Engine System

Abstract

To reliably improve a fuel consumption performance and an exhaust gas performance in an engine system having a main combustion chamber and an auxiliary chamber.SOLUTION: A system comprises a main combustion chamber, an auxiliary chamber, a fuel injection device for injecting fuel to the main combustion engine, a main ignition device for igniting air-fuel mixture in the main combustion chamber, and an auxiliary ignition device for igniting the air-fuel mixture in the auxiliary chamber. In a specific area with an engine speed not higher than a reference speed and an engine load higher than a reference load, the fuel injection device is controlled so that fuel injection timing is included in a compression stroke and fuel injection timing under a low speed condition becomes after fuel injection timing under a high speed condition. The main ignition device and the auxiliary ignition device are controlled so that auxiliary ignition timing is nearer a retard angle than the main ignition timing and an ignition phase difference that is a retard angle amount of the auxiliary ignition timing to the main ignition timing in a low speed condition becomes larger than that in a high speed condition.SELECTED DRAWING: Figure 10

Description

[Technical field]

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

[0002] In the past, in engines mounted on vehicles, etc., it has been considered to provide a main combustion chamber and a pre-chamber communicating therewith in order to improve fuel economy and exhaust gas performance. Specifically, by providing a main combustion chamber and a pre-chamber communicating therewith and ejecting the flame generated in the pre-chamber into the main combustion chamber, it is possible to increase the combustion speed in the main combustion chamber and improve fuel economy, and also to suppress the remaining unburned air-fuel mixture and improve exhaust gas performance.

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

[0004] [Patent Document 1] JP 2007-255370 A Summary of the Invention [Problem to be solved by the invention]

[0005] In the engine of Patent Document 1, fuel is injected into the main combustion chamber and the auxiliary combustion chamber separately, and two fuel injection valves are required for one cylinder. This makes the structure complicated and is disadvantageous in terms of cost. In response to this, in an engine having a main combustion chamber and an auxiliary combustion chamber, it is possible to provide a fuel injection valve only in the main combustion chamber. However, in a configuration in which a fuel injection valve is provided only in the main combustion chamber, the fuel injected from the fuel injection valve may not be sufficiently introduced into the auxiliary combustion chamber, and the mixture may not be properly burned in the auxiliary combustion chamber. In other words, there is a risk that the improvement in fuel efficiency and exhaust gas performance obtained by providing a main combustion chamber and an auxiliary combustion chamber may not be fully obtained.

[0006] The present invention has been made in consideration of the above circumstances, and has an object to reliably improve fuel economy and exhaust gas performance in an engine system equipped with a main combustion chamber and an auxiliary combustion chamber. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides a combustion engine comprising a cylinder block and a cylinder head which define a cylinder, a piston housed in the cylinder so as to be capable of reciprocating motion, a main combustion chamber defined by the cylinder block, the cylinder head, and the piston, an auxiliary chamber which is separated from the main combustion chamber by a partition wall and which communicates with the main combustion chamber through a communication hole formed in the partition wall, a fuel injection device which injects fuel into the main combustion chamber, a main ignition device which ignites an air-fuel mixture in the main combustion chamber, an auxiliary ignition device which ignites an air-fuel mixture in the auxiliary chamber, and a control device which is electrically connected to the fuel injection device, the main ignition device, and the auxiliary ignition device and outputs control electrical signals to each of the devices, wherein when the engine is operated in a specific range where the engine speed is equal to or lower than a predetermined reference speed and the engine load is higher than a predetermined reference load, the control device the fuel injection device is controlled so that a fuel injection timing, which is the timing at which fuel is injected by the fuel injection device, is included in the compression stroke, and the main ignition device and the auxiliary ignition device are each caused to ignite after the fuel injection timing, and when the lower of two conditions in the specific region under which the engine load is the same and the engine speed is different is defined as a low speed condition and the higher of the two conditions is defined as a high speed condition, the fuel injection device is controlled so that the fuel injection timing under the low speed condition is later than the fuel injection timing under the high speed condition, and the main ignition device and the auxiliary ignition device are controlled so that the auxiliary ignition timing, which is the ignition timing of the auxiliary ignition device, is retarded more than the main ignition timing, which is the ignition timing of the main ignition device, and an ignition phase difference, which is the amount of retardation of the auxiliary ignition timing relative to the main ignition timing, is larger under the low speed condition than under the high speed condition.

[0008] In a specific region where the engine speed is equal to or lower than a predetermined reference speed and the engine load is higher than the predetermined reference load, that is, in a low-speed high-load region, if fuel is injected into the main combustion chamber during the intake stroke, preignition, in which the mixture self-ignites before ignition by the ignition device, is likely to occur. In contrast, in the present invention, the fuel injection timing is controlled to be included in the compression stroke in the specific region, so that the occurrence of preignition can be suppressed. Moreover, the fuel injection timing under low-speed conditions, where the engine speed is low and preignition is particularly likely to occur, is made later than the fuel injection timing under high-speed conditions, where preignition is relatively unlikely to occur. Therefore, the occurrence of preignition under low-speed conditions can be more reliably suppressed. Moreover, under high-speed conditions, the mixture of fuel and air up to the vicinity of the compression top dead center can be promoted while suppressing the occurrence of preignition, thereby suppressing the remaining of unburned mixture.

[0009] Here, if fuel is injected during the compression stroke, the fuel does not sufficiently diffuse into the main combustion chamber by the time the compression stroke reaches the top dead center, making it difficult to introduce a sufficient amount of mixture (fuel) into the auxiliary chamber by the compression action of the piston alone. In contrast, in the present invention, the auxiliary ignition timing is set to a timing that is retarded from the main ignition timing. Therefore, the mixture is burned in the main combustion chamber by ignition by the main ignition device, and the mixture (fuel) can be pushed into the auxiliary chamber by utilizing the resulting increase in pressure in the main combustion chamber. Therefore, according to the present invention, in a specific region set for low speed and high load, the occurrence of preignition can be suppressed while proper combustion in the main combustion chamber and the auxiliary combustion chamber can be achieved, thereby improving fuel efficiency and exhaust performance.

[0010] Moreover, in the present invention, the ignition phase difference, which is the amount of retardation of the auxiliary ignition timing relative to the main ignition timing, is made larger under low speed conditions than under high speed conditions. In other words, under low speed conditions, where the fuel injection timing is closer to the compression top dead center and it is more difficult to introduce the mixture (fuel) into the auxiliary chamber only by the compression action of the piston, the period from when the mixture (fuel) starts to be introduced into the auxiliary chamber due to the pressure rise in the main combustion chamber until ignition by the auxiliary ignition device is made longer. Therefore, under low speed conditions, the amount of mixture (fuel) introduced into the auxiliary chamber can be secured, and appropriate combustion in the auxiliary chamber can be more reliably achieved. Also, under high speed conditions, combustion in the auxiliary chamber can be started relatively early after combustion in the main combustion chamber starts, and the combustion period can be shortened, thereby more reliably improving fuel efficiency.

[0011] In the above configuration, preferably, the control device sets the main ignition timing under the low speed condition to a timing that is more retarded than the main ignition timing under the high speed condition, and sets the auxiliary ignition timing under the low speed condition to a timing that is more retarded than the auxiliary ignition timing under the high speed condition (claim 2).

[0012] With this configuration, the period from the fuel injection timing to the main ignition timing, i.e., the fuel-air mixing period until the main ignition timing, can be secured under both low speed and high speed conditions, while the ignition phase difference under the low speed condition can be made larger than the ignition phase difference under the high speed condition, so that appropriate combustion in the main combustion chamber and the auxiliary combustion chamber can be more reliably achieved.

[0013] As a specific configuration for realizing the above configuration, the control device may be configured to make the amount of retardation of the auxiliary ignition timing under the low speed condition relative to the auxiliary ignition timing under the high speed condition greater than the amount of retardation of the main ignition timing under the low speed condition relative to the main ignition timing under the high speed condition (Claim 3).

[0014] Here, since the piston descends during the expansion stroke, if the auxiliary ignition timing is set to a time during the expansion stroke, it is particularly difficult to ensure a sufficient amount of mixture (fuel) in the auxiliary chamber at the auxiliary ignition timing by only the compression action of the piston. In contrast, in the present invention, as described above, the mixture (fuel) can be pushed into the auxiliary chamber by utilizing the pressure increase in the main combustion chamber accompanying combustion. Therefore, even in a configuration in which the control device sets the auxiliary ignition timing in the specific region to a time during the expansion stroke, the amount of mixture (fuel) in the auxiliary chamber can be secured (claim 4).

[0015] In the above configuration, preferably, the control device controls the main ignition device and the auxiliary ignition device so that, when operating in the specific region, the ignition phase difference becomes larger as the engine speed decreases, and the rate of change of the ignition phase difference relative to the engine speed is larger on the high rotation side than on the low rotation side (Claim 5).

[0016] According to this configuration, the ignition phase difference is increased as the engine speed decreases, so that appropriate combustion in the pre-chamber can be reliably achieved while improving fuel economy at each engine speed. However, if the ignition phase difference is excessively increased in a configuration in which the pre-ignition timing is set during the expansion stroke, the pre-ignition timing will be too late in the expansion stroke, reducing the effect of introducing the mixture (fuel) into the pre-chamber and reducing fuel economy. In contrast, in this configuration, the rate of change of the ignition phase difference relative to the engine speed is set to be larger on the high rotation side than on the low rotation side. Therefore, it is possible to prevent the ignition phase difference from becoming too large, that is, to prevent the pre-ignition timing from becoming too late in the expansion stroke, and it is possible to ensure the amount of mixture (fuel) introduced into the pre-chamber while improving fuel economy.

[0017] In the above-mentioned configuration, preferably, the control device sets the main ignition timing during the expansion stroke when the engine is operating in the specific region (claim 6).

[0018] According to this configuration, the period from the fuel injection timing to the main ignition timing, i.e., the period during which the fuel and air are mixed until the main ignition timing, can be secured, and appropriate combustion in the main combustion chamber can be achieved more reliably. Effect of the Invention

[0019] As described above, according to the engine system of the present invention, it is possible to reliably improve fuel economy and exhaust gas performance. [Brief description of the drawings]

[0020] [Figure 1] 1 is a schematic configuration diagram of an engine system according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic cross-sectional view of an engine body. [Diagram 3] 4 is a partial cross-sectional view of the tip portion of the sub-ignition unit as viewed from the side. FIG. [Figure 4] FIG. 4 is a plan view of the tip portion of the auxiliary ignition unit. [Diagram 5] FIG. 2 is a diagram showing a control block of the engine. [Figure 6] 2 is a map showing an operating range of an engine. [Figure 7] 10 is a flowchart showing a control procedure for the injector and the spark plug in a third region. [Figure 8] FIG. 11 is a diagram showing an example of a drive pulse, a main ignition timing, and an auxiliary ignition timing of an injector in a third region. [Figure 9] FIG. 11 is a diagram showing another example of the injector drive pulse, the main ignition timing, and the auxiliary ignition timing in the third region. [Figure 10] FIG. 11 is a diagram showing the relationship between the engine speed and each parameter in a third region. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] (Overall engine configuration) 1 is a schematic diagram showing a preferred embodiment of an engine system of the present invention. The engine system 1 includes an engine body 2, an intake passage 4 through which air (intake air) introduced into the engine body 2 flows, an exhaust passage 6 through which exhaust gas discharged from the engine body 2 flows, and an EGR device 50. 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 fuel containing gasoline is supplied to the engine body 2.

[0022] FIG. 2 is a schematic cross-sectional view of the engine body 2. In this embodiment, the engine body 2 is a multi-cylinder engine having a plurality of cylinders 22. For example, the engine body 2 has four cylinders 22 arranged in a row (arranged in a direction perpendicular to the paper surface of FIG. 1). The engine body 2 includes a cylinder block 52 in which the plurality of cylinders 22 are formed, a cylinder head 54 having a bottom surface 54a that closes the upper end openings of each cylinder 22 and attached to the upper surface of the cylinder block 52, and a plurality of pistons 24 accommodated in each cylinder 22 so as to be reciprocally slidable. In this embodiment, the side from the cylinder block 52 toward the cylinder head 54 is treated as the top, and the opposite side is treated as the bottom, but this is for convenience of explanation and is not intended to limit the installation posture of the engine.

[0023] A main combustion chamber 26 is defined above the piston 24 of each cylinder 22. The main combustion chamber 26 is defined by an inner circumferential surface 22a of the cylinder 22 formed in a cylinder block 52, a bottom surface (lower surface) 54a of a cylinder head 54, and a crown surface 24a of the piston 24. Fuel is supplied to the main combustion chamber 26 by injection from an injector 28, which will be described later. The piston 24 reciprocates up and down due to the expansion force caused by the combustion of the mixture of fuel and air.

[0024] A crankshaft 20, which is an output shaft of the engine body 2, is provided at the lower part of the cylinder block 52 (below the pistons 24). The crankshaft 20 is connected to the pistons 24 of the cylinders 22 via connecting rods 21, and rotates about its central axis in response to the reciprocating motion of the pistons 24.

[0025] In the cylinder head 54, 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 exhaust gas generated in the main combustion chamber 26 to the exhaust passage 6 are formed for each cylinder 22. In the cylinder head 54, an intake valve 10 for opening and closing the opening of the intake port 8 on the main combustion chamber 26 side and an exhaust valve 14 for opening and closing the opening of the exhaust port 12 on the main combustion chamber 26 side are provided for each cylinder 22. In this embodiment, two intake valves 10 and two exhaust valves 14 are provided for each cylinder 22.

[0026] 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 valve mechanisms 16, 18, respectively, disposed in the cylinder head 54. The valve 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 mechanism 18 for the exhaust valve 14 is 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.

[0027] The cylinder head 54 is provided with one set of injector 28, main spark plug 32, and sub-ignition unit 30 for each cylinder 22. The injector 28 corresponds to the "fuel injection device" in the claims, and the main spark plug 32 corresponds to the "main ignition device" in the claims.

[0028] The injector 28 is an injection valve that injects fuel into the main combustion chamber 26. An injection port for injecting fuel is formed at a tip 28x of the injector 28. The injector 28 is attached to the cylinder head 54 so that the tip 28x faces the main combustion chamber 26 from above. In this embodiment, the injector 28 is disposed so that the tip 28x is located at the center of the ceiling surface of the main combustion chamber 26 (more specifically, on the axis of the cylinder 22).

[0029] The main ignition plug 32 ignites the air-fuel mixture in the main combustion chamber 26 by spark discharge. An electrode portion 32x for discharging a spark is provided at the tip of the main ignition plug 32. This electrode portion 32x includes a center electrode 32a and a side electrode (earth) 32b. The main ignition plug 32 is attached to the cylinder head 54 so that the electrode portion 32x faces the main combustion chamber 26 from above. In this embodiment, the main ignition plug 32 is disposed so that the electrode portion 32x is located on the intake port 8 side of the tip portion 28x of the injector 28 on the ceiling surface of the main combustion chamber 26.

[0030] The auxiliary ignition unit 30 is a device for ejecting a flame into the main combustion chamber 26. The auxiliary ignition unit 30 will be described in detail later.

[0031] The intake passage 4 is connected to one side of the cylinder head 54 so as to communicate with the intake ports 8 of each cylinder 22. The intake passage 4 is provided with, in this order from the upstream side, an air cleaner 34 that removes foreign matter from the intake air, an openable and closable throttle valve 36 that adjusts the flow rate of the intake air, and a surge tank 38.

[0032] The downstream end of the intake passage 4 branches into multiple passages. Each branch passage is connected to one intake port 8. For each cylinder 22, the branch passage connected to one of the two intake ports 8 is provided with a swirl valve 56 (see FIG. 5) that opens and closes the branch passage.

[0033] The exhaust passage 6 is connected to one side of the cylinder head 54 (the side opposite to the intake passage 4) so ​​as to communicate with the exhaust ports 12 of each cylinder 22. The exhaust passage 6 is provided with a catalytic device 40 incorporating a catalyst 41 such as a three-way catalyst.

[0034] The EGR device 50 is a device for recirculating a part of the exhaust gas as EGR gas to the intake passage 4 and introducing (recirculating) the EGR gas into the main combustion chamber 26 that is connected to the intake passage 4 via the intake passage 4. The EGR device 50 has an EGR passage 42 that communicates 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 downstream end of the catalytic device 40 and the exhaust passage 6 downstream of the catalyst 41, and the downstream end of the EGR passage 42 is connected to the surge tank 38. The EGR valve 46 is a valve that opens and closes the EGR passage 42 to adjust the flow rate of the EGR gas. The EGR cooler 44 is a heat exchanger that cools the EGR gas. The EGR cooler 44 is disposed downstream of the EGR valve 46.

[0035] (Sub-ignition unit 30) Fig. 3 is a partial cross-sectional side view of the tip portion 30x of the sub-ignition unit 30. Fig. 4 is a plan view of the tip portion 30x of the sub-ignition unit 30 (viewed from the tip side).

[0036] The auxiliary ignition unit 30 has an auxiliary spark plug 62 that ignites the air-fuel mixture by spark discharge. An electrode portion 62x for discharging sparks is provided at the tip of the auxiliary spark plug 62. The electrode portion 62x includes a center electrode 62a and a side electrode (earth) 62b. The auxiliary ignition unit 30 has a cover member 64 that is provided at its tip portion 30x and covers the electrode portion 62x of the auxiliary ignition plug 62. A sub-chamber 60, which is a predetermined space, is defined inside the cover member 64. In other words, the auxiliary ignition plug 62 is disposed so that its electrode portion 62x faces the sub-chamber 60, and ignites the air-fuel mixture in the sub-chamber 60. The cover member 64 has a hollow hemispherical shape that bulges out toward the tip side of the auxiliary ignition unit 30. The auxiliary ignition plug 62 corresponds to the "auxiliary ignition device" in the claims, and the cover member 64 corresponds to the "partition wall" in the claims.

[0037] 2, the auxiliary ignition unit 30 is attached to the cylinder head 54 so that its tip portion 30x faces the main combustion chamber 26 from above. In this embodiment, the auxiliary ignition unit 30 is attached to a position on the ceiling surface of the main combustion chamber 26 closer to the exhaust port 12 than the injector 28. In this embodiment, in this attached state, almost the entire cover member 64 is located inside the main combustion chamber 26.

[0038] The cover member 64 is formed with a plurality of communication holes 66 that penetrate the front and back of the cover member 64 and communicate between the main combustion chamber 26 and the auxiliary chamber 60. The inner space of the cover member 64, i.e., the auxiliary chamber 60, communicates with the main combustion chamber 26 via these communication holes 66. In this manner, in this embodiment, by attaching the auxiliary ignition unit 30 configured as described above to the engine body 2, the auxiliary chamber 60 that is separated from the main combustion chamber 26 by the cover member 64 and communicates with the main combustion chamber 26 via the communication holes 66 is formed in the engine body 2.

[0039] In this embodiment, three communication holes 66 are formed in the cover member 64. As shown in Fig. 4, the three communication holes 66 are formed at 120 degree intervals around the axis of the cover member 64 passing through the apex A of the cover member 64. Also, as shown in Fig. 3, each communication hole 66 is formed at a position 45 degrees from the apex A in a side view. The radius and thickness of the cover member 64 are 5 mm and 1 mm, respectively, and the diameter of each communication hole 66 is 1.2 mm.

[0040] The auxiliary ignition unit 30 ejects a flame into the main combustion chamber 26. Specifically, when fuel is injected from the injector 28 into the main combustion chamber 26 and a mixture of air and fuel is formed in the main combustion chamber 26, a part of this mixture is introduced into the auxiliary chamber 60 through the communication hole 66. When a spark discharge is generated by the auxiliary spark plug 62 with a sufficient amount of mixture present in the auxiliary chamber 60, the mixture starts to burn in the auxiliary chamber 60, and a flame propagates from the vicinity of the electrode portion 62x of the auxiliary spark plug 62 to the surroundings. Then, this flame is ejected / released into the main combustion chamber 26 through the communication hole 66 and propagates to the mixture in the main combustion chamber 26.

[0041] Here, as described above, when ignition is performed by the main spark plug 32, the flame also propagates from the vicinity of the electrode portion 32x of the main spark plug 32 to the surroundings. As a result, if ignition is performed by both the main spark plug 32 and the sub-spark plug 62 and the mixture is appropriately combusted in the main combustion chamber 26 and the sub-chamber 60, the flame will propagate from multiple positions to the mixture in the main combustion chamber 26, increasing the combustion speed of the mixture in the main combustion chamber 26 and improving fuel efficiency, while suppressing the occurrence of knocking and the remaining of unburned mixture.

[0042] (Control system) Fig. 5 is a block diagram showing the control system of the engine. The ECU 100 shown in this figure is a device that controls the engine overall, and is composed of a microcomputer including a processor (CPU) that performs various arithmetic processing, memories such as ROM and RAM, and various input / output buses. The ECU 100 corresponds to the "control device" in the claims.

[0043] Information detected by various sensors is input to the ECU 100. For example, the ECU 100 receives detection values ​​from an airflow sensor SN1, an intake air temperature sensor SN2, an intake pressure sensor SN3, a water temperature sensor SN4, and a crank angle sensor SN5 provided in the engine system 1, and an accelerator opening sensor SN6 provided in the vehicle. The airflow sensor SN1 detects the flow rate of intake air passing through the intake passage 4 and introduced into the engine body 2. The intake air temperature sensor SN2 and the intake 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 engine cooling water that cools the engine body 2. The crank angle sensor SN5 detects the crank angle, which is the rotation angle of the crankshaft 20, and the engine speed. The accelerator opening sensor SN6 detects the accelerator opening, which is the opening of an accelerator pedal (not shown) provided in the vehicle.

[0044] 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 sub spark plug 62, the EGR device 50 (more specifically, the EGR valve 46), etc., and outputs control electrical signals to these devices based on the results of the calculations, etc.

[0045] Fig. 6 is a map showing the engine operating range with the horizontal axis representing engine speed and the vertical axis representing engine load. As shown in Fig. 6, the engine operating range is roughly divided into three ranges A1 to A3 (first range A1, second range A2, third range A3) according to the control contents of the injector 28 and the ignition plugs 32, 62.

[0046] The first region A1 is a low-speed, low-load region where the engine speed is equal to or lower than a predetermined first speed N1 and the engine load is equal to or lower than a predetermined first load Tq1. The third region A3 is a low-speed, high-load region where the engine speed is equal to or lower than the first speed N1 and the engine load is higher than a predetermined second load Tq2. The second region A2 is the other region, and includes a region where the engine speed is equal to or lower than the first speed N1 and where the engine load is higher than the first load Tq1 and equal to or lower than the second load Tq2, and a region where the engine speed is higher than the first speed N1. The second load Tq2 corresponds to the "reference load" in the claims, the first speed N1 corresponds to the "reference speed" in the claims, and the third region A3 corresponds to the "specific region" in the claims.

[0047] In the first region A1, the injector 28 and the spark plugs 32, 62 are controlled to realize HCCI combustion (Homogeneous Compression Charge Ignition). Specifically, in the first region A1, fuel is injected from the injector 28 during the intake stroke. Also, the driving of the spark plugs 32, 62 (ignition by these spark plugs 32, 62) is stopped.

[0048] As described above, the injector 28 faces the main combustion chamber 26, and the fuel injected from the injector 28 can be diffused throughout the main combustion chamber 26. Thus, in the first region A1, fuel is injected from the injector 28 during the intake stroke, so that the fuel and air are sufficiently mixed in the main combustion chamber 26 before the compression top dead center is reached. Then, in the first region A1, this sufficiently mixed mixture (premixed air-fuel) is heated to a high temperature and pressure by the compression of the piston 24, and self-ignites near the compression top dead center.

[0049] 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 leaner (higher) 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 leaner (higher) than the stoichiometric air-fuel ratio (14.7).

[0050] In the second region A2, the injector 28 and the spark plugs 32, 62 are controlled so as to realize flame propagation combustion (SI combustion, SI: Spark Ignition).

[0051] Specifically, in the second region A2, fuel is injected from the injector 28 during the intake stroke, as in the first region A1. Meanwhile, in the second region A2, the main spark plug 32 and the auxiliary spark plug 62 are driven, and ignition is performed by both of these spark plugs 32, 62. Also, the opening of the throttle valve 36 is adjusted so that the air-fuel ratio of the mixture in the main combustion chamber 26 approaches the stoichiometric air-fuel ratio. In the second region A2, a flame kernel is generated around the electrodes 32x, 62x of the spark plugs 32, 62 by ignition by the spark plugs 32, 62, and the mixture in the main combustion chamber 26 and the auxiliary combustion chamber 60 is burned by the flame propagating from the flame kernel to the surroundings.

[0052] (Control content in the third area A3) Next, the control content in the third zone A3, which is a feature of the present invention, will be described. Fig. 7 is a flowchart showing the overall flow of the control procedure for the injector 28, the main spark plug 32, and the sub spark plug 62 in the third zone A3, which is implemented by the ECU 100.

[0053] First, the ECU 100 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.

[0054] Next, the ECU 100 calculates a required torque, which is a torque required of the engine, that is, an engine load (step S2). The ECU 100 calculates the required torque (engine load) based on the engine speed and the accelerator opening degree read in step S1.

[0055] Next, the ECU 100 determines whether or not the engine operating point is in the third region A3 (step S3). Specifically, the ECU 100 determines whether or not the current engine operating point is in the third region A3 based on the engine speed read in step S1 and the required torque (engine load) calculated in step S2.

[0056] If the determination in step S3 is NO and the engine operating point is not a point within the third region A3, the ECU 100 ends the process (performs 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 a point within the third region A3, the ECU 100 proceeds to step S4.

[0057] In step S4, based on the engine speed and engine load, the ECU 100 sets the fuel injection timing, which is the timing when fuel injection by the injector 28 begins, the main ignition timing, which is the ignition timing of the main spark plug 32 (the timing at the crank angle at which the main spark plug 32 ignites, i.e., produces a spark discharge), and the sub-ignition timing, which is the ignition timing of the sub-ignition plug 62 (the timing at the crank angle at which the sub-ignition plug 62 ignites, i.e., produces a spark discharge).

[0058] Next, in step S5, the ECU 100 drives the injector 28 so that fuel injection is started at the fuel injection timing set in step S4. The ECU 100 also drives the main ignition plug 32 so that ignition by the main ignition plug 32 is performed at the main ignition timing set in step S4. The ECU 100 also drives the auxiliary ignition plug 62 so that ignition by the auxiliary ignition plug 62 is performed at the auxiliary ignition timing set in step S4.

[0059] The fuel injection timing, the main ignition timing, and the auxiliary ignition timing in the third region A3 set in step S4 above will now be described in detail.

[0060] 8 and 9 are diagrams showing the drive pulse of the injector 28, the main ignition timing tm, and the auxiliary ignition timing ts at the operation points P1 and P2 included in the third region A3, respectively. As shown in FIG. 6, the operation point P2 is a point at which the engine load Tq3 is the same as that of the operation point P1, and the engine speed is higher than that of the operation point P1. FIG. 10 is a diagram showing the relationship between the engine speed and each parameter in the third region A3. The top graph in FIG. 10 is a graph showing the relationship between the engine speed and the fuel injection timing tinj. The second graph from the top in FIG. 10 is a graph showing the relationship between the engine speed and the ignition phase difference dt described later. The third graph from the top in FIG. 10 is a graph showing the relationship between the engine speed and the main ignition timing tm and the auxiliary ignition timing ts. Note that these graphs show the relationship between the engine speed and each parameter at a constant engine load. In the following, for two operating points (e.g., operating points P1, P2) with the same engine load but different engine speeds, the operating point with the lower engine speed (P1) will be referred to as the low-speed point, and the point with the higher engine speed (P2) will be referred to as the high-speed point.

[0061] In the third region A3, the injector 28 and the spark plugs 32, 62 are controlled so as to achieve SI combustion, similar to the second region A2.

[0062] However, in the third region A3, as in the second region A2, if fuel is injected from the injector 28 during the intake stroke, preignition may occur. Specifically, when the engine load is high, the combustion energy generated in the main combustion chamber 26 increases, causing the temperature in the main combustion chamber 26 to rise. When the engine speed is low, the time per crank angle becomes long. For this reason, in the third region A3, which is a low-speed, high-load region where the engine speed is low and the engine load is high, as in the second region A2, if fuel is injected from the injector 28 during the intake stroke, the amount of heat received by the mixture and the time it takes to receive heat until the top dead center of compression are reached are large, making it more likely that preignition will occur, in which the mixture self-ignites before the desired timing, that is, before ignition by the spark plug, occurs.

[0063] As a result, in the third region A3, retarded SI combustion is performed to start fuel injection from the injector 28 during the compression stroke, and the heat receiving time of the mixture (fuel) until the compression top dead center is shortened, that is, the occurrence of preignition is suppressed. That is, in the third region A3, the fuel injection timing tinj is set to a time during the compression stroke (controlled to be included in the compression stroke), and fuel injection from the injector 28 into the main combustion chamber 26 is started during the compression stroke. Note that the end time of the fuel injection by the injector 28 is not limited to a time during the compression stroke. For example, as shown in FIG. 8, in this embodiment, at an operating point where the engine speed is low in the third region A3, the fuel injection from the injector 28 ends during the expansion stroke.

[0064] Here, even in the third region A3, the lower the engine speed, the higher the possibility of preignition occurring. Thus, 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 fuel injection timing tinj at the low-speed point (P1) is made later than the fuel injection timing tinj at the high-speed point (P2). That is, in the third region A3, among two conditions with the same engine load and different engine speeds, the fuel injection timing tinj at the low-speed condition with the lower engine speed is made later than the fuel injection timing tinj at the high-speed condition with the higher engine speed. In this embodiment, as described later, in the third region A3, the lower the engine speed, the later the fuel injection timing tinj is made (toward the retarded side).

[0065] In this embodiment, in the third region A3, the fuel injection timing tinj is set to be more retarded as the engine speed decreases, as shown in Fig. 10. Note that Fig. 10 shows an example in which the fuel injection timing tinj increases and decreases in proportion to the engine speed, but the relationship is not limited to a proportional relationship.

[0066] In the third region A3, both the main spark plug 32 and the auxiliary spark plug 62 are driven.

[0067] 8 and 9, in the third region A3, the main ignition timing tm is set to be more advanced than the sub ignition timing ts, and ignition is first performed by the main spark plug 32, and then by the sub spark plug 62. In this embodiment, the main ignition timing tm and the sub ignition timing ts in the third region A3 are both set to be timings during the expansion stroke. The ignition phase difference dt is the amount of retardation of the sub ignition timing ts relative to the main ignition timing tm, that is, the period in crank angles from the main ignition timing tm to the sub ignition timing ts.

[0068] In the third region A3, at two operating points (e.g., operating points P1, P2) having the same engine load but different engine speeds, the main ignition timing tm at the low speed point (P1) is made slower than the main ignition timing tm at the high speed point (P2), and the secondary ignition timing ts at the low speed point (P1) is made slower than the secondary ignition timing ts at the high speed point (P2).

[0069] In the third region A3, at two driving points (e.g., driving points P1 and P2) with the same engine load and different engine revolutions, the retard 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 made larger than the retard 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 amount of the sub ignition timing ts relative to the main ignition timing tm) is controlled as follows. That is, at two driving points (e.g., driving points P1 and P2) with the same engine load and different engine revolutions, the ignition phase difference dt at the low speed point (P1) is made larger than the ignition phase difference dt at the high speed point (P2).

[0070] As shown in FIG. 10, in this embodiment, in the third region A3, the main ignition timing tm and the auxiliary ignition timing ts are each set to a later timing as the engine speed decreases.

[0071] In addition, the main ignition timing tm and the auxiliary ignition timing ts are set so that the ignition phase difference dt increases as the engine speed decreases. In other words, the rate of change of the auxiliary ignition timing ts relative to the engine speed is set to be greater than the rate of change of the main ignition timing tm.

[0072] Also, the main ignition timing tm is set so that its rate of change with respect to the engine speed is constant for all engine speeds in the third region A3, while the sub ignition timing ts is set so that its rate of change with respect to the engine speed is greater when the engine speed is equal to or greater than a predetermined engine speed N2 than when the engine speed is less than the engine speed N2. Accordingly, in the third region A3, the rate of change of the ignition phase difference dt with respect to the engine speed is greater on the high rotation side where the engine speed is equal to or greater than the predetermined engine speed N2 than on the low rotation side where the engine speed is less than the engine speed N2.

[0073] In this embodiment, the timings (fuel injection timing tinj, main ignition timing, sub ignition timing ts) set as described above are stored in advance in the form of a map for the engine speed and engine load in the ECU 100. In step S4, the ECU 100 extracts values ​​corresponding to the current engine load and engine speed from the stored map.

[0074] (action, etc.) As described above, in the above embodiment, the main combustion chamber 26 and the auxiliary combustion chamber 60 are provided in the engine body 2, and the fuel consumption performance and exhaust gas performance can be improved by burning the mixture in these two combustion chambers 26, 60. Moreover, the injector 28, which is a device for injecting fuel, is provided only in the main combustion chamber 26 and not in the auxiliary combustion chamber 60, so that the structure of the engine system can be simplified and it is advantageous in terms of cost compared to the case where the injector 28 is provided in each of the main combustion chamber 26 and the auxiliary combustion chamber 60. Furthermore, since the injector 28 is disposed so as to inject fuel into the main combustion chamber 26, the fuel can be uniformly diffused throughout the main combustion chamber 26. Therefore, appropriate HCCI combustion can be realized in the first region A1 of low speed and low load.

[0075] In addition, in the third region A3, which is a low-speed, high-load region, the fuel injection timing tinj is set to a time during the compression stroke, and in two operating points (e.g., operating points P1 and P2) with the same engine load and different engine speeds, the fuel injection timing tinj at the low-speed point (P1) is set later than the fuel injection timing tinj at the high-speed point (P2). Therefore, as described above, in the third region A3, the heat receiving time of the mixture until the compression top dead center is neared is prevented from becoming excessively long, thereby suppressing the occurrence of preignition.

[0076] However, if the fuel injection timing tinj is set to a time during the compression stroke, the fuel does not diffuse throughout the main combustion chamber 26 until near the top dead center of the compression stroke, so it becomes difficult to introduce a sufficient amount of fuel into the auxiliary combustion chamber 60 only by the compression action of the piston 24, and it becomes difficult to realize proper combustion in the auxiliary combustion chamber 60. In particular, in the above embodiment, the auxiliary ignition timing ts is set to a time during the expansion stroke after the piston 24 starts to descend, so that there is a high possibility that the mixture (fuel) in the auxiliary combustion chamber at the auxiliary ignition timing will be insufficient only by the compression action of the piston 24. Also, if ignition is performed by the auxiliary spark plug 62 after waiting for the fuel to diffuse sufficiently and a sufficient mixture to be introduced into the auxiliary combustion chamber 60, and then ignition is performed by the main spark plug 32, the ignition timing of the main spark plug 32 will be very late in the expansion stroke, and there is a high possibility that the mixture in the main combustion chamber 26 will not be properly burned.

[0077] In contrast, in the above embodiment, in the third region A3, the auxiliary ignition timing ts is set to a timing on the retard side of the main ignition timing tm. Therefore, appropriate combustion can be achieved in the main combustion chamber 26 by ignition by the main ignition plug 32 near the top dead center of the compression stroke. In addition, the pressure increase in the main combustion chamber 26 caused by the combustion in the main combustion chamber 26 can push the mixture (fuel) from the main combustion chamber 26 into the auxiliary combustion chamber 60. Therefore, a sufficient amount of mixture (fuel) can be present in the auxiliary combustion chamber 60 when ignition is performed by the auxiliary ignition plug 62, and appropriate combustion can be achieved in the auxiliary combustion chamber 60 as well.

[0078] As described above, according to the embodiment, in the third region A3, the fuel injection timing tinj is set to a period during the compression stroke, thereby suppressing the occurrence of preignition and achieving appropriate combustion in the main combustion chamber 26 and the auxiliary combustion chamber, thereby improving fuel economy and exhaust performance.

[0079] Furthermore, in the above embodiment, in the third region A3, the ignition phase difference dt at the low speed point where the fuel injection timing tinj is relatively retarded is set larger than the ignition phase difference dt at the high speed point where the fuel injection timing tinj is relatively advanced. In other words, the period from when the mixture (fuel) starts being introduced into the auxiliary combustion chamber 60 due to the pressure rise in the main combustion chamber 26 to when the auxiliary spark plug 62 ignites the mixture (fuel), i.e., the introduction period of the mixture (fuel) into the auxiliary combustion chamber 60, is made longer at the low speed point where the fuel injection timing tinj is closer to the compression top dead center and it is more difficult to introduce the mixture (fuel) into the auxiliary combustion chamber 60 only by the compression action of the piston 24. Therefore, at the low speed point, a sufficient amount of the mixture (fuel) can be reliably introduced into the auxiliary combustion chamber 60, and the mixture can be reliably combusted in the auxiliary combustion chamber 60. In addition, at the high speed point, the amount of mixture (fuel) in the auxiliary combustion chamber 60 is secured and combustion in the auxiliary combustion chamber 60 begins relatively early after combustion in the main combustion chamber 26. This ensures proper combustion of the mixture in the auxiliary combustion chamber 60 while shortening the combustion period and improving fuel efficiency more reliably.

[0080] In particular, in the above embodiment, at operating points in the third region A3 where the engine speed is low, fuel injection from the injector 28 ends during the expansion stroke, and the compression action of the piston 24 does not reach some of the fuel, which tends to result in a shortage of the mixture (fuel) amount in the auxiliary chamber 60. In contrast, according to the above embodiment, it is possible to introduce a sufficient amount of mixture (fuel) into the auxiliary chamber 60 even at such operating points where the engine speed is low and fuel injection ends during the expansion stroke.

[0081] In the above embodiment, in the third region A3, the ignition phase difference dt is increased as the engine speed decreases, so that appropriate combustion in the auxiliary combustion chamber 60 can be reliably achieved while improving fuel economy at each engine speed.

[0082] Here, in the above embodiment, since the auxiliary ignition timing ts is set to a time during the expansion stroke in the third region A3, if the ignition phase difference dt is made excessively large, the auxiliary ignition timing ts will be an excessively late time in the expansion stroke. As the expansion stroke progresses, the pressure in the main combustion chamber 26 drops significantly, so the effect of pushing the mixture (fuel) from the main combustion chamber 26 to the auxiliary combustion chamber 60 becomes smaller. Also, if the combustion start timing in the auxiliary combustion chamber 60 becomes an excessively late time in the expansion stroke, there is a risk that fuel consumption performance will worsen. On the other hand, 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 made larger on the high rotation side where the engine speed is equal to or higher than a predetermined engine speed N2 than on the low rotation side where the engine speed is less than the engine speed N2. Therefore, it is possible to avoid the ignition phase difference dt becoming excessive on the low rotation side, that is, to prevent the auxiliary ignition timing ts from becoming an excessively late time in the expansion stroke, and it is possible to reliably improve fuel consumption performance.

[0083] In the above embodiment, in the third region A3, the main ignition timing tm at the low speed point where the fuel injection timing tinj is on the retard side is set to a timing that is more retarded than the main ignition timing tm at the high speed point where the fuel injection timing tinj is relatively advanced. Therefore, the period from the fuel injection timing tinj to the main ignition timing tm, that is, the mixing period of fuel and air until the main ignition timing tm, can be secured at both the low speed point and the high speed point, and appropriate combustion of the mixture in the main combustion chamber 26 can be more reliably achieved.

[0084] In the above embodiment, the main ignition timing tm is set to a timing during the expansion stroke in the third region A3. Therefore, the period from the fuel injection timing tinj to the main ignition timing tm, that is, the period during which the fuel and air are mixed until the main ignition timing tm, can be particularly long, and appropriate combustion in the main combustion chamber 26 can be more reliably achieved.

[0085] (Modification) The specific shape and dimensions of the cover member 64 of the auxiliary ignition unit 30 are not limited to those described above. Moreover, the number and dimensions of the communication holes 66 provided in the cover member 64 are not limited to those described above. Moreover, the mounting position of the auxiliary ignition unit 30 is not limited to those described above. For example, the auxiliary ignition unit 30 may be provided on the exhaust port 12 side with respect to the tip portion 28x of the injector 28.

[0086] In the above embodiment, the upper limit rotation speed of the first region A1 and the upper limit rotation speed of the third region A3 are the same, but they do not have to be the same. In other words, the upper limit rotation speed of the first region A1 does not have to be the first rotation speed N1, which is the upper limit rotation speed of the third region A3.

[0087] Furthermore, the control contents of the first area A1 and the second area A2 are not limited to those described above.

[0088] Further, the detailed structure of the engine body 2, such as the number of cylinders, is not limited to the above. [Explanation of symbols]

[0089] 1 Engine System 2 Engine body 24 Piston 28 Injector (fuel injection device) 26 Main combustion chamber 30 Auxiliary ignition unit 32 Main spark plug (main ignition device) 52 Cylinder block 54 Cylinder head 60 Auxiliary combustion chamber 62 Auxiliary spark plug (auxiliary ignition device) 64 Cover material (partition wall) 66 Communication hole 100 ECU (control unit)

Claims

1. A cylinder block and a cylinder head which form a cylinder; A piston accommodated in the cylinder so as to be capable of reciprocating motion; a main combustion chamber defined by the cylinder block, the cylinder head, and the piston; an auxiliary chamber separated from the main combustion chamber by a partition wall and communicating with the main combustion chamber through a communication hole formed in the partition wall; a fuel injection device that injects fuel into the main combustion chamber; a main ignition device that ignites the air-fuel mixture in the main combustion chamber; an auxiliary ignition device that ignites the air-fuel mixture in the auxiliary chamber; a control device electrically connected to the fuel injection device, the main ignition device, and the auxiliary ignition device to output control electrical signals to each of the devices; When the engine is operated in a specific region where the engine speed is equal to or lower than a predetermined reference speed and the engine load is higher than a predetermined reference load, the control device controlling the fuel injection device so that a fuel injection timing, which is a timing for injecting fuel by the fuel injection device, is included in a compression stroke, and causing the main ignition device and the auxiliary ignition device to perform ignition after the fuel injection timing; when the lower engine speed is defined as a low speed condition and the higher engine speed is defined as a high speed condition, the fuel injection device is controlled so that the fuel injection timing under the low speed condition is later than the fuel injection timing under the high speed condition, an ignition timing of the auxiliary ignition device is retarded more than a main ignition timing of the main ignition device, and an ignition phase difference, which is an amount of retardation of the auxiliary ignition timing with respect to the main ignition timing, is greater under the low speed condition than under the high speed condition.

2. 2. The engine system according to claim 1, the control device sets the main ignition timing under the low speed condition to a timing that is more retarded than the main ignition timing under the high speed condition, and sets the auxiliary ignition timing under the low speed condition to a timing that is more retarded than the auxiliary ignition timing under the high speed condition.

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

4. In the engine system according to any one of claims 1 to 3, The engine system according to claim 1, wherein the control device sets the auxiliary ignition timing in the specific region to a timing during an expansion stroke.

5. 5. The engine system according to claim 4, The control device controls the main ignition device and the auxiliary ignition device so that, when operating in the specific region, the ignition phase difference becomes larger as the engine speed decreases, and 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.

6. 6. The engine system according to claim 4 or 5, The engine system according to claim 1, wherein the control device sets the main ignition timing in the specific region during an expansion stroke.

Images