JP2019199849A - Internal combustion engine control method and its control apparatus - Google Patents

Abstract

To force an oxidizing reaction of exhaust air using plasma without ushering in an increase in ventilation resistance in the exhaust channel.SOLUTION: A plasma generation device 11 is disposed in a secondary air introduction channel 8 that is connected to an exhaust channel 2. When cold-starting an internal combustion engine 1, a secondary air is introduced from the secondary air introduction channel 8, and plasma is generated by the plasma generation device 11 discharging into the secondary air. This makes it possible to dispose the plasma generation device 11 in an exhaust system without increasing ventilation resistance in the exhaust channel 2, suppressing fuel economy and output performance from deteriorating.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an internal combustion engine control method and an internal combustion engine control apparatus.

  For example, Patent Document 1 discloses an exhaust purification device in which a plasma generation device is provided in an exhaust passage. The plasma generator in Patent Document 1 is located on the upstream side of the oxidation catalyst in the exhaust passage, and generates a highly active exhaust gas excitation component in the exhaust by discharge when supplying secondary air to the exhaust passage. Therefore, in Patent Document 1, the DPF (filter for collecting PM) downstream of the oxidation catalyst is heated by urging the combustion of the unburned component with the oxidation catalyst by this highly active exhaust gas excitation component.

JP 2005-320880 A

  However, in Patent Document 1, since the plasma generator is disposed in the exhaust passage, there is a possibility that the ventilation resistance in the exhaust passage increases, and the fuel consumption and output performance deteriorate.

  The internal combustion engine of the present invention introduces secondary air from the secondary air introduction passage when the internal combustion engine starts at a low temperature, and discharges it into the secondary air by the plasma generator provided in the secondary air introduction passage. It is characterized by generating plasma.

  According to the present invention, since the plasma generator is disposed in the secondary air introduction passage, an increase in ventilation resistance in the exhaust passage is suppressed, and deterioration of fuel consumption and output performance can be suppressed.

BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows one Example of the internal combustion engine to which control which concerns on this invention is applied. The timing chart explaining the time of the low temperature start of the internal combustion engine in 1st Example. The flowchart which shows the flow of control in 1st Example. The timing chart explaining the time of the low temperature start of the internal combustion engine in 2nd Example. The flowchart which shows the flow of control in 2nd Example.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an explanatory view showing an embodiment of an internal combustion engine 1 to which the control according to the present invention is applied, and is an explanatory view schematically showing an outline of an exhaust system of the internal combustion engine 1. The internal combustion engine 1 is, for example, a spark ignition gasoline engine, and performs combustion mainly at a stoichiometric air fuel ratio (stoichiometric).

  The internal combustion engine 1 is mounted on a vehicle such as an automobile as a drive source.

  The exhaust passage 2 of the internal combustion engine 1 is provided with a three-way catalyst 3 as a catalyst and a GPF (Gasoline Particulate Filter) 4 as a filter in series. The GPF 4 is disposed on the downstream side of the three-way catalyst 3.

  In addition, although illustration is abbreviate | omitted, the intake passage (not shown) is connected to the internal combustion engine 1, and intake air is supplied.

  The three-way catalyst 3 purifies the exhaust gas discharged from the internal combustion engine 1. When the excess air ratio is approximately “1”, that is, when the exhaust air / fuel ratio becomes approximately the stoichiometric air / fuel ratio, the three-way catalyst 3 The purification rates of the three components of HC, CO, and NOx are all increased.

  The GPF 4 collects PM which is exhaust particulates (Particulate Matter) in the exhaust discharged from the internal combustion engine 1.

  As GPF4, for example, a filter having a wall flow honeycomb structure (so-called plugged type) in which a large number of honeycomb-shaped fine passages are formed in a filter material such as cordierite and the ends thereof are alternately closed is used. It is used. The GPF 4 may support the same type of catalyst as the three-way catalyst 3.

  Brownian motion greatly affects the collection efficiency of exhaust particulates of GPF4 in a gasoline engine. The GPF collection efficiency by the Brownian motion is highly dependent on the temperature of the GPF 4, the particle diameter of the exhaust particulates, and the space velocity of the exhaust gas flowing through the GPF 4.

  That is, the GPF collection efficiency increases as the temperature of the GPF 4 increases. The GPF collection efficiency increases as the particle size of the exhaust particulates decreases. The GPF collection efficiency increases as the space velocity of the exhaust gas flowing through the GPF 4, in other words, the gas flow rate decreases.

  The internal combustion engine 1 also has a turbocharger 5 as a supercharger provided coaxially with a compressor (not shown) provided in the intake passage and a turbine 6 provided in the exhaust passage 2. ing. The turbine 6 is disposed upstream of the three-way catalyst 3.

  Connected to the exhaust passage 2 is a secondary air introduction passage 8 for supplying secondary air fed from the air pump 7.

  By driving the air pump 7, secondary air is supplied (introduced) from the secondary air introduction passage 8 to the exhaust passage 2. In the air pump 7, the amount of secondary air supplied to the exhaust passage 2 is controlled by a control signal from a control unit 9 as a control unit.

  The secondary air introduction passage 8 is connected to the exhaust passage 2 at a position upstream of the three-way catalyst 3. In other words, the secondary air introduction passage 8 is connected to the exhaust passage 2 at a position upstream of the turbine 6.

  In the first embodiment, the secondary air introduction passage 8 is a branch portion 8a branched downstream to the number of cylinders of the internal combustion engine. The branch portion 8a of the secondary air introduction passage 8 is connected to each exhaust port 10 in the cylinder head. The secondary air may be supplied to the exhaust passage 2 from a position after the exhaust from the cylinders merges.

  The secondary air introduction passage 8 is provided with a plasma generator 11 to which electric power is supplied from a power supply unit (not shown). The plasma generator 11 corresponds to a plasma generator, and is disposed on the upstream side of the branch portion 8 a of the secondary air introduction passage 8.

  The plasma generator 11 has an electrode (not shown) that discharges into the secondary air introduction passage 8 to generate plasma. The plasma generator 11 generates plasma in the secondary air introduction passage 8 to excite active species having high activity in the secondary air and activate the secondary air supplied to the exhaust passage 2.

  In the plasma generator 11, the generation of plasma is controlled by a control signal from a control unit 9 as a control unit.

  The control unit 9 includes a crank angle sensor 12 that can detect the engine speed together with the crank angle of the crankshaft, an accelerator opening sensor 13 that detects the amount of depression of an accelerator pedal (not shown), and an upstream side of the three-way catalyst 3. The air-fuel ratio sensor 14 for detecting the exhaust air-fuel ratio at the (inlet), the oxygen sensor 15 for detecting the exhaust air-fuel ratio at the downstream side (outlet) of the three-way catalyst 3, and the exhaust temperature at the upstream side (inlet) of the three-way catalyst 3 Three-way catalyst inlet temperature sensor 16 to detect, three-way catalyst outlet temperature sensor 17 to detect the exhaust temperature on the downstream side (outlet) of the three-way catalyst 3, GPF inlet temperature to detect the exhaust temperature on the upstream side (inlet) of GPF4 Detection signals of sensors such as the sensor 18 and the GPF outlet temperature sensor 19 for detecting the exhaust temperature downstream (outlet) of the GPF 4 are input.

  The air-fuel ratio sensor 14 is a so-called wide-area air-fuel ratio sensor having a substantially linear output characteristic corresponding to the exhaust air-fuel ratio. The oxygen sensor 15 is a sensor that detects only the rich / lean of the air-fuel ratio by changing the output voltage ON / OFF (rich, lean) in a narrow range near the theoretical air-fuel ratio.

  The control unit 9 calculates the required load (engine load) of the internal combustion engine 1 using the detection value of the accelerator opening sensor 13.

  Based on these detection signals, the control unit 9 controls the ignition timing, the air-fuel ratio, the engine speed, etc. of the internal combustion engine 1, the control of the plasma generator 11 and the air pump 7, and the like.

  The control unit 9 calculates the catalyst temperature (the bed temperature of the three-way catalyst 3), which is the temperature of the three-way catalyst 3, using the detected values of the three-way catalyst inlet temperature sensor 16 and the three-way catalyst outlet temperature sensor 17. Yes. The temperature of the three-way catalyst 3 may be corrected and calculated using the detection values of the air-fuel ratio sensor 14 and the oxygen sensor 15. Further, as the temperature of the three-way catalyst 3, a temperature obtained by directly detecting the bed temperature of the three-way catalyst 3 with a temperature sensor may be used.

  Further, the control unit 9 calculates the filter temperature of the GPF 4 (the bed temperature of the GPF 4), which is the temperature of the GPF 4, using the detection values of the GPF inlet temperature sensor 18 and the GPF outlet temperature sensor 19. Note that the temperature of the GPF 4 may be corrected and calculated using the detection values of the air-fuel ratio sensor 14 and the oxygen sensor 15. In addition, as the temperature of the GPF 4, a temperature obtained by directly detecting the bed temperature of the GPF 4 with a temperature sensor may be used.

  In the first embodiment described above, the plasma generator 11 is provided in the secondary air introduction passage 8 connected to the exhaust passage 2.

  Therefore, in the first embodiment described above, the plasma generator 11 can be arranged in the exhaust system without increasing the ventilation resistance in the exhaust passage 2. That is, in the first embodiment described above, the plasma generator 11 can be arranged in the exhaust system without causing deterioration of fuel consumption and output performance.

  Further, in the first embodiment described above, the influence of heat from the exhaust on the plasma generator 11 is reduced, so that the occurrence of a failure of the plasma generator 11 caused by the heat of the exhaust can be suppressed.

  Furthermore, in the first embodiment described above, since moisture in the exhaust gas is less likely to adhere to the plasma generator 11, the occurrence of a failure in the plasma generator 11 caused by the moisture in the exhaust gas is suppressed. be able to.

  For example, in a state where the temperature of the three-way catalyst 3 and GPF 4 disposed in the exhaust passage 2 is low and not activated, such as when the internal combustion engine 1 is started at a low temperature (at the time of cold start), the three-way catalyst 3 or The exhaust performance deteriorates until the temperature of the GPF 4 rises and is activated.

  Therefore, in the first embodiment described above, the temperature of the three-way catalyst 3 and the GPF 4 disposed in the exhaust passage 2 is low and not activated, such as when the internal combustion engine 1 is started at a low temperature (at the time of cold start). Sometimes, the air pump 7 is driven and the plasma generator 11 is activated to generate plasma in the secondary air introduction passage 8.

  Here, the plasma generator 11 generates the plasma until it is determined that the exhaust gas oxidation reaction is sufficiently obtained by the supply of the secondary air without generating the plasma.

  Specifically, the oxidation reaction of HC in the exhaust by supplying secondary air at a timing when a predetermined time has elapsed from the start of low-temperature start of the internal combustion engine 1 (start of cold start) without generating plasma. Is obtained, that is, a state in which the secondary air post-oxidation activity determination is “OK”. If the secondary air post-oxidation determination is “OK”, it can be said that the reaction between the secondary air and the HC in the exhaust gas is sufficiently obtained. When the secondary air post-oxidation determination is not “OK”, the secondary air post-oxidation determination is “NG”.

  After the start of low-temperature start of the internal combustion engine 1 (after the start of cold start), the secondary air is not generated even when plasma is generated at a timing when the exhaust gas temperature is equal to or higher than a predetermined exhaust gas temperature threshold (predetermined temperature). You may determine with the state in which the oxidation reaction of HC in exhaust_gas | exhaustion is fully obtained by supply, ie, the state in which secondary air post-oxidation activity determination is "OK".

  In the first embodiment, since secondary air activated by plasma at the time of low temperature start is introduced into the exhaust passage 2, the exhaust oxidation reaction is further promoted in the exhaust passage 2, the three-way catalyst 3 and the GPF 4, It is possible to reduce the HC in the exhaust from a low temperature and to activate the three-way catalyst 3 and the GPF 4 at an early stage.

  Further, the secondary air post-oxidation activity determination becomes “OK” several seconds after the internal combustion engine 1 is started at a low temperature (cold start). Therefore, when the internal combustion engine 1 is started at a low temperature, the amount of power consumed by the plasma generator 11 (power consumption) after starting the internal combustion engine 1 can be suppressed.

  FIG. 2 is a timing chart for explaining the low temperature start (cold start) of the internal combustion engine 1 in the first embodiment described above.

  The exhaust temperature indicated by a solid line in FIG. 2 indicates the exhaust temperature on the inlet side of the three-way catalyst 3 when plasma is generated in the secondary air at a low temperature start. The exhaust temperature indicated by the alternate long and short dash line in FIG. 2 indicates the exhaust temperature on the inlet side of the three-way catalyst 3 when plasma is not generated in the secondary air at the low temperature start.

  By generating plasma in the secondary air, the oxidation reaction of the exhaust is further promoted, and the rise of the exhaust temperature is promoted.

  Time t0 in FIG. 2 is a timing at which cranking is started. The air pump 7 is driven when cranking is started. That is, the supply of secondary air to the exhaust passage 2 is started from the timing of time t0 in FIG. Moreover, the plasma generator 11 starts discharge into the secondary air introduction passage 8 when cranking is started. That is, plasma is generated in the secondary air introduction passage 8 from the timing of time t0 in FIG.

  Time t1 in FIG. 2 is the timing of the first explosion. Control is performed so that the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio (stoichiometry) from the timing of time t1 in FIG.

  Time t2 in FIG. 2 is a timing at which a predetermined time has elapsed since the start of the internal combustion engine 1, and is a timing at which the above-described secondary air post-oxidation activity determination is determined to be “OK”. Specifically, for example, it is a timing at which a predetermined time has elapsed from time t0. The timing at which a predetermined time has elapsed from time t1 may be determined as the timing at which the above-described secondary air post-oxidation activity determination is determined to be “OK”. The plasma generator 11 ends the discharge into the secondary air introduction passage 8 at the timing of time t2 in FIG. That is, plasma discharge (plasma generation) ends at the timing of time t2 in FIG.

  Time t3 in FIG. 2 is timing when the three-way catalyst 3 is activated. That is, time t3 is a timing at which the temperature of the three-way catalyst 3 becomes equal to or higher than a predetermined catalyst activation temperature set in advance. The three-way catalyst activity determination is “OK” when the temperature of the three-way catalyst 3 is equal to or higher than the catalyst activation temperature, and “NG” when the temperature of the three-way catalyst 3 is lower than the catalyst activation temperature. The air pump 7 stops when the temperature of the three-way catalyst 3 becomes equal to or higher than the catalyst activation temperature. That is, the supply of secondary air to the exhaust passage 2 stops at the timing of time t3 in FIG. Further, the air-fuel ratio is controlled so as to become the stoichiometric air-fuel ratio (stoichiometric) from the timing of time t3 in FIG.

  FIG. 3 is a flowchart showing the flow of control in the first embodiment.

  In step S1, it is determined whether or not the internal combustion engine 1 is cold start (cold start). If the internal combustion engine 1 is at a low temperature start (cold start) in step S1, the process proceeds to step S2. In step S1, if the internal combustion engine 1 is not cold start (cold start), the current routine is terminated.

  In step S <b> 2, the air pump 7 is driven to supply secondary air to the exhaust passage 2.

  In step S <b> 3, plasma is generated in the secondary air introduction passage 8 by the plasma generator 11.

  In step S4, it is determined whether or not an exhaust oxidation reaction can be sufficiently obtained with only secondary air without generating plasma. In other words, in step S4, it is determined whether or not the exhaust oxidation reaction is activated. If it is determined in step S4 that the exhaust oxidation reaction is activated, the process proceeds to step S5. If it is determined in step S4 that the exhaust oxidation reaction is not activated, the process proceeds to step S2.

  In step S5, the plasma generation by the plasma generator 11 is terminated.

  In step S6, it is determined whether or not the three-way catalyst 3 is activated. If it is determined in step S6 that the three-way catalyst 3 is activated, the process proceeds to step S7.

  In step S7, the air pump 7 is stopped and the supply of secondary air to the exhaust passage 2 is terminated.

  The first embodiment described above relates to a method for controlling the internal combustion engine 1 and a control device for the internal combustion engine 1.

  Hereinafter, other embodiments of the present invention will be described. However, the same constituent elements as those of the first embodiment described above are denoted by the same reference numerals, and redundant description will be omitted.

  A control method for the internal combustion engine 1 and a control device for the internal combustion engine 1 in the second embodiment will be described.

  The second embodiment has substantially the same configuration as the first embodiment described above, but after it is determined that an exhaust oxidation reaction can be obtained by supplying secondary air without generating plasma. When the temperature of the GPF 4 is equal to or higher than the predetermined GPF activation temperature and the three-way catalyst 3 is not activated, the plasma is generated in the secondary air by the plasma generator 11 to generate plasma. The GPF activation temperature is a lower limit value of the temperature at which the GPF 4 is activated, and is a lower limit value of a temperature range in which the GPF 4 exhibits the intended exhaust treatment performance. The restarted plasma generation ends when the three-way catalyst 3 is activated.

  By generating plasma in the secondary air and exciting active species having high activity in the secondary air, the secondary air supplied to the exhaust passage 2 is activated. By activating the secondary air, the particle size of the exhaust particulates in the exhaust is reduced, and the collection efficiency of the exhaust particulates in the GPF 4 is increased.

  However, in the situation where the temperature of the GPF 4 is low and the GPF 4 is not activated, the collection efficiency of the GPF 4 is deteriorated as described above, and thus there is a possibility that power is wasted even if plasma is generated.

  Therefore, in this second embodiment, GPF 4 is activated and three-way catalyst 3 is activated even in the state where a sufficient oxidation reaction of HC in the exhaust gas can be obtained by supplying secondary air without generating plasma. If not, the plasma generation is resumed.

  Therefore, in the second embodiment, the exhaust particulate collection efficiency of the GPF 4 can be improved more efficiently when the internal combustion engine 1 is started at a low temperature (at the time of cold start).

  In the second embodiment, substantially the same operational effects as those of the first embodiment described above can be obtained.

  FIG. 4 is a timing chart for explaining the low temperature start (cold start) of the internal combustion engine 1 in the second embodiment described above.

  The exhaust temperature indicated by a solid line in FIG. 4 indicates the exhaust temperature on the inlet side of the three-way catalyst 3 when plasma is generated in the secondary air at a low temperature start. The exhaust temperature indicated by the alternate long and short dash line in FIG. 4 indicates the exhaust temperature on the inlet side of the three-way catalyst 3 when plasma is not generated in the secondary air at the low temperature start.

  By generating plasma in the secondary air, the oxidation reaction of the exhaust is further promoted, and the rise of the exhaust temperature is promoted.

  Time t0 in FIG. 4 is timing when cranking is started. The air pump 7 is driven when cranking is started. That is, the supply of secondary air to the exhaust passage 2 is started from the timing of time t0 in FIG. Moreover, the plasma generator 11 starts discharge into the secondary air introduction passage 8 when cranking is started. That is, plasma is generated in the secondary air introduction passage 8 from the timing of time t0 in FIG.

  Time t1 in FIG. 4 is the timing of the first explosion. Control is performed so that the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio (stoichiometric) from the timing of time t1 in FIG.

  Time t2 in FIG. 4 is a timing at which a predetermined time has elapsed since the start of the internal combustion engine 1, and is a timing at which the above-described secondary air post-oxidation activity determination is determined to be “OK”. Specifically, for example, it is a timing at which a predetermined time has elapsed from time t0. The timing at which a predetermined time has elapsed from time t1 may be determined as the timing at which the above-described secondary air post-oxidation activity determination is determined to be “OK”. The plasma generator 11 ends the discharge into the secondary air introduction passage 8 at the timing of time t2 in FIG. That is, plasma discharge (plasma generation) ends at the timing of time t2 in FIG.

  Time t3 in FIG. 4 is a timing at which the GPF 4 is activated when the temperature of the GPF 4 becomes equal to or higher than a predetermined GPF activation temperature. At this time (at time t3 in FIG. 4), since the three-way catalyst 3 is not activated, the plasma generator 11 resumes the discharge into the secondary air introduction passage 8.

  Time t4 in FIG. 4 is timing when the three-way catalyst 3 is activated. That is, time t3 is a timing at which the temperature of the three-way catalyst 3 becomes equal to or higher than a predetermined catalyst activation temperature set in advance. The air pump 7 stops when the temperature of the three-way catalyst 3 becomes equal to or higher than a predetermined catalyst activation temperature set in advance. That is, the supply of secondary air to the exhaust passage 2 stops at the timing of time t4 in FIG. Further, the air-fuel ratio is controlled so as to become the stoichiometric air-fuel ratio (stoichiometric) from the timing of time t4 in FIG.

  FIG. 5 is a flowchart showing the flow of control in the second embodiment.

  In step S21, it is determined whether or not the internal combustion engine 1 is at a low temperature start (cold start). In step S21, when the internal combustion engine 1 is at a low temperature start (cold start), the process proceeds to step S22. In step S21, if the internal combustion engine 1 is not cold start (cold start), the current routine is terminated.

  In step S <b> 22, the air pump 7 is driven to supply secondary air to the exhaust passage 2.

  In step S <b> 23, plasma is generated in the secondary air introduction passage 8 by the plasma generator 11.

  In step S24, it is determined whether or not an exhaust oxidation reaction can be sufficiently obtained with only secondary air without generating plasma. In other words, in step S24, it is determined whether or not the exhaust oxidation reaction is activated. If it is determined in step S24 that the exhaust oxidation reaction is activated, the process proceeds to step S25. If it is determined in step S24 that the exhaust oxidation reaction is not activated, the process proceeds to step S22.

  In step S25, the plasma generation by the plasma generator 11 is terminated.

  In step S26, it is determined whether or not the three-way catalyst 3 is activated. If it is determined in step S6 that the three-way catalyst 3 is activated, the process proceeds to step S27. If it is determined in step S26 that the three-way catalyst 3 is not activated, the process proceeds to step S28.

  In step S27, the air pump 7 is stopped and the supply of secondary air to the exhaust passage 2 is terminated.

  In step S28, it is determined whether GPF4 is activated. If it is determined in step S28 that GPF4 is activated, the process proceeds to step S29. If it is determined in step S28 that GPF4 is not activated, the process proceeds to step S26.

  In step S 29, plasma is generated in the secondary air introduction passage 8 by the plasma generator 11.

  In step S30, it is determined whether or not the three-way catalyst 3 is activated. If it is determined in step S30 that the three-way catalyst 3 is activated, the process proceeds to step S31. If it is determined in step S30 that the three-way catalyst 3 is not activated, the process proceeds to step S29.

  In step S31, the plasma generation by the plasma generator 11 is finished. From step S31, the process proceeds to step S27.

  In each of the embodiments described above, plasma may be generated in the secondary air introduction passage 8 by the plasma generator 11 when the internal combustion engine 1 is temporarily stopped.

  Specifically, for example, when the internal combustion engine 1 is stopped and the motor travels in a hybrid vehicle, or when the internal combustion engine 1 is idle-stopped, when the internal combustion engine 1 is stopped, the plasma generator 11 is operated for a predetermined time. In this case, plasma may be generated.

  In this way, when the internal combustion engine 1 is temporarily stopped, plasma is generated by the plasma generator 11, whereby high-concentration active species can be mixed into the exhaust gas simultaneously with the start of the internal combustion engine 1. The purification rate can be further improved immediately after the restart of the internal combustion engine.

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Exhaust passage 3 ... Three-way catalyst 4 ... GPF
DESCRIPTION OF SYMBOLS 5 ... Turbocharger 6 ... Turbine 7 ... Air pump 8 ... Secondary air introduction passage 8a ... Branch part 9 ... Control unit 10 ... Exhaust port 11 ... Plasma generator 12 ... Crank angle sensor 13 ... Accelerator opening sensor 14 ... Empty Fuel ratio sensor 15 ... oxygen sensor 16 ... three-way catalyst inlet temperature sensor 17 ... three-way catalyst outlet temperature sensor 18 ... GPF inlet temperature sensor 19 ... GPF outlet temperature sensor

Claims (9)

In a control method for an internal combustion engine capable of introducing secondary air into an exhaust passage connected to the internal combustion engine via a secondary air introduction passage,
During the cold start of the internal combustion engine, the secondary air is introduced from the secondary air introduction passage, and the plasma generator provided in the secondary air introduction passage discharges the secondary air to generate plasma. A control method of an internal combustion engine characterized by the above.   2. The plasma generation by the plasma generator is terminated when it is determined that an oxidation reaction of exhaust gas can be obtained by supplying secondary air without generating plasma. Control method for an internal combustion engine.   The exhaust gas is judged to be in a state in which an oxidation reaction of exhaust gas can be obtained by supplying secondary air without generating plasma when the exhaust gas temperature becomes equal to or higher than a predetermined temperature after starting the cold start of the internal combustion engine. 3. A method for controlling an internal combustion engine according to 2.   3. The internal combustion engine according to claim 2, wherein when a predetermined time elapses from the start of the low-temperature start of the internal combustion engine, it is determined that the oxidation reaction of the exhaust gas can be obtained by supplying the secondary air without generating plasma. How to control the engine. The exhaust passage is provided with a catalyst that purifies the exhaust discharged from the internal combustion engine, and a filter that is located downstream of the catalyst and collects exhaust particulates in the exhaust discharged from the internal combustion engine.
5. The control method for an internal combustion engine according to claim 2, wherein the secondary air introduction passage is connected to the exhaust passage on the upstream side of the catalyst.   After determining that the exhaust oxidation reaction can be obtained by supplying the secondary air without generating plasma, the temperature of the filter becomes a predetermined temperature or higher, and the catalyst is not activated, 6. The method for controlling an internal combustion engine according to claim 5, wherein the plasma generator generates plasma by discharging into secondary air.   7. The method for controlling an internal combustion engine according to claim 6, wherein when it is determined that the catalyst is activated, the plasma generation by the plasma generator is terminated.   8. The method of controlling an internal combustion engine according to claim 1, wherein when the internal combustion engine is temporarily stopped, the plasma generator generates plasma. A secondary air introduction passage capable of introducing secondary air into an exhaust passage connected to the internal combustion engine;
A plasma generator that is provided in the secondary air introduction passage and discharges into the secondary air flowing through the secondary air introduction passage to generate plasma;
A control unit capable of controlling the amount of secondary air supplied to the exhaust passage and the plasma generator;
The control unit of the internal combustion engine, wherein when the internal combustion engine is started at a low temperature, secondary air is supplied to the exhaust passage and plasma is generated in the secondary air by the plasma generator.

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