JP2019031920A - Exhaust emission control device - Google Patents

Abstract

To restore storage capacity of oxygen with an OSC material, and prevent deterioration of fuel economy.SOLUTION: An exhaust emission control device 200 comprises: a three-way catalyst 210 provided in an exhaust passage 140 of an engine, and containing an OSC material; a precursor supply unit 220 configured to supply reductant precursor to an upstream side of the three-way catalyst 210 in an exhaust passage 140, wherein the reductant precursor contains one or both of alcohol or hydrocarbon having three or less carbons; and a supply control unit 240 configured to, when a predetermined fuel cut termination condition is established, control the precursor supply unit 220 to start supplying the reductant precursor.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an exhaust gas purification device that purifies exhaust gas.

  In order to purify hydrocarbons (HydroCarbon: HC), carbon monoxide (CO), and nitrogen oxides (NOx) in the exhaust gas discharged from the engine, a three-way catalyst (Three-Way Catalyst) is provided in the exhaust passage. Is provided.

  By the way, while the fuel cut is being executed, the intake air reaches the three-way catalyst without being burned. For this reason, when the fuel cut ends (when returning from the fuel cut), the amount of oxygen stored by the OSC (Oxygen Storage Capacity) material included in the three-way catalyst reaches saturation (upper limit). There is. When combustion is performed in the engine with the OSC material reaching saturation, the reduction of oxygen in the exhaust gas by the OSC material is not performed, and the reduction efficiency of NOx by the noble metal contained in the three-way catalyst is reduced.

  Therefore, conventionally, after the fuel cut is completed, the air-fuel ratio is made richer than the stoichiometric air-fuel ratio (stoichiometric), the hydrocarbon in the exhaust gas functions as a reducing agent, oxygen is released from the OSC material, and the oxygen storage capacity is restored. (For example, Patent Document 1).

Japanese Patent Laid-Open No. 2005-69188

  However, the technique of excessively injecting fuel as in Patent Document 1 has a problem that the fuel consumption is reduced.

  An object of the present invention is to provide an exhaust gas purifying device capable of suppressing a reduction in fuel consumption while restoring the oxygen storage capacity of the OSC material.

  In order to solve the above problems, an exhaust gas purifying apparatus of the present invention is provided in an exhaust passage of an engine, and includes a three-way catalyst including an OSC material, an alcohol on the upstream side of the three-way catalyst in the exhaust passage, and A precursor supply unit that supplies a reducing agent precursor containing one or both of hydrocarbons having 3 or less carbon atoms, and controls the precursor supply unit when a predetermined fuel cut end condition is satisfied. And a supply control unit for starting the supply of the reducing agent precursor.

  Further, the supply control unit is based on the temperature of the three-way catalyst and the flow rate of the exhaust gas passing through the three-way catalyst in at least a part of the period in which the supply of fuel to the engine is cut, The supply amount of the reducing agent precursor may be controlled.

  The alcohol may be one or more of methanol, ethanol, and propanol.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to suppress the fall of a fuel consumption, recovering the oxygen storage capability by OSC material.

It is the schematic which shows the structure of an engine system. It is a figure explaining an exhaust-gas purification apparatus. It is a flowchart which shows the supply process of the reducing agent precursor by a supply control part.

  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 showing the configuration of the engine system 100. 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 the collective portion of the exhaust manifold 138 through an exhaust passage 140, and a three-way catalyst 210 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 also provided with a crank angle sensor 166 that detects the crank angle of the crankshaft and an accelerator opening sensor 168 that detects the opening of an accelerator (not shown).

  Each of these sensors 160 to 168 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 168 and controls 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 168. 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. The target value deriving unit 182 is stored in advance based on the derived engine speed and a signal indicating the accelerator opening obtained from the accelerator opening sensor 168 (hereinafter referred to as “accelerator opening signal”). The target torque and the target engine speed are derived with reference to the map.

  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 determines a target injection amount of fuel to be supplied to each cylinder 122a based on the target air amount of each cylinder 122a determined by the air amount determination unit 184. 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. The injection amount determination unit 186 sets the target injection amount to zero when the vehicle is decelerating (vehicle speed> 0) and the accelerator opening indicated by the accelerator opening signal acquired from the accelerator opening sensor 168 is zero. The determined fuel cut processing is executed.

  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.

  In this way, the exhaust gas generated by burning the fuel in the combustion chamber 146 is discharged to the outside through the exhaust path 140. The exhaust gas contains hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx), which need to be removed. Therefore, an exhaust gas purification device 200 is provided in the exhaust passage 140 to remove (purify) hydrocarbons, carbon monoxide, and nitrogen oxides.

  FIG. 2 is a diagram for explaining the exhaust gas purifying device 200. As shown in FIG. 2, the exhaust gas purification apparatus 200 includes a three-way catalyst 210, a precursor supply unit 220, an oxygen sensor 230, and a supply control unit 240.

The three-way catalyst 210 is provided in the exhaust path 140. The three-way catalyst 210 includes a support and a noble metal. The carrier includes alumina and OSC material. The OSC material has a function of storing oxygen and releasing the stored oxygen. The OSC material includes, for example, ceria (CeO ₂ ). The noble metal is supported on the support (the surface of the support). The noble metal purifies (removes) hydrocarbons, carbon monoxide, and nitrogen oxides in the exhaust gas discharged from the exhaust port 136. The noble metal is composed of, for example, platinum (Pt), palladium (Pd), rhodium (Rh), or the like.

  The precursor supply unit 220 includes a tank 222, a pipe 224, a pump 226, and a valve 228. The tank 222 stores the reducing agent precursor. Here, the reducing agent precursor is an alcohol. The alcohol is, for example, one or more of methanol, ethanol, and propanol, that is, an alcohol having 3 or less carbon atoms, preferably methanol or ethanol, and more preferably methanol.

  The pipe 224 is provided so that the opening at one end is connected to the tank 222 and the opening at the other end is located in the exhaust path 140. More specifically, the opening at the other end of the pipe 224 is provided on the upstream side (the engine 120 side) of the three-way catalyst 210 in the exhaust path 140.

  The pump 226 is provided in the pipe 224. The pump 226 sends the reducing agent precursor stored in the tank 222 to the exhaust path 140 via the pipe 224. In this embodiment, the pump 226 is driven and controlled by a supply control unit 240 described later so that the delivery flow rate is constant. The valve 228 is constituted by, for example, an on-off valve, and is provided on the downstream side of the pump 226 in the pipe 224. The valve 228 is controlled to open and close by the supply control unit 240.

  The oxygen sensor 230 detects the oxygen concentration in the exhaust gas flowing downstream of the three-way catalyst 210 in the exhaust path 140.

  In the present embodiment, the ECU 110 functions as the supply control unit 240 of the exhaust gas purification device 200. The supply control unit 240 opens the valve 228 to start the supply of the reducing agent precursor when a predetermined fuel cut end condition is satisfied.

  FIG. 3 is a flowchart showing the supply process of the reducing agent precursor by the supply control unit 240. In the present embodiment, the supply process of the reducing agent precursor is repeatedly performed by an interruption that occurs at predetermined time intervals.

(Step S110)
The supply control unit 240 determines whether or not the fuel cut process is being executed. As a result, when it is determined that the fuel cut process is being performed, the supply control unit 240 proceeds to step S120, and when it is determined that the fuel cut process is not being performed, the process is performed to step S140. Move.

(Step S120)
Based on the signal indicating the oxygen concentration acquired from the oxygen sensor 230, the supply control unit 240 determines whether or not the oxygen concentration on the downstream side of the three-way catalyst 210 is greater than or equal to a predetermined threshold value. Here, the threshold value is a value determined based on the target value of the amount of oxygen stored in the OSC material of the three-way catalyst 210. The target value is a value less than the upper limit value of the amount of oxygen stored by the OSC material, and the OSC material can store a predetermined amount of oxygen according to the concentration of oxygen in the exhaust gas. It is a value that can release oxygen.

  When the amount of oxygen stored in the OSC material exceeds the target value, the amount of oxygen that can be taken in from the exhaust gas decreases, so that the oxygen concentration detected by the oxygen sensor 230 becomes equal to or greater than the threshold value. On the other hand, if the amount of oxygen stored in the OSC material is equal to or less than the target value, oxygen can be sufficiently taken in from the exhaust gas, so that the oxygen concentration detected by the oxygen sensor 230 is less than the threshold value.

  If the supply control unit 240 determines that the oxygen concentration is equal to or higher than the threshold value, the supply control unit 240 moves the process to step S130. If the supply control unit 240 determines that the oxygen concentration is lower than the threshold value, the supply control unit 240 ends the supply process.

(Step S130)
Based on the current temperature of the three-way catalyst 210 and the current exhaust gas flow velocity (or accelerator opening), the supply control unit 240 refers to an accumulation amount map stored in advance in a memory (not shown), A current amount (per unit time) of oxygen (hereinafter referred to as “accumulated amount”) accumulated (stored) exceeding the target value in the OSC material of the three-way catalyst 210 is derived.

  The accumulated amount map is a map in which the accumulated amount of oxygen in the OSC material is associated with the temperature of the three-way catalyst 210 and the flow rate of the exhaust gas passing through the three-way catalyst 210. In the accumulation amount map, the oxygen accumulation amount decreases as the temperature of the three-way catalyst 210 increases, and the oxygen accumulation amount decreases as the exhaust gas flow rate increases.

  Then, the supply control unit 240 adds the oxygen accumulation amount derived this time to the integrated value of the oxygen accumulation amount up to the previous time. Thus, the amount of oxygen accumulated in the OSC material during the fuel cut is derived.

(Step S140)
The supply control unit 240 determines whether or not a predetermined fuel cut end condition is satisfied. For example, the supply control unit 240 determines that the fuel cut end condition is satisfied when it is determined that the engine speed is equal to or higher than a predetermined speed and the accelerator opening is switched from zero to a predetermined value or higher. . The predetermined value is a value exceeding zero. As a result, when it is determined that the fuel cut end condition is satisfied, the supply control unit 240 moves the process to step S150. On the other hand, when it is determined that the fuel cut end condition is not satisfied, the supply control unit 240 ends the supply process.

(Step S150)
The supply control unit 240 refers to a supply amount map stored in advance in a memory (not shown) based on the oxygen accumulation amount (the amount of oxygen stored above the target value) derived in step S130, and supplies the OSC material to the OSC material. The supply amount of the reducing agent precursor necessary for reducing the oxygen accumulation amount to the target value is derived. The supply amount map is created based on the actual measurement value, and is a map in which the supply amount of the reducing agent precursor is associated with the oxygen accumulation amount in the OSC material. In the supply amount map, the supply amount of the reducing agent precursor increases as the oxygen accumulation amount increases. Then, the supply control unit 240 derives the valve opening time of the valve 228 in which the derived supply amount of the reducing agent precursor is supplied to the exhaust passage 140.

(Step S160)
The supply control unit 240 starts driving the pump 226 and opens the valve 228. Thus, the reducing agent precursor is supplied from the tank 222 to the three-way catalyst 210 via the exhaust path 140.

Then, the steam reforming reaction represented by the following formula (1) proceeds in the three-way catalyst 210, and carbon dioxide (CO ₂ ) and hydrogen (H) are obtained from the steam (water) contained in the exhaust gas and the reducing agent precursor. ₂ ) is generated.
CH ₃ OH + H ₂ O → CO ₂ + 3H ₂ Formula (1)
In Formula (1), a case where the reducing agent precursor is methanol is taken as an example.

  Hydrogen generated by the progress of the steam reforming reaction functions as a reducing agent, and reduces oxygen accumulated in the OSC material to water. As a result, the amount of oxygen accumulated in the OSC material can be reduced to the target value, and the oxygen storage capacity of the OSC material can be recovered.

  Then, when the valve opening time elapses after the valve 228 is opened, the supply control unit 240 stops the pump 226 and closes the valve 228. Also, the integrated value of the oxygen accumulation amount is reset.

  As described above, the exhaust gas purifying apparatus 200 of the present embodiment can recover the oxygen storage capacity of the OSC material with a simple configuration in which only the reducing agent precursor is supplied.

  Further, in the prior art in which the air-fuel ratio is rich after the fuel cut is completed, hydrocarbons contained in the fuel are used as a reducing agent to release oxygen accumulated in the OSC material. On the other hand, the exhaust gas purification apparatus 200 of this embodiment generates hydrogen from the reducing agent precursor by advancing the steam reforming reaction, and uses hydrogen as the reducing agent. Hydrogen has a higher reducing ability than hydrocarbons. Therefore, the exhaust gas purification apparatus 200 of the present embodiment can recover the oxygen storage capacity of the OSC material only by supplying a small amount of the reducing agent precursor as compared with the conventional technique.

  The steam reforming reaction is a reaction in which a noble metal contained in the three-way catalyst 210 is used as a catalyst and steam is reformed from alcohol or hydrocarbon to generate hydrogen. However, at a temperature as low as the temperature of the three-way catalyst 210 heated only by the exhaust gas, when the reducing agent precursor is a starting material, the steam reforming reaction proceeds, but the hydrocarbon contained in the fuel starts. When it is a substance, the steam reforming reaction hardly proceeds. That is, although the reducing agent precursor can be reformed to hydrogen, the hydrocarbon contained in the fuel cannot be reformed to hydrogen.

  Further, unlike the prior art, since the oxygen storage capacity of the OSC material can be recovered without excessively injecting the fuel, it is possible to suppress a reduction in fuel consumption.

  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 precursor supply unit 220 supplies alcohol to the exhaust path 140 as a reducing agent precursor has been described as an example. However, the precursor supply unit 220 may supply an aqueous solution of alcohol to the exhaust path 140. Further, the precursor supply unit 220 supplies a hydrocarbon having 3 or less carbon atoms, for example, methane, ethane, butane, or the like, as a reducing agent precursor, in place of or in addition to alcohol, to the exhaust path 140. May be. By supplying hydrocarbons having 3 or less carbon atoms, the steam reforming reaction can proceed even at a temperature as low as the temperature of the three-way catalyst 210, and hydrogen can be generated.

  Further, in the above-described embodiment, the supply control unit 240 controls the driving of the pump 226 so that the delivery flow rate (supply flow rate) of the reducing agent precursor is constant, and controls the valve opening time of the valve 228, thereby performing the step. The configuration for supplying the supply amount of the reducing agent precursor derived in S150 has been described as an example. However, the supply control unit 240 may control the flow rate of the pump 226 so that the supply amount of the reducing agent precursor derived in step S150 is supplied to the exhaust passage 140.

  The present invention can be used in an exhaust gas purification device that purifies exhaust gas.

200 Exhaust Gas Purifier 210 Three-way Catalyst 220 Precursor Supply Unit 240 Supply Control Unit

Claims (3)

A three-way catalyst provided in the exhaust passage of the engine and containing an OSC material;
A precursor supply unit that supplies a reducing agent precursor containing either one or both of alcohol and a hydrocarbon having 3 or less carbon atoms to the upstream side of the three-way catalyst in the exhaust passage;
A supply control unit that controls the precursor supply unit to start supply of the reducing agent precursor when a predetermined fuel cut end condition is satisfied;
An exhaust gas purification apparatus comprising:   The supply control unit is configured to reduce the reduction based on the temperature of the three-way catalyst and the flow rate of the exhaust gas passing through the three-way catalyst in at least a part of a period in which the supply of fuel to the engine is cut. The exhaust gas purification device according to claim 1, wherein the supply amount of the agent precursor is controlled.   The exhaust gas purifying device according to claim 1 or 2, wherein the alcohol is one or more of methanol, ethanol, and propanol.

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