JP4737143B2 - Exhaust gas purification device for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

  A particulate filter for collecting particulate matter in the exhaust gas is placed in the exhaust passage of the engine that burns under excess oxygen, and a fuel supply valve that can supply fuel is located upstream of the particulate filter. 2. Description of the Related Art Conventionally, an internal combustion engine is known which is disposed in an engine exhaust passage and is configured to supply fuel from a fuel supply valve when particulate matter deposited on a particulate filter is to be oxidized and removed.

  However, when particulate matter in the exhaust gas adheres to the nozzle hole of the fuel supply valve and this particulate matter is heated by the high-temperature exhaust gas, a so-called deposit is generated, and the fuel supply valve is clogged by this deposit. There is a fear. Therefore, an internal combustion engine in which fuel is regularly supplied from a fuel supply valve so that the fuel supply valve is not clogged even when it is not time to oxidize and remove particulate matter is known. (Refer to patent document 1 etc.).

JP 2007-71175 A

  However, it is not preferable from the viewpoint of energy consumption to supply fuel even though the particulate matter should not be oxidized and removed. This problem may also occur when a reducing agent is supplied to prevent clogging at a supply valve arranged in the exhaust passage in order to supply a reducing agent such as an aqueous urea solution.

  Therefore, there is a need for a new exhaust purification device that can prevent clogging of the supply valve without supplying fuel or reducing agent when fuel or reducing agent should not be supplied.

  According to the present invention, the particulate filter for collecting the particulate matter in the exhaust gas in the exhaust passage of the engine where combustion is performed under excess oxygen, and the reducing agent under excess oxygen. A catalyst suitable for reducing NOx in the exhaust gas is disposed, and a single supply valve capable of selectively supplying fuel or a reducing agent is disposed in the particulate filter and the engine exhaust passage upstream of the catalyst. When the particulate matter deposited on the particulate filter is to be oxidized and removed, the fuel is supplied from the supply valve. When the particulate matter deposited on the particulate filter is not to be removed by oxidation, the reducing valve is supplied from the supply valve. An exhaust emission control device for an internal combustion engine is provided.

  Further, according to the present invention, the particulate filter for collecting particulate matter in the exhaust gas in the exhaust passage of the engine where combustion is performed under an excess of oxygen, and the reduction under the excess of oxygen. A catalyst suitable for reducing NOx in the exhaust gas by the agent is disposed, and a fuel supply valve capable of selectively supplying fuel or a substance other than fuel is disposed in the engine exhaust passage upstream of the particulate filter. In addition, when a reducing agent supply valve capable of selectively supplying a reducing agent or a substance other than the reducing agent is disposed in the engine exhaust passage upstream of the catalyst, the particulate matter deposited on the particulate filter should be oxidized and removed. When supplying fuel from the fuel supply valve and supplying substances other than the reducing agent from the reducing agent supply valve, and particulate matter deposited on the particulate filter should not be oxidized and removed Exhaust purification system of an internal combustion engine so as to supply the reducing agent from the reducing agent supply valve to supply a substance other than fuel is provided from the charge supply valve.

  When the fuel or reducing agent should not be supplied, the supply valve can be prevented from being clogged without supplying the fuel or reducing agent.

  FIG. 1 shows a case where the present invention is applied to a compression ignition type internal combustion engine. The present invention can also be applied to a gasoline engine.

  Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electronically controlled fuel injection valve for injecting fuel into each combustion chamber 2, 4 is an intake manifold, and 5 is an exhaust manifold. Respectively. The intake manifold 4 is connected to the outlet of the compressor 7 c of the exhaust turbocharger 7 via the intake duct 6, and the inlet of the compressor 7 c is connected to the air cleaner 9 via the air flow meter 8. An electrically controlled throttle valve 10 is arranged in the intake duct 6, and a cooling device 11 for cooling intake air flowing in the intake duct 6 is arranged around the intake duct 6. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 11, and the intake air is cooled by the engine cooling water. On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 t of the exhaust turbocharger 7, and the outlet of the exhaust turbine 7 t is connected to the exhaust aftertreatment device 20.

  The exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 12, and an electrically controlled EGR control valve 13 is disposed in the EGR passage 12. A cooling device 14 for cooling the EGR gas flowing in the EGR passage 12 is disposed around the EGR passage 12. In the embodiment shown in FIG. 1, engine cooling water is guided into the cooling device 14, and the EGR gas is cooled by the engine cooling water. On the other hand, each fuel injection valve 3 is connected to a common rail 16 via a fuel supply pipe 15, and this common rail 16 is connected to a fuel tank 18 via an electronically controlled variable discharge pump 17. The fuel in the fuel tank 18 is supplied into the common rail 16 by the fuel pump 17, and the fuel supplied into the common rail 16 is supplied to the fuel injection valve 3 through each fuel supply pipe 15.

  The exhaust aftertreatment device 20 includes a catalytic converter 22 connected to an outlet of the exhaust turbine 7t through an exhaust pipe 21, and the catalytic converter 22 is connected to an exhaust pipe 23. In the catalytic converter 22, a particulate filter 24 for collecting particulate matter in the exhaust gas and suitable for reducing NOx in the exhaust gas with a reducing agent such as ammonia under excess oxygen. The NOx selective reduction catalyst 25 is disposed. The particulate filter 24 carries a catalyst having an oxidation function. Further, a differential pressure sensor 26 for detecting the differential pressure across the particulate filter 24 is attached to the catalytic converter 22.

  Further, an electromagnetically controlled supply valve 27 is attached to the exhaust pipe 21, and an electrically controlled three-way valve 28 is connected to the supply valve 27. The three-way valve 28 is connected on the one hand to the common rail 16 and on the other hand to a tank 30 in which a liquid containing an ammonia generating compound that generates ammonia is stored via a pump 29.

  The supply valve 27 is selectively connected to one of the common rail 16 and the tank 30 by a three-way valve 28. When the supply valve 27 is connected to the common rail 16, fuel is supplied from the supply valve 27 into the exhaust pipe 21. When the supply valve 27 is connected to the tank 30, an ammonia generating compound is contained in the exhaust pipe 21 from the supply valve 27. Liquid is supplied. In the embodiment according to the present invention, the fuel is a hydrocarbon such as light oil.

  The electronic control unit 40 is composed of a digital computer, and is connected to each other by a bidirectional bus 41. A ROM (read only memory) 42, a RAM (random access memory) 43, a CPU (microprocessor) 44, an input port 45 and an output port 46 are connected. It comprises. The air flow meter 8 generates an output voltage proportional to the amount of intake air, and this output voltage is input to the input port 45 via the corresponding AD converter 47. The output signal of the differential pressure sensor 26 is input to the input port 45 through the corresponding AD converter 47. A load sensor 50 that generates an output voltage proportional to the amount of depression of the accelerator pedal 49 is connected to the accelerator pedal 49, and the output voltage of the load sensor 50 is input to the input port 45 via the corresponding AD converter 47. Further, the input port 45 is connected to a crank angle sensor 51 that generates an output pulse every time the crankshaft rotates, for example, 30 °. On the other hand, the output port 46 is connected to the fuel injection valve 3, the throttle valve 10 drive device, the EGR control valve 13, the fuel pump 17, the supply valve 27, the three-way valve 28, and the pump 29 through corresponding drive circuits 48.

  As described above, the liquid containing the ammonia generating compound is supplied into the exhaust pipe 21 upstream of the NOx selective reduction catalyst 25. There are various types of ammonia generating compounds capable of generating ammonia, and therefore various compounds can be used as the ammonia generating compound. In the embodiment according to the present invention, urea is used as the ammonia generating compound, and an aqueous urea solution is used as the liquid containing the ammonia generating compound. Therefore, hereinafter, the present invention will be described by taking as an example the case where the urea aqueous solution is supplied into the exhaust pipe 21 upstream of the NOx selective reduction catalyst 25.

On the other hand, the NOx selective reduction catalyst 25 as described above consists NOx selective reduction catalyst, in the embodiment shown in FIG. 1 titania as a carrier as this NOx selective reduction catalyst, a catalyst V ₂ O carrying vanadium oxide on this carrier ₅ / TiO ₂ (hereinafter referred to as vanadium / titania catalyst) or zeolite Cu / ZSM5 (hereinafter referred to as copper zeolite catalyst) in which copper is supported on this support is used.

In the internal combustion engine shown in FIG. 1, combustion is performed under an excess of oxygen, and the exhaust gas contains excess oxygen. When urea aqueous solution is supplied to the exhaust gas containing excess oxygen, NO contained in the exhaust gas is reduced on the NOx selective reduction catalyst 25 by ammonia NH ₃ generated from urea CO (NH ₂ ) ₂ (for example, 2NH ₃ + 2NO + 1 / 2O ₂ → 2N ₂ + 3H ₂ O).

  That is, urea in the supplied aqueous urea solution first adheres to the NOx selective reduction catalyst 25. At this time, if the temperature of the NOx selective reduction catalyst 25 is high, for example, approximately 350 ° C. or higher, urea is thermally decomposed at once and ammonia is generated.

  On the other hand, when the temperature of the NOx selective reduction catalyst 25 is from about 132 ° C. to about 350 ° C., urea is once stored in the NOx selective reduction catalyst 25, and then a little ammonia from the urea stored in the NOx selective reduction catalyst 25. It is generated and released one by one. The generation of ammonia in this case is considered to be due to the form change of urea on the NOx selective reduction catalyst 25. That is, urea changes to biuret at approximately 132 ° C., biuret changes to cyanuric acid at approximately 190 ° C., and cyanuric acid changes to cyanic acid or isocyanic acid at approximately 360 ° C. Alternatively, as the elapsed time from storage in the NOx selective reduction catalyst 25 becomes longer, urea changes to biuret, biuret changes to cyanuric acid, and cyanuric acid changes to cyanic acid or isocyanic acid. It is considered that ammonia is generated little by little in the process of such morphological change.

  When the urea aqueous solution is supplied to the NOx selective reduction catalyst 25 when the temperature of the NOx selective reduction catalyst 25 is approximately 132 ° C. or less, which is the thermal decomposition temperature of urea, urea in the urea aqueous solution is stored in the NOx selective reduction catalyst 25, Occasionally ammonia is not generated from the stored urea. However, for example, when the engine acceleration operation is subsequently performed and the temperature of the NOx selective reduction catalyst 25 becomes high, ammonia generated from urea stored in the NOx selective reduction catalyst 25 is generated and released little by little.

  That is, in the NOx selective reduction catalyst 25, it is considered that ammonia is generated by the thermal decomposition of urea or the storage of the NOx selective reduction catalyst 25 once it changes its form. In the embodiment according to the present invention, the amount of ammonia generated in the NOx selective reduction catalyst 25 in this way substantially matches the amount necessary for reducing the total amount of NOx flowing into the NOx selective reduction catalyst 25. The aqueous urea solution is supplied from the supply valve 27.

  On the other hand, the particulate matter contained in the exhaust gas is collected on the particulate filter 24 and sequentially oxidized. However, when the amount of particulate matter collected is larger than the amount of particulate matter to be oxidized, particulate matter gradually accumulates on the particulate filter 24. In this case, if the amount of particulate matter deposited increases, the engine output Will be reduced. Therefore, when the amount of deposited particulate matter increases, the deposited particulate matter must be removed. In this case, if the temperature of the particulate filter 24 is raised to about 600 ° C. under excess oxygen, the deposited particulate matter is oxidized and removed.

  Therefore, in the embodiment according to the present invention, when the amount of the particulate matter deposited on the particulate filter 24 exceeds an allowable amount, that is, the differential pressure dP before and after the particulate filter 24 detected by the differential pressure sensor 26 is an allowable value. When the pressure exceeds the value, the fuel is supplied from the supply valve 27 in the presence of excess oxygen, and the temperature of the particulate filter 24 is raised by the oxidation reaction heat of the fuel, thereby removing the deposited particulate matter by oxidation. ing.

  That is, in the embodiment according to the present invention, as shown in FIG. 2, until the differential pressure dP across the particulate filter 24 exceeds the allowable value MAX, that is, particulate matter deposited on the particulate filter 24 is removed by oxidation. If not, the aqueous urea solution is supplied from the supply valve 27 in the form of continuous pulses, and at this time, the fuel is not supplied from the supply valve 27. Next, as indicated by X in FIG. 2, when the differential pressure dP across the particulate filter 24 exceeds the allowable value MAX, that is, when particulate matter deposited on the particulate filter 24 is to be removed by oxidation, the fuel is supplied from the supply valve 27. Are supplied in the form of continuous pulses, and at this time, the urea aqueous solution is not supplied from the supply valve 27. Next, as indicated by Y in FIG. 2, when the front-rear differential pressure dP of the particulate filter 24 decreases to a predetermined set value MIN, the aqueous urea solution is supplied again from the supply valve 27, and the fuel from the supply valve 27 is supplied. The supply is stopped again.

  In this way, the fuel or urea aqueous solution is continuously supplied from the supply valve 27 in the form of continuous pulses, so that the supply valve 27 is prevented from being clogged. Further, when the particulate particulate matter on the particulate filter 24 is to be oxidized and removed, the fuel is supplied from the supply valve 27, so that the particulate particulate matter is reliably removed by oxidation and the particulate particulate matter should be oxidized and removed. If not, no fuel is supplied from the supply valve 27, so the fuel consumption does not increase.

  By the way, when the temperature of the NOx selective reduction catalyst 25 becomes considerably high, the NOx purification rate of the NOx selective reduction catalyst 25 becomes low. When the accumulated particulate matter on the particulate filter 24 is removed by oxidation, the temperature of the NOx selective reduction catalyst 25 is also considerably high. At this time, the NOx purification rate of the NOx selective reduction catalyst 25 is low. Therefore, even if the urea aqueous solution is supplied when the deposited particulate matter is removed by oxidation, urea cannot be effectively used for NOx reduction. In the embodiment according to the present invention, the urea aqueous solution is not supplied when the deposited particulate matter is oxidized and removed. Therefore, the urea aqueous solution can be effectively used for NOx reduction. On the other hand, when the deposited particulate matter is not oxidized and removed, the urea aqueous solution is supplied from the supply valve 27, so that the NOx reduction action is reliably performed.

  Therefore, generally speaking, in the embodiment according to the present invention, the particulate filter 24 for collecting particulate matter in the exhaust gas in the exhaust passage of the engine in which combustion is performed under excess oxygen, And a catalyst 25 suitable for reducing NOx in the exhaust gas with a reducing agent under an excess of oxygen, and a single supply valve 27 capable of selectively supplying fuel or a reducing agent is provided as a particulate filter. 24 and the catalyst 25 are disposed in the engine exhaust passage upstream, and when particulate matter deposited on the particulate filter 24 is to be oxidized and removed, fuel is supplied from the supply valve 27 and deposited on the particulate filter 24. When the particulate matter should not be removed by oxidation, the reducing agent is supplied from the supply valve 27.

  FIG. 3 shows a routine for executing the supply control of the embodiment according to the present invention. This routine is executed by interruption every predetermined time.

  Referring to FIG. 3, first, at step 100, it is judged if the particulate matter deposited on the particulate filter 24 should be oxidized and removed. In the embodiment according to the present invention, it is determined that the deposited particulate matter should be removed by oxidation until the differential pressure dP across the particulate filter 24 exceeds the allowable value MAX and decreases to the set value MIN. It is determined that the particulate matter should not be removed by oxidation. When it is determined that the deposited particulate matter should not be removed by oxidation, the routine proceeds to step 101 where urea aqueous solution is supplied from the supply valve 27. On the other hand, when it is determined that the deposited particulate matter should be removed by oxidation, the process proceeds from step 100 to step 102 where fuel is supplied from the supply valve 27.

  FIG. 4 shows another embodiment according to the present invention. In another embodiment of the present invention, an electromagnetically controlled fuel supply valve 61 is attached to the exhaust pipe 21, and an electrically controlled three-way valve 62 is connected to the fuel supply valve 61. The three-way valve 62 is connected to the common rail 16 on the one hand, and connected to a tank 64 in which substances other than fuel and aqueous urea solution are stored via the pump 63 on the other hand. Further, an electromagnetically controlled urea supply valve 65 is attached to the exhaust pipe 21, and an electrically controlled three-way valve 66 is connected to the urea supply valve 65. The three-way valve 66 is connected on the one hand to a urea tank 68 in which a urea aqueous solution is stored via a urea pump 67, and on the other hand to a tank 64 via a pump 63.

  The fuel supply valve 61 is selectively connected to one of the common rail 16 and the tank 64 by a three-way valve 62. When the fuel supply valve 61 is connected to the common rail 16, fuel is supplied from the fuel supply valve 61 into the exhaust pipe 21. When the fuel supply valve 61 is connected to the tank 64, fuel is supplied from the fuel supply valve 61 into the exhaust pipe 21. Substances other than the urea aqueous solution are supplied. On the other hand, the urea supply valve 65 is selectively connected to one of the urea tank 68 and the tank 64 by a three-way valve 66. When the urea supply valve 65 is connected to the urea tank 68, the urea aqueous solution is supplied from the urea supply valve 65 into the exhaust pipe 21, and when the urea supply valve 65 is connected to the tank 64, the urea supply valve 65 is connected to the exhaust pipe 21. Substances other than the fuel and the aqueous urea solution are supplied.

  Various liquids or gases can be used for substances other than the fuel and the aqueous urea solution. In another embodiment according to the present invention, inexpensive and easy-to-handle water is used as a substance other than the fuel and the urea aqueous solution.

  Next, another embodiment of the present invention will be described with reference to FIG. As shown in FIG. 5, until the differential pressure dP across the particulate filter 24 exceeds the allowable value MAX, that is, when the particulate matter deposited on the particulate filter 24 should not be removed by oxidation, the fuel supply valve 61. From this time, water is supplied in the form of continuous pulses, and at this time, fuel is not supplied from the fuel supply valve 61. Further, the urea aqueous solution is supplied from the urea supply valve 65 in the form of continuous pulses, and at this time, water is not supplied from the urea supply valve 65. Next, as indicated by X in FIG. 5, when the differential pressure dP across the particulate filter 24 exceeds the allowable value MAX, that is, when particulate matter deposited on the particulate filter 24 is to be removed by oxidation, the fuel supply valve 61 The fuel is supplied in the form of continuous pulses, and at this time, water is not supplied from the fuel supply valve 61. Further, water is supplied from the urea supply valve 65 in the form of continuous pulses, and at this time, the urea aqueous solution is not supplied from the urea supply valve 65. Next, as indicated by Y in FIG. 5, when the differential pressure dP across the particulate filter 24 decreases to a predetermined set value MIN, water is supplied again from the fuel supply valve 61, and urea aqueous solution is supplied from the urea supply valve 65. Is supplied again.

  In this way, fuel or water continues to be supplied from the fuel supply valve 61 in the form of continuous pulses, and urea aqueous solution or water continues to be supplied from the urea supply valve 65 in the form of continuous pulses. Therefore, the fuel supply valve 61 and the urea supply The clogging of the valve 65 can be prevented. In addition, since fuel is supplied from the fuel supply valve 61 when the particulate matter on the particulate filter 24 is to be oxidized and removed, the particulate matter is reliably removed by oxidation, and the particulate matter is oxidized and removed. When it should not be, fuel is not supplied from the fuel supply valve 61, so the fuel consumption does not increase. Further, since the urea aqueous solution is supplied from the urea supply valve 65 when the deposited particulate matter should not be removed by oxidation, the NOx reduction action is performed reliably, and when the deposited particulate matter should be removed by oxidation, the urea supply valve 65 is provided. Since no urea aqueous solution is supplied, the consumption of urea aqueous solution does not increase.

  The water supplied from the fuel supply valve 61 or the urea supply valve 65 is for preventing the fuel supply valve 61 or the urea supply valve 65 from being clogged, and a small amount is sufficient. Therefore, in the example shown in FIG. 5, the time interval of the water supply pulse is set longer than the time interval of the fuel supply pulse in the fuel supply valve 61, and the time interval of the water supply pulse is set in the urea supply valve 65. It is set longer than the time interval of the supply pulse.

  Therefore, in general terms, in another embodiment according to the present invention, a particulate filter for collecting particulate matter in exhaust gas in the exhaust passage of an engine that burns under excess oxygen. 24 and a catalyst 25 suitable for reducing NOx in the exhaust gas with a reducing agent under an excess of oxygen are disposed, and a fuel supply valve 61 capable of selectively supplying fuel or a substance other than fuel is put in the patty. The particulate filter 24 is disposed in the engine exhaust passage upstream of the curate filter 24 and the reducing agent supply valve 65 capable of selectively supplying a reducing agent or a substance other than the reducing agent is disposed in the engine exhaust passage upstream of the catalyst 25. When the particulate matter deposited on 24 is to be oxidized and removed, the fuel is supplied from the fuel supply valve 61 and the reducing agent supply valve 65 is supplied with a substance other than the reducing agent. Rate when the filter 24 the deposited particulate matter on not to be removed by oxidation will be referred to from the reducing agent feed valve 65 supplies a substance other than the fuel from the fuel supply valve 61 so as to supply the reducing agent.

  FIG. 6 shows a routine for executing the supply control of another embodiment according to the present invention. This routine is executed by interruption every predetermined time.

  Referring to FIG. 6, first, at step 200, it is judged if the particulate matter deposited on the particulate filter 24 should be removed by oxidation. When it is determined that the deposited particulate matter should not be removed by oxidation, the routine proceeds to step 201 where water is supplied from the fuel supply valve 61 to prevent clogging, and an aqueous urea solution is supplied from the urea supply valve 65. On the other hand, when it is determined that the deposited particulate matter should be oxidized and removed, the routine proceeds from step 200 to step 202 where fuel is supplied from the fuel supply valve 61 and water is supplied from the urea supply valve 65 to prevent clogging. Is done.

1 is an overall view of an internal combustion engine. It is a time chart for demonstrating the Example by this invention. It is a flowchart which shows a supply control routine. It is a general view of the internal combustion engine of another Example by this invention. It is a time chart for demonstrating another Example by this invention. It is a flowchart which shows the supply control routine of another Example by this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Engine body 21 Exhaust pipe 24 Particulate filter 25 NOx selective reduction catalyst 27 Supply valve 61 Fuel supply valve 65 Urea supply valve

Claims (4)

  A particulate filter for collecting particulate matter in the exhaust gas in the exhaust passage of the engine that burns under excess oxygen, and NOx in the exhaust gas by the reducing agent under excess oxygen And a single supply valve capable of selectively supplying fuel or a reducing agent is disposed in the particulate filter and the engine exhaust passage upstream of the catalyst, and is disposed on the particulate filter. An internal combustion engine in which fuel is supplied from a supply valve when deposited particulate matter is to be removed by oxidation, and a reducing agent is supplied from the supply valve when particulate matter deposited on the particulate filter is not to be removed by oxidation. Engine exhaust purification system.   A particulate filter for collecting particulate matter in the exhaust gas in the exhaust passage of the engine that burns under excess oxygen, and NOx in the exhaust gas by the reducing agent under excess oxygen A catalyst suitable for reduction and a fuel supply valve capable of selectively supplying fuel or a substance other than fuel are arranged in the engine exhaust passage upstream of the particulate filter, and other than the reducing agent or reducing agent. A reductant supply valve capable of selectively supplying the above substances is arranged in the engine exhaust passage upstream of the catalyst, and fuel is supplied from the fuel supply valve when the particulate matter deposited on the particulate filter is to be removed by oxidation. At the same time, substances other than the reducing agent are supplied from the reducing agent supply valve, and when the particulate matter deposited on the particulate filter should not be removed by oxidation, the fuel supply valve supplies other than fuel. Exhaust purification system of an internal combustion engine so as to supply the reducing agent from the reducing agent supply valve supplies the material.   The exhaust emission control device for an internal combustion engine according to claim 2, wherein one or both of the substance other than the fuel and the substance other than the reducing agent is water.   The reducing agent is composed of an ammonia generating compound, and the catalyst is a catalyst suitable for reducing NOx in exhaust gas with ammonia under an excess of oxygen, and at least of the ammonia generating compound supplied to the catalyst. A part of the catalyst is stored in the catalyst, and ammonia is generated from an ammonia generating compound stored in the catalyst, and the catalyst has a function of reducing NOx in exhaust gas by the generated ammonia. The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 3.

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