JP5521508B2 - Exhaust gas recirculation device for internal combustion engine - Google Patents

Description

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

  Conventionally, for example, as disclosed in Japanese Patent Application Laid-Open No. 2009-91917, an internal combustion engine including an external EGR (Exhaust Gas Recirculation) system is known. The conventional internal combustion engine includes an EGR passage that connects an exhaust passage and an intake passage via an EGR cooler. The conventional internal combustion engine has a bypass passage extending in parallel with the EGR cooler and a switching valve for selectively switching the flow path to the bypass passage in the EGR passage. The above-mentioned conventional internal combustion engine sufficiently exhibits the effect of the charging efficiency improvement control using the exhaust pressure pulsation in the configuration provided with the EGR passage and the EGR cooler by setting the switching valve in a shut-off state under a predetermined condition. Can do.

JP 2009-91917 A JP 2004-332576 A

  In order to suppress overheating of the exhaust catalyst of the internal combustion engine, or in an internal combustion engine equipped with a supercharger, there is a method of increasing the fuel injection amount in order to suppress the temperature of the supercharger. This fuel increase is also referred to as “OT increase”. In order to avoid deterioration in fuel consumption and emission characteristics of exhaust gas, it is desirable to reduce the OT increase as much as possible. Therefore, in an internal combustion engine equipped with an EGR system, there is a method of performing EGR in a relatively high output range in order to reduce the OT increase.

  However, when the load on the internal combustion engine is to be increased, the amount of air also increases, so the EGR amount must be reduced. For this reason, an amount of EGR gas sufficient to prevent overheating of the exhaust catalyst cannot be introduced, the exhaust temperature rises, and accordingly, an increase in OT is required to prevent overheating of the exhaust catalyst. Therefore, in the above-described method using EGR for reducing the OT increase, it is necessary to rely on the OT increase in order to suppress overheating of the exhaust catalyst, and it is difficult to suppress the OT increase to a sufficiently low level.

  An object of the present invention is to provide an exhaust gas recirculation device for an internal combustion engine that can lower the exhaust gas temperature without relying on an increase in OT.

In order to achieve the above object, a first invention is an exhaust gas recirculation device for an internal combustion engine,
An external EGR passage having one end communicating with the exhaust passage of the internal combustion engine and the other end communicating with the intake passage of the internal combustion engine;
An EGR cooler that cools exhaust gas recirculated from the exhaust passage to the intake passage through the external EGR passage;
Recirculation means for returning the exhaust gas cooled by the EGR cooler to the exhaust passage of the internal combustion engine;
With
The reflux means includes
A gas passage in which one end communicates with the downstream side of the EGR cooler in the external EGR passage, and the other end communicates with the exhaust passage;
A gas that preferentially flows gas in the gas passage in a first direction from the downstream side of the EGR cooler toward the exhaust passage as compared to a second direction opposite to the first direction. Direction control means;
With
The gas direction control means includes a check valve attached to the gas passage with an inlet facing a downstream side of the EGR cooler and an outlet facing the exhaust passage .

In addition, the second invention, one of the first invention,
The recirculation means includes switching means capable of switching between execution and stop of recirculation of the exhaust gas cooled by the EGR cooler to the exhaust passage of the internal combustion engine.

The third invention is the first or second invention , wherein
The recirculation means stops or suppresses recirculation of the exhaust gas cooled by the EGR cooler to the exhaust passage of the internal combustion engine when the catalyst provided in the exhaust passage of the internal combustion engine is warmed up. It is characterized by.

Moreover, 4th invention is 2nd invention.
The reflux means has a gas passage in which one end communicates with the downstream side of the EGR cooler in the external EGR passage and the other end communicates with the exhaust passage;
The switching means includes a switching valve provided in the middle of a circulation path formed by a part of the external EGR passage, a joining portion of the external EGR passage and the gas passage, and the gas passage. It is characterized by.

The fifth invention is the fourth invention, wherein
An EGR valve provided in the middle of the external EGR passage for controlling the amount of exhaust gas recirculated to the intake passage;
The switching valve is provided at a position closer to the exhaust passage than the EGR valve in the external EGR passage,
A first state is formed in which the EGR valve is opened and the switching valve is closed. After the first state is formed, the switching valve is opened after a lapse of a predetermined period of time in which the pressure in the external EGR passage becomes negative. The apparatus further comprises negative pressure generation opening control means for forming a second state for closing the EGR valve.

The sixth invention is the fifth invention, wherein
The EGR cooler and / or the EGR catalyst is provided between the EGR valve and the switching valve in the external EGR passage.

The seventh invention is the fifth or sixth invention, wherein
The internal combustion engine includes an exhaust catalyst provided in the exhaust passage,
When the temperature of the exhaust catalyst is equal to or lower than a predetermined temperature, a first state is formed in which the EGR valve is closed and the switching valve is opened, and after the predetermined state has elapsed after the formation of the first state, the EGR valve And an exhaust accumulation control means for forming a second state in which the switching valve is closed, and forming the first state when the temperature of the exhaust catalyst exceeds the predetermined temperature after the formation of the second state. Features.

According to the first aspect of the invention, the exhaust gas cooled by the EGR cooler is returned to the exhaust passage again, so that the exhaust temperature can be lowered regardless of the increase in OT. The external EGR passage and the gas passage form a circulation path, and an exhaust gas flow from the exhaust passage toward the exhaust passage again through the EGR cooler can be created in the circulation path. Further, a check valve is provided in a direction in which the exhaust gas is recirculated in the exhaust passage. Thereby, according to the pulsation of exhaust, the flow of the exhaust gas recirculated from the downstream of the EGR cooler to the exhaust passage can be generated.

According to the second invention, the recirculation of the exhaust gas to the exhaust passage can be executed and stopped at a desired timing.

According to the third invention, when the exhaust catalyst is warmed up or maintained in temperature, the exhaust gas recirculation can be blocked.

According to the fourth invention, the recirculation of the exhaust gas to the exhaust passage can be stopped reliably and easily by closing the valve provided in the middle of the circulation path.

According to the fifth aspect , the external EGR passage can be cleaned.

According to the sixth aspect , in the seventh aspect, the EGR cooler and the EGR catalyst can be cleaned together.

According to the seventh aspect, the exhaust gas can be accumulated when the temperature of the exhaust catalyst is low. Furthermore, when the temperature of the catalyst becomes high, the accumulated exhaust gas can be returned to the exhaust passage.

1 is a diagram schematically showing a configuration of an exhaust gas recirculation device for an internal combustion engine according to a first embodiment of the present invention. It is an example of the exhaust pressure pulsation of a 4-cylinder internal combustion engine. FIG. 3 is a diagram showing an image of an exhaust gas flow rate in the first embodiment. It is a figure which shows typically the structure of the exhaust gas recirculation apparatus of the internal combustion engine concerning Embodiment 3 of this invention. An example of the map which prescribed | regulated opening / closing control of the EGR valves 31 and 32 in Embodiment 3 of this invention with the relationship between an engine speed and a load is shown. It is a figure for demonstrating operation | movement of the exhaust gas recirculation apparatus concerning Embodiment 4 of this invention. It is a figure for demonstrating operation | movement of the exhaust gas recirculation apparatus concerning Embodiment 6 of this invention.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
FIG. 1 is a diagram schematically showing a configuration of an exhaust gas recirculation device for an internal combustion engine according to a first embodiment of the present invention. In the present embodiment, it is assumed that the exhaust gas recirculation device according to the present embodiment is provided in an internal combustion engine mounted on a vehicle as a power source. In the figure, an internal combustion engine body 10 is an in-line four-cylinder internal combustion engine. The specific configuration of the internal combustion engine according to the present invention is not limited to this, and the internal combustion engine main body 10 may have a different number of cylinders other than the in-line four cylinders or another cylinder arrangement system. There is no limitation on the type of engine.

  An intake system including a surge tank 12 and an exhaust system including an exhaust manifold 14 are connected to the internal combustion engine body 10. An external EGR passage 20 is connected to the exhaust manifold 14. An EGR cooler 22 is provided in the middle of the external EGR passage 20. Although not shown, an exhaust system configuration such as an exhaust pipe, an exhaust catalyst, and an exhaust gas sensor is appropriately connected and connected downstream of the exhaust manifold 14.

  The exhaust gas recirculation apparatus according to this embodiment includes a gas passage 24. One end of the gas passage 24 is connected to the downstream position of the EGR cooler 22, and the other end of the gas passage 24 is connected to the exhaust manifold 14. An EGR valve 31 is provided on the external EGR passage 20 on the surge tank 12 side.

  A check valve 41 is provided at a position between the connection portion with the exhaust manifold 14 and the EGR cooler 22 in the external EGR passage 20. The check valve 41 allows the exhaust gas to flow only in the direction from the exhaust manifold 14 toward the EGR cooler 22. The gas passage 24 is provided with a check valve 42. The check valve 42 allows the exhaust gas to flow only in the direction from the EGR cooler 22 toward the exhaust manifold 14, that is, only in the direction opposite to the check valve 41. According to the first embodiment, when the EGR valve 31 is closed, an exhaust gas loop can be generated by the function of the check valves 41 and 42 accordingly. In this way, the presence of the check valve can form an exhaust gas loop (circulation) path that passes through the EGR cooler 22 and returns to the exhaust manifold 14 again.

  The internal combustion engine of the first embodiment includes an ECU (Electronic Control Unit) 50. The ECU 50 is connected to various sensors (for example, an air flow meter, an engine water temperature sensor, an exhaust gas sensor, etc.) and various actuators (for example, an over-variable valve mechanism, a fuel injection valve, etc.) of the internal combustion engine. About these general structures which an internal combustion engine mounts, since various techniques are already well-known and are not a new matter, description is abbreviate | omitted. Based on the control signal of the ECU 50, the EGR valve 31 is also opened and closed.

  FIG. 2 is an example of exhaust pressure pulsation of a four-cylinder internal combustion engine. FIG. 3 is a diagram showing an image of the exhaust gas flow rate in the first embodiment. The flow rate of the exhaust gas flowing through the check valve 41 and the flow rate of the exhaust gas flowing through the check valve 42 are shown.

  By closing the EGR valve 31 in the high output region, a loop for cooling and recirculating the exhaust gas is formed, and the exhaust temperature can be lowered. Thereby, even if the OT increase is suppressed to a low level, the exhaust temperature can be lowered (temperature control of the exhaust catalyst or the like can be achieved without relying on the OT increase), and the output can be improved, and high speed fuel consumption and practical fuel consumption can be improved.

  In the first embodiment, the check valve 42 is provided in the gas passage 24. However, the present invention is not limited to this. Instead of the check valve 42, a throttle mechanism (throttle valve) may be provided. Thereby, although there is a possibility that the amount of gas that can be cooled is reduced due to a slight backflow in the flow of the loop, there is an advantage that the system can be constructed at low cost.

  In the configuration of the first embodiment, the positions of the check valve 41 and the EGR cooler 22 may be interchanged. That is, the check valve 41 may be provided at a position downstream of the EGR cooler 22 in the external EGR passage 20. Thereby, the check valve 41 does not have to have high heat resistance.

Embodiment 2. FIG.
An internal combustion engine having a twin entry turbocharger may have an EGR system. In this case, the design is usually performed so that the pressure can be different between the two exhaust passages. By connecting the EGR system to the high-pressure exhaust passage and exhausting the exhaust gas, the differential pressure from the intake pressure can be increased and the EGR introduction property can be improved.

  When the exhaust gas extraction position by the EGR system is before T / C, when the EGR gas extracted from the high temperature / high pressure side is returned to the exhaust passage by the loop according to the first embodiment, the exhaust gas on the high temperature / high pressure side is again exhausted. Return to the aisle. Thereby, pressure (temperature) imbalance can be suppressed, maintaining the introduction property of EGR gas. As a result, an increase in OT increase due to pressure (temperature) imbalance (deterioration of fuel consumption associated with this) can be suppressed.

Embodiment 3 FIG.
FIG. 4 is a diagram schematically showing the configuration of the exhaust gas recirculation device for the internal combustion engine according to the third embodiment of the present invention. The hardware configuration illustrated in FIG. 4 is the same as the hardware configuration illustrated in FIG. 1 except that the EGR valve 32 is provided, and thus redundant description is avoided. Similar to the EGR valve 31, the EGR valve 32 is connected to the ECU 50 and is opened and closed by a control signal thereof.

  During warm-up operation or light load operation of the exhaust catalyst, it is common that the EGR valve 31 is closed or its opening degree is minute. In the configuration of the first embodiment, an exhaust gas cooling loop is formed even in such a case. For this reason, there is a possibility that emission characteristics may be deteriorated due to a delay in warming up of the exhaust catalyst or a decrease in the catalyst bed temperature.

  Therefore, in the third embodiment, an EGR valve 32 is provided upstream of the check valve 41, and the EGR valve 32 is closed under the above operating conditions. As a result, the exhaust gas cooling loop can be cut off, and deterioration of the emission characteristics can be prevented.

FIG. 5 shows an example of a map in which the opening / closing control of the EGR valves 31 and 32 in the third embodiment is defined by the relationship between the engine speed and the load. Each of the areas A, B, and C is defined as follows.
Area A: An area where the load is high and the rotation speed is high, and the area where exhaust cooling should be performed.
Region B: An intermediate region between region A and region C, and is a region where EGR is introduced.
Region C: a region where the load is light and the rotational speed is low, and is a region where the exhaust catalyst is warmed up and temperature is maintained.

  In the third embodiment, in the region A, the EGR valve 31 is closed and the EGR valve 32 is opened. Thus, when exhaust cooling is to be performed, an exhaust gas cooling loop can be utilized. In the third embodiment, in the region C, both the EGR valve 31 and the EGR valve 32 are closed. Thereby, when warming up or maintaining the temperature of the exhaust catalyst, the exhaust gas cooling loop can be shut off to prevent the emission characteristics from deteriorating. In region B, EGR is introduced by opening both the EGR valve 31 and the EGR valve 32.

In the third embodiment, the EGR valve 32 corresponds to the “switching means” in the second invention and to the “switching valve” in the fourth invention.
The EGR valve 32 may not have the same flow rate control function as the EGR valve 31, and the EGR valve 32 may be replaced with a valve that can be selectively switched between communication and blocking.
In the third embodiment, the “refluxing means” according to the third aspect of the present invention is realized by controlling the switching of the open / closed states of the EGR valves 31 and 32 according to the map of FIG.

Embodiment 4 FIG.
The fourth embodiment provides a control method capable of cleaning the EGR system. FIG. 6 is a diagram for explaining the operation of the exhaust gas recirculation apparatus according to the fourth embodiment of the present invention. The hardware configuration of the fourth embodiment is basically the same as the configuration shown in FIG. However, in the fourth embodiment, the EGR catalyst (not shown) is provided in the external EGR passage 20.

  Under an operating condition in a light load range (a large negative pressure downstream of the throttle), the ECU 50 performs control so that the EGR valve 31 is opened and the EGR valve 32 is closed. Thereby, the inside of the external EGR passage 20 (inside the pipe) can be brought into a low pressure state. Thereafter, the EGR valve 32 is rapidly opened, so that the exhaust gas passes through the external EGR passage 20 at a high speed. As a result, deposits adhering to the pipe inner wall of the external EGR passage 20, the EGR cooler 22, the EGR catalyst (not shown), and the like can be peeled off by this high-speed flow.

  On the other hand, excessive EGR causes deterioration of combustion. Therefore, in the fourth embodiment, the ECU 50 controls the EGR valve 31 so that the EGR valve 31 is closed simultaneously with or just before the EGR valve 32 is opened. When the EGR valve 31 is opened to close the piping inside the external EGR passage 20 and the EGR valve 32 is closed, the EGR valve 32 is immediately closed. The EGR valve 31 is a residual exhaust gas inside the exhaust of the external EGR passage 20. The valve is opened in a small lift state so that the combustion does not deteriorate due to. Furthermore, the effect of peeling off the deposit may be enhanced by repeating the cycle of low pressure and high speed inflow continuously or intermittently a plurality of times.

Embodiment 5 FIG.
The cleaning control according to the fourth embodiment is preferably performed at a predetermined time (periodic) and at an idle time that is equal to or higher than a predetermined engine water temperature. This is because combustion resistance is afforded by the high engine water temperature and the pressure downstream of the throttle is low. In the case of having a configuration capable of detecting an increase in pressure loss of the EGR system, it is preferable that the operation is performed under the above operating conditions when the pressure loss exceeds a predetermined pressure loss. Therefore, in the fifth embodiment, the ECU 50 according to the fourth embodiment is performed when the engine water temperature is equal to or higher than the predetermined temperature and in the idling operation after a predetermined period after the previous cleaning control is executed. Perform cleaning.

Embodiment 6 FIG.
FIG. 7 is a diagram for explaining the operation of the exhaust gas recirculation apparatus according to the sixth embodiment of the present invention. The hardware configuration of the sixth embodiment is the same as the configuration shown in FIG. At the time of low temperature start, the high HC and low temperature exhaust gas immediately after the start is held for the capacity of the loop path (that is, a part of the external EGR passage 20 and the volume of the gas passage 24 that form the exhaust gas loop path). . Thereafter, after the exhaust catalyst is warmed up, the held exhaust gas is discharged into the exhaust manifold 14.

  Specifically, as shown in FIG. 7, a period in which the EGR valve 31 is closed and the EGR valve 32 is opened is provided before the exhaust catalyst warm-up is completed. During this period, the exhaust gas fills the loop path. The determination that the exhaust catalyst has been warmed up is established when a predetermined condition is appropriately satisfied by, for example, direct measurement using a catalyst bed temperature sensor or indirect measurement using an exhaust temperature sensor or the like, or an elapsed start time. The determination process may be executed on the ECU 50. Thereafter, the EGR valve 32 is closed, and after the warm-up of the exhaust catalyst is completed, the EGR valve 32 is opened. Thereby, the emission characteristics can be improved.

10 Internal combustion engine body 12 Surge tank 14 Exhaust manifold 20 External EGR passage 22 EGR cooler 24 Gas passages 31, 32 EGR valves 41, 42 Check valves

Claims (7)

An external EGR passage having one end communicating with the exhaust passage of the internal combustion engine and the other end communicating with the intake passage of the internal combustion engine;
An EGR cooler that cools exhaust gas recirculated from the exhaust passage to the intake passage through the external EGR passage;
Recirculation means for returning the exhaust gas cooled by the EGR cooler to the exhaust passage of the internal combustion engine;
With
The reflux means includes
A gas passage in which one end communicates with the downstream side of the EGR cooler in the external EGR passage, and the other end communicates with the exhaust passage;
In the gas passage, a gas that preferentially flows a gas in a first direction from the downstream side of the EGR cooler toward the exhaust passage side as compared with a second direction opposite to the first direction. Direction control means;
With
The exhaust gas recirculation apparatus for an internal combustion engine, wherein the gas direction control means includes a check valve attached to the gas passage with an inlet facing a downstream side of the EGR cooler and an outlet facing the exhaust passage. . Before SL reflux means, according to claim 1, characterized in that it comprises a switchable switching means to execute and stop reflux to the exhaust passage of the internal combustion engine of the exhaust gas cooled by the EGR cooler An exhaust gas recirculation device for an internal combustion engine. The recirculation means stops or suppresses recirculation of the exhaust gas cooled by the EGR cooler to the exhaust passage of the internal combustion engine when the catalyst provided in the exhaust passage of the internal combustion engine is warmed up. The exhaust gas recirculation device for an internal combustion engine according to claim 1 or 2 . The reflux means has a gas passage in which one end communicates with the downstream side of the EGR cooler in the external EGR passage and the other end communicates with the exhaust passage;
The switching means includes a switching valve provided in the middle of a circulation path formed by a part of the external EGR passage, a joining portion of the external EGR passage and the gas passage, and the gas passage. The exhaust gas recirculation apparatus for an internal combustion engine according to claim 2 . An EGR valve provided in the middle of the external EGR passage for controlling the amount of exhaust gas recirculated to the intake passage;
The switching valve is provided at a position closer to the exhaust passage than the EGR valve in the external EGR passage,
Forming a first state to close the opening and the switching valve the EGR valve, after the formation of the first state, after a lapse of a predetermined time enough to the external EGR passage becomes a negative pressure, opens the switching valve 5. The exhaust gas recirculation apparatus for an internal combustion engine according to claim 4 , further comprising negative pressure generation opening control means for forming a second state in which the EGR valve is closed. The exhaust gas recirculation device for an internal combustion engine according to claim 5 , wherein the EGR cooler and / or the EGR catalyst is provided between the EGR valve and the switching valve in the external EGR passage. The internal combustion engine includes an exhaust catalyst provided in the exhaust passage,
When the temperature of the exhaust catalyst is equal to or lower than a predetermined temperature, a first state is formed in which the EGR valve is closed and the switching valve is opened, and after the predetermined state has elapsed after the formation of the first state, the EGR valve And an exhaust accumulation control means for forming a second state in which the switching valve is closed, and forming the first state when the temperature of the exhaust catalyst exceeds the predetermined temperature after the formation of the second state. The exhaust gas recirculation device for an internal combustion engine according to claim 5 or 6 , characterized by the above.

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