Engine system

Abstract

To appropriately combust mixed gas in an auxiliary chamber during a cold start-up.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. During a cold start-up in which an engine is started up under a condition that an engine water temperature is lower than a threshold, 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 a sub chamber.

Background Art

[0002] An engine is known that includes a main combustion chamber defined by a cylinder block, a cylinder head, and a piston, a sub chamber adjacent to the main combustion chamber, and a communication hole formed in a wall defining the sub chamber. For example, Patent Document 1 below discloses an engine including a main combustion chamber and a sub chamber, a main fuel injection valve that injects fuel into an intake port, a sub fuel injection valve that injects fuel into the sub chamber, a main ignition plug that ignites an air-fuel mixture in the main combustion chamber, and a sub ignition plug that ignites an air-fuel mixture in the sub chamber. In this engine, the respective fuel injection valves and ignition plugs are controlled so that the air-fuel mixture in the sub chamber burns after the air-fuel mixture in the main combustion chamber burns. When the air-fuel mixture in the sub chamber burns, a flame is ejected from the sub 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 the above Patent Document 1 and provide a fuel injection valve in the main combustion chamber instead of the auxiliary chamber. However, if this is done, there is a high possibility that misfire will occur in the auxiliary chamber, especially during cold start of the engine. That is, during cold start of the engine, atomization and evaporation of fuel are difficult to proceed, so 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 phenomenon that the air-fuel mixture does 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 cold start.

Means for Solving the Problems

[0006] To solve the above problems, the present invention provides 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, 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, an ignition device that ignites the air-fuel mixture in the sub-chamber, a water temperature detection unit that detects the engine water temperature, which is the temperature of cooling water flowing inside the cylinder block and the cylinder head, and a controller electrically connected to the water temperature detection unit, the first fuel injection device, the second fuel injection device, and the ignition device. The controller receives an electrical signal representing the detection information of the engine water temperature from the water temperature detection unit and outputs a control electrical signal to the first and second fuel injection devices and the ignition device. During a cold start when the engine is started under the condition that the detected engine water temperature is less than a predetermined threshold value, the controller controls the second fuel injection device and the ignition device such that fuel is injected from the second fuel injection device during the intake stroke and ignition is performed by the ignition device after the fuel injection. When the engine is normally started under the condition that the detected engine water temperature is equal to or higher than the threshold value, the controller causes the first fuel injection device to inject fuel. , which is characterized by the above.

[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, at the time of cold start of the engine, fuel is injected from the second fuel injection device that injects fuel into the intake air introduction passage during the intake stroke. Therefore, the fuel injected 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 air introduction passage into the main combustion chamber, and the fluidity of the fuel can be enhanced. As a result, 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 hole formed in the partition wall is stabilized. Therefore, it is possible to eliminate the shortage of the concentration of the air-fuel mixture formed in the auxiliary chamber at the time of ignition. That is, before ignition in the auxiliary chamber by the ignition device, it becomes possible to form an air-fuel mixture having a desired concentration suitable for combustion (flame propagation) in the auxiliary chamber. As a result, the air-fuel mixture in the auxiliary chamber can be appropriately burned triggered by the ignition of the ignition device, and a flame can be ejected from the auxiliary chamber into the main combustion chamber through the communication hole. The flame ejected from the communication hole burns the air-fuel mixture in the main combustion chamber at a sufficient speed. Thereby, the thermal efficiency at the time of cold start can be increased, and the fuel consumption performance of the engine can be improved. In addition, during normal start-up when the ignitability is relatively good, fuel is injected from the first fuel injection device. Therefore, the air-fuel mixture based on the fuel directly injected into the main combustion chamber from this first fuel injection device can be efficiently burned.

[0009] Preferably, the intake air introduction passage includes an intake port formed in the cylinder head, and the cylinder head is provided with the second fuel injection device that injects fuel into the intake port and an intake valve that opens and closes the intake port. The controller starts fuel injection to the second fuel injection device before the valve opening timing of the intake valve at the time of cold start.

[0010] According to this configuration, particularly immediately after the intake valve opens and the intake air vigorously flows from the intake port into the main combustion chamber, the fuel injected from the second fuel injection device can be introduced into the main combustion chamber together with the intake air. 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 further includes an additional ignition device that ignites the air-fuel mixture in the main combustion chamber, and the controller causes the additional ignition device to ignite before the ignition timing of the ignition device during cold start.

[0012] Even if ignition (main ignition) in the main combustion chamber by the additional ignition device is performed before ignition (sub-ignition) in the sub-chamber by the ignition device during cold start with low ignitability, this main ignition does not bring about the effect of burning the air-fuel mixture in the main combustion chamber. However, the main ignition brings about the effect 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 subsequent sub-ignition with a higher probability. Thereby, the combustibility of the air-fuel mixture during cold start can be enhanced, and the fuel consumption performance of the engine can be improved.

Advantages of the Invention

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

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Embodiments 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] Figure 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 the present embodiment, the side from the cylinder block 52 toward the cylinder head 54 is regarded as the upper side and the opposite side as the lower side for the sake of 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] A crankshaft 20, which is an output shaft of the engine body 2, is provided below the lower part of the cylinder block 52 (below the piston 24). The crankshaft 20 is connected to the piston 24 of each cylinder 22 via a connecting rod 21, and rotates about the central axis in accordance with the reciprocating motion of the piston 24.

[0022] The crankshaft 20 is detachably connected to a starter motor 45. The starter motor 45 is an electric motor that engages with the crankshaft 20 at the start of the engine and forcibly rotates it (cranks it).

[0023] 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 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.

[0024] 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-VT 16a, which variably sets the opening and closing timing of the intake valve 10.

[0025] 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 "additional ignition device" in the present invention.

[0026] 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 facing 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.

[0027] 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 facing 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.

[0028] 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.

[0029] 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.

[0030] The intake passage 4 is connected to one side surface of the cylinder head 54 so as to communicate with the intake port 8 of each cylinder 22. In the intake passage 4, an air cleaner 34 for removing foreign matters in the intake air, an openable and closable throttle valve 36 for adjusting the intake air flow rate, 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.

[0031] 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.

[0032] [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 "ignition device" in the present invention, and the cover member 64 corresponds to the "partition wall" in the present invention.

[0033] 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.

[0034] The cover member 64 is a cover that constitutes 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.

[0035] The auxiliary chamber 60 is the space around the electrode portion 62x of the auxiliary ignition 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 ignition 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.

[0036] 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 attachment state, substantially the entire cover member 64 is exposed in 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.

[0037] 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.

[0038] 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.

[0039] [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 unit 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.

[0040] Information detected by various sensors provided in the engine system 1 and the like is sequentially input into the ECU 100 as electrical signals. The ECU 100 controls each part of the engine while executing various determinations, calculations, etc. 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, an accelerator opening sensor SN6 is provided in a vehicle equipped with the engine system 1. The ECU 100 is electrically connected to these sensors SN1 to SN6 and sequentially receives the information detected by the sensors SN1 to SN6. Note that the water temperature sensor SN4 corresponds to the "water temperature detection unit" in the present invention.

[0041] The air flow sensor SN1 is a sensor that detects the flow rate of 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 water temperature sensor SN4 is a sensor that detects the engine water temperature, which is the temperature of the cooling water 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 rotation speed 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.

[0042] Furthermore, an operation signal of an ignition switch SW1 provided in the vehicle is also input into the ECU 100. The ignition switch SW1 is a switch operated by a passenger when starting or stopping the engine system 1. Information representing the operation state of the ignition switch SW1 is sequentially input into the ECU 100 as an electrical signal.

[0043] [Control Operation] Next, a specific control example of the engine system 1 will be described with reference to FIGS. 6 to 10. FIGS. 6 and 7 are flowcharts showing the details of the control executed by the ECU 100 during engine operation. FIGS. 8 to 10 are time charts showing the timings of fuel injection and spark ignition. FIG. 8 shows those at cold start, FIG. 9 shows those at normal start, and FIG. 10 shows those during non-idling operation, respectively.

[0044] When the control shown in FIG. 6 starts, the ECU 100 determines whether the ignition switch SW1 has been turned on (step S1). For example, when the ECU 100 receives an IG·ON signal indicating that the ignition switch SW1 has been switched from the off state to the on state from the ignition switch SW1, the ECU 100 determines that the ignition switch SW1 has been turned on.

[0045] If it is determined YES in step S1 and the on operation of the ignition switch SW1 is confirmed, the ECU 100 reads various information (step S2). For example, the ECU 100 reads at least the engine coolant temperature detected by the coolant temperature sensor SN4, 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 executes start control to start the engine (step S3). The details of this start control will be described with reference to FIG. 7. When the start control is started, the ECU 100 controls the intake S-VT 16a so that the opening / closing timing of the intake valve 10 becomes relatively late (step S21). 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 or FIG. 9. That is, the ECU 100 controls the intake S-VT 16a so that the intake valve 10 opens at the time point t1 during the intake stroke and closes at the time point t2 during the compression stroke. In other words, at the start of the engine, 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. Thus, the opening / closing timing of the intake valve 10 by the intake S-VT 16a is set.

[0047] Next, the ECU 100 starts cranking the engine (step S22). That is, the ECU 100 forcibly rotates the crankshaft 20 by driving the starter motor 45 to apply a rotational force to the crankshaft 20. Note that the cranking in this step S22 can be executed simultaneously with the driving of the intake S-VT 16a in the above step S21.

[0048] Next, the ECU 100 determines whether or not the engine coolant temperature acquired from the water temperature sensor SN4 in step S2, that is, the temperature of the engine coolant at the time of ignition on, is less than a predetermined threshold value Tx (step S23). The threshold value Tx is appropriately set according to the characteristics of the engine, and can be set, for example, around 0°C.

[0049] When it is determined YES in step S23 above and it is confirmed that the engine coolant temperature is less than the threshold value Tx, the ECU 100 causes the port injector 28 to inject fuel (step S24). 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. Also, 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, at engine start under the condition that the engine coolant temperature is less than the threshold value Tx (hereinafter referred to as cold start), 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. At cold start of the engine, 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 S24 above 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 becomes negative pressure 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] As described above, at the time of cold starting of the engine, all the required fuel is supplied by injection from the port injector 28. In other words, at the time of cold starting, only the port injector 28 operates as a fuel supply source, and the direct injection injector 26 is stopped.

[0052] Next, the ECU 100 causes the main ignition plug 32 to generate ignition (step S25). Specifically, as shown in FIG. 8, the ECU 100 causes the main ignition plug 32 to generate ignition (main ignition) at an appropriate timing in the compression stroke that is on the retard side of the 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 S25 when the main ignition is performed, an air-fuel mixture derived from the fuel injected from the port injector 28 in step S24 is formed in the main combustion chamber 25, but the main ignition is executed before the main combustion chamber 25 is sufficiently heated and pressurized so that the air-fuel mixture does not ignite due to the main ignition. Although the main ignition executed at such a timing does not lead to the combustion of the air-fuel mixture, it has the effect of heating the main combustion chamber 25 by the discharge energy. This promotes the combustion of the air-fuel mixture by the subsequent sub-ignition.

[0053] Next, the ECU 100 causes the sub-ignition plug 62 to fire (step S26). 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 S25 above and close to the compression top dead center. This sub-ignition burns the air-fuel mixture present inside the cover member 64, that is, inside 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. Note that FIG. 8 shows an example in which sub-ignition is performed in the vicinity of the advanced angle side of the compression top dead center (that is, at the end of the compression stroke), but the timing of 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, sub-ignition may be performed at a timing that coincides with the compression top dead center, or sub-ignition may be performed in the vicinity of the retarded angle side of the compression top dead center (that is, at the initial stage of the expansion stroke).

[0054] Next, the ECU 100 determines whether or not the engine startup has been completed (step S27). For example, the ECU 100 determines that the engine startup has been completed when the engine speed detected by the crank angle sensor SN5 exceeds a predetermined reference speed. While the determination here is NO, that is, while the engine speed is below the reference speed, the control of steps S24 to S26 described above is repeated while changing the target cylinder. That is, the control of burning the air-fuel mixture by performing port injection, main ignition, and sub-ignition in this order is sequentially executed for each cylinder 22 until the engine speed exceeds the reference speed. On the other hand, when the engine speed exceeds the reference speed and the determination in step S27 becomes YES, the flow shifts to step S4 in FIG. 6.

[0055] Next, when it is determined as NO in the above step S23, that is, when the engine coolant temperature is equal to or higher than the threshold value Tx, the control in this case will be described. In this case, the ECU 100 causes the direct injection injector 26 to inject fuel (step S28). Specifically, as shown in FIG. 9, the ECU 100 controls the direct injection injector 26 so that the required fuel for one combustion cycle is injected during the intake stroke. More specifically, the ECU 100 controls the direct injection injector 26 so that the injection pulse of the direct injection injector 26 is included between the valve opening timing t1 of the intake valve 10 and the intake bottom dead center. In other words, at engine start (hereinafter referred to as normal start) under the condition that the engine coolant temperature is equal to or higher than the threshold value Tx, the direct injection injector 26 injects fuel at a timing that overlaps both the intake stroke and the valve opening period of the intake valve 10.

[0056] As described above, at the normal start of the engine, all the required fuel is supplied by the injection from the direct injection injector 26. In other words, at the normal start, only the direct injection injector 26 operates as the fuel supply source, and the port injector 28 is stopped.

[0057] Next, the ECU 100 causes the sub spark plug 62 to generate ignition (step S29). Specifically, as shown in FIG. 9, the ECU 100 causes the sub spark plug 62 to generate ignition (sub ignition) at a timing close to the compression top dead center. Although FIG. 9 shows an example in which the sub ignition is performed in the vicinity of the advanced angle side of the compression top dead center, the timing of the sub ignition may be the timing that coincides with the compression top dead center, or may be in the vicinity of the retarded angle side of the compression top dead center. By this sub ignition, the air-fuel mixture in the sub chamber 60 burns, and the air-fuel mixture in the main combustion chamber 25 burns due to the flame ejected from the communication hole 66 of the cover member 64 accompanying the combustion.

[0058] Next, the ECU 100 determines whether or not the engine has completed starting (step S30). The details of the determination here are the same as those in step S27 described above. Until it is confirmed in step S30 that the starting has been completed, the controls in steps S28 and S29 above (direct injection and sub-ignition) are repeated while changing the target cylinder, and when it is confirmed that the starting has been completed, the flow proceeds to step S4 in FIG. 6.

[0059] Returning to FIG. 6, the control after the engine has completed starting will be described. After the engine has started, the ECU 100 determines whether or not the engine is idling (step S4). As is well known, idling operation is an operation in which the engine generates the minimum combustion torque necessary for stable self-rotation under the conditions that the vehicle is substantially stopped and the accelerator opening is substantially zero. For example, the ECU 100 identifies the engine load and the engine speed from the detection values of the crank angle sensor SN5 and the accelerator opening sensor SN6, etc., and determines that the engine is idling when both the identified engine load and the engine speed are at the lowest levels.

[0060] If it is determined YES in step S4 above and it is confirmed that the engine is idling, the ECU 100 determines whether or not the engine coolant temperature detected by the coolant temperature sensor SN4 is less than the threshold value Tx (step S5).

[0061] If it is determined YES in step S5 above and it is confirmed that the engine coolant temperature is less than the threshold value Tx, the ECU 100 executes control to inject fuel into the port injector 28 and burn the air-fuel mixture based on the injected fuel (step S6). The control here is the same as the control in steps S24 to S26 in the starting control (FIG. 7) described above. That is, the ECU 100 executes control to burn the air-fuel mixture by performing port injection, main ignition, and sub-ignition in this order (see FIG. 8).

[0062] On the other hand, when it is determined as NO in the above step S5 and it is confirmed that the engine coolant temperature is equal to or higher than the threshold value Tx, the ECU 100 executes control to cause the direct injection injector 26 to inject fuel and burn an air-fuel mixture based on the injected fuel (step S7). The control here is the same as the control in steps S28 and S29 in the above-described starting control (Fig. 7). That is, the ECU 100 executes control to burn the air-fuel mixture by performing direct injection and sub-ignition in this order (see Fig. 9).

[0063] After combustion is performed in any one of the above steps S6 and S7, the ECU 100 determines whether or not the ignition switch SW1 has been turned off (step S8). For example, when the ECU 100 receives an IG·OFF signal indicating that the ignition switch SW1 has been switched from the on state to the off state from the ignition switch SW1, the ECU 100 determines that the ignition switch SW1 has been turned off. While the determination here is NO, that is, while the ignition-on state continues, the control after the above step S4 is repeated. On the other hand, when the ignition switch is turned off and the determination in step S8 becomes YES, the flow returns.

[0064] Next, when it is determined as NO in the above step S4, that is, when the engine is not idling, the control will be described. In this case, in each cylinder 22 of the engine, combustion that generates higher torque (i.e., torque contributing to the running of the vehicle) than during idling operation is performed. Hereinafter, such an operation is referred to as non-idling operation. When it corresponds to the non-idling operation, the ECU 100 controls the intake S-VT 16a so that the opening / closing timing of the intake valve 10 becomes the normal timing earlier than during idling operation (step S10). As a result, the intake valve 10 comes to open throughout all or most of the intake stroke. FIG. 10 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 a point t11 near the advanced side of the exhaust top dead center and closes at a point t12 near the retarded side of the intake bottom dead center. Of course, the timing may be slightly advanced or retarded with respect to FIG. 10, and the specific timing can be appropriately set according to the operating conditions of the engine and the like.

[0065] Next, the ECU 100 causes the direct injection injector 26 to inject fuel (step S11). 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. 10 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.

[0066] 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 S12). FIG. 10 shows an example where the main ignition and the sub-ignition are executed in the order of sub-ignition → main ignition, but the order of main ignition → sub-ignition may be reversed. The ignition order can be appropriately set according to conditions such as the engine load and the engine speed during non-idling operation. In any case of the ignition order, the respective times of the main ignition and the sub-ignition are set near the compression top dead center.

[0067] As described above, since the main ignition and the sub-ignition are performed near the compression top dead center, the combustion of the air-fuel mixture starts at a plurality of positions. That is, when 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 flame to jet out from the plurality of communication holes 66, and the air-fuel mixture in the main combustion chamber 25 also burns due to this jetted 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.

[0068] After the ignition in the above step S12, the ECU 100 determines whether the ignition switch SW1 has been turned off (step S8), and depending on the result, repeats the control after the above step S4 or returns the flow.

[0069] [Operation Example] Next, an example of the operation realized by the control of FIGS. 6 and 7 described above will be described using the time chart of FIG. 11. In the operation example of FIG. 11, at time ta, the engine coolant temperature is lower than the threshold value Tx, and the engine is started (cold start) under this condition. After that, at time tb, the engine shifts to the idling operation, and further, from time tc, the non-idling operation (vehicle running) is started. During this period (from time ta to tc), the engine coolant temperature remains lower than the threshold value Tx, and the cold state of the engine continues. After that, the engine is once stopped at time td and restarted at time te. At the time te of this restart, the engine coolant temperature has risen to a value higher than the threshold value Tx, and the engine has shifted to the non-cold state. After time te, the idling operation and the non-idling operation are appropriately performed in the non-cold state.

[0070] When the operation is performed as described above, the fuel injection to each cylinder 22 will transition as follows. That is, during the period from time point ta to time point tc when starting and idling operation in a cold state are performed, fuel injection is performed by the port injector 28, and the direct injection injector 26 is stopped. On the other hand, during the period from time point tc to time point td, since the engine is in a cold state and non-idling operation is performed or the engine is in a non-cold state, fuel injection is performed by the direct injection injector 26, and the port injector 28 is stopped. After time point te when the engine is restarted, since the engine is in a non-cold state, fuel injection is still performed by the direct injection injector 26, and the port injector 28 is stopped.

[0071] [Function and Effect] As described above, in the present embodiment, when the engine is cold-started, that is, when the engine is started under the condition that the engine coolant temperature is less than the threshold value Tx, 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 auxiliary chamber 60 can be appropriately burned during idling operation, and the fuel consumption performance of the engine can be improved.

[0072] That is, in the present embodiment, during cold start, since fuel injection by the port injector 28 starts before the valve opening timing t1 of the intake valve 10, especially immediately after the intake valve 10 opens and intake air flows vigorously 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-ignition 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.

[0073] For example, during cold start when the temperature of the main combustion chamber 25 is low, atomization and evaporation of fuel are difficult to proceed. Thus, if fuel is injected from the direct injection injector 26 instead of the port injector 28, there is a possibility that 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 may not burn (misfire may occur) even if sub-ignition is performed. On the contrary, in this embodiment, since fuel is injected from the port injector 28 during cold start, the fluidity of the fuel can be enhanced to sufficiently homogenize the air-fuel mixture in the main combustion chamber 25, 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 triggered by sub-ignition, and a flame can be ejected from the auxiliary chamber 60 to 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 cold start can be increased, and the fuel consumption performance of the engine can be improved.

[0074] Also, in this embodiment, during cold start of the engine, ignition (main ignition) by the main ignition plug 32 is performed before ignition (sub-ignition) by the sub-ignition plug 62. Even if main ignition is performed prior to sub-ignition during cold start when the ignitability is low, this main ignition does not bring about the effect of burning the air-fuel mixture in the main combustion chamber 25. However, the main ignition brings about the effect of raising 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 auxiliary chamber 60 rises, so that misfire during subsequent sub-ignition can be prevented with a higher probability. Thereby, the combustibility of the air-fuel mixture during cold start can be enhanced, and the fuel consumption performance of the engine can be improved.

[0075] Further, in the present embodiment, during normal starting in which the engine is started under the condition that the engine coolant temperature is equal to or higher than the threshold value Tx, fuel is injected from the direct injection injector 26, and then ignition (sub-ignition) is performed by the sub-ignition plug 62. According to such a configuration, during normal starting in which the ignitability is relatively good, the air-fuel mixture based on the fuel directly injected into the main combustion chamber 25 from the direct injection injector 26 can be efficiently burned.

[0076] [Modification Example] As described above, the preferred embodiments of the present invention have been described. However, the present invention is not limited to the above embodiments and may include, for example, the following modification examples.

[0077] In the above embodiment, when fuel is injected from the port injector 28 during cold starting, the port injector 28 is controlled so that fuel injection starts 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 cold starting 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 limit. For example, the fuel injection of 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.

[0078] In the above 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 limit.

[0079] In the above-described embodiment, as the cover member 64 of the sub-ignition unit 30, a hemispherical (dome-shaped) member 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.

[0080] 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.

Description of Reference Numerals

[0081] 1 Engine system 4 Intake passage (intake introduction passage) 8 Intake port (intake introduction passage) 10 Intake valve 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 (additional ignition device) 52 Cylinder block 54 Cylinder head 60 Sub-chamber 62 Sub-ignition plug (ignition device) 64 Cover member (partition wall) 66 Communication hole 100 ECU (controller) SN4 Water temperature sensor (water temperature detection unit)

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, 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, An ignition device that ignites the air-fuel mixture in the sub-chamber, A water temperature detection unit that detects the engine water temperature, which is the temperature of cooling water flowing inside the cylinder block and the cylinder head, A controller that is electrically connected to the water temperature detection unit, the first fuel injection device, the second fuel injection device, and the ignition device, receives an electrical signal representing the detection information of the engine water temperature from the water temperature detection unit, and outputs a control electrical signal to the first and second fuel injection devices and the ignition device, During cold start when the engine is started under the condition that the detected engine water temperature is lower than a predetermined threshold, the controller controls the second fuel injection device and the ignition device so that fuel is injected from the second fuel injection device during the intake stroke and ignition is performed by the ignition device after the fuel injection. During normal start when the engine is started under the condition that the detected engine water temperature is equal to or higher than the threshold, the controller causes the first fuel injection device to inject fuel. An engine system characterized by this.

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 an intake valve that opens and closes the intake port. The controller starts fuel injection to the second fuel injector before the valve opening timing of the intake valve at cold start. An engine system characterized by this.

3. In the engine system according to claim 1 or 2, further comprising an additional ignition device for igniting the air-fuel mixture in the main combustion chamber, the controller causes the additional ignition device to perform ignition before the ignition timing of the ignition device at cold start. An engine system characterized by this.

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