JP2004132318A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine for controlling exhaust emission while preventing degradation of the fuel consumption and degradation of exhaust emission control capacity of NOx catalyst caused by catalyst poisoning. <P>SOLUTION: A plurality of cylinders are divided into at least two cylinder groups in an exhaust emission control system of an internal combustion engine. In one cylinder group, fuel is injected in the intake stroke or the compression stroke in the cylinders to form premixed gas of fuel and air in the cylinders, and the fuel/air mixture is compressed, ignited and burned by igniting the premixed gas of fuel and air by the compression. In the other cylinder group, in the cylinders, a piston is in a vicinity of a top dead center of compression, and by performing the diffusion combustion with the fuel injected in a high-temperature combustion chamber, the air-fuel ratio of exhaust gas from one cylinder group is set to be richer than the air-fuel ratio of exhaust gas from the other cylinder group. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine.
[0002]
[Prior art]
In lean-burn internal combustion engines typified by diesel engines, various measures have been taken to reduce emissions of nitrogen oxides NOx and unburned fuel components (HC, CO).
[0003]
As one of the countermeasures, there is an exhaust purification device provided with a NOx catalyst in an exhaust passage.
[0004]
When the oxygen concentration of the inflowing exhaust gas is high, that is, when the air-fuel ratio of the exhaust gas is lean, the NOx catalyst stores NOx contained in the exhaust gas, and when the oxygen concentration of the inflowing exhaust gas is low, NOx that was stored when the air-fuel ratio of the fuel was rich was converted to nitrogen dioxide NO. ₂ And NO in the form of NO or NO in the form of NO ₂ Harmless steam H by oxidizing NO and NO with unburned fuel components CO and HC contained in exhaust gas. ₂ O and carbon dioxide CO ₂ It has an exhaust purification function to purify the exhaust gas.
[0005]
However, in a diesel engine, during a normal combustion state, the engine is operated under an excess of air reaching A / F = 25 to 40, and NOx stored by the NOx catalyst is contained in the exhaust gas. It is difficult to reduce and release.
[0006]
To cope with such a problem, conventionally, in the low load operation region, the amount of the inert gas supplied to the combustion chamber is larger than the amount of the inert gas at which the amount of generated smoke is peaked, and the low temperature where almost no smoke is generated. In an internal combustion engine in which normal combustion is performed in which the amount of inert gas supplied to the combustion chamber is smaller than the amount of inert gas at which the amount of smoke generated peaks in the middle and high load operation region in which combustion is performed, A technique has been proposed in which a reducing agent is supplied to an exhaust passage when the combustion is performed, and the supply of the reducing agent is stopped when low-temperature combustion is performed (for example, see Patent Document 1).
[0007]
According to the above-described conventional technology, the amount of inert gas supplied into the combustion chamber is large in a low-load operation region, and a reducing agent is supplied to an exhaust passage in a medium-high load operation region. Becomes the stoichiometric air-fuel ratio or the rich air-fuel ratio, and the NOx stored in the NOx catalyst is reduced and released into the exhaust gas.
[0008]
Further, in a general diesel engine, diffusion combustion is performed in which fuel is injected into a cylinder when a piston is near a top dead center in a compression stroke. A premixed compression ignition combustion system is proposed in which fuel is injected into the cylinder from the beginning of the stroke to the middle stage of the compression stroke, the injected fuel is vaporized and mixed in the compression stroke, and ignited and burned by spontaneous ignition at the end of the compression stroke. (For example, see Patent Document 2). In this premixed compression ignition combustion, fuel and air are burned in a uniformly mixed state, so that generation of NOx and smoke can be suppressed.
[0009]
According to the homogeneous charge compression ignition combustion, it is possible to perform combustion at an air-fuel ratio richer than the diffusion combustion (there is little generation of NOx and smoke even when the air-fuel ratio is rich). By performing at a fuel ratio or a rich air-fuel ratio, the air-fuel ratio of the exhaust gas can be set to a stoichiometric air-fuel ratio or a rich air-fuel ratio, and NOx stored in the NOx catalyst can be reduced and released into the exhaust gas.
[0010]
[Patent Document 1]
JP 2001-152832A
[Patent Document 2]
JP-A-9-158810
[0011]
[Problems to be solved by the invention]
However, in the conventional technology as described above, when the reducing agent is supplied to the exhaust system under normal combustion during a medium to high load operation, the exhaust gas having a lean air-fuel ratio is set to a stoichiometric air-fuel ratio or a rich air-fuel ratio. Requires a large supply of reducing agent. Therefore, when a fuel is used as the reducing agent, the fuel efficiency is deteriorated, and the poisoning of the catalyst by a large amount of the reducing agent may cause a decrease in the exhaust purification ability of the NOx catalyst.
[0012]
Further, in the premixed compression ignition combustion, when the temperature in the cylinder increases, the combustion speed of the air-fuel mixture increases, and the pressure in the cylinder increases rapidly before the piston reaches the top dead center of the compression stroke. Ignition is more likely to occur. Therefore, it is difficult to perform the homogeneous charge compression ignition combustion in the medium-high load operation region where the temperature in the cylinder is high.
[0013]
The present invention has been made in view of the above-described circumstances, and an object of the present invention is to prevent an exhaust purification device for an internal combustion engine from deteriorating fuel efficiency and reducing the exhaust purification capability of a NOx catalyst due to catalyst poisoning. An object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can perform exhaust gas purification.
[0014]
[Means for Solving the Problems]
The present invention employs the following means in order to solve the above problems. That is, the exhaust gas purifying apparatus for an internal combustion engine according to the present invention includes:
An internal combustion engine having a fuel injection valve and having a plurality of cylinders divided into at least two cylinder groups;
A NOx catalyst provided in an exhaust passage of the internal combustion engine;
Fuel injection timing control means for controlling the fuel injection timing of the fuel injection valve,
In one of the cylinder groups, fuel is injected in the cylinder during an intake process or a compression stroke, and a premixed mixture of fuel and air is formed in the cylinder, and the premixed air is compressed. In the other cylinder group, a piston is located near a compression top dead center in the other cylinder group, and a second combustion is performed in which fuel is injected into a high-temperature combustion chamber. Is also good.
[0015]
According to the present invention, a plurality of cylinders are divided into at least two cylinder groups. In one cylinder group, fuel is injected during an intake process or a compression stroke in the cylinder, and a premixed fuel and air mixture is injected into the cylinder. The first combustion that forms and ignites the premixed gas by compression, that is, premixed compression ignition combustion is performed, and in the other cylinder group, the piston is located near the compression top dead center in the cylinder, The greatest feature is that the second combustion in which the fuel is injected into the burned combustion chamber, that is, the diffusion combustion is performed.
[0016]
In the homogeneous charge compression ignition combustion, combustion at a stoichiometric air-fuel ratio or a rich air-fuel ratio can be performed without inducing generation of NOx or smoke. Therefore, according to the exhaust emission control device of the present invention, the air-fuel ratio of the entire exhaust gas can be made richer than when the diffusion combustion is performed in all the cylinders.
[0017]
As a result, the amount of fuel added to the exhaust passage to reduce and release NOx stored in the NOx catalyst into exhaust gas can be reduced or made unnecessary.
[0018]
Therefore, according to the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, it is possible to purify exhaust gas while preventing deterioration of fuel efficiency due to excessive fuel addition and reduction in exhaust gas purifying ability of the NOx catalyst due to catalyst poisoning.
[0019]
Further, the exhaust gas of the lean air-fuel ratio discharged from the cylinder group performing the diffusion combustion and the stoichiometric air-fuel ratio or the exhaust gas of the rich air-fuel ratio discharged from the cylinder group performing the premixed compression ignition combustion alternately use the NOx catalyst. Therefore, the NOx occlusion and the reduction / release are repeated, and the exhaust purification ability of the NOx catalyst is activated.
[0020]
Further, according to the exhaust gas purification apparatus of the present invention, in one of the cylinder groups, the operation is performed in a load region where the homogeneous charge compression ignition combustion is possible, and in the other cylinder group, the diffusion combustion is performed. Operation can be performed with a higher load than one of the cylinder groups.
[0021]
As a result, the entire cylinder can be operated in a higher load range than in the case where the premixed compression ignition combustion is performed in all cylinders.
[0022]
Therefore, according to the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, it is possible to purify exhaust gas in a wider load range than before, while preventing deterioration of fuel efficiency and deterioration of exhaust gas purifying ability of the NOx catalyst due to catalyst poisoning. .
[0023]
In the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the air-fuel ratio of the exhaust gas from the cylinder group performing the premixed compression ignition combustion may be richer than the air-fuel ratio of the exhaust gas from the cylinder group performing the diffusion combustion. Good.
[0024]
As a method of making the air-fuel ratio of the exhaust gas from the cylinder group performing the premixed compression ignition combustion richer than the air-fuel ratio of the exhaust gas from the cylinder group performing the diffusion combustion, the cylinder group performing the premixed compression ignition combustion is used. A method in which the amount of recirculated gas recirculated to the cylinder group performing the diffusion combustion is made larger than the amount of recirculated gas recirculated to the cylinder group performing the diffusion combustion, and the amount of intake air to the cylinder group performing the premixed compression ignition combustion is diffused. For example, a method of reducing the amount of intake air to the cylinder group that performs combustion may be used.
[0025]
When the air-fuel ratio of the exhaust gas from the cylinder group performing the premixed compression ignition combustion is a stoichiometric air-fuel ratio or a rich air-fuel ratio, the NOx stored in the NOx catalyst is reduced without adding fuel to the exhaust gas.・ Can be released.
[0026]
Therefore, in the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, fuel addition means is provided in the exhaust passage, and when fuel is added to the exhaust passage by the fuel addition means, the exhaust gas from the cylinder group performing the diffusion combustion is provided. The fuel may be added when the gas flows near the fuel adding means.
[0027]
According to this configuration, since the air-fuel ratio of the exhaust gas from the cylinder group performing the diffusion combustion becomes rich as compared with the case where the fuel addition is not performed, the reduction and release of NOx from the NOx catalyst can be promoted. it can. Further, since fuel is not added to the exhaust gas from the cylinder group that performs the premixed compression ignition combustion, deterioration of fuel efficiency due to excessive fuel addition and reduction of the exhaust purification ability of the NOx catalyst due to catalyst poisoning are prevented. be able to.
[0028]
Further, in the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the premixed compression ignition combustion is performed in all cylinders, the air-fuel ratio of one cylinder group is set to a rich air-fuel ratio, and the air-fuel ratio of the other cylinder group is set to lean air-fuel ratio. The fuel ratio may be configured.
[0029]
According to this configuration, during the low-load operation in which the premixed compression ignition combustion becomes possible, the exhaust gas having the rich air-fuel ratio and the exhaust gas having the lean air-fuel ratio alternately flow through the NOx catalyst. The exhaust gas purifying ability of the NOx catalyst is more activated.
[0030]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, specific embodiments of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described with reference to the drawings.
[0031]
(First Embodiment)
FIG. 1 is a schematic configuration diagram of an exhaust gas purification device for an internal combustion engine according to a first embodiment of the present invention.
[0032]
The internal combustion engine 1 is a diesel engine, which is a type of a lean-burn internal combustion engine, and includes four cylinders 2a, 2b, 2c, and 2d. Of the four cylinders, the first cylinder group 2a and the third cylinder 2c constitute a first cylinder group 11, and the second cylinder 2b and the fourth cylinder 2d constitute a second cylinder group 12.
[0033]
Here, the configuration around the cylinder of the internal combustion engine 1 will be described. FIG. 2 is a schematic configuration diagram around a cylinder of the internal combustion engine 1.
[0034]
The internal combustion engine 1 includes a cylinder block 1b and a cylinder head 1a fixed above the cylinder block 1b, and a cylinder 2 is formed on the cylinder block 1b. A cooling water passage 1c is provided around the cylinder 2.
[0035]
The cylinder block 1b rotatably supports a crankshaft 73, which is an engine output shaft. The crankshaft 73 is connected to a piston 72 slidably mounted in each cylinder 2.
[0036]
Above the piston 72, a combustion chamber 74 surrounded by the top surface of the piston 72, the wall surface of the cylinder head 1a, and the wall surface of the cylinder 2 is formed.
[0037]
In the cylinder head 1a, an opening end of two intake ports 76 and an opening end of two exhaust ports 77 are formed so as to face the combustion chamber 74, and a fuel injection valve 7 is formed so that an injection hole faces the combustion chamber 74. Installed.
[0038]
Each open end of the intake port 76 is opened and closed by an intake valve 78 supported on the cylinder head 1a so as to be able to move forward and backward, and these intake valves 78 are connected to an electromagnetic drive mechanism 80 ( Hereinafter, it is driven to open and close by an intake-side electromagnetic drive mechanism 80).
[0039]
Each open end of the exhaust port 77 is opened and closed by an exhaust valve 79 supported on the cylinder head 1a so as to be able to advance and retreat, and these exhaust valves 79 are provided by an electromagnetic drive mechanism 81 ( Hereinafter, the opening / closing drive is performed by an exhaust-side electromagnetic drive mechanism 81). The intake-side electromagnetic drive mechanism 80 and the exhaust-side electromagnetic drive mechanism 81 are electrically connected to an ECU 20, which will be described later. The ECU 20 controls the opening / closing timing and lift amount of the intake valve 78 and the exhaust valve 79.
[0040]
Returning to FIG. 1, the internal combustion engine 1 includes a fuel supply system, an intake system, an exhaust system, a control system, and the like as its main components.
[0041]
(Fuel supply system)
The fuel supply system includes a fuel injection valve 7, a common rail (accumulation chamber) 6, a fuel supply pipe 22, a fuel pump 21, and the like, and supplies fuel to each of the cylinders 2a to 2d. The fuel injection valve 7 is an electromagnetically driven on-off valve provided for each of the cylinders 2a to 2d, and each fuel injection valve 7 is connected to a common rail 6 serving as a fuel distribution pipe. The common rail 6 is connected to a fuel pump 21 via a fuel supply pipe 22.
[0042]
In the fuel supply system configured as described above, first, fuel in a fuel tank (not shown) is pumped up by the fuel pump 21. The pumped fuel is supplied to the common rail 6 via the fuel supply pipe 22. The fuel supplied to the common rail 6 is raised to a predetermined fuel pressure in the common rail 6 and distributed to each fuel injection valve 7. The fuel injection valve 7 is electrically connected to the ECU 20, and when a driving voltage is applied to the fuel injection valve 7 and the fuel injection valve 7 is opened, the fuel is injected into the cylinder 2 via the fuel injection valve 7. Is done.
[0043]
(Intake system)
The intake system includes an intake pipe 14, an air cleaner box 18, an intercooler 15, an intake manifold 13, a first intake branch 3a, a second intake branch 3b, a first throttle valve 31, a second throttle valve 32, and the like. An intake passage for supplying air thereto is formed.
[0044]
The intake pipe 14 forms a passage for guiding the air taken in through the air cleaner box 18 and the intake manifold 13 to the first intake branch pipe 3a and the second intake branch pipe 3b. The first intake branch pipe 3a forms a passage for distributing the air flowing through the intake pipe 14 to each of the cylinders 2a and 2c of the first cylinder group 11, and the second intake branch pipe 3b directs the air flowing through the intake pipe 14 to the first. A passage is formed for distribution to the cylinders 2b and 2d of the two-cylinder group 12.
[0045]
Further, a turbocharger 25 (compressor wheel 25a) for compressing the intake air and air compressed by the turbocharger 25 are supplied to the intake pipe 14 from the air cleaner box 18 to the first intake branch pipe 3a and the second intake branch pipe 3b. An intercooler 15 for cooling is provided, and an air flow meter 19 for measuring a flow rate of air flowing into the intake pipe 14 is provided upstream of the turbocharger 25.
[0046]
Further, a first throttle valve 31 for adjusting the amount of air flowing into the first cylinder group 11 is provided immediately upstream of the first intake branch pipe 3a, and a second throttle group 12 is provided immediately upstream of the second intake branch pipe 3b. A second throttle valve 32 for adjusting the amount of air flowing in is provided, and the opening degree of the first throttle valve 31 and the second throttle valve 32 is controlled by the ECU 20 described later.
[0047]
In the intake system configured as described above, first, the air to be supplied to each cylinder 2 flows into the air cleaner box 18 due to the generation of the negative pressure accompanying the operation of the engine. The air that has flowed into the air cleaner box 18 flows into the turbocharger 25 via the intake pipe 14 after dust and dirt are removed in the air cleaner box 18. The air that has flowed into the turbocharger 25 is compressed by the compressor wheel 25a and then cooled by the intercooler 15. Thereafter, the flow rate is adjusted by the first throttle valve 31 or the second throttle valve 32 via the intake manifold 13, and flows into the first intake branch pipe 3a or the second intake branch pipe 3b. The air flowing into the first intake branch pipe is distributed to the respective cylinders 2a and 2c of the first cylinder group 11, and the air flowing into the second intake branch pipe is distributed to the respective cylinders 2b and 2d of the second cylinder group 12. The fuel is supplied to the combustion together with the fuel injected and supplied from the fuel injection valve 7.
[0048]
The exhaust system includes an exhaust pipe 8, a first exhaust branch pipe 4a, and a second exhaust branch pipe 4b, and forms an exhaust passage for discharging exhaust gas discharged from each cylinder 2 to the outside of the engine body. Further, it includes an EGR device 26, a NOx catalyst 10, a fuel addition device 24, and the like, and has a function as an exhaust gas purification device that purifies nitrogen oxides (NOx) and smoke contained in exhaust gas.
[0049]
The first exhaust branch pipe 4a forms a passage for guiding the exhaust gas discharged from each of the cylinders 2a and 2c of the first cylinder group 11 to the exhaust pipe 8, and the second exhaust branch pipe is each of the cylinders 2b and 2d of the second cylinder group 12. A passage for guiding exhaust gas discharged from the exhaust pipe to the exhaust pipe 8 is formed. The exhaust pipe 8 forms a passage for guiding exhaust gas discharged from each cylinder 2 to a muffler (not shown). The exhaust pipe 8 is provided with a NOx catalyst 10, and a fuel addition injector 9 is provided upstream of the NOx catalyst 10. Further, a turbine housing 25b of the turbocharger 25 is provided between the fuel addition injector 9 and the NOx catalyst 10.
[0050]
Further, a first air-fuel ratio sensor 41 and a second air-fuel ratio sensor 42 are provided in the first exhaust branch pipe 4a and the second exhaust branch pipe 4b, respectively, and the first air-fuel ratio sensor 41 discharges from the first cylinder group 11. The second air-fuel ratio sensor 42 detects the air-fuel ratio of the exhaust gas discharged from the second cylinder group 12. Further, a third air-fuel ratio sensor 43 is provided near the fuel addition injector 9 of the exhaust pipe 8 and detects the air-fuel ratio of the exhaust gas flowing near the fuel addition injector 9. Outputs of the first air-fuel ratio sensor 41, the second air-fuel ratio sensor 42, and the third air-fuel ratio sensor 43 are input to the ECU 20, which will be described later.
[0051]
(NOx catalyst)
The NOx catalyst 10 has an exhaust purification function of mainly purifying nitrogen oxides (NOx) in exhaust gas. More specifically, when the oxygen concentration of the exhaust gas flowing into the NOx catalyst 10 is high, nitrogen oxide (NOx) in the exhaust gas is absorbed, and when the oxygen concentration in the exhaust gas is low, that is, the exhaust gas flowing into the NOx catalyst 10 When the air-fuel ratio of the gas is low, the absorbed nitrogen oxides (NOx) are converted to nitrogen dioxide (NOx). ₂ ) And nitric oxide (NO) in the form of reduced and released gases in the exhaust gas, ₂ ) And nitrogen monoxide (NO) through an oxidative reaction with unburned fuel components (CO, HC) contained in the exhaust gas, thereby producing harmless steam (H). ₂ O) and carbon dioxide (CO ₂ ) Has the exhaust purification ability to purify.
[0052]
(Fuel addition device)
The fuel addition device 24 includes the fuel addition injector 9, the addition fuel supply passage 23, the fuel pressure control valve 27, and the like, and adds an appropriate amount of fuel to the exhaust passage upstream of the NOx catalyst 10 as needed. That is, fuel is supplied into the exhaust gas such that the air-fuel ratio of the exhaust gas flowing into the NOx catalyst 10 becomes a desired air-fuel ratio.
[0053]
The fuel addition injector 9 includes an electric on-off valve that opens when a predetermined voltage is applied. The additional fuel supply passage 23 forms a passage for guiding a part of the fuel pumped by the fuel pump 21 to the fuel addition injector 9. The fuel pressure control valve 27 is disposed in the middle of the additional fuel supply path 23, and maintains the fuel pressure in the additional fuel supply path 23 at a predetermined fuel pressure.
[0054]
In the fuel addition device 24 configured as described above, the fuel discharged from the fuel pump 21 is maintained at a predetermined fuel pressure by the fuel pressure control valve 27, and is supplied to the fuel addition injector 9 through the addition fuel supply passage 23. Subsequently, when a predetermined voltage is applied to the fuel addition injector 9, the on-off valve is opened, and the fuel in the addition fuel supply passage 23 is injected and supplied into the exhaust pipe 8 through the fuel addition injector 9. The fuel supplied to the exhaust pipe 8 flows into the NOx catalyst 10 after being stirred in the turbine housing 25b. Therefore, the exhaust gas having a low oxygen concentration and containing hydrocarbon (HC) as an unburned fuel component flows into the NOx catalyst 10, and the above-described exhaust gas purifying action is promoted.
[0055]
(EGR device)
The EGR device 26 includes the EGR passage 16, the first EGR valve 33, the second EGR valve 34, the EGR cooler 17, and the like.
[0056]
The EGR passage 16 is a passage that connects the exhaust pipe 8 with the first intake branch pipe 3a and the second intake branch pipe 3b. A first EGR valve 33 is provided at a connection portion between the EGR passage 16 and the first intake branch pipe 3a, and a second EGR valve 34 is provided at a connection portion between the EGR passage 16 and the second intake branch pipe 3b. The first EGR valve 33 and the second EGR valve 34 are electric open / close valves, and are controlled by the ECU 20 to adjust the amounts of exhaust gas (EGR gas) flowing into the first intake branch pipe 3a and the second intake branch pipe 3b, respectively. Is going. The EGR cooler 17 cools the exhaust gas flowing through the EGR passage 16 using the engine cooling water as a heat medium. In the following description, the exhaust gas flowing into the first intake branch pipe 3a and the second intake branch pipe 3b through the EGR passage 16 may be simply referred to as EGR gas.
[0057]
According to the EGR device 26 configured as described above, a part of the exhaust gas flowing through the exhaust pipe 8 flows into the EGR passage 16 at a flow rate corresponding to the opening amounts of the first EGR valve 33 and the second EGR valve 34. The EGR gas (exhaust gas) flowing into the EGR passage 16 is cooled via the EGR cooler 17 and flows into the first intake branch pipe 3a or the second intake branch pipe 3b. The EGR gas flowing into the first intake branch pipe 3a or the second intake branch pipe 3b forms an air-fuel mixture while mixing with air (fresh air) flowing from the upstream of each intake branch pipe 3a, 3b, and is injected from the fuel injection valve 7. The fuel is used for combustion together with the fuel.
[0058]
In the exhaust gas that becomes the EGR gas, water vapor (H ₂ O) and carbon dioxide (CO ₂ ) And the like. Therefore, when exhaust gas as an inert gas flows into the combustion chamber of each cylinder, the combustion temperature is reduced due to the mixing of the exhaust gas, and the generation of nitrogen oxides (NOx) is suppressed. Also, with the introduction of EGR gas, the amount of oxygen in the combustion chamber of each cylinder also decreases. Therefore, in this regard, nitrogen oxide (NOx) and oxygen (O ₂ ) Is suppressed, and the emission of nitrogen oxides (NOx) is suppressed.
[0059]
(Control system)
The control system includes a ROM (Read Only Memory) 62, a RAM (Random Access Memory) 63, a CPU (Central Control Unit) 64, an input port 65, and an output port 66 connected to each other by a bidirectional bus 61. It is.
[0060]
In addition to the output signals of the above-described sensors, a load sensor 44 for detecting the amount of depression of an accelerator pedal 60, a crank angle sensor 45 for detecting the number of revolutions of the crankshaft 73, and a vehicle speed sensor 46 for measuring the vehicle speed are provided at the input port 65. And the like are input via the corresponding A / D converter 67 or directly. On the other hand, the output port 66 is connected to the fuel injection valve 7, the fuel addition injector 9, the first throttle valve 31, the second throttle valve 32, the first EGR valve 33, the second EGR valve 34, and the intake side via a corresponding drive circuit 68. An electromagnetic drive mechanism 80, an exhaust-side electromagnetic drive mechanism 81, and the like are connected.
[0061]
In the ROM 62, control programs for various devices, a control map referred to when processing the programs, and the like are recorded corresponding to each device. In the RAM 63, output signals of various sensors input to the input port 65, control signals output to the output port 66, and the like are recorded as operation history of the internal combustion engine. The CPU 64 compares the output signals of the various sensors recorded on the RAM 63 with the control map developed on the ROM 62 on a desired program on a desired program, and compares the various control signals output during the processing with the output port 66. Output to the corresponding device via the PC, and various devices are centrally managed.
[0062]
For example, based on output signals from the crank angle sensor 45, the first air-fuel ratio sensor 41, the second air-fuel ratio sensor 42, the third air-fuel ratio sensor 43, and the like, the CPU 64 determines whether the fuel injection valve 7, the fuel addition injector 9, the first throttle The air-fuel ratio of exhaust gas flowing into the NOx catalyst 10 is controlled by controlling the opening / closing timing or opening of the valve 31, the second throttle valve 32, the first EGR valve 33, the second EGR valve 34, the intake valve 78, and the exhaust valve 79. .
[0063]
(Fuel injection control)
Next, the fuel injection timing in each of the cylinders 2a, 2b, 2c, and 2d in the present embodiment will be described.
FIG. 3 is a diagram showing the fuel injection timing and the air-fuel ratio (equivalent ratio) of the exhaust gas in each of the cylinders 2a, 2b, 2c, and 2d in the present embodiment.
[0064]
In the present embodiment, the CPU 64 sets each of the fuel injection valves 7a, 7b, 7c, 7d such that fuel injection is performed in the order of the first cylinder 2a → the third cylinder 2c → the fourth cylinder 2d → the second cylinder 2b. Control.
[0065]
Further, based on the output of the crank angle sensor 45, the CPU 64 determines in the first cylinder 2a and the third cylinder 2c before the piston 72 reaches the top dead center of the compression stroke (for example, as shown in FIG. Fuel injection is performed at a time point (30 ° before the process top dead center), and in the second cylinder 2b and the fourth cylinder 2d, the fuel injection is performed when the piston 72 reaches near the compression process top dead center. .
[0066]
In the cylinders 2b and 2d, the fuel is injected into the cylinders 2b and 2d when the piston 72 reaches the vicinity of the top dead center of the compression stroke. It will be injected. Therefore, a flame is formed at the boundary between the surface of the injected fuel droplet and the high-temperature air. That is, so-called diffusion combustion is performed in the cylinders 2b and 2d.
[0067]
In the cylinders 2a and 2c, the fuel is injected into the cylinders 2a and 2c before the piston 72 reaches the top dead center of the compression process, so that a uniform mixture of the fuel and the air in the cylinders is formed. You. This homogeneous air-fuel mixture is compressed with the rise of the piston 72 and the temperature rises, and the entire air-fuel mixture is ignited near the top dead center of the compression stroke, and combustion proceeds. That is, in the cylinders 2a and 2c, so-called premix compression ignition combustion is performed.
[0068]
In the homogeneous charge compression ignition combustion, since the flame temperature is lower than that in the diffusion combustion, the generation of NOx is suppressed. In addition, since the fuel and the air are burned under a sufficient amount of oxygen in a uniformly mixed state, generation of smoke due to lack of oxygen is suppressed. Therefore, combustion at an air-fuel ratio richer than diffusion combustion can be performed.
[0069]
Also, when the amount of EGR gas recirculated to each cylinder is increased, the generation of NOx is suppressed, and the amount of oxygen in each cylinder is reduced, so that the air-fuel ratio can be made rich. Causes an increase in the amount of smoke generated at the same time. However, in the homogeneous charge compression ignition combustion, generation of smoke is suppressed even if the amount of EGR gas is increased for the above reason.
[0070]
Therefore, in the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, the amount of EGR gas recirculated to the second cylinder group 12 is reduced by the second EGR gas valve 34 so that the generation of smoke is not excessive (for example, As shown in FIG. 3, the air-fuel ratio of the exhaust gas is adjusted to an equivalent ratio of 0.5), and further, based on the outputs of the first air-fuel ratio sensor 41 and the second air-fuel ratio sensor 42, the first cylinder The air-fuel ratio of the exhaust gas from the group 11 is richer than the air-fuel ratio of the exhaust gas from the second cylinder group 12 (for example, as shown in FIG. 3, the equivalent ratio is 1.0, ie, the stoichiometric air-fuel ratio). The amount of EGR gas recirculated to the first cylinder group 11 is adjusted by the first EGR gas valve 33.
[0071]
As a result, the air-fuel ratio of the exhaust gas as a whole becomes rich as compared with the case where diffusion combustion is performed in all the cylinders 2a, 2b, 2c, and 2d, so that the NOx stored in the NOx catalyst 10 is reduced and released. Therefore, the amount of fuel added from the fuel injector 9 to the exhaust pipe 8 can be reduced.
[0072]
Therefore, according to the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, it is possible to purify the exhaust gas while preventing the fuel efficiency from being deteriorated due to excessive fuel addition to the exhaust pipe 8 and the exhaust gas purifying ability of the NOx catalyst 10 from being lowered. Can be.
[0073]
Further, the exhaust gas having a rich air-fuel ratio (for example, stoichiometric air-fuel ratio) from the first cylinder group 11 and the exhaust gas having a lean air-fuel ratio (for example, equivalent ratio 0.5) from the second cylinder group 12 are different. Since the NOx catalyst 10 flows alternately, the NOx storage and the reduction / release are repeated, and the exhaust purification ability of the NOx catalyst 10 is activated.
[0074]
In the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, the air-fuel ratio of the exhaust gas detected by the third air-fuel ratio sensor 43 provided near the fuel addition injector 9 changes the air-fuel ratio of the exhaust gas from the first cylinder group 11. When the fuel ratio is equal to the fuel ratio, the CPU 64 may control the fuel addition timing so that the fuel addition from the fuel addition injector 9 to the exhaust pipe 8 is not performed.
[0075]
That is, according to this control, when the exhaust gas from the second cylinder group 12, that is, the exhaust gas having the lean air-fuel ratio passes through the fuel addition injector 9, the fuel is added to the exhaust pipe 8.
[0076]
Accordingly, since the air-fuel ratio of the exhaust gas from the second cylinder group 12 can be made richer than when no fuel is added, the reduction and release of NOx from the NOx catalyst 10 can be promoted. It becomes. Further, since fuel is not added to the exhaust gas from the first cylinder group 11, deterioration of fuel efficiency due to excessive fuel addition and reduction of the exhaust purification ability of the NOx catalyst 10 due to catalyst poisoning can be prevented.
[0077]
Further, in the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, the opening degree of the first EGR gas valve 33 is increased so that the amount of EGR gas recirculated to the first cylinder group 11 is further increased. The air-fuel ratio of the exhaust gas from the group 11 may be richer than the stoichiometric air-fuel ratio (for example, the equivalent ratio is 1.5). By setting the air-fuel ratio of the exhaust gas from the first cylinder group 11 to the rich air-fuel ratio, the air-fuel ratio of the entire exhaust gas can be set to the stoichiometric air-fuel ratio or the rich air-fuel ratio.
[0078]
As a result, the NOx stored in the NOx catalyst 10 is reduced and released into the exhaust gas without adding fuel to the exhaust pipe 8 from the fuel addition injector 9, so that fuel efficiency is deteriorated and catalyst poisoning is caused. It is possible to further prevent the exhaust purification ability of the NOx catalyst 10 from decreasing.
[0079]
(Second embodiment)
Next, a second embodiment of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described.
The configuration of the exhaust gas purification device for an internal combustion engine according to the present embodiment is the same as that of the exhaust gas purification device for an internal combustion engine according to the first embodiment.
[0080]
In the above-described premixed compression ignition combustion, the air-fuel mixture in the cylinder formed by the intake air or the fuel injected in the compression stroke ignites before the piston 72 reaches the top dead center of the compression stroke, and is relatively ignited. It is preferable that the combustion continues gently and the pressure in the cylinder reaches the maximum pressure immediately after the top dead center. However, if the combustion rate of the air-fuel mixture in the cylinder is higher than the range suitable for premixed compression ignition combustion, the air-fuel mixture ignited before the piston 72 reaches the top dead center of the compression stroke will be burned at once, and the top dead center will be burned. Before reaching the point, the pressure in the cylinder rapidly rises. As described above, if a sudden increase in pressure occurs before the top dead center is reached, so-called premature ignition occurs, as in the case of knocking of a gasoline engine, in which large vibration and noise are generated in the engine. Further, this premature ignition tends to occur in a high-load operation region.
[0081]
Therefore, in the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, the combustion method, the fuel injection timing, and the air-fuel ratio in each of the cylinders 2a, 2b, 2c, and 2d are the same as those in the first embodiment. The load on each cylinder 2a, 2b, 2c, 2d is controlled by adjusting the amount.
[0082]
FIG. 4 is a diagram illustrating the fuel injection timing, the air-fuel ratio (equivalent ratio) of the exhaust gas, and the fuel injection amount in each of the cylinders 2a, 2b, 2c, and 2d in the present embodiment.
[0083]
In the present embodiment, the CPU 64 determines the amount of fuel injection from each of the fuel injection valves 7a and 7c such that the load on the first cylinder 2a and the third cylinder 2c is a load capable of performing homogeneous charge compression ignition combustion. (For example, if the fuel injection amount is 10 mm ³ / St). Further, the fuel injection amount from each of the fuel injection valves 7b and 7d to the second cylinder 2b and the fourth cylinder 2d is adjusted to be larger than the fuel injection amount from the fuel injection valves 7a and 7c (for example, the fuel Injection amount 15mm ³ / St).
[0084]
As a result, the load of the second cylinder group 12 that performs diffusion combustion becomes higher than the load of the first cylinder group 11 that performs premixed compression ignition combustion, so that the premixed compression ignition is performed in all the cylinders 2a, 2b, 2c, and 2d. The load of the entire cylinder can be increased as compared with the case where combustion is performed.
[0085]
Therefore, according to the exhaust gas purifying apparatus for an internal combustion engine according to the present embodiment, it is possible to purify exhaust gas in a wider load range while preventing deterioration of fuel efficiency and reduction in exhaust gas purifying ability of the NOx catalyst due to catalyst poisoning. Becomes possible.
[0086]
(Third embodiment)
Next, a third embodiment of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described.
The configuration of the exhaust gas purification device for an internal combustion engine according to the present embodiment is the same as that of the exhaust gas purification device for an internal combustion engine according to the first embodiment.
[0087]
FIG. 5 is a diagram showing the fuel injection timing and the air-fuel ratio (equivalent ratio) of the exhaust gas in each of the cylinders 2a, 2b, 2c, and 2d in the present embodiment.
[0088]
In the present embodiment, as in the first embodiment, the CPU 64 performs each fuel injection such that fuel injection is performed in the order of the first cylinder 2a → the third cylinder 2c → the fourth cylinder 2d → the second cylinder 2b. The valves 7a, 7b, 7c, 7d are controlled respectively. Further, the CPU 64 sets the fuel injection timing from each of the fuel injection valves 7a, 7b, 7c, 7d such that the piston 72 reaches the top dead center of the compression stroke so that the above-described premixed compression ignition combustion is performed in all cylinders. Control is performed so as to reach a point before reaching (for example, 30 ° before reaching the top dead center in the compression stroke as shown in FIG. 5).
[0089]
Further, the air-fuel ratio of the exhaust gas from the first cylinder group 11 becomes a rich air-fuel ratio (for example, an equivalence ratio of 1.5 as shown in FIG. 5), and the air-fuel ratio of the exhaust gas from the second cylinder group 12 becomes lean. Based on the output of the first air-fuel ratio sensor 41 or the second air-fuel ratio sensor 42, respectively, the first EGR valve 33 or the second EGR so that the air-fuel ratio (equivalent ratio 0.5 as shown in FIG. 5) is obtained. The amount of EGR gas recirculated to each of the cylinder groups 11 and 12 is adjusted by the valve 34.
[0090]
As a result, during low-load operation in which premixed compression ignition combustion is possible, the exhaust gas having a rich air-fuel ratio and the exhaust gas having a lean air-fuel ratio alternately flow through the NOx catalyst 10, so that NOx is stored. And the reduction and release are repeated, so that the exhaust purification ability of the NOx catalyst 10 is further activated.
[0091]
In the embodiment described above, the opening degree of the first EGR valve 33 or the second EGR valve 34 is controlled, and the amount of EGR gas recirculated to each cylinder is adjusted to be used for combustion in the cylinder. Although the air-fuel ratio of the air-fuel mixture is controlled to be a desired air-fuel ratio, the opening degree of the first throttle valve 31 or the second throttle valve 32 is controlled, or the intake valve of each cylinder is controlled using the intake-side electromagnetic drive mechanism 80. The air-fuel ratio of the air-fuel mixture used for combustion in the cylinder may be controlled by controlling the lift amount of the cylinder 78 and adjusting the amount of intake air to each cylinder.
[0092]
In the above-described embodiment, the case where the exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied to a four-cylinder internal combustion engine has been described. For example, four or more cylinders such as an in-line six-cylinder and a V-type eight-cylinder are used. The present invention is also applicable to a multi-cylinder engine having
[0093]
Further, in the internal combustion engine according to the above-described embodiment, one cylinder group is formed by the first cylinder 2a and the third cylinder 2c, and the other cylinder group is formed by the second cylinder 2b and the fourth cylinder 2d. However, in the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, in the plurality of cylinders, it is sufficient that there are a cylinder that performs premixed compression ignition combustion and a cylinder that performs diffusion combustion. Thus, a configuration in which one cylinder group is formed and the other cylinder group is formed by the remaining cylinders, or a configuration in which the cylinder group is divided into three or more cylinder groups may be adopted. As a configuration in which a plurality of cylinders are divided into three or more cylinder groups, a configuration in which six cylinders are divided into three cylinder groups each two in the order of fuel injection in an in-line six-cylinder engine, or in a V-type eight-cylinder engine, An example is a configuration in which eight cylinders are divided into four cylinder groups each of which is two in the order of fuel injection.
[0094]
【The invention's effect】
According to the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, among the at least two cylinder groups, one cylinder group performs premixed compression ignition combustion, and the other cylinder group performs diffusion combustion, whereby all cylinders are subjected to diffusion combustion. The air-fuel ratio of the exhaust gas as a whole can be made richer as compared with the case where diffusion combustion is performed.
[0095]
As a result, the amount of fuel added to the exhaust passage to reduce and release the NOx stored in the NOx catalyst into the exhaust gas is reduced, and therefore, the exhaust purification capability of the NOx catalyst due to deterioration of fuel efficiency and catalyst poisoning. It is possible to purify the exhaust while preventing a decrease in the exhaust gas.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an exhaust gas purification device for an internal combustion engine according to the present invention.
FIG. 2 is a schematic configuration diagram around a cylinder of the internal combustion engine according to the present invention.
FIG. 3 shows a fuel injection timing and an exhaust gas air-fuel ratio (equivalent ratio) in each cylinder according to the first embodiment.
FIG. 4 shows the fuel injection timing, the exhaust gas air-fuel ratio (equivalent ratio), and the fuel injection amount in each cylinder according to the second embodiment.
FIG. 5 shows a fuel injection timing and an exhaust gas air-fuel ratio (equivalent ratio) in each cylinder according to the third embodiment.
[Explanation of symbols]
1 ... internal combustion engine
1a Cylinder head
1b Cylinder block
1c ・ ・ Cooling channel
2 ... Cylinder
3a-1st intake branch pipe
3b-2nd intake branch pipe
4a-1st exhaust branch pipe
4b ··· Second exhaust branch
6 ... Common rail
7 ... Fuel injection valve
8 ・ ・ ・ Exhaust pipe
9 Fuel injector
10. NOx catalyst
11 ・ ・ First cylinder group
12. Second cylinder group
13. Intake manifold
14. Intake pipe
15. Intercooler
16. EGR passage
17. EGR cooler
18. Air cleaner
19. Air flow meter
20 ECU
21 ... Fuel pump
22 .. Fuel supply pipe
23 ... Additional fuel supply path
24 ・ ・ Fuel addition device
25 Turbocharger
25a Compressor wheel
25b Turbine housing
26 EGR device
27 .. Fuel pressure control valve
31 .. First intake valve
32 .. Second intake valve
33..First EGR valve
34 .. Second EGR valve
41 ··· First air-fuel ratio sensor
42..Second air-fuel ratio sensor
43 .. Third air-fuel ratio sensor
44..Load sensor
45 Crank angle sensor
46 Vehicle speed sensor
60 ・ Accelerator pedal
61 ... bidirectional bus
62 ROM
63 RAM
64 CPU
65 Input port
66 output port
67 A / D converter
68..Drive circuit
72 ・ ・ Piston
73 Crankshaft
74 ・ ・ Combustion chamber
76 ... intake port
77 ... Exhaust port
78 ... intake valve
79 ・ ・ Exhaust valve
80 .. Intake side electromagnetic drive mechanism
81 ... Exhaust side electromagnetic drive mechanism

Claims (7)

An internal combustion engine having a fuel injection valve and having a plurality of cylinders divided into at least two cylinder groups;
A NOx catalyst provided in an exhaust passage of the internal combustion engine;
Fuel injection timing control means for controlling the fuel injection timing of the fuel injection valve,
In one of the cylinder groups, fuel is injected in the cylinder during an intake process or a compression stroke to form a premixed mixture of fuel and air in the cylinder, and the premixed gas is compressed. In the other cylinder group, a second combustion in which a piston is near the compression top dead center and fuel is injected into a high-temperature combustion chamber is performed in the other cylinder group. An exhaust gas purification device for an internal combustion engine. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein a load on the other cylinder group is set higher than a load on the one cylinder. 2. The internal combustion engine according to claim 1, further comprising air-fuel ratio control means for making the air-fuel ratio of the exhaust gas from the one cylinder group richer than the air-fuel ratio of the exhaust gas from the other cylinder group. Exhaust gas purification device. Further comprising a recirculation exhaust gas amount adjustment valve for adjusting the amount of recirculation exhaust gas recirculated to the combustion chamber of each cylinder,
The air-fuel ratio control means adjusts the amount of recirculated exhaust gas so that the amount of recirculated exhaust gas recirculated to the one cylinder group is larger than the amount of recirculated exhaust gas recirculated to the other cylinder group. 4. The exhaust gas purifying apparatus for an internal combustion engine according to claim 2, wherein the valve is controlled. An intake air amount adjusting valve that adjusts an amount of air taken into the combustion chamber of each of the cylinders;
The air-fuel ratio control means controls the intake air amount adjusting valve so that the amount of air taken into the one cylinder group is smaller than the amount of air taken into the other cylinder group. 4. The exhaust gas purifying apparatus for an internal combustion engine according to claim 3. Fuel addition means provided upstream of the NOx catalyst in the exhaust passage, for adding fuel to the exhaust passage;
The internal combustion engine according to any one of claims 1 to 5, wherein when the exhaust gas from the other cylinder group flows in the vicinity of the fuel addition means, the addition of fuel by the fuel addition means is performed. Exhaust gas purification device. In all of the cylinder groups, fuel is injected in the cylinder during an intake process or a compression stroke to form a premixed mixture of fuel and air in the cylinder and ignite the premixed gas by compression. Burning,
4. The air-fuel ratio of exhaust gas from the one cylinder group is made richer than the stoichiometric air-fuel ratio, and the air-fuel ratio of exhaust gas from the other cylinder group is made leaner than the stoichiometric air-fuel ratio. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1.

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