JP2013151911A - Internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an internal combustion engine for suppressing combustion from becoming unstable when a working angle of an intake valve is switched.SOLUTION: An internal combustion engine includes: a variable compression ratio mechanism capable of changing a mechanical compression ratio; and a variable working angle mechanism capable of incrementally switching a working angle of an intake valve. A reference mechanical compression ratio associated with the operating state of the internal combustion engine is predetermined. A set mechanical compression ratio is set based on the reference mechanical compression ratio when the working angle of the intake valve should be switched, and the working angle of the intake valve is switched after changing the mechanical compression ratio directed to the set mechanical compression ratio is started.

Description

  The present invention relates to an internal combustion engine.

  In the combustion chamber of the internal combustion engine, the air-fuel mixture is ignited in a compressed state. It is known that the compression ratio when the air-fuel mixture is compressed affects the output and fuel consumption of the internal combustion engine. By increasing the compression ratio, the output torque can be increased and the thermal efficiency can be improved. However, it is known that abnormal combustion such as knocking occurs when the compression ratio is too high. Further, when the air-fuel mixture burns in the combustion chamber, the piston is pushed down, and the thermal efficiency can also be improved by increasing the expansion ratio at this time.

  In the prior art, there is known an internal combustion engine in which the expansion ratio is increased while suppressing the actual compression ratio from becoming too high particularly when the internal combustion engine is operated at a low load. In Japanese Patent Application Laid-Open No. 2007-303423, a variable compression ratio mechanism capable of changing a mechanical compression ratio determined by a stroke volume of a piston and a volume of a combustion chamber, and a variable valve timing mechanism capable of changing a valve closing timing of an intake valve. A spark ignition type internal combustion engine is disclosed. In this publication, the mechanical compression ratio is maximized so that the maximum expansion ratio can be obtained during low-load operation, and the actual compression ratio during low-load operation is controlled to be substantially the same as during medium-high load operation. Is disclosed.

  In JP 2008-106609 A, a first variable mechanism that controls the valve lift and operating angle (open period) of the intake valve, a phase variable mechanism that controls the lift center angle (phase) of the intake valve, A starting device for an internal combustion engine is disclosed that includes a second variable mechanism that controls a nominal compression ratio in a cylinder. This publication discloses that the operating angle and closing timing of the intake valve are controlled in accordance with the mechanical compression ratio when starting the internal combustion engine.

  Japanese Patent Laid-Open No. 2009-085069 discloses a control device for an internal combustion engine having an intake valve valve operating angle variable mechanism capable of switching the valve operating angle of an intake valve in at least two stages. In the case of switching, it is disclosed that the valve timing of the intake valve is controlled to a valve timing at which the closing timing of the intake valve is substantially the same before and after switching of the valve operating angle of the intake valve.

JP 2007-303423 A JP 2008-106609 A JP 2009-085069 A

  As disclosed in the above Japanese Patent Application Laid-Open No. 2007-303423, an internal combustion engine having a variable compression ratio mechanism and a variable valve timing mechanism for changing the closing timing of the intake valve can be operated at an extremely high expansion ratio. it can. Furthermore, a variable working angle mechanism that can change the working angle of the intake valve can be arranged. As the variable working angle mechanism, it is preferable to continuously change the working angle of the intake valve. By providing a variable working angle mechanism that continuously changes the working angle and a variable valve timing mechanism, it is possible to arbitrarily change the valve opening timing, the valve closing timing, and the working angle of the intake valve. It is possible to cope with the operating conditions of

  However, the variable working angle mechanism capable of continuously changing the working angle has a problem that its structure is complicated. Or there exists a problem that an apparatus will become expensive. Therefore, a variable working angle mechanism that can change the working angle of the intake valve stepwise can be employed as the variable working angle mechanism. However, when such a working angle is switched stepwise, there is a problem that the amount of internal EGR (exhaust gas recirculation) changes abruptly and combustion in the combustion chamber becomes unstable.

  For example, when the overlap period during which the intake valve and the exhaust valve are open changes for a long time when the operating angle is switched, the internal EGR amount increases rapidly and changes to a state where it is difficult to burn instantaneously. There is a problem that the combustibility deteriorates. In particular, when the amount of internal EGR increases rapidly, there is a risk of misfire. On the other hand, when the overlap period changes short, the internal EGR amount decreases rapidly, and as a result, abnormal combustion such as knocking may occur. Thus, there is a problem that the operating state of the internal combustion engine becomes unstable due to the deterioration of the stability of the combustion of the fuel.

  An object of the present invention is to provide an internal combustion engine that includes a variable working angle mechanism that switches the working angle of an intake valve in stages, and suppresses unstable combustion when the working angle of the intake valve is switched. .

  The internal combustion engine of the present invention can switch the working angle of the intake valve and the variable compression ratio mechanism that can change the mechanical compression ratio by changing the volume of the combustion chamber when the piston reaches top dead center. Variable working angle mechanism. A reference mechanical compression ratio corresponding to the operating state of the internal combustion engine is determined in advance. When the operating state of the internal combustion engine changes and the operating angle of the intake valve should be switched, after setting the set mechanical compression ratio based on the reference mechanical compression ratio and starting changing the mechanical compression ratio toward the set mechanical compression ratio After switching the operating angle of the intake valve and switching the operating angle of the intake valve, the mechanical compression ratio is changed from the set mechanical compression ratio to the reference mechanical compression ratio.

  In the above invention, when the operating state of the internal combustion engine changes and the operating angle of the intake valve is greatly changed by the variable operating angle mechanism, the set mechanical compression ratio can be set higher than the reference mechanical compression ratio. .

  In the above invention, when the operating state of the internal combustion engine changes and the operating angle of the intake valve is changed to be small by the variable operating angle mechanism, the set mechanical compression ratio can be set lower than the reference mechanical compression ratio. .

  In the said invention, after a mechanical compression ratio reaches | attains a setting mechanical compression ratio, it is preferable to maintain a mechanical compression ratio at a setting mechanical compression ratio by predetermined time length.

  In the above invention, when the operating angle of the intake valve is switched, it is preferable to start the switching of the operating angle after the mechanical compression ratio reaches the set mechanical compression ratio.

  In the above invention, the variable working angle mechanism includes a small working angle cam for opening and closing the intake valve, and a large working angle cam in which the working angle of the intake valve is larger than the small working angle cam. The operating angle of the intake valve can be switched by switching between the cam and the large operating angle cam.

  ADVANTAGE OF THE INVENTION According to this invention, the internal combustion engine which suppresses that combustion becomes unstable when switching the working angle of an intake valve can be provided.

1 is a schematic overall view of an internal combustion engine in an embodiment. It is a general | schematic exploded perspective view of the variable compression ratio mechanism in embodiment. (A) to (C) is a schematic cross-sectional view of a variable compression ratio mechanism for explaining a change in mechanical compression ratio in the embodiment. 1 is a schematic perspective view of a drive device for an intake valve in an embodiment. It is a graph explaining the function of the variable valve mechanism in embodiment. (A) is explanatory drawing of a mechanical compression ratio, (B) is explanatory drawing of an actual compression ratio, (C) is explanatory drawing of an expansion ratio. It is a graph explaining the relationship between the expansion ratio of an internal combustion engine and theoretical thermal efficiency in embodiment. (A) is explanatory drawing of a normal driving cycle, (B) is explanatory drawing of a super-high expansion ratio cycle. It is a graph of operation control of an internal-combustion engine in an embodiment. 1 is a schematic perspective view of a cam switching device for an internal combustion engine in an embodiment. (A) is a graph explaining the open / close state of the intake valve and the exhaust valve during high load operation, and (B) is a graph explaining the open / close state of the intake valve and exhaust valve during low load operation. (A) And (B) is a graph explaining the state when switching an intake cam. 4 is a time chart when the intake cam is switched from a small operating angle cam to a large operating angle cam in the internal combustion engine of the embodiment. 4 is a time chart when the intake cam is switched from a large operating angle cam to a small operating angle cam in the internal combustion engine of the embodiment. It is a flowchart of operation control of an embodiment. It is a graph explaining the relationship between a load, an engine speed, and an actual compression ratio. (A) is a map of the reference valve closing timing IC of the intake valve, and (B) is a map of the reference mechanical compression ratio CR.

  The internal combustion engine in the embodiment will be described with reference to FIGS. The internal combustion engine in the present embodiment includes a variable compression ratio mechanism that can change the mechanical compression ratio and a variable valve mechanism that can change the closing timing of the intake valve, and increases the expansion ratio in a low load region. Super high expansion ratio control.

  FIG. 1 is a schematic overall view of an internal combustion engine in the present embodiment. The internal combustion engine in the present embodiment includes a crankcase 1, a cylinder block 2, and a cylinder head 3. A piston 4 is disposed in a hole formed in the cylinder block 2. A spark plug 6 is disposed at the center of the top surface of the combustion chamber 5 surrounded by the top surface of the piston 4 and the cylinder head 3. An intake port 8 and an exhaust port 10 are formed in the cylinder head 3. An intake valve 7 is disposed at the end of the intake port 8. An exhaust valve 9 is disposed at the end of the exhaust port 10. The intake port 8 is connected to a surge tank 12 via an intake branch pipe 11. Each intake branch pipe 11 is provided with a fuel injection valve 13 for injecting fuel into the corresponding intake port 8. Instead of being attached to each intake branch pipe 11, the fuel injection valve 13 may be arranged so as to inject fuel directly into each combustion chamber 5.

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

  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 axial direction at the connecting portion between the crankcase 1 and the cylinder block 2. A variable compression ratio mechanism A that can change the volume of the combustion chamber 5 at the time is provided. Furthermore, an actual compression action start timing changing mechanism capable of changing the actual compression action start timing is provided. The actual compression operation start timing changing mechanism in the present embodiment includes a variable valve timing mechanism B as a variable valve mechanism that can control the closing timing of the intake valve 7.

  A relative position sensor 22 for detecting the relative positional relationship between the crankcase 1 and the cylinder block 2 is attached to the crankcase 1 and the cylinder block 2. The relative position sensor 22 outputs an output signal indicating a change in the distance between the crankcase 1 and the cylinder block 2. The variable valve timing mechanism B is attached with a valve timing sensor 23 that generates an output signal indicating the closing timing of the intake valve 7. A throttle opening sensor 24 for generating an output signal indicating the throttle valve opening is attached to the actuator 16 for driving the throttle valve.

  The control device for the internal combustion engine in the present embodiment includes an electronic control unit 30. Electronic control unit 30 in the present embodiment includes a digital computer. The digital computer includes 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 connected to each other by a bidirectional bus 31. Output signals of the intake air amount detector 18, the air-fuel ratio sensor 21, the relative position sensor 22, the valve timing sensor 23, and the throttle opening sensor 24 are input to the input port 35 via the corresponding AD converters 37. A load sensor 41 that generates an output voltage proportional to the depression amount L 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. Is done. The required load can be detected from the output of the load sensor 41. Further, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 30 °. From the output of the crank angle sensor 42, the crank angle and the engine speed can be detected.

  On the other hand, the output port 36 is connected to the spark plug 6, the fuel injection valve 13, the actuator 16 for driving the throttle valve, the variable compression ratio mechanism A, and the variable valve timing mechanism B through a corresponding drive circuit 38. These devices are controlled by the electronic control unit 30.

  FIG. 2 is an exploded perspective view of the variable compression ratio mechanism shown in FIG. FIG. 3 shows a schematic sectional view of the internal combustion engine for explaining the operation of the variable compression ratio mechanism. Referring to FIG. 2, a plurality of protrusions 50 are formed below the both side walls of the cylinder block 2 so as to be spaced apart from each other. A cam insertion hole 51 having a circular cross section is formed in each protrusion 50. On the other hand, a plurality of protrusions 52 are formed on the upper wall surface of the crankcase 1 so as to be fitted between the corresponding protrusions 50 at intervals. Each of these protrusions 52 is also formed with a cam insertion hole 53 having a circular cross section.

  The variable compression ratio mechanism in the present embodiment includes a pair of camshafts 54 and 55. On each of the camshafts 54 and 55, a circular cam 58 that is rotatably inserted into each of the cam insertion holes 53 is fixed. These circular cams 58 are coaxial with the rotational axes of the camshafts 54 and 55. On the other hand, on both sides of each circular cam 58, as shown in FIG. 3, eccentric shafts 57 that are eccentrically arranged with respect to the rotation axes of the cam shafts 54 and 55 extend. Another circular cam 56 is eccentrically mounted on the eccentric shaft 57 so as to be rotatable. As shown in FIG. 2, these circular cams 56 are arranged on both sides of each circular cam 58, and these circular cams 56 are rotatably inserted into the corresponding cam insertion holes 51. A cam rotation angle sensor 25 that generates an output signal representing the rotation angle of the cam shaft 55 is attached to the cam shaft 55. The output of the cam rotation angle sensor 25 is input to the electronic control unit 30.

  When the circular cams 58 fixed on the camshafts 54 and 55 are rotated in opposite directions as shown by arrows in FIG. 3A from the state shown in FIG. The circular cam 56 rotates in a direction opposite to the circular cam 58 in the cam insertion hole 51 so as to move away from each other, and as shown in FIG. Position. Next, when the circular cam 58 is further rotated in the direction indicated by the arrow, the eccentric shaft 57 is at the lowest position as shown in FIG.

  3A, 3B, and 3C show the positional relationship among the center a of the circular cam 58, the center b of the eccentric shaft 57, and the center c of the circular cam 56 in each state. It is shown.

  3A to 3C, the relative positions of the crankcase 1 and the cylinder block 2 are determined by the distance between the center a of the circular cam 58 and the center c of the circular cam 56. The cylinder block 2 moves away from the crankcase 1 as the distance between the center a of the cylinder and the center c of the circular cam 56 increases. That is, the variable compression ratio mechanism A changes the relative position between the crankcase 1 and the cylinder block 2 by a crank mechanism using a rotating cam. When the cylinder block 2 moves away from the crankcase 1, the volume of the combustion chamber 5 increases when the piston 4 is located at the compression top dead center. The volume of the combustion chamber 5 when it is located at can be changed.

  As shown in FIG. 2, in order to rotate the camshafts 54 and 55 in opposite directions, a pair of worms 61 and 62 having opposite spiral directions are attached to the rotation shaft of the drive motor 59, respectively. Worm wheels 63 and 64 that mesh with the worms 61 and 62 are fixed to the ends of the camshafts 54 and 55, respectively. In this embodiment, by driving the drive motor 59, the volume of the combustion chamber 5 when the piston 4 is located at the compression top dead center can be changed over a wide range.

  The variable compression ratio mechanism in the present embodiment moves the cylinder block relative to the lower structure including the crankcase. However, the variable compression ratio mechanism is not limited to this form. Any mechanism that can change the ratio can be employed.

  FIG. 4 is a schematic perspective view of the intake valve driving apparatus according to the present embodiment. The internal combustion engine in the present embodiment includes an intake valve drive device. The intake valve drive device has a variable valve timing mechanism for changing the closing timing of the intake valve. The variable valve timing mechanism can advance or retard the period during which the intake valve is open.

  The variable valve timing mechanism in the present embodiment includes a valve control device 71. The valve control device 71 is connected to the intake camshaft 70. A sprocket is connected to the valve control device 71, and a timing chain 72 is engaged with the sprocket. The valve control device 71 in the present embodiment is formed such that the phase of the sprocket and the phase of the intake camshaft 70 can be changed from each other. That is, it is formed so that the phase of the intake camshaft 70 can be advanced or delayed with respect to the phase when the sprocket is rotated by the timing chain 72. The opening / closing timing of the intake valve can be changed by changing the phase of the intake camshaft 70.

  The intake valve drive device of the present embodiment includes a variable working angle mechanism that can switch the working angle of the intake valve in stages. The variable working angle mechanism in the present embodiment has a plurality of intake cams for driving the intake valves. In the present embodiment, there are a small working angle cam 73a and a large working angle cam 73b in which the working angle of the intake valve is larger than that of the small working angle cam 73a. The operating angle of the intake valve 7 can be changed by switching the small operating angle cam 73a and the large operating angle cam 73b. The small working angle cam 73 a and the large working angle cam 73 b are fixed to the intake camshaft 70. The small working angle cam 73 a and the large working angle cam 73 b rotate together with the intake camshaft 70. The cam switching device 75 transmits the driving force of one of the small working angle cam 73 a and the large working angle cam 73 b to the intake valve 7. The variable working angle mechanism will be described later.

  FIG. 5 is a graph illustrating the function of the variable valve timing mechanism B. FIG. 5 shows a state when the period during which the intake valve is open is changed using one intake cam. The solid line shows the time when the phase of the intake camshaft 70 is advanced most by the variable valve timing mechanism B, and the broken line shows the time when the phase of the intake camshaft 70 is most retarded. The period during which the intake valve 7 is open can be arbitrarily set between a range indicated by a solid line and a range indicated by a broken line. Therefore, the closing timing of the intake valve 7 can also be set to an arbitrary crank angle within the range indicated by the arrow C. As the variable valve timing mechanism B, any mechanism that can change the period during which the intake valve is open can be employed.

  Next, the meanings of terms used in the present application will be described with reference to FIG. 6 (A), (B), and (C) show an engine having a combustion chamber volume of 50 ml and a piston stroke volume of 500 ml for the sake of explanation. , (B), (C), the combustion chamber volume represents the volume of the combustion chamber when the piston is located at the compression top dead center.

  FIG. 6A explains the mechanical compression ratio. The mechanical compression ratio is a value mechanically determined only from the stroke volume of the piston and the combustion chamber volume during the compression stroke, and this mechanical compression ratio is expressed by (combustion chamber volume + stroke volume) / combustion chamber volume. In the example shown in FIG. 6A, this mechanical compression ratio is (50 ml + 500 ml) / 50 ml = 11.

  FIG. 6B describes the actual compression ratio. This actual compression ratio is a value determined from the actual piston stroke volume and the combustion chamber volume from when the compression action is actually started until the piston reaches top dead center, and this actual compression ratio is (combustion chamber volume + actual (Stroke volume) / combustion chamber volume. That is, as shown in FIG. 6B, even if the piston starts to rise in the compression stroke, the compression operation is not performed while the intake valve is open, and the actual compression is performed from the time when the intake valve is closed. The action begins. Therefore, the actual compression ratio is expressed as described above using the actual stroke volume. In the example shown in FIG. 6B, the actual compression ratio is (50 ml + 450 ml) / 50 ml = 10.

  FIG. 6C illustrates the expansion ratio. The expansion ratio is a value determined from the stroke volume of the piston and the combustion chamber volume during the expansion stroke, and this expansion ratio is expressed by (combustion chamber volume + stroke volume) / combustion chamber volume. In the example shown in FIG. 6C, this expansion ratio is (50 ml + 500 ml) / 50 ml = 11.

  Next, the super expansion ratio cycle used in the present invention will be described with reference to FIGS. FIG. 7 shows the relationship between the theoretical thermal efficiency and the expansion ratio, and FIG. 8 shows a comparison between a normal cycle and an ultrahigh expansion ratio cycle that are selectively used according to the load in the present invention.

  FIG. 8A shows a normal cycle when the intake valve closes near the bottom dead center and the compression action by the piston is started from the vicinity of the intake bottom dead center. In the example shown in FIG. 8A as well, the combustion chamber volume is set to 50 ml, and the stroke volume of the piston is set to 500 ml, similarly to the example shown in FIGS. 6A, 6B, and 6C. As can be seen from FIG. 8A, in a normal cycle, the mechanical compression ratio is (50 ml + 500 ml) / 50 ml = 11, the actual compression ratio is almost 11, and the expansion ratio is also (50 ml + 500 ml) / 50 ml = 11. That is, in a normal internal combustion engine, the mechanical compression ratio, the actual compression ratio, and the expansion ratio are substantially equal.

  The solid line in FIG. 7 shows the change in the theoretical thermal efficiency when the actual compression ratio and the expansion ratio are substantially equal, that is, in a normal cycle. In this case, it can be seen that the theoretical thermal efficiency increases as the expansion ratio increases, that is, as the actual compression ratio increases. Therefore, in order to increase the theoretical thermal efficiency in a normal cycle, it is only necessary to increase the actual compression ratio. However, the actual compression ratio can only be increased to a maximum of about 12 due to the restriction of the occurrence of knocking at the time of engine high load operation, and thus the theoretical thermal efficiency cannot be sufficiently increased in a normal cycle.

  On the other hand, under such circumstances, it is considered to increase the theoretical thermal efficiency while strictly dividing the mechanical compression ratio and the actual compression ratio. As a result, the theoretical thermal efficiency is governed by the expansion ratio, and the actual compression ratio is compared to the theoretical thermal efficiency. Has little effect. That is, if the actual compression ratio is increased, the explosive force is increased, but a large amount of energy is required for compression. Thus, even if the actual compression ratio is increased, the theoretical thermal efficiency is hardly increased.

  On the other hand, when the expansion ratio is increased, the period during which the pressing force acts on the piston during the expansion stroke becomes longer, and thus the period during which the piston applies the rotational force to the crankshaft becomes longer. Therefore, the larger the expansion ratio, the higher the theoretical thermal efficiency. The broken line ε = 10 in FIG. 7 indicates the theoretical thermal efficiency when the expansion ratio is increased with the actual compression ratio fixed at 10. The increase in the theoretical thermal efficiency when the expansion ratio is increased while maintaining the actual compression ratio ε at a low value, and the theoretical thermal efficiency when the actual compression ratio increases with the expansion ratio as shown by the solid line in FIG. It can be seen that there is no significant difference from the amount of increase.

  Thus, if the actual compression ratio is maintained at a low value, knocking does not occur. Therefore, if the expansion ratio is increased while the actual compression ratio is maintained at a low value, the theoretical thermal efficiency is reduced while preventing the occurrence of knocking. Can be greatly increased. FIG. 8B shows an example where the variable compression ratio mechanism A and variable valve timing mechanism B are used to increase the expansion ratio while maintaining the actual compression ratio at a low value.

  Referring to FIG. 8B, in this example, the variable compression ratio mechanism A reduces the combustion chamber volume from 50 ml to 20 ml. On the other hand, the variable valve timing mechanism B delays the closing timing of the intake valve until the actual piston stroke volume is reduced from 500 ml to 200 ml. As a result, in this example, the actual compression ratio is (20 ml + 200 ml) / 20 ml = 11, and the expansion ratio is (20 ml + 500 ml) / 20 ml = 26. In the normal cycle shown in FIG. 8A, the actual compression ratio is almost 11 and the expansion ratio is 11, as described above. Compared with this case, only the expansion ratio is shown in FIG. 8B. It can be seen that it has been increased to 26. This is why it is called an ultra-high expansion ratio cycle.

  Generally speaking, in an internal combustion engine, the lower the engine load, the worse the thermal efficiency. Therefore, in order to improve the thermal efficiency during engine operation, that is, to improve fuel efficiency, it is necessary to improve the thermal efficiency when the engine load is low. Necessary. On the other hand, in the ultra-high expansion ratio cycle shown in FIG. 8B, since the actual piston stroke volume during the compression stroke is reduced, the amount of intake air that can be sucked into the combustion chamber 5 is reduced. The expansion ratio cycle can only be adopted when the engine load is relatively low. Therefore, in the present invention, when the engine load is relatively low, the super high expansion ratio cycle shown in FIG. 8B is used, and during the high engine load operation, the normal cycle shown in FIG. 8A is used.

Next, an example of operation control of the internal combustion engine in the present embodiment will be described with reference to FIG. FIG. 9 is a graph schematically illustrating general operation control of the super-high expansion ratio control. FIG. 9 shows changes in the intake air amount, the intake valve closing timing, the expansion ratio (mechanical compression ratio), the actual compression ratio, and the throttle valve opening according to the engine load at a certain engine speed. Yes. Incidentally, FIG. 9, unburned HC, the average air-fuel ratio output signal of the air-fuel ratio sensor 21 in the combustion chamber 5 so as to be able to reduce at the same time CO and NO _X in the exhaust gas by the three-way catalyst in the catalytic device 20 This shows a case where feedback control is performed to the theoretical air-fuel ratio based on the above.

  As described above, the normal cycle shown in FIG. 8A is executed during high load operation. Therefore, as shown in FIG. 9, at this time, the mechanical compression ratio is lowered, so the expansion ratio is low, and the closing timing of the intake valve 7 is advanced as shown by the solid line in FIG. At this time, the intake air amount is large, and at this time, the opening degree of the throttle valve 17 is kept fully open, and the pumping loss is suppressed.

  On the other hand, when the engine load becomes low, the closing timing of the intake valve 7 is delayed so as to reduce the intake air amount. At this time, the mechanical compression ratio is increased as the engine load is reduced so that the actual compression ratio is maintained substantially constant. Therefore, the expansion ratio increases as the engine load decreases. At this time, the throttle valve 17 is kept fully open, and the amount of intake air supplied into the combustion chamber 5 is controlled by changing the closing timing of the intake valve 7 without depending on the throttle valve 17. ing.

  As described above, when the engine load is reduced from the high-load operation state, the mechanical compression ratio is increased as the intake air amount is decreased while the actual compression ratio is substantially constant. That is, the volume of the combustion chamber 5 when the piston 4 reaches the compression top dead center is reduced in proportion to the reduction of the intake air amount. Therefore, the volume of the combustion chamber 5 when the piston 4 reaches the compression top dead center changes in proportion to the intake air amount. At this time, in the example shown in FIG. 9, the air-fuel ratio in the combustion chamber 5 is the stoichiometric air-fuel ratio, so the volume of the combustion chamber 5 when the piston 4 reaches the compression top dead center is proportional to the fuel amount. Will change.

  In the embodiment according to the present invention, the closing timing of the intake valve 7 moves away from the intake bottom dead center BDC until the limit closing timing at which the amount of intake air supplied into the combustion chamber can be controlled as the engine load decreases. Will be.

  In the embodiment shown in FIG. 9, when the engine load decreases to the load L <b> 2, the closing timing of the intake valve 7 becomes the limit closing timing that can control the intake air amount supplied into the combustion chamber 5. When the closing timing of the intake valve 7 reaches the limit closing timing, the closing timing of the intake valve 7 is in a region where the load is lower than the engine load L2 when the closing timing of the intake valve 7 reaches the closing timing. It is held at the limit closing timing.

  When the closing timing of the intake valve 7 is held at the limit closing timing, the amount of intake air can no longer be controlled by changing the closing timing of the intake valve 7. In the embodiment shown in FIG. 9, at this time, that is, in a region where the load is lower than the engine load L2 when the closing timing of the intake valve 7 reaches the limit closing timing, the throttle valve 17 causes the combustion chamber 5 to enter the combustion chamber 5. The amount of intake air to be supplied is controlled, and the opening degree of the throttle valve 17 is made smaller as the engine load becomes lower.

  As the engine load is further reduced, the mechanical compression ratio further increases. In the internal combustion engine shown in FIG. 9, when the engine load is reduced to the load L1, the mechanical compression ratio reaches a limit mechanical compression ratio (upper limit mechanical compression ratio) that becomes a structural limit of the combustion chamber 5. When the mechanical compression ratio reaches the limit mechanical compression ratio, the mechanical compression ratio is held at the limit mechanical compression ratio in a region where the load is lower than the engine load L1 when the mechanical compression ratio reaches the limit mechanical compression ratio. Therefore, the mechanical compression ratio is maximized and the expansion ratio is maximized during low load operation. In other words, the mechanical compression ratio is maximized so that the maximum expansion ratio is obtained in low load operation.

  As described above, the expansion ratio is 26 in the ultra-high expansion ratio cycle shown in FIG. The higher the expansion ratio, the better. However, as can be seen from FIG. 7, a considerably high theoretical thermal efficiency can be obtained if it is 20 or more with respect to the practically usable lower limit actual compression ratio ε = 5. Therefore, in this embodiment, the variable compression ratio mechanism A is formed so that the expansion ratio is 20 or more.

  Next, a variable working angle mechanism of the intake valve driving device in the present embodiment will be described. The operating angle corresponding to the period from the valve opening timing to the valve closing timing of the intake valve is determined based on the cross-sectional shape of the intake cam. In the present embodiment, control for switching the intake cam is performed.

  FIG. 10 shows an enlarged schematic perspective view of the cam switching device in the present embodiment. The variable working angle mechanism in the present embodiment includes a cam switching device 75. 4 and 10, cam switching device 75 has a rocker arm body 75a. The rocker arm body 75a is formed to be rotatable about a rotation shaft 76.

  The variable working angle mechanism of the present embodiment has a small working angle cam 73a and a large working angle cam 73b that are different working angles of the intake valves. The small working angle cam 73a and the large working angle cam 73b have different cross-sectional shapes. When the intake camshaft 70 is rotating at a constant rotational speed, the time during which the intake valve 7 is opened by the large operating angle cam 73b is longer than the time during which the intake valve 7 is opened by the small operating angle cam 73a. It is formed so that the length becomes longer. In the present embodiment, the intake valve 7 is driven by one of the intake cams.

  As a small working angle cam in the present embodiment, an intake cam in which the working angle of the intake valve is equivalent to the working angle of an internal combustion engine that does not have a compression ratio variable mechanism in the prior art can be exemplified. For example, an intake cam in which the operating angle of the intake valve is 240 ° or more and 270 ° or less can be employed. On the other hand, as the large working angle cam, for example, an intake cam that drives the intake valve with a large working angle of about 320 ° can be used.

  The cam switching device 75 has a roller 75c that contacts the small working angle cam 73a. The roller 75c is rotatably supported by the rocker arm main body 75a. The cam switching device 75 has a slipper 75b that contacts the large working angle cam 73b. The slipper 75b is supported by a support bar 75f. As shown by an arrow 112, the slipper 75b is formed to be swingable. The slipper 75b is biased toward the large working angle cam 73b by a spring 75g.

  The variable working angle mechanism in the present embodiment has a control oil supply device 74 that supplies control oil to the cam switching device 75. The control oil supply device 74 is formed so that the pressure of the control oil supplied to the cam switching device 75 can be increased or decreased.

  A lock pin 75d is disposed inside the rocker arm main body 75a. The lock pin 75d is urged away from the support rod 75f by a spring 75e. An oil passage for control oil is connected to the lock pin 75d. As the pressure of the control oil increases, the lock pin 75d moves toward the support rod 75f as indicated by an arrow 113. When the lock pin 75d moves in the direction indicated by the arrow 113, the support rod 75f is prevented from moving, and the slipper 75b does not swing.

  When the intake valve 7 is driven by the small operating angle cam 73a, the control oil supplied to the rocker arm main body 75a is brought into a low pressure state. The lock pin 75d is moved away from the support bar 75f by the urging force of the spring 75d, and the support bar 75f is movable. The slipper 75b can swing in the direction indicated by the arrow 112.

  Referring to FIG. 4, when the intake camshaft 70 rotates, the large working angle cam 73b rotates. The slipper 75b is pressed by the cam nose portion of the large working angle cam 73b. However, since the slipper 75b is in a swingable state, the driving of the rocker arm body 75a by the large working angle cam 73b is avoided. That is, the large working angle cam 73b is idling. At this time, the roller 75c is pressed by the small working angle cam 73a, and the rocker arm main body 75a swings. The intake valve 7 is opened and closed by the small working angle cam 73a. The intake valve 7 opens and closes according to the cross-sectional shape (profile) of the small working angle cam 73a. That is, the intake valve 7 can be opened and closed with a small operating angle.

  On the other hand, when increasing the operating angle of the intake valve, the control oil supplied to the oil passage inside the rocker arm body 75a is made high. As the hydraulic pressure of the control oil increases, the lock pin 75d moves in the direction indicated by the arrow 113 and the support rod 75f is fixed. The slipper 75b is in a state where it cannot swing. When the intake camshaft 70 rotates, the slipper 75b is pressed by the large working angle cam 73b, and the rocker arm main body 75a swings. At this time, the large operating angle cam 73b has a larger moving amount (lift amount) and operating angle of the intake valve 7 than the small operating angle cam 73a. For this reason, the small operating angle cam 73a idles. The intake valve 7 opens and closes according to the cross-sectional shape (profile) of the intake cam 73b. That is, the intake valve 7 can be opened and closed at a large operating angle.

  Thus, in the present embodiment, the intake cam can be switched by changing the hydraulic pressure supplied by the control oil supply device. The operating angle of the intake valve can be increased or decreased.

  The variable working angle mechanism is not limited to the above-described form, and any mechanism that can change the working angle of the intake valve in stages can be employed. That is, a variable working angle mechanism that can switch the working angle of the intake valve discontinuously can be employed. In addition, the variable working angle mechanism of the present embodiment is formed so as to switch the working angle in two stages, but is not limited to this form and employs a variable working angle mechanism that can be switched in three or more stages. It doesn't matter.

  FIG. 11 is a graph illustrating the relationship between the state during high load operation and the state during low load operation of the internal combustion engine in the present embodiment. FIG. 11A shows a state during high load operation, and FIG. 11B shows a state during low load operation. The horizontal axis indicates the crank angle, and the vertical axis indicates the valve lift amount of the intake valve or the exhaust valve. In the operation example shown in FIG. 11, the opening timing and closing timing of the exhaust valve are constant.

  The amount of intake air flowing into the combustion chamber depends on the crank angle (movement length of the piston) from when the intake valve is closed until the piston reaches the compression top dead center. In the internal combustion engine of the present embodiment, the closing timing of the intake valve is controlled early during high load operation. During high load operation, the intake valve is opened and closed with a small working angle cam. The valve closing timing θICH of the intake valve during high load operation is set, for example, near the bottom dead center (BDC) of the piston. With this control, the amount of intake air flowing into the combustion chamber can be increased.

  When the engine load becomes low, the intake air amount is controlled to be small, so that the intake valve closing timing θICL is controlled later than the valve closing timing θICH. As the intake air amount decreases, the closing timing of the intake valve is controlled to approach the top dead center (TDC) of the compression stroke.

  In the high load operation of FIG. 11A, the intake valve opens before the intake top dead center, and when the piston starts to descend, the intake valve is open. For this reason, pumping loss can be suppressed. By the way, when the intake valve is driven by a small working angle cam as shown by the dotted line during the low load operation of FIG. 11B, from when the piston reaches the intake top dead center until the intake valve opens. Has a predetermined time. During this time, the pressure in the combustion chamber becomes negative and pumping loss occurs.

  Therefore, in the internal combustion engine of the present embodiment, the opening timing of the intake valve can be advanced to the intake top dead center by switching the intake cam to the large working angle cam. Alternatively, the opening timing of the intake valve can be advanced to the vicinity of the intake top dead center. This control can suppress the pumping loss in the intake stroke and can improve the thermal efficiency.

  During high-load operation, an amount of air equivalent to that of the internal combustion engine in the prior art can be sucked. During low-load operation, throttling that causes pumping loss can be avoided as much as possible, and the operating range where the throttle valve is fully open can be increased. In addition, the amount of intake air finally sealed in the combustion chamber can be reduced. That is, it is possible to make the intake amount according to the low load. Thus, in the internal combustion engine of the present embodiment, it is preferable to use the large working angle cam in the low load operation state and the small working angle cam in the high load operation state.

  It should be noted that the operating angle of the intake valve is set to the above in order to expect the effect of inertia supercharging in an operating state where the engine speed is high during high load operation compared to an operating state where the engine speed is low. It may be smaller than the large working angle. For example, a medium working angle cam can be arranged so that the working angle of the intake valve is about 270 °. Three intake cams having different operating angles can be arranged. For example, a medium operating angle cam can be used in a high load and high rotation operation state, and a large operation angle cam can be used in a high load and low rotation operation state. On the other hand, at the time of low load operation, a small working angle cam can be used regardless of the engine speed.

  Thus, in the internal combustion engine of the present embodiment, it is possible to switch between the high working angle cam and the low working angle cam according to the engine load. Referring to FIG. 9, for example, the intake cam can be switched by a switching load Lx. When the engine load changes to the low load side across the switching load Lx, the operating angle can be greatly changed by switching from the small operating angle cam to the large operating angle cam. Further, when the engine load changes to the high load side across the switching load Lx, the operating angle can be changed small by switching from the large operating angle cam to the small operating angle cam.

  FIG. 12 shows a graph for explaining a state when the intake cam is switched in the present embodiment. FIG. 12A shows a state in which the large working angle cam is selected, and FIG. 12B shows a state in which the small working angle cam is selected. In the internal combustion engine of the present embodiment, when switching the intake cam, the intake cam is switched so that the closing timing of the intake valve is substantially the same. The intake cam is switched by setting the intake valve closing timing θICL by the large working angle cam and the closing timing θICH of the intake valve by the small working angle cam to be substantially the same timing. For example, the intake cam phase can be changed and the intake valve phase (intake camshaft phase) can be changed by the variable valve mechanism so that the closing timing of the intake valve is substantially the same. Alternatively, the large operating angle cam and the small operating angle cam can be fixed to the intake camshaft so that the closing timing of the intake valve is substantially the same in the phase of switching the intake cam.

  By making the intake valve closing timing substantially the same when switching the intake cam, the intake air amount can be made substantially the same, and torque shock caused by fluctuations in the intake air amount can be suppressed. For example, it is possible to suppress a torque shock caused by a reduction in the intake air amount that occurs when the operating angle of the intake valve is instantaneously switched from a small operating angle to a large operating angle.

  However, referring to FIGS. 12A and 12B, when the intake cam is switched, the time length of the overlap OL in which the period during which the intake valve is open and the period during which the exhaust valve is open overlaps each other. Changes. As a result, the internal EGR amount changes between before and after switching of the intake cam. For example, when the required load decreases and the small working angle cam is switched to the large working angle cam, the overlap OL period becomes longer and the internal EGR amount suddenly increases. For this reason, the combustibility of fuel deteriorates. On the contrary, when switching from the large operating angle cam to the small operating angle cam, the overlap OL period is shortened and the internal EGR amount is rapidly decreased. For this reason, abnormal combustion such as knocking may occur.

  Thus, in the variable working angle mechanism in the present embodiment, the working angle of the intake valve is switched discontinuously, so that combustion in the combustion chamber may become unstable. Therefore, in the internal combustion engine of the present embodiment, when the operating state of the internal combustion engine changes and the intake cam is switched together with the change of the closing timing of the intake valve, control for temporarily correcting the mechanical compression ratio is performed. Do. In the present embodiment, a set mechanical compression ratio obtained by correcting the reference mechanical compression ratio based on the operating state of the internal combustion engine is set. When the intake cam is to be switched, the mechanical compression ratio is changed toward the set mechanical compression ratio. After the intake cam is switched, control is performed to maintain the set mechanical compression ratio for a predetermined time and then shift to the reference mechanical compression ratio.

  FIG. 13 is a time chart when the operating angle of the intake valve is switched from a small operating angle to a large operating angle in the internal combustion engine of the present embodiment. As such an operation state, referring to FIG. 11, for example, a case where the required load is shifted to a low load side and the intake cam is switched from the small operating angle cam to the large operating angle cam can be exemplified. In the period from time t2 to time t3, the operating angle of the intake valve is switched by switching from the small operating angle cam to the large operating angle cam.

  In the present embodiment, the change of the mechanical compression ratio is started at time t1 before switching of the working angle cam. Here, the reference mechanical compression ratio is a mechanical compression ratio set based on the operating state of the internal combustion engine. The target mechanical compression ratio is a mechanical compression ratio that can suppress unstable combustion when the intake cam is switched. The set mechanical compression ratio is a mechanical compression ratio that is actually set and changed in consideration of a margin for the target mechanical compression ratio. In the present embodiment, the set mechanical compression ratio is set by adding or subtracting a predetermined compression ratio to the reference mechanical compression ratio.

  The internal combustion engine detects a change in the required load, for example, and sets the reference mechanical compression ratio and the closing timing of the intake valve. At this time, if it is necessary to change the operating angle of the intake valve, the set mechanical compression ratio is further set. When the operating angle of the intake valve is greatly changed by the variable operating angle mechanism, the set mechanical compression ratio is set higher than the reference mechanical compression ratio after the transition. At time t1, the mechanical compression ratio is increased toward the set mechanical compression ratio. In the present embodiment, the mechanical compression ratio has reached the target mechanical compression ratio before time t3 when the change of the working angle ends.

  Thus, the actual compression ratio in the combustion chamber is increased by making the mechanical compression ratio higher than the reference mechanical compression ratio. Even if the operating angle is switched and the internal EGR amount suddenly increases, deterioration of combustibility can be suppressed because the mechanical compression ratio is set high.

  In the present embodiment, after the mechanical compression ratio reaches the set mechanical compression ratio, the mechanical compression ratio is maintained at the set mechanical compression ratio for a predetermined time. At time t4, the mechanical compression ratio is changed from the set compression ratio toward the reference mechanical compression ratio. At time t5, the mechanical compression ratio has reached the reference mechanical compression ratio.

  FIG. 14 shows a time chart when the operating angle of the intake valve is switched from a large operating angle to a small operating angle in the internal combustion engine of the present embodiment. As such an operation state, for example, a case where the required load shifts to a high load side and the intake cam is switched from the large operating angle cam to the small operating angle cam can be exemplified.

  From time t2 to time t3, the intake cam is switched from the large operating angle cam to the small operating angle cam to change the operating angle of the intake valve. When the working angle of the intake valve is changed to be small by the variable working angle mechanism, the set mechanical compression ratio is set lower than the reference mechanical compression ratio after the transition. After the mechanical compression ratio reaches the set mechanical compression ratio, the mechanical compression ratio is maintained at the set mechanical compression ratio until time t4 after the elapse of a predetermined time. The mechanical compression ratio is changed to the reference mechanical compression ratio after the transition from time t4 to time t5. In addition, in the example shown in FIG. 14, a target mechanical compression ratio that avoids unstable combustion due to occurrence of abnormal combustion such as knocking is determined in advance, and the operating angle after reaching the target mechanical compression ratio. Has started to change. Thus, the operating angle may be changed after reaching the target mechanical compression ratio that can suppress the deterioration of the stability of combustion.

  As described above, in the present embodiment, when the operating angle of the intake valve is switched, it is possible to prevent the combustion from becoming temporarily unstable due to the switching of the intake cam. Since such a period of unstable combustion does not continue for a long time, the mechanical compression ratio can be shifted to the reference mechanical compression ratio based on the operating state after a predetermined time has elapsed.

  In the present embodiment, the mechanical compression ratio reaches or exceeds the target mechanical compression ratio before time t3 when the change of the working angle is completed. Combustion is unstable immediately after changing the operating angle by delaying the start of changing the operating angle from the start of changing the mechanical compression ratio so that the target mechanical compression ratio is reached before the switching of the intake cam is completed. Can be suppressed. Thus, it is preferable that the period for changing the operating angle of the intake valve is set so that the mechanical compression ratio reaches the target mechanical compression ratio when the change of the operating angle is completed. For example, the operating angle may be changed after the mechanical compression ratio reaches the set mechanical compression ratio. By performing this control, it is possible to more reliably suppress deterioration in combustibility.

  In the present embodiment, after the mechanical compression ratio reaches the set mechanical compression ratio, a period for maintaining the set mechanical compression ratio is provided, and at time t4 after elapse of a predetermined time, the mechanical compression ratio is set. Is changed toward the standard mechanical compression ratio. By performing this control, it is possible to more reliably suppress the combustion from becoming unstable. The length of time for maintaining the mechanical compression ratio substantially constant can be set based on the length of time during which combustion becomes unstable. Note that immediately after the mechanical compression ratio reaches the set mechanical compression ratio, control for shifting to the reference mechanical compression ratio may be performed without making the mechanical compression ratio substantially constant.

  FIG. 15 shows a flowchart of the operation control of the internal combustion engine in the present embodiment. The flowchart shown in FIG. 15 can be repeatedly performed at predetermined time intervals, for example.

  In step 101, the operating state of the internal combustion engine is detected. As the operating state of the internal combustion engine, for example, the engine speed and the required load can be detected. In step 102, the reference mechanical compression ratio CR and the reference valve closing timing IC of the intake valve are set based on the detected operating state. Referring to FIG. 9, for example, the reference mechanical compression ratio can be set smaller as the load increases. Further, the reference valve closing timing of the intake valve can be advanced as the load increases.

FIG. 16 shows a graph for explaining the relationship between the engine speed and the actual compression ratio with respect to the load. The horizontal axis is the load L, and the vertical axis is the actual compression ratio. FIG. 16 shows a graph of engine speeds N ₁ , N ₂ , N ₃ and N ₄ (where N ₁ <N ₂ <N ₃ <N ₄ ). When the load L is substantially constant, abnormal combustion such as knocking is less likely to occur as the engine speed N increases. For this reason, the higher the engine speed N, the higher the actual compression ratio can be set. For example, when the closing timing of the intake valve is constant, the mechanical compression ratio can be set higher as the engine speed increases.

  FIG. 17 shows a map for setting the reference valve closing timing and the reference mechanical compression ratio in the present embodiment. FIG. 17A is a map of the reference valve closing timing IC. The reference valve closing timing IC can be set by using this map based on the detected engine speed N and load L. FIG. 17B is a map of the reference mechanical compression ratio CR. The reference mechanical compression ratio CR can be set by using this map based on the detected engine speed N and load L.

  Referring to FIG. 15, next, in step 103, it is determined whether or not the intake cam needs to be changed when shifting to a new reference valve closing timing of the intake valve. That is, it is determined whether or not the operating angle needs to be changed. In step 103, if it is not necessary to change the intake cam, the routine proceeds to step 104.

  In step 104, the mechanical compression ratio is changed to the set reference mechanical compression ratio CR. Further, the closing timing of the intake valve is changed to a set reference closing timing IC. At this time, the mechanical compression ratio and the closing timing of the intake valve are changed without changing the intake cam.

  If it is necessary to change the intake cam in step 103, the routine proceeds to step 105. In step 105, it is determined whether or not the change of the intake cam is a change from a small operating angle cam to a large operating angle cam. If the change is from the small working angle cam to the large working angle cam, the routine proceeds to step 106. The operating state of the internal combustion engine is, for example, a case where the engine load is decreasing toward a low load.

  In step 106, a set compression ratio CRd having a higher mechanical compression ratio than the current new reference mechanical compression ratio CR is set (see FIG. 13). In the present embodiment, the set mechanical compression ratio CRd is calculated by adding a predetermined mechanical compression ratio increment ΔCR to the reference mechanical compression ratio CR.

  If it is not a change from the small working angle cam to the large working angle cam in step 105, the routine proceeds to step 107. In this case, the intake cam is changed from the large operating angle cam to the small operating angle cam. The operating state of the internal combustion engine is, for example, a case where the engine load increases toward a high load.

  In step 107, a mechanical compression ratio CRd that is lower than the new reference mechanical compression ratio CR is set (see FIG. 14). In the present embodiment, the set mechanical compression ratio CRd is calculated by subtracting a predetermined mechanical compression ratio decrement ΔCR from the reference mechanical compression ratio CR. When the set mechanical compression ratio CRd is set in step 106 or step 107, the routine proceeds to step 108.

  In step 108, the mechanical compression ratio is changed to the currently set mechanical compression ratio CRd. In step 109, the closing timing of the intake valve is changed to the current reference closing timing IC. At this time, the intake cam is switched in a predetermined phase. In the switching of the intake cam, as described above, it is preferable to perform control to switch with a time delay so that the switching of the intake cam is completed after the mechanical compression ratio reaches the target mechanical compression ratio (FIG. 13). Or refer to FIG.

  In addition, as a setting mechanical compression ratio, it is not restricted to said form, Arbitrary mechanical compression ratios which can suppress the deterioration of combustibility at the time of switching of an operating angle are employable. For example, the mechanical compression ratio when starting the switching of the intake valve may be estimated, and the set mechanical compression ratio may be set based on the estimated mechanical compression ratio. In this case, the mechanical compression ratio when starting the switching of the intake valve can be estimated based on a reference mechanical compression ratio that depends on the operating state. That is, the set mechanical compression ratio can be set based on the reference mechanical compression ratio.

  Next, in step 110, after the mechanical compression ratio reaches the set mechanical compression ratio CRd, the mechanical compression ratio is held at the set mechanical compression ratio for a predetermined time. In the present embodiment, the mechanical compression ratio is kept substantially constant for a predetermined time length.

  Next, in step 111, the mechanical compression ratio is shifted to the reference mechanical compression ratio CR set in step 102 after a predetermined time has elapsed.

  As described above, in the internal combustion engine in the present embodiment, the combustion becomes unstable by temporarily setting the mechanical compression ratio to be higher or lower when changing the operating angle of the intake valve. While suppressing this, the operating angle of the intake valve can be changed.

  By the way, in an internal combustion engine, a variable valve mechanism may be arranged in an exhaust valve drive device. When the variable valve mechanism is arranged in the exhaust valve, the closing timing of the exhaust valve can be adjusted. For this reason, in order to suppress the change of the internal EGR amount when the intake cam is switched, the valve closing timing of the exhaust valve can be changed.

  For example, when the intake cam is changed from the small working angle cam to the large working angle cam, the internal EGR amount is reduced early in consideration of the time delay of the operation of the variable valve mechanism of the exhaust valve drive device. It is possible to change the valve closing timing of the exhaust valve in the direction in which the valve is closed. Since the internal EGR amount increases rapidly, it is possible to perform control for advancing (advancing) the closing timing of the exhaust valve.

  However, if the closing timing of the exhaust valve is changed, the exhaust pulsation in which the pressure oscillates in the engine exhaust passage changes, and the intake air amount may change due to the change in the exhaust pulsation. As a result, torque fluctuation may occur. For this reason, even when a variable valve mechanism is disposed on the exhaust valve, when the intake cam is switched, control is performed to prohibit adjustment of the internal EGR amount by the variable valve mechanism disposed in the exhaust valve drive device. be able to. As in this embodiment, by suppressing the rapid change in the internal EGR amount by changing the mechanical compression ratio, it is possible to more reliably suppress the torque fluctuation when the intake cam is switched.

  In the present embodiment, the internal combustion engine attached to the vehicle has been described as an example. However, the present invention is not limited to this embodiment, and the present invention is applied to an internal combustion engine disposed in an arbitrary device or facility. be able to.

  In the respective drawings described above, the same or equivalent parts are denoted by the same reference numerals. In addition, said embodiment is an illustration and does not limit invention. In the embodiment, the change shown in a claim is included.

DESCRIPTION OF SYMBOLS 1 Crankcase 2 Cylinder block 4 Piston 5 Combustion chamber 6 Spark plug 13 Fuel injection valve 17 Throttle valve 30 Electronic control unit 54,55 Camshaft 56,58 Circular cam 57 Eccentric shaft 59 Drive motor 61 Warm 70 Intake camshaft 71 Valve control Device 73a Small working angle cam 73b Large working angle cam 75 Cam switching device 75b Slipper 75c Roller

Claims (6)

A variable compression ratio mechanism capable of changing the mechanical compression ratio by changing the volume of the combustion chamber when the piston reaches top dead center;
With a variable working angle mechanism that can switch the working angle of the intake valve in stages,
A reference mechanical compression ratio according to the operating state of the internal combustion engine is predetermined,
When the operating state of the internal combustion engine changes and the operating angle of the intake valve should be switched, after setting the set mechanical compression ratio based on the reference mechanical compression ratio and starting changing the mechanical compression ratio toward the set mechanical compression ratio An internal combustion engine characterized by changing the working angle of the intake valve and changing the mechanical compression ratio from the set mechanical compression ratio to the reference mechanical compression ratio after switching the working angle of the intake valve.   The internal combustion engine according to claim 1, wherein when the operating state of the internal combustion engine changes and the operating angle of the intake valve is greatly changed by the variable operating angle mechanism, the set mechanical compression ratio is set higher than the reference mechanical compression ratio. organ.   The set mechanical compression ratio is set to be lower than the reference mechanical compression ratio when the operating state of the internal combustion engine changes and the operating angle of the intake valve is changed to be smaller by the variable operating angle mechanism. Internal combustion engine.   The internal combustion engine according to any one of claims 1 to 3, wherein the mechanical compression ratio is maintained at the set mechanical compression ratio for a predetermined length of time after the mechanical compression ratio reaches the set mechanical compression ratio.   The internal combustion engine according to any one of claims 1 to 4, wherein when the operating angle of the intake valve is switched, the switching of the operating angle is started after the mechanical compression ratio reaches the set mechanical compression ratio.   The variable working angle mechanism includes a small working angle cam for opening and closing the intake valve and a large working angle cam in which the working angle of the intake valve is larger than the small working angle cam. The internal combustion engine according to any one of claims 1 to 5, wherein a working angle of the intake valve is switched by switching a cam.

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