JP6927765B2 - Exhaust purification control device for internal combustion engine - Google Patents

Description

In the present invention, a selective reduction catalyst, an addition valve arranged upstream of the selective reduction catalyst to add urea water to the exhaust gas, and urea water injected from the addition valve are provided in the exhaust passage of the internal combustion engine. The present invention relates to an exhaust gas purification control device for an internal combustion engine, which is applied to an exhaust gas purification device provided with a disperser.

For example, in Patent Document 1 below, urea water is injected from a urea water injection nozzle (addition valve) toward a mixer (dispersor) upstream of a urea SCR catalyst (selective reduction catalyst) in an exhaust passage. An exhaust purification device that promotes mixing of urea water and exhaust gas is described.
It is well known that the amount of urea water injected by the addition valve is an amount that can react with the amount of NOx in the exhaust gas.

Japanese Unexamined Patent Publication No. 2009-2213

By the way, when the temperature of the exhaust gas is low, the urea injected from the addition valve is deposited as a urea-modified product in the disperser. After that, when the temperature of the exhaust gas rises, the urea-modified product accumulated in the disperser is decomposed into ammonia. For this reason, if the temperature of the exhaust gas rises when urea modified products are deposited on the disperser, the amount of urea water injected by the addition valve may be set to an amount that can react with the amount of NOx in the exhaust gas. The amount of ammonia flowing into the catalyst may be excessive.

In order to solve the above problems, the control device of the internal combustion engine includes a selective reduction catalyst in the exhaust passage of the internal combustion engine and an addition valve arranged upstream of the selective reduction catalyst to add urea water to the exhaust. It is applied to an exhaust gas purification device provided with a disperser for dispersing urea water injected from the addition valve, and when the temperature of the exhaust is equal to or higher than a specified temperature, deposits are deposited on the disperser. If it is present, a reduction treatment is performed to reduce the amount of urea water injected from the addition valve as compared with the case where it is not deposited.

When urea water is injected from the addition valve when the exhaust temperature is low, a part of it is deposited as a urea modifier in the disperser. When the temperature of the exhaust gas rises, the urea-modified product deposited on the disperser decomposes and desorbs from the disperser as ammonia. Therefore, according to the above configuration, by setting the specified temperature to the temperature at which ammonia is desorbed, when the desorbed ammonia flows into the selective reduction catalyst, urea is injected from the addition valve by performing a reduction treatment. The amount of water can be reduced. This makes it possible to prevent the amount of ammonia flowing into the selective reduction catalyst from becoming excessive.

The figure which shows the exhaust gas purification control device and the exhaust gas purification device which concerns on 1st Embodiment. The flow chart which shows the procedure of the addition treatment of urea water which concerns on this embodiment. The figure which shows the exhaust gas purification control device and the exhaust gas purification device which concerns on 2nd Embodiment. The flow chart which shows the procedure of the addition treatment of urea water which concerns on this embodiment. The figure which shows the structure for detecting the sedimentation amount of the disperser which concerns on 3rd Embodiment.

<First Embodiment>

In the internal combustion engine 10 shown in FIG. 1, the air sucked into the intake passage 12 flows into the downstream side of the throttle valve 16 via the supercharger 14, and the cylinder 20 and the piston are opened as the intake valve 18 is opened. It flows into the combustion chamber 24 partitioned by 22. A fuel injection valve 26 is provided in the combustion chamber 24, and a mixture of the fuel injected from the fuel injection valve 26 and the air flowing into the combustion chamber 24 is subjected to combustion by compression ignition. The combustion energy of the air-fuel mixture is converted into the rotational energy of the crankshaft 28 via the piston 22. The air-fuel mixture used for combustion in the combustion chamber 24 is discharged to the exhaust passage 32 as exhaust gas as the exhaust valve 30 is opened. The intake passage 12 and the exhaust passage 32 are connected by an EGR passage 34, and the EGR passage 34 is provided with an EGR valve 36 for adjusting the cross-sectional area of the passage.

An oxidation catalyst 38 and a diesel particulate filter (DPF40) are provided downstream of the supercharger 14 in the exhaust passage 32 in this order from the upstream side. Further, downstream of the DPF 40, a selective reduction catalyst (SCR42) and an ammonia oxidation catalyst 44 that oxidizes ammonia are provided in this order from the upstream side.

Further, an addition valve 46 for adding urea water to the exhaust gas is provided between the SCR 42 and the DPF 40, and a disperser 48 for dispersing the urea water is provided downstream of the addition valve 46. The addition valve 46 injects urea water toward the disperser 48, whereby the urea water is dispersed in the disperser 48, and the degree of mixing between the exhaust gas and the urea water is increased. The urea water stored in the tank 50 is pumped up and supplied to the addition valve 46 by the pump 52.

The control device 60 controls the internal combustion engine 10 and controls various operation target devices such as the throttle valve 16, the fuel injection valve 26, the EGR valve 36, and the addition valve 46 to control the amount (torque, exhaust component). To control. The control device 60 controls the control amount, such as the intake air amount Ga detected by the air flow meter 70, the output signal Scr of the crank angle sensor 72, and the exhaust discharged from the supercharger 14 detected by the exhaust temperature sensor 74. Temperature (exhaust temperature Tex) is taken in. Further, the control device 60 has an upstream concentration NOxu which is the concentration of the upstream NOx detected by the upstream NOx sensor 76 and a downstream concentration NOxd which is the concentration of the downstream NOx detected by the downstream NOx sensor 78. To capture. The control device 60 includes a CPU 62, a ROM 64, and a RAM 66, and the CPU 62 executes a program stored in the ROM 64 to control the control amount.

FIG. 2 shows a processing procedure for exhaust gas purification control using the addition valve 46. The process shown in FIG. 2 is realized by the CPU 62 repeatedly executing the program stored in the ROM 64 at a predetermined cycle. In the following, the step number is represented by a number with "S" added at the beginning.

In the series of processes shown in FIG. 2, the CPU 62 first calculates the amount of urea water (equal ratio QSR) that reacts with the NOx flow rate in the exhaust without excess or deficiency based on the upstream concentration NOxu and the exhaust flow rate (S10). ). Here, the CPU 62 calculates the exhaust flow rate based on the intake air amount Ga and the fuel injection amount. Next, the CPU 62 calculates an increase correction amount ΔQ that increases the amount of urea water injected from the addition valve 46 with respect to the equivalent ratio QSR based on the downstream concentration NOxd and the exhaust flow rate (S12). Specifically, the CPU 62 first calculates the NOx flow rate in the exhaust downstream of the SCR 42 based on the downstream concentration NOxd and the exhaust flow rate. Next, the CPU 62 lacks an equal amount ratio QSR to the amount of urea water that can react with the calculated NOx flow rate without excess or deficiency with the amount of urea water that can react with the NOx flow rate in the exhaust upstream of the SCR 42 without excess or deficiency. It is regarded as an amount, and this shortage amount is defined as an increase correction amount ΔQ. When the downstream concentration NOxd is zero, the increase correction amount ΔQ is zero. Then, the CPU 62 sets the command value (injection amount command value QS *) of the urea water injection amount per unit time from the addition valve 46 to a value obtained by increasing the equal amount ratio QSR by the increase correction amount ΔQ (S14). ..

Next, the CPU 62 determines whether or not the exhaust temperature Tex is equal to or higher than the specified temperature Tth (S16). Here, the specified temperature Tth is set to a temperature (for example, 400 ° C.) at which the urea-modified deposits deposited on the disperser 48 decompose. That is, when the exhaust temperature Tex is low (for example, when the temperature is 350 ° C. or lower), the urea water injected from the addition valve 46 is deposited as a urea-modified product in the disperser 48, but the exhaust temperature Tex is high. In some cases, the accumulated urea denatured product is decomposed and desorbed as ammonia. In the treatment of S16, when it is assumed that deposits are deposited on the disperser 48, it is determined whether or not the deposited urea denaturants are at a temperature at which they are decomposed and desorbed as ammonia.

When the CPU 62 determines that the temperature is less than the specified temperature Tth (S16: NO), the CPU 62 calculates the increase amount ΔDi of the deposit amount of the SCR42 deposit based on the increase correction amount ΔQ (S18). That is, when urea water is injected from the addition valve 46 according to the equivalent ratio QSR determined by the treatment of S10, if all of the injected urea water reaches SCR42, the downstream concentration NOxd is considered to be a negligible value. Be done. Therefore, when the downstream concentration NOxd becomes a value larger than zero and the increase correction amount ΔQ becomes a value larger than zero, a part of the urea water injected from the addition valve 46 is a urea-modified product in the disperser 48. It is probable that it did not reach SCR42. Then, it is considered that the amount that did not reach the SCR 42 by depositing on the disperser 48 corresponds to the increase correction amount ΔQ. Therefore, the CPU 62 sets the increase amount ΔDi as the increase correction amount ΔQ.

Then, the CPU 62 increases and corrects the accumulated amount D by the increased amount ΔDi (S20). Next, the CPU 62 determines whether or not the accumulated amount D is equal to or less than the allowable upper limit amount Dth (S22). When the CPU 62 determines that the amount is greater than the allowable upper limit amount Dth (S22: NO), the exhaust temperature Tex is set to a predetermined temperature (for example, 500 ° C.) in order to decompose the deposits of the disperser 48 and desorb them as ammonia. The process of raising the temperature is executed (S24). This can be achieved, for example, by retarding the injection timing of the fuel injection valve 26.

On the other hand, when the CPU 62 determines that the exhaust temperature Tex is equal to or higher than the specified temperature Tth (S16: YES), the CPU 62 desorbs ammonia from the disperser 48 based on the accumulated amount D, the exhaust temperature Tex, and the exhaust flow rate. The quantity ΔDd is calculated (S26). Specifically, the CPU 62 substitutes the exhaust temperature Tex as the temperature of the deposit, and in view of the fact that the desorption rate is higher when the temperature of the deposit is higher than when it is lower, than when the exhaust temperature Tex is lower than when it is low. Also, a large amount of desorption ΔDd is calculated. Further, the CPU 62 calculates the desorption amount ΔDd more when the exhaust flow rate is large than when it is small. Further, the CPU 62 calculates the desorption amount ΔDd more when the deposition amount D is large than when it is small. This can be performed by, for example, a map calculation using map data in which the deposition amount D, the exhaust temperature Tex, and the exhaust flow rate are input parameters, and the desorption amount ΔDd is the output parameter. Here, the map data is a set of data of discrete values of input variables and values of output variables corresponding to the values of the input variables. In the map calculation, for example, if the value of the input variable matches any of the values of the input variable of the map data, the value of the output variable of the corresponding map data is used as the calculation result, and if they do not match, the map data is included. The process may be such that the value obtained by interpolating the values of a plurality of output variables is used as the calculation result. The amount of ammonia desorbed ΔDd is a value converted into the amount of urea water. That is, the desorption amount ΔDd is equal to the amount of urea water capable of producing desorbed ammonia.

Next, the CPU 62 reduces and corrects the injection amount command value QS * by the desorption amount ΔDd (S28). Next, the CPU 62 reduces and corrects the accumulated amount D by the desorption amount ΔDd (S30).

When the processing of S24 and S30 is completed or when affirmative judgment is made in S22, the CPU 62 is added so that the amount of urea water injected from the addition valve 46 per unit time becomes the injection amount command value QS *. An operation signal MS is output to the addition valve 46 in order to operate the valve 46 (S32).
When the process of S32 is completed, the CPU 62 temporarily ends the series of processes shown in FIG.
Here, the operation of the present embodiment will be described.

The CPU 62 injects urea water into the addition valve 46 based on the injection amount command value QS * according to the equivalent ratio QSR. Here, when the exhaust temperature Tex is low, a part of the urea water injected from the addition valve 46 is deposited as a urea modified product in the disperser 48, so that the amount of urea water reaching the SCR 42 is NOx in the exhaust. It may be insufficient for the amount that reacts without excess or deficiency. In that case, the CPU 62 detects the shortage of urea water based on the downstream concentration NOxd, and increases and corrects the equivalent ratio QSR by the increase correction amount ΔQ. Further, the CPU 62 grasps the amount of increase in the amount of deposits accumulated in the disperser 48 according to the amount of increase correction amount ΔQ. Then, when the urea modified product deposited on the disperser 48 is decomposed and ammonia is desorbed due to the increase in the exhaust temperature Tex, the CPU 62 reduces and corrects the injection amount command value QS * by the desorption amount ΔDd. .. As a result, the ammonia desorbed from the disperser 48 and the urea water jetted from the addition valve 46 reach the SCR 42, whereby NOx can be sufficiently purified. Therefore, it is possible to suppress the injection of an excessive amount of urea water with respect to the amount required for purifying NOx.
<Second embodiment>
Hereinafter, the second embodiment will be described with reference to the drawings, focusing on the differences from the first embodiment.

FIG. 3 shows an exhaust gas purification control device and an exhaust gas purification device according to the present embodiment. In FIG. 3, the members corresponding to the members shown in FIG. 1 are designated by the same reference numerals for convenience.
As shown in FIG. 3, in the present embodiment, an ammonia sensor 80 for detecting the ammonia concentration Da is provided between the SCR 42 and the ammonia oxidation catalyst 44.

FIG. 4 shows a processing procedure for exhaust gas purification control using the addition valve 46. The process shown in FIG. 4 is realized by the CPU 62 repeatedly executing the program stored in the ROM 64 at a predetermined cycle. In FIG. 4, the same step numbers are assigned to the processes corresponding to the processes shown in FIG. 2 for convenience.

In the series of processes shown in FIG. 4, when the CPU 62 determines that the exhaust temperature Tex is equal to or higher than the specified temperature Tth (S16: YES), the CPU 62 calculates the desorption amount ΔDd based on the exhaust flow rate and the ammonia concentration Da (S16: YES). S26a). Specifically, the CPU 62 calculates the desorption amount ΔDd to a larger value when the exhaust flow rate is high than when it is low, and calculates the desorption amount ΔDd to a larger value when the ammonia concentration Da is high than when it is low. Specifically, for example, the ROM 64 stores map data in which the ammonia concentration Da and the exhaust flow rate are input variables and the desorption amount ΔDd is an output variable, and the desorption amount ΔDd is calculated by the CPU 62 performing a map calculation. It may be calculated. When the CPU 62 calculates the desorption amount ΔDd, the CPU 62 shifts to the process of S28.
<Third embodiment>
Hereinafter, the third embodiment will be described with reference to the drawings, focusing on the differences from the first embodiment.

FIG. 5 shows a part of the exhaust passage 32 of the internal combustion engine 10 according to the present embodiment. In FIG. 5, the members corresponding to the members shown in FIG. 1 are designated by the same reference numerals for convenience.

As shown in FIG. 5, an upstream pressure sensor 82 for detecting the upstream exhaust pressure Pexu is arranged on the upstream side of the disperser 48, and a downstream exhaust pressure Pexd is arranged on the downstream side of the disperser 48. A downstream pressure sensor 84 for detection is arranged.

Instead of the processing of S18, S20, and S30 in FIG. 2, the CPU 62 calculates the accumulated amount D based on the differential pressure between the upstream exhaust pressure Pexu and the downstream exhaust pressure Pexd. Specifically, the CPU 62 calculates the accumulated amount D to be a larger value when the upstream exhaust pressure Pexu exceeds the downstream exhaust pressure Pexd than when it is small. Specifically, for example, the ROM 64 may store map data in which the differential pressure is used as an input variable and the accumulated amount D is used as an output variable, and the accumulated amount D may be calculated by the CPU 62 performing a map calculation.
<Correspondence>

The correspondence between the matters in the above-described embodiment and the matters described in the above-mentioned "means for solving the problem" column is as follows. The selective reduction catalyst corresponds to SCR42, and the reduction treatment corresponds to the treatment of S28.
<Other Embodiments>
In addition, at least one of each item of the said embodiment may be changed as follows.

-The method for calculating the amount of deposit D is not limited to that exemplified in the above embodiment. For example, instead of the processing of S18, the increase amount ΔDi may be calculated based on the exhaust temperature Tex and the exhaust flow rate. This can be realized by storing the map data in which the exhaust temperature Tex and the exhaust flow rate are input variables and the increase amount ΔDi is the output variable in the ROM 64 and performing the map calculation by the CPU 62. By the way, the exhaust flow rate here is a parameter having a positive correlation with the amount of urea water.

-The exhaust gas purification control device is not limited to the one that includes the CPU 62 and the ROM 64 and executes software processing. For example, a dedicated hardware circuit (for example, ASIC or the like) for hardware processing at least a part of the software processed in the above embodiment may be provided.

10 ... Internal combustion engine, 12 ... Intake passage, 14 ... Supercharger, 16 ... Throttle valve, 18 ... Intake valve, 20 ... Cylinder, 22 ... Piston, 24 ... Combustion chamber, 26 ... Fuel injection valve, 28 ... Crankshaft, 30 ... Exhaust valve, 32 ... Exhaust passage, 34 ... EGR passage, 36 ... EGR valve, 38 ... Oxidation catalyst, 40 ... DPF, 42 ... SCR, 44 ... Ammonia oxidation catalyst, 46 ... Addition valve, 48 ... Disperser, 50 ... Tank, 52 ... Pump, 60 ... Control device, 62 ... CPU, 64 ... ROM, 66 ... RAM, 70 ... Airflow meter, 72 ... Crank angle sensor, 74 ... Exhaust temperature sensor, 76 ... Upstream NOx sensor, 78 ... Downstream NOx sensor, 80 ... ammonia sensor, 82 ... upstream pressure sensor, 84 ... downstream pressure sensor.

Claims (3)

In the exhaust passage of the internal combustion engine, between the selective reduction catalyst, the addition valve arranged upstream of the selective reduction catalyst and adding urea water to the exhaust, and the addition valve and the selective reduction catalyst. In an exhaust gas purification control device for an internal combustion engine, which is applied to an exhaust gas purification device provided with a disperser that is arranged and disperses urea water injected from the addition valve.
The addition valve injects the urea water toward the disperser.
When the temperature of the exhaust is equal to or higher than the specified temperature, the amount of urea water injected from the addition valve is reduced when urea-modified deposits are deposited on the disperser as compared with the case where they are not deposited. run the reduction process,
The reduction treatment is an exhaust gas purification control device for an internal combustion engine, which is a treatment for increasing the reduction amount of the urea water amount when the exhaust flow rate is large as compared with the case where the exhaust flow rate is small. The reduction treatment is a treatment for increasing the amount of reduction in the amount of urea water when the exhaust flow rate is large, and for reducing the amount of urea water when the temperature of the sediment is high, as compared with the case where the amount of urea water is low. The exhaust gas purification control device for an internal combustion engine according to claim 1, which is a process for increasing the amount of urea water, which is a process for increasing the amount of reduction in the amount of urea water as compared with the case where the amount of accumulated sediment is large. The reduction treatment is a treatment in which the reduction amount of the urea water amount is larger than that in the case where the exhaust flow rate is large, and is lower than the case where the ammonia concentration in the exhaust gas flowing out from the selective reduction catalyst is high. The exhaust gas purification control device for an internal combustion engine according to claim 1, which is also a process for increasing the reduction amount of the urea water amount.

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