Control method and control device for internal combustion engine

Abstract

To perform reference position learning of a variable compression ratio mechanism without deteriorating startability.SOLUTION: An internal combustion engine causes a first arm part 22 of a variable compression ratio mechanism 1 to abut on a high compression ratio side stopper 35 during stop, and learns a state where the variable compression ratio mechanism 1 reaches a maximum compression ratio as a reference position on a high compression ratio side at the start. When the internal combustion engine cannot cause the first arm part 22 of the variable compression ratio mechanism 1 to abut on the high compression ratio side stopper 35 during the stop, the internal combustion engine operates the variable compression ratio mechanism 1 so as to reach a minimum compression ratio at the start, and learns a state where the variable compression ratio mechanism 1 reaches the minimum compression ratio as a reference position on a low compression ratio side.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a control method for an internal combustion engine having a variable compression ratio mechanism and a control device for the internal combustion engine. [Background technology]

[0002] For example, Patent Document 1 discloses a technology for accurately adjusting the compression ratio of an internal combustion engine during low-load, low-speed operation, such as during cranking, by changing the compression ratio and abutting a control-shaft-side stopper member fixed to the control shaft of a compression ratio variable mechanism against a main-body-side stopper member press-fitted into the cylinder block to learn a reference position on the high-compression ratio side. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-226133 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Patent Document 1, for example, when the rotation angle of the control shaft is at a position close to the minimum compression ratio during cranking, it takes longer for the control shaft side stopper member to hit the main body side stopper member than when the rotation angle of the control shaft is at a position close to the maximum compression ratio during cranking.

[0005] Therefore, in Patent Document 1, the time required to learn the reference position of the variable compression ratio mechanism varies depending on the rotational angle position of the control shaft at the start of cranking, so if an attempt is made to start the internal combustion engine after learning the reference position of the variable compression ratio mechanism, there is a risk that the startability of the internal combustion engine will deteriorate.

[0006] In other words, there is room for further improvement in learning the reference position of the variable compression ratio mechanism without impairing the startability of the internal combustion engine. [Means for solving the problem]

[0007] When the internal combustion engine of the present invention is stopped, one of the members constituting the variable compression ratio mechanism that moves when the compression ratio is changed to the high compression ratio side abuts against a first stopper, and when started, the internal combustion engine learns a state in which the variable compression ratio mechanism has reached its maximum compression ratio as a reference position on the high compression ratio side.Furthermore, if when stopped, one of the members constituting the variable compression ratio mechanism that moves when the compression ratio is changed to the high compression ratio side does not abut against the first stopper, when started, the internal combustion engine operates the variable compression ratio mechanism to achieve the minimum compression ratio, and learns a state in which the variable compression ratio mechanism has reached its minimum compression ratio as a reference position on the low compression ratio side. [Effects of the Invention]

[0008] According to the present invention, the reference position of the high compression ratio side of the variable compression ratio mechanism can be learned as quickly as possible when starting the internal combustion engine. Also, if the reference position of the high compression ratio side of the variable compression ratio mechanism cannot be learned when starting the internal combustion engine, the reference position of the low compression ratio side of the variable compression ratio mechanism can be learned, thereby enabling the internal combustion engine to be started quickly. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is an explanatory diagram schematically illustrating a variable compression ratio mechanism applied to the present invention. [Figure 2] 1 is an explanatory diagram schematically illustrating a main part of a variable compression ratio mechanism applied to the present invention; [Figure 3] 1 is an explanatory diagram schematically illustrating a main part of a variable compression ratio mechanism applied to the present invention; [Figure 4] 6 is a timing chart showing a case where the reference position on the high compression ratio side of the variable compression ratio mechanism can be learned when the internal combustion engine is started. [Figure 5] 6 is a timing chart showing a case where the reference position on the high compression ratio side of the variable compression ratio mechanism cannot be learned when the internal combustion engine is started. [Figure 6] 4 is a flowchart showing a control flow when an ignition switch is turned on. [Figure 7] 6 is a flowchart showing a control flow when an ignition switch is turned off. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of the present invention will be described in detail below with reference to the drawings.

[0011] 1 to 3 are explanatory diagrams that schematically show a variable compression ratio mechanism 1 that is applied to an internal combustion engine of the present invention.

[0012] Fig. 1 shows a schematic configuration of a variable compression ratio mechanism 1 applied to an internal combustion engine of the present invention, as viewed from the crankshaft axial direction. Fig. 2 is an explanatory diagram that schematically shows the main parts of the variable compression ratio mechanism 1 applied to an internal combustion engine of the present invention, showing a state in which the variable compression ratio mechanism 1 has the maximum compression ratio. Fig. 3 is an explanatory diagram that schematically shows the main parts of the variable compression ratio mechanism 1 applied to an internal combustion engine of the present invention, showing a state in which the variable compression ratio mechanism 1 has the minimum compression ratio.

[0013] An internal combustion engine having a variable compression ratio mechanism 1 is mounted on a vehicle such as an automobile. The variable compression ratio mechanism 1 has a piston 2, an upper link 4 as a first link, a lower link 7 as a second link, a control link 9 as a third link, a first control shaft 10, an actuator 21, a second control shaft 24, and a lever 30. The variable compression ratio mechanism 1 is a multi-link piston-crank mechanism in which the piston 2 and the crank pin 6a of the crankshaft 6 are connected by multiple links.

[0014] The piston 2 is rotatably connected to one end of an upper link 4 via a piston pin 3 .

[0015] The other end of the upper link 4 is rotatably connected to one end of the lower link 7 via an upper pin 5 serving as a first link connecting pin.

[0016] The crankshaft 6 has a plurality of journal portions 6b and crank pins 6a, and the journal portions 6b are rotatably supported by main bearings (not shown) of the cylinder block 11. The crank pins 6a are eccentric from the journal portions 6b by a predetermined amount.

[0017] The lower link 7 is rotatably connected to a crank pin 6 a of the crankshaft 6 .

[0018] One end of the control link 9 is rotatably connected to the other end of the lower link 7 via a control pin 8 serving as a third link connecting pin. The other end of the control link 9 is rotatably connected to an eccentric shaft portion 10a of a first control shaft 10 supported on the engine body side.

[0019] The first control shaft 10 is disposed parallel to the crankshaft 6 and is rotatably supported, for example, by a cylinder block 11. In other words, the other end of the control link 9, which is rotatably connected to the eccentric shaft portion 10a, is swingably supported on the engine body side. The central axis of the eccentric shaft portion 10a is eccentric by a predetermined amount with respect to the center of rotation of the first control shaft 10.

[0020] The variable compression ratio mechanism 1 can change the position of the piston 2 at top dead center by rotating the first control shaft 10 to change the position of the eccentric shaft portion 10a, thereby changing the mechanical compression ratio of the internal combustion engine.

[0021] The first control shaft 10 restricts the degree of freedom of the lower link 7, and its rotational position is changed and maintained by an actuator 21. The first control shaft 10 has a first arm portion 22 as a first movable member, and is rotatably supported inside the internal combustion engine body, which is made up of the cylinder block 11 and an oil pan upper fixed to its lower side (lower part). The first arm portion 22 is a first movable member that is one of the members that make up the variable compression ratio mechanism 1 and that moves when the compression ratio is changed to a higher compression ratio. The first arm portion 22 extends radially outward from the first control shaft 10. In other words, the first arm portion 22 protrudes from the first control shaft 10.

[0022] The actuator 21 is, for example, an electric motor, and is disposed outside the internal combustion engine body. The rotation of the actuator 21 is reduced by a reducer (not shown) and is extracted as the rotation of the second control shaft 24. That is, the second control shaft 24 is connected to the actuator 21 via the reducer. The rotation of the rotating shaft (rotor) of the actuator 21 is transmitted to the second control shaft 24 after being significantly reduced by the reducer.

[0023] The second control shaft 24 is disposed parallel to the first control shaft 10 and extends in the longitudinal direction of the engine. The second control shaft 24 has a second arm portion 26 serving as a second movable member. The second arm portion 26 is one of the members constituting the variable compression ratio mechanism 1 that moves when the compression ratio is changed to a lower compression ratio. The second arm portion 26 extends radially outward from the second control shaft 24. In other words, the second arm portion 26 protrudes from the second control shaft 24.

[0024] The first arm portion 22 and the second arm portion 26 are linked by a long, thin lever 30 that is perpendicular to the first control shaft 10 and the second control shaft 24. In other words, the first control shaft 10, which is disposed inside the internal combustion engine body where lubricating oil (lubricating oil) splashes, and the second control shaft 24, which is provided outside the internal combustion engine body, are mechanically linked by the lever 30.

[0025] The first arm portion 22 and the lever 30 are rotatably connected via a first connecting pin 31. The first connecting pin 31 is parallel to the first control shaft 10 and passes through the tip of the first arm portion 22 and one end of the lever 30.

[0026] The second arm portion 26 and the lever 30 are rotatably connected via a second connecting pin 32. The second connecting pin 32 is parallel to the second control shaft 24 and passes through the tip of the second arm portion 26 and the other end of the lever 30.

[0027] As the compression ratio of the variable compression ratio mechanism 1 is shifted toward the high compression ratio side, as shown in FIG. 2 , the first arm portion 22 abuts against a high compression ratio side stopper 35 serving as a first stopper, thereby restricting movement of the variable compression ratio mechanism 1 toward the high compression ratio side. The high compression ratio side stopper 35 is provided, for example, on a bearing cap (not shown) attached to the cylinder block 11. This bearing cap rotatably supports the journal portion 6b of the crankshaft 6 together with a main bearing of the cylinder block 11. In the variable compression ratio mechanism 1, the first arm portion 22 abuts against the high compression ratio side stopper 35 and comes into surface contact with it, thereby mechanically restricting displacement of the first arm portion 22 toward the high compression ratio side. In other words, the high compression ratio side stopper 35 determines the maximum compression ratio of the variable compression ratio mechanism 1.

[0028] Furthermore, as the compression ratio of the variable compression ratio mechanism 1 is shifted toward the lower compression ratio side, as shown in FIG. 3 , the second arm portion 26 abuts against a low compression ratio side stopper 36 serving as a second stopper, thereby restricting movement of the variable compression ratio mechanism 1 toward the lower compression ratio side. The low compression ratio side stopper 36 is provided, for example, on the housing of the actuator 21. In the variable compression ratio mechanism 1, the second arm portion 26 abuts against the low compression ratio side stopper 36 and comes into surface contact, thereby mechanically restricting displacement of the second arm portion 26 toward the lower compression ratio side. In other words, the low compression ratio side stopper 36 determines the minimum compression ratio of the variable compression ratio mechanism 1.

[0029] The variable compression ratio mechanism 1 rotates the second control shaft 24 by controlling the drive of the actuator 21 according to a command from the control unit 41, and transmits the rotation of the second control shaft 24 to the first control shaft 10 via the lever 30. In other words, the control unit 41 is capable of executing variable compression ratio control by the variable compression ratio mechanism 1.

[0030] The control unit 41 receives detection signals from various sensors, such as a crank angle sensor 42 that detects the engine speed (engine speed) and crank angle position of the internal combustion engine, an accelerator opening sensor 43 that detects the amount of depression of the accelerator pedal operated by the driver (accelerator opening), and a compression ratio sensor 44 that can detect the compression ratio of the variable compression ratio mechanism 1.

[0031] The compression ratio sensor 44 detects the compression ratio of the variable compression ratio mechanism 1 by detecting the rotation angle of a rotating shaft (rotor) (not shown) of the actuator 21. The compression ratio sensor 44 detects the rotation angle of the rotating shaft (rotor) from the phase of the rotating shaft (rotor) of the actuator 21. In this embodiment, the compression ratio of the variable compression ratio mechanism 1 is detected only by the compression ratio sensor 44.

[0032] Furthermore, signals associated with the on / off operation of the ignition switch 45 by the driver are also input to the control unit 41. The control unit 41 corresponds to a control section, and based on these detection signals, in addition to variable compression ratio control by the variable compression ratio mechanism 1, can perform variable valve timing control of the intake valve (not shown) by the intake-side variable valve mechanism 46, supercharging pressure control of the internal combustion engine having a supercharger 47, drive control of the starter motor 48, and learning of the reference position of the variable compression ratio mechanism 1 by driving the actuator 21.

[0033] The intake-side variable valve mechanism 46 is a valve mechanism for the intake valve, and is capable of changing the valve timing (opening and closing timing) of the intake valve.

[0034] The intake-side variable valve mechanism 46 is, for example, a phase variable mechanism that continuously advances or retards the phase of the central angle of the intake valve lift (phase relative to the crankshaft 6). The phase variable mechanism is already known, for example, from Japanese Patent Application Laid-Open No. 2002-89303, and retards the phase of an intake camshaft (not shown), which drives the intake valve to open and close, relative to the crankshaft 6. The valve mechanism for the exhaust valve (not shown) of the internal combustion engine is a general direct-acting valve mechanism.

[0035] The intake-side variable valve mechanism 46 is, for example, hydraulically driven and is capable of changing the valve timing of the intake valve under control of a control signal from the control unit 41. The intake-side variable valve mechanism 46 is capable of varying the effective compression ratio of the internal combustion engine by changing the closing timing of the intake valve.

[0036] The supercharging pressure control of an internal combustion engine is a control of intake pressure, and if the supercharger 47 is a turbo supercharger, it is possible to prevent supercharging by, for example, opening an electric wastegate valve (not shown) provided in an exhaust bypass passage (not shown). The exhaust bypass passage bypasses an exhaust turbine (not shown) of the supercharger 47 provided in the exhaust passage and connects the upstream side and downstream side of the exhaust turbine.

[0037] The supercharger 47 may be an electric supercharger in which a compressor disposed in the intake passage is driven by an electric motor. In this case, supercharging can be prevented by not driving the electric motor that drives the compressor.

[0038] The drive control of the starter motor 48 is to drive the starter motor 48 so that the stopped internal combustion engine can rotate independently when the starter motor 48 becomes capable of being driven.

[0039] The reference position of the variable compression ratio mechanism 1 is learned using the detection signal (detection value) of the compression ratio sensor 44. Specifically, the control unit 41 learns the reference position of the high compression ratio side of the variable compression ratio mechanism 1 using the detection value of the compression ratio sensor 44 when the first arm portion 22 is in a state where it abuts against the high compression ratio side stopper 35. The control unit 41 also learns the reference position of the low compression ratio side of the variable compression ratio mechanism 1 using the detection value of the compression ratio sensor 44 when the second arm portion 26 is in a state where it abuts against the low compression ratio side stopper 36.

[0040] More specifically, when the internal combustion engine is stopped, the control unit 41 operates the variable compression ratio mechanism 1 to achieve the maximum compression ratio, abutting the first arm portion 22 against the high compression ratio side stopper 35, and when the internal combustion engine is next started, the control unit 41 learns the state in which the variable compression ratio mechanism 1 achieves the maximum compression ratio by abutting the first arm portion 22 against the high compression ratio side stopper 35, as the high compression ratio side reference position. Note that when the internal combustion engine is stopped, the variable compression ratio mechanism 1 stops the first arm portion 22 in a state in which it abuts against the high compression ratio side stopper 35.

[0041] Furthermore, if the first arm portion 22 fails to abut against the high compression ratio side stopper 35 when the internal combustion engine is stopped, the control unit 41 operates the variable compression ratio mechanism 1 so that the minimum compression ratio is achieved the next time the internal combustion engine is started, and learns the state in which the variable compression ratio mechanism 1 has reached the minimum compression ratio as the reference position on the low compression ratio side.

[0042] By learning the reference position of the variable compression ratio mechanism 1, the internal combustion engine can change the compression ratio with high precision while the internal combustion engine is running.

[0043] FIG. 4 is a timing chart showing a case where the reference position on the high compression ratio side of the variable compression ratio mechanism 1 can be learned when the internal combustion engine is started.

[0044] 4 is the timing when the driver turns on the ignition switch 45. In the variable compression ratio mechanism 1, the first arm portion 22 was abutted against the high compression ratio side stopper 35 the last time the ignition switch 45 was turned off, so at the timing of time t1, the first arm portion 22 is in a position very close to the high compression ratio side stopper 35 or is in a state in which the first arm portion 22 is abutted against the high compression ratio side stopper 35.

[0045] Time t2 in Fig. 4 is the timing at which learning of the high compression ratio side reference position of the variable compression ratio mechanism 1 is completed. The starter motor 48 and the turbocharger 47 become operable from the timing of time t2. Cranking of the internal combustion engine is started at the timing of time t2. The variable compression ratio mechanism 1 is controlled so that the first arm portion 22 abuts against the high compression ratio side stopper 35 during the period from time t1 to t2 in Fig. 4.

[0046] Time t3 in FIG. 4 is the timing when the ignition switch 45 is turned off by the driver. The starter motor 48 and the turbocharger 47 are disabled from time t3. The internal combustion engine stops at time t3. When the ignition switch 45 is turned off, the variable compression ratio mechanism 1 is controlled so that the compression ratio becomes the minimum compression ratio in order to check its operation. Note that the check of operation with the compression ratio set to the maximum compression ratio also serves as learning of the reference position on the high compression ratio side of the variable compression ratio mechanism 1.

[0047] During the period from time t2 to time t3 in FIG. 4, the variable compression ratio mechanism 1 is controlled so as to follow a target compression ratio according to the engine speed of the internal combustion engine and the accelerator opening.

[0048] Time t4 in Fig. 4 is the timing at which the state in which the second arm portion 26 abuts against the low compression ratio side stopper 36 ends. The variable compression ratio mechanism 1 is controlled so that the compression ratio becomes the maximum compression ratio from the timing of time t4. During the period from time t3 to t4 in Fig. 4, the variable compression ratio mechanism 1 is controlled to reduce the compression ratio so that the second arm portion 26 abuts against the low compression ratio side stopper 36.

[0049] Time t5 in Fig. 4 is the timing at which the first arm portion 22 abuts against the high compression ratio side stopper 35. During the period from time t4 to t5 in Fig. 4, the variable compression ratio mechanism 1 is controlled to increase the compression ratio so that the first arm portion 22 abuts against the high compression ratio side stopper 35. Note that energization of the actuator 21 of the variable compression ratio mechanism 1 ends at time t5, for example. That is, control of the variable compression ratio mechanism 1 ends at the timing of time t5.

[0050] FIG. 5 is a timing chart showing a case where the reference position on the high compression ratio side of the variable compression ratio mechanism 1 cannot be learned when the internal combustion engine is started.

[0051] 5, time t1 is the timing when the ignition switch 45 is turned off by the driver. The starter motor 48 and the turbocharger 47 are disabled from time t1. The internal combustion engine stops at time t1. When the ignition switch 45 is turned off, the variable compression ratio mechanism 1 is controlled so that the compression ratio becomes the minimum compression ratio in order to check its operation.

[0052] 5 is the timing at which the state in which the second arm portion 26 abuts against the low compression ratio side stopper 36 ends. The variable compression ratio mechanism 1 is controlled so that the compression ratio becomes the maximum compression ratio from the timing of time t2. During the period from time t1 to t2 in FIG. 5, the variable compression ratio mechanism 1 is controlled to reduce the compression ratio so that the second arm portion 26 abuts against the low compression ratio side stopper 36.

[0053] Time t3 in FIG. 5 is the timing at which it is determined that the first arm portion 22 has failed to abut against the high compression ratio side stopper 35. During the period from time t2 to t3 in FIG. 4, the variable compression ratio mechanism 1 is controlled to increase the compression ratio so that the first arm portion 22 abuts against the high compression ratio side stopper 35, but for some reason, the first arm portion 22 is unable to abut against the high compression ratio side stopper 35. Note that energization of the actuator 21 of the variable compression ratio mechanism 1 ends, for example, at time t3. In other words, control of the variable compression ratio mechanism 1 ends at the timing of time t3. In the example of FIG. 5, the operation of the variable compression ratio mechanism 1 ends at a position where the compression ratio is approximately halfway between the minimum and maximum compression ratios (an intermediate compression ratio).

[0054] Time t4 in Figure 5 is the timing when the driver turns on the ignition switch 45. The variable compression ratio mechanism 1 failed to cause the first arm portion 22 to abut against the high compression ratio side stopper 35 the last time the ignition switch 45 was turned off, so at time t4 the first arm portion 22 is separated from the high compression ratio side stopper 35 (intermediate compression ratio in the example of Figure 5). The starter motor 48 becomes operable at time t4. Cranking of the internal combustion engine begins at time t4.

[0055] 5 is the timing at which learning of the reference position on the low compression ratio side of the variable compression ratio mechanism 1 is completed. The supercharger 47 becomes operable from the timing of time t5. The variable compression ratio mechanism 1 is controlled so that the second arm portion 26 abuts against the low compression ratio side stopper 36 during the period from time t4 to t5 in FIG.

[0056] Time t6 in FIG. 5 is the timing when the ignition switch 45 is turned off by the driver. The starter motor 48 and the turbocharger 47 are disabled at time t6. The internal combustion engine is stopped at time t6. During the period from time t5 to t6 in FIG. 5, the variable compression ratio mechanism 1 is controlled to follow a target compression ratio that corresponds to the engine speed of the internal combustion engine and the accelerator pedal position. Furthermore, in this trip, the variable compression ratio mechanism 1 has the minimum compression ratio when the ignition switch 45 is turned on, and therefore it is not necessary to set the compression ratio to the minimum compression ratio for operation check. Therefore, control to set the compression ratio to the minimum compression ratio when the ignition switch 45 is turned off is omitted. Note that the operation check of setting the compression ratio to the maximum compression ratio also serves as learning of the reference position on the high compression ratio side of the variable compression ratio mechanism 1.

[0057] 5 is the timing at which the first arm portion 22 abuts against the high compression ratio side stopper 35. During the period from times t6 to t7 in Fig. 5, the variable compression ratio mechanism 1 is controlled to increase the compression ratio so that the first arm portion 22 abuts against the high compression ratio side stopper 35. Note that the supply of electricity to the actuator 21 of the variable compression ratio mechanism 1 ends at time t7, for example. That is, the control of the variable compression ratio mechanism 1 ends at the timing of time t7.

[0058] In an internal combustion engine, the higher the compression ratio, the smaller the combustion chamber volume, and the higher the compression ratio, the larger the proportion of the combustion chamber volume that the same combustion chamber volume change accounts for, so the variation in compression ratio is greater on the high compression ratio side.

[0059] Therefore, when learning the reference position of the variable compression ratio mechanism 1, the reference position on the high compression ratio side is more important than the reference position on the low compression ratio side.

[0060] Furthermore, if an attempt is made to learn the reference position on the high compression ratio side of the variable compression ratio mechanism 1 while the internal combustion engine is in operation, knocking is more likely to occur, and there is a risk that the driving performance will deteriorate.

[0061] In this embodiment, when learning the reference position of the variable compression ratio mechanism 1, the reference position on the high compression ratio side of the variable compression ratio mechanism 1 is basically learned, and if it is not possible to learn the reference position on the high compression ratio side of the variable compression ratio mechanism 1, the reference position on the low compression ratio side of the variable compression ratio mechanism 1 is learned.

[0062] If the first arm portion 22 cannot be brought into contact with the high compression ratio side stopper 35 when the internal combustion engine is stopped, it is difficult to determine what state of compression ratio the variable compression ratio mechanism 1 will provide when the internal combustion engine is started. If the variable compression ratio mechanism 1 is stopped in a state of a low compression ratio on the minimum compression ratio side (for example, near the minimum compression ratio) when the internal combustion engine is stopped, it takes time to change the compression ratio to the maximum compression ratio when the internal combustion engine is started, and therefore it takes time to learn the reference position on the high compression ratio side.

[0063] If the variable compression ratio mechanism 1 can bring the first arm portion 22 into contact with the high compression ratio side stopper 35 when the internal combustion engine is stopped, it can learn the reference position of the high compression ratio side as quickly as possible when the internal combustion engine is started.

[0064] Furthermore, when the variable compression ratio mechanism 1 is unable to learn the reference position on the high compression ratio side when starting the internal combustion engine, it is possible to start the internal combustion engine quickly by learning the reference position on the low compression ratio side.

[0065] Even if the compression ratio of an internal combustion engine is changed to a lower compression ratio while the engine is running, knocking is less likely to occur than when the compression ratio is changed to a higher compression ratio while the engine is running, and the reference position of the variable compression ratio mechanism 1 can be learned without deteriorating the driving performance of the vehicle.

[0066] Since knocking is less likely to occur in an internal combustion engine when the compression ratio is low, cranking can be started without waiting for completion of learning of the reference position on the low compression ratio side of the variable compression ratio mechanism 1. Therefore, even if the internal combustion engine attempts to learn the reference position on the low compression ratio side of the variable compression ratio mechanism 1 when the compression ratio set by the variable compression ratio mechanism 1 is on the high compression ratio side at start-up, the reference position on the low compression ratio side can be learned quickly without impairing driving performance. In other words, the internal combustion engine can be started quickly even if it is not possible to learn the reference position on the high compression ratio side of the variable compression ratio mechanism 1 at start-up.

[0067] If the first arm portion 22 fails to abut against the high compression ratio side stopper 35 when the internal combustion engine is stopped, the supercharger 47 is prohibited from supercharging until learning of the reference position of the low compression ratio side of the variable compression ratio mechanism 1 is completed at the next start.

[0068] Since the compression ratio cannot be accurately determined until the reference position has been learned, the internal combustion engine can suppress knocking during start-up by prohibiting supercharging until the reference position has been learned.

[0069] The control unit 41 records whether or not the first arm portion 22 is in contact with the high compression ratio side stopper 35 when the internal combustion engine is stopped.

[0070] When starting the internal combustion engine, the control unit 41 can speed up the start-up control of the internal combustion engine by reading out a record of whether or not the first arm portion 22 was in a state of being abutted against the high compression ratio side stopper 35 when the internal combustion engine was last stopped.

[0071] In addition, if it is not possible to record whether or not the first arm portion 22 has come into contact with the high compression ratio side stopper 35 when the internal combustion engine is stopped, it may be determined that the first arm portion 22 has not come into contact with the high compression ratio side stopper 35, for example.

[0072] FIG. 6 is a flowchart showing the flow of control when the ignition switch 45 is turned on in the above-described embodiment.

[0073] In step S1, a record of whether or not the first arm portion 22 abutted against (came into contact with) the high compression ratio side stopper 35 when the ignition switch 45 was previously turned off is read.

[0074] In step S2, it is determined from the record read out in step S1 whether or not the first arm portion 22 has been successfully brought into contact with (abutment against) the high compression ratio side stopper 35. If it is determined in step S2 that the first arm portion 22 has been successfully brought into contact with the high compression ratio side stopper 35, the process proceeds to step S3. If it is determined in step S2 that the first arm portion 22 has not been brought into contact with the high compression ratio side stopper 35, the process proceeds to step S8. Note that if, for some reason, there is no record of whether or not the first arm portion 22 has been brought into contact with (abutment against) the high compression ratio side stopper 35, it is determined in step S2 that the first arm portion 22 has not been brought into contact with the high compression ratio side stopper 35.

[0075] In step S3, a command is issued to learn the reference position on the high compression ratio side of the variable compression ratio mechanism 1.

[0076] In step S4, it is determined whether or not learning of the reference position on the high compression ratio side of the variable compression ratio mechanism 1 has been successful. If it is determined in step S4 that learning of the reference position on the high compression ratio side of the variable compression ratio mechanism 1 has been successful, the process proceeds to step S5. If it is determined in step S4 that learning of the reference position on the high compression ratio side of the variable compression ratio mechanism 1 has failed, the process proceeds to step S6.

[0077] In step S5, it becomes possible (permitted) to drive the starter motor 48 and the supercharger 47, and it becomes possible (permitted) to control the variable compression ratio mechanism 1 so that it follows the target compression ratio (variable compression ratio control).

[0078] In step S6, a fail-safe is implemented, that is, in step S6, variable compression ratio control of the variable compression ratio mechanism 1 is not performed, and the compression ratio is fixed.

[0079] In step S7, the starter motor 48 is enabled to be driven.

[0080] In step S8, a command is issued to learn the reference position on the low compression ratio side of the variable compression ratio mechanism 1, and driving of the starter motor 48 is enabled (permitted).

[0081] In step S9, it is determined whether or not learning of the reference position on the low compression ratio side of the variable compression ratio mechanism 1 has been successful. If it is determined in step S9 that learning of the reference position on the low compression ratio side of the variable compression ratio mechanism 1 has been successful, the process proceeds to step S10. If it is determined in step S9 that learning of the reference position on the low compression ratio side of the variable compression ratio mechanism 1 has failed, the process proceeds to step S11.

[0082] In step S10, it becomes possible (permitted) to drive the supercharger 47, and it becomes possible (permitted) to control the variable compression ratio mechanism 1 so that it follows the target compression ratio (variable compression ratio control).

[0083] In step S11, a fail-safe is executed, that is, in step S11, variable compression ratio control of the variable compression ratio mechanism 1 is not performed, and the compression ratio is fixed.

[0084] FIG. 7 is a flowchart showing the flow of control when the ignition switch 45 is turned off in the above-described embodiment.

[0085] In step S21, a record of whether or not the first arm portion 22 abutted against (came into contact with) the high compression ratio side stopper 35 the previous time the ignition switch 45 was turned off is read.

[0086] In step S22, it is determined from the record read out in step S21 whether or not the first arm portion 22 has been successfully brought into contact with (abutment against) the high compression ratio side stopper 35. If it is determined in step S22 that the first arm portion 22 has been successfully brought into contact with the high compression ratio side stopper 35, the process proceeds to step S23. If it is determined in step S22 that the first arm portion 22 has not been brought into contact with the high compression ratio side stopper 35, the process proceeds to step S30. Note that if, for some reason, there is no record of whether or not the first arm portion 22 has been brought into contact with (abutment against) the high compression ratio side stopper 35, it is determined in step S22 that the first arm portion 22 has not been brought into contact with the high compression ratio side stopper 35.

[0087] In step S23, it is determined whether or not learning of the reference position on the high compression ratio side of the variable compression ratio mechanism 1 was successful when the ignition switch 45 was turned on this time. If it is determined in step S23 that learning of the reference position on the high compression ratio side of the variable compression ratio mechanism 1 was successful, the process proceeds to step S24. If it is determined in step S23 that learning of the reference position on the high compression ratio side of the variable compression ratio mechanism 1 was unsuccessful, the process proceeds to step S29.

[0088] In step S24, the variable compression ratio mechanism 1 is instructed to make the second arm portion 26 abut against (contact with) the low compression ratio side stopper 36.

[0089] In step S25, it is determined whether or not the second arm portion 26 has been successfully brought into contact with (abutment against) the low compression ratio side stopper 36. If it is determined in step S25 that the second arm portion 26 has been successfully brought into contact with the low compression ratio side stopper 36, the process proceeds to step S26. If it is determined in step S25 that the second arm portion 26 has not been successfully brought into contact with the low compression ratio side stopper 36, the process proceeds to step S29.

[0090] In step S26, the variable compression ratio mechanism 1 is instructed to make the first arm portion 22 abut against (contact with) the high compression ratio side stopper 35.

[0091] In step S27, it is determined whether or not the first arm portion 22 has been successfully brought into contact with (abutment against) the high compression ratio side stopper 35. If it is determined in step S27 that the first arm portion 22 has been successfully brought into contact with the high compression ratio side stopper 35, the process proceeds to step S28. If it is determined in step S27 that the first arm portion 22 has not been successfully brought into contact with the high compression ratio side stopper 35, the process proceeds to step S29.

[0092] In step S28, the fact that the first arm portion 22 has been successfully brought into contact with (abutted against) the high compression ratio side stopper 35 when the ignition switch 45 is turned off is recorded in the control unit 41.

[0093] In step S29, the fact that the first arm portion 22 failed to abut (contact) against the high compression ratio side stopper 35 when the ignition switch 45 was turned off is recorded in the control unit 41.

[0094] In step S30, it is determined whether or not learning of the reference position on the high compression ratio side of the variable compression ratio mechanism 1 was successful when the ignition switch 45 was turned on this time. If it is determined in step S30 that learning of the reference position on the high compression ratio side of the variable compression ratio mechanism 1 was successful, the process proceeds to step S31. If it is determined in step S30 that learning of the reference position on the high compression ratio side of the variable compression ratio mechanism 1 was unsuccessful, the process proceeds to step S34.

[0095] In step S31, the variable compression ratio mechanism 1 is instructed to make the first arm portion 22 abut against (contact with) the high compression ratio side stopper .

[0096] In step S32, it is determined whether or not the first arm portion 22 has been successfully brought into contact with (abutment against) the high compression ratio side stopper 35. If it is determined in step S32 that the first arm portion 22 has been successfully brought into contact with the high compression ratio side stopper 35, the process proceeds to step S33. If it is determined in step S32 that the first arm portion 22 has not been successfully brought into contact with the high compression ratio side stopper 35, the process proceeds to step S34.

[0097] In step S33, the fact that the first arm portion 22 has been successfully brought into contact with (abutted against) the high compression ratio side stopper 35 when the ignition switch 45 is turned off is recorded in the control unit 41.

[0098] In step S34, the fact that the first arm portion 22 failed to abut (contact) against the high compression ratio side stopper 35 when the ignition switch 45 was turned off is recorded in the control unit 41.

[0099] Although specific embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the invention.

[0100] For example, during a cold start when the temperature of the internal combustion engine is equal to or lower than a predetermined temperature, the intake-side variable valve mechanism 46 may be used to cause the intake valve to close closer to bottom dead center, thereby increasing the effective compression ratio of the internal combustion engine compared to when the temperature of the internal combustion engine is higher than the predetermined temperature. This improves the startability of the internal combustion engine.

[0101] In the above-described embodiment, the intake-side variable valve mechanism 46 may be of a type that can change the opening and closing timings of the intake valves independently. Also, the intake-side variable valve mechanism 46 is not limited to being hydraulically driven, and may be electrically driven by a motor or the like.

[0102] The intake-side variable valve mechanism 46 may also be a variable lift / operating angle mechanism that can change the lift and operating angle of the intake valve. Variable lift / operating angle mechanisms are already known, for example, from Japanese Patent Application Laid-Open No. 2002-89303, and are capable of simultaneously and continuously increasing or decreasing the lift and operating angle of the intake valve.

[0103] In addition, the intake-side variable valve mechanism 46 may be composed of a phase variable mechanism that continuously advances or retards the phase of the central angle of the intake valve lift, and a lift / operating angle variable mechanism that can change the lift amount and operating angle of the intake valve.

[0104] In the above-described embodiment, the supercharger 47 is a turbo supercharger, but the supercharger 47 may be an electric supercharger in which an electric motor drives a compressor disposed in the intake passage. In this case, it is possible to prevent supercharging by not driving the electric motor that drives the compressor.

[0105] Furthermore, the variable compression ratio mechanism 1 may be configured such that, when determining the mechanical maximum compression ratio, a member other than the first arm portion 22 abuts against a corresponding stopper.

[0106] Furthermore, the variable compression ratio mechanism 1 may be configured such that, when determining the mechanical minimum compression ratio, a member other than the second arm portion 26 is abutted against a corresponding stopper, thereby determining the mechanical minimum compression ratio. [Explanation of symbols]

[0107] 1...Variable compression ratio mechanism 2...Piston 4...Upper Link 6...Crankshaft 7...Lower Link 9...Control Link 10...First control axis 11...Cylinder block 21...Actuator 22...First arm section 24...Second control axis 26...Second arm section 30...Lever 35...High compression ratio stopper 36...Low compression ratio stopper 41...Control unit 44...Compression ratio sensor 46...Variable intake valve mechanism 47...Turbocharger

Claims

1. a variable compression ratio mechanism that can change the compression ratio by changing the combustion chamber volume; a first stopper that mechanically restricts one of the members that configure the variable compression ratio mechanism and that moves when the compression ratio is changed to a higher compression ratio side from displacing toward the higher compression ratio side, thereby determining the maximum compression ratio of the variable compression ratio mechanism; a second stopper that mechanically restricts, toward the lower compression ratio side, displacement of one of the members that configure the variable compression ratio mechanism and that moves when the compression ratio is changed to the lower compression ratio side, thereby determining a minimum compression ratio of the variable compression ratio mechanism, when the internal combustion engine is stopped, one of the members constituting the variable compression ratio mechanism that moves when the compression ratio is changed to the high compression ratio side is brought into contact with the first stopper, and when the internal combustion engine is started, the variable compression ratio mechanism is operated so as to achieve the maximum compression ratio, and the state in which the variable compression ratio mechanism has achieved the maximum compression ratio is learned as a reference position on the high compression ratio side; A control method for an internal combustion engine, characterized in that, if one of the members constituting the variable compression ratio mechanism that moves when changing the compression ratio to the high compression ratio side fails to abut against the first stopper when the internal combustion engine is stopped, the variable compression ratio mechanism is operated to achieve the minimum compression ratio when the internal combustion engine is started, and the state in which the variable compression ratio mechanism has achieved the minimum compression ratio is learned as a reference position for the low compression ratio side.

2. 2. The control method for an internal combustion engine according to claim 1, wherein, when the internal combustion engine is stopped, if one of the members constituting the variable compression ratio mechanism that moves when changing the compression ratio to the high compression ratio side fails to abut against the first stopper, when the internal combustion engine is started, cranking is started without waiting for completion of learning of the reference position on the low compression ratio side of the variable compression ratio mechanism.

3. A variable valve mechanism is provided that can vary the valve timing of the intake valve of the internal combustion engine.

3. The control method for an internal combustion engine according to claim 1, wherein, during a cold start in which the temperature of the internal combustion engine is equal to or lower than a predetermined temperature, the effective compression ratio of the internal combustion engine is made higher by the variable valve mechanism than when the temperature of the internal combustion engine is higher than the predetermined temperature.

4. A supercharger is provided to supercharge the intake air of the internal combustion engine.

4. The control method for an internal combustion engine according to claim 1, wherein, if one of the members constituting the variable compression ratio mechanism that moves when changing the compression ratio to the high compression ratio side fails to abut against the first stopper when the internal combustion engine is stopped, supercharging by the supercharger is prohibited when the internal combustion engine is started until learning of a reference position on the low compression ratio side of the variable compression ratio mechanism is completed.

5. 5. A control method for an internal combustion engine according to claim 1, further comprising the step of recording, when the internal combustion engine is stopped, whether or not one of the members constituting the variable compression ratio mechanism that moves when the compression ratio is changed to the high compression ratio side comes into contact with the first stopper.

6. a variable compression ratio mechanism that can change the compression ratio by changing the combustion chamber volume; a first stopper that mechanically restricts one of the members that configure the variable compression ratio mechanism and that moves when the compression ratio is changed to a higher compression ratio side from displacing toward the higher compression ratio side, thereby determining the maximum compression ratio of the variable compression ratio mechanism; a second stopper that mechanically restricts one of the members that constitute the variable compression ratio mechanism, which moves when the compression ratio is changed to a lower compression ratio side, from displacing toward the lower compression ratio side, thereby determining the minimum compression ratio of the variable compression ratio mechanism; when the internal combustion engine is stopped, one of the members constituting the variable compression ratio mechanism that moves when the compression ratio is changed to the high compression ratio side is brought into contact with the first stopper, and when the internal combustion engine is started, the variable compression ratio mechanism is operated so as to achieve the maximum compression ratio, and the state in which the variable compression ratio mechanism has achieved the maximum compression ratio is learned as a reference position on the high compression ratio side; and a control unit that, when the internal combustion engine is stopped, operates the variable compression ratio mechanism to achieve the minimum compression ratio when the internal combustion engine is started, if one of the members that move when changing the compression ratio to the high compression ratio side among the members that make up the variable compression ratio mechanism fails to abut against the first stopper, and learns the state in which the variable compression ratio mechanism has achieved the minimum compression ratio as a reference position for the low compression ratio side.

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