JP4168247B2 - 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 (hereinafter referred to as an engine), and more particularly to an exhaust gas purification apparatus that reacts and purifies NOx in exhaust gas by a NOx catalyst provided in an exhaust system.
[0002]
[Related background]
As an exhaust purification device for this type of engine, there is one that uses an HC adsorbent to efficiently purify NOx in exhaust gas with a NOx catalyst (see, for example, Patent Document 1). The exhaust emission control device described in Patent Document 1 uses NOx fuel injected from an injection nozzle as a reducing agent to react and purify NOx in exhaust gas on a selective reduction type NOx catalyst provided in an exhaust system, and to reduce the NOx catalyst. HC adsorbent is provided on the upstream side.
[0003]
The HC adsorbent has a property of adsorbing HC in the exhaust gas in a relatively low temperature range (adsorption temperature range) and desorbing the adsorbed HC when exceeding a predetermined temperature (desorption start temperature). Therefore, HC in the exhaust gas is adsorbed by the HC adsorbent when the vehicle decelerates when the temperature of the HC adsorbent decreases as the exhaust temperature decreases, and the temperature of the HC adsorbent increases along with the exhaust temperature during subsequent vehicle acceleration. When rising, the adsorbed HC is desorbed from the HC adsorbent and supplied onto the NOx catalyst together with the reducing agent from the fuel injection nozzle. As a result, the HC generated at the time of deceleration is effectively used for the reaction purification of NOx at the time of acceleration, and the HC corresponding to the NOx emission amount that increases with the acceleration is ensured.
[0004]
[Patent Document 1]
Japanese Patent No. 3252793
[0005]
[Problems to be solved by the invention]
As described above, in the technique described in Patent Document 1, although HC is effectively used by the adsorption action of the HC adsorbent, on the other hand, the technique injects light oil as a reducing agent from the fuel injection valve for supplying HC. Therefore, an increase in fuel consumption is inevitable, and an improvement in this point has been demanded.
[0006]
An object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine capable of preventing wasteful fuel consumption while realizing effective utilization of HC by reacting and purifying NOx by HC adsorbed using an HC adsorbent. It is to provide.
[0007]
[Means for Solving the Problems]
  In order to achieve the above object, the invention of claim 1Mounted on the vehicle,An internal combustion switchable between a first combustion mode and a second combustion mode in which the EGR amount is increased from the first combustion mode and the increase in HC is allowed while the smoke emission is suppressed and the NOx emission is reduced. With the agency,Corresponding to idling and vehicle decelerationControl means for causing the internal combustion engine to execute the second combustion mode in a predetermined low load region and causing the internal combustion engine to execute the first combustion mode in a region higher than the predetermined low load region; An HC adsorbent that adsorbs the HC and desorbs the adsorbed HC as the temperature rises, and a NOx catalyst that reacts and purifies the desorbed HC and NOx from the HC adsorbent, and is provided in the exhaust system of the internal combustion engine. The exhaust gas purification catalyst device is provided.
[0008]
Therefore, for example, in a low load range such as during idling or when the vehicle is decelerating, the internal combustion engine executes the second combustion mode by the control means. In the second combustion mode, the EGR is compared with the first combustion mode. By increasing the amount, the increase of HC is allowed while suppressing the emission of smoke and NOx, and the HC at this time is adsorbed by the HC adsorbent of the exhaust purification catalyst device. Thereafter, when the load increases with acceleration of the vehicle or the like, the internal combustion engine executes the first combustion mode, and HC is desorbed from the HC adsorbent of the exhaust purification catalyst device whose temperature has increased with the increase in load, This desorbed HC purifies NOx.
[0009]
Since the HC generated in the second combustion mode executed for the purpose of reducing the NOx emission amount is used in this way, the NOx in the first combustion mode is reactively purified. Therefore, useless fuel consumption can be prevented compared with the case of injecting fuel as NOx reducing agent.
The invention according to claim 2 is the selective reduction type NOx catalyst according to claim 1, wherein the NOx catalyst reduces or decomposes NOx in the presence of desorbed HC.
[0010]
Therefore, the NOx exhausted when the first combustion mode is executed is reduced or decomposed by the HC desorbed from the HC adsorbent as the temperature rises, thereby realizing efficient NOx purification.
The invention of claim 3 is the invention of claim 1, wherein the NOx catalyst stores or adsorbs NOx discharged when the first combustion mode is executed, and when the second combustion mode is executed and when HC is desorbed from the HC adsorbent. This is a NOx catalyst (storage type NOx catalyst or adsorption type NOx catalyst) that releases and reduces NOx.
[0011]
Therefore, NOx exhausted during the execution of the first combustion mode is occluded or adsorbed by the NOx catalyst, and this occluded or adsorbed NOx is desorbed from the HC adsorbent as the temperature rises in the first combustion mode. In addition to being released and reduced by the HC, in addition to the HC increased in the exhaust gas in the second combustion mode, it is released and reduced by the excess HC that has not been adsorbed by the HC adsorbent, thereby realizing efficient NOx purification. In addition, since the opportunity to naturally regenerate the storage-type NOx catalyst or the adsorption-type NOx catalyst increases in this way, the number of processes for forced regeneration, such as rich spikes, is reduced.
[0012]
According to a fourth aspect of the present invention, in the first aspect, the exhaust purification catalyst device integrally includes the HC adsorbent and the NOx catalyst.
Therefore, the HC adsorbent and the NOx catalyst are formed as a layer overlapping each other on a common carrier, or formed as a mixed single layer, and HC desorbed from the HC adsorbent is removed. It is surely captured by the NOx catalyst and used for NOx reaction purification.
[0013]
  According to a fifth aspect of the present invention, in the first aspect, the control means indicates that the index related to the temperature of the exhaust system of the internal combustion engine is the HC adsorbent.Less than or equal to the separation start temperatureIf it is within the adsorption temperature range, the index is equivalent to the HC adsorbent desorption start temperature.valueCompared with the above case, the EGR amount in the second combustion mode is increased.
  Therefore, an index related to the temperature of the exhaust system isLess than or equal to the separation start temperatureWhen it is in the range corresponding to the adsorption temperature range, it corresponds to the desorption start temperaturevalueCompared to the above case, it can be considered that the HC adsorbent retains sufficient HC adsorption capability. Therefore, even if the HC in the exhaust gas is increased by increasing the amount of EGR in the second combustion mode, the increased HC is adsorbed by the HC adsorbent, and then the HC adsorbent is adsorbed on the NOx catalyst in the first combustion mode. Sufficient desorbed HC can be supplied.
[0014]
  A sixth aspect of the present invention is the method according to the first aspect, wherein the control means indicates that the index related to the temperature of the exhaust system of the internal combustion engine is that of the HC adsorbent.Less than or equal to the separation start temperatureIf it is within the adsorption temperature range, the index is equivalent to the HC adsorbent desorption start temperature.valueCompared to the case described above, the predetermined low load region for executing the second combustion mode is expanded.
  Therefore, an index related to the temperature of the exhaust system isLess than or equal to the separation start temperatureWhen it is in the range corresponding to the adsorption temperature range, it corresponds to the desorption start temperaturevalueCompared to the above case, it can be considered that the HC adsorbent can maintain the HC adsorption capacity up to a higher load region. Therefore, the amount of HC adsorbed on the HC adsorbent increases by expanding the region of the second combustion mode, and sufficient desorbed HC can be supplied from the HC adsorbent to the NOx catalyst in the subsequent first combustion mode. It becomes.
[0015]
According to a seventh aspect of the present invention, in the first aspect, when the internal combustion engine is cold started, the control means prohibits execution of the second combustion mode for a predetermined period after the start. Therefore, when the internal combustion engine is cold started, execution of the second combustion mode is prohibited until a predetermined time elapses. Therefore, immediately after the cold start, the second combustion mode for increasing the EGR amount is executed and combustion is not performed. Prevents the situation where the HC adsorbent becomes saturated due to the HC generated in the second combustion mode immediately after the cold start, and prevents the HC from being absorbed in the low load region that is important after that. Is done.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
[First Embodiment]
Hereinafter, a first embodiment in which the present invention is embodied in an exhaust emission control device for a common rail type diesel engine will be described.
FIG. 1 is an overall configuration diagram showing an exhaust emission control device for a diesel engine according to the present embodiment. In this figure, one cylinder of the diesel engine 1 is shown, and the piston 2 disposed in the cylinder block 1a is connected to a crankshaft (not shown) via a connecting rod 3. A fuel injection valve 5 is disposed on the cylinder head 4 of the engine 1 so as to face the cylinder, and the fuel injection valve 5 is connected to a common rail 6 common to each cylinder. A fuel pump 7 is connected to the common rail 6, and high-pressure fuel supplied from the fuel pump 7 is stored in the common rail 6.
[0017]
The fuel injection valve 5 is opened at a predetermined timing near the compression top dead center, and the high-pressure fuel in the common rail 6 is injected from the fuel injection valve 5 toward the cavity 2a of the piston head, and is ignited and burned in compressed air. Then push down the piston 2. Although the configuration of the common rail system is well known and will not be described in detail, the fuel injection amount and the injection timing can be freely set by controlling the open state of the fuel injection valve 5.
[0018]
On the other hand, the cylinder of each cylinder is connected to a common intake passage 9 via an intake port 8 formed in the cylinder head 4, and an air cleaner 10 and an intake throttle valve 12 are provided in the intake passage 9 from the upstream side. ing. The cylinders of the cylinders are connected to a common exhaust passage 14 via an exhaust port 13 of the cylinder head 4. The exhaust passage 14 is connected to an exhaust throttle valve 15, an exhaust purification catalyst device 16, and the illustrated figure from the upstream side. There is no silencer.
[0019]
The exhaust purification catalyst device 16 of the present embodiment is configured as a catalyst having a honeycomb (monolith) cordierite carrier composed of a large number of cells. FIG. 2 shows a quadrant of one cell. An HC adsorption layer 16b is formed on the surface of the cordierite carrier 16a, and a selective reduction type NOx catalyst layer 16c is formed on the surface of the HC adsorption layer 16b. Yes.
[0020]
The HC adsorption layer 16b has zeolite as a main component, adsorbs HC in the exhaust gas in a relatively low adsorption temperature range, and exceeds the desorption start temperature on the high temperature side after passing through the equilibrium range from this adsorption temperature range. Has a function of desorbing. On the other hand, the selective reduction type NOx catalyst layer 16c has a function of reducing or decomposing NOx in an atmosphere where HC exists.
[0021]
The intake air introduced from the air cleaner 10 into the intake passage 9 is introduced into the cylinder through the intake throttle valve 12 as the intake valve 18 of each cylinder is opened, and is compressed as the piston 2 rises. Used for combustion as described above. The exhaust gas after combustion is discharged into the exhaust passage 14 as the exhaust valve 19 is opened, passes through the exhaust throttle valve 15, passes through the exhaust purification catalyst device 16, and is discharged into the atmosphere through the silencer.
[0022]
On the other hand, one end of an EGR passage 23 is connected to the intake passage 9 downstream of the intake throttle valve 12, and an EGR valve 21 and an EGR cooler 25 are provided in the EGR passage 23, and the other end of the EGR passage 23 is connected to the EGR passage 23. The exhaust passage 14 is connected to an upstream position of the exhaust throttle valve 15. The recirculation of EGR from the exhaust passage 14 to the intake passage 9 is performed through the EGR passage 23. When the EGR valve 21 is opened, the exhaust gas cooled by the EGR cooler 25 is recirculated through the EGR passage 23. Note that the EGR rate at this time is appropriately adjusted according to the opening degree of the EGR valve 21, the restriction of the intake air by the intake throttle valve 12, and the restriction of the exhaust gas by the exhaust throttle valve 15.
[0023]
On the other hand, an input / output device (not shown), a storage device (ROM, RAM, etc.) used for storage of a control program, a control map, etc., a central processing unit (CPU), a timer counter, etc. Control unit) 31 is installed. Various sensors such as an accelerator sensor 32 for detecting the accelerator operation amount θacc and a rotation speed sensor 33 for detecting the engine rotation speed Ne are connected to the input side of the ECU 31, and the fuel injection valve 5 and the intake throttle are connected to the output side. Various devices such as the valve 12, the exhaust throttle valve 15, and the EGR valve 12 are connected.
[0024]
The ECU 31 calculates the fuel injection amount Q from a map (not shown) based on the accelerator operation amount θacc and the engine rotation speed Ne, while calculating the fuel injection timing IT from the map (not shown) based on the engine rotation speed Ne and the fuel injection amount Q. The fuel injection valve 5 is driven and controlled based on these calculated values.
Further, the ECU 31 calculates a target excess air ratio λtgt from a map (not shown) based on the calculated values of the engine speed Ne and the fuel injection amount Q, and the EGR valve 21 is calculated from the target excess air ratio λtgt and the actual excess air ratio λ. Is controlled in feedback (that is, EGR rate).
[0025]
On the other hand, the engine 1 of the present embodiment is configured to be able to switch the combustion mode according to the operation region. The combustion mode is switched between the first combustion mode and the second combustion mode. Hereinafter, the exhaust gas characteristics in both combustion modes will be described based on the characteristic diagram of FIG.
HC emissions increase as the excess air ratio λ decreases (exhaust air / fuel ratio becomes rich), and NOx emissions increase as the excess air ratio λ increases (exhaust air / fuel ratio becomes leaner). There is a trade-off relationship. Smoke also tends to increase in a region where the excess air ratio λ is low as in the case of HC. However, in this embodiment, the fuel injection timing IT is greatly advanced in a region where the excess air ratio λ is low. In addition, the premixing time of the injected fuel and air from fuel injection to ignition is secured, and as shown in the figure, the increase in smoke is suppressed in the region where the excess air ratio λ is low. The fuel injection timing IT does not necessarily have to be advanced, and may be controlled to a constant fuel injection timing IT with respect to changes in the excess air ratio λ.
[0026]
In the first combustion mode, the EGR amount is limited to a certain extent and is controlled to the lean excess air ratio λ from the stoichio as in the case of a general diesel engine, and although the NOx emission amount slightly increases, the HC and smoke emission Exhaust gas characteristics with suppressed are realized. Further, in the second combustion mode, the EGR amount is increased and the excess air ratio λ is controlled to be richer than that in the first combustion mode, and although the HC emission amount slightly increases, NOx and smoke emission are suppressed. Exhaust gas characteristics are realized.
[0027]
The setting of the combustion mode is performed by the ECU 31 according to the map shown in FIG. 4, and the engine 1 is controlled according to the setting of the combustion mode (control means). The combustion mode is set in accordance with the engine load (specifically, the fuel injection amount Q or the like is applied) and the engine rotational speed Ne, and the second combustion mode in which the amount of fresh air is limited by a large amount of EGR recirculation is: The engine load and the engine rotational speed Ne are set in a relatively low region, and the first combustion mode is set in a region beyond that.
[0028]
Further, when the engine 1 is cold-started, the ECU 31 is prohibited from executing the second combustion mode until a predetermined time set in advance has elapsed. Therefore, even if the operation region corresponding to the second combustion mode, for example, the idle operation is continued immediately after the cold start, the first combustion mode is executed before the elapse of the predetermined time.
Next, the exhaust gas purification action exhibited by the exhaust gas purification device of the diesel engine 1 configured as described above will be described based on the time chart of FIG. The time chart shows the measurement results of NOx emission amount, catalyst temperature, and PM emission amount (correlated with smoke) when the vehicle is accelerated / decelerated according to a preset travel pattern.
[0029]
The temperature of the exhaust purification catalyst device 16 (the catalyst temperature in the figure) changes following the exhaust temperature change of the engine 1 according to the acceleration / deceleration state of the vehicle with a slight delay. For example, at the time of deceleration, the catalyst temperature decreases to the adsorption temperature range as the exhaust temperature of the engine 1 decreases, and at the time of acceleration, the catalyst temperature increases as the exhaust temperature of the engine 1 increases and starts desorption. The temperature is exceeded (for example, 160 ° C. shown in the figure).
[0030]
On the other hand, at the time of deceleration or the like, the second combustion mode is set from the map of FIG. 4 by the ECU 31 as the engine load and the engine speed Ne decrease, so that the HC in the exhaust gas increases based on the characteristics of FIG. During acceleration, the first combustion mode is set from the map of FIG. 4 by the ECU 31 as the engine load and the engine rotational speed Ne increase. Therefore, NOx in the exhaust gas increases based on the characteristics of FIG.
[0031]
As a result, as shown in FIG. 5, the period in which the catalyst temperature exceeds the desorption start temperature for each acceleration / deceleration of the vehicle is substantially synchronized with the period in which the NOx emission amount increases rapidly. The period during which the catalyst temperature decreases to the adsorption temperature range and the period during which the HC emission amount increases are substantially synchronized. Therefore, when the vehicle decelerates, etc., the increased HC in the exhaust gas is adsorbed by the HC adsorption layer 16b of the exhaust purification catalyst device 16 in the adsorption temperature range, and adsorbed by the HC adsorption layer 16b during subsequent acceleration or the like. HC is desorbed and used for reduction or decomposition of NOx in the exhaust gas on the selective reduction type NOx catalyst layer 16c on the surface side.
[0032]
Here, when the supply amount of desorbed HC is insufficient with respect to NOx in the exhaust gas, it leads to discharge of NOx, and when the supply amount of desorbed HC is excessive, it leads to discharge of HC. Therefore, in the first combustion mode, the ECU 31 controls the exhaust temperature of the engine 1 and the exhaust gas flow rate to adjust the HC desorption state from the HC adsorption layer 16b. For example, the exhaust temperature control is performed by fuel injection in the exhaust stroke, and the desorption of HC becomes more active as the exhaust temperature increases due to the increase in fuel. Further, the exhaust flow rate control is performed by limiting the intake air by the intake throttle valve 12 or by limiting the exhaust gas by the exhaust throttle valve 15, and the HC desorption becomes more active as the exhaust flow rate increases as the valve opening increases. By these exhaust temperature control and exhaust gas flow rate control, the desorbed HC is supplied without excess or deficiency according to the NOx in the exhaust gas, and the exhaust of NOx and HC can be more reliably prevented.
[0033]
As is clear from the above description, according to the exhaust gas purification device of the diesel engine 1 of the present embodiment, HC generated during vehicle deceleration or the like is temporarily adsorbed to the HC adsorption layer 16b of the exhaust gas purification catalyst device 16. Since it is effectively used for the reduction and decomposition of NOx during subsequent acceleration, NOx that rapidly increases during acceleration can be reliably purified.
[0034]
In addition, since HC generated in the second combustion mode executed in the low load low rotation range is used for the purpose of reducing the NOx emission amount, the NOx in the first combustion mode is reactively purified. Compared with the case where light oil is injected as a reducing agent from the fuel injection valve as in the technique described in Patent Document 1, it is possible to prevent wasteful fuel consumption.
[0035]
Further, since the HC adsorption layer 16b and the NOx catalyst layer 16c are formed on the exhaust purification catalyst device 16 so as to overlap each other, the HC desorbed from the HC adsorption layer 16b is reliably captured by the NOx catalyst layer 16c on the surface side. Therefore, the desorbed HC can be used for NOx reaction purification without waste.
On the other hand, when the engine 1 is cold-started, execution of the second combustion mode is prohibited until a predetermined time elapses. Therefore, immediately after the cold start, the second combustion mode for increasing the EGR amount is executed and combustion is performed. Unstable situations can be prevented. In addition, when the second combustion mode is executed immediately after the cold start, the HC adsorption layer 16b of the exhaust purification catalyst device 16 is saturated due to the adsorption of the generated HC, and HC is adsorbed at the time of subsequent critical deceleration, etc. Although there is a possibility that it can be discharged as it is, there is an advantage that such a situation can be prevented and its reliability can be improved.
[0036]
In the present embodiment, the selective reduction type NOx catalyst layer 16c is formed on the surface of the HC adsorption layer 16b of the exhaust purification catalyst device 16, but the HC adsorption layer 16b and the selective reduction type NOx catalyst, for example, as shown in FIG. The layer 16c may be formed as a single layer 16d mixed with the layer 16c. Even in this case, the same function and effect as in the embodiment can be obtained. 2 and FIG. 6, it is not always necessary to form the HC adsorption layer 16b and the NOx catalyst layer 16c on the common carrier 16a. The HC adsorbent may be provided separately.
[0037]
[Second Embodiment]
Next, a second embodiment in which the present invention is embodied in another exhaust gas purification device for a diesel engine 1 will be described. The exhaust purification apparatus of this embodiment differs from that described in the first embodiment in that an occlusion-type NOx catalyst layer 16e is formed instead of the selective reduction-type NOx catalyst layer 16c shown in FIG. The configuration is the same. Accordingly, the NOx storage / release reduction action performed by the storage-type NOx catalyst layer 16e will be described mainly.
[0038]
The storage-type NOx catalyst layer 16e stores NOx in an atmosphere with a high excess air ratio, and once releases NOx in an atmosphere with a low excess air ratio mainly containing HC and CO, then N₂It has a function of reducing to (nitrogen) or the like.
The control of the combustion mode by the ECU 31 is the same as in the first embodiment, and the second combustion mode is executed in a region where the engine load and the engine rotational speed Ne are relatively low according to the map of FIG. The combustion mode is executed. As in the first embodiment, when the vehicle decelerates, etc., HC in the exhaust gas is increased by execution of the second combustion mode, and the HC is adsorbed by the HC adsorption layer 16b in the adsorption temperature range.
[0039]
On the other hand, during the acceleration of the vehicle, etc., NOx in the exhaust gas increases due to the execution of the first combustion mode, but the NOx is occluded in the occlusion-type NOx catalyst layer 16e. At the same time, HC is desorbed from the HC adsorption layer 16b exceeding the desorption start temperature, and NOx on the storage-type NOx catalyst layer 16e is released and reduced by the desorbed HC.
Further, the NOx release reduction from the occlusion-type NOx catalyst layer 16e is also performed in the second combustion mode described above. Of the HC increased in the exhaust gas, surplus HC that has not been adsorbed by the HC adsorption layer 16b is released. Has a reducing action. Note that the NOx release action from the occlusion-type NOx catalyst layer 16e is mainly exerted by CO, but CO increases in the second combustion mode in which the excess air ratio λ is low similarly to the characteristics of HC shown in FIG. Therefore, NOx is released efficiently.
[0040]
As described above, the exhaust emission control device for the engine 1 of the present embodiment temporarily adsorbs HC generated at the time of vehicle deceleration, etc., to the HC adsorption layer 16b as in the first embodiment, and at the time of subsequent acceleration, etc. Effectively used for NOx release and reduction, NOx, which increases rapidly during acceleration, can be reliably purified, and HC generated in the first combustion mode is used to prevent wasteful fuel consumption. it can.
[0041]
In addition, since the opportunity to naturally regenerate the storage-type NOx catalyst layer 16e increases, the number of processes for forced regeneration, such as rich spikes, decreases, and this factor also contributes to the suppression of fuel consumption.
Instead of the occlusion type NOx catalyst layer 16e, an adsorption type NOx catalyst layer that exhibits NOx adsorption action may be formed as a NOx catalyst, and in this case, the same effect as that of this embodiment can be obtained.
[0042]
[Third Embodiment]
Next, a third embodiment in which the present invention is embodied in another exhaust emission control device for a diesel engine 1 will be described. The exhaust purification apparatus of the present embodiment corrects the excess air ratio λ in the second combustion mode based on the temperature of the exhaust purification catalyst apparatus 16 with respect to those described in the first and second embodiments. Are different, and the other configurations are the same. Therefore, the correction process of the excess air ratio λ, which is a difference, will be described mainly.
[0043]
  FIG. 7 is a flowchart showing an excess air ratio correction routine executed by the ECU 31, and the ECU 31 executes the routine at predetermined control intervals while the engine 1 is operating.
  First, in step S2, it is determined whether or not the second combustion mode is being performed. When the determination is NO (negative), the routine is once terminated. If the determination in step S2 is YES (positive), the process proceeds to step S4, where the temperature of the exhaust purification catalyst device 16 is in the adsorption temperature range.(A range corresponding to the adsorption temperature range below the value corresponding to the separation start temperature)It is determined whether or not. Catalyst temperature at this time(Indicator related to exhaust system temperature)May be detected directly by a sensor, for example, exhaust temperature, cooling water temperature, or cooling water temperature at start-up and elapsed time after start-up(Indicator related to exhaust system temperature)It may be estimated based on the relationship betweenNote that the separation start temperature (the value corresponding to the separation start temperature) that defines the adsorption temperature range (the range corresponding to the adsorption temperature range equal to or less than the value corresponding to the separation start temperature) is, for example, 160 ° C. shown in FIG.
[0044]
When the determination in step S4 is NO, the process proceeds to step S6, where the normal value based on FIG. 3 is set as the target value λtgt of the excess air ratio λ in the second combustion mode, and the determination in step S4 is YES In step S8, the target value λtgt of the excess air ratio λ is corrected to the rich side by a predetermined amount. Therefore, the second combustion mode is executed while the excess air ratio λ is controlled based on the set target value λtgt.
[0045]
That is, when the catalyst temperature is in the adsorption temperature range, it means that the HC adsorption layer 16b of the exhaust purification catalyst device 16 has sufficient HC adsorption capability. The amount of HC adsorbed by the HC adsorption layer 16b during the second combustion mode is increased. As a result, in the exhaust purification system of the present embodiment, the desorbed HC from the HC adsorption layer 16b is sufficiently supplied to the NOx catalyst layers 16c and 16e in the subsequent first combustion mode. Compared with the form, the NOx purification effect can be further improved.
[0046]
In step S4, the estimated catalyst temperature is compared with the adsorption temperature range. However, the present invention is not limited to this. For example, instead of the adsorption temperature range, it may be compared with a predetermined temperature set on a lower temperature side.
[Fourth Embodiment]
Next, a fourth embodiment in which the present invention is embodied in another exhaust gas purification device for a diesel engine 1 will be described. The exhaust emission control device of the present embodiment is different in that the second combustion mode region is switched instead of the correction process of the excess air ratio λ described in the third embodiment, and the other configurations are the same. . Therefore, the second combustion mode region switching process, which is a difference, will be described mainly.
[0047]
FIG. 8 is a flowchart showing an area switching routine executed by the ECU 31, and the ECU 31 executes the routine at predetermined control intervals while the engine 1 is operating.
First, when it is determined in step S2 that the second combustion mode is in the same manner as in the third embodiment, the process proceeds to step S4 to determine whether or not the catalyst temperature is in the adsorption temperature range. When the determination is NO, the process proceeds to step S12, and the normal area indicated by the solid line in FIG. 4 is set as the second combustion mode area. When the determination in step S4 is YES, the process proceeds to step S14. As the region of the second combustion mode, the region is enlarged as shown by a two-dot chain line in FIG. Therefore, the second combustion mode is executed based on the set region.
[0048]
That is, when the catalyst temperature is in the adsorption temperature range, it can be considered that the HC adsorption layer 16b can maintain the HC adsorption capacity up to a region where the engine load and the engine rotational speed Ne are higher, so the second combustion mode region is expanded. It is doing. As a result, in the exhaust purification device of the present embodiment, the amount of HC adsorbed on the HC adsorption layer 16b increases as in the third embodiment, so that the desorbed HC from the HC adsorption layer 16b in the subsequent second combustion mode. Is sufficiently supplied to the NOx catalyst layers 16c and 16e, and the NOx purification effect can be further improved as compared with the first and second embodiments.
[0049]
This is the end of the description of the embodiment, but the aspect of the present invention is not limited to this embodiment. For example, in each embodiment, the exhaust gas purification device of the common rail type diesel engine 1 is embodied. However, the present invention is not limited to this, and for example, the exhaust gas purification device of a general diesel engine that controls the fuel injection with a governor. May be used.
[0050]
In each of the above embodiments, the combustion mode is set according to the engine load and the engine speed Ne. However, it is not always necessary to consider the engine speed Ne, and the combustion mode may be set based only on the engine load. Good.
Furthermore, in the third embodiment, the excess air ratio λ in the second combustion mode is corrected based on the catalyst temperature, and in the fourth embodiment, the region of the second combustion mode is switched based on the catalyst temperature. These processes may be combined.
[0051]
【The invention's effect】
As described above, according to the exhaust gas purification apparatus for an internal combustion engine of the first to third aspects of the present invention, since NOx is reacted and purified by HC adsorbed using the HC adsorbent, effective use of HC can be realized, and NOx Since HC generated in the second combustion mode for reducing the emission amount is adsorbed by the HC adsorbent, it is possible to prevent wasteful fuel consumption.
[0052]
  According to the exhaust gas purification apparatus for an internal combustion engine of the fourth aspect of the invention, in addition to the first aspect, since the HC adsorbent and the NOx catalyst are integrated, the desorbed HC is reliably captured by the NOx catalyst, and the NOx is eliminated. It can be used for purification of reaction.
  According to the exhaust gas purification apparatus for an internal combustion engine of the fifth and sixth aspects of the invention, in addition to the first aspect, the index related to the temperature of the exhaust system isLess than or equal to the separation start temperatureIf the adsorption capacity of the HC adsorbent is in the range corresponding to the adsorption temperature range, the amount of HC adsorbed on the HC adsorbent is increased by increasing the EGR amount or expanding the second combustion mode region. Therefore, the NOx purification effect can be further improved.
[0053]
According to the exhaust gas purification apparatus for an internal combustion engine of the seventh aspect of the invention, in addition to the first aspect, since the execution of the second combustion mode is prohibited until a predetermined time elapses during the cold start of the internal combustion engine, In addition to preventing instability, the saturation of the HC adsorbent can prevent the situation in which HC cannot be adsorbed in the low load region, thereby improving its reliability.
[Brief description of the drawings]
FIG. 1 is an overall configuration diagram showing an exhaust emission control device for a diesel engine according to an embodiment.
FIG. 2 is an enlarged cross-sectional view showing a quadrant of a cell of the exhaust purification catalyst device.
FIG. 3 is a characteristic diagram showing exhaust gas characteristics in first and second combustion modes.
FIG. 4 is an explanatory diagram showing a map for setting a combustion mode.
FIG. 5 is a time chart showing measurement results of NOx emission amount, catalyst temperature, and PM emission amount accompanying acceleration / deceleration of the vehicle.
FIG. 6 is an enlarged cross-sectional view showing a quadrant of a cell of another example of the exhaust purification apparatus in which the HC adsorption layer and the NOx catalyst layer are a single layer.
FIG. 7 is a flowchart showing an excess air ratio correction routine executed by an ECU according to a third embodiment.
FIG. 8 is a flowchart showing an area switching routine executed by an ECU according to a fourth embodiment.
[Explanation of symbols]
1 engine (internal combustion engine)
16 Exhaust gas purification catalyst device
16b HC adsorption layer (HC adsorbent)
16c Selective reduction type NOx catalyst layer (selective reduction type NOx catalyst)
16e NOx storage layer (NOx catalyst)
31 ECU (control means)

Claims (7)

A first combustion mode that is mounted on a vehicle, and a second combustion mode that suppresses smoke emission and reduces NOx emission while allowing an increase in HC by increasing the EGR amount from the first combustion mode. An internal combustion engine capable of switching between,
The internal combustion engine is caused to execute the second combustion mode in a predetermined low load range corresponding to idle operation and vehicle deceleration, and the internal combustion engine has the first combustion mode in a region higher in load than the predetermined low load range. Control means for executing the combustion mode;
An HC adsorbent that adsorbs HC in the exhaust gas of the internal combustion engine and desorbs adsorbed HC as the temperature rises, and a NOx catalyst that reacts and purifies the desorbed HC and NOx from the HC adsorbent, An exhaust purification catalyst device for an internal combustion engine, comprising: an exhaust purification catalyst device provided in an exhaust system of the internal combustion engine. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the NOx catalyst is a selective reduction type NOx catalyst that reduces or decomposes NOx in the presence of desorbed HC. The NOx catalyst is a NOx catalyst that occludes or adsorbs NOx discharged when the first combustion mode is executed, and releases and reduces NOx when the second combustion mode is executed and when HC is desorbed from the HC adsorbent. 2. An exhaust emission control device for an internal combustion engine according to claim 1, wherein: 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the exhaust gas purification catalyst apparatus integrally includes the HC adsorbent and the NOx catalyst. When the index related to the temperature of the exhaust system of the internal combustion engine is in a range corresponding to the adsorption temperature range equal to or less than the value corresponding to the start temperature of the HC adsorbent, the control means starts the start of HC adsorbent detachment. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the EGR amount in the second combustion mode is increased as compared with a case where the temperature is equal to or higher than a temperature equivalent value . When the index related to the temperature of the exhaust system of the internal combustion engine is in a range corresponding to the adsorption temperature range equal to or less than the value corresponding to the start temperature of the HC adsorbent, the control means starts the start of HC adsorbent detachment. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein a predetermined low load region in which the second combustion mode is executed is expanded as compared with a case where the temperature is equal to or higher than a temperature equivalent value . 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein when the internal combustion engine is cold-started, the control means prohibits execution of the second combustion mode for a predetermined period after the start-up. .

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