JP4509871B2 - Exhaust purification device - Google Patents

Description

  The present invention relates to an exhaust purification device for purifying engine exhaust, and more particularly to an exhaust purification device including a NOx catalyst that reduces and purifies NOx in exhaust using ammonia as a reducing agent.

A selective reduction type NOx catalyst (SCR catalyst) is disposed in the exhaust passage of the engine 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 exhaust gas purification apparatus is used that purifies NOx in exhaust gas by supplying ammonia to the NOx catalyst as a reducing agent.
In this exhaust purification device, urea water is supplied to the upstream side of the NOx catalyst, and ammonia generated by hydrolysis of the urea water by the heat of the exhaust is supplied to the NOx catalyst. Ammonia supplied to the NOx catalyst is once adsorbed by the NOx catalyst, and NOx purification is performed by promoting the denitration reaction between this ammonia and NOx in the exhaust gas by the NOx catalyst.

At this time, since the urea water is atomized so as to be easily hydrolyzed and supplied into the exhaust gas, the urea water is mixed in the pressurized air in advance by the urea water injection device and is discharged into the exhaust gas from the urea water addition nozzle together with the pressurized air. It comes to be sprayed.
The amount of urea water added varies depending on the amount of NOx to be purified by the NOx catalyst. However, when the amount of urea water added is relatively small, the urea water is taken away by the pressurized air, and urea crystals are precipitated. There is a possibility that clogging may occur in the urea water supply path such as the water injection device, the urea water addition nozzle, or the passage therebetween.

Further, when the engine is stopped after the urea water is supplied from the urea water addition nozzle, the urea water remains in the urea water supply path. Then, the urea water is evaporated and urea crystals are precipitated, which may cause clogging in the urea water supply path.
Patent Document 1 discloses an exhaust emission control device that prevents clogging caused by the soot in the exhaust gas adhering to the urea water addition nozzle, although it is not clogged due to precipitation of urea crystals. Yes.

In the exhaust gas purification apparatus disclosed in Patent Document 1, a pressurized air supply passage and a urea water supply passage are separately formed in the urea water addition nozzle, and together with the pressurized air at the tip of the urea water addition nozzle. Urea water is jetted out. Then, when supplying urea water from the urea water addition nozzle, by supplying pressurized air to the urea water supply passage side of the urea water addition nozzle every predetermined time, the tip of the urea water addition nozzle is supplied. Blows off the adhering soot to prevent clogging.
JP-A-2-223625

The exhaust emission control device disclosed in Patent Document 1 is not intended to prevent clogging caused by precipitation of urea crystals, but only blows off soot by pressurized air. When urea crystals are precipitated, it is difficult to remove them sufficiently.
Further, in the exhaust gas purification device disclosed in Patent Document 1, only the urea water addition nozzle is clogged for the above purpose, and the urea water addition nozzle from the urea water injection device or the urea water injection device on the upstream side thereof is the target. It is impossible to prevent clogging in the passage for supplying urea water to the tank.

Furthermore, in the exhaust gas purification apparatus disclosed in Patent Document 1, pressurized air is always supplied to the urea water supply passage side every predetermined time regardless of whether or not clogging is actually likely to occur. Therefore, the supply of urea water is interrupted more than necessary, and the NOx purification efficiency by the NOx catalyst may be reduced.
The present invention has been made in view of such problems, and an object thereof is to supply urea water without causing clogging to a NOx catalyst that selectively reduces NOx in exhaust gas using ammonia as a reducing agent. An object of the present invention is to provide an exhaust emission control device that can be used.

In order to achieve the above object , an exhaust emission control device according to the present invention is provided in an exhaust passage of an engine and selectively reduces NOx in exhaust using ammonia as a reducing agent, and urea water in the exhaust of the engine. A urea water addition nozzle for supplying ammonia to the NOx catalyst by adding, a urea water injection device for mixing urea water into the pressurized air, and an air supply passage for supplying pressurized air to the urea water injection device; A urea water supply passage for supplying urea water to the urea water injection device, a urea water injection passage for supplying urea water mixed in pressurized air by the urea water injection device to the urea water addition nozzle, and the urea Wash water supply means for supplying wash water to the water injection device, air pressure detection means for detecting the pressure in the air supply passage, injection pressure detection means for detecting the pressure in the urea water injection passage, And a control means for controlling the cleaning water supply means based on the pressure of the pressure and the injection pressure detecting the urea water injection passage detected by means of the said air supply passage detected by the pressure detecting means. The cleaning water supply means supplies the cleaning water to the urea water supply passage by supplying the cleaning water to the urea water supply passage, and supplies the cleaning water to the air supply passage. The operation can be switched to the second mode in which the cleaning water is supplied to the urea water injection device by the control means, and the control means has a predetermined upper limit for the pressure in the air supply passage detected by the air pressure detection means. When the pressure in the urea water injection passage detected by the injection pressure detecting means is equal to or higher than a predetermined upper limit injection pressure, the cleaning water is supplied in the first mode. While controlling the water supply means, the pressure in the air supply passage detected by the air pressure detection means is equal to or higher than a predetermined upper limit air pressure, and before the pressure detected by the injection pressure detection means. When the pressure in the urea water injection passage is equal to or lower than a predetermined lower limit injection pressure, the cleaning water supply means is controlled to supply cleaning water in the second mode (Claim 1). .

According to the exhaust gas purification apparatus configured as described above , the urea water supplied via the urea water supply passage is mixed into the pressurized air supplied via the air supply passage in the urea water injection device, and the urea water It is sent to the urea water addition nozzle through the injection passage. Then, the urea water injected into the exhaust gas together with the pressurized air from the urea water addition nozzle is hydrolyzed by the heat of the exhaust gas to generate ammonia, which is supplied as a reducing agent to the NOx catalyst. On the other hand, the control means controls the wash water supply means based on the pressure in the air supply path detected by the air pressure detection means and the pressure in the urea water injection path detected by the injection pressure detection means, thereby providing an air supply path. The cleaning water is supplied from the cleaning water supply means to the urea water injection device in accordance with the internal pressure and the pressure in the urea water injection passage.
At this time, the pressure in the air supply passage detected by the air pressure detection means is not less than a predetermined upper limit air pressure, and the pressure in the urea water injection passage detected by the injection pressure detection means is not less than a predetermined upper limit injection pressure. In this case, the control means controls the cleaning water supply means so that the cleaning water is supplied from the urea water supply passage to the urea water injection device.
Further, when the pressure in the air supply passage detected by the air pressure detection means is equal to or higher than a predetermined upper limit air pressure, and the pressure in the urea water injection passage detected by the injection pressure detection means is equal to or lower than a predetermined lower limit injection pressure. The control means controls the cleaning water supply means so that the cleaning water is supplied from the air supply passage to the urea water injection device.

More specifically, in such an exhaust purification apparatus, the control means further includes the cleaning water supply means so as to supply the cleaning water to the urea water injection device for a predetermined time after the engine is stopped. Is controlled (claim 2 ).
According to the exhaust emission control device configured as described above, when the engine is stopped, the cleaning water is supplied from the cleaning water supply means to the urea water injection device for a predetermined time.

In addition, these exhaust purification apparatuses are further provided with heating means for heating the washing water supplied to the urea water injection device (Claim 3 ).
According to the exhaust gas purification apparatus configured as described above, the cleaning water heated by the heating means is supplied from the cleaning water supply means to the urea water injection device.

According to the exhaust emission control device of the present invention, the cleaning water is supplied from the cleaning water supply means to the urea water injection device in accordance with both the pressure in the air supply passage and the pressure in the urea water injection passage. The urea water supply path such as the water injection device and the urea water addition nozzle is cleaned with the cleaning water.
Therefore, it is possible to detect clogging in the urea water supply path such as the urea water injection device and the urea water addition nozzle based on both the pressure in the air supply passage and the pressure in the urea water injection passage. It is possible to prevent clogging by washing with washing water when there is a property.

In particular, when the clogging is caused by the precipitation of urea crystals, the urea crystals dissolve well in the washing water, so the urea crystals deposited in the urea water supply path are quickly and reliably removed by the washing water, The occurrence of clogging can be efficiently prevented.
Furthermore, based on both the pressure in the air supply passage and the pressure in the urea water injection passage, cleaning with washing water is performed only when there is a possibility of clogging, thereby preventing clogging more than necessary. The cleaning water is not supplied for this purpose, and the cleaning water is not wasted.
Further, when the pressure in the air supply passage is equal to or higher than the predetermined upper limit air pressure and the pressure in the urea water injection passage is equal to or higher than the predetermined upper limit injection pressure, the wash water is supplied from the urea water supply passage to the urea water injection device. Is supplied.
When the pressure in the air supply passage is equal to or higher than the predetermined upper limit air pressure and the pressure in the urea water injection passage is equal to or higher than the predetermined upper limit injection pressure, clogging may be occurring on the urea water addition nozzle side. In such a case, it is necessary to more aggressively clean the urea water addition nozzle than to clean the urea water injection device. The urea water injection device is originally configured so that urea water is positively mixed into the pressurized air. By supplying the cleaning water from the urea water supply passage, a sufficient amount of the cleaning water can be efficiently obtained. It is supplied to the urea water addition nozzle together with the pressurized air. As a result, the urea crystals deposited on the urea water addition nozzle are dissolved by the washing water, and clogging is prevented.
Further, when the pressure in the air supply passage detected by the air pressure detection means is equal to or higher than a predetermined upper limit air pressure, and the pressure in the urea water injection passage detected by the injection pressure detection means is equal to or lower than a predetermined lower limit injection pressure. The cleaning water is supplied from the air supply passage to the urea water injection device.
When the pressure in the air supply passage is equal to or higher than the predetermined upper limit air pressure and the pressure in the urea water injection passage detected by the injection pressure detecting means is equal to or lower than the predetermined lower limit injection pressure, the urea water addition nozzle The possibility of clogging is low, and there is a high possibility that clogging is occurring on the urea water injector side.
Clogging in the urea water injection device is often caused by urea crystals precipitated in the mixed portion of pressurized air and urea water, but the cleaning water is supplied from the air supply passage located upstream of the urea crystals. By doing so, it is possible to reliably remove the urea crystals deposited in such a place.

Further, according to the exhaust purification device of the second aspect , when the engine is stopped, the cleaning water is supplied from the cleaning water supply means to the urea water injection device for a predetermined time. The urea water remaining in the urea water supply path such as the addition nozzle or the passage between them is removed by the cleaning water, and clogging due to the deposition of urea crystals precipitated from the residual urea can be prevented.

According to the exhaust purification device of claim 3 , since the cleaning water heated by the heating means is supplied to the urea water injection device, the urea crystals are more easily dissolved in the cleaning water, and the deposited urea crystals are It can be quickly removed to reliably prevent clogging.

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 supplies light oil, which is high-pressure fuel stored in the common rail 2, to an injector 4 provided in each cylinder. From this, light oil is injected into each cylinder.

  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 accommodates a NOx catalyst 30 that adsorbs ammonia and selectively reduces NOx in the exhaust gas using the adsorbed ammonia as a reducing agent. The NOx catalyst 30 is provided downstream of the NOx catalyst 30. An oxidation catalyst 32 for oxidizing the outflowing ammonia to N ₂ is accommodated.
An inlet temperature sensor 34 for detecting the inlet side exhaust temperature of the NOx catalyst 30 is provided on the inlet side of the NOx catalyst 30, and an outlet temperature for detecting the outlet side exhaust temperature of the NOx catalyst 30 is provided on the outlet side of the NOx catalyst 30. A sensor 36 is provided.

A urea water addition nozzle 38 that injects urea water into the exhaust gas in the exhaust pipe 20 is provided upstream of the exhaust aftertreatment device 28 in the exhaust pipe 20. The urea water addition nozzle 38 is a urea water injection nozzle. A urea water injection device 42 is connected through a pipe (urea water injection passage) 40.
The air tank 44 stores pressurized air compressed by an air pump (not shown), and the pressurized air in the air tank 44 is supplied to the urea water injection device 42 via an air supply pipe (air supply passage) 46. Is done. The air supply pipe 46 is provided with an air control valve 48 that is an electromagnetic valve for controlling the supply of pressurized air to the urea water injection device 42.

The urea water tank 50 stores urea water, and the urea water in the urea water tank 50 is supplied to the urea water injection device 42 via a urea water supply pipe (urea water supply passage) 52. The urea water supply pipe 52 is provided with a urea water control valve 54 that is an electromagnetic three-way valve.
The urea water control valve 54 is connected to a urea water supply pipe 52 on the urea water injector 42 side and a urea water supply pipe 52 on the urea water tank 50 side, as well as a passage communicating with a wash water tank 56 for storing wash water. A position where the urea water supply from the urea water tank 50 to the urea water injection device 42 is allowed and the supply of the cleaning water from the cleaning water tank 56 to the urea water injection device 42 is cut off (hereinafter referred to as a urea water supply position). And a position that blocks the supply of urea water from the urea water tank 50 to the urea water injection device 42 and permits the supply of cleaning water from the cleaning water tank 56 to the urea water injection device 42 (hereinafter referred to as a cleaning water supply position). And a position where both the supply of urea water from the urea water tank 50 to the urea water injection device 42 and the supply of cleaning water from the wash water tank 56 to the urea water injection device 42 are cut off (hereinafter referred to as a cutoff position). One of has become can be switched to the state.

  The washing water tank 56 is connected to the air supply pipe 46 via the washing water supply pipe 58, and the passage branched from the middle of the washing water supply pipe 58 is connected to the urea water control valve 54 as described above. . Further, a cleaning water control valve which is an electromagnetic valve for allowing or blocking the supply of the cleaning water from the cleaning water tank 56 to the air supply pipe 46 is provided in the cleaning water supply pipe 58 on the air supply pipe 46 side from this branch portion. 60 is provided.

By opening the cleaning water control valve 60, the cleaning water in the cleaning water tank 56 is supplied to the urea water injection device 42 via the air supply pipe 46.
Therefore, the urea water control valve 54 and the cleaning water control valve 60 are controlled to supply the cleaning water to the urea water injection device 42. This corresponds to the washing water supply means of the invention.

The urea water injection device 42 mixes the urea water supplied from the urea water tank 50 into the pressurized air supplied from the air tank 44 as described above, and supplies the urea water to the urea water addition nozzle 38 together with the pressurized air. FIG. 2 shows a simplified schematic structure.
As shown in FIG. 2, the urea water injection device 42 is formed with a main passage 42 a penetrating through the inside, and one end of the main passage 42 a is connected to the air supply pipe 46, and the other end is connected to the urea water injection pipe 40. It is connected.

A throttle 42b having a cross-sectional area smaller than that of the main passage 42a is formed at an intermediate portion of the main passage 42a. One end of the main passage 42a downstream of the throttle 42b is connected to a urea water supply pipe 52. The other end of the water passage 42c is open.
In the urea water injection device 42 configured as described above, pressurized air is supplied into the main passage 42a via the air supply pipe 46, and the pressurized air whose flow velocity is increased by the throttle 42b is the opening portion of the urea water passage 42c. Pass through. At this time, the urea water supplied into the urea water passage 42c through the urea water supply pipe 52 is sucked into the pressurized air, becomes mist, and flows out to the urea water injection pipe 40 together with the pressurized air, It is supplied from the urea water injection pipe 40 to the urea water addition nozzle 38.

The atomized urea water supplied to the urea water addition nozzle 38 is injected into the exhaust gas in the exhaust pipe 20 together with the pressurized air, and is hydrolyzed by the heat of the exhaust gas to become ammonia. The ammonia thus generated is supplied to the NOx catalyst 30 and once adsorbed on the NOx catalyst 30. The denitration reaction with NOx in the exhaust and the adsorbed ammonia in the NOx catalyst 30 is promoted by the NOx catalyst 30, exhaust gas is purified by the NOx is converted to harmless N _2.

At this time, ammonia that has not reacted with NOx and has flowed out of the NOx catalyst 30 is oxidized by the downstream oxidation catalyst 32 to become N ₂ or NOx. The NOx produced here reacts with the ammonia flowing into the oxidation catalyst 32 to become N ₂ , so that the ammonia flowing into the oxidation catalyst 32 becomes harmless N ₂ and is released into the atmosphere. .
The air supply pipe 46 is provided with an air pressure sensor (air pressure detecting means) 62 for detecting the pressure in the air supply pipe 46, and the urea water injection pipe 40 detects the pressure in the urea water injection pipe 40. An injection pressure sensor (injection pressure detecting means) 64 is provided.

The ECU (control means) 66 is a control device for performing comprehensive control including the operation control of the engine 1, and includes a CPU, a memory, a timer counter, and the like, and performs various control amount calculations. Various devices are controlled based on the control amount.
On the input side of the ECU 66, in order to collect information necessary for various controls, in addition to the intake flow rate sensor 16, the inlet temperature sensor 34, the outlet temperature sensor 36, the air pressure sensor 62, and the injection pressure sensor 64, the engine speed is set. A start / stop switch 72 for starting and stopping the engine 1 is connected to the output side in addition to various sensors such as a rotation speed sensor 68 to detect and an accelerator opening sensor 70 to detect the depression amount of the accelerator pedal. Is the injector 4, the intake control valve 12, the EGR valve 22, the exhaust throttle valve 26, the air control valve 48, the urea water control valve 50, the wash water control valve 60, etc. of each cylinder to be controlled based on the calculated control amount Various devices are connected.

  The ECU 66 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 rotational speed detected by the rotational speed sensor 68 and the accelerator opening detected by the accelerator opening sensor 70. 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 66 performs urea water necessary for selectively reducing NOx discharged from the engine 1 by the NOx catalyst 30 based on the engine operating state such as the engine speed and the main injection amount of fuel detected by the speed sensor 68. The supply amount is obtained from map data stored in advance, and the urea water control valve 54 is controlled.
At this time, the urea water control valve 54 switches the urea water supply position and the shut-off position alternately by the ECU 66 based on the urea water supply amount read from the map data, so that the urea water supply amount to the urea water injection device 42 is changed. Is adjusted.

On the other hand, the air control valve 48 is opened when the operation of the engine 1 is started, and the pressurized air in the air tank 44 is supplied to the urea water injection device 42 via the air supply pipe 46.
The urea water whose supply amount is adjusted by the urea water control valve 54 is mixed with the pressurized air supplied by opening the air control valve 64 and the urea water injection device 42 to be atomized, and converted into urea water together with the pressurized air. It is injected from the nozzle 38 into the exhaust gas in the exhaust pipe 20. The urea water thus injected is hydrolyzed by the heat of the exhaust to become ammonia, and the NOx in the exhaust is selectively reduced by the NOx catalyst 30 as described above using this ammonia as a reducing agent.

In the exhaust gas purification apparatus configured as described above, when the amount of supplied urea water is relatively small, the urea crystals are precipitated by removing the water of the urea water, and the urea injection device 42 and the urea addition nozzle 38 are thus removed. There is a possibility that clogging may occur in the urea water supply path.
Therefore, in the present embodiment, the urea water supply control for supplying the urea water is performed while detecting the possibility of such clogging, and the details thereof will be described below.

The urea water supply control is performed at a predetermined control period according to the flowcharts of FIGS. 3 and 4 when the engine 1 is started.
First, based on the position of the start / stop switch 72 and the engine speed detected by the speed sensor 68 in step S2, it is determined whether or not the engine 1 is in operation. This flowchart is started when the engine 1 is started. Immediately after the start, it is determined that the engine 1 is in operation, and the process proceeds to step S4.

In step S4, the value of the driving flag F1 is set to 1. This in-operation flag F1 indicates that the value of 1 indicates that the engine 1 is in operation or that the engine 1 has just stopped, and the value is 0 if the above state is not met. It has become.
Next, when proceeding to step S6, the air control valve 48 is opened, the supply of the pressurized air stored in the air tank 44 to the urea water injector 42 is started, and the routine proceeds to step S8.

In step S8, it is determined whether or not the pressure Pa in the air supply pipe 46 detected by the air pressure sensor 62 is equal to or higher than a preset upper limit pressure (upper limit air pressure) P1.
When substances such as urea crystals that cause clogging accumulate in urea water supply paths such as the urea water injection device 42 and the urea water addition nozzle 38, the pressurized air is not easily discharged from the urea water addition nozzle 38. Therefore, the pressure in the air supply pipe 46 gradually increases with the deposition of substances such as urea crystals. Therefore, the pressure in the air supply pipe 46 when the accumulation of substances such as urea crystals progresses and clogging may occur is obtained in advance through experiments or the like, and this pressure is set as the upper limit pressure P1.

Accordingly, when it is determined in step S8 that the pressure Pa in the air supply pipe 46 is equal to or higher than the upper limit pressure P1, the urea water supply path such as the urea water injection device 42 or the urea water addition nozzle 38 is clogged. If it is determined that the pressure Pa is less than the upper limit pressure P1, it is determined that there is no possibility of clogging.
In this manner, when it is determined that the pressure Pa in the air supply pipe 46 is less than the upper limit pressure P1 and there is no possibility of clogging, the process proceeds to step S10, where urea water is supplied. It is determined whether or not it is possible.

  That is, for example, when the NOx catalyst 30 has not reached the activation temperature immediately after the engine 1 is started, or when the exhaust temperature has not reached a temperature enabling hydrolysis of the urea water, the urea water is being exhausted. However, NOx cannot be purified by the NOx catalyst 30. Therefore, in step S10, based on the engine operating state such as the exhaust temperature at the inlet side of the NOx catalyst 30 detected by the inlet temperature sensor 34, it is determined whether or not the urea water can be supplied.

If it is determined in step S10 that the urea water cannot be supplied, the current control cycle is terminated, and the process is performed again from step S2 in the next control cycle. In the following, the urea water can be supplied. The description will be given assuming that there is something.
If it is determined in step S10 that urea water can be supplied based on the engine operating state, the process proceeds to step S12, and since there is no possibility of clogging at the present time as described above, the cleaning water control valve 60 is closed. To do. The initial state of the cleaning water control valve 60 is the valve closing position. By instructing the valve closing in step S12, the cleaning water control valve 60 is maintained in the closed state.

  Next, in step S14, the supply amount of urea water necessary for purifying NOx in the exhaust gas by the NOx catalyst 30 is obtained, and the urea water control valve 54 is moved from the shut-off position for a time corresponding to the determined supply amount. Switch to the urea water supply position. By doing so, the amount of urea water required to purify NOx in the exhaust gas by the NOx catalyst 30 is injected into the exhaust gas from the urea water addition nozzle 38, and the urea water is hydrolyzed by the heat of the exhaust gas. The generated ammonia is supplied to the NOx catalyst 30 as a reducing agent.

The supply amount of urea water necessary for purifying NOx in the exhaust with the NOx catalyst 30 is determined as follows.
First, the NOx emission amount from the engine 1 is estimated based on the engine operation state such as the engine rotation number detected by the rotation number sensor 68 and the fuel main injection amount calculated by the ECU 66. Further, the NOx purification rate of the NOx catalyst 30 is obtained from the map data stored in advance based on the exhaust temperature at the inlet side of the NOx catalyst 30 detected by the inlet temperature sensor 34. Next, the NOx purification amount by the NOx catalyst 30 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.

After supplying urea water in step S14 in this way, the current control cycle is terminated, and the process is started again from step S2 in the next control cycle.
Therefore, as long as it is determined that there is no possibility of clogging, an appropriate amount of urea water is injected into the exhaust gas from the urea water addition nozzle 38, and the urea water injected from the urea water addition nozzle 38 is caused by the heat of the exhaust gas. Hydrolysis produces ammonia. Using this ammonia as a reducing agent, the NOx in the exhaust is selectively reduced by the NOx catalyst 30 to become harmless N ₂ and discharged into the atmosphere.

On the other hand, if the deposition of substances such as urea crystals progresses and the pressure Pa in the air supply pipe 46 rises, and the pressure Pa in the air supply pipe 46 detected by the air pressure sensor 62 is equal to or higher than the upper limit pressure P1, in step S8. If it is determined, the process proceeds to step S16 because clogging may occur.
In step S16, it is determined whether or not the pressure Pu in the urea water injection pipe 40 detected by the injection pressure sensor 64 is equal to or higher than a preset upper limit pressure (upper limit injection pressure) P2.

  The pressure change in the urea water injection pipe 40 varies depending on the position where substances such as urea crystals that cause clogging are deposited. That is, when a substance such as urea crystals is accumulated at the urea water addition nozzle 38, the pressurized air is less likely to be discharged from the urea water addition nozzle 38 as the deposition progresses. The pressure increases gradually. On the other hand, when substances such as urea crystals are deposited on the urea water injection device 42, it is difficult to supply pressurized air from the urea water injection device 42 to the urea water injection pipe 40 as the deposition proceeds. The pressure in the water jet pipe 40 gradually decreases.

  Therefore, the pressure in the urea water injection pipe 40 when the accumulation of substances such as urea crystals progresses in the urea water addition nozzle 38 and the possibility of clogging increases is obtained in advance through experiments or the like. In step S16, this pressure is determined. Is set as the upper limit pressure P2. It should be noted that, when the pressure Pa in the air supply pipe 46 becomes equal to or higher than the upper limit pressure P1 in step S8, the clogging occurs when the pressure Pu in the urea water injection pipe 40 becomes equal to or higher than the upper limit pressure P2. The value of the upper limit pressure P2 is set so as to increase the possibility of occurrence.

Therefore, when it is determined in step S16 that the pressure Pu in the urea water injection pipe 40 is equal to or higher than the upper limit pressure P2, it is determined that the urea water addition nozzle 38 is likely to be clogged. Become.
In such a case, first, the process proceeds to step S18 to close the washing water control valve 60. However, since the washing water control valve 60 has been in the closed position before proceeding to step S18, the washing is performed here. The water control valve 60 maintains the valve closing position. Then, the process proceeds to the next step S20, the urea water control valve 54 is set to the washing water supply position, and the current control cycle is ended.

Thus, the urea water control valve 58 is set to the closed position and the urea water control valve 54 is set to the cleaning water supply position, so that the urea water supply device 42 has been supplied with urea from the urea water tank 50 until then. Instead of water, cleaning water is supplied from the cleaning water tank 56 via the urea water supply pipe 52 (first mode).
The wash water supplied through the urea water supply pipe 52 is introduced into the urea water passage 42c shown in FIG. On the other hand, the pressurized air supplied through the air supply pipe 46 flows in the main passage 42a, and the flow rate is increased by the throttle 42b, so that the wash water in the urea water passage 42c is sucked into the main passage 42a. As a result, it becomes mist and is supplied from the urea water injection pipe 40 to the urea water addition nozzle 38 together with the pressurized air. At this time, since the cleaning water control valve 60 is in the closed state, the cleaning water indicated by the broken arrow in FIG. 2 is not supplied from the cleaning water supply pipe 58.

The restrictor 42b and the urea water passage 42c positioned on the downstream side thereof are configured in this way so that the urea water is originally sucked into the pressurized air. By supplying cleaning water from the water passage 42c, a sufficient amount of cleaning water can be efficiently supplied to the urea water addition nozzle 38.
The cleaning water supplied to the urea water addition nozzle 38 in this manner flows in the urea water addition nozzle 38 and is injected into the exhaust gas in the exhaust pipe 20, so that urea crystals or the like precipitated in the urea water addition nozzle 38 are collected. The substance is removed together with the cleaning water by dissolving it in the cleaning water, and clogging is prevented.

  When the supply of the washing water to the urea water addition nozzle 38 in steps S16 to S20 is repeated in each control cycle, and substances that cause clogging such as urea crystals deposited in the urea water addition nozzle 38 are removed, While the pressure in the urea water injection pipe 40 decreases, the pressure in the air supply pipe 40 also decreases. If it is determined in step S8 that the pressure Pa in the air supply pipe 46 detected by the air pressure sensor 62 has fallen below the upper limit pressure P1, it is determined that there is no possibility of clogging and the process proceeds to steps S10 to S14.

In steps S10 to S14, the urea water control valve 54 is switched to the urea water supply position as described above, and the urea water is again supplied to the urea water injection device 42. Then, the mist-like urea water mixed in the pressurized air by the urea water injection device 42 is injected from the urea water addition nozzle 38 into the exhaust gas in the exhaust pipe 20.
As described above, when the pressure Pa in the air supply pipe 46 is equal to or higher than the predetermined upper limit pressure P1 and the pressure Pu in the urea water injection pipe 40 is equal to or higher than the predetermined upper limit pressure P2, the urea water supply pipe 52 is used. By supplying cleaning water to the urea water injection device 42, a sufficient amount of cleaning water is efficiently supplied to the urea water addition nozzle 38 that may cause clogging, and the urea water addition nozzle 38 is cleaned. Clogging is reliably prevented.

  On the other hand, when it is determined in step S8 that the pressure Pa in the air supply pipe 46 is equal to or higher than the upper limit pressure P1, and in step S16, it is determined that the pressure Pu in the urea water injection pipe 40 is lower than the upper limit pressure P2. Indicates that the pressure in the air supply pipe 46 increases and clogging may occur, but the pressure in the urea water injection pipe 40 does not increase to the extent that clogging may occur. It will be. That is, although it is unlikely that clogging will occur in the urea water addition nozzle 38, it is determined that clogging may occur on the urea water injection device 42 side.

Therefore, in such a case, the process proceeds to step S22, and whether or not the pressure Pu in the urea water injection pipe 40 detected by the injection pressure sensor 64 is equal to or lower than a preset lower limit pressure (lower limit injection pressure) P3. Determine.
When substances such as urea crystals that cause clogging accumulate in the urea water injection device 42, it becomes difficult for pressurized air to be supplied to the urea water injection pipe 40, and therefore deposition of substances such as urea crystals proceeds. As a result, the pressure in the urea water injection pipe 40 gradually decreases.

  Therefore, the pressure in the urea water injection pipe 40 when the accumulation of substances such as urea crystals progresses in the urea water injection device 42 and the possibility of clogging is increased is obtained in advance by experiments or the like. In step S22, this pressure is determined. Is set as the lower limit pressure P3. In addition, it is more clogged when the pressure Pu in the urea water injection pipe 40 becomes lower than the lower limit pressure P3 as compared with the case where the pressure Pa in the air supply pipe 46 becomes higher than the upper limit pressure P1 in step S8. The value of the lower limit pressure P3 is set so as to increase the possibility of occurrence.

  Therefore, when it is determined in step S22 that the pressure Pu in the urea water injection pipe 40 is equal to or lower than the lower limit pressure P3, it is determined that there is a high possibility that the urea water injection device 42 is clogged. In such a case, the process proceeds to step S24, and after the urea water control valve 54 is set to the shut-off position, the washing water control valve 60 is opened in the next step S26 and the current control cycle is completed.

Thus, by setting the urea water control valve 54 to the shut-off position and opening the wash water control valve 60, neither urea water nor wash water is supplied from the urea water supply pipe 52, and the wash water tank 56 washing water is supplied to the urea water injection device 42 through the air supply pipe 46 together with the pressurized air (second mode).
That is, when the cleaning water control valve 60 is opened, the cleaning water flows into the air supply pipe 46 from the cleaning water supply pipe 58 and flows through the air supply pipe 46 as shown by the broken arrow in FIG. Mixed into the pressurized air. The washing water mixed in the pressurized air flows through the main passage 42a in the urea water injection device 42 together with the pressurized air, and reaches the urea injection pipe 40 through the throttle 42b. At this time, urea water or washing water indicated by a solid arrow in FIG. 2 is not supplied to the urea passage 42c because the urea water control valve 54 is in the blocking position.

When urea water is supplied to the urea injection device 42 by the processing of steps S10 to S14, part of the urea water sucked into the main passage 42a from the urea water passage 42c adheres to the vicinity of the outlet of the throttle 42b, Urea crystals are likely to precipitate due to the removal of moisture.
Therefore, when it is determined that there is a high possibility that the urea water injection device 42 is clogged, the cleaning water is supplied from the air supply pipe 46 in this way, so that the urea crystals deposited on the throttle 42b and the like are collected. Since it is dissolved and removed in the washing water, the occurrence of clogging in the urea water injection device 42 can be reliably prevented.

Since the cleaning water discharged from the urea water injection device 42 is supplied to the urea water addition nozzle 38 via the urea water injection pipe 40, substances such as urea crystals accumulated in the urea water addition nozzle 38 are used. Are also removed by this washing water.
In this way, the supply of the washing water to the urea water injection device 42 in steps S22 to S26 is repeated in each control cycle, and the substances that cause clogging such as urea crystals deposited in the urea water injection device 42 are removed. As the pressure in the air supply pipe 40 decreases, the pressure in the urea water injection pipe 40 increases. If it is determined in step S8 that the pressure Pa in the air supply pipe 46 detected by the air pressure sensor 62 has fallen below the upper limit pressure P1, it is determined that there is no possibility of clogging and the process proceeds to steps S10 to S14.

In steps S10 to S14, the urea water control valve 54 is switched to the urea water supply position as described above, and the urea water is again supplied to the urea water injection device 42. Then, the mist-like urea water mixed in the pressurized air by the urea water injection device 42 is injected from the urea water addition nozzle 38 into the exhaust gas in the exhaust pipe 20.
As described above, when the pressure Pa in the air supply pipe 46 is equal to or higher than the predetermined upper limit pressure P1 and the pressure Pu in the urea water injection pipe 40 is equal to or lower than the predetermined lower limit pressure P3, the air supply pipe 46 By supplying the cleaning water to the urea water injection device 42, the cleaning water is supplied to the urea water injection device 42 where clogging may occur, and the urea water injection from the upstream side of the throttle 42b where clogging is likely to occur. The device 42 is washed to prevent clogging reliably.

  If the pressure Pu in the urea water injection pipe 40 is determined to be greater than the lower limit pressure P3 in step S22 from step S8 to step S16, the pressure in the air supply pipe 46 is Although it indicates that clogging may occur, the pressure in the urea water injection pipe 40 is not increased or decreased to the extent that clogging may occur, and the pressurized air and urea water are within the proper ranges. It is judged that it is still supplied. Therefore, in such a case, the process proceeds to step S10, and urea water is continuously supplied from the urea water addition nozzle 38 into the exhaust pipe 20 through steps S10 to S14.

Next, control when the engine 1 is stopped when urea water is being supplied from the urea water addition nozzle 38 into the exhaust gas in the exhaust pipe 20 in steps S10 to S14 will be described. Note that the ECU 66 continues to operate for at least the time necessary for the urea water supply control according to the flowcharts of FIGS. 3 and 4 even after the engine 1 is stopped.
When the engine 1 is in an operating state, the start / stop switch is set to the stop position, and when the engine 1 is stopped, it is determined in step S2 of FIG. Processing proceeds.

In step S28, it is determined whether or not the value of the driving flag F1 is 1. Since the value of the operating flag F1 has been set to 1 in step S4 until the previous control cycle, the process proceeds to step S30.
In step S30, it is determined whether or not the value of the timer T1 flag F2 is 1. The timer T1 flag F2 indicates whether or not the timer T1 that counts the time elapsed since the engine 1 is stopped is currently counting. If the value is 1, the timer T1 is counting. Yes, 0 indicates reset and stopped.

Since the value of the timer T1 is 0 in the initial state and during the operation of the engine 1, the process proceeds from step S30 to step S32, and the timer T1 starts counting.
In the next step S34, since the timer T1 is counting, the value of the timer T1 flag F2 is set to 1, and the process proceeds to step S36.
In step S36, it is determined whether or not the time counted by the timer T1, that is, the time t1 that has elapsed since the engine 1 was stopped, is equal to or greater than a preset reference time ta. If the time t1 that has elapsed since the engine 1 has stopped has not reached the reference time ta, the process proceeds to step S38.

  In step S38, the urea water control valve 54 is set to the shut-off position, and in the next step S40, the washing water control valve 60 is opened to end the current control cycle. By controlling the urea water control valve 54 and the washing water control valve 60 in this manner, the supply of urea water to the urea water injection device that has been performed is stopped, and the washing water in the washing water tank 56 is discharged. The water is supplied from the cleaning water supply pipe 58 to the urea water injection device 42 via the air supply pipe 46. At this time, the air control valve 48 remains open by the control up to the previous control cycle, and therefore is continuously supplied to the urea water injection device 42 via the air supply pipe 46.

  That is, the cleaning water supplied from the cleaning water tank 56 to the cleaning water supply pipe 58 by the opening of the cleaning water control valve 60 is supplied from the cleaning water supply pipe 58 as indicated by a broken line arrow in FIG. The urea is injected into the urea water injector 42 together with the pressurized air that flows into the pipe 46 and flows through the air supply pipe 46. On the other hand, the urea water (indicated by a solid arrow in FIG. 2) supplied to the urea water passage 42c via the urea water supply pipe 52 is not supplied when the urea water control valve 54 is set to the shut-off position. . The cleaning water supplied to the urea water injection device 42 flows through the urea water injection device 42, and then supplied to the urea water addition nozzle 38 via the urea water injection tube 40, and is discharged from the urea water addition nozzle 38 to the exhaust pipe 20. Discharged inside.

  In this way, the supply of urea water to the urea water injection device 42 is stopped along with the stop of the engine 1 and the cleaning water is supplied, whereby the urea water injection pipe 40 and the urea water injection pipe 40 in the urea water injection device 42 and downstream thereof are provided. The urea water remaining in the urea water addition nozzle 38 is washed away by the washing water and removed. Therefore, occurrence of clogging due to precipitation of urea crystals from the remaining urea water is reliably prevented.

Even after the next control cycle, since the engine 1 is in a stopped state and the value of the operating flag F1 is 1, the process proceeds from step S2 to step S30 through step S28.
Since the value of the timer T1 flag F2 has already been set to 1 in step S34 of the previous control cycle and the count of the timer T1 has already started, the current process proceeds directly from step 30 to step S36.

In step S36, it is determined again whether or not the time counted by the timer T1, that is, the time t1 that has elapsed since the engine 1 was stopped, is equal to or greater than the reference time ta.
Therefore, as long as the time t1 that has elapsed since the engine 1 has stopped has not reached the reference time ta, the cleaning water is supplied to the urea water injection device 42 as described above in steps S38 and S40. The urea water remaining in the urea water injection device 42 or in the urea water injection pipe 40 and the urea water addition nozzle 38 downstream thereof is washed away by the cleaning water and removed.

Thus, the control is repeated, and when the time counted by the timer T1, that is, the time t1 that has elapsed since the engine 1 was stopped, is equal to or greater than the preset reference time ta, the process proceeds from step S36 to step S42. Become.
In step S42, it is determined whether or not the value of the timer T2 flag F3 is 1. The timer T2 flag F3 indicates whether or not the timer T2 is currently counting. If the value is 1, the timer T2 is counting, and if it is 0, the timer T2 is reset and stopped. Indicates. The timer T2 counts an elapsed time after the count time t1 by the timer T1 reaches the reference time ta.

Since the value of the timer T2 is 0 in the initial state and during operation of the engine 1, the process proceeds from step S42 to step S44, and the timer T2 starts counting.
In the next step S46, since the timer T2 is counting, the value of the timer T2 flag F3 is set to 1, and the process proceeds to step S48.
In step S48, it is determined whether or not the time t2 counted by the timer T2 is equal to or greater than a preset reference time tb. If the count time t2 by the timer T2 has not reached the reference time tb, the process proceeds to step S50.

  In step S50, the urea water control valve 54 is continuously set to the shut-off position, and in the next step S52, the washing water control valve 60 is closed to end the current control cycle. By controlling the urea water control valve 54 and the washing water control valve 60 in this manner, the supply of the washing water to the urea water injection device that has been performed by opening the washing water control valve 60 in step S40 is stopped. . On the other hand, since the air control valve 48 remains open, only the pressurized air is supplied to the urea water injector 42 via the air supply pipe 46.

Therefore, when the engine 1 is stopped, the supply of the urea water to the urea water injection device 42 is stopped, and the cleaning water is supplied to the urea water injection device 42 for a predetermined time ta, so that the urea water injection device 42 is supplied. The urea water remaining inside and downstream of the urea water injection pipe 40 and the urea water addition nozzle 38 is washed away by the cleaning water and removed.
Thereafter, the supply of the washing water to the urea water injection device 42 is also stopped, and only the supply of pressurized air is continued.

In the next control cycle, the timer T1 continues counting, and the count time t1 of the timer T1 has already exceeded the reference time ta, so that the process proceeds from step S36 to step S42 through step S28 and step S30.
Since the timer T2 has already started counting in the previous control cycle and becomes 1 of the timer T2 flag F3, it is determined in step S42 that the value of the timer T2 flag F3 is 1, and the process directly proceeds to step S48. .

  In step S48, it is determined whether or not the time t2 counted by the timer T2 is equal to or longer than the reference time tb. Therefore, the time that has elapsed since the count time of the timer T1 has reached the reference time ta, that is, the time that has elapsed after supplying the wash water to the urea water injector 42 for the time ta after the engine is stopped reaches the reference time tb. In the meantime, the processes of step S50 and step S52 are repeated every control cycle. During this time, the urea water control valve 54 is maintained at the shut-off position and the wash water control valve 60 is also maintained at the closed position as described above, so that only the pressurized water is supplied to the urea water injector 42. Will be.

By supplying pressurized air to the urea water injection device 42 in this way, the cleaning water remaining inside the urea water injection device 42, the urea water injection pipe 40, the urea water addition nozzle 38, and the like is compressed air. At the same time, it is discharged from the urea water addition nozzle 38 into the exhaust pipe 20.
If it is determined in step S48 that the time t2 counted by the timer T2 has reached the reference time tb, the process proceeds from step S48 to step S54. In step S54, the air control valve 48 is closed.

  Thereby, the supply of the pressurized air to the urea water injection device 42 is also stopped, and each device for supplying the urea water is in a standby state until the engine 1 is started next. Accordingly, since it is not necessary to perform the process until the next time the engine 1 is started in the urea water supply control, all the flags F1 to F3 are reset in step S56 to set the values to 0 of the initial state. In step S58, the timers T1 and T2 are reset to a standby state, and the control cycle ends.

At this time, if there is no other calculation to be processed, the ECU 66 is in a rest state until the engine 1 is started next time.
Thus, after the engine 1 is stopped, the cleaning water is supplied to the urea water injection device 42 for a predetermined time ta so that the remaining urea water is washed and discharged, and thereafter, the pressurization is performed for the predetermined time tb. By supplying only air to the urea water injection device 42, the remaining cleaning water is discharged. For this reason, the urea water supply path such as the urea water injection device 42, the urea water injection pipe 40, or the urea water addition nozzle 38 is maintained in a clean state after the engine is stopped, and clogging caused by the residue is generated. It can be surely prevented.

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, the cleaning water is stored in the cleaning water tank 56 and supplied to the urea water injection device 42 as it is. However, an electric heater is provided around the cleaning water tank 56 or the cleaning water supply pipe 58. A heating device such as the above may be provided, and the cleaning water supplied to the urea water injection device 42 may be heated in advance. Since the urea crystals are easily dissolved in the washing water whose temperature is increased by heating as described above, the urea crystals can be removed more rapidly. As for the heating device, in addition to the electric heater, for example, the cooling water of the engine 1 may be used and a part of the cooling water may be circulated around the cleaning water tank 56 and the cleaning water supply pipe 58.

Moreover, although general tap water may be used as the washing water, the urea water supply path can be kept cleaner by using pure water containing no impurities.
In the above embodiment, the supply of the cleaning water to the urea water injection device 42 is performed via the air supply pipe 46 by controlling the cleaning water control valve 60 and the urea water control valve 54, and the urea water supply Although the case where it carries out via the pipe | tube 52 can be switched now, it is not restricted to this.

  For example, the urea water control valve 54 is not a three-way valve, but only the supply of urea water is controlled as a simple on-off valve. The cleaning water is supplied from the cleaning water supply pipe 58 by opening / closing the cleaning water control valve 60. It may be performed only through 46. Conversely, although the clogging prevention effect of the urea water injection device 42 is slightly reduced, the cleaning water control valve 60 and the cleaning water supply pipe 58 are eliminated, and the cleaning water is supplied only by switching the urea water control valve 54. You may do it. Further, the urea water control valve 54 is set to the cleaning water supply position and the cleaning water control valve 60 is also opened to supply the cleaning water to the urea water injection device 42 from both the air supply pipe 46 and the urea water supply pipe 52. You may do it.

Further, the pressurized air is always supplied to the urea water injection device 42 from the start to the stop of the engine 1, but depending on the supply state of the urea water and the wash water or the operating state of the engine 1. Thus, the air control valve 48 may be appropriately controlled to open and close to control the supply state.

Further, after the engine 1 is stopped, the cleaning water is supplied for a predetermined time ta, and then only the pressurized air is continuously supplied to the urea water injector 42 for the predetermined time tb. However, at this time, the air control valve 48 may be controlled to open and close, and the pressurized air may be intermittently supplied to the urea water injection device 42.
With respect to the supply of the wash water after the engine is stopped, in the above embodiment, the urea water control valve 54 is set to the shut-off position and the wash water control valve 60 is opened so that the wash water is supplied from the air supply pipe 46 to the urea water injector 42. However, the urea water control valve 54 is set to the cleaning water supply position and the cleaning water control valve 60 is closed to supply the cleaning water from the urea water supply pipe 52 to the urea water injection device 42. You may make it do.

Further, the urea water control valve 54 is set to the cleaning water supply position and the cleaning water control valve 60 is also opened, so that the cleaning water is supplied to the urea water injection device 42 from both the air supply pipe 46 and the urea water supply pipe 52. You may do it.
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 ammonia generated by supplying urea water is used as a reducing agent. Any engine having a NOx catalyst for purifying NOx 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 the schematic which shows the urea water injection apparatus used with the exhaust gas purification apparatus of FIG. It is a figure which shows a part of flowchart of the urea water supply control performed with the exhaust gas purification device of FIG. It is a figure which shows the remainder of the flowchart of the urea water supply control performed with the exhaust gas purification apparatus of FIG.

Explanation of symbols

1 Engine 20 Exhaust pipe (exhaust passage)
30 NOx catalyst 38 Urea water addition nozzle 40 Urea water injection pipe (urea water injection passage)
42 Urea water injection device 54 Urea water control valve (cleaning water supply means)
60 Washing water control valve (washing water supply means)
62 Air pressure sensor (air pressure detection means)
64 Injection pressure sensor (Injection pressure detection means)
66 ECU (control means)

Claims (3)

A NOx catalyst that is disposed in the exhaust passage of the engine and selectively reduces NOx in the exhaust gas using ammonia as a reducing agent;
A urea water addition nozzle for supplying ammonia to the NOx catalyst by adding urea water into the exhaust of the engine;
A urea water injection device for mixing urea water into the pressurized air;
An air supply passage for supplying pressurized air to the urea water injection device;
A urea water supply passage for supplying urea water to the urea water injection device;
A urea water injection passage for supplying urea water mixed in pressurized air by the urea water injection device to the urea water addition nozzle;
Cleaning water supply means for supplying cleaning water to the urea water injection device;
Air pressure detecting means for detecting the pressure in the air supply passage;
Injection pressure detecting means for detecting the pressure in the urea water injection passage;
Control means for controlling the washing water supply means based on the pressure in the air supply passage detected by the air pressure detection means and the pressure in the urea water injection passage detected by the injection pressure detection means. ,
The cleaning water supply means supplies the cleaning water to the urea water injection device by supplying the cleaning water to the urea water supply passage, and supplies the cleaning water to the air supply passage. The operation can be switched to a second mode for supplying cleaning water to the urea water injection device,
The control means is configured such that the pressure in the air supply passage detected by the air pressure detection means is equal to or higher than a predetermined upper limit air pressure, and the pressure in the urea water injection passage detected by the injection pressure detection means is a predetermined pressure. When it is equal to or higher than the upper limit injection pressure, the cleaning water supply means is controlled to supply cleaning water in the first mode, while the pressure in the air supply passage detected by the air pressure detection means is a predetermined value. If the pressure in the urea water injection passage detected by the injection pressure detecting means is equal to or higher than the upper limit air pressure and lower than the predetermined lower limit injection pressure, the cleaning water is supplied in the second mode. An exhaust emission control device for controlling a washing water supply means . Wherein said control means further for a predetermined time after the engine is stopped, according to claim 1, wherein the controller controls the cleaning water supply means to supply the cleaning water to the urea water injector Exhaust purification device. The exhaust emission control device according to claim 1 or 2, further comprising heating means for heating the washing water supplied to the urea water injection device.

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