JP5900701B2 - Control device and control method for internal combustion engine - Google Patents

Description

  The present invention relates to an internal combustion engine that directly injects fuel into a combustion chamber, and more particularly, to a control device and control method for an internal combustion engine that includes a variable compression ratio mechanism.

  2. Description of the Related Art A cylinder direct injection type spark ignition internal combustion engine in which a fuel injection valve is disposed facing a combustion chamber so that fuel is directly injected into the cylinder during an intake stroke or a compression stroke is known.

  Various types of variable compression ratio mechanisms for changing the mechanical compression ratio of an internal combustion engine have been known. For example, the applicants have proposed a number of variable compression ratio mechanisms in which the piston top dead center position is displaced up and down by changing the link geometry of a multi-link piston crank mechanism. Patent Document 1 describes a variable compression ratio mechanism that similarly changes the mechanical compression ratio by displacing the cylinder position up and down with respect to the center position of the crankshaft.

  Patent Document 1 discloses an internal combustion engine having a fuel injection valve in an intake port, in order to suppress oil dilution due to fuel adhering to a cylinder wall (lubricating oil dilution due to mixing of fuel components). Has disclosed that the compression ratio by the variable compression ratio mechanism is lowered in the case of short trip operation in which is not fully completed. This is a technical idea of reducing the pressure difference inside and outside the combustion chamber by reducing the compression ratio and suppressing oil dilution.

  Patent Document 2 describes a technique for obtaining the state of oil dilution from, for example, engine operating conditions during operation of the internal combustion engine.

  In the above-mentioned Patent Document 1, the compression ratio is reduced in the case of short trip operation, and the oil pressure is suppressed by reducing the pressure difference inside and outside the combustion chamber. In this way, the variable compression ratio mechanism has a low compression ratio. If it is controlled to the side, the piston top dead center position is relatively low with respect to the cylinder, and the cylinder wall surface exposed to the combustion chamber increases so that fuel droplets can come into contact with each other, so the amount of fuel adhering to the cylinder wall surface increases. To do. This causes an increase in oil dilution, so that even if the pressure difference inside and outside the combustion chamber is slightly reduced, there is a concern that oil dilution will be promoted. In particular, in an internal combustion engine equipped with an in-cylinder direct injection type fuel injection device that directly injects fuel into a cylinder, a large amount of fuel adheres as droplets to the cylinder wall surface when cold, so that the compression ratio is lowered. The influence of the increase in the cylinder wall surface becomes dominant, and on the contrary, oil dilution deteriorates. Therefore, it is not preferable to reduce the compression ratio.

JP 2009-167858 A JP 2004-316471 A

The present invention includes a variable compression ratio mechanism that changes a mechanical compression ratio by changing a relative positional relationship between a piston and a cylinder, and a fuel injection valve that directly injects fuel into a combustion chamber. A control device for an internal combustion engine,
Oil dilution detection means for detecting a state in which fuel is mixed into oil and the oil is diluted to a predetermined level or more,
When this oil dilution is detected, the compression ratio by the variable compression ratio mechanism is increased.

  If the compression ratio of the variable compression ratio mechanism is controlled to be high when oil dilution is detected, the piston top dead center position is relatively high with respect to the cylinder, and the cylinder wall surface exposed in the combustion chamber at the fuel injection timing is reduced. Accordingly, the amount of fuel injected into the cylinder and adhering to the cylinder wall surface is reduced, and oil dilution is suppressed. Although the pressure difference inside and outside the combustion chamber increases by increasing the compression ratio, as described above, in a direct injection type internal combustion engine in which fuel is directly injected into the combustion chamber, the fuel spray is larger than the pressure difference. The size of the cylinder wall area in contact with is dominant, and the cylinder wall surface exposed in the combustion chamber is reduced, so that oil dilution can be suppressed.

  Here, since the fuel component mixed in the oil is separated from the oil by vaporization in parallel, if the oil dilution is suppressed, the oil dilution is canceled or at least the oil dilution is balanced by the balance between the two. Progress is suppressed.

  In one desirable mode of the present invention, at the time of the above-mentioned oil dilution detection, the ignition timing retardation is further corrected. By correcting the retard of the ignition timing, it is possible to suppress abnormal combustion such as knocking caused by increasing the compression ratio.

  According to the present invention, oil dilution can be effectively suppressed particularly in a direct injection type internal combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS Configuration explanatory drawing which shows the system configuration | structure of the control apparatus of the internal combustion engine which concerns on this invention. The flowchart which shows the flow of control in this Example. The time chart which shows an example of the control with respect to oil dilution.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows the system configuration of an automotive internal combustion engine 1 to which the present invention is applied. The internal combustion engine 1 is a four-stroke cycle direct injection type spark ignition internal combustion engine having a variable compression ratio mechanism 2 using, for example, a multi-link type piston crank mechanism, and is provided on the ceiling wall surface of the combustion chamber 3. A pair of intake valves 4 and a pair of exhaust valves 5 are arranged, and an ignition plug 6 is arranged in the center surrounded by the intake valves 4 and the exhaust valves 5.

  A fuel injection valve 8 that directly injects fuel into the combustion chamber 3 is disposed below the intake port 7 that is opened and closed by the intake valve 4. The fuel injection valve 8 is mounted in a posture inclined obliquely downward, and the nozzle tip is directed to the opposing cylinder wall surface.

  An intake passage (not shown) connected to the intake port 7 is provided with an electronically controlled throttle valve (not shown) whose opening degree is controlled by a control signal from the engine controller 9, and further upstream thereof. On the side, an air flow meter 10 for detecting the intake air amount is disposed.

  In addition, a catalyst device 13 made of a three-way catalyst is interposed in the exhaust passage 12 connected to the exhaust port 11, and an air-fuel ratio sensor 14 for detecting the air-fuel ratio is disposed upstream thereof.

  In addition to the air flow meter 10 and the air-fuel ratio sensor 14, the engine controller 9 includes a crank angle sensor 15 for detecting the engine speed, a water temperature sensor 16 for detecting the coolant temperature, and an accelerator pedal operated by the driver. Detection signals of sensors such as an accelerator opening sensor 17 for detecting the amount of depression of the oil and an oil temperature sensor 18 for detecting the temperature of the lubricating oil are input. Based on these detection signals, the engine controller 9 optimally controls the fuel injection amount and injection timing by the fuel injection valve 8, the ignition timing by the spark plug 6, the opening of a throttle valve (not shown), and the like. Further, as will be described later, the engine controller 9 sequentially estimates the amount of fuel mixed in the oil (hereinafter referred to as oil diluted fuel amount).

  On the other hand, the variable compression ratio mechanism 2 uses a known multi-link type piston crank mechanism described in Japanese Patent Application Laid-Open No. 2004-116434 and is rotatably supported by the crank pin 21a of the crankshaft 21. A lower link 22, an upper link 25 that connects the upper pin 23 at one end of the lower link 22 and the piston pin 24 a of the piston 24, and a control having one end connected to a control pin 26 at the other end of the lower link 22. The link 27 and a control shaft 28 that pivotally supports the other end of the control link 27 are mainly configured. The crankshaft 21 and the control shaft 28 are rotatably supported in a crankcase below the cylinder block 29 via a bearing structure (not shown). The control shaft 28 has an eccentric shaft portion 28a whose position changes with the rotation of the control shaft 28. Specifically, the end portion of the control link 27 is rotatably fitted to the eccentric shaft portion 28a. Match. In the variable compression ratio mechanism 2 described above, the top dead center position of the piston 24 is displaced up and down with the rotation of the control shaft 28, so that the mechanical compression ratio changes.

  As a drive mechanism for variably controlling the compression ratio of the variable compression ratio mechanism 2, an electric motor 31 having a rotation center axis parallel to the crankshaft 21 is disposed below the cylinder block 29. A reduction gear 32 is connected so as to be arranged in series in the direction. As the speed reducer 32, for example, a wave gear mechanism having a large speed reduction ratio is used, and the speed reducer output shaft 32 a is positioned coaxially with the output shaft (not shown) of the electric motor 31. Accordingly, the speed reducer output shaft 32a and the control shaft 28 are positioned in parallel with each other, and the first arm 33 and the control shaft 28 fixed to the speed reducer output shaft 32a are connected to each other so that both of them rotate in conjunction with each other. The fixed second arm 34 is connected to each other by an intermediate link 35.

  That is, when the electric motor 31 rotates, the angle of the speed reducer output shaft 32a changes in a form greatly decelerated by the speed reducer 32. The rotation of the speed reducer output shaft 32a is transmitted from the first arm 33 to the second arm 34 via the intermediate link 35, and the control shaft 28 rotates. Thereby, as mentioned above, the mechanical compression ratio of the internal combustion engine 1 changes. In the illustrated example, the first arm 33 and the second arm 34 extend in the same direction. Therefore, for example, when the speed reducer output shaft 32a rotates in the clockwise direction, the control shaft 28 also rotates in the clockwise direction. Although it is related, the link mechanism can also be configured to rotate in the opposite direction.

  The target compression ratio of the variable compression ratio mechanism 2 is set in the engine controller 9 based on engine operating conditions (for example, required load and engine speed), and the electric motor 31 is driven so as to realize this target compression ratio. Be controlled.

  FIG. 2 is a flowchart showing a control flow of the present invention that is repeatedly executed by the engine controller 9 during operation of the internal combustion engine 1. In step 1, the engine operating conditions (engine speed and load), cooling water temperature, lubricating oil temperature, etc. at that time are read. In step 2, the basic target compression ratio and the basic ignition timing are set based on the engine operating conditions. In step 3, the oil diluted fuel amount at that time is obtained. The oil-diluted fuel amount can be calculated using, for example, the methods disclosed in the above-mentioned Patent Document 2 and Japanese Patent Application Laid-Open No. 2004-137993, and the engine operating conditions and temperature conditions (cooling water temperature and lubricating oil temperature). ), The increase amount of the oil dilution fuel amount and the decrease amount of the oil dilution fuel amount are sequentially obtained and integrated, so that the oil dilution fuel amount at that time can be estimated. The increase in the amount of oil-diluted fuel is mainly caused by mixing of fuel from the cylinder wall into the crankcase, and the decrease in the amount of oil-diluted fuel is mainly due to evaporation of fuel components in the oil. In the present invention, the detection of the oil dilution state is not the main part, and a known detection means can be used as appropriate.

  In step 4, it is determined whether or not the oil has been diluted to a predetermined level or more by comparing the amount of oil diluted fuel obtained in step 3 with a predetermined threshold. If “NO” here, the process proceeds to a step 7 to execute the normal control using the basic target compression ratio and the basic ignition timing.

  On the other hand, if the amount of oil-diluted fuel is greater than or equal to the threshold value in step 4, the process proceeds to step 5 where the target compression ratio is set to a higher compression ratio than the basic target compression ratio and the variable compression ratio mechanism 2 is controlled. Here, a higher compression ratio may be obtained by correcting the basic target compression ratio (for example, addition of a predetermined correction amount or multiplication by a correction coefficient), or fixed control at a maximum compression ratio that can be controlled by the variable compression ratio mechanism 2. You may make it do.

  At the same time, in step 6, a value obtained by performing a predetermined amount of retardation correction from the basic ignition timing is set as the ignition timing. The retard angle correction amount at this time may simply be a constant crank angle, but the compression set in step 5 in order to avoid abnormal combustion such as knocking by setting the compression ratio higher than the basic target compression ratio. It is desirable to correspond to the ratio value.

  FIG. 3 is a time chart showing an example of changes in the compression ratio and ignition timing according to the amount of oil diluted fuel. For example, when the temperature of the internal combustion engine 1 is low, fuel droplets adhere to the cylinder wall and are taken out to the crankcase side. As a result, the amount of oil-diluted fuel increases as shown in the figure. This oil diluted fuel amount is sequentially estimated by the engine controller 9 as described above. In this example, at time t1, the oil diluted fuel amount exceeds a predetermined threshold value, and in response thereto, the compression ratio increases. At the same time, the ignition timing is retarded.

  By increasing the compression ratio in this manner, oil dilution is suppressed as described above. Abnormal combustion such as knocking due to an increase in the compression ratio is suppressed by retarding the ignition timing.

  In the illustrated example, as a result of the oil dilution being suppressed, the oil diluted fuel amount gradually decreases after time t1, and falls below a predetermined threshold at time t2. Along with this, the compression ratio returns to the basic target compression ratio, and the ignition timing also becomes the basic ignition timing.

  As shown in the figure, when the compression ratio increase and ignition timing retardation correction are started, and after the start of the compression ratio increase and ignition timing retardation correction, the oil dilution is performed. Appropriate hysteresis is given to the threshold value of the fuel amount, and the actual threshold value is lower in the latter case.

  As mentioned above, although one Example of this invention was described, this invention is not limited to the said Example, A various change is possible. For example, in the above embodiment, the degree of oil dilution is estimated based on the engine operating conditions, but it is also possible to detect the degree of oil dilution from the increase or decrease of the oil amount or the change of the oil component due to fuel mixing. Is possible. In the above embodiment, the variable compression ratio mechanism 2 that changes the compression ratio by moving the top dead center position of the piston 24 up and down is used. However, the variable compression ratio mechanism of the type that moves the cylinder side up and down is used. However, the present invention can be similarly applied.

Claims (4)

A variable compression ratio mechanism that changes the mechanical compression ratio by changing the relative positional relationship between the piston and cylinder, a fuel injection valve that directly injects fuel into the combustion chamber, and ignition by an ignition plug A control device for an internal combustion engine that performs
Oil dilution detection means for detecting a state in which fuel is mixed into oil and the oil is diluted to a predetermined level or more,
A control device for an internal combustion engine that increases the compression ratio by the variable compression ratio mechanism when detecting the oil dilution.   2. The control device for an internal combustion engine according to claim 1, further comprising correcting the retard of the ignition timing when detecting the oil dilution.   When the target compression ratio of the variable compression ratio mechanism is corrected to a target compression ratio that is higher than the basic target compression ratio set according to the engine operating conditions at the time of detecting the oil dilution, and the cancellation of oil dilution is detected. The control device for an internal combustion engine according to claim 1, wherein the control is made to return to the basic target compression ratio. A variable compression ratio mechanism that changes the mechanical compression ratio by changing the relative positional relationship between the piston and cylinder, a fuel injection valve that directly injects fuel into the combustion chamber, and ignition by an ignition plug In an internal combustion engine that performs
A control method for an internal combustion engine, which detects a state in which fuel is mixed into oil and the oil is diluted to a predetermined level or more, and increases the compression ratio by the variable compression ratio mechanism when the oil dilution is detected.

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