JP5029517B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine.

  In general, when a piston of an internal combustion engine (hereinafter also referred to as “engine”) is at a position corresponding to the top dead center, a dead space exists between the upper surface of the piston and the cylinder head. As a result, the burned gas is not completely scavenged from the combustion chamber of the engine during the exhaust stroke of the engine, and a part of it can remain in the combustion chamber. In particular, the so-called internal EGR control (the overlap period of the intake and exhaust valves (the period during which the intake and exhaust valves are both kept open) is adjusted to return to the intake passage from the exhaust passage through the combustion chamber. Control for positively adjusting the amount of burned gas) or so-called external EGR control (EGR gas by adjusting the opening degree of the EGR valve interposed in the EGR gas passage that connects the intake passage and the exhaust passage) In an engine in which the control of positively adjusting the amount of burned gas recirculated from the exhaust passage to the intake passage through the passage is executed, the concentration of the burned gas remaining in the combustion chamber is large.

  Hereinafter, the burnt gas remaining in the combustion chamber is referred to as “residual burnt gas”, and the concentration of the remaining burnt gas is referred to as “residual burnt gas concentration”. Further, the burned gas recirculated from the exhaust passage to the intake passage by the above-described EGR control is also particularly referred to as “EGR gas”.

  Since the burned gas is composed of an inert gas such as carbon dioxide or water, it does not contribute to the combustion of fuel in the combustion chamber. Residual burnt gas inhibits the mixing of fuel and fresh air (oxygen contained therein) in the combustion chamber. Therefore, as the residual burned gas concentration increases, the degree of mixing decreases, and when the residual burned gas concentration exceeds a certain upper limit (hereinafter referred to as “misfire limit”), misfire may occur.

  On the other hand, it is widely known that fuel cut (hereinafter also referred to as “FC”) for interrupting fuel injection at the time of deceleration is performed from the viewpoint of reducing fuel consumption. No heat is generated by fuel combustion in FC. Therefore, when fuel injection is resumed due to the end of FC due to reacceleration or the like, the temperature of the gas in the combustion chamber is often low. The misfire limit for the residual burned gas concentration decreases as the combustion chamber gas temperature decreases.

  From the above, for example, when FC is executed by deceleration while a large amount of EGR gas is recirculated to the intake passage by the above-described EGR control, fuel injection is resumed by the end of FC by reacceleration. The residual burned gas concentration is high and the combustion chamber gas temperature is low. As a result, misfire is particularly likely to occur.

From the viewpoint of suppressing the occurrence of misfire as described above, in the control device described in Patent Document 1, when fuel injection is resumed by the end of FC, ignition is performed a plurality of times in one combustion cycle. Thereby, it is described that the probability of ignition of the air-fuel mixture increases and the occurrence of misfire can be suppressed.
JP 2004-197704 A

  However, even if the ignition probability is increased by executing ignition a plurality of times as in the apparatus described in the above document, the misfire limit itself for the residual burned gas concentration does not increase. Therefore, it is thought that the suppression effect with respect to misfire generation is still small.

  In view of the above, an object of the present invention is to provide a control device for an internal combustion engine that can positively increase the misfire limit for the residual burned gas concentration and suppress the occurrence of misfire when fuel injection is resumed by the end of FC. It is to provide.

  A first control device for an internal combustion engine according to the present invention includes a fuel injection unit that injects fuel into a combustion chamber of the internal combustion engine, an intake passage of the internal combustion engine, a combustion chamber based on an operating state of the internal combustion engine, An intake valve opening timing control means for changing the opening timing of the intake valve that communicates and shuts off, and a fuel cut that executes FC for interrupting fuel injection from the fuel injection means based on the operating state of the internal combustion engine Means.

  The first control device is characterized in that when the intake valve opening timing control means resumes fuel injection upon completion of the FC, the opening timing of the intake valve is a timing during the intake stroke, and Intake valve delaying control is performed to retard the opening timing of the intake valve so that the timing is delayed from the closing timing of the exhaust valve that communicates and blocks the exhaust passage of the internal combustion engine and the combustion chamber. There is a retarding means.

  Here, the intake valve opening timing control means controls the intake valve opening timing to a normal timing determined based on the operating state of the internal combustion engine, and when fuel injection is resumed by the end of the FC, As the intake valve delay opening control, the intake valve opening timing is changed to the timing during the intake stroke on the retard side of the normal timing instead of the normal timing, and the timing on the retard side of the exhaust valve closing timing. Can be configured to control.

  When the intake valve opening timing is set to a timing that is retarded from the exhaust valve closing timing by the intake valve delay opening control, both the intake and exhaust valves are maintained in the closed state. The intake valve opens in the process in which the piston descends in a closed state (ie, the combustion chamber is sealed). Accordingly, immediately after the intake valve is opened, the pressure difference before and after the passage of the gas passing through the throttle portion of the intake valve is large because the pressure of the gas in the combustion chamber is reduced. As a result, the flow velocity of the intake air flowing into the combustion chamber after opening the intake valve (particularly immediately after the valve opening) (hereinafter referred to as “intake flow velocity”) increases.

  Thereby, the atomization of the fuel spray mixed with the intake air is promoted. When the atomization of the fuel is promoted, the degree of mixing of the fuel spray and the intake air (oxygen contained therein) increases, and the fuel spray (air mixture) is easily ignited. This means that the misfire limit for the residual burned gas concentration described above increases.

  From the above, according to the first control device, when the fuel injection is resumed by the end of FC, the misfire limit can be positively increased by executing the intake valve delay opening control. As a result, the occurrence of misfire can be suppressed.

  The first control apparatus includes a residual burned gas concentration estimating means for estimating a value correlated with a remaining burned gas concentration that is a concentration of burned gas remaining in the combustion chamber, and the retarding means However, it is preferable that the retard amount of the opening timing of the intake valve is determined to be larger as the residual burned gas concentration is higher. The values correlated with the residual burned gas concentration include, for example, the residual burned gas concentration itself (mass concentration of the remaining burned gas in the gas in the combustion chamber), and the residual burned gas amount (residual in the gas in the combustion chamber). The mass of burned gas).

  The greater the residual burned gas concentration (when fuel injection is resumed by the end of FC), the more likely misfire occurs. That is, the greater the residual burned gas concentration, the greater the demand for finer fuel (and hence the higher speed of the intake air flow rate). On the other hand, in the intake valve retarded opening control, the differential pressure increases and the intake flow velocity increases as the retard amount of the intake valve opening timing (from the normal timing) increases.

  On the other hand, the large amount of retardation in the intake valve retarded opening control means that the piston is lowered for a long time while both the intake and exhaust valves are maintained in the closed state. That is, so-called pumping loss increases and the fuel consumption of the engine deteriorates.

  As described above, according to the above configuration, when the residual burned gas concentration is low, the retardation amount is reduced, and deterioration of fuel consumption due to an increase in pumping loss can be suppressed while the occurrence of misfire is suppressed. Further, when the residual burned gas concentration is high, the retard amount is sufficiently increased, and the intake flow velocity can be sufficiently increased (therefore, the misfire limit can be sufficiently increased), and the occurrence of misfire can be reliably suppressed. .

  In this case, the retarding means determines a required intake flow velocity based on the residual burned gas concentration, and the intake valve opening timing (from the normal timing) based on the determined required intake flow velocity. ) Can be configured to determine the amount of retardation. Further, the retarding means may be configured to execute the intake valve retarded opening control only when the residual burned gas concentration is larger than a predetermined value.

  Further, in the first control device, when the fuel injection is resumed by the end of the FC, the compression end temperature increase control for increasing the temperature of the gas in the combustion chamber (compression end temperature) at the compression top dead center. Based on the temperature of the coolant when fuel injection is resumed by the end of the FC. It is preferable that the apparatus further comprises selection means for selecting control to be executed between the intake valve delay opening control by the retard angle means and the compression end temperature increase control by the temperature increase means.

  When the intake flow velocity is increased by the intake valve delay opening control, the droplet fuel adhering to the intake port and the like due to the fuel injection to the intake port before the intake valve is opened flows into the combustion chamber in the form of droplets. It becomes easy to adhere to the spark plug. As a result, a situation in which good ignition cannot be performed particularly at low temperatures (so-called spark plug smoldering) easily occurs. Therefore, the intake valve slow opening control is preferably executed at a relatively high temperature.

  On the other hand, as described above, the misfire limit for the residual burned gas concentration increases as the combustion chamber gas temperature increases. Therefore, in order to suppress the occurrence of misfire, control for increasing the compression end temperature (that is, the compression end temperature increase control) may be executed. However, particularly when the compression end temperature is raised at a high temperature, knocking is likely to occur. Therefore, it is preferable that the compression end temperature increase control is executed at a relatively low temperature.

  From the above, according to the above configuration, misfire can be suppressed by selecting and executing the intake valve slow-opening control at high temperatures, and misfire can be suppressed by selecting and executing the compression end temperature increase control at low temperatures. Generation can be suppressed. Therefore, the occurrence of misfire can be stably suppressed regardless of the temperature of the coolant while suppressing the occurrence of smoldering and knocking of the spark plug.

  A second control device for an internal combustion engine according to the present invention comprises fuel pressure control means for changing the pressure of fuel injected from the fuel injection means instead of the intake valve opening timing control means, and The fuel pressure control means is different from the first control device only in that the fuel pressure control means includes pressure increase means for performing fuel pressure pressure increase control for increasing the fuel pressure when fuel injection is resumed by the end of the FC.

  Here, the fuel pressure control means controls the fuel pressure to a normal pressure determined based on the operating state of the internal combustion engine, and when fuel injection is resumed by the end of the FC, as fuel pressure boost control, The fuel pressure may be configured to be controlled to a pressure higher than the normal pressure instead of the normal pressure.

  When the fuel pressure increases by the fuel pressure increase control, the injection speed of the fuel injected from the fuel injection means increases. Thereby, the atomization of the fuel spray mixed with the intake air is promoted. Accordingly, the misfire limit for the residual burned gas concentration described above increases as in the first control device.

  From the above, according to the second control device, when the fuel injection is resumed by the end of FC, the misfire limit can be positively increased by executing the fuel pressure increase control. As a result, the occurrence of misfire can be suppressed.

  Also in the second control device, similarly to the first control device, the pressure increasing means is configured to determine the pressure increase amount of the fuel pressure to be larger as the residual burned gas concentration is larger. Is preferred.

  Similar to the above, the greater the residual burned gas concentration, the greater the demand for finer fuel (and hence the higher speed of fuel injection). On the other hand, in the fuel pressure increase control, the injection speed increases as the fuel pressure increase amount (from the normal pressure) increases.

  Therefore, according to the above configuration, when the residual burned gas concentration is low, the pressure increase amount is reduced, and the occurrence of misfire can be suppressed without unnecessarily increasing the pressure increase amount. Further, when the residual burned gas concentration is large, the pressure increase amount is sufficiently increased, and the injection speed can be sufficiently increased (therefore, the misfire limit can be sufficiently increased), and misfire occurrence can be reliably suppressed. .

  In this case, the pressure increasing means may be configured to execute the fuel pressure pressure increasing control only when the residual burned gas concentration is larger than a predetermined value. Further, when the fuel injection means includes port fuel injection means for injecting fuel in the intake passage and in-cylinder fuel injection means for directly injecting fuel in the combustion chamber, as the fuel pressure boost control, Either or both of the fuel pressure of the fuel injected from the port fuel injection means (port injection fuel) and the fuel pressure of the fuel injected from the cylinder fuel injection means (cylinder injection fuel) The pressure may be increased (from normal pressure).

  A third control device for an internal combustion engine according to the present invention is provided with no intake valve opening timing control means, the fuel injection means includes at least the in-cylinder fuel injection means, and the in-cylinder fuel injection. When the fuel injection is resumed by the end of the fuel cut, the first means is provided only with the division injection means for performing the injection number increase control for increasing the number of fuel injections (per combustion cycle). Different from the control device.

  Here, the in-cylinder fuel injection means controls the number of injections to a normal number (for example, once), and when the fuel injection is resumed by the end of the FC, It may be configured to control the number of times larger than the normal number of times instead of the normal number of times.

  When the number of injections from the in-cylinder fuel injection means is increased by the injection number increase control, the total surface area of the fuel spray of the in-cylinder injected fuel is increased. As a result, the degree of mixing between the fuel spray and the intake air (oxygen contained therein) increases, and the fuel spray (air mixture) is easily ignited. Therefore, like the first and second control devices, the misfire limit for the residual burned gas concentration is increased.

  From the above, according to the third control device, when the fuel injection is restarted by the end of FC, the misfire limit can be positively increased by executing the injection number increase control. As a result, the occurrence of misfire can be suppressed.

  Also in the third control device, as in the first and second control devices, the split injection means determines that the increase in the number of injections is larger as the residual burned gas concentration is higher. It is suitable to be configured.

  The greater the residual burned gas concentration, the greater the demand for expansion of the total surface area of the fuel spray of the in-cylinder injected fuel. On the other hand, the larger the increase in the number of injections (from the normal number) in the injection number increase control, the larger the total surface area becomes.

  Therefore, according to the said structure, when the residual burned gas density | concentration is small, the increase amount of the said frequency | count of injection is made small and generation | occurrence | production of misfire can be suppressed without increasing the frequency | count of injection unnecessarily. In addition, when the residual burned gas concentration is high, the amount of increase in the number of injections can be made sufficiently large to sufficiently expand the total surface area (thus, the above misfire limit can be made sufficiently large), and the misfire occurrence can be reliably suppressed. it can. In this case, the in-cylinder fuel injection means may be configured to execute the injection number increase control only when the residual burned gas concentration is larger than a predetermined value.

  As described above, in the first to third control devices, an EGR gas passage that communicates an exhaust passage and an intake passage of the internal combustion engine, an EGR gas adjustment valve that is interposed in the EGR gas passage and has an adjustable opening area. And an opening area control means for adjusting the opening area of the EGR gas regulating valve based on the operating state of the internal combustion engine (that is, when the external EGR control is executed), the opening area control. The means is preferably configured to fix the opening area of the EGR gas regulating valve to a minimum value (for example, zero) in the FC.

  According to this, in the FC, the inflow of burned gas (EGR gas) from the intake passage to the combustion chamber is prohibited, but the remaining burned gas (a part) is exhausted every time the exhaust stroke comes. Scavenging into the passage. Therefore, it is possible to effectively reduce the residual burned gas concentration in the FC. As a result, the residual burned gas concentration at the time when fuel injection is resumed by the end of FC can be reduced, and the occurrence of misfire can be suppressed.

  As described above, the intake valve delay opening control, the fuel pressure increase control, and the injection frequency increase control only have to be executed at least when the fuel injection is resumed by the end of the FC. The intake valve delay opening control and the fuel pressure increase control may be executed over a predetermined period from the FC end point (that is, the fuel injection restart point), or before the FC end point in FC. From this stage, the process may be executed from the FC end point to after a lapse of a predetermined period, or from the FC start point to the end of the predetermined period from the FC end point. The injection frequency increase control may be executed over a predetermined period from the FC end point (that is, the fuel injection restart point).

  In the first to third control devices, one of the internal EGR control and the external EGR control may be executed, or both the internal EGR control and the external EGR control may not be executed.

  Hereinafter, embodiments of a control device for an internal combustion engine according to the present invention will be described with reference to the drawings.

(First embodiment)
FIG. 1 shows a system in which a control device according to a first embodiment of the present invention (hereinafter also referred to as “the present device”) is applied to a spark ignition multi-cylinder (four-cylinder) internal combustion engine 10 having a dual injection system. The schematic structure of is shown. The internal combustion engine 10 includes a cylinder block 20 including a cylinder block and an oil pan, a cylinder head 30 fixed on the cylinder block 20, and a gasoline mixture supplied to the cylinder block 20. An intake system 40 and an exhaust system 50 for releasing the exhaust gas from the cylinder block 20 to the outside are included.

  The cylinder block unit 20 includes a cylinder 21, a piston 22, a connecting rod 23, and a crankshaft 24. The heads of the cylinder 21 and the piston 22 form a combustion chamber 25 together with the cylinder head portion 30.

  The cylinder head portion 30 includes an intake port 31 communicating with the combustion chamber 25, an intake valve 32 that opens and closes the intake port 31, an intake camshaft that drives the intake valve 32, and continuously opens and closes the intake valve 32 and the maximum lift amount. Variable intake timing device 33 to be changed, actuator 33a of variable intake timing device 33, exhaust port 34 communicating with combustion chamber 25, exhaust valve 35 for opening and closing exhaust port 34, exhaust camshaft 36 for driving exhaust valve 35, An ignition plug 37, an igniter 38 including an ignition coil that generates a high voltage to be applied to the ignition plug 37, a port injection valve 39P (port injection means) for injecting fuel into the intake port 31, and fuel directly in the combustion chamber 25 An in-cylinder injection valve 39C (in-cylinder injection means) for injection is provided.

  The intake system 40 is provided in an intake pipe 41 including an intake manifold that communicates with the intake port 31 and forms an intake passage together with the intake port 31, an air filter 42 provided at an end of the intake pipe 41, and the intake pipe 41. A throttle valve 43 that makes the opening cross-sectional area of the intake passage variable, and a throttle valve actuator 43a that constitutes throttle valve driving means are provided.

  The exhaust system 50 includes an exhaust manifold 51 that communicates with the exhaust port 34, and an exhaust pipe (exhaust pipe) that is connected to the exhaust manifold 51 (actually, a collection portion of the exhaust manifolds 51 that communicate with each exhaust port 34). ) 52, a three-way catalyst 53 and an EGR gas passage 54 disposed (interposed) in the exhaust pipe 52. The exhaust port 34, the exhaust manifold 51, and the exhaust pipe 52 constitute an exhaust passage.

  The EGR gas passage 54 is configured to communicate the exhaust passage upstream of the three-way catalyst 53 and the intake passage downstream of the throttle valve 43. In the EGR gas passage 54, an EGR gas cooler 55, an EGR valve 56, and an actuator 56a of the EGR valve 56 are interposed. The opening area of the EGR valve 56 can be adjusted by the actuator 56a of the EGR valve 56. Thus, a part of the exhaust gas can be supplied to the intake passage.

  On the other hand, this system includes an air flow meter 61, a throttle position sensor 62, a cam position sensor 63, a crank position sensor 64, a water temperature sensor 65, an exhaust passage upstream of the three-way catalyst 53 (in this example, each exhaust manifold 51 is An air-fuel ratio sensor 66, an EGR valve opening sensor 67, and an accelerator opening sensor 68 are provided.

  The air flow meter 61 detects the flow rate (mass flow rate) of fresh air flowing through the intake passage and outputs a signal representing the fresh air flow rate Ga. The throttle position sensor 62 detects the opening of the throttle valve 43 and outputs a signal representing the throttle valve opening TA. The cam position sensor 63 detects the opening / closing timing of the intake valve 32 and outputs a signal representing the opening / closing timing VVT. The crank position sensor 64 detects the rotational speed of the crankshaft 24 and outputs a signal representing the engine rotational speed NE. The water temperature sensor 65 detects the temperature of the cooling water of the internal combustion engine 10 and outputs a signal representing the cooling water temperature THW. The air-fuel ratio sensor 66 detects the air-fuel ratio of the exhaust gas and outputs a signal representing the air-fuel ratio. The EGR valve opening degree sensor 67 detects the opening degree of the EGR valve 56 and outputs a signal representing the EGR valve opening degree Aegr. The accelerator opening sensor 68 detects the operation amount of the accelerator pedal 81 operated by the driver, and outputs a signal representing the operation amount Accp of the accelerator pedal 81.

  The electric control device 70 includes a CPU 71 connected to each other by a bus, a routine (program) executed by the CPU 71, a table (map), and a ROM 72, a RAM 73, a backup RAM 74, and an interface 75 including an AD converter. It is the microcomputer which consists of.

  The interface 75 is connected to the sensors 61 to 68, supplies signals from the sensors 61 to 68 to the CPU 71, and in response to instructions from the CPU 71, the actuator 33a, the igniter 38, and the port injection valve 39P of the variable intake timing device 33. In-cylinder injection valve 39C, throttle valve actuator 43a, actuator 56a of EGR valve 56, and fuel pump 82 are sent with drive signals.

  As a result, the opening / closing timing of the intake valve 32, the fuel injection pattern of the injection valves 39P, 39C, the opening of the EGR valve 56, the pressure of the fuel injected from the injection valves 39P, 39C, etc. are changed according to the operating state of the engine. It has come to be.

(Suppression of misfire)
In the present apparatus, control for adjusting the flow rate of EGR gas by adjusting the opening degree of the EGR valve 56 (external EGR control described above) is executed. For this reason, the concentration of the burned gas remaining in the combustion chamber 25 after the exhaust stroke (residual burned gas concentration) is large. As the residual burned gas concentration increases, mixing of fuel spray and fresh air (oxygen contained therein) is more likely to be inhibited in the combustion chamber 25. If the residual burned gas concentration exceeds a certain upper limit (misfire limit), misfire may occur.

  Further, in the present apparatus, fuel cut (FC) is executed in which fuel injection from the injection valves 39P and 39C is interrupted during deceleration. Since no heat is generated due to the combustion of the fuel in the FC, when the fuel injection is resumed by the end of the FC due to reacceleration or the like (hereinafter also referred to as “when returning from the FC”), the inside of the combustion chamber 25 The gas temperature is low. The misfire limit for the residual burned gas concentration is smaller as the combustion chamber gas temperature is lower.

  From the above, for example, when FC is executed by deceleration while a large amount of EGR gas is recirculated to the intake passage by external EGR control before the start of FC, etc. The burnt gas concentration is high and the combustion chamber gas temperature is low. As a result, misfire is particularly likely to occur.

  In the present apparatus, in order to suppress the occurrence of misfire that is likely to occur at the time of return from the FC as described above, the intake valve delay opening control described below is executed. This point will be described below with reference to the routine shown in the flowchart of FIG. Note that all the routines described below are executed by the CPU 71.

(Intake valve slow open control)
First, in step 205, it is determined whether the FC condition is established. In this example, for example, the FC condition is satisfied only in a period in which a predetermined state including that the accelerator pedal operation amount Accp is maintained at zero (during deceleration) continues.

  First, a case where the FC condition is not satisfied will be described. In this case, “No” is determined in step 205, and in step 210, the amounts of fuel injected from the injection valves 39P and 39C are respectively set to the corresponding normal amounts. Specifically, each normal amount is determined based on the accelerator pedal operation amount Accp, the engine speed NE, and the like. As a result, the corresponding normal amount of fuel is injected from the injection valves 39P and 39C at the corresponding predetermined timing thereafter.

  Next, in step 215, it is determined whether or not a predetermined time has elapsed since the end of FC. In this case, “Yes” is determined, and in step 220, the opening degree of the EGR valve 56 is set to the normal opening degree. The normal opening is determined based on the accelerator pedal operation amount Accp, the engine speed NE, and the like. Specifically, the actuator 56a is feedback-controlled so that the EGR valve opening Aegr matches the current normal opening.

  Subsequently, at step 225, the opening / closing timing of the intake valve 32 is set to the normal timing. The normal timing is determined based on the accelerator pedal operation amount Accp, the engine speed NE, and the like. Specifically, the variable intake timing device 33 is feedback-controlled so that the opening / closing timing VVT coincides with the current normal timing.

  In this example, the opening / closing timing of the exhaust valve 35 is fixed, and the closing timing of the exhaust valve 35 is set in the vicinity of the intake top dead center during the intake stroke. In the normal timing, the valve opening timing of the intake valve 32 can vary from the exhaust stroke to the intake stroke in the vicinity of the intake top dead center according to the operating state. Therefore, depending on the operating state, the opening timing of the intake valve 32 is advanced from the closing timing of the exhaust valve 35, and an overlap period (a period during which both the intake and exhaust valves are kept open) is formed. Sometimes it is done.

  As described above, when the FC condition is not satisfied, the injection amount, the EGR valve opening degree, and the intake valve opening / closing timing are controlled according to the operating state of the engine (specifically, Accp, NE). The normal operation is executed.

  Next, a case where the FC condition is satisfied will be described. In this case, “Yes” is determined in step 205, and in step 230, the amounts of fuel injected from the injection valves 39P and 39C are both set to zero. As a result, fuel is not injected from the injection valves 39P and 39C. That is, FC is executed.

  Next, at step 235, the opening of the EGR valve 56 is set to zero, and at the next step 240, the current residual burned gas concentration (mass concentration) R is estimated. R is estimated based on one of well-known methods based on the throttle valve opening TA, the EGR valve opening Aegr, the opening / closing timing VVT, and the engine speed NE during normal operation. In FC, using the fact that the opening degree of the EGR valve 56 is zero, R is an estimated value immediately before the start of FC, an elapsed time from the start of FC, etc. based on one of known methods. Estimated based on. During FC, R gradually decreases from the estimated value just before the start of FC.

  Next, in step 245, it is determined whether R is larger than a predetermined value Rth. Rth is, for example, a value equal to the misfire limit described above. If “No” is determined in step 245, that is, if R does not exceed the misfire limit, the opening / closing timing of the intake valve 32 is set to the normal timing in step 225 described above. That is, even during FC, if R ≦ Rth, misfire does not occur (it is difficult), and intake valve slow-opening control is not executed.

  On the other hand, if “Yes” is determined in step 245, that is, if R exceeds the misfire limit, intake valve retarded opening control is executed in step 250. Specifically, the valve opening timing of the intake valve 32 is set in the intake stroke on the retard side with respect to the normal timing, and is set on the retard side with respect to the valve closing timing of the exhaust valve 35. The amount of retardation from the normal timing may be constant or variable.

  In this way, while the FC condition is satisfied, that is, from the start time of FC to the end time of FC, the opening degree of the EGR valve 56 is fixed to zero and (R> Rth) A) The intake valve slow-opening control is continued. In addition, when the FC is terminated due to re-acceleration or the like, “No” is determined in step 215 until the predetermined time elapses after the return from the FC, and the processing from step 235 is executed. Therefore, the opening degree of the EGR valve 56 is still fixed to zero until the predetermined time elapses after the return from the FC, and the intake valve slow opening control is still performed (when R> Rth). Will continue.

  Here, the intake valve slow opening control will be described. When the valve opening timing of the intake valve 32 is set to the retard side of the valve closing timing of the exhaust valve 35 by the intake valve delay opening control, the exhaust valve 35 is closed and thereafter The intake valve 32 opens in the process of lowering the piston while the intake / exhaust valves 32 and 35 are both closed (the process of increasing the volume of the sealed combustion chamber 25). . Therefore, immediately after the intake valve 32 is opened, the pressure of the gas in the combustion chamber 25 is lower than the pressure in the intake passage, so that the differential pressure before and after the passage of the gas passing through the throttle portion of the intake valve 32 is increased. large. As a result, the flow velocity (intake flow velocity) of the intake air flowing into the combustion chamber 25 after the intake valve 32 is opened (especially immediately after the opening) is increased.

  When the intake air flow rate is high, the atomization of the fuel spray mixed with the intake air is promoted. When the atomization of the fuel is promoted, the degree of mixing of the fuel spray and the intake air (oxygen contained therein) increases, and the fuel spray (air mixture) is easily ignited. This means that the misfire limit for the residual burned gas concentration is increased.

  From the above, the execution of the intake valve slow opening control increases the misfire limit due to the increase of the intake flow velocity. Therefore, as in the first embodiment, when the intake valve delay opening control is executed and continued from the FC start time to the time when the predetermined time has elapsed from the FC end time, within this period, The misfire limit is increased by increasing the intake flow velocity. As a result, even when returning from FC, the misfire limit is increased. As a result, the occurrence of misfire when returning from the FC can be suppressed.

  In addition, in the first embodiment, the opening degree of the EGR valve 56 is fixed to zero during the execution of the intake valve delay opening control. Therefore, the opening degree of the EGR valve 56 is maintained at zero throughout the FC. As a result, in the FC, inflow of EGR gas from the intake passage to the combustion chamber 25 is prohibited, but residual burned gas (a part thereof) is scavenged into the exhaust passage every time the exhaust stroke comes. Go. Therefore, it is possible to effectively reduce the residual burned gas concentration in the FC. As a result, the residual burned gas concentration at the time of return from FC can be reduced. This can also prevent the occurrence of misfire when returning from the FC.

  FIG. 3 shows that FC is started by deceleration (Accp = 0) in a high-load operation state in which a large amount of EGR gas is recirculated to the intake passage by external EGR control before FC starts, and then reacceleration (Accp> 0) shows an example of a change in residual burned gas concentration when FC is terminated. As shown in FIG. 3, before the start of FC, the residual burned gas concentration is maintained at a large value. However, since the gas temperature in the combustion chamber 25 is high due to the high load operation state, the misfire limit is also high. Therefore, no misfire occurs in this state.

  On the other hand, when the FC is started, as described above, the opening degree of the EGR valve 56 is maintained at zero. As a result, the residual burned gas concentration rapidly decreases as described above. In addition, in FC, since heat is not generated by the combustion of fuel, the gas temperature in the combustion chamber 25 gradually decreases, and therefore, the misfire limit gradually decreases.

  Here, it is assumed that when the above-described intake valve slow-opening control is not executed, the misfire limit at the time of return from FC is a value indicated by a broken line. In this case, if the above-described intake valve slow-opening control is not executed, the residual burned gas concentration at the time of return from FC exceeds the misfire limit, so misfire is likely to occur. On the other hand, in the first embodiment, the misfire limit is increased to the value indicated by the alternate long and short dash line in FIG. As a result, the occurrence of misfire when returning from the FC can be suppressed.

  The present invention is not limited to the first embodiment, and various modifications can be employed within the scope of the present invention. For example, in the first embodiment, in the intake valve delay opening control, the opening timing of the intake valve 32 is changed by changing the opening / closing timing of the intake valve 32. The valve opening timing of the intake valve 32 may be changed by changing. Further, in the intake valve delay opening control, the opening timing of the intake valve 32 may be changed by changing the opening / closing timing of the intake valve 32 and the maximum lift amount of the intake valve 32.

  In the first embodiment, the intake valve retarded opening control is executed only when the residual burned gas concentration R exceeds Rth. However, the intake valve retarded opening is performed regardless of the magnitude relationship between R and Rth. While the control is executed, the retardation amount from the normal timing may be determined based on R. In this case, the routine shown in the flowchart in FIG. 4 is executed instead of the routine shown in FIG.

  The routine shown in FIG. 4 differs from the routine shown in FIG. 2 only in that step 245 is omitted and steps 405 and 410 are inserted between steps 240 and 250. In step 405, the required intake flow velocity V is determined based on the residual burned gas concentration R estimated in step 240 and the table shown in FIG. In step 410, based on the required intake flow velocity V, the engine speed NE and the valve opening timing of the intake valve 32, a function obtained in advance to obtain the intake flow velocity, and the retard amount from the normal timing based on the normal timing. A is determined. Thereby, the retard amount A is determined to be larger as the residual burned gas concentration R is larger.

  In step 250, as the intake valve retarded opening control, the valve opening timing of the intake valve 32 is set to the retarded side by the retard amount A from the normal timing. As a result, when the residual burned gas concentration R is small, the retardation amount A is reduced, and the deterioration of fuel consumption due to an increase in pumping loss can be suppressed while suppressing the occurrence of misfire as described above. Further, when the residual burned gas concentration R is large, the retardation amount A is made sufficiently large. Therefore, the intake flow velocity can be sufficiently increased, and the misfire limit can be sufficiently increased. As a result, the occurrence of misfire can be reliably suppressed.

  Further, in the first embodiment, only the intake valve delay opening control is executed in order to suppress the occurrence of misfire when returning from the FC, but in order to suppress the occurrence of misfire, the compression end of the gas in the combustion chamber is controlled. Control for increasing the temperature (compression end temperature increase control) may be executed. In this case, the routine shown in the flowchart of FIG. 6 is executed instead of the routine shown in FIG.

  The routine shown in FIG. 6 differs from the routine shown in FIG. 2 only in that step 250 is replaced with steps 605, 610, and 615. In step 605, it is determined whether or not the coolant temperature THW is higher than a predetermined value THWth. If “Yes” is determined here, the intake valve retarded opening control is executed in step 610 as in the first embodiment. On the other hand, if “No” is determined, compression end temperature increase control is executed in step 615.

  Here, as the compression end temperature increase control, for example, control for advancing the closing timing of the intake valve 32 so as to be in the vicinity of the intake bottom dead center can be employed. As a result, the actual compression ratio increases and the compression end temperature rises. Further, when a mechanism for stopping some cylinders of the plurality of cylinders is provided, control for stopping some cylinders may be employed as the compression end temperature increase control. Thereby, the amount of intake air in the intake stroke per cylinder increases and the compression end temperature rises. When a device for heating fuel before injection (for example, fuel in a fuel tank) is provided, control for overheating the fuel before injection can be employed as the compression end temperature increase control. As a result, the temperature of the air-fuel mixture increases and the compression end temperature rises.

  By executing the routine shown in FIG. 6, the intake valve slow-opening control is selected and executed at a high temperature to suppress the occurrence of misfire at the time of return from FC, and the compression end temperature increase control is selected at a low temperature. This is executed to suppress the occurrence of misfire when returning from FC. As a result, it is possible to suppress the occurrence of the smoldering of the spark plug described above by executing the intake valve delay opening control at low temperatures and the above-described knocking by executing the compression end temperature increase control at high temperatures. In addition, the occurrence of misfire at the time of return from FC can be stably suppressed regardless of the coolant temperature THW.

  In the routine shown in FIG. 6, the cooling water temperature THW is divided into two regions, the intake valve slow opening control is executed at high temperatures (THW> THWth), and the compression end temperature increase control is executed at low temperatures (THW ≦ THWth). However, the coolant temperature THW is divided into three regions, and intake valve slow-opening control is executed at high temperatures (THW> THWth1), and intake valve slow-opening control and compression end temperature at medium temperatures (THWth2 <THW ≦ THWth1). The increase control may be executed together, and the compression end temperature increase control may be executed at a low temperature (THW ≦ THWth2).

(Second Embodiment)
Next, an internal combustion engine control apparatus according to a second embodiment of the present invention will be described. In this second embodiment, the intake valve delay is controlled to suppress the occurrence of misfire at the time of return from the FC only when the fuel pressure increase control is executed to suppress the occurrence of the misfire at the time of return from the FC. Different from the first embodiment in which the opening control is executed.

  In the second embodiment, the routine shown in the flowchart in FIG. 7 is executed instead of the routine shown in FIG. The routine shown in FIG. 7 differs from the routine shown in FIG. 2 only in that step 225 is replaced with step 705 and step 250 is replaced with step 710.

  Step 705 is executed during normal operation (that is, a period excluding from the FC start time to the time when a predetermined time has elapsed from the end of FC). In step 705, the pressure of the fuel injected from the injection valves 39P and 39C (fuel pressure) is set to the normal pressure. The normal pressure is determined based on the accelerator pedal operation amount Accp, the engine speed NE, and the like. Specifically, the fuel pump 82 is feedback-controlled so that the fuel pressure matches the normal pressure.

  Step 710 is executed in a period from the FC start time to the time when a predetermined time has elapsed from the end of FC. In step 710, fuel pressure increase control is executed. Specifically, the fuel pressure is set to a value larger than the normal pressure. The amount of pressure increase from the normal pressure may be constant or variable.

  In this way, during the period from the FC start time to the time when a predetermined time has elapsed from the FC end, the opening degree of the EGR valve 56 is fixed to zero, and (when R> Rth), fuel pressure increase control Will continue.

  Here, the fuel pressure increase control will be described. When the fuel pressure increases by the fuel pressure increase control, the injection speed of the fuel injected from the injection valves 39P and 39C increases. Thereby, the atomization of the fuel spray mixed with the intake air is promoted. Therefore, as in the first embodiment, the misfire limit for the residual burned gas concentration increases.

  From the above, the misfire limit becomes larger due to the increase in the injection speed due to the execution of the fuel pressure increase control. Therefore, as in the second embodiment, when the fuel pressure increase control is executed and continued from the FC start time to the time when the predetermined time has elapsed from the FC end time, the injection is performed within this period. Increasing the speed increases the misfire limit (since no fuel is injected in the FC, there is actually no change in the misfire limit in the FC). As a result, the misfire limit is increased when returning from FC. As a result, the occurrence of misfire when returning from the FC can be suppressed.

  FIG. 8 is a diagram corresponding to FIG. 3 described above. In FIG. 8, it is assumed that the misfire limit at the time of return from FC is a value indicated by a broken line when the above-described fuel pressure increase control is not executed. In this case, if the above fuel pressure increase control is not executed, the residual burned gas concentration at the time of return from the FC exceeds the misfire limit, and misfire is likely to occur. On the other hand, in the second embodiment, the misfire limit is increased to the value indicated by the alternate long and short dash line in FIG. As a result, the occurrence of misfire when returning from the FC can be suppressed.

  The present invention is not limited to the second embodiment, and various modifications can be adopted within the scope of the present invention. For example, in the second embodiment, the fuel pressure boost control is executed only when the residual burned gas concentration R exceeds Rth, but the fuel pressure boost control is performed regardless of the magnitude relationship between R and Rth. May be executed, and the amount of pressure increase from the normal pressure may be determined based on R. In this case, the routine shown in the flowchart in FIG. 9 is executed instead of the routine shown in FIG.

  The routine shown in FIG. 9 differs from the routine shown in FIG. 7 only in that step 245 is omitted and step 905 is inserted between steps 240 and 710. In step 905, the pressure increase amount B from the normal pressure is determined based on the residual burned gas concentration R estimated in step 240 and the table shown in FIG. Thereby, the pressure increase amount B is determined to be larger as the residual burned gas concentration R is larger.

  In step 710, as the fuel pressure increase control, the fuel pressure is set to a value larger than the normal pressure by the increase amount B. Thereby, when the residual burned gas concentration R is small, the pressure increase amount B is reduced, and the occurrence of misfire can be suppressed without unnecessarily increasing the pressure increase amount. Further, when the residual burned gas concentration R is large, the pressure increase amount B is sufficiently increased. Therefore, the injection speed can be sufficiently increased and the misfire limit can be sufficiently increased. As a result, the occurrence of misfire can be reliably suppressed.

  In the second embodiment, the fuel pressure of the fuel injected from the injection valves 39P and 39C is increased together as the fuel pressure increase control, but the fuel pressure of the fuel injected from the injection valves 39P and 39C is individually controlled. When the fuel pressure is increased, only one of the fuel pressures of the fuel injected from the injection valves 39P and 39C may be increased as the fuel pressure increase control.

(Third embodiment)
Next, a control device for an internal combustion engine according to a third embodiment of the present invention will be described. In the third embodiment, the intake valve delay is controlled to suppress the misfire occurrence at the time of return from the FC only when the injection number increase control is executed to suppress the occurrence of the misfire at the time of return from the FC. Different from the first embodiment in which the opening control is executed.

  In the third embodiment, the routine shown in the flowchart in FIG. 11 is executed instead of the routine shown in FIG. The routine shown in FIG. 11 differs from the routine shown in FIG. 2 only in that step 225 is replaced with step 1105 and step 250 is replaced with step 1110.

  Step 1105 is executed during normal operation (that is, a period excluding from the FC start time to the time when a predetermined time has elapsed from the end of FC). In step 1105, the number of injections (per combustion cycle) of the fuel injected from the in-cylinder injection valve 39C is set to the normal number (= 1). That is, all of the normal amount of fuel corresponding to the in-cylinder injection valve 39C determined in step 210 is injected by one injection from the in-cylinder injection valve 39C. In this example, the number of injections of fuel injected from the port injection valve 39P (per combustion cycle) is always set to one.

  Step 1110 is executed in a period from the FC start time to the time when a predetermined time has elapsed from the end of FC. In step 1110, injection number increase control is executed. Specifically, the number of injections (per combustion cycle) from the in-cylinder injection valve 39C is set to a plurality of times. With this multiple injections, all of the normal amount of fuel corresponding to the in-cylinder injection valve 39C determined in step 210 is divided and injected. The increase amount of the number of times from the normal number of times (= 1) may be constant or variable.

  In this way, during the period from the FC start time to the time when a predetermined time has elapsed from the FC end, the opening degree of the EGR valve 56 is fixed to zero, and (when R> Rth), the injection frequency increase control Will continue.

  Here, the injection number increase control will be described. When the number of injections from the in-cylinder injection valve 39C is increased by the injection number increase control, the total surface area of the fuel spray of the fuel injected from the in-cylinder injection valve 39C increases. As a result, the degree of mixing between the fuel spray and the intake air (oxygen contained therein) increases, and the fuel spray (air mixture) is easily ignited. Therefore, as in the first and second embodiments, the misfire limit for the residual burned gas concentration is increased.

  From the above, by executing the injection number increase control, the misfire limit increases due to the increase in the total surface area of the fuel spray from the in-cylinder injection valve 39C. Therefore, as in the third embodiment, when the injection number increase control is executed and continued from the FC start time to the time when the predetermined time has elapsed from the FC end time, the cylinder is changed within this period. The misfire limit is increased by increasing the total surface area of the fuel spray from the inner injection valve 39C (since no fuel is injected in the FC, the misfire limit is not actually changed in the FC). As a result, the misfire limit is increased when returning from FC. As a result, the occurrence of misfire when returning from the FC can be suppressed.

  FIG. 12 is a diagram corresponding to FIG. 3 described above. In FIG. 12, it is assumed that the misfire limit at the time of return from FC is a value indicated by a broken line when the above-described injection frequency increase control is not executed. In this case, if the above injection number increase control is not executed, the residual burned gas concentration at the time of return from FC exceeds the misfire limit, and misfire is likely to occur. On the other hand, in the third embodiment, the misfire limit is increased to the value indicated by the alternate long and short dash line in FIG. As a result, the occurrence of misfire when returning from the FC can be suppressed.

  The present invention is not limited to the third embodiment, and various modifications can be employed within the scope of the present invention. For example, in the third embodiment, the injection number increase control is executed only when the residual burned gas concentration R exceeds Rth. However, the injection number increase control is performed regardless of the magnitude relationship between R and Rth. And the number of injections may be determined based on R. In this case, the routine shown in the flowchart in FIG. 13 is executed instead of the routine shown in FIG.

  The routine shown in FIG. 13 differs from the routine shown in FIG. 11 only in that step 245 is omitted and step 1305 is inserted between steps 240 and 1110. In step 1305, the number N of injections is determined based on the residual burned gas concentration R estimated in step 240 and the table shown in FIG. Thereby, the larger the residual burned gas concentration R, the larger the number of injections N is determined.

  In step 1110, the number of injections is set to N as injection number increase control. Thereby, when the residual burned gas concentration R is small, the number of injections N is reduced, and the occurrence of misfire can be suppressed without unnecessarily increasing the number of injections. Further, when the residual burned gas concentration R is large, the number of injections N is sufficiently increased. Therefore, the total surface area can be sufficiently increased, and the misfire limit can be sufficiently increased. As a result, the occurrence of misfire can be reliably suppressed.

  In the first (second) embodiment, the intake valve delay opening control (fuel pressure boosting control) is executed from the FC start time to the time when a predetermined period elapses from the return time from the FC. However, it may be executed at least at the time of return from the FC, may be executed within a predetermined period from the time of return from the FC, or may be returned from the FC in the middle of the FC. It may be executed from the time point to the time point when the predetermined period has elapsed.

  Further, in the third embodiment, the injection number increase control is executed from the FC start time to the time when the predetermined period has elapsed from the return time from the FC, but at least at the return time from the FC. It may be executed as long as it is executed, and may be executed over a predetermined period from the time of return from FC.

  Further, in the first to third control devices, the opening degree of the EGR valve 56 is maintained at zero not only during the FC but also within a predetermined period from the time of return from the FC. May be maintained at zero only during FC, and may be set to the normal opening after the return from FC.

  In addition, in the first to third control devices, external EGR control is executed, but internal EGR control may be executed instead of external EGR control, and both external EGR control and internal EGR control are executed. It does not have to be done.

1 is a schematic configuration diagram of a system in which a control device according to a first embodiment of the present invention is applied to a spark ignition type multi-cylinder internal combustion engine. FIG. 3 is a flowchart showing a routine for execution of intake valve delay opening control executed by a CPU shown in FIG. 1. FIG. It is a figure for demonstrating that a misfire limit increases and execution of misfire is suppressed by execution of intake valve late opening control. It is the flowchart which showed the routine for execution of intake valve late opening control which CPU of the control device which relates to the modification of 1st execution form of this invention executes. FIG. 5 is a graph showing a table that defines a relationship between a residual burned gas concentration and a required intake air flow rate, which is referred to by a CPU that executes the routine shown in FIG. 4. It is the flowchart which showed the routine for selectively performing intake valve late opening control and compression end temperature rise control which CPU of the control device which concerns on the modification of 1st Embodiment of this invention performs. It is the flowchart which showed the routine for execution of fuel pressure boost control which CPU of the control device which relates to 2nd execution form of this invention executes. It is a figure for demonstrating that a misfire limit increases by execution of fuel pressure pressure | voltage rise control, and misfire generation is suppressed. It is the flowchart which showed the routine for execution of fuel pressure boost control which CPU of the control device which relates to the modification of 2nd execution form of this invention executes. 10 is a graph showing a table that defines the relationship between the residual burned gas concentration and the pressure increase amount, which is referred to by a CPU that executes the routine shown in FIG. 9. It is the flowchart which showed the routine for execution of injection frequency increase control which CPU of the control device which concerns on 3rd Embodiment of this invention performs. It is a figure for demonstrating that a misfire limit increases and execution of misfire is suppressed by execution of injection frequency increase control. It is the flowchart which showed the routine for execution of injection frequency increase control which CPU of the control device which concerns on the modification of 3rd Embodiment of this invention performs. It is the graph which showed the table which prescribes | regulates the relationship between the residual burned gas concentration and the frequency | count of injection which the CPU which performs the routine shown in FIG. 13 refers.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Spark ignition type multi-cylinder internal combustion engine, 25 ... Combustion chamber, 32 ... Intake valve, 33 ... Variable intake timing device, 35 ... Exhaust valve, 39C ... In-cylinder injection valve, 39P ... Port injection valve, 54 ... EGR gas passage 56 ... EGR valve, 70 ... electric control device, 71 ... CPU, 82 ... fuel pump

Claims (3)

Fuel injection means for injecting fuel into the combustion chamber of the internal combustion engine;
An intake valve opening timing control means for changing an opening timing of an intake valve for communicating / blocking the intake passage and the combustion chamber of the internal combustion engine based on an operating state of the internal combustion engine;
Fuel cut means for executing fuel cut for interrupting fuel injection from the fuel injection means based on the operating state of the internal combustion engine;
An internal combustion engine control apparatus comprising:
The intake valve opening timing control means includes:
When fuel injection is resumed by the end of the fuel cut, the opening timing of the intake valve is a timing during the intake stroke, and the exhaust valve that closes and connects the exhaust passage of the internal combustion engine and the combustion chamber is closed. In a control device for an internal combustion engine comprising retarding means for performing intake valve retarded opening control for retarding the valve opening timing of the intake valve so that the timing is retarded from the valve timing ,
A residual burned gas concentration estimating means for estimating a value correlated with a burned gas concentration that is a concentration of burned gas remaining in the combustion chamber;
The retard means is
The control apparatus for an internal combustion engine configured to determine a retard amount of the valve opening timing of the intake valve to be larger as the residual burned gas concentration is higher . A control device for an internal combustion engine according to claim 1 ,
Temperature increase means for performing compression end temperature increase control for increasing the temperature of the gas in the combustion chamber at the compression top dead center when fuel injection is resumed by the end of the fuel cut;
Temperature acquisition means for acquiring a value correlated with the temperature of the coolant for cooling the internal combustion engine;
When fuel injection is resumed by the end of the fuel cut, based on the temperature of the coolant, the intake valve delay opening control by the retarding means and the compression end temperature increase control by the temperature increasing means A selection means for selecting a control to be executed;
The control apparatus of the internal combustion engine provided with. A control device for an internal combustion engine according to claim 1 or 2 ,
An EGR gas passage communicating the exhaust passage and the intake passage of the internal combustion engine;
An EGR gas regulating valve interposed in the EGR gas passage and having an adjustable opening area;
An opening area control means for adjusting an opening area of the EGR gas regulating valve based on an operating state of the internal combustion engine;
With
The opening area control means includes
A control device for an internal combustion engine configured to fix an opening area of the EGR gas regulating valve to a minimum value during the fuel cut.

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