JP3601395B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly, to an exhaust gas purification device for supplying exhaust gas having a stoichiometric air-fuel ratio or a rich air-fuel ratio to an exhaust gas purification catalyst disposed in an exhaust passage as required.
[0002]
[Prior art]
NO in exhaust under lean air-fuel ratio_XAn exhaust purification catalyst for purifying exhaust gas is known. As this kind of exhaust purification catalyst, for example, when the air-fuel ratio of the exhaust is a lean air-fuel ratio, NO_XNO when the exhaust air-fuel ratio falls below the stoichiometric air-fuel ratio_XTo release and purify NO_XIt adsorbs hydrocarbons and reducing agent components in the storage reduction catalyst, exhaust gas, and NO in exhaust gas at a lean air-fuel ratio._XAnd selectively react with adsorbed hydrocarbons and the like to form NO_XNO to reduce_XThere are selective reduction catalysts and the like.
[0003]
NO as above_XIn an exhaust purification catalyst for purifying NO, for example, NO_XNO absorbed by the storage reduction catalyst_XRelease and reduction purification, and NO_XIn the selective reduction catalyst, it is necessary to periodically supply exhaust gas containing a large amount of hydrocarbons having a stoichiometric air-fuel ratio or a rich air-fuel ratio to the exhaust purification catalyst in order to cause hydrocarbons and the like to be adsorbed by the selective reduction catalyst.
[0004]
In an engine such as a diesel engine having an in-cylinder fuel injection valve that injects fuel directly into a cylinder, combustion is performed in the cylinder by performing additional fuel injection during expansion or exhaust stroke in addition to main fuel injection ( That is, it is possible to vaporize the fuel without increasing the output torque) and supply it to the catalyst together with the exhaust gas. This makes it possible to supply exhaust gas containing a large amount of hydrocarbons having a stoichiometric air-fuel ratio or a rich air-fuel ratio to the exhaust purification catalyst without causing a large fluctuation in engine output torque.
[0005]
Although it is not related to a diesel engine, an example of an internal combustion engine in which an air-fuel ratio of exhaust gas supplied to an exhaust purification catalyst by additional fuel injection is set to be equal to or lower than a stoichiometric air-fuel ratio is described in, for example, JP-A-9-32619. is there.
In the internal combustion engine of the publication, the fuel vaporized without burning in the cylinder reaches the exhaust purification catalyst together with the exhaust by performing multiple additional fuel injections into the cylinder of the gasoline engine during the expansion stroke or the exhaust stroke of the cylinder. Then, the exhaust gas is burned by the exhaust gas purifying catalyst to raise the temperature of the exhaust gas purifying catalyst and to decompose the substance having a reduced purifying ability attached to the catalyst.
[0006]
[Problems to be solved by the invention]
In Japanese Patent Application Laid-Open No. 9-32619, a gasoline engine is used as an internal combustion engine, and fuel vaporized by performing additional fuel injection is caused to reach an exhaust purification catalyst. However, when attempting to perform additional fuel injection with a diesel engine in order to make the exhaust purification catalyst reach exhaust gas with a stoichiometric air-fuel ratio or rich air-fuel ratio, an extremely large amount of fuel is supplied to the cylinder by additional fuel injection as compared with a gasoline engine. Need to be done.
[0007]
Normally, diesel engines are operated at an extremely lean air-fuel ratio. For example, the operating air-fuel ratio in a normal operation region of a diesel engine is an extremely lean air-fuel ratio of about 30. For this reason, in order to make the exhaust air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio (stoichiometric air-fuel ratio or rich air-fuel ratio) by additional fuel injection in a diesel engine, the additional fuel injection injects approximately the same amount of fuel as the main fuel injection amount. There is a need to.
[0008]
However, in a diesel engine, when a large amount of fuel is injected by additional fuel injection, the injected fuel directly reaches the cylinder inner wall in a liquid state, and the lubricating oil film on the cylinder wall is washed away. There is a problem that gets worse. In order to prevent the occurrence of bore flushing, additional fuel injection is performed when the piston is near the top dead center of the expansion stroke or the exhaust stroke, and almost all the injected fuel enters the combustion chamber on the top surface of the piston and evaporates. What should I do? However, when additional fuel injection is performed near the top dead center of the expansion stroke, for example, the combustion timing of the fuel injected by the main fuel injection and the additional fuel injection timing are close to each other, so that a part of the fuel injected by the additional fuel injection is reduced. A problem arises in that combustion occurs and exhaust smoke is generated. Further, if additional fuel injection is performed near the top dead center of the exhaust stroke, additional fuel injection will be performed during the valve overlap period in which both the exhaust valve and the intake valve are opened. The fuel that has flowed back to the intake port and is again drawn into the cylinder during the intake stroke, so that the fuel injected by the additional fuel injection remains in the next cycle of the cylinder. If unburned fuel due to the additional injection remains in the cylinder, there is a problem that abnormal combustion occurs in which the residual fuel starts burning during the compression stroke, and engine output torque fluctuates due to combustion of the residual fuel.
[0009]
In addition to the above-mentioned problem, in order to make the exhaust air-fuel ratio a stoichiometric air-fuel ratio or a rich air-fuel ratio in a diesel engine, it is necessary to perform a relatively large amount of additional fuel injection. There is a problem that it increases significantly.
In order to prevent the additional fuel injection amount from becoming large, for example, it is conceivable to provide a throttle valve in an intake passage of a diesel engine to reduce the amount of intake air when performing additional fuel injection. However, in this case, the pumping loss due to the restriction of the intake air amount increases, so that there is a problem that even if the intake air amount is restricted, the increase in the fuel consumption of the engine cannot be suppressed.
[0010]
The present invention has been made in view of the above problems, and has an object to provide means capable of preventing bore flushing and increase in fuel consumption when the exhaust air-fuel ratio of an internal combustion engine is set to a stoichiometric air-fuel ratio or a rich air-fuel ratio by additional fuel injection. And
[0011]
[Means for Solving the Problems]
According to the first aspect of the present invention, an exhaust purification catalyst disposed in an exhaust passage of an internal combustion engine having an in-cylinder fuel injection valve that injects fuel directly into a cylinder, and is supplied to the exhaust purification catalyst as needed. Control means for performing additional fuel injection during the cylinder expansion or exhaust stroke from the in-cylinder fuel injection valve in addition to the main fuel injection when setting the air-fuel ratio of the exhaust gas to be the stoichiometric air-fuel ratio or the rich air-fuel ratio. The exhaust gas purifying apparatus for an internal combustion engine further includes variable valve timing means capable of changing at least one valve timing of an intake valve and an exhaust valve, wherein the variable valve timing means is configured such that the control means controls the additional fuel injection. When at least one of the valve timing of the intake valve and the exhaust valve is changed so that the amount of air taken into the cylinder is reduced as compared to when the additional fuel injection is not performed, Exhaust purification system of combustion engine is provided.
[0012]
That is, in the first aspect of the present invention, when performing additional fuel injection, the valve timing of at least one of the intake valve and the exhaust valve is changed by the variable valve timing means, and the amount of air taken into the cylinder is reduced. . Therefore, when performing additional fuel injection, the exhaust air-fuel ratio can be set to the stoichiometric air-fuel ratio or the rich air-fuel ratio with a small amount of fuel, and the occurrence of bore flushing and fuel consumption by injecting a large amount of fuel can be achieved. Can be prevented from increasing.
[0013]
In this case, the change of the valve timing may be performed for one of the intake valve and the exhaust valve, or may be performed for both. Reduction of the intake air amount by changing the valve timing is performed, for example, by delaying the closing timing of the intake valve. By delaying the closing timing of the intake valve, the time from when the cylinder enters the compression stroke to when the intake valve closes becomes longer, so that the air once taken into the cylinder is pushed back to the intake port with the rise of the piston. As a result, the amount of air charged into the cylinder when the intake valve is closed decreases.
[0014]
According to the invention described in claim 2, the control means performs the additional fuel injection in a plurality of times during the expansion or exhaust stroke of the cylinder, and the amount of fuel injected in one additional fuel injection. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein is set smaller than a fuel injection amount at which bore flushing occurs in the cylinder.
That is, according to the second aspect of the present invention, the fuel to be supplied into the cylinder by the additional fuel injection is divided into a plurality of additional fuel injections and injected into the cylinder. Thus, the amount of fuel injected at one time is reduced, so that the occurrence of bore flushing can be completely prevented.
[0015]
According to the third aspect of the invention, an air-fuel ratio sensor for detecting an exhaust air-fuel ratio is further provided in an engine exhaust passage upstream of the exhaust purification catalyst, and the control device is configured to perform the air-fuel ratio when the additional fuel injection is performed. 3. An exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the amount of fuel supplied to the cylinder by additional fuel injection is controlled such that the exhaust air-fuel ratio detected by the sensor becomes a predetermined rich air-fuel ratio.
[0016]
That is, in the third aspect of the invention, the fuel injection amount of the additional fuel injection is feedback-controlled based on the output of the air-fuel ratio so that the exhaust air-fuel ratio becomes a predetermined air-fuel ratio when the additional fuel injection is performed. Therefore, at the time of performing additional fuel injection, the exhaust air-fuel ratio is controlled to the air-fuel ratio truly required for the exhaust purification catalyst, and the amount of fuel supplied to the cylinder by the additional fuel injection is limited to the truly necessary amount. No excess or deficiency occurs.
[0017]
According to the invention as set forth in claim 4, further comprising means for detecting the catalyst temperature, the control means and the variable valve timing means are added so that the detected catalyst temperature becomes a predetermined temperature. 2. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the valve controls the fuel supplied to the cylinder by the fuel injection and the valve timing.
[0018]
That is, in the invention of claim 4, the catalyst temperature is detected, and the valve timing and the fuel injection amount of the additional fuel injection are controlled so that the catalyst temperature becomes a predetermined value. Since the exhaust gas purifying catalyst generally has a lower exhaust gas purifying action at a temperature lower than the activation temperature of the catalyst, it is preferable to always maintain the catalyst temperature at the activation temperature or higher during operation of the engine. However, when the engine is cold started or when the exhaust gas temperature is low, the catalyst temperature may become lower than the activation temperature, and it is necessary to raise the temperature of the catalyst. Particularly, in a diesel engine, the catalyst temperature may decrease when the light load operation is continued because the exhaust gas temperature is low. In the present invention, for example, when the catalyst temperature decreases, the adjustment of the engine valve timing and the additional fuel injection are performed so that the catalyst temperature becomes a predetermined temperature. Based on the detected catalyst temperature, the engine valve timing and the additional fuel injection amount are adjusted so that the catalyst temperature becomes equal to or higher than a predetermined temperature. Therefore, an appropriate amount of air (oxygen) and the additional fuel injection are supplied to the catalyst. Since the unburned fuel reaches the fuel, the fuel burns in the exhaust purification catalyst, and the temperature of the catalyst rises to a predetermined temperature in a short time. The catalyst temperature may be directly detected by a temperature sensor or the like, or may be detected by actually measuring the exhaust gas temperature or estimating based on the operating state, and estimating the catalyst temperature using the exhaust gas temperature. May be.
[0019]
According to the fifth aspect of the present invention, an exhaust purification catalyst disposed in an exhaust passage of an internal combustion engine having an in-cylinder fuel injection valve that injects fuel directly into a cylinder, and supplies the exhaust purification catalyst as needed. Control means for performing additional fuel injection from the in-cylinder fuel injection valve in addition to main fuel injection when setting the air-fuel ratio of the exhaust gas to be stoichiometric or rich air-fuel ratio. Further, there is provided a variable valve timing means capable of changing the opening timing of the engine intake valve, wherein the control means is arranged such that the cylinder is in the exhaust process and the cylinder piston moves to the cylinder inner wall of the fuel injected by the additional fuel injection. Performing the additional fuel injection at a position where the additional fuel injection is prevented, and the variable valve timing means, when the control means performs the additional fuel injection, compared to when the additional fuel injection is not performed. Valves and the exhaust valve to delay the intake valve opening timing so that the valve overlap period is shortened to be opened at the same time, the exhaust gas purification apparatus is provided for an internal combustion engine.
[0020]
That is, in the invention of claim 5, when the cylinder is in the exhaust stroke and the piston is located at a position where the fuel injected by the additional fuel injection does not directly reach the cylinder inner wall, that is, for example, when the piston is in the exhaust stroke top dead center Additional fuel injection is performed when it is nearby. As a result, almost all of the injected fuel is prevented from entering the combustion chamber on the upper surface of the piston and the injected fuel is prevented from directly reaching the inner wall of the cylinder. For example, a large amount of fuel is injected by one additional fuel injection. In such a case, bore flushing is prevented from occurring.
Further, in the present invention, when additional fuel injection is performed, the intake valve opening timing is delayed so that the valve overlap period is shortened. Near the top dead center of the exhaust stroke, the intake valve starts to open, so there is a valve overlap period in which both the intake valve and the exhaust valve open.However, if additional fuel injection is performed during the valve overlap period, the injected fuel will decrease. Since it remains in the cylinder and burns in the next cycle, abnormal combustion and fluctuations in engine output torque occur. According to the present invention, when performing additional fuel injection, the valve opening time of the intake valve is delayed and the valve overlap period is shortened, so that the occurrence of residual fuel in the cylinder due to the additional fuel injection is suppressed, and abnormal combustion and The fluctuation of the engine output torque is prevented.
Further, by delaying the intake valve closing timing together with the intake valve opening timing to reduce the amount of air taken into the cylinder, the additional fuel injection amount is reduced to prevent an increase in the fuel injection amount. It is also possible.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram showing a schematic configuration of an embodiment when the present invention is applied to an automobile diesel engine.
In FIG. 1, reference numeral 1 denotes an internal combustion engine for a vehicle. In the present embodiment, the engine 1 is a six-cylinder diesel engine having six cylinders # 1 to # 6, and each cylinder is provided with an in-cylinder fuel injection valve 111 for directly injecting fuel into the cylinder. The fuel is pressure-fed from a high-pressure fuel injection pump (not shown) to a common rail (accumulator) (not shown) to which each fuel injection valve 111 is connected. Injected in.
[0022]
In FIG. 1, reference numeral 21 denotes a surge tank that connects an intake port of each cylinder to the intake passage 2, and 31 denotes an exhaust manifold that connects an exhaust port of each cylinder to the exhaust passage 3.
In the present embodiment, a supercharger 35 for supercharging the engine 1 is provided, and the exhaust passage 3 is provided at an exhaust outlet of the supercharger 35, and the intake passage 2 is provided at an intake outlet of the supercharger 35. It is connected. The intake passage 2 is provided with an intercooler 25 for cooling intake air supplied from the supercharger 35 and an intake throttle valve 27. The intake throttle valve 27 is used, for example, to throttle the engine intake air amount during idling of the engine and to increase the EGR gas amount described later.
[0023]
In FIG. 1, reference numeral 33 denotes an EGR passage which connects an engine exhaust manifold 31 and a surge tank 21 of an intake system and recirculates a part of the engine exhaust to an intake system, 32 denotes an EGR cooler which cools exhaust gas passing through the EGR passage, and 23 denotes an EGR cooler. An EGR valve arranged in the EGR passage. The EGR valve 23 includes an appropriate actuator (not shown) such as a stepper motor and a negative pressure actuator. The EGR valve 23 takes an opening in accordance with a signal from the ECU 30 and returns to the intake system through the EGR passage 33 (EGR gas). The flow rate is controlled according to the engine operating state.
[0024]
A variable valve timing device for changing the valve timing of the engine is shown at 50 in FIG. In the present embodiment, the variable valve timing device 50 is of a type that can change the opening timing and closing timing of the intake valve in a stepless manner by changing the rotation phase of the intake camshaft with respect to the crankshaft. . In the present invention, the type of the variable valve timing device 50 is not particularly limited, and any known type can be used as long as the opening / closing timing of one or both of the intake valve and the exhaust valve can be changed. Can be used.
[0025]
In FIG. 1, reference numeral 70 denotes the NO disposed in the exhaust passage 3._XIt is a storage reduction catalyst. NO of this embodiment_XThe occlusion reduction catalyst 70 uses, for example, alumina as a carrier, and on the carrier, for example, an alkali metal such as potassium K, sodium Na, lithium Li, or cesium Cs, an alkaline earth such as barium Ba, calcium Ca, lanthanum La, or cerium. It supports at least one component selected from rare earths such as Ce and yttrium Y and a noble metal such as platinum Pt. NO_XWhen the air-fuel ratio of the inflowing exhaust gas is lean, the NOx in the exhaust_X(NO₂, NO) to nitrate ion NO₃ ⁻NO when the inflow exhaust gas becomes rich_XReleases NO_XPerforms the absorption and release action.
[0026]
The mechanism of this absorption and release will be described below by taking platinum Pt and barium Ba as an example, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths, and rare earths.
When the oxygen concentration in the inflowing exhaust gas increases (that is, when the air-fuel ratio of the exhaust gas becomes a lean air-fuel ratio), these oxygens become₂ ⁻Or O^2-NO in the exhaust_XIs O on platinum Pt₂ ⁻Or O^2-With NO₂Is generated. Also, NO in the inflow exhaust₂And the NO generated above₂Is combined with barium oxide BaO as an absorbent while being further oxidized on platinum Pt and nitrate ions NO₃ ⁻Diffuses into the absorbent in the form of Therefore, in a lean atmosphere, NO_XIs NO_XIt becomes absorbed in the form of nitrate in the storage reduction catalyst.
[0027]
Also, when the oxygen concentration in the inflowing exhaust gas decreases (that is, when the air-fuel ratio of the exhaust gas decreases), NO on the platinum Pt becomes NO.₂Since the amount of production is reduced, the reaction proceeds in the reverse direction, and nitrate ion NO₃ ⁻Is NO₂NO in the form of_XIt is released from the storage reduction catalyst. In this case, if components such as HC and CO are present in the exhaust gas, these components cause NO on the platinum Pt.₂Is reduced.
[0028]
In this embodiment, since a diesel engine is used as the engine 1, the engine exhaust usually has a lean air-fuel ratio, and NO_XThe NOx in the storage reduction catalyst 70 is_XAbsorb. But NO_XNO absorbed by the storage reduction catalyst_XWhen the amount increases, the absorbent (such as BaO) becomes saturated with nitrate ions, and NO_XNO in storage exhaust catalyst_XCan not be absorbed. Therefore, in the present embodiment, NO_XAt a certain timing, a rich air-fuel ratio exhaust gas containing a large amount of unburned fuel is supplied to the storage reduction catalyst, and NO_XNO storage reduction catalyst_XAbsorbed before saturation with_XTo reduce and purify NO_XNO of storage reduction catalyst_XPrevents a decrease in absorption capacity.
[0029]
Reference numeral 30 in FIG. 1 denotes an electronic control unit (ECU) of the engine 1. In the present embodiment, the ECU 30 is a microcomputer having a known configuration including a RAM, a ROM, and a CPU. The ECU 30 performs basic control such as fuel injection control of the engine 1 and also has a NO_XNO absorbed from the storage reduction catalyst 70_XIs to be performed, an additional fuel injection is performed to each cylinder of the engine 1 to make the exhaust air-fuel ratio equal to or lower than the stoichiometric air-fuel ratio.
[0030]
In order to perform these controls, a signal corresponding to the amount of engine intake air from an air flow meter 51 provided in the engine intake passage is provided to an input port of the ECU 30 in a cooling water jacket (not shown) of the engine 1. A signal corresponding to the engine cooling water temperature is input from the cooling water temperature sensor 53 via an AD converter (not shown). In the present embodiment, the NO in the exhaust passage 3_XAn air-fuel ratio sensor 41 that outputs a voltage signal corresponding to the exhaust air-fuel ratio is provided at the entrance of the storage reduction catalyst 70,_XAt the outlet of the storage reduction catalyst 70, exhaust temperature sensors 43 for outputting a voltage signal corresponding to the exhaust temperature are arranged. Outputs of the air-fuel ratio sensor 41 and the exhaust temperature sensor 43 are supplied to input ports of the ECU 30 via AD converters (not shown). Further, a pulse signal is input to the input port of the ECU 30 at every constant rotation angle of the engine crankshaft from a rotation speed sensor 55 disposed near the engine crankshaft (not shown). A voltage signal indicating the driver's accelerator pedal depression amount (accelerator opening) is input from an accelerator opening sensor 57 disposed near one accelerator pedal (not shown) via an AD converter (not shown).
[0031]
The ECU 30 performs AD conversion on the output of the air flow meter 51 and the output of the accelerator opening sensor 57, the output of the temperature sensor 53, the air-fuel ratio sensor 41, and the output of the exhaust temperature sensor 43 at predetermined intervals to convert the intake air amount G, the accelerator opening ACCP, and the cooling. Water temperature TW, exhaust air-fuel ratio AF, exhaust temperature T_EXThe engine speed NE is calculated from the interval of the pulse signal from the speed sensor 55 and stored in a predetermined area of the RAM. The ECU 30 calculates an engine basic fuel injection amount based on a relationship previously stored in a ROM based on the accelerator opening ACCP detected by the accelerator opening sensor 57 and the engine speed NE. The main fuel injection amount Q of the engine is set by adding a correction according to the state. In the present invention, the method for setting the fuel injection amount is not particularly limited, and any of the known setting methods for a diesel engine can be used.
[0032]
On the other hand, an output port of the ECU 30 is connected to a fuel injection valve 111 of each cylinder via a fuel injection circuit (not shown) for controlling a fuel injection amount and a fuel injection timing to each cylinder. The fuel pump is controlled to control the amount of fuel pumped from the high-pressure fuel pump to the common rail. Further, an output port of the ECU 30 is further connected to an actuator of the EGR valve 23 via a drive circuit (not shown) to control the amount of EGR gas passing through the EGR valve 23 and a variable valve timing device via a drive circuit (not shown). 50, and controls the intake valve timing.
[0033]
Next, additional fuel injection in the present embodiment will be described.
In the present embodiment, the ECU 30_XNO absorbed by the storage reduction catalyst 70_XIs estimated and this NO_XThe absorption amount is a predetermined value (for example, NO_XNO absorbed by the storage reduction catalyst 70_XApproximately 70% of the amount saturated by the fuel injection), additional fuel injection is performed in each cylinder._XNO from the storage reduction catalyst 70_XTo release and purify.
[0034]
NO_XNO absorbed by the storage reduction catalyst 70_XThe quantity can be estimated, for example, based on engine operating conditions. NO generated by the engine per unit time_XThe amount is determined by the engine operating conditions such as the engine load and the number of revolutions. NO_XNO absorbed per unit time by the storage reduction catalyst 70_XThe amount is the amount of NO released per unit time from the engine._XQuantity, ie NO per unit time of the engine_XA value obtained by multiplying the generation amount by a predetermined coefficient. Therefore, in the present embodiment, an experiment is performed by changing the combination of the engine fuel injection amount (load) and the rotational speed in advance, and the engine releases NO per unit time._XMeasure the amount and use this NO_XThe relationship among the quantity, the engine load, and the rotation speed is stored in the ROM of the ECU 30. Then, based on the actual fuel injection amount and the engine speed at regular intervals (unit time) during engine operation, NO released from the engine per unit time is determined._XThe amount is calculated and this NO_XThe value obtained by multiplying the quantity by a predetermined coefficient is integrated. As a result, the calculated integrated value becomes NO_XNO absorbed by the storage reduction catalyst_XTo match the quantity. Note that additional fuel injection is performed and NO_XNO absorbed from the storage reduction catalyst 70_XIs released after NO is released_XNO of the storage reduction catalyst 70_XThe absorption amount is reset to 0, and NO_XIntegration of the absorption amount is started.
[0035]
Note that NO_XNO of the storage reduction catalyst 70_XAs the absorption increases, NO_XNO in exhaust gas downstream of the storage reduction catalyst 70_XThe concentration increases. Therefore, as described above, NO_XNO of the storage reduction catalyst 70_XInstead of estimating the amount of absorption, for example, NO_XNO in the exhaust passage downstream of the storage reduction catalyst 70_XNO whose concentration can be detected_XA sensor is placed and this NO_XNO detected by sensor_XWhen the concentration exceeds a predetermined value, NO_XNO absorbed by the storage reduction catalyst 70_XThe additional fuel injection may be performed by determining that the amount has increased.
[0036]
The ECU 30 determines NO_XNO of the storage reduction catalyst 70_XWhen it is determined that the absorption amount has increased, the fuel injection valve 111 of each cylinder performs an additional fuel injection in addition to the main fuel injection, thereby setting the exhaust air-fuel ratio of the engine 1 to the rich air-fuel ratio and setting the NO._XNO absorbed from the storage reduction catalyst 70_XRelease.
In the present embodiment, the additional fuel injection amount of each cylinder is set as described below.
[0037]
That is, in the present embodiment, the ratio of the intake air amount of the engine measured by the air flow meter 51 to the sum of the fuel injection amount in the main fuel injection of the engine and the fuel supplied to the engine by the additional fuel injection (that is, the exhaust air-fuel ratio) ) Is determined to be an air-fuel ratio equal to or lower than a predetermined stoichiometric air-fuel ratio (in this embodiment, a rich air-fuel ratio close to the stoichiometric air-fuel ratio).
[0038]
That is, the ECU 30 calculates an engine intake air amount G per one engine revolution G (gram / revolution) based on the engine intake air amount (gram / second) measured by the air flow meter 51 and the engine speed.
Next, the ECU 30 calculates the main fuel injection amount per one time from each of the fuel injection valves 111 based on the accelerator opening and the engine speed, multiplies the number of cylinders, and injects the main fuel into the engine per main engine revolution by the main fuel injection. The total amount of supplied fuel Q (gram / rotation) is calculated.
[0039]
The fuel amount QA to be supplied to the engine 1 by the additional fuel injection per one revolution of the engine is based on the intake air amount G and the total main fuel injection amount Q.
QA = (G / AF₀) -Q (1)
Is calculated as Where AF₀Is a target air-fuel ratio to be reached by additional fuel injection.
[0040]
Fuel quantity QA to be supplied from each fuel injection valve 111 by additional fuel injection per engine stroke cycle_iIs a value obtained by dividing the above QA by the number of cylinders N (N = 6 in this embodiment), that is, QA_i= QA / N.
QA_iIs the total amount of fuel to be supplied to one cylinder by additional fuel injection per one revolution of the engine.
[0041]
However, as described above, a diesel engine is usually operated at a very lean (lean) air-fuel ratio of about 30 at an air-fuel ratio. For this reason, if the exhaust air-fuel ratio is set to be equal to or lower than the stoichiometric air-fuel ratio while the normal operation is continued, it is necessary to inject a large amount of fuel in the additional fuel injection as much as the main fuel injection.
On the other hand, in the late stage of the expansion stroke in which the additional fuel injection is performed and in the exhaust stroke, the temperature in the cylinder is lowered, and the piston is also at the lowered position in the cylinder. For this reason, when a large amount of fuel is injected into the cylinder at this time, the injected fuel does not enter the combustion chamber on the top surface of the piston and reaches the cylinder inner wall in a liquid state, that is, so-called bore flushing occurs. When bore flushing occurs, poor lubrication or the like due to dilution of the lubricating oil or breakage of the oil film tends to occur.
[0042]
For this reason, in a diesel engine, when a large amount of fuel is injected by additional fuel injection, not only does the engine fuel consumption increase, but also there is a problem that bore flushing occurs.
In order to solve this problem, in order to obtain an exhaust air-fuel ratio lower than the stoichiometric air-fuel ratio with a small amount of additional fuel injection, for example, the intake air amount throttle valve 27 in the intake passage is throttled to reduce the engine intake air amount. It is also conceivable to let them. However, when the intake air amount is reduced by the intake throttle, the engine pumping loss due to the throttle loss increases, and the main fuel injection amount must be increased in order to prevent a decrease in engine output. Fuel consumption cannot be reduced so much.
[0043]
Therefore, in this embodiment, by changing the engine valve timing, the amount of air taken into the engine is reduced without increasing the pumping loss in the method described below, and the engine fuel consumption at the time of performing the additional fuel injection is reduced. And the occurrence of bore flushing is prevented.
Hereinafter, the additional fuel injection of the present invention will be described.
(1) First embodiment
In this embodiment, when the exhaust air-fuel ratio is to be lower than the stoichiometric air-fuel ratio, the variable valve timing device 50 is operated to delay the closing timing of the intake valve, thereby reducing the amount of air drawn into the cylinder. I do.
[0044]
FIG. 2 shows the normal operation of the engine 1 in the present embodiment (when the additional fuel injection is not performed) (FIG. 2, (A)) and the additional fuel injection execution (FIG. 2, (B)). FIG. 4 is a timing chart showing setting of engine valve timing.
In FIG. 2, EX and IN indicate the valve lift curves of the exhaust valve and the intake valve, respectively, ETDC and EBDC indicate the top dead center and bottom dead center of the expansion stroke, and ITDC indicates the top dead center of the intake stroke (that is, the exhaust stroke). Top dead center), IBDC indicates the intake stroke and bottom dead center (that is, the bottom dead center of the compression stroke), and CTDC indicates the compression stroke top dead center.
[0045]
As shown in FIG. 2A, during normal operation, the exhaust valve (EX) opens before the bottom dead center (EBDC) of the expansion stroke and closes after the top dead center (ITDC) of the intake stroke. The intake valve (IN) opens before the intake stroke top dead center (ITDC) and closes at a position slightly beyond the intake stroke bottom dead center (IBDC).
On the other hand, in the present embodiment, when the additional fuel injection is performed, the opening and closing timing of the exhaust valve is maintained at the same level as in the normal operation, but the opening and closing timing of the intake valve is greatly delayed. That is, as shown in FIG. 2 (B), in the present embodiment, when additional fuel injection is performed, the intake valve opens after the intake stroke top dead center, and near the center of the compression stroke (the intake bottom dead center IBDC and the compression stroke top dead center). (Between CTDC).
[0046]
As shown in FIG. 2 (B), if the closing timing of the intake valve is delayed, the intake valve is opened until the middle stage of the compression stroke. The intake air is discharged to the intake port as the piston rises during the compression stroke. For this reason, the amount of intake air charged into the cylinder at the time of closing the intake valve is greatly reduced as compared with the normal operation. On the other hand, as described above, in the present embodiment, since the main fuel injection amount is determined by the accelerator opening and the rotation speed, the main fuel injection amount is not significantly reduced even if the intake air amount of the cylinder decreases. Accordingly, in the above equation (1), the intake air amount G decreases and the main fuel injection amount Q does not change, so that the injection amount QA of the additional fuel injection necessary for obtaining the predetermined air-fuel ratio is greatly reduced. You.
[0047]
Further, unlike the intake throttle by the intake throttle valve 27, the reduction of the intake amount due to the delay of the intake valve closing timing does not cause the pumping loss due to the intake throttle. For this reason, the injection amount in the additional fuel injection is reduced by the reduced amount of the intake air, and the increase in the engine fuel consumption when the additional fuel injection is performed is suppressed.
Next, the additional fuel injection operation of the present embodiment will be described. As described above, in the present embodiment, since the intake air amount at the time of additional fuel injection is significantly reduced by delaying the closing timing of the intake valve, the injection amount per cylinder per one engine revolution of the additional fuel injection QA_iIs also greatly reduced. For this reason, the possibility of occurrence of bore flushing is significantly reduced as compared with the case where additional fuel injection is performed without reducing the intake air amount.
[0048]
However, as described above, the additional fuel injection is performed during the expansion stroke and the exhaust stroke in which the temperature in the cylinder decreases. Further, at this time, the piston is at the lowered position, and the fuel injected from the fuel injection valve is in a liquid state and easily reaches the cylinder inner wall. Therefore, in the present embodiment, the fuel amount QA to be supplied to the cylinder by the additional fuel injection_iIs not injected by one fuel injection, and qa is shown in FIG._iAs shown in the above, additional fuel injection is performed a plurality of times during the expansion stroke and the intake stroke. As a result, the amount of fuel injected in one additional fuel injection can be reduced, so that the injected fuel is immediately vaporized, and the occurrence of bore flushing can be more completely prevented. Become.
[0049]
In the present embodiment, the maximum amount of fuel that can be injected in one additional fuel injection without bore flushing is determined in advance by an experiment or the like, and a small value having a margin for the maximum fuel in the additional fuel injection is determined. Maximum fuel injection amount QA_iMAXSet as Then, the total QA of the additional fuel injection amount per cylinder_iAnd QA_iMAXFrom this, the number NI of additional fuel injections is determined. That is, the number NI of additional fuel injections is NI = (QA_i/ QA_iMAX) +1. Then, the fuel injection amount QAI in each additional fuel injection_iIs QA for the first to NI additional fuel injections._iMAX, NI + 1 in the additional fuel injection (QA_i-QA_iMAX× NI).
[0050]
The maximum amount of fuel that can be injected without causing bore flushing can be obtained by previously performing additional fuel injection under the condition that bore flushing is most likely to occur, and measuring the maximum fuel injection amount that does not cause bore flushing. For example, at the end of the expansion stroke, the piston is most lowered and the temperature in the cylinder is also reduced, so that bore flushing is most likely to occur. In this embodiment, when fuel is injected at the end of the expansion stroke, the maximum fuel injection amount that can be injected without causing bore flushing is measured, and a value having a sufficient margin for this maximum fuel injection amount is determined by QA._iMAXSet as QA_iMAXIs generally smaller than the fuel amount corresponding to 20 CC / injection.
[0051]
Further, additional fuel injection is performed not only in one stroke cycle but also in NO cycle._XNO absorbed from the storage reduction catalyst 70_XUntil a supply of the unburned fuel required to release the fuel is performed over a plurality of cycles.
As described above, in the present embodiment, the ECU 30_XNO absorbed by the storage reduction catalyst 70_XWhen the amount increases, the variable valve timing device 50 is controlled to retard the intake valve opening / closing timing by a predetermined amount. The retard amount is set in accordance with the engine load condition, and when the main fuel injection amount is small and the operating air-fuel ratio is high, such as when the load is light, the retard amount of the intake valve timing is set to be large, and the intake air The amount is greatly reduced.
[0052]
Then, when the intake valve timing reaches the predetermined retard amount, the ECU 30 performs additional fuel injection a plurality of times during the expansion stroke and the exhaust stroke of each cylinder. At this time, the amount of fuel injected by one additional fuel injection is set to a small amount that does not cause bore flushing, and the number of additional fuel injections performed during the stroke cycle of the cylinder is calculated by the above equation (1). It is determined by the fuel amount and the fuel amount injected for one additional fuel injection.
[0053]
This makes it possible to significantly reduce the amount of fuel to be supplied to the cylinder by additional fuel injection without causing pumping loss, thereby preventing an increase in fuel consumption during the execution of additional fuel injection, and The occurrence of bore flushing due to the above is completely prevented.
(2) Second embodiment
Next, a second embodiment of the present invention will be described.
[0054]
In the first embodiment, the closing timing of the intake valve is delayed to reduce the intake air amount of the engine, thereby preventing an increase in fuel consumption and the occurrence of bore flushing when performing additional fuel injection. In this embodiment, in addition to the above, the injection amount of each additional fuel injection is feedback-controlled based on the output of the air-fuel ratio sensor 41 disposed in the engine exhaust passage 3.
[0055]
That is, in the present embodiment, the ECU 30 performs NO based on the output of the air-fuel ratio sensor 41 when performing the additional fuel injection._XThe actual air-fuel ratio of the exhaust gas flowing into the storage reduction catalyst 70 is detected. Then, the total fuel amount (total amount of the main fuel injection amount and the additional fuel injection amount) supplied to the cylinder according to the deviation between the predetermined target air-fuel ratio (for example, the stoichiometric air-fuel ratio) and the detected actual exhaust air-fuel ratio. Is corrected. For example, when the exhaust air-fuel ratio at the time of performing the additional fuel injection is higher than the target air-fuel ratio (when the actual exhaust air-fuel ratio is leaner than the target air-fuel ratio), the total fuel amount is increased and the actual exhaust air-fuel ratio becomes higher than the target air-fuel ratio. If it is lower than the air-fuel ratio, the total fuel amount is reduced. The control of the total fuel amount is performed by a known proportional integral derivative control (PID control) based on a deviation between the target air-fuel ratio and the actual air-fuel ratio.
[0056]
Further, the correction of increase or decrease between the main fuel injection amount and the additional fuel injection amount is determined according to the ratio of each injection amount to the total fuel amount.
As described above, in the present embodiment, the amount of fuel supplied to the cylinder is corrected so that the actual exhaust air-fuel ratio detected by the air-fuel ratio sensor 41 matches the target air-fuel ratio._XThe air-fuel ratio of the exhaust gas supplied to the storage reduction catalyst 70 can be controlled very accurately, and the total amount of the main fuel injection amount and the additional fuel injection amount at the time of performing the additional fuel injection is always set to obtain the target air-fuel ratio. Only the amount needed. For this reason, there is no possibility that the fuel amount will be excessive or insufficient, and NO_XNO from the storage reduction catalyst 70_XThe release can be performed efficiently, and it is possible to prevent the supply of excessive fuel and prevent an increase in fuel consumption.
(3) Third embodiment
In the present embodiment, in addition to the control of the first embodiment, NO_XWhen the temperature of the storage reduction catalyst 70 is low, NO_XAn operation of raising the temperature of the storage reduction catalyst to a predetermined temperature is performed. As described above, since the exhaust temperature of a diesel engine is generally lower than that of a gasoline engine, NO_XThere is a case where the temperature of the storage reduction catalyst drops to a temperature lower than the activation temperature of the catalyst (for example, about 350 ° C.). In such a case, NO_XNO of storage reduction catalyst_XStorage capacity and NO_XThe reduction ability at the time of release is reduced, and exhaust gas cannot be sufficiently purified. NO_XEven when the temperature of the storage reduction catalyst is equal to or higher than the activation temperature, it may be necessary to increase the catalyst temperature. For example, SO in exhaust_XThe component is NO_XNO with the same mechanism as the component_XOxide is stored in the storage reduction catalyst to produce stable sulfate. Decompose this sulfate to NO_XFrom storage reduction catalyst to SO_XTo release NO_XIt is necessary to supply exhaust gas with a rich air-fuel ratio while keeping the storage reduction catalyst at a higher temperature than the activation temperature.
[0057]
In the present embodiment, the ECU 30 determines NO based on the output of the exhaust gas temperature sensor 43 disposed in the exhaust passage 3._XThe temperature of the storage reduction catalyst 70 is detected. And NO_XNO from storage reduction catalyst_XIs to be released or SO_XShould be released, additional fuel injection should be performed and NO_XFeedback control is performed on the intake valve timing and the additional fuel injection amount based on the output of the exhaust temperature sensor 43 and the output of the air-fuel ratio sensor 41 so that the temperature of the storage reduction catalyst 70 becomes a predetermined target value. The predetermined target temperature is, for example, NO_XIs to be released when the catalyst activation temperature is about 350 ° C._XIs set to about 550 ° C. when is to be released.
[0058]
Next, the above NO_XThe details of the temperature control of the storage reduction catalyst will be described.
NO_XNO from the storage reduction catalyst 70_XIs to be released or SO_XIs to be released, the ECU 30 returns NO_XNO based on the exhaust gas temperature detected by the exhaust gas temperature sensor 43 disposed at the outlet of the storage reduction catalyst 70_XThe temperature of the storage reduction catalyst 70 is detected. NO_XSince the catalyst bed temperature of the storage reduction catalyst 70 and the exhaust temperature after passing through the catalyst are substantially equal, in this embodiment, the exhaust temperature detected by the exhaust temperature sensor 43 is set to NO._XUsed as the temperature of the storage reduction catalyst 70.
[0059]
Next, the ECU 30 controls the variable valve timing 50 to retard the intake valve closing timing by a predetermined amount and to start additional fuel injection. In this embodiment, the exhaust air-fuel ratio is set so that the exhaust air temperature becomes the highest when the temperature of the catalyst rises (a value near the stoichiometric air-fuel ratio). The feedback control of the additional fuel injection amount is performed so that the air fuel ratio becomes the above-mentioned air-fuel ratio.
[0060]
Further, the ECU 30 determines NO based on the output of the exhaust gas temperature sensor 43._XThe temperature of the storage reduction catalyst 70 is detected, and the detected actual NO_XThe above-mentioned NO of the storage reduction catalyst temperature_XA deviation from the storage reduction catalyst target temperature is calculated, and the intake valve timing is corrected based on the deviation. That is, when the actual temperature is lower than the target temperature, the intake valve timing is advanced to increase the amount of air taken into the cylinder. As described above, in the present embodiment, the additional fuel injection amount is controlled so that the exhaust air-fuel ratio becomes the target air-fuel ratio, and the additional fuel injection amount is also increased in accordance with the intake air amount. The exhaust flow rate increases while maintaining the predetermined temperature, and NO_XThe temperature of the storage reduction catalyst 70 increases. Also, the actual NO_XWhen the temperature of the storage reduction catalyst is lower than the target temperature, the ECU 30 retards the intake valve timing to reduce the amount of air drawn into the cylinder. Also in this case, the additional fuel injection amount is controlled so that the exhaust air-fuel ratio becomes a predetermined air-fuel ratio._XThe temperature of the storage reduction catalyst decreases. NO above_XThe valve timing of the intake valve during temperature control of the storage reduction catalyst is NO_XTarget temperature of storage reduction catalyst and actual NO_XThe control may be performed by proportional integral differential control based on a deviation from the storage reduction catalyst temperature.
[0061]
In the present embodiment, as described above, the intake valve timing and the fuel injection amount are determined by the actual NO_XSince the temperature of the storage reduction catalyst is controlled to reach a predetermined target temperature, exhaust gas having an appropriate temperature and flow rate is always supplied to the catalyst, so that the NO_XIt is possible to control the storage reduction catalyst temperature to the target temperature.
[0062]
(4) Fourth embodiment
Next, a fourth embodiment of the present invention will be described.
In the above-described first embodiment, the occurrence of bore flushing is prevented by dividing the additional fuel injection into the expansion stroke or the exhaust stroke in a plurality of times. On the other hand, this embodiment is different from the first embodiment in that the additional fuel injection is performed in the latter half of the exhaust stroke, and the required amount of fuel is injected by one additional fuel injection.
In the latter half of the exhaust stroke, the piston is in the raised position, so that most of the cylinder inner wall is covered by the piston. Further, since the fuel injected by the additional fuel injection enters the combustion chamber on the upper surface of the piston and is vaporized, the injected fuel does not directly reach the inner wall of the cylinder in a liquid state, so that bore flushing does not occur.
[0063]
However, as described above, in the normal operation, in the latter half of the exhaust stroke, the intake valve starts to open and a valve overlap period occurs, and a part of the fuel injected during this period passes through the opened intake valve through the intake valve. Backflow to port. This backflow fuel flows into the cylinder together with the intake air during the intake stroke, so that unburned fuel remains in the cylinder, and the residual fuel is injected into the main fuel during the compression stroke of the next cycle of the cylinder. If it burns before burning, abnormal combustion will occur. Further, even when abnormal combustion does not occur, both fuel and main fuel by the main fuel injection are burned in the cylinder, so that the generated torque of the cylinder increases and the engine output torque fluctuates. .
In the present embodiment, by delaying the intake valve opening timing at the time of performing the additional fuel injection, the fuel injected by the additional fuel injection is prevented from remaining in the cylinder and burning in the next cycle.
[0064]
3 is a diagram similar to FIG. 2 showing the additional fuel injection timing and the intake valve opening / closing timing in the present embodiment. FIG. 3 (A) shows a normal operation, and FIG. Indicates time.
As shown in FIG. 3, in the present embodiment, at the time of performing the additional fuel injection, the intake valve starts to open after the exhaust stroke top dead center (that is, the intake stroke top dead center ITDC). For this reason, when the additional fuel injection is performed, the intake valve is closed, and a part of the fuel injected by the additional fuel injection is prevented from flowing back to the intake port. This prevents the residual fuel in the cylinder from being generated by the additional fuel injection.
In the present embodiment, the additional fuel injection is performed only once in the latter half of the exhaust stroke (for example, near the top dead center ITDC of the exhaust stroke). Therefore, the fuel injected by the additional fuel injection reaches the inner wall of the cylinder by the piston at the ascending position, so that bore flushing does not occur. The positions of the pistons that can prevent the fuel injected by the additional fuel injection from directly reaching the inner wall of the cylinder are the cylinder inner diameter (cylinder bore diameter), the spray angle of the fuel injection valve, and the projection length of the fuel injection valve into the cylinder. The actual additional fuel injection execution timing is determined for each engine type based on the above conditions.
[0065]
The intake valve opening timing (the delay amount of the valve opening timing) at the time of additional fuel injection can be completely prevented by setting the valve overlap period so that no valve overlap period occurs. Actually, even if some residual fuel is generated, abnormal combustion and engine output torque fluctuation do not occur, so that the intake valve opening timing may be delayed to such an extent that some valve overlap period occurs. In this case, the actual intake valve opening timing may be set to a range in which abnormal combustion or output torque fluctuation does not occur during additional fuel injection by an experiment using an actual engine.
Further, as shown in FIG. 3, if the intake valve closing timing is also delayed at the same time as the intake valve opening timing, the amount of intake air charged into the cylinder is reduced as in the first embodiment. Therefore, it is possible to significantly reduce the additional fuel injection amount and prevent an increase in engine fuel consumption.
Note that also in the present embodiment, the feedback control of the injection amount of the additional fuel injection based on the output of the air-fuel ratio sensor 41 described in the second embodiment and the NO control described in the third embodiment_XIt goes without saying that either one or both of the operation of raising the temperature of the storage reduction catalyst can be used in combination.
[0066]
【The invention's effect】
According to the invention described in each claim, when supplying exhaust gas with a stoichiometric air-fuel ratio or a rich air-fuel ratio to an exhaust purification catalyst by additional fuel injection, occurrence of bore flushing is suppressed while suppressing increase in fuel consumption of the engine. The common effect that it can be completely prevented is obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic configuration of an embodiment when the present invention is applied to an automobile diesel engine.
FIG. 2 is a diagram illustrating intake valve timing when additional fuel injection is performed in the embodiment of FIG. 1;
FIG. 3 is a view similar to FIG. 2, illustrating valve overlap when additional fuel injection is performed in an additional fuel injection embodiment different from FIG. 2;
[Explanation of symbols]
1. Diesel engine
23 ... EGR control valve
30 ... Electronic control unit (ECU)
41 ... Air-fuel ratio sensor
43 ... Exhaust gas temperature sensor
50 ... Variable valve timing device
70 ... NO_XStorage reduction catalyst
111: In-cylinder fuel injection valve

Claims (5)

An exhaust purification catalyst disposed in an exhaust passage of an internal combustion engine having an in-cylinder fuel injection valve that injects fuel directly into a cylinder;
When the air-fuel ratio of the exhaust gas supplied to the exhaust purification catalyst is set to the stoichiometric air-fuel ratio or the rich air-fuel ratio as necessary, in addition to the main fuel injection, during the expansion or exhaust stroke of the cylinder from the in-cylinder fuel injection valve. Control means for performing additional fuel injection, and an exhaust gas purification apparatus for an internal combustion engine comprising:
Further, there is provided a variable valve timing means capable of changing at least one valve timing of the engine intake valve and the exhaust valve,
The variable valve timing means, when the control means performs the additional fuel injection, at least one of the intake valve and the exhaust valve so that the amount of air taken into the cylinder is reduced as compared to when the additional fuel injection is not performed. An exhaust purification device for an internal combustion engine that changes one valve timing. The control means performs the additional fuel injection in a plurality of times during the expansion or exhaust stroke of the cylinder, and determines the amount of fuel injected in one additional fuel injection from the amount of fuel injection in which bore flushing occurs in the cylinder. 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, which is set to be small. Further, an air-fuel ratio sensor for detecting an exhaust air-fuel ratio is provided in an engine exhaust passage upstream of the exhaust purification catalyst,
The control device controls the amount of fuel supplied to the cylinder by the additional fuel injection so that the exhaust air-fuel ratio detected by the air-fuel ratio sensor at the time of performing the additional fuel injection becomes a predetermined rich air-fuel ratio. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1. Further, there is provided a means for detecting the catalyst temperature, wherein the control means and the variable valve timing means are configured such that the fuel supplied to the cylinder by the additional fuel injection so that the detected catalyst temperature becomes a predetermined temperature, and 2. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purifying apparatus controls the valve timing. An exhaust purification catalyst disposed in an exhaust passage of an internal combustion engine having an in-cylinder fuel injection valve that injects fuel directly into a cylinder;
Control means for performing additional fuel injection from the in-cylinder fuel injection valve in addition to main fuel injection when the air-fuel ratio of exhaust gas supplied to the exhaust purification catalyst is set to a stoichiometric air-fuel ratio or a rich air-fuel ratio as necessary. In an exhaust gas purification device for an internal combustion engine comprising:
The engine further includes variable valve timing means capable of changing the opening timing of the engine intake valve, wherein the control means is arranged such that the cylinder is in the exhaust process and the cylinder piston reaches the inner wall of the cylinder of the fuel injected by the additional fuel injection. Perform the additional fuel injection when in the position to prevent
The variable valve timing means controls the intake valve so that the valve overlap period during which the intake valve and the exhaust valve are simultaneously opened is shorter when the control means performs the additional fuel injection than when the additional fuel injection is not performed. An exhaust gas purification device for an internal combustion engine that delays valve opening timing.

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