JP6969423B2 - Exhaust gas purification system for internal combustion engine and exhaust gas purification method for internal combustion engine - Google Patents

Description

The present disclosure relates to an exhaust gas purification system for an internal combustion engine that purifies the exhaust gas discharged from the internal combustion engine, and a method for purifying the exhaust gas of the internal combustion engine.

In internal combustion engines such as diesel engines and lean combustion gasoline engines, NOx storage reduction catalysts (LNT catalyst, LNT: Lean NOx Trap) and selective catalytic reduction catalysts (SCR catalyst, SCR: Selective Catalytic Reduction) are used to reduce NOx. In addition, by adding a filter that collects exhaust fine particles (PM: Particulate Meter) (for example, DPF: Diesel Particulate Filter), we aimed to reduce NOx in a wide operating range from low load to high load. Exhaust gas purification systems are becoming mainstream (see, for example, Patent Document 1).

Special Table 2006-512259

By the way, since an SCR catalyst is used in such an exhaust gas purification system, NH ₃ (ammonia) adsorbed on the SCR catalyst is desorbed by the rapid temperature rise of the exhaust gas during the regeneration control of the filter, and ammonia is produced. Slip may occur. Therefore, the filter regeneration control is started from the state where the amount _{of NH 3} adsorbed in the SCR catalyst is lowered to some extent.

In particular, when the LNT device carrying the LNT catalyst is arranged in front of the SCR device carrying the SCR catalyst, NOx is occluded in the LNT catalyst of the LNT device, and the NH ₃ consumption in the SCR device is reduced. Since the efficiency is lowered, _{the waiting time until the NH 3} adsorption amount is reduced becomes long, and there is a concern that the time until the start of filter regeneration becomes long. If the time until the start of filter regeneration becomes long, there is a concern that NOx emissions will increase.

An object of the present disclosure is to prevent the reducing agent adsorbed on the SCR catalyst of the SCR apparatus from being desorbed and released and flowing out to the downstream side of the SCR apparatus during filter regeneration until the start of filter regeneration. It is an object of the present invention to provide an exhaust gas purification system for an internal combustion engine and an exhaust gas purification method for an internal combustion engine, which can solve the problem of long time and the concern about the increase in NOx emissions associated therewith.

The exhaust gas purification system of the internal combustion engine according to the embodiment of the present invention for achieving the above object includes a NOx adsorption reduction type catalyst device that absorbs NOx in the exhaust gas in order from the upstream side in the exhaust passage of the internal combustion engine. In the exhaust gas purification system of an internal combustion engine equipped with a selective reduction type catalyst device that reduces NOx in the exhaust gas with a reducing agent and a filter device that collects particulate matter in the exhaust gas in the exhaust passage. At the start of the estimation reduction agent adsorption amount calculation means for calculating the estimated reduction agent adsorption amount, which is an estimated value of the reduction agent adsorption amount in the selective reduction type catalyst apparatus, and the filter regeneration for burning and removing the particulate matter of the filter apparatus. A reducing agent adsorption amount determining means for determining whether or not the estimated reducing agent adsorption amount at the start of regeneration calculated by the estimated reducing agent adsorption amount calculating means is equal to or greater than a preset target reducing agent adsorption amount, and the reducing agent. When the estimated reducing agent adsorption amount calculated by the estimated reducing agent adsorption amount calculating means is equal to or larger than the target reducing agent adsorption amount in the adsorption amount determining means, the estimated reduction calculated by the estimated reducing agent adsorption amount calculating means. A control configured to include an adsorption-reducing agent consuming means for controlling the adsorption-reducing agent consumption to reduce the adsorption-reducing agent in the selective reduction type catalyst device so that the amount of the agent adsorbed is smaller than the target adsorbing amount of the reducing agent. Has a device.

Further, the method for purifying the exhaust gas of the internal combustion engine according to the embodiment of the present invention for achieving the above object is a NOx occlusion reduction type catalyst device that occludes NOx in the exhaust gas in the exhaust passage of the internal combustion engine in order from the upstream side. And a selective reduction type catalyst device that reduces NOx in the exhaust gas with a reducing agent, and an exhaust gas purification method for an internal combustion engine provided with a filter device that collects particulate matter in the exhaust gas in the exhaust passage. At the start of filter regeneration in which the estimated reducing agent adsorption amount, which is an estimated value of the reducing agent adsorption amount in the selective reduction catalyst device, is calculated and the particulate matter of the filter device is burned and removed. It is determined whether or not the estimated reducing agent adsorption amount of is equal to or greater than the preset target reducing agent adsorption amount, and if the estimated reducing agent adsorption amount is equal to or greater than the target reducing agent adsorption amount, the estimated reducing agent is calculated. It is a method characterized by performing adsorption-reducing agent consumption control which reduces the adsorption-reducing agent in the selective reduction type catalyst apparatus so that the adsorption amount becomes smaller than the target reducing agent adsorption amount.

According to the exhaust gas purification system of the internal combustion engine and the exhaust gas purification method of the internal combustion engine according to the embodiment of the present invention, the reducing agent adsorbed on the SCR catalyst of the SCR apparatus is desorbed and released during the filter regeneration, and the SCR is released. It is possible to solve the problem that the time until the start of filter reproduction becomes long while avoiding the outflow to the downstream side of the device.

It is a figure which shows typically the structure of the exhaust gas purification system of the internal combustion engine of embodiment of this invention. It is a figure which shows typically the structure of the control device of the exhaust gas purification system of the internal combustion engine of embodiment of this invention. It is a figure which shows an example of the control flow for carrying out the exhaust gas purification method of the internal combustion engine of embodiment of this invention. It is a figure which illustrates the relationship between the engine outlet temperature and NOx purification rate in an LNT catalyst and an SCR catalyst.

Hereinafter, the exhaust gas purification system of the internal combustion engine and the exhaust gas purification method of the internal combustion engine according to the embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 1, the exhaust gas purification system (hereinafter, exhaust gas purification system) 1 of the internal combustion engine according to the embodiment of the present invention passes the exhaust gas G discharged from the engine main body (E: internal combustion engine main body) 10. The LNT device (NOx catalyst device) 21 having a NOx storage function and the CSF device (filter device with catalyst) 22 that collects PM (particulate substance) in the exhaust gas G in the exhaust passage 11 in order from the upstream side. And the urea water supply device 23 that supplies urea water (strictly speaking, it is _{a reducing agent generating substance that generates NH 3} (ammonia: reducing agent), but here, it is used as a reducing agent for the sake of simplicity of explanation). , SCR device (for example, urea SCR catalytic device: selective reduction catalytic device) 24 that reduces and purifies NOx with _{NH 3} generated from urea water, and ASC ( _{for example) that oxidizes and purifies NH 3 flowing out of the SCR device 24.} It is configured to include a DOC device (DOC: Diesel Oxidation Catalyst: oxidation catalyst) 25 called an Amminoa Slip Catalyst (ammonia slip catalyst).

Along with this, a control device 40 for controlling the injection amount U1 of the urea water U injected from the urea water supply device 23 is provided. The control device 40 is usually incorporated in a control device called an engine control unit that controls the entire engine body 10, but it can also be another control device.

That is, the exhaust gas purification system 1 has an LNT device 21 that sucks NOx in the exhaust gas G in the exhaust passage 11 of the internal combustion engine in order from the upstream side, and an SCR that reduces the NOx in the exhaust gas G with a reducing agent. It is provided with a catalyst device 24 and a CSF device 22 for collecting PM in the exhaust gas G in the exhaust passage 11. Further, a control device 40 for controlling the exhaust gas purification system 1 is provided.

As the LNT device 21 for storing NOx, a NOx storage reduction type catalyst device is exemplified, but any catalyst may be used as long as it is a catalyst that stores NOx and purifies NOx in the exhaust gas. It is not limited to the reduction type catalyst device. Further, as a filter device for collecting PM (particulate matter), a CSF device which is one of the filter devices carrying a catalyst is exemplified, but any filter device that requires filter regeneration may be used. The invention is not limited to this CSF.

Further, the exhaust gas purification system shown in FIG. 1 is an example, and the present invention selects to reduce NOx in the exhaust gas with a reducing agent downstream of the NOx occlusion reduction type catalyst device that occludes NOx in the exhaust gas. It may be an exhaust gas purification system in which a reduction type catalyst device is arranged and a filter device requiring filter regeneration is arranged in any of the exhaust passages.

An example of the LNT device 21 is a device carrying a NOx storage-reducing catalyst or the like. This NOx storage reduction type catalyst is composed of a molded body or the like in which a noble metal catalyst such as platinum and a NOx storage material formed of an alkaline earth metal such as barium are supported on a catalyst carrier. Then, when the NOx in the exhaust gas is in a lean state, the NOx storage material is temporarily stored, and the exhaust gas is brought into a rich air-fuel ratio state by NOx purge control before the NOx storage amount is saturated. NOx stored in the occlusal gas is released and reduced by the ternary function of the noble metal catalyst.

The CSF device (filter device with catalyst) 22 is made of a cordierite material, a silicon carbide (SiC) material, or the like, and alternately closes both ends of the honeycomb ceramic cell to use a thin wall of the ceramic as a filter. .. Since this fine particle collection filter has excellent heat resistance, PM collected can be burned and removed by heating during filter regeneration, and the collection performance can be maintained by this filter regeneration process. .. In addition, an oxidation catalyst is supported to facilitate the combustion of PM.

The urea water supply device 23 is an injection device for supplying the urea water U supplied from the urea water tank 23a via the urea water supply pipe 23b to the SCR device 24, and the control device 40 is used to inject the urea water U. The presence / absence and its injection amount U1 are adjusted and controlled.

The SCR device 24 is configured by carrying, for example, a urea selective reduction catalyst in which urea water is used as a reducing agent U and the generated NH _{3 reacts with NOx in the exhaust gas G to form nitrogen and water.} As the urea selective reduction catalyst, include zeolite catalyst such as iron ion exchange aluminosilicate and copper ion-exchanged aluminosilicate, adsorbs NH _3, has a function to reduce and purify NOx in NH ₃ was the suction ing. By using this selective reduction type catalyst device 24, _{instead of using NH 3} directly, urea water is injected into the exhaust gas G _{to react NH 3} generated by hydrolysis from the urea water with NOx. By making it harmless, NOx is made harmless.

Regarding the NOx sensor in the sensor group arranged in the exhaust passage 11, the first NOx sensor 31 for detecting the first NOx concentration Cn1 which is the NOx concentration in the exhaust gas G flowing into the LNT device 21 is the LNT device. It is provided on the entrance side of 21. Further, a second NOx sensor 32 for detecting the second NOx concentration Cn2, which is the NOx concentration in the exhaust gas G flowing into the SCR device 24, is provided on the inlet side of the SCR device 24. Further, a third NOx sensor 33 for detecting the third NOx concentration Cn3, which is the NOx concentration in the exhaust gas G flowing out from the DOC device 25, is provided on the outlet side of the DOC device 25.

Further, regarding the lambda sensor (air-fuel ratio sensor: oxygen concentration sensor), the first lambda sensor 34 for detecting the first air-fuel ratio Ca1 which is the air-fuel ratio (λ) of the exhaust gas G flowing into the LNT device 21 is the LNT. It is provided on the inlet side of the device 21. Further, a second lambda sensor 35 for detecting the second air-fuel ratio Ca2, which is the air-fuel ratio (λ) of the exhaust gas G flowing into the CSF device 22, is provided on the inlet side of the CSF device 22.

Regarding the exhaust gas temperature sensor, the first exhaust gas temperature sensor (first temperature detection device) 36 for detecting the first exhaust gas temperature Tg1, which is the temperature of the exhaust gas G flowing into the LNT device 21, is the LNT device 21. It is installed on the entrance side of. Further, a second exhaust gas temperature sensor (second temperature detection device) 37 for detecting the second exhaust gas temperature Tg2, which is the temperature of the exhaust gas G flowing into the SCR device 24, is provided on the inlet side of the SCR device 24. .. Further, a third exhaust gas temperature sensor 38 for detecting the third exhaust gas temperature Tg3, which is the temperature of the exhaust gas G flowing into the CSF device 22, is provided on the inlet side of the CSF device 22.

That is, the first exhaust gas temperature sensor 36 that measures the first exhaust gas temperature Tg1, which is the temperature of the exhaust gas G flowing into the LNT device 21, and the second exhaust gas, which is the temperature of the exhaust gas G flowing into the SCR device 24. It is configured to include a second exhaust gas temperature sensor 37 that measures the temperature Tg2.

The detected values of these various sensors 31 to 38 are input to the control device 40, and the control device 40 performs various calculations based on these input data and outputs a control command to the engine main body 10. At the same time, a control command is also output to the urea water supply device 23 to adjust and control the injection amount U1 of the reducing agent U injected from the urea water supply device 23.

Further, the exhaust gas purification system 1 raises the exhaust gas temperature according to the control command of the control device 40, and performs filter regeneration control in the CSF device 22 to oxidize and remove the PM collected by the CSF device 22. Alternatively, the temperature of the exhaust gas is raised and the air-fuel ratio of the exhaust gas G is set to a rich air-fuel ratio to release the stored NOx in the LNT device 21 and to be released by the ternary catalyst carried by the LNT device 21. NOx purge control (NOx regeneration control) is performed to reduce and purify the NOx, and the exhaust gas temperature is raised to a temperature higher than the temperature of the NOx purge control to remove the sulfur component stored in the LNT device 21. Sulfur purge control is performed.

As shown in FIG. 2, the control device 40 includes a filter regeneration control means 41 for performing the filter regeneration control, a NOx purge control means 42 for performing NOx purge control, a sulfur purge control means 43 for performing sulfur purge control, and urea water. In addition to the supply control means 44, an estimated NH ₃ adsorption amount calculation means (estimated reducing agent adsorption amount calculation means) 51, an NH ₃ adsorption amount determination means (reducing agent adsorption amount determination means) 52, and an adsorption NH ₃ consumption means ( It is configured to include an adsorption reducing agent consuming means) 53.

The estimated NH ₃ adsorption amount calculation means 51 is a means for calculating the _{estimated NH 3 adsorption amount Se, which is an estimated value of the NH 3} (reducing agent) adsorption amount in the SCR device 24. Further, the NH _{3 adsorption amount determining means 52 has an estimated NH 3} adsorption amount Se at the start of filter regeneration calculated by the _{estimated NH 3} adsorption amount calculation means 51 at the start of filter regeneration for burning and removing PM of the CSF device 22. It is a means for determining whether or not the target NH _{3 adsorption amount St or more is set in advance.}

Further, the adsorption NH ₃ consuming means 53 is the NH ₃ adsorption amount determining means 52, and when the _{estimated NH 3} adsorption amount Se _{calculated by the estimated NH 3} adsorption amount calculation means 51 is equal to or more than the _{target NH 3 adsorption amount St,} Means for controlling the _{adsorption NH 3} consumption to reduce the _{adsorption NH 3} in the SCR device 24 so that the _{estimated NH 3} adsorption amount Se calculated by the estimated NH ₃ adsorption amount calculation means 51 _{is smaller than the target NH 3 adsorption amount St.} Is.

In the adsorption NH ₃ consuming means 53, the first exhaust gas temperature Tg1 detected by the first exhaust gas temperature sensor 36 becomes equal to or higher than the first set temperature Tgc1 preset based on the NOx emission temperature in the LNT device 21. As described above, it is configured to control the consumption of the adsorption-reducing agent for raising or maintaining the temperature of the exhaust gas G. The first set temperature Tgc1 is a temperature at which the NOx purification rate of the LNT device 21 decreases so that there is a temperature at which the NOx purification rate of LNT decreases in relation to the NOx purification rate exemplified in FIG. 4 and the engine outlet temperature. In other words, it is set to a temperature at which the NOx storage capacity decreases, for example, 400 ° C. or higher.

Due to the temperature rise of the NOx storage reduction catalyst of the LNT device 21 due to the temperature rise of the exhaust gas G, the NOx stored in the LNT device 21 is released at the time of filter regeneration before the filter regeneration is started. , The released NOx is allowed to flow into the downstream SCR device 24. _{By reacting the inflowing NOx with the NH 3} adsorbed by the SCR device 24 to reduce and purify the NOx, the adsorbed NH ₃ in the SCR device 24 can be reduced.

The temperature rise of the exhaust gas G at this time is different from the NOx purge control, and it is preferable that the air-fuel ratio (λ) in the exhaust gas G is in a lean state. When the air-fuel ratio is in a rich state, the NOx released from the NOx storage reduction catalyst is reduced and purified by the three-way catalyst, so that the NOx flowing into the SCR device 24 decreases, and the adsorbed NH _{3 in the SCR device 24 decreases.} This is because the reduction effect of is reduced.

Further, in the adsorption NH ₃ consumption means 53, in the adsorption NH ₃ consumption control, the second exhaust gas temperature Tg 2 detected by the second exhaust gas temperature sensor 37 is preset based on the _{NH 3 consumption efficiency in the SCR device 24.} The second exhaust gas temperature Tg2 is raised or maintained so as to be equal to or higher than the second set temperature Tgc2 and lower than _{the preset third set temperature Tgc3 based on the NH 3 emission temperature in the SCR device 24.} It is preferable that it is configured in. This second set temperature Tgc2 has a high NOx purification rate and consumes _{the occluded NH 3} so that there is a temperature at which the NOx purification rate becomes high in SCR in relation to the NOx purification rate exemplified in FIG. 4 and the engine outlet temperature. It is set to a temperature at which the rate increases, for example, about 300 ° C.

Due to the temperature rise of the SCR catalyst of the SCR device 24 due to the temperature rise of the exhaust gas G, NH ₃ adsorbed on the SCR device 24 is reacted with NOx at the time of filter regeneration before the filter regeneration is started. Efficiency of the NOx reduction reaction, i.e., NH ₃ consumption efficiency, the second exhaust gas temperature Tg2 is, becomes larger becomes the second set temperature Tgc2 or set above, short time, storage NH ₃ in the SCR device 24 Will be able to be reduced.

Further, if the SCR catalyst temperature of the SCR device 24 becomes too high, the NOx purification rate in the SCR device 24 decreases, so that the second exhaust gas temperature Tg2 is suppressed to the third set temperature Tgc3 or less set above. This third set temperature Tgc 3 has a low NOx purification rate and a consumption rate of _{occluded NH 3} so that there is a temperature at which the NOx purification rate becomes low in SCR due to the relationship between the NOx purification rate exemplified in FIG. 4 and the engine outlet temperature. Is set to a temperature at which the temperature decreases, for example, about 400 ° C. That is, the second exhaust gas temperature Tg2 rises within the temperature range corresponding to the temperature range Ra in which the NOx purification rate in SCR is high in relation to the NOx purification rate exemplified in FIG. 4 and the engine outlet temperature. Keep warm and maintain.

The exhaust gas purification method for an exhaust gas engine according to the embodiment of the present invention (hereinafter referred to as an exhaust gas purification method) is an LNT device that stores NOx in the exhaust gas G in the exhaust passage 11 of the internal combustion engine in order from the upstream side. This is an exhaust gas purification method including 21 and an SCR device 24 that reduces NOx in the exhaust gas G by NH _3, and a CSF device 22 that collects PM in the exhaust gas G in the exhaust passage 11. , The method is as follows.

In this exhaust gas purification method, the _{estimated NH 3} adsorption amount Se, which is an estimated value _{of the NH 3} adsorption amount in the SCR device 24, is calculated, and the calculated regeneration start is performed at the start of the filter regeneration that burns and removes the PM of the CSF device 22. estimated adsorbed NH ₃ amount Se is determined whether a target adsorbed NH ₃ amount St above a preset time, when the estimated adsorbed NH ₃ amount Se is the target adsorbed NH ₃ amount St above is calculated _{Adsorption NH 3} consumption control is performed to reduce the _{adsorption NH 3} in the SCR device 24 so that the estimated NH ₃ adsorption amount Se _{becomes smaller than the target NH 3 adsorption amount St.}

This above-mentioned control can be carried out by an example control flow as shown in FIG. The control flow of FIG. 3 is called from the advanced control flow when the internal combustion engine starts operation, is executed in parallel with the operation control flow of the other exhaust gas purification system 1, and when the operation of the internal combustion engine ends. Shows that an interrupt occurs, returns to the advanced control flow, and ends with this advanced control flow.

When the control flow of FIG. 3 is called from a higher-level control flow and starts, a filter reproduction request (hereinafter referred to as reproduction control) for requesting filter reproduction control (hereinafter referred to as reproduction control) in the CSF device 22 in "is there a reproduction request?" In step S11 (hereinafter referred to as reproduction control). Hereinafter, it is determined whether or not there is a reproduction request). In this determination, if there is no reproduction request, it returns, returns to the upper control flow, elapses a preset time, is called from the upper control flow again, starts, and repeats this.

If there is a reproduction request in the determination of "reproduction request?" In step S11, the process goes to "stop NOx purge control" in step S12. In the “stop NOx purge control” in step S12, the NOx purge control of the NOx storage reduction catalyst is stopped, and the NOx reduction control (DeNOx control) of the NOx storage reduction catalyst is stopped. That is, the NOx purge control is stopped.

In the "input of the SCR inlet temperature" in the next step S13, the second exhaust gas temperature Tg2 detected by the second exhaust gas temperature sensor 37, that is, the SCR inlet temperature is input. Then, in the " _{setting of the target NH 3 adsorption amount St", the NH 3} adsorption amount Smax that can be adsorbed by the SCR device 24 is greatly affected by the temperature of the SCR catalyst. Therefore, based on this second exhaust gas temperature Tg2, _{Set the target NH 3} adsorption amount St during filter regeneration (hereinafter referred to as regeneration). The target NH _{3 adsorption amount St during regeneration is the target NH 3} at normal times other than during regeneration because the exhaust gas flow rate is small during regeneration and the exhaust gas rises rapidly, so that ammonia slip is likely to occur. It is set to a value smaller than this as compared with the adsorption amount St0.

Furthermore, in the "calculation of the estimated adsorbed NH ₃ amount Se", it calculates the estimated adsorbed NH ₃ amount Se is an estimate of the adsorbed NH ₃ amount in the SCR device 24. The estimated adsorbed NH ₃ amount Se subtracts the consumed amount of NH ₃ from the supply amount of NH _3, further is obtained by subtracting the NH ₃ slip amount (estimated adsorbed NH ₃ amount Se = previously estimated adsorbed NH ₃ amount + supply NH ₃ amount-consumed NH ₃ amount-NH ₃ slip amount).

This supply NH _{3 amount is the supply amount of NH 3} generated by hydrolysis from the urea water U, and this is calculated based on the injection amount U1 of the urea water U supplied from the urea water supply device 23 and the like.

The amount of NH ₃ consumed is the amount of _{NH 3} used to reduce the amount of NOx generated from the engine body 10. This includes the amount of NOx flowing into the SCR device 24, the temperature of the SCR catalyst (for example, the second exhaust gas temperature Tg2 is used as a substitute), the flow rate of the exhaust gas G, _{the ratio of NO and NO 2} , the amount _{of NH 3} adsorbed during the reaction, etc. It is calculated based on. The amount of NOx flowing into the SCR device 24 can be estimated by the amount of NOx per unit time obtained from the second NOx concentration Cn2 on the outlet side of the LNT device 21 and the flow rate of the exhaust gas G.

The NOx amount flowing into the SCR device 24 (SCR inlet NOx amount) is obtained by subtracting the NOx storage desorption amount of the LNT device 21 and the NOx reduction amount of the LNT device 21 from the NOx amount at the engine outlet (SCR). Inlet NOx amount = NOx amount at engine outlet-NOx storage / desorption amount of LNT device-NOx reduction amount of LNT device).

The NOx amount at the engine outlet can be estimated from the engine operating state, or can be calculated from the NOx sensor on the inlet side of the LNT device 21 and the exhaust gas flow rate. Further, the NOx storage desorption amount of the LNT device 21 can be calculated from the LNT temperature, the exhaust gas flow rate, and the NOx storage amount. The NOx reduction amount of the LNT device 21 can be calculated from the LNT temperature, the exhaust gas flow rate, the NOx storage amount, and the air-fuel ratio.

Further, the NH _{3 slip amount is calculated based on the NH 3} adsorption amount in the SCR device 24, the temperature, the flow rate of the exhaust gas G, and the like.

Then, in the determination of “Se ≧ St” in the next step S14, it is determined whether or not _{the estimated NH 3} adsorption amount Se is _{larger than the target NH 3 adsorption amount St. If the estimated NH 3} adsorption amount Se is equal to or greater than the _{target NH 3} adsorption amount St in the determination of “Se ≧ St” in step S14 _{(YES), go to “Adsorption NH 3} consumption control” in step S15 and set in advance. After the elapsed time has elapsed, the process returns to step S13, and the new estimated NH ₃ adsorption amount Se and the new target NH ₃ adsorption amount St, which have changed at this preset time, are compared.

In this adsorption NH ₃ consumption control, the calculated estimated NH ₃ adsorption amount Se _{becomes smaller than the target NH 3} adsorption amount St, or the second exhaust gas temperature Tg2 is the second set temperature Tgc2 and the third set temperature. Control is performed to reduce the _{adsorbed NH 3} in the SCR device 24 so as to be within the range between Tgc 3 and Tgc 3. Specifically, in this adsorption NH ₃ consumption control, the temperature of the exhaust gas G is raised or maintained so that the first exhaust gas temperature Tg1 becomes equal to or higher than the first set temperature Tgc1. To raise the temperature of the exhaust gas G, the fuel injection amount in the engine body 10 may be increased, or the unburned fuel supplied to the exhaust passage 11 by post injection or fuel injection in the exhaust pipe may be oxidized by the LNT device 21 to generate heat. A method of raising the temperature of the exhaust gas G is adopted.

Then, in the determination of “Se ≧ St” in step S14, if the estimated NH ₃ adsorption amount Se is _{less than the target NH 3} adsorption amount St, the process goes to “Regeneration condition satisfied?” In step S16. In the "reproduction condition satisfied?" In step S16, it is determined whether or not the reproduction control start condition in the CSF device 22 is satisfied, and if the reproduction control start condition is not satisfied (NO), it is set in advance. After the elapsed time has elapsed, the process returns to step S13.

On the other hand, if the start condition of the reproduction control is satisfied in the "reproduction condition satisfied?" In the step S16 (YES), the reproduction control in the CSF device 22 is performed by going to the "regeneration control" in the step S17. After the reproduction control is completed, it goes to the return, returns to the upper control flow, elapses a preset time, is called from the upper control flow again, starts, and repeats this.

When the operation of the internal combustion engine is terminated in the middle of the control flow of FIG. 3, an interrupt is used to perform necessary control termination processing (not shown), and then returns to return to the advanced control flow. It ends with the control flow of.

Although the first exhaust gas temperature Tg1 is used instead of the catalyst temperature of the LNT device 21, the third exhaust gas temperature Tg3 may be used, and further, when estimating a more accurate catalyst temperature, It is also possible to use the first exhaust gas temperature Tg1 and the third exhaust gas temperature Tg3 to set a simple average or a weighted average as the catalyst temperature of the LNT device 21.

Further, although the second exhaust gas temperature Tg2 is used instead of the catalyst temperature of the SCR device 24, a fourth exhaust gas temperature sensor is provided in the exhaust passage 11 between the SCR device 24 and the DOC device 25. The fourth exhaust gas temperature Tg4 detected by the fourth exhaust gas temperature sensor may be used, and further, when estimating the catalyst temperature with higher accuracy, the second exhaust gas temperature Tg2 and the fourth exhaust gas temperature Tg4 It is also possible to use a simple average or a weighted average as the catalyst temperature of the SCR device 24.

As described above, according to the exhaust gas purification system 1 of the internal combustion engine and the exhaust gas purification method of the internal combustion engine of this embodiment, NH _{3 adsorbed on the SCR catalyst of the SCR device 24 is removed during filter regeneration.} It is possible to solve the problem that the time until the start of filter reproduction becomes long while avoiding being separated and released and flowing out to the downstream side of the SCR device 24.

In particular, when the LNT device 21 carrying the LNT catalyst is arranged in front of the SCR device 24 carrying the SCR catalyst, NOx is occluded by the LNT catalyst of the LNT device 21 and NH _{3 in the SCR device 24.} Since the efficiency of reducing the consumption is lowered, _{the waiting time until the NH 3} adsorption amount is reduced becomes longer, and the time until the start of filter regeneration becomes longer, but this problem can be solved more effectively.

That is, when the _{amount of NH 3} adsorbed in the SCR device 24 is large and the amount of NOx stored in the LNT device 21 is small, it is necessary to saturate the amount of NOx stored in the LNT device 21 and consume _{the adsorbed NH 3 in the SCR device 24.} It takes time. In such a case, by raising the temperature to a temperature at which the NOx storage efficiency of the LNT device 21 decreases _{, the consumption of the adsorption NH 3} in the SCR device 24 by the NOx released from the LNT device 21 and the NOx storage saturation in the LNT device 21 The overall effect of eliminating the need for the SCR device 24 and improving the reaction efficiency (= improving the NH ₃ consumption efficiency) by increasing the temperature of the SCR catalyst of the SCR device 24 can be obtained, and the time until the start of filter regeneration can be shortened. Can be done. This makes it possible to reduce NOx emissions and suppress PM over-deposition on the CSF device 22.

1 Exhaust gas purification system for internal combustion engine 10 Engine body 11 Exhaust passage 21 LNT device (NOx storage reduction catalyst device)
22 CSF device (filter device with catalyst)
23 Urea water supply device (reducing agent supply device)
24 SCR device (selective reduction catalyst device)
25 DOC device (ASC: oxidation catalyst device)
31 1st NOx sensor 32 2nd NOx sensor 33 3rd NOx sensor 34 1st lambda sensor 35 2nd lambda sensor 36 1st exhaust gas temperature sensor (1st temperature detection device)
37 Second exhaust gas temperature sensor (second temperature detector)
38 Third exhaust gas temperature sensor 40 Control device 41 Filter regeneration control means 42 NOx purge control means 43 Sulfur purge control means 44 Urea water supply control means 51 Estimated NH ₃ occlusion calculation means (estimated reducing agent occlusion calculation means)
52 NH ₃ Adsorption amount determination means (reducing agent adsorption amount determination means)
53 Occlusion NH ₃ Consumption Means (Occlusion Reducing Agent Consumption Means)
G Exhaust gas U Urea water (reducing agent)

Claims (4)

The exhaust passage of the internal combustion engine is provided with a NOx storage reduction type catalyst device for storing NOx in the exhaust gas and a selective reduction type catalyst device for reducing NOx in the exhaust gas with a reducing agent in order from the upstream side. In an exhaust gas purification system of an internal combustion engine equipped with a filter device that collects particulate matter in the exhaust gas in the exhaust passage.
An estimated reducing agent adsorption amount calculating means for calculating an estimated reducing agent adsorption amount, which is an estimated value of the reducing agent adsorption amount in the selective reduction type catalyst device, and
At the start of filter regeneration for burning and removing particulate matter from the filter device, the estimated reducing agent adsorption amount at the start of regeneration calculated by the estimated reducing agent adsorption amount calculation means is equal to or greater than the preset target reducing agent adsorption amount. Reducing agent adsorption amount determining means for determining whether or not,
When the estimated reducing agent adsorption amount calculated by the estimated reducing agent adsorption amount calculation means by the reducing agent adsorption amount determining means is equal to or larger than the target reducing agent adsorption amount, it is calculated by the estimated reducing agent adsorption amount calculation means. It is configured to include an adsorption-reducing agent consuming means for controlling the consumption of the adsorption-reducing agent in the selective reducing-type catalyst device so that the estimated reducing agent adsorbing amount is smaller than the target reducing agent adsorbing amount. An exhaust gas purification system for an internal combustion engine, characterized by having a controlling device. It is provided with a first temperature detecting device for measuring the temperature of the exhaust gas flowing into the NOx storage reduction type catalyst device, and is also provided.
In the adsorption-reducing agent consumption control, the first exhaust gas temperature detected by the first temperature detecting device is preset based on the NOx emission temperature of the NOx-reducing catalyst device. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the exhaust gas temperature is raised or maintained so as to be equal to or higher than the first set temperature. A second temperature detecting device for measuring the temperature of the exhaust gas flowing into the selective reduction catalyst device is provided, and the device is provided with a second temperature detecting device.
In the adsorption-reducing agent consumption control, the second exhaust gas temperature detected by the second temperature detecting device is preset based on the reducing agent consumption efficiency of the selective reducing catalyst device. It is configured to raise or maintain the exhaust gas temperature so as to be equal to or higher than the second set temperature and lower than the third set temperature preset based on the reducing agent discharge temperature in the selective reduction type catalyst device. The exhaust gas purification system for an internal combustion engine according to claim 1 or 2, wherein the exhaust gas purification system is characterized by the above. The exhaust passage of the internal combustion engine is provided with a NOx storage reduction type catalyst device for storing NOx in the exhaust gas and a selective reduction type catalyst device for reducing NOx in the exhaust gas with a reducing agent in order from the upstream side. In an exhaust gas purification method for an internal combustion engine equipped with a filter device that collects particulate matter in the exhaust gas in the exhaust passage.
The estimated reducing agent adsorption amount, which is an estimated value of the reducing agent adsorption amount in the selective reduction type catalyst device, is calculated.
At the start of filter regeneration that burns and removes particulate matter from the filter device, it is determined whether or not the calculated estimated reducing agent adsorption amount at the start of regeneration is equal to or greater than the preset target reducing agent adsorption amount.
When the estimated reducing agent adsorption amount is equal to or larger than the target reducing agent adsorption amount, the adsorption reduction in the selective reduction type catalyst device is performed so that the calculated estimated reducing agent adsorption amount is smaller than the target reducing agent adsorption amount. A method for purifying exhaust gas from an internal combustion engine, which is characterized by controlling the consumption of an adsorption-reducing agent that reduces the amount of the agent.

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