JP2000097010A - Exhaust emission control device for internal-combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control device for internal combustion engine equipped with a particulate trap installed at each exhaust port, a communication passage to put each exhaust port in communication with at least one other exhaust port in the upstream of the exhaust line about the particulate tarp, and an opening/closing valve installed in each communication passage and left open normally, wherein excessive capturing of particulates of each particulate trap is precluded and it is made practicable to sufficiently reduce the total emission of particulates into the atmosphere. SOLUTION: An exhaust emission control device for an internal combustion engine is equipped with a first shutoff valve 7 which is installed in the downstream of the exhaust line about each main particulate trap 4 and is left open normally as capable of shutting the exhaust system of an engine, a bypass passage 8 to make bypassing the first shutoff valve 7, and an auxiliary particulate trap 9 installed in the bypass passage, wherein the first shutoff valve 7 is closed when the opening/closing valves 6a are closed to exhaust particulates from the main particulate traps 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purification device for an internal combustion engine.

[0002]

2. Description of the Related Art The exhaust gas of an internal combustion engine, especially a diesel engine, contains harmful particulates containing carbon as a main component, and it is desired to reduce the amount of particulates discharged into the atmosphere. ing. Therefore, it has been proposed to arrange a particulate trap as a filter for trapping particulates in an exhaust system of a diesel engine. Since such a particulate trap has a large exhaust resistance as the amount of trapped particulates increases, it is necessary to burn the collected particulates and regenerate the particulate trap itself.

[0003] If the exhaust gas is heated to a high temperature as in high-speed high-speed operation of the engine, the particulates spontaneously ignite and burn, so that the particulate trap can be regenerated. Japanese Patent Laying-Open No. 10-54220 proposes disposing a particulate trap for each exhaust port. With this configuration, the particulate trap can be made to approach the engine body, and the heat of the exhaust gas can be effectively used for the regeneration of the particulate trap.

[0004] While the size of the particulate is very small, the pores of the particulate trap are very large compared to the particulate so that the particulate trap itself does not have a large exhaust resistance. Have been. In such a particulate trap, the particulates adhere and accumulate around the pores and are collected. If the deposited particulates grow relatively large and the substantial pore size of the particulate trap is reduced to some extent, the particulate trapping rate in the particulate trap is greatly improved.

[0005] However, if the particulate trap is simply arranged close to the engine body, relatively high-speed exhaust gas immediately after being discharged from each cylinder always passes through each particulate trap. The deposited particulates around the pores are easily broken before growing relatively large, and the particulate collection rate in each particulate trap is kept low without improvement.

In order to solve this problem, in the above-mentioned prior art, each exhaust port communicates with each other by a communication path on the upstream side of the particulate trap. Thereby,
In the exhaust stroke of each cylinder, the exhaust gas is dispersed into each particulate trap,
It is possible to improve the particulate collection efficiency of the particulate trap without hindering the growth of the adhered and deposited particulates.

[0007]

As described above, the particulates are properly collected in each of the particulate traps. However, depending on the operating state of the engine, the exhaust gas does not reach a high temperature for a while. Regeneration of the particulate traps is not performed, and each particulate trap may collect a large amount of particulates. The large amount of collected particulates not only greatly increases the exhaust resistance of the particulate trap, but also generates a large amount of heat of combustion when the exhaust gas burns at a high temperature, and melts the particulate trap. There is a possibility.

Accordingly, in order to prevent such particulates from being excessively collected in each of the particulate traps, when a predetermined amount of the particulates is collected, the particulates are discharged from each of the particulate traps. is necessary. For this reason, by providing a closing valve that can close each communication path and disabling each communication path, relatively high-speed exhaust gas immediately after being discharged from each cylinder passes only the corresponding particulate trap. It is conceivable that the exhaust gas breaks up the accumulation of particulates and discharges them to the downstream side of the particulate trap. However, simply discharging the particulates into the atmosphere does not mean that the total amount of particulates discharged into the atmosphere is sufficiently reduced.

Accordingly, an object of the present invention is to provide a particulate trap disposed at each of the exhaust ports communicating the exhaust collecting section and each of the cylinders in the engine exhaust system, and an exhaust upstream side of each of the particulate traps. In an exhaust gas purifying apparatus for an internal combustion engine having a communication passage for communicating an exhaust port with at least one other exhaust port, and a normally open on-off valve arranged in each communication passage, a particulate matter to each particulate trap is provided. An object of the present invention is to prevent excessive collection of curates and sufficiently reduce the total amount of particulates discharged into the atmosphere.

[0010]

According to a first aspect of the present invention, there is provided an exhaust gas purifying apparatus for an internal combustion engine according to the present invention. A particulate trap, a communication path for communicating each of the exhaust ports with at least one of the other exhaust ports on the exhaust upstream side of each of the main particulate traps, and a normally open port disposed in each of the communication paths. An on-off valve, a normally-open first closing valve capable of closing an engine exhaust system on the exhaust downstream side of each of the main particulate traps, a bypass passage bypassing the first closing valve, and provided in the bypass passage. A sub-particulate trap is provided, and each of the on-off valves is closed to discharge particulates from the main particulate trap. Characterized by closing the first shut-off valve.

According to a second aspect of the present invention, there is provided the exhaust gas purifying apparatus for an internal combustion engine according to the first aspect of the present invention, wherein the bypass passage is provided upstream of the sub-particulate trap. A second closing valve capable of closing a bypass passage is provided, and when closing each on-off valve to discharge ash from the main particulate trap, closing the second closing valve, the first closing valve Thus, the inflow of exhaust gas into the at least one main particulate trap is temporarily suppressed.

[0012]

FIG. 1 is a sectional view of an engine exhaust system to which an exhaust gas purifying apparatus according to a first embodiment of the present invention is attached. In the figure, reference numeral 1 denotes a mounting flange on the exhaust side of a cylinder head, 2 denotes an exhaust collecting portion of each cylinder, and 3 denotes an exhaust port for communicating the exhaust collecting portion 2 with each cylinder. Each of the exhaust ports 3 is provided with a main particulate trap 4.

Each main particulate trap 4 is, for example, a porous material particulate trap made of a porous material such as ceramic. This particulate trap has a plurality of axial spaces subdivided by a plurality of longitudinally extending partitions, and in two adjacent axial spaces, one is an exhaust upstream side and the other is an exhaust downstream side. Is closed by a closing material such as ceramic. Thus, the two adjacent axial spaces serve as a trap passage through which the exhaust gas flowing in from the exhaust upstream side flows out to the exhaust downstream side via the partition wall, and the partition wall made of the porous material serves as a trap wall to allow the exhaust gas to pass therethrough. At the time, it collects particulates.

Each main particulate trap 4
For example, a metal fiber particulate trap composed of a nonwoven fabric of heat-resistant metal fiber and a corrugated sheet of heat-resistant metal may be used. In this particulate trap, two nonwoven fabrics and two corrugated sheets are stacked in a thickness direction differently from each other and spirally wound, and a plurality of axial spaces are formed by the nonwoven fabrics and the corrugated sheets. Things. Examples of the heat-resistant metal fiber constituting the nonwoven fabric and the heat-resistant metal constituting the corrugated sheet include Fe-Cr-Al alloy and Ni-Cr-A.
1 alloy and the like can be used. The two nonwoven fabrics are continuously welded in a spiral shape with one surface in close contact with each other at the exhaust upstream end, and spirally with the other surfaces in close contact with each other at the exhaust downstream end. Welded continuously. In this way, the two axially adjacent spaces in the radial direction serve as a trap passage through which the exhaust gas flowing from the upstream of the exhaust flows to the downstream of the exhaust via any of the nonwoven fabrics. At the time of the collection of particulates.

The exhaust gas purifying apparatus according to this embodiment further includes:
On the exhaust upstream side of each main particulate trap 4, a communication path 6 for communicating each exhaust port 3 with an adjacent exhaust port 3 is provided. Each communication passage 6 is provided with a normally open on-off valve 6a. The downstream side of the exhaust collecting part 2 is open to the atmosphere via a single exhaust passage 5. A normally-open first closing valve 7 that can close the exhaust passage 5 is disposed in the exhaust passage 5. In addition, a bypass passage 8 that bypasses the first closing valve 7 is provided, and a sub-particulate trap 9 is disposed in the bypass passage 8. The sub-particulate trap 9 has a configuration similar to that of the above-mentioned main particulate trap 4 and collects particulates.
It is smaller than the main particulate trap 4 and has better trapping ability. Immediately upstream of the sub-particulate trap 9, a heating means such as a heater or a burner for eliminating the particulates collected by the sub-particulate trap 9 is provided.
A normally closed second closing valve 10 capable of closing the bypass passage 8 is disposed upstream of the sub-particulate trap 9 in the bypass passage 8.

In the exhaust gas purification apparatus thus configured, relatively high-speed exhaust gas discharged from each cylinder is distributed to all the exhaust ports 3 by each communication path 6. Thereby, the change in the flow velocity of the exhaust gas flowing into the specific main particulate trap 4 changes at a relatively low speed as shown in FIG. Although the size of the pores of the main particulate trap 4 is very large as compared with the particulates, since the flowing exhaust gas is slow, the particulates in the exhaust gas are The attached and deposited particulates are collected around the fine pores, and the attached and deposited particulates can easily grow relatively large without being destroyed. Thus, the size of the substantial pores of the main particulate trap 4 is reduced to some extent, and the particulate collection rate in the main particulate trap 4 is increased.

Since each of the main particulate traps 4 is disposed near the engine body, the particulates collected by each of the main particulate traps 4 can have high exhaust gas temperature when the engine is operated at high load and high speed. For example, the heat of the exhaust gas is effectively used and burned, and the regeneration of each main particulate trap 4 is completed.

However, such high-load high-speed operation of the engine may not be performed for a predetermined period. In this case, a relatively large amount of a predetermined amount of particulates is collected in each main particulate trap 4. When the particulates are further collected in each of the main particulate traps 4, the particulates are excessively collected, which not only greatly increases the exhaust resistance of each of the main particulate traps but also generates a large amount of combustion heat during regeneration. May occur and each main particulate trap 4 may be melted.

Therefore, when a predetermined amount of particulates are collected in each main particulate trap 4 without performing regeneration, it is necessary to release the collected particulates from each main particulate trap 4. Becomes In this embodiment, when the engine high-load high-speed operation is not performed for a predetermined period, or when the pressure difference between the upstream side and the downstream side of each main particulate trap becomes equal to or more than a predetermined value, the on-off valve 6a of each communication path 6 , And the first closing valve 7 of the exhaust passage 5 is closed and the second closing valve 10 of the bypass passage 8 is opened as shown by a chain line.

The dashed line in FIG. 3 indicates a change in the flow velocity of the exhaust gas flowing into a specific main particulate trap 4 when each communication passage 6 is closed by each on-off valve 6a. Two peak velocities occur during the journey. The first peak flow velocity is caused by the ejection of high-pressure burned gas in the cylinder simultaneously with the opening of the exhaust valve. Further, the second peak flow velocity is obtained by discharging a large amount of burned gas in the cylinder as the piston rises.

Thus, the burned gas in the cylinder flows into the main particulate trap 4 at two peak flow rates. Each peak flow rate is relatively high, and the accumulation of the particulates collected in the main particulate trap 4 can be easily broken and discharged from the main particulate trap 4. At this time, since the exhaust passage 5 is closed by the first closing valve 7 and the bypass passage 8 is open, the particulates discharged from each main particulate trap 4 are, as shown by the one-dot chain line arrow,
The gas flows into the bypass passage 8 together with the exhaust gas, and is collected by the auxiliary particulate trap 9. In this way, at the time of excessive collection of the main particulates, the particulates discharged from each main particulate trap 4 are directly discharged into the atmosphere, thereby preventing an increase in the total amount of particulates discharged.

The sub-particulate trap 9 has small pores as compared with the main particulate trap 4, so that it traps the particulates better, but on the other hand, the exhaust resistance is increased. However,
A short time is required to close each on-off valve 6a in order to discharge the particulates from each main particulate trap 4, and only during this time the exhaust gas passes through the bypass passage 8.
In addition, since it does not pass through the sub-particulate trap 9, there is no particular problem.

When the discharge of the particulates from each main particulate trap 4 is completed, as shown by the solid line, the first closing valve 7 is opened and the bypass passage 8 is closed by the second closing valve 10, so that the exhaust gas is exhausted. The gas is discharged into the atmosphere through an exhaust passage 7 having a low exhaust resistance as indicated by a solid arrow. Thereafter, the particulates collected in the sub-particulate trap 9 are burned out by the above-mentioned heating means, and the sub-particulate trap 9 is regenerated, so that the next particulates are discharged from each main particulate trap 4. Be provided.

The exhaust gas contains oxides and sulfides such as calcium and phosphorus, which are combustion products of the engine oil that has entered the cylinder. These are called ash and have the same size as particulates,
Although the amount of generation is smaller than that of the particulates, they are collected well in each main particulate trap 4 similarly to the particulates. Since ash is very difficult to burn, even if the particulates are burned off from each main particulate trap 4, the ash remains in the particulate traps and accumulates, increasing the exhaust resistance.

Such ash must also be discharged from each of the main particulate traps 4. However, in each of the main particulate traps 4, the ash accumulation is stronger than the particulates. It is not possible to remove from the particulate trap 4 only by closing each communication passage 6 by 6a.

In the present embodiment, for example, immediately after the high-load high-speed operation of the engine is performed, that is, the high-temperature exhaust gas burns out the particulates collected in each main particulate trap 4 to burn each main particulate trap. Immediately after the completion of the regeneration, each communication passage 6 is closed by the opening / closing valve 6a for closing the opening / closing valve 6a without fail or at every predetermined number of times of regeneration, and the first closing is performed only at the beginning of the exhaust stroke of each cylinder. The valve 7 is operated in the valve closing direction. The solid line in FIG. 3 shows the change in the flow rate of the exhaust gas flowing into the specific particulate trap 4 as a result.

In the early stage of the exhaust stroke, since the first closing valve 7 is operated in the valve closing direction to increase the exhaust resistance in the exhaust system, the amount of burned gas ejected from the cylinder simultaneously with the opening of the exhaust valve. And the first peak flow rate is lower than normal. Thereafter, as the piston rises, the burned gas in the cylinder is forcibly discharged by increasing the amount of burned gas ejected from the cylinder at the same time as the opening of the exhaust valve. Since the first closing valve 7 is sometimes fully opened, the second peak flow rate is much higher than usual. Thereby, the deposited ash can be broken down by the exhaust gas flowing into the main particulate trap 4 at a second peak flow velocity higher than usual and finer, and can be discharged to the downstream side of the particulate trap 4.

As described above, the timing for suppressing the flow of the exhaust gas into the main particulate trap 4 is not limited to the initial stage of the exhaust stroke of each cylinder. In this case, the flow rate of the exhaust gas flowing into each main particulate trap 4 when canceling the inflow suppression in the next exhaust stroke of each cylinder can be increased as compared with normal times. That is, if the flow of the exhaust gas into the main particulate trap 4 is temporarily suppressed together with the closing of each communication passage 6, the above-described effect can be obtained.

Thus, each main particulate trap 4
When the ash is discharged from the second closing valve 10, the second closing valve 10 is closed. This makes it possible to favorably suppress the inflow of exhaust gas into the main particulate trap 4 by the first closing valve 7, and further, the ash removed from the main particulate trap 4 flows into the sub-particle trap 9. And can be released into the atmosphere. Thus, although the mechanism for removing ash is not provided in the sub-particulate trap 9, the ash removed from each main particulate trap does not accumulate in the sub-particulate trap 9,
There is no particular problem.

In this embodiment, the configuration of the bypass passage 8 including the first closing valve 7 and the sub-particulate trap 9 is one on the downstream side of the exhaust collecting section 2, that is, one for all the main particulate traps 4. Although placed, this is not a limitation of the present invention. For example, such a configuration of the first shut-off valve 7 and the bypass passage 8 may be provided for each main particulate trap 4 or for each of two or more main particulate traps 4.

[0031]

As described above, according to the exhaust gas purifying apparatus for an internal combustion engine according to the present invention, the main particulate trap disposed at each of the exhaust ports communicating the exhaust collecting section and each cylinder in the engine exhaust system is provided. A communication passage for communicating each exhaust port with at least one other exhaust port on the exhaust upstream side of each main particulate trap, a normally open on-off valve disposed in each communication passage, and a main particulate A normally closed first closing valve capable of closing the engine exhaust system on the exhaust downstream side of the trap, a bypass passage bypassing the first closing valve, and a sub-particulate trap provided in the bypass passage; When closing the valve and increasing the flow rate of exhaust gas flowing into the main particulate trap to discharge the over-collected particulates, the first closing valve The valve is closed, and the particulates discharged from each main particulate trap are collected by the sub-particulate trap provided in the bypass passage, and a sufficient amount of the particulates discharged into the atmosphere is sufficiently collected. Can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing an embodiment of an exhaust gas purification device for an internal combustion engine according to the present invention.

FIG. 2 is a graph showing a flow rate of exhaust gas flowing into a specific particulate trap when an on-off valve is opened.

FIG. 3 is a graph showing a flow rate of exhaust gas flowing into a specific particulate trap when the on-off valve is closed.

[Explanation of symbols]

 2 ... Exhaust collecting part 3 ... Exhaust port 4 ... Main particulate trap 5 ... Exhaust passage 6 ... Communication passage 6a ... On-off valve 7 ... First closing valve 8 ... Bypass passage 9 ... Sub-particulate trap 10 ... Second closing valve

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Atsushi Tahara 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F-term (reference) 3G090 AA01 AA04 BA01 BA02 BA04 CA00 CA01 CA04 CB22 CB23 CB24 DA04

Claims (2)

[Claims] 1. A main particulate trap disposed at each exhaust port that communicates between an exhaust collecting portion and each cylinder in an engine exhaust system, and each exhaust port is provided on an exhaust upstream side of each main particulate trap. , A normally open on-off valve arranged in each of the communication paths, and an engine exhaust system can be closed on the exhaust downstream side of each of the main particulate traps. A normally open first shut-off valve,
A bypass passage bypassing the first closing valve, comprising a sub-particulate trap provided in the bypass passage, when closing each on-off valve and discharging particulates from the main particulate trap, An exhaust gas purifying apparatus for an internal combustion engine, wherein the first closing valve is closed. 2. A second closing valve capable of closing the bypass passage is provided upstream of the sub-particulate trap in the bypass passage, and each of the on-off valves is closed to close the main particulate trap. When discharging ash, the second closing valve is closed, and the flow of exhaust gas into the at least one main particulate trap is temporarily suppressed by the first closing valve. 2. The exhaust gas purification device for an internal combustion engine according to claim 1.