JPH1071324A - Engine exhaust gas cleaner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove harmful components in a low temperature exhaust gas immediatele after starting an engine by producing a catalyst converter by arranging a catalyst which is produced by depositing transition metals on a carrier with a molecular sieve structure and an oxidation catalyst in the inside and in the outside, respectively. SOLUTION: A catalyst converter 18 is connected in a downstream side of an exhaust gas route 16. This catalyst converter 18 is provided with a first exhaust gas route 22 containing a three way catalyst or a catalyst 20 produced by depositing transition metals on a substance such as zeolite with a molecular sieve structure. A second exhaust gas route 24 is formed in the outer circumference of the first exhaust gas route 22 and in the second exhaust gas route 24, an oxidation catalyst or a combustion catalyst 26 is contained in circular state as to surround the first catalyst 20. Immediatly after the starting of an engine 10, an exhaust gas is at a low temperature and contains large quantities of unburned gas components, is led to the first exhaust gas route 21 and then to the second exhaust gas route 24 by closing a butterfly valve 34 by a temperature sensor 4, and is purified by being brought into contact with the second catalyst 26 and heat is generated during the purification. The generated heat is utilized to heat the first catalyst 20 and activate the catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for purifying exhaust gas discharged from an engine, especially a vehicle engine.

[0002]

2. Description of the Related Art Nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons (HC), which are harmful components in exhaust gas discharged from engines, particularly engines for vehicles such as automobiles.
Platinum (Pt), palladium (P) on a heat-resistant porous carrier such as cordierite
d), one or two noble metals such as rhodium (Rh), and nickel (Ni), cobalt (C
A three-way catalyst in which an oxide such as o) is supported as a catalyst component is widely used. However, this type of three-way catalyst generally has low activity in a low-temperature region of less than 300 ° C., and it is difficult to sufficiently purify harmful components in low-temperature exhaust gas discharged immediately after the start of the engine.

[0003] The three-way catalyst can efficiently purify harmful components in a so-called stoichiometric air-fuel ratio operation region in which the oxygen concentration in the exhaust gas is approximately 1% or less. In the case of more than a few percent, i.e. in the lean-burn region of the Otto cycle engine and in the exhaust gas emitted from a diesel engine operated essentially in excess of oxygen,
The purification efficiency of harmful components is extremely low. On the other hand, by supporting a transition metal on a substance having a molecular sieve structure such as various natural zeolites or synthetic zeolites, NOx and Hx can be obtained even in the lean combustion region where the oxygen concentration in the exhaust gas is high.
A catalyst capable of purifying C has been developed. However, this type of catalyst in which a transition metal is supported on a substance having a molecular sieve structure usually shows excellent activity in a temperature range of about 300 ° C. to 500 ° C., but a temperature of less than 300 ° C. discharged immediately after the engine is started. Efficient purification of harmful components in flue gas has not been achieved with the current technology.

In order to improve the exhaust gas purification efficiency of the three-way catalyst or a catalyst in which a transition metal is supported on a substance having a molecular sieve structure in an operating region where the exhaust gas temperature is low, for example, immediately after the start of the engine, these catalysts are used as an electrothermal catalyst. A method of improving the activation by heating by using a method has already been proposed. The conceptual configuration of the proposed exhaust gas purifying apparatus will be described with reference to FIG.

In FIG. 2, reference numeral 1 generally indicates a catalytic converter, which contains therein a catalyst 2 in which a transition metal is supported on a substance having a three-way catalyst or a molecular sieve structure. An electric heating device 3 is provided on the outer periphery of 2. The upstream side of the converter 1 is connected to an exhaust passage including an exhaust manifold for a vehicle engine (not shown) via an inlet passage 4, and the downstream side communicates with the atmosphere via a muffler and a tail pipe (not shown). It is connected to the discharge passage 5.

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 a 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, and compares the exhaust gas temperature Te with the set temperature T.
If it is lower than o, the actuator 8 such as a relay coil
Is turned on to close the switch 9, and power is supplied to the electric heating device 3 from a power source, for example, a vehicle-mounted battery 10.

By heating the catalyst 2 by the electric heating device 3 to raise the temperature, the activity of the catalyst 2 can be increased, and the purification efficiency of harmful components in low-temperature exhaust gas discharged immediately after the start of the engine can be improved. . However, the electric heating device 3 has a problem that a large amount of electric power is consumed. In particular, the electric heating device 3 is not suitable for an exhaust gas purifying device for a vehicle engine having a limited electric power capacity, and the fuel efficiency of the engine is deteriorated. In addition, the electric heating device often has an electrical failure such as disconnection or short-circuit, so that the durability and reliability are uneasy.

[0008]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and is directed to a three-way catalyst or a substance having a molecular sieve structure housed in a catalytic converter without using external energy such as electric power. By raising the temperature of the catalyst supporting the transition metal, the activity is improved, harmful components in low-temperature exhaust gas discharged from the engine immediately after starting can be effectively purified, and durability and reliability are improved. It is an object of the present invention to provide an excellent exhaust gas purifying apparatus.

[0009]

In order to achieve the above object, the present invention provides a catalyst or a three-way catalyst in which a transition metal is supported on a substance having a molecular sieve structure, and an oxidation catalyst is disposed outside the catalyst or the three-way catalyst. Exhaust gas that has passed through a catalyst or a three-way catalyst in which a transition metal is supported on a substance having the molecular sieve structure, interposed in the exhaust passage of the engine,
The present invention proposes an exhaust gas purifying apparatus for an engine, which is configured to be guided to the oxidation catalyst.

The present invention also provides a first exhaust gas passage which 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. A second exhaust gas passage surrounding and surrounding the catalyst in the exhaust gas passage and containing an oxidation catalyst therein, and interposed between the first and second exhaust gas passages;
In the first position, the first exhaust gas passage communicates with the exhaust gas discharge passage via the second exhaust gas passage,
A valve device for connecting the first exhaust gas passage directly to the exhaust gas discharge passage at the position, a temperature sensor provided in the exhaust passage or the first exhaust gas passage of the engine for detecting an exhaust gas temperature, and an exhaust gas detected by the temperature sensor. A valve control device that positions the valve device at the first position when the temperature is lower than the set value, and positions the valve device at the second position when the temperature is higher than the set value. The present invention proposes an exhaust gas purifying apparatus for an engine.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to the schematic diagram of FIG. Symbol 1 in the figure
Reference numeral 0 denotes a conceptually illustrated engine, for example, an engine for a vehicle such as an automobile. The engine 10 includes an intake manifold 1 that takes in outside air via an air cleaner (not shown).
2, and an exhaust manifold 14 for exhausting combustion gas generated in the engine 10 to the outside air. The exhaust manifold 14 forms an exhaust passage 16 of the engine 10 together with an exhaust pipe connected to an exhaust end thereof.

Downstream of the exhaust passage 16, a catalytic converter indicated generally by reference numeral 18 is connected. The catalytic converter 18 has a three-way catalyst or a substance having a molecular sieve structure in which a transition metal is carried. A first exhaust gas passage 22 containing a catalyst 20 (hereinafter, sometimes referred to as a first catalyst) is provided. A second exhaust gas passage 24 is formed on the outer periphery of the first exhaust gas passage 22, and inside the second exhaust gas passage 24,
An oxidation catalyst or a combustion catalyst 26 (hereinafter, sometimes referred to as a second catalyst) is housed in an annular shape so as to surround the first catalyst 20.

A third exhaust gas passage 28 is formed on the outer periphery of the second exhaust gas passage 24. The third exhaust gas passage 28 communicates with the atmosphere via a muffler and a tail pipe (not shown). Is formed. The first
The exhaust gas passage 22, the second exhaust gas passage 24, and the third exhaust gas passage or the exhaust gas discharge passage 28 are usually made of a heat-resistant and corrosion-resistant thin steel plate.

As shown, 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 communicates with the third exhaust gas passage. Alternatively, it communicates with the upstream end of the exhaust gas discharge passage 28. The second exhaust port 22 adjacent to the downstream open end 30 of the first exhaust gas passage 22
A valve opening 32 is provided in a passage wall near the upstream end of the exhaust gas passage 24, and the valve opening 32 is opened and closed by a butterfly valve 34.

The casing 1 of the catalytic converter 18
The valve shaft 36 of the butterfly valve 34 protruding to the outside of the 8 '
One end of the valve control arm 38 is fixed, and an operating rod 42 of an actuator 40 is pivotally attached to the other free end of the valve control arm 38. The actuator 40 includes an electromagnetic actuator, an air cylinder using compressed air as a working medium,
Other arbitrary actuators can be appropriately adopted.

A portion of the first exhaust gas passage 22 on the upstream side of the first catalyst 20 or an appropriate position of the exhaust passage 16 of the engine;
Preferably, a temperature sensor 44 for detecting the temperature Te of the exhaust gas flowing into the first catalyst 20 is provided in an exhaust passage portion adjacent to the first exhaust gas passage 22, and the exhaust gas temperature information detected by the temperature sensor 44 includes: It is supplied to the control unit 46.

The control unit 46 changes the exhaust gas temperature Te to a preset temperature To, for example, 30
When the exhaust gas temperature Te is lower than the set temperature To as compared with 0 ° C., the actuator 40 is deenergized, and the butterfly valve 34 is held at the valve closing position as shown in the figure, and the exhaust gas temperature Te is higher than the set temperature To. And the actuator 4
By urging 0, the operating rod 42 is displaced downward in the figure, and the valve control arm 34 is rotated clockwise as shown by the dotted line 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 connected to 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.

As described above, the first catalyst 20 is a three-way catalyst or a catalyst having a transition metal supported on a substance having a molecular sieve structure. Here, the three-way catalyst may be alumina, cordierite or the like. A granular or monolithic carrier having excellent heat resistance, based on one or two kinds of noble metals such as platinum (Pt), rhodium (Rh), and palladium (Pd) as a catalyst component, and optionally nickel (Ni) , Iron (Fe), cobalt (Co), manganese (Mn), cerium (Ce), and the like.

A catalyst in which a transition metal is supported on a substance having a molecular sieve structure is generally called zeolite, whose main components are silica and alumina, and whose Si / A1 ratio is 5%.
About 100, which means a metallosilicate having a crystal structure of X-type, Y-type, ZSM-type, or the like, and those obtained by ion-exchanging these zeolites and metallosilicates with a transition metal.

Further, as described above, the second catalyst 26 is an oxidation catalyst or a combustion catalyst. Here, oxygen in the exhaust gas reacts with hydrocarbons (HC) and carbon monoxide (CO). Is a catalyst that oxidizes HC and CO to decompose it into CO ₂ and H ₂ O. The catalyst component is platinum (Pt), a particulate or monolithic carrier such as alumina or cordierite.
Palladium (Pd), platinum-palladium alloy (Pt-P
d) or those supporting a noble metal to which a small amount of rhodium (Rh) is added are typical, but base metal-based ones are also known, meaning a catalyst generically referring to them.

In the exhaust gas purifying apparatus having the above structure, immediately after the start of the engine 10, particularly at the time of low temperature start, whether the engine 10 is an Otto cycle engine using gasoline or a diesel engine using light oil as fuel, The exhaust gas is low in temperature and generally 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 an engine including an exhaust manifold 14. It flows into the catalytic converter 18.

The exhaust gas temperature Te detected by the temperature sensor 44 is set to a preset temperature To (for example, 300 ° C.) in consideration of a temperature at which the first catalyst 20 has a sufficient activity.
When the pressure is lower, the actuator 40 is deenergized by the control unit 46 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 flows into the second exhaust gas passage 24. 2 Contact the catalyst 26. Since the exhaust gas temperature Te is low, harmful components in the exhaust gas are not sufficiently purified by contact with the first catalyst 20, but the second exhaust gas in the second exhaust gas passage 24
By contact with the catalyst 26, HC and CO in the exhaust gas are oxidized and decomposed to generate heat.

The heat generated in the second catalyst 26 is transmitted to the first catalyst 20 disposed radially inward of the second catalyst 26, and the first catalyst 20 is heated and quickly rises in temperature. Second catalyst 2
Exhaust gas that has passed through 6 is cleaned of a considerable part of the harmful components contained therein, HC and CO, and is discharged from the third exhaust gas passage or exhaust gas discharge passage 28 to the atmosphere via a muffler and a tail pipe. There is an advantage that the purification efficiency is increased by an amount corresponding to the removal of harmful components in the exhaust gas by the second catalyst 26, as compared with a conventional device using an electric heating device as a heating means of the first catalyst 20.

By raising the temperature of the first catalyst 20, the catalyst 2
0 is effectively improved, the efficiency of purifying harmful components in the exhaust gas by contact with the catalyst is increased, and the harmful components (HC, HC) in the exhaust gas based on the oxidation reaction of the second catalyst 26 are increased.
Together with the purification of CO), the purification of harmful components in the exhaust gas finally discharged to the atmosphere is promoted.

After the engine 10 is started, when the warm-up progresses and the exhaust gas temperature Te becomes equal to or higher than the set temperature To, the actuator 40 is urged by the control unit 46 and the operating rod 42 is driven downward in the drawing.
The butterfly valve 34 is opened via the valve control arm 38. The opening of the butterfly valve 34 causes the first exhaust gas passage 22 to directly communicate with the downstream side of the third exhaust gas passage or the exhaust gas discharge passage 28 via the valve opening 32.

As a result, the exhaust gas that has passed through the first catalyst 20 hardly flows into the second exhaust gas passage 24 having a high flow resistance due to the presence of the second catalyst 26, and substantially the entire amount of the exhaust gas directly passes through the third exhaust gas passage. Alternatively, the gas flows into the exhaust gas discharge passage 28 and is discharged to the atmosphere via the muffler and the tail pipe. Of course, since the exhaust gas temperature Te is higher than the set temperature To, the first catalyst 20
The purification of the harmful components in the exhaust gas by the exhaust gas is performed more effectively than when the exhaust gas temperature Te is lower than the set temperature To immediately after the start of the engine 10, and the high-temperature exhaust gas does not flow through the second catalyst 26. Durability can be ensured.

According to the above-described configuration, since a catalyst heating device using electric heat as in the conventional exhaust gas purifying device shown in FIG. 2 is not required, the electric load of the engine 10 is not increased, and the electric capacity is limited. It is very suitable for use in an exhaust gas purifying apparatus for a certain vehicle engine.
Therefore, the fuel efficiency of the engine 10 can be improved as compared with the above-mentioned conventional exhaust gas purifying device by an amount corresponding to the smaller electric load. Further, in the case of the electric heating device, there is an advantage that a failure such as disconnection or short-circuit which often occurs does not occur and durability and reliability are excellent.

In the above configuration, the butterfly valve 3
4, other valve devices such as a slide valve and a rotary valve can be adopted.
One or more catalytic converters can be additionally installed. Further, as the first catalyst 20, a three-way catalyst or a catalyst having a transition metal supported on a substance having a molecular sieve structure can be used alone or in combination.

As described in detail above, the exhaust gas purifying apparatus for an engine according to the present invention has a catalyst in which a transition metal is supported on a material having a molecular sieve structure or a three-way catalyst disposed inside, and an oxidation catalyst disposed outside thereof. The catalytic converter with
An exhaust gas passing through a catalyst or a three-way catalyst in which a transition metal is supported on a substance having the molecular sieve structure, which is interposed in an exhaust passage of the engine, is configured to be guided to the oxidation catalyst. Since low-temperature exhaust gas discharged at the time of starting can be effectively purified 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 can be improved, and further, there is an advantage that excellent durability and reliability can be ensured.

Further, the exhaust gas purifying apparatus for an engine according to the present invention is connected to an exhaust passage of the engine and contains therein a first catalyst or a three-way catalyst in which a transition metal is supported by a substance having a molecular sieve structure. An exhaust gas passage, a second exhaust gas passage surrounding and surrounding the catalyst in the first exhaust gas passage and containing an oxidation catalyst therein, and interposed between the first and second exhaust gas passages; A valve device for connecting the first exhaust gas passage to the exhaust gas discharge passage via the second exhaust gas passage at the first position, and a valve device for communicating the first exhaust gas passage directly to the exhaust gas discharge passage at the second position; A temperature sensor provided in the exhaust passage or the first exhaust gas passage for detecting an exhaust gas temperature, and when the exhaust gas temperature detected by the temperature sensor is lower than a set value, the valve device is moved to the first position. And a valve control device for positioning the valve device in the second position when the value is equal to or more than a set value, without using external energy such as an electric heating device, immediately after starting the engine. In addition to being able to effectively purify harmful components in low-temperature exhaust gas, when warm-up progresses and the exhaust gas temperature rises, high-temperature exhaust gas does not flow through the oxidation catalyst, so that its durability can be improved. is there.

[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 provided with 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 ...
1st exhaust gas passage, 24 ... 2nd exhaust gas passage, 26 ... 2nd catalyst, 28 ... 3rd exhaust gas 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)

[Claims] 1. 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 disposed inside, and an oxidation catalyst is disposed outside the catalyst converter, which is interposed in an exhaust passage of the engine. Exhaust gas that has passed through a catalyst or a three-way catalyst in which a substance having a molecular sieve structure supports a transition metal,
An exhaust gas purifying apparatus for an engine, wherein the apparatus is configured to be guided to the oxidation catalyst. 2. A first exhaust gas passage connected to an exhaust passage of an engine and containing a catalyst or a three-way catalyst in which a transition metal is supported on a substance having a molecular sieve structure therein, and a first exhaust gas passage in the first exhaust gas passage. A second exhaust gas passage surrounding and surrounding the catalyst and containing an oxidation catalyst therein; and a first exhaust gas passage interposed between the first and second exhaust gas passages. A valve device for communicating with the exhaust gas discharge passage through the second exhaust gas passage and for communicating the first exhaust gas passage directly with the exhaust gas discharge passage at the second position, and provided in the exhaust passage or the first exhaust gas passage of the engine; A temperature sensor for detecting the temperature of the exhaust gas, the valve device being located at the first position when the temperature of the exhaust gas detected by the temperature sensor is less than a set value, and An exhaust gas purifying apparatus for an engine, comprising: a valve control device positioned at two positions.