JP4349438B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

  The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine that discharges evaporated fuel generated in a fuel tank to the intake side of the internal combustion engine (engine), burns it, and purges it.

Conventionally, as a prior art document related to an air-fuel ratio control apparatus for an internal combustion engine, one disclosed in Patent Document 1 is known. This technique shows a technique for correcting the fuel injection amount by detecting the fuel concentration during purging based on the air-fuel ratio feedback value (coefficient) at the time of purging.
JP 7-83096 A

  By the way, in an air-fuel ratio control apparatus for an internal combustion engine capable of changing the air-fuel ratio, if the air-fuel ratio is changed at the time of purging, the degree of influence on the air-fuel ratio by the purge also changes, so that the required fuel amount (fuel There is a problem in that drivability and emission are deteriorated by changing the correction value for the injection amount) and causing an air-fuel ratio fluctuation.

  Accordingly, the present invention has been made to solve such a problem, and an object thereof is to provide an air-fuel ratio control device for an internal combustion engine that can ensure stable air-fuel ratio controllability even when the air-fuel ratio is changed during purge execution.

According to the air-fuel ratio control apparatus for an internal combustion engine of claim 1, even if the air-fuel ratio is changed by the air-fuel ratio changing means , the predetermined air-fuel ratio is controlled based on the air-fuel ratio feedback correction coefficient and the air-fuel ratio at the time of purge execution. The purge concentration is calculated, and the control parameter related to the purge control means, which is calculated using the purge concentration, is corrected according to the air-fuel ratio by the air-fuel ratio changing means . Thus, even if the air-fuel ratio is changed during the purge execution with the purge rate set to a predetermined ratio, stable air-fuel ratio controllability can be ensured by correcting the parameters in the purge control.

  In the air-fuel ratio control apparatus for the internal combustion engine according to the second aspect, the fuel correction amount by the purge is corrected by the parameter correction means as a parameter in the purge control. In this way, stable air-fuel ratio controllability is ensured by compensating for the deviation of the air-fuel ratio when the air-fuel ratio is changed during the purge execution with the purge rate being a predetermined ratio by the fuel correction by the purge. Can do.

  In the air-fuel ratio control apparatus for an internal combustion engine according to claim 3, the opening degree of the purge valve is corrected as a parameter in the purge control by the parameter correction means. In this way, stable air-fuel ratio controllability is ensured by compensating for the deviation of the air-fuel ratio when the air-fuel ratio is changed at the time of purge execution with the purge rate set to a predetermined ratio by correcting the opening of the purge valve. be able to.

According to the air-fuel ratio control apparatus for an internal combustion engine of claim 4, the purge concentration calculating means determines the degree of influence of the purge on the predetermined air-fuel ratio based on the air-fuel ratio feedback correction coefficient and the air-fuel ratio at the time of purge execution. The fuel correction means calculates a purge correction coefficient as a fuel correction quantity by purging based on the purge concentration and the air-fuel ratio, and corrects the fuel injection quantity supplied to the internal combustion engine by the purge correction coefficient . As described above, even if the air-fuel ratio is changed during the purge execution with the purge rate set to a predetermined ratio, it is possible to secure stable air-fuel ratio controllability by correcting the fuel injection amount in consideration of the influence degree in the purge control. it can.

  Hereinafter, embodiments of the present invention will be described based on examples.

  FIG. 1 is a schematic configuration diagram showing an internal combustion engine to which an air-fuel ratio control apparatus for an internal combustion engine according to an example of an embodiment of the present invention is applied and its peripheral devices.

  In FIG. 1, the internal combustion engine 1 is configured as a four-cylinder four-cycle spark ignition type, and its intake air passes from the upstream side through an air cleaner 2, an intake passage 3, a throttle valve 4, a surge tank 5, and an intake manifold 6. It is mixed with fuel injected from an injector (fuel injection valve) 7 in the intake manifold 6 and distributed and supplied to each cylinder as an air-fuel mixture having a predetermined air-fuel ratio. Further, the high voltage supplied from the ignition circuit 9 is distributed and supplied to the ignition plug 8 provided in each cylinder of the internal combustion engine 1 by the distributor 10, and the air-fuel mixture of each cylinder is ignited at a predetermined timing. The exhaust gas after combustion passes through the exhaust manifold 11 and the exhaust passage 12, and is provided in the exhaust passage 12, and in the three-way catalyst 13 carrying a catalyst component such as platinum and rhodium and an additive such as cerium and lanthanum. Harmful components such as CO (carbon monoxide), HC (hydrocarbon) and NOx (nitrogen oxide) are purified and discharged into the atmosphere.

An intake air temperature sensor 21 and an intake pressure sensor 22 are provided in the intake passage 3. The intake air temperature sensor 21 is an intake air temperature THA on the downstream side of the air cleaner 2, and the intake air pressure sensor 22 is an intake air pressure PM on the downstream side of the throttle valve 4. To detect. The throttle valve 4 is provided with a throttle opening sensor 23 for detecting the throttle opening TA. The throttle opening sensor 23 is substantially fully closed together with an analog signal corresponding to the throttle opening TA. An on / off signal from an idle switch (not shown) that detects this is output. Further, a water temperature sensor 24 is provided in the cylinder block of the internal combustion engine 1, and this water temperature sensor 24 detects the cooling water temperature THW in the internal combustion engine 1. The distributor 10 is provided with a rotation angle sensor 25 for detecting the engine speed NE of the internal combustion engine 1. The rotation angle sensor 25 is provided every two rotations of the crankshaft of the internal combustion engine 1, that is, every 720 ° CA (crank angle). The pulse signal is output 24 times. Further, an A / F sensor 26 that outputs a linear air-fuel ratio signal VOX1 corresponding to the air-fuel ratio λ of the exhaust gas discharged from the internal combustion engine 1 is provided upstream of the three-way catalyst 13 in the exhaust passage 12. An oxygen (O ₂ ) sensor 27 that outputs a voltage signal VOX ₂ corresponding to whether the air-fuel ratio λ of the exhaust gas is rich or lean with respect to the stoichiometric air-fuel ratio λ = 1 is provided on the downstream side of the three-way catalyst 13. Yes.

  An ECU (Electronic Control Unit) 30 that controls the operating state of the internal combustion engine 1 includes a CPU 31 as a known central processing unit, a ROM 32 that stores a control program and a control map, a RAM 33 that stores various data, and a B / B It is configured as a logical operation circuit centered on a U (backup) RAM 34 and the like, and is connected via a bus 37 to an input port 35 for inputting detection signals of each sensor and an output port 36 for outputting control signals to each actuator. Yes. Then, the ECU 30 inputs the intake air temperature THA, the intake air pressure PM, the throttle opening degree TA, the cooling water temperature THW, the engine speed NE, the air-fuel ratio signal VOX1, the voltage signal VOX2, etc. from each sensor via the input port 35. Based on these values, the fuel injection amount TAU, the ignition timing Ig, and the control duty PD are calculated, and control signals are output to the injector 7, the ignition circuit 9, and a purge solenoid valve 45 described later via the output port 36.

  A purge pipe 41 extending from the upper part of the fuel tank (not shown) is communicated with the surge tank 5 in the intake passage 3. In the middle of the purge pipe 41, activated carbon is stored as an adsorbent that adsorbs evaporated fuel generated in the fuel tank. The canister 40 is disposed. The canister 40 is provided with an air opening hole 42 for introducing outside air. The purge pipe 41 has discharge passages 43 and 44 on the surge tank 5 side of the canister 40, and a purge solenoid valve 45 as a variable flow solenoid valve is disposed in the middle of the discharge passages 43 and 44. In the purge solenoid valve 45, the valve body 46 is always urged in a direction to close the seat portion 47 by a spring (not shown), but the valve body 46 opens the seat portion 47 by exciting the coil 48. It has become. Accordingly, the discharge passages 43 and 44 are closed by demagnetization of the coil 48 of the purge solenoid valve 45, and the discharge passages 43 and 44 are opened by excitation of the coil 48. The opening of the purge solenoid valve 45 is adjusted by an ECU 30 described later by duty ratio control based on pulse width modulation.

  Therefore, if a control signal is supplied from the ECU 30 to the purge solenoid valve 45 so that the canister 40 communicates with the surge tank 5 (intake passage 3) of the internal combustion engine 1, new air is introduced from the atmosphere, and this canister The inside of the engine 40 is ventilated and sent from the surge tank 5 into the cylinder of the internal combustion engine 1, a canister purge is performed, and the adsorption function of the canister 40 can be recovered. The purge air amount Qp [l / min], which is new air introduced through the purge solenoid valve 45 at this time, changes the duty ratio [%] of the pulse signal supplied from the ECU 30 to the purge solenoid valve 45. Adjusted by. FIG. 2 is a characteristic diagram showing the purge air amount Qp [l / min] with respect to the duty ratio [%] at this time, and the duty ratio [% of the purge solenoid valve 45 when the negative pressure in the intake passage 3 is constant. ] And the purge air amount Qp [l / min]. As shown in FIG. 2, the purge solenoid valve 45 increases the amount of purge air almost linearly, that is, the amount of air sucked into the internal combustion engine 1 via the canister 40 as the duty ratio is increased from 0%. I know that

  The ECU 30 includes an intake air temperature THA signal from an intake air temperature sensor 21 that detects intake air temperature, an intake air pressure PM signal from an intake air pressure sensor 22 (may be an intake air amount signal from an intake air amount sensor), and a throttle opening sensor 23. The throttle opening degree TA signal, the engine speed NE signal from the rotation angle sensor 25, and the cooling water temperature THW signal from the water temperature sensor 24 are input.

  In addition, the ECU 30 receives the voltage signal VOX2 from the oxygen sensor 27 and performs rich / lean determination of the air-fuel mixture. The ECU 30 greatly changes (skips) a FAF value as an air-fuel ratio feedback correction coefficient, which will be described later, to increase or decrease the fuel injection amount when reversing from rich to lean and when reversing from lean to rich. When rich or lean continues, the FAF value is gradually increased or decreased. Note that this air-fuel ratio feedback control is not performed when the coolant temperature is low or when the engine is running at a high load and high speed. Further, the ECU 30 obtains the basic injection time from the engine speed and the intake pressure, corrects the basic injection time by the FAF value and the like to obtain the final injection time, and causes the injector 7 to perform fuel injection at a predetermined injection timing. .

  In the air-fuel ratio control apparatus for an internal combustion engine according to this embodiment, fuel injection amount setting, target air-fuel ratio setting, purge rate control, evaporation (evaporative fuel) concentration detection, purge rate gradual change control, fuel injection Volume control and purge solenoid valve control programs are executed.

  Hereinafter, the operation of the embodiment will be described for each control.

<Fuel injection amount setting: see FIGS. 3 and 4>
The fuel injection amount setting routine will be described with reference to FIG. 4 based on FIG. FIG. 4 is a map showing the target air-fuel ratio λTG with respect to the coolant temperature THW [° C.]. The fuel injection amount setting routine is executed by the CPU 31 in the ECU 30 every 360 ° CA in synchronization with the rotation of the internal combustion engine 1.

  In FIG. 3, first, in step S101, the intake pressure PM, the engine speed NE, and the like are read as various sensor signals. Next, the process proceeds to step S102, and the basic fuel injection amount TP is calculated based on the various sensor signals read in step S101. Next, the process proceeds to step S103, where it is determined whether the air-fuel ratio F / B (feedback) control condition is satisfied. Here, as is well known, the air-fuel ratio F / B control condition is that the fuel increase after starting is 0%, the fuel is not being cut, and the high-speed / high-load operation is not being performed, and the air-fuel ratio sensor is active. It is established when it is in a state. When the air-fuel ratio F / B control condition is satisfied in step S103, the process proceeds to step S104 to determine whether the three-way catalyst 13 is in an active state. When the determination condition of step S104 is satisfied, the routine proceeds to step S105, where it is determined whether the coolant temperature THW is 60 ° C. or higher. When the determination condition in step S105 is satisfied, the process proceeds to step S106, and the target air-fuel ratio λTG is set as will be described later.

  On the other hand, when the determination condition of step S104 is not satisfied and the three-way catalyst 13 is in an inactive state, or when the determination condition of step S105 is not satisfied and the cooling water temperature THW is less than 60 ° C., the process proceeds to step S107. Based on the map shown in FIG. 4, the target air-fuel ratio λTG with respect to the coolant temperature THW is set. After the target air-fuel ratio λTG is set in step S106 or step S107, the process proceeds to step S108, and the air-fuel ratio feedback correction coefficient FAF is set so that the air-fuel ratio λ becomes the target air-fuel ratio λTG. That is, in step S108, the air-fuel ratio feedback correction coefficient FAF is set according to the target air-fuel ratio λTG and the air-fuel ratio signal VOX1 detected by the A / F sensor 26. On the other hand, when the air-fuel ratio F / B control condition is not satisfied in step S103, the process proceeds to step S109, and the air-fuel ratio feedback correction coefficient FAF is set to 1.0. After the air-fuel ratio feedback correction coefficient FAF is set in step S108 or step S109, the process proceeds to step S110, where the fuel injection amount TAU is expressed by the following equation based on the basic fuel injection amount TP, the air-fuel ratio feedback correction coefficient FAF, and other correction coefficients FALL. Set in (1) and end this routine.

[Equation 1]
TAU = TP × FAF × FALL (1)
A control signal based on the fuel injection amount TAU thus set is output to the injector 7 to control the valve opening time, that is, the actual fuel injection amount. As a result, the air-fuel mixture is adjusted to the target air-fuel ratio λTG. The

<Target air-fuel ratio setting: See FIGS. 5 and 6>
The target air-fuel ratio setting routine will be described based on FIG. 5 and with reference to FIG. FIG. 6 is a time chart showing a transition state of the target air-fuel ratio λTG corresponding to the voltage signal VOX2 which is the output of the oxygen sensor 27. The target air-fuel ratio setting routine is executed by the CPU 31 in the ECU 30 every 360 ° CA in synchronization with the rotation of the internal combustion engine 1.

  In FIG. 5, it is determined in step S201 whether the voltage signal VOX2 from the oxygen sensor 27 is on the rich side (R). When the determination condition in step S201 is satisfied and the air-fuel ratio is on the rich side (R), the process proceeds to step S202, and the predetermined value λM is added to the previous target air-fuel ratio λTGi−1, that is, the current target air-fuel ratio λTGi. Is set to the lean side (L) from the previous time, and this routine is terminated (see FIG. 6). On the other hand, when the determination condition of step S201 is not satisfied and the air-fuel ratio is on the lean side (L), the process proceeds to step S203, and the predetermined value λM is subtracted from the previous target air-fuel ratio λTGi−1, that is, the current target The air-fuel ratio λTGi is set to the richer side (R) than the previous time, and this routine ends (see FIG. 6).

<Modification of target air-fuel ratio setting: see FIG. 7>
A modification of the target air-fuel ratio setting routine will be described with reference to FIG. A modified example of the target air-fuel ratio setting routine is executed by the CPU 31 in the ECU 30 every 360 ° CA in synchronization with the rotation of the internal combustion engine 1.

  In FIG. 7, it is determined in step S301 whether the engine is idling. When the determination condition in step S301 is not satisfied, the process proceeds to step S302, where it is determined whether steady operation is being performed. As this determination condition, for example, the engine speed change amount ΔNE is 200 rpm or less, and the intake pressure change amount ΔPM is 100 mmHg or less. When the determination condition of step S302 is satisfied and the operation is steady, the process proceeds to step S303, and the target air-fuel ratio λTG is set based on a map using the engine speed NE [rpm] and the intake pressure PM [mmHg] as parameters. This routine is terminated. On the other hand, when the idling operation is being performed in step S301 or when the steady operation is not being performed in step S302, the routine proceeds to step S304, the target air-fuel ratio λTG is set to 1.0, and this routine is terminated.

<Purge rate control: See FIGS. 8, 9, and 10>
The purge rate control routine will be described with reference to FIGS. 9 and 10 based on FIG. FIG. 9 is a map showing the fully open purge rate PGRMX [%]. The engine speed NE [rpm] and the intake pressure PM [mmHg] (in this embodiment, the load is the intake pressure. It may be determined by the opening degree). This map shows the ratio of the amount of air flowing through the discharge passages 43 and 44 when the duty ratio of the purge solenoid valve 45 is 100% with respect to the total amount of air flowing into the internal combustion engine 1 through the intake passage 3. , Stored in the ROM 32. FIG. 10 is a map showing the target TAU correction amount KTPRG [%]. The engine speed NE [rpm] and the intake pressure PM [mmHg] (in this embodiment, the load is the intake pressure, but the intake air Amount or throttle opening). This purge rate control routine is executed by the CPU 31 in the ECU 30 about every 4 ms.
In FIG. 8, first, is the air-fuel ratio F / B (feedback) in step S401, whether the coolant temperature THW is 40 ° C. or higher in step S402, or is F / C (fuel cut) in step S403? Are determined respectively. Note that the determination condition in step S401 is to exclude a state such as start-up control, and the determination condition in step S402 is to exclude a state in which fuel increase correction other than purge is corrected by water temperature correction. The determination condition is to prevent purging during F / C. When the determination conditions of step S401 and step S402 are satisfied and the determination condition of step S403 is not satisfied, the process proceeds to step S404 and the purge execution flag XPRG is set to 1.

  Next, the routine proceeds to step S405, where the fully open purge rate PGRMX is read from the map shown in FIG. 9 based on the intake pressure PM and the engine speed NE. Next, the process proceeds to step S406, where the target purge rate PGRO is calculated from the target TAU correction amount KTPRG and the evaporation concentration average value FGPGAV. Here, the target TAU correction amount KTPRG represents how much the fuel injection amount can be corrected to be reduced when the fuel gas is replenished by performing the purge. This target TAU correction amount KTPRG is set in advance based on the margin with respect to the minimum injection pulse of the injector 7, and the intake pressure PM indicating the operating state of the internal combustion engine 1 and the engine speed NE are used as parameters as shown in FIG. Are two-dimensional maps and stored in the ROM 32 in advance. This map is set so that the target TAU correction amount KTPRG tends to decrease when the driving state is such that the basic fuel injection amount TP is small.

  Further, the evaporation concentration average value FGPGAV corresponds to the amount of fuel gas adsorbed to the canister 40, is estimated by the processing described later, and is stored in the RAM 33 while being updated as needed. The target purge rate PGRO corresponds to how much fuel gas should be replenished by purging when the fuel injection amount is assumed to be reduced to the full target TAU correction amount KTPRG. Thus, the larger the evaporation concentration average value FGPGAV, the smaller the value, and the smaller the value, the larger the value.

  After the target purge rate PGRO is calculated in this way, the process proceeds to step S407, and the purge rate gradual change value PGRD is read. The purge rate gradual change value PGRD is a control value provided to avoid this because if the purge rate is suddenly changed greatly, the correction cannot catch up and the optimum air-fuel ratio cannot be maintained. How the purge rate gradual change value PGRD is set will be described in detail in the purge rate gradual change control described later.

  Next, the process proceeds to step S408, and the minimum purge purge rate PGRMX in step S405, the target purge rate PGRO in step S406, and the purge rate gradual change value PGRD in step S407 are the final purge rate PGR for executing the purge control. This routine is terminated. On the other hand, when the determination condition of step S401 or step S402 is not satisfied, or when the determination condition of step S403 is satisfied, the process proceeds to step S409, and the purge execution flag XPRG is set to zero. Next, the process proceeds to step S410, the final purge rate PGR is set to 0, and this routine is finished. Here, that the final purge rate PGR is 0 means that the purge control is not performed.

<Evaporation concentration detection: see FIG. 11>
The evaporation concentration detection routine will be described with reference to FIG. This evaporation concentration detection routine is executed by the CPU 31 in the ECU 30 about every 4 ms.

  In FIG. 11, first, in step S501, it is determined whether or not it is immediately after the ignition switch is turned on. This is to avoid the occurrence of an error if the previously detected value is used because evaporated fuel is further adsorbed to the canister 40 while the internal combustion engine is stopped. If the determination condition in step S501 is not satisfied and the ignition switch is not immediately after turning on, the process proceeds to step S502, and it is determined whether the purge execution flag XPRG is 1 and the purge control is started. If the determination condition in step S502 is not satisfied and the purge execution flag XPRG is 0 and the purge control is before the start, the evaporation concentration cannot be detected, and thus this routine is terminated. On the other hand, when the determination condition in step S502 is satisfied, the process proceeds to step S503, where it is determined whether acceleration or deceleration is being performed. Here, the determination during acceleration / deceleration may be performed by a generally well-known method by detecting an idle switch, slot valve opening change, intake pressure change, vehicle speed, and the like. When the determination condition in step S503 is satisfied and acceleration / deceleration is being performed, the operating state is in a transient state, and the correct evaporation concentration cannot be detected, so this routine ends.

  On the other hand, when the determination condition in step S503 is not satisfied, the process proceeds to step S504, and it is determined whether the initial concentration detection end flag XNFPGG is 1. Since the concentration detection is not completed at first, the determination condition of step S504 is not satisfied, and step S505 is skipped and the process proceeds to step S506, and the air-fuel ratio feedback correction coefficient FAF set in step S108 of FIG. It is determined whether the absolute value of the deviation between the smoothed value FAFAV that has been smoothed (averaged) every predetermined time and the reference value 1 exceeds ω [%] as a predetermined value. This is because the evaporation concentration cannot be detected correctly unless there is a clear deviation in the air-fuel ratio due to the purge control, and ω [%] means a range of variation.

  When the determination condition in step S506 is not satisfied, this routine is terminated. On the other hand, when the determination condition in step S506 is satisfied, the process proceeds to step S507, and the deviation (FAFAV-1) divided by the final purge rate PGR multiplied by the air-fuel ratio λ is added to the previous evaporation concentration FGPG. The current evaporation concentration FGPG is calculated. Therefore, the value of the evaporation concentration FGPG in this embodiment is 1 when the evaporation concentration in the discharge passages 43 and 44 is 0 (air is 100%), and the value of 1 is larger as the evaporation concentration in the discharge passages 43 and 44 is higher. It is set to a small value. Here, in step S507, the annealing value FAFAV and the reference value 1 are replaced, and the evaporation concentration is calculated so that the evaporation concentration FGPG is set to a value larger than 1 as the evaporation concentration increases. It may be.

  When calculating the evaporation concentration FGPG in step S507, the purge control is performed because the final purge rate PGR is multiplied by the air / fuel ratio λ even if the air / fuel ratio λ is changed during the purge execution at the predetermined purge rate PGR. It is possible to eliminate the degree of influence on the evaporation concentration FGPG due to the change of the air-fuel ratio λ at the time.

  Next, the process proceeds to step S508, where it is determined whether the initial concentration detection end flag XNFPGG is 1. Since the concentration detection is not completed at first, the determination condition of step S508 is not satisfied, and the process proceeds to step S509, where the change between the previous detection value and the current detection value of the evaporation concentration FGPG is equal to or less than a predetermined value (θ%). Whether or not the evaporation concentration is stable is determined based on whether or not the current has continued three times or more. When the determination condition in step S509 is satisfied and the evaporation concentration is stable, the process proceeds to step S510, and the initial concentration detection end flag XNFPGG is set to 1. After the processing of step S510, or when the determination condition of step S508 is satisfied and the initial concentration detection end flag XNFPGG is 1, steps S509 and S510 are skipped, or the determination condition of step S509 is not satisfied and the evaporation concentration is stable. If not, step S510 is skipped and the process proceeds to step S511. In step S511, in order to calculate the evaporation concentration average value FGPGAV obtained by averaging the current evaporation concentration FGPG, a predetermined smoothing calculation (for example, 1/64 smoothing calculation) is executed, and this routine is terminated.

  Then, after the initial concentration detection is completed, the determination condition in step S504 is always satisfied, and thus the process proceeds to step S505, where it is determined whether the purge rate PGR exceeds β [%] as a predetermined value. When the determination condition in step S505 is not satisfied and the purge rate PGR is equal to or less than β [%], this routine is terminated. On the other hand, when the determination condition of step S505 is satisfied, the processing after step S506 is executed. This is because when the purge rate PGR is small, that is, when the purge solenoid valve 45 is on the low flow rate side, the opening degree cannot be accurately controlled and the evaporation concentration cannot be detected accurately. In other cases, the evaporation concentration detection is executed only under conditions that allow accurate detection, and a value having as little error as possible is given.

  On the other hand, if it is immediately after the ignition switch is turned on in step S501, the evaporation concentration FGPG is set to 1.0 in step S512, the evaporation concentration average value FGPGAV is set to 1.0 in step S513, and the initial concentration detection flag XNFFGPG is set in step S514. The initial setting is 0, and this routine ends. Here, the evaporation concentration FGPG and the evaporation concentration average value FGPGAV being 1.0 means that the evaporation concentration is 0 (no fuel gas is adsorbed at all). Initially, the adsorption is assumed to be zero. When the initial concentration detection flag XNFPGG is 0, it means that the evaporation concentration has not been detected yet.

<Purge rate gradual change control: see FIG. 12>
A purge rate gradual change control routine will be described with reference to FIG. This purge rate gradual change control routine is executed by the CPU 31 in the ECU 30 about every 4 ms.

  In FIG. 12, first, it is determined in step S601 whether the purge execution flag XPRG is “1”. When the determination condition of step S601 is satisfied, the routine proceeds to step S602, where it is determined whether the deviation | 1-FAFAV | as the air-fuel ratio feedback correction coefficient FAF deviation amount exceeds 5%. When the determination condition of step S602 is not satisfied, the routine proceeds to step S603, where the value obtained by adding 0.1% to the previous final purge rate PGRi-1 is set as the purge rate gradual change value PGRD, and this routine ends. On the other hand, when the determination condition in step S602 is satisfied, the process proceeds to step S604, and it is determined whether the deviation | 1-FAFAV | is 10% or less. When the determination condition in step S604 is satisfied, the process proceeds to step S605, and a value obtained by setting the previous last purge rate PGRi-1 to the last purge rate PGRi-1 is set as the purge rate gradual change value PGRD, and this routine is finished.

  On the other hand, when the determination condition of step S604 is not satisfied, the routine proceeds to step S606, where the value obtained by subtracting 0.1% from the previous final purge rate PGRi-1 is set as the purge rate gradual change value PGRD, and this routine is terminated. . When the determination condition in step S601 is not satisfied and the purge execution flag XPRG is 0, the process proceeds to step S607, the purge rate gradual change value PGRD is set to 0, and this routine is finished.

  In this manner, when the air-fuel ratio feedback correction coefficient FAF is in a state where it deviates by 5% or less with respect to the theoretical air-fuel ratio (FAF = 1), the fuel injection amount TAU correction is sufficient even if the purge rate is further changed. As it catches up, the purge rate is changed more. Further, when the air-fuel ratio feedback correction coefficient FAF remains at a deviation of 5 to 10% with respect to the theoretical air-fuel ratio (FAF = 1), the change of the purge rate and the fuel injection amount TAU correction are relatively balanced. As a result, the purge rate is maintained as it is. The reason why the air-fuel ratio feedback correction coefficient FAF deviates so much as to exceed 10% with respect to the theoretical air-fuel ratio (FAF = 1) is that the fuel injection amount TAU correction cannot catch up as a result of changing the purge rate too much. If this is the case, the displacement may increase further, so the purge rate is restored to the original level.

<Fuel injection amount control: see FIG. 13>
A fuel injection amount control routine will be described with reference to FIG. This fuel injection amount control routine is executed by the CPU 31 in the ECU 30 about every 4 ms.

  In FIG. 13, first, the basic fuel injection amount TP is calculated from the engine speed NE and the load (for example, intake pressure PM) based on the map stored in the ROM 32 in step S701. Next, the process proceeds to step S702, where various basic corrections (cooling water temperature correction, post-startup correction, intake air temperature correction, etc.) are executed. Next, the process proceeds to step S703, where the evaporation concentration average value FGPGAV is multiplied by the final purge rate PGR and the air-fuel ratio λ to calculate the purge correction coefficient FPG.

  This purge correction coefficient FPG means the amount of fuel that is replenished by purging under the conditions determined by the purge rate control process, and also represents the amount of fuel that can be corrected to decrease from the basic fuel injection amount TP. . In this way, when calculating the purge correction coefficient FPG, even if the air-fuel ratio λ is changed during the purge execution at the predetermined purge rate PGR, the evaporation concentration average value FGPGAV is multiplied by the final purge rate PGR. Furthermore, the air-fuel ratio λ is multiplied, and the fuel correction amount due to the change of the air-fuel ratio λ during purge control is taken into consideration.

  Next, the process proceeds to step S704, where the correction coefficient is calculated from the air / fuel ratio feedback correction coefficient FAF, the purge correction coefficient FPG, and the air / fuel ratio learning value KGj by the expression {1+ (FAF-1) + (KGj-1) + FPG}. This is multiplied by the basic fuel injection amount TP and reflected in the fuel injection amount TAU, and this routine is terminated. The air-fuel ratio learning value KGj is set for each operating region of the internal combustion engine.

<Purge solenoid valve control: See FIG. 14>
The purge solenoid valve control routine will be described with reference to FIG. The purge solenoid valve control routine is executed by the CPU 31 in the ECU 30 with a time interruption every 100 ms.

In FIG. 14, first, in step S801, it is determined whether the purge execution flag XPRG is 1 or not. When the determination condition of step S801 is satisfied, the routine proceeds to step S802, where the control duty (duty ratio) PD of the purge solenoid valve 45 is calculated by the following equation (2), and this routine ends.
[Equation 2]
PD = (PGR / PGRMX) × (100−PV) × PPA + PV (2)
In this formula (2), the drive period of the purge solenoid valve 45 is 100 ms. Also, PGR is the final purge rate calculated in FIG. 8, PGRMX is the fully open purge rate in each operating state of the purge solenoid valve 45 (see FIG. 9), PV is a voltage correction value for battery voltage fluctuations, and PPA is atmospheric pressure. It is an atmospheric pressure correction value with respect to fluctuations.

  On the other hand, when the determination condition of step S801 is not satisfied and the purge is not performed, the process proceeds to step S803, the control duty PD of the purge solenoid valve 45 is set to 0, and this routine is ended.

  As described above, the air-fuel ratio control device for the internal combustion engine of the present embodiment determines the opening degree of the purge solenoid valve 45 when the fuel vapor adsorbed by the canister 40 is released to the surge tank 5 side on the intake side of the internal combustion engine 1. Purge control means achieved by the ECU 30 for controlling and correcting the fuel injection amount, air-fuel ratio changing means achieved by the ECU 30 capable of changing the air-fuel ratio λ according to the operating state of the internal combustion engine 1, Parameter correction means achieved by the ECU 30 for correcting the control parameter related to the purge control means in accordance with the air-fuel ratio λ by the air-fuel ratio changing means.

  Therefore, even if the air-fuel ratio λ is changed by the ECU 30 that achieves the air-fuel ratio changing means, the purge rate as the opening of the purge solenoid valve 45 is controlled by the ECU 30 that achieves the purge control means to be a predetermined ratio. Accordingly, the fuel injection amount TAU from the injector 7 is corrected. As a result, even if the air-fuel ratio λ is changed during the purge execution with the purge rate being a predetermined ratio, stable air-fuel ratio controllability can be ensured by correcting the parameters in the purge control.

  In the air-fuel ratio control apparatus for an internal combustion engine according to this embodiment, the parameter correction means achieved by the ECU 30 uses the control parameter as the fuel correction amount by purging. That is, the purge correction coefficient FPG for setting the fuel correction amount by purging as a control parameter according to the air-fuel ratio λ changed by the ECU 30 that achieves the air-fuel ratio changing means in step S703 of the fuel injection amount control routine of FIG. Calculated. As a result, even if the air-fuel ratio λ is changed during the purge execution with the purge rate set to a predetermined ratio, the deviation of the air-fuel ratio feedback correction coefficient FAF is compensated by the fuel correction to ensure stable air-fuel ratio controllability. Can do.

  The air-fuel ratio control apparatus for the internal combustion engine according to the present embodiment is a purge solenoid valve for releasing the fuel vapor adsorbed by the canister 40 corresponding to different air-fuel ratios λ to the surge tank 5 on the intake side of the internal combustion engine 1. The purge control means achieved by the ECU 30 for controlling the opening degree of 45, and the ECU 30 for calculating the degree of influence of the purge by the purge control means for the predetermined air-fuel ratio λ as the purge concentration, that is, the evaporation concentration FGPG. Purge concentration calculating means, and a purge correction coefficient FPG as a fuel correction amount by purging is obtained based on the evaporation concentration FGPG calculated by the purge concentration calculating means, and the fuel injection amount TAU supplied to the internal combustion engine 1 is finally determined And a fuel amount correcting means achieved by the ECU 30 that corrects automatically.

  That is, the degree of influence of the purge on the predetermined air-fuel ratio λ is determined by the ECU 30 that achieves the purge concentration calculating means, and the fuel injection amount TAU supplied to the internal combustion engine 1 is finally determined by the ECU 30 that achieves the fuel amount correcting means. It is corrected to. As a result, even if the air-fuel ratio λ is changed during the purge execution with the purge rate set to a predetermined ratio, the influence degree in the purge control is taken into consideration and the fuel injection amount TAU is corrected to ensure stable air-fuel ratio controllability. Can do.

<Modification of purge solenoid valve control: see FIG. 15>
A modification of the purge solenoid valve control routine will be described with reference to FIG.

  Note that a modification of this purge solenoid valve control routine is executed by the CPU 31 in the ECU 30 with a time interruption every 100 ms.

  In this modification, a change in the air-fuel ratio λ is taken into account when calculating the control duty PD of the purge solenoid valve 45. Corresponding to this modification of the purge solenoid valve control routine, the correction by the air-fuel ratio λ in the evaporation concentration FGPG calculation in step S507 of the evaporation concentration detection routine shown in FIG. 11 and the step S703 of the fuel injection amount control routine shown in FIG. Since it is not necessary to consider both corrections with the air-fuel ratio λ in calculating the purge correction coefficient FPG, the multiplication λ is only an arithmetic expression that is deleted, and the processing in the other steps is the same. The detailed explanation is omitted.

  In FIG. 15, first, it is determined in step S901 whether the purge execution flag XPRG is 1. When the determination condition of step S901 is satisfied, the routine proceeds to step S902, where the control duty PD of the purge solenoid valve 45 is calculated by the following equation (3), and this routine is terminated.

[Equation 3]
PD = {PGR / (PGRMX × λ)} × (100−PV) × PPA + PV (3)
In this formula (3), the drive period of the purge solenoid valve 45 is 100 ms. Also, PGR is the final purge rate calculated in FIG. 8, PGRMX is the fully open purge rate in each operating state of the purge solenoid valve 45 (see FIG. 9), PV is a voltage correction value for battery voltage fluctuations, and PPA is atmospheric pressure. It is an atmospheric pressure correction value with respect to fluctuations.

  As described above, when calculating the control duty PD of the purge solenoid valve 45, the full purge ratio PGRMX is multiplied by the air-fuel ratio λ even when the air-fuel ratio λ is changed during the purge execution at the predetermined purge ratio PGR. The fuel correction by changing the air-fuel ratio λ during the purge control is compensated by the opening correction of the purge solenoid valve 45.

  On the other hand, when the determination condition of step S901 is not satisfied and the purge is not performed, the process proceeds to step S903, the control duty PD of the purge solenoid valve 45 is set to 0, and this routine is ended.

  As described above, in the air-fuel ratio control apparatus for the internal combustion engine according to the present embodiment, the parameter correction means achieved by the ECU 30 sets the control parameter as the control duty PD as the opening degree of the purge solenoid valve 45. That is, the control duty PD of the purge solenoid valve 45 as a control parameter is calculated according to the air-fuel ratio λ changed by the ECU 30 that achieves the air-fuel ratio changing means in step S902 of the purge solenoid valve control routine of FIG. As a result, even if the air-fuel ratio λ is changed at the time of purge execution with the purge rate set to a predetermined ratio, the deviation of the air-fuel ratio feedback correction coefficient FAF is purge-corrected and compensated by the control duty PD of the purge solenoid valve 45, thereby being stable. The air / fuel ratio controllability can be ensured.

FIG. 1 is an overall configuration diagram showing an air-fuel ratio control apparatus for an internal combustion engine according to an example of an embodiment of the present invention. FIG. 2 is a characteristic diagram showing the purge air amount with respect to the duty ratio used in the air-fuel ratio control apparatus for an internal combustion engine according to an example of the embodiment of the present invention. FIG. 3 is a flowchart showing a procedure for setting the fuel injection amount in the CPU in the ECU used in the air-fuel ratio control apparatus for an internal combustion engine according to an example of the embodiment of the present invention. FIG. 4 is a map for setting the target air-fuel ratio in FIG. 3 from the cooling water temperature. FIG. 5 is a flowchart showing a processing procedure for setting the target air-fuel ratio in the CPU in the ECU used in the air-fuel ratio control apparatus for an internal combustion engine according to an example of the embodiment of the present invention. FIG. 6 is a time chart showing the transition state of the target air-fuel ratio corresponding to the output of the oxygen sensor. FIG. 7 is a flowchart showing a processing procedure of a modified example of the target air-fuel ratio setting in the CPU in the ECU used in the air-fuel ratio control apparatus for an internal combustion engine according to an example of the embodiment of the present invention. FIG. 8 is a flowchart showing a processing procedure for purge rate control in the CPU in the ECU used in the air-fuel ratio control apparatus for an internal combustion engine according to an example of the embodiment of the present invention. FIG. 9 is a map for setting the fully open purge rate in FIG. FIG. 10 is a map for setting the target TAU correction amount in FIG. FIG. 11 is a flowchart showing a processing procedure of the evaporation concentration detection in the CPU in the ECU used in the air-fuel ratio control apparatus for an internal combustion engine according to an example of the embodiment of the present invention. FIG. 12 is a flowchart showing a processing procedure of purge rate gradual change control in the CPU in the ECU used in the air-fuel ratio control apparatus for an internal combustion engine according to an example of the embodiment of the present invention. FIG. 13 is a flowchart showing a fuel injection amount control processing procedure in the CPU in the ECU used in the air-fuel ratio control apparatus for an internal combustion engine according to an example of the embodiment of the present invention. FIG. 14 is a flowchart showing a processing procedure of purge solenoid valve control in the CPU in the ECU used in the air-fuel ratio control apparatus for an internal combustion engine according to an example of the embodiment of the present invention. FIG. 15 is a flowchart showing a processing procedure of a modified example of purge solenoid valve control in the CPU in the ECU used in the air-fuel ratio control apparatus for an internal combustion engine according to an example of the embodiment of the present invention.

Explanation of symbols

1 Internal combustion engine 5 Surge tank 7 Injector 30 ECU (electronic control unit)
31 CPU
40 canister 45 purge solenoid valve

Claims (4)

Purge control means for controlling the opening of the purge valve when discharging the fuel vapor adsorbed by the canister to the intake side of the internal combustion engine and correcting the fuel injection amount;
Air-fuel ratio changing means capable of changing the air-fuel ratio according to the operating state of the internal combustion engine;
A purge concentration calculation means for calculating a purge concentration for a predetermined air-fuel ratio based on the air-fuel ratio feedback correction coefficient and the air-fuel ratio at the time of purging;
Parameter correction means for correcting a control parameter related to the purge control means , which is calculated by using the purge concentration in accordance with the air-fuel ratio by the air-fuel ratio changing means, apparatus.   2. The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the parameter correction means uses the control parameter as a fuel correction amount by purging.   The air-fuel ratio control apparatus for an internal combustion engine according to claim 1, wherein the parameter correction means sets the control parameter to an opening of the purge valve. Purge control means for controlling the opening of the purge valve when releasing the fuel vapor adsorbed by the canister corresponding to different air-fuel ratios to the intake side of the internal combustion engine;
The degree of influence of the purging with prior Symbol purge control means, based on the air-fuel ratio feedback correction coefficient during purge execution and the air-fuel ratio, the purge concentration calculating means for calculating a purge concentration for a given air-fuel ratio,
A fuel which calculates a purge correction coefficient as a fuel correction amount by purging based on the purge concentration and air-fuel ratio calculated by the purge concentration calculating means, and corrects the fuel injection amount supplied to the internal combustion engine by the purge correction coefficient An air-fuel ratio control apparatus for an internal combustion engine, comprising: an amount correction means.

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