Engine system

Abstract

The present invention provides an engine system. In an engine system having a combustion chamber and a sub-chamber, fuel consumption performance and exhaust gas performance are improved. The engine system includes an ECU, which is electrically connected to an injector that injects fuel into the main combustion chamber, a main spark plug that performs main ignition on the air-fuel mixture in the main combustion chamber, and a sub-spark plug that performs sub-ignition on the air-fuel mixture in the sub-chamber, and outputs an electrical signal for control to each device. When the engine is operating in a high-load region, i.e., a specific region, where the engine load is higher than a specified reference load, the ECU performs the following control. In a low-rotation region where the engine speed is below a specified reference speed, the ECU performs the sub-ignition after performing the main ignition. In a high-rotation region where the engine speed exceeds the reference speed, only the sub-ignition is performed, or the sub-ignition and the main ignition performed at the same time as or after the sub-ignition are performed.

Description

Technical Field

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

[0002] There is known an engine having a main combustion chamber using a cylinder and an auxiliary chamber communicating with the main combustion chamber. For example, in Patent Document 1, an engine is disclosed in which fuel injection devices and spark plugs are arranged in both the main combustion chamber and the auxiliary chamber. In this engine, after the air-fuel mixture is burned in the main combustion chamber, the air-fuel mixture is burned in the auxiliary chamber, and the flame in the auxiliary chamber is ejected into the main combustion chamber, so that the unburned air-fuel mixture existing in the main combustion chamber is burned. Therefore, it is possible to suppress the remaining of the unburned air-fuel mixture in the main combustion chamber, and further improve the fuel consumption performance and the exhaust gas performance.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2007-255370 Summary of the Invention

[0006] Problems to be Solved by the Invention

[0007] Different from the engine of Patent Document 1, if a structure in which only a fuel injection device is arranged in the main combustion chamber is adopted for the purpose of simplifying the structure or the like, it is difficult to introduce the air-fuel mixture into the auxiliary chamber. For example, in the operating region of low rotation and high load of the engine, sometimes the supply of the flame from the auxiliary chamber is insufficient, resulting in insufficient combustion of the unburned air-fuel mixture. In addition, in the operating region of high rotation and high load, there is also a problem that knocking is likely to occur in the main combustion chamber. As a result of these problems, there is a concern that the improvement effects on the fuel consumption performance and the exhaust gas performance obtained by providing the auxiliary chamber in addition to the main combustion chamber cannot be fully exerted.

[0008] An object of the present invention is to reliably improve the fuel consumption performance and the exhaust gas performance in an engine system having a main combustion chamber and an auxiliary chamber.

[0009] Means for Solving the Problems

[0010] An engine system according to one aspect of the present invention includes: a cylinder block and a cylinder head that form a cylinder; a piston that is reciprocally movably received in the cylinder; a main combustion chamber that is defined by the cylinder block, the cylinder head, and the piston; a sub chamber that is separated from the main combustion chamber by a partition wall and communicates 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 for igniting the air-fuel mixture in the main combustion chamber; a sub ignition device that performs sub ignition for igniting the air-fuel mixture in the sub chamber; and a controller that is electrically connected to the fuel injection device, the main ignition device, and the sub ignition device and outputs control electrical signals to these devices. When the engine is operating in a high load region where the engine load is higher than a specified reference load, the controller performs the following control: in a low rotation region where the engine speed is below a specified reference speed, the sub ignition is performed after the main ignition; in a high rotation region where the engine speed exceeds the reference speed, only the sub ignition is performed, or the sub ignition and the main ignition that is performed at the same time as or after the sub ignition are performed.

[0011] In the operating region where the engine is at high load and low rotation, the movement of the piston is slow, so that the pressing force for pressing the air-fuel mixture into the sub chamber becomes weak. As a result, the flow of the air-fuel mixture in the sub chamber slows down, and the combustion speed in the sub chamber also slows down. Consequently, there is a tendency for the flame ejected from the sub chamber to become weak. According to the above engine system, in the operating region of high load and low rotation, the sub ignition is performed after the main ignition. Thereby, the inflow of the air-fuel mixture into the sub chamber is promoted. That is, by superimposing the combustion pressure generated by the propagation combustion of the flame due to the main ignition on the pressing force of the piston, the pressing force for pressing the air-fuel mixture into the sub chamber increases. Therefore, the flow of the air-fuel mixture in the sub chamber speeds up, and the combustion speed in the sub chamber also speeds up. As a result, a stronger flame can be ejected from the sub chamber, and the unburned air-fuel mixture remaining in the main combustion chamber can be burned well. On the other hand, in the operating region of high load and high rotation, there is a tendency for knocking to easily occur in the main combustion chamber. In the above engine system, in the operating region of high load and high rotation, the sub ignition is performed first to eject the flame from the sub chamber. Thereby, the combustion in the main combustion chamber is accelerated, and knocking can be suppressed.

[0012] In the above engine system, preferably, in the low rotation region, the lower the engine speed is in the low rotation, the more the controller delays the timing of the sub ignition.

[0013] The lower the engine speed rotates, the weaker the pressing force of the piston, and the more likely it is to have a tendency that it is difficult to introduce the air-fuel mixture into the auxiliary chamber. According to the above engine system, the lower the rotation speed, the more delayed the timing of the auxiliary ignition. Therefore, it is possible to sufficiently ensure the time for pressing the air-fuel mixture into the auxiliary chamber according to the engine speed.

[0014] In the above engine system, it is preferable that in the high rotation region, the higher the engine speed rotates, the more the controller advances the timing of the auxiliary ignition.

[0015] There is a tendency that the higher the engine speed rotates, the more likely knocking occurs. According to the above engine system, the higher the rotation speed, the more advanced the timing of the auxiliary ignition. Therefore, the combustion speed can be increased. Therefore, knocking can be suppressed.

[0016] In the above engine system, it is preferable that the controller performs the main ignition after performing the auxiliary ignition in the low rotation region, and the lower the engine speed rotates, the larger the ignition phase difference between the auxiliary ignition and the main ignition is set.

[0017] According to this engine system, the lower the engine speed rotates, the larger the ignition phase difference becomes. Therefore, it is possible to sufficiently ensure the time for pressing the air-fuel mixture into the auxiliary chamber according to the engine speed.

[0018] Advantages of the Invention

[0019] According to the present invention, in an engine system having a main combustion chamber and an auxiliary chamber, it is possible to suppress insufficient flame supply from the auxiliary chamber and knocking, thereby reliably improving fuel consumption performance and exhaust gas performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is a schematic configuration diagram of an engine system according to an embodiment of the present invention.

[0021] Figure 2 is a schematic cross-sectional view of an engine body.

[0022] Figure 3 is a partial cross-sectional view of the front end portion of the auxiliary ignition unit as viewed from the side.

[0023] Figure 4 is a bottom view of the front end portion of the auxiliary ignition unit.

[0024] Figure 5 is a block diagram showing the control structure of the engine system.

[0025] Figure 6 is a map showing the operating region of the engine.

[0026] Figure 7It is a flowchart showing an example of fuel injection and ignition control executed when the operating region is a specific region.

[0027] Figure 8 It is a timing chart showing the fuel injection timing, main ignition timing, and sub-ignition timing in the low rotation region within the specific region.

[0028] Figure 9 It is a timing chart showing the fuel injection timing, main ignition timing, and sub-ignition timing in the high rotation region within the specific region.

[0029] Figure 10 It is a line graph showing the relationship between the engine speed and the main ignition, sub-ignition, and ignition phase difference in the specific region.

[0030] Explanation of reference numerals

[0031] 1 Engine system

[0032] 22 Cylinders

[0033] 24 Pistons

[0034] 26 Main combustion chamber

[0035] 28 Injector (fuel injection device)

[0036] 30 Sub-ignition unit

[0037] 32 Main spark plug (main ignition device)

[0038] 52 Cylinder block

[0039] 54 Cylinder head

[0040] 60 Sub-chamber

[0041] 62 Sub-spark plug (sub-ignition device)

[0042] 64 Cover component (partition wall)

[0043] 66 Communication hole

[0044] 100 ECU (controller)

[0045] A2H Specific region (high load region higher than the reference load)

[0046] P1 Operating point in the low rotation region

[0047] P2 Operating point in the high rotation region

[0048] N2 Second speed (prescribed reference speed)

[0049] Tq21 Boundary load (prescribed reference load)

[0050] tm main ignition period

[0051] ts auxiliary ignition period

[0052] dt ignition phase difference Detailed implementation manners

[0053] Hereinafter, the engine system according to the embodiment of the present invention will be described in detail based on the drawings. In the present embodiment, a case where the engine system is mounted on a vehicle such as an automobile as a power source for driving the vehicle is illustrated.

[0054] [Overall configuration of the engine]

[0055] Figure 1 is a schematic configuration diagram of the engine system 1 according to the embodiment of the present invention. The engine system 1 includes an engine main body 2, an intake passage 4, an exhaust passage 6, and an EGR device 50. The air (intake air) introduced into the engine main body 2 flows inside the intake passage 4, and the exhaust gas discharged from the engine main body 2 flows inside the exhaust passage 6. The engine main body 2 is a four-stroke gasoline engine that mainly uses gasoline as fuel, and fuel containing gasoline is supplied to the engine main body 2.

[0056] Figure 2 is a schematic cross-sectional view of the engine main body 2. The engine main body 2 is a multi-cylinder engine having a plurality of cylinders 22. For example, the engine main body 2 has four cylinders 22 arranged in a row (arranged in a direction orthogonal to the Figure 1 plane of the drawing). The engine main body 2 includes a cylinder block 52, a cylinder head 54, and a plurality of pistons 24. The cylinders 22 are formed by the cylinder block 52 and the cylinder head 54. Inside the cylinder block 52, a plurality of cylindrical spaces forming the plurality of cylinders 22 are provided. The cylinder head 54 has a bottom surface 54a that closes the upper end opening of the cylindrical space, and is mounted on the upper surface of the cylinder block 52. The pistons 24 are respectively reciprocally slidably received in the respective cylinders 22. In addition, in the present embodiment, the side from the cylinder block 52 toward the cylinder head 54 is defined as the upper side, and the opposite side is defined as the lower side. These are set for convenience of description and are not intended to limit the mounting attitude of the engine main body 2.

[0057] Above the piston 24 of each cylinder 22, a space serving as the main combustion chamber 26 is formed. 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 54a of the cylinder head 54, and the top surface 24a of the piston 24. Fuel is supplied to the main combustion chamber 26 by injection from an injector 28 described later. The mixture of the supplied fuel and air burns in the main combustion chamber 26, and the piston 24 reciprocates in the vertical direction by the expansion force generated by the combustion.

[0058] In the lower part of the cylinder block 52 (below the piston 24), a crankshaft 20 serving as an output shaft of the engine main body 2 is provided. The crankshaft 20 is connected to the pistons 24 of the respective cylinders 22 via connecting rods 21, and rotates about the central axis corresponding to the reciprocating motion of the pistons 24.

[0059] On the cylinder head 54, an intake port 8, an intake valve 10, an exhaust port 12, and an exhaust valve 14 are respectively formed for each cylinder 22. The intake port 8 is a port for introducing air supplied from the intake passage 4 into the main combustion chamber 26. The exhaust port 12 is a port for discharging the exhaust gas generated in the main combustion chamber 26 to the exhaust passage 6. The intake valve 10 opens and closes the opening on the main combustion chamber 26 side of the intake port 8. The exhaust valve 14 opens and closes the opening on the main combustion chamber 26 side of the exhaust port 12. In the present embodiment, two intake valves 10 and two exhaust valves 14 are provided for one cylinder 22.

[0060] The intake valve 10 and the exhaust valve 14 are respectively opened and closed in conjunction with the rotation of the crankshaft 20 by valve drive mechanisms 16 and 18 disposed on the cylinder head 54. In the valve drive mechanism 16 for the intake valve 10, 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 in an electric manner is provided. Similarly, in the valve drive mechanism 18 for the exhaust valve 14, 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 in an electric manner is also provided.

[0061] On the cylinder head 54, a set of fuel injectors 28 (fuel injection devices), main spark plugs 32 (main ignition devices), and sub-ignition units 30 are respectively provided for each cylinder 22. The fuel 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 front end portion 28x of the fuel injector 28. The fuel injector 28 is mounted on the cylinder head 54 in such a manner that its front end portion 28x faces the main combustion chamber 26 from above. The fuel injector 28 is disposed in such a manner that its front end portion 28x is located at the center of the top surface of the main combustion chamber 26, and more specifically, on the axis of the cylinder 22.

[0062] The main spark plug 32 performs main ignition, that is, ignites the air-fuel mixture in the main combustion chamber 26 by spark discharge. At the front end of the main spark plug 32, an electrode portion 32x for discharging sparks is provided. The electrode portion 32x includes a center electrode 32a and a side electrode 32b for grounding. The main spark plug 32 is mounted on the cylinder head 54 in such a manner that its electrode portion 32x faces the main combustion chamber 26 from above. The main spark plug 32 is disposed in such a manner that its electrode portion 32x is located at a position on the top surface of the main combustion chamber 26 that is closer to the intake port 8 side than the front end portion 28x of the fuel injector 28.

[0063] The sub-ignition unit 30 is a device for injecting flames into the main combustion chamber 26. The sub-ignition unit 30 will be described in detail later.

[0064] The intake passage 4 is connected to one side surface of the cylinder head 54 so as to communicate with the intake ports 8 of the respective cylinders 22. In the intake passage 4, an air cleaner 34 for removing foreign matters in the intake air, an openable and closable throttle valve 36 for adjusting the flow rate of the intake air, and a surge tank 38 are provided in order from its upstream side. The downstream end of the intake passage 4 branches into a plurality of passages, and these respective branch passages are respectively connected to one intake port 8. In each cylinder 22, in the branch passage connected to one of the two intake ports 8, a swirl valve 56 (see Figure 5 ) for opening and closing it is provided.

[0065] The exhaust passage 6 is connected to one side surface of the cylinder head 54 (the surface opposite to the intake passage 4 side) so as to communicate with the exhaust ports 12 of the respective cylinders 22. In the exhaust passage 6, a catalytic device 40 having a catalyst 41 such as a three-way catalyst incorporated therein is provided.

[0066] The EGR device 50 is a device for returning a part of the exhaust gas as EGR gas to the intake passage 4. The EGR device 50 has an EGR passage 42 that connects the exhaust passage 6 and the intake passage 4, and an EGR valve 46 and an EGR cooler 44 respectively provided in the EGR passage 42. The upstream end of the EGR passage 42 is connected to the exhaust passage 6 that is downstream of the catalytic device 40 and further downstream than the catalyst 41. 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 at a position more upstream than the EGR valve 46.

[0067] [Details of the sub-ignition unit]

[0068] Figure 3 is a partial cross-sectional view of the front end portion 30x of the sub-ignition unit 30 as viewed from the side, Figure 4 is a bottom view of the front end portion 30x as viewed from below. The sub-ignition unit 30 includes a sub-spark plug 62 (sub-ignition device), a cover member 64 (partition wall) attached to the front end of the sub-spark plug 62, and a sub-chamber 60 as an internal space covered by the cover member 64.

[0069] The auxiliary spark plug 62 performs auxiliary ignition, that is, ignites the air-fuel mixture in the auxiliary chamber 60 by spark discharge. An electrode portion 62x for discharging sparks is provided at the front end of the auxiliary spark plug 62. The electrode portion 62x includes a center electrode 62a and a side electrode 62b for grounding. The cover member 64 forms the front end portion 30x of the auxiliary ignition unit 30 and covers the periphery of the electrode portion 62x of the auxiliary spark plug 62. The cover member 64 has a hemispherical shape that bulges downward. The auxiliary chamber 60 is the space inside the cover member 64. Specifically, the auxiliary chamber 60 is the space around the vicinity of the electrode portion 62x of the auxiliary spark plug 62, and is a space divided by the cover member 64. Since it is such a space, the size of the auxiliary chamber 60 is smaller than that of the main combustion chamber 26. The electrode portion 62x of the auxiliary spark plug 62 is disposed so as to face the auxiliary chamber 60, and the above-mentioned auxiliary ignition can be performed.

[0070] As Figure 2 shown, the auxiliary ignition unit 30 is mounted on the cylinder head 54 in such a manner that its front end portion 30x faces the main combustion chamber 26 from above. The auxiliary ignition unit 30 is mounted at a position on the top surface of the main combustion chamber 26 (the bottom surface 54a of the cylinder head 54) closer to the exhaust port 12 side than the fuel injector 28. In this mounted state, almost the entire cover member 64 is located inside the main combustion chamber 26. As a result, the cover member 64 becomes a partition wall that separates the auxiliary chamber 60 from the main combustion chamber 26.

[0071] On the cover member 64, a plurality of communication holes 66 are formed that penetrate through the inside and outside thereof and communicate with the main combustion chamber 26. The inner space of the cover member 64, that is, the auxiliary chamber 60, communicates with the main combustion chamber 26 via these communication holes 66. In the present embodiment, an example in which three communication holes 66 are formed in the cover member 64 is shown. As Figure 4 shown, the three communication holes 66 are arranged at intervals of 120 degrees around the axis of the cover member 64 passing through the vertex A of the cover member 64. In addition, as Figure 3 shown, each communication hole 66 is arranged at a position approximately 45 degrees obliquely above the vertex A in a side view. In the present embodiment, the radius of the cover member 64 is 5 mm, the thickness is 1 mm, and the diameter of each communication hole 66 is 1.2 mm.

[0072] The auxiliary ignition unit 30 having the above structure functions as a device for injecting flames into the main combustion chamber 26. When fuel is injected into the main combustion chamber 26 from the fuel injector 28 and an air-fuel mixture is formed in the main combustion chamber 26, a part of the air-fuel mixture is introduced into the auxiliary chamber 60 via the communication holes 66. When spark discharge (auxiliary ignition) is performed using the auxiliary spark plug 62 in a state where there is a sufficient amount of air-fuel mixture in the auxiliary chamber 60, the air-fuel mixture starts to burn in the auxiliary chamber 60, and the flame propagates from the vicinity of the electrode portion 62x of the auxiliary spark plug 62 to the surroundings. Moreover, the flame is ejected into the main combustion chamber 26 via the communication holes 66, and thus propagates to the air-fuel mixture in the main combustion chamber 26.

[0073] Here, if the main combustion chamber 26 is mainly ignited by the main spark plug 32 for the air-fuel mixture therein, the flame also propagates from around the electrode portion 32x of the main spark plug 32. Thus, if ignition is performed using both the main spark plug 32 and the sub-spark plug 62 to appropriately start the combustion of the air-fuel mixture 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 multiple positions (the positions of the electrode portion 32x and the respective communication holes 66). Therefore, the combustion speed of the air-fuel mixture in the main combustion chamber 26 will increase, improving the fuel consumption performance and suppressing the occurrence of knocking.

[0074] [Control System]

[0075] Figure 5 It is a block diagram showing the control system of the engine system 1. The engine system 1 includes an ECU 100 (controller) that uniformly controls each functional part included in the engine system 1. The ECU 100 is electrically connected to the above-described fuel injector 28 (fuel injection device), main spark plug 32 (main ignition device), sub-spark plug 62 (sub-ignition device), etc., and outputs control electrical signals to these devices. The ECU 100 is composed of a microcomputer, and this microcomputer includes a processor (CPU) that performs various arithmetic processes, memories such as a ROM and a RAM, and various input / output buses.

[0076] The detection information of various sensors is input to the ECU 100. The ECU 100 controls each part of the engine by performing various determinations, calculations, etc. based on the input information from various sensors. 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.

[0077] 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 rotation angle of the crankshaft 20, i.e., the crank angle and the engine speed. The accelerator opening sensor SN6 detects the opening of the accelerator pedal (not shown) provided in the vehicle, i.e., the accelerator opening.

[0078] Figure 6It is a map showing the operating region of the engine with the horizontal axis representing the engine speed and the vertical axis representing the engine load. The operating region of the engine is roughly divided into three regions A1 to A3 (the first region A1, the second region A2, and the third region A3) according to the control contents of the fuel injector 28, the main spark plug 32, and the sub-spark plug 62.

[0079] The first region A1 is a low-rotation and low-load region where the engine speed is below a specified first speed N1 and the engine load is below a specified first load Tq1. The third region A3 is a low-rotation and high-load region where the engine speed is below the first speed N1 and the engine load is higher than a specified second load Tq2. The second region A2 is the other region, in other words, it is a region composed of the region where the engine load is higher than the first load Tq1 and below the second load Tq2 in the region where the engine speed is below the first speed N1, and the region where the engine speed is higher than the first speed N1.

[0080] In the first region A1, the fuel injector 28, the main spark plug 32, and the sub-spark plug 62 are controlled in a manner to achieve HCCI combustion (Homogeneous Compression Charge Ignition). Specifically, fuel is injected from the fuel injector 28 during the intake stroke. In addition, the ignition operations of the main spark plug 32 and the sub-spark plug 62 are stopped.

[0081] The fuel injector 28 is arranged facing the main combustion chamber 26, and the fuel injected from the fuel injector 28 diffuses throughout the main combustion chamber 26. Thus, in the first region A1, by injecting fuel from the fuel injector 28 during the intake stroke, the fuel and air are sufficiently mixed in the main combustion chamber 26 during the period until the top dead center of compression is reached. In the first region A1, the sufficiently mixed mixture (premixed mixture) is heated to a high temperature and high pressure due to the compression of the piston 24, and thus self-ignites near the top dead center of compression. In HCCI combustion, the air-fuel ratio of the mixture can be made lean (increased) to a level where flame propagation cannot occur, thereby improving the fuel consumption performance. Therefore, in the first region A1, the opening degree of the throttle valve 36 is adjusted so that the air-fuel ratio of the mixture in the main combustion chamber 26 becomes leaner than the stoichiometric air-fuel ratio (14.7).

[0082] In the second region A2, the fuel injector 28, the main spark plug 32, and the sub-spark plug 62 are controlled in a manner to achieve flame propagation combustion (SI combustion). In the second region A2, similar to the first region A1, fuel is injected from the fuel injector 28 during the intake stroke. On the other hand, in the second region A2, the main spark plug 32 and the sub-spark plug 62 are driven, and main ignition and sub-ignition are performed using these two spark plugs 32 and 62. In addition, the opening degree of the throttle valve 36 is adjusted such that the air-fuel ratio of the air-fuel mixture in the main combustion chamber 26 is near the stoichiometric air-fuel ratio. In the second region A2, flame kernels are generated around the electrode portions 32x and 62x through main ignition by the main spark plug 32 and sub-ignition by the sub-spark plug 62. Through the propagation of the flame from these flame kernels to the surroundings, the air-fuel mixture in the main combustion chamber 26 and the sub-chamber 60 is combusted.

[0083] In the third region A3, the fuel injector 28, the main spark plug 32, and the sub-spark plug 62 are controlled in a manner to achieve retarded SI combustion in which the fuel injection timing is retarded compared to the second region A2. In the third region A3, fuel is injected from the fuel injector 28 during the compression stroke instead of during the intake stroke. This is because, in the third region A3 of low rotation and high load, if fuel injection is performed during the intake stroke, pre-ignition may occur in which the air-fuel mixture self-ignites before the main ignition.

[0084] In the present embodiment, in a specific region A2H within the second region A2, unique ignition control is performed. The specific region A2H is a high rotation and high load operating region where the engine speed is higher than the first speed N1 and the engine load is higher than the boundary load Tq21 (prescribed reference load). In the specific region A2H, the ECU 100 performs different ignition controls with a prescribed second speed N2 (prescribed reference speed) higher than the first speed N1 as a boundary.

[0085] The ECU 100, in the low rotation region below the second speed N2 (for example Figure 6 the operating point P1), after causing the main spark plug 32 to perform main ignition, causes the sub-spark plug 62 to perform sub-ignition. In other words, in the low rotation region of the specific region A2H, control is performed such that the main ignition is performed prior to the sub-ignition. On the other hand, in the high rotation region (for example the operating point P2) of the specific region A2H, control is performed that gives priority to the sub-ignition compared to the main ignition. Specifically, in the said high rotation region, the ECU 100 performs control of selecting one of the following three modes.

[0086] · Mode A: Only sub-ignition is performed;

[0087] · Mode B: Sub-ignition and main ignition are performed at the same time; or

[0088] ·Mode C: Execute sub-ignition and main ignition in the period after the sub-ignition.

[0089] In the operating region (operating point P1) with relatively low rotation in the specific region A2H of high load, the reciprocating movement of the piston 24 is relatively slow, so that the pressing force for pressing the air-fuel mixture into the sub-chamber 60 becomes weak. Therefore, the flow of the air-fuel mixture in the sub-chamber 60 becomes slow, and the combustion speed in the sub-chamber 60 also becomes slow. As a result, there is a tendency for the flame ejected from the sub-chamber 60 to become weak. In view of this, the ECU 100 executes sub-ignition after executing main ignition in the operating region of high load and low rotation. Thereby, the inflow of the air-fuel mixture into the sub-chamber 60 is promoted. That is, by superimposing the combustion pressure of the flame propagation combustion generated by the main ignition on the pressing force of the piston 24, the pressing force for pressing the air-fuel mixture into the sub-chamber 60 increases. Therefore, the flow of the air-fuel mixture in the sub-chamber 60 speeds up, and the combustion speed in the sub-chamber 60 also speeds up. As a result, a stronger flame can be ejected from the sub-chamber 60 through the communication hole 66, and the unburned air-fuel mixture remaining in the main combustion chamber 26 can be burned well.

[0090] On the contrary, in the operating region (operating point P2) with relatively high rotation in the specific region A2H, there is a tendency for knocking to easily occur in the main combustion chamber 26 originally. In view of this, the ECU 100 ejects a flame from the sub-chamber 60 by executing sub-ignition first in the operating region of high load and high rotation. For example, only sub-ignition (mode A) is executed at a prescribed period, and all the air-fuel mixture in the main combustion chamber 26 is subjected to SI combustion by the flame ejected from the sub-chamber 60. Or, main ignition is executed together with sub-ignition at the same time (mode B), a flame is ejected from the sub-chamber 60, and a flame kernel is formed around the electrode portion 32x of the main spark plug 32, and the air-fuel mixture in the main combustion chamber 26 is subjected to SI combustion. Or, main ignition is executed after executing sub-ignition first (mode C), the air-fuel mixture in the main combustion chamber 26 is first subjected to SI combustion by the flame from the sub-chamber 60, and the remaining air-fuel mixture is burned by the main ignition of the main spark plug 32. Through any one of these controls, the combustion in the main combustion chamber 26 is accelerated, and knocking can be suppressed.

[0091] [Specific control examples in specific regions]

[0092] Next, specific control examples in the above-mentioned specific region A2H will be described. Figure 7 It is a flowchart showing an example of the fuel injection control of the fuel injector 28 and the ignition control of the main spark plug 32 and the sub-spark plug 62 executed by the ECU 100 when the operating region is the specific region A2H. Here, an example of executing the control of the above-mentioned "mode C" in the high rotation region (operating point P2) of the specific region A2H is shown.

[0093] When a prescribed sampling period arrives, the ECU 100 reads various information from Figure 5 the various sensors SN1 to 6 and other sensors shown (step S1). In order to perform the above-described fuel injection control and ignition control, the ECU 100 reads the engine speed detected by the crank angle sensor SN5 and the opening degree of the accelerator pedal detected by the accelerator opening sensor SN6.

[0094] Next, the ECU 100 calculates the torque required for the engine body 2, that is, the required torque, or in other words, the engine load (step S2). The ECU 100 calculates the required torque (engine load) based on the engine speed and the opening degree of the accelerator pedal read in step S1.

[0095] Next, the ECU 100 determines whether the operating point of the engine body 2 is a specific area A2H within the second area A2 (refer to Figure 6 the operating map) (step S3). Specifically, the ECU 100 determines whether the current operating point of the engine is a point within the specific area A2H based on the engine speed read in step S1 and the engine load calculated in step S2.

[0096] When the operating point of the engine body 2 is not a point within the specific area A2H (in step S3, "no"), the ECU 100 executes control corresponding to other operating areas, that is, fuel injection control and ignition control preset for the first area A1, the third area A3, or the area other than the specific area A2H within the second area A2 (step S8). On the other hand, when the operating point of the engine body 2 is a point within the specific area A2H (in step S3, "yes"), the ECU 100 executes the processes of steps S4 to S7. Through these processes, the fuel injection period, that is, the period when the fuel injector 28 starts fuel injection, the main ignition period, that is, the period when the main spark plug 32 ignites (spark discharge), and the sub-ignition period, that is, the period when the sub-spark plug 62 ignites (spark discharge) are set.

[0097] In step S4, the ECU 100 determines whether the operating point of the engine body 2 is a low rotation area within the specific area A2H (step S4). When the operating point is in the low rotation area within the specific area A2H and is below the second rotation speed N2 (for example, the operating point P1) (in step S4, "yes"), the ECU 100 sets the main ignition period and the sub-ignition period in such a way that the sub-ignition is executed after the main ignition (step S5).

[0098] On the contrary, when the operating point is in the high rotation region where the rotational speed exceeds the second rotational speed N2 within the specific region A2H (e.g., the operating point P2) (in step S4, "No"), the ECU 100 sets the main ignition timing and the sub-ignition timing in such a manner that the main ignition is performed after the sub-ignition is executed (step S6). In addition, in either of the above-mentioned low rotation region and high rotation region, the fuel injection timing is set to a specified timing in the intake stroke.

[0099] Thereafter, the ECU 100 drives the fuel injector 28 in such a manner that the fuel injection starts at the set fuel injection timing. In addition, the ECU 100 drives the main spark plug 32 in such a manner that the main ignition is performed at the main ignition timing set by step S5 or S6, and drives the sub-spark plug 62 in such a manner that the sub-ignition is performed at the sub-ignition timing set by step S5 or S6 (step S7). In actual control, for the engine load and the engine speed, a control map associating the fuel injection timing, the main ignition timing, and the sub-ignition timing is stored in advance in the storage area of the ECU 100, and the fuel injection timing and the ignition timing are set with reference to the control map.

[0100] Figure 8 It is a timing chart showing the fuel injection timing, the main ignition timing tm, and the sub-ignition timing ts at the operating point P1 in the low rotation region within the specific region A2H. The fuel injection timing in the low rotation region is in the intake stroke. Specifically, the fuel injection start timing and the fuel injection end timing of the fuel injector 28 are set to be included in the intake stroke. This is because, in the specific region A2H, there is little requirement to delay the fuel injection timing like in the third region A3 to suppress pre-ignition. In addition, the fuel injection end timing may also be close to the compression stroke.

[0101] In the low rotation region within the specific region A2H, as described in Figure 7 step S5, the main ignition timing tm is set to a timing on the advance angle side compared to the sub-ignition timing ts. That is, first, the main ignition is performed using the main spark plug 32, and then, the sub-ignition is performed using the sub-spark plug 62. The main ignition timing tm is set in the compression stroke slightly on the advance angle side compared to the top dead center TDC, and the sub-ignition timing ts is set in the first half of the expansion stroke. By the prior main ignition near the TDC, the SI combustion of the air-fuel mixture in the main combustion chamber 26 starts. In the low rotation region, since the reciprocating movement of the piston 24 is relatively slow, the pressure for pressing the air-fuel mixture into the sub-chamber 60 is weak. However, with the assistance of the pressure rise accompanying the SI combustion, the unburned air-fuel mixture remaining in the main combustion chamber 26 is pressed into the sub-chamber 60 through the communication hole 66. Thus, a sufficient amount of air-fuel mixture accompanied by a rapid flow is introduced into the sub-chamber 60.

[0102] After the main ignition, the sub-ignition is carried out, and the air-fuel mixture introduced into the sub-chamber 60 burns. As described above, the flow of the air-fuel mixture in the sub-chamber 60 is relatively fast, so the combustion speed of the air-fuel mixture after this sub-ignition is also relatively fast. As a result, stronger flames can be ejected from the plurality of communication holes 66. These flames cause the unburned air-fuel mixture in the main combustion chamber 26 to burn all at once. Therefore, the fuel consumption performance and exhaust gas performance can be improved.

[0103] Figure 9 It is a timing chart showing the fuel injection timing, main ignition timing tm, and sub-ignition timing ts at the operating point P2 in the high rotation region within the specific region A2H. The fuel injection timing in the high rotation region is the same as that in the low rotation region described above and is during the intake stroke. As described in step S6 of Figure 7 , the sub-ignition timing ts is set to a period on the advance angle side compared to the main ignition timing tm. That is, contrary to the low rotation region described above, first, the sub-spark plug 62 is used for sub-ignition, and then, the main spark plug 32 is used for main ignition. The sub-ignition timing ts is a period relatively close to the top dead center TDC in the compression stroke, and the main ignition timing tm is a period relatively close to the TDC in the expansion stroke.

[0104] In the high rotation region, since the reciprocating movement of the piston 24 is relatively fast, it is easy to introduce the air-fuel mixture into the sub-chamber 60. Therefore, even if the sub-ignition is carried out first, misfire is not likely to occur. The air-fuel mixture in the sub-chamber 60 burns through the sub-ignition, and its flames are ejected from the plurality of communication holes 66. Taking these flames as the ignition points, the air-fuel mixture in the main combustion chamber 26 starts SI combustion. Through the main ignition after this sub-ignition, the air-fuel mixture remaining in the main combustion chamber 26 burns all at once. Therefore, the combustion speed of the air-fuel mixture in the main combustion chamber 26 is accelerated, and knocking that is likely to occur in the high rotation region can be suppressed.

[0105] [Relationship between engine speed and ignition control]

[0106] Figure 10 It is a line graph showing the relationship between the engine speed and the main ignition timing ( Figure 10 upper graph), sub-ignition timing (middle graph), and ignition phase difference (lower graph) in the specific region A2H. In Figure 10 , the low rotation region and the high rotation region are distinguished with the second speed N2 (prescribed reference speed) as the reference speed. The vertical axis of each line graph is the crank angle. The advance angle side compared to the TDC is the compression stroke, and the retard angle side is the expansion stroke. In Figure 8 , Figure 9 , the ignition control examples at the specific operating point P1 in the low rotation region and the specific operating point P2 in the high rotation region are respectively shown. In Figure 10shows the trend of ignition control in all the rotation regions of a specific region A2H executed by the ECU 100. Additionally, Figure 10 The line graph of

[0107] The main ignition timing is set in the compression stroke in order to perform ignition first in the low rotation region. The main ignition timing in the low rotation region is controlled such that as the engine speed becomes higher, it gradually moves from TDC to the advance angle side more slowly. This control includes the intention that the higher the engine speed, the earlier the SI combustion starts, thereby suppressing the occurrence of self-ignition in the main combustion chamber 26.

[0108] In the high rotation region, the main ignition timing is set in the expansion stroke in order to perform ignition later. That is, at the inversion point of the ignition control, i.e., the second speed N2, the main ignition timing steps from the advance angle side to the retard angle side with respect to TDC. The main ignition timing in the high rotation region is the most retarded at the point of the second speed N2 and moves toward the advance angle side in such a way that the higher the engine speed, the closer it gets to TDC.

[0109] The sub-ignition timing is set in the expansion stroke in order to perform ignition later in the low rotation region. In this low rotation region, the ECU 100 controls such that the lower the engine speed is in the low rotation, the more the sub-ignition timing is retarded. Specifically, the sub-ignition timing is set near TDC at the second speed N2 and is controlled to move more toward the retard angle side as the engine speed decreases. The lower the engine speed, the weaker the pressing force of the piston 24, and there is a tendency that it becomes more difficult to introduce the air-fuel mixture into the sub-chamber 60. Therefore, by retarding the sub-ignition timing more as the engine speed is lower, the period from the main ignition to the sub-ignition can be made longer. Thereby, the time for pressing the air-fuel mixture into the sub-chamber 60 can be sufficiently ensured, and the flame can be reliably ejected from the plurality of communication holes 66.

[0110] The sub-ignition timing is set in the compression stroke in order to perform ignition first in the high rotation region. In this high rotation region, the ECU 100 controls such that the higher the engine speed is in the high rotation, the more the sub-ignition timing is advanced. Specifically, the sub-ignition timing is set near TDC at the second speed N2 and is controlled to move more toward the advance angle side as the engine speed increases. There is a tendency that the higher the engine speed, the more likely knocking occurs. Therefore, if the sub-ignition timing is advanced more as the engine speed is higher as in this control example, the SI combustion based on the flame ejected from the sub-chamber 60 can start from an earlier period. Therefore, the combustion speed of the air-fuel mixture in the main combustion chamber 26 can be made faster, which can contribute to suppressing knocking.

[0111] As Figure 8 、 Figure 9As shown, the ignition phase difference dt is the phase difference in terms of crank angle between the main ignition period tm and the sub-ignition period ts. In the low rotation region of the specific region A2H, the lower the engine speed, the larger the ignition phase difference dt is set. In the low rotation region, the lower the engine speed, the more delayed the sub-ignition period ts. In the low rotation region, the main ignition period tm also moves more towards the retard angle side as the engine speed decreases, but the degree of its movement is smaller than that of the sub-ignition period ts. Therefore, the lower the engine speed, the larger the ignition phase difference dt becomes. Additionally, in the high rotation region, the ignition phase difference dt is substantially constant.

[0112] As described above, the lower the engine speed, the larger the ignition phase difference dt is set, so that the time for injecting the air-fuel mixture into the sub-chamber 60 can be sufficiently ensured according to the engine speed. In other words, setting the ignition phase difference dt larger makes the period between the main ignition that ignites first and the sub-ignition that ignites later longer in the low rotation region. Therefore, the introduction effect of injecting the air-fuel mixture into the sub-chamber 60 accompanying the combustion in the main combustion chamber 26 can be easily obtained.

[0113] [Modification Example]

[0114] The above has described the embodiments of the present invention, but the present invention is not limited to the above embodiments, and the following modified embodiments can be adopted.

[0115] (1) In the control of the high rotation region (P2) shown in Figure 9 、 Figure 10 , an example of the control based on the above "Mode C" is shown. In the case of performing the control of the above "Mode A" (only sub-ignition is executed), only the sub-ignition period ts is set. In this case, in order to suppress knocking, the sub-ignition period shown in Figure 10 can also be integrally shifted towards the advance angle side. Additionally, in the case of performing the control of the above "Mode B" (sub-ignition and main ignition are executed at the same time), the main ignition period tm and the sub-ignition period ts are set to the same period (ignition phase difference dt = 0).

[0116] (2) In the above embodiment, as the cover member 64 of the sub-ignition unit 30, a dome shape having a semi-sphere ( Figure 3 ) and having three communication holes 66 ( Figure 4 ) is shown. The shape of the cover member 64 can also be other shapes such as a frustum of a cone shape or a rectangular parallelepiped shape. Additionally, the number and size of the communication holes 66 can be appropriately set. Additionally, the installation position of the sub-ignition unit 30 is not limited to the Figure 2 form. For example, the sub-ignition unit 30 can also be provided on the intake port 8 side with respect to the front end portion 28x of the fuel injector 28.

[0117] (3) In the above-described embodiment, an example is shown in which a specific region A2H is set within the range of the second region A2 (lower limit engine speed = N1). Instead, the lower limit engine speed of the specific region A2H may be expanded toward the low rotation side as compared with N1. That is, a part on the high rotation side of the third region A3 shown Figure 6 may be incorporated into the specific region A2H.

Claims

1. An engine system, characterized in that, it comprises: a cylinder block and a cylinder head that form a cylinder; a piston that is reciprocally movably received in the cylinder; a main combustion chamber that is delimited by the cylinder block, the cylinder head, and the piston; a sub-chamber that is separated from the main combustion chamber by a partition wall and is in communication 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 for igniting the air-fuel mixture in the main combustion chamber; a sub-ignition device that performs sub-ignition for igniting the air-fuel mixture in the sub-chamber; and a controller that is electrically connected to the fuel injection device, the main ignition device, and the sub-ignition device and outputs control electrical signals to these devices; when the engine is operating in a high load region where the engine load is higher than a specified reference load, the controller performs the following control: in a low rotation region where the engine speed is below a specified reference speed, the sub-ignition is performed after the main ignition; in a high rotation region where the engine speed exceeds the reference speed, only the sub-ignition is performed, or the sub-ignition and the main ignition that is performed at the same time as or after the sub-ignition are performed, in the low rotation region, the lower the engine speed is, the greater the ignition phase difference between the sub-ignition and the main ignition is set by the controller.

2. The engine system according to claim 1, characterized in that, in the low rotation region, the lower the engine speed is, the more the controller delays the timing of the sub-ignition.

3. The engine system according to claim 1, characterized in that, in the high rotation region, the higher the engine speed is, the more the controller advances the timing of the sub-ignition.

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