JP2016050481A - Control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably suppress condensed water induced by an EGR, and to enhance the service life or reliability of a component.SOLUTION: An engine 10 includes a turbosupercharger 30, an LPL-EGR mechanism 40, an HPL-EGR mechanism 50 and an auxiliary supercharging mechanism 60. An ECU 70 includes first control means for driving the auxiliary supercharging mechanism 60 when it is determined that condensed water is generated in an intake passage 12 and generation of the condensed water can be suppressed by the auxiliary supercharging mechanism 60. The ECU 70 further includes second control means for opening a high pressure EGR valve 54 of the HPL-EGR mechanism 50 so that an intake pressure is released to an exhaust passage 22 through a high pressure EGR passage 52 when the intake pressure of an intake manifold 20 is larger than an exhaust pressure of an exhaust manifold 24 after driving of the auxiliary supercharging mechanism 60.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a control device for an internal combustion engine including a turbocharger, an EGR mechanism, and an electric compressor.

  As a conventional technique, for example, as disclosed in Japanese Patent Application Laid-Open No. 2005-226505, an internal combustion engine including a turbocharger, an LPL-EGR mechanism, and an electric compressor is known. In the prior art, a throttle valve, an electric compressor, and a turbo compressor are sequentially arranged from the upstream side to the downstream side of the intake passage. The LPL-EGR mechanism is configured to recirculate EGR gas between the throttle valve and the electric compressor.

JP 2005-226505 A JP 2008-280923 A JP 2013-167218 A JP 2009-002286 A

  In the conventional technology described above, condensed water may be generated in the intake passage when the amount of EGR gas is increased. This condensed water may corrode the injection hole of the fuel injection valve or damage the turbo compressor. In the prior art, there is a problem that the life and reliability of the parts are reduced by the condensed water.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to stably suppress condensate water induced by EGR and improve the life and reliability of parts. It is an object of the present invention to provide a control device for an internal combustion engine that can be made to operate.

A first invention includes a turbo compressor provided in an intake passage and a turbine provided in an exhaust passage, wherein the turbine receives exhaust pressure and drives the turbo compressor to supercharge intake air. A turbocharger,
An LPL-EGR mechanism that recirculates EGR gas taken from the downstream side of the turbine to the intake passage upstream of the turbo compressor;
An HPL-EGR mechanism having an EGR passage for returning EGR gas taken from the upstream side of the turbine to the intake passage on the downstream side of the turbo compressor, and an EGR valve capable of adjusting the amount of EGR gas flowing through the EGR passage; ,
Auxiliary supercharging means capable of supercharging intake air;
A first control means for driving the auxiliary supercharging means when it is determined that condensed water is generated in the intake passage and the auxiliary supercharging means can suppress the generation of condensed water;
After the auxiliary supercharging means is driven, when the intake pressure of the intake manifold is larger than the exhaust pressure of the exhaust manifold, the EGR valve of the HPL-EGR mechanism is opened and the intake pressure is passed through the EGR passage. Second control means for allowing the exhaust passage to escape;
It has.

  According to the first invention, when it is determined that condensed water is generated in the intake passage and it is determined that the generation of condensed water can be suppressed by the auxiliary supercharging means, the auxiliary supercharging means is driven. . Thereby, while raising intake air temperature, A / F can be made lean and generation | occurrence | production of condensed water can be suppressed. Accordingly, it is possible to improve the life and reliability of the component. Further, when the generation of condensed water can be suppressed by the auxiliary supercharging means, it is not necessary to reduce the amount of EGR gas, so that NOx emission can be suppressed and exhaust emission can be reduced. Further, after the auxiliary supercharging means is driven, when the intake pressure of the intake manifold is larger than the exhaust pressure of the exhaust manifold, the gas in the intake passage is released from the high pressure EGR passage to the exhaust manifold. Thereby, generation | occurrence | production of condensed water can further be suppressed.

It is a block diagram for demonstrating the system configuration | structure of the engine by Embodiment 1 of this invention. It is a timing chart which shows the outline | summary of the condensed water suppression control by Embodiment 1 of this invention. In Embodiment 1 of this invention, it is a flowchart which shows an example of the condensed water suppression control performed by ECU. It is explanatory drawing which shows the effect acquired by an auxiliary | assistant supercharging mechanism. It is operation | movement explanatory drawing which shows the state which scavenges a high voltage | pressure EGR channel | path with the gas in an intake passage.

Embodiment 1 FIG.
[Configuration of Embodiment 1]
The first embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a configuration diagram for explaining a system configuration of an engine according to Embodiment 1 of the present invention. The system according to the present embodiment includes an engine 10 as an internal combustion engine. Although FIG. 1 illustrates a four-cylinder engine, the present invention can be applied to an internal combustion engine having an arbitrary number of cylinders. The engine 10 includes an intake passage 12 that sucks air into a combustion chamber (cylinder) of each cylinder.

  In the intake passage 12, an air cleaner 14, a throttle valve 16, an auxiliary supercharging mechanism 60, which will be described later, a turbo compressor 34, an intercooler 36, and a second throttle valve 18 are provided in this order from the upstream. The throttle valve 16 and the second throttle valve 18 adjust the intake air amount of the engine 10. The most downstream portion of the intake passage 12 is constituted by an intake manifold 20 connected to the combustion chamber of each cylinder. The engine 10 also includes an exhaust passage 22 that exhausts exhaust gas from each cylinder. The most upstream part of the exhaust passage 22 is constituted by an exhaust manifold 24 connected to the combustion chamber of each cylinder. The exhaust passage 22 is provided with a catalyst 26 that purifies exhaust gas downstream of a turbine 32 described later.

  The engine 10 includes a turbocharger 30, an LPL-EGR mechanism 40, an HPL-EGR mechanism 50, and an auxiliary supercharging mechanism 60. The turbocharger 30 is composed of, for example, a variable capacity supercharger. That is, the turbocharger 30 includes a turbine 32 provided in the exhaust passage 22, a turbo compressor 34 provided in the intake passage 12, and a variable nozzle (not shown) attached to the turbine 32. . The turbocharger 30 supercharges intake air when the turbine 32 receives exhaust pressure and drives the turbo compressor 34. Further, the opening area of the turbine 32 is configured to increase as the opening of the variable nozzle (VN) increases. Thereby, the turbocharger 30 can drive the variable nozzle to the closed side in, for example, a low rotation region, and improve the supercharging efficiency. In the high rotation region, the variable nozzle can be driven to the open side to reduce the exhaust pressure.

  An LPL (Low Pressure Loop) -EGR mechanism 40 takes out the exhaust gas from the downstream side of the turbine 32 and recirculates the extracted exhaust gas to the intake passage 12 on the upstream side of the turbo compressor 34 as low-pressure EGR gas. The LPL-EGR mechanism 40 includes a low pressure EGR passage 42, a low pressure EGR valve 44, and a low pressure EGR cooler 46. One end side of the low pressure EGR passage 42 is connected to the exhaust passage 22 on the downstream side of the turbine 32 and the catalyst 26. The other end of the low pressure EGR passage 42 is connected to the intake passage 12 on the upstream side of the turbo compressor 34 and the auxiliary supercharging mechanism 60. The low pressure EGR valve 44 adjusts the amount of low pressure EGR gas flowing through the low pressure EGR passage 42.

  The HPL (High Pressure Loop) -EGR mechanism 50 takes out the exhaust gas from the upstream side of the turbine 32 and recirculates the extracted exhaust gas as high-pressure EGR gas to the intake passage 12 on the downstream side of the turbo compressor 34. The HPL-EGR mechanism 50 includes a high pressure EGR passage 52 and a high pressure EGR valve 54. One end side of the high pressure EGR passage 52 is connected to the exhaust passage 22 (for example, the exhaust manifold 24) on the upstream side of the turbine 32. The other end side of the high pressure EGR passage 52 is connected to the intake passage 12 on the downstream side of the turbo compressor 34, the intercooler 36 and the second throttle valve 18. The high pressure EGR valve 54 adjusts the amount of high pressure EGR gas flowing through the high pressure EGR passage 52.

  The auxiliary supercharging mechanism 60 constitutes a specific example of auxiliary supercharging means that supercharges intake air separately from the turbo compressor 34. The auxiliary supercharging mechanism 60 is disposed in the intake passage 12 downstream of the connection portion where the low pressure EGR passage 42 is connected to the intake passage 12 and upstream of the second throttle valve 18. The auxiliary supercharging mechanism 60 includes a bypass valve 62, a bypass passage 64, and an electric compressor 66. The bypass valve 62 is provided in the intake passage 12, and is disposed between the turbo compressor 34 and a connection portion where the low pressure EGR passage 42 is connected to the intake passage 12. The bypass passage 64 branches from the intake passage 12 on the upstream side of the bypass valve 62 and merges with the intake passage 12 on the downstream side of the bypass valve 62. The electric compressor 66 is provided in the bypass passage 64.

  The system of the present embodiment also includes a sensor system that detects the operating state of the engine 10 and an ECU (Electronic Control Unit) 70 that controls the engine 10 based on the output of the sensor system. The sensor system includes a crank angle sensor for detecting the rotation speed of the crankshaft (engine rotation speed) and the crank angle, an air flow sensor for detecting the intake air amount, and various other sensors. The sensor system is connected to the input side of the ECU 70. On the output side of the ECU 70, in addition to the fuel injection valve and spark plug of each cylinder, actuators such as a throttle valve 16, a second throttle valve 18, a low pressure EGR valve 44, a high pressure EGR valve 54, a bypass valve 62, an electric compressor 66, and the like. Is connected. The ECU 70 performs operation control of the engine 10 and executes condensed water suppression control as necessary.

(Condensate suppression control)
In general, if the amount of EGR gas is increased, NOx in the exhaust gas can be reduced. However, the higher the EGR rate, the richer the A / F and the higher the dew point. Therefore, when the water vapor in the EGR gas is cooled in the intake passage 12, condensed water is more likely to be generated, causing problems such as corrosion. Arise. In particular, at the time of supercharging, since the dew point increases as the supercharging pressure increases, the generation of condensed water becomes significant.

  For this reason, in the present embodiment, the condensed water suppression control is executed in a situation where condensed water is likely to be generated in the intake passage 12. FIG. 2 is a timing chart showing an outline of the condensed water suppression control according to the first embodiment of the present invention. This figure illustrates the case where the condensed water suppression control is executed when increasing the EGR gas. In the condensed water suppression control shown in FIG. 2, the auxiliary supercharging mechanism 60 (denoted as e-boost in the drawing) is driven when increasing the EGR gas. Specifically, the middle of the intake passage 12 is closed by the bypass valve 62 and the electric compressor 66 is operated. As a result, the intake air is supercharged by the electric compressor 66.

  Further, in the condensed water suppression control, when the electric compressor 66 is driven, the variable nozzle of the turbocharger 30 is driven more open than usual. In the present specification, “normal” means when the condensed water suppression control is not executed (when the auxiliary supercharging mechanism 60 is not operated).

  After the electric compressor 66 is driven, the high pressure EGR valve 54 of the HPL-EGR mechanism 50 is controlled according to the magnitude relationship between the intake pressure of the intake manifold 20 and the exhaust pressure of the exhaust manifold 24. Specifically, when the intake pressure is larger than the exhaust pressure, the high pressure EGR valve 54 is driven to the valve opening side, and the opening degree of the high pressure EGR valve 54 is made larger than usual. Thereby, the intake pressure is released to the exhaust manifold 24 via the high pressure EGR passage 52, and the dew point of the intake gas can be lowered. On the other hand, when the intake pressure is smaller than the exhaust pressure, the high pressure EGR valve 54 is driven to the closed side, and the opening degree of the high pressure EGR valve 54 is made smaller than usual.

[Specific Processing for Realizing Embodiment 1]
Next, specific processing for realizing the above-described control will be described with reference to FIG. FIG. 3 is a flowchart showing an example of the condensed water suppression control executed by the ECU in the first embodiment of the present invention. The routine shown in this figure is repeatedly executed during engine operation.

  In the routine shown in FIG. 3, first, in step S0, it is determined whether or not EGR is being executed by the LPL-EGR mechanism 40. If the determination in step S0 is not established, it is determined that no condensed water is generated, and this routine is terminated as it is. If the determination in step S0 is established, for example, EGR is executed during high load operation or intermediate load operation, and condensed water can be generated, so the process proceeds to step S1.

  In step S <b> 1, it is determined whether or not the current dew point (temperature at which moisture in the EGR gas begins to condense) of the EGR gas returned to the intake passage 12 is higher than the gas temperature in the intake passage 12. The ECU 70 stores data for calculating the dew point in advance when the auxiliary supercharging mechanism 60 is in operation and when it is not in operation. The gas temperature in the intake passage 12 is detected by a temperature sensor or the like. If the determination in step S1 is not established, it is determined that no condensed water is generated, and this routine is immediately terminated.

  On the other hand, when the determination in step S1 is established, it is determined that condensed water is generated in the intake passage 12, and the process proceeds to step S2. In step S <b> 2, it is determined whether or not the dew point when the auxiliary supercharging mechanism 60 is activated is higher than the gas temperature in the intake passage 12. The gas temperature t in the intake passage 12 when the auxiliary supercharging mechanism 60 is operated can be calculated by the following equation (1). When the intake passage temperature is high but the intake air temperature is extremely low, it is preferable not to operate the auxiliary supercharging mechanism 60.

[Equation 1]
t = (assumed fresh air amount × outside air temperature + intake passage gas amount × intake passage temperature) / assumed total gas amount

  If the determination in step S2 is not established, the generation of condensed water cannot be suppressed even if the auxiliary supercharging mechanism 60 is driven, so the process proceeds to step S3 and EGR reduction control is executed. In step S3, the LPL-EGR valve (low pressure EGR valve 44) is driven to the closed side, and the amount of EGR gas by the LPL-EGR mechanism 40 is decreased.

  On the other hand, when the determination in step S2 is established, it is determined that the generation of condensed water can be suppressed by the auxiliary supercharging mechanism 60, and the auxiliary supercharging mechanism 60 is driven in step S4. As a result, as shown in FIG. 4, the dew point can be lowered by the supercharging of the auxiliary supercharging mechanism 60 and the generation of condensed water can be suppressed. FIG. 4 is an explanatory view showing the effect obtained by the auxiliary supercharging mechanism 60.

  Next, in step S5 in FIG. 3, it is determined whether an acceleration request is generated based on the accelerator opening detected by the accelerator opening sensor, for example. If the determination in step S5 is not established, the variable nozzle of the turbocharger 30 is driven to the open side in step S6, and then the process proceeds to step S7. Thereby, a supercharging pressure can be reduced and generation | occurrence | production of condensed water can be suppressed.

  If the determination in step S5 is established, step S6 is not executed, and the process proceeds to step S7. Thereby, at the time of acceleration, it can avoid that a supercharging pressure falls by opening a variable nozzle, and can ensure operativity.

  Next, in step S <b> 7, it is determined whether or not the intake pressure of the intake manifold 20 is larger than the exhaust pressure of the exhaust manifold 24. The intake pressure and the exhaust pressure may be detected by a pressure sensor, respectively, or may be estimated based on the operating state. If the determination in step S7 is not established, EGR by the HPL-EGR mechanism 50 is executed, for example, during intermediate load operation. In this case, the process proceeds to step S8, and the HPL-EGR valve (high pressure EGR valve 54) is driven closer to the closing side than usual.

  On the other hand, when the determination in step S7 is established, the process proceeds to step S9, and the high pressure EGR valve 54 is fully opened. Thereby, in step S10, the gas in the intake passage 12 can be caused to flow backward from the HPL-EGR passage (the high pressure EGR passage 52) to the exhaust manifold 24 as indicated by the arrow in FIG. As a result, the rich gas staying in the high pressure EGR passage 52 can be scavenged and the generation of condensed water can be suppressed. FIG. 5 is an operation explanatory diagram showing a state in which the high-pressure EGR passage 52 is scavenged by the gas in the intake passage 12.

  Next, in step S11 in FIG. 3, it is determined whether or not the set control time has elapsed since the processing in steps S9 and S10 was started. This control time may be set based on, for example, the time during which scavenging of the high-pressure EGR passage 52 can be completed. If the determination in step S11 is not established, the processes in steps S9 and S10 are continued until the determination is established. Further, when the determination in step S11 is established, this routine ends.

  In addition, according to the routine shown in FIG. 3, the case where condensed water suppression control is repeatedly performed is also considered. However, in this case, since the EGR by the LPL-EGR mechanism 30 is stopped before the execution of the condensed water suppression control and the determination in step S0 is not established, the condensed water suppression control is not repeatedly executed.

  As described above in detail, according to the present embodiment, when it is determined that condensed water is generated in the intake passage 12, and the auxiliary supercharging mechanism 60 determines that the generation of condensed water can be suppressed. The condensed water suppression control can be executed. In the condensed water suppression control, the auxiliary supercharging mechanism 60 can be driven to increase the intake air temperature. Further, the auxiliary supercharging mechanism 60 can make the A / F lean when the A / F becomes rich and the dew point increases due to acceleration or the like. Therefore, according to the condensed water suppression control, generation of condensed water can be suppressed using the auxiliary supercharging mechanism 60, and the life and reliability of the parts can be improved. Further, when the auxiliary supercharging mechanism 60 can suppress the generation of condensed water, the EGR gas does not have to be reduced, so that NOx emission can be suppressed and exhaust emission can be reduced.

  Further, after the auxiliary supercharging mechanism 60 is driven, when the intake pressure of the intake manifold 20 is larger than the exhaust pressure of the exhaust manifold 24, the gas in the intake passage 12 is released from the high pressure EGR passage 52 to the exhaust manifold 24. Can do. Thereby, generation | occurrence | production of condensed water can further be suppressed.

  In the condensed water suppression control, the auxiliary supercharging mechanism 60 is driven, and the variable nozzle of the turbocharger 30 and the high pressure EGR valve 54 are cooperatively controlled. Therefore, the generation of condensed water can be stably suppressed by these synergistic effects. Further, in the present embodiment, whether or not the condensed water is likely to be generated by sequentially calculating the dew point from the state quantity in the intake passage 12 and comparing the calculation result with the output value of the temperature sensor or the like. Can be accurately determined.

  In the first embodiment, steps S0, S1, S2, and S4 in FIG. 3 show specific examples of the first control means, and steps S7, S9, and S10 show specific examples of the second control means. ing. In the first embodiment, the case where the electric compressor 66 is used has been exemplified. However, the present invention is not limited to this. For example, when the MAT is mounted, the electric compressor 66 may not be used. Note that MAT (Motor Assist Turbo) is a system that performs supercharging by forcibly driving a conventional turbocharger with an electric motor. When the MAT is mounted, by operating the MAT instead of the electric compressor 66, it is possible to obtain substantially the same effect as in the first embodiment, so that the electric compressor 66 can be omitted.

10 Engine (Internal combustion engine)
12 Intake passage 14 Air cleaner 16 Throttle valve 18 Second throttle valve 20 Intake manifold 22 Exhaust passage 24 Exhaust manifold 26 Catalyst 30 Turbocharger 32 Turbine 34 Turbo compressor 36 Intercooler 40 LPL-EGR mechanism 42 Low pressure EGR passage 44 Low pressure EGR valve 46 Low pressure EGR cooler 50 HPL-EGR mechanism 52 High pressure EGR passage 54 High pressure EGR valve 60 Auxiliary supercharging mechanism (auxiliary supercharging means)
62 Bypass valve 64 Bypass passage 66 Electric compressor 70 ECU

Claims (1)

A turbocharger having a turbo compressor provided in an intake passage and a turbine provided in an exhaust passage, wherein the turbine receives exhaust pressure and drives the turbo compressor to supercharge intake air;
An LPL-EGR mechanism that recirculates EGR gas taken from the downstream side of the turbine to the intake passage upstream of the turbo compressor;
An HPL-EGR mechanism having an EGR passage for returning EGR gas taken from the upstream side of the turbine to the intake passage on the downstream side of the turbo compressor, and an EGR valve capable of adjusting the amount of EGR gas flowing through the EGR passage; ,
Auxiliary supercharging means capable of supercharging intake air;
A first control means for driving the auxiliary supercharging means when it is determined that condensed water is generated in the intake passage and the auxiliary supercharging means can suppress the generation of condensed water;
After the auxiliary supercharging means is driven, when the intake pressure of the intake manifold is larger than the exhaust pressure of the exhaust manifold, the EGR valve of the HPL-EGR mechanism is opened and the intake pressure is passed through the EGR passage. Second control means for allowing the exhaust passage to escape;
The control apparatus of the internal combustion engine provided with.

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