JPH0232854Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Field of Industrial Application) This invention relates to improvement of an exhaust gas recirculation device for an engine.

(Prior Art) In engines such as automobiles, there is an exhaust gas recirculation device as a means for reducing _NOx in exhaust gas in order to prevent air pollution. This device lowers the combustion temperature of the engine by circulating a portion of the exhaust gas back into the intake system. For example, in the exhaust gas recirculation device disclosed in Japanese Utility Model Application Publication No. 58-77144, the upstream part of the intake manifold and the exhaust passage are connected through an exhaust gas recirculation pipe, and the exhaust gas is sent to the cylinders of the engine through the exhaust gas recirculation pipe. I'm trying to reflux it.

By the way, in an engine having multiple cylinders, in order to distribute the exhaust gas uniformly to each cylinder, it is necessary to sufficiently mix the exhaust gas and fresh air in the intake passage. It is desirable to connect it to the upstream side of the intake passage. Also,
High-temperature exhaust gas passing through the intake passage accelerates corrosion of the passage walls, so in order to prevent this, it is desirable to connect the exhaust gas recirculation pipe to the downstream side of the intake passage. If adopted, it is necessary to equalize the amount of exhaust gas distributed.

In addition, the surge tank extends along the direction in which the cylinders are arranged, and this surge tank is connected to each cylinder by an intake manifold consisting of a plurality of branch pipes, and the intake inlet of the surge tank extends along the direction in which the cylinders are arranged. In engines with openings on a straight line, there tends to be a difference in the amount of exhaust gas distributed between the upstream cylinder near the intake inlet and the downstream cylinder away from the intake inlet. It was desired to be able to homogenize the gas distribution in a particularly effective manner.

(Purpose of the invention) This invention was made in view of the above points, and it is possible to prevent the walls of the intake passage from corroding with a simple structure, and also to direct exhaust gas to each cylinder of the engine. The present invention provides an exhaust gas recirculation device that can evenly distribute and recirculate the exhaust gas.

(Structure of the invention) The exhaust gas recirculation device of this invention includes a surge tank that extends along the direction in which the cylinders are arranged and has an intake inlet opening on a line along the direction in which the cylinders are arranged, and a surge tank that has one end connected to each cylinder. A bent part is formed in the intake passage located upstream of the intake manifold, the other end of which is located on the upstream side of an intake manifold consisting of a plurality of branch pipes connected in sequence in the cylinder arrangement direction of the surge tank, and an exhaust gas recirculation pipe is connected to the outside of the bent part. The supply port of this exhaust gas recirculation device is formed near an extension of the center line of the surge tank. That is, by bending the intake passage, a turbulent flow is generated by the fresh air outside the bend, thereby promoting mixing of the exhaust gas supplied to this portion with the fresh air.

(Embodiment) In FIGS. 1 and 2, 1 is a surge tank forming a part of an intake passage, 2 is an exhaust manifold, and 3 is a cylinder head of an engine. The surge tank 1 extends along the direction in which the cylinders are arranged, and has an intake inlet opening on a line along the direction in which the cylinders are arranged, and a communication pipe 4 is connected to this intake inlet. connected to the duct. Further, this surge tank 1 is connected to each cylinder of the engine via a plurality of branch pipes 5, one end of which is connected to each cylinder, and the other end of which is connected sequentially in the cylinder arrangement direction of the surge tank 1. 1 and each branch pipe 5 constitute an intake manifold 6. The communication pipe 4 located upstream of the intake manifold 6 is bent at a predetermined angle with respect to the center line a of the surge tank 1. An exhaust gas recirculation pipe 7 communicating with the exhaust manifold 2 is connected to the outside of the bending part of the communication pipe 4, and the exhaust gas flowing into the communication pipe 4 through the exhaust gas recirculation pipe 7 is converted into fresh air. The gases are mixed to form a mixed gas, which is distributed to each branch pipe 5 via a surge tank 1. The supply port 8 of the exhaust gas recirculation pipe 7 is formed at a position X on an extension of the center line a of the surge tank 1 outside the bend of the connecting pipe 4. In the example shown, the supply port 8 is at position
Although the opening is not strictly at this position, it may be in this vicinity.

The exhaust gas recirculation pipe 7 is provided with an exhaust gas recirculation control valve 9 that controls the flow rate of exhaust gas.
Further, the inside of the cylinder head cover 10 of the engine and the surge tank 1 are communicated through a blow-by passage 11. In addition, in the figure, 12 is a cooling water pipe.

The exhaust gas recirculation device configured as above is
A supply port 8 of the exhaust gas recirculation pipe 7 is formed outside the bend of the communication pipe 4 located upstream of the intake manifold 6, near a position Therefore, even though the exhaust gas recirculation pipe 7 is connected to the communication pipe 4 located relatively downstream of the intake passage, the exhaust gas does not flow unevenly into a specific branch pipe 5 and flows evenly into each branch pipe 5. It will be distributed to The reason for this will be explained below.

If the exhaust gas recirculation pipe is connected sufficiently upstream of the intake passage in a 4-cylinder diesel engine, the exhaust gas will be distributed approximately equally to each cylinder in various rotational ranges of the engine, as shown in Figure 3. The experimental data was obtained. In addition, in Fig. 3, the EGR rate indicates the percentage of the CO ₂ concentration in the mixed gas to the CO ₂ concentration in the exhaust gas,
The smaller the amount of exhaust gas distributed, the lower the percentage.

As mentioned above, by setting the connection position of the exhaust gas recirculation pipe 7 sufficiently upstream of the intake passage, the amount of exhaust gas distributed can be equalized because the exhaust gas is sufficiently mixed with fresh air while passing through the intake passage. It is thought that this is because the On the other hand, if the exhaust gas recirculation pipe 7 is connected relatively downstream of the intake passage made of a straight pipe, that is, at a position close to the intake manifold 6, the exhaust gas and fresh air will not be sufficiently mixed, and the exhaust gas will be unevenly distributed. As a result, the amount of exhaust gas flowing into each branch pipe 5 becomes uneven. Particularly in a diesel engine with a large amount of intake air, the inertia of fresh air flowing through the intake passage is large, so the exhaust gas is easily carried downstream by this fresh air, and the exhaust gas is directed to the branch pipe 5 located upstream of the surge tank. There is a tendency for the amount of distribution to be insufficient.

On the other hand, when a part of the intake passage is bent as described above, the fresh air collides with the wall outside the bend and flows intensively along the outside wall while creating turbulence. If the exhaust gas is introduced into this portion, the exhaust gas and fresh air will be effectively mixed in a short time. Therefore, even if the exhaust gas recirculation pipe 7 is connected to the downstream side of the intake passage, the distribution of exhaust gas is not impaired. Therefore, it is possible to shorten the length of the intake passage that comes into contact with exhaust gas, thereby preventing corrosion of the passage wall surface, and making it possible to equalize the amount of exhaust gas flowing into each cylinder and to maintain the same combustion conditions. Can be set.

Note that even when the above-mentioned bent portion is formed,
If the opening position of the exhaust gas supply port 8 is arranged downstream of the position X on the extension of the surge tank center line a, the mixing effect due to the turbulent flow will not be obtained as much, so the distribution of the exhaust gas will be difficult. You can't improve your sexuality. Therefore, the limit for moving the exhaust gas supply port 8 to the downstream side of the intake passage is near the position X on the extension of the center line a of the surge tank 1 outside the bend.

The exhaust gas recirculation device according to this invention can be applied not only to diesel engines but also to gasoline engines. In the above embodiment, an example in which a bent portion is formed in the communication pipe 4 has been described, but a structure may be adopted in which the communication pipe 4 is a straight pipe and a bent portion is formed in the intake duct connected thereto. Further, the bent portion may have a structure curved at a predetermined curvature, or may be bent at a predetermined angle.

(Effects of the invention) As explained above, this invention has a simple structure by bending a part of the intake passage and providing the supply port of the exhaust gas recirculation pipe at a specific position of the bend. This allows exhaust gas to be evenly distributed to each cylinder of the engine. Therefore, the combustion conditions in each cylinder are the same, eliminating the difference in output between each cylinder, making it possible to stabilize the engine operating condition, and also fully exhibiting the effect of reducing _NOx in exhaust gas. Moreover, by arranging the exhaust gas supply port on the downstream side of the intake passage to shorten the length of the intake passage that comes into contact with the exhaust gas, it is possible to simultaneously achieve the effect of preventing corrosion of the passage wall surface.

[Brief explanation of the drawing]

Figure 1 is a front view showing an embodiment of this invention, Figure 2 is a front view showing an embodiment of this invention.
The figure is a partially cutaway plan view of Figure 1, and Figure 3 is a graph showing the EGR rate of the engine for each cylinder under various conditions. 1...Surge tank, 4...Communication pipe, 6...Intake manifold, 7...Exhaust gas recirculation pipe, a...
Center line of surge tank.

Claims (1)

[Scope of utility model registration request] A surge tank extends along the cylinder arrangement direction and has an intake inlet opening on a line along the cylinder arrangement direction, and one end is connected to each cylinder and the other end is connected sequentially in the cylinder arrangement direction of the surge tank. A bent part is formed in the intake passage located upstream of the intake manifold, which is made up of multiple branch pipes, and an exhaust gas recirculation pipe is connected to the outside of the bent part, and the supply port of this exhaust gas recirculation pipe is connected to the center of the surge tank. An exhaust gas recirculation device for an engine, characterized in that it is formed near an extension of a line.