JP2004108345A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine capable of efficiently and securely controlling HC when the internal combustion engine is started in cold state. <P>SOLUTION: A three-way conversion catalyst 22 formed of a transition metal included in a catalyst layer is installed in an exhaust emission passage 14. An HC trap 20 adsorbing HC and discharging the adsorbed HC at a specified temperature or higher is installed on the upstream side of the three-way conversion catalyst. In addition, an oxygen supply means 34 supplying oxygen to the three-way conversion catalyst is installed. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification device for an internal combustion engine, and more particularly, to an exhaust gas purification device capable of reliably purifying HC (hydrocarbon) during a cold start of the internal combustion engine.
[0002]
[Related background art]
2. Description of the Related Art Generally, an engine (internal combustion engine) includes an exhaust gas purification device that purifies harmful substances (HC, CO, NOx, etc.) in exhaust gas using a three-way catalyst. However, the three-way catalyst cannot sufficiently exhibit purification performance until the temperature reaches the activation temperature, and even if the three-way catalyst is arranged close to the engine body to achieve early activation, the three-way catalyst is not discharged when the engine is cold started. There is a problem that the HC that is generated cannot be sufficiently purified.
[0003]
In order to solve this problem, a three-way catalyst layer is provided on a zeolite layer effective for adsorbing HC, and HC that adsorbs HC to the zeolite layer and purifies HC desorbed after reaching a certain temperature is purified by the three-way catalyst layer. An adsorption catalyst has been proposed (for example, see Patent Document 1).
On the other hand, the HC adsorbent such as zeolite and the three-way catalyst are separately provided on the exhaust passage, and the air-fuel ratio of the exhaust gas flowing into the three-way catalyst is maintained at the stoichiometric air-fuel ratio, and the HC desorbed from the HC adsorbent is removed A device configured to purify with a three-way catalyst is disclosed (for example, see Patent Document 2).
[0004]
In addition, a hydrocarbon trap and a catalyst made of a catalyst composition that renders the hydrocarbon harmless are separately provided, and an oxygen-containing gas is mixed with the exhaust gas upstream of the catalyst, and the catalyst is heated by an electric heating means to form a catalyst. A device having a configuration for achieving early activation is disclosed (for example, see Patent Document 3).
[0005]
[Patent Document 1]
JP-A-7-124468 [Patent Document 2]
JP-A-5-149130 [Patent Document 3]
Japanese Patent Publication No. Hei 10-513526
[Problems to be solved by the invention]
However, the temperature at which the desorption of HC from the HC adsorption catalyst is started is as low as about 70 ° C. to 150 ° C., whereas the activation temperature of the ternary component is as high as about 250 ° C. to 350 ° C. In the case of 2, there is a problem that the desorbed HC is discharged without purification until the integrally supported three-way component or three-way catalyst is activated.
[0007]
In this case, it is conceivable to set the air-fuel ratio to a lean air-fuel ratio and to retard the ignition timing in the engine control at the time of starting to quickly raise the temperature of the three-way component and the three-way catalyst, but at the same time, desorption of HC from the zeolite And the effect is low. It is also conceivable that the HC adsorption catalyst, the HC adsorption substance and the three-way catalyst are arranged close to the engine body as described above, but the heat resistance temperature of the zeolite is low, and the heat resistance and durability of the HC adsorption catalyst and the HC adsorption substance can be secured. This is not preferable because the exhaust pressure increases and the output performance of the engine deteriorates.
[0008]
Further, when the catalyst is heated by the electric heating means as disclosed in Patent Document 3, it is necessary to separately provide the electric heating means, which leads to an increase in cost, which is not preferable.
The present invention has been made to solve such a problem, and an object of the present invention is to provide an exhaust gas purification device for an internal combustion engine that can efficiently and reliably purify HC during a cold start of the internal combustion engine. Is to do.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, in the exhaust gas purifying apparatus for an internal combustion engine according to claim 1, a three-way catalyst provided in an exhaust passage and including a transition metal in a catalyst layer, and an exhaust gas upstream of the three-way catalyst A trap having a function of adsorbing HC and releasing the adsorbed HC at a certain temperature or higher, and having no catalytic function, and supplying oxygen to the exhaust gas upstream side of the three-way catalyst. Oxygen supply means.
[0010]
As described above, when the three-way catalyst includes a transition metal in the catalyst layer, the transition metal has a high ability to adsorb and oxidize CO (carbon monoxide). A large amount of metal is adsorbed and oxygen is supplied to the three-way catalyst by the oxygen supply means, so that the oxidation reaction of CO is accelerated, and the reaction heat of the oxidation reaction heats and raises the temperature of the three-way catalyst. To an activation temperature (about 250 ° C. to 350 ° C.). In particular, since the HC trap does not have a catalytic function, CO discharged from the internal combustion engine is adsorbed and oxidized by the transition metal of the three-way catalyst without being oxidized on the HC trap, The three-way catalyst is efficiently heated.
[0011]
Therefore, at the time of a cold start of the internal combustion engine, HC is discharged together with CO from the internal combustion engine and is adsorbed by the HC trap. The adsorbed HC is desorbed at a certain temperature (about 150 ° C.) or higher and the downstream three-way catalyst is discharged. At this time, the three-way catalyst has already reached the activation temperature, and the desorbed HC is efficiently and reliably purified by the three-way catalyst.
[0012]
In this case, since the three-way catalyst does not need to be brought close to the internal combustion engine body, the heat resistance and durability of the HC trap are ensured, and the output of the internal combustion engine does not decrease due to an increase in exhaust pressure.
In addition, since HC can be reliably purified without carrying a large amount of expensive noble metal (Pt or the like) on the three-way catalyst, the production cost of the three-way catalyst is reduced.
The oxygen supply means can also be realized by setting the internal combustion engine to a lean air-fuel ratio to increase excess oxygen in the exhaust gas, but preferably, the oxygen supply means is an external supply means comprising an air pump. By doing so, the combustion stability can be ensured by setting the internal combustion engine to the rich air-fuel ratio side, and the output performance of the internal combustion engine is prevented from lowering.
[0013]
In the exhaust gas purifying apparatus for an internal combustion engine according to claim 2, the transition metal contained in the three-way catalyst contains at least nickel.
That is, among the transition metals, nickel has a particularly high ability to adsorb and oxidize CO, and by including nickel in the three-way catalyst, the amount of oxidation reaction of CO in the three-way catalyst is sufficiently ensured and the three-way catalyst is used. The temperature rises favorably, and HC is reliably purified.
[0014]
Preferably, the transition metal included in the three-way catalyst contains at least 10 g / liter or more of a nickel component in the entire catalyst layer.
As a result, the amount of oxidation reaction of CO in the three-way catalyst is sufficiently ensured without shortage, the temperature of the three-way catalyst is satisfactorily increased, and HC is reliably purified.
Further, the exhaust gas purifying apparatus for an internal combustion engine according to claim 3 is characterized in that the HC trap is made of β-type zeolite.
[0015]
That is, β-type zeolite has a particularly high HC adsorbing ability, can sufficiently retain HC in the HC trap until the three-way catalyst is activated, and can purify HC more reliably.
The exhaust gas purifying apparatus for an internal combustion engine according to claim 4, further comprising catalyst temperature detecting means for detecting a temperature of the three-way catalyst, wherein the oxygen supply means includes a three-way catalyst detected by the catalyst temperature detecting means. When the temperature of the catalyst becomes equal to or higher than a predetermined temperature, the supply of oxygen is started.
[0016]
That is, when the temperature of the three-way catalyst becomes equal to or higher than a predetermined temperature (a temperature at which the oxidation reaction of CO by nickel is started, for example, 100 ° C.), the supply of oxygen is started by the oxygen supply means, so that Oxidation of CO is promoted at an appropriate timing, and the temperature of the three-way catalyst is more efficiently increased.
[0017]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described with reference to the accompanying drawings.
Referring to FIG. 1, there is shown a schematic configuration diagram of an exhaust gas purifying apparatus for an internal combustion engine according to the present invention mounted on a vehicle, and the configuration of the exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described with reference to FIG. explain.
[0018]
As the internal combustion engine (hereinafter, simply referred to as an engine) 1, a spark-ignition gasoline engine of an intake pipe injection type is employed. Since the spark-ignition gasoline engine of the intake pipe injection type is known, the detailed description of the configuration is omitted here.
In the cylinder head of the engine 1, an intake port is formed for each cylinder, and one end of an intake manifold 10 is connected to communicate with each intake port. An exhaust port is formed in the cylinder head 2 for each cylinder, and one end of an exhaust manifold 12 is connected to communicate with each exhaust port.
[0019]
An exhaust pipe (exhaust passage) 14 is connected to the exhaust manifold 12. The exhaust pipe 14 is provided with an HC trap 20 located below the floor of the vehicle, and is located downstream of the HC trap 20. A three-way catalyst 22 is interposed.
The HC trap 20 has a porous monolith-type cordierite carrier composed of a large number of cells, and each cell is formed, for example, in a rectangular cross section.
[0020]
On the surface of the cordierite carrier of the HC trap 20, an HC adsorbent mainly composed of β-type zeolite is formed. β-type zeolite has a function of adsorbing HC, particularly olefinic HC, and desorbing and releasing the adsorbed HC when the temperature rises and reaches a certain temperature (about 150 ° C.). The β-type zeolite has a pore size of 7.6 to 7.8%, which is larger than other zeolites (MFI type, Y type, etc.), has a larger adsorption amount, has a higher desorption start temperature (about 150 ° C.), It has the characteristics that the desorption end temperature is high and the HC desorption ratio in the high temperature range is high. That is, by using β-type zeolite as the HC adsorbent of the HC trap 20, it is possible to increase the HC adsorbing ability and adsorb and hold HC as high as possible.
[0021]
Note that a catalyst layer is not formed in the HC trap 20, and CO and NOx are not purified in the HC trap 20.
The three-way catalyst 22 has a porous monolith-type cordierite carrier 23 also composed of a large number of cells, and each cell is formed, for example, in a square cross section. Referring to FIG. 2, a quarter of one cell of the three-way catalyst 22 is shown, and the configuration of the three-way catalyst 22 will be described below with reference to FIG.
[0022]
As shown in the figure, the three-way catalyst 22 has a three-way catalyst layer 24 formed on the lower layer side on the surface of a cordierite carrier 23 and a three-way catalyst nickel containing nickel (Ni) in the upper layer side. A layer 26 is formed.
The lower three-way catalyst layer 24 contains at least one of platinum (Pt), rhodium (Rh) and palladium (Pd) as a noble metal, and when the exhaust air-fuel ratio is near the stoichiometric air-fuel ratio (stoichio). The three components HC, CO, and NOx can be satisfactorily purified.
[0023]
On the other hand, the upper three-way catalyst nickel layer 26 contains at least one of platinum (Pt), rhodium (Rh), and palladium (Pd) as a noble metal as described above, and is one of transition metals. It is configured to include nickel (Ni). Actually, the three-way catalyst contains nickel oxide (NiO). Specifically, the three-way catalyst nickel layer 26 contains at least 10 g (gram) / L (liter) or more of NiO with respect to the entire catalyst layer.
[0024]
Ni or NiO has a function of adsorbing CO in the exhaust gas and promoting the oxidation reaction of the adsorbed CO in the presence of oxygen, and it has been confirmed that the function is high. The larger the content, the more CO in the exhaust gas is adsorbed, and the oxidation reaction can be promoted. The reason why the three-way catalyst nickel layer 26 is formed on the upper layer side is to increase the exposure area to the exhaust gas and facilitate the adsorption of CO.
[0025]
Returning to FIG. 1, an air passage 30 extends from an upstream portion of the three-way catalyst nickel layer 26, and the air passage 30 is connected to a discharge port of an air pump (oxygen supply means) 34 via a check valve 31 and an air filter 32. Have been. That is, when the air pump 34 operates, an amount of air corresponding to the operation amount of the air pump 34 is supplied to the upstream portion of the three-way catalyst nickel layer 26, and oxygen flows into the three-way catalyst nickel layer 26 together with the exhaust gas.
[0026]
Further, the exhaust pipe 14 is provided with a linear air-fuel ratio sensor 16 that detects an exhaust air-fuel ratio by detecting an oxygen concentration contained in exhaust gas flowing into the HC trap 20. A temperature sensor (catalyst temperature detecting means) 28 for detecting the temperature of the catalyst 22, that is, the catalyst temperature Tcat is provided.
Further, an electronic control unit (ECU) 40 including an input / output device, a memory, a CPU, and the like is provided. The ECU 40 controls the exhaust gas purifying apparatus for the engine 1 and the internal combustion engine according to the present invention. Is
[0027]
Various sensors such as the linear air-fuel ratio sensor 16 and the temperature sensor 28 described above are connected to an input side of the ECU 40, and detection information from these sensors is input.
On the other hand, various devices such as a fuel injection valve and an ignition coil (both not shown) of the engine 1 and the air pump 34 are connected to an output side of the ECU 40, and various sensors are connected to the fuel injection valve and the ignition coil. Optimum control signals such as a fuel injection amount and an ignition timing according to the target air-fuel ratio calculated based on the detection information from the sensors are output to the air pump 34. An optimal control signal such as a pump operation timing is output.
[0028]
Hereinafter, the operation of the exhaust gas purification apparatus according to the present invention configured as described above will be described. When the engine 1 is cold and the three-way catalyst 22 is not yet active, the target air-fuel ratio is set to the rich air-fuel ratio in order to warm up the engine 1 and activate the three-way catalyst 22. The engine 1 is started.
When the engine 1 is started with the target air-fuel ratio set to the rich air-fuel ratio in this manner, since the engine 1 is cold and has a small amount of oxygen, the exhaust gas discharged from the engine 1 to the exhaust pipe 14 contains CO together with HC. Are included.
[0029]
The HC and CO thus discharged are adsorbed by the HC trap 20 for HC, and pass through the HC trap 20 having no catalyst layer without purification for CO, and the three-way catalyst 22 Adsorbed on the catalytic nickel layer 26. Specifically, CO is retained in Ni of the three-way catalyst nickel layer 26.
Although the warming-up of the engine 1 proceeds and the temperature Tcat of the three-way catalyst 22 starts to rise due to the rise of the exhaust gas, the temperature Tcat of the three-way catalyst 22 becomes higher than the predetermined temperature (Ni or NiO) based on the temperature information from the temperature sensor 28. When the temperature reaches a temperature at which the oxidation reaction of CO is started, for example, 100 ° C., the air pump 34 is operated with an operation amount corresponding to the CO amount (for example, the target air-fuel ratio). As a result, oxygen is supplied to the three-way catalyst 22, and the CO adsorbed on the three-way catalyst nickel layer 26 causes an oxidation reaction with the oxygen.
[0030]
When the CO adsorbed on the three-way catalyst nickel layer 26 oxidizes at once with oxygen in the air supplied by the air pump 34, a large amount of reaction heat corresponding to the oxidation reaction is sufficiently generated without shortage. Then, the three-way catalyst 22 is rapidly heated by the reaction heat to increase the temperature.
Referring to FIG. 3, the time change of the catalyst temperature Tcat when the three-way catalyst 22 is provided with the three-way catalyst nickel layer 26 and air is supplied upstream of the three-way catalyst 22 is indicated by a solid line (NiO amount: 11.6 g). / L), a broken line (NiO amount: 23.2 g / L), and a dashed line (NiO amount: 34.8 g / L), the catalyst temperature Tcat is sharply increased by supplying air. Will rise. In particular, as the amount of NiO increases, the catalyst temperature Tcat increases significantly.
[0031]
As a result, the temperature Tcat of the three-way catalyst 22 easily reaches the activation temperature (about 250 ° C. to 350 ° C.), and early activation of the three-way catalyst 22 is achieved.
When the temperature Tcat of the three-way catalyst 22 reaches the activation temperature (about 250 ° C.), the operation of the air pump 34 stops.
On the other hand, the HC adsorbed by the HC trap 20 starts to be desorbed when the HC trap 20 reaches a certain temperature (about 150 ° C.) as described above, and the HC released from the HC trap 20 is discharged to the downstream side. It will flow into the three-way catalyst 22.
[0032]
However, since the temperature of the three-way catalyst 22 rises rapidly as described above, the three-way catalyst 22 is already in an active state at the time when HC starts to be desorbed from the HC trap 20, and the HC trap HC released from the catalyst 20 and flowing into the three-way catalyst 22 is reliably purified by the three-way catalyst 22.
As a result, even when the engine 1 is cold started, HC discharged from the engine 1 is efficiently and reliably purified. Since CO is also oxidized well in the three-way catalyst nickel layer 26, the exhaust gas purification efficiency at the time of cold start of the engine 1 is improved as a whole.
[0033]
Although the HC trap 20 has relatively low heat resistance, the heat resistance and durability of the HC trap 20 can be ensured because the three-way catalyst 22 does not need to be located close to the engine 1 while being kept under the floor. Also, there is no decrease in the output of the engine 1 due to the increase in the exhaust pressure.
Furthermore, since HC can be reliably purified without having to carry a large amount of expensive noble metals (such as Pt) on the three-way catalyst 22, the manufacturing cost of the three-way catalyst 22 can be reduced.
[0034]
The description of the embodiment of the present invention is finished above, but the present invention is not limited to the above embodiment.
For example, in the above embodiment, the three-way catalyst 22 is constituted by the lower three-way catalyst layer 24 and the upper three-way catalyst nickel layer 26. However, as shown in FIG. The nickel layer 26 may be provided as a single layer. Considering that the heat resistance of the three-way catalyst nickel layer is inferior to that of the three-way catalyst layer, as shown in FIG. 5, a three-way catalyst nickel layer 26 is provided on the lower side, and the three-way catalyst layer is provided on the upper side. 24 may be provided. In this case, the durability of the three-way catalyst 22 is improved although the CO adsorption capacity is slightly reduced.
[0035]
In the above embodiment, nickel (Ni) having a high CO adsorption and oxidation ability is used as the transition metal. However, any transition metal such as manganese (Mn), silver (Ag), and copper (Cu) is used. It is applicable even if it is an element.
Further, in the above embodiment, air is supplied upstream of the three-way catalyst 22, but air may be supplied upstream of the HC trap 20 within a range that does not affect HC adsorption performance.
[0036]
Further, in the above embodiment, the case where the engine 1 is an intake pipe injection type gasoline engine has been described as an example, but the engine 1 may be a direct injection type gasoline engine or a diesel engine.
Further, in the above embodiment, the air is supplied by using the air pump 34. However, in an engine capable of simultaneously discharging CO and oxygen (for example, a direct injection gasoline engine), the engine 1 has a lean air-fuel ratio. Excess oxygen may be supplied to the three-way catalyst 22 by performing an operation (for example, a lean lean operation). However, when the air pump 34 as the external supply means is used as in the above-described embodiment, the combustion stability can be ensured by setting the engine 1 to a rich air-fuel ratio, and the output performance of the engine 1 at a low water temperature decreases. Can be prevented.
[0037]
In the above embodiment, the temperature of the three-way catalyst 22 is detected using the temperature sensor 28. However, a means for detecting the exhaust gas temperature may be provided, and the temperature of the three-way catalyst 22 may be estimated from the exhaust gas temperature. it can.
[0038]
【The invention's effect】
As described in detail above, according to the exhaust gas purifying apparatus for an internal combustion engine of the first aspect of the present invention, the transition metal is included in the three-way catalyst, so that the CO discharged from the internal combustion engine is stored on the HC trap. The oxygen is supplied to the three-way catalyst by the oxygen supply means and is supplied to the three-way catalyst without being oxidized by the oxidation, thereby promoting the oxidation reaction of CO in the three-way catalyst. The activation temperature (about 250 ° C. to 350 ° C.) can be reached early by heating and raising the temperature of the raw catalyst.
[0039]
Therefore, at the time of cold start of the internal combustion engine, even if HC adsorbed from the HC trap is desorbed at a certain temperature (about 150 ° C.) or more and discharged toward the downstream three-way catalyst, at this time, the three-way catalyst Can be kept active, and HC can be efficiently and reliably purified by the three-way catalyst.
According to the exhaust gas purifying apparatus for an internal combustion engine of the second aspect, since the transition metal contains nickel having a high ability to adsorb and oxidize CO, a sufficient amount of CO oxidation reaction in the three-way catalyst is ensured. As a result, the temperature of the three-way catalyst can be satisfactorily increased to achieve early activation, and HC can be reliably purified.
[0040]
According to the exhaust gas purifying apparatus for an internal combustion engine of the third aspect, the HC trap is made of β-type zeolite having a high HC adsorbing ability, so that the HC is sufficiently held in the HC trap until the three-way catalyst is activated. Therefore, HC can be more reliably purified.
Further, according to the exhaust gas purifying apparatus for an internal combustion engine of the fourth aspect, when the temperature of the three-way catalyst becomes equal to or higher than the predetermined temperature (the temperature at which the oxidation reaction of CO by nickel is started, for example, 100 ° C.) Since the supply of oxygen is started by the oxygen supply means, the oxidation of CO can be promoted at an appropriate timing, and the temperature of the three-way catalyst can be raised more efficiently.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an exhaust gas purification device for an internal combustion engine according to the present invention mounted on a vehicle.
FIG. 2 is a partially enlarged sectional view showing a quarter of one cell of the three-way catalyst according to the present invention.
FIG. 3 is a time chart showing a change over time of a catalyst temperature Tcat when a three-way catalyst is provided with a three-way catalyst nickel layer and air is supplied upstream of the three-way catalyst.
FIG. 4 is a partially enlarged sectional view showing a quarter of one cell of a three-way catalyst according to another embodiment.
FIG. 5 is a partially enlarged cross-sectional view showing a quarter of one cell of a three-way catalyst according to still another embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Engine 14 Exhaust pipe 16 Linear air-fuel ratio sensor 20 HC trap 22 Three-way catalyst 23 Cordierite carrier 24 Three-way catalyst layer 26 Three-way catalyst nickel layer 28 Temperature sensor (catalyst temperature detecting means)
30 air passage 34 air pump (oxygen supply means)
40 ECU (electronic control unit)

Claims (4)

A three-way catalyst provided in the exhaust passage and including a transition metal in the catalyst layer;
An HC trap that is provided on the exhaust gas upstream side of the three-way catalyst, has a function of adsorbing HC and releasing the adsorbed HC at a certain temperature or higher, and has no catalytic function;
Oxygen supply means for supplying oxygen to the exhaust upstream side of the three-way catalyst,
An exhaust gas purifying apparatus for an internal combustion engine, comprising: The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the transition metal contained in the three-way catalyst includes at least nickel. The exhaust gas purifying apparatus for an internal combustion engine according to claim 1, wherein the HC trap is made of β-type zeolite. Further, a catalyst temperature detecting means for detecting the temperature of the three-way catalyst,
4. The oxygen supply unit according to claim 1, wherein the oxygen supply unit starts supplying oxygen when the temperature of the three-way catalyst detected by the catalyst temperature detection unit becomes equal to or higher than a predetermined temperature. An exhaust gas purifying apparatus for an internal combustion engine according to claim 1.

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