JP2004060543A - Air/fuel ratio control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air/fuel ratio control device of an internal combustion engine capable of increasing emission characteristics by accurately controlling an air/fuel ratio to a target air/fuel ratio by surely compensating a fuel injection amount in a period in which residual evaporated fuel (evaporated fuel purged to an intake system after purge-cut) affects the air/fuel ratio. <P>SOLUTION: The transport delay period CPGDLYRX of the evaporated fuel is calculated (S304) based on an engine speed NE. A target purge compensating coefficient KAFEVACZ as the target value of the compensation item of the fuel injection amount is calculated based on parameters (QPGC (k-CPGDLYRX), KAFEVRT (k-CPGDLYRX)) before the transport delay period CPGDLYRX (S306 to S310). <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an air-fuel ratio control device for an internal combustion engine, and more particularly, to determine an amount of fuel injection to be supplied to the internal combustion engine in consideration of the effect of evaporated fuel purged to an intake system of the internal combustion engine, The present invention relates to an air-fuel ratio control device for an internal combustion engine in which the emission characteristics are improved by accurately controlling the air-fuel ratio.
[0002]
[Prior art]
Fuel is supplied to an internal combustion engine of an automobile from a fuel supply pipe and a fuel tank via an injector. Further, the fuel vapor generated in the fuel tank is adsorbed by the canister, and a part of the fuel vapor adsorbed by the canister is purged to the intake system of the internal combustion engine via the purge passage. A purge control valve is provided in the purge passage, and the amount of evaporated fuel purged to the intake system is controlled by adjusting the opening of the purge passage in accordance with the operating state.
[0003]
When such purging is performed, the total amount of fuel supplied to the internal combustion engine is determined by the sum of the amount of fuel supplied through the injector (hereinafter referred to as “fuel injection amount”) and the amount of evaporated fuel purged to the intake system. Therefore, in order to accurately control the air-fuel ratio to be the target air-fuel ratio, it is necessary to consider the influence of the purged fuel vapor. For this reason, conventionally, the fuel injection amount has been corrected in a decreasing direction according to the amount and concentration of the evaporated fuel to be purged.
[0004]
By the way, the evaporated fuel flowing out of the purge control valve is purged into the intake system of the internal combustion engine through the purge passage, so that it takes time from when the fuel flows out of the purge control valve to when it is actually supplied into the cylinder. There is a delay, the so-called transport delay period. That is, even after the purge cut (purge control valve is closed), the evaporated fuel remaining in the purge passage (hereinafter referred to as “residual evaporated fuel”) continues to be supplied to the internal combustion engine via the intake system, and the air-fuel ratio Affect. Therefore, for example, in Japanese Patent No. 2841005, when the purge cut is performed when the influence of the evaporated fuel on the air-fuel ratio is large, the correction of the fuel injection amount is continued for a predetermined period after the purge cut to supply the fuel after the purge cut. The effect of the residual evaporated fuel on the air-fuel ratio is avoided.
[0005]
[Problems to be solved by the invention]
However, in the above-mentioned Japanese Patent No. 2841005, the predetermined period in which the correction is continued is set (fixed) to a period in which it is estimated that all of the residual evaporated fuel in the purge passage will be completely taken into the cylinder after the purge cut. . For this reason, when the influence of the evaporated fuel on the air-fuel ratio becomes small (when the amount of fuel to be purged becomes zero or decreases) within the set period, the total amount of fuel actually supplied to the internal combustion engine decreases. The air-fuel ratio becomes an unintended value on the lean side, and there is a problem that the accuracy of the air-fuel ratio control is reduced and a desired emission characteristic cannot be obtained.
[0006]
On the other hand, if the residual fuel vapor continues to be purged even after the set period and the influence of the fuel vapor on the air-fuel ratio does not decrease, the total amount of fuel actually supplied to the internal combustion engine increases and the air-fuel ratio is not intended. This is a value on the rich side, and similarly, there has been a problem that the accuracy of the air-fuel ratio control is reduced and a desired emission characteristic cannot be obtained.
[0007]
Accordingly, an object of the present invention is to solve the above-mentioned problem, and to surely correct the fuel injection amount during a period in which the residual fuel vapor affects the air-fuel ratio. It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine which is controlled well to improve emission characteristics.
[0008]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, according to claim 1, fuel injection amount calculating means for calculating a fuel injection amount to be supplied to the internal combustion engine based on an operation state of the internal combustion engine, evaporative fuel generated in a fuel tank Means for purging the fuel into the intake system of the internal combustion engine, fuel injection amount correcting means for correcting the calculated fuel injection amount according to the degree of influence of the purged fuel vapor, and purging after the purging is completed. Correction continuation means for continuing the correction of the fuel injection amount when the degree of influence of the adjusted fuel vapor, more specifically, the degree of influence on the air-fuel ratio, and supplying the corrected fuel amount to the internal combustion engine An air-fuel ratio control device for the internal combustion engine, comprising: an air-fuel ratio detection unit configured to detect an air-fuel ratio of exhaust gas discharged from the internal combustion engine. The detected air-fuel ratio is configured to end the continuation of the predetermined air-fuel ratio from the lean side since the at fuel injection amount correction.
[0009]
Since the air-fuel ratio of the exhaust gas discharged from the internal combustion engine is detected and the correction of the fuel injection amount is terminated when the detected air-fuel ratio becomes leaner than the predetermined air-fuel ratio, the residual evaporation The fuel injection amount can be surely corrected during the period in which the fuel affects the air-fuel ratio, and thus the emission characteristics can be improved by accurately controlling the air-fuel ratio to the target air-fuel ratio.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an air-fuel ratio control device for an internal combustion engine according to one embodiment of the present invention will be described with reference to the accompanying drawings.
[0011]
FIG. 1 is a schematic diagram showing an overall configuration of an air-fuel ratio control device for an internal combustion engine according to this embodiment. In FIG. 1, reference numeral 10 denotes an internal combustion engine (hereinafter, referred to as "engine"), and the engine 10 is, for example, an in-line four-cylinder DOHC engine.
[0012]
A throttle valve 14 is arranged upstream of the intake pipe 12 of the engine 10. A throttle valve opening sensor 16 is provided near the throttle valve 14, outputs a signal corresponding to the opening (throttle opening) θTH of the throttle valve 14, and sends the signal to an ECU (electronic control unit) 18.
[0013]
The ECU 18 includes a CPU 20 that performs an operation for controlling each part of the engine 10, a ROM (EEPROM) 22 that stores a program for controlling each part of the engine 10 and various data (tables and the like), and a CPU 20. A RAM 24 which provides a work area for calculation and temporarily stores data sent from each part of the engine 10 and a control signal sent to each part of the engine 10; and an input circuit 26 which receives data sent from each part of the engine 10. And an output circuit 28 for sending a control signal to each part of the engine 10.
[0014]
An injector (fuel injection valve) 30 is provided for each cylinder (not shown) near the intake port immediately downstream of an intake manifold (not shown) downstream of the throttle valve 14. The injector 30 is connected to a fuel tank 34 via a fuel supply pipe 32, and gasoline fuel is pumped by a fuel pump 36 provided in the middle of the fuel supply pipe 32, and the valve opening time is controlled by a control signal from the ECU 18. Controlled.
[0015]
A regulator (not shown) is provided between the injector 30 and the fuel pump 36 to keep the pressure difference between the pressure of the air taken in from the intake pipe 12 and the pressure of the fuel supplied through the fuel supply pipe 32 constant. When the fuel pressure is too high, excess fuel is returned to the fuel tank 34 through a return pipe (not shown). The air taken in via the throttle valve 14 passes through the intake pipe 12, is mixed with fuel injected from the injector 30, and is supplied to each cylinder of the engine 10.
[0016]
An intake pipe pressure sensor 40 and an intake temperature sensor 42 are mounted downstream of the throttle valve 14 of the intake pipe 12, and output electric signals indicating an intake pipe pressure (load) PBA and an intake temperature TA, respectively, and send them to the ECU 18. I do. An engine coolant temperature sensor 44 is attached to a cylinder peripheral wall (not shown) of the cylinder block of the escidin 10 which is filled with coolant, and outputs a signal corresponding to the engine coolant temperature TW.
[0017]
A cylinder discrimination sensor 46 is mounted near a camshaft or a crankshaft (both not shown) of the engine 10 and outputs a cylinder discrimination signal CYL when a specific cylinder reaches a predetermined classical angle position. A TDC sensor 48 and a crank angle sensor 50 are further mounted near the camshaft or crankshaft of the engine 10. The TDC sensor 48 outputs a TDC signal at a predetermined crank angle position related to the TDC position of the piston of each cylinder, and the crank angle sensor 50 outputs a CRK signal at a crank angle (for example, 30 degrees) shorter in cycle than the TDC signal. I do. The CRK signal is counted by the ECU 18, and the engine speed NE is detected.
[0018]
The engine 10 includes an exhaust pipe 54, and discharges combustion gas to the outside via a three-way catalyst 56 which is an exhaust gas purification device provided in the exhaust pipe 54. A wide area air-fuel ratio sensor (hereinafter, referred to as “LAF sensor”) 58 mounted in the middle of the exhaust pipe 54 generates an output indicating the actual air-fuel ratio KACT in the exhaust gas in a range from lean to rich, and sends it to the ECU 18.
[0019]
A vehicle speed sensor 66 is disposed near a drive shaft of a vehicle (not shown) on which the engine 10 is mounted, and generates an output indicating the running speed of the vehicle and sends it to the ECU 18. The output of the vehicle speed sensor 66 is counted by the ECU 18, and the vehicle speed VP is detected. Further, a battery voltage sensor 68 is connected to an unillustrated vehicle-mounted battery, and outputs a signal corresponding to the battery voltage VB. Further, an atmospheric pressure sensor 70 is provided at an appropriate position in an engine room (not shown), and outputs a signal corresponding to the atmospheric pressure PA.
[0020]
The outputs of the various sensors described above are input to the input circuit 26 of the ECU 18. The input circuit 26 shapes the input signal waveform, corrects the voltage level to a predetermined level, and converts an analog signal value to a digital signal value. The CPU 20 processes the converted digital signal, executes an operation according to a program stored in the ROM 22, and sends a control signal to the injector 30, the igniter and other actuators (both not shown) via the output circuit 28. send.
[0021]
Next, the purge mechanism (purge means) 70 will be described. The purge mechanism 70 includes a fuel tank 34, a charge passage 72, a canister 74, a purge passage 76, and some control valves, and controls discharge of fuel vapor from the fuel tank 34.
[0022]
The fuel tank 34 is connected to a canister 74 via a charge passage 72. The charge passage 72 includes a first branch passage 72a and a second branch passage 72b. An internal pressure sensor 78 is attached to the fuel tank 34 side of the charge passage 72, and outputs a signal indicating the internal pressure in the charge passage 72.
[0023]
A two-way valve 80 is provided in the first branch 72a. The two-way valve 80 includes two mechanical valves 80a and 80b. The valve 80a is a positive pressure valve that opens when the tank internal pressure becomes higher than the atmospheric pressure by a predetermined amount. When the valve 80a is in the open state, the fuel vapor flows to the canister 74 and is adsorbed there. The valve 80b is a negative pressure valve that opens when the tank internal pressure becomes lower than the pressure on the canister 74 side by a predetermined amount. When this valve is open, the evaporated fuel adsorbed by the canister 74 returns to the fuel tank 34. A bypass valve 82, which is an electromagnetic valve, is provided in the second branch path 72b. The bypass valve 82 is normally closed, and opens according to a control signal from the ECU 18.
[0024]
The canister 25 incorporates activated carbon that adsorbs evaporated fuel, and has an intake port (not shown) that communicates with the atmosphere via a passage 84. A vent shut valve 86, which is an electromagnetic valve, is provided in the middle of the passage 84. The vent shut valve 86 is normally in an open state, and is closed according to a control signal from the ECU 18.
[0025]
The canister 74 is connected to a downstream side of the throttle valve 14 of the intake pipe 12 via a purge passage 76, that is, to the intake system. A purge control valve 88 as an electromagnetic valve is provided in the middle of the purge passage 76, and the fuel adsorbed by the canister 74 is purged to the intake system of the engine 10 through the purge control valve 88. The purge control valve 88 continuously controls the purge flow rate by changing the duty ratio based on a control signal from the ECU 18.
[0026]
Next, the operation of the apparatus according to this embodiment, specifically, the operation of the ECU 18 will be described with reference to FIG. FIG. 2 is a block diagram illustrating the operation of the ECU 18.
[0027]
As shown in the figure, the device according to this embodiment includes a fuel supply amount calculation unit 100. The fuel supply amount calculation unit 100 receives the output of various sensors and the like, and calculates the fuel injection amount TCYL that is actually injected via the injector 30 according to equation (1).
TCYL = TIM × (KTOTAL × KCMD × KAF-KAFEVACT) Equation (1)
[0028]
In the above equation, TIM is a basic fuel injection amount, and more specifically, a basic fuel injection amount (indicated by a valve opening time of the injector 30) determined by searching a map from the engine speed NE and the intake pipe pressure PBA. ). KTOTAL is a correction coefficient calculated based on detection signals from various sensors, and is set so that the fuel consumption characteristics, acceleration characteristics, and the like of the engine are optimized according to the driving state. KCMD is called a target air-fuel ratio coefficient, and represents the target air-fuel ratio in an equivalent ratio. The target air-fuel ratio coefficient KCMD is proportional to the reciprocal of the air-fuel ratio A / F, that is, the fuel-air ratio F / A, and takes a value of 1.0 at the stoichiometric air-fuel ratio.
[0029]
KAF indicates an air-fuel ratio correction coefficient, and is a coefficient for executing the air-fuel ratio feedback control so that the air-fuel ratio of the air-fuel mixture supplied to the engine matches the target air-fuel ratio. The air-fuel ratio correction coefficient KAF is calculated by the air-fuel ratio controller 102 based on the actual air-fuel ratio detected by the LAF sensor 58. KAFEVACT is a purge correction coefficient, and is a correction term for correcting the fuel injection amount TCYL in a decreasing direction. The calculation of the purge correction coefficient KAFEVACT will be described later.
[0030]
The injector 30 is opened for a time that realizes the fuel injection amount TCYL calculated as described above, and supplies the gasoline fuel in the fuel tank 34 to each cylinder of the engine 10.
[0031]
The fuel supply amount calculation unit 100 calculates the fuel injection amount TCYL as described above, while calculating (estimating) the intake air amount QAIR based on the following equation (2).
QAIR = TIM × NE × 2 × KQAIR × KPA (2)
[0032]
Here, since the basic fuel injection amount TIM is determined from the intake pipe pressure PBA and the like as described above, KQAIR is a coefficient for converting the fuel injection amount determined thereby into an air flow rate, and is a fixed value ( For example, 0.45 L / mms). KPA is a coefficient for correcting a change in flow rate according to the intake pipe pressure PBA.
[0033]
The fuel supply amount calculation unit 100 further calculates the ratio of the evaporated fuel to the intake air amount QAIR, that is, the basic purge flow rate QPGCBASE based on the following equation (3).
QPGCBASE = QAIR × KQPGB Equation (3)
[0034]
Here, KQPGB is a target purge rate, and is set to, for example, 0.04. In this case, it means that the fuel vapor is included in 4% of the intake air amount QAIR.
[0035]
FIG. 3 is a flow chart showing the operation of the apparatus according to this embodiment, more specifically, the operation of the ECU 18 for calculating the intake air amount QAIR and the basic purge flow rate QPGCBASE. The illustrated program is executed every time a signal indicating TDC is output from the TDC sensor 48, for example.
[0036]
First, in S10, the intake air amount QAIR is obtained according to the above-described equation (2). Next, the program proceeds to S12, in which the basic purge flow rate QPGCBASE is obtained according to the above-mentioned equation (3).
[0037]
Returning to the description of FIG. 2, the purge flow rate calculation unit 104 calculates the target purge flow rate QPGCMD based on the basic purge amount QPGCBASE calculated by the fuel supply amount calculation unit 102 according to the following equation (4). The target purge flow rate QPGCMD represents a target value of the purge flow rate for purging the intake system of the engine in the current control cycle.
QPGCMD = QPGCBASE × KPGT Equation (4)
[0038]
Here, KPGT is a purge flow coefficient and is set to a value of 1 or less. By changing the coefficient KPGT, the target purge flow rate QPGCMD can be controlled. Note that the coefficient KPGT is calculated according to the operating state.
[0039]
Further, the purge flow rate calculation unit 104 calculates the purge flow rate QPGC to be purged in the current control cycle (the execution time in the flow chart of FIG. 3) based on the intake air amount QAIR based on the following equation (5).
QPGC (k) = QPGC (k−1) + (QAIR × KDQPGC) Equation (5)
[0040]
Here, k indicates a control cycle (discrete sample time), (k) indicates a current control cycle (current program execution time), and (kn) indicates a control cycle n times before. KDQPGC is a predetermined fixed value (for example, 0.003). As is apparent from the equation (5), the purge flow rate QPGC is controlled so as to gradually reach the target purge flow rate QPGCMD.
[0041]
The purge control valve drive amount calculation unit 106 calculates the duty ratio PGCMD for driving the purge control valve 88 such that the purge flow rate QPGC calculated by the purge flow rate calculation unit 104 is purged to the intake system by the following equation (6). Calculated according to The duty ratio indicates a ratio at which the purge control valve is opened.
PGCMD = PGCMD0 + DPGCVBX + DPGC0
PGCMD0 = QPGC × KDUTY / KDPBG (6)
[0042]
Here, KDUTY is a coefficient for converting the purge flow rate into a duty ratio, and is a fixed value (for example, 3.8% · min / L). KDPBG is a coefficient for correcting the opening degree according to the pressure difference between before and after the purge control valve 88. PGCMD0 represents a duty ratio corresponding to the purge flow rate QPGC, and is hereinafter referred to as a “target duty ratio”. DPGCVBX and DPGC0 are coefficients for correcting the delay (invalid time) because a delay occurs before the purge control valve 88 starts to open depending on the battery voltage VB and the intake pipe pressure PBA, respectively.
[0043]
The purge control valve drive amount calculation unit 106 performs a limit process on the calculated duty ratio PGCMD with predetermined upper and lower limits, and outputs a final duty ratio DOUTPGC. The opening and closing of the purge control valve 88 is controlled in accordance with the final duty ratio DOUTPGC.
[0044]
Further, the rate calculation unit 108 calculates the duty rate PGRATE according to the following equation (7) based on the calculated final duty ratio DOUTPGC.
PGRATE = (DOUTPGC-DPGCVBX-DPGC0) / PGCMD0 Equation (7)
[0045]
Here, the duty rate PGRATE indicates the ratio of the actual duty ratio (after subtracting the invalid time) to the target duty ratio PGCMD0 of the purge flow rate QPGC. Therefore, the value obtained by multiplying QPGC by PGRATE indicates the actual purge flow rate purged by the purge control valve 88 in the current control cycle.
[0046]
FIG. 4 is a flowchart showing the calculation operation of the final duty ratio DOUTPGC. The illustrated program is executed, for example, every 80 msec.
[0047]
First, in step S20, the purge flow rate QPGC is determined.
[0048]
FIG. 5 is a subroutine flowchart showing the operation of calculating the purge flow rate QPGC. Hereinafter, the operation of calculating the purge flow rate QPGC will be described with reference to the same drawing. First, in S100, a purge flow rate coefficient KPGT is obtained. The purge flow coefficient KPGT is calculated according to the operating state as described above.
[0049]
Next, proceeding to S102, a value obtained by multiplying the basic purge flow rate QPGCBASE by the coefficient KPGT in accordance with the above-described equation (4) is set as a temporary variable qpgcmd. It is determined whether it is greater than. When the result in S104 is affirmative, the program proceeds to S105, in which the upper limit value QPGMAX is set to the target purge flow rate QPGCMD. 1 L / min).
[0050]
When the result in S106 is affirmative, the process proceeds to S108, in which the lower limit value QPGMIN is set to the target purge flow rate QPGCMD. When the result in S106 is negative, that is, when the temporary variable qpgcmd is between the upper limit value QPGMAX and the lower limit value QPGMIN, Proceeding to S110, the temporary variable qpgcmd is set to the target purge flow rate QPGCMD.
[0051]
Next, the routine proceeds to S112, where the purge permission flag F. It is determined whether the bit of NEPGACT is set to 1. Purge permission flag F. NEPGACT (initial value: 0), when the bit is set to 1, indicates that the execution of the purge is permitted. This purge permission flag F. The setting of the NEPGACT bit will be described later in detail. When the result in S112 is affirmative, the program proceeds to S114, in which the purge cut flag F.P. It is determined whether the bit of PGREQ is set to 1. Purge cut flag F. PGREQ (initial value 0) indicates that purge cut is being executed when the bit is set to 1.
[0052]
When the result in S114 is affirmative, the program proceeds to S116, in which a predetermined value DQPGCOBD (for example, 2 L / min) is subtracted from the purge flow rate QPGC (k-1) calculated in the previous control cycle (program execution time). Let the value be a temporary variable qpgc. On the other hand, when the result in S114 is NO, the program proceeds to S118, in which a value obtained by multiplying the intake air amount QAIR by a purge addition coefficient KDQPGC is set as a temporary variable qpgc. The purge addition coefficient KDQPGC is a coefficient (for example, 0.003) that determines how much to be added to the intake air amount QAIR as the purge flow rate.
[0053]
Next, the process proceeds to S120, and it is determined whether or not the value of the temporary variable qpgc is equal to or greater than a predetermined upper limit value DQPGCMAX (for example, 2 L / min). When the result in S120 is affirmative, the program proceeds to S122, in which the upper limit value DQPGCMAX is set to the added purge flow rate DQPGC. On the other hand, when the result in S120 is NO, the program proceeds to S124, in which the temporary variable qpgc is set to the added purge flow rate DQPGC.
[0054]
Next, in S126, a value obtained by adding the added purge flow rate DQPGC to the purge flow rate QPGC (k-1) calculated in the previous control cycle is set as a temporary variable qpgc. Thus, the purge flow rate is gradually increased toward the target purge flow rate QPGCMD.
[0055]
Next, the process proceeds to S128, and it is determined whether or not the temporary variable qpgc has exceeded the target purge flow rate QPGCMD as a result of increasing the purge flow rate in S126. When the result in S128 is affirmative, the program proceeds to S130, in which the value of the target purge flow rate QPGCMD is set as the purge flow rate QPGC. On the other hand, when the result in S128 is NO, the program proceeds to S132, in which the temporary variable qpgc is set to the purge flow rate QPGC. Thus, the purge flow rate QPGC purged in the current control cycle is calculated so as not to exceed the target purge flow rate QPGCMD. In S112, the purge permission flag F. When it is determined that the bit of NEPGACT is not 1, the routine proceeds to S134, where the purge flow rate QPGC is set to zero.
[0056]
Returning to the description of the flow chart of FIG. 4, the process proceeds to S22, where it is determined whether the purge flow rate QPGC calculated in S20 is zero. When the result in S22 is affirmative, that is, when the evaporative fuel is not purged, the process proceeds to S24, where the duty ratio PGCMD is set to zero. On the other hand, if the result in S22 is negative, the program proceeds to S26, in which the cycle for driving the purge control valve 88 is set to, for example, 0.80 msec.
[0057]
Next, in S28, a DPGCVBX table (not shown) is searched based on the battery voltage VB to correct the invalid time of the purge control valve 88 according to the battery voltage VB, and the invalid time DPGCVBX is obtained. The DPGCVBX table is set so that the invalid time DPGCVBX decreases as the battery voltage increases.
[0058]
Next, in S30, a KDPBG table (not shown) is searched based on the intake pipe pressure PBA to obtain a differential pressure correction value KDPBG in order to correct the duty ratio fluctuation caused by the differential pressure across the purge control valve 88. . The KDPBG table is set so that the differential pressure correction value KDPBG increases as the engine load (PBA) decreases.
[0059]
Next, in S32, a DPGC0 table (not shown) is searched based on the intake pipe pressure PBA to determine the invalid time DPGC0 in order to correct the invalid time of the purge control valve 88 according to the intake pipe pressure PBA. The characteristics of the DPGC0 table are set such that the invalid time DPGC0 increases as the load increases. Next, the process proceeds to S34 and S36, and the duty ratio PGCMD is obtained according to the above-described equation (6).
[0060]
Next, in S38, it is determined whether the duty ratio PGCMD is equal to or greater than a predetermined upper limit value DOUTPGH (for example, 95%). When the result in S38 is affirmative, the program proceeds to S40, in which the final duty ratio DOUTPGC is set to the upper limit value DOUTPGH. On the other hand, when the result in S38 is NO, the program proceeds to S42, in which it is determined whether the duty ratio PGCMD is equal to or less than a predetermined lower limit value DOUTPGL (for example, 5%). When the result in S42 is affirmative, the final duty ratio DOUTPGC is set to zero in S44. Further, in S46, the values of the duty rate PGRATE and the purge flow rate QRATE (described later) are set to zero, and the value of the high concentration correction coefficient KKEVG (described below) is set to 1.0.
[0061]
On the other hand, when the result in S42 is negative, that is, when the final duty ratio DOUTPGC is between the upper limit value DOUTPGH and the lower limit value DOUTPGL, the final duty ratio DOUTPGC is set to the duty ratio PGCMD in S48, and then the above-described equation (7) is used in S50. ), The duty rate PGRATE is obtained. It should be noted that, even if the result in S38 is affirmative, the program proceeds to S50 and the duty rate PGRATE is calculated.
[0062]
Returning to the description of FIG. 2, the transport delay period calculator 110 calculates the transport delay period CPGDLYRX based on the engine speed NE. The transport delay period CPGDLYRX indicates a time delay from when the evaporated fuel is purged to the purge passage to when it is sent to the intake system of the engine 10. The transport delay period CPGDLYRX is represented by an integer n, and indicates that the transport delay increases as n increases. Alternatively, the transport delay period may be calculated based on the intake air amount QAIR instead of the engine speed NE.
[0063]
The purge coefficient calculation means 112 calculates a vapor concentration coefficient KAFEV based on the air-fuel ratio coefficient KAF and the target air-fuel ratio KCMD calculated by the air-fuel ratio control unit 102, the detected actual air-fuel ratio KACT, and the like.
[0064]
Further, the high density correction coefficient calculation unit 114 calculates the high density correction coefficient KKEVG based on the vapor density coefficient KAFEV calculated by the purge coefficient calculation means 112 and the like. The higher the concentration of the fuel vapor, the greater the influence on the air-fuel ratio. Therefore, the high concentration correction coefficient KKEVG is a coefficient for correcting this.
[0065]
The purge correction coefficient calculation unit 116 calculates the target purge correction coefficient KAFEVACZ according to the following equation (8) based on the various values calculated as described above.
KAFEVACZ = KAFEV × PGRATE × QRATE Equation (8)
[0066]
Here, QRATE is a purge flow rate, and is calculated according to the following equation (9).
QRATE = QPGC / QPGCBASE Equation (9)
[0067]
As is clear from the equations (7) and (9), the value “PGRATE × QRATE” obtained by multiplying the duty rate PGRATE by the purge flow rate QRATE is a ratio of the purge flow rate purged to the intake system in the current control cycle. Represent. Further, since the degree of influence of the evaporated fuel on the air-fuel ratio is expressed depending on the vapor concentration coefficient KAFEV, the target purge correction is calculated by multiplying “PGRATE × QRATE” by the vapor concentration coefficient KAFEV. The coefficient can be determined accurately.
[0068]
The purge correction coefficient calculation unit 116 calculates the purge correction coefficient KAFEVACT based on the calculated target purge correction coefficient KAFEVACZ according to the following equation (10).
KAFEVACT = KAFEVACZ × KKEVG (10)
[0069]
Here, the purge correction coefficient KAFEVACT indicates the ratio of the fuel amount to which the purge flow rate QPGC contributes to the required fuel. The ratio of the fuel amount contributed by the purge flow rate QPGC is first calculated as described above as the target purge correction coefficient KAFEVACZ, and a value corrected by multiplying the target purge correction coefficient KAFEVACZ by the high concentration correction coefficient KEVEVG is used as the final purge correction coefficient KAFEVACT. Is set.
[0070]
The fuel supply amount calculation unit 100 corrects the fuel injection amount TCYL (the amount of fuel to be supplied via the injector 30) in a decreasing direction according to the above equation (1), based on the purge correction coefficient KAFEVACT calculated in this manner. I do. As a result, the total amount of fuel supplied to the engine 10 becomes appropriate, and the actual air-fuel ratio KACT is accurately controlled to follow the target air-fuel ratio.
[0071]
FIG. 6 is a flowchart showing the operation of calculating the purge correction coefficient KAFEVACT. The illustrated program is executed each time a TDC pulse signal is output from the TDC sensor 48, for example.
[0072]
First, in S200, the fuel injection amount correction end flag F. It is determined whether the bit of KACTKV is set to 1. Here, the fuel injection amount correction end flag F. KACTKV (initial value 0) means that when the bit is set to 1, the correction of the fuel injection amount is not executed (end). Note that the fuel injection amount correction end flag F. The setting of the KACTKV bit will be described later in detail.
[0073]
When the result in S200 is negative, the program proceeds to S202, in which a target purge correction coefficient KAFEVACZ is calculated.
[0074]
FIG. 7 is a subroutine flowchart showing the calculation operation. As shown in the figure, first, in S300, the stored value of the ring buffer QPGCn is updated. The ring buffer QPGCn is composed of 24 buffers QPGC0 to QPGC23 (not shown), and stores a total of 24 values from the latest value of the purge flow rate QPGC to 23 times before in a time series. In S300, the value stored in the ring buffer QPGCn is shifted by one. Note that shifting the ring buffer means shifting the data stored in QPGC0 to QPGC22 from QPGC1 to QPGC23, respectively, and emptying QPGC0.
[0075]
Next, in S302, the current value QPGC (k) of the purge flow rate QPGC is stored in the emptied QPGC0 as the latest value, and in S304, the transport delay period table CPGDLYRX is searched based on the engine speed NE, and the transport delay is determined. The period CPGDLYRX is calculated. As described above, the transport delay period CPGDLYRX indicates a time delay from when the evaporated fuel is purged to the purge passage via the purge control valve 88 to when the fuel reaches the intake system of the engine 10.
[0076]
In this embodiment, the transport delay period CPGDLYRX is represented by an integer n, more specifically, the number of TDCs. FIG. 8 shows an example of the transport delay period table CPGDLYRX. As shown in the figure, the transport delay period CPGDLYRX is set such that the transport delay period CPGDLYRX increases as the engine speed NE increases. This is because, as the engine speed NE increases, the number of strokes that is performed from the time when the fuel vapor is purged to the time when the fuel reaches the intake system of the engine increases, that is, the number of TDCs increases.
[0077]
Next, the routine proceeds to S306, where the purge flow rate QRATE is calculated according to the equation (9). At this time, as the purge flow rate QPGC, of the 24 values stored in the ring buffer QPGCn, the value (QPGC (k-CPGDLYRX)) preceding by the transport delay period CPGDLYRX is used.
[0078]
Next, in S308, the value obtained by multiplying the purge flow rate QRATE by the duty rate PGRATE is set as KAFEVRT, and then in S310, the target purge correction coefficient KAFEVACZ is calculated in accordance with the above-described equation (8).
[0079]
Returning to the description of the flow chart of FIG. 6, the process proceeds to S204, where it is determined whether the vapor density coefficient KAFEV is larger than the guard coefficient KEVACTG. The guard coefficient KEVACTG is a coefficient calculated according to the operating state. When the vapor concentration coefficient KAFEV is larger than this value, the target purge correction coefficient KAFEVACZ needs to be corrected in the increasing direction according to the value. It means there is.
[0080]
When the result in S204 is affirmative, the program proceeds to S206, in which a value obtained by dividing the vapor density coefficient KAFEV by the guard coefficient KEVACTG is set as a high density correction coefficient KKEVG. Is calculated. In this case, since the vapor density coefficient KAFEV is larger than the guard coefficient KEVACTG, the high density correction coefficient KKEVG calculated in S208 is a value larger than 1.0. Therefore, in S208, a value obtained by correcting the target purge correction coefficient KAFEVACZ in the increasing direction is set as the final purge correction coefficient KAFEVACT.
[0081]
On the other hand, when the result in S204 is NO, the process proceeds to S208, and the high density correction coefficient KKEVG is set to 1.0. That is, in step S206, the target purge correction coefficient KAFEVACZ is directly used as the final purge correction coefficient KAFEVACT.
[0082]
In S200, the fuel injection amount correction end flag F. If it is determined that the KACTKV bit is set to 1, the process proceeds to S212, where the purge correction coefficient KAFEVACT is set to zero. That is, the fuel supply amount calculation unit 100 does not correct the fuel injection amount TCYL according to the equation (1).
[0083]
As described above, the purge correction coefficient KAFEVACT, which is a correction term of the fuel injection amount TCYL, is calculated based on the parameters (QPGC (k-CPGDLYRX), KAFEVRT (k-CPGDLYRX)) preceding by the evaporated fuel transport delay period CPGDLLYRX. Therefore, the correction of the fuel injection amount TCYL is continued during the transport delay period CPGDLYRX after the purge cut. That is, the evaporative fuel transport delay period CPGDLYRX is obtained, and during that period, the correction of the fuel injection amount TCYL is continued. Therefore, the fuel injection amount TCYL can be reliably corrected during a period in which the residual fuel vapor (vapor fuel purged into the intake system after the purge cut) affects the air-fuel ratio, and the air-fuel ratio is set to the target air-fuel ratio. Emission characteristics can be improved by controlling with high accuracy.
[0084]
Further, since the transport delay period CPGLYRX is determined based on the engine speed NE, it is possible to more accurately calculate the period in which the residual fuel vapor affects the air-fuel ratio. The fuel injection amount TCYL can be more reliably corrected during the influence period, so that the air-fuel ratio can be more accurately controlled to the target air-fuel ratio to improve the emission characteristics.
[0085]
Next, the purge permission flag F. NEPGACT and a fuel injection amount correction end flag F.N. KACTKV will be described. FIG. NEPGACT and a fuel injection amount correction end flag F.N. 9 is a flow chart showing an operation of setting bits of KACTKV. The illustrated program is executed every time a signal indicating TDC is output from the TDC sensor 48, for example.
[0086]
In the following, in S400, it is determined whether or not the detected engine speed NE is higher than a predetermined engine speed NEPGACT (for example, 500 rpm) set near an idle (idling) engine speed. When the result in S400 is affirmative, the program proceeds to S402, in which the fuel injection amount correction end flag F.F. KACTKV bit is set to 0, and the process proceeds to S404, where a purge permission flag F.K. Set the NEPGACT bit to one.
[0087]
Here, the fuel injection amount correction end flag F. KACTKV, as described above, means that when the bit is set to 1, the correction of the fuel injection amount is not executed (ends). The purge permission flag F. NEPGACT indicates that purging is permitted when the bit is set to 1, as described above. That is, when the engine speed NE is higher than the idle speed, the processes from S400 to S404 mean that the correction of the fuel injection amount TCYL is continued and the purge of the evaporated fuel is executed.
[0088]
On the other hand, when the result in S400 is NO, the program proceeds to S406, in which it is determined whether the detected air-fuel ratio (actual air-fuel ratio) KACT is leaner than a predetermined air-fuel ratio KACTKV (for example, 13.9). When the result in S406 is NO, the program proceeds to S408, in which the fuel injection amount correction end flag F.F. The KACTKV bit is reset to 0, and the process proceeds to S410, where the purge permission flag F.K. Reset the NEPGACT bit to 0. That is, since the detected actual air-fuel ratio KACT is richer than the predetermined air-fuel ratio KACTKV, it is considered that the degree of influence of the purged fuel on the air-fuel ratio is large. At the same time, the purge of the fuel vapor is stopped. In other words, the correction in the decreasing direction of the fuel injection amount TCYL is continued even after the purge cut.
[0089]
On the other hand, when the result in S406 is affirmative, the routine proceeds to S412, in which the fuel injection amount correction end flag F.F. The bit of KACTKV is set to 1. That is, since the detected actual air-fuel ratio KACT is leaner than the predetermined air-fuel ratio KACTKV, it is considered that the degree of influence of the purged fuel vapor on the air-fuel ratio is small. End continuation of.
[0090]
As described above, the actual air-fuel ratio KACT of the exhaust gas discharged from the engine 10 is detected, and the correction of the fuel injection amount TCYL is continued when the detected actual air-fuel ratio KACT becomes leaner than the predetermined air-fuel ratio KACTKV. Since the fuel injection amount is ended, the fuel injection amount TCYL can be surely corrected in a period in which the residual fuel vapor affects the air-fuel ratio. Therefore, the air-fuel ratio is accurately controlled to the target air-fuel ratio to improve the emission characteristics. Can be done.
[0091]
As described above, in this embodiment, the fuel injection amount calculation means (various sensors, ECU 18) for calculating the fuel injection amount TCYL to be supplied to the internal combustion engine (engine) 10 based on the operating state of the internal combustion engine (engine) 10 , A fuel supply amount calculation unit 100), a purge unit (purge mechanism 70, ECU 18, fuel supply amount calculation unit 100, purge flow rate calculation unit 104) for purging evaporated fuel generated in the fuel tank 34 into the intake system of the internal combustion engine. Purge control valve drive amount calculation unit 106, S10, S12, S20 to S50, S100 to S134), fuel injection amount correction means for correcting the calculated fuel injection amount TCYL according to the degree of influence of the purged fuel vapor. (Various sensors, ECU 18, fuel supply amount calculation unit 100, purge correction coefficient calculation unit 116, S200 to S212, S300 S310) After the completion of the purge, when the influence of the purged evaporated fuel is large, a correction continuation unit (various sensors, the ECU 18, the purge correction coefficient calculation unit 116) that continues to correct the fuel injection amount TCYL, And a fuel supply means (injector 30, ECU 18, fuel supply amount calculation unit 100) for supplying the corrected fuel injection amount TCYL to the internal combustion engine. And an air-fuel ratio detecting means (LAF sensor 58, ECU 18) for detecting an air-fuel ratio (actual air-fuel ratio) KACT of the exhaust gas to be detected. At the time of the lean side, the continuation of the correction of the fuel injection amount TCYL is terminated (ECU 18, purge correction coefficient calculation 116, S200, S212, S406, S412) is configured as.
[0092]
In the above description, the LAF sensor is used as the air-fuel ratio sensor. ₂ It may be a sensor.
[0093]
Further, the present invention can be applied to an air-fuel ratio control device for a marine vessel propulsion engine such as an outboard motor in which the output shaft of the engine is set in a vertical direction.
[0094]
【The invention's effect】
According to the first aspect, the air-fuel ratio of the exhaust gas discharged from the internal combustion engine is detected, and the continuation of the correction of the fuel injection amount is terminated when the detected air-fuel ratio becomes leaner than the predetermined air-fuel ratio. As a result, the fuel injection amount can be reliably corrected during the period in which the residual fuel vapor affects the air-fuel ratio, and the air-fuel ratio is accurately controlled to the target air-fuel ratio to improve the emission characteristics. be able to.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing an overall configuration of an air-fuel ratio control device for an internal combustion engine according to one embodiment of the present invention.
FIG. 2 is a block diagram showing an operation of an ECU of the device shown in FIG.
FIG. 3 is a flowchart showing an operation of calculating an intake air amount among operations of an ECU of the apparatus shown in FIG. 1;
FIG. 4 is a flowchart showing a calculation operation of a final duty ratio among operations of the ECU of the apparatus shown in FIG. 1;
FIG. 5 is a subroutine flowchart showing an operation of calculating a purge flow rate in the flowchart shown in FIG. 4;
FIG. 6 is a flowchart showing a calculation operation of a purge correction coefficient among operations of the ECU of the apparatus shown in FIG. 1;
FIG. 7 is a subroutine flowchart showing an operation of calculating a target purge correction coefficient in the flowchart shown in FIG. 6;
8 is a diagram showing characteristics of a table used for searching for a transport delay period in the subroutine flow chart shown in FIG. 7;
9 is a flowchart showing an operation of setting bits of a purge permission flag and a fuel injection amount correction end flag among operations of the ECU of the apparatus shown in FIG. 1.
[Explanation of symbols]
10 Internal combustion engine (engine)
18 ECU (electronic control unit)
30 Injector (fuel injection valve)
34 Fuel tank
50 Crank angle sensor
58 LAF sensor (air-fuel ratio sensor)
70 Purge mechanism
100 Fuel supply calculation unit
104 Purge flow rate calculation unit
106 Purge control valve drive amount calculation unit
110 Transportation delay period calculation unit
116 Purge correction coefficient calculation unit

Claims (1)

a. Fuel injection amount calculation means for calculating a fuel injection amount to be supplied to the internal combustion engine based on an operation state of the internal combustion engine,
b. Purging means for purging evaporative fuel generated in a fuel tank into an intake system of the internal combustion engine,
c. Fuel injection amount correction means for correcting the calculated fuel injection amount according to the degree of influence of the purged evaporated fuel,
d. After the completion of the purge, when the influence of the purged evaporated fuel is large, a correction continuation unit that continues to correct the fuel injection amount,
And e. Fuel supply means for supplying the corrected fuel injection amount to the internal combustion engine,
In an air-fuel ratio control device for an internal combustion engine having
f. Air-fuel ratio detection means for detecting an air-fuel ratio of exhaust gas discharged from the internal combustion engine,
And the correction continuation means ends the correction of the fuel injection amount when the detected air-fuel ratio becomes leaner than a predetermined air-fuel ratio. apparatus.

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