JP2002206417A - Exhaust emission control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for burning floating grain of carbon or the like by heat energy of exhaust gas to become harmless, capable of preventing temperature lowering inside a filter in transition from stationary operation to a low load operation state, and surely purifying exhaust gas in no load operation as well. SOLUTION: A heat accumulating part 1 comprising a heat accumulating part 1 and a purifying part 2 has a pair of a right and a left heat accumulating units 3 and 3, and inlet passages 7R and 7L of both units 3 and 3 are connected to an exhaust passage 6 via a first selector valve 10. Inlet and outlet passages 21 and 22 of a purifying unit 4 are connected to outlet passages 8R and 8L of the heat accumulation units 3 and 3 via a second selector valve 23. Exhaust gas is alternately fed to the heat accumulating units 3 and 3 to accumulate heat. Using the accumulated heat, the exhaust gas temperature is increased, thereby lowering of inner temperature in the purifying unit 4 in low load operation is restricted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an engine, and more particularly to an exhaust gas purifying apparatus for removing suspended particulate matter containing carbon as a main component (hereinafter, simply referred to as suspended particles). The engine referred to in the present invention mainly means a compression ignition type internal combustion engine such as a diesel engine or a dual fuel diesel engine, but includes all engines that discharge suspended particles.

[0002]

2. Description of the Related Art As this type of purifying device, there has been proposed a device in which suspended particles are captured by a non-woven fabric filter made of silicon carbide, heated and burned by a motor, and the filter is regenerated (published by Nikkan Kogyo Shimbun, Trigger, May 2000, p. 102). This purifying apparatus includes two filters, and while one of the filters captures suspended particles, the other filter is heated by a heater to perform a regeneration process.

[0003] Japanese Patent Application Laid-Open No. 10-159552 discloses a purifying apparatus in which a first-stage oxidation catalyst and a second-stage ceramic filter are combined. In this purifying device, a reaction represented by (2NO + O ₂ → 2NO ₂ ) is caused by the oxidation catalyst, and (C + 2NO ₂ → CO ₂ ) inside the filter.
By generating the reaction represented by (+ 2NO) and (C + O ₂ → CO ₂ ), the suspended particles can be burned and the filter can be regenerated.

[0004]

In the exhaust gas purifying apparatus of the self-regeneration system described above, the heater can be omitted.
Since the suspended particles can be removed only by the oxidation catalyst and one filter, the purification device can be reduced in size and cost. The problem is that the suspended particles (carbon) react with nitric oxide (2NO ₂ ) and oxygen (O ₂ ) in the exhaust gas and burn. Therefore, when the exhaust gas temperature is low at the time of low load operation or idling operation, etc. , Combustion reaction decreases. as a result,
In a traffic jam or the like, the filter cannot be sufficiently regenerated and an extra load is applied to the engine.

An object of the present invention is to maintain the temperature inside a filter at an active temperature (500 ° C. or higher) without requiring external heating even during a low load operation or an idling operation, thereby enabling the combustion of suspended particles. And to ensure the regeneration of the filter. It is another object of the present invention to provide an exhaust gas purifying apparatus that can be easily installed at low cost on existing vehicles such as trucks and buses.

[0006]

An exhaust gas purifying apparatus according to the present invention comprises: a heat storage unit 1 including two heat storage units 3;
A purifying unit 2 including a purifying unit 4 is provided. Heat storage unit 1
In each of the heat storage units 3, the inlet passages 7 R and 7 L of the heat storage units 3 are connected to the exhaust passage 6 via the first switching valve 10. The purifying unit 2 has a purifying unit 4 and an inlet passage 21 and an outlet passage 22 of the purifying unit 4. The outlet passages 8R and 8L of the heat storage units 3 and 3 are connected to the inlet passage 21 and the outlet passage 22 of the purification unit 4 via the second switching valve 23. The first switching valve 10 includes the two heat storage units 3
The three inlet passages 7R and 7L can be alternatively connected to the upstream passage 6a and the downstream side passage 6b of the exhaust passage 6. The second switching valve 23 is connected to the outlet passage 8L or 8R of the heat storage unit 3 on the side connected to the upstream passage 6a.
Is connected to the inlet passage 21 of the purification unit 4 and the outlet passage 8R of the heat storage unit 3 on the side connected to the downstream passage 6b.
Alternatively, 8L is configured to be connected to the outlet passage 22 of the purification unit 4. Thus, heat storage is performed while alternately supplying the exhaust gas flowing from the upstream passage 6a to the two heat storage units 3 and 3, and the heat storage unit 3 communicating with the upstream passage 6a.
The exhaust gas that has passed through is supplied to the purification unit 4.

The purification unit 4 includes a filter 31 having heat resistance, and an oxidation catalyst 30 is provided in a passage upstream of the filter 31.

[0008] The purification unit 4 can be composed of an oxidation catalyst 30 and a filter 31 arranged in the same container.

The oxidation catalyst 30 can be provided in both heat storage units 3.

[0010] The heat storage unit 3 can be constituted by a catalytic converter.

The first and second switching valves 10 and 23 are simultaneously switched by actuators 18 and 28.

After a predetermined time has elapsed since the first switching valve 10 was switched, the second switching valve 23 is switched.

On the basis of the state in which the exhaust gas temperature in the upstream side exhaust passage 6a reaches a predetermined value, the first and second switching valves 10
・ Switch the switching cycle time of 23 between large and small.

[0014]

The exhaust gas of the engine 5 is alternately sent to the two heat storage units 3.3 at regular time intervals, exchanges heat while passing through the heat storage units 3.3, and is stored therein. . Exhaust gas before purification (hereinafter, simply referred to as untreated gas) that has passed through the heat storage unit 3 is supplied to the purification unit 4.
, Where it undergoes purification treatment. When the exhaust gas is alternately supplied to the heat storage units 3 in this manner, the heat energy of the exhaust gas during normal operation can be stored in each of the heat storage units 3.3. Therefore, even when the operation mode shifts from the normal operation state to the low load operation state, although the internal temperature of the heat storage units 3 gradually decreases, the temperature drops only slowly, and the low-temperature untreated gas is heated and supplied. it can.

That is, since high-temperature untreated gas is supplied to the purification unit 4 even during low-load operation, the tendency of the internal temperature of the purification unit 4 to decrease can be moderated, and the internal temperature becomes lower than the activation temperature. You can delay the time to become. Therefore, according to the exhaust gas purifying apparatus of the present invention, even during low-load operation, the combustion of the suspended particles in the purification unit 4 is reliably performed, the clogging of the filter 31 due to the suspended particles is eliminated, and the self-regeneration function of the filter 31 is achieved. Can be maintained. Accordingly, it is possible to prevent an excessive back pressure from acting on the engine, reduce the energy loss by that much, and contribute to energy saving.

When the oxidation catalyst 30 is provided in the passage on the upstream side of the filter 31, the nitrogen gas in the exhaust gas becomes (2NO +
O ₂ → 2NO ₂ ). The nitrogen dioxide gas and the oxygen contained in the exhaust gas react with the suspended particles trapped in the filter 31 to burn carbon, which is the main component thereof, and render it harmless.
Is self-regenerating, so that it is not necessary to add a heating means such as a heater, so that the structure of the exhaust gas purifying apparatus can be simplified and the cost can be reduced accordingly.

When the purifying unit 4 is constituted by the oxidation catalyst 30 and the filter 31 arranged in the same container, the mounting and maintenance of the purifying unit 4 can be easily performed.

When the oxidation catalyst 30 is provided in both the heat storage units 3 and 3, heat storage and oxidation treatment of exhaust gas can be performed at the same time. Therefore, it is not necessary to separately provide an oxidation catalyst. Cost can be reduced.

When the heat storage unit 3 is constituted by a catalytic converter, the heat storage efficiency is slightly reduced, but the unprocessed gas can be purified at the time of heat storage, so that the exhaust gas can be more reliably purified.

If the first and second switching valves 10 and 23 are simultaneously switched by the actuators 18 and 28, leakage of unprocessed gas due to a delay in response of the switching valves 10 and 23 at the time of passage switching, and a purification unit 4 can reliably prevent the exhaust gas from flowing back.

The reason why the second switching valve 23 is switched after a predetermined time has elapsed after the switching of the first switching valve 10 is to burn the unburned floating particles adhered to the filter 31. When the first switching valve 10 is switched, the exhaust gas flows backward in the passage on the switched side, and due to the pressure wave of the backflow gas, unburned suspended particles adhering to the upstream side wall of the filter 31 are removed from the filter surface wall. Is torn off. By switching the second switching valve 23 so as to follow the first switching valve 10, the exhaust gas in the purification unit 4 flows in a direction opposite to the flow direction of the backflow gas. The suspended particles thus collected are captured by the filter 31 again. That is, the suspended particles are separated from the filter surface wall, dispersed in the exhaust gas, and then captured again. Thereby, the re-captured suspended particles are uniformly dispersed on the filter face wall. Therefore, it is possible to effectively perform the oxidation reaction of the re-captured suspended particles and to prevent the suspended particles from remaining unburned.

The switching cycle time of the first and second switching valves 10 and 23 is switched between large and small with reference to a state in which the exhaust gas temperature in the upstream exhaust passage 6a has reached a predetermined value. Specifically, when the temperature of the exhaust gas is high, the switching cycle time is lengthened to suppress the power consumption of the actuator that switches the two switching valves 10 and 23. When the temperature of the exhaust gas is low, the switching cycle time is shortened to prevent the temperature of the oxidation catalyst 30 from dropping below the activation temperature.

[0023]

1 to 5 show an embodiment of an exhaust gas purifying apparatus according to the present invention. In FIG. 2, the exhaust gas purifying device includes a heat storage unit 1 including two heat storage units 3 and 3 and a purification unit 2 including a purification unit 4. Reference numeral 5 denotes an engine, and reference numeral 6 denotes an exhaust passage derived from an exhaust manifold of the engine 5.

The heat storage section 1 includes a pair of left and right heat storage units 3.
3, the inlet passages 7R and 7L of the unit 3 and the outlet passages 8R and 8L. Each of the inlet passages 7R and 7L is connected to the exhaust passage 6 via the first switching valve 10. . The heat storage unit 3 includes a heat storage element 11 formed of ceramics in a honeycomb shape, and a canister 12 for housing the heat storage element 11, and performs heat exchange when exhaust gas passes through the honeycomb space to partition the honeycomb space. Heat energy can be stored on the wall.

In FIG. 3, the first switching valve 10 is a butterfly valve 13
And a four-way switching valve with a switching element
4 is connected to the exhaust passage on the engine 5 side, that is, the upstream passage 6a, and the outlet 15 is connected to the exhaust passage on the tail pipe side, that is, the downstream passage 6b. Left and right branch openings 16.1
7 are connected to the inlet passages 7R and 7L of the heat storage unit 3, respectively. The butterfly valve 13 can be switched by an actuator (not shown) such as an air cylinder or a solenoid. By switching the butterfly valve 13 between the state shown in FIG. 1 and the state shown in FIG. The exhaust gas can be sent alternately. For example, as shown in FIG. 2, when the exhaust gas is supplied to the left heat storage unit 3 via the inlet passage 7L, the inlet passage 7R of the right heat storage unit 3 is connected to the downstream passage 6b.

The purifying section 2 comprises a purifying unit 4 and an inlet passage 21 and an outlet passage 22 thereof. These two passages 21 are connected to the left and right outlet passages 8R of the heat storage units 3.3.
Connect to 8L via the second switching valve 23. Second
The switching valve 23 is a four-way switching valve having the same butterfly valve 13 as the first switching valve 10, and has an inlet 24 connected to the inlet passage 21 of the purification unit 4 and an outlet 25 connected to the outlet passage 22 of the purification unit 4. . The outlet passages 8R and 8L of the heat storage unit 3 are connected to the left and right branch ports 26 and 27, respectively. The butterfly valve 13 of the second switching valve 23 can be switched by an actuator such as an air cylinder or a solenoid (not shown). By switching the hinge 13 between the state shown in FIG. 1 and the state shown in FIG. Exhaust gas passing through the heat storage unit 3 communicating with the passage 6 a is supplied to the purification unit 4 via the inlet passage 21.

The purifying unit 4 includes the oxidation catalyst 30 of the preceding stage.
And a filter 31 having a high heat resistance at a later stage, and a canister 32 accommodating these. Oxidation catalyst 30
Is formed into a column shape by supporting a catalyst metal on a honeycomb-shaped monolith or supporting a catalyst metal on a granular material such as ceramics, and the outer peripheral surface thereof is covered with a metal fiber mat. The untreated gas passes through the oxidation catalyst 30 (2
(NO + O ₂ → 2NO ₂ ).

The filter 31 is made of a wall-flow type porous ceramic and allows the exhaust gas to pass therethrough, but traps suspended particles (particle size of 10 μm or more) contained in the exhaust gas. These suspended particles are burned and made harmless as the temperature of the filter 31 is heated to 450 ° C. or higher. Specifically, a combustion mode in which carbon and nitrogen oxides represented by (C + 2NO ₂ → CO ₂ + 2NO) react, and (C + O ₂ → CO
₂ ) Through the combustion mode in which carbon and oxygen react as shown in ₂ ),
Suspended particles are rendered harmless.

When the internal temperature of the filter 31 is lower than 500 ° C., the suspended particles are less likely to burn. In particular, when the low-load operation state such as during idling is prolonged, the amount of heat energy of the exhaust gas falls below the amount of energy necessary for maintaining the temperature of the filter 31, so that the internal temperature of the filter 31 gradually decreases. . In order to suppress such a temperature drop and maintain the inside of the filter at an active temperature (450 ° C. or higher) for a long time, a heat storage unit 1 is provided in front of the purification unit 2.

Mainly, when the exhaust gas temperature in the upstream exhaust gas passage 6a becomes 250 ° C. or more in the high rotation high torque operation state or the low rotation high torque operation state,
By switching the first and second switching valves 10 and 23 every 60 seconds, the exhaust gas is alternately supplied to the left and right heat storage units 3 and heat is stored in the heat storage element 11. In this state, since the temperature of the exhaust gas itself is high, the first and second switching valves 10 and 23
Can be extended, and power consumption of the actuator can be suppressed accordingly. If the temperature of the exhaust gas exceeds 750 ° C., the heat storage unit 3 and the oxidation catalyst 30 will be damaged. As shown in FIG. 5, the first switching valve 10 is switched to neutral to prevent the exhaust gas from being supplied to the purification device. I do.

Mainly, when shifting to a low load operation state such as a high rotation low torque operation state or a low rotation low torque operation state, the exhaust gas temperature decreases. However, the exhaust gas is heated by receiving heat released from the heat storage element 11 while passing through the heat storage element 11. By sending the heated exhaust gas to the purification unit 4, the tendency of the temperature inside the filter 31 to decrease can be moderated, so that the inside of the filter 31 can be maintained at the active temperature for a long time. The exhaust gas purified by the purification unit 4 is sent to the heat storage unit 3 communicating with the downstream passage 6b via the outlet passage 22 and the second switching valve 23,
It is discharged into the atmosphere from the downstream passage 6b. When the exhaust gas temperature becomes lower than 250 ° C., the first switching valve 10 and the second switching valve 23 are switched from 60 seconds to 30 seconds,
The switching cycle time of both valves is shortened, and the heat retaining action is promoted to prevent the temperature of the oxidation catalyst 30 from decreasing.

Although the first switching valve 10 and the second switching valve 23 are switched basically at the same time, the switching timing can be shifted as required. When the first switching valve 10 is switched, the exhaust gas flows backward in the passage on the switched side. When the pressure wave of the backflow gas reaches the filter 31, the second switching valve 23 is switched to the first switching valve 10. It switches following. In this case, the unburned suspended particles adhering to the upstream side wall of the filter 31 are momentarily peeled off from the surface wall by the pressure wave of the backflow gas. However, by switching the second switching valve 23, it is captured by the filter 31 again. The suspended particles at this time are once dispersed in the exhaust gas, so that when they are captured again, they are uniformly dispersed. Therefore, it is possible to effectively perform the oxidation reaction of the re-captured suspended particles and to prevent the suspended particles from remaining unburned.

In addition to the above embodiment, the oxidation catalyst 30 can be provided in a passage upstream of the filter 31.
For example, the oxidation catalyst 30 can be provided inside the two heat storage units 3 using the heat storage units 3. In this case, the purification unit 4 can be configured with only the filter 31. The heat storage unit 3 can be constituted by a catalytic converter. First
The second switching valves 10 and 23 do not need to be constituted by four-way switching valves, and other valve structures can be adopted. Filter 3
1 can use a filter made of a porous metal, a filter made of a ceramic fiber in which ceramic fibers are wound around a pipe made of a punched metal, or the like in addition to a porous ceramic of a wall flow type. As long as the filter is used, any material or structure may be used.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of an exhaust gas purification device.

FIG. 2 is a conceptual diagram equivalent to FIG. 1 with a switching valve switched.

FIG. 3 is a sectional view of a first switching valve.

FIG. 4 is a sectional view of a second switching valve.

FIG. 5 is a conceptual diagram of the exhaust gas purifying apparatus in a state where exhaust gas purification is stopped.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat storage part 2 Purification part 3 Heat storage unit 4 Purification unit 7R ・ 7L Inlet passage 8R ・ 8L Outlet passage 10 First switching valve 11 Heat storage element 21 Inlet passage 22 Outlet passage 23 Second switching valve

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) F01N 3/24 F01N 3/24 HL N B01D 53/36 103B (71) Applicant 500082595 Alternative Fuel Systems Inc. Alternative Fuel Syssystems Incorporated Alberta T3C0M5, Canada, Eleventh Avenue ES. Wu. 1207, Suite 420 (71) Applicant 000005083 Hitachi Metals, Ltd. 1-2-1, Shibaura, Minato-ku, Tokyo (72) Inventor Toshihiko Hiraoka 5-13 Koshien Mihocho, Nishinomiya City, Hyogo Prefecture (72) Inventor Akio Ishida 1-13-13 Nishihonmachi, Nishi-ku, Osaka-shi, Osaka Cornes House 6F Japan Ecos Co., Ltd. In-house F-term (reference) 3G090 AA01 BA01 CB00 CB23 CB25 DB03 EA01 EA02 3G091 AA02 AA18 AB13 BA00 BA02 BA04 CA10 CA12 FA12 FB02 GA06 GA21 HA16 HB02 HB03 4D048 AA06 AA14 AB01 AB02 CA01 CC26 CC27 CC28 CC32 CC33 CC51 CD05 4D058 JA32 MA41 NA10 QA01 QA03 QA19 SA08 TA06 UA01 UA25

Claims (8)

[Claims] The heat storage unit includes a heat storage unit including two heat storage units and a purification unit including a purification unit. The heat storage unit includes an inlet passage for both heat storage units.
L is connected to the exhaust passage 6 via the first switching valve 10, and the purifying unit 2 has a purifying unit 4 and an inlet passage 21 and an outlet passage 22 of the unit 4. 3.3 outlet passages 8R and 8L and the inlet passage 21 and the outlet passage 22 of the purification unit 4
The first switching valve 10 is connected via a switching valve 23, and is connected to the inlet passage 7 of the heat storage units 3.3.
R · 7L is configured to be selectively connected to the upstream passage 6a and the downstream side passage 6b of the exhaust passage 6, and the second switching valve 23 is connected to the upstream passage 6a. The outlet passage 8L or 8R of the heat storage unit 3 is connected to the inlet passage 21 of the purification unit 4, and the outlet passage 8R or 8L of the heat storage unit 3 connected to the downstream passage 6b is connected to the outlet passage 22 of the purification unit 4. The exhaust gas flowing from the upstream passage 6a is alternately supplied to the heat storage units 3 and 3 to store heat, and the heat is stored in the upstream passage 6a.
An exhaust gas purifying apparatus for an engine, wherein exhaust gas passing through a heat storage unit 3 communicating with a is supplied to a purifying unit 4. 2. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the purifying unit includes a filter having heat resistance, and the oxidation catalyst is provided in a passage upstream of the filter. 3. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the purifying unit includes an oxidation catalyst and a filter disposed in the same container. 4. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the oxidation catalyst is provided in each of the heat storage units. 5. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the heat storage unit 3 comprises a catalytic converter. 6. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the first and second switching valves 10 and 23 are simultaneously switched by actuators 18 and 28. 7. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the second switching valve is switched after a predetermined time has elapsed after switching the first switching valve. 8. The first and second switching valves 1 based on a state in which the exhaust gas temperature in the upstream side exhaust passage 6a has reached a predetermined value.
The exhaust gas purifying apparatus for an engine according to any one of claims 1 to 7, wherein the switching cycle time of 0.23 is switched between large and small.