JP3733845B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine, and more particularly to a technique for enhancing an exhaust gas purification effect by a catalyst during stratified combustion operation in an internal combustion engine capable of stratified combustion.
[0002]
[Prior art]
  In recent years, the need to improve fuel economy of internal combustion engines has increased from the perspective of preventing global warming,soA lean air-fuel ratio combustion, that is, an internal combustion engine that is operated leaner than the stoichiometric air-fuel ratio is becoming widespread. Among them, especially low load and low rotation rangesoStratified combustion, that is, an air-fuel mixture with an appropriate air-fuel ratio is formed near the spark plug,FurtherSome of them perform combustion in the state where a large amount of excess air exists around them. In this stratified combustion, only the air-fuel mixture in the vicinity of the spark plug contributes to the combustion, so that the air-fuel ratio can be made lean substantially compared with the case of homogeneous combustion, and the fuel efficiency improvement effect is high.
[0003]
  By the way, pollutant components such as HC, CO, NOx in the exhaust gas of the internal combustion engine have been conventionally used.,Purifying using a three-way catalystRu. This three-way catalyst oxidizes HC and CO in the inflowing exhaust gas to produce H₂O and CO₂And also,NOx is reduced to N₂Thus, these polluting components are rendered harmless, and the conversion efficiency is highest when the average air-fuel ratio in the catalyst is stoichiometric, and when the average air-fuel ratio changes to the rich side, the oxygen concentration in the catalyst Reduced HC and CO conversion efficiency (Ie, Oxidation rate)On the other hand,When changing to the lean side, the oxygen concentration becomes excessive and the NOx conversion efficiency (SnowThat is, the reduction rate) decreases.
[0004]
  For these reasons, it is difficult for the above-described lean combustion engine to purify NOx in the exhaust gas to a sufficiently low level by the three-way catalyst. Here, the following can be mentioned as techniques for purifying NOx under a lean air-fuel ratio.
  First, trap and hold NOx in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean,FurtherThere is a so-called NOx trap catalyst for desorbing and purifying NOx retained when the air-fuel ratio of exhaust gas flowing into the exhaust gas is rich (Japanese Patent Laid-Open06-294319).
[0005]
  If this NOx trap catalyst is installed in the exhaust passage of a lean combustion engine, during lean operationInWhen NOx discharged from the combustion chamber is trapped and removed from the exhaust gas, and the amount of NOx retained by the catalyst (hereinafter referred to as “NOx retention amount”) exceeds a predetermined amount, the air-fuel ratio Can be temporarily enriched to desorb and purify the retained NOx.
[0006]
  As another technique, there is a so-called NOx selective reduction catalyst capable of selectively reducing NOx even when lean exhaust gas flows (Japanese Patent Laid-Open No. Hei.0No. 6-285335). Improve selective reduction efficiencyLetRutaMeUpstream of the catalystsoIt is also possible to add a reducing agent.
[0007]
[Problems to be solved by the invention]
  However, for the purification of exhaust gas from an internal combustion engine that performs stratified combustion, even if any of the above-mentioned catalysts is applied, due to the characteristics of stratified combustion, the performance of the catalyst is reduced as a result of the conventional configuration, which is sufficient. There is a problem that an effective exhaust purification effect cannot be obtained. that is,NextBecause of the reason.
[0008]
  For stratified combustionBy the wayA combustible air-fuel ratio mixture distributed in the vicinity of the spark plug can contribute to combustion, and an incombustible air-fuel ratio mixture distributed in the surrounding area cannot contribute to combustion. Exhaust gas generated by contributing to combustion contains a lot of HC, CO, and NOx.On the other handThe exhaust gas generated without contributing to combustion is exhausted without burning the non-combustible air-fuel ratio mixture, and contains a large amount of oxygen.
[0009]
  Exhaust gas generated by stratified combustion,In the conventional configuration in which the catalyst is provided and purified, the exhaust gas generated by contributing to combustion and the exhaust gas generated without contributing to combustion pass through the catalyst in a mixed state. Here, the components to be purified by the catalyst are actually HC, CO, and NOx contained in the exhaust gas generated by contributing to combustion. Therefore, it is not preferable that the exhaust gas mixed as described above flows into the catalyst.
[0010]
  In other words, exhaust gas generated by contributing to combustion flows into the catalyst in a state where exhaust gas generated by contributing to combustion and exhaust gas generated without contributing to combustion are mixed. The time that can remain in the catalyst is shortened by the amount of exhaust gas produced without contributing to combustion flowing in the catalyst. This is equivalent to an increase in the space velocity of the catalyst (= the amount of exhaust gas flowing through the catalyst / the volume of the catalyst). It is.
[0011]
  In view of such circumstances, the present invention makes it possible to increase the conversion efficiency (or trap efficiency) by the catalyst during the stratified combustion operation without increasing the volume of the catalyst, and is sufficiently low even with a relatively small catalyst. An object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can purify exhaust gas to a level.
[0012]
[Means for Solving the Problems]
  An internal combustion engine exhaust gas purification apparatus according to the present invention includes:It has a piston with irregularities on the crown surface and is formed by the irregularities on this crown surfaceAn exhaust gas purification apparatus for an internal combustion engine ENG capable of performing stratified combustion by forming an air-fuel mixture layer in which a region near a spark plug becomes a combustible air-fuel ratio and a peripheral region becomes a lean incombustible air-fuel ratio in the combustion chamber As shown in FIG. 1, in order to separate the exhaust gas actually generated by contributing to combustion from the exhaust gas generated by the stratified combustion, the exhaust gas contributes to combustion and the exhaust gas that contributes to combustion. Not separated into exhaust gasThen, the exhaust gas that has contributed to the combustion flows into the first exhaust passage, and the exhaust gas that has not contributed to the combustion flows into the second exhaust passage that is formed in parallel with the first exhaust passage.Exhaust gas separation means A, andLocated in the middle of the first exhaust passageFirst exhaust purification means B.
  The exhaust gas separation means A makes the valve timing of the first exhaust valve on the first exhaust passage side different from that of the second exhaust valve on the second exhaust passage side, Exhaust gas that contributes to the combustion by setting the opening timing later than the opening timing of the second exhaust valve and setting the closing timing of the first exhaust valve earlier than the closing timing of the second exhaust valve Into the first exhaust passage (claim 1).
  Further, the exhaust gas separating means A includes a first exhaust valve on the first exhaust passage side and a second exhaust on the second exhaust passage side by a fuel injection valve that directly injects fuel into the combustion chamber. Among the valves, fuel is injected in the direction of the first exhaust valve, and exhaust gas that contributes to the combustion flows into the first exhaust passage (Claim 5).
[0013]
  The first exhaust purification means B has a three-way catalyst, and the exhaust gas separation means A is an exhaust gas that has contributed to the combustion.TheSo that the average air-fuel ratio becomes stoichiometric.Flowing into the first exhaust passageAre preferred (claims)6).
  The first exhaust purification means B traps and holds NOx in the exhaust gas when the air-fuel ratio of the inflowing exhaust gas is lean, and holds it when the air-fuel ratio of the inflowing exhaust gas is rich. The exhaust gas separation means A has a trap catalyst that reduces NOx with a reducing agent component in the exhaust gas, and the exhaust gas separation means A contributes to the combustion.TheSo that the average air-fuel ratio becomes leanFlowing into the first exhaust passageAre preferred (claims)7).
[0014]
  The exhaust gas purification apparatus for an internal combustion engine according to the present invention is preferably capable of adding an auxiliary reducing agent to the trap catalyst when the amount of NOx retained by the trap catalyst becomes equal to or greater than a predetermined amount.8).
  The exhaust gas separation means A is configured to provide an exhaust gas that contributes to the combustion when the amount of NOx retained by the trap catalyst exceeds a predetermined amount.TheSo that the average air-fuel ratio becomes richAnd flowing into the first exhaust passageAre preferred (claims)9).
[0015]
  The first exhaust purification means B has a selective reduction type catalyst that can flow exhaust gas having a lean air-fuel ratio and reduce NOx in the exhaust gas that has flowed in with a reducing agent component in the exhaust gas, The exhaust gas separation means A is an exhaust gas that contributes to the combustion.TheSo that the average air-fuel ratio becomes leanFlowing into the first exhaust passageAre preferred (claims)10).
  In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, it is preferable that an auxiliary reducing agent can be added to the selective catalytic reduction catalyst.11).
[0016]
[0017]
  The exhaust gas is separated by the valve timing of the first and second exhaust valves. 1)During stratified combustion operationHeyWhen the first exhaust valve and the second exhaust valve are both open, the opening area of the first exhaust passageButThe opening area of the second exhaust passage is preferably larger than that of the second exhaust passage.2).
  It is preferable that the valve timing of the first exhaust valve can be variably set according to engine operating conditions.3).
[0018]
  Preferably, the first exhaust valve extends the valve opening period in accordance with an increase in at least one of engine speed and load.4).
[0019]
[0020]
  The first exhaust passage and the second exhaust passage join downstream from the first exhaust purification means B,thisIt is preferable that the second exhaust purification means C is provided in the exhaust passage downstream of the junction.12).
  The exhaust gas separation means A provides the first exhaust with respect to the amount of exhaust gas to be exhausted from the combustion chamber when the engine is cold, including when the engine is started.aisleIt is preferable that the ratio of the amount of exhaust gas flowing into the engine is approximately 1.13).
[0021]
[0022]
【The invention's effect】
  According to the invention which concerns on Claim 1, the following effect can be acquired.
  In the internal combustion engine according to the present invention,Stratified combustionInOnly the combustible air-fuel ratio mixture in the region near the spark plug can contribute to combustion, and the surplus air in the peripheral region cannot contribute to combustion. Therefore, in the combustion chamber immediately after combustion, exhaust gas generated by contributing to combustion and exhaust gas generated without contributing to combustion are mixed. Of these, many HC, CO, and NOx pollutants are present in the former exhaust gas.
[0023]
  Therefore, during stratified combustion operationHeyThus, the exhaust gas separation means A did not contribute to combustion with the exhaust gas that contributed to combustion, in order to separate the exhaust gas actually generated and contributed to combustion from the exhaust gas generated by combustion. By separating only the exhaust gas that has contributed to combustion out of these exhaust gases into the first exhaust purification means B, the pollutant component contained in the exhaust gas that has contributed to combustion is the first The exhaust gas purification means B can stay longer than before. Therefore, the exhaust purification effect by the first exhaust purification means B is enhanced.Can.
  According to the first aspect of the present invention, after the exhaust gas that has contributed to combustion is separated from the exhaust gas that has not contributed to combustion by the exhaust gas separation means A, the exhaust gas that has not contributed to combustion is separated from the exhaust gas that has not contributed to combustion. 1 flows in the exhaust passage. Therefore, the exhaust gas that has contributed to the combustion flows into the first exhaust gas purification means B without being mixed with the exhaust gas that has not contributed to the combustion, so that the exhaust gas purification effect by the first exhaust gas purification means B is further increased. Can be increased.
  In addition, as described above, in the combustion chamber immediately after stratified combustion, exhaust gas generated by contributing to combustion and exhaust gas generated without contributing to combustion are mixed, but the former is mainly used. In the combustion chamber around the spark plug, and the latter is distributed near the wall surface around the exhaust gas generated by contributing to the combustion. Therefore, at the time of exhaust, first, exhaust gas generated without contributing to combustion in the vicinity of the exhaust valve is exhausted, followed by exhaust gas generated contributing to combustion, and further generated without contributing to combustion. Exhaust gas is exhausted.
  Therefore, during exhaust, the first exhaust valve opens more late than the opening timing of the second exhaust valve and closes earlier than the closing timing of the second exhaust valve, so that combustion mainly distributed in the approximate center of the combustion chamber. The exhaust gas generated by contributing to the combustion is positively extracted, and the separation of the exhaust gas that has contributed to the combustion and the exhaust gas that has not contributed to the combustion is made favorable so that the combustion contains a lot of pollutant components to be purified. The contributed exhaust gas can flow to the first exhaust purification means B.
  Moreover, according to the invention which concerns on Claim 5, the fuel injection direction is made into the 1st and 2nd exhaust valve, By inclining in the direction of the first exhaust valve, the air-fuel mixture that can contribute to combustion is intensively distributed in the vicinity of the first exhaust valve. Therefore, even if the valve timings of the first exhaust valve and the second exhaust valve are the same, a large amount of exhaust gas generated by contributing to combustion is introduced into the first exhaust passage from the second exhaust passage. Can be imported.
[0024]
  Claim6According to the invention, the three-way catalyst can simultaneously purify HC, CO, and NOx that are pollutants generated by stratified combustion. Further, since only the exhaust gas whose average air-fuel ratio contributed to the combustion of the stoichiometric gas separated by the exhaust gas separation means A flows into the catalyst, the polluted components contained therein can stay in the catalyst for a long time, The conversion efficiency by the catalyst is improved.
[0025]
  Claim7According to the invention, since only the exhaust gas that has been separated by the exhaust gas separation means A and contributed to the lean combustion of the average air-fuel ratio flows into the trap catalyst, the polluted components contained therein are contained in the catalyst. It can stay for a long time, and the trapping efficiency by the catalyst is improved.
  Claim8According to the invention concerning, the following effect can be acquired.
[0026]
  Only the exhaust gas contributing to the combustion separated by the exhaust gas separation means A flows into the trap catalyst, but the exhaust gas contributing to this combustion is in a richer state than the entire exhaust gas generated by the stratified combustion. Therefore, it is possible not only to desorb and reduce the retained NOx by adding an auxiliary reducing agent, but also to reduce the amount of addition and perform this.
[0027]
  Claim9According to this invention, the exhaust gas flowing into the trap catalyst becomes rich by making the average air-fuel ratio of the exhaust gas contributing to combustion rich. For this reason, even during stratified combustion operation, the retained NOx can be desorbed and reduced by the reducing agent component in the exhaust gas.
  Claim10According to the invention according to the present invention, since only the exhaust gas that has been separated by the exhaust gas separation means A and contributes to the lean combustion of the average air-fuel ratio flows into the selective reduction catalyst, the pollutant component contained therein is the catalyst. The conversion efficiency by the catalyst is improved.
[0028]
  Claim11According to the invention, since the auxiliary reducing agent added to the selective catalytic reduction catalyst can stay in the catalyst for a long time, the amount of the auxiliary reducing agent to be added can be reduced.
[0029]
[0030]
[0031]
  Claim2According to the invention relating to this, the exhaust gas flow rate in the first exhaust passage is equal to the exhaust gas flow rate in the second exhaust passage.RSince it can be increased, the exhaust gas generated by contributing to the combustion will more actively flow into the first exhaust passage side. For this reason, a larger amount of contaminating components can be flowed to the first exhaust purification means B.
  Claim3According to the present invention, the valve timing of the first exhaust valve is changed according to the engine operating condition, so that the exhaust gas generated by contributing to combustion can be efficiently extracted to separate the exhaust gas. Can do.
[0032]
  Claim4According to the invention concerning, the following effect can be acquired.
  As the engine speed increases, the actual exhaust time per cycle decreases. At this time, the first exhaust passage of the exhaust gas generated by contributing to the combustion is extended by extending the valve opening period of the first exhaust valve, thereby extending the real time of exhaust by the first exhaust valve. The amount of inflow to the can be maintained as much as possible.
[0033]
  Further, when the load increases, the amount of fuel injection increases accordingly, and the absolute amount of the air-fuel mixture that can contribute to combustion increases. Therefore, in this case as well, by extending the valve opening period of the first exhaust valve, it is possible to flow more exhaust gas generated by contributing to combustion to the first exhaust passage.
[0034]
[0035]
[0036]
[0037]
  Claim12According to the invention, the pollutant component that has passed through the first exhaust gas purification unit B without being purified and the pollutant component in the exhaust gas that has been separated by the exhaust gas separation unit A and passed through the second exhaust passage. It can be purified by the second exhaust purification means C.
  Claim13According to the present invention, in order to warm up (activate) the first exhaust gas purification means B, the heat of the exhaust gas that has not contributed to the combustion is also used in addition to the heat of the exhaust gas that has contributed to the combustion. Therefore, the time required for warming up the first exhaust purification means B can be shortened.
[0038]
[0039]
DETAILED DESCRIPTION OF THE INVENTION
  Embodiments of the present invention will be described below with reference to the drawings.
  FIG. 2 is a cross-sectional view schematically showing the structure of the internal combustion engine (hereinafter referred to as “engine”) 1 according to the first embodiment of the present invention, and includes the exhaust purification device according to the present invention. The structure of the engine 1 will be described with reference to FIG.
[0040]
  An air cleaner 3 is attached to the inlet of the intake passage 2 of the engine 1. Immediately downstream of this, an air flow meter 4 is installed, and a detection signal thereof is sent to an electronic control unit (hereinafter referred to as “ECU”) 41, which will be described later, so that an intake air amount Qa to the engine 1 can be measured. It has become.
  A throttle valve 5 is installed in the intake passage 2 downstream of the air flow meter 4, thereby controlling the intake air amount Qa. Further, a collector 6 and a port section 7 are connected downstream of the throttle valve 5, and air whose flow rate is controlled by the throttle valve 5 passes through these two intake valves 8 (8 a, 8 b) per cylinder. Valve opening periodIn addition,It is supplied to the combustion chamber in the cylinder 9. These intake valves 8a and 8b are controlled signals from the ECU 41.On the basis of theBy the intake side electromagnetic actuator 31 that operates, a predetermined valve timing is obtained.soOpen the intake passage 2.
[0041]
  A piston 10 is inserted into the cylinder 9 so as to be capable of reciprocating. The crown surface of the piston 10 is provided with irregularities 11 for tumble control, and the intake air that has entered the combustion chamber is guided by the irregularities 11 to form a tumble flow. In addition, the port part 7 isthisAngle at which tumble flow is likely to formsoConnectionIsing.
[0042]
  The cylinder 9 has a fuel injection valve 12 in the vicinity of the opening of the port portion 7.,It is installed so as to face the combustion chamber directlyAnd,pointThe fire hydrant 13 is installed so as to be positioned substantially in the center of the combustion chamber. The fuel injection valve 12 injects and supplies a predetermined amount of fuel to the intake air that forms the tumble flow as described above, and the air-fuel mixture thus formed is By operation, predetermined timingsoIgnite and burn.
[0043]
  The fuel injection valve 12 is switched in the injection timing according to the combustion method of the engine 1, and in the case of homogeneous combustion in which the fuel is uniformly distributed in the combustion chamber to obtain an output, the intake strokesoSpray. On the other hand, in the case of stratified combustion that aims to improve fuel efficiency by distributing a mixture of combustible air-fuel ratio that can contribute to combustion in the vicinity of the spark plug 13 and stratifying the mixture, the compression strokesoSpray.
[0044]
  After combustion, the generated exhaust gas is exhausted through the exhaust passage 22 (22a, 22b) from the exhaust ports 21 (21a, 21b) formed by two for each cylinder. Exhaust valves 23 (23a, 23b) for opening and closing the exhaust passages 22a and 22b, respectively, are controlled by a control signal from the ECU 41.On the basis of theIt is driven by the exhaust side electromagnetic actuator 32 which operates.
[0045]
  The exhaust valves 23a and 23b and the exhaust side electromagnetic actuator 32 constitute exhaust gas separation means of the present invention.
  FIG. 3 shows the cylinder 9 as viewed from above. An upstream catalytic converter 24 is provided in the middle of the first exhaust passage 22a of the two exhaust passages 22a and 22b.Ising. The catalytic converter 24 can incorporate any of a three-way catalyst, a NOx trap catalyst, and a NOx selective reduction catalyst according to matching with the engine 1. The exhaust passages 22a and 22b merge downstream of the catalytic converter 24,thisA downstream catalytic converter 25 is connected to the exhaust passage downstream from the junction.ButEstablishmentIsTheNoThe
[0046]
  The downstream catalytic converter 25 passes through the first exhaust passage 22a but is upstream of the catalytic converter 24.ThenIt is for purifying the pollutant components that could not be completely purified and the pollutant components in the exhaust gas that passed through the second exhaust passage 22b before being released to the atmosphere,Similar to upstream catalytic converter 24It can be appropriately selected according to matching with the engine 1.
[0047]
  The upstream catalytic converter 24 constitutes the first exhaust purification means of the present invention, and the downstream catalytic converter 25 constitutes the second exhaust purification means of the present invention.
  In addition, as shown in FIG.₂Sensor 51ButInstallationHas beenThis causes O in exhaust gas₂concentrationButMeasurementIsThe When the engine 1 is operated at the stoichiometric air-fuel ratio, this O₂Information from sensor 51On the basis of theFeedback controlButlineBe called.
[0048]
  The electronic control unit 41 includes a CPU, a ROM, a RAM, an A / D converter, and an input / output interface, and includes an intake air amount Qa and O₂In addition to the concentration, the crankshaft rotation position signal from the crank angle sensor 52 (based on this, the engine speed Ne can be calculated), the accelerator pedal opening signal Aps from the accelerator sensor 53, and the water temperature sensor 54 Enter information such as engine coolant temperature TwOn the basis of theControl signals for the intake side electromagnetic actuator 31 and the exhaust side electromagnetic actuator 32 are generated.
[0049]
  Next, the control contents of the electronic control unit 41 will be described with reference to the flowcharts shown in FIGS. First, the combustion method selection will be described with reference to FIG. 4, and then control according to the combustion method of the exhaust side electromagnetic actuator 32 will be described with reference to FIG.
  FIG. 4 is a flowchart of a combustion method selection routine.
[0050]
  First, after reading various operating conditions in step (hereinafter simply referred to as “S”) 1, the accelerator opening Aps is read in subsequent S2.On the basis of theA target torque TTC is obtained from the map.
  In S3, the engine speed Ne, the target torque TTC,On the basis of theA combustion flag Fcmb (0 to 2) is set. Operating conditions that should improve fuel efficiency through stratified combustionsoThe combustion flag Fcmb is set to 0. In other operating conditions, homogeneous combustion will occur, but in particular areas where fuel economy should be improved.soThe combustion flag Fcmb is set to 1 for homogeneous lean combustion. In a region other than the above two regions, the combustion flag Fcmb is set to 2 for homogeneous stoichiometric combustion.
[0051]
  In S4, it is determined whether or not the water temperature Tw is equal to or higher than a predetermined value TwL. When it is determined that the value is equal to or greater than the predetermined value TwL, the routine returns as it is, and the combustion flag Fcmb set in S3 is maintained. However, if the above determination is negative (that is, the water temperature Tw is less than the predetermined value TwL), the process proceeds to S5 and the combustion flag Fcmb is set to 2. This is because when the engine is cold, there is a possibility that stability may not be obtained when performing lean combustion, so lean combustion is prohibited and combustion is performed at the stoichiometric air-fuel ratio.
[0052]
  Next, control according to the combustion method of the exhaust side electromagnetic actuator 32 will be described. FIG. 5 is a flowchart showing a basic flow of a valve operating angle setting routine for the exhaust valves 23a and 23b.
  First, in S11, various control information is read.
  In S12, it is determined whether the water temperature Tw is equal to or higher than a predetermined value TwL, that is, whether the engine 1 has been warmed up. If it is determined that the value is equal to or greater than the predetermined value TwL, the process proceeds to S14. On the other hand, if the above determination is negative (during cold operation), the process proceeds to S13, the second exhaust valve 23b is stopped and kept closed, and the exhaust by only the first exhaust valve 23a is selected. To do. When the engine is cold, including when the engine is started, it is necessary to increase the catalyst temperature to activate the catalyst.like thatconditionsThenBy providing all the generated exhaust gas to the catalytic converter 24 on the upstream side, a larger amount of heat is given to the catalyst, and the activation time is shortened.
[0053]
  In S14, it is determined whether or not the combustion flag Fcmb is 0, that is, whether or not the selected combustion method is stratified combustion. As a result, when it is determined that the combustion flag Fcmb is 0, the routine proceeds to S15, where the engine speed Ne.as well asTarget torque TTCInThe target valve operating angles of the exhaust valves 23a and 23b are set using the maps assigned in correspondence.
[0054]
  AndFor example, when the operating condition is in the region A, the lift curves of the first and second exhaust valves 23a and 23b are as shown in the profiles Pra1 and Prb1 shown in FIG. The opening timing of the valve 23a is set later than the opening timing of the second exhaust valve 23b, and the closing timing of the first exhaust valve 23a is set earlier than the closing timing of the second exhaust valve 23b.
[0055]
  The target valve operating angle of the first exhaust valve 23a is changed with the change of the engine speed Ne, and particularly with the change of the target torque TTC. (FigureDuring ~And the profile Pra2 shown in FIG. 6B, the opening timing of the first exhaust valve 23a is advanced while the closing timing is delayed and the valve opening period is extended.
[0056]
  On the other hand, when the determination result of S14 is negative, that is, when it is determined that the selected combustion method is homogeneous combustion (homogeneous lean combustion or homogeneous stoichiometric combustion), the process proceeds to S16 and the selected combustion method is selected. Set target valve operating angle for
  FIG. 7 shows CO in the combustion chamber immediately after combustion during stratified charge combustion operation.₂It represents the concentration distribution trend.
[0057]
  When stratified combustion is selected as the combustion method as described above (that is, the combustion flag Fcmb = 0), only the air-fuel mixture in the vicinity of the spark plug 13 can contribute to combustion, and the air-fuel mixture in the vicinity thereof is It is a lean state and cannot contribute to combustion. For this reason, CO in the combustion chamber immediately after combustion₂As shown in the figure, the concentration distribution is high around the spark plug 13,SoThe surroundings are low.
[0058]
  Such CO₂The concentration distribution tendency is substantially maintained even after the exhaust valve 23 is opened and exhaust is started. That is, when the exhaust valve 23 is opened, first, CO generated without contributing to the combustion in the vicinity of the exhaust valve 23 is generated.₂Low-concentration exhaust gas is discharged from the combustion chamber,BurningCO generated by contributing to the combustion concentrated in the center of the firing chamber₂Concentrated exhaust gas continues,FurtherAt a position far from the exhaust valve 23₂The exhaust gas having a low concentration will be discharged. Therefore, CO in the exhaust gas discharged from the combustion chamber to the exhaust passage 22 is obtained.₂The concentration changes with a tendency as shown in FIG.
[0059]
  CO in exhaust gas₂Since the concentration substantially indicates the air-fuel ratio of the exhaust gas, the CO in the exhaust gas₂Changes over time in the concentration, the CO concentration, and the air-fuel ratio of the exhaust gas are as shown in FIGS. CO is generally a region where the air-fuel ratio is rich.soThe CO detection point shown in FIG.₂Corresponding to the peak point of concentration change,thisA depression is detected at the peak point.
[0060]
  In addition, CO produced by contributing to combustion₂High-concentration exhaust gas contains a large amount of NOx generated during combustion, while CO produced without contributing to combustion.₂NOx contained in the exhaust gas having a low concentration is small. Therefore, the exhaust gas containing a large amount of NOx is mainly discharged in the middle of the exhaust stroke. Therefore, with the above-described configuration, the valve opening period of the first exhaust valve 23a is set to the middle stage of the exhaust stroke, that is, the exhaust timing of exhaust gas containing a large amount of NOx generated by contributing to combustion.TogetherAccordingly, only the exhaust gas containing a large amount of NOx can flow to the upstream catalytic converter 24.
[0061]
  Here, when the three-way catalyst is built in the upstream catalytic converter 24, the exhaust gas generated mainly contributing to the stoichiometric to rich combustion of the air-fuel ratio is introduced into the first exhaust passage 22a. By taking in, the average air-fuel ratio in the first exhaust passage 22a can be stoichiometric, and NOx in the exhaust gas can be purified with the highest conversion efficiency of the three-way catalyst.
[0062]
  Even if not all of the NOx can be purified by the catalytic converter 24, the remaining NOx can be purified by incorporating the NOx trap catalyst or NOx selective reduction catalyst in the downstream catalytic converter 25. ThisHereSince NOx to be purified by the downstream catalyst is reduced by the upstream catalyst, fuel consumption and emission can be improved.
[0063]
  When the NOx trap catalyst is built in the upstream catalytic converter 24, the average air-fuel ratio in the first exhaust passage 22a is made lean.
  That is, when trapping NOx in the exhaust gas, the valve opening period of the first exhaust valve 23a is shown in FIG. 9 (a-1).periodAs Δta, the first exhaust valve 23a is opened for a relatively long period including the exhaust gas exhaust timing when the air-fuel ratio is stoichiometric to rich. The lift curves of the first and second exhaust valves 23a and 23b at this time are as shown by profiles Pra3 and Prb3 in FIG. 9A-2, respectively.
[0064]
  On the other hand, when reducing the retained NOx, such as when the NOx retention amount of the NOx trap catalyst becomes equal to or greater than a predetermined amount, the valve opening period of the first exhaust valve 23a is set as shown in FIG. 9 (b-1). Shown inperiodAs Δtb, the exhaust gas with rich air-fuel ratio is dischargedTogetherThus, the first exhaust valve 23a is opened. The lift curves of the first and second exhaust valves 23a and 23b at this time are as shown in the profiles Pra4 and Prb4 of FIG. 9B-2, respectively, and the opening period of the first exhaust valve 23a is NOx. It is narrower than when trapping.
[0065]
  In this way, by making the air-fuel ratio of the exhaust gas flowing into the upstream catalytic converter 24 rich, the retained NOx can be reduced and purified by the reducing agent component in the exhaust gas.
  Further, when a three-way catalyst, a NOx selective reduction catalyst, or the like is built in the upstream catalytic converter 24, NH is placed in the first exhaust passage 22a upstream of the catalytic converter 24._Three, H₂It is also possible to purify NOx by adding auxiliary reducing agents such as CO, HC and the like. The exhaust gas in the first exhaust passage 22a has a conventional lean degree.RSince it is lower (on the rich side), the amount of auxiliary reducing agent added isRLess is enough.
[0066]
  FIG. 10 shows CO in the combustion chamber immediately after combustion in the stratified combustion operation.₂The distribution tendency of concentration is expressed by dividing the difference in load (high and low). FIG. 11 shows the valve open periods of the first and second exhaust valves 23a and 23b when the load is low and when the load is high, and the CO in the exhaust gas discharged from the combustion chamber.₂This is shown in correspondence with the change in concentration over time.
[0067]
  On the low load side, that is, when the fuel injection amount is small, as shown in FIG.₂The high-concentration part is limited to a very narrow range near the spark plug 13, and the CO formed around it.₂The proportion of the low density portion is increased. For this reason, CO in the exhaust gas₂The change in concentration with time forms a temporary peak as shown in FIG. As mentioned above, CO in exhaust gas₂Since the concentration substantially indicates the air-fuel ratio of the exhaust gas, by narrowing the operating angle of the first exhaust valve 23a, the exhaust gas generated by contributing to the combustion is accurately put into the first exhaust passage 22a. Can be captured.
[0068]
  On the other hand, on the high load side, that is, when the fuel injection amount is large, as shown in FIG.₂The high concentration portion expands to a relatively wide range around the spark plug 13. For this reason, CO in the exhaust gas₂The density is maintained at a high density value for a certain period of time as shown in FIG. Therefore, by taking a relatively wide operating angle of the first exhaust valve 23a, more exhaust gas generated by contributing to combustion can be taken into the first exhaust passage 22a.
[0069]
  In this embodiment, since an electromagnetically driven actuator is used as the valve operating device for the intake and exhaust valves, not only the valve timing but also the lift amount can be changed as desired.
  Therefore, the lift curves of the first exhaust valve 23a and the second exhaust valve 23b areAndFor example,When the first and second exhaust valves are set to open along the profiles Pra5 and Prb5 shown in FIG. 12, the lift amount of the first exhaust valve is the same as that of the second exhaust valve. Lift amountRMake it bigger.
[0070]
  Thereby, the opening area of the exhaust port 21a is equal to the opening area of the exhaust port 21b.RBecause it growsExhaust gas flow rate to the first exhaust passage 22a,Exhaust gas flow rate to the second exhaust passage 22bLargeCan be A throttle valve that can adjust the flow area of the second exhaust passage 22b is provided.AlsoSimilar effects can be obtained.
[0071]
  AlsoThe lift curves of the first exhaust valve 23a and the second exhaust valve 23b are set so as to follow the profiles Pra6 and Prb6 shown in FIG. 13, and exhaust gas generated by contributing to combustion is discharged from the combustion chamber. At the timingTogetherIt is also possible to open the first exhaust valve 23a and reduce the lift amount of the second exhaust valve 23b.
[0072]
  In the above description, an example in which the upstream catalytic converter 24 is individually installed for a specific exhaust passage among the plurality of exhaust passages has been described. A catalytic converter may be provided for implementation.
  FIG. 14 shows an example in which all exhaust passages are connected to one upstream catalytic converter 124. Since the catalytic converter 124 has a grid-like passage, the exhaust gas that flows without being mixed after being separated (that is, the exhaust gas that contributes to combustion and the exhaust gas that does not contribute to combustion) There is no mixing in the catalytic converter 124. A downstream catalytic converter may be provided in the exhaust passage downstream of the upstream catalytic converter 124.
[0073]
  Thus, according to the present invention, during stratified charge combustion operation, exhaust gas containing a large amount of NOx that contributes to combustion is actively removed.FirstIt can be taken into the exhaust passage 22a. As a result, the exhaust gas generated by the combustion is separated into the exhaust gas that has contributed to the combustion and the exhaust gas that has not contributed to the combustion, and only the exhaust gas that has contributed to the combustion remains upstream while maintaining the separated state. To the catalytic converter 24 (a part of the collective catalytic converter 124). Therefore, exhaust gas containing a large amount of pollutant can be selectively introduced into the upstream catalytic converter 24, the space velocity of the upstream catalyst can be reduced without increasing the volume, and the conversion efficiency (or trap) by the catalyst can be reduced. Efficiency).
[0074]
  In this embodiment, an electromagnetically driven valve operating device is used, but the present invention is not limited to this, and the same effect can be obtained even if a cam driven variable valve operating device is used. Moreover, you may provide the fixed cam which gives a desired lift curve.
[0075]
[0076]
[0077]
  In addition, although the valve operating apparatus of the intake / exhaust valve can be selected according to the required engine performance, in the illustrated example, the intake valve 8 is connected to the intake side cam 32 via the lifter 31, and the exhaust valve 23 is The exhaust side cam 34 is driven through the lifter 33.
  The method of separating the exhaust gas into exhaust gas that has contributed to combustion and exhaust gas that has not contributed to combustion is the exhaust valve 2 shown above.To 3It is not limited to that. As will be described below, the fuel can be separated depending on the fuel injection direction by the fuel injection valve. Then, next, the first of the present invention.2Embodiments will be described.
[0078]
  Figure15These are top views which show the structure of the engine 201 which concerns on embodiment. The same components as those of the engine 1 are denoted by the same reference numerals as those in FIG.
  In this way, the injection direction of the fuel injection valve 212 that directly injects fuel into the combustion chamber is set toward the port portion (exhaust valve) of the first exhaust passage 22a, and an air-fuel mixture that can contribute to combustion is set. , Concentrate in the vicinity of the opening of the port. As a result, the exhaust gas generated by contributing to the combustion is sent to the second exhaust passage 22b.RFirst exhaustaisleA large amount can be taken into 22a.
[0079]
  In addition to this, figure16As shown in FIG. 2, the position of the piston bowl (concave portion) C formed on the crown surface of the piston 209 is set closer to the opening of the first exhaust passage 22a, and the air-fuel mixture that can contribute to combustion isthisIt is good also as concentrating in the opening part vicinity. ThisIn Case of, Fuel injection valve 212 and piston bowl CButThe exhaust gas separation means of the present invention is configured.
[0080]
[0081]
[0082]
[Brief description of the drawings]
FIG. 1 is a block diagram showing a configuration of the present invention.
FIG. 2 is a sectional view schematically showing the configuration of the internal combustion engine according to the first embodiment of the invention.
FIG. 3 is a plan view of the exhaust system of the internal combustion engine.
FIG. 4 is a flowchart of a combustion method selection routine.
FIG. 5 is a flowchart of a target valve operating angle setting routine.
FIG. 6 is a diagram showing an example of a lift curve of an exhaust valve
FIG. 7 shows CO in the combustion chamber immediately after combustion during stratified charge combustion operation.₂Figure showing the concentration distribution trend
FIG. 8 shows CO in exhaust gas discharged from the combustion chamber after stratified combustion.₂The figure which shows the time change of concentration, CO concentration and air fuel ratio
FIG. 9 is a diagram showing a method for controlling the air-fuel ratio of exhaust gas contributing to combustion.
FIG. 10 CO₂The figure which shows the change tendency according to the target torque of concentration distribution
FIG. 11 is a graph showing a change trend according to a target torque during an exhaust valve opening period.
FIG. 12 is a diagram showing another example of the lift curve of the exhaust valve
FIG. 13 is a view showing another example of the lift curve of the exhaust valve.
FIG. 14 shows an example of a collective upstream catalytic converter.
FIG. 15First of the present invention2The top view which shows schematically the structure of the internal combustion engine which concerns on embodiment of this
FIG. 16The figure which shows the piston shape of an internal combustion engine same as the above
[Explanation of symbols]
  DESCRIPTION OF SYMBOLS 1 ... Engine, 2 ... Intake passage, 8 ... Intake valve, 9 ... Cylinder, 10 ... Piston, 12 ... Fuel injection valve, 13 ... Spark plug, 21 ... Exhaust port, 22 ... Exhaust passage, 23 ... Exhaust valve, 24 ... Upstream catalytic converter, 25 ... downstream catalytic converter, 31 ... intake side electromagnetic actuator, 32 ... exhaust side electromagnetic actuator, 41 ... electronic control unit.

Claims (13)

It has a piston with irregularities formed on the crown surface,
In the combustion chamber formed by the irregularities of the crown surface , a stratified combustion is performed by forming an air-fuel mixture layer in which the region near the spark plug becomes a combustible air-fuel ratio and the peripheral region becomes a lean incombustible air-fuel ratio. An exhaust purification device for an internal combustion engine,
Wherein in order to separate the actual exhaust gas produced contributes to the combustion of the exhaust gas generated by stratified combustion, it is separated into an exhaust gas which has not contributed to the combustion exhaust gas that has contributed to the exhaust gas to the combustion The exhaust gas that contributes to the combustion flows into the first exhaust passage, and the exhaust gas that does not contribute to the combustion flows into the second exhaust passage formed in parallel to the first exhaust passage. Separating means;
First exhaust gas purification means located in the middle of the first exhaust passage ,
The exhaust gas separating means makes the valve timing of the first exhaust valve on the first exhaust passage side different from that of the second exhaust valve on the second exhaust passage side to open the first exhaust valve. The timing is set later than the opening timing of the second exhaust valve, the closing timing of the first exhaust valve is set earlier than the closing timing of the second exhaust valve, and the exhaust gas contributing to the combustion is exhaust purifying apparatus for an internal combustion engine Ru allowed to flow into the first exhaust passage. During the stratified combustion operation, when both the first exhaust valve and the second exhaust valve are open, the opening area of the first exhaust passage is the opening of the second exhaust passage. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purification apparatus is larger than a partial area. The exhaust purification device for an internal combustion engine according to claim 1 or 2, wherein the first exhaust valve can be variably set in valve timing according to engine operating conditions. The exhaust purification device for an internal combustion engine according to claim 3, wherein the first exhaust valve has a valve opening period extended in accordance with an increase in at least one of an engine speed and a load. It has a piston with irregularities formed on the crown surface,
In the combustion chamber formed by the unevenness of the crown surface, a mixture layer in which the region near the spark plug becomes a combustible air-fuel ratio and the peripheral region becomes a lean incombustible air-fuel ratio is formed, and stratified combustion is performed. An exhaust purification device for an internal combustion engine,
In order to separate the exhaust gas generated by actually contributing to combustion from the exhaust gas generated by the stratified combustion, the exhaust gas is separated into exhaust gas that has contributed to combustion and exhaust gas that has not contributed to combustion. The exhaust gas that contributes to the combustion flows into the first exhaust passage, and the exhaust gas that does not contribute to the combustion flows into the second exhaust passage formed in parallel to the first exhaust passage. Separating means;
First exhaust purification means located in the middle of the first exhaust passage,
The exhaust gas separation means includes a fuel injection valve that directly injects fuel into the combustion chamber, and includes a first exhaust valve on the first exhaust passage side and a second exhaust valve on the second exhaust passage side. An exhaust gas purification apparatus for an internal combustion engine that injects fuel in the direction of the first exhaust valve and causes the exhaust gas contributing to the combustion to flow into the first exhaust passage. The first exhaust purification means has a three-way catalyst,
The exhaust gas separating means, the exhaust gas that has contributed to the combustion, so that the average air-fuel ratio of that is stoichiometric, claim 1-5, characterized in that to flow into the first exhaust passage An exhaust emission control device for an internal combustion engine according to one . The first exhaust gas purification means traps and holds NOx in the exhaust gas when the air-fuel ratio of the exhaust gas that has flowed is lean and holds NOx when the air-fuel ratio of the exhaust gas that has flowed is rich A trap catalyst that reduces the exhaust gas with the reducing agent component in the exhaust gas,
The exhaust gas separating means, the exhaust gas that has contributed to the combustion, so that the average air-fuel ratio of that is lean, claim 1-5, characterized in that to flow into the first exhaust passage An exhaust emission control device for an internal combustion engine according to one . 8. The exhaust gas purification apparatus for an internal combustion engine according to claim 7 , wherein an auxiliary reducing agent can be added to the trap catalyst when the amount of NOx retained by the trap catalyst becomes a predetermined amount or more. The exhaust gas separating means, when the NOx holding amount by the trap catalyst becomes equal to or greater than a predetermined amount, the exhaust gas that has contributed to the combustion, so that the average air-fuel ratio of that is rich, the first exhaust The exhaust gas purification apparatus for an internal combustion engine according to claim 7 or 8 , wherein the exhaust gas is caused to flow into the passage . The first exhaust purification means has a selective reduction catalyst capable of flowing exhaust gas having a lean air-fuel ratio and reducing NOx in the exhaust gas that has flowed in with a reducing agent component in the exhaust gas,
The exhaust gas separating means, the exhaust gas that has contributed to the combustion, so that the average air-fuel ratio of that is lean, claim 1-5, characterized in that to flow into the first exhaust passage An exhaust emission control device for an internal combustion engine according to one . 11. The exhaust gas purification apparatus for an internal combustion engine according to claim 10, wherein an auxiliary reducing agent can be added to the selective reduction catalyst. Wherein the first exhaust passage and the second exhaust passage, and merge at the downstream side of the first exhaust gas purification device, the exhaust passage downstream from the merging portion, be provided with a second exhaust gas purification unit The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 11 , wherein The exhaust gas separation means sets the ratio of the amount of exhaust gas flowing into the first exhaust passage to the amount of exhaust gas to be exhausted from the combustion chamber at a cold time including when the engine is started to be approximately 1. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 12 , wherein the exhaust gas purification device is an internal combustion engine.

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