JP5585539B2 - Control device for internal combustion engine - Google Patents

Description

  The present invention relates to a control device for an internal combustion engine.

  In an internal combustion engine with a supercharger, a so-called valve overlap is known in which both an intake valve and an exhaust valve are simultaneously opened when acceleration or a high output is required. In other words, by performing valve overlap, the intake air is blown out to the exhaust side by using supercharging pressure, etc., and the remaining burned gas in the combustion chamber is scavenged to improve the combustibility and output. The exhaust gas amount supplied to the supercharged turbine is increased to increase the supercharging effect and to improve the output.

  In addition, a control system for an internal combustion engine that achieves both improvement in fuel consumption and torque increase by appropriately combining a charging efficiency improvement method using a scavenging effect and a charging efficiency improvement method using a supercharger according to the situation. Proposals have also been made (Patent Document 1).

JP 2009-103084 A

  By the way, in the internal combustion engine which scavenges the burned gas so-called internal EGR remaining in the combustion chamber by providing the valve overlap period as described above, if the valve overlap period is too short, a large amount of internal EGR remains and torque May result in a decrease in. On the other hand, when the valve overlap period is too long, the amount of air blown during the valve overlap period is excessively large, and the exhaust gas contains a large amount of oxygen. The exhaust purification catalyst is likely to be deteriorated or excessively heated, and when a three-way catalyst is used, the purification rate is lowered and the emission may be deteriorated.

  Therefore, in an internal combustion engine that scavenges internal EGR by providing a valve overlap period, it is necessary to accurately grasp the relationship between the valve overlap period and the internal EGR amount. From the viewpoint of improving the scavenging efficiency of internal EGR and the charging efficiency of fresh air, it is particularly important to accurately grasp the minimum valve overlap period in which the residual ratio of internal EGR is 0%. In addition, the relationship between the valve overlap period and the internal EGR amount may have individual differences for each internal combustion engine due to variations in parts constituting the internal combustion engine and variations due to aging.

  In view of the above-described problems, the present invention provides scavenging of internal EGR by providing a valve overlap period in which both the intake valve and the exhaust valve are open during an engine operation state where the intake pressure is higher than the back pressure. In a control apparatus for an internal combustion engine, the minimum valve overlap period in which the residual ratio of internal EGR is 0% and accurately grasps the minimum valve overlap period in consideration of individual differences as described above. It is an object of the present invention to provide a control device for an internal combustion engine that can be used.

  According to the first aspect of the present invention, the internal EGR scavenging is performed by providing a valve overlap period in which both the intake valve and the exhaust valve are open during an engine operation state in which the intake pressure is higher than the back pressure. In the control device for an internal combustion engine to perform, in an engine operation state in which the intake pressure is higher than the back pressure, a plurality of engine operations with different valve overlap periods are performed, and the intake in each engine operation state of the plurality of engine operations Based on the intake air amount measuring means for measuring the air amount and each intake air amount data measured by the intake air amount measuring means, a change tendency of the intake air amount with respect to a change in the valve overlap period is derived, and the change tendency Identifies the boundary valve overlap period during which the trend shifts to a different trend, and this boundary valve overlap period is the minimum value that can make the internal EGR 0%. Comprising a valve overlap period learning means for learning a blanking overlap period, the control device of the internal combustion engine is provided.

In the valve overlap period region where there is sufficient valve overlap period and everything can be scavenged without leaving any internal EGR, the change in intake air volume relative to the change in valve overlap period is It will be influenced by the amount of blowout. On the other hand, in the bubble overlap period region where the valve overlap period is insufficient and a part of the internal EGR remains without being scavenged, the change tendency of the intake air amount with respect to the change of the valve overlap period Is affected by the scavenging amount of the internal EGR during the valve overlap period, and is also affected by the contraction of the internal EGR remaining without scavenging. That is, in the valve overlap period region in which all of the internal EGR can be scavenged without remaining, and in the valve overlap period region in which a part of the internal EGR remains without being scavenged, the valve overlap period The change tendency of the intake air amount with respect to the change is different.

  Based on this, in the present invention described in claim 1, the boundary valve overlap period in which the change tendency of the intake air amount with respect to the change in the valve overlap period shifts to a different tendency is specified, and the boundary valve overlap period Is learned as the minimum valve overlap period in which the internal EGR can be 0%, and the scavenging efficiency of the internal EGR and the charging efficiency of fresh air can be improved. In addition, according to the present invention, the minimum valve overlap period can be learned during engine operation of an internal combustion engine that is actually used, and each internal combustion engine that may be caused by variations due to variations in components constituting the internal combustion engine or aging deterioration, etc. It is possible to accurately grasp the minimum valve overlap period considering individual differences for each engine.

  According to a second aspect of the present invention, the internal combustion engine has a variable compression ratio mechanism that changes the volume of the combustion chamber at the top dead center to make the mechanical compression ratio variable, and is based on the intake air amount measuring means. The measurement of each intake air amount is performed in an engine operation state in which an intake pressure is higher than a back pressure and in a low load side engine operation state in which a predetermined high mechanical compression ratio is obtained by the variable compression ratio mechanism. A control apparatus for an internal combustion engine according to claim 1 is provided.

According to a third aspect of the present invention, the internal combustion engine has a variable compression ratio mechanism that varies the mechanical compression ratio by changing the volume of the combustion chamber at the top dead center, and the intake air amount measuring means is In the engine operation state where the intake pressure is higher than the back pressure, a plurality of engine operations with different valve overlap periods are performed at two different mechanical compression ratios, and the intake air amount in each engine operation state is measured. The valve overlap period learning means is one of the two different mechanical compression ratios when the valve overlap period is the same based on each intake air quantity data measured by the intake air quantity measuring means . calculated for each valve overlap period of intake air amount difference which is the difference between the intake air amount in the engine operation at the intake air amount and the other mechanical compression ratio in the engine operation in the mechanical compression ratio Then, a change tendency of the intake air amount difference with respect to a change in the valve overlap period is derived, a boundary valve overlap period in which the change tendency shifts to a different tendency is specified, and the boundary valve overlap period is set to 0% of the internal EGR. The control device for an internal combustion engine according to claim 1, wherein learning is performed as a minimum valve overlap period that can be determined.

  According to the invention described in each claim, scavenging of the internal EGR is performed by providing a valve overlap period in which both the intake valve and the exhaust valve are open during an engine operation state in which the intake pressure is higher than the back pressure. In a control device for an internal combustion engine to be performed, a minimum valve overlap period in which the residual rate of internal EGR is 0%, and taking into account individual differences for each internal combustion engine due to variations among components and variations due to aging There is a common effect that the overlap period can be accurately grasped.

1 is an overall view of an 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 a figure which shows a variable valve timing mechanism. It is a figure which shows the lift amount of an intake valve and an exhaust valve. It is a figure for demonstrating a mechanical compression ratio, an actual compression ratio, and an expansion ratio. It is a figure which shows the relationship between theoretical thermal efficiency and an expansion ratio. It is a figure for demonstrating a normal cycle and a super-high expansion ratio cycle. It is a figure which shows one Embodiment of the change tendency of the intake air amount with respect to the change of a valve overlap period in the case of the engine driving | running state in which intake pressure is higher than back pressure. It is a flowchart which shows one Embodiment of the control which specifies the minimum valve overlap period which can make internal EGR 0%. It is a figure which shows another one Embodiment of the change tendency of the intake air amount with respect to the change of a valve overlap period. It is a flowchart which shows another embodiment of control which specifies the minimum valve overlap period which can make internal EGR 0%.

  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 the outlet of the compressor 15a of the exhaust turbocharger 15 via an intake duct 14, and the inlet of the compressor 15a is connected to an air cleaner 17 via an intake air amount detector 16 using, for example, heat rays. A throttle valve 19 driven by an actuator 18 is disposed in the intake duct 14.

  On the other hand, the exhaust port 10 is connected to an inlet of an exhaust turbine 15b of an exhaust turbocharger 15 via an exhaust manifold 20, and an outlet of the exhaust turbine 15b is connected to a catalytic converter 22 containing an exhaust purification catalyst via an exhaust pipe 21. The An air-fuel ratio sensor 23 is disposed in the exhaust pipe 21.

  On the other hand, in the embodiment shown in FIG. 1, the piston 4 is brought to 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. A variable compression ratio mechanism A capable of changing the volume of the combustion chamber 5 when positioned is provided, and the closing timing of the intake valve 7 can be controlled in order to change the actual start timing of the compression action, and An intake variable valve timing mechanism B capable of individually controlling the opening timing of the intake valve 7 is provided, and an exhaust variable valve timing mechanism C capable of individually controlling the opening timing and closing timing of the exhaust valve 9. 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 16 and the output signal of the air-fuel ratio sensor 23 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. On the other hand, the output port 36 is connected to the spark plug 6, the fuel injection valve 13, the throttle valve driving actuator 18, the variable compression ratio mechanism A, the intake variable valve timing mechanism B, and the exhaust variable valve timing mechanism C through corresponding drive circuits 38. Connected.

  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 protrusions 50 spaced from each other are formed below both side walls of the cylinder block 2, and cam insertion holes 51 each having a circular cross section are formed in each protrusion 50. Has been. 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 spaced apart from each other. Cam insertion holes 53 each having a circular cross section are formed.

  As shown in FIG. 2, a pair of camshafts 54 and 55 are provided, and on each camshaft 54 and 55, a circular cam 58 is rotatably inserted into each cam insertion hole 53. It 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, an eccentric shaft 57 eccentrically arranged with respect to the rotation axis of each camshaft 54, 55 extends. 56 is mounted eccentrically and 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. As shown in FIG. 2, a cam rotation angle sensor 25 that generates an output signal representing the rotation angle of the camshaft 55 is attached to the camshaft 55.

  When the circular cams 58 fixed on the camshafts 54 and 55 are rotated in opposite directions as indicated by arrows in FIG. 3A from the state shown in FIG. 3A, the eccentric shafts 57 are separated from each other. In order to move in the direction, the circular cam 56 rotates in the opposite direction to the circular cam 58 in the cam insertion hole 51, and as shown in FIG. 3B, the position of the eccentric shaft 57 is changed from the high position to the intermediate height position. It becomes. 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. As the distance between the center a of 58 and the center c of the circular cam 56 increases, the cylinder block 2 moves away from the crankcase 1. 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 positioned at the compression top dead center. Therefore, by rotating the camshafts 54 and 55, the piston 4 is compressed at the 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.

  On the other hand, FIG. 4 shows the intake variable valve timing mechanism B attached to the end of the camshaft 70 for driving the intake valve 7 in FIG. Referring to FIG. 4, the intake variable valve timing mechanism B includes a timing pulley 71 that is rotated in the direction of an arrow by a crankshaft of an engine via a timing belt, a cylindrical housing 72 that rotates together with the timing pulley 71, an intake air A rotating shaft 73 that rotates together with the valve drive camshaft 70 and is rotatable relative to the cylindrical housing 72, and a plurality of partition walls that extend from the inner peripheral surface of the cylindrical housing 72 to the outer peripheral surface of the rotating shaft 73. 74 and vanes 75 extending from the outer peripheral surface of the rotating shaft 73 to the inner peripheral surface of the cylindrical housing 72 between the partition walls 74, and the advance hydraulic chambers 76 on both sides of each vane 75. And a retarding hydraulic chamber 77 are formed.

  The hydraulic oil supply control to the hydraulic chambers 76 and 77 is performed by a hydraulic oil supply control valve 78. The hydraulic oil supply control valve 78 includes hydraulic ports 79 and 80 connected to the hydraulic chambers 76 and 77, a hydraulic oil supply port 82 discharged from the hydraulic pump 81, a pair of drain ports 83 and 84, And a spool valve 85 for controlling communication between the ports 79, 80, 82, 83, and 84.

  When the cam phase of the intake valve driving camshaft 70 should be advanced, the spool valve 85 is moved to the right in FIG. 4 and the hydraulic oil supplied from the supply port 82 is advanced via the hydraulic port 79. The hydraulic oil in the retard hydraulic chamber 77 is discharged from the drain port 84 while being supplied to the hydraulic chamber 76. At this time, the rotary shaft 73 is rotated relative to the cylindrical housing 72 in the direction of the arrow.

  On the other hand, when the cam phase of the intake valve driving camshaft 70 should be retarded, the spool valve 85 is moved to the left in FIG. 4, and the hydraulic oil supplied from the supply port 82 causes the hydraulic port 80 to move. The hydraulic oil in the advance hydraulic chamber 76 is discharged from the drain port 83 while being supplied to the retard hydraulic chamber 77. At this time, the rotating shaft 73 is rotated relative to the cylindrical housing 72 in the direction opposite to the arrow.

  If the spool valve 85 is returned to the neutral position shown in FIG. 4 while the rotation shaft 73 is rotated relative to the cylindrical housing 72, the relative rotation operation of the rotation shaft 73 is stopped, and the rotation shaft 73 is The relative rotation position at that time is held. Therefore, the intake variable valve timing mechanism B can advance or retard the phase of the cam of the intake valve driving camshaft 70 by a desired amount.

  In FIG. 5, the solid line shows the time when the cam phase of the intake valve driving camshaft 70 is advanced the most by the intake variable valve timing mechanism B, and the broken line shows the phase of the cam of the intake valve driving camshaft 70. It shows when the angle is most retarded. Therefore, the valve opening period of the intake valve 7 can be arbitrarily set between the range indicated by the solid line and the range indicated by the broken line in FIG. 5, and therefore the closing timing of the intake valve 7 is also the range indicated by the arrow C in FIG. Any crank angle can be set.

  The intake variable valve timing mechanism B shown in FIG. 1 and FIG. 4 shows an example. For example, a variable valve that can change only the closing timing of the intake valve while keeping the opening timing of the intake valve constant. Various types of variable valve timing mechanisms, such as timing mechanisms, can be used.

  Further, the exhaust variable valve timing mechanism C basically has the same configuration as the intake variable valve timing mechanism B, and the valve opening timing and valve opening period of the exhaust valve 9, that is, the valve opening timing of the exhaust valve 9. The valve closing timing can be arbitrarily changed.

  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 embodiment 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 the normal cycle and the ultra-high expansion ratio cycle that are selectively used according to the load in this embodiment.

  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. Was found to have 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. Thus, the theoretical thermal efficiency when the expansion ratio is increased while the actual compression ratio ε is maintained at a low value, and the theoretical thermal efficiency when the actual compression ratio is increased 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 this embodiment, when the engine load is relatively low, the super high expansion ratio cycle shown in FIG. 8B is used, and during the engine high load operation, the normal cycle shown in FIG. 8A is used.

  Next, an embodiment of overall operation control in the spark ignition type internal combustion engine of the present embodiment will be schematically described. As described above, the normal cycle shown in FIG. 8A is executed during engine high load operation. Therefore, since the mechanical compression ratio is lowered, 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 amount of intake air is large, and at this time, the opening degree of the throttle valve 17 is kept fully open, so that the pumping loss is zero.

  On the other hand, when the engine load becomes low, the closing timing of the intake valve 7 is delayed to reduce the intake air amount. Further, at this time, the mechanical compression ratio is increased as the engine load is lowered so that the actual compression ratio is kept substantially constant. Therefore, the expansion ratio is also increased as the engine load is lowered. At this time, the throttle valve 17 is kept fully open, and therefore the amount of intake air supplied into the combustion chamber 5 is controlled by changing the closing timing of the intake valve 7 regardless of the throttle valve 17. Has been.

  As described above, when the engine load is reduced from the engine 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 decreased in proportion to the decrease in 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.

  When the engine load is further reduced, the mechanical compression ratio is further increased, and when the engine load is reduced to a medium load L1 slightly close to the low load, the mechanical compression ratio becomes a limit mechanical compression ratio (upper limit mechanical compression) that becomes a structural limit of the combustion chamber Ratio). 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. Accordingly, the mechanical compression ratio is maximized and the expansion ratio is maximized at the time of low engine load operation and low engine load operation, that is, at the engine low load operation side. In other words, the mechanical compression ratio is maximized so that the maximum expansion ratio is obtained on the engine low load operation side.

  On the other hand, when the engine load decreases to L1, the closing timing of the intake valve 7 becomes the limit closing timing at which the amount of intake air supplied into the combustion chamber 5 can be controlled. When the closing timing of the intake valve 7 reaches the limit closing timing, the closing timing of the intake valve 7 is reduced in a region where the load is lower than the engine load L1 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. At this time, that is, in the region where the load is lower than the engine load L1 when the closing timing of the intake valve 7 reaches the limit closing timing, the amount of intake air supplied into the combustion chamber 5 is controlled by the throttle valve 17, As the engine load becomes lower, the opening degree of the throttle valve 17 is made smaller.

  On the other hand, the intake air amount can be controlled without depending on the throttle valve 17 by advancing the closing timing of the intake valve 7 as the engine load becomes lower. Therefore, in the example according to the present embodiment, the closing timing of the intake valve 7 is from the intake bottom dead center BDC until the limit closing timing L1 that can control the amount of intake air supplied into the combustion chamber as the engine load decreases. It will be moved away.

  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.

  By the way, as described above, there is a turbocharged internal combustion engine that performs so-called valve overlap in which both the intake valve and the exhaust valve are simultaneously opened when acceleration or high output is required. In other words, by performing valve overlap, the intake air is blown out to the exhaust side by using supercharging pressure, etc., and the remaining burned gas in the combustion chamber is scavenged to improve the combustibility and output. The exhaust gas amount supplied to the supercharged turbine is increased to increase the supercharging effect and to improve the output.

  However, in an internal combustion engine that scavenges burned gas that remains in the combustion chamber, so-called internal EGR, by providing a valve overlap period, if the valve overlap period is too short, a large amount of internal EGR remains and torque decreases. It may bring about. On the other hand, when the valve overlap period is too long, the amount of air blown during the valve overlap period is excessively large, and the exhaust gas contains a large amount of oxygen. The exhaust purification catalyst is likely to be deteriorated or excessively heated, and when a three-way catalyst is used, the purification rate is lowered and the emission may be deteriorated.

  Therefore, in an internal combustion engine that scavenges internal EGR by providing a valve overlap period, it is necessary to accurately grasp the relationship between the valve overlap period and the internal EGR amount. From the viewpoint of improving the scavenging efficiency of internal EGR and the charging efficiency of fresh air, it is particularly important to accurately grasp the minimum valve overlap period in which the residual ratio of internal EGR is 0%. Further, it is conceivable that the relationship between the valve overlap period and the internal EGR amount has individual differences for each internal combustion engine due to variations in parts constituting the internal combustion engine and variations due to aging.

  Therefore, in the control apparatus for an internal combustion engine according to the present invention, scavenging of the internal EGR is performed by providing a valve overlap period in which both the intake valve and the exhaust valve are open when the engine is operating with an intake pressure higher than the back pressure. Is a minimum valve overlap period in which the residual rate of internal EGR is 0%, and takes into account the individual differences for each internal combustion engine as described above. It is comprised with the means comprised so that it could grasp | ascertain with high precision.

  In the control apparatus for an internal combustion engine of the present invention, the intake air amount depends on the valve overlap period and the internal EGR amount, and contracts due to a temperature drop when the internal EGR is mixed with the intake air supplied into the combustion chamber. In consideration of this, it is assumed that the minimum valve overlap period in which the residual ratio of the internal EGR is 0% is learned.

FIG. 9 is a diagram showing an embodiment of a change tendency of the intake air amount with respect to a change in the valve overlap period in an engine operation state in which the intake pressure is higher than the back pressure. In the valve overlap period region where there is sufficient valve overlap period and everything can be scavenged without leaving any internal EGR, the change in intake air volume relative to the change in valve overlap period is It will be influenced by the amount of blowout. On the other hand, in the bubble overlap period region where the valve overlap period is insufficient and a part of the internal EGR remains without being scavenged, the change tendency of the intake air amount with respect to the change of the valve overlap period Is affected by the scavenging amount of the internal EGR during the valve overlap period, and is also affected by the contraction of the internal EGR remaining without scavenging. That is, as shown in FIG. 9, a valve overlap period region in which all of the internal EGR can be scavenged without remaining the internal EGR, and a valve overlap period region in which a part of the internal EGR remains without being scavenged. In, the change tendency of the intake air amount with respect to the change of the valve overlap period is different.

  Based on this, in one embodiment of the control device of the present invention, the boundary valve overlap period in which the change tendency of the intake air amount with respect to the change in the valve overlap period shifts to a different tendency is specified, and the boundary valve over It has valve overlap period learning means for learning the lap period as the minimum valve overlap period that can make the internal EGR 0%. Further, in the present embodiment, in order to identify the boundary valve overlap period in which the change tendency of the intake air amount with respect to the change in the valve overlap period shifts to a different tendency, the engine pressure is higher than the back pressure. And an intake air amount measuring means for performing a plurality of engine operations with different valve overlap periods and measuring an intake air amount in each engine operation state of the plurality of engine operations.

  According to the present invention having the intake air amount measuring means and the valve overlap period learning means, the minimum valve overlap period can be learned during the operation of the actually used internal combustion engine, and the internal combustion engine is configured. It is possible to accurately grasp the minimum valve overlap period that also takes into account individual differences among each internal combustion engine that may be caused by variations in parts due to variations and aging deterioration, etc. Therefore, scavenging efficiency of internal EGR and fresh air It is possible to improve the filling efficiency.

  FIG. 10 is a flowchart showing an embodiment of control for specifying the minimum valve overlap period in which the internal EGR can be 0% using the intake air amount measuring means and the valve overlap learning means. is there.

  In the embodiment shown in FIG. 10, first, in step 101, an engine operating state in which the intake pressure is higher than the back pressure using a turbocharger (supercharger) or the like to perform scavenging of the internal EGR. It is said. Then, in the subsequent step 102 and step 103, each of the large valve overlap period region in which all the internal EGR is scavenged and fresh air is blown out, and the small valve overlap period region in which a part of the internal EGR remains. In the region, the engine is operated in two states with different valve overlap (VOL) periods, and the intake air amount (a1, a2, b1, b2 in FIG. Measure). Then, in the subsequent step 104 and step 105, based on the intake air amount measured in step 102 and step 103, linearly approximates the change tendency of the intake air amount with respect to the change in the valve overlap period in each region, The valve overlap period at the intersection D where the straight lines intersect is specified as a boundary valve overlap period in which the change tendency of the intake air amount with respect to the change in the valve overlap period shifts to a different tendency. Then, the boundary valve overlap period is learned as the minimum valve overlap period in which the internal EGR can be 0%.

  There is no particular limitation on the mechanical compression ratio when the intake air amount is measured by the intake air amount measuring means and the boundary valve overlap period is specified by the valve overlap period learning means. Or it may be performed on either the high compression ratio side. However, in order to learn more accurately the minimum valve overlap period in which the internal EGR can be set to 0%, it is necessary to measure the intake air amount in a plurality of engine operating states with greatly different valve overlap periods. Although advantageous, when the intake air amount measuring means measures the intake air amount in the high load side engine operating state with a low compression ratio, if the valve overlap period is greatly changed, the output torque changes greatly. As a result, there may be a problem in driving.

  Therefore, in one embodiment of the present invention, taking into account problems in terms of drivability and the like, the measurement of each intake air amount by the intake air amount measuring means is performed in an engine operating state where the intake pressure is higher than the back pressure. It is assumed that the operation is performed in a low-load side engine operating state in which the variable compression ratio mechanism has a predetermined high mechanical compression ratio. In the low load side engine operating state in which the predetermined high mechanical compression ratio is achieved by the variable compression ratio mechanism, the combustion limit is high, the valve overlap period can be greatly swung, and the output torque change can also be sucked by the throttle or the like. Therefore, it is possible to more accurately learn the minimum valve overlap period in which the internal EGR can be 0% while suppressing the deterioration of the drivability.

Further, in another embodiment of the control device of the present invention, the intake air amount measuring means performs a plurality of different engine operations with different valve overlap periods when the intake air pressure is higher than the back pressure. The measurement is performed at two mechanical compression ratios, and the intake air amount in each engine operating state is measured. Further, the valve overlap period learning means is one of the two different mechanical compression ratios when the valve overlap period is the same based on each intake air quantity data measured by the intake air quantity measuring means . The difference between the intake air amount in engine operation at the mechanical compression ratio and the intake air amount in engine operation at the other mechanical compression ratio is calculated for each valve overlap period, and the valve overlap period A change tendency of the intake air amount difference with respect to the change in the difference is derived, and a boundary valve overlap period in which the change tendency shifts to a different tendency is specified. Then, the boundary valve overlap period is learned as the minimum valve overlap period in which the internal EGR can be 0%.

  In this embodiment, it is noted that the intake air amount depends on the valve overlap period and the internal EGR amount, and that the internal EGR contracts due to a temperature drop when mixing with the intake air supplied into the combustion chamber, Furthermore, it is assumed that the amount of contraction of the internal EGR differs depending on the mechanical compression ratio, and the minimum valve overlap period in which the residual ratio of the internal EGR is 0% is learned. According to the learning of the minimum valve overlap period according to the present embodiment, the valve overlap period area where all the internal EGR is scavenged and fresh air is blown out, and the valve overlap period area where a part of the internal EGR remains. Even when it is difficult to linearly approximate the change tendency of the intake air amount with respect to the change in the valve overlap period of each region due to the pulsation effect, the residual ratio of the internal EGR becomes 0% more accurately. It is possible to learn the minimum valve overlap period.

  FIG. 11 shows a case where a plurality of engine operations with different valve overlap periods are performed at two different mechanical compression ratios in an engine operation state in which the intake pressure is higher than the back pressure, and the intake air amount in each engine operation state is calculated. It is a figure which shows one Embodiment of the change tendency of the intake air amount with respect to the change of a valve overlap period in embodiment to measure.

The difference between the amount of intake air in engine operation at one mechanical compression ratio and the amount of intake air in engine operation at the other mechanical compression ratio when the valve overlap period is the same. A certain intake air amount difference corresponds to a difference in fuel chamber volume at two different mechanical compression ratios in a valve overlap period region in which there is a sufficient valve overlap period and all of the air can be scavenged without remaining internal EGR. Therefore, it is kept constant as shown in FIG. On the other hand, in the bubble overlap period region where the valve overlap period is insufficient and a part of the internal EGR remains without being scavenged, as described above, the suction with respect to the change of the valve overlap period The change tendency of the air amount is affected by the scavenging amount of the internal EGR during the valve overlap period, and is also affected by the contraction of the internal EGR remaining without being scavenged. Further, the amount of contraction of the internal EGR that remains without being scavenged differs depending on the mechanical compression ratio. Therefore, one of the two different mechanical compression ratios when the valve overlap period is the same. The intake air amount difference, which is the difference between the intake air amount during engine operation at the engine and the intake air amount during engine operation at the other mechanical compression ratio, is not maintained constant. That is, as shown in FIG. 11, a valve overlap period region in which all of the internal EGR can be scavenged without remaining the internal EGR, and a valve overlap period region in which a part of the internal EGR remains without being scavenged. , The change tendency of the intake air amount difference with respect to the change of the valve overlap period is different.

  FIG. 12 shows that when the intake pressure is higher than the back pressure in the engine operation state, a plurality of engine operations with different valve overlap periods are performed at two different mechanical compression ratios, and the intake air amount in each engine operation state is calculated. It is a flowchart which shows one Embodiment of the control which specifies the minimum valve overlap period which can make internal EGR 0% in embodiment to measure.

In the embodiment shown in FIG. 12, first, in step 201, in order to perform scavenging of the internal EGR, the engine operating state in which the intake pressure is higher than the back pressure using a turbocharger (supercharger) or the like. And In subsequent steps 202 and 203, a plurality of engine operations having different valve overlap (VOL) periods are divided into two mechanical compression ratios, that is, a first mechanical compression ratio (low mechanical compression ratio side) and a second mechanical compression ratio. (High mechanical compression ratio side) Measure the intake air amount in each engine operating state. In subsequent steps 204 and 205, based on the intake air amounts measured in steps 202 and 203, the first mechanical compression ratio and the second mechanical compression ratio when the valve overlap period is the same . The intake air amount difference E (see FIG. 11), which is the difference between the intake air amount in the engine operation at one of the mechanical compression ratios and the intake air amount in the engine operation at the other mechanical compression ratio, is represented by each valve overlap period. , A change tendency of the intake air amount difference with respect to a change in the valve overlap period is derived, and a boundary valve overlap period in which the change tendency shifts to a different tendency is specified. More specifically, the first mechanical compression in the case where a plurality of engine operations that increase the valve overlap period by a predetermined value from an engine operation that does not have a valve overlap period is executed, and the valve overlap period is the same. The intake air amount difference E, which is the difference between the intake air amount in engine operation at one mechanical compression ratio and the intake air amount in engine operation at the other mechanical compression ratio, is constant. The valve overlap period that will be maintained is identified as the boundary valve overlap period. Then, the boundary valve overlap period is learned as the minimum valve overlap period in which the internal EGR can be 0%.

DESCRIPTION OF SYMBOLS 1 Crankcase 2 Cylinder block 3 Cylinder head 4 Piston 5 Combustion chamber 7 Intake valve 70 Intake valve drive camshaft A Variable compression ratio mechanism B Intake variable valve timing mechanism C Exhaust variable valve timing mechanism

Claims (3)

In an internal combustion engine control apparatus that scavenges internal EGR by providing a valve overlap period in which both an intake valve and an exhaust valve are open during an engine operation state in which the intake pressure is higher than the back pressure,
When the engine is in an engine operating state in which the intake pressure is higher than the back pressure, a plurality of engine operations with different valve overlap periods are performed, and the intake air amount is measured in each of the engine operating states of the plurality of engine operations. Measuring means;
Based on each intake air amount data measured by the intake air amount measuring means, a change tendency of the intake air amount with respect to a change in the valve overlap period is derived, and a boundary valve overlap period in which the change tendency shifts to a different tendency is obtained. A control apparatus for an internal combustion engine, comprising: a valve overlap period learning unit that identifies and learns the boundary valve overlap period as a minimum valve overlap period in which the internal EGR can be 0%. The internal combustion engine has a variable compression ratio mechanism that varies the mechanical compression ratio by changing the combustion chamber volume at top dead center,
Measurement of each intake air amount by the intake air amount measuring means is an engine operation state in which the intake pressure is higher than the back pressure, and a low load side engine operation state in which the variable compression ratio mechanism has a predetermined high mechanical compression ratio. The control apparatus for an internal combustion engine according to claim 1, wherein The internal combustion engine has a variable compression ratio mechanism that varies the mechanical compression ratio by changing the combustion chamber volume at top dead center,
The intake air amount measuring means performs a plurality of engine operations with different valve overlap periods at two different mechanical compression ratios in an engine operation state where the intake pressure is higher than the back pressure, Measure the intake air volume,
The valve overlap period learning means is one of the two different mechanical compression ratios when the valve overlap period is the same based on each intake air quantity data measured by the intake air quantity measuring means . The difference between the intake air amount in engine operation at the mechanical compression ratio and the intake air amount in engine operation at the other mechanical compression ratio is calculated for each valve overlap period, and the valve overlap period It is possible to derive the change tendency of the difference in intake air amount with respect to the change of the air flow, identify the boundary valve overlap period in which the change tendency shifts to a different tendency, and set the internal EGR to 0% for the boundary valve overlap period The control apparatus for an internal combustion engine according to claim 1, wherein learning is performed as a minimum minimum valve overlap period.

Images