Engine system

Abstract

To reliably improve fuel consumption while restraining a torque shock.SOLUTION: A system comprises a main combustion chamber, an auxiliary chamber, a fuel injection device for injecting fuel to the main combustion chamber, a main ignition device for igniting air-fuel mixture in the main combustion chamber, and an auxiliary ignition device for igniting air-fuel mixture. In a first area, the air-fuel mixture is compression self-ignition combusted, and in a second area, the air-fuel mixture is flame propagation combusted, so as to make an air-fuel rate of the air-fuel mixture lower than the air-fuel rate of the first area. Immediately after it is shifted from the first area to the second area, only the auxiliary ignition is executed, or the auxiliary ignition and the main ignition are executed, and timing of the main ignition is set to the same or slightly later timing of the auxiliary ignition.SELECTED DRAWING: Figure 9

Description

Technical Field

[0001] The present invention relates to an engine system including a main combustion chamber and an auxiliary chamber.

Background Art

[0002] Conventionally, in an engine mounted on a vehicle or the like, in order to improve its fuel consumption performance and exhaust gas performance, it has been studied to provide a main combustion chamber and an auxiliary chamber communicating therewith. Specifically, by providing a main combustion chamber and an auxiliary chamber communicating therewith and ejecting the flame generated in the auxiliary chamber into the main combustion chamber, the combustion speed in the main combustion chamber can be increased to improve the fuel consumption performance, and the residual of unburned air-fuel mixture can be suppressed to improve the exhaust gas performance.

[0003] For example, Patent Document 1 discloses an engine including a main combustion chamber (main chamber in Patent Document 1) partitioned by a cylinder block, a cylinder head, and a piston, an auxiliary chamber communicating therewith, a main fuel injection valve provided in an intake port for supplying fuel to the main combustion chamber through the intake port, a main chamber ignition plug for igniting the air-fuel mixture in the main combustion chamber, an auxiliary fuel injection valve for directly injecting fuel into the auxiliary chamber, and an auxiliary chamber ignition plug for igniting the air-fuel mixture in the auxiliary chamber. In this engine, the air-fuel mixture formed in the main combustion chamber, which is the air-fuel mixture of fuel and air injected from the main fuel injection valve, is first ignited by the main chamber ignition plug, and then the air-fuel mixture formed in the auxiliary chamber, which is the air-fuel mixture of fuel and air injected from the auxiliary fuel injection valve, is ignited by the auxiliary chamber ignition plug.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As a configuration for improving the fuel consumption performance of an engine different from the above, there is a configuration in which an air-fuel mixture is compressed and self-ignited. In compression self-ignition combustion, the air-fuel ratio of the air-fuel mixture can be made higher (leaner) than in flame propagation combustion, making it possible to improve fuel consumption performance. Therefore, in an engine having a sub-chamber and a main combustion chamber, if a configuration is adopted in which the air-fuel mixture is compressed and self-ignited in some operating regions and the air-fuel mixture in the sub-chamber and the main combustion chamber is burned by flame propagation by spark ignition in some operating regions, it is considered that the fuel consumption performance of the engine can be surely improved. However, in this configuration, there is a possibility of torque shock occurring when shifting from the region where compression self-ignition combustion is performed to the region where flame propagation combustion is performed. Specifically, it is necessary to lower the air-fuel ratio of the air-fuel mixture during the above shift, but there is a delay in the decrease of the air-fuel ratio due to intake delay or the like. Therefore, immediately after the shift, spark ignition is performed in a state where the air-fuel ratio of the air-fuel mixture is relatively high, and there is a possibility that appropriate flame propagation combustion cannot be realized and engine torque decreases.

[0006] The present invention has been made in view of the above circumstances, and an object thereof is to provide an engine system capable of surely improving fuel consumption performance while suppressing torque shock.

Means for Solving the Problems

[0007] To solve the above problems, the present invention includes a cylinder block and a cylinder head that form a cylinder, a piston reciprocally accommodated in the cylinder, a main combustion chamber defined by the cylinder block, the cylinder head, and the piston, a sub-chamber separated from the main combustion chamber by a partition wall and communicating with the main combustion chamber through a communication hole formed in the partition wall, a fuel injection device that injects fuel into the main combustion chamber, a main ignition device that performs main ignition to ignite the air-fuel mixture in the main combustion chamber, a sub-ignition device that performs sub-ignition to ignite the air-fuel mixture in the sub-chamber, an air-fuel ratio changing device that can change the air-fuel ratio of the air-fuel mixture in the main combustion chamber, the fuel injection device, the main ignition device, the sub-ignition device, and the air-fuel ratio changing device Each deviceIt is provided with a control device electrically connected thereto and outputting an electric signal for control to each of the devices. In a predetermined first region, the control device stops the main ignition and the sub-ignition and causes the air-fuel mixture in the main combustion chamber to undergo compression self-ignition combustion, and controls the air-fuel ratio changing device so that the air-fuel ratio in the main combustion chamber becomes a predetermined first air-fuel ratio. In a second region adjacent to the first region, the control device causes at least one of the main ignition and the sub-ignition to be executed to cause the air-fuel mixture in the main combustion chamber to undergo flame propagation combustion, and controls the air-fuel ratio changing device so that the air-fuel ratio in the main combustion chamber becomes a second air-fuel ratio lower than the first air-fuel ratio. Immediately after shifting from the first region to the second region, only the sub-ignition is executed, or the sub-ignition and the main ignition are executed and the timing of the main ignition is set to be the same as or later than the timing of the sub-ignition. This is the gist of the invention.

[0008] In the engine system of the present invention, a main combustion chamber, a sub-chamber, a main ignition device, and a sub-ignition device are provided, enabling the combustion of the air-fuel mixture in both the main combustion chamber and the sub-chamber. Therefore, in some operating regions, the combustion speed in the main combustion chamber can be increased by the action of the flame generated in the sub-chamber. Furthermore, in this engine system, in some operating regions (the first region), while the air-fuel ratio of the air-fuel mixture in the main combustion chamber is controlled to a relatively high (higher than the second region) first air-fuel ratio, compression self-ignition combustion is performed. Therefore, the fuel consumption performance can be surely improved.

[0009] Moreover, in this engine system, immediately after the transition from the first region to the second region, sub-ignition is executed, and the main ignition is prohibited so that the main ignition does not precede the sub-ignition, or the timing of the main ignition is set after the timing of the sub-ignition. Therefore, torque shock immediately after the transition to the second region can be suppressed. Specifically, since the sub-chamber is separated from the main combustion chamber by a partition wall and communicates with the main combustion chamber through a communication hole, it is difficult for high-temperature burned gas to be discharged from the sub-chamber, and the inside of the sub-chamber is likely to be maintained at a high temperature. Therefore, even in a state where the air-fuel ratio is high, the air-fuel mixture can be surely flame-propagated and burned by spark ignition from the sub-ignition device in the sub-chamber. From this, if sub-ignition is preferentially executed immediately after the transition from the first region to the second region where the air-fuel ratio is lower than that, even in a state where the air-fuel ratio of the main combustion chamber immediately after the transition has not sufficiently decreased, a flame can be ejected from the sub-chamber into the main combustion chamber, and the air-fuel mixture in the main combustion chamber can be surely flame-propagated and burned by the action of this flame, and a decrease in engine torque can be suppressed.

[0010] In the above configuration, preferably, after the transition from the first region to the second region, in the first combustion cycle in the second region, the sub-ignition and the main ignition are executed such that the timing of the sub-ignition precedes the timing of the main ignition (Claim 2).

[0011] In this configuration, in the first combustion cycle in the second region, after the sub-ignition is executed, the main ignition is executed, so that the flame is propagated from the sub-chamber to the air-fuel mixture in the main combustion chamber, and ignition energy is applied from the main ignition device to the air-fuel mixture in the main combustion chamber heated by the flame propagation. Therefore, in the first combustion cycle in the second region when the air-fuel ratio of the air-fuel mixture is particularly high, the air-fuel mixture in the main combustion chamber can be surely flame-propagated and burned.

[0012] In the above configuration, preferably, after the transition from the first region to the second region, in the second combustion cycle in the second region, the sub-ignition and the main ignition are executed simultaneously (Claim 3).

[0013] According to this configuration, in the second combustion cycle in the second region, when the air-fuel ratio of the air-fuel mixture has decreased to a certain extent but is not yet sufficiently decreased, the flame ejected from the auxiliary chamber into the main combustion chamber and the ignition energy of the main ignition device can surely cause the air-fuel mixture in the main combustion chamber to undergo flame propagation combustion. Further, if the auxiliary ignition and the main ignition performed at a time later than the auxiliary ignition are executed in a state where the air-fuel ratio has decreased to a certain extent, there is a risk that the air-fuel mixture in the main combustion chamber will burn explosively, but this explosive combustion of the air-fuel mixture can be prevented.

[0014] In the above configuration, preferably, after the transition from the first region to the second region, in the third and subsequent combustion cycles in the second region, the control device executes the auxiliary ignition and the main ignition such that the timing of the auxiliary ignition is delayed with respect to the timing of the main ignition (Claim 4).

[0015] In the third and subsequent combustion cycles in the second region, it is considered that the air-fuel ratio in the main combustion chamber has decreased to the original air-fuel ratio (second air-fuel ratio). Therefore, in the third and subsequent combustion cycles, even if the auxiliary ignition is executed after the main ignition is executed, the air-fuel mixture in the main combustion chamber can be appropriately burned.

[0016] In the above configuration, preferably, the 1 air-fuel ratio is set to a value higher than the stoichiometric air-fuel ratio, and the control device controls the fuel injection device so that fuel injection starts during the intake stroke in the first region (Claim 5).

[0017] In this configuration, in the first region, since the air-fuel ratio is leaner (higher) than the stoichiometric air-fuel ratio and a homogeneous air-fuel mixture undergoes compression self-ignition combustion, the 1 fuel consumption performance of the region can be more surely improved.

Advantages of the Invention

[0018] As described above, according to the engine system of the present invention, it is possible to surely improve the fuel consumption performance while suppressing torque shock.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

[0020] (Overall Configuration of Engine) FIG. 1 is a schematic configuration diagram showing a preferred embodiment of the engine system of the present invention. The engine system 1 includes an engine body 2, an intake passage 4 through which air (intake air) introduced into the engine body 2 flows inside, an exhaust passage 6 through which exhaust gas derived from the engine body 2 flows inside, and an EGR device 50. The engine system 1 is mounted on a vehicle as a power source for its running and the like. The engine body 2 is a four-stroke gasoline engine mainly using gasoline as fuel, and fuel containing gasoline is supplied to the engine body 2.

[0021] FIG. 2 is a schematic cross-sectional view of the engine body 2. In the present embodiment, the engine body 2 is a multi-cylinder engine having a plurality of cylinders 22. For example, the engine body 2 has four cylinders 22 arranged in a row (arranged in a direction perpendicular to the plane of FIG. 1). The engine body 2 includes a cylinder block 52 in which a plurality of cylinders 22 are formed inside, a cylinder head 54 having a bottom surface 54a that closes the upper end opening of each cylinder 22 and is attached to the upper surface of the cylinder block 52, and a plurality of pistons 24 respectively accommodated in each cylinder 22 so as to be reciprocally slidable. In the present embodiment, the side from the cylinder block 52 toward the cylinder head 54 is regarded as the upper side and the reverse as the lower side for convenience of explanation, but this is for convenience of explanation and is not intended to limit the installation posture of the engine.

[0022] Above the piston 24 of each cylinder 22, a main combustion chamber 26 is partitioned respectively. The main combustion chamber 26 is defined by the inner peripheral surface 22a of the cylinder 22 formed in the cylinder block 52, the bottom surface (lower surface) 54a of the cylinder head 54, and the crown surface 24a of the piston 24. Fuel is supplied to the main combustion chamber 26 by injection from an injector 28 described later. The piston 24 reciprocates in the vertical direction under the expansion force generated by the combustion of the air-fuel mixture of this fuel and air.

[0023] At the lower part of the cylinder block 52 (below the piston 24), a crankshaft 20, which is the output shaft of the engine body 2, is provided. The crankshaft 20 is connected to the pistons 24 of the respective cylinders 22 via connecting rods 21, and rotates around the central axis in response to the reciprocating motion of the pistons 24.

[0024] In the cylinder head 54, an intake port 8 for communicating the main combustion chamber 26 with the intake passage 4 and introducing the air supplied from the intake passage 4 into the main combustion chamber 26, and an exhaust port 12 for communicating the main combustion chamber 26 with the exhaust passage 6 and leading the exhaust gas generated in the main combustion chamber 26 to the exhaust passage 6 are formed for each cylinder 22. In the cylinder head 54, an intake valve 10 for opening and closing the opening of the intake port 8 on the main combustion chamber 26 side and an exhaust valve 14 for opening and closing the opening of the exhaust port 12 on the main combustion chamber 26 side are provided for each cylinder 22. In the present embodiment, two intake valves 10 and two exhaust valves 14 are provided for each cylinder 22.

[0025] The intake valve 10 and the exhaust valve 14 are respectively driven to open and close in conjunction with the rotation of the crankshaft 20 by valve operating mechanisms 16 and 18 disposed in the cylinder head 54. The valve operating mechanism 16 for the intake valve 10 is provided with a variable valve lift mechanism (intake S-VT) 16a that variably controls the valve lift amount and the opening / closing timing of the intake valve 10 electrically. Similarly, the valve operating mechanism 18 for the exhaust valve 14 is also provided with a variable valve lift mechanism (exhaust S-VT) 18a that variably controls the valve lift amount and the opening / closing timing of the exhaust valve 14 electrically.

[0026] In the cylinder head 54, an injector 28, a main ignition plug 32, and a sub-ignition unit 30 are provided in one set for each cylinder 22. The injector 28 corresponds to the "fuel injection device" in the claims, and the main ignition plug 32 corresponds to the "main ignition device" in the claims.

[0027] The injector 28 is an injection valve that injects fuel into the main combustion chamber 26. An injection port for injecting fuel is formed at the tip 28x of the injector 28. The injector 28 is attached to the cylinder head 54 such that its tip 28x faces the main combustion chamber 26 from above. In the present embodiment, the injector 28 is arranged such that its tip 28x is located at the center of the ceiling surface of the main combustion chamber 26 (specifically, on the axis of the cylinder 22).

[0028] The main ignition plug 32 performs main ignition by generating a spark discharge in the air-fuel mixture within the main combustion chamber 26. An electrode portion 32x for discharging a spark is provided at the tip of the main ignition plug 32. This electrode portion 32x includes a center electrode 32a and a side electrode (ground) 32b. The main ignition plug 32 is attached to the cylinder head 54 such that its electrode portion 32x faces the combustion chamber 5 from above. In the present embodiment, the main ignition plug 32 is arranged such that its electrode portion 32x is located on the intake port 8 side of the tip 28x of the injector 28 on the ceiling surface of the main combustion chamber 26.

[0029] The sub-ignition unit 30 is a device for ejecting a flame into the main combustion chamber 26. Details of the sub-ignition unit 30 will be described later.

[0030] The intake passage 4 is connected to one side surface of the cylinder head 54 so as to communicate with the intake port 8 of each cylinder 22. In the intake passage 4, an air cleaner 34, a throttle valve 36, and a surge tank 38 are provided in order from its upstream side. The air cleaner 34 is a device for removing foreign matters in the intake air, and the surge tank 38 is a tank having a predetermined volume. The throttle valve 36 is a valve that opens and closes the intake passage 4 and adjusts the flow rate of the intake air flowing through the intake passage 4. The opening degree of the throttle valve 36 is changed by driving means for driving the same. The flow rate of the intake air flowing through the intake passage 4, and thus the amount of the intake air (air) flowing into the main combustion chamber 26 through the intake passage 4, is adjusted by the opening degree of the throttle valve 36. Along with the change in the intake air amount, the air-fuel ratio in the main combustion chamber 26 (the ratio of the weight of the air in the main combustion chamber 26 to the weight of the fuel in the main combustion chamber 26) is changed. In the present embodiment, the throttle valve 36 functions as an air-fuel ratio changing device capable of changing the air-fuel ratio of the air-fuel mixture in the main combustion chamber 26.

[0031] The downstream end of the intake passage 4 branches into a plurality of passages. Each branch passage is connected to one intake port 8. For each cylinder 22, a swirl valve 56 (see FIG. 5) for opening and closing the branch passage connected to one of the two intake ports 8 is provided.

[0032] The exhaust passage 6 is connected to one side surface of the cylinder head 54 (the surface opposite to the intake passage 4) so as to communicate with the exhaust port 12 of each cylinder 22. A catalyst device 40 incorporating a catalyst 41 such as a three-way catalyst is provided in the exhaust passage 6.

[0033] The EGR device 50 is a device for recirculating a part of the exhaust gas as EGR gas to the intake passage 4 and introducing (recirculating) it into the main combustion chamber 26 communicating therewith via the intake passage 4. The EGR device 50 has an EGR passage 42 communicating the exhaust passage 6 and the intake passage 4, and an EGR valve 46 and an EGR cooler 44 provided in the EGR passage 42 respectively. The upstream end of the EGR passage 42 is connected to the exhaust passage 6 at the downstream end of the catalyst device 40 and on the downstream side of the catalyst 41, and the downstream end of the EGR passage 42 is connected to the surge tank 38. The EGR valve 46 is a valve that opens and closes the EGR passage 42 to adjust the flow rate of the EGR gas. The EGR cooler 44 is a heat exchanger that cools the EGR gas. The EGR cooler 44 is disposed on the Upper downstream side of the EGR valve 46.

[0034] (Sub-ignition unit) FIG. 3 is a partial cross-sectional view of the tip portion 30x of the sub-ignition unit 30 as viewed from the side. FIG. 4 is a plan view (viewed from the tip side) of the tip portion 30x of the sub-ignition unit 30.

[0035] The sub-ignition unit 30 has a sub-ignition plug 62 that ignites the air-fuel mixture by spark discharge. An electrode portion 62x for discharging a spark is provided at the tip of the sub-ignition plug 62. The electrode portion 62x includes a center electrode 62a and a side electrode (ground) 62b. The sub-ignition unit 30 is provided with a cover member 64 at its tip portion 30x that covers the electrode portion 62x of the sub-ignition plug 62. A sub-chamber 60, which is a predetermined space, is defined inside the cover member 64. In other words, the sub-ignition plug 62 is disposed such that its electrode portion 62x faces the sub-chamber 60, and performs sub-ignition to ignite the air-fuel mixture in the sub-chamber 60. The cover member 64 has a hollow hemispherical shape that bulges toward the tip side of the sub-ignition unit 30. The above-mentioned sub-ignition plug 62 corresponds to the "sub-ignition device" in the claims, and the above-mentioned cover member 64 corresponds to the "partition wall" in the claims.

[0036] As shown in FIG. 2, the sub-ignition unit 30 is attached to the cylinder head 54 such that its tip portion 30x faces the main combustion chamber 26 from above. In the present embodiment, the sub-ignition unit 30 is attached to a position on the ceiling surface of the main combustion chamber 26 on the exhaust port 12 side rather than the injector 28. In the present embodiment, in this attachment state, substantially the entire cover member 64 is located within the main combustion chamber 26.

[0037] A plurality of communication holes 66 that penetrate the front and back of the cover member 64 and communicate the main combustion chamber 26 and the sub-chamber 60 are formed in the cover member 64. The inner space of the cover member 64, that is, the sub-chamber 60, communicates with the main combustion chamber 26 through these communication holes 66. Thus, in the present embodiment, by attaching the sub-ignition unit 30 configured as described above to the engine body 2, a sub-chamber 60 that is separated from the main combustion chamber 26 by the cover member 64 and communicates with the main combustion chamber 26 through the communication holes 66 is formed in the engine body 2.

[0038] In the present embodiment, three communication holes 66 are formed in the cover member 64. As shown in FIG. 4, the three communication holes 66 are formed at 120-degree intervals around the axis of the cover member 64 passing through the vertex A of the cover member 64. Further, as shown in FIG. 3, each communication hole 66 is formed at a position 45 degrees from the vertex A in a side view. The radius and thickness of the cover member 64 are 5 mm and 1 mm, respectively, and the diameter of each communication hole 66 is 1.2 mm.

[0039] The sub-ignition unit 30 ejects a flame into the main combustion chamber 26. Specifically, when fuel is injected into the main combustion chamber 26 from the injector 28 and an air-fuel mixture is formed in the main combustion chamber 26, a part of this mixture is introduced into the sub-chamber 60 through the communication holes 66. When spark discharge is performed by the sub-ignition plug 62 in a state where a sufficient amount of the mixture exists in the sub-chamber 60, the mixture starts to burn in the sub-chamber 60, and the flame propagates from around the electrode portion 62x of the sub-ignition plug 62 to the surroundings. Then, this flame is ejected / discharged into the main combustion chamber 26 through the communication holes 66 and propagates to the mixture in the main combustion chamber 26.

[0040] Here, as described above, when ignition is performed by the main ignition plug 32, the flame propagates from around the electrode portion 32x of the main ignition plug 32 to the surroundings. From this, if ignition is performed by both the main ignition plug 32 and the sub-ignition plug 62 and the air-fuel mixture burns appropriately in the main combustion chamber 26 and the sub-chamber 60, the flame will propagate to the air-fuel mixture in the main combustion chamber 26 from a plurality of positions. As a result, the combustion speed of the air-fuel mixture in the main combustion chamber 26 is increased, the fuel consumption performance is improved, and the occurrence of knocking and the remaining unburned air-fuel mixture are suppressed.

[0041] (Control System) FIG. 5 is a block diagram showing the control system of the engine. The ECU 100 shown in this figure is a device that comprehensively controls the engine, and is composed of a microcomputer including a processor (CPU) that performs various arithmetic processes, memories such as a ROM and a RAM, and various input / output buses. The ECU 100 corresponds to the "control device" in the claims.

[0042] Detection information from various sensors is input to the ECU 100. For example, the detection values of an air flow sensor SN1, an intake air temperature sensor SN2, an intake air pressure sensor SN3, a water temperature sensor SN4, and a crank angle sensor SN5 provided in the engine system 1, and an accelerator opening sensor SN6 provided in the vehicle are input to the ECU 100. The air flow sensor SN1 detects the flow rate of the intake air introduced into the engine body 2 through the intake passage 4. The intake air temperature sensor SN2 and the intake air pressure sensor SN3 respectively detect the temperature and pressure of the intake air introduced into the engine body 2. The water temperature sensor SN4 detects the temperature of the engine cooling water that cools the engine body 2. The crank angle sensor SN5 detects the crank angle, which is the rotation angle of the crankshaft 20, and the engine speed. The accelerator opening sensor SN6 detects the accelerator opening, which is the opening of an accelerator pedal (not shown) provided in the vehicle.

[0043] The ECU 100 performs various determinations, calculations, etc. based on input signals from various sensors. The ECU 100 is electrically connected to an injector 28, a main ignition plug 32, a sub-ignition plug 62, an EGR device 50 (specifically, an EGR valve 46), etc., and outputs an electrical control signal to these devices based on calculation results, etc.

[0044] FIG. 6 is a map showing the operating region of the engine with the engine speed on the horizontal axis and the engine load on the vertical axis. As shown in FIG. 6, the operating region of the engine is roughly divided into two regions A1 and A2 (HCCI region A1, SI region A2) according to the combustion mode. The HCCI region A1 is a low-speed and low-load region where the engine speed is equal to or lower than a predetermined switching speed N1 and the engine load is equal to or lower than a predetermined switching load Tq1, and the SI region A2 is the other region. The HCCI region A1 corresponds to the "first region" in the claims, and the SI region A2 corresponds to the "second region" in the claims.

[0045] (Normal control) The normal control performed in each of the regions A1 and A2 (control when not during the transition from the HCCI region A1 to the SI region A2) will be described.

[0046] (HCCI region) In the HCCI region A1, each part of the engine is controlled by the ECU 100 so that the air-fuel mixture undergoes compression self-ignition combustion.

[0047] Specifically, in the HCCI region A1, the ECU 100 stops the main ignition and the sub-ignition. That is, the ECU 100 stops driving the main ignition plug 32 and the sub-ignition plug 62 to prohibit ignition (spark discharge) by these ignition plugs 32 and 62.

[0048] FIG. 7 is a diagram showing the drive pulse of the injector 28 in the HCCI region A1. As shown in FIG. 7, in the HCCI region A1, the ECU 100 sets the fuel injection timing tinj, which is the timing when fuel injection from the injector 28 starts, to a timing during the intake stroke, and causes the injector 28 to start fuel injection from a predetermined timing during the intake stroke.

[0049] As described above, the injector 28 faces the main combustion chamber 26, and the fuel injected from the injector 28 can be diffused throughout the main combustion chamber 26. Thus, in the HCCI region A1, fuel is injected from the injector 28 during the intake stroke, so that the fuel is diffused almost uniformly throughout the main combustion chamber 26 and sufficiently mixed with air by the time the top dead center of compression is reached. Then, in the HCCI region A1, this sufficiently mixed air-fuel mixture (premixed mixture) is heated to a high temperature and pressure by the compression of the piston 24 and auto-ignites near the top dead center of compression. In this way, in the present embodiment, in the HCCI region A1, fuel and air are pre-mixed to form a mixture with a substantially uniform concentration, that is, a homogeneous mixture, in the main combustion chamber 26, and this mixture (premixed mixture) undergoes HCCI combustion (premixed compression auto-ignition combustion, HCCI: Homogeneous Compression Charge Ignition) in which it auto-ignites by compression near the top dead center of compression.

[0050] In HCCI combustion, the air-fuel ratio of the air-fuel mixture can be made lean (high) to a level at which flame propagation is impossible, thereby improving fuel consumption performance. Thus, in the HCCI region A1, the ECU 100 adjusts the opening degree of the throttle valve 36 so that the air-fuel ratio of the air-fuel mixture in the main combustion chamber 26 becomes lean (high) compared to the stoichiometric air-fuel ratio (14.7).

[0051] Also, in the HCCI region A1, the ECU 100 performs EGR in which EGR gas is recirculated to the intake passage 4 and the main combustion chamber 26. That is, in the HCCI region A1, the EGR valve 46 is opened and the EGR gas is recirculated to the intake passage 4 and the main combustion chamber 26.

[0052] (SI region) In the SI region A2, each part of the engine is controlled by the ECU 100 so that the air-fuel mixture undergoes SI combustion (SI: Spark Ignition), that is, flame propagation combustion.

[0053] Specifically, in the SI region A2, the ECU 100 performs main ignition and sub-ignition. That is, the ECU 100 drives the main ignition plug 32 and the sub-ignition plug 62 to cause ignition (spark discharge) in these ignition plugs 32 and 62. When spark discharge occurs in the ignition plugs 32 and 62, a flame kernel is generated around the electrode portions 32x and 62x of these ignition plugs 32 and 62, and SI combustion is realized in which the flame propagates from the flame kernel to the surroundings.

[0054] FIG. 8 is a diagram showing the drive pulse of the injector 28, the main ignition timing tm which is the ignition timing of the main ignition plug 32 (the timing tm at the crank angle when the main ignition plug 32 ignites, that is, performs spark discharge), and the sub-ignition timing ts which is the ignition timing of the sub-ignition plug 62 (the timing ts at the crank angle when the sub-ignition plug 62 ignites, that is, performs spark discharge) in the SI region A2.

[0055] As shown in FIG. 8, in the SI region A2, the ECU 100 sets the fuel injection timing tinj to a timing during the intake stroke, and starts fuel injection from a predetermined timing during the intake stroke in the injector 28. Note that in a region in the SI region A2 where the engine speed is low and the engine load is high and pre-ignition (a phenomenon in which the air-fuel mixture self-ignites before ignition occurs) is likely to occur, the fuel injection timing may be set to a timing during the compression stroke in order to reliably avoid the occurrence of pre-ignition.

[0056] As shown in FIG. 8, in the SI region A2, the ECU 100 sets the main ignition timing tm to a timing on the advanced side compared to the sub-ignition timing ts. That is, the ECU 100 first causes the main ignition plug 32 to ignite, and then causes the sub-ignition plug 62 to ignite. In the present embodiment, the main ignition timing tm is set to a timing during the compression stroke, and the sub-ignition timing ts is set to a timing during the expansion stroke.

[0057] Also, in the SI region A2, the ECU 100 adjusts the opening degree of the throttle valve 36 so that the air-fuel ratio of the air-fuel mixture in the main combustion chamber 26 becomes the stoichiometric air-fuel ratio.

[0058] As described above, in the HCCI region A1, the air-fuel ratio of the air-fuel mixture in the main combustion chamber 26 is made leaner (higher) than the stoichiometric air-fuel ratio (14.7). Thus, the air-fuel ratio (second air-fuel ratio) of the air-fuel mixture in the main combustion chamber 26 in the SI region A2 is made lower (richer) than the air-fuel ratio (first air-fuel ratio) of the air-fuel mixture in the main combustion chamber 26 in the HCCI region A1. In other words, the ECU 100 controls the throttle valve 36 so that the air-fuel ratio of the main combustion chamber 26 in the SI region A2 is lower than the air-fuel ratio in the HCCI region A1.

[0059] Also, in the SI region A2, the ECU 100 adjusts the opening degree of the EGR valve 46 so that the EGR rate is lower than that in the HCCI region A1. The EGR rate is the ratio (weight ratio) of the EGR gas in all the gases present in the main combustion chamber 26 and the auxiliary chamber 60. In the present embodiment, in the SI region A2, EGR is stopped (the EGR valve 46 is fully closed) and the EGR rate is set to zero in the regions where the engine speed is high and the engine load is high. On the other hand, in the remaining regions of the SI region A2, the EGR rate is set to a value greater than zero and the EGR valve 46 is opened.

[0060] (Transitional control) Next, the control of the main ignition plug 32 and the auxiliary ignition plug 62 performed by the ECU 100 when shifting from the HCCI region A1 to the SI region A2, that is, when the operation point shifts from the operation point P1 in the HCCI region A1 to the operation point P2 in the SI region A2 as shown by the arrow Y1 in FIG. 6, will be described.

[0061] When shifting from the HCCI region A1 to the SI region A2, the ECU 100 performs control that gives priority to the auxiliary ignition over the main ignition. Specifically, at the time of this shift, the ECU 100 · Pattern A: Execute only the auxiliary ignition, · Pattern B: Execute the auxiliary ignition and the main ignition performed after the auxiliary ignition (execute the auxiliary ignition and the main ignition and set the main ignition timing to be the same as or delayed from the auxiliary ignition timing), and performs either one of the two patterns of control selected therefrom.

[0062] Hereinafter, the case of performing the control of "Pattern B" will be described.

[0063] FIG. 9 is a flowchart showing the procedures of the spark plugs 32 and 62 during the transition from the HCCI region A1 to the SI region A2.

[0064] The ECU 100 first reads various information (step S1). The ECU 100 reads the engine speed detected by the crank angle sensor SN5, the accelerator opening detected by the accelerator opening sensor SN6, and the like.

[0065] Next, the ECU 100 calculates the required torque, that is, the engine load, which is the torque required for the engine (step S2). The ECU 100 calculates the required torque (engine load) based on the engine speed read in step S1 and the accelerator opening.

[0066] Next, the ECU 100 determines whether the operating point of the engine has shifted from the HCCI region A1 to the SI region A2 (step S3). Specifically, based on the engine speed read in step S1 and the required torque (engine load) calculated in step S2, if the current operating point of the engine is a point within the SI region A2, the ECU 100 determines that there has been a transition from the HCCI region A1 to the SI region A2.

[0067] If the determination in step S3 is NO and there has been no shift in the operating point of the engine from the HCCI region A1 to the SI region A2, that is, if the current operating point is a point within the HCCI region A1, the ECU 100 performs the control of the spark plugs 32 and 62 in the normal HCCI region A1 described above. Specifically, the ECU 100 stops the ignition by the main spark plug 32 and the sub spark plug 62 (step S4). On the other hand, if the determination in step S3 is YES and the operating point of the engine has shifted from the HCCI region A1 to the SI region A2, the ECU 100 proceeds to step S 5 to proceed.

[0068] Step S 5 In step S, the ECU 100 determines whether the number of ignitions performed after the transition from the HCCI region A1 to the SI region A2 is less than 2 (step S5). That is, it is determined whether it is either a state where no ignition has been performed yet (the number of ignitions is 0) or a state where ignition has been performed only once (the number of ignitions is 1) after the transition to the SI region A2. The number of these ignitions is the number of ignitions of the main ignition plug 32 or the sub - ignition plug 62, and is the same as the number of combustion cycles. Also, the number of these ignitions, that is, the number of combustion cycles, is the number for one cylinder 22. In the present embodiment where a plurality of cylinders 22 are provided in the engine body 2, the ECU 100 determines for each cylinder 22 whether the number of ignitions is less than 2. Also, the ECU 100 individually performs the subsequent steps (S6 - S9) after this step S5 for each cylinder 22.

[0069] If the determination in step S5 is YES and the number of ignitions after the transition to the SI region A2 is less than 2, the ECU 100 further determines whether the number of ignitions after the transition to the SI region A2 is 0, that is, whether it is a state where no ignition has been performed yet after the transition to the SI region A2 (step S6).

[0070] If the determination in step S6 is YES and the number of ignitions after the transition to the SI region A2 is 0, the ECU 100 first causes the sub - ignition plug 62 to perform ignition (sub - ignition), and then causes the main ignition plug 32 to perform ignition (main ignition) (step S7). That is, in the ECU 100, in the first ignition (combustion cycle) in the SI region A2 performed in each cylinder 22 after the transition to the SI region A2, first, the sub - ignition plug 62 is driven to perform ignition (spark discharge), and then the main ignition plug 32 is driven to perform ignition (spark discharge). Note that when step S7 is performed, the number of ignitions changes from 0 to 1.

[0071] FIG. 10(a) is a diagram showing the main ignition timing tm and the sub-ignition timing ts when ignition is first performed after the transition to the SI region A2 (in the first combustion cycle after the transition). As shown in FIG. 10(a), in the first ignition after the transition, both the sub-ignition timing ts and the main ignition timing tm are set to be during the compression stroke. The timing tm_base indicated by the dashed line in FIG. 10(a) is the main ignition timing tm during normal control of the SI region A2. In the first ignition performed after the transition to the SI region A2, both the main ignition timing tm and the sub-ignition timing ts are set to be advanced compared to the main ignition timing tm and the sub-ignition timing ts during normal control.

[0072] Returning to FIG. 9, when the determination in step S6 is NO, the number of ignitions after the transition to the SI region A2 is not 0 but 1, and ignition has already been performed once after the transition, the ECU 100 causes the sub-ignition plug 62 and the main ignition plug 32 to perform ignition (sub-ignition, main ignition) simultaneously (step S8). That is, in the second ignition in the SI region A2 performed in each cylinder 22 after the transition to the SI region A2, the ECU 100 drives the sub-ignition plug 62 and the main ignition plug 32 simultaneously to cause ignition (spark discharge) in these plugs simultaneously. Note that when step S8 is executed, the number of ignitions changes from 1 to 2.

[0073] FIG. 10(b) is a diagram showing the main ignition timing tm and the sub-ignition timing ts when ignition is performed for the second time after the transition to the SI region A2 (in the second combustion cycle after the transition). As shown in FIG. 10(b), in the first ignition after the transition, both the sub-ignition timing ts and the main ignition timing tm are set to be during the compression stroke. Similar to FIG. 10(a), the timing tm_base indicated by the dashed line in FIG. 10(b) is the main ignition timing tm during normal control of the SI region A2. The timing tm1 indicated by the chain line in FIG. 10(b) is the main ignition timing tm at the first ignition shown in FIG. 10(a). As is clear from the comparison of these timings tm1 , tm_base, in the second ignition after the transition to the SI region A2, both the main ignition timing tm and the sub-ignition timing ts are set to be advanced compared to the main ignition timing tm (tm_base) during normal control, and the first main ignition timing after the transition tm1It is set to a timing on the retard side than that.

[0074] Return to step S5. When the determination in step S5 is NO and the number of ignition times after the transition to the SI region A2 is 2 or more, the ECU 100 performs normal control on the spark plugs 32 and 62. That is, the ECU 100 starts normal control when ignition is performed 2 times after the transition to the SI region A2. Fig. 10(c) is a diagram showing the main ignition timing tm and the sub-ignition timing ts at the time of ignition after the third time and later after the transition to the SI region A2 (in the combustion cycles after the third time after the transition), and is a diagram showing a part of Fig. 8. As shown in these diagrams, and as described above, in the normal control performed after the third time and later after the transition to the SI region A2, the ECU 100 sets the main ignition timing tm to a timing on the advance side than the sub-ignition timing ts. Further, the ECU 100 sets the main ignition timing tm to a timing during the compression stroke, and sets the sub-ignition timing ts to a timing during the expansion stroke.

[0075] Fig. 11 is a time chart showing the time change of each parameter at the time of transition from the HCCI region A1 to the SI region A2. Fig. 11 shows, in order from the top, a chart of the engine load, the air-fuel ratio of the main combustion chamber 26, and the ignition timing (the main ignition timing tm and the sub-ignition timing ts).

[0076] In the example of Fig. 11, at time t1, the engine load increases and the operating point of the engine transitions from a point within the HCCI region A1 to a point within the SI region A2.

[0077] With the transition to the SI region A2, the driving of the spark plugs 32 and 62 is started at time t1. As described above, the order of ignition performed first after the transition to the SI region A2 is sub-ignition → main ignition. From time t1 until the first sub-ignition and main ignition are completed in all the cylinders 22, the sub-ignition timing ts is set to a timing on the advance side than the main ignition timing tm.

[0078] In the example of Fig. 11, at time t2, the first ignition (sub-ignition and main ignition) is completed in all cylinders 22, and the second ignition is started at time t2. In the second ignition performed after the transition to the SI region A2, the sub-ignition and the main ignition are carried out simultaneously. From time t2 until the second sub-ignition and main ignition in all cylinders 22 are completed, the sub-ignition timing ts and the main ignition timing tm are set to the same time. Also, as described above, the sub-ignition timing ts and the main ignition timing tm are set to be retarded more in the second ignition than in the first ignition. At time t2, these ignition timings ts and tm are set to a retarded time compared to the time before time t2.

[0079] In the example of Fig. 11, at time t3, the second ignition (sub-ignition and main ignition) is completed in all cylinders 22, and the third ignition is started at time t3. As described above, the control of the spark plugs 32 and 62 after the third ignition becomes normal control. After time t3, the ignition order is main ignition → sub-ignition. Also, as described above, the sub-ignition timing ts and the main ignition timing tm are set to be retarded more during normal control than during the first and second ignitions. At time t3, these ignition timings ts and tm are set to a retarded time compared to the time before time t3.

[0080] Also, during operation within the HCCI region A1 until time t1, the air-fuel ratio is set leaner than the stoichiometric air-fuel ratio. Then, when the operation point transitions to a point within the SI region A2 at time t1, the opening degree of the throttle valve 36 is changed so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. Specifically, the opening degree of the throttle valve 36 is changed to an opening degree on the closed valve side. Also, the opening degree of the EGR valve 46 is adjusted so that the EGR rate decreases. However, there is a delay in the intake air and the EGR gas. Therefore, even if the opening degrees of the throttle valve 36 and the EGR valve 46 are changed at time t1, the air-fuel ratio in the main combustion chamber 26 does not immediately decrease to the stoichiometric air-fuel ratio. From this, for some time after time t1, the air-fuel ratio in the main combustion chamber 26 remains higher (leaner) than the stoichiometric air-fuel ratio, and it is not until around time t3 that the air-fuel ratio in the main combustion chamber 26 decreases to the stoichiometric air-fuel ratio.

[0081] (Function, etc.) As described above, in the engine system 1 of the above embodiment, HCCI combustion is carried out in the HCCI region A1 of low speed and low load. Further, in the SI region A2 which is another region, the air-fuel mixture is combusted (flame propagation combustion) in both the main combustion chamber 26 and the auxiliary chamber 60. Therefore, the fuel consumption performance can be improved in all regions, and the fuel consumption performance of the engine system 1 is surely improved.

[0082] Here, immediately after the transition to the SI region A2, it is difficult to cause flame propagation combustion of the air-fuel mixture in the main combustion chamber 26 only by the spark discharge from the main ignition plug 32. Therefore, if the control of normally igniting the SI region A2, which first drives the main ignition plug 32 and then drives the auxiliary ignition plug 62, is carried out immediately after the transition, the engine torque may decrease and torque shock may occur.

[0083] Specifically, in the SI region A2, when the main ignition plug 32 is driven, its temperature and the temperature around the main ignition plug 32 are maintained at a relatively high temperature. However, in the HCCI region A1, since the driving of the main ignition plug 32 is stopped, the temperature of the main ignition plug 32 and its surroundings can be kept low. Further, since the main combustion chamber 26 communicates with the intake passage 4 via the intake port 8 and communicates with the exhaust passage 6 via the exhaust port 12, unburned gas hardly remains in the main combustion chamber 26, and it is difficult for the main combustion chamber 26 to be heat-insulated by the high-temperature unburned gas. And, as shown in FIG. 11, immediately after the transition from the HCCI region A1 to the SI region A2, the air-fuel ratio is maintained in a high state. Therefore, even if the control of first driving the main ignition plug 32 is carried out immediately after the transition to the SI region A2, a flame kernel may not be appropriately formed around the main ignition plug 32, and there is a possibility that the air-fuel mixture in the main combustion chamber 26 may not burn appropriately.

[0084] In contrast, in the above-described embodiment, at the first ignition after the transition from the HCCI region A1 to the SI region A2, the ignition order is sub-ignition → main ignition. First, the sub-combustion chamber 60 is ignited by the sub-ignition plug 62, and then the main ignition plug 32 ignites. Therefore, the air-fuel mixture in the main combustion chamber 26 can be reliably flame-propagated and burned, and a decrease in engine torque can be suppressed.

[0085] Specifically, the sub-combustion chamber 60 is partitioned from the main combustion chamber 26 by the cover member 64 and communicates with the main combustion chamber 26 only through the communication hole 66. Therefore, high-temperature burned gas tends to remain in the sub-combustion chamber 60, and the sub-combustion chamber 60 is kept warm by the high-temperature burned gas even in the HCCI region A1. Thus, even immediately after the transition from the HCCI region A1 to the SI region A2, the air-fuel mixture in the sub-combustion chamber 60 can be flame-propagated and burned by the spark discharge from the sub-ignition plug 62. Therefore, according to the above-described embodiment, at the first ignition after the transition to the SI region A2, first, the sub-ignition plug 62 ignites, so that the air-fuel mixture in the sub-combustion chamber 60 can be flame-propagated and burned, and a flame can be ejected from the sub-combustion chamber 60 to the main combustion chamber 26 to start the flame-propagated combustion of the air-fuel mixture in the main combustion chamber 26. Then, after the sub-ignition plug 62, the main ignition plug 32 ignites, so that ignition energy is added from the main ignition plug 32 to the air-fuel mixture in the main combustion chamber 26 that has become high temperature by receiving the flame ejected from the sub-combustion chamber 60, and the entire air-fuel mixture in the main combustion chamber 26 can be reliably flame-propagated and burned.

[0086] Here, at the second ignition after the transition to the SI region A2, although the air-fuel ratio of the air-fuel mixture in the main combustion chamber 26 has not sufficiently decreased, it has decreased to some extent, and the air-fuel mixture in the main combustion chamber 26 is in a state where it is relatively easy to burn compared to the first ignition. Therefore, if ignition is performed in the order of sub-ignition → main ignition as in the first ignition, the ignition energy from the main ignition plug 32 is added to the air-fuel mixture in the main combustion chamber 26 that has become high temperature upon receiving the flame from the sub-chamber 60, and there is a risk that the air-fuel mixture in the main combustion chamber 26 will burn explosively. In contrast, in the above embodiment, at the second ignition after the transition to the SI region A2, the sub-ignition and the main ignition are performed simultaneously. Therefore, the air-fuel mixture in the main combustion chamber 26 can be surely burned by flame propagation, and the explosive combustion of the air-fuel mixture in the main combustion chamber 26 can be prevented.

[0087] (Modification example) In the above embodiment, the case where sub-ignition is performed before main ignition at the first ignition after the transition from the HCCI region A1 to the SI region A2 has been described. However, at the first ignition as well, the main ignition and the sub-ignition may be performed simultaneously in the same manner as the second ignition. Also in this case, since the air-fuel mixture in the main combustion chamber 26 is surely burned by flame propagation by the flame ejected from the sub-chamber 60 to the main combustion chamber 26, a decrease in engine torque is suppressed. However, as described above, if sub-ignition is performed before main ignition, the ignition energy from the main ignition plug 32 is applied to the air-fuel mixture heated by the flame ejected from the sub-chamber 60 to the main combustion chamber 26, so that the air-fuel mixture in the main combustion chamber 26 can be more surely burned by flame propagation.

[0088] Also, in the above, the case where the control of "pattern B" is performed at the time of transition from the HCCI region A1 to the SI region A2 has been described. However, even when the control of the above "pattern A" (executing only sub-ignition) is performed, the air-fuel mixture in the main combustion chamber 26 can be surely burned by flame propagation by the flame ejected from the sub-chamber 60 to the main combustion chamber 26, and a decrease in engine torque can be suppressed. When performing the control of "pattern A", at the first ignition and the second ignition after the transition, the driving of the main ignition plug 32 is stopped and ignition is performed only by the sub-ignition plug 62.

[0089] Further, in the above embodiment, when HCCI combustion is carried out in the HCCI region A1 which is a low-speed and low-load region, that is, when fuel injection is started during the intake stroke and the air-fuel ratio of the air-fuel mixture in the main combustion chamber 26 is made leaner than the stoichiometric air-fuel ratio and the air-fuel mixture undergoes compression self-ignition combustion, the combustion carried out in the low-speed and low-load region may be compression self-ignition combustion and does not have to be premixed compression self-ignition combustion. That is, the timing when fuel injection is started in the low-speed and low-load region is not limited to the timing during the intake stroke. Further, the region where compression self-ignition combustion is carried out is not limited to the low-speed and low-load region.

[0090] Further, the normal ignition control of the SI region A2 is not limited to the above. For example, as the normal ignition control of the SI region A2, a control in which only sub-ignition is carried out, or a control in which sub-ignition is carried out before main ignition may be adopted.

[0091] Further, the specific shape and dimensions of the cover member 64 of the sub-ignition unit 30 are not limited to the above. Further, the number and dimensions of the communication holes 66 provided in the cover member 64 are not limited to the above. Further, the mounting position of the sub-ignition unit 30 is not limited to the above. For example, the sub-ignition unit 30 may be provided on the exhaust port 12 side with respect to the tip portion 28x of the injector 28.

[0092] Further, the detailed structure such as the number of cylinders of the engine body 2 is not limited to the above.

Explanation of reference numerals

[0093] 1 Engine system 2 Engine body 4 Intake passage 24 Piston 28 Injector (fuel injection device) 26 Main combustion chamber 30 Sub-ignition unit 32 Main ignition plug (main ignition device) 36 Throttle valve (air-fuel ratio changing device) 52 Cylinder block 54 Cylinder head 60 Auxiliary chamber 62 Auxiliary ignition plug (auxiliary ignition device) 64 Cover member (partition wall) 66 Communication hole 100 ECU (control device)

Claims

1. A cylinder block and a cylinder head that form a cylinder, a piston reciprocally accommodated in the cylinder, a main combustion chamber defined by the cylinder block, the cylinder head, and the piston, a sub-chamber separated from the main combustion chamber by a partition wall and communicating with the main combustion chamber through a communication hole formed in the partition wall, a fuel injection device that injects fuel into the main combustion chamber, a main ignition device that performs main ignition to ignite the air-fuel mixture in the main combustion chamber, a sub-ignition device that performs sub-ignition to ignite the air-fuel mixture in the sub-chamber, an air-fuel ratio changing device capable of changing the air-fuel ratio of the air-fuel mixture in the main combustion chamber, and a control device electrically connected to each of the fuel injection device, the main ignition device, the sub-ignition device, and the air-fuel ratio changing device and outputting an electric signal for control to each of the devices, wherein the control device in a predetermined first region, stops the main ignition and the sub-ignition to cause the air-fuel mixture in the main combustion chamber to undergo compression self-ignition combustion, and controls the air-fuel ratio changing device so that the air-fuel ratio in the main combustion chamber becomes a predetermined first air-fuel ratio, in a second region adjacent to the first region, executes at least one of the main ignition and the sub-ignition to cause the air-fuel mixture in the main combustion chamber to undergo flame propagation combustion, and controls the air-fuel ratio changing device so that the air-fuel ratio in the main combustion chamber becomes a second air-fuel ratio lower than the first air-fuel ratio, immediately after shifting from the first region to the second region, only the sub-ignition is executed, or the sub-ignition and the main ignition are executed and the timing of the main ignition is set to be the same as or later than the timing of the sub-ignition. An engine system characterized by this.

2. In the engine system according to Claim 1, after shifting from the first region to the second region, the control device executes the sub-ignition and the main ignition such that the timing of the sub-ignition precedes the timing of the main ignition in the first combustion cycle in the second region. An engine system characterized by this.

3. In the engine system according to Claim 2, after shifting from the first region to the second region, the control device executes the sub-ignition and the main ignition simultaneously in the second combustion cycle in the second region. An engine system characterized by this.

4. In the engine system according to Claim 3, After the transition from the first region to the second region, in the combustion cycles after the third cycle in the second region, the control device executes the sub-ignition and the main ignition such that the timing of the sub-ignition is delayed with respect to the timing of the main ignition. An engine system characterized by this.

5. In the engine system according to any one of claims 1 to 4, the first air-fuel ratio is set to a value higher than the stoichiometric air-fuel ratio, the control device controls the fuel injection device so that fuel injection starts during the intake stroke in the first region. An engine system characterized by this.

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