JP2010096143A - Device and system for controlling internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To show sufficient cleaning effect in cleaning deposits accumulated in an EGR cooler by making fresh air reversely flow into the EGR cooler. <P>SOLUTION: When an accumulation state is determined in which deposits not less than a prescribed quantity accumulate in the EGR cooler 22, a mode is changed over from a normal mode for recirculating part of exhaust gas to an intake system as EGR gas to a reverse flow mode for making fresh air reversely flow into the EGR cooler 22. Contents of control of the internal combustion engine are changed to rise temperature of fresh air in the reverse flow mode. For example, a temperature of the reversely flowing fresh air is raised by executing low pressure EGR quantity increase (control A), intercooler bypass (control B), refrigerant flow rate reduction (control C), and fuel addition (control D). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an internal combustion engine control device and a control system applied to an internal combustion engine including an EGR cooler that cools EGR gas.

  Conventionally, a part of the exhaust gas discharged from the combustion chamber of the internal combustion engine is recirculated to the intake system of the internal combustion engine as EGR (Exhaust Gas Recirculation) gas, thereby reducing the combustion temperature and reducing NOx in the exhaust gas. EGR systems are known. Further, a technique for improving the NOx reduction effect by increasing the density of the EGR gas by providing an EGR cooler that cools the EGR gas is conventionally known.

  However, as the internal combustion engine is used, foreign substances (deposits) such as soot contained in the exhaust gas accumulate on the EGR cooler. Then, the cooling capacity by the EGR cooler is lowered, and the NOx reduction effect cannot be sufficiently improved.

Therefore, in the control described in Patent Document 1, fresh air taken in from the outside air and flowing through the intake system of the internal combustion engine is caused to flow back to the EGR cooler to remove accumulated deposits and clean the EGR cooler (hereinafter referred to as “backflow”). Cleaning ”).
Japanese Patent Laid-Open No. 11-62722

  However, it has become clear from the following knowledge by the present inventor that a sufficient cleaning effect cannot be obtained simply by reflowing fresh air.

  That is, the deposit deposited on the EGR cooler is a foreign substance in a state where soot and unburned gas in the exhaust gas and condensed water generated by cooling with the EGR cooler are mixed. Such a deposit is in a viscous state (fluid state) at a high temperature where the exhaust gas is circulated through the EGR cooler. However, when fresh air is caused to flow backward through the EGR cooler, the deposit is cooled by the fresh air, and the deposit is lowered in viscosity and becomes in a state where the adhesive force is increased (fixed state). As a result, the deposit is difficult to peel off from the EGR cooler, and a sufficient cleaning effect cannot be obtained.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an internal combustion engine that exhibits a sufficient cleaning effect when cleaning deposits accumulated in the EGR cooler by causing fresh air to flow backward in the EGR cooler. An object of the present invention is to provide an engine control device and a control system therefor.

  Hereinafter, means for solving the above-described problems and the operation and effects thereof will be described.

  The invention according to claim 1 is provided in the EGR pipe that recirculates a part of the exhaust gas discharged from the combustion chamber to the intake system as EGR gas, and / cooled by exchanging heat with the EGR gas. The EGR cooler, the normal mode in which the EGR gas is recirculated, and the reverse flow mode in which fresh air taken in from outside air and flowing through the intake system is caused to flow backward to the EGR cooler. The present invention is applied to an internal combustion engine having a switching valve for switching the flow path of the engine.

  And a deposit determining means for determining whether or not a deposit of a predetermined amount or more is deposited on the EGR cooler; and / or when the deposit is determined to be in the deposit state, the reverse flow mode is set. Backflow control means for controlling the operation of the switching valve; and / or fresh air temperature increase means for changing the control content of the internal combustion engine so as to increase the temperature of the fresh air in the reverse flow mode. .

  The present invention has been made based on the above-mentioned knowledge that “when the deposit is cooled by fresh air, the deposit becomes a sticking state with increased adhesive force and is less likely to peel off from the EGR cooler”. Since the control content of the internal combustion engine is changed so as to increase the temperature of fresh air, it is possible to suppress an increase in the adhesive strength of the deposit. Therefore, since the deposit is easily peeled off from the EGR cooler by flowing back the fresh air, the cleaning effect by the backflow can be sufficiently exhibited.

  As a method for increasing the temperature of fresh air, a method for increasing the temperature of fresh air by increasing the degree of heating fresh air as described in claim 2 and a degree of cooling of fresh air as described in claim 6 are described. And a method for increasing the fresh air temperature by reducing the temperature. If the degree of fresh air heating is increased, the fresh air temperature can be raised so as to raise the temperature of the fresh air that flows backward than the temperature of the outside air taken into the intake system. If the degree of fresh air cooling is decreased, the fresh air temperature can be raised so that the temperature of the fresh air to be backflowed approaches the outside air temperature.

  Moreover, you may combine the invention of Claim 2 and the invention of Claim 6. That is, on the one hand, the fresh air temperature may be increased by increasing the degree of heating the fresh air, and on the other hand, the fresh air temperature may be increased by decreasing the degree of cooling the fresh air. Hereinafter, specific examples for realizing the respective methods of increasing the heating degree and decreasing the cooling degree will be described.

<Method of increasing the degree of heating>
The invention described in claim 3 is applied to an internal combustion engine equipped with a supercharger, a low pressure EGR pipe, and a low pressure EGR valve, and the EGR pipe recirculates the EGR gas from the upstream side of the turbine. High pressure EGR piping arranged to circulate. In other words, the internal combustion engine targeted by the present invention includes a path for recirculating the high pressure EGR before passing through the turbine and a path for recirculating the low pressure EGR after passing through the turbine. In such an internal combustion engine, the fresh air temperature raising means changes the control content of the low pressure EGR valve so as to increase the flow rate of the low pressure EGR gas, thereby increasing the degree of heating of the fresh air. It is characterized by.

  According to this, while the EGR cooler is cleaned by backflow of fresh air in the high pressure EGR path, the exhaust gas having a higher temperature than the outside air is recirculated to the intake system as low pressure EGR gas in the low pressure EGR path. Therefore, the heating degree of fresh air that causes the EGR cooler to flow backward can be easily increased. In addition, although EGR recirculation cannot be performed by the high pressure EGR path in the reverse flow mode, according to the present invention, EGR recirculation can be performed by the low pressure EGR path even in the reverse flow mode. The reduced NOx effect can be exhibited even in the reverse flow mode.

  In the invention of claim 4, the internal combustion engine includes a low pressure EGR cooler that is provided in the low pressure EGR pipe and cools by exchanging heat with the EGR gas, and a filter that collects particulate components in the exhaust gas. And the low-pressure EGR pipe is arranged to recirculate the EGR gas from the downstream side of the filter.

  In the fourth aspect of the invention, in addition to providing the EGR cooler in the high pressure EGR pipe, the low pressure EGR cooler is provided in the low pressure EGR pipe. Therefore, the density of the low pressure EGR gas can be increased and the NOx reduction effect can be improved. However, since the low-pressure EGR pipe is arranged to recirculate EGR gas from the downstream side of the filter, in the case of the low-pressure EGR cooler, no deposit is deposited unlike the high-pressure side EGR cooler. Is unnecessary.

  According to a fifth aspect of the present invention, the internal combustion engine includes a supercharger having a supercharging pressure adjusting mechanism that adjusts the supercharging pressure by adjusting an amount of converting the flow velocity energy of the exhaust gas into the rotational force of the turbine. The fresh air temperature raising means increases the degree of heating of the fresh air by changing the control content of the supercharging pressure adjusting mechanism so as to increase the supercharging pressure.

  If the supercharging pressure is increased in this way, the temperature of the fresh air rises as the pressure increases. Therefore, the heating degree with respect to fresh air can be easily increased only by changing the control content of the supercharging pressure adjusting mechanism so as to increase the supercharging pressure.

<Method of reducing the degree of cooling>
The invention according to claim 7 controls an intercooler that cools fresh air, a bypass pipe that bypasses the fresh air with respect to the intercooler, and a ratio of the fresh air flow rate to the intercooler with respect to the fresh air flow rate to the bypass pipe. The present invention is applied to an internal combustion engine equipped with an intercooler valve. And the said fresh air temperature raising means reduces the cooling degree with respect to the said fresh air by changing the control content of the said intercooler valve so that the ratio of the fresh air flow volume to the said intercooler may be reduced. To do.

  According to this, the degree of cooling with respect to the fresh air can be easily reduced only by changing the control content of the intercooler valve so as to reduce the ratio of the fresh air flow rate to the intercooler.

  In the invention according to claim 8, the EGR cooler is provided with a refrigerant flow rate adjusting valve for adjusting a circulation flow rate of a cooling medium that exchanges heat with the EGR gas, and the fresh air temperature raising means is configured to The degree of cooling with respect to the fresh air is reduced by changing the control content of the refrigerant flow rate adjustment valve so as to reduce the amount of air.

  According to this, the cooling degree with respect to fresh air can be easily reduced only by changing the control content of the refrigerant flow rate adjusting valve so as to reduce the refrigerant flow rate.

  The invention according to claim 9 is applied to an internal combustion engine provided with a supercharger. In addition, the flow path is configured so that the fresh air that has flowed back through the EGR cooler in the reverse flow mode flows into the downstream side of the turbine and is discharged.

  Here, a large amount of deposit peeled off from the EGR cooler is included in the fresh air after washing by backflow, that is, fresh air downstream of the EGR cooler in the backflow mode. If such fresh air after washing flows into the upstream side of the turbine and is exhausted, deposits are attached to the turbine, which may cause a malfunction of the supercharger. In view of this point, in the invention according to claim 9, the flow path is configured so that fresh air that has flowed back through the EGR cooler in the reverse flow mode (that is, fresh air after cleaning) flows into the downstream side of the turbine and is discharged. Therefore, deposits can be avoided from adhering to the turbine, and the above concerns can be resolved.

  A tenth aspect of the invention is an internal combustion engine control system comprising the control device and at least one of the EGR pipe, the EGR cooler, and the switching valve. According to this control system, the various effects described above can be exhibited in the same manner.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a control device for an internal combustion engine according to the present invention will be described below with reference to the drawings.

  First, an outline of an engine (internal combustion engine) to be controlled by the control device according to the present embodiment will be briefly described. In this embodiment, a diesel engine for a four-wheeled vehicle is targeted, and compression ignition of a system in which high-pressure fuel (for example, light oil having an injection pressure “1000 atm” or more) is directly supplied to the combustion chamber by injection (direct injection supply). Expression engine. The engine is assumed to be a multi-cylinder (for example, in-line four-cylinder) four-stroke, reciprocating diesel engine.

  Next, the configuration of the intake / exhaust system of the engine will be described with reference to FIG.

  The engine 10 includes EGR pipes 20 and 30 that recirculate exhaust gas from the exhaust system to the intake system. By returning a part of the exhaust gas to the intake pipe 11, the combustion temperature in the combustion chamber 10a is lowered to reduce the exhaust gas in the exhaust gas. NOx reduction and the like are aimed at. In the present embodiment, the high-pressure EGR pipe 20 that recirculates exhaust gas from the upstream portion (see reference numeral 12a) of the turbine 42, which will be described later, in the exhaust pipe 12, and the downstream portion (reference numeral 12b) of the turbine 42 in the exhaust pipe 12. A low pressure EGR pipe 30 that recirculates the exhaust gas from the exhaust gas. That is, a path for recirculating the low pressure EGR before passing through the turbine 42 through the high pressure EGR pipe 20 and a path for recirculating the low pressure EGR after passing through the turbine 42 through the low pressure EGR pipe 30 are provided.

  Each of the EGR pipes 20 and 30 is provided with EGR flow rate adjusting devices 21 and 31 for adjusting the flow rate of EGR gas (EGR flow rate). The EGR flow rate adjusting devices 21 and 31 include a high-pressure EGR valve 21a and a low-pressure EGR valve 31a that adjust the flow area of the EGR pipes 10 and 20, and electric motors 21b and 31b that drive the EGR valves 21a and 31a. It is configured. When the EGR valves 21a and 31a are fully opened, the EGR flow rate becomes maximum, and when the EGR valves 21a and 31a are fully closed, the EGR flow rate becomes zero.

  A high-pressure EGR cooler 22 and a low-pressure EGR cooler 32 that cool the EGR gas are provided on the upstream side of the EGR valves 21 a and 31 a in the EGR pipes 20 and 30. By cooling the EGR gas in this way, the volume of the EGR gas is reduced (density increase), thereby improving the charging efficiency of the intake air flowing into the combustion chamber 10a. Inside the high-pressure EGR cooler 22, a coolant passage through which coolant (cooling medium) circulates and a gas passage 22a through which EGR gas flows are formed, and the EGR gas flowing through the gas passage 22a passes through the coolant passage. It is cooled by exchanging heat with the circulating coolant.

  Note that engine coolant is applied to the coolant, and the coolant is cooled by exchanging heat with outside air by a radiator (not shown). Then, by adjusting the opening degree of the refrigerant flow rate adjusting valve 22b, the amount (refrigerant flow rate * 3) that flows into the coolant passage in the cooling water circulating through the radiator (see reference numerals * 1 and * 2) is adjusted. To do. Thereby, the cooling capacity of the high pressure EGR cooler 22 is adjusted. In addition, since the structure of the low pressure EGR cooler 32 is the same as that of the high pressure EGR cooler 22, the description is cited.

  A bypass pipe 23 that bypasses the high-pressure EGR gas with respect to the high-pressure EGR cooler 22 is provided on the upstream side of the EGR valve 21 a in the high-pressure EGR pipe 20. In addition, a switching device 24 that switches the flow of EGR gas between the EGR cooler 22 and the bypass pipe 23 is provided at a portion of the high-pressure EGR pipe 20 that is upstream of the EGR cooler 22 and where the bypass pipe 23 branches. Yes. The switching device 24 includes a switching valve 24a that switches between the inlet 20a to the EGR cooler 22 and the inlet 20b to the bypass piping 23 in the EGR pipe 20, and an electric motor 24b that drives the switching valve 24a. Configured.

  Further, the switching valve 24a not only simply opens and closes both the inlets 20a and 20b, but also adjusts the opening degree at an intermediate opening position where both the inlets 20a and 20b are opened, thereby allowing EGR gas to flow through EGR. The distribution ratio between the flow rate to be circulated to the cooler 22 and the flow rate to be bypassed by the bypass pipe 23 is adjusted. As a result, the temperature of the EGR gas is adjusted at the portion where the bypass pipe 23 merges on the downstream side of the EGR cooler 22. According to this, it is possible to improve the NOx reduction effect by adjusting the temperature of the high pressure EGR gas to an optimum value and recirculating the high pressure EGR gas.

  A throttle valve 13 for adjusting the flow rate of fresh air out of the intake air flowing into the combustion chamber 10a is provided upstream of the portion of the intake pipe 11 to which the high pressure EGR pipe 20 is connected. The throttle valve 13 is opened / closed by an electric motor 13a. The fresh air amount becomes maximum when the throttle valve 13 is fully opened, and the fresh air amount becomes zero when the throttle valve 13 is fully closed.

  A turbocharger 40 (supercharger) is disposed between the intake pipe 11 and the exhaust pipe 12. The turbocharger 40 includes a compressor impeller 41 (hereinafter referred to as “compressor”) provided in the intake pipe 11, and a turbine wheel 42 (hereinafter referred to as “turbine”) provided in the exhaust pipe 12. They are connected by a shaft 43. In the turbocharger 40, the turbine 42 is rotated by the flow velocity energy of the exhaust gas flowing through the exhaust pipe 12, and the rotational force is transmitted to the compressor 41 via the shaft 43. Then, the outside air (fresh air) taken in from the inlet 14a of the air cleaner 14 is compressed by the compressor 41. Thereby, the intake air (fresh air) sucked into the combustion chamber 10a is supercharged.

  Further, the turbocharger 40 according to the present embodiment employs a variable capacity turbocharger that can change the ratio of converting the fluid energy of the exhaust into the rotational driving force of the turbine 42. Specifically, the turbine 42 is provided with a plurality of variable vanes 44 for making the flow rate of the exhaust gas sprayed variable. These variable vanes 44 open and close in synchronization with each other. Then, the exhaust flow velocity is adjusted by changing the size of the gap between the adjacent variable vanes 44, that is, the opening degree of the variable vanes 44, and thereby the rotational speed of the turbine 42 is adjusted. Then, by adjusting the rotational speed of the turbine 42, the amount of air forcibly supplied to the combustion chamber 10a, that is, the supercharging pressure is adjusted.

  The air supercharged by the turbocharger 40 is cooled by the intercooler 50 and then fed downstream. The intake air is cooled by the intercooler 50 to reduce the volume (increase in density), thereby improving the charging efficiency of the intake air flowing into the combustion chamber 10a.

  The intake pipe 11 is provided with a bypass pipe 51 that bypasses the supercharged fresh air with respect to the intercooler 50. In addition, a switching device 52 that switches the flow of fresh air between the intercooler 50 and the bypass pipe 51 is provided at a portion of the intake pipe 11 that is upstream of the intercooler 50 and where the bypass pipe 51 branches. . The switching device 52 includes a switching valve 52a for switching the inlet 11a to the intercooler 50 and the inlet 11b to the bypass pipe 51 in the intake pipe 11, and an electric motor 52b for driving the switching valve 52a. Configured.

  A filter 60 (DPF: diesel particulate filter) that collects particulate matter (PM) in the exhaust is disposed downstream of the turbine 42 and upstream of the branching point 12b of the low-pressure EGR pipe 30 in the exhaust pipe 12. ) Is provided. Therefore, the high pressure EGR by the high pressure EGR pipe 20 is exhaust in a state where PM is not collected by the filter 60, whereas the low pressure EGR by the low pressure EGR pipe 30 is exhaust in a state where PM is collected by the filter 60. is there. On the downstream side of the filter 60, an oxidation catalyst (not shown) for purifying HC and CO in the exhaust, a NOx catalyst (not shown) for purifying NOx in the exhaust, and the like are provided. Incidentally, the oxidation catalyst may be provided in the filter 60.

  By the way, as the engine 10 is used, foreign matter (deposit) mainly composed of PM such as soot contained in the exhaust gas accumulates in the gas passage 22a of the high pressure EGR cooler 22. Then, there is a concern that the cooling capacity of the EGR cooler 22 is lowered and the NOx reduction effect cannot be sufficiently improved.

  Therefore, in the present embodiment, the EGR cooler 22 is cleaned by removing the deposited deposit by causing the outside air (fresh air) taken in from the air cleaner 14 to flow back to the EGR cooler 22. In the following description, the state in which the EGR gas is circulated to the EGR cooler 22 in the direction in which the EGR gas is recirculated from the exhaust system to the intake system is referred to as “normal mode”, and the direction in which fresh air flows backward from the intake system to the exhaust system. A state in which fresh air is circulated to the EGR cooler 22 is referred to as “backflow mode”.

  The ECU 60 functions as a deposition determination unit that determines whether or not a predetermined amount or more of deposit is deposited on the EGR cooler 22, and when it is determined that the deposit is in the accumulation state, the normal mode is changed to the reverse flow mode. Switch. Alternatively, the normal mode may be restored on the condition that the execution of the backflow mode is continued for a predetermined time, or the normal mode may be restored when it is determined that the accumulation state is not established.

  As a specific example of the deposition determination, it may be determined that the accumulation state is detected when the differential pressure across the EGR cooler 22 is detected and the differential pressure exceeds a predetermined value. Further, an intake air amount to the combustion chamber 10a is calculated based on an intake air pressure and an intake air temperature detected by an intake air pressure sensor (not shown) installed in the surge tank 16, and an air flow meter (not shown) is calculated from the calculated intake air amount. The actual EGR amount is calculated by subtracting the fresh air amount detected in step), the theoretical EGR amount is calculated from the opening degree of the high pressure EGR valve 21a, and the calculated actual EGR amount is smaller than the theoretical EGR amount by a predetermined amount or more. It is mentioned that it is determined that it is in a deposited state.

  A portion upstream of the high pressure EGR cooler 22 in the high pressure EGR pipe 20 and a portion downstream of the turbine 42 and the upstream portion of the filter 60 (see reference numeral 12 c) of the exhaust pipe 12 are communicated with each other by the backflow bypass pipe 25. ing. Moreover, the state where the EGR pipe 20 communicates with the turbine upstream side portion 12a and the state where the EGR pipe 20 communicates with the turbine downstream side portion 12c via the backflow bypass piping 25 are connected to a portion of the high pressure EGR pipe 20 where the reverse flow bypass pipe 25 branches. And a switching device 26 for switching between and. The switching device 26 includes a switching valve 26a and an electric motor 26b that drives the switching valve 26a. The switching valve 26a switches between opening and closing the flow port 20c to the turbine upstream portion 12a and the flow port 20d to the turbine upstream portion 12a in the EGR pipe 20.

  As shown in FIG. 2, in the normal mode, the EGR pipe 20 is communicated with the turbine upstream side portion 12 a and the switching valve 26 a is operated so as to close the backflow bypass pipe 25. As a result, the exhaust from the turbine upstream portion 12a is recirculated to the intake system as high-pressure EGR gas.

  On the other hand, in the reverse flow mode shown in FIG. 3, the ECU 70 (reverse flow control means) operates the switching valve 26a so as to connect the EGR pipe 20 to the reverse flow bypass pipe 25 and close the flow port 20c to the turbine upstream portion 12a. . As a result, the fresh air that has flowed back through the EGR cooler 22 flows through the backflow bypass pipe 25 and is discharged to the exhaust pipe 12. That is, the fresh air that has cleaned the EGR cooler 22 bypasses the turbine 42, passes through a purification device such as the filter 60, is purified, and then discharged to the outside. The deposit peeled off from the EGR cooler 22 is collected by the filter 60.

  In order to make fresh air flow backward to the EGR cooler 22, it is necessary to set the pressure reverse state in which the pressure on the intake system side is higher than the pressure on the exhaust system side with respect to the EGR cooler 22. That is, it is necessary to control the engine 10 so as to increase the intake pressure and decrease the exhaust pressure.

  Here, when the engine 10 is operating so as to decelerate the output shaft (crankshaft) of the engine 10 and when the supercharging pressure is equal to or higher than a predetermined value and it is required to reduce the pressure (hereinafter, In the case of “decelerated and reduced pressure”, the opening degree of the variable vane 44 is increased so that the ratio of converting the exhaust fluid energy into the rotational driving force of the turbine 42 is reduced. Therefore, at the time of such deceleration and pressure reduction, by increasing the opening of the variable vane 44, the exhaust pressure in the exhaust pipe 12 is lowered, and the pressure on the intake system side is increased due to excessive supercharging. . That is, it is in the pressure reversal state described above.

  Therefore, in the present embodiment, the switching valve 26a is operated so that the EGR pipe 20 communicates with the backflow bypass pipe 25 at the time of deceleration and pressure reduction assumed to be in the pressure reversal state. As a result, fresh air in the intake system flows backward through the EGR cooler 22 and is discharged to the exhaust system through the reverse flow bypass pipe 25.

  The ECU 70 (electronic control unit) controls the operation of various actuators mounted on the engine 10 based on the engine operating state. As specific examples of the engine operating state, the engine speed, the engine load, the amount of accelerator operation by the driver, the amount of fresh air flowing through the air cleaner 14, the pressure in the surge tank 16 (intake pressure), the opening of the throttle valve 13 Detected values such as engine coolant temperature, O2 concentration contained in exhaust gas, NOx concentration, and the like.

  Next, specific examples in which the ECU 70 controls the operation of the various actuators in the normal mode will be listed. The ECU 70 controls the fuel injection amount, the injection timing, and the like by controlling the operation of the fuel injection valve 15. Further, the supercharging pressure is controlled by controlling the operation of the variable vane 44. The intake air amount is controlled by controlling the operation of the throttle valve 13. The high pressure EGR amount and the low pressure EGR amount are controlled by controlling the operation of the EGR valves 21a and 31a. By controlling the operation of the switching valves 24a and 52a, the temperature of the high pressure EGR and the temperature of the low pressure EGR are controlled.

  Further, the ECU 70 controls the switching between the normal mode and the reverse flow mode by controlling the operation of the switching valve 26a of the switching device 26. That is, as described above, the switching valve 26a is operated so as to connect the EGR pipe 20 to the reverse flow bypass pipe 25 at the time of deceleration and pressure reduction assumed to be in the pressure reverse state, thereby switching to the reverse flow mode.

  By the way, in this embodiment, engine operation is performed in a high pressure EGR mode for recirculating high pressure EGR to the intake system, a low pressure EGR mode for recirculating low pressure EGR, and a mixed mode for recirculating both high pressure EGR and low pressure EGR. Switching according to the state.

  In the high-pressure EGR mode, the EGR gas is taken in and circulated from a location near the combustion chamber 10a on the upstream side of the turbine in the exhaust pipe 12, and therefore, the circulation path thereof is compared with the low-pressure EGR mode in which EGR gas is taken in and circulated from the downstream side of the filter. Can be shortened. Therefore, the response time from when the opening degree of the high pressure EGR valve 21a is changed to when the flow rate of the high pressure EGR flowing into the surge tank 16 is actually changed can be shortened. However, when the engine load increases, the operation of the variable vane 44 is controlled so as to increase the supercharging pressure, so that the pressure in the surge tank 16 increases. Then, it becomes difficult for the high-pressure EGR to flow into the surge tank 16, and there is a concern that the high-pressure EGR will not circulate.

  On the other hand, since the filter 60 is generally disposed at a position far from the engine 10 (for example, under the floor of the vehicle), the low pressure EGR mode in which EGR gas is taken in from the downstream side of the filter and circulated is compared with the high pressure EGR mode. The circulation path becomes longer. Therefore, the response time from when the opening degree of the low pressure EGR valve 31a is changed to when the flow rate of the low pressure EGR flowing into the compressor 41 is actually changed becomes long. However, even if the engine load increases, since the low pressure EGR is sucked by the compressor 41, there is no concern that it will not circulate like the high pressure EGR.

  To summarize the above description, the high pressure EGR mode is advantageous in terms of responsiveness, but it is necessary to switch to the low pressure EGR mode that does not cause the possibility of circulation during high load operation of the engine 10. Therefore, in this embodiment, when the normal mode is executed, the low-pressure EGR mode is switched in the high load operation region, the mix mode is switched in the medium load operation region, and the high pressure EGR mode is switched in the low load operation region.

  By the way, in executing the reverse flow mode, it is not possible to obtain a sufficient cleaning effect by simply causing the fresh air to flow backward to the EGR cooler 22. That is, when the deposit accumulated on the EGR cooler 22 is cooled by fresh air, the deposit is in a fixed state with increased adhesive force, and is difficult to peel off from the EGR cooler 22.

  Therefore, the ECU 70 (fresh air temperature raising means) of the present embodiment changes the engine control content in the normal mode to the control content in the reverse flow mode so that the fresh air temperature is higher in the reverse flow mode than in the normal mode. Hereinafter, various controls A to D for increasing the fresh air temperature in the reverse flow mode will be described.

<Control A: Increase in low-pressure EGR amount>
In controlling the low pressure EGR amount and the high pressure EGR amount, switching to the low pressure EGR mode, the mix mode, and the high pressure EGR mode according to the engine load is as described above. In other words, it can be said that when the opening degree of the low pressure EGR valve 31a is controlled to control the low pressure EGR amount, the control is performed according to the engine load in the normal mode shown in FIG.

  On the other hand, in the reverse flow mode shown in FIG. 3, the low pressure EGR amount is increased by controlling the opening of the low pressure EGR valve 31a to a predetermined opening (for example, the maximum opening) regardless of the engine load. Thereby, the heating degree with respect to a fresh air is increased, and the temperature of the fresh air made to flow backward to the EGR cooler 22 can be raised.

  In the reverse flow mode, instead of controlling the low pressure EGR valve 31a to the maximum opening, the target EGR amount is set so that the exhaust oxygen concentration detected by the A / F sensor (not shown) approaches the target exhaust oxygen concentration. The opening degree of the low pressure EGR valve 31a may be controlled so that the target EGR amount is set. According to this, compared with the case where the low pressure EGR valve 31a is fully closed, the fresh air temperature can be increased, and the amount of the high pressure EGR circulated in the normal mode can be supplemented with the low pressure EGR in the reverse flow mode. it can.

  Incidentally, when the EGR flow rate is too low, a sufficient NOx reduction effect cannot be obtained, and when the EGR flow rate is too high, oxygen in the cylinder becomes insufficient and particulates (especially smoke) increase. In order to avoid this, it is required to increase the EGR flow rate to the limit of the smoke generation limit and to reduce NOx without the generation of smoke. Therefore, the target flow rates of the high pressure EGR and the low pressure EGR are set so as to increase to the limit of smoke generation, but the high pressure EGR amount becomes zero in the reverse flow mode. In this regard, if the control is performed such that the shortage of the high pressure EGR amount is compensated by the low pressure EGR in the reverse flow mode, the effects of smoke suppression and NOx reduction can be sufficiently exhibited even in the reverse flow mode.

<Control B: Intercooler bypass>
The NOx reduction effect caused by refluxing the EGR gas varies depending on the temperature of the EGR to be refluxed. Therefore, it is desirable to control the EGR temperature to an optimum value so that the NOx reduction effect is maximized. Therefore, when the opening degree of the switching valve 52a is controlled to control the temperature of the low-pressure EGR gas, the opening degree of the switching valve 52a is controlled so as to be an optimum value according to the engine operating state in the normal mode.

  On the other hand, in the reverse flow mode, the intercooler 50 is controlled by controlling the opening degree of the switching valve 52a to a predetermined opening degree (for example, the opening degree that maximizes the inlet 11b to the bypass pipe 51) regardless of the engine operating state. Increase the flow rate of fresh air that bypasses the air. Thereby, since the degree by which fresh air is cooled by the intercooler 50 can be reduced, the temperature of the fresh air that flows back to the EGR cooler 22 can be increased as compared with the case where a part of the fresh air is cooled by the intercooler 50.

  Further, the target opening degree of the switching valve 52a in the normal mode is corrected to the side that bypasses the intercooler 50, and the opening degree of the switching valve 52a is controlled to be the corrected target opening degree in the reverse flow mode. May be.

<Control C: Refrigerant flow rate decrease>
In controlling the operation of the refrigerant flow rate adjustment valve 22b, in the normal mode, the refrigerant flow rate adjustment valve 22b is fully opened so that the engine coolant (refrigerant) circulates through the coolant passage inside the high pressure EGR cooler 22. Thereby, the cooling function by the high-pressure EGR cooler 22 is sufficiently exhibited.

  On the other hand, in the reverse flow mode, the refrigerant flow rate adjustment valve 22b is fully closed so as to stop the inflow of the refrigerant into the high pressure EGR cooler 22. Thereby, since the cooling function by the high pressure EGR cooler 22 is remarkably lowered, the degree to which fresh air is cooled by the high pressure EGR cooler 22 can be reduced. Therefore, the temperature of the fresh air that flows back to the EGR cooler 22 can be increased.

<Control D: Fuel addition>
As shown in FIG. 1, an addition valve 17 for adding fuel into the high-pressure EGR pipe 20 and an oxidation reaction of the added fuel are provided in a portion of the high-pressure EGR pipe 20 on the surge tank 16 side with respect to the high-pressure EGR cooler 22. The catalyst 18 to be made is provided. In the normal mode, the ECU 70 controls the operation of the addition valve 17 so as to prohibit fuel addition from the addition valve 17.

  On the other hand, in the reverse flow mode, the ECU 70 controls the operation of the addition valve 17 so as to execute fuel addition. As a result, the added fuel undergoes an oxidation reaction on the catalyst 18, and the fresh air is heated by the reaction heat, and the temperature of the fresh air flowing back to the EGR cooler 22 can be raised.

  As described above, according to the present embodiment, the temperature of the fresh air that flows back to the EGR cooler 22 can be increased by executing the various controls A to D in the backflow mode. Therefore, the degree to which the deposit deposited on the EGR cooler 22 is cooled by fresh air can be suppressed, and the increase in the adhesive strength of the deposit can be suppressed. Therefore, since the deposit is easily peeled off from the gas passage 22a of the EGR cooler 22 by flowing back the fresh air, the cleaning effect by the backflow can be sufficiently exhibited.

(Other embodiments)
The present invention is not limited to the description of the above embodiment, and may be modified as follows. Moreover, you may make it combine the characteristic structure of each embodiment arbitrarily, respectively.

  The various controls A to D may be executed in any combination according to various situations such as the engine operating state.

  In the reverse flow mode, the temperature of the reverse flow fresh air may be increased by controlling the variable vane 44 so as to increase the supercharging pressure as compared with the normal mode.

  The high-pressure EGR cooler 22 may be provided with an electric heater that heats fresh air on the upstream side during backflow, and in the backflow mode, the backflow fresh air may be heated by the electric heater to increase the temperature. The electric heater is preferably used also as an electric heater that raises the temperature of the intake air flowing into the combustion chamber 10a during the warm-up operation of the engine 10.

  In an engine equipped with a valve timing adjusting device that adjusts the timing of at least one of the exhaust valve and the intake valve, the temperature of the fresh air that flows back to the EGR cooler 22 can be increased by controlling the timing of the on-off valve. It may be. For example, when controlling the closing timing of the exhaust valve, if the control is performed so that the valve is closed at a retarded angle in the reverse flow mode as compared with that in the normal mode, the exhaust temperature is raised. Therefore, the low pressure EGR temperature rises and the backflow fresh air temperature rises.

  By installing a bypass pipe that bypasses the low pressure EGR cooler 23 and controlling the low pressure EGR to bypass the low pressure EGR cooler 23 in the reverse flow mode, the temperature of the fresh air that flows back to the EGR cooler 22 is increased. Also good.

  In the reverse flow mode, it is desirable to fully open the throttle valve 13 and the high pressure EGR valve 21a. According to this, the cleaning effect of the EGR cooler 22 can be improved by increasing the flow rate of fresh air to flow backward.

  In the embodiment shown in FIG. 1, the backflow bypass pipe 25 is connected to the downstream portion 12 c of the turbine 42 in the exhaust pipe 12, but is connected to a predetermined portion (for example, the upstream portion of the compressor 41) of the intake pipe 11. You may do it. Alternatively, it may be connected to the low pressure EGR pipe 30. However, in these cases, the deposit peeled off from the EGR cooler 22 due to the backflow cleaning adheres to the compressor 41, and there is a concern that the turbocharger 40 may malfunction. On the other hand, in the embodiment shown in FIG. 1, since the deposit peeled off from the EGR cooler 22 is collected by the filter 60, the above-mentioned concern can be solved, which is preferable.

  -When increasing the temperature of the fresh air in the reverse flow mode, the engine control content may be changed by various controls A to D so as to increase the temperature compared with the normal mode, or taken in from the inlet 14a of the air cleaner 14 The engine control content may be changed so that the temperature of the backflow fresh air becomes higher than the fresh air temperature at that time (that is, the outside air temperature). Alternatively, the engine control content may be changed so that the backflow fresh air is not cooled and becomes lower than the outside air temperature.

The schematic diagram which shows the control system of the internal combustion engine concerning one Embodiment of this invention. The figure which shows the flow of EGR and a fresh air when the control system of FIG. 1 is operate | moving in normal mode. The figure which shows the flow of EGR and a fresh air when the control system of FIG. 1 is operate | moving in the reverse flow mode.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 20 ... High pressure EGR piping (EGR piping), 22 ... High pressure EGR cooler (EGR cooler), 26a ... Switching valve, 30 ... Low pressure EGR piping, 31a ... Low pressure EGR valve, 40 ... Turbocharger (supercharger), 41 ... Compressor , 42... Turbine, 70... ECU (deposition determination means, backflow control means, fresh air temperature raising means).

Claims (10)

EGR piping that recirculates a part of the exhaust gas discharged from the combustion chamber to the intake system as EGR gas;
An EGR cooler that is provided in the EGR pipe and cools by exchanging heat with the EGR gas;
Switching for switching the EGR gas and the fresh air flow path to the normal mode for recirculating the EGR gas and the reverse flow mode for causing the fresh air taken in from the outside air to flow through the intake system to flow backward to the EGR cooler A valve,
Applied to an internal combustion engine with
Deposition determination means for determining whether or not a deposit of a predetermined amount or more is deposited on the EGR cooler;
A reverse flow control means for controlling the operation of the switching valve so as to be in the reverse flow mode when it is determined that the accumulation state is present;
Fresh air temperature increasing means for changing the control content of the internal combustion engine to increase the temperature of the fresh air during the reverse flow mode;
A control device for an internal combustion engine, comprising:   2. The control apparatus for an internal combustion engine according to claim 1, wherein the fresh air temperature increasing means changes at least one of the control contents so as to increase a degree of heating the fresh air in the reverse flow mode. . The internal combustion engine includes
A turbine that rotates by the flow velocity energy of the exhaust, and a turbocharger that has a compressor that rotates by the rotational force of the turbine to supercharge the fresh air
Low-pressure EGR piping for recirculating exhaust gas after passing through the turbine as low-pressure EGR gas from the downstream side of the turbine;
A low pressure EGR valve for controlling the flow rate of the low pressure EGR gas;
Is provided,
The EGR pipe is a high-pressure EGR pipe arranged to recirculate the EGR gas from the upstream side of the turbine,
The said fresh air temperature raising means increases the heating degree with respect to the said fresh air by changing the control content of the said low pressure EGR valve so that the flow volume of the said low pressure EGR gas is increased. Control device for internal combustion engine. The internal combustion engine includes
A low pressure EGR cooler that is provided in the low pressure EGR pipe and cools by exchanging heat with the EGR gas;
A filter that collects particulate components in the exhaust;
Is provided,
The control apparatus for an internal combustion engine according to claim 3, wherein the low-pressure EGR pipe is arranged to recirculate the EGR gas from a downstream side of the filter. The internal combustion engine includes a turbine that is rotated by the flow velocity energy of the exhaust, a compressor that is rotated by the rotation force of the turbine and supercharges the fresh air, and an amount that converts the flow velocity energy to the rotation force of the turbine is adjusted. A supercharger having a supercharging pressure adjustment mechanism for adjusting the supercharging pressure by
The fresh air temperature raising means increases the degree of heating of the fresh air by changing the control content of the supercharging pressure adjustment mechanism so as to increase the supercharging pressure. The control apparatus of the internal combustion engine as described in any one of these.   The fresh air temperature raising means changes at least one of the control contents so as to reduce a degree of cooling the fresh air in the reverse flow mode. The internal combustion engine control device described. The internal combustion engine includes
An intercooler for cooling the fresh air;
Bypass piping for bypassing the fresh air to the intercooler;
An intercooler valve that controls the ratio of the fresh air flow rate to the intercooler with respect to the fresh air flow rate to the bypass pipe;
Is provided,
The fresh air temperature increasing means reduces the degree of cooling of the fresh air by changing the control content of the intercooler valve so as to reduce the ratio of the fresh air flow rate to the intercooler. Item 7. A control device for an internal combustion engine according to Item 6. The EGR cooler is provided with a refrigerant flow rate adjustment valve that adjusts the circulation flow rate of the cooling medium that exchanges heat with the EGR gas,
The said fresh air temperature raising means reduces the cooling degree with respect to the said fresh air by changing the control content of the said refrigerant | coolant flow control valve so that the said refrigerant | coolant flow volume may be decreased. Control device for internal combustion engine. The internal combustion engine is provided with a supercharger having a turbine that rotates by the flow velocity energy of exhaust, and a compressor that rotates by the rotational force of the turbine and supercharges the fresh air.
The flow path is configured so that the fresh air that has flowed back through the EGR cooler flows into the downstream side of the turbine and is discharged in the reverse flow mode. A control apparatus for an internal combustion engine according to claim 1.   An internal combustion engine control system comprising: the internal combustion engine control device according to claim 1; and at least one of the EGR pipe, the EGR cooler, and the switching valve.

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