JP2014208987A - Internal combustion engine exhaust recirculation controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine exhaust recirculation controller capable of making clear the association of water in a process of generation of deposits in an EGR mechanism and exerting a control to remove the deposits at appropriate timing for an actual process of generation of deposits.SOLUTION: An exhaust recirculation controller comprises: an EGR mechanism recirculating a part of exhaust gas; temperature acquisition means for acquiring a wall temperature in the EGR mechanism; and removal control means for exerting a removal control to remove deposits deposited in the EGR mechanism by increasing a temperature of the deposits. The removal control means exerts the removal control on the basis of time ΔD for which the wall temperature is equal to or higher than a condensed water continuous generation upper limit temperature Td associated with generation of condensed water and equal to or lower than a condensed water complete dry temperature Te associated with evaporation of the condensed water in the EGR mechanism.

Description

  The present invention relates to an exhaust gas recirculation control device for an internal combustion engine. More specifically, the present invention relates to an exhaust gas recirculation control device that removes deposits accumulated in a recirculation device that recirculates part of exhaust gas of an internal combustion engine to intake air.

  As a technique for reducing NOx in the exhaust gas of an internal combustion engine and improving fuel efficiency, exhaust gas recirculation is known in which a part of the exhaust gas is extracted and reintroduced into the intake air. This exhaust gas recirculation device is called an exhaust gas recirculation device, and is composed of an EGR pipe that connects the exhaust system and the intake system, an EGR valve that opens and closes the EGR pipe, and an EGR cooler that cools the gas in the EGR pipe. Is done.

  When the exhaust gas is recirculated by the exhaust gas recirculation device, components such as particulate matter and unburned hydrocarbons contained in the exhaust gas may be deposited in a solid state in the device. Hereinafter, the deposits in the exhaust gas recirculation apparatus are collectively referred to as deposits. If deposits are excessively accumulated in the apparatus, the gas flow in the EGR pipe may deteriorate or the sealing performance of the EGR valve may deteriorate. Further, since the deposit is viscous, the controllability of the EGR valve may be deteriorated. For this reason, the technique (refer patent documents 1-3) for suppressing the accumulation of the deposit in an exhaust-gas recirculation apparatus, or removing the deposited deposit is proposed.

  The technique of Patent Document 1 focuses on the fact that the temperature of the exhaust gas flowing through the EGR pipe has a correlation with the generation of deposits. More specifically, in the technique of Patent Document 1, about 110 ° C. or less is defined as a deposit generation region, and when the temperature of the exhaust gas is within the deposit generation region, the temperature of the exhaust gas is set higher than that of the deposit generation region. This suppresses the generation of deposits.

  The technique of Patent Document 2 focuses on the fact that not only the temperature of exhaust gas but also the concentration of soluble organic components in exhaust gas has a correlation with the generation of deposits. More specifically, in the technique of Patent Document 2, it is determined whether or not deposits are deposited based on the exhaust temperature and the soluble organic component concentration.

  The technique of Patent Document 3 focuses on the fact that when the temperature of the exhaust gas decreases, the viscosity of components such as carbon in the exhaust gas increases and adhesion to the wall surface (that is, deposit deposition) is facilitated. . More specifically, in the technique of Patent Document 3, when the temperature of the exhaust gas becomes lower than a first temperature at which deposits may accumulate on the wall surface, the amount of exhaust gas that is reduced by the exhaust gas recirculation device is reduced. Control is performed to reduce deposit accumulation by reducing the amount of exhaust itself that is the source of the deposit. In the technique of Patent Document 3, when the temperature of the exhaust gas is higher than the first temperature and becomes equal to or higher than the second temperature at which deposits attached to the wall surface can be removed, the reduction control is canceled, It helps to remove the deposited deposit.

JP-A-8-61156 JP 2007-162556 A JP 2003-138990 A

  All of the above three techniques have been made on the assumption that the temperature of the exhaust at that time is most correlated with the generation of deposits. As described above, since the deposit actually generated in the exhaust gas recirculation apparatus is viscous, it is considered that the moisture in the exhaust gas has some influence on the generation. However, the correlation between the presence of moisture and the formation of deposits has not been sufficiently studied so far, and thus the deposit generation technology of the conventional exhaust gas recirculation system can suppress the generation of deposits with high accuracy. Absent. That is, the conventional technique cannot correctly determine the actual deposit generation area.

  If the deposit generation region cannot be correctly determined, the amount of deposit actually generated in the exhaust gas recirculation apparatus cannot be accurately determined. For this reason, for example, even if the deposit once deposited is removed by exposing the deposit to a high temperature environment as in the technique of Patent Document 3, it is difficult to measure an appropriate timing for starting such deposit removal control.

  The present invention clarifies the involvement of moisture in the deposit generation process in the exhaust gas recirculation apparatus, and controls the internal combustion engine capable of performing control to remove it at an appropriate timing according to the actual deposit generation process. An object of the present invention is to provide an exhaust gas recirculation control device.

  (1) An exhaust gas recirculation control device for an internal combustion engine (for example, engine 1 described later) of the present invention is a recirculation device (for example, an EGR mechanism 6 described later) that recirculates a part of exhaust gas from an exhaust passage of the internal combustion engine to an intake passage. And a temperature acquisition means (for example, a water temperature sensor 82 and ECU 7 described later) for acquiring the reflux device temperature of the reflux device and the temperature of the deposit accumulated in the reflux device is increased to remove the deposit. Removal control means (for example, ECU 7 described later) for performing the removal control (for example, the processing of S153 in FIG. 15 described later). The removal control means is configured such that the reflux device temperature is equal to or higher than a first temperature (for example, a condensate continuous generation upper limit temperature Td described later) associated with the generation of condensed water in the reflux device and the condensation in the reflux device. The removal control is performed based on a time (ΔD) that is equal to or lower than a second temperature (for example, condensed water complete drying temperature Te described later) associated with water evaporation.

  (2) In this case, the first temperature corresponds to the upper limit of the temperature at which condensed water is continuously generated in the reflux device, and the second temperature is a temperature at which all the condensed water in the reflux device evaporates. It is preferable to correspond to the lower limit of. In this case, when the reflux device temperature is equal to or higher than the first temperature and equal to or lower than the second temperature, the condensed water in the reflux device evaporates and decreases.

  (3) In this case, the temperature raising control means determines that the reflux device temperature is the reflux device from the deposit generation time (D1) in which the reflux device temperature is equal to or higher than the first temperature and equal to or lower than the second temperature. It is preferable to perform the removal control based on a time obtained by subtracting the deposit decomposition time (D2) that is equal to or higher than the third temperature associated with the temperature at which the thermal decomposition of the deposit starts.

  (4) In this case, in the removal control, the temperature is higher than the temperature at which the moisture contained in the deposit evaporates and reaches a temperature at which the deposit is thermally decomposed and organic components start to be released (for example, deposit decomposition wall temperature Tb described later). It is preferable to raise the reflux device temperature.

  (5) In this case, the exhaust gas recirculation control device has condensed water in the recirculation device from the state where the recirculation device temperature is equal to or lower than the first temperature until the second temperature is exceeded thereafter. A condensate water generation determination unit (for example, an ECU 7 described later and a unit related to execution of S116 to S120 in FIG. 11) that determines that the state is in a state; It is preferable that the time during which it is determined that the condensed water is present by the condensed water generation determination means is the deposit generation time.

  (1) According to the inventors of the present application, it is clear that the generation of deposits in the reflux apparatus involves the presence of condensed water generated by the exhaust gas cooled in the conduit of the reflux apparatus and the evaporation process. became. More specifically, according to the inventors of the present application, it has been clarified that the deposit amount increases as the time taken for the condensed water once generated to dry out in the reflux apparatus becomes longer (described later). Test 1, 2). Based on such new knowledge, the present invention obtains the reflux device temperature, which is a representative temperature of the reflux device, not the temperature of the exhaust gas flowing through the reflux device, and this reflux device temperature is associated with the generation of condensed water. Deposit removal control is performed based on a time that is equal to or higher than one temperature and equal to or lower than a second temperature associated with evaporation of condensed water.

  According to the present invention, the recirculation device temperature having a stronger correlation with the generation and evaporation of condensed water in the recirculation device than the exhaust temperature is acquired, and this recirculation device temperature belongs to between the first temperature and the second temperature. By determining the execution of the removal control based on the time, the removal control can be started at a more appropriate timing as compared with the case where the execution of the removal control is determined based on the exhaust gas temperature. In addition, according to the inventor of the present application, the time during which the reflux apparatus temperature is equal to or higher than the first temperature related to the generation of condensed water and equal to or lower than the second temperature related to the evaporation of condensed water is the deposit accumulation. It is considered to be roughly proportional to the amount. In the present invention, the removal control can be started at an appropriate timing by performing the removal control of the deposit based on the time considered to be proportional to the deposit amount.

  (2) In the present invention, the first temperature is the upper limit of the temperature at which condensed water is continuously generated in the reflux device, and the second temperature is the lower limit of the temperature at which all the condensed water evaporates. That is, when the reflux device temperature is between the first temperature and the second temperature, it is considered that the condensed water generated so far gradually evaporates in the reflux device. Further, as described above, the deposit amount increases as the time taken for the condensed water to dry out in the reflux apparatus becomes longer. That is, the time during which the reflux device temperature is within the first to second temperature ranges is approximately proportional to the amount of deposit deposited. In the present invention, the removal control can be started at an appropriate timing by performing the removal control of the deposit on the basis of the time substantially proportional to the deposit amount.

  (3) Deposits once deposited can be removed by thermal decomposition. In the present invention, the time during which the reflux apparatus temperature is equal to or higher than the third temperature associated with the temperature at which the thermal decomposition of the deposit starts is defined as the deposit decomposition time. This deposit decomposition time is approximately proportional to the amount of thermally decomposed deposit. That is, the time obtained by subtracting the deposit decomposition time approximately proportional to the total deposit decomposition amount from the deposit generation time approximately proportional to the total deposit accumulation amount is approximately proportional to the deposit accumulation amount at that time. In the present invention, the removal control can be started at an appropriate timing by performing the removal control based on a time substantially proportional to the deposit accumulation amount.

(4) According to the inventor of the present application, when the deposit deposited in the reflux apparatus is heated to raise the temperature, the water first evaporates at about 100 ° C., and then is thermally decomposed from about 150 ° C. to produce CO ₂ or low It became clear that molecular organic components began to be released. Based on such new knowledge, in the present invention, in the removal control, it is possible to reliably remove deposited deposits by raising the reflux apparatus temperature to a temperature at which such thermal decomposition of the deposits starts reliably.

  (5) As described above, it has become clear that the deposit is generated in the process of evaporating the generated condensed water. That is, no matter how the temperature in the reflux device changes, no deposit is generated unless condensed water is present. Therefore, in the present invention, the reflux device is in a state from the state in which the reflux device temperature is equal to or lower than the first temperature and the condensed water can be generated until it exceeds the second temperature and it is estimated that the existing condensed water has evaporated. It is determined that condensed water is present in the interior. Furthermore, in the present invention, it is determined that the condensed water exists, and the time during which the generated condensed water evaporates when the reflux apparatus temperature is within the first to second temperature ranges is generated as a deposit. Time. Thereby, since the deposit accumulation amount can be estimated more accurately, the removal control can be started at a more appropriate timing.

It is a figure which shows the structure of the engine which concerns on one Embodiment of this invention, and its exhaust recirculation control apparatus. It is a figure which shows the result of Test 1. It is a figure which shows the procedure of the test 2 typically. It is a figure which shows the result of Test 2. It is a figure for demonstrating the concept of the deposit production | generation acceleration | stimulation temperature range which concerns on this embodiment. It is a result of test 3, and is a figure which shows the change of the external appearance at the time of heating a deposit. It is a result of the test 3, and it is a figure which shows the change of the component of the gas discharge | released when a deposit is heated, and its instantaneous generation amount. It is a result of the test 3, and is a figure which shows the change of the component of the gas discharge | released when a deposit is heated, and its total generation amount. It is a flowchart which shows the specific procedure of the warming-up control which warms up the engine and its water temperature performed immediately after engine starting. It is a flowchart which shows the procedure which judges introduction of EGR gas. It is a flowchart which shows the procedure which concerns on acquisition of the wall temperature in an EGR mechanism, and the update of a condensed water flag. It is a figure which shows typically the change of the water temperature after an engine stop, and the wall temperature in an EGR mechanism. It is a flowchart which shows the procedure of the control which suppresses deposit accumulation based on the acquired wall temperature. It is a flowchart which shows the specific procedure which calculates the quantity of the deposit accumulated in the EGR mechanism. It is a flowchart which shows the specific procedure which removes the deposit accumulated in the EGR mechanism. It is a figure which shows typically removal control start determination time. It is a time chart which shows the specific example of removal control.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a configuration of an internal combustion engine (hereinafter referred to as “engine”) 1 and an exhaust gas recirculation control device thereof according to an embodiment of the present invention.

  The engine 1 includes an intake pipe 3 through which intake air flows, an exhaust pipe 4 through which exhaust gas flows, a supercharger 5 that pumps intake air using the pressure of the exhaust gas, and a part of the exhaust gas in the exhaust pipe 4 as EGR gas. And an EGR mechanism 6 that recirculates to the intake pipe 3 and an electronic control unit (hereinafter referred to as “ECU (Electronic Control Unit)”) 7 are provided.

  The engine 1 is a diesel engine that uses light oil as fuel and burns it by compression ignition, but the present invention is not limited to this. The engine 1 is provided with a fuel injection valve 11 that directly injects fuel supplied via a fuel pump (not shown) into the cylinder. The fuel injection valve 11 is connected to the ECU 7 via a driver (not shown). The valve opening timing and valve opening time of the fuel injection valve 11, that is, the fuel injection timing and the fuel injection amount are controlled by fuel injection control described later in the ECU 7.

  The supercharger 5 includes a turbine 51 provided in the exhaust pipe 4 and a compressor 52 provided in the intake pipe 3. The turbine 51 is driven by the kinetic energy of the exhaust flowing through the exhaust pipe 4. The compressor 52 is rotationally driven by the turbine 51 and pumps intake air in the intake pipe 3 to the engine 1.

  The intake pipe 3 is provided with a compressor 52 of the supercharger 5 and a throttle valve 32 in order from the upstream side to the downstream side. The throttle valve 32 controls the amount of air supplied to the engine 1 (hereinafter referred to as “intake amount”). The throttle valve 32 is connected to the ECU 7 via a driver (not shown). That is, the throttle valve 32 is called a so-called DBW (Drive By Wire) throttle, which is mechanically disconnected from an accelerator pedal (not shown) operated by the driver's vehicle. The opening degree of the throttle valve 32, that is, the intake air flow rate is controlled by an intake air amount control described later in the ECU 7.

  The exhaust pipe 4 is provided with a turbine 51 of the supercharger 5 and an exhaust purification catalyst 41 for purifying exhaust gas in order from the upstream side to the downstream side.

  The EGR mechanism 6 includes an EGR pipe 61 that communicates the upstream side of the turbine 51 in the exhaust pipe 4 and the downstream side of the compressor 52 in the intake pipe 3, and an EGR valve that opens and closes the EGR gas flow path in the EGR pipe 61. 62 and an EGR cooler 63 that cools the EGR gas.

  The EGR valve 62 is provided in the EGR pipe 61 and includes a valve body 621 that opens and closes an EGR gas flow path, and a solenoid actuator 622 that moves the valve body 621 forward and backward. The solenoid actuator 622 is connected to the ECU 7 via a driver (not shown). The lift amount of the valve body 621, that is, the amount of EGR gas recirculated through the EGR pipe 61 (hereinafter referred to as “EGR amount”) is controlled by an intake air amount control (not shown) in the ECU 7.

  The ECU 7 is an electronic control unit that controls various devices provided in the engine 1 and the EGR mechanism 2, and includes an electronic circuit such as a CPU, a ROM, a RAM, and various interfaces. A plurality of sensors 81 to 86 are connected to the ECU 7 in order to grasp the state of the engine 1 and the state of the EGR mechanism 2.

  The intake air temperature sensor 81 outputs a detection signal to the ECU 7 that is substantially proportional to the intake air temperature upstream of the compressor 52 of the supercharger 5 in the intake pipe 3. Note that the upstream side of the compressor 52 in the intake pipe 3 is substantially equal to the atmospheric pressure.

The water temperature sensor 82 outputs a detection signal to the ECU 7 that is substantially proportional to the temperature of cooling water (hereinafter simply referred to as “water temperature”) flowing in a cooling water passage (not shown) formed in the cylinder block of the engine 1. The ECU 7 uses the water temperature detected by the water temperature sensor 82 as the representative temperature of the engine 1, but is not limited to this.
The accelerator pedal sensor 83 detects the depression amount of the accelerator pedal operated by the driver, and outputs a detection signal corresponding to the depression amount to the ECU 7.

  The crank angle sensor 84 outputs a pulse signal to the ECU 7 for each predetermined crank angle according to the rotation of a crankshaft (not shown) of the engine 1. In the ECU 7, the actual rotational speed of the engine 1 is grasped based on the output of the crank angle sensor.

The LAF sensor 85 is provided upstream of the exhaust purification catalyst 41 in the exhaust pipe 4 and outputs a detection signal substantially proportional to the oxygen concentration (air-fuel ratio) of the exhaust to the ECU 7.
The air flow meter 86 outputs to the ECU 7 a detection signal that is substantially proportional to the flow rate of the intake air upstream of the compressor 52 of the supercharger 5 in the intake pipe 3.

  The ignition switch IG is provided at a position where the driver can operate. When the ignition switch IG is turned on from the off state, the ignition switch IG outputs a start request signal for requesting the start of the engine 1 to the ECU 7. Further, when the ignition switch IG is turned off from the ON state, the ignition switch IG outputs a stop request signal for requesting the engine 1 to stop to the ECU 7.

  The warning light MI is provided at a position that can be visually recognized by the driver. The warning lamp MI is turned on based on a control signal transmitted from the ECU 7, and notifies the driver that a predetermined process is being executed.

  The ECU 7 executes the following intake air amount control and fuel injection control based on the outputs of the plurality of sensors 81 to 86 as described above.

  The intake air amount control unit 71 calculates a required output of the engine 1 by searching a predetermined map based on the engine speed, the accelerator pedal depression amount, the vehicle speed, and the like. The intake air amount control unit 71 searches the predetermined map based on the engine speed, the intake air flow rate, the intake air temperature, the required output, the fuel injection amount calculated by the fuel injection control unit 72 and the like to the engine 1. The target intake air amount that is the target of the intake air amount and the target EGR amount that is the target of the EGR amount are calculated. Further, the intake air amount control unit 71 searches a predetermined map based on the calculated target intake air amount and the target EGR amount, thereby making the target throttle opening and the EGR valve opening that are targets of the throttle valve opening. The target EGR opening degree which is the target of is calculated, control inputs to the throttle valve 32 and the EGR valve 62 are determined so as to be realized, and input to the respective drivers. Thus, the plurality of maps used in the intake air amount control unit 71 to finally determine the control input to the throttle valve 32 and the EGR valve 62 are determined with an emphasis on improving fuel efficiency and purification performance by the exhaust purification catalyst. It is done. Hereinafter, the intake air amount control based on such a map is referred to as normal intake air amount control.

  The fuel injection control unit 72 calculates a basic value for the fuel injection amount and the fuel injection timing by searching a predetermined map based on the engine speed, the intake air flow rate, the intake air temperature, the water temperature, and the like. Further, the fuel injection control unit 72 calculates the fuel injection amount and the fuel injection timing by adding or multiplying the determined basic value by a correction coefficient calculated based on the output of the LAF sensor. A control input for the injection valve 11 is determined and input to the driver. Thus, the plurality of maps used in the fuel injection control unit 72 to finally determine the control input to the fuel injection valve 11 is determined with an emphasis on improving fuel efficiency and purification performance by the exhaust purification catalyst. Hereinafter, the fuel injection control based on such a predetermined map is referred to as normal injection control.

  Next, a description will be given of tests performed to clarify the deposit generation process and decomposition process in the EGR mechanism 2 and the results thereof.

<Test 1>
The deposit that actually deposits in the EGR mechanism is viscous. For this reason, it is considered that the moisture present in the EGR mechanism has some influence on the deposit generation process. Further, when the engine is started after the vehicle has been stopped for a long time, the temperature of the EGR mechanism is substantially equal to the outside air. When the engine exhaust is introduced in such a state where the temperature of the piping and valves of the EGR mechanism is low in this way, condensed water is generated by cooling the water vapor contained in the exhaust in the piping. Therefore, it is considered that condensed water has an influence on the formation of deposits.

  In Test 1 and Test 2, the influence of the condensed water that is likely to be generated immediately after starting the engine on the formation of deposits was verified. More specifically, in Test 1, after the engine of the actual vehicle in a cold state is started, the condensed water generated in the EGR mechanism is stuck to the seat surface of the EGR valve after drying out. The load was measured. Particularly in Test 1, the temperature increase rate of the EGR mechanism that increases the temperature by exhaust heat from the engine by adjusting the fuel injection amount and the intake air amount of the engine at the start, that is, the drying rate of the condensed water is divided into three stages. In each case, the EGR valve sticking load was measured.

FIG. 2 is a diagram showing the results of Test 1. In FIG. In FIG. 2, the horizontal axis represents the time [sec] required for drying the condensed water, and the vertical axis represents the EGR valve sticking load [kgf].
As shown in FIG. 2, the sticking load increases as the drying time of the condensed water generated immediately after the engine starts increases. When the drying time was about 280 seconds, the gloss due to adhesion of tar (deposit) was visually confirmed around the EGR valve and its surroundings. On the other hand, when the drying time was about 30 seconds, no tar adhered to the EGR valve and its surroundings, and no gloss was confirmed. Therefore, assuming that the sticking load is proportional to the deposit amount, it is verified from the results of FIG. 2 that the deposit amount is almost proportional to the time taken to dry the condensed water generated in the EGR mechanism. It was done.

<Test 2>
In the test 1, after starting the engine of the vehicle in the cold state, the engine was continuously started until the generated condensed water was dried. On the other hand, in Test 2, after starting the engine of the vehicle in a cold state in a low temperature environment, the engine is intermittently stopped and started repeatedly, so that a specific part of the EGR mechanism where the EGR gas is in direct contact Temperature (hereinafter referred to as “wall temperature”) did not exceed a predetermined upper limit temperature. In particular, in Test 2, the upper limit temperature for the wall temperature of the EGR mechanism was set to a temperature (for example, 40 ° C.) at which condensed water was continuously generated in the EGR mechanism and the generated condensed water was not dried.

FIG. 3 is a diagram schematically showing the procedure of Test 2. As shown in FIG. In FIG. 3, the horizontal axis represents time [sec], and the vertical axis represents wall temperature [° C.] in the EGR mechanism.
As schematically shown in FIG. 3, in the test 2, the engine is started from a state where the entire vehicle including the EGR mechanism is completely cooled, and then the engine is stopped after performing idle operation for a predetermined idle time. After leaving the vehicle for the soak time, start the engine again. In Test 2, the idle operation over a predetermined idle time and the leaving of the vehicle over a predetermined soak time were repeated so that the wall temperature in the EGR mechanism did not exceed a predetermined upper limit temperature. In an actual vehicle, engine warm-up control is performed immediately after the engine is started, and introduction of EGR gas (EGR valve opening) is started after the water temperature has risen to some extent by this warm-up control. Therefore, in the actual test, unlike what is schematically shown in FIG. 3, there is a delay of about several seconds from the start of the engine until the temperature in the EGR mechanism starts to rise.

In Test 2, the idling operation and the leaving of the vehicle were repeated under the conditions of the outside air temperature = 1 ° C., the water temperature at the start of the test = 3 ° C., the idle time = 1 minute, and the soak time = 2 minutes.
FIG. 4 is a diagram showing the results of Test 2. In FIG. More specifically, FIG. 4 is a view showing the vicinity of the EGR valve in the EGR mechanism after the test 2 is completed. As shown in FIG. 4, condensed water remained in the EGR mechanism after Test 2. In addition, the metal surface of the EGR valve could be visually confirmed through the condensed water, and therefore the formation of deposits could not be confirmed. Therefore, according to the result of Test 2, it was verified that even if a lot of condensed water was generated, no deposit was generated unless the generated condensed water was dried. In other words, it can be said that a large amount of condensed water is not necessarily deposited due to the generation of a large amount of condensed water.

FIG. 5 is a diagram for explaining the concept of the deposit generation acceleration temperature range derived from the results of the tests 1 and 2 described above.
In FIG. 5, the horizontal axis represents the time [s] that has elapsed since the engine was started, and the vertical axis represents the wall temperature [° C.] within the EGR mechanism.

  According to the result of Test 1, the amount of deposit deposition increases as the time taken for the condensed water generated in the EGR mechanism to dry increases. Further, according to the result of Test 2, the amount of condensed water generated in the EGR mechanism is independent of the amount of deposit accumulated, and the deposit accumulates as long as the wall temperature does not exceed the temperature at which the condensed water starts to evaporate. There is no. From these, it is considered that the deposit amount increases as the time taken for the condensed water once generated to dry out in the EGR mechanism is longer. That is, it is considered that the condensed water in the drying process in the EGR mechanism promotes the dissolution and absorption of components such as particulate matter and unburned hydrocarbons in the exhaust gas, thereby promoting the deposition of deposits.

  From the above, as shown in FIG. 5, the deposit generation acceleration temperature range between the temperature Td associated with the generation of condensed water and the temperature Te associated with the evaporation of condensed water with respect to the wall temperature in the EGR mechanism. In this case, the amount of deposit accumulation is considered to be proportional to the time during which the condensed water is generated in the EGR mechanism and the deposit generation acceleration temperature range is passed. The lower limit of the deposit generation promoting temperature range, that is, the temperature Td in FIG. 5 is a wall in which condensed water is continuously generated from the water vapor in the exhaust by cooling the exhaust in the EGR mechanism, and the generated condensed water does not evaporate. It corresponds to the upper limit of temperature, and is referred to as the condensate continuous generation upper limit temperature below. Further, the upper limit of the deposit generation promotion temperature range, that is, the temperature Te, corresponds to the lower limit of the wall temperature at which all the condensed water in the EGR mechanism evaporates and the wall surface is always kept dry. This is called the drying temperature. Therefore, when the wall temperature is equal to or higher than the condensate continuous generation upper limit temperature and equal to or lower than the condensate complete drying temperature, if condensate exists in the EGR mechanism, this tends to evaporate and decrease. In addition, the condensed water continuous generation | occurrence | production upper limit temperature is 40 degreeC, for example, and condensed water complete drying temperature is 100 degreeC, for example.

  When the wall temperature in the EGR mechanism is increased in a manner as indicated by a broken line 51 after the engine is started, and a case where the wall temperature is increased in a manner as indicated by a solid line 52, a solid line 52 is obtained. In the case where the wall temperature is raised in this mode, the time required to pass through the deposit generation promotion temperature range is shorter, so the deposit amount is considered to be small. Therefore, in the present embodiment, when the wall temperature is within the deposit generation promotion temperature range in the presence of condensed water, the deposit generation promotion temperature range is quickly passed by performing the temperature increase control to increase the wall temperature. , Suppress deposit formation and deposition.

  Further, once the wall temperature exceeds the condensed water complete drying temperature Te, it is considered that almost no condensed water is generated in the EGR mechanism unless the wall temperature is lower than the condensed water continuous generation upper limit temperature Td. Therefore, as indicated by a one-dot chain line 53, when the wall temperature falls from a state higher than the condensed water complete drying temperature Te and enters the deposit generation promotion temperature range, the wall temperature does not fall below the condensate continuous generation upper limit temperature thereafter. As long as condensed water is not generated, it is not necessary to raise the wall temperature in order to quickly pass through the deposit generation promotion temperature range.

<Test 3>
In the test 3, the deposit actually generated in the EGR mechanism was collected, and the process of thermally decomposing the deposit by heating it was verified.
FIG. 6 is a diagram showing the change in appearance when the deposit is heated as a result of Test 3. FIG. FIG. 6 shows, in order from the left side, (a) normal temperature, (b) when heated to 100 ° C. or higher, and (c) appearance of the deposit when heated to 150 ° C. or higher.
The actual deposit is affixed to the wall like lacquer in the EGR mechanism. (A) of FIG. 6 is a sample obtained by scraping off the deposit adhered to the wall surface with a spatula. Therefore, as shown in FIG. 6 (a), corners generated when scraping off at room temperature are confirmed.

As shown in FIG. 6 (b), when the scraped deposit is heated to 100 ° C. or higher, the moisture contained in the deposit evaporates and rounds off with a corner. That is, the deposit has thermoplasticity that softens when heated and solidifies again when cooled.
As shown in FIG. 6 (c), when further heating to 150 ° C. or higher, not only moisture but also organic components fly off and become smaller until almost powdered. If this is replaced with an actual vehicle, it can be said that the deposited deposit is thermally decomposed and removed almost completely.

In Test 3, the components of the gas released when the deposit was heated as described above and the generation amount thereof were specified in detail by temperature programmed desorption analysis and gas chromatography.
FIG. 7 is a diagram showing the results of Test 3 and showing changes in components released when the deposit is heated and the instantaneous generation amount [ppm / s]. FIG. 8 shows the total generation amount [ppm]. It is a figure which shows a change.
As shown in FIG. 7, when heating the deposit from room temperature, the instantaneous generation amount of water reaches a peak at approximately 100 ° C., and the softening of the deposit starts. However, since only water is removed from the deposit at about 100 ° C., it will solidify again when it returns from this temperature to room temperature. That is, the deposit cannot be removed at about 100 ° C. When further heated from 100 ° C., it was confirmed that gases such as CO ₂ , low molecular organic gas, acetic acid, cresol, acetone, C ₈ H ₁₀ , SO ₂ , and N ₂ were released from about 150 ° C. In FIG. 7, acetic acid, C ₈ H ₁₀ , SO ₂ , and N ₂ are omitted for clarity of illustration. These CO ₂ , organic gas, and the like are generated by thermal decomposition of the deposit. Therefore, it was confirmed that the deposit once generated cannot be removed unless it is heated to at least about 150 ° C. Hereinafter, a temperature that is higher than the temperature at which the moisture contained in the deposit evaporates and that starts to release organic components and the like when the deposit is thermally decomposed is referred to as a deposit decomposition temperature.

<Deposit generation suppression control>
Next, a specific procedure for deposit accumulation suppression control in consideration of the deposit generation process clarified by the tests 1 and 2 and control at the time of engine start related to this deposit accumulation suppression control will be described with reference to FIG. This will be described with reference to FIG.

  FIG. 9 is a flowchart showing a specific procedure of warm-up control for warming up the engine and its water temperature, which is executed immediately after the engine is started. This process is executed by the ECU when the ignition switch is turned from OFF to ON.

  In S91, the ECU acquires an initial state (for example, intake air temperature, water temperature, etc.) of the engine immediately after starting based on outputs from various sensors. The intake air temperature acquired at the time of starting the engine in step S91 is hereinafter referred to as a start-time intake air temperature sTa, and the water temperature is referred to as a start-time cooling water temperature sTw, which is appropriately used in subsequent processing.

  In S92, it is determined whether or not the engine has been started at a low temperature, more specifically, whether or not condensed water can be generated in the EGR mechanism when engine exhaust is supplied. As will be described later with reference to FIG. 12, the water temperature of the engine can be regarded as substantially equal to the wall temperature in the EGR mechanism. Therefore, when the starting cooling water temperature sTw is equal to or lower than the condensate continuous generation upper limit temperature Td, it is considered that condensed water is generated in the EGR mechanism when exhaust gas is introduced into the EGR mechanism. When the determination in S92 is YES (when sTw ≦ Td), the condensed water flag F_cond is set to 1 (S93), and when NO (when sTw> Td), the condensed water flag F_cond is set to 0. (S94). The condensed water flag F_cond is a flag indicating that condensed water exists in the EGR mechanism or that it is estimated that condensed water is generated when EGR gas is introduced into the EGR mechanism. The condensed water flag F_cond is updated according to the wall temperature in S116 to S120 of FIG.

  In S95, engine warm-up control is started. More specifically, in S95, the fuel injection amount of the engine is continuously increased by a predetermined amount from the amount determined during normal injection control until a predetermined warm-up completion condition is satisfied (S96). As a result, the temperature of the engine, the engine water temperature, the exhaust purification catalyst, etc. rises faster than during normal injection control. The warm-up completion conditions include, for example, that the engine water temperature reaches a predetermined warm-up completion temperature (for example, 60 ° C.) and that the exhaust purification catalyst reaches a predetermined activation temperature. Further, as will be described later with reference to FIG. 10, the EGR valve is not opened until the warm-up of the engine is completed. That is, while the engine warm-up control is being performed in S95, the EGR valve remains closed and no exhaust gas is introduced into the EGR pipe, so that the wall temperature in the EGR mechanism hardly increases.

  FIG. 10 is a flowchart showing a procedure for determining the introduction of EGR gas. This process is executed at a predetermined cycle by the ECU after the ignition switch is turned from OFF to ON.

  In S101, the ECU determines whether or not the engine water temperature Tw exceeds a warm-up completion temperature Twarm (for example, 60 ° C.) (Tw> Twarm?). If the determination in S101 is NO, the EGR valve is closed (S102), and this process ends. Therefore, while the engine warm-up control described in S95 of FIG. 9 is not completed, the EGR valve is closed and EGR gas is not introduced. Further, only when the determination in S101 is YES, the process proceeds to S103 and the introduction of EGR gas is started.

  In S103, by searching a predetermined EGR introduction area determination map based on basic parameters such as the intake speed proportional to the engine speed and the engine load, it is determined whether or not the current engine operating state is within the EGR introduction area. Is determined. If the determination in S103 is NO, the process moves to S102 and the introduction of EGR gas is stopped. When the determination in S103 is YES, the process proceeds to S104, the EGR valve is opened based on the normal intake air amount control, the EGR gas is introduced, and this process is terminated.

  FIG. 11 is a flowchart showing a procedure related to acquisition of wall temperature in the EGR mechanism and update of the condensed water flag F_cond. This process is executed at a predetermined cycle by the ECU after the ignition switch is turned from OFF to ON.

  In S111, it is determined whether or not the EGR gas is currently being introduced. If the determination in S111 is NO, that is, if no EGR gas is introduced, no deposit is deposited, so this process is terminated without performing the processes after S111. When determination of S111 is YES, it moves to S112 and acquires wall temperature. Below, although the case where wall temperature is estimated from the existing sensor is demonstrated (S112-S115), the specific procedure which acquires wall temperature is not restricted to this. For example, an appropriate detection point in the EGR mechanism (for example, the vicinity of an EGR valve where deposit deposition is desired to be suppressed as much as possible, or a point where deposits are likely to occur) is specified, and the temperature of this detection point is set as a wall temperature by a temperature sensor It may be detected directly. That is, the processes of S112 to S115 may be replaced with a process of detecting the wall temperature T based on the output of the temperature sensor.

  In S112, a temperature difference ΔT = | Tw−Ta | between the current water temperature Tw and the intake air temperature Ta is calculated, and the process proceeds to S113. As described above, since the intake air temperature sensor is provided in an environment substantially equal to the atmospheric pressure, the intake air temperature Ta detected here is substantially equal to the outside air temperature. Therefore, the temperature difference ΔT can be regarded as a difference between the water temperature and the outside air temperature, and is a guideline for determining the warm-up state of the entire vehicle. Of course, when there is a sensor for detecting the temperature of the outside air in addition to the intake air temperature sensor, the outside air temperature obtained from the output may be used.

FIG. 12 is a diagram schematically showing changes in the water temperature after the engine is stopped and the wall temperature in the EGR mechanism. In FIG. 12, the horizontal axis represents the time (soak time) [sec] that has elapsed after the engine stopped, and the vertical axis represents the temperature [° C.].
Of the EGR mechanism, the periphery of the EGR valve and the actuator that drives the EGR valve are warmed by engine coolant. Therefore, when the warm-up of the engine is finished, the introduction of EGR gas is started, and a sufficient time has passed thereafter, the wall temperature in the EGR mechanism becomes substantially equal to the water temperature. For this reason, the wall temperature is substantially equal to the water temperature after a sufficient time has elapsed after the engine is warmed up. However, since exhaust gas is introduced into the EGR mechanism, the wall temperature in the EGR mechanism tends to be slightly higher than the water temperature, as shown in FIG. Further, when the engine is stopped, both the wall temperature and the water temperature decrease, and finally both become substantially equal to the outside air temperature.

Therefore, the temperature difference ΔT calculated in S112 is used as a guideline for determining whether the current state of the vehicle is a warm state where the entire vehicle is warmed or a cold state where the vehicle is completely cooled.
Here, more specifically, the warm state means that the engine warm-up is completed, the introduction of EGR gas is started, and then the sufficiently warmed cooling water reaches the various devices in the engine room. This corresponds to the state after sufficient time has elapsed. Further, even immediately after completion of warming up of the engine, for example, when the engine room is started in a state in which the soak time is short and the engine room is not completely cooled, this corresponds to this warm state.
The cold state refers to a state other than the warm state. More specifically, the cold state corresponds to a state immediately after starting the engine (during engine warm-up) or shortly after the engine warm-up is completed and the introduction of EGR gas is started. Even after the engine has been warmed up and enough time has elapsed since the introduction of EGR gas has started, for example, when the engine room is started in a state where the soak time is long and the inside of the engine room has cooled down This corresponds to this cold state.

  Returning to FIG. 11, in S113, it is determined whether or not the temperature difference ΔT is equal to or greater than a predetermined temperature difference ΔTs. If the determination in S113 is YES, it is determined that the current vehicle state is a warm state, and the current water temperature Tw is set as the wall temperature T (S114). If the determination in S113 is NO, it is determined that the current state of the vehicle is a cold state, and the cooling water temperature sTw at the start is set to the wall temperature T. When the current state is a cold state, it is estimated that the engine has just been warmed up. Moreover, since the introduction of EGR gas is not started while the engine is warming up as described above, it is considered that the wall temperature is not much different from the temperature at the start. Therefore, in the cold state, it is appropriate to regard the startup cooling water temperature sTw as the wall temperature T.

  After acquiring the wall temperature T by the above procedure, it is determined whether or not the condensed water flag F_cond is 1 in S116. If the determination in S116 is YES, the process proceeds to S117, and it is determined whether or not the wall temperature T has exceeded the condensed water complete drying temperature Te from the previous execution of S117 to the current execution of S117. If the determination in S117 is YES, it is estimated that all the condensed water present in the EGR mechanism has evaporated from the previous time to this time, so the condensed water flag F_cond is reset from 1 to 0 (S118). The process ends. When the determination in S116 is NO, the process proceeds to S89, and it is determined whether or not the wall temperature T has fallen below the condensate continuous generation upper limit temperature Td from the previous execution of S119 to the current execution of S119. If the determination in S119 is YES, it is estimated that condensed water begins to be generated in the EGR mechanism, so the condensed water flag F_cond is set from 0 to 1 (S120), and this process ends.

  FIG. 13 is a flowchart showing a control procedure for suppressing deposit accumulation based on wall temperature T acquired according to the procedure shown in FIG. This process is executed at a predetermined cycle by the ECU in parallel with other processes in response to the ignition switch being turned from OFF to ON.

  In S131, it is determined whether or not the EGR gas is currently being introduced. If the determination in S131 is NO, that is, if no EGR gas is introduced, no deposit is deposited, so this process is terminated without performing the processes after S132.

  When the determination in S131 is YES, the process proceeds to S132, and it is determined whether or not the condensed water flag F_cond is 1. If the determination in S132 is NO, no condensed water is generated in the EGR mechanism, and therefore no deposit is deposited regardless of the wall temperature, so the processing from S133 is performed. This process is finished without.

  When the determination in S132 is YES, the process proceeds to S133, and it is determined whether or not the wall temperature T acquired in the process of FIG. 11 is within the deposit generation promotion temperature range (Td ≦ T ≦ Te?). If the determination in S133 is YES, that is, if condensed water exists in the EGR mechanism (F_cond = 1) and the wall temperature T is within the deposit generation promotion temperature range, the deposit generation promotion temperature range is quickly passed. Therefore, the process proceeds to S134, and temperature increase control is performed to increase the wall temperature in the EGR mechanism. More specifically, this temperature increase control increases the fuel injection amount of the engine by a predetermined amount from the amount determined during the normal injection control until the wall temperature T exceeds at least the condensed water complete drying temperature Te (S147). Maintain state. As a result, exhaust gas that is hotter than during normal injection control is introduced into the EGR mechanism, so that the wall temperature rises. Further, in the temperature increase control, the wall temperature may be increased by increasing the amount of EGR gas introduced into the EGR mechanism by opening the EGR valve larger than in the normal intake amount control. Furthermore, when a heating device for heating the EGR mechanism is provided, the wall temperature may be increased by driving the heating device in this temperature increase control.

  If the determination in S133 is NO, that is, if there is residual water in the EGR mechanism but the wall temperature is not within the deposit generation promotion temperature range, no deposit is generated, so the temperature increase control in S104 is performed. This process is finished without.

<Deposit removal control>
Next, a specific procedure of deposit removal control in consideration of the deposit decomposition process clarified by the test 3 will be described with reference to FIGS.

  FIG. 14 is a flowchart showing a specific procedure for calculating the amount of deposit accumulated in the EGR mechanism. This process is executed by the ECU at a predetermined cycle in response to the ignition switch being turned from OFF to ON.

  In S141, it is determined whether or not EGR gas is currently being introduced. If the determination in S141 is NO, that is, if no EGR gas is introduced, no deposit is deposited or removed in the EGR mechanism, so this process is performed without performing the processes after S142. Exit.

  When determination of S141 is YES, it moves to S142 and determines whether the condensed water flag F_cond is 1. When the condensed water flag F_cond is 0, no condensed water is generated in the EGR mechanism, and therefore no deposit is deposited regardless of the wall temperature. Further, when the condensed water flag F_cond is 1, condensed water exists in the EGR mechanism. Therefore, when the wall temperature is within the deposit generation promoting temperature range, a deposit can be generated.

  When the determination in S142 is NO, the process proceeds to S143, and it is determined whether or not the wall temperature is higher than a predetermined deposit decomposition wall temperature Tb (T ≧ Tb?). This deposit decomposition wall temperature Tb is a wall temperature associated with the deposit decomposition temperature (about 150 ° C.) that was revealed in Test 3, and is determined experimentally. If the determination in S143 is NO, it is presumed that the pyrolysis of the deposit does not proceed, so this process is terminated without performing the processes after S144. When the determination in S143 is YES, the time D2 when the wall temperature T is equal to or higher than the deposit decomposition wall temperature Tb is integrated (S144), and the process proceeds to S147. As described above, when the wall temperature T becomes equal to or higher than the deposit decomposition wall temperature Tb, it is considered that the thermal decomposition of the deposit attached to the wall surface proceeds. Therefore, the integration time D2 is proportional to the amount of deposits that have been removed, and hereinafter referred to as deposit decomposition time.

  When the determination in S142 is YES, the process proceeds to S145, and it is determined whether or not the wall temperature is within the deposit generation promotion temperature range (Td ≦ T ≦ Te?). If the determination in S145 is NO, it is presumed that deposit accumulation does not proceed, so this process is terminated without performing the processes after S146. When the determination in S145 is YES, the time D1 during which the wall temperature T was within the deposit generation acceleration temperature range is integrated (S146), and the process proceeds to S147. The amount of deposit generated is proportional to the time during which the wall temperature T is within the deposit generation promoting temperature range (drying time). Therefore, the integration time D1 is hereinafter referred to as deposit generation time.

  In S147, a time difference ΔD (= D1−D2) is calculated by subtracting the deposit decomposition time from the deposit generation time, and this process is terminated.

  FIG. 15 is a flowchart showing a specific procedure for removing deposits accumulated in the EGR mechanism. This process is executed by the ECU at a predetermined cycle in response to the ignition switch being turned from OFF to ON.

  In S151, it is determined whether or not EGR gas is currently being introduced. If the determination in S151 is NO, that is, if EGR gas is not introduced, even if deposits are deposited, they cannot be removed, so this processing is performed without performing the processing from S152 onward. finish. When the determination in S151 is YES, the process proceeds to S152, and it is determined whether or not the time difference ΔD is equal to or longer than a predetermined start determination time DL (ΔD ≧ DL?).

FIG. 16 is a diagram schematically illustrating the removal control start determination time DL. In FIG. 16, the vertical axis represents the amount [g] of deposit accumulated in the EGR mechanism, and the horizontal axis represents the time difference ΔD [sec] between the deposit generation time D1 and the deposit decomposition time D2.
First, the deposit generation time D1 is proportional to the amount of deposit generated, and the deposit decomposition time D2 is proportional to the amount of deposit removed. Therefore, the time difference ΔD is proportional to the amount of deposit actually deposited in the EGR mechanism, as shown in FIG. The start determination time DL in S152 is obtained by converting the limit amount of deposit that can be accumulated in the EGR mechanism into time. That is, if deposits are accumulated beyond this limit amount, there is a possibility that the exhaust flow in the EGR pipe and the dynamic characteristics of the EGR valve will be adversely affected.

  Returning to FIG. 15, if the determination in S152 is NO, it is estimated that no deposit has accumulated so as to have an adverse effect in the EGR mechanism, so this process is terminated without performing the processes after S153. If the determination in S152 is YES, the process proceeds to S153, and the removal control is performed to remove the deposit by raising the wall temperature in the EGR mechanism and thus raising the temperature of the deposit accumulated on the wall surface. More specifically, in this removal control, the deposited deposit is removed by continuing to maintain a state where the wall temperature T exceeds at least the deposit decomposition wall temperature Tb for a predetermined time. Here, as means for making the wall temperature T higher than the deposit decomposition wall temperature Tb, as in the temperature rise control in S104, an increase in the fuel injection amount, an increase in the amount of exhaust gas introduced into the EGR mechanism, and a heating device The temperature rise by is appropriately used.

  The state in which the wall temperature is raised by this removal control is maintained until the time difference ΔD proportional to the deposit accumulation amount becomes equal to or shorter than the end determination time Ds (see FIG. 16) smaller than the start determination time DL (S156). While this removal control is being executed, the engine is prohibited from stopping even when the ignition switch is turned off (S154), and the deposit removal control is performed by turning on the warning light. It is preferable to notify the driver that the vehicle is in a state (S155). When the ignition switch is turned off during the execution of the removal control, the time difference ΔT becomes equal to or less than the end determination time Ds, and the engine is stopped after the removal control is completed.

  FIG. 17 is a time chart showing a specific example of the removal control as described above. In FIG. 17, the time elapsed since the engine was started [sec], and the vertical axis represents the time difference ΔD [sec] proportional to the deposit amount [g].

  As described above, when EGR gas is introduced into the EGR mechanism after the engine is started, condensed water is generated. When the wall temperature is within the deposit generation promotion temperature range (Td to Te) in the state where the condensed water exists, the condensed water evaporates and deposits are generated in this process. However, once the deposit is generated, it is thermally decomposed and removed when the wall temperature becomes higher than the deposit decomposition wall temperature Tb.

  In the process shown in FIG. 14, the time during which the wall temperature T was within the deposit generation acceleration temperature range (Td to Te) is integrated as the deposit generation time D1 (S146), and the wall temperature T has exceeded the deposit decomposition wall temperature Tb. The time is integrated as a deposit decomposition time D2 (S144). Therefore, as shown in FIG. 14, the time difference ΔD proportional to the deposit amount increases in a section where the deposit generation time D1 is added and decreases in a section where the deposit decomposition time D2 is added. Then, when the time difference ΔD exceeds the start determination time DL, deposit removal control for increasing the wall temperature is started (S155). The section where the time difference ΔD is constant and does not change is, for example, when EGR gas is not introduced, when condensed water is generated but the wall temperature T does not evaporate lower than the condensed water continuous generation upper limit temperature Td, This corresponds to the case where no condensed water is generated but the wall temperature T is lower than the deposit decomposition wall temperature Tb, and only the moisture in the deposit is released.

The embodiment of the present invention has been described above, but the present invention is not limited to this.
In the above embodiment, the wall temperature of the EGR mechanism is estimated, and the timing for starting deposit suppression control and deposit removal control is determined based on the estimated wall temperature, but the present invention is not limited to this. The timing for starting these deposit suppression control and deposit removal control may be determined based on the wall temperature directly detected by the temperature sensor instead of the estimated wall temperature. In this case, the location where the temperature sensor is provided, that is, the detection location of the temperature sensor may be anywhere as long as a deposit can be generated in the EGR mechanism.

1. Engine (internal combustion engine)
3 ... Intake pipe (intake passage)
4 ... Exhaust pipe (exhaust passage)
6 ... EGR mechanism (reflux device)
7 ... ECU (temperature acquisition means, removal control means, condensed water generation determination means)
82 ... Water temperature sensor (temperature acquisition means)
Td: Condensed water continuous generation upper limit temperature Te: Condensed water complete drying temperature Tb: Deposit decomposition wall temperature

Claims (5)

A recirculation device that recirculates part of the exhaust from the exhaust passage of the internal combustion engine to the intake passage;
Temperature acquisition means for acquiring the reflux device temperature of the reflux device;
An exhaust gas recirculation control device for an internal combustion engine, comprising: removal control means for performing removal control for removing the deposit by raising the temperature of the deposit accumulated in the recirculation device,
The removal control means is configured such that the reflux device temperature is not less than a first temperature associated with the generation of condensed water in the reflux device and not more than a second temperature associated with evaporation of the condensed water in the reflux device. An exhaust gas recirculation control apparatus for an internal combustion engine, wherein the removal control is performed based on a predetermined time. The first temperature corresponds to the upper limit of the temperature at which condensed water is continuously generated in the reflux device,
The second temperature corresponds to the lower limit of the temperature at which all the condensed water in the reflux device evaporates,
2. The exhaust gas recirculation of the internal combustion engine according to claim 1, wherein when the reflux device temperature is equal to or higher than the first temperature and equal to or lower than the second temperature, the condensed water in the reflux device evaporates and decreases. Control device.   The temperature raising control means starts the thermal decomposition of the deposit in the reflux apparatus at the reflux apparatus temperature from the deposit generation time when the reflux apparatus temperature is equal to or higher than the first temperature and equal to or lower than the second temperature. 3. The exhaust gas recirculation control apparatus for an internal combustion engine according to 1 or 2, wherein the removal control is performed based on a time obtained by subtracting a deposit decomposition time that is equal to or higher than a third temperature associated with the temperature.   In the removal control, the reflux device temperature is raised to a temperature higher than a temperature at which moisture contained in the deposit evaporates and higher than a temperature at which the deposit is thermally decomposed and organic components start to be released. Item 4. The exhaust gas recirculation control device for an internal combustion engine according to any one of Items 1 to 3. Condensed water generation determination means for determining that condensed water is present in the reflux device from the state where the reflux device temperature is equal to or lower than the first temperature until the temperature exceeds the second temperature thereafter. Prepared,
The temperature raising control means is defined as a deposit generation time, which is a time during which the condensed water generation determination means determines that the condensed water is present by the reflux apparatus temperature not lower than the first temperature and not higher than the second temperature. The exhaust gas recirculation control apparatus for an internal combustion engine according to claim 3, wherein