Engine System

Abstract

To suppress a combustion fluctuation by estimating a flow condition in a cylinder to perform fuel injection according to a flow condition.SOLUTION: An engine system includes an auxiliary ignition control part 84 for controlling an ignition device 7 so as to perform auxiliary ignition as subsidiary ignition on the advance side compared to a timing for igniting air-fuel mixture with main ignition when an estimated flow rate estimated on the basis of a parameter for a discharge path formed by inspected ignition is lower than a first set value Vp1 or higher than a second set value Vp2 higher than the first set value Vp1. The first set value Vp1 and the second set value Vp2 are each located on the side where the estimated flow rate is higher as an engine speed detected by an operating condition detector (a crank angle sensor SW6) is higher.SELECTED DRAWING: Figure 16

Description

[Technical field]

[0001] The technology disclosed herein belongs to the technical field of engine systems. [Background technology]

[0002] It has been known that the combustion speed can be increased to improve the fuel efficiency of an engine. In an engine equipped with a spark plug, the spark plug ignites the mixture in the combustion chamber, generating a flame around the spark plug, which then propagates throughout the cylinder while reacting with the unburned mixture, completing one cycle of combustion. Therefore, in order to quickly react the unburned mixture with the flame and increase the combustion speed, it is advantageous to have a large flame contact area between the flame and the unburned mixture. For this reason, it is preferable to generate a lot of turbulence in the cylinder.

[0003] It is known that turbulence of the unburned mixture is generated by the collapse of the intake flow before the piston reaches the top dead center during the compression stroke. However, the state of the intake flow can change from cycle to cycle. For this reason, methods for estimating the intake flow have been studied.

[0004] For example, Patent Document 1 describes a technology in which an ignition plug disposed in a combustion chamber is ignited multiple times prior to the ignition timing, the current value in the discharge path of the ignition plug is detected, the flow state of the mixture is estimated according to each current value, and the ignition timing is controlled based on the estimated result. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2014-145306 A Summary of the Invention [Problem to be solved by the invention]

[0006] Here, the inventors of the present application conducted extensive research into improving combustion in accordance with the intake flow based on the current value of the discharge path as described in Patent Document 1, and found that, depending on the position of the vortex center formed in the cylinder by the intake flow, differences in the flow conditions in the cylinder in the latter half of the compression stroke occur, and the flame no longer propagates evenly throughout the cylinder, becoming a factor in combustion fluctuations.

[0007] Specifically, the intake air flow is a combination of vertical and horizontal vortex components, forming an oblique flow in the cylinder. When the intake air flow vortex center is located near the center of the cylinder as viewed from the cylinder axis direction and the direction perpendicular to the cylinder axis (hereinafter referred to as the plan view and side view, respectively), the swirling flow is maintained even in the latter half of the compression stroke, and the degree of turbulence becomes uniform or approximately uniform throughout the cylinder. In this case, the flame propagates evenly or approximately uniformly from near the center to the periphery of the cylinder.

[0008] However, the inventors of the present application found that when the position of the vortex center of the longitudinal vortex component is shifted toward the piston in a side view, the vortex center comes into contact with the top surface of the piston in the latter half of the compression stroke, crushing the lower half of the longitudinal vortex, and the flow inside the cylinder becomes a regular unidirectional flow from the intake side to the exhaust side. When the flow inside the cylinder becomes a regular unidirectional flow, the degree of turbulence is strong in the exhaust side area of ​​the cylinder, but the degree of turbulence is weak in the intake side area. In this case, the flame easily propagates to the exhaust side area, but it is difficult to propagate to the intake side area.

[0009] Furthermore, if the position of the vortex center of the longitudinal vortex component is shifted toward the ceiling of the cylinder in a side view, the vortex center comes into contact with the ceiling in the latter half of the compression stroke, crushing the upper half of the longitudinal vortex, and the flow inside the cylinder becomes a non-unidirectional flow from the exhaust side to the intake side. When the flow inside the cylinder becomes a non-unidirectional flow, the intake side area inside the cylinder is highly turbulent, but the exhaust side area is less turbulent. In this case, the flame easily propagates to the intake side area, but it is difficult to propagate to the exhaust side area.

[0010] On the other hand, the inventors of the present application have discovered that when the position of the vortex center of the lateral vortex component is shifted toward the outside of the cylinder when viewed in a plane, part of the flame attempting to propagate from the center of the cylinder toward the periphery is hindered by the flow of the lateral vortex shifted from the center of the cylinder, making it difficult for the flame to propagate to a specific area.

[0011] The inhibition of flame propagation to a certain region in the cylinder reduces the combustion speed and causes combustion fluctuation. Therefore, in order to suppress the combustion fluctuation of the engine, it is necessary to promote flame propagation to this certain region. Suppressing the combustion fluctuation of the engine is advantageous for improving the fuel efficiency of the engine.

[0012] The technology disclosed herein has been developed in consideration of these points, and its purpose is to suppress combustion fluctuations by estimating the flow conditions within a cylinder and performing auxiliary ignition in accordance with the flow conditions. [Means for solving the problem]

[0013] As a result of extensive research, the inventors of the present application have discovered that by detecting the electrical parameters of the discharge path of the spark plug during the intake stroke or compression stroke, it is possible to estimate the position of the vortex center within the cylinder, and thereby to estimate the intake flow and degree of turbulence in the latter half of the compression stroke.

[0014] Therefore, the technology disclosed herein targets an engine system including an engine having a cylinder with a pent roof type ceiling, an ignition device including an ignition plug arranged in the center of the cylinder, and a fuel injection valve arranged in the center of the cylinder, and further includes an operating state detector that detects the operating state of the engine, and a controller electrically connected to the ignition device, the fuel injection valve, and the operating state detector, wherein the controller sets an injection amount of main fuel and a main fuel injection timing which is the injection timing based on the engine load detected by the operating state detector, and controls the fuel injection valve to inject the main fuel in the amount set at the main fuel injection timing, and controls the spark plug when the mixture is not ignited. a flow velocity estimation unit that controls the ignition device to apply a voltage between the electrodes and detect a parameter related to a current value of a discharge path generated between the electrodes, and estimates the level of the flow velocity of the intake air in the cylinder from the parameter; and an auxiliary ignition control unit that executes auxiliary ignition by controlling the ignition device on the advance side of a timing at which the air-fuel mixture is ignited by main ignition when the estimated flow velocity estimated by the flow velocity estimation unit is less than a predetermined first set value or higher than a second set value higher than the first set value, and imparts energy by ignition into the cylinder, wherein the first set value and the second set value are positioned on the side of the higher estimated flow velocity as the engine speed detected by the operating state detector is higher.

[0015] In this specification, for convenience, the positive unidirectional flow indicates the intake flow from the intake side to the exhaust side, and the anti-unidirectional flow indicates the intake flow from the exhaust side to the intake side, but these may be reversed.

[0016] According to the above-mentioned configuration, since the engine has a combustion chamber with a pent roof type ceiling, the intake air introduced into the cylinder forms a vertical vortex as well as a horizontal vortex, and the flow inside the cylinder becomes an oblique flow inclined with respect to the cylinder axis.

[0017] When main fuel injection is performed from the fuel injector, an air-fuel mixture is formed inside the cylinder. When this mixture does not ignite, a voltage is applied to the spark plug to create a discharge path (test discharge). The stronger the intake air flow around the spark plug, the longer the discharge path created in the spark plug becomes. When the discharge path is extended, the resistance between the electrodes increases, and the voltage drop between the electrodes increases. As a result, the time it takes for the energy applied to the spark plug to be consumed, i.e. the discharge time, becomes shorter.

[0018] From this, the inventors of the present application discovered that by detecting the discharge time of the current, it is possible to estimate the flow velocity of the intake air flow around the spark plug, and to estimate the position of the vortex center in the cylinder based on the estimated flow velocity. Note that the "estimated flow velocity" estimated from the parameters need only be a value that allows the high or low flow velocity to be estimated, and does not have to be the flow velocity value itself.

[0019] For example, the reciprocal of the discharge time can be used as the “estimated flow velocity.” In addition to the discharge time, a current value, a voltage value, a gradient of the current value during discharge, a gradient of the voltage value during discharge, etc. may be used as a parameter for estimating the flow velocity, as long as the high or low of the flow velocity can be estimated.

[0020] Specifically, when the center of the vertical vortex of the intake flow is located near the center of the cylinder, the strength of the intake flow near the spark plug becomes medium, and the estimated flow speed estimated from the parameters falls within the range from the first set value to the second set value. When the center of the vertical vortex shifts toward the ceiling of the cylinder, the strength of the intake flow near the spark plug becomes weak, and the estimated flow speed becomes less than the first set value.

[0021] When the center of the vertical vortex shifts toward the piston, the strength of the intake air flow near the spark plug increases, and the estimated flow velocity becomes higher than the second set value. Therefore, by comparing whether the estimated flow velocity is higher than the first set value or lower than the second set value, it is possible to estimate whether the intake air flow is unidirectional or anti-unidirectional before the mixture in the cylinder is ignited, and to estimate the area with weak turbulence.

[0022] When the center of the lateral vortex of the intake flow is located near the center of the cylinder, the strength of the intake flow near the spark plug becomes moderate, and the estimated flow speed falls within the range from the first set value to the second set value. When the center of the lateral vortex is displaced from the center of the cylinder, the strength of the intake flow near the spark plug becomes weak, and the estimated flow speed becomes lower than the first set value, or the strength of the intake flow near the spark plug becomes strong, and the estimated flow speed becomes higher than the second set value. Therefore, by comparing whether the estimated flow speed is lower than the first set value or higher than the second set value, it is possible to estimate the region where flame propagation is hindered before the mixture in the cylinder is ignited.

[0023] If the estimated flow velocity is determined to be less than the first set value or higher than the second set value, in other words, if the longitudinal vortex is estimated to be flowing in one direction or the opposite direction, or if the transverse vortex is estimated to be deviating from the center of the vortex, auxiliary ignition is performed on the advanced side of the timing of igniting the mixture by main ignition. The auxiliary ignition forms a mixture with a lot of plasma in an area with a weak degree of turbulence or an area where the flame does not easily propagate.

[0024] As a result, in the latter half of the compression stroke, a normal mixture can be placed in the area where the flame propagates, and a relatively high temperature mixture can be placed in the area where the flame does not propagate easily. After this auxiliary ignition, the ignition device uses a spark plug to perform main ignition of the mixture, which promotes flame propagation to the area where the flame does not propagate easily, and the flame propagates evenly or approximately evenly throughout the cylinder. As a result, the combustion speed in the area where the flame does not propagate easily is increased. By performing auxiliary ignition if necessary in each cycle, the combustion speed for each cycle becomes constant or approximately constant, and combustion fluctuations can be suppressed.

[0025] Furthermore, in this configuration, the first and second set values ​​are set to be on the side of the higher estimated flow velocity as the engine speed increases. When the engine speed is high, the intake air flow is compressed while the inertia force is large. Therefore, even if the center of the vortex is located near the cylinder axis, the flow velocity of the intake air during the inspection discharge is higher when the engine speed is high than when the engine speed is low.

[0026] Therefore, by appropriately changing the setting value for executing auxiliary ignition according to the engine speed, it is possible to appropriately promote combustion. As a result, it is possible to stabilize the combustion speed and suppress combustion fluctuations.

[0027] In the engine system, the auxiliary ignition control unit may be configured to increase the energy of the auxiliary ignition when the estimated flow velocity is less than a third set value set in a region lower than the first set value, compared to when the estimated flow velocity is higher than the third set value and less than the first set value, and the third set value may be positioned on the lower engine speed side as the estimated flow velocity is lower.

[0028] That is, when the engine speed is high, the time from the intake stroke to the compression stroke is short, so the inertial force of the intake flow is large even during the compression stroke. When the inertial force of the intake flow is large, the mixture is more likely to be pressed against the cylinder wall. In other words, when the engine speed is high, the mixture is more biased at the time of ignition than when the engine speed is low. The further the estimated flow speed is from the first set value to the low side, the stronger the anti-unidirectional flow is formed, so the greater the effect of the engine speed.

[0029] Therefore, when the estimated flow velocity is less than the third set value, the auxiliary ignition energy is increased. Also, the third set value is set to a position on the side where the estimated flow velocity is higher as the engine speed increases, expanding the conditions for increasing the auxiliary ignition energy as the engine speed increases. This makes it easier for the flame to propagate throughout the cylinder, stabilizing the combustion speed. As a result, the combustion fluctuation can be more effectively suppressed.

[0030] In the engine system, the auxiliary ignition control unit may be configured to increase the energy of the auxiliary ignition when the estimated flow velocity is higher than a fourth set value set in a range higher than the second set value, compared to when the estimated flow velocity is lower than the fourth set value and higher than the second set value, and the fourth set value may be positioned on the lower side of the estimated flow velocity as the engine speed increases.

[0031] As mentioned above, when the engine speed is high, the inertia force of the intake air flow is large even during the compression stroke, so the air-fuel mixture becomes more biased at the time of ignition. Also, as the estimated flow velocity moves higher from the second set value, the more the vertical vortex forms a positive unidirectional flow and the more the vortex center becomes biased in the horizontal vortex, so the effect of the engine speed becomes greater.

[0032] Therefore, when the estimated flow velocity is higher than the fourth set value, the auxiliary ignition energy is increased. Also, the fourth set value is set to a lower side of the estimated flow velocity as the engine speed increases, expanding the conditions for increasing the auxiliary ignition energy as the engine speed increases. This makes it easier for the flame to propagate throughout the cylinder, stabilizing the combustion speed. As a result, the combustion fluctuation can be more effectively suppressed. Effect of the Invention

[0033] As described above, according to the technology disclosed herein, the combustion speed of the engine can be stabilized by executing auxiliary ignition in accordance with the engine speed, thereby suppressing fluctuations in engine combustion. [Brief description of the drawings]

[0034] [Figure 1] FIG. 1 is a diagram illustrating an engine system. [Diagram 2] The upper diagram in FIG. 2 is a plan view illustrating the structure of a combustion chamber of an engine, and the lower diagram is a cross-sectional view taken along line II-II of the upper diagram. [Diagram 3] FIG. 3 is a block diagram of the engine system. [Figure 4] FIG. 4 is a diagram illustrating an ignition device. [Diagram 5] FIG. 5 is a block diagram showing functional blocks relating to engine control. [Figure 6] FIG. 6 is a diagram for explaining the relationship between the center position of the vertical vortex and the flow state inside the cylinder in the latter half of the compression stroke. [Figure 7] FIG. 7 is a diagram illustrating the change in voltage and current between the electrodes of a spark plug when the strength of the flow near the spark plug is different. [Figure 8] FIG. 8 is a diagram showing the relationship between the discharge time detected by the spark plug and the center position of the vertical vortex. [Figure 9] FIG. 9 is a diagram for explaining the relationship between the central position of the lateral vortex and the propagation state of the flame inside the cylinder. [Figure 10] FIG. 10 is a diagram showing the relationship between the discharge time detected by the spark plug and the central position of the lateral vortex. [Figure 11] FIG. 11 is a timing chart illustrating the injection timing of the main fuel injection, the timing of the inspection discharge, the timing of the auxiliary ignition, and the timing of the main ignition. [Figure 12] FIG. 12 is a schematic diagram showing how plasma is generated by auxiliary ignition of an ignition plug. [Figure 13] FIG. 13 is a diagram for explaining the change in flow and the plasma distribution inside the cylinder when the center position of the longitudinal vortex is close to the piston. [Figure 14] FIG. 14 is a diagram for explaining the change in flow and plasma distribution inside the cylinder when the center position of the vertical vortex is close to the ceiling. [Figure 15] FIG. 15 is a diagram for explaining the change in flow and plasma distribution within the cylinder when the central position of the transverse vortex is inclined toward the exhaust side and when the central position of the transverse vortex is inclined toward the intake side. [Figure 16] FIG. 16 is a map for setting the auxiliary ignition period formed by the estimated flow speed and the engine load. [Figure 17]FIG. 17 is a graph showing the relationship between the estimated flow velocity and the auxiliary ignition period when the engine load is constant. [Figure 18] FIG. 18 is a graph showing the relationship between the auxiliary ignition period and engine load when the estimated flow velocity is constant. [Figure 19] FIG. 19 is a timing chart showing the timing of auxiliary ignition for each engine speed. [Figure 20] FIG. 20 is a part of a flowchart of the auxiliary ignition control. [Figure 21] FIG. 21 shows the remainder of the flow chart of the auxiliary ignition control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Hereinafter, an embodiment of an engine system will be described with reference to the drawings. The engine and engine system described here are merely examples.

[0036] Fig. 1 is a diagram illustrating an engine system. Fig. 2 is a diagram illustrating a structure of a combustion chamber of an engine. The positions of the intake side and the exhaust side in Fig. 1 are interchanged with the positions of the intake side and the exhaust side in Fig. 2. Fig. 3 is a block diagram illustrating a control device of the engine.

[0037] The engine system has an engine 1. The engine 1 has a cylinder 11. An intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke are repeated in the cylinder 11. The engine 1 is a four-stroke engine. The engine 1 is mounted on a four-wheeled automobile. The automobile runs when the engine 1 is operated. The fuel for the engine 1 is gasoline in this configuration example.

[0038] (Engine configuration) The engine 1 includes a cylinder block 12 and a cylinder head 13. The cylinder head 13 is placed on top of the cylinder block 12. A plurality of cylinders 11 are formed in the cylinder block 12. The engine 1 is a multi-cylinder engine. Only one cylinder 11 is shown in FIG. 1.

[0039] A piston 3 is inserted into each cylinder 11. The piston 3 is connected to a crankshaft 15 via a connecting rod 14. The piston 3 reciprocates inside the cylinder 11. The piston 3, the cylinder 11, and the cylinder head 13 form a combustion chamber 17.

[0040] The lower surface of the cylinder head 13, i.e., the ceiling of the cylinder 11, is composed of an inclined surface 1311 and an inclined surface 1312, as shown in the lower diagram of Fig. 2. The inclined surface 1311 is an inclined surface 1311 on the side of the intake valve 21, which will be described later, and has an upward gradient toward the center of the cylinder 11. The inclined surface 1312 is an inclined surface 1312 on the side of the exhaust valve 22, and has an upward gradient toward the center of the cylinder 11. The ceiling of the cylinder 11 is a so-called pent roof type.

[0041] An intake port 18 is formed in the cylinder head 13 for each cylinder 11. The intake port 18 is connected to the inside of the cylinder 11. Although detailed illustration is omitted, the intake port 18 is a so-called tumble port. In other words, the intake port 18 has a shape that generates a tumble flow inside the cylinder 11. The ceiling of the pent roof type cylinder 11 and the tumble port generate a vertical vortex inside the cylinder 11.

[0042] An intake valve 21 is disposed in the intake port 18. The intake valve 21 opens and closes the intake port 18. The valve mechanism opens and closes the intake valve 21 at a predetermined timing. The valve mechanism may be a variable valve mechanism that makes the valve timing and / or the valve lift variable. As shown in FIG. 3, the valve mechanism has an intake S-VT (Sequential-Valve Timing) 23. The intake S-VT 23 continuously changes the rotational phase of the intake camshaft within a predetermined angle range. The opening angle of the intake valve 21 does not change. The intake S-VT 23 is of an electric or hydraulic type.

[0043] An exhaust port 19 is formed in the cylinder head 13 for each cylinder 11. The exhaust port 19 communicates with the combustion chamber 17.

[0044] An exhaust valve 22 is disposed in the exhaust port 19. The exhaust valve 22 opens and closes the exhaust port 19. The valve mechanism opens and closes the exhaust valve 22 at a predetermined timing. The valve mechanism may be a variable valve mechanism that makes the valve timing and / or the valve lift variable. As shown in FIG. 3, the valve mechanism has an exhaust S-VT 24. The exhaust S-VT 24 continuously changes the rotational phase of the exhaust camshaft within a predetermined angle range. The opening angle of the exhaust valve 22 does not change. The exhaust S-VT 24 is of an electric or hydraulic type.

[0045] An injector 6 is attached to the cylinder head 13 for each cylinder 11. The injector 6 directly injects fuel into the cylinder 11. The injector 6 is an example of a fuel injection valve. The injector 6 is disposed in a valley of the pent roof where the inclined surface 1311 and the inclined surface 1312 intersect. As shown in FIG. 2, the injector 6 is disposed in the center of the cylinder 11.

[0046] Although detailed illustration is omitted, the injector 6 is a multi-hole type injector having multiple holes. As indicated by the two-dot chain line in Fig. 2, the injector 6 injects fuel in a radial pattern from the center of the cylinder 11 toward the periphery. In the illustrated example, the injector 6 has ten nozzle holes arranged at equal angles in the circumferential direction, but the number and arrangement of the nozzle holes are not particularly limited.

[0047] A fuel supply system 61 is connected to the injector 6. The fuel supply system 61 includes a fuel tank 63 configured to store fuel, and a fuel supply passage 62 connecting the fuel tank 63 and the injector 6 to each other. A fuel pump 65 and a common rail 64 are interposed in the fuel supply passage 62. The fuel pump 65 pressure-feeds fuel to the common rail 64. In this configuration example, the fuel pump 65 is a plunger-type pump driven by the crankshaft 15. The common rail 64 stores the fuel pressure-feed from the fuel pump 65 at a high fuel pressure. When the injector 6 opens, the fuel stored in the common rail 64 is injected into the cylinder 11 from the nozzle of the injector 6. The pressure of the fuel supplied to the injector 6 may be changed according to the operating state of the engine 1. The configuration of the fuel supply system 61 is not limited to the above configuration.

[0048] An ignition plug 25 is attached to the cylinder head 13 for each cylinder 11. The spark plug 25 forcibly ignites the air-fuel mixture inside the cylinder 11. The center electrode and ground electrode of the spark plug 25 are located near the ceiling of the cylinder 11 in the center of the cylinder 11, although detailed illustration is omitted.

[0049] As shown in FIG. 1 or 3, the spark plug 25 is electrically connected to the ignition device 7. The ignition device 7 applies a voltage between the electrodes of the spark plug 25 to cause a discharge and ignite the air-fuel mixture in the cylinder 11. The ignition device 7, which will be described in detail later, causes the spark plug 25 to discharge when the air-fuel mixture is not yet ignited, and detects a parameter related to the current value of the discharge path generated between the electrodes at that time. The flow state in the cylinder 11 can be estimated based on the detected parameter. The configuration of the ignition device 7 will be described later.

[0050] An intake passage 40 is connected to one side of the engine 1. The intake passage 40 is connected to the intake ports 18 of each cylinder 11. The intake air to be introduced into the cylinders 11 flows through the intake passage 40. An air cleaner 41 is disposed at the upstream end of the intake passage 40. The air cleaner 41 filters the intake air. A surge tank 42 is disposed near the downstream end of the intake passage 40. The intake passage 40 downstream of the surge tank 42 constitutes an independent passage that branches off for each cylinder 11. The downstream end of the independent passage is connected to the intake port 18 of each cylinder 11.

[0051] A throttle valve 43 is disposed between the air cleaner 41 and the surge tank 42 in the intake passage 40. The throttle valve 43 adjusts the amount of fresh air introduced into the cylinder 11 by adjusting the opening degree of the valve.

[0052] The engine 1 has a swirl generating section that generates a swirl flow inside the cylinder 11. Although detailed illustration is omitted, the swirl generating section has a swirl control valve 56 attached to the intake passage 40. The swirl control valve 56 is disposed in the second intake passage of the first intake passage and the second intake passage that are parallel to each other. The swirl control valve 56 is an opening adjustment valve that can narrow the cross section of the second intake passage.

[0053] When the opening of the swirl control valve 56 is small, the intake air flow rate flowing into the cylinder 11 from the first intake port 21a shown in FIG. 2 is relatively large and the intake air flow rate flowing into the cylinder 11 from the second intake port 21b is relatively small, so the swirl flow in the cylinder 11 becomes strong. When the opening of the swirl control valve 56 is large, the intake air flow rates flowing into the cylinder 11 from the first intake port 21a and the second intake port 21b become approximately equal, so the swirl flow in the cylinder 11 becomes weak. When the swirl control valve 56 is fully open, no swirl flow is generated. The swirl flow circulates in the counterclockwise direction in FIG. 2, as shown by the white arrow in FIG. 2.

[0054] An exhaust passage 50 is connected to the other side of the engine 1. The exhaust passage 50 communicates with the exhaust ports 19 of each cylinder 11. The exhaust passage 50 is a passage through which exhaust gas discharged from the cylinder 11 flows. Although not shown in detail, the upstream portion of the exhaust passage 50 constitutes an independent passage that branches off for each cylinder 11. The upstream end of the independent passage is connected to the exhaust port 19 of each cylinder 11.

[0055] An exhaust gas purification system having a plurality of catalytic converters is disposed in the exhaust passage 50. The upstream catalytic converter has, for example, a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512. The downstream catalytic converter has a three-way catalyst 513. The exhaust gas purification system is not limited to the configuration shown in the figure. For example, the GPF may be omitted. Furthermore, the catalytic converter is not limited to one having a three-way catalyst. Furthermore, the order of the three-way catalyst and the GPF may be changed as appropriate.

[0056] An EGR passage 52 constituting an external EGR system is connected between the intake passage 40 and the exhaust passage 50. The EGR passage 52 is a passage for recirculating a part of the exhaust gas to the intake passage 40. An upstream end of the EGR passage 52 is connected between the upstream catalytic converter and the downstream catalytic converter in the exhaust passage 50. A downstream end of the EGR passage 52 is connected to a downstream portion of the throttle valve 43 in the intake passage 40.

[0057] A water-cooled EGR cooler 53 is disposed in the EGR passage 52. The EGR cooler 53 cools the exhaust gas. An EGR valve 54 is also disposed in the EGR passage 52. The EGR valve 54 adjusts the flow rate of the exhaust gas flowing through the EGR passage 52. By adjusting the opening of the EGR valve 54, the amount of recirculated cooled exhaust gas can be adjusted.

[0058] (Configuration of engine control device) 3, the control device for the engine 1 includes an ECU (Engine Control Unit) 10 for operating the engine 1. The ECU 10 is a controller based on a known microcomputer, and includes a central processing unit (CPU) 101 for executing programs, a memory 102 configured, for example, of a RAM (Random Access Memory) or a ROM (Read Only Memory) for storing programs and data, and an input / output bus 103 for inputting and outputting electrical signals. The ECU 10 is an example of a controller.

[0059] 1 and 3, various sensors SW1 to SW9 are connected to the ECU 10. The sensors SW1 to SW9 output signals to the ECU 10. The sensors include the following sensors.

[0060] The air flow sensor SW1 is disposed downstream of the air cleaner 41 in the intake passage 40 and measures the flow rate of fresh air flowing through the intake passage 40. The intake air temperature sensor SW2 is disposed downstream of the air cleaner 41 in the intake passage 40 and measures the temperature of fresh air flowing through the intake passage 40. The intake pressure sensor SW3 is attached to the surge tank 42 and measures the pressure of the intake air introduced into the cylinder 11. The cylinder pressure sensor SW4 is attached to the cylinder head 13 corresponding to each cylinder 11 and measures the pressure in each cylinder 11. The water temperature sensor SW5 is attached to the engine 1 and measures the temperature of the coolant. The crank angle sensor SW6 is attached to the engine 1 and measures the rotation angle of the crankshaft 15. The accelerator opening sensor SW7 is attached to the accelerator pedal mechanism and measures the accelerator opening corresponding to the amount of operation of the accelerator pedal. The intake cam angle sensor SW8 is attached to the engine 1 and measures the rotation angle of the intake camshaft. The exhaust cam angle sensor SW9 is attached to the engine 1 and measures the rotation angle of the exhaust camshaft.

[0061] The ECU 10 judges the operating state of the engine 1 based on the signals of these sensors SW1 to SW9, and calculates the control amount of each device according to a predetermined control logic. The control logic is stored in a memory 102. The control logic includes calculating a target amount and / or a control amount by using a map stored in the memory 102.

[0062] The ECU 100 outputs electrical signals related to the calculated control amounts to the injector 6, the spark plug 25, the intake S-VT 23, the exhaust S-VT 24, the fuel supply system 61, the throttle valve 43, the EGR valve 54, and the swirl control valve 56.

[0063] (Ignition device configuration) The ignition device 7 applies a voltage between the center electrode 251 and the ground electrode 252 of the spark plug 25, causing a discharge in the cylinder 11. The ignition device 7 has an ignition coil 70. The center electrode 251 is connected to a secondary coil 70c of the ignition coil 70. The ground electrode 252 is grounded. When the secondary voltage applied between the electrodes by the secondary coil 70c reaches a voltage required for dielectric breakdown, a discharge occurs in the gap between the center electrode 251 and the ground electrode 252.

[0064] The ignition coil 70 has a primary coil 70a, a secondary coil 70c, and an iron core 70b. One end of the primary coil 70a is connected to the capacitor 72, and the other end is connected to the collector of the transistor 73. As described above, one end of the secondary coil 70c is connected to the center electrode 251, and the other end is connected to the ignition controller 75. The ignition controller 75 can measure the secondary voltage that the secondary coil 70c applies between the electrodes of the spark plug 25, and the secondary current that flows from the secondary coil 70c to the spark plug 25.

[0065] The ignition device 7 also includes a capacitor 72 that stores electric energy to pass a primary current through the primary coil 70a of the ignition coil 70, an energy generator 74 that charges the capacitor 72, and a transistor 73 that switches the primary current of the ignition coil 70 on and off. The energy generator 74 includes a power source. An ignition controller 75 controls the energy generator 74 and the transistor 73 to ignite the air-fuel mixture in the cylinder 11 (main ignition) using the spark plug 25 at a predetermined timing.

[0066] As described above, the ignition device 7 causes the spark plug 25 to discharge when the air-fuel mixture is not yet ignited, and estimates the flow state within the cylinder 11 based on the electrical parameters detected at that time.

[0067] (Engine operation control) Next, an explanation will be given of the operation control of the engine 1 by the ECU 10. In order to improve fuel efficiency, the engine 1 increases the combustion speed by generating turbulence in the cylinder 11. Specifically, the engine 1 has an intake port 18 which is a tumble port, and vertical vortices are generated in the cylinder 11.

[0068] Here, the state of the intake air flow may change every cycle, and when the state of the intake air flow in the cylinder 11 changes, the combustion speed changes every cycle, resulting in combustion fluctuations. The engine system disclosed herein suppresses the change in combustion speed every cycle, thereby suppressing combustion fluctuations.

[0069] Specifically, this engine system estimates the state of the intake air flow in the cylinder 11, and executes auxiliary ignition according to the estimated state of the intake air flow to impart ignition energy into the cylinder 11.

[0070] FIG. 5 is a block diagram illustrating the configuration of a control device for the engine 1 that executes suppression control of combustion variation. FIG. 5 illustrates functional blocks of the ECU 10. The ECU 10 has, as functional blocks, a main fuel injection unit 81, a main ignition control unit 82, a flow velocity estimation unit 83, and an auxiliary ignition control unit 84. The main fuel injection unit 81 is a functional block that sets the injection amount and injection timing of the main fuel injection, which is the timing of the main fuel injection, based on the required torque (engine load) of the engine 1, and causes the injector 6 to perform the main fuel injection at the set injection timing. The main ignition control unit 82 is a functional block that causes ignition (i.e., main ignition) at a predetermined timing using the spark plug 25 so that the air-fuel mixture provided in the cylinder 11 is ignited after the main fuel injection.

[0071] The flow velocity estimation unit 83 is a functional block that causes the ignition plug 25 to discharge, i.e., execute an inspection discharge, at a timing when the air-fuel mixture is not ignited in order to inspect the flow state within the cylinder 11. The flow velocity estimation unit 83 is also a functional block that estimates the flow state within the cylinder 11, in particular the high or low flow velocity of the intake air around the spark plug 25, based on parameters detected using the ignition device 7 and the spark plug 25 during the inspection discharge. The auxiliary ignition control unit 84 is a functional block that executes auxiliary ignition as necessary, prior to main ignition, at a timing when the air-fuel mixture is not ignited, based on the flow state within the cylinder 11 estimated by the flow velocity estimation unit 83.

[0072] Hereinafter, the estimation of the state of the intake air flow in the cylinder 11, which is executed by the engine system illustrated in FIG. 5, will be described, and then the auxiliary ignition control according to the estimated state of the intake air flow will be described.

[0073] (Intake flow state estimation) Fig. 6 is a diagram showing the center position of the vertical vortex in the first half of the compression stroke and the flow state in the cylinder 11 in the second half of the compression stroke. Chart 601 in Fig. 6 illustrates the flow state in the cylinder 11 when the center position of the vertical vortex in the first half of the compression stroke is close to the piston 3 in the cylinder 11, and chart 604 illustrates the flow state in the cylinder 11 in the second half of the compression stroke when the crank angle has progressed from the state of chart 601.

[0074] Similarly, chart 602 illustrates the flow conditions within cylinder 11 when the center of the vertical vortex is located midway between piston 3 and the ceiling of cylinder 11 in the first half of the compression stroke, and chart 605 illustrates the flow conditions within cylinder 11 in the second half of the compression stroke when the crank angle has progressed from the state of chart 602.

[0075] Moreover, chart 603 illustrates an example of the flow state within cylinder 11 when the center of the vertical vortex is located near the ceiling of cylinder 11 in the first half of the compression stroke, and chart 606 illustrates an example of the flow state within cylinder 11 in the second half of the compression stroke when the crank angle has progressed from the state of chart 603.

[0076] In addition, the first half of the compression stroke refers to the first half when the compression stroke is divided into two halves, and the second half of the compression stroke refers to the second half when the compression stroke is divided into two halves.

[0077] First, when the center of the vertical vortex in the cylinder 11 is near the center of the cylinder 11 as shown in chart 602, the swirling flow is maintained even in the latter half of the compression stroke as shown in chart 605. As a result, the degree of turbulence becomes uniform or approximately uniform throughout the cylinder 11. In this case, the flame propagates uniformly or approximately uniformly from near the center to the periphery of the cylinder 11. Because the propagation of the flame is promoted by the turbulence in the cylinder 11, the combustion speed is relatively fast.

[0078] As shown in chart 601, when the center of the vertical vortex is shifted to the vicinity of the piston 3 side (here, the lower side of the cylinder 11), as shown in chart 604, the vortex center comes into contact with the top surface of the piston 3 in the latter half of the compression stroke, and the lower half of the vertical vortex is crushed. As a result, as shown by the arrow in chart 604, the flow in the cylinder 11 becomes a unidirectional flow from the intake valve 21 to the exhaust valve 22 (hereinafter, referred to as a positive unidirectional flow). When the flow in the cylinder 11 becomes a positive unidirectional flow, the degree of turbulence in the cylinder 11 becomes uneven. Specifically, the degree of turbulence in the region on the exhaust valve 22 side in the cylinder 11 is strong, but the degree of turbulence in the region on the intake valve 21 side is weak (see the region surrounded by the dashed line in the same figure). At this time, the flame generated by the ignition of the mixture in the center of the cylinder 11 easily propagates to the region on the exhaust valve 22 side, but does not easily propagate to the region on the intake valve 21 side. In the case of chart 604, the burning speed is slower than in the case of chart 605.

[0079] As shown in chart 603, when the position of the vortex center of the vertical vortex is shifted to the vicinity of the ceiling side (here, the upper side of the cylinder) in a side view, as shown in chart 606, the vortex center comes into contact with the ceiling of the cylinder 11 in the latter half of the compression stroke, and the upper half of the vertical vortex is crushed. As a result, as shown by the arrow in chart 606, the flow in the cylinder 11 becomes a unidirectional flow from the exhaust valve 22 to the intake valve 21 (hereinafter, referred to as a non-unidirectional flow). When the flow in the cylinder 11 becomes a non-unidirectional flow, the degree of turbulence in the cylinder 11 becomes uneven. Specifically, in the cylinder 11, the degree of turbulence in the region on the intake valve 21 side is strong, but the degree of turbulence in the region on the exhaust valve 22 side is weak (see the region surrounded by the dashed line in the same figure). In this case, the flame easily propagates to the region on the intake valve 21 side, but does not easily propagate to the region on the exhaust valve 22 side. In the case of chart 606, the burning speed is slower than in the case of chart 605.

[0080] In the engine system, the flow state in the cylinder 11 is detected by the ignition device 7. Specifically, the ignition device 7 performs a discharge (test discharge) in the cylinder 11 during a period when the air-fuel mixture is not ignited in response to a control signal from a flow rate estimation unit 83, and detects the discharge time at that time. The flow velocity estimation unit 83 estimates the flow velocity near the spark plug 25 based on the detected discharge time, and determines the center position of the vertical vortex based on the estimated flow velocity.

[0081] 7 illustrates an example of a time change 701 of the voltage between the electrodes of the spark plug 25 and a time change 702 of the current when the strength of the flow around the spark plug 25 is different. When a voltage is applied between the electrodes by imparting energy to the spark plug 25, a discharge path is formed between the center electrode 251 and the ground electrode 252. The stronger the flow around the spark plug 25, the more the discharge path is carried by the flow and extends. The extension of the discharge path increases the resistance between the electrodes, and promotes a drop in the voltage applied between the electrodes. The stronger the flow around the spark plug 25, the shorter the time it takes for the energy imparted to the spark plug 25 to be consumed, i.e., the discharge time.

[0082] More specifically, as shown by the solid line in Fig. 7, when there is no flow near the spark plug 25, the discharge time is long. The stronger the flow near the spark plug 25, the shorter the discharge time becomes, as shown by the dashed and dotted lines in Fig. 7. In other words, the discharge time of the current between the electrodes of the spark plug 25 is proportional to the strength of the flow near the spark plug 25. If the ignition device 7 detects the discharge time, the flow velocity estimation unit 83 can estimate the strength of the flow near the spark plug 25 (i.e., the flow velocity).

[0083] Fig. 8 shows the relationship between the discharge time detected by the ignition device 7 and the central position of the vertical vortex in the cylinder 11. Fig. 8 shows the relationship between the discharge time and the flow velocity near the spark plug 25. As described above, there is a proportional relationship between the discharge time and the flow velocity, so that the shorter the discharge time, the faster the flow velocity, and the longer the discharge time, the slower the flow velocity.

[0084] As shown in chart 802 of FIG. 8, when the center position of the vertical vortex is midway between the piston 3 and the ceiling of the cylinder 11 during the first half of the compression stroke, the spark plug 25 and the center position of the vortex are separated to a certain extent, so that the flow velocity near the spark plug 25 is between V1 and V2.

[0085] On the other hand, as shown in chart 801, when the center position of the vertical vortex is close to piston 3 in the first half of the compression stroke, the spark plug 25 is far away from the center of the vortex, and the flow velocity near the spark plug 25 is faster than V1.

[0086] Also, as shown in chart 803, when the center position of the vertical vortex is near the ceiling in the first half of the compression stroke, the flow velocity near spark plug 25 is slower than V2 because spark plug 25 is close to the center of the vortex.

[0087] The vertical vortex formed in the cylinder 11 mainly by the tumble flow becomes stable in the compression stroke after the intake valve 21 is closed, and its center position is determined. Therefore, in the first half of the compression stroke, when the spark plug 25 discharges (second discharge described later) and the estimated flow velocity estimated from the discharge time (second discharge time described later) detected by the ignition device 7 is higher than the second set value Vp2 corresponding to the speed V1 (when the discharge time is shorter than the first threshold in FIG. 8), the center position of the vertical vortex can be estimated to be close to the piston 3, and when the estimated flow velocity is lower than the first set value Vp1 corresponding to the speed V2 (when the discharge time is longer than the second threshold in FIG. 8), the center position of the vertical vortex can be estimated to be close to the ceiling. When the estimated flow velocity is between the first set value Vp1 and the second set value Vp2 (when the discharge time is between the first threshold and the second threshold in FIG. 8), the center position of the vertical vortex can be estimated to be the middle position of the cylinder 11.

[0088] In addition, the "estimated flow velocity" mentioned here may be anything that can estimate the flow velocity of the intake air, and does not have to be the flow velocity itself. For example, the reciprocal of the discharge time may be used as the estimated flow velocity.

[0089] Fig. 9 is a diagram showing the relationship between the center position of the transverse vortex during the intake stroke and the flow state inside the cylinder 11 in the latter half of the compression stroke. Chart 901 in Fig. 9 illustrates an example of the flow state inside the cylinder 11 when the center position of the transverse vortex during the intake stroke is inclined toward the exhaust valve 22 inside the cylinder 11. Chart 904 illustrates an example of the flow state inside the cylinder 11 in the latter half of the compression stroke when the crank angle has progressed from the state of chart 901.

[0090] Similarly, chart 902 illustrates an example of the flow state within cylinder 11 when the center of the lateral vortex during the intake stroke is located approximately along the axis of cylinder 11 at the center of cylinder 11. Chart 905 illustrates an example of the flow state within cylinder 11 during the latter half of the compression stroke when the crank angle has progressed from the state of chart 902.

[0091] Moreover, chart 903 illustrates an example of the flow state in cylinder 11 when the position of the center of the lateral vortex during the intake stroke is tilted toward the intake valve 21 in cylinder 11. Chart 906 illustrates an example of the flow state in cylinder 11 in the latter half of the compression stroke when the crank angle has progressed from the state of chart 903.

[0092] First, as shown in chart 902, when the center of the transverse vortex in the cylinder 11 is located along the axis of the cylinder 11 at the center of the cylinder 11, the center of the transverse vortex is located near the axis even in the latter half of the compression stroke, as shown in chart 905. The degree of turbulence in the cylinder 11 is also uniform or approximately uniform throughout the cylinder 11. When the spark plug 25 ignites the air-fuel mixture at the center of the cylinder 11, the flame propagates from the center to the periphery of the cylinder 11 while being bent in the circumferential direction by the transverse vortex, as shown by the dashed arrow in the figure. The flame propagates uniformly or approximately uniformly from near the center to the periphery of the cylinder 11. The flame propagation is promoted by the turbulence in the cylinder 11, so the combustion speed is relatively fast.

[0093] As shown in chart 901, when the position of the center of the transverse vortex is inclined toward the exhaust valve 22, the center of the transverse vortex is misaligned with the center of the cylinder 11. The degree of turbulence in the cylinder 11 becomes uneven throughout the cylinder 11. In addition, when the spark plug 25 ignites the mixture in the center of the cylinder 11 in the latter half of the compression stroke, the flame propagates from the center to the periphery of the cylinder 11 while being bent in the circumferential direction by the transverse vortex, as shown by the dashed arrow in chart 904. At this time, the flow speed of the transverse vortex becomes faster the farther away from the center of the transverse vortex (see the concentric circles in chart 904). In other words, the flow speed of the transverse vortex is relatively faster on the intake valve 21 side, which is far from the center of the transverse vortex. The flame propagating from the center of the cylinder 11 toward the exhaust valve 22 propagates radially outward while being bent in the circumferential direction, whereas the flame propagating from the center of the cylinder 11 toward the intake valve 21 is strongly bent by the fast flow velocity of the lateral vortex, making it difficult for the flame to propagate radially outward. As a result, as shown by the dashed line in chart 904, the area on the intake valve 21 side is an area where flame propagation is difficult. In this case, the combustion speed is slower than in the case of chart 905.

[0094] As shown in chart 903, when the position of the center of the transverse vortex is inclined toward the intake valve 21, the center of the transverse vortex is also misaligned with the center of the cylinder 11. The degree of turbulence in the cylinder 11 is uneven throughout the cylinder 11. In addition, when the spark plug 25 ignites the mixture in the center of the cylinder 11 in the latter half of the compression stroke, the flame propagates from the center to the periphery of the cylinder 11 while being bent in the circumferential direction by the transverse vortex, as shown by the dashed arrow in chart 906. At this time, as shown by the solid arrow, the direction from the center of the cylinder 11 toward the intake valve side is opposite to the flow of the counterclockwise transverse vortex. As a result, the flame propagating from the center of the cylinder 11 to the exhaust valve side propagates radially outward while being bent in the circumferential direction, while the flame propagating from the center of the cylinder 11 to the intake valve side is pushed back by the flow of the transverse vortex, making it difficult to propagate radially outward. As shown by the dashed line in chart 906, the area on the intake valve side is an area where flame propagation is difficult. In this case as well, the combustion speed is slower than in the case of chart 905.

[0095] 10 shows the relationship between the discharge time detected by the ignition device 7 and the central position of the transverse vortex in the cylinder 11. A chart 1000 in FIG.

[0096] As shown in chart 1002 of Fig. 10, a flow velocity distribution occurs in the cylinder 11 during the intake stroke due to the intake air flowing mainly from the first intake passage 18a. If the velocity distribution during the intake stroke is such that the flow velocity is maximum at a specific radial position between the center of the cylinder 11 and the liner, and the flow velocity decreases toward the center from there and toward the liner, the center of the lateral vortex will be along the axis near the center of the cylinder 11. In this case, the flow velocity near the spark plug 25 will be between V3 and V4.

[0097] On the other hand, as shown in chart 1001, when the flow velocity near the liner becomes extremely high during the intake stroke, the center of the lateral vortex tilts toward the exhaust valve 22. In this case, the flow velocity near the spark plug 25 becomes lower than V4.

[0098] Furthermore, as shown in chart 1003, when the flow velocity distribution during the intake stroke is averaged in the radial direction, the center of the lateral vortex is inclined toward the intake valve 21. In this case, the flow velocity near the spark plug 25 is higher than V3.

[0099] The transverse vortex formed in cylinder 11 mainly by the swirl flow stabilizes during the intake stroke after intake valve 21 opens and before it closes. Ignition device 7 causes spark plug 25 to discharge (first discharge, described below) during the intake stroke and detects the discharge time (first discharge time, described below). More specifically, the flow of intake air is prone to variation for a predetermined period of time from the moment intake valve 21 opens. After a predetermined time has elapsed since intake valve 21 opens, the transverse vortex stabilizes until intake valve 21 opens. After a predetermined time has elapsed since intake valve 21 opens, ignition device 7 causes spark plug 25 to discharge and detects the discharge time.

[0100] When the estimated flow velocity is higher than the second set value Vp2 corresponding to the velocity V3 (when the discharge time is shorter than the first threshold in FIG. 10), the flow velocity estimation unit 83 can estimate that the center position of the transverse vortex is inclined toward the intake valve 21 side, and when the estimated flow velocity is longer than the first set value Vp1 corresponding to the velocity V4 (when the discharge time is longer than the second threshold in FIG. 10), the flow velocity estimation unit 83 can estimate that the center position of the transverse vortex is inclined toward the exhaust valve 22 side. When the estimated flow velocity is between the first set value Vp1 and the second set value Vp2 (when the discharge time is between the first threshold and the second threshold in FIG. 10), the flow velocity estimation unit 83 can estimate that the center position of the transverse vortex is along the axis of the cylinder 11 at the center of the cylinder 11. Note that the velocity V4 and the velocity V2 corresponding to the first set value Vp1 are not necessarily the same. Similarly, the velocity V3 and the velocity V1 corresponding to the second set value Vp2 are not necessarily the same.

[0101] (auxiliary ignition control) 11 is a timing chart illustrating the timing of fuel injection by the injector 6, and the timing of discharge (test discharge), auxiliary ignition, and main ignition by the spark plug 25. The crank angle progresses from left to right in FIG.

[0102] As described above, when the center position of the longitudinal vortex and / or the transverse vortex shifts due to the variation in the intake flow, a region where the degree of turbulence is weak and / or a region where flame propagation is difficult occurs in the cylinder 11. The auxiliary fuel places a high-energy air-fuel mixture containing a lot of plasma in such a region where the degree of turbulence is weak and / or a region where flame propagation is difficult, thereby promoting flame propagation to the region.

[0103] First, the main fuel injection unit 81 executes main fuel injection during the intake stroke from when the intake valve 21 opens until when the intake valve 21 closes, and injects fuel into the cylinder 11 through the injector 6 (see main fuel injection 1104). The injected fuel flows and diffuses within the cylinder 11, forming an air-fuel mixture within the cylinder 11.

[0104] As shown in chart 1102, the flow rate estimation unit 83 causes the ignition device 7 and the spark plug 25 to execute a first discharge 1105 during an intake stroke period after a predetermined time constant Δt has elapsed since the intake valve 21 opens. The first discharge 1105 is a discharge for inspection (i.e., an inspection discharge) that is performed during a period in which the mixture is not ignited. The ignition device 7 detects a first discharge time corresponding to the first discharge. The flow velocity estimation unit 83 estimates the flow velocity of the transverse vortex near the ignition plug 25 from the first discharge time detected during the first discharge 1105, and estimates the center position of the transverse vortex.

[0105] The flow rate estimation unit 83 also causes the ignition device 7 and the spark plug 25 to execute a second discharge 1106, for example, in the first half of the compression stroke after the intake valve 21 is closed. The second discharge 1106 is also a test discharge that is performed during a period in which the mixture is not ignited. The ignition device 7 detects a second discharge time corresponding to the second discharge. The flow velocity estimation unit 83 estimates the flow velocity of the longitudinal vortex near the ignition plug 25 from the second discharge time detected during the second discharge 1106, and estimates the center position of the longitudinal vortex.

[0106] When the first discharge time and the second discharge time detected by the ignition device 7 are both between the first threshold value and the second threshold value (that is, when the flow velocity estimated by the flow velocity estimation unit 83 is between the first set value Vp1 and the second set value Vp2), the center position of the vertical vortex is located in the middle between the piston 3 and the ceiling of the cylinder 11, and the center position of the horizontal vortex is along the axis of the cylinder 11 at the center of the cylinder 11. In this case, auxiliary ignition is not required. As shown in the chart 1102 of FIG. 11, the auxiliary ignition control unit 84 stops the execution of auxiliary ignition, and the main ignition control unit 82 uses the spark plug 25 to ignite the mixture at a predetermined timing near the compression top dead center in the latter half of the compression stroke (see main ignition 1107 of FIG. 11). In this case, since the center positions of the horizontal vortex and the vertical vortex are located in the center of the cylinder 11, the degree of turbulence is uniform or approximately uniform throughout the cylinder 11. The flame propagates evenly or nearly evenly from the center to the periphery of the cylinder 11. The combustion speed is relatively high.

[0107] Next, a case where the second discharge time detected by the ignition device 7 is shorter than the first threshold value (i.e., the flow velocity estimated by the flow velocity estimation unit 83 is higher than the second set value Vp2) will be described. In this case, the center position of the vertical vortex is a position in the cylinder 11 close to the piston 3, and a positive unidirectional flow occurs in the cylinder 11 in the latter half of the compression stroke. As shown in chart 1101 of FIG. 11, the auxiliary ignition control unit 84 controls the ignition device 7 to execute the first auxiliary ignition. The spark plug 25 executes the first auxiliary ignition 1108, for example, at a first operation timing in the first half of the compression stroke or the second half of the compression stroke.

[0108] 12, when the ignition device 7 applies energy to the spark plug 25, an arc discharge occurs between the center electrode 251 and the ground electrode 252 of the spark plug 25 (i.e., auxiliary ignition). The plasma generated in the cylinder 11 is carried by the flow in the cylinder 11.

[0109] 13 is a diagram for explaining the change in the flow and the distribution of plasma in the cylinder 11 when the center position of the vertical vortex is located near the piston 3 in the cylinder 11. As described above, when the center position of the vertical vortex is located near the piston 3, as the piston 3 rises from P1301, P1302, P1303, and P1304, the center of the vortex hits the top surface of the piston 3, causing the lower half of the vertical vortex to collapse, and as shown by the black arrow in P1305, the flow in the cylinder 11 in the latter half of the compression stroke becomes a unidirectional flow from the intake valve 21 toward the exhaust valve 22.

[0110] The first auxiliary ignition by the spark plug 25 occurs relatively early in the compression stroke (P3203). The plasma generated in the cylinder 11 is carried by the vertical vortex from the exhaust valve 22 side to the intake valve 21 side before the vortex collapses because the pressure in the cylinder 11 is not so high (see the hatched areas of P1304 and P1305). As a result, the temperature of the mixture near the intake valve 21 can be increased.

[0111] After the first auxiliary ignition 1108 is performed, the main ignition control unit 82 uses the spark plug 25 to ignite the mixture at a predetermined timing near the compression top dead center in the latter half of the compression stroke (see main ignition 1107 in chart 1101). Due to the positive unidirectional flow, the flame is less likely to propagate toward the intake valve 21 side, but since the temperature of the mixture on the intake valve 21 side is high, the flame propagation toward the intake valve 21 side is promoted. The combustion speed increases accordingly, and the combustion speed increases to the same extent as when the discharge time is between the first threshold value and the second threshold value (when the estimated flow speed is between the first set value Vp1 and the second set value Vp2). Therefore, the combustion fluctuation of the engine 1 is suppressed.

[0112] Next, a case where the second discharge time detected by the ignition device 7 is longer than the second threshold value (i.e., the flow velocity estimated by the flow velocity estimation unit 83 is less than the first set value Vp1) will be described. In this case, the center position of the vertical vortex is close to the ceiling of the cylinder 11, and a non-unidirectional flow occurs in the cylinder 11 in the latter half of the compression stroke. As shown in chart 1103 of FIG. 11, the auxiliary ignition control unit 84 controls the ignition device 7 to execute the second auxiliary ignition. The spark plug 25 executes the second auxiliary ignition 1109 at the second injection timing in the latter half of the compression stroke. The execution timing of the second auxiliary ignition 1109 is later than the execution timing of the first auxiliary ignition 1108.

[0113] 14 is a diagram for explaining the change in the flow and the distribution of plasma in the cylinder 11 when the center position of the vertical vortex is located near the ceiling of the cylinder 11. As described above, when the center position of the vertical vortex is located near the ceiling, as the piston 3 rises through P1401, P1402, P1403, and P1404, the center of the vortex hits the ceiling, causing the upper half of the vertical vortex to collapse, and as shown by the black arrow in P1405, the flow in the cylinder 11 in the latter half of the compression stroke becomes a counter-unidirectional flow from the exhaust valve 22 toward the intake valve 21.

[0114] The spark plug 25 executes the second auxiliary ignition 1109 in the latter half of the compression stroke (see P1404). Since the pressure in the cylinder 11 is high in the latter half of the compression stroke, the plasma generated in the cylinder 11 receives the strong compression pressure and remains in the center of the cylinder 11, while flowing toward the exhaust valve 22 where the flow is relatively weak (see the hatched areas in P1404 and P1405). As a result, a high-temperature mixture can be placed near the exhaust valve 22.

[0115] After the second auxiliary ignition 1109 is performed, the main ignition control unit 82 uses the spark plug 25 to ignite the mixture at a predetermined timing near the compression top dead center in the latter half of the compression stroke (see main ignition 1107 in chart 1103). Due to the non-unidirectional flow, the flame is less likely to propagate toward the exhaust valve 22 side, but since the temperature of the mixture on the exhaust valve 22 side is high, the flame propagation toward the exhaust valve 22 side is promoted. The combustion speed increases accordingly, and the combustion speed increases to the same extent as when the discharge time is between the first threshold value and the second threshold value (when the estimated flow speed is between the first set value Vp1 and the second set value Vp2). Therefore, the combustion fluctuation of the engine 1 is suppressed.

[0116] Therefore, by performing auxiliary ignition according to the flow conditions within the cylinder 11, even if the intake flow conditions vary from cycle to cycle and the center position of the vertical vortex varies, the ECU 10 can keep the combustion speed the same or approximately the same, thereby suppressing combustion fluctuations.

[0117] Next, a case where the first discharge time detected by the ignition device 7 is shorter than the first threshold value (i.e., the flow velocity estimated by the flow velocity estimation unit 83 is higher than the second set value Vp2) will be described. In this case, the center position of the lateral vortex is inclined toward the intake valve side of the cylinder 11. As shown in a chart 1101 of FIG. 11, the auxiliary ignition control unit 84 controls the ignition device 7 to execute the first auxiliary ignition. The spark plug 25 executes the first auxiliary ignition 1108 at a first operation timing in, for example, the first half of the compression stroke or the second half of the compression stroke.

[0118] P1501 and P1502 in Fig. 15 are diagrams for explaining the change in flow and plasma distribution inside the cylinder 11 when the center position of the transverse vortex is inclined toward the intake valve 21. When the center of the transverse vortex is inclined toward the intake valve 21, as shown in P1501, the velocity distribution inside the cylinder 11 during the compression stroke has low kurtosis of the flow velocity distribution, and therefore there are no points with extremely high flow velocities.

[0119] After the second discharge, in the first or second half of the compression stroke, the plasma generated at the spark plug 25 at the center of the cylinder 11 is carried radially outward by the flow shown by the solid arrow in Fig. 15, and is also carried circumferentially along the liner (see the dashed arrow in Fig. 15). Because the timing of the auxiliary injection is relatively advanced, the plasma is carried to the intake valve 21 side by utilizing the long time until the ignition timing. As a result, the temperature of the mixture on the intake valve 21 side rises at the ignition timing (P1502).

[0120] After the first auxiliary ignition is performed, the main ignition control unit 82 uses the spark plug 25 to ignite the mixture at a predetermined timing near the compression top dead center in the latter half of the compression stroke (see main ignition 1107 in chart 1101). As described above, the flame is prevented from propagating radially outward by the lateral vortex with the center position shifted, so that the flame is less likely to propagate toward the intake valve 21 side. However, since the temperature of the mixture on the intake valve 21 side is high, the flame propagation toward the intake valve 21 side is promoted. The combustion speed increases accordingly, and the combustion speed increases to the same extent as when the discharge time is between the first threshold value and the second threshold value (when the estimated flow speed is between the first set value Vp1 and the second set value Vp2). The combustion fluctuation of the engine 1 is suppressed.

[0121] Next, a case where the first discharge time detected by the ignition device 7 is longer than the second threshold value, i.e., the flow velocity estimated by the flow velocity estimation unit 83 is lower than the first set value Vp1, will be described. In this case, the center position of the lateral vortex is inclined toward the exhaust valve 22 side in the cylinder 11. As shown in a chart 1103 of FIG. 11, the auxiliary ignition control unit 84 controls the ignition device 7 to perform the second auxiliary ignition 1109. The spark plug 25 performs the second auxiliary ignition 1109 at a second operation timing in the latter half of the compression stroke. The timing of execution of the second auxiliary ignition 1109 is later than the timing of execution of the first auxiliary ignition 1108.

[0122] P1503 and P1504 in Fig. 15 are diagrams for explaining the change in flow and plasma distribution inside the cylinder 11 when the center position of the transverse vortex is inclined toward the exhaust valve 22. When the center of the transverse vortex is inclined toward the exhaust valve 22, as shown in P1503, the velocity distribution inside the cylinder 11 in the latter half of the compression stroke has an extremely fast flow velocity near the liner.

[0123] At a late timing in the latter half of the compression stroke, the plasma generated at the spark plug 25 in the center of the cylinder 11 is transported radially outward and, by riding on the fast circumferential flow, is quickly transported circumferentially along the liner to the intake valve 21 side. As a result, at the ignition timing (P1504), the sprays of the auxiliary fuel overlap, and the temperature of the mixture on the intake valve 21 side increases.

[0124] After the second auxiliary ignition 1109 is performed, the main ignition control unit 82 uses the spark plug 25 to ignite the mixture at a predetermined timing near the compression top dead center in the latter half of the compression stroke (see main ignition 1107 in chart 1103). As described above, the flame is difficult to propagate toward the intake valve side because the propagation direction is bent by the lateral vortex whose center position is shifted, but the flame propagation toward the intake valve side is promoted because the temperature of the mixture on the intake valve side is high. The combustion speed increases accordingly, and the combustion speed increases to the same extent as when the discharge time is between the first threshold value and the second threshold value (when the estimated flow speed is between the first set value Vp1 and the second set value Vp2). Therefore, the combustion fluctuation of the engine 1 is suppressed.

[0125] Therefore, by performing auxiliary ignition according to the flow conditions within the cylinder 11, even if the intake flow conditions vary from cycle to cycle and the center position of the lateral vortex varies, the ECU 10 can keep the combustion speed the same or approximately the same, thereby suppressing combustion fluctuations in the engine 1.

[0126] The energy applied to the spark plug 25 in each of the first discharge, the second discharge, the first auxiliary ignition, the second auxiliary ignition, and the main ignition may be the same or different. In addition, in the first auxiliary ignition and the second auxiliary ignition, a low-temperature plasma may be generated in the cylinder 11 by repeatedly applying, for example, a short-pulse voltage to the spark plug 25. The low-temperature plasma also promotes flame propagation and contributes to an improvement in the combustion speed.

[0127] (Setting the amount of energy for auxiliary ignition) As described above, in this embodiment, the ECU 10 executes the inspection discharge (the above-mentioned first and second discharges) during the intake stroke and the compression stroke, estimates the flow speed of the intake air from the electrical parameters of the discharge path of the inspection discharge, and performs auxiliary ignition (the first and second auxiliary ignitions) according to the estimated flow speed. Note that, hereinafter, the above-mentioned first auxiliary ignition and second auxiliary ignition may be simply referred to as auxiliary ignition without distinction.

[0128] FIG. 16 is a map for setting the amount of energy of auxiliary ignition based on the estimated flow velocity and the engine speed. The amount of energy of auxiliary ignition is set according to the length of the period during which auxiliary ignition is performed (auxiliary ignition period). However, the setting of the amount of energy of auxiliary ignition is not limited to the length of the auxiliary ignition period, and may be performed by the amount of current passed through the spark plug, etc. Also, these may be combined. The vertical axis represents the estimated flow velocity, and the horizontal axis represents the engine speed. This map of FIG. 16 is stored in the memory 102 of the ECU 10. Here, the reciprocal of the discharge time is used as the value of the estimated flow velocity. As described above, the longer the discharge time, the higher the flow velocity of the mixture around the spark plug 25, so that the vertical axis of FIG. 16 can be said to reflect the flow velocity of the mixture. As the estimated flow velocity, the slope of the voltage may be used, or a flow velocity value calculated from the discharge time, etc. based on a graph such as that shown in FIG. 8 may be used. The estimated flow velocity here includes both the flow velocity of the transverse vortex estimated from the parameters of the first discharge and the flow velocity of the longitudinal vortex estimated from the parameters of the second discharge.

[0129] As shown in Fig. 16, auxiliary ignition is performed in a region where the estimated flow velocity is less than a first set value Vp1 and in a region where the estimated flow velocity is higher than a second set value Vp2 that is higher than the first set value Vp1. The first set value Vp1 and the second set value Vp2 shown in Fig. 16 are the first set value Vp1 and the second set value Vp2 described above.

[0130] The region where the estimated flow velocity is less than the first set value Vp1 is divided into two regions, a first region R1 and a second region R2, by the third set value Vp3. The first region R1 is the region where the estimated flow velocity is equal to or less than the third set value Vp3, and the second region R2 is the region where the estimated flow velocity is higher than the third set value Vp3 and equal to or less than the first set value Vp1.

[0131] 16, the region where the estimated flow velocity is higher than the second set value Vp2 is divided into two regions, a third region R3 and a fourth region R4, by the fourth set value Vp4. In the region where the estimated flow velocity is higher than the second set value Vp2, the third region R3 is a region where the estimated flow velocity is higher than the second set value Vp2 and equal to or lower than the fourth set value Vp4, and the fourth region R4 is a region where the estimated flow velocity is higher than the fourth set value Vp4.

[0132] The region where the estimated flow velocity is between the first set value Vp1 and the second set value Vp2 is a fifth region R5.

[0133] As shown in FIG. 16, the first set value Vp1 and the second set value Vp2 have a higher estimated flow velocity as the engine speed increases. That is, the fifth region R5 expands to a region where the estimated flow velocity is higher as the engine speed increases. This is because, when the engine speed is high, the time of the intake stroke in which the piston descends and intakes air is short, and the piston descends at a high speed, so that the intake flow velocity is high and the flow velocity of the intake air at the time of the inspection discharge is high. For this reason, even if the vortex center of the intake air is in an appropriate position, the estimated flow velocity at that time is higher when the engine speed is high than when the engine speed is low. For this reason, the first set value Vp1 and the second set value Vp2 have a higher estimated flow velocity as the engine speed increases, and the fifth region R5 expands as described above.

[0134] In the region where the estimated flow velocity is less than the first set value Vp1, when the auxiliary ignition period in the first region R1 is the first ignition period and the auxiliary ignition period in the second region R2 is the second ignition period, the first ignition period is longer than the second ignition period. That is, since the mixture is more likely to be biased toward the wall side of the cylinder 11 when the engine speed is high, the energy of the auxiliary ignition is increased to widely form a region with a large amount of plasma in a part of the cylinder 11 with a low degree of turbulence. As shown in FIG. 16, the third set value Vp3, which is the boundary at which the auxiliary ignition period is switched, is located on the lower engine speed side as the estimated flow velocity is lower. In the region where the estimated flow velocity is less than the first set value Vp1, the lower the estimated flow velocity is with respect to the first set value Vp1, the more biased the mixture is in the cylinder 11. For this reason, when the estimated flow velocity is low, it is preferable to increase the energy of the auxiliary ignition even when the engine speed is low.

[0135] On the other hand, in a region where the estimated flow velocity is higher than the second set value Vp2, when the auxiliary ignition period in the third region R3 is the third ignition period and the auxiliary ignition period in the fourth region R4 is the fourth ignition period, the fourth ignition period is longer than the third ignition period. In a region where the estimated flow velocity is higher than the second set value Vp2, the higher the estimated flow velocity is relative to the second set value Vp2, the more the intake air is pressed against the side wall of the cylinder 11, resulting in a greater bias in the mixture in the cylinder 11.

[0136] Therefore, it is preferable to increase the auxiliary ignition energy in the fourth region R4 more than in the third region R3. As shown in Fig. 16, the fourth set value Vp4 is located on the side where the estimated flow velocity is lower as the engine speed is higher. When the engine speed is high, the inertia force of the intake flow is large even during the compression stroke, so that the air-fuel mixture becomes more biased at the time of main ignition. Therefore, in the region where the estimated flow velocity is higher than the second set value Vp2, it is preferable to increase the auxiliary ignition energy when the engine speed is high, from when the estimated flow velocity is relatively low.

[0137] In the fifth region R5, the center of the intake swirl is located at an appropriate position, that is, near the cylinder axis and at the center position in the cylinder axis direction, so auxiliary ignition is not performed. The auxiliary ignition period is 0.

[0138] In the map of Figure 16, the shapes of the first set value Vp1, the second set value Vp2, the third set value Vp3, and the fourth set value Vp4 change slightly depending on the value used as the estimated flow velocity, but the relationship of the auxiliary ignition period in each of the regions R1 to R5 does not change.

[0139] FIG. 17 shows the change in the auxiliary ignition period with respect to the estimated flow speed when the engine speed is the engine speed Ro shown in FIG. 16. In the first region R1, the lower the estimated flow speed, the longer the first ignition period. In the second region R2, similar to the first region R1, the lower the estimated flow speed, the longer the second ignition period. This is because, in a region where the estimated flow speed is less than the first set value Vp1, the lower the estimated flow speed, the more likely it is that a region with a low degree of turbulence will be formed in the cylinder 11, and it is necessary to form a region with a large amount of plasma over a wide range. In addition, the first ignition period and the second ignition period change significantly at the third set value Vp3, and are discontinuous. The slope of the first ignition period with respect to the estimated flow speed and the slope of the second ignition period with respect to the estimated flow speed may be the same or different.

[0140] In the region R5 where the estimated flow velocity is between the first set value Vp1 and the second set value Vp2, auxiliary ignition is not performed, so that the auxiliary ignition period is 0, as described above.

[0141] In the third region R3 and the fourth region R4, the higher the estimated flow velocity, the longer the third ignition period and the fourth ignition period are set. As described above, in a region where the estimated flow velocity is higher than the second set value Vp2, the higher the estimated flow velocity, the more likely it is that a region with a low degree of turbulence will be formed in the cylinder 11, and it is necessary to form a region with a large amount of plasma over a wide range.

[0142] Therefore, the amount of energy of the auxiliary ignition is increased as the estimated flow velocity around the spark plug 25 increases, so that a region with a large amount of plasma is appropriately formed on the intake side of the cylinder 11. Also, the third ignition period and the fourth ignition period change significantly at the fourth set value Vp4, and are discontinuous. Note that the slope of the third ignition period with respect to the estimated flow velocity and the slope of the fourth ignition period with respect to the estimated flow velocity may be the same or different.

[0143] On the other hand, Fig. 18 shows the change in the auxiliary ignition period with respect to the engine speed when the estimated flow velocity is the estimated value VA shown in Fig. 16. When the estimated flow velocity is constant, both the first ignition period and the second ignition period are constant regardless of the engine speed. Although not shown, when the estimated flow velocity is constant, the third ignition period and the fourth ignition period are also constant regardless of the engine speed.

[0144] In this way, by adjusting the auxiliary ignition energy (i.e., auxiliary ignition period) based on the estimated flow velocity estimated from the parameters of the discharge path in the test discharge and the engine speed, it is possible to appropriately form a region with a large amount of plasma in a region where flame propagation is difficult in the cylinder 11. As a result, flame propagation becomes easier throughout the cylinder 11, and the combustion speed can be stabilized.

[0145] Figure 19 shows the timing of auxiliary ignition and main ignition by the spark plug 25. Figure 19(a) shows the timing when the engine state belongs to the first region R1, and Figure 19(b) shows the timing when the engine state belongs to the second region R2. Note that Figure 19 shows the case where the estimated flow speed is the same.

[0146] As shown in FIG. 19, whether the engine state is in the first region R1 or the second region R2, the main fuel injection is performed by the injector 6 during the intake stroke.

[0147] After the main fuel injection, a first discharge and a second discharge are performed by the spark plug 25. The first discharge is performed during the intake stroke, and the second discharge is performed after the intake valve 21 closes, particularly in the first half of the compression stroke.

[0148] After the first and second discharges, auxiliary ignition is performed in the latter half of the compression stroke before combustion is started by main ignition. As described above, the first ignition period is set longer than the second ignition period. Therefore, the auxiliary ignition control unit 84 makes the discharge time at the spark plug 25 longer when the engine state is in the first region R1 than when the engine state is in the second region R2.

[0149] Then, after the auxiliary ignition, before the piston 3 reaches the top dead center of compression, the main ignition control unit 82 again operates the ignition plug 25 to execute main ignition to combust the mixture. At this time, a high-energy region with a large amount of plasma has been formed in the part of the cylinder 11 with a low degree of turbulence by the auxiliary ignition, so that the flame quickly propagates throughout the cylinder 11.

[0150] (flowchart) Next, the processing operation of the auxiliary ignition control of the ECU 10 will be described with reference to FIG. 20 and FIG.

[0151] First, in step S1, the ECU 10 acquires information from each of the sensors SW1 to SW9.

[0152] Next, in step S2, the ECU 10 calculates the required torque based on the detection result of the accelerator opening sensor SWO. The required torque calculated in step S2 corresponds to the load to be determined when calculating the auxiliary ignition period.

[0153] Next, in step S3, the ECU 10 sets the injection amount and injection timing of the main fuel injection.

[0154] Next, in step S4, the ECU 10 sets the ignition timing, which is the timing of main ignition for combusting the air-fuel mixture.

[0155] Next, in step S5, the ECU 10 sets the timing of the inspection discharge. In this step S5, the ECU 10 sets the timing of the first discharge and the timing of the second discharge. The ECU 10 sets the timing of the first discharge to the timing of the intake stroke, and sets the timing of the second discharge to the first half of the compression stroke after the intake valve 21 is closed.

[0156] Next, in step S6, the ECU 10 executes the test discharge at the time set in step S5. The ECU 10 acquires from the ignition device 7 the discharge times of the discharge paths generated in the spark plug 25 in the first and second discharges.

[0157] Next, in step S7, the ECU 10 estimates the flow velocity of the mixture in the cylinder 11. Here, the ECU 10 calculates the reciprocal of the discharge time of the inspection discharge in step S6 as the estimated flow velocity.

[0158] Next, in step S8, the ECU 10 determines whether the estimated flow speed calculated in step S7 is equal to or less than the first set value Vp1. If the estimated flow speed is less than the first set value Vp1 (YES), the ECU 10 proceeds to step S9. On the other hand, if the estimated flow speed is higher than the first set value Vp1 (NO), the ECU 10 proceeds to step S12. If at least one of the estimated flow speed of the transverse vortex and the estimated flow speed of the longitudinal vortex is less than the first set value Vp1, the ECU 10 determines the answer to be YES in step S8.

[0159] In step S9, the ECU 10 determines whether the state of the engine 1 belongs to the first region R1, i.e., whether the estimated flow speed is equal to or less than the third set value Vp3, based on the engine speed and the estimated flow speed calculated in step S7. The ECU 10 makes the determination by reading the map shown in Fig. 16. If the state of the engine 1 belongs to the first region R1 (YES), the ECU 10 proceeds to step S10. On the other hand, if the state of the engine 1 belongs to the second region R2 (NO), the ECU 10 proceeds to step S11.

[0160] In the step S10, the ECU 10 sets the auxiliary ignition period to the first ignition period. At this time, the ECU 10 sets the first ignition period to be long or short depending on the estimated flow speed estimated in the step S7. After the step S10, the ECU 10 proceeds to the step S17.

[0161] In the step S11, the ECU 10 sets the auxiliary ignition period to the second ignition period. At this time, the ECU 10 sets the second ignition period to be long or short depending on the estimated flow speed estimated in the step S7. After the step S11, the ECU 10 proceeds to the step S17.

[0162] On the other hand, as shown in Fig. 21, in step S12, which is reached when the result of step S8 is NO, the ECU 10 determines whether or not the estimated flow speed calculated in step S7 is higher than the second set value Vp2. If the result of step S8 is NO, that is, the ECU 10 proceeds to step S14. On the other hand, if the result of step S8 is NO, that is, the ECU 10 proceeds to step S13. If at least one of the first estimated flow speed and the second estimated flow speed is higher than the second set value Vp2, the ECU 10 determines the result of step S12 as YES.

[0163] In step S13, the ECU 10 determines that the state of the engine 1 belongs to the fifth region R5 and thus determines that auxiliary ignition is not required. The ECU 10 returns after step S13.

[0164] In step S14, the ECU 10 determines whether the engine state belongs to the third region R3, i.e., whether the estimated flow speed is equal to or lower than the fourth set value Vp4, based on the engine speed and the estimated flow speed calculated in step S7. The ECU 10 makes the determination by reading the map shown in Fig. 16. If the engine state belongs to the third region R3 (YES), the ECU 10 proceeds to step S15. On the other hand, if the engine state belongs to the fourth region R4 (NO), the ECU 10 proceeds to step S16.

[0165] In the step S15, the ECU 10 sets the auxiliary ignition period to the third ignition period. At this time, the ECU 10 sets the third ignition period to be long or short depending on the estimated flow speed estimated in the step S7. After the step S15, the ECU 10 proceeds to the step S17.

[0166] In the step S16, the ECU 10 sets the auxiliary ignition period to the fourth ignition period. At this time, the ECU 10 sets the fourth ignition period to be long or short depending on the estimated flow speed estimated in the step S7. After the step S16, the ECU 10 proceeds to the step S17.

[0167] Then, as shown in Fig. 20, in step S17 which follows steps S10, S11, S15 and S16, the ECU 10 sets the timing for executing auxiliary ignition. When the estimated flow speed calculated in step S7 is less than a first set value Vp1, the ECU 10 sets the timing for executing auxiliary ignition to the latter half of the compression stroke, whereas when the estimated flow speed calculated in step S7 is higher than a second set value Vp2, the ECU 10 sets the timing for executing auxiliary ignition to the first or second half of the compression stroke. The ECU 10 returns after step S17.

[0168] After the flow chart, the ECU 10 executes the auxiliary ignition. This allows a high-energy region with a large amount of plasma to be formed in a region with a low degree of turbulence according to the state of the vortex in the cylinder 11, and the combustion speed of the entire cylinder 11 can be stabilized.

[0169] (summary) Therefore, in this embodiment, the engine is provided with an operating state detector (sensors SW1 to Sw9) that detects the operating state of the engine, an ignition device 7, an injector 6, and an ECU 10 that is electrically connected to the operating state detector. The ECU 10 has a main fuel injection unit 81 that sets a main fuel injection timing, which is the timing of main fuel injection, based on the engine load detected by the operating state detector (particularly, the accelerator opening sensor SW7), and controls the injector 6 to perform main fuel injection at the main fuel injection timing; a flow velocity estimation unit 83 that controls the ignition device 7 to apply a voltage between the electrodes of the ignition plug 25 and perform an inspection discharge to detect a parameter related to a current value of a discharge path generated between the electrodes during a period when the mixture is not ignited, and estimates the level of the flow velocity of the intake air in the cylinder 11 from the parameter in the inspection discharge; and an auxiliary ignition control unit 84 that performs auxiliary ignition by controlling the ignition device 7 to be on the retard side of the main fuel injection timing when the estimated flow velocity estimated by the flow velocity estimation unit 83 is less than a first set value Vp1 or higher than a second set value Vp2 higher than the first set value Vp1, and imparts energy by ignition into the cylinder 11.

[0170] The first set value Vp1 and the second set value Vp2 are positioned on the side where the estimated flow velocity is higher as the engine speed detected by the operating state detector (especially the crank angle sensor SW6) is higher. In this way, by appropriately changing the set value for executing auxiliary ignition according to the difference in the intake air flow in the cylinder 11 caused by the engine speed, it is possible to appropriately promote the combustion of the air-fuel mixture in the region where the turbulence state is weak and where flame propagation is difficult. As a result, it is possible to stabilize the combustion speed and suppress the combustion fluctuation.

[0171] In particular, in this embodiment, the auxiliary ignition control unit 84 is configured to increase the energy of the auxiliary ignition when the estimated flow velocity is equal to or lower than a third set value Vp3 set in a region lower than the first set value Vp1, compared to when the estimated flow velocity is higher than the third set value Vp3 and less than the first set value Vp1, and the third set value Vp3 is positioned on the lower engine speed side as the estimated flow velocity decreases.

[0172] When the engine speed is high, the time of the intake stroke during which the piston 3 descends to take in air is short, and the speed at which the piston 3 descends is high, so the intake flow rate is high and the inertial force of the intake flow is large even during the compression stroke. If the inertial force of the intake flow is large, the mixture is more likely to be pressed against the side wall of the cylinder 11. In other words, compared to when the engine speed is low, the bias of the mixture at the time of main ignition is greater when the engine speed is high. The further the estimated flow rate is from the first set value Vp1 to the low side, the stronger the anti-unidirectional flow is formed, and the greater the effect of the engine speed.

[0173] Therefore, when the estimated flow velocity is equal to or lower than the third set value Vp3, the auxiliary ignition energy is increased. Furthermore, by setting the third set value Vp3 to a position where the estimated flow velocity is higher as the engine speed increases, the conditions for increasing the auxiliary ignition energy as the engine speed increases are expanded. This makes it easier for the flame to propagate throughout the cylinder 11 even when the engine speed is high, and the combustion speed can be stabilized. As a result, the combustion fluctuation can be more effectively suppressed.

[0174] In this embodiment, the auxiliary ignition control unit 84 is configured to increase the energy of the auxiliary ignition when the estimated flow velocity is higher than a fourth set value Vp4 set in a region higher than the second set value Vp2, compared to when the estimated flow velocity is equal to or lower than the fourth set value Vp4 and higher than the second set value Vp2, and the fourth set value Vp4 is located on the lower side of the estimated flow velocity as the engine speed increases. As the estimated flow velocity moves away from the second set value to the higher side, the more strongly the positive unidirectional flow is formed, and the influence of the engine speed becomes greater.

[0175] Therefore, when the estimated flow velocity is higher than the fourth set value Vp4, the auxiliary ignition energy is increased. Also, the fourth set value Vp4 is set to a lower side of the estimated flow velocity as the engine speed increases, expanding the conditions for increasing the auxiliary ignition energy as the engine speed increases. This makes it easier for flames to propagate throughout the cylinder 11 even when the engine speed is high, stabilizing the combustion speed. As a result, the combustion fluctuation can be more effectively suppressed.

[0176] In the above embodiment, the injector 6 performs the main fuel injection during the intake stroke. However, the present invention is not limited to this, and the injector 6 may perform the main fuel injection during the compression stroke. The spark plug 25 may perform the first discharge after the main fuel injection or before the main fuel injection. Similarly, the spark plug 25 may perform the second discharge after the main fuel injection or before the main fuel injection. [Explanation of symbols]

[0177] 1 Engine 6 Injector (fuel injection valve) 7 Ignition device 10 ECU (controller) 11 Cylinder 21 Intake valve 25 Spark plug 81 Main fuel injection section 83 Flow velocity estimation part 84 Auxiliary ignition control unit SW6 Crank angle sensor (operating condition detector)

Claims

1. An engine system including an engine having a cylinder having a pent roof type ceiling, an ignition device including an ignition plug disposed in a center portion of the cylinder, and a fuel injection valve disposed in a center portion of the cylinder, an operating condition detector for detecting an operating condition of the engine; a controller electrically connected to the ignition device, the fuel injection valve, and the operating condition detector; The controller includes: a main fuel injection unit that sets an injection amount of a main fuel and a main fuel injection timing that is an injection timing of the main fuel based on an engine load detected by the operating state detector, and controls the fuel injection valve so as to inject the main fuel in the amount set at the main fuel injection timing; a flow velocity estimation unit that controls the ignition device to apply a voltage between the electrodes of the spark plug during a period when the air-fuel mixture is not ignited and detects a parameter that is an inverse of a discharge time generated between the electrodes or a gradient of the voltage applied to the electrodes, and estimates the level of the flow velocity of the intake air in the cylinder from the parameter; an auxiliary ignition control unit that executes auxiliary ignition by controlling the ignition device on the advance side of a timing for igniting the air-fuel mixture by main ignition when the estimated flow velocity estimated by the flow velocity estimation unit is less than a first preset value at which a region where flame propagation is difficult occurs in the latter half of the compression stroke due to a deviation in the vortex center of the air-fuel mixture, or is higher than a second preset value higher than the first preset value, thereby providing energy by ignition into the cylinder; having An engine system, characterized in that the first set value and the second set value are positioned on a side where the estimated flow velocity is higher as the engine speed detected by the operating condition detector is higher.

2. 2. The engine system according to claim 1, the auxiliary ignition control unit is configured to increase the energy of the auxiliary ignition when the estimated flow velocity is lower than the first set value and less than a third set value that is set in a region in which the lower the estimated flow velocity, the greater the deviation of the vortex center of the mixture becomes, compared with when the estimated flow velocity is higher than the third set value and less than the first set value; An engine system, wherein the third set value is set to a lower engine speed side as the estimated flow velocity is lower.

3. 3. The engine system according to claim 1, the auxiliary ignition control unit is configured to increase the energy of the auxiliary ignition when the estimated flow velocity is higher than a fourth set value that is set in a region where the higher the estimated flow velocity is, the more the deviation of the vortex center of the air-fuel mixture increases, compared to when the estimated flow velocity is lower than the fourth set value and higher than the second set value; An engine system, wherein the fourth set value is set to a lower side of the estimated flow velocity as the engine speed increases.

Images