JP2011127525A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine, reducing risk of outflow of reduction agent downstream of a selective reduction catalyst, and setting a target adsorption proportion in the selective reduction catalyst used for calculating a target injection amount high. <P>SOLUTION: The exhaust emission control device for an internal combustion engine reduces nitrogen oxide in exhaust gas by using the selective reduction catalyst which can adsorb the reduction agent. The exhaust emission control device for the internal combustion engine includes: a reduction agent supply means supplying the reduction agent to an exhaust passage upstream of the selective reduction catalyst; a catalyst temperature estimation means estimating a temperature of the selective reduction catalyst; a passage area restriction means disposed to an exhaust passage downstream of the selective reduction catalyst; and a control means increasing pressure in the exhaust passage of a region, where the selective reduction catalyst is disposed, by the passage area restriction means, so as to increase an adsorbable amount of the reduction agent in the selective reduction catalyst. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust purification device for an internal combustion engine for reducing nitrogen oxides in exhaust gas discharged from the internal combustion engine. In particular, the present invention relates to an exhaust gas purification apparatus for an internal combustion engine for reducing nitrogen oxides in exhaust gas using a selective reduction catalyst capable of adsorbing a reducing agent.

In many cases, exhaust gas discharged from an internal combustion engine such as a diesel engine contains nitrogen oxides (hereinafter referred to as “NO _x ”). As the exhaust gas purification device for purifying exhaust gas by reducing the NO _X, by injecting liquid reducing agent in the upstream of the selective reduction catalyst disposed in an exhaust passage such as hydrocarbons (HC) or ammonia adsorbing the reducing agent to the selective reduction catalyst, the exhaust purification device for purifying exhaust gas by reacting with a reducing agent to NO _X in the exhaust gas flowing into the selective reduction catalyst are known.

In the selective reduction catalyst used in this type of exhaust purification device, the amount of reducing agent that can be adsorbed is determined. Therefore, when the amount of reducing agent supplied to the selective reduction catalyst exceeds the adsorbable amount, a part of the reducing agent flows out downstream of the selective reduction catalyst, while when the amount of reducing agent adsorbed on the selective reduction catalyst is too small, not be nO _X is flow out to the downstream side of the selective reduction catalyst.

  The adsorbable amount of the reducing agent is a value that depends on the catalyst temperature, and as shown in FIG. 6A, the adsorbable amount Vmax decreases as the catalyst temperature Tcat increases. Therefore, in the situation where the temperature of the selective reduction catalyst decreases, the adsorbable amount increases, so there is very little risk of the reducing agent flowing out, while in the situation where the temperature of the selective reduction catalyst rapidly rises, the adsorbable amount decreases rapidly. Therefore, the adsorbed reducing agent may be released and flow out downstream of the selective reduction catalyst.

  Therefore, in the reducing agent supply device, the reducing agent does not flow downstream of the selective reduction catalyst even in a situation where the catalyst temperature rapidly rises and the adsorbable amount sharply decreases, for example, during regeneration of the particulate filter. Thus, the injection amount of the liquid reducing agent is set. Specifically, the target injection amount of the liquid reducing agent is, for example, a predetermined ratio in which the actual adsorption amount of the reducing agent in the selective reduction catalyst (hereinafter referred to as “estimated adsorption amount”) is smaller than the current adsorbable amount. Thus, it calculates | requires by a calculation based on the catalyst temperature, the operating state of an internal combustion engine, etc. (for example, refer patent document 1).

JP 2006-22729 A (FIG. 3 etc.)

However, as shown in FIG. 6B, the selective reduction catalyst has a higher NO _x purification efficiency η (hereinafter referred to as “the adsorption ratio”) as the ratio R of the estimated adsorption amount Vact to the adsorbable amount Vmax (hereinafter referred to as “adsorption ratio”) increases. It is called “catalytic efficiency”). Therefore, when the target injection amount is calculated so that the estimated adsorption amount Vact is smaller than the adsorbable amount Vmax and the injection control of the liquid reducing agent is performed, the reducing agent flows out downstream of the selective reduction catalyst. If the target adsorption ratio is set too low in order to suppress this, the purification performance of the selective reduction catalyst cannot be fully utilized.

  Accordingly, the inventors of the present invention diligently paid attention to the fact that the selective reduction catalyst has the property that the adsorbable amount of the reducing agent increases as the pressure of the gas (exhaust gas) increases. It has been found that such a problem can be solved by providing the passage area restricting means on the downstream side of the present invention, and the present invention has been completed. That is, the present invention reduces the risk that the reducing agent flows downstream from the selective reduction catalyst, and the internal combustion engine can set a high target adsorption ratio in the selective reduction catalyst used for calculating the target injection amount. An object is to provide an exhaust emission control device.

  According to the present invention, in an exhaust gas purification apparatus for an internal combustion engine for reducing nitrogen oxides in exhaust gas using a selective reduction catalyst capable of adsorbing a reducing agent, reduction is performed in an exhaust passage upstream of the selective reduction catalyst. Reducing agent supply means for supplying the agent, catalyst temperature estimation means for estimating the temperature of the selective reduction catalyst, passage area restriction means provided in the exhaust passage downstream of the selective reduction catalyst, and passage area restriction means And a control means for increasing the adsorbable amount of the reducing agent in the selective reduction catalyst by increasing the pressure in the exhaust passage in the region where the selective reduction catalyst is disposed. Can be provided to solve the above-mentioned problems.

  Further, in configuring the exhaust gas purification apparatus for an internal combustion engine of the present invention, the exhaust gas purification apparatus includes an adsorption amount calculation means for estimating the adsorption amount of the reducing agent in the selective reduction catalyst, and the reducing agent supply means is a reduction in the selective reduction catalyst. The reducing agent is supplied so that the adsorbed amount of the reducing agent becomes a predetermined ratio smaller than the adsorbable amount, and the control means adjusts the pressure in the exhaust passage when the adsorbing amount of the reducing agent exceeds the predetermined amount with respect to the adsorbable amount Is preferably increased.

  In configuring the exhaust gas purification apparatus for an internal combustion engine of the present invention, it is preferable that the control means increases the pressure in the exhaust passage when the temperature increase rate of the selective reduction catalyst exceeds a predetermined threshold value.

  Further, when configuring the exhaust gas purification apparatus for an internal combustion engine of the present invention, the exhaust gas purification apparatus includes a downstream side reducing agent concentration calculating means for detecting a reducing agent concentration on the downstream side of the selective reduction catalyst, and the control means includes a reducing agent. It is preferable to increase the pressure in the exhaust passage when the concentration exceeds a predetermined value.

  Further, in configuring the exhaust gas purification apparatus for an internal combustion engine of the present invention, it is preferable that the control means can execute control for increasing the pressure in the exhaust passage when the selective reduction catalyst is in an activated state.

According to the exhaust gas purification apparatus for an internal combustion engine of the present invention, the passage area restricting means is provided in the exhaust passage downstream of the selective reduction catalyst, and the exhaust pressure in the region where the selective reduction catalyst is disposed by the passage area restricting means. By providing a control means for increasing the adsorbable amount of the selective reduction catalyst, the amount of reducing agent supplied to the selective reduction catalyst exceeds the adsorbable amount and a part of the reducing agent is placed downstream of the selective reduction catalyst. In a situation where there is a possibility of flowing out, it is possible to suppress the outflow of the reducing agent by increasing the adsorbable amount. Therefore, the target adsorption ratio in the selective reduction catalyst used for calculating the target injection amount of the reducing agent can be set higher than before, and the NO _x purification efficiency can be increased.

  Further, in the exhaust gas purification apparatus for an internal combustion engine of the present invention, the control means raises the exhaust pressure when the adsorption ratio of the reducing agent with respect to the adsorbable amount by the selective reduction catalyst exceeds a predetermined ratio, so that the selective reduction catalyst In a situation where the amount of supplied reducing agent may exceed the adsorbable amount, the adsorbable amount is increased and the outflow of the reducing agent can be reduced.

  Further, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, when the rate of increase in the temperature of the selective reduction catalyst exceeds a predetermined threshold, the control means increases the exhaust pressure, so that the adsorbable amount on the selective reduction catalyst is reduced. In a situation where the amount of adsorption can be rapidly reduced, the amount of decrease in the amount that can be adsorbed can be kept small. Accordingly, it is possible to reduce the outflow of the reducing agent to the downstream side of the selective reduction catalyst.

  Further, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, when the outflow amount of the reducing agent on the downstream side of the selective reduction catalyst exceeds a predetermined value, the control means increases the exhaust pressure so that the downstream side of the selective reduction catalyst. It is possible to keep the amount of reducing agent flowing out to a level lower than a certain line.

  Further, in the exhaust gas purification apparatus for an internal combustion engine according to the present invention, when the selective reduction catalyst is in the activated state, the control means executes control to increase the exhaust pressure, thereby increasing the amount of adsorption that can be performed by increasing the exhaust pressure. The effect of increase is remarkably obtained, and the effectiveness of execution of the control of the present invention is easily obtained.

It is a figure showing an example of composition of an exhaust-air-purification device concerning an embodiment of the invention. It is a figure which shows the relationship between exhaust pressure and the adsorption | suction possible amount of a reduction catalyst. It is a block diagram which shows the structural example of the control apparatus concerning the 1st Embodiment of this invention. It is a figure for demonstrating an example of the calculation method of the target injection quantity of a reducing agent. It is a flowchart for demonstrating the control method concerning the 1st Embodiment of this invention. It is a figure which shows the relationship between catalyst temperature and the amount which can be adsorbed, and the relationship between adsorption | suction ratio and catalyst efficiency.

  DESCRIPTION OF EMBODIMENTS Embodiments relating to an exhaust gas purification apparatus 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, in each figure, what has attached | subjected the same code | symbol has shown the same member, and description is abbreviate | omitted suitably.

[First Embodiment]
1. Overall Configuration First, an example of the overall configuration of an exhaust emission control device for an internal combustion engine according to an embodiment of the present invention (hereinafter simply referred to as “exhaust emission control device”) will be described.
FIG. 1 shows a selective reduction catalyst (hereinafter simply referred to as “reduction catalyst”) 13 disposed in an exhaust passage by injecting and supplying an aqueous urea solution as a liquid reducing agent upstream of the reduction catalyst 13. 1 shows a configuration example of an exhaust purification apparatus 10 that selectively reduces and purifies NO _x contained in exhaust gas using ammonia generated from an aqueous urea solution.

The exhaust purification device 10 is provided in the middle of an exhaust passage connected to the internal combustion engine 5, and includes a reduction catalyst 13 for selectively reducing NO _x contained in the exhaust gas, and a reduction catalyst 13. The main components are a reducing agent supply device 40 for injecting and supplying the liquid reducing agent into the upstream exhaust passage, and a passage area restricting means 20 provided on the downstream side of the reduction catalyst 13. Further, the exhaust purification device 10 includes a control device 30 that controls the operation of the reducing agent supply device 40 and the passage area restricting means 20.

In this exhaust purification device 10, an exhaust temperature sensor 26 is provided upstream of the reduction catalyst 13, and a NO _x sensor 15 is provided downstream of the reduction catalyst 13. Instead of the upstream temperature sensor 26, temperature estimation means for estimating the exhaust temperature of each region by calculation may be provided. The NO _x sensor 15 is used to detect the NO _x concentration in the exhaust gas.

  The exhaust purification device 10 of this embodiment is an exhaust purification device in which a urea aqueous solution is used as a liquid reducing agent. The urea aqueous solution is mixed with the exhaust gas on the upstream side of the reduction catalyst 13, and ammonia generated by hydrolysis of the urea aqueous solution is adsorbed by the reduction catalyst 13. However, the liquid reducing agent to be used is not limited to the urea aqueous solution, and any other liquid reducing agent may be used as long as it can supply ammonia to the reducing catalyst 13. Further, unburned fuel capable of supplying HC to the reducing catalyst 13 is used as the liquid reducing agent. It can also be used.

2. Reduction catalyst The reduction catalyst 13 used in the exhaust purification device 10 of the present embodiment adsorbs ammonia produced by hydrolysis of an aqueous urea solution injected into exhaust gas by the reducing agent supply device 40, and flows into the exhaust gas. The catalyst is configured to reduce NO _x in the gas. As the reduction catalyst 13, for example, a zeolite-based reduction catalyst is used.

  As shown in FIG. 6A, the reduction catalyst 13 has a characteristic that the ammonia adsorbable amount Vmax decreases according to the catalyst temperature Tcat. Further, as shown in FIG. 6B, the reduction catalyst 13 has a characteristic that the catalyst efficiency η increases as the adsorption ratio R with respect to the adsorbable amount Vmax increases and the catalyst temperature Tcat increases. . Therefore, the target adsorption ratio Rtgt is determined so that the catalyst efficiency η is as high as possible while considering that a part of ammonia does not flow downstream from the reduction catalyst 13 due to a slight change in the catalyst temperature Tcat. .

  Further, as shown in FIG. 2, the reduction catalyst 13 has a characteristic that the adsorbable amount Vmax increases as the pressure in the region where the reduction catalyst 13 is arranged, that is, the exhaust pressure is higher. This characteristic is explained by the Langmuir adsorption isotherm shown in the following formula (1).

V = a × b × p / (1 + b × p) (1)
V: Adsorption amount a: Proportional constant b: Adsorption rate constant K / Desorption rate constant K ′
p: exhaust pressure

  Further, according to the above formula (1), the adsorbable amount Vmax can be further increased as the value of b is larger, that is, as the catalyst temperature Tcat is smaller in the desorption rate constant K ′. Is understood.

3. Reducing agent supply device A reducing agent supply device 40 includes a reducing agent injection valve 43 fixed to the exhaust pipe 11 upstream of the reducing catalyst 13, a storage tank 41 in which an aqueous urea solution as a liquid reducing agent is stored, and storage. The liquid reducing agent in the tank 41 is constituted by reducing agent pumping means 42 that pumps the liquid reducing agent toward the reducing agent injection valve 43. The reducing agent pressure feeding means 42 and the storage tank 41 are connected by a first supply passage 44, and the reducing agent pressure feeding means 42 and the reducing agent injection valve 43 are connected by a second supply passage 45.

  The reducing agent pumping means 42 is typically an electric pump, which pumps up the liquid reducing agent in the storage tank 41 and pumps it to the reducing agent injection valve 43. The reducing agent injection valve 43 is, for example, a reducing agent injection valve that is controlled to open and close by energization control. The operation of the reducing agent pumping means 42 and the reducing agent injection valve 43 is controlled by the control device 30. The liquid reducing agent pumped to the reducing agent injection valve 43 by the reducing agent pumping means 42 is injected into the exhaust passage when the reducing agent injection valve 43 is opened by a control signal output from the control device 30.

  The configuration of the reducing agent supply device 40 is not limited to the configuration in which the liquid reducing agent is directly injected into the exhaust pipe 11 from the reducing agent injection valve 43 as described above. For example, the liquid reducing agent is atomized using high-pressure air. In addition, an air assist type configuration may be used in which the air is supplied into the exhaust pipe 11.

4). Passage area restricting means The passage area restricting means 20 provided in the exhaust pipe 11 downstream of the reduction catalyst 13 is used to increase the exhaust pressure upstream of the exhaust passage by restricting the area of the exhaust passage. In particular, the object is to increase the exhaust pressure Pgas in the region where the reduction catalyst 13 is disposed.

  The configuration of the passage area restricting means 20 is not particularly limited as long as the area of the exhaust passage can be made variable. In the exhaust purification device 10 of the present embodiment, the passage area restricting means 20 uses a butterfly valve having the same configuration as the exhaust valve provided in the internal combustion engine 5. The operation of the passage area restricting means 20 is controlled by the control device 30.

5. FIG. 3 is a functional block diagram showing a part for controlling the reducing agent supply device 40 and the passage area restricting means 20 in the configuration of the control device 30 provided in the exhaust purification device 10 of the present embodiment. A configuration example is shown.

  The control device 30 includes a catalyst temperature calculation unit 31, a reducing agent injection amount calculation unit 32, a reducing agent supply device control unit 33, and a passage area restricting means control unit 34 as main components. The control device 30 is configured by a known microcomputer, and each unit is specifically realized by executing a program by a microcomputer (not shown).

(1) Catalyst Temperature Calculation Unit The catalyst temperature calculation unit 31 reads the sensor signal of the exhaust temperature sensor 26 and estimates the catalyst temperature Tcat based on the exhaust gas temperature TUgas calculated using this sensor signal. A specific calculation method is not particularly limited.

(2) Reducing agent injection amount calculation unit (estimated adsorption amount calculation unit)
The reducing agent injection amount calculation unit 32 obtains a required amount of ammonia to be supplied to the reduction catalyst 13 and calculates a target injection amount Qudtgt of the liquid reducing agent that generates ammonia corresponding to the required amount. In the calculation of the target injection amount Qudtgt, the current estimated adsorption amount Vact of ammonia in the reduction catalyst 13 is obtained, and the reducing agent injection amount calculation unit 32 also functions as the estimated adsorption amount calculation unit in the present invention. Have both.

FIG. 4 is a diagram conceptually illustrating an example of a calculation process of the target injection amount Qudtgt of the liquid reducing agent by the reducing agent injection amount calculation unit 32 of the control device 30 provided in the exhaust purification device 10 of the present embodiment. .
In this example, first, a map of the adsorbable amount Vmax of the reducing agent is calculated according to the catalyst temperature Tcat estimated by the catalyst temperature calculation unit 31, and the target adsorption rate Rtgt is multiplied by this adsorbable amount Vmax. Find the quantity Vtgt. The adsorbable amount Vmax used here is the adsorbable amount Vmax when the area of the exhaust passage is not narrowed. Thereafter, the current estimated adsorption amount Vact of ammonia in the reduction catalyst 13 obtained at the time of the previous target injection amount calculation is subtracted from the target adsorption amount Vtgt to calculate an excess / deficiency ammonia amount ΔV with respect to the target adsorption amount Vtgt. In addition, the flow rate of ammonia corresponding to the excess / deficiency ammonia amount ΔV is obtained.

In parallel with this, on the basis of the NO _X sensor and the flow rate of the NO _X in the current exhaust gas obtained by the calculation or the like, obtaining the flow rate of ammonia assuming the NO _X can be reduced to 100%. Flow rate of the NO _X can be obtained by multiplying the NO _X concentration Dnox the flow rate of the example exhaust gas. Thereafter, the ammonia for reducing NO _x in the exhaust gas currently flowing by multiplying the obtained ammonia flow rate by the catalyst efficiency η according to the current estimated adsorption amount Vact of ammonia in the reduction catalyst 13. Obtain the flow rate of

Then, the required flow rate of ammonia to be newly supplied is calculated by adding the two calculated flow rates of ammonia. The target injection amount Qudtgt of the liquid reducing agent is calculated as the amount of aqueous urea solution that generates ammonia at the required flow rate to be supplied. Further, the current estimated adsorption amount Vact of ammonia is the integral value of the value obtained by subtracting the flow rate of ammonia for reducing NO _x in the exhaust gas from the required flow rate of ammonia to be newly supplied, that is, excess or deficient ammonia. It is obtained as an integral value of the flow rate of ammonia according to the amount ΔV.

The catalyst efficiency η (%) corresponding to the estimated adsorption amount Vact can be obtained by map calculation. The control device 30 stores in advance a data map map so that the catalyst efficiency η (%) is obtained based on the catalyst temperature Tcat and the ammonia adsorption ratio R. The ammonia adsorption ratio R is obtained as a ratio of the estimated adsorption amount Vact to the adsorbable amount Vmax. However, the estimation method of the catalyst efficiency η (%) is not limited to such a method, and the catalyst temperature Tcat, the estimated adsorption amount Vact of ammonia in the reduction catalyst 13, the exhaust gas flow rate Fgas, the NO on the upstream side of the reduction catalyst 13. _The catalyst efficiency η can be modeled in consideration of the _X concentration, the ratio between the upstream NO concentration and the upstream NO ₂ concentration, the degree of deterioration of the reduction catalyst 13, and the like.

  However, the calculation method of the target injection amount Qudtgt is not limited to the above-described example, and various calculation methods can be employed. Further, the calculation method of the estimated adsorption amount Vact is not limited to the above-described example, and may be obtained separately from the calculation of the target injection amount Qudtgt.

(3) Reductant Supply Device Control Unit The reductant supply device control unit 33 controls the reductant pumping means 42 and based on the liquid reductant target injection amount Qudtgt calculated by the reductant injection amount calculation unit 32. Thus, opening / closing control of the reducing agent injection valve 43 is performed. In the exhaust purification apparatus 10 of the present embodiment, the reducing agent pressure feeding means 42 is feedback controlled so that the pressure of the liquid reducing agent supplied to the reducing agent injection valve 13 is maintained at a predetermined value. Further, in the exhaust purification device 10 of the present embodiment, the reducing agent injection valve 13 has a predetermined injection start cycle, and the energization control is performed based on the drive duty of the reducing agent injection valve 13 according to the target injection amount Qudtgt. Done.

(4) Passage Area Restricting Means Control Unit The passage area restricting means control unit 34 controls the passage area restricting means 20 provided on the downstream side of the reduction catalyst 13. In the present embodiment, the passage area restricting means control unit 34 is set to control the passage area restricting means 20 so that the exhaust passage area is in either a restricted state or a non-restricted state. ing.

  In this embodiment, it is set so that the area of the exhaust passage is reduced when the estimated adsorption amount Vact in the reduction catalyst 13 exceeds the control maximum threshold value Vα. Specifically, the control maximum threshold value Vα is set according to the catalyst temperature Tcat as a value corresponding to the upper limit threshold value Rmax of the ammonia adsorption ratio R, and the passage area restricting means control unit 34 determines the estimated adsorption amount Vact of ammonia. Whether or not exceeds the control maximum threshold value Vα. The upper limit threshold value Rmax of the adsorption ratio is set to a value larger than the target adsorption ratio Rtgt when calculating the target injection amount Qudtgt of the liquid reducing agent.

  When the estimated adsorption amount Vact exceeds the control maximum threshold value Vα, the ammonia supplied to the reduction catalyst 13 exceeds the adsorbable amount Vmax, and a part of the ammonia flows downstream from the reduction catalyst 13. Since there is a fear, the passage area restricting means controller 34 outputs a control signal to the passage area restricting means 20 so as to restrict the passage area.

  When the passage area is reduced, the exhaust pressure Pgas in the region where the reduction catalyst 13 is disposed increases, and the adsorbable amount Vmax in the reduction catalyst 13 increases. As a result, the ratio R ′ of the estimated adsorption amount Vact with respect to the adsorbable amount Vmax ′ after the increase is lower than the adsorption ratio R before the increase, so that the risk of ammonia flowing out downstream from the reduction catalyst 13 is reduced. Is done.

  Further, the passage area restricting means control unit 34 monitors whether or not the estimated adsorption amount Vact falls below the release threshold value Vβ after the passage area is reduced. Specifically, the release threshold value Vβ is set according to the catalyst temperature Tcat as a value corresponding to the release threshold ratio Roff with respect to the ammonia adsorbable amount Vmax when the passage area is not reduced. This cancellation threshold ratio Roff is set to a value smaller than the upper limit threshold Rmax. The release threshold ratio Roff is set to a value larger than the target adsorption ratio Rtgt used for calculating the target injection amount Qudtgt of the liquid reducing agent.

  When the estimated adsorption amount Vact falls below the release threshold value Vβ, the passage area restricting means control unit 34 determines that there is no risk of the ammonia flowing out downstream of the reduction catalyst 13, and based on the area of the exhaust passage. A control signal is output to the passage area restricting means 20 so as to return.

  In the example of the present embodiment, the passage area restricting means controller 34 is configured to restrict the passage area only when the catalyst temperature Tcat is equal to or higher than the activation temperature Tcat0. That is, even when the exhaust pressure is increased by reducing the passage area, the exhaust pressure is not increased in a state where the effect of increasing the adsorbable amount Vmax is small. Therefore, even when the effect of increasing the adsorbable amount Vmax is small, the load on the internal combustion engine 5 by increasing the exhaust pressure can be suppressed. The threshold value of the catalyst temperature Tcat for increasing the exhaust pressure is not limited to the activation temperature, and can be set as appropriate.

  In the example of the present embodiment, the passage area restricting means 20 changes the area of the exhaust passage in two stages, but it can be set so that the area of the exhaust passage is changed in more stages. However, in some cases, it is necessary to previously store data on the exhaust pressure and the adsorbable amount corresponding to the area of each exhaust passage, data on the catalyst efficiency η, and the like.

6). Next, an example of the control method of the exhaust gas purification device performed by the control device 30 of the present embodiment described so far will be specifically described based on the control flow of FIG. The following routine is always executed during the execution of the liquid reducing agent injection control.

First, in step S1 after the start, the flow rate Fgas the exhaust gas, NO _X concentration Dnox in the exhaust gas, the exhaust gas temperature TUgas on the upstream side of the reduction catalyst 13, reads the current estimated adsorption amount Vact. Next, in step S2, the catalyst temperature Tcat is calculated based on the exhaust gas temperature TUgas on the upstream side of the reduction catalyst 13, and the adsorbable amount Vmax, the target adsorption amount Vtgt, the control maximum threshold value Vα according to the catalyst temperature Tcat, The release threshold value Vβ is obtained.

  Next, in step S3, it is determined whether or not the estimated adsorption amount Vact exceeds the target adsorption amount Vtgt. If the estimated adsorption amount Vact is within the target adsorption amount Vtgt, it is less likely that ammonia will flow out downstream of the reduction catalyst 13, and thus the process proceeds to step S11, and after permitting the liquid reductant injection control, the target is set in step S12. The injection amount Qudtgt is calculated, the liquid reducing agent is injected in step S13, and this routine ends.

  On the other hand, in step S3, when the estimated adsorption amount Vact exceeds the target adsorption amount Vtgt, ammonia may flow out downstream of the reduction catalyst 13, and therefore the injection of the liquid reducing agent is prohibited in step S4. To do. Next, in step S5, it is determined whether or not the exhaust passage is restricted by the current passage area restricting means 20. If the exhaust passage is not constricted, the process proceeds to step S8, and it is determined whether or not the estimated adsorption amount Vact exceeds the control maximum threshold value Vα. If the estimated adsorption amount Vact is less than or equal to the control maximum threshold value Vα, the routine is terminated and the process returns to step S1, while if the estimated adsorption amount Vact exceeds the control maximum threshold value Vα, the process proceeds to step S9.

  In step S9, it is determined whether or not the catalyst temperature Tcat is equal to or higher than the activation temperature Tcat0. If the catalyst temperature Tcat is lower than the activation temperature Tcat0, the effect of increasing the adsorbable amount Vmax is small even if the passage area is narrowed and the exhaust pressure is increased, so this routine is terminated and the routine returns to step S1. On the other hand, if the catalyst temperature Tcat is equal to or higher than the activation temperature Tcat0, the process proceeds to step S10, the passage area restricting means 20 is controlled to restrict the passage area, and then this routine is terminated and the process returns to step S1. As a result, the exhaust pressure Pgas in the region where the reduction catalyst 13 is disposed increases, and the adsorbable amount Vmax in the reduction catalyst 13 becomes the increased adsorbable amount Vmax ′.

  In step S5 described above, if the exhaust passage is in a throttled state, the process proceeds to step S6, where it is determined whether or not the estimated adsorption amount Vact is below the release threshold value Vβ. If the estimated adsorption amount Vact is greater than or equal to the release threshold value Vβ, the routine ends with the exhaust passage being narrowed, and the process returns to step S1. On the other hand, if the estimated adsorption amount Vact is less than the release threshold value Vβ, the process proceeds to step S7, the passage area restricting means 20 is controlled to return the passage area to the original, the routine is terminated, and the process returns to step S1. . As a result, the exhaust pressure in the region where the reduction catalyst 13 is disposed is returned to the original state, and the adsorbable amount Vmax in the reduction catalyst 13 is returned to the normal adsorbable amount Vmax.

  As described above, the exhaust gas purification apparatus 10 of the present embodiment reduces the exhaust pressure when the estimated ammonia adsorption amount Vact in the reduction catalyst 13 exceeds the amount corresponding to the upper limit threshold ratio Rmax with respect to the adsorbable amount Vmax. Control is performed to increase the adsorbable amount Vmax of the catalyst 13. Thereby, the possibility that ammonia flows out downstream of the reduction catalyst 13 is reduced. Therefore, the target adsorption ratio Rtgt used for calculating the target injection amount Qudtgt of the liquid reducing agent in a normal state where the passage area is not reduced can be set high, and the catalyst efficiency η can be increased.

[Second Embodiment]
The exhaust emission control apparatus according to the second embodiment of the present invention is the first embodiment in that it is set so that the trigger for reducing the area of the exhaust passage by the passage area restricting means is determined from the change in the catalyst temperature Tcat. It differs from the exhaust gas purification device of the form. The following description will focus on differences from the first embodiment.

  As already described, since the adsorbable amount Vmax of the reduction catalyst 13 has a characteristic of decreasing as the catalyst temperature Tcat increases, the adsorbable amount Vmax when the catalyst temperature Tcat increases rapidly. Decreases rapidly, the ammonia adsorption amount becomes saturated, and the possibility that ammonia flows out downstream of the reduction catalyst 13 increases. Therefore, the exhaust purification device 10 of the present embodiment is set to increase the exhaust pressure Pgas and increase the adsorbable amount Vmax when the catalyst temperature Tcat starts to increase rapidly.

  Specifically, in the present embodiment, the passage area restricting means control unit 34 constituting the control device 30 continuously reads the catalyst temperature Tcat and calculates the change rate X, and the change rate X is a preset temperature. Control is performed so that the area of the exhaust passage is reduced when the rate of increase X0 is exceeded.

  The temperature rise rate X0 can be set to an arbitrary value. For example, the closer the target adsorption rate Rtgt in the liquid reductant injection control to 1, the shorter the time it takes for the estimated adsorption amount Vact to reach the adsorbable amount Vmax, so the higher the set target adsorption rate Rtgt, the higher the temperature It is preferable to set the rate of increase X0 to a small value. The temperature increase rate X0 may be a fixed value, but the smaller the current adsorption rate R, the longer the time it takes for the estimated adsorption amount Vact to reach the adsorbable amount Vmax. Accordingly, it is possible to set a variable value such that the temperature increase rate X0 increases as the adsorption ratio R decreases.

  Further, after the passage area is reduced, the passage area restricting means controller 34 monitors whether or not the estimated adsorption amount Vact is lower than the release threshold value Vβ, as in the first embodiment, and the estimated adsorption amount Vact. Is lower than the release threshold value Vβ, a control signal is output so as to restore the area of the exhaust passage.

  As described above, the exhaust gas purification apparatus 10 according to the present embodiment controls to increase the exhaust pressure and increase the adsorbable amount Vmax of the reduction catalyst 13 when a state in which the adsorbable amount Vmax is rapidly decreased is detected. I do. Thereby, the possibility that ammonia flows out downstream of the reduction catalyst 13 is reduced. Therefore, the target adsorption ratio Rtgt used for calculating the target injection amount Qudtgt of the liquid reducing agent in a normal state where the passage area is not reduced can be set high, and the catalyst efficiency η can be increased.

[Third Embodiment]
The exhaust emission control apparatus according to the third embodiment of the present invention is set so that the trigger for reducing the area of the exhaust passage by the passage area restricting means is determined from the NO _x concentration downstream of the reduction catalyst. This is different from the exhaust purification apparatus of the previous embodiments. The following description will focus on differences from the first embodiment.

  The exhaust purification device of the present embodiment detects the ammonia concentration A in the exhaust gas on the downstream side of the reduction catalyst, increases the exhaust pressure Pgas when the ammonia concentration A exceeds the upper limit threshold A0, and can be adsorbed It is set to increase Vmax.

  Specifically, the exhaust purification apparatus of this embodiment includes an ammonia concentration detection sensor that can detect the ammonia concentration on the downstream side of the reduction catalyst. Further, the control device is provided with an ammonia concentration detection unit that obtains the ammonia concentration based on the sensor signal of the ammonia concentration detection sensor. This ammonia concentration detection unit continuously detects the ammonia concentration A and compares it with the upper limit threshold A0. When the ammonia concentration A exceeds the upper limit threshold A0, the passage area restricting means control unit controls the exhaust passage area. Send instructions to. The upper limit threshold A0 can be set to an arbitrary value according to the presence or absence of a catalyst that decomposes ammonia on the downstream side of the reduction catalyst, the exhaust purification standard, and the like.

  As described above, the exhaust purification apparatus of the present embodiment performs control to increase the exhaust pressure and increase the adsorbable amount Vmax of the reduction catalyst when the ammonia concentration downstream of the reduction catalyst exceeds the upper limit threshold A0. Do. As a result, the possibility of a significant amount of ammonia flowing downstream from the reduction catalyst is reduced. Therefore, the target adsorption ratio Rtgt used for the calculation of the target injection amount Qudtgt of the liquid reducing agent in a normal state where the passage area is not reduced can be set high, and the catalyst efficiency η can be increased.

5: engine, 10: exhaust gas purification device, 11: exhaust pipe, 13: reduction catalyst, 15: NO _X sensor 20: passage area throttle means, 26: exhaust gas temperature sensor, 30: controller, 31: catalyst temperature calculation Unit: 32: reducing agent injection amount calculating unit, 33: reducing agent supply device control unit, 34: passage area restricting means control unit, 40: reducing agent supply device, 41: storage tank, 42: reducing agent pressure feeding unit, 43: Reducing agent injection valve

Claims (5)

In an exhaust gas purification apparatus for an internal combustion engine for reducing nitrogen oxides in exhaust gas using a selective reduction catalyst capable of adsorbing a reducing agent,
Reducing agent supply means for supplying a reducing agent to the exhaust passage upstream of the selective reduction catalyst;
Catalyst temperature estimating means for estimating the temperature of the selective reduction catalyst;
Passage area restricting means provided in the exhaust passage downstream of the selective reduction catalyst;
Control means for increasing the adsorbable amount of the reducing agent in the selective reduction catalyst by increasing the pressure in the exhaust passage in the region where the selective reduction catalyst is arranged by the passage area restricting means;
An exhaust emission control device for an internal combustion engine, comprising: The exhaust purification device includes an adsorption amount calculation means for estimating an adsorption amount of the reducing agent in the selective reduction catalyst,
The reducing agent supply means supplies the reducing agent so that the amount of adsorption of the reducing agent in the selective reduction catalyst is a predetermined ratio smaller than the adsorbable amount,
The exhaust of the internal combustion engine according to claim 1, wherein the control means increases the pressure in the exhaust passage when the amount of the reducing agent adsorbed exceeds the predetermined ratio with respect to the adsorbable amount. Purification equipment.   The exhaust purification of an internal combustion engine according to claim 1 or 2, wherein the control means increases the pressure in the exhaust passage when the rate of temperature increase of the selective reduction catalyst exceeds a predetermined threshold. apparatus. The exhaust purification device includes a downstream side reducing agent concentration calculating means for detecting the reducing agent concentration on the downstream side of the selective reduction catalyst,
The exhaust purification device for an internal combustion engine according to any one of claims 1 to 3, wherein the control means increases the pressure in the exhaust passage when the reducing agent concentration exceeds a predetermined value. .   The said control means can perform control which raises the pressure in the said exhaust passage when the said selective reduction catalyst is in an activated state, The control method as described in any one of Claims 1-4 characterized by the above-mentioned. An exhaust purification device for an internal combustion engine.

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