JP2018155175A - Control device for internal combustion engine - Google Patents

Abstract

To prevent backflow of fresh air in a passage by reliably closing a EGR valve when the backflow of fresh air in an EGR passage cannot be permitted while suppressing excessive reduction of an EGR execution region. A control device for an internal combustion engine of the present invention is applied to an internal combustion engine including an EGR device and a catalyst. The EGR device includes an EGR passage that connects an exhaust path and an intake path of an internal combustion engine, and an EGR valve that is installed in the EGR passage. The catalyst has an oxygen storage capacity and is disposed in the exhaust path downstream of the portion where the EGR passage is connected to the exhaust path. In a region on the high load side in the EGR execution region, which is a region where EGR gas is circulated by the EGR device, the control device determines the opening of the EGR valve when the oxygen storage amount of the catalyst is larger than the reference amount, as the oxygen storage amount. Is configured to have an opening smaller than the opening of the EGR valve in the case where is less than the reference amount. [Selection] Figure 2

Description

  The present invention relates to a control device for an internal combustion engine including an EGR device.

  Patent Document 1 discloses a technique related to control of an internal combustion engine provided with an EGR device that recirculates a part of exhaust gas to an intake passage through an EGR passage. In Patent Document 1, the connection portion side of the EGR passage to the exhaust passage branches into a passage connected to the turbine upstream side of the exhaust passage and a passage connected to the turbine downstream side, and a switching valve is installed at the branch portion. ing. By the control of the switching valve, the EGR gas recirculation path is selectively switched between a path including a path connected to the turbine upstream side and a path including a path connected to the turbine downstream side. In the control of Patent Document 1, when the supercharging pressure is larger than the exhaust pressure of the exhaust system, the passage is connected to a passage connected to the upstream side of the turbine, and higher-pressure exhaust gas on the upstream side of the turbine is taken out as EGR gas. Thereby, the recirculation | reflux of EGR gas when a supercharging pressure becomes high is enabled.

JP 2009-287435 A

  When the load is high, the intake pressure becomes larger than the exhaust pressure, and fresh air may flow backward in the EGR passage. On the other hand, when the system is not configured as in Patent Document 1 having a branch passage connected to the upstream side of the turbine, it is impossible to prevent backflow by switching the EGR gas recirculation path.

  As another method for preventing the backflow of fresh air, for example, it is conceivable that the EGR valve is closed when the intake pressure becomes larger than the exhaust pressure. However, when changing from a low load to a high load, it is conceivable that the EGR valve does not close in time and the backflow cannot be prevented. In order to ensure that the EGR valve can be closed before the backflow, it is conceivable to set the EGR execution region to the low load side. However, setting the EGR execution area to the low load side to narrow the EGR execution area is not preferable from the viewpoint of improving fuel efficiency.

  In order to solve the above problems, the present invention suppresses excessive reduction of the EGR execution area, and more reliably prevents the backflow of fresh air when the backflow of fresh air in the EGR passage cannot be permitted. Therefore, an improved control device for an internal combustion engine is provided.

  In order to achieve the above object, the control apparatus for an internal combustion engine of the present invention is configured as follows. An internal combustion engine to which the present invention is applied includes an EGR device and a catalyst. The EGR device is a device that circulates a part of the exhaust gas of the internal combustion engine as EGR gas to the intake passage, and is installed in the EGR passage connecting the exhaust passage and the intake passage of the internal combustion engine, the EGR passage, and the EGR passage. And an EGR valve that opens and closes. The catalyst is disposed in the exhaust path downstream of the portion where the EGR passage is connected to the exhaust path. This catalyst can occlude oxygen in the exhaust.

  The control device for an internal combustion engine according to the present invention opens the EGR valve when the oxygen storage amount of the catalyst is larger than the reference amount in the region on the high load side in the EGR execution region where the EGR gas is circulated by the EGR device. The degree is configured to be smaller than the opening degree of the EGR valve when the oxygen storage amount is equal to or less than the reference amount. Here, the “small opening” includes a case where the opening is zero, that is, the EGR valve is fully closed.

  According to the above control, when the oxygen storage amount of the catalyst is small and the oxygen storage in the catalyst can be allowed even if the fresh air flows backward, the opening degree of the EGR valve in the EGR execution region can be controlled as usual. it can. Therefore, the EGR amount in the EGR execution region can be ensured as usual, and the fuel efficiency can be improved. On the other hand, when the amount of oxygen stored in the catalyst is large and inflow of fresh air into the catalyst is not allowed, the opening degree of the EGR valve in the EGR execution region on the high load side is set to a smaller opening degree than usual. . As a result, when the operating region shifts from a low load to a high load side where a fresh air backflow can occur, the EGR valve can be closed and the EGR passage can be closed before the fresh air backflow occurs. it can. Accordingly, it is possible to more reliably suppress the unacceptable fresh air backflow while suppressing the reduction of the EGR execution area and improving the fuel consumption.

1 is a diagram schematically showing an overall configuration of a system including a control device for an internal combustion engine and peripheral devices thereof according to an embodiment of the present invention. FIG. 6 is a diagram for illustrating an EGR execution area in the first embodiment. FIG. 6 is a diagram for illustrating an EGR execution area in the first embodiment. 6 is a diagram for explaining a relationship between an oxygen storage amount of a downstream catalyst of Embodiment 1 and a UF rich duration time. FIG. 3 is a flowchart for illustrating a control routine executed by the control device of the first embodiment. FIG. 10 is a diagram for illustrating an EGR execution area in the second embodiment. 6 is a timing chart for explaining control of the second embodiment.

  Embodiments of the present invention will be described below with reference to the drawings. In the drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof is simplified or omitted.

Embodiment 1 FIG.
FIG. 1 is a diagram schematically showing an overall configuration of a system including a control device for an internal combustion engine and its peripheral devices according to the first embodiment. In the system of FIG. 1, the internal combustion engine body 2 includes a plurality of cylinders 4. Although three cylinders are shown in FIG. 1, the number and arrangement of the cylinders 4 are not limited. An intake path is connected to an intake port (not shown) that opens to the combustion chamber of each cylinder 4. The intake path includes an intake manifold 10 and an intake passage 14. An intake manifold 10 integrated with a surge tank is connected to the intake port. An intake passage 14 is connected to the intake manifold 10 for sucking air from the outside. In the intake passage 14, an air cleaner 16, an air flow meter 18, a turbocharger compressor 20, an intercooler 22, and an electronically controlled throttle valve 24 are installed in this order from the upstream side of the intake air.

  An exhaust path is connected to an exhaust port (not shown) that opens to the combustion chamber of each cylinder 4. The exhaust path includes an exhaust manifold 32 and an exhaust passage 34. An exhaust manifold 32 is connected to the exhaust port. An exhaust passage 34 is connected to the exhaust manifold 32 to exhaust the exhaust to the outside. A turbocharger turbine 36, an upstream catalyst 38, and a downstream catalyst 40 are installed in the exhaust passage 34 in order from the upstream side of the exhaust. Both the upstream catalyst 38 and the downstream catalyst 40 are three-way catalysts capable of storing oxygen.

  The system of FIG. 1 also includes an EGR device 50 that recirculates a portion of the exhaust. The EGR device 50 has an EGR passage 52. The EGR passage 52 is a passage for taking out a part of the exhaust gas as EGR gas, and one end thereof is connected to the exhaust passage 34 between the upstream catalyst 38 and the downstream catalyst 40. The other end of the EGR passage 52 is connected to the EGR delivery chamber 54, and the EGR delivery chamber 54 is connected to the intake manifold 10. An EGR cooler 56 and an EGR valve 58 are installed in the EGR passage 52. The EGR valve 58 is used to adjust the amount of EGR gas flowing through the EGR passage 52. Note that the EGR passage 52 is not limited to the configuration in which the tip on the intake side is connected to the EGR delivery chamber 54, and is directly connected to any position of the intake path including the intake passage 14 and the intake manifold 10. It may be a configuration.

  The system shown in FIG. 1 includes sensors for obtaining information related to the operation state at various places. For example, the amount of intake air is measured by an air flow meter 18 installed in the intake passage 14. The intake manifold 10 is provided with a pressure sensor 60 for measuring a surge tank pressure P3, which is a pressure in the surge tank. Further, an exhaust pressure sensor 62 for measuring the exhaust pressure Pegrin at the EGR extraction position of the EGR passage 52 is installed downstream of the upstream catalyst 38 and upstream of the downstream catalyst 40 in the exhaust passage 34.

  The various sensors and actuators described above are electrically connected to the control device 70. The control device 70 is an ECU (Electronic Control Unit). The control device 70 controls the entire engine system, and is mainly composed of a computer including a CPU, a ROM, and a RAM. The ROM stores various control routines including a control routine described later. The control device 70 controls the internal combustion engine by operating each actuator based on a signal from each sensor.

  As described above, the upstream catalyst 38 and the downstream catalyst 40 are three-way catalysts, and purify NOx, HC, and CO with maximum efficiency when the catalyst atmosphere is at the stoichiometric air-fuel ratio. Further, the upstream side catalyst 38 and the downstream side catalyst 40 can store oxygen. When the air-fuel ratio of the inflowing exhaust gas is a lean air-fuel ratio, the upstream side catalyst 38 and the downstream side catalyst 40 store excess oxygen, and the air-fuel ratio of the inflowing exhaust gas is rich. The stoichiometric air-fuel ratio is maintained by releasing a deficient amount of oxygen. Therefore, the control device 70 controls the oxygen storage amounts of the upstream catalyst 38 and the downstream catalyst 40 so as to maintain them in an appropriate range.

  Incidentally, in the internal combustion engine having the EGR device 50 configured as shown in FIG. 1, fresh air flows back from the intake side to the exhaust side via the EGR passage 52 due to the relationship between the surge tank pressure P3 and the exhaust pressure Pegrin. Can happen.

  When a reverse flow of fresh air occurs in the EGR passage 52, fresh air containing a large amount of oxygen flows directly into the downstream side catalyst 40. Here, when the downstream catalyst 40 is in a state where a large amount of oxygen is stored, the downstream catalyst 40 stores the maximum amount of oxygen by further storing the backflowed fresh air, and is no longer discharged at a lean air-fuel ratio. It may happen that NOx in the exhaust gas cannot be purified (that is, an OSA (Oxygen Storage Ability) failure state occurs). Therefore, when the oxygen storage amount of the downstream catalyst 40 is large, the backflow of fresh air from the EGR passage 52 to the exhaust side cannot be allowed.

  On the other hand, if the oxygen storage amount of the downstream catalyst 40 is small, even if fresh air flows backward from the EGR passage 52, it is possible to store oxygen in the downstream catalyst 40, and OSA failure will not occur. .

  From the above viewpoint, in the present embodiment, control is performed to switch the EGR execution region depending on whether the oxygen storage amount of the downstream catalyst 40 is larger or smaller than the reference amount. 2 and 3 are diagrams for explaining the EGR execution region in the present embodiment. FIG. 2 shows the EGR execution region when the oxygen storage amount is large, and FIG. 3 shows the EGR execution region when the oxygen storage amount is small. Yes.

  As shown in FIGS. 2 and 3, the EGR execution area is defined by the engine speed and the load. As shown in FIG. 2, the EGR execution region when the oxygen storage amount of the downstream side catalyst 40 is large and the backflow of fresh air is not allowed, as shown in FIG. 2, a part on the high load side of the normal EGR execution region is cut. A narrow EGR execution area A is assumed. This narrow EGR execution region A is also switched from the low load side in the EGR execution region A to the high load side such that the surge tank pressure P3> the exhaust pressure Pegrin, and the surge tank pressure P3> the exhaust pressure Pegrin. Thus, the EGR valve 58 is set in a range that allows sufficient time to close the EGR valve 58 until a fresh air backflow occurs. In other words, if EGR is being executed in this narrow EGR execution area A, the time for closing the EGR valve 58 can be secured even when shifting to a higher load side than the EGR execution area A. Qi backflow can be prevented. Therefore, it is possible to prevent the downstream side catalyst 40 from being occluded by unintentional reverse flow of fresh air.

  On the other hand, as shown in FIG. 3, when the backflow of fresh air to the downstream side catalyst 40 is allowed, the EGR execution region is wider than the EGR execution region A and is a normal EGR execution region B that is wider on the high load side. And In this EGR execution region B, when the surge tank pressure P3> exhaust pressure Pegrin and a reverse flow of fresh air occurs, the EGR valve 58 may not close in time. May flow backward. However, since the amount of oxygen stored in the downstream catalyst 40 is small, oxygen storage in the downstream catalyst 40 due to unintended reverse flow of fresh air is allowed to some extent. Therefore, when the oxygen storage amount of the downstream catalyst 40 is small, the fuel efficiency improvement is given priority by selecting the wide EGR execution region B.

  Whether or not the backflow of fresh air to the downstream side catalyst 40 is allowed, that is, whether or not the oxygen storage amount of the downstream side catalyst is smaller than the reference amount, continues with the rich air-fuel ratio gas in the downstream side catalyst 40. Judgment is made based on whether or not the UF rich continuation time, which is the inflow time, exceeds the reference time K2. FIG. 4 is a diagram for explaining the relationship between the oxygen storage amount of the downstream catalyst 40 and the UF rich duration in the present embodiment.

  In FIG. 4, the time K is from the state where the downstream side catalyst 40 has stored oxygen to the maximum, until the amount of storage decreases to the minimum level and a state where it is necessary to supply an appropriate amount of oxygen to the downstream side catalyst 40. It's time. In the present embodiment, with respect to this time K, a time that is allowed even if fresh air is introduced to the downstream side catalyst 40 to some extent by the backflow during the strong acceleration operation is obtained in advance by experiments, simulations, and the like. Set as reference time K2.

  FIG. 5 is a flowchart for illustrating a control routine executed by the control device in the present embodiment. The routine of FIG. 5 is repeatedly executed at predetermined control intervals during operation of the internal combustion engine. In the routine of FIG. 5, first, in step S2, it is determined whether or not the UF rich continuation time exceeds the reference time K2.

  If it is determined in step S2 that the UF rich continuation time exceeds the reference time K2, it is considered that the oxygen storage amount of the downstream catalyst 40 is small enough to allow the backflow of fresh air. Accordingly, in this case, the process proceeds to step S4, where a wide EGR execution area B is selected as the EGR execution area, and the current process is temporarily ended.

  On the other hand, if it is determined in step S2 that the UF rich continuation time is equal to or shorter than the reference time K2, the process proceeds to step S6, where the narrow EGR execution area A is selected as the EGR execution area, and the current process is temporarily ended.

Embodiment 2. FIG.
The system of the second embodiment has the same configuration as the system of FIG. The control of the second embodiment executes the same control as the control of the first embodiment except that the EGR execution region selected when the oxygen storage amount of the downstream catalyst 40 is large is different from that of the first embodiment. To do.

  FIG. 6 is a diagram for describing an EGR execution region that is selected when the oxygen storage amount of the downstream catalyst 40 is large in the second embodiment. The EGR execution area has an EGR execution area C on the high load side of the narrow execution area A in the embodiment. In the EGR execution region C, the opening degree of the EGR valve 58 is set smaller than usual. That is, when compared under the same operating conditions, the EGR execution region C and the EGR execution region B are more effective when the EGR execution region C is selected than when the EGR execution region B is selected. The opening degree of the EGR valve 58 becomes small.

  Thereby, although a limit value of the EGR amount that can be supplied that is determined according to the normal combustion limit or the like cannot be supplied, a certain amount of EGR gas can be introduced. Therefore, the fuel consumption can be further improved as compared with the case of the first embodiment in which EGR on the high load side is cut.

  The opening degree of the EGR valve 58 is determined according to the map according to the operating conditions. In the present embodiment, for each of the EGR execution region B and the EGR execution region C, a map that defines the relationship between the operating condition and the opening degree of the EGR valve 58 is prepared, and the opening degree is determined accordingly. To be determined. In the EGR execution area A on the low load side, the same map as the opening degree map of the EGR execution area B can be used.

  FIG. 7 is a timing chart for explaining the control in the second embodiment. In the example shown in FIG. 7, the load increases due to the driver's output request at time t1, changes from a low load to a high load, and at time t2, the differential pressure Pegrin-P3 between the surge tank pressure P3 and the exhaust pressure Pegrin. Is smaller than zero.

  Here, as shown by the solid line of the opening degree of the EGR valve 58 in FIG. 7B, the EGR execution area C is currently selected, and the opening degree of the EGR valve 58 is small according to the map of the EGR execution area C. Is set, the EGR valve 58 is closed by time t2 by starting to close at time t1. Therefore, as shown by the solid line of the fresh air reverse flow rate in (A), the fresh air reverse flow rate remains zero, and no fresh air is introduced into the downstream side catalyst 40.

  On the other hand, as indicated by the broken line of the opening degree of the EGR valve 58 in (B), the EGR execution area B is selected, and the opening degree of the EGR valve 58 is set to a large opening degree according to the normal map of the EGR execution area B. In this case, even when the EGR valve 58 is instructed to close at time t1, the valve closing is not completed until time t3. For this reason, as shown by the hatched portion in (A), a slight backflow of fresh air occurs between the time t2 when the differential pressure becomes negative and the time t3 when the valve closing is completed. However, when the EGR execution region B is selected, since the oxygen storage amount of the downstream side catalyst 40 is small, inflow of fresh air into the downstream side catalyst 40 is allowed.

  Note that the load on the upper limit side of the EGR execution area C of the second embodiment is set to be smaller than the load on the upper limit side of the EGR execution area B. However, in the present embodiment, in the EGR execution region C, a map different from the normal opening degree of the EGR valve 58 is prepared, and the opening degree can be set smaller than normal according to this. Therefore, the load on the upper limit side of the EGR execution area C may be the same as the load on the upper limit side of the EGR execution area B.

  In the first and second embodiments, the case where the upstream catalyst 38 and the downstream catalyst 40 are provided and the EGR passage 52 is connected between the upstream catalyst 38 and the downstream catalyst 40 has been described. However, the present invention is not limited to such a configuration, and can be applied to a system in which a catalyst having an oxygen storage capacity is installed on the downstream side of the connection portion of the EGR passage 52. Therefore, for example, the configuration may be such that the upstream catalyst 38 is not provided, or the EGR passage 52 may be connected to the upstream side of the upstream catalyst 38 or the upstream side of the turbine 36.

  In addition, when referring to the number of each element in the above embodiment, the number, quantity, amount, range, etc., unless otherwise specified or clearly specified to the number, This invention is not limited. The structures, steps, and the like described in this embodiment are not necessarily essential to the present invention unless otherwise specified or clearly specified.

2 Internal combustion engine body 4 Cylinder 10 Intake manifold 14 Intake passage 16 Air cleaner 18 Air flow meter 20 Compressor 22 Intercooler 24 Throttle valve 32 Exhaust manifold 34 Exhaust passage 36 Turbine 38 Upstream catalyst 40 Downstream catalyst 50 EGR device 52 EGR passage 54 Delivery chamber 56 EGR cooler 58 EGR valve 60 Pressure sensor 62 Exhaust pressure sensor 70 Control device

Claims (1)

An EGR passage that connects an exhaust path and an intake path of the internal combustion engine, and an EGR valve that is installed in the EGR path and opens and closes the EGR path, and a part of the exhaust gas of the internal combustion engine is used as the EGR gas. An EGR device that circulates in the intake path;
A control device for an internal combustion engine for controlling an internal combustion engine, wherein the EGR passage is disposed in the exhaust passage downstream of a portion connected to the exhaust passage and has a catalyst capable of storing oxygen in the exhaust. And
In an EGR execution region, which is a region where EGR gas is circulated by the EGR device, on the high load side, the opening degree of the EGR valve when the oxygen storage amount of the catalyst is larger than a reference amount is set as the oxygen storage amount. A control device configured to have an opening smaller than the opening of the EGR valve in a case where is less than or equal to the reference amount;
A control device for an internal combustion engine, comprising:

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