ratio of the engine intake air-fuel mixture is large to a state in which the degree of influence of the purge gas on the air-fuel ratio of the engine air-fuel mixture is small. At this time, the learning value used in each state is not switched immediately and used, but, for example, the first learning which is a standard of the air-fuel ratio of the purge gas is performed in order to suppress the air-fuel ratio fluctuation due to the residual purge gas at the time of the purge cut. Based on the difference between the value and the value based on the second learning value (or the second learning value itself), the switching-time learning value equivalent value (in the direction opposite to the direction in which the second learning value approaches the first learning value). , And FIG. 16), and the final control value of the air-fuel ratio at the time of switching is set using this value.
[0022]
As a result, air-fuel ratio fluctuations caused by residual purge gas when switching from a state in which the degree of influence of the purge gas to the air-fuel ratio of the engine intake air-fuel mixture is large to a state in which the degree of influence of the purge gas on the air-fuel ratio of the engine air-fuel mixture is small are reduced. Since it is possible to prevent the fluctuation of the air-fuel ratio feedback correction value, it is possible to prevent erroneous learning of the first learning value. Therefore, it is possible to prevent deterioration of exhaust emissions and operability when switching from a state in which the degree of influence of the purge gas on the air-fuel ratio of the engine intake air-fuel mixture is large to a state in which the degree of influence of the purge gas on the air-fuel ratio of the engine air-fuel mixture is small. can do.
[0023]
In the invention according to claim 2, if the value based on the second learning value is a value based on the second learning value and the first learning value, the effect of the purge gas on the air-fuel ratio is large. In the air-fuel ratio control, the second learning value learned according to the air-fuel ratio of the purge gas can cope with the air-fuel ratio of the purge gas that changes from moment to moment, and can also be used for the time-dependent changes in the fuel injection valve, air flow meter, oxygen sensor, etc. Since the base air-fuel ratio deviation can be dealt with by the first learning value learned accordingly, the air-fuel ratio control can be made more precise.
[0024]
In the invention according to claim 3, a value proportional to a deviation between the first learning value and a value based on the second learning value is changed to the second learning value within a predetermined time after the instruction to switch the learning value. A value obtained by subtracting from the value based on the set value is set as a switching time learning value equivalent value, and a final air-fuel ratio control value at the time of switching is set using the set switching time learning value equivalent value. After a lapse of a predetermined time after the switching instruction, the air-fuel ratio control value setting means sets a final air-fuel ratio control value using the first learning value. Thus, with a relatively simple configuration, for example, a value based on the relatively small value (lean correction side) based on the second learning value is temporarily set to a smaller value (lean correction side) after the switching instruction, and then compared. Since the first learning value can be switched to a target value (rich correction side), the degree of influence of the purge gas on the air-fuel ratio of the engine intake air-fuel mixture is increased, and the influence of the purge gas on the air-fuel ratio of the engine air-fuel mixture is increased. It is possible to prevent a change in the air-fuel ratio caused by the residual purge gas when switching to a state with a small degree.
[0025]
According to the fourth aspect of the present invention, the switching is performed at the time of the purge cut. Therefore, when the deviation between the first learning value and the value based on the second learning value is large, an empty space caused by the residual purge gas accompanying the switching is obtained. The switching control by the switching-time air-fuel ratio control value setting means as described above is performed only when the fuel ratio fluctuation is large and erroneous learning of the first learning value and deterioration of exhaust emission and drivability become remarkable. Therefore, the configuration can be simplified.
[0026]
According to the fifth aspect of the present invention, the switching is performed on condition that the throttle valve is closed so that the opening of the throttle valve is equal to or less than a predetermined value. Due to the closing operation of the throttle valve, the intake air flow rate decreases, the degree of influence of the residual purge gas remaining in the intake manifold increases, and the air-fuel ratio of the engine intake air-fuel mixture becomes richer. The switching control by the switching air-fuel ratio control value setting means as described above is performed only when the fluctuation is large and the erroneous learning of the first learning value and the deterioration of the exhaust emission and the drivability become remarkable. Therefore, the configuration can be simplified.
[0027]
【Example】
Hereinafter, one embodiment of the present invention will be described with reference to the accompanying drawings.
2, an intake passage 12 of an engine 11 is provided with an air flow meter 13 for detecting an intake air flow rate Qa introduced through an air cleaner (not shown) and a throttle valve 14 for controlling an intake air amount Qa in conjunction with an accelerator pedal. An electromagnetic fuel injection valve 16 as fuel supply means is provided for each cylinder in the downstream manifold portion 15.
[0028]
The fuel injection valve 16 is driven to open by an injection pulse signal from a control unit 17 containing a microcomputer or the like, and injects and supplies fuel.
The exhaust passage 18 is provided with an air-fuel ratio sensor (hereinafter referred to as an oxygen sensor) 19 as a means for detecting the air-fuel ratio of the intake air-fuel mixture by detecting the oxygen concentration in the exhaust gas at the collecting portion of the manifold portion 18A. I have.
[0029]
The distributor (not shown) has a built-in crank angle sensor 20 which counts a crank unit angle signal output from the crank angle sensor 20 in synchronization with the engine rotation for a certain period of time, or a crank reference angle signal. Is measured to detect the engine rotation speed Ne. Further, a water temperature sensor 21 for detecting the cooling water temperature TW is provided.
[0030]
On the other hand, the evaporated fuel stored in the upper space of the fuel tank (not shown) is guided to the canister 23 through the evaporated fuel passage 22 while the engine 11 is stopped, and is temporarily adsorbed by the adsorbent such as activated carbon in the canister 23. You. The upper space of the canister 23 is connected to a purge port 12 </ b> A formed downstream of the throttle valve 14 in the intake passage 12 via a purge passage 24. The purge passage 24 is provided with a purge control valve 25 that is controlled to be energized by the control unit 17.
[0031]
In the above configuration, sensors for detecting operating conditions of the engine 11 (which function as operating condition detecting means) including the air flow meter 13, the crank angle sensor 20, and the water temperature sensor 21 and the operating air-fuel ratio of the engine 11 are detected. An oxygen sensor 19, a fuel injection valve 16 as a fuel supply device, and whether or not an air-fuel ratio feedback control range is determined based on signals from the sensors and the like. An air-fuel ratio feedback control system (an air-fuel ratio control system according to the present invention), which is provided in a control unit 17 and controls the amount of fuel injected from the fuel injection valve 16 (air-fuel ratio control amount) so that the fuel ratio matches the target air-fuel ratio. (Including a fuel ratio basic control value setting means and an air-fuel ratio feedback correction value setting means).
[0032]
On the other hand, for the air-fuel ratio feedback control system, the canister 23, the purge passage 24, the purge control valve 25, and the opening degree of the purge control valve 25 are calculated based on the engine operating condition, A purge device for evaporating fuel is constituted by the purge control means provided to the control unit 17 as software instructing the control unit 25.
[0033]
The entire evaporative fuel processing apparatus includes, in addition to the evaporative fuel purging device, a charging device that guides the evaporative fuel generated in the fuel tank to the canister 23.
As the purge control valve 25, for example, an open / close solenoid valve that controls only the opening and closing of the valve, a valve that directly controls the valve opening by the operation angle of the stepping motor, and a solenoid valve that opens and closes at a predetermined cycle, Various types such as a so-called duty valve that controls the ratio of the valve opening time (ON duty) to the inside are adopted.
[0034]
In this embodiment, the description will be given taking the duty valve as an example.
The determining means, the first learning value setting / updating means, the second learning value setting / updating means, the air-fuel ratio control value setting means, the switching learning value equivalent value setting means, and the switching air-fuel ratio control value setting means in the present invention are controlled by The unit 17 is equipped with software.
[0035]
Here, a calculation routine of the fuel injection amount (injection pulse width) performed by the control unit 17 of the present embodiment will be described with reference to the flowchart of FIG. The present invention absorbs an air-fuel ratio step generated when the learning value is switched between a case where the degree of influence of the purge gas on the air-fuel ratio of the engine intake air-fuel mixture is large and a case where the learning value is small. However, hereinafter, a case where the degree of influence of the air-fuel ratio of the purge gas on the air-fuel ratio of the engine intake air-fuel mixture is large is referred to as a purge control in which the air-fuel ratio of the purge gas is rich, and a case where the air-fuel ratio is small is referred to as non-purge control (purge cut). explain.
[0036]
In step (denoted by S in the figure, the same applies hereinafter), the engine speed Ne is determined based on the detection signal of the crank angle sensor 20.
In step 2, the intake air flow rate Qa is determined based on the detection signal of the air flow meter 13.
In step 3, the engine operating conditions (for example, Tp [or Qa], Ne, water temperature Tw, etc.) are detected, and the air-fuel ratio correction coefficient (K _MR + K _TMR ), A water temperature correction coefficient (Kw) that forcibly corrects to a rich side at low water temperature, a start and post-start increase correction coefficient (Kas), etc., and various correction coefficients COEF (1 + K). _MR + K _TMR + Kw + Kas +...).
[0037]
In step 4, a basic fuel injection pulse width (corresponding to the basic fuel injection amount) Tp = k × Q / Ne (k is a constant) is calculated from the intake air flow rate Qa and the engine rotation speed Ne.
In step 5, the rich / lean determination output signal of the oxygen sensor 19 is read. In step 6, the air-fuel ratio feedback correction coefficient α (corresponding to the air-fuel ratio feedback correction value in the present invention) set in the air-fuel ratio feedback control based on the rich / lean inversion signal of the oxygen sensor 19 is read.
[0038]
The air-fuel ratio feedback correction coefficient α is determined in a predetermined case (for example, at the time of lean control, at the time of starting, before activation of the oxygen sensor, at the time of a high load, Except during deceleration, etc., the air-fuel ratio is increased / decreased by proportional integral (PI) control based on the rich / lean inversion output of the oxygen sensor 19, whereby the air-fuel ratio of the combustion air-fuel mixture is increased to a target air-fuel ratio (stoichiometric air-fuel ratio). ) Feedback control is performed in the vicinity.
[0039]
In step 7, a learning value Lα set by a routine described later is read. In step 8, the final effective fuel injection pulse width Ti (= Tp × (α + Lα−1) × COEF × k + k ′) is calculated and sent to the fuel injection valve 16 as an injection pulse signal to cause fuel injection.
Here, k is a constant determined by calculation for each rotation or calculation for each cycle. K ′ is a coefficient for correcting the valve opening time of the injector 16 due to a decrease in battery voltage or the like.
[0040]
Next, the calculation of the valve opening duty of the purge control valve 25 will be described with reference to the flowchart of FIG.
In step 11, a basic DUTY is obtained by referring to a map or the like (for example, FIG. 5) based on the engine operating state (Ne or Tp [or Qa]).
In step 12, the target purge rate Evptr is obtained from the engine operating state, the total purge amount, and the like, for example, with reference to the map of FIG. 6 for the total purge amount.
[0041]
In step 13, the open duty of the purge control valve 25 is obtained from the product of the basic duty and the target purge rate Evptr.
The basic DUTY map of FIG. 5 and the purge rate map of FIG. 6 will be described. The basic DUTY is such that the engine rotation speed Ne and the engine load (Tp and Tp) are set so that the purge amount is proportional to the engine intake air flow rate Qa. Qa), and increases as the intake air flow rate Qa increases.
[0042]
The target purge rate Evptr is changed, for example, according to the total purge amount (integrated purge amount from the start of the purge). When the purge is advanced (total purge amount is large), the fuel concentration in the purge gas becomes low, so the purge rate is increased. In order to reduce the influence of the engine intake air-fuel mixture on the air-fuel ratio, a large amount of purging is set.
Here, whether or not the air-fuel ratio of the purge gas is rich can be determined by the air-fuel ratio feedback correction coefficient α. The fuel injection of the engine is basically performed (unless the engine is cold or under heat-resistant conditions) so as to achieve the stoichiometric air-fuel ratio. Here, when the purge gas from the canister 23 is introduced into the engine intake system and the operating air-fuel ratio of the engine becomes rich, this is detected by the oxygen sensor 19 disposed in the exhaust passage 18 of the engine 11 and the air-fuel ratio is corrected. Feedback is given. If the air-fuel ratio feedback control is rich, the fuel injection amount is corrected to be reduced, and if it is lean, the fuel injection amount is corrected to be increased.
[0043]
That is,
The calculation of the air-fuel ratio feedback correction coefficient α determines rich / lean of the actual air-fuel ratio with respect to a target air-fuel ratio (for example, a stoichiometric air-fuel ratio) based on the oxygen concentration in the exhaust gas detected by the oxygen sensor 19, At the time of inversion from (lean to rich), the air-fuel ratio feedback correction coefficient α is increased (decreased) by a predetermined proportional amount (P amount), and thereafter, the integral (I ) Gradually increases (decreases) the correction coefficient α.
[0044]
An example of a method of calculating the air-fuel ratio feedback correction coefficient α is shown in a flowchart of FIG.
The air-fuel ratio feedback correction coefficient α is a correction term that is multiplied by the basic fuel injection pulse width Tp, and the fuel ratio is adjusted so that the actual air-fuel ratio approaches the target air-fuel ratio by the above-described proportional / integral control (PI control). The injection amount is feedback controlled.
[0045]
By the way, in the air-fuel ratio feedback correction, since a delay time is included after the correction is performed and the correction result is detected again, an overshoot usually occurs, and the air-fuel ratio is accurately controlled near the stoichiometric mixture ratio. , The rich / lean correction inversion is repeated. However, in a situation where purging is being performed and the operating air-fuel ratio is being continuously corrected to be rich, the injected fuel amount is continuously being reduced and corrected. The feedback correction for repeating the rich / lean operation is resumed in the same manner as at the time.
[0046]
Since the air-fuel ratio feedback correction decrease at this time corresponds to the purge gas concentration, the air-fuel ratio of the purge gas can be estimated based on the average value of the air-fuel ratio feedback correction coefficient α.
Next, a routine for calculating the learning value Lα (at a steady state and when the purge is OFF → ON) is shown in a flowchart of FIG. Note that Lα1, which corresponds to a second learning value of the present invention described below, is a learning value corresponding to the air-fuel ratio of the purge gas in a region where the degree of influence of the purge gas on the air-fuel ratio is large. Lα2 corresponding to the value is a learning value set for each operating condition in a region where the degree of influence of the purge gas on the air-fuel ratio is small (that is, a learning value for correcting a normal deterioration with time or the like).
[0047]
In step 21, it is determined whether or not air-fuel ratio feedback control (λ control) is being performed. If not, control proceeds to step 37, where the air-fuel ratio learning value Lα is set to 1. If the control is being performed, the process proceeds to step S22. In step 22, the air-fuel ratio feedback correction coefficient α calculated in another routine is read, and in step 23, the air-fuel ratio learning value Lα2 when there is no purge fuel calculated in another routine described later is read.
[0048]
In step 24, it is determined whether the purge control is being performed. If the purge is being performed, the process proceeds to step 25. If the purge control is not being performed, the process proceeds to step 29.
In step 25, the current target purge rate Evptr is read (see FIG. 6). In step 26, the air-fuel ratio learning reference value Lαo during the purge control is read, and based on these, the purge control hollow fuel ratio learning value Lα1 is calculated in step 27. (Lα1 = Lαo × Evptr).
[0049]
Here, a calculation method for obtaining the air-fuel ratio learning value Lα1 from the target purge rate Evptr and the air-fuel ratio correction learning reference value Lαo as described above will be described.
FIG. 9 shows the movement of α and Lα1 when the purge rate changes.
That is, if the purge start permission condition has not yet been reached immediately after the start, the purge rate is naturally 0, and the purged air-fuel ratio learning values Lα1 and Lαo are both set to the initial value 1. When the start of the purge is permitted, the purge rate is initially started as low as possible to minimize the influence on the air-fuel ratio. The air-fuel ratio feedback correction coefficient α is reduced by enriching the air-fuel ratio by the fuel in the purge gas so that the air-fuel ratio becomes λ = 1. When the air-fuel ratio is set to λ = 1, α starts reversing again. Here, learning of the purge-time air-fuel ratio learning reference value Lαo is performed, and the value is updated until α = 1. When the purge of the fuel in the canister progresses and the purge rate is set to a large value according to FIG. 6, Lα1 is calculated based on the purge rate Evptr.
[0050]
For example, considering the purge rate Evptr = 1 (%) as a reference, when Evptr = 1 (%), Lαo = Lα1, but when the purge rate changes, the above-mentioned Lα1 = Lαo × Evptr. (%).
Therefore, according to this calculation method, the air-fuel ratio can be correctly corrected even if the purge rate changes based on the air-fuel ratio learning value Lαo at the reference purge rate (for example, 1%).
[0051]
In step 28, the air-fuel ratio feedback correction coefficient α and the purge control hollow fuel ratio learning value Lα1 are respectively compared with the reference values. If both values are within the reference values, the deviation of the air-fuel ratio is small and the influence of the purge fuel is small. Therefore, it is assumed that there is no purge, and the process proceeds to step 29. In this step 29, the purge flag FLGPRG is set to 0, and this is used for the determination that there is no purge fuel (the degree of influence is small). In step 30, since there is no influence of the purge fuel, the final air-fuel ratio learning value Lα is set to the same value as the air-fuel ratio learning value without purge fuel Lα2 (Lα = Lα2).
[0052]
On the other hand, if it is determined in step 28 that at least one of the air-fuel ratio feedback correction coefficient α and the purge control hollow fuel ratio learning value Lα1 is outside the reference value, the air-fuel ratio is largely shifted and the influence of the purge fuel is large. Then, the purge flag FLGPRG is set to 1 and used for the determination that the purge fuel is present (that the degree of influence is large). In step 32, the final air-fuel ratio learning value Lα when the effect of the purge fuel on the air-fuel ratio of the engine intake air-fuel mixture is large is obtained using the air-fuel ratio learning values Lα1 and Lα2 with and without the purge (Lα = Lα1 + Lα2). -1 = Lα12, which corresponds to a value based on the second learning value of the present invention). The reason why (Lα = Lα1 + Lα2-1) is used when the degree of influence of the purge gas on the air-fuel ratio of the engine intake air-fuel mixture is large in this case is because the purge gas has a large influence on the air-fuel ratio. While Lα1 learned according to the air-fuel ratio of the purge gas corresponds to the air-fuel ratio of the purge gas that changes from moment to moment, while Lα2 learned according to the temporal change of the fuel injection valve, the air flow meter, the oxygen sensor, and the like, This is to improve the control accuracy of the air-fuel ratio control by coping with the deviation of the base air-fuel ratio. It should be noted that control accuracy may be slightly reduced without using Lα12, but control may be performed using Lα1. Further, in steps 33 to 36, upper and lower limit values Lαh and Lαl of the air-fuel ratio learning value Lα are determined to prevent the learning value from abnormally changing due to erroneous learning or the like.
[0053]
Next, updating of the air-fuel ratio learning values Lαo and Lα2 with and without the purge will be described with reference to the flowchart of FIG.
In step 41, the air-fuel ratio feedback correction coefficient α obtained according to the flowchart shown in FIG. 7 is read, and in step 42, the average value αp of the maximum value and the minimum value of α is calculated according to the following equation.
[0054]
αp = (Σαmax, min) / n
In step 43, the deviation Δα of the average value αp from the control center is calculated. In step 44, the presence or absence of purge fuel is determined based on the purge flag FLGPRG. If there is no purge fuel (FLGPRG = 0), the process proceeds to step 45. If there is a purge fuel (FLGPRG = 1), the routine proceeds to step 48. In step 45, the previous air-fuel ratio learning value Lα2 when there is no purge fuel is read, and in step 46, the air-fuel ratio learning value Lα2 is updated. This calculation method adds a weight to the deviation Δα of the current α with respect to the previous learning value Lα2 (−1) in the same manner as the conventional calculation method of the air-fuel ratio learning value, and is expressed by the following equation. .
[0055]
Lα2 = Lα2 (−1) + M · Δα
In this equation, M is a weighted value of Δα, and may be a value determined by the engine operating conditions, the size of Δα, or the like.
The air-fuel ratio learning value Lα2 calculated in step 46 is stored in a map memory determined in step 47 by the engine load and the rotational speed as shown in FIG. Therefore, when the engine operating conditions are the same, the same value in the Lα2 map is searched.
[0056]
In step 48, the target purge rate Evptr (%) when the purge is present is read, and in step 49, the previous purge hollow fuel ratio learning reference value Lαo is read. In step 50, the purge hollow fuel ratio learning reference value Lαo is calculated according to the following equation. I do.
Lαo = Lαo (−1) + M · Δα / Evptr
In this equation, Lαo (−1) is the previous value, and M is a weighting coefficient of Δα obtained in the same manner as when there is no purge.
[0057]
Finally, at step 51, the purge hollow fuel ratio learning reference value Lαo obtained by the above calculation is stored in the memory. This memory does not store the learning value memory for each engine operating condition unlike the learning value memory without the purge, but stores the air-fuel ratio correction learning reference value Lαo with the purge only in one memory. Therefore, the air-fuel ratio learning reference value Lαo when there is a purge is updated from the one memory at the same time that the value is frequently updated, and is set to the latest air-fuel ratio correction request value as the purge progresses from the canister. Becomes possible.
[0058]
According to the calculation of the air-fuel ratio learning value described above, the optimum setting can be performed during the purge control, during the non-purge control, and when switching from the non-purge control to the purge control. For example, the operation is performed as shown in FIG. When the purge is changed from OFF to ON on the way, the value of the learning value Lα changes, and the value of the air-fuel ratio feedback correction coefficient α does not disturb. Deterioration can be prevented (FIG. 12A is an example of the related art).
[0059]
However, when switching from the state in which (Lα1 + Lα2-1) is used as the learning value Lα (that is, the purge control [purge ON]) to the use of Lα2 (that is, the non-purge control [purge OFF]), As described above, the air-fuel ratio step due to the residual purge gas occurs, which causes problems such as deterioration of exhaust emission and drivability and erroneous learning. In order to solve this, in the present embodiment, the flow of FIG. Be executed. In the present embodiment, the switching time is described as representative of the purge cut.
[0060]
That is,
In step 61, the engine speed Ne and the engine load Tp (or Qa) are detected.
In step 62, the basic fuel injection amount TP is calculated.
In step 63, it is determined whether or not it is in the purge area. If YES, proceed to Step 64; if NO, proceed to Step 70. The purge region is set in advance based on the operating conditions (Ne, Tp, Tw) and the like. Therefore, the determination can be made by detecting the operating conditions.
[0061]
In step 64, the learning value Lα1 in a region where the influence of the purge gas on the air-fuel ratio is large is read by referring to a map or the like.
In step 65, it is determined whether Lα1 is smaller than a predetermined value A. If YES, it is determined that the residual purge gas has a large effect on the air-fuel ratio of the engine intake air-fuel mixture, and the routine proceeds to step 66. If NO, the process proceeds to step 70, assuming that the effect of the residual purge gas on the air-fuel ratio of the engine intake air-fuel mixture is small.
[0062]
In step 66, it is determined whether or not the purge is cut (whether or not the purge has been changed from ON to OFF) based on the above-described flag and the like. If YES, the process proceeds to step 72, and if NO, the process proceeds to step 67.
In step 67, the learning value Lα2 in an area where the influence of the purge gas on the air-fuel ratio of the engine intake air-fuel mixture is small is read with reference to a map.
[0063]
In step 68, Lα12 (= Lα1 + Lα2-1) is calculated. In this way, when the degree of influence of the purge gas on the air-fuel ratio of the engine intake air-fuel mixture is large, Lα12 is determined by using Lα2 for correcting the base air-fuel ratio and a learning value corresponding to the constantly changing purge gas air-fuel ratio. This is for improving the control accuracy of the air-fuel ratio by synthesizing Lα1 with Lα1.
[0064]
In step 69, the Lα12 is set as Lα in the flow of FIG. Then, a final fuel injection pulse width Ti is calculated in the flow of FIG.
On the other hand, if it is determined in step 66 that the purge cut has been made (that is, the purge has been turned off from ON), the process proceeds to step 72. In step 72, the intake air flow rate Qa (or the throttle valve 14 is determined to be equal to or smaller than a predetermined value B. If YES, it is determined that the tendency of the air-fuel ratio of the engine intake air-fuel mixture to be rich is remarkable by the closing operation of the throttle valve 14, and the routine proceeds to step 73. If NO, it is determined that the enrichment tendency is not so strong, and the routine proceeds to step 70.
[0065]
In the present embodiment, the air-fuel ratio step due to the closing operation of the throttle valve 14 is taken into consideration. However, even if the throttle valve 14 is not closed, the air-fuel ratio step that cannot be tolerated only by purge cut is performed. Occurs, the step 72 may be omitted and the process may proceed directly to the step 73 from the step 66.
In step 70, it is determined that stable air-fuel ratio control can be performed even if the fuel injection pulse width Ti is calculated using the learning value Lα2, and Lα2 is read with reference to a map. It is set as Lα in the flow of FIG. Then, the final fuel injection pulse width Ti is calculated in the flow of FIG.
[0066]
On the other hand, in step 73, ΔLα (= Lα12−Lα2), which is a measure of the air-fuel ratio of the purge gas, is calculated.
In step 74, the amount of weight loss P (the amount of reduction with respect to Lα12, see FIG. 14) allocated corresponding to ΔLα, and the time for setting a predetermined time t (“Lα12−P”) as the learning value Lα, see FIG. ) And are searched for.
[0067]
In step 75, it is determined whether or not the time t has elapsed. If YES, since the predetermined time t has elapsed since the switching, it is determined that stable air-fuel ratio control can be performed even if the fuel injection pulse width Ti is calculated using Lα2, and the routine proceeds to step 70.
In the case of NO, when the fuel injection pulse width Ti is calculated using Lα2, since the air-fuel ratio step is large, the routine proceeds to step 76, where a learning value equivalent value Q (= Lα12) for absorbing this air-fuel ratio step is obtained. -P). The Q corresponds to a switching learning value equivalent value of the present invention.
[0068]
In step 77, the Q (= Lα12−P) is set as Lα in the flow of FIG. Then, the final fuel injection pulse width Ti is calculated in the flow of FIG.
Then, in a step 78, it is determined whether or not the purge is turned on. If yes, return to step 64. On the other hand, if NO, the process returns to step 75 and uses Q (= Lα12−P) as the learning value Lα until the predetermined time t has elapsed.
[0069]
Here, the operation of the above control will be described with reference to the time chart of FIG.
That is,
In order to prevent the enrichment of the air-fuel ratio of the engine intake air-fuel mixture due to the residual purge gas during the purge cut (as described above, the intake air flow rate Qa is reduced by closing the throttle valve 14, this tendency is further strengthened). Instead of switching to the learning time, a value Q (= Lα12−P) obtained by subtracting the value P corresponding to the difference between Lα12 and Lα2 (ΔLα = Lα12−Lα2) from Lα12 for a predetermined time t after the purge cut. Used as Lα. The value of P increases as the value of ΔLα increases (see FIG. 14).
[0070]
In other words, the above-described enrichment immediately after the purge cut tends to be enriched as the air-fuel ratio of the purge gas is enriched. Therefore, P is proportional to the air-fuel ratio of the purge gas (in proportion to ΔLα). By increasing the value, the value of Q (= Lα12−P) is reduced, and the disturbance of the air-fuel ratio feedback correction coefficient α is suppressed. The time t controlled by Q (= Lα12−P) is also set in proportion to ΔLα because it depends on the air-fuel ratio of the purge gas (see FIG. 15).
[0071]
As described above, the variation of α can be suppressed by changing the enrichment of the air-fuel ratio due to the residual purge gas at the time of the purge cut in accordance with ΔLα, which is a measure of the air-fuel ratio of the purge gas. Can be prevented. Therefore, it is possible to prevent the exhaust emission and the operability from being deteriorated during the purge cut.
[0072]
Although the present embodiment has been described by way of example at the time of the purge cut, the present invention is not limited to the purge cut, but the purge gas has a large influence on the air-fuel ratio of the engine intake air-fuel mixture. This is applicable when switching to a state in which the degree of influence of air on the air-fuel ratio is small.
[0073]
【The invention's effect】
As described above, according to the first aspect of the present invention, the degree of influence of the purge gas on the air-fuel ratio of the engine intake mixture is small from the state of the purge gas having a large influence on the air-fuel ratio of the engine intake mixture. The change in the air-fuel ratio when switching to the state can be prevented, and the change in the air-fuel ratio feedback correction value can be suppressed, so that erroneous learning of the first learning value can be prevented. Therefore, it is possible to prevent deterioration of exhaust emissions and operability when switching from a state in which the degree of influence of the purge gas on the air-fuel ratio of the engine intake air-fuel mixture is large to a state in which the degree of influence of the purge gas on the air-fuel ratio of the engine air-fuel mixture is small. can do.
[0074]
According to the second aspect of the present invention, in the air-fuel ratio control in a case where the influence of the purge gas on the air-fuel ratio is large, the air-fuel ratio of the purge gas that changes every moment is determined by the second learning value learned according to the air-fuel ratio of the purge gas. In addition to being able to cope with the fuel ratio, it is possible to cope with the deviation of the base air-fuel ratio by the first learning value that is learned according to the change over time of the fuel injection valve, air flow meter, oxygen sensor, etc. Accuracy can be improved.
[0075]
According to the third aspect of the present invention, the degree of influence of the purge gas on the air-fuel ratio of the engine intake air-fuel mixture is changed from the state in which the degree of influence of the purge gas on the air-fuel ratio of the engine air-fuel mixture is relatively large. A change in the air-fuel ratio caused by the residual purge gas when switching to a small state can be prevented.
According to the fourth aspect of the present invention, since the time of the switching is the time of the purge cut, the configuration can be simplified.
[0076]
According to the fifth aspect of the present invention, the switching is performed under the condition that the throttle valve is closed so that the opening degree of the throttle valve is equal to or less than a predetermined value. Can be achieved.
[Brief description of the drawings]
FIG. 1 is a block diagram of the present invention.
FIG. 2 is an overall configuration diagram of an embodiment of the present invention.
FIG. 3 is a flowchart illustrating a calculation function of a fuel injection pulse width.
FIG. 4 is a flowchart illustrating a calculation function of a valve opening duty of a purge control valve.
Fig. 5 Basic DUTY map
FIG. 6 is a purge rate map.
FIG. 7 is a flowchart illustrating an example of a method of calculating an air-fuel ratio feedback correction coefficient α.
FIG. 8 is a flowchart illustrating an example of a method of calculating an air-fuel ratio learning value.
FIG. 9 is a time chart showing the movement of α and Lα1 when the purge rate changes.
FIG. 10 is a flowchart illustrating an air-fuel ratio learning value updating unit;
FIG. 11 is a diagram showing a map memory of an air-fuel ratio learning value Lα2.
FIG. 12A is a time chart for explaining a conventional disturbance of the air-fuel ratio feedback correction coefficient when the purge is changed from OFF to ON, and FIG. 12B is a diagram illustrating the movement of the air-fuel ratio learning value and the air-fuel ratio feedback correction coefficient according to the present embodiment. Time chart shown
FIG. 13 is a flowchart illustrating a setting routine of a switching learning value equivalent value used when switching from purge ON to purge according to the present embodiment.
FIG. 14 is a correlation diagram between ΔLα, which is a measure of the purge gas air-fuel ratio, and a reduction amount P.
FIG. 15 is a correlation diagram between ΔLα, which is a measure of the purge gas air-fuel ratio, and a predetermined time t.
FIG. 16 is a time chart for explaining the operation when the purge is switched from ON to OFF in the embodiment.
FIG. 17 is a system diagram illustrating an example of a conventional canister purging device.
FIG. 18 is a time chart for explaining a problem when switching from purge ON to OFF in a conventional air-fuel ratio control device.
[Explanation of symbols]
11 organizations
12 Intake passage
13 Air flow meter
16 Fuel injection valve
17 Control unit
18 Exhaust passage
19 Oxygen sensor
20 Crank angle sensor
23 Canister
24 Purge passage
25 Purge control valve

Claims (5)

After adsorbing the evaporative fuel generated in the fuel supply system, the evaporative fuel purge device that purges the evaporative fuel together with air into an intake system such as an intake passage is provided.
Operating condition detecting means for detecting engine operating conditions;
Air-fuel ratio detection means for detecting the air-fuel ratio of the engine intake mixture,
Air-fuel ratio basic control value setting means for setting a basic control value of the air-fuel ratio based on the engine operating condition detected by the operating condition detecting means,
Air-fuel ratio feedback correction value setting means for setting an air-fuel ratio feedback correction value for increasing or decreasing the basic control value of the air-fuel ratio so as to bring the air-fuel ratio detected by the air-fuel ratio detection means closer to a target value,
Determining means for determining the magnitude of the effect on the air-fuel ratio by the fuel vapor purge from the fuel vapor purge device;
When the determining means determines that the influence on the air-fuel ratio is small, the first learning value is set and updated for each operating region so as to reduce the deviation of the air-fuel ratio feedback correction value from the reference value. Learning value setting updating means,
When the determining means determines that the influence on the air-fuel ratio is large, the setting and updating of the first learning value by the first learning value setting and updating means are prohibited, and the deviation of the air-fuel ratio feedback correction value from the reference value is prevented. Learning value setting updating means for setting and updating a second learning value corresponding to the degree of influence of the evaporated fuel purge on the air-fuel ratio so as to reduce
When the influence on the air-fuel ratio is determined to be small by the determination means, the final value is determined based on at least the basic control value of the air-fuel ratio, the air-fuel ratio feedback correction value, and the first learning value. While the control value of the air-fuel ratio is set to a large value, when the determination unit determines that the influence on the air-fuel ratio is large, a value based on the second learning value is used instead of the first learning value. Air-fuel ratio control value setting means for setting a final air-fuel ratio control value,
In an air-fuel ratio control device for an internal combustion engine configured to include
The state in which the influence on the air-fuel ratio due to the fuel vapor purge from the fuel vapor purge device is large is changed to a small state, and the air-fuel ratio control value setting means sets the first value from the value based on the second learning value. When switching to the learning value,
A switching learning value equivalent value that sets a switching learning value equivalent value based on the value based on the second learning value and the first learning value so as to suppress a change in the air-fuel ratio due to the residual purge gas during the switching. Setting means;
A switching air-fuel ratio control value for setting a final air-fuel ratio control value during switching based on the set switching learning value equivalent value, the air-fuel ratio basic control value, and the air-fuel ratio feedback correction value. Setting means;
An air-fuel ratio control device for an internal combustion engine, comprising: 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the value based on the second learning value is based on the second learning value and the first learning value. 3. The switching learning value equivalent value setting means sets a value proportional to a deviation between the first learning value and a value based on the second learning value within a predetermined time after the switching instruction based on the second learning value. Means for setting a value obtained by subtracting from the value as a switching learning value equivalent value,
The switching-time air-fuel ratio control value setting means is a means for setting a final air-fuel ratio control value at the time of switching using a value corresponding to the set switching learning value within a predetermined time after a switching instruction. ,
2. The air-fuel ratio control value setting means sets a final air-fuel ratio control value using the first learning value after a predetermined time has elapsed after the switching instruction. 3. The air-fuel ratio control device for an internal combustion engine according to 2. The air-fuel ratio control device for an internal combustion engine according to any one of claims 1 to 3, wherein the switching is performed during a purge cut. The idle of the internal combustion engine according to any one of claims 1 to 4, wherein the switching is accompanied by a closing operation of the throttle valve such that an opening degree of the throttle valve becomes a predetermined value or less. Fuel ratio control device.

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