JP2017166462A - Evaporated fuel treatment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve fuel economy by efficiently using evaporated fuel, and to restrain deterioration of power performance.SOLUTION: An evaporated fuel treatment device (an exhaust gas emission control device 200) for treating evaporated fuel generated in a fuel tank 220 for storing liquid fuel includes a circulation flow passage 230 which is connected to the fuel tank and in which mixed gas containing the evaporated fuel generated in the fuel tank is circulated, a canister 240 which is provided in the circulation flow passage so as to adsorb the evaporated fuel in the mixed gas, a pump 270 (circulation amount adjusting means) for adjusting a circulation amount of the mixed gas in the circulation flow passage, an NOx storage reduction catalyst 212 provided in an exhaust passage 140 of an engine, and fuel introduction means (a purge flow passage 250, an introduction flow passage 260, and the pump 270) desorbing the evaporated fuel adsorbed to the canister from the canister and introducing the evaporated fuel to the NOx storage reduction catalyst.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an evaporated fuel processing apparatus that processes evaporated fuel generated in a fuel tank.

  Evaporated fuel generated in the fuel tank contains hydrocarbons (HC) that cause air pollution. For this reason, a canister is provided in a vehicle equipped with a fuel tank, and the evaporated fuel generated in the fuel tank is adsorbed by an adsorbent in the canister. When the amount of fuel adsorbed in the canister exceeds a predetermined threshold, the purge flow path connecting the canister and the intake path is opened, and the fuel is desorbed from the adsorbent by the negative pressure in the intake path. Thus, the desorbed fuel is supplied to the intake passage, and the evaporated fuel is processed.

  Also, after the canister is sucked with a pump to desorb the evaporated fuel, the evaporated fuel is introduced upstream of a NOx storage reduction catalyst (Lean NOx Trap, hereinafter referred to as “LNT”) and used as a reducing agent. The technique which performs is also developed (for example, patent document 1).

JP-A-7-127503

  In the technique disclosed in Patent Document 1, the amount of evaporated fuel adsorbed in the canister may not be enough for the reduction of nitrogen oxides stored in the LNT. In this case, it is necessary to perform rich combustion similarly to a general reduction process of LNT, and there is a problem that fuel efficiency is reduced and power performance is reduced.

  Therefore, an object of the present invention is to provide an evaporative fuel processing apparatus that can improve fuel efficiency and suppress a decrease in power performance by efficiently using evaporative fuel.

  In order to solve the above problems, an evaporated fuel processing apparatus of the present invention is an evaporated fuel processing apparatus that processes evaporated fuel generated in a fuel tank that stores liquid fuel, and is connected to the fuel tank, and the fuel tank A circulation channel through which the mixed gas containing the evaporated fuel generated in step circulates, a canister provided in the circulation channel to adsorb the evaporated fuel in the mixed gas, and circulation of the mixed gas in the circulation channel A circulation amount adjusting means for adjusting the amount; a NOx occlusion reduction catalyst provided in an engine exhaust passage; and a fuel introduction means for desorbing the evaporated fuel adsorbed by the canister from the canister and leading to the NOx occlusion reduction catalyst. And.

  The fuel introducing means may desorb the evaporated fuel adsorbed by the canister and guide it to the NOx occlusion reduction catalyst when the occlusion amount of the NOx occlusion reduction catalyst is equal to or greater than a predetermined occlusion threshold.

  Further, the circulation amount adjusting means is a case where the storage amount of the NOx storage reduction catalyst is greater than or equal to the storage threshold, and the amount of adsorption of the evaporated fuel in the canister is the nitrogen stored in the NOx storage reduction catalyst. When the amount is less than a predetermined reduction threshold required for the reduction of the oxide, the circulation amount of the mixed gas is increased, and the fuel introduction means has a storage amount of the NOx storage reduction catalyst equal to or greater than the storage threshold, and the canister If the amount of the evaporated fuel adsorbed in is equal to or greater than the reduction threshold, the evaporated fuel may be desorbed from the canister and guided to the NOx storage reduction catalyst.

  According to the present invention, by efficiently using evaporated fuel, it is possible to improve fuel efficiency and suppress a decrease in power performance.

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 apparatus. It is a flowchart explaining an evaporative fuel process.

  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 collecting portion of the exhaust manifold 138 through an exhaust passage 140, and an exhaust gas purification device 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. Further, the ECU 110 functions as a flow path switching unit 194 when controlling an exhaust gas purification device 200 described later. The flow path switching unit 194 will be described in detail later.

  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 the map stored in advance 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 rotation. Deriving a number.

  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. Further, the injection amount determination unit 186 is based on a signal indicating the crank angle detected by the crank angle sensor 166 in order to inject the fuel of 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 each 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 path 140. The exhaust gas includes hydrocarbons and carbon monoxide (CO). Since nitrogen oxides (NOx) are contained, these must be removed. Therefore, the exhaust gas purification device 200 is provided in the exhaust passage 140, and the exhaust gas purification device 200 removes hydrocarbons, carbon monoxide, and nitrogen oxides.

  FIG. 2 is a schematic diagram showing the configuration of the exhaust gas purification device 200. In FIG. 2, the flow of signals is indicated by broken arrows, the flow of exhaust gas is indicated by white arrows, and the flows of evaporated fuel, mixed gas, and air are indicated by solid arrows. As shown in FIG. 2, the exhaust gas purification apparatus 200 includes a three-way catalyst 210, a NOx occlusion reduction catalyst 212, a fuel tank 220, a circulation passage 230, a canister 240, and a purge flow. The passage 250, the introduction passage 260, the pump 270, the first switching valve 280, the second switching valve 282, and the check valve 284 are configured.

  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).

  More specifically, the NOx occlusion reduction catalyst 212 occludes nitrogen oxides in a lean atmosphere (and a predetermined occlusion temperature range), and removes the occluded nitrogen oxides from a rich atmosphere (and an upper limit value of the occlusion temperature range). Also has a property of reducing at a high reduction temperature or higher).

The engine 120 of this embodiment normally performs lean combustion, and intermittently performs rich combustion intermittently for a short period (for example, several seconds). Nitrogen oxides exhausted during lean combustion are stored in the NOx storage reduction catalyst 212, and the stored nitrogen oxides are reduced during rich combustion.

  The fuel tank 220 stores liquid fuel. The liquid fuel stored in the fuel tank 220 is injected into the combustion chamber 146 through the injector 150. Connected to the fuel tank 220 is a circulation passage 230 through which a mixed gas containing evaporated fuel generated in the fuel tank 220 circulates. The circulation flow path 230 is configured by a pipe having one end connected to the upper portion of the fuel tank 220 and the other end connected to the side surface of the fuel tank 220.

  The canister 240 is provided in the circulation channel 230 and is filled with an adsorbent (for example, activated carbon) that adsorbs evaporated fuel. The purge flow path 250 is configured by a pipe having one end open to the atmosphere and the other end connected to the downstream side of the fuel tank 220 and the upstream side of the canister 240 in the circulation flow path 230. The introduction flow path (fuel introduction means) 260 has one end connected downstream of the canister 240 in the circulation flow path 230 and upstream of the fuel tank 220, and the other end downstream of the three-way catalyst 210 in the exhaust path 140. In this case, the pipe is connected to the upstream side of the NOx storage reduction catalyst 212.

  The pump 270 is provided on the downstream side of the canister 240 in the circulation channel 230 and on the upstream side of the fuel tank 220, and functions as a circulation amount adjusting unit that adjusts the circulation amount of the mixed gas in the circulation channel 230. The pump 270 functions as a fuel introduction unit that sucks air from the purge flow path 250 to desorb the evaporated fuel from the canister 240 (adsorbent) and guides it to the NOx occlusion reduction catalyst 212 via the introduction flow path 260. To do.

  The first switching valve 280 is provided at a connection point between the circulation flow path 230 and the purge flow path 250, and switches the connection on the upstream side of the canister 240 between the upper part of the fuel tank 220 and the purge flow path 250. The second switching valve 282 is provided at a connection location between the circulation flow path 230 and the introduction flow path 260, and switches the connection on the downstream side of the canister 240 between the side surface of the fuel tank 220 and the introduction flow path 260. The check valve 284 is provided in the introduction flow path 260 and prevents the exhaust gas from flowing back into the canister 240.

  The flow path switching unit 194 controls the pump 270, the first switching valve 280, and the second switching valve 282. Hereinafter, specific processing of control by the flow path switching unit 194 will be described.

  FIG. 3 is a flowchart for explaining the evaporated fuel processing. The evaporated fuel process is executed as an interrupt process at predetermined time intervals. In the initial state, the first switching valve 280 communicates between the upper part of the fuel tank 220 and the canister 240 and blocks communication between the purge flow path 250 and the canister 240. The second switching valve 282 communicates between the canister 240 and the side surface of the fuel tank 220 and blocks communication between the canister 240 and the introduction flow path 260. Further, the pump 270 is stopped.

(Step S110)
The flow path switching unit 194 determines whether the nitrogen oxide storage amount of the NOx storage reduction catalyst 212 exceeds a predetermined first predetermined value. Here, the first predetermined value is a predetermined value less than the maximum storage amount of the NOx storage reduction catalyst 212 (for example, about 80% to 90% of the maximum storage amount). As a result, if it is determined that the occlusion amount exceeds the first predetermined value, the process proceeds to step S120, and if it is determined that the occlusion amount is equal to or less than the first predetermined value, the evaporated fuel process is terminated.

  In the present embodiment, an unillustrated ROM provided in the ECU 110 holds an exhaust amount map in which the operating conditions of the engine 120 and the exhaust amount are associated with each other. Then, the flow path switching unit 194 estimates the occlusion amount of the NOx occlusion reduction catalyst 212 by accumulating the exhaust amount corresponding to the operation time under each operation condition with reference to the exhaust amount map.

(Step S120)
The flow path switching unit 194 determines whether the amount of evaporated fuel adsorbed in the canister 240 (adsorbent) exceeds a predetermined reduction threshold. Here, the reduction threshold is the amount of fuel (reducing agent) necessary for reduction of nitrogen oxides stored in the NOx storage reduction catalyst 212. As a result, when it is determined that the adsorption amount exceeds the reduction threshold, the process proceeds to step S130, and when it is determined that the adsorption amount is equal to or less than the reduction threshold, the process proceeds to step S140.

  In the present embodiment, an unillustrated ROM provided in the ECU 110 has an outside air temperature, a circulation amount of the mixed gas (a flow rate of the mixed gas circulating through the circulation flow path 230), and an adsorption of evaporated fuel in the canister 240. An adsorption amount map associated with the amount is stored in advance. Then, the flow path switching unit 194 estimates the adsorption amount of the canister 240 based on the outside air temperature and the circulation amount of the mixed gas with reference to the adsorption amount map.

(Step S130)
The flow path switching unit 194 determines whether or not the current operation state is a predetermined operation state (whether or not the estimated exhaust gas temperature has reached the reduction temperature of the NOx storage reduction catalyst 212). As a result, when it determines with it being a predetermined driving | running state, a process is moved to step S150. If it is determined that it is not in the predetermined operating state, it waits until it reaches the predetermined operating state.

(Step S140)
The flow path switching unit 194 switches and controls the first switching valve 280 to connect the upper portion of the fuel tank 220 and the canister 240 and to block communication between the purge flow path 250 and the canister 240. Further, the flow path switching unit 194 controls the second switching valve 282 to connect the canister 240 and the side surface of the fuel tank 220, and blocks communication between the canister 240 and the introduction flow path 260. Then, the flow path switching unit 194 drives the pump 270.

  Then, the mixed gas generated in the fuel tank 220 is sent from the upper part of the fuel tank 220 to the circulation channel 230, passes through the canister 240, and is reintroduced from the canister 240 to the side surface of the fuel tank 220. The circulation channel 230 and the fuel tank 220 are circulated. This makes it possible to increase the amount of evaporated fuel adsorbed in the canister 240.

(Step S150)
The flow path switching unit 194 switches and controls the first switching valve 280 to connect the purge flow path 250 and the canister 240 and to block communication between the upper part of the fuel tank 220 and the canister 240. The flow path switching unit 194 controls the second switching valve 282 to connect the canister 240 and the introduction flow path 260, and blocks communication between the canister 240 and the side surface of the fuel tank 220.

  As a result, the evaporated fuel adsorbed on the canister 240 is desorbed and introduced into the NOx storage reduction catalyst 212. Therefore, in the NOx occlusion reduction catalyst 212, nitrogen oxides are reduced by the evaporated fuel.

  In this way, the evaporated fuel generated in the fuel tank 220 is once adsorbed to the canister 240, and introduced into the NOx storage reduction catalyst 212 as needed to be used as a reducing agent, thereby efficiently using the evaporated fuel. be able to. That is, the exhaust gas purification apparatus 200 also functions as an evaporative fuel processing apparatus that processes evaporative fuel.

  Further, since the canister 240 is provided closer to the NOx occlusion reduction catalyst 212 than the intake passage 130, the canister 240 can be shortened as compared with the conventional technique in which the evaporated fuel is introduced into the intake passage 130. Therefore, the number of parts can be reduced, and the cost can be reduced.

  Further, since the evaporated fuel can be used as a reducing agent for the NOx storage reduction catalyst 212, the time for performing rich combustion can be shortened, or the amount of fuel injected when performing rich combustion can be reduced. Therefore, it is possible to suppress a reduction in power performance of engine 120 and improve fuel efficiency.

(Step S160)
The flow path switching unit 194 determines whether the nitrogen oxide storage amount of the NOx storage reduction catalyst 212 is equal to or less than a predetermined second predetermined value. As a result, when it is determined that the storage amount is equal to or less than the second predetermined value, the process proceeds to step S170, and when it is determined that the storage amount exceeds the second predetermined value, the process proceeds to step S120. Note that the second predetermined value may be equal to the first predetermined value, or may be any value less than the first predetermined value.

(Step S170)
The flow path switching unit 194 switches and controls the first switching valve 280 to connect the upper portion of the fuel tank 220 and the canister 240 and to block communication between the purge flow path 250 and the canister 240. Further, the flow path switching unit 194 controls the second switching valve 282 to connect the canister 240 and the side surface of the fuel tank 220, and blocks communication between the canister 240 and the introduction flow path 260. Then, the flow path switching unit 194 stops the pump 270.

  As described above, according to the exhaust gas purification apparatus 200 according to the present embodiment, the evaporated fuel generated in the fuel tank 220 can be used as a reducing agent for the NOx storage reduction catalyst 212. Therefore, it is possible to reduce the cost required for processing the evaporated fuel. Even if the adsorption amount of the canister 240 is less than the reduction threshold, the adsorption amount of the canister 240 can be increased by increasing the circulation amount of the mixed gas in the circulation flow path 230. For this reason, it is possible to reduce the fuel injection amount, improve the fuel efficiency, and suppress the deterioration of the power performance.

  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.

  For example, in the above embodiment, the configuration in which the introduction channel 260 is connected to the circulation channel 230 has been described as an example. However, the connection position of the introduction channel 260 is not limited as long as the evaporated fuel adsorbed by the canister 240 can be guided to the NOx storage reduction catalyst 212. For example, one end of the introduction channel 260 may be directly connected to the canister 240.

  In the above embodiment, the configuration in which the other end of the circulation flow path 230 is connected to a portion of the side surface of the fuel tank 220 located above the liquid level of the liquid fuel has been described as an example. However, the configuration of the circulation channel 230 is not limited as long as the mixed gas can be circulated. For example, the other end of the circulation channel 230 may be connected to a portion of the side surface of the fuel tank 220 located below the liquid level of the liquid fuel. In this case, since the liquid fuel is bubbled by the mixed gas, the generation amount of the evaporated fuel can be increased.

  Moreover, in the said embodiment, the flow-path switching part 194 demonstrated and demonstrated the structure which estimates the occlusion amount of the NOx occlusion reduction catalyst 212 based on the displacement map. However, a NOx sensor may be provided in the exhaust passage 140, and the storage amount of the NOx storage reduction catalyst 212 may be estimated based on a signal from the NOx sensor. For example, a NOx sensor is provided on the downstream side of the NOx storage reduction catalyst 212 in the exhaust passage 140, and if the NOx sensor detects NOx, it is determined that the storage amount of the NOx storage reduction catalyst 212 exceeds the first predetermined value. Good.

  Further, a flow path for sending the evaporated fuel desorbed from the canister 240 to the intake system may be provided.

  INDUSTRIAL APPLICABILITY The present invention can be used for an evaporated fuel processing apparatus that processes evaporated fuel generated in a fuel tank.

120 Engine 140 Exhaust passage 146 Combustion chamber 200 Exhaust gas purification device (evaporated fuel processing device)
212 NOx storage reduction catalyst 220 Fuel tank 230 Circulation flow path 240 Canister 250 Purge flow path (fuel introduction means)
260 Introduction channel (fuel introduction means)
270 Pump (circulation amount adjusting means, fuel introducing means)

Claims (3)

An evaporative fuel processing apparatus for processing evaporative fuel generated in a fuel tank that stores liquid fuel,
A circulation passage connected to the fuel tank, through which a mixed gas containing the evaporated fuel generated in the fuel tank circulates;
A canister that is provided in the circulation channel and adsorbs the evaporated fuel in the mixed gas;
A circulation amount adjusting means for adjusting a circulation amount of the mixed gas in the circulation channel;
A NOx storage reduction catalyst provided in the exhaust passage of the engine;
Fuel introduction means for desorbing the evaporated fuel adsorbed by the canister from the canister and leading it to the NOx storage reduction catalyst;
An evaporative fuel processing apparatus comprising:   The fuel introduction means desorbs the evaporated fuel adsorbed by the canister and guides it to the NOx occlusion reduction catalyst when the occlusion amount of the NOx occlusion reduction catalyst is not less than a predetermined occlusion threshold. The evaporative fuel processing apparatus according to 1. The circulation amount adjusting means is a case where the storage amount of the NOx storage reduction catalyst is greater than or equal to the storage threshold, and the amount of adsorption of the evaporated fuel in the canister is the nitrogen oxide stored in the NOx storage reduction catalyst The amount of circulation of the mixed gas is increased when it is less than a predetermined reduction threshold required for the reduction of
The fuel introduction means desorbs the vaporized fuel from the canister when the occlusion amount of the NOx occlusion reduction catalyst is equal to or greater than the occlusion threshold value and the adsorption amount of the vaporized fuel in the canister is equal to or greater than the reduction threshold value. The evaporative fuel processing device according to claim 2, wherein the evaporative fuel processing device is led to the NOx storage reduction catalyst.

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