JP2004278351A - Exhaust gas recirculating device of engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To recirculate EGR gas to an intake system without flowing backward even if pulsation is generated in exhaust gas of an engine by housing an EGR valve and a reed valve in a small space. <P>SOLUTION: An EGR passage is provided with the EGR valve 16 for opening-closing an EGR passage 14 by an operation state of the engine 11, and the reed valve 17 for allowing a flow of the exhaust gas to an intake passage 12 from an exhaust passage 13, and checking an inverse flow. The EGR valve is a butterfly valve having an EGR valve body 16a and a valve driving means 16b. The EGR passage is provided with a bypass passage 14a having both ends respectively communicating with the exhaust passage side and intake passage side EGR passages from a rotary shaft 16d of the EGR valve body. The other end of the bypass passage is opening-closed by the reed valve. The EGR valve body rotates between a fully closing position for closing both the EGR passage and the bypass passage, a half-opening position for closing the EGR passage, and opening the bypass passage, and a fully opening position for opening both the EGR passage and the bypass passage. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an exhaust gas recirculation system for an engine that extracts a part of exhaust gas from an engine from an exhaust system and recirculates the exhaust gas to an intake system to reduce NOx.
[0002]
[Prior art]
Conventionally, as this type of exhaust gas recirculation device, an EGR valve that controls the amount of EGR gas is provided in an EGR passage that connects an exhaust passage and an intake passage while bypassing an engine. 2. Description of the Related Art There is known an EGR device provided with a reed valve for allowing a flow in one direction and preventing a flow in a reverse direction (for example, see Patent Document 1). In this EGR device, a turbocharger is mounted on the engine, and an inflow preventing portion that prevents passage of components of the reed valve is provided in an EGR passage or an intake passage downstream of the reed valve.
[0003]
In the EGR device configured as described above, even if the rotation speed of the engine is in a low or medium speed range and the engine load is in a medium or high load range, that is, the average boost pressure of the turbocharger is increased. Is higher than the average exhaust pressure, the reed valve opens and recirculates the EGR gas to the intake side when the boost pressure instantaneously becomes smaller than the exhaust pressure using the exhaust pulsation, thereby reducing NOx. Emissions can be reduced. Also, even if the reed valve is damaged and the reed and other parts of the reed valve flow into the EGR passage, the reed valve can be captured by the inflow prevention portion, so that the above-mentioned parts can be prevented from entering the engine. .
[0004]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 2000-64913
[Problems to be solved by the invention]
However, in the conventional EGR device disclosed in Patent Document 1, the EGR valve and the reed valve are provided independently of each other in the EGR passage, and a relatively large amount of EGR gas when the EGR valve is fully opened has a small displacement amount. In order to pass through the reed valve, it is necessary to increase the size of the lead itself of the reed valve and the area of the hole opened and closed by the reed.
SUMMARY OF THE INVENTION It is an object of the present invention to provide an EGR valve and a reed valve that can be accommodated in a relatively small space, and that even if pulsation occurs in the exhaust gas of the engine, the EGR gas can be recirculated to the intake system without backflow. It is to provide a circulation device.
[0006]
[Means for Solving the Problems]
As shown in FIGS. 1 and 2, the invention according to claim 1 includes an EGR passage 14 having one end connected to an exhaust passage 13 of the engine 11 and the other end connected to an intake passage 12 of the engine 11, and an EGR passage 14. An EGR valve 16 provided to open and close the EGR passage 14 according to the operating condition of the engine 11, and a reed valve 17 provided in the EGR passage 14 to allow the flow of exhaust gas from the exhaust passage 13 to the intake passage 12 and prevent the reverse flow. An improved exhaust gas recirculation system for an engine comprising:
The characteristic configuration is that the EGR valve 16 is constituted by a butterfly valve having an EGR valve main body 16a rotatably provided in the EGR passage 14 and a valve driving means 16b for driving the EGR valve main body, and one end of the EGR valve is EGR. A bypass passage 14a communicating from the rotation shaft 16d of the valve body 16a to the EGR passage 14 on the exhaust passage 13 side and the other end communicating from the rotation shaft 16d of the EGR valve body 16a to the EGR passage 14 on the intake passage 12 side is EGR. The EGR valve body 16a is provided in the passage 13 so as to open and close the other end of the bypass passage 14a, and the EGR valve main body 16a closes both the EGR passage 14 and the bypass passage 14a. Between a half-open position for closing the bypass passage 14a and a fully open position for opening both the EGR passage 14 and the bypass passage 14a. Some where that is configured to be rotatable.
[0007]
In the exhaust gas recirculation system for an engine according to the first aspect, the exhaust gas discharged from the engine 11 has a pulsation in an extremely low speed rotation range of the engine 11 during idling or a transient operation range of the engine 11 during acceleration or the like. However, when the pressure in the bypass passage 14a becomes higher than the pressure in the EGR passage 14 on the intake passage 12 side, the other end of the bypass passage 14a is opened by the reed valve 17, so that the exhaust gas is discharged. Then, the air is returned to the engine 11 through the intake passage 12. When the pressure in the bypass passage 14a becomes smaller than the pressure in the EGR passage 14 on the side of the intake passage 12, the reed valve 17 does not open the other end of the bypass passage 14a. There is no backflow from the 12 side to the exhaust passage 13 side.
When it is not preferable to flow the exhaust gas into the EGR passage 14, for example, when the exhaust gas contains a large amount of hydrocarbons or the like, the EGR valve main body 16a is located at the fully closed position. As a result, exhaust gas containing a large amount of hydrocarbons does not flow into the EGR passage 14 at all.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, a first embodiment of the present invention will be described with reference to the drawings.
As shown in FIGS. 1 and 2, the intake port of the diesel engine 11 of the vehicle is connected to an intake pipe 12b via an intake manifold 12a, and the exhaust port is connected to an exhaust pipe 13b via an exhaust manifold 13a. . One end of an EGR pipe 14 is connected to the exhaust manifold 13a, and the other end of the EGR pipe 14 is connected to the intake pipe 12b. The EGR pipe 14 includes an EGR valve 16 that opens and closes the EGR pipe 14 according to the operation state of the engine 11, a reed valve 17 that allows the flow of exhaust gas from the exhaust manifold 13a to the intake pipe 12b, and blocks the reverse flow. Is provided. Further, an EGR cooler 18 for cooling exhaust gas flowing through the EGR pipe is provided in the EGR pipe 14 on the intake pipe 12b side of the EGR valve 16. The intake manifold 12a and the intake pipe 12b constitute an intake passage 12, and the exhaust manifold 13a and the exhaust pipe 13b constitute an exhaust passage 13.
[0009]
The EGR valve 16 is constituted by a butterfly valve, and has an EGR valve main body 16a rotatably provided in the EGR pipe 14, and valve driving means 16b for driving the EGR valve main body. The EGR valve body 16a is formed in a disk shape, and has a through hole 16c extending from one peripheral edge to the other peripheral edge through the center. A rotation shaft 16d is rotatably inserted into the EGR pipe 14, and the EGR valve main body 16a is fixed to the rotation shaft 16d by fitting the through hole 16c into the rotation shaft 16d. The valve drive means 16b is a DC motor in this embodiment, and a power transmission means 19 is provided between the output shaft 16e and the rotation shaft 16d of the DC motor 16b.
[0010]
The power transmission means 19 includes a pinion 19a fitted to the output shaft 16e, a rack 19b meshing with the pinion and extending in the longitudinal direction of the EGR pipe 14, and a lever 19c connecting one end of the rack to the rotating shaft 16d. And The rack 19b is slidably held by a slide bearing 19d, and an elongated hole 19e extending in a direction perpendicular to the EGR pipe 14 is formed at one end of the rack 19b. A base end of the lever 19c is fitted on a rotation shaft 16d protruding from the EGR pipe 14, and a pin 19f is slidably inserted into the elongated hole 19e at a tip end of the lever 19c. The rack 19b, the lever 19c, and the slide bearing 19d are housed in a case (not shown). The case is mounted on the outer peripheral surface of the EGR pipe 14, and the DC motor 16b is mounted on the outer surface of the case.
[0011]
On the other hand, on the peripheral wall of the EGR pipe 14 near the EGR valve 16, a bypass passage 14a that bypasses the rotation shaft 16d is provided. One end of the bypass passage 14a communicates with the EGR pipe 14 on the exhaust manifold 13a side from the rotating shaft 16d of the EGR valve body 16a, and the other end connects to the EGR pipe 14 on the intake pipe 12a side from the rotating shaft 16d of the EGR valve body 16a. It is configured to communicate with The reed valve 17 is mounted so as to open and close the other end of the bypass passage 14a. Specifically, the reed valve 17 is formed of a leaf spring, and one end of the reed valve 17 is fixed to an inner wall of the EGR pipe 14 near the other end of the bypass passage 14a by a bolt 21. Thereby, the reed valve 17 is configured to open and close by the differential pressure in the EGR pipe 14 and the bypass passage 14a.
[0012]
Further, the EGR valve main body 16a is in a fully closed position (a position indicated by a solid line in FIG. 1) for closing both the EGR pipe 14 and the bypass passage 14a, and a half-open position (FIG. 1) for closing the EGR pipe 14 and opening the bypass passage 14a. 1 and a fully open position (a position indicated by a two-dot chain line in FIG. 1) that opens both the EGR pipe 14 and the bypass passage 14a. When the EGR valve body 16a is at the fully closed position, the peripheral edge of the EGR valve body 16a is in close contact with the valve seat 14b formed in the EGR pipe 14, so that one end of the bypass passage 14a and the EGR pipe 14 are fully closed. Thus, the flow of exhaust gas from the exhaust manifold 13a to the intake pipe 12b is completely stopped. When the EGR valve main body 16a is located at the half-open position, one end of the bypass passage 14a is opened and the EGR pipe 14 is substantially closed (the gap between the outer peripheral surface of the EGR valve main body 16a and the inner peripheral surface of the EGR pipe 14). Is formed, so that the exhaust gas slightly flows through this gap.) Further, when the EGR valve body 16a is located at the fully open position, one end of the bypass passage 14a and the EGR pipe 14 are fully opened. The DC motor 14b is configured to continuously drive the EGR valve body 16a to the fully closed position, the half open position, and the fully open position in this order or in the reverse order.
[0013]
In the middle of the exhaust pipe 13b, a particulate filter 22 for collecting particulates in exhaust gas is provided. The particulate filter 22 is a catalyst-equipped honeycomb filter having a function as an oxidation catalyst, and has a polygonal cross section partitioned by porous partition walls made of ceramics such as cordierite. The partition walls are coated with a platinum-zeolite catalyst or a platinum-ceria-zeolite catalyst. Further, the exhaust pipe 13b is provided with a hydrocarbon supply means (not shown) for supplying hydrocarbons for burning and removing the particulates accumulated on the particulate filter 22. Although not shown, the hydrocarbon supply means connects a tank for storing light oil (hydrocarbon-based liquid), a nozzle inserted into an exhaust pipe on the exhaust gas upstream side of the particulate filter 22, and a communication between the tank and the nozzle. A pump provided in the supply pipe to supply light oil in the tank to the nozzle.
[0014]
A first pressure sensor 31 for detecting the exhaust gas pressure in the exhaust pipe is provided in the exhaust pipe 13b on the exhaust gas upstream side of the particulate filter 22, and the exhaust pipe 13b on the exhaust gas downstream side of the particulate filter 22 is provided in the exhaust pipe. A second pressure sensor 32 for detecting exhaust gas pressure is provided. Further, a temperature sensor 23 for detecting the temperature of the exhaust gas in the exhaust pipe is provided in the exhaust pipe 13b on the exhaust gas upstream side of the first pressure sensor 31, and the rotational speed of the crankshaft is detected near the crankshaft 11a of the engine 11. A rotation sensor 24 is provided. Further, the load of the engine 11 is detected by the load sensor 26. The control input of the controller 27 is connected to the detection outputs of the first pressure sensor 31, the second pressure sensor 32, the temperature sensor 23, the rotation sensor 24, and the load sensor 26, and the control output of the controller 27 is connected to the DC motor 16b and the pump. Connected. The controller 27 is provided with a memory 28. In this memory, the injection timing of light oil according to the amount of particulates deposited on the particulate filter 22 is stored as a map. Further, the memory 28 stores, as a map, a change in the exhaust gas temperature, a rotation speed of the engine 11, a change in the load of the engine 11, and an opening degree of the EGR valve body 16a according to the presence or absence of the injection of the light oil.
[0015]
The operation of the exhaust gas recirculation device for an engine configured as described above will be described.
In an extremely low-speed rotation range of the engine 11 such as immediately after the engine 11 is started and the warm-up operation is completed or a signal is waited, the controller 27 controls the DC motor 16b based on the detection outputs of the temperature sensor 23, the rotation sensor 24, and the load sensor 26. Control. The rotation of the DC motor causes the rack 19b meshing with the pinion 19a to move in parallel to rotate the lever 19c, and the EGR valve main body 16a reaches the half-open position (the position indicated by the broken line in FIG. 1). At this time, since the rotation speed of the engine 11 is extremely low at about 600 rpm, pulsation occurs in the exhaust gas discharged from the engine 11. However, since one end of the bypass passage 14a is open, when the pressure in the bypass passage 14a becomes larger than the pressure in the EGR pipe 14 on the intake pipe 12b side, the reed valve 17 is elastically deformed and the bypass passage 14a The other end is opened, and the exhaust gas is returned to the engine 11 from the bypass passage 14a through the EGR cooler 18, the intake pipe 12b, and the intake manifold 12a. As a result, the combustion temperature of the fuel in the engine 11 decreases, and the generation of NOx can be suppressed. When the pressure in the bypass passage 14a becomes smaller than the pressure in the EGR pipe 14 on the side of the intake pipe 12b, the reed valve 17 does not open the other end of the bypass passage 14a. There is no backflow from the 12b side to the exhaust manifold 13a side. The controller 27 also controls the DC motor 16b in the transient operation range of the vehicle such as during acceleration, as described above.
[0016]
When the vehicle is traveling at a constant speed, the controller 27 controls the DC motor 16b according to the traveling state, that is, based on the detection outputs of the temperature sensor 23, the rotation sensor 24, and the load sensor 26. Due to the rotation of the DC motor, the rack 19b meshing with the pinion 19a moves in parallel to rotate the lever 19c, and the EGR valve body 16a moves from the half-open position (the position shown by the broken line in FIG. 1) to the fully open position (the two-dot chain line in FIG. 1). (A position indicated by) is temporarily fixed at a predetermined position. As a result, an optimal amount of exhaust gas is returned from the EGR pipe 14 or the EGR pipe and the bypass passage 14a to the engine 11 through the EGR cooler 18, the intake pipe 12b, and the intake manifold 12a. As a result, the combustion temperature of the fuel in the engine 11 decreases, and the generation of NOx can be suppressed.
[0017]
Further, when a predetermined amount or more of particulates accumulates on the particulate filter 22, the differential pressure between the detection outputs of the first and second pressure sensors 31, 32 becomes equal to or more than a predetermined value. At this time, the controller 27 controls the pump to inject light oil from the nozzle, and at the same time, controls the DC motor 16b to rotate the EGR valve body 16a to the fully closed position. Hydrocarbons are generated by the injection of the light oil, and the hydrocarbons are oxidized and burned by the oxidizing action of platinum carried on the particulate filter when flowing into the particulate filter 22, and are captured by the filter 22 by reaction heat generated at this time. The collected particulates are burned. In addition, one end of the bypass passage 14a and the EGR pipe 14 are completely closed by the EGR valve body 16a, and the exhaust gas containing a large amount of hydrocarbons does not flow into the EGR cooler 18, so that the adhesion of the hydrocarbons to the EGR cooler 18 can be prevented. Thus, clogging of the EGR cooler 18 can be prevented.
[0018]
3 and 4 show a second embodiment of the present invention. 1 and 2, the same reference numerals as those in FIGS. 3 and 4 indicate the same parts.
In this embodiment, a turbocharger 51 is mounted on the engine 11. The turbocharger includes a turbine case 51a provided in an exhaust pipe 13b on the exhaust gas upstream side of the particulate filter 22, and a compressor provided in an intake pipe 12b on the intake upstream side of a connection at the other end of the EGR pipe 14. A case 51b and an intercooler 52 provided in the intake pipe 12b between the connection portion at the other end of the EGR pipe 14 and the compressor case 51b to cool intake air compressed by the turbocharger 51 are provided. Although not shown, a turbine wheel is rotatably provided in the turbine case 51a, and a compressor wheel is rotatably provided in the compressor case 51b, and these wheels are connected by a shaft. The compressor wheel rotates via the turbine wheel and the shaft by the energy of the exhaust gas discharged from the engine 11, and the rotation of the compressor wheel compresses the intake air in the intake pipe 12b. The valve driving means 16b of the EGR valve 16 is a stepping motor in this embodiment. An output shaft of the stepping motor 16b is connected to a rotation shaft 16d via a speed reducer 59 as a power transmission means. If the torque of the stepping motor is large, the output shaft of the stepping motor may be directly connected to the rotation shaft. Except for the above, the configuration is the same as that of the first embodiment.
[0019]
In the exhaust gas recirculation device for an engine configured as described above, the stepping motor 56b is used as the valve driving means, and the speed reducer 59 is used as the power transmission means, so that the installation space for these members is smaller than in the first embodiment. Can be smaller. Further, in a transient operation region of the vehicle such as during acceleration, the intake air is supercharged by the turbocharger 51, so that the intake pressure in the intake pipe 12b increases. At this time, the controller 27 controls the stepping motor 56b to rotate the EGR valve body 16a to the half-open position (the position indicated by the broken line in FIG. 1). In addition, although pulsation occurs in the exhaust gas discharged from the engine 11, one end of the bypass passage 14a is open, so that the pressure in the bypass passage 14a becomes larger than the pressure in the EGR pipe 14 on the intake pipe 12b side. Then, the reed valve 17 is elastically deformed, the other end of the bypass passage 14a is opened, and the exhaust gas is returned to the engine 11 from the bypass passage 14a through the EGR cooler 18, the intake pipe 12b, and the intake manifold 12a. As a result, the combustion temperature of the fuel in the engine 11 decreases, and the generation of NOx can be suppressed. The operation other than the above is substantially the same as the operation of the first embodiment, and therefore, the description thereof will not be repeated.
[0020]
In the first embodiment, a DC motor is used as the valve driving means. In the second embodiment, a stepping motor is used as the valve driving means. However, a linear solenoid or an air cylinder may be used. .
In the first and second embodiments, the first pressure sensor, the second pressure sensor, the temperature sensor, the rotation sensor, and the load sensor are connected to the control input. NOx sensor for detecting the NOx concentration of the O ₂ sensor and the exhaust gas for detecting may be connected to a control input to the controller a. With these, the opening degree of the EGR valve can be controlled in accordance with the operating condition, so that NOx emission can be further suppressed.
Further, in the first embodiment, in order to oxidize and burn the particulates deposited on the particulate filter, light oil is injected from a nozzle of the hydrocarbon supply means to generate hydrocarbons, and the hydrocarbons are particulated. The unburned hydrocarbons are supplied to the filter, but unburned hydrocarbons are generated by performing post-injection after the main injection of fuel to the engine without using the hydrocarbon supply means. It may be supplied to a filter.
[0021]
【The invention's effect】
As described above, according to the present invention, the EGR valve is constituted by the butterfly valve having the EGR valve body and the valve driving means, and one end of which is connected to the EGR passage on the exhaust passage side from the rotation axis of the EGR valve body. The other end of the passage communicates with the EGR passage on the intake passage side from the rotation axis of the EGR valve body, the reed valve opens and closes the other end of the bypass passage, and the EGR valve body is in the fully closed position, half open position, and fully open position. Pulsation occurs in the exhaust gas discharged from the engine in the extremely low speed rotation range of the engine or in the transient operation range of the engine, but the pressure in the bypass passage is reduced by the EGR on the intake passage side. When the pressure becomes higher than the pressure in the passage, the other end of the bypass passage is opened by the reed valve. As a result, the exhaust gas is recirculated from the bypass passage to the engine through the intake passage, so that the combustion temperature of the fuel in the engine is reduced and the generation of NOx can be suppressed.
[0022]
When it is not preferable to flow exhaust gas into the EGR passage, only the EGR valve body is positioned at the fully closed position, and no exhaust gas flows into the EGR passage.
Further, in comparison with a conventional EGR device in which the EGR valve and the reed valve are independently provided in the EGR passage to increase the size of the device, the present invention incorporates the reed valve into the butterfly valve type EGR valve. The valve and reed valve can be accommodated in a relatively small space.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing an exhaust gas recirculation device for an engine according to a first embodiment of the present invention.
FIG. 2 is a side view of a main part of an EGR pipe showing a rotation mechanism of an EGR valve main body by a DC motor and power transmission means.
FIG. 3 is a configuration diagram showing an exhaust gas recirculation device for an engine according to a second embodiment of the present invention.
FIG. 4 is a cutaway perspective view of an EGR pipe showing a rotation mechanism of an EGR valve main body by a stepping motor.
[Explanation of symbols]
11 Diesel engine 12 Intake passage 13 Exhaust passage 14 EGR pipe (EGR passage)
14a Bypass passage 16, 56 EGR valve 16a EGR valve main body 16b DC motor (valve driving means)
16d rotating shaft 17 reed valve 56b stepping motor (valve driving means)

Claims (2)

An EGR passage (14) having one end connected to an exhaust passage (13) of the engine (11) and the other end connected to an intake passage (12) of the engine (11); An EGR valve (16) that opens and closes the EGR passage (14) in accordance with the operating condition of the engine (11); and an exhaust gas (13) provided in the EGR passage (14) from the exhaust passage (13) to the intake passage (12). An exhaust gas recirculation system for an engine, comprising: a reed valve (17) for allowing flow and preventing reverse flow,
A butterfly valve having an EGR valve body (16a) in which the EGR valve (16) is rotatably provided in the EGR passage (14) and valve driving means (16b) for driving the EGR valve body (16a); Is composed of
One end communicates with the EGR passage (14) on the exhaust passage (13) side from the rotating shaft (16d) of the EGR valve body (16a), and the other end rotates on the rotating shaft (16d) of the EGR valve body (16a). A bypass passage (14a) communicating with the EGR passage (14) closer to the intake passage (12) is provided in the EGR passage (14);
The reed valve (17) is mounted to open and close the other end of the bypass passage (14a),
The EGR valve body (16) is in a fully closed position in which both the EGR passage (14) and the bypass passage (14a) are closed, and the EGR passage (14) is closed and the bypass passage (14a) is opened. An exhaust gas recirculation device for an engine, wherein the exhaust gas recirculation device is configured to be rotatable between a half-open position to open both the EGR passage (14) and the bypass passage (14a). The valve driving means (16b) is a DC motor, a stepping motor, a linear solenoid or an air cylinder which continuously drives the EGR valve body (16a) to the fully closed position, the half open position and the fully open position in this order or in the reverse order. Item 7. An exhaust gas recirculation device for an engine according to Item 1.

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