JP2006274951A - Four cycle spark ignition engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress torque shock due to momentary increase of torque at a time of transition from a zone performing compression self ignition operation to a zone performing spark ignition in a spark ignition engine. <P>SOLUTION: This engine performs compression self ignition using internal EGR by valve reopening action of an exhaust valve during intake stroke, and is provided with a combustion control means 120 performing compression self ignition by opening an intake valve in neighborhood of intake top dead center and closing the intake valve before bottom dead center and reopening the exhaust valve in a partial load zone and performing spark ignition under a condition where valve reopening action of the exhaust valve is stopped with valve closing timing of the intake valve set at predetermined timing after bottom dead center in an engine heavy load zone. Also a throttle valve control means 123 reducing throttle valve opening at a time of transition from the compression self ignition operation zone to the spark ignition operation zone is provided. Moreover, a torque reduction means 140 reducing combustion torque of the engine for predetermined period right after the transition is provided. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a four-cycle spark-ignition engine, and more particularly, to an operation mode and spark ignition for performing premixed compression auto-ignition combustion (HCCI), which is referred to as “compression auto-ignition” in this specification. The present invention relates to a four-cycle spark ignition engine having an operation mode to be performed.

In general, a technique is known in which internal EGR gas is used to improve the ignitability of an air-fuel mixture, and to ensure the EGR rate required in a wide operation region in order to enhance exhaust performance (for example, Patent Document 1). In the configuration according to this prior art, the exhaust valve is opened during the intake stroke to realize so-called internal EGR.
JP 2001-107759 A

  The technique for obtaining the internal EGR by opening the exhaust valve in the intake stroke as described above can be used for compression self-ignition for improving fuel efficiency. That is, even in a spark ignition engine (gasoline engine), the air-fuel mixture can be self-ignited by setting the combustion chamber at a high temperature and high pressure at the end of the compression stroke, as in the case of a diesel engine. Since the entire chamber burns at once, the combustion efficiency is increased, the fuel consumption is greatly improved, the generation of NOx is suppressed, and the emission is advantageously improved. When the exhaust valve is opened during the intake stroke as described above, a large amount of internal EGR can be obtained, and thereby the in-cylinder temperature can be increased and compression self-ignition can be performed.

  However, with such a method, if a large amount of internal EGR is performed in a high load region, torque cannot be increased and knocking is likely to occur. Therefore, compression self-ignition operation is performed in a predetermined partial load region, and high load In the region, it is necessary to stop the internal EGR so as to cause combustion by spark ignition.

  In such a case, the engine torque temporarily increases due to a sudden increase in the amount of fresh air accompanying the stoppage of the introduction of the internal EGR at the time of transition from the region where compression self-ignition operation is performed to the region where spark ignition is performed. There is a problem that the torque increases and a torque shock is likely to occur.

  In view of the above circumstances, the present invention provides a four-cycle spark ignition engine capable of suppressing a torque shock due to a temporary torque increase at the time of transition from a region where compression self-ignition operation is performed to a region where spark ignition is performed. The challenge is to do.

  In order to solve the above-described problems, the present invention provides an internal EGR with an in-cylinder temperature in a predetermined operating region of an engine by a restart valve operation that opens the exhaust valve again in the intake stroke in addition to the valve opening operation in the exhaust stroke. In a four-cycle spark ignition type engine that is enhanced to perform compression self-ignition, the exhaust valve driving means that enables switching between execution and stop of the restart operation of the exhaust valve, and the opening / closing timing of the intake valve are made variable. Compressed self-ignition by opening the intake valve near the intake top dead center and closing it before the bottom dead center in the partial load range of the intake valve driving means and the engine, and by restarting the exhaust valve On the other hand, in the high load range of the engine, control is performed so that spark ignition is performed in a state where the closing timing of the intake valve is set to a predetermined timing after bottom dead center and the restart valve operation of the exhaust valve is stopped Combustion control hand And a throttle valve control means for controlling the opening of the throttle valve provided in the intake passage to be small at the time of transition from the operation region where the compression self-ignition is performed to the operation region where the spark ignition is performed, And a torque reduction means for reducing the combustion torque of the engine for a predetermined period immediately after the transition.

  According to this configuration, when the operating state of the engine is in the partial load region, a large amount of internal EGR is introduced by the resuming valve operation of the exhaust valve, and thereby compression self-ignition is performed. When the operating state shifts from this state to the high load range, the restart valve operation of the exhaust valve is stopped and switched to the spark ignition operation. At this time, the throttle valve opening is reduced in order to suppress an increase in the amount of fresh air due to the introduction stop of the internal EGR, etc., but this alone causes a delay until the pressure downstream of the throttle valve actually decreases. In the meantime, the amount of fresh air temporarily increases and the combustion torque of the engine increases. On the other hand, when the torque reduction means works, a temporary increase in combustion torque immediately after the transition is suppressed.

  In the present invention, the predetermined period immediately after the transition is, for example, a period until the intake pipe pressure downstream of the throttle valve is reduced to an appropriate intake pipe pressure in the operating range in which spark ignition is performed. Thereby, the torque reduction means works so as to suppress this only during a period in which a tendency to temporarily increase the combustion torque occurs.

  The torque reduction means is configured to change the intake valve closing timing until the predetermined period elapses after switching from a state in which the restart valve operation of the exhaust valve is performed immediately after the transition to a state in which the restart valve operation is stopped. It is preferable that the angle is advanced with respect to the predetermined time set in the operating range in which spark ignition is performed. In this case, the predetermined period is shorter than the normal setting in the operating range in which spark ignition is performed, because the opening period of the intake valve is shortened by advancing the closing timing of the intake valve. The amount of air flowing into the inside is reduced, and the torque is reduced.

  Further, it is preferable that the torque reducing means adjusts the closing timing of the intake valve according to the intake pipe pressure downstream of the throttle valve during a predetermined period immediately after the transition. In this way, the torque is moderately reduced to the extent that it is commensurate with a temporary increase in combustion torque.

  Further, the torque reducing means is configured to take in the in-cylinder air at a later time than the predetermined timing set in the operating range in which spark ignition is performed during a predetermined period immediately after the transition. It may be a time when blowback to the port occurs. Even in this case, the amount of air filling is reduced by blowing back the in-cylinder air to the intake port, and the torque is reduced.

  In this case, the torque reducing means retards the ignition timing in addition to delaying the intake valve closing timing further than the predetermined timing in a predetermined period immediately after the transition. It may be. By doing so, the torque is reduced by both the delay of the closing timing of the intake valve and the retard of the ignition timing, and the in-cylinder gas is blown back and cooled at the intake port, thereby igniting. An increase in the in-cylinder temperature due to the timing retard is suppressed, and the occurrence of knocking during the subsequent high load operation can be suppressed.

  Further, in the present invention, there is provided means for discriminating a low temperature state in which the temperature state in the cylinder is equal to or lower than a predetermined temperature, and the torque reducing means retards the ignition timing in a predetermined period immediately after the transition in the low temperature state. You may make it make it. In this way, when the temperature in the cylinder is low, the torque is reduced by the ignition timing retard, and since the temperature is low, knocking may occur even if the cylinder temperature rises somewhat due to the ignition timing retard. There is no problem.

  As described above, according to the four-cycle spark ignition engine of the present invention, from the operation region where the internal EGR is introduced by the resuming valve operation of the exhaust valve and the compression self-ignition is performed, to the operation region where the spark ignition is performed. When the transition is made, the opening of the throttle valve is reduced and the combustion torque of the engine is reduced only for a predetermined period immediately after the transition. Can be prevented.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 is a configuration diagram showing a schematic configuration of a four-cycle spark ignition type engine 10 according to an embodiment of the present invention, and FIG. 2 is provided with one cylinder of the engine body 20 according to FIG. 2 is a schematic cross-sectional view showing the structure of an intake / exhaust valve and the like.

  In these drawings, the engine body 20 of the illustrated four-cycle spark ignition type engine 10 integrally includes a cylinder block 22 that rotatably supports a crankshaft 21 and a cylinder head 23 that is disposed above the cylinder block 22. Have.

  The cylinder block 22 and the cylinder head 23 are provided with a plurality of cylinders 24. Each cylinder 24 is provided with a piston 25 connected to the crankshaft 21 and a combustion chamber 26 formed in the cylinder 24 by the piston 25 in the same manner as a known configuration. The cylinder block 22 is provided with a crank angle sensor 27 that detects the rotation angle (crank angle) of the crankshaft 21.

  A fuel injection valve 28 that directly injects fuel into the combustion chamber 26 is provided at the side of each combustion chamber 26. An ignition plug 29 is provided at the top of each combustion chamber 26, and the plug tip faces the combustion chamber 26. An ignition circuit 29a capable of controlling the ignition timing by electronic control is connected to the ignition plug 29.

  The engine body 20 includes an intake system 30 that supplies fresh air into the cylinder 24 and an exhaust system 50 that exhausts burned gas burned in the combustion chamber 26 of the cylinder 24.

  The intake system 30 includes an intake pipe 31 for supplying fresh air into the cylinder 24, and an intake manifold 32 communicating with the downstream side of the intake pipe 31. The intake manifold 32 branches from the surge tank and corresponds to each. A branch intake pipe 33 connected to the cylinder 24 is provided. In the illustrated embodiment, each cylinder 24 is formed with a pair of intake ports 24a (see FIG. 1), and the downstream end of the branched intake pipe 33 corresponds to the intake port 24a of each cylinder 24. And it is formed in two forks.

  An airflow sensor 34 is provided in the intake pipe 31 of the intake system 30. Further, the intake pipe 31 is provided with a throttle valve 35 for adjusting the intake flow rate. The throttle valve 35 is configured to be opened and closed by an actuator 36. Further, a pressure sensor 37 for detecting the intake pipe pressure is provided in the intake pipe 31 downstream of the throttle valve 35.

  Each intake port 24a provided in each cylinder 24 is provided with an intake valve 40. In the illustrated embodiment, two intake valves 40 are provided for each cylinder corresponding to the intake port. Each intake valve 40 is configured to be driven by a valve operating mechanism 41. This valve operating mechanism 41 has intake valve driving means for making the opening / closing timing of the intake valve variable. In this embodiment, the valve opening timing (phase angle) of the intake valve 40 can be changed as the intake valve driving means. A VCT (Variable Camshaft Timing Mechanism) 42 and a VVE (Variable Valve Event) 43 capable of changing the lift amount (valve opening amount) of the intake valve 40 in a stepless manner are provided.

  FIG. 3 is a perspective view showing a specific configuration of the valve mechanism 41 according to the embodiment of FIG.

  As shown in the figure, the valve operating mechanism 41 includes a cam shaft 41a extending along the direction in which the cylinders 24 are arranged (see FIG. 1), and a VCT 42 and a VVE 43 are incorporated into the cam shaft 41a. ing.

  The VCT 42 includes a rotor (input member) 42a fixed to the end of the camshaft 41a, a casing (output member) 42b disposed concentrically on the outer periphery of the rotor 42a, and the casing 42b. And a sprocket 42c disposed on the outer periphery of the sprocket 42 relatively rotatably. A chain 42d for transmitting driving force from the crankshaft 21 (see FIG. 2) is wound around the sprocket 42c. Further, a hydraulic oil chamber (not shown) is formed between the rotor 42a and the casing 42b, and the rotor 42a and the casing 42b are integrally rotated or relatively rotated by hydraulic control of the electromagnetic valve 42e. It can be switched to operation. As a result, the VCT 42 constitutes an operating timing variable mechanism that can simultaneously change the valve opening start timing and the valve closing timing of the intake valve 40 by shifting the phase of the camshaft 41a with respect to the crankshaft 21. As will be described later, the electromagnetic valve 42e is driven and controlled by the ECU 100, and the rotor 42a and the casing 42b are switched between connected and disconnected by this drive control.

  Next, the VVE 43 includes a pair of intake cams 43a and 43b corresponding to each intake valve 40 for each cylinder. These intake cams 43a and 43b are connected to each other by a sleeve-like connecting portion 43c provided therebetween, and are attached to the camshaft 41a so as to be relatively rotatable.

  4A and 4B are cross-sectional views showing the main part of the VVE in FIG. 3, where FIG. 4A shows the lift amount being 0 in the large lift control state, and FIG. 4B is the maximum lift amount in the large lift control state. (C) shows the time when the lift amount is 0 in the small lift control state, and (D) shows the time when the lift amount is maximum in the small lift control state.

  As shown in FIG. 3 and FIGS. 4A to 4D, in order to swing intake cams 43a and 43b attached to the camshaft 41a so as to be relatively rotatable, the camshaft 41a includes a cylinder 24. An eccentric cam 43d provided for each is fixed. As is apparent from FIGS. 4A to 4D, the eccentric cam 43d is eccentric with respect to the cam shaft 41a. An offset link 43e is rotatably attached to the outer periphery of the eccentric cam 43d. A protrusion 43f protruding in the radial direction is integrally provided on the outer peripheral portion of the offset link 43e. A connecting pin 43g parallel to the camshaft 41a passes through the projecting portion 43f, and one end of each of the link arms 43h and 43i is rotatable on both side surfaces of the offset link 43e by the connecting pin 43g. Is attached. One link arm 43h connects the offset link 43e and the intake cam 43b, and the other end of the link arm 43h is rotatable to the vicinity of the bulging portion of the intake cam 43b by a pin 43j parallel to the cam shaft 41a. It is connected to. The other link arm 43i is for connecting the offset link 43e to the control shaft 43k that changes the phase of the offset link 43e. With respect to the end of the control arm 43m fixed to the control shaft 43k, The other end of the ring arm 43i is rotatably connected by a pin 43n parallel to the camshaft 41a.

  As shown in FIG. 3, a fan-shaped worm wheel 43p is fixed in the middle of the control shaft 43k, and a worm gear 43q that meshes with the worm wheel 43p is rotationally driven by a stepping motor 43r. Yes. As will be described later, the stepping motor 43r is driven and controlled by the ECU 100. By this driving control, the phase of the control arm 43m is determined, and thereby the phase of the offset link 43e is determined. The rotation trajectory of the intake cam 43b that drives 61 changes in the axial direction of the intake valve 40, and the valve lift amount is changed steplessly.

  As shown in FIG. 4B, the tappet 61 is fixed to the end of the valve stem 40 a of the intake valve 40. On the other hand, the valve stem 40a of the intake valve 40 is guided by a known valve guide 40b. A spring seat portion 40c is integrally formed on the outer periphery of the valve guide 40b. The spring seat portion 40c is contracted between the spring seat portion 61a formed in the inner back portion of the tappet 61. A valve spring 40d is seated.

  The intake cam 43b is joined to the tappet 61 and receives the urging force of the valve spring 40d.

  In this state, when the control shaft 43k and the control arm 43m are rotated by the stepping motor 43r and the pin 43n is positioned below the control shaft 43k as shown in FIGS. 4A and 4B, the intake cam 43b is swung. The moving angle becomes large, and a large lift control state in which the lift amount of the valve at the lift peak is the largest is achieved. Further, when the pin 43n is moved upward by the rotation of the control arm 43m or the like, the swing angle of the intake cam 43b is reduced accordingly, and as shown in FIGS. 4C and 4D, the pin 43n Is positioned above the camshaft 41a, the small lift control state with the smallest valve lift amount is achieved.

  In the large lift control state shown in FIGS. 4A and 4B, the intake cam 43b presses the tappet 61 on the tip side of the cam nose, as shown in FIG. 4B, and the intake valve 40 passes through the tappet 61. And a lift peak state (a state where the intake cam 43b greatly lifts the intake valve 40 via the tappet 61) and a lift of the intake valve 40 (the intake valve 40) as shown in FIG. It swings between the state where the amount becomes zero. 4C and 4D, which are in a small lift control state, similarly swing between a lift peak state (pressing the tappet 61 on the base end side of the cam nose) and a lift amount 0 state (same as above). (See Figures (D) and (C)).

  FIG. 5 schematically shows the control states of FIGS. 4B and 4D, where FIG. 5A corresponds to the large lift control position, and FIG. 5B corresponds to the small lift control position. 5A and 5B, the control arm 43m and the link arms 43h and 43i are simply represented by straight lines, and the rotation locus of the center of the eccentric cam 43d (the center of the outer ring of the offset link 43e) is shown. It is shown as a symbol T0.

  First, the profile of the intake cam 43b itself will be described with reference to FIG. 5A. On the peripheral surface of the intake cam 43b, a base circle surface (base circle section) θ1 having a constant curvature radius within a predetermined angle range, Following the θ1, a cam surface (lift section) θ2 having a gradually increasing radius of curvature is formed.

  The solid line in FIG. 5A shows the state of FIG. 4B where the intake valve 40 is in the vicinity of the lift peak. At this time, the pin 43j is pulled up most by the link arm 43h, and the intake cam 43b The cam nose tip side of the cam surface θ2 is in contact with the tappet 61. On the other hand, the phantom line shows a state in which the valve lift amount H is 0 (FIG. 4A). At this time, the base circle surface θ1 of the intake cam 43b is in contact with the tappet 61 and the intake valve 40 is closed. It is in a state.

  When the camshaft 41a (eccentric cam 43d) rotates in the clockwise direction in the figure, one end side (lower end side in the figure) of the offset link 43e moves along the axis X of the camshaft 41a as indicated by the arrow in the figure. Although revolving around, the displacement of the other end of the offset link 43e is regulated by a link arm 43i connected thereto. That is, the link arm 43i swings between the position of the solid line and the position of the phantom line around the pin 43n positioned below the control shaft 43k, and accordingly, the other end side of the offset link 43e. The (connecting pin 43g) reciprocates around the pin 43n every time the eccentric cam 43d rotates once (the movement locus of the connecting pin 43g is indicated as T1).

  With the reciprocating arc motion T1 of the connecting pin 43g, the other end portion (pin 43j) of the link arm 43h whose one end portion is connected to the offset link 43e by the same connecting pin 43g reciprocates along a locus indicated by T2 in the drawing. The intake cam 43b, which moves in an arc and is connected to the link arm 43h by the pin 43j, swings between the position of the solid line and the position of the phantom line in the figure. That is, when the connecting pin 43g moves upward, the pin 43j is pulled upward by the link arm 43h, and the cam nose of the intake cam 43b pushes down the tappet 61, whereby the valve spring 40d (see FIG. 4B). The intake valve 40 is lifted while compressing.

  On the other hand, when the connecting pin 43g moves downward, the pin 43j is pushed downward by the link arm 43h, and the cam nose of the intake cam 43b rises. Therefore, the reaction force of the compressed valve spring 40d The tappet 61 is pushed up and moves upward so as to follow the rise of the cam nose, the intake valve 40 is pulled up, and the intake port of the intake passage 24a is closed.

  That is, in the large lift control state, the intake cam 43b swings greatly so as to press the tappet 61 by substantially the entire base circle surface θ1 and cam surface θ2 of the peripheral surface, and thus corresponds to such a large swing angle. This increases the lift amount of the valve.

  Further, from the above-mentioned large lift control state, the control arm 43m is rotated upward about the axis of the control shaft 43k until it becomes substantially horizontal, as shown in FIG. 4 (D) and FIG. 5 (B), When the pin 43n, which is the rotation axis of the link arm 43i, is positioned closer to the front side in the rotational direction of the camshaft 41a than the large lift control state, the small lift control state is established. In FIG. 5B, as in FIG. 5A, the state where the intake valve 40 is in the vicinity of the lift peak is indicated by a solid line, and the state where the lift amount H is 0 is indicated by a virtual line.

  In FIG. 5B, when the camshaft 41a (eccentric cam 43d) rotates, the displacement of the connecting pin 43g of the offset link 43e is restricted by the link arm 43i, as in the large lift control state, and the side of the control shaft 43k. A reciprocating arc motion T3 is performed around the pin 43n positioned at (the link arm 43i reciprocates between the solid line position and the virtual line position in the figure). The pin 43j of the link arm 43h performs a reciprocating arc motion T4 in accordance with the reciprocating arc motion T3 of the connecting pin 43g, and the intake cam 43b connected to the link arm 43h by the pin 43j is positioned in the solid line in the figure. The intake valve 40 is opened and closed by swinging between the imaginary line and the position of the imaginary line.

  That is, in the small lift control state, the swing angle of the intake cam 43b is smaller than that in the large lift control state, and the intake cam 43b has a base circle surface θ1 on its peripheral surface and a cam surface θ2 continuous therewith. The tappet 61 is pressed only by a part, and the lift amount of the valve is reduced.

  In this embodiment, as shown in FIG. 2, two sets of VVE 43 are provided for a four-cylinder engine, and each VVE 43 can individually adjust the lift amount of the exhaust valve by two cylinders. Yes.

  By the VCT 42 and VVE 43 described above, the intake valve 40 is configured to be able to change its opening / closing timing and the valve lift amount H.

  Next, as shown in FIGS. 1 and 2, the exhaust system 50 collects bifurcated branch exhaust pipes 51 connected to the exhaust ports 24b formed in pairs in each cylinder 24 on the downstream exhaust side. The exhaust manifold 52 is connected to the downstream manifold of the exhaust manifold 52, and an exhaust pipe 53 for discharging burned gas from the exhaust manifold 52 is provided.

  Each exhaust port 24b is provided with an exhaust valve 60. The exhaust valves 60 are also provided in pairs for each cylinder 24. Each exhaust valve 60 is driven by a valve operating mechanism 62. The valve mechanism 62 is configured to enable a restart valve operation for reopening the exhaust valve 60 in the intake stroke in addition to the valve opening operation in the exhaust stroke, and to execute and stop the restart valve operation. As an exhaust valve driving means that makes it possible to switch between, a valve operation switching mechanism 70 having a lost motion function is provided.

  That is, the valve mechanism 62 includes a transmission mechanism 64 and a camshaft 62 a that is driven by the driving force of the crankshaft 21 via the transmission mechanism 64, and the exhaust valve 60 has a different phase with respect to one exhaust valve 60. Two sets of exhaust cams 62b and 62c for driving the exhaust gas are provided on the camshaft 62a, and a valve operation switching mechanism 70 is provided between the exhaust cams 62b and 62c and one exhaust valve 60. The valve operation switching mechanism 70 can be switched between a state in which the drive of both the exhaust cams 62b and 62c is transmitted to the exhaust valve 60 and a state in which only the drive of the one exhaust cam 62b is transmitted to the exhaust valve 60. . One of the two sets of exhaust cams 62b and 62c is a first exhaust cam 62b that opens the exhaust valve 60 in order to discharge the burned gas in the cylinder 24 during the exhaust stroke, and the other is an intake stroke that will be described later. A second exhaust cam 62c that reopens the exhaust valve 60 to recirculate the exhaust gas into the cylinder. In the present embodiment, the first exhaust cams 62b form a pair, and the second exhaust cam 62c is disposed between the first exhaust cams 62b and 62b in the axial direction of the cam shaft 62a (see FIG. 7). The other exhaust valve 60 is driven via a direct acting tappet by one exhaust cam provided on the camshaft 62a, and is always opened only in the exhaust stroke.

  A specific structure of the valve operation switching mechanism 70 will be described with reference to FIGS.

  6 is an exploded perspective view of the valve operation switching mechanism 70, FIG. 7 is a front sectional view of the valve operation switching mechanism 70, and FIG. 9 is a plan sectional view of the valve operation switching mechanism 70.

  Referring to these drawings, the valve operation switching mechanism 70 is for realizing a so-called lost motion in which the second exhaust cam 62c turns on / off the function of pushing down the stem 60a of the exhaust valve 60. Then, it is embodied in a tappet type.

  That is, the valve operation switching mechanism 70 includes a rectangular housing 71, a side tappet 72 that is housed in the housing 71 so as to be movable up and down, and is fixed to the end of the stem 60 a of the exhaust valve 60. The side tappet 72 is assembled so as to be relatively displaceable, and has a center tappet 73. The first exhaust cam 62 b is in contact with the side tappet 72, and the second exhaust cam 62 c is in contact with the center tappet 73.

  The side tappet 72 is formed in a substantially cylindrical shape, and has an accommodation recess 72a in a diametrical direction perpendicular to the camshaft 62a when seen in a plan view. Insertion holes 72c parallel to the camshaft 62a are formed in the wall portions 72b on both sides of the housing recess 72a. The bottomed sleeve-like holders 75a and 75b are fixed to the respective insertion holes 72c in such a posture that the openings face each other. A bearing 76 is fixed to the outside of one sleeve-like holder 75 a, and a rolling element 76 a held by the bearing 76 is in rolling contact with a vertical groove 71 a formed on the inner wall of the housing 71. As a result, the side tappet 72 is movable along the axial direction (the direction in which the exhaust valve 60 is opened and closed) in a state where the rotation in the circumferential direction is restricted. A spring seat 72d that receives the valve spring 60d is fixed to the lower portion of the side tappet 72.

  On the other hand, the center tappet 73 is an “I” -shaped structure that follows the outline of the receiving recess 72 a of the side tappet 72 as viewed in plan, and is defined by the receiving recess 72 a and a locking portion provided in the housing 71. In the stroke S, the side tappet 72 is assembled so as to be movable up and down and faces the exhaust cam 62c.

  The center tappet 73 is always urged toward the exhaust cam 62c by a pair of coil springs 77 arranged at the bottom of the accommodation recess 72a of the side tappet 72. The spring coefficient of the coil spring 77 is set so that the urging force is sufficiently smaller than that of the valve spring 60d. Therefore, in the free state, the upper surface of the wall portion 72b of the side tappet 72 and the upper surface of the center tappet 73 are flush with each other as shown in FIG. The center tappet 73 is provided with a pin hole 73a that communicates concentrically with the insertion hole 72c in the free state. A pin unit 78 is accommodated in the pin hole 73a.

  The pin unit 78 includes a lock plunger 78a that can be moved in and out of one sleeve-shaped holder 75a, a coil spring 78b interposed between the lock plunger 78a and the sleeve-shaped holder 75a, and a lock plunger 78a. A lock pin 78c concentrically disposed on the opposite side of the coil spring 78b, and an unlocking plunger 78d accommodated in the other sleeve-like holder 75b so as to be able to advance and retract in order to drive the lock pin 78c toward the lock plunger 78a. In addition, a pair of bushes 78e and 78f fixed to both opening ends of the pin hole 73a to support the lock pin 78c, a flange 78g and a bearing 76 integrally formed at a substantially central portion of the lock pin 78c are arranged. Between the side bush 78e and the lock pin via the flange 78g. 8c and a coil spring 78h for energizing the to the unlocked plunger 78d side. In the free state, the lock plunger 78 a and the lock pin 78 c are interposed between the wall 72 b and the center tappet 73, respectively, so that the center tappet 73 is locked to the side tappet 72. In this state, when the side tappet 72 is driven by the first exhaust cam 62b, the exhaust valve 60 is opened, and when the center tappet 73 is driven by the second exhaust cam 62c, the side tappet 72 is also exhausted via the side tappet 72. The valve 60 is opened.

  Further, on the side opposite to the side on which the bearing 76 is provided, a hydraulic oil passage PH is formed in the wall portion 72b and the sleeve-like holder 75b fixed thereto. Then, when hydraulic fluid is supplied from the hydraulic fluid circuit 79 to the hydraulic fluid passage PH under the control of the ECU 100, which will be described later, the unlocking plunger 78d is driven to the left in FIGS. 7 and 8, and the lock pin 78c is moved. At the same time, the lock plunger 78a is pushed into the corresponding wall 72b, and the lock by these members is released. When the center tappet 73 is driven by the second exhaust cam 62c in this unlocked state, the center tappet 73 moves up and down in the housing recess 72a of the side tappet 72, and the force is absorbed by the coil spring 77 and exhausted. It is not transmitted to the valve 60. As a result, the exhaust valve 60 is opened only when the side tappet 72 is driven by the first exhaust cam 62b, and the exhaust valve 60 is opened by the second cam 62c (the exhaust valve is restarted during the intake stroke). ) Can be stopped. The hydraulic oil circuit 79 is provided with an electromagnetic valve 79a, and the electromagnetic valve 79a is controlled by the ECU 100 as a control device.

  In this embodiment, as shown in FIG. 2, by providing two sets of hydraulic oil passages 79 and electromagnetic valves 79a, the valve operation switching mechanism 70 can be operated individually for each of the two cylinders. .

  The four-cycle spark ignition engine 10 is provided with an ECU 100.

  As shown in FIG. 1, the ECU 100 includes a CPU 101, a memory 102, an interface 103, and a bus 104 that connects these units 101 to 103.

  The memory 102 of the ECU 100 stores control maps, data, and programs. When the CPU 101 executes these control maps, data, and programs, as shown in FIG. 2, operations such as engine speed and engine load are performed. An operating state determining unit 110 that determines the state, a combustion control unit 120 that controls combustion of the engine according to the determined operating state, and a throttle valve control unit 130 that controls the throttle valve 35 according to the determined operating state. And a torque reduction means 140 that performs control to reduce the combustion torque of the engine at the time of transition from the operation region where compression self-ignition is performed to the operation region where spark ignition is performed.

  The combustion control means 120 includes a VCT control means 121 that controls the electromagnetic valve 42e of the VCT 42 provided in the valve mechanism 41 of the intake system 30, and a VVE control that controls a stepping motor 43r of the VVE 43 provided in the intake system 30. Exhaust valve control means 123 for switching control of a valve operation switching mechanism 70 provided for the exhaust valve 60 by driving control of the means 122 and the electromagnetic valve 79a, and ignition control for controlling ignition by the spark plug 29 Means 124.

  Various detection means such as a crank angle sensor 27, an air flow sensor 34, a pressure sensor 37, and an accelerator opening sensor 66 are connected to the ECU 100 as input elements. On the other hand, as control elements, the actuator 36 of the throttle valve 35, the electromagnetic valve 42e provided in the VCT 42 of the valve operating mechanism 41, the electromagnetic valve 79a of the hydraulic oil circuit 79 that drives each valve operation switching mechanism 70, and the intake system 30 are provided. The VVE 43 stepping motor 43r, an ignition circuit 29a for controlling ignition by the ignition plug 29, the fuel injection valve 28, and the like are connected.

  Next, the control characteristics stored in the ECU 100 will be described with reference to FIGS.

  FIG. 9 is a characteristic diagram showing an example of operation region setting for performing control according to the operation state by the combustion control means 120 of the ECU 100.

  As shown in the figure, as an operation region set in the ECU 100, a region A where a so-called compression self-ignition operation (denoted as HCCI in the drawing) is performed, and a spark ignition operation (denoted as SI in the diagram) is performed. Area B is set. The region A of the compression self-ignition operation is a region below a predetermined engine load in a low / medium rotation region where the engine speed ne is relatively low. The spark ignition operation region B is a region other than the compression self-ignition operation region A, that is, a region on the high rotation side and the high load side.

  The operating state determining means 110 of the ECU 100 detects the operating state of the engine from the crank angle sensor 27, the accelerator opening sensor 66, and the like, and determines whether the operating state is in the above-described region A or B.

  FIGS. 10A to 10C are diagrams illustrating the characteristics of the opening operation of the intake valve 40 and the exhaust valve 60 according to the operating state. The characteristics of the valve opening operation according to this operating state will be described.

  In the region A, as shown in FIG. 10A, the valve opening operation EX1 of the exhaust valve 60, the valve opening operation INa of the intake valve 40, and the restart valve operation EX2 of the exhaust valve 60 are set. That is, the exhaust valve 60 is opened in the exhaust stroke (EX1), and then the exhaust valve 60 is closed and the intake valve 40 is opened (INa) in the vicinity of the intake top dead center, and the exhaust valve 60 is opened in the middle of the intake stroke. The restart valve operation is performed (EX2), and the intake valve 40 is set to close before the bottom dead center. Then, the control by the VCT control means 121, the VVE control means 122 and the exhaust valve control means 123 is performed so that the intake valve 40 and the exhaust valve 60 are opened and closed according to such settings.

  Note that when the operating state changes in the region A, the valve closing timing of the intake valve 40 is adjusted to change in a period before the bottom dead center accordingly. That is, the VCT control means 121 and the VVE control means 122 function as valve closing timing adjusting means. As the engine load increases in the region A, the valve closing timing of the intake valve 40 approaches the bottom dead center and the intake valve opens. The valve period is adjusted to be long and the intake valve lift amount is also increased.

  On the other hand, in the region B, as shown in FIG. 10B, the exhaust valve 60 performs only the valve opening operation EX1 in the exhaust stroke, stops the restart valve operation EX2 in the intake stroke, and the intake valve 40 The valve opening characteristic (INb) is set so that the intake valve closing timing is retarded (preferably delayed until after bottom dead center) and the valve opening period and the valve lift amount are larger than the valve opening characteristic at A. Is done. Then, the VCT control means 121, the VVE control means 122, and the exhaust valve control means 123 are controlled so that the intake valve 40 and the exhaust valve 60 are opened and closed in accordance with such settings, and the ignition control means 124 is controlled. Spark ignition is performed.

  In addition, when the region A is shifted to the region B, the restart valve operation EX2 of the exhaust valve 60 is stopped and spark ignition is performed, but the amount of fresh air accompanying the absence of the introduction of the internal EGR by the restart valve operation EX2 In order to correct the increasing tendency, the throttle valve control unit 120 controls the throttle valve 35 so that the opening degree of the throttle valve 35 becomes smaller, and the torque reduction unit 140 controls the engine combustion torque to decrease only for a predetermined period immediately after the transition. Done. As control immediately after the transition by the torque reducing means 140, in this embodiment, as shown in FIG. 10C, the valve opening characteristics (INc, INc ′) of the intake valve 40 are normal valve opening characteristics in the region B. Correction is made to decrease the intake air amount with respect to (INb). Specifically, the intake valve closing time is advanced and the lift amount is reduced by advancing the intake valve closing timing as compared with the normal valve opening characteristic (INb), and the valve opening characteristic in the region A ( The characteristics are close to INa).

  Note that the valve opening characteristics (INc, INc ′) of the intake valve 40 immediately after this transition are adjusted according to the intake pipe pressure as will be described in detail later.

  FIG. 11 shows the stroke of each cylinder of the four-cylinder four-cycle engine and the change in the ignition state during the transition from the compression self-ignition operation to the spark ignition operation. In this figure, F indicates fuel injection, CI indicates self-ignition, and SI indicates spark ignition.

  As shown in this figure, in each cylinder, four strokes of suction, compression, expansion, and exhaust are sequentially performed during one cycle (two engine revolutions). In general, in a four-cylinder four-cycle engine, if the first to fourth cylinders (# 1 to # 4) are sequentially arranged from one end side in the cylinder row direction, the second cylinder (# 2), the first cylinder (# 1), the first cylinder Each of the above strokes is performed with a phase difference of 180 ° in crank angle in the order of the third cylinder (# 3) and the fourth cylinder (# 4).

  In this embodiment, the first and second cylinders (# 1, # 2) are the first group, and the third and fourth cylinders (# 3, # 4) are the second group, and two cylinders for each group. The valve opening characteristics of the intake valve 40 and the exhaust valve 60 are controlled.

In this case, when the operation state determination means determines that the shift from the compression self-ignition operation region (region A in FIG. 9) to the spark ignition operation region (region B in FIG. 9) is performed, Since the characteristics of the valve cannot be switched during the operation of the valve, immediately after the transition determination time t ₀ , immediately after the restart valve operation of the cylinder with the slower restart valve operation of the exhaust valve 60 out of the two cylinders is completed for each group. The exhaust valve opening characteristic is switched so that the restart valve operation is stopped by controlling the electromagnetic valve 79a. As shown in FIG. 11, the exhaust valve opening characteristic switching timing is indicated by the one-dot chain line ellipse in FIG. 11, the compression stroke of the first cylinder (expansion stroke of the second cylinder) in the first group, and the timing of the second group. This is the compression stroke of the four cylinders (the expansion stroke of the third cylinder). After the exhaust valve opening operation is thus stopped, spark ignition is performed.

  FIGS. 12 and 13 are flowcharts showing an example of control by the combustion control means 120 of the ECU 100 and the like. This flowchart will be described with reference to FIGS.

  The ECU 100 first determines in step S1 whether or not the engine is warm and the operating state is in the region A. If the determination is NO, that is, the operating state is in the high load region (region B). Or when the engine is cold, in step S2, the opening and closing characteristics of the intake and exhaust valves (see FIG. 10 (B)) obtained from the SI (spark ignition operation) mode map for all cylinders according to the engine speed and load. Spark ignition operation is performed at the ignition timing.

  When the determination in step S1 is YES, in step S3, all the cylinders have the intake / exhaust valve opening characteristics obtained from the map of the HCCI (compression self-ignition operation) mode according to the engine speed and load, that is, the intake air The valve has a small lift characteristic when the closing timing is before the bottom dead center, and the exhaust valve has a characteristic of executing a restart valve operation, thereby performing a compression self-ignition operation.

  Next, in step S4, it is determined whether or not the operating state has shifted from region A to region B. If not, step S3 is repeated and the compression self-ignition operation is continued.

  When the operating state shifts from the region A to the region B, the throttle valve 35 is closed in step S5. At the same time, in step S6, it is first determined whether or not the cylinder in which the exhaust valve opening characteristic can be switched is the first group. That is, as shown in FIG. 11, the timing when the valve opening characteristics of the exhaust valve can be switched is different between the first group and the second group, and which group comes first depending on the timing of transition from the region A to the region B. Since whether or not it can be switched to is changed, it is determined in step S6.

  If the determination in step S6 is YES (or after the processing in step S18 described later), in step S7, the resuming valve operation of the exhaust valve 60 is performed after a predetermined timing (initial stage of the compression stroke of the first cylinder) in the first group. Stop. Subsequently, in step S8, it is determined whether or not the stop of the restart valve operation of the exhaust valve 60 in the first group is completed. If completed, in step S9, the intake valve opening characteristics and the ignition timing are corrected. I do. In the present embodiment, the reference intake pipe pressure during the spark ignition operation is obtained based on the SI mode map, and the actual intake pipe pressure before the intake stroke is detected by the pressure sensor, and the reference intake pipe pressure, the actual intake pipe pressure, The intake valve opening characteristic and the ignition timing are corrected according to the difference.

  In this case, as shown in FIG. 10C, the intake valve opening characteristic is corrected so that the valve closing period is shortened before the bottom dead center and the lift amount is also reduced. In particular, the larger the absolute value of the difference, the smaller the valve opening period and the lift amount, and the closer the absolute value of the difference is, the closer to the valve opening characteristic in the SI mode.

  Note that the intake valve opening characteristics may be corrected so that the closing timing is delayed from the normal closing timing in the SI mode so that the effective compression ratio is reduced and the intake air is blown back. Good. Further, the ignition timing may be corrected so as to retard as the absolute value of the difference increases.

  In step S10 following step S9, it is determined whether or not the stop of the restart valve operation in all groups is completed. If not, flag F is set to “1” in step S11, and in step S12. In the second group of cylinders, the HCCI mode intake valve small lift characteristic (see FIG. 10A) corresponding to the intake pipe pressure before the intake stroke is set.

  If the determination in step S6 is NO, or after the process in step S12, the process proceeds to step S13. In step S13, when a predetermined timing (initial stage of the compression stroke of the fourth cylinder) has passed in the second group, the restart valve operation of the exhaust valve is stopped. Next, in step S14, it is determined whether or not the flag F is “1”. If the determination is YES, it is determined in step S15 whether the stop of the restart valve operation of the exhaust valve in the second group has been completed. Determine.

  If the stop of the restart valve operation of the exhaust valve in the second group is completed, in step S16, the intake valve opening characteristics and the like are corrected by the same processing as in step S9 for the cylinders in the second group. Subsequently, in step S17, it is determined whether or not the stop of the restart valve operation in all groups is completed. If not completed, in step S18, the same process as in step S12 is performed for the first group of cylinders, and then the process proceeds to step S7.

  When it is determined in step S10 or step S17 that the stop of the restart valve operation of all the groups has been completed, the flag F is set to “0” in step S19 and detected by the pressure sensor in step S20. It is determined whether or not the actual intake pipe pressure has decreased to a reference intake pipe pressure (appropriate intake pipe pressure) during SI operation. If this determination is NO, in step S21, correction of the intake valve opening characteristics and the like is performed for all the cylinders by the same process as in step S9, and then the process returns to step S20. If the determination in step S20 is YES, in step S21, the intake / exhaust valve opening characteristics obtained from the SI mode map for all cylinders in accordance with the engine speed and load (see FIG. 10B). The spark ignition operation is performed at the ignition timing.

  The control operation according to this embodiment as described above is schematically shown in a time chart as shown in FIG.

That is, when the operating state such as by the accelerator opening increases the transition from the region A of the compression-ignition operation to the area B of the spark ignition operation, the throttle opening is small at the transition point t _0, and migration resume valve operation of the exhaust valve in a predetermined time t ₁ after the time point t ₀ is stopped, switching switched to spark ignition operation from the compression-ignition operation. Incidentally, showing the time t ₁ of the switched is different between the cylinders of the cylinder and a second group of the first group, the one of the group for the sake of simplicity in FIG. 14 only.

  When the restart valve operation of the exhaust valve is stopped as described above and the operation is switched from the compression self-ignition operation to the spark ignition operation, the introduction of the internal EGR is stopped and the fresh air amount tends to increase. Thus, the throttle opening is reduced to suppress the increase in the fresh air amount, but the intake pipe pressure downstream of the throttle valve does not decrease until the intake of each cylinder is performed several times. For this reason, if the intake valve is switched to the SI mode valve opening characteristic simultaneously with the stop of the restart operation of the exhaust valve (two-dot chain line portion 201 in FIG. 14), the intake pipe pressure is reduced until the intake pipe pressure decreases. The torque temporarily increases suddenly (two-dot chain line portion 202 in FIG. 14), and a torque shock occurs.

  On the other hand, in this embodiment, the valve opening characteristic of the intake valve is corrected so as to limit the fresh air intake amount of the engine until the intake pipe pressure decreases to an appropriate intake pipe pressure during the spark ignition operation. For example, when the valve closing timing is advanced from the bottom dead center (solid line portion 301 in FIG. 14), the valve opening period is shortened and the lift amount is also reduced. As a result, a sudden increase in torque is suppressed (solid line portion 302 in FIG. 14), and torque shock is prevented.

  As a correction of the intake valve opening characteristic until the intake pipe pressure decreases, the intake air is blown back even if it is corrected so that it closes later than the normal closing timing in the SI mode. The air filling amount is reduced, and a sudden increase in torque can be suppressed. The torque is also reduced by retarding the ignition timing. In particular, if the intake valve is closed slowly and the ignition timing retard is used in combination, the effect of suppressing the sudden increase in torque is enhanced by both actions. While there is a concern that knocking may occur during high load operation, if the intake valve is closed slowly, the in-cylinder gas is blown back into the intake passage and cooled here, thereby suppressing an increase in the in-cylinder temperature. This is advantageous for suppressing knocking during high-load operation.

  15 and 16 are flowcharts showing another example of control by the combustion control means 120 of the ECU 100 and the like.

  Also in this example, steps S1 to S5 are the same as the example shown in FIG.

  In step S101 following step S5, the in-cylinder temperature state (cylinder wall temperature) is estimated from the operating state of the engine (such as the duration of low-temperature combustion compression self-ignition operation), the intake air temperature, the engine coolant temperature, etc. It is determined whether or not the in-cylinder temperature state is a low temperature state equal to or lower than a predetermined temperature.

  If the determination in step S101 is no, high temperature mode compatible control is performed in step S102. As the high temperature mode compatible control, the processes in steps S6 to S22 in the flowcharts of FIGS.

  If the determination in step S101 is YES, in step S103, it is first determined whether or not the cylinder in which the exhaust valve opening characteristic can be switched is the first group. If this determination is YES (or after the process of step S116 described later), the restart valve operation of the exhaust valve is stopped when a predetermined timing (initial stage of the compression stroke of the first cylinder) has passed in the first group in step S104. In step S105, the intake valve opening characteristics of the first group are changed to the SI mode.

  Subsequently, in step S106, it is determined whether or not the stop of the restart valve operation of the exhaust valve 60 in the first group is completed. If completed, the ignition timing retard amount is set in step S107, and the retard Control the ignition timing by the amount. In the present embodiment, the reference intake pipe pressure during the spark ignition operation is obtained based on the SI mode map, and the actual intake pipe pressure before the intake stroke is detected by the pressure sensor, and the reference intake pipe pressure, the actual intake pipe pressure, The ignition timing retard amount is set according to the difference. In this case, the ignition timing retard amount is increased as the absolute value of the difference increases.

  In step S108 following step S107, it is determined whether the stop of the restart valve operation in all groups is completed. If not, the flag F is set to “1” in step S109.

  If the determination in step S103 is NO, or after the process in step S109, the process proceeds to step S110. In step S110, when a predetermined timing (initial stage of the compression stroke of the fourth cylinder) has passed in the second group, the restart operation of the exhaust valve is stopped, and in step S111, the intake valve opening characteristic of the second group is set to the SI mode. change.

  Next, in step S112, it is determined whether or not the flag F is “1”. If the determination is YES, it is determined in step S113 whether the stop of the restart valve operation of the exhaust valve in the second group is completed. Determine.

  If the stop of the resuming valve operation of the exhaust valve in the second group is completed, the ignition timing retard amount is set and executed in the same process as in step S107 for the cylinders in the second group in step S114. Subsequently, in step S115, it is determined whether or not the stop of the restart valve operation in all groups is completed. If not completed, the process proceeds to step S104.

  When it is determined in step S108 or step S115 that the stop of the restart valve operation of all the groups has been completed, the flag F is set to “0” in step S116 and the actual value detected by the pressure sensor in step S117. It is determined whether or not the intake pipe pressure has decreased to the reference intake pipe pressure during SI operation. If this determination is NO, in step S118, the ignition timing retard amount is set and executed for all the cylinders by the same process as in step S9, and then the process returns to step S117. If the determination in step S117 is YES, in step S119, all cylinders perform a spark ignition operation at the ignition timing obtained from the SI mode map according to the engine speed and load.

  According to the example shown in this flowchart, when the in-cylinder temperature is in a low temperature state, when the operation state shifts from the compression self-ignition operation region A to the spark ignition operation region B, the throttle opening is reduced, The engine torque is reduced by retarding the ignition timing with respect to the normal ignition timing in the spark ignition operation only during a period until the intake pipe pressure is reduced to an appropriate intake pipe pressure during the spark ignition operation. Therefore, a temporary rapid increase in torque immediately after the transition from the region A of the compression self-ignition operation to the region B of the spark ignition operation can be suppressed.

  In addition, when the ignition timing is retarded, the in-cylinder temperature (cylinder wall temperature) is likely to rise. However, since the ignition timing is retarded when the in-cylinder temperature is in a low temperature state, the in-cylinder temperature is somewhat reduced from this low temperature state. Even if it rises, it is sufficiently avoided that knocking occurs during the subsequent high load operation.

1 is a configuration diagram showing a schematic configuration of a four-cycle spark ignition engine according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing the structure of one cylinder of the engine according to FIG. 1 and intake and exhaust valves provided for the cylinder. It is a perspective view which shows the specific structure of the valve mechanism which concerns on embodiment of FIG. FIG. 4 is a cross-sectional view showing the main part of the VVE shown in FIG. 3, (A) shows when the lift amount is 0 in the large lift control state, and (B) shows when the lift amount is maximum in the large lift control state. (C) shows when the lift amount is 0 in the small lift control state, and (D) shows when the lift amount is maximum in the small lift control state. 4 (B) and 4 (D) schematically represent control states, where (A) corresponds to a large lift control position and (B) corresponds to a small lift control position. It is a disassembled perspective view of the valve operation switching mechanism provided with respect to the exhaust valve. It is front sectional drawing of the said valve operation switching mechanism. It is a top sectional view of the above-mentioned valve operation change mechanism. It is a characteristic view which shows an example of the driving | operation area | region setting for performing control according to the driving | running state in the engine which concerns on embodiment of FIG. It is a figure which shows the valve opening characteristic of an exhaust valve intake valve, Comprising: (A) is a characteristic in the case of a partial load area, (B) is a characteristic in the case of a high load area, (C) Transition to a high load area The characteristics in the case immediately after are shown. It is explanatory drawing which shows the stroke of each cylinder of a 4-cylinder 4 cycle engine, and the change of the ignition state at the time of the transition from compression self-ignition operation to spark ignition operation. It is a flowchart which shows an example of control by the combustion control means etc. of ECU. It is a continuation part of the flowchart of FIG. 14 is a time chart schematically showing a control operation shown in the flowcharts of FIGS. It is a flowchart which shows another example of control by the combustion control means etc. of ECU. It is a continuation part of the flowchart of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Spark ignition type engine 24 cylinder 29 Spark plug 29a Ignition circuit 40 Intake valve 41 Valve mechanism 42 VCT
43 VVE
60 Exhaust valve 62 Valve mechanism 62b, 62c Exhaust cam 70 Valve operation switching mechanism 100 ECU
120 Combustion control means 121 VCT control means 122 VVE control means 123 Exhaust valve control means 124 Ignition control means 130 Throttle valve control means 140 Torque reduction means

Claims (7)

In the predetermined engine operating range, in addition to the valve opening operation in the exhaust stroke, the reopening valve operation that opens the exhaust valve again in the intake stroke increases the in-cylinder temperature by the internal EGR and performs compression self-ignition. In a 4-cycle spark ignition engine,
Exhaust valve drive means that enables switching between execution and stop of the restart valve operation of the exhaust valve;
Intake valve driving means for making the opening / closing timing of the intake valve variable;
In the partial load region of the engine, the intake valve is opened near the intake top dead center and closed before the bottom dead center, and the compression valve self-ignition is performed by restarting the exhaust valve, Combustion control means for controlling the spark valve ignition to be performed in a state where the closing timing of the intake valve is a predetermined timing after bottom dead center and the restart valve operation of the exhaust valve is stopped in a high load region of the engine;
Throttle valve control means for controlling the opening of the throttle valve provided in the intake passage to be small at the time of transition from the operation region in which the compression self-ignition is performed to the operation region in which the spark ignition is performed;
A four-cycle spark ignition engine characterized by comprising torque reducing means for reducing the combustion torque of the engine for a predetermined period immediately after the transition. The four-cycle spark ignition engine according to claim 1,
The four-cycle spark ignition engine characterized in that the predetermined period immediately after the transition is a period until the intake pipe pressure downstream of the throttle valve is reduced to an appropriate intake pipe pressure in an operating range in which spark ignition is performed. . The four-cycle spark ignition engine according to claim 1 or 2,
The torque reduction means is configured to change the intake valve closing timing until the predetermined period elapses after switching from a state in which the restart valve operation of the exhaust valve is performed immediately after the transition to a state in which the restart valve operation is stopped. A four-cycle spark ignition engine characterized by being advanced with respect to a predetermined time set in an operating range in which spark ignition is performed. The four-cycle spark ignition engine according to claim 3,
The four-cycle spark ignition engine characterized in that the torque reducing means adjusts the closing timing of the intake valve in accordance with the intake pipe pressure downstream of the throttle valve in a predetermined period immediately after the transition. The four-cycle spark ignition engine according to claim 1 or 2,
In the predetermined period immediately after the transition, the torque reducing means sets the closing timing of the intake valve to the intake port for in-cylinder air further later than the predetermined timing set in the operating range in which spark ignition is performed. A four-cycle spark-ignition engine characterized by the timing at which the engine blows back. The four-cycle spark ignition engine according to claim 5,
The four-cycle spark ignition type, wherein the torque reduction means retards the ignition timing in addition to delaying the closing timing of the intake valve further than the predetermined timing in a predetermined period immediately after the transition. engine. The four-cycle spark ignition engine according to any one of claims 1 to 6,
Means for determining a low temperature state in which the temperature state in the cylinder is equal to or lower than a predetermined temperature;
The four-cycle spark ignition engine characterized in that the torque reduction means retards the ignition timing in a predetermined period immediately after the transition in the low temperature state.

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