JP5679210B2 - Exhaust gas purification apparatus and exhaust gas purification method - Google Patents

Description

  The present invention relates to an exhaust gas purification device and an exhaust gas purification method for purifying exhaust gas discharged from an engine. In particular, the present invention relates to promotion of catalyst warm-up when the temperature of the catalyst is low and does not reach the activation temperature immediately after the engine is started.

  Exhaust gas discharged from engines such as automobiles contains harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). As one of the exhaust gas purifying device technologies for purifying this harmful component, there is an exhaust gas purifying device that installs a catalyst in the exhaust gas flow path to purify the harmful component in the exhaust gas.

  One of the problems related to such an exhaust gas purification apparatus is that immediately after the engine is started, the temperature of the catalyst is low, the desired catalytic activity cannot be expressed, and the catalyst does not sufficiently exhibit the purification function. . For this reason, there has been conventionally devised that the temperature of the catalyst is quickly raised and activated when the engine is started. For example, Patent Document 1 describes an electrically heated catalyst device that raises the temperature of a catalyst carrier by energizing a catalyst carrier made of a conductive material. In the invention described in Patent Document 1, since the local heat generating part connected to the catalyst carrier so as to be locally energized is provided, local heat is generated by this, and the heat of the local heat generating part is generated. The catalyst itself is heated.

JP 07-054444 A JP 2003-073123 A International Publication No. 2008/093471

  However, an electrically heated catalyst device that raises the temperature of the catalyst by energizing a catalyst carrier made of a conductive material promotes warming up of the catalyst using electric power, resulting in a deterioration in fuel consumption rate and an increase in cost.

  Therefore, the present invention was created to solve the above-described conventional problems, and its purpose is to efficiently perform the oxidation reaction of the catalyst itself without relying on the power consumption as described above when starting the engine. By heating the catalyst, the warming up of the catalyst is promoted and the purification function of the catalyst is exhibited.

The present inventor has studied from various angles and has come up with the present invention capable of realizing the above object. Hereinafter, the present invention will be described in detail.
In exhaust gas purification devices that purify exhaust gas emitted from engines such as automobiles, three-way catalysts are used to purify harmful components such as hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx). Is widely used. In general, in a three-way catalyst, the air-fuel ratio is close to the stoichiometric air-fuel ratio (stoichiometric), and it is possible to efficiently purify the harmful components by oxidation and reduction. To do. Therefore, it is widely practiced to expand the air-fuel ratio range in which the catalyst can exhibit activity by using an oxygen storage substance in combination as a promoter. For example, in Patent Document 2, as a catalyst for exhaust gas purification that has both a high specific surface area required for a catalyst and a high oxygen storage / release capability, the heat resistance is a composite oxide of ceria (CeO ₂ ) and zirconia (ZrO ₂ ). High-performance ceria-zirconia composite oxide, which is a pyrochlore structure ceria-zirconia composite oxide containing a so-called pyrochlore phase in the crystal structure (hereinafter referred to as “pyrochlore structure ceria-zirconia composite oxide”). Is disclosed. On the other hand, in Patent Document 3, two catalyst carriers are arranged on the upstream side and the downstream side of the exhaust gas passage, and the downstream catalyst carrier contains a pyrochlore structure ceria-zirconia composite oxide, so that the hydrocarbon concentration is reduced. An exhaust gas purification device that exhibits excellent purification performance against nitrogen oxides even when it fluctuates is disclosed.

Ordinary ceria containing a cubic phase in the crystal structure has oxygen storage / release ability and the following reaction formula:
4CeO ₂ ← → 2Ce ₂ O ₃ + O ₂ (1)
As shown, a reversible reaction for occluding and releasing oxygen can be realized. Ordinary ceria is stable in an oxidized state (the left side of the above reaction formula (1); CeO ₂ ). Even if it is reduced to Ce ₂ O ₃ , it reacts with oxygen at room temperature to become CeO ₂ . At startup, the catalyst carrier starts from an oxidized state.

However, the pyrochlore structure ceria-zirconia composite oxide has the following reaction formula:
4CeZrO ₄ (κ phase) ← → 2Ce ₂ Zr ₂ O ₇ (pyrochlore phase) + O ₂ (2)
As shown, a reversible reaction for occluding and releasing oxygen can be realized. However, since the pyrochlore structure ceria-zirconia composite oxide is different from the above-mentioned normal ceria, it is both stable to absorb and release oxygen and has a slow reaction rate. Oxygen is not occluded under low temperature conditions (for example, 400 ° C. or lower). Therefore, oxygen can be occluded from the start of the engine if the engine is stopped and kept in a relatively low temperature condition (for example, 400 ° C. or lower) while being in a reduced state. Therefore, by utilizing such an exothermic reaction during occlusion, warming up of the catalyst can be promoted and emission can be reduced. The present invention utilizes the exothermic reaction of the pyrochlore structure ceria-zirconia composite oxide itself.

Specifically, the present invention provides an exhaust gas purification device for realizing the above object. An exhaust gas purification apparatus according to the present invention is an exhaust gas purification apparatus provided in an exhaust system of an engine, and controls a catalyst portion disposed in an exhaust pipe through which exhaust gas flows and an oxygen concentration of exhaust gas introduced into the catalyst portion. A control unit, and the catalyst unit includes a support having a pyrochlore structure ceria-zirconia composite oxide and at least one noble metal catalyst supported on the support.
Here, the control unit is for warming up the catalyst unit realized by oxidizing the pyrochlore structure ceria-zirconia composite oxide in the catalyst unit and generating heat by the exhaust gas introduced into the catalyst unit. At the time of starting the engine, an oxidizing exhaust gas is supplied to the catalyst unit.

  By providing the exhaust gas purification device having such a configuration in the exhaust system of the engine, at the time of starting the engine, in place of the catalyst warm-up by energizing the conductive material as in the conventional electric heating type catalyst device described above, The exhaust gas introduced into the catalyst part and the pyrochlore structure ceria-zirconia composite oxide in the catalyst are subjected to an oxidation reaction, and the composite oxide generates heat, thereby promoting warming-up of the catalyst part. The purification function can be exhibited. As a result, the emission of the engine can be reduced by warming up the catalyst by the oxidation exothermic reaction of the composite oxide.

Further, in a preferable aspect of the exhaust gas purifying apparatus disclosed herein, the exhaust gas purification apparatus includes a main oxygen sensor that measures an oxygen concentration in the exhaust gas upstream of the exhaust pipe from the catalyst unit, and the control unit includes the above-described control unit. It is electrically connected to the main oxygen sensor.
The control unit is configured to cause the pyrochlore structure ceria-zirconia composite oxide of the catalyst unit to be oxidized and generate heat based on the oxygen concentration measured by the main oxygen sensor when starting the engine. The air-fuel ratio (A / F) of the air-fuel mixture supplied to is controlled to the oxidizing atmosphere side, and oxidizing exhaust gas generated by the combustion of the air-fuel mixture is supplied to the catalyst section.

In this specification, the “oxidizing atmosphere” refers to an atmosphere in which the reaction from the right side to the left side in the reaction formula (2) is dominant. On the other hand, in this specification, the “reducing atmosphere” refers to an atmosphere in which the reaction from the left side to the right side predominates in the reaction formula (2).
In the present specification, “oxidative exhaust gas” refers to exhaust gas capable of forming an oxidizing atmosphere in the catalyst portion. Typically, it refers to exhaust gas (hereinafter, also referred to as “lean exhaust gas”) formed by burning an air-fuel mixture having a lean air-fuel ratio. On the other hand, in this specification, “reducing exhaust gas” refers to exhaust gas capable of forming an oxidizing atmosphere in the catalyst portion. Typically, it refers to exhaust gas (hereinafter, also referred to as “rich exhaust gas”) that is obtained by burning an air-fuel mixture rich in air-fuel ratio.

  By providing the exhaust gas purifying apparatus having such a configuration in the exhaust system of the engine, by controlling the air-fuel ratio of the air-fuel mixture to the oxidizing atmosphere side (typically leaner than the stoichiometric ratio) at the time of engine start, The exhaust gas introduced into the catalyst part can be made oxidizing (that is, containing oxidizable oxygen). Thereby, the pyrochlore structure ceria-zirconia composite oxide in the catalyst can be positively oxidized, and the composite oxide generates heat, promotes warming-up of the catalyst portion, and the catalyst. The purification function of the part can be exhibited.

Moreover, in another preferable aspect of the exhaust gas purifying apparatus disclosed herein, air injection (AI) upstream of the exhaust pipe from the catalyst portion, and exhaust gas upstream of the exhaust pipe from the catalyst portion. A main oxygen sensor for measuring the oxygen concentration therein, and the control unit is electrically connected to the AI and the main oxygen sensor .
The control unit is configured to generate heat by oxidizing the pyrochlore structure ceria-zirconia composite oxide of the catalyst unit based on the oxygen concentration measured by the main oxygen sensor when starting the engine. An oxygen-containing gas is injected from the AI, and oxidizing exhaust gas generated by the injection is supplied to the catalyst unit.

  By providing the exhaust gas purifying apparatus having such a configuration in the exhaust system of the engine, the oxygen-containing gas is injected into the exhaust gas when the engine is started, so that the pyrochlore structure ceria-zirconia composite oxide in the catalyst is actively oxidized. The complex oxide generates heat by the oxidation reaction, and warming up of the catalyst can be further promoted. It is also possible to simultaneously perform the process of controlling the air-fuel ratio of the above-mentioned exhaust gas mixture to an oxidizing atmosphere and the process of injecting an oxygen-containing gas into the exhaust gas. By carrying out simultaneously, the warming-up of the said catalyst part can be accelerated | stimulated more rapidly, and the purification function of this catalyst part can be exhibited.

Further, in another preferable aspect of the exhaust gas purification device disclosed herein, the exhaust gas purification device includes a sub oxygen sensor that measures an oxygen concentration in the exhaust gas downstream of the exhaust pipe from the catalyst unit, and the control unit includes The sub oxygen sensor is further electrically connected.
Then, the control unit measures the oxygen concentration of the exhaust gas downstream of the catalyst unit by the sub oxygen sensor at the time of engine stop request, and the atmosphere of the catalyst unit is an oxidizing atmosphere based on the oxygen concentration In this determination, if it is determined that the atmosphere of the catalyst portion is an oxidizing atmosphere, the air-fuel ratio of the air-fuel mixture supplied to the engine is reduced to the reducing atmosphere side (typically Is controlled to be richer than the stoichiometric ratio), so that the atmosphere of the catalyst portion is made a reducing atmosphere before the engine is stopped. On the other hand, if it is determined by the above determination that the atmosphere of the catalyst part is a reducing atmosphere, the air-fuel ratio is controlled to the oxidizing atmosphere side, and after the atmosphere of the catalyst part has changed to the oxidizing atmosphere, the above-described empty space is again obtained. By controlling the fuel ratio to the reducing atmosphere side, the atmosphere of the catalyst section is made the reducing atmosphere before the engine is stopped.

  According to the exhaust gas purification apparatus having such a configuration, when the engine stop request is made, the control unit can supply the reducing exhaust gas to the catalyst unit, so that the engine can be stopped by setting the atmosphere of the catalyst unit to a reducing atmosphere. . Thus, by making the atmosphere of the catalyst part a reducing atmosphere, the pyrochlore structure ceria-zirconia composite oxide in the catalyst part is in a reduced state (that is, a compound shown on the right side of the above reaction formula (2)). The engine can be stopped. Then, when the engine is next started, oxidizing exhaust gas can be supplied to the reduced composite oxide. Accordingly, the pyrochlore structure ceria-zirconia composite oxide generates heat by the oxidation reaction based on the oxidizing exhaust gas, and the catalyst part can be quickly warmed up.

Further, in another preferable aspect of the exhaust gas purification device disclosed herein, the exhaust gas purification device includes a sub oxygen sensor that measures an oxygen concentration in the exhaust gas downstream of the exhaust pipe from the catalyst unit, and the control unit includes The sub oxygen sensor is further electrically connected.
When the engine stop request is made, the control unit measures the oxygen concentration of the exhaust gas downstream of the catalyst unit by the sub oxygen sensor, and controls the air-fuel ratio of the air-fuel mixture supplied to the engine to the reducing atmosphere side. And determining whether the atmosphere of the catalyst part at the time of engine stop request is an oxidizing atmosphere or a reducing atmosphere based on the oxygen concentration, and in the determination, the atmosphere of the catalyst part is determined to be an oxidizing atmosphere. In such a case, the control of the air-fuel mixture on the reducing atmosphere side is continued until the atmosphere of the catalyst section is reversed to the reducing atmosphere, so that the atmosphere of the catalyst section is made the reducing atmosphere before the engine is stopped. On the other hand, when it is determined that the atmosphere of the catalyst part is a reducing atmosphere, the sub oxygen sensor measures the output value of oxygen concentration or the displacement of the output value, and the engine stop is performed with the measurement value set in advance. The engine is configured to stop when reaching an acceptable level reducing atmosphere determination condition.

  According to the exhaust gas purifying apparatus having such a configuration, when the engine stop request is made, the air-fuel mixture is controlled to the reducing atmosphere side. When the atmosphere of the catalyst part is a reducing atmosphere, the engine part can be allowed to stop inside the catalyst part. The engine can be stopped in a reducing atmosphere. According to such control, when the sub oxygen sensor determines that the atmosphere of the catalyst unit is a reducing atmosphere, the control unit omits the control of changing the atmosphere of the catalyst unit to the oxidizing atmosphere and then the reducing atmosphere. Therefore, it is possible to control until the engine stops more quickly.

Moreover, this invention provides the following exhaust gas purification methods as another side surface for implement | achieving the objective mentioned above.
That is, it is a method for purifying exhaust gas discharged from an engine in which an exhaust system is provided with a catalyst having a carrier having a pyrochlore structure ceria-zirconia composite oxide and at least one noble metal catalyst supported on the carrier. .
In this method, at the time of starting the engine, the pyrochlore structure ceria-zirconia composite oxide is oxidized to generate heat in the composite oxide to warm up the catalyst. The oxidizing exhaust gas is supplied to the catalyst.

  According to this exhaust gas purification method, the pyrochlore structure ceria-zirconia composite oxide in the catalyst is replaced with the catalyst warm-up by energization of the conductive material as performed in the above-described conventional electrically heated catalyst device. By utilizing the heat generated by the oxidation reaction, the catalyst can be warmed up when the engine is started. By warming up the catalyst by the oxidation exothermic reaction of the composite oxide, it is possible to reduce emissions at the time of engine start. In addition, the exhaust gas purification method disclosed here can be suitably realized by the above-described exhaust gas purification device.

  Further, in a preferred aspect of the exhaust gas purification method disclosed herein, the oxygen concentration of the exhaust gas is measured at the time of engine start, and the pyrochlore structure ceria-zirconia composite oxide of the catalyst is oxidized based on the oxygen concentration. The air-fuel ratio (A / F) of the air-fuel mixture supplied to the engine is controlled to the oxidizing atmosphere side so that the catalyst can generate heat, and the oxidizing exhaust gas generated by the air-fuel mixture is supplied to the catalyst. It is characterized by doing.

  According to this exhaust gas purification method, the exhaust gas introduced into the catalyst can be made oxidizing by controlling the air-fuel ratio of the air-fuel mixture to the oxidizing atmosphere side. As a result, the pyrochlore structure ceria-zirconia composite oxide in the catalyst can be actively oxidized, and the composite oxide generates heat by the oxidation reaction, thereby promoting warm-up of the catalyst. Further, the emission of the engine can be reduced by warming up the catalyst by the oxidation exothermic reaction of the composite oxide.

  Further, in another preferable aspect of the exhaust gas purification method disclosed herein, the oxygen concentration of the exhaust gas is measured at the time of starting the engine, and the pyrochlore structure ceria-zirconia composite oxide of the catalyst is based on the oxygen concentration. Oxygen-containing gas is supplied to the exhaust gas so that the catalyst can generate heat (typically, an oxygen-containing gas such as air is injected into the exhaust pipe using a mechanism such as AI) The oxidizing exhaust gas produced by the above process is supplied to the catalyst.

  According to the exhaust gas purification method, by supplying an oxygen-containing gas to the exhaust gas from the outside, the pyrochlore structure ceria-zirconia composite oxide in the catalyst can be actively oxidized, and the oxidation reaction causes the oxidation reaction to occur. The composite oxide generates heat and can promote warming up of the catalyst.

  In another preferred embodiment of the exhaust gas purification method disclosed herein, when the engine stop request is made, the oxygen concentration of the catalyst is measured, and whether the atmosphere of the catalyst is an oxidizing atmosphere based on the oxygen concentration. Alternatively, it is determined whether the atmosphere is a reducing atmosphere. If it is determined that the catalyst is an oxidizing atmosphere, the engine is stopped by controlling the air-fuel ratio of the air-fuel mixture supplied to the engine to the reducing atmosphere side. Before the catalyst atmosphere is reduced. On the other hand, if it is determined by the determination that the catalyst atmosphere is a reducing atmosphere, the air-fuel ratio is controlled to the oxidizing atmosphere side, and after the catalyst atmosphere is changed to the oxidizing atmosphere, the air-fuel ratio is again set. By controlling to the reducing atmosphere side, the catalyst atmosphere is made a reducing atmosphere before the engine is stopped.

  According to this exhaust gas purification method, when the engine is requested to be stopped, the engine can be stopped by setting the atmosphere of the catalyst to a reducing atmosphere (the pyrochlore structure ceria-zirconia composite oxide in the catalyst is kept in a reduced state). . In this way, by setting the atmosphere of the catalyst to a reducing atmosphere, the engine is stopped after the composite oxide in the catalyst is brought into a reduced state, so that the reduced state in the catalyst is reduced at the next engine start. An oxidizing exhaust gas can be supplied to the composite oxide. Therefore, the composite oxide generates heat by the oxidation reaction based on the oxidizing exhaust gas, and the catalyst can be warmed up.

  Further, in another preferable aspect of the exhaust gas purification method disclosed herein, when the engine stop request is made, the oxygen concentration of the catalyst is measured, and the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to the reducing atmosphere side. Determining whether the atmosphere of the catalyst at the time of engine stop request is an oxidizing atmosphere or a reducing atmosphere based on the oxygen concentration, and in the determination, determining that the atmosphere of the catalyst is an oxidizing atmosphere Continues the control of the air-fuel mixture on the reducing atmosphere side until the atmosphere of the catalyst is reversed to the reducing atmosphere, thereby bringing the atmosphere of the catalyst into the reducing atmosphere before the engine is stopped. On the other hand, if it is determined by the above determination that the atmosphere of the catalyst is a reducing atmosphere, the control on the reducing atmosphere side of the air-fuel mixture is continued and the catalyst is set to a level at which a preset engine stop is acceptable. It is characterized in that the engine is stopped at the stage where the reducing atmosphere of the inside proceeds.

  According to the exhaust gas purification method, when the engine stop request is made, the air-fuel mixture is controlled to the reducing atmosphere side, and when the catalyst atmosphere is the reducing atmosphere, the reducing atmosphere at a level that allows the engine to stop within the catalyst. The engine can be stopped. According to such control, when it is determined that the catalyst atmosphere described above is a reducing atmosphere, it is possible to omit the control of changing the catalyst atmosphere from an oxidizing atmosphere to a reducing atmosphere. it can.

It is the figure which showed typically the engine exhaust system with which the exhaust gas purification apparatus which concerns on one Embodiment of this invention is comprised. It is the figure which demonstrated typically the control part provided in the exhaust gas purification apparatus which concerns on one Embodiment of this invention. It is a whole view showing typically composition of a catalyst part concerning one embodiment of the present invention. It is a flowchart explaining control of the exhaust gas purification apparatus which concerns on one Embodiment of this invention. It is a flowchart explaining control of the exhaust gas purification apparatus which concerns on other embodiment of this invention. It is a flowchart explaining control of the exhaust gas purification apparatus which concerns on other embodiment of this invention.

  Several preferred embodiments of the present invention will be described below with reference to the drawings. Note that matters other than matters specifically mentioned in the present specification and necessary for the implementation of the present invention can be grasped as design matters of those skilled in the art based on the prior art in this field. The present invention can be implemented based on the contents disclosed in the present specification and technical knowledge in the field.

<Exhaust gas purification device>
First, an exhaust gas purification apparatus 100 according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. As shown in FIGS. 1 and 2, the exhaust gas purification apparatus 100 includes an engine unit 1, a control unit 30, and a catalyst unit 40.

A. As shown in FIG. 1, in the exhaust gas purifying apparatus 100 according to the present embodiment, the engine unit 1 is mainly composed of an automobile gasoline engine (the engine unit 1 includes an accelerator for driving the engine). And other controls.) Hereinafter, the configuration of the gasoline engine 1 will be briefly described. The gasoline engine 1 described below is merely an example of the engine unit 1. The exhaust gas purifying apparatus 100 according to the present invention can also use an engine other than a gasoline engine (for example, a diesel engine) as the engine unit 1.

  A cylinder head 13 is connected to the engine unit 1 on a cylinder block 12, and pistons 15 are fitted to a plurality of cylinder bores 14 formed in the cylinder block 12 so as to be movable up and down. A crankshaft (not shown) is rotatably supported at the lower part of the cylinder block 12, and each piston 15 is connected to the crankshaft via a connecting rod 16. In the following, only one cylinder will be described.

  The combustion chamber 17 includes a cylinder block 12, a cylinder head 13, and a piston 15, and an intake port 18 and an exhaust port 19 are formed in an upper portion of the combustion chamber 17, that is, a lower portion of the cylinder head 13. . The lower ends of the intake valve 20 and the exhaust valve 21 are located with respect to the intake port 18 and the exhaust port 19. Therefore, when the intake valve 20 and the exhaust valve 21 move up and down at a predetermined timing, the intake port 18 and the exhaust port 19 are opened and closed, and the intake port 18 and the combustion chamber 17 and the combustion chamber 17 and the exhaust port 19 communicate with each other. can do.

An intake pipe 23 is connected to the intake port 18 via an intake manifold 22. An air cleaner 24 is attached to the air intake port of the intake pipe 23, and a throttle valve 25 is provided on the downstream side of the air cleaner 24. The intake manifold 18 is provided with an injector 26 for injecting fuel (engine) into each intake port 18, and the cylinder head 13 is positioned above the combustion chamber 17 and ignites an air-fuel mixture. 27 is attached.
On the other hand, an exhaust pipe 29 is connected to the exhaust port 19 via an exhaust manifold 28.

B. Catalyst Part Next, the catalyst part 40 will be described in detail.
The catalyst unit 40 is provided in the exhaust pipe 29 that communicates with the engine 1. Specifically, as shown in FIG. 1, the catalyst unit 40 is provided on the downstream side of the exhaust pipe 29.

  A main oxygen sensor 50 a is disposed in the exhaust pipe 29 upstream of the catalyst unit 40. The main oxygen sensor 50a is for measuring the oxygen concentration of the exhaust gas flowing in the exhaust pipe 29 upstream from the catalyst unit 40. The main oxygen sensor 50a can be arranged at any position if the oxygen concentration of the exhaust gas can be measured. The position is not limited to the position illustrated in FIG. A sub oxygen sensor 50 b is disposed in the exhaust pipe 29 downstream of the catalyst unit 40. The sub oxygen sensor 50b is for estimating the oxygen concentration in the catalyst unit 40 by measuring the oxygen concentration of the exhaust gas flowing in the exhaust pipe 29 downstream of the catalyst unit 40. The sub oxygen sensor 50b The arrangement position is not limited to the position illustrated in FIG. 1 as long as the oxygen concentration in the catalyst unit 40 can be estimated. The main oxygen sensor 50a and the sub oxygen sensor 50b only need to be able to detect the oxygen concentration in the exhaust pipe 29, and the specific configuration thereof does not particularly limit the present invention. For example, as the main oxygen sensor 50a and the sub oxygen sensor 50b, a zirconia oxygen sensor used in a normal automobile exhaust gas system can be used, but not limited to this, other means capable of measuring the oxygen concentration can be substituted.

  An air injection (AI) 52 is disposed in the exhaust pipe 29 upstream of the catalyst unit 40. The AI 52 is for injecting an oxygen-containing gas into the exhaust pipe 29 on the upstream side of the catalyst unit 40 and flowing an oxidizing exhaust gas into the catalyst unit 40. Therefore, the arrangement position of the AI 52 is not limited to the position illustrated in FIG. 1 as long as an oxygen-containing gas (typically air) can flow through the catalyst unit 40.

  The catalyst unit 40 disclosed herein is composed of a base material, a support supported on the base material, and a noble metal catalyst (typically a metal catalyst belonging to the platinum group) supported on the support. Yes.

  As a base material, the thing of the various raw materials and form used for this kind of conventional use can be used. For example, cordierite having high heat resistance, a honeycomb substrate having a honeycomb structure formed of ceramics such as silicon carbide (SiC) or an alloy (stainless steel, etc.) can be suitably employed. As an example, as shown in FIG. 3, a honeycomb base material 42 having a cylindrical outer shape, and cells (through holes) 46 of exhaust gas passages are provided in the cylinder axis direction, and rib walls 44 that partition the cells 46. The exhaust gas can be contacted. The shape of the substrate may be a foam shape, a pellet shape, etc. in addition to the honeycomb shape. In addition to the cylindrical shape, the overall shape of the base material may be an elliptical cylindrical shape or a polygonal cylindrical shape.

The catalyst support of the catalyst unit 40 according to the present embodiment has at least a pyrochlore structure ceria-zirconia composite oxide. The pyrochlore-structure ceria-zirconia composite oxide is stable both in storing and releasing oxygen and has a slow reaction rate. Therefore, it is reduced to a relatively low temperature condition (for example, 400 ° C. or lower). This makes it difficult to store oxygen. Therefore, if the engine is stopped and kept in a relatively low temperature condition (for example, 400 ° C. or lower) while being in a reduced state, oxygen can be occluded from the start of the engine. Therefore, warm-up of the catalyst can be promoted by utilizing the exothermic reaction at the time of occlusion. In carrying out the present invention, it is only necessary to have a pyrochlore structure ceria-zirconia composite oxide as a support, and other supports (for example, alumina (Al ₂ O ₂₎ for the purpose of improving mechanical strength and the like. ₃ )) can be used in combination.

The noble metal catalyst supported on the catalyst carrier is composed of metal catalyst particles having an oxidation catalyst ability or a reduction catalyst ability. As such metal catalyst particles, for example, metal catalyst particles such as platinum (Pt), palladium (Pd), rhodium (Rh), silver (Ag), and composite particles containing the metal catalyst particles are preferably used. Can do.
In this embodiment, it is preferable that the catalyst part 40 is comprised with what is called a three-way catalyst. Preferred examples of the metal particles constituting the three-way catalyst include a combination of rhodium (Rh) having a strong reduction catalyst ability and platinum (Pt) and / or palladium (Pd) having a strong oxidation catalyst ability. .

C. Control unit (ECU: Engine Control Unit)
The control unit (ECU) 30 is mainly composed of a digital computer, and functions as a control device in the operation of the exhaust gas purification device 100. The control unit 30 includes, for example, a ROM that is a read-only storage device, a RAM that is a readable / writable storage device, a CPU that performs arbitrary computation and determination, an input port, and an output port.
As schematically shown in FIG. 2, the control unit 30 is a unit that performs control among the engine unit 1, the main oxygen sensor 50 a, the sub oxygen sensor 50 b, and the AI 52, and includes the engine unit 1, the main oxygen sensor 50 a, The oxygen sensor 50b and the AI 52 are electrically connected.

  Output signals from the main oxygen sensor 50a and the sub oxygen sensor 50b are input to the input ports of the control unit 30 via corresponding AD converters (not shown). On the other hand, the output port of the control unit 30 is connected to the injector 26, the step motor for driving the throttle valve 25, the spark plug 27, the AI 52, and the like via corresponding drive circuits. Thereby, the control unit 30 can control the fuel injection timing of the injector 26, the ignition timing of the spark plug 27, and the like, and the detected intake air amount, throttle opening (or accelerator opening), engine speed The fuel injection amount, injection timing, ignition timing, etc. are determined based on the engine operating state.

  In the exhaust gas purification apparatus 100 having the configuration shown in FIG. 1, the control unit 30 is based on the oxygen concentration of the exhaust gas upstream of the catalyst unit 40 detected by the main oxygen sensor 50a, and the air-fuel mixture burned in the engine unit 1 is empty. The fuel ratio (A / F) can be estimated. Further, the control unit 30 can determine whether the atmosphere in the catalyst unit 40 is an oxidizing atmosphere or a reducing atmosphere based on the oxygen concentration of the exhaust gas downstream of the catalyst unit 40 detected by the sub oxygen sensor 50b.

  It should be noted that the configuration of the control unit 30 itself as described above does not characterize the present invention, and may be conventionally employed in this type of internal combustion engine (automobile engine), and further detailed description thereof is omitted.

  Next, an embodiment of the exhaust gas purification method executed in the above-described exhaust gas purification apparatus 100 will be described with reference to the flowchart of FIG. In such an exhaust gas purifying apparatus 100, when the engine is started, the catalyst carrier pyrochlore in the catalyst unit 40 is replaced with the catalyst warm-up by energizing the conductive material as is done in the above-described conventional electrically heated catalyst apparatus. The warming-up of the catalyst unit 40 can be promoted by the oxidation exothermic reaction of the structural ceria-zirconia composite oxide.

  As shown in FIG. 4, the exhaust gas purifying apparatus has “engine start request determination (S10)”, “engine start (S11)”, “air-fuel ratio control (oxidizing atmosphere side) start of air-fuel mixture or AI-ON ( S12) ”and“ End of air-fuel ratio control of air-fuel mixture or AI-OFF (S13) ”. Hereinafter, each step will be described.

1-A. Determination of engine start request (S10)
First, in the exhaust gas purification apparatus 100 according to the present embodiment, an engine start request is determined in step S10. When the control unit 30 receives the engine start request signal, it determines that “the engine start request is present” (YES), and performs step S11. On the other hand, if the control unit 30 has not received the engine start request signal, it is determined (NO) as “no engine start request”, and the control process ends without performing the following control.

1-B. Engine start (S11)
If the determination result in step S10 is YES, the engine is started. The control unit 30 transmits an engine start signal for starting the engine to a cell motor (not shown) to start the engine.

1-C. Start air-fuel ratio control (oxidizing atmosphere side) of air-fuel mixture or AI-ON (S12)
After performing step S11, the control unit 30 oxidizes the exhaust gas flowing upstream of the catalyst unit 40 in order to warm up the catalyst unit 40 by the oxidation exothermic reaction of the pyrochlore structure ceria-zirconia composite oxide of the catalyst carrier. (That is, exhaust gas capable of forming an oxidizing atmosphere in the catalyst unit 40), and the oxidizing exhaust gas is introduced into the catalyst unit 40. That is, the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to the oxidizing atmosphere side, and oxidizing exhaust gas generated by the combustion of the air-fuel mixture is supplied to the catalyst unit 40. Alternatively, the oxygen-containing gas is supplied to the exhaust pipe 29 by the AI 52, and the oxidizing exhaust gas generated by the supply is supplied to the catalyst unit 40.

  Here, “controlling the air-fuel ratio of the air-fuel mixture to the oxidizing atmosphere side” means forcibly controlling the air-fuel ratio of the air-fuel mixture to lean. By this control, lean exhaust gas can be supplied to the catalyst. In the exhaust gas purification apparatus 100, when the lean control is executed, the control unit 30 creates a lean control signal, and the lean control signal is transmitted to the injector 26, the throttle valve 25, and the like. At this time, the injector 26 reduces the fuel supplied to the intake port 18 by reducing the fuel injection amount. In addition, the opening of the throttle valve increases, and the amount of air supplied to the intake port 18 increases. As a result, the air-fuel ratio of the air-fuel mixture supplied to the engine 1 becomes lean, that is, the oxidizing atmosphere side.

1-D. End of air-fuel ratio control of air-fuel mixture or AI-OFF (S13)
In step S12, supply of oxidizing exhaust gas into the catalyst unit 40 is started, and after a predetermined time has elapsed and the warming-up of the catalyst by the supply is completed, the control unit 30 performs the control of the air-fuel mixture performed in step S12. Stop control of the air-fuel ratio to the oxidizing atmosphere. Alternatively, the supply of the oxygen-containing gas to the exhaust pipe 29 by the AI 52 performed in step S12 is stopped.

The exhaust gas purification method executed in the exhaust gas purification apparatus 100 according to one embodiment of the present invention has been described above. Next, another embodiment of the exhaust gas purification method that can be executed by the exhaust gas purification apparatus 100 having the above configuration will be described with reference to the flowchart of FIG.
In FIG. 5, the pyrochlore structure ceria-zirconia composite oxide in the catalyst unit 40 is reduced to the reduced state (on the right side of the above reaction formula (2)) by making the atmosphere in the catalyst unit 40 a reducing atmosphere at the time of engine stop request. Stop the engine). Then, at the next engine start, by supplying oxidizing exhaust gas to the reduced composite oxide in the catalyst unit 40, the composite oxide is oxidized by an oxidation reaction based on the oxidizing exhaust gas. It generates heat and can quickly warm up the catalyst.

  As shown in FIG. 5, the exhaust gas purification method executed in the exhaust gas purification apparatus 100 includes “catalyst oxygen concentration measurement (S20, S23, S26)”, “catalyst atmosphere determination (S21)”, “air mixture”. Air / fuel ratio control (oxidation atmosphere side) start (S22) ”,“ catalyst oxidation state determination (S24) ”,“ air-fuel ratio control (reduction atmosphere side) start of mixture (S25) ”,“ catalyst reduction state determination ” (S27) ”and“ engine stop (S28) ”are included. Hereinafter, each step will be described.

2-A. Measurement of oxygen concentration of catalyst (S20)
First, in step S20, in order to determine whether the atmosphere in the catalyst unit 40 is a reducing atmosphere or an oxidizing atmosphere, the control unit 30 uses the sub oxygen sensor 50b to detect exhaust gas downstream of the catalyst unit 40. Then, the oxygen concentration in the catalyst unit 40 is determined. For example, when a zirconia oxygen sensor is used as the sub oxygen sensor 50b, the oxygen concentration is represented by a voltage value.

2-B. Determination of atmosphere in catalyst (S21)
In step S21, it is determined based on the oxygen concentration of the catalyst unit 40 obtained in step S20 whether the atmosphere in the catalyst unit 40 is an oxidizing atmosphere or a reducing atmosphere.
Specifically, a predetermined value for the atmosphere in the catalyst unit 40 is set in advance, and it is determined whether or not the oxygen concentration (voltage value) exceeds the predetermined value. For example, when a zirconia oxygen sensor is used as the sub oxygen sensor 50b, the measured value (output voltage value) of the oxygen sensor is high in a reducing atmosphere. On the other hand, when the atmosphere is an oxidizing atmosphere, the measured value (output voltage value) of the oxygen sensor is low. In this case, when the measured value of the sub oxygen sensor 50b exceeds the predetermined value, it is determined that the atmosphere in the catalyst unit 40 is a reducing atmosphere, and then Step S22 is performed. On the other hand, when the measured value of the sub oxygen sensor 50b falls below the predetermined value, it is determined that the atmosphere in the catalyst unit 40 is an oxidizing atmosphere, and step S25 is performed.

2-C. Start air-fuel ratio control (oxidizing atmosphere side) of air-fuel mixture (S22)
If it is determined from step S21 that the atmosphere of the catalyst unit 40 is a reducing atmosphere, the atmosphere of the catalyst unit 40 is changed to an oxidizing atmosphere, and the atmosphere of the catalyst unit 40 is changed to an oxidizing atmosphere. It is necessary to control the atmosphere of the portion 40 to the reducing atmosphere side.
The reason for this control is that there is a time delay between the actual atmosphere of the catalyst unit 40 and the measured value of the sub oxygen sensor 50b (zirconia oxygen sensor). In other words, the sub-oxygen sensor 50b measures the exhaust gas downstream of the catalyst unit 40, that is, the oxygen concentration of the exhaust gas that has passed through the catalyst unit 40, and determines the atmosphere of the exhaust gas downstream of the catalyst unit 40 from the oxygen concentration. This is because the atmosphere of the catalyst part 40 is determined. That is, even if the exhaust gas atmosphere downstream of the catalyst unit 40 is a reducing atmosphere, the atmosphere of the catalyst unit 40 is not necessarily a reducing atmosphere. For example, even if the exhaust gas atmosphere downstream of the catalyst unit 40 is a reducing atmosphere, the atmosphere in the catalyst unit 40 may be an oxidizing atmosphere.
Therefore, in step S22, first, in order to make the atmosphere of the catalyst unit 40 an oxidizing atmosphere, a process of controlling the air-fuel ratio of the air-fuel mixture supplied to the engine to the oxidizing atmosphere side is performed. Specifically, the control unit 30 forcibly controls the air-fuel ratio of the air-fuel mixture to lean, and supplies lean exhaust gas to the catalyst unit 40 by the control.

2-D. Measurement of oxygen concentration of catalyst (S23)
While the control of the air-fuel ratio of the air-fuel mixture to the oxidizing atmosphere side is performed in step S22, in step S23, the control unit 30 determines whether the atmosphere in the catalyst unit 40 is an oxidizing atmosphere. The oxygen concentration (voltage value) of the exhaust gas downstream of the catalyst unit 40 is measured by the sub oxygen sensor 50b (for example, zirconia oxygen sensor), and the oxygen concentration in the catalyst unit 40 is determined based on the oxygen concentration.

2-E. Determination of oxidation state of catalyst (S24)
Based on the measured value of the oxygen concentration of the catalyst unit 40 obtained in step S23, it is determined whether or not the atmosphere of the catalyst unit 40 has become an oxidizing atmosphere. Specifically, a predetermined value (voltage value) for determining that the atmosphere in the catalyst unit 40 is an oxidizing atmosphere is set in the control unit 30 in advance, and the measured value (voltage value) of the sub oxygen sensor 50b is the above value. It is determined whether or not the value is below a predetermined value. When the measured value of the sub oxygen sensor 50b falls below the predetermined value, it is determined that the inside of the catalyst unit 40 is in an oxidizing atmosphere (YES), and then Step S25 is performed. On the other hand, when the measured value of the sub oxygen sensor 50b exceeds the predetermined value, it is determined that the inside of the catalyst unit 40 is still in a reducing atmosphere (NO), and Step S23 is performed again.

2-F. Start air-fuel ratio control (reducing atmosphere side) of air-fuel mixture (S25)
When it is determined in step S21 or step 24 that the atmosphere of the catalyst unit 40 is an oxidizing atmosphere, the control unit 30 sets the air-fuel mixture supplied to the engine in order to make the atmosphere of the catalyst unit 40 a reducing atmosphere. The air-fuel ratio is controlled to the reducing atmosphere side.

  Here, “controlling the air-fuel ratio of the air-fuel mixture to the reducing atmosphere side” means forcibly controlling the air-fuel ratio of the air-fuel mixture to be rich. By this control, rich exhaust gas can be supplied to the catalyst. In the exhaust gas purification apparatus 100, when rich control is executed, the control unit 30 creates a rich control signal, and the rich control signal is transmitted to the injector 26, the throttle valve 25, and the like. At this time, the injector 26 increases the fuel supplied to the intake port 18 by increasing the fuel injection amount. Further, the opening degree of the throttle valve 25 increases, and the amount of air supplied to the intake port 18 decreases. Thereby, the air-fuel ratio of the air-fuel mixture supplied to the engine 1 is rich, that is, the reducing atmosphere side.

2-G. Measurement of oxygen concentration of catalyst (S26)
While the control of the air-fuel ratio of the air-fuel mixture to the reducing atmosphere side is being performed in step S25, in step S26, the control unit 30 determines whether the atmosphere in the catalyst unit 40 is an oxidizing atmosphere. The oxygen concentration of the exhaust gas downstream of the catalyst unit 40 is measured by the sub oxygen sensor 50b, and the oxygen concentration in the catalyst unit 40 is determined based on the oxygen concentration.

2-H. Determination of catalyst reduction state (S27)
Based on the measured value (voltage value) of the oxygen concentration of the catalyst unit 40 obtained in step S26, it is determined whether or not the atmosphere of the catalyst unit 40 has become a reducing atmosphere. Specifically, a predetermined value (voltage value) for determining that the atmosphere in the catalyst unit 40 is a reducing atmosphere is set in the control unit 30 in advance, and the measured value of the sub oxygen sensor 50b exceeds the predetermined value. It is determined whether or not. When the measured value of the sub oxygen sensor 50b exceeds the predetermined value, it is determined that the inside of the catalyst unit 40 is in a reducing atmosphere (YES), and then Step S28 is performed. On the other hand, when the measured value of the sub oxygen sensor 50b falls below the predetermined value, it is determined that the inside of the catalyst unit 40 is still in an oxidizing atmosphere (NO), and Step S26 is performed again.

2-I. Engine stop (S28)
When it is determined in step S27 that the atmosphere of the catalyst unit 40 is a reducing atmosphere, the control unit 30 transmits an engine stop signal to the engine 1 and stops the engine.

The exhaust gas purification method executed in the exhaust gas purification apparatus 100 according to one embodiment of the present invention has been described above. Next, an exhaust gas purification method that can be executed by the exhaust gas purification apparatus 100 according to another embodiment of the present invention will be described with reference to the flowchart of FIG.
According to such an exhaust gas purification method, when the engine stop request is made, the air-fuel mixture is controlled to the reducing atmosphere side, and when the catalyst atmosphere is the reducing atmosphere, a reduction level at which the engine can be forced to stop inside the catalyst. Turn the engine to the atmosphere. According to such a method, the control performed when the atmosphere of the catalyst unit 40 is determined as the reducing atmosphere, which is performed in the above-described exhaust gas purification method, is omitted. Therefore, it is possible to control until the engine stops more quickly.

  As shown in FIG. 6, the method for purifying exhaust gas according to the present embodiment includes “catalyst oxygen concentration measurement (S30, S33)”, “air-fuel ratio control (reducing atmosphere side) start of air-fuel mixture (S31)”. “Catalyst atmosphere determination at engine stop request (S32)”, “Catalyst reduction state determination (S34)”, “Catalyst oxygen concentration output value measurement or catalyst oxygen concentration output displacement measurement (S35)”, Each step includes "catalyst reduction state determination (S36)" and "engine stop (S37)". Hereinafter, each step will be described.

3-A. Measurement of oxygen concentration of catalyst (S30)
First, in step S30, in order to determine whether the atmosphere of the catalyst unit 40 at the time of the engine stop request is a reducing atmosphere or an oxidizing atmosphere, the control unit 30 determines whether the sub oxygen sensor 50b (for example, zirconia oxygen) The oxygen concentration (voltage value) of the exhaust gas downstream of the catalyst unit 40 is measured by a sensor), and the oxygen concentration of the catalyst unit 40 is determined.

3-B. Start air-fuel ratio control (reducing atmosphere side) of air-fuel mixture (S31)
After performing step S30, in step S31, the controller 30 first sets the atmosphere of the catalyst unit 40 to a reducing atmosphere regardless of whether the atmosphere of the catalyst unit 40 is a reducing atmosphere or an oxidizing atmosphere. Controls the air-fuel ratio of the air-fuel mixture supplied to the engine to the reducing atmosphere side, that is, forcibly controls the air-fuel ratio of the air-fuel mixture to rich, and starts processing to supply rich exhaust gas to the catalyst unit 40 by this control. To do.

3-C. Determination of catalyst atmosphere at the time of engine stop request (S32)
After controlling the air-fuel ratio of the air-fuel mixture to the reducing atmosphere side in step S31, based on the measured value (voltage value) of the oxygen concentration of the catalyst unit 40 obtained in step S30, the catalyst unit at the time of engine stop request It is determined whether the atmosphere of 40 is an oxidizing atmosphere or a reducing atmosphere.
Specifically, a predetermined value for the atmosphere in the catalyst unit 40 is preset in the control unit 30, and the measured value (voltage value) of the oxygen concentration of the sub oxygen sensor 50b is compared with the predetermined value. For example, when a zirconia oxygen sensor is used as the sub oxygen sensor 50b, the value (output voltage value) of the oxygen sensor is high in a reducing atmosphere. On the other hand, in the case of an oxidizing atmosphere, the value (output voltage value) of the oxygen sensor is low. In this case, when the measured value of the sub oxygen sensor 50b exceeds the predetermined value, it is determined that the atmosphere in the catalyst unit 40 is a reducing atmosphere, and then Step S35 is performed. On the other hand, when the measured value of the sub oxygen sensor 50b falls below the predetermined value, it is determined that the atmosphere in the catalyst unit 40 is an oxidizing atmosphere, and step S33 is performed.

3-D. Measurement of catalyst oxygen concentration (S33)
After determining in step S32 that the atmosphere of the catalyst unit 40 at the time of the engine stop request is an oxidizing atmosphere, in step S33, in order to determine whether the catalyst unit 40 is in a reduced state, the control unit 30 The oxygen concentration of the exhaust gas downstream of the catalyst unit 40 is measured by the sub oxygen sensor 50b, and the oxygen concentration of the catalyst unit 40 is determined based on the oxygen concentration.

3-E. Determination of catalyst reduction state (S34)
In step S34, based on the measured value (voltage value) of the oxygen concentration of the catalyst unit 40 obtained in step S33, it is determined whether or not the atmosphere of the catalyst unit 40 has become a reducing atmosphere.
Specifically, a predetermined value (voltage value) for determining that the atmosphere in the catalyst unit 40 is a reducing atmosphere is set in advance, and whether or not the measured value of the sub oxygen sensor 50b exceeds the predetermined value. judge. When the measured value of the sub oxygen sensor 50b exceeds the predetermined value, it is determined that the inside of the catalyst unit 40 is in a reducing atmosphere (YES), and then Step S37 is performed. On the other hand, when the measured value of the sub oxygen sensor 50b falls below the predetermined value, it is determined that the inside of the catalyst unit 40 is still in an oxidizing atmosphere (NO), and Step S33 is performed again.

3-F. Output value measurement of catalyst oxygen concentration or output displacement measurement of catalyst oxygen concentration (S35)
On the other hand, when it is determined in step S32 that the atmosphere of the catalyst unit 40 is a reducing atmosphere, the control unit 30 measures the output voltage value of the oxygen concentration of the catalyst unit 40 by the sub oxygen sensor 50b. Alternatively, the displacement of the output voltage of the oxygen concentration of the catalyst unit 40 is measured by the sub oxygen sensor 50b.

3-G. Determination of catalyst reduction state (S36)
In step S35, after the output voltage value of the oxygen concentration of the catalyst unit 40 or the displacement of the output voltage of the oxygen concentration of the catalyst unit 40 is measured by the sub oxygen sensor 50b, the reduction state of the catalyst unit 40 is determined. In other words, whether the reducing atmosphere in the catalyst unit 40 is a reducing atmosphere at a level that allows the engine to be stopped (that is, the stage where the reducing atmosphere in the catalyst unit 40 has advanced to a level at which the engine can be stopped). Judgment is made.
Among these, when the output voltage value is adopted as a determination condition as to whether or not the engine can be stopped, a predetermined value of the output voltage that determines that the reducing atmosphere in the catalyst unit 40 is a reducing atmosphere at a level that allows the engine to stop (Hereinafter also referred to as “predetermined output voltage value”) is set in the control unit 30 in advance, and it is determined whether or not the output voltage value is equal to or greater than the predetermined output voltage value. If the output voltage value is equal to or higher than the output voltage predetermined value, it is determined that the reducing atmosphere in the catalyst unit 40 is a reducing atmosphere at a level that allows the engine to be stopped (YES), and then step S37 is performed. . On the other hand, when the output voltage value falls below the predetermined output voltage value, it is determined that the reducing atmosphere of the catalyst unit 40 is not yet a reducing atmosphere that allows the engine to be stopped (NO), and Step S35 is performed again.

  On the other hand, when the displacement of the output voltage is adopted as the determination condition as to whether or not the engine can be stopped, for example, when a zirconia oxygen sensor used in a general automobile is used as the sub oxygen sensor 50b, the time of the zirconia oxygen sensor Take advantage of the nature of delays. In other words, since there is a time delay between the actual atmosphere of the catalyst unit 40 and the measured value of the sub oxygen sensor 50b (zirconia oxygen sensor), this property is utilized. The zirconia oxygen sensor follows the actual reduction state of the catalyst unit 40, reacts with a delay in time, and increases in value, so that the catalyst unit 40 depends on the degree of increase in the value (that is, displacement of the output voltage). It can be determined whether or not the reduction atmosphere has become a reduction atmosphere at a level that allows the engine to be stopped.

  In this case, a predetermined value (hereinafter also referred to as “output voltage displacement predetermined value”) of the displacement of the output voltage that determines that the reducing atmosphere in the catalyst unit 40 is a reducing atmosphere at a level that allows the engine to be stopped is controlled. It is set in the unit 30 in advance, and it is determined whether or not the displacement of the output voltage is equal to or greater than a predetermined value of the output voltage displacement. If the displacement of the output voltage is equal to or greater than the output voltage displacement predetermined value, it is determined that the reducing atmosphere in the catalyst unit 40 is a reducing atmosphere at a level that allows the engine to be stopped (YES), and then step S37 is performed. carry out. On the other hand, if the displacement of the output voltage is less than the predetermined value of the output voltage displacement, it is determined that the reducing atmosphere of the catalyst unit 40 is not yet a reducing atmosphere that allows engine stop (NO), and Step S35 is performed again. To do.

3-H. Engine stop (S37)
When it is determined in step S34 or step S36 that the atmosphere of the catalyst unit 40 is a reducing atmosphere, the control unit 30 transmits an engine stop signal to the engine 1 and stops the engine.

Heretofore, several preferred embodiments of the exhaust gas purifying apparatus and the exhaust gas purifying method according to the present invention have been described in detail.
With the exhaust gas purifying apparatus 100 of the present invention, when the engine is started, the control unit 30 controls the air-fuel ratio of the air-fuel mixture to the oxidizing atmosphere side or supplies the oxygen-containing gas into the exhaust pipe by the AI 52, so that the catalyst The exhaust gas introduced into the section 40 can be made oxidizing (that is, containing oxidizable oxygen). As a result, the pyrochlore structure ceria-zirconia composite oxide in the catalyst unit 40 can be actively oxidized, the composite oxide generates heat by the oxidation reaction, and warming up of the catalyst unit 40 is promoted. The purification function of the part 40 can be exhibited.

  Further, in the exhaust gas purification apparatus 100 according to another embodiment of the present invention, when the engine stop request is made, the control unit 30 controls the air-fuel ratio of the air-fuel mixture supplied to the engine to the reducing atmosphere side, so that the catalyst unit 40 By making the atmosphere of the reduction atmosphere, the engine can be stopped after the pyrochlore structure ceria-zirconia composite oxide in the catalyst unit 40 is brought into the reduction state. As a result, when the engine is next started, by supplying oxidizing exhaust gas to the reduced composite oxide in the catalyst unit 40, the composite oxide is formed by an oxidation reaction based on the oxidizing exhaust gas. It generates heat and can quickly warm up the catalyst.

1 Engine 12 Cylinder Block 13 Cylinder Head 14 Cylinder Bore 15 Piston 16 Connecting Rod 17 Combustion Chamber 18 Intake Port 19 Exhaust Port 20 Intake Valve 21 Exhaust Valve 22 Intake Manifold 23 Intake Pipe 24 Air Cleaner 25 Throttle Valve 26 Injector 27 Spark Plug 28 Exhaust Manifold 29 Exhaust pipe 30 Control unit 40 Catalyst unit 42 Honeycomb substrate 44 Rib wall (partition)
46 cells (through holes)
50a Main oxygen sensor 50b Sub oxygen sensor 52 AI
100 Exhaust gas purification device

Claims (8)

An exhaust gas purification device provided in an exhaust system of an engine,
A catalyst unit disposed in an exhaust pipe through which exhaust gas flows;
A control unit for controlling the oxygen concentration of the exhaust gas introduced into the catalyst unit;
A sub-oxygen sensor that measures the oxygen concentration in the exhaust gas downstream of the exhaust pipe from the catalyst unit;
With
The catalyst part includes a support having a pyrochlore structure ceria-zirconia composite oxide, and at least one noble metal catalyst supported on the support,
The control unit is electrically connected to the sub oxygen sensor,
Here, the control unit is for warming up the catalyst unit realized by oxidizing the pyrochlore structure ceria-zirconia composite oxide in the catalyst unit and generating heat by the exhaust gas introduced into the catalyst unit. At the time of engine start, it is configured to supply oxidizing exhaust gas to the catalyst unit,
The control unit measures an oxygen concentration of exhaust gas downstream of the catalyst unit by the sub oxygen sensor at the time of an engine stop request, and based on the oxygen concentration, the atmosphere of the catalyst unit is an oxidizing atmosphere or It is determined whether the atmosphere is a reducing atmosphere. If it is determined that the catalyst unit is an oxidizing atmosphere, the engine is stopped by controlling the air-fuel ratio of the air-fuel mixture supplied to the engine to the reducing atmosphere side. When the atmosphere of the catalyst portion is set to a reducing atmosphere before, and the determination determines that the atmosphere of the catalyst portion is a reducing atmosphere, the air-fuel ratio is controlled to the oxidizing atmosphere side, and the atmosphere of the catalyst portion is Is changed to an oxidizing atmosphere, and again, the air-fuel ratio is controlled to the reducing atmosphere side so that the atmosphere of the catalyst section is made the reducing atmosphere before the engine is stopped. An exhaust gas purifying apparatus.   An exhaust gas purification device provided in an exhaust system of an engine,
  A catalyst unit disposed in an exhaust pipe through which exhaust gas flows;
  A control unit for controlling the oxygen concentration of the exhaust gas introduced into the catalyst unit;
  A sub-oxygen sensor that measures the oxygen concentration in the exhaust gas downstream of the exhaust pipe from the catalyst unit;
With
  The catalyst part includes a support having a pyrochlore structure ceria-zirconia composite oxide, and at least one noble metal catalyst supported on the support,
  The control unit is electrically connected to the sub oxygen sensor,
  Here, the control unit is for warming up the catalyst unit realized by oxidizing the pyrochlore structure ceria-zirconia composite oxide in the catalyst unit and generating heat by the exhaust gas introduced into the catalyst unit. At the time of engine start, it is configured to supply oxidizing exhaust gas to the catalyst unit,
  The control unit measures the oxygen concentration of the exhaust gas downstream of the catalyst unit by the sub oxygen sensor at the time of engine stop request, and controls the air-fuel ratio of the air-fuel mixture supplied to the engine to the reducing atmosphere side, When it is determined whether the atmosphere of the catalyst part at the time of engine stop request is an oxidizing atmosphere or a reducing atmosphere based on the oxygen concentration, and in the determination, it is determined that the atmosphere of the catalyst part is an oxidizing atmosphere Continues the control on the reducing atmosphere side of the air-fuel mixture until the atmosphere of the catalyst section is reversed to the reducing atmosphere, thereby setting the atmosphere of the catalyst section to a reducing atmosphere before the engine is stopped, while the atmosphere of the catalyst section is Is determined to be a reducing atmosphere, the sub oxygen sensor measures the output value of oxygen concentration or the displacement of the output value, and the measurement value is preset. Engine stop when it reaches the determination condition in the level of the reducing atmosphere is acceptable, and is configured to stop the engine, the exhaust gas purifying apparatus. A main oxygen sensor for measuring the oxygen concentration in the exhaust gas upstream of the exhaust pipe from the catalyst unit;
The control unit is electrically connected to the main oxygen sensor,
Here, at the time of engine start, the control unit is configured so that the pyrochlore structure ceria-zirconia composite oxide of the catalyst unit is oxidized based on the oxygen concentration measured by the main oxygen sensor so that heat can be generated. The air-fuel ratio (A / F) of the air-fuel mixture supplied to the engine is controlled to the oxidizing atmosphere side, and oxidizing exhaust gas generated by combustion of the air-fuel mixture is supplied to the catalyst unit. Item 3. The exhaust gas purifying apparatus according to Item 1 or 2 . Air injection (AI) on the upstream side of the exhaust pipe from the catalyst part ,
A main oxygen sensor for measuring the oxygen concentration in the exhaust gas upstream of the exhaust pipe from the catalyst unit;
With
The control unit is electrically connected to the AI and the main oxygen sensor ,
Here, at the time of engine start, the control unit is configured so that the pyrochlore structure ceria-zirconia composite oxide of the catalyst unit is oxidized based on the oxygen concentration measured by the main oxygen sensor so that heat can be generated. The exhaust gas purification apparatus according to any one of claims 1 to 3 , wherein an oxygen-containing gas is injected from the AI, and oxidizing exhaust gas generated by the injection is supplied to the catalyst unit. A method for purifying exhaust gas discharged from an engine provided with an exhaust system in which a catalyst having a pyrochlore structure ceria-zirconia composite oxide and at least one noble metal catalyst supported on the carrier is provided,
At the time of engine start, the pyrochlore structure ceria-zirconia composite oxide is oxidized to heat the composite oxide to warm up the catalyst. Of exhaust gas to the catalyst ,
At the time of engine stop request, the oxygen concentration of the catalyst is measured to determine whether the atmosphere of the catalyst is an oxidizing atmosphere or a reducing atmosphere based on the oxygen concentration. In the determination, the catalyst is oxidized If it is determined that the atmosphere is, by controlling the air-fuel ratio of the air-fuel mixture supplied to the engine to the reducing atmosphere side, the atmosphere of the catalyst is reduced to the reducing atmosphere before the engine is stopped. When it is determined that the catalyst atmosphere is a reducing atmosphere, the air-fuel ratio is controlled to the oxidizing atmosphere side, and after the catalyst atmosphere is changed to the oxidizing atmosphere, the air-fuel ratio is controlled again to the reducing atmosphere side. Thus, the exhaust gas purifying method is characterized in that the atmosphere of the catalyst is made a reducing atmosphere before the engine is stopped .   A method for purifying exhaust gas discharged from an engine provided with an exhaust system in which a catalyst having a pyrochlore structure ceria-zirconia composite oxide and at least one noble metal catalyst supported on the carrier is provided,
  At the time of engine start, the pyrochlore structure ceria-zirconia composite oxide is oxidized to heat the composite oxide to warm up the catalyst. Of exhaust gas to the catalyst,
  At the time of engine stop request, the oxygen concentration of the catalyst is measured, the air-fuel ratio of the air-fuel mixture supplied to the engine is controlled to the reducing atmosphere side, and the atmosphere of the catalyst at the time of engine stop request is oxidized based on the oxygen concentration It is determined whether the atmosphere is an atmosphere or a reducing atmosphere. If it is determined in this determination that the atmosphere of the catalyst is an oxidizing atmosphere, the control of the reducing atmosphere side of the mixture is controlled by the atmosphere of the catalyst. By continuing until the atmosphere is reversed, the atmosphere of the catalyst is made a reducing atmosphere before the engine is stopped. On the other hand, if it is determined by the determination that the atmosphere of the catalyst is a reducing atmosphere, the mixture is reduced. Continue control on the atmosphere side, and stop the engine when the reducing atmosphere in the catalyst has progressed to a level where a preset engine stop is acceptable Exhaust gas purification method, characterized in that, characterized in that. When the engine is started, the oxygen concentration of the exhaust gas is measured, and the pyrochlore structure ceria-zirconia composite oxide of the catalyst is oxidized based on the oxygen concentration and supplied to the engine so that the catalyst can generate heat. The exhaust gas according to claim 5 or 6, wherein an air-fuel ratio (A / F) of the air-fuel mixture is controlled to the oxidizing atmosphere side, and oxidizing exhaust gas generated by the air-fuel mixture is supplied to the catalyst. Purification method. At the time of engine start, the oxygen concentration of the exhaust gas is measured, and based on the oxygen concentration, the pyrochlore structure ceria-zirconia composite oxide of the catalyst is oxidized, and the exhaust gas is allowed to generate heat. The exhaust gas purification method according to any one of claims 5 to 7 , wherein an oxidizing exhaust gas generated by supplying an oxygen-containing gas is supplied to the catalyst.

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