Sulfur removal method

Abstract

To suppress outflow of hydrocarbon and carbon monoxide to the outside.SOLUTION: A sulfur removal method includes: operating an engine and warming up a NOx occlusion reduction catalyst provided in an exhaust flow passage connected to the engine; controlling the engine so that an excess air ratio of the engine becomes a target value that is less than 1 when a temperature of the NOx occlusion reduction catalyst reaches a temperature enabling reduction of a sulfur constituent occluded in the NOx occlusion reduction catalyst; stopping the engine; and closing a downstream side of the NOx occlusion reduction catalyst in the exhaust flow passage.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for removing sulfur. [Background technology]

[0002] An exhaust system of an engine mounted on a vehicle such as an automobile may be provided with a NOx storage reduction catalyst that removes nitrogen oxides (NOx) contained in exhaust gas. The NOx storage reduction catalyst removes NOx from exhaust gas by storing NOx while the engine's air-fuel ratio is kept lean. NOx removal processing is then performed at a predetermined timing to remove NOx from the NOx storage reduction catalyst. The NOx removal processing is a process in which, when the NOx storage reduction catalyst is at or above the NOx desorption temperature, the engine's air-fuel ratio is made richer than the stoichiometric air-fuel ratio to desorb and reduce NOx from the NOx storage reduction catalyst. The NOx desorption temperature is, for example, 250°C or higher.

[0003] The NOx storage reduction catalyst unintentionally stores not only NOx in exhaust gas but also sulfur components contained in fuel or lubricating oil. Even if the above-mentioned NOx removal process is performed, sulfur components cannot be removed from the NOx storage reduction catalyst. Therefore, as the engine operates, sulfur components gradually accumulate in the NOx storage reduction catalyst. As the amount of accumulated sulfur components in the NOx storage reduction catalyst increases, the amount of NOx that can be stored decreases.

[0004] Therefore, for example, Patent Document 1 discloses that when a vehicle is running under high load and the temperature of the NOx storage reduction catalyst reaches the desorption temperature of sulfur oxides, a sulfur removal process is performed to make the engine air-fuel ratio rich. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-120268 Summary of the Invention [Problem to be solved by the invention]

[0006] However, with the technology of Patent Document 1, there is a risk that hydrocarbons (HC) and carbon monoxide (CO) contained in the exhaust gas may leak to the outside during the sulfur removal process.

[0007] In view of the above problems, an object of the present invention is to provide a method for removing sulfur that can suppress the outflow of hydrocarbons and carbon monoxide to the outside. [Means for solving the problem]

[0008] In order to solve the above problem, a sulfur removal method according to one embodiment of the present invention includes: Operating an engine to warm up a NOx storage reduction catalyst provided in an exhaust passage connected to the engine; When the temperature of the NOx storage reduction catalyst reaches a temperature at which the sulfur components stored in the NOx storage reduction catalyst can be reduced, controlling the engine so that the excess air ratio of the engine becomes a target value less than 1; stopping the engine; closing a downstream side of the NOx storage reduction catalyst in the exhaust passage; Includes. [Effects of the Invention]

[0009] According to the present invention, it is possible to suppress the outflow of hydrocarbons and carbon monoxide to the outside. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram showing the configuration of an engine system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a block diagram showing an example of a functional configuration of the control device according to the embodiment of the present invention. [Figure 3]FIG. 3 is a flowchart showing an example of the process flow of the sulfur removal method according to the embodiment of the present invention. [Figure 4] FIG. 4 is a schematic diagram showing the configuration of an engine system according to a second modified example. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Specific dimensions, materials, numerical values, etc. shown in the embodiments are merely examples for facilitating understanding of the invention and do not limit the present invention unless otherwise specified. In this specification and drawings, elements having substantially the same functions and configurations are designated by the same reference numerals to avoid redundant explanation, and elements not directly related to the present invention are not shown.

[0012] <Engine system configuration> The configuration of an engine system 100 according to an embodiment of the present invention will be described with reference to FIGS.

[0013] 1 is a schematic diagram showing the configuration of an engine system 100 according to an embodiment of the present invention. In FIG. 1, dashed arrows indicate the flow of signals.

[0014] 1, the engine system 100 is mounted on, for example, a vehicle 10. The engine system 100 includes an engine 110, an intake passage 120, a throttle valve 122, an exhaust passage 130, a NOx storage reduction catalyst 140, a muffler 150, an intake air amount sensor 160, a temperature sensor 162, and a control device 170.

[0015] The engine 110 functions as a drive source for the vehicle 10. In other words, the vehicle 10 is an engine vehicle. The engine 110 is a gasoline engine or a diesel engine. The vehicle 10 may also be a hybrid vehicle that includes a motor as a drive source in addition to the engine 110.

[0016] The intake passage 120 is connected to the engine 110. For example, an intake manifold is connected to an intake port of the engine 110. The intake passage 120 is connected to a collection portion of the intake manifold. The intake passage 120 is formed of, for example, a pipe. A throttle valve 122 is provided in the intake passage 120.

[0017] The exhaust flow path 130 is connected to the engine 110. For example, an exhaust manifold is connected to the exhaust port of the engine 110. The exhaust flow path 130 is connected to the collection point of the exhaust manifold. The exhaust flow path 130 is formed, for example, by piping. Exhaust gas exhausted from the engine 110 flows through the exhaust flow path 130. Hereinafter, the upstream side in the flow direction of the exhaust gas may simply be referred to as "upstream". Also, the downstream side in the flow direction of the exhaust gas may simply be referred to as "downstream".

[0018] In the exhaust flow path 130, a NOx storage reduction catalyst 140 and a muffler 150 are provided in that order from the engine 110.

[0019] The NOx storage reduction catalyst (LNT: Lean NOx Trap) 140 contains, for example, barium (Ba) and potassium (K). The NOx storage reduction catalyst 140 may further contain a three-way catalyst. The three-way catalyst contains, for example, platinum (Pt), palladium (Pd), rhodium (Rh), and an OSC material. The OSC material is, for example, ceria.

[0020] The NOx storage reduction catalyst 140 stores nitrogen oxides while the engine 110 is performing lean combustion. Hereinafter, nitrogen oxides may be referred to as "NOx." Lean combustion is an operation mode in which the air-fuel ratio of the engine 110 is made leaner than the stoichiometric air-fuel ratio. The exhaust gas purified by the NOx storage reduction catalyst 140 is exhausted through the muffler 150.

[0021] The intake air amount sensor 160 is provided in the intake flow path 120 on the upstream side of the throttle valve 122. The intake air amount sensor 160 detects the amount of intake air flowing into the engine 110.

[0022] The temperature sensor 162 is provided in the exhaust flow path 130 between the engine 110 and the NOx storage reduction catalyst 140. In other words, the temperature sensor 162 is provided upstream of the NOx storage reduction catalyst 140 in the exhaust flow path 130. The temperature sensor 162 detects the temperature of the exhaust gas sent to the NOx storage reduction catalyst 140. The temperature detected by the temperature sensor 162 can be considered to be the temperature of the NOx storage reduction catalyst 140.

[0023] The control device 170 has one or more processors 170a and one or more memories 170b connected to the processors 170a. The processor 170a includes, for example, a CPU (Central Processing Unit). The memory 170b includes, for example, a ROM (Read Only Memory) and a RAM (Random Access Memory). The ROM is a storage element that stores programs used by the CPU, calculation parameters, etc. The RAM is a storage element that temporarily stores data such as variables and parameters used in processing executed by the CPU.

[0024] The control device 170 communicates with each device provided in the vehicle 10, such as the engine 110, the throttle valve 122, the intake air amount sensor 160, and the temperature sensor 162. The communication between the control device 170 and each device is realized, for example, by using CAN (Controller Area Network) communication.

[0025] 2 is a block diagram showing an example of a functional configuration of the control device 170 according to an embodiment of the present invention. For example, as shown in FIG. 2, the control device 170 includes a control unit 180, an acquisition unit 182, and a calculation unit 184.

[0026] Note that various processes including the processes described below performed by the control unit 180, the acquisition unit 182, and the calculation unit 184 may be executed by the processor 170a. In detail, the various processes are executed by the processor 170a executing programs stored in the memory 170b.

[0027] The functions of the control device 170 according to this embodiment may be divided among multiple devices, or multiple functions may be realized by one device. When the functions of the control device 170 are divided among multiple devices, the multiple devices may be connected to each other via a communication bus such as a CAN.

[0028] The control unit 180 controls the operation of each device in the engine system 100. For example, the control unit 180 controls the engine 110 and the throttle valve 122.

[0029] The control unit 180 controls the air-fuel ratio of the engine 110, for example, by controlling the amount of fuel injected into the combustion chamber of the engine 110 and the opening of the throttle valve 122. In this embodiment, the control unit 180 performs lean combustion processing, NOx removal processing, and sulfur removal processing. The lean combustion processing and NOx removal processing are performed, for example, while the vehicle 10 is traveling. The sulfur removal processing is performed, for example, while the vehicle 10 is stopped.

[0030] Lean burn processing is processing that sets the operating mode of the engine 110 to lean burn. In lean burn processing, the air-fuel ratio of the engine 110 is made leaner than the stoichiometric air-fuel ratio, that is, the excess air ratio of the engine 110 is made greater than 1 (λ>1). Note that λ represents the excess air ratio. While lean burn processing is being performed, NOx is contained in the exhaust gas, and the NOx contained in the exhaust gas is stored in the NOx storage reduction catalyst 140. Note that the longer the time that lean burn processing is performed, the greater the amount of NOx stored in the NOx storage reduction catalyst 140.

[0031] When the amount of NOx stored in the NOx storage reduction catalyst 140 exceeds a predetermined amount, the control unit 180 performs a NOx removal process. The predetermined amount is determined, for example, based on the maximum amount of NOx stored by the NOx storage reduction catalyst 140. The predetermined amount is a value slightly smaller than the maximum amount of NOx stored by the NOx storage reduction catalyst 140. For example, the predetermined amount is a value obtained by multiplying the maximum amount of NOx stored by the NOx storage reduction catalyst 140 by a predetermined ratio.

[0032] The NOx removal process is a process for removing NOx from the NOx storage reduction catalyst 140. In the NOx removal process, the temperature of the NOx storage reduction catalyst 140 is set to the NOx desorption temperature, and the operation mode of the engine 110 is set to rich combustion. Rich combustion is an operation mode in which the air-fuel ratio of the engine 110 is made richer than the stoichiometric air-fuel ratio, that is, the excess air ratio of the engine 110 is made less than 1 (λ<1). The NOx desorption temperature is a temperature at which NOx can be desorbed from the NOx storage reduction catalyst 140 and can be reduced. The NOx desorption temperature is, for example, 250°C or higher.

[0033] The sulfur removal process is a process for removing sulfur oxides from the NOx storage reduction catalyst 140. In the sulfur removal process, the temperature of the NOx storage reduction catalyst 140 is set to the desorption temperature of the sulfur components, and the operation mode of the engine 110 is set to rich combustion. The desorption temperature of the sulfur components is a temperature at which the sulfur components can be desorbed from the NOx storage reduction catalyst 140 and can be reduced. The desorption temperature of the sulfur components is higher than the desorption temperature of NOx. The desorption temperature of the sulfur components is, for example, 550°C or higher. The sulfur components are, for example, sulfur oxides (SOx). The sulfur removal process will be described in detail later.

[0034] Acquisition unit 182 acquires various information used in the processes performed by control unit 180 and calculation unit 184, and outputs the information to control unit 180 and calculation unit 184. For example, acquisition unit 182 acquires information from engine 110, intake air amount sensor 160, and temperature sensor 162.

[0035] The calculation unit 184 calculates the amount of NOx stored in the NOx storage reduction catalyst 140 and the amount of sulfur components stored in the NOx storage reduction catalyst 140. The amount of NOx and the amount of sulfur components calculated by the calculation unit 184 are stored in, for example, memory 170b. Hereinafter, the amount of NOx may be referred to as the "NOx amount" and the amount of sulfur components may be referred to as the "sulfur component amount."

[0036] For example, while the control unit 180 is performing lean burn processing, the calculation unit 184 calculates the amount of NOx stored in the NOx storage reduction catalyst 140 for each unit time. Then, the calculation unit 184 adds the calculated NOx amount to the NOx amount stored in the memory 170b, thereby updating the NOx amount stored in the memory 170b for each unit time. Then, when the NOx removal processing or the sulfur removal processing is completed, the calculation unit 184 resets the NOx amount stored in the memory 170b to zero. Furthermore, when the operation of the engine 110 is restarted after the completion of the NOx removal processing or the completion of the sulfur removal processing, the calculation unit 184 resumes calculating the NOx amount.

[0037] The calculation unit 184 calculates the amount of NOx stored per unit time in the NOx storage reduction catalyst 140 based on, for example, the flow rate per unit time of the exhaust gas sent to the NOx storage reduction catalyst 140 and the concentration of NOx contained in the exhaust gas. Note that the calculation unit 184 may obtain the concentration of NOx sent to the NOx storage reduction catalyst 140 based on a detection value of a NOx sensor (not shown). The NOx sensor is provided, for example, between the engine 110 and the NOx storage reduction catalyst 140 in the exhaust flow path 130. The NOx sensor is a sensor that detects the concentration of NOx. Furthermore, the concentration of NOx sent to the NOx storage reduction catalyst 140 may be estimated based on the rotation speed of the engine 110, the detection value of the intake air mass sensor 160, the excess air ratio, and the ignition timing.

[0038] Furthermore, for example, the calculation unit 184 calculates the amount of sulfur components stored in the NOx storage reduction catalyst 140 for each unit time. Then, the calculation unit 184 adds the calculated amount of sulfur components to the amount of sulfur components stored in the memory 170b, thereby updating the amount of sulfur components stored in the memory 170b for each unit time. Then, when the sulfur removal process is completed, the calculation unit 184 resets the amount of sulfur components stored in the memory 170b to zero. Furthermore, when the operation of the engine 110 is resumed after the sulfur removal process is completed, the calculation unit 184 resumes calculation of the amount of sulfur components.

[0039] The calculation unit 184 calculates the amount of sulfur components per unit time stored in the NOx storage reduction catalyst 140 based on, for example, the flow rate per unit time of the exhaust gas sent to the NOx storage reduction catalyst 140 and the concentration of sulfur components contained in the exhaust gas. The calculation unit 184 may obtain the concentration of sulfur components sent to the NOx storage reduction catalyst 140 based on a detection value of a sulfur sensor (not shown). The sulfur sensor is provided, for example, between the engine 110 and the NOx storage reduction catalyst 140 in the exhaust flow path 130. The sulfur sensor is a sensor that detects, for example, the concentration of SOx. The concentration of sulfur components sent to the NOx storage reduction catalyst 140 may also be estimated based on the rotation speed of the engine 110, the detection value of the intake air mass sensor 160, the excess air ratio, and the ignition timing.

[0040] Furthermore, when the control unit 180 performs the NOx removal process, the calculation unit 184 refers to the NOx amount stored in the memory 170b and calculates the amount of reducing agent capable of reducing the NOx stored in the NOx storage reduction catalyst 140. In the NOx removal process, the control unit 180 injects into the engine an amount of fuel necessary for the amount of reducing agent calculated by the calculation unit 184 to be supplied to the NOx storage reduction catalyst 140. The reducing agent is fuel-derived hydrocarbons and carbon monoxide contained in the exhaust gas emitted from the engine 110.

[0041] Furthermore, the calculation unit 184 calculates a target value of the excess air ratio based on the amount of sulfur components stored in the NOx storage reduction catalyst 140.

[0042] <Sulfur removal method> Next, a sulfur removal method according to an embodiment of the present invention will be described with reference to FIG.

[0043] 3 is a flowchart showing an example of the processing flow of the sulfur removal method according to the embodiment of the present invention. The sulfur removal method according to the present embodiment is performed, for example, while the vehicle 10 is stopped. The sulfur removal method according to the present embodiment is performed, for example, in a facility where inspection, repair, maintenance, etc. of the vehicle 10 are performed. The processing flow shown in FIG. 3 is started, for example, in response to a predetermined operation input by an operator of the facility.

[0044] 3, the sulfur removal method according to this embodiment includes a warm-up process step S110, a calculation process step S112, a temperature determination process step S114, an engine control process step S116, a first time elapse determination process step S118, an engine stop process step S120, a closing process step S122, a second time elapse determination process step S124, and an opening process step S126. In this embodiment, the processes from the warm-up process step S110 to the engine stop process step S120 correspond to the sulfur removal process performed by the engine system 100. Each process will be described below.

[0045] [Warm-up processing step S110] In warm-up processing step S110, the control unit 180 operates the engine 110 to warm up the NOx occlusion reduction catalyst 140 provided in the exhaust flow path 130 connected to the engine 110. In this embodiment, the control unit 180 warms up the NOx occlusion reduction catalyst 140 in a state in which the engine 110 is controlled so that the excess air ratio of the engine 110 becomes 1, for example. In other words, the control unit 180 controls the engine 110 so that the air-fuel ratio of the engine 110 becomes the stoichiometric air-fuel ratio. For example, the control unit 180 adjusts the amount of fuel injected into the engine 110, the rotation speed of the engine 110, the ignition timing of the engine 110, and the like so that the air-fuel ratio of the engine 110 becomes the stoichiometric air-fuel ratio and the temperature of the NOx occlusion reduction catalyst 140 is warmed up to the desorption temperature Ts of the sulfur components.

[0046] [Calculation processing step S112] In engine control processing step S116, which will be described later, the engine 110 is subjected to rich combustion to remove sulfur components from the NOx storage reduction catalyst 140. Therefore, in calculation processing step S112, the calculation unit 184 calculates a target value of the excess air ratio based on the amount of sulfur components occluded in the NOx storage reduction catalyst 140. For example, the calculation unit 184 refers to the amount of sulfur components stored in the memory 170b and calculates the amount of reducing agent capable of reducing the sulfur components adsorbed in the NOx storage reduction catalyst 140. Then, the calculation unit 184 calculates a target value of the excess air ratio that can fill the exhaust flow path 130 with the calculated amount of reducing agent. Note that, at this time, the calculation unit 184 may take into account the amount of oxygen adsorbed in the NOx storage reduction catalyst 140 in addition to the amount of sulfur components adsorbed in the NOx storage reduction catalyst 140. Note that, in calculation processing step S112, the excess air ratio calculated by the calculation unit 184 is less than 1.

[0047] [Temperature determination processing step S114] In temperature determination processing step S114, the control unit 180 determines whether the temperature Tcat of the NOx storage reduction catalyst 140 is equal to or higher than the desorption temperature Ts of the sulfur components. For example, the control unit 180 regards the detection value of the temperature sensor 162 acquired by the acquisition unit 182 as the temperature Tcat of the NOx storage reduction catalyst 140, and determines whether the detection value of the temperature sensor 162 is equal to or higher than the desorption temperature Ts. As a result, if it is determined that the temperature Tcat is equal to or higher than the desorption temperature Ts (YES in step S114), the control unit 180 proceeds to engine control processing step S116. On the other hand, if it is determined that the temperature Tcat is not equal to or higher than the desorption temperature Ts, that is, if it is determined that the temperature Tcat is lower than the desorption temperature Ts (NO in step S114), the control unit 180 repeats temperature determination processing step S114.

[0048] [Engine control processing step S116] In engine control processing step S116, control unit 180 controls engine 110 so that the excess air ratio of engine 110 is less than 1. That is, in engine control processing step S116, control unit 180 causes rich combustion in engine 110. In this embodiment, control unit 180 adjusts the amount of fuel injected into engine 110, the opening of throttle valve 122, and the like so that the excess air ratio becomes the target value calculated in calculation processing step S112.

[0049] [First time passage determination processing step S118] In a first time elapse determination process step S118, the control unit 180 determines whether or not a first target time has elapsed since the start of the engine control process step S116. The first target time is the time it takes for the exhaust gas exhausted from the engine 110 to reach the outlet of the exhaust flow path 130. The first target time is, for example, 5 seconds or more and 15 seconds or less. The outlet of the exhaust flow path 130 is, for example, the outlet of the muffler 150. If the control unit 180 determines that the first target time has elapsed (YES in step S118), the control unit 180 proceeds to the engine stop process step S120. On the other hand, if the control unit 180 determines that the first target time has not elapsed (NO in step S118), the control unit 180 repeats the first time elapse determination process step S118.

[0050] [Engine stop processing step S120] In the engine stop processing step S120, the control unit 180 stops the engine 110.

[0051] [Closing processing step S122] In the closing process step S122, the downstream side of the NOx storage reduction catalyst 140 in the exhaust passage 130 is closed. For example, an operator of the facility closes the outlet of the exhaust passage 130 with a plug.

[0052] [Second time passage determination processing step S124] In the second time elapse determination process step S124, it is determined whether or not a second target time has elapsed since the start of the closing process step S122. The second target time is the time from the start of the closing process step S122 until the sulfur components stored in the NOx storage reduction catalyst 140 are removed by the reducing agent. If it is determined that the second target time has elapsed (YES in step S124), the process proceeds to the opening process step S126. On the other hand, if it is determined that the second target time has not elapsed (NO in step S124), the second time elapse determination process step S124 is repeated.

[0053] [Release processing step S126] In the opening process step S126, the downstream side of the NOx storage reduction catalyst 140 in the exhaust passage is opened. For example, a plug is removed from the outlet of the exhaust passage by an operator of the facility.

[0054] When the release processing step S126 is completed, the processing flow shown in FIG. 3 ends.

[0055] <Effects of sulfur removal methods> The effects of the sulfur removal method according to the embodiment of the present invention will be described.

[0056] The sulfur removal method according to this embodiment includes operating the engine 110 to warm up the NOx occlusion reduction catalyst 140 provided in the exhaust flow path 130 connected to the engine 110, controlling the engine 110 so that the excess air ratio of the engine 110 becomes a target value less than 1 when the temperature of the NOx occlusion reduction catalyst 140 reaches a temperature at which the sulfur components occluded in the NOx occlusion reduction catalyst 140 can be reduced, stopping the engine 110, and closing the downstream side of the NOx occlusion reduction catalyst 140 in the exhaust flow path 130. Therefore, the sulfur removal method according to this embodiment makes it possible to send hydrocarbons and carbon monoxide, which function as reducing agents, to the NOx occlusion reduction catalyst 140 by making the excess air ratio of the engine 110 less than 1 when the temperature of the NOx occlusion reduction catalyst 140 reaches a temperature at which the sulfur components can be reduced. Then, by stopping the engine 110 and closing the exhaust flow path 130 downstream of the NOx occlusion reduction catalyst 140, it is possible to fill the exhaust flow path 130 with reducing agent while preventing air from flowing into the exhaust flow path 130 from the outside. This makes it possible to prevent a decrease in the efficiency of reducing sulfur components due to oxygen contained in the air. Furthermore, by closing the exhaust flow path 130 downstream of the NOx occlusion reduction catalyst 140, it is possible to prevent the reducing agent from leaking to the outside. And, because it is possible to prevent the reducing agent from leaking to the outside, it is possible to remove the sulfur components occluded in the NOx occlusion reduction catalyst 140 with a small amount of reducing agent.

[0057] Furthermore, in the sulfur removal method according to this embodiment, the target value of the excess air ratio is preferably determined based on the amount of sulfur components stored in the NOx storage reduction catalyst 140. This enables the sulfur removal method according to this embodiment to remove sulfur components from the NOx storage reduction catalyst 140.

[0058] Furthermore, in the sulfur removal method according to this embodiment, warming up the NOx occlusion reduction catalyst 140 preferably includes warming up the NOx occlusion reduction catalyst 140 while controlling the engine 110 so that the excess air ratio of the engine 110 is 1. When the engine 110 is at a stoichiometric air-fuel ratio where the excess air ratio is 1, the temperature of the exhaust gas is higher than when the engine 110 is in a rich state where the excess air ratio is less than 1. Therefore, by setting the excess air ratio of the engine 110 to 1, the NOx occlusion reduction catalyst 140 can be warmed up earlier than when rich combustion is performed. Furthermore, when the engine 110 is at a stoichiometric air-fuel ratio where the excess air ratio is 1, the amount of reducing agent contained in the exhaust gas is smaller than when the engine 110 is in a rich state where the excess air ratio is less than 1. Therefore, by setting the excess air ratio of the engine 110 to 1, it is possible to suppress the outflow of reducing agent from the exhaust passage 130 to the outside more than when rich combustion is performed.

[0059] In this embodiment, the engine 110 is provided in a vehicle 10, and the sulfur removal method according to this embodiment is preferably performed while the vehicle 10 is stopped. This makes it possible to remove sulfur components from the NOx storage reduction catalyst 140 while avoiding operational problems and deterioration of fuel economy that may occur when sulfur removal processing is performed while the vehicle 10 is in operation.

[0060] [First Modification] In the calculation processing step S112 of the above embodiment, the calculation unit 184 calculates the target value of the excess air ratio based on the amount of sulfur components stored in the NOx storage reduction catalyst 140. However, the calculation unit 184 may calculate the excess air ratio based on, for example, the amount of NOx stored in the NOx storage reduction catalyst 140 in addition to the amount of sulfur components stored in the NOx storage reduction catalyst 140.

[0061] In calculation processing step S112 according to the first modified example, the calculation unit 184 refers to the amount of NOx and the amount of sulfur components stored in the memory 170b, for example, and calculates the amount of reducing agent capable of reducing the NOx and sulfur components stored in the NOx storage reduction catalyst 140. Then, the calculation unit 184 calculates a target value of the excess air ratio that can fill the exhaust flow path 130 with the calculated amount of reducing agent. Note that, even in calculation processing step S112 according to the first modified example, the excess air ratio calculated by the calculation unit 184 is less than 1.

[0062] In the sulfur removal method according to the first modification, the target value of the excess air ratio is determined based on the amount of nitrogen oxides stored in the NOx storage reduction catalyst 140 in addition to the amount of sulfur components stored in the NOx storage reduction catalyst 140. This makes it possible to remove NOx in addition to removing the sulfur components when NOx remains in the NOx storage reduction catalyst 140.

[0063] [Second Modification] In the above embodiment, the engine system 100 is described as an example in which no on-off valve is provided in the exhaust passage 130. However, the engine system 200 may be provided with an on-off valve in the exhaust passage 130.

[0064] 4 is a schematic diagram showing the configuration of an engine system 200 according to a second modified example. In FIG. 4, dashed arrows indicate the flow of signals.

[0065] As shown in Fig. 4, an engine system 200 according to the second modification is mounted on, for example, a vehicle 10. The engine system 200 according to the second modification includes an engine 110, an intake passage 120, a throttle valve 122, an exhaust passage 130, a NOx storage reduction catalyst 140, a muffler 150, an intake air mass sensor 160, a temperature sensor 162, a control device 170, and an on-off valve 210. Components that are substantially the same as those in the engine system 100 described above are denoted by the same reference numerals, and description thereof will be omitted. The engine system 200 according to the second modification is different from the engine system 100 in that it includes the on-off valve 210 and is controlled by the control device 170, but is otherwise the same.

[0066] 4, the on-off valve 210 is provided in the exhaust flow path 130 downstream of the NOx storage reduction catalyst 140. The on-off valve 210 is provided, for example, at the outlet of the muffler 150 in the exhaust flow path 130. The on-off valve 210 opens and closes the exhaust flow path 130.

[0067] In the second modification, the control unit 180 of the control device 170 controls the opening and closing of the on-off valve 210. For example, the control unit 180 keeps the on-off valve 210 open except when the sulfur removal method is performed.

[0068] In the second modified example, the control unit 180 closes the on-off valve 210 in the above-described closing process step S122, thereby closing the downstream side of the NOx storage reduction catalyst 140 in the exhaust passage .

[0069] In the second modified example, in the second time elapse determination process step S124, the control unit 180 determines whether or not the second target time has elapsed since the start of the closing process step S122. In the second modified example, if the control unit 180 determines that the second target time has elapsed (YES in step S124), the control unit 180 proceeds to the opening process step S126. On the other hand, if the control unit 180 determines that the second target time has not elapsed (NO in step S124), the control unit 180 repeats the second time elapse determination process step S124.

[0070] Then, in the second modified example, the control unit 180 opens the on-off valve 210 in the above-described opening process step S126, thereby opening the exhaust passage 130 on the downstream side of the NOx storage reduction catalyst 140.

[0071] As described above, the sulfur removal method using the engine system 200 according to the second modified example not only achieves the same effects as the sulfur removal method according to the above embodiment, but also eliminates the need for equipment workers to attach and detach plugs.

[0072] While the preferred embodiments of the present invention have been described above with reference to the accompanying drawings, it goes without saying that the present invention is not limited to such embodiments. It is clear that those skilled in the art can conceive of various modifications and alterations within the scope of the claims, and it is understood that such modifications and alterations also fall within the technical scope of the present invention.

[0073] For example, the processes described herein using flowcharts do not necessarily have to be performed in the order shown in the flowcharts, and additional process steps may be employed or some process steps may be omitted.

[0074] In the above embodiment, the target value of the excess air ratio in calculation step S112 is determined based on the amount of sulfur components stored in the NOx storage reduction catalyst. However, the target value of the excess air ratio determined in calculation step S112 may be less than 1, and the amount of sulfur components stored in the NOx storage reduction catalyst may not be taken into consideration. For example, calculation step S112 may be omitted, and the target value of the excess air ratio in engine control processing step S116 may be set to a fixed value less than 1.

[0075] In the warm-up processing step S110 of the above embodiment, the case where the engine 110 is controlled so that the excess air ratio of the engine 110 becomes 1 has been taken as an example. However, in the warm-up processing step S110, there is no limitation on the excess air ratio as long as the engine is operated to warm up the NOx storage reduction catalyst 140. For example, the NOx storage reduction catalyst 140 may be warmed up by performing lean combustion or rich combustion of the engine 110.

[0076] In the above embodiment, the sulfur removal method is performed while the vehicle 10 is stopped. However, the sulfur removal method may be performed while the vehicle 10 is traveling.

[0077] Furthermore, for example, in the above-described second modified example, the on-off valve 210 is provided at the outlet of the muffler 150 in the exhaust flow path 130. However, there are no limitations on the installation position of the on-off valve 210 as long as it is provided downstream of the NOx storage reduction catalyst 140. For example, the on-off valve 210 may be provided between the NOx storage reduction catalyst 140 and the muffler 150 in the exhaust flow path 130. Also, for example, the on-off valve 210 may be provided inside the muffler 150. [Explanation of symbols]

[0078] 10 vehicles 100 Engine System 110 Engine 120 intake passage 122 Throttle valve 130 Exhaust flow path 140 NOx storage reduction catalyst 150 muffler 160 Intake air volume sensor 162 Temperature Sensor 170 Control device 170a processor 170b memory 180 Control Unit 182 Acquisition Department 184 Arithmetic section 190 Memory section 200 Engine System 210 On-off valve

Claims

1. operating an engine to warm up a NOx storage reduction catalyst provided in an exhaust passage connected to the engine; When the temperature of the NOx storage reduction catalyst reaches a temperature at which the sulfur components stored in the NOx storage reduction catalyst can be reduced, controlling the engine so that the excess air ratio of the engine becomes a target value less than 1; stopping the engine; closing a downstream side of the NOx storage reduction catalyst in the exhaust passage; A method for removing sulfur, comprising:

2. 2. The sulfur removal method according to claim 1, wherein the target value of the excess air ratio is determined based on the amount of sulfur components stored in the NOx storage reduction catalyst.

3. 3. The sulfur removal method according to claim 2, wherein the target value of the excess air ratio is determined based on the amount of nitrogen oxides stored in the NOx storage-reduction catalyst in addition to the amount of sulfur components stored in the NOx storage-reduction catalyst.

4. 3. The sulfur removal method according to claim 1, wherein warming up the NOx storage reduction catalyst includes warming up the NOx storage reduction catalyst while controlling the engine so that an excess air ratio of the engine is 1.

5. The engine is mounted in a vehicle, The sulfur removal method according to claim 1 or 2, which is carried out while the vehicle is stopped.

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