JP2013029064A - Exhaust emission control system of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further enhance exhaust emission control during start of an internal combustion engine, in an exhaust emission control system of an internal combustion engine comprising an electric heating type catalyst (EHC) provided at an exhaust passage and an exhaust purifying catalyst provided at the exhaust passage downstream of the EHC.SOLUTION: When energization to an EHC is performed during a period from when an operation of an internal combustion engine is stopped to when an engine rotation speed of the internal combustion becomes substantially zero, a flow rate of exhaust passing through the EHC and the exhaust purifying catalyst during the period is larger than that when the energization to the EHC is not performed during the period.

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine including an electrically heated catalyst provided in an exhaust passage of the internal combustion engine.

Electric heating catalyst (Electric Heating Catalyst)
In the following, there is also known an EHC). EHC is provided in the exhaust passage of the internal combustion engine and generates heat when energized.

  In Patent Document 1, a filter carrying a catalyst is provided in an exhaust passage downstream of EHC, an exhaust throttle valve is provided in an exhaust passage downstream of the filter, and exhaust gas upstream of EHC is further provided. A configuration is disclosed in which one end of an EGR passage is connected to the passage, and the other end of the EGR passage is connected to an intake passage downstream of the intake throttle valve. Further, in Patent Document 1, when the internal combustion engine is in a fuel-free injection state, the EGR control valve is fully opened, and the intake throttle valve and the exhaust throttle valve are fully closed, so that low-temperature exhaust can be generated in the filter. A technique for suppressing inflow and energizing the EHC is described.

  Patent Document 2 includes a motor, a battery that supplies electric power to the motor, a generator that charges the battery, and an internal combustion engine that rotationally drives the generator, and a charge amount of the battery is less than a predetermined amount. In the hybrid vehicle for starting the internal combustion engine, a configuration in which an electric heater for heating the catalyst provided in the exhaust passage of the internal combustion engine is further provided and a regenerative power generation mechanism for recharging the battery in the motor is disclosed. . Patent Document 2 describes a technique for supplying a regenerative current of a regenerative power generation mechanism to an electric heater when the internal combustion engine is stopped and the amount of charge of a battery is below a certain level.

  In Patent Document 3, if the estimated catalyst temperature is equal to or lower than the catalyst activation temperature when the engine is stopped, the energization of the battery to the electric heater that energizes and heats the catalyst based on the deviation between the estimated catalyst temperature and the catalyst activation temperature. A technique is described in which time is calculated and power is supplied from the battery to the electric heater for the calculated energization time.

JP 2006-274806 A JP-A-6-178401 JP-A-9-250333 JP 2001-082130 A

  After the operation of the internal combustion engine is stopped (that is, after the fuel injection in the internal combustion engine is stopped), it takes a certain amount of time until the engine speed of the internal combustion engine becomes zero. During this period, since the temperature of the exhaust gas discharged from the internal combustion engine is low, the temperature of the exhaust purification catalyst provided in the exhaust passage of the internal combustion engine decreases. If the temperature of the exhaust purification catalyst is lowered and its exhaust purification capability is reduced, it becomes difficult to sufficiently purify the exhaust gas in the exhaust purification catalyst when the internal combustion engine is restarted. There is a risk of increased emissions of hazardous substances.

The present invention has been made in view of the above problems, and is provided with an E provided in an exhaust passage.
In an exhaust gas purification system of an internal combustion engine provided with HC and an exhaust gas purification catalyst provided in an exhaust passage downstream of the EHC, an object is to further promote the purification of exhaust gas at the start of the internal combustion engine.

An internal combustion engine exhaust gas purification system according to a first aspect of the invention includes:
An electrically heated catalyst that is provided in the exhaust passage of the internal combustion engine and generates heat when energized;
An exhaust purification catalyst provided downstream of the electrically heated catalyst;
If the electric heating catalyst is energized during the period from when the operation of the internal combustion engine is stopped until the engine speed of the internal combustion engine becomes substantially zero, the electric heating catalyst is energized during the period. Exhaust flow rate control means for increasing the flow rate of the exhaust gas that passes through the electric heating catalyst and the exhaust purification catalyst during the period than when not being performed,
It has.

  Here, the operation of the internal combustion engine being stopped means that fuel injection in the internal combustion engine is stopped.

  According to the present invention, when the electric heating catalyst is energized during the period from when the operation of the internal combustion engine is stopped until the engine rotational speed of the internal combustion engine becomes substantially zero, the EHC and exhaust gas purification are performed. By increasing the flow rate of the exhaust gas that passes through the catalyst, the amount of heat of EHC is easily supplied to the exhaust gas purification catalyst by the exhaust gas. Therefore, it is possible to suppress the temperature reduction of the exhaust purification catalyst. As a result, when the internal combustion engine is restarted, the exhaust purification in the exhaust purification catalyst can be further promoted.

  The exhaust purification system for an internal combustion engine according to the present invention automatically stops the operation of the internal combustion engine when a predetermined automatic stop condition is satisfied, and then automatically starts the internal combustion engine when the predetermined automatic start condition is satisfied. -A starting means may be further provided. In this case, when the EHC is energized by the exhaust flow rate control means, the period during which the flow rate of the exhaust gas passing through the EHC and the exhaust purification catalyst is increased is automatically stopped and It may be a period from when the operation of the internal combustion engine is automatically stopped by the starting means until the engine speed of the internal combustion engine becomes substantially zero. According to this, when the internal combustion engine is automatically started, exhaust purification in the exhaust purification catalyst can be further promoted.

  In the present invention, when the EHC is energized, when the temperature of the exhaust purification catalyst is equal to or higher than a predetermined threshold, the EHC and the EHC and the EHC are not energized than when the EHC is not energized. Execution of control for increasing the flow rate of the exhaust gas passing through the exhaust purification catalyst may be prohibited. According to this, the excessive temperature rise of the exhaust purification catalyst can be suppressed. The predetermined threshold value may be a threshold value at which it is possible to determine that the exhaust purification catalyst is overheated when control is performed to increase the flow rate of exhaust gas that passes through the EHC and the exhaust purification catalyst.

  In the present invention, the exhaust flow rate control means includes an intake throttle valve provided in the intake passage of the internal combustion engine, and an upstream side of the EHC in the exhaust system of the internal combustion engine and a downstream side of the intake throttle valve in the intake system of the internal combustion engine. You may have the high-pressure EGR valve provided in the high-pressure EGR channel to connect. When the EHC is energized during a period from when the operation of the internal combustion engine is stopped until the engine rotational speed of the internal combustion engine becomes substantially zero, the exhaust flow rate control means is configured to take an intake throttle valve or a high pressure EGR valve. By adjusting at least one of the opening degrees, the flow rate of the exhaust gas passing through the EHC and the exhaust purification catalyst during the period may be made larger than when the EHC is not energized during the period. .

Specifically, the flow rate of the exhaust gas passing through the EHC and the exhaust purification catalyst can be increased by increasing the opening degree of the intake throttle valve and decreasing the opening degree of the high pressure EGR valve.

An internal combustion engine exhaust purification system according to a second aspect of the present invention includes:
An electrically heated catalyst that is provided in the exhaust passage of the internal combustion engine and generates heat when energized;
An exhaust purification catalyst provided in an exhaust passage downstream of the electrically heated catalyst;
Automatic stop / start means for automatically stopping the operation of the internal combustion engine when a predetermined automatic stop condition is satisfied, and then automatically starting the internal combustion engine when the predetermined automatic start condition is satisfied;
An intake throttle valve provided in the intake passage of the internal combustion engine;
A high pressure EGR valve provided in a high pressure EGR passage connecting the upstream side of the electrically heated catalyst in the exhaust system of the internal combustion engine and the downstream side of the intake throttle valve in the intake system of the internal combustion engine;
An exhaust gas purification system for an internal combustion engine comprising:
When the operation of the internal combustion engine is automatically stopped by the automatic stop / start means, the electric heating catalyst is energized for a period until the engine rotation speed of the internal combustion engine becomes substantially zero, and the intake throttle valve or the The opening degree of at least one of the high pressure EGR valves is adjusted in a direction in which the flow rate of the exhaust gas passing through the electric heating catalyst and the exhaust purification catalyst increases.

  Also according to the present invention, it is possible to suppress the temperature reduction of the exhaust purification catalyst when the internal combustion engine is automatically stopped. As a result, when the internal combustion engine is automatically started, exhaust purification in the exhaust purification catalyst can be further promoted.

  According to the present invention, in an exhaust gas purification system for an internal combustion engine including an EHC provided in an exhaust passage and an exhaust purification catalyst provided in an exhaust passage downstream of the EHC, the operation of the internal combustion engine is stopped. The temperature reduction of the exhaust purification catalyst can be suppressed. Therefore, the purification of exhaust gas when the internal combustion engine is restarted can be further promoted.

1 is a diagram illustrating a schematic configuration of an internal combustion engine and an intake / exhaust system thereof according to Embodiment 1. FIG. 2 is a flowchart illustrating a flow of exhaust flow control when the operation of the internal combustion engine is automatically stopped according to the first embodiment. When the exhaust gas flow rate control according to the first embodiment is executed, the temperature Tcco of the oxidation catalyst, the engine rotational speed Ne of the internal combustion engine, the energization state (ON or OFF) of the EHC, the opening degree Dhegrv of the high-pressure EGR valve, and the throttle valve It is a time chart which shows transition of the opening degree Dthv. 6 is a flowchart showing a flow of exhaust flow control when the operation of the internal combustion engine is automatically stopped according to a modification of the first embodiment. It is a figure which shows schematic structure of the internal combustion engine which concerns on Example 2, and its intake / exhaust system. 6 is a flowchart showing a flow of exhaust flow control when the operation of the internal combustion engine is automatically stopped according to a second embodiment. When the exhaust gas flow rate control according to the second embodiment is executed, the temperature Tcco of the oxidation catalyst, the engine rotational speed Ne of the internal combustion engine, the energization state (ON or OFF) of the EHC, the opening degree Dhegrv of the high pressure EGR valve, the second throttle It is a time chart which shows transition of the opening degree Dsthv of a valve, and the opening degree Dlegrv of a low pressure EGR valve. 6 is a flowchart showing a flow of exhaust flow control when the operation of the internal combustion engine is automatically stopped according to a modification of the second embodiment. The temperature Tcco of the oxidation catalyst, the engine rotational speed Ne of the internal combustion engine, the energization state (ON or OFF) to the EHC, the opening degree Dhegrv of the high-pressure EGR valve when the exhaust flow control according to the modification of the second embodiment is executed It is a time chart which shows transition of the opening degree Dsthv of a 2nd throttle valve, and the opening degree Doutv of an exhaust throttle valve.

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

<Example 1>
Here, a case where the present invention is applied to an exhaust gas purification system for a diesel engine for driving a vehicle will be described as an example. However, the internal combustion engine according to the present invention is not limited to a diesel engine, and may be a gasoline engine or the like.

[Schematic configuration of internal combustion engine and its intake and exhaust system]
A schematic configuration of an internal combustion engine and an intake / exhaust system thereof according to the present embodiment will be described with reference to FIG. The internal combustion engine 1 is a diesel engine for driving a vehicle having four cylinders 2. Each cylinder 2 is provided with a fuel injection valve 3 that directly injects fuel into the cylinder 2.

  An intake manifold 4 and an exhaust manifold 5 are connected to the internal combustion engine 1. An intake passage 6 is connected to the intake manifold 4. An exhaust passage 7 is connected to the exhaust manifold 5. A compressor 8 a of a turbocharger 8 is installed in the intake passage 6. A turbine 8 b of a turbocharger 8 is installed in the exhaust passage 7.

  An intercooler 10 is provided in the intake passage 6 downstream of the compressor 8a. The intercooler 10 cools intake air by exchanging heat between outside air and intake air.

  An air flow meter 9 and a throttle valve (intake throttle valve) 12 are provided upstream of the compressor 8 a in the intake passage 6. The air flow meter 9 detects the intake air amount of the internal combustion engine 1. The throttle valve 12 adjusts the flow rate of the intake air flowing through the intake passage 6 by changing the cross-sectional area of the intake passage 6.

  On the downstream side of the turbine 8b in the exhaust passage 7, an EHC 15, an oxidation catalyst 16, and a particulate filter 11 are provided in this order from the upstream side along the flow of exhaust. The EHC 15 is a catalyst that generates heat when energized. Electric power is supplied to the EHC 15 from an alternator 17 or a battery (not shown) described later. The particulate filter 11 collects PM (Particulate Matter) in the exhaust gas. In this embodiment, the oxidation catalyst 16 corresponds to the exhaust purification catalyst according to the present invention. However, the exhaust purification catalyst according to the present invention is not limited to the oxidation catalyst, and may be another catalyst such as a NOx storage reduction catalyst or a selective reduction NOx catalyst. An exhaust temperature sensor 23 is provided in the exhaust passage 7 between the oxidation catalyst 16 and the particulate filter 11.

  Further, the intake and exhaust system of the internal combustion engine 1 according to the present embodiment is provided with a high pressure EGR device 30 as an EGR device for introducing a part of the exhaust gas flowing through the exhaust system into the intake system as EGR gas. The high pressure EGR device 30 includes a high pressure EGR passage 31, a high pressure EGR valve 32, and a high pressure EGR cooler 33. The high pressure EGR passage 31 has one end connected to the exhaust manifold 5 and the other end connected to the intake manifold 4. Here, the EGR gas introduced from the exhaust manifold 5 to the intake manifold 4 through the high pressure EGR passage 31 is referred to as high pressure EGR gas. In the present embodiment, the high pressure EGR passage 31 and the high pressure EGR valve 32 correspond to the EGR passage and the EGR valve according to the present invention.

The high pressure EGR valve 32 and the high pressure EGR cooler 33 are provided in the high pressure EGR passage 31. The high pressure EGR valve 32 adjusts the flow rate (high pressure EGR gas amount) of the high pressure EGR gas introduced into the intake manifold 4 by changing the flow path cross-sectional area of the high pressure EGR passage 31. The high pressure EGR cooler 33 cools the high pressure EGR gas by exchanging heat between the high pressure EGR gas flowing through the high pressure EGR passage 31 and the cooling water of the internal combustion engine 1.

  The internal combustion engine 1 configured as described above is provided with an electronic control unit (ECU) 20. An air flow meter 9 and an exhaust temperature sensor 23 are electrically connected to the ECU 20. Further, a crank angle sensor 21 and an accelerator opening sensor 22 are electrically connected to the ECU 20. The crank angle sensor 21 outputs a pulse signal corresponding to the engine speed of the internal combustion engine 1. The accelerator opening sensor 22 outputs a signal corresponding to the accelerator opening of the vehicle on which the internal combustion engine 1 is mounted. Output signals from these sensors are input to the ECU 20.

  In addition, the fuel injection valve 3, the throttle valve 12, the alternator 17, and the high-pressure EGR valve 32 are electrically connected to the ECU 20. These devices are controlled by the ECU 20.

  In the present embodiment, the ECU 20 automatically stops the operation of the internal combustion engine 1 when the predetermined automatic stop condition is satisfied (that is, stops the fuel injection from the fuel injection valve 3), and then the predetermined automatic start condition. When the above is established, the internal combustion engine 1 is automatically started (that is, fuel injection from the fuel injection valve 3 is resumed), and automatic stop / start control is performed.

  Here, as an automatic stop condition, the operating state of the internal combustion engine is a decelerating operation (that is, in a vehicle equipped with the internal combustion engine 1, the shift position is the drive position and the accelerator opening is zero). ) Or idling (that is, in a vehicle equipped with the internal combustion engine 1, the shift position is the drive position, the accelerator opening is zero, and the brake is depressed). Further, as an automatic start condition, it can be exemplified that the accelerator opening is larger than zero (that is, the accelerator pedal is depressed in a vehicle equipped with the internal combustion engine 1).

  Further, the rotation of the crankshaft of the internal combustion engine 1 can be transmitted to the alternator 17 via a transmission mechanism (not shown). When the operation state of the internal combustion engine 1 is a deceleration operation and the operation of the internal combustion engine 1 is automatically stopped, regeneration is performed by the alternator 17 until the engine rotation speed of the internal combustion engine 1 becomes substantially zero. . The electric power generated by the regeneration may be stored in a battery, or may be directly supplied to an electric device such as the EHC 15. Whether the electric power generated by the regeneration is supplied to the battery or directly to an electric device such as the EHC 15 is controlled by the ECU 20.

[Exhaust flow control during engine shutdown]
When the operation of the internal combustion engine 1 is automatically stopped, the temperature of the exhaust gas discharged from the internal combustion engine 1 is greatly reduced. When the temperature of the exhaust gas decreases, the temperature of the oxidation catalyst 16 decreases. If the oxidation capacity of the oxidation catalyst 16 is lowered due to a decrease in the temperature of the oxidation catalyst 16, it is difficult to sufficiently oxidize harmful substances in the exhaust gas in the oxidation catalyst 16 when the internal combustion engine 1 is automatically started. That is, it may be difficult to sufficiently purify the exhaust gas.

  Therefore, in this embodiment, when the operation of the internal combustion engine 1 is automatically stopped, the exhaust gas that passes through the EHC 15 and the oxidation catalyst 16 (hereinafter referred to as catalyst passage) in order to suppress the temperature drop of the oxidation catalyst 16 during the engine operation stop period. Exhaust flow rate control is performed to control the flow rate (sometimes referred to as exhaust). Specifically, when the EHC 15 is energized when the operation of the internal combustion engine 1 is automatically stopped, the EHC 15 is energized for a period until the engine speed of the internal combustion engine 1 becomes substantially zero. The flow rate of the exhaust gas passing through the catalyst is increased as compared with the case where it is not performed.

  When the EHC 15 is energized, the exhaust gas passing through the catalyst is heated by the EHC 15. Therefore, in this case, the engine rotational speed becomes substantially zero after the operation of the internal combustion engine 1 is automatically stopped by increasing the flow rate of the exhaust gas passing through the catalyst as compared with the case where the EHC 15 is not energized. In the period up to, the amount of heat of the EHC 15 is easily supplied to the oxidation catalyst 16 by exhaust. As a result, the temperature drop of the oxidation catalyst 16 can be suppressed. On the other hand, when the EHC 15 is not energized, the exhaust gas passing through the catalyst is not heated by the EHC 15, so that low-temperature exhaust gas is supplied to the oxidation catalyst 16. Therefore, in this case, the engine rotational speed becomes substantially zero after the operation of the internal combustion engine 1 is automatically stopped by reducing the flow rate of the exhaust gas passing through the catalyst as compared with the case where the EHC 15 is energized. In the period up to, it is possible to suppress the oxidation catalyst 16 from being cooled by the low temperature exhaust. As a result, the temperature drop of the oxidation catalyst 16 can be suppressed.

  Control of the flow rate of the catalyst passing exhaust as described above is realized by adjusting the opening degree of the throttle valve 12 and the high pressure EGR valve 32. Specifically, the flow rate of the exhaust gas passing through the catalyst can be increased by increasing the opening degree of the throttle valve 12 and decreasing the opening degree of the high pressure EGR valve 32.

  FIG. 2 is a flowchart showing a flow of exhaust flow control when the operation of the internal combustion engine 1 is automatically stopped according to the present embodiment. This flow is stored in advance in the ECU 20 and is repeatedly executed by the ECU 20. FIG. 3 shows the temperature of the oxidation catalyst 16, the engine speed Ne of the internal combustion engine 1 and the energization status to the EHC 15 (ON is energized and OFF is de-energized when the exhaust flow control is executed. FIG. 6 is a time chart showing changes in the opening degree Dhegrv of the high-pressure EGR valve 32 and the opening degree Dthv of the throttle valve 12. In FIG. 3, the horizontal axis represents time t.

  In the flow shown in FIG. 2, it is determined in step S101 whether or not the operation of the internal combustion engine 1 has been automatically stopped. If a negative determination is made in step S101, the execution of this flow is once terminated. If an affirmative determination is made, the process of step S102 is executed next. In FIG. 3, at time t1, a predetermined automatic stop condition is satisfied, and the operation of the internal combustion engine 1 is automatically stopped. Thereafter, the engine speed Ne of the internal combustion engine 1 gradually decreases.

  In step S102, it is determined whether the EHC 15 is energized. If a negative determination is made in step S102, the process of step S105 is executed next, and if an affirmative determination is made, the process of step S103 is executed next.

  In step S103, the high-pressure EGR valve 32 is controlled to be fully closed, and the throttle valve 12 is controlled to be fully open. By controlling the high pressure EGR valve 32 to be fully closed, the flow rate of the high pressure EGR gas flowing through the high pressure EGR passage 31 becomes substantially zero. As a result, substantially all of the exhaust discharged from the internal combustion engine 1 flows into the EHC 15. Further, the throttle valve 12 is controlled to be fully opened, so that the flow rate of intake air increases as much as possible. Therefore, the flow rate of the exhaust gas passing through the catalyst can be increased as much as possible by executing the process of step S103.

  However, the opening degree of the high pressure EGR valve 32 does not necessarily need to be fully closed and the opening degree of the throttle valve 12 does not have to be fully opened, and the high pressure EGR valve 32 is not compared with the case where the EHC 15 is not energized. May be reduced and the opening of the throttle valve 12 may be increased. Thereby, compared with the case where electricity supply to EHC15 is not performed, the flow volume of catalyst passage exhaust gas can be increased.

Next, in S104, it is determined whether or not the engine speed Ne of the internal combustion engine 1 has become substantially zero. When the engine rotational speed Ne of the internal combustion engine 1 becomes substantially zero, the flow rate of the exhaust gas from the internal combustion engine 1 becomes substantially zero. Here, when the engine speed Ne of the internal combustion engine 1 calculated based on the detection value of the crank angle sensor 21 by the ECU 20 becomes equal to or less than a predetermined value, it is determined that the engine speed Ne has become substantially zero. If a negative determination is made in step S104, the process of step S103 is executed again. On the other hand, if an affirmative determination is made in step S104, the process of step S105 is then executed. In FIG. 3, at the time t2, the engine speed Ne of the internal combustion engine 1 becomes substantially zero. When the engine speed Ne of the internal combustion engine 1 becomes substantially zero, energization to the EHC 15 is stopped.

  In step S105, the high-pressure EGR valve 32 is controlled to be fully opened, and the opening degree of the throttle valve 12 is reduced to a predetermined opening degree Dthv0. The predetermined opening degree Dthv0 is an opening degree in the vicinity of full closing, and is a predetermined lower limit value of the opening degree of the throttle valve 12. Thereby, the flow rate of exhaust gas passing through the catalyst can be reduced as much as possible.

  However, the opening degree of the high-pressure EGR valve 32 does not necessarily need to be fully opened, and is larger than the period until the engine rotation speed Ne becomes substantially zero (that is, when the EHC 15 is energized). That's fine. Further, the opening degree of the throttle valve 12 may be made smaller than the period until the engine rotational speed Ne becomes substantially zero.

  In addition, when a negative determination is made in step S102, the process of step S105 is executed next. That is, the high pressure EGR valve 32 is controlled to be fully opened and the throttle valve 12 is opened even during a period until the engine rotational speed Ne of the internal combustion engine 1 becomes substantially zero (a period from time t1 to t2 in FIG. 3). The degree is controlled to a predetermined opening degree Dthv0. Thereby, compared with the case where electricity supply to EHC15 is performed, the flow volume of catalyst passage exhaust gas can be decreased.

  In FIG. 3, the high pressure EGR valve 32 is controlled to be fully closed and the throttle valve 12 is controlled to be fully open during the period from time t1 to t2. In the time chart showing the transition of the temperature Tcco of the oxidation catalyst 16 in FIG. 3, the broken lines indicate the same degree of opening of the high pressure EGR valve 32 and the throttle valve 12 from the time t2 in the period from the time t1 to the time t2. The temperature of the oxidation catalyst 16 when controlled is shown, and the solid line shows the temperature of the oxidation catalyst 16 when the exhaust gas flow rate control according to the present embodiment as described above is executed.

  When the exhaust gas flow rate control according to the present embodiment is executed, when the operation of the internal combustion engine 1 is automatically stopped, the EHC 15 is energized for a period until the engine rotation speed becomes substantially zero. The flow rate of exhaust gas passing through the catalyst during the period can be increased as compared with the case where the EHC 15 is not energized during the period. As a result, the amount of heat of the EHC 15 is easily supplied to the oxidation catalyst 16 by exhaust. In addition, when the operation of the internal combustion engine 1 is automatically stopped and the EHC 15 is not energized for a period until the engine rotation speed becomes substantially zero, the EHC 15 is energized during the period. As a result, the flow rate of exhaust gas passing through the catalyst can be reduced. Thereby, cooling of the oxidation catalyst 16 by low temperature exhaust can be suppressed.

  Therefore, when the operation of the internal combustion engine 1 is automatically stopped, the temperature of the oxidation catalyst 16 can be suppressed from decreasing. As a result, when the internal combustion engine 1 is automatically started, the oxidation of harmful substances in the oxidation catalyst 16 can be further promoted. That is, when the internal combustion engine 1 is automatically started, it becomes possible to further promote the purification of exhaust gas at the oxidation catalyst 16.

[Modification]
Here, a modification of the present embodiment will be described. If the EHC 15 is energized when the operation of the internal combustion engine 1 is automatically stopped, and the temperature of the oxidation catalyst 16 at that point is high to some extent, When the flow rate of exhaust gas passing through the catalyst is increased by executing the exhaust gas flow rate control, an excessive amount of heat is supplied from the EHC 15 to the oxidation catalyst 16, and as a result, the oxidation catalyst 16 may overheat.

  Therefore, in the present modification, when the temperature of the oxidation catalyst 16 is equal to or higher than a predetermined threshold at the time when the operation of the internal combustion engine 1 is automatically stopped, even when the EHC 15 is energized, Exhaust flow rate control that increases the flow rate of exhaust gas passing through the catalyst is prohibited. Here, the predetermined threshold is a value by which it can be determined that there is a possibility that the oxidation catalyst 16 will overheat when the exhaust flow control is performed to increase the flow rate of the exhaust gas passing through the catalyst as described above. Etc., based on the above.

  FIG. 4 is a flowchart showing a flow of exhaust flow control when the operation of the internal combustion engine 1 is automatically stopped according to this modification. This flow is stored in advance in the ECU 20 and is repeatedly executed by the ECU 20. Note that the processing in steps other than step S203 in this flow is the same as the processing in each step of the flow shown in FIG. For this reason, the same reference numbers are assigned to steps in which the same processes as the steps of the flow shown in FIG. 2 are executed, and the description thereof is omitted.

  In this flow, if an affirmative determination is made in step S102, that is, if it is determined that the EHC 15 is energized, the process of step S203 is executed next. In step S203, it is determined whether or not the temperature Tcco of the oxidation catalyst 16 calculated based on the detected value of the exhaust temperature sensor 23 is lower than a predetermined threshold T0.

  When a negative determination is made in step S203, that is, when it is determined that the temperature Tcco of the oxidation catalyst 16 is equal to or higher than a predetermined threshold value, the process of step S105 is performed next as in the case where the EHC 15 is not energized. Executed. On the other hand, when an affirmative determination is made in step S203, the process of step S103 is performed next.

  According to this modification, it is possible to prevent the oxidation catalyst 16 from overheating after the operation of the internal combustion engine 1 is automatically stopped.

  In this embodiment, the flow rates of the exhaust gas passing through the catalyst are controlled by adjusting the opening degrees of both the high pressure EGR valve 32 and the throttle valve 12, but it is not always necessary to adjust the opening degrees of both of them. For example, in step S103 in the flow shown in FIG. 2, only one of the control for fully closing the high pressure EGR valve 32 or the control for fully opening the throttle valve 12 may be executed. Even when only one of these controls is executed, the flow rate of exhaust gas passing through the catalyst can be increased.

  Further, in this embodiment, when the operation of the internal combustion engine 1 is automatically stopped and the EHC 15 is not energized, the EHC 15 may be energized at that time. The energization is continued until the engine rotational speed of the internal combustion engine 1 becomes substantially zero, and at least one of the opening degree of the high pressure EGR valve 32 and the opening degree of the throttle valve 12 is opened as described above. The degree may be controlled so that the flow rate of the exhaust gas passing through the catalyst increases. According to this, even when the EHC 15 is not energized at the time when the operation of the internal combustion engine 1 is automatically stopped, the temperature drop of the oxidation catalyst 16 can be suppressed after the automatic stop. As a result, it becomes possible to further promote the purification of exhaust gas at the oxidation catalyst 16.

Further, the control of the exhaust flow rate according to the present embodiment is not only performed when the operation of the internal combustion engine 1 is automatically stopped, but also the operation of the internal combustion engine 1 is stopped by the operation of the driver of the vehicle equipped with the internal combustion engine 1. Sometimes it may apply. That is, when the operation of the internal combustion engine 1 is stopped by the driver's operation, if the EHC 15 is energized during the period until the engine rotational speed becomes substantially zero, the EHC 15 is energized during the period. The flow rate of exhaust gas passing through the catalyst may be increased as compared with the case where it is not performed. Also in this case, when the operation of the internal combustion engine 1 is stopped by the operation of the driver and then the operation of the internal combustion engine 1 is restarted in a short time, the exhaust gas purification by the oxidation catalyst 16 can be further promoted.

<Example 2>
[Schematic configuration of internal combustion engine and its intake and exhaust system]
A schematic configuration of the internal combustion engine and its intake / exhaust system according to the present embodiment will be described with reference to FIG. Here, differences from the configuration according to the first embodiment will be mainly described, and the same reference numerals are given to the same components as those in the first embodiment, and the description thereof will be omitted.

  The intake and exhaust system of the internal combustion engine 1 according to the present embodiment is provided with a low pressure EGR device 34 as an EGR device in addition to the high pressure EGR device 30. The low pressure EGR device 34 has a low pressure EGR passage 35, a low pressure EGR valve 36, and a low pressure EGR cooler 37. One end of the low pressure EGR passage 35 is connected to the exhaust passage 7 downstream of the particulate filter 11, and the other end is connected to the intake passage 6 downstream of the throttle valve 12 and upstream of the compressor 8a. ing. Here, the EGR gas introduced from the exhaust passage 7 into the intake passage 6 through the low pressure EGR passage 35 is referred to as low pressure EGR gas. In this embodiment, the throttle valve 12 is the first throttle valve 12.

  The low pressure EGR valve 36 and the low pressure EGR cooler 37 are provided in the low pressure EGR passage 35. The low pressure EGR valve 36 adjusts the flow rate (low pressure EGR gas amount) of the low pressure EGR gas introduced into the intake passage 6 by changing the flow path cross-sectional area of the low pressure EGR passage 35. The low pressure EGR cooler 37 cools the low pressure EGR gas by exchanging heat between the low pressure EGR gas flowing through the low pressure EGR passage 35 and the cooling water of the internal combustion engine 1.

  A second throttle valve 13 is provided in the intake passage 6 on the downstream side of the intercooler 10. Similar to the first throttle valve 12, the second throttle valve 13 adjusts the flow rate of the intake air flowing through the intake passage 6 by changing the flow passage cross-sectional area of the intake passage 6.

  Further, an exhaust throttle valve 14 is provided downstream of the connection portion of the low pressure EGR passage 35 in the exhaust passage 7. The exhaust throttle valve 14 adjusts the flow rate of the exhaust gas flowing through the exhaust passage 7 by changing the cross-sectional area of the exhaust passage 7. The ECU 20 is electrically connected to the second throttle valve 13 and the exhaust throttle valve 14. These devices are controlled by the ECU 20.

[Exhaust flow control during engine shutdown]
Also in this embodiment, the same automatic stop / start control as that in the first embodiment is performed. Then, when the EHC 15 is energized when the operation of the internal combustion engine 1 is automatically stopped, as in the first embodiment, during the period until the engine speed of the internal combustion engine 1 becomes substantially zero, the EHC 15 is returned to. The flow rate of the exhaust gas passing through the catalyst is increased as compared with the case where the current is not energized.

  In this embodiment, the flow rate of the exhaust gas passing through the catalyst is controlled by adjusting the opening degree of the second throttle valve 13 and the high pressure EGR valve 32. Specifically, the flow rate of the exhaust gas passing through the catalyst can be increased by increasing the opening degree of the second throttle valve 13 and decreasing the opening degree of the high pressure EGR valve 32.

In this embodiment, the exhaust gas circulation through the low pressure EGR passage 35 is further promoted during a period from when the operation of the internal combustion engine 1 is automatically stopped until the engine rotation speed becomes substantially zero. Specifically, the flow rate of the low pressure EGR gas flowing through the low pressure EGR passage 35 is increased by decreasing the opening degree of the first throttle valve 12 and increasing the opening degree of the low pressure EGR valve 36. Thereby, the circulation of the exhaust gas passing through the low pressure EGR passage 35 can be promoted.

  The exhaust gas whose temperature has been increased by passing through the EHC 15, the oxidation catalyst 16, and the particulate filter 11 becomes low-pressure EGR gas. Therefore, during the period from when the operation of the internal combustion engine 1 is automatically stopped until the engine rotational speed becomes substantially zero, the exhaust gas circulation through the low pressure EGR passage 35 is promoted, thereby reducing the temperature drop due to the exhaust of the oxidation catalyst 16. It becomes possible to suppress more.

  FIG. 6 is a flowchart showing a flow of exhaust flow control when the operation of the internal combustion engine 1 is automatically stopped according to the present embodiment. This flow is stored in advance in the ECU 20 and is repeatedly executed by the ECU 20. FIG. 7 shows the temperature of the oxidation catalyst 16, the engine rotational speed Ne of the internal combustion engine 1 and the energization status to the EHC 15 (ON is energized and OFF is de-energized) when the exhaust flow control is executed. FIG. 6 is a time chart showing the transition of the opening degree Dhegrv of the high pressure EGR valve 32, the opening degree Dsthv of the second throttle valve 12, and the opening degree Dlegrv of the low pressure EGR valve 36. In FIG. 7, the horizontal axis represents time t.

  The flow shown in FIG. 6 is obtained by replacing steps S103 and S105 of the flow shown in FIG. 2 with steps S303 and S304 and steps S305 and S306. Therefore, steps S303 to S306 different from the flow shown in FIG. 2 will be described, and descriptions of other steps will be omitted.

  In this flow, when an affirmative determination is made in step S102, that is, when it is determined that energization to the EHC 15 is performed, the process of step S303 is executed next. In step S303, the high-pressure EGR valve 32 is controlled to be fully closed, and the second throttle valve 13 is controlled to be fully open. Thereby, the flow rate of exhaust gas passing through the catalyst can be increased as much as possible.

  However, the opening degree of the high pressure EGR valve 32 is not necessarily fully closed and the opening degree of the second throttle valve 13 is not necessarily fully opened, and is higher than that when the EHC 15 is not energized. The opening degree of the valve 32 may be reduced and the opening degree of the second throttle valve 13 may be increased. Thereby, compared with the case where electricity supply to EHC15 is not performed, the flow volume of catalyst passage exhaust gas can be increased.

  Next, in step S304, the low pressure EGR valve 36 is controlled to be fully open, and the first throttle valve 12 is controlled to be fully closed. Thereby, the flow volume of the exhaust gas circulating through the low pressure EGR passage 35 can be increased as much as possible.

  However, the opening degree of the low pressure EGR valve 36 is not necessarily fully opened and the opening degree of the first throttle valve 12 is not necessarily fully closed. Compared to the case where the EHC 15 is not energized, the low pressure EGR valve 36 is not necessarily opened. What is necessary is just to enlarge the opening degree of the valve 36 and to make the opening degree of the 1st throttle valve 12 small. As a result, the flow rate of the exhaust gas circulated through the low pressure EGR passage 35 can be increased as compared with the case where the EHC 15 is not energized.

In this embodiment, when an affirmative determination is made in step S104, that is, when it is determined that the engine speed Ne of the internal combustion engine 1 has become substantially zero, the process of step S305 is executed next. In step S305, the high pressure EGR valve 32 is controlled to be fully opened, and the opening degree of the second throttle valve 13 is reduced and controlled to a predetermined opening degree Dsthv0. The predetermined opening degree Dsthv0 is an opening degree near the fully closed state, and is a predetermined lower limit value of the opening degree of the second throttle valve 13. Thereby, the flow rate of exhaust gas passing through the catalyst can be reduced as much as possible.

  However, the opening degree of the high-pressure EGR valve 32 does not necessarily need to be fully opened, and is larger than the period until the engine rotation speed Ne becomes substantially zero (that is, when the EHC 15 is energized). That's fine. Further, the opening of the second throttle valve 13 may be made smaller than the period until the engine speed Ne becomes substantially zero.

  Next, in step S306, the low-pressure EGR valve 36 is controlled to be fully closed, and the first throttle valve 12 is controlled to be fully open. However, it is not always necessary to fully close the opening of the low pressure EGR valve 36 and fully open the opening of the first throttle valve 12, and the period until the engine speed Ne becomes substantially zero (that is, the EHC 15). Compared to when the power is applied to the first throttle valve 12, the opening degree of the low pressure EGR valve 36 may be reduced and the opening degree of the first throttle valve 12 may be increased.

  Also, if a negative determination is made in step S102, the process of step S305 is then executed. That is, even during the period until the engine speed Ne of the internal combustion engine 1 becomes substantially zero (period from time t1 to t2), the high-pressure EGR valve 32 is controlled to be fully opened, and the opening of the second throttle valve 13 Is controlled to a predetermined opening degree Dsthv0. Thereby, compared with the case where electricity supply to EHC15 is performed, the flow volume of catalyst passage exhaust gas can be decreased. Next, the process of step S306 is executed. That is, even during the period until the engine rotational speed Ne of the internal combustion engine 1 becomes substantially zero, the low pressure EGR valve 36 is controlled to be fully closed, and the opening degree of the first throttle valve 12 is controlled to be fully open.

  In FIG. 7, the operation of the internal combustion engine 1 is automatically stopped at time t1, and the engine speed of the internal combustion engine 1 becomes substantially zero at time t2. At time t1, the EHC 15 is energized, and the energization is continued until time t2. During the period from time t1 to t2, the high pressure EGR valve 32 is controlled to be fully closed, the second throttle valve 13 is controlled to be fully open, the low pressure EGR valve 36 is controlled to be fully open, and the first throttle valve 12 is fully closed. Controlled.

  In the time chart showing the transition of the temperature Tcco of the oxidation catalyst 16 in FIG. 7, the broken lines indicate the high pressure EGR valve 32, the second throttle valve 12, the low pressure EGR valve 36, and the first throttle valve even during the period from time t1 to time t2. 12 shows the temperature of the oxidation catalyst 16 when the opening degree 12 is controlled to the same opening degree as after the time t2, and the solid line shows the oxidation catalyst when the exhaust gas flow control according to the present embodiment as described above is executed. 16 temperatures are shown.

  When the exhaust gas flow rate control according to the present embodiment is executed, when the operation of the internal combustion engine 1 is automatically stopped, the EHC 15 is energized for a period until the engine rotation speed becomes substantially zero. The flow rate of exhaust gas passing through the catalyst during the period can be increased as compared with the case where the EHC 15 is not energized during the period. Further, when the EHC 15 is energized during this period, the flow rate of the exhaust gas circulated through the low pressure EGR passage 35 can be increased as compared with the case where the EHC 15 is not energized during the period. That is, the exhaust gas circulation through the low-pressure EGR passage 35 can be promoted.

  Thereby, when the operation of the internal combustion engine 1 is automatically stopped, the temperature of the oxidation catalyst 16 can be further suppressed from decreasing. As a result, when the internal combustion engine 1 is automatically started, the oxidation of harmful substances in the oxidation catalyst 16 can be further promoted. When the internal combustion engine 1 is automatically started, the exhaust gas purification by the oxidation catalyst 16 can be further promoted.

In this embodiment, the flow rate of the exhaust gas passing through the catalyst is controlled by adjusting the opening degrees of both the high pressure EGR valve 32 and the second throttle valve 13, but it is not always necessary to adjust the opening degrees of both. . For example, in step S303 in the flow shown in FIG. 6, only one of the control for fully closing the high-pressure EGR valve 32 or the control for fully opening the second throttle valve 13 may be executed. Even when only one of these controls is executed, the flow rate of exhaust gas passing through the catalyst can be increased.

  In this embodiment, the flow rate of the exhaust gas circulated through the low-pressure EGR passage 35 is controlled by adjusting the opening degrees of both the low-pressure EGR valve 36 and the first throttle valve 12. There is no need to adjust the degree. For example, in step S304 in the flow shown in FIG. 6, only one of the control for fully opening the low pressure EGR valve 36 or the control for fully closing the first throttle valve 12 may be executed. Even when only one of these controls is executed, the flow rate of the exhaust gas circulated through the low pressure EGR passage 35 can be increased.

[Modification]
Here, a modification of the present embodiment will be described. The flow rate of the exhaust gas circulated through the low-pressure EGR passage 35 can be controlled by adjusting the opening degree of the exhaust throttle valve 14 instead of the first throttle valve 12. Specifically, the flow rate of the low pressure EGR gas flowing through the low pressure EGR passage 35 can be increased by reducing the opening of the exhaust throttle valve 14.

  Therefore, in the present embodiment, in the exhaust flow rate control when the operation of the internal combustion engine 1 is automatically stopped, the flow rate of the low pressure EGR gas flowing through the low pressure EGR passage 35 using the exhaust throttle valve 14 instead of the first throttle valve 12. To control.

  FIG. 8 is a flowchart showing a flow of exhaust flow control when the operation of the internal combustion engine 1 is automatically stopped according to this modification. This flow is stored in advance in the ECU 20 and is repeatedly executed by the ECU 20. FIG. 9 shows the temperature of the oxidation catalyst 16, the engine rotational speed Ne of the internal combustion engine 1 and the energization state to the EHC 15 when the exhaust flow control is executed (ON indicates an energized state, OFF indicates a non-energized state). FIG. 6 is a time chart showing transitions of the opening degree Dhegrv of the high-pressure EGR valve 32, the opening degree Dsthv of the second throttle valve 12, and the opening degree Doutv of the exhaust throttle valve 14. In FIG. 9, the horizontal axis represents time t.

  The flow shown in FIG. 8 is obtained by replacing steps S304 and S306 in the flow shown in FIG. 6 with steps S404 and S406. Therefore, steps S404 and S406 different from the flow shown in FIG. 6 will be described, and descriptions of other steps will be omitted.

  In step S404, the low pressure EGR valve 36 is controlled to be fully opened, and the exhaust throttle valve 14 is controlled to be fully closed. Thereby, the flow volume of the exhaust gas circulating through the low pressure EGR passage 35 can be increased as much as possible. However, the opening degree of the exhaust throttle valve 14 does not necessarily need to be fully closed, and the opening degree may be made smaller than when the EHC 15 is not energized. As a result, the flow rate of the exhaust gas circulated through the low pressure EGR passage 35 can be increased as compared with the case where the EHC 15 is not energized.

  In step S406, the low pressure EGR valve 36 is controlled to be fully closed, and the exhaust throttle valve 14 is controlled to be fully open. However, it is not always necessary to fully open the opening of the exhaust throttle valve 14, compared to the period until the engine speed Ne becomes substantially zero (that is, when the EHC 15 is energized). What is necessary is just to enlarge an opening degree.

In FIG. 9, the operation of the internal combustion engine 1 is automatically stopped at time t1, and the engine speed of the internal combustion engine 1 becomes substantially zero at time t2. At time t1, the EHC 15 is energized, and the energization is continued until time t2. During the period from time t1 to t2, the high pressure EGR valve 32 is controlled to be fully closed, the second throttle valve 13 is controlled to be fully open, the low pressure EGR valve 36 is controlled to be fully open, and the exhaust throttle valve 14 is fully closed. Be controlled.

  In the time chart showing the transition of the temperature Tcco of the oxidation catalyst 16 in FIG. 9, the broken lines indicate the high pressure EGR valve 32, the second throttle valve 12, the low pressure EGR valve 36, and the exhaust throttle valve 14 even during the period from time t1 to time t2. Indicates the temperature of the oxidation catalyst 16 when the opening is controlled to be the same as the opening after time t2, and the solid line indicates the oxidation catalyst 16 when the exhaust flow control according to the present modification as described above is executed. Shows the temperature.

  Also in this modification, when the operation of the internal combustion engine 1 is automatically stopped and the EHC 15 is energized for a period until the engine rotation speed becomes substantially zero, the EHC 15 is energized during the period. The flow rate of the exhaust gas circulated through the low pressure EGR passage 35 can be increased as compared with the case where it is not performed. That is, the exhaust gas circulation through the low-pressure EGR passage 35 can be promoted.

  In this modification, the flow rate of the exhaust gas circulated through the low pressure EGR passage 35 is controlled by adjusting the opening amounts of both the low pressure EGR valve 36 and the exhaust throttle valve 14. There is no need to adjust. For example, in step S404 in the flow shown in FIG. 8, only one of the control for fully opening the low pressure EGR valve 36 or the control for fully closing the exhaust throttle valve 14 may be executed. Even when only one of these controls is executed, the flow rate of the exhaust gas circulated through the low pressure EGR passage 35 can be increased.

  In the present embodiment, the flow rate of the exhaust gas circulated through the low pressure EGR passage 35 may be controlled by using the first throttle valve 12 and the exhaust throttle valve 14 together.

  As in the modification of the first embodiment, in this embodiment, if the temperature of the oxidation catalyst 16 is equal to or higher than a predetermined threshold when the operation of the internal combustion engine 1 is automatically stopped, the EHC 15 is energized. Even when the engine is closed, execution of the exhaust gas flow rate control for increasing the flow rate of the exhaust gas passing through the catalyst as described above may be prohibited.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 4 ... Intake manifold 5 ... Exhaust manifold 6 ... Intake passage 7 ... Exhaust passage 11 ... Particulate filter 12 ... Throttle valve (first throttle valve)
13. Second throttle valve 14 Exhaust throttle valve 15 Electric heating catalyst (EHC)
16. ・ Oxidation catalyst 17 ・ ・ Alternator 20 ・ ・ ECU
21 ·· Crank angle sensor 23 · · Exhaust temperature sensor 30 · · High pressure EGR device 31 · · High pressure EGR passage 32 · · High pressure EGR valve 34 · · Low pressure EGR device 35 · · Low pressure EGR passage 36 · · Low pressure EGR valve

Claims (5)

An electrically heated catalyst that is provided in the exhaust passage of the internal combustion engine and generates heat when energized;
An exhaust purification catalyst provided in an exhaust passage downstream of the electrically heated catalyst;
If the electric heating catalyst is energized during the period from when the operation of the internal combustion engine is stopped until the engine speed of the internal combustion engine becomes substantially zero, the electric heating catalyst is energized during the period. Exhaust flow rate control means for increasing the flow rate of the exhaust gas that passes through the electric heating catalyst and the exhaust purification catalyst during the period than when not being performed,
An internal combustion engine exhaust gas purification system. Automatic stop / starting means for automatically stopping the operation of the internal combustion engine when a predetermined automatic stop condition is satisfied, and then automatically starting the internal combustion engine when the predetermined automatic start condition is satisfied;
Exhaust gas that passes through the electrically heated catalyst and the exhaust purification catalyst when the electrically heated catalyst is energized by the exhaust gas flow rate control means than when the electrically heated catalyst is not energized. 2. The internal combustion engine according to claim 1, wherein a period during which the flow rate of the internal combustion engine is increased is a period from when the operation of the internal combustion engine is automatically stopped by the automatic stop / start means until the engine rotation speed of the internal combustion engine becomes substantially zero. Engine exhaust purification system.   When the electric heating catalyst is energized, if the temperature of the exhaust purification catalyst is equal to or higher than a predetermined threshold, the exhaust gas flow control means energizes the electric heating catalyst. The exhaust purification system for an internal combustion engine according to claim 1 or 2, wherein execution of control for increasing a flow rate of exhaust gas that passes through the electric heating catalyst and the exhaust purification catalyst is prohibited as compared with a case where there is no exhaust gas. The exhaust flow rate control means is
An intake throttle valve provided in an intake passage of the internal combustion engine, and an EGR passage connecting an upstream side of the electrically heated catalyst in the exhaust system of the internal combustion engine and a downstream side of the intake throttle valve in the intake system of the internal combustion engine Having an EGR valve provided,
When the electric heating catalyst is energized during the period from when the operation of the internal combustion engine is stopped until the engine speed of the internal combustion engine becomes substantially zero, at least one of the intake throttle valve and the EGR valve By adjusting the opening degree, the flow rate of the exhaust gas that passes through the electric heating catalyst and the exhaust purification catalyst during the period is made smaller than when the electric heating catalyst is not energized during the period. The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 3, which is increased. An electrically heated catalyst that is provided in the exhaust passage of the internal combustion engine and generates heat when energized;
An exhaust purification catalyst provided in an exhaust passage downstream of the electrically heated catalyst;
Automatic stop / start means for automatically stopping the operation of the internal combustion engine when a predetermined automatic stop condition is satisfied, and then automatically starting the internal combustion engine when the predetermined automatic start condition is satisfied;
An intake throttle valve provided in the intake passage of the internal combustion engine;
An EGR valve provided in an EGR passage connecting the upstream side of the electrically heated catalyst in the exhaust system of the internal combustion engine and the downstream side of the intake throttle valve in the intake system of the internal combustion engine;
An exhaust gas purification system for an internal combustion engine comprising:
When the operation of the internal combustion engine is automatically stopped by the automatic stop / start means, the electric heating catalyst is energized for a period until the engine rotation speed of the internal combustion engine becomes substantially zero, and the intake throttle valve or the An exhaust gas purification system for an internal combustion engine that adjusts the opening degree of at least one of the EGR valves in a direction in which the flow rate of exhaust gas passing through the electric heating catalyst and the exhaust gas purification catalyst increases.

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