JP4379232B2 - Exhaust gas purification device - Google Patents

Description

  The present invention relates to an exhaust gas purification device suitable for an internal combustion engine such as an automobile, and more particularly to an exhaust gas purification device capable of maintaining a high purification performance of a catalyst in a wide temperature range.

  In general, an exhaust system of an internal combustion engine (engine) for an automobile is provided with, for example, an underfloor catalytic converter (UCC) located under the floor of a vehicle. In this underfloor catalytic converter, the underfloor catalytic converter is mainly built in the catalytic converter. A three-way catalyst purifies and reduces HC (hydrocarbon), CO (carbon monoxide), and NOx (nitrogen oxide) in the exhaust gas. In recent years, a vehicle including a three-way catalyst in an underfloor catalytic converter and a NOx occlusion catalyst (NOx trap catalyst) that occludes NOx in an oxidizing atmosphere and releases and reduces the occluded NOx in a reducing atmosphere has been put into practical use. Yes.

  Furthermore, recently, in addition to the underfloor catalytic converter, a pre-stage catalytic converter (MCC, FCC) is additionally provided in the exhaust manifold that is susceptible to high-temperature combustion gas from the engine or immediately after the exhaust manifold in order to activate the catalyst early. In this way, an exhaust gas purification device that can exhibit high exhaust purification performance even immediately after the cold start of the engine has been developed and put into practical use.

JP 7-279713 A

  By the way, in recent years, high catalyst purification performance has been required with the tightening of exhaust gas regulations. However, in the conventional catalyst as described above, exhaust gas purification considered to be due to CO poisoning of noble metals in a high temperature range (a temperature range that is frequently exposed when the catalyst functions). There is a drop in performance.

  For example, as can be seen from the graph showing the NOx purification temperature characteristic of FIG. 4, NOx has a characteristic that the performance decreases when the bed (center) temperature of the catalyst is around 700 ° C., regardless of the amount of noble metal (PGM). This has been confirmed by the present inventors, and similar characteristics have been confirmed in HC and CO. In FIG. 4, the vertical axis represents the NOx purification efficiency, and the horizontal axis represents the catalyst bed temperature.

This is because the temperature range is a region where the form of ceria (CeO ₂ : OSC (oxygen storage function) agent) changes, and the reactivity of oxygen transfer to the noble metal is reduced, which adversely affects the NOx purification performance. It is thought that has been given.

  In Patent Document 1, based on the knowledge that when the temperature of the palladium catalyst exceeds about 500 ° C., the NOx purification rate is reduced due to CO poisoning, and when the air-fuel ratio is inclined to the rich side, CO poisoning proceeds. Taking advantage of these two characteristics, when the temperature of the palladium catalyst is about 500 ° C. or less, the excess air ratio of the control center of the internal combustion engine becomes 0.989 to 0.996 so that the rich side, and about 500 ° C. or more. A technique is disclosed in which fuel injection amount control means for changing the air-fuel ratio to the lean side is sometimes set so that the control center excess air ratio of the internal combustion engine becomes 0.998 to 1.003 in the vicinity of the theoretical air-fuel ratio.

  However, the technique disclosed in Patent Document 1 has a problem that versatility is low because the temperature range for changing the air-fuel ratio is limited to about 500 ° C. because the temperature is limited to the palladium catalyst.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an exhaust gas purification device that can maintain a high purification performance of a catalyst in a wide temperature range regardless of engine control.

In order to achieve the above object, an invention according to claim 1 is an exhaust gas purifying apparatus having a catalyst having an oxygen storage function, and an exhaust gas state detecting means provided downstream of the catalyst for detecting the state of the exhaust gas. a catalyst temperature detection means for detecting a temperature of the catalyst, before and CO poisoning determining means for determining the CO poisoning of the catalyst based on the state of Sharing, ABS air gas, CO poisoning determination based on the temperature of the catalyst Threshold change means for changing the determination threshold of the means, and oxygen supply means for supplying excess oxygen to the catalyst when the catalyst is poisoned by CO.

According to the invention of claim 1, by supplying excess oxygen to the catalyst by a secondary air supply device or the like under the required conditions, the oxidation reaction with CO covering the noble metal active point is promoted, and the recovery of the catalyst activity is achieved. In addition , the CO poisoning of the catalyst can be more accurately determined .

  Hereinafter, an exhaust gas purifying apparatus according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of an exhaust gas purifying apparatus for an internal combustion engine showing an embodiment of the present invention, FIG. 2 is a flowchart of CO poisoning recovery control, and FIG. 3 is a test result of poisoning recovery by lean spike. It is a graph.

  As shown in FIG. 1, as an internal combustion engine body (hereinafter simply referred to as an engine) 1, for example, a spark ignition gasoline engine is employed. The engine 1 can easily realize an operation at a lean air-fuel ratio (lean operation) in addition to an operation at a stoichiometric air-fuel ratio (stoichio) or an operation at a rich air-fuel ratio (rich operation).

  An ignition plug 3 is attached to each cylinder head 2 of the engine 1 and an electromagnetic fuel injection valve 4 is attached to each intake port. An ignition coil (not shown) that outputs a high voltage is connected to the spark plug 3. A fuel supply device (not shown) having a fuel tank is connected to the fuel injection valve 4 via a fuel pipe.

  An intake port 5 is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of an intake manifold 6 is connected so as to communicate with each intake port 5. Further, an exhaust port 7 is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of an exhaust manifold 8 is connected so as to communicate with each exhaust port 7. In the figure, 9 is an intake valve for opening and closing the intake port 5, and 10 is an exhaust valve for opening and closing the exhaust port 7.

An exhaust pipe (exhaust passage) 11 is connected to the exhaust manifold 8, and a three-way catalytic converter 12 as a UCC is interposed in the exhaust pipe 11. The catalyst in the three-way catalytic converter 12 carries ceria (CeO ₂ ) as an oxygen storage function (O ₂ Storage Component: OSC). The exhaust pipe 11 directly below the three-way catalytic converter 12 may be an exhaust temperature sensor (catalyst temperature calculation means) 13 and an O ₂ sensor (exhaust gas state detection means, a linear A / F (air / fuel ratio) sensor or NOx sensor. ) 14 is interposed.

  In this embodiment, a known secondary air supply device (oxygen supply means) including an air pump 15a, a secondary air control valve (ACV) 15b, an electromagnetic valve 15c, and the like is provided between the intake manifold 6 and the exhaust manifold 8. 15 is provided so that the atmosphere (excess oxygen) can be introduced into the exhaust manifold 8 under a predetermined condition described later.

The vehicle is provided with an ECU (electronic control unit) 16 having an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a central processing unit (CPU), a timer counter, and the like. Thus, comprehensive control including the engine 1 is performed. That is, various sensors such as the exhaust temperature sensor 13 and the O ₂ sensor 14 described above are connected to the input side of the ECU 16 in addition to a throttle position sensor, an air flow sensor, a crank angle sensor, and an accelerator position sensor (not shown). Detection information from these sensors is input.

  On the other hand, an ignition plug 3, a fuel injection valve 4, a throttle valve (not shown), and the like are connected to the output side of the ECU 16 through the ignition coil described above. The ignition plug 3, the fuel injection valve 4, the throttle valve, and the like are connected. Respectively output optimum values such as ignition timing, fuel injection amount, and throttle opening th calculated based on detection information from various sensors. Thus, ignition is performed at an appropriate timing by the spark plug 3, and an appropriate amount of fuel is injected from the fuel injection valve 4 at an appropriate timing so that a predetermined air-fuel ratio (A / F) is obtained.

  In this embodiment, the ECU 16 performs CO poisoning recovery control in order to prevent catalyst performance deterioration (see FIG. 4) due to temporary CO poisoning of the catalyst in the three-way catalytic converter 12. That is, the electromagnetic valve 15c is controlled to open and close and the air pump 15a is driven and controlled under a predetermined condition, and the atmosphere is introduced into the exhaust manifold 8 by the secondary air supply device 15.

The CO poisoning recovery control will be described in detail based on the flowchart shown in FIG.
First, in step P1, it is determined whether or not the catalyst in the three-way catalytic converter 12 is within the CO poisoning detection range. That is, it is determined by the exhaust temperature sensor 13 whether the temperature of the catalyst is within a temperature range of, for example, 600 to 800 ° C. (preferably around 700 ° C.).

If yes, the output from the O ₂ sensor (rear O ₂ ) 14 is monitored in step P2, and then it is determined in step P3 whether or not the catalyst is deteriorated by CO poisoning. That is, the fluctuation of the output signal of the O ₂ sensor 14 is compared with the threshold value (CO poisoning determination means).

If yes in step P3, atmospheric air is introduced into the exhaust manifold 8 by the secondary air supply device 15 in step P4 (O ₂ supply start). On the other hand, if no, the process returns to Step P1.

Next, in step P5, it is determined whether or not the catalyst has been released from CO poisoning. That is, the fluctuation of the output signal of the O ₂ sensor 14 is compared with the threshold value (CO poisoning determination means).

If yes in Step P5, the introduction of the atmosphere into the exhaust manifold 8 by the secondary air supply device 15 is stopped (O ₂ supply end) in Step P6, and the CO poisoning recovery control is ended.

  In this way, the temperature of the catalyst is in a temperature range of, for example, 600 to 800 ° C. (This is a temperature region in which the purification efficiency is lowered after the purification efficiency is once improved with respect to the transition of the catalyst temperature to a high temperature. In the temperature region where the form changes), when temporary poisoning of CO is detected, oxygen (secondary air) is supplied for a short period (several seconds), so that CO The oxidation reaction is promoted, and the catalytic activity can be recovered.

  As shown in the graph showing the test result of the poisoning recovery by the lean spike in FIG. 3, the present inventors perform the lean spike under the condition shifted to the rich side in the air-fuel ratio feedback control, so that the catalyst is poisoned by CO. Confirmed to recover from.

  Further, in this embodiment, since the atmosphere is introduced into the exhaust manifold 8 by the secondary air supply device 15, the air-fuel ratio of the exhaust gas can be controlled regardless of the engine control, and the control by the ECU 16 is simple.

  In the above embodiment, the three-way catalytic converter 19 is described as an example, but the present invention can also be applied to a NOx trap catalyst. Further, the threshold for determining CO poisoning may be changed based on the temperature of the catalyst (threshold changing means). In this case, in the temperature range where the function of the oxygen storage agent is lowered (600 to 800 ° C. in the case of ceria), the determination of CO poisoning is lowered and the other temperature range is raised. In this way, it is possible to determine the CO poisoning of the catalyst in the entire temperature range, and in particular, it is possible to determine the CO poisoning early in the temperature range where the oxygen storage function is lowered, and in the other temperature range, the temporary operating state Excessive determination due to (for example, rich operation) can be suppressed.

1 is a schematic configuration diagram of an exhaust gas purification device for an internal combustion engine showing an embodiment of the present invention. It is a flowchart of CO poisoning recovery control similarly. It is a graph which similarly shows the test result of the poisoning recovery | restoration by a lean spike. It is a graph which shows a NOx purification temperature characteristic.

Explanation of symbols

1 engine, 2 cylinder head, 3 spark plug, 4 fuel injection valve, 5 intake port, 6 intake manifold, 7 exhaust port, 8 exhaust manifold, 9 intake valve, 10 exhaust valve, 11 exhaust pipe, 12 three-way catalytic converter, 13 exhaust temperature sensor, 14 O ₂ sensor, 15 secondary air supply device, 16 ECU (electronic control unit).

Claims (1)

In an exhaust gas purification apparatus having a catalyst having an oxygen storage function,
Exhaust gas state detection means provided downstream of the catalyst for detecting the state of exhaust gas;
Catalyst temperature detecting means for detecting the temperature of the catalyst;
And CO poisoning determining means for determining the CO poisoning of the catalyst based on the state of the prior Sharing, ABS air gas,
A threshold value changing means for changing a determination threshold value of the CO poisoning determining means based on the temperature of the catalyst;
An oxygen supply means for supplying excess oxygen to the catalyst when determining the CO poisoning of the catalyst;
An exhaust gas purification device comprising:

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