JP2008286096A - Exhaust gas after treatment device for internal combustion engine - Google Patents

Exhaust gas after treatment device for internal combustion engine Download PDF

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Publication number
JP2008286096A
JP2008286096A JP2007131478A JP2007131478A JP2008286096A JP 2008286096 A JP2008286096 A JP 2008286096A JP 2007131478 A JP2007131478 A JP 2007131478A JP 2007131478 A JP2007131478 A JP 2007131478A JP 2008286096 A JP2008286096 A JP 2008286096A
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Japan
Prior art keywords
urea
urea water
means
aqueous solution
stirring
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Pending
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JP2007131478A
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Japanese (ja)
Inventor
Kenji Funai
Yusuke Motoe
勇介 本江
賢二 船井
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Denso Corp
株式会社デンソー
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Priority to JP2007131478A priority Critical patent/JP2008286096A/en
Publication of JP2008286096A publication Critical patent/JP2008286096A/en
Application status is Pending legal-status Critical

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Classifications

    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066Selective catalytic reduction [SCR]
    • F01N3/208Control of selective catalytic reduction [SCR], e.g. dosing of reducing agent
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/009Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/009Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
    • F01N13/0093Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series the purifying devices are of the same type
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066Selective catalytic reduction [SCR]
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2251/00Reactants
    • B01D2251/20Reductants
    • B01D2251/206Ammonium compounds
    • B01D2251/2067Urea
    • BPERFORMING OPERATIONS; TRANSPORTING
    • B01PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01DSEPARATION
    • B01D2257/00Components to be removed
    • B01D2257/40Nitrogen compounds
    • B01D2257/404Nitrogen oxides other than dinitrogen oxide
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2290/00Movable parts or members in exhaust systems for other than for control purposes
    • F01N2290/02Movable parts or members in exhaust systems for other than for control purposes with continuous rotary movement
    • F01N2290/06Movable parts or members in exhaust systems for other than for control purposes with continuous rotary movement driven by auxiliary drive
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00Adding substances to exhaust gases
    • F01N2610/02Adding substances to exhaust gases the substance being ammonia or urea
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00Adding substances to exhaust gases
    • F01N2610/10Adding substances to exhaust gases the substance being heated, e.g. by heating tank or supply line of the added substance
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2610/00Adding substances to exhaust gases
    • F01N2610/14Arrangements for the supply of substances, e.g. conduits
    • F01N2610/1406Storage means for substances, e.g. tanks or reservoirs
    • FMECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01NGAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2900/00Details of electrical control or of the monitoring of the exhaust gas treating apparatus
    • F01N2900/06Parameters used for exhaust control or diagnosing
    • F01N2900/18Parameters used for exhaust control or diagnosing said parameters being related to the system for adding a substance into the exhaust
    • F01N2900/1806Properties of reducing agent or dosing system
    • F01N2900/1811Temperature
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02ATECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection
    • Y02A50/20Air quality improvement or preservation
    • Y02A50/23Emission reduction or control
    • Y02A50/232Catalytic converters
    • Y02A50/2322Catalytic converters for exhaust after-treatment of internal combustion engines in vehicles
    • Y02A50/2325Selective Catalytic Reactors [SCR]
    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02TCLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00Road transport of goods or passengers
    • Y02T10/10Internal combustion engine [ICE] based vehicles
    • Y02T10/20Exhaust after-treatment
    • Y02T10/24Selective Catalytic Reactors for reduction in oxygen rich atmosphere

Abstract

<P>PROBLEM TO BE SOLVED: To prevent situation that concentration of water solution and temperature gets unstable, and urea is deposited due to freezing of urea water solution in a tank during vehicle travel or parking in a cold district. <P>SOLUTION: An addition valve 3 adding urea water solution as reducer is provided on an SCR catalyst 23 installed in an exhaust gas passage 11 of an internal combustion engine, and is connected to a urea water solution tank 4 by a urea water solution channel 31. The engine is provided with a mixing means 5 having a mixing blade 51 mixing urea water solution in the urea water solution tank 4, and a urea water solution temperature detection means 71 monitoring freezing of the urea water solution in the urea water solution tank. A controller unit 7 monitors a freezing state from the temperature, and controls the mixing means 5 to prevent freezing during engine drive and parking. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust aftertreatment device including a urea reduction catalyst in an exhaust passage of an internal combustion engine.

  As a technique for reducing nitrogen oxide (NOx) discharged from a vehicle internal combustion engine, an exhaust aftertreatment device (urea SCR system) using a urea reduction catalyst is known. A typical configuration example of a urea SCR system is shown in FIG. 5. An SCR catalyst 102 that selectively reduces urea by the action of a reducing agent is disposed in an exhaust pipe 101 of an engine, and the inlet side thereof is provided. A urea aqueous solution serving as a reducing agent is injected from the installed addition valve 103. The urea aqueous solution added to the exhaust pipe 101 causes a thermal decomposition reaction and a hydrolysis reaction in the exhaust pipe 101, and the generated ammonia purifies NOx on the SCR catalyst.

  The urea aqueous solution serving as the reducing agent is stored in a urea water tank 104 mounted on the vehicle, and is supplied from the urea water supply pipe 105 to the addition valve 103 through the filter 106. Urea aqueous solution is suitable for urea SCR system because it is easy to handle and non-toxic compared to ammonia, and among them, 32.5% aqueous solution with the lowest freezing temperature (-11 ° C) is mainly used. It has become.

  However, when the usage environment is extremely low, such as in a cold region or a severe winter season, the temperature in the vicinity of the urea water tank 104 may decrease to the freezing point (−11 ° C.) of the urea aqueous solution. For this reason, the urea aqueous solution may be locally frozen or totally frozen in the urea water tank, and it is necessary to take measures against freezing at low temperatures.

As a conventional technique, for example, in Patent Document 1, a gap corresponding to an increase in the volume of liquid frozen in the tank chamber is provided between the highest liquid level in the tank and the tank upper wall surface above the tank. A liquid tank configuration is disclosed in which damage to the tank due to increase is prevented. Furthermore, a frozen urea aqueous solution can be thawed by arranging a heater at the bottom of the tank or by installing a heat insulating material incorporating the heater outside the tank.
Japanese Patent Laid-Open No. 2004-324651

  In the technique of Patent Document 1, when the freezing of the tank contents is detected based on the measured value of the filling level measuring device or the like, the heater is operated to melt the frozen tank contents. The heater is preferably a heater composed of a plurality of heating tubes using a heat exchange medium of an engine cooling circuit, and prevents freezing of the liquid during the running operation. It can also be formed as an electric heater.

  However, once a part of the urea aqueous solution in the tank is frozen, there is a problem that the concentration of the urea aqueous solution supplied to the addition valve becomes unstable. This unstable factor is due to the fact that the inside of the tank is partially frozen and unfrozen urea water (high concentration aqueous solution) is sucked and discharged by the pump. And when partial freezing advances, the urea water of a non-freezing site | part will become a still higher concentration aqueous solution, and it will become supersaturated locally (for example, 50% or more), and a urea component will precipitate as a crystal | crystallization. When this precipitation occurs, even after the tank contents frozen by the heater operation are completely thawed, the precipitated urea component becomes difficult to dissolve in the aqueous solution. Becomes a low-concentration urea aqueous solution.

  In addition, it is possible to operate the heater at an early stage in order to prevent freezing, but in that case, the concentration of the urea aqueous solution tends to vary due to temperature unevenness in the tank. This is due to the fact that a temperature difference occurs between the area around the heater and the part away from the tank, making it difficult for the entire tank to reach a uniform temperature, and the solubility of urea in water varies depending on the temperature. Furthermore, if the urea aqueous solution in the tank is left stationary for a long time in a cryogenic environment, the tank will freeze completely, making it difficult to quickly supply the urea aqueous solution when starting the engine. Become. Further, even when thawing is started in the heater, more time is required until the entire thawing is performed, and the supply concentration becomes unstable during the thawing process.

  As described above, in the conventional technique, it is difficult to realize a desired NOx purification performance by supplying a urea solution having a stable target concentration to the addition valve.

  The present invention has been made in view of the above problems, and an object thereof is to prevent the urea aqueous solution in the tank from freezing when the vehicle is traveling or parked in a cold region. In particular, it is possible to prevent the concentration of aqueous solution from becoming unstable due to local freezing and temperature unevenness, or precipitation of urea, or preventing freezing and causing troubles in the supply of urea in the tank. The aqueous solution is maintained at a uniform and stable concentration.

The invention of claim 1 is a urea reduction catalyst installed in an exhaust passage of an internal combustion engine;
Urea addition means for adding an aqueous urea solution as a reducing agent upstream of the urea reduction catalyst;
In the exhaust aftertreatment device comprising the urea addition means and a urea water tank connected by a urea water supply path,
Stirring means for stirring the urea aqueous solution stored in the urea water tank;
Freezing monitoring means for monitoring freezing of the urea aqueous solution in the urea water tank;
A stirring operation control means is provided for controlling the stirring operation of the urea aqueous solution by the stirring means based on the freeze monitoring information from the freeze monitoring means.

  According to the invention of claim 1, when there is a risk of freezing in the urea water tank, the stirring operation control means operates the stirring means to forcibly stir the urea aqueous solution in the tank. The concentration becomes uniform and the effect of preventing freezing is obtained. Therefore, local freezing and temperature unevenness occur, the aqueous solution concentration becomes unstable, and urea is prevented from precipitating, and a uniform urea aqueous solution can be supplied stably.

  More specifically, the stirring means has a stirring member installed in the urea water tank and a driving means for driving the stirring member to mechanically supply the urea aqueous solution. The tank can be uniformly mixed easily by adopting a stirring configuration.

  According to a third aspect of the present invention, a urea water heating means for heating the urea aqueous solution in the urea water tank may be provided. Freezing can be more effectively prevented by using the stirring member together.

  Specifically, the stirring member is disposed near the center of the bottom surface of the urea water tank, and the urea water heating means is disposed near the outer periphery of the bottom surface of the urea water tank. can do.

  Preferably, urea aqueous solution heating means is arranged near the outer periphery of the bottom surface of the urea water tank that tends to become low temperature to prevent the urea aqueous solution from freezing. Moreover, the effect which prevents precipitation of solid urea is acquired by arrange | positioning the stirring member in the center part of the bottom face which tends to become high concentration, and making concentration and temperature uniform.

  According to a fifth aspect of the present invention, there is provided a second stirring means having a pump that pumps the urea aqueous solution to the urea water supply passage, and a return passage that returns the excess urea aqueous solution from the urea water supply passage to the urea water tank. It can also be provided. The second stirring means has an action of stirring the urea aqueous solution by the fluid circulation accompanying the driving of the pump, and the effect of stirring the urea aqueous solution easily can be enhanced using the existing configuration.

  In the invention of claim 6, the freeze monitoring means includes temperature detection means for detecting a temperature inside or outside the urea water tank, and the stirring operation control means is configured to detect the urea water based on a detection result of the temperature detection means. The presence or absence of the possibility of freezing of the urea aqueous solution in the tank is determined, and the operation of the agitation means and urea water heating means is switched between inactive and inactive based on the determination result.

  The presence or absence of the possibility of freezing of the urea aqueous solution in the urea water tank can be easily determined based on the temperature inside or outside the urea water tank, and by operating the stirring means and the urea water heating means based on the results, The effect is easily obtained.

  In the invention of claim 7, the agitation operation control means is configured such that the agitation means controls the agitation means when the urea aqueous solution in the urea water tank becomes at least partially frozen or lower based on a detection result of the temperature detection means. Then, the urea water heating means is operated, and when the temperature of the urea aqueous solution reaches a predetermined temperature at which there is no risk of freezing, the operations of the stirring means and the urea water heating means are stopped.

  Specifically, when the temperature of the urea aqueous solution falls below, for example, a predetermined temperature higher than the freezing temperature, it is determined that the urea aqueous solution is partially frozen, and the stirring unit and the urea water heating unit are operated. By continuing this until a predetermined temperature at which there is no risk of freezing, the inside of the tank can be uniformly stirred without temperature unevenness to prevent freezing.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the overall configuration of an exhaust aftertreatment device for an internal combustion engine according to a first embodiment of the present invention. As the internal combustion engine of the present embodiment, a multi-cylinder (for example, four-cylinder) diesel engine 1 mounted on a vehicle (not shown) is employed. A turbine of a turbocharger 12 is installed in the exhaust passage 11 of the engine 1 downstream of the exhaust manifold, and when the turbine is driven by exhaust, a compressor in an intake passage (not shown) rotates to compress intake air. It has become.

The exhaust discharged from the engine 1 passes through an exhaust aftertreatment device installed in the exhaust passage 11 downstream of the turbocharger 12 and is then released to the outside of the vehicle. The exhaust aftertreatment device includes an oxidation catalyst 21 and a NOx catalyst 22 in order from the upstream side as a catalyst for purifying NOx in the exhaust, and the NOx catalyst 22 is oxidized in the subsequent stage of the urea reduction catalyst (SCR catalyst) 23. The catalyst 24 is integrally accommodated. The oxidation catalyst 21 disposed in the front stage of the SCR catalyst 23 converts the nitrogen monoxide (NO) in the exhaust gas to nitrogen dioxide (NO 2 ) to increase the NO 2 ratio in the NOx and facilitates the subsequent NOx reduction reaction. To. At the same time, it has an action of oxidizing hydrocarbons (HC) and carbon monoxide (CO) in the exhaust. Of course, the SCR catalyst 23 and the subsequent oxidation catalyst 24 may not be integrated but may be provided separately.

  The SCR catalyst 23 selectively reduces and purifies NOx by the action of a reducing agent. For this reason, a reducing agent addition valve 3 for supplying a reducing agent to the SCR catalyst 23 is disposed between the oxidation catalyst 21 and the NOx catalyst 22. In the present invention, urea, which is a precursor of ammonia, is used as the reducing agent, and is injected and supplied from the addition valve 3 into the exhaust passage 11 in a urea aqueous solution that is easy to handle. The oxidation catalyst 24 at the latter stage of the SCR catalyst 23 is for suppressing the ammonia generated from urea from being released without reacting with NOx. The ammonia passing through the SCR catalyst 23 is oxidized and decomposed to be harmless. To do.

  The urea aqueous solution supplied to the addition valve 3 is stored in the urea water tank 4. The urea water tank 4 and the addition valve 3 are connected by a urea water supply path 31, and a urea solution is sucked out by driving a pump 41 disposed in the lower part of the urea water tank 4. It is pumped to the addition valve 3 via a filter (not shown) interposed in the middle. A pressure regulator 32 for adjusting the pressure is installed at the upper part of the urea water tank 4 and connected to the urea water supply path 31. When the supply pressure exceeds a predetermined pressure, the valve is opened and surplus from the return port 33. The urea aqueous solution is returned to the upper part of the urea water tank 4. The addition valve 3 can have, for example, a known air assist type injection valve structure. In the air assist type, the urea water supply path 31 is connected to the addition valve 3, while an air supply path (not shown) is connected to supply assisting air, and the tip nozzle portion is opened and closed to open the urea aqueous solution in the exhaust passage 11. Inject.

As illustrated, the addition valve 3 is attached to the wall of the exhaust passage 11 in an inclined manner. At this time, the injection direction of the nozzle portion protruding into the exhaust passage 11 is parallel to the exhaust flow, and the urea aqueous solution is evenly supplied to the entire inlet side end surface of the SCR catalyst 23. Urea in the injected urea water is thermally decomposed and hydrolyzed by exhaust heat to generate ammonia (Equations 1 and 2). The generated ammonia acts as a NOx reducing agent on the SCR catalyst 23 and promotes the NOx reduction reaction (Formula 3). On the other hand, ammonia slip that has passed through the SCR catalyst 23 without contributing to the reduction of NOx is purified by the oxidation catalyst 24 (Equation 4).
(NH 2 ) 2 CO + H 2 O → NH 3 + NHCO (Formula 1)
NHCO + H 2 O → NH 3 + CO 2 (Formula 2)
NO + NO 2 + 2NH 3 → 2N 2 + 3H 2 O (Formula 3)
4NH 3 + 3O 2 → 2N 2 + 6H 2 O (Formula 4)

  The urea water tank 4 is a sealed container having a predetermined capacity and contains a urea aqueous solution as an ammonia precursor, usually a 32.5% aqueous solution having the lowest freezing temperature (−11 ° C.). However, when used in a cold region, there is a possibility that the temperature will be further lowered and freezing will occur locally, which causes the concentration of the aqueous solution supplied to the addition valve 3 to become unstable. The urea aqueous solution stored in the urea water tank 4 in a low temperature environment has a low temperature at the part contacting the bottom and side surfaces of the tank exposed to the outside air, and solid urea is precipitated due to partial freezing and high concentration due to temperature unevenness. Prone to occur. Under this condition, the unfrozen urea aqueous solution pumped from inside the tank has a higher concentration than the above-mentioned concentration, and once precipitated solid urea is difficult to redissolve in the aqueous solution. When the state is reached, a phenomenon occurs in which the concentration is lower than the predetermined concentration.

  Therefore, in the present invention, a stirring means for stirring the urea aqueous solution in the urea water tank 4 is provided, and the operation of the stirring means is controlled based on the freeze monitoring information of the urea aqueous solution, whereby the urea in the urea water tank 4 is controlled. Stir the aqueous solution uniformly to prevent freezing due to local temperature drop. In the present embodiment, as a stirring means, a stirring blade 51 serving as a stirring member is provided in the vicinity of the center of the bottom surface of the urea water tank 4, and an in-tank stirring means 5 that drives the drive shaft 52 by using the in-vehicle battery 6 as power is provided. .

  In addition, it is more effective if a urea water heating means for heating the urea aqueous solution in the urea water tank 4 is provided and operated auxiliary. In the present embodiment, an electrical heater 42 is disposed as a urea water heating means in the vicinity of the outer peripheral portion of the bottom surface in the urea water tank 4, and energization is controlled by the controller unit 7.

  As shown in the figure, specifically, the heater 42 may be formed in a thin annular shape and disposed on the outer peripheral wall side of the bottom surface of the urea water tank 4. The urea aqueous solution in the vicinity of the peripheral side surface of the urea water tank 4 that is easily frozen is heated by energization heating to the heater 42 to be prevented from freezing, and a convection flow (vertical flow) is generated due to the temperature rise. Promotes heating of the aqueous solution. Further, the stirring blade 51 which is the stirring means 5 is a hollow region in the annular heater 42 and is disposed at the substantially central portion of the bottom surface of the urea water tank 4 to generate a swirling flow in the circumferential direction of the urea water tank 4. . Thereby, the urea aqueous solution heated by the heater 42 effectively raises the temperature of the peripheral side surface of the urea water tank 4. In addition, the urea aqueous solution is uniformly stirred by the flow in the tank to eliminate unevenness in concentration and temperature.

  At this time, the pump 41 may be disposed on the side of the stirring blade 51 as shown in the drawing, and the suction port may be opened at a position facing the upper surface of the heater 42. As described above, by arranging the suction port of the pump 41 at the portion heated by the heater 42 and uniformly stirred by the stirring blade 51, the uniform urea aqueous solution can be sucked.

  Further, urea water temperature detecting means 71 for detecting the urea aqueous solution temperature in the lower part of the urea water tank 4 is provided as a freeze monitoring means for monitoring the freezing of the urea aqueous solution, and the detection result is given to the controller unit 7 as the stirring operation control means. Output. It is also possible to provide outside air temperature detection means 72 outside the urea water tank 4 and reflect the detection result. The motor that drives the tank agitation means 5 can be electric or hydraulic.

  The controller unit 7 rotates the stirring blade 51 of the stirring means 5 when the partial freezing of the urea aqueous solution is predicted from the detected urea water temperature or outside air temperature and it is determined that the tank stirring means 5 needs to be operated. Drive to forcibly stir the aqueous urea solution. If the stirring blade 51 is disposed at the bottom of the urea water tank 4 that tends to be low in temperature as in this embodiment, the effect of preventing freezing by stirring is high. In addition, a urea water heating means for heating the urea aqueous solution in the urea water tank 4 can be provided and operated auxiliary. In the present embodiment, an electrical heater 42 is disposed as a urea water heating means in the vicinity of the side surface in the urea water tank 4, and energization is controlled by the controller unit 7.

  According to the above configuration, a flow is formed in the urea water tank 4 by the operation of the tank agitating means 5, so that concentration unevenness and temperature unevenness are eliminated, and freezing and solid urea precipitation are less likely to occur. In particular, in addition to the stirring operation, the urea water heating means 42 is used in combination to promote the temperature rise of the urea aqueous solution near the side surface of the tank that is likely to freeze, thereby preventing local freezing or easily thawing and refreezing. To prevent. Further, since the heater 42 is installed on the bottom surface of the urea water tank 4, the urea aqueous solution whose temperature has risen moves upward, so that convection easily occurs in the tank. This natural convection can be expected to have an agitation effect according to the tank agitation means 5, so that the urea aqueous solution can be more effectively prevented from freezing.

  Further, when the pump 41 is operated, vertical convection is generated in the tank by the suction by the pump 41 and the return flow from the pressure regulator 32. By utilizing the stirring effect by the fluid circulation as the second stirring means, the antifreezing effect can be enhanced by a synergistic effect with the convection by the tank stirring means 5 and the heater 42. At this time, it is desirable that the return port 33 from the pressure regulator 32 and the suction port by the pump 41 are located on a diagonal line, and it is easy to obtain the stirring effect by the circulating flow. Further, the reflux port from the pressure regulator 32 can be extended to the vicinity of the inner bottom portion of the urea water tank 4, and upstream and downstream are easily generated by introducing a high-temperature return flow into the tank bottom portion.

  In this way, the stirring effect is enhanced by the interference between the flow generated in the tank by the tank stirring means 5, the heater 42, and the pump 41, and the concentration and temperature of the urea aqueous solution are kept uniform. In this embodiment, a horizontal swirling flow is formed by the tank agitating means 5 and a flow perpendicular to the vertical convection by the heater 42 and the pump 41 is generated. The entire tank 4 can be stirred uniformly, and a urea solution having a desired concentration can be stably supplied.

  The urea water heating means such as the heater 42 is not limited to the urea water tank 4, and the installation location can be appropriately selected such as being disposed outside the urea water tank 4 or embedded in the wall of the urea water tank 4. Moreover, the normally well-known heat insulation structure for suppressing a temperature fall, such as covering the outer periphery of the urea water tank 4 with a heat insulating material, can be employed.

  The control of the stirring operation by the controller unit 7 can add conditions such as when the engine is stopped or when the pump 41 is stopped to the temperature conditions inside and outside the urea water tank 4, and when these conditions are satisfied, the tank stirring means 5 and the heater 42 are operated. Further, for the control when the engine is stopped, a battery remaining amount detecting means 61 for detecting the remaining amount of the battery 6 as a power source is provided, and it is preferable to control so that the battery does not run out at the next engine start. When the engine is stopped, the inside of the urea water tank 4 may be forcibly stirred by operating the tank stirring means 5 intermittently. Further, when the pump 41 is operated, an agitation action due to the circulation of the urea aqueous solution can be expected in the urea water tank 4, so that the agitation operation more than necessary may be suppressed only when the pump 41 is stopped.

Next, an example of control according to the present embodiment will be described using a flowchart.
At the time of driving the engine 1 of the vehicle equipped with the post-exhaust device of the present embodiment, the controller unit 7 repeats the freeze monitoring processing routine of FIG. 3 every predetermined control cycle. In FIG. 3, in step S1, it is determined whether or not there is a “freezing prevention request”. The “freezing prevention request” is set such that, for example, when the ignition key is turned off, this request is transmitted. Alternatively, a changeover switch may be provided so that the request is transmitted by an operation by the driver. If it is determined in step S1 that there is a “freezing prevention request”, the process proceeds to step S2, and if there is no “freezing prevention request”, this process is terminated.

  In step S2, the urea water temperature detection means 71 detects the urea water temperature T, and in step S3, the detected urea water temperature T is a temperature (Tb) at which the tank agitation means 5 and the heater 42 are required to operate in advance. It is determined whether it is below. The operation required temperature (Tb) is a temperature at which the urea aqueous solution in the urea water tank 4 is estimated to be partially frozen, and is set to −5 ° C., for example. Here, the operation required temperature (Tb) is set to a temperature higher than the freezing temperature (−11 ° C.) in order to avoid local freezing due to temperature unevenness or the like. If the urea water temperature T is equal to or higher than the operation request temperature (Tb) and the negative determination is made in step S3, it is determined that there is no possibility of freezing of urea water or precipitation of solid urea, and the present process is terminated.

  When the urea water temperature T is lower than the operation required temperature (Tb) (Tb> T), the process proceeds to step S4, and the tank stirring means 5 and the heater 42 are operated. Next, at step S5, it is determined whether or not the urea water temperature T re-detected by the urea water temperature detecting means 71 exceeds a preset temperature (Tb + ΔT) that requires the tank stirring means 5 and the heater 42 to stop operating. (The step of redetecting the urea water temperature T is omitted). The operation stop request temperature (Tb + ΔT) is sufficiently higher than Tb, and even when freezing occurs in the urea water tank 4, it is a temperature at which full thawing is possible, and ΔT is, for example, 5 ° C.

  When the urea water temperature T exceeds the operation stop request temperature (Tb + ΔT) (T> Tb + ΔT), the process proceeds to step S6, the operation of the tank stirring means 5 and the heater 42 is stopped, and this process is temporarily ended. . When a negative determination is made in step S5, the operation of the tank stirring means 5 and the heater 42 is continued until an affirmative determination is made.

  In this way, the control flow can always execute the control logic as long as the “freezing prevention request” is being transmitted regardless of whether the ignition key is on or off. Therefore, by controlling the operation of the heater 42 and the stirring means 5 according to the urea water temperature T while the vehicle is running and parked, it is possible to effectively prevent freezing of urea aqueous solution and precipitation of solid urea by power saving. can do.

  However, when parking and stopping for a long time, there is a concern that the battery will run out. Therefore, when the engine 1 is stopped, the operation time of the motor of the stirring unit 5 and the heater 42 is restricted, or the detection result of the battery remaining amount detecting unit 61 is compared with a preset threshold value, and the remaining battery amount is less than the threshold value. Sometimes the agitation means 5 and the heater 42 are deactivated to prevent the battery from running out. Thereby, freezing at the time of parking and stopping and precipitation of solid urea can be prevented, and the urea aqueous solution can be stably supplied at the next engine start.

  FIG. 3 illustrates another example of control based on the configuration of the present embodiment, using a flowchart. In this control example, when the ignition key is in the ON state, the operation of the stirring means 5 and the heater 42 is controlled based on the monitoring information of the urea water temperature T. In addition, when the engine is operated, a circulating flow is generated as the pump 41 is operated, so that the freezing is suppressed by utilizing the stirring action by these fluid flows.

  In step S11 of FIG. 3, when the ignition key is turned on, the process proceeds to step S12 where the urea water temperature detecting means 71 detects the urea water temperature T. In the subsequent step S13, it is determined whether or not the detected urea water temperature T is higher than the urea water temperature Ta at which the pump 41 can be operated. The operable temperature Ta of the pump 41 is set to a freezing temperature of the urea aqueous solution, for example, −11 ° C. for a 32.5% urea aqueous solution. If the urea water temperature T exceeds the operable temperature Ta (Ta <T) and the determination in step S13 is affirmative, the process proceeds to step S14.

  In step S14, it is determined whether or not the urea aqueous solution discharge request (QR) is present. If there is a discharge request (QR), the pump 41 is operated in step S15, and the process proceeds to the next step S16. In step S16, it is determined whether or not the detected urea water temperature T is higher than the operable temperature Ta of the pump 41 and lower than the required operation temperature (Tb) of the tank stirring means 5 and the heater 42. When an affirmative determination is made in step S16 (Ta <T <Tb), the process proceeds to step S17, and the tank stirring means 5 and the heater 42 are operated. Next, in step S18, it is determined whether the urea water temperature T redetected by the urea water temperature detecting means 71 exceeds the operation stop request temperature (Tb + ΔT) of the tank stirring means 5 and the heater 42 (urea water temperature). The step of redetecting T is omitted).

  When the urea water temperature T exceeds the operation stop request temperature (Tb + ΔT) (T> Tb + ΔT), the process proceeds to step S19, the operations of the tank stirring means 5 and the heater 42 are stopped, and the process proceeds to step S20. If negative determinations are made in steps S13, 14, and 16, the process proceeds to step S20 while the stop of the pump 41 is maintained. In step S20, it is determined whether or not the ignition key is in an off state. If an affirmative determination is made, the present process is temporarily terminated. When the ignition key is in the on state and step S20 is negatively determined, step S12 and subsequent steps are repeated.

  In this way, if the ignition key is on, based on this control flow, the urea water temperature T is monitored, and according to the result and the urea water discharge request 3 from the urea SCR system, the tank agitation means 5 and The operation of the heater 42 and the pump 41 is controlled. At this time, in addition to the swirling flow by the stirring means 5 and the natural convection by the heater 42, a circulating flow is generated by the operation of the pump 41, so the stirring effect in the urea water tank 4 is enhanced. Therefore, freezing of the urea aqueous solution can be effectively suppressed, and the urea aqueous solution can be stably supplied to the SCR catalyst 23 from the addition valve 3 of the urea SCR system.

  FIG. 4A is a diagram showing the state of the concentration and temperature in the tank when a urea water tank having no conventional stirring means is left for a long time. As shown in the figure, the temperature increases and the concentration tends to decrease as it goes from the tank bottom to the top and from the outer periphery to the inner periphery. Further, near the bottom periphery of the low temperature, the urea water is likely to freeze and become ice, and solid urea tends to precipitate near the bottom center where the concentration is high.

  From this state, even if the tank is heated with, for example, a heater, as shown in FIG. 4B, the ice melts, but the solid urea at the center of the high-concentration bottom does not melt, and the density unevenness is eliminated. It ’s difficult. Thus, once the precipitation occurs, it is difficult to dissolve without external influences (turbulent flow or the like). However, in the present invention, the inside of the urea water tank can be forcibly stirred by providing a stirring means. In particular, as shown in FIG. 1, when the stirring means 5 is installed at the center of the bottom of the urea water tank 4 to form a swirling flow by forced stirring, mixing with the outer periphery of the bottom of low temperature and low concentration is promoted. The effect of suppressing solid urea precipitation due to concentration is high. Therefore, the entire tank can be agitated to make the temperature and concentration uniform.

  In addition, another power supply can also be installed as a means for preventing the battery from running off when parked. Also in this case, the basic configuration is the same as that of the first embodiment of FIG. 1 described above, and the tank stirring means 5 having the stirring blades 51 is provided as the stirring means. In the first embodiment, the agitation operation is performed while monitoring the remaining battery level when the vehicle is parked or stopped. For example, the battery 6 and the AC are connected to the motor serving as the power source 53 of the agitation unit 5 via a switch. A / DC converter can also be connected. When the engine key is stopped, the switch is switched to the AC / DC converter side, and electric power is supplied from a household power supply via a power plug connected to the AC / DC converter.

  In this way, when the engine is stopped (parking and stopping), power is supplied from a separate power source, so that there is no risk of the battery running out when parking and stopping, and freezing in a low temperature environment can be prevented. In addition, depending on the switching mode of the switch, it is possible to charge the battery from the household power supply.

  Alternatively, a solar cell may be connected to the battery 6 so that electricity can be supplied to the motor serving as the power source 53 of the stirring means 5 even when the engine is stopped. A wind power generator may be used instead of the solar cell 65. In this way, when parked or stopped, a solar cell can be used and the motor can be driven while charging the battery 6. Therefore, there is no risk of the battery running out when parked and stopped, and freezing in a low temperature environment is prevented. Can do.

  Although the preferred embodiment of the present invention has been described above, the exhaust aftertreatment device of the present invention is not limited to the above-illustrated configuration, and can be applied to various configurations in a generally known urea SCR system. It is.

1 is an overall schematic configuration diagram of an exhaust aftertreatment device according to a first embodiment of the present invention. It is a flowchart of an example of control in a 1st embodiment. It is a flowchart of the other example of the control in 1st Embodiment. FIG. 5A is a diagram for explaining a conventional state of concentration and temperature in a tank, and FIG. 5A is a diagram illustrating when the tank is left for a long time, and FIG. It is a whole schematic block diagram of the conventional exhaust aftertreatment device.

Explanation of symbols

1 Engine 11 Exhaust passages 21, 24 Oxidation catalyst 23 SCR catalyst (urea reduction catalyst)
3 Addition valve (urea addition means)
31 Urea water supply path 32 Pressure regulator 33 Return port 4 Urea water tank 41 Pump 42 Heater (heating means)
5 Stirring means 51 Stirring blade 52 Drive shaft 6 Battery 61 Battery remaining amount detecting means 7 Control unit (stirring operation control means)
71 Urea water temperature detection means (temperature detection means)
72 Outside air temperature detection means (temperature detection means)

Claims (7)

  1. A urea reduction catalyst installed in the exhaust passage of the internal combustion engine;
    Urea addition means for adding an aqueous urea solution as a reducing agent upstream of the urea reduction catalyst;
    In the exhaust aftertreatment device comprising the urea addition means and a urea water tank connected by a urea water supply path,
    Stirring means for stirring the urea aqueous solution stored in the urea water tank;
    Freezing monitoring means for monitoring freezing of the urea aqueous solution in the urea water tank;
    An exhaust aftertreatment device for an internal combustion engine, comprising: stirring operation control means for controlling the stirring operation of the urea aqueous solution by the stirring means based on the freeze monitoring information from the freeze monitoring means.
  2.   The exhaust aftertreatment device for an internal combustion engine according to claim 1, wherein the stirring means includes a stirring member installed in the urea water tank and a driving means for driving the stirring member to mechanically stir the urea aqueous solution. .
  3.   The exhaust aftertreatment device for an internal combustion engine according to claim 2, further comprising urea water heating means for heating the urea aqueous solution in the urea water tank.
  4.   The exhaust aftertreatment device for an internal combustion engine according to claim 3, wherein the stirring member is disposed in the vicinity of the center of the bottom surface of the urea water tank, and the urea water heating means is disposed in the vicinity of the outer peripheral portion of the bottom surface of the urea water tank.
  5.   A pump that pumps the urea aqueous solution to the urea water supply path; and a return path that returns the excess urea aqueous solution from the urea water supply path to the urea water tank. The exhaust aftertreatment device for an internal combustion engine according to any one of claims 2 to 4, further comprising a second stirring means for stirring.
  6.   The freeze monitoring means includes temperature detection means for detecting the temperature inside or outside the urea water tank, and the stirring operation control means freezes the urea aqueous solution in the urea water tank from the detection result of the temperature detection means. 6. The exhaust gas aftertreatment of an internal combustion engine according to claim 3, wherein the presence or absence of the possibility is determined, and the agitation unit and the urea water heating unit are switched between operation and non-operation based on the determination result. apparatus.
  7.   The agitation operation control means operates the agitation means and the urea water heating means when the urea aqueous solution in the urea water tank becomes at least partially frozen or lower based on the detection result of the temperature detection means. The exhaust aftertreatment device for an internal combustion engine according to claim 6, wherein the operation of the stirring means and the urea water heating means is stopped when the temperature of the urea aqueous solution reaches a predetermined temperature at which the urea aqueous solution is not frozen.
JP2007131478A 2007-05-17 2007-05-17 Exhaust gas after treatment device for internal combustion engine Pending JP2008286096A (en)

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DE102008000549A DE102008000549A1 (en) 2007-05-17 2008-03-06 Exhaust gas post processing apparatus for internal combustion engine of vehicle, has stirring operation control part controlling stirring operation of aqueous solution based on freezing monitoring information from freezing monitoring part

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JP2010164014A (en) * 2009-01-19 2010-07-29 Mazda Motor Corp Exhaust emission control device of engine
CN102312708A (en) * 2010-07-08 2012-01-11 通用汽车环球科技运作有限责任公司 Method of operating a vehicle under frozen diesel emission fluid conditions
JP2013532253A (en) * 2010-06-16 2013-08-15 エミテック ゲゼルシヤフト フユア エミツシオンステクノロギー ミツト ベシユレンクテル ハフツング Device for making available a reducing agent with a system heating element
WO2014133785A1 (en) * 2013-02-28 2014-09-04 Tenneco Automotive Operating Company Inc. Urea common rail
JP2014202094A (en) * 2013-04-02 2014-10-27 株式会社デンソー Control device of urea water addition device
JP2015520823A (en) * 2012-05-25 2015-07-23 エミテック ゲゼルシヤフト フユア エミツシオンステクノロギー ミツト ベシユレンクテル ハフツング Container having a heating device for a tank for storing liquid additives
JP2016050499A (en) * 2014-08-29 2016-04-11 ヤンマー株式会社 Combine-harvester
DE102017124687A1 (en) 2016-12-22 2018-06-28 Denso Corporation Urea water motion controller

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EP2549072A1 (en) * 2011-07-20 2013-01-23 Inergy Automotive Systems Research (Société Anonyme) Vehicular fluid injection system, controller and method for heating said fluid injection system
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JP2010164014A (en) * 2009-01-19 2010-07-29 Mazda Motor Corp Exhaust emission control device of engine
JP2013532253A (en) * 2010-06-16 2013-08-15 エミテック ゲゼルシヤフト フユア エミツシオンステクノロギー ミツト ベシユレンクテル ハフツング Device for making available a reducing agent with a system heating element
CN102312708A (en) * 2010-07-08 2012-01-11 通用汽车环球科技运作有限责任公司 Method of operating a vehicle under frozen diesel emission fluid conditions
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WO2014133785A1 (en) * 2013-02-28 2014-09-04 Tenneco Automotive Operating Company Inc. Urea common rail
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JP2014202094A (en) * 2013-04-02 2014-10-27 株式会社デンソー Control device of urea water addition device
JP2016050499A (en) * 2014-08-29 2016-04-11 ヤンマー株式会社 Combine-harvester
DE102017124687A1 (en) 2016-12-22 2018-06-28 Denso Corporation Urea water motion controller

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