Engine system

Abstract

To appropriately combust mixed gas in an auxiliary chamber during idling operation.SOLUTION: An engine system 1 comprises: a main combustion chamber 25; an auxiliary chamber 60 which is separated from the main combustion chamber 25 by a bulkhead (64) and communicated with the main combustion chamber 25 through a communication hole 66 formed on the bulkhead (64); an intake air introduction passage (8) in which intake air to be introduced into the main combustion chamber 25 is circulated; a first fuel injection device (26) which injects fuel into the main combustion chamber 25; a second fuel injection device (28) which injects the fuel into the intake air introduction passage (8); an ignition device (62) which ignites mixed gas in the auxiliary chamber 60; and a control unit (100) which controls respective devices. When an engine is in idling operation, the control unit (100) controls the second fuel injection device (28) and the ignition device (62) so that the fuel is injected from the second fuel injection device (28) in an air intake stroke and the fuel is ignited with the ignition device (62) after fuel is injected.SELECTED DRAWING: Figure 8

Description

Technical Field

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

Background Art

[0002] There is known an engine including a main combustion chamber defined by a cylinder block, a cylinder head, and a piston, and an auxiliary chamber adjacent to the main combustion chamber, and having a communication hole formed in a wall defining the auxiliary chamber. For example, Patent Document 1 below discloses an engine including a main combustion chamber and an auxiliary chamber, a main fuel injection valve that injects fuel into an intake port, an auxiliary fuel injection valve that injects fuel into the auxiliary chamber, a main ignition plug that ignites an air-fuel mixture in the main combustion chamber, and an auxiliary ignition plug that ignites an air-fuel mixture in the auxiliary chamber. In this engine, the respective fuel injection valves and the respective ignition plugs are controlled so that the air-fuel mixture in the auxiliary chamber burns after the air-fuel mixture in the main combustion chamber burns. When the air-fuel mixture in the auxiliary chamber burns, a flame is ejected from the auxiliary chamber into the main combustion chamber through the communication hole, and the unburned air-fuel mixture in the main combustion chamber burns by this ejected flame (torch flame). Thereby, it is suppressed that unburned air-fuel mixture remains in the main combustion chamber, and it is said that fuel consumption performance and exhaust gas performance are improved.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Here, it is conceivable to modify the engine of Patent Document 1 above and provide a fuel injection valve in the main combustion chamber instead of the auxiliary chamber. However, if this is done, the possibility of misfire occurring in the auxiliary chamber becomes high, especially during idling operation. That is, during idling operation, since the fuel injection amount is small and the fuel pressure (fuel injection pressure) is also low, the required time from when fuel is injected into the main combustion chamber until the air-fuel mixture in the main combustion chamber becomes homogeneous tends to be long. This means that it is difficult for the concentration of the air-fuel mixture introduced from the main combustion chamber into the auxiliary chamber through the communication hole to increase. When the concentration of the air-fuel mixture in the auxiliary chamber is low, there is a high possibility that even if the air-fuel mixture in the auxiliary chamber is ignited by the auxiliary spark plug, the air-fuel mixture will not burn, that is, misfire will occur.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide an engine system capable of appropriately burning the air-fuel mixture in the auxiliary chamber during idling operation.

Means for Solving the Problems

[0006] As means for solving the above problems, the engine system of 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, an auxiliary 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, an intake introduction passage through which intake air introduced into the main combustion chamber flows, An intake valve that opens and closes the intake introduction passage, a first fuel injection device that injects fuel into the main combustion chamber, a second fuel injection device that injects fuel into the intake introduction passage, A main ignition device that ignites the air-fuel mixture in the main combustion chamber, an ignition device that ignites the air-fuel mixture in the auxiliary chamber Sub and a controller electrically connected to the first fuel injection device, the second fuel injection device The rec Main ignition device And the sub-ignition device and outputs an electric signal for control to each of the devices. When the engine is operating in idling operation, the controller causes fuel to be injected from the second fuel injection device during the intake stroke and after the fuel injection, the SubSo that ignition is performed by the ignition device, the second fuel injection device and the Sub ignition device are controlled Together with this, the main ignition device is made to ignite before the ignition timing of the sub-ignition device. The ignition timing by the main ignition device during the idling operation is set to a timing such that the air-fuel mixture existing in the main combustion chamber does not ignite, on the retard side from the closing timing of the intake valve and on the advance side from top dead center of compression. , which is characterized by the following.

[0007] In the present invention, "fuel is injected during the intake stroke" means that at least a part of the required fuel for one combustion cycle is injected during the intake stroke, and does not necessarily mean that all of the required fuel is injected during the intake stroke.

[0008] According to the present invention, during idling operation, since fuel is injected during the intake stroke from the second fuel injection device that injects fuel into the intake introduction passage, the injected fuel from the second fuel injection device can be introduced into the main combustion chamber together with the intake air that vigorously flows from the intake introduction passage into the main combustion chamber, and the fluidity of the fuel can be enhanced. As a result, Sub before ignition in the auxiliary chamber by the ignition device, fuel and air can be sufficiently mixed, and a sufficiently homogeneous air-fuel mixture can be formed in the main combustion chamber. When the air-fuel mixture in the main combustion chamber is homogenized, the concentration of the air-fuel mixture introduced from the main combustion chamber into the auxiliary chamber through the communication holes formed in the partition wall is stabilized, so that the concentration deficiency of the air-fuel mixture formed in the auxiliary chamber at the ignition time can be eliminated. That is, Sub before ignition in the auxiliary chamber by the ignition device, it becomes possible to form an air-fuel mixture with a desired concentration suitable for combustion (flame propagation) in the auxiliary chamber. As a result, Sub the air-fuel mixture in the auxiliary chamber can be appropriately burned triggered by the ignition of the ignition device, and the flame can be ejected from the auxiliary chamber into the main combustion chamber through the communication holes. The flame ejected from the communication holes burns the air-fuel mixture in the main combustion chamber at a sufficient speed. As a result, the thermal efficiency during idling operation can be increased, and the fuel consumption performance of the engine can be improved. Also, during the idling operation, since the main ignition device ignites before the ignition timing of the sub-ignition device, the ignitability of the air-fuel mixture can be enhanced. That is, even if the main ignition (ignition in the main combustion chamber by the main ignition device) is performed before the sub-ignition (ignition in the sub-chamber by the sub-ignition device) during the idling operation where the fuel injection amount is small, this main ignition does not bring about the action of burning the air-fuel mixture in the main combustion chamber. However, the main ignition brings about the action of raising the temperature in the main combustion chamber by discharge energy. When the temperature in the main combustion chamber rises, the temperature of the air-fuel mixture introduced from the main combustion chamber to the sub-chamber rises, so it is possible to prevent misfire during the subsequent sub-ignition with a higher probability. Thereby, the combustibility of the air-fuel mixture during the idling operation can be enhanced, and the fuel consumption performance of the engine can be improved.

[0009] Preferably, the intake introduction passage includes an intake port formed in the cylinder head, and in the cylinder head, there are the second fuel injection device that injects fuel into the intake port and the one that opens and closes the intake port The An intake valve is provided, and the controller starts fuel injection to the second fuel injection device before the valve opening timing of the intake valve during the idling operation.

[0010] According to this configuration, the injected fuel from the second fuel injection device can be introduced into the main combustion chamber together with the intake air, particularly immediately after the intake valve opens and the intake air vigorously flows from the intake port into the main combustion chamber. Thereby, the air-fuel mixture in the main combustion chamber can be sufficiently homogenized, and the concentration of the air-fuel mixture in the auxiliary chamber can be sufficiently ensured.

[0011] Preferably, the engine system A variable valve mechanism that variably sets the opening and closing timing of the intake valve further includes, and the controller, during the idling operation, Control the variable valve mechanism so that the intake valve closes in the middle of the compression stroke and the closing timing of the intake valve is on the retard side compared to non-idling operation. .

[0013] When the engine is operating in a non-idling state, it is preferable that the controller injects fuel into the first fuel injection device.

[0014] According to this configuration, during non-idling operation with relatively good ignitability, the air-fuel mixture based on the fuel directly injected into the main combustion chamber from the first fuel injection device can be efficiently burned.

Advantages of the Invention

[0015] As described above, according to the engine system of the present invention, the air-fuel mixture in the auxiliary chamber can be appropriately burned during idling operation.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Mode for Carrying Out the Invention

[0017] Hereinafter, based on the drawings, an engine system according to an embodiment of the present invention will be described in detail. The engine system exemplified in this embodiment is an in-vehicle engine system 1 mounted on a vehicle such as an automobile as a power source for driving the vehicle to travel.

[0018] [Overall Configuration of Engine] FIG. 1 is a schematic configuration diagram of the engine system 1. 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, and an exhaust passage 6 through which exhaust gas derived from the engine body 2 flows. The engine body 2 is a four-stroke gasoline engine that receives the supply of fuel containing gasoline.

[0019] FIG. 2 is a schematic cross-sectional view of the engine body 2. 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, 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. That is, a plurality of cylindrical spaces corresponding to the plurality of cylinders 22 are formed inside the cylinder block 52, and the cylinder head 54 is attached to the upper surface of the cylinder block 52 so as to close the cylindrical space from above. The piston 24 is reciprocally slidably accommodated in each cylinder 22. In this embodiment, the side from the cylinder block 52 toward the cylinder head 54 is regarded as the upper side, and the opposite side is regarded as the lower side for convenience of explanation, but this is for convenience of explanation and does not limit the installation posture of the engine body 2.

[0020] Above the piston 24 of each cylinder 22, a main combustion chamber 25 is formed. The main combustion chamber 25 is a space defined by the inner peripheral surface 22a of the cylinder block 52 that defines the side peripheral surface (cylinder liner) of the cylinder 22, the bottom surface 54a of the cylinder head 54 that defines the upper surface of the cylinder 22, and the crown surface 24a of the piston 24. Fuel is supplied to the main combustion chamber 25 by injection from injectors 26 and 28 described later. The air-fuel mixture supplied burns in the main combustion chamber 25, and the piston 24 reciprocates in the vertical direction under the expansion force generated by the combustion.

[0021] Below 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 piston 24 of each cylinder 22 via a connecting rod 21, and rotates around the central axis in accordance with the reciprocating motion of the piston 24.

[0022] The cylinder head 54 is formed with an intake port 8 and an exhaust port 12 that communicate with the main combustion chamber 25 of each cylinder 22. Further, the cylinder head 54 is equipped with a combination of an intake valve 10 and an exhaust valve 14 for each cylinder 22. The intake port 8 is a port for introducing the air supplied from the intake passage 4 into the main combustion chamber 25. The exhaust port 12 is a port for leading the burned gas (exhaust gas) generated in the main combustion chamber 25 to the exhaust passage 6. The intake valve 10 is a valve that opens and closes the opening on the main combustion chamber 25 side of the intake port 8. The exhaust valve 14 is a valve that opens and closes the opening on the main combustion chamber 25 side of the exhaust port 12. In the present embodiment, two intake valves 10 and two exhaust valves 14 are provided for each cylinder 22.

[0023] The intake valve 10 and the exhaust valve 14 are respectively opened and closed by valve operating mechanisms 16, 18 disposed in the cylinder head 54. The valve operating mechanisms 16, 18 include, for example, a pair of camshafts linked to the crankshaft 20, and open and close the intake valve 10 and the exhaust valve 14 of each cylinder 22 in conjunction with the rotation of the crankshaft 20. The valve operating mechanism 16 for the intake valve 10 incorporates an electronically controlled variable valve mechanism, the intake S-VT16a, which variably sets the opening and closing timing of the intake valve 10.

[0024] The cylinder head 54 is equipped with a combination of a direct injection injector 26, a port injector 28, a main ignition plug 32, and a sub-ignition unit 30 for each cylinder 22. Note that the direct injection injector 26 corresponds to the "first fuel injection device" in the present invention, and the port injector 28 corresponds to the "second fuel injection device" in the present invention. Further, the main ignition plug 32 corresponds to the " Main ignition device" in the present invention.

[0025] The direct injection injector 26 is an injection valve that injects fuel into the main combustion chamber 25. The direct injection injector 26 has a tip portion 26a that faces the main combustion chamber 25 from above. A nozzle is formed in the tip portion 26a of the direct injection injector 26, and fuel is injected from the nozzle toward the main combustion chamber 25. The direct injection injector 26 is attached to the cylinder head 54 such that its tip portion 26a is located at the center of the ceiling surface of the main combustion chamber 25, more specifically, on the axis of the cylinder 22.

[0026] The port injector 28 is an injection valve that injects fuel into the intake port 8. The port injector 28 has a tip portion 28a that faces the intake port 8 from above. A nozzle is formed in the tip portion 28a of the port injector 28, and fuel is injected from the nozzle toward the intake port 8. The fuel injected from the port injector 28 into the intake port 8 is introduced into the main combustion chamber 25 together with the intake air flowing through the intake port 8.

[0027] The main ignition plug 32 is a plug that performs main ignition to ignite the air-fuel mixture in the main combustion chamber 25. An electrode portion 32x for discharging a spark is provided at the tip of the main ignition plug 32. The electrode portion 32x includes a center electrode 32a and a side electrode 32b for grounding. The main ignition plug 32 is attached to the cylinder head 54 such that its electrode portion 32x faces the main combustion chamber 25 from above. The electrode portion 32x of the main ignition plug 32 is disposed on the intake side of the ceiling surface of the main combustion chamber 25 with respect to the tip portion 26a of the direct injection injector 26.

[0028] The sub-ignition unit 30 is a device for ejecting a flame into the main combustion chamber 25. The structure of the sub-ignition unit 30 will be described in detail later.

[0029] 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 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 this order from the upstream side. The portion of the intake passage 4 downstream of the surge tank 38 branches into a plurality of passages, and each of these branched passages is connected to the intake port 8 of each cylinder 22. Note that the combination of the intake passage 4 and the intake port 8 corresponds to the "intake introduction passage" in the present invention.

[0030] The exhaust passage 6 is connected to one side surface (the surface opposite to the intake passage 4) of the cylinder head 54 so as to communicate with the exhaust port 12 of each cylinder 22. A catalyst device 40 having a catalyst 41 such as a three-way catalyst incorporated therein is provided in the exhaust passage 6.

[0031] [Details of the 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, and FIG. 4 is a plan view of the tip portion 30x as viewed from below. As shown in this figure, the sub-ignition unit 30 includes a sub-ignition plug 62, a cover member 64 that covers the tip of the sub-ignition plug 62, and a sub-chamber 60 that is the internal space of the cover member 64. Note that the sub-ignition plug 62 corresponds to the " Sub ignition device" in the present invention, and the cover member 64 corresponds to the "partition wall" in the present invention.

[0032] The sub-ignition plug 62 is a plug that performs sub-ignition for igniting the air-fuel mixture in the sub-chamber 60. An electrode portion 62x that discharges 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 62b for grounding.

[0033] The cover member 64 is a cover that forms the outer contour of the tip portion 30x of the sub-ignition unit 30, and is attached so as to cover the periphery of the electrode portion 62x of the sub-ignition plug 62. The cover member 64 has a hemispherical (dome-shaped) shape that bulges downward.

[0034] The auxiliary chamber 60 is the surrounding space of the electrode portion 62x of the auxiliary spark plug 62 and is surrounded by the cover member 64. Since it is such a space, the size of the auxiliary chamber 60 is smaller compared to the size of the main combustion chamber 25. The electrode portion 62x of the auxiliary spark plug 62 is disposed so as to face the auxiliary chamber 60, and the auxiliary ignition is performed by discharging a spark into the auxiliary chamber 60.

[0035] As shown in FIG. 2, the auxiliary ignition unit 30 is attached to the cylinder head 54 such that its tip portion 30x faces the main combustion chamber 25 from above. The tip portion 30x of the auxiliary ignition unit 30 is disposed on the exhaust side of the tip portion 26a of the direct injection injector 26 in the ceiling surface of the main combustion chamber 25. In this mounting state, substantially the entire cover member 64 is exposed to the main combustion chamber 25. In other words, the cover member 64 functions as a partition wall separating the auxiliary chamber 60 and the main combustion chamber 25.

[0036] A plurality of communication holes 66 penetrating through the front and back of the cover member 64 and communicating with the main combustion chamber 25 are formed in the cover member 64. The auxiliary chamber 60, which is the inner space of the cover member 64, communicates with the main combustion chamber 25 through 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 shown in FIG. 4, the three communication holes 66 are arranged at intervals of 120 degrees around the axis of the cover member 64 passing through the vertex Q of the cover member 64. Further, as shown in FIG. 3, each communication hole 66 is disposed at a position obliquely upward by about 45 degrees from the vertex Q 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.

[0037] The sub-ignition unit 30 having the above configuration functions as a device for ejecting a flame into the main combustion chamber 25. When fuel is ejected from at least one of the direct injection injector 26 and the port injector 28 into the main combustion chamber 25 and an air-fuel mixture is formed in the main combustion chamber 25, a part of this air-fuel mixture is introduced into the sub-chamber 60 through the communication hole 66. When sub-ignition is performed with the air-fuel mixture present in the sub-chamber 60 and a spark is discharged from the electrode portion 62x of the sub-ignition plug 62, the air-fuel 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, the flame is ejected into the main combustion chamber 25 through the communication hole 66 and propagates to the air-fuel mixture in the main combustion chamber 25.

[0038] [Control system] FIG. 5 is a functional block diagram showing the control system of the engine system 1. As shown in this figure, the engine system 1 includes an ECU 100 that comprehensively controls each functional part provided in the engine system 1. The ECU 100 is a controller configured by 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 is electrically connected to devices such as the above-described direct injection injector 26, port injector 28, main ignition plug 32, sub-ignition plug 62, intake S-VT 16a, and throttle valve 36, and outputs control electrical signals to these devices.

[0039] Information detected by various sensors provided in the engine system 1 and the like is sequentially input to the ECU 100 as electrical signals. The ECU 100 controls each part of the engine while performing various determinations and calculations based on the input type information from the various sensors. Specifically, the engine system 1 is provided with 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. In addition, a vehicle equipped with the engine system 1 is provided with an accelerator opening sensor SN6. The ECU 100 is electrically connected to these sensors SN1 to SN6 and sequentially receives the information detected by these sensors SN1 to SN6.

[0040] The air flow sensor SN1 is a sensor that 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 are sensors that respectively detect the temperature and pressure of the intake air introduced into the engine body 2. The coolant temperature sensor SN4 is a sensor that detects the engine coolant temperature, which is the temperature of the coolant flowing through the inside of the cylinder block 52 and the cylinder head 54 to cool the engine body 2. The crank angle sensor SN5 is a sensor that detects the crank angle, which is the rotation angle of the crankshaft 20, and the engine speed, which is the number of rotations of the crankshaft 20. The accelerator opening sensor SN6 is a sensor that detects the accelerator opening, which is the opening of an accelerator pedal (not shown) provided in the vehicle.

[0041] Figure 6 is an engine operation map with the engine speed on the horizontal axis and the engine load on the vertical axis. The engine operation region is divided into an idle region A1 and a non-idle region A2 depending on whether the direct injection injector 26 or the port injector 28 is used.

[0042] The idle region A1 is a region corresponding to the idling operation of the engine, and is an operation region where both the engine load and the engine speed are at the lowest levels. Corresponding to this idle region A1 means that the engine is being operated under the conditions that the vehicle is substantially stopped and the accelerator opening is substantially zero. That is, in the idle region A1, combustion that generates the minimum torque required for the engine to perform stable self-rotation is performed in each cylinder 22 of the engine body 2. The fuel required for combustion in each cylinder 22 is supplied by injection from the port injector 28. In other words, in the idle region A1, only the port injector 28 operates as the fuel supply source, and the direct injection injector 26 is stopped.

[0043] The non-idle region A2 is the remaining operating region excluding the idle region A1. In the non-idle region A2, in order to generate torque contributing to the running of the vehicle, combustion that generates higher torque than in the idle region A1 is performed in each cylinder 22. The fuel required for combustion in each cylinder 22 is supplied by injection from the direct injection injector 26. In other words, in the non-idle region A2, only the direct injection injector 26 operates as the fuel supply source, and the port injector 28 is stopped.

[0044] [Control Operation] Next, a specific control example of the engine system 1 will be described with reference to FIGS. 7 to 9. FIG. 7 is a flowchart showing the details of the control executed by the ECU 100 during engine operation. FIG. 8 is a time chart showing the timings of fuel injection and spark ignition executed in the idle region A1. FIG. 9 is a time chart showing the timings of fuel injection and spark ignition executed in the non-idle region A2. (a) shows the case of low-speed conditions where the engine speed is relatively low within the non-idle region A2, and (b) shows the case of high-speed conditions where the engine speed is relatively high within the non-idle region A2.

[0045] When the control shown in FIG. 7 starts, the ECU 100 reads various information (step S1). Specifically, the ECU 100 reads at least the engine speed detected by the crank angle sensor SN5 and the accelerator opening detected by the accelerator opening sensor SN6.

[0046] Next, the ECU 100 calculates the required torque, that is, the engine load, required for the engine (step S2). Specifically, the ECU 100 calculates the required torque (engine load) based on the engine speed and the accelerator opening read in step S1 above.

[0047] Next, the ECU 100 determines whether the engine is operating in the idle region A1 (step S3). Specifically, the ECU 100 determines whether the current operating point of the engine corresponds to the idle region A1 based on the engine speed read in step S1 and the required torque (engine load) calculated in step S2.

[0048] If it is determined YES in step S3 and it is confirmed that the engine is operating in the idle region A1, the ECU 100 controls the intake S-VT 16a so that the opening / closing timing of the intake valve 10 becomes relatively late (step S4). Specifically, the ECU 100 controls the intake S-VT 16a so that the lift curve, which is the change in the lift amount of the intake valve 10, becomes a curve as shown in FIG. 8, that is, the intake valve 10 opens at the time point t1 in the middle of the intake stroke and closes at the time point t2 in the middle of the compression stroke. In other words, in the idle region A1, the intake valve 10 opens with a delay of a predetermined crank angle from the exhaust top dead center (TDC between the exhaust stroke and the intake stroke), which is the start of the intake stroke, and closes with a delay of a predetermined crank angle from the intake bottom dead center (BDC between the intake stroke and the compression stroke), which is the end of the intake stroke. The opening / closing timing of the intake valve 10 by the intake S-VT 16a is set.

[0049] Next, the ECU 100 causes the port injector 28 to inject fuel (step S5). Specifically, as shown in FIG. 8, the ECU 100 controls the port injector 28 so that the required fuel for one combustion cycle is mainly injected at the beginning of the intake stroke. FIG. 8 shows an example in which the injection pulse of the port injector 28 is included between the exhaust top dead center (the start of the intake stroke) and the valve opening timing t1 of the intake valve 10. In this case, the fuel injection by the port injector 28 starts after the exhaust top dead center and ends before the valve opening timing t1 of the intake valve 10. However, this is merely an example, and timings other than those in FIG. 8 are also allowed. For example, the port injector 28 may inject fuel over a period straddling the valve opening timing t1 of the intake valve 10. Further, the port injector 28 may inject fuel at a timing such that a part of the fuel injection period (injection pulse) is included in the exhaust stroke and the remaining part is included in the intake stroke. In other words, in the idle region A1, the timing of fuel injection by the port injector 28 may be any timing as long as the injection starts before the valve opening timing t1 of the intake valve 10 and at least a part of the required fuel is injected during the intake stroke. In the idle region A1, the ECU 100 controls the port injector 28 so that fuel is injected from the port injector 28 at such a timing.

[0050] Here, it is assumed that at least a part of the fuel injected from the port injector 28 before the intake valve 10 opens in step S5 adheres to the wall surface of the intake port 8. However, even if fuel adheres to the wall surface of the intake port 8, the adhered fuel evaporates as the intake port 8 is depressurized immediately after the intake valve 10 opens, and is introduced into the main combustion chamber 25 without waste together with the intake air flowing through the intake port 8.

[0051] Next, the ECU 100 causes the main ignition plug 32 to fire (step S6). Specifically, as shown in FIG. 8, the ECU 100 causes the main ignition plug 32 to fire (main ignition) at an appropriate timing during the compression stroke that is on the retard side of the valve closing timing t2 of the intake valve 10 and on the advance side of the top dead center of compression (TDC between the compression stroke and the expansion stroke). However, the main ignition here is not for directly burning the air-fuel mixture. In other words, the timing of the main ignition is set to a timing such that the air-fuel mixture present in the main combustion chamber 25 does not ignite (burn). That is, at the time of step S6 when the main ignition is performed, an air-fuel mixture derived from the fuel injected from the port injector 28 in step S5 is formed in the main combustion chamber 25, but the main ignition is executed before the main combustion chamber 25 becomes sufficiently high temperature and high pressure so that the air-fuel mixture does not ignite by the main ignition. The main ignition executed at such a timing does not lead to the combustion of the air-fuel mixture, but has the effect of raising the temperature of the main combustion chamber 25 by the discharge energy. This promotes the combustion of the air-fuel mixture by the subsequent sub-ignition.

[0052] Next, the ECU 100 causes the sub-ignition plug 62 to fire (step S7). Specifically, as shown in FIG. 8, the ECU 100 causes the sub-ignition plug 62 to fire (sub-ignition) at a timing later than the main ignition in step S6 and close to the top dead center of compression. This sub-ignition burns the air-fuel mixture present inside the cover member 64, that is, in the sub-chamber 60. When the air-fuel mixture in the sub-chamber 60 burns, the flame is ejected into the main combustion chamber 25 through the plurality of communication holes 66 of the cover member 64, and the air-fuel mixture in the main combustion chamber 25 burns in response to the ejection of the flame. Although FIG. 8 shows an example in which the sub-ignition is performed near the advance side of the top dead center of compression (that is, at the end of the compression stroke), the timing of the sub-ignition may be any timing as long as the air-fuel mixtures in the sub-chamber 60 and the main combustion chamber 25 burn, and is not limited to that shown in FIG. 8. For example, the sub-ignition may be performed at a timing that coincides with the top dead center of compression, or the sub-ignition may be performed near the retard side of the top dead center of compression (that is, at the beginning of the expansion stroke).

[0053] Next, when it is determined as NO in the above step S3, that is, when the engine is operating in the non-idle region A2, the control in this case will be described. In this case, the ECU 100 controls the intake S-VT 16a so that the opening / closing timing of the intake valve 10 becomes the normal timing, which is earlier than when it is in the idle region A1 (step S9). As a result, the intake valve 10 comes to open for all or most of the period of the intake stroke. FIG. 9 shows an example where the opening period of the intake valve 10 overlaps with the entire intake stroke. In this case, the intake valve 10 opens at the time point t11 near the advanced angle side of the exhaust top dead center and closes at the time point t12 near the retarded angle side of the intake bottom dead center. Of course, the timing may be slightly advanced or retarded with respect to FIG. 9, and the specific timing can be appropriately set according to the conditions within the non-idle region A2.

[0054] Next, the ECU 100 causes the direct injection injector 26 to inject fuel (step S10). Specifically, the ECU 100 controls the direct injection injector 26 so that the required fuel for one combustion cycle is injected between the opening timing t11 of the intake valve 10 and the compression top dead center. FIG. 9 shows an example where the injection pulse of the direct injection injector 26 is included in the intake stroke (between the exhaust top dead center and the intake bottom dead center), but all or part of the injection pulse may be included in the compression stroke.

[0055] Next, the ECU 100 controls the main ignition plug 32 and the sub-ignition plug 62 so that ignition by the main ignition plug 32 (main ignition) and ignition by the sub-ignition plug 62 (sub-ignition) are executed in an appropriate order (step S11).

[0056] For example, when the engine is operating at the first operation point P1 (FIG. 6) where the engine speed is relatively low among the non-idle regions A2, the ECU 100 controls the main ignition plug 32 and the sub-ignition plug 62 so that, as shown in FIG. 9(a), the main ignition and the sub-ignition are executed in the order of sub-ignition → main ignition. In this case, the timing of the sub-ignition can be set near the advanced angle side of the compression top dead center (the end of the compression stroke), and the timing of the main ignition can be set near the retarded angle side of the compression top dead center (the initial stage of the expansion stroke).

[0057] On the other hand, when the engine is operating at a second operating point P2 (Fig. 6) where the engine speed is higher than the first operating point P1 in the non-idle region A2, the ECU 100 controls the main ignition plug 32 and the sub-ignition plug 62 so that the main ignition and the sub-ignition are executed in the order of main ignition → sub-ignition as shown in Fig. 9(b). In this case, the timing of the main ignition can be set in the vicinity of the advanced side of top dead center of compression (the end of the compression stroke), and the timing of the sub-ignition can be set in the vicinity of the retarded side of top dead center of compression (the beginning of the expansion stroke).

[0058] In either case of Figs. 9(a) and 9(b), since the main ignition and the sub-ignition are performed near top dead center of compression, the combustion of the air-fuel mixture starts at a plurality of positions. That is, as the air-fuel mixture in the main combustion chamber 25 starts to burn due to the flame propagation from the electrode portion 32x of the main ignition plug 32, the air-fuel mixture in the sub-chamber 60 starts to burn due to the flame propagation from the electrode portion 62x of the sub-ignition plug 62. Further, the combustion of the air-fuel mixture in the sub-chamber 60 causes the ejection of flames from the plurality of communication holes 66, and the air-fuel mixture in the main combustion chamber 25 also burns due to this ejected flame. By starting the combustion from a plurality of positions in this way, the combustion speed of the air-fuel mixture in the main combustion chamber 25 is increased, and the fuel consumption performance is improved.

[0059] [Operation and Effect] As described above, in the present embodiment, when the engine is operating in the idle region A1, fuel is injected from the port injector 28, and then ignition (sub-ignition) is performed by the sub-ignition plug 62. The port injector 28 starts fuel injection before the valve opening timing t1 of the intake valve 10, and the sub-ignition plug 62 performs sub-ignition near top dead center of compression. According to such a configuration, there is an advantage that the air-fuel mixture in the sub-chamber 60 can be appropriately burned during idling operation, and the fuel consumption performance of the engine can be improved.

[0060] That is, in the present embodiment, during idling operation, fuel injection by the port injector 28 is started before the valve opening timing t1 of the intake valve 10. Therefore, particularly immediately after the intake valve 10 opens and intake air vigorously flows from the intake port 8 into the main combustion chamber 25, the injected fuel from the port injector 28 can be introduced into the main combustion chamber 25 together with the intake air, and the fluidity of the fuel can be enhanced. As a result, fuel and air can be sufficiently mixed before ignition (sub-ignition) by the sub spark plug 62, and a sufficiently homogeneous air-fuel mixture can be formed in the main combustion chamber 25. When the air-fuel mixture in the main combustion chamber 25 is homogenized, the concentration deficiency of the air-fuel mixture formed in the auxiliary chamber 60 at the time of sub-ignition is eliminated, so that the air-fuel mixture can be appropriately burned starting from sub-ignition.

[0061] For example, during idling operation when the fuel injection amount is small, the fuel pressure (fuel injection pressure) is low and the fluidity of the fuel is likely to decrease. If fuel is injected from the direct injection injector 26 instead of the port injector 28, the air-fuel mixture in the main combustion chamber 25 may not be sufficiently homogenized by the time of sub-ignition. In this case, the concentration of the air-fuel mixture in the auxiliary chamber 60 may not rise sufficiently, and there is a possibility that the air-fuel mixture will not burn (misfire will occur) even if sub-ignition is performed. On the other hand, in the present embodiment, since fuel is injected from the port injector 28 during idling operation, the fluidity of the fuel can be enhanced and the air-fuel mixture in the main combustion chamber 25 can be sufficiently homogenized, and the concentration of the air-fuel mixture introduced from the main combustion chamber 25 into the auxiliary chamber 60 through the communication hole 66 can be stabilized. As a result, an air-fuel mixture with a desired concentration suitable for combustion (flame propagation) can be formed in the auxiliary chamber 60 before sub-ignition, so that the air-fuel mixture in the auxiliary chamber 60 can be appropriately burned starting from sub-ignition, and a flame can be ejected from the auxiliary chamber 60 into the main combustion chamber 25 through the communication hole 66. The flame ejected from the communication hole 66 burns the air-fuel mixture in the main combustion chamber 25 at a sufficient speed. Thereby, the thermal efficiency during idling operation can be increased, and the fuel consumption performance of the engine can be improved.

[0062] Further, in the present embodiment, when the engine is idling, ignition by the main ignition plug 32 (main ignition) is performed before ignition by the sub-ignition plug 62 (sub-ignition). Even if main ignition is performed prior to sub-ignition during idling operation with a small fuel injection amount, this main ignition does not cause the air-fuel mixture in the main combustion chamber 25 to burn. However, the main ignition raises the temperature in the main combustion chamber 25 by discharge energy. When the temperature in the main combustion chamber 25 rises, the temperature of the air-fuel mixture introduced from the main combustion chamber 25 into the sub-chamber 60 also rises, so it is possible to prevent misfire during subsequent sub-ignition with a higher probability. Thereby, the combustibility of the air-fuel mixture during idling operation can be enhanced, and the fuel consumption performance of the engine can be improved.

[0063] Further, in the present embodiment, when the engine is operating in the non-idle region A2 (non-idling operation), fuel is injected from the direct injection injector 26, and then ignition by the main ignition plug 32 and the sub-ignition plug 62 is performed in an appropriate order. According to such a configuration, during non-idling operation with relatively good ignitability, the air-fuel mixture based on the fuel directly injected from the direct injection injector 26 into the main combustion chamber 25 can be efficiently burned.

[0064] [Modification Example] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments and may include, for example, the following modification examples.

[0065] In the above embodiment, when fuel is injected from the port injector 28 during idling operation, the port injector 28 was controlled so that fuel injection was started before the valve opening timing t1 of the intake valve 10 (see FIG. 8). However, the timing of fuel injection from the port injector 28 during idling operation may be any timing as long as at least a part of the required fuel for one combustion cycle is included in the intake stroke, and various changes are possible within that range. For example, fuel injection from the port injector 28 may be started at the same time as or immediately after the valve opening timing t1 of the intake valve 10.

[0066] In the above-described embodiment, fuel is injected from the port injector 28 provided in the cylinder head 54 into the intake port 8. However, instead of such a port injector 28, for example, an injector that injects fuel into the downstream portion of the intake passage 4 (the portion between the surge tank 38 and the engine body 2) may be provided. In other words, the second fuel injection device in the present invention may be any device that injects fuel at any position in the intake introduction passage through which the intake air introduced into the main combustion chamber flows, and the mounting position of the second fuel injection device can be appropriately changed within that range.

[0067] In the above-described embodiment, as the cover member 64 of the sub-ignition unit 30, a hemispherical (dome-shaped) one having three communication holes 66 was exemplified (see FIGS. 3 and 4). However, the shape of the cover member 64 may be other shapes such as a frustum of a cone shape or a rectangular parallelepiped shape. Further, the number and size of the communication holes 66 can be set as appropriate. Furthermore, the mounting position of the sub-ignition unit 30 is not limited to the position shown in FIG. 2. For example, the sub-ignition unit 30 may be provided on the intake port 8 side with respect to the tip portion 26a of the direct injection injector 26.

[0068] In the above-described embodiment, in addition to the sub-ignition unit 30 (sub-ignition plug 62), the main ignition plug 32 was provided. However, the main ignition plug 32 is not essential and may be omitted.

Explanation of Reference Numerals

[0069] 1 Engine system 4 Intake passage (intake introduction passage) 8 Intake port (intake introduction passage) 10 Intake valve 16a Intake S-VT (Variable Valve Mechanism) 22 Cylinder 24 Piston 25 Main combustion chamber 26 Direct injection injector (first fuel injection device) 28 Port injector (second fuel injection device) 32 Main ignition plug ( Main Ignition device) 52 Cylinder block 54 Cylinder head 60 Sub-chamber 62 Sub-ignition plug ( Sub ignition device) 64 Cover member (partition wall) 66 Communication hole 100 ECU (controller)

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, An intake introduction passage through which intake air introduced into the main combustion chamber flows, An intake valve that opens and closes the intake introduction passage, A first fuel injection device that injects fuel into the main combustion chamber, A second fuel injection device that injects fuel into the intake introduction passage, A main ignition device that ignites the air-fuel mixture in the main combustion chamber, A sub-ignition device that ignites the air-fuel mixture in the sub-chamber, It includes a controller electrically connected to the first fuel injection device, the second fuel injection device, the main ignition device, and the sub-ignition device, and outputting an electrical signal for control to each of the devices, When the engine is idling, the controller controls the second fuel injection device and the sub-ignition device so that fuel is injected from the second fuel injection device during the intake stroke and ignition is performed by the sub-ignition device after the fuel injection, and causes the main ignition device to ignite before the ignition timing of the sub-ignition device, The ignition timing of the main ignition device during the idling operation is set to a timing such that the air-fuel mixture existing in the main combustion chamber does not ignite, on the retard side of the closing timing of the intake valve and on the advance side of top dead center of compression, characterized by an engine system.

2. In the engine system according to Claim 1, The intake introduction passage includes an intake port formed in the cylinder head, The cylinder head is provided with the second fuel injection device that injects fuel into the intake port and the intake valve that opens and closes the intake port, The engine system is characterized in that the controller starts fuel injection to the second fuel injector before the valve opening timing of the intake valve during the idling operation.

3. In the engine system according to claim 1 or 2, further comprising a variable valve mechanism for variably setting the opening and closing timing of the intake valve, the controller controls the variable valve mechanism such that the intake valve closes during the compression stroke and the valve closing timing of the intake valve is retarded compared to the non-idling operation during the idling operation. The engine system is characterized by this.

4. In the engine system according to any one of claims 1 to 3, when the engine is operating in a non-idling state, the controller injects fuel into the first fuel injector. The engine system is characterized by this.

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