JP6642220B2 - Exhaust gas purification device - Google Patents

Description

  The present invention relates to an exhaust gas purification device including a catalyst for purifying exhaust gas from a spark ignition type internal combustion engine.

  2. Description of the Related Art An internal combustion engine mounted on a vehicle or the like is provided with a catalyst for purifying exhaust gas, and the catalyst exerts a desired purifying action when in an active state. Therefore, it is required that the exhaust gas be passed through the catalyst when the temperature of the catalyst is higher than the activation temperature.

  DESCRIPTION OF RELATED ART Conventionally, what was described in patent document 1 and 2 is known as an exhaust gas purification apparatus which purifies exhaust gas with a catalyst. In Patent Documents 1 and 2, when the temperature of the catalyst after the stop of the internal combustion engine is high, the inside of the cylinder is scavenged with secondary air. As a result, in the devices described in Patent Literatures 1 and 2, it is possible to prevent hydrocarbons (HC) from remaining in the cylinder and the exhaust path and being discharged without being purified at the next cold start.

  Further, when the catalyst described in Patent Documents 1 and 2 uses palladium, which has a high low-temperature activity in an oxidized state, as the catalyst, the palladium is oxidized with the scavenging by the secondary air. Can improve the purification ability.

JP 2003-90215 A JP-A-11-210520

  In recent years, rhodium, which is more excellent in exhaust gas purification ability, has been used as a catalyst together with palladium in accordance with stricter exhaust gas regulations. This rhodium has a characteristic that, contrary to palladium, its low-temperature activity in an oxidized state is low.

  However, those described in Patent Documents 1 and 2 show that when the internal combustion engine is cold-started with the catalyst oxidized, the decrease in the low-temperature activity of rhodium exceeds the increase in the low-temperature activity of palladium, and the catalyst as a whole Low temperature activity. For this reason, it has been required to activate the catalyst at an early stage when the internal combustion engine is cold started.

  The present invention has been made in view of the above circumstances, and has as its object to provide an exhaust gas purification device that can activate a catalyst at an early stage when a cold start of an internal combustion engine is performed.

The present invention is an exhaust purification device including a catalyst for purifying exhaust gas from a spark ignition type internal combustion engine, and a control unit for controlling the internal combustion engine, wherein the control unit is configured to stop the internal combustion engine when stopped. Performing an oxidation control to control the internal combustion engine to oxidize the catalyst, and at the next cold start of the internal combustion engine, the internal combustion engine to supply the unburned mixture generated by the ignition cut to the catalyst. It is characterized in that HC concentration control is performed.

  ADVANTAGE OF THE INVENTION According to this invention, a catalyst can be activated early at the time of the cold start of an internal combustion engine.

FIG. 1 is a configuration diagram of an exhaust gas purification device according to an embodiment of the present invention. FIG. 2 is a flowchart illustrating a flow of an operation including oxidation control of the exhaust gas purification device according to the embodiment of the present invention. FIG. 3 is a flowchart illustrating an operation flow including HC concentration control of the exhaust gas purification apparatus according to the embodiment of the present invention. FIG. 4 is a timing chart illustrating a flow of an operation including HC concentration control of the exhaust emission control device according to the embodiment of the present invention. FIG. 5 is an enlarged view of the period of the predetermined time Time HCFC in the timing chart of FIG. FIG. 6 is a diagram illustrating an effect of the exhaust gas purification device according to the embodiment of the present invention, and is a diagram illustrating an improvement in the purification rate of the catalyst during a warm-up process. FIG. 7 is a diagram illustrating an effect of the exhaust gas purification device according to the embodiment of the present invention, and is a diagram illustrating a decrease in harmful components.

  Hereinafter, an embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows an internal combustion engine 10 and an ECM (Engine Control Module) 30 as a control unit for electrically controlling the internal combustion engine 10.

  In FIG. 1, an internal combustion engine 10 is composed of, for example, an in-line four-cylinder gasoline engine that operates using gasoline as fuel. The internal combustion engine 10 includes a cylinder and a piston (not shown), and performs a series of four strokes including an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke while the piston makes two reciprocations in the cylinder. It is a gasoline engine.

  Note that the number of cylinders of the internal combustion engine 10 is not limited to four cylinders. Further, the internal combustion engine 10 is not limited to a gasoline engine, and may be any internal combustion engine having an igniter for forcibly burning a mixture of fuel and air.

  The internal combustion engine 10 includes an injector (not shown), and the injector injects fuel into an intake port or a combustion chamber (not shown). The injector is electrically connected to the ECM 30, and the fuel injection amount and the fuel injection timing are adjusted by the ECM 30.

  The internal combustion engine 10 includes an ignition coil 11 and a spark plug 17. The ignition plug 17 is electrically connected to the ECM 30 via the ignition coil 11. The ignition coil 11 boosts the ignition signal received from the ECM 30 to a high voltage and supplies it to the ignition plug 17.

  The spark plug 17 ignites the air-fuel mixture by generating a spark when discharging high-voltage electricity. The ignition timing and the discharge energy amount of the ignition plug 17 are controlled by the ECM 30. Thus, the internal combustion engine 10 is a spark ignition type internal combustion engine.

  The internal combustion engine 10 includes an exhaust pipe 13, and an internal space of the exhaust pipe 13 forms an exhaust passage 13 </ b> A through which exhaust gas generated in a combustion chamber of the internal combustion engine 10 passes.

  A catalyst 14 is provided in the exhaust passage 13A, and the catalyst 14 purifies exhaust gas from the internal combustion engine 10. Specifically, the catalyst 14 is formed of a three-way catalyst, and simultaneously reduces three kinds of harmful components of hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxide (NOx) in exhaust gas by reduction and oxidation. Purify.

  The catalyst 14 is composed of a RoPd catalyst in which rhodium (Ro) and palladium (Pd) are supported on a monolithic carrier such as a ceramic. Palladium has a property of improving its low-temperature activity (low-temperature activity) in an oxidized state.

  On the other hand, rhodium has a property that its low-temperature activity is reduced in an oxidized state. Rhodium is more expensive but more active than palladium. Here, the low temperature is a temperature corresponding to the catalyst temperature when the internal combustion engine 10 starts a cold operation. The cold start means starting from a state in which the internal combustion engine 10 is cooled to the same level as the outside air temperature. Note that, in addition to rhodium and palladium, platinum (Pt) may be further used for the catalyst 14.

  An exhaust gas temperature sensor 22 is provided upstream of the catalyst 14 in the exhaust passage 13A. The exhaust gas temperature sensor 22 detects the temperature of the exhaust gas passing through the exhaust passage 13A, and transmits a detection signal (exhaust gas temperature) to the ECM 30. In the present embodiment, the exhaust gas temperature sensor 22 is provided near the inlet of the catalyst 14.

  The catalyst 14 is provided with a catalyst temperature sensor 23, which detects the temperature of the catalyst 14 and transmits a detection signal (exhaust gas temperature) to the ECM 30.

  The internal combustion engine 10 includes an electric pump 19. The electric pump 19 communicates with the intake manifold 18 through a passage 20. Further, the electric pump 19 communicates with the vicinity of the inlet of the catalyst 14 in the exhaust passage 13 </ b> A through the passage 21.

  The electric pump 19 is electrically connected to the ECM 30 and is driven by a drive signal from the ECM 30 to supply the air in the intake manifold 18 as secondary air to the exhaust passage 13A near the inlet of the catalyst 14.

  The ECM 30 includes a microcomputer including a CPU, a RAM, a ROM, an input / output interface, and the like, and is configured to electrically control an operation state of the internal combustion engine 10. The ECM 30 is mounted on a vehicle (not shown) together with the internal combustion engine 10.

  The CPU uses the temporary storage function of the RAM and performs signal processing according to a program stored in the ROM in advance. Various control constants, various maps, and the like are stored in the ROM in advance.

  Various sensors including an exhaust gas temperature sensor 22 and a catalyst temperature sensor 23 are connected to the input side of the ECM 30.

  Various controlled objects including a spark plug 17, an injector, and a throttle valve are connected to the output side of the ECM 30.

  The ECM 30 controls the operation of the internal combustion engine 10 by controlling the fuel injection amount and fuel injection timing of the injector, the ignition timing of the ignition plug 17 and the throttle opening of the throttle valve based on the detection signals of various sensors. Control the state.

  In the present embodiment, the ECM 30 controls the internal combustion engine 10 such that the catalyst 14 is activated early when the internal combustion engine 10 starts cold operation. Specifically, the ECM 30 performs an oxidation control for controlling the internal combustion engine 10 to oxidize the catalyst 14 when the internal combustion engine 10 is stopped. Further, the ECM 30 performs HC concentration control for controlling the internal combustion engine 10 to supply the unburned air-fuel mixture to the catalyst 14 at the next cold start of the internal combustion engine 10. The ECM 30 constitutes a control unit in the present invention.

  The ECM 30 supplies secondary air to the catalyst 14 until the catalyst temperature of the catalyst 14 rises to a predetermined temperature or higher in order to oxidize the catalyst 14 in the oxidation control.

  The ECM 30 generates an unburned air-fuel mixture by intentional misfire due to ignition cut in the HC concentration control, and supplies the unburned air-fuel mixture to the catalyst 14. The ECM 30 advances the ignition timing at least immediately before the ignition cut. The ECM 30 supplies the unburned mixture set in stoichiometry to the catalyst 14 in the HC concentration control.

  The ECM 30 includes an oxidation control unit 31 and an HC concentration control unit 32. The oxidation control is performed by the oxidation control unit 31 of the ECM 30. The HC concentration control is performed by the HC concentration control unit 32 of the ECM 30.

  Next, an operation including an oxidation control performed by the ECM 30 will be described with reference to FIG. The operation in FIG. 2 is repeatedly executed at a predetermined short cycle.

  In FIG. 2, first, the ECM 30 determines whether or not “history after starting the internal combustion engine” is present (step S1). Here, the ECM 30 confirms whether or not there is a history of the internal combustion engine 10 being in a predetermined driving state (hereinafter, a history after the internal combustion engine is started). For example, the ECM 30 determines that there is a history after the start of the internal combustion engine when there is a history that the engine speed has become equal to or more than the predetermined speed, or when there is a history that the traveling distance has become equal to or more than the predetermined distance.

  If the determination in step S1 is NO (there is no history after the start of the internal combustion engine), the ECM 30 ends the current operation.

  If the determination in step S1 is YES (there is a history after the start of the internal combustion engine), the ECM 30 determines whether or not the ignition switch 24 (indicated as IG in the figure) has been switched from on to off (step S2). .

  If the determination in step S2 is NO (i.e., the ignition switch 24 remains ON), the ECM 30 ends the current operation.

  When the determination in step S2 is YES (when the ignition switch 24 is turned off), the ECM 30 drives the electric pump 19 to start supplying secondary air to the catalyst 14 (step S3). When the ignition switch 24 is turned off, the internal combustion engine 10 stops.

  After step S3, the ECM 30 determines whether the catalyst temperature has risen to a predetermined temperature or higher (step S4), and repeats step S4 until the catalyst temperature rises to a predetermined temperature or higher.

  If it is determined in step S4 that the catalyst temperature has risen to a predetermined temperature or higher, the ECM 30 stops supplying secondary air (step S5).

  After step S5, the ECM 30 shuts off the main relay (not shown) (step S6), and ends the current operation. When the main relay is shut off, the ECM 30 stops supplying power and stops operating.

  As described above, when the ignition switch 24 is turned off and the internal combustion engine 10 is stopped, the secondary air is supplied to the catalyst 14. Therefore, rhodium and palladium of the catalyst 14 are oxidized by the secondary air being supplied to the catalyst 14 in a state where the temperature of the catalyst 14 is high immediately after the internal combustion engine 10 is stopped.

  Rhodium is in an improved low-temperature activity by being oxidized. Palladium is in a state where its low-temperature activity is reduced by being oxidized. The above-described oxidation control corresponds to steps S3, S4, and S5 in FIG.

  In step S4, instead of determining whether the catalyst temperature has risen to a predetermined temperature or higher, it may be determined whether the elapsed time from the start of the supply of the secondary air is longer than a predetermined time. The predetermined time in this case is a time required for the catalyst 14 to be oxidized, and is a value obtained in advance through experiments or the like.

  Next, an operation including the HC concentration control executed by the ECM 30 will be described with reference to FIGS. Here, FIG. 3 is a flowchart illustrating an operation including HC concentration control. The flowchart of FIG. 3 is repeatedly executed in a predetermined short cycle.

  FIGS. 4 and 5 are timing charts showing changes in the operating state of the internal combustion engine 10 at the time of cold start. 4 shows the engine speed, exhaust gas temperature, catalyst temperature, temperature difference (temperature difference between exhaust gas temperature and catalyst temperature), gradient of temperature difference, HC generation ignition cut control flag, HC generation ignition The time series changes of the cut flag and the HC purification rate are shown. On the other hand, FIG. 5 is a partially enlarged view of FIG. 4, and shows a time series change of the HC generation ignition cut control flag, the HC generation ignition cut flag, and an embodiment of the ignition cut.

  In FIG. 3, first, the ECM 30 determines whether or not the catalyst temperature is lower than a predetermined temperature TempCat (Step S11). The predetermined temperature TempCat is used as a threshold value for distinguishing between an operating state when the internal combustion engine 10 is restarted immediately after stopping and an operating state when the internal combustion engine 10 starts cold. The predetermined temperature TempCat is a suitable value obtained in advance by an experiment or the like.

  When the determination in step S11 is NO (when the catalyst temperature is equal to or higher than the predetermined temperature TempCat), the internal combustion engine 10 is in an operating state when it is restarted immediately after stopping, and the ECM 30 sequentially processes step S15 and step S20 described below. And the current operation is ended without performing the ignition cut described later.

  If the determination in step S11 is YES (the catalyst temperature is lower than the predetermined temperature TempCat), the internal combustion engine 10 is in an operating state after the cold start, and the ECM 30 proceeds to step S12.

  In step S12, the ECM 30 calculates a temperature difference between the catalyst temperature and the exhaust gas temperature. This temperature difference is a value obtained by subtracting the exhaust gas temperature from the catalyst temperature. For this reason, the absolute value of the temperature difference increases as a negative value immediately after the cold start of the internal combustion engine 10, and then decreases as the catalyst temperature increases (see FIG. 4).

  In step S12, the ECM 30 calculates the gradient of the temperature difference between the catalyst temperature and the exhaust gas temperature. The gradient of the temperature difference is a value obtained by dividing the temperature difference between the previous processing and the current processing by the processing cycle.

Next, the ECM 30 determines whether the gradient of the temperature difference is greater than 0 (Step S13). Here, the case where the gradient of the temperature difference between the catalyst temperature and the exhaust gas temperature is larger than 0 is the case where the temperature difference has changed in the positive direction past the minimum point (time t3 in FIG. 4). That is,
When the catalyst 14 starts to be activated, the catalyst 14 generates heat as the exhaust gas is purified, so that the temperature difference between the catalyst temperature and the exhaust gas temperature reaches a minimum point. Therefore, in the present embodiment, it is determined that the catalyst 14 has started to be activated on condition that the temperature difference has reached the minimum point, and the HC concentration control is started at this timing.

  If the determination in step S13 is NO (the gradient of the temperature difference is 0 or less), the ECM 30 sequentially proceeds to step S15 and step S20 described below, and performs the current operation without performing ignition cut described later. finish.

  If the determination in step S13 is YES (if the gradient of the temperature difference is greater than 0), the ECM 30 proceeds to step S14.

  In step S14, the ECM 30 sets the "HC generation ignition cut control flag" to ON, sets the "HC generation ignition cut time" to 0 (initializes), and sets the "ignition cut counter" to 0. (initialize.

  This step S14 is a preparation step for performing the ignition cut in step S18 described later. The HC generation ignition cut control flag is a parameter for managing whether or not to perform the ignition cut. The HC generation ignition cut time and the ignition cut counter are parameters for managing the ignition cut time and the number of times, respectively. After performing step S14, the ECM 30 proceeds to step S15.

  In step S15, the ECM 30 determines whether or not the HC generation ignition cut control flag is ON.

  If the determination in step S15 is YES (if the HC generation ignition cut control flag is ON), the ECM 30 proceeds to step S16.

  In step S16, the ECM 30 determines whether the HC generation ignition cut time is less than the predetermined time Time HCFC. The predetermined time TimeHCFC is a length of time during which the ignition cut is performed (see FIG. 5), and is a suitable value obtained in advance by an experiment or the like.

  If the determination in step S16 is YES (the HC generation ignition cut time is less than the predetermined time Time HCFC), the ECM 30 proceeds to step S17.

  In step S17, the ECM 30 determines whether the value of the ignition cut counter is equal to or greater than a predetermined value INTERVALFC. The predetermined value INTERVALFC is an interval between ignition cuts, and is a suitable value obtained in advance by an experiment or the like.

  If the determination in step S17 is YES (if the value of the ignition cut counter is equal to or greater than the predetermined value INTERVALFC), the ECM 30 proceeds to step S18.

  In step S18, the ECM 30 sets (initializes) the value of the ignition cut counter to 0, performs ignition cut, and sets (initializes) the ignition cut control correction when HC occurs.

  By performing the ignition cut in step S18, an unburned air-fuel mixture is generated. Then, the unburned air-fuel mixture generated by the ignition cut is supplied to the catalyst 14 through the exhaust passage 13A. This step S18 corresponds to the aforementioned HC concentration control. During the execution of the HC concentration control, the concentration of hydrocarbons (HC) in the catalyst 14 sharply increases in a spike every time the ignition is cut.

  Here, the ignition cut control correction is an advance correction of the ignition timing in order to cope with a torque reduction accompanying the ignition cut. This advance angle correction is performed for ignition timing (ignition opportunity) at which ignition cut is not performed. The correction amount of the advance angle correction is updated in step S19 described later.

  Note that the ECM 30 also maintains the air-fuel ratio at stoichiometry (stoichiometric air-fuel ratio) when executing step S18. That is, in the present embodiment, the unburned air-fuel mixture is generated by the ignition cut, and the fuel injection amount is not increased for the purpose of generating the unburned air-fuel mixture. Further, the fuel injection timing is not changed for the purpose of generating the unburned air-fuel mixture.

  As for the cylinders for which the ignition cut is to be performed, the ignition cut may be performed only for a specific cylinder, or the ignition cut may be performed for all cylinders.

  After performing Step S18, the ECM 30 proceeds to Step S21. In step S21, the ECM 30 counts up the HC generation ignition cut time, counts up the ignition cut counter, and ends the current HC concentration control operation.

  On the other hand, when the determination in step S15 is NO (when the HC generation ignition cut control flag is OFF) and when the determination in step S16 is NO (when the HC generation ignition cut time is equal to or longer than the predetermined time Time HCFC) ), The ECM 30 turns off the HC generation ignition cut control flag in step S20, and ends the current operation. Therefore, when the determination in step S15 is NO and when the determination in step S16 is NO, ignition cut is not performed.

  When the determination in step S17 is NO (when the value of the ignition cut counter is smaller than the predetermined value INTERVALFC), the ECM 30 updates the correction amount of the HC cut-off ignition cut control (step S19).

  In step S19, the ECM 30 advances the ignition timing according to the time until the time of the next ignition cut (see FIG. 5). Thus, the torque can be increased by the advance correction of the ignition timing before the torque reduction accompanying the ignition cut occurs, and the engine stall at the time of the ignition cut is prevented.

  In FIG. 4, when the internal combustion engine 10 is cold-started at time t1, the exhaust gas temperature and the catalyst temperature rise.

  Thereafter, at time t2, since the internal combustion engine 10 has just started cold start, the catalyst temperature rises later than the exhaust gas temperature. The temperature difference obtained by subtracting the exhaust gas temperature from the catalyst temperature increases in the negative direction. At this time t2, the catalyst temperature has not reached the predetermined temperature TempCat.

  Thereafter, at time t3, when the slope of the temperature difference exceeds the minimum point and becomes larger than 0, the HC generation ignition cut control flag is set to ON. The HC generation ignition cut control flag is set to ON for a predetermined time period TimeHCFC from time t3 to time t4.

  When the HC generation ignition cut control flag is set to ON at time t3, the count of the HC generation ignition cut time starts, and the count of the ignition cut counter starts, as shown in FIG.

  Thereafter, at time t3 (a), time t3 (b), and time t3 (c), the value of the ignition cut counter reaches the predetermined value INTERVALFC, and the ignition cut is performed. That is, the ignition cut is performed once every predetermined number of times determined from the predetermined value INTERVALFC.

  In other words, the ignition cut is not performed continuously at all the ignition opportunities during the predetermined time HCFC, but is performed intermittently in such a manner that the ignition is thinned out. Thus, it is possible to prevent the engine from stalling due to the ignition cut.

  Thereafter, at time t4, a predetermined time TimeHCFC is reached, and the HC generation ignition cut flag is set to off.

  Immediately before time t3 (a), immediately before time t3 (b), and immediately before time t3 (c), the value of the ignition cut counter is smaller than the predetermined value INTERVALFC. The ignition timing at an unillustrated ignition timing (ignition opportunity) where cutting is not performed is advanced and the torque is increased.

  Immediately after time t3 (a), immediately after time t3 (b), and immediately after time t3 (c), the advance correction of the ignition timing is continued. As described above, the advance correction of the ignition timing needs to be performed at least immediately before the ignition cut, but may be continued until immediately after the ignition cut.

  It should be noted that the condition in which the internal combustion engine 10 is idling while warming up may be set as the execution condition of the HC concentration control. In this case, the ECM 30 performs the HC enrichment control further on the condition that a shift selector (not shown) is in the P (parking) range or the N (neutral) range. When the range is switched to the (running) range, the HC concentration control is stopped.

  As described above, according to the exhaust emission control device of the present embodiment, when the internal combustion engine 10 is stopped, the ECM 30 performs the oxidation control that controls the internal combustion engine 10 to oxidize the catalyst 14. Further, the ECM 30 performs HC concentration control for controlling the internal combustion engine 10 to supply the unburned air-fuel mixture to the catalyst 14 at the next cold start of the internal combustion engine 10.

  For this reason, the unburned air-fuel mixture is supplied to the catalyst 14 that has been oxidized by the oxidation process when the internal combustion engine 10 is stopped in the HC concentration control at the time of starting the cold engine. As a result, palladium, which has improved low-temperature activity in an oxidized state, reacts with this fuel to generate heat. Then, oxygen is released from the surface of rhodium by the heat generated by the palladium.

  That is, rhodium is reduced. When the reduced rhodium is activated, the activity of the entire catalyst 14 can be increased.

  As described above, in the exhaust gas purification apparatus of the present embodiment, the unburned air-fuel mixture acts as a reducing agent on the catalyst 14, and the reaction heat is exchanged between palladium and rhodium. The catalyst 14 can be activated at an early stage.

  FIG. 6 shows a process in which the warming-up of the catalyst 14 progresses. The process of the warming-up is shown on the horizontal axis according to the temperature change, and the HC purification rate at that time is shown on the vertical axis. In FIG. 6, in the present embodiment (referred to as an example in the figure), when the exhaust gas temperature rises to 260 ° C. after the next cold start after the oxidation control is performed, the HC concentration control is performed. Thus, the HC purification rate is rapidly increasing. That is, by performing the HC concentration control after the oxidation control, the catalyst 14 can be activated at an early stage, and the HC purification rate can be improved at an early stage.

  On the other hand, in Comparative Example 1 indicated by the broken line, only the oxidation control was performed, and the HC concentration control was not performed at the next cold start, so that the catalyst 14 could not be activated early, and the HC purification rate was reduced. Can not be improved. Further, in Comparative Example 2 indicated by the dashed line, neither the oxidation control nor the HC concentration control is performed, so that the catalyst 14 cannot be activated at an early stage, and the HC purification rate cannot be improved at an early stage.

  For this reason, as shown in FIG. 7, in the present embodiment (referred to as an example in the figure), the discharge amount of hydrocarbons (HC) is reduced to a lower discharge amount, which is smaller than Comparative Example 2 and equivalent to Comparative Example 1. Can be reduced.

  Further, in the present embodiment, the emission amount of nitrogen oxides (NOx) can be reduced as compared with Comparative Examples 1 and 2.

  Further, in the present embodiment, the emission amount of carbon monoxide (CO) can be reduced as compared with Comparative Example 1 and Comparative Example 2. Note that each value in FIG. 7 is a relative value using Comparative Example 2 as a reference value (1.0).

  Further, according to the exhaust purification device of the present embodiment, the ECM 30 supplies the secondary air to the catalyst 14 in the oxidation control until the catalyst temperature of the catalyst 14 rises to a predetermined temperature or higher.

  Thus, by supplying the secondary air based on the catalyst temperature, the degree of oxidation of rhodium of the catalyst 14 can be adjusted so as not to be excessive or insufficient. Further, since the degree of oxidation of rhodium in the catalyst 14 can be adjusted so as not to be excessive or insufficient, it is possible to prevent unnecessary consumption of battery power for driving the electric pump 19.

  Further, since the degree of oxidation of rhodium in the catalyst 14 can be adjusted so as not to be excessive or insufficient, the fuel consumed for the HC concentration control can be suppressed to a necessary and sufficient amount.

  Further, according to the exhaust gas purification apparatus of the present embodiment, the ECM 30 supplies the unburned air-fuel mixture set in the stoichiometry to the catalyst 14 in the HC concentration control.

  Thereby, the reaction heat can be maximized without excess and deficiency of the air and the fuel in the catalyst 14, so that the catalyst 14 can be activated at an early stage.

  Further, according to the exhaust purification device of the present embodiment, the ECM 30 supplies the unburned air-fuel mixture generated by the ignition cut to the catalyst 14 in the HC concentration control.

  Thus, an unburned air-fuel mixture can be generated without increasing the fuel injection amount and controlling the air-fuel mixture to a rich side, so that a decrease in fuel efficiency can be prevented.

  Further, according to the exhaust emission control device of the present embodiment, the ECM 30 advances the ignition timing at least immediately before the ignition cut in the HC concentration control.

  Thus, the torque is increased by the advance correction of the ignition timing prior to the torque reduction due to the ignition cut, so that the engine stall at the time of the ignition cut can be prevented.

  Here, in the HC concentration control of the present embodiment, the concentration of hydrocarbons (HC) in the catalyst 14 is increased by supplying the mixture of the unburned mixture to the catalyst 14. Instead of increasing the concentration of hydrocarbons (HC), the concentration of carbon monoxide (CO) in the catalyst 14 may be increased. The activation of the catalyst 14 can also be promoted by increasing the concentration of carbon monoxide (CO). However, the calorific value during the oxidation reaction in the catalyst 14 is larger when the concentration of hydrocarbon is increased than when the concentration of carbon monoxide is increased. Therefore, it is preferable to increase the concentration of the hydrocarbon as in the present embodiment.

  Further, as a method of supplying combustion to the catalyst 14 as a reducing agent, a method of directly introducing an unburned air-fuel mixture into the exhaust pipe 13 may be used.

  Further, as a method of compensating for the torque reduction accompanying the ignition cut, a motor capable of transmitting power to the internal combustion engine 10 may be operated instead of the advance correction of the ignition timing. In this case, an ISG (Integrated Starter Generator) in which a starter and a generator are integrated, or a motor for traveling can be used as the motor.

  When the air-fuel ratio is corrected to the rich side based on the cooling water temperature or the like, the ignition timing may not be corrected because the possibility of engine stall due to ignition cut is low.

  When the internal combustion engine 10 is a direct injection engine, the fuel injection timing may be changed so that the injection timing is when the valve overlap in the latter half of the exhaust stroke is large.

  In this case, a part of the unburned air-fuel mixture generated in the combustion chamber can be supplied to the catalyst 14 via the exhaust valve by the differential pressure between the intake pressure and the exhaust pressure. Therefore, not only the unburned air-fuel mixture due to the ignition cut but also the unburned air-fuel mixture due to the fuel injection at the time of valve overlap can be supplied to the catalyst 14.

  As described above, the embodiments of the present invention have been disclosed. However, it is apparent that those skilled in the art can make changes without departing from the scope of the present invention. All such modifications and equivalents are intended to be included in the following claims.

Reference Signs List 10 internal combustion engine 14 catalyst 17 spark plug 19 electric pump 22 exhaust gas temperature sensor 23 catalyst temperature sensor 24 ignition switch 30 ECM (control unit)
31 oxidation control unit 32 HC concentration control unit

Claims (4)

A catalyst for purifying exhaust gas from a spark ignition type internal combustion engine,
A control unit for controlling the internal combustion engine, comprising:
The control unit includes:
When the internal combustion engine is stopped, performing oxidation control to control the internal combustion engine to oxidize the catalyst,
An exhaust gas purification apparatus, comprising: performing HC concentration control for controlling the internal combustion engine so that unburned air-fuel mixture generated by ignition cut is supplied to the catalyst at the next cold start of the internal combustion engine.   2. The exhaust gas purification apparatus according to claim 1, wherein in the oxidation control, the control unit supplies secondary air to the catalyst until the catalyst temperature of the catalyst rises to a predetermined temperature or higher. 3.   3. The exhaust gas purification apparatus according to claim 1, wherein the control unit supplies an unburned air-fuel mixture set in stoichiometry to the catalyst in the HC concentration control. 4. The exhaust gas purifying apparatus according to any one of claims 1 to 3, wherein the control unit performs an advance correction of the ignition timing at least immediately before the ignition cut in the HC concentration control .

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