JP2007263006A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device provided with a mechanism for preventing accumulation of deposition urea in a breather of a reducer tank. <P>SOLUTION: In the exhaust emission control device having the reducer tank 1 storing liquid reducer provided with the breather 8 opening an inside of the reducer tank to atmosphere includes a blowing pipe 10 branching off of a tank connection part 8a of the breather 8, an air tank 11 feeding air to the blowing pipe 10, and is provided with a breather cleaning device blowing air into the reducer tank 1 from the blowing pipe 10 through the tank connection part 8a of the breather 8. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for purifying exhaust gas of an internal combustion engine using selective catalytic reduction (SCR).

  As an exhaust purification device for purifying nitrogen oxide (NOx) contained in exhaust gas of an internal combustion engine, particularly a diesel engine, a selective catalytic reduction type exhaust purification device using a liquid reducing agent such as urea water has been proposed. This apparatus employs a configuration in which a liquid reducing agent is added into the exhaust passage upstream of the reduction catalyst in order to increase the purification efficiency of the nitrogen oxide reduction catalyst interposed in the exhaust passage.

In such an exhaust purification device, when a liquid reducing agent containing urea such as urea water is used, it is important to prevent precipitation of urea as described in Patent Document 1. The technology of Patent Document 1 solves urea precipitation in a nozzle portion that is exposed to exhaust gas and becomes high temperature.
Japanese Utility Model Publication No. 4-118133

  As described in Patent Document 1, prevention of urea precipitation is focused on components in the exhaust passage exposed to high temperatures. However, in places that are not exposed to high temperatures, that is, in a breather (atmosphere open pipe) provided in a reducing agent tank for storing a liquid reducing agent, urea precipitation phenomenon has recently occurred in the tank connection pipe. Has been reported. This is because liquid reducing agent droplets containing urea adhere to the breather tube that opens in the tank, and the moisture evaporates under certain conditions due to vibration during driving and mist-like urea water. It is thought that this phenomenon occurs, but if the precipitated urea accumulates, the breather may be blocked, so it is better to take measures.

  The present invention focuses on this point, and proposes an exhaust emission control device having a mechanism for preventing accumulation of precipitated urea in a breather of a reducing agent tank.

  According to the present invention, a reducing agent tank having a configuration in which urea-containing liquid reducing agent is added to the exhaust upstream side of the reduction catalyst interposed in the exhaust passage of the internal combustion engine, and storing the liquid reducing agent, In the exhaust gas purification apparatus provided with a breather for releasing the inside of the reducing agent tank to the atmosphere, including a blowing pipe branched from a tank connecting portion of the breather and an air tank for sending air to the blowing pipe, and connecting the breather to the tank from the blowing pipe A breather cleaning device for blowing air into the reducing agent tank through the section is provided.

According to this breather cleaning device, cleaning can be performed by blowing the precipitated urea away into the liquid reducing agent by blowing the inside of the breather tube into the reducing agent tank with the air fed from the blowing tube.
Such a breather cleaning device can include a valve that can be controlled to be opened and closed interposed in the blow-in pipe, and a control unit that opens the valve for a predetermined time during the internal combustion engine stop process. In other words, for example, the ECU (electronic control unit) of the exhaust gas purification apparatus can be set as a control means, and the timing for performing the air blow can be set during the stop process in which the internal combustion engine stops operating.

  According to the present invention, the liquid reducing agent containing urea is added to the exhaust upstream side of the reduction catalyst interposed in the exhaust passage of the internal combustion engine while the addition amount is controlled by the addition device, The reducing agent tank that stores the liquid reducing agent, a breather that opens the inside of the reducing agent tank to the atmosphere, a reducing agent feed pipe that sends the liquid reducing agent from the reducing agent tank to the adding device, and the adding device to the reducing agent tank In an exhaust emission control device having a reducing agent return pipe for returning a liquid reducing agent, the reducing agent return pipe is placed through the reducing agent return pipe by arranging the opening of the reducing agent return pipe in the vicinity of the opening of the breather in the reducing agent tank. A breather cleaning device is provided for spraying the liquid reducing agent returned to the agent tank to the opening of the breather.

  An exhaust gas purification apparatus that uses a liquid reducing agent may stop the addition of the liquid reducing agent exhaust gas depending on the operating state of the internal combustion engine. A process of returning the liquid reducing agent remaining in the pipe or the like to the reducing agent tank is executed. At the time of the processing, since the liquid reducing agent is pumped by air and returned from the reducing agent return pipe to the reducing agent tank, the liquid reducing agent blows out from the reducing agent return pipe vigorously. In the breather cleaning apparatus of the present embodiment, the precipitated urea is cleaned by using the liquid reducing agent blown out from the reducing agent return pipe and sprayed to the opening of the breather to suppress accumulation.

  For this purpose, the opening of the reducing agent return pipe is arranged in the vicinity of the breather opening. The portion of the reducing agent return pipe in the reducing agent tank is bent, and the opening at the tip of the bent portion is the opening of the breather. It is arranged so as to face the part, or the part in the reducing agent tank in the breather is bent so that the opening at the tip of the bent part is located below the opening of the reducing agent return pipe Is possible. Among these, in the case of the aspect which bends the inside of the reducing agent tank of the reducing agent return pipe, the injection amount adjusting hole can be formed in the bent part of the reducing agent return pipe.

  Furthermore, according to the present invention, the liquid reducing agent containing urea is added to the exhaust upstream side of the reduction catalyst interposed in the exhaust passage of the internal combustion engine while the addition amount is controlled by the adding device, The reducing agent tank that stores the liquid reducing agent, a breather that opens the inside of the reducing agent tank to the atmosphere, a reducing agent feed pipe that sends the liquid reducing agent from the reducing agent tank to the adding device, and the adding device to the reducing agent tank In an exhaust emission control device having a reducing agent return pipe for returning a liquid reducing agent, a reducing agent return pipe is connected to a tank connecting portion of the breather, and the reducing agent tank is connected from the reducing agent return pipe to the breather tank connecting portion. A breather cleaning device is provided in which the liquid reducing agent returns to the inside.

This embodiment also utilizes the liquid reductant return process as described above, and the momentum of the liquid reductant is blown back from the reductant return pipe into the reductant tank through the tank connecting portion of the breather. In this method, the precipitated urea is washed.
In addition to the above, according to the present invention, the reduction reducing agent that stores the liquid reducing agent has a configuration in which a liquid reducing agent containing urea is added to the exhaust upstream side of the reduction catalyst interposed in the exhaust passage of the internal combustion engine. In an exhaust gas purification apparatus provided with a breather that opens the inside of the reducing agent tank to the atmosphere in the reducing agent tank, the pump is disposed in the reducing agent tank and discharges the liquid reducing agent in the reducing agent tank, and is discharged by the pump. A breather cleaning device for returning the liquid reducing agent discharged by the pump from the discharge pipe into the reducing agent tank through the tank connecting portion of the breather. It is characterized by that.

In this breather cleaning apparatus, a dedicated pump is provided in the reducing agent tank, and the precipitated urea is cleaned by pumping the liquid reducing agent by the pump and flowing it into the breather tube. In this case, since the pump is a dedicated pump, the cleaning can be performed not only at the time of returning the liquid reducing agent as described above but also at an appropriate timing according to the situation.
The pump of the breather cleaning device of this aspect includes a cylinder, a piston sliding in the cylinder, an intake / exhaust pipe communicating with one compartment in the cylinder divided into two by the piston, and from the air tank to the intake / exhaust pipe during intake An intake / exhaust switching valve that feeds air and opens the intake / exhaust pipe to the atmosphere when exhausting, an urging means for urging the piston so as to expand the volume of the other compartment in the cylinder divided into two by the piston, A check valve provided at the reducing agent suction port of the compartment and allowing only the liquid reducing agent to flow into the other compartment, and the discharge pipe communicates with the other compartment in the cylinder. The pump can be configured as described above.

  Further, the breather cleaning device of this aspect can include a check valve interposed in the discharge pipe so that the liquid reducing agent once discharged into the discharge pipe does not flow back into the pump.

  The exhaust emission control device of the present invention includes a breather cleaning device, and urea precipitated in a breather pipe provided in a reducing agent tank is used by air blow or a liquid reducing agent returned to the reducing agent tank. Alternatively, by circulating the liquid reducing agent in the reducing agent tank, it is possible to wash away and suppress the accumulation of urea in the breather tube, thereby preventing a decrease in the breather function.

FIG. 1 schematically shows an example of an exhaust purification device to which a breather cleaning device is applied.
The illustrated exhaust purification device uses an aqueous urea solution as a liquid reducing agent, and purifies NOx contained in the exhaust by a catalytic reduction reaction. In the exhaust passage of the internal combustion engine, an oxidation catalyst S1 that oxidizes nitrogen monoxide (NO) to nitrogen dioxide (NO ₂ ) from the exhaust upstream side to the downstream side, an injection nozzle N that injects and supplies a liquid reducing agent, A NOx reduction catalyst S2 that reduces and purifies NOx with ammonia obtained by hydrolyzing the liquid reducing agent, and an ammonia oxidation catalyst S3 that oxidizes ammonia that has passed through the NOx reduction catalyst S2 are arranged in this order. The liquid reducing agent injected and supplied from the injection nozzle N is hydrolyzed by exhaust heat and water vapor in the exhaust to generate ammonia. The generated ammonia reacts with NOx in the exhaust gas in the NOx reduction catalyst S2, and is purified into water and harmless gas. At this time, in order to improve the NOx purification rate by the NOx reduction catalyst S2, NO is oxidized to NO ₂ by the oxidation catalyst S1, it is improved to that ratio between NO and NO ₂ in the exhaust gas suitable for catalytic reduction reaction The Further, the ammonia that has passed through the NOx reduction catalyst S2 is oxidized by the ammonia oxidation catalyst S3 disposed downstream of the exhaust gas, so that the ammonia is prevented from being released into the atmosphere as it is.

  The liquid reducing agent stored in the reducing agent tank 1 is sucked out to the adding device A equipped with a pump through the reducing agent feed pipe 2 having a suction port located at the bottom of the tank, and contributes to the injection by the adding device A. The excess liquid reducing agent that did not exist is returned to the reducing agent tank 1 through the reducing agent return pipe 3. The adding device A is controlled by an ECU (electronic control unit), and mixes the liquid reducing agent with air and supplies it to the injection nozzle N while controlling the addition amount according to the operating state of the internal combustion engine.

  The reducing agent tank 1 in this exhaust purification device detects the concentration of the liquid reducing agent, the replenishing port 4 for replenishing the liquid reducing agent, the water level meter 5 for detecting the remaining amount of the liquid reducing agent, and the upper part thereof. A densitometer 6 is installed. Each of the water level meter 5 and the concentration meter 6 hangs down into the reducing agent tank 1. Further, in the reducing agent tank 1, a heat exchanger pipe 7 is circulated for circulating the cooling water of the internal combustion engine as a heat medium.

In the upper space in the reducing agent tank 1, a breather 8 that opens the space to the atmosphere and the reducing agent return pipe 3 are opened.
The opening in the tank of the breather 8 is located above the liquid level of the liquid reducing agent, but when the liquid reducing agent droplets adhere due to shaking or condensation during operation of the internal combustion engine, the moisture evaporates. Urea may precipitate out. If the deposited urea accumulates, the opening may be narrowed and the breather function may be lowered. Therefore, the urea is washed away by a breather cleaning apparatus such as the embodiment shown in FIGS. Hereinafter, each embodiment will be described.

  The breather cleaning apparatus according to the first embodiment shown in FIG. 2 includes a blowing pipe 10 branched from a tank connection portion 8a of the breather 8 and an air tank 11 that sends air into the blowing pipe 10. That is, the air stored in the air tank 11 is blown into the reducing agent tank 1 from the blowing pipe 10 through the tank connection portion 8a of the breather 8, thereby blowing urea precipitated in the pipe of the breather 8 to reduce the reducing agent tank 1. It is a mechanism that blows inward.

  As the air tank 11, for example, an air reservoir for auxiliary equipment of a vehicle can be used, and blowing can be performed vigorously with the compressed air. An opening / closing control valve, for example, a magnetic (electromagnetic control) valve 12, is interposed in the blowing pipe 10, and the ECU shown in FIG. The timing at which the valve 12 is opened and the air blow is performed may be set at the time of the internal combustion engine stop process accompanying turning off the ignition key so as not to affect the purification operation of the exhaust purification device. That is, the ECU executes a stop process for returning the liquid reducing agent remaining in the adding device A from the reducing agent return pipe 3 into the reducing agent tank 1 along with the key-off. Air blow can be executed with the time open. The predetermined time can be set by being stored in advance in the memory of the ECU, or can be set by a mechanism that the valve 12 is normally closed so that the valve 12 is opened for a certain time when an open signal is received from the ECU. .

  FIG. 2A shows an example in which the blowing pipe 10 is branched from the tank connecting portion 8a of the breather 8 at a substantially right angle. In this case, the air blown from the blow pipe 10 can be divided into a flow toward the reducing agent tank 1 and a flow toward the outside air in the breather 8, but on the other hand, the example shown in FIG. When the blowing pipe 10 is branched obliquely from the tank connection portion 8a to form a Y-shaped branch as shown above, the air in the blowing pipe 10 is mostly flowed into the reducing agent tank 1, and the air blowing effect can be further enhanced. It becomes.

The breather cleaning apparatus according to the second embodiment shown in FIG. 3 is an example in which the opening 3 a of the reducing agent return pipe 3 is arranged in the vicinity of the opening 8 b of the breather 8 in the reducing agent tank 1. With this arrangement, the liquid reducing agent that is returned into the reducing agent tank 1 through the reducing agent return pipe 3 can be blown against the opening 8 b of the breather 8.
The exhaust gas purification apparatus as shown in FIG. 1 may stop the addition of the liquid reducing agent depending on the operating state (exhaust temperature, etc.) of the internal combustion engine. When the addition is stopped or when the internal combustion engine is stopped, the liquid reducing agent remaining in the apparatus is returned from the adding apparatus A to the reducing agent tank 1. When returning the residual liquid reducing agent, air is used to return from the reducing agent return pipe 3 to the reducing agent tank 1, so that the liquid reducing agent blows out from the reducing agent return pipe 3 vigorously. The sprayed urea can be washed by spraying the blowing liquid reducing agent onto the opening 8b of the breather 8.

  FIG. 3A shows that the portion of the reducing agent return pipe 3 in the reducing agent tank 1 is bent into a bent portion 3b, and the opening 3a at the tip of the bent portion 3b is formed in the opening 8b of the breather 8. It is an example arrange | positioned so that it may oppose. In this case, the amount of liquid blown to the opening 8b of the breather 8 can be adjusted by opening the injection amount adjusting hole 3c in the bent portion 3b of the reducing agent return pipe 3 to release a part of the liquid reducing agent. it can. On the other hand, FIG. 3B shows that a portion of the breather 8 in the reducing agent tank 1 is bent into a bent portion 8c, and an opening 8b at the tip of the bent portion 8c is an opening of the reducing agent return pipe 3. It is an example arrange | positioned so that it may be located below 3a. In this case, the tip of the bent portion 8c of the breather 8 is preferably cut obliquely so that the opening 8b is inclined upward.

  The breather cleaning apparatus according to the third embodiment shown in FIG. 4 is an example in which the reducing agent return pipe 3 is connected to the tank connection portion 8 a of the breather 8. According to this embodiment, the liquid reducing agent returns from the reducing agent return pipe 3 to the reducing agent tank 1 through the tank connecting portion 8a of the breather 8. Accordingly, cleaning can always be performed by using the return flow of the liquid reducing agent during operation of the exhaust gas purification device, and the tank of the breather 8 is utilized by using the liquid reducing agent blowback of the reducing agent return pipe 3 as in the second embodiment. Precipitated urea in the connecting portion 8a can be washed.

FIG. 4A shows an example of a tank connecting portion 8a that is a Y-shaped branch that branches the breather 8 diagonally, and FIG. 4B shows a Y that branches the reducing agent return pipe 3 diagonally. It is an example of the tank connection part 8a made into the character branch. In either case, the precipitated urea in the tank connection portion 8a can be washed away.
The breather cleaning apparatus according to the fourth embodiment shown in FIG. 5 is arranged in the reducing agent tank 1 and discharges the liquid reducing agent in the reducing agent tank 1. 8 and the discharge pipe 14 that feeds into the tank connection portion 8a. The liquid reducing agent discharged by the pump 13 is returned from the discharge pipe 14 into the reducing agent tank 1 through the tank connecting portion 8a of the breather 8, thereby cleaning the precipitated urea. Since the breather cleaning pump 13 is provided, it can be operated at an appropriate timing according to the situation by the control of the ECU of FIG.

A check valve 15 is interposed in the discharge pipe 14 so that the liquid reducing agent discharged from the pump 13 to the discharge pipe 14 does not flow back to the pump 13.
The pump 13 in the example shown in FIG. 5A includes a cylinder 16, a piston 17 that slides in the cylinder 16, and an intake / exhaust pipe 19 that communicates with one compartment 18 in the cylinder 16 that is divided into two by the piston 17. When the intake air is supplied, air is supplied from the air tank 20 to the intake / exhaust pipe 19 and when the exhaust gas is exhausted, the intake / exhaust pipe 19 is opened to the atmosphere, thereby switching the intake / exhaust of the intake / exhaust pipe 19 and the piston 17 into the cylinder 16 divided into two. An urging means for urging the piston 17 so as to expand the chamber volume of the other compartment 22, in this example, a coil spring 23, and a reducing agent suction port of the other compartment 22 are provided, and liquid to the compartment 22 is provided. And a check valve 24 that allows only the reducing agent inflow.

  The pump 13 is a pump configured to discharge the liquid reducing agent in the compartment 22 to the discharge pipe 14 by communicating the discharge pipe 14 with the compartment 22 and expanding the volume of the compartment 18. Although the pump can be electrically driven, the pump 13 having a simple mechanism that does not have a heat source that causes urea precipitation is more suitable. For example, an auxiliary air reservoir for a vehicle can be used for the air tank 20.

  The switching valve 21 is controlled by the ECU shown in FIG. 1, and forms an intake passage from the air tank 20 to the intake / exhaust pipe 19 when the internal combustion engine is stopped when the ignition key is turned off as described above. Switching to the formation of an exhaust passage for opening the trachea 19 to the outside air. When the switching valve 21 is set to the intake passage side and air is sent from the air tank 20 to the intake / exhaust pipe 19, the piston 17 is pushed and the volume of the compartment 18 is expanded, and the volume of the compartment 22 on the opposite side is reduced. The liquid reducing agent contained in the compartment 22 is discharged to the discharge pipe 14 through the check valve 15. The discharged liquid reducing agent is discharged from the discharge pipe 14 through the connecting portion 8a of the breather 8 into the reducing agent tank 1, and at this time, the urea deposited on the connecting portion 8a is washed away.

  When the switching valve 21 is on the exhaust path side, the air in the compartment 18 is released from the intake / exhaust pipe 19 to the outside air, so that the pressure in the compartment 18 decreases. As a result, when the urging force by the coil spring 23 is won, the piston 17 slides, the volume of the compartment 18 is reduced, and the volume of the opposite compartment 22 is expanded. Since the negative pressure is generated by the expansion, the liquid reducing agent flows into the compartment 22 from the reducing agent suction port that is opened when the check valve 24 is pushed up. Once the liquid reducing agent has flowed in, the check valve 24 closes even if it tries to exit the compartment 22, so that it remains in the compartment 22. Therefore, when air is next fed into the compartment 18 and pressure is applied, the liquid reducing agent in the compartment 22 is pushed out to the discharge pipe 14 through the check valve 15.

FIG. 5B shows another example of the connection form of the discharge pipe 14 and the breather 8.
The discharge pipe 14 of this example is inserted into the tank connecting portion 8 a of the breather 8 through the breather opening 8 b in the reducing agent tank 1. The insertion portion 14a has a diameter smaller than the inner diameter of the connection portion 8a and is provided with a large number of vent holes 14b in the tube wall, and a flange 14b protrudes from the end portion and is locked to the step of the connection portion 8a. To do. The liquid reducing agent flowing through the discharge pipe 14 is discharged from the vent 14b and the opening 14d at the tip, and returns to the reducing agent tank 1 while washing the inside of the breather 8. On the other hand, when the liquid reducing agent is not flowing through the discharge pipe 14, the air in the upper space in the reducing agent tank 1 is released to the outside air by the breather 8 through the opening 14 d from the vent 14 b.

The figure which showed embodiment of an exhaust gas purification apparatus. The figure which showed 1st Embodiment of the breather washing | cleaning apparatus which concerns on this invention. The figure which showed 2nd Embodiment of the breather washing | cleaning apparatus which concerns on this invention. The figure which showed 3rd Embodiment of the breather washing | cleaning apparatus which concerns on this invention. The figure which showed 4th Embodiment of the breather washing | cleaning apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Reducing agent tank 2 Reducing agent feed pipe 3 Reducing agent return pipe 8 Breather 10 Blowing pipe 11 Air tank 12 Magnetic valve 13 Common end 13 Pump 14 Discharge pipe 15 Check valve 16 Cylinder 17 Piston 18 One compartment 19 Intake / exhaust pipe 20 Air tank 21 Switching valve 22 Other compartment 23 Energizing means 24 Check valve

Claims (10)

A liquid reducing agent containing urea is added to the exhaust upstream side of the reduction catalyst interposed in the exhaust passage of the internal combustion engine, and the reducing agent tank for storing the liquid reducing agent is disposed inside the reducing agent tank. In an exhaust purification device equipped with a breather that opens to the atmosphere,
A breather cleaning device that includes a blowing pipe branched from a tank connecting portion of the breather, and an air tank that feeds air into the blowing pipe, and blows air into the reducing agent tank from the blowing pipe through the tank connecting portion of the breather. An exhaust emission control device comprising:   2. The exhaust according to claim 1, wherein the breather cleaning device includes a valve that can be controlled to be opened and closed interposed in the blowing pipe, and a control unit that opens the valve for a predetermined time during the internal combustion engine stop process. Purification equipment. Reduction that stores the liquid reducing agent in a configuration in which a liquid reducing agent containing urea is added to the upstream side of the exhaust of the reduction catalyst interposed in the exhaust passage of the internal combustion engine while the addition amount is controlled by an adding device. A breather for releasing the inside of the reducing agent tank to the atmosphere, a reducing agent feed pipe for sending the liquid reducing agent from the reducing agent tank to the adding device, and a liquid reducing agent from the adding device to the reducing agent tank. In an exhaust gas purification apparatus comprising a reducing agent return pipe for returning,
By arranging the opening of the reducing agent return pipe in the vicinity of the opening of the breather in the reducing agent tank, the liquid reducing agent returned into the reducing agent tank through the reducing agent return pipe is opened in the breather. An exhaust emission control device comprising a breather cleaning device that blows on the part.   The breather cleaning device is formed by bending a portion of the reducing agent return pipe in the reducing agent tank so that an opening at a tip of the bent portion is opposed to the opening of the breather. The exhaust emission control device according to claim 3.   The exhaust emission control device according to claim 4, wherein an injection amount adjusting hole is formed in a bent portion of the reducing agent return pipe.   The breather cleaning device is formed by bending a portion of the breather in the reducing agent tank so that an opening at a tip of the bent portion is positioned below the opening of the reducing agent return pipe. The exhaust emission control device according to claim 3, wherein: Reduction that stores the liquid reducing agent in a configuration in which a liquid reducing agent containing urea is added to the upstream side of the exhaust of the reduction catalyst interposed in the exhaust passage of the internal combustion engine while the addition amount is controlled by an adding device. A breather for releasing the inside of the reducing agent tank to the atmosphere, a reducing agent feed pipe for sending the liquid reducing agent from the reducing agent tank to the adding device, and a liquid reducing agent from the adding device to the reducing agent tank. In an exhaust gas purification apparatus comprising a reducing agent return pipe for returning,
A breather cleaning device which connects the reducing agent return pipe to the tank connecting portion of the breather and returns the liquid reducing agent from the reducing agent return pipe to the reducing agent tank through the tank connecting portion of the breather; An exhaust purification device characterized by that. A liquid reducing agent containing urea is added to the exhaust upstream side of the reduction catalyst interposed in the exhaust passage of the internal combustion engine, and the reducing agent tank for storing the liquid reducing agent is disposed inside the reducing agent tank. In an exhaust purification device equipped with a breather that opens to the atmosphere,
A pump that is disposed in the reducing agent tank and discharges the liquid reducing agent in the reducing agent tank; and a discharge pipe that feeds the liquid reducing agent discharged by the pump into the tank connecting portion of the breather. An exhaust emission control device comprising a breather cleaning device for returning the liquid reducing agent discharged by the pump from the discharge pipe into the reducing agent tank through the tank connecting portion of the breather.   The pump of the breather cleaning device includes a cylinder, a piston sliding in the cylinder, an intake / exhaust pipe communicating with one of the compartments in the cylinder divided by the piston, and an air tank to the intake / exhaust pipe during intake An intake / exhaust switching valve that feeds air and opens the intake / exhaust pipe to the atmosphere when exhausting; and an urging means that urges the piston to expand the volume of the other compartment in the cylinder divided into two by the piston; A check valve provided at the reducing agent suction port of the other compartment and allowing only the liquid reducing agent to flow into the other compartment, and is provided in the other compartment in the cylinder. The exhaust emission control device according to claim 8, wherein the discharge pipe is in communication.   The exhaust gas purification device according to claim 8 or 9, wherein the breather cleaning device includes a check valve interposed in the discharge pipe.

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