Engine System

Abstract

The present invention provides an engine system. In an engine system having a main combustion chamber and a sub-chamber, fuel consumption performance and exhaust gas performance are reliably improved. A main combustion chamber, a sub-chamber, a fuel injection device for injecting fuel into the main combustion chamber, a main ignition device for igniting a mixture in the main combustion chamber, and a sub-ignition device for igniting a mixture in the sub-chamber are provided. In a specific area where the engine speed is below a reference speed and the engine load is higher than the reference load, the fuel injection device is controlled in such a manner that the fuel injection period is included in the compression stroke and the fuel injection period under low speed conditions is later than the fuel injection period under high speed conditions. Furthermore, the main ignition device and the sub-ignition device are controlled in such a manner that the sub-ignition period is closer to the delayed angle side than the main ignition period and the delayed angle amount of the sub-ignition period relative to the main ignition period, i.e., the ignition phase difference, is larger under low speed conditions than under high speed conditions.

Description

Technical Field

[0001] The present invention relates to an engine system including a main combustion chamber and a sub-chamber. Background Art

[0002] In the past, in order to improve the fuel consumption performance and exhaust gas performance of engines mounted on vehicles, etc., research has been conducted to provide a main combustion chamber and a sub-chamber connected thereto. Specifically, if a main combustion chamber and a sub-chamber connected thereto are provided so that the flame generated in the sub-chamber is ejected into the main combustion chamber, the combustion speed in the main combustion chamber can be increased to achieve an improvement in fuel consumption performance, and the residue of unburned mixed gas can be suppressed to achieve an improvement in exhaust gas performance.

[0003] For example, Patent Document 1 discloses an engine including a main combustion chamber (main chamber in Patent Document 1) divided by a cylinder block, a cylinder head, and a piston, a sub-chamber connected thereto, a main fuel injection valve provided at an intake port and supplying fuel to the main combustion chamber via the intake port, a main chamber spark plug igniting a mixture in the main combustion chamber, a sub-fuel injection valve directly injecting fuel into the sub-chamber, and a sub-chamber spark plug igniting a mixture in the sub-chamber. In this engine, a mixture formed in the main combustion chamber, which is a mixture of fuel and air injected from the main fuel injection valve, is first ignited by the main chamber spark plug, and then a mixture formed in the sub-chamber, which is a mixture of fuel and air injected from the sub-fuel injection valve, is ignited by the sub-chamber spark plug.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2007-255370 Summary of the invention

[0007] Problems to be solved by the invention

[0008] In the engine of Patent Document 1, the main combustion chamber and the sub-chamber are configured to inject fuel independently, and two fuel injection valves are required for one cylinder. Therefore, the structure is complicated and disadvantageous in terms of cost. In contrast, it is conceivable to set a fuel injection valve only for the main combustion chamber in an engine having a main combustion chamber and a sub-chamber. However, in a structure in which a fuel injection valve is set only for the main combustion chamber, there is a concern that the fuel injected from the fuel injection valve will not be fully introduced into the sub-chamber, and the mixed gas in the sub-chamber will not be properly burned. In other words, there is a concern that the improvement effect of fuel consumption performance and exhaust gas performance obtained by setting the main combustion chamber and the sub-chamber cannot be fully obtained.

[0009] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to reliably improve fuel efficiency and exhaust gas performance in an engine system including a main combustion chamber and a sub chamber.

[0010] Means for solving problems

[0011] As a technical solution for solving the above-mentioned problems, the present invention is characterized in that it comprises: a cylinder block and a cylinder head forming a cylinder; a piston which is reciprocally accommodated in the cylinder; a main combustion chamber which is divided by the cylinder block, the cylinder head and the piston; a sub-chamber which is separated from the main combustion chamber by a partition wall and is connected to the main combustion chamber through a connecting hole formed in the partition wall; a fuel injection device which injects fuel into the main combustion chamber; a main ignition device which ignites the mixture in the main combustion chamber; a sub-ignition device which ignites the mixture in the sub-chamber; and a control device which is electrically connected to the fuel injection device, the main ignition device and the sub-ignition device and outputs an electrical signal for control to these devices; when the engine is running in a specific range where the engine speed is below a specified reference speed and the engine load is higher than a specified reference load, the control device performs the following control: The fuel injection device is controlled in such a manner that an injection period, i.e., a fuel injection period, at which the injection device injects fuel is included in a compression stroke, and the main ignition device and the auxiliary ignition device are respectively ignited after the fuel injection period. When the lower engine speed of two conditions in the specific area with the same engine load and different engine speeds is set as a low-speed condition and the higher engine speed is set as a high-speed condition, the fuel injection device is controlled in such a manner that the fuel injection period under the low-speed condition is later than the fuel injection period under the high-speed condition. The main ignition device and the auxiliary ignition device are controlled in such a manner that the ignition period, i.e., the auxiliary ignition period, is closer to the retarded angle side than the ignition period, i.e., the main ignition period, and the retarded angle amount, i.e., the ignition phase difference, of the auxiliary ignition period relative to the main ignition period is larger under the low-speed condition than under the high-speed condition.

[0012] In a specific region where the engine speed is below a predetermined reference speed and the engine load is higher than a predetermined reference load, in other words, in a low-speed high-load region, if fuel is injected into the main combustion chamber during the intake stroke, pre-ignition is likely to occur, that is, the mixture self-ignites before being ignited by the ignition device. In contrast, in the present invention, in a specific region, the fuel injection period is controlled in a manner that is included in the compression stroke, so that the occurrence of pre-ignition can be suppressed. In addition, compared with the fuel injection period under high-speed conditions where pre-ignition is relatively difficult to occur, the fuel injection period under low-speed conditions where pre-ignition is particularly likely to occur due to the low engine speed is set to be later. Therefore, the occurrence of pre-ignition under low-speed conditions can be more reliably suppressed. In addition, under high-speed conditions, the occurrence of pre-ignition can be suppressed and the mixing of fuel and air can be promoted until near the compression top dead center, thereby suppressing the residue of unburned mixture.

[0013] Here, if fuel injection is performed during the compression stroke, the fuel will not be fully diffused in the main combustion chamber until near the compression top dead center, so it is difficult to introduce a sufficient amount of air-fuel mixture (fuel) into the sub-chamber only by the compression action of the piston. In contrast, in the present invention, the sub-ignition timing is set to a timing that is closer to the delayed angle side than the main ignition timing. Therefore, the air-fuel mixture can be burned in the main combustion chamber by ignition performed by the main ignition device, and the pressure increase in the main combustion chamber generated thereby can be used to pressurize the air-fuel mixture (fuel) into the sub-chamber. Therefore, according to the present invention, in a specific area set to low speed and high load, the occurrence of pre-ignition can be suppressed, and proper combustion can be achieved in the main combustion chamber and the sub-chamber, thereby improving fuel consumption performance and exhaust performance.

[0014] Furthermore, in the present invention, under low-speed conditions, the retard angle amount of the auxiliary ignition timing relative to the main ignition timing, that is, the ignition phase difference is larger than that under high-speed conditions. In other words, for low-speed conditions where it is more difficult to introduce the mixture (fuel) into the auxiliary chamber only by the compression action of the piston because the fuel injection timing is closer to the compression top dead center, the period from the start of the introduction of the mixture (fuel) into the auxiliary chamber accompanied by the pressure rise in the main combustion chamber to the ignition by the auxiliary ignition device is set to be longer. Therefore, under low-speed conditions, the amount of the mixture (fuel) introduced into the auxiliary chamber can be ensured and proper combustion in the auxiliary chamber can be achieved more reliably. In addition, under high-speed conditions, the combustion in the auxiliary chamber can be started at a relatively early period after the start of combustion in the main combustion chamber, which can shorten the combustion period and more reliably improve fuel consumption performance.

[0015] In the above solution, preferably, the control device sets the main ignition timing under the low speed condition to a timing closer to the retarded angle side than the main ignition timing under the high speed condition, and sets the auxiliary ignition timing under the low speed condition to a timing closer to the retarded angle side than the auxiliary ignition timing under the high speed condition. (Technical Solution 2).

[0016] According to this scheme, the period from the fuel injection period to the main ignition period can be ensured under both low-speed conditions and high-speed conditions, in other words, the mixing period of fuel and air until the main ignition period can be ensured, and the ignition phase difference under low-speed conditions can be made larger than the ignition phase difference under high-speed conditions. Therefore, proper combustion in the main combustion chamber and the sub-chamber can be further reliably achieved.

[0017] As a specific scheme to implement the above scheme, the following scheme can be listed: the control device makes the delay angle amount of the auxiliary ignition period under the low-speed condition relative to the auxiliary ignition period under the high-speed condition larger than the delay angle amount of the main ignition period under the low-speed condition relative to the main ignition period under the high-speed condition (Technical Solution 3).

[0018] Here, since the piston descends during the expansion stroke, when the auxiliary ignition timing is set to the period during the expansion stroke, it is particularly difficult to set the air-fuel mixture (fuel) in the auxiliary chamber at the auxiliary ignition timing to a sufficient amount only by the compression action of the piston. In contrast, in the present invention, as described above, the pressure rise in the main combustion chamber accompanying the combustion can be used to pressurize the auxiliary chamber with the air-fuel mixture (fuel). Therefore, even in the scheme in which the control device sets the auxiliary ignition timing in the specific area to the period during the expansion stroke, the amount of the air-fuel mixture in the auxiliary chamber can be ensured (technical solution 4).

[0019] In the above solution, preferably, when operating in the specific area, the control device controls the main ignition device and the auxiliary ignition device in such a manner that the lower the engine speed, the larger the ignition phase difference, and the rate of change of the ignition phase difference with respect to the engine speed is larger on the high speed side than on the low speed side. (Technical Solution 5).

[0020] According to this scheme, since the ignition phase difference is set to be larger as the engine speed is lower, it is possible to achieve good fuel efficiency and reliably achieve proper combustion in the sub chamber at all engine speeds. However, in the scheme in which the sub ignition timing is set to a period in the expansion stroke, if the ignition phase difference is too large, the sub ignition timing will become a period that is too late in the expansion stroke, so the effect of introducing the mixture (fuel) into the sub chamber becomes smaller and the fuel efficiency is reduced. In contrast, in this scheme, the rate of change of the ignition phase difference with respect to the engine speed is larger on the high rotation side than on the low rotation side. Therefore, it is possible to avoid an excessively large ignition phase difference, in other words, it is possible to avoid the sub ignition timing from becoming a period that is too late in the expansion stroke, and it is possible to ensure the amount of the mixture (fuel) introduced into the sub chamber and achieve good fuel efficiency.

[0021] In the above solution, preferably, when operating in the specific region, the control device sets the main ignition timing to the expansion stroke. (Solution 6).

[0022] According to this aspect, the period from the fuel injection timing to the main ignition timing, in other words, the mixing period of fuel and air until the main ignition timing can be ensured, and appropriate combustion in the main combustion chamber can be achieved more reliably.

[0023] Effects of the Invention

[0024] As described above, according to the engine system of the present invention, it is possible to reliably improve fuel efficiency and exhaust gas performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic configuration diagram of an engine system according to an embodiment of the present invention.

[0026] Figure 2 This is a schematic cross-sectional view of the engine body.

[0027] Figure 3 This is a partial cross-sectional view of the front end portion of the auxiliary ignition unit as viewed from the side.

[0028] Figure 4 It is a bottom view of the front end portion of the auxiliary ignition unit.

[0029] Figure 5 A diagram showing a control module of an engine.

[0030] Figure 6 It is a map showing the operating range of the engine.

[0031] Figure 7 This is a flowchart showing the control procedure of the injector and the spark plug in the third area.

[0032] Figure 8FIG. 1 is a diagram showing an example of the drive pulse of the injector, the main ignition timing, and the auxiliary ignition timing in the third region.

[0033] Fig. 9 FIG. 2 is a diagram showing another example of the drive pulse of the injector, the main ignition timing, and the auxiliary ignition timing in the third region.

[0034] Fig.10 This is a diagram showing the relationship between the engine speed and various parameters in the third region.

[0035] Description of Reference Numerals

[0036] 1 Engine system

[0037] 2 Engine body

[0038] 24 Piston

[0039] 28 Injector (fuel injection device)

[0040] 26 Main combustion chamber

[0041] 30 Auxiliary ignition unit

[0042] 32 Main spark plug (main ignition device)

[0043] 52 Cylinder Block

[0044] 54 Cylinder head

[0045] 60 Auxiliary combustion chamber

[0046] 62 Auxiliary spark plug (auxiliary ignition device)

[0047] 64 Cover part (partition wall)

[0048] 66 connecting hole

[0049] 100 ECU (control unit) DETAILED DESCRIPTION

[0050] [Overall structure of the engine]

[0051] Figure 1 1 is a schematic diagram showing a preferred embodiment of the engine system of the present invention. The engine system 1 includes an engine body 2, an intake passage 4, an exhaust passage 6, and an EGR device 50. The air (intake air) introduced into the engine body 2 flows inside the intake passage 4, and the exhaust gas led out from the engine body 2 flows inside the exhaust passage 6. The engine system 1 is mounted on a vehicle as a power source for driving the vehicle. The engine body 2 is a four-stroke gasoline engine that mainly uses gasoline as fuel, and the fuel containing gasoline is supplied to the engine body 2.

[0052] Figure 2 2 is a schematic cross-sectional view of the engine body 2. In the present embodiment, the engine body 2 is a multi-cylinder engine having a plurality of cylinders 22. For example, the engine body 2 has a plurality of cylinders 22 arranged in a row (along the same direction as the cylinders 22). Figure 1 The engine body 2 includes a cylinder block 52, a cylinder head 54, and a plurality of pistons 24. The cylinder block 52 has a plurality of cylinders 22 formed therein, and the cylinder head 54 has a bottom surface 54a that blocks the upper end opening of each cylinder 22 and is mounted on the upper surface of the cylinder block 52. The plurality of pistons 24 are respectively accommodated in each cylinder 22 so as to be reciprocatingly slidable. In addition, in the present embodiment, the side from the cylinder block 52 toward the cylinder head 54 is set as the upper side, and the opposite side is set as the lower side, but this is for the convenience of explanation and is not intended to limit the installation posture of the engine.

[0053] A main combustion chamber 26 is defined above the piston 24 of each cylinder 22. The main combustion chamber 26 is defined by the inner peripheral surface 22a of the cylinder 22 formed in the cylinder block 52, the bottom surface (lower surface) 54a of the cylinder head 54, and the top surface 24a of the piston 24. Fuel is supplied to the main combustion chamber 26 by injection from an injector 28 described later. The piston 24 reciprocates in the up-and-down direction by the expansion force generated by the combustion of the fuel-air mixture.

[0054] A crankshaft 20 as an output shaft of the engine body 2 is provided at the bottom 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 around a central axis in accordance with the reciprocating motion of the piston 24.

[0055] The cylinder head 54 is provided with an intake port 8 for introducing air supplied from the intake passage 4 into the main combustion chamber 26 and an exhaust port 12 for leading the exhaust gas generated in the main combustion chamber 26 to the exhaust passage 6 for each cylinder 22. The cylinder head 54 is provided with an intake valve 10 for opening and closing the opening of the intake port 8 on the main combustion chamber 26 side and an exhaust valve 14 for opening and closing the opening of the exhaust port 12 on the main combustion chamber 26 side for each cylinder 22. In the present embodiment, two intake valves 10 and two exhaust valves 14 are provided for one cylinder 22.

[0056] The intake valve 10 and the exhaust valve 14 are driven to open and close in conjunction with the rotation of the crankshaft 20 by the valve drive mechanisms 16 and 18 provided in the cylinder head 54. The valve drive mechanism 16 for the intake valve 10 is provided with a variable valve lift mechanism (intake S-VT) 16a that electrically variably controls the valve lift amount and opening and closing timing of the intake valve 10. Similarly, the valve drive mechanism 18 for the exhaust valve 14 is also provided with a variable valve lift mechanism (exhaust S-VT) 18a that electrically variably controls the valve lift amount and opening and closing timing of the exhaust valve 14.

[0057] The cylinder head 54 is provided with a set of injectors 28, main spark plugs 32 and auxiliary ignition units 30 for each cylinder 22. The injectors 28 correspond to the "fuel injection device" in the claims, and the main spark plugs 32 correspond to the "main ignition device" in the claims.

[0058] The fuel injector 28 is an injection valve that injects fuel into the main combustion chamber 26. An injection port for injecting fuel is formed at the front end portion 28x of the fuel injector 28. The fuel injector 28 is mounted on the cylinder head 54 in such a manner that the front end portion 28x faces the main combustion chamber 26 from above. In the present embodiment, the fuel injector 28 is arranged in such a manner that the front end portion 28x is located at the center of the top surface of the main combustion chamber 26 (specifically, on the axis of the cylinder 22).

[0059] The main spark plug 32 ignites the mixture in the main combustion chamber 26 by spark discharge. An electrode portion 32x for emitting sparks is provided at the front end of the main spark plug 32. The electrode portion 32x includes a center electrode 32a and a side electrode (ground) 32b. The main spark plug 32 is mounted on the cylinder head 54 in such a manner that its electrode portion 32x faces the main combustion chamber 26 from above. In the present embodiment, the main spark plug 32 is arranged in such a manner that its electrode portion 32x is located on the top surface of the main combustion chamber 26 at a position closer to the intake port 8 than the front end portion 28x of the injector 28.

[0060] The auxiliary ignition unit 30 is a device for ejecting flames into the main combustion chamber 26. The details of the auxiliary ignition unit 30 will be described later.

[0061] The intake passage 4 is connected to one side 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 filter 34 for removing foreign matter in the intake air, a throttle valve 36 that can be opened and closed to adjust the flow rate of the intake air, and a surge tank 38 are provided in order from the upstream side.

[0062] The downstream end of the intake passage 4 branches into a plurality of passages. Each branch passage is connected to one intake port 8. For each cylinder 22, a vortex valve 56 (see FIG. 5 ) is provided in the branch passage connected to one of the two intake ports 8 to open and close the branch passage. Figure 5 ).

[0063] 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. The exhaust passage 6 is provided with a catalyst device 40 having a catalyst 41 such as a three-way catalyst built therein.

[0064] The EGR device 50 is a device for allowing a part of the exhaust gas to flow back to the intake passage 4 as EGR gas, and to be introduced (flowed back) to the main combustion chamber 26 connected to the intake passage 4. The EGR device 50 has an EGR passage 42 that connects the exhaust passage 6 with the intake passage 4, and an EGR valve 46 and an EGR cooler 44 that are respectively provided in the EGR passage 42. The upstream end of the EGR passage 42 is connected to the exhaust passage 6 that is at the downstream end of the catalytic device 40 and is more downstream than the catalyst 41, and the downstream end of the EGR passage 42 is connected to the surge tank 38. The EGR valve 46 is a valve that opens and closes the EGR passage 42 to adjust the flow rate of the EGR gas. The EGR cooler 44 is a heat exchanger that cools the EGR gas. The EGR cooler 44 is arranged at a position more upstream than the EGR valve 46.

[0065] [Sub-ignition unit 30]

[0066] Figure 3 It is a partial cross-sectional view of the front end portion 30x of the auxiliary ignition unit 30 as seen from the side. Figure 4 It is a bottom view of the front end portion 30 x of the auxiliary ignition unit 30 (seen from the front end side).

[0067] The auxiliary ignition unit 30 has an auxiliary spark plug 62 for igniting the air-fuel mixture by spark discharge. An electrode portion 62x for emitting sparks is provided at the front end of the auxiliary spark plug 62. The electrode portion 62x includes a center electrode 62a and a side electrode (ground) 62b. The auxiliary ignition unit 30 has a cover member 64 provided at its front end portion 30x and covering the electrode portion 62x of the auxiliary spark plug 62. A prescribed space, namely, the auxiliary chamber 60 is divided inside the cover member 64. In other words, the auxiliary spark plug 62 is arranged in such a manner that its electrode portion 62x faces the auxiliary chamber 60, and ignites the air-fuel mixture in the auxiliary chamber 60. The cover member 64 is in a hollow hemispherical shape that bulges toward the front end side of the auxiliary ignition unit 30. The auxiliary spark plug 62 described above is equivalent to the "auxiliary ignition device" in the claims, and the cover member 64 described above is equivalent to the "partition wall" in the claims.

[0068] like Figure 2 As shown, the auxiliary ignition unit 30 is mounted on the cylinder head 54 in such a manner that its front end portion 30x faces the main combustion chamber 26 from above. In the present embodiment, the auxiliary ignition unit 30 is mounted on the top surface of the main combustion chamber 26 at a position closer to the exhaust port 12 than the injector 28. In the present embodiment, in this mounted state, the cover member 64 is almost entirely located in the main combustion chamber 26.

[0069] The cover member 64 is provided with a plurality of communication holes 66 that penetrate the inside and outside thereof and connect the main combustion chamber 26 with the sub-chamber 60. The inner space of the cover member 64, i.e., the sub-chamber 60, is connected to the main combustion chamber 26 via these communication holes 66. Thus, in the present embodiment, by installing the sub-ignition unit 30 configured as described above in the engine body 2, the sub-chamber 60 that is separated from the main combustion chamber 26 by the cover member 64 and connected to the main combustion chamber 26 via the communication holes 66 is formed in the engine body 2.

[0070] In this embodiment, three communication holes 66 are formed in the cover member 64. Figure 4 As shown, three communication holes 66 are formed at intervals of 120 degrees around the axis of the cover member 64 passing through the vertex A of the cover member 64. Figure 3 As shown, each communicating hole 66 is formed at a position separated by 45 degrees from the vertex A in a side view. In addition, the radius and thickness of the cover member 64 are set to 5 mm and 1 mm, respectively, and the diameter of each communicating hole 66 is set to 1.2 mm.

[0071] The auxiliary ignition unit 30 ejects flames into the main combustion chamber 26. Specifically, when fuel is injected from the fuel injector 28 into the main combustion chamber 26 to form a mixture of air and fuel in the main combustion chamber 26, a portion of the mixture is introduced into the auxiliary chamber 60 through the connecting hole 66. When spark discharge is performed by the auxiliary spark plug 62 in a state where a sufficient amount of mixture exists in the auxiliary chamber 60, the mixture starts to burn in the auxiliary chamber 60, and the flame propagates to the surroundings from the vicinity of the electrode portion 62x of the auxiliary spark plug 62. Moreover, the flame is ejected / released into the main combustion chamber 26 through the connecting hole 66, and propagates to the mixture in the main combustion chamber 26.

[0072] Here, if ignition is performed by the main spark plug 32 as described above, the flame will also propagate to the surroundings from the vicinity of the electrode portion 32x of the main spark plug 32. Therefore, if ignition is performed by both the main spark plug 32 and the auxiliary spark plug 62, and the air-fuel mixture is properly burned in the main combustion chamber 26 and the auxiliary chamber 60, the flame will propagate to the air-fuel mixture in the main combustion chamber 26 from multiple positions, and the combustion speed of the air-fuel mixture in the main combustion chamber 26 will be increased, so that the fuel consumption performance can be improved, and the occurrence of knocking and the residue of unburned air-fuel mixture can be suppressed.

[0073] [Control system]

[0074] Figure 5 ECU 100 is a block diagram showing an engine control system. ECU 100 shown in this figure is a device for controlling the engine in a unified manner and is composed of a microcomputer including a processor (CPU) for performing various calculations, memories such as ROM and RAM, and various input and output buses. ECU 100 is equivalent to the "control device" in the claims.

[0075] The detection information of various sensors is input to the ECU 100. For example, the detection values ​​of the air flow sensor SN1, the intake air temperature sensor SN2, the intake air pressure sensor SN3, the water temperature sensor SN4, the crank angle sensor SN5, and the throttle opening sensor SN6 provided in the engine system 1 are input to the ECU 100. The air flow sensor SN1 detects the flow rate of the intake air introduced into the engine body 2 through the intake passage 4. The intake air temperature sensor SN2 and the intake air pressure sensor SN3 respectively detect the temperature and pressure of the intake air introduced into the engine body 2. The water temperature sensor SN4 detects the temperature of the engine cooling water for cooling the engine body 2. The crank angle sensor SN5 detects the rotation angle of the crankshaft 20, i.e., the crank angle, and the engine speed. The throttle opening sensor SN6 detects the opening of the throttle pedal (not shown) provided in the vehicle, i.e., the throttle opening.

[0076] The ECU 100 performs various determinations and calculations based on input signals from various sensors. The ECU 100 is electrically connected to the injector 28, the main spark plug 32, the auxiliary spark plug 62, the EGR device 50 (specifically, the EGR valve 46), etc., and outputs control electrical signals to these devices based on calculation results.

[0077] Figure 6 This is a graph showing the engine's operating range, with the horizontal axis being the engine speed and the vertical axis being the engine load. Figure 6 As shown, the operating range of the engine is roughly divided into three ranges A1 to A3 (first range A1, second range A2, and third range A3) according to the control contents of the injector 28 and the spark plugs 32 and 62.

[0078] The first region A1 is a low-speed, low-load region where the engine speed is below the prescribed first speed N1 and the engine load is below the prescribed first load Tq1. The third region A3 is a low-speed, high-load region where the engine speed is below the first speed N1 and the engine load is higher than the prescribed second load Tq2. The second region A2 is another region, which is composed of a region where the engine speed is below the first speed N1, a region where the engine load is higher than the first load Tq1 and below the second load Tq2, and a region where the engine speed is higher than the first speed N1. The above-mentioned second load Tq2 is equivalent to the "reference load" in the claims, the first speed N1 is equivalent to the "reference speed" in the claims, and the third region A3 is equivalent to the "specific region" in the claims.

[0079] In the first region A1, the injector 28 and the spark plugs 32 and 62 are controlled so as to realize HCCI combustion (Homogeneous Compression Charge Ignition). Specifically, in the first region A1, the fuel is injected from the injector 28 during the intake stroke. In addition, the driving of the spark plugs 32 and 62 (the ignition by these spark plugs 32 and 62) is stopped.

[0080] As described above, the injector 28 faces the main combustion chamber 26, and the fuel injected from the injector 28 can be diffused throughout the main combustion chamber 26. Therefore, in the first region A1, by injecting the fuel from the injector 28 during the intake stroke, the fuel and the air are fully mixed in the main combustion chamber 26 until the compression top dead center is reached. Then, in the first region A1, the fully mixed mixed gas (premixed gas) is compressed by the piston 24 to a high temperature and high pressure, and self-ignites near the compression top dead center.

[0081] In HCCI combustion, the air-fuel ratio of the mixture (the ratio of the weight of air in the main combustion chamber 26 to the weight of fuel in the main combustion chamber 26) can be made lean (increased) to a level where flame propagation is impossible, thereby improving fuel efficiency. Thus, in the first region A1, the opening of the throttle valve 36 is adjusted so that the air-fuel ratio of the mixture in the main combustion chamber 26 becomes lean (higher) than the theoretical air-fuel ratio (14.7).

[0082] In the second region A2, the injector 28 and the spark plugs 32 and 62 are controlled so as to achieve flame propagation combustion (SI combustion, SI: Spark Ignition).

[0083] Specifically, in the second region A2, similarly to the first region A1, fuel is injected from the injector 28 during the intake stroke. On the other hand, in the second region A2, the main spark plug 32 and the auxiliary spark plug 62 are driven, and ignition is performed by the two spark plugs 32 and 62. In addition, the opening of the throttle valve 36 is adjusted so that the air-fuel ratio of the air-fuel mixture in the main combustion chamber 26 is close to the theoretical air-fuel ratio. In the second region A2, a flame core is generated around the electrode portions 32x and 62x of the spark plugs 32 and 62 by ignition, and the flame propagates from the flame core to the surroundings, so that the air-fuel mixture in the main combustion chamber 26 and the auxiliary chamber 60 is burned.

[0084] [Control contents in the third area A3]

[0085] Next, the control contents in the third area A3 which is a feature of the present invention will be described. Figure 71 is a flowchart showing the overall flow of a control procedure of the injector 28, the main spark plug 32, and the auxiliary spark plug 62 in the third area A3, which is performed by the ECU 100.

[0086] The ECU 100 first reads various information (step S1 ). The ECU 100 reads the engine speed detected by the crank angle sensor SN5 , the accelerator opening detected by the accelerator opening sensor SN6 , and the like.

[0087] Next, the ECU 100 calculates the torque required of the engine, that is, the required torque, in other words, the engine load (step S2). The ECU 100 calculates the required torque (engine load) based on the engine speed and the accelerator opening read in step S1.

[0088] Next, ECU 100 determines whether the engine operating point is in third region A3 (step S3). Specifically, ECU 100 determines whether the current engine operating point is in third region A3 based on the engine speed read in step S1 and the required torque (engine load) calculated in step S2.

[0089] If the determination in step S3 is "No" and the engine operating point is not within the third region A3, the ECU 100 ends the process (implements control of the first region A1 or the second region A2). On the other hand, if the determination in step S3 is "Yes" and the engine operating point is within the third region A3, the ECU 100 proceeds to step S4.

[0090] In step S4, the ECU 100 sets the fuel injection timing when the fuel injection is started by the injector 28, i.e., the fuel injection timing, the ignition timing of the main spark plug 32, i.e., the main ignition timing (the main spark plug 32 ignites, in other words, the period in crank angle when spark discharge is performed), and the ignition timing of the auxiliary spark plug 62, i.e., the auxiliary ignition timing (the auxiliary spark plug 62 ignites, in other words, the period in crank angle when spark discharge is performed), based on the engine speed and the engine load.

[0091] Next, in step S5, the ECU 100 drives the injector 28 to start the injection of the fuel at the fuel injection timing set in step S4. In addition, the ECU 100 drives the main spark plug 32 to perform ignition with the main spark plug 32 at the main ignition timing set in step S4. In addition, the ECU 100 drives the auxiliary spark plug 62 to perform ignition with the auxiliary spark plug 62 at the auxiliary ignition timing set in step S4.

[0092] Next, the details of the fuel injection timing, the main ignition timing, and the auxiliary ignition timing in the third area A3 set in the above-mentioned step S4 will be described.

[0093] Figure 8 and Fig. 9 1 and 2 are diagrams showing the drive pulse of the injector 28, the main ignition timing tm, and the auxiliary ignition timing ts at the operating points P1 and P2 included in the third region A3. Figure 6 As shown, the operating point P2 is a point where the engine load is Tq3 which is the same as that of the operating point P1 and the engine speed is higher than that of the operating point P1. Fig.10 : is a graph showing the relationship between the engine speed and various parameters in the third area A3. Fig.10 The uppermost line graph of FIG. 1 is a line graph showing the relationship between the engine speed and the fuel injection timing tinj. Fig.10 The second graph from the top is a graph showing the relationship between the engine speed and the ignition phase difference dt described later. Fig.10 The third line graph from the top is a line graph showing the relationship between the engine speed and the main ignition timing tm and the auxiliary ignition timing ts. In addition, these line graphs show the relationship between the engine speed and each parameter when the engine load is constant. Hereinafter, among two operating points (for example, operating points P1 and P2) with the same engine load and different engine speeds, the operating point (P1) with a lower engine speed is appropriately referred to as a low speed point, and the point (P2) with a higher engine speed is appropriately referred to as a high speed point.

[0094] In the third region A3, similarly to the second region A2, the injector 28 and the spark plugs 32 and 62 are controlled so as to realize SI combustion.

[0095] However, in the third region A3, if the fuel is injected from the injector 28 during the intake stroke as in the second region A2, pre-ignition may occur. Specifically, when the engine load is high, the combustion energy generated in the main combustion chamber 26 becomes larger, so the temperature in the main combustion chamber 26 becomes higher. When the engine speed is low, the time per crank angle becomes longer. Therefore, in the low-speed and high-load region where the engine speed is low and the engine load is high, that is, in the third region A3, if the fuel is injected from the injector 28 during the intake stroke as in the second region A2, the amount of heat received by the mixture until the vicinity of the compression top dead center and the heating time become larger, so pre-ignition is likely to occur, that is, the mixture self-ignites at the desired timing, in other words, before ignition by the spark plug.

[0096] Thus, in the third region A3, delayed SI combustion is implemented in which the fuel injection from the injector 28 is started during the compression stroke, so that the heating time of the mixture (fuel) reaching the vicinity of the compression top dead center is suppressed to be shorter, in other words, the occurrence of pre-ignition is suppressed. That is, in the third region A3, the fuel injection period tinj is set to a period in the compression stroke (controlled to be included in the compression stroke), and the fuel injection from the injector 28 into the main combustion chamber 26 is started during the compression stroke. In addition, the end period of the fuel injection by the injector 28 is not limited to the period in the compression stroke. For example, Figure 8 As shown, in the present embodiment, at an operating point in the third region A3 where the engine speed is relatively low, the fuel injection from the injector 28 ends at a period in the expansion stroke.

[0097] Here, in the third region A3, the lower the engine speed, the higher the possibility of pre-ignition. Therefore, in the third region A3, in two operating points (for example, operating points P1 and P2) with the same engine load and different engine speeds, the fuel injection period tinj of the low speed point (P1) is later than the fuel injection period tinj of the high speed point (P2). In other words, in the third region A3, in two conditions with the same engine load and different engine speeds, the fuel injection period tinj under the low speed condition with a lower engine speed is later than the fuel injection period tinj under the high speed condition with a higher engine speed. In the present embodiment, as described later, in the third region A3, the lower the engine speed, the later the fuel injection period tinj (the period closer to the delay angle side).

[0098] In this embodiment, if Fig.10 As shown in FIG. 1 , in the third region A3, the lower the engine speed, the closer the fuel injection timing tinj is to the delayed angle side. Fig.10 2 shows an example in which the fuel injection timing tinj increases or decreases in proportion to the engine speed, but the relationship between them is not limited to a proportional relationship.

[0099] In the third region A3, both the main spark plug 32 and the auxiliary spark plug 62 are driven.

[0100] like Figure 8 and Fig. 9As shown, in the third region A3, the main ignition timing tm is set to a period closer to the advanced angle side than the auxiliary ignition timing ts, and ignition is first performed by the main spark plug 32, and then ignition is performed by the auxiliary spark plug 62. In the present embodiment, the main ignition timing tm and the auxiliary ignition timing ts in the third region A3 are both set to a period in the expansion stroke. The above-mentioned ignition phase difference dt is the amount of retardation of the auxiliary ignition timing ts relative to the main ignition timing tm, in other words, the period from the main ignition timing tm to the auxiliary ignition timing ts in crank angle.

[0101] In the third area A3, among two operating points (for example, operating points P1 and P2) with the same engine load and different engine speeds, the main ignition period tm of the low-speed point (P1) is later than the main ignition period tm of the high-speed point (P2), and the sub-ignition period ts of the low-speed point (P1) is later than the sub-ignition period ts of the high-speed point (P2).

[0102] In the third region A3, at two operating points (e.g., operating points P1 and P2) with the same engine load and different engine speeds, the retard angle amount of the sub-ignition timing ts at the low speed point (P1) relative to the sub-ignition timing ts at the high speed point (P2) is set to be larger than the retard angle amount of the main ignition timing tm at the low speed point (P1) relative to the main ignition timing tm at the high speed point (P2). Accordingly, in the third region A3, the ignition phase difference dt (the retard angle amount of the sub-ignition timing ts relative to the main ignition timing tm) is controlled as follows. In other words, at two operating points (e.g., operating points P1 and P2) with the same engine load and different engine speeds, the ignition phase difference dt at the low speed point (P1) is set to be larger than the ignition phase difference dt at the high speed point (P2).

[0103] like Fig.10 As shown, in the present embodiment, in the third region A3, the main ignition timing tm and the sub ignition timing ts are set to later timings as the engine speed decreases.

[0104] In addition, the main ignition timing tm and the sub-ignition timing ts are set so that the ignition phase difference dt increases as the engine speed decreases. In other words, the change rate of the sub-ignition timing ts with respect to the engine speed is set to be greater than the change rate of the main ignition timing tm with respect to the engine speed.

[0105] In addition, the main ignition timing tm is set so that its change rate with respect to the engine speed is constant at all engine speeds in the third region A3, while the sub-ignition timing ts is set so that its change rate with respect to the engine speed is larger when the engine speed is equal to or higher than a predetermined engine speed N2 than when the engine speed is lower than the engine speed N2. Accordingly, in the third region A3, the change rate of the ignition phase difference dt with respect to the engine speed is larger on the high speed side when the engine speed is equal to or higher than the predetermined engine speed N2 than on the low speed side when the engine speed is lower than the engine speed N2.

[0106] In the present embodiment, each of the timings set as described above (fuel injection timing tinj, main ignition timing, and sub-ignition timing ts) is stored in advance in the form of a map with respect to the engine speed and the engine load in the ECU 100. In the above-mentioned step S4, the ECU 100 extracts values ​​corresponding to the current engine load and engine speed from the map stored in the ECU 100.

[0107] [Function, etc.]

[0108] As described above, in the above embodiment, since the main combustion chamber 26 and the sub-chamber 60 are provided in the engine body 2, the fuel consumption performance and the exhaust gas performance can be improved by the combustion of the mixed gas in the two combustion chambers 26 and 60. In addition, the injector 28 as a device for injecting fuel is only provided in the main combustion chamber 26, and is not provided in the sub-chamber 60. Therefore, compared with the case where the injector 28 is provided in the main combustion chamber 26 and the sub-chamber 60, the structure of the engine system can be simplified and it is more cost-effective. In addition, by arranging the injector 28 to inject fuel into the main combustion chamber 26, the fuel can be uniformly diffused in the entire main combustion chamber 26. Therefore, in the first area A1 of low speed and low load, appropriate HCCI combustion can be achieved.

[0109] In the third region A3, which is a low-speed and high-load region, the fuel injection period tinj is set to a period in the compression stroke, and at two operating points (e.g., operating points P1 and P2) with the same engine load and different engine speeds, the fuel injection period tinj at the low-speed point (P1) is later than the fuel injection period tinj at the high-speed point (P2). Therefore, as described above, in the third region A3, it is possible to avoid the heating time of the mixture until it reaches the vicinity of the compression top dead center becoming too long, thereby suppressing the occurrence of pre-ignition.

[0110] However, when the fuel injection timing tinj is set to a time during the compression stroke, since the fuel does not diffuse into the entire main combustion chamber 26 until near the compression top dead center, it is difficult to introduce a sufficient amount of fuel into the sub chamber 60 by the compression action of the piston 24 alone, and it is difficult to achieve proper combustion in the sub chamber 60. In particular, in the above-mentioned embodiment, since the sub ignition timing ts is set to a time after the piston 24 starts to descend during the expansion stroke, if only the compression action of the piston 24 is used, there is a high possibility that the air-fuel mixture (fuel) in the sub chamber at the sub ignition timing is insufficient. In addition, if the ignition is performed by the sub spark plug 62 only after the fuel is sufficiently diffused and a sufficient amount of air-fuel mixture is introduced into the sub chamber 60, and then the ignition is performed by the main spark plug 32, the ignition timing of the main spark plug 32 will become a very late time in the expansion stroke, so there is a high possibility that the air-fuel mixture in the main combustion chamber 26 will not burn properly.

[0111] In contrast, in the above-described embodiment, in the third region A3, the auxiliary ignition timing ts is set to a timing closer to the retarded angle side than the main ignition timing tm. Therefore, proper combustion can be achieved in the main combustion chamber 26 by ignition by the main spark plug 32 near the compression top dead center. In addition, the mixture (fuel) can be pressed from the main combustion chamber 26 to the auxiliary chamber 60 by the pressure increase in the main combustion chamber 26 caused by the combustion in the main combustion chamber 26. Therefore, a sufficient amount of the mixture (fuel) can be present in the auxiliary chamber 60 when ignition is performed by the auxiliary spark plug 62, and proper combustion can be achieved even in the auxiliary chamber 60.

[0112] Thus, according to the above embodiment, in the third area A3, the fuel injection timing tinj is set to the timing in the compression stroke, thereby suppressing the occurrence of pre-ignition and achieving proper combustion in the main combustion chamber 26 and the sub chamber, thereby improving fuel efficiency and exhaust performance.

[0113] Furthermore, in the above-mentioned embodiment, in the third region A3, the ignition phase difference dt at the low speed point where the fuel injection timing tinj is closer to the retarded angle side is set to be larger than the ignition phase difference dt at the high speed point where the fuel injection timing tinj is closer to the advanced angle side. In other words, for the low speed point where it is more difficult to introduce the air-fuel mixture (fuel) into the sub chamber 60 only by the compression action of the piston 24 because the fuel injection timing tinj is closer to the compression top dead center, the period from the start of the introduction of the air-fuel mixture (fuel) into the sub chamber 60 with the pressure rise of the main combustion chamber 26 to the ignition by the sub spark plug 62, that is, the period of introduction of the air-fuel mixture into the sub chamber 60 is set to be longer. Therefore, at the low speed point, a sufficient amount of the air-fuel mixture (fuel) can be reliably introduced into the sub chamber 60 and appropriate combustion of the air-fuel mixture in the sub chamber 60 can be reliably achieved. In addition, at high-speed points, the amount of mixture (fuel) in the sub-chamber 60 can be ensured, and combustion in the sub-chamber 60 can be started at a relatively early period after the start of combustion in the main combustion chamber 26, thereby achieving proper combustion of the mixture in the sub-chamber 60, shortening the combustion period and more reliably improving fuel consumption performance.

[0114] In particular, in the above embodiment, at the operating point in the third region A3 where the engine speed is low, a portion of the fuel is not compressed by the piston 24 during the expansion stroke at the time when the fuel injection from the injector 28 ends, and thus the amount of the mixed gas (fuel) in the sub chamber 60 is likely to be insufficient. In contrast, according to the above embodiment, even at such an operating point where the engine speed is low and the fuel injection ends during the expansion stroke, a sufficient amount of the mixed gas (fuel) can be introduced into the sub chamber 60.

[0115] In the above embodiment, the ignition phase difference dt is set to be larger as the engine speed is lower in the third region A3. Therefore, appropriate combustion in the sub chamber 60 can be reliably achieved with good fuel efficiency at each engine speed.

[0116] Here, in the above embodiment, in the third region A3, since the auxiliary ignition timing ts is set to a period in the expansion stroke, if the ignition phase difference dt is too large, the auxiliary ignition timing ts will become a period that is too late in the expansion stroke. If the expansion stroke advances, the pressure in the main combustion chamber 26 will drop significantly, so the effect of pressing the air-fuel mixture (fuel) from the main combustion chamber 26 into the auxiliary chamber 60 will decrease. In addition, if the combustion start timing in the auxiliary chamber 60 becomes a period that is too late in the expansion stroke, the fuel efficiency performance may be deteriorated. In contrast, in the above embodiment, in the third region A3, the rate of change of the ignition phase difference dt with respect to the engine speed is larger on the high rotation side where the engine speed is a predetermined engine speed N2 or more than the low rotation side where the engine speed is less than the speed N2. Therefore, it is possible to avoid the ignition phase difference dt being too large on the low rotation side, in other words, it is possible to avoid the auxiliary ignition timing ts from becoming a period that is too late in the expansion stroke, and it is possible to reliably make the fuel efficiency performance good.

[0117] In the above embodiment, in the third region A3, the main ignition timing tm at a low speed point where the fuel injection timing tinj is closer to the retarded angle side is set to a timing closer to the retarded angle side than the main ignition timing tm at a high speed point where the fuel injection timing tinj is closer to the advanced angle side. Therefore, the period from the fuel injection timing tinj to the main ignition timing tm can be ensured at both the low speed point and the high speed point, in other words, the mixing period of the fuel and the air can be ensured until the main ignition timing tm, and the proper combustion of the mixture in the main combustion chamber 26 can be achieved more reliably.

[0118] In the above embodiment, in the third region A3, the main ignition timing tm is set to the period during the expansion stroke. Therefore, the period from the fuel injection timing tinj to the main ignition timing tm, in other words, the period of mixing the fuel and the air until the main ignition timing tm, can be made particularly long, and proper combustion in the main combustion chamber 26 can be achieved more reliably.

[0119] [Modifications]

[0120] The specific shape and size of the cover member 64 of the auxiliary ignition unit 30 are not limited to the above. In addition, the number and size of the communication holes 66 provided in the cover member 64 are not limited to the above. In addition, the installation position of the auxiliary ignition unit 30 is not limited to the above. For example, the auxiliary ignition unit 30 may also be provided on the intake port 8 side relative to the front end portion 28x of the injector 28.

[0121] In the above embodiment, the upper speed limit of the first area A1 is the same as the upper speed limit of the third area A3, but they may not be the same. In other words, the upper speed limit of the first area A1 may not be the first speed N1 which is the upper speed limit of the third area A3.

[0122] In addition, the control contents of the first area A1 and the second area A2 are not limited to those described above.

[0123] In addition, the detailed structure of the engine body 2 such as the number of cylinders is not limited to the above.

Claims

1. An engine system, characterized in that: have: A cylinder block and a cylinder head forming the cylinder; A piston is reciprocatably received in the cylinder; a main combustion chamber, which is divided by the cylinder block, the cylinder head and the piston; a sub-chamber separated from the main combustion chamber by a partition wall and communicating with the main combustion chamber through a communication hole formed in the partition wall; a fuel injection device for injecting fuel into the main combustion chamber; A main ignition device, which ignites the mixed gas in the main combustion chamber; A secondary ignition device, which ignites the mixed gas in the secondary chamber; as well as a control device electrically connected to the fuel injection device, the main ignition device, and the auxiliary ignition device and outputting electrical signals for control to these devices; When the engine is operated in a specific range where the engine speed is lower than a predetermined reference speed and the engine load is higher than a predetermined reference load, the control device performs the following control: The fuel injection device is controlled so that the injection timing of the fuel injected by the fuel injection device is included in the compression stroke, and the main ignition device and the auxiliary ignition device are ignited respectively after the fuel injection timing, When the lower engine speed of two conditions in the specific region where the engine load is the same and the engine speed is different is set as the low speed condition, and the higher engine speed is set as the high speed condition, the fuel injection device is controlled in such a manner that the fuel injection timing under the low speed condition is later than the fuel injection timing under the high speed condition, The main ignition device and the auxiliary ignition device are controlled in such a manner that the ignition timing of the auxiliary ignition device, i.e., the auxiliary ignition timing, is closer to the retarded angle side than the ignition timing of the main ignition device, i.e., the main ignition timing, and the retarded angle amount of the auxiliary ignition timing relative to the main ignition timing, i.e., the ignition phase difference, is larger under the low speed condition than under the high speed condition.

2. The engine system according to claim 1, characterized in that: The control device sets the main ignition timing under the low speed condition to a timing on the retarded angle side compared with the main ignition timing under the high speed condition, and sets the auxiliary ignition timing under the low speed condition to a timing on the retarded angle side compared with the auxiliary ignition timing under the high speed condition.

3. The engine system according to claim 2, characterized in that: The control device makes the retardation amount of the auxiliary ignition timing under the low speed condition relative to the auxiliary ignition timing under the high speed condition greater than the retardation amount of the main ignition timing under the low speed condition relative to the main ignition timing under the high speed condition.

4. The engine system according to any one of claims 1 to 3, characterized in that: The control device sets the sub-ignition timing in the specific region to a timing in an expansion stroke.

5. The engine system according to claim 4, characterized in that: When operating in the specific area, the control device controls the main ignition device and the auxiliary ignition device in such a manner that the lower the engine speed, the larger the ignition phase difference, and the rate of change of the ignition phase difference with respect to the engine speed is larger on the high speed side than on the low speed side.

6. The engine system according to claim 4, characterized in that: The control device sets the main ignition timing in the specific region in an expansion stroke.

7. The engine system according to claim 5, characterized in that: The control device sets the main ignition timing in the specific region in an expansion stroke.

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