JP2012255366A - Control device and control method for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a control device for an internal combustion engine which can effectively reduce a PM exhaust amount while securing stability of combustion immediately after cold start of the internal combustion engine at the warm-up of an exhaust purifying catalyst, and a control method for the internal combustion engine.SOLUTION: An engine 10 includes an injector 21 for directly jetting fuel into a combustion chamber 22, an ignition plug 36, a variable valve timing mechanism 33 for varying opening/closing timing of an intake valve 31, and a three-way catalyst 38 provided to an exhaust pipe 35. An ECU 50 performs control for delaying ignition timing by an ignition plug 36 by jetting fuel in the intake stroke and compression stroke of the engine 10 with the injector 21 and increasing a fuel injection amount in the compression stroke more than a fuel injection amount in the intake stroke while increasing an overlap amount of opening periods of the intake valve 31 and exhaust valve 32 by the variable valve timing mechanism 33 when executing the cold start of the engine 10.

Description

  The present invention relates to a control device for an internal combustion engine that executes control for warming up an exhaust purification catalyst provided in an exhaust passage of the internal combustion engine, and a control method for the internal combustion engine.

  Conventionally, in order to warm up the exhaust purification catalyst early, a rich air-fuel mixture is formed around the spark plug by compression stroke injection to improve ignitability, and so-called afterburning is caused by retarding the ignition timing, and exhaust gas is exhausted. Some increase the temperature.

  However, if compression stroke injection is performed during cold start of the engine, a large amount of PM (Particulate Matter) is discharged because the amount of fuel adhering to the piston increases or the air-fuel mixture partially becomes too thick There is a thing. For this reason, in response to the recent introduction of PM regulations, reduction of PM emissions has become an issue.

  Here, if the injection timing in the compression stroke is delayed too much, the air-fuel ratio around the spark plug becomes excessively rich, and the PM emission amount may increase. In this regard, in consideration of the fact that fuel atomization is promoted as the engine temperature increases, there is one that advances the injection timing in the compression stroke as the engine temperature increases (see, for example, Patent Document 1). ). According to the device described in Patent Document 1, it is possible to reduce the PM emission amount by suppressing the air-fuel ratio around the spark plug from being excessively rich.

Japanese Patent No. 4000926

  However, in the one described in Patent Document 1, the injection timing in the compression stroke cannot be advanced until the engine temperature rises, and the PM emission amount is effectively reduced immediately after the cold start of the engine. I can't.

  It is also conceivable to reduce the fuel injection amount in the compression stroke in order to reduce the PM emission immediately after the cold start of the engine. However, in order to retard the ignition timing, it is necessary to ensure the stability of combustion, and there is a limit to reducing the fuel injection amount in the compression stroke. For this reason, the effect of reducing the PM emission amount is naturally limited. In order to inject a small amount of fuel in the compression stroke, it is necessary to reduce the minimum injection amount of the injector, which causes an increase in the cost of the injector and increases the variation in the injection amount.

  The present invention has been made in view of such circumstances, and when warming up the exhaust purification catalyst, the PM emission amount is effectively reduced while ensuring the stability of combustion immediately after the cold start of the internal combustion engine. An object of the present invention is to provide a control device for an internal combustion engine and a control method for the internal combustion engine.

  The present invention employs the following means in order to solve the above problems.

  According to a first aspect of the present invention, there is provided a fuel injection valve that directly injects fuel into a cylinder of an internal combustion engine, an ignition plug that ignites a mixture of fuel and air injected by the fuel injection valve, A control device applied to an internal combustion engine comprising: a variable valve mechanism that makes opening / closing timing of at least one of an intake valve and an exhaust valve variable; and an exhaust purification catalyst provided in an exhaust passage of the engine, When the engine is cold-started, the variable valve mechanism increases the internal EGR amount by changing the opening / closing timing of at least one of the intake valve and the exhaust valve, and the fuel injection valve controls the engine. Control for injecting fuel in the intake stroke and compression stroke, and making the fuel injection amount in the compression stroke larger than the fuel injection amount in the intake stroke, and retarding the ignition timing by the spark plug Characterized in that it comprises a control means for executing.

  According to the above configuration, the fuel is directly injected into the cylinder of the internal combustion engine by the fuel injection valve. The mixture of fuel and air injected by the fuel injection valve is ignited by the spark plug. Further, the opening / closing timing of at least one of the intake valve and the exhaust valve of the engine is changed by the variable valve mechanism.

  Here, when the engine is cold-started, an internal EGR (exhaust gas recirculation) amount is increased by changing the opening / closing timing of at least one of the intake valve and the exhaust valve by the variable valve mechanism. Generally, when the amount of internal EGR is increased, fuel combustion becomes unstable. In this respect, fuel is injected by the fuel injection valve in the intake stroke and the compression stroke of the engine, and the fuel injection amount in the compression stroke is made larger than the fuel injection amount in the intake stroke. Therefore, the air-fuel ratio of the air-fuel mixture around the spark plug can be further enriched, and the ignitability of the air-fuel mixture and the stability of combustion can be ensured.

  At this time, even if the air-fuel ratio around the spark plug becomes rich, fuel atomization can be promoted by the heat of the internal EGR. For this reason, it can suppress that a fuel adheres in a cylinder or the droplet of a fuel becomes large. Immediately after the engine is cold started, the temperature in the cylinder is low and the fuel is difficult to atomize. Therefore, by promoting the atomization of the fuel by the heat of the internal EGR, the PM emission amount can be effectively reduced. it can.

  And since the ignition timing by the spark plug is retarded, it is possible to increase the temperature of the exhaust and promote warm-up of the exhaust purification catalyst. As a result, when the catalyst is warmed up, the PM emission amount can be effectively reduced while ensuring the stability of combustion immediately after the cold start of the engine.

  As a means for increasing the internal EGR, for example, a variable valve mechanism can be used to increase the overlap amount during the valve opening period of the intake valve and the exhaust valve. Here, increasing the overlap amount means increasing the overlap amount as compared to before the execution of the control, and includes generating an overlap from a state where the overlap amount is zero. Further, retarding the ignition timing by the spark plug is retarding the ignition timing as compared to before the execution of the control, and includes reducing the advance amount of the ignition timing.

  Generally, in an intake valve whose opening / closing timing is changed by a variable valve mechanism, the valve opening period is set to be larger than 180 ° CA (Crank Angle). For this reason, when the rotational speed of the internal combustion engine is low, the intake air is blown back in a valve opening period after BDC (Bottom Dead Center).

  In this regard, the invention according to claim 2 employs a configuration in which the control means increases the internal EGR amount by advancing the opening / closing timing of the intake valve by the variable valve mechanism. . For this reason, while increasing the amount of internal EGR, it is possible to decrease the blowback of the intake air, and it is possible to increase the charging efficiency of the intake air, and thus the actual compression ratio. Therefore, the combustion of fuel can be made more stable, and the internal EGR amount can be further increased. As a result, fuel atomization can be further promoted, and the PM emission amount can be further reduced.

  Specifically, as described in claim 3, the control means ends the control before the engine warm-up is completed on the condition that the exhaust purification catalyst warm-up is completed. It is possible to adopt a configuration such as. That is, the above-described control for promoting the warm-up of the exhaust purification catalyst is executed for a relatively short period immediately after the cold start of the engine, and is executed for 15 to 25 seconds, for example. For this reason, in general, even when the exhaust purification catalyst has been warmed up, the warming up of the internal combustion engine has not yet been finished, and the control is finished before the warming up of the engine is finished. It will be. In recent PM regulations, it is necessary to reduce the amount of PM emission in such a short period.

  According to a fourth aspect of the present invention, there is provided a fuel injection valve that directly injects fuel into a cylinder of an internal combustion engine, an ignition plug that ignites a mixture of fuel and air injected by the fuel injection valve, A control method for an internal combustion engine, comprising: a variable valve mechanism that varies an opening / closing timing of at least one of an intake valve and an exhaust valve; and an exhaust purification catalyst provided in an exhaust passage of the engine. When the engine is started for a while, the variable valve mechanism increases the internal EGR amount by changing the opening / closing timing of at least one of the intake valve and the exhaust valve, and the fuel injection valve increases the intake stroke of the engine. Fuel is injected during the compression stroke, and the fuel injection amount in the compression stroke is made larger than the fuel injection amount in the intake stroke, and the ignition timing by the spark plug is retarded. .

  According to the said process, there can exist an effect similar to the invention described in Claim 1.

The figure which shows the outline of an engine control system. The figure which shows the pattern of the valve profile by a variable valve timing mechanism. The time chart which shows the execution aspect of catalyst warm-up control. The flowchart which shows the process sequence of catalyst warm-up control. The graph which shows the reduction effect of PM discharge amount and HC discharge amount by catalyst warm-up control. The graph which shows the relationship between the overlap amount by each variable valve timing mechanism, PM discharge amount, and HC discharge amount.

  Hereinafter, an embodiment will be described with reference to the drawings. In the present embodiment, a cylinder injection type multi-cylinder four-cycle gasoline engine mounted on a vehicle is used as a control target, and control of various actuators in this engine is executed. First, an outline of the engine control system will be described with reference to FIG.

  In the in-cylinder injection engine 10 (internal combustion engine), an air flow meter 12 for detecting an intake air amount is provided upstream of the intake pipe 11. A throttle valve 14 whose opening degree is adjusted by a throttle actuator 13 such as a DC motor is provided on the downstream side of the air flow meter 12. The opening degree of the throttle valve 14 (throttle opening degree) is detected by a throttle opening degree sensor built in the throttle actuator 13. A surge tank 16 is provided on the downstream side of the throttle valve 14. The surge tank 16 is provided with an intake pipe pressure sensor 17 for detecting the intake pipe pressure. The surge tank 16 is connected to an intake manifold 18 that introduces air into each cylinder of the engine 10.

  The cylinder block 20 is provided with an electromagnetically driven injector 21 (fuel injection valve), and fuel is directly injected into the combustion chamber 22 (cylinder) by the injector 21. High pressure fuel is supplied to the injector 21 through a high pressure pump (not shown) and a fuel pipe (delivery pipe). The high pressure pump increases the fuel pressure to about 10 to 20 MPa, for example.

  An intake valve 31 and an exhaust valve 32 are provided at the intake port and the exhaust port of the engine 10, respectively. The intake air is introduced into the combustion chamber 22 by the opening operation of the intake valve 31 (intake valve), and the exhaust gas after combustion is discharged to the exhaust pipe 35 (exhaust passage) by the opening operation of the exhaust valve 32 (exhaust valve). An intake camshaft and an exhaust camshaft (not shown) are rotated based on the rotation of the crankshaft of the engine 10. The intake valve 31 and the exhaust valve 32 are reciprocally driven by the cam provided on the intake camshaft and the cam provided on the exhaust camshaft, respectively.

  The intake valve 31 and the exhaust valve 32 are provided with variable valve timing mechanisms 33 and 34 (variable valve operating mechanisms) that make opening / closing timings of these valves variable. The variable valve timing mechanisms 33 and 34 respectively change the relative rotational phase between the clan shaft of the engine 10 and the intake camshaft and the relative rotational phase of the clan shaft of the engine 10 and the exhaust camshaft. In the present embodiment, electric variable valve timing mechanisms are used as the variable valve timing mechanisms 33 and 34.

  A spark plug 36 (ignition plug) is attached to each cylinder of the cylinder head of the engine 10, and a high voltage is applied to the spark plug 36 at a desired ignition timing through an ignition coil (not shown). By applying this high voltage, a spark discharge is generated between the opposing electrodes of each spark plug 36, and the mixture of fuel and air is ignited in the combustion chamber 22 for combustion.

  The exhaust pipe 35 is provided with catalysts 37 and 38 (exhaust gas purification catalyst) for purifying exhaust gas. The upstream catalyst 37 and the downstream catalyst 38 are three-way catalysts that purify CO, HC, and NOx in the exhaust. An air-fuel ratio sensor 39 is provided upstream of the three-way catalyst 37 in the exhaust pipe 35, and an air-fuel ratio sensor 40 is provided downstream of the three-way catalyst 37. The air-fuel ratio sensors 39 and 40 both detect the air-fuel ratio of the air-fuel mixture using exhaust as a detection target. For example, as the upstream air-fuel ratio sensor 39, an A / F sensor capable of detecting the air-fuel ratio in a wide range is used. As the downstream air-fuel ratio sensor 40, an O2 sensor that outputs a binary electromotive force signal in accordance with rich / lean is used (however, the combination of the A / F sensor and the O2 sensor is arbitrary).

  In addition, the cylinder block 20 includes a coolant temperature sensor 42 that detects the coolant temperature, and a crank angle sensor 43 that outputs a rectangular crank angle signal for each predetermined crank angle of the engine 10 (for example, at a cycle of 30 ° CA). It is attached.

  The surge tank 16 and the exhaust pipe 35 are connected via an EGR pipe 45, and an electromagnetically driven EGR valve 46 is provided in the middle of the EGR pipe 45. Note that the exhaust side connection portion of the EGR pipe 45 may be downstream of the three-way catalyst 37. By adjusting the opening degree of the EGR valve 46 (EGR opening degree), the amount of exhaust gas recirculated from the exhaust pipe 35 to the intake passage side (external EGR amount) is controlled. Reference numeral 47 in the figure is an accelerator sensor for detecting the amount of accelerator operation by the driver.

  The outputs of the various sensors described above are input to an electronic control unit (hereinafter referred to as ECU 50) that controls the engine. The ECU 50 (control device) is configured mainly by a microcomputer including a CPU, a ROM, a RAM, and the like, and executes various control programs stored in the ROM, so that the fuel injection amount of the injector 21 according to the engine operating state. The fuel injection timing, the ignition timing of the spark plug 36, and the like are controlled. Further, the ECU 50 drives the intake and exhaust side variable valve timing mechanisms 33 and 34 to open and close the intake valve 31 and the exhaust valve 32, and thus the overlap amount during the valve opening period of the intake valve 31 and the exhaust valve 32. To control.

  Here, in the present embodiment, the opening / closing timing of the intake valve 31 is advanced by the variable valve timing mechanism 33 on the intake side when a warm-up control request for the three-way catalyst 37, 38 immediately after the cold start of the engine 10 is requested. As a result, the overlap amount during the opening / closing period of the intake valve 31 and the exhaust valve 32 is increased, and thus the internal EGR amount in the combustion chamber 22 is increased. Specifically, the internal EGR amount is increased by “intake air blow-back” by opening the intake valve 31 during the opening period of the exhaust valve 32 in the exhaust stroke.

  With reference to FIG. 2, the pattern of the valve profile by the variable valve timing mechanisms 33 and 34 will be described. Here, patterns other than the “intake air blow-back” are also described. In FIG. 2, the valve profile of the exhaust valve 32 is indicated by a solid line, and the valve profile of the intake valve 31 is indicated by a dotted line.

  2A shows a normal valve profile. The exhaust valve 32 is opened during the exhaust stroke, and the intake valve 31 is opened during the intake stroke. At this time, the valve opening periods of the intake valve 31 and the exhaust valve 32 are each greater than 180 ° CA. For this reason, when the rotational speed of the engine 10 is low, the intake air is blown back slightly in the valve opening period after the BDC in the intake valve 31. In addition, there is a slight overlap in the valve opening period between the intake valve 31 and the exhaust valve 32 in the vicinity of the TDC (Top Dead Center) of the piston.

  Further, (b) shows a valve profile in the case of performing “exhaust re-intake”, and the exhaust valve 32 is from the first half of the exhaust stroke (slightly after BDC) to the first half of the intake stroke (slightly after TDC). The valve is open. At this time, since there is a period in which the intake valve 31 and the exhaust valve 32 are simultaneously opened in the intake stroke, the exhaust (burned gas) once discharged to the exhaust port in the exhaust stroke is in the combustion chamber 22 (in the cylinder). Re-inhaled. For this reason, the amount of internal EGR increases as compared with the valve profile of (a).

  (C) shows a valve profile when “intake air blow-back” is performed, and the intake valve 31 is opened from the latter half of the exhaust stroke (slightly before TDC) to the latter half of the intake stroke (slightly before BDC). I speak. At this time, in the exhaust stroke, since there is a period in which the intake valve 31 and the exhaust valve 32 are simultaneously opened, the burned gas existing in the combustion chamber 22 (inside the cylinder) is blown back to the intake port. Then, the burned gas blown back to the intake port is sucked into the combustion chamber 22 in the intake stroke, so that the internal EGR amount increases as compared with the valve profile of (a). Further, since there is no valve opening period after BDC in the intake valve 31, it is possible to increase the overlap amount and to reduce intake blow-back.

  (D) shows a valve profile when both “intake air blow-back” and “exhaust gas re-intake” are performed. The exhaust valve 32 opens from the first half of the exhaust stroke (slightly after the BDC) to the first half of the intake stroke (slightly after the TDC), and the intake valve 31 starts from the second half of the exhaust stroke (slightly before the TDC). The valve opens during the latter half of the intake stroke (slightly before BDC). At this time, in the exhaust stroke, burned gas blows back from the combustion chamber 22 (inside the cylinder) to the intake port, and in the intake stroke, exhaust gas is re-intaked from the exhaust port into the combustion chamber 22 (inside the cylinder). Occurs. For this reason, the amount of internal EGR increases as compared with the valve profile of (a).

  In this way, when the internal EGR amount is increased, fuel combustion generally becomes unstable. On the other hand, the atomization of the injected fuel can be promoted by the heat of the internal EGR. For this reason, it is possible to suppress the fuel from adhering to the combustion chamber 22 and the fuel droplets from becoming large. In particular, immediately after the engine 10 is cold started, the temperature in the combustion chamber 22 is low and the fuel is difficult to atomize. For this reason, it is unlikely that excessive fuel will atomize and the air-fuel ratio will become excessively rich, and promoting fuel atomization by the heat of the internal EGR will reduce PM emissions and HC emissions. It is valid.

  Next, the combustion mode control executed by the ECU 50 will be described. When fuel is injected from the injector 21 in the intake stroke, the injected fuel diffuses into the combustion chamber 22 to form a homogeneous mixture, and is ignited and burned by the spark plug 36. Such combustion is called homogeneous combustion. Further, when fuel is injected from the injector 21 in the compression stroke (particularly in the latter half), the injected fuel is concentrated around the spark plug 36 by, for example, riding on a tumble flow using the convex portion of the piston crown surface. A layered air-fuel mixture is formed in the gas and is ignited by the spark plug 36 and burned. Such combustion is called stratified combustion.

  The ECU 50 controls the combustion mode according to the operating state of the engine 10. That is, during normal operation (here, after the warm-up of the three-way catalysts 37 and 38 is completed), homogeneous stoichiometric combustion is performed by intake stroke injection, while at the time of ignition delay control by catalyst warm-up request, compression stroke injection is performed. Perform stratified combustion.

  In the present embodiment, when the warm-up control of the three-way catalysts 37 and 38 immediately after the cold start of the engine 10 is requested, the fuel injection is divided and the intake stroke injection and the compression stroke injection are performed, so that A relatively rich air-fuel ratio layered mixture is formed, and a relatively lean air-fuel ratio mixture is formed in the entire combustion chamber 22 surrounding the mixture. At this time, the air-fuel ratio of the entire air-fuel mixture in the combustion chamber 22 is controlled to be substantially stoichiometric, and such a combustion mode is called stratified stoichiometric combustion (stratified stoichiometric combustion by split injection). In the stratified stoichiometric combustion, a rich air-fuel mixture is formed around the spark plug 36 by compression stroke injection, and the ignitability of the air-fuel mixture and the stability of combustion are improved. As a result, the ignition timing by the spark plug 36 can be retarded, and the afterburning effect is produced by the retardation of the ignition timing to increase the exhaust gas temperature.

  In particular, since the combustion may become unstable by increasing the internal EGR amount as described above, the fuel injection amount in the compression stroke is made larger than the fuel injection amount in the intake stroke. Thereby, the air-fuel ratio of the air-fuel mixture around the spark plug 36 is further enriched, and the ignitability of the air-fuel mixture and the stability of combustion are ensured. Therefore, when the three-way catalysts 37 and 38 are warmed up, the PM emission amount and the HC emission amount can be reduced while ensuring combustion stability immediately after the cold start of the engine 10.

  Next, a mode in which control for warming up the three-way catalysts 37 and 38 (catalyst warm-up control) when the engine 10 is cold started will be described. FIG. 3 is a time chart showing an execution mode of catalyst warm-up control.

  As shown in the figure, when the cold start of the engine 10 is started, the ECU 50 executes the start-up injection control for the injector 21 as shown in (d), and also shown in (e). As described above, the start time VVT control is executed for the variable valve timing mechanisms 33 and 34. Specifically, in start-up injection control, fuel is injected in the intake stroke by the injector 21, and homogeneous stoichiometric combustion is executed. In the starting VVT control, the opening / closing timings of the intake valve 31 and the exhaust valve 32 are controlled by the variable valve timing mechanisms 33 and 34 so that the overlap amount during the opening period of the intake valve 31 and the exhaust valve 32 is minimized (approximately 0 or 0). . At this time, the ECU 50 sets the ignition timing by the ignition plug 36 to an ignition timing suitable for starting the engine 10 (ignition timing advanced from TDC). Thereby, as shown to (a), the rotational speed of the engine 10 rises.

  At timing t1, the rotational speed of the engine 10 reaches the start determination rotational speed, and the ECU 50 determines that the start of the engine 10 is completed. And N range idle control corresponding to the non-running state of a vehicle is performed. At a timing t2 when a predetermined period (for example, 2 seconds) has elapsed from the determination, as shown in (b), the ECU 50 changes the catalyst warm-up control execution flag from “0” to “1”.

  When the catalyst warm-up control execution flag is “1”, the ECU 50 executes the catalyst warm-up control described above. That is, as shown in (d), fuel injection (split injection) is performed by the injector 21 in the intake stroke and exhaust stroke, and stratified stoichiometric combustion by split injection is performed. At this time, the fuel injection amount in the compression stroke is made larger than the fuel injection amount in the intake stroke. Further, as shown in (e), the opening / closing timing of the intake valve 31 is advanced by the variable valve timing mechanism 33 on the intake side so that the overlap amount during the opening period of the intake valve 31 and the exhaust valve 32 is increased. Let At this time, the ECU 50 sets the ignition timing by the ignition plug 36 to an ignition timing suitable for warming up the three-way catalysts 37 and 38 (ignition timing delayed from TDC). The ignition timing is gradually changed from the ignition timing when the engine 10 is started to the ignition timing when the three-way catalysts 37 and 38 are warmed up. By this catalyst warm-up control, warm-up of the three-way catalysts 37 and 38 is promoted in a state where the PM discharge amount and the HC discharge amount are reduced.

  The ECU 50 changes the catalyst warm-up control execution flag from “1” to “0” at a timing t3 when a predetermined period (for example, 20 seconds) has elapsed since the start of the catalyst warm-up control. The catalyst warm-up control is terminated by changing the catalyst warm-up control execution flag to “0”. As a condition for terminating the catalyst warm-up control, the temperature of the three-way catalysts 37 and 38 estimated based on the operating state of the engine 10 may be employed.

  Then, the ECU 50 executes D range idle control corresponding to the traveling preparation state of the vehicle. Specifically, in the D range idle injection control, fuel is injected by the intake stroke injection by the injector 21, and homogeneous stoichiometric combustion is executed. In the D-range idle VVT control, the variable valve timing mechanisms 33 and 34 control the opening / closing timing of the intake valve 31 and the exhaust valve 32 so that the overlap amount during the valve opening period is minimized. At this time, the ECU 50 sets the ignition timing by the spark plug 36 to an ignition timing suitable for idle operation of the engine 10 (ignition timing advanced from TDC). In the D-range idle control, since the three-way catalysts 37 and 38 have been warmed up, the rotational speed of the engine 10 is made lower than that during the catalyst warm-up control.

  When the accelerator pedal of the vehicle is operated by the driver at the timing t4, the ECU 50 executes the on-travel control corresponding to the traveling state of the vehicle. Specifically, in the traveling injection control, appropriate fuel injection is executed by the injector 21 in accordance with the load of the engine 10 and the like. In the running VVT control, the opening / closing timings of the intake valve 31 and the exhaust valve 32 are controlled by the variable valve timing mechanisms 33 and 34 according to the load of the engine 10 and the like. At this time, the ECU 50 sets the ignition timing by the ignition plug 36 to an appropriate ignition timing according to the load of the engine 10 and the like.

  Next, a detailed processing procedure of control (catalyst warm-up control) for warming up the three-way catalysts 37 and 38 when the engine 10 is cold-started will be described. FIG. 4 is a flowchart showing a processing procedure for catalyst warm-up control. This series of processing is repeatedly executed by the ECU 50 with a predetermined cycle.

  First, it is determined whether or not the engine 10 is in a cold state (S11). Specifically, based on the detection value of the coolant temperature sensor 42, it is determined whether or not the engine 10 is in a cold state. In this determination, when it is determined that the engine 10 is not in the cold state (S11: NO), this series of processes is temporarily ended (END).

  On the other hand, if it is determined in the above determination that the engine 10 is in a cold state (S11: YES), it is determined whether there is a request for catalyst warm-up control (S12). Specifically, when the catalyst warm-up control execution flag is “1”, it is determined that there is a request for catalyst warm-up control. When the catalyst warm-up control execution flag is “0”, the catalyst warm-up control execution flag is determined. Determine that there is no request. As described above, the catalyst warm-up control execution flag is set to a predetermined value after the ECU 50 determines that the rotation speed of the engine 10 has reached the start determination rotation speed when the engine 10 is cold started and the start of the engine 10 is completed. When a period (for example, 2 seconds) elapses, the value is changed from “0” to “1”. Further, the catalyst warm-up control execution flag is changed from “1” to “0” when a predetermined period (for example, 20 seconds) has elapsed since the catalyst warm-up control was started. Normally, the catalyst warm-up control execution flag is changed from “1” to “0” before the warm-up of the engine 10 ends (for example, the cooling water temperature of the engine 10 becomes 80 ° C. or higher). . In this determination, if it is determined that there is no request for catalyst warm-up control (S12: NO), this series of processing is temporarily ended (END).

  On the other hand, when it is determined in the above determination that there is a request for catalyst warm-up control (S12: YES), the overlap amount of the valve opening period of the intake valve 31 and the exhaust valve 32 is increased (S13). Specifically, the state is changed from a state where the overlap amount is minimum (approximately 0 or 0) to a predetermined overlap amount state. Specifically, the opening / closing timing of the intake valve 31 is advanced by a predetermined amount by the variable valve timing mechanism 33 on the intake side. The advance amount by the variable valve timing mechanism 33 is set to the maximum advance amount within a range where the combustion stability of the fuel does not deteriorate from the combustion limit. In setting the advance amount, in the catalyst warm-up control, fuel is injected into the intake stroke and the compression stroke of the engine 10 by the injector 21, and the fuel injection amount in the compression stroke is larger than the fuel injection amount in the intake stroke. Consider increasing the retard of the ignition timing by the spark plug 36.

  Subsequently, split injection is performed in the intake stroke and the compression stroke of the engine 10, and the fuel injection amount in the compression stroke is made larger than the fuel injection amount in the intake stroke (S14). Specifically, in each cylinder of the engine 10 in the idling operation state, the injector 21 injects an appropriate amount of fuel for warming up the three-way catalysts 37 and 38 in the intake stroke and the compression stroke. At this time, the fuel injection amount is distributed so that the fuel injection amount in the compression stroke is larger than the fuel injection amount in the intake stroke. That is, the fuel injection rate in the compression stroke is set higher than the fuel injection rate in the intake stroke. When setting the fuel injection amount in the compression stroke and the fuel injection amount in the intake stroke, the variable valve timing mechanism 33 on the intake side controls the valve opening period of the intake valve 31 and the exhaust valve 32 in the catalyst warm-up control. Consider increasing the overlap amount and retarding the ignition timing by the spark plug 36.

  Subsequently, the ignition timing by the spark plug 36 is retarded (S15). Specifically, as described above, the ignition timing by the spark plug 36 is set to an ignition timing suitable for warming up the three-way catalysts 37 and 38 (ignition timing retarded from TDC). When the ignition timing is retarded, the ignition timing is gradually changed from the ignition timing at the start of the engine 10 (ignition timing advanced from TDC) to the ignition timing when the three-way catalysts 37 and 38 are warmed up. Thereafter, this series of processing is temporarily terminated (END). In addition, about the process of S13-S15, those orders can also be changed and performed. Moreover, the process of S13-S15 is corresponded to the process as a control means.

  FIG. 5 is a graph showing the effect of reducing the PM emission amount and the HC emission amount by the catalyst warm-up control. Here, immediately after the cold start of the engine 10, the fuel injection amount in the intake stroke and the fuel injection amount in the compression stroke are summed to obtain a fuel amount suitable for warming up the three-way catalyst 37, 38. Spraying. Note that the ignition timing is retarded to an ignition timing suitable for catalyst warm-up control.

  As shown in (a), as the advance amount of the variable valve timing mechanism 33 on the intake side increases, the overlap amount during the valve opening period of the intake valve 31 and the exhaust valve 32, and hence the internal EGR amount, is increased. Since it increases, combustion stability deteriorates. When the fuel injection rate in the compression stroke is large (fuel injection amount in the intake stroke <fuel injection amount in the compression stroke), the fuel injection rate in the compression stroke is small (fuel injection amount in the intake stroke> The deterioration of the combustion stability with respect to the increase in the advance angle becomes more gradual than the fuel injection amount in the compression stroke).

  Here, it is not possible to use a region where the combustion stability is worse than the combustion limit, and it is necessary to burn the fuel in a range where the combustion stability is better than the combustion limit. For this reason, when the fuel injection rate in the compression stroke is large, the advance amount of the variable valve timing mechanism 33 on the intake side can be increased as compared with the case where the fuel injection rate in the compression stroke is small. As described above, as the internal EGR amount is increased, atomization of the injected fuel can be promoted, and the PM emission amount and the HC emission amount can be reduced.

  As shown in (b) and (c), when the advance amount of the variable valve timing mechanism 33 on the intake side is zero, the fuel in the intake stroke is greater when the fuel injection rate in the compression stroke is larger. The PM emission amount and the HC emission amount are larger than when the injection rate is small. However, the PM discharge amount and the HC discharge amount decrease as the advance amount increases, and the advance amount can be further increased when the fuel injection rate in the compression stroke is large. As a result, in combustion at the combustion limit, when the fuel injection rate in the compression stroke is large, the PM emission amount and the HC emission amount can be reduced as compared with the case where the fuel injection rate in the compression stroke is small.

  FIG. 6 is a graph showing the relationship between the overlap amount by each variable valve timing mechanism 33, 34, the PM discharge amount, and the HC discharge amount. Here, immediately after the cold start of the engine 10, the fuel injection amount in the intake stroke and the fuel injection amount in the compression stroke are summed to obtain a fuel amount suitable for warming up the three-way catalyst 37, 38. Spraying. In addition, the fuel injection amount in the compression stroke is larger than the fuel injection amount in the intake stroke (corresponding to the case where the fuel injection rate in the compression stroke is large). Note that the ignition timing is retarded to an ignition timing suitable for catalyst warm-up control.

  As shown in (a), the internal EGR amount increases as the overlap amount of the valve opening period of the intake valve 31 and the exhaust valve 32 increases, so that the combustion stability deteriorates. Here, as described above, when the advance amount of the variable valve timing mechanism 33 on the intake side is increased, there is no valve opening period after the BDC in the intake valve 31, so that the intake air blowback is reduced. Can do. For this reason, it is possible to increase the charging efficiency of the intake air, and thus the actual compression ratio, and it is possible to further stabilize the fuel combustion. Therefore, when the advance amount of the intake side variable valve timing mechanism 33 is increased, the combustion stability with respect to the increase in the overlap amount is worse than when the retard amount of the exhaust side variable valve timing mechanism 34 is increased. Becomes moderate.

  Here, it is not possible to use a region where the combustion stability is worse than the combustion limit, and it is necessary to burn the fuel in a range where the combustion stability is better than the combustion limit. For this reason, when the advance amount of the variable valve timing mechanism 33 on the intake side is increased, the overlap amount can be increased as compared with the case where the retard amount of the variable valve timing mechanism 34 on the exhaust side is increased. As the internal EGR amount is increased, atomization of the injected fuel can be promoted, and the PM emission amount and the HC emission amount can be reduced.

  As shown in (b) and (c), the PM discharge amount and the HC discharge amount decrease as the overlap amount increases, and when the advance amount of the variable valve timing mechanism 33 on the intake side is increased, the overlap amount is increased. The amount can be increased further. As a result, in combustion at the combustion limit, when the advance amount of the intake side variable valve timing mechanism 33 is increased, the PM emission is larger than when the retard amount of the exhaust side variable valve timing mechanism 34 is increased. Amount and HC emission can be reduced.

  The embodiment described above has the following advantages.

  When the engine 10 is cold-started, the overlap amount during the valve opening period of the intake valve 31 and the exhaust valve 32 is increased by the variable valve timing mechanism 33 on the intake side. For this reason, the burnt gas sucked back into the combustion chamber 22 increases, and the so-called internal EGR amount increases. Generally, when the amount of internal EGR is increased, fuel combustion becomes unstable. In this respect, fuel is injected by the injector 21 in the intake stroke and the compression stroke of the engine 10, and the fuel injection amount in the compression stroke is made larger than the fuel injection amount in the intake stroke. Therefore, the air-fuel ratio of the air-fuel mixture around the spark plug 36 can be further enriched, and the ignitability of the air-fuel mixture and the stability of combustion can be ensured.

  At this time, even if the air-fuel ratio around the spark plug 36 becomes rich, the atomization of fuel can be promoted by the heat of the internal EGR. For this reason, it is possible to suppress the fuel from adhering to the combustion chamber 22 and the fuel droplets from becoming large. In particular, immediately after the engine 10 is cold started, the temperature in the combustion chamber 22 is low and the fuel is difficult to atomize. Therefore, by promoting the atomization of the fuel by the heat of the internal EGR, the PM emission amount and the HC emission amount are reduced. It can be effectively reduced.

  And since the ignition timing by the spark plug 36 is retarded, it is possible to increase the temperature of the exhaust and promote the warm-up of the three-way catalysts 37, 38. As a result, when the three-way catalysts 37 and 38 are warmed up, immediately after the cold start of the engine 10, the PM emission amount can be effectively reduced while ensuring the combustion stability.

  The overlap amount is increased by advancing the opening / closing timing of the intake valve 31 by the variable valve timing mechanism 33 on the intake side. For this reason, the overlap amount can be increased, the intake blow-back can be decreased, and the intake charging efficiency, and hence the actual compression ratio, can be increased. Therefore, the combustion of fuel can be made more stable, and the overlap amount can be further increased. As a result, fuel atomization can be further promoted, and the PM emission amount can be further reduced.

  The control for promoting the warm-up of the three-way catalysts 37 and 38 is executed for a relatively short period (for example, 20 seconds) immediately after the engine 10 is cold started. For this reason, in general, even when the three-way catalysts 37 and 38 have been warmed up, the warming up of the engine 10 has not been finished yet, and the above control is performed before the warming up of the engine 10 is finished. Will be terminated. For recent PM regulations, it is important to reduce the amount of PM emission in such a short period.

  The present invention is not limited to the above-described embodiment, and can be implemented as follows, for example.

  In the above embodiment, the opening / closing timing of the intake valve 31 is advanced by the variable valve timing mechanism 33 on the intake side, thereby increasing the overlap amount of the intake valve 31 and the exhaust valve 32 during the valve opening period. . However, the amount of overlap can be increased by retarding the opening / closing timing of the exhaust valve 32 by the variable valve timing mechanism 34 on the exhaust side. Moreover, the overlap amount can be increased by executing both of these controls. It is not always necessary to increase the overlap amount, and the internal EGR amount can be increased by changing the opening / closing timing of the intake valve 31 and the exhaust valve 32 while keeping the overlap amount constant.

  DESCRIPTION OF SYMBOLS 10 ... In-cylinder injection engine (internal combustion engine), 21 ... Injector (fuel injection valve), 22 ... Combustion chamber, 31 ... Intake valve (intake valve), 32 ... Exhaust valve (exhaust valve), 33, 34 ... Variable valve Timing mechanism (variable valve mechanism), 35 ... exhaust pipe, 36 ... spark plug (ignition plug), 37 ... three-way catalyst (exhaust gas purification catalyst), 38 ... three-way catalyst (exhaust gas purification catalyst), 50 ... ECU (control) Means, control device).

Claims (4)

A fuel injection valve for directly injecting fuel into the cylinder of the internal combustion engine;
A spark plug for igniting a mixture of fuel and air injected by the fuel injection valve;
A variable valve mechanism for varying the opening and closing timing of at least one of the intake valve and the exhaust valve of the engine;
An exhaust purification catalyst provided in an exhaust passage of the engine;
A control device applied to an internal combustion engine comprising:
When the engine is cold started, an internal EGR amount is increased by changing the opening / closing timing of at least one of the intake valve and the exhaust valve by the variable valve mechanism, and the engine is controlled by the fuel injection valve. Control means for performing control for injecting fuel in the intake stroke and compression stroke of the engine and increasing the fuel injection amount in the compression stroke to be greater than the fuel injection amount in the intake stroke to retard the ignition timing by the spark plug A control device for an internal combustion engine, comprising:   2. The control device for an internal combustion engine according to claim 1, wherein the control means increases the internal EGR amount by advancing the opening / closing timing of the intake valve by the variable valve mechanism.   3. The control device for an internal combustion engine according to claim 1, wherein the control means finishes the control before the warm-up of the engine is finished on condition that the warm-up of the exhaust purification catalyst is finished. . A fuel injection valve for directly injecting fuel into the cylinder of the internal combustion engine;
A spark plug for igniting a mixture of fuel and air injected by the fuel injection valve;
A variable valve mechanism for varying the opening and closing timing of at least one of the intake valve and the exhaust valve of the engine;
An exhaust purification catalyst provided in an exhaust passage of the engine;
An internal combustion engine control method comprising:
When the engine is cold started, an internal EGR amount is increased by changing the opening / closing timing of at least one of the intake valve and the exhaust valve by the variable valve mechanism, and the engine is controlled by the fuel injection valve. An internal combustion engine characterized in that fuel is injected during the intake stroke and the compression stroke, and the fuel injection amount in the compression stroke is made larger than the fuel injection amount in the intake stroke to retard the ignition timing by the spark plug. How to control the engine.

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