JPH10212992A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To purge fuel collected by a canister with a good efficiency, in an air-fuel ratio control device of an internal combustion engine provided with the canister for collecting evaporation fuel generated in a fuel tank. SOLUTION: In an air-fuel ratio control device for an internal combustion engine, a fuel injection valve 33 for injecting fuel into the internal combustion engine is provided, and a canister 40 for collecting evaporation fuel generated in a fuel tank 34 is arranged. A surge tank 36 and the canister 40 are communicated with each other through a purge control valve 38. An intake side air-fuel ratio sensor 35 is arranged downstream from the surge tank 36. The purge control valve 38 and the fuel injection valve 33 are controlled so as to set the air-fuel ratio of mixture supplied to the combustion chamber 24, and so as to supply fuel collected by the canister 40 into the internal combustion engine preferentially.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly to an air-fuel ratio control for an air-fuel mixture supplied to an internal combustion engine having a canister for capturing fuel vapor generated in a fuel tank. The present invention relates to an air-fuel ratio control device for an internal combustion engine suitable as a device.

[0002]

2. Description of the Related Art Conventionally, for example, Japanese Patent Application Laid-open No.
As disclosed in Japanese Patent No. 54, there is known an internal combustion engine including a canister for capturing fuel vapor generated in a fuel tank. The conventional internal combustion engine includes a purge control valve that controls a conduction state between the canister and the intake passage,
A fuel injection valve for injecting fuel into the intake passage, and O ₂ for detecting oxygen concentration in exhaust gas flowing through the exhaust passage
It has a sensor.

[0003] During operation of the internal combustion engine, an intake negative pressure is generated in the intake passage. The intake negative pressure generated in the intake passage is guided to the canister by opening the purge control valve. The fuel captured by the canister is purged into the intake passage by introducing the intake negative pressure to the canister. Therefore, in the above-described conventional internal combustion engine, fuel corresponding to the opening of the purge control valve is purged from the canister into the inside of the intake passage.

[0004] The oxygen concentration in the exhaust gas flowing through the exhaust passage becomes leaner as the air-fuel mixture supplied to the internal combustion engine becomes richer in fuel, and becomes richer as the air-fuel mixture becomes leaner in fuel. Therefore, according to the conventional internal combustion engine, the air-fuel ratio of the air-fuel mixture can be detected based on the output signal of the O ₂ sensor.

[0005] The conventional internal combustion engine controls the purge control valve and the fuel injection valve such that the air-fuel ratio of the air-fuel mixture detected based on the output signal of the O ₂ sensor matches the target air-fuel ratio. Therefore, according to the conventional internal combustion engine, the fuel trapped in the canister can be appropriately purged while the air-fuel ratio of the air-fuel mixture matches the target air-fuel ratio.

[0006]

The canister is saturated by capturing a given volume of fuel. When the canister is saturated, the canister cannot capture the evaporated fuel generated in the fuel tank thereafter. Therefore, in order to efficiently capture the evaporated fuel and consume it as fuel, it is desirable that the canister not be saturated.

To prevent the canister from being saturated,
During operation of the internal combustion engine, it is effective to promptly purge fuel trapped in the canister into the intake passage. Therefore, in order to efficiently capture the evaporated fuel and consume it as fuel, it is desirable that a large amount of fuel be purged from the canister during operation of the internal combustion engine.

However, in the above-mentioned conventional internal combustion engine, a control method for similarly increasing or decreasing the amount of fuel injected from the fuel injection valve and the amount of fuel purged from the canister based on the air-fuel ratio of the air-fuel mixture. Is used. That is, in the above-described conventional internal combustion engine, even in a situation where a larger amount of fuel can be purged, the target fuel is purged together with the fuel purged from the canister and the fuel injected from the fuel injection valve. A control method for supplying fuel for achieving a fuel ratio is used. In this regard, the above-described conventional internal combustion engine leaves room for further enhancing the capability of capturing the evaporated fuel.

[0009] The present invention has been made in view of the above-mentioned points, and has been made in comparison with the fuel injected by the fuel injection valve.
It is an object of the present invention to provide an air-fuel ratio control device for an internal combustion engine that exhibits excellent performance with respect to capturing and effectively utilizing evaporated fuel by preferentially supplying fuel purged from a canister to the internal combustion engine. I do.

[0010]

The above object is achieved by the present invention.
In an air-fuel ratio control device for an internal combustion engine that controls an air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine, a fuel injection valve that injects fuel to the internal combustion engine and an evaporative fuel generated in a fuel tank are provided. A purge control valve for controlling a conduction state between an intake passage of the internal combustion engine and the canister; an air-fuel ratio detecting means for detecting an air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine; and the air-fuel ratio detection. Based on the air-fuel ratio detected by the means, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine becomes a predetermined air-fuel ratio, and the fuel captured by the canister is supplied to the internal combustion engine preferentially. As described above, the present invention is achieved by an air-fuel ratio control device for an internal combustion engine including the purge control valve and the air-fuel ratio control means for controlling the fuel injection valve.

In the present invention, the evaporated fuel generated in the fuel tank is captured by the canister and then purged into the intake passage during operation of the internal combustion engine. The amount of fuel purged from the canister into the intake passage changes according to the amount of fuel captured by the canister and the opening of the purge control valve. The air-fuel ratio control means controls the air-fuel ratio of the mixture supplied to the internal combustion engine to a predetermined air-fuel ratio by controlling the purge control valve and the fuel injection valve. At this time, the air-fuel ratio control means controls the purge control valve and the fuel injection valve so that the fuel in the canister is preferentially supplied to the internal combustion engine. When the canister and the fuel injection valve are controlled as described above, a large amount of fuel can be efficiently purged from the canister to the intake passage.

[0012] The object of the present invention is as described in claim 2.
The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the air-fuel ratio control unit is configured to perform a process when the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine is richer than a predetermined air-fuel ratio.
An injection amount reducing means for preferentially reducing the amount of fuel injected from the fuel injection valve as compared to the fuel purged from the canister; and an air-fuel ratio of a mixture supplied to the internal combustion engine having a predetermined air-fuel ratio Purge amount increasing means for preferentially increasing the amount of fuel purged from the canister in comparison with the amount of fuel injected from the fuel injection valve when the fuel is leaner than that of the internal combustion engine. This is also achieved by the air-fuel ratio control device.

In the present invention, when the air-fuel mixture supplied to the internal combustion engine is rich in fuel, the amount of fuel injected from the fuel injection valve is preferentially reduced. When the mixture supplied to the internal combustion engine is lean, the amount of fuel purged from the canister is preferentially increased. According to the above process, the purge amount of the fuel captured by the canister is controlled to the maximum value that does not make the air-fuel ratio fuel-rich, and the amount of fuel injected from the fuel injection valve reduces the air-fuel ratio. It is controlled to the minimum value that does not make the fuel lean.

According to a third aspect of the present invention, in the air-fuel ratio control device for an internal combustion engine according to any one of the first and second aspects, the air-fuel ratio detecting means is disposed in the intake passage. An air-fuel ratio control device for an internal combustion engine, which is provided with an intake-side air-fuel ratio sensor that outputs a signal corresponding to a ratio between an amount of air flowing through the intake passage and an amount of fuel purged from the canister, This is effective in accurately controlling the air-fuel ratio while purging a large amount of fuel from the canister.

In the present invention, the air-fuel ratio sensor detects an air-fuel ratio of an air-fuel mixture formed by air sucked into the intake passage and fuel purged from the canister. The air-fuel ratio sensor is provided in the intake passage. Therefore, the air-fuel ratio sensor accurately detects the above-described air-fuel ratio with excellent responsiveness. When a large amount of fuel is purged from the canister to the internal combustion engine, a large change occurs in the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine with a change in the purge amount. In the present invention, it is possible to quickly detect a change in the purge amount and perform the air-fuel ratio control with excellent responsiveness.

[0016]

FIG. 1 is a system configuration diagram of an internal combustion engine 10 equipped with an air-fuel ratio control device according to one embodiment of the present invention. The internal combustion engine 10 includes an electronic control unit 12
(Hereinafter, referred to as ECU 12).
The internal combustion engine 10 includes a cylinder block 14.
A water jacket 16 is provided on the cylinder block 14.
Are formed. Cooling water circulates inside the water jacket 16 during operation of the internal combustion engine 10.

The cylinder block 14 is provided with a water temperature sensor 18 such that its tip is exposed to the water jacket 16. The water temperature sensor 18 outputs an electric signal corresponding to the cooling water temperature THW. Water temperature sensor 1
The output signal of 8 is supplied to the ECU 12. ECU
12 calculates the coolant temperature THW based on the signal supplied from the coolant temperature sensor 18.

A piston 20 is slidably disposed inside the cylinder block 14. A cylinder head 22 is fixed to an upper portion of the cylinder block 14. Inside the internal combustion engine 10, the inner wall of the cylinder block 14, the upper surface of the piston 20, and the cylinder head 22
A combustion chamber 24 is separated by a bottom surface of the combustion chamber.

The cylinder head 22 is formed with an intake port 26 and an exhaust port 24 communicating with the combustion chamber 24. In addition, the cylinder head 22 incorporates an intake valve 30 and an exhaust valve 31 that make the intake port 26 and the exhaust port 28 conductive or shut off.

The intake port 26 has an intake manifold 3
Two are communicating. The intake manifold 32 is provided with a fuel injection valve 33 that injects fuel into the intake manifold 32.
The fuel injection valve 33 is provided corresponding to each cylinder of the internal combustion engine 10. Fuel is supplied from a fuel tank 34 to the fuel injection valve 33 at a predetermined pressure. Fuel injection valve 33
The valve is opened only while the drive signal is being supplied from the ECU 12, and fuel is injected at a predetermined pressure into the intake manifold 32 from the tip thereof. In the intake manifold 32, the valve opening time of the fuel injection valve 33, that is, the ECU 12
Injects an amount of fuel corresponding to the time length of the drive signal supplied to the fuel injection valve 33 from the. Hereinafter, this time length is referred to as a fuel injection time TAU.

The intake manifold 32 is provided with an intake-side air-fuel ratio sensor 35. Intake side air-fuel ratio sensor 35
Is provided with an oxygen concentration sensor for outputting an electric signal corresponding to the oxygen concentration, and a heater for heating the oxygen concentration sensor. The intake-side air-fuel ratio sensor 35 is provided with a through hole (not shown) for guiding the air flowing through the intake manifold 32 to around the oxygen concentration sensor.

The heater of the intake air-fuel ratio sensor 35 always heats the oxygen concentration sensor while the internal combustion engine 10 is operating. Therefore, when a mixture of air and fuel is introduced around the oxygen concentration sensor, the mixture burns around the oxygen concentration sensor. When the air-fuel mixture burns around the oxygen concentration sensor, an oxygen concentration corresponding to the air-fuel ratio of the air-fuel mixture is generated around the oxygen concentration sensor. And the oxygen concentration sensor
An electric signal corresponding to the oxygen concentration is output. Therefore, according to the output signal of the oxygen concentration sensor, that is, the output signal of the intake-side air-fuel ratio sensor 35, the air-fuel ratio of the air-fuel mixture flowing inside the intake manifold 32 can be detected.
The output signal of the intake-side air-fuel ratio sensor 35 is supplied to the ECU 12. The ECU 12 includes an intake-side air-fuel ratio sensor 35.
, The air-fuel ratio of the air-fuel mixture flowing through the intake manifold 32 is detected.

The intake manifold 32 includes a surge tank 3
It communicates with 6. A purge passage 37 communicates with the surge tank 36. A purge control valve 38 is provided in the purge passage 37. The purge control valve 38 is a valve mechanism that controls the conduction state of the purge passage 37, and the ECU 1
2 is driven by duty. The ECU 12 supplies a drive signal having an appropriate duty ratio to the purge control valve 38. The purge control valve 38 realizes an opening according to the duty ratio.

The other end of the purge passage 37 is connected to a canister 40.
The fuel purge holes 42 communicate with each other. Canister 40
Has an activated carbon 44 therein. Further, the canister 40 has an air introduction hole 46 on the side opposite to the fuel purge hole 42 with the activated carbon 44 interposed therebetween, for opening the internal space of the canister 40 to the atmosphere. Further, the canister 40
Is on the same side as the fuel purge hole 42 with respect to the activated carbon 44,
A vapor introduction hole 48 is provided. A vapor passage 49 communicating with the fuel tank 34 communicates with the vapor introduction hole 48. The vapor passage 49 communicates with the fuel tank 34 at a position always above the liquid level of the fuel.

An intake pipe 50 communicates with the surge tank 36. A throttle valve 52 that operates in conjunction with an accelerator pedal is provided inside the intake pipe 50. A throttle opening sensor 54 that outputs an electric signal corresponding to the opening TA of the throttle valve 52 is provided near the throttle valve 52. The output signal of the throttle opening sensor 54 is supplied to the ECU 12. E
The CU 12 detects the throttle opening TA based on a signal supplied from the throttle opening sensor 54. Also,
When a signal indicating that the throttle valve 52 is fully closed is supplied from the throttle opening sensor 54, the ECU 12 determines that the internal combustion engine 10 is in an idle operation.

At the end of the intake pipe 50, an air filter 56 is provided.
Are in communication. The air filtered by the air filter 58 flows through the intake pipe 50. The surge tank 36 is provided with an intake pressure sensor 58 that outputs an electric signal corresponding to the internal pressure. Inside the surge tank 36,
A pressure is generated according to the amount of intake air that is taken into the internal combustion engine 10 through the intake pipe 50. The output signal of the intake pressure sensor 58 is supplied to the ECU 12. The ECU 12 detects an intake air amount Q of the internal combustion engine 10 based on an output signal of the intake pressure sensor 58.

An exhaust manifold 60 communicates with the exhaust port 28 of the internal combustion engine 10. Exhaust manifold 6
0 is provided with an O ₂ sensor 62. The O ₂ sensor 62 outputs an electric signal corresponding to the oxygen concentration in the exhaust gas. The oxygen concentration in the exhaust gas becomes leaner as the air-fuel ratio A / F of the air-fuel mixture supplied to the internal combustion engine 10 becomes richer, and becomes richer as the air-fuel ratio A / F becomes leaner.

The O ₂ sensor 62 outputs a high signal of about 0.9 V when the air-fuel ratio A / F of the mixture supplied to the internal combustion engine 10 is richer than the stoichiometric air-fuel ratio SA / F. And the air-fuel ratio A / F is the stoichiometric air-fuel ratio S−A /
When the fuel is leaner than F, a low signal of about 0.1 V is output. The output signal of the O ₂ sensor 62 is
12 are provided. The ECU 12 includes an O ₂ sensor 62
, It is determined whether the air-fuel ratio A / F of the air-fuel mixture is rich or lean.

The internal combustion engine 10 has a crank angle sensor 64 for detecting the rotation angle of the crank shaft. The crank angle sensor 64 generates a reference signal each time the rotation angle of the crankshaft reaches a predetermined rotation angle, and generates a pulse signal each time the crankshaft rotates by a predetermined rotation angle. The output signal of the crank angle sensor 64 is supplied to the ECU 12. The ECU 12 includes a crank angle sensor 64
The engine speed NE and the rotation angle of the internal combustion engine 10 are detected on the basis of the output signal supplied from.

In the system of the present embodiment, for example, immediately after the internal combustion engine 10 is stopped,
Evaporated fuel is generated when the vehicle is stopped in a high-temperature environment, or when the vehicle is traveling on a congested road in a high-temperature environment. Evaporated fuel generated inside the fuel tank 34 is guided to the canister 40 through a vapor passage 49,
Then, it is adsorbed on activated carbon 44.

The ECU 12 appropriately opens the purge control valve 38 when the internal combustion engine 10 is operating in a predetermined operating state. During the operation of the internal combustion engine 10, an intake negative pressure is generated inside the surge tank 36. Therefore, when the purge control valve 38 is opened as described above, the purge passage 37
, The intake negative pressure is guided to the fuel purge hole 42 of the canister 40.

When an intake negative pressure is introduced into the fuel purge hole 42 of the canister 40, the internal pressure of the canister 40 becomes negative pressure, and air is sucked into the canister 40 from the air introduction hole 46. The air flowing from the air introduction hole 46 passes through the activated carbon 44 and flows from the fuel purge hole 42 to the purge passage 37. The fuel adsorbed on the activated carbon 44 separates from the activated carbon 44 when the air passes through the activated carbon 44, and is purged together with the air into the purge passage 37.

The fuel discharged from the canister 40 into the purge passage 37 as described above flows into the surge tank 36 and is then drawn into the combustion chamber 24 together with the air drawn from the air filter 58. Therefore, according to the system of the present embodiment, after the fuel vapor generated in the fuel tank 34 is temporarily captured by the canister 40, it can be effectively consumed as fuel during the operation of the internal combustion engine 10.

By the way, in a situation where a vehicle equipped with the internal combustion engine 10 is traveling on a congested road in a high temperature environment,
A large amount of evaporated fuel is likely to be continuously supplied to the canister 34. If such a situation continues without the fuel trapped in the canister 40 being purged, the canister 40 eventually becomes saturated, and the evaporated fuel cannot be captured by the canister 40. Therefore, in order to efficiently capture and consume the evaporated fuel as fuel, it is necessary to prevent the canister 40 from reaching a saturated state.

In order to prevent the canister 40 from being saturated, it is effective to quickly purge the fuel trapped in the canister 40 during the operation of the internal combustion engine 10. In the present embodiment, during operation of the internal combustion engine 10, the fuel in the canister 40 is purged in preference to injecting fuel from the fuel injection valve 33. Therefore, according to the internal combustion engine 10, a large amount of fuel trapped in the canister 40 can be promptly purged to effectively prevent the canister 40 from becoming saturated.

The above functions are realized by the ECU 12 executing an injection amount control routine shown in FIG. 2 and a purge control routine shown in FIG. Hereinafter, the contents of the processing executed by the ECU 12 to realize the above functions in the internal combustion engine 10 will be described.

FIG. 2 shows that the ECU 12 determines the fuel injection time TAU.
Is a flowchart of an example of an injection amount control routine executed to calculate the injection amount. The routine shown in FIG.
0 is an NE interrupt routine that is started each time a predetermined rotation angle is rotated. When this routine is started, first, the process of step 90 is executed.

In step 90, a reference fuel injection time TAUmn is calculated based on the operating state of the internal combustion engine 10. In this step 90, the reference fuel injection time TA
Umn is specifically calculated based on the engine speed NE, the intake pressure PM, the coolant temperature THW, and the like. The reference fuel injection time TAUmn is used to set the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 24 to a target air-fuel ratio corresponding to the operating state of the internal combustion engine 10 in a state where fuel is not purged from the canister 40. Is the injection time corresponding to the amount of fuel required.
When the process of step 90 is completed, the process proceeds to step 92.
Is performed.

In step 92, the fuel injection time TAU is calculated. In this step 92, the fuel injection time T
AU is calculated by multiplying the reference fuel injection time TAUmn by an injection time correction coefficient K. The injection time correction coefficient K is a variable whose upper limit is 1.0, and is calculated in a purge control routine described later. When the process of step 92 ends, the current routine ends.

FIG. 3 shows a flowchart of an example of a purge control routine executed by the ECU 12. FIG.
Is an NE interruption routine that is started each time the internal combustion engine 10 rotates by a predetermined rotation angle. When the routine shown in FIG. 3 is started, first, the process of step 100 is executed.

In step 100, it is determined whether a predetermined purge condition is satisfied in the internal combustion engine 10. In step 100, it is determined that the purge condition is satisfied when the temperature THW of the cooling water of the internal combustion engine 10 is 80 ° C. or higher and the intake-side air-fuel ratio sensor 35 is activated. By the way, the intake-side air-fuel ratio sensor 35
After the internal combustion engine 10 is started, it is heated by a built-in heater and activated to output a voltage signal of a predetermined value or more. For this reason, the ECU 12 determines that the intake-side air-fuel ratio sensor 35 is activated when a voltage signal of a predetermined value or more is output from the intake-side air-fuel ratio sensor 35. If it is determined in step 100 that the purge condition is satisfied, the process of step 102 is executed next.

In step 102, a target value Vt is calculated. The target value Vt is a voltage value output from the intake-side air-fuel ratio sensor 35 when a mixture having a target air-fuel ratio according to the operating state of the internal combustion engine 10 flows around the intake-side air-fuel ratio sensor 35. A matching value. Internal combustion engine 10
Is determined in accordance with the engine speed NE and the intake pressure PM. Therefore, the target value Vt uniquely determined with respect to the target air-fuel ratio is also different from the engine speed N.
It can be determined based on E and the intake pressure PM.

FIG. 4 shows that the target value V
4 shows an example of a map referred to when calculating t. EC
U12 stores therein a two-dimensional map relating to the target value Vt shown in FIG. In step 102, the target value Vt is calculated based on the engine speed NE and the intake pressure PM by referring to a map shown in FIG. When the processing in step 102 is completed, the processing in step 104 is executed next.

In step 104, it is determined whether or not the output signal Vox of the intake air-fuel ratio sensor 35 is equal to or higher than the target value Vt. Output signal Vox of intake side air-fuel ratio sensor 35
Becomes larger as the air-fuel ratio of the air-fuel mixture flowing therearound is leaner than the target air-fuel ratio. Therefore, Vox
If ≧ Vt is satisfied, it can be determined that the air-fuel ratio of the air-fuel mixture flowing around the intake-side air-fuel ratio sensor 35 is leaner than the target air-fuel ratio.

In the internal combustion engine 10, a mixture of air sucked from the air filter 56, air and fuel sucked from the purge passage 37 flows around the intake-side air-fuel ratio sensor 35. Therefore, in step 104 above,
If it is determined that Vox ≧ Vt holds (the mixture is lean), the amount of fuel purged from the canister 40 is insufficient with respect to the amount of fuel for achieving the target air-fuel ratio. It can be determined that there is. In this case, following step 104, the process of step 106 is executed.

In step 106, the duty ratio DUTY of the drive signal supplied to the purge control valve 38 is set to 10
It is determined whether it is 0% or more, that is, whether the purge control valve 38 has already been fully opened. As a result, when it is determined that DUTY ≧ 100% is satisfied, it can be determined that the amount of fuel purged from the canister 40 has already reached the maximum value. In this case, the process of step 108 is performed thereafter.

In step 108, a process for setting the duty ratio DUTY of the drive signal to 100% is executed. When the process of step 108 is completed, the process proceeds to step 110.
Is performed. In the processing after step 110, as described above, the amount of fuel purged from the canister 40 has reached the maximum value, and the amount of fuel is insufficient for achieving the target air-fuel ratio. Is performed under certain circumstances. Under such circumstances, in order to set the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 24 to the target air-fuel ratio, it is necessary to compensate for the shortage of fuel by the fuel injection valve 33.

In step 110, first, a deviation ΔV = Vox−Vt between the output signal Vox of the intake air-fuel ratio sensor 35 and the target value Vt is calculated to realize the above function. When the process of step 110 is completed, the process proceeds to step 112
Is performed. FIG. 5 shows an intake-side air-fuel ratio sensor 35.
And the air-fuel ratio of the air-fuel mixture flowing around
The relationship with the deviation ΔV calculated with 0 is shown. As shown in FIG. 5, the deviation ΔV is determined as the air-fuel ratio of the air-fuel mixture flowing around the intake-side air-fuel ratio sensor 35 becomes leaner than the target air-fuel ratio, that is, the amount of fuel purged from the canister 40. Becomes larger as the amount of fuel for achieving the target air-fuel ratio becomes insufficient. Therefore, the deviation ΔV
Can be grasped as a characteristic value of the amount of fuel to be injected from the fuel injection valve 33 to achieve the target air-fuel ratio.

In step 112, a calculation process of the injection time correction coefficient K is executed based on the deviation ΔV. As described above, the injection time correction coefficient K is a coefficient that is multiplied by the reference fuel injection time TAUmn when calculating the fuel injection time TAU. In this step 112, the injection time correction coefficient K is calculated specifically with reference to the map shown in FIG.

FIG. 6 shows the injection time correction in relation to the deviation ΔV.
4 shows an example of a map in which a coefficient K is determined. As shown in FIG.
The injection time correction coefficient K is such that the deviation ΔV has its maximum value “Vox
_MAX-Vt "approaches the maximum value" 1.0 "
Stipulated. Vox _MAXIs the intake air-fuel ratio
The maximum value of the voltage signal output from the
When air flows around the intake-side air-fuel ratio sensor 35,
This is the value of the voltage signal output by the intake air-fuel ratio sensor 35.
You.

When the injection time correction coefficient K is calculated according to the map shown in FIG. 6, the larger the deviation ΔV, the more the reference fuel injection time TAUmn is set to the upper limit value, and
Can be set for a long time. Further, the smaller the deviation ΔV, the shorter the fuel injection time TAU can be set, that is, the smaller the amount of fuel injected from the fuel injection valve 33 can be.

In step 114, a process for driving the purge control valve 38 with the drive duty ratio DUTY set in the current processing cycle is executed. According to the above-described processing routine, the execution of step 114 causes the purge control valve 38 to be controlled to the fully open state. When the process of step 114 ends, the current routine ends.

As described above, according to the internal combustion engine 10, even if the purge control valve 38 is fully opened, the fuel required for realizing the target air-fuel ratio cannot be purged from the canister 40, the fuel cannot be supplied. The fuel injection time T is set so that the fuel is injected from the injection valve 33 in an amount to compensate for the shortage.
The AU can be set. For this reason, the internal combustion engine 10
According to this, even under such circumstances, the air-fuel ratio of the air-fuel mixture sucked into the combustion chamber 24 can be accurately controlled to the target air-fuel ratio.

In this routine, at step 106, D
If it is determined that UTY ≧ 100% is not satisfied, the fuel injection valve 33 is increased by further increasing the opening of the purge control valve 38, that is, by further increasing the amount of fuel purged from the canister 40. It can be determined that there is a possibility that fuel for realizing the target air-fuel ratio can be secured without injecting fuel from the fuel cell. In this case, the process of step 116 is executed next.

In step 116, a process for increasing the drive duty ratio DUTY of the purge control valve 38 by a predetermined value ΔD is executed. When the process of step 116 ends, the process of step 118 is executed next. In step 118, processing for setting the injection time correction coefficient K to "0" is performed. When the injection time correction coefficient K is set to “0”, the fuel injection time TAU is calculated to be “0” in the injection amount control routine shown in FIG. Therefore, when the process of step 118 is executed, the supply of fuel by the fuel injection valve 33 is stopped thereafter. This step 118
Is performed, the process of step 114 is then performed.

At step 114, the predetermined value Δ
The purge control valve 38 is controlled at the drive duty ratio DUTY increased by D. According to the above processing, the amount of fuel purged from the canister 40 can be increased toward the amount of fuel for achieving the target air-fuel ratio.

As described above, according to the internal combustion engine 10, when it is determined that the air-fuel mixture is lean under the condition that the purge control valve 38 is not fully opened, the fuel is not injected from the fuel injection valve 33, The amount of fuel is increased by increasing the opening of the purge control valve 38. For this reason, according to the internal combustion engine 10, a large amount of fuel captured by the canister 40 can be quickly and rapidly purged during the operation of the internal combustion engine 10.

In this routine, at step 104, V
If it is determined that ox ≧ Vt is not established, the air-fuel ratio of the air-fuel mixture flowing around the intake-side air-fuel ratio sensor 35 is richer than the target air-fuel ratio, that is, the canister 4
From 0, it can be determined that the amount of fuel being purged is excessive for achieving the target air-fuel ratio. In this case, in order to achieve the target air-fuel ratio, it is necessary to reduce the amount of fuel purged from the canister 40 while stopping the fuel injection from the fuel injection valve 33. In this case, in the present routine, the process of step 120 is executed after step 104.

In step 120, a process for reducing the drive duty ratio DUTY of the purge control valve 38 by a predetermined value ΔD is executed. When the processing in step 120 is completed, the processing in steps 118 and 114 is performed, and then the current routine is terminated.

According to the above-described process, when the amount of fuel to be purged is excessive, the fuel injection from the fuel injection valve 33 is stopped, and the purge control valve is controlled until the amount of fuel to be purged becomes appropriate. 38 can be reduced. Therefore, according to the internal combustion engine 10, when a large amount of fuel is captured inside the canister 40, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 24 is accurately controlled to the target air-fuel ratio while the canister 40 is controlled. Quickly captures the fuel captured by
In addition, a large amount can be purged.

In this routine, if it is determined in step 100 that the purge condition is not satisfied, it can be determined that the fuel should not be purged from the canister 40. In this case, the ECU 12 executes the processing of step 122 following step 100.

In step 122, the drive duty ratio D
A process for setting UTY to “0” is executed. This step 1
When the process of step S22 ends, the process of step S124 is executed. In step 124, the injection time correction coefficient K
Is set to the maximum value “1.0”. When the process of step 124 is performed, the reference fuel injection time TAUmn is calculated as the fuel injection time TAU in the injection amount control routine shown in FIG. Step 12
When the process of step 4 is completed, the process of step 114 is performed, and then the current routine is terminated.

According to the above-described processing, when the purge condition is not satisfied, the purge control valve 38 is fully closed, and all of the fuel necessary for achieving the target air-fuel ratio is supplied from the fuel injection valve 33. Can be supplied. As mentioned above,
According to the internal combustion engine 10, the canister 40 is set so that the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 24 becomes the target air-fuel ratio and that the fuel is injected from the fuel injection valve 33.
The fuel injection valve 33 and the purge control valve 38 are controlled such that the fuel trapped in the fuel cell is purged. For this reason,
According to the internal combustion engine 10, the fuel trapped in the canister 40 can be efficiently purged, and the canister 40 can be effectively prevented from becoming saturated.

In this embodiment, the drive duty ratio DUTY of the purge control valve 38 and the injection time correction coefficient K
Is calculated based on the output signal of the intake air-fuel ratio sensor 35 as described above. In a system such as the internal combustion engine 10 having an O ₂ sensor also on the exhaust manifold 60 side, it is also possible to calculate the drive duty ratio DUTY and the injection time correction coefficient K using the output signal of the O ₂ sensor 60. .

However, the part where the fuel captured by the canister 40 is purged toward the internal combustion engine 10,
That is, the portion where the purge passage 37 opens into the surge tank 36 and the O ₂ sensor 62 are largely separated. Therefore, after the amount of fuel purged from the canister 40 changes, there is a certain delay time before the effect of the change is reflected on the output signal of the O ₂ sensor 62.

On the other hand, the intake-side air-fuel ratio sensor 35 is disposed near a portion where the purge passage 37 opens into the surge tank 35. Therefore, when the amount of fuel purged from the canister 40 changes, the change quickly changes to O _2.
This is reflected in the output signal of the sensor 62. Therefore, by calculating the drive duty ratio DUTY and the injection time correction coefficient K based on the output signal of the intake-side air-fuel ratio sensor 35 as in the system of the present embodiment, the air-fuel ratio can be improved with excellent responsiveness. Control can be performed.

As described above, the O ₂ sensor 62 is connected to the combustion chamber 2.
A high-level signal or a low-level signal is output according to whether the air-fuel mixture supplied to 4 is lean or rich compared to the stoichiometric air-fuel ratio S / A / F. Therefore, according to the O ₂ sensor 62, it is possible to more accurately determine whether the air-fuel mixture is fuel-lean or fuel-rich as compared with the intake-side air-fuel ratio sensor 35. In this embodiment, the ECU
12 executes the routine shown in FIG. 3 based on the output signal of the air-fuel ratio sensor 35 on the intake side while the O ₂ sensor 62
Is output to the control of the fuel injection valve 33 and the control of the purge control valve 38. For this reason, according to the internal combustion engine 10, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 24 can be controlled extremely accurately.

In this embodiment, when the fuel for achieving the target air-fuel ratio cannot be covered only by the fuel purged from the canister 40, the shortage is compensated by the fuel injection valve 33. However, the method of filling the shortage is not limited to this. For example, a heater may be provided inside the fuel tank 34, and when the purge fuel is insufficient, a large amount of fuel vapor may be generated inside the fuel tank 34 by heating the heater. Further, a communication line for directly communicating the internal combustion engine 10 with the fuel tank 34 may be provided, and when the purge fuel is insufficient, the evaporated fuel may be directly sucked from the communication line.

In the above embodiment, the air-fuel ratio sensor 35 on the intake side is the "air-fuel ratio detecting means" according to the first aspect.
The "air-fuel ratio control means" according to claim 1 is realized by the ECU 12 executing the injection amount control routine shown in FIG. 2 and the purge control routine shown in FIG. In the above-described embodiment, the ECU 12 executes the processing of steps 106 to 112, and the “injection amount reducing means” according to claim 2 executes the processing of steps 106 and 116. The "purge amount increasing means" according to claim 2 is realized respectively.

Next, a second embodiment of the present invention will be described with reference to FIG. FIG.
In the system configuration shown in FIG.
And the purge control routine shown in FIG. 7 is executed instead of the routine shown in FIG.

The routine shown in FIG. 7 is a flowchart of an example of a control routine executed by the ECU 12 to control the purge control valve 38 and calculate the injection time correction coefficient K in the system of the present embodiment. The control routine shown in FIG. 7 is an NE interrupt routine that is started every time the internal combustion engine 10 rotates by a predetermined rotation angle. In FIG. 7, steps that execute the same processing as the steps shown in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted.

In the routine shown in FIG. 7, if it is determined in step 100 that the purge condition is satisfied, the process of step 130 is executed. Step 1
If it is determined that the purge condition is not satisfied in 00, then the processing of step 122 and thereafter, which will be described later, is executed.

In step 130, it is determined whether or not "1" is set in the saturation flag f. As will be described later, the saturation flag f is a flag that is set to “1” when it is estimated that a large amount of fuel is trapped inside the canister 40 so that the canister 40 is saturated. The saturation flag f is reset to “0” by initial processing when the internal combustion engine 10 is started. Therefore,
Immediately after the start of the internal combustion engine 10, it is determined that "1" is not set in the saturation flag f. In this case, the processing after step 102 is executed thereafter.

At step 104 in the routine shown in FIG.
If it is determined that Vox ≧ Vt is satisfied, that is, if it is determined that the amount of fuel purged from the canister 40 is insufficient compared with fuel for achieving the target air-fuel ratio, The same processing as the routine shown in FIG. 3 is executed. On the other hand, in step 104, Vox ≧ V
If t is not satisfied, that is, if it is determined that the amount of fuel purged from the canister 40 is excessive compared to the fuel for achieving the target air-fuel ratio, step 1
After the end of the process of step 20, the process of step 132 is executed.

In step 132, it is determined whether the drive duty ratio DUTY of the purge control valve 38 is larger than a predetermined value α%. When a large amount of fuel is captured inside the canister 40, a large amount of fuel is purged from the canister 40 to the internal combustion engine 10 by only slightly opening the purge control valve 38. Further, when the internal combustion engine 10 is operating at a low load such as an idle state, the amount of fuel required to achieve the target air-fuel ratio becomes extremely small. Therefore, when a large amount of fuel is captured by the canister 40 and the internal combustion engine 10 is operating at a low load,
In some cases, the duty ratio DUTY of the drive signal to be applied to the purge control valve 38 to achieve the target air-fuel ratio becomes an extremely small value.

Α% used as the determination value in step 132 is the minimum DUTY at which the purge control valve 38 can be accurately driven. Therefore, when the drive duty ratio DUTY exceeds the predetermined value α, the opening degree of the purge control valve 38 is accurately controlled and the canister 40
The amount of fuel purged from the fuel cell can be accurately controlled. For this reason, if it is determined in step 132 that DUTY> α is satisfied, the processes of steps 118 and 114 are executed thereafter in the same manner as in the first embodiment.

On the other hand, when the drive duty ratio DUTY is equal to or less than α%, the opening of the purge control valve 38 cannot be accurately controlled. Therefore, in such a situation, the amount of fuel purged from the canister 40 to the internal combustion engine 10 cannot be accurately controlled by controlling the purge control valve 38. In the present embodiment, in step 132, D
If it is determined that UTY> α is not satisfied, the process of step 134 is executed next.

At step 134, "1" is set to the saturation flag f to indicate that the canister 40 is saturated. When the processing of step 134 is completed,
Thereafter, after the processes of steps 122 and 124 are executed, the current routine is terminated.

According to the above-described processing, when the canister 40 is saturated and the internal combustion engine 10 is operating at a low load, the fuel injection valve is prevented from being purged from the canister 40. The fuel can be appropriately supplied to the internal combustion engine 10 from the internal combustion engine 33. Therefore, according to the system of the present embodiment, even in such a situation,
The operating state of the internal combustion engine 10 can be maintained at an appropriate state.

After the saturation flag f is set to "1" in step 134, this routine is started.
In step 130, it is determined that f = 1 is established. In this case, the process of step 136 is executed following step 130. In step 136, it is determined whether a predetermined high-speed and high-load condition is satisfied in the internal combustion engine 10. In this step 136, when the internal combustion engine 10 is operating in a state of requesting fuel exceeding a predetermined amount, it is determined that the predetermined high-speed high-load condition is satisfied.

If it is determined that the predetermined high-speed, high-load condition is not satisfied, it can be determined that the drive duty ratio DUTY for purging the required fuel has an extremely small value. In this case, it is determined that the purge control should not be resumed, and thereafter, the processing of step 122 and subsequent steps is executed, and then the current routine is terminated.

On the other hand, if it is determined in step 136 that the high-speed / high-load condition is satisfied, it can be determined that the drive duty ratio DUTY for purging the required fuel has a sufficiently large value. In this case, the process of step 138 is executed next to restart the purge control.

In step 138, step 136 is performed.
Then, it is determined whether or not a predetermined time has elapsed after it is determined that the high-speed and high-load condition is satisfied, that is, whether or not the predetermined time has elapsed after the purge control is restarted.
As a result, when it is determined that the predetermined time has not elapsed, it can be determined that a large amount of fuel is still captured in the canister 40, that is, it is determined that the saturated state of the canister 40 has not been eliminated. In this case, following step 138, the processing of step 102 and thereafter is executed.

On the other hand, if it is determined in step 138 that the predetermined time has elapsed, it can be determined that the saturation state of the canister 40 has already been restarted by restarting the purge control. In this case, the process of step 140 is performed next.

In step 140, a process for resetting the saturation flag f to "0" is executed. This step 1
When this routine is started again after the processing of step 40 is executed, it is determined in step 130 that f = 1 is not established. When the processing in step 140 is completed, the processing in step 102 and thereafter is executed.

According to the above-described processing, even when the internal combustion engine 10 is operating at a low load, accurate purge control can be executed when the canister 40 is not saturated. When the internal combustion engine 10 is operating at a low load and the canister 40 is in a saturated state, the execution of the inaccurate purge control is prohibited, and the fuel injection valve 33 is operated.
Can be used to supply fuel. Further, when the internal combustion engine 10 satisfies a high-speed and high-load condition after the canister 40 is saturated, the saturated state of the canister 40 can be eliminated while executing accurate purge control. Therefore, according to the system of the present embodiment, the internal combustion engine 1
Regardless of the operation state of 0, the fuel in the canister 40 can be efficiently purged in a wide operation range while always accurately controlling the air-fuel ratio.

In the above embodiment, the ECU 12
7 together with the injection amount control routine shown in FIG.
The “air-fuel ratio control means” according to claim 1 is realized by executing the processing of the middle steps 100 to 124. In the above-described embodiment, the ECU 12 executes the processing of steps 106 to 112, and the “injection amount reducing means” according to claim 2 executes the processing of steps 106 and 116. The "purge amount increasing means" according to claim 2 is realized respectively.

[0088]

As described above, according to the first and second aspects of the present invention, a large amount of fuel trapped in the canister can be efficiently purged. Therefore, according to the air-fuel ratio control device of the present invention, it is possible to effectively prevent the canister from becoming saturated.

Further, according to the present invention, while purging a large amount of fuel from the canister toward the intake passage, the purge amount can be detected accurately and with excellent responsiveness. it can. Therefore, the air-fuel ratio control apparatus according to the present invention can control the air-fuel ratio with excellent accuracy while purging a large amount of fuel from the canister to the internal combustion engine.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of an internal combustion engine corresponding to a first embodiment of the present invention.

FIG. 2 is a flowchart of an example of an injection amount control routine executed in the internal combustion engine according to the first embodiment of the present invention.

FIG. 3 is a flowchart of an example of a purge control routine executed in the internal combustion engine according to the first embodiment of the present invention.

FIG. 4 is an example of a map of a target value Vt referred to during execution of a purge control routine shown in FIG. 3;

FIG. 5 shows an output signal Vox and a target value V of an intake air-fuel ratio sensor.
FIG. 9 is a characteristic diagram showing a deviation ΔV from the relationship between the target air-fuel ratio and the concentration of the air-fuel mixture.

FIG. 6 is an example of a map of an injection time correction coefficient K referred to during execution of a purge control routine shown in FIG. 3;

FIG. 7 is a flowchart of an example of a purge control routine executed in the internal combustion engine according to the second embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 10 internal combustion engine 12 electronic control unit (ECU) 35 intake-side air-fuel ratio sensor 38 purge control valve 40 canister 34 fuel tank TAU fuel injection time TAUmn standard fuel injection time K injection time correction coefficient DUTY purge control valve drive duty ratio Vt target Value Vox Output value of intake-side air-fuel ratio sensor ΔV deviation α DUT that can accurately control the purge control valve
Lower limit of Y

Claims (3)

[Claims] 1. An air-fuel ratio control device for an internal combustion engine for controlling an air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine, comprising: a fuel injection valve for injecting fuel into the internal combustion engine; A purge control valve for controlling a conduction state between an intake passage of the internal combustion engine and the canister; an air-fuel ratio detecting unit for detecting an air-fuel ratio of a mixture of air and fuel; and the air-fuel ratio detecting unit. Based on the detected air-fuel ratio, the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine becomes a predetermined air-fuel ratio, and the fuel captured by the canister is supplied to the internal combustion engine preferentially. Air-fuel ratio control means for controlling the purge control valve and the fuel injection valve. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein said air-fuel ratio control means determines that an air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine is richer than a predetermined air-fuel ratio. An injection amount reducing means for preferentially reducing an amount of fuel injected from the fuel injection valve compared to fuel purged from the canister; and an air-fuel ratio of an air-fuel mixture supplied to the internal combustion engine having a predetermined air-fuel ratio. Purge amount increasing means for preferentially increasing the amount of fuel purged from the canister in comparison with the amount of fuel injected from the fuel injection valve when the fuel is lean relative to the fuel ratio. An air-fuel ratio control device for an internal combustion engine. 3. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein said air-fuel ratio detecting means is provided in said intake passage, and flows through said intake passage. An air-fuel ratio control device for an internal combustion engine, comprising: an intake-side air-fuel ratio sensor that outputs a signal corresponding to a ratio between the amount of air to be purged and the amount of fuel purged from the canister.