JP2009133291A - Exhaust emission control device for internal combustion engine and its control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To quickly raise a temperature of a reduction catalyst and early start injection control of a reduction agent by switching a flowing direction of exhaust gas from a normal direction to a reverse direction, when the temperature of the exhaust gas is raised while the temperature of the reduction catalyst becomes less than a reference temperature and the injection control of the reduction agent is stopped. <P>SOLUTION: This exhaust emission control device includes exhaust gas flow path switch means for switching a flowing direction of exhaust gas to a normal direction directing to a reduction catalyst from a particulate filter or a reverse direction directing to the particulate filter from the reduction catalyst. The device includes a control device including a reduction agent injection control part for controlling injection of the reduction agent from a reduction agent supplying part while the temperature of the reduction catalyst is not less than a predetermined temperature, and a control part of the exhaust gas flow path switch means for controlling the exhaust gas flow path switch means so that the flowing direction of the exhaust gas becomes a reverse direction when the temperature of the reduction catalyst is less than a predetermined temperature and the temperature of the exhaust gas is determined as raising. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to an exhaust emission control device for an internal combustion engine and a control method therefor. In particular, with both particulate filter and reduction catalyst, it relates to an exhaust purifying apparatus and a control method thereof for an internal combustion engine for purifying particulate matter and NO _X in the exhaust gas.

The exhaust gas discharged from diesel engines, contain contaminants such as particulates and NO _X (nitrogen oxides). Therefore, conventionally, an internal combustion engine has been provided with an exhaust gas purification device for purifying exhaust gas.

Among these, for particulates, a particulate filter is disposed in the exhaust passage so as to collect particulates in the exhaust gas passing therethrough.
For NO _x , a selective reduction type reduction catalyst (SCR catalyst) is provided in the exhaust passage of the engine, and ammonia is supplied to the reduction catalyst as a reducing agent, thereby reducing NO _x in the exhaust gas passing therethrough. There is known an SCR system which is made to purify. In this SCR system, the urea solution is supplied to the upstream side of the reduction catalyst, and this urea solution is thermally decomposed by the heat of the exhaust gas and further hydrolyzed on the catalyst to produce ammonia, which is once adsorbed on the reduction catalyst. Is done. A denitration reaction between NO _x and ammonia in the exhaust gas passing therethrough is promoted by the reduction catalyst, and is efficiently decomposed and released into nitrogen, water, carbon dioxide, and the like.

Recently, sometimes it is enhanced purifying reference exhaust gas, includes both these particulate filter and reduction catalyst, the exhaust gas purifying device intended both to remove particulates and NO _X in the exhaust gas Is being put to practical use (see, for example, Patent Documents 1 and 2).

JP 2007-239486 A (FIG. 3) JP2007-255285A (FIG. 3)

By the way, in the particulate filter, when the amount of the collected particulates becomes large, the pressure loss of the exhaust gas becomes large, which may cause a problem in the internal combustion engine or the like. Therefore, when the collected amount of particulates exceeds a certain amount, forced regeneration of the particulate filter that forcibly burns the particulates is performed. In addition to this forced regeneration, an oxidation catalyst is disposed upstream of the particulate filter, and NO ₂ (nitrogen dioxide) produced by oxidizing NO (nitrogen monoxide) in the exhaust gas in a normal operation state. ) Is used to oxidize (burn) the particulates collected by the particulate filter, and continuous regeneration is performed.

In the exhaust gas purification apparatus provided with both the particulate filter and the reduction catalyst as exemplified in Patent Documents 1 and 2, the particulate filter is continuously regenerated using NO ₂ in the exhaust gas as described above. For this purpose, it is necessary to arrange the oxidation catalyst, the particulate filter, and the reduction catalyst in this order from the upstream side. That is, when the reduction catalyst is arranged on the upstream side of the particulate filter, NO ₂ in the exhaust gas is reduced by the reduction catalyst.

On the other hand, SCR system startup and idling of the internal combustion engine, when the temperature temperature is lower reduction catalyst in the exhaust gas is low, because of low production efficiency of the ammonia be injected urea solution, reduction of the NO _X The efficiency may decrease and the urea solution may adhere to the exhaust passage. Therefore, in the SCR system, the urea solution injection control is performed only when the temperature of the reduction catalyst is equal to or higher than the reference temperature.
However, the reduction catalyst used in the SCR system has a characteristic that the amount of saturated adsorption of ammonia increases as the temperature decreases, while a temperature of about 120 to 140 ° C. is required to generate ammonia from the urea solution. Therefore, a sufficient amount of ammonia cannot be obtained at low temperatures. Therefore, when the temperature of the reduction catalyst is lowered and the urea solution injection is stopped, the ammonia adsorption rate is reduced and the NO _x reduction efficiency is easily lowered. Therefore, when the temperature of the exhaust gas rises after starting the internal combustion engine, or when the exhaust gas temperature is returned to the normal operation state after the idling operation, the temperature of the reduction catalyst is raised early so that the urea solution can be injected. It is desirable to increase the NO _x reduction efficiency in the reduction catalyst.

However, in the exhaust gas purification apparatus in which the particulate filter is arranged on the upstream side of the reduction catalyst as described in Patent Documents 1 and 2, even if the temperature of the exhaust gas starts to rise, the downstream side Before reaching the reduction catalyst, heat is first taken away by the upstream particulate filter. Therefore, it takes time until the temperature of the reduction catalyst rises and reaches the reference temperature or higher at which the reducing agent injection control is performed, and a considerable amount of time is required until the efficient reduction reaction of NO _x is resumed. It will take.

  Therefore, the inventors of the present invention have made diligent efforts to provide means for switching the flow direction of the exhaust gas to the forward direction or the reverse direction, and the temperature of the exhaust gas starts to rise in a state where the injection control of the reducing agent is stopped. The present inventors have found that such a problem can be solved by switching the flow direction of the exhaust gas in the reverse direction. That is, the object of the present invention is to correct the flow direction of the exhaust gas when the temperature of the reduction catalyst is lower than the reference temperature and the injection control of the reducing agent is stopped and the exhaust gas temperature rises. To provide an exhaust purification device for an internal combustion engine and a control method for the exhaust purification device for an internal combustion engine capable of switching from the direction to the reverse direction, quickly increasing the temperature of the reduction catalyst, and starting the injection control of the reducing agent at an early stage It is.

  According to the present invention, the reduction catalyst disposed in the exhaust passage of the internal combustion engine, the reducing agent supply unit that is provided upstream of the reduction catalyst and supplies the reducing agent into the exhaust passage, and the reducing agent supply unit And a particulate filter disposed in the exhaust passage on the exhaust upstream side, and an exhaust gas purification apparatus for an internal combustion engine, wherein the exhaust gas flows in a forward direction from the particulate filter toward the reduction catalyst, or In addition to the exhaust gas flow path switching means for switching in the reverse direction from the reduction catalyst to the particulate filter, the catalyst temperature detection unit for detecting the temperature of the reduction catalyst, and the temperature of the reduction catalyst is a predetermined temperature or higher, A reducing agent injection control unit that controls the injection of reducing agent from the reducing agent supply unit, an exhaust temperature detection unit that detects the temperature of the exhaust gas, and an exhaust gas when the temperature of the reduction catalyst is less than a predetermined temperature. When the exhaust gas temperature rise determination unit for determining whether the temperature of the exhaust gas rises and the exhaust gas temperature rise determination unit determine that the temperature of the exhaust gas rises, the flow direction of the exhaust gas is reversed. An exhaust gas purification apparatus for an internal combustion engine, characterized by comprising a control device including an exhaust gas flow path switching means control unit for controlling the exhaust gas flow path switching means, and to solve the above-described problems Can do.

  In configuring the exhaust emission control device of the present invention, the exhaust passage is provided on the upstream side of the particulate filter, and communicates with the downstream side of the reduction catalyst, the first branch portion, and the reduction catalyst. Between the first branch portion and the particulate filter, the exhaust gas flowing in the opposite direction is further passed The exhaust gas flow path switching means comprises a flow path switching valve provided in the first branch section, the second branch section, and the third branch section. It is preferable.

  In configuring the exhaust emission control device of the present invention, it is preferable that the exhaust passage is folded back between the particulate filter and the reduction catalyst so that the particulate filter and the reduction catalyst are brought close to each other.

In configuring the exhaust emission control device of the present invention, it is preferable that an oxidation catalyst is provided between the third branch portion and the particulate filter and between the second branch portion and the reduction catalyst.

  In configuring the exhaust emission control device of the present invention, it is preferable to provide an oxidation catalyst upstream of the first branch portion.

  In configuring the exhaust emission control device of the present invention, it is preferable that the exhaust gas temperature rise determination unit determine whether the temperature of the exhaust gas continuously rises for a predetermined time or more.

  Further, in configuring the exhaust emission control device of the present invention, it is preferable that the exhaust gas temperature increase determination unit determines whether or not the temperature of the exhaust gas increases and exceeds the reference temperature.

According to another aspect of the present invention, there is provided a reduction catalyst disposed in an exhaust passage of an internal combustion engine, a reducing agent supply unit that is provided upstream of the reduction catalyst and supplies a reducing agent into the exhaust passage, And a particulate filter disposed in the exhaust passage upstream of the agent supply unit, and a control method for an exhaust gas purification device for an internal combustion engine comprising:
The exhaust purification device includes an exhaust gas flow switching means for switching the flow direction of the exhaust gas to the forward direction from the particulate filter to the reduction catalyst, or to the reverse direction from the reduction catalyst to the particulate filter, In a state where the temperature of the reduction catalyst is equal to or higher than a predetermined temperature, the injection of the reducing agent from the reducing agent supply unit is controlled.
When the temperature of the reduction catalyst is lower than the predetermined temperature and the injection control of the reducing agent is stopped, it is determined whether or not the temperature of the exhaust gas is increased, and when it is determined that the temperature of the exhaust gas is increased This is a control method for an exhaust gas purification device for an internal combustion engine that controls the exhaust gas flow path switching means so that the flow direction of the exhaust gas is opposite.

According to the exhaust gas purification apparatus for an internal combustion engine of the present invention, when the exhaust gas flow rate switching means and the control unit thereof are provided, when the exhaust gas temperature rise determination means determines that the temperature of the exhaust gas rises, The flow path of the exhaust gas is switched so that the exhaust gas passes through the reduction catalyst before the particulate filter. Therefore, it is possible to efficiently raise the temperature of the reduction catalyst without taking the amount of heat of the exhaust gas discharged from the internal combustion engine by the particulate filter. As a result, the time taken to return the exhaust gas flow path to the positive direction and start the injection control of the reducing agent is greatly shortened, the ammonia adsorption rate of the reduction catalyst increases rapidly, and the NO _x efficiency increases. The reduction reaction starts early.

  In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the exhaust passage is configured to have a plurality of branch portions, and a flow path switching valve is provided at each branch portion, so that the flow path of the exhaust gas is corrected. It can be easily switched in the direction or the reverse direction.

  Further, in the exhaust gas purification apparatus for an internal combustion engine of the present invention, the heat retention of the exhaust gas purification apparatus can be improved by folding the exhaust passage between the particulate filter and the reduction catalyst and bringing the particulate filter and the reduction catalyst close to each other. The temperature of the reduction catalyst can be made difficult to decrease.

Further, in the exhaust gas purification apparatus for an internal combustion engine of the present invention, by providing an oxidation catalyst between the third branch portion and the particulate filter, when the exhaust gas flows in the positive direction, HC (carbonization) is caused by the oxidation catalyst. Hydrogen) and CO (carbon monoxide) can be oxidized to enable continuous regeneration of the particulate filter and improvement of reduction efficiency with the reduction catalyst. An exhaust purification device, by providing the oxidation catalyst between the reduction catalyst second branch portion, to decompose the ammonia that has not been used in the reduction of the NO _X by the oxidation catalyst, the release of ammonia into the atmosphere Can be prevented.
Further, when the exhaust gas flows in the opposite direction, the temperature of the exhaust gas is further raised by the oxidation action of HC and CO by the oxidation catalyst between the second branch part and the reduction catalyst and flows into the reduction catalyst. Therefore, the heating efficiency of the reduction catalyst is improved, and the time until the start of the injection control of the reducing agent can be greatly shortened.

  In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the exhaust gas may flow in either the forward direction or the reverse direction by providing an oxidation catalyst in the exhaust passage upstream of the first branch portion. The exhaust gas can pass through the oxidation catalyst and then flow into the particulate filter or the reduction catalyst. Therefore, with one oxidation catalyst, it is possible to realize continuous regeneration of the particulater, efficient temperature increase of the reduction catalyst, and the like.

  Further, in the exhaust gas purification apparatus for an internal combustion engine of the present invention, the exhaust gas temperature rise determination unit determines whether or not the exhaust gas temperature continuously rises for a predetermined time or longer, whereby the temperature of the exhaust gas is temporarily increased. It is possible to prevent the flow path of the exhaust gas from being switched in the reverse direction when it rises and then falls again.

  In the exhaust gas purification apparatus for an internal combustion engine according to the present invention, the exhaust gas temperature increase determination unit determines whether or not the temperature of the exhaust gas rises and exceeds a reference temperature, whereby the temperature of the reduction catalyst is reduced. When the temperature at which the injection control is performed is not reached, it is possible to prevent the flow path of the exhaust gas from being switched in the reverse direction.

Further, according to the control method for the exhaust gas purification apparatus for an internal combustion engine of the present invention, when the exhaust gas temperature increase determining means determines that the temperature of the exhaust gas increases, the exhaust gas is reduced before the particulate filter. By switching the flow path of the exhaust gas so as to pass through, the temperature of the reduction catalyst can be efficiently raised by the amount of heat of the exhaust gas discharged from the internal combustion engine. Therefore, the time from returning the exhaust gas flow direction to the positive direction and starting the injection control of the reducing agent is greatly shortened, and the ammonia adsorption rate can be quickly increased. As a result, an efficient reduction reaction of NO _x is started at an early stage, and the exhaust gas purification efficiency can be increased.

DESCRIPTION OF EMBODIMENTS Embodiments relating to an exhaust purification device for an internal combustion engine and a control method for the exhaust purification device for an internal combustion engine according to the present invention will be specifically described below with reference to the drawings. However, this embodiment shows one aspect of the present invention and does not limit the present invention, and can be arbitrarily changed within the scope of the present invention.
In addition, what attached | subjected the same code | symbol in each figure has shown the same member, and description is abbreviate | omitted suitably.

1. FIG. 1 is a diagram schematically showing the configuration of an exhaust gas purification device for an internal combustion engine (hereinafter simply referred to as “exhaust gas purification device”) according to the present embodiment.
An exhaust purification device 10 shown in FIG. 1 is connected to an exhaust system of an internal combustion engine 11, collects particulates by a particulate filter 20, and selects NO _x by a reduction catalyst 21 using a urea aqueous solution as a reducing agent. This is an exhaust purification device 10 that reduces automatically. The exhaust purification device 10 injects a reducing agent into the exhaust passage upstream of the first oxidation catalyst 19, the particulate filter 20, the reduction catalyst 21, the second oxidation catalyst 22, and the reduction catalyst 21. And a reducing agent injection valve (reducing agent supply device) 35 for this purpose. An upstream NO _x sensor 33 and a first temperature sensor 31 are disposed upstream of the reduction catalyst 21, and a second temperature sensor 32 is disposed downstream of the reduction catalyst 21, and the second oxidation catalyst. A downstream side NO _X sensor 34 is disposed downstream of 22. Further, the third temperature sensor 30 is also disposed in the exhaust passage 12 connected to the internal combustion engine 11.

The exhaust emission control device 10 also has a control device (hereinafter referred to as “DCU: Dosing Control Unit”) 29 for controlling the amount of reducing agent injected and supplied into the exhaust passage via the reducing agent injection valve 35. I have. The DCU 29 not only receives information from various sensors and the like provided in the exhaust emission control device 10 but also a control unit (hereinafter referred to as “ECU: Engine Control”) for controlling the operating state of the internal combustion engine. It is sometimes referred to as “Unit”.) 13 is connected, and information regarding the operating state of the internal combustion engine 11 including the fuel injection amount, the injection timing, the rotational speed, and the like is input. As will be described later, the DCU 29 performs drive control of a reducing agent supply device (not shown) including the reducing agent injection valve 35 based on various signals that are input.
In the present embodiment, the ECU 13 and the DCU 29 are composed of separate control units so that information can be exchanged between them. However, the ECU 13 and the DCU 29 may be configured as a single control unit. Absent.

In FIG. 1, an exhaust passage 12 through which exhaust gas discharged from the internal combustion engine 11 flows is connected to the internal combustion engine 11, and this exhaust passage 12 is connected to a muffler (not shown) on the downstream side. Yes. As the internal combustion engine 11 that exhausts exhaust gas, a diesel engine or a gasoline engine is typical, but it is suitable to target a diesel engine in which purification of particulates or NO _x is currently a problem. Further, the ECU 13 detects the operating state of the internal combustion engine such as the rotational speed of the internal combustion engine 11, the fuel injection amount, and the fuel injection timing.

  Further, the exhaust passage 12 connected to the internal combustion engine 11 branches into an upstream exhaust passage 16 and a downstream exhaust passage 17 at the first branch portion 14. Among these, the upstream side exhaust passage 16 is provided with a first oxidation catalyst 19 and a particulate filter 20, and the downstream side exhaust passage 17 is provided with a reduction catalyst 21 and a second oxidation catalyst 22. Yes. The upstream exhaust passage 16 and the downstream exhaust passage 17 are folded back and communicated with each other, and the upstream exhaust passage 16 and the downstream exhaust passage 17 are in contact with each other, and are disposed in the upstream exhaust passage 16. Further, the particulate filter 20 and the reduction catalyst 21 disposed in the downstream side exhaust passage 17 are disposed close to each other. Thus, the exhaust gas purification device 10 is made compact by the upstream exhaust passage 16 and the downstream exhaust passage 17 being folded back and in contact with each other. Further, the exhaust emission control device 10 is made compact, and the particulate filter 20 and the reduction catalyst 21 are arranged close to each other, so that the exhaust heat is radiated to the outside and the heat retention is improved.

Further, in the first branch portion 14 where the upstream exhaust passage 16 and the downstream exhaust passage 17 branch, the flow of the exhaust gas flowing from the internal combustion engine 11 is sent to the upstream exhaust passage 16 side or the downstream exhaust passage. A first flow path switching valve 23 and a second flow path switching valve 24 for switching to the passage 17 side are provided. In a normal operation state, the second flow path switching valve 24 is closed, while the first flow path switching valve 23 is opened so that the exhaust gas flows to the upstream exhaust passage 16 side. Yes.
In addition, in the example of the exhaust gas purification apparatus 10 of the present embodiment, the first branch portion 14 has two flow path switching valves. However, depending on the configuration of the valve, one flow path switching valve may be used. It can also be configured to switch the flow path.

Further, a second branch portion 15 is provided between the second flow path switching valve 24 and the second oxidation catalyst 22 in the downstream side exhaust passage 17, and the second branch portion 15 is discharged in the forward direction. A path 26 is connected. The forward discharge path 26 is provided with a third flow path switching valve 27 for switching whether or not exhaust gas can flow into the forward discharge path 26.
Similarly, a third branch portion 18 is provided between the first flow path switching valve 23 and the first oxidation catalyst 19 in the upstream exhaust passage 16, and the third branch portion 18 has a reverse direction. A discharge path 25 is connected. The reverse direction discharge path 25 is provided with a fourth flow path switching valve 28 for switching whether or not exhaust gas can flow into the reverse direction discharge path 25.

As described above, the exhaust gas purification apparatus 10 of the present embodiment includes the first to fourth flow path switching valves 23, 24, 27, and 28 as exhaust gas flow path switching means, and is provided in the DCU 29 described later. The opening / closing control of each valve is performed by the controller of the exhaust gas flow path switching means.
For example, when the internal combustion engine is in a normal operation state and the exhaust gas flow direction is set to the positive direction, as shown in FIG. 2A, the first flow path switching valve 23 and the third flow path While the switching valve 27 is opened, the second flow path switching valve 24 and the fourth flow path switching valve 28 are closed. In this case, the exhaust gas discharged from the internal combustion engine 11 passes through the first oxidation catalyst 19, the particulate filter 20, the reduction catalyst 21, and the second oxidation catalyst 22 in this order, and flows into the forward discharge path 26. It is.
When the exhaust gas flow direction is reversed, the second flow path switching valve 24 and the fourth flow path switching valve 28 are opened, as shown in FIG. The flow path switching valve 23 and the third flow path switching valve 27 are closed. In this case, the exhaust gas discharged from the internal combustion engine 11 passes through the second oxidation catalyst 22, the reduction catalyst 21, the particulate filter 20, and the first oxidation catalyst 19 in this order, and then flows into the reverse discharge path 25. It is.

Further, in the exhaust gas purification apparatus 10 shown in FIG. 1, the particulate filter 20 disposed in the upstream side exhaust passage 16 is for collecting particulates contained in the exhaust gas, and is used for the first oxidation. It is disposed downstream of the catalyst 19.
The first oxidation catalyst 19 is mainly used for oxidizing NO in the exhaust gas to generate NO ₂ and oxidizing HC and CO in a state where the exhaust gas flows in the forward direction. The generated NO ₂ oxidizes (combusts) the particulates collected by the particulate filter 20 and is used for continuous regeneration of the particulate filter 20. In addition, the reduction rate of NO _x in the reduction catalyst 21 is optimized by the ratio of NO ₂ and NO not used for particulate oxidation.
As the first oxidation catalyst 19 and the particulate filter 20, known ones can be used.

Further, the reduction catalyst 21 disposed in the downstream side exhaust passage 17 is used for reducing and purifying NO _x contained in the exhaust gas using a reducing agent in a state where the exhaust gas flows in the forward direction. The reduction catalyst 21 provided in the exhaust purification apparatus 10 of the present embodiment adsorbs ammonia generated by decomposition of the reducing agent injected and supplied from the reducing agent injection valve 35 and is included in the inflowing exhaust gas. the are NO _X is a catalyst having a function of selectively reducing. The reduction catalyst 21 that can be used is not particularly limited as long as it has a function of adsorbing ammonia. For example, a catalyst made of a zeolite-based material can be used.

3 and 4 are diagrams showing the characteristics of such a reduction catalyst having an ammonia adsorption function.
FIG. 3 shows a saturated adsorption amount curve showing the relationship between the temperature of the reduction catalyst having an ammonia adsorption function and the saturated adsorption amount of ammonia. A solid line A in FIG. 3 shows a saturated adsorption amount curve, and the temperature of the reduction catalyst and the saturated adsorption amount are in an inversely proportional relationship, and the saturated adsorption amount decreases as the temperature increases. Understood.
Further, FIG. 4, in the reduction catalyst having ammonia adsorption function shows the relationship between the reduction efficiency of the actual adsorption rate and NO _X of ammonia to saturation adsorption amount, of the NO _X as the adsorption rate of ammonia is high It is understood that the reduction efficiency is good.

Further, in the exhaust purification apparatus 10 shown in FIG. 1, the second oxidation catalyst 22 is disposed downstream of the reduction catalyst 21, and mainly performs NO _X reduction reaction in a state where the exhaust gas flows in the forward direction. It is used to oxidize and purify ammonia that has passed through the reduction catalyst 21 without being used. That is, when the flowing downstream ammonia slip without being adsorbed by the reduction catalyst 21, by oxidizing ammonia, and is used to release to the relatively low toxicity NO _X. Further, in a state where the exhaust gas flows in the reverse direction, the temperature of the exhaust gas is raised by oxidation heat generated by oxidation of HC and CO in the exhaust gas when the exhaust gas passes through the second oxidation catalyst 22. Thus, the temperature of the reduction catalyst 21 can be increased efficiently.
As the second oxidation catalyst 22, a known catalyst can be used.

  Further, a reducing agent injection valve 35 is attached at a turn-back position where the upstream side exhaust passage 16 and the downstream side exhaust passage 17 communicate with each other. The reducing agent injection valve 35 constitutes a part of a reducing agent supply device (not shown), and injects a liquid reducing agent into the exhaust passage upstream of the reduction catalyst 21 while the exhaust gas flows in the forward direction. To supply. In the present invention, the configuration of the reducing agent supply device (not shown) is not particularly limited. For example, in addition to the form of supplying the reducing agent pumped by the pump through the reducing agent injection valve, It is also possible to use an air assist type in which a liquid reducing agent is atomized using high pressure air and then supplied into the exhaust passage.

Moreover, as a reducing agent, if ammonia is produced | generated by the time it reaches | attains a reduction catalyst, it can use suitably, A urea aqueous solution and ammonia aqueous solution are mentioned as a typical thing.
For example, when an aqueous urea solution is used, urea injected into the exhaust passage is thermally decomposed by heat in the exhaust gas to generate ammonia, and further hydrolyzed in the reduction catalyst to further generate ammonia. Adsorbed on the reduction catalyst. This ammonia reacts with NO _x in the exhaust gas flowing into the reduction catalyst, and is decomposed into nitrogen (N ₂ ), carbon dioxide (CO ₂ ), and water (H ₂ O) and released.

Moreover, the 1st temperature sensor 31, the 2nd temperature sensor 32, and the 3rd temperature sensor 30 are used in order to measure the temperature of the exhaust gas in each location. The DCU 29 estimates the temperature of the reduction catalyst 21 using temperature signals output from the first temperature sensor 31 and the second temperature sensor 32. About each of these temperature sensors, a well-known thing can be used.
Note that when the temperature of the exhaust gas discharged from the internal combustion engine 11 is estimated based on the operating state of the internal combustion engine, the third temperature sensor 30 can be omitted. In addition, when the reduction catalyst 21 can be directly provided with a temperature sensor, the first temperature sensor 31 and the second temperature sensor 32 can be omitted.

Further, the upstream-side NO _X sensor 33 and the downstream-side NO _X sensor 34 is used to measure the concentration of NO _X exhaust gas at each occurrence. Since the NO _x amount discharged from the internal combustion engine is obtained from the detected value of the upstream NO _x sensor 33, the DCU 29 calculates the injection amount of the reducing agent according to the discharged NO _x amount. The upstream NO _x sensor 33 may be omitted, and the exhaust NO _x amount may be estimated based on the operating state of the internal combustion engine 11.
Further, the detection value of the downstream NO _X sensor 34, since the amount of NO _X discharged into the atmosphere without being reduced in the reduction catalyst 21 is required, the DCU29 of the exhaust gas purifying apparatus 10 of the present embodiment, the NO _X The amount of reducing agent injection is calculated in consideration of the amount.

2. Exhaust purification control unit (DCU)
The DCU 29 provided in the exhaust purification device 10 of the present embodiment is configured around a microcomputer having a known configuration. FIG. 5 shows an example of the configuration of the DCU 29 related to the reducing agent injection control and the exhaust gas flow path switching control, expressed in functional blocks.

  The DCU 29 provided in the exhaust purification apparatus of the present embodiment includes a catalyst temperature detection unit (indicated as “catalyst temperature detection” in FIG. 5) that detects the temperature of the reduction catalyst, and a catalyst temperature that predicts the transition of the temperature of the reduction catalyst. A transition determination unit (indicated as “catalyst temperature transition determination” in FIG. 5), an actual adsorption amount calculation unit (indicated as “actual adsorption amount calculation” in FIG. 5) for calculating the actual adsorption amount of ammonia in the reduction catalyst, a reduction A first injection control unit (indicated as “first injection control” in FIG. 5) that controls the injection amount of the agent in accordance with the first target adsorption amount, and a control of the injection amount of the reducing agent to the second target. A second injection control unit (indicated as “second injection control” in FIG. 5) performed according to the amount of adsorption, and an injection stop control unit (in FIG. 5) that stops injection when the temperature of the reduction catalyst is lower than the reference temperature. "Injection stop control") and the temperature of the exhaust gas discharged from the internal combustion engine Exhaust gas temperature detection unit (indicated as “exhaust gas temperature detection” in FIG. 5) and exhaust gas for determining whether or not the predicted temperature transition of the exhaust gas rises when the temperature of the reduction catalyst is lower than the reference temperature An exhaust gas flow path switching means that controls the exhaust gas flow path switching means so that the flow direction of the exhaust gas is the forward direction or the reverse direction. The control unit ("channel switching control" in FIG. 5) and the like are configured as main elements. Each of these units is specifically realized by executing a program by a microcomputer (not shown). Although not shown, the DCU 29 is provided with a RAM (Random Access Memory) for storing the temperature information of the reduction catalyst, the injection instruction value of the reducing agent, and the like.

Among these, the catalyst temperature detection unit estimates the temperature of the reduction catalyst based on the temperature signals detected by the first temperature sensor 31 and the second temperature sensor 32. In the case where the reduction catalyst 21 can be directly provided with a temperature sensor, the catalyst temperature detection unit only needs to be able to receive a temperature signal from the temperature sensor.
Further, the exhaust gas temperature detection unit detects an exhaust gas temperature signal detected by the third temperature sensor 30. In the case where the third temperature sensor 30 is not provided, the exhaust gas temperature detection unit is based on the engine speed signal, the intake air amount, the fuel injection amount, the fuel injection timing, etc. output from the ECU 13. Thus, the temperature of the exhaust gas to be discharged is determined by calculation.

In addition, the catalyst temperature transition determination unit in the DCU 29 of the present embodiment predicts the transition of the reduction catalyst temperature based on the rotational speed signal and torque signal of the internal combustion engine sent from the ECU 13, and reduces the temperature of the reduction catalyst. However, it is determined whether or not the temperature falls below a reference temperature at which the reducing agent injection control is performed.
For example, the temperature of the reduction catalyst is predicted to be lower than the reference temperature when the rotational speed of the internal combustion engine is lower than a predetermined threshold value or when the torque is negative. In addition to this, the temperature signal of the exhaust gas detected by the third temperature sensor and the temperature of the reduction catalyst calculated by the catalyst temperature detection unit are continuously read, and the temperature transition is predicted and determined from the result. It may be.

Further, the injection stop control unit sends an injection stop control signal to the reducing agent supply device when the temperature of the reduction catalyst calculated by the catalyst temperature detection unit becomes lower than a predetermined reference temperature. It has become. This reference temperature is set to a temperature (catalytic activity temperature) at which it is difficult for the reduction catalyst to produce ammonia due to hydrolysis of the reducing agent. As an example, it is a value within the range of 120 to 140 ° C. Therefore, when the temperature of the reduction catalyst is lower than the prescribed reference temperature, the reducing agent is not supplied, and the actual adsorption amount of ammonia in the reduction catalyst is continuously reduced. That is, if the current temperature of the reduction catalyst does not reach the activation temperature range of the catalyst, NO _x cannot be efficiently reduced on the reduction catalyst even if a reducing agent is added. In the exhaust emission control device, the reducing agent injection control is performed only under the condition that the temperature of the reduction catalyst 21 reaches the activation temperature region.

In addition, the actual adsorption amount calculation unit estimates the amount of ammonia actually adsorbed on the reduction catalyst. For example, the value obtained by subtracting the amount of ammonia used to reduce NO _x contained in the exhaust gas from the amount of ammonia generated corresponding to the amount of reducing agent actually injected is added to the reduction catalyst, and is already adsorbed on the reduction catalyst. By adding the amount of ammonia that has been added, the actual adsorption amount of ammonia in the reduction catalyst is calculated.

  Further, in the first injection control unit, when the catalyst temperature transition determination unit predicts that the temperature of the reduction catalyst does not fall below the reference temperature, the first injection control unit has a value smaller than the saturated adsorption amount of the reduction catalyst. The injection amount of the reducing agent is determined according to the target adsorption amount of 1, and a control signal is sent to the reducing agent supply device. That is, when the temperature of the reduction catalyst is maintained at the reference temperature or higher, the first injection control unit performs the injection control in the normal mode.

The first injection control unit in the DCU 29 of the present embodiment is a reduction catalyst at the time of determining the catalyst temperature transition based on the first target adsorption amount curve indicating the relationship between the temperature of the reduction catalyst and the first target adsorption amount. The first target adsorption amount corresponding to the temperature is read, and the reducing agent is injected so that an amount of ammonia corresponding to the difference from the actual adsorption amount of ammonia calculated by the actual adsorption amount calculation unit is adsorbed to the reduction catalyst. The quantity is configured to be calculated.
The first target adsorption amount curve is set so as to have a ratio of, for example, about 70 to 90% with respect to the saturated adsorption amount, as indicated by a broken line B in FIG. By making the first target adsorption amount smaller than the saturated adsorption amount, it is possible to prevent ammonia from being supplied in an amount exceeding the saturated adsorption amount of the reduction catalyst and flowing out to the downstream side of the reduction catalyst. Further, even when the temperature of the reduction catalyst suddenly increases, ammonia slip to the downstream side of the reduction catalyst can be prevented. Further, when the first target adsorption amount is set at such a ratio, the NO _x reduction efficiency does not significantly decrease.

  In the second injection control unit, when the catalyst temperature transition determination unit predicts that the temperature of the reduction catalyst is lower than the reference temperature, the value is larger than the first target adsorption amount and smaller than the saturated adsorption amount. The injection amount of the reducing agent is determined in accordance with the second target adsorption amount, and a control signal is sent to the reducing agent supply device. That is, when the internal combustion engine shifts to an idling state, or when the internal combustion engine is stopped at the time of deceleration, etc., when the temperature of the reduction catalyst is lower than the reference temperature, the second injection control unit performs the increase mode. Injection control is performed.

The second injection control unit in the DCU 29 of the present embodiment uses the second target adsorption amount curve indicating the relationship between the temperature of the reduction catalyst and the second target adsorption amount to determine the reduction catalyst at the time of temperature transition determination. The second target adsorption amount corresponding to the temperature is read, and the injection amount of the reducing agent so that the amount of ammonia corresponding to the difference from the actual adsorption amount of ammonia calculated by the actual adsorption amount calculation unit is adsorbed to the reduction catalyst. Is calculated.
This second target adsorption amount curve can be set to have a ratio of, for example, about 85 to 95% with respect to the saturated adsorption amount, as indicated by a one-dot chain line C in FIG. By setting the second target adsorption amount to a value larger than the first target adsorption amount, a relatively large amount is always maintained even in a state where the saturated adsorption amount continuously increases while ammonia is hardly generated. Ammonia can be adsorbed. In addition, if the saturated adsorption amount is continuously increased, even when the injection amount of the reducing agent is increased, an amount of ammonia exceeding the saturated adsorption amount of the reduction catalyst is supplied. The possibility of flowing out downstream is also reduced.

In particular, as in the present embodiment, when the reduction catalyst injection control is stopped when the temperature of the reduction catalyst is lower than the reference temperature, the temperature of the reduction catalyst decreases and is lower than the reference temperature. When there is a possibility that the amount of fuel is reduced, injection control in the increase mode is performed, and a relatively large amount of ammonia can be adsorbed on the reduction catalyst until the injection of the reducing agent is stopped. Therefore, even when the temperature of the reduction catalyst is low and the reducing agent is not hydrolyzed and ammonia cannot be newly adsorbed, it is possible to prevent the NO _x reduction efficiency from being significantly reduced. .

Further, in the exhaust gas temperature rise determination unit in the DCU 29 of the present embodiment, while the temperature of the reduction catalyst is lower than the reference temperature at the cold start or idling state, etc., while the reducing agent injection control is stopped, The temperature of the exhaust gas is determined based on the rotational speed signal, torque signal, intake air amount, fuel injection amount, etc. output from the ECU 13 and the exhaust gas temperature information detected by the exhaust gas temperature detector. It is determined whether or not the temperature of the exhaust gas will rise.
At this time, if it is determined whether or not the temperature of the exhaust gas continuously increases for a predetermined time or more, the temperature increase of the exhaust gas is not temporary, and the temperature of the reduction catalyst is surely increased to the activation temperature. It is possible to determine the state in which it can be raised. Although this predetermined time is arbitrarily set, for example, it can be set based on whether or not the temperature of the reduction catalyst can be raised to the activation temperature.
Alternatively, as a result of the rise in the exhaust gas temperature, it is possible to reliably raise the temperature of the reduction catalyst to the activation temperature by determining whether or not the exhaust gas temperature exceeds a predetermined threshold value. It becomes possible to determine the state where the user can

Further, the control unit of the exhaust gas flow path switching means outputs operation signals for the first to fourth flow path switching valves in order to switch the flow direction of the exhaust gas to the forward direction or the reverse direction. .
In the exhaust purification system of this embodiment, when the internal combustion engine is in a normal operating state, the valve opening signal is output to the first flow path switching valve and the third flow path switching valve, while the second A valve closing signal is output to the flow path switching valve and the fourth flow path switching valve. As a result, the exhaust gas flows in the forward direction, passes through the first oxidation catalyst, the particulate filter, the reduction catalyst, and the second oxidation catalyst in this order, and then flows into the forward discharge path.
On the other hand, when the exhaust gas temperature increase determination unit determines that the temperature of the exhaust gas increases, a valve opening signal is output to the second flow path switching valve and the fourth flow path switching valve, while the first A valve closing signal is output to the flow path switching valve and the third flow path switching valve. As a result, the exhaust gas flows in the reverse direction, passes through the second oxidation catalyst, the reduction catalyst, the particulate filter, and the first oxidation catalyst in this order, and then flows into the reverse discharge path.

When the internal combustion engine is in a normal operation state by opening / closing control of the first to fourth flow path switching valves, the particulate filter is arranged upstream in the exhaust gas flow direction by flowing the exhaust gas in the forward direction. In addition, since the reduction catalyst is disposed on the downstream side, it is possible to continuously regenerate the particulate filter using NO ₂ present in the exhaust gas. On the other hand, in a state where the temperature of the reduction catalyst is lowered and the injection control of the reducing agent is stopped, when the exhaust gas temperature rises, the exhaust gas is allowed to flow in the reverse direction, thereby upstream of the exhaust gas flow direction Because the reduction catalyst is placed in the downstream and the particulate filter is placed on the downstream side, the heat quantity of the exhaust gas is transferred to the reduction catalyst without being taken away by the particulate filter, and the temperature of the reduction catalyst is efficiently raised. Can do. Therefore, the temperature of the reduction catalyst quickly rises to the reference temperature or higher, and the injection control of the reducing agent by the first injection control unit is resumed early while returning the exhaust gas flow to the positive direction again.

3. Control Method of Exhaust Gas Purification Device for Internal Combustion Engine Next, an example of a routine of a control method of the exhaust gas purification device performed using the control device of the exhaust gas purification device of the present embodiment shown in FIG. Will be described with reference to FIG. This routine is always executed in the operating state of the internal combustion engine.

First, the reducing agent injection control method will be described with reference to the flowchart of FIG.
In step S11 after the start, the DCU reads signals indicating the rotational speed Ne and torque Tr of the internal combustion engine. Next, at step S12, it is determined whether or not the read rotational speed Ne and torque Tr of the internal combustion engine are equal to or less than predetermined threshold values Ne0 and Tr0. If either the rotational speed Ne or the torque Tr of the internal combustion engine exceeds the predetermined threshold values Ne0, Tr0, NO is determined in step S12 and the process proceeds to step S20.

  In this embodiment, in steps S11 to S12, the prediction of the temperature transition of the reduction catalyst is predicted from the values of the engine speed Ne and the torque Tr in the internal combustion engine, but various prediction methods are conceivable. For example, it is predicted from changes in the engine speed Ne and torque Tr, predicted from changes in the temperature of the exhaust gas detected by the third temperature sensor, and further, the first temperature sensor and the second temperature sensor. It can be predicted from the change transition of the estimated temperature of the reduction catalyst calculated by the temperature sensor.

After step S20, the reducing agent injection control in the normal mode is performed.
In the control of the reducing agent in the normal mode, first, in step S20, the temperature Tt of the reduction catalyst is calculated based on the temperature signals detected by the first temperature sensor and the second temperature sensor, and then in step S21. Then, it is determined whether or not the temperature Tt of the reduction catalyst is equal to or higher than a predetermined reference temperature Tt0. In step S21, it is determined whether or not the temperature Tt of the reduction catalyst is equal to or higher than the temperature at which the reducing agent is hydrolyzed and ammonia is generated. When the temperature Tt of the reduction catalyst is lower than the predetermined reference temperature Tt0, it is determined as NO in Step S21, and the process proceeds to Step S41 described later without performing the injection of the reducing agent. On the other hand, if the temperature Tt of the reduction catalyst is equal to or higher than the predetermined reference temperature Tt0, YES is determined in step S21, and in step S22, ammonia corresponding to the temperature Tt of the reduction catalyst is determined from the first target adsorption amount curve NT1. The target adsorption amount NT is obtained, and the process proceeds to step S16.

  On the other hand, if both the rotational speed Ne and the torque Tr of the internal combustion engine are equal to or less than the predetermined threshold values Ne0 and Tr0 in step S12 described above, it is determined as YES and the process proceeds to step S13. In this case, there is a possibility that the temperature Tt of the reduction catalyst continuously decreases and becomes lower than the reference temperature Tt0. Therefore, the injection control of the reducing agent in the increasing mode is performed after step S13.

  In the reducing agent injection control in the increasing mode, first, in step S13, the temperature Tt of the reducing catalyst is calculated based on the temperature signals detected by the first temperature sensor and the second temperature sensor, and then in step S14. Then, it is determined whether or not the temperature Tt of the reduction catalyst is equal to or higher than a predetermined reference temperature Tt0. In step S14, as in step S21, it is determined whether or not the temperature Tt of the reduction catalyst is equal to or higher than the temperature at which the reducing agent is hydrolyzed and ammonia is generated. When the temperature Tt of the reduction catalyst is lower than the predetermined reference temperature Tt0, it is determined as NO in Step S14, and the process proceeds to Step S41 described later without performing the injection of the reducing agent. On the other hand, if the temperature Tt of the reduction catalyst is equal to or higher than the predetermined reference temperature Tt0, YES is determined in step S14, and ammonia corresponding to the temperature Tt of the reduction catalyst is determined from the second target adsorption amount curve NT2 in step S15. The target adsorption amount NT is obtained, and the process proceeds to step S16.

In step S16, where the target adsorption amount NT is obtained in step S15 or step S22, the actual adsorption amount NR of ammonia currently adsorbed on the reduction catalyst is calculated. For example, the value obtained by subtracting the amount of ammonia used for the reduction of NO _x contained in the exhaust gas from the amount of ammonia corresponding to the amount of reducing agent actually injected so far is added to the reduction catalyst. By adding the amount of ammonia adsorbed (previous value), the actual adsorption amount NR of ammonia in the reduction catalyst is calculated.

  Next, in step S17, the current ammonia adsorption amount NR obtained in step S16 is subtracted from the ammonia target adsorption amount NT obtained in step S15 or step S22 to calculate a shortage amount ΔN. Next, in step S18, it is determined whether or not the value of the ammonia shortage amount ΔN obtained in step S17 is 0 or more. As a result, when it is less than 0, it is determined as NO, and it is not necessary to newly supply ammonia, and thus the process ends. On the other hand, if it is 0 or more, it is determined as YES and the process proceeds to step S19, where a reducing agent injection instruction value U that is a value of the reducing agent amount to be injected from the reducing agent supply device is calculated.

Here, an example of a flow of calculation of the reducing agent injection instruction value U performed in step S19 is shown in FIG.
In this example, first, in step S31, a reducing agent required amount U1 that can generate ammonia for the ammonia shortage amount ΔN calculated in step S17 is calculated.
Then, in step S32, after reading the signal indicating the exhaust NO _X concentration Nd detected by the exhaust gas flow rate Gf and the upstream-side NO _X sensor discharged from the internal combustion engine, in step S33, these exhaust gas flow rate Gf and it calculates the discharge amount of NO _X Nf from exhaust NO _X concentration Nd. Then, in step S34, it calculates the amount NC ammonia required for reducing the emission amount of NO _X Nf content of NO _X, in step S35, the reducing agent required amount amount NC partial ammonia ammonia can be generated U2 Is calculated.
Next, in step S36, the reducing agent required amount U1 calculated in step S21 and the reducing agent required amount U2 calculated in step S35 are added to calculate a reducing agent injection instruction value U.

In the example of FIG. 7, determine the discharge amount of NO _X Nf flowing at that time, although the amount of ammonia NC corresponding to the discharge amount of NO _X Nf to be added to the injection instruction value U1 of the reducing agent, step S32~ skip step S36, only in consideration of the target adsorption amount NT without considering the amount of NO _X Nf discharged, also a reducing agent required amount U1 calculated in step S21 as it is as the injection instruction value U Good.

  After calculating the reducing agent injection instruction value U in this manner, in step S20, a control signal corresponding to the reducing agent injection instruction value U is output to the reducing agent supply device, and the process is terminated.

Next, regarding the exhaust gas flow path switching control method that is performed in the state in which it is determined in step S14 or step S21 described above that the temperature of the reduction catalyst is lower than the reference temperature and the reducing agent injection control is stopped, This will be described with reference to the flowchart of FIG.
First, in step S41 after the start, the DCU 29 reads the rotational speed Ne, the torque Tr, the intake air amount As, the fuel injection amount Q, and the temperature Tg detected by the third temperature sensor of the internal combustion engine, and then proceeds to step S42. move on.

Next, in step S42, the exhaust gas temperature Tg is determined based on the internal combustion engine speed Ne, torque Tr, intake air amount As, fuel injection amount Q, and exhaust gas temperature Tg read in step S41. Predict whether it will rise in the future.
If it is predicted that the temperature Tg of the exhaust gas will not rise, NO is determined in step S42 and the process returns to the start position. On the other hand, when it is predicted that the temperature Tg of the exhaust gas will rise, YES is determined in step S42, and the process proceeds to step S43.

  Next, in step S43, the second flow path switching valve V2 and the fourth flow path switching valve V4 are closed, while the first flow path switching valve V1 and the third flow path switching valve V3 are opened. It is determined whether or not it is in the state. In step S43, it is determined whether or not the flow path of the exhaust gas is in a positive direction so that the exhaust gas passes through the reduction catalyst after passing through the particulate filter. When it is determined that the temperature of the exhaust gas will rise for the first time after the temperature of the reduction catalyst falls below the reference temperature and the reducing agent injection control is stopped, YES is always determined in step S43.

  If YES is determined in step S43, the second flow path switching valve V2 and the fourth flow path switching valve V4 are opened in step S44, while the first flow path switching valve V1 and the third flow path are opened. The path switching valve V3 is closed, and after the exhaust gas passes through the reduction catalyst, the flow path of the exhaust gas is switched in the reverse direction so as to pass through the particulate filter, and the process proceeds to step S45. On the other hand, if the flow direction of the exhaust gas has already been reversed in step S43, it is determined as NO and the process proceeds to step S45. That is, at the stage of proceeding to step S45, the flow direction of the exhaust gas is always switched to the reverse direction, so that the exhaust gas passes through the reduction catalyst before the particulate filter. Therefore, the reduction catalyst can be efficiently heated without the heat quantity of the exhaust gas being taken away by the particulate filter.

  Next, in step S45, it is determined whether or not the temperature Tt of the reduction catalyst is equal to or higher than a predetermined reference temperature Tt0. In step S45, it is determined whether or not the temperature Tt of the reduction catalyst is equal to or higher than the temperature at which the reducing agent is hydrolyzed and ammonia is generated. If the temperature Tt of the reduction catalyst is lower than the reference temperature Tt0, NO is determined in step S45, and the process returns to the start position. The state of the flow path switching valve when it is returned from step S45 to step S41 is that the second flow path switching valve V2 and the fourth flow path switching valve V4 are opened while the first flow path switching valve is open. V1 and the third flow path switching valve V3 are closed. Therefore, in the determination of the next step S43, it is always determined as NO, and the process proceeds to step S45.

  On the other hand, when the temperature Tt of the reduction catalyst is equal to or higher than the predetermined reference temperature Tt0 in step S45, YES is determined in step S45, and the process proceeds to step S46. In step S46, the second flow path switching valve V2 and the fourth flow path switching valve V4 are closed, while the first flow path switching valve V1 and the third flow path switching valve V3 are opened, and the exhaust gas. After passing through the particulate filter, the flow of exhaust gas is switched in the positive direction so as to pass through the reduction catalyst. After step S46 is completed, the reducing agent injection control is performed again according to the flow of FIG.

As described above, according to the control method of the exhaust gas purification apparatus of the present embodiment, when it is predicted that the temperature of the reduction catalyst becomes lower than the reference temperature at which the injection control of the reducing agent is stopped, Compared with normal injection control, NO _x reduction efficiency after reducing agent injection control is stopped by controlling the injection of reducing agent with a larger amount of ammonia adsorbed on the catalyst. And can be improved relatively.
In addition, when the exhaust gas temperature is predicted to rise while the reducing agent injection control is stopped, the exhaust gas is allowed to pass through the reduction catalyst before the particulate filter. By switching the flow path, the temperature of the reduction catalyst can be raised efficiently without the amount of heat of the exhaust gas being taken away by the particulate filter. Therefore, the temperature of the reduction catalyst can be quickly increased to or higher than the reference temperature at which the injection control of the reducing agent takes place, an efficient reduction and purification of the NO _X early by switching again the flow path of the exhaust gas in the forward direction It can be resumed.

4). Modifications The configuration of the exhaust gas purification apparatus for an internal combustion engine according to the present invention is not limited to the configuration shown in FIG. 1, and various modifications are possible. Hereinafter, modifications of the exhaust emission control device will be described with reference to the drawings. In each figure, the same reference numerals as those in FIG. 1 denote the same members, and the description will focus on the differences from the configuration of the exhaust gas purification apparatus in FIG.

(1) First Modification FIG. 9 shows a first modification of the exhaust emission control device.
In the example of the exhaust gas purification apparatus 40 shown in FIG. 9, the exhaust gas flow path configuration switched in the forward direction or reverse direction by the exhaust gas flow path switching means is the same as that of the exhaust gas purification apparatus shown in FIG. However, instead of the first oxidation catalyst 21 in the upstream exhaust passage 16 and the second oxidation catalyst 22 in the downstream exhaust passage 17 shown in FIG. 1, one oxidation catalyst is provided in the exhaust passage 12 connected to the internal combustion engine 11. 36 is arranged.
In the configuration of the exhaust gas purification device 40, when the flow direction of the exhaust gas is positive, the first flow path switching valve 23 and the third flow path switching valve 27 are provided as shown in FIG. While being opened, the second flow path switching valve 24 and the fourth flow path switching valve 28 are closed. Therefore, the exhaust gas discharged from the internal combustion engine 11 sequentially passes through the oxidation catalyst 36, the particulate filter 20, and the reduction catalyst 21, and flows to the forward discharge path 26.
On the other hand, when the flow direction of the exhaust gas is reverse, as shown in FIG. 10B, the second flow path switching valve 24 and the fourth flow path switching valve 28 are opened, while the first flow path switching valve 24 is opened. The flow path switching valve 23 and the third flow path switching valve 27 are closed. Therefore, the exhaust gas discharged from the internal combustion engine 11 sequentially passes through the oxidation catalyst 36, the reduction catalyst 21, and the particulate filter 20, and flows to the reverse discharge path 25.

In this example of the exhaust gas purification device 40, even if only one oxidation catalyst 36 is used, the exhaust gas always passes through the oxidation catalyst 36 regardless of whether the exhaust gas flows in the forward direction or the reverse direction. Can be made. Therefore, part of NO, HC, and CO in the exhaust gas is oxidized to generate NO ₂ , CO _{2, and the} like. Therefore, when the exhaust gas flows in the forward direction, the particulate filter is continuously regenerated and NO _X is generated. When the exhaust gas flows in the opposite direction, the temperature of the exhaust gas further increases, and the reduction catalyst can be efficiently heated.
However, in such a configuration, when exhaust gas is flowed in the positive direction and injection control of the reducing agent is performed, ammonia that has not been used for reduction of NO _{x by} the reduction catalyst passes through the oxidation catalyst. Therefore, more precise control of the reducing agent injection is required.

(2) Second Modification FIG. 11 shows a second modification of the exhaust emission control device.
In the example of the exhaust emission control device 50 shown in FIG. 11, the main exhaust passage 51 is configured in a straight line without being folded back, and the first oxidation catalyst 53, the particulate filter 20, the reduction catalyst 21, and the second oxidation catalyst. 55 are arranged in this order from the upstream side. Further, the exhaust passage 51 is provided with a first branch portion 57 upstream of the first oxidation catalyst 53, and the first branch portion 57 has a first branch portion downstream of the second oxidation catalyst 55. A first bypass passage 61 leading to the three branch portions 59 is connected. A second branch part 63 is provided between the first branch part 57 of the exhaust passage 51 and the first oxidation catalyst 53, and the second branch part 63 includes a third branch part 59. A second bypass passage 67 that leads to the fourth branching portion 65 on the further downstream side is connected.

A first flow path switching valve 71 is disposed in the exhaust passage 51 between the first branch portion 57 and the second branch portion 63, and the first branch portion 57 of the first bypass passage 61 A second flow path switching valve 73 is disposed in the vicinity, and a third flow path switching valve 75 is disposed in the vicinity of the second branch portion 63 of the second bypass passage 67.
Similarly, a fourth flow path switching valve 77 is disposed in the exhaust passage 51 between the third branch portion 59 and the fourth branch portion 65, and the third branch portion 59 of the first bypass passage 61. A fifth flow path switching valve 79 is disposed in the vicinity of the second bypass passage 67, and a sixth flow path switching valve 81 is disposed in the vicinity of the fourth branch portion 65 of the second bypass passage 67.

In the example of the exhaust gas purification device 50 shown in FIG. 11, first to sixth flow path switching valves 71, 73, 75, 77, 79, 81 are provided as exhaust gas flow path switching means. By controlling the opening and closing, the flow direction of the exhaust gas can be switched between the forward direction and the reverse direction.
That is, when the exhaust gas flow direction is positive, as shown in FIG. 12 (a), the first flow path switching valve 71 and the fourth flow path switching valve 77 are opened, while the second flow path switching valve 77 is opened. The flow path switching valve 73, the third flow path switching valve 75, the fifth flow path switching valve 79, and the sixth flow path switching valve 81 are closed. Therefore, the exhaust gas discharged from the internal combustion engine 11 sequentially passes through the first oxidation catalyst 53, the particulate filter 20, the reduction catalyst 21, and the second oxidation catalyst 55, and flows downstream.
On the other hand, when the flow direction of the exhaust gas is opposite, as shown in FIG. 12B, the second flow path switching valve 73, the third flow path switching valve 75, and the fifth flow path switching valve. 79 and the sixth flow path switching valve 81 are opened, while the first flow path switching valve 71 and the fourth flow path switching valve 77 are closed. Therefore, the exhaust gas discharged from the internal combustion engine 11 flows into the first bypass passage 61 side at the first branch portion 57, and the second oxidation catalyst 55, the reduction catalyst 21, the particulate filter 20, and the first oxidation filter. The catalyst 53 sequentially passes and flows downstream via the second bypass passage 67.

  The example of the exhaust gas purification device 50 is compact as the exhaust gas purification device 10 shown in FIG. 1 and does not have a structure with improved heat retention, but the temperature of the reduction catalyst is lower than the reference temperature, and the injection control of the reducing agent is performed. When the temperature of the exhaust gas is predicted to rise while the engine is stopped, the flow path of the exhaust gas can be switched so that the flow of the exhaust gas is reversed. Therefore, the reduction catalyst can be efficiently heated without the heat quantity of the exhaust gas being taken away by the particulate filter.

It is a figure which shows the structural example of the exhaust gas purification apparatus of the internal combustion engine of this embodiment. It is a figure for demonstrating the flow path of the exhaust gas which flows into a normal direction and a reverse direction. It is a figure which shows the relationship between the temperature of a reduction catalyst, and the saturated adsorption amount of ammonia. Is a diagram showing the relationship between the reduction efficiency of the adsorption rate and NO _X ammonia. It is a block diagram which shows the structural example of the control apparatus of an exhaust gas purification apparatus. It is a flowchart which shows an example of the injection control method of a reducing agent. It is a flowchart which shows an example of the calculation method of the injection instruction value of a reducing agent. It is a flowchart which shows an example of switching control of an exhaust gas flow path. It is a figure which shows the 1st modification of an exhaust gas purification apparatus. It is a figure for demonstrating the flow path of the exhaust gas which flows into the normal | positive direction and the reverse direction in the 1st modification of an exhaust gas purification apparatus. It is a figure which shows the 2nd modification of an exhaust gas purification apparatus. It is a figure for demonstrating the flow path of the exhaust gas which flows into the normal direction and the reverse direction in the 2nd modification of an exhaust gas purification apparatus.

Explanation of symbols

10: exhaust purification device (SCR system), 11: internal combustion engine, 12: exhaust passage, 13: ECU, 14: first branching portion, 15: second branching portion, 16: upstream exhaust passage, 17: downstream Side exhaust passage, 18: third branch, 19: first oxidation catalyst, 20: particulate filter, 21: reduction catalyst, 22: second oxidation catalyst, 23: first flow path switching valve, 24 : Second flow path switching valve, 25: reverse discharge path, 26: forward discharge path, 27: third flow path switching valve, 28: fourth flow path switching valve, 29: control unit (DCU) , 30: third temperature sensor, 31: a first temperature sensor, 32: second temperature sensor, 33: upstream NO _X sensor, 34: downstream NO _X sensor, 35: reducing agent injection valve, 36: Oxidation catalyst, 40: exhaust purification device, 50: exhaust purification device, 51: exhaust passage, 53: first Oxidation catalyst, 55: second oxidation catalyst, 57: first branch, 59: third branch, 61: first bypass passage, 63: second branch, 65: fourth branch Part, 67: second bypass passage, 71: first flow path switching valve, 73: second flow path switching valve, 75: third flow path switching valve, 77: fourth flow path switching valve, 79: Fifth flow path switching valve, 81: Sixth flow path switching valve

Claims (8)

A reduction catalyst disposed in an exhaust passage of the internal combustion engine; a reducing agent supply unit that is provided upstream of the reduction catalyst and supplies a reducing agent into the exhaust passage; and an exhaust upstream of the reducing agent supply unit An exhaust gas purification apparatus for an internal combustion engine, comprising: a particulate filter disposed in the exhaust passage on a side;
An exhaust gas flow switching means for switching the flow direction of the exhaust gas to the forward direction from the particulate filter to the reduction catalyst or the reverse direction from the reduction catalyst to the particulate filter;
A catalyst temperature detector for detecting the temperature of the reduction catalyst;
A reducing agent injection control unit that performs injection control of the reducing agent from the reducing agent supply unit in a state where the temperature of the reducing catalyst is equal to or higher than a predetermined temperature;
An exhaust gas temperature detector for detecting the temperature of the exhaust gas;
An exhaust gas temperature increase determination unit that determines whether or not the temperature of the exhaust gas increases when the temperature of the reduction catalyst is lower than the predetermined temperature;
The exhaust gas flow for controlling the exhaust gas flow path switching means so that the flow direction of the exhaust gas becomes the opposite direction when the exhaust gas temperature rise determination unit determines that the temperature of the exhaust gas rises A control unit of the path switching means;
An exhaust emission control device for an internal combustion engine, comprising: a control device including: The exhaust passage is provided on the upstream side of the particulate filter, and is provided between the first branch portion communicating with the downstream side of the reduction catalyst, the first branch portion, and the reduction catalyst, A second branch part that allows the exhaust gas flowing in the forward direction to flow further downstream; and a second branch part that is provided between the first branch part and the particulate filter, and further flows the exhaust gas that flows in the reverse direction further downstream. And a third branch that flows through
2. The exhaust gas flow path switching means comprises flow path switching valves provided in the first branch section, the second branch section, and the third branch section. An exhaust purification device for an internal combustion engine.   3. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, wherein the exhaust passage is folded between the particulate filter and the reduction catalyst, and the particulate filter and the reduction catalyst are brought close to each other.   The internal combustion engine according to claim 2 or 3, further comprising an oxidation catalyst between the third branch portion and the particulate filter and between the second branch portion and the reduction catalyst. Engine exhaust purification system.   The exhaust gas purification apparatus for an internal combustion engine according to claim 2 or 3, further comprising an oxidation catalyst upstream of the first branch portion.   The exhaust purification of an internal combustion engine according to any one of claims 1 to 5, wherein the exhaust gas temperature increase determination unit determines whether the temperature of the exhaust gas continuously increases for a predetermined time or more. apparatus.   The exhaust of the internal combustion engine according to any one of claims 1 to 5, wherein the exhaust gas temperature rise determination unit determines whether or not the temperature of the exhaust gas rises and exceeds a reference temperature. Purification equipment. A reduction catalyst disposed in an exhaust passage of the internal combustion engine; a reducing agent supply unit that is provided upstream of the reduction catalyst and supplies a reducing agent into the exhaust passage; and an exhaust upstream of the reducing agent supply unit In a control method of an exhaust gas purification device for an internal combustion engine, comprising a particulate filter disposed on the exhaust side on the side,
The exhaust gas purification device switches the exhaust gas flow path for switching the flow direction of the exhaust gas in the forward direction from the particulate filter to the reduction catalyst or in the reverse direction from the reduction catalyst to the particulate filter. Means for controlling the injection of the reducing agent from the reducing agent supply unit in a state where the temperature of the reduction catalyst is equal to or higher than a predetermined temperature.
In a state where the temperature of the reduction catalyst is lower than the predetermined temperature and the injection control of the reducing agent is stopped, it is determined whether or not the temperature of the exhaust gas is increased, and when the temperature of the exhaust gas is increased A control method for an exhaust gas purification apparatus for an internal combustion engine, wherein, when judged, the exhaust gas flow path switching means is controlled so that the flow direction of the exhaust gas is in the opposite direction.

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