Engine System

Abstract

To reliably enhance fuel economy performance while curbing a torque shock.SOLUTION: An engine system comprises: a main combustion chamber; an auxiliary chamber; a fuel injection device which injects fuel into the main combustion chamber; a main ignition device which ignites mixed gas in the main combustion chamber; and an auxiliary ignition device which ignites the mixed gas in the auxiliary chamber. The engine system controls the main ignition device and the auxiliary ignition device, in a predetermined region, so that an auxiliary ignition timing which is an ignition timing of the auxiliary ignition device is delayed with respect to a main ignition timing which is an ignition timing of the main ignition device. When an air-fuel ratio shortage condition, in which an air-fuel ratio in the main combustion chamber is lower than a target value while a vehicle is accelerated in the predetermined region, meets, the engine system increases an ignition phase difference which is a delay amount of the auxiliary ignition timing with respect to the main ignition timing.SELECTED DRAWING: Figure 9

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 separately into the main combustion chamber and the auxiliary combustion chamber, 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 combustion state of the mixture in the auxiliary combustion chamber and the main combustion chamber changes depending on the flow rate of the mixture from the main combustion chamber to the auxiliary combustion chamber. Therefore, ingenuity is required in order to reliably burn the mixture in both the main combustion chamber and the auxiliary combustion chamber during acceleration when the amount of air introduced into the main combustion chamber may be insufficient.

[0006] The present invention has been made in consideration of the above circumstances, and has an object to appropriately combust an air-fuel mixture in the auxiliary combustion chamber and the main combustion chamber during acceleration 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 system mounted on a vehicle, comprising a cylinder block and a cylinder head which form a cylinder, a piston housed in the cylinder so as to be capable of reciprocating motion, a main combustion chamber defined by the cylinder block, the cylinder head, and the piston, an auxiliary chamber which is separated from the main combustion chamber by a partition wall and which communicates with the main combustion chamber through a communication hole formed in the partition wall, a fuel injection device which injects fuel into the main combustion chamber, a main ignition device which ignites the air-fuel mixture in the main combustion chamber, an auxiliary ignition device which ignites the air-fuel mixture in the auxiliary chamber, and a control system for controlling the fuel injection device, the main ignition device, and the auxiliary ignition device. and a control device electrically connected to the ignition devices to output an electric signal for control to each of the devices, the control device controls 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, in a predetermined region. a target value of the air-fuel ratio of the main combustion chamber in the predetermined region is set to a constant value, and when a rate of change in an accelerator pedal opening of the vehicle is equal to or greater than a predetermined reference rate of change during acceleration of the vehicle in the predetermined region, it is determined that an air-fuel ratio deficiency condition exists in which the air-fuel ratio of the main combustion chamber is insufficient with respect to the constant target value, When the vehicle accelerates in the predetermined range, The aboveWhen an air-fuel ratio deficiency condition is established, an ignition phase difference, which is an amount of retardation of the auxiliary ignition timing with respect to the main ignition timing, is increased for correction.

[0008] In the present invention, ignition is performed by the main ignition device in a predetermined region, and then ignition is performed by the auxiliary ignition device. Therefore, the mixture is burned in the main combustion chamber by ignition by the main ignition device, and the resulting increase in pressure in the main combustion chamber can be used to push the mixture into the auxiliary chamber. Therefore, the mixture can be burned appropriately in both the main combustion chamber and the auxiliary combustion chamber, improving fuel efficiency and exhaust gas performance.

[0009] Moreover, in the present invention, the ignition phase difference is increased during acceleration when the air-fuel ratio in the main combustion chamber is insufficient relative to the target value and it is therefore difficult to introduce sufficient air from the main combustion chamber into the auxiliary chamber. When the ignition phase difference is increased, the period from when the mixture starts to be introduced into the auxiliary chamber due to the increase in pressure in the main combustion chamber until ignition by the auxiliary ignition device is extended. Therefore, even during acceleration when it is difficult to introduce sufficient air into the auxiliary chamber, the amount of air in the auxiliary chamber can be secured and appropriate combustion of the mixture in the auxiliary chamber can be achieved. This combustion of the mixture in the auxiliary chamber can promote combustion in the main combustion chamber, which can achieve appropriate combustion of the mixture in the main combustion chamber while increasing engine torque and improving acceleration.

[0011] Also, when the rate of change of the accelerator pedal opening is equal to or greater than a predetermined reference rate of change, it is determined that the air-fuel ratio deficiency condition is established. Therefore, it is possible to easily determine whether or not the air-fuel ratio deficiency condition exists based on the rate of change in the accelerator pedal depression.

[0012] In the above-mentioned configuration, preferably, when the air-fuel ratio deficiency condition is established, the control device increases the correction amount of the ignition phase difference as the deficiency amount of the air-fuel ratio of the main combustion chamber with respect to the target value increases (see claim 2 ).

[0013] According to this configuration, when the deficit of the air-fuel ratio in the main combustion chamber is large and it is particularly difficult to introduce air from the main combustion chamber to the auxiliary combustion chamber, the correction amount of the ignition phase difference is particularly large, so that engine torque can be ensured. Also, when the deficit of the air-fuel ratio in the main combustion chamber is relatively small and it is relatively easy to introduce air from the main combustion chamber to the auxiliary combustion chamber, it is possible to prevent the ignition phase difference from becoming excessive, and thus the combustion period from becoming excessive, thereby improving fuel efficiency.

[0014] In the above-mentioned configuration, the control device preferably corrects the main ignition timing to the advance side when the air-fuel ratio deficiency condition is satisfied. 3 ).

[0015] According to this configuration, the engine torque can be increased by increasing the ignition phase difference as well as by advancing the main ignition timing, thereby ensuring good acceleration performance.

[0016] In the above-mentioned configuration, preferably, when the air-fuel ratio deficiency condition is established, if the amount of deficiency of the air-fuel ratio of the main combustion chamber with respect to the target value is equal to or greater than a predetermined value, the control device corrects the auxiliary ignition timing to the retard side (claim 4 ).

[0017] According to this configuration, when the air-fuel ratio is particularly insufficient with respect to the target value and it becomes difficult to introduce air into the auxiliary combustion chamber, the auxiliary ignition timing is retarded in conjunction with the advancement of the main ignition timing, thereby reliably increasing the ignition phase difference. Therefore, the combustion in the auxiliary combustion chamber and the combustion in the main combustion chamber can be more reliably promoted, and the acceleration can be more reliably improved. Effect of the Invention

[0018] As described above, according to the engine system of the present invention, the air-fuel mixture can be appropriately combusted in the auxiliary combustion chamber and the main combustion chamber. [Brief description of the drawings]

[0019] [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] FIG. 11 is a diagram showing an example of a drive pulse and an ignition timing of an injector in a second region. [Figure 8] FIG. 13 is a diagram showing the relationship between the rate of change of the accelerator opening and the amount of air-fuel ratio deficiency. [Figure 9] 4 is a flowchart showing a control procedure for a main spark plug and an auxiliary spark plug. [Figure 10] 5A to 5C are diagrams showing an example of the main ignition timing and the auxiliary ignition timing during acceleration in the second region, where (a) is a diagram during slow acceleration, (b) is a diagram during rapid acceleration, and (c) is a diagram during intermediate acceleration. [Figure 11] 4 is a graph showing a relationship between a rate of change of an accelerator opening and an amount of correction for an ignition timing and an amount of correction for an ignition phase difference. [Figure 12] 4 is a time chart showing the time changes of each parameter during acceleration in a second region.

[0020] (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.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] In the cylinder head 54, an intake port 8 for communicating the main combustion chamber 26 with the intake passage 4 to introduce air supplied from the intake passage 4 into the main combustion chamber 26, and an exhaust port 12 for communicating the main combustion chamber 26 with the exhaust passage 6 to lead 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.

[0025] 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.

[0026] 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.

[0027] 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).

[0028] The main spark plug 32 performs main ignition by igniting 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 spark plug 32. This electrode portion 32x includes a center electrode 32a and a side electrode (earth) 32b. 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. In this embodiment, the main spark 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.

[0029] 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.

[0030] 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 an air cleaner 34, a throttle valve 36, and a surge tank 38, in this order from the upstream side. The air cleaner 34 is a device for removing foreign matter from the intake air, and the surge tank 38 is a tank having a predetermined volume. The throttle valve 36 is a valve for opening and closing the intake passage 4 to adjust the flow rate of the intake air flowing through the intake passage 4. The opening degree of the throttle valve 36 is changed by a driving means for driving the throttle valve 36. The flow rate of the intake air flowing through the intake passage 4, and thus the amount of intake air (air) flowing through the intake passage 4 into the main combustion chamber 26, is adjusted by the opening degree of the throttle valve 36.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] (auxiliary ignition unit) 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).

[0035] The auxiliary ignition unit 30 has an auxiliary spark plug 62 that ignites the 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 provided at its tip portion 30x and covering 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 performs auxiliary ignition to ignite the 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.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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.

[0041] (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.

[0042] 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 detect the temperature and pressure of the intake air introduced into the engine body 2, respectively. 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 70 provided in the vehicle.

[0043] 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.

[0044] Fig. 6 is a map showing the operating range of an engine, with the horizontal axis representing engine speed and the vertical axis representing engine load. As shown in Fig. 6, the operating range of an engine is roughly divided into two regions A1 and A2 (first region A1 and second region A2) according to the combustion mode. The first region A1 is a low-speed, low-load region where the engine speed is equal to or lower than a predetermined switching speed N1 and the engine load is equal to or lower than a predetermined switching load Tq1, and the second region A2 is the other region. The second region A2 corresponds to the "predetermined region" in the claims.

[0045] (1st area) 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.

[0046] 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 top dead center of compression is reached. Then, in the first region A1, the sufficiently mixed mixture (premixed air) is heated and pressurized by the compression of the piston 24, and self-ignites near the top dead center of compression. In HCCI combustion, the air-fuel ratio of the mixture (the ratio of the weight of air in the main combustion chamber 26 to the weight of fuel in the main combustion chamber 26) can be made lean (high) 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 is leaner (higher) than the theoretical air-fuel ratio (14.7).

[0047] In addition, in the first region A1, the ECU 100 performs EGR to recirculate the EGR gas to the intake passage 4 and the main combustion chamber 26. That is, in the first region A1, the EGR valve 46 is opened to recirculate the EGR gas to the intake passage 4 and the main combustion chamber 26.

[0048] (Control during normal operation in the second region) The control during normal operation (control when not accelerating) performed in the second region A2 will be described.

[0049] In the second region A2, the ECU 100 controls each part of the engine so that the air-fuel mixture undergoes SI (Spark Ignition) combustion, that is, flame propagation combustion.

[0050] Specifically, in the second region A2, the ECU 100 performs main ignition and auxiliary ignition. That is, the ECU 100 drives the main ignition plug 32 and the auxiliary ignition plug 62 to cause these ignition plugs 32, 62 to perform ignition (spark discharge). When the ignition plugs 32, 62 perform spark discharge, a flame kernel is generated around the electrode portions 32x, 62x of these ignition plugs 32, 62, and SI combustion is realized in which the flame propagates from the flame kernel to the surroundings.

[0051] FIG. 7 is a diagram showing the drive pulse of the injector 28 in the second region A2, the main ignition timing tm which is the ignition timing of the main ignition plug 32 (the timing tm at the crank angle at which the main ignition plug 32 ignites, i.e., produces a spark discharge), and the sub-ignition timing ts which is the ignition timing of the sub-ignition plug 62 (the timing ts at the crank angle at which the sub-ignition plug 62 ignites, i.e., produces a spark discharge).

[0052] 7, in the second region A2, the ECU 100 sets the fuel injection timing tinj to a timing during the intake stroke, and causes the injector 28 to start fuel injection at a predetermined timing during the intake stroke. In the second region A2 where the engine speed is low and the engine load is high and where preignition (a phenomenon in which the air-fuel mixture self-ignites before ignition) is likely to occur, the fuel injection timing may be set to a timing during the compression stroke in order to reliably avoid the occurrence of preignition.

[0053] As shown in FIG. 7, in the second region A2, the ECU 100 sets the auxiliary ignition timing ts to a timing that is more retarded than the main ignition timing tm. That is, the ECU 100 first causes the main spark plug 32 to ignite, and then causes the auxiliary spark plug 62 to ignite. 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. The basic ignition timings (basic main ignition timing tm_base, basic auxiliary ignition timing ts_base), which are the ignition timings tm and ts during normal operation, are set in advance for each operating point and stored in the ECU 100. In this embodiment, the basic main ignition timing tm_base and the basic auxiliary ignition timing ts_base are set in advance for each engine speed and engine load and stored in a map, and the ECU 100 extracts the timings corresponding to the engine speed and engine load from this map and sets them as the main ignition timing tm and the auxiliary ignition timing ts.

[0054] In the second region A2, the ECU 100 adjusts the opening of the throttle valve 36 so that the air-fuel ratio of the mixture in the main combustion chamber 26 becomes the stoichiometric air-fuel ratio. That is, in the second region A2, the target value of the air-fuel ratio of the main combustion chamber 26 is set to the stoichiometric air-fuel ratio, and the throttle valve 36 is controlled so as to realize this target value.

[0055] In the second region A2, the ECU 100 adjusts the opening of the EGR valve 46 so that a preset target EGR rate is achieved at each operating point. The EGR rate is the ratio (weight ratio) of EGR gas to the total gas present in the main combustion chamber 26 and the auxiliary combustion chamber 60. In this embodiment, in the second region A2 where the engine speed is high and the engine load is high, the target EGR rate is set to zero and EGR is stopped (the EGR valve 46 is fully closed). On the other hand, in the remaining region of the second region A2, the EGR rate is set to a value greater than zero and the EGR valve 46 is opened.

[0056] (Acceleration control in the second range) Next, we will explain the control of the main spark plug 32 and the auxiliary spark plug 62 performed by the ECU 100 during acceleration within the second region A2, that is, when the operating point shifts from operating point P1 in the second region A2 to operating point P2 in the second region A2 where the engine load is higher, as shown by the arrow in Figure 6.

[0057] When the vehicle starts accelerating, that is, when the driver depresses the accelerator pedal 70 to accelerate the vehicle, the ECU 100 increases the amount of fuel injected from the injector 28 to increase the engine load. The ECU 100 also adjusts the opening of the throttle valve 36 and the EGR valve 46 to increase the amount of air introduced into the main combustion chamber 26. However, there is a delay in the flow of gas. Therefore, immediately after the start of acceleration, the burnt gas in the main combustion chamber 26 is not sufficiently discharged, and the change in the opening of the throttle valve 36, etc. is not immediately reflected in the amount of air in the main combustion chamber 26, so that the amount of air introduced into the main combustion chamber 26 does not increase sufficiently, and the air-fuel ratio of the main combustion chamber 26 may be insufficient relative to the target value. If the air-fuel ratio of the main combustion chamber 26 is insufficient relative to the target value, that is, if the amount of air introduced into the main combustion chamber 26 is insufficient, a sufficient mixture (air) is not introduced into the auxiliary combustion chamber 60, and the mixture does not burn properly in the auxiliary combustion chamber 60. Furthermore, if the air-fuel mixture does not burn properly in the auxiliary combustion chamber 60, the flame from the auxiliary combustion chamber 60 will not have the effect of promoting combustion in the main combustion chamber 26, so engine torque will not be increased sufficiently, and acceleration may decrease.

[0058] Here, if the ignition phase difference dt, which is the amount of retardation of the auxiliary ignition timing ts relative to the main ignition timing tm (i.e., the period in crank angles from the main ignition timing tm to the auxiliary ignition timing ts), is increased, the period from when the mixture starts being introduced into the auxiliary combustion chamber 60 due to the pressure increase in the main combustion chamber 26 until ignition by the auxiliary spark plug 62 becomes longer. As a result, if the ignition phase difference dt is increased, the introduction of air into the auxiliary combustion chamber 60 can be promoted to achieve proper combustion of the mixture in the auxiliary combustion chamber 60, and a flame can be ejected from the auxiliary combustion chamber 60 into the main combustion chamber 26 to promote combustion of the mixture in the main combustion chamber 26. In other words, the mixture can be properly burned in the main combustion chamber 26, and the engine torque can be increased to improve acceleration.

[0059] Therefore, when accelerating in the second region A2 and an air-fuel ratio deficiency condition is satisfied, that is, the air-fuel ratio in the main combustion chamber 26 is insufficient with respect to the target value (stoichiometric air-fuel ratio), the ECU 100 corrects the ignition phase difference dt to increase it. Specifically, when the air-fuel ratio deficiency condition is satisfied, the ECU 100 corrects at least one of the main ignition timing tm and the auxiliary ignition timing ts so that the ignition phase difference dt is increased compared to that during normal operation. Hereinafter, the amount of deficiency of the air-fuel ratio in the main combustion chamber 26 with respect to the target value (stoichiometric air-fuel ratio) is simply referred to as the air-fuel ratio deficiency. Note that, in this specification, the state in which the air-fuel ratio in the main combustion chamber 26 is insufficient with respect to the target value (stoichiometric air-fuel ratio) is not limited to a state in which the amount of deficiency is strictly zero or more, but also includes a state in which the air-fuel ratio is substantially insufficient, that is, a state in which the air-fuel ratio is insufficient to an extent that affects the engine torque.

[0060] In the following, strong acceleration refers to acceleration when the air-fuel ratio deficiency condition is satisfied and the air-fuel ratio in the main combustion chamber 26 is insufficient relative to the target value (stoichiometric air-fuel ratio) (acceleration that is substantially insufficient to an extent that affects engine torque). In addition, gentle acceleration refers to acceleration when the air-fuel ratio deficiency condition is not satisfied and the air-fuel ratio in the main combustion chamber 26 is not insufficient (not substantially insufficient) relative to the target value (stoichiometric air-fuel ratio) and the amount of deficiency is kept small enough that it does not affect engine torque.

[0061] FIG. 8 is a diagram showing the relationship between the rate of change of the accelerator opening (the rate of change of the opening of the accelerator pedal 70) at the start of acceleration in the second region A2 and the amount of air-fuel ratio deficiency. As shown in FIG. 8, the greater the rate of change of the accelerator opening at the start of acceleration, the greater the amount of air-fuel ratio deficiency. Thus, in this embodiment, the ECU 100 judges whether the acceleration is strong or slow (whether the air-fuel ratio deficiency condition is met) based on the rate of change of the accelerator opening at the start of acceleration. Specifically, the ECU 100 judges that slow acceleration has started when the rate of change of the accelerator opening is less than a predetermined first judgment value (and greater than 0) and the amount of air-fuel ratio deficiency is less than the first deficiency (greater than 0) and is suppressed to an amount that does not affect engine torque, and judges that strong acceleration has started when the rate of change of the accelerator opening is equal to or greater than the first judgment value and the amount of air-fuel ratio deficiency is equal to or greater than the predetermined first deficiency and affects engine torque.

[0062] In this embodiment, as described later, during strong acceleration, the control of the ignition timing is made different depending on whether the rate of change of the accelerator opening is equal to or greater than a second judgment value that is greater than the first judgment value. In the following, as appropriate, acceleration in which the rate of change of the accelerator opening at the start of acceleration is equal to or greater than the second judgment value, that is, acceleration in which the air-fuel ratio deficiency is equal to or greater than a predetermined second deficiency that is greater than the first deficiency, is referred to as sudden acceleration. Also, acceleration in which the rate of change of the accelerator opening is equal to or greater than the first judgment value and less than the second judgment value, that is, acceleration in which the air-fuel ratio deficiency is equal to or greater than the first deficiency and less than the second deficiency, is referred to as intermediate acceleration. The second deficiency corresponds to the "predetermined value" in the claims.

[0063] Next, a specific control procedure for the spark plugs 32, 62 during acceleration in the second region A2 will be described with reference to the flowchart of FIG.

[0064] 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.

[0065] 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.

[0066] Next, the ECU 100 sets the basic ignition timings (basic main ignition timing tm_base, basic sub ignition timing ts_base) (step S3). As described above, in this embodiment, the ECU 100 extracts values ​​corresponding to the current engine speed and engine load from a map that is preset and stored for the main ignition timing tm and the sub ignition timing ts, and sets the extracted values ​​to the basic main ignition timing tm_base and the basic sub ignition timing ts_base.

[0067] Next, the ECU 100 determines whether or not the vehicle has started accelerating (step S4). Specifically, the ECU 100 determines that the vehicle has started accelerating when the rate of change in the accelerator opening changes from a state equal to or less than 0 to a value greater than 0.

[0068] If the determination in step S4 is YES, that is, if it is determined that the vehicle has started accelerating, the ECU 100 determines in step S5 whether or not the rate of change in the accelerator opening is equal to or greater than a first determination value, that is, whether or not the vehicle is undergoing strong acceleration (step S4). The first determination value is a value greater than 0, and is preset and stored in the ECU 100.

[0069] If the determination in step S4 is YES and the rate of change in the accelerator opening is equal to or greater than the first determination value, the ECU 100 determines whether or not the rate of change in the accelerator opening is equal to or greater than the second determination value, that is, whether or not the acceleration is rapid (step S5). As described above, the second determination value is a value greater than the first determination value, and is set in advance and stored in the ECU 100. The determinations in steps S4 to S6 are made based on the accelerator opening read in step S1.

[0070] When the determination in step S5 is YES and the rate of change in the accelerator opening is equal to or greater than the second determination value, that is, when rapid acceleration is occurring, the ECU 100 corrects the ignition timing (step S8).

[0071] Fig. 10(a) is an enlarged view of a part of Fig. 7, showing the main ignition timing tm when the main ignition timing tm is the basic main ignition timing tm_base and the auxiliary ignition timing ts when the auxiliary ignition timing ts is the basic auxiliary ignition timing ts_base. Fig. 10(b) shows the main ignition timing tm and the auxiliary ignition timing ts during rapid acceleration.

[0072] As shown in FIG. 10(b), during rapid acceleration (step S8), the ECU 100 corrects the main ignition timing tm to a timing more advanced than the basic main ignition timing tm_base. That is, the ECU 100 determines the main ignition timing tm to be a timing more advanced than the basic main ignition timing tm_base. Also, the ECU 100 corrects the sub ignition timing ts to a timing more retarded than the basic sub ignition timing ts_base set in step S3. That is, the ECU 100 determines the sub ignition timing ts to be a timing more retarded than the basic sub ignition timing ts_base. As a result, the ignition phase difference dt is increased. That is, the ignition phase difference dt is increased with respect to the basic ignition phase difference dt_base, which is the ignition phase difference when the ignition timing is the basic ignition timing. After determining the ignition timing in step S8, the ECU 100 proceeds to step S9.

[0073] 9, if the determination in step S6 is NO and the rate of change in the accelerator opening is less than the second determination value (and equal to or greater than the first determination value), that is, during intermediate acceleration, the ECU 100 proceeds to step S7. In step S7, the ECU 100 also corrects the ignition timing.

[0074] FIG. 10(c) is a diagram showing the main ignition timing tm and the auxiliary ignition timing ts during intermediate acceleration. As shown in FIG. 10(c), even during intermediate acceleration (step S7), the ECU 100 corrects the main ignition timing tm to a timing more advanced than the basic main ignition timing tm_base, as in the case of rapid acceleration (step S8). That is, the ECU 100 determines the timing more advanced than the basic main ignition timing tm_base as the main ignition timing tm. On the other hand, during intermediate acceleration (step S7), the ECU 100 does not correct the auxiliary ignition timing ts, and determines the basic auxiliary ignition timing ts_base set in step S3 as the auxiliary ignition timing ts. After the ignition timing is determined in step S7, the process proceeds to step S9.

[0075] FIG. 11 is a diagram showing the relationship between the rate of change of the accelerator opening at the start of acceleration and the correction amount of the ignition timing and the correction amount of the ignition phase difference. As shown in FIG. 11, when the rate of change of the accelerator opening is equal to or greater than the first judgment value and during strong acceleration (during intermediate acceleration and rapid acceleration), the ECU 100 increases the correction amount (advance amount) of the main ignition timing tm as the rate of change of the accelerator opening at the start of acceleration increases, that is, as the air-fuel ratio deficiency increases. When the rate of change of the accelerator opening is equal to or greater than the second judgment value and during rapid acceleration, the ECU 100 increases the correction amount (retard amount) of the sub-ignition timing ts as the rate of change of the accelerator opening at the start of acceleration increases, that is, as the air-fuel ratio deficiency increases. Thus, during strong acceleration, the correction amount (increase amount) of the ignition phase difference dt is increased as the rate of change of the accelerator opening at the start of acceleration increases and the air-fuel ratio deficiency increases.

[0076] In this embodiment, the ECU 100 stores in advance a map that indicates the relationship between a preset rate of change in the accelerator opening and the correction amounts for the ignition timings tm, ts. The ECU 100 extracts from the map a correction amount that corresponds to the rate of change in the accelerator opening at the start of acceleration, and corrects the basic main ignition timings tm_base, ts_base using the extracted correction amount.

[0077] 9, if the determination in step S4 is NO, i.e., it is not the start of acceleration, the ECU 100 determines whether the ignition timing is being corrected and whether the elapsed time from the start of the correction is less than a predetermined reference period (step S10). The reference period is preset and stored in the ECU 100.

[0078] If the determination in step S10 is YES, the ignition timing has been corrected, and the reference period has not yet elapsed since the correction was started, the ECU 100 continues the correction of the ignition timing (step S11). However, the ECU 100 gradually decreases the correction amount of the ignition timing over time. That is, the ECU 100 sets the correction amount so that the correction amount of the ignition timing becomes smaller as the elapsed time from the start of strong acceleration becomes longer, and determines the timing obtained by correcting the basic ignition timing with this correction amount as the ignition timing. During rapid acceleration, the correction amounts of both the main ignition timing tm and the sub ignition timing ts are gradually decreased, and during intermediate acceleration, the correction amount of the main ignition timing tm is gradually decreased. In this way, in this embodiment, once the correction of the ignition timing is started with the start of strong acceleration (intermediate acceleration or rapid acceleration), the correction of the ignition timing is continued until the reference period has elapsed. After the ignition timing is determined in step S11, the process proceeds to step S9.

[0079] On the other hand, if the determination in step S10 is NO, and the ignition timing has not been corrected, or the time that has elapsed since the ignition timing was corrected is equal to or longer than the reference period, the ECU 100 does not correct the ignition timing, and determines the basic ignition timing set in step S3 as the ignition timing (step S12). After determining the ignition timing in step S12, the process proceeds to step S9.

[0080] In step S9, which is performed after any one of steps S7, S8, S11, and S12, the ECU 100 drives the main spark plug 32 and the auxiliary spark plug 62 so that ignition is performed at the main ignition timing tm and the auxiliary ignition timing ts set in any one of the above steps. After performing step S9, the process returns to step S1 again. Note that the above steps S1 to S12 are repeatedly performed at predetermined timings during operation in the second region A2.

[0081] Fig. 12 is a time chart showing the change over time of each parameter when the above control is performed during acceleration in the second region A2. In Fig. 12, the thin line shows the change over time during slow acceleration, the dashed line shows the change over time during medium acceleration, and the thick line shows the change over time during rapid acceleration.

[0082] In the example of FIG. 12, at time t1, the rate of change in the accelerator opening becomes greater than 0, and acceleration begins.

[0083] As shown by the thin line, during slow acceleration, even if acceleration starts, the air-fuel ratio is maintained at approximately the theoretical air-fuel ratio, and the air-fuel ratio deficiency is maintained at approximately zero. Here, in the example of FIG. 12, the correction amounts of the ignition timings tm and ts before time t1 are zero, and slow acceleration starts in a state where the ignition timing is not corrected. That is, the example of slow acceleration in FIG. 12 is an example in which the determination in step S4 is YES, the determination in step S5 is NO, and the determination in step S10 is NO. As a result, in this example, step S12 is performed, and the ignition timing is not corrected after time t1, and the correction amounts of the main ignition timing tm and the sub ignition timing ts are set to zero even after time t1, and the correction amount of the ignition phase difference dt is also maintained at zero.

[0084] On the other hand, as shown by the dashed line, during intermediate acceleration, immediately after the start of acceleration, the air-fuel ratio becomes lower than the theoretical air-fuel ratio, and the air-fuel ratio deficiency becomes a value greater than 0. As described above, at the start of intermediate acceleration, the determinations of steps S4 and S5 are YES and the determination of step S6 is NO, so that step S7 is executed. That is, the sub ignition timing ts is not corrected, while the main ignition timing tm is corrected to the advance side. Thus, as shown by the dashed line, during intermediate acceleration, immediately after time t1, the correction amount (advance amount) of the main ignition timing tm is increased, and the correction amount of the ignition phase difference dt is also increased. Also, as described above, once the correction of the ignition timing is started, the correction of the ignition timing is continued until the reference period has elapsed. Thus, from time t1 to time t2 at which the reference period has elapsed, the correction amounts of the main ignition timing tm and the ignition phase difference dt are set to values ​​greater than zero. During this period, the correction amount (advance amount) of the main ignition timing tm is gradually decreased, and the correction amount (increase amount) of the ignition phase difference dt is also gradually decreased accordingly. Here, the reference period is set to be approximately the same as the period from the start of strong acceleration until the air-fuel ratio returns to the stoichiometric air-fuel ratio, and in the example of Fig. 12, the correction amount (advance amount) of the main ignition timing tm and the correction amount (increase amount) of the ignition phase difference dt become zero at almost the same time as the shortage amount of the air-fuel ratio becomes almost zero at time t2.

[0085] Also, as shown by the thick line, during rapid acceleration, immediately after the start of acceleration, the air-fuel ratio becomes lower than the theoretical air-fuel ratio, and the air-fuel ratio deficiency becomes a value greater than 0. During rapid acceleration, this deficiency becomes particularly large, and is greater than that during intermediate acceleration. As described above, at the start of rapid acceleration, the determinations of steps S4, S5, and S6 are YES, and step S8 is executed. That is, the auxiliary ignition timing ts is corrected to the retard side, and the main ignition timing tm is corrected to the advance side. As a result, as shown by the thick line in FIG. 12, during rapid acceleration, immediately after time t1, the correction amount (advance amount) of the main ignition timing tm and the correction amount (retard amount) of the auxiliary ignition timing ts are increased, and the correction amount of the ignition phase difference dt is significantly increased. During rapid acceleration, the correction amount (advance amount) of the main ignition timing tm, the correction amount (retard amount) of the sub ignition timing ts, and the correction amount (increase amount) of the ignition phase difference dt are gradually decreased from time t1, and these correction amounts are set to zero at time t2, which is a reference period after time t1.

[0086] (effect, etc.) As described above, in the engine system 1 of the above embodiment, in the second zone A2, ignition is performed by the main ignition plug 32, and then ignition is performed by the auxiliary ignition plug 62. Therefore, the air-fuel mixture is burned in the main combustion chamber 26 by ignition by the main ignition plug 32, and the resulting increase in pressure in the main combustion chamber 26 can be used to push the air-fuel mixture into the auxiliary combustion chamber 60. Therefore, the air-fuel mixture can be burned in both the main combustion chamber 26 and the auxiliary combustion chamber 60, improving fuel efficiency and exhaust gas performance.

[0087] Moreover, during strong acceleration where the air-fuel ratio in the second region A2 is insufficient (substantially insufficient) with respect to the target value (theoretical air-fuel ratio) and where it is difficult to introduce a sufficient amount of mixture into the auxiliary combustion chamber 60 and acceleration performance may decrease, the ignition phase difference dt is increased and the period during which the mixture is introduced into the auxiliary combustion chamber 60 is lengthened. Therefore, according to the engine system 1 of the above embodiment, appropriate combustion of the mixture in the auxiliary combustion chamber 60 can be achieved. Then, a flame is ejected from the auxiliary combustion chamber 60 into the main combustion chamber 26 to promote combustion in the main combustion chamber (to achieve appropriate combustion in the main combustion chamber), thereby increasing the engine torque and improving acceleration performance.

[0088] During slow acceleration when the air-fuel ratio is not short (substantially not short) of the target value (theoretical air-fuel ratio) and the amount of mixture in the auxiliary combustion chamber 60 is secured, the increasing correction of the ignition phase difference dt is stopped. Therefore, during slow acceleration, the acceleration performance is improved while combustion in the auxiliary combustion chamber 60 is started relatively early after combustion in the main combustion chamber 26, thereby shortening the combustion period and improving fuel efficiency more reliably.

[0089] In addition, in the above embodiment, a determination is made as to whether or not strong acceleration is occurring (whether or not the air-fuel ratio deficiency condition is met) for correcting the ignition timing and the ignition phase difference dt based on the rate of change of the accelerator opening, and this determination can be made easily.

[0090] In the above embodiment, the main ignition timing tm is corrected to the advance side during strong acceleration. Therefore, in addition to the effect of increasing engine torque by lengthening the ignition phase difference dt, the effect of increasing engine torque by advancing the ignition timing can be obtained, and acceleration can be reliably improved.

[0091] In the above embodiment, during strong acceleration, especially during rapid acceleration when the rate of change of the accelerator opening is high and the air-fuel ratio deficiency is large, the sub-ignition timing ts is retarded in addition to the advance correction of the main ignition timing tm. Therefore, when the air-fuel ratio deficiency is particularly large and it becomes more difficult to introduce air into the sub-combustion chamber 60, the ignition phase difference dt can be reliably lengthened to ensure the amount of mixture in the sub-combustion chamber 60. Therefore, acceleration can be reliably improved.

[0092] (Modification) In the above embodiment, the determination of whether the vehicle is in slow acceleration or strong acceleration, and the determination of whether the vehicle is in intermediate acceleration or strong acceleration, are performed based on the rate of change in the accelerator opening, but the parameters used for these determinations are not limited to the accelerator opening. For example, the above determinations may be performed based on the detection results of the airflow sensor SN1 or the detection results of a sensor provided in the exhaust passage 6 that can detect the air-fuel ratio.

[0093] In the above embodiment, the ignition timing correction is started with the start of strong acceleration, and then the correction is terminated when a reference period has elapsed. However, the timing for terminating the ignition timing correction is not limited to this. For example, the correction may be terminated when it is determined that the air-fuel ratio of the main combustion chamber 26 is insufficient with respect to the target value based on the detection result of a sensor such as the air flow sensor SN1, becoming equal to or less than a predetermined value. In the above embodiment, the ignition timing correction is started, and then the correction amount of the ignition timing is gradually reduced over time. However, the correction amount after the ignition timing correction is started may be set based on the air-fuel ratio insufficiency.

[0094] In the above embodiment, the air-fuel ratio deficiency condition is determined to be satisfied when the amount of air-fuel ratio deficiency is equal to or greater than a first amount of deficiency that is greater than 0, and the ignition timing and the ignition phase difference dt are corrected. However, the air-fuel ratio deficiency condition may be determined to be satisfied when the amount of air-fuel ratio deficiency is greater than 0. In other words, the first amount of deficiency may be set to 0.

[0095] In the above embodiment, the target value of the air-fuel ratio in the main combustion chamber 26 of the second region A2 is the stoichiometric air-fuel ratio, but this target value is not limited to the stoichiometric air-fuel ratio.

[0096] Furthermore, the specific shape and dimensions of the cover member 64 of the sub-ignition unit 30 are not limited to those described above. Furthermore, the number and dimensions of the communication holes 66 provided in the cover member 64 are not limited to those described above. Furthermore, the attachment position of the sub-ignition unit 30 is not limited to those described above. For example, the sub-ignition unit 30 may be provided on the exhaust port 12 side with respect to the tip portion 28x of the injector 28.

[0097] Further, the detailed structure of the engine body 2, such as the number of cylinders, is not limited to the above. [Explanation of symbols]

[0098] 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) 36 Throttle valve (air-fuel ratio change device) 52 Cylinder block 54 Cylinder head 60 Antechamber 62 Auxiliary spark plug (auxiliary ignition device) 64 Cover material (partition wall) 66 Communication hole 70 Accelerator pedal 100 ECU (control unit)

Claims

1. In an engine system mounted on a vehicle, A cylinder block and a cylinder head which form a cylinder; A piston accommodated in the cylinder so as to be capable of reciprocating motion; a main combustion chamber defined by the cylinder block, the cylinder head, and the piston; an auxiliary chamber separated from the main combustion chamber by a partition wall and communicating with the main combustion chamber through a communication hole formed in the partition wall; a fuel injection device that injects fuel into the main combustion chamber; a main ignition device that ignites the air-fuel mixture in the main combustion chamber; an auxiliary ignition device that ignites the air-fuel mixture in the auxiliary chamber; a control device electrically connected to the fuel injection device, the main ignition device, and the auxiliary ignition device to output control electrical signals to each of the devices, The control device includes: controlling the main ignition device and the auxiliary ignition device so that, in a predetermined region, 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; setting a target value of the air-fuel ratio of the main combustion chamber in the predetermined region to a constant value; determining that an air-fuel ratio deficiency condition is established, that is, the air-fuel ratio in the main combustion chamber is insufficient with respect to the constant target value, when a rate of change in an accelerator pedal opening provided on the vehicle is equal to or greater than a predetermined reference rate of change during acceleration of the vehicle in the predetermined range; an ignition phase difference, which is an amount of retardation of the auxiliary ignition timing relative to the main ignition timing, is increased when the air-fuel ratio deficiency condition is satisfied during acceleration of the vehicle in the predetermined range.

2. 2. The engine system according to claim 1, The control device is configured to increase a correction amount of the ignition phase difference as an amount of deficiency of the air-fuel ratio of the main combustion chamber from a target value increases when the air-fuel ratio deficiency condition is satisfied.

3. 3. The engine system according to claim 1, The control device corrects the main ignition timing to an advance side when the air-fuel ratio deficiency condition is established.

4. 4. The engine system according to claim 3, the control device corrects the auxiliary ignition timing to a retarded side when the air-fuel ratio in the main combustion chamber is in deficit with respect to a target value of the air-fuel ratio by a predetermined value or more when the air-fuel ratio deficiency condition is established.

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