JP5589906B2 - gasoline engine - Google Patents

Description

  The present invention includes a cylinder having an intake port and an exhaust port formed therein, an intake valve capable of opening and closing the intake port, an exhaust valve capable of opening and closing the exhaust port, and a spark plug, and at least partially. The present invention relates to a gasoline engine in which a piston is reciprocated by burning an air-fuel mixture containing gasoline and air in a combustion chamber.

  Conventionally, in the gasoline engine field, a combustion mode in which an air-fuel mixture is forcibly ignited by spark discharge from an ignition plug has been common, but in recent years, instead of combustion by such spark ignition, so-called compression self-ignition Research is underway to apply combustion to gasoline engines. Compressed self-ignition combustion is a method in which an air-fuel mixture generated in a combustion chamber in a cylinder is compressed by a piston, and the air-fuel mixture is self-ignited regardless of spark ignition in a high-temperature and high-pressure environment. Compressed self-ignition combustion is combustion in which self-ignition occurs at various locations in the combustion chamber at the same time, and is said to have a shorter combustion period and higher thermal efficiency than combustion by spark ignition.

  Here, in order to stably realize the compression self-ignition combustion, it is necessary to more reliably increase the temperature in the cylinder. On the other hand, for example, in the engine disclosed in Patent Document 1 below, in some operation regions, the exhaust valve is opened from a predetermined time during the exhaust stroke to the vicinity of the exhaust top dead center, and in the intake stroke. By opening the exhaust valve again, the exhaust in the exhaust port is recirculated to the cylinder to increase the internal EGR amount in the cylinder, thereby increasing the temperature in the cylinder.

JP 2007-85241 A

  The demand for improving the fuel efficiency of the engine is still high, and in addition to the realization of compression self-ignition combustion with high thermal efficiency as described above, reduction of pump loss is desired.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gasoline engine that can appropriately perform compression self-ignition combustion and reduce pump loss.

In order to solve the above problems, the present invention provides a cylinder in which an intake port and an exhaust port are formed, and an intake valve capable of opening and closing the intake port and an exhaust valve capable of opening and closing the exhaust port are provided. The piston is reciprocated by burning a mixture of fuel and air containing gasoline at least partially in the combustion chamber of the cylinder, and compressed in at least a part of a specific operation region of the engine operation region. A gasoline engine that performs self-ignition combustion, wherein in all operating regions of the engine, first exhaust valve driving means that drives the exhaust valve so that the exhaust valve opens during an exhaust stroke; and the exhaust valve The exhaust valve is driven so as to open during the intake stroke, and only in a limited region of the specific operation region. And a second exhaust valve driving means for opening driving the exhaust valve during the intake stroke, the first exhaust valve driving means and the second exhaust valve driving means drives the common exhaust valve, the first exhaust valve A maximum lift amount in the ramp portion on the valve closing side of the first valve lift curve, which is a valve lift curve of the exhaust valve when the exhaust valve is driven only by the driving means, and the exhaust valve only by the second exhaust valve driving means. The maximum lift amount in the ramp portion on the valve opening side of the second valve lift curve, which is the valve lift curve of the exhaust valve when the valve is driven, is the maximum in the ramp portion on the valve opening side of the first valve lift curve. to be greater than the maximum lift amount in the lamp unit of the lift amount and valve-closing side of the second valve lift curves, drives the exhaust valve, in the limited region, said first exhaust valve driving means The exhaust valve is closed at a timing retarded from the exhaust top dead center, and the second exhaust valve driving means starts opening the exhaust valve at a timing advanced from the exhaust top dead center. The first lift curve and the second lift curve are crossed so that the exhaust valve is continuously operated from a timing that is advanced from the exhaust top dead center to a timing that is retarded from the exhaust top dead center. And the ramp portion on the valve closing side of the first valve lift curve intersects the ramp portion on the valve opening side of the second valve lift curve in the limited region and at this intersection. The lift amount of the exhaust valve is larger than the maximum lift amount of the ramp portion on the valve opening side of the first valve lift curve and the maximum lift amount of the ramp portion on the valve closing side of the second valve lift curve. The exhaust valve is driven (claim) Item 1).

  According to the present invention, the exhaust valve is configured to open not only during the exhaust stroke but also during the intake stroke only in the limited region. Therefore, the internal EGR amount can be appropriately suppressed in other regions while the internal EGR amount is sufficiently secured in the limited region, and the internal EGR amount can be made appropriate in all regions. In particular, compression self-ignition combustion is performed in the limited region. Therefore, in this limited region, the amount of internal EGR is sufficiently ensured and the air-fuel mixture is brought to a high temperature, so that proper compression self-ignition combustion can be realized. In addition, in the limited region, the exhaust valve is continuously driven to open from the advance side to the retard side with the exhaust top dead center in between. Therefore, the pump loss, which is a resistance generated when the piston descends after exhaust top dead center, is suppressed to a low level. This further increases fuel efficiency.

In this configuration, the same exhaust valve is switched between when the first exhaust valve driving means opens only in the exhaust stroke and when the second exhaust valve driving means opens in the exhaust stroke and intake stroke. It is configured to be Therefore, for example, the number of exhaust valves can be reduced as compared with a case where an exhaust valve that opens only in the exhaust stroke and an exhaust valve that opens in the exhaust stroke and the intake stroke are provided separately. Alternatively, in the case where a plurality of exhaust valves are provided, the exhaust valves that are opened only in the exhaust stroke and the exhaust valves that are opened in the exhaust stroke and the intake stroke are provided separately in the exhaust stroke. By opening all the exhaust valves, the opening amount of the exhaust valves can be increased to improve the scavenging performance.

The lift amount of the exhaust valve at the timing when the valve lift curves intersect is the maximum lift amount of the ramp portion on the valve closing side of the second valve lift curve and the maximum lift amount of the ramp portion on the valve opening side of the first valve lift curve. It is larger than that and is sufficiently secured. Therefore, the internal EGR amount is sufficiently secured and the pump loss is sufficiently reduced.

  The ramp part on the closed side of the valve lift curve of the exhaust valve referred to here means that the valve lift acceleration changes rapidly (the negative amount of acceleration) in the valve lift curve part after the maximum lift amount. It means the part after the period when the value suddenly decreases. That is, the exhaust valve is configured so that the lift speed immediately before the seating becomes gentle so that the impact and sound when sitting on the valve seat become smaller, and the ramp portion has a gentle lift speed. Say part.

Further, where the valve opening side of the lamp part of the valve lift curve of the exhaust valve means, among the timing previous valve lift curve portion lift amount becomes maximum, the previous partial period in which the acceleration of the valve lift is increased abruptly Say. In other words, the exhaust valve is configured such that the lift speed immediately after leaving the seat is gentle so that the impact when the seat is separated from the valve seat becomes smaller, and the lift speed of the ramp portion becomes gentle. Say part.

  Here, when the same exhaust valve is switched by the first exhaust valve driving means and the second exhaust valve driving means, the speed change of the exhaust valve at the time of switching is small from the viewpoint of durability and noise. It is preferable that the movement of the exhaust valve does not change rapidly.

On the other hand, in the present invention , when the first valve lift curve and the second valve lift curve intersect, that is, when the exhaust valve drive source switches from the first exhaust valve drive means to the second exhaust valve drive means, Switching the exhaust valve so that it is positioned on the ramp portion on the valve opening side of the second valve lift curve (portion where the lift speed of the exhaust valve becomes gentle) and the ramp portion on the valve closing side of the first valve lift curve , that is, the switching change the lift speed of the timing Te smell exhaust valves are configured to be smaller. Therefore, a sudden change in the movement of the exhaust valve accompanying the switching is suppressed.
In the present invention, it is preferable that the first valve lift curve and the second valve lift curve intersect at an exhaust top dead center in the limited region (Claim 2).
In this way, the lift amount of the exhaust valve at the exhaust top dead center is increased and sufficiently secured. Therefore, the internal EGR amount is sufficiently secured and the pump loss is sufficiently reduced.

In this configuration, a constant lift portion in which the lift amount of the exhaust valve is constant for a predetermined period is provided in the valve opening side ramp portion of the second valve lift curve, and the first exhaust valve driving means and the second exhaust valve are provided. In the limited region, the valve driving means is configured so that the ramp portion on the valve closing side of the first valve lift curve and the constant lift portion of the ramp portion on the valve opening side of the second valve lift curve intersect each other. It is preferable to drive the exhaust valve (claim 3 ).

  By so doing, since the lift change of the exhaust valve driven by the second exhaust valve driving means is stopped at the switching time, the noise accompanying the switching and the load on the exhaust valve can be kept small.

As described above, according to the present invention, since the exhaust valve is continuously opened from the advance side to the retard side across the exhaust top dead center, the pump loss is suppressed to a small level. , at least part of a region of the confined area, after the exhaust valve is started opened by the second exhaust valve driving means, in the case of opening the intake valve, it is particularly effective (claim 4 ).

  That is, when the intake valve is opened after the second exhaust valve is opened in this way, the gas from the intake port side to the cylinder is lowered when the piston is lowered because the intake valve is not sufficiently opened at the exhaust top dead center. However, if the exhaust valve is opened as described above, the increase in pump loss can be reliably suppressed by the inflow of gas from the exhaust port.

  As described above, according to the present invention, it is possible to provide a gasoline engine capable of improving fuel efficiency by suppressing pump loss more reliably while realizing proper compression self-ignition combustion.

It is a figure showing the whole gasoline engine composition concerning one embodiment of the present invention. It is a block diagram which shows the control system of the said engine. It is a schematic sectional drawing for demonstrating the structure of the exhaust VVL. It is a figure which shows an example of the control map for selecting the combustion form according to the driving | running state of an engine. It is the figure which showed the valve lift curve of the exhaust valve at the time of driving with a normal exhaust cam. It is the figure which showed the valve lift curve of the exhaust valve at the time of driving with a sub exhaust cam. It is the figure which showed the valve lift curve of the exhaust valve at the time of driving with a normal exhaust cam and a sub exhaust cam.

(1) Overall Configuration of Engine FIG. 1 is a diagram showing an overall configuration of an engine according to an embodiment of the present invention. The engine shown in the figure is a reciprocating piston type multi-cylinder gasoline engine mounted on a vehicle as a power source for driving driving. An engine body 1 of this engine includes a cylinder block 3 having a plurality of cylinders 2 (only one of which is shown in the drawing) arranged in a direction orthogonal to the paper surface, and a cylinder head 4 provided on the upper surface of the cylinder block 3. And a piston 5 inserted in each cylinder 2 so as to be slidable back and forth. The fuel supplied to the engine body 1 is mainly composed of gasoline. The fuel only needs to have gasoline as a main component, and the contents thereof may be all gasoline, or may be gasoline containing ethanol (ethyl alcohol) or the like.

  The piston 5 is connected to the crankshaft 7 via a connecting rod 8. In response to the reciprocating motion of the piston 5, the crankshaft 7 rotates about its central axis.

  A combustion chamber 6 is formed above the piston 5. An intake port 9 and an exhaust port 10 are opened in the combustion chamber 6. The cylinder head 4 is provided with an intake valve 11 and an exhaust valve 12 for opening and closing the ports 9 and 10, respectively. The illustrated engine is a so-called double overhead camshaft (DOHC) engine. Two intake ports 9 and two exhaust ports 10 are provided for each cylinder, and two intake valves 11 and two exhaust valves 12 are also provided.

  Here, the “combustion chamber”, in a narrow sense, refers to a space formed above the piston 5 when it is at top dead center, but the combustion chamber 6 here refers to the upper and lower sides of the piston 5. It refers to the space formed above it regardless of position (combustion chamber in a broad sense).

  The intake valve 11 and the exhaust valve 12 are driven to open and close in conjunction with the rotation of the crankshaft 7 by valve mechanisms 13 and 14 including a pair of camshafts (not shown) disposed in the cylinder head 4. The

  A CVVL 15 is incorporated in the valve operating mechanism 13 for the intake valve 11. The CVVL 15 is called a continuously variable valve lift mechanism and continuously (steplessly) changes the lift amount of the intake valve 11. The CVVL 15 is provided so that the lift amounts of all the intake valves 11 of the engine can be changed. When the CVVL 15 is driven, the lift amounts of the pair of intake valves 11 in each cylinder 2 are changed simultaneously. It has become.

  The CVVL 15 having such a configuration is already known, and as a specific example thereof, a link mechanism that reciprocally swings the cam for driving the intake valve 11 in conjunction with the rotation of the camshaft, and the arrangement of the link mechanism (lever ratio). And a stepping motor that changes the swing amount of the cam (the amount by which the intake valve 11 is pushed down) by electrically driving the control arm (for example, JP, 2007-85241, A).

  The valve operating mechanism 14 for the exhaust valve 12 can open the exhaust valve 12 during the intake stroke in addition to the exhaust stroke, and enables or disables the function of opening the exhaust valve 12 during the intake stroke. A variable valve lift mechanism VVL16 that can be switched is incorporated. In the present embodiment, the VVL 16 is provided corresponding to all the exhaust valves 12 of the engine.

  The VVL 16 having such a configuration is already known, and examples thereof include those shown in FIG. 3 disclosed in Japanese Patent Application Laid-Open No. 2007-85241.

  The structure of the VVL 16 will be briefly described.

  The VVL 16 is provided on the camshaft to drive the exhaust valve 12 at different phases, and a pair of exhaust cams 62b and 62c, and a lost motion mechanism provided between the exhaust cams 62b and 62c and the exhaust valve 12. 70. One exhaust cam 62b is a cam (normal exhaust cam) for opening the exhaust valve 12 during the exhaust stroke, and forms a pair of two. The other exhaust cam 62c is a sub exhaust cam for opening the exhaust valve 12 during the intake stroke, and is disposed between the normal exhaust cams 62b. Of the VVL 16, the normal exhaust cam 62b functions as first exhaust valve driving means for driving the exhaust valve 12 to open during the exhaust stroke. Of the VVL 16, the sub exhaust cam 62c functions as second exhaust valve driving means for driving the exhaust valve 12 to open during the intake stroke.

  The lost motion mechanism 70 enables or disables transmission of the driving force of the sub exhaust cam 62c to the exhaust valve 12. The lost motion mechanism 70 includes a pin unit 78 that can integrally connect the sub exhaust cam 62c and the normal exhaust cam 62b to lock the sub exhaust cam 62c to the normal exhaust cam 62b. When the hydraulic oil is supplied to the hydraulic oil passage PH formed in the lost motion mechanism 70, the pin unit 78 moves from the position where the respective cams are locked to the position where the lock is released, thereby releasing the connection. To do.

  In the state where the hydraulic oil is not supplied to the hydraulic oil passage PH and the sub exhaust cam 62c and the normal exhaust cam 62b are integrally connected by the pin unit 78, the exhaust valve 12 is moved by the normal exhaust cam 62b. The valve is pushed down to open during the exhaust stroke, and is pushed down by the sub exhaust cam 62c to open during the intake stroke. On the other hand, in a state where hydraulic oil is supplied to the hydraulic oil passage PH and the connection by the pin unit 78 is released, the push-down force of the sub exhaust cam 62c is not transmitted to the exhaust valve 12, and the exhaust valve 12 And is opened only during the exhaust stroke.

  Supply and stop of the working oil to the working oil passage PH are switched by opening and closing an electromagnetic valve provided in a working oil circuit that supplies the working oil to the working oil pressure PH. This solenoid valve opens and closes in response to a command from the ECU 50.

  In the present invention, the exhaust valve 12 is opened during the exhaust stroke because the exhaust valve 12 is opened mainly during the exhaust stroke, that is, the time when the exhaust valve 12 reaches the maximum lift is during the exhaust stroke. In addition to the case where the exhaust valve 12 starts opening and closing during the exhaust stroke, the case where the exhaust valve 12 starts opening during the expansion stroke and the case where it closes during the intake stroke are included. Similarly, when the exhaust valve 12 opens during the intake stroke, the exhaust valve 12 opens mainly during the intake stroke, and the time when the exhaust valve 12 reaches the maximum lift is during the intake stroke. That is, in addition to the case where the exhaust valve 12 starts opening and closing in the intake stroke, the case where the exhaust valve 12 starts opening in the exhaust stroke and the case where the exhaust valve 12 closes in the compression stroke are included. In the present embodiment, as will be described later, the normal exhaust cam 62b closes the exhaust valve 12 on the retard side from the exhaust top dead center TDC when the exhaust valve 12 is opened and closed by itself. When the sub exhaust cam 62c opens and closes the exhaust valve 12 only by itself, the sub exhaust cam 62c starts opening the exhaust valve 12 on the advance side from the exhaust top dead center TDC. The normal exhaust cam 62b starts to open the exhaust valve 12 near the exhaust bottom dead center BDC. The sub exhaust cam 62c closes the exhaust valve 12 near the intake bottom dead center BDC.

  In the normal exhaust cam 62b, when the exhaust valve 12 is opened only by the normal exhaust cam 62b, the valve lift curve of the exhaust valve 12 (the valve lift curve of the normal cam) is h1 in FIGS. It is comprised so that it may become a shape as shown in. The normal valve lift curve h1 is set such that the maximum lift amount h1_c of the lamp portion L1_c on the valve closing side is larger than the maximum lift amount h1_o of the lamp portion L1_o on the valve opening side.

  When the exhaust valve 12 is opened only by the sub exhaust cam 62c, the sub exhaust cam 62c has the valve lift curve of the exhaust valve 12 (the valve lift curve of the sub exhaust cam 62c) shown in FIGS. It is configured to have a shape as shown in h2. The valve lift curve h2 of the sub exhaust cam 62c is such that the ramp portion L2_o on the valve opening side is continuous to the constant speed ramp portion L2_o1 where the exhaust valve 12 lifts at a constant speed greater than 0, and the constant speed ramp portion L2_o1. And a constant lift ramp portion L2_o2 in which the valve lift speed is zero for a predetermined period and the lift amount is kept constant. In other words, if the exhaust valve 12 is only driven by the sub exhaust cam 62c, after the valve is opened, the exhaust valve 12 is lifted at a constant speed for a predetermined period, then held at the lift amount for a predetermined period, and then accelerated and lifted. . Further, the valve lift curve h2 of the sub exhaust cam 62c is set so that the maximum lift amount h2_o of the valve-opening side ramp portion L2_o is larger than the maximum lift amount h2_c of the valve-closing side ramp portion L2_c.

  The ramp portion on the valve opening side is a portion for a while after the exhaust valve is separated from the valve seat, and the lift speed before the time when the acceleration of the valve lift suddenly increases is gentle. Part. The ramp part on the valve closing side is the part immediately before the exhaust valve is seated on the valve seat, and the lift speed after the period when the acceleration of the valve lift changes suddenly (the negative amount of acceleration decreases sharply) Is a gentle part. In the present embodiment, the lift speed of the exhaust valve 12 is substantially constant in the ramp portion L1_o on the valve opening side and the ramp portion L1_c on the valve closing side of the valve lift curve h1. In the ramp portion L2_c on the valve closing side of the valve lift curve h2, the lift speed of the exhaust valve 12 is substantially constant.

  As shown in FIG. 7, the normal exhaust cam 62b and the sub exhaust cam 62c are configured such that the normal valve lift curve h1 and the valve lift curve h2 of the sub exhaust cam 62c intersect each other in the vicinity of the exhaust top dead center TDC. The exhaust valve 12 is opened and closed. In this embodiment, these valve lift curves h1 and h2 intersect at the exhaust top dead center TDC. That is, the normal exhaust cam 62b closes the exhaust valve 12 on the retard side with respect to the exhaust top dead center TDC when the exhaust valve 12 is opened and closed by itself. When the sub exhaust cam 62c opens and closes the exhaust valve 12 only by itself, the sub exhaust cam 62c starts opening the exhaust valve 12 on the advance side from the exhaust top dead center TDC.

  Further, the normal exhaust cam 62b and the sub exhaust cam 62c are arranged such that the exhaust valve 12 is closed when the valve lift curves h1 and h2 intersect (at the exhaust top dead center TDC). On the side of the ramp portion L1_c, on the point where the lift amount of the exhaust valve 12 is larger than the maximum lift amount h1_o of the ramp portion L1_o on the valve opening side of the valve lift curve h1 of the normal cam, and the exhaust valve 12 is positioned on the lamp portion L2_o on the valve opening side of the valve lift curve h2 of the sub exhaust cam 62c (more specifically, on the constant lift ramp portion L2_o2). As described above, the lift amount h2_o of the constant lift ramp portion L2_o2 is set larger than the maximum lift amount h2_c of the ramp portion L2_c on the valve closing side of the valve lift curve h2 of the sub exhaust cam 62c. Accordingly, when the valve lift curves h1 and h2 intersect, the lift amount of the exhaust valve 12 is the maximum lift amount h1_o of the ramp portion L1_o on the valve opening side of the valve lift curve h1 of the normal cam and the valve lift of the sub exhaust cam 62c. It becomes larger than the maximum lift amount h2_c of the ramp portion L2_c on the valve closing side of the curve h2.

  In the VVL 16 configured as described above, when the hydraulic oil is not supplied to the hydraulic oil path PH and the sub exhaust cam 62c and the normal exhaust cam 62b are integrally connected by the pin unit 78, first, The normal exhaust cam 62b starts to open the exhaust valve 12 near the exhaust bottom dead center BDC. Thereafter, the exhaust valve 12 is driven in the direction in which the lift amount increases by the normal exhaust cam 62b, and after reaching the maximum lift amount, the exhaust valve 12 is driven in the direction in which the lift amount decreases by the normal exhaust cam 62b. At the intersection of the valve lift curves h1 and h2 at the exhaust top dead center TDC, the drive source of the exhaust valve 12 is switched from the normal exhaust cam 62b to the sub exhaust cam 62c, and the sub exhaust cam 62c is connected to the exhaust valve. 12 is continuously opened. By the sub exhaust cam 62c, the exhaust valve 12 is maintained in a constant lift amount for a while from the exhaust top dead center TDC, and then driven in a direction in which the lift amount increases again in the intake stroke. Is driven in a decreasing direction. In the present embodiment, the exhaust valve 12 is closed after the intake bottom dead center BDC.

  As described above, when the valve lift curves h1 and h2 intersect, that is, when the drive source of the exhaust valve 12 is switched from the normal exhaust cam 62b to the sub exhaust cam 62c, the exhaust valve 12 is connected to the normal cam 62b. The valve lift curve h1 is located on the valve closing side L1_c of the valve lift curve h1 and on the constant lift ramp portion L2_o2 of the valve lift curve h2 of the sub exhaust cam 62c62c. For this reason, at the time of the switching, the exhaust valve 12 is temporarily maintained at a constant lift without being switched from the operation in the direction in which the lift amount decreases to the operation in the direction in which the immediate lift amount increases, and then the lift amount increases. Move to the movement of the direction. Thus, in this embodiment, the speed change of the exhaust valve 12 at the time of the switching is suppressed to be small, and noise and scavenging deterioration of the exhaust valve 12 and the like are suppressed.

  On the other hand, in a state where hydraulic oil is supplied to the hydraulic oil path PH and the connection between the sub exhaust cam 62c and the normal exhaust cam 62b by the pin unit 78 is released, the exhaust valve 12 is driven only by driving the normal exhaust cam. As shown in FIG. 5, the exhaust valve 12 starts to open near the exhaust bottom dead center BDC, and then closes at a predetermined timing that is retarded from the exhaust top dead center TDC.

  When the exhaust valve 12 is opened during the intake stroke in addition to during the exhaust stroke due to the action of the VVL 16, the high-temperature exhaust flows back from the exhaust port 10 to the combustion chamber 6 during the exhaust stroke, and the combustion chamber 6 A large amount of exhaust remains. That is, a large amount of internal EGR gas is secured. On the other hand, when the exhaust valve 12 is opened only during the exhaust stroke, the internal EGR gas amount is suppressed to a small amount or not.

  Here, in the present embodiment, the timing when the exhaust valve 12 starts to open means that the lift amount of the exhaust valve 12 is a predetermined lift amount, and between the exhaust port 10 and the combustion chamber 6 via the exhaust valve 12. The time when an effective exhaust flow occurs. The exhaust valve 12 is closed when the lift amount of the exhaust valve 12 is a predetermined lift amount, and an effective exhaust flow between the exhaust port 10 and the combustion chamber 6 via the exhaust valve 12. The time when there is no. The predetermined lift amount is, for example, 0.4 mm.

  The maximum lift amount h1_o of the ramp portion L1_o on the valve opening side of the normal valve lift curve h1 and the maximum lift amount h2_c of the ramp portion L2_c on the valve closing side of the sub valve lift curve h2 are set to 0.4 mm, for example. The predetermined lift amount is set. Therefore, as described above, in the present embodiment in which the lift amount of the exhaust valve 12 is equal to or greater than the maximum lift amounts h1_o, h2_c when the valve lift curves h1 and h2 intersect, the effective amount at the intersection is obtained. Exhaust gas flows into the combustion chamber 6 from the exhaust port 10 via the exhaust valve 12. For example, the lift amount of the exhaust valve 12 when the valve lift curves h1 and h2 intersect, and hence the lift amount h2_o2 of the constant lift ramp portion L2_o2, is set to 1 mm. Further, the maximum lift amount h1_c of the ramp portion L1_c on the valve closing side of the normal valve lift curve h1 is set to 1 mm.

  Returning to FIG. 1 again, the cylinder head 4 of the engine body 1 is provided with one set of spark plugs 20 and injectors 21 for each cylinder 2.

  The injector 21 is provided so as to face the combustion chamber 6 from the ceiling surface (the lower surface of the cylinder head 4 covering the combustion chamber 6). The injector 21 injects fuel mainly composed of gasoline supplied through the fuel supply pipe 23 into the combustion chamber 6 from its tip.

  The spark plug 20 is disposed adjacent to the injector 21 so as to face the combustion chamber 6 from above. The spark plug 20 discharges a spark from the tip in response to power supply from an ignition circuit (not shown).

  An intake passage 28 and an exhaust passage 29 are connected to the intake port 9 and the exhaust port 10 of the engine body 1, respectively.

  The intake passage 28 is provided with a common passage portion 28c composed of a single passage, a surge tank 28b provided at an upstream end portion of the common passage portion 28c, and branched for each cylinder 2. The surge tank 28b And a branch passage portion 28 a that connects the intake port 9 of each cylinder 2.

  The exhaust passage 29 is provided for each cylinder 2 by branching to a common passage portion 29c composed of a single passage, and connects the upstream end of the common passage portion 29c and the exhaust port 10 of each cylinder 2. And a branch passage portion 29a.

  An external EGR device 30 is provided between the intake passage 28 and the exhaust passage 29 to recirculate a part of the exhaust gas passing through the exhaust passage 29 to the intake passage 28. The external EGR device 30 is provided with an EGR passage 31 communicating with the common passage portions 28c and 29c of the intake passage 28 and the exhaust passage 29 and a flow rate of exhaust gas that is provided in the middle of the EGR passage 31 and passes through the EGR passage 31. An EGR valve 32 to be controlled and a water-cooled EGR cooler 33 for cooling the exhaust gas passing through the EGR passage 31 are provided.

  A throttle valve 25 for adjusting the amount of intake air passing through the intake passage 28 is provided in the common passage portion 28 c of the intake passage 28. However, in this embodiment, the lift amount of the intake valve 11 is adjusted by the CVVL 15, the amount of internal EGR gas in the combustion chamber 6 is adjusted by the VVL 16, and further, the return to the intake passage 28 is returned by the external EGR device 30. The amount of exhaust gas is adjusted. Therefore, it is possible to adjust the amount of air (fresh air) introduced into the combustion chamber 6 without operating the throttle valve 25 based on these operations. For this reason, the throttle valve 25 is kept fully open or close to it except when the engine is stopped.

  A catalyst converter 35 for purifying exhaust gas is provided in the common passage portion 29 c of the exhaust passage 29. For example, a three-way catalyst is incorporated in the catalytic converter 35, and harmful components in the exhaust gas passing through the exhaust passage 29 are purified by the action of the three-way catalyst.

  Various sensors are attached to the engine body. For example, a water temperature sensor SW1 for detecting the temperature of the engine coolant, a rotation angle (crank angle) of the crankshaft 7, and a crank angle sensor SW2 for detecting the engine speed, and the camshaft angle are detected to detect the cylinder temperature. A cam angle sensor SW3 that outputs a signal for determination (determination of whether each cylinder is in an intake stroke, compression stroke, expansion stroke, or exhaust stroke) is attached to the engine body.

(2) Control System FIG. 2 is a block diagram showing an engine control system. The ECU 50 shown in the figure is a device for comprehensively controlling each part of the engine, and includes a well-known CPU, ROM, RAM, and the like.

  Various information is input to the ECU 50 from various sensors such as the water temperature sensor SW1, the crank angle sensor SW2, and the cam angle sensor SW3 provided in the engine body. The ECU 50 also receives information from various sensors provided in the vehicle. For example, information on the accelerator opening is input to the ECU 50 from an accelerator opening sensor SW4 that detects the opening of an accelerator pedal (not shown) that is depressed by the driver.

  The ECU 50 includes a determination unit 51, an injector control unit 52, an intake control unit 53, an internal EGR control unit 54, an external EGR control unit 55, and an ignition control unit 56 as main functional elements.

  Based on the engine speed Ne and the load T (target torque) specified from the detected values of the crank angle sensor SW2 and the accelerator opening sensor SW4, the determination means 51 determines whether the current engine operating range is as shown in FIG. It is determined which operating region is in the control map.

  Specifically, in the control map of FIG. 4, the first operation region (limited region) A <b> 1 is set in the region where the load T is relatively low over the entire rotational speed region. In addition, the second operation region A2 is set in a region where the load T is higher than the first operation region A1. The control map composed of the first and second operation areas A1 and A2 is for a warm state where the coolant temperature detected by the engine coolant temperature sensor SW1 is equal to or higher than a predetermined value (for example, 80 ° C.). The description of the control map when the engine is in a cold state is omitted here.

  The injector control means 52 controls the amount and timing of fuel injected from the injector 21 into the combustion chamber 6. Specifically, the injector control means 52 calculates a target fuel injection amount and injection timing based on the load T, the engine speed Ne, and the like, and drives the injector 21 based on the calculation result.

  The intake control means 53 drives the CVVL 15 to change the lift amount (valve opening amount) of the intake valve 11. For example, the intake control means 53 increases the lift amount of the intake valve 11 to introduce a large amount of air (fresh air) into the combustion chamber 6 when the engine load T is high. On the other hand, the intake control means 53 reduces the lift amount of the intake valve 11 when the engine load T is low. Further, the intake control means 53 drives the intake valve 11 so that the valve opening start timing of the intake valve 11 advances as the engine speed Ne increases in order to secure a fresh air amount.

  The internal EGR control means 54 opens and closes the solenoid valve to switch between supply and stop of hydraulic fluid to the hydraulic fluid passage PH of the VVL 16 to connect and disconnect the sub exhaust cam 62c and the normal exhaust cam 62b. Thus, the internal EGR gas amount is adjusted by switching between the execution and stop of the valve opening during the intake stroke of the exhaust valve 12.

  The external EGR control means 55 adjusts the amount of exhaust gas recirculated from the exhaust passage 29 to the intake passage 28, that is, the amount of external EGR, by changing the opening degree of the EGR valve 32 provided in the EGR passage 31.

  The ignition control means 56 controls the timing (ignition timing) at which the spark plug 20 performs spark discharge. However, in this embodiment, as will be described later, in any of the first and second operation regions A1 and A2 shown in FIG. 4, a combustion mode (compressed self-ignition combustion) that self-ignites the air-fuel mixture regardless of spark ignition. ) Is selected. Therefore, the ignition control means 56 stops spark ignition from the spark plug 20 at least when the engine is warm. The ignition control means 56 sets the spark plug 20 only when it is difficult to self-ignite the air-fuel mixture (for example, when forced combustion by spark ignition is necessary), such as when the engine is started or when it is operated in a cold state. Operate.

(3) Specific control procedure for each operation region Next, the control performed by the ECU 50 in the first operation region A1 and the second operation region A2 will be specifically described.

  First, when the engine is started, the ECU 50 displays the engine operating point (load T and rotational speed Ne) based on the detected values of the crank angle sensor SW2 and the accelerator opening sensor SW4. It is sequentially determined which operation region corresponds to the control map of No. 4. Then, the following control is executed depending on whether the determined operation region is the first operation region A1 or the second operation region A2 in FIG. 4.

  As a premise of this explanation, it is assumed that the engine coolant temperature is sufficiently warm (that is, the engine is warm). In the present embodiment, the ECU 50 performs control so that compression self-ignition combustion is realized even when the operating point of the engine is in any of the operating regions A1 and A2 during the warm period. That is, the entire engine operation region is set as a specific region in which compression self-ignition combustion is performed. However, in order to perform appropriate compression self-ignition combustion, it is necessary to change the fuel injection timing from the injector 21 and the presence or absence of internal EGR or external EGR depending on the operation regions A1 and A2. Therefore, the ECU 50 controls the injector 21, CVVL15, VVL16, EGR valve 32, and the like while sequentially determining the operating point of the engine.

(I) 1st operation area A1
In the first operation region A1, general premixed compression self-ignition combustion is performed in which a mixture of fuel and air injected before the compression stroke is self-ignited by the compression action of the piston 5. Specifically, in the first operation region A1, fuel is injected from the injector 21 into the combustion chamber 6 at a predetermined time during the intake stroke, and the fuel injected by this fuel injection is introduced into the combustion chamber 6 from the intake passage 28. The air-fuel mixture with the air (fresh air) is increased in temperature and pressure by the compression action of the piston 5, and self-ignites near the compression top dead center (TDC between the compression stroke and the expansion stroke).

  Here, in the first operation region A1, since the load T is relatively low and the amount of fuel injected from the injector 21 is small, misfire may occur unless the in-cylinder temperature is intentionally increased. Therefore, in the first operating region A1, the solenoid valve is driven to open and hydraulic oil is supplied to the hydraulic fluid passage PH of the VVL 16 to connect the sub exhaust cam 62c and the normal exhaust cam 62b. The valve 12 is continuously opened in the exhaust stroke and the intake stroke with the exhaust top dead center TDC interposed therebetween. Then, a large amount of hot exhaust gas in the exhaust port 10 flows back to the combustion chamber 6 to increase the amount of internal EGR in the combustion chamber 6. Thus, when a large amount of high-temperature internal EGR gas is ensured, the temperature of the air-fuel mixture in the combustion chamber 6 becomes high, and self-ignition of the air-fuel mixture is promoted.

  Here, when the exhaust valve 12 is closed after the exhaust top dead center TDC, the pressure in the combustion chamber 6 decreases as the piston 5 decreases, so that work for lowering the piston 5 is required. And pump loss occurs. On the other hand, in the present embodiment, as described above, the exhaust valve 12 is continuously opened in the exhaust stroke and the intake stroke with the exhaust top dead center TDC interposed therebetween. Therefore, since exhaust flows into the combustion chamber 6 from the exhaust port as the piston is lowered, the effect of suppressing the pump loss can be obtained in addition to the effect that the amount of internal EGR gas can be sufficiently secured. it can.

  As described above, in the first operation region A1, the external EGR is stopped as the internal EGR gas amount is increased. That is, the recirculation of the exhaust gas from the exhaust passage 29 to the intake passage 28 is stopped by setting the opening degree of the EGR valve 32 provided in the EGR passage 31 to be fully closed.

  In the first operation region A1, the excess air ratio λ, which is a value obtained by dividing the air-fuel ratio (actual air-fuel ratio) of the air-fuel mixture in the combustion chamber 6 by the theoretical air-fuel ratio (14.7), is about 2-2. It is set to a significantly lean value of about .4. Therefore, control for increasing or decreasing the lift amount of the intake valve 11 (valve lift curve IN) is executed by driving the CVVL 15, and the amount of fresh air introduced into the combustion chamber 6 is considerably larger than the fuel injection amount from the injector 21. Controlled to be excessive. Specifically, in the first operation region A1, the intake valve 11 is opened during the intake stroke, and is controlled to advance as the engine speed decreases. Note that the closing timing of the intake valve 11 is controlled to be constant.

  In this way, when the air-fuel mixture set to be significantly lean is burned, the combustion temperature is greatly lowered, so that the cooling loss can be reduced and the thermal efficiency (fuel consumption) can be improved. Note that when λ = 2 to 2.4, the NOx purification action by the three-way catalyst can hardly be expected. However, if λ = 2 to 2.4, the amount of NOx produced by combustion (raw NOx amount) ) Is greatly reduced, the amount of NOx contained in the exhaust gas can be suppressed to a sufficiently small value without providing a special catalyst (for example, a NOx trap catalyst) in addition to the three-way catalyst.

  Further, as described above, in the low speed region of the first operating region A1, the intake valve 11 is opened on the relatively retarded angle side after the exhaust top dead center TDC. Therefore, when the exhaust valve 12 is closed near the exhaust top dead center TDC, the amount of negative pressure in the combustion chamber 6 increases and the pump loss increases. However, in this embodiment, the pump loss can be suppressed to a low level. it can.

(Ii) Second operation area A2
In the second operation region A2 in which the load T is higher than the first operation region A1 and the rotation speed Ne is set to a relatively low region, fuel is supplied from the injector 21 in multiple times with the compression top dead center in between. The divided injection to be injected is executed, and the mixture of the injected fuel and fresh air self-ignites over a relatively long time. In the second operation region A2 where the fuel injection amount is large, if the fuel is injected at a time, the in-cylinder pressure rapidly increases due to a rapid combustion in which all of the injected large amount of fuel burns in a short time. In addition, the combustion noise may increase significantly. Therefore, in the present embodiment, by dividing and injecting fuel as described above and combusting each fuel in different spaces, relatively mild combustion continuously occurs, so that the combustion noise as described above is reduced. The increase is avoided.

  Here, in the second operation region A2, the engine load T is high and the total amount of injected fuel is large. Therefore, the amount of heat generated with combustion increases, and the combustion chamber 6 tends to have a high temperature. For this reason, if the internal EGR amount is increased even in the second operation region A2, the combustion chamber 6 may become increasingly hot and abnormal combustion such as pre-ignition or knocking may occur. Therefore, in the second operation region A2, control for switching from the internal EGR to the external EGR is performed in order to prevent an excessively high temperature of the combustion chamber 6 and to avoid abnormal combustion as described above. Specifically, the solenoid valve is driven to open, the supply of hydraulic oil to the hydraulic fluid path PH of the VVL 16 is stopped, and the connection between the sub exhaust cam 62c and the normal exhaust cam 62b is released. The exhaust valve 12 is opened only during the exhaust stroke, and internal EGR is prohibited. On the other hand, the EGR valve 32 provided in the EGR passage 31 is opened to a predetermined opening, and an operation of recirculating the exhaust gas from the exhaust passage 29 to the intake passage 28 is executed. As a result, the exhaust gas that has passed through the EGR passage 31 with the EGR cooler 33 (that is, cooled by the EGR cooler 33) recirculates to the intake passage 28 and is contained in the mixture while the temperature in the combustion chamber 6 is kept low. The amount of EGR gas that is an inert gas is ensured.

  In addition, the CVVL 15 is driven to increase the lift amount of the intake valve 11 in order to introduce a large amount of fresh air corresponding to the fuel injection amount set to increase in this way into the combustion chamber 6.

In the second operation region A2, the mixture of fuel and fresh air injected at each timing is locally λ == locally so that the harmful components can be sufficiently purified only by the three-way catalyst. The excess air ratio is set to about 1.
(4) Operational Effect According to the gasoline engine according to this embodiment configured as described above, the exhaust valve 12 is configured to open during the intake stroke in addition to during the exhaust stroke. Therefore, in the first operation region A1 where internal EGR is required, the exhaust valve 12 opens during the intake stroke in addition to during the exhaust stroke, so that a sufficient amount of internal EGR gas can be secured and the internal EGR can be secured. Since the exhaust valve 12 is opened only during the exhaust stroke in the second operation region A2 that does not require the internal EGR gas, the amount of internal EGR gas can be reduced, and appropriate combustion can be achieved in each operation region. Moreover, the exhaust valve 12 is continuously opened from the advance side to the retard side with the exhaust top dead center TDC interposed therebetween. For this reason, the internal EGR amount is sufficiently ensured to realize proper compression self-ignition combustion, and the pump loss is suppressed to be small, so that the fuel efficiency is improved.

  Here, in the present embodiment, compression self-ignition combustion is performed in the entire engine operation region at the warm time, and the exhaust valve 12 is in the intake stroke in addition to the exhaust stroke on the low load side and the high load side. However, the present invention is not limited to this, and the present invention is not limited to this, and compression self-ignition combustion that requires a large amount of internal EGR gas is performed in a part of the engine operation region. In addition, the present invention can be applied to a gasoline engine configured to keep the internal EGR gas amount small in at least some other regions, and the fuel efficiency improvement effect can be obtained in such a gasoline engine as a whole.

Also, normal valve closing side of the lamp unit the maximum lift amount h1_c of L1_c the valve lift curve h1 is set larger than the maximum lift amount h1_o the opening side of the lamp unit L1_o, of the valve-closing side ramp portion L1_c Of these, the valve lift curve h2 of the sub exhaust cam 62c62c intersects with the valve lift curve h2 of the sub exhaust cam 62c62c at a timing larger than the maximum lift amount h1_o of the lamp portion L1_o on the valve opening side. It is possible to secure the internal EGR gas amount by securing it and to suppress a rapid change in the speed of the exhaust valve 12.

Similarly, the maximum lift amount h2_o of the lamp portion L2_o on the valve opening side of the valve lift curve h2 of the sub exhaust cam 62c is set to be larger than the maximum lift amount h2_c of the lamp portion L2_c on the valve closing side. Since it intersects with the normal valve lift curve h1 at a timing larger than the maximum lift amount h2_c of the valve-side ramp portion L2_c among the valve-side ramp portions L2_o, the lift amount of the exhaust valve 12 before and after this intersection. Can be secured sufficiently to secure the amount of internal EGR gas, and a rapid change in the speed of the exhaust valve 12 can be suppressed. In particular, as in the above-described embodiment, the constant lift ramp portion L2_o2 in which the lift amount is maintained constant is provided in the ramp portion L2_o on the valve opening side of the valve lift curve h2 of the sub exhaust cam 62c. If the portion L2_o2 and the normal valve lift curve h1 intersect, the amount of change in the speed of the exhaust valve 12 can be further reduced.

  Further, the intersection timing of the valve lift curve h1 of the normal exhaust cam 62b and the valve lift curve h2 of the sub exhaust cam 62c is not limited to the exhaust top dead center TDC.

5 Piston 6 Combustion chamber 12 Exhaust valve 62b Normal exhaust cam (first exhaust valve drive means)
62c Sub exhaust cam (second exhaust valve drive means)
h1 1st valve lift curve h2 2nd valve lift curve A1 1st operation area (limited area, specific operation area)
A2 Second operation area (specific operation area)

Claims (4)

Fuel and air containing at least partially gasoline and having an intake port and an exhaust port, and a cylinder provided with an intake valve capable of opening and closing the intake port and an exhaust valve capable of opening and closing the exhaust port A gas engine that reciprocates the piston by combusting the air-fuel mixture in the combustion chamber of the cylinder and performs compression self-ignition combustion in at least a specific operation region of the engine operation region,
First exhaust valve driving means for driving the exhaust valve so that the exhaust valve is opened during the exhaust stroke in the entire operation region of the engine;
A second exhaust valve that drives the exhaust valve so that the exhaust valve opens during the intake stroke, and that opens the exhaust valve during the intake stroke only in at least a limited region of the specific operation region. Driving means,
The first exhaust valve driving means and the second exhaust valve driving means are:
Drive a common exhaust valve,
The maximum lift amount in the lamp portion on the valve closing side of the first valve lift curve, which is the valve lift curve of the exhaust valve when the exhaust valve is driven only by the first exhaust valve drive means, and the second exhaust valve drive means The maximum lift amount at the ramp portion on the valve opening side of the second valve lift curve which is the valve lift curve of the exhaust valve when the exhaust valve is driven alone is the valve opening side of the first valve lift curve. Driving the exhaust valve to be larger than the maximum lift amount in the ramp portion and the maximum lift amount in the ramp portion on the valve closing side of the second valve lift curve,
In the limited region , the first exhaust valve driving means closes the exhaust valve at a timing retarded from the exhaust top dead center, and the second exhaust valve driving means causes the exhaust valve to close from the exhaust top dead center. Also, by opening the valve at the advance timing, the first lift curve and the second lift curve are crossed so that the exhaust valve is exhausted from the advance timing with respect to the exhaust top dead center. The valve is continuously opened until the time behind the dead center ,
In the limited region, the exhaust valve lift at the intersection is such that the ramp portion on the valve closing side of the first valve lift curve intersects the ramp portion on the valve opening side of the second valve lift curve. The exhaust valve is driven so that the amount is larger than the maximum lift amount of the ramp portion on the valve opening side of the first valve lift curve and the maximum lift amount of the ramp portion on the valve closing side of the second valve lift curve. A gasoline engine characterized by The gasoline engine according to claim 1,
The gasoline engine according to claim 1, wherein the first valve lift curve and the second valve lift curve intersect at an exhaust top dead center in the limited region.   The gasoline engine according to claim 1 or 2,
  A constant lift portion in which the lift amount of the exhaust valve is constant for a predetermined period is provided on the valve opening side ramp portion of the second valve lift curve,
  The first exhaust valve driving means and the second exhaust valve driving means are:
  The exhaust valve is driven so that the ramp portion on the valve closing side of the first valve lift curve intersects the constant lift portion of the ramp portion on the valve opening side of the second valve lift curve in the limited region. A gasoline engine characterized by that. The gasoline engine according to any one of claims 1 to 3,
  Intake valve drive means for driving the intake valve,
  The intake valve driving means opens the intake valve after the exhaust valve is started to open by the second exhaust valve driving means in at least a part of the limited area. engine.

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