JP2009115060A - Variable compression ratio internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make an actual compression ratio promptly reach near a target compression ratio even the target compression ratio is a value within a low compression ratio region. <P>SOLUTION: A variable compression ratio internal combustion engine includes a variable compression ratio mechanism (A) which can change a compression ratio of the internal combustion engine by rotating an actuator 59. The actuator is controlled so that a rotation angle of the actuator becomes a target rotation angle corresponding to a target compression ratio set in accordance with an engine operating state. If an actual compression ratio is required to be changed to a target compression ratio within a low compression ratio region, the actual rotation angle is allowed to exceed the target rotation speed to be overshot when changing the rotation angle of the actuator to the target rotation angle. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a variable compression ratio internal combustion engine.

  In recent years, techniques for changing the compression ratio of an internal combustion engine have been proposed for the purpose of improving the fuel efficiency and output performance of the internal combustion engine. As such a technique, for example, a cylinder block and a crankcase are connected so as to be relatively movable, and a camshaft is provided in the connecting portion, and the camshaft is rotated to connect the cylinder block and the crankcase to the cylinder axis. There is a technique in which the volume of the combustion chamber is changed by relative movement in the direction, thereby changing the compression ratio of the internal combustion engine (see, for example, Patent Documents 1 and 2).

  In the variable compression ratio internal combustion engine disclosed in Patent Documents 1 and 2, the camshaft is rotated by a drive motor. If the camshaft is rotated by the drive motor in this way, the camshaft may be over-rotated, and the over-rotation of the camshaft causes the internal combustion engine compression ratio to overshoot beyond the target compression ratio. It may end up.

  Therefore, in the variable compression ratio internal combustion engine disclosed in Patent Document 1, when changing the compression ratio of the internal combustion engine to the target compression ratio in order to suppress such overshoot due to over-rotation of the camshaft, the actual compression ratio is actually reduced. When the compression ratio reaches the vicinity of the target compression ratio, the rotational speed of the drive motor is reduced. In the variable compression ratio internal combustion engine, the rotational speed of the drive motor is similarly reduced when the actual compression ratio is near the maximum compression ratio or the minimum compression ratio that can be taken by the variable compression ratio mechanism. .

JP 2007-56837 A JP 2003-206871 A

  However, in a variable compression ratio internal combustion engine as disclosed in Patent Document 1, the relationship between the rotation angle of the drive motor and the compression ratio is not linear, and particularly in the low compression ratio region, the change in the rotation angle of the drive motor The rate of change in compression ratio is small. Therefore, for example, as disclosed in Patent Document 1, if the rotational speed of the drive motor is reduced when the compression ratio is in the vicinity of the minimum compression ratio, that is, within the low compression ratio region, the compression ratio is reduced. Reaching the target compression ratio will be delayed.

  Here, normally, when the compression ratio is lowered, the amount of intake air supplied into the combustion chamber of the internal combustion engine is also increased at the same time. For this reason, when the target compression ratio is in the low compression ratio region and the actual compression ratio is moved from the medium to high compression ratio region to the low compression ratio region, the amount of intake air supplied into the combustion chamber is increased. In spite of this, a situation may occur in which the compression ratio is not sufficiently low due to a delay in changing the compression ratio. In such a situation, the compression end temperature (temperature of the mixture in the combustion chamber when the piston is at compression top dead center) and the compression end pressure (the temperature of the mixture in the combustion chamber when the piston is at compression top dead center). Abnormal combustion may occur in the combustion chamber due to an increase in pressure, and knocking may occur.

  The present invention has been made in view of the above problems, and its purpose is to quickly reach the actual compression ratio near the target compression ratio even if the target compression ratio is a value in the low compression ratio region. An object of the present invention is to provide a variable compression ratio internal combustion engine that can be made to operate.

In order to solve the above-described problem, the first invention includes a variable compression ratio mechanism capable of changing the compression ratio of the internal combustion engine by rotating the actuator, and the rotation angle of the actuator is set according to the engine operating state. In a variable compression ratio internal combustion engine in which the actuator is controlled to have a target rotation angle corresponding to the target compression ratio, the actual compression ratio should be changed to the target compression ratio in the low compression ratio region. When the rotation angle of the actuator is changed to the target rotation angle, the actual rotation angle is allowed to overshoot beyond the target rotation angle.
According to the first invention, when the target compression ratio is in the low compression ratio region, the rotation angle of the actuator exceeds the target rotation angle and is overshot. In the low compression ratio region, the ratio of the change in the compression ratio to the change in the rotation angle of the actuator is small. Therefore, even if the overshoot occurs in the low compression ratio region and the actuator rotation angle deviates from the target rotation angle, the compression ratio is It is maintained near the target compression ratio. For this reason, the compression ratio can be quickly reached near the target compression ratio.

  In the second invention, in the first invention, when the actual compression ratio should be changed to the target compression ratio in the low compression ratio region, the actual rotation ratio is changed when the rotation angle of the actuator is changed to the target rotation angle. The actuator is controlled so that the rotation angle exceeds the target rotation angle and overshoots.

  According to a third invention, in the second invention, a sensor capable of detecting a rotation angle or a compression ratio of the actuator is further provided so that the rotation angle of the actuator becomes a target rotation angle based on an output of the sensor. The actuator is feedback-controlled, and controlling the actuator so that the actual rotation angle exceeds the target rotation angle and overshoots is performed by increasing the control gain in the feedback control.

  According to a fourth aspect, in the second aspect, controlling the actuator so that the actual rotation angle exceeds the target rotation angle and overshoots the corrected target rotation with the actual rotation angle exceeding the target rotation angle. This is done by controlling the actuator so as to be at an angle.

  In the fifth invention, in any one of the first to fourth inventions, when the actual compression ratio should be changed to the target compression ratio in the middle compression ratio region, the rotation angle of the actuator is set to the target rotation angle. It is prohibited that the actual rotation angle exceeds the target rotation angle and overshoots when changing to.

  In the sixth invention, in the fifth invention, when the actual compression ratio should be changed to the target compression ratio in the intermediate compression ratio region, the actual rotation ratio is changed when the rotation angle of the actuator is changed to the target rotation angle. The actuator is controlled so that the rotation angle does not overshoot beyond the target rotation angle.

  In the seventh invention, in the first invention, when the actual compression ratio should be changed to the target compression ratio in the low compression ratio region, the overshoot allowable range with respect to the target rotation angle of the actuator is the actual compression ratio. This is larger than the overshoot allowable range with respect to the target rotation angle of the actuator when the target compression ratio is to be changed within the intermediate compression ratio region.

  In the eighth invention, in the first or seventh invention, when the actual compression ratio should be changed to the target compression ratio in the high compression ratio region, the overshoot allowable range with respect to the target rotation angle of the actuator is an actual When the compression ratio is to be changed to the target compression ratio in the middle compression ratio region, the overshoot allowable range for the target rotation angle of the actuator is larger.

  According to the present invention, even when the target compression ratio is in the low compression ratio region, the compression ratio can quickly reach the vicinity of the target compression ratio.

  Hereinafter, a variable compression ratio internal combustion engine according to a first embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 shows a side sectional view of a spark ignition type internal combustion engine.

  Referring to FIG. 1, 1 is a crankcase, 2 is a cylinder block, 3 is a cylinder head, 4 is a piston, 5 is a combustion chamber, 6 is a spark plug disposed at the center of the top surface of the combustion chamber 5, and 7 is an intake air 8 is an intake port, 9 is an exhaust valve, and 10 is an exhaust port. The intake port 8 is connected to a surge tank 12 via an intake branch pipe 11, and a fuel injection valve 13 for injecting fuel into the corresponding intake port 8 is arranged in each intake branch pipe 11. The fuel injection valve 13 may be arranged in each combustion chamber 5 instead of being attached to each intake branch pipe 11.

  The surge tank 12 is connected to an air cleaner 15 via an intake duct 14, and a throttle valve 17 driven by an actuator 16 and an intake air amount detector 18 using, for example, heat rays are arranged in the intake duct 14. On the other hand, the exhaust port 10 is connected to a catalytic converter 20 containing, for example, a three-way catalyst via an exhaust manifold 19, and an air-fuel ratio sensor 21 is disposed in the exhaust manifold 19.

  On the other hand, in the embodiment shown in FIG. 1, the piston 4 is positioned at the compression top dead center by changing the relative position of the crankcase 1 and the cylinder block 2 in the cylinder axis direction at the connecting portion between the crankcase 1 and the cylinder block 2. Is provided with a variable compression ratio mechanism A capable of changing the volume of the combustion chamber 5 when the engine is operated, and a variable valve timing capable of controlling the closing timing of the intake valve 7 in order to change the actual start timing of the compression action. A mechanism B is provided.

  The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. A ROM (Read Only Memory) 32, a RAM (Random Access Memory) 33, a CPU (Microprocessor) 34, an input port 35 and an output port 36. It comprises. The output signal of the intake air amount detector 18 and the output signal of the air-fuel ratio sensor 21 are input to the input port 35 via the corresponding AD converters 37, respectively. A load sensor 41 that generates an output voltage proportional to the amount of depression of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. The Further, a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 30 ° is connected to the input port 35. Further, the cylinder block 2 is provided with a relative position sensor 43 for detecting the relative position between the cylinder block 2 and the crankcase 1, and the output voltage of the relative position sensor 43 is passed through a corresponding AD converter 37. Input to the input port 35. On the other hand, the output port 36 is connected to the spark plug 6, the fuel injection valve 13, the throttle valve drive actuator 16, the variable compression ratio mechanism A, and the variable valve timing mechanism B through corresponding drive circuits 38.

  Next, the configuration of the variable compression ratio mechanism A of the present embodiment will be described with reference to FIGS. 2 is an exploded perspective view of the variable compression ratio mechanism A shown in FIG. 1, and FIG. 3 is a side sectional view of the internal combustion engine schematically shown.

  Referring to FIG. 2, a plurality of block-side protrusions 50 are formed below the both side walls of the cylinder block 2 so as to be spaced from each other. A cam insertion hole 51 is formed. These block side cam insertion holes 51 are formed on the same axis so as to be parallel to the arrangement direction of the cylinders.

  On the other hand, a plurality of case-side protrusions 52 are formed on the upper wall surface of the crankcase 1 so as to be fitted between the corresponding block-side protrusions 50 spaced apart from each other. Case-side cam insertion holes 53 each having a circular cross section are also formed in the portion 52. The case side cam insertion holes 53 are also formed on the same axis so as to be parallel to the cylinder arrangement direction, similarly to the block side cam insertion holes 51.

  As shown in FIG. 2, a pair of camshafts 54 and 55 are provided, and on the camshafts 54 and 55, every other one is rotatably inserted into each case-side cam insertion hole 53. A circular cam 56 is fixed. These case-side circular cams 56 are coaxial with the rotational axes of the camshafts 54 and 55. On the other hand, an eccentric shaft 57 arranged eccentrically with respect to the rotation axis of each camshaft 54, 55 extends between the case side circular cams 56, as shown in FIG. A circular cam 58 is eccentrically mounted for rotation. As shown in FIG. 2, these block-side circular cams 58 are arranged between the case-side circular cams 56, and these block-side circular cams 58 are rotatably inserted into the corresponding block-side cam insertion holes 51. ing.

  As shown in FIG. 2, a pair of worm gears 61, 62 having opposite spiral directions are attached to the rotation shaft 60 of the drive motor 59 in order to rotate the camshafts 54, 55 in opposite directions, respectively. Gears 63 and 64 that mesh with the worm gears 61 and 62 are fixed to end portions of the camshafts 54 and 55, respectively. In this embodiment, by driving the drive motor 59, the volume of the combustion chamber when the piston 4 is located at the compression top dead center can be changed over a wide range.

  Next, a method for changing the compression ratio by the variable compression ratio mechanism A having the above-described configuration will be described in detail with reference to FIGS. FIG. 4 is a diagram modeling the movement of the center of the case-side circular cam 56, the eccentric shaft 57, and the block-side circular cam 58. 3 and 4, a is the center of the case-side circular cam 56, b is the center of the eccentric shaft 57, and c is the center of the block-side circular cam 58. In this embodiment, the diameter of the block-side circular cam 58 is larger than the diameter of the case-side circular cam 56 as shown in FIG. The distance m between the center b of the eccentric shaft 57 is longer than the distance n between the center a of the case side circular cam 56 and the center b of the eccentric shaft 57.

  When the drive motor 59 is driven from the state shown in FIGS. 3A and 4A, the case-side circular cams 56 are opposite to each other as indicated by solid arrows in FIG. When the camshafts 54 and 55 are rotated to rotate, the eccentric shaft 57 moves upward around the center a of the case-side circular cam 56. Along with the movement of the eccentric shaft 57, the block-side circular cam 58 is also rotated in the directions opposite to each other in the directions indicated by solid arrows in FIG. When the case-side circular cam 56 rotates 90 ° from the state shown in FIGS. 3A and 4A, the state shown in FIGS. 3B and 4B is obtained.

  Further, when the drive motor 59 is driven to rotate the camshafts 54 and 55 so that the case-side circular cam 56 rotates in opposite directions as indicated by arrows in FIG. It moves further upward around the center a of the side circular cam 56. As the eccentric shaft 57 moves, the block-side circular cam 58 is also rotated in the direction opposite to the direction indicated by the arrow in FIG. When the case-side circular cam 56 rotates 90 ° from the state shown in FIGS. 3B and 4B, the state shown in FIGS. 3C and 4C is obtained.

  Here, the block-side circular cam 58 and the case-side circular cam 56 are accommodated in the block-side cam insertion port 51 and the case-side cam insertion port 53, respectively, and cannot move in a direction perpendicular to the cylinder axis. . Accordingly, the block-side circular cam 58 or the case-side circular cam 56 can be relatively moved only in a direction parallel to the cylinder axis. Therefore, the cams 56 and 58 are always positioned on the same straight line l parallel to the cylinder axis. To do. Therefore, the case-side circular cams 56 fixed on the camshafts 54 and 55 are rotated in opposite directions as shown by solid arrows in FIG. 3A from the state shown in FIG. As a result, the center c of the block-side circular cam 58 is moved upward away from the center a of the case-side circular cam 56.

  3A to 3C, the relative position between the crankcase 1 and the cylinder block 2 is determined by the distance between the center a of the case-side circular cam 56 and the center c of the block-side circular cam 58. As the distance between the center a of the case-side circular cam 56 and the center c of the block-side circular cam 58 increases, the cylinder block 2 moves away from the crankcase 1. When the cylinder block 2 moves away from the crankcase 1, the volume of the combustion chamber 5 when the piston 4 is located at the compression top dead center increases. Therefore, the volume of the combustion chamber 5 when the piston 4 is located at the compression top dead center (hereinafter referred to as “combustion chamber volume”) can be changed by rotating the camshafts 54 and 55.

  Even if the volume of the combustion chamber 5 when the piston 4 is located at the compression top dead center is changed by rotating the camshafts 54 and 55 in this way, the stroke volume of the piston 4 during the compression stroke (the piston 4 The volume of the combustion chamber 5 that changes when moving from the intake bottom dead center to the compression top dead center does not change. Therefore, the compression ratio represented by (combustion chamber volume + stroke volume) / combustion chamber volume changes according to the change of the combustion chamber volume. That is, according to the variable compression ratio mechanism A of the present embodiment, the compression ratio of the internal combustion engine can be changed by rotating the camshafts 54 and 55 by the drive motor 59.

  The variable compression ratio mechanism A shown in FIGS. 1 to 4 is an example, and any type of variable compression ratio mechanism can be used as long as the compression ratio can be changed by driving an actuator such as a drive motor. Can be used.

  By the way, in the internal combustion engine having the variable compression ratio mechanism A configured as described above, the rotation angle of the camshafts 54 and 55 or the drive motor 59 and the compression ratio are not proportional. Below, this reason is demonstrated easily. In this specification, the relationship between the rotation angle of the camshafts 54 and 55 and the compression ratio will be described as an example, but the same applies to the relationship between the rotation angle of the drive motor 59 and the compression ratio.

図５はｍ：ｎを２：１とした場合における回転角度θに対する相対距離Ｌを示す図である。図５からわかるように、カムシャフト５４、５５の回転角度θに対して相対距離Ｌは比例しない。 Referring to the model shown in FIG. 4, when the rotation angle of the camshafts 54 and 55 from the state shown in FIGS. 3A and 4A is θ, the cylinder block 3 relative to the crankcase 1 The relative distance L is expressed as the following formula (1).

FIG. 5 is a diagram showing the relative distance L with respect to the rotation angle θ when m: n is 2: 1. As can be seen from FIG. 5, the relative distance L is not proportional to the rotation angle θ of the camshafts 54 and 55.

In the model as shown in FIG. 6A, the compression ratio ε is expressed by the following equation (2) using the height h of the combustion chamber 5 determined according to the relative distance L and the stroke s of the piston 4. It is expressed as follows.
ε = ((π · (D / 2) ² · (h + s) / (π · (D / 2) ² · h)
= (H + s) / h (2)

  As shown in FIG. 6B, the rate of change of the compression ratio ε with respect to the change in the height h increases as the compression ratio becomes higher and the height h of the combustion chamber 5 decreases. That is, the compression ratio ε does not change in proportion to the height of the combustion chamber 5.

  Due to the synergistic effect of these two principles, the rotation angle of the camshafts 54 and 55 and the compression ratio are not proportional. Specifically, the relationship between the rotation angle θ of the camshafts 54 and 55 and the compression ratio ε is as shown in FIG. 7A, for example, and the compression ratio ε per unit rotation angle of the camshafts 54 and 55 is The amount of change (hereinafter referred to as “compression ratio change rate”) is as shown in FIG. That is, when the rotation angle θ of the camshafts 54 and 55 is small, that is, when the compression ratio is low, and when the rotation angle θ of the camshafts 54 and 55 is large, that is, when the compression ratio is high, the compression ratio change rate is small. On the contrary, when the rotation angle θ of the camshafts 54 and 55 is around 90 °, that is, when the compression ratio is medium, the compression ratio change rate is large. FIG. 7 shows the relationship between the rotation angle, the compression ratio, and the compression ratio change rate when m: n is 2: 1, but it is also fundamental when m: n is set to other ratios. A similar tendency is observed.

  By the way, in the variable compression ratio mechanism A of the present embodiment, the rotation angle of the camshafts 54 and 55 is feedback-controlled based on the output of the relative position sensor 43 so that the compression ratio becomes the target compression ratio. Any control method may be used as the feedback control. Hereinafter, a case where PID control is used as feedback control will be described as an example.

  FIG. 8 is a flowchart showing a control routine for controlling the rotation angle of the drive motor 59. The illustrated control routine is performed by interruption at predetermined time intervals. First, in step S11, a target rotation angle θt set by target rotation angle setting control, which will be described later, is acquired according to the target compression ratio calculated based on the engine load and the like. Next, in step S12, the current rotation angle θ (n) of the camshafts 54 and 55 is calculated based on the output of the relative position sensor 43. Note that n is a value representing the number of times the rotation angle θ is calculated, and for example, n−1 means the rotation angle θ calculated in the previous control routine.

In step S13, a difference Δθ (n) between the target rotation angle θt calculated in step S11 and the current rotation angle θ (n) calculated in step S12 is calculated (Δθ (n) = θt−θ. (N)). Next, in step S14, the proportional term Vp is calculated by the following equation (3) based on the difference Δθ (n) calculated in step S13. Next, in step S15, the integral term Vi is calculated by the following equation (4) based on the difference Δθ (n) calculated in step S13. Further, in step S16, the differential term Vd is calculated by the following equation (5) based on the difference Δθ (n) calculated in step S13. Note that Kp, Ki, and Kd in the equations (3) to (5) indicate a proportional coefficient, an integral coefficient, and a differential coefficient, respectively, and are constant values in this embodiment.

  In step S17, the proportional term Vp calculated in step S14, the integral term Vi calculated in step S15, and the differential term Vd calculated in step S16 are added to calculate the drive voltage Vm of the drive motor 59. Next, in step S 18, the drive voltage 59 calculated in step S 17 is applied to the drive motor 59, and the cam shafts 54 and 55 are rotated by the drive motor 59.

  Incidentally, as described above, in the low compression ratio region, the compression ratio change rate with respect to the rotation angle of the camshafts 54 and 55 is small. Therefore, for example, when the target compression ratio is within this low compression ratio region, the rotation angle of the camshafts 54 and 55 reaches a target rotation angle corresponding to the target compression ratio slowly. For this reason, when the target compression ratio is in the low compression ratio region, the responsiveness of the variable compression ratio mechanism A is lowered.

  Further, when reducing the compression ratio, the intake air amount is often increased. That is, when the compression ratio is high (for example, 14 or more), if the intake air amount supplied into the combustion chamber 5 is large, the compression end temperature and the compression end pressure become too high and knocking occurs. For this reason, when the compression ratio is high, generally, the opening degree of the throttle valve 17 is reduced so that knocking does not occur, or the closing timing of the intake valve 7 is inhaled by the variable valve timing mechanism B. The amount of intake air supplied into the combustion chamber 5 is reduced by moving away from the bottom dead center. On the other hand, when the compression ratio is low (for example, 13 or less), the possibility of knocking is low even if the intake air amount supplied into the combustion chamber 5 is large. For this reason, when the compression ratio is low, the opening degree of the throttle valve 17 is increased, and the closing timing of the intake valve 7 is moved to the vicinity of the intake bottom dead center by the variable valve timing mechanism B. The amount of intake air supplied into the combustion chamber 5 is increased.

  However, when the target compression ratio is changed within the low compression ratio region, if the responsiveness of the variable compression ratio mechanism A is low, only the amount of intake air supplied into the combustion chamber 5 before the compression ratio decreases is obtained. It will increase. For this reason, although the compression ratio is high, the amount of intake air supplied into the combustion chamber 5 increases, and knocking may occur.

  Therefore, in the embodiment of the present invention, when the compression ratio is changed into the low compression ratio region, the actual compression ratio exceeds the target compression ratio and overshoots in order to quickly reach the target compression ratio. I try to allow it. In particular, in the present embodiment, the actual compression ratio overshoots exceeding the target compression ratio, that is, the actual rotation angle of the camshafts 54 and 55 exceeds the target rotation angle corresponding to the target compression ratio. The drive motor 59 is controlled to shoot.

FIG. 9 is a time chart showing changes in the rotation angle θ of the camshafts 54 and 55 and the compression ratio ε when the target compression ratio is changed within the low compression ratio region. In the illustrated example, a transition is shown when the target compression ratio shifts from the maximum compression ratio εmax to the minimum compression ratio εmin due to, for example, a sudden depression of the accelerator pedal 40 at time t ₀ . Further, the solid line in FIG. 9A is the transition of the actual rotation angle of the camshafts 54 and 55, the broken line is the transition of the target rotation angle, the alternate long and short dash line is the transition of the corrected target rotation angle described later, and the two-dot chain line is later described. The transition of the actual rotation angle when normal control is performed without performing control as in this embodiment is shown. Similarly, the solid line in FIG. 9B indicates the transition of the actual compression ratio ε, the broken line indicates the transition of the target compression ratio, and the alternate long and two short dashes line indicates the transition of the actual compression ratio when the normal control is performed. Yes.

First, when the target compression ratio is changed from the maximum compression ratio εmax to the minimum compression ratio εmin at time t ₀ , the target rotation angle also changes from the rotation angle corresponding to the maximum compression ratio εmax (180 ° in the illustrated example) to the minimum compression ratio. The angle is changed to a rotation angle corresponding to εmin (0 ° in the illustrated example). In the case of normal control, the drive motor 59 is controlled so that the rotation angle θ of the camshafts 54 and 55 becomes 0 °, which is the target rotation angle after the change. However, in the present embodiment, as shown by the one-dot chain line in FIG. 9, the corrected target rotation angle that exceeds the changed target rotation angle and is smaller than this target rotation angle (in the example shown in FIG. 9). For example, −10 °) is set, and the drive motor 59 is controlled so that the rotation angle θ of the camshafts 54 and 55 becomes the corrected target rotation angle.

  Thus, by controlling the drive motor 59 so that the rotation angle of the camshafts 54 and 55 becomes the corrected target rotation angle, the actual rotation angle θ of the camshafts 54 and 55 can be quickly reached the target rotation angle. Can do. This state is clear from FIG. 9A, and the rotation angle is the correction target as compared with the case where the normal control is performed so that the rotation angle becomes the target rotation angle (two-dot chain line in the figure). When the rotation angle is controlled to be the same (solid line in the figure), the target rotation angle is reached faster. Accordingly, as shown in FIG. 9B, the rotation angle is compared with the case where the normal control is performed so that the rotation angle becomes the target rotation angle (two-dot chain line in the figure). Is controlled so as to be the corrected target rotation angle (solid line in the figure), the target compression ratio is reached faster.

  In this embodiment, as a result of controlling the rotation angle to be the corrected target rotation angle, when the actual rotation angle of the camshafts 54 and 55 reaches the target rotation angle, the rotation angle thereafter becomes the target rotation angle. To control. However, even if the target value of the rotation angle of the camshafts 54 and 55 is changed from the corrected target rotation angle to the target rotation angle after the actual rotation angle reaches the target rotation angle in this way, FIG. As shown, the rotation angles of the camshafts 54 and 55 overshoot beyond the target rotation angle.

  However, as described with reference to FIG. 7B, the compression ratio change rate is low in the low compression ratio region, that is, in the region where the rotation angle of the camshafts 54 and 55 is small. For this reason, even if the rotation angle of the camshafts 54 and 55 exceeds the target rotation angle and overshoots, the actual compression ratio does not change greatly from the target compression ratio as shown in FIG. It is maintained near the compression ratio. Finally, the actual compression ratio is set to the target compression ratio.

  As described above, according to the compression ratio control method of the present embodiment, the compression ratio can be quickly reached near the target compression ratio, and after reaching the vicinity of the target compression ratio, the compression ratio is set near the target compression ratio. Can be maintained.

  On the other hand, as described with reference to FIG. 7, the compression ratio change rate with respect to the rotation angle of the camshafts 54 and 55 is large in the intermediate compression ratio region. Therefore, for example, when the target compression ratio is in the middle compression ratio region, the responsiveness of the variable compression ratio mechanism A is high. Further, since the rate of change of the compression ratio with respect to the rotation angle of the camshafts 54 and 55 is large in the medium compression ratio region, as described above, the actual rotation angle of the camshafts 54 and 55 overshoots beyond the target rotation angle. When the drive motor 59 is controlled, the compression ratio greatly exceeds the target rotation angle.

  Therefore, in the embodiment of the present invention, when the compression ratio is changed into the middle compression ratio region, the actual compression ratio exceeds the target compression ratio so that the compression ratio does not greatly exceed the target compression ratio. It is prohibited to shoot. In particular, in the present embodiment, the actual compression ratio does not overshoot beyond the target compression ratio, that is, the actual rotation angle of the camshafts 54 and 55 exceeds the target rotation angle corresponding to the target compression ratio. The drive motor 59 is controlled so as not to occur.

  FIG. 10 is a flowchart showing a control routine for setting control of the target rotation angle for executing the above-described compression ratio control method of the present embodiment. Hereinafter, in the description of the control routine, the target rotation angle corresponding to the target compression ratio will be described as the reference target rotation angle.

  Referring to FIG. 10, first, in step S21, it is determined whether a condition for rapidly changing the rotation angle to the target rotation angle when the target compression ratio is in the low compression ratio region, that is, a rapid change condition is satisfied. Is done. The rapid change condition is satisfied when, for example, the accelerator pedal 40 is depressed faster than a predetermined speed, or knocking is detected by a knock sensor (not shown) for detecting knocking in the combustion chamber 5. As a result, the target compression ratio may be changed to a compression ratio in the low compression ratio region. That is, in this embodiment, even when the target compression ratio is changed to a compression ratio in the low compression ratio region, the rapid change condition is not necessarily satisfied, and in addition to that, the compression ratio is rapidly changed to the low compression ratio. The rapid change condition is established when it is necessary to change to the target compression ratio in the region. However, when the target compression ratio is changed to a compression ratio in the low compression ratio region, the rapid change condition may always be satisfied.

  If it is determined in step S21 that the rapid change condition is not satisfied, the process proceeds to step S24. In step S24, the target rotation angle θt used in step S11 of FIG. 8 is set as the reference target rotation angle θtb. Here, the reference target rotation angle θtb is a rotation angle corresponding to the target compression ratio calculated according to the engine load or the like. The reference target rotation angle θtb is calculated in advance by obtaining a map as shown in FIG. 7 through experiments or the like and based on the target compression ratio.

  On the other hand, if it is determined in step S21 that the rapid change condition is satisfied, the process proceeds to step S22. In step S22, the target rotation angle θt used in step S11 of FIG. 8 is set as the corrected target rotation angle θtm. Here, the corrected target rotation angle θtm is a rotation angle shifted from the reference target rotation angle θtb described above in a direction away from the current rotation angle by a fixed rotation angle. The corrected target rotation angle θtm is calculated by calculating the reference target rotation angle θtb as described above and adding or subtracting a predetermined value from the reference target rotation angle θtb.

  Next, in step S23, it is determined whether or not the actual rotation angle θt of the camshafts 54 and 55 has reached the reference target rotation angle θtb. When it is determined in step S23 that the actual rotation angle θt has not reached the reference target rotation angle θtb, step S22 is repeated until the target rotation angle θtb reaches the reference target rotation angle θtb, and the target rotation angle θt becomes the corrected target rotation. The angle θtm is maintained. Thereafter, when it is determined in step S23 that the actual rotation angle θt has reached the reference target rotation angle θtb, the process proceeds to step S24, where the target rotation angle θt is set as the reference target rotation angle θtb.

  Next, the variable compression ratio internal combustion engine of the second embodiment of the present invention will be described. The configuration of the variable compression ratio internal combustion engine of the present embodiment is basically the same as the configuration of the variable compression ratio internal combustion engine of the first embodiment. However, in the variable compression ratio internal combustion engine of the present embodiment, when the target compression ratio is changed to a compression ratio in the low compression ratio region, the rotation angle of the camshafts 54 and 55 is set without setting the corrected target rotation angle. The variable compression ratio mechanism A is controlled so as to be the target rotation angle, and the control gain in the feedback control of the rotation angle of the camshafts 54 and 55 is changed.

FIG. 11 is a time chart similar to FIG. 9 showing the transition of the control gain, the rotation angle θ of the camshafts 54 and 55, and the compression ratio ε when the target compression ratio is changed within the low compression ratio region. is there. In the illustrated example, a transition is shown when the target compression ratio shifts from the wife band compression ratio εmax to the minimum compression ratio εmin due to, for example, a sudden depression of the accelerator pedal 40 at time t ₀ .

First, when the target compression ratio is changed from the maximum compression ratio εmax to the minimum compression ratio εmin at time t ₀ , the target rotation angle also changes from the rotation angle corresponding to the maximum compression ratio εmax (180 ° in the illustrated example) to the minimum compression ratio. The angle is changed to a rotation angle corresponding to εmin (0 ° in the illustrated example). Then, the drive motor 59 is controlled so that the actual rotation angle θ of the camshafts 54 and 55 becomes 0 °, which is the changed target rotation angle.

  At this time, in this embodiment, when the target rotation angle is changed to the rotation angle corresponding to the low compression ratio region, the control gain is increased with the change of the target rotation angle. Here, the control gain means the ratio of output to input in the control. Normally, the larger the control gain, the larger the control amount (rotation amount) of the camshafts 54 and 55 under the same conditions. When PID control is performed as shown in FIG. 8, increasing the control gain means increasing at least one of the proportional coefficient Kp, the integral coefficient Ki, and the differential coefficient Kd.

  By increasing the control gain in this manner, the actual rotation angle θ of the camshafts 54 and 55 can be quickly reached the target rotation angle as shown in FIG. Along with this, the compression ratio can be quickly reached the target compression ratio. In particular, in this embodiment, the control gain is increased so that the rotation angle of the camshafts 54 and 55 exceeds the target rotation angle and overshoots. Therefore, the rotation angle θ of the camshafts 54 and 55 can reach the target rotation angle very quickly.

  In the present embodiment, once the actual rotation angle of the camshafts 54 and 55 reaches the target rotation angle, the control gain is returned to the original value thereafter. Here, even if the control gain is returned to the original value after the actual rotation angle reaches the target rotation angle, the rotation angles of the camshafts 54 and 55 overshoot beyond the target rotation angle. However, as described with reference to FIG. 7B, since the compression ratio change rate is low in the low compression ratio region, even if the rotation angle θ of the camshafts 54 and 55 exceeds the target rotation angle, it actually The compression ratio is maintained near the target compression ratio.

  As described above, the compression ratio control method according to the second embodiment can quickly reach the vicinity of the target compression ratio and can reach the vicinity of the target compression ratio. Can be maintained.

  In this embodiment, the control gain is such that the angle at which the rotation angle of the camshafts 54, 55 overshoots beyond the target rotation angle (hereinafter referred to as “overshoot allowable angle deviation”) is less than the value shown in FIG. Is set to be As can be seen from FIG. 12, the overshoot allowable angle deviation in the low compression ratio region and the high compression ratio region is smaller than the overshoot allowable angle deviation in the medium compression ratio region. This is because the compression ratio change rate in the medium compression ratio region is larger than the compression ratio change rate in the low compression ratio region and the high compression ratio region. In other words, the amount that can be overshot when the compression ratio exceeds the target compression ratio is substantially constant in all compression ratio regions.

  FIG. 13 is a flowchart showing a control routine of control gain setting control for executing the above-described compression ratio control method of the present embodiment. Steps S31 and S33 shown in FIG. 13 are the same as steps S21 and S23 shown in FIG.

  If it is determined in step S31 that the rapid change condition is not satisfied, the process proceeds to step S34. In step S34, the proportional coefficient Kp, the integral coefficient Ki, and the differential coefficient Kd used in steps 14, 15, and 16 in FIG. 8 are set as the reference proportional coefficient Kpb, the reference integral coefficient Kib, and the reference differential coefficient Kdb, respectively. These coefficients Kpb, Kib, and Kdb are set to values that reach the target rotation angle the fastest in a range where the rotation angle of the camshafts 54 and 55 does not exceed the target rotation angle and overshoot, for example.

  On the other hand, if it is determined in step S31 that the rapid change condition is satisfied, the process proceeds to step S32. In step S32, the proportionality coefficient Kp, the integral coefficient Ki, and the differential coefficient Kd used in steps 14, 15, and 16 in FIG. 8 are set as the corrected proportional coefficient Kpm, the corrected integral coefficient Kim, and the corrected differential coefficient Kdm, respectively. Here, the modified proportionality coefficient Kpm, the modified integral coefficient Kim, and the modified differential coefficient Kdm are set to values equal to or larger than the standard proportional coefficient Kpb, the standard integral coefficient Kib, and the standard differential coefficient Kdb, respectively (Kpm ≧ Kpb, Kim ≧ Kib, Kdm ≧ Kdb).

  Next, if it is determined in step S33 that the actual rotation angle θ has not reached the target rotation angle θt, step S32 is repeated until the target rotation angle θt is reached. Thereafter, when it is determined that the actual rotation angle θ has reached the target rotation angle θt, the process proceeds to step S34, where the proportional coefficient Kp, the integral coefficient Ki, and the differential coefficient Kd are the reference proportional coefficient Kpb and the reference integral coefficient, respectively. Let Kib be the reference differential coefficient Kdb.

  FIG. 14 is a side view showing one example of gears 63 and 64 that mesh with the worm gears 61 and 62 used in the embodiment of the present invention. The gears 63 and 64 may be circular as shown in FIG. 2, or may be substantially semicircular as shown in FIG.

  However, as described above, in the above embodiment, for example, when the target rotation angle is 0 °, the camshafts 54 and 55 are controlled to overshoot beyond the target rotation angle. For this reason, the gears 63 and 64 must be formed so that the camshafts 54 and 55 can mesh with the worm gears 61 and 62 even when the rotation angle of the camshafts 54 and 55 is 0 ° or less.

  Therefore, in the embodiment of the present invention, the meshing angle α of the gears 63 and 64 is 180 ° or more. In particular, in the gears 63 and 64 of the present embodiment, meshing margin areas β and β ′ are provided on both sides of the meshing area corresponding to the maximum compression ratio to the minimum compression ratio. As a result, the gears 63 and 64 mesh with the worm gears 61 and 62 even when the rotation angle of the camshafts 54 and 55 is 0 ° or less and 180 ° or more.

  In the above description, the drive motor 59 is controlled so that the rotation angle of the camshafts 54 and 55 becomes the target rotation angle by feedback control. However, the rotation can be performed by any control such as open loop control as well as feedback control. You may control so that an angle may turn into a target rotation angle.

1 is an overall view of a spark ignition internal combustion engine. It is a disassembled perspective view of a variable compression ratio mechanism. 1 is a schematic side sectional view of an internal combustion engine. It is the figure which modeled the motion of the center of a block side circular cam, an eccentric shaft, and a case side circular cam. It is a figure which shows the relative displacement amount with respect to a rotation angle. It is a figure for demonstrating the relationship between the height of a combustion chamber, and a compression ratio. It is a figure which shows the relationship between a rotation angle, a compression ratio, and a compression ratio change rate. It is a flowchart which shows the control routine of rotation angle control of a drive motor. It is a time chart showing transition of the rotation angle of the camshaft and the compression ratio ε when the target compression ratio is changed within the low compression ratio region. It is a flowchart which shows the control routine of the setting control of a target rotation angle. It is a time chart showing transition of a control gain, a rotation angle of a camshaft, and a compression ratio. It is a figure which shows an overshoot allowable angle deviation. It is a flowchart which shows the control routine of control gain setting control. It is a side view which shows one example of the gearwheel meshing with a worm gear.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crankcase 2 Cylinder block 3 Cylinder head 4 Piston 5 Combustion chamber 7 Intake valve 54, 55 Camshaft 56 Case side circular cam 57 Eccentric shaft 58 Block side circular cam 59 Drive motor 63, 64 Gear A Variable compression ratio mechanism B Variable valve Timing mechanism

Claims (8)

A variable compression ratio mechanism capable of changing the compression ratio of the internal combustion engine by rotating the actuator is provided so that the rotation angle of the actuator becomes a target rotation angle corresponding to a target compression ratio set according to the engine operating state. In a variable compression ratio internal combustion engine in which the actuator is controlled
When the actual compression ratio should be changed to the target compression ratio in the low compression ratio region, when the rotation angle of the actuator is changed to the target rotation angle, the actual rotation angle exceeds the target rotation angle and overshoots. A variable compression ratio internal combustion engine that is allowed to do.   When the actual compression ratio should be changed to the target compression ratio in the low compression ratio region, when the rotation angle of the actuator is changed to the target rotation angle, the actual rotation angle exceeds the target rotation angle and overshoots. The variable compression ratio internal combustion engine according to claim 1, wherein the actuator is controlled to do so. A sensor capable of detecting the rotation angle or compression ratio of the actuator, and feedback-controlling the actuator so that the rotation angle of the actuator becomes a target rotation angle based on the output of the sensor;
The variable compression ratio internal combustion engine according to claim 2, wherein controlling the actuator so that the actual rotation angle overshoots beyond the target rotation angle is performed by increasing a control gain in feedback control.   Controlling the actuator so that the actual rotation angle overshoots beyond the target rotation angle is achieved by controlling the actuator so that the actual rotation angle becomes a corrected target rotation angle exceeding the target rotation angle. The variable compression ratio internal combustion engine according to claim 2, wherein the internal combustion engine is performed.   When the actual compression ratio should be changed to the target compression ratio in the medium compression ratio region, the actual rotation angle exceeds the target rotation angle and overshoots when the rotation angle of the actuator is changed to the target rotation angle. The variable compression ratio internal combustion engine according to any one of claims 1 to 4, which is prohibited to perform.   When the actual compression ratio should be changed to the target compression ratio in the medium compression ratio region, the actual rotation angle exceeds the target rotation angle and overshoots when the rotation angle of the actuator is changed to the target rotation angle. The variable compression ratio internal combustion engine according to claim 5, wherein the actuator is controlled so as not to occur.   When the actual compression ratio should be changed to the target compression ratio in the low compression ratio region, the allowable overshoot range for the target rotation angle of the actuator is to change the actual compression ratio to the target compression ratio in the medium compression ratio region. The variable compression ratio internal combustion engine according to claim 1, wherein the variable compression ratio internal combustion engine is larger than an allowable overshoot range with respect to a target rotation angle of the actuator in a power case.   When the actual compression ratio should be changed to the target compression ratio in the high compression ratio region, the overshoot allowable range for the target rotation angle of the actuator is to change the actual compression ratio to the target compression ratio in the medium compression ratio region. The variable compression ratio internal combustion engine according to claim 1 or 7, which is larger than an allowable overshoot range with respect to a target rotation angle of the actuator in a power case.

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