JP2009167838A - Control device of flex fuel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control device of a flex fuel engine, stabilizing combustion at engine cold time, even when using alcohol-containing fuel. <P>SOLUTION: An internal combustion engine 20 has: a valve characteristic changing mechanism 30 for changing an opening-closing characteristic of an intake valve 31; and a cylinder injection valve 28 directly injecting fuel into a cylinder 21. An electronic control device 10 delays the valve opening timing of the intake valve 31 more than the valve closing timing of an exhaust valve 32 by the valve characteristic changing mechanism 30 when determining the effect of hardly atomizing injection fuel based on the ethanol concentration estimated by an ethanol concentration sensor 45, and executes pressure-reduced cylinder injection for injecting the fuel from the cylinder injection valve 28 when a piston 22 is lowered and both the intake valve 31 and the exhaust valve 32 are closed. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a control apparatus for a flex fuel engine capable of using an alcohol-containing fuel in which gasoline and alcohol are mixed at an arbitrary ratio.

  In recent years, the use of alcohol with low emissions such as CO (carbon monoxide) and HC (hydrocarbon) as fuel for internal combustion engines has attracted attention. In addition to gasoline, gasoline and alcohol are mixed in any proportion. Attention has been focused on a flex fuel engine (see, for example, Patent Document 1) that can also use an alcohol-containing fuel. Some countries and regions also have tax incentives for vehicles with alcohol-containing fuels or flex-fuel engines that can use them. In particular, the use of flex fuel engines is expanding.

By the way, since alcohol is less likely to atomize than gasoline, in such a flex-fuel engine, misfiring is likely to occur compared to an engine using only gasoline as fuel, and the engine combustion state becomes unstable. Tend. However, such instability of the engine combustion state is almost negligible after the engine temperature rises.
JP 2006-152990 A

  However, in a situation where fuel with a high alcohol concentration is used, particularly in a situation where the temperature in the cylinder is low, such as when the engine is cold started, it may be difficult to achieve a stable engine combustion state.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a control apparatus for a flex fuel engine that can stabilize combustion when the engine is cold even when alcohol-containing fuel is used. There is to do.

In the following, means for achieving the above object and its effects are described.
According to a first aspect of the present invention, there is provided a control apparatus for a flex fuel engine comprising a valve characteristic changing mechanism for changing an opening / closing characteristic of an intake valve and an in-cylinder injection valve for directly injecting fuel into a cylinder. An alcohol concentration estimating means for estimating the intake valve opening timing by the valve characteristic changing mechanism when it is determined that the injected fuel is difficult to atomize based on the alcohol concentration estimated by the alcohol concentration estimating means. The pressure reducing in-cylinder injection injects fuel from the in-cylinder injection valve when the piston is descending and the intake valve and the exhaust valve are both closed. The gist is to execute.

  According to the above configuration, since the fuel is injected when the piston is lowered and the inside of the cylinder is depressurized with both the intake valve and the exhaust valve closed, atomization of the injected fuel is promoted. Thus, even when an alcohol-containing fuel that is difficult to atomize when the engine is cold is used, combustion can be stabilized. However, when such decompression in-cylinder injection is executed, the opening timing of the intake valve is limited, so that it is not possible to set the optimal opening timing for the intake inertia effect. There is a concern that the intake air amount is limited as described above. Therefore, in the invention described in claim 1, such reduced pressure in-cylinder injection is performed only when it is determined that the injected fuel is difficult to atomize based on the alcohol concentration. As a result, the reduced pressure in-cylinder injection is executed in accordance with the properties of the fuel, and it is possible to stabilize the combustion when the engine is cold while suppressing the occurrence of the above inconvenience as much as possible.

  According to a second aspect of the present invention, in the control apparatus for a flex fuel engine according to the first aspect, the in-cylinder injection is performed when the engine cooling water temperature is lower than a predetermined determination water temperature, The gist of the invention is to further include setting means for setting the determination water temperature higher as the estimated alcohol concentration is higher.

  The higher the alcohol concentration of the injected fuel, the more difficult it is to atomize, and this tendency becomes prominent especially when the engine is cold, so that combustion tends to become unstable. Therefore, in the invention described in claim 2, the in-cylinder injection is performed when the engine cooling water temperature is lower than the predetermined determination water temperature, and the determination water temperature is set higher as the alcohol concentration of the fuel is higher. I have to. If such a configuration is adopted, the judgment water temperature can be set in consideration of the change in the degree of fuel atomization due to the difference in the alcohol concentration of the fuel, and it is accurately determined that the injected fuel is difficult to atomize based on the engine cooling water temperature. This makes it possible to execute the reduced pressure in-cylinder injection.

  According to a third aspect of the present invention, the flex fuel engine control device according to the first or second aspect further comprises a port injection valve for injecting fuel into the intake port in addition to the in-cylinder injection valve. The gist.

  When the alcohol concentration of the fuel is high, the amount of fuel required for obtaining the same engine output is increased as compared with the case where the alcohol concentration is low. Therefore, a large amount of fuel must be injected at the time of high engine load, and there is a concern that it is difficult to appropriately perform fuel injection only by the in-cylinder injection valve. In this respect, in the configuration of the third aspect, since fuel can be injected from the port injection valve to the intake port in addition to the in-cylinder injection valve, when the fuel having a high alcohol concentration as described above is used. An appropriate amount of fuel can be supplied to the cylinder even when the engine is at a high load.

  According to a fourth aspect of the present invention, in the control apparatus for a flex fuel engine according to the third aspect, when the fuel injection of the port injection valve is performed simultaneously with the in-cylinder injection, the estimated alcohol concentration is The gist is to increase the ratio of the fuel injection amount of the in-cylinder injection valve as it is higher.

  An in-cylinder injection valve and a port, such as an internal combustion engine that includes both an in-cylinder injection valve and a port injection valve and injects fuel from both of these fuel injection valves based on a ratio set based on the engine operating state In a flex fuel engine equipped with both injection valves, when the above-described decompression in-cylinder injection and port injection by the port injection valve are executed, the estimated alcohol concentration is as in the invention of claim 4. A configuration in which the ratio of the fuel injection amount of the in-cylinder injection valve is increased as the ratio is higher can be employed. According to such a configuration, the amount of fuel injected by the reduced pressure in-cylinder injection, that is, the amount of fuel that promotes atomization can be increased as the alcohol concentration is high and the injected fuel is difficult to atomize. Combustion during cold can be stabilized. Further, as the alcohol concentration of the fuel is higher in this way, by increasing the ratio of the fuel injection amount of the in-cylinder injection valve, the fuel injection amount of the port injection valve is reduced, and the fuel is injected in a state that is difficult to atomize. Therefore, the amount of fuel that does not contribute to combustion can be reduced. As a result, the amount of unburned fuel components contained in the exhaust can be reduced, and deterioration of exhaust properties can be suppressed.

  According to a fifth aspect of the present invention, in the control apparatus for a flex fuel engine according to the third or fourth aspect, when the fuel injection of the port injection valve is performed simultaneously with the in-cylinder injection, the port injection is performed. The gist of the invention is that the fuel injection timing of the valve is synchronized with the opening timing of the intake valve, and the fuel injection to the intake port is started after the intake valve is opened.

  In a flex fuel engine having both a cylinder injection valve and a port injection valve as described above, when fuel is injected from the port injection valve before the intake valve is opened when the engine is cold, the fuel May stay in the intake port in a liquid state without being atomized. If the fuel staying in the intake port is sucked into the cylinder as the intake valve is opened, it may adhere to the spark plug in a liquid state and cause misfire. Therefore, in the invention according to the fifth aspect, in addition to the pressure reduction in-cylinder injection, the fuel injection after the intake valve is opened after the start timing of the fuel injection by the port injection valve is synchronized with the opening timing of the intake valve. Like to start. By adopting such a configuration, it is possible to suppress the fuel that has accumulated in the intake port from adhering, and to stabilize the combustion when the engine is cold, in addition to the effect of promoting atomization by the reduced pressure in-cylinder injection. become able to.

  According to a sixth aspect of the present invention, in the control apparatus for a flex fuel engine according to any one of the first to fifth aspects, the reduced pressure in-cylinder injection is performed when the estimated alcohol concentration is equal to or higher than a predetermined concentration. The gist is to be executed.

  As described above, the higher the alcohol concentration of the fuel, the more difficult the atomized fuel is atomized when the engine is cold. Therefore, the estimated alcohol concentration is equal to or higher than the predetermined concentration as in the invention of claim 6. Based on the above, it is also possible to estimate that the injected fuel is difficult to atomize and to perform a reduced pressure in-cylinder injection.

  According to a seventh aspect of the present invention, in the control apparatus for a flex fuel engine according to any one of the first to sixth aspects, the decompression in-cylinder injection is performed on the condition that the engine is started. The gist.

  When starting the engine, the temperature in the cylinder is low and the atomization of the injected fuel is difficult to promote, so the startability is likely to deteriorate. This is especially true for flex-fuel engines that use alcohol-containing fuel. The startability deteriorates more easily.

  In this regard, according to the configuration of the seventh aspect, it is possible to improve the engine combustion state at the time of starting the engine and suppress deterioration of the engine startability.

(First embodiment)
Hereinafter, a first embodiment in which a control device for a flex fuel engine according to the present invention is embodied in an electronic control device 10 that comprehensively controls a vehicle equipped with a flex fuel engine will be described with reference to FIGS. To do.

  FIG. 1 is a schematic diagram illustrating a schematic configuration of an electronic control device 10 according to the present embodiment and an internal combustion engine 20 that is a control target thereof. The internal combustion engine 20 is a flex fuel engine that can use an ethanol-containing fuel in which gasoline and ethanol are mixed at an arbitrary ratio.

  As shown in FIG. 1, a piston 22 is accommodated in the cylinder 21 of the internal combustion engine 20 so as to be able to reciprocate. Thus, a combustion chamber 23 is defined by the top surface of the piston 22 and the inner peripheral surface of the cylinder 21. Although the internal combustion engine 20 is a multi-cylinder internal combustion engine having a plurality of cylinders 21, only one of the plurality of cylinders 21 is shown in FIG.

  An ignition plug 24 is provided above each combustion chamber 23 so as to face the piston 22, and an intake port 25 and an exhaust port 26 communicating with each combustion chamber 23 are formed. The intake port 25 is connected to an intake manifold (not shown) to constitute a part of the intake passage, and the exhaust port 26 is connected to an exhaust manifold (not shown) to constitute a part of the exhaust passage.

  As shown in FIG. 1, in the internal combustion engine 20 of the present embodiment, a port injection valve 27 for injecting fuel toward the combustion chamber 23 is provided in each intake port 25, and each combustion The chamber 23 is provided with an in-cylinder injection valve 28 that directly injects fuel into the combustion chamber 23.

  As shown in FIG. 1, an intake valve 31 for communicating / blocking the intake port 25 and the combustion chamber 23, and an exhaust valve 32 for communicating / blocking the exhaust port 26 and the combustion chamber 23, are provided above each combustion chamber 23. And are provided. These valves 31 and 32 are driven to open and close by an intake camshaft and an exhaust camshaft (not shown) connected to a crankshaft that is rotated as the piston 22 reciprocates.

  The internal combustion engine 20 includes a valve characteristic changing mechanism 30 that changes the opening / closing characteristics of the intake valve 31. The valve characteristic changing mechanism 30 includes a valve timing changing mechanism that changes the opening / closing timing of the intake valve 31 by changing the relative rotational phase of the intake camshaft with respect to the crankshaft, and an intake valve by changing the operating angle of the intake cam. The lift amount changing mechanism for changing the lift amount and the valve opening period of 31 is included.

  In the internal combustion engine 20, the valve characteristic of the intake valve 31, that is, the opening / closing timing, the lift period, and the lift amount can be changed by the valve characteristic changing mechanism 30. Specifically, the valve timing changing mechanism can advance or retard the opening / closing timing of the intake valve 31 with respect to the crank angle CA, which is the rotation angle of the crankshaft. For example, as shown in FIG. As shown by the broken line, the opening / closing timing of the intake valve 31 can be retarded.

  Further, the lift amount changing mechanism can change the lift amount and the valve opening period of the intake valve 31 accompanying the action of the intake cam, that is, the operating angle. For example, as shown by the broken line in FIG. The lift amount of 31 and the valve opening period can be reduced.

  Thereby, according to the valve characteristic changing mechanism 30 combining the valve timing changing mechanism and the lift amount changing mechanism, the opening / closing timing, the lift amount, and the valve opening period of the intake valve 31 can be arbitrarily set. Therefore, by controlling the valve characteristic changing mechanism 30 to retard the opening / closing timing of the intake valve 31, and reducing the lift amount and the valve opening period, the intake valve 31 is shown in FIG. When the both exhaust valves 32 and the exhaust valve 32 are closed, the decompression period during which the piston 22 descends and the inside of the cylinder 21 is decompressed can be set.

  The electronic control device 10 controls the internal combustion engine 20 such as changing the valve characteristic through the valve characteristic changing mechanism 30. The electronic control unit 10 includes a crank angle sensor 40 that detects a crank angle CA that is a rotation angle of the crankshaft and an engine rotation speed NE that is a rotation speed of the crankshaft, and a cam position sensor 41 that detects a rotation angle CAMA of the camshaft. , A water temperature sensor 42 for detecting the engine cooling water temperature THW, an air flow meter 43 for detecting the intake air amount GA of the internal combustion engine 20, an accelerator position sensor 44 for detecting the accelerator operation amount ACCP by the driver, and detecting the ethanol concentration CE of the fuel. Various sensors such as an ethanol concentration sensor 45 are connected.

  The electronic control unit 10 takes in signals output from these various sensors, executes various arithmetic processes, and comprehensively controls each part of the engine based on the results. Specifically, cylinder discrimination is performed based on output signals from the crank angle sensor 40 and the cam position sensor 41, and the fuel injection timing and ignition timing for each cylinder 21 are set based on the crank angle CA.

  Further, the intake air amount GA is regulated by controlling the valve characteristic changing mechanism 30 and the throttle valve provided in the intake passage based on the engine rotational speed NE and the accelerator operation amount ACCP, and the port is combined with the intake air amount GA. The fuel injection amount is adjusted by controlling the injection valve 27 and the in-cylinder injection valve 28.

  Further, in the internal combustion engine 20 of the present embodiment, fuel is injected from both the port injection valve 27 and the in-cylinder injection valve 28 according to the engine operating state. Specifically, the cylinder injection valve out of the fuel injection amount injected in one fuel injection stroke based on the engine load KL calculated based on the intake air amount GA and the engine rotational speed NE and the engine rotational speed NE. A ratio of 28 fuel injection amounts, so-called in-cylinder injection ratio, is set. An amount of fuel based on the in-cylinder injection ratio out of the fuel injection amount injected in one fuel injection stroke is injected from the in-cylinder injection valve 28, and other fuel is injected from the port injection valve 27. At this time, depending on the engine operating state, fuel is injected from only the port injection valve 27 or only the in-cylinder injection valve 28, that is, the in-cylinder injection ratio is set to “0%” or “100%”. is there.

  By the way, ethanol is more difficult to atomize than gasoline, so when using ethanol-containing fuel, it is easier to misfire than when only gasoline is used as fuel, and the engine combustion state becomes unstable. Tend. However, such instability of the engine combustion state is almost negligible after the engine temperature rises.

  However, in a situation where a fuel having a high ethanol concentration CE is used, particularly in a situation where the temperature in the cylinder 21 is low, such as when the engine is cold started, it may be difficult to realize a stable engine combustion state. is there.

  Therefore, in the internal combustion engine 20, it is determined that the injected fuel is difficult to atomize based on the ethanol concentration CE of the fuel detected by the ethanol concentration sensor 45, and the fuel injection mode is changed based on this determination. In order to secure a stable engine combustion state.

  Hereinafter, with reference to FIG. 3, the control concerning the change of the fuel injection mode based on the ethanol concentration CE will be described. FIG. 3 is a flowchart showing a flow of a series of processes for control related to the change of the fuel injection mode. This series of processes is repeatedly executed at a predetermined cycle by the electronic control unit 10 during engine operation including when the engine is started.

  When this series of processing is started, the electronic control unit 10 first reads the engine coolant temperature THW and the fuel ethanol concentration CE in step S100. In step S110, it is determined whether the engine coolant temperature THW is lower than the determination coolant temperature THWjdg. Here, the determination water temperature THWjdg is determined based on the fact that the engine cooling water temperature THW is lower than this value, that the temperature of the intake port 25 and the cylinder 21 is low and the possibility that the injected fuel is difficult to atomize is high. The possible value is set based on the result of an experiment or the like performed in advance.

  If it is determined in step S110 that the engine cooling water temperature THW is lower than the determination water temperature THWjdg (step S110: YES), the process proceeds to step S120, and it is determined whether the ethanol concentration CE is higher than the determination concentration CEjdg. To do. The determination concentration CEjdg is set based on a result of an experiment or the like that is performed in advance as a value that can determine that it is highly likely that the injected fuel is difficult to atomize based on the fact that the ethanol concentration CE of the fuel is higher than this concentration. ing.

  If it is determined in step S120 that the ethanol concentration CE is higher than the determination concentration CEjdg (step S120: YES), that is, it is determined that the engine cooling water temperature THW is lower than the determination water temperature THWjdg and the ethanol concentration CE is higher than the determination concentration CEjdg. If so, it is determined that the injected fuel is difficult to atomize, and the process proceeds to step S130.

  In step S130, the in-cylinder injection ratio set based on the engine load KL and the engine speed NE is changed based on the ethanol concentration CE. Specifically, the correction amount of the in-cylinder injection ratio is calculated based on the ethanol concentration CE, and the correction amount is added to the in-cylinder injection ratio calculated based on the engine load KL and the engine rotation speed NE. Increase in-cylinder injection ratio.

  The calculation of the correction amount is executed with reference to a calculation map stored in advance in the electronic control unit 10. In this calculation map, the correction amount of the in-cylinder injection ratio is set to a larger value as the ethanol concentration CE is higher in proportion to the ethanol concentration CE as shown in FIG. Therefore, by changing the in-cylinder injection ratio through step S130, the in-cylinder injection ratio increases as the ethanol concentration CE increases.

  When the increased in-cylinder injection ratio is set as a new in-cylinder injection ratio, the routine proceeds to step S140, where the valve characteristic changing mechanism 30 is controlled to show the opening timing of the intake valve 31 as shown in FIG. In addition, the exhaust valve 32 is retarded from the closing timing, and the lift amount and the valve opening period are decreased. The fuel in the in-cylinder injection valve 28 is in a period in which both the intake valve 31 and the exhaust valve 32 are closed and the piston 22 is lowered, that is, in a decompression period in which the inside of the cylinder 21 is in a decompressed state as described above. The fuel injection timing is set so that the injection is started. At the same time, the injection start timing of the port injection valve 27, which is normally set before the opening timing of the intake valve 31, is retarded so as to coincide with the opening timing of the intake valve 31. FIG. 5 shows the relationship between the crank angle CA and the lift amounts of the intake valve 31 and the exhaust valve 32, the timing when the fuel injection of the in-cylinder injection valve 28 is started, and the fuel injection of the port injection valve 27. The relationship with the time is shown.

  Thus, the fuel injection timing in the in-cylinder injection valve 28 is set so as to execute the reduced-pressure in-cylinder injection that starts the fuel injection of the in-cylinder injection valve 28 during the depressurization period, and the port injection valve simultaneously with the opening of the intake valve 31. When the fuel injection timing is changed by delaying the fuel injection timing so as to start the fuel injection 27, this process is temporarily ended.

  On the other hand, when it is determined in step S110 that the engine cooling water temperature THW is equal to or higher than the determination water temperature THWjdg (step S110: NO), and when it is determined in step S120 that the ethanol concentration CE is less than the determination concentration CEjdg (step S120). : NO), the process proceeds to step S150 without determining that the injected fuel is difficult to atomize.

  Then, based on the in-cylinder injection ratio set on the basis of the engine load KL and the engine speed NE, without executing the decompression in-cylinder injection and retarding the fuel injection timing of the port injection valve 27 as described above. Normal fuel injection is executed by both the port injection valve 27 and the in-cylinder injection valve 28, and this process is temporarily terminated.

According to the first embodiment described above, the following effects can be obtained.
(1) Since the piston 22 descends with both the intake valve 31 and the exhaust valve 32 closed, the fuel injection of the in-cylinder injection valve 28 starts during the decompression period in which the inside of the cylinder 21 is decompressed. The atomization of the injected fuel is promoted, and the combustion can be stabilized even when an ethanol-containing fuel that is difficult to atomize when the engine is cold is used. However, when such decompression in-cylinder injection is executed, the valve opening timing of the intake valve 31 is limited, so that it is not possible to set an optimal valve opening timing aiming at the intake inertia effect, There is a concern that the intake air amount GA is limited more than necessary. Therefore, in the internal combustion engine 20 of the present embodiment, such reduced pressure in-cylinder injection is performed only when it is determined that the injected fuel is difficult to atomize based on the ethanol concentration CE being higher than the determination concentration CEjdg. . As a result, the reduced pressure in-cylinder injection is executed in accordance with the properties of the fuel, and it is possible to stabilize the combustion when the engine is cold while suppressing the occurrence of the above inconvenience as much as possible.

  (2) When the ethanol concentration CE of the fuel is high, the amount of fuel required for obtaining the same engine output is increased as compared with the case where the fuel concentration CE is low. Accordingly, a large amount of fuel must be injected at the time of high engine load, and there is a concern that it is difficult to appropriately perform fuel injection only by the in-cylinder injection valve 28.

  In this regard, in the above embodiment, since the fuel can be injected from the port injection valve 27 to the intake port 25 in addition to the in-cylinder injection valve 28, the fuel having a high ethanol concentration CE as described above is used. An appropriate amount of fuel can be supplied to the cylinder 21 even when the engine is at a high load.

  (3) In the above embodiment, as the ethanol concentration CE is higher, the in-cylinder injection ratio that is the ratio of the fuel injection amount of the in-cylinder injection valve 28 is increased. According to such a configuration, the amount of fuel injected by the reduced pressure in-cylinder injection, that is, the amount of fuel that promotes atomization can be increased as the ethanol concentration CE is higher and the injected fuel is more difficult to atomize. Combustion when the engine is cold can be stabilized. Further, by increasing the in-cylinder injection ratio as the ethanol concentration CE of the fuel is higher in this way, the fuel injection amount of the port injection valve 27 is reduced, and the amount of fuel injected in a state that is difficult to atomize. Therefore, the amount of fuel that does not contribute to combustion can be reduced. As a result, the amount of unburned fuel components contained in the exhaust can be reduced, and deterioration of exhaust properties can be suppressed.

  (4) Further, when the fuel is injected from the port injection valve 27 before the intake valve 31 is opened when the engine is cold, the fuel may remain in the intake port 25 in a liquid state without being atomized. is there. If the fuel staying in the intake port 25 is sucked into the cylinder 21 as the intake valve 31 is opened, it may adhere to the spark plug 24 in a liquid state and cause misfire. On the other hand, in the internal combustion engine 20 of the above-described embodiment, the intake valve 31 opens in synchronization with the opening timing of the intake valve 31 in synchronism with the opening timing of the intake valve 31 together with the decompression in-cylinder injection. Sometimes, the fuel injection of the port injection valve 27 is started. By adopting such a configuration, it is possible to suppress the fuel that has accumulated in the intake port 25 from adhering, and to stabilize the combustion when the engine is cold, in addition to the effect of promoting atomization by the reduced pressure in-cylinder injection. Will be able to.

The first embodiment can also be implemented in the following forms that are appropriately modified.
In step S130, the in-cylinder injection ratio is increased by adding the correction amount calculated based on the ethanol concentration CE to the in-cylinder injection ratio calculated based on the engine load KL and the engine speed NE. Although the configuration has been shown, a configuration in which the in-cylinder injection ratio is increased by multiplying the correction coefficient calculated based on the ethanol concentration CE may be employed. That is, if the in-cylinder injection ratio is changed so that the fuel injection ratio of the in-cylinder injection valve 28 increases as the ethanol concentration CE is higher, the changing method can be appropriately changed.

  As shown in FIG. 4, the configuration in which the correction amount of the in-cylinder injection ratio is set to a gradually larger value as the ethanol concentration CE is higher in proportion to the ethanol concentration CE is shown. As the ethanol concentration CE increases, It is also possible to adopt a configuration in which the correction amount is set to a large value step by step.

As shown in FIG. 6, the process of changing the in-cylinder injection ratio based on the ethanol concentration CE (step S130 in FIG. 3) is omitted, the engine cooling water temperature THW is lower than the determination water temperature THWjdg, and the ethanol concentration When CE is higher than the determination concentration CEjdg, it may be determined that the injected fuel is difficult to atomize, and the decompression in-cylinder injection and the delay of the fuel injection timing of the port injection valve 27 may be executed.
(Second Embodiment)
Hereinafter, the second embodiment will be described with reference to FIGS. 7 and 8. In the first embodiment, it is determined that the injected fuel is not easily atomized based on the fact that the engine cooling water temperature THW is lower than the preset determination water temperature THWjdg and the ethanol concentration CE is higher than the determination concentration CEjdg, and the pressure is reduced. The delay of the in-cylinder injection and the fuel injection timing of the port injection valve 27 is executed. In contrast, in the present embodiment, the determination water temperature THWjdg is variably set based on the ethanol concentration CE, and the fuel property is determined based on the fact that the engine cooling water temperature THW is lower than the determination water temperature TWHjdg set based on the ethanol concentration CE. The retarded in-cylinder injection and the retardation of the fuel injection timing of the port injection valve 27 are executed in a manner corresponding to the change.

Hereinafter, description of points common to the first embodiment will be omitted, and control related to a change in the fuel injection mode, which is a difference between the two embodiments, will be described.
FIG. 7 is a flowchart showing a flow of a series of processes for control according to the change of the fuel injection mode in the present embodiment. This series of processing is repeatedly executed by the electronic control unit 10 during engine operation including when the engine is started, as in the first embodiment. In FIG. 7, the same reference numerals are assigned to the same processes as those in the first embodiment.

  When this series of processing is started, the electronic control unit 10 first reads the engine coolant temperature THW and the fuel ethanol concentration CE in step S100, as in the first embodiment. In step S105, the determination water temperature THWjdg is set based on the ethanol concentration CE.

  Specifically, the determination water temperature THWjdg is calculated based on the ethanol concentration CE with reference to a calculation map stored in advance in the electronic control unit 10. In this calculation map, as shown in FIG. 8, the determination water temperature THWjdg is set to a larger value as the ethanol concentration CE is higher in proportion to the ethanol concentration CE. Therefore, the determination water temperature THWjdg is set higher as the ethanol concentration CE is higher through step S105.

  When the determination water temperature THWjdg is thus set, the process proceeds to step S110, and it is determined whether or not the engine cooling water temperature THW is lower than the determination water temperature THWjdg set through step S105.

  If it is determined in step S110 that the engine coolant temperature THW is lower than the determination coolant temperature THWjdg (step S110: YES), the process proceeds to step S140, and the reduced pressure in-cylinder injection is executed as in the first embodiment. At the same time, the injection timing is retarded so that the fuel injection start timing of the port injection valve 27 coincides with the opening timing of the intake valve 31.

  On the other hand, when it is determined in step S110 that the engine coolant temperature THW is equal to or higher than the determination coolant temperature THWjdg (step S110: NO), the process proceeds to step S150, and normal fuel injection is executed.

According to the second embodiment described above, the following effects can be obtained in addition to the effects (1), (3), and (4).
(5) As the ethanol concentration CE is higher, the injected fuel is less likely to atomize, and this tendency becomes particularly prominent when the engine is cold, so that combustion tends to become unstable. Therefore, in the second embodiment, the reduced pressure in-cylinder injection is executed when the engine cooling water temperature THW is lower than the determination water temperature THWjdg, and the determination water temperature THWjdg is set higher as the fuel ethanol concentration CE is higher. I have to. Therefore, the determination water temperature THWjdg can be set in consideration of a change in the degree of fuel atomization due to the difference in the ethanol concentration CE of the fuel, and it is accurately determined that the injected fuel is difficult to atomize based on the engine cooling water temperature THW. Thus, the in-cylinder injection can be executed.

The second embodiment can also be carried out in the following forms that are appropriately modified.
As shown in FIG. 8, a configuration is shown in which the determination water temperature THWjdg is gradually set to a larger value as the ethanol concentration CE is higher in proportion to the ethanol concentration CE. However, the determination is made step by step as the ethanol concentration CE increases. A configuration in which the water temperature THWjdg is set to a large value may be employed.

  As shown in FIG. 9, step S130 in the first embodiment is added to the control related to the change of the fuel injection mode of the second embodiment, and the determination water temperature THWjdg is set based on the ethanol concentration CE. In addition, a configuration in which the in-cylinder injection ratio is corrected based on the ethanol concentration CE may be employed.

In addition, the said 1st and 2nd embodiment can also be implemented with the following forms which changed this suitably.
The decompression in-cylinder injection is not limited as long as the fuel is injected from the in-cylinder injection valve 28 at least during the decompression period in which the inside of the cylinder 21 is in a decompressed state. That is, a part of the fuel injection period from the in-cylinder injection valve 28 at the time of decompression in-cylinder injection may overlap the opening period of the intake valve 31.

  In the first and second embodiments, the fuel injection timing in the port injection valve 27 is started so as to start the fuel injection of the port injection valve 27 at the same time when the intake valve 31 is opened together with the decompression in-cylinder injection. A configuration for retarding the angle is shown. On the other hand, the delay of the injection timing of the port injection valve 27 is that fuel is injected into the intake port 25 while the intake valve 31 is closed, so that the fuel is injected into the intake port 25 and the intake valve 31. Any material can be used as long as it can be prevented from adhering and staying in a liquid state. That is, not only the configuration in which fuel injection is started simultaneously with the opening timing of the intake valve 31, but also a configuration in which fuel injection is started after a predetermined period of time has elapsed since the intake valve 31 is opened.

  Although the decompression in-cylinder injection is executed and the injection start timing of the port injection valve 27 is retarded so that the fuel injection by the port injection valve 27 is started simultaneously with the opening of the intake valve 31, The fuel injection by the injection valve 27 can be started before the intake valve 31 is opened in the same manner as the normal fuel injection after the warm-up is completed, and it is possible to execute only the in-cylinder injection.

  In the above embodiment, the present invention is applied to the internal combustion engine 20 that changes the ratio of the fuel injection amount of the in-cylinder injection valve 28 and the fuel injection amount of the port injection valve 27 based on the engine load KL and the engine rotational speed NE. The configuration was shown. In contrast, the present invention can be applied to any internal combustion engine 20 that includes at least the in-cylinder injection valve 28 and the port injection valve 27. In other words, the present invention can also be applied to an internal combustion engine in which fuel is injected by only one of the port injection valve 27 and the in-cylinder injection valve 28 while the reduced pressure in-cylinder injection is executed only when the engine is started.

Even if the port injection valve 27 is not provided, an internal combustion engine provided with at least the in-cylinder injection valve 28 can execute reduced pressure in-cylinder injection to stabilize the fuel when the engine is cold.
When starting the engine, the temperature of the cylinder 21 and the intake port 25 is low, and the atomization of the injected fuel is difficult to be promoted, so the startability is likely to deteriorate. Therefore, particularly in a flex fuel engine, such a startability deterioration is more likely to occur. Therefore, it is also possible to adopt a configuration in which the fuel injection timing is retarded so that fuel injection of the port injection valve 27 is started simultaneously with the decompression in-cylinder injection or the opening of the intake valve 31 on condition that the engine is started. it can. According to such a configuration, the engine combustion state at the time of engine start can be improved and deterioration of engine startability can be suppressed.

  As the alcohol concentration estimation means, the ethanol concentration sensor 45 that directly detects the ethanol concentration CE has been exemplified, but instead of such a configuration, the air-fuel ratio or ignition for suppressing knocking based on the difference in fuel properties between gasoline and alcohol A configuration in which the alcohol concentration is estimated from the difference in the correction amount in the timing feedback control can also be adopted.

  As the valve characteristic changing mechanism 30, a combination of a valve timing changing mechanism that changes the opening / closing timing of the intake valve 31 and a lift amount changing mechanism that changes the lift amount and valve opening period of the valve is illustrated. On the other hand, the valve characteristic changing mechanism changes at least the valve opening timing of the intake valve 31, such as only the valve timing changing mechanism, in addition to changing the valve opening / closing timing, lift amount, and lift period independently. Anything is possible.

  As an example of a flex fuel engine, the internal combustion engine 20 that can use an ethanol-containing fuel in which gasoline and ethanol are mixed in an arbitrary ratio has been illustrated, but an alcohol-containing fuel in which gasoline and alcohol are mixed in an arbitrary ratio can be used As long as it is a flexible fuel engine, the control according to the present invention can be applied in the same manner even in a flex fuel engine that can use other alcohol-containing fuels such as methanol and butanol. .

1 is a schematic diagram showing a schematic configuration of an electronic control device according to a first embodiment of the present invention and a flex fuel engine that is a control target thereof. (A), (b), (c) is explanatory drawing which shows the change mode of the valve opening timing and lift amount of an intake valve by the valve characteristic change mechanism concerning the embodiment. The flowchart which shows the flow of a series of processes of control concerning the change of the fuel-injection aspect in the embodiment. The graph which shows the relationship between the ethanol concentration concerning the same embodiment, and the correction amount of the cylinder injection ratio. Explanatory drawing which shows the relationship between the fuel injection timing of the cylinder injection valve concerning this embodiment, the fuel injection timing of a port injection valve, and the valve opening / closing timing. The flowchart which shows the flow of a series of processes of control concerning the change of the fuel-injection aspect in the example of a change of the embodiment. The flowchart which shows the flow of a series of processes of control concerning the change of the fuel-injection aspect in 2nd Embodiment of this invention. The graph which shows the relationship between the ethanol concentration concerning the same embodiment, and determination water temperature. The flowchart which shows the flow of a series of processes of control concerning the change of the fuel-injection aspect in the example of a change of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Electronic controller, 20 ... Internal combustion engine, 21 ... Cylinder, 22 ... Piston, 23 ... Combustion chamber, 24 ... Spark plug, 25 ... Intake port, 26 ... Exhaust port, 27 ... Port injection valve, 28 ... In-cylinder injection Valve, 30 ... Valve characteristic changing mechanism, 31 ... Intake valve, 32 ... Exhaust valve. DESCRIPTION OF SYMBOLS 40 ... Crank angle sensor, 41 ... Cam position sensor, 42 ... Water temperature sensor, 43 ... Air flow meter, 44 ... Accelerator position sensor, 45 ... Ethanol concentration sensor

Claims (7)

In a control apparatus for a flex fuel engine comprising a valve characteristic changing mechanism that changes the opening / closing characteristics of an intake valve and an in-cylinder injection valve that injects fuel directly into a cylinder.
Comprising an alcohol concentration estimating means for estimating the alcohol concentration of the fuel;
When it is determined that the injected fuel is difficult to atomize based on the alcohol concentration estimated by the alcohol concentration estimating means, the valve characteristic changing mechanism delays the opening timing of the intake valve from the closing timing of the exhaust valve. A flex fuel that performs reduced pressure in-cylinder injection that injects fuel from the in-cylinder injection valve when the piston is descending and the intake valve and the exhaust valve are both closed. Engine control device. The reduced pressure in-cylinder injection is executed when the engine cooling water temperature is lower than a predetermined determination water temperature,
The control apparatus for a flex fuel engine according to claim 1, further comprising setting means for setting the determination water temperature to be higher as the estimated alcohol concentration is higher. The control apparatus for a flex fuel engine according to claim 1, further comprising a port injection valve that injects fuel into an intake port in addition to the in-cylinder injection valve. The fuel injection amount ratio of the in-cylinder injection valve is increased as the estimated alcohol concentration is higher when fuel injection of the port injection valve is performed simultaneously with the decompression in-cylinder injection. Control system for flex fuel engines. When the fuel injection of the port injection valve is performed simultaneously with the in-cylinder injection, the fuel injection timing of the port injection valve is synchronized with the opening timing of the intake valve, and after the intake valve is opened, The control apparatus for a flex fuel engine according to claim 3 or 4, wherein fuel injection to the intake port is started. The control apparatus for a flex fuel engine according to any one of claims 1 to 5, wherein the decompression in-cylinder injection is executed when the estimated alcohol concentration is equal to or higher than a predetermined concentration. The control apparatus for a flex fuel engine according to any one of claims 1 to 6, wherein the decompression in-cylinder injection is executed on condition that the engine is started.

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