JP3731491B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine for causing an evaporative fuel generated in a fuel tank to be sucked into an intake side of the internal combustion engine (engine) and burnt.
[0002]
[Prior art]
Conventionally, evaporative fuel generated in a fuel tank is stored in a canister, and evaporative fuel stored in the canister is discharged to the intake side of an internal combustion engine together with air for combustion. In some cases, the concentration of the evaporated fuel sucked into the intake side of the internal combustion engine from the canister is detected based on the change amount of the air-fuel ratio feedback value at that time (for example, Japanese Patent Laid-Open No. 2-130240).
[0003]
[Problems to be solved by the invention]
However, in the above-described conventional system, the evaporated fuel concentration is detected by changing the canister purge amount by a certain value. Therefore, when the concentration detection is performed when the amount of evaporated fuel adsorbed to the canister is large, the internal combustion engine There is a problem that the air-fuel ratio of the mixture of fuel and air supplied to the engine greatly fluctuates, resulting in deterioration of idle stability and exhaust emission of the internal combustion engine.
[0004]
Therefore, the present invention has an object to suppress fluctuations in the air-fuel ratio during detection of the evaporated fuel concentration and prevent deterioration of idle stability and exhaust emission even when the amount of evaporated fuel adsorbed to the canister is large. Is.
[0005]
[Means for solving problems]
Therefore, the invention according to claim 1 of the present application stores the evaporated fuel generated in the fuel tank in the canister, and discharges the evaporated fuel stored in the canister together with air to the intake side of the internal combustion engine through the discharge passage. An air-fuel ratio control device for an internal combustion engine, comprising: an air-fuel ratio detection means for detecting an air-fuel ratio of the internal combustion engine; fuel and air supplied to the internal combustion engine in accordance with the air-fuel ratio detected by the air-fuel ratio detection means; An air-fuel ratio feedback means for feedback-controlling the air-fuel ratio of the air-fuel mixture; a flow rate control valve for changing a purge rate of air containing evaporated fuel discharged from the canister to the intake side of the internal combustion engine through the discharge passage; A concentration detection purge rate control means for changing the purge rate by the flow rate control valve when detecting the concentration of the evaporated fuel, and a purge rate control means for changing the purge rate. A concentration detecting means for detecting the concentration of the evaporated fuel based on the air-fuel ratio and the purge rate before and after the change of the change rate, and the concentration detecting means again after the concentration detecting means detects the concentration of the evaporated fuel. A fuel concentration correction means at the time of concentration detection that reflects the amount of fuel fuel vapor already detected in the fuel supply amount of the internal combustion engine according to the purge rate at the time of concentration detection. An air-fuel ratio control apparatus for an internal combustion engine is provided.
[0006]
As a result, when the concentration detection means detects the concentration of the evaporated fuel again after the concentration detection means detects the concentration of the evaporated fuel, the purged fuel at the time of this concentration detection is detected. Since the fuel concentration correction means at the time of concentration detection is reflected in the fuel supply amount of the internal combustion engine according to the rate, fluctuations in the air-fuel ratio can be suppressed even when the concentration of the evaporated fuel is detected again.
[0007]
Further, the invention according to claim 2 stores the evaporated fuel generated in the fuel tank in the canister, and discharges the evaporated fuel stored in the canister together with air to the intake side of the internal combustion engine through the discharge passage. An air-fuel ratio control apparatus for an engine, comprising: an air-fuel ratio detection means for detecting an air-fuel ratio of the internal combustion engine; and an air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine in accordance with the air-fuel ratio detected by the air-fuel ratio detection means An air-fuel ratio feedback means for performing feedback control, a flow rate control valve for changing a purge rate of air including evaporated fuel discharged from the canister to the intake side of the internal combustion engine through the discharge passage, and a concentration of the evaporated fuel Detected value When updating the concentration, the purge rate control means for concentration update that changes the purge rate by the flow rate control valve according to the fuel vapor concentration already detected, and before and after the purge rate is changed by the purge rate control means An air-fuel ratio control device for an internal combustion engine is provided that includes a concentration update means for updating the concentration of the evaporated fuel by the air-fuel ratio and the purge rate.
[0008]
As a result, the purge rate at the time of concentration update is changed by the concentration detection purge rate control means according to the concentration detected last time. Detected value It is possible to suppress fluctuations in the air-fuel ratio even when updating the engine.
[0009]
According to a third aspect of the present invention, the evaporated fuel generated in the fuel tank is stored in the canister, and the evaporated fuel stored in the canister is discharged together with air to the intake side of the internal combustion engine through the discharge passage. An air-fuel ratio control apparatus for an engine, comprising: an air-fuel ratio detection means for detecting an air-fuel ratio of the internal combustion engine; and fuel and air supplied to the internal combustion engine in accordance with the air-fuel ratio detected by the air-fuel ratio detection means An air-fuel ratio feedback means for feedback-controlling the air-fuel ratio of the air-fuel mixture, a flow rate control valve for changing the purge rate of air containing evaporated fuel discharged from the canister to the intake side of the internal combustion engine through the discharge passage, Concentration detection purge rate control means for changing the purge rate by the flow rate control valve when detecting the concentration of the evaporated fuel, and the purge rate control means for setting the purge rate. The concentration detecting means for detecting the concentration of the evaporated fuel based on the air-fuel ratio feedback value of the air-fuel ratio feedback means and the purge rate before and after the control, and when the concentration of the evaporated fuel is detected by the concentration detecting means An air-fuel ratio control apparatus for an internal combustion engine is provided, which comprises a concentration detection lower limit guard changing means for expanding the lower limit guard of the air-fuel ratio feedback value by the air-fuel ratio feedback means.
[0010]
As a result, the lower limit guard of the air-fuel ratio feedback value is expanded at the time of concentration detection, so that the fuel injection amount can be corrected to be larger than that at the time of normal air-fuel ratio feedback, so that fluctuation of the air-fuel ratio at the time of concentration detection can be suppressed.
[0011]
Embodiment
DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment as an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, a multi-cylinder engine 1 is mounted on a vehicle, and an intake pipe 2 and an exhaust pipe 3 are connected to the engine 1. An electromagnetic injector 4 is provided at the inner end of the intake pipe 2, and a throttle valve 5 is provided upstream thereof. Further, the exhaust pipe 3 is provided with an oxygen sensor 6 as air-fuel ratio detection means, and the sensor 6 outputs a voltage signal corresponding to the oxygen concentration in the exhaust gas.
[0012]
The fuel supply system that supplies fuel to the injector 4 includes a fuel tank 7, a fuel pump 8, a fuel filter 9, and a pressure regulating valve 10. The fuel (gasoline) in the fuel tank 7 is pumped by the fuel pump 8 to each injector 4 via the fuel filter 9 and the fuel supplied to each injector 4 is adjusted to a predetermined pressure by the pressure regulating valve 10. Is done.
[0013]
A purge pipe 11 extending from the upper part of the fuel tank 7 communicates with a surge tank 12 of the intake pipe 2, and a canister containing activated carbon as an adsorbent for adsorbing evaporated fuel generated in the fuel tank in the middle of the purge pipe 11. 13 is disposed. The canister 13 is provided with an air opening hole 14 for introducing outside air. The purge pipe 11 has a discharge passage 15 on the surge tank 12 side of the canister 13, and a variable flow solenoid valve 16 (hereinafter referred to as a purge solenoid valve) is provided in the middle of the discharge passage 15. The purge solenoid valve 16 is always urged by a spring (not shown) in the direction in which the valve body 17 closes the seat portion 18, but the valve body 17 opens the seat portion 18 by exciting the coil 19. It has become. Accordingly, the discharge passage 15 is closed by demagnetizing the coil 19 of the purge solenoid valve 16, and the discharge passage 15 is opened by exciting the coil 19. The opening degree of the purge solenoid valve 16 is adjusted by a CPU 21 described later by duty ratio control based on pulse width modulation.
[0014]
Therefore, if a control signal is supplied from the CPU 21 to the purge solenoid valve 16 so that the canister 13 communicates with the intake pipe 2 of the engine 1, new air Qa is introduced from the atmosphere, which ventilates the inside of the canister 13. Then, it is fed into the cylinder from the intake pipe 2 of the engine 1 and canister purge is performed, so that the adsorption function of the canister 13 can be recovered. The introduction amount Qp (l / min) of the fresh air Qa at this time is adjusted by changing the duty of the pulse signal supplied from the CPU 21 to the purge solenoid valve 13. FIG. 2 is a characteristic diagram of the purge amount at this time, and shows the relationship between the duty of the purge solenoid valve 13 and the purge amount when the negative pressure in the intake pipe is constant. It can be seen that the purge amount, that is, the amount of air sucked into the engine 1 through the canister 13 increases almost directly as it increases from%.
[0015]
The CPU 21 passes the throttle opening signal from the throttle sensor 5 a that detects the opening degree of the throttle valve 5, the engine speed signal from the rotation speed sensor (not shown) that detects the rotation speed of the engine 1, and the throttle valve 5. An intake pressure signal from the intake pressure sensor 5B that detects the pressure of the intake air, a coolant temperature signal from the water temperature sensor 5C that detects the temperature of the engine coolant, and an intake temperature sensor (not shown) that detects the intake air temperature The intake air temperature signal from is input.
[0016]
Further, the CPU 21 inputs a signal (voltage signal) from the oxygen sensor 6 and performs rich / lean determination of the air-fuel mixture. Then, the CPU 21 changes (skips) the feedback correction coefficient in a stepwise manner to increase or decrease the fuel injection amount when it is reversed from rich to lean and when it is reversed from lean to rich, and when it is rich or lean, the feedback correction coefficient Is gradually increased or decreased. Note that this feedback control is not performed when the engine coolant temperature is low or during high load / high speed running. The CPU 21 obtains the basic injection time from the engine speed and the intake pressure, corrects the basic injection time by a feedback correction coefficient or the like to obtain the final injection time, and performs fuel injection at a predetermined injection timing by the injector 4. Let it be done.
[0017]
The ROM 34 stores a program and a map for controlling the operation of the entire engine. The RAM 35 temporarily stores various data such as detection data such as the opening degree of the throttle valve 5 and the engine speed. The CPU 21 controls the operation of the engine based on the program in the ROM 34.
[0018]
FIG. 3 shows a full-open purge rate map, which is determined by the engine speed Ne and the load (this time, the intake pipe pressure, in addition to the intake air amount and the throttle opening). This map shows the ratio of the amount of air flowing through the discharge passage 15 when the duty of the purge solenoid valve 16 is 100% with respect to the total amount of air flowing into the engine 1 through the intake pipe 2, and is stored in the ROM 34.
[0019]
This system is operated by operating air-fuel ratio feedback (FAF) control, purge rate control, initial evaporated fuel (evaporation) concentration detection, continuous evaporation concentration detection, fuel injection amount control, air-fuel ratio learning control, and purge solenoid valve control. . First, in order to detect an unknown evaporation concentration level, first-time evaporation concentration (FAF change amount per unit purge rate) is detected. Secondly, the fuel injection amount is manipulated based on the detected evaporation concentration and the current purge rate. Third, when the operation state is stable every predetermined time, the updated evaporation concentration is detected, the evaporation concentration is updated, and the fuel injection amount is manipulated in the same manner as described above. Then, air-fuel ratio learning control is performed based on the behavior of the FAF value as a result of operating the fuel injection amount.
[0020]
Hereinafter, the operation of the embodiment will be described for each control.
[0021]
Air-fuel ratio feedback control
The air-fuel ratio feedback control will be described with reference to FIG. This air-fuel ratio feedback control is executed by the base routine of the CPU 21 about every 4 ms.
[0022]
First, it is determined in step S40 whether feedback (F / B) control is possible. This F / B condition is mainly when all of the following conditions are satisfied. (1) Not at start-up. (2) The fuel is not being cut. (3) Cooling water temperature (THW) ≧ 40 ° C. (3) TAU> TAUmin. (4) The oxygen sensor is active.
[0023]
If the condition is satisfied, the process proceeds to step S41, where it is determined whether the concentration has been detected. If not, the process proceeds to step S42, where the oxygen sensor output is compared with a predetermined determination level, and each has a delay time (H · ImseC). Then, the air-fuel ratio flag XOXR is operated. For example, rich when XOXR = 1, lean when XOXR = 0. In step S43, the FAF value is manipulated based on the XOXR. That is, when XOXR changes (0 → 1), (1 → 0), the FAF value is skipped by a predetermined amount, and while XOXR continues to be 1 or 0, integration control of the FAF value is performed. Then, the process proceeds to the next step S44, and after checking the upper and lower limits of the FAF value, the process proceeds to step S45 and the smoothing process is performed at every skip or every predetermined time based on the determined FAF value. An annealing value FAFAV is obtained. When the F / B control is not established in step S40 and immediately after the end of concentration detection in step S41 (when a concentration detection flag to be described later has changed from 1 to 0), the process proceeds to step S46 and FAF is set. The value is 1.0.
[0024]
Purge rate control
The main routine for purge rate control is shown in FIG. This routine is also executed by the base routine of the CPU 21 about every 4 ms.
[0025]
In step S501, it is determined whether or not the air-fuel ratio is F / B under the same conditions as in step S40 in FIG. 4. In step S502, it is determined whether or not the cooling water temperature is 50 ° C. or higher. When the water temperature is equal to or higher than the predetermined value 50 ° C., the purge stop flag XIPGR is set to 0 in step S503 in order to execute the purge rate control. In the next step S504, it is determined whether or not the fuel is being cut. When the fuel is being cut, the routine proceeds to step S505, where the fuel cut purge rate (PGR) is controlled. If it is determined in step 504 that the fuel is not being cut, the process proceeds to step S506, and it is determined from the initial concentration detection flag XFFPGPG whether the evaporation concentration from the canister has been detected. When no detection has been made (first time), the process proceeds to step S507 to perform the initial concentration detection PGR control. After detecting the initial concentration, the process proceeds to step S508 to activate the counter CPGKAN. Based on the coefficient value of the counter, it is determined whether a predetermined time (for example, 60 seC) has elapsed in the next step S509, and the process proceeds to step S510 every predetermined time. Detection is performed and the evaporation concentration (FGPG) is updated. In other cases, the process proceeds to step S511 to perform normal purge rate control. When the purge rate condition is not satisfied in steps S501 and S502, the process proceeds to step S512 to set the purge rate to 0, and then proceeds to step S513 to set the purge stop flag XIPGR to 1.
[0026]
FIG. 6 shows a normal purge rate control subroutine in step S511 of FIG. First, in step S601, the FAF value (or FAF annealing value) is 1.0.
Which of the three areas ((1), (2), (3)) with respect to the reference is detected. Here, as shown in FIG. 7A, the region (1) is within 1.0 ± F%, and the region (2) is within 1.0 ± F% and within ± G% (provided that F <G). The area {circle over (3)} indicates a time of 1.0 ± G% or more.
[0027]
If it is region (1), the process proceeds to step S602, and the purge rate (PGR) is increased by a predetermined value D%. In the area (2), the process proceeds to step S603, and there is no increase / decrease in PGR. In the area {circle over (3)}, the process proceeds to step S604 and PGR is decreased by a predetermined value E%. Here, the predetermined values D and E are preferably changed according to the evaporation concentration (FGPG) as shown in FIG. In the next step S605, the upper and lower limits of PGR are checked. Here, the upper limit value is the value of various conditions such as the purge start time shown in FIG. 7C, the water temperature shown in FIG. 7D, and the operating conditions (full open purge rate map) shown in FIG. The smallest value is set.
[0028]
FIG. 8 shows the PGR control subroutine at the time of fuel cut in step S505 of FIG. First, in step S801, PGR is set to 0 so that the evaporation from the canister 13 does not enter the engine 1. Next, the process proceeds to step S802, and if the concentration is being detected, each flag during the concentration detection is reset in order to cancel the detection (for example: XPGIDL, XPGRUN, XPGNO1, XPGNO2 = 0).
[0029]
FIG. 9 shows an initial concentration detection PGR control subroutine in step S507 in FIG. This control is divided into idle and running. During idling, if it is determined in step S901 that the idle flag XIDL is 1, in step S902, the vehicle speed SPD is 0 km / h, and in step S903 that the FAF value has been skipped three or more times, the process proceeds to step S904, and the concentration during idling is being detected. The flag XPGIDL is set to 1. Further, XPGIDL proceeds to step S905 when XIDL is 0 or SPD is greater than 0 km / h, and resets XPGIDL to 0 so as to stop density detection. When traveling, the process proceeds from step S901 to step S906, where XPGIDL is not 1. Therefore, the process proceeds to step S907. If the running density detection flag XPGRUN is 1, the process proceeds to step S908, where the learning area is the same. If the FAF value is skipped three times or more and acceleration / deceleration is not being performed (for example, change in intake pipe pressure of the engine 1 DLPM <19.5 mmHg), the process further proceeds to step S909 to set the running concentration detection flag XPGRUN to 1. To do. If XPPGUN is not 1 in step S907, the process proceeds to step S910. If acceleration / deceleration is not being performed (for example, DLPM <19.5 mmHg) and the FAF value is skipped three or more times in the same engine operating range, the process proceeds to step S911. Then, after storing the engine operating region at that time, the routine further proceeds to step S909, where the running concentration detection flag XPGRUN is set to 1. If the region / DLPM deviates from the predetermined value in step S908, the process proceeds to step S912, where XPGRUN is set to 0, and the density detection flag is cancelled.
[0030]
The operation of the purge rate after XPGIDL becomes 1 or XPGRUN becomes 1 is as follows. First, if it is determined that the FAF value (or the annealing value) before changing the purge rate in step S913: FAFB is determined. (The determination of this FAFB will be described later with reference to FIG. 13). In the next step S914, a value reduced by a predetermined value A% (for example, 15%) is obtained with reference to the FAFB, and a predetermined value ± α% is obtained with respect to this value. A dead zone (for example, 2%) is provided. As a result, as shown in FIG. 10, three areas (1), (2), and (3) are determined. In step S915, it is determined in which region the FAF value (or the annealing value) is, and if it is region {circle around (1)}, the flow proceeds to step S916 to increase the purge rate PGR by a predetermined value B%, and region {circle around (2)}. If so, the process proceeds to step S917, and there is no increase or decrease in PGR. If it is region (3), the process proceeds to step S918, and PGR is decreased by a predetermined value C%. Finally, the process proceeds to step S819, where the upper and lower limits of the PGR are checked, and the PGR is limited to a range of 0% (lower limit) to 20% (upper limit).
[0031]
FIG. 11 shows the density update PGR control subroutine in step S510 of FIG. This control is also performed separately during idling and during driving. The conditions for operating the concentration detection flag (XPGNO1, XPGNO2) are the same as in the initial concentration detection routine. The operation of the purge rate is as follows: when idling, XIDL is 1 in step S1101, SPD is 0 km / h in step S1102. If it is determined in step S1103 that the FAF value is skipped three times or more, the process proceeds to steps S1104 and S1105, and further, the FAF value (or the smoothed value) when XPGNO1 becomes 1 and its predetermined change amount F% (for example, 10%). It is confirmed that the value does not reach the upper and lower limits of the FAF value, the predetermined change amount F% is divided by the evaporation concentration (FGPG), and the PGR when XPGNO1 becomes 1 is added to the divided value. Thus, PGR is determined in step S1106. Finally, the process proceeds to step S1107 to check the upper and lower limits of PGR.
[0032]
When running, as in the case of idling, when the predetermined change amount G% (for example, 7%) is divided by the evaporation concentration (FGPG) in steps S1117 through steps S1108 to S1116, and this divided value becomes 1 Subtract from PGR. Finally, the process proceeds to step S1118 to check the upper and lower limits of PGR. Here, the reason for performing addition during idling and subtraction during traveling is that the opening of the purge solenoid valve is small during idling and the opening during driving is large.
[0033]
Evaporation concentration detection
FIG. 12 shows a main routine of the evaporation concentration detection executed by the base routine of the CPU 21 about every 4 ms. This routine is controlled separately for initial density detection and density update. That is, when XFFPGG is 1 in step S121 and XPGIDL is 1 or XPGRUN is 1 in step S122, the process proceeds to step S123 to detect the initial concentration of evaporation. When 1 or XPGNO2 is 1, the process proceeds to step S125 and the evaporation concentration is updated.
[0034]
FIG. 13 shows the initial concentration detection subroutine in step S123 of FIG. First, in step S131, it is determined whether or not the previous concentration detection flag is 0. If the previous concentration detection flag is 0, the concentration detection flag (XPGIDL, XPGRUN, XPGNO1, XPGNO2) for purge rate control is set to 1 this time. Therefore, the process proceeds to step S132, and the PGR and FAF values (or smoothed values) at that time are stored as PGRB and FAFB. In the next step S133, if the FAF value (or the annealing value) enters the dead zone described in the purge rate control and the FAF value is skipped three or more times, the process proceeds to step S134, and the PGR / FAF value (or the annealing) at that time Value) is stored as PGRC, FAFC. In the next step S135, the difference ΔFAF between FAFB and FAFC is divided by the difference ΔPGR between PGRB and PGRC to obtain the evaporation concentration FGPG. When this density detection is completed, flag and counter processing is performed in steps S136, S137, and S138 (for example, XFFFGPG is set to 1 and CPGKAN is set to 0). If NO in step S133, the process proceeds to step S139, and if the FAF value is skipped three or more times after the PGR reaches the upper limit, the evaporation concentration is low, so the FAF value does not increase to the dead zone even if the purge amount is increased. In step S134, the evaporation concentration FGPG is obtained in the same manner as described above. If NO in step S139, the process returns without obtaining the evaporation concentration FGPG.
[0035]
FIG. 14 shows the density update subroutine in step S125 of FIG. This density update subroutine includes steps S141, S142, and S144 to S148 similar to steps S131, S132, and S134 to S138 of the initial density detection subroutine of FIG. 13, and eliminates the determination of the dead zone of the FAF value in step S133 of FIG. Step S143 is only for determining whether or not the FAF value is skipped three times or more, and Step S139 is omitted. Thereby, the concentration update of the detected evaporation is executed when the FAF value is skipped three times after the PGR is updated by ΔPGR for the concentration update.
[0036]
Fuel injection amount control
FIG. 15 shows fuel injection amount control that is executed about every 4 ms in the base routine of the CPU 21.
[0037]
First, in step S151, the basic fuel injection amount (TP) is obtained from the engine speed and load (for example, intake pipe pressure) based on the data stored as a map in the ROM 34 in step S151, and various basic corrections are performed in next step S152. (Cooling water temperature, intake air temperature after startup, etc.) Second, if the evaporation concentration is being detected in step S153 (XPGIDL, XPGRUN, XPGNO1, XPGNO2 = 1), the process proceeds to step S154 and the purge correction coefficient FPG (when PGR is multiplied by FGPG) when each flag is set to 1. (Fixed value). Otherwise, proceed to step S155 to match the PGR change,
[0038]
[Expression 1]
FPG = (FGPG-1) × PGR
To obtain FPG. Finally, in step S156, the FAF, FPG, and air-fuel ratio learning value (KGj) for each engine operation region are
[0039]
[Expression 2]
1+ (FAF-1) + (KGj-1) + FPG
As a correction coefficient by the above calculation, it is reflected in the fuel injection amount.
[0040]
Purge solenoid valve control
FIG. 16 shows a purge solenoid valve control routine executed by the CPU 21 by interruption every 100 ms. If XIPGR is 1 in step S161 or if fuel cut is in progress in step S162, the routine proceeds to step S163, where the duty of the purge solenoid valve 16 is set to 0. Otherwise, the process proceeds to step S164, where the purge solenoid valve 16 drive cycle is 100 ms.
[0041]
[Equation 3]
Duty = (PGR / PGRfo) × (100 ms−PV) × PPa + PV
The duty of the purge solenoid valve 16 is obtained by the following equation. Here, PGR is the purge rate obtained in FIGS. 6, 9, and 11, PGRfo is the purge rate in each operating state when the purge solenoid valve 16 is fully open (see FIG. 3), and PV is the battery voltage fluctuation The voltage correction value, PPa, is an atmospheric pressure correction value with respect to a change in atmospheric pressure.
[0042]
Air-fuel ratio learning control
FIG. 17 shows the air-fuel ratio learning control routine. During the air-fuel ratio feedback, the cooling water temperature THW is 80 ° C or higher, the increase after start is 0, the warm-up increase is 0, the battery voltage is 11.5V or higher, which has entered the current operation range and skipped 5 times or more from the FAF value In step S1702, it is determined that all the conditions have been completed, and if all of the evaporation concentration detecting flags XPGIDL, XPGRUN, XPGUO1, and XPGN2 are other than 1, it is determined in step S1701 and learning control is performed. After the FAFAV value is read in step S1703, learning control is performed separately for idle time KG0 (step S1708) and travel time (step S1710) according to the determination result of whether or not the vehicle is idle in step S1705. A predetermined number (for example, seven) of regions KG1 to KG7 is divided according to (for example, the pressure in the intake pipe). In addition, the learning value is updated only when the engine speed is within a predetermined engine speed in steps S1706 and S1709 (600 to 1000 rpm during idling and 1000 to 3200 rpm during traveling). Further, at the time of idling, the learning value is updated in step S1707 when the intake pipe pressure PM is 173 mmHg or more. The update method of the learning values KG0 to KG7 in each region is such that when the difference between the FAF smoothing value and 1.0 is larger than a predetermined value (for example, 2%), the learning values KG0 to KG7 in that region are set to a predetermined value (K %, L%). (Steps S1711 to S1714). Finally, the upper and lower limits of KGj are checked (step S1715). Here, the upper limit value of KGj is set to 1.2, for example, the lower limit value is set to 0.8, and the upper and lower limit values can be set for each engine operating region.
[0043]
FIG. 18 shows a subroutine of step S44 of FIG. 4. First, in step S181, the basic upper and lower limit values of FAF are set (for example, set to an upper limit value of 1.2 and a lower limit value of 0.8). Next, the process proceeds to step S182, and if any of the evaporative concentration detection flags is 1, the process proceeds to step S183, and the lower limit value of FAF is set to a value smaller than the basic lower limit value (for example, 0.6). After return. If all of the evaporation concentration detection flags are other than 1 in step S182, the process proceeds to step S184 to determine whether or not a predetermined time (for example, 3 seconds) has elapsed since all of the evaporation concentration detection flags have become 0. When the predetermined time has not elapsed, the process proceeds to step S183, and when the predetermined time has elapsed, the process directly returns. As a result, the lower limit value of the FAF is set to a value smaller than the basic value during the evaporative concentration detection and until a predetermined time elapses, whereby the FAF value sticks to the lower limit value at the time of concentration detection or update. It prevents the detection and update of the concentration from becoming impossible.
[0044]
A time chart of the embodiment described above is shown in FIG. (A) shows the detected evaporation concentration value FGPG, (B) shows the fuel loss correction coefficient FPG, (C) shows the purge rate PGR, the solid line in (d) shows the FAF value, and the one-dot chain line shows the FAF value. Indicates the lower limit.
[0045]
Other Embodiment A In the above-described embodiment, the fuel loss correction coefficient FPG during concentration update is fixed to the value immediately before it, but as shown in the time chart of FIG. 20, the fuel loss correction coefficient during concentration update is fixed. By changing the FPG in accordance with the fuel vapor concentration already detected and the purge rate at the time of concentration update, the fluctuation of the FAF value at the time of concentration update can be further reduced. In this embodiment, the fuel control in FIG. 15 is replaced with that in FIG. 21 and the concentration update subroutine in FIG. 14 is replaced with that in FIG. 22 in the embodiment shown in FIGS. Here, in FIG. 21, steps S153 and S154 are omitted from FIG. 15, and FIG. 22 is an update step S145 in which the evaporation density change amount is reflected in the previous FGPG value as compared with FIG. It is what I did.
[0046]
Other Example B
In each of the embodiments described above, the present invention is applied to the case where the pressure of the intake air downstream of the throttle valve 5 is detected by the intake pressure sensor 5B and the basic fuel injection amount is calculated from the engine speed and the intake pipe pressure. However, the present invention can also be applied to an apparatus in which the basic fuel injection amount is calculated based on the engine speed and the intake air amount using an intake air amount sensor that detects the intake air amount upstream of the throttle valve 5. In this way, when the intake air amount upstream of the throttle valve 5 is detected, the flow rate of bypass air including the evaporation gas introduced downstream of the throttle valve 5 via the discharge passage 15 cannot be detected as the intake air amount. The basic fuel injection amount is determined by excluding the flow rate of the bypass air. Therefore, when the concentration of the evaporation gas in the bypass air is low, the higher the purge rate, the greater the air-fuel ratio of the air-fuel mixture sucked into the combustion chamber of the internal combustion engine. On the contrary, the FAF value that should be decreased as the value increases is increased, making it impossible to detect the initial concentration of evaporative gas. Therefore, in this embodiment, as shown in FIG. 23, an area larger than the FAFB before changing the purge rate is added to the FAF determination area shown in FIG. 10, and the initial concentration is detected in this area. Ban. For this reason, in this embodiment, the initial concentration detection purge control subroutine of FIG. 9 is changed to that of FIG. 24 and the evaporation concentration detection of FIG. Further, the purge solenoid valve control of FIG. 16 is replaced with that of FIG.
[0047]
Here, in FIG. 24, an area larger than FAFB is added as the area confirmation step S915 to that of FIG. 9, and when it is determined that this area, the process proceeds to step S920 to set the purge rate to 0, In S921, the area 4 flag XRYU4 is set to 1 and then the process returns. In FIG. 25, region 4 confirmation step S126 is inserted before step S121 in FIG. 12, and when it is determined in step S126 that region 4 flag XRYU4 is not 1, the process proceeds to step S121. The same operation as in FIG. 12 is performed, and when it is determined in step S126 that the region 4 flag XRYU4 is 1, the process proceeds to step S127, the evaporation concentration is set to 1.0, and then the process returns. Further, in FIG. 26, an area 4 confirmation step S165 is inserted before step S161 with respect to that of FIG. 16, and when it is determined in this step S165 that the area 4 flag XRYU4 is not 1, the process proceeds to step S161. The same operation as that in FIG. 16 is performed, and when it is determined in step S165 that the region 4 flag XRYU4 is 1, the process proceeds to step S163.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram showing an embodiment of the present invention.
FIG. 2 is a characteristic diagram of a purge solenoid valve in the embodiment.
FIG. 3 is a fully open purge rate map in the embodiment.
FIG. 4 is a flowchart of air-fuel ratio feedback control in the embodiment.
FIG. 5 is a flowchart of purge rate control in the embodiment.
FIG. 6 is a flowchart of a normal purge rate control subroutine in the embodiment.
FIGS. 7A to 7E are graphs showing various characteristics used in a normal purge rate control subroutine in the embodiment.
FIG. 8 is a flowchart of a fuel cut purge rate control subroutine in the embodiment.
FIG. 9 is a flowchart of an initial concentration detection purge rate control subroutine in the embodiment.
FIG. 10 is an area determination characteristic diagram used in an initial concentration detection purge rate control subroutine in the embodiment.
FIG. 11 is a flowchart of a concentration update purge rate control subroutine in the embodiment.
FIG. 12 is a flowchart of evaporation concentration detection in the embodiment.
FIG. 13 is a flowchart of an initial concentration detection subroutine in the embodiment.
FIG. 14 is a flowchart of a density update subroutine in the embodiment.
FIG. 15 is a flowchart of fuel injection amount control in the embodiment.
FIG. 16 is a flowchart of purge solenoid valve control in the embodiment.
FIG. 17 is a flowchart of air-fuel ratio learning control in the embodiment.
FIG. 18 is a flowchart of an upper / lower limit check subroutine for air-fuel ratio feedback control in the embodiment.
FIG. 19 is a time chart showing waveforms of respective parts in the embodiment.
FIG. 20 is a time chart showing waveforms of respective parts in another embodiment A of the apparatus of the present invention.
FIG. 21 is a flowchart of fuel injection amount control in the other embodiment A;
FIG. 22 is a flowchart of a density update subroutine in the other embodiment A;
FIG. 23 is an area determination characteristic diagram used in an initial concentration detection purge rate control subroutine in another embodiment B of the apparatus of the present invention;
FIG. 24 is a flowchart of an initial concentration detection purge rate control subroutine in the other embodiment B;
FIG. 25 is a flowchart of evaporation concentration detection in the other embodiment B.
FIG. 26 is a flowchart of purge solenoid valve control in the other embodiment B;
[Explanation of symbols]
1 Multi-cylinder engine
2 Intake pipe
5 Throttle valve
5a Throttle sensor
5B Intake pressure sensor
6 Oxygen sensor
7 Fuel tank
13 Canister
15 Release passage
16 Purge solenoid valve
21 CPU

Claims (3)

An air-fuel ratio control device for an internal combustion engine that stores evaporated fuel generated in a fuel tank in a canister and discharges the evaporated fuel stored in the canister together with air to an intake side of the internal combustion engine through a discharge passage,
Air-fuel ratio detection means for detecting the air-fuel ratio of the internal combustion engine;
Air-fuel ratio feedback means for feedback-controlling the air-fuel ratio of the mixture of fuel and air supplied to the internal combustion engine in accordance with the air-fuel ratio detected by the air-fuel ratio detection means;
A flow rate control valve for changing a purge rate of air containing evaporated fuel discharged from the canister to the intake side of the internal combustion engine through the discharge passage;
A concentration detection purge rate control means for changing a purge rate by the flow rate control valve when detecting the concentration of the evaporated fuel;
Concentration detecting means for detecting the concentration of the evaporated fuel based on the air-fuel ratio before and after the purge rate is changed by the purge rate control means and the purge rate; and
When the concentration detection means detects the concentration of the evaporated fuel again after the concentration detection means detects the concentration of the evaporated fuel, the already detected amount of the evaporated fuel concentration is used as the purge rate at the time of this concentration detection. An air-fuel ratio control apparatus for an internal combustion engine, comprising: a fuel concentration correction means for detecting the concentration that is reflected in the fuel supply amount of the internal combustion engine accordingly. An air-fuel ratio control device for an internal combustion engine that stores evaporated fuel generated in a fuel tank in a canister and discharges the evaporated fuel stored in the canister together with air to an intake side of the internal combustion engine through a discharge passage,
Air-fuel ratio detection means for detecting the air-fuel ratio of the internal combustion engine;
Air-fuel ratio feedback means for feedback-controlling the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine according to the air-fuel ratio detected by the air-fuel ratio detection means;
A flow rate control valve for changing a purge rate of air containing evaporated fuel discharged from the canister to the intake side of the internal combustion engine through the discharge passage;
A concentration update purge rate control means for changing a purge rate by the flow rate control valve according to the amount of evaporated fuel concentration already detected when the concentration detection value of the evaporated fuel is updated;
An air-fuel ratio control apparatus for an internal combustion engine, comprising: an air-fuel ratio before and after the purge rate is changed by the purge rate control means; and a concentration update means for updating the concentration of the evaporated fuel based on the purge rate. An air-fuel ratio control device for an internal combustion engine that stores evaporated fuel generated in a fuel tank in a canister and discharges the evaporated fuel stored in the canister together with air to an intake side of the internal combustion engine through a discharge passage,
Air-fuel ratio detection means for detecting the air-fuel ratio of the internal combustion engine;
Air-fuel ratio feedback means for feedback-controlling the air-fuel ratio of the mixture of fuel and air supplied to the internal combustion engine in accordance with the air-fuel ratio detected by the air-fuel ratio detection means;
A flow rate control valve for changing a purge rate of air containing evaporated fuel discharged from the canister to the intake side of the internal combustion engine through the discharge passage;
A concentration detection purge rate control means for changing a purge rate by the flow rate control valve when detecting the concentration of the evaporated fuel;
Concentration detecting means for detecting the concentration of the evaporated fuel based on the air-fuel ratio feedback value of the air-fuel ratio feedback means before and after the purge rate is changed by the purge rate control means and the purge rate;
An air-fuel ratio control apparatus for an internal combustion engine, comprising: a concentration detection lower limit guard changing means for expanding a lower limit guard of an air-fuel ratio feedback value by the air-fuel ratio feedback means when the concentration detection means detects the concentration of the evaporated fuel.

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