JP4196593B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust emission control device that purifies harmful components contained in exhaust gas of an internal combustion engine.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, this type of exhaust emission control device is configured to include, for example, a filter structure (hereinafter referred to as a filter) for purifying particulates such as soot contained in the exhaust of a diesel engine together with NOx in the exhaust passage of the engine. The As a filter having such a function, for example, a filter in which a noble metal catalyst is supported on a porous ceramic structure is known. The filter having such a structure has a function of once collecting fine particles such as soot contained in the exhaust and oxidizing and removing the same, and also absorbs nitrogen oxide (NOx) contained in the exhaust and a reducing component in the exhaust. It also has a function of repeating the action of reducing and purifying under a high amount condition (in a rich atmosphere).
[0003]
By the way, due to the characteristics of the filter that once collects the particulates in the exhaust gas and then oxidizes and removes them, the particulate collection efficiency may vary depending on the state of the exhaust gas that passes through the filter (for example, temperature, particulate concentration, etc.). The oxidation removal efficiency may be exceeded, and in such a case, there is a concern that the filter may be clogged.
[0004]
As a measure against such a problem, an exhaust passage structure as shown in FIG. 6 is considered (for example, JP-A-7-189656). In the passage structure 200 shown in FIG. 6, by operating a passage switching valve (for example, a butterfly valve) 201, the flow of exhaust gas from one end to the other end of both ends of the filter 202 (forward flow: FIG. 6 (a)) and the flow in the opposite direction (reverse flow: the mode shown in FIG. 6 (b)) can be switched alternatively. When the exhaust gas passes through the filter 202, the temperature of the exhaust gas exhaust side at both ends of the filter 202 locally rises due to the oxidation reaction heat of the fine particles originating from the exhaust gas. For this reason, if the passage structure as described above is adopted and the flow of the exhaust gas passing through the filter 202 is periodically switched, the temperature of the filter 202 is increased at both ends thereof, and the filter The distribution of the fine particles collected in 202 is made uniform. As a result, the fine particles are oxidized and removed more efficiently, and the occurrence of clogging is suitably suppressed.
[0005]
[Problems to be solved by the invention]
By the way, in the passage structure as described above, a part of the exhaust gas flowing from the upstream is, for example, a passage switching valve and an exhaust passage at a portion where a passage switching valve (or a mechanism having the same function) is provided. It passes through the gap existing between the inner wall of the exhaust gas and is discharged downstream (outside) of the exhaust passage without passing through the filter. Such exhaust passage is particularly noticeable when the passage switching valve is operated.
[0006]
The present invention has been made in view of such circumstances, and an object of the present invention is to provide a filter in an exhaust gas purification apparatus for an internal combustion engine having a filter for collecting particulates in exhaust gas in an exhaust passage. An object of the present invention is to provide an exhaust gas purification apparatus for an internal combustion engine that can reduce the consumption of reducing components necessary for functioning and can improve the efficiency of an exhaust gas purification function using a filter.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, (1) the present invention is provided in an exhaust system of an internal combustion engine, and includes a first exhaust passage provided in the middle of the passage with a filter for collecting particulates in the exhaust. A filter for collecting particulates is connected to a second exhaust passage provided in the middle of the passage, a passage opening end on the upstream side of the first exhaust passage, and a passage opening end on the upstream side of the second exhaust passage. A collecting space portion, a first collecting passage connected to the collecting space portion, a passage opening end downstream of the first exhaust passage, and a passage opening end downstream of the second exhaust passage; A second exhaust passage, a third exhaust passage communicating between the collective space portion and the second collective passage, and the first exhaust passage and the second exhaust passage provided in the collective space portion. An adjustment valve mechanism for adjusting a connection state of the first collecting passage with respect to the third exhaust passage; The provided, the introduced exhaust through the first collecting passage, an exhaust gas purification device for an internal combustion engine to be discharged through the second manifolds, the adjusting valve mechanism As a single valve body that can rotate in the collective space portion, by rotating in the collective space portion, The first exhaust passage, the second exhaust passage, the connection state of the first collecting passage to the third exhaust passage, at least the first exhaust passage is connected to the first collecting passage, A first connection state in which the second exhaust passage and the third exhaust passage are blocked from the first collecting passage, and the second exhaust passage is connected to the first collecting passage. On the other hand, the first exhaust passage and the third exhaust passage are disconnected from the first exhaust passage, and the third connection passage is connected to the first collecting passage. And the first connection state and the second connection state are switched to each other without going through the third connection state. With a single valve body capable of This is the gist.
[0008]
In each of the exhaust passages, the upstream passage opening end means the passage opening end on the exhaust side, and the downstream passage opening end means the passage opening end on the exhaust side.
[0009]
In addition, the function of “connecting and blocking other passages with respect to a predetermined passage” widely means a function of relatively changing the connection state between the passages. For example, 90% passage open state may mean connection between the passages, and 20% passage open state may mean blockage between the passages. Further, based on the function of “connecting and blocking other paths with respect to the predetermined path” described above, the distance between the paths may be adjusted to an intermediate stage between “connection” and “blocking”. .
[0010]
According to this configuration, the exhaust gas moving from the first collecting passage as the starting point and the second collecting passage as the ending point is the filter provided in the first exhaust passage, and the filter provided in the second exhaust passage. Passes through at least one of them. For this reason, when switching the two types of exhaust flow paths, it is possible to avoid a problem that fine particles to be collected by any of the filters pass through the second collecting passage.
[0011]
That is, when the first exhaust passage provided with a filter for collecting particulates in the exhaust, the second exhaust passage provided with a filter for collecting particulates in the exhaust, and both the filters are clogged, etc. And a third exhaust passage having a separate exhaust passage, and a function of a filter for collecting particulates in the exhaust in the first exhaust passage, and an exhaust in the second exhaust passage. In addition to being able to switch between the functions of the filter that collects the particulates inside, the structure of the exhaust passage that does not allow exhaust to flow into the third exhaust passage when switching between the two functions is easily realized. can do.
[0012]
(2) Means for estimating or detecting the amount of particulates collected by the filter of the first exhaust passage and the amount of particulates collected by the filter of the second exhaust passage, and the estimation Alternatively, the adjustment valve mechanism is driven in accordance with the amount of the detected fine particles, and the connection state of the first collecting passage with respect to the first exhaust passage, the second exhaust passage, and the third exhaust passage is changed to the third exhaust passage. And a control means for shifting to the connected state.
[0013]
According to this configuration, for example, when a problem such as clogging occurs in the filter of the first exhaust passage or the filter of the second exhaust passage, the exhaust passage is secured reliably and promptly to increase the exhaust pressure. Can be suppressed.
[0014]
(3) The filter provided in the first exhaust passage and the filter provided in the second exhaust passage occlude NOx contained in the exhaust in an oxidizing atmosphere and reduce the occluded NOx in a reducing atmosphere. It is preferable to have a function of reducing with.
[0015]
According to this configuration, the action of purifying fine particles and the action of purifying NOx by each filter can be synergistically enhanced. Further, NOx occluded in the catalyst in the first exhaust passage can be efficiently released and reduced without increasing the pressure of the exhaust upstream of the first collecting passage. In other words, the exhaust gas purification function of the catalyst (or filter) provided in the first exhaust passage and the exhaust gas purification function of the catalyst (or filter) provided in the second exhaust passage are alternately used to efficiently Exhaust gas purification can be performed continuously.
[0016]
(4) In the first exhaust passage, a first reduction is provided between a passage opening end forming the first collecting passage and the filter, and a reducing agent is added to the first exhaust passage. In the second exhaust passage, a second agent that is provided between a passage opening end that forms the second collecting passage and the filter, and that adds a reducing agent into the second exhaust passage. And a reducing agent addition means.
[0017]
Using the same configuration, for example, under a predetermined condition, the first exhaust passage is a sealed space, and the reducing agent is added using the first reducing agent adding means, whereby the gas having a high reducing component concentration is While retaining in the sealed space, a sufficient exhaust flow rate is secured in a route starting from the first collecting passage and ending at the second collecting passage through the second exhaust passage. In this way, NOx occluded in the filter of the first exhaust passage can be efficiently released and reduced without increasing the pressure of the exhaust upstream of the first collecting passage. Also, under other conditions, the second exhaust passage is a sealed space, and the reducing agent is added using the second reducing agent adding means so that a gas having a high reducing component concentration stays in the sealed space. On the other hand, a sufficient exhaust flow rate is ensured in a route starting from the first collecting passage and ending at the second collecting passage through the first exhaust passage. By applying such a configuration, NOx occluded in the filter of the second exhaust passage can be efficiently released and reduced without increasing the pressure of the exhaust upstream of the first collecting passage. That is, according to the same configuration, the exhaust gas purification function of the filters provided in the two types of exhaust passages (the function of temporarily storing, releasing, and reducing NOx) is alternately used to continue efficient exhaust gas purification. Can be done automatically.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which an exhaust gas purification apparatus for an internal combustion engine according to the present invention is applied to a diesel engine system will be described.
[0019]
[Engine system structure and function]
In FIG. 1, an internal combustion engine (hereinafter referred to as an engine) 1 is an in-line four-cylinder diesel engine system that includes a fuel supply system 10, a combustion chamber 20, an intake system 30, an exhaust system 40, and the like as main parts.
[0020]
First, the fuel supply system 10 includes a supply pump 11, a common rail 12, a fuel injection valve 13, a shutoff valve 14, a metering valve 16, fuel addition valves 17a and 17b, an engine fuel passage P1, an addition fuel passage P2, and the like. Is done.
[0021]
The supply pump 11 makes the fuel pumped up from a fuel tank (not shown) into a high pressure and supplies it to the common rail 12 via the engine fuel passage P1. The common rail 12 has a function as a pressure accumulation chamber that holds (accumulates) the high-pressure fuel supplied from the supply pump 11 at a predetermined pressure, and distributes the accumulated fuel to each fuel injection valve 13. The fuel injection valve 13 is an electromagnetic valve provided with an electromagnetic solenoid (not shown) therein, and is appropriately opened to inject and supply fuel into the combustion chamber 20.
[0022]
On the other hand, the supply pump 11 distributes and supplies part of the fuel pumped up from the fuel tank to the fuel addition valves 17a and 17b via the addition fuel passage P2. In the addition fuel passage P2, a shutoff valve 14 and a metering valve 16 are sequentially arranged from the supply pump 11 toward the fuel addition valves 17a and 17b. The shutoff valve 14 shuts off the fuel supply P2 in an emergency and stops the fuel supply. The metering valve 16 controls the pressure (fuel pressure) PG of fuel supplied to the fuel addition valves 17a and 17b. The fuel addition valves 17a and 17b are electromagnetic valves provided with electromagnetic solenoids (not shown) therein, and the fuel functioning as a reducing agent is introduced into the filter casing 100 of the exhaust system 40 at an appropriate amount and at an appropriate timing. Add supply.
[0023]
The intake system 30 forms a passage (intake passage) for intake air supplied into each combustion chamber 20. On the other hand, the exhaust system 40 forms a passage (exhaust passage) for exhaust gas discharged from each combustion chamber 20.
[0024]
The engine 1 is provided with a known supercharger (turbocharger) 50. The turbocharger 50 includes rotating bodies 52 and 53 connected via a shaft 51. One rotating body (turbine wheel) 52 is exposed to exhaust in the exhaust system 40, and the other rotating body (compressor wheel) 53 is exposed to intake air in the intake system 30. The turbocharger 50 having such a configuration performs so-called supercharging in which the compressor wheel 53 is rotated using the exhaust flow (exhaust pressure) received by the turbine wheel 52 to increase the intake pressure.
[0025]
In the intake system 30, an intercooler 31 provided in the turbocharger 50 forcibly cools the intake air whose temperature has been raised by supercharging. The throttle valve 32 provided further downstream than the intercooler 31 is an electronically controlled on-off valve whose opening degree can be adjusted steplessly, and changes the flow area of the intake air under predetermined conditions. And the function of adjusting the supply amount (flow rate) of the intake air.
[0026]
Further, an exhaust gas recirculation passage (EGR passage) 60 that connects the intake system 30 and the exhaust system 40 is formed in the engine 1. The EGR passage 60 has a function of returning a part of the exhaust to the intake system 30 as appropriate. The EGR passage 60 is opened and closed steplessly by electronic control, and an EGR valve 61 that can freely adjust the flow rate of exhaust gas (EGR gas) flowing through the passage, and exhaust gas that passes (refluxs) the EGR passage 60. An EGR cooler 62 for cooling is provided.
[0027]
In the exhaust system 40, a filter casing 100 is provided downstream of the turbocharger 50 (turbine wheel 52). Inside the filter casing 100, a particulate filter (not shown) having a function of purifying particulates contained in exhaust gas and purifying NOx is housed.
[0028]
In addition, each part of the engine 1 is attached with various sensors that output signals relating to the environmental conditions of the part and the operating state of the engine 1.
[0029]
That is, the rail pressure sensor 70 outputs a detection signal corresponding to the fuel pressure stored in the common rail 12. The added fuel pressure sensor 71 outputs a detection signal corresponding to the pressure in the added fuel passage P2. The air flow meter 72 outputs a detection signal corresponding to the flow rate (intake amount) GA of intake air downstream of the throttle valve 32 in the intake system 30. The oxygen concentration sensor 73 outputs a detection signal corresponding to the oxygen concentration in the exhaust gas downstream of the filter casing 100 of the exhaust system 40. The exhaust gas temperature sensor 74 outputs a detection signal corresponding to the temperature in the exhaust gas downstream of the filter casing 100. The differential pressure sensor 75 outputs a detection signal corresponding to the difference between the exhaust pressure upstream of the filter casing 100 and the exhaust pressure downstream. The accelerator position sensor 76 is attached to an accelerator pedal (not shown) of the engine 1 and outputs a detection signal corresponding to the depression amount ACC to the pedal. The crank angle sensor 77 outputs a detection signal (pulse) every time the output shaft (crankshaft) of the engine 1 rotates by a certain angle. These sensors 70 to 77 are electrically connected to an electronic control unit (ECU) 90.
[0030]
The ECU 90 includes a central processing unit (CPU) 91, a read-only memory (ROM) 92, a random access memory (RAM) 93, a backup RAM 94, a timer counter 95, and the like. These units and an external input including an A / D converter The circuit 96 and an external output circuit 97 are provided with a logic operation circuit configured by being connected by a bidirectional bus 98.
[0031]
The ECU 90 configured as described above inputs the detection signals of the various sensors via an external input circuit, grasps various parameters relating to the operating state of the engine 1 based on these signals, and determines the engine 1 based on these parameters. Various controls are implemented to optimize the operating state of
[0032]
The filter casing 100 and the ECU 90 that controls its function together constitute an exhaust purification device of the engine 1.
[0033]
[Overview of fuel injection control]
The ECU 90 performs fuel injection control based on the operating conditions of the engine 1 grasped from the detection signals of various sensors. In the present embodiment, the fuel injection control is related to the fuel injection into each combustion chamber 20 through each fuel injection valve 13 by setting parameters such as the fuel injection amount Q, the injection timing, and the injection pattern. This is a series of processes for executing the opening / closing operation of the individual fuel injection valves 13 based on the set parameters.
[0034]
The ECU 90 repeats such a series of processes every predetermined time during the operation of the engine 1. The fuel injection amount Q and the injection timing are basically a map set in advance based on the accelerator pedal depression amount ACC and the engine speed NE (a parameter that can be calculated based on the pulse signal of the crank angle sensor). Determined with reference to (not shown).
[0035]
Further, regarding the setting of the fuel injection pattern, the ECU 90 obtains engine output by performing fuel injection in the vicinity of compression top dead center for each cylinder as well as fuel output prior to main injection (hereinafter referred to as pilot injection). ) And fuel injection following the main injection (hereinafter referred to as post-injection) are performed for the selected cylinder at the time appropriately selected as the sub-injection. When a fuel injection mode involving pilot injection or post injection is applied, the amount of light HC and CO that are not completely burned in the combustion chamber 20 and discharged to the exhaust system 40 increases, and these HC and CO are exhausted. Inside, an exothermic reaction takes place, particularly via a NOx catalyst. That is, by performing the pilot injection, the temperature of the exhaust gas flowing into the filter casing 100 and the NOx catalyst can be increased.
[0036]
[Structure of filter casing]
Next, the structure and function of the filter casing 100 provided in the exhaust system 40 will be described in detail.
[0037]
FIG. 2 is a cross-sectional view schematically showing the main internal structure of the filter casing 100.
[0038]
As shown in FIG. 2, three types of passage spaces such as a first exhaust passage 110, a second exhaust passage 120, and a third exhaust passage 130 are defined in the filter casing 100. Particulate filters (hereinafter referred to as filters) 111 and 121 are accommodated in the middle of the first exhaust passage 110 and the second exhaust passage 120, and the oxidation catalyst 131 is disposed in the middle of the third exhaust passage 130. Is housed.
[0039]
One passage opening end of the first exhaust passage 110, one passage opening end of the second exhaust passage 120, and one passage opening end of the third exhaust passage 130 are each in the first collective space 140. To the first collecting passage 40a upstream of the filter casing 100 of the exhaust system 40. The rotary valve 141 provided in the first collective space 140 includes a rotating shaft 140a that rotates based on a command signal from the ECU 90, and a valve body 140b that is attached to the outer periphery of the rotating shaft 140a. It has a function as an adjusting valve mechanism for adjusting the connection state between 120, 130, and 40a.
[0040]
On the other hand, the other passage opening end of the first exhaust passage 110, the other passage opening end of the second exhaust passage 120, and the other passage opening end of the third exhaust passage 130 are each in the second collective space. It is connected to the second collecting passage 40 b downstream of the filter casing 100 of the exhaust system 40 via the portion 150.
[0041]
Further, in the first exhaust passage 110, a fuel addition valve in which an injection hole faces the first exhaust passage 110 between the passage opening end connected to the first collecting space 140 and the filter 111. 17a is provided. Similarly, in the second exhaust passage 120, the fuel addition is made between the filter 121 and the passage opening end connected to the first collecting space portion 140 so that the injection hole faces the first exhaust passage 110. A valve 17a is provided. As described above, the fuel addition valves 17a and 17b are electromagnetic valves provided with electromagnetic solenoids (not shown) therein, and the fuel functioning as a reducing agent can be added and supplied at an appropriate amount and at an appropriate timing.
[0042]
The porous material forming the filters 111 and 121 is a ceramic material such as cordierite, which is coated with a coating material such as alumina, titania, zirconia, or zeolite, and has a property of transmitting exhaust gas. Further, the filters 111 and 121 are so-called wall flows each having an exhaust inflow passage whose upstream end is opened in parallel with each other and whose downstream end is closed, and an exhaust outflow passage whose upstream end is closed and its downstream end is opened. It is a type. And, for example, potassium (K), sodium (Na), lithium (Li), cesium (Cs) functioning as a NOx occlusion agent on the surface of the partition wall between the two exhaust passages and in the pores formed inside. ), An alkaline earth such as barium (Ba), calcium (Ca), a rare earth such as lanthanum (La) or yttrium (Y), and platinum that functions as an oxidation catalyst (noble metal catalyst). A noble metal such as Pt) is supported. As described above, the NOx storage agent and the noble metal catalyst mixed in the carrier layer as the constituent elements of the filters 111 and 121 constitute a NOx catalyst (storage reduction type NOx catalyst).
[0043]
The filters 111 and 121 having such a structure purify particulates such as soot and harmful components such as NOx contained in the exhaust gas based on the following mechanism.
[0044]
The NOx storage agent stores NOx in a state where the oxygen concentration in the exhaust gas is high (in a lean atmosphere), and is in a state where the oxygen concentration in the exhaust gas is low (a state where the concentration of the reducing component is high) (in a rich atmosphere). ) It has the characteristic of releasing NOx. Further, when NOx is released into the exhaust gas, if HC, CO, or the like is present in the exhaust gas, the noble metal catalyst promotes an oxidation reaction of these HC and CO, so that NOx is an oxidizing component, and HC and CO is removed. A redox reaction as a reducing component occurs between the two. That is, HC and CO are CO ₂ And H ₂ Oxidized to O, NOx is N ₂ Reduced to
[0045]
On the other hand, if the NOx storage agent stores a predetermined limit amount of NOx even when the oxygen concentration in the exhaust gas is high, the NOx storage agent does not store NOx any more. In the engine 1, for example, the concentration of the reducing component in the exhaust gas is increased by intermittently supplying the reducing component to the NOx catalysts 111 and 121 in the filter casing 100 through the fuel addition valves 17a and 17b. Before the NOx occlusion amount of the NOx catalyst (NOx occlusion agent) reaches the limit amount, this reducing component periodically releases and reduces and purifies NOx occluded in the NOx catalyst, and the NOx occlusion capacity of the NOx occlusion agent. Will be restored (function replayed).
[0046]
Further, the NOx storage agent has a characteristic of generating active oxygen as a secondary process in the process of repeatedly storing, releasing, and purifying NOx in cooperation with the noble metal catalyst. When the exhaust gas passes through the filters 111 and 121, particulates such as soot contained in the exhaust gas are captured by the structure (porous material). Here, since the active oxygen produced by the NOx storage agent has an extremely high reactivity (activity) as an oxidant, fine particles deposited on or near the surface of the NOx catalyst among the captured fine particles It reacts quickly with oxygen (without emitting a luminous flame) and is purified. Further, the filters 111 and 121 efficiently raise the temperature of themselves by the reaction heat generated from the NOx catalyst to enhance the decomposition action of the fine particles.
[0047]
The oxidation catalyst 131 accommodated in the middle of the third exhaust passage 130 is formed of a straight flow type honeycomb structure whose surface is coated with a noble metal such as Pd and Pt, and passes through the honeycomb structure. It promotes the oxidation of hydrocarbons (HC), carbon monoxide (CO) and nitrogen monoxide (NO) in the exhaust.
[0048]
FIG. 3 shows the internal structure of the filter 111 provided in the first exhaust passage 110. 3A is an enlarged plan view of the exhaust inflow surface of the filter 111, and FIG. 3B is an exhaust passage route inside the filter 111 (III-III in FIG. 3A). It is sectional drawing which shows a cross section schematically. Note that the filter 121 provided in the second exhaust passage 120 also has the same internal structure as the filter 111.
[0049]
As shown in FIGS. 3A and 3B, the filter 111 includes a plurality of passages 111b partitioned by a porous material (for example, cordierite) 111a having a honeycomb structure. One end of each passage 111b is closed by a stopper 111c, and the other end is open. Therefore, the exhaust gas flowing in from the opening end of each passage flows into the other adjacent passage by passing through the porous material forming the inner wall of the passage, and is discharged from the opening end of the other passage. .
[0050]
For example, as shown in FIG. 3B, when exhaust is introduced from one surface 111d of the filter 111, it flows in the filter 111 along a path indicated by a solid arrow in the same figure. Further, when exhaust is introduced from the other surface 111e of the filter 111, it flows in the filter 111 along a path indicated by a dashed arrow in the figure.
[0051]
[Various controls for utilizing the filter casing function]
The ECU 90 performs control (flow path switching control) for changing the exhaust flow path in the filter casing 100 through operation of the rotary valve 141 so that efficient exhaust purification is performed in the filter casing 100, the fuel addition valve 17a, Various controls related to the function of the filter casing 100, such as control for adding and supplying fuel (reducing agent) through 17b (reducing agent addition control), are executed at appropriate timing.
[0052]
(1) Catalyst regeneration control
Next, flow path switching control (catalyst regeneration control) for NOx catalyst regeneration that is executed to release and reduce NOx stored in the NOx catalyst in the filters 111 and 121 will be described.
[0053]
As the operation of the engine 1 continues, the amount of NOx stored in the NOx catalyst in the filters 111 and 121 gradually increases. The engine 1 periodically performs fuel addition control for supplying fuel (reducing component) into the exhaust gas that passes through the filters 111 and 121 through the fuel addition valves 17a and 17b. By performing the fuel addition control, the NOx occluded in the NOx catalyst can be released and reduced and purified before the NOx occlusion amount of the NOx catalyst reaches the limit amount, and the NOx occlusion capacity of the NOx catalyst can be recovered. In addition, the particulate matter trapped by the filters 111 and 121 is also efficient due to the reaction heat generated from the NOx catalyst accompanying the periodic implementation of fuel addition control and the action of active oxygen generated by the NOx catalyst (NOx storage agent). Will be decomposed and removed.
[0054]
Here, in order for the reducing component supplied through the fuel addition control to efficiently react with the NOx occluded in the NOx catalyst, the flow of the exhaust gas passing through the NOx catalyst is made sufficiently gentle during the control, It is necessary to provide sufficient opportunity for the exhaust gas containing the reducing component at a concentration to react with the NOx stored in the NOx catalyst. On the other hand, if the exhaust flow stays, the pressure in the exhaust system 40 increases, and there is a concern that this increase in pressure affects the combustion state of the engine 1 and the like.
[0055]
Therefore, in the engine 1 according to the present embodiment, when the fuel addition control is performed, the exhaust gas containing the reducing component gradually passes through the NOx catalyst, while the exhaust system 40 as a whole secures a sufficient exhaust gas flow rate. An exhaust passage is formed.
[0056]
FIG. 4A and FIG. 4B are schematic views illustrating the basic type of the exhaust passage formed in the filter casing 100 when performing catalyst regeneration control.
[0057]
First, when the rotary valve 141 is in the state shown in FIG. 4A, a passage space connecting the first collecting passage 40a and the first exhaust passage 110 is secured, while the first collecting passage 40a has On the other hand, the second exhaust passage 120 and the third exhaust passage 130 are blocked or at least a substantial passage cross section at the boundary portion between each passage (between the passages 40a and 120 or between the passages 40a and 130) is reduced. Is done. That is, an exhaust passage is formed that flows into the filter casing 100 from the first collecting passage 40a and is discharged to the second collecting passage 40b through the first exhaust passage 110. Further, the gas in the second exhaust passage 120 stays in the passage 120. The ECU 90 operates the rotary valve 141 at an appropriate timing to form such an exhaust passage in the filter casing 100, and additionally supplies fuel (reducing agent) to the second exhaust passage 120 through the fuel addition valve 17b. .
[0058]
Next, when the rotary valve 141 is in the state shown in FIG. 4B, a passage space connecting the first collecting passage 40a and the second exhaust passage 120 is secured, while the first collecting passage 40a. On the other hand, the substantial passage cross section at the boundary portion between at least the first exhaust passage 110 and the third exhaust passage 130 (between the passages 40a and 120 or between the passages 40a and 130) is reduced. That is, an exhaust passage is formed that flows into the filter casing 100 from the first collecting passage 40a and is discharged to the second collecting passage 40b through the second exhaust passage 120. Further, the gas in the second exhaust passage 110 stays in the passage 110. The ECU 90 operates the rotary valve 141 at an appropriate timing to form such an exhaust passage in the filter casing 100, and additionally supplies fuel (reducing agent) to the first exhaust passage 110 through the fuel addition valve 17a. .
[0059]
In this way, in the engine 1, NOx is temporarily stored in the filters 111 and 121 accommodated in the filter casing 100, and then periodically released / reduced, whereby NOx in exhaust gas generated in association with engine operation. Purify continuously.
[0060]
By the way, it is normal that the fuel of the internal combustion engine contains a sulfur compound. In addition to NOx, there are also sulfur components originating from the sulfur compound in the fuel. Sulfur components present in the exhaust are combined with the NOx catalyst at a higher efficiency than NOx, and moreover under conditions sufficient to release the NOx stored in the catalyst (the concentration of the reducing component in the exhaust is low). Even under conditions exceeding the predetermined value, it is not easily released from the catalyst. For this reason, as the engine operation continues, so-called S poisoning occurs in which the sulfur component in the exhaust gas is gradually accumulated in the NOx catalyst.
[0061]
As S poisoning progresses, the limit value of the NOx occlusion amount by the NOx catalyst and the NOx occlusion efficiency decrease, and as a result, the NOx purification efficiency decreases.
[0062]
The sulfur component accumulated in the NOx catalyst is released from the catalyst by satisfying the conditions for further increasing the concentration of the reduced component in the exhaust gas and the temperature of the NOx catalyst than the conditions achieved by the normal catalyst regeneration control. It has been known.
[0063]
For this reason, in the engine 1, control (hereinafter referred to as S poison recovery control) for supplying a reducing component into the exhaust gas and setting the NOx catalyst to a high temperature state (for example, about 600 ° C.) is appropriately performed during operation of the engine 1. By executing at the timing, the sulfur component accumulated in the NOx catalyst is released. In order to bring the NOx catalyst into such a high temperature state, for example, the supply of reducing components to the filters 111 and 121 may be continued for a longer period than in the case of the catalyst regeneration control. Even when the sulfur poisoning recovery control is performed, the form of the exhaust passage shown in FIG. 4A and the sulfur component accumulated in the filter 111 are released when the sulfur component accumulated in the filter 121 is released. In this case, the form of the exhaust passage shown in FIG. 4B can be applied.
[0064]
When performing the catalyst regeneration control and the S poison recovery control, the temperature of the filters 111 and 121 is a predetermined value so that the fuel added through the fuel addition valves 17a and 17b reacts efficiently via the NOx catalyst. It is preferable that a condition exceeding (for example, about 300 ° C.) is satisfied. For this reason, when starting the catalyst regeneration control or the S poison recovery control, for example, the temperature of the filters 111 and 121 is estimated based on the detection signal of the exhaust temperature sensor 74, and this temperature does not exceed a predetermined value. It is preferable to increase the temperature of the NOx catalyst by performing pilot injection, post injection, or the like.
[0065]
(2) Clogging detection
A method for detecting the occurrence of clogging in each of the filters 111 and 121 housed in the filter casing 100 will be described.
[0066]
For example, when the NOx catalyst regeneration control is performed by applying the exhaust passage shown in FIG. 4A, a change in the detection signal of the oxygen concentration sensor 73 or the exhaust temperature sensor 74 is observed before and after the control is performed. Then, it can be determined whether or not the filter 111 is clogged. That is, when the filter 111 functions normally, the oxygen concentration of the exhaust gas detected downstream of the filter casing 100 becomes low (exhaust gas) in response to the execution of the NOx catalyst regeneration control (the valve opening operation of the fuel addition valve 17a). And the exhaust gas temperature increases, so that the detection signals (outputs) of the oxygen concentration sensor 73 and the exhaust temperature sensor 74 change. When the filter 111 is clogged, the output changes of the oxygen concentration sensor 73 and the exhaust temperature sensor 74 in response to the opening operation of the fuel addition valve 17a become slow. Based on this, clogging of the filter 111 is detected. Further, based on the detection signal of the differential pressure sensor 75, it can be determined whether or not the filter 111 is clogged. That is, when the filter 111 is clogged, when the exhaust flow path in the filter casing 100 is switched to the state shown in FIG. Remarkably increased. The ECU 90 recognizes the variation in the pressure difference through the detection signal of the differential pressure sensor 75 and detects clogging of the filter 111.
[0067]
Further, when the NOx catalyst regeneration control is performed by applying the exhaust passage shown in FIG. 4B, the filter 121 is clogged according to the same principle as the detection of the clogging of the filter 111. It can be determined whether or not.
[0068]
That is, in NOx catalyst regeneration control and S poison recovery control, when NOx is released / reduced or fine particles are decomposed and removed in one of the two filters 111 and 121 provided in the filter casing 100. In the other filter, NOx is occluded (fine particles are captured). For this reason, NOx and particulates in the exhaust gas flowing into the filter casing 100 do not pass through downstream without passing through any of the filters 111 and 121.
[0069]
(3) Channel switching control based on clogging detection
When clogging is detected for only one of the filters 111 and 121, the ECU 90 operates the rotary valve 141, and the exhaust gas flowing into the filter casing 100 functions as a normally functioning filter (clogged. An exhaust passage that is introduced only into the filter) is formed. Further, when the filters 111 and 121 are clogged, the rotary valve 141 is brought into the state shown in FIG. By setting the rotary valve 141 in such a state, an exhaust passage that flows into the filter casing 100 from the first collecting passage 40a and is discharged to the second collecting passage 40b through the third exhaust passage 130 is formed. Is done. When the filters 111 and 121 are clogged and the exhaust cannot be moved through the first exhaust passage 110 or the second exhaust passage 120, such an exhaust passage is formed in the filter casing 100. Thus, it is possible to avoid an increase in the exhaust pressure upstream of the filter casing 100.
[0070]
As described above, according to the exhaust purification device of the engine 1, the simple configuration of the device is used, and the exhaust gas flowing into the filter casing 100 always secures an exhaust passage through which at least one filter passes. It is possible to perform a switching operation for flowing exhaust from each end. By carrying out such an operation, not only can the removal action of the particulates and the like by the filters 111 and 121 be maintained for a long period of time, but also temporary passage of the particulates and the like downstream of the filter casing 100. It can be avoided reliably.
[0071]
In addition, when supplying exhaust in a reducing atmosphere to a filter carrying a NOx catalyst and releasing / reducing NOx occluded in the NOx catalyst, a predetermined space (exhaust passage) including the filter is in a sealed state or close to a sealed state. In addition, the efficiency of the NOx release / reduction action and the fine particle decomposition action is increased by adding and supplying a reducing agent to the sealed space, while another exhaust passage is secured in the filter casing 100 so as to be upstream of the filter casing 100. Do not increase the pressure. Further, another filter is arranged in the exhaust passage secured in the filter casing 100, and NOx in the exhaust flowing along the exhaust passage is occluded (fine particles are captured). Therefore, it is possible to reliably avoid the downstream passage of NOx and fine particles in the exhaust gas flowing into the filter casing 100, and to reduce the consumption of the reducing agent required for regeneration of the NOx catalyst.
[0072]
In addition, even when one of the filters 111 and 121 is clogged, the function of the filter without clogging can be utilized to the maximum, and the exhaust purification function can be maintained.
[0073]
Further, even when the filters 111 and 121 are clogged, the exhaust pressure is exhausted through the third exhaust passage 130, so that the pressure increase in the exhaust system 40 can be suppressed.
[0074]
The third exhaust passage 130 may also be provided with a catalyst or filter having an exhaust purification function, such as an oxidation catalyst, a NOx catalyst, or a particulate filter. Thus, if a catalyst or a filter is also provided in the third exhaust passage 130, when clogging occurs in both the filters 111 and 121, the exhaust gas is caused to flow through the third exhaust passage 130 to thereby filter the filter casing 100. The exhaust purification capability of the filter casing 100 can be maintained by preliminarily functioning the catalyst and the filter provided in the third exhaust passage 130 while suppressing the upstream pressure rise.
[0075]
Note that the detection signal of the oxygen concentration sensor 73, the exhaust temperature sensor 74, or the differential pressure sensor 75 under a specific condition is also a parameter that indirectly reflects the total amount of particulates captured by the filters 11 and 121. For example, when the filter casing 100 is in the state of FIG. 4A, the detection signals of the sensors 71, 74, and 75 reflect the amount of particulates captured by the filter 111, and the filter casing 100 is in FIG. ), The detection signals of the sensors 71, 74, and 75 reflect the amount of particles and the like captured by the filter 121. Therefore, the outputs of these sensors are used as criteria for determining whether or not clogging has occurred in the filters 111 and 121, as well as for timing of fuel addition control, and for decomposing particulates captured by the filters. It can also be used as a criterion for determining the necessary amount of reducing agent (fuel) added.
[0076]
[Modifications, etc.]
Note that, by adopting a regulating valve mechanism and a passage structure as shown in FIG. 5 in place of the configuration of the filter casing 100 provided with the rotary valve 141 as the regulating valve mechanism, an effect equivalent to that of the present embodiment can be obtained. Can do.
[0077]
FIG. 5 shows an example of an exhaust passage structure that can be used in place of the filter casing 100. As shown in the side view of FIG. 5 (a) and the top view of FIG. 5 (b), the passage structure of this example has a passage switching portion between the first collecting passage 40a and the second collecting passage 40b. 142 and three branch passages 110 ′, 120 ′, and 130 ′. Further, filters 111 ′ and 121 ′ having characteristics equivalent to those of the filters 111 and 121 provided in the filter casing 100 are provided in the middle of the branch passages 110 ′ and 120 ′. The exhaust gas flowing from the first collecting passage 40a is guided to one of the three branch passages 110 ′, 120 ′, and 130 ′ through the passage switching portion 142. The passage switching unit 142 incorporates a valve body (adjusting valve mechanism) 143.
[0078]
5C is a side sectional view of the valve body 143, and FIG. 5D is a front view of the valve body 143 viewed from the upstream side of the exhaust passage (exhaust passage 40a side). Note that FIG. 5D corresponds to the VC-VC cross section of FIG.
[0079]
As shown in FIGS. 5C and 5D, the valve body 143 has a through hole 143a. The valve body 143 rotates around the point O in the direction of arrow α based on a command signal from the ECU 90, so that the through-hole 143a has any one of the branch passages 110 ′, 120 ′, and 130 ′ with respect to the exhaust passage 40a. Alternatively, the distribution ratio of the exhaust gas flowing into the branch passages 110 ′, 120 ′, and 130 ′ is changed. Also by applying the passage structure having such a configuration, the first exhaust passage (branch passage 110) is based on the function of the adjustment valve mechanism (valve element 143) provided in the passage switching portion 141 (passage space portion). ′), The connection state of the first collecting passage 40a to the second exhaust passage (branch passage 120 ′) and the third exhaust passage (branch passage 130 ′) is at least the branch passage 110 with respect to the first collecting passage 40a. ', While the branch passage 120' and the branch passage 130 'are cut off or close to the first collecting passage 40a, and the first collecting passage 40a is connected to the first collecting passage 40a. The second exhaust passage 120 'is connected, while the collecting passage 120' and the branch passage 130 'are cut off or close to the branch passage 110', and the first collecting passage 40a. Vs. Exhaust having a function of adjusting to the third connection state to which the branch passage 130 ′ is connected and switching the first connection state and the second connection state to each other without going through the third connection state A purification device can be implemented.
[0080]
In addition, when the filter 111 or the filter 121 is clogged, control for removing particulates or the like clogged in the filter (particle removal control) may be performed. As the fine particle removal control, for example, a method in which a clogged filter is exposed to a high temperature condition to decompose fine particles clogged in the filter can be considered. Specifically, the temperature of the exhaust gas may be increased by performing the above-described pilot injection, post injection, or fuel addition. Further, by adopting a known variable valve timing mechanism, the operation timing (so-called valve timing) of the intake valve and the exhaust valve of the engine 1 may be controlled to raise the temperature of the exhaust. Alternatively, a well-known variable turbo mechanism may be employed in the turbocharger 50 to control the supercharging pressure independently of the intake air amount (intake air pressure) and raise the exhaust gas temperature.
[0081]
In addition, the control for switching (adjusting) the connection states (first, second, and third connection states) between the passages in the present embodiment, including the passage structure of the modified example, In addition to selectively switching between a fully open state and a closed state, a substantial passage cross section at the boundary portion between them is controlled by, for example, continuously adjusting the arrangement of the valve body 140b and the valve body 141. There may be. Accordingly, various conditions (exhaust flow path states) can be set according to the state of the filters and catalysts provided in the filter casings 100 and 100 ′ or the operating state of the engine 1.
[0082]
In the present embodiment, the exhaust purification device of the present invention is applied to an in-line four-cylinder diesel engine as an internal combustion engine. However, the present invention can also be applied to a gasoline engine that performs lean combustion. Further, the present invention can be applied not only to an in-line four-cylinder internal combustion engine but also to an internal combustion engine having a different number of mounted cylinders.
[0083]
【The invention's effect】
As described above, according to the exhaust emission control device of the present invention, the first exhaust passage provided with the filter that collects the particulates in the exhaust gas and the second filter that also includes the filter that collects the particulates in the exhaust gas. Exhaust passage and a third exhaust passage that forms a separate exhaust passage when both filters are clogged or the like, and in the first exhaust passage, particulates in the exhaust are captured. The function of the collecting filter and the function of the filter that collects particulates in the exhaust gas in the second exhaust passage can be switched and used separately, and when the two functions are switched, the exhaust gas is discharged into the third exhaust passage. A structure that does not flow can be easily realized.
[0084]
Further, the exhaust gas moving from the first collecting passage as the starting point and the second collecting passage as the ending point is at least one of a filter provided in the first exhaust passage and a filter provided in the second exhaust passage. To pass. For this reason, when switching the two types of exhaust flow paths, it is possible to avoid a problem that fine particles to be collected by any of the filters pass through the second collecting passage.
[0085]
In particular, when each filter has a function of storing NOx contained in the exhaust gas in an oxidizing atmosphere and reducing the stored NOx in a reducing atmosphere, the purifying action of fine particles and the NOx cleaning action of each filter are synergistic. Can be enhanced. Further, NOx occluded in the catalyst in the first exhaust passage can be efficiently released and reduced without increasing the pressure of the exhaust upstream of the first collecting passage. In other words, the exhaust gas purification function of the catalyst (or filter) provided in the first exhaust passage and the exhaust gas purification function of the catalyst (or filter) provided in the second exhaust passage are alternately used to efficiently Exhaust gas purification can be performed continuously.
[0086]
That is, based on a simple device configuration, it is possible to achieve both improvement in exhaust characteristics and reduction in reducing agent consumption.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a diesel engine system according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing the internal structure of the filter casing according to the embodiment.
FIG. 3 is a plan view showing the structure of a particulate filter.
FIG. 4 is a schematic diagram for explaining the relationship between various forms of exhaust passages formed in the filter casing and the state of each rotary valve.
FIG. 5 is a schematic diagram showing a modification of the exhaust emission control device according to the embodiment;
FIG. 6 is a schematic diagram showing an example of a conventional exhaust purification device.
[Explanation of symbols]
1 engine (internal combustion engine)
10 Fuel supply system
11 Supply pump
12 Common rail
13 Fuel injection valve
20 Combustion chamber
30 Intake system
40 Exhaust system
40a First collecting passage
40b Second collecting passage
50 turbocharger
60 EGR passage
61 EGR valve
71 Added fuel pressure sensor
73 Oxygen concentration sensor
74 Exhaust temperature sensor
75 Differential pressure sensor
90 Electronic control unit (ECU)
100 Filter casing
110 First exhaust passage
111,121 filters
111a Porous material
120 Second exhaust passage
130 Third exhaust passage
140 First collective space section (collective space section)
141 Rotary valve
P1 Engine fuel passage
P2 added fuel passage

Claims (4)

Provided in the exhaust system of the internal combustion engine,
A first exhaust passage provided with a filter in the middle of the passage for collecting particulates in the exhaust;
A second exhaust passage that also includes a filter in the middle of the passage for collecting particulates in the exhaust;
A collective space portion connected to a passage opening end on the upstream side of the first exhaust passage and a passage opening end on the upstream side of the second exhaust passage;
A first collecting passage connected to the collecting space portion;
A second collecting passage connected to a passage opening end downstream of the first exhaust passage and a passage opening end downstream of the second exhaust passage;
A third exhaust passage communicating between the collective space portion and the second collective passage;
An adjustment valve mechanism that is provided in the collective space portion and adjusts a connection state of the first collective passage to the first exhaust passage, the second exhaust passage, and the third exhaust passage;
With
An exhaust gas purification apparatus for an internal combustion engine for discharging exhaust gas introduced through the first collecting passage through the second collecting passage,
As the adjustment valve mechanism ,
A single valve body that is rotatable in the assembly space,
By rotating in the assembly space part,
At least a connection state of the first collecting passage with respect to the first exhaust passage, the second exhaust passage, and the third exhaust passage,
A first connection state in which the first exhaust passage is connected to the first collecting passage, and the second exhaust passage and the third exhaust passage are blocked from the first collecting passage. When,
A second connection state in which the second exhaust passage is connected to the first collecting passage and the first exhaust passage and the third exhaust passage are blocked from the first exhaust passage. When,
A third connection state in which the third exhaust passage is connected to the first collecting passage;
And a single valve body capable of switching the first connection state and the second connection state to each other without going through the third connection state.
An exhaust emission control device for an internal combustion engine. Means for estimating or detecting the amount of particulates collected by the filter of the first exhaust passage and the amount of particulates collected by the filter of the second exhaust passage;
The adjustment valve mechanism is driven in accordance with the amount of the estimated or detected fine particles, and the connection state of the first collecting passage to the first exhaust passage, the second exhaust passage, and the third exhaust passage is changed to the first exhaust passage. Control means for shifting to the connection state of No. 3,
The exhaust emission control device for an internal combustion engine according to claim 1, comprising:   The filter provided in the first exhaust passage and the filter provided in the second exhaust passage have a function of storing NOx contained in the exhaust in an oxidizing atmosphere and reducing the stored NOx in a reducing atmosphere. The exhaust emission control device for an internal combustion engine according to claim 1 or 2. In the first exhaust passage, a first reducing agent adding means is provided between a passage opening end forming the first collecting passage and the filter, and adds a reducing agent into the first exhaust passage. When,
In the second exhaust passage, a second reducing agent adding means is provided between a passage opening end forming the second collecting passage and the filter, and adds a reducing agent into the second exhaust passage. When,
The exhaust emission control device for an internal combustion engine according to claim 3, further comprising:

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