JP2008180137A - Air-fuel ratio control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an air-fuel ratio control device capable of converging the air-fuel ratio to the target air-fuel ratio, while restraining an increase in an engine speed of an internal combustion engine. <P>SOLUTION: This internal combustion engine 10 has a throttle valve 14 arranged in an intake passage 12 and capable of varying opening, an intake valve 30 communicating and cutting-off the intake passage 12 and a combustion chamber 18 and capable of varying a maximum lift quantity, a fuel injection valve 20 injecting fuel introduced to the combustion chamber 18, and an air-fuel ratio sensor 25 detecting the air-fuel ratio of an air-fuel mixture introduced to the combustion chamber 18. An electronic control device 70 controls quantity of the fuel injected by the fuel injection valve 20 in response to a driving state of the throttle valve 14 and the intake valve 30 so that the air-fuel ratio detected by the air-fuel ratio sensor 25 becomes the stoichiometric air-fuel ratio, and controls a lift quantity for reducing throttle opening and the throttle opening by setting the maximum lift quantity of the intake valve 30 to a predetermined minimum lift quantity or more, when the quantity of fuel of the fuel injection valve 20 is estimated as a minimum injection quantity or less. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an air-fuel ratio control apparatus that converges an air-fuel ratio of an internal combustion engine to a target air-fuel ratio.

  Conventionally, an air-fuel ratio control device for an internal combustion engine calculates an air-fuel ratio that is a weight ratio of air and fuel by detecting an oxygen concentration in exhaust gas, and performs fuel injection so that the air-fuel ratio becomes a target air-fuel ratio. Air-fuel ratio feedback control for increasing / decreasing the fuel injection amount by the valve is performed.

  By the way, in the internal combustion engine, so-called fuel dilution occurs in which the injected fuel is not sufficiently vaporized at the time of cold start or the like and is mixed into the lubricating oil. Thus, the fuel mixed in the lubricating oil evaporates as the temperature of the internal combustion engine rises, and is supplied again to the combustion chamber by the blow-by gas recirculation device. In addition, the combustion chamber is supplied with the fuel vapor evaporated from the fuel tank adsorbed by the charcoal canister by being purged into the intake system. Thus, when the amount of fuel supplied from other than the fuel injection valve increases, the air-fuel ratio tends to become rich, and in the air-fuel ratio control, control is performed to reduce the amount of fuel injected from the fuel injection valve. Done. However, if the amount of fuel supplied by other than these fuel injection valves increases, the amount of fuel injected from the fuel injection valves becomes the minimum injection amount that is the limit of the controllable amount, and the fuel injection amount is reduced to this amount. Since the amount cannot be reduced below the amount, appropriate air-fuel ratio control cannot be performed.

Thus, for example, the air-fuel ratio control apparatus described in Patent Document 1 increases the air-fuel ratio by increasing the intake air amount when the injection amount by the fuel injection valve becomes equal to or less than the minimum injection amount and air-fuel ratio control cannot be performed. Is changed from the rich state to the lean state, and the fuel can be supplied from the fuel injection valve at a minimum injection amount or more so that air-fuel ratio control can be performed. Specifically, in an internal combustion engine to which the control device of Patent Document 1 is applied, an air valve is provided in an air supply passage that bypasses the intake throttle valve in the intake passage. Normally, the air valve is closed and fuel injection is performed. Even if the fuel injection amount by the valve becomes the minimum injection amount, if the rich state continues, this air valve is opened to increase the intake air amount.
JP-A 64-69747

  By the way, for example, during idle operation after high-speed traveling, the amount of evaporated fuel purged from the fuel tank to the intake system and the amount of evaporated fuel returned to the intake system together with the blow-by gas due to fuel dilution increase. As described above, even if the fuel injection amount by the fuel injection valve is set to the minimum injection amount, the air-fuel ratio tends to be rich. On the other hand, during idle operation, idle rotation speed control for controlling the engine rotation speed to a constant target rotation speed is executed. In such a case, if the intake air amount is increased in the manner described in Patent Document 1, the engine speed will increase even during idle operation, giving the passenger a sense of incongruity due to the occurrence of noise or vibration. There is a fear.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an air-fuel ratio control apparatus that can converge an air-fuel ratio to a target air-fuel ratio while suppressing an increase in the rotational speed of the internal combustion engine. It is to provide.

Hereinafter, means for solving the above-described problems and the effects thereof will be described.
According to the first aspect of the present invention, there is provided a throttle valve that adjusts the cross-sectional area of the intake passage, an intake valve that adjusts the communication state between the intake passage and the combustion chamber, and fuel that is introduced into the combustion chamber. An air-fuel ratio control apparatus for controlling the air-fuel ratio in an internal combustion engine, comprising: a fuel injection valve configured to detect the air-fuel ratio of an air-fuel mixture of air introduced into the combustion chamber and the fuel; First control means for controlling an amount of the fuel injected by the fuel injection valve in accordance with a drive state of the throttle valve and the intake valve so that the air-fuel ratio detected by the control becomes a target air-fuel ratio; When the amount of the fuel injected by the fuel injection valve is less than or equal to a predetermined minimum injection amount, the drive state of the throttle valve is controlled so as to reduce the flow passage cross-sectional area of the intake passage. , And summarized in that and a second control means for controlling the driving state of the intake valve to increase the amount of the air introduced into the combustion chamber.

  According to the above configuration, the first control means controls the amount of fuel injected by the fuel injection valve in accordance with the drive state of the throttle valve and the intake valve so that the air-fuel ratio becomes the target air-fuel ratio. To do. Then, when the amount of fuel injected by the fuel injection valve is less than or equal to the predetermined minimum injection amount, the second control means controls the drive state of the throttle valve so as to reduce the flow passage cross-sectional area of the intake passage. At the same time, the drive state of the intake valve is controlled so as to increase the amount of air introduced into the combustion chamber.

  The time when the amount of fuel injected by the fuel injection valve is less than or equal to the predetermined minimum injection amount may be when the actual amount of fuel injected by the fuel injection valve is less than or equal to the predetermined minimum injection amount. Further, when the amount of fuel injected by the fuel injection valve at the time of low load of the internal combustion engine is estimated in advance by a calculation formula or the like, the estimated amount of fuel may be equal to or less than a predetermined minimum injection amount. Then, when it is estimated in advance that the amount of this fuel is less than or equal to the predetermined minimum injection amount, when the internal combustion engine shifts to a low load state, the amount of air that is originally introduced into the combustion chamber according to this load is compared. The intake valve drive state is controlled so that the amount is as small as possible, but the intake valve drive state is controlled to introduce more air into the combustion chamber than is normally supplied according to this load. To do.

  In this way, if the amount of air introduced into the combustion chamber increases, the air-fuel ratio detected by the sensor changes from the rich side to the lean side with respect to the target air-fuel ratio, thereby the first control means. Controls to increase the amount of fuel injected by the fuel injection valve. Therefore, the amount of fuel injected by the fuel injection valve becomes larger than the minimum injection amount, and control for setting the air-fuel ratio to the target air-fuel ratio becomes possible, so that deterioration of emissions can be suppressed.

  Further, in the present invention, the driving state of the throttle valve is controlled so as to reduce the flow passage cross-sectional area of the intake passage, so that the pumping loss increases in the intake stroke of the internal combustion engine. Therefore, although the amount of air supplied to the combustion chamber and the fuel injection amount increase and the energy generated by the internal combustion engine increases, the load on the internal combustion engine also increases, so that the rotation speed of the internal combustion engine is prevented from increasing. can do. As a result, the air-fuel ratio can be converged to the target air-fuel ratio without giving a sense of incongruity due to noise or vibration to the occupant during idling.

  The predetermined minimum injection amount is set slightly larger than the minimum injection amount that enables accurate injection amount control of the fuel injection valve and the minimum injection amount determined by the characteristics of the fuel injection valve. A predetermined injection amount can be employed. As an intake valve that adjusts the communication state between the intake passage and the combustion chamber, a variable valve mechanism that makes the maximum lift amount of the intake valve variable, and the maximum lift amount and opening / closing timing of the intake valve are made variable freely. What is driven by an electromagnetic valve mechanism can be employed.

  According to a second aspect of the present invention, in the first aspect of the present invention, the first control means is configured such that the throttle valve and the intake air are set such that the air-fuel ratio detected by the sensor becomes a target air-fuel ratio. The amount of fuel to be injected by the fuel injection valve is derived as a required injection amount in accordance with the driving state of the valve, and is injected by the fuel injection valve when the required injection amount is smaller than the predetermined minimum injection amount. The amount of the fuel is set to the same predetermined minimum injection amount, and the second control means is configured such that when the required injection amount becomes equal to or less than the predetermined minimum injection amount, the smaller the required injection amount, the more the combustion The gist is to control the drive state of the intake valve so that the amount of air introduced into the chamber increases.

  For example, if the required injection amount is much smaller than the predetermined minimum injection amount, the air-fuel ratio may remain in a rich state if the amount of air introduced into the combustion chamber is slightly increased. The fuel ratio cannot be controlled quickly. On the other hand, when the required injection amount is approximately the same as the predetermined minimum injection amount, if the amount of air introduced into the combustion chamber is significantly increased, the air-fuel ratio changes from the rich state to the lean state. As the fuel consumption increases significantly, the amount of fuel injected by the fuel injection valve becomes unnecessarily large, and the fuel consumption deteriorates.

  In this regard, according to the above configuration, when the required injection amount is equal to or less than the predetermined minimum injection amount, control is performed so that the smaller the required injection amount, the greater the amount of air introduced into the combustion chamber. The air-fuel ratio control can be performed quickly and accurately without causing the above problems.

  According to a third aspect of the present invention, in the first aspect, the first control means calculates an air-fuel ratio feedback correction coefficient for making the air-fuel ratio detected by the sensor a target air-fuel ratio. Thus, the amount of fuel to be injected by the fuel injection valve is derived as a required injection amount in accordance with the driving state of the throttle valve and the intake valve, and is injected by the fuel injection valve based on the required injection amount. When the feedback correction coefficient is calculated as a value that decreases the required injection amount, the second control means has a large extent that the correction coefficient decreases the required injection amount. The gist is to control the drive state of the intake valve so that the amount of the air introduced into the combustion chamber increases.

  For example, when the feedback correction coefficient is calculated as a value that significantly reduces the required injection amount, this is estimated when the amount of fuel injected by the fuel injection valve is estimated in advance at a low load of the internal combustion engine. There is a high possibility that the amount of fuel to be discharged will be equal to or less than a predetermined minimum injection amount. When the feedback correction coefficient is a value that greatly reduces the required injection amount in this way, the fuel injection valve can be operated at a low load of the internal combustion engine by slightly increasing the amount of air introduced into the combustion chamber. There is a possibility that the amount of fuel injected by the fuel injection becomes less than the minimum injection amount and the air-fuel ratio becomes rich. On the other hand, even if this feedback correction coefficient is calculated as a value that decreases the required injection amount, if this decrease is not so large, the fuel injection valve is not increased without increasing the amount of air introduced into the combustion chamber. The amount of fuel injected can be made larger than the minimum injection amount. Therefore, according to the above-described configuration, the amount of air introduced into the combustion chamber is controlled so as to increase as the feedback correction coefficient decreases the required injection amount. be able to.

  Specifically, as described in claim 4, in the invention according to any one of claims 1 to 3, the intake valve is configured so that the amount of air introduced into the combustion chamber is variable. The maximum lift amount is variably configured, and the second control means determines that the maximum lift amount of the intake valve is predetermined when the amount of the fuel injected by the fuel injection valve is equal to or less than a predetermined minimum injection amount. It is possible to employ a configuration in which the amount of air introduced into the combustion chamber is increased by limiting the amount to be equal to or greater than the minimum lift amount. In the invention according to claim 2, when the invention according to claim 4 is adopted, the predetermined minimum lift amount may be set to be larger as the required injection amount is smaller. In the invention described in claim 3, when the invention described in claim 4 is adopted, the predetermined minimum lift amount increases as the feedback correction coefficient decreases the required injection amount. It should be set as follows.

  According to a fifth aspect of the present invention, in the invention according to any one of the first to fourth aspects, the second control means is configured such that the fuel injected by the fuel injection valve dilutes the lubricating oil of the internal combustion engine. The gist is to execute the control by the second control means on condition that the degree of fuel dilution has reached a predetermined dilution reference value.

  In the above configuration, when the fuel dilution reaches a predetermined dilution reference value, the evaporation amount of the fuel diluted with the lubricating oil increases, and this large amount of fuel is supplied to the combustion chamber, so that it is injected by the fuel injection valve. There is a high possibility that the amount of fuel becomes the minimum injection amount. Therefore, according to said structure, when the influence by this fuel dilution is large, control by a 2nd control means can be performed.

  Hereinafter, an embodiment in which an air-fuel ratio control apparatus according to the present invention is embodied will be described with reference to FIGS. FIG. 1 is a schematic diagram of an in-vehicle internal combustion engine to which an air-fuel ratio control apparatus according to the present invention is applied.

  As shown in FIG. 1, the internal combustion engine 10 exhausts exhaust gas generated by combustion in the combustion chamber 18 formed in each cylinder 11, an intake passage 12 that feeds intake air into the combustion chamber 18, and combustion in the combustion chamber 18. The exhaust passage 28 is provided.

  A throttle valve 14 is provided in the intake passage 12. A throttle motor 16 is connected to the throttle valve 14. The throttle valve 14 is adjusted in opening degree (throttle opening degree) through the drive control of the throttle motor 16, thereby adjusting the cross-sectional area of the intake passage 12.

  A fuel injection valve 20 and a spark plug 22 are disposed in the combustion chamber 18 formed in each cylinder 11. The fuel injection valve 20 is configured such that the amount of fuel injected is controlled by controlling the length of the valve opening time. The fuel injection valve 20 cannot accurately control the fuel injection amount if the valve opening time is too short. Therefore, the minimum injection corresponding to the shortest valve opening time that enables accurate injection amount control is possible. The amount is set.

  The fuel is directly injected into the combustion chamber 18 by the fuel injection valve 20 and mixed with the air introduced from the intake passage 12. The fuel / air mixture is ignited and burned by spark discharge from the spark plug 22, and the piston 24 reciprocates due to the combustion energy, and the crankshaft 23 rotates. The air-fuel mixture after combustion is sent out from the combustion chamber 18 to the exhaust passage 28 as exhaust.

  A crankcase 13 is formed below each cylinder 11 forming the combustion chamber 18. An oil pan 29 is attached to the lower portion of the crankcase 13, and lubricating oil for the internal combustion engine 10 is stored in the oil pan 29. The crankcase 13 and the intake passage 12 are connected to each other by a blow-by gas recirculation device 17 so as to be freely communicated and blocked. The gas in the crankcase 13 can be supplied to the intake passage 12 by the blow-by gas recirculation device 17. It is configured to be possible.

An air-fuel ratio sensor 25 and an exhaust purification catalyst 26 are disposed in the exhaust passage 28.
The exhaust purification catalyst 26 is constituted by a three-way catalytic converter that reduces harmful components such as CO, HC and NOx contained in exhaust gas generated by combustion. The exhaust purification catalyst 26 can simultaneously reduce these three components when the air-fuel ratio, which is the weight ratio of the air combusted in the combustion chamber 18, becomes the stoichiometric air-fuel ratio (14.7). Therefore, the air-fuel ratio of the air-fuel mixture supplied to the combustion chamber 18 is controlled to be the stoichiometric air-fuel ratio. That is, the target air-fuel ratio in the present embodiment is set to the stoichiometric air-fuel ratio.

  FIG. 2 shows the output current characteristics of the air-fuel ratio sensor 25. As shown in FIG. 2, the output current of the air-fuel ratio sensor 25 becomes the reference current Id at the stoichiometric air-fuel ratio, and becomes smaller than the reference current Id as the air-fuel ratio becomes richer than the stoichiometric air-fuel ratio. Changes in a manner that becomes larger than the reference current Id as it becomes leaner than the stoichiometric air-fuel ratio. That is, the air-fuel ratio sensor 25 has a characteristic that the output current changes linearly and continuously according to the air-fuel ratio of the exhaust gas. When feedback control is performed using the air-fuel ratio sensor 25 to change the air-fuel ratio to the stoichiometric air-fuel ratio, the fuel injection valve 20 causes the output current of the air-fuel ratio sensor 25 to become the reference current Id. The amount of fuel to be injected is corrected to increase or decrease.

  In the internal combustion engine 10, the intake passage 12 and the combustion chamber 18 are connected and cut off by the opening / closing operation of the intake valve 30, and the combustion chamber 18 and the exhaust passage 28 are connected and cut off by the opening / closing operation of the exhaust valve 32. Is done. The intake valve 30 opens and closes with the rotation of the intake camshaft 34 to which the rotation of the crankshaft 23 is transmitted, and the exhaust valve 32 similarly rotates with the rotation of the exhaust camshaft 36 to which the rotation of the crankshaft 23 is transmitted. Open and close.

  Further, between the intake camshaft 34 and the intake valve 30, a variable valve mechanism 42 is provided as a lift amount variable mechanism that variably sets the maximum lift amount of the intake valve 30. The variable valve mechanism 42 is driven by an electric motor 44. FIG. 3 is a time chart showing how the lift amount of the intake valve 30 is changed by driving the electric motor 44. As shown in FIG. 3, the lift amount (specifically, the maximum lift amount) of the intake valve 30 changes in synchronization with the lift operation angle. For example, the lift operation angle increases as the maximum lift amount increases. Go. Therefore, the increase in the lift operating angle means that the valve opening timing and the valve closing timing of the intake valve 30 move away from each other and the valve opening period of the intake valve 30 becomes longer, and the amount of air introduced into the combustion chamber 18 is increased. Means to grow.

  Further, the vehicle is equipped with an electronic control device 70 as an air-fuel ratio control device that controls the operation of the internal combustion engine 10. The electronic control unit 70 includes a central processing unit that executes various processes relating to engine control, a memory for storing a program for engine control and information necessary for the control, an input port for inputting a signal from the outside, an external Are provided with an output port for outputting a signal.

  Detection signals from the following various sensors are input to the electronic control unit 70. The various sensors include the air-fuel ratio sensor 25, the throttle sensor 50 for detecting the throttle opening, the intake air amount sensor 52 for detecting the intake air amount passing through the intake passage 12, and the temperature of the engine coolant (THW). A water temperature sensor 54 for detection and an accelerator sensor 56 for detecting a depression amount (accelerator depression amount) of an accelerator pedal not shown. Further, a crank sensor 58 for detecting the rotation angle (crank angle) and rotation speed (engine rotation speed NE) of the crankshaft 23, a cam sensor 60 for detecting the rotation angle (cam angle) of the intake camshaft 34, A lift sensor 62 or the like is also included for detecting the lift operating angle of the intake valve 30 (specifically, the operation amount of the variable valve mechanism 42).

This electronic control unit 70 has functions as the first control unit and the second control unit of the present invention, and controls the operation of the internal combustion engine 10 as follows.
The electronic control unit 70 adjusts the output of the internal combustion engine 10 based on the accelerator depression amount operated by the driver. Specifically, an accelerator depression amount detected by the accelerator sensor 56 is input to the electronic control device 70, and the electronic control device 70 controls the variable valve mechanism 42 based on the accelerator depression amount, thereby the intake valve. Adjust the maximum lift amount of 30. Then, the electronic control unit 70 operates as a first control means so that the air-fuel ratio detected by the air-fuel ratio sensor 25 becomes the stoichiometric air-fuel ratio in accordance with the drive states of the intake valve 30 and the throttle valve 14. The amount of fuel injected by the injection valve 20 is controlled. That is, the amount of air introduced into the combustion chamber 18 changes based on the accelerator depression amount, and the amount of fuel injected by the fuel injection valve 20 by the electronic control unit 70 in response to the change in the amount of air. By controlling the output, the output of the internal combustion engine 10 is adjusted and the air-fuel ratio is controlled to be the stoichiometric air-fuel ratio. The electronic control unit 70 may keep the opening degree of the throttle valve 14 at a constant opening degree, or may change the opening degree according to the operating state of the internal combustion engine 10.

  The electronic control unit 70 then serves as the second control means when the amount of fuel injected by the fuel injection valve 20 is estimated to be equal to or less than the minimum injection amount in advance, and the intake valve 30 based on the accelerator depression amount. Instead of this control, the drive state of the intake valve 30 is controlled so that the amount of air introduced into the combustion chamber 18 is larger than the amount of air based on the accelerator depression amount. Further, the electronic control device 70 as the second control means controls the driving state of the throttle valve 14 so as to reduce the flow passage cross-sectional area of the intake passage 12 when the intake valve 30 is controlled. Specifically, the electronic control unit 70 sets the minimum lift amount of the intake valve 30 when it is estimated that the fuel amount of the fuel injection valve 20 is equal to or less than the minimum injection amount. Then, when the maximum lift amount based on the accelerator depression amount is less than the minimum lift amount, the electronic control unit 70 sets the re-maximum lift amount of the intake valve 30 to the minimum lift amount and sets the throttle opening at that time. Less than the opening in the engine operating state. The lift amount and throttle opening degree control by the second control means is executed on condition that the degree of fuel dilution of the lubricating oil has reached a predetermined reference value or more as will be described later.

  Next, the operation control of the internal combustion engine 10 by the electronic control unit 70 will be described in more detail based on FIGS. FIG. 4 is a time chart showing the control state of the internal combustion engine 10, where (a) shows the maximum lift amount L of the intake valve 30, (b) shows the throttle opening degree O, and (c) shows the fuel injection amount Q. Each is shown.

  During normal operation (for example, high speed traveling) of the internal combustion engine 10, the maximum lift amount L of the intake valve 30 is controlled to increase as the accelerator depression amount operated by the driver increases. For example, it changes in the mode shown in FIG. At this time, the throttle valve 14 is set to the fully open state O1.

The electronic control unit 70 serves as a first control means such that the air-fuel ratio detected by the air-fuel ratio sensor 25 according to the driving state of the throttle valve 14 and the intake valve 30 becomes the target air-fuel ratio (theoretical air-fuel ratio). , the amount of fuel to be injected is the fuel injection valve 20 is derived as the required injection amount Q _fin, the amount of fuel injected by the fuel injection valve 20 to control the amount corresponding to the required injection amount Q _fin. Specifically, if the required injection amount Q _fin is larger than the minimum injection amount Q _min of the fuel injection valve 20, the electronic control unit 70 determines the amount of fuel injected by the fuel injection valve 20 from the derived required injection. controlled to be the amount Q _fin, the required injection amount Q _fin is equal to or less than the minimum injection quantity Q _min, controlling the amount of fuel injected by the fuel injection valve so that the minimum injection quantity Q _min To do. That is, when the required injection amount Q _fin becomes equal to or less than the minimum injection amount Q _min , the first control means causes the fuel injection valve 20 to supply the fuel with the minimum injection amount Q _min regardless of the derived required injection amount Q _fin. It will control to inject.

The first control means derives the required injection amount Q _fin by the following equation 1, for example.
Q _fin = Q _base + K _p · (I−Id) (1)
Here, “Q _base ” is the reference injection amount Q _base of the fuel injection valve 20 derived from the engine speed NE and the amount of air introduced into the combustion chamber 18, and is indicated by a broken line in FIG. As shown, it increases or decreases as the maximum lift amount L of the intake valve 30 changes. “K _p ” is a feedback gain, “I” is an output current of the air-fuel ratio sensor 25, and “Id” is an output current of the air-fuel ratio sensor indicating the theoretical air-fuel ratio, that is, a reference current Id. That is, _Kp · (I−Id) is a feedback correction coefficient for setting the air-fuel ratio to the stoichiometric air-fuel ratio. This feedback correction coefficient is a negative value if the air-fuel ratio when the fuel injection amount is the reference injection amount Q _base is rich relative to the stoichiometric air-fuel ratio, and the air-fuel ratio in that case is lean relative to the stoichiometric air-fuel ratio. If so, the value becomes a positive value, and the absolute value increases as the air-fuel ratio deviates from the stoichiometric air-fuel ratio when the fuel injection amount is the reference injection amount Q _base . Then, the required injection amount Q _fin derived in this way increases and decreases as shown by the solid line in FIG.

  In this manner, the energy generated by the combustion generated in the combustion chamber 18 is adjusted in accordance with the accelerator depression amount of the driver, and an output corresponding to the driver's output request for the internal combustion engine 10 is obtained. Air-fuel ratio feedback control is performed in which the amount of fuel injected by the fuel injection valve 20 is controlled to increase or decrease based on the output current.

Here, in the internal combustion engine 10, since the fuel injected by the fuel injection valve 20 is not sufficiently vaporized mainly at the time of cold start or the like, a large amount of fuel adheres to the inner peripheral surface of the cylinder 11, and this fuel Is mixed with the lubricating oil, so that the lubricating oil is diluted with the fuel, so-called fuel dilution occurs. The lubricating oil containing such fuel is scraped off by the oil pan 29 as the piston 24 reciprocates, and the fuel (diluted fuel) mixed in the lubricating oil in the oil pan 29 increases as the temperature of the lubricating oil increases. When evaporated, the evaporated fuel is supplied to the intake passage 12 via the blow-by gas recirculation device 17. When this diluted fuel is introduced into the combustion chamber 18, the feedback correction coefficient calculated based on the detected value of the air-fuel ratio sensor 25 becomes a value that decreases the required injection amount _Qfin . As shown after time t1, the required injection amount Q _fin deviates from Q _base .

In the state where the fuel supply to the combustion chamber 18 due to such fuel dilution is large, the following problems occur when the idle operation or slow driving with a small accelerator depression amount is performed. That is, in idle operation, slow drive, etc., the maximum lift amount L of the intake valve 30 is reduced and the amount of air introduced into the combustion chamber 18 is reduced, and accordingly, the reference injection amount Q _base is derived small. . Therefore, the degree of fuel by fuel dilution is introduced more into the combustion chamber 18 the feedback correction coefficient is to reduce the required injection amount Q _fin is increased, the required injection amount Q _fin is derived below the minimum injection amount Q _min It becomes. If the operation state with a small accelerator depression amount continues, the amount of fuel injected by the fuel injection valve 20 continues to be the minimum injection amount _Qmin , and the air-fuel ratio sensor 25 continues to exceed the reference current Id. Since the state of detecting a small rich state continues, air-fuel ratio control cannot be performed appropriately.

  Therefore, in the present embodiment, the electronic control device 70 as the second control means performs the lift amount and throttle opening control when the lubricating oil is diluted with fuel, thereby performing the air-fuel ratio control. We are trying to do it properly. FIG. 5 shows a flowchart of the lift amount and throttle opening control routine of the intake valve 30 executed by the electronic control unit 70.

  In the lift amount and throttle opening control, first, in step S1, a fuel dilution determination is performed. This fuel dilution determination is performed based on FIGS. FIG. 6 shows the relationship between the coolant temperature THW, the dilution rate k indicating the amount of fuel dissolved in the lubricating oil of the fuel injected by the fuel injection valve 20, and the evaporation rate d indicating the amount of fuel evaporated from the lubricating oil. FIG. 7 shows a flowchart of the fuel dilution determination routine of this lubricating oil.

  As shown in FIG. 6, when the cooling water temperature THW is lower than the predetermined set temperature THW1, as described above, the fuel injected by the fuel injection valve 20 is not easily vaporized. As the coolant temperature THW decreases, the coolant temperature THW increases. On the other hand, when the cooling water temperature THW is higher than the predetermined set temperature THW1, the fuel (diluted fuel) mixed in the lubricating oil in the oil pan 29 is likely to evaporate as the temperature of the lubricating oil rises, and this evaporation rate d Increases as the coolant temperature THW increases.

Then, as shown in FIG. 7, when the fuel dilution determination routine is started, first, in step S11, it is determined whether or not the current coolant temperature THW is lower than the set temperature THW1. If it is determined in step S11 that the current cooling water temperature THW is lower than the set temperature THW1, since the fuel dilution of the lubricating oil is currently in progress, the process proceeds to step S12 and the current lubricating oil fuel A dilution rate _Di is derived. Since the current fuel dilution rate D _i is more than that of the previous fuel dilution rate D _i−1 , the fuel dilution has progressed by the amount of fuel injected from the fuel injection valve 20, so that the injected fuel is equal to the required injection amount Q _fin. Is obtained by adding the product of the dilution ratio k to the previous fuel dilution ratio _Di-1 . If it is determined in step S11 that the current cooling water temperature THW is equal to or higher than the set temperature THW1, the current state is that the diluted fuel is evaporating from the lubricating oil. A fuel dilution rate _Di is derived. In step S13, the current fuel dilution rate D _i is derived by subtracting the fuel evaporation rate d from the previous fuel dilution rate D _i−1 . Thus, after the current fuel dilution rate D _i is derived in step S12 or step S13, the process proceeds to step S14, and the derived fuel dilution rate D _i is a predetermined value indicating that the fuel dilution is proceeding. It is determined whether or not the dilution reference value D1 is greater than or equal to. If the fuel dilution rate D _i is greater than the predetermined dilution reference value D1, the process proceeds to step S15, where the dilution flag XD is set to “1” to indicate that fuel dilution is in progress, and the fuel dilution rate D _i is diluted. When the value is smaller than the reference value D1, the process proceeds to step S16, the dilution flag XD is set to “0” to indicate that the fuel dilution is not progressing so much, and the process proceeds to the end.

  Then, in step S1 in the lift amount and throttle opening control routine shown in FIG. 5, if the dilution flag XD is "1", the process proceeds to step S2, and if the dilution flag XD is "0", the process proceeds to the end. . That is, when the fuel dilution is not progressing so much, the process is finished as it is. In step S2 of the lift amount and throttle opening control routine, it is determined whether or not there is a request for reducing the amount of fuel injected by the fuel injection valve 20. More specifically, the decrease request determination in step S2 is performed based on a decrease request determination routine shown in the flowchart of FIG.

First, in the reduction request determining routine, in step S21, the feedback correction coefficient K (I-Id) is added by adding the feedback correction coefficient K (I-Id) used in the above-described calculation formula for the required injection amount _Qfin. The integral term SK is calculated. Specifically, the current feedback correction coefficient K (I−Id) is added to the previous integral term SK _i−1 to calculate the current integral term SK _i . Then, the process proceeds to step S22, and whether the calculated integral term SK _i (feedback correction coefficient K (I−Id)) is smaller than a predetermined reference value SK1 indicating that the required injection amount Q _fin is _largely reduced. It is determined whether or not. If the current integral term SK _i is less than the predetermined reference value SK1, the process proceeds to step S23 to indicate that there is a reduction request by setting the reduction request flag XSK to “1”, and the current integral term SK _i is predetermined. If it is less than the reference value SK1, the process proceeds to step S23 to set the decrease request flag XSK to “0”, indicating that there is no decrease request (or not so large), and to the end.

In this reduction request determination, it may be determined whether there is a reduction request by determining whether the feedback correction coefficient K (I-Id) is less than a predetermined reference value. . In this case, however, the reduction request flag XSK is set to “1” even when the feedback correction coefficient K (I−Id) temporarily becomes a very small value due to, for example, a sudden change in operating conditions. Become. Therefore, whether or not the determination is made by calculating the integral term SK _i as described above is not affected by the temporary change of the feedback correction coefficient K (I−Id), and whether or not the current tendency is to request a reduction. Can be determined more accurately.

  In the lift amount and throttle opening control routine shown in FIG. 5, the lift amount guard process based on the reduction request is performed in step S3. Specifically, the lift amount guard process is performed based on a lift amount guard process routine shown in the flowchart of FIG.

First, in the lift amount guard process routine, in step S31, the minimum lift amount L _min is set based on the integral term SK _i calculated by the reduction request in the previous step S2. This minimum lift amount L _min is derived so that the minimum lift amount L _min increases as the integral term SK decreases, as shown in the map of the minimum lift amount L _min with respect to the integral term SK in FIG. . In other words, the fact that the integral term SK is small means that the required injection amount Q _fin is reduced to a large extent, and even when the amount of air introduced into the combustion chamber 18 is not so small, the required injection amount Q _fin is Since it tends to be equal to or less than the minimum injection amount _Qmin , the minimum lift amount _Lmin that is the lower limit value of the maximum lift amount L of the intake valve 30 is set large. Then, the flow proceeds to step S32, the maximum lift amount L _a of the intake valve 30 which is derived from the accelerator pedal depression amount, whether small is determined than the minimum lift amount L _min set in step S31. The maximum maximum lift amount L _a which is derived from the accelerator depression amount is equal to or minimum lift amount L _min or more, the routine goes to end, the maximum lift amount L of the intake valve 30, which is derived based on the accelerator depression amount It is set to the lift amount _{L a.} On the other hand, the maximum lift amount L _a which is derived from the accelerator pedal depression amount, is smaller than the minimum lift amount L _min, the sequence proceeds to step S33, the maximum lift amount L of the intake valve 30 is set to the minimum lift amount L _min Move to the end.

When the lift amount guard process is performed in this way, in the lift amount and throttle opening control routine shown in FIG. 5, the routine proceeds to step S4, where the throttle opening O is set. In step S4, when the maximum lift amount of the intake valve 30 is set to the maximum lift amount L _a which is derived based on the accelerator depression amount is set in a state of the throttle opening O is as fully open state O1 Is done. On the other hand, when the maximum lift amount L _a derived from the accelerator depression amount is smaller than the minimum lift amount L _min in the previous step S3, the maximum lift amount L of the intake valve 30 is set to the minimum lift amount L _min Is controlled so that the throttle opening degree O becomes an opening degree O2 smaller than the opening degree calculated based on the engine operating state at that time, and the routine proceeds to the end. As described above, the lift amount and the throttle opening degree control by the electronic control unit 70 are performed.

Below, based on previous FIG. 4, the effect of the said control by the electronic control apparatus 70 is demonstrated. As shown in FIG. 4C, for example, the diluted fuel evaporated from the lubricating oil is returned to the intake passage 12 together with the blow-by gas, so that the amount of evaporated fuel introduced into the combustion chamber gradually increases from time t1. Thus, the required injection amount Q _fin starts to deviate from Q _base . After the time t2, when the dilution level of the fuel reaches a predetermined dilution reference value and the dilution determination flag is “1”, the integral term SK of the feedback correction coefficient K (I−Id) at this time is set. Based on this, the minimum lift amount L _min that is the lower limit value of the maximum lift amount L of the intake valve 30 is set. In the time t3 time t4, for example, the maximum lift amount L _a of idling or slow speed operation is performed intake valve 30 based on the accelerator depression amount is, the minimum lift amount as shown in the dashed line A in FIGS. 4 (a) L becomes smaller than _min . At this time, setting the maximum lift amount L of the intake valve 30 to the maximum lift amount L _a, since the reference injection amount Q _base is changed as shown in chain line B one point of FIG. 4 (c), the required injection amount Q _fin As shown by a two-dot chain line C in FIG. 4C, the fuel injection amount changes below the minimum injection amount _Qmin . Therefore, the fuel injection valve 20 injects the fuel with the minimum injection amount _Qmin , and the air-fuel ratio control cannot be performed appropriately. Therefore, by performing the above-described lift amount and throttle opening control, the lift amount guard process for setting the maximum lift amount L to the minimum lift amount L _min is performed during the period from time t3 to time t4. As a result, the fuel injection valve 20 can inject the required injection amount Q _fin that is larger than the minimum injection amount corresponding to the minimum lift amount L _min , and control for setting the air-fuel ratio to the stoichiometric air-fuel ratio is possible. Thus, the deterioration of emissions can be suppressed.

Further, as shown in FIG. 4B, during the period from time t3 to time t4 when the maximum lift amount L becomes the minimum lift amount L _min , the throttle opening degree O is set from the fully open state O1 during normal operation of the internal combustion engine 10. Since the opening degree O2 is set to be small, the pumping loss increases in the intake stroke of the internal combustion engine 10. Therefore, since the guard process is performed so that the maximum lift amount of the intake valve 30 is equal to or greater than the minimum lift amount L _{min, the} intake air amount and the fuel injection amount are larger than the output request of the internal combustion engine 10 based on the accelerator depression amount. Although the energy generated by the internal combustion engine 10 is increased, the load on the internal combustion engine 10 is also increased, so that an increase in the rotational speed of the internal combustion engine 10 can be suppressed. In other words, during idle operation or slow drive, the engine speed increases, and the air-fuel ratio can be converged to the target theoretical air-fuel ratio without causing the passenger to feel uncomfortable due to noise or vibration. .

As described above in detail, according to the present embodiment, the following effects can be obtained.
(1) The electronic control unit 70 of the present embodiment sets the minimum lift amount L _min of the intake valve 30 when the amount of fuel injected by the fuel injection valve 20 is estimated to be the minimum injection amount Q _min. I am doing so. When the maximum lift amount L _a based on the accelerator depression amount is smaller than the minimum lift amount L _min, performs lift guard processing for the maximum lift amount L of the intake valve 30 and the minimum lift amount L _min, throttle opening The degree O is made small. Therefore, since the amount of fuel injected by the fuel injection valve 20 can be made larger than the minimum injection amount, control for setting the air-fuel ratio to the stoichiometric air-fuel ratio becomes possible, and deterioration of emissions can be suppressed. .

Further, when the lift amount guard process is performed, the driving state of the throttle valve 14 is controlled so as to reduce the throttle opening degree O. Therefore, the pumping loss increases in the intake stroke of the internal combustion engine 10. Therefore, to maximum lift L of the intake valve 30 increases than the maximum lift amount L _a based on the accelerator depression amount, even when large energy the internal combustion engine 10 to generate than the output request of the internal combustion engine by the driver Since the load on the internal combustion engine 10 also increases, it is possible to suppress an increase in the rotational speed of the internal combustion engine 10. As a result, the air-fuel ratio can be converged to the target air-fuel ratio without giving a sense of incongruity due to noise or vibration to the occupant during idling.

(2) In the present embodiment, the minimum lift amount _Lmin is set to increase as the integral term SK of the feedback correction coefficient K (I-Id) decreases. That is, when the feedback correction coefficient K (I-Id) (integral term SK) is very small, that is, when the feedback correction coefficient K (I-Id) is large enough to reduce the required injection amount _Qfin , the intake air be not very small lift amount of the valve 30, the required injection amount _{Q fin} can easily be less than the minimum injection quantity _{Q min.} On the other hand, it is calculated as a value the feedback correction coefficient K (I-Id) decreases the required injection amount Q _fin, when the maximum lift amount L of the intake valve 30 is not so small, the required injection amount Q _fin is minimum injection The amount is less than Q _min . Therefore, the greater the extent to which the feedback correction coefficient K (I−Id) decreases the required injection amount Q _fin , the greater the amount of air introduced into the combustion chamber 18 is controlled. Can be done.

  (3) The electronic control unit 70 of the present embodiment executes the lift amount and throttle opening degree control on the condition that the degree of fuel dilution has reached a predetermined dilution reference value D1. Thereby, when the influence of the fuel introduced into the combustion chamber 18 due to the fuel dilution is large, the electronic control unit 70 can perform the lift amount and throttle opening control as the second control means.

(Second Embodiment)
In the second embodiment of the present invention, air-fuel ratio control is performed by using an oxygen sensor instead of the air-fuel ratio sensor 25 of the first embodiment as a sensor for detecting the air-fuel ratio. That is, in the internal combustion engine of the present embodiment, although not shown, an oxygen sensor is provided in the exhaust passage 28 instead of the air-fuel ratio sensor.

  FIG. 11 is a time chart showing the control state of the internal combustion engine 10 in the present embodiment, where (a) is the maximum lift amount L of the intake valve 30, (b) is the output voltage V of the oxygen sensor, and (c) is described later. The feedback correction coefficient FAF is shown.

  In this oxygen sensor, as shown in FIG. 11B, when the air-fuel ratio is the stoichiometric air-fuel ratio, the output voltage V becomes the reference voltage Vd, and when the air-fuel ratio changes across the stoichiometric air-fuel ratio, the output voltage V It has characteristics that change suddenly. Specifically, the output voltage V of the oxygen sensor shows a value smaller than the reference voltage Vd when the air-fuel ratio is lean with respect to the stoichiometric air-fuel ratio, and the air-fuel ratio is rich with respect to the stoichiometric air-fuel ratio. Sometimes, the value is larger than the reference voltage Vd. In other words, this oxygen sensor does not detect the air-fuel ratio as a linear continuous value like the air-fuel ratio sensor 25 of the first embodiment, but determines whether the air-fuel ratio is rich with respect to the stoichiometric air-fuel ratio. Detect only the state of.

In the present embodiment, the first control means derives the required injection amount Q _fin by the following equations 2 and 3.
Q _fin = Q _base + FAF Equation 2
FAF = RS + RI ... Formula 3
Here, “FAF” is a feedback correction coefficient, which is calculated by the skip amount RS and the integral amount RI as shown in Expression 3, and changes as shown in FIG. Hereinafter, a change mode of the feedback correction coefficient FAF will be described.

When the air-fuel ratio is rich with respect to the stoichiometric air-fuel ratio, the output voltage V of the air-fuel ratio sensor becomes larger than the reference voltage Vd as described above. Then, as shown at a point V1 in FIG. 11, when the air-fuel ratio is still rich, the integral amount RI of the feedback correction coefficient FAF is decreased, and the feedback correction coefficient FAF is indicated by a point F1. It gradually becomes smaller from the state. When the feedback correction coefficient FAF is gradually reduced in this way, the required injection amount Q _fin is also gradually reduced by Equation 2, so that the air-fuel ratio changes from the rich side to the lean side with respect to the theoretical air-fuel ratio, As indicated by a point V2 in FIG. 11, the output voltage V changes from a value larger than the reference voltage Vd to a smaller value.

At this time, the skip amount RS is added to the feedback correction coefficient FAF, and the state shown at the point F2 changes to the state shown at the point F3. The skip amount RS is set to a value at which the air-fuel ratio does not reverse at a stretch from the lean side to the rich side with respect to the stoichiometric air-fuel ratio. Therefore, the air-fuel ratio remains lean with respect to the stoichiometric air-fuel ratio for a while, and the output voltage V continues to be lower than the reference voltage Vd. Then, the integration amount RI of the feedback correction coefficient FAF is increased, and the feedback correction coefficient FAF gradually increases from the state indicated by the point F3. When the feedback correction coefficient FAF is gradually increased in this way, the required injection amount Q _fin is gradually derived, so that the air-fuel ratio changes from the lean side to the rich side with respect to the stoichiometric air-fuel ratio. As indicated by the point V3, the output voltage V changes from a value smaller than the reference voltage Vd to a larger value.

At this time, the skip amount RS is subtracted from the feedback correction coefficient FAF, and the feedback correction coefficient FAF changes from the state indicated by the point F4 to the state indicated by the point F5. The skip amount RS is set to a value at which the air-fuel ratio does not reverse at a stretch from the rich side to the lean side with respect to the stoichiometric air-fuel ratio. The feedback correction coefficient FAF changes as described above based on the output voltage of the oxygen sensor, and the feedback correction coefficient FAF derived in this way is added to the reference injection amount Q _base to derive the required injection amount Q _fin. The

Here, for example, when the amount of fuel supplied to the combustion chamber 18 increases due to factors other than the fuel injection valve 20 due to the influence of the fuel dilution described above, for example, after the time t1, the oxygen sensor has a long-term air-fuel ratio. It shows that it is rich with respect to the theoretical air-fuel ratio. At this time, since the integral amount RI of the feedback correction coefficient FAF is continuously decreased, the feedback correction coefficient FAF subsequently increases or decreases around a value smaller than 0. When the integral amount RI becomes smaller than, for example, a preset integral reference value RI1, for example, when the maximum lift amount L of the intake valve 30 becomes small and the reference injection amount Q _base becomes small, for example, during idling. , Q _fin may be less than the minimum injection amount.

That is, during the normal operation of FIG. 11, the maximum lift amount L of the intake valve 30 is relatively large, and at this time, the reference injection amount Q _base is also relatively large. Therefore, even when the feedback correction coefficient FAF is small, the required injection The amount Q _fin is not less than the minimum injection amount. However, for example, when the idle operation is started and the maximum lift amount L of the intake valve 30 based on the accelerator depression amount is smaller than the minimum lift amount L _min as shown by a one-dot chain line A in FIG. Accordingly, since the reference injection amount Q _base becomes small, there is a possibility that the required injection amount Q _fin becomes equal to or less than the minimum injection amount when the feedback correction coefficient FAF is small as described above.

Therefore, in the present embodiment, as shown in FIG. 11, when the integral amount RI of the feedback correction coefficient FAF becomes smaller than the integral reference value RI1 (time t2), the integral amount RI (feedback correction coefficient FAF) is calculated. The minimum lift amount L _min of the intake valve 30 is set to increase as the value decreases. Then, as in the first embodiment, when the maximum lift amount L of the intake valve 30 based on the accelerator depression amount is smaller than the minimum lift amount L _min, and the minimum lift amount L _min the maximum lift amount L of the intake valve 30 A lift amount guard process is performed. Although not shown, when the lift amount guard process is performed, a process is performed to make the throttle opening smaller than the opening calculated based on the engine operating state at that time.

As described above, in the present embodiment, an oxygen sensor is used instead of the air-fuel ratio sensor. However, even when this oxygen sensor is used, the maximum lift amount L of the intake valve 30 is calculated by integrating the feedback correction coefficient. performs lift guard process for minimizing the lift amount L _min or more based on the amount RI, and to perform the processing for reducing the throttle opening. Therefore, the effect according to the effect similar to the said 1st Embodiment can be show | played.

(Other embodiments)
In addition, you may change the said embodiment as follows.
In each of the above embodiments, the maximum lift amount guard process of the intake valve 30 is performed by estimating that the fuel injected by the fuel injection valve 20 is less than the minimum injection amount by the feedback correction coefficient in advance. . However, the electronic control unit 70 performs control to increase the maximum lift amount of the intake valve 30 after the required injection amount Q _fin that is actually derived becomes equal to or less than the minimum injection amount after, for example, idle operation is started. You may make it perform. In this case, the maximum lift amount of the intake valve 30 may be set larger as the required injection amount Q _fin decreases. Thereby, air-fuel ratio control can be performed quickly and accurately. As control for increasing the maximum lift amount of the intake valve 30, instead of setting the minimum lift amount, which is the lower limit value of the maximum lift amount, so as not to become smaller than the minimum lift amount, the intake valve 30 The maximum lift amount may be set to a value larger than the opening calculated based on the accelerator opening at that time.

  In the above description, the electronic control unit 70 controls the throttle opening to be small when controlling the maximum lift amount of the intake valve 30 to be large. It should be noted that the throttle opening may be controlled to be smaller than the fully open state during normal operation such as during high-speed traveling, for example, when idle operation is started. In such a case, the throttle opening is reduced as the idle operation starts, and the throttle opening is further reduced when the maximum lift amount of the intake valve 30 is increased. You may make it perform control which makes it small in a step.

In the case where the control by the second control means is performed from when the required injection amount Q _fin actually becomes equal to or less than the minimum injection amount in this way, when the minimum injection amount is temporarily reached, the second control means The control may be started, or the control by the second control unit may be started when a time that is equal to or less than the minimum injection amount continues for a predetermined time or more. In other words, even if the amount of fuel injected by the fuel injection valve 20 temporarily becomes a predetermined minimum injection amount, if the amount immediately exceeds that predetermined minimum injection amount, appropriate air-fuel ratio control can be performed immediately. Therefore, in such a case, the control by the second control unit may not be performed.

  In each of the above embodiments, the second control means is provided on the condition that fuel dilution is proceeding by determining whether or not the fuel dilution is proceeding beyond a predetermined reference value in consideration of the effect of fuel dilution. The control by is done. However, the control by the second control unit may be performed when the amount of fuel injected by the fuel injection valve 20 is equal to or less than the minimum injection amount without performing the fuel dilution determination. The reason why the amount of fuel injected by the fuel injection valve 20 is less than or equal to the minimum injection amount is that the evaporated fuel in the fuel tank adsorbed by the charcoal canister is purged to the intake system, or the fuel injection valve 20 There are changes over time in the characteristics. Regardless of these factors, the control by the second control means may be performed when the amount of fuel injected by the fuel injection valve 20 is less than or equal to the minimum injection amount. Further, instead of determining the fuel dilution, it may be determined whether or not these factors have reached a predetermined standard, and then the control by the second control means may be performed.

In the above-described embodiments, when the feedback correction coefficient is calculated as a value to reduce the required injection amount Q _fin, as the degree of the correction coefficient decreases the same required injection amount Q _fin is large, introduced into the combustion chamber 18 The driving state of the intake valve 30 was controlled so that the amount of air to be increased. In contrast, when the amount of fuel injected by the fuel injection valve 20 is less than or equal to the minimum injection amount, the drive state of the intake valve 30 is set so that the amount of air introduced into the combustion chamber 18 is increased by a certain amount. May be controlled.

  In each of the above embodiments, the target air-fuel ratio is the stoichiometric air-fuel ratio, but the target air-fuel ratio is not the stoichiometric air-fuel ratio, and may be set to a value larger or smaller than the stoichiometric air-fuel ratio, for example.

  In each of the above embodiments, the fuel injection valve 20 is disposed in the combustion chamber 18 and directly injects fuel into the combustion chamber 18. However, fuel is injected from the fuel injection valve 20 into the intake port of the intake passage 12. You may make it do. In this case, the injected fuel is easily vaporized, so that the fuel dilution is relatively less likely to occur. However, when the fuel dilution is caused by some factor, or by the fuel injection valve 20 due to a factor other than the fuel dilution. When the amount of fuel to be injected is less than or equal to the minimum injection amount, the control by the second control means may be performed.

  In each of the above embodiments, the minimum injection amount is set to the minimum injection amount that enables accurate injection amount control of the fuel injection valve, but is slightly larger than the minimum injection amount determined by the characteristics of the fuel injection valve. You may make it employ | adopt the set predetermined injection amount.

  In the above embodiment, the variable valve mechanism that makes the maximum lift amount of the intake valve variable is used. However, as the intake valve that adjusts the communication state between the intake passage and the combustion chamber, the maximum lift of the intake valve is used. It is also possible to use one driven by an electromagnetic valve mechanism in which the amount and opening / closing timing are freely variable.

1 is a schematic diagram of an internal combustion engine to which an electronic control device as an air-fuel ratio control device is applied in a first embodiment according to the present invention. FIG. The graph which shows the output characteristic of the air fuel ratio sensor provided in the exhaust passage of the internal combustion engine. The graph which shows the change aspect of the lift amount and lift action angle of the intake valve of the internal combustion engine. 4 is a time chart showing the control state of the internal combustion engine, where (a) shows the maximum lift amount of the intake valve, (b) shows the throttle opening, and (c) shows the fuel injection amount. The flowchart which shows the lift amount and throttle opening control routine which the electronic control apparatus performs. The graph which shows the fuel dilution state of the lubricating oil with respect to the cooling water temperature of the internal combustion engine. The flowchart which shows the fuel dilution determination routine of the lubricating oil which the electronic control apparatus performs. The flowchart which shows the weight reduction request | requirement determination routine which the electronic control apparatus performs. The flowchart which shows the lift amount guard processing routine which the electronic control apparatus performs. The graph which shows the minimum lift amount with respect to the integral term of the feedback correction coefficient based on the detected value of the same air-fuel ratio sensor. In 2nd Embodiment which concerns on this invention, it is a time chart which shows the control state of an internal combustion engine, (a) is the maximum lift amount of an intake valve, (b) is the output voltage of an oxygen sensor, (c) is feedback correction. Indicates the coefficient.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Internal combustion engine, 11 ... Cylinder, 12 ... Intake passage, 13 ... Crankcase, 14 ... Throttle valve, 16 ... Throttle motor, 17 ... Blow-by gas recirculation device, 18 ... Combustion chamber, 20 ... Fuel injection valve, 22 ... Ignition Plug, 23 ... Crankshaft, 24 ... Piston, 25 ... Air-fuel ratio sensor, 26 ... Exhaust purification catalyst, 28 ... Exhaust passage, 29 ... Oil pan, 30 ... Intake valve, 32 ... Exhaust valve, 34 ... Intake camshaft, 36 ... exhaust camshaft, 42 ... variable valve mechanism, 44 ... electric motor, 50 ... throttle sensor, 52 ... intake air amount sensor, 54 ... water temperature sensor, 56 ... accelerator sensor, 58 ... crank sensor, 60 ... cam sensor, 62 ... Lift sensor, 70: electronic control unit.

Claims (5)

A throttle valve that adjusts the cross-sectional area of the intake passage, an intake valve that adjusts the communication state between the intake passage and the combustion chamber, a fuel injection valve that injects fuel introduced into the combustion chamber, and the combustion chamber An air-fuel ratio control apparatus for controlling the air-fuel ratio in an internal combustion engine comprising a sensor for detecting an air-fuel ratio of an air-fuel mixture of air and the fuel introduced into the fuel,
First control for controlling the amount of the fuel injected by the fuel injection valve according to the driving state of the throttle valve and the intake valve so that the air-fuel ratio detected by the sensor becomes a target air-fuel ratio Means,
When the amount of the fuel injected by the fuel injection valve is less than or equal to a predetermined minimum injection amount, the throttle valve drive state is controlled so as to reduce the flow passage cross-sectional area of the intake passage, and the combustion An air-fuel ratio control apparatus comprising: a second control unit that controls a driving state of the intake valve so as to increase an amount of the air introduced into the chamber. In claim 1,
The first control means is an amount of fuel to be injected by the fuel injection valve in accordance with a driving state of the throttle valve and the intake valve so that the air-fuel ratio detected by the sensor becomes a target air-fuel ratio. Is calculated as the required injection amount, and when the required injection amount is smaller than the predetermined minimum injection amount, the amount of the fuel injected by the fuel injection valve is set to the predetermined minimum injection amount,
The second control means is configured such that when the required injection amount is equal to or less than the predetermined minimum injection amount, the amount of air introduced into the combustion chamber increases as the required injection amount decreases. An air-fuel ratio control apparatus for controlling a driving state of an intake valve. In claim 1,
The first control means calculates an air-fuel ratio feedback correction coefficient for making the air-fuel ratio detected by the sensor a target air-fuel ratio, so that the fuel according to the driving state of the throttle valve and the intake valve Deriving the amount of fuel to be injected by the injection valve as a required injection amount, and controlling the amount of fuel injected by the fuel injection valve based on the required injection amount,
When the feedback correction coefficient is calculated as a value that decreases the required injection amount, the second control means is introduced into the combustion chamber as the correction coefficient decreases the required injection amount. An air-fuel ratio control apparatus that controls the drive state of the intake valve so that the amount of air increases. In any one of Claims 1-3,
The intake valve is configured to have a variable maximum lift so that the amount of air introduced into the combustion chamber is variable.
The second control means is configured such that the maximum lift amount of the intake valve is equal to or greater than a predetermined minimum lift amount when the amount of the fuel injected by the fuel injection valve is equal to or smaller than a predetermined minimum injection amount. An air-fuel ratio control apparatus characterized by increasing the amount of air introduced into the combustion chamber by limiting. In any one of Claims 1-4,
The second control means performs the second control on the condition that the degree of fuel dilution by which the fuel injected by the fuel injection valve dilutes the lubricating oil of the internal combustion engine has reached a predetermined dilution reference value. An air-fuel ratio control apparatus that performs the control by means.

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