JP2017036695A - Control device of diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimum a period for limiting the introduction of an EGR gas into an intake passage while suppressing the creation of condensed water in the intake passage, in a diesel engine.SOLUTION: In an intake passage of a diesel engine, an intercooler is arranged at a downstream side with respect to a compressor of a supercharger, and a throttle valve is arranged at a downstream side with respect to the intercooler. Furthermore, an EGR device for introducing an EGR gas into the intake passage at a downstream side with respect to the throttle valve is arranged. At this time, when a temperature of a heat medium in the intercooler is lower than a target heat medium temperature, the introduction of the EGR gas into the intake passage is limited. Then, when the introduction of the EGR gas is limited, a pressure ratio of the supercharger is increased, and an opening of the throttle valve is reduced compared with the case that operation states of the diesel engine are the same, and the temperature of the heat medium in the intercooler is not lower than the target heat medium temperature.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a control device for a diesel engine provided with an EGR device that introduces part of exhaust gas into an intake passage as EGR gas.

  2. Description of the Related Art Conventionally, a diesel engine having an EGR device that introduces a part of exhaust gas into an intake passage as EGR gas in order to reduce NOx emission is known. The EGR device introduces an amount of EGR gas corresponding to the operating state of the diesel engine into the intake passage. Here, the EGR gas contains moisture. Therefore, in a diesel engine equipped with an EGR device, condensed water may be generated by introducing EGR gas during low-temperature intake air. In Patent Document 1, in the configuration in which EGR gas is introduced into the intake passage upstream of the intercooler, the condensed water generated by the condensation of moisture contained in the EGR gas is cooled by the intercooler. When there is a possibility of freezing (that is, when the temperature of the cooling water circulating through the intercooler is lower than the freezing determination temperature), a technique for closing the EGR valve provided in the EGR passage is disclosed.

  Patent Document 2 discloses a low-pressure EGR passage connecting an exhaust passage downstream of a turbocharger turbine and an intake passage upstream of the turbocharger compressor, and an intake air downstream of the turbocharger compressor. The diesel engine of the structure provided with the intercooler provided in the channel | path is disclosed. Patent Document 2 discloses a technique for controlling the flow rate of EGR gas flowing through the low-pressure EGR passage so that the temperature of the intake air passing through the intercooler becomes a temperature within a predetermined range.

JP 2011-190743 A JP 2007-211595 A JP 2001-090616 A International Publication No. 2014/122773

  As described above, when EGR gas is introduced into the intake passage through which low-temperature intake air flows, condensed water may be generated in the intake passage. If condensed water is generated in the intake passage, corrosion of various intake system components provided in the intake passage and the intake passage itself may be accelerated. Therefore, while there is a possibility that condensed water is generated in the intake passage, it is necessary to limit the introduction of EGR gas into the intake passage by the EGR device. However, while the introduction of EGR gas is limited, the EGR gas cannot sufficiently obtain the NOx emission reduction effect from the diesel engine.

  The present invention has been made in view of the above problems, and in a diesel engine, a period for limiting the introduction of EGR gas into the intake passage is suppressed as much as possible while suppressing the generation of condensed water in the intake passage. The purpose is to shorten.

A control device for a diesel engine according to the present invention is a supercharger having a compressor provided in an intake passage, and is a ratio of a pressure of intake air flowing out from the compressor to a pressure of intake air flowing into the compressor And a throttle valve that is provided in an intake passage downstream of the compressor and controls the flow rate of intake air, and an intake air that is downstream of the compressor and upstream of the throttle valve A heat medium passage through which a liquid heat medium circulates is provided, and an intercooler in which heat is exchanged between the heat medium and the intake air, and a part of the exhaust gas flowing through the exhaust passage is used as EGR gas. A diesel engine control device comprising: an EGR device introduced into an intake passage downstream of the throttle valve; When the temperature of the internal heat medium is lower than a predetermined target heat medium temperature, the introduction of EGR gas into the intake passage by the EGR device is limited until the temperature of the heat medium rises above the target heat medium temperature. And when the control unit restricts the introduction of EGR gas into the intake passage by the EGR device, the control unit restricts circulation of the heat medium in the heat medium passage, and diesel Compared with the case where the engine operating state is the same and the temperature of the heat medium in the intercooler is equal to or higher than the target heat medium temperature, the pressure ratio of the supercharger is increased and the opening of the throttle valve is decreased. To do.

  In the present invention, EGR gas is introduced into the intake passage downstream of the throttle valve. Hereinafter, the intake air after the introduction of the EGR gas may be referred to as “EGR mixed intake air”. In the present invention, an intercooler is provided in the intake passage between the compressor of the supercharger and the throttle valve. A heat medium passage through which the liquid heat medium circulates passes through the intercooler. In the intercooler, heat exchange is performed between the heat medium of the liquid in the intercooler and the intake air flowing through the intake passage. Here, if the temperature of the heat medium in the intercooler is higher than the temperature of the intake air, the temperature of the intake air can be raised by heat exchange with the heat medium. In the intercooler, the temperature of the intake air is higher than the dew point temperature of the EGR mixed intake air formed by mixing the intake air with the EGR gas in the intake passage downstream of the intercooler. If the temperature can be raised to the temperature, the generation of condensed water can be suppressed even if the EGR gas is introduced into the intake passage downstream of the intercooler.

  Therefore, in the present invention, when the temperature of the heat medium in the intercooler is lower than the predetermined target heat medium temperature, the control unit does not perform the EGR until the temperature of the heat medium rises above the target heat medium temperature. Limit the introduction of EGR gas into the intake passage by the device. Here, the target heat medium temperature is an EGR formed by mixing the intake air temperature with the EGR gas in the intake passage downstream of the intercooler by heat exchange with the heat medium in the intercooler. The temperature is set as a temperature at which the temperature of the mixed intake air can be increased to a level higher than the dew point temperature of the EGR mixed intake air. “Restricting the introduction of EGR gas into the intake passage” means that the introduction of EGR gas into the intake passage is stopped, or the operation state of the diesel engine is the same and the heat medium in the intercooler is This means that the flow rate of the EGR gas is reduced compared to when the temperature is equal to or higher than the target heat medium temperature. In other words, in the present invention, when EGR gas is introduced into the intake passage by the EGR device, introduction of EGR gas is restricted while there is a possibility that condensed water is generated. And even if EGR gas is introduced into the intake passage, if the generation of condensed water can be suppressed, the EGR gas introduction restriction is released.

In the present invention, the control unit limits circulation of the heat medium in the heat medium passage when the EGR device restricts introduction of EGR gas into the intake passage. Here, “restricting the circulation of the heat medium in the heat medium passage” means that the circulation of the heat medium in the heat medium passage is stopped or the operation state of the diesel engine is the same and the heat medium in the intercooler This means that the flow rate of the heat medium circulating in the heat medium passage is reduced as compared to when the temperature of the heat medium is equal to or higher than the target heat medium temperature. Further, when the control unit restricts the introduction of EGR gas into the intake passage by the EGR device, the operation state of the diesel engine is the same, and the temperature of the heat medium in the intercooler is equal to or higher than the target heat medium temperature. Compared to sometimes, increase the pressure ratio of the turbocharger and reduce the opening of the throttle valve. In addition to increasing the pressure ratio of the turbocharger, by reducing the opening of the throttle valve, a portion downstream of the turbine in the intake passage and upstream of the throttle valve, that is, an intercooler is installed. It is possible to efficiently increase the pressure of the intake air in the portion where it is present. Thereby, the temperature of the intake air flowing into the intercooler and the temperature of the intake air in the intercooler can be increased more quickly. When the temperature of the intake air in the intercooler becomes higher than the temperature of the heat medium in the intercooler, the temperature of the heat medium increases due to heat exchange between the intake air and the heat medium. That is, by increasing the pressure ratio of the supercharger and reducing the opening of the throttle valve, the temperature of the heat medium in the intercooler can be quickly increased to the target heat medium temperature or more.

  Therefore, according to the present invention, when the introduction of the EGR gas to the intake passage is restricted because the temperature of the heat medium in the intercooler is lower than the target heat medium temperature, the introduction restriction of the EGR gas is made earlier. It can be canceled. Therefore, it is possible to shorten the period for limiting the introduction of the EGR gas into the intake passage as much as possible while suppressing the generation of condensed water in the intake passage.

  Since the heat medium in the intercooler is a liquid, the specific heat is larger than that of the intake air. Therefore, once the temperature of the heat medium in the intercooler rises above the target heat medium temperature, the pressure ratio of the supercharger is then reduced and the opening of the throttle valve is increased, so that the intercooler Even if the temperature of the inflowing intake air decreases, a rapid temperature decrease of the temperature of the heat medium in the intercooler hardly occurs. Therefore, in the intercooler, the temperature of the intake air is changed by heat exchange with the heat medium, and the temperature of the EGR mixed intake air formed by mixing the intake air with EGR gas is higher than the dew point temperature of the EGR mixed intake air. Can be raised to a certain extent.

  Further, when the opening degree of the throttle valve is reduced in order to efficiently increase the pressure of the intake air in the portion of the intake passage where the intercooler is installed, the pump loss increases. As a result, the torque of the diesel engine may be reduced. However, in a diesel engine, torque can be increased by increasing the fuel injection amount. Therefore, even when the opening degree of the throttle valve is reduced, a desired torque can be output by increasing the fuel injection amount in accordance with the reduction amount of the opening degree of the throttle valve.

  In the present invention, when the control unit restricts the introduction of EGR gas into the intake passage by the EGR device, the operation state of the diesel engine is the same, and the temperature of the heat medium in the intercooler is the target. When the pressure ratio of the supercharger is increased and the opening of the throttle valve is reduced as compared with the case where the temperature is equal to or higher than the heat medium temperature, the control unit is requested by the diesel engine to open the throttle valve at the present time. It may be controlled to be equal to or more than the minimum opening that can secure the target intake air amount for achieving the operating state. According to this, even when the opening degree of the throttle valve is reduced because the temperature of the heat medium in the intercooler is lower than the target heat medium temperature, it is possible to achieve the operation state required for the diesel engine. .

The EGR device according to the present invention may have an EGR passage, an EGR cooler, a bypass passage, and a control valve. The EGR passage has one end connected to the exhaust passage and the other end connected to the intake passage downstream of the throttle valve, and is a passage through which EGR gas flows. The EGR cooler is provided in the EGR passage and is a cooler that cools the EGR gas flowing through the EGR passage. The bypass passage is connected to the EGR passage, and is a passage through which EGR gas flows by bypassing the EGR cooler. The control valve is a valve configured to be able to change the ratio between the flow rate of EGR gas flowing through the EGR cooler and the flow rate of EGR gas flowing through the bypass passage. At this time, the control unit reduces the flow rate of the EGR gas as compared with the case where the operation state of the diesel engine is the same and the temperature of the heat medium in the intercooler is equal to or higher than the target heat medium temperature. In the case where the introduction of EGR gas into the intake passage is restricted by the control unit, the control unit uses the control valve when the operation state of the diesel engine is the same and the temperature of the heat medium in the intercooler is equal to or higher than the target heat medium temperature. Compared to, the ratio of the flow rate of the EGR gas flowing in the bypass passage may be increased.

  According to this, when the temperature of the heat medium in the intercooler is lower than the target heat medium temperature, in addition to the decrease in the flow rate of the EGR gas, the temperature decrease of the EGR gas is suppressed. Therefore, the generation of condensed water in the intake passage can be further suppressed. The control valve includes a valve configured to be able to switch whether the EGR gas flows to the EGR cooler or the bypass passage. Further, “increasing the ratio of the flow rate of EGR gas flowing through the bypass passage by the control valve” includes “switching by the control valve so that EGR gas flows through the bypass passage”.

  In the control device for a diesel engine according to the present invention, the target heat medium temperature may be set based on the temperature of the outside air, the pressure of the outside air, or the humidity of the outside air. For example, when the temperature of the outside air is low, the target heat medium temperature may be set to a lower temperature than when the temperature of the outside air is high. Further, the target heat medium temperature may be set to a lower temperature when the outside air pressure is higher than when the outside air pressure is low. Further, when the outside air humidity is low, the target heat medium temperature may be set to a lower temperature than when the outside air humidity is high. According to these, when the condensed water tends to be relatively difficult to be generated, the target heat medium temperature is lowered. Therefore, the period during which the introduction of EGR gas into the intake passage is restricted can be further shortened.

  ADVANTAGE OF THE INVENTION According to this invention, in the diesel engine, the period which restrict | limits introduction of EGR gas to an intake passage can be shortened as much as possible, suppressing the production | generation of the condensed water in an intake passage.

1 is a diagram illustrating a schematic configuration of an internal combustion engine and an intake / exhaust system thereof according to Embodiment 1. FIG. Immediately after starting the internal combustion engine according to the first embodiment, the temperature Tw of the cooling water in the intercooler, the opening degree Dvn of the nozzle vane, the rotational speed Nt of the turbocharger, the pressure ratio Rp of the turbocharger, the opening degree Dth of the throttle valve, 6 is a time chart showing transitions of inflow intake air temperature Tgin, EGR valve opening degree Degr, flow rate Qegr of EGR gas introduced into the intake manifold, and fuel injection amount Qf from the fuel injection valve. It is a flowchart which shows the flow of EGR control which concerns on Example 1, and warm-up control of an intercooler. It is a map which shows the correlation with the temperature Tair of external air and the target cooling water temperature Twt based on Example 1. FIG. It is a map which shows the correlation with the pressure Pair of external air and the target cooling water temperature Twt based on Example 1. FIG. It is a map which shows the correlation with the humidity Hair of external air and the target cooling water temperature Twt based on Example 1. FIG. It is a flowchart which shows the flow of EGR control which concerns on the modification 1 of Example 1, and warm-up control of an intercooler. 6 is a map showing a correlation between an engine load of an internal combustion engine and a reference EGR gas flow rate ratio and a target EGR gas flow rate ratio according to a first modification of the first embodiment. FIG. 3 is a diagram illustrating a schematic configuration of an intake / exhaust system of an internal combustion engine according to a second embodiment.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the present embodiment are not intended to limit the technical scope of the invention to those unless otherwise specified.

<Example 1>
[Schematic configuration]
Here, a case where the present invention is applied to a control device for a diesel engine for driving a vehicle will be described as an example. FIG. 1 is a diagram showing a schematic configuration of an internal combustion engine and its intake / exhaust system according to the present embodiment. The internal combustion engine 1 is a diesel engine for driving a vehicle having four cylinders 2. Each cylinder 2 is provided with a fuel injection valve 3 that directly injects fuel into the cylinder 2.

  An intake manifold 4 and an exhaust manifold 5 are connected to the internal combustion engine 1. An intake passage 6 is connected to the intake manifold 4. An exhaust passage 7 is connected to the exhaust manifold 5. The “intake passage” according to the present invention includes not only the intake passage 6 but also the intake manifold 4. The “exhaust passage” according to the present invention includes not only the exhaust passage 7 but also the exhaust manifold 5.

  A compressor 8 a of a turbocharger 8 is installed in the intake passage 6. A turbine 8 b of a turbocharger 8 is installed in the exhaust passage 7. The turbine 8b is provided with a nozzle vane 8c. The pressure ratio of the turbocharger 8 is controlled by changing the opening of the nozzle vane 8c. Here, the pressure ratio of the turbocharger 8 is the ratio of the pressure of the intake air flowing out from the compressor 8a to the pressure of the intake air flowing into the compressor 8a. That is, the turbocharger 8 is a variable capacity turbocharger that can control the pressure ratio by controlling the opening degree of the nozzle vane 8c. A reducing agent addition valve 14 and an exhaust purification catalyst 9 are installed downstream of the turbine 8b in the exhaust passage 7. The exhaust purification catalyst 9 is a catalyst for reducing NOx in the exhaust. Examples of the exhaust purification catalyst 9 include a storage reduction type NOx catalyst and a selective reduction type NOx catalyst. The reducing agent addition valve 14 is provided on the upstream side of the exhaust purification catalyst 9. The reducing agent addition valve 14 adds a reducing agent to the exhaust gas in order to supply the reducing agent to the exhaust purification catalyst 9.

  An air flow meter 11 is provided in the intake passage 6 upstream of the compressor 8a. The air flow meter 11 is a sensor that detects the flow rate of intake air flowing into the internal combustion engine 1. A throttle valve 10 is provided in the intake passage 6 downstream of the compressor 8a. The throttle valve 10 controls the flow rate of the intake air flowing into the internal combustion engine 1.

  An intercooler 40 is provided in the intake passage 6 downstream of the compressor 8 a and upstream of the throttle valve 10. The intercooler 40 is a water-cooled intercooler. A cooling water passage 41 through which the cooling water circulates passes through the intercooler 40. A pump 42 and a radiator 43 are provided in the cooling water passage 41. The pump 42 is an electric pump for pumping cooling water flowing through the cooling water passage 41. In the radiator 43, the cooling water circulating through the cooling water passage 41 is cooled by heat exchange between the cooling water flowing through the cooling water passage 41 and the outside air. In the intercooler 40, heat exchange is performed between the intake air flowing through the intake passage 6 and the cooling water in the cooling water passage 41. As the cooling water flowing through the cooling water passage 41, any known heat medium may be used as long as it is a liquid heat medium. A cooling water circulation path (not shown) through which the cooling water circulates through the internal combustion engine 1 and the cooling water passage 41 are separate systems.

An upstream temperature sensor 12 is provided in the intake passage 6 downstream of the compressor 8 a and upstream of the intercooler 40. A downstream temperature sensor 13 is provided in the intake passage 6 downstream of the intercooler 40 and upstream of the throttle valve 10. The upstream temperature sensor 12 is a sensor that detects the temperature of the intake air flowing into the intercooler 40 (hereinafter also referred to as “inflow intake air temperature”). The downstream temperature sensor 13 is a sensor that detects the temperature of the intake air that has flowed out of the intercooler 40 (hereinafter also referred to as “outflow intake air temperature”).

  Further, an EGR device 30 is provided in the intake and exhaust system of the internal combustion engine 1 according to the present embodiment. The EGR device 30 introduces EGR gas having a flow rate according to the operating state of the internal combustion engine 1 into the intake manifold 4. The EGR device 30 includes an EGR passage 31, an EGR valve 32, an EGR cooler 33, a bypass passage 34, and a switching valve 35. One end of the EGR passage 31 is connected to the exhaust manifold 5, and the other end is connected to the intake manifold 4. Through this EGR passage 31, a part of the exhaust is introduced into the intake manifold 4 as EGR gas. The EGR valve 32 is provided in the EGR passage 31. The EGR valve 32 controls the flow rate of EGR gas introduced into the intake manifold 4.

  The EGR cooler 33 is provided upstream of the EGR valve 32 in the EGR passage 31. The EGR cooler 33 is a cooler for cooling the EGR gas flowing through the EGR passage 31. In the EGR cooler 33, heat exchange is performed between the EGR gas and the cooling water. Although a cooling water passage through which the cooling water flowing through the EGR cooler 33 circulates is omitted, it is a separate system from the cooling water passage 41 that passes through the intercooler 40. The bypass passage 34 is a passage through which the EGR gas flows by bypassing the EGR cooler 33. One end of the bypass passage 34 is connected to the upstream side of the EGR cooler 33 in the EGR passage 31, and the other end of the bypass passage 34 is downstream of the EGR cooler 33 in the EGR passage 31 and from the EGR valve 32. Is also connected upstream. The switching valve 35 is a three-way valve provided at a connection portion between one end of the bypass passage 34 and the EGR passage 31. The switching valve 35 is configured to be able to switch whether the EGR gas flows to the EGR cooler 33 or the bypass passage 34.

  The internal combustion engine 1 is also provided with an electronic control unit (ECU) 20. An air flow meter 11, an upstream temperature sensor 12, and a downstream temperature sensor 13 are electrically connected to the ECU 20. Further, a crank angle sensor 21, an accelerator opening sensor 22, an outside air temperature sensor 23, an outside air humidity sensor 24, and an outside air pressure sensor 25 are electrically connected to the ECU 20. The crank angle sensor 21 is a sensor that outputs a pulse signal corresponding to the engine speed of the internal combustion engine 1. The accelerator opening sensor 22 is a sensor that outputs a signal corresponding to the accelerator opening of a vehicle on which the internal combustion engine 1 is mounted. The outside air temperature sensor 23 is a sensor that detects the temperature of the outside air of the vehicle on which the internal combustion engine 1 is mounted. The outside air humidity sensor 24 is a sensor that detects the humidity of outside air of a vehicle on which the internal combustion engine 1 is mounted. The outside air pressure sensor 25 is a sensor that detects the pressure of outside air of a vehicle on which the internal combustion engine 1 is mounted. Output signals from these sensors are input to the ECU 20.

  Further, the fuel injection valve 3, the throttle valve 10, the nozzle vane 8 c, the reducing agent addition valve 14, the pump 42, the EGR valve 32, and the switching valve 35 are electrically connected to the ECU 20. These devices are controlled by the ECU 20.

[EGR control and intercooler warm-up control]
For example, a relatively low temperature intake air may flow through the intake passage 6 and the intake manifold 4 as when the internal combustion engine 1 is started under a low temperature outside air. If EGR gas is introduced into the intake manifold 4 through the EGR passage 31 at this time, the temperature of the intake air (EGR mixed intake air) after the introduction of EGR gas becomes equal to or lower than the dew point temperature, so that condensation occurs in the intake manifold 4. Water may be generated. If such condensed water is generated, corrosion of the intake manifold 4 and the like may be accelerated. Therefore, it is necessary to limit the introduction of EGR gas into the intake manifold 4 while the temperature of the intake air flowing into the intake manifold 4 is so low that the temperature of the EGR mixed intake air is lower than the dew point temperature.

  However, when the introduction of EGR gas is restricted, the effect of reducing the NOx emission amount from the internal combustion engine 1 by the EGR gas cannot be sufficiently obtained. Further, when the activation of the exhaust purification catalyst 9 is insufficient, such as immediately after the start of the internal combustion engine 1, the NOx purification function (that is, the NOx reduction function) of the exhaust purification catalyst 9 is not sufficiently exhibited. Therefore, in order to reduce NOx in the exhaust, it is desirable to shorten the period for limiting the introduction of EGR gas to the intake manifold 4 as much as possible.

  Here, when the temperature of the cooling water in the intercooler 40 is lower than the inflow intake air temperature, the intake air is cooled in the intercooler 40 by heat exchange with the cooling water. On the other hand, when the temperature of the cooling water in the intercooler 40 is higher than the inflow intake air temperature, the temperature of the intake air rises due to heat exchange with the cooling water in the intercooler 40. In the intercooler 40, the temperature of the intake air is changed by the heat exchange with the cooling water, and the temperature of the EGR mixed intake air formed by the intake air being mixed with the EGR gas in the intake manifold 4 is the temperature of the EGR mixed intake air. If the temperature can be raised to a temperature higher than the dew point temperature, the generation of condensed water can be suppressed even if the EGR gas is introduced into the intake manifold 4.

  Therefore, in the present embodiment, the temperature of the cooling water in the intercooler 40 is estimated based on the outflow intake air temperature detected by the downstream temperature sensor 13. Then, based on the temperature of the cooling water in the intercooler 40, it is determined whether or not the EGR gas is introduced into the intake manifold 4.

  2 shows the temperature Tw of the cooling water in the intercooler 40, the opening Dvn of the nozzle vane 8c, the rotational speed Nt of the turbocharger 8, the pressure ratio Rp of the turbocharger 8 and the throttle valve 10 immediately after the internal combustion engine 1 is started. 7 is a time chart showing changes in the opening degree Dth, the inflow intake air temperature Tgin, the opening degree Degr of the EGR valve 32, the flow rate Qegr of the EGR gas introduced into the intake manifold 4, and the fuel injection amount Qf from the fuel injection valve 3. . In FIG. 2, the horizontal axis represents time t. Note that the operation of the pump 42 is stopped immediately after the internal combustion engine 1 is started. That is, the circulation of the cooling water in the cooling water passage 41 is stopped. Therefore, the cooling water stays in the intercooler 40.

  FIG. 2 shows the transition of the values of the above parameters under the condition where the operating state of the internal combustion engine 1 is constant. In FIG. 2, Twt represents a predetermined target cooling water temperature. In FIG. 2, Degr1 represents a reference value (hereinafter referred to as “reference EGR opening”) of the opening degree Degr of the EGR valve 32 set according to the operating state of the internal combustion engine 1. In FIG. 2, Dth1 represents a reference value (hereinafter referred to as “reference EGR opening”) of the opening Dth of the throttle valve 10 set according to the operating state of the internal combustion engine 1. In FIG. 2, Dvn1 represents a reference value (hereinafter referred to as “reference vane opening”) of the opening degree Dvn of the nozzle vane 8c set according to the operating state of the internal combustion engine 1. In FIG. 2, Rp1 represents the pressure ratio of the turbocharger 8 when the opening degree Dvn of the nozzle vane 8c is controlled to the reference vane opening degree Dvn1 (hereinafter referred to as “reference pressure ratio”). In FIG. 2, Qf1 represents a reference value (hereinafter referred to as “reference injection amount”) of the fuel injection amount Qf set according to the engine load of the internal combustion engine 1.

As shown in FIG. 2, when the temperature Tw of the cooling water in the intercooler 40 is lower than the target cooling water temperature Twt, the EGR valve 32 is closed. 2, when the temperature Tw of the cooling water in the intercooler 40 reaches the target cooling water temperature Twt at the time indicated by t1, the EGR valve 32 is opened, and the EGR gas is introduced into the intake manifold 4. That is, when the temperature Tw of the cooling water in the intercooler 40 is lower than the target cooling water temperature Twt, EGR to the intake manifold 4 is continued until the temperature Tw of the cooling water rises above the target cooling water temperature Twt. Gas introduction is stopped. When the temperature Tw of the cooling water in the intercooler 40 reaches the target cooling water temperature Twt, the introduction stop of the EGR gas to the intake manifold 4 is released. Here, the target cooling water temperature Twt is the dew point temperature of the EGR mixed intake air that is formed by mixing the intake air temperature with the EGR gas in the intake manifold 4 in the intercooler 40. The temperature can be raised to a higher level.

  According to the above, while the temperature Tw of the cooling water in the intercooler 40 is lower than the target cooling water temperature Twt, that is, while the EGR gas is introduced into the intake manifold 4, there is a possibility that condensed water may be generated. The introduction of EGR gas is stopped. Then, when the temperature Tw of the cooling water in the intercooler 40 becomes equal to or higher than the target cooling water temperature Twt, that is, even if the EGR gas is introduced into the intake manifold 4, the generation of condensed water can be suppressed. Gas introduction is performed. At this time, after time t1, the opening degree Degr of the EGR valve 32 is controlled to the reference EGR opening degree Degr1.

  Further, in the present embodiment, while the temperature Tw of the cooling water in the intercooler 40 is lower than the target cooling water temperature Twt, that is, while the introduction of EGR gas is stopped, it stays in the intercooler 40. Intercooler warm-up control is performed to promote the temperature rise of the cooling water. Specifically, as shown in FIG. 2, while the introduction of the EGR gas to the intake manifold 4 is stopped (while the EGR valve 32 is closed), the opening degree Dvn of the nozzle vane 8c is determined as follows. Is controlled to an opening smaller than the reference vane opening Dvn1 corresponding to the operating state of the internal combustion engine 1 (as described above, in FIG. 2, the operating state of the internal combustion engine 1 is before and after time t1. Since it is constant, the reference vane opening Dvn1 is also a constant value). Thereby, the pressure ratio Rp of the turbocharger becomes higher than the reference pressure ratio Rp1 corresponding to the current operating state of the internal combustion engine 1. Further, while the introduction of the EGR gas to the intake manifold 4 is stopped, the opening degree Dth of the throttle valve 10 is smaller than the reference throttle opening degree Dth1 corresponding to the current operating state of the internal combustion engine 1. (As described above, in FIG. 2, since the operating state of the internal combustion engine 1 is constant before and after the time t1, the reference throttle opening Dth1 is also constant). When the cooling water temperature Tw in the intercooler 40 reaches the target cooling water temperature Twt, the opening degree Dvn of the nozzle vane 8c is controlled to the reference vane opening degree Dvn1. Thereby, the pressure ratio Rp of the turbocharger becomes the reference pressure ratio Rp1. When the temperature Tw of the cooling water in the intercooler 40 reaches the target cooling water temperature Twt, the opening Dth of the throttle valve 10 is controlled to the reference throttle opening Dth1.

  When the opening degree Dth of the throttle valve 10 is made smaller than the reference throttle opening degree Dth1, the pump loss of the internal combustion engine 1 is smaller than when the opening degree Dth of the throttle valve 10 is controlled to the reference throttle opening degree Dth1. Increase. Therefore, the fuel injected from the fuel injection valve 3 is controlled while the opening Dth of the throttle valve 10 is controlled to be smaller than the reference throttle opening Dth1 (that is, while the introduction of EGR gas is stopped). The injection amount Qf is increased from the reference injection amount Qf1. Here, the diesel engine is normally operated at a lean air-fuel ratio. Therefore, even in the case where the opening Dth of the throttle valve 10 is controlled to be smaller than the reference throttle opening Dth1 in the internal combustion engine 1, there is a surplus in the combustion chamber with respect to the fuel of the reference injection amount Qf1. There will be air. Therefore, when the fuel injection amount is increased from the reference injection amount Qf1, the increased amount of fuel also contributes to combustion. Therefore, even when the pump loss of the internal combustion engine 1 is increasing, it is possible to output a desired torque by increasing the fuel injection amount in the internal combustion engine 1 beyond the reference injection amount Qf1.

According to the above, while the introduction of the EGR gas is stopped, when the introduction of the EGR gas is performed, that is, the operation state of the internal combustion engine 1 is the same and the temperature Tw of the cooling water in the intercooler 40 is the same. The pressure ratio Rp of the turbocharger 8 is made higher and the opening degree Dth of the throttle valve 10 is made smaller than when the temperature is equal to or higher than the target coolant temperature Twt. When the pressure ratio Rp of the turbocharger 8 increases, the amount of intake air flowing into the intake passage 6 on the downstream side of the compressor 8a increases. Further, when the opening degree Dth of the throttle valve 10 is reduced, the outflow of intake air from the intake passage 6 upstream of the throttle valve 10 to the intake passage 6 downstream thereof is further restricted. Therefore, by increasing the pressure ratio Rp of the turbocharger 8 and decreasing the opening degree Dth of the throttle valve 10, a portion of the intake passage 6 that is downstream of the compressor 8 a and upstream of the throttle valve 10, that is, an interface The pressure of the intake air at the portion where the cooler 40 is installed can be increased efficiently. As a result, the inflow intake air temperature Tgin and the temperature of the intake air in the intercooler 40 can be increased more quickly. At this time, the circulation of the cooling water in the cooling water passage 41 is stopped, and the cooling water stays in the intercooler 40. Therefore, when the temperature of the intake air rises, the temperature rise of the cooling water by heat exchange with the intake air in the intercooler 40 is promoted. Therefore, the temperature Tw of the cooling water in the intercooler 40 can be increased more quickly to the target cooling water temperature Twt or more.

  The cooling water in the intercooler 40 has a specific heat larger than that of the intake air. Therefore, after the temperature Tw of the cooling water in the intercooler 40 once rises above the target cooling water temperature Twt, the pressure ratio Rp of the turbocharger 8 is reduced to the reference pressure ratio Rp1, and the opening degree Dth of the throttle valve 10 is the reference. Even if the inflow intake air temperature Tgin is decreased by increasing the throttle opening Dth1, the temperature of the cooling water in the intercooler 40 can be rapidly increased if the circulation of the cooling water in the cooling water passage 41 is continued. Temperature drop is unlikely to occur. Therefore, after the time t1 in FIG. 2, the outflow intake air temperature can be made higher than the inflow intake air temperature by exchanging heat with the cooling water in the intercooler 40. That is, in the intercooler 40, the temperature of the intake air is increased to such an extent that the temperature of the EGR mixed intake air formed by mixing the intake air with the EGR gas is higher than the dew point temperature of the EGR mixed intake air. it can. Further, while the pressure ratio Rp of the turbocharger 8 is higher than the reference pressure ratio Rp1 and the opening degree Dth of the throttle valve 10 is smaller than the reference throttle opening degree Dth1, the intercooler 40 itself and the compressor 8a And the temperature of the intake passage 6 between the throttle valve 10 and the throttle valve 10 also increase as the intake air temperature rises. The intercooler 40 itself and the intake passage 6 itself have a specific heat larger than that of the intake air. Therefore, as shown in FIG. 2, the temperature of the cooling water in the intercooler 40 can be generally maintained due to the influence of the temperature of the intercooler 40 itself and the intake passage 6 itself rising after the time t1.

  By controlling the warm-up of the intercooler as described above, the temperature Tw of the cooling water in the intercooler 40 can be quickly increased to the target cooling water temperature Twt or more, so that the EGR gas to the intake manifold 4 can be increased. Implementation can be performed earlier. Therefore, it is possible to shorten the period for limiting the introduction of EGR gas to the intake manifold 4 as much as possible while suppressing the generation of condensed water in the intake manifold 4.

  Further, when the opening degree of the nozzle vane 8c of the turbocharger 8 is reduced, so-called internal EGR gas, which is exhaust gas remaining in the cylinder 2 without being exhausted from the cylinder 2 in the exhaust stroke, tends to increase. Therefore, according to the warm-up control of the intercooler as described above, the opening degree Dnv of the nozzle vane 8c is made smaller than the reference vane opening degree Dvn1 while the introduction of the EGR gas to the intake manifold 4 is stopped. Thus, the internal EGR gas increases as compared with the case where the opening degree Dnv of the nozzle vane 8c is controlled to the reference vane opening degree Dvn1. As a result, the effect of reducing the NOx emission amount from the internal combustion engine 1 by the internal EGR gas can be obtained.

Note that the execution timing of the above-described intercooler warm-up control is not limited to when the internal combustion engine 1 is started. That is, during the operation of the internal combustion engine 1, the above-described warm-up control of the intercooler is also performed when the temperature Tw of the cooling water in the intercooler 40 falls below the target cooling water temperature Twt.

[Control flow]
FIG. 3 is a flowchart showing the flow of EGR control and intercooler warm-up control according to this embodiment. This flow is stored in the ECU 20 and is repeatedly executed by the ECU 20 at a predetermined interval.

  In this flow, first, in S101, the temperature Tw of the cooling water in the intercooler 40 is calculated based on the detected value of the downstream temperature sensor 13. The detected value of the downstream temperature sensor 13, that is, the correlation between the outflow intake air temperature and the temperature Tw of the cooling water in the intercooler 40 is stored in advance in the ECU 20 as a map. In S101, the temperature Tw of the cooling water is calculated using this map. Next, in S102, it is determined whether or not the temperature Tw of the cooling water in the intercooler 40 calculated in S101 is equal to or higher than the target cooling water temperature Twt. As described above, the target cooling water temperature Twt is the same as the temperature of the intake air by the heat exchange with the cooling water in the intercooler 40, and the temperature of the EGR mixed intake air formed by the intake air mixing with the EGR gas. This is a temperature that can be raised to a level higher than the dew point temperature of the EGR mixed intake air. Such a target cooling water temperature Twt is determined in advance based on experiments or the like and is stored in the ECU 20. In this embodiment, the target cooling water temperature Twt is set as a constant value.

  If an affirmative determination is made in S102, then the process of S103 is executed. As will be described later, when a negative determination is made in S102, the driving of the pump 42 is prohibited. In S103, the prohibited driving of the pump 42 is permitted. As a result, normal drive control is performed for the pump 42.

  Here, even when the drive control of the normal pump 42 is being performed, the pump 42 is always driven, and the cooling water circulation in the cooling water passage 41 is not continuously performed. In the normal drive control of the pump 42, the pump 42 is controlled to maintain the outflow intake air temperature detected by the detection of the downstream temperature sensor 13 in the vicinity of a predetermined target outflow intake air temperature. That is, when the outflow intake air temperature is lower than the target outflow intake air temperature, even in the normal drive control of the pump 42, the drive of the pump 42 is stopped and the cooling water circulation in the cooling water passage 41 is not performed. Here, the target outflow intake air temperature is set to a temperature equal to or higher than the target cooling water temperature Twt.

  Therefore, even if the drive of the prohibited pump 42 is permitted in S103, if the outflow intake air temperature is lower than the target outflow intake air temperature, the pump 42 does not immediately start to drive. 42 stops driving. It should be noted that, when this flow is executed the last time, an affirmative determination is made in S102, and if the drive of the pump 42 has already been permitted and normal drive control is being performed on the pump 42, S103 In, normal drive control is continued.

Next, in S104, the opening degree Degr of the EGR valve 32 is controlled to the reference EGR opening degree Degr1 corresponding to the current operating state of the internal combustion engine 1. That is, the introduction of EGR gas into the intake manifold 4 is executed. Next, in S105, the opening degree Dvn of the nozzle vane 8c is controlled to the reference vane opening degree Dvn1 according to the current operating state of the internal combustion engine 1. As a result, the pressure ratio Rp of the turbocharger 8 is controlled to the reference pressure ratio Rp1. Next, in S106, the opening degree Dth of the throttle valve 10 is controlled to the reference throttle opening degree Dth1 corresponding to the current operating state of the internal combustion engine 1. Note that the correlation between the operating state of the internal combustion engine 1 and each of the reference EGR opening degree Degr1, the reference vane opening degree Dvn1, and the reference throttle opening degree Dt1 is determined in advance based on experiments or the like, and is stored in the ECU 20 as a map. It is remembered.

  Next, in S107, the fuel injection amount Qf from the fuel injection valve 3 is set to a reference injection amount Qf1 corresponding to the current operating state of the internal combustion engine 1. Thereby, when the temperature Tw of the cooling water in the intercooler 40 is equal to or higher than the target cooling water temperature Twt, and the introduction of the EGR gas to the intake manifold 4 is being executed, the fuel injection amount Qf in the internal combustion engine 1 is the reference. The injection amount Qf1 is controlled. The correlation between the operating state of the internal combustion engine 1 and the reference injection amount Qf1 is determined in advance based on experiments and the like, and is stored in the ECU 20 as a map.

  On the other hand, if a negative determination is made in S102, the driving of the pump 42 is prohibited in S108. That is, the circulation of the cooling water in the cooling water passage 41 is stopped. Next, in S109, the EGR valve 32 is closed. That is, the introduction of EGR gas to the intake manifold 4 is stopped. Next, in S110, the opening degree Dvn of the nozzle vane 8c is controlled to a target vane opening degree Dvn2 smaller than the reference vane opening degree Dvn1 corresponding to the current operating state of the internal combustion engine 1. As a result, the pressure ratio Rp of the turbocharger 8 becomes higher than the reference pressure ratio Rp1 corresponding to the current operating state of the internal combustion engine 1. Next, in S111, the opening degree Dth of the throttle valve 10 is controlled to a target throttle opening degree Dth2 that is smaller than the reference throttle opening degree Dth1 corresponding to the current operating state of the internal combustion engine 1.

  As described above, when the opening degree Dvn of the nozzle vane 8c is controlled to the target vane opening degree Dvn2, the pressure ratio Rp of the turbocharger 8 is increased from the reference pressure ratio Rp1, and the opening degree Dth of the throttle valve 10 is set to the target throttle. By controlling the opening degree Dth2, the intake pressure in the portion of the intake passage 6 downstream of the compressor 8a and upstream of the throttle valve 10 increases. That is, compared with the case where the pressure ratio Rp of the turbocharger 8 is set to the reference pressure ratio Rp1 and the opening degree Dth of the throttle valve 10 is set to the reference throttle opening degree Dth1, the pressure of the intake air in the portion in the intake passage 6 is higher. Get higher. As a result, the temperature of the intake air in that portion increases. At this time, the target vane opening degree Dvn2 and the target throttle opening degree Dth2 may be set so that the inflow intake air temperature detected by the upstream temperature sensor 12 is equal to or higher than a predetermined target inflow intake air temperature. At this time, the target inflow intake air temperature is a temperature equal to or higher than the target cooling water temperature Twt. By raising the inflow intake air temperature above the target inflow intake air temperature, the temperature of the cooling water in the intercooler 40 can be raised above the target cooling water temperature Twt.

  Here, as the opening degree Dvn of the nozzle vane 8c and the opening degree Dth of the throttle valve 10 are reduced, the pressure of the intake air in the portion downstream of the compressor 8a in the intake passage 6 and upstream of the throttle valve 10 becomes higher. Become. As a result, the temperature of the intake air at that portion further increases. Therefore, the target vane opening degree Dvn2 and the target throttle opening degree Dth2 may be set based on the difference between the current inflow intake air temperature detected by the upstream temperature sensor 12 and the target inflow intake air temperature. In this case, the target vane opening degree Dvn2 and the target throttle opening degree Dth2 are set to smaller values as the difference between the current inflow intake air temperature and the target inflow intake air temperature is larger.

  Alternatively, the opening degree Dvn of the nozzle vane 8c and the opening degree Dth of the throttle valve 10 may be gradually reduced until the inflow intake air temperature detected by the upstream temperature sensor 12 reaches the target inflow intake air temperature. . In this case, the opening degree Dvn of the nozzle vane 8c and the opening degree Dth of the throttle valve 10 are gradually reduced by a predetermined amount. When the inflow intake air temperature reaches the target inflow intake air temperature, the opening degree Dvn of the nozzle vane 8c and the opening degree Dth of the throttle valve 10 are maintained at the opening degree at that time.

  Next, in S112, the fuel injection amount Qf from the fuel injection valve 3 is set to a target injection amount Qf2 that is larger than the reference injection amount Qf1 corresponding to the current operating state of the internal combustion engine 1. At this time, the amount of increase from the reference injection amount Qf1 is determined according to the amount of increase in the pump loss of the internal combustion engine 1 due to the opening degree Dth of the throttle valve 10 being controlled to the target throttle opening degree Dth2. Specifically, the amount of increase from the reference injection amount Qf1 is determined according to the difference between the reference throttle opening Dth1 and the target throttle opening Dth2. That is, the larger the amount of decrease in the target throttle opening Dth2 with respect to the reference throttle opening Dth1, the greater the increase in the target injection amount Qf2 with respect to the reference injection amount Qf1. Thereby, when the temperature Tw of the cooling water in the intercooler 40 is lower than the target cooling water temperature Twt and the introduction of the EGR gas into the intake manifold 4 is stopped, the fuel injection amount Qf in the internal combustion engine 1 is the target injection. The amount is controlled to Qf2.

  By controlling the fuel injection amount Qf in the internal combustion engine 1 to the target injection amount Qf2, the internal combustion engine 1 resulting from an increase in pump loss due to the opening degree Dth of the throttle valve 10 being controlled to the target throttle opening degree Dth2. The decrease in torque can be compensated. However, it is not always necessary to increase the fuel injection amount Qf in the internal combustion engine 1 to the target injection amount Qf2 as long as the amount of decrease in the torque of the internal combustion engine 1 caused by the increase in pump loss is within the allowable range.

  When a high load operation is required for the internal combustion engine 1, if the opening degree Dth of the throttle valve 10 is excessively reduced, the intake air amount supplied to the internal combustion engine 1 becomes insufficient. There is also a fear. In such a state, even if the fuel injection amount Qf in the internal combustion engine 1 is increased from the reference injection amount Qf1, it becomes difficult to achieve the operating state required for the internal combustion engine 1. Therefore, a lower limit value may be set for the target throttle opening degree Dth2. In this case, the lower limit value of the target throttle opening degree Dth2 is set to the minimum opening degree that can secure the target intake air amount for achieving the operation state currently required for the internal combustion engine 1. Specifically, the lower limit value of the target throttle opening Dth2 may be set based on the current accelerator opening detected by the accelerator opening sensor 22. In this case, the correlation between the accelerator opening and the lower limit value of the target throttle opening Dth2 is stored in advance in the ECU 20 as a map. Then, using this map, the lower limit value of the current target throttle opening Dth2 is set. The ECU 20 controls the opening degree Dth of the throttle valve 10 to be equal to or higher than the lower limit value set in this manner, so that the internal combustion engine 1 can be operated at a high load while the intercooler warm-up control is being executed. Even if it is required, it is possible to achieve the operation state required for the internal combustion engine 1.

  In the above-described flow, when a negative determination is made in S102, that is, when the temperature Tw of the cooling water in the intercooler 40 is lower than the target cooling water temperature Twt, the driving of the pump 42 is prohibited. However, even if the cooling water temperature Tw in the intercooler 40 is lower than the target cooling water temperature Twt, the driving of the pump 42 is not necessarily prohibited. That is, even when the temperature Tw of the cooling water in the intercooler 40 is lower than the target cooling water temperature Twt, the driving of the pump 42 may be permitted. However, in this case, when the pump 42 is driven, the cooling water passage is compared with the case where the operation state of the internal combustion engine 1 is the same and the temperature Tw of the cooling water in the intercooler 40 is equal to or higher than the target cooling water temperature Twt. The pump 42 is controlled so that the flow rate of the cooling water circulating through 41 decreases. Thus, by reducing the flow rate of the cooling water circulating in the cooling water passage 41, that is, the flow rate of the cooling water flowing in the intercooler 40, the temperature of the cooling water due to heat exchange with the intake air in the intercooler 40 is reduced. Ascending is easily promoted. However, when it is necessary to quickly increase the temperature Tw of the cooling water in the intercooler 40 to the target cooling water temperature Twt or more, the cooling water is prohibited by prohibiting the driving of the pump 42 as described in the above flow. It is preferable to stop the circulation of the cooling water in the passage 41.

  In the above-described flow, the target cooling water temperature Twt is set to a predetermined constant value. However, the target cooling water temperature Twt may be set according to the state of the outside air (atmosphere). FIG. 4 is a map showing the correlation between the outside air temperature Tair detected by the outside air temperature sensor 23 and the target cooling water temperature Twt. FIG. 5 is a map showing the correlation between the outside air pressure Pair detected by the outside air pressure sensor 25 and the target cooling water temperature Twt. FIG. 6 is a map showing the correlation between the outside air humidity Hair detected by the outside air humidity sensor 24 and the target cooling water temperature Twt.

  Generally, the lower the temperature of the outside air and the higher the pressure of the outside air, the higher the possibility that the amount of moisture contained in the intake air per unit volume is small. For this reason, the lower the temperature of the outside air and the higher the pressure of the outside air, the more difficult the condensed water is generated in the intake manifold 4. Therefore, as shown in FIG. 4, the target cooling water temperature Twt may be lowered as the outside air temperature Tair is lower. Further, as shown in FIG. 5, the target cooling water temperature Twt may be lowered as the outside air pressure Pair increases. Further, the lower the humidity of the outside air, the smaller the amount of water contained in the intake air per unit volume. Therefore, the lower the humidity of the outside air, the less likely the condensed water is generated in the intake manifold 4. Therefore, as shown in FIG. 6, the target coolant temperature Twt may be lowered as the outside air humidity Hair is lower. According to these, when the condensed water tends to be relatively difficult to be generated, the target cooling water temperature Twt is lowered. Therefore, the period during which the introduction of EGR gas to the intake manifold 4 is restricted can be shortened.

  When the target cooling water temperature Twt is set according to the state of the outside air, the correlation between the outside air temperature Tair, the outside air pressure Pair, or the outside air humidity Hair and the target cooling water temperature Twt as shown in FIGS. Is stored in the ECU 20 in advance. The target coolant temperature Twt is set by the ECU 20 using the stored map. 4 to 6, the target cooling water temperature Twt is continuously changed in accordance with the change in the outside air temperature Tair, the outside air pressure Pair, or the outside air humidity Hair. However, the target cooling water temperature Twt may be changed stepwise in accordance with the change in the outside air temperature Tair, the outside air humidity Hair, or the outside air pressure Pair.

  In this embodiment, the temperature Tw of the cooling water in the intercooler 40 is calculated based on the detection value of the downstream temperature sensor 13. However, the intercooler 40 may be provided with a cooling water temperature sensor that detects the temperature Tw of the cooling water in the intercooler 40. And in S101 of the flowchart shown in FIG. 3, you may read the detected value of this cooling water temperature sensor.

  Further, in this embodiment, the introduction of EGR gas to the intake manifold 4 was stopped while the temperature Tw of the cooling water in the intercooler 40 was lower than the target cooling water temperature Twt. However, it is not always necessary to stop the introduction of the EGR gas into the intake manifold 4. That is, while the cooling water temperature Tw in the intercooler 40 is lower than the target cooling water temperature Twt, the operation state of the internal combustion engine 1 is the same, and the cooling water temperature in the intercooler 40 is equal to or higher than the target cooling water temperature Twt. The flow rate of the EGR gas may be decreased as compared with the case of. In this case, the flow rate of the EGR gas is reduced to the extent that the amount of condensed water generated due to the introduction of the EGR gas into the intake manifold 4 is within the allowable range. In this case, in step S109 of the flowchart shown in FIG. 3, the opening degree Degr of the EGR valve 32 is controlled to be smaller than the reference EGR opening degree Degr1 corresponding to the current operating state of the internal combustion engine 1. As described above, the amount of condensed water generated in the intake manifold 4 can also be suppressed by reducing the flow rate of the EGR gas.

In the present embodiment, the turbocharger 8 in which the nozzle vanes 8c are provided in the turbine 8b corresponds to the supercharger according to the present invention. Further, in this embodiment, the ECU 20 functions as a control unit according to the present invention by executing the processing from S103 to S106 and S108 to S111 in the flowchart shown in FIG.

[Modification 1]
FIG. 7 is a flowchart showing a flow of EGR control and intercooler warm-up control when the internal combustion engine according to the first modification of the present embodiment is started. This flow is stored in the ECU 20 and is repeatedly executed by the ECU 20 at a predetermined interval. In the flowchart shown in FIG. 7, steps that perform the same processes as those in the flowchart shown in FIG. 3 are given the same reference numerals, and descriptions thereof are omitted.

  In this flow, after the opening degree Degr of the EGR valve 32 is controlled to the reference EGR opening degree Degr1 in S104, the process of S205 is executed. In S205, the bypass passage 34 is shut off by the switching valve 35. That is, the flow path of the EGR gas is controlled to the EGR cooler 33 side. Thereby, the EGR gas cooled by the EGR cooler 33 is introduced into the intake manifold 4. Next, the process of S105 is executed. The target cooling water temperature Tw is set so that the temperature of the EGR mixed intake air formed by mixing the EGR gas cooled by the EGR cooler 33 and the intake air in the intake manifold 4 becomes higher than the dew point temperature. 40 is set to a temperature at which the temperature of the intake air can be raised.

  Further, after the drive of the pump 42 is prohibited in S108, the process of S209 is executed. In S209, the opening degree Degr of the EGR valve 32 is controlled to a target EGR opening degree Degr2 smaller than the reference EGR opening degree Degr1 corresponding to the current operating state of the internal combustion engine 1. Thereby, the flow rate of the EGR gas is reduced as compared with the case where the opening degree Degr of the EGR valve 32 is controlled to the reference EGR opening degree Degr1, that is, in the case where an affirmative determination is made in S102. Next, in S210, the switching valve 35 shuts off the EGR cooler 33 side. That is, the flow path of EGR gas is controlled to the bypass passage 34 side. Next, the process of S110 is performed.

  In this modification, when the temperature Tw of the cooling water in the intercooler 40 is lower than the target cooling water temperature Twt, the amount of EGR is smaller than when the temperature Tw of the cooling water in the intercooler 40 is equal to or higher than the target cooling water temperature Twt. Gas is introduced 4 into the intake manifold. At this time, EGR gas flows through the bypass passage 34. Therefore, the EGR gas is suppressed from being cooled by the EGR cooler 33. Thereby, the temperature fall of EGR gas is suppressed. Therefore, the temperature of the EGR mixed intake air can be increased as compared with the case where the same amount of EGR gas cooled by the EGR cooler 33 is introduced into the intake manifold 4. Therefore, when the temperature Tw of the cooling water in the intercooler 40 is lower than the target cooling water temperature Twt, the EGR gas is reduced in addition to the cooling of the EGR gas. The production | generation of the condensed water at the time of being introduce | transduced into 4 can be suppressed more.

  In this modification, the switching valve 35 corresponds to a control valve according to the present invention. Moreover, in this modification, ECU20 functions as a control part which concerns on this invention by performing the process by S103 to S106, S108 to S111, S205, S209, and S210 in the flowchart shown in FIG. .

In this modification, instead of the switching valve 35, the ratio of the flow rate of the EGR gas flowing through the EGR cooler 33 and the flow rate of the EGR gas flowing through the bypass passage 34 (hereinafter, referred to as “EGR gas flow rate ratio”). ) May be adopted so that it can be changed continuously or stepwise. In this case, the control valve is controlled by the ECU 20, whereby the EGR gas flow rate ratio is changed according to the operating state of the internal combustion engine 1. At this time, when the flow rate of EGR gas is decreased because the temperature Tw of the cooling water in the intercooler 40 is lower than the target cooling water temperature Twt, the operating state of the internal combustion engine 1 is the same and the Compared with the case where the temperature Tw of the cooling water in the cooler 40 is equal to or higher than the target cooling water temperature Twt, the ratio of the flow rate of the EGR gas flowing through the bypass passage 34 is increased.

  Specifically, in the above-described flow, when the opening degree Degr of the EGR valve 32 is controlled to the reference EGR opening degree Degr1 in S104, the control valve sets the EGR gas flow rate ratio to the current operating state of the internal combustion engine 1. The reference EGR gas flow rate ratio is controlled accordingly. On the other hand, in the flow described above, when the opening degree Degr of the EGR valve 32 is controlled to the target EGR opening degree Degr2 smaller than the reference EGR opening degree Degr1 in S209, the control valve sets the EGR gas flow rate ratio to the current internal combustion engine. The target EGR gas flow rate ratio is controlled such that the ratio of the flow rate of the EGR gas flowing through the bypass passage 34 is larger than the reference EGR gas flow rate ratio corresponding to the operation state of 1. Note that the correlation between the operating state of the internal combustion engine 1 and each of the reference EGR gas flow rate ratio and the target EGR gas flow rate ratio may be determined in advance based on experiments or the like and stored in the ECU 20 as a map.

  FIG. 8 is an example of a map showing the correlation between the engine load of the internal combustion engine, the reference EGR gas flow rate ratio, and the target EGR gas flow rate ratio. In FIG. 8, the horizontal axis represents the engine load Qe of the internal combustion engine 1, and the vertical axis represents the ratio Rb of the flow rate of EGR gas flowing through the bypass passage 34. In FIG. 8, a line L1 indicates the reference EGR gas flow rate ratio, and a line L2 indicates the target EGR gas flow rate ratio. In the map shown in FIG. 8, the reference EGR gas flow rate ratio and the target EGR gas flow rate ratio are set such that the higher the engine load Qe of the internal combustion engine 1 is, the smaller the ratio Rb of the flow rate of EGR gas flowing through the bypass passage 34 is. Each is set. When the engine load Qe of the internal combustion engine 1 is the same, the target EGR gas flow rate ratio has a larger ratio of the flow rate of EGR gas flowing through the bypass passage 34 than the reference EGR gas flow rate ratio. (L2> L1).

  According to the control of the EGR gas flow rate ratio as described above, when the temperature Tw of the cooling water in the intercooler 40 is lower than the target cooling water temperature Twt, the temperature Tw of the cooling water in the intercooler 40 is the target cooling water temperature. The ratio of the flow rate of the EGR gas flowing through the bypass passage 34 is larger than when Twt or more. Therefore, even when the EGR gas flow rate ratio is controlled as described above, when the temperature Tw of the cooling water in the intercooler 40 is lower than the target cooling water temperature Twt, in addition to the flow rate of the EGR gas being reduced, Temperature drop can be suppressed. Therefore, the generation of condensed water when EGR gas is introduced into the intake manifold 4 can be further suppressed.

<Example 2>
The configuration of the intake and exhaust system of the internal combustion engine according to the present embodiment is different from that of the first embodiment in that the turbocharger is a two-stage twin turbo. Since the configuration other than the turbocharger in the internal combustion engine and the intake / exhaust system thereof according to the present embodiment is the same as that of the first embodiment, the description thereof is omitted.

  FIG. 9 is a diagram illustrating a schematic configuration of the turbocharger according to the present embodiment. In the present embodiment, in the intake passage 6, a compressor (low pressure side compressor) 81 a of the low pressure side turbocharger 81 and a compressor (high pressure side compressor) 82 a of the high pressure side turbocharger 82 are sequentially arranged in series from the upstream side. In the exhaust passage 7, a turbine (high-pressure turbine) 82 b of the high-pressure turbocharger 82 and a turbine (low-pressure turbine) 81 b of the low-pressure turbocharger 81 are sequentially arranged in series from the upstream side.

  The intake passage 6 is provided with an intake-side bypass passage 61 that bypasses the high-pressure compressor 82a. One end of the intake-side bypass passage 61 is connected to the intake passage 6 between the low-pressure compressor 81a and the high-pressure compressor 82a, and the other end of the intake-side bypass passage 61 is downstream (and intercooler) from the high-pressure compressor 82a. It is connected to the intake passage 6 on the upstream side of 40. The exhaust passage 7 is provided with a first exhaust-side bypass passage 71 that bypasses the high-pressure turbine 82b and a second exhaust-side bypass passage 72 that bypasses the low-pressure turbine 81b. One end of the first exhaust side bypass passage 71 is connected to the exhaust passage 7 upstream from the high pressure side turbine 82b, and the other end of the first exhaust side bypass passage 71 is between the high pressure side turbine 82b and the low pressure side turbine 81b. The exhaust passage 7 is connected. One end of the second exhaust-side bypass passage 72 is connected to the exhaust passage 7 between the high-pressure turbine 82b and the low-pressure turbine 81b, and the other end of the second exhaust-side bypass passage 72 is downstream of the low-pressure turbine 81b. The exhaust passage 7 is connected.

  An intake control valve (ACV) 63 is provided in the intake side bypass passage 61. An exhaust control valve (ECV) 73 is provided in the first exhaust side bypass passage 71. An exhaust bypass valve (EBV) 74 is provided in the second exhaust side bypass passage 72. ACV63, ECV73, and EBV74 are electrically connected to ECU20. These valves are controlled by the ECU 20. In FIG. 9, arrows indicate the flow of intake and exhaust.

  In the present embodiment, the ratio of the pressure of the intake air flowing out from the high pressure side compressor 82a to the pressure of the intake air flowing into the low pressure side compressor 81a corresponds to the “pressure ratio of the supercharger” according to the present invention. In this embodiment, the pressure ratio between the low-pressure side turbocharger 81 and the high-pressure side turbocharger 82 can be controlled by changing the opening degree of at least one of the ACV 63, the ECV 73, and the EBV 74. Therefore, in the intercooler warm-up control according to the present embodiment, instead of the opening degree control of the nozzle vane 8c in the intercooler warm-up control according to the first embodiment, at least one of ACV63, ECV73, and EBV74 is used. Opening control is performed.

  More specifically, also in the present embodiment, when the temperature Tw of the cooling water in the intercooler 40 is higher than the target cooling water temperature Twt, the EGR gas is introduced into the intake manifold 4. In this case, the ECU 20 controls the openings of the ACV 63, the ECV 73, and the EBV 74 to the respective reference openings. Each reference opening degree of ACV63, ECV73, and EBV74 is determined in advance according to the operating state of the internal combustion engine 1, and is stored in the ECU 20 as a map. On the other hand, when the temperature Tw of the cooling water in the intercooler 40 is lower than the target cooling water temperature Twt, the EGR valve 32 is controlled by the ECU 20 until the temperature Tw of the cooling water rises above the target cooling water temperature Twt. Is closed, the introduction of EGR gas into the intake manifold 4 is stopped. The ECU 20 opens the throttle valve 10 while the coolant temperature Tw in the intercooler 40 is lower than the target coolant temperature Twt (that is, while the introduction of EGR gas to the intake manifold 4 is stopped). The degree is controlled to be smaller than the reference throttle opening, and at least one of ACV63, ECV73, and EBV74 is controlled to be smaller than the reference opening. When the coolant temperature Tw in the intercooler 40 reaches the target coolant temperature Twt, the ECU 20 controls the opening degree Dvn of the nozzle vane 8c to the reference vane opening degree Dvn1, and the ACV63, ECV73, and EBV74. The opening is controlled to each reference opening.

According to the control as described above, while the introduction of the EGR gas is stopped, when the introduction of the EGR gas is performed, that is, the operation state of the internal combustion engine 1 is the same and the cooling water in the intercooler 40 is The opening degree of the throttle valve 10 is made smaller and the pressure ratio between the low-pressure side turbocharger 81 and the high-pressure side turbocharger 82 is made higher than when the temperature Tw is equal to or higher than the target cooling water temperature Twt. Therefore, in the first embodiment, as in the case where the opening degree of the throttle valve 10 is made smaller than the reference throttle opening degree and the pressure ratio of the turbocharger 8 is made higher than the reference pressure ratio, the inflow intake air temperature Tgin and the intercooler 40 inside The intake air temperature can be increased more quickly. As a result, the temperature rise of the cooling water by heat exchange with the intake air in the intercooler 40 is promoted. Therefore, the temperature Tw of the cooling water in the intercooler 40 can be increased more quickly to the target cooling water temperature Twt or more. Therefore, as in the case where the warm-up control of the intercooler according to the first embodiment is performed, a period for limiting the introduction of EGR gas to the intake manifold 4 while suppressing the generation of condensed water in the intake manifold 4 is allowed. As short as possible.

  Also in the present embodiment, as in the first embodiment, while the temperature of the cooling water in the intercooler 40 is lower than the target cooling water temperature, the ECU 20 does not stop the introduction of the EGR gas to the intake manifold 4. By controlling the opening degree of the EGR valve 32 to the target EGR opening degree that is smaller than the reference EGR opening degree, the operating state of the internal combustion engine 1 is the same, and the temperature of the cooling water in the intercooler 40 is the target cooling water temperature. Compared to the above case, the flow rate of the EGR gas may be decreased.

  In the present embodiment, the supercharger according to the present invention is configured including the low-pressure side turbocharger 81, the high-pressure side turbocharger 82, the ACV 63, the ECV 73, and the EBV 74. In the present embodiment, the ECU 20 functions as a control unit according to the present invention by controlling the ACV 63, the ECV 73, or the EBV 74 in addition to the EGR valve 32 and the throttle valve 10 as described above.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 4 ... Intake manifold 5 ... Exhaust manifold 6 ... Intake passage 7 ... Exhaust passage 8 ... Turbocharger 8a, compressor 8b, turbine 8c, nozzle vane 10, -Throttle valve 11 -Air flow meter 12 -Upstream temperature sensor 13 -Downstream temperature sensor 20 -ECU
21 ·· Crank angle sensor 22 · · accelerator opening sensor 23 · · outside air temperature sensor 24 · · outside air humidity sensor 25 · · outside air pressure sensor 30 · · EGR device 31 · · EGR passage 32 · · EGR valve 33 · · EGR Cooler 34, bypass passage 35, switching valve 40, intercooler 41, cooling water passage 42, pump 43, radiator 61, intake side bypass passage 63, intake control valve (ACV)
71..First exhaust side bypass passage 72..Second exhaust side bypass passage 73..Exhaust control valve (ECV)
74..Exhaust bypass valve (EBV)
··· Low pressure side turbocharger 81a · · Low pressure side compressor 81b · · Low pressure side turbine 82 · · High pressure side turbocharger 82a · · High pressure side compressor 82b · · High pressure side turbine

Claims (6)

A supercharger having a compressor provided in an intake passage, the supercharger capable of controlling a pressure ratio that is a ratio of the pressure of intake air flowing out of the compressor to the pressure of intake air flowing into the compressor;
A throttle valve that is provided in the intake passage downstream of the compressor and controls the flow rate of intake air;
A heat medium passage is provided in an intake passage downstream of the compressor and upstream of the throttle valve, through which a liquid heat medium circulates, and heat exchange is performed between the heat medium and the intake air. Intercooler to be performed,
A diesel engine control device comprising: an EGR device that introduces a portion of exhaust gas flowing through the exhaust passage into the intake passage downstream of the throttle valve as EGR gas,
When the temperature of the heat medium in the intercooler is lower than a predetermined target heat medium temperature, the EGR gas to the intake passage by the EGR device is increased until the temperature of the heat medium rises above the target heat medium temperature. It has a control unit that restricts introduction,
When the control unit restricts the introduction of EGR gas into the intake passage by the EGR device, the control unit restricts circulation of the heat medium in the heat medium passage, and the operation state of the diesel engine is the same. A control device for a diesel engine that increases the pressure ratio of the supercharger and reduces the opening of the throttle valve compared to when the temperature of the heat medium in the intercooler is equal to or higher than the target heat medium temperature. .   When the control unit restricts the introduction of EGR gas into the intake passage by the EGR device, the operation state of the diesel engine is the same, and the temperature of the heat medium in the intercooler is the target heat medium temperature. When the pressure ratio of the supercharger is increased and the opening degree of the throttle valve is reduced as compared with the above case, the control unit is required to provide the opening degree of the throttle valve to the diesel engine at the present time. The control device for a diesel engine according to claim 1, wherein the control device controls the intake air amount to be equal to or greater than a minimum opening degree that can secure a target intake air amount for achieving a certain operating state. The EGR device is
An EGR passage having one end connected to the exhaust passage and the other end connected to an intake passage downstream of the throttle valve;
An EGR cooler that is provided in the EGR passage and cools EGR gas flowing through the EGR passage;
A bypass passage connected to the EGR passage, in which EGR gas flows by bypassing the EGR cooler;
A control valve configured to be able to change the ratio of the flow rate of EGR gas flowing through the EGR cooler and the flow rate of EGR gas flowing through the bypass passage;
Have
The controller reduces the EGR gas flow rate when the operating state of the diesel engine is the same and the temperature of the heat medium in the intercooler is lower than the target heat medium temperature, thereby reducing the EGR gas flow rate. Limiting the introduction of EGR gas into the intake passage by the device,
Further, when the control unit restricts the introduction of EGR gas into the intake passage by the EGR device, the control unit controls the control valve so that the operation state of the diesel engine is the same and the inside of the intercooler is The diesel engine control device according to claim 1 or 2, wherein a ratio of a flow rate of the EGR gas flowing through the bypass passage is increased as compared with a case where the temperature of the heat medium is equal to or higher than the target heat medium temperature. The control device for a diesel engine according to any one of claims 1 to 3, wherein when the temperature of the outside air is low, the target heat medium temperature is set to a lower temperature than when the temperature of the outside air is high.   The diesel engine control device according to any one of claims 1 to 4, wherein the target heat medium temperature is set to a lower temperature when the outside air pressure is high than when the outside air pressure is low.   The control device for a diesel engine according to any one of claims 1 to 5, wherein when the outside air humidity is low, the target heat medium temperature is set to a lower temperature than when the outside air humidity is high.

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