JP2009046996A - Egr system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technique capable of restraining troubles such as instability of combustion or increase of HC emission during the transition of the acceleration of an internal combustion engine before completion of warm-up in an EGR system using both an HPLEGR means and an LPLEGR means or switching them in accordance with an operation state of the internal combustion engine. <P>SOLUTION: This system is provided with the HPLEGR means for introducing a part of exhaust gas on the upstream side of a turbine of a turbocharger to an intake passage on the downstream side of a compressor of the turbocharger, the LPLEGR means for introducing a part of the exhaust gas on the downstream side of the turbine to an intake passage on the upstream side of the compressor, an EGR control means increasing an EGR amount by the LPLEGR means as the load gets higher and increasing the EGR amount by the HPLEGR means as the load gets lower, and a combustion stabilizing means for stabilizing combustion of the fuel in the internal combustion engine when the acceleration transition state is detected in the halfway of the warm-up of the internal combustion engine. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an EGR system for an internal combustion engine.

As a technique for reducing the NOx emission amount from the internal combustion engine, an EGR system is known in which a part of the exhaust gas is returned to the intake system and is again taken into the internal combustion engine. Further, in an internal combustion engine equipped with a turbocharger, HPLEGR means for returning a part of the exhaust gas to the internal combustion engine via an HPL passage that connects an exhaust passage upstream of the turbine of the turbocharger and an intake passage downstream of the compressor of the turbocharger. And an LPLEGR means for returning part of the exhaust gas to the internal combustion engine via an LPL passage that connects an exhaust passage downstream from the turbine and an intake passage upstream from the compressor, and HPLEGR according to the operating state of the internal combustion engine An EGR system that performs EGR by using or switching between the means and the LPLEGR means has also been developed (see, for example, Patent Document 1). Note that HPL means High Pressure Loop and LPL means Low Pressure Loop. These names are generally used because the pressure of the EGR gas flowing through the HPL passage is relatively high, while the pressure of the EGR gas flowing through the LPL passage is relatively low.
JP 2004-150319 A JP 2005-127247 A JP 2006-37763 A

  In such an EGR system, when the operating state of the internal combustion engine is low load, EGR is mainly performed by the HPLEGR means, and as the load becomes higher, the amount of exhaust gas (HPLEGR gas) returned to the internal combustion engine by the HPLEGR means is reduced. EGR is performed by increasing the amount of exhaust gas (LPLEGR gas) returned to the internal combustion engine by the LPLEGR means, and performing EGR control in which EGR is mainly performed by the LPLEGR means when the operating state of the internal combustion engine is high. A system is conceivable.

  By the way, HPLEGR gas and LPLEGR gas have different temperature characteristics. Since the HPL passage is provided in the vicinity of the main body of the internal combustion engine and its path length is relatively short, the HPLEGR gas is relatively difficult to be cooled in the flow process until it returns to the internal combustion engine through the HPL passage. For this reason, the temperature of the HPLEGR gas tends to be relatively high. In contrast, the LPL passage has a relatively long path length, and an intercooler is disposed on the circulation path of the LPLEGR gas. Therefore, the LPLEGR gas passes through the LPL passage and returns to the internal combustion engine. It is relatively easy to cool. Therefore, the temperature of the LPLEGR gas tends to be relatively low.

  Here, in the internal combustion engine before warming-up is completed (while warming up), the temperature of the engine member including the intake system is low, and therefore the temperature of the intake air is likely to decrease. Therefore, when the amount of low-temperature LPLEGR gas is increased by the EGR control during the acceleration transition when the operating state of the internal combustion engine shifts from a low load to a high load, the intake air temperature decreases excessively and becomes lower than the target intake air temperature. There was a case. When the intake air temperature becomes lower than the target intake air temperature, the in-cylinder temperature becomes lower than expected, which may increase the ignition delay and increase the HC emission amount or cause a combustion failure such as misfire.

The present invention has been devised in view of such problems, and in an EGR system that performs EGR by using or switching HPLEGR means and LPLEGR means in accordance with the operating state of the internal combustion engine, the internal combustion engine before warm-up is completed. It is an object of the present invention to provide a technique for suppressing the occurrence of problems such as instability of combustion and increase in HC emissions during a transition in which the operating state changes.

In order to achieve the above object, an EGR system for an internal combustion engine of the present invention comprises:
A turbocharger having a turbine provided in an exhaust passage of an internal combustion engine and a compressor provided in an intake passage;
By adjusting the valve opening degree of the HPL EGR valve provided in the HPL passage through an HPL passage connecting the exhaust passage upstream of the turbine and the intake passage downstream of the compressor, a part of the exhaust gas is internal combustion engine. HPLEGR means to return to
By adjusting the valve opening degree of the EPL valve for LPL provided in the LPL passage through the LPL passage connecting the exhaust passage downstream from the turbine and the intake passage upstream from the compressor, a part of the exhaust gas is internal combustion engine. LPLEGR means to return to
As the operating state of the internal combustion engine becomes higher, the amount of exhaust (LPLEGR gas) returned to the internal combustion engine by the LPLEGR means or the ratio of LPLEGR gas in all EGR gases (LPLEGR ratio) is increased. EGR control means for increasing the amount of exhaust (HPLEGR gas) returned to the internal combustion engine by the HPLEGR means or the ratio of HPLEGR gas (HPLEGR ratio) in the total EGR gas as the state becomes lower,
Combustion stabilization means for stabilizing the combustion of fuel in the internal combustion engine during a transition when the internal combustion engine is warming up and transitioning from an operating state to an operating state on a higher load side than the operating state; ,
It is characterized by providing.

  According to this configuration, the LPLEGR gas amount or the LPLEGR ratio is increased by the EGR control means at the time of transition from one operating state to a higher operating state than the operating state. When the LPLEGR gas amount or the LPLEGR ratio is increased, the temperature of the LPLEGR gas is relatively low as described above, and therefore, compared with the state before the operation state shifts (before the LPLEGR gas amount or the LPLEGR ratio is increased). As a result, the temperature of the intake air drawn into the combustion chamber decreases. The increase amount of the LPLEGR gas amount or the LPLEGR ratio is determined in advance by an adaptation operation or the like so that the intake air temperature thus lowered matches the target intake air temperature corresponding to the operating state after the transition.

  However, when the internal combustion engine is warming up, since the engine member including the intake system is in a low temperature state as described above, the temperature of the intake air is likely to decrease due to heat transfer between the intake air flowing through the intake system and the engine member. . Therefore, when the LPLEGR gas amount or LPLEGR ratio is increased by a predetermined increase amount determined in advance as described above during a transition such as acceleration during warm-up, the intake air temperature is excessively lowered than expected and the target It may be lower than the intake air temperature. In that case, since the in-cylinder temperature is lower than expected, combustion may become unstable, leading to problems such as misfires and an increase in HC emissions.

  On the other hand, according to the present invention, at the time of acceleration in the middle of warming up, combustion of fuel is stabilized by the combustion stabilization means, and misfire and increase in HC emissions can be suppressed.

  In the present invention, the combustion stabilization means includes, for example, means for advancing the fuel injection timing, means for increasing the pilot injection amount, means for increasing the effective compression ratio, means for increasing the internal EGR amount, and the intake passage. Means for increasing the amount of intercooler bypass, which is the amount of intake air flowing through the bypass passage, having a bypass passage for bypassing the intercooler, means for increasing the HPLEGR ratio, means for increasing the amount of HPLEGR gas, and a turbocharger with a variable nozzle mechanism Various means such as a means for closing the variable nozzle opening and a means for operating the glow plug can be employed. These means can be combined as much as possible to constitute a combustion stabilization means.

  The in-cylinder temperature (compression end temperature) can be increased by means such as advance of the fuel injection timing, increase of the pilot injection amount, increase of the effective compression ratio, increase of the internal EGR amount, operation of the glow plug, etc. , Fuel combustion can be stabilized. Further, according to means such as an increase in the intercooler bypass amount, an increase in the HPLEGR ratio, an increase in the HPLEGR gas amount, and a reduction in the variable nozzle opening, the intake air temperature (the temperature in the intake manifold) can be increased. Similarly, the combustion of fuel can be stabilized.

  The correction by the various means is performed with respect to a specified value (target value) corresponding to the operation state after the transition when the operation state of the internal combustion engine is shifted from the operation state to the operation state on the higher load side than the operation state. Do it.

  According to the present invention, in an EGR system that performs EGR by using or switching HPLEGR means and LPLEGR means according to the operating state of the internal combustion engine, instability of combustion during a transient state in which the operating state changes in the internal combustion engine before warm-up is completed. The occurrence of problems such as an increase in HC emission can be suppressed.

  The best mode for carrying out the present invention will be exemplarily described in detail below 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 only to those unless otherwise specified.

  FIG. 1 is a conceptual diagram schematically showing a schematic configuration of an internal combustion engine to which the EGR system according to the present embodiment is applied and its intake system and exhaust system. The internal combustion engine 1 is a water-cooled four-cycle diesel engine having four cylinders 2.

  Each cylinder 2 of the internal combustion engine 1 communicates with the intake passage 3 via an intake manifold 17. An HPL passage 41, which will be described later, is connected in the vicinity of the connection portion between the intake manifold 17 and the intake passage 3. A second throttle valve 9 that adjusts the amount of intake air flowing through the intake passage 3 is disposed in the intake passage 3 upstream from the connection location of the HPL passage 41. An intercooler 8 for cooling the intake air is disposed in the intake passage 3 upstream of the second throttle valve 9. A compressor 11 of a turbocharger 13 is disposed in the intake passage 3 upstream from the intercooler 8. An LPL passage 31 described later is connected to the intake passage 3 upstream of the compressor 11. A first throttle valve 6 that adjusts the amount of fresh air flowing into the intake passage 3 is disposed in the intake passage 3 upstream from the connection point of the LPL passage 31. An air flow meter 7 that measures the amount of fresh air flowing into the intake passage 3 is provided in the intake passage 3 upstream of the first throttle valve 6. An air cleaner (not shown) is connected to the intake passage 3 further upstream. Hereinafter, the intake passage 3, the intake manifold 17, the intercooler 8, the compressor 11, and the like disposed therein may be collectively referred to as “intake system”.

  In the intake system configured as described above, the air from which dust or dust has been removed through the air cleaner flows into the intake passage 3. The air flowing into the intake passage 3 passes through the compressor 11 and is pressurized, then passes through the intercooler 8, is cooled, and is led to the intake passage 3 by an LPLEGR device 30 and an HPLEGR device 40 described later. It flows into the intake manifold 17 while being mixed with the EGR gas, and is distributed to the intake port of each cylinder 2 through each branch pipe of the intake manifold 17. The intake air distributed to the intake port is drawn into each cylinder 2 when the intake valve is opened.

  Each cylinder 2 of the internal combustion engine 1 communicates with the exhaust passage 4 via an exhaust manifold 18. An HPL passage 41 is connected in the vicinity of the connection portion between the exhaust manifold 18 and the exhaust passage 4. A turbine 12 of the turbocharger 13 is disposed in the exhaust passage 4 downstream from the connection location of the HPL passage 41. The turbocharger 13 is a variable capacity turbocharger provided with a nozzle vane 5 that makes the flow area of exhaust gas passing through the turbine 12 variable. An exhaust purification device 10 is disposed in the exhaust passage 4 downstream from the turbine 12. The exhaust purification device 10 stores NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and stores the NOx that has been stored when the oxygen concentration of the exhaust gas becomes low, and reduces and purifies the NOx. And a particulate filter capable of collecting particulate matter (PM) therein and capable of oxidizing and removing the collected PM in a timely manner. The configuration of the exhaust purification device 10 is not limited to this example. An exhaust throttle valve 19 that adjusts the amount of exhaust gas flowing through the exhaust passage 4 is disposed in the exhaust passage 4 downstream of the exhaust purification device 10. An LPL passage 31 is connected to the exhaust passage 4 downstream from the exhaust throttle valve 19. The exhaust throttle valve 19 may be arranged in the exhaust passage 4 downstream from the connection point of the LPL passage 31. Hereinafter, the exhaust passage 4, the exhaust manifold 18, and the turbine 12, the exhaust purification device 10, and the like arranged in these may be collectively referred to as “exhaust system”.

  In the exhaust system configured as described above, the burned gas burned in each cylinder 2 of the internal combustion engine 1 is discharged to the exhaust manifold 18 and flows into the exhaust passage 4. Exhaust gas flowing into the exhaust passage 4 is driven to rotate the turbine 13 and then passes through the exhaust gas purification device 10 so that harmful substances contained therein are purified. A part of the exhaust discharged from the cylinder 2 is guided to the intake passage 3 as EGR gas by the HPLEGR device 40 and / or the LPLEGR device 30 described later. The exhaust gas purified by the exhaust gas purification device 10 is released into the atmosphere through the muffler.

  The internal combustion engine 1 includes an HPLEGR device 40 that guides a part of the exhaust gas flowing through the exhaust passage 4 upstream of the turbine 12 to the intake passage 3 downstream of the compressor 11 and returns the exhaust gas to the internal combustion engine 1. The HPLEGR device 40 includes an HPL passage 41 that connects the exhaust passage 4 upstream of the turbine 12 and the intake passage 3 downstream of the second throttle valve 9, and intakes a part of the exhaust through the HPL passage 41. It flows into the passage 3. The exhaust gas returned to the internal combustion engine 1 by the HPLEGR device 40 is hereinafter referred to as “HPLEGR gas”.

  An HPLEGR cooler 43 that cools the HPLEGR gas is disposed in the HPL passage 41. An HPLEGR valve 42 that changes the flow area of the HPL passage 41 is disposed in the HPL passage 41 on the downstream side (the intake passage 3 side) of the HPLEGR cooler 43. The amount of HPLEGR gas flowing through the HPL passage 41 is adjusted by adjusting the opening degree of the HPLEGR valve 42. As means for adjusting the HPLEGR gas amount, means for adjusting the back pressure by adjusting the opening of the second throttle valve 9, adjusting the back pressure, or adjusting the opening of the nozzle vane 5 is used. You can also. In this embodiment, the HPLEGR device 40 corresponds to the HPLEGR means in the present invention.

  The internal combustion engine 1 is provided with an LPLEGR device 30 that guides a part of the exhaust gas flowing through the exhaust passage 4 downstream of the turbine 12 to the intake passage 3 upstream of the compressor 11 and returns the exhaust gas to the internal combustion engine 1. The LPLEGR device 30 has an LPL passage 31 that connects the exhaust passage 4 downstream from the exhaust throttle valve 19 and the intake passage 3 upstream from the compressor 11, and a part of the exhaust is taken into the intake passage via the LPL passage 31. 3 is allowed to flow. The exhaust gas returned to the internal combustion engine by the LPLEGR device 30 is hereinafter referred to as “LPLEGR gas”.

An LPLEGR cooler 33 for cooling the LPLEGR gas is disposed in the LPL passage 31. An LPLEGR valve 32 that changes the flow area of the LPL passage 31 is disposed in the LPL passage 31 on the downstream side (intake passage 3 side) of the LPLEGR cooler 33. LPLEGR
By adjusting the opening of the valve 32, the amount of LPLEGR gas flowing through the LPL passage 31 is adjusted. As means for adjusting the LPLEGR gas amount, means for adjusting the differential pressure between the upstream and downstream of the LPL passage 31 by adjusting the opening of the first throttle valve 6 may be used. In this embodiment, the LPLEGR device 30 corresponds to the LPLEGR means in the present invention.

  When the EGR is performed by the HPLEGR device 40 and the LPLEGR device 30 configured as described above, the combustion temperature of the fuel is lowered and the generation amount of NOx can be reduced.

  The internal combustion engine 1 is provided with an electronic control unit (ECU) 20 that controls the internal combustion engine 1. The ECU 20 is a microcomputer provided with a CPU, a ROM, a RAM, an input / output port, and the like. In addition to the air flow meter 7 described above, the ECU 20 outputs a water temperature sensor 14 that outputs an electric signal corresponding to the temperature of the cooling water circulating in the water jacket of the internal combustion engine 1, and an electric signal corresponding to the operation amount of the accelerator pedal. Sensors such as an accelerator opening sensor 15 and a crank position sensor 16 that outputs a pulse signal each time the crankshaft of the internal combustion engine 1 rotates by a predetermined angle (for example, 10 °) are electrically connected, and output from each sensor A signal is input to the ECU 20. Also, the ECU 20 is electrically connected to devices such as the first throttle valve 6, the second throttle valve 9, the nozzle vane 5, the exhaust throttle valve 19, the LPLEGR valve 32, and the HPLEGR valve 42, and a control output from the ECU 20. These devices are controlled by signals.

  ECU20 acquires the driving | running state of the internal combustion engine 1, and a driver | operator's request | requirement based on the signal input from each said sensor. For example, the ECU 20 calculates the rotational speed of the internal combustion engine 1 based on a signal input from the crank position sensor 16 and calculates the load of the internal combustion engine 1 based on a signal input from the accelerator opening sensor 15. The target injection timing, the target intake air temperature, and the like are read in accordance with the operating state acquired in this way, and the above-described devices are controlled so that the actual values of these parameters become target values.

  Here, the EGR control performed in the EGR system of the present embodiment will be described.

  As shown in FIG. 2, in the EGR system of the present embodiment, EGR is performed by using or switching the HPLEGR device 40 and the LPLEGR device 30 in accordance with the operating state of the internal combustion engine 1. In FIG. 2, the horizontal axis represents the rotational speed of the internal combustion engine 1, and the vertical axis represents the load of the internal combustion engine 1. As shown in FIG. 2, in the EGR control of this embodiment, EGR is performed mainly using the HPLEGR device 40 when the operating state of the internal combustion engine 1 is low load and low rotation. Further, as the load or the rotational speed increases, the EGR amount (HPLEGR gas amount) performed using the HPLEGR device 40 is decreased, and the EGR amount (LPLEGR gas amount) performed using the LPLEGR device 30 is increased to increase the HPLEGR. EGR is performed using the apparatus 40 and the LPLEGR apparatus 30 together. Further, when the operating state of the internal combustion engine 1 is high load or high rotation, EGR is mainly performed using the LPLEGR device 30.

In FIG. 2, a region displayed as “HPL” mainly represents a region in an operating state where EGR is performed using the HPLEGR device 40. This region is hereinafter referred to as “HPLEGR region”. Further, an area displayed as “LPL” mainly represents an operating state area where EGR is performed using the LPLEGR device 30. This region is hereinafter referred to as “LPLEGR region”, and the medium load or medium rotation region indicated as “MIX” between the HPLEGR region and the LPL region EGR is performed by the EGR using the HPLEGR device 40 and the LPLEGR device 30 together. Represents the area to be called. This region is hereinafter referred to as “MIXGR region”. As described above, in the MIXGR region, control is performed such that the HPLEGR gas amount is decreased and the LPLEGR gas amount is increased as the operating state of the internal combustion engine 1 becomes a higher load or higher rotation side. In other words, the higher the load or the higher the rotation side, the lower the HPLEGR gas ratio (HPLEGR ratio) in the total EGR gas and the higher the LPLEGR gas ratio (LPLEGR ratio) in the total EGR gas.

  The target values of the HPLEGR gas amount and the LPLEGR gas amount corresponding to each operation state are engine performance such as NOx emission amount, smoke generation amount, HC generation amount, fuel consumption, etc. when the internal combustion engine 1 is in steady operation in the operation state. And various characteristics relating to the exhaust performance are determined in advance by an adaptation operation so as to achieve predetermined regulation values and desired target values, and stored in the ROM of the ECU 20. The ECU 20 reads the target value of the HPLEGR gas amount and the LPLEGR gas amount corresponding to the operating state from the ROM according to the acquired operating state, and the amount of exhaust gas returned to the intake system using the HPLEGR device 40 and the LPLEGR device 30 is determined. The HPLEGR valve 42, the LPLEGR valve 32, the first throttle valve 6, the second throttle valve 9, the exhaust throttle valve 19, the nozzle vane 5, and the like are controlled so that the respective target values are obtained. In the present embodiment, the ECU 20 that performs the above-described EGR control corresponds to the EGR control means in the present invention.

  By the way, HPLEGR gas and LPLEGR gas have different temperature characteristics. Since the HPL passage 41 is provided in the vicinity of the main body of the internal combustion engine 1 and has a relatively short path length, the HPLEGR gas is relatively difficult to cool in the flow process until it returns to the internal combustion engine 1 through the HPL passage 41. For this reason, the temperature of the HPLEGR gas tends to be relatively high. On the other hand, the LPL passage 31 has a relatively long path length, and further, the intercooler 8 is disposed on the LPLEGR gas flow path, so that the LPLEGR gas passes through the LPL passage 31 and returns to the internal combustion engine 1. It is relatively easy to cool in the distribution process. Therefore, the temperature of the LPLEGR gas tends to be relatively low.

  Here, a case where the internal combustion engine 1 is in a state of warming up (before completion of warming up) will be considered. In the internal combustion engine 1 that is warming up, the temperature of the engine members including the intake system is low, so the temperature of the intake air is likely to decrease. Therefore, if the amount of low-temperature LPLEGR gas is increased in accordance with the above-described EGR control during an acceleration transition in which the operation state of the internal combustion engine 1 shifts from a certain operation state to an operation state on the higher load side than the operation state, the intake air temperature becomes excessive. May fall below the target intake air temperature. If the intake air temperature becomes lower than the target intake air temperature, the in-cylinder temperature becomes lower than expected, so that there is a possibility that the ignition delay will increase and the HC emission amount will increase, or a combustion failure such as misfire will occur.

  Therefore, in the EGR system of the present embodiment, when the acceleration transient state of the internal combustion engine 1 is detected while the internal combustion engine 1 is in the middle of warming up, the HPLEGR gas amount is changed to the operation state of the transition destination due to the acceleration transient ( The basic HPLEGR gas amount is increased according to the high load side operation state), and the LPLEGR gas amount is decreased from the basic LPLEGR gas amount determined according to the operation state of the transition destination. By correcting the increase in the HPLEGR gas amount and correcting the decrease in the LPLEGR gas amount, the amount of the high-temperature HPLEGR gas increases and the amount of the low-temperature LPLEGR gas decreases, so that the intake air temperature (the temperature in the intake manifold 17) is excessive. The decrease can be suppressed. Therefore, it is possible to suppress occurrence of problems such as defective combustion even in a situation where the intake air temperature may be lower than the target intake air temperature (that is, an acceleration transient state during warm-up).

  FIG. 3 shows an example of changes in the HPLEGR gas amount, the LPLEGR gas amount, and the intake air temperature when the above-described HPLEGR gas amount increase correction and LPLEGR gas amount decrease correction are performed during acceleration transition during the warm-up of the internal combustion engine 1. FIG. Here, the intake air temperature means the temperature in the intake manifold 17. The same applies to the following description unless otherwise specified.

FIG. 3A is a diagram showing a change in intake air temperature. A broken line C1 indicates a change in the intake air temperature when the correction is not performed, and a solid line C2 indicates a change in the intake air temperature when the correction is performed. FIG. 3B is a diagram showing a change in the amount of HPLEGR gas. A broken line C3 indicates a change in the HPLEGR gas amount when the correction is not performed, and a solid line C4 indicates a change in the HPLEGR gas amount when the correction is performed. FIG. 3C is a diagram showing a change in the LPLEGR gas amount. A broken line C5 indicates a change in the LPLEGR gas amount when the correction is not performed, and a solid line C6 indicates a change in the LPLEGR gas amount when the correction is performed.

  When the operation state of the internal combustion engine 1 shifts from a low load to a high load (t1), the HPLEGR gas amount corresponds to the operation state after the shift (the operation state on the high load side) as indicated by a broken line C3. The basic HPLEGR gas amount (high load basic HPLEGR gas amount) is changed to GHPLHI, and the LPLEGR gas amount is changed to the basic LPLEGR gas amount (high load basic LPLEGR gas amount) corresponding to the operating state after the transition, as shown by the broken line C5. ) If it is changed to GLPLHI, as shown by the broken line C1, the intake air temperature is excessively lowered and becomes lower than the target intake air temperature (high load target intake air temperature) TINHI corresponding to the operating state after the transition. .

  On the other hand, in this embodiment, as shown by the solid line C4, the HPLEGR gas amount is the basic HPLEGR gas amount (low load basic HPLEGR gas amount) GHPLLO corresponding to the operating state before the transition (the operating state on the low load side). Gradually, from the high load basic HPLEGR gas amount GHPLHI, and as shown by the solid line C6, the LPLEGR gas amount corresponds to the basic LPLEGR gas amount (low load basic LPLEGR gas amount) GLPLLO corresponding to the operating state before the transition. To the high load basic LPLEGR gas amount GLPLHI. Then, the amount of high-temperature HPLEGR gas is high during the period (acceleration transient period) from the time point (t1) when the operating state shifts to the high load side to the time point (t2) when the intake air temperature matches the high load target intake air temperature TINHI. Since the amount of the load basic HPLEGR gas is larger and the amount of the low temperature LPLEGR gas is smaller than the amount of the high load basic LPLEGR gas, a decrease in the intake air temperature is suppressed and, as shown by the solid line C2, during the acceleration transient period The intake air temperature is suppressed from becoming lower than the high load target intake air temperature TINHI. Accordingly, the in-cylinder temperature is suppressed from becoming lower than expected, and the occurrence of defects such as poor combustion can be suppressed.

  In FIG. 3, the HPLEGR gas amount (LPLEGR gas amount) is continuously changed from the low load basic HPLEGR gas amount (low load basic LPLEGR gas amount) to the high load basic HPLEGR gas amount (high load basic LPLEGR gas amount). However, if the condition that the HPLEGR gas amount (LPLEGR gas amount) during the acceleration transient period is larger (smaller) than the high load basic HPLEGR gas amount (high load basic LPLEGR gas amount) is satisfied, the HPLEGR gas is satisfied. The method of changing the amount (LPLEGR gas amount) is not limited to the example shown in FIG. For example, it can be changed step by step.

  Hereinafter, a specific execution procedure when the ECU 20 performs the above-described correction control of the EGR gas amount will be described with reference to FIG. FIG. 4 is a flowchart showing the EGR gas amount correction control routine. This routine is repeatedly executed by the ECU 20 during operation of the internal combustion engine 1.

  First, in step S101, the ECU 20 acquires the operating state of the internal combustion engine 1. Specifically, the rotational speed, accelerator opening, fuel injection amount, cooling water temperature, and the like of the internal combustion engine 1 are acquired based on the signals from the various sensors described above.

In step S102, the ECU 20 calculates a target intake air temperature based on the operating state of the internal combustion engine 1 acquired in step S101. The target intake air temperature in this case is a target value of the temperature of the intake air sucked into the cylinder of the internal combustion engine 1 and corresponds to the temperature of the intake air passing through the intake manifold 17.

  In step S103, the ECU 20 determines whether or not the internal combustion engine 1 is being warmed up. If an affirmative determination is made in step S103, the ECU 20 proceeds to step S104. On the other hand, if a negative determination is made in step S103, the ECU 20 once ends the execution of this routine.

  In step S104, the ECU 20 determines whether or not the internal combustion engine 1 is in an acceleration transient state. Specifically, for example, when the detected value by the accelerator opening sensor 15 is increased by a predetermined amount or more, it can be determined that the acceleration is in a transient state. If an affirmative determination is made in step S104, the ECU 20 proceeds to step S105. On the other hand, if a negative determination is made in step S104, the ECU 20 once ends the execution of this routine.

  In step S105, the ECU 20 increases the HPLEGR gas amount from the high load basic HPLEGR gas amount and decreases the LPLEGR gas amount from the high load basic LPLEGR gas amount.

  In step S106, the ECU 20 determines whether or not the intake air temperature has become equal to the target intake air temperature. Here, the intake air temperature is a detected value by the air flow meter 7, a detected value by the water temperature sensor 14, a detected value by a sensor (not shown) for detecting the opening degree of the LPLEGR valve 32, or an opening command value for the LPLEGR valve 32, an HPLEGR valve. The detected value by the sensor (not shown) for detecting the opening of 42, the opening command value for the HPLEGR valve 42, the detected value by the crank angle sensor 16, the detected value by the accelerator opening sensor 15, and the opening of the exhaust throttle valve 19 Based on parameters such as a detected value by a sensor (not shown) or an opening command value for the exhaust throttle valve 19, a detected value by a sensor (not shown) that detects the opening of the nozzle vane 5, or an opening command value for the nozzle vane 5. Then, it is estimated by a model that calculates the intake air temperature. The ECU 20 repeats step S106 until an affirmative determination is made. If a positive determination is made in step S106, the ECU 20 proceeds to step S107.

  In step S107, the ECU 20 returns the HPLEGR gas amount to the high load basic HPLEGR gas amount, and returns the LPLEGR gas amount to the high load basic LPLEGR gas amount.

  In the present embodiment, the ECU 20 that executes steps S103 to S105 corresponds to the combustion stabilization means in the present invention. The HPLEGR gas amount increase correction and the LPLEGR gas amount decrease correction are canceled when the intake air temperature becomes equal to the target intake air temperature.

  Next, a second embodiment of the present invention will be described. Since the schematic configuration of the internal combustion engine to which the EGR system of the present embodiment is applied and its intake and exhaust system are the same as those of the first embodiment, detailed description thereof is omitted.

  In this embodiment, when the acceleration transient state of the internal combustion engine 1 is detected during the warm-up of the internal combustion engine 1, the fuel injection timing is changed to the operation state of the transition destination due to the acceleration transient (the operation state on the high load side). It is advanced from the basic fuel injection timing (high load basic fuel injection timing) determined accordingly. By correcting the advance of the fuel injection timing, the combustion temperature of the fuel rises, so that the combustion is stabilized. Accordingly, even when the intake air temperature is lower than the target intake air temperature corresponding to the operation state of the transition destination during acceleration transition during warm-up, it is possible to suppress the occurrence of problems such as defective combustion.

FIG. 5 is a diagram illustrating an example of changes in the fuel injection timing and the intake air temperature when the above-described fuel injection timing advance correction is performed during acceleration transition during the warm-up of the internal combustion engine 1. Here, the intake air temperature means the temperature of the intake air in the intake manifold 17. The same applies to the following description unless otherwise specified.

  FIG. 5A is a diagram showing a change in intake air temperature. A solid line C1 indicates a change in the intake air temperature. In the present embodiment, the intake air temperature changes in the same manner when the correction is not performed and when the correction is not performed. That is, unlike the first embodiment, this embodiment does not attempt to suppress the combustion failure by suppressing the decrease in the intake air temperature in the intake manifold 17. FIG. 5B is a diagram showing a change in the fuel injection timing. A broken line C3 indicates a change in the fuel injection timing when the correction is not performed, and a solid line C4 indicates a change in the fuel injection timing when the correction is performed.

  When the operation state of the internal combustion engine 1 shifts from a low load to a high load, the target intake air temperature changes from the target intake air temperature TINLO corresponding to the low load operation state to the target intake air temperature TINHI corresponding to the high load operation state. The intake air temperature gradually decreases as indicated by the solid line C1. However, when the internal combustion engine 1 is warmed up, the intake system including the intake manifold 17 and the intake passage 3 is in a low temperature state, so that the intake air temperature excessively decreases. Then, at time t0 when time Δt has elapsed from time t1 when the operating state has shifted, as shown by a solid line C1, the intake air temperature decreases to a temperature lower than the target intake air temperature TINHI corresponding to the high load operating state.

  On the other hand, in this embodiment, as shown by the solid line C4 during the acceleration transition period from the time point (t1) when the operating state shifts to the high load side to the time point (t2) when the intake air temperature matches the target intake air temperature TINHI. The fuel injection timing is set to the injection timing θFTA that is on the advance side of the high load basic fuel injection timing θFHI. As the fuel injection timing is corrected to advance in this manner, the combustion temperature of the fuel rises. Therefore, even in a situation where the intake air temperature is lower than the target intake air temperature TINHI in the acceleration transient state during warm-up, poor combustion occurs. The occurrence of problems such as these can be suppressed.

  FIG. 5 illustrates the case where the fuel injection timing during the acceleration transition period is fixed to a constant injection timing θFTA on the advance side of the high load basic fuel injection timing θFHI, but it is advanced from the high load basic fuel injection timing θFHI. If the condition of being on the corner side is satisfied, the method of changing the fuel injection timing during the acceleration transient period is not limited to this. For example, the injection timing may be continuously changed from the basic fuel injection timing θFLO corresponding to the low load operation state to the high load basic fuel injection timing θFHI, or may be changed stepwise.

  Hereinafter, a specific execution procedure when the ECU 20 performs the above-described fuel injection timing correction control will be described with reference to FIG. FIG. 6 is a flowchart showing the fuel injection timing correction control routine. This routine is repeatedly executed by the ECU 20 during operation of the internal combustion engine 1.

  First, in step S201, the ECU 20 acquires the operating state of the internal combustion engine 1. Specifically, the rotational speed, accelerator opening, fuel injection amount, cooling water temperature, and the like of the internal combustion engine 1 are acquired based on the signals from the various sensors described above.

  In step S202, the ECU 20 calculates a target intake air temperature based on the operating state of the internal combustion engine 1 acquired in step S201. The target intake air temperature in this case is a target value of the temperature of the intake air sucked into the cylinder of the internal combustion engine 1 and corresponds to the temperature of the intake air in the intake manifold 17.

In step S203, the ECU 20 determines whether or not the internal combustion engine 1 is being warmed up. If an affirmative determination is made in step S203, the ECU 20 proceeds to step S204. On the other hand, if a negative determination is made in step S203, the ECU 20 once ends the execution of this routine.

  In step S204, the ECU 20 determines whether or not the internal combustion engine 1 is in an acceleration transient state. Specifically, for example, when the detected value by the accelerator opening sensor 15 is increased by a predetermined amount or more, it can be determined that the acceleration is in a transient state. If an affirmative determination is made in step S204, the ECU 20 proceeds to step S205. On the other hand, if a negative determination is made in step S204, the ECU 20 once ends the execution of this routine.

  In step S205, the ECU 20 advances the fuel injection timing from the high load basic fuel injection timing.

  As shown by the solid line C1 in FIG. 5A, the intake air temperature is the operating state on the high load side at time t0 when time Δt has elapsed from time t1 when the operating state of the internal combustion engine 1 has shifted from the low load to the high load. It further decreases beyond the target intake air temperature TINHI corresponding to, and then gradually increases and changes to match the target intake air temperature TINHI. As will be described later, the fuel injection timing advance angle correction control of this embodiment is terminated when the intake air temperature coincides with the target intake air temperature TINHI. Therefore, if it is determined whether or not the intake air temperature matches the target intake air temperature TINHI before time t0, an affirmative determination is made in the determination at time t0, and the fuel injection timing advance angle correction control is terminated. It will end up.

  In order to prevent this, in this embodiment, the advance correction control of the fuel injection timing is performed before the time t0 when the intake air temperature decreases immediately after the operating state changes and temporarily matches the target intake air temperature TINHI. The intake air temperature is not judged to determine the end of the process. Specifically, in step S206, immediately after the operating state of the internal combustion engine 1 changes, a time t0 when the intake air temperature falls below the target intake air temperature TINHI when the intake air temperature decreases is calculated. This time t0 is the operating state on the low load side before the transition, the operating state on the high load side after the transition, the coolant temperature, the detected value by the crank angle sensor 16, the detected value by the accelerator opening sensor 15, the exhaust throttle valve 19 It is estimated by a model determined in advance based on various parameters such as a detected value or command value of the opening degree, a detected value or command value of the opening degree of the nozzle vane 5 and the like.

  In step S207, the ECU 20 determines whether or not the current time t is equal to or greater than the time t0 calculated in step S206. The ECU 20 does not proceed to the next step S208 until an affirmative determination is made in step S207.

  In step S208, the ECU 20 determines whether or not the intake air temperature has become equal to the target intake air temperature. The ECU 20 repeats step S208 until an affirmative determination is made. If an affirmative determination is made in step S208, the ECU 20 proceeds to step S209.

  In step S209, the ECU 20 returns the fuel injection timing to the high load basic fuel injection timing.

  In this embodiment, the ECU 20 that executes Steps S203 to S205 corresponds to the combustion stabilization means in the present invention.

  Next, Embodiment 3 of the present invention will be described. Since the schematic configuration of the internal combustion engine to which the EGR system of the present embodiment is applied and its intake and exhaust system are the same as those of the first embodiment, detailed description thereof is omitted.

  In the present embodiment, when the acceleration transient state of the internal combustion engine 1 is detected during the warm-up of the internal combustion engine 1, the internal EGR amount is converted to the operation state of the transition destination due to the acceleration transient (high load side operation state). The basic internal EGR amount (high load basic internal EGR amount) determined according to Thereby, since the in-cylinder temperature rises, combustion can be stabilized. Therefore, even when the intake air temperature is lower than the target intake air temperature corresponding to the operation state of the transition destination during acceleration transition during warm-up, it is possible to suppress the occurrence of problems such as defective combustion.

  FIG. 7 is a diagram illustrating an example of changes in the intake air temperature, the in-cylinder temperature, and the internal EGR amount when the above-described internal EGR amount increase correction is performed during acceleration transition during the warm-up of the internal combustion engine 1. Here, the intake air temperature means the temperature of the intake air in the intake manifold 17. The same applies to the following description unless otherwise specified.

  FIG. 7A is a diagram showing a change in intake air temperature. A solid line C1 indicates a change in the intake air temperature. In the present embodiment, the intake air temperature changes in the same manner when the correction is not performed and when the correction is not performed. That is, unlike the first embodiment, this embodiment does not attempt to suppress the combustion failure by suppressing the decrease in the intake air temperature in the intake manifold 17. FIG. 7B is a diagram showing a change in the in-cylinder temperature. Here, the in-cylinder temperature means an average gas temperature in the cylinder. The same applies to the following description unless otherwise specified. A broken line C2 indicates a change in the in-cylinder temperature when the correction is not performed, and a solid line C3 indicates a change in the in-cylinder temperature when the correction is performed. FIG. 7C is a diagram showing changes in the internal EGR amount. A broken line C4 indicates a change in the internal EGR amount when the correction is not performed, and a solid line C5 indicates a change in the internal EGR amount when the correction is performed.

  When the operation state of the internal combustion engine 1 shifts from a low load to a high load, the target intake air temperature changes from the target intake air temperature TINLO corresponding to the low load operation state to the target intake air temperature TINHI corresponding to the high load operation state. The intake air temperature gradually decreases as indicated by the solid line C1. However, when the internal combustion engine 1 is warmed up, the intake system including the intake manifold 17 and the intake passage 3 is in a low temperature state, so that the intake air temperature excessively decreases. Then, at time t0 when time Δt has elapsed from time t1 when the operating state has shifted, as shown by a solid line C1, the intake air temperature decreases to a temperature lower than the target intake air temperature TINHI corresponding to the high load operating state.

  In contrast, in this embodiment, as shown by the solid line C5 during the acceleration transition period from the time (t1) when the operating state shifts to the high load side to the time (t2) when the intake air temperature matches the target intake air temperature TINHI. The internal EGR amount is gradually reduced from the basic internal EGR amount (low load basic internal EGR amount) GEGRIL corresponding to the low load side operation state to the high load basic internal EGR amount GEGRHI. Then, during the period (acceleration transient period) from the time (t1) when the operating state shifts to the high load side to the time (t2) when the intake air temperature matches the high load target intake air temperature TINHI, Since it becomes larger than the EGR amount GEGRIHI, the in-cylinder temperature rises as shown by the solid line C3. Thereby, even in a situation where the intake air temperature is lower than the high load target intake air temperature, combustion is stabilized and it is possible to suppress the occurrence of problems such as poor combustion.

  FIG. 7 illustrates the case where the internal EGR amount is continuously changed from the low load basic internal EGR amount GEGRLO to the high load basic internal EGR amount GEGRHI. However, the internal EGR amount during the acceleration transient period is high. If the condition that the amount is larger than the EGR amount is satisfied, the way of changing the internal EGR amount is not limited to the example shown in FIG. For example, it can be decreased step by step.

Hereinafter, a specific execution procedure in the case where the ECU 20 performs the above-described correction control of the internal EGR amount will be described with reference to FIG. FIG. 8 is a flowchart showing the internal EGR amount correction control routine. This routine is repeatedly executed by the ECU 20 during operation of the internal combustion engine 1.

  First, in step S301, the ECU 20 acquires the operating state of the internal combustion engine 1. Specifically, the rotational speed, accelerator opening, fuel injection amount, cooling water temperature, and the like of the internal combustion engine 1 are acquired based on the signals from the various sensors described above.

  In step S302, the ECU 20 calculates a target intake air temperature based on the operating state of the internal combustion engine 1 acquired in step S301. The target intake air temperature in this case is a target value of the temperature of the intake air sucked into the cylinder of the internal combustion engine 1 and corresponds to the temperature of the intake air in the intake manifold 17.

  In step S303, the ECU 20 determines whether or not the internal combustion engine 1 is warming up. If an affirmative determination is made in step S303, the ECU 20 proceeds to step S304. On the other hand, if a negative determination is made in step S303, the ECU 20 once ends the execution of this routine.

  In step S304, the ECU 20 determines whether or not the internal combustion engine 1 is in an acceleration transient state. Specifically, for example, when the detected value by the accelerator opening sensor 15 is increased by a predetermined amount or more, it can be determined that the acceleration is in a transient state. If an affirmative determination is made in step S304, the ECU 20 proceeds to step S305. On the other hand, if a negative determination is made in step S304, the ECU 20 once ends the execution of this routine.

  In step S305, the ECU 20 increases the internal EGR amount from the high load basic internal EGR amount.

  As for the increase correction control of the internal EGR amount of the present embodiment, the correction is canceled when the intake air temperature coincides with the target intake air temperature as in the case of the advance correction control of the fuel injection timing of the second embodiment. Yes.

  Therefore, in the present embodiment, as in the second embodiment, immediately after the operating state of the internal combustion engine 1 shifts from a low load to a high load, the intake air temperature decreases to a temperature lower than the target intake air temperature TINHI. In order to prevent the increase correction control of the internal EGR amount from being terminated at the same time, after the internal EGR amount increase correction control is started (after the operating state of the internal combustion engine 1 shifts from a low load to a high load). ) A delay is provided until it is determined whether or not the intake air temperature matches the target intake air temperature TINHI.

  That is, in step S306, immediately after the operating state of the internal combustion engine 1 changes, the time t0 when the intake air temperature falls below the target intake air temperature TINHI when the intake air temperature decreases is calculated. This time t0 is the operating state on the low load side before the transition, the operating state on the high load side after the transition, the coolant temperature, the detected value by the crank angle sensor 16, the detected value by the accelerator opening sensor 15, the exhaust throttle valve 19 It is estimated by a model determined in advance based on various parameters such as a detected value or command value of the opening degree, a detected value or command value of the opening degree of the nozzle vane 5 and the like.

  In step S307, the ECU 20 determines whether the current time t is equal to or greater than the time t0 calculated in step S306. The ECU 20 does not proceed to the next step S308 until an affirmative determination is made in step S307.

  In step S308, the ECU 20 determines whether or not the intake air temperature has become equal to the target intake air temperature. The ECU 20 repeats step S308 until an affirmative determination is made. If an affirmative determination is made in step S308, the ECU 20 proceeds to step S309.

  In step S309, the ECU 20 returns the internal EGR amount to the high load basic internal EGR amount.

  In the present embodiment, the ECU 20 that executes Steps S303 to S305 corresponds to the combustion stabilization means in the present invention.

  As a means for increasing the internal EGR amount, for example, a method of increasing the valve overlap amount in which both the exhaust valve and the intake valve are opened from the exhaust stroke to the intake stroke by controlling the VVT mechanism, And a method of increasing the back pressure in the exhaust passage 4 with the opening of the exhaust throttle valve 19 and the nozzle vane 5 being closed.

  Next, a fourth embodiment of the present invention will be described. Since the schematic configuration of the internal combustion engine to which the EGR system of the present embodiment is applied and its intake and exhaust system are the same as those of the first embodiment, detailed description thereof is omitted.

  In this embodiment, when the acceleration transient state of the internal combustion engine 1 is detected during the warm-up of the internal combustion engine 1, the VN opening is changed to the operation state (the high load side operation state) at the transition destination due to the acceleration transient. The basic VN opening amount (high load basic VN opening amount) is corrected to a closing side opening amount, and the HPLEGR gas amount is determined according to the operating state on the high load side (high load basic amount). Increase from HPLEGR gas amount). As a result, the supercharging pressure rises and the intake air temperature (temperature in the intake manifold 17) rises, so that an excessive decrease in the intake air temperature can be suppressed. Therefore, it is possible to suppress occurrence of problems such as defective combustion even in a situation where the intake air temperature may be lower than the target intake air temperature (that is, an acceleration transient state during warm-up). At this time, since the HPLEGR gas amount is corrected to increase, an excessive decrease in the intake air temperature can be more reliably suppressed, and a decrease in the EGR rate due to an increase in the supercharging pressure can be suppressed. Can also be suppressed.

  FIG. 9 shows changes in HPLEGR gas amount, VN opening amount, supercharging pressure, and intake air temperature when the above-described VN opening correction and HPLEGR gas amount increase correction are performed during acceleration transients during the warm-up of the internal combustion engine 1. It is a figure which shows an example. Here, the intake air temperature means the temperature of intake air in the intake manifold 17. The same applies to the following description unless otherwise specified.

  FIG. 9A is a diagram showing a change in intake air temperature. A broken line C1 indicates a change in the intake air temperature when the correction is not performed, and a solid line C2 indicates a change in the intake air temperature when the correction is performed. FIG. 9B is a diagram showing a change in supercharging pressure. A broken line C3 indicates a change in the supercharging pressure when the correction is not performed, and a solid line C4 indicates a change in the supercharging pressure when the correction is performed. FIG. 9C is a diagram showing changes in the VN opening. A broken line C5 indicates a change in the VN opening when the correction is not performed, and a solid line C6 indicates a change in the VN opening when the correction is performed. FIG. 9D is a diagram showing a change in the amount of HPLEGR gas. A broken line C7 indicates a change in the HPLEGR gas amount when the correction is not performed, and a solid line C8 indicates a change in the HPLEGR gas amount when the correction is performed.

As indicated by the solid line C6, the target intake air temperature (high load target intake air temperature) TINHI corresponding to the operating state on the high load side from the time point (t1) when the operating state of the internal combustion engine 1 shifts from the low load to the high load. During the period up to the time point (t2) that coincides with (acceleration transient period), the VN opening is set to the opening VNTA on the closing side from the high load basic VN opening. As a result, as indicated by a solid line C4, the supercharging pressure during the acceleration transition period becomes a pressure PINTA higher than the basic supercharging pressure PINHI corresponding to the operating state on the high load side. As a result, a decrease in the intake air temperature is suppressed, and as shown by a solid line C2, the intake air temperature is suppressed from becoming lower than the high load target intake air temperature TINHI during the acceleration transient period. Thus, the in-cylinder temperature is suppressed from becoming lower than expected, and the occurrence of defects such as poor combustion can be suppressed. Further, as shown by the solid line C8, the amount of the high-temperature HPLEGR gas is increased from the amount of the high load basic HPLEGR gas, so that it is possible to further suppress the decrease in the intake air temperature and to reduce the EGR accompanying the increase in the supercharging pressure. A decrease in the rate is suppressed, and an increase in the amount of NOx generated can also be suppressed.

  In FIG. 9, the case where the VN opening and the HPLEGR gas amount during the acceleration transition period are set to constant values is illustrated. However, if the condition that the opening is closer to the closing side than the high load basic VN opening is satisfied. The method of changing the VN opening during the acceleration transition period is not limited to this. As long as the condition that the amount of HPLEGR gas is larger than the high load basic HPLEGR gas amount is satisfied, the method of changing the amount of HPLEGR gas during the acceleration transient period is not limited to this. For example, the basic amount corresponding to the low-load operation state can be continuously changed to the basic amount corresponding to the high-load operation state.

  Hereinafter, a specific execution procedure when the correction control is executed by the ECU 20 will be described with reference to FIG. FIG. 10 is a flowchart showing the correction control routine. This routine is repeatedly executed by the ECU 20 during operation of the internal combustion engine 1.

  First, in step S401, the ECU 20 acquires the operating state of the internal combustion engine 1. Specifically, the rotational speed, accelerator opening, fuel injection amount, cooling water temperature, and the like of the internal combustion engine 1 are acquired based on the signals from the various sensors described above.

  In step S402, the ECU 20 calculates a target intake air temperature based on the operating state of the internal combustion engine 1 acquired in step S401. The target intake air temperature in this case is a target value of the temperature of the intake air sucked into the cylinder of the internal combustion engine 1 and corresponds to the temperature of the intake air in the intake manifold 17.

  In step S403, the ECU 20 determines whether or not the internal combustion engine 1 is being warmed up. If an affirmative determination is made in step S403, the ECU 20 proceeds to step S404. On the other hand, if a negative determination is made in step S403, the ECU 20 once ends the execution of this routine.

  In step S404, the ECU 20 determines whether or not the internal combustion engine 1 is in an acceleration transient state. Specifically, for example, when the detected value by the accelerator opening sensor 15 is increased by a predetermined amount or more, it can be determined that the acceleration is in a transient state. If an affirmative determination is made in step S404, the ECU 20 proceeds to step S405. On the other hand, if a negative determination is made in step S404, the ECU 20 once ends the execution of this routine.

  In step S405, the ECU 20 sets the VN opening to an opening closer to the high load basic VN opening, and increases the HPLEGR gas amount than the high load basic HPLEGR gas amount.

  In step S406, the ECU 20 determines whether or not the intake air temperature has become equal to the target intake air temperature. The ECU 20 repeats step S406 until an affirmative determination is made. If an affirmative determination is made in step S406, the ECU 20 proceeds to step S407.

  In step S407, the ECU 20 returns the VN opening to the high load basic VN opening, and returns the HPLEGR gas amount to the high load basic HPLEGR gas amount.

  In this embodiment, the ECU 20 that executes Steps S403 to S405 corresponds to the combustion stabilization means in the present invention.

  In addition, when an acceleration transient state is detected in the middle of warming up, combustion failure can be suppressed by means other than the above embodiments. For example, means for increasing the pilot injection amount, means for increasing the effective compression ratio (for example, controlling the VVT mechanism to change the closing timing of the intake valve to the bottom dead center side of the intake stroke at the crankshaft angle), HPLEGR gas In the EGR system having a configuration in which the HPLEGR cooler 43 is bypassed, the means for increasing the HPLEGR cooler bypass amount, the means for increasing the LPLEGR gas amount for bypassing the LPLEGR cooler 33, and the amount of intake air for bypassing the intercooler 8 are increased. Means, means for operating the glow plug, etc. can be implemented as combustion stabilization means. In addition, these various means and the above embodiments may be combined as much as possible to implement the combustion stabilization means of the present invention.

It is a figure which shows schematic structure of the internal combustion engine to which the EGR system in an Example is applied, and its intake / exhaust system. It is a figure which shows an example of the EGR control map according to the driving | running state in an Example. It is a figure which shows an example of the change of the intake air temperature at the time of performing correction control of Example 1, HPLEGR gas amount, and LPLEGR gas amount. 3 is a flowchart illustrating a correction control routine according to the first embodiment. It is a figure which shows an example of the change of the intake temperature and fuel injection timing at the time of performing correction control of Example 2. FIG. 6 is a flowchart illustrating a correction control routine according to a second embodiment. FIG. 10 is a diagram illustrating an example of changes in intake air temperature, in-cylinder temperature, and internal EGR amount when correction control according to the third embodiment is performed. 10 is a flowchart illustrating a correction control routine according to a third embodiment. It is a figure which shows an example of the change of the intake temperature at the time of performing correction control of Example 4, a supercharging pressure, the VN opening degree, and the HPLEGR gas amount. 10 is a flowchart illustrating a correction control routine according to a fourth embodiment.

Explanation of symbols

1 Internal combustion engine 2 Cylinder 3 Intake passage 4 Exhaust passage 5 Nozzle vane 6 First throttle valve 7 Air flow meter 8 Intercooler 9 Second throttle valve 10 Exhaust purification device 11 Compressor 12 Turbine 13 Turbocharger 14 Water temperature sensor 15 Accelerator opening sensor 16 Crank Angle sensor 17 Intake manifold 18 Exhaust manifold 19 Exhaust throttle valve 20 ECU
30 LPLEGR device 31 LPL passage 32 LPLEGR valve 33 LPLEGR cooler 40 HPLEGR device 41 HPL passage 42 HPLEGR valve 43 HPLEGR cooler

Claims (2)

A turbocharger having a turbine provided in an exhaust passage of an internal combustion engine and a compressor provided in an intake passage;
By adjusting the valve opening degree of the HPL EGR valve provided in the HPL passage through an HPL passage connecting the exhaust passage upstream of the turbine and the intake passage downstream of the compressor, a part of the exhaust gas is internal combustion engine. HPLEGR means to return to
By adjusting the valve opening degree of the EPL valve for LPL provided in the LPL passage through the LPL passage connecting the exhaust passage downstream from the turbine and the intake passage upstream from the compressor, a part of the exhaust gas is internal combustion engine. LPLEGR means to return to
As the operating state of the internal combustion engine becomes higher, the amount of exhaust gas returned to the internal combustion engine by the LPLEGR means or the ratio of exhaust gas returned to the internal combustion engine by the LPLEGR means in the total EGR gas is increased. EGR control means for increasing the amount of exhaust gas returned to the internal combustion engine by the HPLEGR means or the ratio of exhaust gas returned to the internal combustion engine by the HPLEGR means in the total EGR gas as the state becomes lower load;
Combustion stabilization means for stabilizing the combustion of fuel in the internal combustion engine during a transition when the internal combustion engine is warming up and transitioning from an operating state to an operating state on a higher load side than the operating state; ,
An EGR system for an internal combustion engine comprising: In claim 1,
The combustion stabilization means includes means for advancing the fuel injection timing, means for increasing the pilot injection amount, means for increasing the effective compression ratio, means for increasing the internal EGR amount, bypass for bypassing the intercooler to the intake passage Means for increasing the amount of intercooler bypass that is the amount of intake air flowing through the bypass passage, means for increasing the ratio of exhaust gas returned to the internal combustion engine by the HPLEGR means in all EGR gas, and flowing through the HPL passage It has at least one of a means for increasing the amount of HPLEGR gas that is the amount of EGR gas, a means for the turbocharger to have a variable nozzle mechanism to close the variable nozzle opening, and a means for operating a glow plug An internal combustion engine EGR system characterized.

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