JP2010084600A - Exhaust gas recirculation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas recirculation device capable of efficiently functioning an internal combustion engine even when only a low-pressure EGR (Exhaust Gas Recirculation) device is operated. <P>SOLUTION: This exhaust gas recirculation device for an internal combustion engine 10 including a turbocharger 14 is provided with the low-pressure EGR device 20, a high-pressure EGR device 25, and an exhaust gas cutout valve 29 which turns on/off the inflow of the exhaust gas into the high-pressure EGR device 25 (a high-pressure EGR device passage 26) and which is closed when the high-pressure EGR device 25 is stopped to operate. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust gas recirculation device, and more particularly to an exhaust gas recirculation device for recirculating (recirculating) exhaust gas from an internal combustion engine equipped with a turbocharger.

An EGR (Exhaust Gas Recirculation) device for returning a part of exhaust gas from an exhaust manifold to an intake manifold is attached to an internal combustion engine equipped with a turbocharger. Further, in addition to the EGR device (hereinafter referred to as a high pressure EGR device), a part of the exhaust from the turbine downstream portion of the exhaust passage is returned to the portion of the intake passage upstream of the compressor in the internal combustion engine provided with the turbocharger. For this purpose, a low-pressure EGR device is installed.

In order to stably drive the turbine during transient operation, the exhaust manifold of the internal combustion engine is provided with a partition valve capable of dividing the manifold into a part including the turbine inlet and the remaining part, and the turbine inlet is It has also been proposed to attach an EGR device to a portion that is not included (see, for example, Patent Document 1). That is, it has also been proposed that all exhaust gas from several cylinders of the internal combustion engine can be supplied to the EGR device.
JP 2006-307749 A

  If an exhaust gas recirculation device including a high pressure EGR device and a low pressure EGR device is attached to an internal combustion engine equipped with a turbocharger, it is possible to recirculate EGR gas in a wider operating range. However, in the existing exhaust gas recirculation device, when only the low pressure EGR device is operated (when the operation of the high pressure EGR device is stopped), the presence of the high pressure EGR device adversely affects the performance of the internal combustion engine. Yes.

  Accordingly, an object of the present invention is to provide an exhaust gas recirculation device capable of functioning an internal combustion engine efficiently (with good fuel consumption and low NOx generation amount) even when only a low pressure EGR device is operated. There is.

  In order to solve the above problems, an exhaust gas recirculation apparatus for an internal combustion engine in which a compressor of a turbocharger is attached to an intake passage and a turbine of the turbocharger is attached to an exhaust passage of the present invention is the exhaust passage. A low pressure EGR passage for taking a part of the exhaust flowing through the exhaust passage from a portion of the exhaust passage downstream of the turbine and leading it to a portion of the intake passage upstream of the compressor, and the low pressure EGR passage provided in the low pressure EGR passage. A low pressure EGR valve for adjusting the amount of exhaust gas flowing in the EGR passage, and a part of the exhaust gas flowing through the exhaust passage is taken out from a portion of the exhaust passage upstream from the turbine, and is downstream of the compressor in the intake passage. A high pressure EGR passage connected to the exhaust passage through an exhaust cutoff valve for leading to the portion, and the high pressure EGR passage A high-pressure EGR valve for adjusting the amount of exhaust gas flowing in the high-pressure EGR passage, an amount corresponding to the operating state of the internal combustion engine by each of the low-pressure EGR passage and the high-pressure EGR passage (including “ An EGR control unit that controls the low-pressure EGR valve and the high-pressure EGR valve so that exhaust of zero ") is recirculated, and stops the recirculation of the exhaust gas through the high-pressure EGR passage; An EGR control unit that closes the exhaust cutoff valve and opens the high-pressure EGR valve and the exhaust cutoff valve when the exhaust gas recirculation is started by the high-pressure EGR passage.

  That is, the exhaust gas recirculation device of the present invention includes an exhaust cutoff valve for turning ON / OFF the exhaust gas flowing from the exhaust passage to the high pressure EGR passage. Further, the exhaust cutoff valve provided in the exhaust gas recirculation device is closed while the recirculation (recirculation) of the EGR gas by the high pressure EGR passage is stopped.

  Therefore, the internal combustion engine to which the exhaust gas recirculation device of the present invention is attached is more stopped during operation of the high pressure EGR device (EGR gas through the high pressure EGR passage) than the internal combustion engine to which the exhaust gas recirculation device not equipped with an exhaust cutoff valve is attached. The function of the exhaust system during the recirculation stop) is reduced by the volume of the high-pressure EGR passage upstream of the high-pressure EGR valve.

  When the exhaust system volume is small, the exhaust pressure increases. If the exhaust pressure increases, the amount of energy flowing into the turbine increases, resulting in an increase in supercharging pressure. Moreover, since the exhaust gas recirculation device of the present invention is a device that can recirculate exhaust gas even when the operation of the high pressure EGR device is stopped (equipment having a low pressure EGR passage or the like), it can be used. Thus, the internal combustion engine can be made to function as an internal combustion engine with better fuel efficiency in the LPL region and less NOx generation in the LPL region.

  The exhaust gas recirculation device of the present invention can also be configured as a device in which the high-pressure EGR valve and the exhaust cutoff valve are opened and closed simultaneously. However, if the EGR gas is stored in the high pressure EGR passage (between the high pressure EGR valve and the exhaust cutoff valve), the reintroduction of the EGR gas can be performed quickly. For this reason, as the EGR control unit of the exhaust gas recirculation apparatus, a “unit that closes the exhaust cutoff valve after closing the high pressure EGR valve when stopping the exhaust gas recirculation through the high pressure EGR passage” should be adopted. Is desirable.

  Further, the time required for storing EGR gas in the high-pressure EGR passage varies depending on the operation state (exhaust flow rate or the like). For this reason, when the EGR control unit as described above is employed, the time from when the high pressure EGR valve is closed to when the exhaust cutoff valve is closed is determined from the operating state of the internal combustion engine. desirable.

  If the high-pressure EGR valve and the exhaust cutoff valve are opened at the same time, depending on the operation details (contents / history of operations performed by the driver), the exhaust pressure suddenly increases when resuming EGR gas introduction through the high-pressure EGR passage. As a result, torque shock may occur or controllability may deteriorate. For this reason, in order to prevent the exhaust pressure from changing suddenly, the EGR control unit of the exhaust gas recirculation device is configured as follows: “When the exhaust gas recirculation through the high-pressure EGR passage is started, It is desirable to employ a “unit that opens the high-pressure EGR valve”.

  However, even if the exhaust shut-off valve and the high pressure EGR valve are opened almost simultaneously, there may be no problem. Therefore, when the EGR control unit as described above is employed, the timing for closing the exhaust shut-off valve is It is desirable to be determined from the operating state of the internal combustion engine.

  According to the exhaust gas recirculation device of the present invention, even when only the low-pressure EGR device is operated, the internal combustion engine can function efficiently (with good fuel consumption and a small amount of NOx generation).

  Hereinafter, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a configuration of an internal combustion engine system to which an exhaust gas recirculation apparatus according to an embodiment of the present invention is applied.

  An internal combustion engine (internal combustion engine body) 10 used in this internal combustion engine system is a diesel engine having four cylinders equipped with an intake valve, an exhaust valve, a fuel injection device, and the like. The internal combustion engine 10 is provided with a VVT (variable valve timing mechanism) 11 for opening and closing the intake valve and the exhaust valve of each cylinder at a timing (suitable) according to the operating state. The internal combustion engine 10 is also provided with a crank position sensor (not shown) for detecting the engine speed.

  A combustion chamber of each cylinder of the internal combustion engine 10 is connected to an intake pipe 13 via an intake manifold 12. The combustion chamber of each cylinder is also connected to an exhaust pipe 17 via an exhaust manifold 16.

  A supercharging pressure sensor (not shown) for measuring the supercharging pressure is attached to the intake manifold 12. In the middle of the intake pipe 13, a compressor housing 14a, which is a component of the turbocharger 14, and an intercooler (I / C in the figure) 15 for cooling the compressed air from the compressor housing 14a are arranged. Further, a throttle valve and an air flow meter (not shown) are also arranged in the middle of the intake pipe 13.

  In the middle of the exhaust pipe 17, a turbine housing 14b (a component of the turbocharger 14) that is a drive source of the compressor housing 14a and a filter 18 for collecting PM (particulate matter) in the exhaust are disposed. .

  The internal combustion engine system includes a low pressure EGR device 20, a high pressure EGR device 25, and an exhaust cutoff valve 29. The low pressure EGR device 20 includes a low pressure EGR passage 21 that connects a downstream portion of the exhaust pipe 17 with respect to the filter 18 and a upstream portion of the intake pipe 13 with respect to the compressor housing 14a, and exhaust gas that flows in the low pressure EGR passage 21 (hereinafter referred to as “low pressure EGR passage 21”). , Also referred to as “low pressure EGR gas”), and a low pressure EGR cooler (E / C in the figure) 22 and a low pressure EGR valve 23 for adjusting the amount of low pressure EGR gas returned into the intake pipe 13. It is a configured device.

  The high pressure EGR device 25 flows in the high pressure EGR passage 26 for returning a part of the exhaust gas passing through the exhaust manifold 16 (hereinafter also referred to as “high pressure EGR gas”) to the intake manifold 12 and the high pressure EGR passage 26. This is an apparatus constituted by a high pressure EGR cooler (E / C in the figure) 27 for cooling the high pressure EGR gas and a high pressure EGR valve 28 for adjusting the amount of the high pressure EGR gas returned into the intake manifold 12. The exhaust cutoff valve 29 is an electromagnetic valve provided between the exhaust manifold 16 end of the high pressure EGR passage 26 of the high pressure EGR device 25 on the exhaust manifold 16 side. The exhaust shut-off valve 29 is a valve that can only perform open / close control (the amount of gas flowing through the valve cannot be adjusted).

  The internal combustion engine system also includes an accelerator position sensor (not shown) for detecting the accelerator opening. Further, the internal combustion engine system integrates a throttle valve, a fuel injection device, a VVT 11, a low pressure EGR device 20 (low pressure EGR valve 23), a high pressure EGR device 25 (high pressure EGR valve 28), etc., based on the outputs of the various sensors described above. An ECU (electronic control unit) 30 is also provided.

  The control performed by the ECU 30 for the VVT 11, the low pressure EGR device 20 and the high pressure EGR device 25 is basically the same as that of an existing ECU for an internal combustion engine equipped with two types of EGR devices and a VVT. .

That is, the ECU 30 is a unit that controls the VVT 11 so that a scavenging effect is obtained (so that the valley of the exhaust pulsation is close to the intake / exhaust TDC (Top Dead Center)).

The ECU 30 is also a unit that controls the EGR devices 20 and 25 (EGR valves 23 and 28), as schematically shown in FIG. That is, in the ECU 30, the operating state of the internal combustion engine 10 (the operating state specified from the combination of the engine load and the engine speed) is an LPL (Low Pressure Loop) region in which only the low pressure EGR device 20 should be operated, the low pressure In order to determine whether it belongs to an MPL (Middle Pressure Loop) region where both the EGR device 20 and the high-pressure EGR device 25 should be operated, or an HPL (High Pressure Loop) region where only the high-pressure EGR device 25 should be operated Information (so-called map) is set.

  Then, when the operating state changes, the ECU 30 refers to the information to determine whether it is necessary to stop / start the operation of the EGR devices 20 and 25, and the content according to the determination result Is a unit that performs control of the EGR device 20 or 25. The ECU 30 is also a unit that controls the recirculation amount of the EGR gas by the low pressure EGR device 20 and / or the high pressure EGR device 25 in each region in accordance with the operating state.

  As described above, the control performed by the ECU 30 on the VVT 11 and the like is basically the same as that of the existing ECU. However, the ECU 30 is a unit configured (programmed) so as to also perform opening / closing control of the exhaust cutoff valve 29 when the operation of the high pressure EGR device 25 is started / stopped.

  Specifically, the ECU 30 is shown in FIG. 3 when the operating state belonging to the MPL region changes to that belonging to the LPL region (when the operation of the high pressure EGR device 25 needs to be stopped). The MPL → LPL transition process of the procedure is started.

  The ECU 30 that has started the MPL → LPL transition process first performs a process for completely closing the high-pressure EGR valve 28 (control process for the high-pressure EGR valve 28: step S101).

  Thereafter, the ECU 30 performs a process for calculating a standby time (step S102). Here, the standby time is the time required for exhaust to fill the high pressure EGR passage 26 (portion upstream of the high pressure EGR valve 28 in the high pressure EGR passage 26) in the current operation state.

  Various algorithms for calculating the standby time as described above are conceivable, but the processing that the ECU 30 according to the present embodiment performs in step S102 calculates the exhaust flow rate from the intake flow rate, the fuel injection amount, etc. at that time. In this process, the standby time associated with the calculated exhaust flow rate is read from the exhaust flow rate / standby time table. The exhaust flow rate / standby time table is a table (information) stored in the ROM in the ECU 30 in which standby times for various exhaust flow rates are set.

  ECU30 which finished the process of step S102 waits for the calculated waiting time to pass (step S103). The ECU 30 performs a process for closing the exhaust cutoff valve 29 (control process for the exhaust cutoff valve 29: step S104) when the standby time has elapsed (when the process of step S103 is completed). The MPL → LPL transition process is terminated.

Further, when the operation state belonging to the LPL region changes to that belonging to the MPL region (when the operation of the high-pressure EGR device 25 needs to be started), the ECU 30 performs the LPL of the procedure shown in FIG. → Execute MPL transition processing.

  That is, when it becomes necessary to start the operation of the high pressure EGR device 25, the ECU 30 first performs a process for opening the exhaust cutoff valve 29 (step S201).

  Thereafter, the ECU 30 performs a process (step S202) for monitoring whether the change speed (the change amount of the supercharging pressure per unit time) of the supercharging pressure (the pressure detected by the supercharging pressure sensor) is equal to or lower than the predetermined speed. Start.

  Then, the ECU 30 performs a process for opening the high-pressure EGR valve 28 (step S203) when the change speed of the supercharging pressure becomes equal to or lower than the predetermined speed (step S202; YES), and then the LPL → MPL transition. The process ends.

  As is apparent from the above description, the exhaust gas recirculation device (low pressure EGR device 20, high pressure EGR device 25, exhaust shutoff valve 29, part for controlling the exhaust shutoff valve 29 of the ECU 30, etc.) according to the present embodiment is a constituent element. The apparatus is provided with an exhaust cutoff valve 29 for turning ON / OFF the inflow of exhaust gas from the exhaust manifold 16 to the high pressure EGR device 25. Further, the exhaust gas recirculation device is also a device in which the exhaust cutoff valve 29 is closed while the operation of the high pressure EGR device 25 is stopped.

  Therefore, if the exhaust gas recirculation device according to the present embodiment is used, the exhaust gas in which the operation of the high pressure EGR device 25 is stopped is more than that of the internal combustion engine system in which the exhaust gas recirculation device not provided with the exhaust cutoff valve 29 is used. An internal combustion engine system in which the system volume is small by the volume of the upstream portion of the high-pressure EGR passage 26 can be constructed.

  When the exhaust system volume is small, the exhaust pressure increases. If the exhaust pressure increases, the amount of energy flowing into the turbine housing 14b increases, and the boost pressure increases. Moreover, since the exhaust gas recirculation device is a device that can recirculate the exhaust gas even when the operation of the high pressure EGR device 25 is stopped (the device including the low pressure EGR device 20), the exhaust gas recirculation device according to the present embodiment is used. By doing so, it is possible to realize an internal combustion engine system that has better fuel efficiency in the LPL region and less NOx generation in the LPL region.

  Further, as schematically shown in FIG. 5, if the exhaust gas recirculation apparatus according to the present embodiment is used for an internal combustion engine equipped with a VVT (FIG. 5B), an exhaust cutoff valve 29 equivalent one is obtained. Since the exhaust pulsation becomes larger (the pressure difference between the intake pressure and the exhaust pressure during the positive overlap becomes larger) than when the exhaust gas recirculation device not provided (FIG. 5A) is used, it is higher. A scavenging effect is obtained (the amount of fresh air increases). Therefore, if the exhaust gas recirculation apparatus according to the present embodiment is used in an internal combustion engine equipped with VVT, the torque at low speed can be increased.

  Finally, the reason why the exhaust gas recirculation apparatus according to the embodiment is configured as an apparatus that does not simultaneously open and close the high pressure EGR valve 28 and the exhaust cutoff valve 29 will be described.

  The reason why the exhaust gas recirculation device is configured as a device that does not simultaneously close the high pressure EGR valve 28 and the exhaust cutoff valve 29 (the device that performs the processing of FIG. 3) is that EGR gas is stored in the upstream portion of the high pressure EGR passage 26. This is because the operation of the high-pressure EGR device 25 (introduction of EGR gas into the intake manifold 12) can be resumed quickly.

However, even if EGR gas is stored in the upstream portion of the high pressure EGR passage 26, if the high pressure EGR valve 28 and the exhaust cutoff valve 29 are opened at the same time, torque shock may occur or controllability may deteriorate. It will be. This is because in this case, the amount of EGR gas introduced into the exhaust manifold 16 and the amount of energy flowing into the turbine housing 14b change relatively abruptly.

  Then, if the high pressure EGR valve 28 and the exhaust cutoff valve 29 are opened in the procedure of FIG. 4, the amount of EGR gas introduced into the exhaust manifold 16 and the amount of energy flowing into the turbine housing 14b change rapidly. Can be prevented. For this reason, the exhaust gas recirculation device is configured as a device in which the high pressure EGR valve 28 and the exhaust cutoff valve 29 cannot be opened at the same time (opened by the procedure of FIG. 4).

<Deformation>
The exhaust gas recirculation device described above can be variously modified. For example, the effect of “improves fuel consumption in the LPL region where the high pressure EGR device 25 is stopped” is that the exhaust cutoff valve 29 is provided between the exhaust passage (exhaust manifold and exhaust pipe) of the internal combustion engine and the high pressure EGR device 25. It can be obtained if the exhaust cutoff valve 29 is closed when the high pressure EGR device 25 is stopped (when the high pressure EGR gas is not recirculated).

  For this reason, the exhaust gas recirculation device is different from the above-described one in which the opening / closing timing of the high pressure EGR valve 28 is different from that described above, for example, a device that calculates the standby time (see FIG. 3) by another algorithm or the standby time is not calculated (standby time). Can be transformed into a device). Further, the exhaust gas recirculation device is modified into a device that opens the exhaust shut-off valve 29 after a certain time has elapsed after opening the high-pressure EGR valve 28, or a device that opens and closes the high-pressure EGR valve 28 and the exhaust shut-off valve 29 simultaneously. You can also

  However, the exhaust gas recirculation apparatus is an apparatus in which the EGR gas flow rate is adjusted by the exhaust cutoff valve 29 (an apparatus having an exhaust cutoff valve 29 capable of adjusting the gas flow rate and not provided with the high pressure EGR valve 28 in the high pressure EGR passage 26). ) Is not desirable. This is because, when the above configuration is adopted, the high-pressure EGR gas does not exist in the EGR passage 26 when the operation of the high-pressure EGR device 25 is started. Furthermore, although the vicinity of the exhaust manifold 16 is hot, a general valve is liable to malfunction at high temperatures. Therefore, the exhaust gas recirculation apparatus adopting the above configuration has low reliability and high pressure EGR gas. This is because recirculation cannot be started promptly.

1 is a configuration diagram of an internal combustion engine system in which an exhaust gas recirculation apparatus according to an embodiment of the present invention is used. It is a figure for demonstrating the basic control content with respect to the high voltage | pressure EGR apparatus and low voltage | pressure EGR apparatus by ECU. It is a flowchart of the MPL-> LPL transition process which ECU performs. It is a flowchart of the LPL-> MPL transition process which ECU performs. It is a figure for demonstrating the effect acquired by using the exhaust gas recirculation apparatus which concerns on embodiment.

Explanation of symbols

10 ... Internal combustion engine 11 ... VVT
12 ... Intake manifold 13 ... Intake pipe 14 ... Turbocharger 14b ... Turbine housing 14a ... Compressor housing 15 ... Intercooler 16 ... Exhaust manifold 17 ... Exhaust pipe 18. .. Filter 20 ... Low pressure EGR device 21 ... Low pressure EGR passage 22 ... Low pressure EGR cooler 23 ... Low pressure EGR valve 25 ... High pressure EGR device 26 ... High pressure EGR passage 27 ... High pressure EGR cooler 28 ... High pressure EGR valve 29 ... Exhaust shut-off valve 30 ... ECU

Claims (5)

An exhaust gas recirculation device for an internal combustion engine in which a compressor of a turbocharger is attached to an intake passage, and a turbine of the turbocharger is attached to an exhaust passage,
A low-pressure EGR passage for taking a part of the exhaust flowing through the exhaust passage from a portion of the exhaust passage downstream of the turbine and leading it to a portion of the intake passage upstream of the compressor;
A low-pressure EGR valve provided in the low-pressure EGR passage for adjusting the amount of exhaust gas flowing through the low-pressure EGR passage;
A part of the exhaust gas flowing through the exhaust passage is connected to the exhaust passage through an exhaust cutoff valve for taking out a part of the exhaust passage upstream from the turbine and guiding it to a portion downstream of the compressor in the intake passage. High pressure EGR passage,
A high pressure EGR valve provided in the high pressure EGR passage for adjusting the amount of exhaust gas flowing through the high pressure EGR passage;
An EGR control unit that controls the low-pressure EGR valve and the high-pressure EGR valve so that an amount of exhaust according to an operating state of the internal combustion engine is recirculated by the low-pressure EGR passage and the high-pressure EGR passage, The EGR valve and the exhaust cutoff valve are closed when the exhaust gas recirculation through the high pressure EGR passage is stopped, and the high pressure EGR valve and the exhaust cutoff valve are opened when the exhaust gas recirculation through the high pressure EGR passage is started. An exhaust gas recirculation apparatus comprising: a control unit. 2. The exhaust gas recirculation device according to claim 1, wherein when the EGR control unit stops exhaust gas recirculation through the high pressure EGR passage, the exhaust gas recirculation device closes the exhaust gas shutoff valve after closing the high pressure EGR valve. . 3. The exhaust gas recirculation apparatus according to claim 2, wherein the EGR control unit is a unit that determines a time period from when the high-pressure EGR valve is closed to when the exhaust gas shut-off valve is closed based on an operating state of the internal combustion engine. 4. The unit according to claim 1, wherein the EGR control unit is a unit that opens the high-pressure EGR valve after opening the exhaust cutoff valve when starting recirculation of exhaust gas through the high-pressure EGR passage. 5. The exhaust gas recirculation device according to any one of the above. The exhaust gas recirculation apparatus according to claim 4, wherein the EGR control unit is a unit that determines a timing at which the high-pressure EGR valve is opened from an operating state of the internal combustion engine.

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