JP7622401B2 - Engine System - Google Patents

Description

The technology disclosed herein belongs to the technical field of engine systems.

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

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

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

JP 2014-145306 A

Here, the inventors of the present application conducted extensive research into improving combustion in response to the intake flow based on the current value of the discharge path as described in Patent Document 1, and discovered that the position of the vortex center formed in the cylinder by the intake flow causes differences in the flow conditions in the cylinder in the latter half of the compression stroke, preventing the flame from propagating uniformly throughout the entire cylinder, which becomes a factor in combustion fluctuations.

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

However, the inventors of the present application have discovered that if the position of the vortex center of the vertical vortex component is shifted toward the piston in a side view, the vortex center comes into contact with the top surface of the piston in the latter half of the compression stroke, crushing the lower half of the vertical vortex, and the flow inside the cylinder becomes a positive unidirectional flow from the intake side to the exhaust side. When the flow inside the cylinder becomes a positive unidirectional flow, the exhaust side area inside the cylinder is highly turbulent, but the intake side area is less turbulent. In this case, the flame easily propagates to the exhaust side area, but is less likely to propagate to the intake side area.

Furthermore, if the position of the vortex center of the vertical vortex component is shifted toward the ceiling of the cylinder in a side view, the vortex center will come into contact with the ceiling in the latter half of the compression stroke, crushing the upper half of the vertical vortex, and the flow inside the cylinder will become a non-unidirectional flow from the exhaust side to the intake side. When the flow inside the cylinder becomes a non-unidirectional flow, the intake side area inside the cylinder will be highly turbulent, but the exhaust side area will be less turbulent. In this case, the flame will easily propagate to the intake side area, but will have difficulty propagating to the exhaust side area.

On the other hand, the inventors have found that when the position of the vortex center of the transverse vortex component is shifted toward the outside of the cylinder in a plan view, part of the flame attempting to propagate from the center to the periphery of the cylinder is hindered by the flow of the transverse vortex that is shifted from the center of the cylinder, making it difficult for the flame to propagate to a specific area.

Hindered flame propagation to some areas within the cylinder reduces the combustion speed, which causes combustion fluctuations. Therefore, in order to suppress engine combustion fluctuations, it is necessary to promote flame propagation to these areas. Suppressing engine combustion fluctuations is advantageous for improving engine fuel efficiency.

The technology disclosed here has been developed in light of these issues, and its purpose is to suppress combustion fluctuations by estimating the flow conditions within the cylinder and performing auxiliary ignition according to those flow conditions.

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

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

For the sake of convenience, in this specification, unidirectional flow refers to intake flow from the intake side to the exhaust side, and anti-unidirectional flow refers to intake flow from the exhaust side to the intake side, but these may be reversed.

With the above configuration, the engine has a pent roof type combustion chamber in the ceiling, so the intake air introduced into the cylinder forms vertical vortices as well as horizontal vortices. The flow inside the cylinder is an oblique flow inclined with respect to the cylinder axis.

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

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

For example, the inverse of the discharge time can be used as the "estimated flow velocity." In addition to the discharge time, other parameters for estimating the flow velocity can be used, such as the current value, the voltage value, the slope of the current value during discharge, and the slope of the voltage value during discharge, as long as the high or low flow velocity can be estimated.

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

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

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

If the estimated flow velocity is determined to be less than the first set value or higher than the second set value, in other words, if the longitudinal vortex is estimated to be flowing in one direction or the opposite direction, or if the transverse vortex is estimated to be biased in the vortex center, auxiliary ignition is performed on the advanced side of the timing at which the mixture is ignited by main ignition. The auxiliary ignition creates a mixture with a lot of plasma in areas with weak turbulence or areas where flames are difficult to propagate.

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

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

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

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

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

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

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

As mentioned above, when the engine speed is high, the inertia force of the intake flow is large even during the compression stroke, so the mixture becomes more biased at the time of ignition. Also, the higher the estimated flow velocity is from the second set value, the stronger the positive unidirectional flow is formed in the vertical vortex, and the stronger the bias of the vortex center becomes in the horizontal vortex, so the greater the effect of the engine speed.

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

As described above, the technology disclosed herein makes it possible to stabilize the engine combustion speed by performing auxiliary ignition according to the engine speed. This makes it possible to suppress fluctuations in engine combustion.

FIG. 1 is a diagram illustrating an engine system. 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. FIG. 3 is a block diagram of the engine system. FIG. 4 is a diagram illustrating an ignition device. FIG. 5 is a block diagram showing functional blocks related to engine control. FIG. 6 is a diagram for explaining the relationship between the center position of the vertical vortex and the flow state inside the cylinder in the latter half of the compression stroke. FIG. 7 is a diagram illustrating the change in voltage and current between the electrodes of a spark plug when the strength of the flow near the spark plug is different. FIG. 8 is a diagram showing the relationship between the discharge time detected by the spark plug and the center position of the longitudinal vortex. FIG. 9 is a diagram for explaining the relationship between the central position of the lateral vortex and the propagation state of the flame inside the cylinder. FIG. 10 is a diagram showing the relationship between the discharge time detected by the spark plug and the central position of the lateral vortex. FIG. 11 is a timing chart illustrating the injection timing of the main fuel injection, the timing of the inspection discharge, the timing of the auxiliary ignition, and the timing of the main ignition. FIG. 12 is a diagram showing a schematic diagram of plasma being generated by auxiliary ignition of an ignition plug. FIG. 13 is a diagram for explaining the change in flow and the distribution of plasma inside the cylinder when the center position of the longitudinal vortex is close to the piston. FIG. 14 is a diagram for explaining the change in flow and plasma distribution inside the cylinder when the center position of the vertical vortex is close to the ceiling. FIG. 15 is a diagram for explaining the change in flow and plasma distribution within the cylinder when the center position of the transverse vortex is inclined toward the exhaust side and when the center position of the transverse vortex is inclined toward the intake side. FIG. 16 is a map for setting the auxiliary ignition period formed by the estimated flow speed and the engine load. FIG. 17 is a graph showing the relationship between the estimated flow velocity and the auxiliary ignition period when the engine load is constant. FIG. 18 is a graph showing the relationship between auxiliary ignition duration and engine load when the estimated flow velocity is constant. FIG. 19 is a timing chart showing the timing of auxiliary ignition for each engine speed. FIG. 20 is a part of a flowchart of the auxiliary ignition control. FIG. 21 shows the remainder of the flow chart of the auxiliary ignition control.

Embodiments of the engine system will be described below with reference to the drawings. The engine and engine system described here are examples.

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

The engine system has an engine 1. The engine 1 has a cylinder 11. In the cylinder 11, an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke are repeated. 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.

(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.

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.

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 Figure 2. The inclined surface 1311 is the inclined surface 1311 on the intake valve 21 side, which will be described later, and has an upward slope toward the center of the cylinder 11. The inclined surface 1312 is the inclined surface 1312 on the exhaust valve 22 side, and has an upward slope toward the center of the cylinder 11. The ceiling of the cylinder 11 is a so-called pent roof type.

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

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 varies the valve timing and/or the valve lift. As shown in FIG. 3, the valve mechanism has an intake S-VT (Sequential-Valve Timing) 23. The intake S-VT 23 continuously changes the rotational phase of the intake camshaft within a predetermined angle range. The opening angle of the intake valve 21 does not change. The intake S-VT 23 is electrically or hydraulically operated.

An exhaust port 19 is formed in the cylinder head 13 for each cylinder 11. The exhaust port 19 is connected to the combustion chamber 17.

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 varies the valve timing and/or the valve lift. As shown in FIG. 3, the valve mechanism has an exhaust S-VT 24. The exhaust S-VT 24 continuously changes the rotational phase of the exhaust camshaft within a predetermined angle range. The opening angle of the exhaust valve 22 does not change. The exhaust S-VT 24 is electric or hydraulic.

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

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

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 pumps 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 pumped from the fuel pump 65 at 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 depending on the operating state of the engine 1. The configuration of the fuel supply system 61 is not limited to the above configuration.

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

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 and ignite the mixture in the cylinder 11. The ignition device 7, which will be described in detail later, causes the spark plug 25 to discharge when the mixture is not ignited, and detects a parameter related to the current value of the discharge path generated between the electrodes at that time. The flow state in the cylinder 11 can be estimated based on the detected parameter. The configuration of the ignition device 7 will be described later.

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. The intake 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 intake air. A surge tank 42 is disposed near the downstream end of the intake passage 40. The intake passage 40 downstream of the surge tank 42 constitutes an independent passage that branches off for each cylinder 11. The downstream end of the independent passage is connected to the intake port 18 of each cylinder 11.

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

The engine 1 has a swirl generating section that generates a swirl flow inside the cylinder 11. Although not shown in detail, the swirl generating section has a swirl control valve 56 attached to the intake passage 40. The swirl control valve 56 is disposed in the second intake passage of the first and second intake passages that are parallel to each other. The swirl control valve 56 is an opening adjustment valve that can narrow the cross section of the second intake passage.

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

An exhaust passage 50 is connected to the other side of the engine 1. The exhaust passage 50 is connected to the exhaust port 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.

An exhaust gas purification system having multiple catalytic converters is arranged 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. In addition, 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.

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

A water-cooled EGR cooler 53 is provided in the EGR passage 52. The EGR cooler 53 cools the exhaust gas. An EGR valve 54 is also provided 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 cooled exhaust gas recirculated can be adjusted.

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

As shown in Figures 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:

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

The ECU 10 determines the operating state of the engine 1 based on the signals from 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 the memory 102. The control logic includes calculating the target amount and/or the control amount using a map stored in the memory 102.

The ECU 100 outputs electrical signals related to the calculated control quantities 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.

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

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

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

As mentioned above, the ignition device 7 causes the spark plug 25 to discharge when the mixture is not ignited, and estimates the flow state within the cylinder 11 based on the electrical parameters detected at that time.

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

Here, the state of the intake air flow may change with each cycle, and when the state of the intake air flow in the cylinder 11 changes, the combustion speed changes with each cycle. As a result, this leads to combustion fluctuations. The engine system disclosed herein suppresses the change in combustion speed with each cycle, thereby suppressing combustion fluctuations.

Specifically, this engine system estimates the state of the intake air flow in cylinder 11, performs auxiliary ignition according to the estimated state of the intake air flow, and provides ignition energy in cylinder 11.

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

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

Below, we will explain how the engine system shown in FIG. 5 estimates the state of the intake air flow in the cylinder 11, and then we will explain the auxiliary ignition control according to the estimated state of the intake air flow.

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

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

Chart 603 illustrates the flow state inside cylinder 11 when the center of the vertical vortex is close to the ceiling of cylinder 11 during the first half of the compression stroke, and chart 606 illustrates the flow state inside cylinder 11 during the second half of the compression stroke when the crank angle has progressed from the state of chart 603.

The first half of the compression stroke refers to the first half when the compression stroke is divided into two halves, and the second half of the compression stroke refers to the second half when the compression stroke is divided into two halves.

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

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

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

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

Figure 7 illustrates an example of the time change 701 of the voltage between the electrodes of the spark plug 25 and the time change 702 of the current between the electrodes when the strength of the flow near the spark plug 25 is different. When a voltage is applied between the electrodes by imparting energy to the spark plug 25, a discharge path is formed between the center electrode 251 and the ground electrode 252. The stronger the flow near 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 in the voltage applied between the electrodes. The stronger the flow near 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.

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

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

As shown in chart 802 of FIG. 8, when the center position of the vertical vortex is halfway between the piston 3 and the ceiling of the cylinder 11 during the first half of the compression stroke, the spark plug 25 and the center position of the vortex are some distance apart, so the flow velocity near the spark plug 25 is between V1 and V2.

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

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

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

The "estimated flow velocity" referred to here is not necessarily the flow velocity itself, but may be anything that can estimate the high or low flow velocity of the intake air. For example, the reciprocal of the discharge time may be used as the estimated flow velocity.

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

Similarly, chart 902 illustrates the flow state in cylinder 11 when the center of the lateral vortex during the intake stroke is located in the center of cylinder 11 and is approximately aligned with the axis of cylinder 11. Chart 905 illustrates the flow state in cylinder 11 during the latter half of the compression stroke when the crank angle has progressed from the state of chart 902.

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

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

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

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

Figure 10 shows the relationship between the discharge time detected by the ignition device 7 and the central position of the lateral vortex in the cylinder 11. Chart 1000 in Figure 10 shows the relationship between the discharge time and the flow velocity near the spark plug 25.

As shown in chart 1002 of FIG. 10, a flow velocity distribution occurs within the cylinder 11 during the intake stroke, mainly due to the intake air flowing in from the first intake passage 18a. If the velocity distribution during the intake stroke is such that the flow velocity is maximum at a specific radial position between the center of the cylinder 11 and the liner, and the flow velocity decreases toward the center from there, and 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.

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

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

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

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

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

As mentioned above, when the center position of the vertical vortex and/or the horizontal vortex shifts due to variations in the intake flow, areas where the degree of turbulence is weak and/or where flame propagation is difficult are generated in the cylinder 11. The auxiliary fuel places a high-energy mixture containing a lot of plasma in such areas where the degree of turbulence is weak and/or where flame propagation is difficult, thereby promoting flame propagation to those areas.

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

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

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

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

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

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

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

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

After the first auxiliary ignition 1108 is performed, the main ignition control unit 82 uses the spark plug 25 to ignite the mixture at a predetermined timing near the compression top dead center in the latter half of the compression stroke (see main ignition 1107 in chart 1101). Due to the positive unidirectional flow, the flame is less likely to propagate toward the intake valve 21 side, but the higher temperature of the mixture on the intake valve 21 side promotes flame propagation toward the intake valve 21 side. This increases the combustion speed, which is about the same as when the discharge time is between the first and second thresholds (when the estimated flow speed is between the first set value Vp1 and the second set value Vp2). This suppresses combustion fluctuations in the engine 1.

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

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

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

After the second auxiliary ignition 1109 is performed, the main ignition control unit 82 uses the spark plug 25 to ignite the mixture at a predetermined timing near the compression top dead center in the latter half of the compression stroke (see main ignition 1107 in chart 1103). Due to the anti-unidirectional flow, the flame is less likely to propagate toward the exhaust valve 22 side, but the high temperature of the mixture on the exhaust valve 22 side promotes flame propagation toward the exhaust valve 22 side. This increases the combustion speed, which is about the same as when the discharge time is between the first and second thresholds (when the estimated flow speed is between the first set value Vp1 and the second set value Vp2). This suppresses combustion fluctuations in the engine 1.

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

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

P1501 and P1502 in Figure 15 are diagrams explaining the change in flow and plasma distribution inside the cylinder 11 when the center position of the transverse vortex is tilted toward the intake valve 21. When the center of the transverse vortex is tilted toward the intake valve 21, as shown in P1501, the velocity distribution inside the cylinder 11 during the compression stroke has low kurtosis of the flow velocity distribution, so there are no points with extremely fast flow velocities.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

In the fifth region R5, the center of the intake vortex is located in an appropriate position, i.e., near the cylinder axis and in the center position in the cylinder axis direction, so auxiliary ignition is not performed. The auxiliary ignition period is 0.

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

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

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

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

Therefore, the higher the estimated flow velocity around the spark plug 25, the larger the amount of energy of the auxiliary ignition is, so as to appropriately form a region with a large amount of plasma on the intake side of the cylinder 11. In addition, the third ignition period and the fourth ignition period change significantly at the fourth set value Vp4, and are discontinuous. Note that the slope of the third ignition period relative to the estimated flow velocity and the slope of the fourth ignition period relative to the estimated flow velocity may be the same or different.

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

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

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

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

After the main fuel injection, the spark plug 25 generates a first and a second discharge. The first discharge occurs during the intake stroke, and the second discharge occurs after the intake valve 21 closes, particularly in the first half of the compression stroke.

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

After the auxiliary ignition, before the piston 3 reaches the top dead center of compression, the main ignition control unit 82 activates the spark plug 25 again, and main ignition is performed to combust the mixture. At this time, the auxiliary ignition creates a high-energy region with a lot of plasma in the part of the cylinder 11 with low turbulence, so the flame quickly spreads throughout the entire cylinder 11.

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

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

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

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

Next, in step S4, the ECU 10 sets the ignition timing. This ignition timing is the timing of the main ignition to combust the mixture.

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

Next, in step S6, the ECU 10 executes the inspection discharge at the time set in step S5. The ECU 10 acquires from the ignition device 7 the discharge times of the discharge paths that occurred in the spark plug 25 during the first and second discharges.

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

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

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

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

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

On the other hand, as shown in FIG. 21, in step S12, which is reached when step S8 is NO, the ECU 10 determines whether the estimated flow speed calculated in step S7 is higher than the second set value Vp2. If the estimated flow speed is higher than the second set value Vp2 (YES), the ECU 10 proceeds to step S14. On the other hand, if the estimated flow speed is equal to or lower than the second set value Vp2 (NO), the ECU 10 proceeds to step S13. If at least one of the first estimated flow speed and the second estimated flow speed is higher than the second set value Vp2, the ECU 10 determines YES in step S12.

In step S13, the ECU 10 determines that the state of the engine 1 belongs to the fifth region R5 and that auxiliary ignition is not required. After step S13, the ECU 10 returns.

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

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

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

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

After the flow chart, the ECU 10 executes auxiliary ignition. This allows a high-energy region with a lot of plasma to be formed in an area with low turbulence according to the state of the vortex inside the cylinder 11, and the combustion speed of the entire cylinder 11 can be stabilized.

(summary)
Therefore, in this embodiment, there is provided an operating condition detector (sensors SW1 to SW9) that detects the operating condition of the engine, an ignition device 7, an injector 6, and an ECU 10 that is electrically connected to the operating condition detector. The ECU 10 has a main fuel injection unit 81 that sets a main fuel injection timing, which is the timing of main fuel injection, based on the engine load detected by the operating state detector (in particular, the accelerator opening sensor SW7), and controls the injector 6 to inject main fuel at the main fuel injection timing; a flow velocity estimation unit 83 that controls the ignition device 7 to apply a voltage between the electrodes of the spark plug 25 and execute an inspection discharge for detecting a parameter related to a current value of a discharge path generated between the electrodes during a period when the air-fuel mixture is not ignited, and estimates the level of the flow velocity of the intake air in the cylinder 11 from the parameter in the inspection discharge; and an auxiliary ignition control unit 84 that executes auxiliary ignition by controlling the ignition device 7 to be on the retard side of the main fuel injection timing when the estimated flow velocity estimated by the flow velocity estimation unit 83 is less than a first set value Vp1 or higher than a second set value Vp2 higher than the first set value Vp1, and imparts energy by ignition into the cylinder 11.

The first set value Vp1 and the second set value Vp2 are positioned on the side where the estimated flow velocity is higher as the engine speed detected by the operating state detector (particularly the crank angle sensor SW6) is higher. In this way, by appropriately changing the set value for executing auxiliary ignition in accordance with the difference in the intake flow in the cylinder 11 due to the engine speed, it is possible to appropriately promote the combustion of the mixture in areas where the turbulence state is weak and flame propagation is difficult. As a result, the combustion speed can be stabilized and combustion fluctuations can be suppressed.

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

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

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

In addition, in this embodiment, the auxiliary ignition control unit 84 is configured to increase the energy of the auxiliary ignition when the estimated flow velocity is higher than a fourth set value Vp4 set in a region higher than the second set value Vp2, compared to when the estimated flow velocity is equal to or lower than the fourth set value Vp4 and higher than the second set value Vp2, and the fourth set value Vp4 is located on the lower side of the estimated flow velocity as the engine speed increases. The further the estimated flow velocity moves away from the second set value to the higher side, the stronger the positive unidirectional flow is formed, and the greater the effect of the engine speed.

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

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

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 unit 83 Flow velocity estimation unit 84 Auxiliary ignition control unit SW6 Crank angle sensor (operating state detector)

Claims (3)

An engine system including an engine having a cylinder having a pent roof type ceiling, an ignition device including an ignition plug disposed in a center portion of the cylinder, and a fuel injection valve disposed in a center portion of the cylinder,
an operating condition detector for detecting an operating condition of the engine;
a controller electrically connected to the ignition device, the fuel injection valve, and the operating condition detector;
The controller includes:
a main fuel injection unit that sets an injection amount of a main fuel and a main fuel injection timing that is an injection timing of the main fuel based on an engine load detected by the operating state detector, and controls the fuel injection valve so as to inject the main fuel in the amount set at the main fuel injection timing;
a flow velocity estimation unit that controls the ignition device to apply a voltage between the electrodes of the spark plug during a period when the air-fuel mixture is not ignited and detects a parameter that is an inverse of a discharge time generated between the electrodes or a gradient of the voltage applied to the electrodes , and estimates the level of the flow velocity of the intake air in the cylinder from the parameter;
an auxiliary ignition control unit that executes auxiliary ignition by controlling the ignition device on the advance side of a timing for igniting the air-fuel mixture by main ignition when the estimated flow velocity estimated by the flow velocity estimation unit is less than a first preset value at which a region where flame propagation is difficult occurs in the latter half of the compression stroke due to a deviation in the vortex center of the air-fuel mixture, or is higher than a second preset value higher than the first preset value, thereby providing energy by ignition into the cylinder;
having
An engine system, characterized in that the first set value and the second set value are positioned on a side where the estimated flow velocity is higher as the engine speed detected by the operating condition detector is higher. 2. The engine system according to claim 1,
the auxiliary ignition control unit is configured to increase the energy of the auxiliary ignition when the estimated flow velocity is lower than the first set value and less than a third set value that is set in a region in which the lower the estimated flow velocity, the greater the deviation of the vortex center of the mixture becomes , compared with when the estimated flow velocity is higher than the third set value and less than the first set value;
An engine system, wherein the third set value is set to a lower engine speed side as the estimated flow velocity is lower. 3. The engine system according to claim 1,
the auxiliary ignition control unit is configured to increase the energy of the auxiliary ignition when the estimated flow velocity is higher than a fourth set value that is set in a region where the higher the estimated flow velocity is, the more the deviation of the vortex center of the air-fuel mixture increases , compared to when the estimated flow velocity is lower than the fourth set value and higher than the second set value;
An engine system, wherein the fourth set value is set to a lower side of the estimated flow velocity as the engine speed increases.

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