Control device for a flexible fuel internal combustion engine

Abstract

An object of the present application is to effectively reduce the amount of fuel adhering to the cylinder. A control device for a flexible fuel internal combustion engine capable of using alcohol fuel is configured to implement, in a case where the amount of fuel adhering to the cylinder, i.e., the cylinder adhesion amount, exceeds a determination value (S100: YES), a cylinder negative pressure increase process (S120) that increases the cylinder negative pressure.

Description

Technical Field

[0001] This invention relates to a control device for a flexible fuel internal combustion engine capable of using alcohol-containing fuels. Background Technology

[0002] Compared to other fuels such as gasoline, alcohols have lower volatility. Therefore, in flexible fuel internal combustion engines as described above, fuel may sometimes adhere to the cylinder walls, such as the bore walls or piston crowns. Moreover, the fuel adhering to the cylinder is discharged into the exhaust passage in an unburned state, which can sometimes lead to worsened emissions.

[0003] In contrast, Patent Document 1 describes a control device for a flexible fuel internal combustion engine that suppresses the deterioration of low-temperature startability by performing compression stroke injection during engine startup. This control device sets the fuel injection pressure based on the fuel's alcohol concentration and coolant temperature to initiate combustion before the injected fuel adheres to the cylinder, thereby performing compression stroke injection during startup and promoting fuel vaporization.

[0004] Patent Document 1: Japanese Patent Application Publication No. 2010-37968 Summary of the Invention

[0005] In the aforementioned conventional control devices, fuel adhesion to the cylinder is suppressed by promoting the vaporization of the injected fuel. However, while this method can suppress the increase in the amount of fuel adhering to the cylinder, it cannot effectively reduce the amount of fuel already adhering to the cylinder. Therefore, in the aforementioned conventional control devices, if a large amount of fuel adheres to the cylinder, the deterioration of emissions cannot be adequately suppressed.

[0006] The control device for the flexible fuel internal combustion engine that solves the above-mentioned problem is applicable to flexible fuel internal combustion engines that can use alcohol-containing fuels, and is configured to determine whether the amount of fuel adhering to the cylinder of the flexible fuel internal combustion engine is high, i.e., the amount of fuel adhering to the cylinder is high, and if it is determined that the amount of fuel adhering to the cylinder is high, to perform a cylinder negative pressure increase process that increases the negative pressure in the cylinder.

[0007] Invention Effects

[0008] The control device for the aforementioned flexible fuel internal combustion engine has the effect of effectively reducing the amount of fuel adhering to the cylinder. Attached Figure Description

[0009] Figure 1 This is a diagram schematically illustrating the structure of a flexible fuel internal combustion engine according to one embodiment of an applicable control device.

[0010] Figure 2 This is a schematic diagram illustrating the structure of one embodiment of the control device for a flexible fuel internal combustion engine.

[0011] Figure 3 It means Figure 1 The flowchart shows the processing steps of the in-cylinder adhesion suppression control performed by the control device.

[0012] Figure 4 It is a graph showing the relationship between the cylinder wall temperature and the evaporation rates of ethanol and gasoline in the adhering fuel. Detailed Implementation

[0013] The following is for reference. Figures 1-4 An embodiment of the control device for a flexible fuel internal combustion engine will be described in detail.

[0014] <Structure of a Flexible Fuel Internal Combustion Engine>

[0015] First, refer to Figure 1 The structure of the flexible fuel internal combustion engine 10 to which the control device of this embodiment is applied will be described. The flexible fuel internal combustion engine 10 is configured as an on-board internal combustion engine capable of using gasoline, alcohol, and mixtures thereof as fuel.

[0016] The flexible fuel internal combustion engine 10 includes a cylinder 12 with a piston 11. The piston 11 is connected to the output shaft, or crankshaft 14, of the flexible fuel internal combustion engine 10 via a connecting rod 13. The connecting rod 13 and the crankshaft 14 constitute a crank mechanism that converts the reciprocating linear motion of the piston 11 into the rotational motion of the crankshaft 14. Inside the cylinder 12, a combustion chamber 15 for combustion of the air-fuel mixture is formed by the piston 11. In the combustion chamber 15, an intake passage 16 for supplying combustion air is connected via an intake valve 18. Furthermore, an exhaust passage 17 for exhaust gas generated by combustion is connected via an exhaust valve 19. Additionally, the flexible fuel internal combustion engine 10 includes a variable valve timing mechanism (hereinafter referred to as VVT mechanism 20) that sets the valve timing of the intake valve 18 to be variable. Furthermore, the flexible fuel internal combustion engine 10 includes a crankshaft angle sensor 31 for detecting the rotation angle of the crankshaft 14, i.e., the crankshaft angle.

[0017] In the intake passage 16 of the flexible fuel internal combustion engine 10, an air flow meter 21, a throttle valve 22, and an intake pressure sensor 23 are provided. The air flow meter 21 is a sensor that detects the flow rate of the intake air passing through the intake passage 16, i.e., the intake air volume. The throttle valve 22 is a valve that adjusts the intake air volume by changing the flow path area of ​​the intake air. The intake pressure sensor 23 is a sensor that detects the pressure of the intake air downstream of the throttle valve 22 in the intake passage 16, i.e., the intake manifold pressure. Furthermore, the flexible fuel internal combustion engine 10 is provided with an injector 26 that injects fuel into the intake air introduced into the combustion chamber 15, and an ignition device 27 that ignites the air-fuel mixture in the combustion chamber 15 by spark discharge. On the other hand, in the exhaust passage 17 of the flexible fuel internal combustion engine 10, an air-fuel ratio sensor 24 and an exhaust purification catalyst 25 are provided. The air-fuel ratio sensor 24 is a sensor that detects the air-fuel ratio of the air-fuel mixture burning in the combustion chamber 15. The exhaust purification catalyst 25 is an exhaust purification device that purifies harmful substances in exhaust gas.

[0018] The flexible fuel internal combustion engine 10 includes an exhaust gas recirculation (EGR) system that recirculates a portion of the exhaust gas flowing in the exhaust passage 17 into the intake air. The EGR system includes an EGR passage 28, an EGR cooler 29, and an EGR valve 30. The EGR passage 28 is a passage connecting the exhaust passage 17, which allows the recirculated exhaust gas (i.e., EGR gas) to flow into the intake air, and the intake passage 16. The EGR cooler 29 is a heat exchanger that cools the EGR gas flowing into the intake air through the EGR passage 28. The EGR valve 30 is a valve that adjusts the flow rate of the EGR gas flowing into the intake air through the EGR passage 28, i.e., the external EGR quantity.

[0019] <Structure of the control device for the flexible fuel internal combustion engine 10>

[0020] Next, refer to Figure 2 For applicable Figure 1The structure of the control device for the flexible fuel internal combustion engine 10 will be described. In this embodiment, the control device is configured as an electronic control unit 40 comprising a processing unit 41, a storage unit 42, an input circuit 43, and an output circuit 44. The storage unit 42 stores control programs or data. The processing unit 41 executes the program stored in the storage unit 42. The input circuit 43 is connected to the aforementioned air flow meter 21, intake pressure sensor 23, air-fuel ratio sensor 24, and crankshaft angle sensor 31. Furthermore, the input circuit 43 is connected to a water temperature sensor 32 for detecting the coolant temperature of the flexible fuel internal combustion engine 10 and an alcohol concentration sensor 33 for detecting the alcohol concentration of the fuel injected by the injector 26. On the other hand, the output circuit 44 is connected to actuators of the flexible fuel internal combustion engine 10, such as the VVT ​​mechanism 20, throttle valve 22, injector 26, ignition device 27, and EGR valve 30. The electronic control unit 40 calculates the operating parameters of the actuators of the flexible fuel internal combustion engine 10 based on the detection results of the sensors connected to the input circuit 43. Then, the electronic control unit 40 outputs command signals from the output circuit 44 to the actuators based on the calculated operating parameters, thereby controlling the flexible fuel internal combustion engine 10. Examples of the operating parameters of the flexible fuel internal combustion engine 10 include intake valve timing, throttle valve opening, fuel injection quantity, fuel injection timing, ignition timing, and EGR opening. Intake valve timing refers to the valve timing of the intake valve 18 set by the VVT ​​mechanism 20, and throttle valve opening refers to the opening ratio of the throttle valve 22. Furthermore, fuel injection quantity and fuel injection timing refer to the amount of fuel injected by the injector 26 and the start time of fuel injection, respectively. Ignition timing refers to the time when the air-fuel mixture is ignited by the ignition device 27, and EGR opening refers to the opening ratio of the EGR valve 30.

[0021] For example, the electronic control unit 40 sets the throttle valve opening in the following manner. The electronic control unit 40 calculates the current intake air filling efficiency of the combustion chamber 15 based on the engine speed obtained from the crankshaft angle detection result and the current throttle valve opening. Filling efficiency represents the ratio of the dry weight of the fresh air drawn into the combustion chamber 15 under standard atmospheric conditions to the dry weight of the fresh air occupying the stroke volume of the cylinder 12. Filling efficiency is sometimes also referred to as engine load rate. On the other hand, with the air-fuel ratio of the mixture burned in the combustion chamber 15 set to a target value, the electronic control unit 40 calculates the filling efficiency required to obtain the desired output of the flexible fuel internal combustion engine 10 as the target filling efficiency value. Then, the electronic control unit 40 adjusts the throttle valve opening setting value to obtain the target filling efficiency, thereby setting the throttle valve opening commanded by the throttle valve 22. Furthermore, if the EGR opening increases and the external EGR quantity increases, the throttle valve opening to obtain the target filling efficiency becomes larger. Furthermore, if the valve timing of the intake valve 18 is advanced by the VVT ​​mechanism 20, increasing the valve overlap between the intake valve 18 and the exhaust valve 19, the amount of exhaust gas backflushed from the exhaust passage 17 to the combustion chamber 15, i.e., the so-called internal EGR, increases. Then, by increasing the internal EGR, the throttle valve opening to achieve the target filling efficiency becomes larger. The electronic control unit 40 sets the throttle valve opening in a manner that reflects the influence of both the external and internal EGR. Additionally, even with the same filling efficiency, when the throttle valve opening is larger, the in-cylinder negative pressure is smaller compared to when the throttle valve opening is smaller. The in-cylinder negative pressure refers to the negative pressure formed in the combustion chamber 15 during the intake stroke.

[0022] Furthermore, the electronic control unit 40 performs fuel cut-off control to stop the fuel supply to the flexible fuel internal combustion engine 10 during the vehicle's inertial driving when the throttle is closed. The electronic control unit 40 also performs intermittent stop control by stopping the flexible fuel internal combustion engine 10 during stop times at traffic lights and restarting it based on the driver's pre-driving preparation operation. Additionally, in hybrid vehicles capable of motor-driven operation, where the flexible fuel internal combustion engine 10 is installed, the control to stop the flexible fuel internal combustion engine 10 can also be implemented as intermittent stop control during motor-driven operation, in addition to stop times.

[0023] <In-cylinder adhesion suppression and control>

[0024] The electronic control unit 40, as part of the control of the flexible fuel internal combustion engine 10, performs in-cylinder adhesion suppression control to suppress in-cylinder adhesion. In-cylinder adhesion refers to fuel adhering to the walls of the cylinder 12 bore, the top surface of the piston 11, and other surfaces exposed in the combustion chamber 15.

[0025] Figure 3The diagram illustrates the processing flow executed by the electronic control unit 40 for in-cylinder adhesion suppression control. During operation of the flexible fuel internal combustion engine 10, the electronic control unit 40 repeatedly executes the process according to each preset control cycle. Figure 3 The handling. If Figure 3 Upon commencement of the process, the electronic control unit 40 first determines in step S100 whether the amount of fuel adhering to the cylinder exceeds a preset threshold. This threshold is set to be less than the upper limit of the permissible amount of fuel adhering to the cylinder, as determined from emission and other perspectives. Then, if the electronic control unit 40 determines that the amount of fuel adhering to the cylinder is below the threshold (no), it terminates the current control cycle. Figure 3 In contrast, if the electronic control unit 40 determines that the amount of fuel adhering to the cylinder exceeds a predetermined value, it proceeds to step S110. Then, in step S110, the electronic control unit 40 disables the fuel cut-off control and intermittent stop control of the flexible fuel internal combustion engine 10. Furthermore, after implementing the cylinder negative pressure increase process in the subsequent step S120, the electronic control unit 40 ends the current control cycle. Figure 3 The processing.

[0026] The electronic control unit 40 estimates the in-cylinder injection quantity used in the determination in step S100 in the following manner. First, the electronic control unit 40 calculates the fuel evaporation quantity based on the current estimated value of the in-cylinder fuel adhesion quantity, the cylinder wall temperature 12, the in-cylinder negative pressure, and the alcohol concentration of the fuel. The fuel evaporation quantity represents the amount of fuel that evaporates from the cylinder wall. At the same time, the electronic control unit 40 calculates the new adhesion quantity based on the fuel injection quantity, the cylinder wall temperature 12, the in-cylinder negative pressure, and the alcohol concentration of the fuel. The new adhesion quantity represents the amount of fuel that is not completely vaporized after being injected from the injector 26 and adheres to the cylinder. Then, the electronic control unit 40 updates the estimated value of the in-cylinder adhesion quantity by subtracting the fuel evaporation quantity from the previous value and adding the subtracted value to the new adhesion quantity to obtain the updated value, thereby estimating the in-cylinder adhesion quantity.

[0027] <Treatment for Increased Negative Pressure Inside the Cylinder>

[0028] For Figure 3 The in-cylinder negative pressure increase process implemented in step S120 will be described. The in-cylinder negative pressure increase process is a process of adjusting the operating amount of the flexible fuel internal combustion engine 10 to increase the in-cylinder negative pressure, that is, to reduce the internal pressure of the combustion chamber 15 during the intake stroke. As examples of the in-cylinder negative pressure increase process, the processes (A) to (E) below can be cited.

[0029] (A) Handling of changing the operating point of the flexible fuel internal combustion engine 10: By changing the operating point of the flexible fuel internal combustion engine 10 on the side where engine speed increases and filling efficiency decreases, the cylinder negative pressure can be increased. This change in operating point can be implemented, for example, by operating the transmission in a vehicle equipped with the flexible fuel internal combustion engine 10 in a manner that increases the gear ratio. Furthermore, in the case of the flexible fuel internal combustion engine 10 being equipped in a hybrid vehicle, this change in operating point can also be performed through coordinated control of the flexible fuel internal combustion engine 10 and the electric motor.

[0030] (B) Reducing the throttle valve opening: Reducing the throttle valve opening decreases the filling efficiency, which in turn increases the cylinder negative pressure. However, simply reducing the throttle valve opening will reduce the output of the flexible fuel internal combustion engine 10. Therefore, it is preferable to improve combustion efficiency by reducing the throttle valve opening and advancing the ignition timing, thereby maintaining the output of the flexible fuel internal combustion engine 10.

[0031] (C) Reduction of External EGR Amount: When the EGR valve 30 is opened, fresh air and EGR gas are introduced into the combustion chamber 15 during exhaust gas recirculation. If the EGR opening is reduced to decrease the external EGR amount, the total amount of gas filling the combustion chamber 15 decreases, thus increasing the in-cylinder negative pressure. Furthermore, if the external EGR amount is further reduced, the combustion efficiency improves, therefore the throttle valve opening required to achieve the target filling efficiency is smaller than before the reduction. This reduction in the throttle valve opening increases the in-cylinder negative pressure.

[0032] (D) Reduction of Internal EGR: If the timing of the intake valve 18 is advanced by a certain degree through the VVT ​​mechanism 20, a state in which the intake valve 18 and the exhaust valve 19 are open simultaneously occurs, known as valve overlap. During valve overlap, exhaust gas is backflushed from the exhaust passage 17 into the combustion chamber 15. The amount of exhaust gas recirculated to the intake air due to this backflushing during valve overlap, i.e., the internal EGR, increases with the increase of valve overlap and decreases with the decrease of valve overlap. Furthermore, valve overlap is a quantity expressed in crankshaft angle as the length of the period during which valve overlap occurs. Similar to the reduction of external EGR, reducing the valve overlap to decrease the internal EGR also increases the cylinder vacuum.

[0033] (E) Reduction of ignition timing delay in catalyst preheating control: Sometimes, after the flexible fuel internal combustion engine 10 is started, the ignition timing is delayed to increase the exhaust temperature, thereby implementing catalyst preheating control to promote the preheating of the exhaust purification catalyst 25. During the execution of this catalyst preheating control, the reduction of the ignition timing delay in catalyst preheating control can be implemented as a process of increasing in-cylinder negative pressure. If the ignition timing delay is reduced, the combustion efficiency is improved, and therefore the throttle valve opening to obtain the target charging efficiency is smaller than before the delay is reduced. Then, if the throttle valve opening is reduced, the charging efficiency decreases, and therefore the in-cylinder negative pressure increases.

[0034] <The Role of the Implementation Method>

[0035] In the flexible fuel internal combustion engine 10, a portion of the fuel injected from the injector 26 sometimes remains incompletely vaporized and adheres to the cylinder 12 walls, such as the bore walls or the top surface of the piston 11. As during a cold start, when the temperature inside the cylinder 12 is low, the fuel adhering to the walls is difficult to volatilize, thus increasing the amount of fuel adhering to the cylinder walls. If the amount of fuel adhering to the cylinder walls increases, the adhering fuel is discharged into the exhaust passage 17 in an unburned state, potentially leading to worsened emissions.

[0036] The flexible fuel internal combustion engine 10 is configured to use alcohol, gasoline, and mixtures thereof as fuel; however, when the alcohol concentration of the fuel is high, there is a tendency for a significant increase in in-cylinder adhesion during cold starts. Furthermore, fuels composed of almost 100% ethanol are commonly available as alcohol fuels for vehicles.

[0037] Figure 4The diagram shows the relationship between the wall temperature of cylinder 12 and the volatilization rates of gasoline and ethanol components in the fuel adhering to the wall of cylinder 12. Gasoline is a mixture of various hydrocarbons with different molecular weights and therefore does not have a definite boiling point. Therefore, gasoline components volatilize to a certain extent even at low wall temperatures. In contrast, ethanol, as a pure substance, has a definite boiling point BP. Therefore, within a wall temperature range below the boiling point BP of ethanol, ethanol hardly volatilizes, and within a wall temperature range above the boiling point BP of ethanol, the volatilization rate of ethanol becomes almost 100%. Therefore, if the wall temperature of cylinder 12 remains below the boiling point BP of ethanol, ethanol components in the fuel adhering to the wall will remain. Therefore, when using fuel with a high ethanol concentration, the increase in in-cylinder adhering amount during cold starts becomes significant. Furthermore, besides cold starts, if combustion in the flexible fuel internal combustion engine 10 is stopped by fuel cut-off control or intermittent stop control, the interior of cylinder 12 cools down, and therefore sometimes the in-cylinder adhering amount increases after combustion resumes. Incidentally, the boiling point BP of ethanol varies with air pressure; it is a low temperature at low pressure and a high temperature at high pressure. Therefore, when the cylinder pressure is high, that is, when the pressure inside the combustion chamber 15 is low during the intake stroke, the boiling point BP of ethanol in the combustion chamber 15 is lower compared to when the cylinder pressure is low.

[0038] In contrast, when the amount of fuel adhering to the cylinder exceeds a predetermined value (S100: Yes), the electronic control unit 40 performs a cylinder negative pressure increase process to increase the cylinder negative pressure of the flexible fuel internal combustion engine 10. If the cylinder negative pressure increases, that is, if the pressure inside the cylinder 12 decreases, the volatilization of the adhering fuel is promoted, thus reducing the amount of fuel adhering to the cylinder. Moreover, if the cylinder negative pressure increases, the vaporization of the fuel injected by the injector 26 is also promoted, thus reducing the amount of new fuel adhering and suppressing the increase of the amount of fuel adhering to the cylinder.

[0039] Furthermore, by implementing the in-cylinder negative pressure increase treatment in the following manner, the reduction effect of in-cylinder adhering amount based on the in-cylinder negative pressure increase treatment can be further improved. If the boiling point BP of ethanol in combustion chamber 15 is reduced to below the wall temperature of cylinder 12 by increasing the in-cylinder negative pressure, the ethanol adhering to the fuel in the cylinder can be effectively evaporated. The wall temperature of cylinder 12 is determined, for example, by estimating based on the cooling water temperature of flexible fuel internal combustion engine 10. Moreover, the relationship between the in-cylinder negative pressure and the boiling point BP of ethanol in combustion chamber 15 can be determined in advance through experiments, etc. Therefore, when performing the in-cylinder negative pressure increase treatment, if the electronic control unit 40 calculates the magnitude of the in-cylinder negative pressure at which the boiling point BP of ethanol in combustion chamber 15 is below the wall temperature, and increases the in-cylinder negative pressure to a magnitude greater than or equal to that magnitude, the reduction effect of in-cylinder adhering amount can be improved.

[0040] Furthermore, when the amount of fuel adhering to the cylinder exceeds a predetermined value, the electronic control unit 40 disables the fuel cut-off control and intermittent stop control of the flexible fuel internal combustion engine 10. If combustion in the flexible fuel internal combustion engine 10 stops due to fuel cut-off or intermittent stop, the inside of the cylinder 12 cools down, and the amount of fuel adhering to the cylinder tends to increase after combustion resumes. Therefore, by disabling fuel cut-off control and intermittent stop control, it is possible to suppress further increase in the amount of fuel adhering to the cylinder when a large amount of fuel has already adhered. Moreover, if the flexible fuel internal combustion engine 10 is operated at a low load under conditions where fuel cut-off is normally implemented, the negative pressure inside the cylinder decreases, promoting the volatilization of fuel adhering to the cylinder. Therefore, even if fuel cut-off control is disabled, the amount of fuel adhering to the cylinder can be reduced.

[0041] <Effects of the Implementation Method>

[0042] The control device for the flexible fuel internal combustion engine 10 in this embodiment has the following effects.

[0043] (1) The electronic control unit 40 determines whether there is a large amount of fuel adhering to the cylinder, and if it determines that there is a large amount of fuel adhering to the cylinder, it performs a process to increase the negative pressure in the cylinder. By increasing the negative pressure in the cylinder, the volatilization of fuel adhering to the cylinder and the vaporization of fuel injected by the injector 26 are promoted. Therefore, the amount of fuel adhering to the cylinder can be effectively reduced.

[0044] (2) When the electronic control unit 40 determines that there is a high amount of fuel adhering to the cylinder, it prohibits the fuel cut-off of the flexible fuel internal combustion engine 10. If fuel cut-off is implemented, the inside of the cylinder 12 cools down during its implementation, making it easier for the amount of fuel adhering to the cylinder to increase after combustion restarts. By prohibiting fuel cut-off when there is a high amount of fuel adhering to the cylinder, it is possible to suppress the further increase of the amount of fuel adhering to the cylinder after combustion restarts. Furthermore, if fuel cut-off is prohibited, the flexible fuel internal combustion engine 10 operates under a high negative pressure in the cylinder during the period when fuel cut-off would normally be implemented. As a result, the volatilization of fuel adhering to the cylinder can also be promoted, thus reducing the amount of fuel adhering to the cylinder.

[0045] (3) When the electronic control unit 40 determines that the cylinder has a high amount of in-cylinder adhesion, it prohibits the intermittent stopping of the flexible fuel internal combustion engine 10. If combustion is stopped by intermittent stopping, the inside of the cylinder 12 becomes cold, and therefore the amount of in-cylinder adhesion is likely to increase after combustion restarts. By prohibiting intermittent stopping when the amount of in-cylinder adhesion is high, it is possible to suppress the further increase of the amount of in-cylinder adhesion after combustion restarts.

[0046] (Other implementation methods)

[0047] The above-described embodiments can be implemented with the following modifications. The above-described embodiments and the following modifications can be combined with each other within the scope of technical inconsistency.

[0048] • Multiple combinations of the above processes (A) to (E) can also be used to implement the in-cylinder negative pressure increase process.

[0049] • As long as the treatment can increase the in-cylinder negative pressure, the treatments other than (A) to (E) above can also be implemented as in-cylinder negative pressure increasing treatments. For example, the treatment of reducing the amount of internal EGR by reducing the back pressure of the flexible fuel internal combustion engine 10 can also be implemented as in-cylinder negative pressure increasing treatment.

[0050] In the above embodiment, it is determined whether the in-cylinder adhesion amount is high based on the estimated in-cylinder adhesion amount. This determination can also be made by other methods. For example, it can be determined that the flexible fuel internal combustion engine 10 is in a high-cylinder adhesion amount state if it continues to operate for a predetermined time or more under conditions where the in-cylinder adhesion amount is likely to increase. Driving conditions for the flexible fuel internal combustion engine 10 that make it easy to increase in-cylinder adhesion amount include, for example, low in-cylinder negative pressure, low temperature inside the cylinder 12, and high alcohol concentration in the fuel.

[0051] • If a state of high in-cylinder adhesion is detected, either the fuel cut-off control or the intermittent stop control can be disabled, while the other continues. Alternatively, if a state of high in-cylinder adhesion is detected, neither the fuel cut-off control nor the intermittent stop control can be disabled.

[0052] The control device described in the above embodiments and their modifications can also be applied to internal combustion engines capable of using alcohol-containing fuels. Figure 1 Flexible fuel internal combustion engines with different structures.

[0053] Symbol Explanation

[0054] 10-Flexible fuel internal combustion engine, 11-Piston, 12-Cylinder, 13-Connecting rod, 14-Crankshaft, 15-Combustion chamber, 16-Intake passage, 17-Exhaust passage, 18-Intake valve, 19-Exhaust valve, 20-VVT mechanism, 21-Air flow meter, 22-Throttle valve, 23-Intake pressure sensor, 24-Air-fuel ratio sensor, 25-Exhaust gas purification catalyst, 26-Injector, 27-Ignition device, 28-EGR passage, 29-EGR cooler, 30-EGR valve, 31-Crankshaft angle sensor, 32-Water temperature sensor, 33-Alcohol concentration sensor, 40-Electronic control unit, 41-Processing unit, 42-Storage device, 43-Input circuit, 44-Output circuit.

Claims

1. A control device for a flexible fuel internal combustion engine, applicable to a flexible fuel internal combustion engine capable of using alcohol-containing fuels, characterized in that... It determines whether the amount of fuel adhering to the cylinder of the flexible fuel internal combustion engine is high, and if it is determined that the amount of fuel adhering to the cylinder is high, it performs a process to increase the negative pressure in the cylinder.

2. The control device for a flexible fuel internal combustion engine according to claim 1, characterized in that, If it is determined that the cylinder has a high amount of adsorption, the fuel cut-off of the flexible fuel internal combustion engine is prohibited.

3. The control device for a flexible fuel internal combustion engine according to claim 1, characterized in that, If it is determined that the cylinder has a high amount of adsorption, the intermittent stopping of the flexible fuel internal combustion engine is prohibited.

4. The control device for a flexible fuel internal combustion engine according to claim 1, characterized in that, The negative pressure inside the cylinder is increased by reducing the amount of exhaust gas recirculated into the cylinder.

5. The control device for a flexible fuel internal combustion engine according to claim 1, characterized in that, The cylinder negative pressure is increased by changing the operating point of the flexible fuel internal combustion engine on the side where the engine speed increases and the intake air filling efficiency decreases.

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