JP2009191623A - Exhaust gas circulation device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure an early temperature rise in engine oil and the proper temperature of the engine oil by using an EGR cooler. <P>SOLUTION: An EGR valve 16 is arranged in its middle in an EGR passage 15. A first EGR cooler 17 is arranged upstream of the EGR valve 16. A second EGR cooler 18 is arranged downstream of the EGR valve 16. Engine cooling water is supplied to the first EGR cooler 17, and exhaust gas passing through the EGR passage 15 is cooled by this engine cooling water. The engine oil is supplied to the second EGR cooler 18, and heat is exchanged between this engine oil and the exhaust gas passing through this EGR passage 15. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

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

  In recent internal combustion engines, an exhaust gas circulation (EGR) device is generally employed to reduce NOx in the exhaust gas regardless of whether it is a gasoline engine, a diesel engine, or a rotary engine. In a gasoline engine, pumping loss can be reduced by EGR, so that exhaust gas recirculation is performed by EGR in a partial load region. In a diesel engine, a large amount of EGR tends to be performed to significantly reduce NOx.

  Patent Document 1 discloses that engine oil is used as a refrigerant of an EGR cooler for cooling the exhaust gas recirculated to the intake system. Specifically, the invention disclosed in Patent Document 1 raises the temperature of the engine oil early at the start of the engine, and if the engine oil becomes too hot, the viscosity decreases and it becomes difficult to form an appropriate oil film. In order to prevent this, in addition to cooling the engine oil with an oil cooler that uses engine cooling water as a refrigerant, an EGR cooler that uses engine oil as a refrigerant is installed in the EGR device. And EGR cooler to cool the EGR gas while cooling the engine oil, but when the engine is started or at low load, the engine oil is stopped to be supplied to the oil cooler and the oil cooler is bypassed. By supplying the oil to the EGR cooler, the temperature of the engine oil is raised quickly.

Japanese Patent Laid-Open No. 2005-295992

  The invention disclosed in Patent Document 1 uses an oil cooler and an EGR cooler in combination to ensure an early rise in engine oil temperature and an appropriate engine oil temperature.

  An object of the present invention is to provide an exhaust gas circulation device for an internal combustion engine that can quickly raise the temperature of engine oil and ensure an appropriate temperature of the engine oil using an EGR cooler.

According to the present invention, the above technical problem is
An EGR passage connecting an exhaust passage through which engine exhaust gas passes and an intake passage for supplying air to the engine;
An EGR valve that is interposed in the EGR passage and adjusts the flow rate of exhaust gas recirculated from the exhaust passage to the intake passage;
First and second EGR coolers interposed in the EGR passage;
Exhaust gas passing through the first EGR cooler is subjected to heat exchange with engine cooling water or air supplied to the first EGR cooler,
The exhaust gas passing through the second EGR cooler exchanges heat with the engine oil supplied to the second EGR cooler,
This is achieved by providing an exhaust gas circulation device for an internal combustion engine, wherein the second EGR cooler is disposed downstream of the first EGR cooler in the exhaust gas flow direction of the EGR passage.

  That is, an air-cooled or water-cooled first EGR cooler is disposed upstream of the second EGR cooler, engine oil is supplied to a second EGR cooler located downstream of the first EGR cooler, and engine oil and exhaust gas are supplied by the second EGR cooler. Therefore, when the engine is cold, the temperature of the engine oil can be raised quickly by the heat of the exhaust gas. Further, by disposing the second EGR cooler downstream by the first EGR cooler, the exhaust gas cooled by the first EGR cooler can be heat-exchanged with the engine oil by the second EGR cooler, so that an appropriate temperature of the engine oil can be ensured. it can.

  In a preferred embodiment of the present invention, the EGR valve is disposed upstream of the second EGR cooler. As a result, in an operating state where the exhaust gas is excessively hot, the EGR valve can be fully closed to prevent the exhaust gas from entering the second EGR cooler, thereby suppressing an excessive temperature rise of the engine oil. be able to.

  In a preferred embodiment of the present invention, the EGR valve is disposed downstream of the first EGR cooler. As a result, when the exhaust gas is excessively hot, the EGR valve can be fully closed to prevent the exhaust gas from entering the second EGR cooler, and the first EGR cooler positioned upstream from the EGR valve. Since the exhaust gas can be cooled by the above, it is possible to prevent an excessively high temperature exhaust gas from attacking the EGR valve and causing a thermal damage to the EGR valve, thereby prematurely degrading the EGR valve. Can be suppressed.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  In FIG. 1, 1 is a water-cooled gasoline engine, and a combustion chamber 5 is defined by a cylinder block 2, a cylinder head 3, and a piston 4. The cylinder head 3 is formed with an intake port 6 and an exhaust port 7 that face the combustion chamber 5. The intake port 6 is opened and closed by an intake valve 8, and the exhaust port 7 is opened and closed by an exhaust valve 9. Reference numeral 10 in FIG. 1 is a fuel injection valve. A spark plug is disposed on the top of the combustion chamber 5.

  A throttle valve 12 is disposed in the intake passage 11 connected to the intake port 6, and air purified by an air cleaner (not shown) is supplied to the intake passage 11. On the other hand, an exhaust gas purification catalyst 14 is disposed in the exhaust passage 13 connected to the exhaust port 7, and the exhaust gas emitted from the exhaust port 7 is purified by the exhaust gas purification catalyst 14 and then released to the outside.

  The intake passage 11 and the exhaust passage 13 are connected to each other by an EGR passage 15. The EGR passage 15 is provided with an EGR valve 16 in the middle thereof, and the flow rate of exhaust gas recirculated to the intake passage 11 through the EGR passage 15 is adjusted by the EGR valve 16.

  The EGR passage 15 is provided with a first EGR cooler 17 in a passage portion on the upstream side of the EGR valve 16, that is, a passage portion 15 a on the exhaust passage 13 side, and on the other hand, a passage portion on the downstream side of the EGR valve 16, that is, an intake passage. A second EGR cooler 18 is disposed in the passage portion 15b on the 11th side. By opening the EGR valve 16, the exhaust gas in the exhaust passage 13 is recirculated to the intake passage 11 through the EGR passage 15, while the recirculation of the exhaust gas is stopped by closing the EGR valve 16.

  Engine cooling water is supplied to the first EGR cooler 17, and the exhaust gas (EGR gas) passing through the EGR passage 15 is cooled by the engine cooling water. That is, the refrigerant of the first EGR cooler 17 is engine cooling water. On the other hand, engine oil is supplied to the second EGR cooler 18, and heat exchange is performed between the engine oil and exhaust gas (EGR gas) passing through the EGR passage 15.

  In FIG. 2, U is a controller (control unit) configured using a microcomputer, and EGR control as will be described later is performed by this controller U. The controller U includes an engine speed sensor 20 for detecting the engine speed and an accelerator position sensor 21 for detecting an accelerator position as an engine load, as well as an intake system for detecting the temperature of air introduced into the intake passage 11. Signals such as an air temperature sensor 22, an intake pressure sensor 23 that detects the pressure of the intake passage 11, and an intake air amount sensor 24 that detects the amount of air introduced into the intake passage 11 are input. The controller U controls the EGR valve 16, the throttle valve 12, and the fuel injection valve 10 described above.

  The outline of the control by the controller U will be described. FIG. 3 shows the division of the EGR execution region using the engine speed and the accelerator opening as parameters. In other words, the EGR valve 16 is opened and exhaust gas recirculation is executed through the EGR passage 15 in the first region where the rotation is low and the load is a predetermined load or less (partial load). On the other hand, in the second region where the engine speed is high or the load is high, the EGR valve 16 is closed and the exhaust gas recirculation is stopped.

  Next, an example of EGR return control by the controller U will be described with reference to the flowchart of FIG. In the following description, “S” indicates a step. First, after signals from various sensors are read in S1, it is determined in S2 whether or not the current operating state is the first region from the engine speed and the accelerator opening. When the determination in S2 is YES, the process proceeds to S3, and EGR for returning the exhaust gas in the exhaust passage 13 to the intake passage 11 is executed. On the other hand, when it is determined NO in S2, it is determined that the current operation state is the second region, the process proceeds to S4, the EGR valve 16 is fully closed, and the exhaust gas recirculation is stopped.

  In the above-described embodiment, since engine cooling water is used as the refrigerant of the first EGR cooler 17 on the exhaust passage 13 side, the hot engine exhaust gas passing through the exhaust passage 13 is used to quickly cool engine cooling water. The temperature can be raised. Further, the engine oil in the cold state can be raised in temperature early using the heat of the exhaust gas passing through the EGR passage 15.

  Further, when the engine speed is 2000 to 3000 rpm, the temperature of the exhaust gas becomes 500 to 700 ° C., but the exhaust gas after being taken into the EGR passage 15 and water-cooled with the engine cooling water in the first EGR cooler 17 is 100 to 200. The temperature drops to ° C. Therefore, in the process in which the exhaust gas whose temperature has been lowered to 100 to 200 ° C. passes through the passage portion 15b on the intake passage 11 side, the second EGR cooler 18 exchanges heat with the engine oil so that the engine oil has a temperature of 80 to 100 ° C. It becomes easy to maintain at an appropriate temperature.

  Further, since the EGR valve 16 is closed in the second region of FIG. 3, that is, the high rotation or high load region, the engine oil passing through the second EGR cooler 18 is not unnecessarily heated. In the second region where the EGR valve 16 is fully closed, the heat of the exhaust gas that has entered the passage portion 15a on the exhaust passage 13 side in the EGR passage 15 is cooled by water by the first EGR cooler 17, so that the temperature is extremely high. It is possible to prevent the heat of the exhaust gas from directly attacking the EGR valve 16 and causing thermal damage to the EGR valve 16.

  As described above, the embodiment of the present invention has been described. When the engine 1 is, for example, an air-cooled type, air is used as the refrigerant of the first EGR cooler 17, and the outside air is forcibly supplied to the first EGR cooler 17 to be supplied to the first EGR cooler. The exhaust gas passing through 17 may be air-cooled.

1 is an overall schematic diagram of an embodiment. It is a block diagram which shows the whole system | strain of EGR control. It is a figure which shows the example of a setting of the area | region which performs EGR control. It is a flowchart which shows the outline | summary of an example of EGR control.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Gasoline engine 6 Intake port 7 Exhaust port 11 Intake passage 13 Exhaust passage 14 Exhaust gas purification catalyst 15 EGR passage 16 EGR valve 17 1st EGR cooler 18 2nd EGR cooler

Claims (4)

An EGR passage connecting an exhaust passage through which engine exhaust gas passes and an intake passage for supplying air to the engine;
An EGR valve that is interposed in the EGR passage and adjusts the flow rate of exhaust gas recirculated from the exhaust passage to the intake passage;
First and second EGR coolers interposed in the EGR passage;
Exhaust gas passing through the first EGR cooler is subjected to heat exchange with engine cooling water or air supplied to the first EGR cooler,
The exhaust gas passing through the second EGR cooler exchanges heat with the engine oil supplied to the second EGR cooler,
The exhaust gas circulation device for an internal combustion engine, wherein the second EGR cooler is disposed downstream of the first EGR cooler in the exhaust gas flow direction of the EGR passage.   The exhaust gas circulation device for an internal combustion engine according to claim 1, wherein the EGR valve is disposed upstream of the second EGR cooler.   The exhaust gas circulation device for an internal combustion engine according to claim 2, wherein the EGR valve is disposed downstream of the first EGR cooler.   The exhaust gas circulation device for an internal combustion engine according to any one of claims 1 to 3, wherein the EGR valve is fully closed in a high load, high rotation region.

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