JP4591300B2 - 4-cycle spark ignition engine - Google Patents

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.

  In addition to this, as a technique for performing the compression self-ignition, it is considered to provide a means for heating the intake air.

  By the way, when compression self-ignition is performed by internal EGR or intake air heating as described above, knocking is likely to occur in a high load region, and torque cannot be increased by a large amount of internal EGR. It is necessary to perform the compression self-ignition operation in the region and stop the compression self-ignition in the high load region so that the combustion by the spark ignition is performed.

  In this case, immediately after switching from the high load region where spark ignition was performed to the partial load region and switching to compression self-ignition operation, the combustion chamber temperature was In addition to being high, there is a problem that knocking is likely to occur temporarily because the in-cylinder temperature is excessively increased by a hot internal EGR or the like.

  In view of the above circumstances, the present invention suppresses the occurrence of knocking immediately after switching from the high load region where the spark ignition has been performed to the partial load region and switching to the compression self-ignition operation, thereby reducing the combustion state of the engine. A four-cycle spark ignition engine that can be kept in good condition is provided.

In order to solve the above problems, the present invention controls the combustion state in a compression self-ignition operation mode in which the air-fuel mixture in the combustion chamber is combusted by compression self-ignition in the partial load region of the engine. In a spark ignition engine in which the combustion state is controlled to a normal operation mode in which ignition is stopped and the air-fuel mixture in the combustion chamber is combusted by spark ignition, in the compression self-ignition operation mode, the exhaust valve is operated in the exhaust stroke. In addition to the valve opening operation, it opens in the intake stroke, or the intake valve opens in the exhaust stroke in addition to the valve opening operation in the intake stroke, thereby increasing the in-cylinder temperature by internal EGR and performing compression self-ignition a combustion control means for so to a fuel injection valve for injecting fuel directly into a combustion chamber of the engine, and determines the operating condition determining means for operating condition of the engine, the operating condition determining hands Based on the determination by, along with the operating state of the engine to inject fuel in the intake stroke in either operating mode when in the vicinity of the boundary between at least the compression operation region and the operating region of the normal operation mode-ignition operation mode, At least a part of the injected fuel is injected in the latter half of the compression stroke in a temporary period immediately after the transition from the normal operation mode to the compression self-ignition operation mode due to a change in the operation state from the high load region to the partial load region. Thus, the fuel injection control means for controlling the fuel injection from the fuel injection valve is provided.

  According to this configuration, immediately after the transition from the normal operation mode to the compression self-ignition operation mode, the compression self-compression is performed in a state in which the temperature of the combustion chamber is high due to the high-temperature combustion in the normal operation mode in the high load range until then. In contrast to the tendency that the in-cylinder temperature becomes excessively high by switching to the ignition operation mode, the in-cylinder temperature is appropriately lowered by the latent heat of vaporization of the fuel injected in the latter half of the compression stroke, and knocking is suppressed.

In the present invention, the fuel injection control means performs fuel injection divided into an intake stroke and a latter half of the compression stroke in a temporary period immediately after the transition from the normal operation mode to the compression self-ignition operation mode. It is preferable to control. If it does in this way, the effect | action which suppresses overheating by the injection in the latter half of a compression stroke will be acquired, aiming at the vaporization of the fuel, atomization, and spreading | diffusion (homogenization of air-fuel mixture) by intake stroke injection.

Further, the fuel injection control means performs control for injecting at least a part of the injected fuel in the latter half of the compression stroke immediately after the transition from the normal operation mode to the compression self-ignition operation mode for each cylinder. Just do it for minutes.

  That is, when the cylinder temperature is increased by the internal EGR and the compression self-ignition is performed, immediately after the transition to the compression self-ignition operation mode, particularly in the period of one cycle, the combustion in the previous normal operation mode is performed. Since the high temperature exhaust gas is introduced into the cylinder and the temperature in the cylinder tends to become excessively high, overheating is effectively suppressed by injecting fuel to each cylinder in the latter half of the compression stroke. The

  As described above, according to the four-cycle spark ignition type engine of the present invention, immediately after the transition from the normal operation mode to the compression self-ignition operation mode, the fuel is injected in the latter half of the compression stroke, and the in-cylinder temperature is caused by the latent heat of vaporization. By being pulled down, the tendency for the in-cylinder temperature to become excessively high is corrected, knocking is suppressed, and the combustion state can be kept good.

  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 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 fuel injection control means 140 for controlling the fuel injection from the fuel injection valve 28.

  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 means for controlling ignition by the spark plug 29 124.

  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, the operation region set in the ECU 100 includes a region A in a compression self-ignition operation mode (denoted as HCCI in the drawing) for performing so-called compression self-ignition, and a normal operation mode for performing spark ignition operation. Region B (denoted as SI in the figure) is set. The region A of the compression self-ignition operation mode is a region below a predetermined engine load in a low / medium rotation region where the engine speed ne is relatively low. The region B in the normal operation mode is a region other than the region A in the compression self-ignition operation mode, 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.

  10A and 10B are diagrams showing 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 opening operation EX1 of the exhaust valve 60, the opening operation INa of the intake valve 40, and the resumption valve operation EX2 of the exhaust valve 60 are set as the control of the compression self-ignition operation mode. Is done. 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, as the normal operation mode control, the exhaust valve 60 performs only the valve opening operation EX1 in the exhaust stroke, and stops the restart valve operation EX2 in the intake stroke. The intake valve 40 is opened so that the intake valve closing timing is retarded (preferably delayed until after bottom dead center) compared to the valve opening characteristics in the region A, and the valve opening period and the valve lift amount are increased. The valve characteristic (INb) is set. 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.

  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 spark ignition operation to the compression self-ignition operation. In this figure, F and F1, F2 indicate fuel injection, C indicates self-ignition, and S 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 transition from the spark ignition operation region (region B in FIG. 9) to the compression self-ignition operation region (region A in FIG. 9) is made, it is not possible to switch the characteristics of the intake and exhaust valves in the stroke, after the transition determination time t _0, for each group, just after the intake stroke of the slower cylinder intake stroke among the two cylinders, solenoid valves 79a Is controlled to switch the exhaust valve opening characteristic to a state where the restart valve operation is performed. 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). In addition to the switching of the exhaust valve opening characteristic, the intake valve opening characteristic is also switched from the characteristic (INb) shown in FIG. 10 (B) to the small lift characteristic (INa) shown in FIG. 10 (A). After the opening characteristics of the exhaust valve and the intake valve are switched in this way, compression self-ignition is performed.

  Further, as a control of the fuel injection by the fuel injection control means 140, at least near the boundary between the operation region in the normal operation mode and the operation region in the compression self-ignition operation mode, the fuel injection F is in the intake stroke in any mode. However, immediately after the transition from the normal operation mode to the compression self-ignition operation mode, at least a part of the injected fuel is controlled to be injected in the latter half of the compression stroke. That is, fuel injection is performed in the latter half of the compression stroke for at least one cycle from the first intake stroke after the opening characteristics of the exhaust valve and the intake valve are switched in each cylinder. The divided injections F1 and F2 are performed in the latter half of the compression stroke.

  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 operating state is in the region A. If the determination is YES, the ECU 100 performs compression self-ignition operation in accordance with the engine speed and load for all the cylinders in step S2. The valve opening characteristics of the intake and exhaust valves determined from the map of the mode (HCCI mode) (see FIG. 10A), that is, the intake valve closes before the bottom dead center and the characteristics of small lift, the exhaust valve is the restart valve The characteristic is to execute the operation, and the compression self-ignition operation is performed.

  If the determination in step S1 is NO, that is, if the operating state is in the high load side or high speed side region (region B), in step S3, all the cylinders are in the normal operation mode (depending on the engine speed and load). The spark ignition operation is performed with the valve opening characteristics (see FIG. 10B) and ignition timing of the intake / exhaust valves obtained from the SI mode map.

  In step S4 following step S3, it is determined whether or not the operating state has shifted from region B to region A. If not, step S3 is repeated and the normal operation mode is continued.

  When the operating state shifts from the region B to the region A, in step S5, it is first determined whether or not the cylinder in which the valve opening characteristics of the intake and exhaust valves can be switched is the first group. That is, as shown in FIG. 11, the time when the valve opening characteristics can be switched is different between the first group and the second group, and either group is switched first depending on the transition time from the region B to the region A. Since whether or not it becomes possible changes, it is determined in step S5.

  If the determination in step S5 is YES (or if the determination in step S15 described later is NO), in step S6, the exhaust valve is restarted when the predetermined timing (initial stage of the compression stroke of the first cylinder) has passed in the first group. The intake valve is switched to have a small lift characteristic. Subsequently, in step S7, it is determined whether or not the switching of the valve opening characteristics in the first group is completed. If completed, in step S8, fuel injection is performed for one cycle in the first group of cylinders. The compression self-ignition operation is performed in a state where the fuel injection from the valve 28 is divided injection of the intake stroke and the compression stroke.

  In step S9 following step S8, it is determined whether or not the switching of the valve opening characteristics of the intake / exhaust valves in all the groups has been completed. If not, the flag F is set to “1” in step S10.

  If the determination in step S5 is NO, or after the process in step S10, the process proceeds to step S11. In step S11, when a predetermined timing (the initial stage of the compression stroke of the fourth cylinder) has passed in the second group, the exhaust valve is switched to the restart valve characteristic and the intake valve is switched to the small lift characteristic. Next, in step S12, it is determined whether or not the flag F is “1”. If the determination is YES, it is determined in step S13 whether or not the switching of the valve opening characteristics in the second group is completed. . Note that the determination in step S13 also proceeds if the determination in step S7 is NO.

  If the switching of the valve opening characteristics in the second group has been completed, in step S14, the fuel injection from the fuel injection valve 28 is divided into the intake stroke and the compression stroke for one cycle in the second group of cylinders. In this state, compression self-ignition operation is performed.

  Subsequently, in step S15, it is determined whether or not the switching of the valve opening characteristics in all groups has been completed. If not completed, the process proceeds to step S6.

  When it is determined in step S9 or step S15 that the switching of the valve opening characteristics in all the groups has been completed, the flag F is set to “0” in step S16, and the fuel injection valve 28 in step S17. The compression self-ignition operation is performed in a state where the fuel injection from is made as a batch injection in the intake stroke.

  According to the engine of the present embodiment as described above, the combustion state is controlled to the compression self-ignition operation mode in the operation region A that is equal to or lower than the predetermined load in the low and medium rotation region. That is, as shown in FIG. 10A, the intake valve 40 is controlled to have a small lift characteristic, and the exhaust valve 60 is controlled to perform a restart valve operation during the intake stroke. As a result, exhaust gas is introduced from the exhaust port into the combustion chamber during the exhaust valve restart valve operation, and a large amount of internal EGR is obtained. The in-cylinder temperature is increased by this internal EGR, and combustion by compression self-ignition is performed. As a result, combustion efficiency is increased and fuel efficiency is greatly improved. On the other hand, in the operation region B on the high load side or the high rotation side, if compression self-ignition is performed, knocking is likely to occur and torque cannot be increased by a large amount of internal EGR. As shown, the restart valve operation of the exhaust valve 60 is stopped and the intake valve 40 is set to a normal lift characteristic, and the combustion state is controlled to the normal operation mode in which the air-fuel mixture is burned by spark ignition in this state.

  By the way, as indicated by an arrow in FIG. 9, knocking is likely to occur temporarily immediately after the transition from the normal operation mode to the compression self-ignition operation mode by changing the operation state from the region B to the region A. There is a natural tendency to become.

  That is, immediately after the transition to the compression self-ignition operation mode, the in-cylinder temperature is high because it was in the region B on the relatively high load side, and the spark ignition operation is less efficient than the compression self-ignition operation. Since the exhaust gas temperature is high, at the time of the first exhaust valve restart valve operation immediately after the transition to the compression self-ignition operation mode, the high-temperature exhaust gas in the previous spark ignition operation is introduced into the cylinder as the internal EGR. For this reason, especially in the first cycle immediately after the transition to the compression self-ignition operation mode, the in-cylinder temperature becomes too high and knocking is likely to occur.

  On the other hand, in this embodiment, immediately after the transition from the normal operation mode to the compression self-ignition operation mode, a part of the fuel is injected into each cylinder for one cycle in the latter half of the compression stroke. The in-cylinder temperature is appropriately lowered by the latent heat of vaporization of the fuel injected in the latter half of the compression stroke, and the occurrence of knocking is suppressed. Then, as in this embodiment, when the divided injection is divided into the intake stroke and the latter half of the compression stroke, the fuel injected in the intake stroke is sufficiently vaporized and atomized and burned before ignition. Since it is diffused uniformly throughout the chamber, combustion by compression self-ignition is performed satisfactorily.

  The specific structure of the engine of the present invention is not limited to the above embodiment, and can be variously changed.

  For example, in the above embodiment, split injection is performed as control for preventing knocking immediately after shifting to the compression self-ignition operation mode. However, fuel may be injected all at once in the latter half of the compression stroke.

  In addition, split injection is performed for each cylinder for each cycle immediately after the transition to the compression self-ignition operation mode. However, the in-cylinder temperature after the transition to the compression self-ignition operation mode is affected by the operation state until then. When the tendency of becoming excessively high reaches several cycles, the divided injection or the batch injection in the latter half of the compression stroke may be performed over several cycles.

  As a control of the intake and exhaust valves during the compression self-ignition operation, instead of opening the exhaust valve again in the intake stroke as in the above embodiment, the intake valve is opened in the exhaust stroke in addition to opening in the intake stroke. In this way, a part of the burned gas in the combustion chamber flows out to the intake port side during the intake valve opening operation in the exhaust stroke, and this is the next intake stroke. Since it is returned to the combustion chamber, a large amount of internal EGR is also obtained in this case, and the in-cylinder temperature is increased. Further, in these methods, compression self-ignition is enabled by a large amount of internal EGR, but instead of this, or in combination with this, it is possible to enable compression self-ignition by heating the intake air by the intake air heating means. Good. In this case as well, when shifting to the compression self-ignition operation mode, the in-cylinder temperature tends to become excessively high due to the influence of the previous operation state, so one cycle or several immediately after the transition to the compression self-ignition operation mode. In the cycle period, it is desirable to suppress knocking by appropriately lowering the in-cylinder temperature by the divided injection or batch injection in the latter half of the compression stroke.

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) shows the characteristic in the case of a partial load area, (B) shows the characteristic in the case of a high load area. 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 spark ignition operation to compression self-ignition operation. It is a flowchart which shows an example of control by ECU. It is a continuation part of the flowchart of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Spark ignition type engine 24 cylinder 28 Fuel injection valve 29 Spark plug 29a Ignition circuit 40 Intake valve 60 Exhaust valve 100 ECU
120 Combustion control means 140 Fuel injection control control means

Claims (3)

In the partial load region of the engine, the combustion state is controlled in a compression self-ignition operation mode in which the air-fuel mixture in the combustion chamber is combusted by compression self-ignition, and in the high engine load region, the compression self-ignition is stopped to In a spark ignition engine in which the combustion state is controlled to a normal operation mode in which the fuel is burned by spark ignition,
In the compression self-ignition operation mode, the exhaust valve is opened during the intake stroke in addition to the valve opening operation during the exhaust stroke, or the intake valve is opened during the exhaust stroke in addition to the valve opening operation during the intake stroke. Combustion control means for increasing the in-cylinder temperature by internal EGR and performing compression self-ignition,
A fuel injection valve that injects fuel directly into the combustion chamber of the engine;
An operating state determining means for determining an operating state of the engine;
Based on the determination by the operation state determination means, when the engine operation state is at least near the boundary between the operation region of the compression self-ignition operation mode and the operation region of the normal operation mode, the fuel in the intake stroke in any operation mode And at least a part of the injected fuel in a temporary period immediately after the transition from the normal operation mode to the compression self-ignition operation mode due to a change in the operation state from the high load region to the partial load region. A four-cycle spark ignition engine comprising fuel injection control means for controlling fuel injection from the fuel injection valve so as to inject in the latter half of the compression stroke. The fuel injection control means controls to perform fuel injection divided into an intake stroke and a second half of the compression stroke in a temporary period immediately after the transition from the normal operation mode to the compression self-ignition operation mode. The four-cycle spark ignition engine according to claim 1, The fuel injection control means performs control for injecting at least a part of the injected fuel in the latter half of the compression stroke immediately after the transition from the normal operation mode to the compression self-ignition operation mode, for each cycle for each cylinder. 4-cycle spark ignition engine according to claim 1 or 2, characterized in that.

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