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: An engine system 1 comprises an injector 28 for injecting fuel to a main consumption chamber 26, a main ignition plug 32 for mainly igniting air-fuel mixture of the main combustion chamber 26, and an ECU 100 electrically connected to an auxiliary ignition plug 62 for auxiliary igniting the air-fuel mixture in an auxiliary chamber 60, and outputting control electric signals to each device. The ECU 100 performs control for executing the auxiliary ignition after the main ignition is executed in a low load area where, an engine load is equal to or less than a prescribed reference load, and retarding a timing of the auxiliary ignition compared with a low rotation area not higher than a predetermined reference speed (N1) in a high rotation area with an engine speed higher than the reference speed.SELECTED DRAWING: Figure 7

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] There is known an engine equipped with a main combustion chamber using a cylinder and an auxiliary combustion chamber communicating with the main combustion chamber. For example, Patent Document 1 discloses an engine in which a fuel injector and an ignition plug are disposed in both the main combustion chamber and the auxiliary combustion chamber. In this engine, an air-fuel mixture is combusted in the main combustion chamber, and then combusted in the auxiliary combustion chamber. The flame in the auxiliary combustion chamber is then ejected into the main combustion chamber, thereby combusting the unburned air-fuel mixture present in the main combustion chamber. This prevents the unburned air-fuel mixture from remaining in the main combustion chamber, thereby improving fuel economy and exhaust gas performance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-255370 Summary of the Invention [Problem to be solved by the invention]

[0004] Unlike the engine of Patent Document 1, if a fuel injection device is placed only in the main combustion chamber for the purpose of structural simplification, it may be difficult to introduce the air-fuel mixture into the pre-chamber. For example, when the engine is operating at a low load, the amount of air taken into the main combustion chamber is relatively small, making it difficult to introduce the air-fuel mixture into the pre-chamber. Therefore, even if ignition is performed using the spark plug in the pre-chamber, misfire may occur due to insufficient air-fuel mixture. As a result, the improvements in fuel economy and exhaust gas emissions achieved by providing a pre-chamber in addition to the main combustion chamber may not be fully realized.

[0005] An object of the present invention is 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]

[0006] an auxiliary ignition device that performs main ignition to ignite an air-fuel mixture in the main combustion chamber; and a controller that 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. The controller executes the auxiliary ignition after the main ignition when the engine load is in a low load range below a predetermined reference load. The higher the engine rotation speed, the larger the ignition phase difference between the auxiliary ignition and the main ignition is set, and In a high rotation region where the engine rotation speed is higher than a predetermined reference rotation speed, the timing of the auxiliary ignition is retarded compared to a low rotation region where the engine rotation speed is equal to or lower than the reference rotation speed.

[0007] When the engine is operating at low load, the amount of air taken into the main combustion chamber is relatively small, making it difficult to introduce the air-fuel mixture into the pre-combustion chamber. Even if pre-ignition is performed by the pre-ignition device when there is not enough air-fuel mixture in the pre-combustion chamber, misfire may occur. If a misfire occurs, a flame cannot be ejected from the pre-combustion chamber and cannot contribute to the combustion of the unburned air-fuel mixture remaining in the main combustion chamber. According to the engine system described above, pre-ignition is performed after main ignition is performed. This promotes the flow of the air-fuel mixture into the pre-combustion chamber. That is, the combustion pressure of the flame propagation combustion generated by the main ignition is superimposed on the pushing force of the piston, increasing the force pushing the air-fuel mixture into the pre-combustion chamber. This promotes the introduction of the air-fuel mixture into the pre-combustion chamber, preventing the above-mentioned misfire. The execution of pre-ignition allows a flame to be ejected from the pre-combustion chamber, thereby successfully combusting the unburned air-fuel mixture remaining in the main combustion chamber. Furthermore, with the above engine system, the ignition phase difference increases as the engine speed increases, so that the time required to push the air-fuel mixture into the auxiliary chamber can be ensured sufficiently in accordance with the engine speed.

[0008] Furthermore, in the low-load, high-speed range, the timing of the auxiliary spark is retarded compared to the low-speed range. The higher the engine speed, the shorter the time available for forcing the mixture into the auxiliary chamber. Therefore, by retarding the timing of the auxiliary spark in the high-speed range, sufficient time can be ensured for the combustion pressure of the flame propagation combustion of the main ignition to force the mixture into the auxiliary chamber. This further reduces misfires during auxiliary spark.

[0009] In the above engine system, it is preferable that the controller advances the timing of the main ignition as the engine speed increases.

[0010] According to this engine system, the timing of the main ignition is advanced as the engine speed increases, so that sufficient time can be secured to push the air-fuel mixture into the pre-chamber according to the engine speed. [Effects of the Invention]

[0013] According to the present invention, in an engine system having a main combustion chamber and an auxiliary combustion chamber, misfires in the auxiliary combustion chamber can be suppressed, and fuel economy and exhaust gas performance can be reliably improved. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a schematic configuration diagram of an engine system according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view of the engine body. [Figure 3] FIG. 3 is a partial cross-sectional side view of the tip of the sub-chamber plug. [Figure 4] FIG. 4 is a plan view of the tip of the sub-chamber plug. [Figure 5] FIG. 5 is a block diagram showing the control configuration of the engine system. [Figure 6] Figure 6 is a map showing the engine operating range. [Figure 7]FIG. 7 is a flowchart showing an example of fuel injection and ignition control that is executed when the operating region is in the specific region. [Figure 8] FIG. 8 is a time chart showing the fuel injection timing, the main ignition timing, and the auxiliary ignition timing in the low rotation speed region within the specific region. [Figure 9] FIG. 9 is a time chart showing the fuel injection timing, the main ignition timing, and the auxiliary ignition timing in the high rotation speed region within the specific region. [Figure 10] FIG. 10 is a chart showing the relationship between the engine speed and the main ignition, the auxiliary ignition, and the ignition phase difference in the specific region. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, an engine system according to an embodiment of the present invention will be described in detail with reference to the drawings. In this embodiment, the engine system is an engine system mounted on a vehicle such as an automobile as a power source for driving the vehicle.

[0016] [Overall engine configuration] 1 is a schematic diagram of an engine system 1 according to an embodiment 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 body 2 is a four-stroke gasoline engine that uses gasoline as its main fuel, and fuel containing gasoline is supplied to the engine body 2.

[0017] FIG. 2 is a schematic cross-sectional view of the engine body 2. The engine body 2 is a multi-cylinder engine having a plurality of cylinders 22. For example, the engine body 2 has four cylinders 22 aligned in a row (aligned in a direction perpendicular to the plane of FIG. 1). The engine body 2 includes a cylinder block 52, a cylinder head 54, and a plurality of pistons 24. The cylinders 22 are defined by the cylinder block 52 and the cylinder head 54. A plurality of cylindrical spaces defining the plurality of cylinders 22 are provided inside the cylinder block 52. The cylinder head 54 has a bottom surface 54a that closes the upper end openings of the cylindrical spaces, and is attached to the upper surface of the cylinder block 52. The pistons 24 are accommodated in each cylinder 22 so that they can slide back and forth. In this embodiment, the side from the cylinder block 52 toward the cylinder head 54 is referred to as the top, and the opposite is referred to as the bottom. These terms are used for convenience of explanation and are not intended to limit the installation orientation of the engine body 2.

[0018] A space that serves as a main combustion chamber 26 is formed 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 the cylinder block 52, a bottom surface 54a of the 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 supplied mixture of fuel and air is combusted in the main combustion chamber 26, and the expansion force caused by the combustion causes the piston 24 to reciprocate up and down.

[0019] A crankshaft 20, which is the output shaft of the engine body 2, is provided at the bottom of the cylinder block 52 (below the pistons 24). The crankshaft 20 is connected to the pistons 24 of each cylinder 22 via connecting rods 21, and rotates around its central axis in response to the reciprocating motion of the pistons 24.

[0020] An intake port 8 and an intake valve 10, and an exhaust port 12 and an exhaust valve 14 are formed in the cylinder head 54 for each cylinder 22. The intake port 8 is a port for introducing air supplied from the intake passage 4 into the main combustion chamber 26. The exhaust port 12 is a port for directing exhaust gas generated in the main combustion chamber 26 to the exhaust passage 6. The intake valve 10 opens and closes the opening of the intake port 8 on the side of the main combustion chamber 26. The exhaust valve 14 opens and closes the opening of the exhaust port 12 on the side of the main combustion chamber 26. In this embodiment, two intake valves 10 and two exhaust valves 14 are provided for each cylinder 22.

[0021] The intake valve 10 and the exhaust valve 14 are driven to open and close by valve trains 16, 18, respectively, which are disposed in a cylinder head 54, in conjunction with the rotation of a crankshaft 20. The valve train 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 train 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.

[0022] The cylinder head 54 is provided with one set of injector 28 (fuel injection device), main spark plug 32 (main ignition device), and auxiliary ignition unit 30 for each cylinder 22. The injector 28 is an injection valve that injects fuel into the main combustion chamber 26. A nozzle hole 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. 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.

[0023] The main spark plug 32 performs main ignition by spark discharge, igniting the air-fuel mixture in the main combustion chamber 26. An electrode portion 32x for discharging the spark is provided at the tip of the main spark plug 32. The electrode portion 32x includes a center electrode 32a and a side electrode 32b for grounding. The main spark plug 32 is attached to the cylinder head 54 so that the electrode portion 32x faces the combustion chamber 5 from above. The main spark plug 32 is disposed so that the electrode portion 32x is located on the ceiling surface of the main combustion chamber 26 closer to the intake port 8 than the tip portion 28x of the injector 28.

[0024] The secondary ignition unit 30 is a device for injecting a flame into the main combustion chamber 26. The secondary ignition unit 30 will be described in detail below.

[0025] 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 order from the upstream side, an air cleaner 34 that removes foreign matter from the intake air, an openable / closable throttle valve 36 that adjusts the flow rate of intake air, and a surge tank 38. The downstream end of the intake passage 4 branches into multiple passages, and each of these branch passages is connected to one intake port 8. In 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.

[0026] 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.

[0027] The EGR device 50 is a device for recirculating a part of the exhaust gas to the intake passage 4 as EGR gas. 5The exhaust gas turbine engine 0 has an EGR passage 42 that connects the exhaust passage 6 and 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 converter 40, which is connected to the exhaust passage 6 downstream of the catalyst 41. 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 EGR gas. The EGR cooler 44 is a heat exchanger that cools the EGR gas. The EGR cooler 44 is connected to the downstream end of the catalytic converter 40, which is connected to the exhaust passage 6 downstream of the catalyst 41. above It is located on the stream side.

[0028] [Details of the auxiliary ignition unit] Fig. 3 is a partial cross-sectional view of the tip portion 30x of the auxiliary ignition unit 30 as seen from the side, and Fig. 4 is a plan view of the tip portion 30x as seen from below. The auxiliary ignition unit 30 includes an auxiliary spark plug 62 (auxiliary ignition device), a cover member 64 (partition wall) attached to the tip of the auxiliary spark plug 62, and an auxiliary chamber 60 which is an internal space covered by the cover member 64.

[0029] The auxiliary spark plug 62 performs auxiliary ignition by igniting the air-fuel mixture in the auxiliary combustion chamber 60 through spark discharge. The tip of the auxiliary spark plug 62 is provided with an electrode portion 62x that discharges sparks. The electrode portion 62x includes a center electrode 62a and a side electrode 62b for grounding. The cover member 64 constitutes the tip portion 30x of the auxiliary ignition unit 30 and covers the periphery of the electrode portion 62x of the auxiliary spark plug 62. The cover member 64 has a hemispherical shape that bulges downward. The auxiliary combustion chamber 60 is the space inside the cover member 64. More specifically, the auxiliary combustion chamber 60 is the space surrounding the electrode portion 62x of the auxiliary spark plug 62 and is a space partitioned by the cover member 64. Because of this space, the size of the auxiliary combustion chamber 60 is smaller than the size of the main combustion chamber 26. An electrode portion 62x of the auxiliary spark plug 62 is disposed so as to face the auxiliary chamber 60, thereby enabling the auxiliary ignition to be performed.

[0030] 2, the auxiliary ignition unit 30 is attached to the cylinder head 54 so that its tip end 30x faces the main combustion chamber 26 from above. The auxiliary ignition unit 30 is attached to the ceiling surface of the main combustion chamber 26 (the bottom surface 54a of the cylinder head 54) at a position closer to the exhaust port 12 than the injector 28. In this attached state, almost the entire cover member 64 is located inside the main combustion chamber 26. As a result, the cover member 64 serves as a partition wall separating the auxiliary combustion chamber 60 from the main combustion chamber 26.

[0031] 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 with the main combustion chamber 26. The auxiliary chamber 60, which is the space inside the cover member 64, communicates with the main combustion chamber 26 via these communication holes 66. In this embodiment, an example is shown in which three communication holes 66 are formed in the cover member 64. As shown in FIG. 4, the three communication holes 66 are arranged at 120-degree intervals around the axis of the cover member 64 that passes through the vertex A of the cover member 64. Also, as shown in FIG. 3, each communication hole 66 is arranged at a position diagonally upward by approximately 45 degrees from the vertex A in a side view. In this embodiment, the cover member 64 has a radius of 5 mm, a thickness of 1 mm, and a diameter of each communication hole 66 of 1.2 mm.

[0032] The auxiliary ignition unit 30 having the above configuration functions as a device for injecting a flame into the main combustion chamber 26. 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 portion of this mixture is introduced into the auxiliary combustion chamber 60 through the communication hole 66. When a sufficient amount of mixture is present in the auxiliary combustion chamber 60 and a spark discharge (auxiliary ignition) is caused by the auxiliary spark plug 62, the mixture begins to burn in the auxiliary combustion chamber 60, and a flame propagates from the vicinity of the electrode portion 62x of the auxiliary spark plug 62 to the surrounding area. This flame is then ejected into the main combustion chamber 26 through the communication hole 66 and propagates to the mixture in the main combustion chamber 26.

[0033] Here, when main ignition is performed on the air-fuel mixture in the main combustion chamber 26 by the main spark plug 32, a flame also propagates from the vicinity of the electrode portion 32x of the main spark plug 32 to the surrounding area. In this way, if ignition is performed by both the main spark plug 32 and the auxiliary spark plug 62 and the air-fuel mixture starts to burn appropriately in the main combustion chamber 26 and the auxiliary combustion chamber 60, flames will propagate to the air-fuel mixture in the main combustion chamber 26 from multiple positions (the positions of the electrode portion 32x and each communication hole 66). Therefore, the combustion speed of the air-fuel mixture in the main combustion chamber 26 is increased, which in turn improves fuel efficiency and suppresses the occurrence of knocking.

[0034] [Control system] 5 is a block diagram showing a control system of the engine system 1. The engine system 1 includes an ECU 100 (controller) that performs overall control of each functional unit of the engine system 1. The ECU 100 is electrically connected to the injector 28 (fuel injection device), main spark plug 32 (main ignition device), and auxiliary spark plug 62 (auxiliary ignition device), and outputs control electrical signals to these devices. The ECU 100 is configured with a microcomputer that includes a processor (CPU) that performs various arithmetic processing, memories such as ROM and RAM, and various input / output buses.

[0035] Information detected by various sensors is input to the ECU 100. The ECU 100 performs various determinations and calculations based on the information input from the various sensors to control various parts of the engine. Detected values from an air flow sensor SN1, an intake air temperature sensor SN2, an intake air pressure sensor SN3, a water temperature sensor SN4, and a crank angle sensor SN5 provided in the engine system 1, and an accelerator opening sensor SN6 provided in the vehicle, are input to the ECU 100.

[0036] The air flow sensor SN1 detects the flow rate of intake air that passes through the intake passage 4 and is introduced into the engine body 2. The intake air temperature sensor SN2 and the intake air pressure sensor SN3 respectively detect the temperature and pressure of the intake air that is introduced into the engine body 2. The water temperature sensor SN4 detects the temperature of the engine coolant 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 position sensor SN6 detects the accelerator position, which is the position of an accelerator pedal (not shown) provided on the vehicle.

[0037] 6 is a map showing the engine operating range, with the horizontal axis representing engine speed and the vertical axis representing engine load. The engine operating range is roughly divided into three ranges A1 to A3 (first range A1, second range A2, and third range A3) depending on the control details of the injector 28, main spark plug 32, and sub spark plug 62.

[0038] The first region A1 is a low-speed, low-load region where the engine speed is equal to or less than a predetermined first speed N1 and the engine load is equal to or less 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 less 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, that is, the region where the engine speed is equal to or less than the first speed N1, and is made up of a region where the engine load is higher than the first load Tq1 and equal to or less than the second load Tq2, and a region where the engine speed is higher than the first speed N1.

[0039] In the first region A1, the injector 28, the main spark plug 32, and the auxiliary spark plug 62 are controlled to achieve HCCI combustion (Homogeneous Compression Charge Ignition). Specifically, fuel is injected from the injector 28 during the intake stroke. In addition, the ignition operations of the main spark plug 32 and the auxiliary spark plug 62 are stopped.

[0040] The injector 28 is disposed facing the main combustion chamber 26, and fuel injected from the injector 28 is dispersed 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 thoroughly mixed in the main combustion chamber 26 before the top dead center of compression is reached. In the first region A1, this thoroughly mixed mixture (premixed air-fuel) is heated and pressurized by the compression of the piston 24, causing it to self-ignite near the top dead center of compression. In HCCI combustion, the air-fuel ratio of the mixture is made lean (high) to a level where flame propagation is impossible, thereby improving fuel economy. Therefore, 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 is leaner than the stoichiometric air-fuel ratio (14.7).

[0041] In the second region A2, the injector 28, the main spark plug 32, and the auxiliary spark plug 62 are controlled to achieve flame propagation combustion (SI combustion). 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 main ignition and auxiliary ignition are performed by these spark plugs 32, 62. The opening of the throttle valve 36 is also 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, flame kernels are generated around the electrodes 32x, 62x by main ignition by the main spark plug 32 and auxiliary ignition by the auxiliary spark plug 62. Flames propagate from these flame kernels to the surrounding areas, causing the mixture in the main combustion chamber 26 and the auxiliary combustion chamber 60 to combust.

[0042] In the third region A3, the injector 28, the main spark plug 32, and the auxiliary spark plug 62 are controlled to achieve retarded SI combustion, in which the fuel injection timing is more retarded than in the second region A2. In the third region A3, fuel is injected from the injector 28 during the compression stroke, not the intake stroke. This is because if fuel injection is performed during the intake stroke in the third region A3, which is low rotation and high load, pre-ignition, in which the air-fuel mixture self-ignites before the main ignition, may occur.

[0043] In this embodiment, a specific ignition control is executed in a specific region A2H within the second region A2. The specific region A2H is a high-speed, low-load operating region where the engine speed is higher than the first engine speed N1 and the engine load is lower than the boundary load Tqs (predetermined reference load). In the specific region A2H, the ECU 100 causes the main spark plug 32 to execute main ignition and then causes the auxiliary spark plug 62 to execute auxiliary ignition. In other words, in the specific region A2H, control is executed to cause main ignition to precede auxiliary ignition.

[0044] Furthermore, in the specific region A2H, the ECU 100 executes a different ignition control using a predetermined second rotation speed N2 (predetermined reference rotation speed) higher than the first rotation speed N1 as a guide. twist In a high rotation range where the rotation speed is the highest (for example, at operating point P2), the timing of the sub-ignition is controlled to be retarded compared to a low rotation range where the rotation speed is equal to or lower than the second rotation speed N2 (for example, at operating point P1 in FIG. 6). This retard control may be performed in a manner where the timing is retarded stepwise from the second rotation speed N2 as a boundary, or in a manner where the amount of retard increases linearly from operating point P1 to P2.

[0045] In the specific range A2H where the engine body 2 is operated at a low load, the amount of air taken into the main combustion chamber 26 is relatively small. In other words, because of the low load, the amount of air is inherently small, making it difficult for the mixture to be introduced into the auxiliary combustion chamber 60. Even if auxiliary ignition is performed by the auxiliary spark plug 62 when there is not enough mixture in the auxiliary combustion chamber 60, misfire may occur. If a misfire occurs, a flame cannot be ejected from the communication hole 66 of the auxiliary combustion chamber 60, and therefore cannot contribute to the combustion of the unburned mixture present in the main combustion chamber 26.

[0046] In consideration of this, in the specific region A2H, the ECU 100 executes the main ignition and then the auxiliary ignition. This promotes the inflow of the mixture into the auxiliary combustion chamber 60. That is, the combustion pressure of the flame propagation combustion generated by the main ignition is superimposed on the pushing force of the piston 24, increasing the pushing force of the mixture into the auxiliary combustion chamber 60. As a result, the introduction of the mixture into the auxiliary combustion chamber 60 is promoted, and the above-mentioned misfire does not occur, and a flame can be ejected from the auxiliary combustion chamber 60 by executing the auxiliary ignition. Therefore, the unburned mixture remaining in the main combustion chamber 26 can be combusted well.

[0047] Furthermore, in the specific region A2H, in a relatively high rotational speed operating region (e.g., operating point P2), the timing of the auxiliary ignition is retarded compared to a relatively low rotational speed operating region (e.g., operating point P1). The higher the engine speed, the shorter the time available for forcing the mixture into the auxiliary combustion chamber 60. In contrast, by retarding the timing of the auxiliary ignition in the high rotational speed region, the crank angle period from the main ignition to the auxiliary ignition can be lengthened. This ensures sufficient time for the combustion pressure of the flame propagation combustion to force the mixture into the auxiliary combustion chamber 60. Therefore, misfires during the auxiliary ignition can be further suppressed.

[0048] [Specific control examples in specific areas] Next, a specific example of control in the specific region A2H will be described. Fig. 7 is a flowchart showing an example of fuel injection control of the injector 28 and ignition control of the main spark plug 32 and the sub spark plug 62, which are executed by the ECU 100 when the operating region is the specific region A2H.

[0049] When a predetermined sampling period arrives, the ECU 100 reads various pieces of information from the various sensors SN1 to SN6 and other sensors shown in Fig. 5 (step S1). For the fuel injection control and ignition control described above, the ECU 100 reads the engine speed detected by the crank angle sensor SN5 and the accelerator pedal opening detected by the accelerator pedal opening sensor SN6.

[0050] Next, the ECU 100 calculates the required torque, that is, the engine load, which is the torque required of the engine body 2 (step S2). The ECU 100 calculates the required torque (engine load) based on the engine speed and accelerator pedal opening degree read in step S1.

[0051] Next, the ECU 100 determines whether or not the operating point of the engine main body 2 is in a specific region A2H (see the operating map in FIG. 6) within the second region A2 (step S3). Specifically, the ECU 100 determines whether or not the current operating point of the engine is within the specific region A2H based on the engine speed read in step S1 and the engine load calculated in step S2.

[0052] If the operating point of the engine main body 2 is not within the specific region A2H (NO in step S3), the ECU 100 executes control according to another operating region, i.e., preset fuel injection control and ignition control for the first region A1, the third region A3, or the second region A2 other than the specific region A2H (step S8). On the other hand, if the operating point of the engine main body 2 is within the specific region A2H (YES in step S3), the ECU 100 executes the processes of steps S4 to S7. These processes set the fuel injection timing at which the injector 28 starts fuel injection, the main ignition timing at which the main ignition plug 32 performs ignition (spark discharge), and the auxiliary ignition timing at which the auxiliary ignition plug 62 performs ignition (spark discharge).

[0053] If the determination in step S3 is YES, the ECU 100 sets the main ignition timing and the auxiliary ignition timing so that auxiliary ignition is performed after the main ignition. In the following step S4, the ECU 100 determines whether the operating point of the engine body 2 is in a high rotation region within the specific region A2H (step S4). If the operating point is in a high rotation region (e.g., operating point P2) within the specific region A2H that exceeds the second rotation speed N2 (YES in step S4), the ECU 100 sets the auxiliary ignition timing to the retard side compared to the case of the low rotation region described below (step S5). On the other hand, if the operating point is in a low rotation region (e.g., operating point P2) within the specific region A2H that is equal to or lower than the second rotation speed N2 (NO in step S4), the ECU 100 sets the auxiliary ignition timing to the advance side compared to the case of the high rotation region described above (step S6). In both the low rotation region and the high rotation region, the fuel injection timing is set to a predetermined time during the intake stroke.

[0054] Thereafter, the ECU 100 drives the injector 28 so that fuel injection begins at the set fuel injection timing. The ECU 100 also drives the main spark plug 32 so that main ignition is performed first, and drives the auxiliary spark plug 62 so that auxiliary ignition occurs at the auxiliary ignition timing set in step S5 (retard side) or S6 (advance side) (step S7). In actual control, a control map formed by linking the fuel injection timing, main ignition timing, and auxiliary ignition timing to the engine load and engine speed is stored in advance in a memory area of the ECU 100, and the fuel injection timing and ignition timing are set by referring to the control map.

[0055] FIG. 8 is a time chart showing the fuel injection timing, main ignition timing tm, and auxiliary ignition timing ts at an operating point P1 in the low rotation speed region within the specific region A2H. The fuel injection timing in the low rotation speed region is during the intake stroke. Specifically, the start and end timings of fuel injection from the injector 28 are set to be included in the intake stroke. This is because in the specific region A2H, unlike the third region A3, there is little need to retard the fuel injection timing to prevent pre-ignition. Note that the fuel injection end timing may occur during the compression stroke.

[0056] As described above, in the specific region A2H, main ignition is prior and secondary ignition is subsequent. Therefore, even in the low-speed region within the specific region A2H, the main ignition timing tm1 is set to a timing more advanced than the secondary ignition timing ts1. That is, main ignition by the main spark plug 32 is performed first, followed by secondary ignition by the secondary spark plug 62. The main ignition timing tm1 is set in the latter half of the compression stroke, advanced from top dead center (TDC), and the secondary ignition timing ts is set in the first half of the expansion stroke, retarded from TDC. The prior main ignition initiates SI combustion of the mixture in the main combustion chamber 26. Because the specific region A2H is a low-load region, the amount of air taken into the main combustion chamber 26 is relatively small, making it difficult for the mixture to be introduced into the secondary combustion chamber 60. However, with the assistance of the pressure increase associated with the SI combustion, the unburned mixture remaining in the main combustion chamber 26 is forced into the secondary combustion chamber 60 through the communication hole 66. As a result, a sufficient amount of the mixture is introduced into the sub-chamber 60.

[0057] The air-fuel mixture introduced into the auxiliary combustion chamber 60 is combusted by the auxiliary ignition following the main ignition. As described above, since a sufficient amount of air-fuel mixture is introduced into the auxiliary combustion chamber 60, misfires are unlikely to occur, and the air-fuel mixture in the auxiliary combustion chamber 60 is combusted by the auxiliary ignition. As a result, it is possible to increase the reliability of ejecting flames from the multiple communication holes 66. These flames combust the unburned air-fuel mixture in the main combustion chamber 26 all at once. This can therefore improve fuel economy and exhaust gas performance.

[0058] FIG. 9 is a time chart showing the fuel injection timing, main ignition timing tm, and auxiliary ignition timing ts at the operating point P2 in the high rotation region within the specific region A2H. The fuel injection timing in the high rotation region is during the intake stroke, as in the low rotation region described above. The auxiliary ignition timing ts2 in the high rotation region is set to be more retarded than the auxiliary ignition timing ts1 in the low rotation region. Furthermore, the main ignition timing tm2 in the high rotation region is set to be more advanced than the main ignition timing tm1 in the low rotation region.

[0059] The higher the engine speed, the shorter the time available for the combustion pressure of the flame propagation combustion based on the main ignition to push the unburned mixture into the pre-ignition chamber 60. Therefore, by retarding the pre-ignition timing ts2 and advancing the main ignition timing tm2 in the high engine speed range, the time available for the pushing can be secured longer, thereby further suppressing misfires in the pre-ignition.

[0060] [Relationship between engine speed and ignition control] FIG. 10 is a chart showing the relationship between engine speed and main ignition timing (upper part of FIG. 10), auxiliary ignition timing (middle part), and ignition phase difference (lower part) in the specific region A2H. In FIG. 10, the low rotation region and the high rotation region are separated using the second rotation number N2 (predetermined reference rotation number) as the reference rotation number. The vertical axis of each chart represents the crank angle, with the advance side of TDC representing the compression stroke and the retard side representing the expansion stroke. FIGS. 8 and 9 show examples of ignition control at a specific operating point P1 in the low rotation region and a specific operating point P2 in the high rotation region, respectively. FIG. 10 shows the tendency of ignition control executed by ECU 100 throughout the entire rotation region of the specific region A2H. The chart in FIG. 10 shows the relationship between each parameter and engine speed at a constant engine load.

[0061] The main ignition timing is set to the compression stroke because it is a pre-ignition in the full rotation range of the specific region A2H. The ECU 100 controls the main ignition timing to be more advanced as the engine speed increases. This control makes it possible to lengthen the crank angle period for forcing the mixture into the auxiliary combustion chamber 60 as the engine speed increases. Therefore, the mixture can be sufficiently forced into the auxiliary combustion chamber 60. Note that the degree of advancement of the main ignition timing does not necessarily have to be linear as shown in FIG. 10; for example, it may change in slope or stepwise at the second rotation speed N2.

[0062] The secondary ignition timing may be a trailing ignition in the entire rotation range and is set in the expansion stroke. The ECU 100 performs control to retard the secondary ignition timing as the engine speed increases. This retardation can increase the period from the main ignition to the secondary ignition. As a result, sufficient time can be ensured for pushing the air-fuel mixture into the auxiliary chamber 60, and the air-fuel mixture in the auxiliary chamber 60 can be reliably burned by the secondary ignition.

[0063] As shown in FIGS. 8 and 9, the ignition phase differences dt1 and dt2 are the phase differences on the crank angle between the main ignition timings tm1 and tm2 and the secondary ignition timings ts1 and ts2. As shown in the lower part of FIG. 10, in the specific region A2H, the ignition phase difference is set to be larger as the engine speed increases (dt1 < dt2). Increasing the ignition phase difference leads to an increase in the period between the main ignition as the leading ignition and the secondary ignition as the trailing ignition. Therefore, the period for pushing the air-fuel mixture into the auxiliary chamber 60 can be sufficiently ensured according to the engine speed.

[0064] [Modified Example] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and the following modified embodiments can be adopted.

[0065] (1) In the above embodiment, as the cover member 64 of the secondary ignition unit 30, an embodiment having a semi-spherical dome shape (FIG. 3) and three communication holes 66 (FIG. 4) is exemplified. The shape of the cover member 64 may be other shapes such as a frustum of a cone shape or a rectangular parallelepiped shape. Also, the number and size of the communication holes 66 can be set as appropriate. Further, the mounting position of the secondary ignition unit 30 is not limited to the embodiment of FIG. 2. For example, the secondary ignition unit 30 may be provided on the intake port 8 side with respect to the tip portion 28x of the injector 28.

[0066] (2) In the above embodiment, the specific region A2H is set within the range of the second region A2 (lower limit engine speed = N1). Alternatively, the lower limit engine speed of the specific region A2H may be extended to a lower rotational speed side than N1. In other words, a portion of the high rotational speed side of the first region A1 shown in FIG. 6 may be incorporated into the specific region A2H. [Explanation of symbols]

[0067] 1 Engine System 22 cylinders 24 pistons 26 Main combustion chamber 28 Injector (fuel injection device) 30 Sub-ignition unit 32 Main spark plug (main ignition device) 52 Cylinder block 54 Cylinder head 60 Antechamber 62 Auxiliary spark plug (auxiliary ignition device) 64 Cover member (partition wall) 66 Communication hole 100 ECU (Controller) A2H Specific area (low load area below standard load) P1 Low RPM driving point P2 High RPM driving point N2 Second rotation speed (predetermined reference rotation speed) Tqs boundary load (predetermined reference load) tm main ignition timing ts sub ignition timing dt ignition phase difference

Claims

1. a cylinder block and a cylinder head that form a cylinder; a piston accommodated in the cylinder so as to be capable of reciprocating; 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 performs main ignition to ignite the air-fuel mixture in the main combustion chamber; an auxiliary ignition device that performs auxiliary ignition to ignite the air-fuel mixture in the auxiliary chamber; a controller electrically connected to the fuel injection device, the main ignition device, and the auxiliary ignition device, and outputting control electrical signals to each of the devices; The controller, in a low load region where the engine load is equal to or less than a predetermined reference load, executing the main ignition and then executing the secondary ignition; The higher the engine rotation speed, the larger the ignition phase difference between the auxiliary ignition and the main ignition is set, and An engine system in which the timing of the auxiliary ignition is retarded in a high rotation range where the engine rotation speed is higher than a predetermined reference rotation speed, compared to a low rotation range where the engine rotation speed is equal to or lower than the reference rotation speed.

2. 2. The engine system according to claim 1, The controller advances the main ignition timing as the engine speed increases.

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