JP4521824B2 - Exhaust purification device - Google Patents

Description

  The present invention relates to an exhaust purification device for purifying engine exhaust, and in particular, includes a particulate filter that collects particulates in exhaust, and a NOx catalyst that reduces and purifies NOx in exhaust using ammonia as a reducing agent. The present invention relates to an exhaust purification device.

As an exhaust purification device for purifying NOx (nitrogen oxide), which is one of the pollutants contained in the exhaust discharged from the engine, an ammonia selective reduction type NOx catalyst is disposed in the exhaust passage of the engine, and the reduction is performed. 2. Description of the Related Art Exhaust gas purification devices that purify NOx in exhaust gas by supplying ammonia, which is an agent, to an ammonia selective reduction type NOx catalyst are used.
In such an exhaust purification device, urea water is supplied to the upstream side of the ammonia selective reduction type NOx catalyst, and ammonia generated by hydrolysis of the urea water by the heat of exhaust gas is supplied to the ammonia selective reduction type NOx catalyst. . Ammonia supplied to the ammonia selective reduction type NOx catalyst is once adsorbed by the ammonia selective reduction type NOx catalyst, and the NOx removal reaction between this ammonia and NOx in the exhaust gas is promoted by the ammonia selective reduction type NOx catalyst. Purification is performed.

On the other hand, in a diesel engine or the like, in order to purify exhaust gas by removing particulates contained in exhaust gas, a particulate filter is disposed in the exhaust passage so as to collect particulates in the exhaust gas.
In this particulate filter, since the exhaust resistance gradually increases as the collected particulate matter accumulates in the particulate filter, the temperature of the particulate filter is raised when the particulate accumulation amount reaches a predetermined amount, The exhaust gas purification function of the particulate filter is maintained by forcibly incinerating the particulate and forcibly regenerating the particulate filter.

An exhaust gas purification apparatus that includes both such a particulate filter and an ammonia selective reduction type NOx catalyst using ammonia as a reducing agent and purifies particulates and NOx in exhaust gas is disclosed in, for example, Patent Document 1 It is disclosed.
In the exhaust gas purification apparatus disclosed in Patent Document 1, a particulate filter is disposed in the exhaust passage of the engine, and an ammonia selective reduction type NOx catalyst is disposed downstream of the particulate filter. After the particulates are collected by the particulate filter, the exhaust gas is supplied to the ammonia selective reduction type NOx catalyst, and the ammonia generated from the urea water is used as a reducing agent, and the NOx in the exhaust gas is ammonia selective reduction type NOx. The catalyst is selectively reduced and purified.

Even in the exhaust gas purification device disclosed in Patent Document 1, exhaust gas resistance gradually increases when particulates are collected and deposited on the particulate filter. Therefore, it is necessary to raise the temperature of the particulate filter and perform forced regeneration. Therefore, fuel, that is, HC (hydrocarbon) is supplied to the oxidation catalyst provided on the upstream side of the particulate filter, and the temperature of the particulate filter is increased by combustion of HC in the oxidation catalyst, thereby being deposited on the particulate filter. The particulates are incinerated for forced regeneration.
JP 2003-176711 A

  When forced regeneration is performed in the exhaust gas purification apparatus disclosed in Patent Document 1, the exhaust gas that has passed the heated particulate filter and has reached a high temperature is supplied to the ammonia selective reduction type NOx catalyst. For this reason, when urea water is supplied in such a state, the ammonia generated from the urea water and supplied to the ammonia selective reduction type NOx catalyst is oxidized and converted into NOx, and the exhaust gas discharged into the atmosphere is discharged. There is a risk that the NOx concentration may be increased.

  Accordingly, when forced regeneration is performed by raising the temperature of the particulate filter, ammonia cannot be supplied to the ammonia selective reduction type NOx catalyst. On the other hand, if ammonia cannot be supplied to the ammonia selective reduction type NOx catalyst, NOx in the exhaust gas cannot be purified by the ammonia selective reduction type NOx catalyst. As a result, during the forced regeneration of the particulate filter, the NOx in the exhaust gas is exhausted. There is a problem that it cannot be sufficiently purified.

  The present invention has been made in view of such problems, and an object of the present invention is to provide an exhaust capable of satisfactorily purifying NOx in the exhaust even during forced regeneration of the particulate filter. It is to provide a purification device.

  In order to achieve the above object, an exhaust emission control device according to the present invention is provided with an oxidation catalyst disposed in an exhaust passage of an engine and a downstream side of the oxidation catalyst, and purifies NOx in exhaust gas using HC as a reducing agent. An HC selective reduction type NOx catalyst, a particulate filter disposed between the oxidation catalyst and the HC reduction type NOx catalyst, for collecting particulates in the exhaust, the oxidation catalyst and the HC reduction type NOx An ammonia selective reduction NOx catalyst that is disposed between the catalyst and purifies NOx in the exhaust gas using ammonia as a reducing agent, and forcibly regenerates the particulate filter by raising the temperature of the particulate filter by supplying HC to the oxidation catalyst HC supply means for performing ammonia, ammonia supply means for supplying ammonia to the ammonia selective reduction type NOx catalyst, and HC from the HC supply means When the forced regeneration is performed, the supply of ammonia from the ammonia supply unit is stopped, and when it is determined that the HC selective reduction type NOx catalyst is activated, the amount of HC supplied from the HC supply unit And a control means for increasing the amount by a predetermined amount from the amount necessary for forced regeneration of the particulate filter (claim 1).

According to the exhaust gas purification apparatus configured as described above, particulates in the exhaust gas are collected by the particulate filter, and exhausted by the ammonia selective reduction type NOx catalyst using ammonia supplied from the ammonia supply means as a reducing agent. NOx is purified.
When forced regeneration of the particulate filter is performed, the temperature of the particulate filter is raised by supplying HC from the HC supply unit, while the control unit stops supplying ammonia from the ammonia supply unit and If it is determined that the selective reduction type NOx catalyst is activated, the amount of HC supplied from the HC supply means is increased by a predetermined amount from the amount necessary for forced regeneration of the particulate filter.

By such an increase, surplus HC that was not consumed by the forced regeneration of the particulate filter is supplied to the downstream HC selective reduction type NOx catalyst, and the HC selective reduction type NOx catalyst uses the supplied HC as a reducing agent to exhaust gas. NOx in the inside is selectively reduced and purified.
More specifically, in such an exhaust purification device, the control means is detected by an engine NOx emission amount detection means for detecting the amount of NOx discharged from the engine and the engine NOx emission amount detection means. HC increase calculation means for determining the predetermined amount based on the NOx emission amount from the engine (claim 2).

In the exhaust emission control device configured as described above, the predetermined amount determined by the HC increase calculation means based on the NOx emission amount from the engine detected by the engine NOx emission amount detection means is used for the increase.
In this case, preferably, the amount of NOx discharged from the engine may be estimated based on the operating state of the engine.

Alternatively, the amount of NOx exhausted from the engine may be directly detected by an engine exhaust NOx sensor provided in the exhaust passage.
Further, the exhaust purification device further includes a catalyst NOx emission amount detecting means for detecting an amount of NOx discharged from the HC selective reduction type NOx catalyst, and the HC increase calculating means is provided by the engine NOx emission amount detecting means. Based on the detected NOx emission from the engine and the NOx emission from the HC selective reduction NOx catalyst detected by the catalyst NOx emission detection means, the NOx purification rate of the HC selective reduction NOx catalyst is calculated. The predetermined amount is obtained and corrected according to the NOx purification rate (Claim 3).

In the exhaust gas purification apparatus configured as described above, the engine NOx emission amount detected by the engine NOx emission amount detection means and the NOx emission amount of the HC selective reduction type NOx catalyst detected by the catalyst NOx emission amount detection means. A predetermined amount corrected according to the obtained NOx purification rate of the HC selective reduction type NOx catalyst is used for the increase.
In order to achieve the above object, an exhaust emission control device according to the present invention is provided with an oxidation catalyst disposed in an exhaust passage of an engine and a downstream side of the oxidation catalyst, and NOx in exhaust gas using HC as a reducing agent. HC selective reduction type NOx catalyst for purifying gas, a particulate filter disposed between the oxidation catalyst and the HC reduction type NOx catalyst, for collecting particulates in exhaust gas, the oxidation catalyst and the HC reduction An ammonia selective reduction-type NOx catalyst that is disposed between the NOx catalyst and purifies NOx in the exhaust gas using ammonia as a reducing agent, and a temperature raising unit that raises the temperature of the particulate filter to perform forced regeneration; An ammonia supply means for supplying ammonia to the ammonia selective reduction type NOx catalyst; and an HC supply means for NOx catalyst for supplying HC to the HC selective reduction type NOx catalyst; When the temperature of the particulate filter is raised by the temperature raising means and the forced regeneration is performed, the supply of ammonia from the ammonia supply means is stopped and the HC selective reduction type NOx catalyst is activated And a control means for supplying HC from the NOx catalyst HC supply means to the HC selective reduction type NOx catalyst (claim 4).

According to the exhaust gas purification apparatus configured as described above, particulates in the exhaust gas are collected by the particulate filter, and exhausted by the ammonia selective reduction type NOx catalyst using ammonia supplied from the ammonia supply means as a reducing agent. NOx is purified.
When the particulate filter is forcibly regenerated, the temperature of the particulate filter is raised by the temperature raising means, while the control means stops the supply of ammonia from the ammonia supply means and the HC selective reduction type NOx catalyst is activated. HC is supplied from the NOx catalyst HC supply means to the HC selective reduction type NOx catalyst. The HC selective reduction type NOx catalyst selectively reduces and purifies NOx in the exhaust gas using the supplied HC as a reducing agent.

  According to the exhaust emission control device of claims 1 to 3, when the particulate filter is forcibly regenerated, the supply of ammonia from the ammonia supply means is stopped, so that the supplied ammonia is oxidized and generated. NOx is not discharged into the atmosphere. At this time, if the HC selective reduction type NOx catalyst is activated, the amount of HC supplied from the HC supply means is increased by a predetermined amount from the amount required for forced regeneration of the particulate filter. Excess HC not consumed for forced regeneration of the filter is used as a reducing agent in the HC selective reduction type NOx catalyst, and NOx in the exhaust gas is purified by the HC selective reduction type NOx catalyst. As a result, it is possible to satisfactorily purify NOx in the exhaust gas even during forced regeneration of the particulate filter.

Further, according to the exhaust gas purification apparatus of the second aspect, the predetermined amount of the increase is determined based on the NOx emission amount from the engine detected by the engine NOx emission amount detecting means, so the NOx is purified. Therefore, a necessary amount of HC can be supplied to the HC selective reduction type NOx catalyst with higher accuracy.
Furthermore, according to the exhaust purification system of claim 3, the NOx emission amount of the engine detected by the engine NOx emission amount detection means and the NOx emission of the HC selective reduction type NOx catalyst detected by the catalyst NOx emission amount detection means. The predetermined amount of the increase is corrected according to the NOx purification rate of the HC selective reduction type NOx catalyst obtained from the quantity, so that the purification ability of the HC selective reduction type NOx catalyst can be exhibited to the maximum extent possible. A necessary amount of HC can be supplied with high accuracy, and wasteful consumption of HC can be eliminated.

  According to the exhaust gas purification apparatus of the fourth aspect, when forced regeneration of the particulate filter is performed, the supply of ammonia from the ammonia supply means is stopped, so that the supplied ammonia is oxidized and generated. NOx is not discharged into the atmosphere. At this time, if the HC selective reduction type NOx catalyst is activated, the HC selective reduction type NOx catalyst purifies NOx in the exhaust gas using HC supplied from the HC supply means for NOx catalyst as a reducing agent. As a result, it is possible to satisfactorily purify NOx in the exhaust gas even during forced regeneration of the particulate filter.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a system configuration diagram of a four-cylinder diesel engine (hereinafter referred to as an engine) to which an exhaust emission control device according to an embodiment of the present invention is applied. The exhaust emission control device according to the present invention is based on FIG. The structure of will be described.
The engine 1 includes a high-pressure accumulator chamber (hereinafter referred to as a common rail) 2 common to each cylinder, and light oil, which is high-pressure fuel supplied from a fuel injection pump (not shown) and stored in the common rail 2, is supplied to each cylinder. The oil is supplied to the provided injectors 4, and light oil is injected from the injectors 4 into the respective cylinders.

  The intake passage 6 is equipped with a turbocharger 8. The intake air drawn from an air cleaner (not shown) flows into the compressor 8a of the turbocharger 8 from the intake passage 6, and the intake air supercharged by the compressor 8a is intercooler. 10 and the intake control valve 12 are introduced into the intake manifold 14. An intake flow rate sensor 16 for detecting the intake air flow rate to the engine 1 is provided upstream of the compressor 8 a in the intake passage 6.

On the other hand, an exhaust port (not shown) through which exhaust is discharged from each cylinder of the engine 1 is connected to an exhaust pipe (exhaust passage) 20 via an exhaust manifold 18. An EGR passage 24 that communicates the exhaust manifold 18 and the intake manifold 14 via the EGR valve 22 is provided between the exhaust manifold 18 and the intake manifold 14.
The exhaust pipe 20 passes through the turbine 8 b of the turbocharger 8 and is connected to an exhaust aftertreatment device 28 via an exhaust throttle valve 26. The rotating shaft of the turbine 8b is connected to the rotating shaft of the compressor 8a, and the turbine 8b receives the exhaust flowing in the exhaust pipe 20 and drives the compressor 8a.

The exhaust aftertreatment device 28 includes an upstream casing 30 and a downstream casing 34 that is communicated with the downstream side of the upstream casing 30 through a communication passage 32.
In the upstream casing 30, an oxidation catalyst 36 is accommodated, and an oxidation catalyst temperature sensor 38 for detecting the outlet side exhaust temperature of the oxidation catalyst 36 is provided.
Further, a particulate filter (hereinafter referred to as a filter) 40, an ammonia selective reduction type NOx catalyst 42, and an HC selective reduction type NOx catalyst 44 are accommodated in the downstream casing 34 from the upstream side.

The filter 40 is made of a honeycomb-type ceramic carrier, and a large number of passages communicating with the upstream side and the downstream side are arranged side by side, and the upstream side opening and the downstream side opening of the passage are alternately closed, The exhaust of the engine 1 is purified by collecting the particulates.
The ammonia selective reduction type NOx catalyst 42 purifies the exhaust of the engine 1 by selectively reducing NOx in the exhaust gas using ammonia as a reducing agent, and the HC selective reduction type NOx catalyst 44 is in the exhaust gas using HC as a reducing agent. The exhaust of the engine 1 is purified by selectively reducing the NOx.

The HC NOx selective reduction catalyst 48 oxidizes CO generated when the particulates are incinerated in forced regeneration of the filter 40 to be described later, is also a function of discharge into the atmosphere as CO _2.
By disposing the filter 40 on the downstream side of the oxidation catalyst 36, NO ₂ generated from NO in the exhaust gas by the oxidation catalyst 36 is supplied to the filter 40. Particulates collected and accumulated in the filter 40 are removed from the filter 40 by reacting with the NO ₂ and oxidizing, and the filter 40 is continuously regenerated.

  An upstream pressure sensor 46 that detects the exhaust pressure upstream of the filter 40 and a downstream pressure sensor 48 that detects the exhaust pressure downstream of the filter 40 are provided in the downstream casing 34 before and after the filter 40. . Further, on the downstream side of the HC selective reduction type NOx catalyst 44, a NOx catalyst temperature sensor 50 for detecting the outlet side exhaust temperature of the HC selective reduction type NOx catalyst 44 is provided.

  Fuel is supplied from a fuel injection pump (not shown) to the exhaust pipe 20 between the exhaust throttle valve 26 and the exhaust aftertreatment device 28, and a fuel addition valve 52 for injecting fuel into the exhaust gas in the exhaust pipe 20. (HC supply means) is provided. The fuel addition valve 52 supplies HC to the oxidation catalyst 36 by injecting fuel into the exhaust gas when forced regeneration of the filter 40 becomes necessary, and becomes high temperature due to oxidation of HC in the oxidation catalyst 36. Exhaust gas is supplied to the filter 40 to raise the temperature of the filter 40.

Further, the communication passage 32 of the exhaust aftertreatment device 28 is provided with an injection nozzle (ammonia supply means) 54 for injecting urea water into the exhaust in the communication passage 32, and the injection nozzle 54 is a urea water injection pipe. The urea water injection device 58 is connected via 56.
The urea water injection device 58 is supplied from a urea water tank 62 by a urea water supply pump (not shown) into pressurized air supplied from an air tank 60 that stores compressed air compressed by an air pump (not shown). The supplied urea water is ejected, and urea water is supplied to the injection nozzle 54 via the urea water injection pipe 56 together with the pressurized air, and is connected to the air tank 60 via the air supply pipe 64, A urea water tank 62 is connected via a urea water supply pipe 66.

  An air control valve 68 is provided in the air supply pipe 64, and the supply amount of pressurized air to the urea water injector 58 is adjusted by controlling the opening and closing of the air control valve 68. In addition, a urea water control valve 70 is provided in the urea water supply passage 66, and the urea water supply amount to the urea water injection device 58 is adjusted by opening and closing the urea water control valve 70. That is, by controlling the opening and closing of the air control valve 68 and the urea water control valve 70, the amount of urea water injected from the injection nozzle 54 into the exhaust gas is adjusted.

The urea water injected from the injection nozzle 54 is hydrolyzed by the heat of the exhaust to become ammonia, and is supplied to the ammonia selective reduction type NOx catalyst 42. The ammonia selective reduction type NOx catalyst 42 adsorbs the supplied ammonia and promotes a denitration reaction between the adsorbed ammonia and NOx in the exhaust gas, thereby purifying NOx and making it harmless N ₂ .
At this time, ammonia that has not reacted with NOx and has flowed out of the ammonia selective reduction type NOx catalyst 42 is oxidized by the oxidation function of the HC selective reduction type NOx catalyst 44 to become N ₂ or NOx. The NOx produced here reacts with HC flowing into the HC selective reduction type NOx catalyst 44 and becomes N ₂ , so the ammonia flowing into the HC selective reduction type NOx catalyst 44 becomes harmless N ₂ and enters the atmosphere. To be released.

A NOx sensor (catalyst NOx) that detects the concentration of NOx in the exhaust discharged from the exhaust aftertreatment device 28, that is, the concentration of NOx exhausted from the HC selective reduction type NOx catalyst 44, is disposed downstream of the exhaust aftertreatment device 28. (Discharge amount detecting means) 72 is provided.
The ECU (control means) 74 is a control device for performing comprehensive control including operation control of the engine 1, and includes a CPU, a memory, a timer counter, and the like, and calculates various control amounts. Various devices are controlled based on the control amount.

  On the input side of the ECU 74, in order to collect information necessary for various controls, the intake flow rate sensor 16, the oxidation catalyst temperature sensor 38, the upstream pressure sensor 46, the downstream pressure sensor 48, the NOx catalyst temperature sensor 50, and the NOx sensor 72 described above. In addition, various sensors such as an engine speed sensor 76 for detecting the engine speed and an accelerator opening sensor 78 for detecting the depression amount of the accelerator pedal are connected, and the output side is controlled based on the calculated control amount. Various devices such as the injector 4, the intake control valve 12, the EGR valve 22, the exhaust throttle valve 26, the fuel addition valve 52, the air control valve 68, and the urea water control valve 70 of each cylinder are connected.

  The ECU 74 also performs calculation of the fuel supply amount to each cylinder of the engine 1 and control of fuel supply from the injector 4 based on the calculated fuel supply amount. The fuel supply amount (main injection amount) necessary for the operation of the engine 1 is stored in advance based on the engine speed detected by the speed sensor 76 and the accelerator opening detected by the accelerator opening sensor 78. Read from the map and decide. The amount of fuel supplied to each cylinder is adjusted by the valve opening time of the injector 4, and each injector 4 is driven to open in a driving time corresponding to the determined fuel amount, and main injection is performed in each cylinder. Thus, the amount of fuel necessary for the operation of the engine 1 is supplied.

Further, the ECU 74 uses the ammonia selective reduction type NOx catalyst 42 to selectively reduce NOx discharged from the engine 1 based on the engine operating state such as the engine speed and the main injection amount of fuel detected by the speed sensor 76. A necessary urea water supply amount is obtained from map data stored in advance, and the air control valve 68 and the urea water control valve 70 are controlled to open and close.
The urea water whose supply amount has been adjusted by the urea water control valve 70 is mixed with the pressurized air whose supply amount has been adjusted by the air control valve 68 by the urea water injection device 58, and communicated from the injection nozzle 54 together with the pressurized air. The fuel is injected into the exhaust gas in the exhaust gas 32. The urea water thus injected and supplied is hydrolyzed by the heat of the exhaust to become ammonia and is adsorbed by the ammonia selective reduction type NOx catalyst 42. Ammonia selective reduction type NOx catalyst 42 promotes denitration reaction between the NOx in the exhaust gas with ammonia adsorbed, NOx in the exhaust gas becomes a harmless N _2.

At this time, ammonia that has flowed out without being adsorbed by the ammonia selective reduction type NOx catalyst 42 is discharged into the atmosphere as harmless N ₂ by the HC selective reduction type NOx catalyst 44 as described above.
In the exhaust gas purification apparatus configured as described above, the exhaust gas discharged from the engine 1 is introduced into the exhaust gas after-treatment device 28 through the exhaust pipe 20, and particulates in the exhaust gas are collected by the filter 40, and As described above, the particulates deposited on the filter 40 are oxidized and removed by continuous regeneration using NO ₂ supplied from the oxidation catalyst 36. Further, urea water is supplied from the injection nozzle 54 by the urea water supply control, and NOx in the exhaust gas is selectively reduced by the ammonia selective reduction NOx catalyst 42 using ammonia generated from the urea water as a reducing agent, and is harmless. N ₂ is discharged into the atmosphere.

The urea water supply control at this time is performed at a predetermined control cycle according to the flowchart of FIG. 2 when the engine 1 is started.
First, in step S2, it is determined whether urea water can be supplied into the exhaust gas. For example, when the ammonia selective reduction type NOx catalyst 46 has not reached the activation temperature immediately after the engine 1 is started, or when the exhaust temperature has not reached a temperature at which the urea water can be hydrolyzed, ammonia is not used. Since NOx as a reducing agent cannot be purified, urea water cannot be supplied into the exhaust gas. Accordingly, in step S2, it is determined whether urea water can be supplied based on the engine operating state such as the exhaust temperature on the outlet side of the oxidation catalyst 36 detected by the oxidation catalyst temperature sensor 38.

If it is determined in step S2 that urea water cannot be supplied, the current control cycle is terminated, and the processing is performed again from step S2 in the next control cycle. In the following, the operation in which the engine 1 can supply urea water is performed. The description will be made assuming that it is in a state.
If it is determined in step S2 that urea water can be supplied, the process proceeds to step S4, where it is determined whether the value of the forced regeneration flag F1 is 1. The forced regeneration flag F1 indicates whether or not forced regeneration of the filter 40 is performed. In the forced regeneration control described later, whether or not forced regeneration is necessary is determined, and a value is set according to the determination result. Yes, a value of 1 indicates that forced regeneration is performed, and a value of 0 indicates that forced regeneration is not performed.

  When the filter 40 is forcibly regenerated, the exhaust temperature and the temperature of the ammonia selective reduction type NOx catalyst 42 increase with the forced regeneration of the filter 40. When urea water is supplied into the exhaust gas from the injection nozzle 54 in this state, the urea water is directly oxidized and converted into NOx because of the high-temperature exhaust gas and the ammonia selective reduction type NOx catalyst 42, and NOx in the exhaust gas is exhausted. It will increase the concentration.

For this reason, if it is determined in step S4 that the value of the forced regeneration flag F1 is 1, the current control cycle is terminated without doing anything, and the processing is repeated from step S2 in the next control cycle. Therefore, while the filter 40 is being forcedly regenerated, the supply of urea water from the injection nozzle 54 is stopped.
On the other hand, when the value of the forced regeneration flag F1 is 0, since the forced regeneration of the filter 40 is not performed, it is assumed that there is no possibility of the increase in the NOx concentration as described above even if the urea water is supplied. Proceed to step S6.

  In step S6, the amount of urea water to be supplied is determined from the amount of ammonia necessary for purifying NOx in the exhaust gas by the ammonia selective reduction type NOx catalyst 42. Specifically, first, the NOx emission amount from the engine 1 is estimated based on the engine operating state such as the engine speed detected by the speed sensor 76 and the fuel main injection amount calculated by the ECU 74. Further, based on the exhaust temperature on the outlet side of the oxidation catalyst 36 detected by the oxidation catalyst temperature sensor 38, the NOx purification rate of the ammonia selective reduction type NOx catalyst 42 is obtained from a previously stored map. Then, the NOx purification amount by the ammonia selective reduction type NOx catalyst 42 is obtained from the estimated NOx emission amount and the NOx purification rate, and the ammonia amount corresponding to the NOx purification amount is obtained. The necessary urea water supply amount is obtained from the ammonia amount thus obtained.

Next, when the process proceeds from step S6 to step S8, the air control valve 68 and the urea water control valve 70 are controlled to be opened and closed so that the amount of urea water obtained in step S6 is injected and supplied from the injection nozzle 54 into the exhaust gas. Then, urea water is injected from the injection nozzle 54 into the exhaust gas in the communication passage 32 together with the pressurized air.
The urea water injected from the injection nozzle 54 is hydrolyzed by the heat of the exhaust to generate ammonia. This ammonia is supplied to the ammonia selective reduction type NOx catalyst 42 and adsorbed on the ammonia selective reduction type NOx catalyst 42, and the denitration reaction between the NOx in the exhaust and the adsorbed ammonia is promoted by the ammonia selective reduction type NOx catalyst 42. NOx in the exhaust gas is selectively reduced and converted into harmless N ₂ .

At this time, the ammonia that has not reacted with NOx and has flowed out of the ammonia selective reduction type NOx catalyst 42 is oxidized by the oxidation function of the HC selective reduction type NOx catalyst 44 to become N ₂ or NOx. The NOx produced here reacts with HC in the exhaust gas flowing into the HC selective reduction type NOx catalyst 44 and becomes N ₂ , so that the ammonia flowing into the HC selective reduction type NOx catalyst 44 becomes harmless N _2. Released into the atmosphere.

After supplying urea water in step S8 in this way, the current control cycle is terminated, and the processing is performed again from step S2 in the next control cycle.
If forced regeneration of the filter 40 is required while supplying urea water from the injection nozzle 54, the value of the forced regeneration flag F1 is switched from 0 to 1 by forced regeneration control described later, so that the steps from step S4 to step S4 are performed. The process does not proceed to S6, but the process in the control cycle ends in step S4 as described above. Therefore, when the filter 40 is forcibly regenerated, the supply of urea water from the injection nozzle 54 is stopped.

  By performing the urea water supply control as described above, when the filter 40 is not forcibly regenerated, urea water is supplied into the exhaust gas from the injection nozzle 54 and ammonia as a reducing agent is supplied to the ammonia selective reduction type NOx catalyst 42. When the filter 40 is forcibly regenerated, the supply of urea water from the injection nozzle 54, that is, the supply of ammonia to the ammonia selective reduction type NOx catalyst 42 is stopped.

On the other hand, the particulates collected and deposited by the filter 40 are oxidized and removed by continuous regeneration using NO ₂ generated by oxidizing NO in the exhaust gas by the oxidation catalyst 36 as an oxidizing agent. However, in an operating state where the exhaust temperature of the engine 1 is low, for example, at a low speed or low load operation, the exhaust temperature does not rise to the activation temperature of the oxidation catalyst 36, and NO in the exhaust is not oxidized and the filter 40 is continuously regenerated. It may not be done enough. If such a state continues, particulates may be excessively accumulated in the filter 40 and the filter 40 may be clogged. Therefore, the temperature of the filter 40 is appropriately increased according to the particulate accumulation state in the filter 40. However, forced regeneration is performed.

The forced regeneration control for forcibly regenerating the filter 40 is performed in a predetermined control cycle according to the flowchart of FIG.
First, in step S12 of FIG. 3, it is determined whether or not the value of the forced regeneration flag F1 is “1”. The initial set value of the forced regeneration flag F1 is 0, and the process proceeds from step S12 to step S14 in the first control cycle.

  In step S14, it is determined whether or not forced regeneration of the filter 40 is necessary. Specifically, based on the differential pressure before and after the filter 40 obtained from the detection values of the upstream pressure sensor 46 and the downstream pressure sensor 48 and the exhaust flow rate to the filter 40 calculated from the detection value of the intake flow sensor 16, the filter 40. The amount of particulate deposition on the surface is estimated, and when this estimated amount of deposition is equal to or greater than the forced regeneration start determination value, it is determined that forced regeneration is necessary.

When the estimated accumulation amount of particulates is less than the forced regeneration start determination value, it is determined that the current forced regeneration is unnecessary, this control cycle is terminated, and the processing is performed again from step S12 in the next control cycle. .
On the other hand, if it is determined that forced regeneration is necessary, the process proceeds to step S16, the value of the forced regeneration flag F1 is set to 1 to indicate that forced regeneration is being performed, and the process proceeds to the next step S18.

  When the value of the forced regeneration flag F1 becomes 1 in step S16, in the urea water supply control, the supply of urea water from the injection nozzle 54 is stopped as described above, and ammonia as a reducing agent is added to the ammonia selective reduction type NOx catalyst 42. It will not be supplied. In the ammonia selective reduction type NOx catalyst 42, the ammonia supplied so far is adsorbed, and the NOx is purified by the adsorbed ammonia for a while after the supply of ammonia is stopped.

In step S18, it is determined whether or not the oxidation catalyst 36 is activated by determining whether or not the exhaust temperature Tfc on the outlet side of the oxidation catalyst 36 detected by the oxidation catalyst temperature sensor 38 is 250 ° C. or higher. .
If the exhaust gas temperature Tfc on the outlet side of the oxidation catalyst 36 is less than 250 ° C., it is determined that the oxidation catalyst 36 is not activated, and the process proceeds to step S20 to control the temperature increase of the oxidation catalyst 36.

  In this temperature increase control, the temperature of the oxidation catalyst 36 is raised to an activation temperature (for example, 250 ° C.) by supplying high-temperature exhaust gas to the oxidation catalyst 36. The intake control valve 12 and the exhaust throttle valve 26 are heated. Is controlled in the closing direction to raise the temperature of the exhaust discharged from the engine 1, and the first fuel is added from the fuel addition valve 52 into the exhaust as necessary. The fuel supplied into the exhaust gas by the addition of the first fuel burns in the exhaust gas whose temperature has risen, and the high-temperature exhaust gas is supplied to the oxidation catalyst 36, whereby the temperature of the oxidation catalyst 36 increases.

Next, when proceeding to step S28, as in step S14, is the particulate accumulation amount estimated based on the differential pressure across the filter 40 and the exhaust flow rate to the filter 40 equal to or less than the forced regeneration end determination value? Determine whether or not.
As described above, since the oxidation catalyst 36 is not yet fully activated, the incineration of particulates is not performed, and it is determined that the estimated accumulation amount of particulates is larger than the forced regeneration end determination value. After the current control cycle, the forced regeneration control is performed again from step S12 in the next control cycle.

In this case, since the value of the forced regeneration flag F1 is already 1, the process proceeds from step S12 to step S18.
If it is determined in step S18 that the exhaust temperature Tfc on the outlet side of the oxidation catalyst 36 is less than 250 ° C. and the oxidation catalyst 36 is not yet activated, the control of the intake control valve 12 and the exhaust throttle valve 26 is performed again in step S20. Catalyst temperature increase control is performed by adding the first fuel.

Therefore, as long as the exhaust gas temperature Tfc on the outlet side of the oxidation catalyst 36 is less than 250 ° C. and the oxidation catalyst 36 is not activated, the catalyst temperature increase control in step S20 is repeatedly performed every control cycle.
In this way, the catalyst temperature rise control is repeated, and when it is determined that the exhaust temperature Tfc on the outlet side of the oxidation catalyst 36 is 250 ° C. or higher and the oxidation catalyst 36 is activated, the process proceeds from step S18 to step S22.

  In step S22, the exhaust temperature Tpc on the outlet side of the HC selective reduction type NOx catalyst 44 detected by the NOx catalyst temperature sensor 50 corresponds to the temperature of the HC selective reduction type NOx catalyst 44, and this exhaust temperature Tpc is selected as the HC selection. It is determined whether or not the HC selective reduction NOx catalyst 44 is activated by determining whether or not the activation temperature lower limit value Tal of the reduction NOx catalyst 44 is equal to or higher than the activation temperature upper limit value Tah.

  If it is determined that the exhaust temperature Tpc corresponding to the temperature of the HC selective reduction type NOx catalyst 44 is not within the activation temperature range, the process proceeds to step S24. In step S24, the fuel amount Qfs that is preset and stored so that the temperature of the exhaust gas flowing into the filter 40 becomes a predetermined temperature (for example, 600 ° C.) is added to the fuel to be supplied from the fuel addition valve 52 by the second fuel addition. The amount Qf is set, and the fuel addition amount Qf, that is, HC, is supplied from the fuel addition valve 52 into the exhaust gas. This predetermined temperature is obtained in advance as a temperature at which the particulates deposited on the filter 40 burn most efficiently. Therefore, the fuel amount Qfs corresponds to the amount of HC necessary for the forced regeneration of the filter 40.

When the second fuel is added in this manner, the added HC reaches the oxidation catalyst 36 and burns at the oxidation catalyst 36 at the activation temperature. The exhaust temperature rises due to this combustion, and the particulates accumulated on the filter 40 are incinerated, whereby the filter 40 is forcibly regenerated.
On the other hand, the exhaust temperature Tpc on the outlet side of the HC selective reduction type NOx catalyst 44 detected by the NOx catalyst temperature sensor 50, that is, the temperature of the HC selective reduction type NOx catalyst 44 is the activation temperature lower limit value Tal of the HC selective reduction type NOx catalyst 44. If it is determined in step S22 that the HC selective reduction type NOx catalyst 44 is activated as described above and is not more than the activation temperature upper limit value Tah, the process proceeds to step S26.

In step S26, a predetermined amount Qa is added to the fuel amount Qfs that is preset and stored so that the temperature of the exhaust gas flowing into the filter 40 becomes the predetermined temperature (for example, 600 ° C.), and the fuel addition by the second fuel addition is performed. An amount Qf is set, and a fuel addition amount Qf of fuel, that is, HC, is supplied from the fuel addition valve 52 into the exhaust.
When the second fuel is added in this manner, the added HC reaches the oxidation catalyst 36 and burns at the oxidation catalyst 36 at the activation temperature. The exhaust temperature rises due to this combustion, and the particulates accumulated on the filter 40 are incinerated, whereby the filter 40 is forcibly regenerated. At this time, since the amount of HC supplied by the second fuel addition is increased by a predetermined amount Qa from the amount necessary for forced regeneration of the filter 40, the surplus HC is not selectively burned without burning. The type NOx catalyst 44 is reached.

  By the way, when forced regeneration of the filter 40 is performed, urea water is not supplied from the injection nozzle 54 as described above, and ammonia as a reducing agent is not supplied to the ammonia selective reduction type NOx catalyst 42. NOx purification by the reduced NOx catalyst is not performed. Therefore, the NOx in the exhaust reaches the HC selective reduction type NOx catalyst 44 without being purified by the ammonia selective reduction type NOx catalyst 42.

The NOx in the exhaust gas that has reached the HC selective reduction type NOx catalyst 44 is selectively reduced by the HC selective reduction type NOx catalyst 44 using the HC supplied by the second fuel addition as a reducing agent, and becomes harmless N _2. Released into the atmosphere.
In this manner, the amount of fuel supplied in the second fuel addition is increased by a predetermined amount Qa from the amount necessary for forced regeneration of the filter 40, whereby the HC selective reduction type NOx catalyst 44 purifies NOx in the exhaust gas. Therefore, in step S22, the predetermined amount Qa is determined based on the NOx emission amount from the engine 1 and the NOx release amount from the HC selective reduction type NOx catalyst 44.

  Specifically, the ECU 74 estimates and detects the NOx emission amount from the engine 1 based on the engine operation state such as the engine rotation number detected by the rotation number sensor 76 and the fuel main injection amount calculated by the ECU 74. Then, the ECU 74 sets the amount of HC necessary for purification as the basic amount of the second fuel addition with respect to the NOx emission amount detected from the engine 1 in this way.

  Further, the ECU 74 stores in advance the reference NOx purification rate of the HC selective reduction NOx catalyst 44 at that temperature based on the exhaust temperature downstream of the HC selective reduction NOx catalyst 44 detected by the NOx catalyst temperature 50. Read from the map. Then, from the NOx emission amount from the engine 1 estimated as described above and the NOx emission amount from the HC selective reduction type NOx catalyst 44 detected by the NOx sensor 72, the actual HC selective reduction type NOx catalyst 44 is detected. The NOx purification rate is obtained and compared with the reference NOx purification rate read from the map.

If the actual NOx purification rate does not reach the reference NOx purification rate as a result of the comparison, the basic NOx purification function of the HC selective reduction type NOx catalyst 44 is not sufficiently exhibited because HC is insufficient. Correct the amount by increasing.
On the other hand, when the actual NOx purification rate reaches the reference NOx purification rate, the NOx purification function of the HC selective reduction type NOx catalyst 44 is sufficiently exerted, but there is a possibility that HC is excessively supplied. If there is, the basic amount is corrected to decrease.

  In this way, the predetermined amount Qa is determined based on the NOx emission amount from the engine 1 and the NOx release amount from the HC selective reduction type NOx catalyst 44, whereby the NOx of the HC selective reduction type NOx catalyst 44 is determined. The predetermined amount Qa is determined so that an optimal amount of HC that can sufficiently perform the purification function is supplied. Therefore, the NOx purification function of the HC selective reduction type NOx catalyst 44 can be exhibited as effectively as possible, and HC supplied more than necessary is not discharged into the atmosphere as it is.

As described above, in the present embodiment, the ECU 74 corresponds to the engine NOx emission amount detection means and the HC increase calculation means.
Further, instead of estimating and detecting the NOx emission amount from the engine 1 based on the operating state of the engine 1 as described above, the engine NOx emission amount detecting means is provided in the exhaust pipe 20 upstream of the exhaust aftertreatment device as engine NOx emission amount detecting means. An exhaust NOx sensor may be provided and detected directly by the engine exhaust NOx sensor.

  Thus, by performing the second fuel addition in step S24 or step S26, the particulates deposited on the filter 40 are incinerated, and the amount of particulates deposited on the filter 40 decreases. If it is determined in step S28 that the particulate accumulation amount estimated based on the differential pressure before and after the filter 40 and the exhaust flow rate to the filter 40 is equal to or less than the forced regeneration end determination value, the forced regeneration of the filter 40 is completed. As a result, the process proceeds to step S30.

In step S30, since the forced regeneration of the filter 40 has been completed, the value of the forced regeneration flag F1 is set to 0 to indicate that forced regeneration is not being performed, and the current control cycle ends.
In step S30, when the value of the forced regeneration flag F1 becomes 0, in the urea water supply control, the supply of urea water is resumed as described above, and ammonia as the reducing agent is supplied again to the ammonia selective reduction type NOx catalyst 42. It becomes like this.

When the forced regeneration of the filter 40 is completed, the HC supply to the HC selective reduction type NOx catalyst 44 due to the addition of the second fuel is eliminated, but the NOx in the exhaust gas is restarted by restarting the ammonia supply to the ammonia selective reduction type NOx catalyst 42. Is subsequently purified by the ammonia selective reduction type NOx catalyst 42.
In the control cycle after the forced regeneration of the filter 40 is completed, the value of the forced regeneration flag F1 is 0, so that the process proceeds from step S12 to step S14. Until it is determined that the forced regeneration is necessary, the processes in steps S12 and S14 are repeated.

By performing the urea water supply control and the forced regeneration control as described above, when the filter 40 is not forcibly regenerated, the ammonia selective reduction type NOx catalyst 42 is supplied by the urea water supply by the urea water supply control. By selectively reducing NOx using ammonia as a reducing agent, NOx in the exhaust gas is purified.
Further, when the filter 40 is forcibly regenerated, the supply of urea water is stopped by the urea water supply control, and an increase in NOx concentration in the exhaust due to NOx generation from the urea water is prevented. At this time, if the HC selective reduction-type NOx catalyst 44 is activated, HC increased by a predetermined amount Qa from the HC supply amount necessary for forced regeneration of the filter 40 is supplied to the oxidation catalyst 36, whereby the oxidation catalyst 36. Thus, HC that has reached the HC selective reduction type NOx catalyst 44 without being burned becomes a reducing agent, and the NOx in the exhaust gas is selectively reduced by the HC selective reduction type NOx catalyst 44, and the NOx in the exhaust gas is purified.

Therefore, even during forced regeneration of the filter 40, NOx in the exhaust gas can be purified well.
Although the description of the exhaust emission control device according to one embodiment of the present invention is finished above, the present invention is not limited to the above embodiment.
For example, in the above-described embodiment, the amount of HC supplied for forced regeneration of the filter 40 is increased by a predetermined amount Qa when the second fuel is added from the fuel addition valve 52, whereby the HC to the HC selective reduction type NOx catalyst is increased. However, the method of supplying HC to the HC selective reduction type NOx catalyst is not limited to this, and a fuel supply valve 80 for NOx catalyst may be provided separately from the fuel addition valve 52. Good.

  FIG. 4 is a configuration diagram of the exhaust aftertreatment device 28 and its surroundings in such a modification. In FIG. 4, the same reference numerals as those in the above embodiment are used for the same members as in the above embodiment, and the NOx catalyst fuel supply valve (NOx catalyst HC supply means) 80 is provided in the above embodiment. Only the difference is. Further, the configuration of this modification other than the portion shown in FIG. 4 is the same as that of the above embodiment.

  The NOx catalyst fuel supply valve 80 is disposed between the ammonia selective reduction type NOx catalyst 42 and the HC selective reduction type NOx catalyst 44. Fuel is supplied to the NOx catalyst fuel supply valve 80 from a fuel injection pump (not shown) in the same manner as in the above embodiment, and the ECU 74 controls the opening and closing thereof, so that the exhaust into the downstream casing 34 is discharged. The fuel supply amount is controlled.

In such a modification, the urea water supply control performed by the ECU 74 is the same as that in the above embodiment, and thus the description thereof is omitted.
Further, the forced regeneration control of the filter 40 is performed according to the flowchart shown in FIG. 5, but Steps S22 and S26 are deleted from the flowchart of the forced regeneration control in the embodiment shown in FIG. As soon as it is determined that is activated, in step S24, only the temperature of the filter 40 is increased by adding the second fuel, which is different from the above embodiment. Therefore, the forced regeneration control of FIG. 5 will be described with respect to this difference, and description of the other steps will be omitted.

That is, in the forced regeneration control of this modification, as in the previous embodiment, if it is determined in step 18 that the exhaust temperature Tfc on the outlet side of the oxidation catalyst 36 is 250 degrees or more and the oxidation catalyst 36 is activated, the process proceeds to step S24.
In step S24, as in step 24 of the above embodiment, the fuel amount Qfs set in advance so that the temperature of the exhaust gas flowing into the filter 40 becomes a predetermined temperature (for example, 600 ° C.) The fuel addition amount Qf to be supplied from the addition valve 52 is set, and fuel of the fuel addition amount Qf, that is, HC, is supplied from the fuel addition valve 52 into the exhaust gas.

Then, HC supplied from the fuel addition valve 52 reaches the oxidation catalyst 36 and burns with the oxidation catalyst 36 at the activation temperature. The exhaust temperature rises due to this combustion, and the particulates accumulated on the filter 40 are incinerated, whereby the filter 40 is forcibly regenerated. Therefore, in this modification, the fuel addition valve 52 corresponds to the temperature raising means.
As described above, in the forced regeneration control of this modification, the second fuel addition is performed only for increasing the temperature of the filter 40 without increasing the amount for supplying HC to the HC selective reduction type NOx catalyst.

The supply of HC to the HC selective reduction type NOx catalyst 44 is performed in a predetermined control cycle in accordance with the flowchart shown in FIG.
First, in step S40, it is determined whether or not the value of the forced regeneration control flag F1 is 1. When the value of the forced regeneration flag F1 is 0, the forced regeneration of the filter 40 is not performed, and the urea water is supplied by the urea water supply control. NOx purification is performed. Therefore, NOx purification by the HC selective reduction type NOx catalyst 44 is unnecessary, and the current control cycle is terminated without doing anything.

On the other hand, when the value of the forced regeneration flag F1 is 1, since the forced regeneration of the filter 40 is performed and the supply of urea water is stopped by the urea water supply control, the ammonia selective reduction type NOx catalyst 42 is stopped. This means that NOx purification is not performed.
Therefore, in this case, the process proceeds to step S42, and the exhaust temperature Tpc on the outlet side of the HC selective reduction type NOx catalyst 44 detected by the NOx catalyst temperature sensor 50, that is, the temperature of the HC selective reduction type NOx catalyst 44 is the HC selective reduction type. It is determined whether or not the HC selective reduction NOx catalyst 44 is activated by determining whether or not the activation temperature lower limit value Tal of the NOx catalyst 44 is equal to or greater than the activation temperature upper limit value Tah.

If it is determined that the temperature of the HC selective reduction type NOx catalyst 44 is not within the activation temperature range, the NOx purification by the HC selective reduction type NOx catalyst 44 cannot be performed even if HC is supplied, and thus the current control cycle ends. .
On the other hand, in step S42, the exhaust temperature Tpc on the outlet side of the HC selective reduction type NOx catalyst 44, that is, the temperature of the HC selective reduction type NOx catalyst 44 is equal to or higher than the activation temperature lower limit value Tal of the HC selective reduction type NOx catalyst 44 and If it is not greater than the value Tah and it is determined that the HC selective reduction NOx catalyst 44 is activated, the process proceeds to step S44.

In step S44, an amount of Qa required for NOx purification by the HC selective reduction type NOx catalyst 44, that is, HC, is supplied from the NOx catalyst fuel supply valve 80, and the supplied HC is supplied to the HC selective reduction type NOx catalyst 44. To reach.
On the other hand, when the filter 40 is forcibly regenerated, the NOx in the exhaust gas that has passed through the ammonia selective reduction type NOx catalyst reaches the HC selective reduction type NOx catalyst 44.

The NOx in the exhaust gas that has reached the HC selective reduction type NOx catalyst 44 is selectively reduced by the HC selective reduction type NOx catalyst 44 using the HC supplied from the NOx catalyst fuel supply valve 80 as a reducing agent, and harmless N ₂ . Become discharged into the atmosphere.
At this time, the amount of fuel supplied from the NOx catalyst fuel supply valve 80 is determined in the same manner as the predetermined amount Qa in the above embodiment.

By controlling the supply of HC to the HC selective reduction type NOx catalyst 44 in this way, the NOx in the exhaust gas can be purified well even during the forced regeneration of the filter 40 as in the above embodiment. Is possible.
This is the end of the description of the modification of the embodiment, but the modification of the embodiment is not limited to this.

For example, in the embodiment, the fuel addition valve 52 is used as the HC supply means, and the first and second fuel additions are performed from the fuel addition valve 52, so that the temperature of the oxidation catalyst 36 and the filter 40 is increased. Instead of this, the first and second additional fuel injections may be performed from the injector 4 by post injection different from the main injection.
In this case, in order to activate the oxidation catalyst 36 when the filter 40 is forcibly regenerated, the intake control valve 12 and the exhaust throttle valve 26 are controlled in the closing direction in the same manner as in the above embodiment, and the injectors in the expansion stroke of each cylinder 4 to perform the first additional fuel injection. The injection timing of the first additional fuel is relatively earlier than the end of the expansion stroke. By injecting the additional fuel into the cylinder at such timing, the additional fuel and the high-temperature combustion gas in the cylinder are generated. As a result of mixing, additional fuel is combusted in the exhaust port and the exhaust manifold 18, and high temperature exhaust gas is supplied to the oxidation catalyst 36, whereby the temperature of the oxidation catalyst 36 rises.

  Further, in order to raise the temperature of the filter 40 to a temperature at which particulates can be incinerated, the second additional fuel is injected from the injector 4 in the exhaust stroke. By injecting the second additional fuel into each cylinder at such injection timing, the second additional fuel reaches the oxidation catalyst 36 without being burned in the cylinder or the exhaust manifold 18 and is at the activation temperature. Combustion is performed by the front-stage oxidation catalyst 36. By this combustion, the exhaust temperature rises to an optimum temperature for particulate combustion, and the particulates accumulated on the filter 40 are incinerated, so that the filter 40 is forcibly regenerated.

  When the second additional fuel injection is performed in this manner, the increased amount of HC is reduced to HC by increasing the fuel amount Qfs necessary for forced regeneration of the filter 40 by a predetermined amount Qa, as in the above embodiment. The selective reduction type NOx catalyst 44 is reached. Since this HC is used as a reducing agent, NOx purification by the HC selective reduction type NOx catalyst 44 is performed, so that the same effect as in the above embodiment can be obtained.

In the embodiment, the ammonia selective reduction type NOx catalyst 42 is arranged on the downstream side of the filter 40 in the downstream casing 34, but the filter 40 is arranged on the downstream side of the ammonia selective reduction type NOx catalyst 42. Even if it does in this way, the same effect can be acquired.
Further, although the exhaust aftertreatment device 28 is divided into the upstream casing 30 and the downstream casing, the oxidation catalyst 36, the filter 40, the ammonia selective reduction type NOx catalyst 42, and the HC selective reduction type NOx are provided in a single casing. The catalyst 44 may be accommodated.

In the above embodiment, the injection nozzle 54 for supplying urea water is arranged on the upstream side of the filter 40, but it may be arranged between the filter 40 and the ammonia selective reduction type NOx catalyst 42. As long as it is arranged upstream of the ammonia selective reduction type NOx catalyst 42, any position may be used.
Furthermore, in the above-described embodiment, ammonia is supplied to the ammonia selective reduction type NOx catalyst 42 by supplying urea water from the injection nozzle 54. However, the ammonia itself is reduced to the ammonia selective reduction type by the injection nozzle 54 or other means. The NOx catalyst 42 may be supplied.

In the above embodiment, the exhaust temperature at the outlet side of the HC selective reduction type NOx catalyst 44 is used as the temperature of the HC selective reduction type NOx catalyst 44. However, the exhaust temperature at the inlet side of the HC selective reduction type NOx catalyst 44 is detected. The temperature in the HC selective reduction type NOx catalyst 44 may be detected and used.
Further, in the above embodiment, whether the forced regeneration of the filter 40 is necessary or not is determined based on the accumulated amount of particulates estimated based on the differential pressure before and after the filter 40 and the exhaust flow rate to the filter 40. The method is not limited to this, and may be performed based on the integrated value of the fuel supply amount to the engine 1 after the previous forced regeneration, and various known methods can be employed.

  Finally, in the above embodiment, the present invention is applied to an exhaust emission control device for a diesel engine. However, the engine type is not limited to this, and the oxidation catalyst 36, the filter 40, the ammonia selective reduction type NOx. Any engine provided with the catalyst 42 and the HC selective reduction type NOx catalyst 44 can be applied.

1 is an overall configuration diagram of an exhaust emission control device according to an embodiment of the present invention. It is a flowchart of the urea water supply control performed with the exhaust gas purification device of FIG. It is a flowchart of the forced regeneration control performed with the exhaust gas purification device of FIG. It is a block diagram which shows the exhaust after-treatment apparatus and its periphery in the modification of the exhaust gas purification apparatus of FIG. 5 is a flowchart of forced regeneration control performed by the exhaust gas purification apparatus of FIG. 5 is a flowchart of HC supply control to an HC selective reduction type NOx catalyst performed by the exhaust purification device of FIG. 4.

Explanation of symbols

1 Engine 20 Exhaust pipe (exhaust passage)
36 Oxidation catalyst 40 Particulate filter 42 Ammonia selective reduction type NOx catalyst 44 HC selective reduction type NOx catalyst 52 Fuel addition valve (HC supply means, temperature raising means)
54 Injection nozzle (ammonia supply means)
74 ECU (control means)
80 NOx catalyst fuel supply valve (HC supply means for NOx catalyst)

Claims (4)

An oxidation catalyst disposed in the exhaust passage of the engine;
An HC selective reduction type NOx catalyst that is disposed downstream of the oxidation catalyst and purifies NOx in the exhaust gas using HC as a reducing agent;
A particulate filter disposed between the oxidation catalyst and the HC reducing NOx catalyst and collecting particulates in the exhaust;
An ammonia selective reduction type NOx catalyst that is disposed between the oxidation catalyst and the HC reduction type NOx catalyst and purifies NOx in exhaust gas using ammonia as a reducing agent;
HC supply means for performing forced regeneration by raising the temperature of the particulate filter by supplying HC to the oxidation catalyst;
Ammonia supply means for supplying ammonia to the ammonia selective reduction type NOx catalyst;
When the forced regeneration is performed by supplying HC from the HC supply means, the supply of ammonia from the ammonia supply means is stopped, and it is determined that the HC selective reduction type NOx catalyst is activated. An exhaust emission control device comprising: control means for increasing the amount of HC supplied from the HC supply means by a predetermined amount from that required for forced regeneration of the particulate filter. The control means includes
Engine NOx emission detection means for detecting the amount of NOx discharged from the engine;
The exhaust emission control device according to claim 1, further comprising: an HC increase calculation unit that determines the predetermined amount based on a NOx emission amount from the engine detected by the engine NOx emission amount detection unit. A catalyst NOx emission amount detecting means for detecting the amount of NOx emitted from the HC selective reduction type NOx catalyst;
The HC increase amount calculating means includes the NOx emission amount from the engine detected by the engine NOx emission amount detecting means, and the NOx emission amount from the HC selective reduction type NOx catalyst detected by the catalyst NOx emission amount detecting means. The exhaust gas purification apparatus according to claim 2, wherein a NOx purification rate of the HC selective reduction type NOx catalyst is obtained from the above, and the predetermined amount is corrected according to the NOx purification rate. An oxidation catalyst disposed in the exhaust passage of the engine;
An HC selective reduction type NOx catalyst that is disposed downstream of the oxidation catalyst and purifies NOx in the exhaust gas using HC as a reducing agent;
A particulate filter disposed between the oxidation catalyst and the HC reducing NOx catalyst and collecting particulates in exhaust;
An ammonia selective reduction type NOx catalyst that is disposed between the oxidation catalyst and the HC reduction type NOx catalyst and purifies NOx in the exhaust gas using ammonia as a reducing agent;
A temperature raising means for forcibly regenerating by raising the temperature of the particulate filter;
Ammonia supply means for supplying ammonia to the ammonia selective reduction type NOx catalyst;
HC supply means for NOx catalyst for supplying HC to the HC selective reduction type NOx catalyst;
When the particulate filter is heated by the temperature raising means to perform the forced regeneration, the supply of ammonia from the ammonia supply means is stopped and the HC selective reduction type from the HC supply means for NOx catalyst is stopped. An exhaust purification device comprising: control means for supplying HC to the NOx catalyst.

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