JP2007009810A - METHOD FOR CONTROLLING SULFUR PURGE OF NOx ELIMINATION SYSTEM AND NOx ELIMINATION SYSTEM - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for controlling sulfur purge of an NOx elimination system and the NOx elimination system capable of raising temperature of an NOx elimination catalyst device to a temperature at which sulfur purge can be done in a short period of time at a time of sulfur purge and capable of quickly and efficiently making air fuel ratio of exhaust gas rich enough to perform sulfur purge. <P>SOLUTION: In sulfur purge control for recovering the NOx elimination catalyst device 22 from sulfur poisoning in the NOx elimination system 1 provided with the NOx elimination catalyst device 22 in an exhaust gas passage 3 of an engine E and provided with an exhaust gas throttle valve 9 in the exhaust gas passage 3, an EGR valve 11 is fully opened and the exhaust gas throttle valves 8, 9 are controlled to close during sulfur purge control. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sulfur purge control method and a NOx purification system for a NOx purification system provided with an NOx purification catalyst device and an exhaust throttle valve in an exhaust passage of an internal combustion engine.

  Exhaust gas regulations on automobiles are becoming stricter, and it is becoming a situation that cannot be caught up by technological development on the engine side alone. For this reason, it is indispensable to purify the exhaust gas with an aftertreatment device, and NOx (nitrogen oxide) is reduced and removed from the exhaust gas of internal combustion engines such as diesel engines and some gasoline engines and various combustion devices. Various researches and proposals have been made on NOx catalysts for the purpose and diesel particulate filter devices (hereinafter referred to as DPF devices) that remove particulate matter (hereinafter referred to as PM) in these exhaust gases. .

  Among these, as NOx reduction catalysts, NOx occlusion reduction type catalysts, NOx direct reduction type catalysts, ammonia selective reduction type NOx catalysts (Selective Catalystic Reduction: SCR catalyst) and the like have been proposed.

  An apparatus carrying a NOx occlusion reduction type catalyst comprises a noble metal catalyst having an oxidation function and a NOx occlusion material having a NOx occlusion function such as an alkali metal, and thereby, depending on the oxygen concentration in the exhaust gas. Two functions of NOx occlusion and NOx release / purification are demonstrated.

  That is, when the air-fuel ratio of the exhaust gas flowing into the NOx occlusion reduction type catalyst device is lean, the nitrogen monoxide in the exhaust gas is oxidized by the noble metal catalyst to become nitrogen dioxide, and this nitrogen dioxide becomes the NOx occlusion material. Occluded as nitrate. On the other hand, when the air-fuel ratio of the exhaust gas is in a rich state, nitrate is decomposed from the NOx storage material and NOx is released, and this NOx is caused by unburned hydrocarbons in the exhaust gas due to the catalytic action of the noble metal catalyst. Reduced to nitrogen by carbon oxide or the like. For this reason, when the NOx occlusion capacity of the NOx occlusion material approaches saturation, regeneration control for recovering the NOx occlusion ability that makes the air-fuel ratio in the exhaust gas rich is performed.

  However, this NOx occlusion material occludes NOx in the form of nitrate, but also functions as a sulfur occlusion material because it occludes the sulfur content in the fuel in the form of sulfate. In addition, since SOx is less likely to be released than NOx, the nitrate formation reaction is inhibited by the sulfur content. Therefore, there is a problem of sulfur poisoning in which the NOx occlusion ability decreases with each mileage.

  Further, an apparatus carrying a NOx direct reduction catalyst is configured by carrying a catalyst component such as rhodium (Rh) or palladium (Pd) on a support such as β-type zeolite, and directly reduces NOx. . And during this reduction, oxygen is adsorbed to the metal that is the active substance of the catalyst and the NOx reduction performance deteriorates. Therefore, in order to recover the NOx reduction performance, the air-fuel ratio of the exhaust gas is made rich, Regeneration control for NOx reduction performance recovery is performed to regenerate and activate the active substance of the catalyst.

  However, even in this NOx direct reduction type catalyst device, there is a problem of sulfur poisoning in which the sulfur content contained in the fuel is adsorbed and the NOx reduction ability decreases with an increase in the amount of adsorption of the sulfur content.

  In addition, an apparatus that supports an ammonia selective reduction type NOx catalyst has a honeycomb structure support (catalyst structure) formed of cordierite, aluminum oxide, titanium oxide, etc., and titania-vanadium, zeolite, chromium oxide, manganese oxide. , Molybdenum oxide, titanium oxide, tungsten oxide and the like. In this catalyst device, ammonia-based solution such as urea aqueous solution, ammonia, ammonia water or the like is added to exhaust gas flowing into the catalyst device, and NOx is purified by selective reduction reaction of the generated ammonia with NOx. .

  In this ammonia selective reduction type NOx catalyst device, since the reduction reaction can be continuously performed, regeneration control is not particularly required. However, in this ammonia selective reduction type NOx catalyst device, sulfur contained in the fuel is also included. There is a problem of sulfur poisoning in which NO is reduced and the NOx reduction ability decreases with an increase in the amount of sulfur adsorbed.

  As a countermeasure against sulfur poisoning of these catalyst devices, sulfur purge control is required to remove sulfur by a reducing agent such as carbon monoxide or hydrocarbon. In this sulfur purge control, the catalyst temperature is kept at a higher temperature (for example, a high temperature state of 600 ° C. or higher) than in the regeneration control for recovery of the NOx storage capability and the NOx direct reduction capability, and the storage material is stored. The sulfur component is thermally decomposed and released into the exhaust gas as an oxide, and the released sulfur oxide is reduced by reacting with a reducing agent in a reducing atmosphere in which oxygen is insufficient.

  In this sulfur purge control, the air-fuel ratio of the exhaust gas flowing into the catalyst device carrying these NOx purification catalysts is made rich, and the exhaust temperature and the catalyst temperature are increased by post injection or in-pipe injection in the cylinder injection. Air-fuel ratio rich control is performed.

  As one of the sulfur purge controls, in the NOx storage reduction catalyst (NOx storage reduction catalyst device), unnecessary temperature increase control is reduced, fuel efficiency is improved, and SOx poisoning recovery is achieved even in light load conditions for a short time. In order to enable this, it is estimated before the engine operating condition necessary for SOx poisoning recovery control is reached, based on the information of the navigation system, the history of the running state of the vehicle, etc. An exhaust emission control device for an internal combustion engine capable of performing temperature rise control has been proposed (see, for example, Patent Document 1).

  However, in order to regenerate the sulfur poisoning of the NOx purification catalyst device, it is indispensable to control the temperature of the exhaust gas. Making the air-fuel ratio rich state causes a significant deterioration in fuel consumption under normal engine control. Further, if the sulfur purge control is performed during traveling, drivability such as traveling performance and riding comfort deteriorates.

  Furthermore, when the internal combustion engine is in a high load state, in order to make the air-fuel ratio of the exhaust gas rich, it is oxidized by the oxidation catalyst upstream of the NOx purification catalyst, and the released sulfur content is reduced. When the reducing agent is added, the reducing agent that has passed through the oxidation catalyst burns in the NOx purification catalyst device, and the catalyst temperature rises, causing a problem of inducing thermal deterioration of the catalyst.

Therefore, it is preferable to stop the vehicle so that the engine is in a stable state. However, since the exhaust gas temperature decreases when the engine is in the idle state, the catalyst temperature is raised to a temperature at which sulfur purge can be performed quickly and efficiently. Is important.
JP 2003-155925 A

  The present invention has been made in order to solve the above-described problems. The object of the present invention is to increase the temperature of the NOx purification catalyst device to a temperature at which sulfur purging can be performed in a short time and to exhaust gas during sulfur purging. It is an object of the present invention to provide a sulfur purge control method for a NOx purification system and a NOx purification system that can make the air-fuel ratio of the air-fuel ratio rich state in which sulfur purge can be performed quickly and efficiently.

  A sulfur purge control method for a NOx purification system for achieving the above object is a NOx purification system in which a NOx purification catalyst device is disposed in an exhaust passage of an internal combustion engine and an exhaust throttle valve is disposed in an exhaust passage. A sulfur purge control method for recovering the NOx purification catalyst device from sulfur poisoning, wherein the EGR valve is fully opened and the exhaust throttle valve is closed during the sulfur purge control. And

  According to this configuration, when the sulfur purge control is executed, the exhaust pressure is increased by closing the exhaust throttle valve such as the exhaust brake or the exhaust throttle to perform the exhaust throttle. Due to this effect, high temperature combustion gas can remain in the cylinder (inside the cylinder), or can flow backward from the exhaust valve into the cylinder, so-called internal EGR can be caused to raise the cylinder internal temperature and the exhaust gas temperature. .

  In addition, since the EGR valve is fully opened, the increase in exhaust pressure can further increase the EGR rate that is limited by the pipe diameter of the EGR path, the lift amount of the EGR valve, the performance of the EGR cooler, and the like. By combustion at this high EGR rate, the air-fuel ratio of the exhaust gas can be brought into a rich state in which sulfur purge can be performed quickly.

  Further, since the exhaust gas can be raised to a high temperature, the temperature of the NOx purification catalyst device can be increased in a short time, and the NOx purification catalyst device can be maintained at a high temperature. As a result, the sulfur purge can be efficiently performed, and the sulfur purge time can be shortened.

  In the above-described sulfur purge control method of the NOx purification system, when it is determined that the sulfur purge control of the NOx purification catalyst device is necessary, an instruction to stop the vehicle on which the internal combustion engine and the NOx purification catalyst device are mounted is generated. When the vehicle stops after the instruction, if the engine speed of the internal combustion engine when the vehicle is stopped is increased to a predetermined engine speed higher than the engine speed of normal idle operation, Since it becomes possible to avoid performing the control, it is possible to prevent the drivability from deteriorating in the sulfur purge during traveling.

  Further, in the above-described sulfur purge control method of the NOx purification system, if the intake throttle valve is controlled to be closed during the sulfur purge control, the intake air amount and the pressure on the intake manifold side can be reduced. The temperature inside the cylinder and the exhaust temperature rise can be made easier.

  In addition, a NOx purification system for achieving the above object includes a NOx purification catalyst device disposed in an exhaust passage of an internal combustion engine, an exhaust throttle valve disposed in the exhaust passage, and the NOx purification catalyst device. And a control device that performs sulfur purge control for recovering sulfur from poisoning, wherein the control device fully opens the EGR valve and controls the exhaust throttle valve during the sulfur purge control. It is configured to perform valve closing control.

  With this configuration, during the sulfur purge, the NOx purification catalyst device can be heated to a temperature at which sulfur purge can be performed in a short time, and the air-fuel ratio of the exhaust gas can be brought into a rich state in which sulfur purge can be performed quickly.

  In the NOx purification system, when the control device determines that the sulfur purge control is necessary, an instruction to stop the vehicle on which the internal combustion engine and the NOx purification catalyst device are mounted is generated. When the vehicle is stopped, the engine speed of the internal combustion engine when the vehicle is stopped is controlled to increase to a predetermined engine speed higher than the engine speed of normal idle operation. Therefore, it is possible to prevent the drivability from being deteriorated during the sulfur purge during traveling.

  Furthermore, in the above NOx purification system, if the control device is configured to control the intake throttle valve to be closed during the sulfur purge control, the intake air amount and the pressure on the intake manifold side can be reduced. Cooling by fresh air can be reduced, and heat retention in the cylinder and exhaust temperature rise can be made easier.

  In the above NOx purification system, examples of the NOx purification catalyst device include a NOx occlusion reduction type catalyst device, a NOx direct reduction type catalyst device, and an ammonia selective reduction type NOx catalyst device.

  According to the sulfur purge control method and NOx purification system of the NOx purification system according to the present invention, the exhaust pressure can be increased by using an exhaust throttle such as an exhaust brake or an exhaust throttle when performing the sulfur purge. it can.

  This exhaust pressure increase makes it easy to increase the amount of exhaust gas in the cylinder and maintain the temperature in the cylinder at a high temperature or to raise the exhaust gas to a high temperature. The NOx purification catalyst device can be maintained at a high temperature.

  In addition, by fully opening the EGR valve, the amount of exhaust gas in the cylinder can be increased, and the air-fuel ratio of the exhaust gas can be brought into a rich state where sulfur purge can be performed quickly.

  Therefore, the sulfur purge can be performed quickly and efficiently, and the time required for the sulfur purge can be shortened.

  Hereinafter, a sulfur purge control method and a NOx purification system of a NOx purification system according to an embodiment of the present invention will be described with reference to the drawings.

  Here, the NOx occlusion reduction type catalyst device will be described as an example of the NOx purification catalyst device. However, the present invention is directed to a NOx purification catalyst device that performs sulfur purge in an air-fuel ratio rich state, such as a NOx direct reduction type catalyst device. Is applicable. Further, a DPF (diesel particulate filter) device is provided on the downstream side of the NOx occlusion reduction type catalyst device so that smoke is collected by the DPF device against smoke deterioration in the sulfur purge control. Also good.

  The rich state of exhaust gas here does not necessarily require rich combustion in the cylinder, but the amount of air and fuel supplied into the exhaust gas flowing into the NOx occlusion reduction type catalyst device (combusted in the cylinder). Or a rich state in which the amount of fuel is larger than the stoichiometric air-fuel ratio. This amount of fuel includes the amount of reducing agent (fuel) injected directly into the exhaust gas by exhaust pipe injection.

  FIG. 1 shows a configuration of a NOx purification system 1 according to an embodiment of the present invention. In this exhaust gas purification system 1, an exhaust gas purification device 20 having an oxidation catalyst device 21 and a NOx occlusion reduction catalyst device (NOx purification catalyst device) 22 is disposed in an exhaust passage 3 of an engine (internal combustion engine) E.

This oxidation catalyst device 21 has a catalyst coating layer of active aluminum oxide (Al ₂ O ₃ ), platinum (Pt), palladium (Pd), rhodium on the surface of a carrier made of honeycomb cordierite or heat-resistant steel. It is formed by supporting a catalytically active component made of a noble metal such as (Rh). The oxidation catalyst device 21 oxidizes reducing agents such as HC and CO in the inflowing exhaust gas to bring the exhaust gas into a low oxygen state and raise the exhaust temperature by combustion heat (oxidation reaction heat).

The NOx occlusion reduction type catalyst device 22 has a monolithic catalyst formed of cordierite, silicon carbide (SiC), ultra-thin plate stainless steel, etc., and a catalyst coating layer of aluminum oxide (Al ₂ O ₃ ), titanium oxide (TiO), or the like. And a catalyst metal layer such as platinum (Pt) and palladium (Pd) and a NOx storage material (NOx storage material) such as barium (Ba) are supported on the catalyst coat layer. The monolith catalyst structural material carrier has a large number of cells, and the catalyst coat layer provided on the inner wall of the cells has a large surface area to increase the contact efficiency with the exhaust gas. .

  In this NOx occlusion reduction type catalytic device 22, when the exhaust gas having a high oxygen concentration is in an air-fuel ratio lean state, the NOx occlusion material occludes NOx in the exhaust gas, thereby purifying NOx in the exhaust gas. Further, when the air-fuel ratio rich state of the exhaust gas with low or zero oxygen concentration is released, the stored NOx is released and the released NOx is reduced by the catalytic action of the catalytic metal. Thereby, the outflow of NOx into the atmosphere is prevented.

  A mass air flow sensor (MAF sensor) 5 for measuring the intake air amount and an intake throttle valve 7 for adjusting the intake air amount are disposed in the intake passage 2, and the exhaust passage 3 on the upstream side of the exhaust gas purification device 20 is disposed in the intake passage 2. An exhaust brake 8 is disposed, or an exhaust throttle 9 is disposed in the exhaust passage 3 on the downstream side. The EGR passage 4 is provided with an EGR cooler 10 and an EGR valve 11 that adjusts the amount of EGR.

  A first oxygen sensor 25 is disposed upstream of the oxidation catalyst device 21, and a second oxygen concentration sensor 26 is disposed downstream of the NOx storage reduction catalyst device 22. Since the first oxygen concentration sensor 25 detects the oxygen concentration (air-fuel ratio, excess air ratio λ) necessary for controlling the rich depth, a wide-range λ sensor is used. On the other hand, the second oxygen concentration sensor 26 only needs to be able to detect whether or not the air-fuel ratio has become rich in order to measure the rich period, so a binary λ sensor that is detected by binary values of lean and rich is used.

  Further, a first temperature sensor 27 is disposed upstream of the oxidation catalyst device 21 to detect the temperature of the exhaust gas, and a second temperature sensor 28 is disposed between the oxidation catalyst device 21 and the NOx occlusion reduction type catalyst device 22. To do. In addition, a third temperature sensor 29 is disposed on the downstream side of the NOx storage reduction catalyst device 22. From the exhaust gas temperatures detected by these temperature sensors 27 to 29, the catalyst temperature of the oxidation catalyst device 21 and the catalyst temperature Tc of the NOx storage reduction type catalyst device 22 are estimated or calculated.

  In addition, when direct injection in the exhaust pipe is performed in the fuel system rich control, an HC supply valve that supplies hydrocarbon (HC) F that serves as a NOx reducing agent to the exhaust passage 3 upstream of the exhaust gas purification device 20 ( Fuel injection valve) 24 is provided. The HC supply valve 24 directly injects fuel (reducing agent) F such as light oil as fuel of the engine E from a fuel tank (not shown) into the exhaust passage 3 so that the air-fuel ratio of the exhaust gas G can be purged with sulfur. It is for making a rich state, and serves as means for air-fuel ratio rich control by injection in the exhaust pipe.

  A control device (ECU: engine control unit) 30 that performs overall control of the operation of the engine E and performs recovery control of the NOx purification capability of the NOx storage reduction catalyst device 22 and sulfur purge control is provided. Detection values from the first and second oxygen concentration sensors 25, 26 and the first to third temperature sensors 27, 28, 29, etc. are input to the control device 30, and the intake throttle valve ( (Intake throttle valve) 7, exhaust brake 8, exhaust throttle 9, fuel EGR valve 11, fuel injection valve 12 of the fuel injection common rail electronic control fuel injection device, and the like are output.

  In this NOx purification system 1, the air A passes through the air purifier 13 in the intake passage 2 and the mass air flow sensor (MAF sensor) 5, and is compressed and pressurized by the compressor of the turbocharger 6. The amount is adjusted and enters the cylinder from the intake manifold. The exhaust gas G generated in the cylinder exits from the exhaust manifold to the exhaust passage 3, drives the turbine of the turbocharger 6, and then passes through the exhaust gas purification device 20 to become purified exhaust gas Gc. Then, it is discharged into the atmosphere through a silencer (not shown). A part of the exhaust gas G passes through the EGR cooler 10 in the EGR passage 4 as EGR gas Ge, and the amount thereof is adjusted by the EGR valve 11 and recirculated to the intake manifold.

  In the NOx purification system 1 provided with the NOx occlusion reduction type catalyst device 22, when the estimated NOx occlusion amount becomes the NOx occlusion saturation amount by the catalyst regeneration control means incorporated in the control device 30 of the engine E, Fuel F such as hydrocarbons is supplied into the exhaust gas G as a reducing agent by post injection, injection in the exhaust pipe by the HC supply valve 24, or the like. The reducing agent F is oxidized by the upstream oxidation catalyst device 21 to make the exhaust gas G rich in the air-fuel ratio and release the absorbed NOx. This released NOx is reduced by a noble metal catalyst. This regeneration process restores the NOx storage capacity.

  Note that regeneration control other than sulfur purge control is not the subject of the present invention, and this catalyst regeneration control includes well-known EGR control, intake system rich control such as intake throttle and exhaust throttle, and post injection in in-cylinder fuel injection. Since regeneration control having fuel system rich control such as direct injection in the exhaust pipe or the like can be used, description thereof will be omitted.

  In the present invention, in the NOx purification system 1, sulfur purge is executed by the sulfur purge control means incorporated in the control device 30 of the engine E according to the sulfur purge control flow illustrated in FIG. 2. The sulfur purge control of FIG. 2 is provided as part of the catalyst control incorporated in the overall engine control, and is repeatedly executed along with the regeneration control for recovering the NOx storage capacity of the NOx storage reduction catalyst 22. It is shown as a thing.

  When the sulfur purge control of FIG. 2 is called from the normal operation control and started at every time interval (interval) of the sulfur purge start check, it is determined in step S11 whether the sulfur purge is necessary. As this determination method, it is determined whether or not the fuel consumption or travel distance after the previous sulfur purge exceeds a predetermined fuel consumption or predetermined travel distance, or by using a NOx concentration sensor. When the purification performance can be estimated, the determination is made from the estimated deterioration state of the NOx purification performance.

  If it is determined in step S11 that sulfur purge is not necessary, the process goes to return and returns to normal operation control. When it is determined that sulfur purge is necessary, an instruction to stop the vehicle is issued to the driver of the vehicle equipped with the engine E. This stop request instruction is made by lighting a lamp or a voice message.

  In the next step S13, it is determined whether or not the driver has stopped the vehicle, and if not, the process returns to step S12 to stop the vehicle while maintaining normal driving control. Wait to do. The vehicle is stopped when the engine speed has reached the idling speed, the vehicle speed has become zero, the parking brake has been turned on, or the neutral position when the gear position is MT (manual transmission). In the AT (automatic transmission), it is determined from one or several combinations of determination methods such as whether or not the vehicle is parked and whether or not the exhaust gas temperature is equal to or lower than a predetermined temperature. If it is confirmed in step S13 that the vehicle is stopped, the process goes to step S14.

  Thereby, it is possible to avoid the influence of the deterioration of the running performance that occurs when the sulfur purge is executed during the running state. Further, since the exhaust gas temperature hardly fluctuates while the vehicle is stopped, feedback control with a temperature threshold set is facilitated.

  In step S14, exhaust gas temperature increase control, which is pre-temperature increase, is performed for a predetermined time (time related to the catalyst temperature check interval). In this exhaust gas temperature raising control, after-injection and post-injection are performed in the cylinder injection so that the temperature of the exhaust gas G discharged from the engine E rises, and if necessary, the inside of the exhaust pipe by the HC supply valve 24 Injection is performed, and the injected hydrocarbon F is oxidized by the oxidation catalyst 21 to raise the temperature of the exhaust gas. At the same time as the temperature rise combustion, the exhaust brake 8 or the exhaust throttle 9 is closed to perform exhaust throttling. At the same time, the idle speed is increased from the rotational speed during normal idle operation to a rotational speed 1.2 to 1.3 times the rotational speed, for example, from 600 rpm to 700 rpm to 800 rpm to idle up. . In this exhaust gas temperature raising control, the air-fuel ratio of the exhaust gas G flowing into the NOx occlusion reduction type catalyst device 22 is 5 to 10 in terms of excess air ratio.

  Since the exhaust pressure is increased by this exhaust throttle, so-called internal EGR occurs because high-temperature combustion gas remains in the cylinder or flows backward from the exhaust valve into the cylinder. Therefore, the temperature in the cylinder and the exhaust gas temperature can be increased efficiently and quickly.

  In the next step S15, it is determined whether or not the catalyst temperature Tc has exceeded a predetermined first temperature (first temperature threshold) Tc1, and if not, the process returns to step S14 to continue the exhaust gas temperature raising control. On the other hand, when the catalyst temperature Tc exceeds a predetermined first temperature (first temperature threshold: about 600 ° C., for example) Tc1, the process goes to step S16. Since this catalyst temperature Tc is difficult to directly measure the catalyst temperature, the detected value of the upstream second temperature sensor 28 (exhaust gas temperature) and the detected value of the downstream third temperature sensor 29 (exhaust gas temperature) For example, it is calculated as an average temperature.

  In step S16, it is determined whether or not the catalyst temperature Tc exceeds a predetermined second temperature (second temperature threshold value: for example, about 750 ° C.) Tc2, and if not, the process goes to step S17. Then, go to step S19. This prevents the catalyst temperature Tc from rising abnormally and the NOx occlusion reduction type catalytic device 22 from being damaged by overheating. In step S19, the sulfur purge control is finished. Here, the exhaust gas temperature raising control is finished, and the temperature raising combustion, the exhaust throttling, and the idle-up are stopped. Then, the process returns to normal operation control.

  In step S17, air-fuel ratio rich control is performed. In this air-fuel ratio rich control, the exhaust throttle that closes the exhaust brake 8 or the exhaust throttle 9 is continued, the EGR valve 11 is fully opened, and the intake throttle valve 7 is further closed to perform the intake throttle. Further, after-injection and post-injection are continued in the in-cylinder injection, and hydrocarbon F, which is a reducing agent, is injected by exhaust pipe injection by the HC supply valve 24 to add the reducing agent.

  By this in-cylinder injection, the temperature of the exhaust gas G discharged from the engine E is raised, and a part of the reducing agent F injected from the HC supply valve 24 is oxidized by the oxidation catalyst 21, and this oxidation reaction heat causes The temperature of the exhaust gas G is further raised. Also, by these controls, the air-fuel ratio of the exhaust gas G is brought into a rich state where sulfur purge is possible. This air-fuel ratio rich state is a rich state including a stoichiometric state in which a sulfur component is released from the NOx occlusion material of the NOx occlusion reduction type catalyst device 22, and is 0.9 to 1 in terms of excess air ratio (λ). 2.

  The air-fuel ratio rich control in step S17 is performed for a predetermined time (a time related to the sulfur purge control completion check interval and the catalyst temperature check interval), and the process goes to step S18.

  In step S18, it is determined whether or not the sulfur purge control is completed. For this determination, for example, a method is used in which it is determined that the sulfur purging is completed when the duration of the predetermined time has elapsed, and when it has not elapsed, it is determined that it has not been completed. Can do.

  When it is determined in step S18 that the sulfur purge control has not been completed, the process returns to step S16 to check whether the catalyst temperature Tc exceeds the predetermined second temperature Tc2, and until the sulfur purge control is completed. The air-fuel ratio rich control in step S17 is repeated. If it is determined in step S18 that the sulfur purge control has been completed, the process goes to step S19 to perform the sulfur purge control end operation.

  By this air-fuel ratio rich control, the catalyst temperature Tc is set to a high temperature state of, for example, 600 ° C. or more, and the atmosphere around the catalyst of the NOx storage reduction catalyst device 22 is made rich to the air-fuel ratio rich state. The compound is thermally decomposed, and the sulfur content is released into the exhaust gas G as an oxide. The released sulfur oxide is reduced by reacting with the remaining reducing agent F in a reducing atmosphere in which oxygen is insufficient.

  In this air-fuel ratio rich control, since the EGR valve 11 is fully opened, the EGR rate limited by the pipe diameter of the EGR passage 4, the lift amount of the EGR valve 11, the performance of the EGR cooler 10, etc. Can be further increased. The combustion at this high EGR rate can reduce the oxygen concentration of the exhaust gas G when exhausted from the engine E. Further, by adding oxygen consumption due to oxidation of the reducing agent F in the oxidation catalyst 21, a NOx purification catalyst can be obtained. The air-fuel ratio of the exhaust gas G flowing into the device 22 can be quickly made rich.

  Moreover, since the exhaust gas G can be raised to a high temperature, the NOx purification catalyst device 22 can be heated in a short time, and the NOx purification catalyst device 22 can be maintained at a high temperature. As a result, the sulfur purge can be efficiently performed, and the sulfur purge time can be shortened.

  In the completion operation of the sulfur purge control in step S19, the exhaust brake 8 or the exhaust throttle 9 is opened to the normal operation state, the EGR valve 11 is closed to the normal operation state, and the intake throttle valve 7 is opened to the normal operation state. . Thereby, the exhaust throttle for exhausting sulfur, the fully open EGR, and the intake throttle are stopped. Further, after-injection and post-injection in cylinder injection, and injection in the exhaust pipe by the HC supply valve 24 are stopped. After completing these end operations, return to return to normal operation state control.

  According to the above-described sulfur purge control method and NOx purification system 1 of the NOx purification system, when the sulfur purge is executed, the EGR valve 11 is fully opened and the exhaust throttle of the exhaust brake 8 or the exhaust throttle 9 is used. The exhaust pressure can be increased.

  This exhaust pressure increase increases the amount of exhaust gas in the cylinder, so that it is easy to maintain the temperature in the cylinder at a high temperature or to raise the exhaust gas G to a high temperature. A certain NOx occlusion reduction type catalytic device 22 can be heated, and the NOx occlusion reduction type catalytic device 22 can be maintained at a high temperature.

  In addition, the air-fuel ratio of the exhaust gas G can be quickly made rich by increasing the amount of exhaust gas in the cylinder.

  Therefore, during the sulfur purge, the NOx purification catalyst device can be heated to a temperature at which sulfur purge can be performed in a short time, and the air-fuel ratio of the exhaust gas can be brought into a rich state in which sulfur purge can be performed quickly. Sulfur purge can be performed efficiently, and the sulfur purge time can be shortened.

It is a figure showing the whole NOx purification system composition of an embodiment concerning the present invention. It is a figure which shows an example of the flow of sulfur purge control.

Explanation of symbols

E engine (internal combustion engine)
1 NOx purification system 3 Exhaust passage 8 Exhaust brake (exhaust throttle valve)
9 Exhaust throttle (exhaust throttle valve)
21 oxidation catalyst 22 NOx occlusion reduction type catalyst (NOx purification catalyst device)
24 HC supply valve
G exhaust gas Gc purified exhaust gas Tc catalyst temperature TC1 predetermined first temperature (first temperature threshold)
Tc2 Predetermined second temperature (second temperature threshold)

Claims (4)

A sulfur purge control method for recovering a NOx purification catalyst device from sulfur poisoning in a NOx purification system in which a NOx purification catalyst device is provided in an exhaust passage of an internal combustion engine and an exhaust throttle valve is provided in an exhaust passage. There,
A sulfur purge control method for a NOx purification system, wherein the EGR valve is fully opened and the exhaust throttle valve is closed during the sulfur purge control. A NOx purification catalyst device disposed in an exhaust passage of the internal combustion engine, an exhaust throttle valve disposed in the exhaust passage, and a control device that performs sulfur purge control for recovering the NOx purification catalyst device from sulfur poisoning; NOx purification system with
The NOx purification system, wherein the control device fully opens the EGR valve and closes the exhaust throttle valve during the sulfur purge control.   When the control device determines that the sulfur purge control is necessary, the control device generates an instruction to stop the vehicle on which the internal combustion engine and the NOx purification catalyst device are mounted, and when the vehicle stops after the instruction, 3. The NOx purification system according to claim 2, wherein control is performed to increase the engine speed of the internal combustion engine when stopped to a predetermined engine speed higher than the engine speed of normal idle operation.   The NOx purification system according to claim 2 or 3, wherein the control device controls the intake throttle valve to close during the sulfur purge control.

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