JPH0338424B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an exhaust gas recirculation device for a multi-cylinder diesel engine.

Generally, in automotive diesel engines,
It is well known that exhaust gas recirculation (EGR) devices are used to reduce _NO

Conventionally, as a diesel mechanism EGR device, there is one shown in FIG. 1 (Japanese Utility Model Publication No. 53-19299).

This first consists of the intake passage (intake manifold) 2 and exhaust passage (exhaust manifold) 3 of the engine body 1.
are communicated through the EGR passage 4. A fixed orifice 5 is provided in the middle of the EGR passage 4, and an intake throttle valve 6 is interposed in the intake passage 2 located upstream of the connecting portion of the EGR passage 4.

Therefore, when EGR is not required, the intake throttle valve 6 is fully opened. In this way, almost no negative pressure is generated in the intake passage 2, and moreover, the above-mentioned
Since the EGR passage 4 is restricted by the fixed orifice 5, almost no exhaust gas flows back to the intake passage 2 side.

On the other hand, when EGR is required, the intake throttle valve 6 is closed to throttle the intake air. This way,
Negative pressure is generated in the intake passage 2 downstream of the intake throttle valve 6 according to the opening degree of the throttle valve 6, and due to the pressure difference between the intake passage 2 and the exhaust passage 3 at this time, the exhaust gas is
It is recirculated to the intake passage 2 side through the EGR passage 4.

In this way, the EGR amount was controlled by the opening degree of the intake throttle valve 6.

However, in such a conventional EGR device, as mentioned above, when the intake throttle valve 6 is fully open (for example, in a high engine load range or a high engine speed range),
In order to prevent EGR from occurring, reflux resistance was created by providing a fixed orifice 5 in the EGR passage 4 or reducing the passage diameter of the EGR passage 4.
When EGR is required (e.g. low engine load, medium load range, etc.)
In order to obtain a sufficient amount of EGR, the intake throttle valve 6
It was necessary to generate a large negative pressure in the intake passage 2 by reducing the opening degree of the intake passage 2 considerably.

As a result, the amount of fresh air taken into the engine is extremely reduced, the excess air ratio is reduced, and exhaust smoke and unburned HC
There was a problem that the concentration increased.

As a countermeasure to this, the fixed orifice 5 is removed and the diameter of the EGR passage 4 is made thicker.
There is also a method of installing a reflux cutoff valve in the middle of passage 4, but with this, EGR is completely disabled when EGR is not required.
In addition to cutting the maximum
This solves the EGR amount problem, but since the EGR amount is greatly affected by slight changes in the opening of the intake throttle valve 6 during EGR, there will be variations in EGR amount control, and it will depend on the engine operating state. A problem arises in that optimal EGR control cannot be performed.

The present invention aims to solve these conventional problems.

In order to achieve the above object, the present invention provides an exhaust recirculation system for a multi-cylinder diesel engine in which the intake passage and the exhaust passage of the engine body are connected through an exhaust recirculation passage, and a part of the engine exhaust gas is recirculated to the intake passage. The end of the exhaust gas recirculation passage on the exhaust passage side is connected to the individual exhaust passages of a plurality of cylinders, and the exhaust passage is located in the middle of the plurality of exhaust passages downstream of the connection part with the exhaust recirculation passage. As you do,
Exhaust cutoff valves are installed that open and close sequentially depending on the engine operating state.

Based on such a configuration, the exhaust gas cut-off of predetermined cylinders is sequentially closed depending on the operating state, and the exhaust gas of the cylinder is forcibly introduced into the intake passage, so there is no need for intake throttling or the like. The required amount of exhaust gas is recirculated without fail depending on the operating condition.

Embodiments of the present invention will be described below based on the drawings.

FIG. 2 shows an example in which the present invention is applied to a diesel engine consisting of four cylinders.

In the figure, reference numeral 10 denotes an engine body equipped with the first cylinder #1 to the fourth cylinder #4, and the engine body 10 has an intake and exhaust manifold 1 that forms part of the intake and exhaust passages.
1 and 12 are attached, and each branch portion 11 thereof
Each cylinder #1 of the engine body 10 through A, 12A
It is communicated to #4.

Then, the gathering part 11B of the intake manifold 11
An air cleaner 14 is attached to the upstream end of the intake pipe 13 connected to the intake pipe 13, and a diffusion chamber 16 is interposed in the middle of the intake pipe 13 to which one end of an EGR passage 15, which will be described later, is open and connected. On the other hand, an exhaust pipe 17 is communicated with the collection part 12B of the exhaust manifold 12, and the exhaust pipe 17 is opened to the outside after a catalytic converter and a muffler (not shown) are interposed therebetween.

EGR with one end connected to the above diffusion chamber 16
The other end of the passage 15 is branched in the middle, one of which is connected to a branch portion 12A that leads to the fourth cylinder #4 of the exhaust manifold 12, and the other to a branch portion 12A that also leads to the third cylinder #3. Ru.

4th cylinder #4 to which the above EGR passage 15 is connected
and each branch portion 12A of the third cylinder #3 has the corresponding
Exhaust cutoff valves 18 and 18', which open and close in response to commands from the valve control device 21, are installed in the EGR passage 15 so as to be located downstream of the connection with the EGR passage 15. The first cylinder is located upstream of the branch part of the fourth cylinder #4 to the branch part 12A.
A second recirculation control valve 20' is interposed in the middle of the passage section 15' connected to the branch section 12A to the third cylinder #3.

The first exhaust cutoff valve 18 and the recirculation control valve 20 are connected to each other via a link mechanism 19, and the second exhaust cutoff valve 1
8' and the recirculation control valve 20' are connected via a link mechanism 19' so as to open and close reciprocally.

Next, the action will be explained.

In operating ranges where EGR is not required, such as in high engine load ranges, the valve control device 21 controls the exhaust cutoff valves 18 and 18' to fully open. At this time, the recirculation control valves 20, 20' interposed in the middle of the EGR passages 15, 15' are controlled to operate reciprocally with the exhaust cutoff valves 18, 18' via the link mechanism 19, respectively. Therefore, it becomes fully closed.

As a result, all the branch parts 12A of the exhaust manifold 12 communicate only with the collecting part 12B side, that is, the third cylinder #3 and the fourth cylinder #4.
The exhaust gas from the exhaust gas from the first cylinder #1 to the second cylinder #2 joins with the exhaust gas from the first cylinder #1 to the second cylinder #2 at the collecting portion 12B, and is then discharged to the outside via the exhaust pipe 17. As a result, EGR is reliably shut off when EGR is not required.
The high output of the engine is ensured.

On the other hand, in a normal operating range where the load is relatively low, the exhaust cutoff valve 18 installed in the branch portion 12A of the fourth cylinder #4 is fully closed. At this time, as described above, the recirculation control valve 20 is fully opened due to the reciprocal operation. In this state, the exhaust gas discharged from the fourth cylinder #4 cannot flow from the branch part 12A to the collecting part 12B, so the entire amount passes through the EGR passage 15 which is in communication state and reaches the middle of the intake pipe 13. introduced into a diffusion chamber 16,
Here, after being mixed with fresh air from the air cleaner 14, it is sucked into each cylinder #1 to #4 from the collecting portion 11B of the intake manifold 11 via each branch portion 11A. At this time, the above-mentioned diffusion chamber 16
Since the cylinder has a certain volume, mixing of EGR gas and fresh air is promoted, and EGR is uniformly applied to each cylinder #1 to #4.

By the way, since the configuration is such that the entire amount of exhaust gas for one cylinder is recirculated as EGR gas, the effective EGR rate, that is, the CO ₂ concentration in the cylinder intake gas, increases as the engine load increases. In the end, the EGR rate will automatically be adjusted according to the load, but in extremely low load operating ranges such as idling or light engine braking, the
The amount of EGR may be insufficient.

Therefore, in such an operating range, not only the first exhaust cutoff valve 18 but also the branch section 1 of the third cylinder #3
The second shutoff valve 18' installed in 2A is also controlled to be fully closed. At this time, the second recirculation control valve 20' is fully opened via the link mechanism 19'. This results in
The exhaust gas from the third cylinder #3 joins the exhaust gas from the fourth cylinder #4 via the passage 15', and is recirculated to the intake manifold 11 via the EGR passage 15. In other words, the exhaust gas for two cylinders is recirculated, ensuring that the required amount is recirculated.
EGR can be applied to reliably reduce _NOx even in extremely low load ranges.

In this way, when you want to perform EGR, you can perform EGR reliably, albeit in an on-off manner, and the amount of _NOx generated can be reliably reduced.
In addition, EGR can be performed without throttling the intake air (that is, there is no need for an intake throttle valve like in the conventional example), so smoke and
It does not cause the problem of increased generation of HC.

In the above embodiment, the reflux cutoff valves 20 and 20' were installed in the middle of the EGR passages 15 and 15' so that EGR can be reliably stopped when EGR is not required. Install a fixed orifice or EGR passage 15,
The inner diameter of 15' may be made smaller.

Figure 3 is a modification of Figure 2 and shows the EGR passage 1.
The reflux control valve 20 installed in the EGR passage 1
This is an example in which it is relocated to the EGR passage 15 located downstream of the branch point 5', and its operation and effect are the same as those shown in FIG.

FIG. 4 shows an example in which the present invention is applied to a six-cylinder diesel mechanism, in which exhaust gas for EGR is taken out from three cylinders #4 to #6, the fourth to sixth cylinders.

That is, each branch 12A leading to the fourth to sixth cylinders #4 to #6 has an EGR passage 15,
15', 15'' are connected to these branches 12A and EGR passages 15, 15', 15'',
Exhaust cutoff valves 18, 18', 18'' and recirculation control valves 20, 20', 20'' are installed, respectively, and these three exhaust cutoff valves 18, 18', 18'', etc. are controlled by a valve control device 21. Each can be opened and closed independently.

Therefore, according to this embodiment, the same effects as those in FIG. 2 can be obtained, and the maximum
It has the advantage that the EGR amount can be kept the same and the EGR amount can be set in three stages.

As explained above, according to this invention, EGR
The passage is connected to an exhaust passage that communicates only with a specific cylinder, and an exhaust cutoff valve is provided downstream of the connection of the exhaust passage with the EGR passage, which opens and closes depending on the engine operating state. Almost all of the exhaust gas from a particular cylinder can be recirculated to the intake passage, so there is no need for an intake throttle. As a result, there will be no drastic decrease in the amount of fresh air intake due to intake throttling.
The effect is that an increase in exhaust smoke and unburned HC concentration is avoided, and a stable EGR amount can be ensured.

In addition, in this invention, exhaust gas for EGR is introduced sequentially from specific multiple cylinders depending on the operating condition, so
EGR can be applied and therefore _NOx can be reliably reduced over a wide range of operation.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of a conventional example, FIG. 2 is a schematic diagram of an embodiment of the present invention, and FIGS. 3 and 4 are schematic diagrams of other embodiments of the present invention. 10... Engine body, 11... Intake manifold, 11A... Branch section, 12... Exhaust manifold, 12A... Branch section, 15... EGR
Passage, #1 to #6...1st to 6th cylinder, 1
8, 18', 18''...Exhaust cutoff valve.

Claims (1)

[Claims] 1. In an exhaust recirculation system for a multi-cylinder diesel engine in which the intake passage and exhaust passage of the engine body are connected through an exhaust recirculation passage and a part of the engine exhaust gas is recirculated to the intake passage, the exhaust passage side of the exhaust recirculation passage is The ends of the cylinders are connected to individual exhaust passages of a plurality of cylinders, and the ends of the exhaust passages are connected to individual exhaust passages of a plurality of cylinders, and depending on the engine operating state, a pipe is located in the middle of these plurality of exhaust passages, downstream of the connection part with the exhaust gas recirculation passage. An exhaust gas recirculation device for a multi-cylinder diesel engine characterized by interposing exhaust cutoff valves that open and close sequentially.