JP3269400B2 - Air-fuel ratio control device for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an air-fuel ratio control device for controlling an air-fuel ratio of a combustible air-fuel mixture supplied to an internal combustion engine. More specifically, the present invention relates to an air-fuel ratio control device for an internal combustion engine that controls an air-fuel ratio on the assumption that fuel vapor generated in a fuel tank is added to a combustible mixture.

[0002]

2. Description of the Related Art Conventionally, there is an air-fuel ratio control device for controlling an air-fuel ratio of a combustible air-fuel mixture (air-fuel mixture) supplied to a combustion chamber of an internal combustion engine (engine). In general, the air-fuel ratio required for an engine changes according to the engine speed, load state, warm-up state, and the like. Thus, in the above control device, the computer controls the fuel supply device to adjust the amount of fuel supplied to the combustion chamber in accordance with the required air-fuel ratio of the engine. That is, the computer adjusts the air-fuel ratio of the air-fuel mixture by correcting the amount of fuel supplied from the fuel supply device to the combustion chamber so that the actual air-fuel ratio detected by the sensor matches the required air-fuel ratio. . By adjusting the air-fuel ratio, various characteristics such as output characteristics, exhaust characteristics, and drivability of the engine are optimized according to various operating conditions of the engine.

[0003] On the other hand, as one of the devices mounted on vehicles and the like, there is a fuel vapor processing device. This processing device collects fuel vapor generated in a fuel tank in a canister. This processing device purges the fuel vapor collected in the canister from the canister to the intake passage as needed. The fuel purged to the intake passage is added to the original mixture supplied to the combustion chamber by the fuel supply device.

[0004] By the way, it is necessary to adapt the air-fuel ratio control even in an engine equipped with the above processing device. For that purpose, since fuel vapor by purge is added to the original air-fuel mixture supplied to the combustion chamber, it is necessary to control the air-fuel ratio in consideration of the amount of the purged fuel.

Japanese Patent Laying-Open No. 7-269399 discloses an example of an air-fuel ratio control device which controls the air-fuel ratio in anticipation that fuel vapor generated in a fuel tank will be purged into an intake passage. As shown in FIG.
An injector 72 provided in the engine 71 injects fuel pumped from a fuel tank 73 by a pump 74 to each cylinder of the engine 71. The control unit 75 controls the injector 72 so that the actual air-fuel ratio detected by the air-fuel ratio sensor 76 matches the target air-fuel ratio that changes according to the operating state of the engine 71. Thereby, the amount of fuel supplied to each cylinder is adjusted, and the air-fuel ratio of the air-fuel mixture is controlled.

The canister 77 contains an adsorbent made of activated carbon or the like. The canister 77 collects the fuel vapor generated in the fuel tank 73 through the vapor line 78 and adsorbs the fuel vapor on the adsorbent. A purge line 79 extending from the canister 77 communicates with the intake passage 80. Purge line 79
The purge control valve 81 provided in the, selectively opens and closes the line 79 as needed. When operating the engine 71,
When the control unit 75 opens the purge control valve 81, the negative pressure generated in the intake passage 80 acts on the canister 77 through the purge line. By the action of the negative pressure, the fuel collected in the canister 77 is separated from the adsorbent and is purged to the intake passage 80 through the purge line 79. At the time of this fuel purging, the control unit 75 calculates the ratio of the amount of purge fuel to the amount of intake air flowing through the intake passage 80 as a purge rate according to the operating state of the engine 71. The controller 75 limits the temporal change rate of the purge rate to a predetermined threshold value or less. The control unit 75 controls the opening of the purge control valve 81 according to the calculated purge rate. The control unit 75 learns the concentration of the purge fuel based on the detection value of the air-fuel ratio sensor 76.
When the degree of progress of the fuel concentration learning is small, the control unit 75 calculates the rate of change of the opening degree of the purge control valve 81 as:
It is set smaller than when the degree of learning progress is large. With this setting, the control unit 75 suppresses fluctuation (roughness) of the air-fuel ratio when the purge rate is changed.

[0007]

In the apparatus disclosed in the above publication, there is a response delay in the change in the amount of fuel purged to the intake passage 80 through the purge line 79. Further, the responsiveness of the purge control valve 81 to the change in the amount of purge fuel with respect to the rate of change in the degree of opening of the purge control valve 81 varies depending on the operating state of the engine 71, for example, the conditions such as the engine speed and the engine load. Therefore, when the rate of change of the opening of the purge control valve 81 is regulated in accordance with the degree of progress of the concentration learning as in the above-described apparatus, there is a response delay in the purge fuel amount,
There is a possibility that the roughness of the air-fuel ratio controlled by the engine 71 cannot be completely suppressed. This delay is caused by the operation delay of the purge control valve 81 itself, the length of the path of the purge line 81, and the like, and is inevitable.

The present invention has been made in view of the above circumstances, and has as its object to add (purge) fuel vapor generated in a fuel tank to a combustible mixture supplied to an internal combustion engine. An object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine, which is capable of stably adjusting the air-fuel ratio of the internal combustion engine irrespective of a response delay due to a change in a purged fuel amount.

[0009]

In order to achieve the above object, according to the present invention, as shown in FIG. 1, a flammable mixture of fuel and air supplied to an internal combustion engine M1 is provided. An air-fuel ratio control apparatus for controlling an air-fuel ratio according to claim 1, wherein the fuel vapor is generated in a fuel supply means M2 for supplying fuel to the internal combustion engine M1 and a fuel tank M3 for storing fuel. Processing means M4 for flowing to the engine M1 for processing, and the internal combustion engine M through the processing means M4.
An adjusting valve M5 for adjusting the flow rate of the fuel vapor supplied to the fuel cell 1, an operating state detecting means M6 for detecting an operating state of the internal combustion engine M1, and an air-fuel ratio of the combustible mixture being the target air-fuel ratio. Calculating means M7 for calculating the amount of fuel to be supplied to the internal combustion engine M1 based on the detected operating state; and controlling the fuel supply means M2 based on the calculated amount of supplied fuel. First control means M8 and second calculation means M9 for calculating the flow rate of fuel vapor to be supplied to the internal combustion engine M1 based on the detected operating state
A second control means M10 for controlling the opening of the regulating valve M5 based on the calculated flow rate of the fuel vapor, and an upper limit value relating to a rate of change of the controlled opening of the regulating valve M5. ,
Limiting means M for limiting the rate of change to a set upper limit
11 and correction means M12 for increasing and correcting the calculated supplied fuel amount when the rate of change is restricted by the restriction means M11.

According to the configuration of the above invention, the first calculating means M7 determines the amount of fuel to be supplied to the internal combustion engine M1 such that the air-fuel ratio of the combustible mixture becomes the target air-fuel ratio. It is calculated based on the operating state of the internal combustion engine M1 detected by M6. The first control unit M8 controls the fuel supply unit M2 based on the calculated supplied fuel amount. The second calculating means M9 calculates the flow rate of the fuel vapor to be supplied to the internal combustion engine M1 based on the detected operating state. The second control unit M10 controls the opening of the regulating valve M5 based on the calculated flow rate of the fuel vapor. As a result, the fuel vapor generated in the fuel tank M3 is transferred to the processing unit M4.
To the internal combustion engine M1.

Here, when the fuel vapor is supplied to the internal combustion engine M1 through the processing means M4, the limiting means M11 sets an upper limit value relating to the rate of change of the degree of opening of the regulating valve M5, and the rate of change is set. Limit to the upper limit. Then, the correcting means M1
In step 2, when the change rate is limited to the upper limit, the calculated supplied fuel amount is increased and corrected.

Therefore, it is assumed that the operating state of the internal combustion engine M1, for example, the amount of air supplied to the internal combustion engine M1 changes, and the opening of the regulating valve M5 is controlled in accordance with the change. At this time, the flow rate of the fuel vapor supplied to the internal combustion engine M1 through the processing means M4 is limited to the flow rate according to the upper limit value by limiting the change rate of the opening degree of the adjustment valve M5 to the upper limit value. become. Then, instead of adjusting the air-fuel ratio of the combustible mixture by increasing the amount of fuel vapor supplied to the internal combustion engine M1, the amount of fuel supplied from the fuel supply means M2 to the internal combustion engine M1 is increased and corrected. Thus, the air-fuel ratio is adjusted. For this reason, the air-fuel ratio of the combustible air-fuel mixture is quickly adjusted toward the target air-fuel ratio regardless of the presence or absence of the fuel vapor supply delay.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which an air-fuel ratio control apparatus for an internal combustion engine according to the present invention is embodied in an automobile will be described below in detail with reference to the drawings.

FIG. 2 is a schematic configuration diagram showing an air-fuel ratio control device of an internal combustion engine provided with a fuel vapor processing device. A gasoline engine system mounted on an automobile includes a fuel tank 1 for storing fuel. The tank 1 has an inlet pipe 2 for injecting fuel therein, that is, for refueling. The pipe 2 includes an oil supply port 2a at the tip.
When refueling the tank 1, a refueling nozzle (not shown) is inserted into the refueling port 2a. The cap 3 that closes the filler port 2a is removable.

A pump 4 built in the tank 1 sucks and discharges the fuel stored in the tank 1. A main line 5 extending from the pump 4 is connected to a delivery pipe 6.
A plurality of injectors 7 provided in the pipe 6 are arranged corresponding to a plurality of cylinders (not shown) provided in an internal combustion engine (engine) 8. A return line 9 extending from the delivery pipe 6 is connected to the fuel tank 1. When the pump 4 operates, the fuel discharged from the pump 4 reaches the delivery pipe 6 through the main line 5,
It is distributed to each injector 7. When each injector 7 operates, fuel is injected into the intake passage 10. Each injector 7 constitutes fuel supply means of the present invention for supplying fuel to each cylinder of the engine 8.

The intake passage 10 includes an air cleaner 11 and a surge tank 10a. The air purified through the air cleaner 11 is introduced into the intake passage 10. A combustible air-fuel mixture of the fuel injected from each injector 7 and the air introduced into the intake passage 10 (hereinafter simply referred to as “air-fuel mixture”) is supplied to each cylinder of the engine 8 and is subjected to combustion. The surplus fuel without being distributed to each injector 7 in the delivery pipe 6 returns to the tank 1 through the return line 9. The exhaust gas after combustion is discharged from each cylinder of the engine 8 through the exhaust passage 12 to the outside.

In this embodiment, cranking at the time of starting the engine 8 is performed based on the operation of a starter (not shown). The fuel vapor processing apparatus according to this embodiment collects and processes the fuel vapor generated in the tank 1 without releasing it to the atmosphere. This processing apparatus has a canister 14 for collecting fuel vapor generated in the tank 1 through a vapor line 13. The canister 14 contains a plurality of adsorbents 15 made of activated carbon or the like. The interior of the canister 14 is occupied by a layered adsorbent 15, and the spaces 14a, 1 located above and below the adsorbent 15.
4b.

The first atmospheric valve 16 provided on the canister 14 is a check valve. This atmospheric valve 16 is a canister 1
4 is opened when the internal pressure is lower than the atmospheric pressure to allow the introduction of outside air (atmospheric pressure) into the canister 14 and prevent the flow of gas in the opposite direction. An air pipe 17 extending from the atmosphere valve 16 is connected to the air cleaner 11. Therefore, the outside air purified by the air cleaner 11 is introduced into the canister 14. The second atmospheric valve 18 provided on the canister 14 is a check valve. The atmospheric valve 18 opens when the internal pressure of the canister 14 becomes higher than the atmospheric pressure, and allows the gas (internal pressure) to be led out from the canister 14 to the outlet pipe 19, and prevents the gas flow in the opposite direction.

A vapor control valve 20 provided on the canister 14 controls fuel vapor flowing from the tank 1 to the canister 14. The control valve 20 has an internal pressure (hereinafter referred to as “tank-side internal pressure”) PT on the side of the tank 1 including the vapor line 13.
And the internal pressure on the side of the canister 14 (hereinafter referred to as “canister-side internal pressure”) PC, thereby allowing fuel vapor to flow into the canister 14. That is, the control valve 20 opens when the canister-side internal pressure PC becomes substantially equal to the atmospheric pressure and is smaller than the tank-side internal pressure PT to allow the fuel vapor to flow into the canister 14. In addition, the vapor control valve 20 allows the gas to flow from the canister 14 to the tank 1 when the canister-side internal pressure PC is higher than the tank-side internal pressure PT.

Purge line 2 extending from canister 14
1 communicates with the surge tank 10a. The canister 14 causes the adsorbent 15 to adsorb and collect only the fuel component in the fuel vapor introduced through the vapor line 13. The canister 14 supplies only gas containing no fuel component to the atmosphere valve 18.
Is discharged through the outlet pipe 19 to the outside. During operation of the engine 8, the intake negative pressure generated in the intake passage 10 acts on the purge line 21. At this time, the fuel collected in the canister 14 or the tank 1
The fuel which is introduced into the canister 14 and is not adsorbed by the adsorbent 15 is purged to the intake passage 10 through the purge line 21. A purge control valve 22 provided in the purge line 21 adjusts the amount of fuel passing through the purge line 21 according to the necessity of the engine 8. The purge control valve 22 includes a casing and a valve (both not shown).
The control valve 22 is an electromagnetic valve that receives a supply of an electric signal to move the valve body, and receives a duty signal to control the opening degree in duty. In this embodiment, the vapor line 13, the canister 14, and the purge line 21 constitute processing means of the present invention. Further, the purge control valve 22 constitutes the regulating valve of the present invention.

This processing apparatus includes a pressure sensor 4 for detecting the flow of fuel vapor from the tank 1 to the canister 14.
Including 1. The pressure sensor 41 is configured to be able to individually detect the tank-side internal pressure PT and the canister-side internal pressure PC with the vapor control valve 20 as a boundary. That is, the pressure sensor 41
The three-way switching valve 23 provided in conjunction with has three ports. The three-way switching valve 23 is an electromagnetic valve that receives a supply of an electric signal and switches communication between ports. One port of the three-way switching valve 23 is connected to the pressure sensor 41. The other two ports of the three-way switching valve 23 are connected to the vapor line 13 on the tank 1 side and the canister 14 with the vapor control valve 20 as a boundary. By switching the three-way switching valve 23 as needed, the pressure sensor 41
Selectively communicate with the vapor line 13 or the canister 14. In response to this switching, the pressure sensor 41 selectively detects the tank-side internal pressure PT and the canister-side internal pressure PC. In this embodiment, in order for the pressure sensor 41 to preferentially detect the tank-side internal pressure PT, the three-way switching valve 23 is used.
The three-way switching valve 23 is configured such that the pressure sensor 41 communicates with the vapor line 13 when no electric signal is supplied to the fuel cell.

Various sensors 42, 43, 44, 45, 4
Reference numerals 6 and 47 constitute driving state detecting means of the present invention for detecting the driving state of the engine 8 and the automobile. An intake air temperature sensor 42 provided in the vicinity of the air cleaner 11 detects a temperature (intake air temperature) THA of the air taken into the intake passage 10 and outputs a signal corresponding to the magnitude. The intake air amount sensor 43 provided near the air cleaner 11 is connected to the intake passage 1.
An air amount (intake amount) Q taken into 0 is detected, and a signal corresponding to the magnitude is output. A water temperature sensor 44 provided in the engine 8 detects the temperature (cooling water temperature) THW of the cooling water flowing inside the engine block 8a, and outputs a signal corresponding to the magnitude. The rotation speed sensor 45 provided in the engine 8 detects the rotation speed (engine rotation speed) NE of the crankshaft 8b of the engine 8, and outputs a signal corresponding to the magnitude. The oxygen sensor 46 provided as an air-fuel ratio detecting means provided in the exhaust passage 12
The oxygen concentration Ox in the exhaust gas passing through is detected, and a signal corresponding to the magnitude is output. The sensor 46 detects the concentration of oxygen in the air-fuel mixture supplied to each cylinder of the engine 8 as a specific component. A vehicle speed sensor 47 provided in the vehicle detects the vehicle speed SPD and outputs a signal corresponding to the magnitude.

An electronic control unit (ECU) 51 constituting the first calculating means, the second calculating means, the first controlling means, the second controlling means, the limiting means and the correcting means of the present invention comprises various sensors 41-41. The signal output from 47 is input. ECU
Reference numeral 51 executes air-fuel ratio control for controlling the amount of fuel injected from each injector 7 so that the air-fuel ratio of the air-fuel mixture in the engine 8 becomes a target air-fuel ratio suitable for the operating state of the engine 8. The ECU 51 controls the fuel vapor processing device to control the execution of the fuel purge. The ECU 51 sets the purge control valve 22 to the required duty ratio DPG in order to purge an amount of fuel suitable for the operating state of the engine 8.
A duty signal required for the purge control valve 22 is output. Here, the fuel purged from the canister 14 to the intake passage 10 affects the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber. Therefore, the ECU 51
Determines the opening of the purge control valve 22 according to the operating state of the engine 8. When fuel vapor is being supplied to the engine 8, the ECU 51 performs control based on the control result of the air-fuel ratio control and the value of the oxygen concentration Ox detected by the oxygen sensor 46.
The learning value related to the concentration of the fuel vapor added to the air-fuel mixture is learned. Generally, when the air-fuel ratio increases, the concentration of CO contained in the exhaust gas of the engine increases, and the oxygen concentration Ox
Decrease. Therefore, the ECU 51 determines the value of the oxygen concentration Ox in the exhaust gas detected by the oxygen sensor 46,
The concentration learning value FGHPG of the fuel vapor to be purged is learned. The ECU 51 determines a duty value DPG corresponding to the opening of the purge control valve 22 based on the learning value FGHPG, and outputs a duty signal corresponding to the value to the control valve 22. The ECU 51 uses the learning value FGHPG to calculate
The fuel amount adjusted by the air-fuel ratio control is corrected.

The ECU 51 switches the three-way switching valve 23 as required based on the detection values of the various sensors 41 to 47, and selectively selects the value of the tank-side internal pressure PT and the value of the canister-side internal pressure PC detected by the pressure sensor 41. input.

As shown in the block circuit diagram of FIG.
U51 is a central processing unit (CPU) 52, a read-only memory (ROM) 53, and a random access memory (RA).
M) 54, a backup RAM 55 and a timer counter 56. The ECU 51 includes these units 52 to 56,
A logical operation circuit is formed by connecting the external input circuit 57 and the external output circuit 58 by a bus 59. ROM53
Stores in advance a predetermined control program relating to air-fuel ratio control, fuel purge and the like. The RAM 54 temporarily stores the calculation result of the CPU 52. The backup RAM 55 stores data stored in advance. The timer counter 56 can perform a plurality of timing operations simultaneously. External input circuit 57
Includes a buffer, a waveform shaping circuit, a hard filter (a circuit including an electric resistor and a capacitor), and an A / D converter. The external output circuit 58 includes a drive circuit and the like. The various sensors 41 to 47 are connected to the external input circuit 57. Each injector 7, the purge control valve 22, and the three-way switching valve 23 are connected to an external output circuit 58.

The CPU 52 reads the detection signals of the various sensors 41 to 47 input via the external input circuit 57 as input values. The CPU 52 controls each injector 7, the purge control valve 22, and the three-way switching valve 23 to execute air-fuel ratio control, fuel purge control, and the like based on the input values.

Next, a description will be given of the contents of control processing executed by the ECU 51 (CPU 52). RO of ECU51
The M53 stores in advance control programs and function data relating to the following various routines.

FIGS. 4 and 5 are flowcharts showing a "fuel purge control routine" relating to the fuel purge control.
The ECU 51 (CPU 52) periodically executes the processing of this routine every predetermined time (for example, “102 ms”).

In step 100, the CPU 52 determines whether or not a precondition for executing the fuel purge control is satisfied. In this embodiment, when the precondition is satisfied is when all of the following conditions are satisfied. That is, the value of the cooling water temperature THW detected by the water temperature sensor 44 is “80 ° C.” or more. "30 seconds" or more has elapsed since the start of the engine 8. The value of the post-start increase FASE used for calculating the fuel injection amount TAU described later is set to “0”. Similarly, the value of the warm-up amount FWL used for calculating the fuel injection amount TAU is “0”.
Must be set to Similarly, the value of the high temperature increase FHOT used for calculating the fuel injection amount TAU is set to “0”. Forcible prohibition of fuel injection due to a high value of the engine speed NE, that is, "fuel cut" is not being performed. Further, feedback control of the air-fuel ratio is performed in connection with the air-fuel ratio control.

If the above precondition is satisfied in step 100, the CPU 52 sets the purge execution flag XPGEX to "1" in step 101, and shifts the processing to step 103. If the precondition is not satisfied in step 100, the CPU 52 sets the purge execution flag XPGEX to “0” and sets the learning condition counter CPGKGO to “0” in step 102, and shifts the processing to step 104.

Step 10 after shifting from step 101
In 3, the CPU 52 determines whether or not the fuel vapor concentration learning has been completed. In this embodiment, the time when the fuel vapor concentration learning is completed is a time when any one of the following conditions is satisfied. That is, the previous set value of the learning end flag XFPGE indicating that the fuel vapor concentration learning has been completed is “1”. The average of the air-fuel ratio correction value FAF described later, that is, the value of the average air-fuel ratio correction value FAFAV is in the range of “0.98 to 1.02”. The value of the learning condition counter CPGKGO is “0 second” or less.

If the density learning has been completed in step 103, or if the process has shifted from step 102, in step 104, the CPU 52 sets a skip counter CSEVP for measuring the elapsed time after the start of the density learning to " After that, the process proceeds to step 105. If the density learning has not been completed in step 103, the CPU 52 shifts the processing to step 105 as it is.

In step 105, the CPU 52 determines whether or not the purge execution flag XPGEX is "1". When the flag XPGEX is “0”, the precondition for executing the fuel purge is not satisfied, and the CPU 52 determines in step 106 whether the fuel purge is to be restarted.
Reset PGRST to "0". This flag XPG
When EX is “1”, the CPU 52 shifts the processing to step 107 because the precondition for fuel purge execution is satisfied.

In step 107, the CPU 52 determines whether the guard flag XFPGMN relating to the purge correction value FHPG is "0", whether the guard flag XFPGMN is "1", and whether the previous purge execution flag XPGEXO is "1". Judge. Here, the guard flag XFPGM
N is a lower limit value FHP of a purge correction value FHPG described later.
After the GMN is calculated, the value is set to “1” when the condition of the following equation (1) is satisfied.

TFHPGCL (= FHPG) ≦ FHPGMN (1) If the above condition is satisfied in step 107, in step 108, the CPU 52 sets the purge restart flag XPGRST to “1”, and proceeds to step 109. Transition. If the above conditions are not satisfied, CP
U52 shifts the processing to step 109 as it is.

In step 109, the CPU 52 determines whether or not a condition for terminating the fuel vapor concentration learning is satisfied. In this embodiment, the end condition is satisfied when all of the following conditions are satisfied. That is, the learning condition counter CPGKGO has a value of “0” or less. A duty value DPG for driving the purge control valve 22 is equal to or more than a predetermined value D1 (for example, “15%”). The previous learning start flag XFPGSO described later
Is “1”. Engine 8 is not idle. Here, the value equal to or greater than the predetermined value D1 is a value that can ensure linearity in the relationship between the duty value DPG and the opening of the purge control valve 22. The learning start flag XFPGS is set to “1” when the learning of the fuel vapor is started.

If the termination condition is satisfied in step 109, the CPU 52 proceeds to step 110
The learning end flag XFPGE is set to “1”, and the subsequent processing proceeds to step 111. If the termination condition is not satisfied, the CPU 52 proceeds to step 11
Move to 1.

In step 111, the CPU 52 determines whether or not a condition for stopping the fuel vapor concentration learning has been satisfied. In this embodiment, when the stop condition is satisfied is when at least one of the following conditions is satisfied. That is, the engine 8 is being cranked (the starter flag XSTEFI indicating that the starter is in the on state is “1”). The fuel vapor concentration learning has been completed (the learning end flag XFPGE is "1"), and the previous concentration determination is not rich (the rich determination flag XEVPR is "0"). The fuel vapor concentration learning is not completed (learning end flag XFPGE is “0”), and the engine 8 is not idling (the idle counter CPGKG0 is “0” or less. That the concentration learning has not been completed (learning end flag XFPGE
Is "0"), and the fuel purge is not being executed (the purge execution flag XPGEX is "0" or less).

If the stop condition is satisfied in step 111, the CPU 52 returns to step 112
The learning start flag XFPGS is set to “0”, and the process proceeds to step 115. If the stop condition is not satisfied, the CPU 52 shifts the processing to Step 113.

In step 113, the CPU 52 determines whether or not the value of the skip counter CSEVP is "3" or more. If the above value is “3” or more, since the air-fuel ratio of the air-fuel mixture is being controlled, the CPU 52 sets the learning start flag XFPGS to “0” in step 114, and proceeds to step 115. If the above value is less than “3”, the CPU 52 shifts the processing to step 115 as it is because the control of the air-fuel ratio is not performed.

In step 115, the CPU 52 determines whether or not a condition for terminating the fuel vapor concentration learning is satisfied. In this embodiment, when the end condition is satisfied is when at least one of the following conditions is satisfied. That is, the learning start flag XFPGS is “0”. The value of the previous rich determination flag XEVPR is “1”, and the value of the idle counter CPGKG0 is “4.2 seconds” or more.

In step 115, if the termination condition is satisfied, it means that the engine 8 has been in the idling state for a relatively long time. Therefore, in order to learn the concentration of the fuel vapor again, in step 116, the CP
U52 sets a learning end flag XFPGE to “0”,
The process moves to step 117. If the termination condition is not satisfied, the CPU 52 proceeds to step 11
Move to 7.

In step 117, the CPU 52 calculates the value of the full-open purge flow rate QPRGMX. This flow rate Q
PRGMX indicates the amount of fuel vapor flowing into the intake passage 10 through the purge line 21. This value varies depending on the magnitude of the intake negative pressure generated in the intake passage 10. In this embodiment, the CPU 52 determines the negative pressure equivalent amount GN and the flow rate QPRGMX.
The flow rate QPRGMX is calculated by referring to predetermined function data in relation to The CPU 52 divides the value of the intake air amount Q by the value of the engine speed NE to obtain the value of the negative pressure equivalent amount GN. In the above function data, as the negative pressure equivalent amount GN increases, the flow rate QPRGM
X is set to be small.

In step 118, the CPU 52 determines whether or not a fuel cut has been performed. If the fuel cut has been performed, in step 119, the CPU
52 sets the duty value DPG for determining the opening degree of the purge control valve 22 to “0%”, and executes the processing in step 12
Go to 5. If fuel cut is not performed, CP
U52 shifts the processing to step 120.

In step 120, the CPU 52 determines whether or not the guard flag XFPGMN is "1". When the flag XFPGMN is “1”, it means that the condition of the above equation (1) is satisfied after the lower limit value FHPGMN of the purge correction value FHPG is calculated. Therefore,
In step 121, the CPU 52 calculates a target purge flow rate QPRG. The CPU 52 calculates the target purge flow rate QPRG according to the following equation (2).

QPRG = PGR * QAIPG (2) In the equation (2), “PGR” indicates a purge rate described later, and “QAIPG” is detected by the intake air amount sensor 43 when the fuel purge is being performed. This corresponds to the value of the intake air amount Q.

On the other hand, in step 120, the flag X
If FPGMN is “0”, the CPU 52 calculates the target purge flow rate QPRG in Step 122. The CPU 52 calculates the target purge flow rate QPRG according to the following equation (3).

QPRG = PGRB * QAIPG (3) In equation (3), “PGRQB” indicates a basic purge rate described later. After shifting from steps 121 and 122, in step 123, the CPU 52 sets the duty value DPG.
Is calculated as an upper limit duty value DPGMXG. The CPU 52 calculates the upper limit duty value DPGMXG according to the following equation (4). The ECU 51 executing the process of step 123 corresponds to an upper limit value setting unit for setting a duty upper limit value DPGMXG corresponding to an upper limit value related to a change rate of the duty value DPG corresponding to the opening degree of the purge control valve 22.

DPGMXG = DPGO + 10 (%) ≦ 100 (%) (4) In equation (4), “DPGO” means the value of the duty value DPG calculated last time.

In step 124, CPU 52 calculates duty value DPG. The CPU 52 calculates the duty value DPG according to the following equation (5). DPG = QPRG / QPRGMX ≦ DPGMXG (5) The ECU 5 that executes the processing of steps 119 and 124
Reference numeral 1 corresponds to a second calculating means of the present invention for calculating a duty value DPG corresponding to a flow rate of fuel vapor to be supplied to the engine 8 based on an operation state of the engine 8. Further, E which executes the processing of steps 123 and 124
The CU 51 corresponds to limiting means of the present invention for limiting the rate of change of the duty value DPG to the set upper limit duty value DPGMXG.

After shifting from steps 119 and 124, in step 125, the CPU 52 sets the duty value DPG
Is greater than or equal to the duty upper limit value DPGMXG and the learning start flag XFPGS is “1”. If this determination is affirmative, in step 126, the CPU 52 sets the guard flag XDPGOG to “1”. If the determination result is negative, the CPU 52 determines in step 127 that the guard flag XD
Set PGOG to “0”. Therefore, the guard flag X
DPGOG is set to “1” when the learning of the fuel vapor is started and the calculated duty value DPG is equal to or greater than the duty upper limit value DPGMXG, and is set to “0” otherwise. Step 125 to step 127
Corresponds to a judging means for judging whether or not the rate of change of the duty value DPG is limited to the upper limit duty value DPGMXG.

At step 128 after shifting from steps 126 and 127, the CPU 52 performs duty control on the opening of the purge control valve 22 based on the duty value DPG calculated this time, and once terminates the subsequent processing. The ECU 51 executing the process of step 128 corresponds to a second control unit of the present invention for controlling the opening of the purge control valve 22 based on the calculated duty value DPG.

FIGS. 6 and 7 show the basic purge rate PG described above.
9 is a flowchart illustrating a “first calculation routine” for calculating an RB and a purge rate PRG, and a base purge correction value FHPGB and a concentration learning value FGHPG described below. The CPU 52 periodically executes the processing of this routine every predetermined time (for example, “102 ms”).

In step 200, the CPU 52 determines whether or not the learning start flag XFPGS is "1". If the flag XFPGS is “0”, it means that the learning of the concentration of the fuel vapor has not been started.
In 01, the CPU 52 sets the basic purge rate PGRB to “0”. Further, in step 225, C
The PU 52 sets a guard value D to be described later to “0”, and shifts the processing to step 230.

In step 200, the flag XFPG
If S is “1”, since the learning of the concentration of the fuel vapor has been started, the CPU 52
Sets the value of the basic purge rate PGRB as a temporary replacement value (replacement value) D, and shifts the processing to step 203.

In step 203, the CPU 52 determines whether or not the learning end flag XFPGE is "1". When the flag XFPGE is “1”, the CPU 52 shifts the processing to step 220 because the learning of the concentration of the fuel vapor has been completed. When the flag XFPGE is “0”, the CPU 52 shifts the processing to step 204 because the learning of the concentration of the fuel vapor has not been completed.

In step 204, the CPU 52 determines whether or not the rich / lean flag XOXR is "1". The CPU 52 determines whether the air-fuel ratio of the mixture supplied to the combustion chamber of the engine 8 is rich or lean based on a separate routine. This flag XOXR
Indicates the result of the determination, and is set to “1” when the determination is rich, and is set to “0” when the determination is lean.

In step 204, the flag XOXR
Is “1”, since the air-fuel ratio is rich,
In step 205, the CPU 52 sets the air-fuel ratio correction value F
It is determined whether the AF is smaller than “0.93”. If this determination result is affirmative, in step 206, the CPU 52 sets a result obtained by subtracting “0.005” from the guard value D as a new guard value D, and proceeds to step 212. If the determination result is negative, the CPU 52 shifts the processing to step 212 as it is.

On the other hand, in step 204, the flag X
When OXR is “0”, the CPU 52 shifts the processing to step 207 because the air-fuel ratio is lean.
In step 207, the CPU 52 sets the guard flag X
It is determined whether or not DPGOG is “1”. If the flag XDPGOG is “1”, the CPU 52 shifts the processing to step 208 because the calculated duty value DPG is equal to or greater than the duty upper limit value DPGMXG.

In step 208, the CPU 52 calculates the guard value D according to the following equation (6), and proceeds to step 212. D = QPRGMX / (QAIPG * DPGMXG) (6) On the other hand, in step 207, this flag XDPGO
If G is “0”, the calculated duty value DPG
Is less than the duty upper limit value DPGMXG,
The CPU 52 shifts the processing to step 209.

In step 209, the CPU 52 determines whether or not the rich / lean flag XOXR is "1". When the rich / lean flag XOXR is “1”, since the determination of the air-fuel ratio is rich, CP
U52 shifts the processing to step 212. When the rich / lean flag XOXR is “0”, the CPU 52 shifts the processing to step 210 because the determination of the air-fuel ratio is lean.

In step 210, the CPU 52 determines whether or not the air-fuel ratio correction value FAF is larger than "0.98". If this determination is affirmative, step 2
In step 11, the CPU 52 sets the guard value D to "0.00".
The result of adding “5” is set as a new guard value D,
The process moves to step 212. If the determination is negative, the CPU 52 proceeds to step 21
Move to 2.

In step 212, the CPU 52 sets the guard value D calculated this time as the base purge rate PGRB. In step 213, the CPU 52 sets the base purge correction value FHPGB as the guard value D.

In step 214, the CPU 52 determines whether or not the rich / lean flag XOXR is "1". When the flag XOXR is “1”, the CPU 52 shifts the processing to step 215 because the determination result of the air-fuel ratio is rich.

In step 215, the CPU 52 determines whether or not the air-fuel ratio correction value FAF is smaller than "0.98". If this determination is affirmative, step 2
At 16, the CPU 52 changes the guard value D to “0.00”.
The result obtained by subtracting “104” is set as a new guard value D, and the process proceeds to step 230. If the result of the determination is negative, the CPU 52 shifts the processing to step 230 as it is.

On the other hand, in step 214, the flag X
When OXR is “0”, the determination result of the air-fuel ratio is lean, and thus the CPU 52 shifts the processing to step 217. In step 217, the CPU 52 determines whether or not the air-fuel ratio correction value FAF is larger than “1.03”. If this determination is affirmative, step 21
8, the CPU 52 sets the guard value D to "0.0010
The result of adding “4” is set as a new guard value D,
The process moves to step 230. If the determination result is negative, the CPU 52 proceeds to step 23
Move to 0.

On the other hand, if the learning end flag XFPGE is "1" at step 203, the CPU 52 shifts the processing to step 220 since the fuel vapor concentration learning has been completed.

In step 220, the CPU 52 determines whether or not the purge execution flag XPGEX is "1". If the flag XPGEX is “0”, the fuel purge has not been performed, and the CPU 52 proceeds to step 240 without performing any processing. This flag XP
When GEX is “1”, since the fuel purge has been executed, the CPU 52 shifts the processing to step 221.

At step 221, the CPU 52 determines whether or not the value of the average air-fuel ratio correction value FAFAV is smaller than "0.9". If this is the case,
The CPU 52 shifts the processing to step 222. In step 222, the CPU 52 determines that the average air-fuel ratio correction value FA
FAV, air-fuel ratio correction value FAF, and base purge correction value F
HPGB is set to “0.03”, and the process proceeds to step 230.

On the other hand, if the decision result in the step 221 is negative, the CPU 52 executes the process in a step 223.
Move to. In step 223, the CPU 52 determines whether or not the value of the average air-fuel ratio correction value FAFAV is larger than “1.1”. If this is the case,
The CPU 52 shifts the processing to step 224. In step 224, the CPU 52 sets the average air-fuel ratio correction value FA
FAV, air-fuel ratio correction value FAF, and purge correction value FHPG
Are set to “0.03”, respectively, and the process proceeds to step 23.
Move to 0.

In step 230, the CPU 52 sets the guard value D as the base purge correction value FHPGB. At step 231, the CPU 52 determines whether or not the learning start flag XFPGS is “1”. When the flag XFPGS is “0”, the learning of the concentration of the fuel vapor has not been started, and the CPU 52 shifts the processing to step 234. In step 234,
The CPU 52 sets the value of the base purge correction value FHPGB as the concentration learning value FGHPG, and shifts the processing to step 235.

On the other hand, in step 231, the flag X
If FPGS is “1”, the learning of the fuel vapor has been started, and the CPU 52 proceeds to step 232.
Move to. In step 232, the CPU 52 determines whether or not the duty value DPG is larger than “30%”. If the result of the determination is negative, the CPU 52 shifts the processing to step 240 as it is. If this determination result is affirmative, the CPU 52 executes the process in step 23
Move to 3.

In step 233, the CPU 52 determines the value of the base purge correction value FHPGB and the base purge rate PG
The ratio with the value of RB is set as a concentration learning value FGHPG,
The process moves to step 235.

In step 235, the CPU 52 determines whether or not the density learning value FGHPG is equal to or less than "0.02". If this determination result is affirmative, the CPU 52
In step 236, the rich determination flag XEVP
R is set to “1”, and the process proceeds to step 240. When the determination result is negative, the CPU 52 sets the rich determination flag XEVPR to “0” in step 237, and shifts the processing to step 240.

In step 240, the CPU 52 determines whether the purge execution flag XPGEX is "0" or the learning start flag XFPGS is "0". If this determination result is affirmative, the CPU 52 shifts the processing to step 245 because the fuel purge has not been performed or the fuel vapor concentration learning has not been performed. In step 245, the CPU 52 sets the purge rate P
RG is set to “0”, and the subsequent processing is temporarily ended.

On the other hand, if the decision result in the step 240 is negative, the CPU 52 executes a process in a step 241 to determine whether or not the guard flag XFPGMN is "1". When the flag XFPGMN is “1”, the purge correction value FHPG is equal to or less than the lower limit value FHPGMN, and the CPU 52 temporarily ends the subsequent processing. If the flag XFPGMN is “0”, the CPU 52 shifts the processing to step 242 because the purge correction value FHPG is larger than the lower limit FHPGMN.

At step 242, the CPU 52 determines whether or not the guard flag XDPGOG is "1". When the flag XDPGOG is “1”, the calculated duty value DPG is equal to the duty upper limit value DPGM.
Since it is XG or more, the CPU 52 shifts the processing to step 244. In step 244, the CPU 5
2 calculates the value of the purge rate PGR according to the following equation (7), and then temporarily ends the subsequent processing.

PGR = QPRGMX / (QAIPG * DPGMXG) (7) On the other hand, if the flag XDPGOG is “0” in step 242, the duty value DPG is smaller than the duty upper limit value DPGMXG, and thus step 243 is executed.
In, the CPU 52 sets the value of the base purge rate PGRB as the purge rate PGR, and temporarily ends the subsequent processing.

FIGS. 8 and 9 show the aforementioned base purge correction value FHPGB, purge correction value FHPG, and its lower limit value FH.
PGMN, base purge rate PGRB and purge rate PGR
9 is a flowchart showing a “second calculation routine” for calculating the second calculation. The CPU 52 periodically executes the processing of this routine at predetermined time intervals.

In step 300, the CPU 52 calculates the lower limit value FHPGMN of the purge correction value FHPG.
The CPU 52 calculates the lower limit value FHPGMN by the following equation (8).
Calculated according to FHPGMN = (tKPGTAU−FMW) / tTAUEVP−FAFKG (8) where “tKPGTAU” is a fuel injection amount TA described later.
It is a constant for determining the guard of U. “FMW” represents the intake passage 1 of the fuel injected from the injector 7.
It means a correction amount for predicting and correcting the amount of fuel attached to the 0 wall. “TTAUEVP” is (FAFKG +
FHPG) and the calculated value of the fuel injection amount when the values of the wall adhesion correction amount FMW are not reflected. "FAFK
"G" means the sum of the air-fuel ratio correction value FAF and the learning value KGX.

At step 301, the CPU 52 determines whether or not the guard flag XDPGOG is "1". When the flag XDPGOG is “1”, the calculated duty value DPG is equal to the duty upper limit value DPGM.
Since it is XG or more, the CPU 52 shifts the processing to step 302.

In step 302, the CPU 52 calculates a guard value D according to the following equation (9). D = FGHGP * QPRGMX / (QAIPG * DPGMXG) (9) On the other hand, if the flag XDPGOG is “0” in step 301, the calculated duty value DPG is smaller than the duty upper limit value DPGMXG,
U52 shifts the processing to step 303. Step 3
03, the CPU 52 sets the base purge correction value FHP
GB is set as the guard value D.

After shifting from steps 302 and 303, in step 304, the CPU 52 determines whether or not the guard value D calculated as described above is larger than the lower limit value FHPGMN. If the guard value D is equal to or smaller than the lower limit value FHPGMN, the CPU 52 sets the guard flag XFPGMN to “1” in step 305. Guard value D
Is larger than the lower limit value FHPGMN, the CPU 52 sets the guard flag XFPGMN to “0” in step 306.

Step 30 shifts from step 306
At 7, it is determined whether various flag conditions are satisfied. In this embodiment, when various flag conditions are satisfied is when all of the following conditions are satisfied. That is,
The guard flag XDPGOG is “1”. The learning end flag XFPGE is “0”. The purge execution flag XPGEX is “1”. If the above condition is satisfied, in step 308, the CPU 52 sets the guard value D as the base purge correction value FHPGB, and proceeds to step 310. If the above condition is not satisfied, the CPU 52 shifts the processing to step 310 as it is.

At step 310, CPU 52 determines whether fuel purging has not been performed or not. CPU
52 is when at least one of the following conditions is satisfied:
It is determined that the fuel purge has not been performed. That is, the purge restart flag XPGRST is “0”. The purge rate PGR is “0”. Here, if there is no execution of the fuel purge, in step 311, the CPU 52 sets the guard value D to “0” and shifts the processing to step 318. If the fuel purge has been performed, the CPU 52 shifts the processing to step 312.

At step 312, CPU 52 determines whether guard flag XFPGMN is "1" or not. If the flag XFPGMN is “0”, the purge correction value FHPG is larger than the lower limit value FHPGMN, and the CPU 52 proceeds to step 31
Move to 8. When the flag XFPGMN is “1”, the purge correction value FHPG is set to the lower limit value FHPGMN.
Because of the following, in step 313, the CPU
52 sets the lower limit value FHPGMN of the purge correction value FHPG as the guard value D.

At step 314, CPU 52 determines whether or not learning end flag XFPGE is "1". If the flag XFPGE is "1", the learning of the concentration of the fuel vapor has been completed, and the CPU 52 proceeds directly to step 318. This flag X
If FPGE is “0”, the CPU 52 determines that the fuel vapor concentration learning has not ended, and the CPU 52 proceeds to step 3.
Move to 15.

At step 315, the CPU 52 determines whether or not the density learning value FGHPG is smaller than "0". If the density learning value FGHPG is smaller than “0”, the CPU 52 determines in step 316 that the guard value DGH
Is set to “0”, and the process proceeds to step 317.
If the concentration learning value FGHPG is “0” or more, the CPU
52 shifts the processing to step 317 as it is.

In step 317, the CPU 52 sets the guard value D as the base purge correction value FHPGB. In step 318 after a transition from steps 312, 314, and 317, the CPU 52 sets the guard value D as the purge correction value FHPG.

Thereafter, at step 320, the CPU
52 determines whether the guard flag XFPGMN is "1". When the flag XFPGMN is “0”, the purge correction value FHPG is larger than the lower limit value FHPGMN, and the CPU 52 temporarily terminates the subsequent processing. When the flag XFPGMN is “1”, the purge correction value FHPG is set to the lower limit value FHPG.
Since it is MN or less, the CPU 52 shifts the processing to step 321.

In step 321, the CPU 52 determines whether the lower limit value FHPGMN is larger than "0" or the concentration learning value FGHPG is larger than "0". If this determination result is affirmative, in step 322, the CPU 52 sets the guard value D to “0”.
If this determination result is negative, in step 323, the CPU 52 determines the guard value D according to the following equation (10).
Is calculated.

D = FHPGMN / FGHPG (10) The process proceeds from Steps 322 and 323, and in Step 324, the CPU 52 determines whether or not the purge execution flag XPGEX is “1”. This flag XPGEX
Is "1", since the fuel purge is being executed, the CPU 52 sets the guard value D as the purge rate PGR in step 325, and proceeds to step 32.
Move to 6. When the flag XPGEX is “0”, since the fuel purge has not been executed, the CPU 5
2 shifts the processing to step 326.

In step 326, CPU 52 determines whether or not learning end flag XFPGE is "1". When the flag XFPGE is "1", the learning of the concentration of the fuel vapor has been completed, and the CPU 52 temporarily terminates the subsequent processing. When the flag XFPGE is “0”, since the learning of the concentration of the fuel vapor has not been completed, in step 327, the CPU 52 sets the guard value D as the base purge rate PGRB, and temporarily ends the subsequent processing.

In this embodiment, the ECU 51 executing the above-mentioned “second calculation routine” determines the calculated fuel injection amount TA when the rate of change of the duty value DPG is limited.
It corresponds to a correction value calculating means for calculating a purge correction value FHPG for increasing the amount of U.

FIG. 10 is a flowchart showing a "fuel injection control routine" for controlling the fuel injection from each injector 7. The CPU 52 executes this routine periodically at predetermined time intervals.

In step 400, the CPU 52 calculates the basic injection amount TAUb based on the values of the intake air amount Q detected by the sensors 43 and 45 and the engine speed NE. The CPU 52 calculates a value of the basic injection amount TAUb based on function data having a relationship between the parameters Q, NE, and TAUb stored in the ROM 53 in advance.

In step 410, the CPU 52 calculates a temperature correction value KT based on the intake air temperature THA and the cooling water temperature THW detected by the sensors 42 and 44.
In step 420, the CPU 52 sets the basic injection amount TA
Based on the value of Ub, the temperature correction value KT, the air-fuel ratio correction value FAF, and the purge correction value FHPG, the value of the fuel injection amount TAU to be injected this time is calculated according to the following equation (11). TAU = TAUb × (KT + FAF + FHPG) + FASE + FWL + FHOT (11) In this equation (11), the air-fuel ratio correction value FAF is used to correct the fuel injection amount TAU according to whether the combustible mixture is rich or lean. The CPU 52 determines whether the air-fuel ratio is rich or lean based on the detection value of the oxygen sensor 46 according to a separate routine, thereby obtaining the correction value FAF.
Is calculated. Various parameters FASE, FWL, FHO
T is the increase value described above. The purge correction value FHPG is calculated as described above.

Therefore, according to the equation (11), since the air-fuel ratio correction value FAF is reflected in the calculation of the fuel injection amount TAU, the fuel injection amount calculation is performed so that the air-fuel ratio of the mixture becomes the target air-fuel ratio. The value of TAU is obtained. Since the purge correction value FHPG is reflected in the calculation of the fuel injection amount TAU, the value of the fuel injection amount TAU according to the change rate of the purge fuel amount added to the air-fuel mixture is obtained.

In this embodiment, the purge control valve 22
Is opened and the fuel purge is performed, a value reduced by “16%” from the original basic injection amount TAUb is applied as the value of the basic injection amount TAUb in anticipation of the purge fuel amount in advance.

At step 430, the CPU 52 adjusts the amount of fuel to be supplied to the engine 8 by controlling each injector 7 based on the value of the fuel injection amount TAU calculated this time. After ending the processing of step 430, the CPU 52 once ends the subsequent processing.

In this embodiment, steps 400 to 420
The ECU 51 executing the processing of (1) corresponds to a first calculating means of the present invention for calculating the fuel injection amount TAU to be supplied to the engine 8 so that the air-fuel ratio of the combustible mixture becomes the target air-fuel ratio. ECU that executes processing of step 430
51 corresponds to first control means of the present invention for controlling the injector 7 based on the calculated fuel injection amount TAU. Further, the ECU that executes the process of step 430
Reference numeral 51 corresponds to correction means of the present invention for increasing and correcting the fuel injection amount TAU based on the purge correction value FHPG.

FIGS. 11A to 11D are time charts showing an example of the behavior of the various parameters Q, DPG, XDPGOG, and FHPG described above. Time t1 to t2
In this case, it is assumed that the engine 8 is accelerated from the steady operation state and the intake air amount Q sharply increases. At this time, according to the increase in the intake air amount Q, the duty value DP
The rate of change of G becomes larger than the predetermined upper limit value, and there is a possibility that the adjustment of the purge fuel amount is delayed. Therefore, the guard flag XDPGOG indicating this becomes “1”, and the purge correction value FHPG increases, so that the fuel injection amount T
The AU is increased.

Thereafter, from time t2 to time t3, although the intake air amount Q increases to some extent, the duty value DP
The rate of change of G is not larger than the predetermined upper limit, and the adjustment of the purge fuel amount is suitably performed. Therefore, guard flag X
DPGOG becomes “0”, the purge correction value FHPG does not increase, and the fuel injection amount TAU is not increased.

Subsequently, from time t3 to t4, the intake air amount Q sharply increases again, and the duty value DPG
Is greater than a predetermined upper limit. At this time, the guard flag XDPGOG indicating this becomes “1”, the purge correction value FHPG increases, and the fuel injection amount TAU is increased.

Then, it is assumed that the intake value Q further increases from time t4 to t5, so that the duty value DPG reaches the upper limit “100%”. At this time, the guard flag XDPGOG becomes “1” and the purge correction value F
The HPG increases according to the change in the intake air amount Q, and the fuel injection amount T
The AU is increased.

As described above, according to the air-fuel ratio control device of this embodiment, the ECU 51 injects the fuel from each injector 7 so that the air-fuel ratio of the combustible mixture supplied to the engine 8 becomes the target air-fuel ratio. Fuel injection amount TAU to be
Is calculated based on the operating state of the engine 8. ECU
51 controls each injector 7 based on the calculated fuel injection amount TAU.

Here, the fuel vapor generated in the fuel tank 1 is collected by the canister 14 and purged to the intake passage 10 through the purge line 21 as required. ECU5
1 calculates a duty value DPG corresponding to the flow rate of fuel vapor to be supplied to the engine 8 based on the operating state of the engine 8. The ECU 51 calculates the calculated duty value D.
The opening of the purge control valve 22 is controlled based on the PG. As a result, fuel vapor generated in the fuel tank 1 is added to the original combustible air-fuel mixture formed by being injected from each injector 7 through the canister 14, the purge line 21, the purge control valve 22, the intake passage 10, and the like. 8 for combustion.

Here, when the fuel vapor is supplied to the engine 8 by purging, the ECU 51 sets the purge control valve 22
, That is, the upper limit value related to the change rate of the duty value DPG, that is, the upper limit duty value DPGMXG, and the change rate is limited to the set upper limit duty value DPG. Then, when the rate of change of the duty value DPG is limited to the upper limit duty value DPG, the ECU 51 increases the calculated fuel injection amount TAU by the purge correction value FHPG.

Therefore, for example, it is assumed that the engine 8 is accelerated from the steady operation state, the intake air amount Q supplied to the engine 8 changes, and the opening of the purge control valve 22 increases. At this time, the rate of change of the opening degree of the purge control valve 22, that is, the rate of change of the duty value DPG is equal to the upper limit duty value DPGMX.
By being limited to G, the flow rate of the fuel vapor supplied to the engine 8 is limited to a flow rate according to the upper limit duty value DPGMXG. Then, instead of adjusting the air-fuel ratio of the combustible air-fuel mixture by increasing and correcting the flow rate of the fuel vapor supplied to the engine 8, the amount of fuel supplied from each injector 7, that is, the fuel injection amount TAU is purge corrected. The air-fuel ratio is adjusted by performing the increase correction based on the value FHPG. For this reason, even if there is a response delay in the fuel purged from the canister 14 to the intake passage 10 with respect to the change in the opening degree of the purge control valve 22, regardless of the delay,
The air-fuel ratio of the combustible mixture of the engine 8 is quickly adjusted toward the target air-fuel ratio. That is, the purge control valve 22 itself has an unavoidable operation delay,
Even if there is an inevitable response delay in the purge fuel due to the length of the path 1, etc., the air-fuel ratio is quickly and suitably adjusted regardless of the delay. As a result, the purge control valve 2
2, the air-fuel ratio of the engine 8 can be stably adjusted irrespective of the response delay in the adjustment of the purge fuel flow rate. In this sense, the control accuracy of the air-fuel ratio in the engine 8 can be improved.

According to this embodiment, in order to adjust the actual air-fuel ratio in the engine 8 to the target air-fuel ratio, the ECU
51 increases the opening of the purge control valve 22 in accordance with the increase in the intake air amount Q. Then, the ECU 51 sets the purge control valve 22
The duty value DPG is “100%” except when the rate of change of the duty value DPG related to the opening of the motor is larger than a predetermined value.
Only when the fuel injection amount TAU reaches the purge correction value FH
Increase correction is performed based on PG. Therefore, the duty value DP
When G does not reach “100%”, the fuel injection amount TAU is increased and corrected only when there is a possibility that the response to the fuel purge is delayed. For this reason, unnecessary increase correction in the fuel injection amount TAU can be suppressed as much as possible, and at the same time, fuel vapor can be used efficiently.

According to this embodiment, the ECU 51 calculates the air-fuel ratio correction value FAF based on the air-fuel ratio obtained based on the detection result of the oxygen sensor 46. The ECU 51 performs feedback control of the air-fuel ratio of the combustible mixture by correcting the fuel injection amount TAU based on the correction value FAF. Thus, the actual air-fuel ratio of the combustible mixture can be accurately converged to the target air-fuel ratio.

According to this embodiment, the ECU 51 learns the concentration learning value FGHPG of the fuel vapor purged from the canister 14 to the intake passage 10 based on the air-fuel ratio obtained based on the detection result of the oxygen sensor 46. ECU 51
Reflects the concentration learning value FGHPG in the calculation of the purge correction value FHPG used for increasing the fuel injection amount TAU. Therefore, a more appropriate fuel injection amount TAU according to the operating state of the engine 8 can be calculated, and the air-fuel ratio of the engine 8 can be adjusted more appropriately.

The present invention can be embodied in another embodiment as follows. In the following embodiments,
The same operation and effect as those of the above embodiment can be obtained. (1) In the above embodiment, the air-fuel ratio correction value FAF is calculated based on the oxygen concentration Ox detected by the oxygen sensor 46. The fuel injection amount TAU is calculated based on the air-fuel ratio correction value FAF.
, The air-fuel ratio in the engine 8 is feedback-controlled. On the other hand, without correcting the fuel injection amount TAU based on the air-fuel ratio correction value FAF, that is, without performing feedback control of the air-fuel ratio,
The air-fuel ratio may be controlled.

(2) In the above embodiment, the canister 14
Has two atmospheric valves 16 and 18, but these valves 16 and 18 may be omitted and the canister 14 may be provided with only a hole communicating with the atmosphere. In this case, the hole communicating with the atmosphere serves as the air introduction part of the present invention.

Further, in addition to those described in the claims,
The technical ideas that can be grasped from the above embodiments will be described below together with their effects. (A) In the invention according to claim 1, an air-fuel ratio detecting means for detecting an air-fuel ratio of the combustible air-fuel mixture;
Wherein the control means further performs feedback control of the fuel supply means based on the detected air-fuel ratio.

According to this configuration, the actual air-fuel ratio can be made to converge to the target air-fuel ratio. (B) In the invention as set forth in claim 1, an air-fuel ratio detecting means for detecting an air-fuel ratio of the combustible air-fuel mixture, and a concentration of the fuel vapor processed by the processing means based on the detected air-fuel ratio. An air-fuel ratio control device for an internal combustion engine, further comprising: learning means for learning the value; and reflection means for reflecting the learned concentration to a correction amount that is increased and corrected by the correction means.

According to this configuration, the air-fuel ratio of the internal combustion engine can be more appropriately adjusted by reflecting the result of learning the concentration of the fuel vapor in the correction amount.

[0118]

According to the first aspect of the present invention, the internal combustion engine is configured to add the fuel vapor generated in the fuel tank to the combustible mixture supplied from the fuel supply unit to the internal combustion engine by the processing unit. Is assumed. Then, the amount of fuel to be supplied to the internal combustion engine is calculated based on the operating state of the internal combustion engine so that the air-fuel ratio of the combustible mixture becomes the target air-fuel ratio, and the fuel supply means is controlled based on the calculated supplied fuel amount. I do. The flow rate of the fuel vapor to be supplied to the internal combustion engine is calculated based on the operating state of the internal combustion engine, and the opening of the flow control valve is controlled based on the calculated flow rate. Further, an upper limit value for the rate of change of the opening degree of the regulating valve is set, and when the rate of change is restricted to the upper limit value, the calculated supplied fuel amount is increased and corrected.

Therefore, when the rate of change of the opening of the regulating valve is limited to the upper limit value, the air-fuel ratio is adjusted by increasing the amount of fuel vapor supplied to the internal combustion engine. The air-fuel ratio is adjusted by increasing the amount of fuel supplied to the engine. For this reason, the air-fuel ratio of the combustible air-fuel mixture is quickly adjusted toward the target air-fuel ratio regardless of the presence or absence of the fuel vapor supply delay. As a result, it is possible to stably adjust the air-fuel ratio regardless of the response delay of the change in the amount of fuel to be purged.

[Brief description of the drawings]

FIG. 1 is a basic conceptual configuration diagram according to a first invention.

FIG. 2 is a schematic configuration diagram showing an air-fuel ratio control device for an internal combustion engine.

FIG. 3 is a block circuit diagram showing an ECU.

FIG. 4 is a flowchart showing a “fuel purge control routine”.

FIG. 5 is a flowchart showing a continuation of FIG. 4;

FIG. 6 is a flowchart showing a continuation of FIG. 5;

FIG. 7 is a flowchart illustrating a “first calculation routine”;

FIG. 8 is a flowchart showing a continuation of FIG. 7;

FIG. 9 is a flowchart showing a continuation of FIG. 8;

FIG. 10 is a flowchart showing a “second calculation routine”.

FIG. 11 is a flowchart showing a continuation of FIG. 10;

FIG. 12 is a flowchart showing a continuation of FIG. 11;

FIG. 13 is a flowchart showing a “fuel injection control routine”.

FIG. 14 is a time chart showing the behavior of various parameters.

FIG. 15 is a schematic configuration diagram showing a conventional air-fuel ratio control device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Fuel tank, 7 ... Injector as fuel supply means, 8 ... Engine as internal combustion engine, vapor line 1
3, 14: canister, 21: purge line (13, 1)
Reference numerals 4 and 21 constitute processing means. ), 22: a purge control valve as a regulating valve, 43: an intake air sensor, 45: a rotational speed sensor, 46: an oxygen sensor (43, 45, 46 constitute operating state detecting means), 51: an ECU (51) Are the first calculation means, the first control means, the second calculation means, the second
, Control means, limiting means and correction means. ).

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) F02D 41/00-41/40 F02M 25/08

Claims (1)

(57) [Claims] 1. An air-fuel ratio control device for controlling an air-fuel ratio of a combustible mixture of fuel and air supplied to an internal combustion engine, comprising: fuel supply means for supplying fuel to the internal combustion engine. Processing means for flowing fuel vapor generated in a fuel tank for storing the fuel to the internal combustion engine for processing, and adjusting a flow rate of fuel vapor supplied to the internal combustion engine through the processing means. An operating valve for detecting an operating state of the internal combustion engine; and detecting the amount of fuel to be supplied to the internal combustion engine so that an air-fuel ratio of the combustible mixture becomes a target air-fuel ratio. First calculation means for calculating based on the operating state to be performed; first control means for controlling the fuel supply means based on the calculated supplied fuel amount; and supply to the internal combustion engine. Rube A second calculating means for calculating a flow rate of the fuel vapor based on the detected operating state; and a second calculating means for controlling an opening of the regulating valve based on the calculated flow rate of the fuel vapor. Control means, an upper limit value related to a rate of change of the opening degree of the regulating valve to be controlled, limiting means for limiting the rate of change to the set upper limit value, and the rate of change by the limiting means. An air-fuel ratio control device for an internal combustion engine, comprising: a correction unit for increasing and correcting the calculated supplied fuel amount when the amount is limited.