JP2010019134A - Exhaust emission control device of internal-combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine equipped with defrosting function capable of quickly defrosting urea solution inside a urea solution storage tank even when the urea solution is frozen. <P>SOLUTION: The exhaust emission control device 2, comprising a catalyst device 8 provided for an exhaust gas passage 10 of an engine 4 and containing an SCR catalyst 28 and an injection nozzle unit 32 for injecting the urea solution stored in the storage tank 38 to the upstream side of the SCR catalyst 28, is equipped with a case 20 for housing the storage tank 38 with play, a sub exhaust gas passage 18 diverging from a main exhaust gas passage 14 at the downstream side of the catalyst device 8 and interposed by the case 20 at the middle part, and a switching valve 16 provided at the diverging position of the sub exhaust gas passage 18 for switching a flowing direction of exhaust gas. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification apparatus that purifies exhaust gas by reducing nitrogen oxides in exhaust gas of an internal combustion engine (hereinafter referred to as an engine) with a reducing agent, and more particularly, when the reducing agent is frozen, it is thawed in a short time. The present invention relates to an exhaust purification device having a thawing function that can be performed.

  As an exhaust purification device for purifying nitrogen oxides in engine exhaust gas, a selective reduction catalyst system (hereinafter referred to as a urea SCR system) using urea as an additive is known. This urea SCR system includes an injection nozzle unit on the upstream side of a selective reduction type NOx catalyst (hereinafter referred to as SCR catalyst) in an exhaust passage, and an aqueous urea solution is injected and supplied from the injection nozzle unit into the exhaust gas. Urea is supplied and the urea is hydrolyzed to produce ammonia, and the ammonia is used to reduce nitrogen oxides in the exhaust gas to harmless nitrogen and water in the SCR catalyst.

In this urea SCR system, the aqueous urea solution is stored in a storage tank, and the aqueous urea solution is supplied from the storage tank toward the injection nozzle unit.
By the way, the urea aqueous solution freezes when it becomes −11 ° C. or lower. Therefore, when an automobile equipped with the urea SCR system is used in a cold region, or when passing through a cold region such as a highland, the urea aqueous solution in the storage tank is frozen and the urea aqueous solution cannot be supplied to the injection nozzle. There may be a problem that the urea aqueous solution cannot be injected from the injection nozzle.

Therefore, as an exhaust emission control device that employs a urea SCR system having a function of preventing the urea aqueous solution from freezing, for example, an exhaust emission control device for an engine described in Patent Document 1 can be cited.
The exhaust emission control device described in Patent Document 1 is provided with a circulation path for engine coolant to pass through a storage tank for urea aqueous solution, and the heat of the engine coolant that has been used for cooling the engine and has become high temperature causes Freezing prevention or thawing is performed.
Japanese Patent Laying-Open No. 2005-083223

  By the way, in the exhaust emission control device of Patent Document 1, when the urea aqueous solution is completely frozen in an environment where the ambient temperature is lower than or equal to the freezing point of the urea aqueous solution, The temperature rise is delayed and it takes time to thaw the urea aqueous solution. If the urea aqueous solution is not thawed, the urea aqueous solution cannot be injected, so the urea SCR system does not function. Therefore, the nitrogen oxides in the exhaust gas cannot be purified until the urea aqueous solution is completely thawed. The problem that it is not possible arises.

  Further, in the exhaust gas purification device of Patent Document 1, a supply passage for supplying the urea aqueous solution from the storage tank to the SCR catalyst becomes long, and it is necessary to take a measure for separately providing a heater device for thawing and heat retention in the supply passage. The problem of increased manufacturing costs is inevitable. Furthermore, the thawing of the urea aqueous solution frozen in the urea aqueous solution storage tank takes a longer time than the thawing of the urea aqueous solution frozen in the urea aqueous solution supply passage. is necessary.

  The present invention has been made to solve such problems, and the object of the present invention is to rapidly thaw the urea aqueous solution even if the urea aqueous solution in the urea aqueous solution storage tank is frozen. An object of the present invention is to provide an exhaust emission control device for an internal combustion engine having a thawing function.

  In order to achieve the above object, an exhaust gas purification apparatus for an internal combustion engine according to the present invention is provided in a main exhaust passage of an internal combustion engine, and a selective reduction type NOx catalyst and an aqueous urea solution in a storage tank are placed upstream of the selective reduction type NOx catalyst. In the exhaust gas purification apparatus for an internal combustion engine, including a urea aqueous solution supply means for supplying the exhaust gas into the exhaust gas, a case in which the storage tank is accommodated with play and an exhaust gas flowing in the main exhaust passage are bypassed, The exhaust gas bypass means for guiding the exhaust gas through the exhaust gas is provided (claim 1).

According to the exhaust gas purification apparatus for an internal combustion engine of claim 1, since the exhaust gas of the internal combustion engine that is relatively hot immediately after the start is introduced into the case in which the storage tank for the aqueous urea solution is accommodated, the exhaust gas is stored by such exhaust gas. The tank is warmed, so that the frozen urea aqueous solution can be thawed in a short time.
Specifically, the exhaust gas bypass means is branched from the main exhaust passage on the downstream side of the selective reduction type NOx catalyst, the sub exhaust passage having the case interposed in the middle thereof, and the sub exhaust passage A switching valve that is provided at the branch position and switches the flow direction of the exhaust gas, and the switching valve connects the upstream portion and the downstream portion of the main exhaust passage, and closes the sub exhaust passage. It is preferable that the position includes a second switching position that connects the upstream portion of the main exhaust passage and the sub exhaust passage, and closes the downstream portion of the men-in exhaust passage. .

According to the exhaust gas purification apparatus for an internal combustion engine according to the second aspect, the high-temperature exhaust gas can be easily introduced into the case in which the storage tank for the urea aqueous solution is accommodated by the switching valve.
Further, it is preferable that the case has a configuration in which the storage tank is accommodated so as to ensure a gap between an inner surface of the case and an outer surface excluding the upper surface of the storage tank.
According to the exhaust gas purification apparatus for an internal combustion engine of the third aspect, a gap is secured between the inner surface of the case and the urea aqueous solution storage tank, and high-temperature exhaust gas is introduced into this gap. For this reason, since the wide range of the outer periphery of the storage tank is in contact with the high temperature exhaust gas, the frozen urea aqueous solution can be thawed efficiently.

Further, it is preferable to include a temperature sensor disposed in the storage tank and a control unit that controls switching of the switching valve based on information from the temperature sensor.
According to the exhaust gas purification apparatus for an internal combustion engine of claim 4, the temperature of the urea aqueous solution storage tank is detected by the temperature sensor, and when the urea aqueous solution is detected to be frozen, the switching valve is driven and controlled, To flow into the sub exhaust passage, and high temperature exhaust gas is introduced into the case. When the thawing is completed and the urea aqueous solution reaches a predetermined temperature, the switching valve is driven and controlled so that the exhaust gas flows only into the main exhaust passage. Thereby, temperature control of urea aqueous solution can be performed easily.

  According to the exhaust gas purification apparatus for an internal combustion engine according to the first to fourth aspects, even if the urea aqueous solution is frozen, it can be thawed in a short time, so that the exhaust gas can be purified early after the engine is started. For this reason, the time during which the nitrogen oxides in the exhaust gas cannot be purified can be shortened as much as possible, the purification device can function effectively early after the engine is started, and the purification efficiency of the exhaust gas is increased as compared with the prior art.

  Further, since the exhaust gas is used for thawing the urea aqueous solution, a storage tank for the urea aqueous solution can be installed in the vicinity of the exhaust purification catalyst. For this reason, it is not necessary to route the coolant circulation path from the engine to a place away from the engine, and the apparatus for thawing urea aqueous solution can be simplified, contributing to reduction of manufacturing cost, suppression of failure occurrence, and freedom of layout. .

Hereinafter, an embodiment of an exhaust emission control device according to the present invention will be described with reference to the drawings.
FIG. 1 shows the configuration of an exhaust emission control device for a diesel engine according to an embodiment.
The exhaust purification device 2 is provided in an exhaust passage 10 of an engine 4 configured as an in-line 6-cylinder internal combustion engine.
The exhaust gas of the engine 4 is discharged from the exhaust manifold 6 through the exhaust passage 10, and at this time, the exhaust purification device 2 disposed in the exhaust passage 10 purifies harmful components in the exhaust gas.

  The exhaust purification device 2 includes a catalyst device 8 disposed in the exhaust passage 10, and the catalyst device 8 has a housing 22. In this case 22, a front-stage oxidation catalyst 24, a diesel particulate filter (hereinafter referred to as DPF) 26, an SCR catalyst 28, and a rear-stage oxidation catalyst 30 are accommodated in this order from the upstream side. An injection nozzle 34 of the injection nozzle unit 32 is disposed between the DPF 26 and the SCR catalyst 28. The injection nozzle 34 injects urea aqueous solution to supply urea as an additive to the SCR catalyst 28. More specifically, the injection nozzle unit 32 further includes an electromagnetic valve 36 connected to the base end of the injection nozzle 34, and the electromagnetic valve 36 is attached to the outer surface of the housing 22.

  And the solenoid valve 36 of the injection nozzle 34 is connected to the storage tank 38 of urea aqueous solution via the circulation path 41 provided with the supply pump (not shown). The storage tank 38 has a box shape made of stainless steel, and an aqueous urea solution pressurized to a predetermined pressure can be supplied from the storage tank 38 to the injection nozzle 34 through the electromagnetic valve 36. Therefore, when the electromagnetic valve 36 is opened, the injection nozzle 34 injects the urea aqueous solution into the exhaust gas from the injection hole (not shown) at the tip thereof. In FIG. 1, the supply pipe and return pipe of the circulation path 41 are indicated by reference numerals 40 and 42, and the supply pipe 40 has a suction port 50 positioned in the urea aqueous solution in the storage tank 38, and the return pipe. 42 has a discharge port 52 positioned above the surface of the urea aqueous solution. The storage tank 38 also has a supply port (not shown) for replenishing the urea aqueous solution.

  Further, the storage tank 38 includes a sensor unit 44. The sensor unit 44 includes a temperature sensor, a concentration sensor, and the like, and these sensors are electrically connected to an electronic control unit (hereinafter referred to as ECU) 54. The above-described electromagnetic valve 36 is electrically connected to the ECU 54 together with other sensors and devices (not shown). In addition to the sensor unit 44, the ECU 54 calculates an optimal urea aqueous solution injection amount based on information from various sensors, controls the opening and closing of the electromagnetic valve 36 according to the injection amount, and injects the urea aqueous solution from the injection nozzle 34. Let

As apparent from FIG. 1, the storage tank 38 is accommodated in the case 20.
The case 20 also has a box shape made of stainless steel, and has a size capable of accommodating the storage tank 38 with a margin. More specifically, the storage tank 38 is accommodated with the upper wall 46 exposed from the case 20, the above-described replenishing port is provided in the upper wall 46, and each of the pipes 40, 42 and the sensor unit 44 are located at The wall 46 passes through and is attached to the upper wall 46. Thus, the structure which exposes the upper wall 46 can perform maintenance of the storage tank 38 easily.

  Specifically, the case 20 is provided with a through hole 58 in the upper wall 56 through which the storage tank 38 can be inserted. Therefore, the storage tank 38 is accommodated in the case 20 through the through hole 58, and the outer periphery of the upper end of the storage tank 38 is welded to the inner periphery of the through hole 58. As a result, the upper wall 56 of the case 20 and the upper wall 46 of the storage tank 38 are flush with each other. At this time, any joining method may be employed for joining the case 20 and the storage tank 38 as long as airtightness can be maintained. In addition to welding, for example, a flange may be provided on the outer periphery of the upper end of the storage tank 38, and the flange portion may be fastened to the upper wall 56 of the case 20 with a bolt via a seal member.

As is apparent from FIG. 1, a gap 60 is secured around the storage tank 38 accommodated in the case 20. The gap 60 is formed on the peripheral wall and bottom of the storage tank 38 and the corresponding inner surface of the case 20. Is formed between.
The gap 60 described above forms part of the sub exhaust passage 18. That is, an inlet 64 is formed in one side wall 62 of the case 20, and an upstream exhaust pipe 69 of the sub exhaust passage 18 extends from the inlet 64. A lead-out port 68 is provided in the other side wall 66 facing the one side wall 62 of the case 20, and a downstream exhaust pipe 70 of the sub exhaust passage 18 extends from the lead-out port 68.

The upstream exhaust pipe 69 is connected to the branch port 72 of the main exhaust passage 14 via the switching valve 16 at a downstream position of the catalyst device 8. The switching valve 16 is switched to flow exhaust gas from the engine 4 to either the main exhaust passage 14 or the sub exhaust passage 18 (upstream exhaust pipe 69).
That is, the switching valve 16 includes a valve housing 71. In addition to the aforementioned branch port 72, the valve housing 71 includes an inlet port 74 and an outlet port 76 that connect the upstream side portion and the downstream side portion of the main exhaust passage 14. Have. A valve body 78 is disposed in the valve housing 71. The valve body 78 communicates the inlet port 74 and the outlet port 76 and closes the branch port 72, and the inlet port 74 and the branch port. 72 and a second switching position for closing the outlet port 76, and switching operation is possible between these switching positions.

Therefore, the switching valve 16 further includes a drive unit (not shown) for switching the valve body 78, and this drive unit is electrically connected to the ECU 54 described above. The ECU 54 performs the switching operation of the valve body 78 through the drive unit based on the temperature information of the aqueous urea solution from the sensor unit 44 in the storage tank 38 described above.
A fuel injection valve (not shown) of the engine 4 is also electrically connected to the ECU 54. The ECU 54 sets a fuel injection amount (not shown) based on the engine rotational speed Ne and the accelerator operation amount θacc, and a map (not shown) sets the fuel injection timing based on the engine rotational speed Ne and the fuel injection amount. The engine 4 is driven via the fuel injection valve based on the fuel injection amount and the fuel injection timing set according to these maps.

During driving of the engine 4, exhaust gas from the engine 4 is introduced into the catalyst device 8 through the exhaust manifold 6 and the main exhaust passage 14 of the exhaust passage 10. In the introduced exhaust gas, hydrocarbons and carbon monoxide in the exhaust gas are changed to carbon dioxide and water by the pre-stage oxidation catalyst 24, and particulate matter (hereinafter referred to as PM) in the exhaust gas is captured by the DPF 26. Be collected.
Thereafter, the exhaust gas reaches the SCR catalyst 36 on the downstream side.

  Here, when the urea aqueous solution in the storage tank 38 is not frozen and the temperature of the urea aqueous solution is an appropriate temperature, the temperature sensor of the sensor unit 44 in the storage tank 38 indicates information indicating that the urea aqueous solution is an appropriate temperature. Based on this information, the ECU 54 switches the valve body 78 to the first switching position indicated by A in FIG. 1 via the drive portion of the switching valve 16, and the valve body 78 causes the sub exhaust passage 18 to switch. The upstream exhaust pipe 69 is closed and the main exhaust passage 14 is opened. Further, under the control of the ECU 54, the urea aqueous solution is injected from the injection nozzle 34 into the exhaust gas at an optimal injection amount. As a result, the SCR catalyst 28 efficiently exhibits the NOx purification action for the exhaust gas.

Therefore, the purified exhaust gas is discharged to the outside through the switching valve 16 and the downstream portion 80 of the main exhaust pipe 14.
On the other hand, when the engine is used in a cold region and the urea aqueous solution in the storage tank 38 is frozen, the ECU 54 performs the switching control of the switching valve 16 as follows in order to perform the thawing operation of the urea aqueous solution.

  That is, first, the sensor unit 44 in the storage tank 38, that is, its temperature sensor detects that the urea aqueous solution in the storage tank 38 is −11 ° C. or less, and informs the ECU 54 that the urea aqueous solution is frozen. , The ECU 54 switches the valve body 78 of the switching valve 16 to the second switching position indicated by B in FIG. 1 based on the information. Therefore, in this case, the main exhaust passage 14 is closed at the downstream portion 80 from the switching valve 16, and the main exhaust passage 14 is connected to the sub exhaust passage 18. On the other hand, at this time, the ECU 54 stops the injection of the urea aqueous solution from the injection nozzle 34.

  Even if the engine 4 is operated in this state, the SCR catalyst of the catalyst device 8 is not functioning, so NOx in the exhaust gas is not purified. However, hydrocarbons and carbon monoxide in the exhaust gas are purified by the oxidation catalyst, and the exhaust gas in which PM is collected by the DPF is discharged. Such exhaust gas is introduced into the upstream exhaust pipe 69 of the sub exhaust passage 18 through the switching valve 16 and introduced into the gap 60 of the case 20. Thereafter, the exhaust gas is discharged from the case 20 to the outside through the downstream exhaust pipe 70 of the sub exhaust passage 18. Here, since the temperature of the exhaust gas discharged from the engine 4 is sufficiently high, the high-temperature exhaust gas introduced into the gap 60 thaws the frozen urea aqueous solution in the storage tank 38.

  Thereafter, when the urea aqueous solution in the storage tank 38 is thawed and the temperature reaches an appropriate temperature, the valve body 78 of the switching valve 16 is again switched to the first switching position A in FIG. 1 as described above. . As a result, the upstream exhaust pipe 69 of the sub exhaust passage 18 is closed, and no further exhaust gas is introduced into the case 20. On the other hand, the ECU 54 injects the urea aqueous solution from the injection nozzle 34, whereby the SCR catalyst 28 purifies NOx in the exhaust gas.

In addition, when the vehicle passes through a cold region while traveling, the temperature of the aqueous urea solution in the storage tank 38 may decrease and freeze. Even in such a case, the switching operation of the switching valve 16 and the injection control of the injection nozzle 34 are similarly performed, and the urea aqueous solution is quickly thawed.
As described above, the exhaust gas purification device 2 of the present invention uses exhaust gas for thawing the urea aqueous solution. Even immediately after the engine is started, the exhaust gas temperature is much higher than the engine coolant temperature. Thawing is completed in a shorter time than when the aqueous urea solution frozen by the coolant is thawed, and the aqueous urea solution can be injected from the injection nozzle 34 at an early stage after the engine is started. For this reason, NOx emissions can be suppressed as short as possible even when starting in cold regions.

  Further, in the exhaust purification device 2 of the present invention, the case 20 including the storage tank 38 can be disposed in the vicinity of the catalyst device 8, so that the urea aqueous solution is supplied from the storage tank 38 to the injection nozzle unit 32. The piping can also be shortened. For this reason, when a heater for preventing freezing is attached to such a pipe, it is only necessary to lay the heater in a short range, which contributes to a reduction in the manufacturing cost of the urea SCR system.

  The present invention is not limited to the above-described embodiments, and various modifications can be made. For example, in the above embodiment, the exhaust gas purification device of the diesel engine 4 provided with the SCR catalyst 28 for NOx purification has been described. However, the exhaust gas purification device of the present invention may be used for a gasoline engine provided with a urea SCR system. .

1 is an overall configuration diagram illustrating an exhaust emission control device for a diesel engine according to Embodiment 1. FIG.

Explanation of symbols

2 Exhaust purification device 4 Engine (internal combustion engine)
DESCRIPTION OF SYMBOLS 10 Exhaust passage 14 Main exhaust passage 16 Switching valve 18 Sub exhaust passage 20 Case 28 SCR catalyst 38 Storage tank 60 Gap 64 Inlet port 68 Outlet port 69 Upstream exhaust pipe 70 Downstream exhaust pipe

Claims (4)

Exhaust gas purification of an internal combustion engine provided in a main exhaust passage of the internal combustion engine and including a selective reduction type NOx catalyst and urea aqueous solution supply means for supplying urea aqueous solution in a storage tank into exhaust gas upstream of the selective reduction type NOx catalyst In the device
A case for accommodating the storage tank with play;
An exhaust gas purification apparatus for an internal combustion engine, comprising exhaust gas bypass means for bypassing exhaust gas flowing in the main exhaust passage and guiding the exhaust gas through the case. The exhaust gas bypass means is
A sub-exhaust passage branched from the main exhaust passage on the downstream side of the selective reduction type NOx catalyst and having the case interposed in the middle thereof;
A switching valve that is provided at a branch position of the sub exhaust passage and switches a flow direction of the exhaust gas,
The switching valve connects an upstream portion and a downstream portion of the main exhaust passage, and has a first switching position for closing the sub exhaust passage, an upstream portion of the main exhaust passage, and the sub exhaust passage. 2. The exhaust gas purification apparatus for an internal combustion engine according to claim 1, further comprising a second switching position for connecting and closing a downstream portion of the men-in exhaust passage.   The exhaust purification of an internal combustion engine according to claim 1 or 2, wherein the case contains the storage tank so as to secure a gap between an inner surface thereof and an outer surface excluding the upper surface of the storage tank. apparatus. A temperature sensor disposed in the storage tank;
The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3, further comprising control means for controlling switching of the switching valve based on information from the temperature sensor.

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