Control system for flex-fuel engines

Abstract

It effectively reduces the amount of fuel adhering inside the cylinder. [Solution] A control device applied to a flex fuel engine that can use alcohol-containing fuel is configured to perform an in-cylinder negative pressure increase process (S120) when the amount of fuel adhering to the inside of the cylinder, which is the amount of fuel adhering to the inside of the cylinder, exceeds a determination value (S100: YES).

Description

Technical Field

[0001] The present invention relates to a control device for a flex fuel engine capable of using fuel containing alcohol.

Background Art

[0002] Compared with other fuels such as gasoline, alcohol has low volatility. Therefore, in a flex fuel engine as described above, fuel may adhere to the inner wall surface of the cylinder, such as the bore wall of the cylinder or the top surface of the piston. Then, the fuel adhering to the inside of the cylinder may be discharged into the exhaust passage without being burned, which may deteriorate emissions.

[0003] On the other hand, Patent Document 1 describes a control device for a flex fuel engine that suppresses deterioration of low-temperature starting performance by performing compression stroke injection at the start of the flex fuel engine. This control device sets the injection pressure of the fuel so that combustion starts before the injected fuel adheres to the inside of the cylinder based on the alcohol concentration of the fuel and the coolant water temperature, and performs compression stroke injection at the start to promote vaporization of the fuel.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the above conventional control device, by promoting vaporization of the injected fuel, adhesion of the fuel to the inside of the cylinder is suppressed. However, this alone can suppress an increase in the amount of adhesion inside the cylinder, but it cannot actively reduce the amount of fuel already adhering to the inside of the cylinder. Therefore, in the above conventional control device, once a large amount of fuel adheres to the inside of the cylinder, deterioration of emissions cannot be sufficiently suppressed.

Means for Solving the Problems

[0006] The control device for a flex fuel engine that solves the above problems is a control device that can be used with a flex fuel engine that can use alcohol-containing fuel, and is configured to determine whether or not the amount of fuel adhering to the inside of the cylinder of the flex fuel engine is high, and if it is determined that the amount of fuel adhering to the inside of the cylinder is high, to perform an in-cylinder negative pressure increase process that increases the in-cylinder negative pressure. [Effects of the Invention]

[0007] The control device for the above-mentioned flex-fuel engine has the effect of effectively reducing the amount of fuel adhering inside the cylinder. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic diagram showing the configuration of a flex-fuel engine to which one embodiment of the control device is applied. [Figure 2] Figure 2 is a schematic diagram showing the configuration of one embodiment of a control device for a flex-fuel engine. [Figure 3] Figure 3 is a flowchart showing the processing procedure for in-cylinder adhesion suppression control performed by the control device in Figure 1. [Figure 4] Figure 4 is a graph showing the relationship between the cylinder wall temperature and the respective volatility rates of ethanol and gasoline in the adhering fuel. [Modes for carrying out the invention]

[0009] Below, one embodiment of the control device for a flex-fuel engine will be described in detail with reference to Figures 1 to 4. <Configuration of a flex-fuel engine> First, with reference to Figure 1, the configuration of the flex-fuel engine 10 to which the control device of this embodiment is applied will be described. The flex-fuel engine 10 is configured as an on-board internal combustion engine that can use gasoline, alcohol, and mixtures thereof as fuel.

[0010] The flex-fuel engine 10 includes a cylinder 12 in which a piston 11 is installed. The piston 11 is connected to a crankshaft 14, which is the output shaft of the flex-fuel 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 the combustion of the fuel-air mixture is partitioned by the piston 11. An intake passage 16, which is the introduction path for intake air used for combustion, is connected to the combustion chamber 15 via an intake valve 18. An exhaust passage 17, which is the discharge path for exhaust gases generated by combustion, is also connected to the combustion chamber 15 via an exhaust valve 19. The flex-fuel engine 10 is equipped with a variable valve timing mechanism (hereinafter referred to as VVT mechanism 20) that makes the valve timing of the intake valve 18 variable. The flex-fuel engine 10 is also equipped with a crank angle sensor 31 that detects the crank angle, which is the rotation angle of the crankshaft 14.

[0011] The intake passage 16 of the flex-fuel engine 10 is equipped with an airflow meter 21, a throttle valve 22, and an intake pressure sensor 23. The airflow meter 21 is a sensor that detects the intake air volume, which is the flow rate of intake air flowing through the intake passage 16. The throttle valve 22 is a valve that adjusts the intake air volume by changing the flow area of ​​the intake air passage. The intake pressure sensor 23 is a sensor that detects the intake manifold pressure, which is the intake air pressure in the intake passage 16 downstream of the throttle valve 22. Furthermore, the flex-fuel engine 10 is equipped 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, the exhaust passage 17 of the flex-fuel engine 10 is equipped with an air-fuel ratio sensor 24 and an exhaust gas purification catalyst 25. The air-fuel ratio sensor 24 is a sensor that detects the air-fuel ratio of the air-fuel mixture burned in the combustion chamber 15. The exhaust gas purification catalyst 25 is an exhaust gas purification device that purifies harmful substances in the exhaust gas.

[0012] The flex-fuel engine 10 is equipped with an EGR (Exhaust Gas Recirculation) system that recirculates a portion of the exhaust gas flowing through the exhaust passage 17 into the intake air. The EGR system comprises an EGR passage 28, an EGR cooler 29, and an EGR valve 30. The EGR passage 28 is a passage that connects the exhaust passage 17 and the intake passage 16 for the flow of exhaust gas, so-called EGR gas, which is recirculated into the intake air. The EGR cooler 29 is a heat exchanger for cooling the EGR gas that flows into the intake air through the EGR passage 28. The EGR valve 30 is a valve that adjusts the external EGR amount, which is the flow rate of EGR gas that flows into the intake air through the EGR passage 28.

[0013] <Configuration of the control device for the flex-fuel engine 10> Next, with reference to Figure 2, the configuration of the control device applied to the flex fuel engine 10 in Figure 1 will be described. The control device in this embodiment is configured as an electronic control unit 40 comprising an arithmetic processing unit 41, a storage device 42, an input circuit 43, and an output circuit 44. The storage device 42 stores control programs and data. The arithmetic processing unit 41 executes the programs stored in the storage device 42. The input circuit 43 is connected to the aforementioned airflow meter 21, intake pressure sensor 23, air-fuel ratio sensor 24, and crank angle sensor 31. The input circuit 43 is also connected to a water temperature sensor 32 for detecting the coolant temperature of the flex fuel 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 flex fuel 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 amounts for the actuators of the flex fuel engine 10 based on the detection results of each sensor connected to the input circuit 43. The electronic control unit 40 then controls the flex fuel engine 10 by outputting command signals to the actuators from the output circuit 44 according to the calculated operating amounts. Examples of operating amounts for the flex fuel engine 10 include intake valve timing, throttle opening, fuel injection amount, fuel injection timing, ignition timing, and EGR opening. Intake valve timing represents the valve timing of the intake valve 18 set by the VVT ​​mechanism 20, and throttle opening represents the opening ratio of the throttle valve 22. Fuel injection amount and fuel injection timing represent the amount of fuel injected by the injector 26 and the start time of fuel injection, respectively. Ignition timing represents the timing at which the ignition device 27 ignites the air-fuel mixture, and EGR opening represents the opening ratio of the EGR valve 30.

[0014] For example, the electronic control unit 40 sets the throttle opening in the following manner. The electronic control unit 40 determines the current intake efficiency of the combustion chamber 15 from the engine speed obtained from the crank angle detection result and the current throttle opening. The intake efficiency represents the ratio of the dry weight of fresh air drawn into the combustion chamber 15 to the dry weight of fresh air occupying the stroke volume of the cylinder 12 under standard atmospheric conditions. The intake efficiency is sometimes called the engine load ratio. On the other hand, the electronic control unit 40 calculates the value of the target intake efficiency required to obtain the required output of the flex fuel engine 10, with the air-fuel ratio of the mixture burned in the combustion chamber 15 set to a target value. The electronic control unit 40 then sets the throttle opening to command the throttle valve 22 by adjusting the throttle opening setting value so that the target intake efficiency can be obtained. Note that if the EGR opening is increased and the amount of external EGR increases, the throttle opening at which the target intake efficiency can be obtained will increase. Furthermore, when the valve timing of the intake valve 18 is advanced by the VVT ​​mechanism 20, increasing the valve overlap amount of the intake valve 18 and the exhaust valve 19, the amount of exhaust gas blown back from the exhaust passage 17 into the combustion chamber 15, the so-called internal EGR amount, increases. This increase in internal EGR also results in a larger throttle opening that can achieve the target volumetric efficiency. The electronic control unit 40 sets the throttle opening in a manner that reflects the effects of both the external and internal EGR amounts. Note that even if the volumetric efficiency is the same, when the throttle opening is increased, the in-cylinder negative pressure is smaller compared to when the throttle opening is decreased. In-cylinder negative pressure represents the negative pressure formed in the combustion chamber 15 during the intake stroke.

[0015] Furthermore, the electronic control unit 40 implements fuel cut control, which stops the fuel supply to the flex fuel engine 10 while the vehicle is coasting when the accelerator is released. The electronic control unit 40 also implements intermittent stop control, which stops the flex fuel engine 10 when the vehicle is stopped, such as at a traffic light, and restarts the flex fuel engine 10 in response to the driver's preparation operation to start driving. In the case of a hybrid vehicle capable of motor-driven operation equipped with a flex fuel engine 10, intermittent stop control may be implemented to stop the flex fuel engine 10 not only when the vehicle is stopped but also when it is running on the motor.

[0016] <In-cylinder adhesion suppression control> The electronic control unit 40 performs in-cylinder adhesion suppression control as part of the control of the flex fuel engine 10 to suppress fuel adhesion inside the cylinder. In-cylinder adhesion refers to the adhesion of fuel to the walls exposed to the combustion chamber 15, such as the bore wall of the cylinder 12 and the top surface of the piston 11.

[0017] Figure 3 shows the processing flow performed by the electronic control unit 40 for in-cylinder deposit suppression control. During operation of the flex fuel engine 10, the electronic control unit 40 repeatedly performs the processing shown in Figure 3 at predetermined control cycles. When the processing in Figure 3 begins, the electronic control unit 40 first determines in step S100 whether the amount of fuel depositing in the cylinder exceeds a predetermined judgment value. The judgment value is set to a value smaller than the upper limit of the acceptable amount of in-cylinder depositing, which is set from the perspective of emissions, etc. If the electronic control unit 40 determines that the amount of in-cylinder depositing is less than or equal to the judgment value (NO), it terminates the processing in Figure 3 for the current control cycle. On the other hand, if the electronic control unit 40 determines that the amount of in-cylinder depositing exceeds the judgment value (YES), it proceeds to step S110. In step S110, the electronic control unit 40 prohibits fuel cut control and intermittent stop control of the flex fuel engine 10. Furthermore, in the following step S120, the electronic control unit 40 performs in-cylinder negative pressure increase processing and then terminates the processing in Figure 3 for the current control cycle.

[0018] The electronic control unit 40 estimates the in-cylinder injection amount used for the determination in step S100 in the following manner. First, the electronic control unit 40 calculates the fuel evaporation amount based on the current estimated value of the in-cylinder fuel adhesion amount, the wall temperature of the cylinder 12, the in-cylinder negative pressure, and the alcohol concentration of the fuel. The fuel evaporation amount represents the amount of fuel that evaporates from the wall surface inside the cylinder. At the same time, the electronic control unit 40 calculates the new adhesion amount based on the fuel injection amount, the wall temperature of the cylinder 12, the in-cylinder negative pressure, the alcohol concentration of the fuel, etc. The new adhesion amount represents the amount of fuel that adheres inside the cylinder without being completely vaporized after injection from the injector 26. Then, the electronic control unit 40 updates the estimated value of the in-cylinder adhesion amount so that the value obtained by subtracting the fuel evaporation amount from the value before update and adding the new adhesion amount to the subtracted value becomes the value after update, thereby estimating the in-cylinder adhesion amount.

[0019] 〈In-cylinder Negative Pressure Increase Process〉 The in-cylinder negative pressure increase process implemented in step S120 of FIG. 3 will be described. The in-cylinder negative pressure increase process is a process of adjusting the operation amount of the flex-fuel engine 10 so that the in-cylinder negative pressure increases, that is, the internal pressure of the combustion chamber 15 during the intake stroke becomes lower. Examples of the in-cylinder negative pressure increase process include the following processes (A) to (E).

[0020] (A) Process of changing the operating point of the flex-fuel engine 10: By changing the operating point of the flex-fuel engine 10 to the side where the engine speed increases and the filling efficiency decreases, the in-cylinder negative pressure can be increased. The change of the above operating point can be implemented, for example, by operating the transmission so as to increase the gear ratio in a vehicle equipped with the flex-fuel engine 10. Also, when the flex-fuel engine 10 is mounted on a hybrid vehicle, it is also possible to change the above operating point through the coordinated control of the flex-fuel engine 10 and the motor.

[0021] (B) Throttle opening reduction process: The negative pressure in the cylinder can also be increased by reducing the throttle opening and decreasing the volumetric efficiency. However, simply reducing the throttle opening will reduce the output of the flex fuel engine 10. Therefore, it is desirable to maintain the output of the flex fuel engine 10 by advancing the ignition timing along with reducing the throttle opening to improve combustion efficiency.

[0022] (C) Processing to reduce the amount of external EGR: When the EGR valve 30 is open and exhaust gas is being recirculated, EGR gas is introduced into the combustion chamber 15 along with fresh air. When the EGR opening is reduced and the amount of external EGR is decreased, the total amount of gas filling the combustion chamber 15 decreases, so the in-cylinder negative pressure increases. Further reducing the amount of external EGR improves combustion efficiency, so the throttle opening at which the target filling efficiency is obtained becomes smaller than before the reduction. This reduction in throttle opening also increases the in-cylinder negative pressure.

[0023] (D) Processing to reduce the amount of internal EGR: When the valve timing of the intake valve 18 is advanced beyond a certain point by the VVT ​​mechanism 20, a state known as valve overlap occurs in which the intake valve 18 and the exhaust valve 19 are open simultaneously. During the valve overlap period, exhaust gas is blown back from the exhaust passage 17 to the combustion chamber 15. The amount of exhaust gas recirculated to the intake due to this blowback during valve overlap, i.e., the amount of internal EGR, increases with increasing valve overlap and decreases with decreasing valve overlap. The amount of valve overlap is expressed in terms of the crank angle, representing the length of the period during which valve overlap occurs. Similar to reducing the amount of external EGR, the in-cylinder negative pressure can also be increased by reducing the amount of internal EGR by reducing the amount of valve overlap.

[0024] (E) Reducing the amount of ignition timing retardation in catalyst warm-up control: After starting the flex fuel engine 10, catalyst warm-up control may be implemented to promote the warm-up of the exhaust gas purification catalyst 25 by retarding the ignition timing to increase the exhaust gas temperature. During the execution of such catalyst warm-up control, a process to reduce the amount of ignition timing retardation in catalyst warm-up control can be implemented as a process to increase in-cylinder negative pressure. Reducing the amount of ignition timing retardation improves combustion efficiency, so the throttle opening at which the target charging efficiency is obtained becomes smaller than before the retardation. And as the throttle opening decreases, the charging efficiency decreases, so the in-cylinder negative pressure increases.

[0025] <Effect of the Embodiment> In the flex-fuel engine 10, some of the fuel injected from the injector 26 may not vaporize completely and may adhere to the walls of the cylinder 12, such as the bore wall of the cylinder 12 or the top surface of the piston 11. When the temperature inside the cylinder 12 is low, such as during a cold start, the fuel adhering to the walls does not vaporize easily, so the amount of fuel adhering to the cylinder increases. When the amount of fuel adhering to the cylinder increases, there is a risk that the adhering fuel will be discharged into the exhaust passage 17 unburned, which may worsen emissions.

[0026] The flex-fuel engine 10 is configured to use alcohol, gasoline, and mixtures thereof as fuel, but when the alcohol concentration of the fuel is high, there is a tendency for a significant increase in in-cylinder deposits when cold. Generally, alcohol fuels for vehicles that are commercially available contain nearly 100% ethanol.

[0027] Figure 4 shows the relationship between the wall temperature of cylinder 12 and the volatility of the 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, so it does not have a clear boiling point. Therefore, the gasoline component volatilizes to some extent even when the wall temperature is low. In contrast, ethanol, being a pure substance, has a clear boiling point BP. Therefore, in the range of wall temperatures below the boiling point BP of ethanol, the ethanol component hardly volatilizes, and in the range of wall temperatures above the boiling point BP of ethanol, the volatility of the ethanol component is almost 100%. Consequently, if the wall temperature of cylinder 12 remains lower than the boiling point BP of ethanol, the ethanol component in the fuel adhering to the wall will continue to remain. Therefore, when using fuel with a high alcohol concentration, the increase in the amount of deposits inside the cylinder when cold is significant. In addition to cold starts, if the combustion of the flex-fuel engine 10 is stopped by fuel cut control or intermittent stop control, the inside of cylinder 12 cools down, and the amount of deposits inside the cylinder may increase after combustion restarts. Incidentally, the boiling point BP of ethanol changes with atmospheric pressure, becoming lower when the pressure is low and higher when the pressure is high. Therefore, when the negative pressure inside the cylinder is large, that is, when the internal pressure of the combustion chamber 15 is low during the intake stroke, the boiling point BP of ethanol inside the combustion chamber 15 is lower than when the negative pressure inside the cylinder is small.

[0028] In response to this, the electronic control unit 40 increases the in-cylinder negative pressure of the flex fuel engine 10 by performing an in-cylinder negative pressure increase process when the amount of deposits in the cylinder exceeds a certain value (S100: YES). When the in-cylinder negative pressure increases, that is, when the pressure inside the cylinder 12 decreases, the vaporization of the deposited fuel is promoted, and the amount of deposits in the cylinder decreases. Furthermore, when the in-cylinder negative pressure increases, the vaporization of the fuel injected by the injector 26 is also promoted, so the amount of new deposits decreases and the increase in the amount of deposits in the cylinder is suppressed.

[0029] Furthermore, the effect of reducing the amount of deposits inside the cylinder by increasing the in-cylinder negative pressure can be further improved by performing the in-cylinder negative pressure increase treatment in the following manner. By increasing the in-cylinder negative pressure, the boiling point BP of ethanol in the combustion chamber 15 is lowered to below the wall temperature of the cylinder 12, thereby effectively volatilizing the ethanol in the fuel that has adhered inside the cylinder. The wall temperature of the cylinder 12 can be determined, for example, by estimation based on the coolant temperature of the flex fuel engine 10. In addition, the relationship between the in-cylinder negative pressure and the boiling point BP of ethanol in the combustion chamber 15 can be determined in advance by experimentation. Therefore, when performing the in-cylinder negative pressure increase treatment, the electronic control unit 40 calculates the magnitude of the in-cylinder negative pressure at which the boiling point BP of ethanol in the combustion chamber 15 falls below the wall temperature, and by increasing the in-cylinder negative pressure beyond that magnitude, the effect of reducing the amount of deposits inside the cylinder can be improved.

[0030] Furthermore, the electronic control unit 40 prohibits fuel cut control and intermittent stop control of the flex fuel engine 10 when the amount of fuel deposits in the cylinder exceeds a predetermined value. When combustion in the flex fuel engine 10 stops due to fuel cut or intermittent stop, the inside of the cylinder 12 cools down, making it easier for the amount of fuel deposits in the cylinder to increase after combustion restarts. Therefore, by prohibiting fuel cut control and intermittent stop control, it is possible to suppress further increases in the amount of fuel deposits in the cylinder when a large amount of fuel has already accumulated inside the cylinder. In addition, if the flex fuel engine 10 is operated at low load in a situation where fuel cut would normally be performed, the negative pressure inside the cylinder decreases, promoting the vaporization of fuel deposited inside the cylinder. Therefore, prohibiting fuel cut control can also reduce the amount of fuel deposits in the cylinder.

[0031] <Effects of the Embodiment> The control device for the flex-fuel engine 10 of this embodiment provides the following effects. (1) The electronic control unit 40 determines whether or not 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 cylinder negative pressure increase process to increase the cylinder negative pressure. The increase in cylinder negative pressure promotes the vaporization of fuel adhering to the cylinder and the vaporization of fuel injected by the injector 26. As a result, the amount of fuel adhering to the cylinder can be effectively reduced.

[0032] (2) The electronic control unit 40 prohibits fuel cut-off of the flex fuel engine 10 when it determines that there is a large amount of fuel deposit inside the cylinder. If fuel cut-off is performed, the inside of the cylinder 12 cools down during the cut-off, making it easier for the amount of fuel deposit inside the cylinder to increase after combustion restarts. By prohibiting fuel cut-off when there is a large amount of fuel deposit inside the cylinder, it is possible to suppress a further increase in the amount of fuel deposit inside the cylinder after combustion restarts. In addition, when fuel cut-off is prohibited, the flex fuel engine 10 operates with a large negative pressure inside the cylinder during the period when fuel cut-off would normally be performed. This also promotes the vaporization of fuel deposits inside the cylinder, thus reducing the amount of fuel deposit inside the cylinder.

[0033] (3) The electronic control unit 40 prohibits intermittent stopping of the flex fuel engine 10 when it determines that there is a large amount of deposit inside the cylinder. Stopping combustion by intermittent stopping causes the inside of the cylinder 12 to cool down, making it easier for the amount of deposit inside the cylinder to increase after combustion is restarted. By prohibiting intermittent stopping when there is a large amount of deposit inside the cylinder, it is possible to suppress a further increase in the amount of deposit inside the cylinder after combustion is restarted.

[0034] (Other embodiments) The above embodiment can be implemented with the following modifications. The above embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0035] • A combination of several of the above processes (A) to (E) may be used to increase the in-cylinder negative pressure. Any process other than those described in (A) to (E) above may be performed as an in-cylinder negative pressure increasing process, as long as it can increase the in-cylinder negative pressure. For example, a process that reduces the amount of internal EGR by lowering the back pressure of the flex fuel engine 10 may be performed as an in-cylinder negative pressure increasing process.

[0036] In the above embodiment, it was determined whether or not the amount of deposits in the cylinder was high based on the estimation result of the amount of deposits in the cylinder. This determination may be made by other methods. For example, it may be determined that the amount of deposits in the cylinder is high if the flex fuel engine 10 is operated for a predetermined time or longer under conditions that tend to increase the amount of deposits in the cylinder. Operating conditions for the flex fuel engine 10 that tend to increase the amount of deposits in the cylinder include, for example, low negative pressure in the cylinder, low temperature inside the cylinder 12, and high alcohol concentration of the fuel.

[0037] If it is determined that there is a large amount of deposit inside the cylinder, either fuel cut control or intermittent stop control may be prohibited, while the other is allowed to continue. Alternatively, if it is determined that there is a large amount of deposit inside the cylinder, neither fuel cut control nor intermittent stop control may be prohibited.

[0038] The control devices of the above embodiments and their modifications are applicable to flex-fuel engines with configurations different from those shown in Figure 1, as long as they are internal combustion engines capable of using alcohol-containing fuels. [Explanation of Symbols]

[0039] 10...Flex fuel 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...Airflow meter, 22...Throttle valve, 23...Intake pressure sensor, 24...Air-fuel ratio sensor, 25...Exhaust catalytic converter, 26...Injector, 27...Ignition system, 28...EGR passage, 29...EGR cooler, 30...EGR valve, 31...Crank angle sensor, 32...Water temperature sensor, 33...Alcohol concentration sensor, 40...Electronic control unit, 41...Computer processing unit, 42...Memory device, 43...Input circuit, 44...Output circuit.

Claims

1. A control device applicable to a flex-fuel engine that can use alcohol-containing fuels, The system determines whether the amount of fuel adhering to the cylinders of the flex-fuel engine is high, and if it is determined that the amount of fuel adhering to the cylinders is high, it performs an in-cylinder negative pressure increase process to increase the in-cylinder negative pressure. Control device for a flex-fuel engine.

2. A control device for a flex fuel engine according to claim 1, which prohibits fuel cut-off of the flex fuel engine when it is determined that the amount of deposits inside the cylinder is high.

3. A control device for a flex fuel engine according to claim 1, which prohibits intermittent shutdown of the flex fuel engine when it is determined that the amount of deposit inside the cylinder is high.

4. The control device for a flex fuel engine according to claim 1, wherein the increase in the in-cylinder negative pressure is achieved by reducing the amount of exhaust gas recirculated into the cylinder.

5. The control device for a flex fuel engine according to claim 1, wherein the increase in the in-cylinder negative pressure is achieved by changing the operating point of the flex fuel engine to the side where the intake air charging efficiency decreases as the engine rotational speed increases.

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