JP4244490B2 - Internal combustion engine having variable valve mechanism - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an internal combustion engine mounted on an automobile or the like, and more particularly to an internal combustion engine provided with a variable valve mechanism that can change the opening / closing timing and / or lift amount of an intake valve and / or an exhaust valve.
[0002]
[Prior art]
2. Description of the Related Art In recent years, internal combustion engines mounted on automobiles have hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) contained in the exhaust before the exhaust discharged from the internal combustion engine is released into the atmosphere. It is desired to purify harmful gas components such as
[0003]
In response to such demands, hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NOx) in the exhaust gas are purified when the air-fuel ratio of the inflowing exhaust gas is a predetermined air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio. The three-way catalyst is disposed in the exhaust passage of the internal combustion engine, and the air-fuel ratio of the exhaust gas flowing into the three-way catalyst becomes a predetermined air-fuel ratio (the air-fuel ratio of the air-fuel mixture burned in the internal combustion engine). A technique for purifying harmful gas components in exhaust gas by executing air-fuel ratio feedback control for controlling the exhaust gas is known.
[0004]
On the other hand, in an internal combustion engine mounted on an automobile, a lean combustion internal combustion engine that can burn an air-fuel mixture with a higher air-fuel ratio (lean air-fuel ratio) than the stoichiometric air-fuel ratio has been developed in order to reduce fuel consumption. ing.
[0005]
In a lean burn internal combustion engine, the air-fuel ratio of the exhaust gas becomes a lean air-fuel ratio, and reducing components such as hydrocarbons (HC) contained in the exhaust gas are reduced. Therefore, only with a three-way catalyst, nitrogen oxides (NOx) in the exhaust gas are emitted. Cannot be fully reduced and purified.
[0006]
For this reason, a technique for arranging an NOx storage reduction catalyst in the exhaust passage of an internal combustion engine has been proposed. The NOx storage reduction catalyst stores nitrogen oxide (NOx) in the exhaust when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst is a lean air-fuel ratio, and flows into the NOx storage reduction catalyst. When the air-fuel ratio of the exhaust gas is the stoichiometric air-fuel ratio or the rich air-fuel ratio, the stored nitrogen oxides (NOx) are released, and the released nitrogen oxides (NOx) are released into hydrocarbons (HC) ) And carbon monoxide (CO) to react with a reducing agent such as nitrogen (N₂).
[0007]
When such a NOx storage reduction catalyst is disposed in the exhaust passage of a lean combustion internal combustion engine, when the internal combustion engine is operated in lean combustion and exhaust gas with a lean air-fuel ratio is exhausted from the internal combustion engine, The contained nitrogen oxides (NOx) are stored in the NOx storage reduction catalyst.
[0008]
Further, when the internal combustion engine is operated at a stoichiometric air-fuel ratio or a rich air-fuel ratio and exhaust gas of the stoichiometric or rich air-fuel ratio is discharged from the internal combustion engine, nitrogen oxides stored in the NOx storage reduction catalyst are stored. (NOx) is released from the NOx storage reduction catalyst and nitrogen (N₂).
[0009]
By the way, since the amount of nitrogen oxide (NOx) that can be stored by the NOx storage reduction catalyst is limited, if the lean combustion operation of the internal combustion engine is continued for a long time, the storage capacity of the NOx storage reduction catalyst is saturated. The nitrogen oxide (NOx) contained in the exhaust gas may be released into the atmosphere without being purified.
[0010]
Therefore, conventionally, when the NOx storage capacity of the NOx storage reduction catalyst is saturated when the internal combustion engine is operating with lean combustion, the operation state of the internal combustion engine is switched from the lean combustion operation to the rich air-fuel ratio operation. So-called rich spike control is performed in which air-fuel ratio exhaust gas is supplied to the NOx storage reduction catalyst.
[0011]
[Problems to be solved by the invention]
By the way, if the fuel injection amount is simply increased in the rich spike control, the torque of the internal combustion engine increases abruptly. Therefore, it is necessary to increase the fuel injection amount while reducing the intake air amount of the internal combustion engine.
[0012]
For this reason, when the execution of the rich spike control is started, the throttle valve is controlled to decrease the intake air amount of the internal combustion engine, and the fuel injection valve is increased to increase the amount of fuel supplied into the cylinder. Will be controlled.
[0013]
However, since there is a distance between the throttle valve and the cylinder, there is a so-called intake response delay that takes time from when the throttle valve is changed until the intake air amount in the cylinder decreases to the desired amount, The transition period until the operating state of the internal combustion engine switches from the lean combustion operation to the desired rich air-fuel ratio operation becomes longer.
[0014]
Further, even when the execution of rich spike control is terminated, the throttle valve is controlled to increase the intake air amount of the internal combustion engine and the fuel injection valve is controlled to decrease the amount of fuel supplied to the cylinder. As a result, an intake response delay occurs as in the start of execution of the rich spike control, and the transition period until the operating state of the internal combustion engine switches from the rich air-fuel ratio operation to the lean combustion operation becomes longer.
[0015]
Thus, when the transition period of the engine operating state becomes long, the execution period of the rich spike control becomes long, and there is a possibility that a deterioration in drivability and an unnecessary increase in fuel consumption are induced.
[0016]
The present invention has been made in view of various circumstances as described above, and performs exhaust gas purification efficiently in a short period of time in a lean combustion internal combustion engine capable of combusting an oxygen-rich mixture. It is an object of the present invention to improve drivability and reduce fuel consumption by providing a technology capable of achieving the above.
[0017]
[Means for Solving the Problems]
The present invention employs the following means in order to solve the above-described problems. That is, an internal combustion engine having a variable valve mechanism according to the present invention is:
A lean combustion internal combustion engine capable of combusting an oxygen-rich mixture.
A NOx catalyst provided in an exhaust passage of the internal combustion engine for purifying nitrogen oxides contained in the exhaust;
A variable valve mechanism capable of changing the opening / closing timing and / or lift amount of the intake valve and / or exhaust valve of the internal combustion engine;
Purification support means for controlling the variable valve mechanism to supply exhaust gas in a state suitable for purifying the predetermined gas component to the NOx catalyst at a time when the predetermined gas component is to be purified in the NOx catalyst;
It is characterized by having.
[0018]
In the internal combustion engine having the variable valve mechanism configured as described above, when the predetermined gas component is to be purified in the NOx catalyst, the purification assisting means performs exhaust in a state suitable for purifying the predetermined gas component. The variable valve mechanism is controlled so as to be discharged from the internal combustion engine.
[0019]
Here, since the intake valve and the exhaust valve are provided so as to face the cylinder, changes in the opening / closing timing and / or the lift amount of the intake valve and / or the exhaust valve are exhausted from the state of the gas in the cylinder and the inside of the cylinder. It will be immediately reflected in the exhaust status.
[0020]
Therefore, when the variable valve mechanism is controlled so that exhaust in a state suitable for purifying a predetermined gas component is discharged from the internal combustion engine, the state of the exhaust discharged from the internal combustion engine is immediately Therefore, the control period for purifying the predetermined gas component is not unnecessarily prolonged.
[0021]
In the internal combustion engine having the variable valve mechanism according to the present invention, examples of the predetermined gas component include nitrogen oxide (NOx) and sulfur oxide (SOx).
[0022]
When purifying nitrogen oxides (NOx) in a NOx catalyst, a reducing agent for reducing the nitrogen oxides (NOx) is required. Therefore, the purification support means is in a state where the exhaust state contains a large amount of reducing agent. What is necessary is just to control a variable valve mechanism so that it may become.
[0023]
Examples of a method for increasing the amount of reducing agent contained in the exhaust gas include a method in which the air-fuel ratio of the exhaust gas is made rich by operating at least one cylinder of the internal combustion engine at the rich air-fuel ratio. .
[0024]
When operating at least one cylinder of the internal combustion engine at a rich air-fuel ratio, the purification support means controls the variable valve mechanism so that the valve opening period of the intake valve of the cylinder is shortened, for example, In the case where the air-fuel ratio of the air-fuel mixture combusted in the cylinder is reduced to a rich air-fuel ratio, and the amount of reducing agent contained in the exhaust gas is further increased, the purification assisting means In other words, the variable valve mechanism is controlled so that the opening period of the intake valve of a predetermined cylinder is shortened, and at the same time, the fuel injection valve is controlled to increase the amount of fuel supplied to the cylinder.
[0025]
As a reducing agent for nitrogen oxides (NOx), hydrocarbons (HC) are generally used, but hydrogen (H₂) And hydrocarbon (HC) oxidation, carbon monoxide (CO) has a higher reducing ability than hydrocarbon (HC).₂) Or carbon monoxide (CO) in a large amount, the variable valve mechanism may be controlled.
[0026]
Hydrogen contained in exhaust (H₂) Is increased, for example, the opening timing of the exhaust valve is advanced to the middle of the expansion stroke before the exhaust stroke bottom dead center, and the gas in the middle of combustion is discharged from the cylinder as exhaust gas The method of doing can be illustrated.
[0027]
As a method for increasing the amount of carbon monoxide (CO) contained in the exhaust, for example, the opening timing of the exhaust valve is retarded until the bottom dead center of the exhaust stroke, and the gas sufficiently oxidized in the cylinder is A method of discharging as exhaust gas can be exemplified.
[0028]
Next, when purifying sulfur oxide (SOx) in the NOx catalyst, particularly when eliminating sulfur poisoning of the NOx catalyst, the NOx catalyst needs to be in a high temperature and rich atmosphere. The variable valve mechanism may be controlled so that the exhaust state is at a high temperature and a rich air-fuel ratio.
[0029]
As a method for increasing the temperature of the exhaust, for example, a method of advancing the valve opening timing of the exhaust valve so that burned gas immediately after being burned in each cylinder is discharged from each cylinder can be exemplified. As a method of making the air-fuel ratio rich, the intake valve opening timing is retarded and / or the intake valve closing timing is advanced in order to shorten the intake valve opening period, or in the cylinder A method for controlling the fuel injection valve to increase the amount of fuel supplied can be exemplified.
[0030]
When the internal combustion engine according to the present invention includes an ignition plug, the opening timing of the exhaust valve is advanced, and the ignition timing of the ignition plug is retarded to delay the combustion timing of the air-fuel mixture. The temperature of burned gas when the exhaust valve is opened may be further increased.
[0031]
Here, as the NOx catalyst according to the present invention, for example, when the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is a lean air-fuel ratio, nitrogen oxide (NOx) contained in the exhaust gas is occluded, and the NOx catalyst When the air-fuel ratio of the exhaust gas flowing into the exhaust gas is the stoichiometric air-fuel ratio or the rich air-fuel ratio, the NOx storage reduction catalyst that releases and reduces the stored nitrogen oxides (NOx) or the exhaust gas flowing into the NOx catalyst Examples include a selective reduction type NOx catalyst that reduces or decomposes nitrogen oxides (NOx) in the exhaust gas when the air-fuel ratio is a lean air-fuel ratio and a reducing agent is present.
[0032]
Further, in the internal combustion engine having the variable valve mechanism according to the present invention, the purification assisting means does not change the torque of the internal combustion engine when supplying exhaust gas in a state suitable for purifying the predetermined gas component to the NOx catalyst. Thus, it is preferable to control the variable valve mechanism.
[0033]
In this case, exhaust gas purification with high responsiveness is realized while suppressing torque fluctuation of the internal combustion engine.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a specific embodiment of an internal combustion engine having a variable valve mechanism according to the present invention will be described with reference to the drawings.
[0035]
<Embodiment 1>
A first embodiment of an internal combustion engine having a variable valve mechanism according to the present invention will be described with reference to FIGS.
[0036]
1 and 2 are diagrams showing a schematic configuration of an internal combustion engine and an intake / exhaust system thereof according to the present embodiment. The internal combustion engine 1 shown in FIGS. 1 and 2 is a four-cycle water-cooled gasoline engine including four cylinders 21.
[0037]
The internal combustion engine 1 includes a cylinder block 1b in which four cylinders 21 and a cooling water channel 1c are formed, and a cylinder head 1a fixed to the upper portion of the cylinder block 1b.
[0038]
A crankshaft 23 serving as an engine output shaft is rotatably supported on the cylinder block 1b. The crankshaft 23 is connected to a piston 22 slidably loaded in each cylinder 21.
[0039]
A combustion chamber 24 surrounded by the top surface of the piston 22 and the wall surface of the cylinder head 1 a is formed above the piston 22 of each cylinder 21. An ignition plug 25 is attached to the cylinder head 1 a so as to face the combustion chamber 24 of each cylinder 21, and an igniter 25 a for applying a drive current to the ignition plug 25 is connected to the ignition plug 25. .
[0040]
Two open ends of the intake port 26 and two open ends of the exhaust port 27 are formed at a portion of the cylinder head 1a facing the combustion chamber 24 of each cylinder 21. The cylinder head 1a is provided with an intake valve 28 that opens and closes each open end of the intake port 26 and an exhaust valve 29 that opens and closes each open end of the exhaust port 27 so as to freely advance and retract.
[0041]
The cylinder head 1a includes an electromagnetic drive mechanism 30 (hereinafter referred to as an intake-side electromagnetic drive mechanism 30) that drives the intake valve 28 to advance and retreat using electromagnetic force generated when an excitation current is applied. The same number as 28 is provided. Each intake side electromagnetic drive mechanism 30 is electrically connected to a drive circuit 30a (hereinafter referred to as an intake side drive circuit 30a) for applying an excitation current to the intake side electromagnetic drive 30.
[0042]
In the cylinder head 1a, an electromagnetic drive mechanism 31 (hereinafter referred to as an exhaust-side electromagnetic drive mechanism 31) that drives the exhaust valve 29 forward and backward using electromagnetic force generated when an excitation current is applied is provided in the exhaust valve. The same number as 29 is provided. Each exhaust side electromagnetic drive mechanism 31 is electrically connected to a drive circuit 31a (hereinafter referred to as an exhaust side drive circuit 31a) for applying an excitation current to the exhaust side electromagnetic drive mechanism 31.
[0043]
The intake side electromagnetic drive mechanism 30 and the exhaust side electromagnetic drive mechanism 31 described above implement the variable valve mechanism according to the present invention.
Here, specific configurations of the intake-side electromagnetic drive mechanism 30 and the exhaust-side electromagnetic drive mechanism 31 will be described. Since the intake side electromagnetic drive mechanism 30 and the exhaust side electromagnetic drive mechanism 31 have the same configuration, only the intake side electromagnetic drive mechanism 30 will be described as an example.
[0044]
FIG. 3 is a cross-sectional view showing the configuration of the intake-side electromagnetic drive mechanism 30. In FIG. 3, the cylinder head 1 a of the internal combustion engine 1 includes a lower head 10 fixed to the upper surface of the cylinder block 1 b and an upper head 11 provided on the upper portion of the lower head 10.
[0045]
The lower head 10 is formed with two intake ports 26 for each cylinder 21, and a valve seat 12 for seating a valve element 28 a of the intake valve 28 at the opening end of each intake port 26 on the combustion chamber 24 side. Is provided.
[0046]
The lower head 10 is formed with a through hole having a circular cross section from the inner wall surface of each intake port 26 to the upper surface of the lower head 10, and a cylindrical valve guide 13 is inserted into the through hole. The valve shaft 28b of the intake valve 28 passes through the inner hole of the valve guide 13, and the valve shaft 28b is movable forward and backward in the axial direction.
[0047]
A core mounting hole 14 having a circular cross section into which the first core 301 and the second core 302 are fitted is provided in a portion of the upper head 11 where the shaft center is the same as the valve guide 13. The lower portion 14b of the core mounting hole 14 is formed larger in diameter than the upper portion 14a. Hereinafter, the lower portion 14b of the core mounting hole 14 is referred to as a large diameter portion 14b, and the upper portion 14a of the core mounting hole 14 is referred to as a small diameter portion 14a.
[0048]
An annular first core 301 and second core 302 made of a soft magnetic material are fitted in the small diameter portion 14a in series in the axial direction with a predetermined gap 303 interposed therebetween. The upper end of the first core 301 and the lower end of the second core 302 are respectively formed with a flange 301a and a flange 302a. The first core 301 is from above and the second core 302 is from below the core mounting holes. 14 and the flanges 301a and 302a abut against the edge of the core mounting hole 14, whereby the first core 301 and the second core 302 are positioned, and the gap 303 is held at a predetermined distance. It is like that.
[0049]
A cylindrical upper cap 305 is provided above the first core 301. The upper cap 305 is fixed to the upper surface of the upper head 11 by passing a bolt 304 through a flange portion 305a formed at the lower end thereof. In this case, the lower end of the upper cap 305 including the flange portion 305 a is fixed in a state where the lower end of the upper cap 305 is in contact with the peripheral edge of the upper surface of the first core 301. become.
[0050]
On the other hand, a lower cap 307 made of an annular body having an outer diameter substantially the same diameter as the large-diameter portion 14 b of the core mounting hole 14 is provided at the lower portion of the second core 302. A bolt 307 passes through the lower cap 307, and the bolt 307 fixes the lower cap 307 to the downward step surface of the step portion of the small diameter portion 14a and the large diameter portion 14b. In this case, the lower cap 307 is fixed in a state where it is in contact with the peripheral edge of the lower surface of the second core 302, and as a result, the second core 302 is fixed to the upper head 11.
[0051]
A first electromagnetic coil 308 is gripped in the groove formed on the surface of the first core 301 on the gap 303 side, and the groove formed on the surface of the second core 302 on the surface of the gap 303 is The second electromagnetic coil 309 is gripped. At this time, the first electromagnetic coil 308 and the second electromagnetic coil 309 are arranged at positions facing each other with the gap 303 therebetween. The first and second electromagnetic coils 308 and 309 are electrically connected to the intake side drive circuit 30a described above.
[0052]
An armature 311 made of an annular soft magnetic material having an outer diameter smaller than the inner diameter of the gap 303 is disposed in the gap 303. A columnar armature shaft 310 extending in the vertical direction along the axis of the armature 311 is fixed to the hollow portion of the armature 311. The armature shaft 310 has an upper end passing through the hollow portion of the first core 301 and reaching the upper cap 305 above it, and a lower end passing through the hollow portion of the second core 302 and a large diameter portion below it. 14b, and is held by the first core 301 and the second core 302 so as to be movable back and forth in the axial direction.
[0053]
A disk-shaped upper retainer 312 is joined to the upper end of the armature shaft 310 extending into the upper cap 305, and an adjustment bolt 313 is screwed into the upper opening of the upper cap 305. An upper spring 314 is interposed between the upper retainer 312 and the adjusting bolt 313. A spring seat 315 having an outer diameter substantially the same as the inner diameter of the upper cap 305 is interposed on the contact surface between the adjustment bolt 313 and the upper spring 314.
[0054]
On the other hand, the upper end portion of the valve shaft 28b of the intake valve 28 is in contact with the lower end portion of the armature shaft 310 extending into the large diameter portion 14b. A disc-shaped lower retainer 28 c is joined to the outer periphery of the upper end portion of the valve shaft 28 b, and a lower spring 316 is interposed between the lower surface of the lower retainer 28 c and the upper surface of the lower head 10.
[0055]
In the intake-side electromagnetic drive mechanism 30 configured as described above, when no excitation current is applied from the intake-side drive circuit 30a to the first electromagnetic coil 308 and the second electromagnetic coil 309, the intake-side electromagnetic drive mechanism 30 starts from the upper spring 314. A biasing force in the downward direction (that is, the direction in which the intake valve 28 is opened) acts on the armature shaft 310 and the upward direction from the lower spring 316 to the intake valve 28 (that is, the intake valve 28 is closed). As a result, the armature shaft 310 and the intake valve 28 come into contact with each other and are elastically supported at a predetermined position, that is, held in a so-called neutral state.
[0056]
The urging force of the upper spring 314 and the lower spring 316 is set so that the neutral position of the armature 311 coincides with an intermediate position between the first core 301 and the second core 302 in the gap 303. When the neutral position of the armature 311 is deviated from the above-described intermediate position due to initial tolerance or aging of components, the adjustment bolt 313 can be adjusted so that the neutral position of the armature 311 matches the above-described intermediate position. It has become.
[0057]
The axial lengths of the armature shaft 310 and the valve shaft 28b are such that when the armature 311 is positioned at an intermediate position of the gap 303, the valve element 28a is fully opened and fully closed. And an intermediate position (hereinafter referred to as a middle open position).
[0058]
In the intake-side electromagnetic drive mechanism 30 described above, when an excitation current is applied to the first electromagnetic coil 308 from the intake-side drive circuit 30a, the intake-side drive circuit 30a is connected between the first core 301, the first electromagnetic coil 308, and the armature 311. When an electromagnetic force is generated in a direction that displaces the armature 311 toward the first core 301, and an excitation current is applied to the second electromagnetic coil 309 from the intake side drive circuit 30 a, An electromagnetic force in a direction to displace the armature 311 toward the second core 302 is generated between the second electromagnetic coil 309 and the armature 311.
[0059]
Therefore, in the intake side electromagnetic drive mechanism 30 described above, the excitation current from the intake side drive circuit 30a is alternately applied to the first electromagnetic coil 308 and the second electromagnetic coil 309, whereby the armature 311 moves forward and backward. As a result, the valve shaft 28b is driven to advance and retract, and at the same time, the valve body 28a is driven to open and close.
[0060]
At that time, it is possible to control the opening / closing timing of the intake valve 28 by changing the excitation current application timing and the magnitude of the excitation current to the first electromagnetic coil 308 and the second electromagnetic coil 309.
[0061]
Further, a valve lift sensor 317 for detecting the displacement of the intake valve 28 is attached to the intake side electromagnetic drive mechanism 30 described above. The valve lift sensor 317 includes a disk-shaped target 317a attached to the upper surface of the apparator 312 and a gap sensor 317b attached to a portion of the adjustment bolt 313 facing the apparator 312.
[0062]
In the valve lift sensor 317 configured as described above, the target 317a is integrally displaced with the armature 311 of the intake-side electromagnetic drive mechanism 30, and the gap sensor 317b is set at a distance between the gap sensor 317b and the target 317a. A corresponding electrical signal is output.
[0063]
At this time, the output signal value of the gap sensor 317b when the armature 311 is in the neutral state is stored in advance, and the difference between the output signal value and the output signal value of the gap sensor 317b at the present time is calculated, thereby obtaining the armature. 311 and the displacement of the intake valve 28 can be specified.
[0064]
Here, returning to FIGS. 1 and 2, an intake branch pipe 33 including four branch pipes is connected to the cylinder head 1 a of the internal combustion engine 1, and an intake port 26 of each cylinder 21 is connected to each of the intake branch pipes 33. It communicates with the branch pipe. A fuel injection valve 32 is attached to the cylinder head 1 a in the vicinity of the connection portion with the intake branch pipe 33 so that its injection hole faces the intake port 26.
[0065]
The intake branch pipe 33 is connected to a surge tank 34 for suppressing intake air pulsation. An intake pipe 35 is connected to the surge tank 34, and the intake pipe 35 is connected to an air cleaner box 36 for removing dust, dust and the like in the intake air.
[0066]
An air flow meter 44 that outputs an electric signal corresponding to the mass of air flowing through the intake pipe 35 (intake air mass) is attached to the intake pipe 35. A throttle valve 39 for adjusting the flow rate of the intake air flowing through the intake pipe 35 is provided in a portion of the intake pipe 35 downstream of the air flow meter 44.
[0067]
The throttle valve 39 is composed of a stepper motor or the like, and a throttle actuator 40 that opens and closes the throttle valve 39 according to the magnitude of applied power, and a throttle that outputs an electrical signal corresponding to the opening of the throttle valve 39. A position sensor 41 and an accelerator position sensor 43 that is mechanically connected to the accelerator pedal 42 and outputs an electric signal corresponding to the operation amount of the accelerator pedal 42 are attached.
[0068]
On the other hand, an exhaust branch pipe 45 formed so that four branch pipes merge with one collecting pipe immediately downstream of the internal combustion engine 1 is connected to the cylinder head 1a of the internal combustion engine 1, and the exhaust branch pipes thereof. Each of the 45 branch pipes communicates with the exhaust port 27 of each cylinder 21.
[0069]
The exhaust branch pipe 45 is connected to an exhaust purification catalyst 46. The exhaust purification catalyst 46 is connected to an exhaust pipe 47, and the exhaust pipe 47 is connected to a muffler (not shown) downstream.
[0070]
The exhaust purification catalyst 46 includes hydrocarbon (HC) and carbon monoxide (CO) contained in the exhaust when the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 46 is a predetermined air-fuel ratio in the vicinity of the theoretical air-fuel ratio. And a three-way active function for purifying nitrogen oxides (NOx) and, when the air-fuel ratio of the exhaust gas flowing into the exhaust purification catalyst 46 is a lean air-fuel ratio, occludes nitrogen oxides (NOx) contained in the exhaust gas. An NOx storage reduction catalyst having a NOx storage reduction function that reduces and purifies nitrogen oxide (NOx) while releasing the stored nitrogen oxide (NOx) when the air-fuel ratio of the inflowing exhaust gas is the stoichiometric air-fuel ratio or rich air-fuel ratio. is there.
[0071]
The NOx storage reduction catalyst 46 is made of, for example, an alkali metal such as potassium (K), sodium (Na), lithium (Li), cesium (Cs), barium (Ba), calcium on a support made of alumina. It is configured by supporting at least one selected from an alkaline earth such as (Ca), a rare earth such as lanthanum (La) and yttrium (Y), and a noble metal such as platinum (Pt). However, in the present embodiment, an occlusion reduction type NOx catalyst in which barium (Ba) and platinum (Pt) are supported on a support made of alumina will be described as an example.
[0072]
In the NOx storage reduction catalyst 46 configured as described above, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 46 becomes a lean air-fuel ratio, the oxygen concentration in the exhaust gas increases, so oxygen (O₂) Is O₂ ^-Or O^2-It adheres to the surface of platinum (Pt) in the form of Further, nitric oxide (NO) contained in the exhaust gas is oxygen (O) on the surface of platinum Pt.₂ ^-Or O^2-) To react with nitrogen dioxide (NO₂) (2NO + O₂→ 2NO₂).
[0073]
Subsequently, nitrogen dioxide (NO₂) Is oxidized on platinum (Pt) and combined with barium oxide (BaO) to form nitrate ions (NO)._3-) And its nitrate ion (NO_3-) Is absorbed by the NOx storage reduction catalyst 46.
[0074]
Such NOx absorption action is continued unless the air-fuel ratio of the inflowing exhaust gas is a lean air-fuel ratio and the NOx absorption capacity of the NOx storage reduction catalyst 46 is saturated.
On the other hand, when the oxygen concentration of the exhaust gas flowing into the NOx storage reduction catalyst 46 decreases, nitrogen dioxide (NO₂Nitrate ions (NO) bound to barium oxide (BaO)._3-) On the contrary, nitrogen dioxide (NO₂) And nitrogen monoxide (NO), and desorbs from the NOx storage reduction catalyst 46.
[0075]
At that time, if the air-fuel ratio of the inflowing exhaust gas is the stoichiometric air-fuel ratio or the rich air-fuel ratio, a relatively large amount of hydrocarbon (HC) or carbon monoxide (CO) is contained in the exhaust gas, and these hydrocarbons ( HC) and carbon monoxide (CO) are oxygen (O) on platinum (Pt) of the NOx storage reduction catalyst 46.₂ ^-Or O^2-) And nitrogen dioxide (NO) released from the NOx storage reduction catalyst 46.₂) Or nitrogen monoxide (NO) is a reducing component in the exhaust gas (oxygen (O) on platinum (Pt) of the NOx storage reduction catalyst 46).₂ ^-Or O^2-) To react with partially oxidized hydrocarbons (HC), carbon monoxide (CO) and other active species) to react with nitrogen (N₂).
[0076]
That is, the hydrocarbon (HC) and carbon monoxide (CO) contained in the exhaust gas flowing into the NOx storage reduction catalyst 46 are oxygen (O) on platinum (Pt).₂ ^-Or O^2-) And immediately oxidized to oxygen, then oxygen on platinum (Pt) (O₂ ^-Or O^2-) After the consumption of hydrocarbons (HC) and carbon monoxide (CO)₂) And nitric oxide (NO) to convert these nitrogen oxides (NOx) to nitrogen (N₂).
[0077]
Therefore, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 46 is a lean air-fuel ratio, the NOx storage reduction catalyst 46 stores nitrogen oxides (NOx) contained in the exhaust gas, and stores the NOx. When the air-fuel ratio of the exhaust gas flowing into the reduction-type NOx catalyst 46 is the stoichiometric air-fuel ratio or the rich air-fuel ratio, the stored nitrogen oxide (NOx) is reduced and purified.
[0078]
Next, an electric signal corresponding to the air-fuel ratio of the exhaust flowing through the exhaust branch pipe 45, in other words, the air-fuel ratio of the exhaust flowing into the NOx storage reduction catalyst 46 is applied to the collecting pipe of the exhaust branch pipe 45. An output air-fuel ratio sensor 48 is attached.
[0079]
An electric signal corresponding to the concentration of nitrogen oxide (NOx) contained in the exhaust gas flowing out from the NOx storage reduction catalyst 46 is provided at a portion of the exhaust pipe 47 located immediately downstream of the NOx storage reduction catalyst 46. An output NOx sensor 49 is attached.
[0080]
The internal combustion engine 1 includes a crank position sensor 51 including a timing rotor 51a attached to an end of the crankshaft 23 and an electromagnetic pickup 51b attached to a cylinder block 1b in the vicinity of the timing rotor 51a. And a water temperature sensor 52 attached to the cylinder block 1b so as to detect the temperature of the cooling water flowing through the cooling water passage 1c.
[0081]
The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 20 for controlling the operating state of the internal combustion engine 1.
[0082]
Various sensors such as a throttle position sensor 41, an accelerator position sensor 43, an air flow meter 44, an air-fuel ratio sensor 48, a NOx sensor 49, a crank position sensor 51, a water temperature sensor 52, and a valve lift sensor 317 are connected to the ECU 20 via electric wiring. The output signals of the sensors are input to the ECU 20.
[0083]
The ECU 20 is connected to an igniter 25a, an intake side drive circuit 30a, an exhaust side drive circuit 31a, a fuel injection valve 32, a throttle actuator 40, and the like via electric wiring, and the ECU 20 uses output signal values of various sensors as parameters. The igniter 25a, the intake side drive circuit 30a, the exhaust side drive circuit 31a, the fuel injection valve 32, and the throttle actuator 40 can be controlled.
[0084]
Here, as shown in FIG. 4, the ECU 20 includes a CPU 401, a ROM 402, a RAM 403, a backup RAM 404, an input port 405, and an output port 406 that are connected to each other via a bidirectional bus 400. A connected A / D converter (A / D) 407 is provided.
[0085]
The A / D 407 outputs analog signals such as a throttle position sensor 41, an accelerator position sensor 43, an air flow meter 44, an air-fuel ratio sensor 48, a NOx sensor 49, a water temperature sensor 52, a valve lift sensor 317, and the like. It is connected to the sensor via electrical wiring. The A / D 407 converts the output signal of each sensor described above from an analog signal format to a digital signal format, and transmits the converted signal to the input port 405.
[0086]
The input port 405 outputs analog signal format signals such as the throttle position sensor 41, accelerator position sensor 43, air flow meter 44, air-fuel ratio sensor 48, NOx sensor 49, water temperature sensor 52, valve lift sensor 317, etc. And a sensor that outputs a signal in the form of a digital signal, such as the crank position sensor 51, is directly connected to the sensor.
[0087]
The input port 405 inputs output signals of various sensors directly or via the A / D 407 and transmits these output signals to the CPU 401 and the RAM 403 via the bidirectional bus 400.
[0088]
The output port 406 is connected to the igniter 25a, the intake side drive circuit 30a, the exhaust side drive circuit 31a, the fuel injection valve 32, the throttle actuator 40, and the like through electrical wiring. The output port 406 receives a control signal output from the CPU 401 via the bidirectional bus 400, and inputs the control signal to the igniter 25a, the intake side drive circuit 30a, the exhaust side drive circuit 31a, the fuel injection valve 32, or It transmits to the actuator 40 for throttles.
[0089]
The ROM 402 includes a fuel injection amount control routine for determining a fuel injection amount, a fuel injection timing control routine for determining fuel injection timing, an intake valve opening / closing timing control routine for determining opening / closing timing of the intake valve 28, The exhaust valve opening / closing timing control routine for determining the opening / closing timing of the exhaust valve 29, the intake side excitation current control routine for determining the amount of excitation current to be applied to the intake side electromagnetic drive mechanism 30, and the exhaust side electromagnetic drive mechanism 31 Exhaust side excitation current amount control routine for determining the amount of excitation current to be applied, ignition timing control routine for determining the ignition timing of the spark plug 25 of each cylinder 21, and opening degree of the throttle valve 39 In addition to application programs such as a throttle opening control routine, nitrogen acid stored in the NOx storage reduction catalyst 46 is stored. A purification support control routine for reducing and purifying chemicals (NOx) is stored.
[0090]
The ROM 402 stores various control maps in addition to the application programs described above. The above-described control map is, for example, a fuel injection amount control map showing the relationship between the operation state of the internal combustion engine 1 and the fuel injection amount, a fuel injection timing control map showing the relationship between the operation state of the internal combustion engine 1 and the fuel injection timing, An intake valve opening / closing timing control map showing the relationship between the operating state of the internal combustion engine 1 and the opening / closing timing of the intake valve 28; an exhaust valve opening / closing timing control map showing the relationship between the operating state of the internal combustion engine 1 and the opening / closing timing of the exhaust valve 29; Excitation current amount control map showing the relationship between the operation state of the internal combustion engine 1 and the excitation current amount to be applied to the intake side electromagnetic drive mechanism 30 and the exhaust side electromagnetic drive mechanism 31, the operation state of the internal combustion engine 1, and each ignition plug 25 These are an ignition timing control map showing the relationship with the ignition timing, a throttle opening degree control map showing the relationship between the operating state of the internal combustion engine 1 and the opening degree of the throttle valve 39, and the like.
[0091]
The RAM 403 stores output signals of the sensors, calculation results of the CPU 401, and the like. The calculation result is, for example, the engine speed calculated based on the output signal of the crank position sensor 51. Various data stored in the RAM 403 is rewritten to the latest data every time the crank position sensor 51 outputs a signal.
[0092]
The backup RAM 45 is a non-volatile memory that retains data even after the operation of the internal combustion engine 1 is stopped, and stores learning values and the like related to various controls.
The CPU 401 operates in accordance with an application program stored in the ROM 402, and executes fuel injection control, ignition control, intake valve opening / closing control, exhaust valve opening / closing control, throttle control, NOx purification control, and the like.
[0093]
At that time, the CPU 401 determines the operating state of the internal combustion engine 1 using output signal values of the crank position sensor 51, the accelerator position sensor 43, the air flow meter 44, and the like as parameters, and performs various controls according to the determined operating state. Execute.
[0094]
For example, if the CPU 401 determines that the operation state of the internal combustion engine 1 is in the low and medium load operation region, the throttle opening is performed in order to realize the lean combustion operation with the oxygen-rich mixture (lean air-fuel ratio mixture). The fuel injection amount, the opening / closing timing of the intake valve 28, the opening / closing timing of the exhaust valve 29, and the ignition timing are controlled.
[0095]
When it is determined that the operation state of the internal combustion engine 1 is in the high load operation region, the CPU 401 determines the throttle opening, the fuel injection amount, the intake air in order to realize the stoichiometric operation with the stoichiometric air-fuel mixture (stoichiometric mixture). The opening / closing timing of the valve 28, the opening / closing timing of the exhaust valve 29, and the ignition timing are controlled.
[0096]
Further, when the internal combustion engine 1 is in a lean combustion operation, the air-fuel ratio of the exhaust becomes a lean air-fuel ratio, so that nitrogen oxide (NOx) contained in the exhaust is stored in the NOx storage reduction catalyst 46. However, when the lean combustion operation of the internal combustion engine 1 is continued for a long period of time, the NOx storage capacity of the NOx storage reduction catalyst 46 is saturated, and nitrogen oxide (NOx) in the exhaust gas enters the NOx storage reduction catalyst 46. May be released into the atmosphere without being removed or purified.
[0097]
On the other hand, when the internal combustion engine 1 is in a lean combustion operation and the NOx storage capacity of the NOx storage reduction catalyst 46 is saturated, the CPU 401 assists in purification to temporarily set the air / fuel ratio of the exhaust to a rich air / fuel ratio. By executing the control, nitrogen oxides (NOx) stored in the NOx storage reduction catalyst 46 are reduced and purified, and the NOx storage capability of the NOx storage reduction catalyst 46 is regenerated.
[0098]
Hereinafter, the purification support control according to the present embodiment will be specifically described.
In the purification support control, the CPU 401 executes a purification support control routine as shown in FIG. This purification support control routine is a routine stored in the ROM 402 in advance, and is a routine that is repeatedly executed by the CPU 401 every predetermined time (for example, every time the crank position sensor 51 outputs a pulse signal).
[0099]
In the purification support control routine, the CPU 401 first determines whether or not the NOx storage capacity of the storage reduction type NOx catalyst 46 is saturated in S501.
As a method for determining whether or not the NOx storage capacity of the NOx storage reduction catalyst 46 is saturated, for example, the operation history of the internal combustion engine 1 (deviation between the execution time of the lean combustion operation and the execution time of the stoichiometric operation) is used. Based on this, the NOx amount stored in the NOx storage reduction catalyst 46 is estimated, and the estimated value is compared with the maximum nitrogen oxide (NOx) amount that the NOx storage reduction catalyst 46 can store. The determination method estimates the amount of nitrogen oxide (NOx) stored in the NOx storage reduction catalyst 46 from the catalyst bed temperature of the NOx storage reduction catalyst 46 and the output signal value of the air-fuel ratio sensor 48, and the estimated value A method of estimating by comparing the maximum amount of nitrogen oxide (NOx) that can be occluded by the NOx storage reduction catalyst 46, or the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 46 is predetermined. It can be exemplified determining method or the like based on the output signal value of the NOx sensor 49 when a fuel ratio.
[0100]
Hereinafter, the maximum nitrogen oxide (NOx) amount that can be stored by the NOx storage reduction catalyst 46 is referred to as the maximum NOx storage amount.
If the CPU 401 determines that the NOx storage capacity of the NOx storage reduction catalyst 46 is not saturated in S501, the CPU 401 terminates the execution of this routine once, and the NOx storage capacity of the NOx storage reduction catalyst 46 is determined in S501. If it is determined that it is saturated, the process proceeds to S502.
[0101]
In S502, the CPU 401 is required to reduce and purify all nitrogen oxides (NOx) stored in the NOx storage reduction catalyst 46, in other words, nitrogen oxides (NOx) having the maximum NOx storage amount. The amount of reducing agent (hereinafter referred to as the target reducing agent amount) is calculated.
[0102]
Note that the maximum NOx occlusion amount of the NOx storage reduction catalyst 46 can be obtained experimentally in advance, so that the target reduction required to purify the maximum NOx occlusion amount of nitrogen oxides (NOx). The amount of the agent may be obtained experimentally in advance and stored in the ROM 402 or the like.
[0103]
In step S503, the CPU 401 reads the output signal value (accelerator opening) of the accelerator position sensor 43 and the engine speed from the RAM 403, and uses the accelerator opening and the engine speed as parameters to request the torque required for the internal combustion engine 1 ( In the following, the required engine torque is calculated.
[0104]
In S504, the CPU 401 calculates the maximum amount of air that can be sucked per cylinder (hereinafter referred to as a target cylinder intake amount) in order to achieve the required engine torque calculated in S503.
[0105]
The torque generated when the internal combustion engine 1 is operated at a predetermined rich air-fuel ratio (for example, the lowest air-fuel ratio of the air-fuel ratio combustible in the internal combustion engine 1), and per cylinder at that time The relationship between the intake air amount and the intake air amount may be obtained experimentally, and the relationship may be mapped in advance so that the CPU 401 calculates the target cylinder intake air amount using the map and the requested engine torque. .
[0106]
In S505, the CPU 401 uses the target cylinder intake amount calculated in S502 and the target reducing agent amount calculated in S504 as parameters to cover the target reducing agent amount with exhaust from a single cylinder 21. The air-fuel ratio of the air-fuel mixture to be combusted in the single cylinder 21 (hereinafter referred to as the target rich air-fuel ratio) is calculated.
[0107]
In S506, the CPU 401 calculates the lowest air-fuel ratio (hereinafter referred to as a rich limit air-fuel ratio) in the air-fuel ratio range in which a combustible air-fuel mixture can be formed in the cylinder 21 of the internal combustion engine 1 in S505. The target rich air-fuel ratio is compared.
[0108]
If it is determined in S506 that the target rich air-fuel ratio is greater than or equal to the rich limit air-fuel ratio, the CPU 401 reduces the target reducing agent amount by operating the single cylinder 21 at the target rich air-fuel ratio only once. It is considered that the agent can be supplied to the NOx storage reduction catalyst 46, and the process proceeds to S507.
[0109]
In S507, the CPU 401 arbitrarily selects one cylinder 21 from the plurality of cylinders 21 of the internal combustion engine 1, and the intake air amount of the selected cylinder 21 (hereinafter referred to as the selected cylinder 21) is the target cylinder intake air. The target opening / closing timing of the intake valve 28 (hereinafter referred to as the target intake valve opening / closing timing) is determined so as to be an amount.
[0110]
In step S508, the CPU 401 calculates the target fuel injection amount of the selected cylinder 21 by dividing the target cylinder intake air amount by the target rich air-fuel ratio.
In S509, the CPU 401 selects the selected cylinder 21 so that the torque generated when the selected cylinder 21 is operated at the target cylinder intake air amount and the target rich air-fuel ratio becomes the required engine torque calculated in S503. And the target opening / closing timing of the exhaust valve 29 (hereinafter referred to as the target exhaust valve opening / closing timing) are determined.
[0111]
In S510, the CPU 401 determines the intake side drive circuit 30a of the selected cylinder 21 according to the target intake valve opening / closing timing, the target fuel injection amount, the target exhaust valve opening / closing timing, and the target ignition timing determined in S507 to S509. The fuel injection valve 32, the exhaust side drive circuit 31a, and the igniter 25a are controlled.
[0112]
Here, since the intake valve 28 of each cylinder 21 is provided at a position facing the combustion chamber 24, when the opening / closing timing of the intake valve 28 is changed, the actual intake air amount of each cylinder 21 causes a response delay. Will be changed immediately.
[0113]
Therefore, when the intake side drive circuit 30a is controlled so that the opening / closing timing of the intake valve 28 of the selected cylinder 21 matches the target intake valve opening / closing timing, the actual intake air amount of the selected cylinder 21 immediately becomes the target. The cylinder intake amount.
[0114]
Therefore, when the intake valve 28 and the fuel injection valve 32 of the selected cylinder 21 are driven according to the target intake valve opening / closing timing and the target fuel injection amount, the selected cylinder 21 is immediately operated at the target rich air-fuel ratio, In the exhaust stroke of the selected cylinder 21, exhaust containing an amount of reducing agent corresponding to the target amount of reducing agent is discharged.
[0115]
The exhaust discharged from the selected cylinder 21 flows into the NOx storage reduction catalyst 46 through the exhaust branch 45, so that all the nitrogen oxides (NOx) stored in the NOx storage reduction catalyst 46 are reduced. And will be purified.
[0116]
That is, by operating the single cylinder 21 of the internal combustion engine 1 only once with the target rich air-fuel ratio, all of the nitrogen oxide (NOx) stored in the NOx storage reduction catalyst 46 is reduced and purified. become.
[0117]
On the other hand, if it is determined in S506 that the target rich air-fuel ratio is lower than the rich limit air-fuel ratio, the CPU 401 supplies the target reducing agent amount of reducing agent even if the single cylinder 21 is operated only once with the rich air-fuel ratio. It is considered that the NOx storage reduction catalyst 46 cannot be supplied, and the process proceeds to S511.
[0118]
In S511, the CPU 401 sets the rich limit air-fuel ratio as a new target rich air-fuel ratio (hereinafter referred to as a new target rich air-fuel ratio).
In S512, the CPU 401 arbitrarily selects one cylinder 21 from the plurality of cylinders 21 of the internal combustion engine 1, and the intake air amount of the selected cylinder 21 (hereinafter referred to as the selected cylinder 21) is calculated in S504. The target intake valve opening / closing timing is determined so as to obtain the target cylinder intake amount.
[0119]
In S513, the CPU 401 calculates the target fuel injection amount of the selected cylinder 21 by dividing the target cylinder intake air amount calculated in S504 by the new target rich air-fuel ratio newly set in S511.
[0120]
In S514, the CPU 401 selects the selected cylinder 21 so that the torque generated when the selected cylinder 21 is operated at the target cylinder intake air amount and the new target rich air-fuel ratio becomes the required engine torque calculated in S503. Target ignition timing and target exhaust valve opening / closing timing are determined.
[0121]
In S515, the CPU 401 determines the intake side drive circuit 30a of the selected cylinder 21 according to the target intake valve opening / closing timing, the target fuel injection amount, the target exhaust valve opening / closing timing, and the target ignition timing determined in S512 to S514. The fuel injection valve 32, the exhaust side drive circuit 31a, and the igniter 25a are controlled.
[0122]
In S516, the CPU 401 supplies the amount of reducing agent supplied to the NOx storage reduction catalyst 46 from the selected cylinder 21 operated in accordance with the target cylinder intake air amount and the new target rich air-fuel ratio (hereinafter referred to as supply reducing agent amount). ) Is calculated.
[0123]
In S517, the CPU 401 subtracts the supply reducing agent amount calculated in S516 from the target reducing agent amount calculated in S502 to obtain a new target reducing agent amount (hereinafter referred to as a new target reducing agent amount). calculate. Then, the CPU 401 replaces the target reducing agent amount with the new target reducing agent amount, and executes the processes after S505 described above.
[0124]
In this case, two or more cylinders 21 are operated at a rich air-fuel ratio, and the total amount of reducing agent contained in the exhaust discharged from these cylinders 21 becomes the target reducing agent amount.
[0125]
As a result, all the nitrogen oxides (NOx) stored in the NOx storage reduction catalyst 46 are reduced and purified by the target reducing agent amount of the reducing agent.
In this way, the purification support means according to the present invention is realized by the CPU 401 executing the purification support control routine.
[0126]
That is, in the above-described purification support control, the intake air amount of each cylinder 21 can be independently controlled by using an electromagnetically driven valve mechanism, so that the nitrogen oxides stored in the NOx storage reduction catalyst 46 are stored. In the case of reducing and purifying (NOx), a desired amount of reducing agent is supplied to the NOx storage reduction catalyst 46 by changing the intake air amount of the minimum necessary number of cylinders 21 and operating at a rich air-fuel ratio. It becomes possible to do.
[0127]
At this time, since the intake air amount of the cylinder 21 to be operated at the rich air-fuel ratio is adjusted by the opening / closing timing of the intake valve 28, there is no response delay of intake, and the intake air amount and the empty air of the cylinder 21 do not occur. It is possible to immediately switch the fuel ratio to the desired intake air amount and rich air-fuel ratio.
[0128]
Therefore, according to the purification support control according to the present embodiment, when reducing and purifying nitrogen oxide (NOx) stored in the NOx storage reduction catalyst 46, a desired amount of reducing agent is stored in a short time. It becomes possible to supply to the reduced NOx catalyst 46, and the rich air-fuel ratio operation period related to the purification of nitrogen oxides (NOx) is not unnecessarily prolonged, and the drivability and the fuel consumption are deteriorated. Is prevented.
[0129]
Further, in the purification support control according to the present embodiment, the target cylinder intake air amount and the target fuel injection amount of the selected cylinder 21 are set such that the generated torque of the selected cylinder 21 is operated at another cylinder 21 (normal lean air-fuel ratio). Therefore, even when only the selected cylinder 21 is operated at the rich air-fuel ratio (target rich air-fuel ratio) when the internal combustion engine 1 is operated at the lean air-fuel ratio, it is set to coincide with the generated torque of the cylinder 21). Torque fluctuation does not occur.
[0130]
In the present embodiment, the target cylinder intake air amount is determined so that the torque generated in the selected cylinder 21 coincides with the torque generated in the other cylinders 21. The maximum amount of air that can be sucked in the stroke (hereinafter referred to as the maximum cylinder intake amount) may be set as the target cylinder intake amount.
[0131]
When the maximum cylinder intake air amount is set as the target cylinder intake air amount, the amount of exhaust that can be discharged by the single cylinder 21 in one exhaust stroke becomes the largest, and accordingly, the single cylinder 21 Since the amount of reducing agent that can be discharged in one exhaust stroke is the largest, the rich air-fuel ratio operation period for the purpose of purifying nitrogen oxide (NOx) stored in the NOx storage reduction catalyst 46 is increased. It can be made even shorter.
[0132]
However, when the maximum cylinder intake air amount is set as the target cylinder intake air amount, the generated torque of the selected cylinder 21 is expected to be significantly larger than the generated torque of the other cylinders 21. The opening / closing timing and / or ignition timing of the exhaust valve 29 of the engine 21 is controlled, or the opening / closing timing of the exhaust valve 29 of the cylinder 21 that is in the exhaust stroke when the selected cylinder 21 is in the expansion stroke. It is preferable to suppress.
[0133]
<Embodiment 2>
A second embodiment of an internal combustion engine having a variable valve mechanism according to the present invention will be described below with reference to FIGS. Here, a configuration different from that of the first embodiment will be described, and the description of the same configuration will be omitted.
[0134]
In the first embodiment described above, when the internal combustion engine 1 is operating in lean combustion, if the NOx storage capacity of the NOx storage reduction catalyst 46 is saturated, the air-fuel ratio of the exhaust discharged from at least one cylinder 21 is reached. In the present embodiment, the operation state of the internal combustion engine 1 is lean. However, in the present embodiment, the nitrogen oxide (NOx) stored in the NOx storage reduction catalyst 46 is reduced and purified. An example in which only a specific cylinder 21 is always operated at a rich air-fuel ratio when in the combustion operation region will be described.
[0135]
The specific cylinder 21 may be a single cylinder 21 or a plurality of cylinders 21. Here, an example in which only the single cylinder 21 is operated at a rich air-fuel ratio will be described. .
[0136]
Since the internal combustion engine 1 according to the present embodiment includes the four cylinders 21, when the operation state of the internal combustion engine 1 is in the lean combustion operation region, the single cylinder 21 is operated at a rich air-fuel ratio. The remaining three cylinders 21 are operated at a lean air-fuel ratio.
[0137]
That is, when one specific cylinder 21 of the four cylinders 21 of the internal combustion engine 1 is always operated at a rich air-fuel ratio, the remaining one cylinder 21 is operated after the three cylinders 21 are continuously operated at a lean air-fuel ratio. Is always operated at a rich air-fuel ratio, and in accordance with this, exhaust gas having a lean air-fuel ratio is exhausted continuously from the three cylinders 21, and then exhaust gas having a rich air-fuel ratio is necessarily exhausted from the remaining one cylinder 21.
[0138]
In this case, the NOx storage reduction catalyst 46 stores nitrogen oxides (NOx) contained in the exhaust gas of the three cylinders 21 operated at a lean air-fuel ratio (hereinafter referred to as lean operation cylinders 21), and then rich-empty. The operation of releasing and reducing nitrogen oxide (NOx) stored by the reducing agent contained in the exhaust gas of the cylinder 21 operated at the fuel ratio (hereinafter referred to as the rich operation cylinder 21) is repeated.
[0139]
At that time, by optimizing the air-fuel ratio and the amount of exhaust exhausted by the rich operation cylinder 21 in one exhaust stroke, all the nitrogen oxides (NOx) stored in the NOx storage reduction catalyst 46 (that is, NOx) (that is, It is possible to reduce and purify all the nitrogen oxides (NOx) discharged from the three lean operation cylinders 21.
[0140]
By the way, the combustion pressure generated when the air-fuel mixture is combusted in the rich operation cylinder 21 becomes higher than the combustion pressure generated when the air-fuel mixture is combusted in the lean operation cylinder 21. If this combustion pressure is directly reflected in the rotational torque of the crankshaft 23, torque fluctuations occur between the cylinders.
[0141]
Therefore, in the present embodiment, the CPU 401 sets the opening / closing timing of the exhaust valve 29 of the cylinder 21 or the opening / closing timing of the exhaust valve 29 of the rich operation cylinder 21 that becomes the exhaust stroke when the rich operation cylinder 21 enters the expansion stroke. By controlling, the generated torque of the rich operating cylinder 21 is reduced to the generated torque of the lean operating cylinder 21.
[0142]
For example, the fourth (# 4) cylinder 21 of the internal combustion engine 1 is the rich operation cylinder 21, and the first (# 1) cylinder 21, the second (# 2) cylinder 21, and the third (# 3) cylinder 21 are lean. In the case of the operating cylinder 21, as shown in FIG. 6, the opening of the exhaust valve 29 of the third (# 3) cylinder 21 that becomes the exhaust stroke when the fourth (# 4) cylinder 21 enters the expansion stroke. Delay the timing to the middle of the exhaust stroke.
[0143]
In this case, when the fourth (# 4) cylinder 21 is in the expansion stroke, the piston 22 of the third (# 3) cylinder 21 is in the cylinder during the period from the exhaust stroke bottom dead center to the exhaust valve 29 opening. Since the burned gas remaining in the cylinder is compressed, a part of the torque generated in the fourth (# 4) cylinder 21 is offset by the compression work of the third (# 3) cylinder 21, and as a result, 4 The torque generated in the number (# 4) cylinder 21 is suppressed.
[0144]
Further, the fourth (# 4) cylinder 21 of the internal combustion engine 1 is set to the rich operation cylinder 21, and the first (# 1) cylinder 21, the second (# 2) cylinder 21, and the third (# 3) cylinder 21 are lean. In the case of the operating cylinder 21, as shown in FIG. 7, the opening timing of the exhaust valve 29 of the fourth (# 4) cylinder 21 may be advanced halfway through the expansion stroke.
[0145]
In this case, the burned gas in the fourth (# 4) cylinder 21 is discharged from the cylinder during the expansion stroke and the pressure in the cylinder decreases, so the pressure acting on the piston 22 decreases, and as a result, Only a part of the combustion pressure generated in the fourth (# 4) cylinder 21 is reflected in the rotational torque of the crankshaft 23.
[0146]
Hereinafter, the purification support control according to the present embodiment will be specifically described.
When the purification support control is executed, the CPU 401 executes a purification support control routine as shown in FIG. This purification support control routine is a routine stored in the ROM 402 in advance, and is a routine that is repeatedly executed by the CPU 401 every predetermined time (for example, every time the crankshaft 23 rotates 720 °).
[0147]
In the purification support control routine, first, in step S <b> 801, the CPU 401 reads various data such as the engine speed and the output signal value (accelerator opening) of the accelerator position sensor 43 from the RAM 403.
[0148]
In S802, the CPU 401 determines the operating state of the internal combustion engine 1 from the engine speed and the accelerator opening read out in S801.
In S803, the CPU 401 determines whether or not the engine operating state determined in S802 is in the lean combustion operation region.
[0149]
If the CPU 401 determines that the engine operation state is not in the lean combustion operation region in S803, the CPU 401 ends the execution of this routine. If the CPU 401 determines in S803 that the engine operation state is in the lean combustion operation region, the process proceeds to S804. move on.
[0150]
In S804, the CPU 401 calculates the required engine torque using the engine speed and the accelerator opening read in S801 as parameters. At that time, the relationship between the engine speed, the accelerator opening, and the required engine torque may be experimentally obtained in advance, and the relationship may be mapped and stored in the ROM 402.
[0151]
In S805, the CPU 401 calculates a torque required per cylinder 21 (hereinafter referred to as a required cylinder torque) based on the required engine torque calculated in S804. Note that the processing of S803 described above may be executed next to S805.
[0152]
In step S806, the CPU 401 causes the air-fuel mixture to be burned in the lean operation cylinder 21 so that the generated torque of the lean operation cylinder 21 is the same as the required cylinder 21 torque and the fuel injection amount of the lean operation cylinder 21 is minimized. The air-fuel ratio (hereinafter referred to as a target lean air-fuel ratio) and an air amount (hereinafter referred to as a target lean cylinder intake amount) to be taken in by the lean operation cylinder 21 are determined.
[0153]
In S807, the CPU 401 determines the target intake valve opening / closing timing and the target exhaust valve opening / closing timing of the lean operation cylinder 21 according to the target lean air-fuel ratio and the target lean cylinder intake air amount determined in S806, and the target lean cylinder intake air amount. Is divided by the target lean air-fuel ratio, and the target fuel injection amount of the lean operation cylinder 21 is calculated.
[0154]
In step S808, the CPU 401 first performs nitrogen oxidation discharged from the lean operation cylinder 21 when the single lean operation cylinder 21 is operated in accordance with the target lean air-fuel ratio and the target lean cylinder intake air amount determined in S806. Estimate the amount of matter (NOx). Next, the CPU 401 calculates the total amount of nitrogen oxides (NOx) discharged from the three lean operation cylinders 21 by multiplying the estimated value by three.
[0155]
In step S809, the CPU 401 calculates the amount of reducing agent (target reduction amount) necessary to reduce the total NOx amount of nitrogen oxide (NOx) estimated in step S808.
[0156]
In S810, the CPU 401 first calculates the lowest air-fuel ratio (hereinafter referred to as a target rich air-fuel ratio) in the air-fuel ratio range in which a combustible mixture can be formed in the rich operation cylinder 21. Subsequently, the CPU 401 calculates the amount of the reducing agent contained per unit amount of the exhaust gas having the target rich air-fuel ratio, and divides the target reducing agent amount by the calculated reducing agent amount so that the rich operating cylinder 21 The amount of exhaust to be discharged, in other words, the amount of air to be taken into the rich operation cylinder 21 (hereinafter referred to as the target rich cylinder intake amount) is calculated.
[0157]
In step S811, the CPU 401 determines the target intake valve opening / closing timing of the rich operation cylinder 21 based on the target rich cylinder intake amount calculated in step S810, and divides the target rich cylinder intake amount by the target rich air-fuel ratio. Thus, the target fuel injection amount of the rich operation cylinder 21 is calculated.
[0158]
In S812, the CPU 401 estimates a torque that can be generated by the rich operation cylinder 21 when the rich operation cylinder 21 is operated according to the target rich air-fuel ratio and the target rich cylinder intake air amount calculated in S810.
[0159]
In S813, the CPU 401 determines the target exhaust valve opening / closing timing of the rich operation cylinder 21 so that the torque estimated in S812 decreases to the required cylinder torque calculated in S805.
[0160]
In S814, the CPU 401 determines the intake-side drive circuit 30a, the exhaust-side drive circuit 31a, and the lean-side drive circuit 31a of the lean operation cylinder 21 according to the target intake valve opening / closing timing, the target exhaust valve opening / closing timing, and the target fuel injection amount determined in S807. In addition to controlling the fuel injection valve 32, the intake side drive circuit 30a of the rich operation cylinder 21 and the exhaust gas according to the target intake valve opening / closing timing, the target exhaust valve opening / closing timing, and the target fuel injection amount determined in S811 and 813. The side drive circuit 31a and the fuel injection valve 32 are controlled.
[0161]
In this case, in the internal combustion engine 1, after the three lean operation cylinders 21 are continuously operated at the target lean air-fuel ratio, one rich operation cylinder 21 is operated at the target rich air-fuel ratio, and accordingly After the three lean operation cylinders 21 continuously exhaust the exhaust gas with the target lean air-fuel ratio, the one rich operation cylinder 21 discharges the exhaust gas with the target rich air-fuel ratio.
[0162]
At that time, the exhaust gas discharged from the rich operation cylinder 21 contains a reducing agent in an amount corresponding to the total amount of nitrogen oxides (NOx) included in the exhaust gas discharged from the three lean operation cylinders 21. When the exhaust gas from the three lean operation cylinders 21 flows in, the NOx storage reduction catalyst 46 stores nitrogen oxide (NOx) contained in the exhaust gas, and then the exhaust gas from the rich operation cylinder 21 flows in. Then, it becomes possible to release and purify all the nitrogen oxides (NOx) that have been occluded.
[0163]
Therefore, according to the purification support control as described above, the storage and reduction of nitrogen oxides (NOx) in the NOx storage reduction catalyst 46 is performed every cycle. Therefore, the storage amount of nitrogen oxides (NOx) It is easy to match the supply amount of the reducing agent, and the calculation load on the CPU 401 can be reduced.
[0164]
Further, in the purification support control as described above, by controlling the opening / closing timing of the exhaust valve 29 of the rich operation cylinder 21, the generated torque of the rich operation cylinder 21 and the generated torque of the lean operation cylinder 21 are made uniform. The torque fluctuation of the internal combustion engine 1 does not occur.
[0165]
In the present embodiment, the example in which the rich operation cylinder 21 of the internal combustion engine 1 is fixed to the specific cylinder 21 has been described. However, the cylinder 21 that is the rich operation cylinder 21 is changed at a predetermined cycle to generate deposits. The smoldering of the spark plug 25 may be suppressed.
[0166]
<Embodiment 3>
Next, a third embodiment of an internal combustion engine having a variable valve mechanism according to the present invention will be described with reference to FIG. Here, a configuration different from the first and second embodiments described above will be described, and the description of the same configuration will be omitted.
[0167]
In the first and second embodiments described above, when the reducing agent is supplied to the NOx storage reduction catalyst 46, the exhaust discharged from the cylinder 21 by operating the specific cylinder 21 at a rich air-fuel ratio. Although an example in which a relatively large amount of hydrocarbon (HC) contained therein is supplied as a reducing agent to the NOx storage reduction catalyst 46 has been described, in the present embodiment, nitrogen oxidation is performed as compared with hydrocarbon (HC). Hydrogen (H, which has strong reducing power of NOx)₂) Or carbon monoxide (CO) as a reducing agent will be described as an example of supply to the NOx storage reduction catalyst 46.
[0168]
In this case, when the CPU 401 needs to operate the predetermined cylinder 21 at a rich air-fuel ratio for the purpose of regenerating the NOx storage capacity of the NOx storage reduction catalyst 46, a rich operation control routine as shown in FIG. 9 is performed. Execute. This rich operation control routine is a routine stored in the ROM 402 in advance.
[0169]
In the rich operation control routine, the CPU 401 first determines in S901 whether or not it is necessary to supply a reducing agent to regenerate the NOx storage capacity of the NOx storage reduction catalyst 46.
[0170]
If it is determined in S901 that it is not necessary to supply a reducing agent to regenerate the NOx storage capacity of the NOx storage reduction catalyst 46, the CPU 401 once ends the execution of this routine.
[0171]
On the other hand, if it is determined in S901 that it is necessary to supply a reducing agent to regenerate the NOx storage capacity of the NOx storage reduction catalyst 46, the CPU 401 proceeds to S902.
[0172]
In S902, the CPU 401 determines whether or not the engine speed of the internal combustion engine 1 is equal to or higher than a predetermined speed, or whether or not the engine load is equal to or higher than a predetermined load.
If it is determined in S902 that the engine speed is equal to or higher than the predetermined speed and / or the engine load is equal to or higher than the predetermined load, the CPU 401 proceeds to S903 and opens the exhaust valve 29 of the rich operation cylinder 21. Advance the angle.
[0173]
This is hydrogen (H₂) Is generated by thermal decomposition when hydrocarbon (HC) contained in the air-fuel mixture burns, and then combines with oxygen and carbon as water (H₂O) and hydrocarbons (HC) are generated, and therefore, by opening the exhaust valve 29 during the combustion of the air-fuel mixture, hydrogen (H₂It is possible to generate exhaust gas that contains a relatively large amount of hydrogen. However, when the engine speed is relatively high or the engine load is relatively large, hydrogen (H₂) Is easily generated.
[0174]
In this case, the exhaust gas discharged from the rich operation cylinder 21 includes hydrogen (H) having a reducing power stronger than that of hydrocarbon (HC).₂) Is contained in a relatively large amount, and when such exhaust flows into the NOx storage reduction catalyst 46, nitrogen oxides (NOx) stored in the NOx storage reduction catalyst 46 are efficiently consumed in a short time. Will be reduced.
[0175]
On the other hand, if the engine speed is lower than the predetermined speed and the engine load is smaller than the predetermined load in S902, the CPU 401 proceeds to S904 and retards the opening timing of the exhaust valve 29 of the rich operation cylinder 21. .
[0176]
This is because carbon monoxide (CO) is produced by oxidizing the hydrocarbon (HC) remaining after combustion of the air-fuel mixture at a high temperature and in an oxidizing atmosphere. This is because it is possible to generate exhaust gas containing a relatively large amount of carbon monoxide (CO) by delaying the valve opening timing of the exhaust valve 29.
[0177]
In this case, since the exhaust discharged from the rich operation cylinder 21 contains a relatively large amount of carbon monoxide (CO) having a stronger reducing power than hydrocarbon (HC), such exhaust is stored in the NOx storage reduction type. When flowing into the catalyst 46, the nitrogen oxide (NOx) stored in the NOx storage reduction catalyst 46 is efficiently reduced in a short time.
[0178]
As described above, the CPU 401 executes the rich operation control routine, so that the storage capacity of the storage reduction type NOx catalyst 46 can be regenerated in a shorter time than when hydrocarbon (HC) is used as a reducing agent. This makes it possible to further shorten the period during which the predetermined cylinder 21 is operated at a rich air-fuel ratio for the purpose of regenerating the NOx storage capacity of the NOx storage reduction catalyst 46, thereby further reducing fuel consumption. It becomes possible to reduce.
[0179]
<Embodiment 4>
Next, a fourth embodiment of an internal combustion engine having a variable valve mechanism according to the present invention will be described with reference to FIG. Here, a configuration different from the first to third embodiments described above will be described, and the description of the same configuration will be omitted.
[0180]
In the first to third embodiments described above, the NOx storage capability of the NOx storage reduction catalyst 46 is regenerated by reducing and purifying the nitrogen oxide (NOx) stored in the NOx storage reduction catalyst 46. In the present embodiment, an example of regenerating the SOx poisoning of the NOx storage reduction catalyst 46 will be described.
[0181]
The NOx storage reduction catalyst 46 stores nitrogen oxides (NOx) contained in the exhaust when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 46 is a lean air-fuel ratio. The sulfur component contained in the exhaust gas is also absorbed by a mechanism similar to that of nitrogen oxide (NOx), and as a result, so-called SOx poisoning occurs in which the NOx storage capacity of the NOx storage reduction catalyst 46 is reduced.
[0182]
Specifically, the sulfur (S) component contained in the fuel of the internal combustion engine 1 is burned to cause SO.₂And SO_ThreeSuch sulfur oxides (SOx) are produced, and these sulfur oxides (SOx) flow into the NOx storage reduction catalyst 46 together with the exhaust gas.
[0183]
At that time, if the air-fuel ratio of the exhaust gas is a lean air-fuel ratio, oxygen O 2 is deposited on the surface of platinum (Pt) supported on the support of the NOx storage reduction catalyst 46.₂ ^-Or O^2-Is attached, the sulfur oxide (SOx) contained in the exhaust gas is oxygen O described above.₂ ^-Or O^2-Reacts with SO_3-And SO_Four-Form.
[0184]
SO formed on platinum (Pt) of NOx storage reduction catalyst 46_3-And SO_Four-Is further oxidized on platinum (Pt) and sulfate ions (SO_Four ^2-) Is absorbed by the NOx storage reduction catalyst 46. Sulfate ion (SO) absorbed in the NOx storage reduction catalyst 46_Four ^2-) Combines with barium oxide (BaO) to form barium sulfate (BaSO)._Four).
[0185]
Barium sulfate (BaSO_Four) Is less decomposed than nitrogen oxide (NOx) and has a characteristic of being easily coarsened. Therefore, even if the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 46 becomes a rich air-fuel ratio. It remains in the NOx storage reduction catalyst 46 without being decomposed.
[0186]
Therefore, barium sulfate (BaSO 4) in the NOx storage reduction catalyst 46 is obtained._Four) Increases with time, so the amount of barium oxide (BaO) capable of acting on the storage of nitrogen oxides (NOx) decreases, and as a result, the NOx of the NOx storage reduction catalyst 46 is reduced. The storage capacity will be reduced.
[0187]
In order to eliminate SOx poisoning of the NOx storage reduction catalyst 46, the atmospheric temperature of the NOx storage reduction catalyst 46 is set to a high temperature (for example, 500 ° C. to 700 ° C.) and the exhaust gas flowing into the NOx storage reduction catalyst 46 is exhausted. It is necessary to make the air-fuel ratio of the air-fuel ratio rich.
[0188]
That is, when the atmospheric temperature of the NOx storage reduction catalyst 46 becomes high, barium sulfate (BaSO) produced in the NOx storage reduction catalyst 46 is increased._Four) Is SO_3-And SO_Four-Pyrolyzed to At that time, if the air-fuel ratio of the exhaust flowing into the NOx storage reduction catalyst 46 is a rich air-fuel ratio, SO_3-And SO_Four-Reacts with hydrocarbons (HC) and carbon monoxide (CO) contained in the exhaust gas to form gaseous SO_2-To be released from the NOx storage reduction catalyst 46.
[0189]
As a method for making the NOx storage reduction catalyst 46 to have a high temperature and rich atmosphere, for example,
A rich air-fuel ratio exhaust gas containing a relatively large amount of unburned fuel components and oxygen is supplied to the NOx storage reduction catalyst 46, and the unburned fuel components and oxygen are reacted (burned) in the NOx storage reduction catalyst 46. Thus, a method of making the NOx storage reduction catalyst 46 into a high temperature and rich atmosphere can be exemplified.
[0190]
Here, as a method of generating exhaust gas containing a relatively large amount of unburned fuel components and oxygen, (1) the internal combustion engine 1 is operated with a rich air-fuel ratio mixture so that the air-fuel ratio of the exhaust gas is made rich. A method of generating exhaust gas containing unburned fuel components and oxygen by supplying secondary air into the exhaust gas in the exhaust passage upstream of the NOx storage reduction catalyst 46, and (2) the internal combustion engine 1 By operating some of the cylinders 21 with a rich air-fuel ratio mixture and simultaneously operating the remaining cylinders 21 with a lean air-fuel mixture, exhaust gas containing a sufficient amount of unburned fuel components and a sufficient amount A method of mixing with exhaust gas containing oxygen, etc. can be exemplified, but in this embodiment, an electromagnetically driven valve operating mechanism in which the opening / closing timing of the intake valve 28 and the exhaust valve 29 can be arbitrarily set The characteristics of The following method was adopted.
[0191]
That is, in the present embodiment, the CPU 401 uses the fuel to operate each cylinder 21 of the internal combustion engine 1 with a rich air-fuel ratio mixture when it becomes necessary to eliminate the SOx poisoning of the NOx storage reduction catalyst 46. After controlling the injection valve 32, the valve opening timing of the exhaust valve 29 is advanced to the middle of the expansion stroke, so that the air-fuel mixture during combustion is discharged as exhaust.
[0192]
In this case, the exhaust gas of the internal combustion engine 1 becomes an exhaust gas that has a higher temperature and contains a large amount of unburned fuel components and oxygen as compared with the case where the burned gas after combustion is exhausted. .
[0193]
When the amount of unburned fuel component and oxygen remaining in the exhaust gas is further increased, the CPU 401 retards the ignition timing of the spark plug 25 of each cylinder 21 to delay the combustion timing of the air-fuel mixture. May be.
[0194]
By the way, when the air-fuel mixture in the middle of combustion is discharged from each cylinder 21, the combustion pressure generated in each cylinder 21 is reduced, and the efficiency with which the combustion pressure is transmitted to the crankshaft 23 is reduced. Torque will drop.
[0195]
On the other hand, the CPU 401 changes the opening / closing timing of the intake valve 28 to increase the intake air amount of each cylinder 21 and corrects the fuel injection amount to be increased. When increasing the intake air amount of each cylinder 21, the CPU 401 may change the opening degree of the throttle valve 39 in addition to the opening / closing timing of the intake valve 28.
[0196]
Hereinafter, the purification support control according to the present embodiment will be specifically described.
When executing the purification support control, the CPU 401 executes a purification support control routine as shown in FIG. This purification support control routine is a routine stored in the ROM 402 in advance, and is a routine that is repeatedly executed by the CPU 401 every predetermined time (for example, every time the crank position sensor 51 outputs a pulse signal).
[0197]
In the purification support control routine, the CPU 401 first determines the degree of SOx poisoning of the NOx storage reduction catalyst 46 in S1001. As a method for determining the degree of SOx poisoning of the NOx storage reduction catalyst 46, for example, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 46 is a lean air-fuel ratio, the NOx catalyst 46 is more effective than the NOx storage reduction catalyst 46. A determination method based on the output signal value of the NOx sensor 49 disposed downstream, or an integrated value of time during which the internal combustion engine 1 is operated at a lean air-fuel ratio, an integrated value of the intake air amount, and / or a fuel injection amount A method for estimating the degree of SOx poisoning of the NOx storage reduction catalyst 46 based on the integrated value or the like can be exemplified.
[0198]
In S1002, the CPU 401 determines whether or not the SOx poisoning degree determined in S1001 exceeds a predetermined reference value. The reference value described above is a value obtained experimentally in advance and is a value stored in advance in the ROM 402 or the like.
[0199]
If it is determined in S1002 that the SOx poisoning degree of the NOx storage reduction catalyst 46 is equal to or less than the reference value, the CPU 401 considers that it is not necessary to execute the SOx poisoning elimination process for the NOx storage reduction catalyst 46, The execution of this routine is temporarily terminated.
[0200]
On the other hand, if it is determined in S1002 that the SOx poisoning degree of the NOx storage reduction catalyst 46 exceeds the reference value, the CPU 401 needs to execute the SOx poisoning elimination process for the NOx storage reduction catalyst 46. And go to S1003.
[0201]
In S1003, the CPU 401 reads out the engine speed and the output signal value (accelerator opening) of the accelerator position sensor 43 from the RAM 403, and calculates the required engine torque of the internal combustion engine 1 using these values as parameters.
[0202]
In step S1004, the CPU 401 satisfies the required engine torque calculated in step S1003, and supplies the exhaust containing the unburned fuel component and oxygen to the storage reduction type NOx catalyst 46 in order to open and close the intake valve 28, The opening / closing timing of the valve 29, the fuel injection amount, and the ignition timing are determined.
[0203]
Specifically, the CPU 401 first determines the air-fuel ratio of the air-fuel mixture to be combusted in each cylinder 21. Subsequently, the CPU 401 corrects the opening timing of the exhaust valve 29 and corrects the ignition timing of the spark plug 25 so as to discharge the air-fuel mixture in the middle of combustion as exhaust gas in each cylinder 21.
[0204]
Then, the CPU 401 performs suction so that the actual engine torque when the internal combustion engine 1 is operated according to the air-fuel ratio, the exhaust valve opening timing, and the ignition timing matches the required engine torque calculated in S1003. The air amount and the fuel injection amount are determined, and the opening / closing timing of the intake valve 28 is determined according to the determined intake air amount.
[0205]
In S1005, the CPU 401 follows the intake valve opening / closing timing, exhaust valve opening / closing timing, fuel injection amount, and ignition timing determined in S1004, according to the intake side drive circuit 30a, the exhaust side drive circuit 31a, the fuel injection valve 32, and the spark plug 25. To start the SOx poisoning elimination process.
[0206]
In this case, the internal combustion engine 1 discharges exhaust gas containing high amounts of unburned fuel components and oxygen while satisfying the required engine torque. Exhaust gas that is discharged from the internal combustion engine 1 and contains a large amount of unburned fuel components and oxygen flows into the NOx storage reduction catalyst 46 through the exhaust branch 45. The NOx storage reduction catalyst 46 is heated by receiving heat from the exhaust gas, and is generated by the reaction between unburned fuel components in the exhaust gas and oxygen on platinum (Pt) of the NOx storage reduction catalyst 46. The temperature is further raised by reaction heat.
[0207]
When the ambient temperature of the NOx storage reduction catalyst 46 increases in this way, barium sulfate (BaSO) in the NOx storage reduction catalyst 46 is increased._Four) Is SO_3-Or SO_Four-Pyrolyzed to SO_3-Or SO_Four-Reacts with hydrocarbons (HC) and carbon monoxide (CO) in the exhaust to produce gaseous SO_2-To be released from the NOx storage reduction catalyst 46.
[0208]
In S1006, the CPU 401 determines whether or not the SOx poisoning of the NOx storage reduction catalyst 46 has been eliminated. As a method of determining whether or not the SOx poisoning of the NOx storage reduction catalyst 46 has been eliminated, the SOx poisoning degree of the NOx storage reduction catalyst 46 and the time required to eliminate the SOx poisoning (SOx poisoning elimination time) The method of determining whether or not the execution time of the SOx poisoning elimination process is equal to or longer than the SOx poisoning elimination time, or the exhaust passage downstream from the NOx storage reduction catalyst 46 is experimentally obtained in advance. An example is a method in which an SOx sensor that outputs an electrical signal corresponding to the SOx concentration in the exhaust gas is disposed, and whether or not the output signal value of the SOx sensor is less than a predetermined value.
[0209]
If it is determined in S1006 that the SOx poisoning of the NOx storage reduction catalyst 46 has not yet been eliminated, the CPU 401 continues to execute the process of S1005.
[0210]
If it is determined in S1006 that the SOx poisoning of the NOx storage reduction catalyst 46 has been eliminated, the CPU 401 proceeds to S1007, where the opening / closing timing of the intake valve 28, the opening / closing timing of the exhaust valve 29, and the ignition timing are set to normal timing. In addition to controlling the intake side drive circuit 30a, the exhaust side drive circuit 31a, and the spark plug 25, the fuel injection valve 32 is controlled to return the fuel injection amount to the normal fuel injection amount.
[0211]
According to such purification support control, by changing the opening / closing timing of the intake valve 28 and the exhaust valve 29, the exhaust state can be immediately brought into a state containing high temperature, unburned fuel components and oxygen. Therefore, it is possible to shorten the time required for the SOx poisoning elimination process, so that the rich air-fuel ratio operation period related to the SOx poisoning elimination process does not become unnecessarily long, the deterioration of the drivability and the fuel consumption amount. Is prevented from deteriorating.
[0212]
In this embodiment, when SOx poisoning of the NOx storage reduction catalyst 46 is eliminated, the internal combustion engine 1 is operated with a rich air-fuel ratio mixture and the opening timing of the exhaust valve 29 is advanced. As described above, when both the intake valve 28 and the exhaust valve 29 of each cylinder 21 of the internal combustion engine 1 are open, that is, during the valve overlap period, the fuel injection valve 32 is operated, and unburned fuel is discharged. By supplying to the NOx storage reduction catalyst 46, the unburned fuel is combusted by the NOx storage reduction catalyst 46, so that the NOx storage reduction catalyst 46 has a high temperature and rich atmosphere in a shorter time. May be.
[0213]
【The invention's effect】
In the internal combustion engine having the variable valve mechanism according to the present invention, when the predetermined gas component is to be purified in the NOx catalyst, the exhaust gas in a state suitable for purifying the predetermined gas component is discharged from the internal combustion engine. Thus, the variable valve mechanism is controlled.
[0214]
Since the intake valve and the exhaust valve of the internal combustion engine are provided so as to face the cylinder, the opening / closing timing and / or the lift amount of the intake valve and / or the exhaust valve by the variable valve mechanism change the state of the gas in the cylinder and This is immediately reflected in the state of exhaust discharged from the cylinder.
[0215]
Therefore, according to the internal combustion engine having the variable valve mechanism according to the present invention, when the predetermined gas component is to be purified, the state of the exhaust actually discharged from the internal combustion engine immediately purifies the predetermined gas component. Therefore, it is possible to shorten the execution period of the control related to the purification of the predetermined gas component.
[0216]
In particular, when it is necessary to operate the internal combustion engine with a rich air-fuel ratio or stoichiometric air-fuel mixture to purify the predetermined gas component, the internal combustion engine is made rich or stoichiometric for the purpose of purifying the predetermined gas component. Since the operating period can be shortened, the fuel injection amount can be minimized and the deterioration of drivability can be suppressed.
[Brief description of the drawings]
FIG. 1 is a plan view showing a schematic configuration of an internal combustion engine having a variable valve mechanism according to the present invention.
FIG. 2 is a sectional view showing a schematic configuration of an internal combustion engine having a variable valve mechanism according to the present invention.
FIG. 3 is a diagram showing an internal configuration of an intake side electromagnetic drive mechanism
FIG. 4 is a block diagram showing the internal configuration of the ECU
FIG. 5 is a flowchart showing a purification support control routine according to the first embodiment.
FIG. 6 is a timing chart (1) showing opening / closing timings of intake and exhaust valves in the purification support control according to the second embodiment.
FIG. 7 is a timing chart (2) showing opening / closing timings of intake and exhaust valves in the purification support control according to the second embodiment.
FIG. 8 is a flowchart showing a purification support control routine according to the second embodiment.
FIG. 9 is a flowchart showing a rich operation control routine according to the third embodiment.
FIG. 10 is a flowchart showing a purification support control routine according to the fourth embodiment.
[Explanation of symbols]
1 ... Internal combustion engine
20 ... ECU
25 ... Spark plug
26 ... Intake port
27 ... Exhaust port
28 ... Intake valve
29 ... Exhaust valve
30 ... Intake side electromagnetic drive mechanism
30a ... Intake side drive circuit
31 ... Exhaust side electromagnetic drive mechanism
31a..Exhaust side drive circuit
32 ... Fuel injection valve
46 ... NOx storage reduction catalyst
49 ... NOx sensor
51 ... Crank position sensor

Claims (4)

A lean combustion internal combustion engine capable of combusting an oxygen-rich mixture.
A fuel injection valve for injecting fuel into each cylinder of the internal combustion engine or an intake passage upstream from each cylinder;
The al is provided in an exhaust passage of the internal combustion engine is, when the air-fuel ratio of the exhaust gas flowing is lean occludes nitrogen oxides contained in the exhaust air-fuel ratio of the exhaust flowing the stoichiometric air-fuel ratio or a rich air a storage reduction the NO x catalyst for reducing while releasing nitrogen oxides was occluded when a ratio,
A variable valve mechanism capable of changing the opening / closing timing and / or lift amount of the intake valve and / or exhaust valve of the internal combustion engine;
To when to reduce nitrogen oxides occluded in the said storage reduction the NO x catalyst, retards the opening timing of the exhaust valve of the predetermined cylinder causes operated a predetermined cylinder of the internal combustion engine at a rich air-fuel ratio and purification of support means for controlling said fuel injection valve and the variable valve mechanism in order to,
An internal combustion engine having a variable valve mechanism.   The purification assisting means retards the opening timing of the exhaust valve of the predetermined cylinder when the engine speed of the internal combustion engine is lower than a predetermined speed and the engine load is smaller than the predetermined load, and the engine speed of the internal combustion engine 2. The internal combustion engine having a variable valve mechanism according to claim 1, wherein when the number is higher than a predetermined rotational speed or the engine load is larger than the predetermined load, the valve opening timing of the exhaust valve of the predetermined cylinder is advanced. . The purification assisting means controls the variable valve mechanism so that torque fluctuation of the internal combustion engine does not occur when supplying exhaust gas in a state suitable for purifying the predetermined gas component to the NOx catalyst. An internal combustion engine having the variable valve mechanism according to claim 1 or 2 . The variable valve mechanism, any one of the preceding claims, characterized in that an electromagnetic drive valve operating mechanism that can change the opening and closing timing and or lift of the intake valve and or the exhaust valve by electromagnetic force internal combustion engine having a variable valve mechanism according to.

Images