JP2010007560A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device capable of easily adjusting the amount of a reducing agent fed into an exhaust pipe. <P>SOLUTION: The exhaust pipe 11 forms an exhaust passage 12 through which exhaust gas is discharged from the combustion chamber of an internal combustion engine. An addition valve 16 is installed upstream of a catalyst part 14 provided in the exhaust pipe 11 and injects a fluid into the exhaust passage 12. A solution of the reducing agent fed with pressure by a pump 22 is injected from the addition valve 16 and is fed to the catalyst part 14 together with the exhaust gas so as to reduce the exhaust gas for its purification. On the way of a fluid passage 11, the reducing agent fed from a reducing agent storage part 31 is dissolved in a solvent by a reducing agent dissolving means 32, and the solution of the reducing agent is obtained. Dissolution of the reducing agent by the means 32 takes place on the way of the fluid passages 28 and 29, so that it is possible to easily prepare the solution in different concentrations. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus for an engine as an internal combustion engine, and more particularly to an exhaust gas purification apparatus that is suitably employed in a urea SCR (Selective Catalytic Reduction) system.

In recent years, a urea SCR system has been developed as an exhaust purification device for purifying nitrogen oxide (hereinafter referred to as “NOx”) in exhaust gas with high efficiency in engines applied to automobiles, particularly diesel engines. Yes.
In the urea SCR system, an SCR catalyst is provided in an exhaust pipe connected to the engine body, and a urea water addition valve for adding an aqueous urea solution as a reducing agent solution into the exhaust pipe is provided upstream thereof. A urea water supply pipe is connected to the urea water supply valve. For example, when a pump disposed in the urea water tank is driven to discharge, the urea aqueous solution is added from the urea water tank through the urea water supply pipe. The valve is supplied.

In such a system, the urea aqueous solution is injected into the exhaust pipe by the urea water addition valve, so that the urea aqueous solution is supplied to the SCR catalyst together with the exhaust, and NOx is reduced on the SCR catalyst to purify the exhaust. . That is, ammonia (NH ₃ ) is generated by hydrolyzing the urea aqueous solution with exhaust heat, and this ammonia reacts with NOx in the exhaust, whereby NOx is reduced to N ₂ .

Conventionally, it has been common to store and use an aqueous urea solution in a liquid state in a tank. In recent years, a urea SCR system that mixes solid urea and water in a urea water tank on a vehicle has been proposed (for example, see Patent Document 1).
JP 2002-166130 A

  However, in the conventional method, even if solid urea is mixed in a urea water tank and a urea aqueous solution is generated on the vehicle as in Patent Document 1, for example, the concentration of the urea aqueous solution injected into the exhaust pipe is uniform. For example, when it is desired to increase the amount of urea supplied into the exhaust pipe, there is a problem that the injection time must be lengthened and the spray state is deteriorated. In addition, when it is desired to reduce the amount of urea supplied into the exhaust pipe, there is a problem that the injection time must be precisely controlled. For this reason, it is difficult to adjust the amount of urea supplied into the exhaust pipe.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an exhaust purification device capable of easily adjusting the amount of reducing agent supplied into the exhaust pipe.

  The exhaust emission control device according to claim 1 includes an exhaust pipe, a catalyst unit, an addition valve, a fluid passage, a pump, a pump drive control unit, a solvent storage unit, a reducing agent storage unit, and a reducing agent dissolution unit. Here, the exhaust pipe forms an exhaust passage for exhausting exhaust from the combustion chamber of the internal combustion engine. The addition valve injects fluid into the exhaust passage, and the addition valve is located upstream of the catalyst portion provided in the exhaust pipe. The fluid ejected by the addition valve is a reducing agent solution or solvent in which a reducing agent is dissolved in a solvent. A pump pumps such fluid to the addition valve, and the pump is controlled by pump drive control means. When the reducing agent solution is injected from the addition valve, the injected reducing agent solution is supplied to the catalyst unit together with the exhaust, and the exhaust is reduced and purified. In particular, in the present invention, the reducing agent supplied from the reducing agent reservoir is dissolved in the solvent in the middle of the fluid passage by the reducing agent dissolving means to obtain a reducing agent solution.

  That is, the reducing agent was dissolved in the solvent in the middle of the fluid passage. Therefore, unlike the case where the reducing agent is dissolved in the tank, reducing agent solutions having various concentrations can be obtained by adjusting the amount of the reducing agent. For example, when it is desired to increase the amount of reducing agent supplied to the exhaust passage, the amount of urea supplied to the exhaust passage can be increased without increasing the injection time by increasing the concentration of the reducing agent solution. It is possible to prevent deterioration of the spray state due to the increase in length. Further, when it is desired to reduce the amount of reducing agent supplied to the exhaust passage, the amount of urea supplied to the exhaust passage can be reduced by lowering the concentration of the reducing agent solution, so that it is not necessary to precisely control the spraying time. .

  Further, if the concentration of the reducing agent solution and the injection time are adjusted, the amount of reducing agent added can be controlled in a wider range. Furthermore, since a desired amount of reducing agent can be supplied by adjusting the concentration of the reducing agent solution, there is no need to change the design of the addition valve for each engine displacement, and parts can be shared. it can. Furthermore, if the concentration of the reducing agent solution is increased, the injection amount can be reduced, and for example, an optimal nozzle hole shape for atomization such as a tapered nozzle hole can be employed.

The amount of NOx in the exhaust gas varies depending on the operating condition, for example, it is large during acceleration, high load, high speed traveling, and small during steady operation. Therefore, it is desirable to adopt the following configuration.
The exhaust emission control device according to claim 2 includes a reducing agent amount control means. The reducing agent amount control means controls the amount of the reducing agent dissolved in the solvent by the reducing agent dissolving means. For example, if the relationship between the operating state of the internal combustion engine and the NOx emission amount and the relationship between the exhausted NOx amount and the reducing agent amount necessary for purification are stored in advance in map data or the like, the operating state of the internal combustion engine Accordingly, the amount of reducing agent dissolved in the solvent can be controlled so that the optimum amount of reducing agent is added to the exhaust passage.

If the exhaust gas purification device is stopped with the reducing agent solution remaining in the fluid passage or the addition valve, there is a problem that the solvent evaporates and the reducing agent is deposited or the remaining reducing agent is altered. . Therefore, it is desirable to adopt the following configuration.
According to a third aspect of the present invention, the reducing agent amount control means of the exhaust emission control device can stop the supply of the reducing agent in a state where the pump driving by the pump driving control means and the fluid injection by the addition valve are continued.

  For example, after the internal combustion engine is stopped, if the supply of the reducing agent is stopped, and only the solvent is pumped and injected from the addition valve without dissolving the reducing agent, the reducing agent remains in the fluid passage and the addition valve. Can be prevented. Thereby, precipitation and quality change of the reducing agent in the fluid passage and the addition valve can be prevented. In this configuration, there is provided a residual determination means for determining whether or not the reducing agent remains in the fluid, and after determining that the reducing agent does not remain in the fluid, the pump drive and the addition valve It is preferable to stop the ejection of the fluid.

By the way, when water is used as the solvent, there is a possibility that the solvent will freeze and hinder use. Therefore, a heating means may be provided. Examples of the heating means include heating by a heater and heat exchange using engine cooling water. Moreover, you may employ | adopt the following structures.
According to a fourth aspect of the present invention, there is provided an exhaust purification device comprising a fluid recovery means for recovering the fluid in the fluid passage. For example, it is conceivable that the solvent is recovered in the solvent reservoir by rotating the pump in the reverse direction using the pump drive control means. Moreover, it is good also as a structure which provides a collection | recovery path | route and a collection | recovery tank separately. When the configuration according to claim 3 is adopted, only the solvent is sent to the fluid passage and the addition valve, and the reducing agent is removed. Then, the pump is reversely rotated by the pump drive control means to recover the solvent in the solvent reservoir. May be. As a result, freezing of the fluid remaining in the fluid passage or the like is prevented, and it is possible to suppress problems such as damage to the reducing agent supply system due to expansion of the volume of the fluid.

The reducing agent dissolving means of the exhaust gas purification apparatus according to claim 5 has a mixing means for promoting dissolution of the reducing agent in the solvent. Examples of the mixing means include a screw stirrer and an ultrasonic vibrator. Thereby, melt | dissolution to the solvent of a reducing agent can be accelerated | stimulated.
Solid urea is suitably used as the reducing agent stored in the reducing agent storage section of the exhaust emission control device according to claim 6. As represented by the aforementioned urea SCR system, the NOx purification device that reduces and purifies NOx by ammonia generated by hydrolyzing urea can purify NOx in the exhaust gas with a high purification rate. For example, if this device is used in a diesel engine, it will be possible to improve the fuel efficiency and particulate matter (PM) in the exhaust by permitting the generation of NOx during the combustion process, thereby contributing to the improvement of automobile performance. Will be able to.

Solid urea used for the exhaust emission control device according to claim 7 is in a powder form. If powdered solid urea is used, it has good solubility in a solvent and enables stable quantification. As the particle shape of the powdered solid urea, it is desirable to select a particle shape having good solubility in a solvent and capable of stable quantification.
The solvent used in the exhaust emission control device according to claim 8 is water. It is preferable to use water as the solvent because there is no environmental load even if it is sprayed into the exhaust gas.

  The solvent used for the exhaust emission control device according to claim 9 is a substance having a freezing point lower than that of water. A substance having a freezing point of −35 ° C. or lower is particularly preferable, and alcohols such as ethanol and methanol are exemplified. If such a substance is employed as a solvent, it is harder to freeze than water, so that troubles in use can be suppressed.

(First embodiment)
Hereinafter, an exhaust emission control device according to the present invention will be described with reference to the drawings. The exhaust purification device of this embodiment purifies NOx in exhaust using a selective reduction catalyst, and is constructed as a urea SCR system.
As shown in FIG. 1, the exhaust gas purification apparatus 1 according to the present embodiment includes an exhaust pipe 11, an addition valve 16, a solvent tank 21 as a solvent storage unit, a pump 22, fluid passages 28 and 29, a urea supply unit 30, and electronic control. An apparatus (hereinafter referred to as “ECU”) 40 and the like are provided.

  The exhaust pipe 11 is connected to a diesel engine as an internal combustion engine (not shown) and forms an exhaust passage 12 for discharging exhaust gas from the diesel engine. The exhaust pipe 11 is provided with an oxidation catalyst 13, a selective reduction catalyst (hereinafter referred to as “SCR catalyst”) 14 as a catalyst part, and an ammonia removing part 15. Further, in the exhaust pipe 11, an addition valve 16 capable of injecting fluid into the exhaust passage 12 is provided between the oxidation catalyst 13 and the SCR catalyst 14. A NOx sensor 17 is provided on the downstream side of the SCR catalyst 14.

The oxidation catalyst 13 is a platinum-based oxidation catalyst, and oxidizes a part of nitrogen monoxide (NO) contained in the exhaust to nitrogen dioxide (NO ₂ ).
The SCR catalyst 14 promotes a reduction reaction of NOx, and the reaction is represented, for example, by the following reaction formula.
4NO + 4NH ₃ + O ₂ → 4N ₂ + 6H ₂ O (Formula 1)
6NO ₂ + 8NH ₃ → 7N ₂ + 12H ₂ O (Formula 2)
NO + NO ₂ + 2NH ₃ → 2N ₂ + 3H ₂ O (Formula 3)
In these reactions, ammonia (NH ₃ ) serving as a NOx reducing agent is generated by hydrolyzing the aqueous urea solution injected from the addition valve 16 provided upstream of the SCR catalyst 14 with exhaust heat. The reaction formula of this hydrolysis reaction is shown in (Formula 4).
(NH ₂ ) ₂ CO + 2H ₂ O → 2NH ₃ + CO ₂ (Formula 4)
The ammonia removal unit 15 is an oxidation catalyst provided on the downstream side of the SCR catalyst 14, and prevents discharge of ammonia that has not been reacted (ammonia slip).

The addition valve 16 has substantially the same configuration as that of an existing fuel injection valve (injector), and a known configuration can be adopted. Therefore, the configuration will be briefly described here. The addition valve 16 is configured as an electromagnetic on-off valve that includes a drive unit including an electromagnetic solenoid and a valve body unit having a needle for opening and closing the injection hole. The addition valve 16 is opened based on a drive signal from the ECU 40. Valve or close. That is, when the electromagnetic solenoid is energized based on the drive signal, the needle moves in the valve opening direction along with the energization, and the injection hole is released by the movement of the needle and the fluid is injected into the exhaust passage 12.
The NOx sensor 17 is provided on the downstream side of the SCR catalyst 14 and can detect the amount of NOx in the exhaust gas.

  The solvent tank 21 is comprised with the airtight container with an oil supply cap, and the water as a solvent is stored. A pump 22 is provided in the solvent tank 21 so as to be immersed in water. The pump 22 is pressurized to a predetermined pressure and fluid is fed to the addition valve 16. The pump 22 is an electric pump that is rotationally driven by a drive signal from the ECU 40, and has a configuration in which the motor rotation direction rotates forward and backward by changing the excitation order of the three-phase armature coils. When the pump 22 is driven to rotate forward, water is discharged from the solvent tank 21, and when the pump 22 is driven to rotate backward, the water is collected in the solvent tank 21. The pump 22 functions as “fluid recovery means” in “Claims”, and in particular, reverse rotation driving corresponds to the function as “fluid recovery means”.

The pressure regulator 23 adjusts the pressure of the fluid supplied to the addition valve 16. When the supply pressure exceeds a set value, the water in the fluid passage 28 is returned to the solvent tank 21. Become.
The fluid passage 28 is a passage that communicates the solvent tank 21 and the urea supply unit 30. A water pressure sensor 24 and a water temperature sensor 25 are provided in the fluid passage 28. The fluid passage 29 is a passage that communicates the urea supply unit 30 and the addition valve 16. A filter 26 and a urea sensor 27 are provided in the fluid passage 29.

The filter 26 filters the fluid, and foreign matters in the fluid are removed by the filter 26 and supplied to the addition valve 16.
The urea sensor 27 detects the urea concentration of the urea aqueous solution. For example, a sensor that detects the urea concentration based on the electrical resistance value of the resistance temperature detector heated by the heater can be used.

The urea supply unit 30 is disposed between the fluid passage 28 and the fluid passage 29, and includes a urea powder storage unit 31 as a reducing agent storage unit and a dissolution unit 32 as a reducing agent dissolving means.
The urea powder storage unit 31 stores powdered solid urea. The stored powdery solid urea is supplied to the dissolution unit 32 under the control of the ECU 40. The powdered solid urea stored in the urea powder storage unit 31 is desirably replenished for every predetermined distance, for example, 20,000 km.

  The dissolving portion 32 constitutes a part of the fluid passage and communicates the fluid passage 28 and the fluid passage 29. In the dissolving part 32, the powdery solid urea supplied from the urea powder storing part 31 is dissolved in the water flowing in from the fluid passage 28 to obtain an aqueous urea solution as a reducing agent solution. The obtained aqueous urea solution flows out to the fluid passage 29.

  The ECU 40 is constituted by a microcomputer having a CPU, a ROM, an I / O, a bus line connecting these, and the like. For example, the exhaust emission control device 1 is controlled by a computer program stored in the ROM. The sensors described above are electrically connected to the input side of the ECU 40, and various actuators such as the addition valve 16, the pump 22, and the urea supply unit 30 are electrically connected to the output side. In the ROM, the relationship between the operating state of a diesel engine (not shown) and the NOx emission amount, and the relationship between the NOx amount to be discharged and the urea amount necessary for purifying the NOx are stored in advance as map data. . Further, the ECU 40 can communicate with other ECUs (not shown) such as an ECU for controlling a diesel engine and an ECU for controlling an in-vehicle navigation device via a communication line with a predetermined communication protocol such as CAN (Control Area Network). It is connected to the.

Next, operation | movement of the exhaust gas purification apparatus 1 in this embodiment is demonstrated.
In the exhaust emission control device 1 according to the present embodiment, water is pumped to the dissolving part 32 via the fluid passage 28 by the forward rotation of the pump 22. The powdery solid urea stored in the urea powder storage unit 31 is quantified and supplied to the dissolution unit 32. A method for quantifying powdered solid urea will be described later with reference to FIG. In the dissolving part 32, powdered solid urea is dissolved by the flow of water pumped by the pump 22, and an aqueous urea solution is obtained. An aqueous urea solution obtained by dissolving powdered solid urea in water is delivered to the fluid passage 29. The aqueous urea solution is filtered by the filter 26, supplied to the addition valve 16, and injected into the exhaust passage 12. The urea aqueous solution injected into the exhaust passage 12 is hydrolyzed by exhaust heat to generate ammonia as shown in (Formula 4). The produced ammonia is supplied to the SCR catalyst 14 together with the exhaust gas, and NOx is reduced and purified by the reduction reactions shown in (Formula 1) to (Formula 3).

Here, based on FIG. 2, a method for quantifying powdered solid urea (hereinafter referred to as “urea quantification cycle”) will be described. In the present embodiment, the dissolving part 32 is provided on the lower side in the gravity direction of the urea powder storing part 31, and three electromagnetic valves are provided between the urea powder storing part 31 and the dissolving part 32. The three electromagnetic valves provided between the urea powder storage unit 31 and the dissolution unit 32 are a first electromagnetic valve 36, a second electromagnetic valve 37, and a first electromagnetic valve in order from the urea powder storage unit 31 side to the dissolution unit 32 side. 3 solenoid valves 38. The first solenoid valve 36, the second solenoid valve 37, and the third solenoid valve 38 are opened or closed under the control of the ECU 40. In FIG. 2, the valve open state is indicated by a dotted line, and the valve closed state is indicated by a solid line.
A metering chamber 311 is formed between the first solenoid valve 36 and the second solenoid valve 37, and a buffer chamber 312 is formed between the second solenoid valve 37 and the third solenoid valve 38. The volume of the buffer chamber 312 is larger than the volume of the metering chamber 311.
The dissolution part 32 is provided on the anti-urea powder storage part 31 side of the third electromagnetic valve 38, the dissolution part inlet 281 of the dissolution part 32 communicates with the fluid passage 28, and the dissolution part outlet 282 communicates with the fluid passage 29. is doing. When the pump 22 is driven to rotate in the forward direction, a flow of water from the dissolving portion inlet 281 to the dissolving portion outlet 282 is formed. In the description of the urea determination cycle using FIG. 2, it is assumed that the pump 22 is driven to rotate forward.

  In FIG. 2A, the first electromagnetic valve 36, the second electromagnetic valve 37, and the third electromagnetic valve 38 are all closed. At this time, the quantitative chamber 311 is filled with powdered solid urea, and the buffer chamber 312 is free of powdered solid urea. Next, as shown in FIG. 2B, the second electromagnetic valve 37 is opened. The first solenoid valve 36 and the third solenoid valve 38 remain closed. When the second electromagnetic valve 37 is opened, the powdered solid urea that has filled the metering chamber 311 moves to the buffer chamber 312 by gravity. When the total amount of powdered solid urea that has filled the fixed amount chamber 311 moves to the buffer chamber 312, the second electromagnetic valve 37 is closed as shown in FIG. Subsequently, as shown in FIG. 2D, the first electromagnetic valve 36 and the third electromagnetic valve 38 are opened. The second electromagnetic valve 37 remains closed. By opening the first electromagnetic valve 36, the powdery solid urea stored in the urea powder storage unit 31 is supplied to the metering chamber 311. By opening the third electromagnetic valve 38, the powdered solid urea in the buffer chamber 312 is supplied to the dissolution unit 32. Since the pump 22 is driven to rotate in the forward direction, a flow of water from the dissolving portion inlet 281 to the dissolving portion outlet 282 is formed in the dissolving portion 32. By this flow of water, the powdery solid urea supplied from the buffer chamber 312 is dissolved in water, and an aqueous urea solution is obtained. The obtained aqueous urea solution flows out from the dissolution unit outlet 282. Thereafter, as shown in FIG. 2A, the first electromagnetic valve 36 and the third electromagnetic valve 38 are closed. The determination chamber 311 is filled with powdered solid urea, and the buffer chamber 312 returns to the state without powdered solid urea.

  By repeating the urea quantification cycle described with reference to FIGS. 2A to 2D, powdery solid urea for the volume of the quantification chamber 311 is quantified and dissolved in water by the dissolution unit 32, and urea An aqueous solution is obtained. At this time, the opening / closing of the electromagnetic valve can be adjusted by the control of the ECU 40 to adjust the urea concentration of the generated urea aqueous solution. For example, if you want to increase the urea concentration, control the opening and closing of the solenoid valve so that the urea metering cycle is performed early, and if you want to reduce the urea concentration, open and close the solenoid valve so that the urea metering cycle is performed slowly. And so on.

  By the way, the present invention is characterized in that the amount of powdered solid urea dissolved in the dissolving section 32 can be adjusted. Therefore, the urea supply process in the exhaust emission control device 1 of the present embodiment will be described based on the flowchart shown in FIG. In the present embodiment, the flow rate and water pressure of water pumped by the pump 22 are constant. Further, the injection time of the urea aqueous solution in the addition valve 16 is constant, and the amount of urea supplied to the exhaust passage 12 is defined by the concentration of the urea aqueous solution.

In the first step S101 (hereinafter, “step” is omitted and simply indicated by the symbol “S”), the operating state of the diesel engine is acquired.
In S102, it is determined whether or not the operation state of the diesel engine acquired in S101 is stopped. When the operation state of the diesel engine acquired in S101 is stopped (S102: YES), the process proceeds to S111. When the operation state of the diesel engine acquired in S101 is not stopped (S102: NO), the process proceeds to S103.

In S <b> 103, the pump 22 is driven to rotate forward, and the water stored in the solvent tank 21 is pumped to the fluid passage 28.
In subsequent S104, the amount of NOx in the exhaust is obtained from the map data stored in advance according to the operating state of the diesel engine acquired in S101. Then, the urea amount necessary for purifying the determined NOx amount in the exhaust gas is obtained from map data stored in advance. In this embodiment, since the injection time of the urea aqueous solution in the addition valve 16 is constant, the concentration of the urea aqueous solution is determined based on the obtained urea amount. Moreover, since the flow rate of the water pumped by the pump 22 is constant, the amount of powdered solid urea supplied from the urea powder reservoir 31 is determined based on the determined concentration of the aqueous urea solution.

  In S <b> 105, the amount of powdery solid urea determined in S <b> 104 is supplied from the urea powder storage unit 31 to the dissolving unit 32. The powdery solid urea supplied to the dissolving section 32 is dissolved by the flow of water flowing in from the fluid passage 28 to obtain an aqueous urea solution. The obtained aqueous urea solution flows out to the fluid passage 29.

In S106, an aqueous urea solution obtained by dissolving powdered solid urea in water is supplied to the addition valve 16 and injected into the exhaust passage 12. The injected urea aqueous solution is hydrolyzed by exhaust heat to generate ammonia (NH ₃ ), and the generated ammonia (NH ₃ ) reduces and purifies NOx in the exhaust. Then, the process returns to S101.

  In S111, where the operation state of the diesel engine acquired in S101 is stopped (S102: YES), the supply of powdered solid urea from the urea powder storage unit 31 is stopped. Then, the forward rotation drive of the pump 22 is continued (S112), and the ejection of the fluid from the addition valve 16 is continued (S113). That is, the supply of powdered solid urea is stopped and the supply of water by the forward rotation driving of the pump 22 is continued, so that the urea concentration of the fluid supplied to the addition valve 16 gradually decreases.

  In subsequent S114, it is determined whether or not urea remains in the addition valve 16. Whether or not urea remains in the addition valve 16 can be determined, for example, by the passage of a predetermined time after the urea sensor 27 provided in the fluid passage 28 detects that the urea concentration is “0”. it can. When it is determined that urea remains in the addition valve 16 (S114: NO), the process returns to S112, and the forward rotation drive of the pump 22 and the injection of fluid from the addition valve 16 are continued. When it is determined that no urea remains in the addition valve 16 (S114: YES), the injection of fluid from the addition valve 16 is stopped (S115). Then, the pump 22 is driven to rotate reversely, and the water in the fluid passage is collected in the solvent tank 21 (S116).

  In S117, it is determined whether or not the collection of water in the fluid passage 28 has been completed. When it is determined that the collection of water in the fluid passage 28 has not been completed (S117: NO), the process returns to S116 and the reverse rotation driving of the pump 22 is continued. When it is determined that the collection of water in the fluid passage 28 has been completed (S117: YES), the driving of the pump 22 is stopped and the urea supply process is terminated.

  The ECU 40 in this embodiment constitutes “pump drive control means” and “reducing agent amount control means”. S103, S112, S116 and S118 in FIG. 3 correspond to processing as a function of “pump drive control means”, and S104, S105 and S111 in FIG. 3 correspond to functions as “reducing agent amount control means”. It corresponds to processing.

  As described above, in the exhaust emission control device 1 according to the present embodiment, the dissolving portion 32 is provided between the fluid passage 28 and the fluid passage 29 to form a part of the fluid passage. Further, the urea amount is determined according to the operating state of the diesel engine (S104), and the determined urea amount is supplied from the urea powder storage unit 31 to the dissolution unit 32 and dissolved by the flow of water to obtain an aqueous urea solution ( S105). Then, the obtained urea aqueous solution is injected from the addition valve 16 into the exhaust passage 12, and NOx in the exhaust is reduced and purified (S106). Since powdery solid urea is dissolved in water in the middle of the fluid passage, the urea concentration of the urea aqueous solution can be adjusted according to the amount of NOx.

  That is, when the amount of NOx discharged is large, for example, during acceleration, high load, high speed traveling, etc., the amount of urea supplied from the urea powder storage unit 31 and dissolved in the dissolution unit 32 is increased, and the urea concentration of the urea aqueous solution is increased. Can be high. Thereby, since the amount of urea injected into the exhaust passage 12 can be increased without increasing the injection time, it is possible to prevent the deterioration of the spray state due to the increase of the injection time. Further, when the amount of NOx discharged is small, for example, during steady running, the amount of urea supplied from the urea powder storage unit 31 and dissolved in the dissolution unit 32 is reduced, and the urea concentration of the urea aqueous solution is reduced, thereby reducing the exhaust passage. 12 can reduce the amount of urea injected into the fuel tank 12. In order to reduce the amount of urea supplied into the exhaust passage 12 using a urea aqueous solution having a high urea concentration, it is necessary to precisely control the injection time, but in this embodiment, the urea concentration of the urea aqueous solution is lowered. Therefore, it is not necessary to precisely control the injection time.

  Furthermore, since a desired amount of urea can be supplied to the exhaust passage 12 by adjusting the urea concentration of the aqueous urea solution, there is no need to change the design of the addition valve for each engine displacement, and parts can be shared. You can plan. Furthermore, if the concentration of the urea aqueous solution is increased, the amount of injection from the addition valve 16 can be reduced, and for example, it is possible to adopt an optimal nozzle hole shape for atomization such as a tapered nozzle hole. The aqueous solution can be sprayed in a good spray state.

  Further, when it is determined that the operation state of the diesel engine is stopped (S102: YES), the exhaust purification device 1 according to the present embodiment stops the supply of powdered solid urea (S111), and the pump 22 is The rotation drive is continued (S112), and the ejection of fluid from the addition valve 16 is continued (S113). If it is determined that no urea remains in the addition valve 16 (S114: YES), the injection of fluid from the addition valve 16 is stopped (S115).

  That is, after the diesel engine is stopped, the supply of powdered solid urea is stopped until it is determined that no urea remains in the addition valve 16, and the pump is driven without dissolving the solid urea for powder. Thus, only water is pumped and injected from the addition valve, so that urea can be prevented from remaining in the addition valve 16 and the fluid passage 29. Therefore, precipitation and alteration of urea in the addition valve 16 and the fluid passage 29 can be prevented.

  Furthermore, the exhaust gas purification apparatus 1 according to the present embodiment determines that urea does not remain in the addition valve 16 (S114: YES), stops the injection of fluid from the addition valve 16 (S115), and then reverses the pump 22 The water is rotated and the water in the fluid passages 28 and 29 is collected (S116). Thereby, since water does not remain in the fluid passages 28 and 29, etc., the freezing of water under low temperature conditions is prevented, and the use of the exhaust gas purification device 1 is damaged due to the expansion of the volume of the water. Can be suppressed.

(Second Embodiment)
Next, another embodiment of the present invention will be described with reference to FIGS. In the following embodiments, the same or equivalent components as those in the first embodiment are denoted by the same reference numerals, and description thereof will not be repeated.

  In the said 1st Embodiment, although the pump 22 is provided in the state immersed in water in the solvent tank 21, in 2nd Embodiment, as shown in FIG. 4, the pump 522 of the exhaust gas purification apparatus 5 is a solvent. It is not in the tank 521 but is provided between the fluid passage 528 and the fluid passage 529. Further, the urea supply unit 30 is provided between the fluid passage 527 and the fluid passage 528.

The pump 522 pressurizes the fluid to a predetermined pressure and pumps the fluid to the addition valve 16. A water pressure sensor 24 and a urea sensor 27 are provided in the fluid passage 529. The pressure regulator 523 adjusts the pressure of the fluid supplied to the addition valve 16, and when the supply pressure exceeds a set value, the fluid in the fluid passage 529 is fluidized via the return passage 533. Return to passage 528. The upstream side of the pump 522 is not pressurized, and the pressure on the upstream side of the pump 522 is atmospheric pressure.
The fluid passage 527 is provided with a water temperature sensor 25, and the fluid passage 528 is provided with a filter 26.

  In the present embodiment, since the dissolving portion 32 is provided between the fluid passage 527 and the fluid passage 528 to form a part of the fluid passage, the same effects as those of the above-described embodiment are obtained. Moreover, since the melt | dissolution part 32 is located in the upstream of the pump 522 and is under atmospheric pressure, it is not necessary to make the melt | dissolution part 32 into a pressure | voltage resistant structure. Further, since the powdered solid urea can be dissolved in water at atmospheric pressure, the structure can be simplified.

(Other embodiments)
In the above embodiment, the exhaust gas purification apparatus applied to a diesel engine has been described. However, the internal combustion engine to which the present invention is applied is not limited to a diesel engine, and may be a gasoline engine. In the above embodiment, the exhaust pipe is provided with the oxidation catalyst, the SCR catalyst, and the ammonia removing unit. However, in other embodiments, the particulate matter (PM) in the exhaust is supplied to the exhaust pipe. A DPF (Diesel Particulate Filter) that is a continuous regeneration type PM removal filter that collects may be provided.

  In the above embodiment, the dissolving portion is configured to dissolve powdered solid urea in water by the flow of water. However, in other embodiments, the dissolving portion may include a mixing unit for promoting dissolution. For example, it is good also as a structure which has the screw stirrer 51 as a mixing means shown in FIG. 5, and the ultrasonic transducer | vibrator 52 as a mixing means shown in FIG. The mixing means is not limited to a screw stirrer or an ultrasonic vibrator, and may have any configuration as long as it can promote dissolution of a reducing agent in a solvent.

  In the above embodiment, the determination of powdered solid urea is performed by controlling three solenoid valves. In other embodiments, any method can be used as long as the powdered solid urea can be determined. For example, the amount may be determined by rotating a screw, or the weight may be measured and a fixed amount may be supplied. In the above embodiment, the urea powder storage unit is provided on the upper side in the gravity direction of the dissolution unit and integrally configured as the urea supply unit. However, in other embodiments, the urea powder storage unit is provided separately from the dissolution unit. The powdered solid urea may be quantified in advance and supplied to the dissolving portion.

  In the above embodiment, the solvent stored in the solvent tank is water, but in other embodiments, a substance having a freezing point lower than that of water can be used. A substance having a freezing point of −35 ° C. or lower is particularly preferable, and alcohols such as ethanol and methanol are preferably used. If such a substance is used, even if it remains in the fluid passage, it does not freeze, so that it is possible to prevent the use from being hindered without a fluid recovery means. If ethanol or methanol is used, the solvent evaporates quickly and the reaction is accelerated. Further, if ethanol or methanol is used, the viscosity is lower than that of water, so that when sprayed from the addition valve, atomization tends to occur and the reaction is promoted.

  In the above embodiment, the flow rate and water pressure of the solvent supplied from the pump, and the injection time from the addition valve are constant, but in other embodiments, the pump is controlled by the ECU according to the operating state of the internal combustion engine. The flow rate and water pressure of the supplied solvent, the injection time from the addition valve, and the concentration of the urea aqueous solution may be adjusted. In this way, it is possible to adjust the amount of urea added to the exhaust passage in a wider range or to control it to achieve an optimal spray state.

  Further, in the above embodiment, the ECU controls only the exhaust emission control device. However, in another embodiment, the ECU may control the entire vehicle including the engine. In another embodiment, the amount of urea to be added may be controlled using information obtainable from CAN. For example, when the map data and the current position of the vehicle are acquired and passed through an entrance toll gate of a highway, the amount of urea is increased because it is expected to accelerate. Moreover, it is good also as urea addition amount according to the driving | operation characteristic of each driver | operator by identifying a driver | operator.

  As mentioned above, this invention is not limited to the said embodiment at all, In the range which does not deviate from the meaning of invention, it can implement with a various form.

It is a block diagram which shows the structure of the exhaust gas purification apparatus of 1st Embodiment of this invention. It is a schematic diagram explaining the urea determination method by 1st Embodiment of this invention. It is a flowchart which shows the urea injection process by 1st Embodiment of this invention. It is a block diagram which shows the structure of the exhaust gas purification apparatus of 2nd Embodiment of this invention. It is a schematic diagram which shows the mixing means of the exhaust gas purification apparatus by other embodiment of this invention. It is a schematic diagram which shows the mixing means of the exhaust gas purification apparatus by other embodiment of this invention.

Explanation of symbols

  1: exhaust purification device, 11: exhaust pipe, 12: exhaust passage, 14: SCR catalyst (catalyst part), 16: addition valve, 21: solvent tank (solvent storage part), 22: pump (pump, fluid recovery means) , 28: fluid passage, 29: fluid passage, 31: powder urea reservoir (reducing agent reservoir), 32: dissolving portion (reducing agent dissolving means, fluid passage), 40: ECU (pump driving means, reducing agent amount control) means).

Claims (9)

An exhaust pipe forming an exhaust passage for exhausting exhaust from the combustion chamber of the internal combustion engine;
A catalyst part provided in the exhaust passage for purifying exhaust;
An addition valve that is provided on the upstream side of the catalyst section of the exhaust pipe and injects a reducing agent solution in which a reducing agent is dissolved in a solvent or a fluid that is the solvent into the exhaust passage;
A fluid passage leading to the addition valve;
A pump that pumps the fluid through the fluid passage to the addition valve;
Pump drive control means for controlling the drive of the pump;
An exhaust purification device comprising:
A solvent reservoir for storing the solvent delivered to the fluid passage by driving the pump under the control of the pump drive control means;
A reducing agent reservoir for storing the reducing agent;
In the middle of the fluid passage, reducing agent dissolving means for obtaining the reducing agent solution by dissolving the reducing agent supplied from the reducing agent reservoir in the solvent;
An exhaust emission control device comprising:   The exhaust emission control device according to claim 1, further comprising a reducing agent amount control means for controlling the amount of the reducing agent dissolved in the solvent by the reducing agent dissolving means.   The reducing agent amount control means can stop the supply of the reducing agent dissolved in the solvent in a state where the pump driving by the pump driving control means and the injection of the fluid by the addition valve are continued. The exhaust emission control device according to claim 2.   The exhaust emission control device according to any one of claims 1 to 3, further comprising a fluid recovery unit that recovers the fluid in the fluid passage.   The exhaust gas purification apparatus according to any one of claims 1 to 4, wherein the reducing agent dissolving means includes a mixing means for promoting dissolution of the reducing agent in the solvent.   The exhaust gas purification apparatus according to any one of claims 1 to 5, wherein the reducing agent stored in the reducing agent storage unit is solid urea.   The exhaust purification apparatus according to claim 6, wherein the solid urea stored in the reducing agent storage unit is in a powder form.   The exhaust gas purification apparatus according to any one of claims 1 to 7, wherein the solvent stored in the solvent storage unit is water.   The exhaust gas purifying apparatus according to any one of claims 1 to 7, wherein the solvent stored in the solvent storage unit is a substance having a freezing point lower than that of water.

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