JP6432550B2 - Exhaust gas purification system for internal combustion engine - Google Patents

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine.

  Conventionally, a filter may be provided in an exhaust passage of an internal combustion engine. This filter has a function of collecting particulate matter (hereinafter also referred to as PM) in the exhaust gas. The collected PM gradually accumulates on the filter. During operation of the internal combustion engine, the temperature of the filter reaches the oxidizable temperature of PM and oxygen exists in the ambient atmosphere of the filter (hereinafter, this situation may be referred to as “PM oxidizable situation”). Is formed, the PM deposited on the filter is oxidized and removed. However, if a PM oxidizable state is not formed during operation of the internal combustion engine, the amount of PM deposited on the filter will continue to increase. Therefore, a technique for performing filter regeneration processing to oxidize and remove PM deposited on the filter is known. The filter regeneration process is a process for forcibly forming a PM oxidizable state.

  Patent Document 1 discloses a technique for performing a filter regeneration process when the operation of the internal combustion engine is stopped when the operation of the internal combustion engine is stopped and the PM accumulation amount in the filter is larger than a predetermined amount. In the configuration disclosed in Patent Document 1, a catalyst having an oxidation function is supported on a filter. The filter is provided with an electric heater for heating the filter. Further, a fuel addition valve and a secondary air supply valve are installed in the exhaust passage upstream of the filter. Then, while the operation of the internal combustion engine is stopped, the filter is heated by heating the filter with an electric heater. Furthermore, by adding the fuel from the fuel addition valve while the filter is heated by the electric heater, the temperature of the filter is raised to the oxidizable temperature of PM by the oxidation heat generated by the oxidation of the fuel in the catalyst, and the secondary PM is oxidized and removed by supplying secondary air from the air supply valve.

  Patent Document 2 discloses a technique for performing filter regeneration processing during operation of an internal combustion engine. In the filter regeneration process disclosed in Patent Document 2, the temperature of the filter is raised to a predetermined temperature by heating the filter with an electric heater during operation of the internal combustion engine, and then the filter is heated by the electric heater. Next, PM is oxidized and removed by supplying air to the filter from an air supply valve.

JP 2007-187006 A JP 2000-097012 A

  If the operation of the internal combustion engine is stopped without the PM oxidizable state being formed for a relatively long period of time, the operation of the internal combustion engine may be stopped with a large amount of PM deposited on the filter. In this case, a large amount of PM is deposited on the filter even at the next start of operation of the internal combustion engine. After the start of the operation of the internal combustion engine, when the operation state of the internal combustion engine becomes a high load operation, the temperature of the filter rapidly rises to the oxidizable temperature of PM, and when the oxidizable state is formed, the accumulated PM Oxidation of can proceed rapidly. In such a case, if a large amount of PM is accumulated on the filter, the temperature of the filter may be excessively increased, and there is a possibility that the filter may be defective.

  In order to suppress the occurrence of the excessive temperature rise of the filter after the start of the operation of the internal combustion engine, the filter is heated by an electric heater while the operation of the internal combustion engine is stopped, as in the related art described above. It is conceivable to remove PM accumulated on the filter by supplying air to the filter. However, a relatively large amount of electric power is required to raise the temperature of the filter to the oxidizable temperature of PM by heating with an electric heater while the internal combustion engine is stopped.

  The present invention has been made in view of the above problems, and provides a technique capable of more suitably removing PM accumulated on a filter by using an electric heater when the operation of the internal combustion engine is stopped. The purpose is to do.

  In the present invention, when the condition for stopping the operation of the internal combustion engine is satisfied, if the PM accumulation amount in the filter is larger than the predetermined accumulation amount, the exhaust temperature of the internal combustion engine can be heated by the electric heater to oxidize the temperature of the filter. The operation of the internal combustion engine is stopped after the temperature is raised. Then, after the temperature of the filter rises to the oxidizable temperature of PM, air is supplied to the filter.

  More specifically, an exhaust gas purification system for an internal combustion engine according to the present invention includes a filter that is provided in an exhaust passage of the internal combustion engine and collects particulate matter in the exhaust gas, and an electric that heats the exhaust gas flowing into the filter. An exhaust gas purification system for an internal combustion engine, comprising: a heater; and an air supply unit that supplies air to the filter, an estimation unit that estimates an accumulation amount of particulate matter in the filter, and an operation stop of the internal combustion engine When the condition is satisfied, if the accumulation amount of the particulate matter in the filter estimated by the estimation unit is larger than a predetermined accumulation amount, the temperature of the exhaust gas is heated by the electric heater while continuing the operation of the internal combustion engine By executing the control, the temperature of the filter is raised to a predetermined temperature that is the oxidizable temperature of the particulate matter, and the temperature of the filter is increased to the predetermined temperature. In the filter that is estimated by the estimation unit when a condition for stopping the operation of the internal combustion engine is satisfied, and a temperature increase control unit that stops the operation of the internal combustion engine and heating of the exhaust gas by the electric heater. When the accumulation amount of particulate matter is larger than the predetermined accumulation amount When the temperature of the filter is lower than the predetermined temperature, the temperature of the filter reaches the predetermined temperature by executing the temperature increase control by the temperature increase control unit. And an air supply control unit that supplies air to the filter by the air supply unit.

  In the present invention, even when the operation stop condition of the internal combustion engine is satisfied, if the PM accumulation amount in the filter is larger than the predetermined accumulation amount, the operation of the internal combustion engine is not immediately stopped but the operation is continued for a certain period. The In the present invention, “operation stop of the internal combustion engine” means that fuel injection from the fuel injection valve in the internal combustion engine is stopped, and combustion of the fuel is not performed in the internal combustion engine. Accordingly, even after the fuel injection in the internal combustion engine is stopped, even if the rotation of the internal combustion engine (that is, the rotation of the crankshaft) is continued for a certain period by the inertia force in a state where the fuel is not burned, the fuel injection After the stop, the operation of the internal combustion engine is interpreted as being stopped. In the present invention, “continuing the operation of the internal combustion engine” means that fuel injection from the fuel injection valve in the internal combustion engine is continued, and fuel combustion in the internal combustion engine is continued. Further, in the present invention, the “operation stop condition of the internal combustion engine” means a condition for stopping fuel injection from the fuel injection valve in the internal combustion engine, that is, a condition for stopping combustion of fuel in the internal combustion engine. Further, the “predetermined accumulation amount” in the present invention is based on the assumption that the oxidizable state is formed when the temperature of the filter rapidly rises to the oxidizable temperature of PM after the start of the next operation of the internal combustion engine, and the oxidation of PM proceeds rapidly However, it is an amount that can be determined that the possibility of overheating of the filter is low.

Then, while the operation of the internal combustion engine is continued, the exhaust gas flowing into the filter is heated by the electric heater. Control in which the operation of the internal combustion engine is continued and the exhaust is heated by the electric heater is referred to as “temperature increase control” in the present invention. And in this invention, the temperature of a filter is raised to predetermined temperature by performing this temperature rising control. In this temperature increase control, not only the electric energy of the electric heater but also the thermal energy of the exhaust contributes to the temperature rise of the filter. Furthermore, in the present invention, air is not supplied from the air supply unit to the filter until the temperature of the filter reaches a predetermined temperature. Therefore, in order to raise the temperature of the filter to a predetermined temperature, it is not necessary to heat the air supplied from the air supply unit by the electric heater in addition to the exhaust. As a result, the power consumed by the electric heater for raising the temperature of the filter to a predetermined temperature can be reduced.

  Moreover, in this invention, after the temperature of a filter reaches predetermined temperature by performing temperature rising control, air is supplied to a filter by an air supply part. As a result, a situation in which PM oxidation is possible is formed, so that PM deposited on the filter is oxidized. Therefore, even if the operation of the internal combustion engine and the heating of the exhaust gas by the electric heater are stopped after the temperature of the filter is raised to a predetermined temperature, while the PM oxidizable state is formed (that is, the filter temperature is PM During the oxidizable temperature), the PM deposited on the filter is oxidized and removed. Therefore, according to the present invention, when the operation of the internal combustion engine is stopped, the PM accumulated on the filter can be more suitably removed using the electric heater.

  In the present invention, the temperature increase control unit may stop the operation of the internal combustion engine and the heating of the exhaust gas by the electric heater when the temperature of the filter reaches a predetermined temperature after the start of the temperature increase control. According to this, the operation continuation period of the internal combustion engine for raising the temperature of the filter and the operation period of the electric heater can be minimized. Therefore, the fuel consumption and power consumption for raising the temperature of the filter can be reduced as much as possible.

  Moreover, in this invention, you may employ | adopt the structure which has an air injection valve which injects secondary air in the exhaust passage upstream from a filter as a structure of an air supply part. In such a configuration, the air supply unit supplies air to the filter by injecting secondary air from the air injection valve.

  Further, in the present invention, a configuration having an electric motor that rotates the internal combustion engine (that is, rotates the crankshaft of the internal combustion engine) may be adopted as the configuration of the air supply unit. In such a configuration, the air supply unit supplies air to the filter by rotating the internal combustion engine with an electric motor in a state where the operation of the internal combustion engine is stopped. In this case, it is possible to supply air to the filter without separately providing a device for supplying secondary air.

  According to the present invention, when the operation of the internal combustion engine is stopped, the PM deposited on the filter can be more suitably removed using the electric heater.

1 is a diagram illustrating a schematic configuration of an exhaust system of an internal combustion engine according to Embodiment 1 of the present invention. When the engine stop regeneration process according to the first embodiment of the present invention is executed, the operating states of the fuel injection valve, the electric heater, and the air injection valve, the temperature of the filter, and the PM accumulation amount in the filter It is a time chart which shows a change. It is a flowchart which shows the flow of the regeneration process at the time of an engine stop based on Example 1 of this invention. It is a figure which shows schematic structure of the exhaust system of the internal combustion engine which concerns on Example 2 of this invention. It is a flowchart which shows the flow of the regeneration process at the time of an engine stop which concerns on Example 2 of this invention.

  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, an embodiment when the exhaust gas purification system for an internal combustion engine according to the present invention is applied to a gasoline engine for driving a vehicle will be described. However, the internal combustion engine according to the present invention is not limited to a gasoline engine, and may be a diesel engine or the like.

[Schematic configuration of exhaust system]
FIG. 1 is a diagram showing a schematic configuration of an exhaust system of an internal combustion engine according to the present embodiment. The internal combustion engine 1 is a gasoline engine for driving a vehicle. The internal combustion engine 1 is provided with a fuel injection valve 2 for injecting fuel to be used for combustion in the cylinder. The fuel injection valve 2 may be a port injection valve that injects fuel into the intake port, or an in-cylinder injection valve that directly injects fuel into the cylinder. An exhaust passage 3 is connected to the internal combustion engine 1. The exhaust passage 3 is configured to include an exhaust manifold. The arrows in FIG. 1 indicate the flow direction of the exhaust gas in the exhaust passage 3.

  An exhaust purification catalyst 4 is provided in the exhaust passage 3. Examples of the exhaust purification catalyst 4 include an oxidation catalyst and a three-way catalyst. A filter 5 is provided in the exhaust passage 3 on the downstream side of the exhaust purification catalyst 4. The filter 5 is a wall flow type filter formed of a porous base material and has a function of collecting PM in exhaust gas. The filter 5 may carry a catalyst having an oxidation function.

  An electric heater 6 capable of heating the gas (exhaust gas) flowing into the filter 5 is installed downstream of the exhaust purification catalyst 4 in the exhaust passage 3 and immediately upstream of the filter 5. Further, a temperature sensor 7 for detecting the temperature of gas (exhaust gas) flowing out from the filter 5 is provided downstream of the filter 5 in the exhaust passage 3. Furthermore, an air injection valve 8 that injects secondary air into the exhaust passage 3 is provided upstream of the exhaust purification catalyst 4 in the exhaust passage 3. The air injection valve 8 is supplied with air fed by an air pump through an air supply passage. In FIG. 1, the air supply passage and the air pump are not shown.

  The internal combustion engine 1 is provided with an electronic control unit (ECU) 10. The ECU 10 is a unit that controls the operating state and the like of the internal combustion engine 1. A temperature sensor 7 is electrically connected to the ECU 10, and a detection value of the temperature sensor 7 is input to the ECU 10. Then, the ECU 10 estimates the temperature of the filter 5 based on the detection value of the temperature sensor 7. In addition, the fuel injection valve 2, the electric heater 6, and the air injection valve 8 are electrically connected to the ECU 10. The operation of these devices is controlled by the ECU 10.

  Further, the ECU 10 is electrically connected to an ignition switch 11 installed in a vehicle on which the internal combustion engine 1 is mounted. Then, the ECU 10 controls the operation of the fuel injection valve 2 of the internal combustion engine 1 based on the output signal of the ignition switch 11. That is, when the ignition switch 11 is turned off by the user of the vehicle during the operation of the internal combustion engine 1, the fuel injection from the fuel injection valve 2 is stopped by the ECU 10. At this time, ignition by the ignition plug (not shown) is also stopped by the ECU 10. Thereby, the combustion of the fuel in the internal combustion engine 1 is not performed. That is, the operation of the internal combustion engine 1 is stopped. However, in this embodiment, as will be described later, the operation of the internal combustion engine 1 is not necessarily stopped immediately when the ignition switch 11 is turned off.

[Regeneration processing when the engine is stopped]
During the operation of the internal combustion engine 1, the amount of PM deposited on the filter 5 increases as the collected PM gradually accumulates. However, in the internal combustion engine 1, so-called fuel cut control may be performed during the travel of the vehicle, in which fuel injection from the fuel injection valve 2 is stopped and fuel combustion is not performed in the internal combustion engine 1. . When such fuel cut control is executed, air is supplied to the filter 5. Therefore, when the fuel cut control is executed in a state where the temperature of the filter 5 has reached the oxidizable temperature of PM, a PM oxidizable state is formed. When the PM oxidizable state is formed, the PM deposited on the filter 5 is oxidized and removed, so that the amount of PM deposited on the filter 5 decreases.

  However, under conditions where the exhaust gas temperature is so low that the temperature of the filter 5 does not reach the PM oxidizable temperature, even if the fuel cut control is executed, the PM oxidizable state is not formed. For this reason, the PM oxidizable state can be obtained as in the case where the operation of the internal combustion engine 1 is stopped after the operation at the engine load whose exhaust temperature is so low that the temperature of the filter 5 does not reach the oxidizable temperature of PM. In some cases, the operation of the internal combustion engine 1 is stopped without being formed for a relatively long period of time. In such a case, the operation of the internal combustion engine 1 is stopped with a large amount of PM accumulated on the filter 5. At this time, when the operation state of the internal combustion engine 1 becomes a high load operation after the start of the next operation of the internal combustion engine 1, the temperature of the filter 5 rapidly rises to the oxidizable temperature of PM, and a PM oxidizable state is formed. There is a possibility that the temperature of the filter 5 is excessively increased due to rapid progress of oxidation of the deposited PM.

  Therefore, in this embodiment, the filter regeneration process is executed when the operation of the internal combustion engine 1 is stopped in order to suppress the occurrence of excessive temperature rise of the filter 5 after the start of the next operation of the internal combustion engine 1. Hereinafter, a filter regeneration process (hereinafter also referred to as an engine stop regeneration process) when stopping the operation of the internal combustion engine 1 will be described with reference to FIG. FIG. 2 shows the time of the operating states of the fuel injection valve, the electric heater, and the air injection valve, the filter temperature, and the PM accumulation amount in the filter when the engine stop regeneration process according to the present embodiment is executed. It is a time chart which shows a typical transition.

  In FIG. 2, the time t1 represents the timing when the ignition switch 11 is turned off. In the present embodiment, turning off the ignition switch 11 corresponds to the establishment of the “operation stop condition for the internal combustion engine” according to the present invention. In the present embodiment, the PM accumulation amount in the filter 5 is estimated by the ECU 10 during the operation of the internal combustion engine 1. Here, any known method may be applied as a method for estimating the PM accumulation amount in the filter 5. For example, during the operation of the internal combustion engine 1, the PM accumulation amount in the filter 5 may be estimated by integrating the amount of PM discharged from the internal combustion engine 1 and the oxidation amount of PM in the filter 5. The amount of PM discharged from the internal combustion engine 1 can be estimated based on the fuel injection amount in the internal combustion engine 1 and the like. The amount of PM oxidation in the filter 5 can be estimated based on the operating state of the internal combustion engine 1, the temperature of the filter 5, and the like. In this embodiment, the ECU 10 estimates the PM accumulation amount in the filter 5, thereby realizing the “estimator” according to the present invention. In this embodiment, when the ignition switch 11 is turned off, if the PM accumulation amount in the filter 5 is larger than the predetermined accumulation amount Fpm1, the regeneration process at the time of engine stop is executed. Here, the predetermined accumulation amount Fpm1 is determined even if the oxidation of PM proceeds rapidly because the oxidizable state is formed by the temperature of the filter 5 rapidly rising to the oxidizable temperature of PM after the start of the next operation of the internal combustion engine 1. The amount set as an amount that can be determined that the possibility of overheating of the filter 5 is low. Such a predetermined deposition amount Fpm1 can be set in advance based on experiments or the like.

  In the engine stop regeneration process according to the present embodiment, as shown in FIG. 2, even when the ignition switch 11 is turned off at time t1, the fuel injection from the fuel injection valve 2 is not immediately stopped but continued. The That is, the operation of the internal combustion engine 1 is continued after time t1. Even after time t1, the exhaust gas flows into the exhaust passage 3 while the operation of the internal combustion engine 1 is continued. Then, the electric heater 6 is turned on from time t1. That is, heating of the exhaust gas flowing into the filter 5 by the electric heater 6 is started from time t1. Thereby, the temperature of the filter 5 rises. At time t2, the temperature of the filter 5 reaches the first predetermined temperature Tf1. Here, the first predetermined temperature Tf1 is the oxidizable temperature of PM, and the PM deposited on the filter 5 is oxidized by the formation of the PM oxidizable condition, and the oxidation heat of the filter 5 Even if the temperature further rises, the temperature of the filter 5 is a temperature that is determined in advance based on experiments or the like as a temperature that falls below the upper limit (Tflimit in FIG. 2) of the allowable range (a range in which excessive temperature rise is not caused). .

  When the temperature of the filter 5 reaches the first predetermined temperature Tf1 at this time t2, the fuel injection from the fuel injection valve 2 is stopped and the electric heater 6 is turned off. That is, at the time t2, the operation of the internal combustion engine 1 is stopped and the heating of the exhaust gas by the electric heater 6 is stopped. In this embodiment, during the period from time t1 to time t2, the operation of the internal combustion engine 1 is continued and the exhaust by the electric heater 6 is heated, so that the temperature increase control according to the present invention is executed. become. Then, secondary air injection from the air injection valve 8 is started from time t2. As a result, air is supplied to the filter 5 whose temperature has reached the oxidizable temperature of PM. As a result, a situation where PM oxidation is possible is formed.

  When the PM oxidizable state is formed at time t2, PM deposited on the filter 5 starts to oxidize. Therefore, the PM accumulation amount in the filter 5 gradually decreases from the time t2. Further, when the PM deposited on the filter 5 starts to be oxidized from the time t2, the temperature of the filter 5 further increases for a while due to the oxidation heat. However, since the electric heater 6 is turned off at time t2, no heat energy is supplied from the electric heater 6 to the filter 5. The amount of heat generated by the oxidation of PM in the filter 5 is carried away by the air injected from the air injection valve 8 and supplied to the filter 5. Therefore, as shown in FIG. 2, the temperature of the filter 5 starts to decrease after a while from the time t2. That is, the temperature of the filter 5 further increased from the temperature at the time point t2 reaches a peak before exceeding the upper limit value Tflimit of the allowable range, and then decreases.

  At time t3, the temperature of the filter 5 reaches the second predetermined temperature Tf2. Here, the second predetermined temperature Tf2 is a temperature lower than the first predetermined temperature Tf1, and is a temperature determined in advance as a lower limit value of the oxidizable temperature of PM based on experiments or the like. That is, after the time t3, the temperature of the filter 5 falls below the lower limit value of the oxidizable temperature of PM, so that even if air is supplied to the filter 5, the PM oxidizable state is not formed. Therefore, PM deposited on the filter 5 is not oxidized. Therefore, at time t3, the injection of secondary air from the air injection valve 8 is stopped. Thereby, the execution of the regeneration process when the engine is stopped is stopped.

  According to the regeneration process at the time of engine stop as described above, a PM oxidizable state is formed in the period from time t2 to time t3. Therefore, during this period, PM deposited on the filter 5 can be oxidized and removed. Thereby, the PM accumulation amount in the filter 5 at the start of the next operation of the internal combustion engine 1 can be reduced. As a result, even after the next operation of the internal combustion engine 1 is started, even if the temperature of the filter 5 suddenly rises to the oxidizable temperature of the PM due to the operation state of the internal combustion engine 1 becoming a high load operation, the oxidation heat of the PM Therefore, it is possible to suppress the temperature of the filter 5 from excessively rising.

Further, according to the above-described regeneration process when the engine is stopped, the operation of the internal combustion engine 1 is continued without stopping immediately even when the ignition switch 11 is turned off. Then, while the operation of the internal combustion engine 1 is continued, the exhaust gas flowing into the filter 5 is heated by the electric heater 6 to raise the temperature of the filter 5 to the first predetermined temperature Tf1. Therefore, not only the electric energy of the electric heater 6 but also the heat energy of the exhaust contributes to the temperature increase of the filter 5. Furthermore, according to the engine stop regeneration process, secondary air is not injected from the air injection valve 8 until the temperature of the filter 5 reaches the first predetermined temperature Tf1 after the timing t1. Therefore, in order to raise the temperature of the filter 5 to the first predetermined temperature Tf1, it is necessary to heat the secondary air injected from the air injection valve 8 by the electric heater 6 in addition to the exhaust discharged from the internal combustion engine 1. Absent. Therefore, the temperature of the filter 5 can be raised more efficiently to the first predetermined temperature Tf1 than when the exhaust gas and the secondary air are heated by the electric heater 6 while the secondary air is injected from the air injection valve 8. it can. Thereby, the electric power consumed by the electric heater 6 in order to raise the temperature of the filter 5 to the first predetermined temperature Tf1 can be reduced.

  Next, the flow of regeneration processing at the time of engine stop according to the present embodiment will be described with reference to FIG. FIG. 3 is a flowchart showing a flow of regeneration processing at the time of engine stop according to the present embodiment. This flow is stored in the ECU 10, and is executed by the ECU 10 when the ignition switch 11 is turned off, that is, when the operation stop condition of the internal combustion engine 1 is satisfied. When the operation stop condition of the internal combustion engine 1 is not satisfied during the execution of this flow (that is, when the ignition switch 11 is turned on), the execution of this flow is stopped in the middle.

  In this flow, the current PM accumulation amount in the filter 5 is read in S101. Note that the PM accumulation amount in the filter 5 is estimated by the ECU 10 executing a flow different from the main flow. Then, the estimated PM accumulation amount is stored in the ECU 10. In S101, the stored PM accumulation amount is read. Next, in S102, it is determined whether or not the PM accumulation amount Fpm in the filter 5 read in S101 is larger than the predetermined accumulation amount Fpm1 described above. If a negative determination is made in S102, that is, if the PM accumulation amount Fpm in the filter 5 when the ignition switch 11 is turned off is equal to or less than the predetermined accumulation amount Fpm1, PM is oxidized after the start of the next operation of the internal combustion engine 1. Even if it progresses rapidly, the possibility that the filter 5 will overheat is low. Therefore, in this case, the process of S111 is performed next. In S111, the fuel injection from the fuel injection valve 2 in the internal combustion engine 1 is stopped. In this case, ignition by the spark plug is also stopped. As a result, the operation of the internal combustion engine 1 is stopped. Thereafter, the execution of this flow is terminated.

  On the other hand, if an affirmative determination is made in S102, then the process of S103 is executed. In S103, fuel injection from the fuel injection valve 2 is continued. In this case, ignition by the spark plug is also continued. Thereby, the operation of the internal combustion engine 1 is continued. Note that the fuel injection amount from the fuel injection valve 2 when the operation of the internal combustion engine 1 is continued may be the same as the fuel injection amount during normal idling operation, or during normal idling operation. It may be less than the fuel injection amount. Next, in S104, the electric heater 6 is turned on. Thereby, the exhaust gas flowing into the filter 5 is heated by the electric heater 6. In the present embodiment, the “temperature increase control” according to the present invention is executed by executing the processes of S103 and S104.

Next, in S105, it is determined whether or not the temperature Tf of the filter 5 is equal to or higher than the first predetermined temperature Tf1. As described above, the first predetermined temperature Tf1 is the oxidizable temperature of PM, and the PM deposited on the filter 5 is oxidized by forming a PM oxidizable condition, and the filter heat is oxidized by the oxidation heat. Even if the temperature of 5 further rises, the temperature of the filter 5 is a temperature that falls below the upper limit value of the allowable range. In the present embodiment, the first predetermined temperature Tf1 corresponds to the “predetermined temperature” according to the present invention. If the result in S105 is negative, that is, if the temperature Tf of the filter 5 has not yet reached the first predetermined temperature Tf1, the processes of S103 and S104 are executed again. On the other hand, if a positive determination is made in S105, the process of S106 is then executed. In S106, the electric heater 6 is turned off. Thereby, heating of the exhaust gas flowing into the filter 5 by the electric heater 6 is stopped. Next, in S107, fuel injection from the fuel injection valve 2 is stopped. In this case, ignition by the spark plug is also stopped. As a result, the operation of the internal combustion engine 1 is stopped.

  Next, in S108, injection of secondary air from the air injection valve 8 is executed. Thereby, air is supplied to the filter 5. As a result, a PM oxidizable situation is formed. Therefore, PM deposited on the filter 5 is oxidized. In S108, the target injection set so that the amount of secondary air injection from the air injection valve 8 is supplied to the filter 5 in such an amount that the PM oxidizable state can be formed. Controlled by quantity. This target injection amount is predetermined based on experiments and the like. Next, in S109, it is determined whether or not the temperature of the filter 5 has become lower than the second predetermined temperature Tf2. As described above, the second predetermined temperature Tf2 is a temperature set as the lower limit value of the oxidizable temperature of PM. Note that, since the operation of the internal combustion engine 1 is stopped at the time when the process of S109 is executed, no exhaust gas flows through the exhaust passage 3, but the air injected from the air injection valve 8 is injected into the exhaust passage 3. Flowing. The temperature of the air that has flowed out of the filter 5 can be detected by the temperature sensor 7. The ECU 10 can estimate the temperature of the filter 5 based on the temperature of the air detected by the temperature sensor 7. If a negative determination is made in S109, that is, if the temperature Tf of the filter 5 has not yet decreased to the second predetermined temperature Tf2, the process of S108 is executed again.

  On the other hand, if an affirmative determination is made in S109, the process of S110 is then performed. In S110, the injection of secondary air from the air injection valve 8 is stopped. Thereafter, the execution of this flow is terminated.

  According to the above flow, when the PM accumulation amount Fpm in the filter 5 is larger than the predetermined accumulation amount Fpm1 when the operation of the internal combustion engine 1 is stopped, the electric power consumed by the electric heater 6 is reduced and accumulated in the filter 5. PM can be removed and reduced.

  In the present embodiment, the air supply device according to the present invention includes the air injection valve 8. Here, in this embodiment, secondary air is injected into the exhaust passage 3 upstream of the exhaust purification catalyst 4 by the air injection valve 8. As a result, when air is supplied to the filter 5, air heated by the heat of the exhaust purification catalyst 4 is supplied to the filter 5. Thereby, the temperature drop of the filter 5 due to heat being removed from the filter 5 by air can be reduced. In addition, when an exhaust system structure other than the exhaust purification catalyst 4 such as a turbocharger turbine is provided in the exhaust passage 3 upstream of the filter 5, the exhaust gas upstream of the exhaust system structure is provided. An air injection valve 8 may be provided in the passage 3. According to this, when the secondary air injected from the air injection valve 8 is supplied to the filter 5, the air can be warmed by the heat of the exhaust system structure. Therefore, the same effect as described above can be obtained. However, it is not essential in the present invention that the air injection valve is provided in the exhaust passage upstream of the exhaust purification catalyst and other exhaust system structures.

  Further, in the present embodiment, the temperature increase control unit according to the present invention is realized by the ECU 10 executing the processes of S102 to S107 in the flow shown in FIG. In the present embodiment, the ECU 10 executes the processes of S102, S105, and S108 in the flow shown in FIG. 3, thereby realizing the air supply control unit according to the present invention.

  Further, in the engine stop regeneration process according to the present embodiment, the operation of the internal combustion engine 1 and the heating of the exhaust gas by the electric heater 6 were stopped when the temperature of the filter 5 reached the first predetermined temperature. However, even after the time when the temperature of the filter 5 reaches the first predetermined temperature, the operation of the internal combustion engine 1 and the heating of the exhaust gas by the electric heater 6 may be continued. Even in this case, since the injection of the secondary air from the air injection valve 8 is executed after the time when the temperature of the filter 5 reaches the first predetermined temperature, the operation of the internal combustion engine 1 continues and the electric heater 6 is a part of the period during which the exhaust gas is heated by 6 (that is, the period during which the temperature raising control according to the present invention is executed) and the period during which the secondary air injection from the air injection valve 8 is executed. It will overlap. However, as described above, if the temperature of the filter 5 has reached the first predetermined temperature, the temperature of the filter 5 may not be increased any further due to the continued operation of the internal combustion engine 1 and the heating of the exhaust gas by the electric heater 6. When air is supplied to the filter 5 by executing the injection of secondary air from the air injection valve 8, a PM oxidizable state is formed, so that PM deposited on the filter 5 can be oxidized. Then, when the temperature of the filter 5 reaches the first predetermined temperature, the operation of the internal combustion engine 1 for raising the temperature of the filter 5 is stopped by stopping the operation of the internal combustion engine 1 and the heating of the exhaust gas by the electric heater 6. In addition, the operation period of the electric heater 6 can be minimized. Thereby, the fuel consumption and power consumption for heating up the filter 5 can be reduced as much as possible.

  In the engine stop regeneration process according to the present embodiment, the timing for stopping the operation of the internal combustion engine 1 (the timing for stopping the fuel injection from the fuel injection valve 2) and the timing for turning off the electric heater 6 are not necessarily the same. It may not be time. Further, in the regeneration process at the time of engine stop according to the present embodiment, the timing when the secondary air injection from the air injection valve 8 is stopped is not necessarily the second value in which the temperature of the filter 5 is the lower limit value of the oxidizable temperature of PM. It does not have to be when the predetermined temperature is reached. However, by injecting the secondary air from the air injection valve 8 until the temperature of the filter 5 reaches the second predetermined temperature, it is possible to form a PM oxidizable state for as long a period as possible. Therefore, PM deposited on the filter 5 can be reduced as much as possible.

  Further, the engine stop regeneration process according to the present embodiment is not limited to the case where the operation of the internal combustion engine 1 is stopped by turning off the ignition switch 11 by the user of the vehicle, and a predetermined automatic stop condition is satisfied. Then, it may be executed when automatic operation stop control is performed in which the operation of the internal combustion engine 1 is automatically stopped. In this case, when the automatic stop condition is satisfied, the above-described regeneration process flow when the engine is stopped is executed. In this case, the time when the automatic stop condition is satisfied corresponds to “when the operation stop condition of the internal combustion engine is satisfied” according to the present invention. In addition, when it is considered that one of the automatic stop conditions includes a PM accumulation amount condition that is a condition related to the PM accumulation amount in the filter 5, the present invention is performed when a condition other than the PM accumulation amount condition is satisfied. This corresponds to “when the operation stop condition of the internal combustion engine is satisfied”.

<Example 2>
Next, an embodiment in which the exhaust gas purification system for an internal combustion engine according to the present invention is applied to a hybrid system having an electric motor in addition to the internal combustion engine as a vehicle drive source will be described.

FIG. 1 is a diagram showing a schematic configuration of an exhaust system of an internal combustion engine according to the present embodiment. Here, only differences from the configuration according to the first embodiment will be described. In this embodiment, the internal combustion engine 1 is an internal combustion engine constituting the hybrid system 20. The hybrid system 20 includes an electric motor 12 serving as a drive source for the vehicle. Electric power is supplied to the electric motor 12 from a battery (not shown). The electric motor 12 is electrically connected to the ECU 10 and its operation is controlled by the ECU 10. Further, the hybrid system 20 is configured so that the internal combustion engine 1 can be rotated by the electric motor 12 even when the operation of the internal combustion engine 1 is stopped (that is, the crankshaft of the internal combustion engine 1 can be rotated). Yes.) In the present embodiment, the air injection valve 8 included in the configuration according to the first embodiment is not provided in the exhaust passage 3 of the internal combustion engine 1.

  In this embodiment, in addition to the case where the ignition switch 11 is turned off by the user of the vehicle as described in the first embodiment, the driving source of the vehicle is switched from the internal combustion engine 1 to the electric motor 12 by the ECU 10. Then, the operation of the internal combustion engine 1 is stopped. In other words, in this embodiment, even when the condition for selecting the electric motor 12 as the vehicle drive source is satisfied, the operation stop condition for the internal combustion engine 1 is satisfied.

  Also in the present embodiment, when the operation stop condition of the internal combustion engine 1 is satisfied, if the PM accumulation amount in the filter 5 is larger than the predetermined accumulation amount, the regeneration process at the time of engine stop is executed. However, as described above, in this embodiment, no air injection valve that injects air into the exhaust passage of the internal combustion engine 1 is provided. Therefore, in the engine stop regeneration process according to the present embodiment, the method of supplying air to the filter 5 is different from the engine stop regeneration process according to the first embodiment.

  Even in the engine stop regeneration process according to the present embodiment, the operation of the internal combustion engine 1 is not immediately stopped even if the operation stop condition of the internal combustion engine 1 is satisfied, and the operation of the internal combustion engine 1 is continued and the electric heater 6 is used. By heating the exhaust, the temperature of the filter 5 is raised to the first predetermined temperature Tf1. Further, when the temperature of the filter 5 reaches the first predetermined temperature Tf1, the fuel injection from the fuel injection valve 2 is stopped and the operation of the internal combustion engine 1 is stopped. Then, after the temperature of the filter 5 reaches the first predetermined temperature Tf1, the internal combustion engine 1 is rotated by the electric motor 12 in a state where the operation of the internal combustion engine 1 is stopped (that is, the crankshaft of the internal combustion engine is rotated). .) As a result, air flows into the internal combustion engine 1 through the intake passage, and the air is discharged from the internal combustion engine 1 to the exhaust passage 3. Then, the air discharged from the internal combustion engine 1 to the exhaust passage 3 is supplied to the filter 5.

  Next, the flow of the regeneration process at the time of engine stop according to the present embodiment will be described with reference to FIG. FIG. 5 is a flowchart showing a flow of regeneration processing at the time of engine stop according to the present embodiment. This flow is stored in the ECU 10, and when the ignition switch 11 is turned off, or when the condition for selecting the electric motor 12 as the vehicle drive source is satisfied, that is, the operation stop condition of the internal combustion engine 1 Is executed by the ECU 10. Further, when the operation stop condition of the internal combustion engine 1 is not satisfied during the execution of this flow (that is, when the ignition switch 11 is turned on, or when the internal combustion engine 1 is selected as a vehicle drive source) When the above is established, the execution of this flow is stopped halfway. Note that among the steps in this flow, steps that execute the same processes as the steps in the flow shown in FIG. 3 are given the same reference numerals, and descriptions thereof are omitted.

  In this flow, when the fuel injection from the fuel injection valve 2 is stopped in S107 and the operation of the internal combustion engine 1 is stopped, the process of S208 is executed next. In S208, the internal combustion engine 1 is rotated by the electric motor 12 in a state where the operation of the internal combustion engine 1 is stopped. Thereby, air is supplied to the filter 5. As a result, a PM oxidizable situation is formed. Therefore, PM deposited on the filter 5 is oxidized. In S208, the engine rotation speed of the internal combustion engine 1 becomes a target rotation speed that is set so that an amount of air that can form a PM oxidizable state is supplied to the filter 5. The electric motor 12 is controlled. This target rotation speed is determined in advance based on experiments and the like.

  Also, in this flow, when an affirmative determination is made in S109, that is, when the temperature Tf of the filter 5 has decreased to the second predetermined temperature Tf2, the process of S210 is executed. In S210, the rotation of the internal combustion engine 1 by the electric motor 12 is stopped. Thereafter, the execution of this flow is terminated.

  According to the engine stop regeneration process according to the present embodiment, when the operation of the internal combustion engine 1 is stopped, the PM accumulation amount Fpm in the filter 5 is equal to the predetermined accumulation amount Fpm1 as in the engine stop regeneration process according to the first embodiment. In the case of more, PM accumulated on the filter 5 can be removed and reduced while reducing the power consumed by the electric heater 6. Moreover, according to the structure which concerns on a present Example, it is possible to supply air to the filter 5 without providing the apparatus for supplying secondary air like the air injection valve 8 which concerns on Example 1 separately. Become.

  In the present embodiment, the air supply device according to the present invention includes the electric motor 12. However, in the present invention, the electric motor for rotating the internal combustion engine in a state where the operation of the internal combustion engine is stopped does not necessarily have to be an electric motor serving as a vehicle drive source in the hybrid system. For example, a starter motor used when starting the internal combustion engine may be used as an electric motor for rotating the internal combustion engine in a state where the operation of the internal combustion engine is stopped in the present invention.

  In the present embodiment, the ECU 10 executes the processes of S102, S105, and S208 in the flow shown in FIG. 5, thereby realizing the air supply control unit according to the present invention.

  Further, unlike the first embodiment, in the engine stop regeneration process according to the present embodiment, the operation of the internal combustion engine 1 and the supply of air to the filter 5 cannot be executed at the same time. Therefore, in this embodiment, the operation of the internal combustion engine 1 is stopped when the temperature of the filter 5 reaches the first predetermined temperature, and the operation of the internal combustion engine 1 is not continued after that time.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Fuel injection valve 3 ... Exhaust passage 4 ... Exhaust purification catalyst 5 ... Filter 6 ... Electric heater 7 ... Temperature sensor 8 ... Air injection valve 10. ・ ECU
11 ・ ・ Ignition switch 12 ・ ・ Electric motor

Claims (5)

A filter provided in an exhaust passage of the internal combustion engine for collecting particulate matter in the exhaust; an electric heater for heating the exhaust flowing into the filter; and an air supply unit for supplying air to the filter. An exhaust purification system for an internal combustion engine,
An estimation unit that estimates the amount of particulate matter deposited in the filter;
If the accumulation amount of the particulate matter in the filter estimated by the estimation unit is larger than a predetermined accumulation amount when the operation stop condition of the internal combustion engine is satisfied, the operation of the internal combustion engine is continued and the electric heater The temperature of the filter is raised to a predetermined temperature that is an oxidizable temperature of the particulate matter by executing a temperature rise control for heating the exhaust gas, and the internal combustion engine is raised after the temperature of the filter is raised to the predetermined temperature. And a temperature rise control unit for stopping heating of the exhaust gas by the electric heater,
If the accumulation amount of the particulate matter in the filter estimated by the estimation unit is larger than the predetermined accumulation amount when the operation stop condition of the internal combustion engine is satisfied, the temperature increase control unit performs the temperature increase control And an air supply control unit that supplies air to the filter by the air supply unit after the temperature of the filter reaches the predetermined temperature. The predetermined accumulation amount is assumed that after the start of the next operation of the internal combustion engine, the temperature of the filter rapidly rises to the oxidizable temperature of the particulate matter so that an oxidizable situation is formed and the oxidation of the particulate matter proceeds rapidly. 2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the amount is such that the possibility that an excessive temperature rise of the filter is unlikely to occur is low. It said heating control unit, after the execution start of the temperature increase control, according to claim 1 the temperature of the filter stops the heating of the exhaust gas by operating and the electric heater of the internal combustion engine at the time reaches the predetermined temperature or 2 2. An exhaust gas purification system for an internal combustion engine according to 1. The air supply unit includes an air injection valve that injects secondary air into the exhaust passage upstream of the filter, and supplies air to the filter by injecting secondary air from the air injection valve. The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 3 . The air supply unit includes an electric motor that rotates the internal combustion engine, and supplies air to the filter by rotating the internal combustion engine by the electric motor in a state where the operation of the internal combustion engine is stopped. The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 3 .

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