JP2000008840A - Function recovery device and function recovery method for exhaust gas purification catalyst - Google Patents

Abstract

[PROBLEMS] To use H as a catalyst for purifying exhaust gas of diesel engines.
Purification function deteriorates due to adhesion of C, SOF, PM, etc. (poisoning)
To provide a means that does not require large energy consumption, such as raising the exhaust gas temperature, as a function recovery means in the event of the above. SOLUTION: A pulsation generating means is attached to an exhaust pipe 12 provided with a catalytic converter 13 to give a pulsation to the flow of the exhaust gas when the amount of adhesion exceeds a predetermined limit, so that the pulsating exhaust gas is shocked. The desorption of HC and the like from the catalyst 13a is promoted by a mechanical or physical action of a simple flow. As the pulsation generating means, for example, an exhaust pipe opening / closing valve 25 operated by an exhaust pipe opening / closing actuator 26 is provided, or in some cases, means for pulsatingly flowing exhaust gas is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst system for purifying nitrogen oxides (NOx) and the like contained in exhaust gas of a diesel engine by a catalyst. Organic matter (SOF),
Alternatively, the present invention relates to an exhaust purification catalyst function recovery device and method for recovering the purification function of a catalyst from a so-called "catalyst poisoning" state in which the function of the catalyst is reduced by the attachment of exhaust particulates (PM) or the like to the catalyst. .

[0002]

2. Description of the Related Art A catalyst purification system using a catalytic converter for purifying nitrogen oxides (NOx) contained in exhaust gas discharged from a diesel engine has been studied. NOx is purified by reacting and reducing with hydrocarbons (HC) in the exhaust gas in the catalytic converter. In the case of a diesel engine, NOx is purified.
Since the amount is small, NOx cannot be sufficiently purified. Therefore, HC such as fuel is provided upstream of the catalytic converter.
Is being added.

However, if HC is continuously added to the exhaust gas for a long time, the HC added to react with NOx
Reacts with the catalyst itself, so that HC emits NOx
There is a problem that so-called "catalyst poisoning" occurs in which HC adheres to the active point of the catalyst before it is consumed by reacting with the catalyst, thereby significantly reducing the catalyst activity. Reduction of the purification function of the catalyst due to catalyst poisoning is caused not only by HC but also by soluble organic matter (SOF) and exhaust particulates (P) contained in exhaust gas of a diesel engine.
It also occurs when M) adheres to the catalyst.

[0004] HC, SOF, PM, etc. (hereinafter referred to as "HC
), The catalyst adsorbed on the catalyst is increased by increasing the catalyst temperature.
A recovery operation for desorbing or burning C and the like is required. When the engine is operated at a high speed or a high load, the exhaust gas temperature rises, so that HC and the like can be naturally removed from the poisoned catalyst. When poisoning occurs, the temperature of the exhaust gas must be raised in some way to restore the functioning of the poisoned catalyst, since the poisoned catalyst does not always enter a high-speed, high-load operating state. Need to be done.

For this purpose, conventionally, for example,
As disclosed in Japanese Patent Application Laid-Open No. 21718 or Japanese Patent Application Laid-Open No. Hei 6-200737, the delay of fuel injection timing into the cylinder of the engine, the closing of the intake throttle valve, the exhaust gas recirculation (EG
R), the exhaust gas temperature is raised to about 400 ° C. by directly heating the exhaust gas by an electric heater or the like, whereby the catalyst temperature is also raised to desorb HC and the like from the catalyst.

[0006]

However, the purification characteristics of the poisoned catalyst are shifted to a high temperature side by more than 10 ° C. as compared with the non-poisoned catalyst, so that the temperature of the gas entering the poisoned catalyst is low. Needs to be considerably higher than the activation start temperature at which the catalyst starts to be activated. Therefore, when the exhaust gas temperature is increased by the conventional method as described above, in order to increase the fuel injection amount of the engine as compared with the normal operation state,
In practice, it is very difficult to increase the exhaust gas temperature to a temperature sufficient for the function recovery of the poisoned catalyst, with the problem that the fuel efficiency of the engine is considerably reduced.

[0007] In view of the above-mentioned problems in the prior art, the present invention does not rely on the means of increasing the temperature of the exhaust and the catalyst, which require large energy consumption, but rather by means of physical or mechanical means for purifying the catalyst. It is an object of the present invention to provide a novel catalyst function recovery device and a function recovery method capable of recovering a catalyst.

The present invention also provides a novel catalyst function recovery device and a function recovery method capable of suppressing the progress of catalyst poisoning due to HC or the like during a deceleration operation of a vehicle equipped with an engine. It is intended to provide.

[0009]

According to the present invention, there is provided, as means for solving the above-mentioned problems, an apparatus and a method for recovering the function of an exhaust gas purifying catalyst described in the claims. I do.

According to the function recovery device of the first aspect, the pulsation is forcibly generated in the exhaust flowing through the exhaust passage by the pulsation generating means provided in the exhaust passage, so that the flow velocity of the exhaust flow is pulsated. Change. As a result, the flow velocity of the exhaust gas flowing through the catalyst is rapidly reduced and accelerated repeatedly, so that the mechanical or physical action of the impact of the flow and the same action as the exhaust flow on the surface of the catalyst are performed. Since the thickness of the boundary layer becomes thin and the exhaust and the chemical action of the catalyst become stronger, HC or the like adhering to the surface of the catalyst is desorbed, and the purification function of the catalyst can be restored.

In the function recovery device according to the second aspect, the pulsation generating means is specifically an exhaust passage opening / closing valve provided in the middle of the exhaust passage. In the device, the exhaust passage opening / closing valve is automatically opened / closed by a command from the control means.
The exhaust passage opening / closing valve may be provided on the downstream side of the exhaust gas purification catalyst, or may be provided on the upstream side.

In the function recovery device according to the present invention, when the exhaust passage opening / closing valve is provided in the exhaust passage upstream of the exhaust purification catalyst, the exhaust passage opening / closing valve is connected to the downstream side of the exhaust passage opening / closing valve. Since the on-off valve, the reserve tank, and the vacuum pump are sequentially inserted in series in the middle of the bypass passage connecting the upstream side, the exhaust passage opening / closing valve is closed by a command from the control means, and at the same time, the bypass passage is closed. When the on-off valve is opened, the upstream side of the catalyst becomes a negative pressure, and the exhaust gas flowing through the catalyst flows backward. As a result, the pulsation of the exhaust gas increases, the action of desorbing HC and the like from the catalyst becomes stronger, and the recovery of the purification function of the catalyst is promoted.

According to the function recovery method of the present invention, since the pulsation is forcibly generated in the exhaust flowing through the exhaust passage by the pulsation generating means attached to the exhaust passage, the flow velocity of the exhaust flow is pulsated. Change. As a result, the flow velocity of the exhaust gas flowing through the catalyst is rapidly reduced and accelerated repeatedly, so that the mechanical or physical action of the impact of the flow and the same action as the exhaust flow on the surface of the catalyst are performed. Since the thickness of the boundary layer becomes thin and the exhaust and the chemical action of the catalyst become stronger, HC or the like adhering or adsorbed on the surface of the catalyst is desorbed, and the purification function of the catalyst can be restored. . Further, in the function recovery method according to the eighth aspect, when the flow rate of the exhaust gas flowing through the exhaust passage is pulsatively changed, a reverse flow of the exhaust gas flowing through the catalyst is also generated. Can be removed.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an apparatus and a method for recovering the function of an exhaust gas purifying catalyst according to the present invention will be described in detail with reference to the illustrated embodiments. As a first embodiment of the present invention, FIG. 1 shows an overall configuration of a vehicle-mounted diesel engine to which the function recovery device and method of the present invention are applied. The engine 11 is a 4200 cc 6 cylinder direct injection diesel engine. Exhaust gas discharged from the engine 11 contains HC, NOx, etc., and these harmful components flow into the 3.4 L catalytic converter 13 through the exhaust pipe 12 having an inner diameter of 60 mm, and are rendered harmless. After being released into the atmosphere. The catalyst in the catalytic converter 13 is, for example, a type of porous zeolite coated with an alumina layer and then loaded with platinum. NOx reacts with HC remaining in the exhaust gas with the aid of this catalyst. , Is rendered harmless by being reduced.

As is generally the case, the exhaust gas of the diesel engine 11 does not contain a sufficient amount of HC as a reducing agent to completely purify NOx.
A hydrocarbon addition device is provided in the exhaust pipe 12 to make up for the shortage of HC. In the embodiment shown, only the injector 17 at the end of the hydrocarbon addition device is shown on the exhaust pipe 12. The injector 17
Exhaust pipe 12 using light oil used as fuel as hydrocarbon
This is a device for injecting and adding to exhaust gas flowing through the inside, and the injection operation is controlled by a computer 16.

The computer 16 is provided for controlling the entire system of the engine 11. The computer 16 is provided at the entrance of the catalytic converter 13 to check the activation state of the catalyst 13 a provided inside the catalytic converter 13. Exhaust temperature sensor 14 attached to detect incoming gas temperature
And a catalyst temperature sensor 15 attached to the catalyst 13a and detecting its temperature.
3 and 24 are input to the computer 16. In addition, a rotation speed signal 21 detected by a rotation speed sensor (not shown) of the engine 11 and a throttle opening signal 22 detected by a sensor attached to a throttle lever are also input to the computer 16.

A feature of the first embodiment is that, for example, a butterfly-type exhaust pipe that is rotatably driven to open and close the exhaust pipe 12 intermittently is provided in a portion of the exhaust pipe 12 downstream of the catalytic converter 13. An opening / closing valve 25 is provided. The exhaust pipe opening / closing valve 25 is controlled to be opened / closed by an exhaust pipe opening / closing actuator 26 such as a motor that operates in response to a command from the computer 16. The exhaust pipe opening / closing valve 25 may be a valve other than the butterfly type, such as a solenoid valve, as long as it can open and close the exhaust pipe 12 at short intervals. Further, even if the exhaust pipe opening / closing valve 25 is not newly provided in the engine 11, if the exhaust pipe 12 is provided with an exhaust brake, it can be used as it is.

The state of the catalyst 13a is determined by the computer 16 when the catalyst temperature signal 24 detected by the catalyst temperature sensor 15 is higher than the exhaust temperature signal 23 detected by the exhaust temperature sensor 14, for example. It can be estimated that it is in an active state. Conversely, when the exhaust gas temperature signal 23 is equal to or higher than the predetermined value and the catalyst temperature signal 24 is lower than the exhaust gas temperature signal 23,
Since it is clear that a does not perform a normal purification function, the computer 16 determines that the catalyst 13a is in a poisoned state.

If the catalyst 13a is poisoned by HC added to the exhaust gas flowing through the exhaust pipe 12 from the injector 17, the amount of HC adsorbed on the catalyst 13a may be estimated. Several methods can be used for this estimation. For example, as an indirect method, the relationship between the operating conditions of the engine 11 and the component concentration of the exhaust gas flowing into the catalytic converter 13 is measured in advance, and the H
There is a method of estimating the current HC adsorption amount by performing a cumulative calculation from the start of use of the catalyst 13a in consideration of the adsorption of C, the desorption from the catalyst, the reaction of HC in the catalyst, and the like.

As a more direct method, the HC concentration at the inlet and the outlet of the catalytic converter 13 is measured by an HC sensor (not shown), and the difference is further detected by the catalyst 1.
The amount of HC adsorbed on the catalyst 13a can be estimated in consideration of the reaction in 3a. As a more direct method, there is a method of directly analyzing the amount of HC adsorption on the catalyst 13a. The HC adsorption amount of the catalyst 13a can be estimated by any of the above methods or other known methods. Therefore, the computer 16 detects the poisoning state of the catalyst 13a by HC or the like by using any of these methods or a combination of some of these methods, and thereby recovers the function according to the degree of the poisoning. Determine if the operation needs to be performed.

When the function recovery operation is to be performed, it is determined from the rotational speed signal 21 and the throttle opening signal 22 that the vehicle equipped with the engine 11 is in a deceleration operation state among the operation states of the engine 11. It is carried out only at the time determined by 16. When the function recovery operation is performed under these conditions, in the case of the first embodiment, the computer 16 operates the exhaust pipe opening / closing valve 25 via a drive circuit and an actuator 26 (not shown), and the exhaust pipe 12 are periodically opened and closed at predetermined intervals, for example.

Therefore, when the computer 16 determines that it is time to perform the function recovery operation of the catalyst 13a, a drive signal is sent from the drive circuit, which has been commanded by the computer 16, to the exhaust pipe opening / closing actuator 26 in the deceleration operation state of the vehicle. The output, the exhaust pipe opening / closing valve 25 opens and closes the exhaust pipe 12. As a result, the flow of exhaust gas in the exhaust pipe 12 is interrupted,
Since the flow velocity of the exhaust gas flowing through the gap of the carrier a rapidly repeats deceleration and acceleration, the mechanical or physical direct action of the impact of the flow is the same as that of the carrier of the catalyst 13a. Since the thickness of the boundary layer of the exhaust flow on the surface becomes thinner and the chemical action of the exhaust and the catalyst becomes stronger, HC and the like adhering to the surface of the catalyst 13a are desorbed. Thereby, the function of the catalyst 13a can be restored.

FIG. 2 shows the overall configuration of a diesel engine according to a second embodiment of the present invention. In FIG. 2, substantially the same parts as those in the first embodiment are denoted by the same reference numerals, and redundant description is omitted. I do. In the case of the second embodiment, the exhaust pipe 12
Among them, on the upstream side of the catalytic converter 13, similarly to the first embodiment, an exhaust pipe opening / closing valve 25 operated by a command of the computer 16 is provided to open and close the exhaust pipe, and the exhaust pipe opening / closing valve 25 is provided downstream of the exhaust pipe opening / closing valve 25. A bypass passage 30 is provided for connecting each part of the exhaust pipe 12 on the upstream side and the exhaust pump 12 on the upstream side.
1 and the reserve tank 32 are inserted and arranged. At this time, the direction of the flow in the bypass passage 30 by the vacuum pump 31 is set to be from the downstream side to the upstream side. Then, the reserve tank 32 and the exhaust pipe opening / closing valve 25
An opening / closing valve 33 such as an electromagnetic valve controlled to be opened / closed by the computer 16 is inserted into a part of the bypass passage 30 connecting the exhaust pipe 12 on the downstream side of the air conditioner.

The vacuum inside the reserve tank 32 is always kept at a predetermined level or higher by the operation of the vacuum pump 31, and the vacuum is usually used for an existing object such as a brake. As in the case of the first embodiment, the computer 16 transmits the rotation speed signal 21 and the throttle opening signal 2
The computer 16 integrates the poisoning state of the catalyst 13a by HC or the like based on the second and the like, and when the computer 16 determines that the function of the catalyst 13a is deteriorated, when the vehicle enters the deceleration operation state, the exhaust pipe opening and closing is performed. The actuator 26 is driven to close the exhaust pipe opening / closing valve 25. And
At the same time, since the computer 16 opens the on-off valve 33, the downstream side of the exhaust pipe opening / closing valve 25, that is, the upstream side of the catalytic converter 13 is connected to the reserve tank 32, and the upstream side of the catalytic converter 13 is depressurized.

As a result, the exhaust gas flowing through the gap of the carrier of the catalyst 13a not only temporarily reverses, but also opens and closes the on-off valve 33 and opens the exhaust pipe opening and closing valve 25 in response to a command from the computer 16. When the exhaust gas flows in the normal direction in the exhaust pipe 12 when the valve is opened, the change in the flow velocity of the exhaust gas flowing through the catalyst 13a increases more than in the normal case. In this manner, not only does the exhaust gas flowing through the catalytic converter 13 pulsate greatly, but also the action and effect of the first embodiment are further enhanced by the increase in the flow velocity, so that the exhaust gas flowing on the catalyst 13a The desorbed HC and the like can be efficiently desorbed, and the purification function of the catalyst 13a can be restored.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram showing an overall configuration of a diesel engine as a first embodiment of the present invention.

FIG. 2 is a system configuration diagram showing an overall configuration of a diesel engine as a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 ... Diesel engine 12 ... Exhaust pipe (exhaust passage) 13 ... Catalyst converter 13a ... Catalyst 14 ... Exhaust temperature sensor 15 ... Catalyst temperature sensor 16 ... Computer 17 ... Injector 21 ... Engine speed signal 22 ... Throttle opening signal 25 ... Exhaust pipe opening / closing valve 26 ... Exhaust pipe opening / closing actuator 30 ... Bypass passage 31 ... Vacuum pump 32 ... Reservoir tank 33 ... Open / close valve

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinya Hirota 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Co., Ltd. (72) Inventor Iwa ▲ saki ▼ ▲ English ▼ 2 1 Toyota Town Toyota City, Aichi Prefecture Toyota (72) Inventor Toshiaki Tanaka 1 Toyota Town, Toyota City, Aichi Prefecture F-term (reference) 3G091 AA02 AA18 AA28 AB05 BA11 BA14 BA33 CA18 DA03 DB10 EA01 EA07 EA17 EA18 EA30 FA19 FC02 GA20 GB01X GB06W GB09X GB10X HA36 HA39

Claims (8)

[Claims] An exhaust purification catalyst provided in an exhaust passage of a diesel engine, and a pulsation which is attached to the exhaust passage and acts on exhaust flowing through the exhaust passage to forcibly generate a pulsation in the flow of the exhaust gas. Generating means, and a determining means for determining whether or not the function of the catalyst is reduced due to the attachment of at least one of hydrocarbons, soluble organic substances, and exhaust particulates contained in the exhaust to the catalyst; and Control means for activating the pulsation generating means when the determining means determines that the catalyst has deteriorated in function by a predetermined level or more, the functional recovery of the exhaust gas purifying catalyst. apparatus. 2. The function recovery device according to claim 1, wherein the pulsation generating means includes an exhaust passage opening / closing valve provided in the exhaust passage. 3. The function recovery device according to claim 2, wherein the exhaust passage opening / closing valve is opened / closed by a command from the control means. 4. The function recovery device according to claim 2, wherein the exhaust passage opening / closing valve is provided downstream of the exhaust gas purification catalyst. 5. The function recovery device according to claim 2, wherein the exhaust passage opening / closing valve is provided upstream of the exhaust gas purification catalyst. 6. A bypass passage for connecting a downstream side and an upstream side of the exhaust passage opening / closing valve is provided, and a bypass passage is provided in the middle of the bypass passage from a position connected to a downstream side of the exhaust passage opening / closing valve. An opening / closing valve that is controlled to open / close opposite to the exhaust passage opening / closing valve by a command of the control means so as to generate an exhaust flow toward a position connected to the storage tank, a reserve tank for storing vacuum, and a reserve tank. 6. The function recovery device according to claim 5, wherein a vacuum pump for generating a vacuum is connected in series and inserted. 7. An exhaust purification catalyst provided in the middle of an exhaust passage of a diesel engine, and a pulsation attached to the exhaust passage and acting on exhaust flowing through the exhaust passage to forcibly generate a pulsation in the flow of the exhaust gas. Generating means, and determining means for determining whether or not at least one of hydrocarbons, soluble organic substances, and exhaust particulates contained in the exhaust gas is attached to the catalyst, thereby deteriorating the function of the catalyst. In the exhaust gas purifying catalyst system, when the determining means determines that the catalyst has deteriorated by a predetermined level or more, the flow rate of exhaust flowing through the exhaust passage by operating the pulsation generating means. A method for recovering the function of the exhaust gas purifying catalyst, wherein the substance adhering to the catalyst is desorbed by pulsatingly changing the pressure. 8. When the pulsation generating means is operated to pulsatively fluctuate the flow rate of the exhaust gas flowing through the exhaust passage, a backflow of the exhaust gas flowing through the catalyst is also generated, whereby the substance attached to the catalyst is generated. The method for recovering function according to claim 7, wherein the method is performed.