JP2007285130A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an internal combustion engine capable of using an alcohol fuel for an engine fuel, and favorably enhancing the low-temperature startability. <P>SOLUTION: An internal combustion engine 1 capable of using an alcohol fuel for an engine fuel has an electric-driven turbocharger 12 for turbocharging sucked air, and also has a cooling passage 50 having an intercooler 18 for cooling sucked air which is turbocharged by the turbocharger 12, a bypass passage 60 for introducing the turbocharged sucked air into a combustion chamber without passing through the cooling passage 50, and a flow passage change-over valve 40 for adjusting the bypass amount of the turbocharged sucked air to be introduced in the bypass passage 60. A control device 25 turbocharges the sucked air by the turbocharger 12 when starting the internal combustion engine 1, and controls the drive of the flow passage change-over valve 40 so that the turbocharged sucked air is introduced in the bypass passage 60. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an internal combustion engine that can use alcohol fuel as engine fuel.

  In recent years, an internal combustion engine capable of using alcohol fuel and gasoline fuel in combination as engine fuel is being put into practical use. Such an internal combustion engine can be operated with only alcohol fuel, only gasoline fuel, or a mixed fuel in which alcohol fuel and gasoline fuel are mixed.

  Such an alcohol fuel has a characteristic that it is less likely to vaporize at a lower temperature than a gasoline fuel. Therefore, the higher the alcohol concentration in the engine fuel, such as when the concentration of alcohol fuel itself is high, or when the ratio of alcohol fuel is high in a mixed fuel in which alcohol fuel and gasoline fuel are mixed, the lower the temperature startability. There is a problem that gets worse.

Therefore, in the internal combustion engine described in Patent Document 1, a heater is provided in the intake passage to superheat the intake air, thereby improving the low-temperature startability when using such alcohol fuel.
JP-A-4-231665

  By the way, when a heater is provided in the intake passage, the structure of the intake passage becomes complicated. Further, when the starter motor is driven when the engine is started, relatively large power is consumed. Therefore, when an electric heater is used as the heater provided in the intake passage, there is a possibility that inconveniences such as insufficient driving force of the starter motor and insufficient heat generation of the electric heater may occur.

  There is also an internal combustion engine in which a reserve fuel tank is provided in a vehicle and gasoline fuel is put therein, and fuel in the reserve fuel tank is used when starting the engine. With such an internal combustion engine, the engine can be started with gasoline fuel, so that it is possible to suitably ensure low temperature startability. However, in this internal combustion engine, it is necessary to replenish gasoline fuel in the reserve fuel tank, which imposes a burden on the vehicle user. In addition, there is a problem that the cost increases as much as the reserve fuel tank is provided.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an internal combustion engine that can improve cold startability more suitably in an internal combustion engine that can use alcohol fuel as an engine fuel. It is in.

In the following, means for achieving the above object and its effects are described.
According to the first aspect of the present invention, in an internal combustion engine that can use alcohol fuel as engine fuel, a supercharger that supercharges intake air, and supercharging control of intake air by the supercharger when the internal combustion engine is started The gist of the present invention is to provide a supercharging control means for performing the above.

  According to this configuration, when the engine is started, the intake air temperature rises by supercharging the intake air with the supercharger. For this reason, when alcohol fuel that is hard to vaporize at low temperatures is injected into the intake air, the temperature of the alcohol fuel rises and is likely to vaporize, thereby improving engine startability. Therefore, in an internal combustion engine that can use alcohol fuel as the engine fuel, the cold startability can be improved more suitably.

  According to a second aspect of the present invention, the internal combustion engine according to the first aspect further comprises concentration detecting means for detecting an alcohol concentration in the engine fuel, wherein the supercharging control means is configured to detect an excess of intake air by the supercharger. The gist is to determine whether or not to perform supply based on the alcohol concentration.

  If the alcohol concentration in the engine fuel is low, the influence of the alcohol concentration on the cold startability is reduced. Therefore, in this configuration, it is determined based on the alcohol concentration whether or not the intake air is supercharged by the supercharger. Therefore, unnecessary supercharging can be suppressed compared to the case where supercharging is always performed when starting the engine. In this configuration, the alcohol concentration when the low-temperature startability deteriorates to an unacceptable degree is examined in advance, and the concentration is set as a determination value. And when the alcohol concentration detected by the said density | concentration detection means is below the determination value, it is good to determine that supercharging by a supercharger is performed.

  The invention according to claim 3 is the internal combustion engine according to claim 1, further comprising intake air temperature detecting means for detecting an intake air temperature before supercharging, wherein the supercharging control means is configured to reduce intake air by the supercharger. The gist is to determine whether to perform supercharging based on the intake air temperature.

  Since the alcohol fuel is easily vaporized when the intake air temperature before supercharging is high, the influence of the alcohol concentration on the low-temperature startability is reduced. Therefore, in this configuration, whether to supercharge intake air by the supercharger is determined based on the intake air temperature before supercharging. Therefore, unnecessary supercharging can be suppressed compared to the case where supercharging is always performed when starting the engine. In this configuration, the intake air temperature when the low-temperature startability deteriorates to an unacceptable degree is examined in advance, and the intake air temperature is set as a determination value. Then, when the intake air temperature detected by the intake air temperature detecting means is equal to or lower than the determination value, it may be determined that supercharging by the supercharger is performed.

  According to a fourth aspect of the present invention, in the internal combustion engine according to the first aspect of the present invention, the internal combustion engine further comprises concentration detecting means for detecting an alcohol concentration in the engine fuel, and the supercharging control means The gist is to variably set the supercharging pressure.

  Although the intake air temperature rises as the boost pressure of the intake air is increased, there is a disadvantage that knocking is likely to occur with the increase. Here, as described above, if the alcohol concentration in the engine fuel is low, the alcohol concentration has less influence on the cold startability. Therefore, in this configuration, the supercharging pressure of the intake air is variably set based on the alcohol concentration. Like to do. Therefore, when the intake air is supercharged in order to improve the low temperature startability, the above inconvenience caused by the rise in the intake air temperature can be suitably suppressed. In this configuration, it is desirable to set the supercharging pressure to be lower as the alcohol concentration is lower.

  Further, as described above, the alcohol fuel is easily vaporized in a state where the intake air temperature before supercharging is high, so that the influence of the alcohol concentration on the low-temperature startability is reduced. Therefore, according to the invention described in claim 5, it is provided with intake air temperature detecting means for detecting the intake air temperature before supercharging, and the supercharging control means controls the supercharging pressure of the intake air based on the intake air temperature. Also by adopting a configuration such as variably setting, it is possible to suitably suppress the inconvenience caused by the rise of the intake air temperature when supercharging the intake air in order to improve the low temperature startability. In this configuration, it is desirable to set the supercharging pressure to be lower as the intake air temperature is higher.

  Further, according to the invention described in claim 6, there is provided a concentration detecting means for detecting the alcohol concentration in the engine fuel, and an intake air temperature detecting means for detecting the intake air temperature before supercharging. By adopting a configuration in which the supercharging pressure of intake air is variably set based on the alcohol concentration and the intake air temperature, the intake air temperature rises when supercharging the intake air in order to improve low temperature startability This makes it possible to more appropriately suppress inconveniences that occur. Even in this configuration, it is desirable to set the boost pressure to be lower as the intake air temperature is higher, and to be lower as the alcohol concentration is lower.

According to a seventh aspect of the present invention, in the internal combustion engine according to any one of the first to sixth aspects, the supercharger is an electric supercharger driven by an electric motor. The gist.
Since the amount of exhaust gas is small when starting the engine, especially during cranking, a turbocharger (so-called exhaust-driven turbocharger) that pumps intake air using the flow of exhaust gas is used when starting the engine. In this case, a sufficient supercharging pressure cannot be obtained. In this respect, in the same configuration, by providing the electric supercharger, a sufficient supercharging pressure can be obtained even when the engine is started. Further, the variable setting of the supercharging pressure can be easily performed.

  According to an eighth aspect of the present invention, in the internal combustion engine according to any one of the first to sixth aspects, the supercharger is a supercharger to which a driving force is transmitted from an output shaft of the internal combustion engine. The gist of the present invention is to include a switching means capable of selecting transmission and cutting of the driving force.

  In a supercharger in which driving force is transmitted from an output shaft of an internal combustion engine, a so-called mechanically driven supercharger, the drive shaft is connected to the engine output shaft via switching means such as a clutch. Therefore, when the engine is started, the switching means is switched so that the driving force from the output shaft is transmitted to the supercharger, whereby the rotation of the output shaft due to cranking is transmitted to the supercharger. It becomes possible to supercharge intake air.

  According to a ninth aspect of the present invention, in the internal combustion engine according to any one of the first to eighth aspects, the cooling passage for cooling the intake air supercharged by the supercharger, and the supercharged suction A bypass passage for introducing air into the combustion chamber without passing through the cooling passage; an adjusting means for adjusting the amount of bypass in the supercharged intake air introduced into the bypass passage; and starting of the internal combustion engine At this time, the gist of the present invention is to include bypass control means for controlling the bypass amount of the supercharged intake air.

  In an internal combustion engine having a supercharger, a cooling device, a so-called intercooler, may be provided in an intake passage through which the supercharged intake air passes in order to suppress a rise in temperature of the supercharged intake air. Here, in order to suppress the deterioration of low temperature startability due to alcohol fuel, supercharging is performed at the time of engine start, and even if the intake air temperature is increased, the suction that is supercharged in the cooling passage provided with such a cooling device If air passes, the temperature of intake air will fall. In this regard, in this configuration, the bypass passage that introduces the supercharged intake air into the combustion chamber without passing through the cooling passage, and the bypass amount that is introduced into the bypass passage in the supercharged intake air are adjusted. Adjusting means to be provided. When the internal combustion engine is started, the bypass amount of the supercharged intake air is controlled. Therefore, by adjusting the bypass amount, it is possible to suitably suppress the temperature drop of the supercharged intake air.

  A tenth aspect of the present invention is the internal combustion engine according to the ninth aspect, further comprising concentration detecting means for detecting an alcohol concentration in the engine fuel, wherein the bypass control means is configured to bypass the supercharged intake air. The gist is to determine whether to introduce into the passage based on the alcohol concentration.

  The higher the temperature of the intake air introduced into the combustion chamber, the more easily the alcohol fuel is vaporized. However, there is a risk that inconveniences such as knocking are more likely to occur as the temperature of the intake air is higher. Here, as described above, if the alcohol concentration in the engine fuel is low, the influence of the alcohol concentration on the low-temperature startability is reduced. Therefore, it is necessary to introduce the supercharged intake air into the bypass passage. This reduces the need to introduce the supercharged intake air into the combustion chamber without cooling. Therefore, in this configuration, whether to introduce the supercharged intake air into the bypass passage is determined based on the alcohol concentration. Accordingly, when the engine is started, the frequency of occurrence of the above-described problem can be suppressed as compared with the case where the supercharged intake air is always introduced into the bypass passage. In this configuration, the alcohol concentration when the low-temperature startability deteriorates to an unacceptable degree is examined in advance, and the concentration is set as a determination value. Then, when the alcohol concentration detected by the concentration detecting means is equal to or lower than the determination value, it is preferable to determine that the supercharged intake air is introduced into the bypass passage.

  The invention according to claim 11 is the internal combustion engine according to claim 9, further comprising intake air temperature detecting means for detecting the intake air temperature before supercharging, wherein the bypass control means The gist is to determine whether to introduce into the bypass passage based on the intake air temperature.

  As described above, since the alcohol fuel is easily vaporized in a state where the intake air temperature before supercharging is high, the influence of the alcohol concentration on the low-temperature startability is reduced. Also, the higher the temperature of the intake air introduced into the combustion chamber, the more easily the alcohol fuel is vaporized. However, there is a possibility that inconveniences such as knocking are more likely to occur as the temperature of the intake air is higher. Therefore, in this configuration, whether to introduce the supercharged intake air into the bypass passage is determined based on the intake air temperature before supercharging. Accordingly, when the engine is started, the frequency of occurrence of the above-described problem can be suppressed as compared with the case where the supercharged intake air is always introduced into the bypass passage. In this configuration, the intake air temperature when the low-temperature startability deteriorates to an unacceptable degree is examined in advance, and the intake air is set as a determination value. Then, when the intake air temperature detected by the intake air temperature detecting means is equal to or lower than the determination value, it may be determined that the supercharged intake air is introduced into the bypass passage.

  A twelfth aspect of the present invention is the internal combustion engine according to the ninth aspect, further comprising concentration detecting means for detecting an alcohol concentration in the engine fuel, wherein the bypass control means determines the bypass amount based on the alcohol concentration. The gist is to variably set.

  As described above, if the alcohol concentration in the engine fuel is low, the alcohol concentration has less influence on the cold startability. Therefore, the amount of supercharged intake air introduced into the bypass passage, that is, the bypass amount is reduced. can do. On the other hand, the higher the temperature of the intake air introduced into the combustion chamber, the more easily the alcohol fuel is vaporized, but there is a risk that inconveniences such as knocking are likely to occur. Therefore, in this configuration, the bypass amount is variably set based on the alcohol concentration. Therefore, in order to improve the low temperature startability, when introducing the supercharged intake air into the bypass passage, the above disadvantage that may occur due to introduction of the high temperature intake air into the combustion chamber is suitably suppressed. Will be able to. In the same configuration, it is desirable to set the amount of bypass to increase as the alcohol concentration increases.

  In addition, as described above, alcohol fuel tends to vaporize in a state where the intake air temperature before supercharging is high, and the influence of alcohol concentration on low temperature startability is reduced. Therefore, the supercharged intake air is passed to the bypass passage. The amount to be introduced, that is, the bypass amount can be reduced. Therefore, according to the invention of claim 13, it is provided with an intake air temperature detecting means for detecting the intake air temperature before supercharging, and the bypass control means variably sets the bypass amount based on the intake air temperature. Also by adopting such a configuration, it is possible to suitably suppress the occurrence of knocking or the like when introducing the supercharged intake air into the bypass passage in order to improve the low temperature startability. In the same configuration, it is desirable to set the bypass amount to be smaller as the intake air temperature is higher.

  Further, according to the invention as set forth in claim 14, there is provided a concentration detection means for detecting the alcohol concentration in the engine fuel, and an intake air temperature detection means for detecting the intake air temperature before supercharging. In order to improve low temperature startability by adopting a configuration in which the bypass amount is variably set based on the alcohol concentration and the intake air temperature, when introducing the supercharged intake air into the bypass passage, It is possible to more suitably suppress the occurrence of inconvenience that knocking or the like is likely to occur. Even in the same configuration, it is desirable to set the bypass amount to be smaller as the intake air temperature is higher, and to be larger as the alcohol concentration is higher.

  Incidentally, examples of the alcohol concentration detecting means include a sensor that detects the alcohol concentration based on the electric conductivity and capacitance of the fuel. The intake air temperature detecting means includes an intake air temperature sensor provided in the intake passage.

(First embodiment)
Hereinafter, a first embodiment of an internal combustion engine according to the present invention will be described with reference to FIGS. 1 and 2.

  FIG. 1 shows a schematic configuration of an internal combustion engine 1 according to the present embodiment. The internal combustion engine 1 in the present embodiment is a four-cylinder in-line internal combustion engine, but an internal combustion engine having another number of cylinders or an internal combustion engine having another cylinder arrangement (for example, a V-type internal combustion engine). ).

  The internal combustion engine 1 is provided with a plurality of cylinders # 1 to # 4. A cylinder head 2 is provided above each cylinder. The cylinder head 2 is provided with an intake port for introducing intake air into the cylinder, an exhaust port for exhausting combustion gas to the outside of the cylinder, and an air-fuel mixture in which fuel and air are mixed for spark ignition. Spark plugs are provided corresponding to the cylinders # 1 to # 4.

  Further, fuel injection valves 4a to 4d are attached to the intake ports corresponding to the cylinders # 1 to # 4, respectively. These fuel injection valves 4a to 4d inject fuel toward the intake ports.

  The fuel injection valves 4 a to 4 d are connected to the delivery pipe 9. The delivery pipe 9 is connected to the fuel pump 10 via the fuel pipe 27. The fuel pump 10 sucks the fuel in the fuel tank 11 and feeds the fuel to the delivery pipe 9. The fuel supplied to the delivery pipe 9 is injected from the fuel injection valves 4a to 4d when the fuel injection valves 4a to 4d are opened. The fuel tank 11 stores only alcohol fuel, only gasoline fuel, and mixed fuel in which alcohol fuel and gasoline fuel are mixed, and the internal combustion engine 1 has alcohol fuel, gasoline fuel, or a mixed fuel thereof. Is used as engine fuel.

An exhaust manifold 8 is connected to each exhaust port, and the exhaust manifold 8 is connected to an exhaust passage 26.
An intake manifold 7 is connected to each intake port, and the intake manifold 7 is connected to the intake passage 3. A throttle valve 16 for adjusting the intake air amount is provided in the intake passage 3.

  In the middle of the intake passage 3, a supercharger 12 is provided for supercharging intake air introduced into the combustion chambers in the cylinders # 1 to # 4. A compressor wheel that pumps intake air is provided in the supercharger 12, and the compressor wheel is rotationally driven by an electric motor 12a. Thus, since the supercharger 12 is an electric supercharger, the following effects can be obtained. In other words, since the amount of exhaust gas is small when the engine is started, especially during cranking, a turbocharger (so-called exhaust-driven turbocharger) that pumps intake air by utilizing the flow of exhaust gas has such an engine. Sufficient supercharging pressure cannot be obtained at the start. In this respect, since the electric supercharger 12 uses the electric motor 12a as its drive source, a sufficient supercharging pressure can be obtained even when the engine is started. Further, the supercharging pressure can be variably set by changing the rotation speed of the electric motor 12a.

  A thermal air flow meter 19 for detecting the intake air amount and the intake air temperature is provided in the intake passage 3 and upstream of the supercharger 12. The thermal air flow meter 19 is provided with a temperature sensor such as a thermistor that functions as a temperature detection element and a heater that is a heating element. Then, energization control is performed on the heater so that the heater temperature is always higher than the intake air temperature THA before supercharging detected by the temperature sensor, and the intake air is based on the energization amount. Mass flow rate is detected.

  Further, an intercooler 18 for cooling intake air whose temperature has increased due to supercharging is provided in the intake passage 3 on the downstream side of the intake air from the supercharger 12. The portion where the cooler 18 is provided functions as a cooling passage 50.

  A flow path switching valve 40 is provided in the intake passage 3 between the intercooler 18 and the supercharger 12. The flow path switching valve 40 is a three-way valve, and its in-side port is connected to the discharge port of the supercharger 12 via the intake passage 3. The first out-side port of the flow path switching valve 40 is connected to the cooling passage 50 side. A second out-side port of the flow path switching valve 40 is connected to the bypass passage 60. The bypass passage 60 is a passage for introducing the supercharged intake air into the combustion chamber without passing through the cooling passage 50, one end of which is the second out-side port and the other end is the intake air. In the passage 3, the cooling passage 50 is connected to the intake downstream side. Then, by adjusting the valve opening degree of the flow path switching valve 40, the amount of intake air introduced into the bypass passage 60 in the supercharged intake air (hereinafter referred to as bypass amount) is adjusted. Hereinafter, a state in which the valve body of the flow path switching valve 40 is driven so that all of the supercharged intake air is introduced into the cooling passage 50 is referred to as a fully open state. All of the heated intake air is cooled. The state in which the valve body of the flow path switching valve 40 is driven so that all of the supercharged intake air is introduced into the bypass passage 60 is referred to as a fully closed state. All of the warm intake air is introduced into the combustion chamber without being cooled. Therefore, the temperature of the intake air introduced into the combustion chamber increases as the valve opening degree of the flow path switching valve 40 decreases.

  On the other hand, the crankshaft 13 that is the output shaft of the internal combustion engine 1 is provided with a flywheel 6 having a gear portion on the outer periphery. When the engine is started, the pinion gear 71 provided on the starter motor 70 is connected to the flywheel. Cranking is performed by meshing with the gear portion 6.

  In addition to the thermal air flow meter 19, the internal combustion engine 1 is equipped with various sensors for detecting the engine operating state such as the engine speed. An ignition switch 24 for detecting an engine start request by the driver is also provided. When the ignition switch 24 is turned on, it is determined that there is an engine start request by the driver, and the starter motor 70 is turned on. Driven by this, cranking, that is, engine starting is performed.

  The outputs of these various sensors and switches are input to the control device 25. The control device 25 includes a central processing control device (CPU), a read only memory (ROM) that stores various programs and maps in advance, a random access memory (RAM) that temporarily stores CPU calculation results, an input interface, and an output. It is mainly composed of a microcomputer equipped with an interface. Then, the control device 25 performs, for example, fuel injection control and fuel injection timing control of the fuel injection valves 4a to 4d, discharge pressure control of the fuel pump 10, opening control of the throttle valve 16, and rotation speed control of the electric motor 12a. Various controls of the internal combustion engine 1 such as supercharging pressure control and opening control of the valve body of the flow path switching valve 40 are performed.

  The internal combustion engine 1 is an internal combustion engine that can use alcohol fuel as its engine fuel. However, such alcohol fuel has a characteristic that it is less likely to vaporize at a lower temperature than gasoline fuel. There is a problem that the cold startability deteriorates as the alcohol concentration in the engine fuel increases. Therefore, in the present embodiment, the low temperature startability is suitably improved in an internal combustion engine that can use alcohol fuel and gasoline fuel as engine fuel by performing an intake air temperature rise process described below.

FIG. 2 shows a processing procedure for the intake air temperature increase processing executed by the control device 25.
When this process is started, it is first determined whether or not there is a request for starting the internal combustion engine 1 (S100). Here, an affirmative determination is made when the ignition switch 24 is in the ON state. If there is no start request (S100: NO), this process is terminated.

  On the other hand, when there is a start request (S100: YES), it is determined that the engine is currently being started and cranking is being performed, and the electric motor 12a of the supercharger 12 is driven (S110). When the electric motor 12a is driven in this manner, the supercharger 12 performs supercharging of the intake air and the intake air temperature rises. For this reason, when alcohol fuel that is hard to vaporize at low temperatures is injected into the intake air, the temperature of the alcohol fuel rises and is likely to vaporize, thereby improving engine startability. In addition, as a rotational speed of the electric motor 12a at this time, a speed capable of ensuring a supercharging pressure capable of promoting the vaporization of the alcohol fuel is set.

  Here, in order to suppress the deterioration of the low temperature startability due to the alcohol fuel, even if supercharging is performed at the time of engine start to increase the temperature of the intake air, the supercharged intake air is provided with a cooling passage 50 provided with the intercooler 18. If it passes, the temperature of the intake air will fall.

  Therefore, next, the flow path switching valve 40 is switched to the bypass side (S120). Here, the flow path switching valve 40 is driven so that the valve body of the flow path switching valve 40 is fully closed. Thus, the amount of the supercharged intake air is controlled so as to maximize the bypass amount B. Accordingly, all of the supercharged intake air is not cooled by the intercooler 18, but is introduced into the combustion chamber while maintaining its high temperature state, and the temperature drop of the supercharged intake air is suppressed. It is done.

  Next, it is determined whether or not the internal combustion engine 1 has completed an explosion, that is, whether or not the internal combustion engine 1 has rotated independently without borrowing the power of the starter motor 70 (S130). Here, an affirmative determination is made when the engine speed has increased to the extent that it can be determined that a complete explosion has occurred.

If the complete explosion has not been reached (S130: NO), the processes of step S110 and step S120 are repeated until the complete explosion occurs.
On the other hand, when the explosion is complete (S130: YES), the electric motor 12a of the supercharger 12 is stopped (S140), and the flow path switching valve 40 is switched to the intercooler side (S150). In step S150, the flow path switching valve 40 is driven so that the valve element of the flow path switching valve 40 is fully opened. Then, this process ends.

  In the present embodiment, when the internal combustion engine 1 is started and completely exploded, the electric motor 12a of the supercharger 12 is stopped and the flow path switching valve 40 is switched to the intercooler side. Yes. In addition, if the electric motor 12a of the supercharger 12 is stopped after a predetermined time has elapsed from the complete explosion and the flow path switching valve 40 is switched to the intercooler side, the predetermined time elapses from the complete explosion. It is also possible to stabilize the combustibility of the air-fuel mixture during

As described above, according to the present embodiment, the following operational effects can be obtained.
(1) A supercharger 12 that supercharges intake air is provided to the internal combustion engine 1 that can use alcohol fuel as engine fuel, and the intake air is supercharged by the supercharger 12 when the engine is started. Therefore, when the engine is started, the intake air temperature rises, alcohol fuel is easily vaporized, and engine startability is improved. Therefore, in the internal combustion engine 1 that can use alcohol fuel as the engine fuel, the cold startability can be improved more suitably.

  (2) A cooling passage 50 that cools the intake air supercharged by the supercharger 12, and a bypass passage 60 that introduces the supercharged intake air into the combustion chamber without passing through the cooling passage 50. And a flow path switching valve 40 for adjusting the amount of bypass introduced into the bypass passage 60 in the intake air. When the engine is started, the bypass amount of the supercharged intake air is controlled. More specifically, all of the supercharged intake air is introduced into the bypass passage 60. Accordingly, it is possible to suitably suppress a decrease in the temperature of the intake air generated when the supercharged intake air passes through the cooling passage 50.

(3) The electric supercharger 12 driven by the electric motor 12a is provided. Therefore, a sufficient supercharging pressure can be obtained even when the engine is started.
(Second Embodiment)
Next, a second embodiment of the internal combustion engine according to the present invention will be described with reference to FIGS.

  The present embodiment is different from the first embodiment only in that an alcohol sensor 80 for detecting the alcohol concentration AD is provided and the detected alcohol concentration AD is used when the intake air temperature rise process is executed. Therefore, in the following, this embodiment will be described focusing on such differences.

  As shown in FIG. 3, the fuel pipe 27 of the internal combustion engine 1 in the present embodiment is provided with an alcohol sensor 80 that detects an alcohol concentration AD in the engine fuel, and the detection signal is input to the control device 25. The As the alcohol sensor 80, a sensor that detects the alcohol concentration based on the electric conductivity, capacitance, etc. of the fuel may be used as appropriate. In the present embodiment, the alcohol sensor 80 is provided in the fuel pipe 27. However, if the alcohol concentration AD in the engine fuel can be detected, the mounting position can be arbitrarily changed. it can.

  In this embodiment, the intake air temperature rise process shown in FIG. As shown in FIG. 4, in the processing procedure in the intake air temperature increase process of the present embodiment, the processes in steps S200 to S250 are performed instead of the processes in steps S110 and S120 of the intake air temperature increase process in the first embodiment. Done.

  That is, if it is determined in step S100 that there is a start request (S100: YES), the alcohol concentration AD detected by the alcohol sensor 80 is read (S200).

  Next, it is determined whether or not the alcohol concentration AD is equal to or higher than a predetermined determination value α (S210). This determination value α is a preset value, and the alcohol concentration at which the low temperature startability deteriorates to an unacceptable level is set. Then, when the alcohol concentration AD is less than the determination value α (S210: NO), this process is terminated. That is, this process is terminated without supercharging by the supercharger 12 and introduction of the supercharged intake air into the bypass passage 60.

  On the other hand, when the alcohol concentration AD is equal to or higher than the determination value α (S210: YES), the target boost pressure Pp is set based on the alcohol concentration AD (S220). Here, the target supercharging pressure Pp is set to be lower as the alcohol concentration AD is lower and the engine fuel is more easily vaporized.

  Further, a target bypass amount Bp, which is a target value of the bypass amount B introduced into the bypass passage 60 in the supercharged intake air, is set based on the alcohol concentration AD (S230). Here, the target bypass amount Bp is set to increase as the alcohol concentration AD is higher and the engine fuel is harder to vaporize.

  Next, the electric motor 12a of the supercharger 12 is driven based on the target supercharging pressure Pp (S240). Here, the rotational speed of the electric motor 12a is controlled so that the target boost pressure Pp is obtained.

  Further, the flow path switching valve 40 is driven based on the target bypass amount Bp (S250). Here, the valve opening degree of the flow path switching valve 40 is controlled so that the target bypass amount Bp is obtained.

  Next, it is determined whether or not the internal combustion engine 1 has been completely detonated (S130). If the detonation has not been completed (S130: NO), the processes of step S240 and step S250 are repeated until the detonation is complete. Executed.

  On the other hand, when the explosion is complete (S130: YES), the electric motor 12a of the supercharger 12 is stopped (S140), and the flow path switching valve 40 is switched to the intercooler side (S150). Then, this process ends.

According to this embodiment described above, the following functions and effects can be obtained in addition to the functions and effects of the first embodiment.
(4) If the alcohol concentration AD in the engine fuel is low, the alcohol concentration AD has less influence on the low temperature startability. Therefore, an alcohol sensor 80 for detecting the alcohol concentration AD in the engine fuel is provided, and it is determined based on the alcohol concentration AD whether or not the intake air is supercharged by the supercharger 12. Therefore, unnecessary supercharging can be suppressed compared to the case where supercharging is always performed when starting the engine.

  (5) Although the alcohol fuel is more easily vaporized as the temperature of the intake air introduced into the combustion chamber is higher, there is a risk that inconveniences such as knocking are more likely to occur as the temperature of the intake air is higher. Here, as described above, if the alcohol concentration AD in the engine fuel is low, the influence of the alcohol concentration AD on the low-temperature startability is reduced. Therefore, it is necessary to introduce the supercharged intake air into the bypass passage 60. In other words, the necessity of introducing the supercharged intake air into the combustion chamber without cooling is reduced. Therefore, whether to introduce the supercharged intake air into the bypass passage 60 is determined based on the alcohol concentration AD. Accordingly, when the engine is started, the frequency of occurrence of the above-described problem can be suppressed as compared with the case where the supercharged intake air is always introduced into the bypass passage 60.

  (6) Although the intake air temperature rises as the supercharging pressure of the intake air is increased, there is a disadvantage that knocking is likely to occur with the increase. Here, as described above, if the alcohol concentration AD in the engine fuel is low, the influence of the alcohol concentration AD on the low-temperature startability is reduced. Therefore, the supercharging pressure of the intake air is variably set based on the alcohol concentration AD. Therefore, when the intake air is supercharged in order to improve the low temperature startability, the above inconvenience caused by the rise in the intake air temperature can be suitably suppressed.

(7) As described above, if the alcohol concentration AD in the engine fuel is low, the influence of the alcohol concentration AD on the low-temperature startability decreases, so the amount of supercharged intake air introduced into the bypass passage 60, That is, the bypass amount B can be reduced. On the other hand, the higher the temperature of the intake air introduced into the combustion chamber, the more easily the alcohol fuel is vaporized. However, there is a risk that the higher the temperature of the intake air, the easier the knocking occurs. Therefore, the bypass amount B is variably set based on the alcohol concentration AD. Therefore, when introducing the supercharged intake air into the bypass passage 60 in order to improve the low-temperature startability, it is possible to suppress the occurrence frequency of the above problems.
(Third embodiment)
Next, a third embodiment of the internal combustion engine according to the present invention will be described with reference to FIG.

  The present embodiment is different from the second embodiment only in that not only the alcohol concentration AD but also the intake air temperature THA that is the temperature of the intake air before supercharging is used when the intake air temperature rise process is executed. Therefore, in the following, this embodiment will be described focusing on such differences.

  In the present embodiment, the intake air temperature rise process shown in FIG. As shown in FIG. 5, in the processing procedure in the intake air temperature increase process of the present embodiment, instead of the process of step S200 of the intake air temperature increase process in the second embodiment, the process of step S400 is also performed in steps S220 and S220. Instead of the process of S230, the processes of Step S410 and Step S420 are performed.

  That is, if it is determined in step S100 that there is a start request (S100: YES), the alcohol concentration AD detected by the alcohol sensor 80 and the intake air temperature THA detected by the thermal air flow meter 19 are read. (S400).

  Next, it is determined whether or not the alcohol concentration AD is equal to or higher than the determination value α (S210). Then, when the alcohol concentration AD is less than the determination value α (S210: NO), this process is terminated. That is, this process is terminated without supercharging by the supercharger 12 and introduction of the supercharged intake air into the bypass passage 60.

  On the other hand, if the alcohol concentration AD is greater than or equal to the determination value α (S210: YES), the target boost pressure Pp is set based on the alcohol concentration AD and the intake air temperature THA (S410). Here, the target boost pressure Pp is set to be lower as the intake air temperature THA is higher and the engine fuel is more easily vaporized. Further, the target supercharging pressure Pp is set to be lower as the alcohol concentration AD is lower.

  Next, the target bypass amount Bp, which is the target value of the bypass amount B introduced into the bypass passage 60 in the supercharged intake air, is set based on the alcohol concentration AD and the intake air temperature THA (S420). Here, the target bypass amount Bp is set to increase as the intake air temperature THA is lower and the engine fuel is harder to vaporize. Further, the higher the alcohol concentration AD is, the higher the target bypass amount Bp is set.

  Next, the electric motor 12a of the supercharger 12 is driven based on the target supercharging pressure Pp (S240). Here, the rotational speed of the electric motor 12a is controlled so that the target boost pressure Pp is obtained.

  Further, the flow path switching valve 40 is driven based on the target bypass amount Bp (S250). Here, the valve opening degree of the flow path switching valve 40 is controlled so that the target bypass amount Bp is obtained.

  Next, it is determined whether or not the internal combustion engine 1 has been completely detonated (S130). If the detonation has not been completed (S130: NO), the processes of step S240 and step S250 are repeated until the detonation is complete. Executed.

  On the other hand, when the explosion is complete (S130: YES), the electric motor 12a of the supercharger 12 is stopped (S140), and the flow path switching valve 40 is switched to the intercooler side (S150). Then, this process ends.

According to this embodiment described above, the following functions and effects can be obtained in addition to the functions and effects of the second embodiment.
(8) When the intake air temperature THA before supercharging is high, the alcohol fuel is easily vaporized, and the influence of the alcohol concentration on the low-temperature startability is reduced. Therefore, the target boost pressure Pp of the intake air is variably set based on the alcohol concentration AD in the engine fuel and the intake air temperature THA before supercharging. Therefore, when the intake air is supercharged in order to improve the low temperature startability, knocking or the like that is likely to occur when the intake air temperature rises can be more suitably suppressed.

  (9) When the intake air temperature THA before supercharging is high, the alcohol fuel is easily vaporized, and the influence of the alcohol concentration on the low-temperature startability is reduced. Therefore, the supercharged intake air is introduced into the bypass passage 60. The amount, that is, the bypass amount B can be reduced. Therefore, the target bypass amount Bp is variably set based on the alcohol concentration AD and the intake air temperature THA before supercharging. Therefore, when introducing the supercharged intake air into the bypass passage 60 in order to improve the cold startability, knocking or the like that is likely to occur due to the introduction of the high-temperature intake air into the combustion chamber is more suitably suppressed. Will be able to.

  In the present embodiment, the target boost pressure Pp and the target bypass amount Bp of intake air may be variably set based only on the intake air temperature THA before supercharging. Even in this case, when the intake air is supercharged in order to improve the low temperature startability, it is possible to suitably suppress the above-described inconvenience caused by the rise in the intake air temperature. Further, in order to improve the low temperature startability, the occurrence of knocking or the like can be suitably suppressed when the supercharged intake air is introduced into the bypass passage 60.

Moreover, each said embodiment can also be changed and implemented as follows.
-In 2nd and 3rd embodiment, it is good also considering either one of the target supercharging pressure Pp and the target bypass amount Bp as a fixed value.

  As described above, since the alcohol fuel is easily vaporized when the intake air temperature THA before supercharging is high, the influence of the alcohol concentration on the low-temperature startability is reduced. Accordingly, in the first to third embodiments, it may be determined based on the intake air temperature THA whether or not the intake air is supercharged by the supercharger 12. Also in this case, unnecessary supercharging can be suppressed as compared with the case where supercharging is always performed when starting the engine. In this case, the intake air temperature when the low-temperature startability deteriorates to an unacceptable extent is examined in advance, and the intake air temperature is set as the start lower limit value L. Then, when the intake air temperature THA is equal to or lower than the starting lower limit value L, it may be determined that the supercharger 12 performs supercharging.

  Similarly, in the first to third embodiments, whether to introduce the supercharged intake air into the bypass passage 60 may be determined based on the intake air temperature THA. Also in this case, when the engine is started, compared with the case where the supercharged intake air is always introduced into the bypass passage 60, the occurrence frequency of the above-described problem, that is, the problem that knocking or the like is likely to occur can be suppressed. It becomes like this. In this case as well, it may be determined that the supercharged intake air is introduced into the bypass passage 60 when the intake air temperature THA is equal to or lower than the starting lower limit value L.

  In this modification, the control device 25 may execute the execution determination process shown in FIG. That is, the intake air temperature THA is read and compared with the starting lower limit value L (S500). If the intake air temperature THA is lower than the starting lower limit value L (S500: YES), the intake air temperature increasing process in each of the above embodiments is executed. In step S510, the present process is terminated. On the other hand, when the intake air temperature THA is equal to or higher than the starting lower limit value L (S500: NO), the execution of the intake air temperature rise process in each of the above embodiments is prohibited (S520), and this process is terminated. Variations can be implemented.

  -In 1st-3rd embodiment and its modification, you may make it abbreviate | omit various processes regarding the drive control of the bypass passage 60, the flow-path switching valve 40, and the flow-path switching valve 40. FIG. Even in this case, the above-described effects can be obtained by supercharging the intake air.

In the second and third embodiments and modifications thereof, the process of comparing the alcohol concentration AD with the determination value α (the process of step S210) may be omitted.
-The higher the intake air temperature THA, the more easily the alcohol fuel is vaporized. Therefore, even if the alcohol concentration is high, engine startability can be ensured to some extent. Therefore, the determination value α may be variably set based on the intake air temperature THA. In this case, as the intake air temperature THA becomes higher, the determination value α becomes larger. As the intake air temperature THA becomes higher, supercharging by the supercharger 12 or introduction of intake air into the bypass passage 60 is performed. It is desirable to be able to suppress it.

The supercharger 12 is a type of supercharger that supercharges intake air by rotation of a compressor turbine, but may be changed to a supercharger that supercharges intake air by other methods.
In the first embodiment, the intake air is supercharged using the electric supercharger 12. In addition, as shown in FIG. You may make it supercharge using the supercharger with which driving force is transmitted from the crankshaft 13 which is an output shaft of the internal combustion engine 1, what is called a mechanical drive supercharger 200. FIG. The supercharger 200 includes a pair of rotors and the like inside thereof, and the intake air is supercharged as each rotor rotates. The drive shafts of these rotors are connected to the crankshaft 13 via switching means that can select transmission and disconnection of the driving force, for example, the clutch mechanism 201. When supercharging is performed, the clutch mechanism 201 is brought into a state capable of transmitting the driving force in response to a control signal from the control device 25. When such a supercharger is provided, the crankshaft 13 is rotated by cranking by switching the state of the clutch mechanism 201 so that the driving force from the crankshaft 13 is transmitted to the supercharger 200 when the engine is started. It is possible to supercharge the intake and intake air by using it. By the way, for those that can change the driving force transmitted from the crankshaft 13 to the supercharger, the supercharging pressure can be arbitrarily changed regardless of the engine rotational speed by changing the driving force. Is possible. Therefore, if the supercharger can arbitrarily change the supercharging pressure, the supercharger 12 in the second and third embodiments can be changed to such a supercharger.

The schematic diagram which shows the structure of the internal combustion engine to which this is applied about 1st Embodiment which actualized the internal combustion engine concerning this invention. The flowchart which shows the process sequence about the intake air temperature rise process in the embodiment. The schematic diagram which shows the structure of the internal combustion engine to which this is applied about 2nd Embodiment which actualized the internal combustion engine concerning this invention. The flowchart which shows the process sequence about the intake air temperature rise process in the embodiment. The flowchart which shows the process sequence about the intake air temperature rise process performed in 3rd Embodiment. The flowchart which shows the process sequence about the feasibility process performed in the modification of 1st-3rd embodiment. The schematic diagram which shows the structure of the internal combustion engine in the modification of 1st Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine, 2 ... Cylinder head, 3 ... Intake passage, 4a-4d ... Fuel injection valve, 6 ... Flywheel, 7 ... Intake manifold, 8 ... Exhaust manifold, 9 ... Delivery pipe, 10 ... Fuel pump, 11 ... Fuel tank, 12 ... supercharger, 12a ... electric motor, 13 ... crankshaft, 16 ... throttle valve, 18 ... intercooler, 19 ... thermal air flow meter, 25 ... control device, 24 ... ignition switch, 26 ... exhaust passage 27 ... Fuel piping, 40 ... Flow path switching valve, 50 ... Cooling passage, 60 ... Bypass passage, 70 ... Starter motor, 71 ... Pinion gear, 80 ... Alcohol sensor, 200 ... Supercharger, 201 ... Clutch mechanism, # 1 ... 1st cylinder, # 2 ... 2nd cylinder, # 3 ... 3rd cylinder, # 4 ... 4th cylinder.

Claims (14)

In an internal combustion engine that can use alcohol fuel as engine fuel,
A supercharger for supercharging the intake air;
An internal combustion engine comprising: a supercharging control unit that performs supercharging control of intake air by the supercharger when starting the internal combustion engine. The internal combustion engine according to claim 1,
Concentration detection means for detecting alcohol concentration in engine fuel is provided,
The internal combustion engine, wherein the supercharging control means determines whether or not to supercharge intake air by the supercharger based on the alcohol concentration. The internal combustion engine according to claim 1,
Intake temperature detection means for detecting the intake air temperature before supercharging,
The internal combustion engine, wherein the supercharging control means determines whether or not to supercharge intake air by the supercharger based on the intake air temperature. The internal combustion engine according to claim 1,
Concentration detection means for detecting alcohol concentration in engine fuel is provided,
The internal combustion engine, wherein the supercharging control means variably sets a supercharging pressure of intake air based on the alcohol concentration. The internal combustion engine according to claim 1,
An intake air temperature detecting means for detecting the intake air temperature before supercharging,
The internal combustion engine, wherein the supercharging control means variably sets a supercharging pressure of intake air based on the intake air temperature. The internal combustion engine according to claim 1,
Concentration detecting means for detecting alcohol concentration in engine fuel;
An intake air temperature detecting means for detecting the intake air temperature before supercharging,
The internal combustion engine, wherein the supercharging control means variably sets a supercharging pressure of intake air based on the alcohol concentration and the intake air temperature. The internal combustion engine according to any one of claims 1 to 6, wherein the supercharger is an electric supercharger that is driven by an electric motor. The supercharger is a supercharger to which a driving force is transmitted from an output shaft of the internal combustion engine, and includes a switching unit capable of selecting transmission and disconnection of the driving force. The internal combustion engine according to item. The internal combustion engine according to any one of claims 1 to 8,
A cooling passage for cooling the intake air supercharged by the supercharger;
A bypass passage for introducing the supercharged intake air into the combustion chamber without passing through the cooling passage;
Adjusting means for adjusting the amount of bypass introduced into the bypass passage in the supercharged intake air;
An internal combustion engine comprising: bypass control means for controlling the bypass amount of the supercharged intake air when starting the internal combustion engine. The internal combustion engine according to claim 9,
Concentration detection means for detecting alcohol concentration in engine fuel is provided,
The internal combustion engine, wherein the bypass control means determines whether or not to introduce the supercharged intake air into the bypass passage based on the alcohol concentration. The internal combustion engine according to claim 9,
Intake temperature detection means for detecting the intake air temperature before supercharging,
The internal combustion engine, wherein the bypass control means determines whether or not to introduce the supercharged intake air into the bypass passage based on the intake air temperature. The internal combustion engine according to claim 9,
Concentration detection means for detecting alcohol concentration in engine fuel is provided,
The internal combustion engine, wherein the bypass control means variably sets the bypass amount based on the alcohol concentration. The internal combustion engine according to claim 9,
An intake air temperature detecting means for detecting the intake air temperature before supercharging,
The internal combustion engine, wherein the bypass control means variably sets the bypass amount based on the intake air temperature. The internal combustion engine according to claim 9,
Concentration detecting means for detecting alcohol concentration in engine fuel;
An intake air temperature detecting means for detecting the intake air temperature before supercharging,
The internal combustion engine, wherein the bypass control means variably sets the bypass amount based on the alcohol concentration and the intake air temperature.

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