JPH11343913A - Air-fuel ratio controller for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To warm catalysts in an early stage by supplying unburned oxygen and unburned fuel in the catalysts and reacting them without a rich/lean operation of each cylinder or a forced rich/lean switching operation every predetermined time during the warming condition of the catalysts. SOLUTION: This controller comprises a fuel injection valve 7 for supplying fuel to an intake port of an internal combustion engine, a catalyst converter 12 arranged in an exhaust passage of the internal combustion engine, and an O2 sensor 13 for detecting the air-fuel ratio. Prior to activating the catalysts, i.e., before the temperature of the catalyst converter 12 is increased to the active temperature, the air-fuel ratio is remained lean and the unburned oxygen is increased, while the fuel injection time during the valve opening of an intake valve 17 is longer than that after activating the catalysts so as to increase the unburned fuel.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an air-fuel ratio control device for an internal combustion engine.

[0002]

2. Description of the Related Art Conventionally, in order to quickly raise the temperature of a three-way catalyst disposed in an exhaust passage of an internal combustion engine to an activation temperature after starting the internal combustion engine, that is, to warm up the three-way catalyst, 2. Description of the Related Art There is known an air-fuel ratio control device for an internal combustion engine that supplies unburned fuel and unburned oxygen remaining in a main catalyst and reacts them. An example of this type of air-fuel ratio control device for an internal combustion engine is disclosed in, for example, Japanese Patent Application Laid-Open No. 62-178740. The air-fuel ratio control device for an internal combustion engine described in Japanese Patent Application Laid-Open No. Sho 62-178740 has a plurality of cylinders, and performs rich operation in one cylinder to supply unburned fuel to a three-way catalyst. At the same time, the three-way catalyst is warmed up by supplying unburned oxygen to the three-way catalyst by performing a lean operation in another cylinder.

[0003]

However, Japanese Unexamined Patent Publication No. Sho 62
In the case of the air-fuel ratio control device for an internal combustion engine described in Japanese Patent No. 178740, it is necessary to perform the rich operation in one cylinder and the lean operation in the other cylinder during the warm-up period of the three-way catalyst. Since it is necessary to perform different air-fuel ratio control for each cylinder, the air-fuel ratio control becomes complicated.

[0004] Air-fuel ratio control of an internal combustion engine that can supply unburned fuel and unburned oxygen to the three-way catalyst to warm up the three-way catalyst without having to perform different air-fuel ratio control for each cylinder. An example of the device is described in, for example, Japanese Patent Application Laid-Open No. 5-33705. The air-fuel ratio control device for an internal combustion engine described in Japanese Patent Application Laid-Open No. 5-33705 has a rich operation for supplying unburned fuel to the three-way catalyst and a lean operation for supplying unburned oxygen to the three-way catalyst. Are forcibly switched and executed at predetermined time intervals to warm up the three-way catalyst.

However, in the case of the air-fuel ratio control apparatus for an internal combustion engine described in Japanese Patent Application Laid-Open No. 5-33705, it is necessary to switch between rich operation and lean operation during the warm-up period of the three-way catalyst. That is, since it is necessary to change the air-fuel ratio control every predetermined time, the air-fuel ratio control is still complicated.

[0006] In view of the above problems, the present invention eliminates the need for performing rich operation in one cylinder and performing lean operation in another cylinder during the warm-up period of the catalyst. The present invention provides an air-fuel ratio control device for an internal combustion engine that can supply unburned fuel and unburned oxygen to a catalyst and warm up the catalyst without having to forcibly switch and execute the process every predetermined time. Aim.

[0007]

According to the first aspect of the present invention, a fuel injection means for supplying fuel to an internal combustion engine, a catalyst disposed in an exhaust passage of the internal combustion engine, and an air-fuel ratio are detected. In the air-fuel ratio control device of the internal combustion engine including the air-fuel ratio detection means, before the catalyst is activated before the temperature of the catalyst rises to the activation temperature, while maintaining the air-fuel ratio lean,
An air-fuel ratio control device for an internal combustion engine is provided, wherein the amount of unburned fuel reaching the catalyst is increased after the activation of the catalyst.

According to the first aspect of the present invention, the air-fuel ratio control device for an internal combustion engine increases the amount of unburned fuel reaching the catalyst before the catalyst is activated while maintaining the air-fuel ratio lean before the catalyst is activated. It is possible to supply both unburned fuel and oxygen to the catalyst while maintaining a constant fuel ratio, that is, without having to change the air-fuel ratio, and therefore to warm up the catalyst early.

According to the second aspect of the present invention, the fuel injection means supplies fuel to the intake port of the internal combustion engine, and the fuel injection means supplies the fuel before the catalyst is activated, that is, before the catalyst temperature rises to the activation temperature. The air-fuel ratio detected by the fuel ratio detecting means is maintained lean to increase unburned oxygen, and the unburned fuel reaching the catalyst is increased by increasing the fuel injection time during the opening period of the intake valve from after activation of the catalyst. An air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the amount of fuel is increased.

According to the third aspect of the present invention, the air-fuel ratio control apparatus for an internal combustion engine according to the second aspect of the present invention is characterized in that the fuel injection end timing is delayed before the activation of the catalyst as compared with after the activation of the catalyst. Provided.

The air-fuel ratio control device for an internal combustion engine according to the second and third aspects supplies unburned oxygen remaining to the catalyst by maintaining the air-fuel ratio lean before the catalyst is activated. Further, by increasing the fuel injection time during the opening period of the intake valve before the catalyst is activated and after the catalyst is activated, the amount of fuel that is not sufficiently mixed with the intake air in the intake port is increased, and the unburned fuel remaining on the catalyst is increased. Supply fuel. Therefore, it is not necessary to change the air-fuel ratio, and only by extending the fuel injection time during the opening period of the intake valve, the unburned oxygen and the unburned fuel supplied to the catalyst are reacted, and the catalyst is quickly warmed up. can do.

According to a fourth aspect of the present invention, there is provided an intake valve, an exhaust valve, and a variable valve timing device capable of changing a valve overlap period during which the intake valve and the exhaust valve are both opened. 3. The air-fuel ratio control device for an internal combustion engine according to claim 2, wherein the valve overlap period is made longer before the catalyst is activated and the amount of unburned fuel is increased by increasing the valve overlap period. .

[0013] The air-fuel ratio control device for an internal combustion engine according to claim 4 further increases the amount of fuel flowing through the combustion chamber of the internal combustion engine by making the valve overlap period longer before the catalytic activity than after the catalytic activity. Then, unburned fuel remaining in the catalyst is supplied to the catalyst. As a result, the catalyst is warmed up even earlier.

According to a fifth aspect of the present invention, there is provided an intake valve, an exhaust valve, and a variable valve timing device capable of changing a valve overlap period during which the intake valve and the exhaust valve are both opened. Before the catalyst is activated before the temperature of the catalyst rises to the activation temperature, the air-fuel ratio detected by the air-fuel ratio detection means is maintained lean to increase unburned oxygen, and the valve overflows after the catalyst is activated. 2. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the amount of unburned fuel reaching the catalyst is increased by lengthening the lap period to increase the amount of unburned fuel blow-through. .

According to the sixth aspect of the invention, the air-fuel ratio control apparatus for an internal combustion engine according to the fifth aspect, wherein the exhaust valve closing timing is delayed before the activation of the catalyst compared with after the activation of the catalyst. Is provided.

According to a seventh aspect of the present invention, there is provided the air-fuel ratio control apparatus for an internal combustion engine according to the fifth aspect, wherein the fuel injection means directly injects fuel into a cylinder of the internal combustion engine. Is done.

According to an eighth aspect of the present invention, there is provided the air-fuel ratio control apparatus for an internal combustion engine according to the fifth aspect, wherein the fuel injection means injects fuel to an intake port of the internal combustion engine. You.

The air-fuel ratio control device for an internal combustion engine according to the fifth to eighth aspects supplies the unburned oxygen remaining on the catalyst by maintaining the air-fuel ratio lean before the catalyst is activated. Further, the amount of fuel flowing through the combustion chamber of the internal combustion engine is increased by making the valve overlap period longer before the catalyst activation than after the catalyst activation, and unburned fuel remaining on the catalyst is supplied. Therefore, the unburned oxygen and the unburned fuel supplied to the catalyst can react with each other only by extending the valve overlap period without changing the air-fuel ratio, and the catalyst can be warmed up at an early stage.

[0019]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is an overall schematic diagram showing a first embodiment of an air-fuel ratio control apparatus for an internal combustion engine according to the present invention. In FIG. 1, an air flow meter 3 is provided in an intake passage 2 of an engine body 1. The air flow meter 3 directly measures the amount of intake air, and has a built-in potentiometer to generate an analog voltage output signal proportional to the amount of intake air. This output signal is supplied to the A / D converter 101 with a built-in multiplexer of the control circuit 10. The distributor 4 has its shaft converted to, for example, a crank angle of 72.
A crank angle sensor 5 for generating a reference position detection pulse signal every 0 ° and a crank angle sensor 6 for generating a reference position detection pulse signal every 30 ° in terms of crank angle are provided. The pulse signals of these crank angle sensors 5 and 6 are supplied to the input / output interface 102
And the output of the crank angle sensor 6 is C
It is supplied to the interrupt terminal of the PU 103.

Further, the intake passage 2 is provided with a fuel injection valve 7 for supplying pressurized fuel from a fuel supply system to an intake port for each cylinder. The water jacket 8 of the cylinder block of the engine body 1 is provided with a water temperature sensor 9 for detecting the temperature of the cooling water. The water temperature sensor 9 generates an analog voltage electric signal corresponding to the cooling water temperature THW. This output is also supplied to the A / D converter 101.

The exhaust system downstream of the exhaust manifold 11 has a catalytic converter 12 containing a three-way catalyst for simultaneously purifying three harmful components HC, CO and NOx in the exhaust gas.
Is provided. In the present embodiment, the catalyst contained in the catalytic converter 12 is a three-way catalyst, but in other embodiments, the catalyst contained in the catalytic converter is not limited to a three-way catalyst. Returning to the description of the present embodiment, the exhaust manifold 11, that is, on the upstream side of the catalytic converter 12,
An O ₂ sensor 13 is provided. The O ₂ sensor 13 generates an electric signal corresponding to the concentration of the oxygen component in the exhaust gas.
That is, the O ₂ sensor 13 generates a different output voltage to the A / D converter 101 by the control circuit 10 depending on whether the air-fuel ratio is lean or rich with respect to the stoichiometric air-fuel ratio. Further, the temperature sensor 16 arranged in the catalytic converter 12 generates an output voltage that differs depending on the catalyst temperature of the catalytic converter 12 to the A / D converter 101 by the control circuit 10.

The control circuit 10 is configured as, for example, a microcomputer, and includes an A / D converter 101, an input / output interface 102, a CPU 103, and a ROM 10
4, a RAM 105, a backup RAM 106, a clock generation circuit 107, and the like.

In the control circuit 10, the down counter 108, the flip-flop 109, and the driving circuit 1
Reference numeral 10 is for controlling the fuel injection valve 7. That is, when the control circuit 10 calculates the fuel injection amount TAU, the fuel injection amount TAU is preset in the down counter 108 and the flip-flop 109 is also set. As a result, the drive circuit 110 starts energizing the fuel injection valve 7. On the other hand, when the down counter 108 counts a clock signal (not shown) and its carry-out terminal finally becomes "1" level, the flip-flop 1
09 is set, and the drive circuit 110 stops energizing the fuel injection valve 7. That is, the fuel injection valve 7 is energized by the above-described fuel injection amount TAU, so that an amount of fuel corresponding to the fuel injection amount TAU is sent to the combustion chamber of the engine body 1.

A variable valve timing device 19 connected to a drive circuit 111 is provided to change the valve timing of the intake valve 17 and the exhaust valve 18. The variable valve timing device 19 changes the valve timing of the intake valve 17 and the exhaust valve 18 so that the intake valve 17
The valve overlap period during which both the exhaust valve 18 and the exhaust valve 18 are open can be changed.

The CPU 103 generates an interrupt at A
For example, when the A / D conversion of the / D converter 101 is completed, when the input / output interface 102 receives a pulse signal of the crank angle sensor 6, or when an interrupt signal from the clock generation circuit 107 is received. The intake air amount data Q and the cooling water temperature data THW of the air flow meter 3 are taken in by an A / D conversion routine executed at predetermined time intervals, and are taken into RA.
It is stored in a predetermined area of M105. That is, the RAM 10
5, the data Q and THW are updated every predetermined time. The rotation speed data Ne is calculated by an interruption of the crank angle sensor 6 at every 30 ° CA, and is stored in the RAM.
105 is stored in a predetermined area.

Hereinafter, an air-fuel ratio control method by the air-fuel ratio control device for an internal combustion engine according to the present embodiment will be described. FIG. 2 is a flowchart showing the air-fuel ratio control method of the present embodiment. The air-fuel ratio control device of the internal combustion engine executes the air-fuel ratio control shown in FIG. 2 at a predetermined cycle. As shown in FIG. 2, when starting the air-fuel ratio control, the air-fuel ratio control device for the internal combustion engine first determines in step 201 whether the air-fuel ratio control feedback control condition is satisfied, that is, the output value of the O ₂ sensor It is determined whether or not to determine the fuel injection amount TAU based on this. When the determination is NO, the process proceeds to step 202, where the intake air amount Q and the engine speed N are determined based on the output value of the O ₂ sensor.
e, and calculates a fuel injection amount TAU based on a predetermined air-fuel ratio correction coefficient FAF stored in the RAM in advance.
The fuel of the calculated fuel injection amount TAU is injected, and this routine ends. On the other hand, when the determination is YES, the process proceeds to step 203.

In step 203, the air-fuel ratio control device for the internal combustion engine determines whether the catalyst temperature Tb of the catalytic converter is at a temperature suitable for executing step 205 described below, that is, whether the unburned fuel and the unburned fuel It is determined whether or not the catalyst temperature is appropriate for warming up the catalytic converter by supplying oxygen to the catalytic converter and causing it to react. When the catalyst temperature Tb is equal to or lower than the predetermined threshold TbL and the unburned fuel and the unburned oxygen cannot react properly in the catalytic converter, the process proceeds to step 204. Further, the catalyst temperature Tb is equal to or higher than a predetermined threshold TbH, and the catalyst temperature Tb is equal to the activation temperature Tb.
Since bH has been reached, the process also proceeds to step 204 when there is no need to warm up the catalytic converter. On the other hand, Tb
If L <Tb <TbH and it is necessary to warm up the catalytic converter, the routine proceeds to step 205.

In step 204, the air-fuel ratio control device of the internal combustion engine performs normal F / B control, that is, O ₂
The fuel injection amount T is set so that the output value of the sensor indicates the stoichiometric air-fuel ratio.
AU is calculated, the fuel of the calculated fuel injection amount TAU is injected, and this routine ends. In step 204, the fuel injection end timing is set so that the injected fuel is appropriately burned. That is, the fuel injection is terminated before the intake valve is opened so that the injected fuel and the intake air are sufficiently mixed in the intake port.

On the other hand, in step 205, the air-fuel ratio control device for the internal combustion engine performs a lean operation, that is, O ₂
The fuel injection amount TAU is calculated so that the output value of the sensor does not indicate the stoichiometric air-fuel ratio but indicates lean. By performing the lean operation, unburned oxygen remaining after combustion in the combustion chamber can be supplied to the catalytic converter. Subsequently, in step 206, the fuel injection end timing is delayed from that in step 204 so that the fuel injection end timing is during the opening period of the intake valve, and this routine ends. According to step 206, fuel that is injected during the opening of the intake valve and is not sufficiently mixed with the intake air can be supplied into the combustion chamber. As a result, unburned fuel remaining unburned during combustion in the combustion chamber can be supplied. And the unburned fuel can be supplied to the catalytic converter. By reacting the unburned fuel and unburned oxygen supplied to the catalytic converter to generate heat, the catalytic converter can be warmed up.

FIG. 3 is a graph showing the relationship between the fuel injection end timing and the unburned fuel amount according to the present embodiment. As shown in FIG. 3, when the fuel injection end timing is delayed, that is, when the fuel injection is ended during the opening period of the intake valve, the unburned fuel amount is determined in the normal F / B control, that is, It is larger than the unburned fuel amount when the fuel injection is terminated before the opening operation of the intake valve.

FIG. 4 is a graph showing the effect of the warm-up of this embodiment. As shown in FIG. 4, when Step 204 similar to the conventional normal F / B control is executed, that is, when Step 205 and Step 206 are not supplied much to the catalytic converter, Steps 205 and 206 are performed. At the time of execution, that is, when unburned fuel and unburned oxygen are supplied to the catalytic converter, the catalyst temperature rises earlier.

As described above, in the present embodiment, the fuel injection is terminated before the opening operation of the intake valve in step 204, and the fuel injection is terminated during the opening period of the intake valve in step 206. . However, in order to achieve the same effect as the above-described effect in the modification of the present embodiment, the fuel injection amount during the opening period of the intake valve before the activation of the catalyst only needs to be larger than that after the activation of the catalyst. The present invention is not limited to the fuel injection ending timing.

Hereinafter, a second embodiment of the air-fuel ratio control apparatus for an internal combustion engine according to the present invention will be described. The configuration of the present embodiment is the same as the configuration of the first embodiment shown in FIG.
FIG. 5 is a flowchart showing the air-fuel ratio control method of the present embodiment. In FIG. 5, the same steps as those in FIG. 2 described above are denoted by the same reference numerals, and description thereof will be omitted. That is, the air-fuel ratio control method of the present embodiment differs from the air-fuel ratio control method of the first embodiment in steps 204 'and 506.

In step 204 ', the air-fuel ratio control device for the internal combustion engine performs the normal F / B control as in the first embodiment.
The control is performed, that is, the fuel injection amount TAU is calculated so that the output value of the O ₂ sensor indicates the stoichiometric air-fuel ratio, the fuel of the calculated fuel injection amount TAU is injected, and this routine ends. In step 204 ', a valve overlap period during which both the intake valve and the exhaust valve are opened is set so that the injected fuel is appropriately burned. That is, the valve overlap period is set so that the injected fuel does not flow into the exhaust passage.

In step 506, the air-fuel ratio control device of the internal combustion engine delays the exhaust valve closing timing from step 204 'to extend the valve overlap period so that the injected fuel flows through the exhaust passage, This routine ends. According to step 506, unburned fuel that has blown through the combustion chamber and has not been burned in the combustion chamber can be supplied to the catalytic converter. By reacting the unburned fuel and unburned oxygen supplied to the catalytic converter to generate heat, the catalytic converter can be warmed up.

FIG. 6 is a graph showing the relationship between the exhaust valve closing timing and the amount of unburned fuel in this embodiment. As shown in FIG. 6, when the exhaust valve closing timing is delayed, that is, when the valve overlap period is lengthened, the amount of unburned fuel that has blown out is determined by the normal F / B control, that is, the normal valve overflow. It is larger than the unburned fuel amount when set during the lap period.

FIG. 7 is a graph showing the effect of the warm-up of this embodiment. As shown in FIG. 7, when Step 204 ′ similar to the conventional normal F / B control is executed, that is, when Steps 205 and 506 are not supplied much to the catalytic converter, unburned fuel and unburned oxygen are not supplied. When you execute
That is, the catalyst temperature rises earlier when unburned fuel and unburned oxygen are supplied to the catalytic converter.

Although the fuel injection valve 7 of this embodiment supplies fuel to the intake port, as a modification of this embodiment, fuel is supplied directly to the cylinder instead of the fuel injection valve 7. Even when the fuel injection valve is provided, the same effects as those described above can be obtained.

Hereinafter, a third embodiment of the air-fuel ratio control apparatus for an internal combustion engine according to the present invention will be described. The configuration of the present embodiment is the same as the configuration of the first embodiment shown in FIG.
FIG. 8 is a flowchart showing the air-fuel ratio control method of the present embodiment. 8, the same steps as those in FIG. 2 described above are denoted by the same reference numerals, and description thereof will be omitted. In other words, the air-fuel ratio control method of the present embodiment is different from the first embodiment in that step 204 ″ is incorporated instead of step 204, and that step 506 similar to that of the second embodiment is incorporated after step 206. It is different from the air-fuel ratio control method of the embodiment.

In step 204 ″, the air-fuel ratio control device for the internal combustion engine performs the normal F / B control as in the first embodiment.
The control is performed, that is, the fuel injection amount TAU is calculated so that the output value of the O ₂ sensor indicates the stoichiometric air-fuel ratio, the fuel of the calculated fuel injection amount TAU is injected, and this routine ends. In step 204 ", the fuel injection end timing and the valve overlap period are set so that the injected fuel burns properly. That is, the injected fuel and the intake air are sufficiently mixed in the intake port. The fuel injection is terminated before the intake valve is opened so that the fuel is mixed, and the valve overlap period is set so that the injected fuel does not flow into the exhaust passage.

The air-fuel ratio control device for the internal combustion engine performs step 2
At step 06, the fuel injection end timing is delayed from step 204 ″ so that the fuel injection end timing is during the opening period of the intake valve. At step 206, the fuel is injected during the intake valve opening period and the intake air is sufficiently supplied. Unmixed fuel can be supplied into the combustion chamber.
In step 6, the exhaust valve closing timing is delayed to extend the valve overlap period from step 204 "so that the injected fuel blows into the exhaust passage, and the valve overlap period is ended. This routine is terminated. Unburned fuel left unburned during combustion can be generated and the unburned fuel can be supplied to the catalytic converter.Step 506 further removes unburned fuel that has blown through the combustion chamber and has not been burned in the combustion chamber. As a result, the unburned fuel and unburned oxygen supplied to the catalytic converter react with each other to generate heat, so that the catalytic converter can be warmed up. According to the embodiment, since more unburned fuel can be supplied to the catalytic converter than in the first and second embodiments, the three-way catalyst is warmed up more quickly. Rukoto can.

As described above, in the present embodiment, the fuel injection is terminated before the intake valve is opened in step 204 ″, and the fuel injection is terminated during the intake valve opening period in step 206. However, in order to achieve the same effect as the above-described effect in the modification of the present embodiment, it is sufficient that the fuel injection amount during the opening period of the intake valve before the catalyst is activated is larger than that after the catalyst is activated. In addition, in the internal combustion engine having the fuel injection valve having a constant injection speed (the amount of fuel injected per unit time), the intake air before the catalyst is activated is not limited to the above-described fuel injection end timing. If the fuel injection time during the valve opening period is longer than after the activation of the catalyst, the same effects as those described above can be obtained.

Although the fuel injection valve 7 of this embodiment supplies fuel to the intake port, as a modification of this embodiment, fuel is supplied directly to the cylinder instead of the fuel injection valve 7. It is also possible to provide a fuel injection valve.

Incidentally, in all the embodiments described above,
Although the O ₂ sensor is used to detect the air-fuel ratio, in other embodiments, any known air-fuel ratio detecting means such as an A / F sensor can be used.

[0046]

According to the first aspect of the invention, it is possible to supply both unburned fuel and oxygen to the catalyst while maintaining the air-fuel ratio constant, that is, without changing the air-fuel ratio. Therefore, the catalyst can be warmed up early.

According to the second and third aspects of the present invention, it is not necessary to change the air-fuel ratio, and only by extending the fuel injection time during the intake valve opening period, the unburned oxygen supplied to the catalyst can be reduced. By reacting with unburned fuel, the catalyst can be warmed up early. In detail, during the warm-up period of the catalyst, it is not necessary to perform rich operation in one cylinder and lean operation in another cylinder, and forcibly switch between rich operation and lean operation at predetermined time intervals. Unburned fuel remaining unburned can be supplied to the catalyst, and the amount of fuel that is not sufficiently mixed with the intake air in the intake port can be increased to supply unburned fuel remaining unburned to the catalyst. as a result,
The unburned oxygen and unburned fuel supplied to the catalyst are caused to react with each other, so that the catalyst can be warmed up at an early stage.

According to the fourth aspect of the present invention, it is possible to increase the amount of fuel flowing through the combustion chamber of the internal combustion engine and supply unburned fuel remaining on the catalyst. As a result, the catalyst can be warmed up even earlier.

According to the invention as set forth in claims 5 to 8, the unburned oxygen and the unburned fuel supplied to the catalyst are reacted only by extending the valve overlap period without changing the air-fuel ratio. At the very least, the catalyst can be warmed up early. In detail, during the warm-up period of the catalyst, it is not necessary to perform rich operation in one cylinder and lean operation in another cylinder, and forcibly switch between rich operation and lean operation at predetermined time intervals. Unburned unburned fuel can be supplied to the catalyst and the amount of fuel flowing through the combustion chamber of the internal combustion engine can be increased, and unburned fuel remaining in the catalyst can be supplied. As a result, the unburned oxygen and the unburned fuel supplied to the catalyst react with each other, and the catalyst can be warmed up at an early stage.

[Brief description of the drawings]

FIG. 1 is an overall schematic diagram showing a first embodiment of an air-fuel ratio control device for an internal combustion engine of the present invention.

FIG. 2 is a flowchart illustrating an air-fuel ratio control method according to the first embodiment.

FIG. 3 is a graph showing a relationship between a fuel injection end timing and an unburned fuel amount according to the first embodiment.

FIG. 4 is a graph showing a warming-up effect of the first embodiment.

FIG. 5 is a flowchart illustrating an air-fuel ratio control method according to a second embodiment.

FIG. 6 is a graph showing a relationship between an exhaust valve closing timing and an unburned fuel amount according to the second embodiment.

FIG. 7 is a graph showing a warming-up effect of the second embodiment.

FIG. 8 is a flowchart illustrating an air-fuel ratio control method according to a third embodiment.

[Explanation of symbols]

7 ... fuel injection valves 10 ... control circuit 12 ... catalytic converter 13 ... O ₂ sensor 16 ... Temperature sensor

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI F02D 13/02 F02D 13/02 J 41/06 305 41/06 305 330 330A 41/14 310 41/14 310A 41/34 41 / 34 F

Claims (8)

[Claims] 1. An air-fuel ratio control device for an internal combustion engine, comprising: fuel injection means for supplying fuel to the internal combustion engine; a catalyst disposed in an exhaust passage of the internal combustion engine; and air-fuel ratio detection means for detecting an air-fuel ratio. In the method, before the temperature of the catalyst rises to the activation temperature, before the catalyst is activated, the amount of unburned fuel reaching the catalyst is increased from that after the catalyst is activated while maintaining the air-fuel ratio lean. Air-fuel ratio control device for internal combustion engine. 2. The air-fuel ratio detected by the air-fuel ratio detecting means before the catalyst is activated, that is, before the temperature of the catalyst rises to an activation temperature, wherein the fuel injection means supplies fuel to an intake port of the internal combustion engine. To increase the amount of unburned fuel that reaches the catalyst by maintaining the lean and increasing the unburned oxygen and increasing the fuel injection time during the intake valve opening period after the activation of the catalyst. An air-fuel ratio control device for an internal combustion engine according to claim 1. 3. The air-fuel ratio control device for an internal combustion engine according to claim 2, wherein the fuel injection end timing is delayed before the catalyst is activated and after the catalyst is activated. 4. An intake valve, an exhaust valve, and a variable valve timing device capable of changing a valve overlap period during which the intake valve and the exhaust valve are both opened, wherein the variable valve timing device is provided before and after the catalyst is activated. 3. The air-fuel ratio control device for an internal combustion engine according to claim 2, wherein the valve overlap period is extended to increase the blow-through amount of unburned fuel. 5. An intake valve, an exhaust valve, and a variable valve timing device capable of changing a valve overlap period during which the intake valve and the exhaust valve are both opened, wherein the temperature of the catalyst rises to an activation temperature. Before the catalyst is activated, the air-fuel ratio detected by the air-fuel ratio detecting means is kept lean to increase unburned oxygen, and the valve overlap period is made longer than after the catalyst is activated to increase the unburned fuel. The air-fuel ratio control device for an internal combustion engine according to claim 1, wherein the amount of unburned fuel reaching the catalyst is increased by increasing the blow-through amount of the fuel. 6. The air-fuel ratio control device for an internal combustion engine according to claim 5, wherein the closing timing of the exhaust valve is delayed before the activation of the catalyst as compared with after the activation of the catalyst. 7. The air-fuel ratio control device for an internal combustion engine according to claim 5, wherein said fuel injection means directly injects fuel into a cylinder of the internal combustion engine. 8. The air-fuel ratio control device for an internal combustion engine according to claim 5, wherein said fuel injection means injects fuel to an intake port of the internal combustion engine.