WO2019159932A1

WO2019159932A1 - Internal combustion engine exhaust gas purification system, and exhaust gas purification method for internal combustion engine

Info

Publication number: WO2019159932A1
Application number: PCT/JP2019/004998
Authority: WO
Inventors: 洋阿野田
Original assignee: いすゞ自動車株式会社
Priority date: 2018-02-19
Filing date: 2019-02-13
Publication date: 2019-08-22
Also published as: JP2019143513A; JP6969423B2; CN111788372A

Abstract

Provided is an internal combustion engine exhaust gas purification system in which a control device, at the start of filter regeneration for combusting and removing particulate matter from a filter device, determines whether an estimated amount of adsorbed reducing agent at the start of regeneration in a selective reducing catalyst device is greater than or equal to a preset target amount. If the estimated amount of adsorbed reducing agent is greater than or equal to the target amount, the control device implements a control to reduce the adsorbed reducing agent in the selective reducing catalyst device so that the estimated amount of adsorbed reducing agent in the selective reducing catalyst device becomes smaller than the target amount.

Description

Exhaust gas purification system for internal combustion engine and exhaust gas purification method for internal combustion engine

The present disclosure relates to an exhaust gas purification system and an exhaust gas purification method for purifying exhaust gas discharged from an internal combustion engine.

In internal combustion engines such as diesel engines and lean burn gasoline engines, NOx storage reduction catalysts (LNT catalyst, LNT: Lean NOx Trap) and selective reduction catalysts (SCR catalyst, SCR: Selective Catalytic Reduction) are used to reduce NOx. And a filter that collects exhaust particulates (PM: Particulate Matter) (for example, DPF: Diesel Particulate Matter Filter) was added to reduce NOx in a wide operating range from low to high loads. Exhaust gas purification systems have become mainstream (see, for example, Patent Document 1).

Japan Special Table 2006-512529

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

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

The purpose of the present disclosure is to prevent the reductant adsorbed on the SCR catalyst of the SCR device from desorbing and releasing and flowing out downstream of the SCR device during filter regeneration, An object of the present invention is 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 that the time is lengthened and the accompanying increase in NOx emission amount.

An exhaust gas purification system for an internal combustion engine according to an aspect of the present disclosure includes a NOx occlusion reduction type catalyst device that occludes NOx in exhaust gas in an exhaust passage of the internal combustion engine in order from the upstream side, and NOx in exhaust gas as a reducing agent. In the exhaust gas purification system for an internal combustion engine, the selective reduction type catalytic device further comprising a selective reduction type catalytic device that reduces the amount of particulate matter in the exhaust gas in the exhaust passage. A calculating unit that calculates an estimated reducing agent adsorption amount that is an estimated value of the reducing agent adsorption amount in the filter, and at the start of filter regeneration that burns and removes particulate matter of the filter device, A determination unit that determines whether or not the estimated reducing agent adsorption amount is equal to or greater than a preset target amount; and the estimated reductant adsorption amount that is calculated by the calculation unit at the determination unit is greater than or equal to the target amount In some cases, a consumption unit that performs adsorption / reduction agent consumption control for reducing the adsorption / reduction agent in the selective catalytic reduction device so that the estimated reduction agent adsorption amount calculated by the calculation unit is smaller than the target amount. It has the control apparatus comprised.

In addition, an exhaust gas purification method for an internal combustion engine according to an aspect of the present disclosure includes a NOx occlusion reduction type catalyst device that stores NOx in exhaust gas in the exhaust passage of the internal combustion engine in order from the upstream side, and NOx in exhaust gas. In the exhaust gas purification method for an internal combustion engine, comprising the selective reduction type catalytic device for reducing with a reducing agent and the filter device for collecting particulate matter in the exhaust gas in the exhaust passage. An estimated reducing agent adsorption amount that is an estimated value of the reducing agent adsorption amount in the catalyst device is calculated, and the estimated reducing agent adsorption amount at the start of regeneration calculated at the start of filter regeneration for burning and removing the particulate matter of the filter device If the estimated reducing agent adsorption amount is equal to or greater than the target amount, the calculated estimated reducing agent adsorption amount is less than the target amount. As a method which is characterized in that the adsorbent reducing agent adsorption reducing agent consumption control to reduce in the selective reduction catalyst device.

According to the exhaust gas purification system for an internal combustion engine and the exhaust gas purification method for an internal combustion engine according to an aspect of the present disclosure, the reductant adsorbed on the SCR catalyst of the SCR device is desorbed and released during filter regeneration. It is possible to solve the problem that the time until the filter regeneration starts becomes long while avoiding the flow out to the downstream side of the apparatus.

FIG. 1 is a diagram schematically illustrating a configuration of an exhaust gas purification system for an internal combustion engine according to an embodiment of the present disclosure. FIG. 2 is a diagram schematically illustrating a configuration of a control device for an exhaust gas purification system for an internal combustion engine according to an embodiment of the present disclosure. FIG. 3 is a diagram illustrating an example of a control flow for carrying out the exhaust gas purification method for an internal combustion engine according to the embodiment of the present disclosure. FIG. 4 is a diagram illustrating the relationship between the engine outlet temperature and the NOx purification rate in the LNT catalyst and the SCR catalyst.

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

As shown in FIG. 1, an exhaust gas purification system (hereinafter referred to as an exhaust gas purification system) 1 for an internal combustion engine according to an embodiment is an exhaust gas through which an exhaust gas G discharged from an engine body (E: internal combustion engine body) 10 passes. In the passage 11, in order from the upstream side, an LNT device (NOx catalyst device) 21 having a NOx occlusion function, a CSF device (filter device with catalyst) 22 for collecting PM (particulate matter) in the exhaust gas G, A urea water supply device 23 for supplying urea water (strictly speaking, a reducing agent generating substance that generates NH ₃ (ammonia: a reducing agent), but here a reducing agent for simplification); SCR device (for example, urea SCR catalyst device: selective reduction catalyst device) 24 that reduces and purifies NOx with NH ₃ generated from water, and ASC that oxidizes and purifies NH ₃ flowing out from SCR device 24 A DOC device (DOC: Diesel Oxidation Catalyst) 25 (Ammonia Slip Catalyst: ammonia slip catalyst) is provided.

In addition, 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 performs overall control of the engine body 10, but may be a separate control device.

That is, the exhaust gas purification system 1 includes an LNT device 21 that stores 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 NOx in the exhaust gas G with a reducing agent. In addition to the catalyst device 24, the exhaust passage 11 includes a CSF device 22 that collects PM in the exhaust gas G. Moreover, the control apparatus 40 for controlling this exhaust gas purification system 1 is provided.

The NOx occlusion reduction type catalyst device is illustrated as the LNT device 21 that occludes NOx, but any catalyst that occludes NOx and purifies NOx in exhaust gas may be used, and the present disclosure discloses this NOx occlusion. The present invention is not limited to a reduction catalyst device. Further, as a filter device for collecting PM (particulate matter), a CSF device which is one of filter devices carrying a catalyst is illustrated, but any filter device that needs filter regeneration may be used. The disclosure is not limited to this CSF.

Further, the exhaust gas purification system shown in FIG. 1 is an exemplification, and the present disclosure selects NOx in the exhaust gas with a reducing agent downstream of the NOx occlusion reduction type catalyst device that stores NOx in the exhaust gas. What is necessary is just an exhaust gas purification system in which a reduction-type catalyst device is disposed and a filter device requiring filter regeneration is disposed in any of the exhaust passages.

The LNT device 21 is exemplified by a device carrying a NOx storage reduction catalyst or the like. This NOx occlusion reduction type catalyst is composed of a molded body carrying a NOx occlusion material formed of a noble metal catalyst such as platinum and an alkaline earth metal such as barium on a catalyst carrier. Then, when NOx in the exhaust gas is in a lean state, the NOx storage material is temporarily stored, and before the NOx storage amount is saturated, the exhaust gas is brought into a rich air-fuel ratio state by NOx purge control, so that the NOx storage material NOx occluded in the catalyst is released and reduced by the three-way function of the noble metal catalyst.

The CSF device (filter device with catalyst) 22 is formed of cordierite material, silicon carbide (SiC) material, or the like, and uses a thin ceramic wall as a filter by alternately closing both ends of the honeycomb ceramic cell. . Since this particulate collection filter is excellent in heat resistance, it is possible to burn and remove PM collected by heating at the time of filter regeneration, and the collection performance can be maintained by this filter regeneration treatment. . Further, an oxidation catalyst is supported in order to make PM combustion easier.

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

The SCR device 24 is configured to carry, for example, a urea selective reduction catalyst that reacts with NOx in the exhaust gas G by NH ₃ generated using urea water as a reducing agent U 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 catalyst device 24, NH ₃ is not directly used, but urea water is injected into the exhaust gas G to react NH ₃ and NOx generated by hydrolysis from the urea water. To make NOx harmless.

As for the NOx sensors 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. 21 is provided on the inlet side. Further, a second NOx sensor 32 for detecting a second NOx concentration Cn2, which is a 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 a third NOx concentration Cn3 that 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 an LNT. It is provided on the inlet side of the device 21. A second lambda sensor 35 that detects the second air-fuel ratio Ca2 that 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.

As for the exhaust gas temperature sensor, a 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 provided in the LNT device 21. It is provided on the entrance side. Further, a second exhaust gas temperature sensor (second temperature detection device) 37 for detecting a 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 a third exhaust gas temperature Tg3 that 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 that is the temperature of the exhaust gas G that flows into the LNT device 21, and the second exhaust gas that is the temperature of the exhaust gas G that flows into the SCR device 24. A second exhaust gas temperature sensor 37 for measuring the temperature Tg2 is provided.

The detection 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 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 performs filter regeneration control in which the temperature of the exhaust gas is raised in accordance with the control command of the control device 40 and the PM collected in the CSF device 22 is oxidized and removed in the CSF device 22. The exhaust gas temperature is raised and the air-fuel ratio of the exhaust gas G is set to a rich air-fuel ratio, so that the stored NOx in the LNT device 21 is released and released by the three-way catalyst supported by the LNT device 21. NOx purge control (NOx regeneration control) for reducing and purifying the NOx is performed, or 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 unit 41 that performs the above-described filter regeneration control, a NOx purge control unit 42 that performs NOx purge control, a sulfur purge control unit 43 that performs sulfur purge control, urea water In addition to the supply control unit 44, an estimated NH ₃ adsorption amount calculation unit (calculation unit) 51, an NH ₃ adsorption amount determination unit (determination unit) 52, and an adsorption NH ₃ consumption unit (consumption unit) 53 are configured. ing.

The estimated NH ₃ adsorption amount calculation unit 51 is a means for calculating an estimated NH ₃ adsorption amount Se that is an estimated value of the NH ₃ (reducing agent) adsorption amount in the SCR device 24. Further, the NH ₃ adsorption amount determination unit 52 calculates the estimated NH ₃ adsorption amount Se at the start of filter regeneration calculated by the estimated NH ₃ adsorption amount calculation unit 51 at the start of filter regeneration for burning and removing PM of the CSF device 22. It is means for determining whether or not the target NH ₃ adsorption amount St is greater than or equal to a preset value.

Further, the adsorption NH ₃ consumption unit 53 is the NH ₃ adsorption amount determination unit 52, and when the estimated NH ₃ adsorption amount Se calculated by the estimated NH ₃ adsorption amount calculation unit 51 is equal to or more than the target NH ₃ adsorption amount St, Means for performing adsorption NH ₃ consumption control for reducing the adsorbed NH ₃ in the SCR device 24 so that the estimated NH ₃ adsorption amount Se calculated by the estimated NH ₃ adsorption amount calculating unit 51 is smaller than the target NH ₃ adsorption amount St. It is.

In the adsorption NH ₃ consumption unit 53, the first exhaust gas temperature Tg1 detected by the first exhaust gas temperature sensor 36 is equal to or higher than the first set temperature Tgc1 set in advance based on the NOx release temperature in the LNT device 21. Thus, it is comprised so that adsorption | suction reduction agent consumption control which raises or maintains the exhaust gas G may be performed. The first set temperature Tgc1 is a temperature at which the NOx purification rate in the LNT device 21 decreases so that there is a temperature at which the NOx purification rate of the LNT decreases due to the relationship between the NOx purification rate illustrated in FIG. 4 and the engine outlet temperature. In other words, the temperature is set to a temperature at which the NOx occlusion ability decreases, for example, 400 ° C. or higher.

Due to the temperature rise of the NOx occlusion reduction type catalyst of the LNT device 21 caused by the temperature rise of the exhaust gas G, the NOx occluded in the LNT device 21 is released before the filter regeneration is started at the time of filter regeneration. The released NOx flows into the SCR device 24 on the downstream side. The inflowing NOx reacts with NH ₃ adsorbed by the SCR device 24 to reduce and purify NOx, whereby the adsorbed NH ₃ in the SCR device 24 can be reduced.

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

Further, the adsorption NH ₃ consumption unit 53 sets the second exhaust gas temperature Tg2 detected by the second exhaust gas temperature sensor 37 in advance based on the NH ₃ consumption efficiency in the SCR device 24 in the adsorption NH ₃ consumption control. The second exhaust gas temperature Tg2 is raised or maintained so as to be equal to or higher than the second preset temperature Tgc2 and lower than or equal to a preset third preset temperature Tgc3 based on the NH ₃ release temperature in the SCR device 24. It is preferable that it is comprised. This second set temperature Tgc2 is a relationship between the NOx purification rate illustrated in FIG. 4 and the engine outlet temperature, so that the NOx purification rate is high such that there is a temperature at which the NOx purification rate becomes high in SCR, and the consumption of stored NH ₃ The temperature at which the rate increases is set to about 300 ° C., for example.

Due to the temperature rise of the SCR catalyst of the SCR device 24 caused by the temperature rise of the exhaust gas G, NH ₃ adsorbed on the SCR device 24 is reacted with NOx before starting filter regeneration during filter regeneration. The efficiency of this NOx reduction reaction, that is, the NH ₃ consumption efficiency, increases when the second exhaust gas temperature Tg2 becomes equal to or higher than the second set temperature Tgc2 set above, and therefore, the occluded NH ₃ in the SCR device 24 in a short time. Can 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 the second exhaust gas temperature Tg2 is suppressed to the third set temperature Tgc3 or less set above. The third set temperature Tgc3 is a relationship between the NOx purification rate and the engine outlet temperature illustrated in FIG. 4, and the NOx purification rate is low and the consumption rate of the occluded NH ₃ so that there is a temperature at which the NOx purification rate becomes low in SCR. Is set to a temperature at which the temperature decreases, for example, about 400 ° C. That is, the second exhaust gas temperature Tg2 is increased within a temperature range corresponding to the temperature range Ra in which the NOx purification rate in the SCR is high in the relationship between the NOx purification rate and the engine outlet temperature illustrated in FIG. Warm and maintain.

An exhaust gas purification method for an internal combustion engine (hereinafter referred to as an exhaust gas purification method) according to an embodiment of the present disclosure stores an NOx in the exhaust gas G in the exhaust passage 11 of the internal combustion engine in order from the upstream side. 21 and an SCR device 24 for reducing NOx in the exhaust gas G with NH ₃ , and an exhaust gas purification method provided with a CSF device 22 for collecting PM in the exhaust gas G in the exhaust passage 11. The method is as follows.

In this exhaust gas purification method, an 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 started at the start of filter regeneration for removing the PM of the CSF device 22 by combustion. 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 for reducing the adsorbed NH ₃ in the SCR device 24 is performed so that the estimated NH ₃ adsorption amount Se is smaller than the target NH ₃ adsorption amount St.

The above control can be performed 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, and 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 the upper control flow and starts, a filter regeneration request (hereinafter, referred to as regeneration control) in the CSF device 22 is requested by “regeneration request?” In step S11. Hereinafter, it is determined whether or not there is a reproduction request. In this determination, if there is no regeneration request, the process returns, returns to the upper control flow, and after a preset time has elapsed, it is called again from the upper control flow and started, and this is repeated.

If it is determined in step S11 that there is a regeneration request ?, if there is a regeneration request, the process proceeds to “stop NOx purge control” in step S12. In “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 next “input of SCR inlet temperature” in step S13, the second exhaust gas temperature Tg2 detected by the second exhaust gas temperature sensor 37, that is, the SCR inlet temperature is inputted. In the “setting of the target NH ₃ adsorption amount St”, the NH ₃ adsorption amount Smax that can be adsorbed in the SCR device 24 is greatly influenced by the temperature of the SCR catalyst. Therefore, based on the second exhaust gas temperature Tg2, A target NH ₃ adsorption amount St during filter regeneration (hereinafter referred to as regeneration) is set. Target adsorbed NH ₃ amount St at the time of reproduction, reproduction, exhaust gas flow rate is small, since the exhaust gas is KyuNoboru temperature, since ammonia slip is likely to occur, the target NH ₃ in the normal non-playback Compared with the adsorption amount St0, a value smaller than this is set.

Further, in “calculation of estimated NH ₃ adsorption amount Se”, an estimated NH ₃ adsorption amount Se that is an estimated value of the NH ₃ adsorption amount in the SCR device 24 is calculated. 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 consumed NH ₃ amount is the amount of NH ₃ used to reduce the NOx amount generated from the engine body 10. This is because the amount of NOx flowing into the SCR device 24 and the temperature of the SCR catalyst (for example, substitute for the second exhaust gas temperature Tg2), the flow rate of the exhaust gas G, the ratio of NO to NO ₂ , the NH ₃ adsorption amount during the reaction, etc. 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.

Further, the NOx amount (SCR inlet NOx amount) flowing into the SCR device 24 is obtained by subtracting the NOx occlusion / 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 occlusion / desorption amount of LNT device−NOx reduction amount of LNT device).

The amount of NOx 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. The NOx occlusion / desorption amount of the LNT device 21 can be calculated from the LNT temperature, the exhaust gas flow rate, and the NOx occlusion amount. The NOx reduction amount of the LNT device 21 can be calculated from the LNT temperature, the exhaust gas flow rate, the NOx occlusion amount, and the air-fuel ratio.

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

In the next determination of “Se ≧ St” in 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. In the determination of “Se ≧ St” in step S14, if the estimated NH ₃ adsorption amount Se is equal to or larger than the target NH ₃ adsorption amount St (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 the preset time, are compared.

In this adsorption NH ₃ consumption control, the calculated estimated NH ₃ adsorption amount Se is smaller than the target NH ₃ adsorption amount St, or the second exhaust gas temperature Tg2 is set to the second set temperature Tgc2 and the third set temperature. Control to reduce the adsorbed NH ₃ in the SCR device 24 is performed so as to be within a range between the Tgc 3 and the 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. As for the temperature rise of the exhaust gas G, the fuel injection amount in the engine body 10 is increased, or the unburned fuel supplied to the exhaust passage 11 by post injection or in-pipe fuel injection is oxidized by the LNT device 21 to generate heat. For example, a method of increasing the temperature of the exhaust gas G is adopted.

If the estimated NH ₃ adsorption amount Se is smaller than the target NH ₃ adsorption amount St in the determination of “Se ≧ St” in step S14, the process proceeds to “regeneration condition satisfied?” In step S16. In “regeneration condition satisfied?” In step S16, it is determined whether or not the start condition for regeneration control in the CSF device 22 is satisfied. If the start condition for regeneration control 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 regeneration control start condition is satisfied in “Regeneration condition established?” In step S16 (YES), the process goes to “regeneration control” in step S17 to perform regeneration control in the CSF device 22. After the reproduction control is completed, the process goes to return and returns to the upper control flow. After a preset time elapses, it is called again from the upper control flow and started, and this is repeated.

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

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. Furthermore, when estimating a more accurate catalyst temperature. Using the first exhaust gas temperature Tg1 and the third exhaust gas temperature Tg3, a simple average or a weighted average can be used as the catalyst temperature of the LNT device 21.

Further, 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. Furthermore, when a more accurate catalyst temperature is estimated, the second exhaust gas temperature Tg2 and the fourth exhaust gas temperature Tg4 are used. It is also possible to use the simple average or the weighted average as the catalyst temperature of the SCR device 24.

As described above, according to the exhaust gas purification system 1 for an internal combustion engine and the exhaust gas purification method for an 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 regeneration is lengthened while avoiding being released 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 the front stage of the SCR device 24 carrying the SCR catalyst, NOx is occluded in the LNT catalyst of the LNT device 21 and NH ₃ in the SCR device 24 is stored. Since the reduction efficiency of consumption decreases, the waiting time until the NH ₃ adsorption amount decreases increases and the time until filter regeneration starts increases, but this problem can be solved more effectively.

That is, when the NH ₃ adsorption amount in the SCR device 24 is large and the NOx occlusion amount of the LNT device 21 is small, it is necessary to saturate the NOx occlusion amount of the LNT device 21 and consume the adsorption NH ₃ of the SCR device 24. Takes time. In such a case, by raising the temperature to a temperature at which the NOx occlusion efficiency of the LNT device 21 is reduced, the consumption of adsorbed NH ₃ in the SCR device 24 due to the NOx released from the LNT device 21 and the NOx occlusion saturation in the LNT device 21. And a comprehensive effect of improving the reaction efficiency (= improvement of NH ₃ consumption efficiency) by increasing the temperature of the SCR catalyst of the SCR device 24, and shortening the time until the start of filter regeneration Can do. As a result, the NOx emission amount can be reduced, and PM overdeposition on the CSF device 22 can be suppressed.

This application is based on a Japanese patent application (Japanese Patent Application No. 2018-027008) filed on February 19, 2018, the contents of which are incorporated herein by reference.

In the exhaust gas purification system and the exhaust gas purification method of the present disclosure, during filter regeneration, the reducing agent adsorbed on the SCR catalyst of the SCR device is prevented from being desorbed and released and flowing out to the downstream side of the SCR device. However, this is useful in that it solves the problem that the time until the filter regeneration starts becomes long and the concern about the increase in the NOx emission amount associated therewith.

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification system 10 of internal combustion engine Engine body 11 Exhaust passage 21 LNT device (Occlusion reduction type 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 equipment (ASC: oxidation catalyst equipment)
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 detection device)
38 Third exhaust gas temperature sensor 40 Control device 41 Filter regeneration control unit 42 NOx purge control unit 43 Sulfur purge control unit 44 Urea water supply control unit 51 Estimated NH ₃ occlusion amount calculation unit (calculation unit)
52 NH ₃ adsorption amount determination unit (determination unit)
53 Occlusion NH ₃ Consumption Department (Consumption Department)
G exhaust gas U urea water (reducing agent)

Claims

The exhaust passage of the internal combustion engine includes, in order from the upstream side, a NOx storage reduction catalyst device that stores NOx in the exhaust gas, and a selective reduction catalyst device that reduces NOx in the exhaust gas with a reducing agent. In the exhaust gas purification system of the internal combustion engine, comprising a filter device for collecting particulate matter in the exhaust gas in the exhaust passage,
A calculating unit that calculates an estimated reducing agent adsorption amount that is an estimated value of the reducing agent adsorption amount in the selective catalytic reduction device;
A determination unit that determines whether or not the estimated reducing agent adsorption amount at the start of regeneration calculated by the calculation unit is greater than or equal to a preset target amount at the start of filter regeneration that burns and removes particulate matter of the filter device When,
In the determination unit, when the estimated reducing agent adsorption amount calculated by the calculation unit is equal to or greater than the target amount, the estimated reducing agent adsorption amount calculated by the calculation unit is less than the target amount. An exhaust gas purification system comprising a control unit comprising a consumption unit that performs adsorption / reduction agent consumption control for reducing adsorption / reduction agent in the selective catalytic reduction device.
A first temperature detector for measuring the temperature of the exhaust gas flowing into the NOx occlusion reduction catalyst device;
In the adsorption reducing agent consumption control, the consumption unit performs a first setting in which the first exhaust gas temperature detected by the first temperature detection device is preset based on the NOx release temperature in the storage reduction catalyst device. The exhaust gas purification system according to claim 1, wherein the exhaust gas temperature is raised or maintained so as to be equal to or higher than the temperature.
A second temperature detecting device for measuring the temperature of the exhaust gas flowing into the selective catalytic reduction device,
In the adsorption reducing agent consumption control by the consumption unit, a second exhaust gas temperature detected by the second temperature detection device is preset based on a reducing agent consumption efficiency in the selective catalytic reduction device. The exhaust gas temperature is raised or maintained so as to be equal to or higher than a preset temperature and lower than or equal to a preset third preset temperature based on the reducing agent release temperature in the selective catalytic reduction device. The exhaust gas purification system according to claim 1 or 2, characterized in that.
The exhaust passage of the internal combustion engine includes, in order from the upstream side, a NOx storage reduction catalyst device that stores NOx in the exhaust gas, and a selective reduction catalyst device that reduces NOx in the exhaust gas with a reducing agent. In the exhaust gas purification method for an internal combustion engine, comprising a filter device for collecting particulate matter in the exhaust gas in the exhaust passage,
Calculating an estimated reducing agent adsorption amount that is an estimated value of the reducing agent adsorption amount in the selective catalytic reduction device,
At the start of filter regeneration for burning and removing particulate matter of the filter device, it is determined whether or not the estimated reducing agent adsorption amount at the start of regeneration is equal to or greater than a preset target amount,
When the estimated reducing agent adsorption amount is equal to or larger than the target amount, the adsorption reduction for reducing the adsorption reducing agent in the selective catalytic reduction device so that the calculated estimated reducing agent adsorption amount is smaller than the target amount. Exhaust gas purification method characterized by performing agent consumption control.