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 chamber, a main ignition device for igniting air-fuel mixture in the main combustion chamber, and an auxiliary ignition device for igniting air-fuel mixture. In a specific area for executing EGR, auxiliary ignition timing is set nearer a retard angle side than main ignition timing. Among two conditions in a specific area with a same engine speed and a different EGR rate, under a high EGR condition with a large EGR rate, an ignition phase difference which is a retard angle amount of the auxiliary ignition timing to the main ignition timing is made larger than under a low EGR condition with a small EGR rate.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 an engine that includes a cylinder block and a cylinder head that form a cylinder, a piston that is accommodated in the cylinder so as to be able to reciprocate, a main combustion chamber defined by the cylinder block, the cylinder head, and the piston, an auxiliary chamber that is separated from the main combustion chamber by a partition wall and communicates with the main combustion chamber through a communication hole formed in the partition wall, a fuel injection device that injects fuel into the main combustion chamber, a main ignition device that ignites the air-fuel mixture in the main combustion chamber, an auxiliary ignition device that ignites the air-fuel mixture in the auxiliary chamber, an EGR device that recirculates a portion of the exhaust gas discharged from the cylinder to an intake passage through which intake air introduced into the cylinder flows, and a control device that is electrically connected to the fuel injection device, the main ignition device, the auxiliary ignition device, and the EGR device and outputs an electric signal for control to each of the devices. and when the engine is operated in a specific region in which the EGR device recirculates a portion of the exhaust gas to the intake passage as EGR gas, the control device controls the main ignition device and the auxiliary ignition device so that the auxiliary ignition timing, which is the ignition timing of the auxiliary ignition device, is retarded relative to the main ignition timing, which is the ignition timing of the main ignition device, and when the engine speed is the same and two conditions in the specific region in which the EGR rate, which is the proportion of the EGR gas in the total gas present in the main combustion chamber and the auxiliary chamber, are different, the one with the smaller EGR rate is a low EGR condition and the one with the larger EGR rate is a high EGR condition, the control device controls the main ignition device and the auxiliary ignition device so that 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 high EGR condition than under the low EGR condition.

[0008] When the EGR gas is recirculated into the intake passage and thus into the cylinder, the ratio of the mixture (fuel and air mixture) to the gas in the main combustion chamber becomes smaller. Therefore, when the EGR gas is recirculated into the intake passage, the mixture is less likely to enter the auxiliary chamber, and proper combustion in the auxiliary chamber is less likely to be realized. In contrast, in the present invention, in a specific region where the EGR gas is recirculated into the intake passage, the auxiliary ignition timing is set to a timing that is retarded from the main ignition timing. If the auxiliary ignition timing is set to a timing that is retarded from the main ignition timing, the mixture is burned in the main combustion chamber by ignition by the main ignition device, and the mixture can be pushed into the auxiliary chamber by utilizing the resulting pressure increase in the main combustion chamber. Therefore, according to the present invention, proper combustion can be realized in the auxiliary chamber in addition to the main combustion chamber while introducing the EGR gas into the cylinder, and fuel efficiency and exhaust performance can be reliably improved.

[0009] Moreover, in the present invention, the ignition phase difference, which is the amount of retardation of the auxiliary ignition timing with respect to the main ignition timing, is made larger when the EGR rate is large (high EGR condition) than when it is small (low EGR condition) at the same engine speed. In other words, the period from when the introduction of the mixture (fuel) into the auxiliary chamber due to the pressure rise in the main combustion chamber begins to be longer when the EGR rate is large than when the EGR rate is small, until ignition by the auxiliary ignition device is performed, is made longer. Therefore, when the EGR rate is large and it is difficult for the mixture to enter the auxiliary chamber, the amount of the mixture introduced into the auxiliary chamber can be secured, and appropriate combustion can be reliably achieved in the main combustion chamber and the auxiliary chamber. Also, when the EGR rate is small and it is relatively easy for the mixture to enter the auxiliary chamber, combustion in the auxiliary chamber can be started relatively early after the start of combustion in the main combustion chamber, and the combustion period can be shortened to more reliably improve fuel efficiency.

[0010] In the above configuration, preferably, the control device controls the main ignition device and the auxiliary ignition device so that the ignition phase difference becomes larger as the EGR rate becomes higher during operation in the specific region (claim 2).

[0011] In this way, the ignition phase difference can be set to an appropriate value according to the EGR rate, thereby achieving appropriate combustion in the pre-chamber and further improving fuel economy.

[0012] Here, since the pressure in the main combustion chamber decreases over time during the expansion stroke, it becomes difficult for the mixture to flow from the main combustion chamber to the auxiliary chamber, especially when ignition is performed by the auxiliary ignition device during the expansion stroke. In contrast, in the present invention, as described above, the mixture can be pushed into the auxiliary chamber by utilizing the increase in pressure in the main combustion chamber caused by combustion in the main combustion chamber. Therefore, even in a configuration in which the control device sets the auxiliary ignition timing during operation in the specific region, the amount of mixture in the auxiliary chamber can be secured (claim 3).

[0013] In the above-mentioned configuration, preferably, when the engine is operated in the specific region, the control device sets the main ignition timing to a timing during the compression stroke (claim 4).

[0014] With this configuration, the pressure increase in the main combustion chamber due to the compression action of the piston and the pressure increase in the main combustion chamber due to combustion can be utilized to more reliably introduce the air-fuel mixture into the auxiliary combustion chamber, thereby more reliably achieving proper combustion of the air-fuel mixture in the auxiliary combustion chamber. Effect of the Invention

[0015] 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]

[0016] [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] 6 is a flowchart showing a control procedure for the injector and the spark plug in a second 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 second region. [Figure 9] 10 is a diagram showing another example of the injector drive pulse, the main ignition timing, and the auxiliary ignition timing in the second region. FIG. [Figure 10] FIG. 11 is a diagram showing the relationship between the engine speed and each parameter in a second region. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] (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.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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).

[0025] 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 combustion chamber 5 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] (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).

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] (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.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] The first region A1 is a low-speed, low-load region where the engine speed is equal to or lower than a predetermined first rotation speed N1 and the engine load is equal to or lower than a predetermined first load Tq1. The second region A2 is a low-speed, medium-load region where the engine speed is equal to or lower than a predetermined second rotation speed N2 and the engine load is higher than the first load Tq1 and equal to or lower than a predetermined second load Tq2. The third region A3 is the other region. The second region A2 corresponds to the "specific region" in the claims.

[0043] 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.

[0044] 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.

[0045] 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).

[0046] In the other regions (second region A2 and third region A3) except the first region A1, the main ignition plug 32 and the sub-ignition plug 62 are driven to realize flame propagation combustion. That is, in these regions A2 and A3, a flame kernel is generated around the electrode portions 32x, 62x of the ignition plugs 32, 62 by spark discharge from the electrode portions 32x, 62x, and the flame propagates from the flame kernel to the surroundings to realize SI combustion (SI: Spark Ignition) in which the mixture in the main combustion chamber 26 and the sub-chamber 60 is burned. In addition, in these regions A2 and A3, 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 close to the theoretical air-fuel ratio.

[0047] Here, in a region where the engine load is particularly low, the combustion is likely to become unstable if EGR, which recirculates the EGR gas to the intake passage 4 and the main combustion chamber 26, is performed. Also, in a region where the engine load or engine speed is particularly high, if EGR is performed, there is a risk that a sufficient amount of air will not be introduced into the main combustion chamber 26. For this reason, EGR is stopped in the third region A3. That is, in the third region A3, the EGR valve 46 is fully closed. On the other hand, in the second region A2 of the low-speed medium load region, EGR is performed because it is expected that the implementation of EGR will improve fuel efficiency by reducing pumping loss and cooling loss. That is, in the second region A2, the EGR valve 46 is opened and the EGR gas is recirculated to the intake passage 4 and the main combustion chamber 26.

[0048] (Control content in the second area A2) Next, the control content in the second region A2, which is a feature of the present invention, will be described. Fig. 7 is a flowchart showing the overall flow of the control procedure of the EGR valve 46, the injector 28, the main spark plug 32, and the sub spark plug 62 in the second region A2, which is implemented by the ECU 100.

[0049] 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.

[0050] 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.

[0051] Next, the ECU 100 determines whether or not the engine operating point is in the second region A2 (step S3). Specifically, the ECU 100 determines whether or not the current engine operating point is in the second region A2 based on the engine speed read in step S1 and the required torque (engine load) calculated in step S2.

[0052] If the determination in step S3 is NO and the engine operating point is not a point within the second region A2, the ECU 100 ends the process (performs control of the first region A1 or the third region A3). On the other hand, if the determination in step S3 is YES and the engine operating point is a point within the second region A2, the ECU 100 proceeds to step S4.

[0053] In step S4, the ECU 100 sets a target value of the EGR rate based on the engine speed and the engine load. The EGR rate is the ratio of the EGR gas to the total gas present in the main combustion chamber 26 and the auxiliary combustion chamber 60. In detail, the EGR rate is the ratio of the total weight of the EGR gas present in the main combustion chamber 26 and the auxiliary combustion chamber 60 to the total weight of the gas present in the main combustion chamber 26 and the auxiliary combustion chamber 60.

[0054] Next, the ECU 100 calculates the opening degree of the EGR valve 46 at which the target EGR rate set in step S4 is realized (step S5). For example, the ECU 100 calculates the opening degree of the EGR valve 46 at which the target EGR rate is realized based on the target EGR rate set in step S4, the engine speed, the amount of intake air detected by the airflow sensor SN1, and the like.

[0055] In addition, 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 ignition plug 32 (the timing at the crank angle at which the main ignition 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) (step S6).

[0056] Next, in step S7, the ECU 100 sets the opening of the EGR valve 46 to the opening calculated in step S5. In detail, the ECU 100 issues a command to a drive device that drives the EGR valve 46 to open and close, thereby setting the opening of the EGR valve 46 to the opening set in step S4. The ECU 100 also drives the injector 28 so that fuel injection is started at the fuel injection timing set in step S6. 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.

[0057] The fuel injection timing, the main ignition timing, and the auxiliary ignition timing set in step S6, and the target EGR rate set in step S4 will be described in detail below.

[0058] 8 and 9 are diagrams showing the drive pulse, main ignition timing tm, and sub ignition timing ts of the injector 28 at driving points P1 and P2 included in the second region A2, respectively. As shown in Fig. 6, driving point P2 is a point where the engine speed N10 is the same as driving point P1 and the engine load is higher than that of driving point P1.

[0059] As shown in FIGS. 8 and 9, in the second region A2, the fuel injection timing tinj is set to a timing during the intake stroke, and fuel injection from the injector 28 into the main combustion chamber 26 begins during the intake stroke.

[0060] In the second region A2, since EGR is performed, the target EGR rate is set to a value greater than 0. Here, as the engine load increases, the amount of air to be introduced into the main combustion chamber 26 increases. Therefore, if a large amount of EGR gas is recirculated to the intake passage 4 and the main combustion chamber 26 when the engine load is high, there is a risk that a sufficient amount of air cannot be introduced into the main combustion chamber 26. For this reason, in the second region A2, for two operating points (e.g., operating points P1 and P2) having the same engine speed but different engine loads, the target EGR rate for the operating point (P1) with a low engine load is set to a higher value than the target EGR rate for the operating point (P2) with a high engine load.

[0061] As described above, the target EGR rate is realized by adjusting the opening degree of the EGR valve 46. As a result, in the second region A2, at two operating points (e.g., operating points P1 and P2) having the same engine speed but different engine loads, the EGR rate at the operating point (P1) where the engine load is low is greater than the EGR rate at the operating point (P2) where the engine load is high.

[0062] 8 and 9, in the second region A2, the main ignition timing tm is set to a timing more advanced than the auxiliary ignition timing ts, and ignition is performed first by the main spark plug 32, and then by the auxiliary spark plug 62. In this embodiment, the main ignition timing tm is set to a timing during the compression stroke, and the auxiliary ignition timing ts is set to a timing during the expansion stroke.

[0063] The above ignition order is realized throughout the second region A2, but the amount of retardation of the sub ignition timing ts relative to the main ignition timing tm, that is, the ignition phase difference dt, which is the period in crank angles from the main ignition timing tm to the sub ignition timing ts, is changed depending on the operating point. As shown in Fig. 8 and Fig. 9, in the second region A2, for two operating points (e.g., operating points P1 and P2) with the same engine speed and different engine loads, the ignition phase difference dt for the operating point (P1) with a low engine load is made larger than the ignition phase difference dt for the operating point (P2) with a high engine load. As described above, the EGR rate is higher when the engine load is low. Thus, for two operating points (e.g., operating points P1 and P2) with the same engine speed and different engine loads, the ignition phase difference dt for the operating point (P1) with a high EGR rate is made larger than the operating point (P2) with a low EGR rate.

[0064] In this embodiment, for two operating points (e.g., operating points P1 and P2) with the same engine speed but different engine loads, the main ignition timing tm is set so that the main ignition timing tm at the operating point (P1) where the engine load is low and the EGR rate is high is more advanced than the main ignition timing tm at the operating point (P2) where the engine load is high and the EGR rate is low. Also, the auxiliary ignition timing ts is set so that the auxiliary ignition timing ts at the operating point (P1) where the engine load is low and the EGR rate is high is more retarded than the main ignition timing tm at the operating point (P2) where the engine load is high and the EGR rate is low. By setting these timings, the ignition phase difference dt at the operating point (P1) where the engine load is low and the EGR rate is high is made larger than the ignition phase difference dt at the operating point (P2) where the engine load is high and the EGR rate is low. In addition, among two operating points (for example, operating points P1 and P2) having the same engine speed but different engine loads, the operating point (P1) with a low engine load and a high EGR rate corresponds to the "high EGR condition" in the claims, and the operating point (P2) with a high engine load and a low EGR rate corresponds to the "low EGR condition" in the claims.

[0065] Fig. 10 is a diagram showing the relationship between the engine load and each parameter in the second region A2. The top graph in Fig. 10 is a graph showing the relationship between the engine load and the target EGR rate and therefore the EGR rate (actual EGR rate). The second graph from the top in Fig. 10 is a graph showing the relationship between the engine load and the ignition phase difference dt. The third graph from the top in Fig. 10 is a graph showing the relationship between the engine load and the main ignition timing tm and the sub ignition timing ts. These graphs show the relationship between the engine load and each parameter at a constant engine speed.

[0066] As shown in Fig. 10, in the second region A2, the target EGR rate is set to a higher value as the engine load decreases, and the EGR rate (actual EGR rate) is controlled to a higher value as the engine load decreases. In this embodiment, the target EGR rate and the EGR rate are increased almost in proportion to the decrease in the engine load.

[0067] In the second region A2, the lower the engine load, that is, the higher the EGR rate, the more the main ignition timing tm is set to the advanced side and the sub ignition timing ts is set to the retarded side. The lower the engine load, that is, the higher the EGR rate, the larger the ignition phase difference dt is controlled to. In this embodiment, the main ignition timing tm is advanced and the sub ignition timing ts is retarded in approximately proportion to the decrease in the engine load, that is, the increase in the EGR rate. This increases the ignition phase difference dt in approximately proportion to the decrease in the engine load, that is, the increase in the EGR rate. In this embodiment, the ignition timings tm and ts are set so that the advance amount of the main ignition timing tm relative to the change in the engine load, that is, the change in the EGR rate, is larger than the retard amount of the sub ignition timing ts.

[0068] In this embodiment, the target EGR rate and each timing (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 steps S4 and S6, the ECU 100 extracts values ​​corresponding to the current engine load and engine speed from the stored map.

[0069] (effect, etc.) As described above, in the above embodiment, in the second region A2 where EGR is performed, the main ignition timing tm is set to a timing more advanced than the sub-ignition timing ts, and the air-fuel mixture in the main combustion chamber 26 is ignited by the main ignition plug 32, and then the air-fuel mixture in the sub-combustion chamber 60 is ignited by the sub-ignition plug 62. Therefore, the air-fuel mixture can be appropriately combusted in both the main combustion chamber 26 and the sub-combustion chamber 60.

[0070] Specifically, in the second region A2, EGR is performed, and EGR gas is introduced into the main combustion chamber 26 in addition to air. Therefore, in the second region A2, it becomes difficult to push a sufficient amount of mixture from the main combustion chamber 26 into the auxiliary combustion chamber 60 only by the compression action of the piston 24. In particular, in the above embodiment, the auxiliary ignition timing ts is set in the second region A2 during the expansion stroke, that is, during the period when the pressure in the main combustion chamber 26 is decreasing, so there is a risk that a sufficient amount of mixture cannot be introduced from the main combustion chamber 26 to the auxiliary combustion chamber 60 only by the compression action of the piston 24. If a sufficient amount of mixture is not introduced into the auxiliary combustion chamber 60, even if the auxiliary ignition plug 62 ignites (sparks), misfires occur and the mixture is not properly burned in the auxiliary combustion chamber 60.

[0071] On the other hand, if the ignition order is as described above and the main spark plug 32 ignites before the sub-spark plug 62 ignites, the pressure rise caused by the combustion of the mixture in the main combustion chamber 26 can promote the flow of the mixture into the sub-combustion chamber 60, and a sufficient amount of the mixture can be forced into the sub-combustion chamber 60. In particular, in the above embodiment, the main ignition timing tm is set to a timing during the compression stroke. Therefore, by utilizing the pressure rise in the main combustion chamber 26 caused by the compression action of the piston 24 and the pressure rise in the main combustion chamber 26 caused by combustion, a sufficient amount of the mixture can be reliably introduced into the sub-combustion chamber 60.

[0072] Therefore, according to the above embodiment, the air-fuel mixture can be appropriately combusted in the auxiliary combustion chamber 60 in addition to the main combustion chamber 26, and fuel economy and exhaust gas performance can be reliably improved.

[0073] Moreover, for two operating points (e.g., operating points P1 and P2) that are included in the second region A2 and have the same engine speed but different engine loads, the ignition phase difference dt at the operating point (P1) where the engine load is low and the EGR rate is high is made larger than the ignition phase difference dt at the operating point (P2) where the engine load is high and the EGR rate is low. In other words, the period from when the main ignition plug 32 ignites and the pressure in the main combustion chamber 26 rises, and the introduction of the mixture (fuel) into the auxiliary combustion chamber 60 begins, until the auxiliary ignition plug 62 ignites, is made longer when the EGR rate is high than when it is low.

[0074] Therefore, even if the air-fuel mixture is particularly difficult to enter the auxiliary combustion chamber 60 due to a high EGR rate, a sufficient amount of the air-fuel mixture can be reliably introduced into the auxiliary combustion chamber 60 before the ignition of the auxiliary spark plug 62, and appropriate combustion of the air-fuel mixture in the auxiliary combustion chamber 60 can be more reliably achieved. Also, if the air-fuel mixture is relatively easy to enter the auxiliary combustion chamber 60 due to a low EGR rate, combustion in the auxiliary combustion chamber 60 can start relatively early after combustion starts in the main combustion chamber 26, shortening the combustion period and further improving fuel efficiency.

[0075] In particular, in the above embodiment, in the second region A2, the lower the engine load and the higher the EGR rate, the larger the ignition phase difference dt is set, so that the ignition phase difference dt can be set to an appropriate value according to the EGR rate, and appropriate combustion in the auxiliary combustion chamber 60 can be reliably achieved, and the fuel economy can be further improved by shortening the combustion period.

[0076] (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.

[0077] In the above embodiment, the case has been described in which the ignition phase difference dt is increased as the EGR rate increases in the second region A2, but the relationship between the EGR rate and the ignition phase difference dt is not limited to that in the above embodiment, and may be such that, among two operating points with the same engine speed and different EGR rates included in the second region A2, the ignition phase difference dt at the operating point with the higher EGR rate is greater than the ignition phase difference dt at the operating point with the lower EGR rate. For example, the second region A2 may be divided into a high EGR rate side and a low EGR rate side, and the ignition phase difference dt at the high EGR rate side may be greater than the ignition phase difference dt at the low EGR rate side, while the ignition phase difference dt at both the high EGR rate side and the low EGR rate side may be constant regardless of the EGR rate.

[0078] Furthermore, the control contents of the first area A1 and the second area A2 are not limited to those described above.

[0079] Further, the detailed structure of the engine body 2, such as the number of cylinders, is not limited to the above. [Explanation of symbols]

[0080] 1 Engine System 2 Engine body 4 Intake passage 24 Piston 28 Injector (fuel injection device) 26 Main combustion chamber 30 Auxiliary ignition unit 32 Main spark plug (main ignition device) 46 EGR valve 50 EGR 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; an EGR device that recirculates a portion of exhaust gas discharged from the cylinder to an intake passage through which intake air introduced into the cylinder flows; a control device electrically connected to the fuel injection device, the main ignition device, the auxiliary ignition device, and the EGR device to output control electrical signals to each of the devices; When the engine is operated in a specific region in which the EGR device recirculates a portion of the exhaust gas to the intake passage as EGR gas, the control device Controlling the main ignition device and the auxiliary ignition device so that an auxiliary ignition timing, which is an ignition timing of the auxiliary ignition device, is retarded relative to a main ignition timing, which is an ignition timing of the main ignition device; an engine system comprising: an engine control unit for controlling the main ignition device and the auxiliary ignition device so that an ignition phase difference, which is an amount of retardation of the auxiliary ignition timing relative to the main ignition timing, is larger under the high EGR condition than under the low EGR condition when the engine speed is the same and the EGR rate, which is the proportion of EGR gas in the total gas present in the main combustion chamber and the auxiliary combustion chamber, is different from the two conditions in the specific region in which the smaller EGR rate is defined as a low EGR condition and the larger EGR rate is defined as a high EGR condition.

2. 2. The engine system according to claim 1, The control device controls the main ignition device and the auxiliary ignition device so that the ignition phase difference becomes larger as the EGR rate becomes higher during operation in the specific region.

3. 3. The engine system according to claim 1, The engine system according to claim 1, wherein the control device sets the auxiliary ignition timing during an expansion stroke when the engine is operating in the specific region.

4. In the engine system according to any one of claims 1 to 3, The control device sets the main ignition timing during a compression stroke when the engine is operating in the specific region.

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