JP3849183B2 - Engine exhaust gas purification device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a purification device for exhaust gas discharged from an engine, particularly a vehicle engine.
[0002]
[Prior art]
Cordierite as a catalyst for efficiently purifying nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HC), which are harmful components in exhaust gas discharged from engines, particularly automobile engines such as automobiles, simultaneously. A heat-resistant porous carrier such as platinum (Pt), palladium (Pd), rhodium (Rh) or other precious metals as a base, and oxides such as nickel (Ni) or cobalt (Co) as required A three-way catalyst having a catalyst added with a catalyst as a catalyst component is widely used. However, this type of three-way catalyst generally has low activity in a low temperature region below 300 ° C., and it is difficult to sufficiently purify harmful components in the low temperature exhaust gas discharged immediately after the engine is started.
[0003]
The three-way catalyst can efficiently purify harmful components in a so-called theoretical air-fuel ratio operation region where the oxygen concentration in the exhaust gas is approximately 1% or less, but the oxygen concentration in the exhaust gas is several percent or more. In this case, that is, in exhaust gas discharged from a lean combustion region of an Otto cycle engine and a diesel engine operating in an essentially oxygen-excess state, the purification efficiency of harmful components is remarkably low.
On the other hand, NOx and HC can be purified even in the above lean combustion region where the oxygen concentration in the exhaust gas is high by loading a transition metal on a substance having a molecular sieve structure such as various natural zeolites or synthetic zeolites. Catalysts have been developed. However, a catalyst in which a transition metal is supported on a substance having a molecular sieve structure of this kind generally exhibits excellent activity in a temperature range of about 300 ° C. to 500 ° C., but the temperature is less than 300 ° C. discharged immediately after starting the engine. Efficient purification of harmful components in the exhaust gas has not been achieved with the current technology.
[0004]
Therefore, in an operating region where the exhaust gas temperature is low, such as immediately after the engine is started, these catalysts are heated by electric heating as a means to improve the exhaust gas purification efficiency by the catalyst having the transition metal supported on the three-way catalyst or the molecular sieve structure. A method for improving the activation has already been proposed. The conceptual configuration of the proposed exhaust gas purification apparatus will be described with reference to FIG.
[0005]
In FIG. 2, reference numeral 1 generally indicates a catalytic converter, in which a catalyst 2 in which a transition metal is supported on the above three-way catalyst or a substance having a molecular sieve structure is accommodated. Is provided with an electric heating device 3. Further, the upstream side of the converter 1 is connected to an exhaust passage including an exhaust manifold of a vehicle engine (not shown) via an inlet passage 4, and the downstream side communicates with the atmosphere via a muffler, a tail pipe and the like (not shown). It is connected to the discharge passage 5.
[0006]
The inlet passage 4 is provided with a temperature sensor 6 for detecting the temperature of the exhaust gas, and the exhaust gas temperature information detected by the temperature sensor 6 is supplied to the control unit 7. The control unit 7 compares the exhaust gas temperature Te detected by the temperature sensor 6 with a preset set temperature To. When the exhaust gas temperature Te is lower than the set temperature To, the control unit 7 is provided with an actuator 8 such as a relay coil. Then, the switch 9 is closed, and power is supplied to the electric heating device 3 from a power source, for example, the in-vehicle battery 10.
[0007]
By heating the catalyst 2 by the electric heating device 3 and raising the temperature, the activity of the catalyst 2 can be increased, and the purification efficiency of harmful components in the low-temperature exhaust gas discharged immediately after starting the engine can be improved.
However, the electric heating device 3 has a problem that it consumes a large amount of electric power, and it is not suitable for an exhaust gas purification device for a vehicle engine that has a limit in power capacity, and the fuel consumption of the engine deteriorates. In addition, since the electric heating device is often prone to electrical failure such as disconnection or short circuit, there is a concern about durability and reliability.
[0008]
[Problems to be solved by the invention]
The present invention was devised in view of the above circumstances. A catalyst in which a transition metal is supported on a three-way catalyst or a substance having a molecular sieve structure housed in a catalytic converter is used without using external energy such as electric power. To provide an exhaust gas purifying apparatus that can improve the activity by heating, effectively purify harmful components in the low temperature exhaust gas discharged from the engine immediately after starting, and has excellent durability and reliability It is intended.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a catalytic converter in which a catalyst or a three-way catalyst in which a transition metal is supported on a substance having a molecular sieve structure is arranged on the inside, and an oxidation catalyst is arranged on the outside of the catalyst. When the temperature of the exhaust gas flowing into the catalyst having the molecular sieve structure loaded with a transition metal or the three-way catalyst is lower than a preset temperature, the transition to the substance having the molecular sieve structure is made. The exhaust gas that has passed through the catalyst carrying the metal or the three-way catalyst is guided to the oxidation catalyst, and the catalyst or the three-way catalyst carrying the transition metal on the substance having the molecular sieve structure is heated by the reaction heat in the oxidation catalyst. The present invention proposes an exhaust gas purifying apparatus for an engine characterized by being configured as described above.
[0010]
The present invention is also directed to a first exhaust gas passage that is connected to an exhaust passage of an engine and contains therein a catalyst or a three-way catalyst in which a transition metal is supported on a substance having a molecular sieve structure, and the first exhaust gas passage. A second exhaust gas passage which is disposed outside the catalyst and contains an oxidation catalyst therein, and is interposed between the first and second exhaust gas passages, and at the first position, the first exhaust gas passage. Is connected to the exhaust gas exhaust passage through the second exhaust gas passage, and in the second position, the valve device that directly connects the first exhaust gas passage to the exhaust gas exhaust passage, and the engine exhaust passage or the first exhaust gas passage. A temperature sensor provided to detect the exhaust gas temperature; and when the exhaust gas temperature detected by the temperature sensor is lower than a set value, the valve device is positioned at the first position, and when the exhaust gas temperature is higher than the set value, the valve device is raised. It proposes a exhaust gas purifying apparatus for an engine, characterized in that it comprises a valve control device that is positioned at the second position.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
A preferred embodiment of the present invention will be described below with reference to the schematic configuration diagram of FIG. Reference numeral 10 in the figure is a conceptually shown engine, for example, an engine for a vehicle such as an automobile. The engine 10 is generated in an intake manifold 12 that takes in outside air via an air cleaner (not shown) and the engine 10. An exhaust manifold 14 for exhausting combustion gas to the outside air is provided, and the exhaust manifold 14 forms an exhaust passage 16 of the engine 10 together with an exhaust pipe connected to the exhaust end thereof.
[0012]
A catalytic converter generally indicated by reference numeral 18 is connected downstream of the exhaust passage 16, and the catalytic converter 18 has a catalyst 20 (a transition metal supported on a substance having a three-way catalyst or molecular sieve structure therein) ( In some cases, the first exhaust gas passage 22 containing the first catalyst) is provided. A second exhaust gas passage 24 is formed on the outer periphery of the first exhaust gas passage 22, and an oxidation catalyst or a combustion catalyst 26 (hereinafter, depending on the case) so as to surround the first catalyst 20 in the second exhaust gas passage 24. (Referred to as second catalyst) is accommodated in a ring shape.
[0013]
A third exhaust gas passage 28 is formed on the outer periphery of the second exhaust gas passage 24, and the third exhaust gas passage 28 forms an exhaust gas exhaust passage communicating with the atmosphere via a muffler and a tail pipe, which are not shown. ing.
The first exhaust gas passage 22, the second exhaust gas passage 24, and the third exhaust gas passage or the exhaust gas exhaust passage 28 are usually made of a thin steel plate having heat resistance and corrosion resistance.
[0014]
As shown in the drawing, the downstream end of the first exhaust gas passage 22 communicates directly with the upstream end of the second exhaust gas passage 24, and the downstream end of the second exhaust gas passage 24 directly connects to the third exhaust gas passage or exhaust gas exhaust. It communicates with the upstream end of the passage 28. A valve opening 32 is provided in a passage wall near the upstream end of the second exhaust gas passage 24 adjacent to the downstream opening end 30 of the first exhaust gas passage 22, and the valve opening 32 is opened and closed by a butterfly valve 34.
[0015]
One end of the valve control arm 38 is fixed to the valve shaft 36 of the butterfly valve 34 protruding outside the casing 18 ′ of the catalytic converter 18, and the operating rod of the actuator 40 is attached to the free end of the other end of the valve control arm 38. 42 is pivotally attached. As the actuator 40, an electromagnetic actuator, an air cylinder using compressed air as a working medium, and other arbitrary actuators can be appropriately employed.
[0016]
Exhaust gas temperature flowing into the first catalyst 20 in a portion upstream of the first catalyst 20 in the first exhaust gas passage 22 or in an appropriate position of the engine exhaust passage 16, preferably in an exhaust passage portion adjacent to the first exhaust gas passage 22. A temperature sensor 44 for detecting Te is provided, and the exhaust gas temperature information detected by the temperature sensor 44 is supplied to the control unit 46.
[0017]
The control unit 46 compares the exhaust gas temperature Te with a preset set temperature To, for example, 300 ° C., and when the exhaust gas temperature Te is lower than the set temperature To, the actuator 40 is deactivated, as shown in the figure. The butterfly valve 34 is held in the closed position, and when the exhaust gas temperature Te becomes equal to or higher than the set temperature To, the actuator 40 is energized to displace the operating rod 42 downward in the figure, and the valve control arm 34 is indicated by a dotted line. Rotate clockwise as shown to open the butterfly valve 34. By opening the butterfly valve 34, the downstream open end 30 of the first exhaust gas passage 22 is directly communicated with the third exhaust gas passage or the exhaust gas discharge passage 28 via the valve opening 32. The control unit 46, the actuator 40, the operating rod 42 and the valve control arm 38 constitute a valve control device.
[0018]
As described above, the first catalyst 20 is a catalyst in which a transition metal is supported on a three-way catalyst or a substance having a molecular sieve structure. Here, the three-way catalyst has heat resistance such as alumina and cordierite. Based on one or two kinds of noble metals such as platinum (Pt), rhodium (Rh), palladium (Pd), etc. as a catalyst component on an excellent granular or monolithic carrier, nickel (Ni), iron ( It means a catalyst on which an oxide such as Fe), cobalt (Co), manganese (Mn), or cerium (Ce) is added.
[0019]
The catalyst having a transition sieve supported on a substance having the molecular sieve structure is generally called zeolite, the main components are silica and alumina, the Si / A1 ratio is about 5 to 100, and the crystal structure is X-type. , Y-type, ZSM-type metallosilicates, and the like, and zeolites and metallosilicates ion-exchanged with transition metals.
[0020]
Further, as described above, the second catalyst 26 is an oxidation catalyst or a combustion catalyst. Here, the oxygen, hydrocarbon (HC), and carbon monoxide (CO) in the exhaust gas are reacted to generate HC, A catalyst that oxidizes CO and decomposes it into CO ₂ and H ₂ O, and is applied to a granular or monolithic carrier such as alumina or cordierite, and as a catalyst component, platinum (Pt), palladium (Pd), platinum-palladium alloy (Pt -Pd), or those in which a noble metal added with a small amount of rhodium (Rh) is supported, but base metal-based ones are also known and mean catalysts collectively. .
[0021]
In the exhaust gas purifying apparatus having the above-described configuration, immediately after the engine 10 is started, particularly at a low temperature start, whether the engine 10 is an Otto cycle engine using gasoline as fuel or a diesel engine using light oil as fuel, the exhaust gas is It is usually low-temperature and contains a large amount of HC as unburned fuel and CO based on incomplete combustion. This low-temperature exhaust gas passes through an exhaust passage 16 of the engine including the exhaust manifold 14 and is converted to a catalytic converter 18. Flow into.
[0022]
When the exhaust gas temperature Te detected by the temperature sensor 44 is lower than a preset temperature To (for example, 300 ° C.) that is set in consideration of the temperature at which the first catalyst 20 has sufficient activity, the control unit 46 controls the actuator 40. Is deactivated and the butterfly valve 34 is closed, so that the exhaust gas flowing through the first exhaust gas passage 221 and passing through the first catalyst 20 flows into the second exhaust gas passage 24 and contacts the second catalyst 26. Since the exhaust gas temperature Te is low, the contact with the first catalyst 20 does not sufficiently purify harmful components in the exhaust gas, but the exhaust gas temperature Te is in contact with the second catalyst 26 in the second exhaust gas passage 24. HC and CO are oxidized and decomposed to generate heat.
[0023]
The heat generated in the second catalyst 26 is transmitted to the first catalyst 20 disposed on the inner side in the radial direction, and the first catalyst 20 is heated to rapidly rise in temperature. Exhaust gas that has passed through the second catalyst 26 is purified from the third exhaust gas passage or the exhaust gas discharge passage 28 through the muffler and tail pipe, and is discharged into the atmosphere from the third exhaust gas passage or the exhaust gas discharge passage 28 after the toxic components contained therein are purified. Therefore, there is an advantage that the purification efficiency is increased by the amount by which harmful components in the exhaust gas are removed by the second catalyst 26, compared to the conventional apparatus using an electric heating device as the heating means of the first catalyst 20.
[0024]
As the temperature of the first catalyst 20 is increased, the activity of the catalyst 20 is effectively improved, so that the purification efficiency of harmful components in the exhaust gas by contact with the catalyst is increased, and the oxidation reaction of the second catalyst 26 is performed. Combined with the purification of harmful components (HC, CO) in the exhaust gas based on this, the purification of harmful components in the exhaust gas finally discharged to the atmosphere is promoted.
[0025]
When the exhaust gas temperature Te becomes equal to or higher than the set temperature To after the engine 10 is started, the actuator 40 is energized by the control unit 46 and the operating rod 42 is driven downward in the drawing, via the valve control arm 38. Then the butterfly valve 34 is opened. By opening the butterfly valve 34, the first exhaust gas passage 22 communicates directly with the downstream side of the third exhaust gas passage or the exhaust gas discharge passage 28 via the valve opening 32.
[0026]
As a result, the exhaust gas that has passed through the first catalyst 20 hardly flows to the second exhaust gas passage 24 side where the flow resistance is large due to the presence of the second catalyst 26, and a substantial amount of the exhaust gas directly passes through the third exhaust gas passage or exhaust gas exhaust. It flows into the passage 28 and is released to the atmosphere through the muffler and the tail pipe. Of course, since the exhaust gas temperature Te is higher than the set temperature To, the purification of harmful components in the exhaust gas by the first catalyst 20 is more effective than when the exhaust gas temperature Te immediately after the start of the engine 10 is lower than the set temperature To. In addition, since the high temperature exhaust gas does not flow through the second catalyst 26, the durability can be ensured.
[0027]
According to the above configuration, there is no need for an electric heating catalyst heating device like the conventional exhaust gas purification device shown in FIG. 2, so the electric load of the engine 10 is not increased and the electric capacity is limited. It is extremely suitable when employed in an exhaust gas purification device for an engine, and the fuel consumption of the engine 10 can be improved over the conventional exhaust gas purification device by the amount of electric load of the engine 10 being small. Furthermore, in the case of an electric heating device, there is an advantage that there is no occurrence of failure such as disconnection or short circuit that often occurs, and durability and reliability are excellent.
[0028]
In the above configuration, other valve devices such as a slide valve and a rotary valve can be employed in place of the butterfly valve 34, and one or more catalytic converters are additionally installed downstream of the catalytic converter 18. be able to. The first catalyst 20 may be a three-way catalyst or a catalyst in which a transition metal is supported on a substance having a molecular sieve structure. Each catalyst may be used alone, or a combination of both catalysts may be used.
[0029]
As described in detail above, the exhaust gas purifying apparatus for an engine according to the present invention has a catalyst or a three-way catalyst in which a transition metal is supported on a substance having a molecular sieve structure disposed inside, and an oxidation catalyst disposed outside thereof. A catalytic converter is disposed in the exhaust passage of the engine, and is configured to guide exhaust gas that has passed through a catalyst having a molecular sieve structure loaded with a transition metal or a three-way catalyst to the oxidation catalyst. And, since it is possible to effectively purify the low temperature exhaust gas discharged at the start of the engine without using an electrothermal catalyst heating device, it is particularly suitable for a vehicle engine having a limited electric capacity, There is an advantage that the fuel consumption of the engine can be improved, and there is an advantage that excellent durability and reliability can be secured.
[0030]
In addition, an exhaust gas purification apparatus for an engine according to the present invention includes a first exhaust gas passage that is connected to an exhaust passage of an engine and contains therein a catalyst having a molecular sieve structure loaded with a transition metal or a three-way catalyst. The first exhaust gas passage is interposed between the first exhaust gas passage and the second exhaust gas passage which surrounds the catalyst in the first exhaust gas passage and is disposed outside the first exhaust gas passage and accommodates the oxidation catalyst therein. A valve device that communicates the first exhaust gas passage with the exhaust gas exhaust passage via the second exhaust gas passage at the position, and a valve device that communicates the first exhaust gas passage directly with the exhaust gas exhaust passage at the second position; and an exhaust passage of the engine Or a temperature sensor that is provided in the first exhaust gas passage and detects the exhaust gas temperature; and when the exhaust gas temperature detected by the temperature sensor is less than a set value, the valve device is positioned at the first position; and And a valve control device that positions the valve device in the second position when the value is equal to or greater than a predetermined value, and without using external energy such as an electric heating device, There is an advantage that harmful components can be effectively purified, and when the warm-up proceeds and the exhaust gas temperature rises, high-temperature exhaust gas does not flow through the oxidation catalyst, so that the durability can be improved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a preferred embodiment of the present invention.
FIG. 2 is a schematic configuration diagram showing an exhaust gas purifying device including a conventional electrothermal catalyst heating device.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Engine, 14 ... Exhaust manifold, 16 ... Exhaust passage, 18 ... Catalytic converter, 20 ... First catalyst, 22 ... First exhaust passage, 24 ... Second exhaust passage, 26 ... Second catalyst, 28 ... Third exhaust Passage or exhaust gas discharge passage 34: Butterfly valve (valve device) 38 ... Valve control arm 40 ... Actuator 44 ... Temperature sensor 46 ... Control unit

Claims (2)

A catalyst converter in which a transition metal is supported on a substance having a molecular sieve structure or a three-way catalyst is disposed on the inside, and a catalytic converter having an oxidation catalyst disposed on the outside is disposed in the exhaust passage of the engine, and has the molecular sieve structure. When the temperature of the exhaust gas flowing into the catalyst or the three-way catalyst in which the transition metal is supported on the substance is lower than the preset set temperature, the catalyst or the three-way catalyst in which the transition metal is supported on the substance having the molecular sieve structure An engine characterized in that exhaust gas that has passed through is guided to the oxidation catalyst, and a catalyst or a three-way catalyst in which a transition metal is supported on a substance having the molecular sieve structure is heated by heat of reaction in the oxidation catalyst. Exhaust gas purification equipment. Surrounding the first exhaust gas passage, which is connected to the exhaust passage of the engine and contains a catalyst or a three-way catalyst in which a transition metal is supported on a substance having a molecular sieve structure, and the catalyst in the first exhaust gas passage. A second exhaust gas passage disposed outside thereof and containing an oxidation catalyst therein and interposed between the first and second exhaust gas passages, and at the first position, the first exhaust gas passage is connected to the second exhaust gas passage. And a valve device for communicating the first exhaust gas passage directly with the exhaust gas exhaust passage at the second position, and detecting the exhaust gas temperature provided in the exhaust passage of the engine or the first exhaust gas passage. And when the exhaust gas temperature detected by the temperature sensor is lower than a set value, the valve device is positioned at the first position, and when the exhaust gas temperature is equal to or higher than the set value, the valve device is positioned at the second position. The exhaust gas purification apparatus for an engine, characterized in that it comprises a cell valve controller.

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