JPH08135517A - Exhaust gas cooling device - Google Patents

Abstract

PURPOSE: To improve the heat exchange performance of a heat exchanger by reducing as far as possible a contamination accumulated in an exhaust gas cooling heat exchanger used for EGR(exhaust gas recirculation). CONSTITUTION: A heat exchanger 5 is installed in an intake pipe 1 and, when exhaust gas is recirculated, a door 10 is positioned at solid lines so as to cool the exhaust gas returned from an exhaust manifold into the intake pipe 1 through an interconnecting pipe by the heat exchanger 5. Though the heat exchanger 5 is contaminated with the exhaust gas at this time, the door 10 is positioned at dotted lines when the exhaust gas is not recirculated so as to pass sucked air through the heat exchanger 5. Then contamination is removed by the sucked air.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas cooling device used for EGR (exhaust gas recirculation).

[0002]

2. Description of the Related Art In recent years, EGR (exhaust gas recirculation) has been carried out in order to regulate vehicle exhaust gas and improve fuel efficiency. Recently, there is an increasing need to increase EGR due to the further tightening of regulations. However, since the exhaust gas used for EGR is at a high temperature, increasing the EGR too much deteriorates the intake efficiency of the engine and eventually causes the output of the engine to be reduced.

In order to solve this problem, a device for cooling the exhaust gas used for EGR may be provided. As a conventional technique of such a cooling device, for example, Japanese Utility Model Publication 1-88.
There is a 77 publication. This is configured such that exhaust gas flows inside an element composed of a pair of upper and lower metal plates, and engine cooling water flows along the outer periphery of the element, whereby heat exchange between exhaust gas and engine cooling water is performed. There is.

[0004]

However, in the above apparatus, since the medium flowing inside the element is the exhaust gas, dirt such as soot accumulates inside the element due to long-term use, which deteriorates the heat exchange performance. Cause. In view of the above problems, the present invention aims to improve the heat exchange performance of a heat exchanger in an exhaust gas cooling device used for EGR by minimizing the accumulation of dirt in a heat exchanger that cools the exhaust gas. With the goal.

[0005]

In order to achieve the above object, in the invention according to claim 1, among the exhaust gas flowing through the exhaust pipe (18) of the engine (16), the engine (1
6) The intake pipe (1, 1) is connected via a communication passage (11, 20) communicating the exhaust pipe (18) and the intake pipe (1, 17).
In the exhaust gas cooling device for cooling the exhaust gas recirculated to 7), the inside of the intake pipe (1, 17) is connected to the intake pipe (1, 17) and the communication passage (11, 20). A heat exchanger (5) for cooling the exhaust gas from the communication passages (11, 20) is provided at a site downstream of the connection portion (9).

According to a second aspect of the invention, in the exhaust gas cooling device according to the first aspect, the intake pipe (1,1)
A heat exchange passage (3) through which the intake air passes through the heat exchanger (5) and a bypass passage (4) through which the intake air bypasses the heat exchanger (5) are formed in the inside of (7), and the connection portion ( 9) Heat exchange passage opening / closing means (10, 12, 14, 15, 2) for opening / closing the heat exchange passage (3) at a position upstream of the heat exchange passage.
2, 23) are provided to control the heat exchange passage opening / closing means (10, 12, 14, 15, 22, 23) so as to close the heat exchange passage (3) when the recirculation is permitted. At the same time, the heat exchange passage opening / closing means (1) is configured to open the heat exchange passage (3) when the recirculation is prohibited.
0, 12, 14, 15, 22, 23) are provided for opening / closing control means (step 200, step 500).

According to a third aspect of the present invention, in the exhaust gas cooling device according to the second aspect, the heat exchange passage opening / closing means (10, 12, 14, 15, 22, 23) includes the heat exchange passage (3 ) When closing the communication passage (11, 2
0) is opened, and the communication passages (11, 20) are closed when the heat exchange passage (3) is opened.

According to a fourth aspect of the invention, in the exhaust gas cooling device according to any one of the first to fourth aspects,
The heat exchanger (5) is configured such that a medium having a temperature lower than that of the exhaust gas and higher than that of the intake air flows through the inside of the heat exchanger (5). Adjustment means (8) for adjusting the inflow amount of the medium is provided, and is configured to inhibit the inflow of the medium into the heat exchanger (5) when the recirculation is inhibited. Is characterized by.

The reference numerals in parentheses of the above means indicate the correspondence with the concrete means of the embodiments described later.

[0010]

According to the invention described in claim 1, since the heat exchanger is provided in the inside of the intake pipe at a portion downstream of the connecting portion between the intake pipe and the communication passage, the recirculation is performed. When allowed, the exhaust gas returned from the connecting portion into the intake pipe flows through the heat exchanger and is cooled. Further, since this heat exchanger is provided inside the intake pipe, clean intake air flows through the heat exchanger. Therefore, even if dirt such as soot accumulates in the heat exchanger when the exhaust gas flows through the heat exchanger, the dirt is removed by clean intake air, so that the dirt accumulated in the heat exchanger is reduced and the heat exchange The heat exchange performance of the vessel is improved.

According to the second aspect of the present invention, the heat exchanger is provided in the heat exchange passage of the heat exchange passage and the bypass passage formed inside the intake pipe, and further on the upstream side of the connecting portion. A heat exchange passage opening / closing means for opening / closing the heat exchange passage in the portion is provided. Then, by the control of the control means of the opening / closing control means, when the recirculation is allowed, the heat exchange passage in the portion is closed, thereby preventing intake air from being mixed into the heat exchange passage downstream of the connecting portion. To be

Therefore, when the recirculation is permitted, the exhaust gas returned from the connecting portion into the heat exchanger passage flows into the heat exchanger without being mixed with intake air. Therefore, since the temperature of the exhaust gas before flowing through the heat exchanger becomes higher than that when the returned exhaust gas flows through the heat exchanger in a state of being mixed with intake air, the heat exchange rate in the heat exchanger is high. As a result, the exhaust gas temperature after passing through the heat exchanger can be lowered.

Further, when the recirculation is prohibited, the heat exchange passage in the portion is opened so that the intake air flows through the heat exchanger. At this time, since the exhaust gas does not flow through the heat exchanger, the dirt accumulated in the heat exchanger is removed by the intake air. Further, in the third aspect of the invention, since both the means for opening / closing the heat exchange passage and the means for opening / closing the communication passage are used as the heat exchange passage opening / closing means, the number of parts can be reduced.

According to the fourth aspect of the invention, when the recirculation is prohibited, that is, when the exhaust gas is not passed through the heat exchanger, the medium having a temperature higher than that of the intake air does not flow through the heat exchanger. Therefore, the intake air can be prevented from being heated by the heat exchanger, which can prevent the engine output from being lowered due to the intake air temperature becoming high.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a partial cross-sectional view showing the main part of this embodiment. In FIG. 1, reference numeral 1 denotes an intake pipe that constitutes a passage for intake air (about 40 to 50 ° C.) flowing from the left to the right in the drawing. A partition plate 2 is provided inside the intake pipe 1, and a first passage 3 and a second passage 4 are formed inside the intake pipe 1 by the partition plate 2.

A heat exchanger 5 is provided in the first passage 3. This heat exchanger 5 is a medium (specifically, engine cooling water, which is introduced into the heat exchanger 5 through an inlet hot water pipe 6).
About 70 to 80 (° C.)) and the exhaust gas (about 400 to 500 (° C.)) flowing through the first passage 3 are heat-exchanged, and the engine cooling water after heat exchange is discharged from the outlet hot water pipe 7. To be done. Further, the inlet hot water pipe 6 is provided with a hot water valve 8 which opens and closes a passage of the inlet hot water pipe 6, and the amount of cooling water flowing into the heat exchanger 5 is adjusted by opening and closing the hot water valve. .

An opening 9 for introducing exhaust gas, which will be described later, into the first passage 3 is provided in a portion of the wall surface of the intake pipe 1 facing the first passage 3 and upstream of the heat exchanger 5. Are formed. Further, a door 10 that rotates between a solid line position and a broken line position in the drawing is provided at a position upstream of the opening 9 in the first passage 3. One end of a pipe 11 is connected to the opening 9 and the diaphragm portion 1 having a diaphragm 12 at the other end of the pipe 11.
3 is provided. A negative pressure from a vacuum pump (see FIG. 2), which will be described later, is applied to a chamber 13a of the diaphragm portion 13 below the diaphragm 12 in the figure via a negative pressure inlet 13b. When this negative pressure is applied, a force acts on the diaphragm 12 in the direction of pushing it down in the figure.

Further, an elastic body 14 (specifically, a coil spring) is provided in the chamber 13a for exerting a force for pushing the diaphragm 12 upward in the drawing. The elastic force of the coil spring 14 and the negative pressure are provided. The position of the diaphragm 12 is determined by the balance with the force. When the diaphragm 12 is vertically displaced in the drawing, the door 10 is rotated between the solid line position and the broken line position in the drawing via the connecting rod 15 that connects the diaphragm 12 and the door 10.

Further, the protruding pipe 1 is provided on the side surface side of the pipe 11.
1a is formed, and a connecting pipe 19 (see FIG. 2) communicating with the exhaust manifold 17 (see FIG. 2) is connected to the protruding pipe 11a. Then, exhaust gas described later is introduced into the pipe 11 through the projecting pipe 11a. That is, in this embodiment, the communication passage referred to in the invention of claim 1 is constituted by the pipe 11 and the communication pipe 19.

Next, the overall structure of this embodiment will be described with reference to FIG. In the figure, 16 is a diesel engine. Reference numerals 17 and 18 in the drawing denote an engine intake manifold and an exhaust manifold, respectively.
Is a mission. And as shown in the figure, the intake pipe 1
The downstream end of the is connected to the intake manifold 17. Further, a communication pipe 20 that communicates with the exhaust manifold 18 is connected to the protruding pipe 11a.

A vacuum pump 22 is connected to the negative pressure inlet 13b via a negative pressure passage 21. In the middle of the negative pressure passage 21, a negative pressure control valve 23 for controlling the magnitude of the negative pressure applied to the chamber 13a is provided.
The negative pressure control valve 23 is controlled based on a control signal from the engine control device 24. This control device 24 is a well-known device having a microcomputer, an A / D converter, etc., which are not shown, inside thereof, and a water temperature sensor 25 for detecting the engine cooling water temperature, a rotation speed sensor 26 for detecting the engine speed, a throttle valve The signal from the throttle position sensor 27 or the like for detecting the opening of the A / D converter is A / D converted by the A / D converter, and the microcomputer performs a predetermined calculation described later based on the A / D converted signal. The control signal is output to the negative pressure control valve 23 based on the calculation result.

Next, the operation of the above configuration will be described with reference to the flowchart of FIG. First, when an automatic control process of the control device 24 is started in step 100 by turning on an ignition key (not shown), in the next step 200, the negative pressure control valve 23 is controlled so that a negative pressure is applied to the chamber 13a. To do. Then, this negative pressure causes the diaphragm 12 to overcome the elastic force of the coil spring 14 and be pushed downward in FIG. Then, the door 10 is at the position indicated by the broken line in the figure, and the communication passage is closed and the first passage 3 is opened.

At this time, since the communication passage is closed by the door 10, recirculation (EGR) of exhaust gas from the exhaust manifold 18 into the intake pipe 1 is prohibited. Here, the reason why the recirculation is prohibited is to avoid deterioration of the starting characteristic of the engine 16 due to recirculation of exhaust gas having a low oxygen concentration. Further, at this time, the first passage 3 is opened so that clean intake air flows through the heat exchanger 5.

Then, in the next step 300, it is determined based on the value of the water temperature sensor 25 whether or not the engine cooling water temperature is equal to or higher than a predetermined temperature (45 (° C.) in this embodiment).
That is, it is determined whether the engine 16 has warmed enough to improve the output performance of the engine 16. The process of step 200 is performed until it is determined to be YES, and the engine 16
Improve the starting characteristics of.

If YES is determined, it is then determined in step 400 whether the load on the engine 16 is large (for example, during acceleration) based on the values of the rotation speed sensor 26 and the throttle position sensor 27. If it is determined to be larger (YES), the process returns to step 200 again. Here, the process returns to step 200 in order to improve the engine output characteristic by prohibiting the recirculation when the load is high.

On the other hand, if it is determined to be small (NO), the negative pressure control valve 23 is closed in step 500. Then, the pressure in the chamber 13a becomes atmospheric pressure, and the coil spring 1
The diaphragm 12 is pushed upward by the elastic force of 4. Then, the door 10 comes to the position shown by the solid line in the figure, the communication passage is opened, and the first communication passage 3 is closed.

At this time, since the communication passage is opened, the recirculation is permitted and the exhaust gas is returned into the first passage 3.
The exhaust gas is cooled by the engine cooling water in the heat exchanger 5, and the cooled exhaust gas and the second passage 4 are cooled.
The intake air that has passed through is mixed with the intake air and is taken into the intake manifold 17. Here, when the exhaust gas is cooled as described above, the heat exchanger 5 may be contaminated by soot of the exhaust gas or the like, and water produced by cooling reacts with the exhaust gas component to generate a highly corrosive acidic liquid. There is a nature.
However, in this embodiment, the exhaust gas is prevented from entering the first passage 3 from the time when the engine 16 is started until the water temperature reaches the predetermined temperature or when the engine is under a high load, that is, when the recirculation is not performed. In addition, clean intake air is made to flow through the heat exchanger 5.

Therefore, since the dirt of the heat exchanger 5 is removed by the intake air at this time, the dirt accumulated in the heat exchanger 5 is reduced and the heat exchange performance of the heat exchanger 5 is improved. In addition, since the heat exchanger 5 is less likely to be contaminated with dirt, the possibility that the acidic liquid will be generated is reduced. Further, in this embodiment, when the recirculation is performed, the door 10 closes the first passage 3 to prevent intake air from entering the first passage 3. In this case, the temperature of the exhaust gas passing through the heat exchanger 5 can be increased as compared with the case where the intake air enters the first passage 3. As a result, the temperature difference between the temperature of the engine cooling water in the heat exchanger 5 and the temperature of the exhaust gas passing through the heat exchanger 5 becomes large, so the exhaust gas that is discarded to the outside of the intake pipe 1 via the heat exchanger 5. The amount of heat of the gas can be increased, and as a result, the temperature of the intake air taken into the intake manifold 17 can be lowered.

Still in this embodiment, means for opening / closing the first passage 3 and means for opening / closing the communication passage are provided in the door 10, the diaphragm 12, the coil spring 14, the connecting rod 15, the vacuum pump 22, and the negative pressure control valve 23. Since they are also used, the number of parts can be reduced as compared with the case where each means is provided separately. Further, in this embodiment, means for achieving the object of the present invention are as follows: the intake pipe 1 is connected to the intake manifold 17, the communicating pipe 20 is connected to the protruding pipe 11a, and the negative pressure passage is connected to the negative pressure introducing port 13b. Since 21 is connected, the means is compact and the same can be applied to various vehicle types.

(Other Embodiments) When the above-mentioned recirculation is not performed, that is, when the door 10 is at the position shown by the broken line in the figure, the hot water valve 8 may be controlled so as to close the inlet hot water pipe 6. As a result, the intake of about 40 to 50 (° C) is about 7
It is possible to prevent heating by engine cooling water of 0 to 80 (° C).

In each of the above-mentioned embodiments, the first pipe is provided in the intake pipe 1.
An example in which the passage 3 and the second passage 4 are provided and the heat exchanger 5 is provided only in the first passage 3 has been described, but such a passage is not provided, and heat is exchanged over the entire passage in the intake pipe 1. The device 5 may be provided. Even in this case, when the recirculation is prohibited, the heat exchanger is dirty by the intake air.

[Brief description of drawings]

FIG. 1 is a partial sectional view showing an essential part of an embodiment of the present invention.

FIG. 2 is an overall configuration diagram of the above embodiment.

FIG. 3 is a control flowchart of a control device 23 of the above embodiment.

[Explanation of symbols]

1 ... Intake pipe, 3 ... 1st passage (heat exchanger passage), 4 ... 2nd
Passage (bypass passage), 5 ... Heat exchanger, 8 ... Hot water valve (adjusting means), 9 ... Opening (connecting portion), 10 ... Door (heat exchange passage opening / closing means), 16 ... Engine, 17 ... Intake manifold ( Intake pipe), 18 ... Exhaust manifold (exhaust pipe), 20 ... Communication pipe (communication passage), 2
2 ... Vacuum pump, 23 ... Negative pressure control valve, 24 ... Control device

Claims (4)

[Claims] 1. An exhaust gas cooling device for cooling, of exhaust gas flowing through an exhaust pipe of an engine, exhaust gas recirculated to the intake pipe through a communication passage that connects the exhaust pipe of the engine and the intake pipe. In the inside of the intake pipe, a heat exchanger that cools the exhaust gas from the communication passage is provided at a site downstream of a connection portion between the intake pipe and the communication passage. Exhaust gas cooling device. 2. A heat exchange passage through which the intake air passes through the heat exchanger and a bypass passage through which the intake air bypasses the heat exchanger are formed inside the intake pipe, and the heat exchange passage is provided at a portion upstream of the connection portion. A heat exchange passage opening / closing means for opening / closing the heat exchange passage is provided, the heat exchange passage opening / closing means is controlled to close the heat exchange passage when the recirculation is permitted, and the recirculation is prohibited. The exhaust gas cooling device according to claim 1, further comprising opening / closing control means for controlling the heat exchange passage opening / closing means so as to open the heat exchange passage. 3. The heat exchange passage opening / closing means is configured to open the communication passage when closing the heat exchange passage, and to close the communication passage when opening the heat exchange passage. The exhaust gas cooling device according to claim 2. 4. The heat exchanger is configured such that a medium having a temperature lower than that of the exhaust gas and a temperature higher than that of the intake gas flows inside the heat exchanger, and the medium flows into the heat exchanger. 5. An adjusting means for adjusting the amount is provided, and is configured to prohibit the inflow of the medium into the heat exchanger when the recirculation is prohibited. The exhaust gas cooling device as described above.