WO2013187141A1

WO2013187141A1 - Control device and control method for internal combustion engine

Info

Publication number: WO2013187141A1
Application number: PCT/JP2013/062376
Authority: WO
Inventors: 小原　徹也
Original assignee: 日産自動車株式会社
Priority date: 2012-06-15
Filing date: 2013-04-26
Publication date: 2013-12-19

Abstract

With the present invention, when an EGR control valve is opened and a throttle valve is closed, the reverse flow of intake air containing EGR gas is detected from a change in the mass flow volume of the intake air passing through a compressor (the compressor flow-through volume Qcomp). After the reverse flow of the intake air is detected, the EGR control valve is closed until the intake air that has passed to the upstream side is again drawn into the compressor. Thus, it is possible to prevent the addition of EGR gas to intake air which already contains EGR gas, and thus it is possible to supply intake air having a stable EGR ratio to cylinders of an internal combustion engine (1), and to improve fuel consumption performance and drivability.

Description

Control device and control method for internal combustion engine

The present invention relates to a control device and a control method for an internal combustion engine that recirculates part of exhaust gas upstream of a supercharger.

Patent Document 1 discloses an internal combustion engine in which a part of exhaust gas is introduced from a downstream side of a catalyst for purifying exhaust gas to a compressor upstream side of a supercharger provided in an intake passage, a compressor, a throttle valve downstream of the compressor, If an air release valve that opens to the atmosphere is provided and the engine is decelerated during EGR execution, the EGR gas staying in the intake passage is released into the atmosphere by opening the air release valve, and the state is shifted to the acceleration state. Prior to this, a technique for reducing the amount of EGR gas sucked into the cylinder at the time of acceleration by closing the air release valve and improving the acceleration response is disclosed.

However, in such Patent Document 1, since the gas released to the atmosphere from the atmosphere release valve is not measured, the amount of EGR gas sucked into the cylinder during acceleration cannot be grasped, and fuel consumption and driving May deteriorate.

JP 2011-111212 A

The control apparatus for an internal combustion engine according to the present invention, in an internal combustion engine in which a part of exhaust gas is introduced into the intake passage from the upstream side of the supercharger as EGR gas, the flow of intake air including EGR gas toward the upstream side of the intake passage When this is detected, the introduction of EGR gas into the intake passage is prohibited.

According to the present invention, it is possible to prevent the EGR gas from being further added to the intake air containing the EGR gas, and to supply the intake air with a stable EGR rate into the cylinder. Can be improved.

1 is a system diagram showing the overall configuration of an internal combustion engine to which the present invention is applied. Explanatory drawing which showed typically the mode of the intake system at the time of high load steady operation. Explanatory drawing which showed typically the mode of the intake system at the time of recirculation valve opening. Explanatory drawing which showed the mode of the intake system at the time of reacceleration typically. Explanatory drawing which showed typically the intake system before and behind a compressor. Timing chart when the backflow of intake air is detected. The flowchart which shows the flow of control at the time of detecting the backflow of intake air.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a system diagram showing an overall configuration of an internal combustion engine 1 to which the present invention is applied.

The internal combustion engine 1 is mounted on a vehicle such as an automobile as a drive source, and an intake passage 2 and an exhaust passage 3 are connected to each other. A throttle valve 5 is provided in the intake passage 2 connected to the internal combustion engine 1 via the intake manifold 4, and an air flow meter 6 and an air cleaner 7 for detecting the intake air amount are provided upstream thereof. Yes. An exhaust catalyst 9 such as a three-way catalyst is provided for exhaust purification in the exhaust passage 3 connected to the internal combustion engine 1 via the exhaust manifold 8.

The internal combustion engine 1 has a turbocharger 10 that is coaxially provided with a compressor 11 disposed in the intake passage 2 and a turbine 12 disposed in the exhaust passage 3. The compressor 11 is located upstream from the throttle valve 5 and is located downstream from the air flow meter 6. The turbine 12 is located on the upstream side of the exhaust catalyst 9. Note that reference numeral 13 in FIG. 1 denotes an intercooler provided on the upstream side of the throttle valve 5.

A recirculation passage 14 that bypasses the compressor 11 and connects the upstream side and the downstream side of the compressor is connected to the intake passage 2. A recirculation valve 15 that controls the intake flow rate in the recirculation passage 14 is interposed in the recirculation passage 14.

The exhaust passage 3 is connected to an exhaust bypass passage 16 that bypasses the turbine 12 and connects the upstream side and the downstream side of the turbine 12. A waste gate valve 17 that controls the exhaust gas flow rate in the exhaust bypass passage 16 is interposed in the exhaust bypass passage 16.

Also, the internal combustion engine 1 can perform exhaust gas recirculation (EGR), and an EGR passage (exhaust gas recirculation passage) 20 is provided between the exhaust passage 3 and the intake passage 2. One end of the EGR passage 20 is connected to the exhaust passage 3 at a position downstream of the exhaust catalyst 9, and the other end is connected to the intake passage 2 at a position downstream of the air cleaner 7 and upstream of the compressor 11. Even during supply, a part of the exhaust gas can be recirculated to the intake passage 2. An EGR control valve 21 and an EGR cooler 22 are interposed in the EGR passage 20. The valve opening degree of the EGR control valve 21 is controlled by the control unit 25 so as to obtain a predetermined EGR rate corresponding to the operating conditions.

In addition to the detection signal of the air flow meter 6 described above, the control unit 25 includes a crank angle sensor 26 that detects a crank angle of a crankshaft (not shown), a downstream side of the intercooler 13 and an upstream side of the throttle valve 5. An intake air temperature sensor 27 and an intake pressure sensor 28 for detecting a temperature T [K] and a pressure (absolute pressure) P [kPa] in the intake passage 2 at a position, and an accelerator for detecting a depression amount of an accelerator pedal (not shown). Detection signals of sensors such as the opening sensor 29 are input.

Based on these detection signals, the control unit 25 controls the ignition timing and the air-fuel ratio of the internal combustion engine 1 and controls the valve opening of the EGR control valve 21 to control the intake passage from the exhaust passage 3. 2 performs exhaust gas recirculation control (EGR control) for recirculating part of the exhaust gas. Note that the valve openings of the throttle valve 5, the recirculation valve 15, and the waste gate valve 17 are also controlled by the control unit 25. The recirculation valve 15 is not controlled to be opened and closed by the control unit 25, and a so-called check valve that opens only when the pressure on the downstream side of the compressor 11 exceeds a predetermined pressure can be used. is there.

In such an internal combustion engine 1, when the throttle valve 5 is closed during deceleration from a high load range, the recirculation valve 15 is opened so that the pressure on the downstream side of the compressor 11 does not become too high. There is.

As shown in FIG. 2, during high load steady operation, the EGR control valve 21 opens at a predetermined opening with the recirculation valve 15 closed, and the intake passage 2 and the EGR passage 14 merge. On the downstream side of the EGR merging portion 31, the intake air has a predetermined EGR rate.

When the vehicle decelerates during high-load steady operation, when the recirculation valve 15 is opened, the intake air on the downstream side of the compressor 11 is pushed out to the upstream side of the compressor 11 through the recirculation passage 14. In the merging portion 31, the intake air that already contains the EGR gas flows toward the upstream side. At this time, if the EGR control valve 21 is open, the EGR gas is further added to the intake air that already contains the EGR gas. As a result, as shown in FIG. 3, intake air having an EGR rate higher than the EGR rate corresponding to the opening degree of the EGR control valve 21 is generated upstream of the EGR merging portion 31.

When the vehicle accelerates from this state, the throttle valve 5 opens and the recirculation valve 15 closes, so that the intake air flows toward the downstream side in the EGR junction 31. Therefore, if the EGR control valve 21 is open at this time, EGR gas is further added to the intake air having a high EGR rate generated upstream of the EGR merging portion 31, as shown in FIG. In this way, intake air with a higher EGR rate is supplied to the internal combustion engine 1.

That is, if the recirculation valve 15 is opened while the EGR control valve 21 is open, the EGR gas is doubled (see FIG. 3) and tripled (see FIG. 4), Therefore, intake air having a stable EGR rate cannot be supplied into the cylinder of the internal combustion engine 1.

Therefore, in this embodiment, when the throttle valve 5 is closed when the EGR control valve 21 is opened, the EGR gas is determined from the change in the mass flow rate of the intake air passing through the compressor 11 (compressor passing mass flow rate Qcomp [kg / s]). Detects backflow of intake air containing Then, the EGR control valve 21 is closed until the intake air that has passed upstream of the compressor 11 is re-inhaled after the reverse flow of the intake air is detected.

The compressor passing mass flow rate Qcomp is the sum of the mass flow rates passing through the compressor 11 and the recirculation valve 15, and the throttle valve passing mass flow rate Qth [kg / s] passing through the throttle valve 5, the intake air temperature sensor 27, and It is calculated using the detected value of the intake pressure sensor 28 (the temperature T [K] and the pressure P [kPa] described above).

Specifically, as shown in FIG. 5, the section from the compressor 11 to the throttle valve 5 is a closed system A having a volume V, and the intake air temperature sensor 27 and the intake pressure sensor 28 located in the closed system A are Using the detected value, the intake air density ρA in the closed system A is calculated from the gas state equation. Further, the mass change of the intake air in the closed system A is calculated from the change in the intake density ρA. Then, using this mass change and the throttle valve passing mass flow rate Qth, the compressor passing mass flow rate Qcomp is calculated from the mass conservation law in the closed system A.

The compressor passage mass flow rate Qcomp in the present embodiment is a positive value when flowing toward the downstream side of the intake passage 2 and a negative value when flowing toward the upstream side of the intake passage 2. The throttle valve passage mass flow rate Qth is calculated from the differential pressure across the throttle valve 5 and the opening ratio of the throttle valve 5. The pressure on the upstream side of the throttle valve 5 is detected by the intake pressure sensor 28. The pressure on the downstream side of the throttle valve 5 can be estimated using, for example, a detection value of the air flow meter 6.

FIG. 6 is a timing chart when the backflow of the intake air containing the EGR gas is detected.

The opening of the throttle valve 5 is reduced from time t1, and the throttle valve 5 is closed at time t3. At this time, the compressor passage mass flow rate Qcomp gradually decreases from the time t1, and becomes a negative value at the time t2. In other words, from time t2, the intake air passing through the compressor 11 toward the upstream side is greater than the intake air passing through the compressor 11 toward the downstream side.

Therefore, if the compressor passing mass flow rate Qcomp is a negative value, it is determined that the intake air including the EGR gas flows toward the upstream side of the intake passage 2. In this embodiment, at time t2, it is determined that the intake air including EGR gas has flowed (backward) toward the upstream side of the intake passage 2, and the EGR control valve 21 is closed, and EGR is prohibited from this timing. .

As a result, it is possible to prevent the EGR gas from being further added to the intake air containing the EGR gas, and to supply the intake air having a stable EGR rate into the cylinder of the internal combustion engine 1. Fuel efficiency and drivability can be improved.

Then, the integration of the compressor passage mass flow rate Qcomp is started from time t2, and the integration value (back flow integration value) during the period (time t2 to t4) when the compressor passage mass flow rate Qcomp is a negative value and the compressor passage mass flow rate Qcomp. The EGR control valve 21 is kept closed until the integrated value (forward flow rate integrated value) from the negative value to the positive value (period t4 to t5) becomes the same amount. In FIG. 6, the area between the characteristic line of the compressor passing mass flow rate Qcomp and the straight line P where the compressor passing mass flow rate Qcomp is “0” is an integrated value, and the Qcomp characteristic line and the straight line during the period from time t2 to t4. The area B1 sandwiched between P corresponds to the backflow integrated value, and the area B2 sandwiched between the Qcomp characteristic line and the straight line P during the period from time t4 to t5 corresponds to the forward flow integrated value.

Thus, even at time t4, even if the intake air flow becomes a forward flow passing through the compressor 11 toward the downstream side, the opening of the EGR control valve 21 is prohibited, and all the intake air that has passed through the compressor 11 upstream is At the time t5 at which re-inhalation is performed, the EGR control valve 21 is allowed to open and the EGR prohibition is released. That is, when the intake flow is flowing backward, the intake reverse flow rate integrated value is calculated, and when the intake flow is switched from the reverse flow to the forward flow, the intake forward flow rate integrated value is calculated. Then, after the backflow integrated value and the forward flow integrated value become the same amount, that is, after the area B1 and the area B2 in FIG.

Therefore, it is possible to reliably prevent the EGR gas from being added twice or triple to the intake air containing the EGR gas.

Further, by using the backflow integrated value and the forward flow integrated value, it is possible to accurately estimate whether or not the EGR gas is contained in the intake air in the merging portion 31, and a more stable EGR rate can be obtained. The intake air can be supplied to the internal combustion engine 1.

Note that the forward flow rate integrated value can be calculated by integrating the detected value of the air flow meter 6 instead of the compressor passing mass flow rate Qcomp.

FIG. 7 is a flowchart showing the flow of control when the backflow of the intake air containing EGR gas is detected.

In S1, it is determined whether or not the compressor passing mass flow rate Qcomp is a negative value (Qcomp <0). If the compressor passing mass flow rate Qcomp is a negative value, the process proceeds to S2, and if not, the process proceeds to S3. In S2, it is determined that the intake air including the EGR gas has flowed toward the upstream side of the intake passage 2 (back flow), the flag that is the back flow detection flag is set to “1”, and the flow proceeds to S3. That is, when the Flag is “1”, the intake air flowing into the EGR junction 31 contains EGR gas.

In S3, it is determined whether or not the flag state is “1”. If “1”, the process proceeds to S4, and if “0”, the process proceeds to S8.

In S4, the compressor passing mass flow rate Qcomp is integrated, and in S5, it is determined whether or not the integrated value (ΣQcomp) of the compressor passing mass flow rate Qcomp is a negative value. If it is determined in S5 that the integrated value of the compressor passage mass flow rate Qcomp is a negative value, the process proceeds to S6, the EGR control valve 21 is closed, and EGR is prohibited. On the other hand, if the integrated value of the compressor passing mass flow rate Qcomp is not a negative value in S5, the process proceeds to S7. In S7, it is determined that all the intake air that has passed through the compressor 11 upstream has been re-inhaled, and the flag state is switched from "1" to "0", and the process proceeds to S8. That is, when the Flag is “0”, the intake air flowing into the EGR merging portion 31 does not contain EGR gas. In S8, the opening of the EGR control valve 21 is permitted and the prohibition of EGR is canceled.

In the above-described embodiment, when the compressor passing mass flow rate Qcomp becomes a negative value, EGR is prohibited because the intake air including EGR gas becomes a flow (back flow) toward the upstream side of the intake passage 2. However, when the recirculation valve 15 is opened, the EGR may be prohibited on the assumption that the intake air containing the EGR gas becomes a flow (back flow) toward the upstream side of the intake passage 2.

Further, EGR may be prohibited only while the recirculation valve 15 is open. In this case, EGR gas is added again after the recirculation valve 15 is closed with respect to the intake air that flows from the downstream side to the upstream side of the compressor 11 while the recirculation valve 15 is opened. Therefore, more EGR gas is added during the transition than in the above-described embodiment. However, when the amount of EGR gas added is small, intake air with a stable EGR rate is put into the cylinder of the internal combustion engine 1. It can be supplied.

Claims

In a control apparatus for an internal combustion engine, comprising: a supercharger provided in an intake passage; and an exhaust gas recirculation unit that introduces a part of exhaust gas into the intake passage from the upstream side of the supercharger as EGR gas.
Intake state detection means for detecting the state of intake air in the intake passage,
A control apparatus for an internal combustion engine, which prohibits introduction of EGR gas by the exhaust gas recirculation means when the intake state detection means detects a flow of intake air including EGR gas toward the upstream side of the intake passage.
The intake state detection means detects the flow of intake air including EGR gas toward the upstream side of the intake passage, prohibits the introduction of EGR gas by the exhaust gas recirculation means, and then the intake state detection means includes EGR gas. 2. The control device for an internal combustion engine according to claim 1, wherein when the flow of intake air toward the downstream side of the intake passage is detected and a predetermined period has elapsed, introduction of EGR gas by the exhaust gas recirculation means is permitted.
The intake state detection means switches between the integrated value of the reverse flow rate of the intake air while the intake air containing EGR gas flows backward to the upstream side of the intake passage and the forward flow from the reverse flow toward the downstream side of the intake passage. And calculating the integrated value of the forward flow rate of the intake air, and detecting the state of the intake air in the intake passage from the integrated value of the reverse flow rate and the integrated value of the forward flow rate,
3. The control device for an internal combustion engine according to claim 2, wherein when the integrated value of the reverse flow becomes equal to the integrated value of the forward flow, introduction of EGR gas by the exhaust gas recirculation means is permitted.
Temperature pressure detecting means for detecting an intake air temperature and an intake air pressure between the supercharger and a throttle valve located downstream of the supercharger;
4. The control apparatus for an internal combustion engine according to claim 3, wherein the intake air state detection means calculates the reverse flow rate and the forward flow rate using intake air temperature and intake air pressure.
5. The forward flow rate is calculated according to claim 3, further comprising an air flow meter positioned upstream of the supercharger and detecting an intake air amount in the intake passage, and calculating the forward flow rate using detection of the air flow meter. Control device for internal combustion engine.
A bypass passage connected to the intake passage so as to communicate the upstream side and the downstream side of the supercharger, and a bypass valve for opening and closing the bypass passage,
2. The control device for an internal combustion engine according to claim 1, wherein the intake state detection means detects a state in which the bypass valve is open as a state in which intake air including EGR gas flows backward to the upstream side of the intake passage. .
The control apparatus for an internal combustion engine according to claim 6, wherein the intake state detection means determines that the time when the bypass valve is opened is that the intake air including EGR gas starts a reverse flow upstream of the intake passage.
When a flow of intake air including EGR gas that is a part of exhaust gas toward the upstream side of the intake passage is detected, introduction of EGR gas introduced from the upstream side of the supercharger provided in the intake passage is introduced into the intake passage. Control method of internal combustion engine to be prohibited.