JP2016186300A - Exhaust emission control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the nitrogen oxide occluding efficiency of a NOx occlusion reduction catalyst by cooling exhaust gas in a simple configuration.SOLUTION: An exhaust emission control device includes: a NOx occlusion reduction catalyst 212 provided in a main exhaust passage (an exhaust passage 140) into which exhaust gas exhausted from a combustion chamber 146 of an engine 120 is guided, for occluding nitrogen oxide in a predetermined temperature range; a water adsorbing material 230 provided in a bypass passage 220 branching from the main exhaust passage and merging with the main exhaust passage for adsorbing water at lower than a water adsorbing temperature being not higher than an upper limit value in the predetermined temperature range and releasing the water at not lower than the water adsorbing temperature; and a flow path control part for, when the temperature of the exhaust gas on the upstream side of the NOx occlusion reduction catalyst exceeds the upper limit value in the predetermined temperature range, controlling a flow path for the exhaust gas so that the exhaust gas, after passing through the water adsorbing material arranged in the bypass passage, passes through the NOx occlusion reduction catalyst.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an exhaust gas purification device that purifies exhaust gas discharged from a combustion chamber of an engine.

  In order to improve fuel efficiency, an engine capable of performing lean combustion in which fuel is burned at an air-fuel ratio leaner than the stoichiometric air-fuel ratio (stoichiometric) has been developed. When lean combustion is performed, nitrogen oxides (NOx) are more likely to be generated than when combustion is performed at a stoichiometric air-fuel ratio. For this reason, an NOx occlusion reduction catalyst (LNT: Lean NOx Trap) that removes nitrogen oxides from the exhaust gas may be provided in the exhaust path of the engine that can execute the lean combustion.

  Since the NOx occlusion reduction catalyst occludes nitrogen oxides in a predetermined temperature range (hereinafter referred to as “occlusion temperature range”), it is necessary to maintain the exhaust gas within the occlusion temperature range. Therefore, for example, a bypass path is provided in the exhaust path, and the bypass path is air-cooled to cool the exhaust gas to the occlusion temperature range (for example, Patent Document 1), or fins are provided in the outer periphery of the bypass path. A technique (for example, Patent Document 2) in which exhaust gas is cooled by heat radiation from the fin to the outside, or the exhaust gas is cooled by water-cooling the bypass passage is disclosed.

JP 2001-214734 A JP-A-8-28254

  However, in the techniques for air-cooling the bypass passages described in Patent Documents 1 and 2, the exhaust gas cooling effect is low, and the temperature of the exhaust gas may not be lowered to the occlusion temperature range. Moreover, in the technique for water-cooling the bypass path described in Patent Document 2, a complicated mechanism for circulating water is required, and thus there is a problem that maintenance of the mechanism is troublesome.

  Accordingly, an object of the present invention is to provide an exhaust gas purifying apparatus that can cool exhaust gas with a simple configuration and can improve the storage efficiency of nitrogen oxides by a NOx storage reduction catalyst.

  In order to solve the above-described problems, an exhaust gas purification apparatus according to the present invention is provided in a main exhaust passage through which exhaust gas discharged from a combustion chamber of an engine is guided, and stores NOx in a predetermined temperature range. The reduction catalyst is provided in a bypass passage branched from the main exhaust passage and joined to the main exhaust passage, and adsorbs water below a predetermined water absorption temperature below an upper limit value of a predetermined temperature range and absorbs water above the water absorption temperature. When the temperature of the water absorbing material to be released and the exhaust gas upstream of the NOx storage reduction catalyst exceeds the upper limit of the predetermined temperature range, the exhaust gas is passed through the water absorbing material arranged in the bypass passage, and then stored in the NOx A flow path control unit that controls the flow path of the exhaust gas so as to pass through the reduction catalyst.

  In addition, when the temperature of the exhaust gas upstream of the NOx occlusion reduction catalyst is within a predetermined temperature range, the flow path control unit passes the exhaust gas through the NOx occlusion reduction catalyst and then is disposed in the bypass passage. The flow path of the exhaust gas may be controlled so as to pass through the water absorbing material.

  The bypass path is branched from the upstream side of the NOx storage reduction catalyst in the main exhaust path and joined to the downstream side of the NOx storage reduction catalyst, the first subflow path, and the first subflow path in the main exhaust path. A main exhaust passage is branched from between the second sub passage communicating with the downstream side of the joining location with the one sub passage, the branch portion of the first sub passage in the main exhaust passage, and the NOx storage reduction catalyst. And a third sub-flow channel that merges downstream of the merged location with the first sub-flow channel, and the water-absorbing material is connected to the second sub-flow channel in the first sub-flow channel and the main exhaust Provided between the junction with the passage and the upstream side of the branch point of the first sub-flow path in the main exhaust path and the downstream side of the branch point of the main exhaust path or the first sub-flow path. The first to switch the exhaust gas flow path In order to communicate the replacement means and the upstream side of the communication location of the second sub-channel in the first sub-channel and the downstream side of the communication location of the first sub-channel, or the second sub-channel, The second switching means for switching the flow path of the exhaust gas, the upstream side of the joining location with the first sub-flow passage in the main exhaust passage, and the downstream side of the joining location in the main exhaust passage, or the first sub-flow passage A third switching means for switching the flow path of the exhaust gas so as to communicate, an upstream side of the branch point of the third sub-flow path in the main exhaust path, and a downstream side of the branch position of the main exhaust path, or the third sub And a fourth switching means for switching the flow path of the exhaust gas so as to communicate with the flow path. The flow path control unit includes a first switching means, a second switching means, a third switching means, and a fourth switching means. The switching means may be subjected to switching control.

  According to the present invention, the exhaust gas can be cooled with a simple configuration, and the nitrogen oxide storage efficiency by the NOx storage reduction catalyst can be improved.

It is the schematic which shows the structure of an engine system. It is the schematic which shows the structure of an exhaust-gas purification | cleaning unit. It is a flowchart for demonstrating the flow of a flow-path switching process. It is a figure for demonstrating the flow of exhaust gas. It is the schematic which shows the structure of the exhaust-gas purification | cleaning unit concerning a modification. It is a flowchart for demonstrating the flow of the flow-path switching process concerning a modification. It is a figure for demonstrating the flow of the exhaust gas concerning a modification.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The dimensions, materials, and other specific numerical values shown in the embodiments are merely examples for facilitating understanding of the invention, and do not limit the present invention unless otherwise specified. In the present specification and drawings, elements having substantially the same function and configuration are denoted by the same reference numerals, and redundant description is omitted, and elements not directly related to the present invention are not illustrated. To do.

  FIG. 1 is a schematic diagram illustrating a configuration of an engine system 100 according to the present embodiment. In FIG. 1, the signal flow is indicated by broken arrows. As shown in FIG. 1, the engine system 100 is provided with an ECU (Engine Control Unit) 110 formed of a microcomputer including a central processing unit (CPU), a ROM storing programs and the like, a RAM as a work area, and the like. The ECU 110 performs overall control of the engine 120. However, the configuration and processing related to the present embodiment will be described in detail below, and the description of the configuration and processing unrelated to the present embodiment will be omitted.

  The engine 120 is a multi-cylinder engine having a plurality of cylinders 122a, and an intake manifold 126 is communicated with an intake port 124 of each cylinder 122a formed in the cylinder block 122. An intake passage 130 is communicated with a collection portion of the intake manifold 126 via an air chamber 128, an air cleaner 132 is provided on the upstream side of the intake passage 130, and a throttle valve 134 is provided on the downstream side of the air cleaner 132.

  An exhaust manifold 138 communicates with the exhaust port 136 of each cylinder 122 a formed in the cylinder block 122 of the engine 120. A muffler 142 is communicated with a collective portion of the exhaust manifold 138 via an exhaust passage 140 (main exhaust passage), and an exhaust gas purification unit 200 described later is provided in the exhaust passage 140.

  The engine 120 is provided with a spark plug 148 for each of the cylinders 122a so that the tip thereof is located in the combustion chamber 146. An injector 150 is provided in the combustion chamber 146 of each cylinder 122a.

  In the engine system 100, an intake air amount sensor 160 that detects the amount of intake air flowing into the engine 120 between the air cleaner 132 and the throttle valve 134 in the intake passage 130, and the temperature of the air flowing into the engine 120 are detected. An intake air temperature sensor 162 is provided. The engine system 100 is also provided with a throttle opening sensor 164 that detects the opening of the throttle valve 134. The engine system 100 is provided with a crank angle sensor 166 that detects the crank angle of the crankshaft.

  The engine system 100 also includes an intake valve (not shown) that can open and close the combustion chamber 146 and the intake port 124, and an exhaust valve (not shown) that can open and close the combustion chamber 146 and the exhaust port 136. A VVT actuator 152 that drives a cam (not shown) to be opened and closed, and a cam sensor 168 that detects a rotation angle of the cam are provided. The engine system 100 is also provided with an accelerator opening sensor 170 that detects the opening of an accelerator (not shown).

  Each of these sensors 160 to 170 is connected to ECU 110 and outputs a signal indicating the detected value to ECU 110.

  ECU 110 acquires signals output from sensors 160 to 170 to control engine 120. When the ECU 110 controls the engine 120, the signal acquisition unit 180, the target value derivation unit 182, the air amount determination unit 184, the injection amount determination unit 186, the throttle opening determination unit 188, the ignition timing determination unit 190, and the drive control unit 192. Function as.

  The signal acquisition unit 180 acquires signals indicating values detected by the sensors 160 to 170. The target value deriving unit 182 derives the current engine speed based on the signal indicating the crank angle acquired from the crank angle sensor 166. Further, the target value deriving unit 182 refers to a pre-stored map based on the derived engine speed and a signal indicating the accelerator opening acquired from the accelerator opening sensor 170, and the target torque and the target engine speed. Is derived.

  The air amount determination unit 184 determines a target air amount to be supplied to each cylinder 122a based on the target engine speed and the target torque derived by the target value deriving unit 182. The throttle opening determination unit 188 derives the total target air amount of each cylinder 122a determined by the air amount determination unit 184, and determines the target throttle opening for intake of the total amount of air from the outside.

  The injection amount determination unit 186, based on the target air amount of each cylinder 122a determined by the air amount determination unit 184, for example, the fuel supplied to each cylinder 122a so that the air-fuel ratio is leaner than the stoichiometric air-fuel ratio. A target injection amount is determined. In addition, the injection amount determination unit 186 performs each injection based on a signal indicating the crank angle detected by the crank angle sensor 166 in order to inject the determined target injection amount from the injector 150 in the intake stroke or compression stroke of the engine 120. The target injection timing and target injection period of the injector 150 are determined.

  Based on the target engine speed derived by the target value deriving unit 182 and a signal indicating the crank angle detected by the crank angle sensor 166, the ignition timing determining unit 190 is a target of the spark plug 148 in each cylinder 122a. Determine the ignition timing.

  The drive control unit 192 drives a throttle valve actuator (not shown) so that the throttle valve 134 opens at the target throttle opening determined by the throttle opening determination unit 188. Further, the drive control unit 192 drives the injector 150 at the target injection timing and the target injection period determined by the injection amount determination unit 186, thereby causing the injector 150 to inject fuel of the target injection amount. Further, the drive control unit 192 ignites the spark plug 148 at the target ignition timing determined by the ignition timing determination unit 190.

  Thus, the exhaust gas generated by the combustion of the fuel in the combustion chamber 146 is discharged to the outside through the exhaust passage 140. The exhaust gas includes hydrocarbon (HC: HydroCarbon), one Since carbon oxide (CO) and nitrogen oxide (NOx) are contained, it is necessary to remove them. Therefore, the exhaust gas purification unit 200 is provided in the exhaust path 140, and the exhaust gas purification unit 200 removes hydrocarbons, carbon monoxide, and nitrogen oxides.

  The ECU 110 functions as the flow path control unit 194 when controlling the exhaust gas purification unit 200. The processing of the flow path control unit 194 will be described in detail later.

  FIG. 2 is a schematic diagram showing the configuration of the exhaust gas purification unit 200. In FIG. 2, the signal flow is indicated by broken arrows. As shown in FIG. 2, the exhaust gas purification unit 200 includes a three-way catalyst 210, a NOx storage reduction catalyst 212, a bypass passage 220, a water absorbing material 230, a first switching means 240, The second switching unit 242, the third switching unit 244, and the fourth switching unit 246 are included.

  The three-way catalyst 210 is provided in the exhaust path 140. The three-way catalyst 210 includes, for example, platinum (Pt), palladium (Pd), and rhodium (Rh). The three-way catalyst 210 removes hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas discharged from the exhaust port 136. Remove.

  The NOx occlusion reduction catalyst 212 is provided on the downstream side of the three-way catalyst 210 in the exhaust passage 140, temporarily occludes nitrogen oxides that could not be removed by the three-way catalyst 210, and the occluded nitrogen oxides have a predetermined timing. Reduce (purify).

  Specifically, the NOx occlusion reduction catalyst 212 occludes nitrogen oxides in a predetermined occlusion temperature range (for example, a temperature range of 300 ° C. to 500 ° C.), and the reduction is higher than the upper limit value of the occlusion temperature range. It has a characteristic of reducing nitrogen oxides at a temperature (for example, 550 ° C.) or higher. On the other hand, in the state where the air-fuel ratio is lean in the engine 120, that is, in the state where lean combustion (lean burn) is being performed, the state where the stoichiometric air-fuel ratio is set, or the state where the air-fuel ratio is rich, that is, rich combustion (rich rich) The amount of nitrogen oxide emission is larger than that in the state where the burn is performed, and the temperature of the exhaust gas is lower.

  Therefore, it is desirable that the NOx occlusion reduction catalyst 212 occludes nitrogen oxides in a state where lean combustion is performed, and reduces nitrogen oxides in a state where rich combustion is being performed. That is, it is preferable that the temperature of the exhaust gas is within the storage temperature range in the state where lean combustion is being performed, and the temperature of the exhaust gas is equal to or higher than the reduction temperature in the state where rich combustion is being performed. The engine 120 of the present embodiment normally performs lean combustion and intermittently performs rich combustion for a short period (for example, several seconds), so that the NOx storage reduction catalyst 212 performs nitrogen oxide during lean combustion. And nitrogen oxides are reduced during rich combustion.

  Here, in the state where the rich combustion is performed, the temperature of the exhaust gas becomes equal to or higher than the reduction temperature, so that the nitrogen oxide can be reduced. However, in the state where the lean combustion is performed, the temperature of the exhaust gas falls within the storage temperature range. It may exceed the reduction temperature. If it does so, there exists a possibility that the storage efficiency of the NOx storage reduction catalyst 212 may fall, and the removal rate of a nitrogen oxide may reduce.

  Therefore, the exhaust gas purification unit 200 according to the present embodiment includes a bypass 220, a water absorbing material 230, a first switching unit 240, a second switching unit 242, a third switching unit 244, and a fourth switching unit 246. When the temperature exceeds the storage temperature range (for example, when the temperature of the exhaust gas exceeds 500 ° C.), the exhaust gas flow path is switched from the exhaust path 140 to the bypass path 220 to cool to the storage temperature range.

  Specifically, the bypass path 220 is a flow path that branches (communication) from the exhaust path 140 and merges (communication) with the exhaust path 140, and includes a first sub flow path 222, a second sub flow path 224, 3 sub-channels 226 are included. The first sub flow path 222 is a flow path branched from the upstream side of the NOx storage reduction catalyst 212 in the exhaust path 140 and joined to the downstream side of the NOx storage reduction catalyst 212. The second sub flow path 224 is a flow path that connects the first sub flow path 222 and the downstream side of the joining point of the first sub flow path 222 in the exhaust path 140. The third sub flow path 226 is branched from between the branch point of the first sub flow path 222 in the exhaust passage 140 and the NOx occlusion reduction catalyst 212, and is the junction of the first sub flow path 222 in the exhaust path 140. It is a flow path that joins the downstream side.

  The water absorbing material 230 is made of, for example, a porous ceramic, and has a predetermined water absorption temperature (for example, 400) that is equal to or lower than the upper limit (for example, 500 ° C.) of the storage temperature range in which the NOx storage and reduction catalyst 212 stores nitrogen oxides. Adsorbs water (liquid or gas) at a temperature lower than (° C.) and releases water at a temperature higher than the water absorption temperature. In the present embodiment, the water absorbing material 230 has a water absorption temperature within the storage temperature range. The water absorbing material 230 is provided in the first sub-channel 222 between a communication location with the second sub-channel 224 and a junction location with the exhaust channel 140.

  Further, the water absorbing material 230 may be made of a ceramic having an electron bias, for example, a ceramic containing an alkali metal or an alkaline earth metal. Thereby, the water absorption efficiency of the water absorbing material 230 can be improved.

  The 1st switching means 240 is comprised by the switching valve provided in the branch location of the 1st subflow path 222 in the exhaust path 140, for example. The first switching means 240 includes an upstream side (three-way catalyst 210 side) of the first switching means 240 in the exhaust path 140 and a downstream side (NOx storage reduction catalyst 212 side) of the first switching means 240 in the exhaust path 140, or The flow path of the exhaust gas is switched so as to communicate with the first sub flow path 222. In other words, the first switching means 240 is located upstream of the branch point of the first sub-channel 222 in the exhaust path 140 and downstream of the branch point of the first sub-channel 222 in the exhaust path 140 or the first sub-flow path. The flow path of the exhaust gas is switched so as to communicate with the path 222.

  The 2nd switching means 242 is comprised by the switching valve provided in the communication location with the 2nd subchannel 224 in the 1st subchannel 222, for example. The second switching unit 242 includes an upstream side of the second switching unit 242 in the first sub-channel 222 and a downstream side (water absorbing material 230 side) of the first switching unit 240 in the first sub-channel 222, or a second The flow path of the exhaust gas is switched so as to communicate with the sub flow path 224. In other words, the second switching unit 242 is configured such that the upstream side of the first sub-channel 222 in communication with the second sub-channel 224, the downstream side of the communication location in the first sub-channel 222, or the second sub-flow path. The flow path of the exhaust gas is switched so as to communicate with the path 224.

  The 3rd switching means 244 is comprised by the switching valve provided in the confluence | merging location of the 1st subflow path 222 in the exhaust path 140, for example. The third switching unit 244 includes an upstream side of the third switching unit 244 in the exhaust passage 140 (NOx storage reduction catalyst 212 side) and a downstream side of the third switching unit 244 in the exhaust passage 140 (muffler 142 side), or The flow path of the exhaust gas is switched so as to communicate with the one sub flow path 222. That is, the third switching unit 244 communicates the upstream side of the joining point with the first sub flow path 222 in the exhaust passage 140 and the downstream side of the joining place in the exhaust passage 140 or the first sub flow path 222. Thus, the flow path of the exhaust gas is switched.

  The 4th switching means 246 is comprised by the switching valve provided in the branch location of the 3rd subflow path 226 in the exhaust path 140, for example. The fourth switching unit 246 includes an upstream side (three-way catalyst 210 side) of the fourth switching unit 246 in the exhaust passage 140 and a downstream side (NOx storage reduction catalyst 212 side) of the fourth switching unit 246 in the exhaust passage 140, or The flow path of the exhaust gas is switched so as to communicate with the third sub flow path 226. That is, the fourth switching unit 246 communicates the upstream side of the branch point of the third sub flow path 226 in the exhaust path 140 with the downstream side of the branch position of the exhaust path 140 or the third sub flow path 226. Then, the flow path of the exhaust gas is switched.

  The flow path control unit 194 controls the first switching unit 240, the second switching unit 242, the third switching unit 244, and the fourth switching unit 246 according to the operating conditions.

(Flow path switching process)
Next, the flow path switching process by the flow path control unit 194 will be described. FIG. 3 is a flowchart for explaining the flow of the flow path switching process, and FIG. 4 is a diagram for explaining the flow of the exhaust gas. In FIG. 4, the flow of exhaust gas is indicated by arrows. In the present embodiment, the flow path switching process is repeatedly performed by an interrupt that occurs at predetermined time intervals.

(Step S310)
As shown in FIG. 3, the flow path control unit 194 first determines that the temperature of the exhaust gas upstream of the NOx storage reduction catalyst 212 (here, between the three-way catalyst 210 and the first switching means 240) is the storage temperature range. Or less than the upper limit value (for example, 500 ° C.). In the present embodiment, the flow path control unit 194 estimates the exhaust gas temperature based on the engine speed derived by the target value deriving unit 182 and the signal indicating the accelerator opening acquired from the accelerator opening sensor 170. To do. More specifically, ECU 110 stores in advance an exhaust gas temperature map in which the engine speed and the accelerator opening are associated with the exhaust gas temperature. Then, the flow path control unit 194 refers to the exhaust gas temperature map stored in advance based on the signal indicating the engine speed and the accelerator opening, and determines the temperature of the exhaust gas upstream of the NOx storage reduction catalyst 212. Deriving an estimate. The estimated value thus derived is regarded as the temperature of the exhaust gas, and the flow path control unit 194 determines whether the temperature of the exhaust gas is less than the upper limit value of the storage temperature range.

  As a result, when it is determined that the temperature of the exhaust gas is less than the upper limit value of the storage temperature range (YES in step S310), the process proceeds to step S312 and is not less than the upper limit value of the storage temperature range (storage temperature). If it is determined that the value exceeds the upper limit of the range (NO in step S310), the process proceeds to step S314.

(Step S312)
The flow path control unit 194 has a first switching means 240 and a second switching so that the exhaust gas passes through the water absorbing material 230 after passing through the NOx storage reduction catalyst 212 (see FIG. 4A). The means 242, the third switching means 244, and the fourth switching means 246 are switched and controlled (water absorption flow path switching process), and the flow path switching process ends. That is, the flow path control unit 194 is configured such that the exhaust gas flow path includes the exhaust path 140, the three-way catalyst 210, the NOx storage reduction catalyst 212, the water absorbing material 230 (first sub flow path 222), the second sub flow path 224, The first switching unit 240, the second switching unit 242, the third switching unit 244, and the fourth switching unit 246 are controlled to be switched to the exhaust path 140.

  Thus, the water in the exhaust gas can be adsorbed by the water absorbing material 230 while the NOx storage reduction catalyst 212 stores the nitrogen oxides in the exhaust gas. Further, since the exhaust gas from which nitrogen oxides have been removed is guided to the water absorbing material 230, it is possible to prevent the water absorbing material 230 from being deteriorated by nitrogen oxides.

  4A, the exhaust gas passes through the NOx storage reduction catalyst 212 and then reaches the water absorbing material 230. That is, after being cooled by the NOx storage reduction catalyst 212, the water absorbing material 230 is discharged. To reach. Therefore, when the temperature of the exhaust gas upstream of the NOx storage reduction catalyst 212 is less than the upper limit value of the storage temperature range, the exhaust gas passing through the water absorbing material 230 is lower than the water absorbing temperature, and the water absorbing material At 230, water in the exhaust gas can be adsorbed.

(Step S314)
The flow path control unit 194 determines whether the temperature of the exhaust gas upstream of the NOx storage reduction catalyst 212 is equal to or higher than the heat resistance temperature (for example, 1000 ° C.) of the water absorbing material 230. As a result, if it is determined that the temperature is equal to or higher than the heat resistant temperature (YES in step S314), the process proceeds to step S318. If it is determined that the temperature is not equal to or higher than the heat resistant temperature (NO in step S314), the process proceeds to step S316. Move.

(Step S316)
The flow path control unit 194 is configured so that the exhaust gas passes through the water absorbing material 230 and then becomes a flow path that passes through the NOx storage reduction catalyst 212 (see FIG. 4B). The unit 242, the third switching unit 244, and the fourth switching unit 246 are controlled to be switched (discharge channel switching process), and the channel switching process is ended. In other words, in the flow path control unit 194, the exhaust gas flow path becomes the exhaust path 140, the water absorbing material 230 (first sub flow path 222), the NOx storage reduction catalyst 212, the third sub flow path 226, and the exhaust path 140. As described above, the first switching unit 240, the second switching unit 242, the third switching unit 244, and the fourth switching unit 246 are controlled to be switched.

  Thereby, the water adsorbed by the water absorbing material 230 can be released by the heat of the exhaust gas, and the released water can be guided to the NOx storage reduction catalyst 212. Therefore, the NOx storage reduction catalyst 212 can be cooled with the released water, and the NOx storage reduction catalyst 212 can be within the storage temperature range.

(Step S318)
The flow path control unit 194 is configured so that the exhaust gas becomes a flow path that passes through the NOx occlusion reduction catalyst 212 without passing through the water absorbing material 230 (see FIG. 4C). The means 244 and the fourth switching means 246 are controlled to be switched (main flow path switching process), and the flow path switching process is terminated. That is, the flow path control unit 194 includes the first switching unit 240 and the third switching unit 244 so that the exhaust gas flow path becomes the exhaust path 140, the three-way catalyst 210, the NOx storage reduction catalyst 212, and the exhaust path 140. The fourth switching means 246 is controlled to be switched.

  Thereby, when the temperature of the exhaust gas is equal to or higher than the heat resistant temperature of the water absorbing material 230, it is possible to avoid the situation where the exhaust gas is guided to the water absorbing material 230, and it is possible to prevent deterioration of the water absorbing material 230. Further, since the NOx storage reduction catalyst 212 is passed, nitrogen oxides can be reliably removed (reduced) from the exhaust gas.

  As described above, according to the exhaust gas purification apparatus of the present embodiment configured by the exhaust gas purification unit 200 and the flow path control unit 194, the NOx occlusion can be achieved with a simple configuration in which the water absorbing material 230 is provided in the bypass passage 220. The reduction catalyst 212 can be cooled. As a result, the NOx occlusion reduction catalyst 212 can be lowered to the occlusion temperature range, and the nitrogen oxide occlusion efficiency by the NOx occlusion reduction catalyst 212 can be improved.

  In addition, a complicated mechanism for circulating water is not required as compared with the conventional configuration in which the exhaust gas is cooled by water cooling, and the maintenance labor can be reduced. Furthermore, according to the exhaust gas purification apparatus of the present embodiment, the exhaust gas is cooled using the water in the exhaust gas that has been disposed of in the past, so it is not necessary to procure water dedicated to cooling, and water is required. Cost can be reduced.

(Modification)
FIG. 5 is a diagram for explaining an exhaust gas purification unit 400 according to a modification. As shown in FIG. 5, the exhaust gas purification unit 400 includes a three-way catalyst 210, a NOx storage reduction catalyst 212, a bypass passage 420, a water absorbing material 230, and a switching means 440. In addition, about the component substantially the same as the exhaust gas purification unit 200 of embodiment mentioned above, the same code | symbol is attached | subjected and description is abbreviate | omitted, and here the bypass path 420 and the switching means 440 from which a structure differs are explained in full detail. To do.

  The bypass passage 420 is a passage that branches off from the upstream side of the NOx storage reduction catalyst 212 in the exhaust passage 140 and joins the upstream side of the NOx storage reduction catalyst 212 on the downstream side of the branch point. In the modification, the water absorbing material 230 is provided in the bypass passage 420.

  The switching unit 440 is configured by, for example, a switching valve provided at a branch point of the bypass path 420 in the exhaust path 140 and switches the exhaust gas flow path to the exhaust path 140 or the bypass path 420.

  In the present embodiment, the flow path control unit 194 performs switching control of the switching unit 440.

(Flow path switching process)
Next, the flow path switching process by the flow path control unit 194 according to the modification will be described. FIG. 6 is a diagram for explaining the flow of the flow path switching process according to the modification. Further, in the modification, the flow path switching process is repeatedly performed by interruptions generated at predetermined time intervals.

(Step S510)
As shown in FIG. 6, the flow path control unit 194 first determines the temperature of the exhaust gas upstream of the NOx storage reduction catalyst 212 (here, between the three-way catalyst 210 and a branch point of the bypass passage 420). The lower limit value of the storage temperature range (for example, 300 ° C.) and less than the water absorption temperature (for example, 400 ° C.), or the upper limit value of the storage temperature range (for example, 500 ° C.) It is determined whether the temperature is lower than the heat resistant temperature (for example, 1000 ° C.). As a result, when it is determined that it is equal to or higher than the lower limit value of the occlusion temperature range and lower than the water absorption temperature, or higher than the upper limit value of the occlusion temperature range and lower than the heat resistant temperature (YES in step S510). Moves the process to step S512. On the other hand, if it is determined that the temperature is not the temperature from the lower limit value of the occlusion temperature range to the water absorption temperature and the temperature from the upper limit value of the occlusion temperature range to the heat resistant temperature (NO in step S510), the process proceeds to step S514. .

(Step S512)
The flow path control unit 194 controls the switching means 440 to switch the flow path of the exhaust gas as a flow path that passes through the bypass path 420 (water absorbing material 230) and passes through the NOx storage reduction catalyst 212. The process ends.

(Step S514)
The flow path control unit 194 controls the switching means 440 so that the exhaust gas flow path passes through the NOx occlusion reduction catalyst 212 without passing through the bypass path 420 (water absorbing material 230). The switching process is terminated.

  As shown in FIG. 7, the flow path control unit 194 performs the processes of steps S510, S512, and S514 until the exhaust gas temperature reaches the lower limit value of the storage temperature range, as shown in FIG. The flow path is a flow path that passes through the NOx storage reduction catalyst 212 without passing through the bypass path 420. Thereby, the NOx storage reduction catalyst 212 can be efficiently heated to the storage temperature.

  When the temperature of the exhaust gas reaches the lower limit value of the storage temperature range, the flow path control unit 194 switches the flow path of the exhaust gas to the bypass path 420. Thereby, the water in exhaust gas can be made to adsorb | suck to the water absorbing material 230. FIG.

  When the temperature of the exhaust gas reaches the water absorption temperature, the flow path control unit 194 switches the flow path of the exhaust gas to a flow path that passes through the NOx storage reduction catalyst 212 without passing through the bypass path 420. As a result, even though the NOx occlusion reduction catalyst 212 is within the occlusion temperature range, that is, there is no need to cool the NOx occlusion reduction catalyst 212, water is released from the water absorbing material 230. It can be avoided.

  When the NOx occlusion reduction catalyst 212 exceeds the upper limit value of the occlusion temperature range, the flow path control unit 194 switches the exhaust gas flow path to the bypass path 420. Thereby, the NOx occlusion reduction catalyst 212 can be cooled, and the NOx occlusion reduction catalyst 212 can be in the occlusion temperature range.

  When the temperature of the exhaust gas exceeds the lower limit value of the reduction temperature and becomes equal to or higher than the heat-resistant temperature of the water absorbing material 230, the flow path control unit 194 passes through the exhaust gas flow path without passing through the bypass path 420. The flow path is switched to 212. Thereby, the situation where exhaust gas is led to the water absorbing material 230 can be avoided, and the water absorbing material 230 can be prevented from deteriorating.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this embodiment. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Is done.

  In the above embodiment, the configuration in which the ECU 110 functions as the flow path control unit 194 has been described as an example. However, the flow path control unit 194 may be configured separately from the ECU 110.

  Further, in the above-described embodiment, the flow path control unit 194 is described by taking as an example a configuration that estimates the temperature of the exhaust gas with reference to the temperature map based on the signal indicating the engine speed and the accelerator opening. did. However, a temperature sensor may be provided and the temperature sensor may measure the temperature of the exhaust gas.

  Further, in the above embodiment, the flow path control unit 194 has the first switching means 240, the first switching means 240 based on the temperature of the exhaust gas flowing between the three-way catalyst 210 and the branch location of the first sub flow path 222. The configuration for controlling the switching of the 2 switching unit 242, the third switching unit 244, and the fourth switching unit 246 has been described as an example. However, the flow path control unit 194, for example, based on the temperature of the exhaust gas upstream of the three-way catalyst 210, the first switching unit 240, the second switching unit 242, the third switching unit 244, the fourth switching unit 246. May be switched.

  Similarly, in the above modification, an example of a configuration in which the flow path control unit 194 performs switching control of the switching unit 440 based on the temperature of the exhaust gas flowing between the three-way catalyst 210 and the branch point of the bypass passage 420 is taken as an example. And explained. However, the flow path control unit 194 may perform switching control of the switching unit 440 based on, for example, the temperature of the exhaust gas upstream of the three-way catalyst 210.

  Further, in the above modification, the flow path control unit 194 allows the exhaust gas flow when the temperature of the exhaust gas upstream of the NOx storage reduction catalyst 212 exceeds the upper limit value of the storage temperature range and is lower than the heat resistance temperature. The configuration for switching the path to the bypass path 420 has been described as an example. However, the flow path control unit 194 may switch the flow path of the exhaust gas to the exhaust path 140 when the temperature of the exhaust gas becomes equal to or higher than the lower limit value of the reduction temperature lower than the heat resistance temperature. As a result, it is possible to avoid a situation in which the exhaust gas that has reached the lower limit of the reduction temperature is cooled by the water absorbing material 230, and it is possible to reduce the nitrogen oxides in the exhaust gas with the NOx storage reduction catalyst 212. It becomes.

  Moreover, in the said embodiment, the structure which exhaust gas always passes the NOx storage reduction catalyst 212 was mentioned as an example, and was demonstrated. However, when the engine 120 is burning stoichiometrically, the NOx storage reduction catalyst 212 does not have to pass because the three-way catalyst 210 can remove nitrogen oxides. That is, the flow path control unit 194 includes the first switching unit 240 and the fourth switching unit so that the exhaust gas flow path becomes the exhaust path 140, the three-way catalyst 210, the third sub-flow path 226, and the exhaust path 140. 246 may be switched. With this configuration, it is possible to prevent the NOx storage reduction catalyst 212 from being deteriorated.

  Moreover, in the said embodiment, the case where the three-way catalyst 210 and the NOx storage reduction catalyst 212 were comprised separately was demonstrated as an example. However, the three-way catalyst 210 and the NOx storage reduction catalyst 212 may be arranged in one casing.

  INDUSTRIAL APPLICABILITY The present invention can be used for an exhaust gas purification device that purifies exhaust gas discharged from a combustion chamber of an engine.

120 Engine 140 Exhaust path 146 Combustion chamber 194 Flow path control unit (exhaust gas purification device)
200, 400 Exhaust gas purification unit (exhaust gas purification device)
212 NOx storage reduction catalyst 220, 420 Bypass path 222 First sub flow path 224 Second sub flow path 226 Third sub flow path 230 Water absorbing material 240 First switching means 242 Second switching means 244 Third switching means 246 Fourth switching means

Claims (3)

A NOx occlusion reduction catalyst which is provided in a main exhaust passage through which exhaust gas discharged from the combustion chamber of the engine is guided and occludes nitrogen oxides in a predetermined temperature range;
Provided in a bypass passage that branches off from the main exhaust passage and merges with the main exhaust passage, adsorbs water below a predetermined water absorption temperature below the upper limit value of the predetermined temperature range, and absorbs water above the water absorption temperature. A water absorbing material to be released;
When the temperature of the exhaust gas upstream of the NOx occlusion reduction catalyst exceeds the upper limit value of the predetermined temperature range, the exhaust gas is passed through the water absorbing material disposed in the bypass passage, and then the NOx occlusion is performed. A flow path control unit for controlling the flow path of the exhaust gas so as to pass through the reduction catalyst;
An exhaust gas purifying device comprising: The flow path controller
When the temperature of the exhaust gas upstream of the NOx storage reduction catalyst is within the predetermined temperature range, the exhaust gas is passed through the NOx storage reduction catalyst, and then the water absorbing material disposed in the bypass passage The exhaust gas purification device according to claim 1, wherein the exhaust gas flow path is controlled so as to pass through the exhaust gas. The bypass path is
A first sub-channel branched from the upstream side of the NOx storage reduction catalyst in the main exhaust passage and joined to the downstream side of the NOx storage reduction catalyst;
A second sub-flow path that communicates the first sub-flow path and a downstream side of a joining point of the first sub-flow path in the main exhaust path;
A first branch is formed between the branch point of the first sub-flow path in the main exhaust path and the NOx occlusion reduction catalyst, and joins downstream of the merge point with the first sub-flow path in the main exhaust path. Three sub-channels;
With
The water absorbing material is provided between a communication location with the second sub flow channel in the first sub flow channel and a merge location with the main exhaust channel,
The exhaust gas is connected so that the upstream side of the branch point of the first sub-flow path in the main exhaust path communicates with the downstream side of the branch point of the main exhaust path or the first sub-flow path. First switching means for switching the flow path;
The upstream side of the first sub-channel and the second sub-channel is connected to the upstream side of the communication point with the second sub-channel, and the downstream side of the communication point of the first sub-channel or the second sub-channel. Second switching means for switching the flow path of the exhaust gas;
The exhaust gas so as to communicate the upstream side of the junction with the first sub-flow path in the main exhaust path and the downstream side of the junction in the main exhaust path or the first sub-flow path. Third switching means for switching the flow path of
The exhaust gas is connected so that the upstream side of the branch point of the third sub-flow path in the main exhaust path communicates with the downstream side of the branch point of the main exhaust path or the third sub-flow path. A fourth switching means for switching the flow path;
With
3. The exhaust according to claim 1, wherein the flow path control unit performs switching control of the first switching unit, the second switching unit, the third switching unit, and the fourth switching unit. Gas purification device.

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