JP5556387B2 - Control device for variable valve system - Google Patents

Description

  The present invention relates to a control device for a variable valve system capable of changing the opening / closing timing of an engine valve.

  When the exhaust purification catalyst is not warmed to the activation temperature immediately after the engine is started, unburned fuel components contained in the exhaust cannot be efficiently purified by the exhaust purification catalyst. Therefore, when the exhaust purification catalyst is not warmed, it is necessary to reduce the amount of unburned fuel discharged together with the exhaust from the combustion chamber of the internal combustion engine as much as possible.

  Therefore, when the exhaust purification catalyst is not warmed, it is desirable to adjust the opening / closing timing of the engine valve, that is, the intake valve or the exhaust valve of the internal combustion engine so as to minimize the amount of unburned fuel discharged from the internal combustion engine. .

  However, when the valve overlap is increased by adjusting the opening / closing timing of the engine valve in order to suppress the discharge of unburned fuel from the internal combustion engine, a part of the exhaust gas is filled in the combustion chamber together with the air-fuel mixture. Therefore, the amount of air-fuel mixture introduced into the combustion chamber is reduced, and the amount of fuel provided for combustion is reduced.

  In addition, when heavy fuel that is difficult to vaporize is used or when the engine temperature is particularly low, when the fuel is difficult to atomize, a portion of the fuel injected from the injector remains in a liquid state while being in the intake passage The amount of fuel contained in the air-fuel mixture introduced into the combustion chamber decreases and the air-fuel mixture tends to become lean.

  For this reason, when the fuel is difficult to atomize and the air-fuel mixture is lean, if the valve overlap is increased by repeatedly changing the valve timing of the engine valve, the fuel to be used for combustion Insufficient amount of water is likely to cause unstable combustion, and cold hesitation in which an appropriate torque cannot be obtained is likely to occur.

  On the other hand, in the control apparatus for the variable valve system described in Patent Document 1, when heavy fuel that is difficult to atomize is used, the control amount of the variable valve system is reduced to reduce the overlap. I am doing so. Furthermore, Patent Document 1 also describes that when the engine temperature is low and it is estimated that the fuel is particularly difficult to atomize, changing the opening / closing timing of the engine valve by the variable valve system itself is prohibited. Yes.

  As described above, when the configuration in which the change of the opening / closing timing of the engine valve is limited when the fuel is difficult to atomize, cold hesitation caused by increasing the valve overlap can be suppressed. It becomes like this.

Japanese Patent Laid-Open No. 11-210509

  By the way, when the change of the opening / closing timing of the engine valve is uniformly limited based on the fact that the fuel is difficult to atomize as described above, the internal combustion engine is controlled by controlling the opening / closing timing of the engine valve. It becomes impossible to reduce the amount of unburned fuel that is discharged, and it becomes difficult to improve the exhaust properties when the engine is cold.

  The present invention has been made in view of the above circumstances, and its purpose is to change the opening and closing timing of the engine valve while suppressing the occurrence of cold hesitation when the exhaust purification catalyst is cold and the engine is cold. Another object of the present invention is to provide a control device for a variable valve system that can suppress the occurrence of cold hesitation while suppressing the discharge of unburned fuel from the internal combustion engine.

In the following, means for achieving the above object and its effects are described.
A control device for a variable valve system for achieving the above object is a control device for a variable valve system that performs cold control for changing an opening / closing timing of an engine valve before the exhaust purification catalyst warms to an activation temperature, Is a control device for a variable valve system that restricts the change of the opening / closing timing by the cold control when it is difficult to atomize, and outputs a detection value proportional to the air-fuel ratio of the air-fuel mixture subjected to combustion. When the sensor element of the fuel ratio sensor is activated and the air fuel ratio of the air-fuel mixture subjected to combustion can be estimated based on the detection value of the air fuel ratio sensor, the restriction is relaxed and the air fuel ratio is reduced. The gist of the invention is to execute cold control for controlling the opening / closing timing of the engine valve in accordance with the detection value of the sensor.

According to the above configuration, when the air-fuel ratio of the air-fuel mixture subjected to combustion can be estimated, the restriction on changing the opening / closing timing is eased even when the fuel is difficult to atomize. Will come to be. In the above configuration , the opening / closing timing of the engine valve is controlled according to the detection value output from the air-fuel ratio sensor.

  Therefore, even in situations where the fuel is difficult to atomize and the air-fuel mixture tends to become lean, the opening and closing timing of the engine valve is set so that the amount of fuel provided for combustion is not insufficient based on the detection value of the air-fuel ratio sensor. Will be able to control. As a result, the discharge of unburned fuel from the internal combustion engine can be suppressed as much as possible while suppressing the occurrence of cold hesitation.

That is, according to the above configuration , when the engine is cold when the exhaust purification catalyst is not warm, by changing the opening / closing timing of the engine valve while suppressing the occurrence of cold hesitation, the unburned fuel is discharged from the internal combustion engine. It is possible to suppress the occurrence of cold hesitation while suppressing.

In the above configuration, in the cold control the sensor element of the air-fuel ratio sensor is performed when activated, specifically, while setting the basic control amount based on the load factor of the internal combustion engine, the air-fuel ratio It is possible to adopt a configuration in which the opening / closing timing of the engine valve is controlled based on the target control amount calculated by correcting this basic control amount so that the valve overlap becomes smaller as the detection value of the sensor becomes higher. Is preferred .

  As described above, when the detected value of the air-fuel ratio sensor is high and the amount of fuel contained in the air-fuel mixture subjected to combustion is estimated to be small, if the valve overlap is reduced, The valve overlap becomes smaller as the introduced air-fuel mixture becomes leaner. Therefore, when the air-fuel mixture is lean, it is possible to suppress the valve overlap from becoming large, and to prevent the amount of fuel used for combustion from becoming insufficient and the combustion from becoming unstable. Can do.

  In addition, since the target control amount is set based on the detection value of the air-fuel ratio sensor and the opening / closing timing of the engine valve is controlled based on the target control amount, the unburned fuel is within the range where combustion does not become unstable. The opening / closing timing of the engine valve can be controlled so that the discharge amount can be reduced as much as possible. Therefore, it is possible to effectively suppress the occurrence of cold hesitation while suppressing the discharge of unburned fuel from the internal combustion engine as much as possible.

Further, in the above configuration, activation promotion processing for activating the sensor element at an early stage may be executed until the sensor element of the air-fuel ratio sensor is activated .

According to the above Ki構 formed, since the sensor element of the air-fuel ratio sensor is to activate prematurely, the changing of the opening-closing timing restriction is to be alleviated early based on the detected value of the air-fuel ratio sensor opening The timing change can be started early. Thereby, the opportunity to change the opening / closing timing through the cold control is increased, and the discharge of unburned fuel can be more effectively suppressed.

  The specific contents of the activation promotion process include a method of increasing the energization amount to the heater that heats the sensor element of the air-fuel ratio sensor, or by retarding the ignition timing in each cylinder of the internal combustion engine. For example, a method of warming the sensor element of the air-fuel ratio sensor by using the heat of the exhaust gas can be employed. It is also possible to apply a method of warming the sensor element of the air-fuel ratio sensor by increasing the idling rotational speed, which is the engine rotational speed during idling operation, to increase the temperature of the exhaust gas during idling operation.

  By the way, if the opening timing of the exhaust valve is retarded, the period from when ignition is performed to when the exhaust valve is opened becomes longer, so the exhaust gas is discharged after the mixture starts to burn in the combustion chamber. The period until it starts to be discharged to the exhaust port becomes longer. Therefore, it is possible to ensure a long time for burning the fuel contained in the air-fuel mixture in the combustion chamber, and to reduce the amount of unburned fuel discharged from the combustion chamber together with the exhaust gas. .

Therefore, in the above configuration, as the cold control executed in order to suppress the emission of unburned fuel, it is preferable to apply the control to retard the opening timing of the exhaust valve.

  On the other hand, when a configuration is adopted in which the opening / closing timing of the intake valve is advanced, a part of the exhaust is blown back to the intake port, so the exhaust port is warmed by the blown back exhaust, and fuel atomization is promoted. Become so. As a result, an increase in fuel for bringing the air-fuel ratio of the air-fuel mixture close to the stoichiometric air-fuel ratio can be reduced, and as a result, the amount of unburned fuel discharged together with the exhaust gas can be reduced.

Therefore, in the above configuration, as the cold control executed in order to suppress the emission of unburned fuel, it is preferable to employ a control to advance the closing timing of the intake valve.

  In order to retard the opening timing of the exhaust valve, if the exhaust camshaft is displaced to the retarded side and the entire opening / closing timing of the exhaust valve is retarded, the closing timing of the exhaust valve is also retarded. As a result, the valve overlap increases. If the valve overlap increases due to the retarded timing of the exhaust valve closing, part of the exhaust gas is introduced into the combustion chamber during the intake stroke, and the amount of air-fuel mixture introduced into the combustion chamber decreases. To come. In a situation where the fuel is difficult to atomize and the air-fuel mixture tends to become lean, if the amount of air-fuel mixture introduced into the combustion chamber decreases, the amount of fuel provided for combustion will be significantly insufficient and combustion will become unstable It becomes easy to become.

Therefore, in addition to the opening and closing timing of the exhaust valve, when provided with a variable valve system that can change the opening period of the equal and exhaust valves to change the working angle, the opening timing of the exhaust valve It is desirable to retard the valve opening period of the exhaust valve and retard the valve opening timing of the exhaust valve while preventing the valve closing timing from being retarded as much as possible. By adopting such a configuration, the valve opening timing of the exhaust valve is retarded through cold control, while an increase in valve overlap can be suppressed, and the valve overlap as described above increases. It is possible to suppress the discharge of unburned fuel while suppressing the resulting unstable combustion.

When the engine temperature becomes high, the fuel is easily atomized, and most of the fuel injected from the injector is introduced into the combustion chamber without adhering to the wall surface of the intake passage. Therefore, in the above configuration, as a method for estimating the fuel is in a state difficult to atomize, the fuel to adopt a configuration of estimating that the state hard to atomize based on engine temperature is less than the reference engine temperature be able to.

By adopting such a configuration, it is possible to estimate whether or not the fuel is difficult to atomize based on the estimated engine temperature by estimating the engine temperature.
The reference engine temperature may be set based on the results of experiments and the like performed in advance so that it can be estimated that the fuel is difficult to atomize based on the engine temperature being lower than the reference engine temperature. Good.

Further, when the fuel being used is a heavy fuel that is difficult to vaporize, the fuel is difficult to atomize. Therefore, in the said structure, it can also be estimated that a fuel is a state which is hard to atomize based on the fuel currently used being heavy fuel.

  As a specific method for determining whether or not the fuel being used is heavy fuel, it is possible to monitor changes in the pressure in the fuel tank and determine whether or not the fuel is likely to vaporize based on the result. It is possible to adopt a configuration for determining whether or not, a method for determining the properties of fuel using a sensor, and the like. Also, apply a configuration that monitors how the engine speed rises during cold start and estimates that the fuel is heavy fuel that is difficult to vaporize at low temperatures when the engine speed does not rise quickly. Can do.

When the sensor element of the air-fuel ratio sensor is activated, a detection value indicating the concentration of oxygen contained in the exhaust gas is output from the air-fuel ratio sensor. Therefore, in the above configuration, it is possible to adopt a configuration in which it is estimated that the air-fuel ratio sensor is activated based on the fact that the detection value is output from the air-fuel ratio sensor. Then, when it is estimated that the air-fuel ratio sensor is activated, the restriction on the change of the opening / closing timing in the cold control is relaxed, and the opening / closing timing is changed based on the detection value output from the air-fuel ratio sensor. That's fine.

Further, in the above configuration, it is also possible to adopt a configuration in which it is estimated that the sensor element of the air-fuel ratio sensor is activated based on the execution of the air-fuel ratio feedback control, and the restriction on changing the opening / closing timing is relaxed. .

  Since the engine cooling water temperature at the time of starting the engine is estimated to be approximately equal to the engine temperature at the time of starting the engine, if the amount of increase in engine temperature accompanying engine operation is estimated based on the amount of increase in engine cooling water temperature after engine starting The engine temperature can be estimated based on the engine coolant temperature at the time of starting the engine and the amount of increase in the engine coolant temperature after the engine is started.

  Therefore, if the value of the increase amount of the engine coolant temperature estimated to be obtained when the engine temperature rises to the reference engine temperature is set in advance as the reference value, the engine coolant temperature after engine startup When the increase amount of the engine is less than the reference value, it can be estimated that the engine temperature is less than the reference engine temperature. Therefore, if a calculation map in which these reference values are plotted for each engine cooling water temperature at the time of starting the engine is prepared in advance, the engine cooling water temperature at the time of starting the engine and the engine after the engine is started by referring to this calculation map. Based on the amount of increase in the cooling water temperature, it is possible to estimate whether or not the fuel is difficult to atomize.

  Further, when estimating whether or not the fuel is difficult to atomize by referring to such a calculation map, an increase in the engine coolant temperature required until the sensor element of the air-fuel ratio sensor is activated in this calculation map. It is possible to estimate that the sensor element of the air-fuel ratio sensor has been activated by adding information indicating the magnitude of the quantity and referring to this calculation map.

  That is, if the value of the increase amount of the engine coolant temperature estimated to be obtained when the sensor element of the air-fuel ratio sensor is activated is plotted on this calculation map for each engine coolant temperature at the time of engine start. It is possible to estimate that the sensor element of the air-fuel ratio sensor has been activated based on the increase amount of the engine coolant temperature reaching the plotted increase amount.

Therefore, in the above configuration, an arithmetic map is provided for estimating that the engine temperature is lower than the reference engine temperature based on the engine cooling water temperature at the time of starting the engine and the amount of increase in the engine cooling water temperature after the engine is started. In the calculation map for estimating whether or not the fuel is difficult to atomize, the sensor element of the air-fuel ratio sensor is added to the calculation map based on the amount of increase in the engine coolant temperature after the engine is started. By adding information for estimating whether or not the sensor is activated, it is possible to estimate that the sensor element of the air-fuel ratio sensor has been activated with reference to the calculation map. By referring to the engine cooling water temperature at the time of starting the engine and the amount of increase in the engine cooling water temperature after starting the engine, it is possible to realize a configuration that relaxes the restriction on changing the opening / closing timing.

  Since the intake air amount of the internal combustion engine has a high correlation with the magnitude of combustion heat accompanying engine operation, the integrated intake air amount, which is the integrated value of the intake air amount after engine startup, is It has a high correlation with the temperature rise. That is, it is estimated that the amount of increase in engine temperature after engine startup increases as the integrated intake air amount increases.

Therefore, instead of the configuration for estimating the amount of increase in the engine temperature on the basis of the amount of increase in institutional coolant temperature, to estimate the amount of increase of the engine temperature on the basis of a totalized amount of intake air, and the engine coolant temperature at engine starting Further, it is possible to adopt a configuration that estimates whether or not the fuel is difficult to atomize based on the integrated intake air amount after engine startup.

  In this case, the value of the cumulative intake air amount estimated to be obtained when the engine temperature rises to the reference engine temperature according to the engine coolant temperature at the time of starting the engine is set as the reference value. When the integrated intake air amount after start-up is less than this reference value, it may be estimated based on that that the engine temperature is less than the reference engine temperature.

  If a calculation map in which these reference values are plotted for each engine coolant temperature at the time of starting the engine is prepared in advance, by referring to this calculation map, the engine coolant temperature at the time of engine start and the integrated intake air after the engine start Based on the amount, it can be estimated whether or not the fuel is in a state of being difficult to atomize.

  Further, when estimating whether or not the fuel is difficult to atomize by referring to such a calculation map, the calculated intake air amount required until the sensor element of the air-fuel ratio sensor is activated is calculated in this calculation map. It is possible to estimate that the sensor element of the air-fuel ratio sensor is activated by adding information indicating the size and referring to the calculation map.

  That is, if the value of the integrated intake air amount estimated to be obtained when the sensor element of the air-fuel ratio sensor is activated is plotted on this calculation map according to the engine coolant temperature at the time of engine start, Based on the fact that the integrated intake air amount has reached the plotted value, it is possible to estimate that the sensor element of the air-fuel ratio sensor has been activated.

Therefore, with the engine coolant temperature at agencies start, the calculation map for the engine temperature based on the accumulated intake air amount after engine start is estimated to be less than the reference engine temperature, with reference to this computation map In this calculation map, it is determined whether or not the sensor element of the air-fuel ratio sensor is activated based on the integrated intake air amount after the engine is started. By adding information for estimation, it becomes possible to estimate that the sensor element of the air-fuel ratio sensor has been activated with reference to the calculation map, and with reference to the calculation map, Based on the engine coolant temperature and the integrated intake air amount after engine startup, it is possible to realize a configuration that relaxes the restriction on changing the opening / closing timing.

It should be noted that the mode of restricting the change of the opening / closing timing by the cold control when the fuel is difficult to atomize includes prohibiting the execution of the cold control when the fuel is difficult to atomize. Therefore, in the above configuration, the execution of cold control is prohibited when the fuel is difficult to atomize, while the sensor element of the air-fuel ratio sensor is activated and used for combustion based on the detected value of the air-fuel ratio sensor. When it becomes possible to estimate the air-fuel ratio of the air-fuel mixture, the cold control is executed to cancel the prohibition of cold control and control the opening and closing timing of the engine valve according to the detection value of the air-fuel ratio sensor It is also possible to adopt a configuration to

1 is a schematic diagram showing an outline configuration of an electronic control device according to an embodiment of the present invention and an internal combustion engine that is a control target of the electronic control device. FIG. The flowchart which shows the flow of a series of processes concerning the control premise flag setting routine of the embodiment. The calculation map referred in order to set the control premise flag concerning the embodiment. The flowchart which shows the flow of a series of processes concerning the cold control of the embodiment. An arithmetic map for calculating a basic target displacement angle based on the engine rotation speed and the load factor. The graph which shows the relationship between an air fuel ratio and a correction coefficient. Explanatory drawing which shows the relationship between integrated intake air amount and a final target displacement angle. The example of a change of the calculation map referred in order to set a control premise flag. The flowchart which shows the flow of a series of processes concerning the control premise flag setting routine as a modification.

  Hereinafter, an embodiment in which a control device for a variable valve system according to the present invention is embodied as an electronic control device that comprehensively controls an internal combustion engine will be described with reference to FIGS. FIG. 1 is a schematic diagram showing the relationship between the electronic control device 100 according to the present embodiment and the internal combustion engine 10 that is the control target.

  As shown in FIG. 1, a piston 13 is slidably accommodated in a cylinder 12 formed in a cylinder block 11 of the internal combustion engine 10. The piston 13 is connected to the crankshaft 16 via a connecting rod 15. The cylinder block 11 is formed with a water jacket 14 through which engine cooling water circulates so as to surround each cylinder 12.

  A cylinder head 17 is assembled to the upper portion of the cylinder block 11, and a combustion chamber 18 is defined by the inner peripheral surface of the cylinder 12, the top surface of the piston 13, and the cylinder head 17. Although the internal combustion engine 10 is a multi-cylinder internal combustion engine having a plurality of cylinders 12, only one of the plurality of cylinders 12 is shown in FIG.

  An ignition plug 19 is provided above each combustion chamber 18 in the cylinder head 17 so as to face the piston 13. In addition, the cylinder head 17 is formed with an intake port 21 and an exhaust port 22 communicating with each combustion chamber 18. The intake port 21 is provided with an injector 20 that injects fuel toward the combustion chamber 18.

  The intake port 21 is connected to the intake manifold and forms a part of the intake passage 30. The exhaust port 22 is connected to the exhaust manifold to form a part of the exhaust passage 40.

  As shown in FIG. 1, the intake passage 30 is provided with a throttle valve 33 that adjusts an intake air amount Ga that is driven by a motor 33 a and introduced into the combustion chamber 18. On the other hand, as shown on the left side of FIG. 1, the exhaust passage 40 is provided with an exhaust purification catalyst 45 carrying a three-way catalyst for purifying hydrocarbons, carbon monoxide, and nitrogen oxides contained in the exhaust. It has been.

  As shown in FIG. 1, the cylinder head 17 is provided with an intake valve 31 for communicating / blocking the intake passage 30 and the combustion chamber 18, and exhaust for communicating / blocking the exhaust passage 40 and the combustion chamber 18. A valve 41 is provided. Each valve 31 and 41 is always urged in the valve closing direction by the urging force of the valve spring. An intake camshaft 32 that drives the intake valve 31 and an exhaust camshaft 42 that drives the exhaust valve 41 are rotatably supported inside the cylinder head 17.

  The camshafts 32 and 42 are connected to the crankshaft 16 through a timing chain (not shown), and when the crankshaft 16 rotates twice, the camshafts 32 and 42 rotate one time respectively. Yes. As a result, when the crankshaft 16 rotates with engine operation, the intake camshaft 32 and the exhaust camshaft 42 rotate, and the intake valve 31 is lifted in the valve opening direction by the action of the cam crest formed on the intake camshaft 32. The exhaust valve 41 is lifted in the valve opening direction by the action of the cam crest formed on the exhaust camshaft 42.

  Further, as indicated by a two-dot chain line in FIG. 1, the internal combustion engine 10 is provided with an intake side valve timing changing mechanism 51 and an exhaust side valve timing changing mechanism 52 as variable valve systems. The intake-side valve timing changing mechanism 51 is provided at a portion where the intake camshaft 32 and the timing chain are connected. By changing the rotational phase of the intake camshaft 32 with respect to the rotational phase of the crankshaft 16, the intake side valve timing changing mechanism 51 The opening / closing timing of the valve 31 is changed. On the other hand, the exhaust side valve timing changing mechanism 52 is provided at a portion where the exhaust camshaft 42 and the timing chain are connected, and changes the rotational phase of the exhaust camshaft 42 relative to the rotational phase of the crankshaft 16. The opening / closing timing of the exhaust valve 41 is changed.

  These valve timing changing mechanisms 51 and 52 are hydraulically driven type that change the phase angle of each camshaft 32 and 42 by using the hydraulic pressure of hydraulic oil pumped by an oil pump (not shown) connected to the crankshaft 16. This is a valve timing changing mechanism.

  The internal combustion engine 10 is provided with various sensors that detect the state of each part of the internal combustion engine 10. For example, the water temperature sensor 60 provided in the cylinder block 11 detects the engine cooling water temperature that is the temperature of the engine cooling water circulating in the water jacket 14. A crank position sensor 61 provided in the vicinity of the crankshaft 16 detects a rotation angle of the crankshaft 16, and the electronic control unit 100 indicates an engine rotation speed indicating the number of rotations of the crankshaft 16 per unit time based on this rotation angle. NE is calculated. The throttle position sensor 63 detects the throttle opening that is the opening of the throttle valve 33. An air flow meter 64 provided in the intake passage 30 detects an intake air amount Ga that is an amount of air introduced into the combustion chamber 18 through the intake passage 30. The intake side cam position sensor 65 provided in the vicinity of the intake camshaft 32 outputs a signal corresponding to the rotational phase of the intake camshaft 32. An exhaust side cam position sensor 66 provided in the vicinity of the exhaust camshaft 42 outputs a signal corresponding to the rotational phase of the exhaust camshaft 42. An air-fuel ratio sensor 67 provided in a portion upstream of the exhaust purification catalyst 45 in the exhaust passage 40 outputs a detection value proportional to the air-fuel ratio of the air-fuel mixture provided for combustion according to the concentration of oxygen contained in the exhaust gas. To do. Further, the downstream side of the exhaust purification catalyst 45 in the exhaust passage 40 is bordered by an oxygen concentration corresponding to the oxygen concentration when the air-fuel ratio of the air-fuel mixture subjected to combustion is adjusted to the stoichiometric air-fuel ratio. An oxygen sensor 68 whose output value changes suddenly is provided.

  These various sensors are electrically connected to an electronic control unit 100 that controls the internal combustion engine 10 in an integrated manner. In addition, an accelerator position sensor 62 attached to the accelerator pedal 53 is also connected to the electronic control device 100. The accelerator position sensor 62 detects an accelerator operation amount indicating the amount of depression of the accelerator pedal 53 by the driver.

  The electronic control unit 100 temporarily stores a central processing unit (CPU) that performs various types of arithmetic processing related to engine control, a read-only memory (ROM) that stores programs and data for engine control, and results of arithmetic processing. A random access memory (RAM) or the like for storage. The electronic control unit 100 reads the detection signals of the various sensors 60 to 68, executes various arithmetic processes, and comprehensively controls the internal combustion engine 10 based on the results.

  Specifically, the electronic control unit 100 adjusts the intake air amount Ga by changing the throttle opening by controlling the motor 33a based on the engine speed NE and the accelerator operation amount. In addition, the target fuel injection amount is set so that the air-fuel ratio of the air-fuel mixture introduced into the combustion chamber 18 approaches the stoichiometric air-fuel ratio, the injector 20 is driven to adjust the fuel injection amount, and the air-fuel ratio is adjusted. Air-fuel ratio feedback control is performed in which the fuel injection amount is feedback controlled based on the output values of the fuel ratio sensor 67 and the oxygen sensor 68.

  Further, the electronic control unit 100 drives the intake side valve timing changing mechanism 51 and the exhaust side valve timing changing mechanism 52 based on the engine rotational speed NE and the load factor KL to set the opening / closing timings of the intake valve 31 and the exhaust valve 41. change.

  The electronic control apparatus 100 according to the present embodiment includes an engine in which the exhaust purification catalyst 45 is not warmed to the activation temperature in addition to normal valve timing control (hereinafter referred to as warm control) performed after the warm-up is completed. Execute cold control to suppress the discharge of unburned fuel when cold.

  When the exhaust purification catalyst 45 is not warmed to the activation temperature, just after the engine is started, the unburned fuel component contained in the exhaust cannot be efficiently purified by the exhaust purification catalyst 45. Therefore, when the exhaust purification catalyst 45 is not warmed, it is necessary to reduce the amount of unburned fuel discharged together with the exhaust from the combustion chamber 18 of the internal combustion engine 10 as much as possible.

  Therefore, when the exhaust purification catalyst 45 is not warmed, the electronic control unit 100 is a cold that delays the closing timing of the exhaust valve 41 so as to minimize the amount of unburned fuel discharged from the internal combustion engine 10. Execute control.

  When the valve closing timing of the exhaust valve 41 is retarded, the period from when ignition is performed until the exhaust valve 41 is opened becomes longer, so the air-fuel mixture starts to burn in the combustion chamber 18. The period until exhaust begins to be exhausted to the exhaust port 22 becomes longer. Therefore, it is possible to ensure a long time for burning the fuel contained in the air-fuel mixture in the combustion chamber 18 and to reduce the amount of unburned fuel discharged from the combustion chamber 18 together with the exhaust gas. It becomes like this.

  However, when the valve closing timing of the exhaust valve 41 is retarded in order to suppress the discharge of unburned fuel from the internal combustion engine 10, the valve overlap becomes large, and a part of the exhaust together with the mixture is in the combustion chamber 18. As a result, the amount of the air-fuel mixture introduced into the combustion chamber 18 decreases, and the amount of fuel used for combustion decreases.

  Further, when the fuel is difficult to atomize, such as when heavy fuel that is difficult to vaporize is used, or when the engine temperature is particularly low, the fuel injected from the injector 20 is partially in the liquid state and is aspirated. It adheres to the wall surface of the passage 30 and the amount of fuel contained in the air-fuel mixture introduced into the combustion chamber 18 is reduced, so that the air-fuel mixture tends to become lean.

  Therefore, when the fuel is difficult to atomize and the air-fuel mixture is lean, if the valve overlap is delayed and the valve overlap is increased, the valve overlap is increased, and the fuel is used for combustion. Insufficient amount of fuel is likely to cause instability of combustion, and cold hesitation in which an appropriate torque cannot be obtained easily occurs.

  On the other hand, as described in Patent Document 1, when it is estimated that the engine temperature is low and the fuel is particularly difficult to atomize, the change of the opening / closing timing of the engine valve by the variable valve system itself is performed. Prohibition is also possible.

  However, when the change of the opening / closing timing of the engine valve is uniformly restricted based on the fact that the fuel is difficult to atomize, it is discharged from the internal combustion engine 10 by controlling the opening / closing timing of the engine valve. It becomes impossible to reduce the amount of unburned fuel, and it becomes difficult to improve exhaust properties when the engine is cold.

  Therefore, in the present embodiment, even if the fuel is difficult to atomize, the sensor element of the air-fuel ratio sensor 67 is activated, and the air-fuel ratio of the air-fuel mixture subjected to combustion can be estimated. In some cases, the prohibition of cold control is canceled and the valve closing timing of the exhaust valve 41 is retarded based on the detection value of the air-fuel ratio sensor 67.

Hereinafter, a series of processes related to the cold control executed by the electronic control apparatus 100 according to the present embodiment will be described in detail with reference to FIGS.
The electronic control unit 100 executes a control premise flag setting routine shown in FIG. 2 and a routine shown in FIG. 4 when the exhaust purification catalyst 45 is cold until it is not warmed to the activation temperature. 2 is a flowchart showing a flow of a series of processes related to the control premise flag setting routine, and FIG. 4 is a flowchart showing a flow of a series of processes in the routine related to cold control.

  The control premise flag setting routine is a routine for setting a control premise flag to be referred to for determining whether or not to perform cold control, and during the cold before the exhaust purification catalyst 45 is completely activated. The electronic control device 100 is repeatedly executed at a predetermined control cycle.

  As shown in FIG. 2, when the control premise flag setting routine is started, the electronic control unit 100 first determines whether or not the engine temperature is lower than the reference engine temperature in step S100. Here, referring to the calculation map as shown in FIG. 3, whether or not the engine temperature is lower than the reference engine temperature based on the engine cooling water temperature at the time of starting the engine and the amount of increase in the engine cooling water temperature after the engine is started. Determine whether.

  The reference engine temperature is set based on the result of an experiment or the like that is performed in advance so that it can be estimated that the fuel is not easily atomized based on the engine temperature being lower than the reference engine temperature. Yes. The reference engine temperature is set to a value lower than the engine temperature when the exhaust purification catalyst 45 is warmed to the activation temperature and fully activated.

  Since the engine cooling water temperature at the time of starting the engine is estimated to be substantially equal to the engine temperature at the time of starting the engine, the amount of increase in engine temperature accompanying engine operation is estimated based on the amount of increase in engine cooling water temperature after engine starting. For example, the current engine temperature can be estimated based on the engine cooling water temperature at the time of starting the engine and the amount of increase in the engine cooling water temperature after the engine is started.

  Therefore, if the value of the increase amount of the engine coolant temperature estimated to be obtained when the engine temperature rises to the reference engine temperature is set in advance as the reference value, the engine coolant temperature after engine startup When the increase amount of the engine is less than the reference value, it can be estimated that the engine temperature is less than the reference engine temperature.

  In this calculation map, it is estimated that the boundary line A for determining whether or not the engine temperature is lower than the reference engine temperature is obtained when the engine temperature rises to the reference engine temperature. The value of the amount of increase in the engine coolant temperature is set based on the alternate long and short dash line Y plotted for each engine coolant temperature when the engine is started.

  In this step S100, when the amount of increase in the engine cooling water temperature after the engine is started is included in a region below the boundary line A shown in FIG. 3, the engine temperature is lower than the reference engine temperature based on that. Judgment is made. On the other hand, if the amount of increase in the engine cooling water temperature after engine startup is on the boundary line A shown in FIG. 3 or if it is included in the region above the boundary line A, the engine temperature is Determine that the temperature is above the reference engine temperature.

  Note that the boundary line A is set so as not to fall below the amount of increase in the engine coolant temperature necessary to secure the hydraulic pressure necessary to drive the exhaust side valve timing changing mechanism 52 indicated by the broken line X in FIG. ing. That is, when the boundary A is in a state where the hydraulic pressure is not secured and the exhaust side valve timing changing mechanism 52 cannot be driven, it is determined that the engine temperature is not higher than the reference engine temperature. Is set to

  If it is determined in step S100 that the engine temperature is lower than the reference engine temperature (step S100: YES), that is, if it is estimated that the engine temperature is low and the fuel is difficult to atomize, step Proceeding to S110, the electronic control unit 100 determines whether or not the sensor element of the air-fuel ratio sensor 67 is activated.

  When the sensor element of the air-fuel ratio sensor 67 is activated, a detection value indicating the concentration of oxygen contained in the exhaust gas is output from the air-fuel ratio sensor 67. Therefore, here, based on whether or not the detection value is output from the air-fuel ratio sensor 67, it is determined whether or not the sensor element of the air-fuel ratio sensor 67 is activated. Specifically, when the detection value is output from the air-fuel ratio sensor 67, it is determined that the sensor element of the air-fuel ratio sensor 67 is activated, while the detection value is not output from the air-fuel ratio sensor 67. Next, it is determined that the sensor element of the air-fuel ratio sensor 67 is not activated.

  If it is determined in step S110 that the sensor element of the air-fuel ratio sensor 67 is not activated (step S110: NO), the process proceeds to step S120, and the electronic control unit 100 sets the control premise flag to “OFF”. Set to.

  And it progresses to step S130 and performs the activation promotion process for activating the sensor element of the air fuel ratio sensor 67 at an early stage. In this activation promotion process, the amount of power supplied to the heater provided in the air-fuel ratio sensor 67 is increased to warm the sensor element and promote the activation of the sensor element.

When the activation promotion process is executed in this way, the electronic control unit 100 once ends this control premise flag setting routine.
On the other hand, when it is determined in step S110 that the sensor element of the air-fuel ratio sensor 67 is activated (step S110: YES), the process proceeds to step 140, and the electronic control unit 100 sets the control premise flag to “ Set to “ON”.

  Further, when it is determined in step S100 that the engine temperature is equal to or higher than the reference engine temperature (step S100: NO), that is, when it is estimated that the engine temperature is high and the fuel is not easily atomized. The electronic control unit 100 skips step S110 and proceeds to step S140, and sets the control premise flag to “ON”.

When the control premise flag is set in this way, the electronic control unit 100 once ends this control premise flag setting routine.
The routine shown in FIG. 4 is a routine for determining whether or not to execute cold control based on the control premise flag set through the control premise flag setting routine, and actually executing cold control based on the determination. The electronic control device 100 is repeatedly executed at a predetermined control period when it is cold before the exhaust purification catalyst 45 is completely activated.

When this routine is started as shown in FIG. 4, the electronic control unit 100 first determines whether or not the control premise flag is set to “ON” in step S200.
If it is determined in step S200 that the control premise flag is set to “ON” (step S200: YES), the process proceeds to step S210, and the electronic control unit 100 executes the cold control priority process. To do. This cold control priority process is a process executed in order to avoid the interference between the warm control and the cold control, and the electronic control unit 100 can change the variable valve by the warm control through the cold control priority process. The system is prohibited from being driven, and shifts to a state in which control of the variable valve system through cold control is preferentially executed.

  When the cold control priority process is executed through step 210, the process proceeds to step S220, in which the electronic control unit 100 is the basic value of the control amount of the exhaust side valve timing changing mechanism 52 for retarding the opening / closing timing of the exhaust valve 41. A basic target displacement angle Tb as a basic control amount is calculated based on the engine speed NE and the load factor KL. The load factor KL is a value indicating the intake air amount Ga per unit rotational speed, and is calculated by dividing the intake air amount Ga by the engine rotational speed NE.

  Here, the basic target displacement angle Tb is calculated with reference to the calculation map as shown in FIG. This calculation map has m parameters KL1 to KLm for the load factor KL and n parameters NE1 to NEn for the engine speed NE (m and n are positive integers). . For this reason, in this calculation map, a total of (m × n) values are stored as values of the basic target displacement angle Tb corresponding to each parameter combination. Thereby, for example, when the value of the load factor KL is “KL1” and the value of the engine rotational speed NE is “NE1”, “Tb (KL1, NE1)” by referring to the calculation map of FIG. Is calculated as the basic target displacement angle Tb.

When the basic target displacement angle Tb is calculated with reference to the calculation map shown in FIG. 5, the process proceeds to step S230, and the electronic control unit 100 limits the target displacement angle based on the air-fuel ratio.
Specifically, the air-fuel ratio of the air-fuel mixture subjected to combustion is estimated based on the detection value of the air-fuel ratio sensor 67, and the correction coefficient K is calculated according to the estimated air-fuel ratio. Then, a target displacement angle limited based on the air-fuel ratio is calculated by setting a value calculated by multiplying the basic target displacement angle Tb by the correction coefficient K as a target displacement angle.

  As shown in FIG. 6, the correction coefficient K is set to “1.0” when the air-fuel ratio of the air-fuel mixture subjected to combustion is equal to or lower than the stoichiometric air-fuel ratio, while the air-fuel ratio is higher than the stoichiometric air-fuel ratio. It is calculated based on the air-fuel ratio so as to become smaller. As a result, the target displacement angle is set to a smaller value and the retard amount of the opening / closing timing of the exhaust valve 41 becomes smaller as the air-fuel ratio is higher, that is, as the air-fuel ratio subjected to combustion is leaner. .

  When the target displacement angle is limited based on the air-fuel ratio through step S230, the process proceeds to step S240, and the electronic control unit 100 determines the final target displacement based on the integrated intake air amount ΣGa that is the integrated value of the intake air amount Ga after engine startup. The angle Tf is calculated.

  Since the intake air amount Ga has a high correlation with the magnitude of the combustion heat accompanying engine operation, the integrated intake air amount ΣGa, which is the integrated value of the intake air amount Ga after engine startup, is increased in the temperature of the exhaust purification catalyst 45. High correlation with quantity. That is, it is estimated that as the integrated intake air amount ΣGa is larger, the temperature of the exhaust purification catalyst 45 increases and the exhaust purification catalyst 45 is activated.

  Therefore, here, the degree of activation of the exhaust purification catalyst 45 is estimated based on the integrated intake air amount ΣGa, and the amount of reflection of the target displacement angle to the displacement angle control in the actual exhaust side valve timing changing mechanism 52 is calculated as the exhaust gas amount. The purification catalyst 45 is reduced as the activation progresses.

  Specifically, as indicated by a one-dot chain line in FIG. 7, the upper limit guard value is set so that the cumulative intake air amount ΣGa becomes smaller as it becomes larger than “S1” and becomes “0” when it reaches “S2”. Is set. “S1” is the cumulative intake air amount ΣGa when the exhaust purification catalyst 45 starts to be activated, and “S2” is the cumulative intake air amount ΣGa when the exhaust purification catalyst 45 is fully activated.

  Then, the target displacement angle is limited by this upper limit guard value as shown by the solid line in FIG. 7, and when the target displacement angle is larger than this upper limit guard value as shown by the broken line, the final target displacement angle Tf is set to The value is set equal to the upper guard value. As a result, the retard amount of the opening / closing timing of the exhaust valve 41 controlled through the cold control is increased as the exhaust purification catalyst 45 is activated and the unburned fuel contained in the exhaust can be efficiently cleaned. Get smaller.

  When the final target displacement angle Tf is calculated based on the integrated intake air amount ΣGa in this way, the process proceeds to step S250, and the electronic control unit 100 drives the variable valve system based on the final target displacement angle Tf. That is, the exhaust valve timing changing mechanism 52 is driven so that the displacement angle of the exhaust camshaft 42 coincides with the final target displacement angle Tf to control the delay amount of the opening / closing timing of the exhaust valve 41.

When the cold control for delaying the opening / closing timing of the exhaust valve 41 is executed through steps S220 to S250, the electronic control unit 100 once ends this routine.
On the other hand, if it is determined in step S200 that the control premise flag is set to “OFF” (step S200: NO), the process proceeds to step S215, and the electronic control unit 100 performs the cold control priority process. Is released. And this routine is once complete | finished, without performing step S220-250. That is, this routine is temporarily terminated without executing the cold control.

  As described above, in the present embodiment, whether or not to perform the cold control is switched with reference to the control premise flag. As a result, even if it is estimated that the fuel is difficult to atomize, when it is estimated that the air-fuel ratio sensor 67 is activated, the cooling is performed based on the detection value of the air-fuel ratio sensor 67. Inter-control is executed.

  That is, in this embodiment, when it is estimated that the engine temperature is lower than the reference engine temperature and the fuel is difficult to atomize, the execution of the cold control is not uniformly prohibited, but the air-fuel ratio When the sensor 67 is activated, the prohibition of the cold control is canceled and the cold control is executed based on the detection value of the air-fuel ratio sensor 67.

According to the embodiment described above, the following effects can be obtained.
(1) When the air-fuel ratio sensor 67 is activated and the air-fuel ratio of the air-fuel mixture subjected to combustion can be estimated, cold control is performed even when the fuel is difficult to atomize. Will be executed. At this time, the opening / closing timing of the exhaust valve 41 is controlled according to the detection value output from the air-fuel ratio sensor 67.

  Therefore, even in a situation where the fuel is difficult to atomize and the air-fuel mixture is likely to become lean, the exhaust valve 41 is opened and closed so that the amount of fuel provided for combustion is not insufficient based on the detection value of the air-fuel ratio sensor 67. The timing can be controlled. Thereby, discharge | emission of the unburned fuel from the internal combustion engine 10 can be suppressed as much as possible, suppressing generation | occurrence | production of cold hesitation.

  In other words, when the exhaust purification catalyst 45 is not warm, the occurrence of cold hesitation is suppressed, and the opening / closing timing of the exhaust valve 41 is retarded to suppress the discharge of unburned fuel from the internal combustion engine 10. However, the occurrence of cold hesitation can be suppressed.

  (2) In the cold control, a basic target displacement angle Tb that is a basic control amount is set based on the load factor KL of the internal combustion engine 10. The opening / closing timing of the exhaust valve 41 is set based on the target displacement angle calculated by correcting the basic target displacement angle Tb so that the valve overlap becomes smaller as the detection value of the air-fuel ratio sensor 67 becomes higher. Control.

  Therefore, the valve overlap decreases as the detected value of the air-fuel ratio sensor 67 is higher and the amount of fuel contained in the air-fuel mixture subjected to combustion is estimated to be smaller, and the mixture introduced into the combustion chamber 18 The more you feel better, the smaller the valve overlap. Therefore, when the air-fuel mixture is lean, it is possible to suppress the valve overlap from becoming large, and to prevent the amount of fuel provided for combustion from becoming insufficient and the combustion from becoming unstable. Can do.

  In addition, since the target displacement angle is set based on the detection value of the air-fuel ratio sensor 67 and the opening / closing timing of the exhaust valve 41 is controlled based on the target displacement angle, unburned within the range where combustion does not become unstable. The opening / closing timing of the exhaust valve 41 can be controlled so that the amount of fuel discharged can be reduced as much as possible. Therefore, it is possible to effectively suppress the occurrence of cold hesitation while suppressing the discharge of unburned fuel from the internal combustion engine 10 as much as possible.

  (3) Until the sensor element of the air-fuel ratio sensor 67 is activated, an activation promotion process for activating the sensor element at an early stage is executed. Therefore, the sensor element of the air-fuel ratio sensor 67 is activated early. Therefore, the prohibition of the cold control is released early, and the cold control based on the detection value of the air-fuel ratio sensor 67 can be started early. Thereby, the opportunity to perform cold control can be increased, and the discharge of unburned fuel can be more effectively suppressed.

  (4) By delaying the opening / closing timing of the exhaust valve 41 through cold control, the opening timing of the exhaust valve 41 is retarded. When the opening timing of the exhaust valve 41 is retarded, the period from when ignition is performed to when the exhaust valve 41 is opened becomes longer, so the air-fuel mixture starts to burn in the combustion chamber 18. The period until exhaust begins to be exhausted to the exhaust port 22 becomes longer. Therefore, it is possible to ensure a long time for burning the fuel contained in the air-fuel mixture in the combustion chamber 18 and to reduce the amount of unburned fuel discharged from the combustion chamber 18 together with the exhaust gas. It becomes like this.

In addition, the said embodiment can also be implemented with the following forms which changed this suitably.
In order to retard the valve opening timing of the exhaust valve 41, when the exhaust camshaft 42 is displaced to the retard side and the entire opening / closing timing of the exhaust valve 41 is retarded, the valve closing timing of the exhaust valve 41 Will also be retarded and the valve overlap will increase. When the valve overlap increases due to the delay of the closing timing of the exhaust valve 41, a part of the exhaust gas is introduced into the combustion chamber 18 in the intake stroke, and the mixture gas introduced into the combustion chamber 18 The amount will decrease. In a situation where the fuel is difficult to atomize and the air-fuel mixture tends to become lean, if the amount of the air-fuel mixture introduced into the combustion chamber 18 decreases, the amount of fuel supplied to the combustion is remarkably insufficient and combustion is not possible. It becomes easy to become stable.

  Therefore, when a variable valve system that can change the valve opening period of the exhaust valve 41 in addition to the opening / closing timing of the exhaust valve 41 by changing the operating angle or the like, the valve opening timing of the exhaust valve 41 is provided. It is desirable that the valve opening timing of the exhaust valve 41 is shortened so that the valve closing timing is not retarded as much as possible.

  By adopting such a configuration, the valve opening timing of the exhaust valve 41 can be retarded through cold control, while increasing the valve overlap can be suppressed, and the above valve overlap increases. This makes it possible to suppress the discharge of unburned fuel while suppressing the instability of combustion caused by.

  In the above embodiment, it is determined whether or not the engine temperature is lower than the reference engine temperature with reference to the calculation map shown in FIG. Based on the above, it is estimated whether the air-fuel ratio sensor 67 is activated, and the control premise flag is set based on these results. On the other hand, it is also possible to employ a configuration in which the control premise flag is set by referring to an arithmetic map as shown in FIG.

  Note that the broken line X and the alternate long and short dash line Y in the calculation map shown in FIG. 8 are the same as the broken line X and the alternate long and short dash line Y in FIG. A two-dot chain line Z in FIG. 8 indicates the amount of increase in the engine coolant temperature required until the sensor element of the air-fuel ratio sensor 67 is activated. In the calculation map of FIG. 8, a boundary line B is set along the two-dot chain line Z in a portion where the two-dot chain line Z is located below the one-dot chain line Y. Therefore, in the boundary line B set in this calculation map, the portion where the two-dot chain line Z protrudes below the one-dot chain line Y is positioned below the boundary line A shown in FIG. ing.

  In the case of adopting a configuration in which the control premise flag is set based on this calculation map instead of the control premise flag setting routine described with reference to FIG. 4, the amount of increase in the engine cooling water temperature after engine start is the boundary. When the area is below the line B, the control premise flag is set to “OFF” to prohibit the execution of the cold control. On the other hand, when the rising amount of the engine cooling water enters the region above the boundary line B, the control precondition flag is set to “ON”, the prohibition of the cold control is canceled, and the cold control is executed.

  If the boundary line B is set by adding information based on the increase amount of the engine cooling water temperature when the air-fuel ratio sensor 67 is activated to the calculation map in this way, the increase of the engine cooling water temperature is referred to by referring to the calculation map. By performing the cold control when the amount enters the region above the boundary line B, the same effect as in the above embodiment can be obtained. That is, when the fuel is difficult to atomize (when it is in a region below the boundary line A in FIG. 3), the hatched lines in FIG. The area where the cold control is executed can be expanded by the area corresponding to the portion C. Therefore, as in the above-described embodiment, it is possible to increase the opportunity to execute the cold control while suppressing the occurrence of cold hesitation, and to suppress the discharge of unburned fuel from the internal combustion engine 10.

  In addition, when the fuel being used is a heavy fuel that is difficult to vaporize, the fuel is difficult to atomize. Therefore, it replaces with the structure which determines whether the engine temperature of step S100 is less than reference | standard engine temperature, and the structure which determines whether the fuel currently used is heavy fuel as shown in FIG. By adopting (Step S105), it is also possible to estimate that the fuel is difficult to atomize based on the heavy fuel used.

As a specific method for determining whether or not the fuel being used is heavy fuel, it is possible to monitor changes in the pressure in the fuel tank and determine whether or not the fuel is likely to vaporize based on the result. It is possible to employ a configuration for determining whether or not, and a method for determining the properties of fuel using a sensor. In addition, a configuration that monitors how the engine speed NE rises during cold start and estimates that it is a heavy fuel that is difficult to vaporize at low temperatures when the engine speed NE does not rise quickly is applied. You can also
The method for determining whether or not the air-fuel ratio sensor 67 is activated can be changed as appropriate. For example, it is possible to adopt a configuration in which it is estimated that the sensor element of the air-fuel ratio sensor 67 is activated based on the execution of the air-fuel ratio feedback control, and the prohibition of the cold control is canceled.

  In addition, when the air-fuel ratio sensor 67 is activated and the air-fuel ratio feedback control is executed, the oxygen sensor 68 detects that the air-fuel ratio is adjusted to an appropriate air-fuel ratio in the vicinity of the theoretical air-fuel ratio. The value will be output. Therefore, when it is determined that the air-fuel ratio is adjusted to an appropriate air-fuel ratio near the stoichiometric air-fuel ratio based on the output value of the oxygen sensor 68 as shown in step S115 of FIG. It is also possible to adopt a configuration in which it is estimated that the sensor element is activated and the control premise flag is set to “ON”.

  -The specific content of the activation promotion process can be changed as appropriate. For example, in addition to the method of increasing the energization amount to the heater that heats the sensor element of the air-fuel ratio sensor 67 as in the above embodiment, the temperature of the exhaust gas is retarded by retarding the ignition timing in each cylinder 12 of the internal combustion engine 10. And a method of warming the sensor element of the air-fuel ratio sensor 67 using the heat of the exhaust can be employed. It is also possible to apply a method of warming the sensor element of the air-fuel ratio sensor 67 by increasing the idling rotational speed, which is the engine rotational speed NE during idling, to increase the temperature of the exhaust during idling.

-Moreover, the structure which abbreviate | omits activation promotion processing as FIG. 9 shows is also employable.
In the above embodiment, the configuration for estimating the engine temperature based on the engine cooling water temperature at the time of starting the engine and the amount of increase in the engine cooling water temperature after the engine starting has been shown. The method can be changed as appropriate. For example, since the intake air amount Ga has a high correlation with the magnitude of combustion heat accompanying engine operation, the integrated intake air amount ΣGa, which is the integrated value of the intake air amount Ga after engine startup, is the engine after engine startup. It has a high correlation with the temperature rise. That is, it is estimated that the larger the integrated intake air amount ΣGa, the larger the amount of increase in engine temperature after engine startup.

  Therefore, instead of the configuration in which the increase amount of the engine temperature is estimated based on the increase amount of the engine coolant temperature as in the above embodiment, the increase amount of the engine temperature is estimated based on the integrated intake air amount ΣGa, and the engine is started. It is also possible to employ a configuration for estimating whether or not the fuel is difficult to atomize based on the engine cooling water temperature and the integrated intake air amount ΣGa after the engine is started.

  In this case, the integrated intake air amount ΣGa, which is estimated to be obtained when the engine temperature rises to the reference engine temperature in accordance with the engine coolant temperature at the time of engine start, is set as a reference value, and the engine start When the later integrated intake air amount ΣGa is less than this reference value, it may be estimated based on that that the engine temperature is less than the reference engine temperature.

  Therefore, if a calculation map in which these reference values are plotted for each engine coolant temperature at the time of starting the engine is prepared in advance, by referring to this calculation map, the engine coolant temperature at the time of engine start and the integration after the engine start Based on the intake air amount ΣGa, it is possible to estimate whether or not the fuel is difficult to atomize.

  In addition, when estimating whether or not the fuel is difficult to atomize with reference to such a calculation map, the integrated intake air amount required until the sensor element of the air-fuel ratio sensor 67 is activated in this calculation map. It is possible to estimate that the sensor element of the air-fuel ratio sensor 67 is activated by adding information indicating ΣGa and referring to the calculation map.

  That is, if the integrated intake air amount ΣGa estimated to be obtained when the sensor element of the air-fuel ratio sensor 67 is activated is plotted on this calculation map according to the engine coolant temperature at the time of engine start, It is possible to estimate that the sensor element of the air-fuel ratio sensor 67 has been activated based on the fact that the integrated intake air amount ΣGa has reached this plotted value.

A configuration in which the engine temperature is estimated based on the temperature of oil flowing inside the internal combustion engine 10 such as the temperature of the lubricating oil instead of the engine cooling water temperature may be employed.
-The content of cold control is specific if the displacement angle is controlled so that the valve overlap becomes smaller as the air-fuel ratio increases so that the occurrence of cold hesitation is suppressed according to the air-fuel ratio. The specific aspect can be changed as appropriate.

  For example, in the above embodiment, the target calculated by setting the basic target displacement angle Tb based on the engine speed NE and the load factor KL and correcting the basic target displacement angle Tb according to the air-fuel ratio. Although the configuration in which the final target displacement angle Tf is set based on the air-fuel ratio is shown, the setting method of the basic target displacement angle Tb and the setting method of the final target displacement angle Tf can be changed as appropriate.

For example, the limitation of the reflection amount by the upper limit guard value shown in step S240 in FIG. 4 can be omitted.
-Although the structure which retards the opening / closing timing of the exhaust valve 41 in cold control was shown, the structure which advances the opening / closing timing of the intake valve 31 can also be employ | adopted. When the configuration in which the opening / closing timing of the intake valve 31 is advanced is adopted, a part of the exhaust gas is blown back to the intake port 21 by advancing the opening / closing timing of the intake valve 31. The intake port 21 is warmed and fuel atomization is promoted. As a result, an increase in fuel for bringing the air-fuel ratio of the air-fuel mixture close to the stoichiometric air-fuel ratio can be reduced, and as a result, the amount of unburned fuel discharged together with the exhaust gas can be reduced.

  When the opening / closing timing of the intake valve 31 is advanced, the overlap in the state in which the piston 13 is raised, that is, in the state in which the pressure in the cylinder 12 is increased, increases. As a result, the amount of exhaust gas blown back into the combustion chamber becomes very large, and the amount of fuel introduced into the combustion chamber 18 in the subsequent intake stroke decreases. On the other hand, when the opening / closing timing of the exhaust valve 41 is retarded as in the above embodiment, the overlap in the state where the piston 13 is lowered, that is, in the state where the pressure in the cylinder 12 is low, is increased. Will be. Therefore, in this overlap, since the exhaust has already started to escape to the exhaust port 22, the amount of exhaust introduced into the combustion chamber 18 becomes smaller than when the opening / closing timing of the intake valve 31 is advanced. Therefore, in the cold control that is executed when the fuel is difficult to atomize and the air-fuel mixture is likely to become lean, the above-described cold control that advances the opening / closing timing of the intake valve 31 is performed. Executing cold control for retarding the opening / closing timing of the exhaust valve 41 as in the embodiment is advantageous in suppressing the occurrence of cold hesitation.

  Therefore, in order to suppress the occurrence of cold hesitation, it is desirable to employ a configuration in which the opening / closing timing of the exhaust valve 41 is retarded through cold control as in the above embodiment.

  ・ Warm control, which is the control of the variable valve system after completion of warm-up, and cold control, which is the control of the variable valve system during cold, are provided separately, and the warm control and the cold control are separately provided. Although the configuration to be executed is shown, the present invention can also be applied to a control device for a variable valve system in which warm control and cold control are not separated. The present invention can also be applied to a control device for a variable valve system that drives the variable valve system only when it is cold.

  In the above embodiment, as an example of a configuration for restricting the change of the opening / closing timing when the air-fuel ratio sensor 67 is not activated, the cold control is executed when the air-fuel ratio sensor 67 is not activated. The configuration to prohibit is shown.

  On the other hand, when the air-fuel ratio sensor 67 is not activated, the configuration for restricting the change of the opening / closing timing cannot be a cause of cold hesitation when the air-fuel ratio sensor 67 is not activated. It is also possible to adopt a configuration in which the change of the opening / closing timing is limited so that the opening / closing timing is changed only within an extremely narrow range.

  That is, when the air-fuel ratio sensor 67 is not activated, the change in the opening / closing timing is limited so that the opening / closing timing is changed only in a very narrow range where cold hesitation cannot occur, while the air-fuel ratio sensor 67 is activated. The configuration can be relaxed and the opening / closing timing can be changed based on the output value of the air-fuel ratio sensor 67.

DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Cylinder block, 12 ... Cylinder, 13 ... Piston, 14 ... Water jacket, 15 ... Connecting rod, 16 ... Crankshaft, 17 ... Cylinder head, 18 ... Combustion chamber, 19 ... Spark plug, 20 ... Injector, 21 ... intake port, 22 ... exhaust port, 30 ... intake passage, 31 ... intake valve, 32 ... intake camshaft, 33 ... throttle valve, 33a ... motor, 40 ... exhaust passage, 41 ... exhaust valve, 42 ... exhaust Camshaft, 45 ... Exhaust gas purification catalyst, 51 ... Intake side valve timing change mechanism, 52 ... Exhaust side valve timing change mechanism, 53 ... Accelerator pedal, 60 ... Water temperature sensor, 61 ... Crank position sensor, 62 ... Accelerator position sensor, 63 ... Throttle position sensor, 64 ... D Furometa, 65 ... intake side cam position sensor, 66 ... exhaust side cam position sensor, 67 ... air-fuel ratio sensor, 68 ... oxygen sensor, 100 ... electronic control unit.

Claims (12)

A control device for a variable valve system that performs cold control for changing the opening and closing timing of the engine valve before the exhaust purification catalyst warms to the activation temperature, and is operated by the cold control when the fuel is difficult to atomize. A control device for a variable valve system that limits timing changes,
The sensor element of the air-fuel ratio sensor that outputs a detected value proportional to the air-fuel ratio of the air-fuel mixture subjected to combustion is activated, and the air-fuel ratio of the air-fuel mixture supplied to combustion is estimated based on the detected value of the air-fuel ratio sensor When it becomes possible to perform the cold control to relax the restriction and control the opening and closing timing of the engine valve according to the detection value of the air-fuel ratio sensor ,
In the cold control executed after the sensor element of the air-fuel ratio sensor is activated, a basic control amount that is a basic value of the control amount when changing the opening / closing timing of the engine valve based on the load factor of the internal combustion engine While setting
The engine is based on a target control amount calculated by correcting the basic control amount according to the detected value of the air-fuel ratio sensor so that the valve overlap becomes smaller as the detected value of the air-fuel ratio sensor becomes higher. A control device for a variable valve system, characterized by controlling the opening and closing timing of the valve. A control device for a variable valve system that performs cold control for changing the opening and closing timing of the engine valve before the exhaust purification catalyst warms to the activation temperature, and is operated by the cold control when the fuel is difficult to atomize. A control device for a variable valve system that limits timing changes,
The sensor element of the air-fuel ratio sensor that outputs a detected value proportional to the air-fuel ratio of the air-fuel mixture subjected to combustion is activated, and the air-fuel ratio of the air-fuel mixture supplied to combustion is estimated based on the detected value of the air-fuel ratio sensor When it becomes possible to perform the cold control to relax the restriction and control the opening and closing timing of the engine valve according to the detection value of the air-fuel ratio sensor ,
A control apparatus for a variable valve system, wherein the valve opening timing of the exhaust valve is retarded through the cold control. In addition to the opening and closing timing of the exhaust valve, a variable valve system control device that controls a variable valve system capable of changing a valve opening period of the exhaust valve,
The control apparatus for a variable valve system according to claim 2 , wherein the cold control retards the valve opening timing of the exhaust valve and shortens the valve opening period of the exhaust valve. A control device for a variable valve system that performs cold control for changing the opening and closing timing of the engine valve before the exhaust purification catalyst warms to the activation temperature, and is operated by the cold control when the fuel is difficult to atomize. A control device for a variable valve system that limits timing changes,
The sensor element of the air-fuel ratio sensor that outputs a detected value proportional to the air-fuel ratio of the air-fuel mixture subjected to combustion is activated, and the air-fuel ratio of the air-fuel mixture supplied to combustion is estimated based on the detected value of the air-fuel ratio sensor When it becomes possible to perform the cold control to relax the restriction and control the opening and closing timing of the engine valve according to the detection value of the air-fuel ratio sensor ,
A control device for a variable valve system, wherein the opening / closing timing of the intake valve is advanced through the cold control. The variable valve system according to any one of claims 1 to 4 , wherein an activation promotion process for activating the sensor element at an early stage is executed until the sensor element of the air-fuel ratio sensor is activated. Control device. In the control apparatus of the variable valve system according to any one of claims 1 to 5 ,
A control apparatus for a variable valve system, characterized in that it is estimated that fuel is difficult to atomize based on an engine temperature being lower than a reference engine temperature. In the control apparatus of the variable valve system according to any one of claims 1 to 5 ,
A control apparatus for a variable valve system, characterized in that it is estimated that fuel is difficult to atomize based on heavy fuel used. The control device for a variable valve system according to any one of claims 1 to 7 , wherein the restriction is relaxed based on a detection value output from the air-fuel ratio sensor. The variable valve according to any one of claims 1 to 7 , wherein the restriction is relaxed based on air-fuel ratio feedback control in which a fuel injection amount is feedback-controlled based on a detection value of the air-fuel ratio sensor. System control unit. A control device for a variable valve system that performs cold control for changing the opening and closing timing of the engine valve before the exhaust purification catalyst warms to the activation temperature, and is operated by the cold control when the fuel is difficult to atomize. A control device for a variable valve system that limits timing changes,
The sensor element of the air-fuel ratio sensor that outputs a detected value proportional to the air-fuel ratio of the air-fuel mixture subjected to combustion is activated, and the air-fuel ratio of the air-fuel mixture supplied to combustion is estimated based on the detected value of the air-fuel ratio sensor When it becomes possible to perform the cold control to relax the restriction and control the opening and closing timing of the engine valve according to the detection value of the air-fuel ratio sensor,
Based on the fact that the engine temperature is lower than the reference engine temperature, it is estimated that the fuel is difficult to atomize,
A calculation map for estimating that the engine temperature is lower than the reference engine temperature based on the engine cooling water temperature at the time of starting the engine and the amount of increase in the engine cooling water temperature after starting the engine,
A control device for a variable valve system that estimates whether or not fuel is difficult to atomize with reference to the calculation map,
Information for estimating whether or not the sensor element of the air-fuel ratio sensor has been activated based on the amount of increase in engine coolant temperature after engine startup has been added to the calculation map,
When it is estimated that the sensor element of the air-fuel ratio sensor is activated with reference to the calculation map, the restriction is relaxed.
A control apparatus for a variable valve system. A control device for a variable valve system that performs cold control for changing the opening and closing timing of the engine valve before the exhaust purification catalyst warms to the activation temperature, and is operated by the cold control when the fuel is difficult to atomize. A control device for a variable valve system that limits timing changes,
The sensor element of the air-fuel ratio sensor that outputs a detected value proportional to the air-fuel ratio of the air-fuel mixture subjected to combustion is activated, and the air-fuel ratio of the air-fuel mixture supplied to combustion is estimated based on the detected value of the air-fuel ratio sensor When it becomes possible to perform the cold control to relax the restriction and control the opening and closing timing of the engine valve according to the detection value of the air-fuel ratio sensor,
Based on the fact that the engine temperature is lower than the reference engine temperature, it is estimated that the fuel is difficult to atomize,
Calculation map for estimating that the engine temperature has exceeded the reference engine temperature based on the engine coolant temperature at the start of the engine and the integrated intake air amount that is the integrated value of the intake air amount of the internal combustion engine after the engine is started With
A control device for a variable valve system that estimates whether or not fuel is difficult to atomize with reference to the calculation map,
Information for estimating whether the sensor element of the air-fuel ratio sensor is activated based on the integrated intake air amount is added to the calculation map,
When it is estimated that the sensor element of the air-fuel ratio sensor is activated with reference to the calculation map, the restriction is relaxed.
A control apparatus for a variable valve system. The control apparatus for a variable valve system according to any one of claims 1 to 11 , wherein execution of the cold control is prohibited when the fuel is in a state in which it is difficult to atomize,
When the sensor element of the air-fuel ratio sensor is activated and the air-fuel ratio of the air-fuel mixture subjected to combustion can be estimated based on the detection value of the air-fuel ratio sensor, the cold control is prohibited. A control apparatus for a variable valve system, wherein the cold valve control is performed to release and control the opening / closing timing of the engine valve in accordance with a detection value of the air-fuel ratio sensor.

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