JP2007056701A - Spark ignition four-cycle engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To develop a suitable compressed self-ignitability according to the operation load area of an engine. <P>SOLUTION: In the compressed self-igniting operation area, only intake ports 24a for flowing out an intake air in the direction to weak a swing flow EX<SB>F</SB>generated by the re-opening operation of one exhaust port 24b is opened on the low load side, and an intake valve and an exhaust valve are controlled to open the intake ports 24a, 24a on the high load side. In the compressed self-igniting operation area, the mixing of fresh air with the burned gas is promoted, the temperature in the entire cylinder is rapidly raised, and a compressed self-ignition without residues is assured in a lean state on the low load side. A fresh air-fuel mixture is stratified in a deviated state around an ignition plug in a combustion chamber, and the assisting of ignition is also facilitated while preventing knocking from occurring on the high load side. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a spark ignition type four-cycle engine, and more particularly, to an operation mode and spark ignition for performing premixed compression auto-ignition combustion (HCCI: “Compression self-ignition” in this specification). The present invention relates to a spark ignition type four-cycle 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

  By the way, in order to improve the performance of the engine using the internal EGR gas in total, in the compression self-ignition operation region, it is required to prevent misfire on the low load side and to prevent knocking on the high load side. However, in the configuration of Patent Document 1, only the valve opening timing of the internal EGR is adjusted based on the determination of the operation state, so that the compression self-ignition performance is improved according to the load region, or knocking is performed. It was not possible to prevent.

  In particular, simply performing the reopening valve operation of the exhaust port in the intake stroke causes the problem that compression self-ignition becomes difficult because the inside of the cylinder is stratified in a state where burned gas is unevenly distributed around the ignition plug of the combustion chamber. there were.

  The present invention has been made in view of the above problems, and an object thereof is to provide a spark ignition type four-cycle engine capable of exhibiting a suitable compression self-ignition performance in accordance with an engine operating load region.

  In order to solve the above-described problems, the present invention provides a cylinder that forms a combustion chamber at the top, a spark plug that is disposed in the center of the combustion chamber, and a longitudinal axis of the cylinder centered on the spark plug. A plurality of intake ports and exhaust ports arranged on opposite sides, and an intake valve provided for each intake port and an exhaust valve provided for each exhaust port, and a plurality of exhaust ports in a predetermined operating region of the engine Among these, a spark ignition type four-cycle engine in which the burned gas is recirculated into the cylinder by a resuming valve operation that opens one exhaust port opening in an intake stroke, and a compression self-ignition operation is performed. Operating state determining means for determining the state, and valve opening / closing control means for controlling the opening / closing timing of the intake port and the exhaust port based on the determination of the operating state determining means, The closing control means closes the intake port that opens in the intake stroke before the intake bottom dead center, and weakens the swirl flow generated by the restart valve operation of the one exhaust port in the predetermined operating region on the low load side. The spark ignition type four-cycle engine is characterized in that only the intake port that flows out the intake air in the direction is opened, and the intake valve and the exhaust valve are controlled to open a plurality of intake ports on the high load side. In this mode, in a predetermined operating region of the engine, the intake port that the intake valve opens in the intake stroke is closed before the intake bottom dead center, and the exhaust valve is restarted in the intake stroke, so that The fuel gas recirculates and tries to form a swirl in a predetermined direction. Here, in this aspect, in the predetermined operating region, on the low load side, fresh air is introduced into the cylinder in a direction that disturbs the swirl by the exhaust valve. Promoted. As a result, the temperature in the entire cylinder rises quickly, and it is possible to reliably perform the compression self-ignition without remaining unburned in a lean state. On the other hand, on the high load side, when a plurality of intake ports are opened, fresh air is introduced into the cylinder while forming a relatively strong swirl at the beginning of the intake stroke. Even after being introduced, stratification is promoted with fresh air unevenly distributed around the ignition plug of the combustion chamber. As a result, knocking is prevented.

  In a preferred aspect, the valve opening / closing control means opens an intake valve adjacent to the exhaust valve performing the restart valve operation on a low load side in a predetermined operation region. In this aspect, the fresh air introduced in the intake stroke and the burned gas introduced by the restart valve operation collide in the cylinder, and the mixing of the fresh air and the burned gas is further promoted.

  In a preferred embodiment, each intake port has a throat axis in the vicinity of the opening formed in parallel along a direction intersecting with the longitudinal axis of the cylinder in a plan view, and is opened on the low load side. The intake port is set to face in the direction close to the tangential line in the left-right direction on the plane of the cylinder as it goes downstream of the throat axis, and the exhaust port that performs the restart valve operation is adjacent to the intake port on the left and right Is. In this aspect, fresh air and burned gas from the intake port collide on the upstream side of the exhaust swirl, and mixing of fresh air and burned gas is further promoted.

  In a preferred embodiment, ignition control means for controlling the ignition timing of the ignition plug is provided, and the ignition control means performs ignition so that ignition is performed before the ignition timing on the high load side in the predetermined operating region of the engine. It controls the plug. In this mode, on the high load side, since a plurality of intake ports are opened, fresh air is introduced into the cylinder while forming a relatively strong swirl at the beginning of the intake stroke. Even after the gas is introduced, stratification is promoted with fresh air unevenly distributed around the ignition plug of the combustion chamber. Therefore, by performing ignition before the ignition timing, it is possible to reliably ignite the air-fuel mixture in the cylinder while avoiding knocking.

  As described above, according to the present invention, on the low load side, mixing of fresh air and burned gas is promoted, and it is possible to reliably perform compression self-ignition without remaining unburned in a lean state. In addition, on the high load side, it is possible to promote the stratification in a state in which fresh air is unevenly distributed around the ignition plug of the combustion chamber and to prevent knocking, which is suitable according to the operating load region of the engine. It has a remarkable effect that it can exhibit a good compression self-ignition performance.

  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 spark ignition type four-cycle engine 10 according to an embodiment of the present invention, and FIG. 2 is provided with one cylinder of an engine body 20 according to FIG. 2 is a schematic cross-sectional view showing the structure of the intake valve 40 and the exhaust valve 60. FIG. 3 is a schematic plan view showing the structure of one cylinder of the engine body 20 and the intake valve 40 and the exhaust valve 60 provided thereto.

  In these drawings, the engine body 20 of the illustrated spark ignition type four-cycle engine 10 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.

Referring to FIG. 3, the throat portions at the downstream ends of the intake ports 24 a provided in the cylinders 24 are all aligned along the longitudinal axis L of the cylinder 24 with the spark plug 29 as the center. Further, in the present embodiment, the throat portion in the vicinity of the downstream end of each intake port 24a is formed such that the throat axis L _IN extends obliquely from the rear to the front and intersects the axis L. For this reason, the fresh air introduced from the intake ports 24a, 24a is configured to form a swirl in the counterclockwise direction in the drawing.

  With reference to FIGS. 1 and 2, 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.

  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 camshaft 41 a of a valve operating mechanism 41. The valve mechanism 41 has a VCT (Variable Camshaft Timing Mechanism) 42 configured by an OCV (Oil Control Valve System) or the like, but the configuration itself is publicly known, and thus detailed description thereof is omitted.

  As shown in FIG. 3, in the pair of front and rear intake valves 40, a known tappet 61 is provided in the front intake valve 40, and this tappet 61 is fixed to the camshaft 41 a of the valve operating mechanism 41. It is comprised so that it may drive. On the other hand, the rear intake valve 40 is provided with a valve operation switching mechanism 70 having a lost motion function as will be described in detail later.

  Next, the exhaust system 50 includes an exhaust manifold 52 in which bifurcated branch exhaust pipes 51 connected to an exhaust port 24b formed in pairs for each cylinder 24 are gathered on the downstream exhaust side, and the exhaust manifold. 52 and an exhaust pipe 53 for discharging burned gas from the exhaust manifold 52.

  Each exhaust port 24b is provided with an exhaust valve 60.

  Referring to FIG. 3, 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 operating mechanism 62 is configured to enable a reopening valve operation for opening the exhaust valve 60 again in the intake stroke in addition to the valve opening operation in the exhaust stroke.

  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. In the present embodiment, the exhaust valve 60 provided with the valve operation switching mechanism 70 is the front exhaust valve 60 in the front-rear direction as shown in FIG. 3, and the rear exhaust valve 60 does not perform the restart valve operation. It is configured as follows. 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 and recirculates the burned 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. 5).

  A specific structure of the valve operation switching mechanism 70 provided in the exhaust system 50 will be described with reference to FIGS.

  4 is an exploded perspective view of the valve operation switching mechanism 70 provided in the exhaust system 50, FIG. 5 is a front sectional view of the valve operation switching mechanism 70, and FIG. 7 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 where the bearing 76 is provided, a hydraulic fluid circuit 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 circuit PH under the control of the ECU 100, which will be described later, the unlocking plunger 78d is driven to the left in FIG. 5 and FIG. 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 exhaust cam 62c (the exhaust valve restart valve in the intake stroke). Operation) 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 the present embodiment, as shown in FIG. 1, a hydraulic oil circuit 79 and an electromagnetic valve 79a are provided so that the valve operation switching mechanism 70 of the exhaust system 50 can be operated.

  Further, the valve operation switching mechanism 70 provided in the intake system 30 is completely the same in principle as the valve operation switching mechanism 70 described with reference to FIGS. 4 to 6, and the intake cam 43a is the second exhaust cam 62c. And is configured to perform a lost motion at a predetermined timing. Then, the lost motion of the intake cam 43a is controlled by driving the hydraulic oil circuit 179 and the electromagnetic valve 179a as shown in FIG.

  Next, the spark ignition type four-cycle 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 140 that controls the throttle valve 35 according to the determined operating state. Functionally.

  The combustion control means 120 drives and controls the VCT control means 121 that controls the electromagnetic valve of the VCT 42 provided in the valve mechanism 41 of the intake system 30 and the electromagnetic valves 179a and 79a provided in the intake and exhaust systems 30 and 50. As a result, valve opening / closing control means 123 for switching control of the valve operation switching mechanism 70 provided for the intake valve 40 and the exhaust valve 60 and ignition control means 124 for controlling ignition by the spark plug 29 are included.

  Various detection means such as a crank angle sensor 27, an air flow sensor 34, 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 provided in the VCT 42 of the valve operating mechanism 41, the electromagnetic valves 79a and 179a of the hydraulic oil circuits 79 and 179 that drive each valve operation switching mechanism 70, and the spark plug An ignition circuit 29a for controlling ignition by 29, a fuel injection valve 28, and the like are connected.

  Next, the control characteristics stored in the ECU 100 will be described.

  FIG. 7 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 operation state determination means 110 of the ECU 100 has a function of detecting the operation state of the engine from the crank angle sensor 27, the accelerator opening sensor 66, and the like, and determining whether the operation state is in the above-described region A or B. It is.

  The VCT control means 121 of the combustion control means 120 is based on the determination of the operating state determination means 110, so that the valve opening mechanism 41 and the movement of the intake valve 40 and the exhaust valve 60 are advanced or retarded individually. The function of controlling the solenoid valve of the valve mechanism 62 is exhibited.

  The valve opening / closing control means 123 operates the electromagnetic valves 79a and 179a provided in the hydraulic oil circuits 79 and 179 based on the determination of the operating state determination means 110, and as shown in Table 1, the intake valve 40 and the exhaust valve 60 are operated. The valve opening function is controlled.

  FIG. 8 is a schematic plan view showing the flow of fresh air and burned gas during the restart valve operation in one cylinder of the engine body, where (A) is a low load and (B) is a high load. FIG. 9 is a timing chart showing the crank angle and the in-cylinder temperature during the compression self-ignition operation.

  Referring to FIGS. 8A and 9, first, when the operation state is the state of FIG. 7A, that is, in the compression self-ignition operation region, the operation state determination means 110 is in the low load side operation region. When it is determined that there is, the valve opening / closing control means 123 drains the hydraulic oil of the hydraulic oil circuit 79 so that the front exhaust valve 60 executes the restart valve operation and supplies the hydraulic oil to the hydraulic oil circuit 179. Then, the rear intake valve 40 is controlled so as to be kept closed in the intake stroke by the lost motion.

As a result, in the compression-ignition operation region A, in the low load side, open front side of the intake valve 40 in the intake stroke, as indicated by the arrow IN _F, in a state in which fresh air is introduced into the cylinder 24, the front side The exhaust valve 60 performs the restart valve operation. As a result, the exhaust swirl that is about to be generated in the direction indicated by the arrow EX _{F due} to the restart valve operation is disturbed by colliding with the flow of fresh air, so that fresh air and burned gas are efficiently mixed, The inside fresh air and burned gas become homogeneous. For this reason, even if the internal EGR rate due to the restart valve operation of the exhaust valve 60 is relatively low, the in-cylinder temperature of the cylinder 24 at the time of low load rises quickly, and the compression self-ignition is surely maintained while maintaining a lean state. Can be realized.

  Referring to FIGS. 8B and 9, when in the compression self-ignition operation region, when the operation state determination unit 110 determines that the operation region is on the high load side, the valve opening / closing control unit 123 The hydraulic oil in the hydraulic oil circuits 79 and 179 is drained so that the front exhaust valve 60 performs the restart valve operation, and the rear intake valve 40 is opened together with the front intake valve 40 in the intake stroke. To control.

In this result, the compression-ignition operation region A, the high load side, open on both sides of the intake valve 40 before and after the intake stroke, as indicated by the arrow IN _F, since the fresh air is introduced into the cylinder 24, compared A strong intake swirl IN _S is generated in the cylinder. As a result of the restart valve operation of the front exhaust valve 60 in this state, the exhaust swirl that is about to occur in the direction indicated by the arrow EX _F by the restart valve operation collides with a strong fresh air flow and is disturbed. The stratification is promoted in a state where fresh air is unevenly distributed around the ignition plug 29 of the combustion chamber 26. For this reason, it becomes possible to prevent the in-cylinder temperature from excessively rising and knocking due to the internal EGR.

  The ignition control unit 124 drives the ignition circuit 29a at a predetermined timing based on the determination of the operating state determination unit 110, and executes ignition by the spark plug 29. In the present embodiment, in addition to normal spark ignition in the spark ignition operation region B, when the compression self-ignition operation region A is in the high load side operation region, the spark plug 29 is driven before the compression self-ignition starts. The so-called ignition assist is executed.

As described above, in the high load side, open on both sides of the intake valve 40 before and after the intake stroke, as indicated by the arrow IN _F of FIG. 8 (B), since the fresh air is introduced into the cylinder 24, compared A strong intake swirl IN _S is generated in the cylinder. In this state, as a result of the restart valve operation of the front exhaust valve 60, stratification is promoted in a state where fresh air is unevenly distributed around the ignition plug 29 of the combustion chamber 26. For this reason, it is possible to reliably execute the ignition assist by operating the spark plug 29 while preventing knocking.

  The throttle valve control means 140 is configured to drive the actuator 36 and control the valve opening amount of the throttle valve 35 based on the determination of the operation state determination means 110.

As described above, in this embodiment, the intake port 24a that the intake valve 40 opens in the intake stroke in the predetermined operation region of the engine 10, that is, the compression self-ignition operation region A, is closed before the intake bottom dead center and exhausted. When the valve 60 restarts in the intake stroke, the burned gas recirculates in the cylinder and tries to form a swirl in a predetermined direction indicated by an arrow EX _F in FIGS. In the present embodiment, in the compression-ignition operation region A, the low-load side, as shown by the arrow IN _F in FIG. 8 (A), the cylinder fresh air in the direction to disturb the swirl of the exhaust valve 60 Therefore, mixing of fresh air and burned gas is promoted. As a result, the temperature in the entire cylinder rises quickly, and it is possible to reliably perform the compression self-ignition without remaining unburned in a lean state. On the other hand, in the high load side, by opening the front and rear side of the intake port 24a, as shown by the arrow IN _S in FIG. 8 (B), the fresh air cylinder while forming a relatively strong swirl to the intake stroke initial Therefore, even after the burned gas is introduced by the restart valve operation of the exhaust valve 60, stratification is promoted in a state where fresh air is unevenly distributed around the ignition plug 29 of the combustion chamber 26. As a result, knocking is prevented.

  In the present embodiment, the valve opening / closing control means 123 opens the intake valve 40 adjacent to the exhaust valve 60 performing the restart valve operation on the low load side in the compression self-ignition operation region A. For this reason, in this embodiment, the fresh air introduced in the intake stroke and the burned gas introduced by the restart valve operation collide in the cylinder, and the mixing of the fresh air and the burned gas is further promoted.

In the present embodiment, each intake port 24a is formed such that the throat axis L _IN near the opening is formed in parallel along the direction intersecting with the front / rear axis L of the cylinder 24 in plan view, and the low an intake port 24a which is opened at the load side, as the go downstream side of the throat axis L _iN is set to the side in close proximity toward the peripheral surface of the cylinder 24, an exhaust port 24b for performing the restart valve operation Is adjacent to the intake port 24a on the left and right. For this reason, in this embodiment, fresh air and burned gas from the intake port 24a collide on the upstream side of the exhaust swirl, and mixing of fresh air and burned gas is further promoted.

  In the present embodiment, ignition control means 124 for controlling the ignition timing of the ignition plug 29 is provided, and the ignition control means 124 is arranged in the compression self-ignition operation region A of the engine 10 before the ignition timing on the high load side. The ignition plug 29 is controlled via the ignition circuit 29a so as to execute ignition. Therefore, in this embodiment, on the high load side, stratification is promoted in a state where fresh air is unevenly distributed around the spark plug 29 of the combustion chamber 26, so that knocking is avoided by so-called ignition assist by the spark plug 29. However, the air-fuel mixture in the cylinder can be ignited with certainty.

  The above-described embodiments are merely examples of preferred specific examples of the present invention, and the present invention is not limited to the above-described embodiments. It goes without saying that various modifications are possible within the scope of the claims of the present invention.

1 is a configuration diagram showing a schematic configuration of a spark ignition type 4-cycle engine according to an embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a structure of one cylinder of the engine according to FIG. 1 and an intake valve and an exhaust valve provided for the cylinder. 1 is a schematic plan view showing the structure of one cylinder of an engine body and intake and exhaust valves provided for the cylinder. 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 schematic plan view showing the flow of fresh air and burned gas during the restart valve operation in one cylinder of the engine body, (A) when the load is low and (B) when the load is high. It is a timing chart which shows the crank angle at the time of compression self-ignition operation, and cylinder temperature.

Explanation of symbols

A Compression self-ignition operation region B Spark ignition operation region 10 Spark ignition type 4-cycle engine 20 Engine body 24 Cylinder 24a Intake port 24b Exhaust port 25 Piston 26 Combustion chamber 29 Spark plug 30 Intake system 40 Intake valve 50 Exhaust system 60 Exhaust valve 70 Valve operation switching mechanism (an example of components of valve opening / closing control means)
79, 179 Hydraulic oil circuit (an example of components of valve opening / closing control means)
79a, 179a Solenoid valve (an example of components of valve opening / closing control means)
101 CPU
110 Operation state determination means 120 Combustion control means 121 VCT control means 123 Valve opening / closing control means 124 Ignition control means

Claims (4)

A cylinder forming a combustion chamber at the top; a spark plug disposed in a central portion of the combustion chamber; and a plurality of intake ports disposed on opposite sides of the front and rear axes of the cylinder around the spark plug; An exhaust port, an intake valve provided for each intake port, and an exhaust valve provided for each exhaust port. In a predetermined operating region of the engine, an opening of one exhaust port of the plurality of exhaust ports is an intake stroke. A spark ignition type four-cycle engine in which the burned gas is recirculated into the cylinder by a restart valve operation opened at
An operating state determining means for determining the operating state of the engine;
Valve opening / closing control means for controlling the opening / closing timing of the intake port and the exhaust port based on the determination of the operating state determining means, and the valve opening / closing control means comprises:
The intake port that opens in the intake stroke is closed before the intake bottom dead center, and in the predetermined operating region, the intake air flows out in the direction of weakening the swirl flow generated by the restart valve operation of the one exhaust port in the predetermined operating region. The spark ignition type four-cycle engine is characterized in that the intake valve and the exhaust valve are controlled so as to open only a plurality of intake ports on the high load side. The spark ignition type four-cycle engine according to claim 1,
The spark ignition type four-cycle engine characterized in that the valve opening / closing control means opens an intake valve adjacent to an exhaust valve performing a restart valve operation on a low load side in a predetermined operating region. The spark ignition type four-cycle engine according to claim 1 or 2,
Each intake port has a throat axis in the vicinity of the opening formed in parallel in a direction intersecting the front and rear axis of the cylinder in plan view, and the intake port opened on the low load side is: The exhaust port that is set to face in the direction close to the tangent in the left-right direction on the plane of the cylinder as it goes downstream of the throat axis line, and that performs the restart valve operation, is adjacent to this intake port on the left and right This is a spark ignition type 4-cycle engine. The spark ignition type four-cycle engine according to any one of claims 1 to 3,
Ignition control means for controlling the ignition timing of the ignition plug is provided, and the ignition control means controls the ignition plug so that ignition is executed before the ignition timing on the high load side in the predetermined operating region of the engine. A spark ignition type 4-cycle engine characterized by being a thing.

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