Engine System

Abstract

To stabilize combustion of an engine by suppressing combustion fluctuation at a high load.SOLUTION: An engine system includes an engine 1 in which a fuel injection valve 6 and an ignition plug 25 are installed in a central part in a cylinder 11 having a pent-roof ceiling part. A controller 10 includes: a main fuel injection part 81 controlling a fuel injection valve 6 so as to inject main fuel; a flow speed estimation part 83 estimating flow speed of an air-fuel mixture by controlling an ignition device 7 at the timing of inhibiting ignition of the air-fuel mixture; and an auxiliary fuel injection part 84 executing auxiliary fuel injection. The auxiliary fuel injection part 84 executes the auxiliary fuel injection when the estimated flow speed is smaller than a predetermined value Vp1, and increases injection amount of the auxiliary fuel injection when a determination that the estimated flow speed is a predetermined comparison value or smaller is made in a region with a relatively large engine load, compared to when a determination that the estimated flow speed is larger than the comparison value is made in a region with a relatively low engine load.SELECTED DRAWING: Figure 16

Description

[Technical field]

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

[0002] In order to improve the fuel efficiency of an engine, it is preferable to increase the combustion speed. When an engine is equipped with a spark plug, the mixture in the cylinder is ignited by the spark plug, generating a flame around the spark plug. This flame propagates and reacts with the unburned mixture, completing one cycle of combustion. Therefore, in order to increase the combustion speed in such an engine, it is advantageous to have a large contact area between the flame and the unburned mixture, as this will result in a quicker reaction. For this reason, it is preferable to stabilize the flow of the mixture in the cylinder while generating a lot of turbulence.

[0003] It is known that turbulence in a cylinder occurs when the mixture collapses before the piston reaches the compression top dead center during the compression stroke. However, the state of the mixture can change from cycle to cycle. For this reason, methods for estimating the mixture flow have been studied.

[0004] For example, Patent Document 1 describes a technique for estimating the flow state of the air-fuel mixture and controlling the ignition timing based on the estimation result. Specifically, an ignition plug is ignited multiple times before the ignition timing, a current value of the discharge path of the ignition plug is detected, and the flow state of the air-fuel mixture is estimated according to each current value. Then, the ignition timing is controlled based on the estimation 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] However, as a result of extensive research, the inventors of the present application have discovered that the position of the vortex center of the flow formed in the cylinder causes differences in the state of the flow in the latter half of the compression stroke, and that these differences are one of the factors causing combustion fluctuations.

[0007] Specifically, the flow of the mixture may become an oblique flow due to the combination of a tumble flow component that constitutes a vertical vortex and a swirl flow component that constitutes a horizontal vortex. In such a case, the center of the vortex of the flow is originally set to be located near the center of the cylinder when viewed from the axial direction of the cylinder and the direction perpendicular to the axial direction (hereinafter referred to as the plan view and the side view).

[0008] If the center of the vortex is located near the center of the cylinder, in the latter half of the compression stroke, the flow will swirl around the spark plug in both plan and side views. In this case, the degree of turbulence will be approximately uniform throughout the cylinder. The flame will also propagate in a balanced manner, achieving the desired combustion.

[0009] However, due to variations from cycle to cycle, the vortex center of the swirl component of the mixture flow may tilt and be positioned radially outward from the center of the cylinder in a plan view. In such cases, the swirl flow becomes less rotatable, and in parts of the cylinder away from the vortex center, the flow speed decreases due to the influence of the wall, and the degree of turbulence also weakens. In such parts, it is difficult for the flame to propagate. This causes localized combustion delays, resulting in combustion fluctuations.

[0010] Therefore, in order to improve the fuel efficiency of an engine, if there are any areas in a cylinder where combustion is delayed, it is necessary to speed up combustion in that area and promote flame propagation.

[0011] In particular, the higher the engine load, the greater the amount of intake air introduced into the cylinder. As the intake air volume increases, the flow inside the cylinder also becomes stronger. This increases the inertial force acting on the swirl component of the mixture flow, so the vortex center of the swirl component tends to be located even further away from the center of the cylinder. As a result, the flow inside the cylinder becomes more uneven, and combustion fluctuations become more pronounced.

[0012] The technology disclosed herein has been made in consideration of the above points, and its purpose is to suppress combustion fluctuations during high load operation and stabilize engine combustion. [Means for solving the problem]

[0013] As a result of extensive research, the inventors have discovered that by detecting the current value of the discharge path generated between the electrodes of the spark plug before the mixture starts to burn during the intake stroke or compression stroke, it is possible to estimate the position of the vortex center in the cylinder and to estimate the state of the mixture flow in the latter half of the compression stroke when the mixture is ignited. The technology disclosed herein is based on this finding.

[0014] In other words, the technology disclosed herein relates to an engine system including an engine in which a fuel injection valve and an ignition plug are installed in the center of a cylinder having a pent roof-shaped ceiling, and intake air is introduced into the cylinder from the ceiling, an operating condition detector that detects the operating condition of the engine, and a controller electrically connected to each of the ignition device that activates the spark plug, the fuel injection valve, and the operating condition detector.

[0015] The controller has: a main fuel injection unit that sets a main fuel injection amount 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 so that the set amount of main fuel is injected at the main fuel injection timing; a flow velocity estimation unit that controls the ignition device to create a discharge path between electrodes of the spark plug at a predetermined timing when the mixture is not ignited and detect a parameter related to a current value of the discharge path and estimates the level of the flow velocity of the mixture based on the parameter; and an auxiliary fuel injection unit that controls the fuel injection valve based on the estimated flow velocity estimated by the flow velocity estimation unit to perform auxiliary fuel injection at a timing retarded from the main fuel injection timing, and the auxiliary fuel injection unit performs the auxiliary fuel injection when the estimated flow velocity is less than a predetermined value.

[0016] Furthermore, when the auxiliary fuel injection section determines that the estimated flow velocity is smaller than the predetermined value and equal to or less than a predetermined comparison value set corresponding to the engine load region in a relatively high engine load region, it increases the injection amount of the auxiliary fuel injection compared to when the estimated flow velocity is determined to be larger than the comparison value in a relatively low engine load region.

[0017] That is, according to this engine system, the engine has a cylinder with a pent roof type ceiling, and a fuel injection valve and an ignition plug are installed in the center. Then, as the intake air is introduced into the cylinder from the pent roof type ceiling, a flow including a vertical vortex (a so-called tumble flow component) and a horizontal vortex (a so-called swirl flow component) is formed inside the cylinder. The flow is an oblique flow inclined with respect to the axis of the cylinder.

[0018] The flow velocity estimation unit of the controller controls the ignition device to apply a high voltage between the electrodes of the spark plug to generate a discharge path when the air-fuel mixture is not ignited, and to detect a parameter related to a current value of the discharge path. For example, the controller controls the ignition device to detect a discharge time of the current flowing through the electrodes.

[0019] The stronger the flow near the spark plug, the longer the discharge path that is generated between the electrodes. As the discharge path extends, the resistance between the electrodes increases, accelerating the drop in the voltage applied between the electrodes. As a result, the time it takes for the energy applied to the spark plug to be consumed, that is, the discharge time, becomes shorter. The ignition device can estimate the flow speed of the mixture near the spark plug by detecting the discharge time of the current.

[0020] The inventors have found that it is possible to estimate the position of the vortex center of the swirl flow component of the flow in the cylinder based on the estimated flow velocity. Based on this finding, they have focused on the fact that it is possible to estimate the occurrence and position of a portion where flame propagation is difficult before igniting the mixture. Therefore, in this engine system, the flow velocity estimation unit estimates the flow velocity of the mixture, and the auxiliary fuel injection unit executes auxiliary fuel injection based on the estimated flow velocity.

[0021] That is, the auxiliary fuel injection unit injects auxiliary fuel when the estimated flow velocity is less than a predetermined value. When the estimated flow velocity is less than the predetermined value, there are areas in the cylinder where flames are difficult to propagate at the timing in the latter half of the compression stroke when the mixture is ignited. In response to this, by injecting auxiliary fuel, it is possible to distribute a mixture with a high fuel concentration to the areas where flames are difficult to propagate. As a result, local combustion delays are improved and combustion fluctuations can be suppressed.

[0022] Furthermore, in this engine system, when the auxiliary fuel injection section determines that the estimated flow velocity is smaller than a predetermined value and equal to or less than a predetermined comparison value set corresponding to the engine load region in a region where the engine load is relatively high, it increases the amount of auxiliary fuel injection compared to when the estimated flow velocity is determined to be greater than the comparison value in a region where the engine load is relatively low.

[0023] In other words, at high loads, the amount of intake air introduced is greater than at low loads, and the flow within the cylinder is also stronger accordingly. This makes it easier for the vortex center of the swirl flow component to be located further away from the center of the cylinder, resulting in significant combustion fluctuations. Therefore, this engine system adopts the above-mentioned configuration, which adjusts the amount of auxiliary fuel injection in response to changes in engine load, and increases the area where the amount of auxiliary fuel injection is increased as the load increases.

[0024] This engine system uses auxiliary fuel injection to distribute a rich fuel mixture to areas of the cylinder where the flow is weak, in an appropriate state that corresponds to changes in engine load. This makes it possible to stabilize flame propagation during combustion, even when the engine load changes from high to low. As a result, combustion fluctuations are suppressed, engine combustion is stabilized, and engine fuel efficiency is improved.

[0025] The flow velocity estimation unit may control the ignition device to detect the parameter after an intake valve of the engine is opened and the introduction of intake air into the cylinder is started, by the time the intake valve is closed and the introduction of intake air into the cylinder is stopped.

[0026] The vortex center of the swirl component of the intake air flow is stable when the intake air is introduced into the cylinder. Therefore, by the ignition device detecting the parameters during the aforementioned period, the controller can accurately estimate the position of the vortex center of the swirl component in the cylinder.

[0027] The ignition device may detect the parameter after a predetermined time constant has elapsed since the intake valve is opened.

[0028] The intake air is prone to variation for a certain period of time from the moment the intake valve opens. Therefore, by prohibiting the ignition device from detecting parameters for this certain period of time, the position of the vortex center of the swirl flow component in the cylinder can be estimated with even greater accuracy. Effect of the Invention

[0029] According to an engine system to which the disclosed technology is applied, even if the engine load changes, an appropriate amount of auxiliary fuel is injected accordingly. As a result, even if there are areas in the cylinder where combustion is delayed, the combustion in those areas can be accelerated and flame propagation can be promoted. As a result, combustion fluctuations are suppressed, and engine combustion can be stabilized. [Brief description of the drawings]

[0030] [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 central position of the lateral vortex and the propagation state of the flame inside the cylinder. [Figure 7] FIG. 7 is a diagram illustrating the time variations in voltage and current between the electrodes of the 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 central position of the lateral vortex. [Figure 9] FIG. 9 is a timing chart illustrating the injection timing of the main fuel, the discharge timing, the injection timing of the auxiliary fuel, and the main ignition timing. [Figure 10] FIG. 10 is a diagram explaining the change in flow within the cylinder and the distribution of auxiliary fuel when the center position of the cross vortex is inclined toward the exhaust valve side and when the center position of the cross vortex is inclined toward the intake valve side. [Figure 11]FIG. 11 is a flowchart illustrating an example of an engine control procedure executed by the ECU. [Figure 12A] FIG. 12A is a diagram for explaining the flow state of a lateral vortex due to differences in engine load. [Figure 12B] FIG. 12B is a diagram for explaining the flow state of a lateral vortex depending on the engine load. [Figure 13] FIG. 13 is a map for setting the injection amount of the auxiliary fuel injection formed by the estimated flow speed and the engine load in the engine system of the application example. [Figure 14] FIG. 14 is a graph showing the relationship between the estimated flow velocity and the injection amount of auxiliary fuel injection when the engine load is constant. [Figure 15] FIG. 15 is a graph showing the relationship between the injection amount of auxiliary fuel injection and the engine load when the estimated flow velocity is constant. [Figure 16] FIG. 16 is a timing chart showing the timing for auxiliary fuel injection in the engine system of the application example. [Figure 17] FIG. 17 is a part of a flowchart of the auxiliary fuel injection control. [Figure 18] FIG. 18 shows the remaining part of the flowchart of the auxiliary fuel injection control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Hereinafter, an embodiment of the disclosed technology will be described with reference to the drawings. In the description, a basic engine system will be described first. Then, an engine system to which the disclosed technology is applied will be described as an application example. Note that the engine and engine system described here are merely examples.

[0032] <Basic engine system> 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.

[0033] 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.

[0034] (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.

[0035] 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.

[0036] 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.

[0037] 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 tumble flow inside the cylinder 11.

[0038] 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 is of an electric or hydraulic type. The intake S-VT 23 continuously changes the rotational phase of the intake camshaft within a predetermined angle range. The opening period of the intake valve 21 does not change.

[0039] An exhaust port 19 is formed in the cylinder head 13 for each cylinder 11. The exhaust port 19 communicates with the inside of the cylinder 11.

[0040] 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 is of an electric or hydraulic type. The exhaust S-VT 24 continuously changes the rotational phase of the exhaust camshaft within a predetermined angle range. The opening period of the exhaust valve 22 does not change.

[0041] An injector 6 is attached to the cylinder head 13 for each cylinder 11. As shown in Fig. 2, the injector 6 is disposed in the center of the cylinder 11. More specifically, the injector 6 is disposed in the valley of the pent roof where the inclined surface 1311 and the inclined surface 1312 intersect.

[0042] The injector 6 directly injects fuel into the cylinder 11. The injector 6 is an example of a fuel injection valve. Although detailed illustration is omitted, the injector 6 is a multi-hole type injector having a plurality of nozzles. As shown by the two-dot chain line in FIG. 2, the injector 6 injects fuel in a radial manner 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.

[0043] 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.

[0044] 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.

[0045] As shown in FIG. 1 or FIG. 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 (arc discharge) and ignite the air-fuel mixture in the cylinder 11. The ignition device 7 also causes the spark plug 25 to discharge when the air-fuel mixture is not ignited, and detects a parameter related to the current value of the discharge path generated between the electrodes at that time, as will be described in detail later. The detected parameter is used to estimate the flow state in the cylinder 11. The configuration of the ignition device 7 will be described later.

[0046] An intake passage 40 is connected to one side of the engine 1. The intake passage 40 is connected to the intake port 18 of each cylinder 11. Air introduced into the cylinder 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 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.

[0047] 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 air introduced into the cylinder 11 by adjusting the opening degree of the valve.

[0048] The engine 1 has a swirl generating section that generates a swirl flow in 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 18b of the first intake passage 18a and the second intake passage 18b (see FIG. 2) that are parallel to each other, downstream of the surge tank 42. The swirl control valve 56 is an opening adjustment valve that can narrow the cross section of the second intake passage 18b. When the opening of the swirl control valve 56 is small, the amount of intake air flowing into the cylinder 11 from the first intake passage 18a shown in FIG. 2 is relatively large and the amount of intake air flowing into the cylinder 11 from the second intake passage 18b is relatively small, so that the swirl flow in the cylinder 11 becomes strong. When the opening of the swirl control valve 56 is large, the flow rates of intake air flowing into the cylinder 11 from the first intake passage 18a and the second intake passage 18b become approximately equal, weakening the swirl flow in the cylinder 11. When the swirl control valve 56 is fully opened, no swirl flow is generated. The swirl flow circulates counterclockwise in FIG. 2, as indicated by the outlined arrow.

[0049] 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.

[0050] 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.

[0051] An EGR passage 52 is connected between the intake passage 40 and the exhaust passage 50. The EGR passage 52 is a passage for recirculating a portion 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 between the throttle valve 43 and the surge tank 42 in the intake passage 40.

[0052] 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.

[0053] 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 I / F circuit 103 for inputting and outputting electric signals. The ECU 10 is an example of a controller.

[0054] 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. Air flow sensor SW1: disposed downstream of the air cleaner 41 in the intake passage 40, and measures the flow rate of air flowing through the intake passage 40. Intake air temperature sensor SW2: is disposed downstream of the air cleaner 41 in the intake passage 40 and measures the temperature of the air flowing through the intake passage 40. Intake pressure sensor SW3: Attached to the surge tank 42 and measures the pressure of the air introduced into the cylinder 11 Cylinder pressure sensor SW4: Attached to the cylinder head 13 corresponding to each cylinder 11, and measures the pressure inside each cylinder 11. Water temperature sensor SW5: Attached to engine 1 and measures the temperature of the cooling water. Crank angle sensor SW6: is attached to the engine 1 and measures the rotation angle of the crankshaft 15. Accelerator opening sensor SW7: Attached to the accelerator pedal mechanism, measures the accelerator opening corresponding to the amount of accelerator pedal operation. Intake cam angle sensor SW8: Attached to the engine 1 and measures the rotation angle of the intake camshaft. Exhaust cam angle sensor SW9: Attached to the engine 1 and measures the rotation angle of the exhaust camshaft.

[0055] 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.

[0056] 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.

[0057] The ECU 10, which is electrically connected to various sensors and various devices, constitutes a plurality of functional blocks for operating the engine 1, as will be described later.

[0058] (Ignition device configuration) 4 illustrates the configuration of the ignition device 7. The ignition device 7 applies a voltage between the center electrode 251 and the ground electrode 252 of the spark plug 25, and causes a discharge in the cylinder 11. The ignition device 7 has an ignition coil 70. The ignition coil 70 has a primary coil 70a, a secondary coil 70c, and an iron core 70b. The ignition device 7 also has a capacitor 72, a transistor 73, an energy generating device 74, and an ignition controller 75.

[0059] The center electrode 251 is connected to the 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.

[0060] One end of the primary coil 70a is connected to a capacitor 72. The capacitor 72 stores electric energy for causing a primary current to flow through the primary coil 70a. The energy generator 74 includes a power source. The energy generator 74 charges the capacitor 72.

[0061] One end of the primary coil 70a is connected to the collector of the transistor 73. The transistor 73 turns the primary current of the ignition coil 70 on and off.

[0062] 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.

[0063] The ignition controller 75 controls the energy generator 74 and the transistor 73 to ignite the air-fuel mixture in the cylinder 11 using the spark plug 25 at a predetermined timing.

[0064] The ignition controller 75 can also 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. As described above, the ignition device 7 causes the spark plug 25 to discharge when the air-fuel mixture is not ignited, and detects parameters related to the current value at that time.

[0065] (Engine operation control) Next, the operation control of the engine 1 by the ECU 10 will be described. The engine 1 is a spark ignition engine. An injector 6 injects an amount of fuel corresponding to the operating state of the engine 1 into a cylinder 11 during the intake stroke or compression stroke. An air-fuel mixture is provided in the cylinder 11. An ignition plug 25 ignites the mixture at a predetermined timing near the top dead center of the compression stroke, and the mixture is burned.

[0066] In order to improve fuel efficiency, the engine 1 generates turbulence in the cylinder 11. When turbulence occurs in the cylinder 11, the combustion speed increases. Specifically, in the engine 1, the ceiling of the cylinder 11 is of a pent roof type, and the intake port 18 is a tumble port. The intake air introduced into the cylinder 11 generates a tumble flow. The engine 1 also has a swirl control valve 56. By closing the swirl control valve 56, the intake air introduced into the cylinder 11 generates a swirl flow. By combining the tumble flow and the swirl flow, an oblique flow that is a combination of a vertical vortex and a horizontal vortex is formed in the cylinder 11.

[0067] Here, the state of the intake air flow in the cylinder 11 is not the same in every cycle, but may change from cycle to cycle due to various factors. If the state of the intake air flow in the cylinder 11 changes, the combustion speed may change. If the combustion speed changes from cycle to cycle, this will cause combustion fluctuations in the engine 1. The engine system and the control method for the engine 1 disclosed herein suppress the change in combustion speed from cycle to cycle, thereby suppressing the combustion fluctuations in the engine 1.

[0068] More specifically, the engine system estimates the flow conditions within the cylinder 11 on a cycle-by-cycle basis and injects supplemental fuel into the cylinder 11, if necessary, based on the estimated flow conditions.

[0069] 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 and a main ignition control unit 82. The main fuel injection unit 81 is a functional block that sets the amount and injection timing of the main fuel corresponding to the required torque of the engine 1, and causes the injector 6 to inject the main fuel. The main ignition control unit 82 is a functional block that ignites the air-fuel mixture provided in the cylinder 11 at a predetermined timing using the spark plug 25 after the injection of the main fuel.

[0070] The ECU 10 also has a determination unit 83 and an auxiliary fuel injection unit 84. The determination unit 83 is a functional block that determines the flow state within the cylinder 11 based on parameters detected using the ignition device 7 and the spark plug 25, as described below. The auxiliary fuel injection unit 84 is a functional block that injects auxiliary fuel into the cylinder 11 as necessary, before the spark plug 25 ignites the air-fuel mixture, based on the flow state within the cylinder 11 determined by the determination unit 83.

[0071] Hereinafter, the estimation of the flow state within the cylinder 11 executed by the engine control device illustrated in FIG. 5 will be described, and then the auxiliary fuel injection control according to the estimated flow state will be described.

[0072] (Estimation of flow state) Fig. 6 is a diagram showing the relationship between the central position of the transverse vortex during the intake stroke and the flow state inside cylinder 11 in the latter half of the compression stroke. Chart 601 in Fig. 6 illustrates an example of the flow state inside cylinder 11 when the central position of the transverse vortex during the intake stroke is inclined toward the exhaust valve inside cylinder 11, and chart 604 illustrates an example of the flame propagation state after the latter half of the compression stroke when the crank angle has progressed from the state of chart 601.

[0073] Similarly, chart 602 illustrates the flow conditions within cylinder 11 during the intake stroke when the center of the lateral vortex is located approximately along the axis of cylinder 11 at the center of cylinder 11, and chart 605 illustrates the flame propagation conditions in the latter half of the compression stroke when the crank angle has progressed from the state of chart 602.

[0074] Moreover, chart 603 illustrates an example of the flow state within cylinder 11 when the position of the center of the vertical vortex during the intake stroke is tilted toward the intake valve inside cylinder 11, and chart 606 illustrates an example of the flow state within cylinder 11 in the latter half of the compression stroke when the crank angle has progressed from the state of chart 603.

[0075] First, as shown in chart 602, when the center of the transverse vortex in the cylinder 11 is located along the axis of the cylinder 11 in the central part of the cylinder 11 in a plan view, the center of the transverse vortex is located near the axis even in the latter half of the compression stroke, as shown in chart 605. 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 in the central part of the cylinder 11, the flame propagates from the central part 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 605. The flame propagates uniformly or approximately uniformly from near the center to the periphery of the cylinder 11. The propagation of the flame is promoted by the turbulence in the cylinder 11, so the combustion speed is relatively fast.

[0076] As shown in chart 601, when the position of the center of the transverse vortex is inclined toward the exhaust valve side in a plan view, 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 near the compression top dead center 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 604. At this time, the flow speed of the transverse vortex increases with distance from the center of the transverse vortex (see the concentric circles in chart 604). In other words, the flow speed of the transverse vortex is relatively faster on the intake valve side, which is far from the center of the transverse vortex. 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, whereas the flame propagating from the center of the cylinder 11 to the intake valve side is strongly bent by the fast flow velocity of the lateral vortex, making it difficult to propagate radially outward. As a result, as shown by the dashed line in chart 604, the area on the intake valve side is an area where flame propagation is difficult. In this case, the combustion speed is slower than in the case of chart 605.

[0077] As shown in chart 603, when the position of the center of the transverse vortex is inclined toward the intake valve side in a plan view, 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 near the compression top dead center 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 606. 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 shown by the solid arrow. 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 606, 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 605.

[0078] In the engine system, the ignition device 7 detects the flow state in the cylinder 11. Specifically, the ignition device 7 discharges electricity in the cylinder 11 when the air-fuel mixture is not ignited, and detects the duration of the discharge. The determination unit 83 estimates the strength of the flow near the spark plug 25 based on the detected discharge duration, and determines the center position of the vertical vortex based on the estimated flow strength.

[0079] 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 (see charts 703 and 704). 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, accelerating the drop of 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.

[0080] 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 (see chart 703). The stronger the flow near the spark plug 25, the shorter the discharge time is (see chart 704), 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 determination unit 83 can estimate the strength of the flow near the spark plug 25 (i.e., the flow speed).

[0081] 8 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 800 in FIG.

[0082] To form a swirl flow, the intake air mainly flows into the cylinder 11 from the first intake passage 18a. As shown in chart 802 of Fig. 8, a flow velocity distribution occurs in the cylinder 11 during the intake stroke due to the intake air mainly flowing in from the first intake passage 18a. If the velocity distribution during the intake stroke is as shown in the figure, that is, if 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 and decreases 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.

[0083] On the other hand, as shown in chart 801, 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. In this case, the flow velocity near the spark plug 25 becomes slower than that of V4.

[0084] Furthermore, as shown in chart 803, when the maximum flow velocity in the flow velocity distribution during the intake stroke is relatively low and the kurtosis of the flow velocity distribution is low, the center of the lateral vortex is inclined toward the intake valve side. In this case, the flow velocity near spark plug 25 is faster than V3.

[0085] The lateral vortex formed inside cylinder 11 mainly by the swirl flow stabilizes during the intake stroke from when intake valve 21 opens until when it closes. Ignition device 7 causes spark plug 25 to discharge during the intake stroke and detects the discharge time. 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 lateral vortex stabilizes until intake valve 21 closes. Ignition device 7 causes spark plug 25 to discharge after a predetermined time (time constant Δt, described later) has elapsed since intake valve 21 opens, and detects the discharge time.

[0086] If the discharge time is shorter than a first threshold corresponding to speed V3, the judgment unit 83 can estimate that the central position of the transverse vortex is inclined toward the intake valve, and if the discharge time is longer than a second threshold corresponding to speed V4, the judgment unit 83 can estimate that the central position of the transverse vortex is inclined toward the exhaust valve, and if the discharge time is between the first and second thresholds, the judgment unit 83 can estimate that the central position of the transverse vortex is along the axis of cylinder 11 at the center of cylinder 11.

[0087] (Auxiliary fuel injection control) 9 is a timing chart illustrating the timing of fuel injection by the injector 6 and the timing of discharge and ignition by the spark plug 25. The crank angle progresses from left to right in FIG.

[0088] As described above, when the center position of the lateral vortex shifts due to the variation in the intake flow, regions where the degree of turbulence is weak and / or where flame propagation is difficult are generated in the cylinder 11. The auxiliary fuel locally distributes a mixture with a high fuel concentration in such regions where the degree of turbulence is weak and / or where flame propagation is difficult, thereby promoting flame propagation to those regions.

[0089] First, the main fuel injection unit 81 injects main fuel into the cylinder 11 through the injector 6 during the intake stroke from when the intake valve 21 opens until when the intake valve 21 closes (see main fuel injection 904). The main fuel flows and diffuses into the cylinder 11, forming an air-fuel mixture in the cylinder 11.

[0090] As shown in chart 902, the determination unit 83 causes the ignition device 7 and the spark plug 25 to perform a test discharge 905 during the intake stroke period after a predetermined time constant Δt has elapsed since the intake valve 21 opens. The discharge 905 is a discharge that is performed during a period in which the air-fuel mixture is not ignited. The ignition device 7 detects a discharge time corresponding to the discharge. The determination unit 83 estimates the center position of the lateral vortex from the discharge time detected during the discharge 905.

[0091] When the discharge time detected by the ignition device 7 is between the first threshold value and the second threshold value, the center position of the transverse vortex is along the axis of the cylinder 11 at the center of the cylinder 11. In this case, the injection of auxiliary fuel is not necessary. As shown in the chart 902 of FIG. 9, the auxiliary fuel injection unit 84 stops the injection of auxiliary fuel, 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 907 of FIG. 9). In this case, since the center position of the transverse vortex is located at the center of the cylinder 11, the degree of turbulence is uniform or approximately uniform throughout the cylinder 11. The flame propagates uniformly or approximately uniformly from the center to the periphery of the cylinder 11. The combustion speed is relatively fast.

[0092] Next, a case where the discharge time detected by the ignition device 7 is smaller than the first threshold value (the discharge time is shorter than the first threshold value) 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 901 of FIG. 9, the auxiliary fuel injection unit 84 causes the injector 6 to inject a predetermined amount of auxiliary fuel, that is, first auxiliary fuel 908. The injector 6 injects the first auxiliary fuel 908 at a first injection timing, for example, in the first half of the compression stroke or the second half of the compression stroke.

[0093] P1001 and P1002 in Fig. 10 are diagrams for explaining the change in flow and distribution of the first auxiliary fuel in the cylinder 11 when the center position of the transverse vortex is inclined toward the intake valve side. When the center of the transverse vortex is inclined toward the intake valve side, as shown in P1001, the velocity distribution in 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.

[0094] In the first or second half of the compression stroke, the first auxiliary fuel injected radially from the center of the cylinder 11 is carried by the flow and transported in the circumferential direction. Although the timing of the injection of the auxiliary fuel is relatively advanced, the spray of the auxiliary fuel injected on the intake valve side is carried by a flow with a slower flow velocity and moves a smaller amount, while the spray of the auxiliary fuel injected on the exhaust valve side is carried by a flow with a faster flow velocity, so that at the ignition timing (P1002), the sprays of the auxiliary fuel overlap and the fuel concentration of the mixture on the intake valve side increases.

[0095] After the injection of the first auxiliary fuel, 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 907 in chart 901). As described above, the flame is prevented from propagating radially outward by the lateral vortex with the center position shifted, so that the flame does not easily propagate toward the intake valve side. However, the high fuel concentration of the mixture on the intake valve side promotes flame propagation toward the intake valve side. This increases the combustion speed, 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. The combustion fluctuation of the engine 1 is suppressed.

[0096] Next, a case where the discharge time detected by the ignition device 7 is greater than the second threshold (the discharge time is longer than the second threshold) will be described. In this case, the center position of the lateral vortex is inclined toward the exhaust valve side of the cylinder 11. As shown in a chart 903 in FIG. 9, the auxiliary fuel injection unit 84 causes the injector 6 to inject a predetermined amount of auxiliary fuel, that is, a second auxiliary fuel 909. The injector 6 injects the second auxiliary fuel 909 at a second injection timing in the latter half of the compression stroke. The injection timing of the second auxiliary fuel 909 is later than the injection timing of the first auxiliary fuel 908.

[0097] P1003 and P1004 in Fig. 10 are diagrams for explaining the change in flow and distribution of the second auxiliary fuel in the cylinder 11 when the center position of the transverse vortex is inclined toward the exhaust valve side. When the center of the transverse vortex is inclined toward the exhaust valve side, as shown in P1003, the velocity distribution in the cylinder 11 in the latter half of the compression stroke has an extremely fast flow velocity near the liner.

[0098] At a late timing in the latter half of the compression stroke, the second auxiliary fuel is injected radially from the center of the cylinder 11, and the auxiliary fuel injected toward the intake valve side is transported by a slow flow and remains on the intake valve side. On the other hand, the auxiliary fuel injected toward the exhaust valve side is transported by a fast flow and is quickly carried in the circumferential direction to the intake valve side. As a result, at the ignition timing (P1004), the sprays of the auxiliary fuel overlap, and the fuel concentration of the mixture on the intake valve side increases.

[0099] After the injection of the second auxiliary fuel 909, 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 907 in chart 903). 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 high fuel concentration of the mixture on the intake valve side promotes flame propagation toward the intake valve side. This increases the combustion speed, 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. Therefore, the combustion fluctuation of the engine 1 is suppressed.

[0100] Therefore, by injecting auxiliary fuel 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.

[0101] The energy imparted to the spark plug 25 during discharge and main ignition may be the same or different.

[0102] (Control procedure of engine control device) Next, the control procedure of the control device for the engine 1 described above will be described with reference to the flowchart of Fig. 11. First, in step S1, the ECU 10 acquires the sensor values ​​of the sensors SW1 to SW9. In the following step S2, the ECU 10 calculates the required torque of the engine 1 based on the acquired sensor values. In step S3, the ECU 10 determines the injection amount and injection timing of the main injection to satisfy the required torque. In addition, the ECU 10 also performs the steps S In step 4, the main ignition timing is determined.

[0103] In step S5, the ECU 10 determines the timing of discharge. In this step, the ECU 10 also determines a time constant Δt for performing discharge. The ECU 10 may adjust the time constant Δt according to, for example, the operating state of the engine 1, i.e., the load and / or the rotation speed of the engine 1.

[0104] In the following step S6, the ECU 10 causes the injector 6 to perform a main injection 904 in accordance with the injection amount and injection timing determined in step S3. As illustrated in Fig. 9, the injector 6 performs the main injection 904 during the intake stroke.

[0105] In step S7, the ECU 10 causes the ignition device 7 to execute the discharge 905. The ignition device 7 executes the discharge 905 during the intake stroke and detects the discharge time.

[0106] In step S8, the ECU 10 determines whether the discharge time is less than the first threshold value. If the determination in step S8 is YES, the process proceeds to step S10. If the determination in step S8 is NO, the process proceeds to step S9.

[0107] In step S9, the ECU 10 determines whether the discharge time is greater than the second threshold. If the determination in step S9 is YES, the process proceeds to step S11. If the determination in step S9 is NO, the process proceeds to step S13. That is, if the determination in step S9 is NO, auxiliary fuel is not injected.

[0108] In step S10, the ECU 10 determines the injection amount and injection timing of the first auxiliary fuel 908. As described above, the injection timing of the first auxiliary fuel 908 is more advanced than the injection timing of the second auxiliary fuel 909. In step S11, the ECU 10 determines the injection amount and injection timing of the second auxiliary fuel 909. The injection timing of the second auxiliary fuel 909 is more retarded than the injection timing of the first auxiliary fuel 908. The injection amount and injection timing of the first auxiliary fuel 908 and the injection amount and injection timing of the second auxiliary fuel 909 may be determined in accordance with the operating state of the engine 1.

[0109] Once the injection amount and injection timing of the auxiliary fuel have been determined, in the next step S12, the ECU 10 injects the auxiliary fuel in the first or second half of the compression stroke (in the case of the first auxiliary fuel 908), or in the second half of the compression stroke (in the case of the second auxiliary fuel 909), and in step S13, the ECU 10 ignites the mixture using the spark plug 25.

[0110] <Applications of engine systems> Next, an application example of the above-mentioned engine system that can improve the combustion stability of the engine 1 in response to changes in engine load will be described. The technology disclosed here relates to this engine system.

[0111] At high loads, that is, when the torque (engine load) required to be output from the engine 1 increases, the amount of intake air and the amount of fuel introduced into the cylinder 11 increase in response to that demand. In particular, when the amount of intake air increases, the flow velocity of the intake air introduced into the cylinder 11 also increases, and accordingly, the flow inside the cylinder 11 (hereinafter also referred to as in-cylinder flow) also becomes stronger.

[0112] When this happens, the vortex center of the swirl flow component that constitutes the transverse vortex in the in-cylinder flow tends to be tilted even further due to the action of inertial force and to be located away from the center of the cylinder 11. As a result, the in-cylinder flow in the cylinder 11 varies more, resulting in noticeable combustion fluctuations.

[0113] 12A and 12B show examples of the state of the swirl flow component of the in-cylinder flow during the intake stroke when the vortex center is offset in plan view. The two-dot chain lines A1 and A2 indicate the areas where flames are difficult to propagate, which occur in the latter half of the compression stroke. FIG. 12A shows the case where the mixture flow rate is low near the center of the cylinder 11 and the vortex center is offset (corresponding to a state slower than V4 in FIG. 8). FIG. 12B shows the case where the mixture flow rate is high near the center of the cylinder 11 and the vortex center is offset (corresponding to a state faster than V3 in FIG. 8). The dashed line shows the state at low load. The solid line shows the state at high load. The Ex side shows the exhaust side, the In side shows the intake side, the R side shows the rear side, and the F side shows the front side.

[0114] As described above, the intake air is introduced into the cylinder 11 mainly from the rear side of the intake side so as to flow in along the circumferential direction of the cylinder 11. Under high load, the intake air is introduced into the cylinder 11 with greater force than under low load. Therefore, under high load, the flow rate of the intake air increases in the radially outer portion of the cylinder 11. In addition, in the vicinity of the liner that constitutes the inner wall of the cylinder 11, the flow rate of the intake air decreases rapidly the closer it gets to the liner due to contact resistance with the wall surface.

[0115] On the other hand, the flow velocity of the intake air does not change significantly regardless of the engine load near the center of the cylinder 11. Therefore, the flow velocity of the mixture near the center of the cylinder 11 can be stably estimated by the spark plug 25. The position of the vortex center of the swirl flow component can also be stably estimated.

[0116] As a result of this change in the state of the in-cylinder flow, the position of the vortex center of the swirl flow component shifts from position C1 to position C2, radially outward of the cylinder 11. Furthermore, as shown in Fig. 12A, when the vortex center is biased toward the exhaust side, the position of the vortex center of the swirl flow component shifts further toward the exhaust side of the cylinder 11. As shown in Fig. 12B, when the vortex center is biased toward the intake side, the position of the vortex center of the swirl flow component shifts further toward the intake side of the cylinder 11.

[0117] Thus, at high loads, the vortex center of the swirl component of the in-cylinder flow is more likely to vary and become more unevenly distributed than at low loads. As a result, the area where flame propagation is difficult, which occurs in the latter half of the compression stroke, expands from state A1 to state A2, and the in-cylinder flow is more likely to vary within the cylinder 11. As a result, there is a risk that combustion fluctuations will become more pronounced.

[0118] Therefore, in this application example, a device has been devised to suppress combustion fluctuations even in such a case, and to stabilize the combustion of the engine 1 even under high load. The specific contents of this engine system will be described below.

[0119] The engine system of this application example is further configured such that the injection amount of auxiliary fuel injection is adjusted depending on the level of the engine load.

[0120] Specifically, in the above-mentioned engine system, the determination unit 83 estimates the position of the vortex center of the swirl flow component from the discharge time detected by the ignition device 7. Then, based on the estimation result, the auxiliary fuel injection unit 84 is configured to inject auxiliary fuel at a predetermined timing.

[0121] On the other hand, in this engine system, the determination unit 83 further estimates an estimated flow velocity related to the flow velocity of the mixture, specifically, an estimated flow velocity near the center of the cylinder 11, from the discharge time detected by the ignition device 7. That is, the determination unit 83 of this engine system constitutes a flow velocity estimation unit (hereinafter, the determination unit 83 is also referred to as a flow velocity estimation unit 83).

[0122] The auxiliary fuel injection unit 84 performs auxiliary fuel injection with an injection amount according to the level of the load, based on the estimated flow velocity estimated by the flow velocity estimation unit 83. That is, when the estimated flow velocity is determined to be smaller than a predetermined value and equal to or less than a predetermined comparison value set corresponding to the engine load region in a region where the engine load is relatively high, the auxiliary fuel injection unit 84 increases the injection amount of the auxiliary fuel injection compared to when the estimated flow velocity is determined to be larger than the comparison value in a region where the engine load is relatively low.

[0123] (Setting the amount of auxiliary fuel injection) 13 is a map for setting the injection amount of auxiliary fuel injection based on the estimated flow speed and the engine load. The vertical axis represents the estimated flow speed, that is, the flow speed of the mixture near the spark plug 25 estimated by the flow speed estimation unit 83. The horizontal axis represents the judged load, that is, the engine load judged by the accelerator opening sensor SW7 (an example of an operating state detector). The map of FIG. 13 is stored in the memory 102 of the ECU 10.

[0124] Here, as described above, the estimated flow velocity corresponds to the reciprocal of the discharge time. The shorter the discharge time, the higher the flow velocity of the mixture around the electrode of the spark plug 25 (see FIG. 8). Therefore, the vertical axis of FIG. 13 can be said to be the reciprocal of the discharge time. In the case of this engine system, the auxiliary fuel injection unit 84 performs auxiliary fuel injection based on the estimation result of the flow velocity estimation unit 83. Note that, instead of the estimated flow velocity or the reciprocal of the discharge time, the gradient of the voltage applied to the electrode can also be used. In other words, these correspond to parameters related to the current value.

[0125] The first predetermined value Vp1 shown in Fig. 13 corresponds to the flow velocity V4 of the mixture near the center of the cylinder 11, which corresponds to the above-mentioned second threshold value. The second predetermined value Vp2 shown in Fig. 13 corresponds to the flow velocity V3 of the mixture near the center of the cylinder 11, which corresponds to the above-mentioned first threshold value. Therefore, auxiliary fuel injection is performed in both a region where the estimated flow velocity is less than the first predetermined value Vp1 (low-speed auxiliary injection region) and a region where the estimated flow velocity is greater than the second predetermined value Vp2 (high-speed auxiliary injection region).

[0126] (Low speed side auxiliary injection area) The low-speed auxiliary injection region is divided into two regions, a first region R1 and a second region R2, by a first boundary B1. The first region R1 has a lower estimated flow velocity than the second region R2. The first boundary B1 is inclined so that the estimated flow velocity increases as the load increases.

[0127] Incidentally, although details will be described later, whether the state of the engine 1 belongs to the first region R1 or the second region R2 is determined by the auxiliary fuel injection unit 84 by comparing the state quantity of the engine 1 with a predetermined comparison value corresponding to the first boundary B1. Whether the engine 1 belongs to each of the third region R3, the fourth region R4, and the fifth region R5 described later is also determined by the auxiliary fuel injection unit 84 by comparing the state quantity of the engine 1 with a predetermined comparison value corresponding to the second boundary B2 or the third boundary B3.

[0128] The first region R1 is a region where the injection amount of the auxiliary fuel injection is set to be relatively large, and the second region R2 is a region where the injection amount of the auxiliary fuel injection is set to be relatively small. If the injection amount in the first region R1 is a first injection amount and the injection amount in the second region R2 is a second injection amount, the first injection amount is larger than the second injection amount.

[0129] As described above, the position of the vortex center of the swirl flow component in the in-cylinder flow correlates with the flow velocity of the mixture near the center of the cylinder 11 detected during the intake stroke (see FIG. 8). When the flow velocity is between the first predetermined value Vp1 and the second predetermined value Vp2, the vortex center of the swirl flow component in the in-cylinder flow is located near the center of the cylinder 11, and an appropriate swirling flow is formed that swirls around the spark plug 25. This results in stable combustion. The combustion speed is also relatively fast.

[0130] In contrast, when the flow velocity is less than the first predetermined value Vp1 or higher than the second predetermined value Vp2, the vortex center of the swirl flow component of the in-cylinder flow is located away from the center of the cylinder 11 toward the outer periphery on the exhaust side or the intake side in a plan view. The inclination of the central axis forms a swirling flow that is biased toward the center of the cylinder 11. Therefore, in the latter half of the compression stroke where the mixture is ignited, a portion that is difficult to burn (hereinafter also referred to as a difficult-to-burn portion) is generated on the intake side in the cylinder 11.

[0131] In the difficult-to-burn portion, even if the air-fuel mixture is ignited by the spark plug 25, the flame does not easily propagate. In other words, combustion is delayed locally. This makes it easier for combustion to fluctuate, reduces the combustion speed, and deteriorates fuel economy.

[0132] The lower the estimated flow speed is and the further it is from the first predetermined value Vp1, or the higher the estimated flow speed is and the further it is from the second predetermined value Vp2, the greater the effect of the misalignment of the vortex center. In other words, combustion is delayed further in the combustion-resistant region. Furthermore, as described above, the effect is even greater at high loads than at low loads (see FIGS. 12A and 12B). In other words, combustion is delayed further in the combustion-resistant region.

[0133] Therefore, in this engine system, the injection amount of the auxiliary fuel injection is adjusted according to the engine load, and when the engine load is high, the region where the injection amount of the auxiliary fuel injection is increased is set to be larger compared to when the engine load is low. This makes it possible to suppress combustion fluctuations even when the influence of the positional deviation of the vortex center becomes large and is intensified by changes in the engine load.

[0134] Specifically, as described above, the region where the estimated flow velocity is lower than the first predetermined value Vp1 is divided by the first boundary B1 into a first region R1 where the auxiliary fuel injection amount is large and a second region R2 where the auxiliary fuel injection amount is small.

[0135] The first region R1 is a region where the estimated flow velocity is farther from the first predetermined value Vp1 than the second region R2. That is, in the first region R1, combustion is more likely to be delayed in the difficult-to-combust area than in the second region R2. Therefore, by setting the injection amount of the auxiliary fuel injection to be larger in the first region R1 than in the second region R2, it is possible to suppress the delay of combustion in the difficult-to-combust area.

[0136] Furthermore, the first boundary B1 is inclined so that the estimated flow speed increases as the load increases, corresponding to the range of engine load. As a result, the first range R1 is relatively increased and the second range R2 is relatively decreased as the engine load increases. Therefore, at high load, the ratio of the auxiliary fuel injection amount to be large is higher than at low load, that is, the injection amount is increased, so that combustion fluctuations can be effectively suppressed even when the engine load changes from high to low.

[0137] (High-speed side auxiliary injection area) The high-speed auxiliary injection region is divided into three regions, the third region R3, the fourth region R4, and the fifth region R5, by the second boundary B2 and the third boundary B3. The fourth region R4 has a higher estimated flow speed than the third region R3, and the fifth region R5 has a higher estimated flow speed than the fourth region R4. The second boundary B2 and the third boundary B3 are inclined so that the estimated flow speed decreases as the load increases. In this example, the inclination angle of the third boundary B3 is smaller than that of the second boundary B2.

[0138] The third region R3 is a region in which the injection amount of the auxiliary fuel injection is set relatively small, similar to the second region R2, and the fourth region R4 is a region in which the injection amount of the auxiliary fuel injection is set relatively large, similar to the first region R1. If the injection amount in the third region R3 is the third injection amount and the injection amount in the fourth region R4 is the fourth injection amount, the fourth injection amount is larger than the third injection amount. The fifth injection amount, which is the injection amount in the fifth region R5, will be described later.

[0139] The fourth region R4 is a region where the estimated flow velocity is farther from the second predetermined value Vp2 than the third region R3. That is, in the fourth region R4, combustion is more likely to be delayed in the combustion-hardened portion than in the third region R3. Therefore, by setting the injection amount of the auxiliary fuel injection in the fourth region R4 to be larger than that in the third region R3, the combustion delay can be suppressed.

[0140] Furthermore, the fourth boundary B4 is inclined so that the estimated flow speed decreases as the load increases, corresponding to the range of engine load. As a result, the fourth range R4 relatively increases and the third range R3 relatively decreases as the engine load increases. Therefore, at high loads, the ratio of the auxiliary fuel injection amount to be large increases compared to low loads, that is, the injection amount is increased, so that a delay in the combustion speed can be suppressed even when the engine load changes from high to low.

[0141] The graph in Fig. 14 shows the change in the injection amount of auxiliary fuel injection with respect to the high and low estimated flow speeds when the engine load is the engine load Tq1 shown in Fig. 13. As shown in Fig. 14, in the first region R1, the lower the estimated flow speed, the larger the first injection amount is. Also, in the second region R2, similar to the first region R1, the lower the estimated flow speed, the larger the second injection amount is.

[0142] The first injection amount and the second injection amount change significantly at the first boundary B1 and are discontinuous. In other words, there is a predetermined quantitative difference between the first injection amount and the second injection amount. The injection amount of the auxiliary fuel injection is switched in a stepwise manner at the first boundary B1. Note that the change in the first injection amount with respect to the estimated flow speed, that is, the slope of the graph, and the slope of the second injection amount with respect to the estimated flow speed may be the same or different.

[0143] When the estimated flow velocity is between the first predetermined value Vp1 and the second predetermined value Vp2, auxiliary fuel injection is not performed, and the injection amount is therefore "0."

[0144] In the third region R3, the third injection amount is increased as the estimated flow velocity increases. Similarly to the third region R3, in the fourth region R4, the fourth injection amount is increased as the estimated flow velocity increases. The third injection amount and the fourth injection amount also change significantly at the second boundary B2 and are discontinuous. The slope of the third injection amount relative to the estimated flow velocity and the slope of the fourth injection amount relative to the estimated flow velocity may be the same or different.

[0145] The fifth injection amount is constant regardless of the value of the estimated flow velocity. The fifth injection amount is equal to the maximum value of the fourth injection amount. That is, the fifth region R5 is a region where the flow velocity of the mixture is very high. Therefore, a very strong inertial force acts on the flow inside the cylinder. Therefore, the mixture is more likely to flow and be distributed to positions further away from the center of the cylinder 11. Therefore, if the injection amount of the auxiliary fuel is increased, a rich mixture with a very high fuel concentration is formed in the radially outer part of the cylinder 11.

[0146] As a result, the mixture may ignite before the latter half of the compression stroke where ignition occurs. In addition, if a rich mixture is burned, a large amount of soot may be generated due to poor combustion. Therefore, in order to prevent such problems, the fifth injection amount in the fifth region R5 is set to a constant value without increasing the injection amount even if the estimated flow velocity value increases.

[0147] The third boundary B3 is inclined so that the estimated flow speed decreases as the engine load increases. This is because the higher the engine load, the larger the injection amount of the main fuel injection becomes, and the more likely it is that a rich mixture will be formed.

[0148] The graph in Fig. 15 shows the change in the injection amount of auxiliary fuel injection with respect to the level of engine load when the estimated flow velocity shown in Fig. 13 has a value of VA or VB. As shown in Fig. 15, when the estimated flow velocity has a same value, both the first injection amount and the second injection amount are constant regardless of the level of engine load. When the estimated flow velocity has a same value, the third injection amount and the fourth injection amount are also constant regardless of the level of engine load.

[0149] In this way, in this engine system, the amount of auxiliary fuel injection is adjusted based on the engine load and the estimated flow velocity estimated from the parameters detected during the intake stroke. This makes it possible to suppress combustion fluctuations that become more pronounced as the engine load increases, and to stabilize combustion in the engine 1 even when the engine load changes from high to low.

[0150] FIG. 16 shows a specific example of combustion control in response to high and low engine loads. FIG. 16 shows the timing of fuel injection by the injector 6 and ignition by the spark plug 25. FIG. 16(a) is a timing chart of combustion control in the second region R2. An example of this is shown in FIG. 13 with reference symbol P2 (second engine state P2). FIG. 16(b) is a timing chart of combustion control in the first region R1. An example of this is shown in FIG. 13 with reference symbol P1 (first engine state P1).

[0151] The first engine state P1 corresponds to a time when the estimated flow speed is determined to be equal to or less than the comparison value indicated by the first boundary B1 in a region where the engine load is relatively high, and the second engine state P2 corresponds to a time when the estimated flow speed is determined to be greater than the comparison value indicated by the first boundary B1 in a region where the engine load is relatively low.

[0152] 16, whether the state of the engine 1 is on the low load side or the high load side, the injector 6 performs main fuel injection at the main fuel injection timing in the intake stroke. The amount of main fuel injected is set according to the engine load, so that the amount of injection of the main fuel is greater in a first engine state P1 located on the high load side than in a second engine state P2 located on the low load side.

[0153] After the main fuel injection, a test discharge is performed by the ignition device 7. This test discharge is performed during the intake stroke. In other words, the test discharge here corresponds to the discharge performed during the intake stroke in the engine system described above. Therefore, in the test discharge, the discharge time is detected as a parameter related to the current between the electrodes of the spark plug 25. Then, based on the length of the discharge time, the flow velocity estimation unit 83 estimates the flow velocity of the mixture near the center of the cylinder 11, along with estimating the position of the vortex center of the swirl flow component of the in-cylinder flow.

[0154] The inspection discharge is performed after the intake valve is opened to start the supply of intake air to the cylinder 11, and before the intake valve is closed to stop the supply of intake air to the cylinder 11. Specifically, the inspection discharge is performed in the period after the intake top dead center and before the compression bottom dead center. As described above, the flow state of the swirl flow component of the in-cylinder flow is stable when the intake air is introduced into the cylinder 11, so that the flow speed can be estimated with high accuracy.

[0155] However, as mentioned above, the inspection discharge is not executed immediately after the start of intake. A time constant Δt is set to prohibit the execution of the inspection discharge for a predetermined period, and the execution of the inspection discharge is prohibited until the time constant Δt has elapsed after the intake valve is opened. This is because the flow state of the swirl flow component is unstable immediately after the start of intake.

[0156] After the inspection discharge, in the latter half of the compression stroke, before the air-fuel mixture is ignited, auxiliary fuel injection is performed by the injector 6. At this time, as described above, in this engine system, the first injection amount in the first region R1 is set to be larger than the second injection amount in the second region R2. Furthermore, as in the first engine state P1, the first injection amount on the high load side of the first region R1 is set to be larger than the second injection amount on the low load side of the second region R2, as in the second engine state P2.

[0157] After the auxiliary fuel injection, the spark plug 25 is actuated just before the piston 3 reaches the top dead center of the compression stroke, thereby igniting the mixture in the cylinder 11. At this time, as described above, a rich mixture of fuel is formed in the difficult-to-combust area due to the auxiliary fuel injection.

[0158] In particular, on the high load side, the first region R1 where the injection amount of the auxiliary fuel injection is large is relatively expanded toward the side where the estimated flow velocity is high, and on the low load side, the second region R2 where the injection amount of the auxiliary fuel injection is small is relatively expanded toward the side where the estimated flow velocity is low. As a result, when the engine is located in the high load side region, the injection amount of the auxiliary fuel injection is large even if the estimated flow velocity is relatively close to the first predetermined value Vp1, as in the first engine state P1. On the other hand, when the engine is located in the low load side region, the injection amount of the auxiliary fuel injection is small even if the estimated flow velocity is relatively far from the first predetermined value Vp1, as in the second engine state P2.

[0159] In other words, the amount of auxiliary fuel injection is generally larger on the high load side than on the low load side, so that a more fuel-rich mixture is more likely to be formed in the difficult-to-burn area at the time of ignition. Therefore, even if the engine load increases and the delay in combustion in the difficult-to-burn area becomes significant, flame propagation can be promoted. In other words, because the combustion fluctuation can be suppressed, the combustion in the engine 1 can be stabilized even at high load.

[0160] (flowchart) Next, the processing operation of the auxiliary injection control by the ECU 10 in this engine system will be described with reference to FIGS.

[0161] First, in step S1, the ECU 10 acquires information detected by each of the sensors SW1 to 9. The ECU 10 determines the operating state of the engine from this information. Each of the sensors SW1 to 9 corresponds to an operating state detector.

[0162] Next, in step S2, the ECU 10 calculates the required torque based on the detection result of the accelerator opening sensor SW7. The required torque calculated in step S2 corresponds to the load to be determined when calculating the injection amount of the auxiliary fuel injection.

[0163] Next, in step S3, the ECU 10 sets the injection amount and injection timing of the main fuel injection based on the required torque. The main fuel injection is performed within a predetermined period of the intake stroke before the timing at which the inspection discharge is performed.

[0164] Next, in step S4, the ECU 10 sets the ignition timing, which is the timing for actually igniting the air-fuel mixture (main ignition timing).

[0165] Next, in step S5, the ECU 10 sets the timing of the inspection discharge, which is a predetermined timing that takes into consideration the time constant Δt within the intake stroke period, as described above.

[0166] Next, in step S6, the ECU 10 controls the ignition device 7 to perform the test discharge at the time set in step S5. The ECU 10 acquires from the ignition device 7 the discharge time of the discharge path generated in the ignition plug 25 during the test discharge.

[0167] Next, in step S7, the ECU 10, specifically the flow velocity estimation unit 83, estimates the flow velocity of the air-fuel mixture in the cylinder 11. Here, the ECU 10 calculates the reciprocal of the discharge time of the inspection discharge as the estimated flow velocity.

[0168] Next, in step S8, the ECU 10 determines whether the calculated estimated flow speed is less than a first predetermined value Vp1. If the ECU 10 determines that the estimated flow speed is less than the first predetermined value Vp1, the ECU 10 proceeds to step S9. On the other hand, if the ECU 10 determines that the estimated flow speed is not less than the first predetermined value Vp1, the ECU 10 proceeds to step S12.

[0169] In step S9, the ECU 10 judges whether the state of the engine belongs to the first region R1 or not based on the calculated engine load (judgment load) and the calculated estimated flow speed. 13 The map shown in is read and a judgment is made.

[0170] The ECU 10 judges whether the estimated flow speed is equal to or less than the value (first comparison value) indicated by the first boundary B1 based on the calculated judgment load. The first comparison value is a value (a value corresponding to the estimated flow speed) on the first boundary B1 at the same engine load as the judgment load. When the ECU 10 judges that the engine state belongs to the first region R1, that is, the estimated flow speed is equal to or less than the first comparison value, the ECU 10 proceeds to step S10.

[0171] On the other hand, when the ECU 10 determines that the engine state belongs to the second region R2, that is, that the engine state is greater than the first comparison value, the ECU 10 proceeds to step S11.

[0172] In step S10, the ECU 10 sets the injection amount of the auxiliary fuel injection to the first injection amount. At this time, the ECU 10 sets the first injection amount to large or small depending on whether the estimated flow velocity is high or low (see FIG. 14).

[0173] In step S11, the ECU 10 sets the injection amount of the auxiliary fuel injection to the second injection amount. At this time, the ECU 10 sets the second injection amount to large or small depending on whether the estimated flow velocity is high or low (see FIG. 14).

[0174] After step S10, the process proceeds to step S19. After step S11, the process proceeds to step S19.

[0175] 18, in step S12, the ECU 10 determines whether the calculated estimated flow speed is higher than a second predetermined value Vp2. When the ECU 10 determines that the estimated flow speed is higher than the second predetermined value Vp2, the ECU 10 proceeds to step S14.

[0176] On the other hand, when the ECU 10 determines that the estimated flow speed is not higher than the second predetermined value Vp2, the ECU 10 proceeds to step S13 and does not perform auxiliary fuel injection because an appropriate in-cylinder flow with the vortex center located near the center of the cylinder 11 is formed in the cylinder 11. The ECU 10 returns after step S13.

[0177] In step S14, the ECU 10 judges whether or not the state of the engine belongs to the third region R3 based on the judged load and the estimated flow speed. The ECU 10 makes the judgment by reading the map shown in FIG.

[0178] The ECU 10 judges whether the estimated flow speed is equal to or lower than the value (second comparison value) indicated by the second boundary B2 based on the judgment load. When the ECU 10 judges that the engine state belongs to the third region R3, that is, the estimated flow speed is equal to or lower than the second comparison value, the ECU 10 proceeds to step S15.

[0179] On the other hand, when the ECU 10 determines that the engine state belongs to the fourth region R4 or the fifth region R5, that is, that the engine state is greater than the second comparison value, the ECU 10 proceeds to step S16.

[0180] In step S15, the ECU 10 sets the injection amount of the auxiliary fuel injection to the third injection amount. Note that, at this time, the ECU 10 sets the third injection amount to large or small depending on whether the estimated flow speed is high or low. After step S15, the process proceeds to step S19.

[0181] On the other hand, in step S16, the ECU 10 determines whether the engine state belongs to the fourth region R4. The ECU 10 determines whether the estimated flow speed is equal to or less than the value (third comparison value) indicated by the third boundary B3 based on the judgment load. When the ECU 10 determines that the engine state belongs to the fourth region R4, that is, the estimated flow speed is equal to or less than the third comparison value, the ECU 10 proceeds to step S17. On the other hand, when the ECU 10 determines that the engine state belongs to the fifth region R5, that is, the estimated flow speed is greater than the third comparison value, the ECU 10 proceeds to step S18.

[0182] In step S17, the ECU 10 sets the injection amount of the auxiliary fuel injection to a fourth injection amount. At this time, the ECU 10 sets the fourth injection amount to a large or small amount depending on the high or low of the estimated flow velocity. After step S17, the process proceeds to step S19.

[0183] In step S18, the ECU 10 sets the injection amount of the auxiliary fuel injection to the fifth injection amount. After step S18, the process proceeds to step S19.

[0184] 17, in step S19, the ECU 10 sets the injection timing of the auxiliary fuel injection. The ECU 10 sets the injection timing of the auxiliary fuel injection to a timing earlier than the main ignition timing set in step S4 on the advance side.

[0185] The ECU 10 returns after step S19. After such auxiliary injection control, the ECU 10 operates the injector 6 to perform auxiliary fuel injection.

[0186] In this way, with this engine system, even when the engine load is high, a rich fuel mixture can be appropriately distributed to areas in the cylinder 11 where flames are less likely to propagate. This makes it possible to stabilize combustion in the engine 1 and improve fuel efficiency.

[0187] The engine system according to the disclosed technology is not limited to the above-described embodiment, and includes various other configurations.

[0188] For example, the injector 6 is not limited to performing main injection during the intake stroke, but may perform main injection during the compression stroke. The main injection is not limited to being performed once, but may be performed multiple times. The swirl generating section is not essential as long as a transverse vortex is formed in the cylinder 11.

[0189] Furthermore, the engine 1 to which the technology disclosed herein can be applied is not limited to the configuration described above, and the technology disclosed herein can be applied to engines of various configurations. [Explanation of symbols]

[0190] 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 section (judgment section) 84 Auxiliary fuel injection section B1 First comparison value (comparison value) SW7 Accelerator opening sensor (driving state detector) Vp1 1st predetermined value

Claims

1. an engine in which a fuel injection valve and an ignition plug are installed in the center of a cylinder having a pent roof type ceiling, and intake air is introduced into the cylinder from the ceiling; an operating condition detector for detecting an operating condition of the engine; a controller electrically connected to each of an ignition device that activates the spark plug, the fuel injection valve, and the operating state detector; An engine system comprising: The controller includes: a main fuel injection unit that sets an injection amount of a main fuel and a main fuel injection timing, which 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 that the set amount of the main fuel is injected at the main fuel injection timing; a flow velocity estimation unit that controls the ignition device to generate a discharge path between electrodes of the spark plug at a predetermined timing when the mixture is not ignited, and detects a parameter that is an inverse of a discharge time or a gradient of a voltage applied to the electrodes, and estimates a flow velocity of the mixture based on the parameter; an auxiliary fuel injection unit that controls the fuel injection valve based on the estimated flow velocity estimated by the flow velocity estimation unit to perform auxiliary fuel injection at a timing retarded from the main fuel injection timing; having the auxiliary fuel injection unit executes the auxiliary fuel injection when the estimated flow velocity is less than a predetermined value at which a difficult-to-burn portion occurs in a latter half of a compression stroke due to a deviation of a vortex center in the flow of the mixture, the auxiliary fuel injection unit further has a predetermined comparison value of the estimated flow velocity which is set in correspondence with an engine load range so as to become higher as the engine load becomes higher in order to determine an injection amount of the auxiliary fuel injection, and is set so that when the engine load is high, the range in which the injection amount of the auxiliary fuel injection is made larger becomes larger than when the engine load is low, and comparing the comparison value with the estimated flow velocity corresponding to the engine load, when it is determined that the estimated flow velocity is equal to or lower than the comparison value in a region where the engine load is relatively high, the amount of auxiliary fuel injection is increased compared to when the estimated flow velocity is determined to be greater than the comparison value in a region where the engine load is relatively low.

2. 2. The engine system according to claim 1, The flow velocity estimation unit controls the ignition device to detect the parameter after an intake valve of the engine is opened and the introduction of intake air into the cylinder is started, by the time the intake valve is closed and the introduction of intake air into the cylinder is stopped.

3. 3. The engine system according to claim 2, The engine system according to claim 1, wherein the ignition device detects the parameter after a predetermined time constant has elapsed since the intake valve is opened.

Images