JPH09112256A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To sufficiently control exhaust emission by a catalyst when an engine is idled. SOLUTION: When a diesel engine with a plurality of cylinders, for example four cylinders, is idled, the whole amount of exhaust emission emitted from the half of the cylinders 1a, 1d is returned to the suction sides of the remaining half of the cylinders 1b, 1c via EGR passages 8a, 8b, thereby the suction air is burned twice consecutively in the cylinders to greatly increase the temperature of exhaust emission while the flow of exhaust emission remains small, which makes a catalyst 1 active and then promotes up oxidization by the catalyst 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purification device for an internal combustion engine, which enhances exhaust gas performance when the internal combustion engine is idling.

[0002]

2. Description of the Related Art Recently, diesel engines (internal combustion engines)
In automobiles (vehicles) equipped with, an oxidation catalyst is provided as a main catalyst in an exhaust system of a diesel engine to purify HC contained in exhaust gas.

Most of the main catalysts used in the exhaust emission control device function in a region occupying most of the range of use of the engine, so that the medium temperature type is used. Such a catalyst is actively heated by the heat of the exhaust gas passing through the catalyst to a temperature at which the catalyst starts its activity, thereby actively performing an oxidation reaction.

By the way, such a structure for purifying exhaust gas with a catalyst has a problem that the exhaust temperature required to activate the catalyst cannot be secured when the engine is idle, that is, when the load is extremely low.

Therefore, as disclosed in Japanese Utility Model Application Laid-Open No. 4-37826, it has been proposed to utilize the reduced-cylinder operation so that the exhaust gas can be oxidized by the catalyst even at a low exhaust temperature such as during idling. There is.

This is because at a low load including idling (no load), a part of a plurality of cylinders is suspended and only the remaining cylinders are operated (reduced cylinder operation), and the cylinders that are operating during this operation. This is a technology that guides only the exhaust gas discharged from the exhaust gas to the catalyst and secures the temperature of the exhaust gas necessary for activation of the catalyst.

[0007]

By the way, in the cut-off cylinder operation in which a part of the cylinders of the engine is deactivated, the cylinder is deactivated,
The behavior is such that the dynamic balance becomes worse than during all-cylinder combustion operation. In particular, during idle operation such as when the engine is started (when the water temperature is low), the vibration of the engine is significant due to resonance that occurs due to fluctuations in rotation (due to friction, etc.).

For this reason, even if the exhaust gas can be purified, vibration and noise from the engine are large and the comfort of the vehicle to be secured may be impaired. Therefore, it is possible to suppress the resonance by increasing the engine speed during idling (idle up).

However, increasing the idle speed increases the flow rate of exhaust gas. With this,
It is difficult to oxidize the HC component of the exhaust gas by effectively using the ability of the catalyst, and there is a problem that the exhaust gas cannot be effectively purified during idling.

Therefore, improvement of exhaust gas purification during idling is required. The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an exhaust gas purification device for an internal combustion engine, which can sufficiently purify exhaust gas with a catalyst during idling.

[0011]

In order to achieve the above object, the invention set forth in claim 1 is a first EGR which connects an exhaust passage of at least one cylinder and an intake passage of another cylinder.
The exhaust gas purification device is configured to include a passage, a first valve that closes the exhaust passage when idling and opens the first EGR passage, and a catalyst that purifies exhaust gas from another cylinder.

That is, the invention described in claim 1 is
When the internal combustion engine is idle (extremely low rotation speed), the first valve operates to close the first exhaust passage and open the first EGR passage.

Then, the exhaust gas discharged from at least one cylinder is guided as it is to the intake passage of another cylinder through the opened first EGR passage. Here, at the time of idling, the intake air amount for the fuel is large, and even after combustion, it still contains a large amount of oxygen.

Thus, the combustion using the exhaust gas as the suction gas is performed in the other cylinders. Then, the exhaust gas that has finished burning in this cylinder is guided to the catalyst.

At this time, since the exhaust gas is the gas after being continuously burned in the two cylinders, the exhaust temperature has risen considerably. Moreover, the exhaust gas discharged from the first cylinder is
Since it is introduced into the subsequent cylinder as it is, the flow rate of exhaust gas passing through the catalyst is small.

Therefore, when the internal combustion engine is idle, the catalyst is sufficiently activated and exhaust gas can be sufficiently purified. In addition to the above-mentioned object, the invention according to claim 2 is the same as the structure according to claim 1 in order to further efficiently purify with a catalyst. There is a valve.

In addition to the above object, the invention described in claim 3 is in addition to the structure described in claim 1 or claim 2 in order to further increase the temperature of the exhaust gas and decrease the flow rate of the exhaust gas. , A second EGR passage communicating an exhaust passage of a cylinder communicating with the EGR passage and an intake passage of another cylinder, and an on-off valve opening the second EGR passage at idling.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to one embodiment shown in FIGS. FIG. 1 shows a schematic configuration of an exhaust emission control device provided in an exhaust system of an engine. In FIG. 1, reference numeral 1 denotes a diesel engine of a plurality of cylinders mounted on a vehicle such as a bus or a truck for traveling (for example, an in-line 4-cylinder engine ( Internal combustion engine).

The first to fourth cylinders 1a to 1d of the diesel engine 1 are provided with valve operating systems (mechanisms having intake and exhaust valves: not shown).
Further, each of the cylinders 1a to 1d is provided with fuel injection nozzles 2a to 2d connected to a fuel injection device (not shown) represented by, for example, a column type or a distribution type, and for all the cylinders 1a to 1d. The fuel is injected at a predetermined injection timing with an injection amount according to the engine load.

On the other hand, the intake passages 3a and 3d extending from the intake sides of the first cylinder 1a and the fourth cylinder 1d, respectively,
They are connected to an intake passage 4b which joins each other and is connected to an air cleaner (not shown).

The intake passages 3b and 3c extending from the intake side of the second cylinder 1b and the third cylinder 1c, respectively, are joined together and similarly connected to an intake passage 4a connected to an air cleaner (not shown). is there.

Exhaust passages 5a and 5d (both corresponding to the first exhaust passage) extending from the exhaust side of the first cylinder 1a and the fourth cylinder 1d, respectively, are joined to each other and opened to the atmosphere. Second cylinder 1 connected to exhaust passage 6
b, exhaust passages 5b, 5c (exhaust passages) extending from the exhaust side of the third cylinder 1c, respectively, are joined so as to join each other and then join the main exhaust passage 6. A catalyst, for example, an oxidation catalyst 7 is interposed in the merging portion 5e where the exhaust passages 5b and 5c merge.

The downstream side of the exhaust passage 5a (first cylinder 1a) and the upstream side of the intake passage 3c (third cylinder 1c) are communicated with each other via, for example, the intake passage 3b. The bypass passage 8a (corresponding to the first EGR passage) is connected to the.

Further, the downstream side of the exhaust passage 5d (fourth cylinder 1d) and the upstream side of the intake passage 3b (second cylinder 1b) are also connected to each other via the intake passage 3c. The bypass passage 8b (corresponding to the first EGR passage) is connected to the.

As a result, the exhaust gas discharged from the first cylinder 1a and the fourth cylinder 1d is supplied to the bypass passages 8a and 8b.
Through to the intake side of the third cylinder 1c and the second cylinder 1b.

In the present embodiment, considering that the bypass passages 8a and 8b are installed in a space-saving manner,
The bypass passage 8a has a piping structure that intersects the intake passage 3b of the second cylinder 1b, and the bypass passage 8b has a piping structure that shares the intersecting portion 3e and communicates with the intake passage 3b.

On the inlet side of these bypass passages 8a and 8b, the inlet of the bypass passage is closed and the exhaust passages 5a and 5d are opened at position A (shown by the broken line in FIG. 1), and the inlet of the bypass passage is opened. For switching the flow paths by opening / closing between the B position (shown by the solid line in FIG. 1) where the exhaust passages 5a, 5d are closed, for example, first switching valves 9a, 9b of Solenoid drive type (first valve). Equivalent to) is provided.

The first switching valves 9a and 9b are the controller 1
0 (for example, a microcomputer and its peripheral circuits). In addition, the controller 10 includes a rack position sensor 11 for detecting an engine load, for example, a rack position of a control rack of a fuel injection device (which controls displacement of an injection amount by displacing an accelerator opening: not shown). Are connected.

The controller 10 includes each first switching valve 9
The function of setting the open / close positions of a and 9b to the B position when the engine load is no load, that is, when the engine is idling, and to the A position when the engine is operating other than idling, opens the bypass passages 8a and 8b only when idling. Bypass paths 8a and 8b during operation other than idling
Is closed.

As a result, only when idling, the first
The exhaust gas from the cylinder 1a and the fourth cylinder 1d is introduced into the intake passages 3b and 3c of the other half of the other cylinders, that is, the second cylinder 1b and the third cylinder 1c. .

On the outlet side of each of the bypass passages 8a and 8b, the bypass passage outlet is closed and the intake passages 3b and 3c are opened at the C position (shown by a broken line in FIG. 1) and the bypass passage outlet is opened. , The intake passages 3b and 3c are closed to open and close with the D position (shown by the solid line in FIG. 1) to switch the flow passages. For example, second switching valves 12a and 12b of solenoid drive type (second Equivalent to the valve) is provided.

The second switching valves 12a and 12b are also connected to the controller 10. The controller 10 has a function of setting the opening / closing positions of the second switching valves 12a and 12b to the D position when the engine load is not loaded, that is, when the engine is idling, and to the C position when the engine is operating other than idling. Each intake passage 3b,
No fresh air (intake air taken in from the air cleaner) enters the 3c.

In other words, the second cylinder 1 only when idle
b. The inflow of fresh air into the third cylinder 1c is restricted so that the exhaust gas exhausted from half of the four cylinders is returned to the remaining cylinders as much as possible. Specifically, at the time of idling, the exhaust gas from the first and fourth cylinders 1a and 1d is completely returned to the second and third cylinders 1b and 1c so that the exhaust gas temperature is the highest and the exhaust gas flow rate is the lowest. .

On the other hand, on the upstream side of the exhaust passage 8b of the second cylinder 1b (cylinder to which the first EGR passage is connected) and on the upstream side of the intake passage 3d of a cylinder other than the same cylinder 1b, for example, the fourth cylinder 1d. Between the two, so that they can communicate with each other
3a (corresponding to the second EGR passage) is connected.

The upstream side of the exhaust passage 5c of the third cylinder 1c (cylinder to which the first EGR passage is connected) and the upstream side of the intake passage 3a of a cylinder other than the same cylinder 1c, for example, the first cylinder 1a. Bypass 1 to connect the two
3b (corresponding to the second EGR passage) is connected.

The bypass passages 13a and 13b are provided with open / close valves 14a and 14b, which are normally closed type two-way valves.
Is provided. These on-off valves 14a and 14b are set to open only when idling according to a command from the controller 10.

As a result, at the time of idling, a part of the exhaust gas after being burned twice is recirculated to the intake side of the upstream cylinder again. By such a double combustion structure and a structure in which a part of the exhaust gas after the double combustion is recirculated, the HC component contained in the exhaust gas is sufficiently oxidized by the oxidation catalyst 7 during idling.

The operation of this exhaust purification system is shown in FIG. Next, based on the flowchart shown in FIG.
The operation of the exhaust emission control device will be described.

First, the diesel engine 1 is started.
Then, the valve train and the fuel injection device are driven. As a result, the fuel pressure-fed from the fuel injection device is injected from the fuel injection nozzles 2a to 2d into the cylinders 1a to 1d at a predetermined injection timing, an optimum amount (amount corresponding to the engine load),
In each of the cylinders 1a to 1d, a cycle of repeating intake, compression, combustion (explosion), and exhaust is repeatedly performed.

At this time, the controller 10 determines the first switching valves 9a, 9b, the second switching valves 12a, 12b from the rack position of the fuel injection device output from the rack position sensor 11.
The switching timing of 12b and the on-off valves 14a and 14b is determined.

Specifically, the controller 10 determines whether or not the rack position is the position during idle operation as shown in step S1. At this time, if the operation is other than idle, the controller 10 determines that the flow path change for activating the oxidation catalyst 7 is not necessary, and proceeds to step S2 to set the first switching valves 9a and 9b to the A position, Set the second switching valves 12a and 12b to the C position, and open / close valve 14
Actuate a and 14b to the closed position respectively.

Then, as shown in FIG. 2, both the inlet and the outlet of each bypass 8a, 8b are closed. Further, both bypass paths 13a and 13b are also closed. As a result, fresh air (intake air from the air cleaner) is introduced into all the cylinders 1a to 1d (4 cylinders) through the intake passages 3a to 3d. Also, all cylinders 1a-1d
The exhaust gas is discharged from the exhaust gas through the exhaust passages 5a to 5d.

The second cylinder 1b and the third cylinder 1c
The exhaust gas exhausted from is discharged to the atmosphere through the oxidation catalyst 7 and the main exhaust passage 6. Further, the exhaust gas exhausted from the first cylinder 1a and the fourth cylinder 1d merges with the exhaust gas exiting the oxidation catalyst 7 and is released to the atmosphere.

On the other hand, if the diesel engine 1 is in the idling operation, the routine proceeds from step S1 to step S3. Then, the controller 3 sets the first switching valves 9a and 9b to the B position and the second switching valves 12a and 9b as shown in FIG.
12b is switched to the D position, and on-off valves 14a and 14b are switched to the open position.

By switching the first switching valves 9a, 9b, the flow paths from the exhaust passages 5a, 5d to the atmosphere are closed, and instead, the inlets of the bypass passages 8a, 8b are exhausted passages 5a, 5d.
The flow path is switched so that it is connected to.

By switching the second switching valves 12a and 12b, the flow paths from the intake passage 4a to the intake passages 3b and 3c are closed, and instead the outlets of the bypass passages 8a and 8b are connected to the intake passages 3b and 3c. The switching of the flow path is performed.

As a result, the exhaust gas after being burned in the first cylinder 1a and the fourth cylinder 1d passes through the bypass passages 8a and 8b as it is, the remaining half of the cylinders, that is, the second cylinder 1b and the third cylinder. Is sucked in from the intake side of the cylinder 1c.

Here, at the time of idling, the intake air amount with respect to the fuel is large and still contains a large amount of oxygen even after combustion in the first cylinder 1a and the fourth cylinder 1d. Therefore, in the second cylinder 1b and the third cylinder 1c, combustion using the same exhaust gas as the intake gas is performed.

As a result, the diesel engine 1 is idle-operated in a multiple combustion cycle in which the intake air sucked into half of all the cylinders burns twice in succession.

Next, the second cylinder 1b and the third cylinder 1c
The exhaust gas, which has been burnt at, is guided to the oxidation catalyst 7. At the same time, a part of the exhaust gas recirculates to the intake side of the first cylinder 1a and the fourth cylinder 1d that perform the first combustion through the bypass passages 13a and 13b.

At this time, the exhaust gas passing through the oxidation catalyst 7 is continuously burned in two cylinders (first cylinder 1a and third cylinder 1c, fourth cylinder 1d and second cylinder 1b). Since it is the latter gas, the exhaust temperature has risen considerably.

Moreover, since the exhaust gas discharged from the first cylinders 1a and 1d is introduced into the subsequent cylinders 1b and 1c) as it is, the exhaust gas flow rate of each cylinder 1a to 1d sucks in fresh air and burns. It is much less than when you let it.

Therefore, even during idling, the oxidation catalyst 7
Is sufficiently activated, and the HC component contained in the exhaust gas is oxidized by the oxidation catalyst 7. As a result, sufficient purification of exhaust gas can be expected even during idling.

Moreover, all the cylinders 1a to 1d are burned without stopping as described in the section "Prior Art", so that the dynamic balance of the engine is kept good and the cylinder cut-off operation is performed. The resonance and noise are not generated, and the comfort of the vehicle is not impaired.

In addition, since the second combustion has a fairly high suction temperature, the second combustion is active, and the H
The amount of C emission decreases. In particular, at the time of idling, if the intake passages 1b and 1c are closed to restrict the introduction of fresh air, the total amount of exhaust gas from the first cylinder 1a and the fourth cylinder 1d can be sucked into the other cylinders 1b and 1c without waste. Therefore, the oxidation catalyst 7 can efficiently purify the exhaust gas.

Further, if a structure in which a part of the exhaust gas generated by the second combustion is recirculated to the suction side of the cylinders 1a, 1d which perform the first combustion, the temperature of the fresh air sucked by the cylinders 1a, 1d is further increased. Is raised, and the temperature of the exhaust gas is raised accordingly. At the same time, the flow rate of the exhaust gas also decreases due to the recirculation.

This fact makes it possible to further accelerate the oxidation reaction in the oxidation catalyst 7 by the same reflux, and the oxidation catalyst 7 can be operated in any idling operation at low ambient temperature.
Good exhaust gas purification can be expected.

Particularly, the HC of the idle operation by the all-cylinder combustion operation of the diesel engine 1 (combustion of fresh air sucked into each cylinder) and the idle operation of the combination of the multiple combustion of the present invention and EGR for fresh air are carried out. As a result of detecting the emission amount, the HC emission amount during the idle operation of the present invention shown by the solid line as shown in FIG. 4 is higher than the HC emission amount during the idle operation of the all-cylinder combustion operation indicated by the broken line compared to the engine emission amount. From the start, it was confirmed that the amount of HC emission was remarkably small, specifically, it was suppressed to less than half.

In the above-described embodiment, since the engine is a four-cylinder engine, the combustion timing is taken into consideration, and the first cylinder 1a to the third cylinder 1c are changed to the fourth cylinder by the bypass passages 8a and 8b. Exhaust gas was returned from 1d to the second cylinder 1b, but conversely, from the third cylinder 1c to the first cylinder 1a.
The exhaust gas may be returned from the second cylinder 1b to the fourth cylinder 1d. Of course, bypass paths 13a and 13b
Also, not only from the second cylinder 1b to the fourth cylinder 1d, from the third cylinder 1c to the first cylinder 1a, but from the fourth cylinder 1d to the second cylinder 1b, from the first cylinder 1a The exhaust gas may be returned to the third cylinder 1c.

Although the present invention is applied to a four-cylinder diesel engine, the present invention is not limited to this and may be applied to other diesel engines having a plurality of cylinders. Needless to say, the present invention is applied to the diesel engine, but the present invention is not limited to this, and may be applied to other internal combustion engines such as a gasoline engine.

[0061]

As described above, according to the invention described in claim 1, the exhaust gas passing through the catalyst is maintained while maintaining the idling operation excellent in dynamic balance in which all the cylinders are burned by the multiple combustion. The temperature of the gas can be raised considerably. Moreover, since the exhaust flow rate of the exhaust gas is small, the catalyst can be sufficiently activated even during idling.

Therefore, the exhaust gas can be sufficiently purified by the catalyst when the internal combustion engine is idle. Moreover, since combustion is performed in all the cylinders without stopping, the dynamic balance of the internal combustion engine is maintained in good condition, and resonance and noise such as the cut-off cylinder operation are not generated.

Moreover, since the second combustion becomes active due to the rise in the suction temperature, there is also an advantage that the amount of HC discharged becomes small. According to the invention as set forth in claim 2, in addition to the effect of the invention as set forth in claim 1, due to the restriction of the introduction of fresh air, the entire amount of exhaust gas exhausted from the first exhaust passage can be sucked into other cylinders without waste. The effect that the exhaust gas can be efficiently purified by the catalyst is obtained.

According to the invention of claim 3, claim 1
Alternatively, in addition to the effect of the second aspect of the invention, the temperature of the exhaust gas can be further increased by the recirculation, and at the same time, the flow rate of the exhaust gas can be reduced.

As a result, the oxidation reaction in the catalyst can be further promoted, and good exhaust gas purification by the catalyst can be expected in any idling operation at low ambient temperature.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining the configuration of an exhaust emission control device for an internal combustion engine according to an embodiment of the present invention, together with the flows of intake air and exhaust gas during idling.

FIG. 2 is a view showing the flow of intake air and exhaust gas when the exhaust emission control device is in an operation other than idling.

FIG. 3 is a flowchart for explaining control of the exhaust emission control device during idling and during other operations.

FIG. 4 is a diagram showing the amount of HC emission from the engine start in idle operation of the exhaust emission control device in comparison with the amount of HC emission in idle operation by all-cylinder combustion operation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Diesel engine (internal combustion engine) 1a-1d ... 1st cylinder-4th cylinder (cylinder) 3a-3d ... Intake passage 5a, 5d ... Exhaust passage (1st exhaust passage) 7 ... Oxidation catalyst (catalyst) 8a , 8b ... Bypass path (first EGR passage) 9a, 9b ... First switching valve (first valve) 10 ... Controller 12a, 12b ... Second switching valve (second valve) 13a, 13b ... Bypass path (second EGR passage) 14a, 14b ... Open / close valves.

Continuation of front page (51) Int.Cl. ⁶ Identification number Reference number within the agency FI Technical display area F02M 25/07 ZAB F02M 25/07 570G 570 570M 580A 580 580B B01D 53/36 103Z (72) Inventor Shigeru Haruto Tokyo 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation (72) Inventor Taizo Shimada 5-33-8, Shiba, Minato-ku, Tokyo Tokyo Mitsubishi Motors Corporation

Claims (3)

[Claims] 1. In an internal combustion engine having a plurality of cylinders, a first EGR passage that connects an exhaust passage of at least one cylinder and an intake passage of another cylinder, and the first EGR that closes the exhaust passage during idling.
An exhaust gas purification apparatus for an internal combustion engine, comprising: a first valve that opens a passage; and a catalyst that purifies exhaust gas from the other cylinder. 2. The exhaust gas purification device for an internal combustion engine according to claim 1, further comprising a second valve that closes the intake passage during idling. 3. A second EGR passage that connects an exhaust passage of a cylinder communicating with the EGR passage and an intake passage of another cylinder, and an opening / closing valve that opens the second EGR passage during idling. The exhaust emission control device for an internal combustion engine according to claim 1 or 2, characterized in that.