JP2009036029A - Exhaust emission control device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem NOx elimination performance is lowered when the supply of the active oxygen and an air-fuel ratio control are performed concurrently, in a conventional exhaust emission control device supplying active oxygen to the upstream side of a catalyst when the temperature of exhaust gas is below the activation temperature of the catalyst after the starting of an engine. <P>SOLUTION: A control unit 20 operates an air supply pump 13 and an active oxygen generating device 14 when the temperature of the exhaust gas detected by an exhaust gas temperature sensor 16 after the starting of the engine 1 is below the activation temperature of the exhaust gas control catalyst 11 to supply the active oxygen into an exhaust gas passage 3 on the upstream side of the catalyst 11, and perform air-fuel ratio control so that the air-fuel ratio oscillates between a rich side and a lean side with respect to a theoretical air-fuel ratio after the starting of the engine 1. When the air-fuel ratio is oscillated to the lean side more than the theoretical air-fuel ratio by the air-fuel ratio control, the supply amount of the active oxygen by the air supply pump 13 and the active oxygen generating device 14 is reduced more than in the case where the air-fuel ratio is oscillated to the lean side more than the theoretical air-fuel ratio by the air-fuel ratio control. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device, and more particularly, to an exhaust gas purification device configured to supply an active oxygen component upstream of an exhaust gas purification catalyst disposed in an exhaust passage of an engine, and to improve exhaust emission. It belongs to the technical field.

  In general, in a vehicle such as an automobile using fossil fuel such as gasoline as an energy source, the exhaust gas temperature is relatively low for several tens of seconds immediately after the engine is started, and the exhaust gas purification catalyst disposed in the exhaust passage of the engine It is known that hydrocarbon (HC) and carbon monoxide (CO), which are unburned exhaust gas components, are difficult to purify because catalytic metals such as platinum (Pt) and palladium (Pd) are not activated. ing. As one method for improving this, conventionally, a manifold catalyst called “straight catalyzer” in which the catalyst is disposed directly under the exhaust manifold has been widely adopted. However, this method shortens the time until the catalyst temperature rises to the activation temperature, and is not a fundamental solution to the problem.

  Therefore, hydrocarbon adsorbents such as zeolite are used as the material for the manifold catalyst. That is, after the engine is started, when the exhaust gas temperature is relatively low, unburned hydrocarbons discharged from the engine are adsorbed in the pores of the hydrocarbon adsorbent, and when the exhaust gas temperature rises to about 200 ° C, Unburned hydrocarbons adsorbed on the hydrocarbon adsorbent are released and reacted with a catalytic metal activated to some extent at about 200 ° C. However, since aluminosilicate porous materials such as zeolite have the property that the crystal structure tends to collapse at high temperatures, this method has a problem that the purification performance of the catalyst gradually decreases with time. .

In order to cope with this problem, there has been proposed a method for oxidizing and purifying unburned exhaust gas components using an active oxygen component such as ozone (O ₃ ) without using a hydrocarbon adsorbent such as zeolite. For example, in Patent Document 1, ozone, which is an active oxygen component, is generated by applying a high voltage to air, and this ozone is supplied upstream of the catalyst in the exhaust passage, so that the HC contained in the exhaust gas is reduced. A technique is disclosed in which a part is converted to CO, and this CO is further oxidized to CO ₂ with a subsequent catalyst.

Patent Document 2 also discloses a means for generating and supplying active oxygen components. That is, in Patent Document 2, a discharge unit and a hydrogen supply unit are provided on the upstream side of the NOx occlusion reduction catalyst disposed in the exhaust pipe of the engine, and it is easy to occlude NO by oxygen radicals or ozone generated by the discharge unit. An exhaust emission control device configured to reduce and purify NO ₂ that is oxidized to NO ₂ and stored in a NOx storage reduction catalyst, and NO ₂ released from the NOx storage reduction catalyst by hydrogen supplied to an exhaust pipe by a hydrogen supply means. It is disclosed.

  Here, in general, active oxygen components such as ozone have a strong oxidizing power and have a relatively long life from generation to decomposition at a relatively low temperature of about room temperature. Supplying the active oxygen component to the exhaust passage upstream of the catalyst until reaching the catalyst activation temperature is considered to be an effective method for oxidizing and purifying unburned exhaust gas components of HC and CO.

JP-A-2005-207316 (paragraphs 0046 to 0050) JP-A-2005-344688 (paragraphs 0005 to 0007)

  By the way, the three-way catalyst capable of simultaneously purifying hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxide (NOx) has a purification window with a theoretical air-fuel ratio (A / F = 14.7). When the three-way catalyst is provided in the engine exhaust passage, the remaining oxygen in the exhaust gas flowing through the exhaust passage is located upstream of the three-way catalyst. An air-fuel ratio sensor that detects whether the air-fuel ratio is richer or leaner than the stoichiometric air-fuel ratio is provided from the concentration.After the engine is started, the fuel injection amount is determined based on the signal from the air-fuel ratio sensor. It is customary to perform an increasing / decreasing air-fuel ratio control. As a result of the air-fuel ratio control, the air-fuel ratio periodically fluctuates between the rich side and the lean side across the theoretical air-fuel ratio.

  Under such circumstances, as described above, after the engine is started, while the exhaust gas temperature is lower than the catalyst activation temperature, active oxygen components such as ozone are supplied to the exhaust passage upstream of the three-way catalyst. The following problems occur. In other words, the currently used active oxygen component supply means generates active oxygen components from oxygen in the air as a raw material, so that when supplying the active oxygen components to the exhaust passage, oxygen is also supplied together. Also, since it is difficult to strictly separate oxygen and active oxygen, the oxygen concentration in the exhaust gas increases with the supply of the active oxygen component.

  In consideration of the life of the active oxygen component, the supply point of the active oxygen component is arranged immediately upstream of the catalyst. Therefore, the position of the air-fuel ratio sensor for controlling the air-fuel ratio is more than the supply point of the active oxygen component. As a result, even if the air-fuel ratio control is normally performed based on the signal of the air-fuel ratio sensor, the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is biased to the lean side as a whole. Therefore, particularly when the air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio by the air-fuel ratio control, the oxygen concentration in the exhaust gas becomes excessive around the three-way catalyst. Although the unburned exhaust gas component is effectively oxidized and purified, a problem arises in that the NOx purification performance deteriorates.

  The present invention solves the above-described problem in the exhaust gas purification apparatus configured to supply the active oxygen component to the exhaust passage upstream of the catalyst when the exhaust gas temperature is equal to or lower than the catalyst activation temperature after the engine is started. In order to cope with this, it is an object to suppress the problem of NOx purification performance deterioration that occurs when the supply of the active oxygen component and the air-fuel ratio control are performed in parallel.

  In order to solve the above problems, the present invention uses the following means.

  That is, the invention according to claim 1 of the present application is an exhaust gas purification catalyst disposed in an exhaust passage of an engine, and an active oxygen component supply capable of supplying an active oxygen component to an exhaust passage upstream of the exhaust gas purification catalyst. An exhaust gas purifying device having an exhaust gas temperature detecting means for detecting an exhaust gas temperature, and an exhaust gas temperature detected by the exhaust gas temperature detecting means after starting the engine is the exhaust gas purifying device. Active oxygen component supply control means for operating the active oxygen component supply means when the temperature is below the activation temperature of the catalyst, and so that the air-fuel ratio fluctuates between the rich side and the lean side with the stoichiometric air-fuel ratio sandwiched after the engine is started When the air-fuel ratio is on the lean side of the stoichiometric air-fuel ratio by the control by the air-fuel ratio control means and the control by the air-fuel ratio control means, the active oxygen component is compared to when it is on the rich side. Characterized in that the active oxygen component supply amount adjusting means to lose weight the supplied amount of the active oxygen component by the supply control means is provided.

  Next, an invention according to claim 2 of the present application is directed to an exhaust gas purification catalyst disposed in an exhaust passage of an engine, and an active oxygen component capable of supplying an active oxygen component to an exhaust passage upstream of the exhaust gas purification catalyst. An exhaust gas purification device having a supply means, wherein the exhaust gas temperature detection means detects the temperature of the exhaust gas, and the temperature of the exhaust gas detected by the exhaust gas temperature detection means after the engine is started is the exhaust gas An active oxygen component supply control means for operating the active oxygen component supply means when the purification catalyst is below the activation temperature; and an exhaust gas temperature detected by the exhaust gas temperature detection means after the engine is started is the exhaust gas Until the predetermined temperature lower than the activation temperature of the purification catalyst is exceeded, the air-fuel ratio is controlled to swing between the rich side and the lean side across the theoretical air-fuel ratio, and the temperature of the exhaust gas is set to the predetermined temperature. Air-fuel ratio control means for controlling the air-fuel ratio so that the air-fuel ratio fluctuates between a rich side and a lean side across a predetermined amount rich side of the air-fuel ratio from the stoichiometric air-fuel ratio, and control by the air-fuel ratio control means Therefore, when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio, the active oxygen component supply amount adjusting means for reducing the supply amount of the active oxygen component by the active oxygen component supply control means compared to when it is on the rich side, And the active oxygen component supply amount adjusting means supplies the active oxygen component supply amount when the air-fuel ratio is on the lean side after the exhaust gas temperature exceeds the predetermined temperature and before the exhaust gas temperature exceeds the predetermined temperature. It is characterized by increasing the amount.

  Note that “reducing the supply amount of the active oxygen component” described in claims 1 and 2 includes setting the supply amount of the active oxygen component to zero, that is, stopping the supply of the active oxygen component. .

  Similarly, the “exhaust gas temperature detecting means” described in claims 1 and 2 may be, for example, one that is disposed in the exhaust passage and directly detects the temperature of the exhaust gas, or the load, the rotational speed, etc. The exhaust gas temperature may be indirectly detected from the engine operating state.

  Next, the invention according to claim 3 of the present application is the exhaust gas purifying apparatus according to claim 2, wherein the active oxygen component supply amount adjusting means has a temperature of the exhaust gas exceeding the predetermined temperature. After that, the supply amount of the active oxygen component when the air-fuel ratio is on the rich side is increased as compared with the time until it exceeds.

  The “predetermined temperature” described in claims 2 and 3 is, for example, the temperature at which the temperature rise curve of the exhaust gas purification catalyst disposed in the exhaust passage of the engine starts to increase rapidly (the temperature rise rate per hour is Temperature that starts to increase rapidly).

  First, according to the first aspect of the present invention, in the exhaust gas purification apparatus configured to be able to supply the active oxygen component upstream of the exhaust gas purification catalyst disposed in the exhaust passage of the engine, after the engine is started, Air-fuel ratio control is performed so that the air-fuel ratio fluctuates between the rich side and the lean side across the stoichiometric air-fuel ratio. Similarly, after the engine is started, when the exhaust gas temperature is lower than the catalyst activation temperature, supply of the active oxygen component is performed. Therefore, as long as the exhaust gas temperature is lower than the catalyst activation temperature after the engine is started, air-fuel ratio control and supply of active oxygen components are performed simultaneously.

  In this case, when the air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio by the air-fuel ratio control, the supply amount of the active oxygen component is reduced compared to when the air-fuel ratio is controlled to the rich side ( In particular, when the air-fuel ratio is on the lean side by the air-fuel ratio control, not only the active oxygen component but also the supply amount of oxygen is reduced, thereby purifying the exhaust gas. The oxygen concentration in the exhaust gas flowing into the catalyst is prevented from becoming excessive when lean, and the problem of NOx purification performance deterioration is effectively suppressed.

  Next, according to the second aspect of the present invention, in the exhaust gas purifying apparatus having the same configuration as that of the first aspect, the exhaust gas temperature is lower than the catalyst activation temperature after the engine is started (described above). Thus, the air-fuel ratio is controlled so that the air-fuel ratio fluctuates between the rich side and the lean side across the stoichiometric air-fuel ratio until the temperature rise curve of the catalyst on the exhaust passage exceeds the temperature at which it suddenly increases. After the gas temperature exceeds the predetermined temperature, the air-fuel ratio is controlled so that the air-fuel ratio fluctuates between the rich side and the lean side with the air-fuel ratio richer than the stoichiometric air-fuel ratio by a predetermined amount. However, after the temperature exceeds the predetermined temperature, the oxygen concentration in the exhaust gas generally decreases, and the concentration of the unburned exhaust gas components of HC and CO in the exhaust gas generally increases.

  In that case, after the exhaust gas temperature exceeds the predetermined temperature, the supply amount of the active oxygen component when the air-fuel ratio is on the lean side is increased as compared to before the exhaust gas temperature exceeds the predetermined temperature. Corresponding to HC and CO, the active oxygen component as an oxidant increases during lean, and as a result, a large amount of oxidation reaction of unburned exhaust gas components of HC and CO occurs in the catalyst during lean and the catalyst rises. The temperature will increase. Thereby, the time until the catalyst temperature rises to the activation temperature is shortened, and the purification performance is improved.

  Moreover, since the supply amount of the active oxygen component is increased during the lean period when the supply amount of the active oxygen component is originally reduced, the supply amount of the active oxygen component can be reduced without imposing an excessive burden on the active oxygen component supply means. It is possible to increase the amount easily.

  According to the third aspect of the present invention, after the exhaust gas temperature exceeds the predetermined temperature, the supply amount of the active oxygen component when the air-fuel ratio is on the rich side is also increased compared to the exhaust gas temperature exceeding the predetermined temperature. As a result, the active oxygen component as an oxidizer increases not only when lean, but also when rich, corresponding to the increased HC and CO as a whole. As a result, the oxidation reaction of unburned exhaust gas components of HC and CO It occurs in a larger amount in the catalyst at the time of lean and rich, and the temperature rise property of the catalyst is further increased. Thereby, the time until the catalyst temperature rises to the activation temperature is further shortened, and the purification performance is further improved. Hereinafter, the present invention will be described in more detail through the best mode for carrying out the invention.

  FIG. 1 is an overall configuration diagram including a control system of an exhaust gas purifying apparatus 10 according to the best embodiment of the present invention. The engine 1 has an intake passage 2 and an exhaust passage 3, and a throttle valve 4 that controls the amount of intake air is disposed in the intake passage 2, and platinum (Pt), palladium (Pd), rhodium ( A three-way catalyst 11 containing a catalyst metal such as Rh) is disposed as an exhaust gas purification catalyst.

Active oxygen component supply means is disposed in the exhaust passage 2 upstream of the three-way catalyst 11. That is, the active oxygen supply passage 12 is merged immediately upstream of the three-way catalyst 11, on the active oxygen supply passage 12, an air supply pump 13, ozone (O ₃₎ activity to generate active oxygen ingredient such as An oxygen generator 14 is provided. For example, the active oxygen generator 14 generates ozone by silently discharging the air introduced by the air supply pump 13.

Further, in the exhaust passage 3, the air-fuel ratio is higher than the stoichiometric air-fuel ratio from the residual oxygen concentration in the exhaust gas flowing through the exhaust passage 3 upstream from the confluence (active oxygen component supply point) of the active oxygen supply passage 12. An air-fuel ratio sensor (O ₂ sensor) 15 that detects whether it is on the rich side or the lean side, and an exhaust gas temperature sensor 16 that detects the temperature of the exhaust gas flowing through the exhaust passage 3 are provided. Note that the temperature of the three-way catalyst 11 substantially corresponds to the exhaust gas temperature detected by the exhaust gas temperature sensor 16.

  The control unit 20 of the exhaust gas purification apparatus 10 inputs an opening degree signal from the throttle valve 4, an air-fuel ratio signal from the air-fuel ratio sensor 15, and a temperature signal from the exhaust gas temperature sensor 16. Based on the input result, air-fuel ratio control for the engine 1 and active oxygen supply control for the air supply pump 13 and the active oxygen generator 14 are executed.

  In the present embodiment, the air-fuel ratio control is performed according to the flowchart shown in FIG. That is, the control unit 20 reads various signals and determines whether or not the exhaust gas temperature T is equal to or lower than the predetermined temperature TC in step S1. The predetermined temperature TC is a temperature at which the temperature rise curve of the three-way catalyst 11 disposed in the exhaust passage 3 of the engine 1 starts to increase rapidly (temperature at which the rate of temperature increase per hour starts to increase rapidly: for example, 100 ° C.). (See time t1 in FIG. 4).

  As a result, if YES, air-fuel ratio control is performed in step S2 so that the air-fuel ratio fluctuates between the rich side and the lean side with the theoretical air-fuel ratio A interposed therebetween. More specifically, based on the output signal from the air-fuel ratio sensor 15, the fuel injection amount in the engine 1 is increased / decreased through feedback control or learning control, and the air-fuel ratio Air-fuel ratio control is performed so as to swing toward the lean side.

  On the other hand, if NO in step S1, it is determined in step S3 whether or not the exhaust gas temperature T is equal to or lower than the catalyst activation temperature TH. The catalyst activation temperature TH is a temperature (light-off temperature: for example, 200 ° C.) when the three-way catalyst 11 is activated and the exhaust gas purification rate becomes 50% (see time t2 in FIG. 4).

  If the result is YES, air-fuel ratio control is performed in step S4 so that the air-fuel ratio fluctuates between the rich side and the lean side with the predetermined air-fuel ratio B interposed therebetween. The predetermined air-fuel ratio B is an air-fuel ratio richer than the theoretical air-fuel ratio A by a predetermined amount (see FIG. 4). More specifically, based on the output signal from the air-fuel ratio sensor 15, the fuel injection amount in the engine 1 is increased or decreased via feedback control or learning control, and in that case, the fuel injection amount is generally increased. (By shifting the air-fuel ratio to the rich side), air-fuel ratio control is performed so that the air-fuel ratio fluctuates between the rich side and the lean side with the predetermined air-fuel ratio B interposed therebetween.

  On the other hand, if NO in step S3, air-fuel ratio control is performed in step S5 so that the air-fuel ratio fluctuates between the rich side and the lean side across the theoretical air-fuel ratio A as in step S2.

  In the present embodiment, the active oxygen supply control is performed according to the flowchart shown in FIG. That is, the control unit 20 reads various signals, confirms that the engine is cold start in step S11, and then determines whether the exhaust gas temperature T is equal to or lower than the predetermined temperature TC in step S12. (See time t1 in FIG. 4).

  If the result is YES, it is determined in step S13 whether or not the air-fuel ratio is 14.7 or less, that is, whether or not the air-fuel ratio is richer than the theoretical air-fuel ratio A. As a result, when YES, in step S14, the ozone supply amount to the exhaust passage 3 is set to the first supply amount OS1 to generate and supply ozone, and when NO, in step S15, the exhaust passage The ozone supply amount to 3 is set to the second supply amount OS2 to generate and supply ozone. Here, the second supply amount OS2 is smaller than the first supply amount OS1.

  On the other hand, if NO in step S12, it is determined in step S16 whether or not the exhaust gas temperature T is equal to or lower than the catalyst activation temperature TH (see time t2 in FIG. 4).

  If the result is YES, in step S17, it is determined whether or not the air-fuel ratio is 14.7 or less, that is, whether or not the air-fuel ratio is richer than the theoretical air-fuel ratio A. As a result, when YES, in step S18, the ozone supply amount to the exhaust passage 3 is set to the third supply amount OS3 to generate and supply ozone, and when NO, in step S19, the exhaust passage The ozone supply amount to 3 is set to the fourth supply amount OS4 to generate and supply ozone. Here, the fourth supply amount OS4 is smaller than the third supply amount OS3. The third supply amount OS3 is larger than the first supply amount OS1, and the fourth supply amount OS4 is larger than the second supply amount OS2. Furthermore, the fourth supply amount OS4 is smaller than the first supply amount OS1.

  On the other hand, if NO in step S16, the end is reached. That is, the supply of active oxygen to the exhaust passage 3 is completed (time t2 in FIG. 4).

  As a result of the control as described above, as shown in FIG. 4, the exhaust gas temperature, the active oxygen supply amount, and the air-fuel ratio change over time. Note that the temperature of the three-way catalyst 11 changes substantially in response to the exhaust gas temperature shown in FIG.

  In FIG. 4, the change (solid line) in the exhaust gas temperature indicated by the symbol “a” is obtained when the air-fuel ratio control in FIG. 2 and the active oxygen supply control in FIG. 3 are performed. On the other hand, the change (chain line) in the exhaust gas temperature indicated by symbol a is performed only in the air-fuel ratio control so that the air-fuel ratio fluctuates between the rich side and the lean side across the theoretical air-fuel ratio A (that is, the air-fuel ratio is reduced). This is the case when the active oxygen supply control is performed with the active oxygen supply amount fixed, without performing the air / fuel ratio control so as to swing between the rich side and the lean side across the predetermined air / fuel ratio B.

  The solid line a has a shorter time until the catalyst temperature T rises to the activation temperature TH than the chain line a. That is, the change in the exhaust gas temperature (temperature of the three-way catalyst 11) up to time t1 is the same in the solid line A and the chain line A, but in the solid line A, the temperature is the activation temperature at a relatively early time t2. In contrast to the temperature rising to TH, in the chain line a, the temperature rises to the activation temperature TH at a later time.

  Further, the change (solid line) in the active oxygen supply amount indicated by the symbol C is obtained when the active oxygen supply control in FIG. 3 is performed. In this case, the supply of active oxygen ends at the time t2. On the other hand, the change (dashed line) in the active oxygen supply amount indicated by reference sign D is obtained when the active oxygen supply amount is fixed (fixed to the first supply amount OS1). In this case, the supply of active oxygen ends at a time later than the time t2.

  The change (dotted line) in the air-fuel ratio indicated by reference character O is in the engine 1 when the air-fuel ratio control of FIG. 2 is performed. That is, until time t1, air-fuel ratio control is performed so that the air-fuel ratio fluctuates between the rich side and the lean side across the theoretical air-fuel ratio A, and from time t1 to time t2, the air-fuel ratio reaches the predetermined air-fuel ratio B. Air-fuel ratio control is performed so as to swing between the rich side and the lean side, and after time t2, the air-fuel ratio control is performed so that the air-fuel ratio swings again between the rich side and the lean side across the theoretical air-fuel ratio A. Is done.

  On the other hand, the change (solid line) in the air-fuel ratio indicated by reference numeral is in the three-way catalyst 11 when the active oxygen supply control of FIG. Further, the change in the air-fuel ratio (chain line) indicated by the symbol is in the three-way catalyst 11 when the active oxygen supply amount is fixed (fixed to the first supply amount OS1). In the solid line power, the air-fuel ratio in the catalyst 11 is moved to the rich side as a whole compared to the chain line key. That is, in the chain line key, the active oxygen supply amount is fixed to the first supply amount OS1, whereas in the solid line power, the active oxygen supply amount is reduced to the second supply amount OS2 and the fourth supply amount OS4 when lean. This prevents the oxygen concentration in the exhaust gas flowing into the three-way catalyst 11 from becoming excessive.

  As described above, the exhaust gas purification apparatus 10 according to the present embodiment supplies the active oxygen component to the upstream of the three-way catalyst 11 disposed in the exhaust passage 3 of the engine 1 by the air supply pump 13 and the active oxygen generator 14. It can be supplied. Then, after the engine 1 is started, air-fuel ratio control is performed so that the air-fuel ratio fluctuates between the rich side and the lean side across the theoretical air-fuel ratio A (S2). When the activation temperature is equal to or lower than the activation temperature TH (YES in S12, YES in S16), the active oxygen component is supplied (S14, S15, S18, S19), so that the exhaust gas temperature T is the catalyst activation temperature after the engine 1 is started. While it is lower than TH (until time t2), the air-fuel ratio control and the supply of active oxygen components are performed simultaneously.

  In this case, when the air-fuel ratio is controlled to be leaner than the stoichiometric air-fuel ratio A by air-fuel ratio control (NO in S13, NO in S17), compared to when the air-fuel ratio is controlled to be rich ( Since the supply amount of the active oxygen component is reduced (OS2 <OS1, OS4 <OS3), particularly when the air-fuel ratio is on the lean side by the air-fuel ratio control, the active oxygen component supply amount is decreased (YES in S13, YES in S17). Not only the components but also the supply amount of oxygen is reduced, which prevents the oxygen concentration in the exhaust gas flowing into the three-way catalyst 11 from becoming excessive during lean, effectively reducing the NOx purification performance problem. It will be suppressed.

  In addition, after the engine 1 is started, until the exhaust gas temperature T exceeds a predetermined temperature TC lower than the catalyst activation temperature TH (YES in S1), the air-fuel ratio becomes rich and lean with respect to the theoretical air-fuel ratio A. (S2), after the exhaust gas temperature T exceeds the predetermined temperature TC (NO in S1), the air-fuel ratio is a predetermined air-fuel ratio richer than the stoichiometric air-fuel ratio A by a predetermined amount. Since the air-fuel ratio control is performed so as to swing between the rich side and the lean side across B (S4), after the exhaust gas temperature T exceeds the predetermined temperature TC (time t1 to t2), oxygen in the exhaust gas The concentration generally decreases, and the concentration of unburned exhaust gas components of HC and CO in the exhaust gas generally increases.

  In that case, after the exhaust gas temperature T exceeds the predetermined temperature TC (NO in S12: time t1 to t2), the air-fuel ratio is leaner than that until it exceeds (YES in S12: time t1). Since the supply amount of the active oxygen component when it is on the side is increased (OS4 of S19> OS2 of S15), the active oxygen component as the oxidant increases in response to the increased HC and CO as a whole. As a result, the oxidation reaction of the unburned exhaust gas components of HC and CO occurs in a large amount in the three-way catalyst 11 at the time of lean, and the temperature rise performance of the three-way catalyst 11 is increased. Thereby, the time until the catalyst temperature T rises to the activation temperature TH is shortened, and the purification performance is improved.

  Moreover, since the supply amount of the active oxygen component is increased when the supply amount of the active oxygen component is originally reduced (OS2 <OS1), the air supply pump 13 serving as the active oxygen component supply unit and the generation of active oxygen are generated. It is possible to easily increase the supply amount of the active oxygen component without imposing an excessive burden on the device 14.

  In addition, after the exhaust gas temperature T exceeds the predetermined temperature TC (NO in S12: time t1 to t2), the air-fuel ratio is on the rich side as compared to until it exceeds (YES in S12: until time t1). The amount of active oxygen component supplied is also increased (OS3 in S18> OS1 in S14), so that the active oxygen component as an oxidizer corresponding to the increased HC and CO as a whole is not only lean but rich. As a result, the oxidation reaction of the unburned exhaust gas components of HC and CO occurs in a large amount in the three-way catalyst 11 at the time of lean and rich, and the temperature rise performance of the three-way catalyst 11 is further enhanced. Become. Thereby, the time until the catalyst temperature T rises to the activation temperature TH is further shortened, and the purification performance is further improved.

  The above embodiment is the best embodiment of the present invention, but it goes without saying that various modifications and changes may be made without departing from the scope of the claims. For example, in the above-described embodiment, the exhaust gas temperature is directly detected by the exhaust gas temperature sensor 16 disposed in the exhaust passage 3, but the present invention is not limited to this, and the engine load (intake air amount or throttle valve 4 opening degree) is not limited thereto. ) And engine speed such as the engine speed can also be indirectly detected.

  In the above embodiment, when the exhaust gas temperature T is equal to or lower than the predetermined temperature TC, the second supply amount OS2 of the active oxygen component when the air-fuel ratio is leaner than the stoichiometric air-fuel ratio A is not zero. However, the present invention is not limited to this, and it is also possible to make it zero, that is, to stop the supply of active oxygen components.

  As described above in detail with reference to specific examples, the present invention is a technology capable of suppressing the problem of NOx purification performance degradation that occurs when the supply of active oxygen components and air-fuel ratio control are performed in parallel. Therefore, in the technical field of exhaust gas purification devices, particularly exhaust gas purification devices configured to supply an active oxygen component upstream of an exhaust gas purification catalyst disposed in an exhaust passage of an engine. Is expected to be available.

1 is an overall configuration diagram including a control system for an exhaust gas purifying apparatus according to a best embodiment of the present invention. It is a flowchart which shows one example of the specific operation | movement of the air fuel ratio control which the control unit of the said exhaust gas purification apparatus performs. It is a flowchart which shows one example of the specific operation | movement of the active oxygen supply control which the control unit of the said exhaust gas purification apparatus performs. It is a time chart showing the effect | action of the said active oxygen supply control.

Explanation of symbols

1 Engine 3 Exhaust passage 10 Exhaust gas purification device 11 Exhaust gas purification catalyst (three-way catalyst)
12 Active oxygen supply passage 13 Air supply pump (active oxygen component supply means)
14 Active oxygen generator (active oxygen component supply means)
15 Air-fuel ratio sensor 16 Exhaust gas temperature sensor (exhaust gas temperature detection means)
20 control unit (active oxygen component supply control means, air-fuel ratio control means, active oxygen component supply amount adjustment means)

Claims (3)

An exhaust gas purification catalyst disposed in the exhaust passage of the engine;
An exhaust gas purification device having active oxygen component supply means capable of supplying an active oxygen component to an exhaust passage upstream of the exhaust gas purification catalyst,
Exhaust gas temperature detecting means for detecting the temperature of the exhaust gas;
Active oxygen component supply control means for operating the active oxygen component supply means when the temperature of the exhaust gas detected by the exhaust gas temperature detection means is equal to or lower than the activation temperature of the exhaust gas purification catalyst after the engine is started;
Air-fuel ratio control means for controlling the air-fuel ratio to swing between the rich side and the lean side across the stoichiometric air-fuel ratio after engine startup;
When the air-fuel ratio is leaner than the stoichiometric air-fuel ratio by the control by the air-fuel ratio control means, the active oxygen component supply amount by the active oxygen component supply control means is reduced compared to when the air-fuel ratio is on the rich side. An exhaust gas purifying device comprising an oxygen component supply amount adjusting means. An exhaust gas purification catalyst disposed in the exhaust passage of the engine;
An exhaust gas purification device having active oxygen component supply means capable of supplying an active oxygen component to an exhaust passage upstream of the exhaust gas purification catalyst,
Exhaust gas temperature detecting means for detecting the temperature of the exhaust gas;
Active oxygen component supply control means for operating the active oxygen component supply means when the temperature of the exhaust gas detected by the exhaust gas temperature detection means is equal to or lower than the activation temperature of the exhaust gas purification catalyst after the engine is started;
After the engine is started, the air-fuel ratio is on the rich side across the stoichiometric air-fuel ratio until the exhaust gas temperature detected by the exhaust gas temperature detecting means exceeds a predetermined temperature lower than the activation temperature of the exhaust gas purification catalyst. After the exhaust gas temperature exceeds the predetermined temperature, the air-fuel ratio is a predetermined amount richer than the stoichiometric air-fuel ratio. Air-fuel ratio control means for controlling to swing to
When the air-fuel ratio is leaner than the stoichiometric air-fuel ratio by the control by the air-fuel ratio control means, the active oxygen component supply amount by the active oxygen component supply control means is reduced compared to when the air-fuel ratio is on the rich side. An oxygen component supply amount adjusting means, wherein the active oxygen component supply amount adjusting means is when the air-fuel ratio is on the lean side after the temperature of the exhaust gas exceeds the predetermined temperature and before it exceeds. An exhaust gas purification device characterized by increasing the supply amount of the active oxygen component. The exhaust gas purification device according to claim 2,
The active oxygen component supply amount adjusting means increases the supply amount of the active oxygen component when the air-fuel ratio is on the rich side, after the temperature of the exhaust gas exceeds the predetermined temperature, compared to before the temperature exceeds. An exhaust gas purification device characterized by the above.

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