JP2009156155A - Internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress plug wetting phenomenon when the evaporation characteristic of fuel is bad. <P>SOLUTION: An internal combustion engine includes a compression ratio/expansion ratio variable means (intake valve variable means 32) which is capable of varying the relationship in magnitude between actual compression ratio and actual expansion ratio, and is characterized by including a fuel evaporation characteristic determination means (electronic control unit 1), and a compression ratio/expansion ratio control means (electronic control unit 1) which controls the compression ratio/expansion ratio variable means such that the actual compression ratio of this evaporation characteristic becomes larger than in the case of higher evaporation characteristic, when the evaporation characteristic of fuel F determined by this evaporation characteristic determination means shows lower evaporation characteristic. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an internal combustion engine that can be operated using fuels having different fuel properties and can be operated even when an expansion ratio is larger than a compression ratio.

  In recent years, in the automobile industry, various efforts have been made to cope with changes in the environment surrounding automobiles. For example, in the field of internal combustion engines, efforts have been made for so-called multi-fuel internal combustion engines that can be operated even with fuels having different fuel properties. A vehicle equipped with this kind of multi-fuel internal combustion engine is generally called a flexible fuel vehicle (FFV). For example, any of gasoline fuel, alcohol fuel, or a mixed fuel thereof is used. However, it is known to improve the environmental performance such as the suppression of the consumption of fossil fuels such as gasoline fuel, which can be operated and the limits of reserves continue to be sought. For example, the following Patent Document 1 discloses a multi-fuel internal combustion engine that is operated using an alcohol mixed fuel composed of gasoline fuel and alcohol fuel.

  In the field of internal combustion engines, there is a so-called Atkinson cycle (or Miller cycle) that increases thermal efficiency while suppressing the occurrence of knocking by making the actual expansion ratio larger than the actual compression ratio, thereby improving fuel efficiency. The ones adopted are also known. For example, this type of internal combustion engine is disclosed in Patent Document 2 below.

  Patent Document 3 listed below relates to a technique for controlling the advance of the closing timing of the intake valve when the alcohol concentration of the fuel is high, thereby increasing the valve overlap so as to suppress emission of formaldehyde. It is disclosed. Patent Document 4 below discloses a technique for controlling the valve overlap amount in accordance with the fuel property so that the drivability remains unchanged even if the fuel property changes. In the technique of Patent Document 4, the fuel property is determined as light, medium, or heavy, and the valve overlap amount is reduced as the fuel is heavier. Patent Document 5 below discloses a technique for controlling the advance timing of the intake valve closing timing when the fuel has a low octane number fuel compared to a high octane number fuel, thereby obtaining a high torque.

JP-A-2-305335 JP 2004-52551 A Japanese Patent Laid-Open No. 5-1574 JP 11-210509 A JP 2001-271682 A

  By the way, in general, an internal combustion engine often supplies a larger amount of fuel into the combustion chamber when the engine is cold during the warm-up operation than after the completion of the warm-up operation. End up. Conventionally, in the field of internal combustion engines, attention has been paid to the above-described operation in the Atkinson cycle as a technique that not only eliminates such inconvenience but also can improve fuel consumption performance even after the completion of warm-up operation.

  However, when the operation in the Atkinson cycle is applied to the above-described multi-fuel internal combustion engine, the following inconvenience occurs depending on the state of the engine and the fuel property of the fuel supplied to the combustion chamber. For example, the higher the alcohol concentration of the fuel, the worse the evaporation characteristics. Therefore, when the fuel used has low evaporation characteristics and the engine temperature is low, the injected fuel is in a condition that does not easily evaporate. There is a risk of floating and adhering to the ignition center of the spark plug, causing a so-called plug covering phenomenon. For this reason, in this case, despite the fact that even the conditions that make it difficult to ignite the fuel are all the same, it is much more difficult to ignite and it is highly likely that starting itself is impossible at low temperature starting. . This can occur regardless of whether it is a so-called port injection type internal combustion engine or a so-called in-cylinder direct injection type internal combustion engine, but the in-cylinder leading the injected fuel to the ignition center of the spark plug. It can be said that the direct injection type appears more prominently. When the operation in the Atkinson cycle is carried out under such conditions, the actual compression ratio becomes low, so that more fuel remains as droplet fuel in the combustion chamber, causing plug covering phenomenon. The situation has become difficult to avoid.

  Therefore, an object of the present invention is to provide an internal combustion engine that can improve the disadvantages of the conventional example and suppress the plug covering phenomenon when the fuel evaporation characteristic is poor.

  In order to achieve the above object, according to the first aspect of the present invention, there is provided an internal combustion engine having a compression ratio / expansion ratio variable means capable of changing a relationship between the actual compression ratio and the actual expansion ratio. Fuel evaporation characteristic determining means for determining the evaporation characteristic of the supplied fuel, and when the fuel evaporation characteristic determined by the fuel evaporation characteristic determining means shows a low evaporation characteristic, the evaporation characteristic is higher than the high evaporation characteristic. Compression ratio / expansion ratio control means for controlling the compression ratio / expansion ratio variable means so as to increase the actual compression ratio is provided.

  In order to achieve the above object, according to a second aspect of the present invention, in the internal combustion engine according to the first aspect, when the fuel evaporation characteristic is a high evaporation characteristic, the actual expansion ratio is made larger than the actual compression ratio. Therefore, the compression ratio / expansion ratio control means is configured. When the compression ratio / expansion ratio control means is operated with the actual expansion ratio larger than the actual compression ratio, the fuel evaporation characteristic determination means determines that the fuel evaporation characteristic is the low evaporation characteristic. The compression ratio / expansion ratio variable means is controlled so as to increase the actual compression ratio as compared with the case where the evaporation characteristic is a high evaporation characteristic.

  In the internal combustion engine according to claim 1 or 2, since the compression end temperature rises by increasing the actual compression ratio, even if a fuel with low evaporation characteristics is used, the fuel is formed into droplets in the combustion chamber. Can be suppressed. Therefore, according to the internal combustion engine of the first or second aspect, the plug covering phenomenon caused by the droplet fuel can be suppressed.

  Here, the compression ratio / expansion ratio control means is preferably configured to increase the actual compression ratio in accordance with the evaporation characteristics of the fuel, as in the third aspect of the invention.

  Further, the compression ratio / expansion ratio variable means can utilize intake valve opening / closing timing variable means capable of changing the opening / closing timing of the intake valve. In this case, since the compression end temperature increases while the actual compression ratio increases as the closing timing of the intake valve approaches the bottom dead center, the compression ratio / expansion ratio control means can increase the actual compression ratio. The intake valve opening / closing timing variable means may be controlled so that the closing timing of the intake valve approaches the bottom dead center.

  In this case, the compression ratio / expansion ratio control means can vary the intake valve opening / closing timing so that the closing timing of the intake valve is at or near the bottom dead center when the actual compression ratio is increased. It is preferable to be configured to control the means.

  Further, the compression ratio / expansion ratio variable means may be configured to further have a function of changing the operating angle of the intake valve and a function of changing the lift amount of the intake valve. Good. In this case, the compression ratio / expansion ratio control means controls the advance of the closing timing of the intake valve in order to increase the actual compression ratio, so that the opening timing of the intake valve is advanced from the top dead center. If so, the opening timing of the intake valve is at least retarded and the lift amount of the intake valve is increased.

  When the valve closing timing of the intake valve is advanced to increase the actual compression ratio, the valve closing timing is used to keep the intake valve operating angle constant and to minimize fluctuations in the intake air amount. The valve opening timing is also advanced by the same amount as the advance amount. However, when the valve opening timing is advanced from the top dead center in accordance with the advance control of the valve opening timing, the intake valve and the piston may interfere with each other. The internal combustion engine according to claim 6 controls the intake valve opening timing by at least retarding and increasing the lift amount of the intake valve, thereby suppressing the intake air amount fluctuation and suppressing the interference between the intake valve and the piston. By avoiding this, it is possible to suppress the plug covering phenomenon which is the main purpose.

  The internal combustion engine according to the present invention raises the compression end temperature by increasing the actual compression ratio and uses a fuel with low evaporation characteristics (particularly, using a fuel with low evaporation characteristics when the engine is cold). Even when the plug is covered, it is possible to prevent the fuel from becoming droplets and suppress the plug covering phenomenon. For this reason, the internal combustion engine can ensure engine output, and can also ensure startability at low temperature start.

  Embodiments of an internal combustion engine according to the present invention will be described below in detail with reference to the drawings. The present invention is not limited to the embodiments.

  A first embodiment of an internal combustion engine according to the present invention will be described with reference to FIGS.

  The internal combustion engine of the first embodiment is operated even when using fuels having different fuel properties such as hydrocarbon fuels such as gasoline fuel, alcohol fuels (ethanol, methanol, butanol, etc.) or alcohol mixed fuels. This is a multi-fuel internal combustion engine mounted on a so-called flexible fuel vehicle. The alcohol mixed fuel is a mixed fuel of an alcohol fuel and at least one fuel having a different fuel property, and here, it is assumed that it is mixed with a hydrocarbon fuel (for example, gasoline fuel). In this alcohol-mixed fuel, the fuel properties change according to the fuel mixing ratio of the reference fuel.

  The internal combustion engine is configured to enable operation in a so-called Atkinson cycle (or Miller cycle) in which the expansion ratio is larger than the compression ratio. The electronic control unit (ECU) shown in FIG. 1 performs various control operations such as combustion control. The electronic control unit 1 includes a CPU (Central Processing Unit) (not shown), a ROM (Read Only Memory) that stores a predetermined control program and the like, and a RAM (Random Access Memory) that temporarily stores the calculation result of the CPU. , And a backup RAM for storing information prepared in advance.

  First, the configuration of the internal combustion engine of the first embodiment will be described with reference to FIG. Although only one cylinder is shown in FIG. 1, the present invention is not limited to this, and can be applied to a multi-cylinder multifuel internal combustion engine. In the first embodiment, description will be made assuming that a plurality of cylinders are provided.

  The internal combustion engine includes a cylinder head 11, a cylinder block 12, and a piston 13 that form a combustion chamber CC. Here, the cylinder head 11 and the cylinder block 12 are fastened with bolts or the like via the head gasket 14 shown in FIG. 1, and the recess 11a on the lower surface of the cylinder head 11 and the cylinder bore 12a of the cylinder block 12 formed thereby. The piston 13 is disposed so as to be capable of reciprocating in the space. And the combustion chamber CC mentioned above is comprised by the space enclosed by the wall surface of the recessed part 11a of the cylinder head 11, the wall surface of the cylinder bore 12a, and the top surface 13a of the piston 13. FIG.

  This internal combustion engine sends air and fuel into the combustion chamber CC in accordance with operating conditions such as engine speed and engine load, and executes combustion control in accordance with the operating conditions. The air is sucked from the outside through the intake passage 21 and the intake port 11b of the cylinder head 11 shown in FIG. On the other hand, the fuel is supplied using the fuel supply device 50 shown in FIG.

  First, the air supply path will be described.

  On the intake passage 21 of the internal combustion engine, an air cleaner 22 for removing foreign matters such as dust contained in air introduced from the outside, and an intake air amount detection means 23 for detecting the amount of intake air from the outside are provided. ing. As the intake air amount detection means 23, an air amount detection sensor such as an air flow meter that directly detects the intake air amount GA, an intake pipe pressure sensor that detects the pressure in the intake passage 21 (ie, intake pressure), and the like are conceivable. . When the latter intake pipe pressure sensor is used, the intake air amount is obtained indirectly from the intake pressure and the engine speed. In this internal combustion engine, the detection signal of the intake air amount detection means 23 is sent to the electronic control unit 1, and the electronic control unit 1 calculates the intake air amount, the engine load and the like based on the detection signal. The engine speed can be grasped from the detection signal of the crank angle sensor 16 that detects the rotation angle of the crankshaft 15.

  A throttle valve 24 capable of adjusting the flow rate of the air flowing into the combustion chamber CC and a throttle valve for opening and closing the throttle valve 24 on the intake passage 21 downstream of the intake air amount detection means 23. And an actuator 25. In the electronic control unit 1 of the first embodiment, the throttle valve actuator 25 is driven and controlled according to the operating conditions, and the throttle valve that adjusts the valve opening angle of the throttle valve 24 so that the valve opening degree according to the operating conditions is obtained. Control means are provided. Here, the throttle valve actuator 25 and the throttle valve control means constitute a throttle valve opening control means. Further, this internal combustion engine is provided with a throttle opening sensor 26 that detects the valve opening of the throttle valve 24 and transmits the detection signal to the electronic control unit 1.

  On the other hand, one end of the intake port 11b opens into the combustion chamber CC, and an intake valve 31 for opening and closing the opening is disposed at the opening portion. The number of openings may be one or more, and an intake valve 31 is provided for each opening. Therefore, in this internal combustion engine, air is sucked into the combustion chamber CC from the intake port 11b by opening the intake valve 31 and closed to the combustion chamber CC by closing the intake valve 31. Air inflow is blocked.

  Here, the internal combustion engine of the first embodiment is provided with the intake valve variable means 32 shown in FIG. 1 for changing the operation of the intake valve 31. The intake valve varying means 32 of the first embodiment is an intake valve opening / closing timing varying means such as a so-called variable valve timing mechanism that changes the opening / closing timing of the intake valve 31, and its operation is the intake valve operation control of the electronic control unit 1. Controlled by means. In other words, in the internal combustion engine of the first embodiment, the intake valve operation control means drives and controls the intake valve variable means 32 in accordance with the operating conditions and the like, whereby the opening and closing timing of the intake valve 31 is in accordance with the operating conditions and the like. It can be changed to a suitable one. In this internal combustion engine, a so-called electromagnetically driven valve capable of opening and closing the intake valve 31 at a desired opening and closing timing using electromagnetic force is obtained in order to obtain the same effect as the intake valve variable means 32. May be used.

  Next, the fuel supply device 50 will be described.

  As this fuel supply device 50, the fuel in one fuel tank is injected into the intake port 11b and / or into the combustion chamber CC, and the fuel having different fuel properties stored in a plurality of fuel tanks is mixed into the fuel mixing device. It can be considered that the mixture is mixed in the intake port 11b and / or injected into the combustion chamber CC. In this embodiment, a port injection type in which the fuel F stored in one fuel tank 41 is injected into the intake port 11b and led to the combustion chamber CC together with the intake air is shown as a representative example.

  Specifically, the fuel supply device 50 distributes the fuel F in the fuel passage 51 to each cylinder, and a feed pump 52 as a fuel pump that sucks the fuel F from the fuel tank 41 and sends it to the fuel passage 51. A fuel delivery pipe 53 and a fuel injection valve (fuel injection means) 54 for each cylinder that injects fuel F supplied from the fuel delivery pipe 53 into each intake port 11b.

  The fuel supply device 50 controls the feed pump 52 and the fuel injection valve 54 to be controlled by the fuel injection control means of the electronic control unit 1 according to the operating conditions, whereby the target fuel injection amount and the fuel corresponding to the operating conditions are controlled. The fuel F is configured to be injected under fuel injection conditions such as the injection timing and the fuel injection period. For example, the fuel injection control means causes the fuel F to be sucked up from the fuel tank 41 by the feed pump 52 and causes the fuel injection valve 54 to perform injection under the fuel injection conditions corresponding to the operating conditions.

  The fuel F supplied to the intake port 11b in this way is supplied into the combustion chamber CC together with the opening of the intake valve 31, while being mixed with the air described above in the intake port 11b. Here, the target fuel injection amount of the fuel F fed into the combustion chamber CC and the intake air amount of the air are determined by the air-fuel ratio control means of the electronic control unit 1 according to the target air-fuel ratio corresponding to the operating conditions. For example, the air-fuel ratio control means executes the air-fuel ratio control to the target air-fuel ratio by adjusting the fuel injection amount of the fuel F.

  The air-fuel ratio-controlled air-fuel mixture in the combustion chamber CC is burned by the ignition operation of the spark plug 61 when the ignition timing according to the operating conditions is reached. The in-cylinder gas (combustion gas) after being burned is discharged from the combustion chamber CC to the exhaust port 11c shown in FIG. 1 and discharged to the atmosphere through the exhaust passage 81.

  An exhaust valve 71 that opens and closes an opening between the exhaust port 11c and the combustion chamber CC is disposed. The number of openings may be one or more, and the exhaust valve 71 described above is provided for each opening. Accordingly, in this internal combustion engine, combustion gas is discharged from the combustion chamber CC to the exhaust port 11c by opening the exhaust valve 71, and closing the exhaust valve 71 to the combustion gas exhaust port 11c. Is blocked.

  Here, the internal combustion engine of the first embodiment is provided with the exhaust valve variable means 72 shown in FIG. 1 for changing the operation of the exhaust valve 71. The exhaust valve variable means 72 of the first embodiment is an exhaust valve open / close timing variable means such as a so-called variable valve timing mechanism for changing the open / close timing of the exhaust valve 71, similar to the intake valve variable means 32 described above. The operation is controlled by the exhaust valve operation control means of the electronic control unit 1. In other words, in the internal combustion engine of the first embodiment, the exhaust valve operation control means drives and controls the exhaust valve variable means 72 in accordance with the operating conditions and the like, whereby the opening / closing timing of the exhaust valve 71 is in accordance with the operating conditions and the like. It can be changed to a suitable one. In this internal combustion engine, a so-called electromagnetically driven valve capable of opening / closing the exhaust valve 71 at a desired opening / closing timing using electromagnetic force is obtained in order to obtain the same effect as the exhaust valve variable means 72. May be used.

An exhaust purification device 82 is disposed on the exhaust passage 81 to purify harmful components in the exhaust gas. Further, on the exhaust passage 81 of the first embodiment, an exhaust sensor 83 is disposed on the upstream side (combustion chamber CC side) of the exhaust purification device 82. The exhaust sensor 83 is a sensor for obtaining information when calculating or estimating the actual air-fuel ratio of the air-fuel mixture in the combustion chamber CC. For example, as the exhaust sensor 83, an O ₂ sensor that detects the amount of oxygen in the exhaust gas or an A / F sensor (broadband λ sensor) that detects the excess air ratio (λ value) in the exhaust gas can be used. .

  Further, in the internal combustion engine of the first embodiment, the compression ratio / expansion that can change the relationship between the actual compression ratio and the actual expansion ratio in order to realize the operation in the above-described Atkinson cycle (Miller cycle). A ratio variable means is provided. The operation of the compression ratio / expansion ratio variable means is controlled by the compression ratio / expansion ratio control means of the electronic control unit 1, and is excellent in fuel consumption performance by making the actual expansion ratio larger than the actual compression ratio. Realize operation in the Atkinson cycle (Miller cycle).

  The compression ratio / expansion ratio variable means of the first embodiment varies the actual compression ratio (that is, makes the actual compression ratio smaller than the actual expansion ratio), and thereby makes the actual expansion ratio larger than the actual compression ratio. And Specifically, in order to make the actual compression ratio smaller than the actual expansion ratio, for example, the valve closing timing of the intake valve 31 is advanced or compared with the normal Otto cycle operation in which the actual compression ratio and the actual expansion ratio are equal. You can delay. That is, when the valve closing timing of the intake valve 31 is controlled to advance than during normal Otto cycle operation, the intake valve 31 is closed earlier than the bottom dead center, so that the combustion chamber CC is sufficiently closed. Since the compression process is started without taking in air, the actual compression ratio can be reduced. On the other hand, when the closing timing of the intake valve 31 is retarded than during normal Otto cycle operation, the intake valve 31 closes at a later time after bottom dead center and is once taken into the combustion chamber CC. Since a part of the air is returned to the intake port 11b and enters the compression stroke, the actual compression ratio can be reduced. For this reason, as the compression ratio / expansion ratio variable means of the first embodiment, an intake valve closing timing variable means capable of changing the closing timing of the intake valve 31 may be used. In the first embodiment, as described above, the intake valve variable means 32 serving as the intake valve opening / closing timing variable means is prepared, and the working angle of the intake valve 31 (the interval from the valve opening timing to the valve closing timing). The intake valve variable means 32 is used as the compression ratio / expansion ratio variable means from the viewpoint of suppressing the amount of variation in the intake air amount as much as possible without changing the intake valve 31 opening period.

  The compression ratio / expansion ratio control means of the first embodiment lowers the closing timing of the intake valve 31 by driving the intake valve variable means 32 when the internal combustion engine is operated in the Atkinson cycle (Miller cycle). The actual compression ratio is made smaller than the actual expansion ratio by advancing or retarding the point, thereby reducing the actual compression ratio. Further, during the operation, in order to suppress the fluctuation amount of the intake air amount due to the change in the closing timing of the intake valve 31, the valve opening timing advances in the same direction as the valve closing timing while maintaining the operating angle of the intake valve 31. Angle or retard. In the combustion chamber CC, even if the operating angle of the intake valve 31 is maintained as described above, the intake air amount is smaller than that during normal Otto cycle operation.

  By the way, when the operation in the Atkinson cycle (Miller cycle) is realized by the advance angle control or the retard angle control of the closing timing of the intake valve 31, this internal combustion engine not only lowers the actual compression ratio but also as described above. In addition, since the intake air amount into the combustion chamber CC is also reduced compared to the normal time, the in-cylinder temperature at the compression top dead center (so-called compression end temperature) is lowered. Here, in the internal combustion engine of the first embodiment that enables the operation with the fuel F having various fuel properties, the low evaporation characteristic fuel (that is, the fuel with a high alcohol concentration such as a single component alcohol fuel). Sometimes F is supplied into the combustion chamber CC. For this reason, when the engine temperature is low and the operation in the Atkinson cycle (Miller cycle) is performed in such a case as when the engine is cold, the low evaporation characteristics supplied in the combustion chamber CC of the internal combustion engine are obtained. There is a high possibility that the fuel F cannot be sufficiently evaporated and a part of the fuel F floats as droplet fuel. In this case, the droplet fuel may adhere to the ignition center of the spark plug 61 and cause a so-called plug covering phenomenon. The plug covering phenomenon at that time is likely to occur as the fuel injection amount increases. In particular, since the plug covering phenomenon is highly likely to occur during a cold start when the in-cylinder temperature is the lowest, the start of the internal combustion engine may be impossible during the cold start.

  The internal combustion engine that can be operated in the Atkinson cycle (Miller cycle) is also applied to a so-called hybrid vehicle that also uses a motor generator as a vehicle drive source. Specifically, in this hybrid vehicle, an operation in the Atkinson cycle (Miller cycle) is executed in order to reduce the load on the motor generator when the internal combustion engine is activated. That is, by operating the internal combustion engine in the Atkinson cycle (Miller cycle), the effect of depressurization in the combustion chamber CC appears, so that the load on the motor generator is reduced. However, when the plug covering phenomenon is caused as described above, there is a possibility that the internal combustion engine cannot be started in the first place. Therefore, for example, improvement of the output performance of the vehicle by assisting the output of the internal combustion engine is required. Sometimes, there is a possibility that the requested output performance cannot be exhibited. In order to improve fuel efficiency, this hybrid vehicle may be operated in the Atkinson cycle (mirror cycle) even during normal operation after startup.

  Therefore, in the first embodiment, when operating with the low evaporation characteristic fuel F when the engine is cold, compared to the normal Atkinson cycle (Miller cycle) operation, that is, when operating with the high evaporation characteristic fuel F The actual compression ratio is increased to increase the compression end temperature. The compression ratio / expansion ratio control means adjusts the amount by which the actual compression ratio is increased according to the evaporation characteristics of the fuel F, the fuel injection amount, and the like. The compression ratio / expansion ratio control means may allow the actual compression ratio to remain smaller than the actual expansion ratio as long as the actual compression ratio increases as a result. The actual compression ratio may be larger than the actual expansion ratio.

  Specifically, when operating with the low-evaporation characteristic fuel F when the engine is cold, the lower the dead-center of the intake valve 31 is, the lower the evaporation characteristic of the fuel F and the larger the fuel injection amount. The compression ratio / expansion ratio control means is configured to approach (BDC). That is, in this case, the closing timing of the intake valve 31 is set to the bottom dead center (BDC) or closer to the bottom dead center (BDC) depending on the evaporation characteristics of the fuel F, the fuel injection amount, and the like. Set to the advance side or retard side. Therefore, in this case, as shown in FIG. 2, the actual compression ratio increases and the compression end temperature can be increased.

  In addition, the electronic control unit 1 according to the first embodiment is provided with a fuel evaporation characteristic determination unit capable of grasping the evaporation characteristic of the fuel F. This fuel evaporation characteristic determination means grasps the current evaporation characteristic of the fuel F based on the fuel property information learned during the operation so far or the fuel property information detected or estimated at the present time. For example, the evaporation characteristic can be grasped by using a detection value of the alcohol concentration sensor 91 shown in FIG. 1 provided on the fuel supply device 50.

  Hereinafter, the operation of the internal combustion engine of the first embodiment when the engine is cold will be described based on the flowchart of FIG.

  First, the compression ratio / expansion ratio control means of the electronic control unit 1 according to the first embodiment detects the engine temperature T of the internal combustion engine (step ST5), and the engine temperature T is lower than the predetermined temperature α. It is determined whether or not (step ST10).

  For example, in the first embodiment, the engine cooling water temperature detected by the water temperature sensor 17 shown in FIG. In addition, the predetermined temperature α means that the fuel F has a low evaporation characteristic, and that the fuel F has an Atkinson cycle (Miller cycle) operation and an Otto cycle operation. What is necessary is just to set the minimum temperature among the engine temperatures which evaporate (that is, atomize) when supplied into the combustion chamber CC and hardly generate droplet fuel. In other words, the predetermined temperature α is equal to the fuel F supplied into the combustion chamber CC regardless of the evaporation characteristic of the fuel F and the operation mode. Can be said to be the lowest temperature among the engine temperatures at which the compression end temperature can be almost atomized at the compression top dead center.

  If it is determined in step ST10 that the engine temperature T is equal to or higher than the predetermined temperature α, the compression ratio / expansion ratio control means may indicate that the fuel F supplied into the combustion chamber CC has a low evaporation characteristic. It is determined that it will not evaporate and cause the plug covering phenomenon, and this calculation processing is finished. When the determination is made, the compression ratio / expansion ratio control means executes a normal Atkinson cycle (mirror cycle) operation with an actual expansion ratio larger than the actual compression ratio in order to improve fuel efficiency. Like that.

  On the other hand, when it is determined in step ST10 that the engine temperature T is lower than the predetermined temperature α and it is determined that the engine is cold, the fuel evaporation characteristic determining means of the electronic control unit 1 is in the combustion chamber CC. It is determined what kind of fuel property (specifically, evaporation characteristics) the fuel F supplied to (step ST15).

  Further, the air-fuel ratio control means of the electronic control unit 1 uses the fuel F based on the detected engine temperature T, fuel properties (evaporation characteristics) of the fuel F, engine speed, engine load (intake air amount), and the like. Is calculated (step ST20). The fuel injection amount is calculated during air-fuel ratio control that is normally performed in the technical field of internal combustion engines.

  The compression ratio / expansion ratio control means is based on the engine temperature T in step ST5, the fuel properties (evaporation characteristics) in step ST15, the fuel injection amount in step ST20, the engine speed, the engine load (intake air amount), and the like. Whether or not the closing timing of the intake valve 31 needs to be changed with respect to that during normal Atkinson cycle (Miller cycle) operation when the engine is cold (hereinafter referred to as “normally closing timing”). Judgment is made (step ST25).

  The normal valve closing timing to be compared here is, for example, the valve closing timing of the intake valve 31 when performing the Atkinson cycle (Miller cycle) operation when the engine is cold and the fuel F is highly evaporated. A preset valve closing angle that can be a compression end temperature that can atomize most of the fuel F in the combustion chamber CC (in other words, suppress plug plug phenomenon caused by droplet fuel). That is.

  Accordingly, in this step ST25, it is determined based on the engine temperature T or the like whether or not the fuel F in the combustion chamber CC can be almost atomized when operating with the normal valve closing timing. If the compression end temperature is so low that a part of the fuel may become droplet fuel, it is determined that the closing timing of the intake valve 31 needs to be changed. For example, when the fuel property (evaporation characteristic) of the fuel F is good even when the engine temperature T is low, or when the fuel injection amount is small, compression sufficient to atomize the fuel F even at the normal closing timing. It is determined that the end temperature can be obtained, and it is determined that there is no need to change the valve closing timing of the intake valve 31. Further, even when the engine temperature T is low and the fuel property (evaporation characteristic) is poor, if the fuel injection amount is small, the fuel F in the combustion chamber CC may be almost atomized. For this reason, when there is such a possibility, it is determined that the compression end temperature sufficient to atomize the fuel F can be obtained even when the valve closing timing is normally maintained, and there is no need to change the valve closing timing of the intake valve 31. . Note that the engine temperature T, the degree of fuel properties (evaporation characteristics), and the fuel injection amount in these cases may be prepared in advance, for example, as map data by conducting experiments and simulations.

  If it is determined in step ST25 that it is not necessary to change the valve closing timing of the intake valve 31, that is, if it is determined that a sufficient compression end temperature can be obtained even with the normal valve closing timing, the compression ratio / expansion ratio control is performed. The means ends this calculation process while keeping the closing timing of the intake valve 31 at the normal closing timing.

  On the other hand, when the compression ratio / expansion ratio control means determines that it is necessary to change the closing timing of the intake valve 31 in step ST25, the engine temperature T in step ST5 and the fuel property (evaporation characteristics) in step ST15. Intake that can raise the compression end temperature until the fuel F in the combustion chamber CC is almost atomized based on the fuel injection amount in step ST20, the engine speed, the engine load (intake air amount), and the like. The valve closing timing of the valve 31 is obtained (step ST30). In this step ST30, for example, the closing timing of the intake valve 31 is brought closer to the bottom dead center as the engine temperature T is lower, the evaporation characteristic is worse, and the fuel injection amount is larger.

  Then, the compression ratio / expansion ratio control means calculates the phase control amount of the intake valve 31 from the difference between the closing timing and the normal closing timing of the intake valve 31 obtained in step ST30 (step ST35).

  In step ST35, the difference in valve closing timing is directly used as the phase control amount. That is, if the operating angle of the intake valve 31 is changed, the amount of intake air changes greatly. Therefore, in the first embodiment, the closing timing of the intake valve 31 is changed to the bottom dead center side by the difference. At the same time, the valve opening timing of the intake valve 31 is also changed by the difference. In this case, if the valve closing timing of the intake valve 31 is controlled to advance, the valve opening timing of the intake valve 31 is also controlled to advance, and if the valve closing timing is controlled to retard, the intake valve opening timing is also controlled. The phase control amount is determined so that the retard angle is controlled.

  The compression ratio / expansion ratio control means of the first embodiment controls the intake valve variable means 32 so as to achieve the phase control amount obtained in step ST35, and executes phase control of the intake valve 31 (step ST40). .

  As a result, the valve opening timing and the valve closing timing of the intake valve 31 are changed with respect to the Atkinson cycle (mirror cycle) operation during normal engine cold. For this reason, in the internal combustion engine at that time, the closing timing of the intake valve 31 is changed to the bottom dead center side with respect to the Atkinson cycle (Miller cycle) operation when the engine is cold, so that the actual compression ratio is It becomes larger and the compression end temperature rises than during the Atkinson cycle (Miller cycle) operation.

  As described above, the internal combustion engine of the first embodiment is supplied into the combustion chamber CC by increasing the actual compression ratio and increasing the compression end temperature even when the low evaporation characteristic fuel F is used when the engine is cold. Further, since the evaporation (atomization) of the fuel F is promoted, the generation of droplet fuel in the combustion chamber CC is suppressed, and the plug covering phenomenon of the spark plug 61 can be suppressed. For this reason, in this internal combustion engine, the engine output can be ensured, and further the startability at the low temperature start can be ensured.

  A second embodiment of the internal combustion engine according to the present invention will be described with reference to FIGS.

  In the first embodiment described above, the phase of the intake valve 31 is changed corresponding to the new valve closing timing while maintaining the operating angle of the intake valve 31. For example, the phase of the intake valve 31 is changed from the upper diagram of FIG. 4 to the middle diagram. The upper diagram of FIG. 4 is a diagram showing the opening timing and closing timing of the intake valve 31 during normal Atkinson cycle (Miller cycle) operation. The closing timing of the intake valve 31 is lower than the bottom dead center. This is set on the retard side. On the other hand, the middle diagram of FIG. 4 is a diagram showing the opening timing and closing timing of the intake valve 31 when the low-evaporation characteristic fuel F is used when the engine is cold, and the phase of the intake valve 31 in the first embodiment. This is when only the change is executed and the closing timing of the intake valve 31 is advanced to the bottom dead center side.

  Here, depending on the position after the change of the closing timing of the intake valve 31 and the operating angle of the intake valve 31, when the phase of the intake valve 31 is changed to increase the actual compression ratio as in the first embodiment. 4, when the opening timing of the intake valve 31 is changed to the advance side with respect to the top dead center (TDC), as shown in the middle diagram of FIG. The valved intake valve 31 may collide with the piston 13 or the intake valve 31.

  Therefore, in the second embodiment, in addition to the phase control of the intake valve 31, the operating angle and lift amount of the intake valve 31 are also changed to avoid interference between the piston 13 and the intake valve 31.

  Specifically, the internal combustion engine of the second embodiment first changes the intake valve varying means 32 in the internal combustion engine of the first embodiment described above. The intake valve varying means 32 according to the second embodiment functions as an intake valve opening / closing timing varying means for changing the opening / closing timing of the intake valve 31 and as an intake valve working angle varying means for changing the operating angle of the intake valve 31. And a function as an intake valve lift amount varying means for changing the lift amount of the intake valve 31. In other words, in the internal combustion engine of the second embodiment, the intake valve operation control means of the electronic control device 1 drives and controls the intake valve variable means 32 according to the operating conditions and the like. And the lift amount can be changed to a suitable one according to the operating conditions. In the internal combustion engine of the second embodiment, an electromagnetically driven valve may be used to obtain the same operation effect as that of the intake valve varying means 32.

  In the second embodiment, the intake valve varying means 32 is used as the compression ratio / expansion ratio varying means as in the first embodiment. Accordingly, the operation of the intake valve variable means 32 is also controlled by the compression ratio / expansion ratio control means of the electronic control unit 1. The compression ratio / expansion ratio control means of the second embodiment has a control function related to the operating angle and lift amount of the intake valve 31 in addition to the same control function as that of the first embodiment.

  Here, when there is a possibility of interference between the piston 13 and the intake valve 31 as shown in the middle diagram of FIG. 4, the valve is opened at least from the position of the opening / closing timing of the intake valve 31 by the same phase control as in the first embodiment. The compression ratio / expansion ratio control means is configured to move the position of the time to or near top dead center. In other words, the compression ratio / expansion ratio control means changes the operating angle of the intake valve 31 by controlling the delay of at least the position of the valve opening timing toward the top dead center.

  Here, if the valve opening timing of the intake valve 31 is changed to near the top dead center, the operating angle of the intake valve 31 becomes small. Therefore, if the lift amount of the intake valve 31 is not changed, the intake air amount is reduced. It will decrease. Due to the reduction of the intake air amount, the fuel F in the combustion chamber CC is liable to be formed into droplets, and the engine output may be reduced. Therefore, in the second embodiment, the compression ratio / expansion ratio control means is configured to increase the lift amount of the intake valve 31 to compensate for the decrease in the intake air amount in order to suppress fluctuations in the intake air amount.

  For example, in the lower diagram of FIG. 4, the valve opening timing of the intake valve 31 is moved to the retard side from the top dead center and the valve closing timing of the first embodiment is changed as shown in the middle diagram of FIG. 4. The piston is moved slightly to the retard side than that by the phase control, and further, the lift amount of the intake valve 31 is increased in addition to the change of the working angle of the intake valve 31, thereby suppressing the fluctuation of the intake air amount. 13 and the intake valve 31 are avoided, and the main proposition of suppressing the plug covering phenomenon is achieved. That is, the lower diagram of FIG. 4 is a diagram showing the opening timing and closing timing of the intake valve 31 when using the low evaporation characteristic fuel F when the engine is cold, and only the phase control of the intake valve 31 in the first embodiment. In other words, the operation angle control and lift amount control of the intake valve 31 are also executed. 4 shows the opening / closing timing of the intake valve 31, and therefore the lift amount control is not shown in the lower diagram of FIG.

  Hereinafter, the operation of the internal combustion engine of the second embodiment when the engine is cold will be described based on the flowchart of FIG. Since steps ST5 to ST35 in FIG. 5 are the same as steps ST5 to ST35 in FIG. 3 of the first embodiment, description thereof will be omitted.

  The compression ratio / expansion ratio control means of the second embodiment obtains the phase control amount of the intake valve 31 in step ST35, and then the opening timing of the intake valve 31 by the phase control causes interference between the piston 13 and the intake valve 31. Judgment is made as to whether or not there is a possibility of causing it (step ST36).

  Here, if it is determined that the interference between the piston 13 and the intake valve 31 does not occur, the compression ratio / expansion ratio control means proceeds to step ST41 described later, and the phase of the intake valve 31 is determined based on the phase control amount of step ST35. To change. That is, in this case, the opening / closing timing of the intake valve 31 is changed by performing only the phase control of the intake valve 31 as in the first embodiment, and the plug cover of the spark plug 61 is made without causing the piston 13 and the intake valve 31 to interfere with each other. The phenomenon can be suppressed.

  On the other hand, the compression ratio / expansion ratio control means may cause interference between the piston 13 and the intake valve 31 in step ST36 due to the fact that the closing timing of the intake valve 31 is calculated to be advanced in step ST30. If it is determined that there is, the opening timing of the intake valve 31 that can avoid such interference is calculated (step ST37). In this step ST37, the valve opening timing of the intake valve 31 is obtained at or near the top dead center.

  Since the operating angle of the intake valve 31 is reduced by changing the valve opening timing in step ST37, the compression ratio / expansion ratio control means of the second embodiment is configured to reduce the intake air amount. A working angle and a lift amount are obtained (step ST38). In this step ST38, if a change in the intake air amount can be avoided only by an increase in the lift amount, only a new lift amount is calculated. If the increase in the operating angle and the lift amount are not intended, the change in the intake air amount is calculated. If it cannot be avoided, a new operating angle and lift amount are calculated.

  The compression ratio / expansion ratio control means includes the closing timing of the intake valve 31 obtained in step ST30, the opening timing of the intake valve 31 obtained in step ST37, and the operating angle of the intake valve 31 obtained in step ST38. Based on the lift amount, the opening / closing timing of the intake valve 31 that can avoid both the plug covering phenomenon and the interference between the piston 13 and the intake valve 31 is calculated (step ST39). For example, in this case, the closing timing of the intake valve 31 obtained in step ST30 is slightly moved to the retard side, and the opening timing of the intake valve 31 obtained in step ST37 is slightly advanced. And move.

  In this case, the compression ratio / expansion ratio control means drives and controls the intake valve variable means 32 so that the opening / closing timing recalculated in step ST39, and performs an Atkinson cycle (mirror cycle) operation when the engine is cold. The opening / closing timing of the intake valve 31 is changed with respect to the hour (step ST41).

  As a result, in the internal combustion engine at that time, the closing timing of the intake valve 31 is changed to the bottom dead center side than during the Atkinson cycle (mirror cycle) operation when the engine is cold, so the actual compression ratio is It becomes larger and the compression end temperature rises. Further, in the internal combustion engine at that time, the valve opening timing of the intake valve 31, the operating angle of the intake valve 31 and the lift amount are also adjusted as described above, so that the piston 13 and the intake air are suppressed while suppressing fluctuations in the intake air amount. Interference with the valve 31 can be avoided.

  Thus, the internal combustion engine of the second embodiment is supplied into the combustion chamber CC by raising the compression end temperature even when the low evaporation characteristic fuel F is used when the engine is cold, as in the first embodiment. Further, since the evaporation (atomization) of the fuel F is promoted, the generation of the droplet fuel can be suppressed, and the plug covering phenomenon of the spark plug 61 can be suppressed. In this case, since the interference between the piston 13 and the intake valve 31 can be avoided while suppressing fluctuations in the intake air amount, the fuel F in the combustion chamber CC can be formed into droplets as the intake air amount decreases. A decrease in engine output is also avoided. Therefore, the internal combustion engine of the second embodiment can more effectively suppress the occurrence of the plug covering phenomenon while avoiding interference between the piston 13 and the intake valve 31 and a decrease in engine output. For this reason, in this internal combustion engine, it is possible not only to ensure engine output and startability at low temperature start, but also to prevent damage to the piston 13 and the intake valve 31.

  As described above, the internal combustion engine according to the present invention is useful as a technique capable of suppressing the plug covering phenomenon even when the fuel evaporation characteristic is poor.

It is a figure shown about an example of the internal combustion engine which concerns on this invention. It is a figure explaining the relationship between the valve closing timing of an intake valve, an actual compression ratio, and compression end temperature. It is a flowchart explaining the arithmetic processing operation | movement of Example 1 of the internal combustion engine which concerns on this invention. It is a figure explaining the opening / closing timing of the intake valve of Example 2. FIG. It is a flowchart explaining the arithmetic processing operation | movement of Example 2 of the internal combustion engine which concerns on this invention.

Explanation of symbols

1 Electronic Control Unit 17 Water Temperature Sensor 31 Intake Valve 32 Intake Valve Variable Means 50 Fuel Supply Device 54 Fuel Injection Valve 61 Spark Plug 83 Exhaust Sensor 91 Alcohol Concentration Sensor CC Combustion Chamber F Fuel

Claims (6)

In an internal combustion engine provided with a compression ratio / expansion ratio variable means capable of changing the relationship between the actual compression ratio and the actual expansion ratio,
A fuel evaporation characteristic determining means for determining an evaporation characteristic of the fuel supplied to the combustion chamber; and when the fuel evaporation characteristic determined by the fuel evaporation characteristic determining means shows a low evaporation characteristic, the evaporation characteristic is a high evaporation characteristic. An internal combustion engine comprising: a compression ratio / expansion ratio control means for controlling the compression ratio / expansion ratio variable means so that the actual compression ratio becomes larger than in the case of the above.   The compression ratio / expansion ratio control means is configured to be able to operate with an actual expansion ratio larger than the actual compression ratio when the fuel evaporation characteristic is a high evaporation characteristic. When the fuel evaporation characteristic determining means determines that the fuel evaporation characteristic is a low evaporation characteristic when the fuel evaporation characteristic is increased, the fuel compression characteristic determination means determines that the actual compression ratio is larger than when the evaporation characteristic is a high evaporation characteristic. 2. The internal combustion engine according to claim 1, wherein the compression ratio / expansion ratio variable means is controlled.   The internal combustion engine according to claim 1 or 2, wherein the compression ratio / expansion ratio control means is configured to increase an actual compression ratio in accordance with an evaporation characteristic of the fuel. The compression ratio / expansion ratio variable means is intake valve opening / closing timing variable means capable of changing the opening / closing timing of the intake valve,
The compression ratio / expansion ratio control means is configured to control the intake valve opening / closing timing variable means to bring the closing timing of the intake valve close to bottom dead center when increasing the actual compression ratio. An internal combustion engine according to claim 1, 2 or 3.   The compression ratio / expansion ratio control means is configured to control the intake valve opening / closing timing variable means so that the closing timing of the intake valve is at or near the bottom dead center when the actual compression ratio is increased. The internal combustion engine according to claim 4. The compression ratio / expansion ratio variable means further has a function of changing a working angle of the intake valve and a function of changing a lift amount of the intake valve,
The compression ratio / expansion ratio control means advances the closing timing of the intake valve to increase the actual compression ratio, so that the opening timing of the intake valve is advanced from the top dead center. The internal combustion engine according to claim 4 or 5, wherein the opening timing of the intake valve is at least retarded and the lift amount of the intake valve is increased.

Images