JP2007309285A - Cycle variable stroke engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cycle variable stroke engine having a simple structure and equipped with a piston stroke characteristic changing means suitable for necessary torque reduction. <P>SOLUTION: This cycle variable stroke engine is provided with a cycle variable stroke mechanism rotating a crankshaft 9 by a reciprocating piston 22 and making piston stroke characteristics different between an exhaust top dead center position and a compression top dead center position of the piston 22 in one cycle; the piston stroke characteristic changing means comprising a variable valve train 30 capable of switching operation timing of an air feed/discharge valve at approximately 360°of a crank rotating angle; and a control means 47 capable of switching ignition timing at approximately 360°of the crank rotating angle. By switching the operation timing of the air feed/discharge valve and ignition timing at approximately 360°of the crank rotating angle by the control means 47 and the variable valve train 30, the exhaust top dead center and the compression top dead center in one cycle are switched to change the piston stroke characteristics. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a cycle variable stroke engine having a piston stroke characteristic in which a crankshaft is rotated by a reciprocating piston and an exhaust top dead center position (TDC) and a compression top dead center position (TDC) of the piston in one cycle are different. In particular, the present invention relates to a cycle variable stroke engine suitable for changing piston stroke characteristics.

  In order to make it possible to change the engine compression ratio, a cycle variable stroke engine has been proposed in which the piston position at the exhaust top dead center is different from the piston position at the compression top dead center (see Patent Document 1).

This is because the upper link connected to the piston pin of the piston and the lower link connected to the crank pin of the crankshaft are connected to each other, and one end of a control link that restricts the freedom of the upper link and the lower link to the lower link. And the other end of this control link is fitted to the eccentric shaft portion of the rotary shaft so as to be rotatable around the center of oscillation, and the rotational angular speed of this rotary shaft is set to 1/2 of the rotational angular speed of the crankshaft. Configured. Furthermore, the piston stroke characteristics can be changed by changing the rotation phase of the rotation shaft relative to the rotation phase of the crankshaft. As a result, the piston position at the exhaust top dead center is set lower than the piston position at the compression top dead center, avoiding interference between the piston and the intake and exhaust valves near the exhaust top dead center, and increasing the compression ratio. I am trying to figure it out.
Japanese Patent Laid-Open No. 2003-13764

  However, in the above conventional example, the piston stroke characteristics are changed by changing the rotational phase of the rotating shaft relative to the rotational phase of the crankshaft. Therefore, the torque required for changing the phase is large and the structure is complicated and large. As a result, there has been a problem of fuel consumption reduction and cost increase.

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to provide a cycle variable stroke engine having piston stroke characteristic changing means having a simple structure and capable of reducing necessary torque.

  The present invention includes a cycle variable stroke mechanism in which a crankshaft is rotated by a reciprocating piston, and a piston stroke characteristic different between an exhaust top dead center position and a compression top dead center position of a piston in one cycle is provided. A variable valve mechanism capable of switching the valve operation timing to a crank rotation angle of about 360 degrees, and a control means for switching the variable valve mechanism and switching the ignition timing to a crank rotation angle of about 360 degrees. The control means switches between the exhaust top dead center and the compression top dead center in one cycle by switching the operation timing and ignition timing of the air supply / exhaust valve in the variable valve mechanism to around 360 degrees as the crank rotation angle. The piston stroke characteristic is changed.

  Therefore, in the present invention, the cycle variable is provided with a cycle variable stroke mechanism having a piston stroke characteristic that is different between the exhaust top dead center position and the compression top dead center position of the piston in one cycle by rotating the crankshaft by the reciprocating piston. By switching the piston stroke characteristics of the stroke engine around 360 degrees with the operation timing and ignition timing of the supply / exhaust valve in the variable valve mechanism as the crank rotation angle, the exhaust top dead center and compression top dead center in one cycle are changed. By changing the piston stroke characteristics by switching, the torque required to change the characteristics is smaller, the structure is simplified, and the cost is lower than when the piston stroke characteristics are changed by the phase switching means of the cycle variable stroke mechanism. This is also advantageous in terms of fuel consumption.

  Hereinafter, a cycle variable stroke engine of the present invention will be described based on each embodiment.

(First embodiment)
1 to 9 show a first embodiment of a cycle variable stroke engine to which the present invention is applied, FIG. 1 is a sectional view of the cycle variable stroke engine, FIG. 2 is a schematic configuration diagram of a cycle variable stroke mechanism, and FIG. FIG. 4 to FIG. 6 are configuration diagrams of the stroke characteristic changing means, FIG. 7 is a control flowchart for changing the stroke characteristics, FIG. 8 is a time chart for changing the stroke characteristics, and FIG. 9 is a schematic view showing another embodiment of the stroke characteristic changing means.

  The cycle variable stroke engine in the present embodiment includes a cycle variable stroke mechanism shown in FIGS. 1 and 2 and a stroke characteristic changing unit shown in FIGS.

  A cycle variable stroke mechanism of a cycle variable stroke engine will be described first with reference to FIGS. A plurality of cylinders 21 are formed along a cylinder row in a cylinder block 20 that constitutes a part of the engine body, and pistons 22 are arranged in the cylinders 21 so as to be able to be moved up and down. The piston pin 1 of each piston 22 is mechanically linked to the crankpin 2 of the crankshaft 9 by a plurality of links, specifically, the upper link 3 and the lower link 4. One end of the upper link 3 is rotatably connected to the piston pin 1, the lower link 4 is rotatably connected to the crank pin 2, and the other end of the upper link 3 and the lower link 4 are connected via a first connecting pin 24. They are connected to each other in a rotatable manner. The crankshaft 9 is provided with a counterweight 9a.

  One end 5 a of a control link 5 is rotatably connected to the lower link 4 via a second connecting pin 25, and the other end 5 b of the control link 5 is around a swing center 5 c provided in the cylinder block 20. It is supported so that it can swing. The connecting positions of the crank pin 2, the first connecting pin 24, and the second connecting pin 25 that are connected to the lower link 4 are not arranged on the same straight line but are arranged in a substantially triangular shape.

  The support center of the swing center 5c of the control link 5 with respect to the cylinder block 20 is configured to be changed by the rotating shaft 6 that rotates in conjunction with the rotation of the crankshaft 9. That is, the rotating shaft 6 extends in the cylinder row direction, and is rotatably supported by the plurality of journal portions 8 on the cylinder block 20 side via the bearing bracket 26. The rotating shaft 6 has a cylindrical or columnar eccentric shaft portion (eccentric portion) 7 which is eccentric with respect to the axial center of the journal portion 8 which is the rotation center 6a of the rotating shaft 6 itself. The other end 5 b of the control link 5 is rotatably fitted on the outer peripheral surface of each eccentric shaft portion 7. That is, the other end 5b of the control link 5 is rotatably supported by the eccentric shaft portion 7, and the shaft center of the eccentric shaft portion 7 becomes the swing center 5c of the control link 5 with respect to the engine body.

  Further, a drive pulley 12A fixed to one end of the crankshaft 9, a driven pulley 12B fixed to one end of the rotating shaft 6, and a pulley belt 13 bridged between both pulleys 12A and 12B, are separated from the crankshaft 9. A rotational power transmission mechanism that transmits rotational power to the rotary shaft 6 is configured. The radius of the driven pulley 12B is set to be twice the radius of the drive pulley 12A so that the rotational speed of the rotary shaft 6 with respect to the crankshaft 9 is halved. Since the reduction ratio of the rotational motion transmitted from the crankshaft 9 to the rotary shaft 6 is set to 1/2, the rotary shaft 6 makes one rotation during one cycle of the engine.

  Therefore, when the rotary shaft 6 rotates in conjunction with the crankshaft 9, the support position of the swing center 5c of the control link 5 moves via the eccentric shaft portion 7 for each cycle, so that it is twice in one cycle. The piston stroke characteristics of the piston reciprocating motion can be different from each other. That is, the piston stroke characteristics can be different between the exhaust-intake stroke and the compression-expansion stroke.

  3A, the crankshaft 9 is rotated in a direction away from the rotary shaft 6 from the top dead center, and the support position of the swing center 5c of the control link 5 is determined via the eccentric shaft portion 7 in the left half of the figure. The piston stroke characteristic is shown when the rotary shaft 6 is rotated so that the position is lowered from the rotation center 6a of the rotation shaft 6 in the cycle and the position is raised from the rotation center 6a of the rotation shaft 6 in the right half cycle in the figure. ing.

  The swing center 5c of the control link 5 is the most lowered position at the top dead center in the left half cycle in the drawing, that is, the piston position is raised through the lower link 4, and the right half in the drawing. The highest position at the top dead center in the cycle, that is, the piston position is lowered with the lower link 4 interposed therebetween, and the piston height position at the exhaust top dead center becomes higher than the piston height position at the compression top dead center. I am doing so.

  Further, accompanying the increase in the vertical position of the piston 22 at the exhaust top dead center, the piston speed from the bottom dead center position to the top dead center in the exhaust stroke is relatively increased by the stroke increase, Also, in the intake stroke starting from the exhaust top dead center, the piston speed to the intake bottom dead center is relatively increased. On the contrary, the piston speed from the bottom dead center position to the top dead center in the compression stroke is relatively decreased by the stroke reduction accompanying the downward movement of the piston 22 at the compression top dead center. Also, in the expansion stroke starting from the compression top dead center, the piston speed to the expansion bottom dead center is relatively reduced.

  Next, the stroke characteristic changing means applied to the cycle variable stroke engine of the present embodiment will be described with reference to FIGS. This stroke characteristic changing means is constituted by a variable valve lift mechanism (VVL) that switches a cam for opening and closing the intake valve and the exhaust valve. The basic configuration has been previously proposed by the present applicant, and is publicly known, for example, from Japanese Patent Laid-Open No. 8-49514. Therefore, only the outline will be described for the intake valve, but the structure for the exhaust valve is similarly configured.

  As shown in FIGS. 4 and 5, the variable valve lift mechanism 30 constituting the stroke characteristic changing means has a camshaft 31 for each cylinder, a high speed cam (high lift, large operating angle) 32, and profiles on both sides thereof. The low-speed cam 33 (low lift, small working angle) is formed. The high speed cam 32 and the low speed cam 33 are arranged with their phases reversed by 180 degrees. The high-speed cam 32 has a cam profile with a large operating angle and a large lift for the purpose of increasing engine output, while the low-speed cam 33 has a cam profile with a small operating angle and a small lift for the purpose of reducing fuel consumption. .

  The rocker shaft 34 is provided with a pair of rocker arms 36 that can open and close the valves 35 and 35 so as to be swingable. A high-speed sub-rocker 37 corresponding to the high-speed cam 32 swings between the rocker shafts 34 at the bases of the rocker arms 36 and 36. The low-speed sub-rockers 38 and 38 corresponding to the low-speed cam 33 are attached to the bases of the rocker arms 36 and 36 so as to freely swing. FIG. 5 is a cross-sectional view taken along the line AA including the low-speed sub-rocker 38, and FIG. 6 is a cross-sectional view taken along the line BB including the high-speed sub-rocker 37.

  As shown in FIG. 6, the rocker arms 36 and 36 have a prop 40 </ b> A attached to a shaft 39 inserted between the arms 36 below the high-speed sub-rocker 37, and a plunger 41 </ b> A provided at the base of the rocker arms 36 and 36 moves backward. When in the position (solid line position), the tip of the prop 40A is engaged with the high-speed sub-rocker 37 by a return spring (not shown). In this state, the rocking movement of the high-speed sub-rocker 37 by the high-speed cam 32 is performed via the prop 40A. , 36 are driven, and the valves 35, 35 are driven to open and close. When the plunger 41A provided at the base of the rocker arms 36, 36 is advanced, the tip of the prop 40A is disengaged from the engagement with the high-speed sub-rocker 37 against a return spring (not shown). An oil gallery for introducing hydraulic pressure from an oil pump 44 is connected to the hydraulic chamber 42A of the plunger 41A via an oil passage 43 formed in the rocker shaft 34, and a control valve 45 is installed in the middle of the oil gallery. is doing.

  Further, as shown in FIG. 5, a prop 40 </ b> B is attached to each outer side of the rocker arm 36 on a shaft 39 inserted between the arms 36 below the low-speed sub rocker 38, and is provided at the base of the rocker arms 36 and 36. When the plunger 41B is in the retracted position (solid line position), the tip of the prop 40B is disengaged from the low-speed sub-rocker 38 by a return spring (not shown). In this state, the low-speed cam 33 swings and moves the low-speed sub-rocker 38. The rocker arms 36 and 36 are not transmitted. When the plunger 41B provided at the base of the rocker arms 36, 36 is advanced, the tip of the prop 40B is engaged with the low-speed sub-rocker 38 against a return spring (not shown). In this state, the low-speed sub-rocker 38 is swung by the low-speed cam 33. The movement drives the rocker arms 36, 36 via the prop 40B, and opens and closes the valves 35, 35.

  A lost motion mechanism 46 is provided between the low-speed sub-rocker 38 and the high-speed sub-rocker 37 and the base of the rocker arms 36 and 36 so that the low-speed sub-rocker 38 and the high-speed sub-rocker 37 are always in contact with the low-speed cam 33 or the high-speed cam 32. 47 is a control device for the variable valve lift mechanism 30. An engine speed signal, an engine load signal, and the like are input to the control device 47, and the control valve 45 is controlled by the control device 47 based on these signals. In addition, the control device 47 outputs drive command signals to the fuel injection device and the ignition timing control device.

  Therefore, when the control valve 45 is closed, the hydraulic pressure from the oil pump 44 to the hydraulic chambers 42A and 42B is cut off (or reduced in pressure), and as shown by the solid lines in FIGS. In this state, the high-speed cam 32 opens and closes the valves 35 and 35 via the high-speed sub-rocker 37 and the rocker arms 36 and 36. . In this case, the opening and closing timing of the valves 35 and 35 is an angular position corresponding to the phase of the high speed cam 32, and as shown in FIG. 3B, the exhaust valve (EXH.V) and the intake valve (INT.V). Is opened and closed. Therefore, a cycle variable stroke engine having a stroke characteristic in which the piston position at the exhaust top dead center is higher than the piston position at the compression top dead center is configured. The ignition timing in this case is set immediately before the compression top dead center on the right side in the drawing.

  By setting the exhaust top dead center (exhaust TDC) height higher than the compression top dead center (compression TDC) height, the in-cylinder residual gas is reduced, and the compression stroke after the intake bottom dead center is started. Combustion can be stabilized even under a condition where the effective compression ratio is low such that the intake valves 35 are closed at the time.

  Further, the crank angle from the exhaust top dead center (exhaust TDC) to the intake bottom dead center (intake BDC) is smaller than the crank angle from the intake bottom dead center (intake BDC) to the compression top dead center (compression TDC). Combustion can be improved by enhancing the in-cylinder gas flow by increasing the piston speed in the intake stroke.

  Moreover, since the exhaust top dead center (exhaust TDC) height is set higher than the compression top dead center (compression TDC) height, the piston speed in the vicinity of the compression top dead center can be increased by a general single link piston crank. Since it becomes moderate around 20% compared with the mechanism, it is possible to stabilize the combustion by assisting the generation and growth of the initial flame kernel even in the cold machine where the combustion speed is slow.

  When the control valve 45 is opened, a predetermined hydraulic pressure is supplied to the hydraulic chambers 42A and 42B, and the tips of the props 40A and 40B are engaged with the low-speed sub-rocker 38 and the high-speed sub-rocker 38 as shown by the dotted lines in FIGS. The low-speed sub rocker 38 and the rocker arms 36 and 36 are connected to each other. In this state, the low-speed cam 33 opens and closes the valves 35 and 35 via the low-speed sub rocker 38 and the rocker arms 36 and 36. In this case, the opening / closing timing of the valve 35 is an angular position corresponding to the phase of the low-speed cam 33, and the exhaust valve (EXH.V) and the intake valve (INT.V) are opened / closed as shown in FIG. The exhaust / intake / compression / expansion strokes before switching become the compression / expansion / exhaust / intake strokes after the switching, respectively. Therefore, a cycle variable stroke engine having a stroke characteristic in which the piston position at the exhaust top dead center is lower than the piston position at the compression top dead center is configured. The ignition timing in this case is set immediately before the compression top dead center on the left side in the drawing.

  By setting the exhaust top dead center (exhaust TDC) height to be lower than the compression top dead center (compression TDC) height, the cylinder residual gas is increased, the pump loss for the reciprocating motion of the piston is reduced, and high compression is achieved. The fuel consumption can be improved by the ratio.

  Although not shown, by providing a variable valve timing mechanism (VTC) that changes the opening / closing timing of the valve 35 by changing the rotational phase of the camshaft 31 of these supply / discharge valves according to the operating state of the engine. The engine operating state can be controlled more finely.

  Next, a stroke characteristic changing method by the stroke characteristic changing means of the cycle variable stroke engine in the present embodiment will be described with reference to FIG. FIG. 7 is a flowchart of the piston stroke characteristic change control, which is executed every time preset by the control device.

  First, in step S1, a piston stroke characteristic is calculated from the required load / engine speed, and then in step S2, it is determined whether or not the calculated piston stroke characteristic has been changed. If there is no change in the piston stroke characteristics, the current process is terminated. If there is a change in the piston stroke characteristics, the process proceeds to step S3. In step S3, the changed compression ratio is read, and the process proceeds to step S4.

  In step S4, it is determined whether or not the compression ratio after the change is on the low compression ratio side. If the compression ratio is on the low compression ratio side, the process of changing the piston stroke characteristics in step S5 is started. In the case of the low compression ratio side, the in-cylinder residual gas is reduced, the knock limit is expanded, the intake stroke is increased, and the output is improved.

  If the determination in step S4 is not the low compression ratio side, the process proceeds to step S6, the engine oil / water temperature is read, and it is determined whether or not the engine is cold in step S7. The process is interrupted, and when the engine is not cold, the process proceeds to step S5, and the piston stroke characteristic changing process is started. As described above, when the engine is on the high compression ratio side, it is determined whether or not the engine is cold, and the piston stroke characteristic change process is started only when the engine is not cold. That is, if the stroke characteristic is changed to the high compression ratio side when the engine is cold, the exhaust temperature is lowered due to high efficiency and the early activation of the catalyst is prevented, so that the piston stroke characteristic is not changed.

  The process of changing the stroke characteristics in step S5 is executed in the order of fuel injection / ignition stop, valve operation timing change, fuel injection timing / ignition timing change / resumption. FIG. 8 is a time chart of the piston stroke characteristic change control. Hereinafter, the piston stroke characteristic change control will be described based on the time chart of FIG.

  In FIG. 8, N is the engine rotation at the time of the change command, N + 1 to N + 2 are in the middle of the change, and N + 3 is the engine rotation immediately after the change. When changing the piston stroke characteristics, the first stage of the exhaust stroke or compression stroke is performed so that the cams 32 and 33 do not collide with the sub-rockers 37 and 38 and a large amount of high-temperature and high-pressure gas is not blown back to the intake side. The switching is started when all the cams are in the base circle. Here, switching from the high-speed cam 32 to the low-speed cam 33 will be described. However, even when changing from the low-speed cam 33 to the high-speed cam 32, the operation is performed in the same order.

  When a piston stroke characteristic change command is issued (time t0 when the compression stroke is started), first, ignition ignition for the last combustion before switching is executed (time t1 near the top dead center of the compression stroke). Since it is necessary to discharge the last combustion exhaust gas before switching, the exhaust cam is operated as it is during the exhaust stroke, and the exhaust valve EXH. V is opened and closed (time t2-t3). Further, after the last ignition ignition, the fuel injection and the ignition ignition are stopped. Therefore, fuel injection is not started at the end point t3 of the exhaust stroke. Thereby, discharge | emission of unburned gas can be prevented.

  During the exhaust stroke for exhausting the last combustion exhaust gas before the switching, the control valve 45 on the intake cam side is switched, the hydraulic pressure is applied to the plungers 41A and 41B, and the props 40A and 40B are moved to the low speed side (FIG. 5, 6 to change the intake operation timing (time t2-t3). With this change, the exhaust valve EXH. The high speed cam 32 on the intake side pushes down the high speed rocker 37 from the time t3 in the vicinity of the top dead center where V is closed (time t3 to t4), but the prop 40A is switched to the low speed side. 37 is only lost motion (idle motion), the rocker arm 36 is not pushed down, and the intake valve 35 is kept closed. In this piston lowering stroke (time point t3-t4) and the subsequent piston rising stroke (time point t4-t5), the intake valve 35 remains closed, and air is not introduced and compressed.

  As the intake cam side is switched to the low speed side, the low speed cam 33 pushes down the low speed rocker 38 and pushes down the rocker arm 36 via the prop 40B to open and close the intake valve 35 in the subsequent piston lowering stroke. (Time t5-t6), the intake stroke by the low speed cam 33 is executed. During this intake stroke, the control valve on the exhaust cam side is switched, the hydraulic pressure is applied to the plunger, the prop is switched to the low speed side, and the exhaust operation timing is changed (time t5-t6). Due to this change, the high speed cam on the exhaust side pushes down the high speed rocker from time t6 near the bottom dead center when the intake valve 35 is closed (time t6 to t7), but the prop is switched to the low speed side. The high-speed rocker only performs lost motion, and the rocker arm is not pushed down, and the exhaust valve is kept closed. In this piston up stroke (time t6-t7) and the subsequent piston down stroke (time t7-t8), the exhaust valve EXH. V remains closed and no air is exhausted or introduced.

  As the exhaust cam side is switched to the low speed side, the low speed cam on the exhaust cam side pushes down the low speed rocker and pushes down the rocker arm via the prop to open and close the exhaust valve in the subsequent piston raising stroke ( From time t8 to t9), the exhaust stroke by the low speed cam is executed. During this exhaust stroke (time t8-t9), fuel injection from the fuel injection device at the low-speed fuel injection timing is resumed.

  In the subsequent piston lowering step (time t9-t10), the low-speed rocker 38 is pushed down by the low-speed cam 33 on the intake cam side switched to the low-speed side, and the intake valve 35 is opened and closed via the prop 40B / rocker arm 36. The intake air containing fuel is introduced, the intake air is compressed in the subsequent piston ascending stroke (time t10-t11), and the ignition ignition is restarted at the ignition timing switched to the low speed. Thereafter, the intake cam side and the exhaust cam side Both are opened and closed in low speed mode.

  The switching of the opening / closing timing of the supply / exhaust valve is executed for each cylinder, and during that period, fuel injection to that cylinder is stopped. Therefore, while there are cylinders that stopped fuel injection, the load per remaining cylinder is present. By increasing the engine torque fluctuations are suppressed.

  As described above, the piston stroke characteristics are changed by switching approximately 360 ° CA (crank angle) so that the intake / exhaust valve operating timing and ignition timing become piston stroke characteristics that achieve both fuel efficiency reduction and output improvement according to the operating conditions. This means that the torque required to change the characteristics is smaller and the structure is simpler than the case where the piston stroke characteristics are changed by the phase switching means of the cycle variable stroke mechanism. It will be advantageous.

  In the above embodiment, the piston stroke characteristic changing means that makes the intake / exhaust valve closing timing variable has been described using a variable operating angle mechanism (VVL) that changes the opening / closing timing of the intake / exhaust valve. As shown, the intake valve INT. V and exhaust valve EXH. V may be an electromagnetic configuration that opens and closes by an electrical signal. Note that this variable valve mechanism has been previously proposed by the applicant of the present invention. However, since this variable valve mechanism is publicly known, for example, in Japanese Patent Application Laid-Open No. 2001-173470, only the outline thereof will be described.

  In the electromagnetic drive device (variable valve operating device) of the intake valve 35 and the exhaust valve, a plate-like movable element 82 is attached to the valve shaft 81 of the valve body 80, and the movable element 82 is attached to a neutral position by springs 83 and 84. It is fast. A valve opening electromagnetic coil 85 is disposed below the movable element 82, and a valve closing electromagnetic coil 86 is disposed above the movable element 82.

  When opening the valve, after energizing the upper valve closing electromagnetic coil 86, the lower valve opening electromagnetic coil 85 is energized to attract the mover 82 downward, The valve body 80 is lifted and opened. Conversely, when closing the valve, by energizing the lower valve opening electromagnetic coil 85 and then energizing the upper valve closing electromagnetic coil 86 to attract the mover 82 upward, The valve body 80 is seated on the seat portion and closed. With the variable valve mechanism having such a configuration, the intake / exhaust timing can be controlled according to the load by variable control of the intake / exhaust valve closing timing.

  In the present embodiment, the following effects can be achieved.

  (A) The crankshaft 9 is rotated by the reciprocating piston 22, and a cycle variable stroke mechanism having different piston stroke characteristics at the exhaust top dead center position and the compression top dead center position of the piston 22 in one cycle is provided. A variable valve mechanism 30 that can be switched around 360 degrees with the operation timing of the air supply / exhaust valve as a crank rotation angle, and a control means that switches the variable valve mechanism 30 and switches the ignition timing around 360 degrees with a crank rotation angle. 47, and the control means 47 switches the operation timing and ignition timing of the air supply / exhaust valve in the variable valve mechanism 30 to around 360 degrees with respect to the crank rotation angle, so that the exhaust top dead center and compression in one cycle can be achieved. The piston stroke characteristics are changed by switching the top dead center.

  That is, in a cycle variable stroke in which the exhaust TDC and the compression TDC are different, it is possible to realize a reduction in fuel consumption or an improvement in output by setting an appropriate piston stroke characteristic. For example, if the piston position at the exhaust top dead center is set lower than the piston position at the compression top dead center, the fuel consumption can be reduced by reducing the pump loss and increasing the expansion ratio due to the increase in the cylinder residual gas. Further, if the piston position at the exhaust top dead center is made higher than the piston position at the compression top dead center, the output is improved by the expansion of the knock limit and the increase of the intake stroke amount due to the residual gas reduction. Therefore, if the piston stroke characteristics are changed according to the operating conditions, both fuel consumption reduction and output improvement can be achieved.

  According to the above switching method, the torque required for the characteristic change is small, the structure is simplified, and the fuel efficiency is reduced as compared with the case where the piston stroke characteristic is changed by the phase switching means of the cycle variable stroke mechanism. This is also advantageous.

  (A) As the variable valve mechanism 30, a hydraulic pressure capable of switching between an intake side camshaft 31 and an exhaust side camshaft formed with a plurality of cams 32, 33 each having a phase difference of 180 degrees and a cam for opening and closing the intake valve 35. An actuating intake side variable valve lift mechanism, a hydraulically actuated exhaust side variable valve lift mechanism capable of switching a cam for opening and closing the exhaust valve, and a control means 47 for controlling the supply of hydraulic pressure to these mechanisms By configuring, only one of a plurality of cams having a phase difference of 180 degrees is selectively operated, so that the response at the time of change is excellent.

  (C) When switching the piston stroke characteristics by the control means 47, the fuel injection is stopped until the switching is completed, thereby preventing the discharge of unburned gas and the backflow of the compressed high-temperature gas mixture to the intake side. be able to.

  (D) The control means 47 fixes the piston top characteristic at which the exhaust top dead center position is higher than the compression top dead center position when the engine is cold, thereby reducing the residual gas in addition to lowering the thermal efficiency due to the lower compression ratio. Thus, combustion is stabilized, ignition timing retard is possible, and the exhaust gas temperature is raised to enable early activation of the catalyst.

(Second Embodiment)
10 to 12 show a second embodiment of a cycle variable stroke engine to which the present invention is applied, FIG. 10 is a system configuration diagram of the stroke characteristic changing means, and FIG. 11 is a schematic diagram of a phase variable mechanism of the stroke characteristic changing means. FIG. 12 is a time chart accompanying the change in stroke characteristics. In this embodiment, the structure which changes a stroke characteristic by switching the opening / closing phase of an air supply / exhaust valve is added to 1st Embodiment. 1 to 8 are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  In the cycle variable stroke engine of this embodiment, on the premise that the cycle variable stroke mechanism in the first embodiment is used, by using the valve timing mechanism (VTC) of the supply / exhaust valve shown in FIGS. It constitutes a change means.

  As shown in FIG. 10, the piston stroke characteristic changing means by the valve timing mechanism (VTC) of the intake / exhaust valve is an intake / exhaust valve variable valve mechanism of the internal combustion engine, which lifts and changes the lift / operating angle of the intake / exhaust valve. The operating angle variable mechanism 51 is combined with a phase variable mechanism 71 that advances or retards the phase of the center angle of the lift (phase with respect to a crankshaft not shown). The lift / operating angle variable mechanism 51 has been previously proposed by the applicant of the present application. However, since it has been publicly known, for example, in Japanese Patent Application Laid-Open No. 11-107725, only the outline thereof will be described.

  First, the lift / operating angle variable mechanism 51 will be described. The lift / operating angle variable mechanism 51 includes a drive shaft 52 rotatably supported by a cam bracket (not shown) above the cylinder head, an eccentric cam 53 fixed to the drive shaft 52 by press-fitting, and the like. A control shaft 62 that is rotatably supported by the same cam bracket at a position above the drive shaft 52 and arranged in parallel to the drive shaft 52, and a rocker arm that is swingably supported by an eccentric cam portion 68 of the control shaft 62. 56, and a swing cam 59 that contacts the tappet 35A disposed at the upper end of each intake valve 35.

  The eccentric cam 53 and the rocker arm 56 are linked by a link arm 54, and the rocker arm 56 and the swing cam 59 are linked by a link member 58. The drive shaft 52 is driven by the crankshaft of the engine via a timing chain or a timing belt. The eccentric cam 53 has a circular outer peripheral surface centered at a point offset from the shaft center of the drive shaft 52 by a predetermined amount, and an annular portion of the link arm 54 is rotatably fitted to the outer peripheral surface. Yes.

  The rocker arm 56 has a substantially central portion supported by the eccentric cam portion 68 so as to be swingable. The one end portion of the rocker arm 56 is linked to the arm portion of the link arm 54 via a connecting pin 55 and the other end portion. Further, the upper end portion of the link member 58 is linked via the connecting pin 57. The eccentric cam portion 68 is eccentric from the axis of the control shaft 62, and the rocking center of the rocker arm 56 changes according to the angular position of the control shaft 62.

  The swing cam 59 is fitted to the outer periphery of the drive shaft 52 and is rotatably supported, and a lower end portion of the link member 58 is linked to an end portion extending sideways through a connecting pin 67. . On the lower surface of the swing cam 59, a base circle surface concentric with the drive shaft 52 and a cam surface extending in a predetermined curve from the base circle surface are continuously formed. The base circle surface and the cam surface are in contact with the upper surface of the tappet 35 </ b> A according to the swing position of the swing cam 59. In other words, the base circle surface is a section where the lift amount becomes 0 as a base circle section, and when the swing cam 59 swings and the cam surface comes into contact with the tappet 35A, it gradually lifts. A slight lap section is provided between the base circle section and the lift section.

  The control shaft 62 is configured to rotate within a predetermined angle range by a lift / operating angle control actuator 63 provided at one end. The lift / operating angle control actuator 63 includes, for example, a servo motor that drives the control shaft 62 via the worm gear 65, and is controlled by a control signal from the engine control unit 69. The rotation angle of the control shaft 62 is detected by the control shaft sensor 64.

  When the drive shaft 52 rotates, the lift / operating angle variable mechanism 51 configured as described above moves the link arm 4 up and down by the cam action of the eccentric cam 53, and the rocker arm 56 swings accordingly. The swing of the rocker arm 56 is transmitted to the swing cam 59 via the link member 58 to swing the swing cam 59. By the cam action of the swing cam 59, the tappet 60 is pressed and acts to lift the intake valve 35.

  When the angle of the control shaft 62 is changed via the lift / operation angle control actuator 63, the initial position of the rocker arm 56 changes and the initial swing position of the swing cam 59 changes. For example, if the eccentric cam portion 68 is positioned upward in the figure, the rocker arm 56 is positioned upward as a whole, and the end of the swing cam 59 on the side of the connecting pin 67 is relatively lifted upward. Become. That is, the initial position of the swing cam 59 is inclined in a direction in which the cam surface is separated from the tappet 35A. Therefore, when the swing cam 59 swings with the rotation of the drive shaft 52, the base circle surface is kept in contact with the tappet 35A long, and the period during which the cam surface is in contact with the tappet 35A is short. Accordingly, the lift amount is reduced as a whole, and the angle range from the opening timing to the closing timing, that is, the operating angle is also reduced.

  On the contrary, if the eccentric cam portion 68 is positioned downward in the figure, the rocker arm 56 is positioned downward as a whole, and the end portion on the connecting pin 67 side of the swing cam 59 is pushed downward relatively. It becomes a state. That is, the initial position of the swing cam 59 is inclined in a direction in which the cam surface approaches the tappet 60. Therefore, when the swing cam 59 swings with the rotation of the drive shaft 52, the portion that contacts the tappet 60 immediately shifts from the base circle surface to the cam surface. Therefore, the lift amount is increased as a whole, and the operating angle is also increased.

  Since the initial position of the eccentric cam portion 68 can be continuously changed, the valve lift characteristic is continuously changed accordingly. That is, the lift and the operating angle can be continuously expanded and reduced simultaneously. Depending on the layout of each part, for example, the opening timing and closing timing of the intake valve 61 change substantially symmetrically with the change in the lift and operating angle.

  The phase variable mechanism 71 includes a sprocket 72 provided at a front end portion of the drive shaft 52, and a phase control actuator 73 that relatively rotates the sprocket 72 and the drive shaft 52 within a predetermined angle range. , Is composed of. The sprocket 72 is linked to the crankshaft 9 via a timing chain or a timing belt (not shown). As shown in FIG. 11, the phase control actuator 73 is a hydraulic rotary actuator, and is connected to a cylinder chamber on the advance side through a switching valve 74 that is controlled to be switched by a control signal from an engine control unit 69. By introducing pressure oil into 75A, the rotary piston (vane) 76 and cam drive shaft 52 are advanced (180 degrees), and pressure oil is introduced into the cylinder chamber 75B on the retard side to thereby rotate the piston (vane). 76 and cam drive shaft 52 are actuated to retard (180 degrees). By the action of the phase control actuator 73, the sprocket 72 and the drive shaft 52 rotate relatively, and the lift center angle in the valve lift is delayed by 180 degrees (360 degrees in crank angle) in the cam drive shaft 52.

  That is, the lift characteristic curve itself does not change, and the whole advances or retards. This change can also be obtained continuously. The control state of the phase variable mechanism 71 is detected by a drive shaft sensor 66 that responds to the rotational position of the drive shaft 52. The lift / operating angle variable mechanism 51 and the phase variable mechanism 71 are optimally controlled by the ECU in accordance with the engine operating conditions.

  Next, the stroke characteristic changing method by the stroke characteristic changing means of the cycle variable stroke engine in the present embodiment will be described. The flowchart of the piston stroke characteristic change control is the same as that of the first embodiment (FIG. 7). Hereinafter, the order of the fuel injection / ignition stop, the change of the valve operation timing, the change / restart of the fuel injection timing / ignition timing, which is the stroke characteristic change processing in step S5, will be described. Based on the time chart of the piston stroke characteristic change control in FIG. 12, the piston stroke characteristic change control will be described.

  In FIG. 12, N is the engine rotation at the time of the change command, N + n to N + m are during the change, and N + (m + 1) is the engine rotation immediately after the change. Here, switching from a low compression ratio (high-speed mode) to a high compression ratio (low-speed mode) will be described, but in the same order when changing from a high compression ratio (low-speed mode) to a low compression ratio (high-speed mode). Actuated.

  When a change command for the piston stroke characteristic is issued (time t0 when the compression stroke is started), first, after the intake stroke before switching is completed, the intake valve lift is substantially zero (time t0-t1), and the valve timing is changed. The piston crown and intake valve INT. Interference with V is prevented.

  Further, the ignition ignition for the last combustion before the switching is executed (time t1 near the top dead center of the compression stroke), and the last combustion exhaust gas before the switching needs to be discharged. The cam is operated as it is and the exhaust valve EXH. V is opened and closed (time t2-t3).

  Further, after the last ignition ignition, the fuel injection and the ignition ignition are stopped. Therefore, fuel injection is not started at the end point t3 of the exhaust stroke. Thereby, discharge | emission of unburned gas can be prevented.

  After the end of the exhaust stroke for discharging the last combustion exhaust gas before the switching (after time t3), the switching valve 74 to the intake-side phase variable mechanism 71 is switched, and the operating oil pressure is retarded. Then, the opening / closing phase of the intake valve 35 is delayed by 180 degrees (crank angle 360 degrees (opened from time t5)). In addition, the change in the intake valve timing at this point is executed after the last combustion exhaust gas discharge before switching, so that there is a large overlap with the exhaust valve in the middle of the intake valve timing change and a large amount of high temperature and high pressure Gas is prevented from blowing back to the intake side. At the same time, the exhaust valve EXH. The lift amount of V is substantially zero (time t3-t4), and the piston crown surface and the exhaust valve EXH. Interference with V is prevented.

  By switching the intake-side phase variable mechanism 71 to the retard side, the intake valve INT. V is opened / closed, but since the valve lift is maintained at zero, the intake valve INT. V remains closed and no air is introduced or compressed.

  During this intake stroke (time t5 to t6), the exhaust-side switching control valve is switched to the retarded angle side, the operating hydraulic pressure is supplied to the retarded-side cylinder chamber, and the exhaust valve EXH. The open / close phase of V is retarded by 180 degrees (crank angle 360 degrees (opened from time t5)). In addition, the intake valve INT. The valve lift amount on the intake side is changed to the target lift amount from time t6 near the bottom dead center where V is closed (time t6 to t7). The exhaust valve EXH. Due to the change of the V opening / closing timing to the retard side, in the subsequent piston ascent stroke (time t6-t7), the exhaust valve EXH. V is not opened or closed.

  The piston up stroke and piston down stroke between time points t6 and t8 correspond to the compression stroke and expansion stroke after switching, the air supply / exhaust valve is not opened and closed, and air is not discharged or introduced.

  As the exhaust side is switched to the retard side, the exhaust valve EXH. V is opened and closed (time t8-t9), and the exhaust stroke is executed. During this exhaust stroke (time t8-t9), fuel injection from the fuel injection device at the retarded fuel injection timing is resumed. At the same time, the exhaust valve EXH. The valve lift amount of V is changed to the target lift amount.

  In the subsequent piston lowering step (time t9-t10), the intake valve INT. V is opened and closed, and intake air containing fuel is introduced. The intake air is compressed in the subsequent piston ascending stroke (time t10-t11), and ignition ignition is restarted at the ignition timing switched to low speed. The exhaust cam side is also opened and closed in the retard mode.

  The switching of the opening / closing timing of the supply / exhaust valve is executed for each cylinder, and during that period, fuel injection to that cylinder is stopped. Therefore, while there are cylinders that stopped fuel injection, the load per remaining cylinder is present. By increasing the engine torque fluctuations are suppressed.

  As described above, the piston stroke characteristics are changed by switching approximately 360 ° CA (crank angle) so that the intake / exhaust valve operating timing and ignition timing become piston stroke characteristics that achieve both fuel efficiency reduction and output improvement according to the operating conditions. This means that the torque required to change the characteristics is smaller and the structure is simpler than the case where the piston stroke characteristics are changed by the phase switching means of the cycle variable stroke mechanism. It will be advantageous.

  In the present embodiment, in addition to the effects (a), (c), and (d) in the first embodiment, the following effects can be achieved.

  (E) Since the variable valve mechanism is constituted by the hydraulically operated variable valve timing mechanism 71 capable of switching the rotational phases of the intake camshaft (52) and the exhaust camshaft by 180 degrees, it has already been put into practical use. This can be realized by the valve timing mechanism of the intake / exhaust valve, which can suppress the cost increase.

  (F) As a variable valve mechanism, a drive shaft 52 that is rotationally driven by the crankshaft 9 and has a drive cam 53 fixed to the outer periphery thereof, a rocker arm 56 that swings by rotation of the drive cam 53 linked to one end, A rocking cam 59 that opens and closes the air supply / exhaust valve linked to the other end of the rocker arm 56, an actuator 63 that changes the rocking fulcrum of the rocker arm 56, and drive control of the actuator 63 according to the engine operating state. Control means 69, and the drive cam 53 is formed in an eccentric ring shape whose axis is offset from the axis of the drive shaft 52, and the drive cam 53 and one end of the rocker arm 56 are connected to the link arm 54. And the fitting hole of the base portion of the link arm 54 is rotatably fitted to the outer peripheral surface of the drive cam 53 so that the drive cam 53 The control means 69 is configured to convert the eccentric rotational force into a linear motion and transmit it to the rocker arm 56, and the control means 69 is configured to supply and exhaust air until the target valve timing is reached when the piston stroke characteristic is changed. By setting the valve lift amount of the valve to zero, it is possible to reliably avoid interference between the piston crown surface and the supply / exhaust valve.

1 is a cross-sectional view of a cycle variable stroke engine showing an embodiment of the present invention. The schematic block diagram of a cycle variable stroke mechanism similarly. The characteristic view which shows the piston stroke characteristic (A) of a cycle variable stroke engine, and ignition timing and valve opening / closing timing (B, C). The schematic block diagram of a stroke characteristic change means. Sectional drawing of the stroke characteristic change means in alignment with the AA of FIG. Sectional drawing of the stroke characteristic change means in alignment with the BB line of FIG. The control flowchart which concerns on a stroke characteristic change. Time chart for changing stroke characteristics. Schematic which shows another Example of a stroke characteristic change means. The system block diagram of the stroke characteristic change means which shows 2nd Embodiment of this invention. The schematic diagram of the phase variable mechanism of a stroke characteristic change means. Time chart for changing stroke characteristics.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piston pin 2 Crank pin 3 Upper link 4 Lower link 5 Control link 5C Oscillation center 6 Rotating shaft 7 Eccentric shaft part 9 Crankshaft 30 Variable valve lift mechanism 31 Cam shaft 32, 33 Cam 34 Rocker shaft 35 Intake valve 36, 56 Rocker arm 37, 38 Sub rocker 40A, 40B Prop 51 Lift / operating angle variable mechanism 52 ... Drive shaft 53 ... Eccentric cam 58 ... Link member 59 ... Swing cam 61 ... Intake valve 62 ... Control shaft 69 ... Engine control unit 71 ... Phase variable mechanism

Claims (6)

The reciprocating piston rotates the crankshaft and has a cycle variable stroke mechanism that makes the piston stroke characteristics different between the exhaust top dead center position and the compression top dead center position in one cycle. A variable valve mechanism capable of switching around 360 degrees with a crank rotation angle, and a control means for switching the variable valve mechanism and switching the ignition timing around 360 degrees with a crank rotation angle.
The control means switches between the exhaust top dead center and the compression top dead center in one cycle by switching the operation timing and ignition timing of the supply / exhaust valve in the variable valve mechanism to around 360 degrees as the crank rotation angle. Cycle variable stroke engine characterized by changing stroke characteristics. The variable valve mechanism includes an intake-side camshaft and an exhaust-side camshaft that form a plurality of cams each having a phase difference of 180 degrees,
A hydraulically operated intake side variable valve lift mechanism capable of switching a cam for opening and closing the intake valve;
A hydraulically operated exhaust-side variable valve lift mechanism capable of switching a cam for opening and closing the exhaust valve;
The cycle variable stroke engine according to claim 1, characterized by comprising control means for controlling the supply of hydraulic pressure to these mechanisms.   2. The cycle variable according to claim 1, wherein the variable valve mechanism is constituted by a hydraulically operated variable valve timing mechanism capable of switching the rotation phases of the intake camshaft and the exhaust camshaft by 180 degrees. Stroke engine. The variable valve mechanism is rotationally driven by a crankshaft, and a drive shaft having a drive cam fixed on the outer periphery;
A rocker arm that swings by rotation of the drive cam linked to one end;
A swing cam that opens and closes the air supply / exhaust valve in linkage with the other end of the rocker arm;
An actuator for changing the rocking fulcrum of the rocker arm;
Control means for driving the actuator according to the engine operating state,
The drive cam is formed in an eccentric ring shape whose axis is offset from the axis of the drive shaft,
The drive cam and one end portion of the rocker arm are rotatably linked via a link arm, and a fitting hole provided in a base portion of the link arm is rotatably fitted to the outer peripheral surface of the drive cam, thereby decentering the drive cam. Consists of a variable valve system that converts rotational force into linear motion and transmits it to the rocker arm.
4. The cycle variable stroke engine according to claim 3, wherein when the piston stroke characteristic is changed, the control unit sets the valve lift amount of the supply / exhaust valve to zero until the target valve timing is reached.   5. The cycle variable stroke engine according to claim 1, wherein when the piston stroke characteristic is switched, the control unit stops fuel injection until the switching is completed. 6.   The cycle according to any one of claims 1 to 5, wherein the control means fixes an exhaust top dead center position to a piston stroke characteristic higher than a compression top dead center position when the engine is cold. Variable stroke engine.