JP4032760B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device for an internal combustion engine.
[0002]
[Prior art]
In recent years, an internal combustion engine mounted on an automobile or the like, particularly a diesel engine or a lean burn gasoline engine that can burn an oxygen-rich mixture (so-called lean air-fuel mixture) is used as an exhaust system of the internal combustion engine. Techniques for arranging NOx storage agents have been proposed. As one of the NOx storage agents, nitrogen oxide (NOx) in the exhaust gas is stored when the oxygen concentration of the inflowing exhaust gas is high, and when the oxygen concentration of the inflowing exhaust gas is reduced and the reducing agent is present, the storage is performed. Nitrogen (Nx) while releasing nitrogen oxide (NOx)₂The NOx storage reduction catalyst is known to reduce to (3).
[0003]
When the NOx storage reduction catalyst is arranged in the exhaust system of the internal combustion engine, when the internal combustion engine is operated in lean combustion and the air-fuel ratio of the exhaust gas becomes high, nitrogen oxide (NOx) in the exhaust gas becomes the NOx storage reduction catalyst. When the air-fuel ratio of the exhaust gas stored and flowing into the NOx storage reduction catalyst becomes low, nitrogen oxide (NOx) stored in the NOx storage reduction catalyst is released while nitrogen (N₂).
[0004]
By the way, in the NOx storage reduction catalyst, sulfur oxide (SOx) generated by combustion of sulfur contained in the fuel is also stored by the same mechanism as NOx. The stored SOx is less likely to be released than NOx and accumulates in the NOx catalyst. This is called sulfur poisoning (SOx poisoning), and the NOx purification rate decreases. Therefore, it is necessary to perform poisoning recovery processing for recovering from SOx poisoning at an appropriate time. This poisoning recovery process is performed by circulating the exhaust gas having a reduced oxygen concentration while keeping the NOx catalyst at a high temperature (for example, about 600 to 650 ° C.) through the NOx catalyst.
[0005]
However, since the temperature of the exhaust gas during the lean combustion operation is low, it is difficult to raise the temperature of the catalyst to the temperature required for recovery from SOx poisoning. In such a case, the oxygen concentration of the exhaust gas can be lowered while raising the temperature of the catalyst by supplying the fuel into the exhaust gas.
[0006]
For example, in the exhaust gas purification apparatus for an internal combustion engine described in Japanese Patent Application Laid-Open No. 11-343836, when it is necessary to recover poisoning of the NOx storage reduction catalyst, the exhaust gas flowing into the NOx storage reduction catalyst is required. While maintaining the air-fuel ratio in the vicinity of the stoichiometric air-fuel ratio, the air-fuel ratio is intermittently made smaller than the stoichiometric air-fuel ratio. As a result, most of the time during the recovery from poisoning is maintained at an air-fuel ratio in the vicinity of the theoretical air-fuel ratio, so that generation of hydrocarbons (HC) and carbon monoxide (CO) in the exhaust can be suppressed. Become.
[0007]
In addition, by intermittently reducing the air-fuel ratio below the stoichiometric air-fuel ratio, the average air-fuel ratio during recovery from poisoning becomes leaner than the stoichiometric air-fuel ratio, but it is possible to recover the sulfur poisoning of the NOx catalyst. It has become.
[0008]
[Problems to be solved by the invention]
In the exhaust purification device described in the above publication, when the temperature of the NOx storage reduction catalyst and the storage amount of the sulfur oxide satisfy the start conditions for the poisoning recovery control, the temperature increase control of the NOx storage reduction catalyst is performed. .
[0009]
However, in a so-called low compression ratio engine (ε <16.5), the compression end temperature becomes low, so when trying to raise the temperature of the exhaust gas flowing into the NOx catalyst by a normal method under conditions of low temperature and light load. , You may misfire.
[0010]
That is, the amount of recirculated exhaust gas is increased by an exhaust gas recirculation device (hereinafter referred to as an EGR device) that reduces the intake air to raise the exhaust gas temperature and recirculates a part of the exhaust gas to the intake air system. Thus, the decrease in intake air temperature and exhaust gas temperature is suppressed, and the unburned fuel component is increased in the exhaust gas by retarding the fuel injection timing. When the NOx storage agent is subjected to an oxidation reaction to increase the temperature of the NOx storage agent (hereinafter referred to as temperature increase control), combustion of the internal combustion engine becomes extremely unstable and may cause misfire. is there.
[0011]
In other words, in the case of a low compression ratio engine, there is a region where the above-described temperature increase control for the NOx catalyst cannot be performed due to misfire.
[0012]
  The present invention has been made to solve the above problems, and even in a low compression ratio engine, without misfiring under low temperature and light load conditions,The temperature of the NOx catalyst is raised by retarding fuel injection and increasing the amount of fuel that reaches the NOx catalyst unburned.It is a technical problem to provide a technique capable of controlling the temperature rise.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the exhaust gas purification apparatus for an internal combustion engine of the present invention employs the following means. That is, the exhaust gas purification apparatus for an internal combustion engine of the present invention stores NOx in the exhaust when the air-fuel ratio of the inflowing exhaust is lean, and releases and reduces the stored NOx when the air-fuel ratio of the inflowing exhaust becomes the stoichiometric air-fuel ratio or rich. NOx storage agent toBy retarding fuel injection and increasing the fuel that reaches the NOx storage agent unburnedNOx storage agentRaise the temperatureA temperature raising means for performing temperature rise control, an operating state detecting means for detecting an operating state of the internal combustion engine, and a combustion heater for supplying vaporized fuel to the intake system, the temperature raising means, Based on the operating state of the internal combustion engine detected by the operating state detecting means, the NOx storage agent is brought to a predetermined temperature.By the temperature rise controlWhen the temperature is raised, the fuel heated and vaporized by the combustion heater is supplied to the intake system.
[0014]
The greatest feature of the present invention is an exhaust purification device for an internal combustion engine with a low compression ratio.When temperature rise control is executedWhen it is necessary to raise the temperature of the NOx storage agent under conditions that are likely to misfire, by supplying vaporized fuel to the intake system using a combustion heater, under any low temperature light load condition,Execute temperature rise controlIt is possible to raise the temperature of the NOx storage agent to the required temperature without misfire.
[0015]
In the exhaust gas purification apparatus for an internal combustion engine configured as described above, the vaporized fuel is supplied to the intake system when the temperature increase control is executed. As a result, as a means for raising the temperature of the NOx storage agent, it is effective that a misfire occurs even if control is performed to retard the fuel injection and increase the fuel that reaches the NOx storage agent unburned. It is suppressed.
[0016]
The combustion heater preferably includes an electronic ignition means, and is heated to a temperature at which the fuel is only vaporized without suppressing the electric energy supplied to the electronic ignition means. The use of the combustion heater here means that the electric energy supplied to the glow or the like as an ignition device is not supplied to the extent that the fuel is combusted, but only to vaporize the fuel, to a certain temperature, preferably about 600 ° C. Let it be heated.
[0017]
As a result, the supplied fuel is vaporized and decomposed into components having a low boiling point, reformed and supplied to the combustion chamber, so that the main combustion is stabilized and the injection timing retardation amount causing misfire increases. Therefore, the exhaust temperature can be raised to a higher temperature.
[0018]
The NOx storage agent may be carried on a particulate filter that temporarily captures particulates in the exhaust.
[0019]
In addition, when excess oxygen is present in the surroundings, an active oxygen release agent that absorbs oxygen and retains oxygen when the surrounding oxygen concentration decreases and releases the retained oxygen as active oxygen is supported on the filter. The fine particles deposited on the filter can be oxidized by the released active oxygen.
[0020]
The active oxygen release agent may be selected from alkali metals, alkaline earth metals, rare earths, or transition metals.
[0021]
In the exhaust gas purification apparatus for an internal combustion engine configured as described above, for example, when it becomes necessary to recover NOx storage agent poisoning (catalyst poisoning by hydrocarbons or sulfur oxides), the main combustion is in a stable state. The NOx storage agent is heated to a temperature required for poisoning recovery by the oxidation reaction heat of the fuel supplied into the exhaust gas. Thereafter, when the operating state of the internal combustion engine shifts to the light load region, the poisoning is recovered.
[0022]
In addition, when the NOx occlusion agent is carried on a particulate filter that temporarily captures particulates in the exhaust (hereinafter referred to as a filter), the temperature rises to raise the filter temperature in order to oxidize and remove the particulates captured by the filter. Perform temperature control.
[0023]
As described above, in the present invention, when it is necessary to increase the temperature of the NOx storage agent for various purposes, it is possible to perform temperature increase control without stabilizing the main combustion and causing misfire.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, specific embodiments of an exhaust emission control device for an internal combustion engine according to the present invention will be described with reference to the drawings. Here, the case where the exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied to a diesel engine for driving a vehicle will be described as an example.
[0025]
FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine to which the exhaust purification apparatus according to the present embodiment is applied and its intake and exhaust system, and FIG. 2 is a diagram showing details of a combustion heater.
[0026]
The internal combustion engine 1 shown in FIG. 1 is a four-cylinder water-cooled four-cycle diesel engine. An intake branch pipe (not shown) is connected to the internal combustion engine 1, and each branch pipe of the intake branch pipe communicates with a combustion chamber of each cylinder through an intake port. The intake branch pipe is connected to an intake pipe 9, and the intake pipe 9 is connected to an air cleaner box 10. An air flow meter 11 that outputs an electrical signal corresponding to the mass of the intake air flowing through the intake pipe 9 is attached to the intake pipe 9 downstream of the air cleaner box 10.
[0027]
The internal combustion engine 1 is provided with a combustion multipurpose heater (hereinafter referred to as a combustion heater) 60, which will be described.
[0028]
As shown in FIG. 2, the combustion heater 60 includes an outer cylinder 140, an intermediate cylinder 141 provided in the outer cylinder 140, and an intermediate cylinder 141, and independent of the internal combustion engine 1. And a combustion cylinder 142 for burning the fuel for use.
[0029]
The combustion cylinder 142 includes a vaporization glow plug (not shown) for vaporizing the fuel and an ignition glow plug (not shown) for igniting the fuel vaporized by the vaporization glow plug. . Note that the vaporization glow plug and the ignition glow plug may be combined with a single glow plug.
[0030]
Between the intermediate cylinder 141 and the combustion cylinder 142, a combustion gas passage 201 for flowing the combustion gas generated in the combustion cylinder 142 is formed. A combustion gas discharge port 145 that communicates the combustion gas passage 201 and the outside of the outer cylinder 140 is formed at an appropriate portion of the intermediate cylinder 141.
[0031]
Next, the fuel introduction pipe 27 is connected to the combustion cylinder 142. As shown in FIG. 1, the fuel introduction pipe 27 is connected to the fuel pump 26, and the fuel discharged from the fuel pump 26 is supplied to the combustion cylinder 142 through the fuel introduction pipe 27. ing.
[0032]
On the other hand, a housing 148 in which a blower fan 149 for sending combustion air to the combustion tube 142 and a motor 150 for rotationally driving the blower fan 149 is attached to the outer tube 140.
[0033]
The housing 148 is formed with an intake port 151 for taking combustion air into the housing 148. As shown in FIG. 2, the intake port 151 is connected to an intake introduction passage 18, and this intake introduction passage 18 is connected to the intake pipe 9 downstream of the air cleaner 10.
[0034]
In the middle of the intake air introduction passage 18, an opening / closing valve 29 for opening and closing the intake air flow in the intake air introduction passage 18 is provided. The open / close valve 29 is provided with an actuator (not shown) configured by a step motor or the like to drive the open / close valve 29. By opening and closing the on-off valve 29, intake air is sent to the combustion heater 60 when necessary, and the vaporized fuel is mixed therewith. Further, the opening / closing valve 29 is closed during normal operation, and the intake air reaches the internal combustion engine 1 without passing through the combustion heater 60.
[0035]
On the other hand, an exhaust port 145 is provided at one end of the combustion gas passage 201, and one end of the heater exhaust passage 31 is connected to the exhaust port 145. On the other hand, the other end of the heater exhaust passage 31 is connected to the intake pipe 9 downstream of the intake introduction passage 18.
[0036]
Further, an in-heater cooling water channel 200 for flowing cooling water of the internal combustion engine 1 is formed between the outer cylinder 140 and the intermediate cylinder 141. The outer cylinder 140 has a cooling water introduction port 143 for taking cooling water into the heater cooling water channel 200 and a cooling water discharge port 144 for discharging cooling water in the heater cooling water channel 200. Is formed.
[0037]
As shown in FIG. 2, the cooling water introduction port 143 communicates with a water jacket (not shown) of the internal combustion engine 1 via a cooling water introduction pipe 22, and the cooling water discharge port 144 communicates with the water jacket and cooling water. It communicates via the discharge pipe 23.
[0038]
An electric water pump 24 is provided in the middle of the cooling water introduction pipe 22 so that the cooling water flowing in the water jacket of the internal combustion engine 1 is forcibly sent to the cooling water introduction port 143. .
[0039]
In the middle of the cooling water discharge pipe 23, a heater core 30 of an indoor heating device is disposed, and heat of the cooling water flowing through the cooling water discharge pipe 23 is transmitted to the heating air.
[0040]
Further, the exhaust water mixed with the vaporized fuel discharged from the combustion type heater 60 is cooled by the cooling water flowing through the in-heater cooling water channel 200, and can be adjusted so that it becomes a predetermined temperature.
[0041]
The combustion heater 60 configured in this way needs to supply vaporized fuel to the combustion chamber of the internal combustion engine 1, promote preheating of the internal combustion engine 1 body, promote warm-up, improve the performance of the indoor heating device, and the like. Activated when it occurs.
[0042]
Specifically, in the combustion type heater 60, the motor 150 operates the blower fan 149 to supply a part of the intake air flowing through the intake pipe 3 to the combustion cylinder 142 of the combustion type heater 60, and the fuel pump 26 is shown in the figure. The fuel in the fuel tank not to be sucked up is supplied to the combustion cylinder 142 of the combustion heater 60. Then, the glow plug of the combustion cylinder 142 is energized, and the mixer of the intake air sent by the blower fan 149 and the fuel supplied by the fuel pump 26 is heated and vaporized by the glow plug.
[0043]
Here, when vaporized fuel is supplied to the internal combustion engine 1, that is, when temperature rise control of the particulate filter 20 described later is performed, the electric energy supplied to the glow plug is suppressed, and the fuel is vaporized without ignition. Heat to a temperature around 600 ° C. In the case where vaporization and ignition glow plugs are provided separately, the fuel is vaporized and not ignited by energizing only the vaporization glow plug. Thereby, since the light oil which is the supplied fuel is decomposed and reformed into vaporized and low boiling point components and supplied to the combustion chamber, the main combustion is stabilized.
[0044]
The fuel vaporized in the combustion cylinder 145 is pushed out from the combustion cylinder 145 to the combustion gas passage 201 by the pressure of the intake air sent out by the blower fan 149, and then discharged from the combustion gas passage 201 to the combustion gas discharge port 145. The combustion gas discharged to the discharge port 145 is sent to the combustion chamber of the internal combustion engine 1 through the heater exhaust passage 31 and the intake pipe 9.
[0045]
When the vaporized fuel is not supplied, that is, when warm air at the start of the internal combustion engine 1 or circulation of cooling water to the heater core 30 is required, the temperature of the glow plug is heated to nearly 1,000 ° C. Is vaporized, ignited and continuously burned while supplying air. In this case, the supplied fuel is completely burned, and most of the combustion energy possessed by the fuel is used to raise the temperature of the supplied air. Accordingly, the water pump 24 is operated to pump the cooling water in the water jacket of the internal combustion engine 1 to the cooling water introduction port 143 of the combustion heater 60, whereby the cooling water is heated.
[0046]
The cooling water pumped by the water pump 24 to the cooling water introduction port 143 of the combustion heater 60 is guided from the cooling water introduction port 143 to the heater cooling water channel 200 and discharged through the heater cooling water channel 200. It is discharged to the port 144.
[0047]
At that time, the heat of the combustion gas flowing through the combustion gas passage 201 is transmitted to the cooling water flowing through the heater cooling water channel 200 through the wall surface of the intermediate cylinder 144, and the temperature of the cooling water rises. Thus, the cooling water channel 200 in the heater and the combustion gas channel 201 realize a heat exchange unit.
[0048]
The cooling water heated in this way is discharged from the cooling water discharge port 144 to the cooling water discharge pipe 23, returned to the water jacket of the internal combustion engine 1 through the heater core 30, and circulates in the water jacket. In the heater core 30, a part of the heat of the cooling water is transmitted to the heating air, and the heating air is heated.
[0049]
Further, in FIG. 1, the intake pipe 9 downstream of the combustion heater 60 is provided with a compressor housing 15a of a centrifugal supercharger (turbocharger) 15 that operates using the heat energy of the exhaust as a drive source, and is downstream of the compressor housing 15a. The intake pipe 9 is provided with an intercooler 16 for cooling the intake air that has been compressed in the compressor housing 15a and has reached a high temperature.
[0050]
In the intake system configured in this way, the intake air that has flowed into the air cleaner box 10 is removed through the intake pipe 9 after dust and dirt in the intake air are removed by an air filter (not shown) in the air cleaner box 10. Then, it flows into the compressor housing 15a via the combustion heater 60 or not.
[0051]
The intake air flowing into the compressor housing 15a is compressed by the rotation of the compressor wheel built in the compressor housing 15a. The intake air compressed to a high temperature in the compressor housing 15a is cooled by the intercooler 16, and then the flow rate is adjusted by the intake throttle valve 13 as necessary to flow into the intake branch pipe. As described above, the intake throttle valve 13 for adjusting the flow rate of the intake air flowing through the intake pipe 9 is provided at a portion located downstream of the compressor housing 15a. The intake throttle valve 13 is provided with an intake throttle actuator 14 that is configured by a step motor or the like and that drives the intake throttle valve 13 to open and close.
[0052]
The intake air that has flowed into the intake branch pipe is distributed to the combustion chamber of each cylinder 2. The fuel injected from the fuel injection valve of each cylinder 2 is combusted using the ignition source. When a mixture of vaporized fuel and intake air supplied from the combustion heater 60 is supplied to the combustion chamber, the sum of the vaporized fuel and fuel injected in the combustion chamber should be supplied in the fuel chamber. The total amount of fuel.
[0053]
On the other hand, an exhaust branch pipe is connected to the internal combustion engine 1, and each branch pipe of the exhaust branch pipe communicates with a combustion chamber of each cylinder via an exhaust port (not shown).
[0054]
The exhaust branch pipe is connected to the turbine housing 15 b of the centrifugal supercharger 15. The turbine housing 15b is connected to an exhaust pipe 19, and the exhaust pipe 19 is connected to a muffler (not shown) downstream.
[0055]
In the middle of the exhaust pipe 19, a particulate filter (hereinafter simply referred to as a filter) 20 carrying an NOx storage reduction catalyst is provided. An exhaust gas temperature sensor 24 that outputs an electrical signal corresponding to the temperature of the exhaust gas flowing through the exhaust pipe 19 is attached to the exhaust pipe 19 upstream of the filter 20.
[0056]
In the exhaust system configured in this way, the air-fuel mixture (burned gas) combusted in each cylinder 2 of the internal combustion engine 1 is discharged to the exhaust branch pipe through the exhaust port, and then the centrifugal supercharger from the exhaust branch pipe 15 flows into the turbine housing 15b. The exhaust gas flowing into the turbine housing 15b rotates the turbine wheel that is rotatably supported in the turbine housing 15b using the thermal energy of the exhaust gas. At that time, the rotational torque of the turbine wheel is transmitted to the compressor wheel of the compressor housing 15a described above.
[0057]
Exhaust gas discharged from the turbine housing 15b flows into the filter 20 through the exhaust pipe 19, and particulates (PM) in the exhaust gas are collected and harmful gas components are removed or purified. The exhaust gas from which PM has been collected by the filter 20 and from which harmful gas components have been removed or purified is discharged into the atmosphere via the muffler.
[0058]
The exhaust branch pipe and the intake branch pipe communicate with each other via an exhaust gas recirculation passage (hereinafter referred to as an EGR passage) 25 that recirculates a part of the exhaust gas flowing through the exhaust branch pipe to the intake branch pipe. . In the middle of the EGR passage 25, a flow rate adjusting valve is configured with an electromagnetic valve or the like, and changes the flow rate of exhaust gas (hereinafter referred to as EGR gas) flowing through the EGR passage 25 in accordance with the magnitude of applied power. (Hereinafter referred to as an EGR valve) 26 is provided.
[0059]
In the exhaust gas recirculation mechanism configured as described above, when the EGR valve 26 is opened, the EGR passage 25 becomes conductive, and a part of the exhaust gas flowing through the exhaust branch pipe flows into the EGR passage 25, and the intake air Guided to the branch pipe.
[0060]
The EGR gas recirculated from the exhaust branch pipe to the intake branch pipe via the EGR passage 25 is guided to the combustion chamber of each cylinder while being mixed with fresh air flowing from the upstream of the intake branch pipe.
[0061]
Here, the EGR gas contains water (H₂O) and carbon dioxide (CO₂) And the like, and since an inert gas component having a high heat capacity is not included, if the EGR gas is contained in the mixture, the combustion temperature of the mixture is lowered. Therefore, the amount of nitrogen oxide (NOx) generated is suppressed.
[0062]
Next, the filter 20 according to the present embodiment will be described.
[0063]
FIG. 3 is a cross-sectional view of the filter 20. FIG. 3A is a diagram showing a cross section in the horizontal direction of the filter 20. FIG. 3B is a view showing a longitudinal section of the filter 20.
[0064]
As shown in FIGS. 3A and 3B, the filter 20 is a so-called wall flow type having a plurality of exhaust flow passages 50 and 51 extending in parallel with each other. These exhaust flow passages include an exhaust inflow passage 50 whose downstream end is closed by a plug 52 and an exhaust outflow passage 51 whose upstream end is closed by a plug 53. In addition, the hatched part in FIG. Therefore, the exhaust inflow passages 50 and the exhaust outflow passages 51 are alternately arranged via the thin partition walls 54. In other words, the exhaust inflow passage 50 and the exhaust outflow passage 51 are arranged such that each exhaust inflow passage 50 is surrounded by four exhaust outflow passages 51 and each exhaust outflow passage 51 is surrounded by four exhaust inflow passages 50.
[0065]
The filter 20 is formed of a porous material such as cordierite, so that the exhaust gas flowing into the exhaust inflow passage 50 is adjacent to the surrounding partition wall 54 as shown by an arrow in FIG. To the exhaust outlet passage 51.
[0066]
In the present invention, a carrier layer made of alumina, for example, is formed on the peripheral wall surfaces of each exhaust inflow passage 50 and each exhaust outflow passage 51, that is, on both side surfaces of each partition wall 54 and on the pore inner wall surface in the partition wall 54. The NOx storage reduction catalyst is supported on the carrier.
[0067]
Next, the function of the NOx storage reduction catalyst carried by the filter 20 according to the present embodiment will be described.
[0068]
The filter 20 uses, for example, alumina as a carrier, and an alkali metal such as potassium (K), sodium (Na), lithium (Li), or cesium (Cs), and barium (Ba) or calcium (Ca). ), An alkaline earth such as lanthanum (La) or yttrium (Y), and a noble metal such as platinum (Pt). In the present embodiment, barium (Ba) and platinum (Pt) are supported on a support made of alumina, and O 2 is further supported.₂Ceria with storage capability (Ce₂O_ThreeThe NOx storage reduction catalyst is added.
[0069]
The NOx catalyst configured in this manner occludes nitrogen oxide (NOx) in the exhaust when the oxygen concentration of the exhaust flowing into the NOx catalyst is high.
[0070]
On the other hand, the NOx catalyst releases the stored nitrogen oxides (NOx) when the oxygen concentration of the exhaust gas flowing into the NOx catalyst decreases. At that time, if a reducing component such as hydrocarbon (HC) or carbon monoxide (CO) is present in the exhaust, the NOx catalyst converts nitrogen oxide (NOx) released from the NOx catalyst to nitrogen (N₂).
[0071]
By the way, when the internal combustion engine 1 is in a lean combustion operation, the air-fuel ratio of the exhaust discharged from the internal combustion engine 1 becomes a lean atmosphere, and the oxygen concentration of the exhaust becomes high. Therefore, nitrogen oxides (NOx) contained in the exhaust Is stored in the NOx catalyst. However, if the lean combustion operation of the internal combustion engine 1 is continued for a long time, the NOx storage capacity of the NOx catalyst is saturated, and nitrogen oxides (NOx) in the exhaust gas are stored in the NOx catalyst. Will be released to the atmosphere without being removed.
[0072]
In particular, in a diesel engine such as the internal combustion engine 1, the lean air-fuel ratio mixture is burned in the most operating region, and the exhaust air-fuel ratio becomes the lean air-fuel ratio in the most operating region accordingly. The NOx storage capacity of the catalyst is easily saturated.
[0073]
Therefore, when the internal combustion engine 1 is operated in lean combustion, before the NOx storage capacity of the NOx catalyst is saturated, the oxygen concentration in the exhaust gas flowing into the NOx catalyst is lowered and the concentration of the reducing agent is increased, so that the NOx catalyst is used. It is necessary to release and reduce the stored nitrogen oxides (NOx).
[0074]
As methods for reducing the oxygen concentration in this way, methods such as fuel addition in exhaust, low temperature combustion, and fuel injection during the expansion stroke into the cylinder 2 can be considered.
[0075]
In the present embodiment, unburned fuel can be supplied into the exhaust gas by performing sub-injection with a timing delayed from the main injection separately from the main injection of fuel in the cylinder 2. As a result, fuel (light oil) as a reducing agent is added to the exhaust gas flowing through the exhaust pipe 19 upstream from the filter 20 to reduce the oxygen concentration of the exhaust gas flowing into the filter 20 and increase the concentration of the reducing agent.
[0076]
The exhaust gas having a low oxygen concentration formed as described above flows into the filter 20 and releases nitrogen oxide (NOx) stored in the filter 20 while nitrogen (N₂).
[0077]
The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 35 for controlling the internal combustion engine 1. The ECU 35 is a unit that controls the operation state of the internal combustion engine 1 in accordance with the operation conditions of the internal combustion engine 1 and the request of the driver.
[0078]
Various sensors such as the air flow meter 11 and the exhaust temperature sensor 24 are connected to the ECU 35 via electric wiring, and output signals from the various sensors described above are input to the ECU 35.
[0079]
On the other hand, a fuel injection valve, an intake throttle actuator 14, an EGR valve 26, and the like are connected to the ECU 35 via electric wiring, and the ECU 35 can control the above-described parts.
[0080]
Here, as shown in FIG. 4, the ECU 35 includes a CPU 351, a ROM 352, a RAM 353, a backup RAM 354, an input port 356, and an output port 357 connected to each other by a bidirectional bus 350. , An A / D converter (A / D) 355 connected to the input port 356 is provided.
[0081]
The input port 356 receives an output signal from a sensor that outputs a digital signal format signal, such as the crank position sensor 33, and transmits the output signal to the CPU 351 and the RAM 353.
[0082]
The input port 356 is input via an A / D 355 of a sensor that outputs a signal in an analog signal format, such as the air flow meter 11, the exhaust gas temperature sensor 24, the accelerator opening sensor 36, and the like, and outputs them. The signal is transmitted to the CPU 351 and the RAM 353.
[0083]
The output port 357 is connected to the fuel injection valve, the intake throttle actuator 14, the EGR valve 26, the water-cooled exhaust cooler 28, the on-off valve 29, etc. via electrical wiring, and the control signal output from the CPU 351 is described above. The data is transmitted to the fuel injection valve, the intake throttle actuator 14, the EGR valve 26, and the like.
[0084]
The ROM 352 adds a reducing agent to the fuel injection control routine for controlling the fuel injection valve, the intake throttle control routine for controlling the intake throttle valve 13, the EGR control routine for controlling the EGR valve 26, and the filter 20. Application programs such as a NOx purification control routine for releasing NOx occluded in this way, a poisoning recovery control routine for recovering SOx poisoning of the filter 20, and a particulate combustion control routine for burning and removing particulates collected by the filter 20 Is remembered.
[0085]
The ROM 352 stores various control maps in addition to the application programs described above. The control map is, for example, a fuel injection amount control map showing the relationship between the operating state of the internal combustion engine 1 and the basic fuel injection amount (basic fuel injection time), and the relationship between the operating state of the internal combustion engine 1 and the basic fuel injection timing. The fuel injection timing control map shown, the intake throttle valve opening control map showing the relationship between the operating state of the internal combustion engine 1 and the target opening of the intake throttle valve 13, the operating state of the internal combustion engine 1 and the target opening of the EGR valve 26 Are an EGR valve opening degree control map showing the relationship of the above, a reducing agent addition amount control map showing the relationship between the operating state of the internal combustion engine 1 and the target addition amount of the reducing agent (or the target air-fuel ratio of the exhaust gas).
[0086]
The RAM 353 stores output signals from the sensors, calculation results of the CPU 351, and the like. The calculation result is, for example, an engine speed calculated based on a time interval at which a crank position sensor (not shown) outputs a pulse signal. These data are rewritten to the latest data every time the crank position sensor outputs a pulse signal.
[0087]
The backup RAM 354 is a nonvolatile memory capable of storing data even after the internal combustion engine 1 is stopped.
[0088]
The CPU 351 operates in accordance with an application program stored in the ROM 352 and executes fuel-injection valve control, intake throttle control, EGR control, NOx purification control, poisoning recovery control, particulate combustion control, and the like.
[0089]
In the poisoning recovery control, the CPU 351 performs a poisoning recovery process to recover the poisoning due to the oxide of the filter 20.
[0090]
Here, the fuel of the internal combustion engine 1 may contain sulfur (S), and when such fuel burns in the internal combustion engine 1, sulfur dioxide (SO₂) And sulfur trioxide (SO_Three) And other sulfur oxides (SOx).
[0091]
Sulfur oxide (SOx) flows into the filter 20 together with the exhaust gas, and is stored in the filter 20 by the same mechanism as nitrogen oxide (NOx).
[0092]
Specifically, when the oxygen concentration of the exhaust gas flowing into the filter 20 is high, sulfur dioxide (SO₂) And sulfur trioxide (SO_Three) And other sulfur oxides (SOx) are oxidized on the surface of platinum (Pt), and sulfate ions (SO_Four ^2-) Is stored in the filter 20. Furthermore, sulfate ions (SO_Four ^2-) Combines with barium oxide (BaO) to form sulfate (BaSO)._Four).
[0093]
By the way, sulfate (BaSO_Four) Is barium nitrate (Ba (NO_Three)₂) And is difficult to decompose, and even if the oxygen concentration of the exhaust gas flowing into the filter 20 is lowered, it remains in the filter 20 without being decomposed.
[0094]
Sulfate (BaSO_Four) Increases, the amount of barium oxide (BaO) that can participate in the storage of nitrogen oxides (NOx) decreases accordingly, so that the NOx storage capacity of the filter 20 decreases, so-called SOx poisoning. Will occur.
[0095]
As a method for recovering SOx poisoning of the filter 20, the temperature of the atmosphere of the filter 20 is raised to a high temperature range of approximately 600 to 650 ° C., and the oxygen concentration of the exhaust gas flowing into the filter 20 is lowered to reduce the filter 20. Barium sulfate (BaSOSO)_Four) SO_Three ^-Or SO_Four ^-Pyrolyzed, and then SO_Three ^-Or SO_Four ^-Reacts with hydrocarbons (HC) and carbon monoxide (CO) in the exhaust to produce gaseous SO₂ ^-An example of the method for reduction is shown.
[0096]
Therefore, in the poisoning recovery process according to the present embodiment, the CPU 351 first executes the catalyst temperature increase control for increasing the bed temperature of the filter 20 and then lowers the oxygen concentration of the exhaust gas flowing into the filter 20.
[0097]
In the catalyst temperature increase control, the CPU 351 first starts this control when it is in a situation where sulfur poisoning should be recovered, that is, when a flag for executing these controls is set.
[0098]
As a starting condition, in the case of sulfur poisoning regeneration, determination is made based on an accumulated fuel consumption, an output signal from a NOx sensor (not shown), a vehicle travel distance, and the like. Here, since the NOx storage reduction catalyst carried on the filter 20 is poisoned by the sulfur component in the fuel, the accumulated amount of fuel consumption is stored in the RAM 353, and when the amount of fuel addition reaches a predetermined amount. It may be a start condition for sulfur poisoning recovery control. Further, as sulfur poisoning proceeds, the amount of NOx absorbed by the NOx storage reduction catalyst decreases, and the amount of NOx flowing downstream of the filter 20 increases. Therefore, a NOx sensor (not shown) may be provided downstream of the filter 20, and this output signal may be monitored, and the start condition of the sulfur poisoning recovery control may be when the flow rate of NOx exceeds a predetermined amount. Further, when the vehicle travel distance exceeds a predetermined value, it is determined that the sulfur poisoning needs to be restored, and a sulfur poisoning recovery control flag is set at this time.
[0099]
When this flag is set, the CPU 351 first grasps the operating state of the internal combustion engine 1 based on information from the accelerator opening sensor 36 and the crank position sensor 33. If the operating state of the internal combustion engine 1 is light, the combustion heater 60 is operated, the on-off valve 29 is opened, the vaporized fuel (light oil) is sent to the intake pipe 9 and supplied to the combustion chamber. At the same time, the timing of fuel injection in each cylinder is retarded. By delaying the fuel injection timing in this way, it is possible to increase the fuel supplied into the exhaust gas as an unburned component without burning in the cylinder.
[0100]
FIG. 5 is a diagram showing a comparison between when vaporized fuel (combustible gas) is supplied to the combustion chamber by the combustion heater 60 and when it is not supplied. Here, when the vaporized fuel is not supplied, the exhaust temperature is 400 ° C. or lower, but it can be seen that the exhaust temperature can be raised to about 600 ° C. by supplying this.
[0101]
When the temperature of the mixture of vaporized fuel and intake air that has passed through the combustion heater 60 is equal to or higher than a predetermined temperature, the temperature is controlled and cooled by adjusting the amount of cooling water flowing through the heater cooling water channel 200.
[0102]
The reason why the exhaust temperature rises as described above is that the misfire limit when the fuel injection timing is retarded is expanded to the side away from the top dead center, and there are many high-temperature unburned fuel components in the exhaust. Because it comes to exist. These unburned fuel components are oxidized in the filter 20, and the bed temperature of the filter 20 is raised by the heat generated during the oxidation.
[0103]
In this catalyst temperature increase control, in addition to the above method, the CPU 351 provides a reducing agent injection valve (not shown) in the exhaust passage 19 and injects fuel from the reducing agent injection valve, whereby the fuel is supplied to the filter 20. The temperature of the filter 20 may be increased by heat generated during the oxidation. At this time, the amount of fuel injected from the reducing agent injection valve is set such that the injection interval is shorter than the fuel injection performed at the time of NOx release / reduction and the air-fuel ratio at that time is higher.
[0104]
However, if the temperature of the filter 20 is excessively increased, thermal degradation of the filter 20 may be induced. Therefore, the secondary injected fuel amount and the added fuel amount are feedback controlled based on the output signal value of the exhaust temperature sensor 24. It is preferable to do so.
[0105]
When the bed temperature of the filter 20 rises to a high temperature range of, for example, 630 ° C. by the catalyst temperature raising method as described above, the CPU 351 supplies fuel into the exhaust gas so as to reduce the oxygen concentration of the exhaust gas flowing into the filter 20.
[0106]
If excessive fuel is supplied, the fuel burns rapidly in the filter 20 and the filter 20 may be overheated, or the filter 20 may be unnecessarily cooled by the excessive fuel. It is preferable to perform feedback control of the fuel supply amount based on an output signal of an air-fuel ratio sensor (not shown).
[0107]
When the poisoning recovery process is performed in this manner, the oxygen concentration of the exhaust gas flowing into the filter 20 becomes low under the condition where the bed temperature of the filter 20 is high, so that barium sulfate (BaSO) stored in the filter 20 is stored._Four) Is SO_Three ^-Or SO_Four ^-They are pyrolyzed into SO_Three ^-Or SO_Four ^-Reacts with hydrocarbon (HC) and carbon monoxide (CO) in the exhaust gas and is reduced, and SOx poisoning of the filter 20 is recovered.
[0108]
Next, the CPU 351 reads the output signal of the exhaust temperature sensor 24 and estimates the temperature of the filter 20. The temperature of the filter 20 is estimated from the intake air amount (output signal of the air flow meter 11), the rotation speed, the load, the fuel injection amount, and the like. Alternatively, the temperature of the filter 20 may be obtained by mapping values obtained by experiments in advance. Furthermore, a temperature sensor may be provided in the filter 20 to directly measure the temperature of the filter 20.
[0109]
In this way, the obtained actual temperature is compared with the target temperature of the filter 20 (for example, 630 ° C. in SOx poisoning recovery). When the actual filter 20 temperature is higher than the target temperature, the fuel addition amount is decreased. On the other hand, when the actual filter 20 temperature is lower than the target temperature, the fuel addition amount is increased. .
[0110]
In the low load region, the temperature of the filter 20 is maintained at, for example, 630 ° C. necessary for SOx poisoning recovery so that SOx poisoning recovery can be started immediately.
[0111]
When the temperature of the filter 20 is raised to a predetermined temperature in this way, the oxygen concentration is reduced as described above to perform SOx poisoning recovery.
<Other embodiments>
In the above embodiment, as an example of the temperature increase control, the case of SOx poisoning recovery of the NOx storage agent carried on the filter 20 has been described. However, the temperature of the filter 20 needs to be increased by the temperature increase control. However, the present invention is not limited to this, and particulates in the exhaust gas captured by the filter 20 may be removed from the filter 20.
[0112]
The filter 20 has a catalyst supported on the surface in contact with the exhaust, and can lower the ignition temperature of the fine particles by the catalytic action and burn and remove the fine particles at a relatively low temperature. As such a filter, for example, a filter carrying a mixture of a white metal metal and an alkaline earth metal oxide is known. In this filter, fine particles can be ignited at a relatively low temperature of about 350 ° C. to 400 ° C., and this can be burned continuously.
[0113]
However, the filter 20 may be clogged when the fine particles accumulate on the filter 20 next time. In this case, it is necessary to burn and remove the particulate matter at an appropriate time so that the amount of particulate matter deposited is relatively small so that the filter is not damaged by the temperature rise due to the rapid combustion of the deposited particulate matter. In that case, filter regeneration control is performed in which the temperature of the filter 20 is raised to about 600 ° C. to burn and remove the fine particles.
[0114]
In this filter regeneration control, the CPU 351 determines whether or not particulate removal by oxidation (hereinafter referred to as filter regeneration) is necessary. In this case, for example, when the differential pressure in the exhaust pipe 19 before and after the filter 20 detected by a differential pressure sensor (not shown) exceeds a predetermined value, it is estimated that a certain amount or more of fine particles have accumulated on the filter 20. can do. If a certain amount or more of fine particles accumulate in this way, a filter regeneration control flag is set.
[0115]
If this flag is set, the CPU 351 executes the temperature rise control to increase the filter bed temperature to a temperature range where the particulates can burn. This specific method is the same as the method described in the previous embodiment. In this way, the bed temperature of the filter 20 is raised to a predetermined temperature.
[0116]
When such filter regeneration control is executed, the particulates that have accumulated on the filter 20 are combusted and removed from the filter 20 to regenerate the particulate collection ability of the filter 20.
[0117]
As described above, in the exhaust gas purification apparatus for an internal combustion engine according to the present embodiment, the fuel vaporized by the combustion heater 60 is sent into the combustion chamber of the internal combustion engine 1 when the temperature increase control for the filter 20 is performed. Therefore, even when the intake air is throttled during the temperature rise control and the fuel injection in the combustion chamber is retarded, it is possible to suppress misfire without causing unstable combustion.
[0118]
【The invention's effect】
In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, misfire is suppressed even when the intake throttle and fuel injection are retarded under low temperature and light load conditions for a low compression ratio engine. Temperature rise control is possible.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an internal combustion engine to which an exhaust gas purification apparatus for an internal combustion engine according to an embodiment of the present invention is applied and an intake / exhaust system thereof.
FIG. 2 is a schematic configuration diagram of a combustion heater.
FIG. 3A is a diagram showing a transverse cross section of a particulate filter. (B) is a figure which shows the longitudinal direction cross section of a particulate filter.
FIG. 4 is a block diagram showing an internal configuration of an ECU.
FIG. 5 is a graph showing the relationship between exhaust temperature and misfire limit.
[Explanation of symbols]
1 ... Internal combustion engine
9. Intake pipe
18 ... Exhaust introduction passage
19 ... Exhaust pipe
20 ... Particulate filter
24 ... Exhaust temperature sensor
25 ... EGR passage
26 ... EGR valve
30 ... Heater core
31 ... Heater exhaust passage
35 ... ECU
60 ... Combustion heater

Claims (5)

NOx occlusion agent that occludes NOx in the exhaust when the air-fuel ratio of the inflowing exhaust is lean, and releases and reduces the stored NOx when the air-fuel ratio of the inflowing exhaust becomes the stoichiometric air-fuel ratio or rich,
A temperature increasing means for performing temperature increase control for increasing the temperature of the NOx storage agent by retarding fuel injection and increasing the amount of fuel that reaches the NOx storage agent unburned ;
An operating state detecting means for detecting an operating state of the internal combustion engine;
A combustion heater for supplying vaporized fuel to the intake system,
When the temperature raising means raises the NOx storage agent to a predetermined temperature by the temperature raising control based on the operating state of the internal combustion engine detected by the operating state detecting means, it is heated and vaporized by the combustion heater. An exhaust gas purification apparatus for an internal combustion engine, characterized in that the supplied fuel is supplied to an intake system.   2. The internal combustion engine according to claim 1, wherein the combustion heater includes an electronic ignition means, and is heated to a temperature at which the fuel is only vaporized without suppressing the electric energy supplied to the electronic ignition means. Engine exhaust purification system.   The exhaust purification device for an internal combustion engine according to claim 1 or 2, wherein the NOx storage agent is carried on a particulate filter that temporarily captures particulates in the exhaust.   When excess oxygen is present in the surroundings, oxygen is occluded and retained, and when the surrounding oxygen concentration is lowered, an active oxygen release agent that releases the retained oxygen as active oxygen is carried on the filter, The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3, wherein fine particles deposited on the filter are oxidized by the released active oxygen.   The exhaust gas purification apparatus for an internal combustion engine according to claim 4, wherein the active oxygen release agent is selected from an alkali metal, an alkaline earth metal, a rare earth, or a transition metal.

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