JP4325078B2 - Internal combustion engine having variable valve mechanism - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an internal combustion engine including an electromagnetically driven valve mechanism that opens and closes intake and exhaust valves using electromagnetic force.
[0002]
[Prior art]
Conventionally, in order to reduce the nitrogen oxides stored in the NOx storage reduction catalyst, the cylinders are divided into a pair of cylinders, and a rich mixture is burned in some cylinders to contain high concentrations of unburned HC and CO. Exhaust is formed, and the lean mixture is burned in the remaining cylinders to form exhaust containing high-concentration oxygen. These exhausts are guided to the NOx storage reduction catalyst, and unburned HC and CO in the exhaust are stored in NOx. The temperature of the NOx occlusion reduction catalyst is increased by burning with the catalyst, and the entire air-fuel ratio flowing into the NOx occlusion reduction catalyst at this time is adjusted to be rich, thereby regenerating the NOx occlusion reduction catalyst. Such a catalyst regeneration apparatus is known (see JP-A-8-61052).
[0003]
By the way, in general, the exhaust purification catalyst has not been activated for a while after the engine is started, and therefore a good exhaust purification action of the exhaust purification catalyst cannot be expected during this period. Therefore, an internal combustion engine in which an additional start-up catalyst, for example, a three-way catalyst is arranged in the engine exhaust passage upstream of the exhaust purification catalyst is known. The start-up catalyst is arranged adjacent to the internal combustion engine and has a small heat capacity, and is activated more quickly than the exhaust purification catalyst after the internal combustion engine is started. Therefore, the exhaust purification catalyst is activated after the internal combustion engine is started. In the meantime, the amount of unburned HC, CO, etc. released into the atmosphere can be reduced.
[0004]
However, if this starting catalyst is applied to the catalyst regeneration device as described above, the NOx storage reduction catalyst cannot be sufficiently regenerated for the following reason.
In this case, the exhaust gas of each cylinder group flows into the NOx occlusion reduction catalyst after flowing through the start-up catalyst, which is an exhaust gas containing high concentration unburned HC and CO and exhaust gas containing high concentration oxygen. Means that the catalyst flows into the catalyst almost simultaneously. As a result, most of the unburned HC and CO in the exhaust gas is burned and consumed in the start-up catalyst, so that the amount of unburned HC and CO burned in the NOx storage reduction catalyst is reduced. Therefore, the NOx storage reduction catalyst cannot be heated sufficiently, and NOx cannot be sufficiently released and reduced from the NOx storage reduction catalyst.
[0005]
Therefore, the cylinders are divided into a plurality of cylinder groups, and each cylinder group is connected to a common combined exhaust passage through a branch exhaust passage, and a NOx storage reduction catalyst is disposed in the combined exhaust passage. The multi-cylinder internal combustion engine which can make the air-fuel ratio of exhaust discharged from at least one cylinder group out of the remaining cylinder groups rich, with the air-fuel ratio of exhaust discharged from some cylinder groups as lean Is known in which a start-up catalyst is arranged in each exhaust branch passage (see JP-A-11-62563).
[0006]
In this way, exhaust gas containing high concentration of HC and exhaust gas containing high concentration of oxygen are prevented from flowing into the start-up catalyst at the same time, so that high-concentration HC and oxygen are consumed by the start-up catalyst. The NOx occlusion reduction catalyst can be supplied without causing it.
[0007]
[Problems to be solved by the invention]
However, in order to create a rich and lean state for each cylinder group as described above, the fuel supply amount for each cylinder group must be changed greatly, resulting in variations in torque generated for each cylinder group. There is a possibility that the engine cannot be rotated smoothly. In other words, since the intake air amount of all the cylinders is almost constant, the torque of the rich cylinder increases and torque fluctuation occurs.
[0008]
Further, in order to solve the above torque fluctuation, there is a problem that if the ignition delay is executed so that the torque of the rich cylinder is matched with the torque of the lean cylinder, combustion is deteriorated and fuel consumption is reduced.
[0009]
The present invention has been made in view of the above-described problems, and provides an internal combustion engine capable of suppressing torque variation when a rich and lean state is created for each cylinder group. Let it be an issue.
[0010]
[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 an electromagnetically driven valve according to the present invention includes a plurality of divided cylinder groups, branch exhaust pipes to which these cylinder groups are connected, and a start-up catalyst disposed in these branch exhaust pipes. A NOx occlusion reduction catalyst provided downstream of the junction of the branch exhaust pipe, and an exhaust gas adjusting means for exhausting rich and lean air-fuel ratio exhaust gas for each of the predetermined cylinder groups. The gas adjusting means adjusts exhaust gas by changing the opening / closing timing of an intake / exhaust valve driven by at least an electromagnetically driven valve mechanism provided in the cylinder.
[0011]
The exhaust gas of the predetermined cylinder group can alternately repeat an over-farming state and a lean state.
In the present invention, so-called electromagnetically driven valves are used, and the intake and exhaust valve opening / closing timing is changed independently for each cylinder, so that the intake air amount and the fuel injection amount are changed to suppress the torque fluctuation for each cylinder. To be able to. At this time, in an internal combustion engine provided with a plurality of start-up catalysts, the air amount and fuel amount of the cylinder group are controlled so that rich exhaust gas flows into some start-up catalysts, and other start-up catalysts are used. Controls the amount of air and fuel in the cylinder group so that lean exhaust gas flows in.
[0012]
The start-up catalyst does not purify rich or lean exhaust gas outside the exhaust purification window, that is, does not react. Therefore, these exhaust gases pass directly through the start-up catalyst and are provided downstream of the junction of the branch exhaust pipe. It flows into the NOx storage reduction catalyst. In this case, the exhaust gas flowing into the NOx occlusion reduction catalyst is adjusted so that the rich and lean exhaust gases are mixed in the junction and become a stoichiometric or slightly rich exhaust gas.
[0013]
For example, when the air-fuel ratio of the inflowing exhaust gas is a lean air-fuel ratio, the NOx storage-reduction catalyst stores nitrogen oxide (NOx) contained in the exhaust gas, and the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is theoretically When the air-fuel ratio or rich air-fuel ratio is the NOx occlusion reduction catalyst that reduces the nitrogen oxide (NOx) that has been occluded, and the air-fuel ratio of the exhaust gas flowing into the NOx catalyst is the lean air-fuel ratio; Examples thereof include a selective reduction type NOx catalyst that reduces or decomposes nitrogen oxides (NOx) in the exhaust when a reducing agent is present.
[0014]
In the present invention, poisoning judging means for judging whether or not the NOx storage reduction catalyst is poisoned is provided, and when it is judged that the NOx storage reduction catalyst is poisoned, the plurality of cylinder groups. And temporarily making the air-fuel ratio of exhaust exhausted from some of the cylinder groups lean, and temporarily making the air-fuel ratio of exhaust exhausted from at least one of the remaining cylinder groups rich, As a result, the NOx storage reduction catalyst can be poisoned and regenerated.
[0015]
The internal combustion engine of the present invention further includes a fuel injection valve that injects fuel into each cylinder or into an intake passage upstream of each cylinder, and the exhaust gas adjusting means increases the fuel injection amount of the cylinder group. It is possible to control the fuel injection valve.
[0016]
Further, the exhaust gas adjusting means controls the electromagnetically driven valve so that the torque fluctuation of the internal combustion engine does not occur, but can control the electromagnetically driven valve to reduce the intake air amount of the predetermined cylinder group. .
[0017]
That is, in a rich air-fuel ratio cylinder, the intake air amount is reduced in order to reduce the torque, but in order to reduce the intake air amount, the intake amount of fresh air itself is reduced by reducing the lift amount of the intake valve. There are methods such as delaying the opening timing of the intake valve, increasing the closing timing of the intake valve, increasing the opening timing of the exhaust valve, and delaying the closing timing of the exhaust valve. By one or a combination of two or more of these methods, the combustion time of the fuel in the cylinder is shortened to reduce the torque.
[0018]
As described above, since the exhaust gas does not react with the start-up catalyst, it is possible to supply a necessary amount of exhaust gas having a reducing power to the downstream NOx storage reduction catalyst, and at the same time, the air amount for each cylinder group is adjusted. Thus, torque fluctuations can be suppressed because the torques of the rich cylinder and the lean cylinder are controlled to be uniform.
[0019]
According to the present invention, the intake air amount and the injected fuel amount can be adjusted by changing the valve timing independently for each cylinder. Therefore, the rich cylinder group and the lean cylinder group are controlled by controlling the air-fuel ratio for each cylinder. In this manner, the reduction reaction at the NOx occlusion reduction catalyst can be promoted while suppressing the reaction at the start-up catalyst.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of an internal combustion engine having a variable valve mechanism according to the present invention will be described with reference to FIGS.
[0021]
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 having four cylinders # 1, # 2, # 3, and # 4. Each of these cylinders is connected to a common surge tank 34 via a corresponding branch pipe 33, and this surge tank 34 is connected to an air cleaner 36 via an intake pipe 35.
[0022]
An air flow meter 44 that outputs an electrical 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 at a portion of the intake pipe 35 downstream of the air flow meter 44.
[0023]
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.
[0024]
In the internal combustion engine 1, each cylinder is a first cylinder group 1a composed of a first cylinder # 1 and a fourth cylinder # 4, and a second cylinder group composed of a second cylinder # 2 and a third cylinder # 3. It is divided into 1b. The first cylinder group 1a is connected via a first exhaust manifold 8a to a casing 10a containing a first start-up catalyst 9a, and the second cylinder group 1b is connected to a second exhaust manifold 8b via a second exhaust manifold 8b. Is connected to a casing 10b containing the starting catalyst 9b. These casings 10 a and 10 b are connected to a casing 13 containing a NOx storage reduction catalyst 12 through a common merged exhaust pipe 11.
[0025]
The combustion order of the internal combustion engine of FIG. 1 is # 1- # 3- # 4- # 2, so that the exhaust strokes of the cylinders do not overlap each other in each cylinder group.
The internal combustion engine 1 includes a cylinder block 1b in which a cooling water channel 1c is formed, and a cylinder head 1a fixed to the upper portion of the cylinder block 1b in addition to the cylinders. A crankshaft 23 serving as an engine output shaft is rotatably supported on the cylinder block 1b. The crankshaft 23 is connected to pistons 22 that are slidably loaded in the cylinders # 1 to # 4.
[0026]
A combustion chamber 24 surrounded by the top surface of the piston 22 and the wall surface of the cylinder head 1a is formed above the piston 22 of each cylinder # 1 to # 4. An ignition plug 25 is attached to the cylinder head 1a so as to face the combustion chambers 24 of the cylinders # 1 to # 4. The ignition plug 25 has an igniter 25a for applying a drive current to the ignition plug 25. It is connected.
[0027]
Two opening ends of the intake port 26 and two opening ends of the exhaust port 27 are formed at a portion of the cylinder head 1a facing the combustion chamber 24 of each cylinder # 1 to # 4. 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.
[0028]
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.
[0029]
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.
[0030]
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.
[0031]
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.
[0032]
In the lower head 10, two intake ports 26 are formed for each cylinder # 1 to # 4, and a valve element 28 a of the intake valve 28 is seated at the open end of each intake port 26 on the combustion chamber 24 side. The valve seat 120 is provided.
[0033]
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 130 is inserted into the through hole. The valve shaft 28b of the intake valve 28 passes through the inner hole of the valve guide 130, and the valve shaft 28b can be moved forward and backward in the axial direction.
[0034]
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 130. 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.
[0035]
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.
[0036]
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.
[0037]
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.
[0038]
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.
[0039]
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.
[0040]
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.
[0041]
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.
[0042]
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.
[0043]
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.
[0044]
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).
[0045]
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.
[0046]
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.
[0047]
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.
[0048]
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.
[0049]
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.
[0050]
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.
[0051]
1 and 2, the cylinder head 1a of the internal combustion engine 1 is connected to an intake branch pipe 33 composed of four branch pipes, and the intake ports 26 of the cylinders # 1 to # 4 are connected to the intake branch. It communicates with each branch pipe of the pipe 33. 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.
[0052]
By the way, the starting catalysts 9a and 9b are mainly for purifying exhaust gas, particularly HC, as much as possible after the engine is started and before the NOx storage reduction catalyst 12 is activated. Since the starting catalysts 9a and 9b are activated quickly after the engine is started, these starting catalysts 9a and 9b are disposed adjacent to the engine combustion chamber and have a smaller heat capacity than the NOx storage reduction catalyst 12. . In the internal combustion engine of FIG. 1, the starting catalysts 9a and 9b are formed of a three-way catalyst. The three-way catalyst uses, for example, alumina as a carrier, and a noble metal such as platinum Pt, palladium Pd, iridium Ir, and rhodium Rh is supported on the carrier. This three-way catalyst can function as an oxidation catalyst for oxidizing HC and CO in the inflowing exhaust gas.
[0053]
In the internal combustion engine of FIG. 1, the NOx occlusion reduction catalyst 12 uses, for example, alumina as a carrier, and on this carrier, for example, an alkali metal such as potassium K, sodium Na, lithium Li, cesium Cs, or an alkali such as barium Ba, calcium Ca. At least one selected from rare earths such as earth, lanthanum La, and yttrium Y, and noble metals such as platinum Pt, palladium Pd, iridium Ir, and rhodium Rh are supported. If the ratio of the total amount of air to the total amount of fuel supplied in the exhaust passage upstream of a certain position in the exhaust passage, the combustion chamber, and the intake passage is the air-fuel ratio of the exhaust flowing through that position, this NOx The occlusion reduction catalyst 12 occludes NOx when the air-fuel ratio of the inflowing exhaust gas is lean, and performs NOx absorption / release action to release the stored NOx when the oxygen concentration in the inflowing exhaust gas decreases.
[0054]
Note that, when fuel or air is not supplied into the exhaust passage upstream of the NOx storage reduction catalyst 12, the air-fuel ratio of the exhaust flowing in coincides with the air-fuel ratio of the exhaust discharged from the internal combustion engine 1, and therefore in this case The NOx storage reduction catalyst 12 stores NOx when the air-fuel ratio of the exhaust discharged from the internal combustion engine 1 is lean, and releases the stored NOx when the oxygen concentration in the exhaust discharged from the internal combustion engine 1 decreases. Become.
[0055]
If the above-mentioned NOx occlusion reduction catalyst is arranged in the engine exhaust passage, this NOx occlusion reduction catalyst actually performs the NOx absorption / release action, but there is a part that is not clear about the detailed mechanism of this absorption / release action. However, this absorption / release action is considered to be performed by the mechanism shown in FIG. This mechanism will be described by taking as an example the case where platinum Pt and barium Ba are supported on the support, but the same mechanism can be obtained by using other noble metals, alkali metals, alkaline earths, and rare earths.
[0056]
That is, when the air-fuel ratio of the inflowing exhaust gas becomes considerably lean, the oxygen concentration in the inflowing exhaust gas greatly increases. As shown in FIG.₂Is O_2-Or O^2-It adheres to the surface of platinum Pt.
[0057]
On the other hand, NO in the inflowing exhaust is O on the surface of platinum Pt.₂ ^- Or O^2-Reacts with NO₂ (2NO + O₂ → 2NO₂ ). Then the generated NO₂ As shown in FIG. 8 (A), a part of is oxidized in the storage material while being further oxidized on platinum Pt and combined with barium oxide BaO._Three ^-It diffuses into the storage material in the form of In this way, NOx is occluded in the occlusion material.
[0058]
NO on the surface of platinum Pt as long as the oxygen concentration in the inflowing exhaust is high₂ As long as the NOx storage capacity of the storage material is not saturated.₂ Is stored in the storage material and nitrate ion NO._Three ^-Is generated. On the other hand, the oxygen concentration in the inflowing exhaust gas decreases and NO₂When the production amount of NO decreases, the reaction proceeds in the reverse direction (NO_Three ^- → NO₂), So nitrate ion NO in the storage material_Three ^-Is NO₂ Is released from the storage material in the form of That is, when the oxygen concentration in the inflowing exhaust gas decreases, NOx is released from the NOx storage reduction catalyst. When the air-fuel ratio of the inflowing exhaust gas is made rich, the oxygen concentration in the inflowing exhaust gas is lowered. Therefore, if the air-fuel ratio of the inflowing exhaust gas is made rich, NOx is released from the NOx storage reduction catalyst.
[0059]
On the other hand, if the air-fuel ratio of the exhaust gas flowing in at this time is made rich, the exhaust gas flowing into the NOx storage reduction catalyst contains high concentrations of HC or CO. These HC and CO are oxygen O on platinum Pt.₂ ^- Or O^2- It reacts with and is oxidized. In addition, if the air-fuel ratio of the inflowing exhaust gas is made rich, the oxygen concentration in the inflowing exhaust gas will extremely decrease, so NO is stored in the storage material.₂ Is released and this NO₂Is reduced by reacting with HC or CO as shown in FIG. In this way, NO on the surface of platinum Pt.₂ NO from storage to next when no longer exists₂ Is released. Therefore, when the air-fuel ratio of the inflowing exhaust gas is made rich, NOx is released from the NOx storage reduction catalyst in a short time.
[0060]
When the air-fuel ratio of the inflowing exhaust gas becomes lean in this way, NOx is stored in the NOx storage-reduction catalyst 12, and when the air-fuel ratio of the inflowing exhaust gas is made rich, NOx is released from the NOx storage-reduction catalyst 12 in a short time. .
[0061]
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.
[0062]
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.
[0063]
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 through electric wiring. The output signals of the sensors are input to the ECU 20.
[0064]
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.
[0065]
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.
[0066]
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.
[0067]
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.
[0068]
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.
[0069]
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.
[0070]
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 excitation current amount to be applied, ignition timing control routine for determining the ignition timing of the spark plugs 25 of the cylinders # 1 to # 4, and the opening degree of the throttle valve 39 In addition to application programs such as a throttle opening control routine for determination, the NOx storage reduction catalyst 12 stores the It stores a control routine for reducing and purifying NOx.
[0071]
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.
[0072]
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.
[0073]
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.
[0074]
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.
[0075]
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, and the opening / closing timing of the exhaust valve 29 are controlled.
[0076]
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 and the opening / closing timing of the exhaust valve 29 are controlled.
[0077]
In addition, 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 12. However, when the lean combustion operation of the internal combustion engine 1 is continued for a long period of time, the NOx occlusion capacity of the NOx occlusion reduction catalyst 12 is saturated, and nitrogen oxides (NOx) in the exhaust gas are removed by the NOx occlusion reduction catalyst 12 or There is a risk of being released into the atmosphere without being purified.
[0078]
On the other hand, when the internal combustion engine 1 is in a lean combustion operation and the NOx occlusion capacity of the NOx occlusion reduction catalyst 12 is saturated, the CPU 401 temporarily sets the air / fuel ratio of the exhaust to be a rich air / fuel ratio, thereby reducing the NOx occlusion reduction catalyst. The NOx storage capacity of the NOx storage reduction catalyst 12 was regenerated by reducing and purifying the nitrogen oxide (NOx) stored in the NOx12.
[0079]
By the way, as described above, the starting catalysts 9a and 9b are for purifying exhaust gas as much as possible until the NOx storage reduction catalyst 12 is activated. In this embodiment, the exhaust of the first cylinder group 1a flows through the start-up catalyst 9a without being mixed with the exhaust of the second cylinder group 1b, and the exhaust of the second cylinder group 1b is the first cylinder group 1a. The start-up catalyst 9b flows without being mixed with the exhaust gas. Therefore, the amount of HC consumed in the start-up catalyst 9a when the air-fuel ratio of the exhaust of the first cylinder group 1a is made rich and the air-fuel ratio of the exhaust of the second cylinder group 1b is made lean is reduced, and The amount of oxygen consumed in the hour catalyst 9b is reduced. Therefore, a large amount of HC and oxygen can be reliably supplied to the NOx storage reduction catalyst 12, and thus the temperature of the NOx storage reduction catalyst 12 can be reliably increased.
[0080]
However, if the amount of fuel injection is increased for some cylinders as described above, the torque generated in these cylinders will be larger than that for other cylinders with a small amount of fuel injection.
[0081]
Therefore, the amount of fuel injection is low, that is, the torque generated in the lean cylinder is obtained, and the intake / exhaust valve opening / closing timings of these cylinders are controlled so that the generated torque of the cylinder with high fuel injection matches this. In this way, the torque is prevented from varying from cylinder to cylinder.
[0082]
Also, in a cylinder with a large amount of fuel injection and a reduced intake air amount to reduce torque, the air-fuel ratio of the exhaust discharged from the combustion chamber becomes rich, but the excess fuel that did not burn in the combustion chamber In addition, partial oxidation is performed without being completely oxidized in the combustion chamber or the exhaust passage upstream of the NOx occlusion reduction catalyst 12, so that the NOx occlusion reduction catalyst 12 can easily reduce NOx.
[0083]
More specifically, in the internal combustion engine of FIG. 1, normally, fuel injection is performed once in one combustion cycle of all cylinders. At this time, the air-fuel ratio of the air-fuel mixture supplied by fuel injection is lean, for example, about 16.0. Therefore, the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 12 is made lean. On the other hand, when NOx should be released from the NOx occlusion reduction catalyst 12, the air-fuel ratio of the air-fuel mixture supplied into the combustion chamber is rich in the first cylinder group 1a, for example, about 12.0. In the second cylinder group 1b, lean, for example, about 16.0 is set. These exhaust gases join at the junction of the branch exhaust pipe and flow into the rich exhaust gas, that is, the air-fuel ratio 14.0 to the NOx storage reduction catalyst 12. Therefore, the reduction of the NOx occlusion reduction catalyst 12 is promoted by this reducing exhaust gas.
[0084]
As described above, when the NOx occlusion amount of the NOx occlusion reduction catalyst 12 becomes equal to or greater than a certain amount, the first cylinder group 1a performs fuel injection for a certain period of time, thereby exhausting the exhaust gas flowing into the NOx occlusion reduction catalyst 12. The fuel ratio is temporarily made rich so that NOx is released from the NOx storage reduction catalyst 12 and reduced.
[0085]
However, the inflowing exhaust gas contains sulfur, and the NOx storage reduction catalyst 12 stores not only NOx but also sulfur, for example, SOx. The storage mechanism of the sulfur content in the NOx storage reduction catalyst 12 is considered to be the same as the storage mechanism of NOx. That is, in the case where platinum Pt and barium Ba are supported on the carrier as in the case of the NOx occlusion mechanism described above, oxygen O2 is generated when the air-fuel ratio of the exhaust gas flowing in is lean as described above. It adheres to the surface of platinum Pt in the form of O2 − or O 2−, and SOx, for example, SO2 in the inflowing exhaust gas reacts with O2 − or O 2− on the surface of platinum Pt to become SO3.
[0086]
Next, the generated SO3 is further oxidized on the platinum Pt, occluded in the occlusion material and bonded to the barium oxide BaO, and diffused in the occlusion material in the form of sulfate ions SO4 2-. The sulfate ion SO4 2- then combines with barium ion Ba 2+ to produce sulfate BaSO4.
[0087]
However, this sulfate BaSO4 is difficult to decompose, and even if the air-fuel ratio of the inflowing exhaust gas is simply made rich, the sulfate BaSO4 remains without being decomposed. Accordingly, the sulfate BaSO4 increases as time elapses, and the amount of NOx that can be stored by the NOx occlusion reduction catalyst 12 decreases as time elapses. That is, the NOx occlusion reduction catalyst 12 is poisoned by sulfur.
[0088]
The sulfate BaSO4 produced in the NOx occlusion reduction catalyst 12 is decomposed when the air-fuel ratio of exhaust flowing in when the temperature of the NOx occlusion reduction catalyst 12 is high, or when the stoichiometric air-fuel ratio is reached, and sulfate ions SO4 2- are converted into SO3. Is released from the storage material, that is, the NOx storage reduction catalyst 12 is poisoned and regenerated.
[0089]
Therefore, in the internal combustion engine of FIG. 1, it is determined whether the NOx storage reduction catalyst 12 is poisoned by the sulfur component, and when it is determined that the NOx storage reduction catalyst 12 is poisoned by the sulfur component, the NOx storage reduction catalyst 12 is removed. A predetermined set temperature, that is, a temperature higher than that required to release the sulfur component from the NOx storage reduction catalyst 12, and the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 12 are temporarily made rich. Thereby, the sulfur content is released from the NOx storage reduction catalyst 12, and the NOx storage reduction catalyst 12 is poisoned and regenerated. The SO3 released at this time is immediately reduced to SO2 by HC and CO in the inflowing exhaust gas.
Hereinafter, the exhaust gas adjustment control according to the present embodiment will be specifically described.
[0090]
<Embodiment 1>
In this control, the CPU 401 executes a control routine as shown in FIG. This 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).
[0091]
In the exhaust gas adjustment control routine, the CPU 401 first determines in step S501 whether the NOx storage capacity of the NOx storage reduction catalyst 12 is saturated.
As a method for determining whether or not the NOx storage capacity of the NOx storage reduction catalyst 12 is saturated, for example, based on 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). The NOx occlusion / reduction catalyst 12 is estimated and the NOx occlusion / reduction catalyst 12 is estimated, and the estimated value is compared with the maximum nitrogen oxide (NOx) amount that the NOx occlusion / reduction catalyst 12 can occlude. The amount of nitrogen oxide (NOx) stored in the NOx storage reduction catalyst 12 is estimated from the catalyst bed temperature of the NOx storage reduction catalyst 12 and the output signal value of the air-fuel ratio sensor 48, and the estimated value and the NOx storage reduction catalyst 12 are estimated. Is estimated by comparing the maximum amount of nitrogen oxide (NOx) that can be occluded, or the air-fuel ratio of the exhaust gas flowing into the NOx occlusion reduction catalyst 12 is predetermined. It can be exemplified determining method or the like based on the output signal value of the NOx sensor 49 when it is an air-fuel ratio.
[0092]
Hereinafter, the maximum amount of nitrogen oxide (NOx) that can be stored by the NOx storage reduction catalyst 12 is referred to as the maximum NOx storage amount.
When the CPU 401 determines in S501 that the NOx occlusion capacity of the NOx occlusion reduction catalyst 12 is not saturated, the execution of this routine is temporarily terminated.
[0093]
On the other hand, if it is determined in S501 that the NOx storage capacity of the NOx storage reduction catalyst 12 is saturated, the process proceeds to S502. In S502, the CPU 401 performs reduction necessary for reducing and purifying all nitrogen oxides (NOx) stored in the NOx storage reduction catalyst 12, in other words, nitrogen oxides (NOx) having the maximum NOx storage amount. The amount of the agent (hereinafter referred to as the target reducing agent amount) is calculated.
[0094]
The maximum NOx occlusion amount of the NOx occlusion reduction catalyst 12 can be experimentally determined in advance, so that the target reducing agent necessary for purifying the maximum NOx occlusion amount of nitrogen oxide (NOx). The amount may be obtained experimentally in advance and stored in the ROM 402 or the like.
[0095]
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.
[0096]
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.
[0097]
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. .
[0098]
In S505, the CPU 401 covers the target reducing agent amount with exhaust from the first cylinder group 1a using the target cylinder intake amount calculated in S502 and the target reducing agent amount calculated in S504 as parameters. Thus, the air-fuel ratio of the air-fuel mixture to be combusted in the first cylinder 1a (hereinafter referred to as the target rich air-fuel ratio) is calculated.
[0099]
In step S506, the CPU 401 calculates the smallest air-fuel ratio (hereinafter referred to as a rich limit air-fuel ratio) in the air-fuel ratio range in which a combustible mixture can be formed in the cylinder group 1a of the internal combustion engine 1, and calculates in step S505. The target rich air-fuel ratio is compared.
[0100]
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, that is, the target rich air-fuel ratio is greater than the rich limit air-fuel ratio, the CPU 401 sets the first cylinder group 1a to one. It is considered that the target reducing agent amount of reducing agent can be supplied to the NOx storage reduction catalyst 12 by operating at the target rich air-fuel ratio only once, and the process proceeds to S507.
[0101]
In S507, the CPU 401 determines the target opening / closing timing of the intake valve 28 (hereinafter referred to as the target intake valve opening / closing timing) so that the intake air amount of the first cylinder group 1a of the internal combustion engine 1 becomes the target cylinder intake amount. To do.
[0102]
In S508, the CPU 401 calculates the target fuel injection amount of the first cylinder group 1a by dividing the target cylinder intake air amount by the target rich air-fuel ratio.
In step S509, the CPU 401 determines that the torque generated when the first cylinder group 1a is operated at the target cylinder intake air amount and the target rich air-fuel ratio becomes the required engine torque calculated in step S503. A target opening / closing timing (hereinafter referred to as a target exhaust valve opening / closing timing) of the exhaust valve 29 of the first cylinder group 1a is determined.
[0103]
In S510, the CPU 401 determines the intake side drive circuit 30a of the first cylinder group 1a, the fuel injection according to the target intake valve opening / closing timing, the target fuel injection amount, and the target exhaust valve opening / closing timing determined in S507 to S509. The valve 32, the exhaust side drive circuit 31a, and the igniter 25a are controlled.
[0104]
Here, since each intake valve 28 of the cylinder group 1a is provided at a position facing the combustion chamber 24, when the opening / closing timing of the intake valve 28 is changed, the first cylinder # 1 and the fourth cylinder # 4 The actual intake air amount is immediately changed without causing a response delay.
[0105]
Therefore, when the intake side drive circuit 30a is controlled so that the opening / closing timing of the intake valve 28 of the first cylinder group 1a matches the target intake valve opening / closing timing, the actual intake air amount of the cylinder group 1a is Immediately, the target cylinder intake amount is obtained.
[0106]
Therefore, when the intake valve 28 and the fuel injection valve 32 of the cylinder group 1a are driven according to the target intake valve opening / closing timing and the target fuel injection amount, the cylinder group 1a is immediately operated at the target rich air-fuel ratio. In the exhaust stroke of the first cylinder group 1a, exhaust containing an amount of reducing agent corresponding to the target reducing agent amount is discharged.
[0107]
The exhaust discharged from the first cylinder group 1a flows into the NOx occlusion reduction catalyst 12 via the exhaust branch pipe 45, so that all the nitrogen oxides (NOx) occluded in the NOx occlusion reduction catalyst 12 are removed. It will be reduced and purified.
[0108]
That is, by operating the first cylinder group 1a of the internal combustion engine 1 only once with the target rich air-fuel ratio, all of the nitrogen oxides (NOx) stored in the NOx storage reduction catalyst 12 are reduced and purified. become.
[0109]
On the other hand, when it is determined in S506 that the target rich air-fuel ratio is smaller than the rich limit air-fuel ratio, the CPU 401 reduces the target reducing agent amount even if the first cylinder group 1a is operated at the rich air-fuel ratio only once. It is considered that the agent cannot be supplied to the NOx storage reduction catalyst 12, and the process proceeds to S511.
[0110]
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 determines the target intake valve opening / closing timing so that the intake air amount of the first cylinder group 1a of the internal combustion engine 1 becomes the target cylinder intake amount calculated in S504.
[0111]
In S513, the CPU 401 calculates the target fuel injection amount in the first cylinder group 1a by dividing the target cylinder intake air amount calculated in S504 by the new target rich air-fuel ratio newly set in S511. To do.
[0112]
In S514, the CPU 401 causes the torque generated when the first cylinder group 1a is operated at the target cylinder intake air amount and the new target rich air-fuel ratio to be the required engine torque calculated in S503. The target exhaust valve opening / closing timing of the first cylinder group 1a is determined.
[0113]
In S515, the CPU 401 determines the intake side drive circuit 30a of the first cylinder group 1a, the fuel injection according to the target intake valve opening / closing timing, the target fuel injection amount, and the target exhaust valve opening / closing timing determined in S512 to S514. The valve 32, the exhaust side drive circuit 31a, and the igniter 25a are controlled.
[0114]
In S516, the CPU 401 supplies the amount of reducing agent supplied to the NOx occlusion reduction catalyst 12 from the cylinder group 1a operated according to the target cylinder intake air amount and the new target rich air-fuel ratio (hereinafter referred to as supply reducing agent amount). Is calculated.
[0115]
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.
[0116]
In this case, the first cylinder # 1 and the fourth cylinder # 4 constituting the first cylinder group 1a are operated at a rich air-fuel ratio, and the reducing agent contained in the exhaust discharged from these cylinders The total amount is the target reducing agent amount.
[0117]
As a result, all the nitrogen oxides (NOx) stored in the NOx storage reduction catalyst 12 are reduced and purified by the target reducing agent amount of the reducing agent.
As described above, when the CPU 401 executes the exhaust gas adjustment control routine, the exhaust gas adjustment means of the present invention is realized.
[0118]
That is, in the exhaust gas adjustment control described above, the intake air amount of the cylinders # 1 to # 4 can be independently controlled by using the electromagnetically driven valve mechanism, so that the NOx occlusion reduction catalyst 12 occludes. When reducing and purifying nitrogen oxide (NOx), a desired amount of reducing agent is supplied to the NOx occlusion reduction catalyst 12 by changing the intake air amount of one cylinder group and operating at a rich air-fuel ratio. Is possible.
[0119]
At this time, since the intake air amount of the first cylinder group 1a 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 air, and the first cylinder # 1 It is possible to immediately switch the intake air amount and air-fuel ratio to the fourth cylinder # 4 to the desired intake air amount and rich air-fuel ratio.
[0120]
Therefore, according to the exhaust gas adjustment control according to the present embodiment, when nitrogen oxide (NOx) stored in the NOx storage reduction catalyst 12 is reduced and purified, a desired amount of reducing agent can be removed in a short period of time. It becomes possible to supply to the storage reduction catalyst 12, and the period of rich air-fuel ratio operation related to the purification of nitrogen oxides (NOx) is not unnecessarily prolonged, thereby preventing deterioration of drivability and fuel consumption. Is done.
[0121]
Further, in the exhaust gas adjustment control according to the present embodiment, the target cylinder intake air amount and the target fuel injection amount of the first cylinder group 1a are determined by the generated torque of the first cylinder group 1a being the second cylinder group 1b. Since it is set so as to coincide with the generated torque of the (cylinder group operated at a normal lean air-fuel ratio), only the first cylinder group 1a is rich when the internal combustion engine 1 is operated at the lean air-fuel ratio. Torque fluctuations do not occur even when operated at a fuel ratio (target rich air-fuel ratio).
[0122]
In the present embodiment, the target cylinder intake air amount is determined so that the torque generated in the first cylinder group 1a matches the torque generated in the second cylinder group 1b. The maximum air amount that the group 1a can inhale in one intake stroke (hereinafter referred to as the maximum cylinder intake amount) may be set as the target cylinder intake amount.
[0123]
When the maximum cylinder intake air amount is set as the target cylinder intake air amount, the first cylinder group 1a has the largest amount of exhaust that can be discharged in one exhaust stroke. Since the amount of reducing agent 1a that can be discharged in one exhaust stroke is the largest, the period of rich air-fuel ratio operation for the purpose of purifying nitrogen oxide (NOx) stored in the NOx storage reduction catalyst 12 Can be further shortened.
[0124]
However, when the maximum cylinder intake air amount is set as the target cylinder intake air amount, the generated torque of the first cylinder group 1a is expected to be significantly larger than the generated torque of the second cylinder group 1b. Therefore, it is preferable to suppress the torque generated in the first cylinder group by controlling the opening / closing timing of the intake valve 28 and the exhaust valve 29 of the first cylinder group 1a.
<Embodiment 2>
Hereinafter, a second 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 that of the first embodiment will be described, and the description of the same configuration will be omitted.
[0125]
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 12 is saturated, at least the exhaust of the exhaust discharged from the first cylinder group 1a is empty. In the present embodiment, the first cylinder of the internal combustion engine 1 has been described in which the nitrogen oxide (NOx) stored in the NOx storage reduction catalyst 12 is temporarily reduced to a rich air-fuel ratio. An example in which the group 1a and the second cylinder group 1b are operated so as to alternately repeat the rich air-fuel ratio and the lean state for each cycle will be described.
[0126]
The internal combustion engine 1 according to the present embodiment includes four cylinders # 1, # 2, # 3, and # 4. When all of these cylinders are operated at a lean air-fuel ratio for each cycle, the rich engine The operation is switched at the air-fuel ratio. That is, when the four cylinders # 1, # 2, # 3, and # 4 of the internal combustion engine 1 are operated at a rich air-fuel ratio, the cylinders # 1, # 2, # 3, and # 4 are continuously leaned in the next cycle. It is operated at an air fuel ratio. In this case, the exhaust gas with a rich air-fuel ratio is always discharged after the exhaust gas with a lean air-fuel ratio is continuously discharged.
[0127]
In such a case, the NOx occlusion reduction catalyst 12 occludes nitrogen oxide (NOx) contained in the exhaust when operated at a lean air-fuel ratio, and then the reduction contained in the exhaust of the cylinder operated at a rich air-fuel ratio. The operation of releasing and reducing the nitrogen oxide (NOx) stored by the agent is repeated.
[0128]
At that time, by optimizing the air-fuel ratio and amount of exhaust discharged in the exhaust stroke in the rich operation, all the nitrogen oxides (NOx) stored in the NOx storage reduction catalyst 12 (the exhausted during the lean operation) All nitrogen oxides (NOx)) can be reduced and purified.
[0129]
By the way, the combustion pressure generated when the air-fuel mixture burns during the rich operation becomes higher than the combustion pressure generated when the air-fuel mixture combusts during the lean operation. When reflected in the rotational torque of 23, torque fluctuation occurs between the cylinders.
[0130]
Therefore, in the present embodiment, during the rich operation, the CPU 401 controls the opening / closing timing of the exhaust valve 29 during the rich operation to reduce the generated torque during the rich operation to the generated torque during the lean operation. .
[0131]
For example, the valve opening timings of the exhaust valves 29 of the cylinders # 1, # 2, # 3, and # 4 may be advanced halfway through the expansion stroke. In this case, the burned gas in the cylinder is discharged from the cylinder in the middle of the expansion stroke and the pressure in the cylinder decreases, so the pressure acting on the piston 22 decreases, and as a result, the combustion pressure generated in the cylinder decreases. Only a part is reflected in the rotational torque of the crankshaft 23.
[0132]
Hereinafter, the control according to the present embodiment will be specifically described.
When executing this control, the CPU 401 executes an exhaust gas adjustment control routine as shown in FIG. This exhaust gas adjustment 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 °).
[0133]
In this control routine, the CPU 401 first 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 in S801.
[0134]
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.
[0135]
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.
[0136]
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.
[0137]
In S805, the CPU 401 calculates a torque required for each cylinder (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.
[0138]
In step S806, the CPU 401 causes the generated torque of the lean operation cylinders # 1, # 2, # 3, and # 4 to be the same as the required cylinder torque, and the fuel of the lean operation cylinders # 1, # 2, # 3, and # 4. The air-fuel ratio of the air-fuel mixture to be burned in the lean operating cylinders # 1, # 2, # 3, and # 4 (hereinafter referred to as the target lean air-fuel ratio) and the lean operating cylinders # 1 and # are set so that the injection amount is minimized. 2, # 3 and # 4 determine the amount of air to be taken in (hereinafter referred to as the target lean cylinder intake amount).
[0139]
In S807, the CPU 401 determines the target intake valve open / close timing and target exhaust valve open / close timing of the cylinder during the lean operation 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 The target fuel injection amount for each cylinder during lean operation is calculated by dividing the amount by the target lean air-fuel ratio.
[0140]
In S808, the CPU 401 first discharges from each cylinder during lean operation when each cylinder during lean operation is operated according to the target lean air-fuel ratio and the target lean cylinder intake air amount determined in S806. Estimate the amount of nitrogen oxides (NOx). In this case, the CPU 401 may calculate the total amount of nitrogen oxides (NOx) discharged during four lean operations by multiplying the estimated value in a single cylinder by four.
[0141]
In step S809, the CPU 401 calculates the amount of reducing agent (target reduction amount) necessary for reducing the total NOx amount of nitrogen oxides (NOx) estimated in step S808.
[0142]
In S810, the CPU 401 first calculates the lowest air-fuel ratio (hereinafter referred to as a target rich air-fuel ratio) in an air-fuel ratio range in which a combustible mixture can be formed in the cylinder during rich operation. 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, whereby the cylinder during the rich operation. The amount of exhaust to be discharged from # 1, # 2, # 3, and # 4, in other words, the amount of air to be taken into cylinders # 1, # 2, # 3, and # 4 during rich operation (hereinafter referred to as target rich cylinder) (Referred to as intake air amount).
[0143]
In S811, the CPU 401 determines the target intake valve opening / closing timing of the cylinders # 1, # 2, # 3, and # 4 during the rich operation based on the target rich cylinder intake air amount calculated in S810, and the target rich cylinder. The target fuel injection amount for cylinders # 1, # 2, # 3, and # 4 during the rich operation is calculated by dividing the cylinder intake amount by the target rich air-fuel ratio.
[0144]
In S812, the CPU 401 estimates the torque that can be generated by the cylinders # 1, # 2, # 3, and # 4 during the rich operation according to the target rich air-fuel ratio and the target rich cylinder intake air amount calculated in S810.
[0145]
In S813, the CPU 401 opens and closes the target exhaust valves of the cylinders # 1, # 2, # 3, and # 4 during the rich operation so that the torque estimated in S812 decreases to the required cylinder torque calculated in S805. Determine timing.
In S814, the CPU 401 performs intake of the cylinders # 1, # 2, # 3, and # 4 during lean operation 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. The side drive circuit 30a, the exhaust side drive circuit 31a, and the fuel injection valve 32 are controlled, and rich 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 intake side drive circuit 30a, the exhaust side drive circuit 31a, and the fuel injection valve 32 of the cylinders # 1, # 2, # 3, and # 4 during operation are controlled.
[0146]
In this case, in the internal combustion engine 1, after the cylinders # 1, # 2, # 3, and # 4 in the lean operation are continuously operated at the target lean air-fuel ratio, the operation is switched to the rich operation, and the cylinders # 1 and # 2 , # 3 and # 4 are operated at the target rich air-fuel ratio. Accordingly, after the cylinders # 1, # 2, # 3, and # 4 in the lean operation continuously exhaust the exhaust gas having the target lean air-fuel ratio, the cylinders # 1, # 2, # 3, and # are in the rich operation. 4 exhausts exhaust gas having a target rich air-fuel ratio.
[0147]
At that time, the exhaust discharged from the cylinders # 1, # 2, # 3, and # 4 during the rich operation is included in the exhaust discharged from the cylinders # 1, # 2, # 3, and # 4 during the lean operation. Since the amount of reducing agent corresponding to the total amount of nitrogen oxide (NOx) is contained, the NOx storage reduction catalyst 12 is exhausted from the cylinders # 1, # 2, # 3, and # 4 during lean operation. When inflowing, nitrogen oxides (NOx) contained in the exhaust gas are occluded, and when exhaust gas from the cylinder during the rich operation flows in subsequently, all of the occluded nitrogen oxides (NOx) are released and purified. It becomes possible to do.
[0148]
Therefore, according to the exhaust gas adjustment control as described above, the storage and reduction of nitrogen oxide (NOx) in the NOx storage and reduction catalyst 12 is performed for each cycle, so the storage amount and reduction of nitrogen oxide (NOx) are performed. It is easy to match the supply amount of the agent, and the calculation load on the CPU 401 can be reduced.
[0149]
Further, in the exhaust gas adjustment control as described above, the opening and closing timings of the exhaust valves 29 of the cylinders # 1, # 2, # 3, and # 4 during the rich operation are controlled, whereby the cylinders # 1 and # during the rich operation are controlled. 2, # 3, # 4 and the generated torque of cylinders # 1, # 2, # 3, # 4 during lean operation are made uniform, so that torque fluctuations of the internal combustion engine 1 do not occur. .
[0150]
Further, it is possible to suppress the generation of deposits and the smoldering of the spark plug 25 due to the constant operation of some cylinders.
In the present embodiment, an example is described in which the rich operation is performed on all of the cylinders # 1, # 2, # 3, and # 4 during the rich operation of the internal combustion engine 1. However, the rich cylinder is set to any specific cylinder. You may make it fix and perform rich operation with a predetermined period.
<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 to third embodiments described above will be described, and the description of the same configuration will be omitted.
[0151]
In the first to third embodiments described above, the NOx storage capacity of the NOx storage reduction catalyst 12 is regenerated by reducing and purifying the nitrogen oxide (NOx) stored in the NOx storage reduction catalyst 12. As described above, in the present embodiment, an example of regenerating the SOx poisoning of the NOx storage reduction catalyst 12 will be described.
[0152]
The NOx occlusion reduction catalyst 12 occludes nitrogen oxide (NOx) contained in the exhaust when the air-fuel ratio of the exhaust gas flowing into the NOx occlusion reduction catalyst 12 is a lean air-fuel ratio. The sulfur component contained in the NOx 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 occlusion capacity of the NOx occlusion reduction catalyst 12 decreases.
[0153]
Specifically, the sulfur (S) component contained in the fuel of the internal combustion engine 1 is burned to cause SO.₂Or SO_ThreeSuch sulfur oxides (SOx) are generated, and these sulfur oxides (SOx) flow into the NOx occlusion reduction catalyst 12 together with the exhaust gas.
[0154]
At this 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 carrier of the NOx storage reduction catalyst 12.₂ ^-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-Or SO_Four-Form.
[0155]
SO formed on platinum (Pt) of the NOx storage reduction catalyst 12_3-Or SO_Four-Is further oxidized on platinum (Pt) and sulfate ions (SO_Four ^2-) Is absorbed by the NOx storage reduction catalyst 12. Sulfate ion (SO) absorbed in the NOx storage reduction catalyst 12_Four ^2-) Combines with barium oxide (BaO) to form barium sulfate (BaSO)._Four).
[0156]
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 12 becomes a rich air-fuel ratio, it is decomposed. Instead, it remains in the NOx storage reduction catalyst 12.
[0157]
Accordingly, the barium sulfate (BaSO) in the NOx storage reduction catalyst 12 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 storage of the NOx storage reduction catalyst 12 decreases. The ability will be reduced.
[0158]
In order to eliminate SOx poisoning of the NOx occlusion reduction catalyst 12, the atmospheric temperature of the NOx occlusion reduction catalyst 12 is raised to a high temperature (for example, 500 ° C. to 700 ° C.) and the air-fuel ratio of the exhaust gas flowing into the NOx occlusion reduction catalyst 12 Needs to be a rich air-fuel ratio.
[0159]
That is, when the atmospheric temperature of the NOx storage reduction catalyst 12 becomes high, the barium sulfate (BaSO) produced in the NOx storage reduction catalyst 12 is increased._Four) Is SO_3-Or SO_Four-Pyrolyzed to At that time, if the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 12 is a rich air-fuel ratio, SO_3-Or 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 12.
[0160]
As a method for making the NOx storage reduction catalyst 12 have a high temperature and a 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 12, and the NOx storage reduction catalyst The method of making the NOx occlusion reduction catalyst 12 into a high temperature and rich atmosphere by reacting (combusting) the unburned fuel component and oxygen in 12 can be exemplified.
[0161]
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. And 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 12, and (2) one of the internal combustion engine 1 By operating a part of the cylinders with a rich air-fuel ratio mixture and simultaneously operating the remaining cylinders with a lean air-fuel mixture, exhaust gas containing a sufficient amount of unburned fuel components and a sufficient amount of oxygen are produced. A method of mixing with exhaust gas can be exemplified, but in the present embodiment, the characteristics of the electromagnetically driven valve mechanism that can arbitrarily set the opening and closing timing of the intake valve 28 and the exhaust valve 29 are shown. Use Methods, such as has been adopted.
[0162]
In other words, in the present embodiment, the CPU 401 renders each cylinder # 1, # 2, # 3, # 4 of the internal combustion engine 1 rich empty when it becomes necessary to eliminate the SOx poisoning of the NOx storage reduction catalyst 12. The fuel injection valve 32 is controlled so as to operate with the air-fuel mixture, and the 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. .
[0163]
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. .
[0164]
By the way, when the air-fuel mixture in the middle of combustion is discharged from each cylinder # 1, # 2, # 3, # 4, the combustion pressure generated in each cylinder decreases and the combustion pressure is transmitted to the crankshaft 23. Efficiency will fall and the torque of the internal combustion engine 1 will fall.
[0165]
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, and corrects the fuel injection amount to be increased. When increasing the intake air amount of each cylinder # 1 to # 4, 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.
[0166]
Hereinafter, the exhaust gas adjustment control according to the present embodiment will be specifically described.
In executing the exhaust gas adjustment control, the CPU 401 executes an exhaust gas adjustment control routine as shown in FIG. This exhaust gas adjustment 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).
[0167]
In the exhaust gas adjustment control routine, the CPU 401 first determines the degree of SOx poisoning of the NOx occlusion reduction catalyst 12 in S1001. As a method for determining the degree of SOx poisoning of the NOx storage reduction catalyst 12, for example, when the air-fuel ratio of the exhaust gas flowing into the NOx storage reduction catalyst 12 is a lean air-fuel ratio, the NOx storage reduction catalyst 12 is disposed downstream of the NOx storage reduction catalyst 12. A determination method based on the output signal value of the NOx sensor 49, or an integrated value of the time when the internal combustion engine 1 is operated at a lean air-fuel ratio, an integrated value of the intake air amount, and / or an integrated value of the fuel injection amount, etc. A method for estimating the degree of SOx poisoning of the NOx storage reduction catalyst 12 based on the above can be exemplified.
[0168]
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.
[0169]
If it is determined in S1002 that the SOx poisoning degree of the NOx storage reduction catalyst 12 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 12, and this routine The execution of is temporarily terminated.
[0170]
On the other hand, if it is determined in S1002 that the SOx poisoning degree of the NOx storage reduction catalyst 12 exceeds the reference value, the CPU 401 considers that it is necessary to execute the SOx poisoning elimination process for the NOx storage reduction catalyst 12. , The process proceeds to S1003.
[0171]
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.
[0172]
In step S1004, the CPU 401 satisfies the required engine torque calculated in step S1003, and supplies the NOx storage reduction catalyst 12 with exhaust gas containing unburned fuel components and oxygen. The opening / closing timing of 29 and the fuel injection amount are determined.
[0173]
Specifically, the CPU 401 first determines the air-fuel ratio of the air-fuel mixture to be combusted in each cylinder # 1 to # 4. Subsequently, the CPU 401 corrects the advance timing of the opening timing of the exhaust valve 29 so that the air-fuel mixture in the middle of combustion in each cylinder # 1 to # 4 is discharged as exhaust.
[0174]
Then, the CPU 401 determines the intake air amount and the fuel injection so that the actual engine torque when the internal combustion engine 1 is operated according to the air-fuel ratio and the exhaust valve opening timing coincides with the required engine torque calculated in S1003. The amount is determined, and the opening / closing timing of the intake valve 28 is determined according to the determined intake air amount.
[0175]
In S1005, the CPU 401 controls the intake side drive circuit 30a, the exhaust side drive circuit 31a, the fuel injection valve 32, and the spark plug 25 according to the intake valve opening / closing timing, the exhaust valve opening / closing timing, and the fuel injection amount determined in S1004. Then, execution of the SOx poisoning elimination process is started.
[0176]
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 occlusion reduction catalyst 12 via the exhaust branch pipe 45. The NOx occlusion reduction catalyst 12 receives the heat of the exhaust gas and raises the temperature, and the reaction heat generated by the reaction between the unburned fuel component in the exhaust gas and oxygen on platinum (Pt) of the NOx occlusion reduction catalyst 12 To further increase the temperature.
[0177]
When the atmospheric temperature of the NOx storage reduction catalyst 12 rises in this way, barium sulfate (BaSO) in the NOx storage reduction catalyst 12 is increased._Four) Is SO_3-Or SO_Four-They are pyrolyzed into 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 occlusion reduction catalyst 12.
[0178]
In S1006, the CPU 401 determines whether or not the SOx poisoning of the NOx storage reduction catalyst 12 has been eliminated. As a method of determining whether or not the SOx poisoning of the NOx storage reduction catalyst 12 has been eliminated, the SOx poisoning degree of the NOx storage reduction catalyst 12 and the time required to eliminate the SOx poisoning (SOx poisoning elimination time) The relationship is experimentally obtained in advance, and a method for 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 in the exhaust passage downstream from the NOx storage reduction catalyst 12 A method of arranging SOx sensors that output electrical signals corresponding to the SOx concentration and determining whether or not the output signal values of those SOx sensors are less than a predetermined value can be exemplified.
[0179]
If it is determined in S1006 that the SOx poisoning of the NOx occlusion reduction catalyst 12 has not yet been eliminated, the CPU 401 continues to execute the process of S1005.
[0180]
If it is determined in S1006 that the SOx poisoning of the NOx occlusion reduction catalyst 12 has been eliminated, the CPU 401 proceeds to S1007 and performs intake air to return the opening / closing timing of the intake valve 28 and the opening / closing timing of the exhaust valve 29 to normal timing. The side drive circuit 30a and the exhaust side drive circuit 31a are controlled, and the fuel injection valve 32 is controlled to return the fuel injection amount to the normal fuel injection amount.
[0181]
According to such exhaust gas adjustment 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 related to the SOx poisoning elimination process, and therefore, the rich air-fuel ratio operation period related to the SOx poisoning elimination process is not unnecessarily lengthened, and the drivability is deteriorated and the fuel consumption is reduced. The deterioration of the amount is prevented.
[0182]
In the present embodiment, when SOx poisoning of the NOx storage reduction catalyst 12 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 the cylinders # 1 to # 4 of the internal combustion engine 1 are open, that is, during the valve overlap period, the fuel injection valve 32 is operated, and unburned. Is supplied to the NOx occlusion reduction catalyst 12 so that the unburned fuel is combusted in the NOx occlusion reduction catalyst 12 so that the NOx occlusion reduction catalyst 12 is brought to a high temperature and rich atmosphere in a shorter time. May be.
[0183]
In this embodiment, torque control is performed by changing the opening / closing timing of the exhaust valve. However, torque is controlled by adjusting the amount of intake air into the cylinder by changing the opening / closing timing of the intake valve. In this case, efficiency is better in terms of fuel consumption than torque control by an exhaust valve.
[0184]
【The invention's effect】
As described above, according to the present invention, only the rich or lean air-fuel ratio exhaust gas passes through the start-up catalyst, so that the reaction at the start-up catalyst is suppressed and the reduction reaction at the NOx storage reduction catalyst is promoted. The torque generated in the cylinder group that can be made rich is controlled to match the torque generated in the lean cylinder. Therefore, variation in torque is suppressed, and deterioration of drivability due to torque fluctuation is prevented.
[Brief description of the drawings]
FIG. 1 is a plan view showing a schematic configuration of an internal combustion engine having an electromagnetically driven valve according to the present invention.
FIG. 2 is a cross-sectional view showing a schematic configuration of an internal combustion engine having an electromagnetically driven valve according to the present invention.
FIG. 3 is a diagram showing a 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 an exhaust gas adjustment control routine according to the first embodiment.
FIG. 6 is a flowchart showing an exhaust gas adjustment control routine according to the second embodiment.
FIG. 7 is a flowchart showing a purification support control routine according to the third embodiment.
FIG. 8 is a diagram showing an outline of the NOx storage / release action of the NOx storage reduction catalyst.
[Explanation of symbols]
1 ... Internal combustion engine
1a: first cylinder group
1b ... second cylinder group
9a, 9b ... Starting catalyst
12 ... NOx storage reduction catalyst
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)

Cylinder group divided into a plurality of parts, branch exhaust pipes to which these cylinder groups are respectively connected, a start-up catalyst disposed in these branch exhaust pipes, and NOx provided downstream of the junction of the branch exhaust pipes It has a storage reduction catalyst, the exhaust gas regulating means the air-fuel ratio for each Jo Tokoro cylinder group to discharge the rich and lean exhaust gas, and
The exhaust gas adjusting means is a target required for reducing and purifying NOx stored in the NOx storage reduction catalyst when it is determined that the NOx storage capacity of the NOx storage reduction catalyst is saturated. A reducing agent amount is calculated, a required engine torque is calculated, a target cylinder intake amount per cylinder that achieves the required engine torque is calculated, and the target reduction is calculated based on the target reducing agent amount and the target cylinder intake amount. A target rich air-fuel ratio to be combusted in the cylinders of the predetermined cylinder group is calculated in order to cover the agent amount with exhaust from the predetermined cylinder group, and the intake air amount of the cylinders of the predetermined cylinder group becomes the target cylinder intake amount Thus, the target intake valve opening / closing timing of the intake valve driven by the electromagnetically driven valve mechanism provided in the cylinder of the predetermined cylinder group is determined, and the target cylinder intake air amount is determined from the target rich air-fuel ratio to the predetermined cylinder group A target fuel injection amount is calculated and provided in the cylinders of the predetermined cylinder group so that a torque generated when the predetermined cylinder group is operated at the target cylinder intake air amount and the target rich air-fuel ratio becomes the required engine torque. A variable valve operating system that determines a target exhaust valve opening / closing timing of an exhaust valve driven by an electromagnetically driven valve mechanism and performs exhaust gas adjustment for operating the predetermined cylinder group at the target rich air-fuel ratio. An internal combustion engine having a mechanism. The exhaust gas adjusting means calculates the target rich air-fuel ratio, and then calculates the target rich air-fuel ratio that is the smallest rich air-fuel ratio in the range of air-fuel ratio that can form a combustible mixture in the predetermined cylinder group. When the target rich air-fuel ratio is determined to be equal to or greater than the rich limit air-fuel ratio, the target intake valve opening / closing timing is determined, the target fuel injection amount is calculated, and the target exhaust valve opening / closing is calculated. 2. An internal combustion engine having a variable valve mechanism according to claim 1, wherein timing is determined and exhaust gas adjustment is performed to operate the predetermined cylinder group at the target rich air-fuel ratio. When the exhaust gas adjusting means compares the rich limit air-fuel ratio with the target rich air-fuel ratio after calculating the target rich air-fuel ratio, and determines that the target rich air-fuel ratio is smaller than the rich limit air-fuel ratio The rich limit air-fuel ratio is set as a new new target rich air-fuel ratio, and the electromagnetic drive provided in the cylinders of the predetermined cylinder group so that the intake air amount of the cylinders of the predetermined cylinder group becomes the target cylinder intake air amount A target intake valve opening / closing timing of an intake valve driven by a valve mechanism is determined, a target fuel injection amount of the predetermined cylinder group is calculated from the target cylinder intake air amount from the new target rich air-fuel ratio, and the predetermined cylinder group Target cylinder intake and new target rich
Determining a target exhaust valve opening / closing timing of an exhaust valve driven by an electromagnetically driven valve mechanism provided in a cylinder of the predetermined cylinder group so that a torque generated when operated at an air-fuel ratio becomes the required engine torque, A predetermined cylinder group is operated at the new target rich air-fuel ratio, and a supply reducing agent amount supplied from the predetermined cylinder group operated according to the target cylinder intake air amount and the new target rich air-fuel ratio to the NOx occlusion reduction catalyst is determined. Calculating a new new target reducing agent amount by subtracting the supplied reducing agent amount from the target reducing agent amount, substituting the target reducing agent amount with the new target reducing agent amount, and calculating the target rich air-fuel ratio. The internal combustion engine having a variable valve mechanism according to claim 2, wherein the process returns to the calculation process. A fuel injection valve for injecting fuel into an intake passage upstream of each cylinder of the internal combustion engine is provided, and the exhaust gas adjusting means controls the fuel injection valve to increase the fuel injection amount of the cylinder group. An internal combustion engine having the variable valve mechanism according to any one of claims 1 to 3.

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