JP2022117700A - Control device of internal combustion engine - Google Patents

Abstract

To provide a control device of an internal combustion engine which can quickly restore an oxygen occlusion amount of an exhaust emission purification catalyst while preventing misfire of the internal combustion engine caused by the excessive enrichment of an air-fuel ratio after releasing a fuel cut.SOLUTION: According to a control device of an engine, even if an accelerator pedal is not turned on during the execution of a fuel cut, the fuel cut is released at timing at which an oxygen occlusion amount of a three-way catalyst exceeds a first threshold, and discharges oxygen which is occluded by the three-way catalyst by controlling an air-fuel ratio of an exhaust gas which flows into the three-way catalyst to a theoretical air-fuel ratio, or weakly enriching the air-fuel ratio rather than the theoretical air-fuel ratio during a period from when the fuel cut is released to when the accelerator pedal is turned on.SELECTED DRAWING: Figure 2

Description

The present invention relates to a control device for an internal combustion engine.

In the exhaust passage of an internal combustion engine mounted on a vehicle, there is an exhaust gas such as a three-way catalyst that purifies substances such as HC (hydrocarbon), CO (carbon monoxide), and NOx (nitrogen oxide) emitted from the internal combustion engine. A purification catalyst is provided.

This type of exhaust purification catalyst stores oxygen (O ₂ ) to accelerate the reduction reaction of NOx when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, and stores oxygen (O 2 ) when the air-fuel ratio is richer than the stoichiometric air-fuel ratio. The oxygen released is released and the oxidation reaction of HC, CO, etc. is accelerated.

By the way, for the purpose of reducing fuel consumption, for example, fuel cut control is performed to stop the supply of fuel to the cylinders of the internal combustion engine when the vehicle is decelerating.

However, when fuel cut control is performed, a large amount of oxygen is contained in the exhaust gas flowing into the exhaust purification catalyst, and the oxygen stored in the exhaust purification catalyst becomes saturated. performance deteriorates.

Conventionally, an engine exhaust purification device described in Patent Document 1 is known as a device for preventing deterioration of NOx purification performance after cancellation of fuel cut.

The exhaust purification device described in Patent Document 1 calculates the O ₂ storage amount of the exhaust purification catalyst, and when the engine is restarted, the target air-fuel ratio is adjusted according to the O ₂ storage amount of the exhaust purification catalyst calculated during the previous operation. is corrected to the rich side, the oxygen storage amount of the exhaust purification catalyst is quickly recovered when the engine is restarted.

JP-A-2000-54826

In an internal combustion engine, if the target air-fuel ratio is corrected to the rich side according to the _O2 storage amount of the exhaust purification catalyst, misfires may easily occur due to factors such as the characteristics of the fuel used and the structure of the combustion chamber. For this reason, the exhaust purification device described in Patent Document 1 has less room to correct the air-fuel ratio to the rich side.

The present invention has been made with a focus on the circumstances as described above. It is an object of the present invention to provide a control device for an internal combustion engine capable of recovering quickly.

The present invention is a control device for an internal combustion engine in which an exhaust purification catalyst capable of storing oxygen is installed in an exhaust passage, and when a predetermined fuel cut condition including at least an accelerator pedal being turned off is satisfied, and a fuel cut execution unit that cancels the fuel cut when a predetermined fuel cut cancellation condition including at least the accelerator pedal being turned on is satisfied; when the accelerator pedal is turned on at the same time, the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is controlled to be richer than the stoichiometric air-fuel ratio to release the oxygen stored in the exhaust purification catalyst. wherein the oxygen release unit detects that the oxygen storage amount of the exhaust purification catalyst exceeds a first threshold value even when the accelerator pedal is not turned on during execution of the fuel cut. As a condition, the fuel cut is canceled, and the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is set to the stoichiometric air-fuel ratio or the rich air-fuel ratio after the fuel cut is canceled until the accelerator pedal is turned on. It is characterized by controlling the air-fuel ratio to a slightly rich air-fuel ratio closer to the stoichiometric air-fuel ratio than the air-fuel ratio.

As described above, according to the present invention, after the fuel cut is canceled, the oxygen storage amount of the exhaust purification catalyst can be recovered quickly while preventing the internal combustion engine from misfiring due to excessive enrichment of the air-fuel ratio.

FIG. 1 is a schematic configuration diagram of an internal combustion engine equipped with a control device according to one embodiment of the present invention. FIG. 2 is a flow chart of the oxygen storage amount control process executed by the internal combustion engine control apparatus according to the embodiment of the present invention. FIG. 3 is a timing chart of the oxygen storage amount control process executed by the internal combustion engine control apparatus according to one embodiment of the present invention. FIG. 4 is a flowchart of an oxygen storage amount control process that accompanies a combustion suspension operation that is executed by the control device for an internal combustion engine according to one embodiment of the present invention. FIG. 5 is a flowchart of an oxygen storage amount control process that accompanies a combustion suspension operation that is executed by the control device for an internal combustion engine according to one embodiment of the present invention.

A control device for an internal combustion engine according to an embodiment of the present invention is a control device for an internal combustion engine in which an exhaust gas purification catalyst capable of storing oxygen is installed in an exhaust passage, and is provided with a predetermined fuel including at least an accelerator pedal off. Execution of fuel cut to stop the fuel supply to the internal combustion engine when the cut condition is satisfied, and to cancel the fuel cut when a predetermined fuel cut cancellation condition including at least turning on of the accelerator pedal is satisfied. and when the accelerator pedal is turned on during fuel cut, the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is controlled to be richer than the stoichiometric air-fuel ratio, and the oxygen occluded by the exhaust purification catalyst and an oxygen release unit that releases the oxygen storage amount of the exhaust purification catalyst exceeding the first threshold value even when the accelerator pedal is not turned on during execution of the fuel cut. The fuel cut is canceled under the condition that the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is increased from the stoichiometric air-fuel ratio or the rich air-fuel ratio from the time the fuel cut is canceled until the accelerator pedal is turned on. is also controlled to a slightly rich air-fuel ratio close to the stoichiometric air-fuel ratio.

As a result, the control device for an internal combustion engine according to one embodiment of the present invention prevents misfires of the internal combustion engine due to excessive enrichment of the air-fuel ratio after canceling the fuel cut, while reducing the oxygen storage amount of the exhaust purification catalyst. can recover quickly.

An internal combustion engine control apparatus according to an embodiment of the present invention will be described below with reference to the drawings.
1 to 5 are diagrams showing a control system for an internal combustion engine according to one embodiment of the present invention.

First, the configuration will be explained.
In FIG. 1, a vehicle 1 equipped with an internal combustion engine control device according to an embodiment of the present invention includes an engine 2 as an internal combustion engine and an ECU (Engine Control Unit) 3 as a control device. there is

The vehicle 1 is a bi-fuel vehicle that uses gasoline, which is liquid fuel, and compressed natural gas (hereinafter referred to as CNG), which is gaseous fuel.

Gasoline and CNG, which have different fuel characteristics, have different starting performance when starting the engine 2. Gasoline has higher engine starting performance than CNG, CNG has better fuel efficiency than gasoline, and after combustion The amount of harmful substances in the exhaust gas is small.

The engine 2 comprises at least one or more cylinders, for example a first cylinder 2a, a second cylinder 2b, a third cylinder 2c and a fourth cylinder 2d. The first cylinder 2a, the second cylinder 2b, the third cylinder 2c, and the fourth cylinder 2d of this embodiment constitute cylinders.

The engine 2 is not limited to an in-line four-cylinder engine, and may be, for example, a V-type engine, and the number of cylinders is not limited to four.

The engine 2 includes a piston, a cylinder, a connecting rod, etc., all of which are not shown, and performs a series of four strokes consisting of an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke while the piston reciprocates the cylinder twice. The engine is composed of

A piston housed in a cylinder is connected to a crankshaft via a connecting rod. The connecting rod converts the reciprocating motion of the piston into rotational motion of the crankshaft.

Spark plugs 4A, 4B, 4C, and 4D and an intake manifold 5 are provided in the cylinder head of the engine 2 .

The spark plugs 4A to 4D are arranged in the cylinder head of the engine 2 with the electrodes projecting into the combustion chambers of the first cylinder 2a to the fourth cylinder 2d of the engine 2, and the ignition timing is controlled by the ECU 3. be done.

A cylinder head of the engine 2 is provided with an intake port (not shown). A downstream end of the intake manifold 5 is attached to the cylinder head of the engine 2 . An intake passage 5a is formed inside the intake manifold 5, and each of the intake passages 5a communicates with an intake port.

An upstream end of the intake manifold 5 is connected to an intake pipe 6 . An air cleaner 7 is connected to the upstream end of the intake pipe 6 . The air cleaner 7 cleans outside air taken in from an air intake duct (not shown).

The outside air purified by the air cleaner 7 is introduced from the intake pipe 6 into the intake manifold 5, and then from the intake passage 5a of the intake manifold 5 through the intake port to the first cylinder 2a to the fourth cylinder 2d.

Here, upstream and downstream indicate upstream and downstream with respect to the direction of air flow, with the air cleaner 7 side being upstream with respect to the engine 2 and the engine 2 side being downstream with respect to the air cleaner 7 .

A throttle valve 8 is provided on the upstream side of the intake pipe 6, and the throttle valve 8 adjusts the amount of air passing through the intake pipe 6 (intake intake amount). The throttle valve 8 is, for example, an electronically controlled throttle valve that is opened and closed by a motor (not shown).

The throttle valve 8 is electrically connected to the ECU 3, and the amount of depression of the accelerator pedal 9 (accelerator opening) is controlled by the ECU 3.

The depression amount of the accelerator pedal 9 is detected by an accelerator opening sensor 10 . The accelerator opening sensor 10 is electrically connected to the ECU 3 . The accelerator opening sensor 10 detects the amount of depression of the accelerator pedal 9 as the opening of the accelerator pedal 9 (hereinafter referred to as accelerator opening) and transmits a signal corresponding to the accelerator opening to the ECU 3 .

A first cylinder 2a to a fourth cylinder 2d of the engine 2 are provided with a gasoline injector 12 and a CNG injector 13, respectively.

The gasoline injector 12 is connected to a gasoline tank (not shown) via a fuel pipe (not shown). Gasoline stored in the gasoline tank is pressure-fed by a fuel pump (not shown) to a gasoline injector 12, and injected by the gasoline injector 12 into each of the first cylinder 2a to the fourth cylinder 2d.

Gasoline injected from the first cylinder 2a to the fourth cylinder 2d mixes with intake air introduced from the first cylinder 2a to the fourth cylinder 2d from the intake manifold 5 through the intake port to form an air-fuel mixture.

The CNG injector 13 is connected to a CNG tank (not shown) via a fuel pipe (not shown). The CNG stored in the CNG tank is pressure-fed to the CNG injector 13 by a fuel pump (not shown), and injected by the CNG injector 13 into each of the first to fourth cylinders 2a to 2d.

The CNG injected from the first cylinder 2a to the fourth cylinder 2d mixes with the intake air introduced from the first cylinder 2a to the fourth cylinder 2d from the intake manifold 5 through the intake port to form an air-fuel mixture.

The selection of whether to supply either gasoline or CNG to the engine 2 is, for example, an automatic selection automatically performed by the ECU 3 according to the operating state of the engine 2, and an automatic selection by the driver who drives the vehicle 1. Manual selection is made by operating a selection switch.

The gasoline injector 12 and the CNG injector 13 of this embodiment are so-called in-cylinder fuel injection valves that inject fuel from the first cylinder 2a to the fourth cylinder 2d.

A cylinder head of the engine 2 is provided with exhaust ports (not shown) communicating with the first cylinder 2a to the fourth cylinder 2d, respectively. An exhaust manifold 14 is connected to the engine 2, and an exhaust passage 14a is formed inside the exhaust manifold 14. As shown in FIG.

Exhaust gas from the first cylinder 2a to the fourth cylinder 2d generated by combustion of the air-fuel mixture gathers in the exhaust passage 14a of the exhaust manifold 14, and the exhaust gas gathered in the exhaust passage 14a is discharged to the three-way catalyst 15. be.

An upstream end of the three-way catalyst 15 is connected to a downstream end of the exhaust manifold 14 . The three-way catalyst 15 is composed of a ceramic or other carrier on which precious metals such as palladium and rhodium are attached. three kinds of harmful substances (NOx) are purified simultaneously by oxidation and reduction reactions.

The three-way catalyst 15 has an oxygen storage capacity of absorbing and releasing oxygen according to the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 15 . That is, the three-way catalyst 15 has an auxiliary catalyst capable of storing oxygen.

The ability of the three-way catalyst 15 to purify unburned gases (HC, CO) and nitrogen oxides (NOx) is extremely high when the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 15 is at the stoichiometric air-fuel ratio.

Further, the three-way catalyst 15 stores excessive oxygen in the exhaust gas when the air-fuel ratio of the exhaust gas is leaner than the stoichiometric air-fuel ratio. On the other hand, when the air-fuel ratio of the exhaust gas is on the richer side than the stoichiometric air-fuel ratio, the three-way catalyst 15 releases oxygen insufficient to oxidize the unburned gas.

As a result, even if the air-fuel ratio of the exhaust gas deviates from the stoichiometric air-fuel ratio, the air-fuel ratio on the surface of the three-way catalyst 15 is maintained close to the stoichiometric air-fuel ratio, and the unburned gas and NOx at the three-way catalyst 15 is purified.

The three-way catalyst 15 of this embodiment constitutes an exhaust purification catalyst. Note that the exhaust purification catalyst may be other than the three-way catalyst as long as it has catalytic action and oxygen storage capacity.

An upstream end of an exhaust pipe 16 is connected to a downstream end of the three-way catalyst 15, and the exhaust pipe 16 discharges exhaust gas purified by the three-way catalyst 15 to the outside (atmosphere). A muffler 17 is provided in the exhaust pipe 16, and the muffler 17 muffles the exhaust sound.

The exhaust manifold 14 and the exhaust pipe 16 of this embodiment constitute an exhaust passage, and the three-way catalyst 15 constitutes an exhaust purification device provided in the exhaust passage.

The vehicle 1 is provided with a MAF sensor 21 , a MAP sensor 22 , an air-fuel ratio sensor 23 , an oxygen sensor 24 and a crank angle sensor 25 .

A MAF (Mass Air Flow) sensor 21 is provided upstream of the throttle valve 8 inside the intake pipe 6 , measures the intake air amount of the intake pipe 6 , and transmits the measured intake air amount to the ECU 3 .

The MAP sensor 22 is provided upstream of the throttle valve 8 inside the intake pipe 6 , measures the intake pressure (MAP: Manifold Absolute Pressure) of the intake pipe 6 , and transmits the measured intake pressure to the ECU 3 .

The air-fuel ratio sensor 23 is provided upstream of the three-way catalyst 15, detects the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 15, and transmits the detected air-fuel ratio to the ECU3.

The oxygen sensor 24 detects the oxygen concentration in the exhaust gas that has passed through the three-way catalyst 15 and transmits the detected oxygen concentration to the ECU 3 . Specifically, the oxygen sensor 24 detects whether the exhaust gas that has passed through the three-way catalyst 15 is leaner or richer than the stoichiometric air-fuel ratio.

A crank angle sensor 25 detects a reference position and rotation angle of the crankshaft of the engine 2 and transmits a crank angle signal to the ECU 3 . The ECU 3 calculates the rotation speed of the engine 2 based on the crank angle signal input from the crank angle sensor 25 .

The ECU 3 is composed of a computer unit having a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a flash memory, an input port, and an output port.

The ROM of the computer unit stores various constants, various maps, etc., as well as programs for realizing the functions of the computer unit.

The ECU 3 controls the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 15 to a target air-fuel ratio (theoretical air-fuel ratio). Specifically, the ECU 3 controls the amount of intake air and the amount of fuel (the amount of gasoline or amount of CNG).

That is, the ECU 3 controls the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 15 to the target air-fuel ratio by performing fuel injection control based on the excess air ratio λ.

Here, the excess air ratio λ is the value obtained by dividing the actual amount of intake air actually supplied to the engine by the theoretically required minimum mass of air, and is an index indicating the degree of excess air in the air-fuel mixture. be.

The excess air ratio λ is also equal to the value obtained by dividing the actual air-fuel ratio by the stoichiometric air-fuel ratio. A mixture when the excess air ratio λ is 1 is called a stoichiometric mixture (theoretical air-fuel ratio), and a mixture when the excess air ratio λ is greater than 1 is called a lean mixture (the air-fuel ratio is lean). An air-fuel mixture in which the excess air ratio λ is less than 1 is called a rich air-fuel mixture (the air-fuel ratio is rich).

Further, the ECU 3 executes a fuel cut to stop the supply of fuel to the engine 2 when a predetermined fuel cut condition is satisfied, and cancels the fuel cut when a predetermined fuel cut cancellation condition is satisfied.

Predetermined fuel cut conditions include, for example, that the vehicle speed is lower than a predetermined value, that the brake pedal (not shown) is depressed, that the accelerator pedal 9 is not depressed (that the accelerator pedal 9 is off), and the like. included.

Even during deceleration of the vehicle 1, the ECU 3 can execute a fuel cut to the engine 2 to automatically stop the engine 2 when the fuel cut condition described above is satisfied.

Predetermined fuel cut cancellation conditions include, for example, that the accelerator pedal 9 is depressed, that the brake pedal is released, and the like. The ECU 3 of this embodiment constitutes a control device and a fuel cut execution section for the internal combustion engine.

The ECU 3 constantly calculates the oxygen excess/deficiency of the exhaust gas detected by the air-fuel ratio sensor 23, and estimates the oxygen storage amount of the three-way catalyst 15 by integrating the oxygen excess/deficiency. The excess/deficiency of oxygen is the amount of oxygen that becomes excessive or insufficient when the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 15 is set to the stoichiometric air-fuel ratio.

When the accelerator pedal 9 is turned on during fuel cut, the ECU 3 controls the intake air amount and the fuel injection amount to make the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 15 richer than the stoichiometric air-fuel ratio. The air-fuel ratio is controlled to release the oxygen stored in the three-way catalyst 15 .

Further, the ECU 3 cancels the fuel cut on the condition that the oxygen storage amount of the three-way catalyst 15 exceeds the first threshold value even when the accelerator pedal 9 is not turned on during execution of the fuel cut. , during the period from when the fuel cut is canceled until the accelerator pedal 9 is turned on, the intake air amount and the fuel injection amount are controlled to control the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 15 to the stoichiometric air-fuel ratio. .

That is, when the oxygen storage amount of the three-way catalyst 15 exceeds the first threshold during fuel cut, the ECU 3 cancels the fuel cut and adjusts the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 15 to The air-fuel ratio is controlled to the stoichiometric air-fuel ratio, and when the accelerator pedal 9 is turned on, the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 15 is controlled to be richer than the stoichiometric air-fuel ratio.

The first threshold value is a value corresponding to the oxygen storage amount and is stored in the ROM of the ECU 3 . The ECU 3 of this embodiment constitutes an oxygen release section.

The oxygen storage amount control processing of the three-way catalyst 15 by the control device for the engine 2 according to this embodiment configured as described above will be described with reference to the flowchart shown in FIG. 2 and the timing chart shown in FIG.

The oxygen storage amount control process shown in FIG. 2 is a process executed by the ECU 3. The ECU 3 starts the oxygen storage amount control process after an ignition switch (not shown) is turned on. End the oxygen storage amount control process.

In step S1, the ECU 3 executes normal engine control processing. This normal engine control process is basic control for operating the engine 2, and includes control of fuel injection timing and injection amount, ignition timing control of the spark plugs 4A to 4D, and the like.

In step S2, the ECU 3 determines whether or not the fuel cut condition is satisfied, and returns to step S1 when determining that the fuel cut condition is not satisfied.

When the ECU 3 determines in step S2 that the fuel cut condition is satisfied, the ECU 3 executes fuel cut (step S3).

Next, the ECU 3 determines whether or not the oxygen amount (OSC) stored in the three-way catalyst 15 exceeds the first threshold A1 (step S4), and determines whether the oxygen amount (OSC) stored in the three-way catalyst 15 is equal to or less than the first threshold value A1, the process returns to step S3.

The first threshold A1 is set to, for example, the maximum oxygen storage amount that the three-way catalyst 15 can store or an oxygen storage amount less than the maximum oxygen storage amount. Note that the first threshold A1 is not limited to this.

When the ECU 3 determines in step S4 that the amount of oxygen stored in the three-way catalyst 15 exceeds the first threshold value A1, there is a possibility that the oxygen stored in the three-way catalyst 15 is saturated. Then, even if the accelerator pedal 9 is not depressed, the fuel cut is canceled and the fuel injection control is started (step S5).

Next, the ECU 3 executes normal engine control processing to control the fuel injection amount so that the air-fuel ratio becomes the stoichiometric air-fuel ratio (step S6).

Next, the ECU 3 determines whether or not the throttle valve 8 has been opened, that is, whether or not the accelerator pedal 9 has been depressed, based on the information detected by the accelerator position sensor 10 after the fuel cut is canceled (step S7). .

Hereinafter, depressing the accelerator pedal 9 will be referred to as "accelerator ON", and releasing the accelerator pedal 9 will be referred to as "accelerator OFF". When the accelerator is on, the accelerator opening is greater than 0, and when the accelerator is off, the accelerator opening is 0.

When the ECU 3 determines that the accelerator is off in step S7, the process returns to step S6.

In step S7, when the ECU 3 determines that the accelerator is on, it controls the intake air amount and the fuel injection amount so that the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio. An oxygen purge process for releasing oxygen is executed (step S8).

Next, the ECU 3 determines whether or not the oxygen amount (OSC) occluded in the three-way catalyst 15 is equal to or less than the second threshold A2 (step S9). ) is greater than the second threshold value A2, the process returns to step S8.

The second threshold A2 is set, for example, to the minimum oxygen storage amount at which the three-way catalyst 15 stores zero oxygen, or to an oxygen storage amount larger than the minimum oxygen storage amount. Note that the second threshold A2 is not limited to this.

When the ECU 3 determines in step S9 that the amount of oxygen stored in the three-way catalyst 15 (OSC) is equal to or less than the second threshold value A2, the three-way catalyst 15 is pushed to a state where the reduction reaction of NOx can be promoted. It is determined that the oxygen stored in is released, and after completing the oxygen purge process (step S10), the process returns to step S1.

FIG. 3 is a timing chart of the oxygen storage amount control process, and the dashed-dotted line after timing t2 indicates the characteristics of the conventional fuel cut process.

In FIG. 3, the ECU 3 controls the air-fuel ratio of the exhaust gas to be the theoretical air-fuel ratio (stoichiometric indicated by λ) until the timing t1 when the fuel cut is started, and at the timing t1 when the accelerator opening is turned off. A fuel cut is performed to set the fuel injection amount to zero.

Since the exhaust gas flowing into the three-way catalyst 15 contains a large amount of oxygen during execution of the fuel cut, the exhaust gas flowing into the three-way catalyst 15 has an air-fuel ratio leaner than the stoichiometric air-fuel ratio.

If the fuel cut is continued until timing t3 when the accelerator is turned on as in the conventional art (see Y1), the exhaust gas flowing into the three-way catalyst 15 has an air-fuel ratio leaner than the stoichiometric air-fuel ratio (see Y2), and the three-way catalyst The amount of oxygen stored in 15 continues to increase (see Y3).

Conventionally, when the fuel injection is restarted at the timing t3 when the accelerator is turned on, the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 15 is adjusted to the theoretical air-fuel ratio in order to quickly release the oxygen stored in the three-way catalyst 15. It is necessary to make the fuel ratio richer than the fuel ratio (see Y4), and misfire may easily occur.

According to the control device of the engine 2 of this embodiment, even when the accelerator pedal 9 is not turned on during fuel cut, the oxygen storage amount of the three-way catalyst 15 exceeds the first threshold value A1. At timing t2, the fuel cut is canceled and the fuel injection is restarted (see X1 and X2), and the exhaust gas flowing into the three-way catalyst 15 is exhausted until the accelerator pedal 9 is turned on after the fuel cut is canceled. By controlling the fuel ratio to the stoichiometric air-fuel ratio (see X3), the oxygen stored in the three-way catalyst 15 is released.

As a result, the amount of oxygen stored in the three-way catalyst 15 can be maintained at the first threshold value A1 or below the first threshold value A1 during execution of the fuel cut.

Therefore, it is possible to eliminate the need to release oxygen from the three-way catalyst 15 by making the air-fuel ratio of the exhaust gas excessively rich (see Y4) when canceling the fuel cut as in the conventional art. Oxygen can be released from the three-way catalyst 15 at a rich air-fuel ratio X5 close to the stoichiometric air-fuel ratio. As a result, the oxygen storage amount of the three-way catalyst 15 can be quickly restored while preventing the engine 2 from misfiring.

Even if the accelerator pedal 9 is not turned on during execution of the fuel cut, the ECU 3 cancels the fuel cut on the condition that the oxygen storage amount of the three-way catalyst 15 exceeds the first threshold value A1. Then, after the fuel cut is canceled and before the accelerator pedal 9 is turned on, the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 15 is adjusted to the rich air-fuel ratio by controlling the intake air amount and the fuel injection amount. The air-fuel ratio may be controlled to a slightly rich air-fuel ratio closer to the stoichiometric air-fuel ratio.

Moreover, the engine 2 of this embodiment uses CNG, which is a gaseous fuel. When gaseous fuel is used, misfires are more likely to occur when the air-fuel ratio is enriched than when liquid fuel is used, and the limit value at which the air-fuel ratio can be enriched is low.

Therefore, by applying this control to the engine 2 that uses gaseous fuel, it is possible to quickly restore the oxygen storage amount of the three-way catalyst 15 while preventing the engine 2 from misfiring. In addition, LPG (Liquefied Petroleum gas) etc. may be used as gaseous gas.

Further, the ECU 3 performs combustion suspension operation when the oxygen storage amount of the three-way catalyst 15 does not become equal to or less than the second threshold value A2 after the accelerator pedal 9 is turned on. That is, the engine 2 of this embodiment can be switched between all-cylinder operation and combustion suspension operation in which ignition of some of the cylinders 2a to 2d is suspended.

In the combustion pause operation, the ECU 3, for example, sets the second cylinder 2b and the third cylinder 2c as combustion pause cylinders, supplies a mixture of intake air and fuel to the second cylinder 2b and the third cylinder 2c, and performs ignition. The output of the ignition signal to the plugs 4B and 4C is stopped to stop the combustion of the air-fuel mixture in the second cylinder 2b and the third cylinder 2c.

On the other hand, the ECU 3 sets the first cylinder 2a and the fourth cylinder 2d as combustion cylinders, supplies a mixture of intake air and fuel to the first cylinder 2a and the fourth cylinder 2d, and supplies ignition signals to the spark plugs 4B and 4C. to burn the air-fuel mixture in the first cylinder 2a and the fourth cylinder 2d.

When the oxygen storage amount of the three-way catalyst 15 does not become equal to or less than the second threshold value after a predetermined time has elapsed since the fuel cut was canceled, the ECU 3 suspends the combustion of the second cylinder 2b and the third cylinder 2c, and restores the combustion cylinder. The air-fuel ratio of the exhaust gas flowing into (the first cylinder 2a and the fourth cylinder 2d) is controlled to the stoichiometric air-fuel ratio, and the air-fuel ratio of the exhaust gas flowing into the combustion paused cylinder (the second cylinder 2b and the third cylinder 2c) is adjusted to The air-fuel ratio is controlled to be richer than the stoichiometric air-fuel ratio.

Next, the oxygen storage amount control process of the three-way catalyst 15 that accompanies combustion suspension operation will be described with reference to the flowchart shown in FIG. 4 and the timing chart shown in FIG.

The oxygen storage amount control process shown in FIG. 4 is a process executed by the ECU 3. When the ignition switch is turned on, the ECU 3 starts the oxygen storage amount control process, and when the ignition switch is turned off, the oxygen storage amount control process is executed. Terminate the volume control process.

Note that the same step numbers are assigned to step S in which the same processing as in the flowchart of FIG. 2 is performed, and the description thereof is omitted.

FIG. 5 is a timing chart of the oxygen storage amount control process that accompanies the combustion suspension operation. The solid line in FIG. 5 indicates the characteristics of the oxygen storage amount control process shown in FIG. 3, and the two-dot chain line after timing t3 indicates the characteristics of the fuel injection amount, ignition signal, and air-fuel ratio to the idle cylinder during combustion suspension operation. show.

Further, in FIG. 5, the dotted line after timing t3 indicates the behavior of the fuel injection amount to the combustion cylinder, the ignition signal, and the air-fuel ratio during the combustion suspension operation. Regarding the amount of oxygen in the three-way catalyst, the chain double-dashed line after timing t3 indicates the change in the amount of oxygen stored in the three-way catalyst 15 during the combustion suspension operation.

In step S9 of FIG. 4, when the ECU 3 determines that the amount of oxygen stored in the three-way catalyst 15 is equal to or less than the second threshold value A2, after completing the oxygen purge (step S10), step S1 Return processing to .

In step S9, if the ECU 3 determines that the amount of oxygen stored in the three-way catalyst 15 is greater than the second threshold value A2, it determines whether a predetermined time T has passed since the fuel cut was canceled. is determined (step S11).

When the ECU 3 determines in step S11 that the predetermined time T has not passed since the fuel cut was canceled, the process returns to step S8.

When the ECU 3 determines in step S11 that the predetermined time T has passed since the fuel cut was canceled, it starts combustion suspension control (step S12).

When the combustion pause control is started, the ECU 3 sets the first cylinder 2a and the fourth cylinder 2d as combustion cylinders, and sets the second cylinder 2b and the third cylinder 2c as combustion pause cylinders.

Next, the ECU 3 turns on the ignition of the spark plugs 4A and 4D of the first cylinder 2a and the fourth cylinder 2d (step S13), and the air-fuel mixture supplied to the first cylinder 2a and the fourth cylinder 2d is equal to the stoichiometric air-fuel ratio. The fuel injection amount is controlled so as to become (step S14).

Further, the ECU 3 turns off the ignition of the spark plugs 4B, 4C of the second cylinder 2b and the third cylinder 2c (step S15), and the air-fuel mixture supplied to the second cylinder 2b and the third cylinder 2c has an air-fuel ratio higher than the stoichiometric air-fuel ratio. The fuel injection amount is controlled so that the air-fuel ratio becomes even richer (step S16).

In other words, the ignition of the second cylinder 2b and the third cylinder 2c is prohibited, but the excess fuel is injected to the second cylinder 2b and the third cylinder 2c compared to the fuel injected at the stoichiometric air-fuel ratio.

In steps S13 and S14, as shown in FIG. 5, when the oxygen storage amount of the three-way catalyst 15 does not become equal to or less than the second threshold value A2 after the lapse of a predetermined time T from timing t3 (timing t4), the ECU 3 Combustion shutdown control is started.

When starting the combustion pause control, the ECU 3 turns on the ignition of the spark plugs 4A and 4D of the first cylinder 2a and the fourth cylinder 2d (see X11), and the air-fuel mixture supplied to the first cylinder 2a and the fourth cylinder 2d. is the stoichiometric air-fuel ratio (see X12) (see X13).

In steps S15 and S16, as shown in FIG. 5, the ECU 3 turns off the ignition of the spark plugs 4B and 4C of the second cylinder 2b and the third cylinder 2c (see X14) when the combustion pause control is started at the timing t4. , the amount of fuel injected into the second cylinder 2b and the third cylinder 2c is controlled so that the air-fuel ratio (see X15) is richer than the stoichiometric air-fuel ratio (see X16).

As described above, the engine 2 of this embodiment has a plurality of cylinders 2a to 2d, and is capable of combustion suspension operation in which ignition of some of the cylinders 2a to 2d is suspended.

Next, the ECU 3 determines whether or not the oxygen amount (OSC) occluded by the three-way catalyst 15 is equal to or less than the second threshold A2 (step S17). ) is greater than the second threshold value A2, the process returns to step S12.

When the ECU 3 determines in step S17 that the amount of oxygen (OSC) stored in the three-way catalyst 15 is equal to or less than the second threshold value A2, the three-way catalyst 15 is pushed to a state where the reduction reaction of NOx can be promoted. It is determined that the oxygen stored in has been released, and after completing the oxygen purge process (step S18), the process returns to step S1.

As described above, according to the control device for the engine 2 of this embodiment, when the oxygen storage amount of the three-way catalyst 15 does not become equal to or less than the second threshold value A2 after the lapse of the predetermined time T after the fuel cut is canceled, The combustion of the second cylinder 2b and the third cylinder 2c is suspended, the air-fuel ratio of the exhaust gas flowing into the combustion cylinder (the first cylinder 2a and the fourth cylinder 2d) is controlled to the stoichiometric air-fuel ratio, and the combustion suspension cylinder (the second The air-fuel ratio of the exhaust gas flowing into the cylinder 2b and the third cylinder 2c) is controlled to be richer than the stoichiometric air-fuel ratio.

As a result, the air and unburned fuel discharged from the combustion paused cylinders (the second cylinder 2b and the third cylinder 2c) are mixed with the exhaust gas from the combustion cylinders (the first cylinder 2a and the fourth cylinder 2d) and burned. and the air-fuel ratio of the exhaust gas flowing into the three-way catalyst 15 can be further enriched.

Therefore, as shown in FIG. 5, the release of oxygen stored in the three-way catalyst 15 can be promoted more effectively than in the all-cylinder operation (see X17), and the oxygen storage amount of the three-way catalyst 15 can be rapidly increased. (see X18).

In addition, it is possible to increase the load required for the combustion cylinders (the first cylinder 2a and the fourth cylinder 2d), thereby avoiding the operation of the engine 2 in a low load range where stalling is likely to occur.

Although embodiments of the present invention have been disclosed, it will be apparent that modifications may be made by those skilled in the art without departing from the scope of the invention. All such modifications and equivalents are intended to be included in the following claims.

2... engine (internal combustion engine), 2a... first cylinder (cylinder), 2b... second cylinder (cylinder), 2c... third cylinder (cylinder), 2d... fourth cylinder (cylinder), 3...ECU (fuel cut execution unit, oxygen release unit), 14...exhaust manifold (exhaust passage), 15...three-way catalyst (exhaust purification device), 16...exhaust pipe (exhaust passage)

Claims (3)

A control device for an internal combustion engine in which an exhaust purification catalyst capable of storing oxygen is installed in an exhaust passage,
When a predetermined fuel cut condition including at least the accelerator pedal being turned off is satisfied, a fuel cut is executed to stop the fuel supply to the internal combustion engine, and a predetermined fuel cut cancellation condition including at least the accelerator pedal being turned on. a fuel cut execution unit that cancels the fuel cut when is established;
When the accelerator pedal is turned on during execution of the fuel cut, the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is controlled to be richer than the stoichiometric air-fuel ratio, and the exhaust purification catalyst stores the air-fuel ratio. and an oxygen release part for releasing oxygen,
The oxygen release unit performs the fuel cut on the condition that the oxygen storage amount of the exhaust purification catalyst exceeds a first threshold value even when the accelerator pedal is not turned on during execution of the fuel cut. is released, and the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst is adjusted to the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio from the rich air-fuel ratio during the period from the fuel cut being canceled to the accelerator pedal being turned on. A control device for an internal combustion engine characterized by controlling to a slightly rich air-fuel ratio close to the air-fuel ratio. 2. A control apparatus for an internal combustion engine according to claim 1, wherein said internal combustion engine uses at least gaseous fuel. The internal combustion engine has a plurality of cylinders, and is capable of combustion suspension operation by suspending ignition of a part of the plurality of cylinders,
The oxygen release part has a second threshold corresponding to an oxygen storage amount smaller than the oxygen storage amount corresponding to the first threshold,
The oxygen release unit suspends combustion of a part of the plurality of cylinders when the oxygen storage amount of the exhaust purification catalyst does not become equal to or less than the second threshold value after a predetermined time has elapsed since the fuel cut was canceled. and controlling the air-fuel ratio of the exhaust gas flowing into the combustion cylinder to a stoichiometric air-fuel ratio, and controlling the air-fuel ratio of the exhaust gas flowing into the combustion paused cylinder to a richer air-fuel ratio than the stoichiometric air-fuel ratio. 2. The control device for an internal combustion engine according to 1.

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