JP7468306B2 - 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. This flame reacts with the unburned mixture as it propagates throughout the cylinder, 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.

In addition, the intake flow rate varies depending on the engine load, so the flow conditions inside the cylinder also vary depending on the engine load. Therefore, in order to stabilize the combustion speed, measures that take the engine load into account are necessary.

The technology disclosed here has been developed in light of these points, and its purpose is to estimate the degree of turbulence in the cylinder and control the spark plug according to this degree of turbulence to suppress combustion fluctuations, thereby stabilizing the combustion speed.

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 is directed to 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 a main fuel injection amount and a main fuel injection timing, which is the injection timing, based on the engine load detected by the operating state detector, and controlling the fuel injection valve to inject the amount of main fuel set at the main fuel injection timing, a main ignition control unit that controls the ignition device to perform main ignition to ignite the air-fuel mixture in order to combust the mixture in the cylinder after the main fuel injection timing, The system has a flow velocity estimation unit that controls the ignition device to apply a voltage between the electrodes of the spark plug and detect a parameter related to the current value of the discharge path generated between the electrodes when the mixture does not ignite, and estimates the high or low flow velocity of the intake air based on the parameter; and an auxiliary ignition control unit that controls the ignition device to perform auxiliary ignition to provide auxiliary ignition energy to the mixture at a timing that is retarded from the main fuel injection timing and advanced from the main ignition when the estimated flow velocity is set in a region lower than the predetermined value and is equal to or less than a comparison value set corresponding to the engine load, and controls the ignition device to increase the ignition energy provided by the auxiliary ignition when the estimated flow velocity is set in a region lower than the predetermined value and is equal to or less than a comparison value set corresponding to the engine load, compared to when the estimated flow velocity is higher than the comparison value.

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 cylinder with a pent roof type 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 the main fuel injection is performed from the fuel injection valve, a mixture is formed in the cylinder. When this mixture does not ignite, a voltage is applied to the spark plug to generate a discharge path. The stronger the intake air flow around the spark plug, the longer the discharge path generated in the spark plug. 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 during which the energy applied to the spark plug is consumed, i.e., the discharge time, becomes shorter. From this, the inventors of the present application found that by detecting the discharge time of the current, the flow speed of the intake air flow around the spark plug can be estimated, and the position of the vortex center in the cylinder can be estimated 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 and low flow speeds 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 speed". In addition, as parameters for estimating the flow velocity, in addition to the discharge time, the current value, voltage value, the slope of the current value during discharge, the slope of the voltage value during discharge, etc. may be used as long as the high or low flow velocity can be estimated.

Specifically, the closer the center of the vertical vortex of the intake flow is to the ceiling of the cylinder, the weaker the intake flow around the spark plug and the lower the estimated flow speed. On the other hand, the closer the center of the vertical vortex of the intake flow is to the piston side of the cylinder, the stronger the intake flow around the spark plug and the higher the estimated flow speed. This makes it possible to estimate whether the intake flow is unidirectional or anti-unidirectional before the mixture in the cylinder is ignited, and to estimate the areas with weak turbulence.

After estimating the flow velocity of the mixture and estimating the region with a weak degree of turbulence, the auxiliary ignition control unit causes the ignition device to execute auxiliary ignition at a timing retarded from the main fuel injection and advanced from the main ignition. The auxiliary ignition generates plasma around the spark plug. The generated high-temperature plasma reaches a region where flame is difficult to propagate (region with a weak degree of turbulence, hereinafter referred to as a specific region) in the latter half of the compression stroke due to the intake flow. This makes it possible to increase the temperature of the mixture in the specific region in advance. Then, by igniting the mixture with the ignition device, flame propagation to the specific region is promoted, and the flame propagates evenly or approximately evenly throughout the cylinder. As a result, the combustion speed in the region with a weak degree of turbulence can be increased. Furthermore, when the estimated flow velocity is less than a predetermined value, the ignition energy provided by the auxiliary ignition is adjusted according to the engine load. That is, when the estimated flow velocity is low, the flow of the mixture in the latter half of the compression stroke becomes a counter-unidirectional flow from the exhaust side to the intake side. Also, when the engine load is low, the intake amount and the injection amount of the main fuel injection are small. For this reason, flame propagation is much more difficult on the exhaust side, which is located on the opposite side of the mixture flow. On the other hand, when the engine load is high, the intake air volume and the main fuel injection volume are large, so even if the flow velocity of the mixture around the spark plug is low, the exhaust side has a certain amount of fuel concentration, so the effect on flame propagation is small. Thus, when the estimated flow velocity is low, the effect on flame propagation differs depending on the engine load.

In this configuration, a comparison value is set according to the engine load, and when the estimated flow rate is equal to or lower than the comparison value, the amount of ignition energy provided by the auxiliary ignition is increased compared to when the estimated flow rate is less than a predetermined value and higher than the comparison value. This makes it possible to appropriately increase the temperature of the mixture over a wide range on the exhaust side. Therefore, the combustion rate on the exhaust side can be appropriately increased according to the engine load, and the combustion rate can be stabilized.

In the engine system, the comparison value may be configured to be closer to the predetermined value the lower the engine load is.

With this configuration, the lower the engine load, the larger the area in which the ignition energy provided by the auxiliary ignition is increased. This makes it possible to further stabilize the combustion speed.

In the engine system, the flow velocity estimation unit may be configured to control the ignition device to detect the parameter after the intake valve of the engine is closed.

That is, when the intake valve closes, the introduction of intake air into the combustion chamber is completed, and the position of the center of the vortex formed in the cylinder is stable. Therefore, by detecting parameters after the intake valve closes, the degree of turbulence in the latter half of the compression stroke can be estimated with high accuracy. As a result, the combustion speed can be stabilized.

In the engine system, the flow velocity estimation unit may be configured to control the ignition device to detect the parameter during the compression stroke.

During the compression stroke, the vortex center of the longitudinal vortex component of the intake flow becomes stable. Therefore, by detecting the parameters at a stage where the position of the vortex center becomes stable, the degree of turbulence in the latter half of the compression stroke can be estimated with high accuracy. As a result, the combustion speed can be stabilized.

In the engine system, the auxiliary ignition control unit may be configured to increase the ignition energy provided by the auxiliary ignition when the estimated flow velocity is equal to or lower than the comparison value when the engine load is constant, as the estimated flow velocity is lower.

In other words, the lower the estimated flow velocity, the earlier the unidirectional flow from the exhaust side to the intake side occurs. In response to this, by increasing the ignition energy applied by the auxiliary ignition, more plasma is concentrated in areas with weaker turbulence. This makes combustion faster on the exhaust side as well, stabilizing the combustion speed.

As explained above, the technology disclosed herein makes it possible to increase the temperature of the mixture in the low turbulence region in the cylinder by providing ignition energy through auxiliary ignition. This makes it possible to stabilize the combustion speed at low loads.

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 relating to 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 showing the relationship between the discharge time detected by the spark plug and the center position of the longitudinal vortex. FIG. 8 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. 9 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. 10 is a schematic diagram showing how plasma is generated by auxiliary ignition of an ignition plug. FIG. 11 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. 12 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. 13 is a map for setting the ignition period of the auxiliary ignition formed based on the estimated flow speed and the engine load. FIG. 14 is a graph showing the relationship between the estimated flow velocity and the ignition period of the auxiliary ignition when the engine load is constant. FIG. 15 is a graph showing the relationship between engine load and the ignition period of the auxiliary ignition when the estimated flow velocity is constant. FIG. 16 is a timing chart showing the timing of auxiliary ignition for each engine load. FIG. 17 is a part of a flowchart of the auxiliary ignition control. FIG. 18 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 underside 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 vertical vortex 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 makes the valve timing and/or the valve lift variable. As shown in FIG. 3, the valve mechanism has an intake S-VT (Sequential-Valve Timing) 23. The intake S-VT 23 is an electric or hydraulic type. The intake S-VT 23 continuously changes the rotational phase of the intake camshaft within a predetermined angle range. The opening period of the intake valve 21 does not change.

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

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

The injector 6 injects fuel directly into the cylinder 11. The injector 6 is an example of a fuel injection valve. Although detailed illustration is omitted, the injector 6 is a multi-hole type injector having multiple nozzles. 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.

A spark plug 25 is attached to each cylinder 11 in the cylinder head 13. The spark plug 25 forcibly ignites the air-fuel mixture inside the cylinder 11. The center electrode and ground electrode of the spark plug 25 are located near the ceiling of the cylinder 11 in the center of the cylinder 11, 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 (arc 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 detected parameter is used to estimate the flow state in the cylinder 11. 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 in the cylinder 11. The swirl generating section has a swirl control valve 56 attached to the intake passage 40, although detailed illustration is omitted. The swirl control valve 56 is disposed in the second intake passage 18b of the first intake passage 18a and the second intake passage 18b (see FIG. 2) that are parallel to each other, downstream of the surge tank 42. The swirl control valve 56 is an opening adjustment valve that can narrow the cross section of the second intake passage 18b. When the opening of the swirl control valve 56 is small, the intake flow rate flowing into the cylinder 11 from the first intake passage 18a shown in FIG. 2 is relatively large and the intake flow rate flowing into the cylinder 11 from the second intake passage 18b is relatively small, so that the swirl flow in the cylinder 11 becomes strong. When the swirl control valve 56 is open, the intake air flow rates from the first intake passage 18a and the second intake passage 18b into the cylinder 11 are approximately equal, weakening the swirl flow in the cylinder 11. When the swirl control valve 56 is fully open, no swirl flow occurs. The swirl flow circulates counterclockwise in FIG. 2, as shown by the white arrow.

In addition, instead of generating a swirl flow using the swirl control valve 56, the intake port 18 of the engine 1 may be configured as a helical port capable of generating a swirl flow.

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 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 a program, a memory 102 configured, for example, of a RAM (Random Access Memory) or a ROM (Read Only Memory) for storing programs and data, and an I/F circuit 103 for inputting and outputting electric signals. The ECU 10 is an example of a controller.

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

The center electrode 251 is connected to the secondary coil 70c of the ignition coil 70. The ground electrode 252 is grounded. When the secondary voltage applied between the electrodes by the secondary coil 70c reaches the voltage required for dielectric breakdown, a discharge occurs in the gap between the center electrode 251 and the ground electrode 252.

One end of the primary coil 70a is connected to a capacitor 72. The capacitor 72 stores electrical energy to pass a primary current through the primary coil 70a. The energy generating device 74 includes a power source. The energy generating device 74 charges the capacitor 72.

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

As mentioned above, one end of the secondary coil 70c is connected to the center electrode 251, and the other end is connected to the ignition controller 75.

The ignition controller 75 controls the energy generating device 74 and the transistor 73 to ignite the mixture in the cylinder 11 using the spark plug 25 at a predetermined timing.

The ignition controller 75 can also measure the secondary voltage that the secondary coil 70c applies between the electrodes of the spark plug 25 and the secondary current that flows from the secondary coil 70c to the spark plug 25. As described above, the ignition device 7 causes the spark plug 25 to discharge when the mixture is not ignited, and detects parameters related to the current value at that time.

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

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

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

More specifically, this engine system estimates the flow conditions within the cylinder 11 for each cycle and performs auxiliary ignition as necessary based on the estimated flow conditions.

Figure 5 is a block diagram illustrating the configuration of a control device for engine 1 that executes suppression control of combustion fluctuations. Figure 5 illustrates the functional blocks of ECU 10. ECU 10 has a main fuel injection unit 81 and a main ignition control unit 82 as functional blocks. 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 ignites the mixture in the cylinder 11 at a predetermined timing using the spark plug 25 after the main fuel injection.

The ECU 10 has a flow velocity estimation unit 83 and an auxiliary ignition control unit 84. The flow velocity estimation unit 83 is a functional block that causes the spark plug 25 to perform an inspection discharge (hereinafter referred to as inspection discharge) when the mixture is not ignited in order to inspect the flow state in the cylinder 11. The flow velocity estimation unit 83 is a functional block that estimates the flow state in the cylinder 11, particularly the high or low flow rate of the intake air around the spark plug 25, based on electrical 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 performs auxiliary ignition as necessary to provide ignition energy before the mixture is ignited by the discharge of the spark plug 25 based on the flow state in the cylinder 11 estimated by the flow velocity estimation unit 83. As will be described in detail later, "providing ignition energy by auxiliary ignition" means generating plasma by auxiliary ignition.

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 11) 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 combustion speed is slower than in the case of chart 605.

In the engine system, the flow state in the cylinder 11 is detected by the ignition device 7. Specifically, the ignition device 7 discharges in the cylinder 11 when the mixture is not ignited in response to a control signal from the flow velocity 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 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 path does not extend much, so the discharge time is long. The stronger the flow near the spark plug 25, the longer the discharge path (see chart 704), so the discharge time becomes shorter, as shown by the dashed lines in charts 701 and 702. In other words, the discharge time of the current between the electrodes of the spark plug 25 is proportional to the strength of the flow near the spark plug 25. If the ignition device 7 detects the discharge time, the flow velocity estimation unit 83 can estimate the strength of the flow near the spark plug 25 (i.e., the flow velocity).

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 spark plug 25 and the center of the vortex are close to each other, so the flow speed near the spark plug 25 is slower than V2.

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 and the estimated flow velocity estimated from the discharge time detected by the ignition device 7 is higher than the second predetermined value Vp2 corresponding to the speed V1 (in FIG. 8, when the discharge time is shorter than the first threshold), it can be estimated that the center position of the vertical vortex is close to the piston 3, and when the estimated flow velocity is lower than the first predetermined value Vp1 corresponding to the speed V2 (in FIG. 8, when the discharge time is longer than the second threshold), it can be estimated that the center position of the vertical vortex is close to the ceiling. When the estimated flow velocity is between the first predetermined value Vp1 and the second predetermined value Vp2, it can be estimated that the center position of the vertical vortex is 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 flow velocity of the intake air. For example, the reciprocal of the discharge time may be used as the estimated flow velocity.

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

As mentioned above, when the center position of the longitudinal vortex and/or transverse vortex shifts due to variations in the intake flow, areas where the degree of turbulence is weak and/or areas where flame propagation is difficult (hereinafter referred to as specific areas) are generated in the cylinder 11. Auxiliary ignition raises the temperature of the mixture by locally disposing plasma in such specific areas, thereby promoting flame propagation to the specific 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 (see main fuel injection 1104 in FIG. 11) into the cylinder 11 through the injector 6. The injected fuel flows and diffuses into the cylinder 11, forming an air-fuel mixture in the cylinder 11.

The flow velocity estimation unit 83 causes the ignition device 7 and the spark plug 25 to execute an inspection discharge 1106, for example, in the first half of the compression stroke after the intake valve 21 closes. The inspection discharge 1106 is a discharge that is performed during the period after the main fuel injection when the mixture is not ignited. The ignition device 7 detects the discharge time of the inspection discharge 1106. The flow velocity estimation unit 83 estimates the flow velocity of the longitudinal vortex around the ignition plug 25 from the discharge time detected during the inspection discharge 1106, and estimates the center position of the longitudinal vortex.

When the discharge time detected by the ignition device 7 is 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 predetermined value Vp1 and the second predetermined value Vp2), the center position of the vertical vortex is located halfway between the piston 3 and the ceiling of the cylinder 11. In this case, auxiliary ignition is not required. As shown in the chart 1102 of FIG. 9, the auxiliary ignition control unit 84 stops 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. 9). In this case, since the center position of the vertical vortex is located in the center of the cylinder 11, the degree of turbulence is uniform or approximately uniform throughout the cylinder 11. The flame propagates uniformly or approximately uniformly from the center to the periphery of the cylinder 11. The combustion speed is relatively fast.

Next, a case where the 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 predetermined 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 of FIG. 9, the auxiliary ignition control unit 84 controls the ignition device 7 to perform the first auxiliary ignition 1108. The ignition device 7 performs the first auxiliary ignition 1108, for example, at the second injection timing in the first half of the compression stroke or the second half of the compression stroke.

As shown in Figure 10, when auxiliary ignition is performed, plasma is generated between the electrodes 251, 252 of the spark plug 25. The generated plasma flows with the intake air flow. The temperature of the mixture in the area where the plasma is retained is raised by the plasma. The mixture warmed by the plasma promotes reaction, making it easier for flames to propagate. Increasing the ignition energy of the auxiliary ignition, lengthening the ignition time of the auxiliary ignition, or increasing the auxiliary ignition voltage increases the amount of plasma. Increasing the amount of plasma makes it possible to raise the temperature of the mixture over a wide range.

Figure 11 is a diagram explaining the change in flow inside the cylinder 11 and the distribution of plasma generated by the first auxiliary ignition 1108 when the center position of the vertical vortex is located near the piston 3 in the cylinder 11. As described above, when the center position of the vertical vortex is located near the piston 3, as the piston 3 rises from P1201, P1202, P1203, and P1204, 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 P1205, 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.

The plasma generated in the cylinder 11 at a relatively early timing (P1203) of the compression stroke 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 P1204 and P1205). As a result, the temperature of the mixture near the intake valve 21 can be raised.

After the first auxiliary ignition 1108, 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 and second predetermined values Vp1 and 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 predetermined 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. 9, the auxiliary ignition control unit 84 controls the ignition device 7 to execute the second auxiliary ignition 1109. The ignition device 7 executes the second auxiliary ignition 1109 at the second ignition timing in the latter half of the compression stroke.

Figure 12 is a diagram explaining the change in flow inside the cylinder 11 and the distribution of plasma generated by the second auxiliary ignition 1109 when the center position of the vertical vortex is located near the ceiling of the cylinder 11. As described above, when the center position of the vertical vortex is located near the ceiling, as the piston 3 rises from P1301, P1302, P1303, and P1304, the center of the vortex hits the ceiling, crushing the upper 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 counter-unidirectional flow from the exhaust valve 22 toward the intake valve 21.

The injector 6 executes a second auxiliary ignition in the latter half of the compression stroke (see P1304). 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, where the flow is relatively weak (see the hatched areas of P1304 and P1305). As a result, the temperature of the mixture near the exhaust valve 22 can be increased.

After the second auxiliary ignition 1109, 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 and second predetermined values Vp1 and 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.

(Setting the auxiliary ignition period)
As described above, in this embodiment, the ECU 10 performs a test discharge during the intake stroke, estimates the flow speed of the mixture based on the electrical parameters of the discharge path of the test discharge, and biases the plasma to areas with low turbulence.

Here, when the estimated flow velocity is low, that is, when the center of the vertical vortex is located on the ceiling side of the cylinder 11, the flow velocity of the intake air in the combustion chamber 17 is low even in the latter half of the compression stroke. Furthermore, when the engine load is low, the intake air flow rate and the main fuel injection are even smaller. Therefore, when the center of the vertical vortex is located on the ceiling side of the cylinder 11, in the latter half of the compression stroke, the degree of turbulence is weak on the exhaust valve 22 side located on the opposite side to the mixture flow, making it difficult for flame to propagate. As a result, the combustion speed becomes unstable. Therefore, in this embodiment, the ECU 10 (strictly speaking, the auxiliary ignition control unit 84) is configured to adjust the amount of ignition energy (hereinafter referred to as auxiliary ignition energy) provided by auxiliary ignition in the auxiliary ignition control according to the estimated flow velocity and the engine load. Specifically, the amount of auxiliary ignition energy is adjusted by adjusting the period of auxiliary ignition.

Figure 13 is a map for setting the ignition period of the auxiliary ignition based on the estimated current and the determined load. The vertical axis is the estimated flow speed, and the horizontal axis is the engine load. This map in Figure 13 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 shorter 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 Figure 13 reflects the level of the intake air flow speed in the cylinder 11. Note that the value of the estimated flow speed may be a flow speed value calculated from the discharge time, etc., based on a graph such as that shown in the upper diagram 700 of Figure 7.

As shown in FIG. 13, auxiliary ignition is performed in a region where the estimated flow velocity is less than a first predetermined value Vp1, and in a region where the estimated flow velocity is higher than a second predetermined value Vp2 that is higher than the first predetermined value Vp1. Here, the first predetermined value Vp1 is the reciprocal of the discharge time corresponding to the velocity V1, and the second predetermined value Vp2 is the reciprocal of the discharge time corresponding to the velocity V2.

The region where the estimated flow velocity is less than the first predetermined value Vp1, i.e., the region where the center of the vertical vortex is biased toward the ceiling of the cylinder 11, is divided into two regions, a first region R1 and a second region R2, by the first comparison value B1. The first region R1 is the region where the estimated flow velocity is equal to or less than the first comparison value B1, and the second region R2 is the region where the estimated flow velocity is less than the first predetermined value Vp1 and higher than the first comparison value B1. The lower the engine load, the closer the first comparison value B1 is to the first predetermined value Vp1. As a result, the first region R1 is a region where there are many ranges where the engine load is relatively low, and the second region R2 is a region where there are many ranges where the engine load is relatively high.

13, the region where the estimated flow velocity is higher than the second predetermined value Vp2, i.e., the region where the center of the vertical vortex is biased toward the piston 3, is divided into three regions, the third region R3, the fourth region R4, and the fifth region R5, by the second comparison value B2 and the third comparison value B3. The third region R3 is a region where the estimated flow velocity is higher than the second predetermined value Vp2 and is equal to or lower than the second comparison value B2, the fourth region R4 is a region where the estimated flow velocity is higher than the second comparison value B2 and is equal to or lower than the third comparison value B3, and the fifth region R5 is a region where the estimated flow velocity is higher than the third comparison value B3. The second comparison value B2 has a value closer to the second predetermined value Vp2 as the engine load increases. On the other hand, the third comparison value B3 has a value where the estimated flow velocity is slightly lower as the engine load increases. As a result, the third region R3 is a region where the range of relatively low engine loads is large, and the fourth region R4 is a region where the range of relatively high engine loads is large. The fifth region R5 extends from low to high engine loads.

In the region where the estimated flow velocity is less than the first predetermined value Vp1, the period of auxiliary ignition is longer than the second ignition period when the ignition period in the first region R1 is the first ignition period and the ignition period in the second region R2 is the second ignition period. That is, when the engine load is low, the intake flow rate and the injection amount of the main fuel injection are small, and the flame is hardly propagated on the exhaust side where the degree of turbulence is weak. On the other hand, when the engine load is high, the intake flow rate and the injection amount of the main fuel injection are large, and a mixture with a certain fuel concentration is present on the exhaust side where the degree of turbulence is weak, so the effect on the flame propagation to the exhaust side is small. Therefore, when the engine load is low and the estimated flow velocity is low, the period of auxiliary ignition is made longer than when the engine load is high, and the plasma is widely distributed on the exhaust valve 22 side in the cylinder 11.

As shown in FIG. 13, the first region R1, i.e., the region in which the ignition period of the auxiliary ignition is increased, spreads toward the high load side as the estimated flow velocity decreases. The lower the estimated flow velocity, the more the vortex center of the vertical vortex is biased toward the ceiling of the cylinder 11. Therefore, the lower the estimated flow velocity, the earlier the anti-unidirectional flow from the exhaust valve 22 side to the intake valve 21 side occurs. If the anti-unidirectional flow from the exhaust valve 22 side to the intake valve 21 side occurs early, the mixture is pressed against the intake valve 21 side for a long period of time. Therefore, when the estimated flow velocity is low, the concentration of fuel on the exhaust valve 22 side is likely to be low even when the engine load is high. Therefore, when the estimated flow velocity is low, the ignition period of the auxiliary ignition is lengthened even when the engine load is high, and the auxiliary ignition energy provided in the cylinder 11 is increased.

On the other hand, in the region where the estimated flow velocity is higher than the second predetermined value Vp2, when the ignition period of the auxiliary ignition is the third ignition period in the third region R3 and the fourth ignition period in the fourth region R4, the fourth ignition period is longer than the third ignition period. When the flow velocity of the intake air is high, the inertial force and centrifugal force of the vertical vortex become large. As described above, when the flow velocity of the intake air is high, that is, when the vortex center of the vertical vortex is biased toward the piston side, the flow of the intake air in the latter half of the compression stroke becomes a positive unidirectional flow from the intake valve 21 side to the exhaust valve 22 side. For this reason, it becomes difficult for the flame to propagate on the intake valve 21 side. When the engine load is high, the intake flow rate and the injection amount of the main fuel injection are large, and the inertial force and centrifugal force of the vertical vortex are large, so that the mixture is significantly biased toward the exhaust valve 22 side in the latter half of the compression stroke. On the other hand, when the engine load is low, the inertial force and centrifugal force of the vertical vortex are small, so the air-fuel mixture is less biased in the latter half of the compression stroke. Therefore, when the estimated flow velocity is high, the fourth ignition period is longer than the third ignition period so that plasma is formed in a wider area on the intake valve 21 side when the engine load is high than when the engine load is low.

As shown in FIG. 12, the third region R3, i.e., the region where the ignition period of the auxiliary ignition is relatively short, spreads toward the high load side as the estimated flow velocity decreases. The higher the estimated flow velocity, the more the vortex center of the vertical vortex is biased toward the piston 3 side. Therefore, the closer the estimated flow velocity is to the second predetermined value Vp2, the longer it takes for a positive unidirectional flow to occur from the intake valve 21 side to the exhaust valve 22 side. Therefore, when the estimated flow velocity is close to the second predetermined value Vp2, the bias of the mixture is small even when the engine load is high. Therefore, when the estimated flow velocity is the second predetermined value Vp2, the amount of auxiliary ignition energy may be small and the injection amount of auxiliary ignition may be short even when the engine load is high.

The fifth ignition period, which is the ignition period of the auxiliary ignition in the fifth region R5, will be described later.

In addition, in the map of FIG. 13, the shapes of the comparison values B1 to B3 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 14 shows the ignition period of the auxiliary ignition with respect to the estimated flow speed when the engine load is the engine load Tq1 shown in Figure 13. That is, Figure 14 shows the relationship between the amount of auxiliary ignition energy and the estimated speed when the engine load is constant. As shown in Figure 14, 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. The lower the estimated flow speed, the more the vortex center of the vertical vortex is biased toward the ceiling. Therefore, the earlier the anti-unidirectional flow from the exhaust valve 22 side to the intake valve 21 side occurs, making it difficult for the flame to propagate to the exhaust valve 22 side. Therefore, the lower the estimated flow speed, the longer the ignition period of the auxiliary ignition is, and by generating more plasma, the plasma is distributed over a wide area on the exhaust valve 22 side. Also, the first ignition period and the second ignition period change significantly at the boundary of the first comparison value B1, and are discontinuous. The slope of the first ignition period relative to the estimated flow velocity and the slope of the second ignition period relative to the estimated flow velocity may be the same or different.

As shown in FIG. 14, when the estimated flow velocity is between the first predetermined value Vp1 and the second predetermined value Vp2, auxiliary ignition is not performed, so the ignition period is 0.

As shown in FIG. 14, in the third region R3 and the fourth region R4, the higher the estimated flow velocity, the longer the third and fourth ignition periods are. The higher the estimated flow velocity, i.e., the higher the flow velocity of the intake air around the spark plug 25, the higher the inertial force and centrifugal force of the vertical vortex in the latter half of the compression stroke, and the more likely the mixture is to be biased toward the exhaust valve 22. Therefore, the higher the flow velocity of the vertical vortex around the spark plug 25, i.e., the higher the estimated flow velocity, the longer the ignition period of the auxiliary ignition is to appropriately distribute the plasma to the intake valve 21 side of the cylinder 11. In addition, the third ignition period and the fourth ignition period change significantly at the boundary of the second comparison value B2 and are discontinuous. Note that the slope of the third ignition period with respect to the estimated flow velocity and the slope of the fourth ignition period with respect to the estimated flow velocity may be the same or different.

As shown in FIG. 14, the fifth ignition period is constant regardless of the estimated flow velocity. The fifth ignition period is the same as the maximum period of the fourth ignition period at the same engine load. That is, the fifth region R5 is a region where the flow velocity of the intake air is very high, the centrifugal force of the vertical vortex is quite large, and the mixture is likely to be biased toward the wall side (liner wall side or ceiling side) of the combustion chamber 17. For this reason, if the ignition period of the auxiliary ignition is lengthened and a lot of plasma is generated, the temperature of the mixture near the wall side on the intake valve 21 side will rise. If the temperature of the mixture rises excessively, there is a risk that the mixture will ignite before the main ignition. Therefore, the fifth ignition period in the fifth region R5 is a constant value. The reason why the third comparison value B3 is located on the side of the lower estimated flow velocity as the engine load increases is because when the engine load is high, the amount of fuel injected is large and ignition is easy.

On the other hand, Figure 15 shows the ignition period of auxiliary ignition with respect to engine load when the estimated flow velocity is the estimated value VA shown in Figure 13. As shown in Figure 8, when the estimated flow velocity is constant, both the first ignition period and the second ignition period are constant regardless of the engine load. 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 load.

In this way, by adjusting the ignition period of the auxiliary ignition based on the estimated flow velocity estimated from the parameters of the discharge path in the test discharge and the engine load, it is possible to appropriately distribute plasma to areas in the cylinder 11 where flame propagation is difficult, and to heat the mixture in those areas. As a result, flame propagation becomes easier throughout the cylinder 11, and the combustion speed can be stabilized.

Figure 16 shows the timing of fuel injection by the injector 6 and ignition by the spark plug 25. Figure 16 (a) shows the timing when the state of the engine 1 belongs to the first region R1, and (b) shows the timing when the state of the engine 1 belongs to the second region R2. Note that Figure 16 shows the case where the estimated flow speed is the same.

As shown in FIG. 16, main fuel injection is performed by the injector 6 during the intake stroke regardless of whether the state of the engine 1 is in the first region R1 or the second region R2. The injection amount at this time is greater when the engine is in the second region R2, where the engine load is relatively high. The main fuel injection unit 81 increases the injection amount of the main fuel injection by lengthening the opening period of the injector 6.

After the main fuel injection, a test discharge is performed by the spark plug 25. This test discharge is performed after the intake valve 21 is closed, particularly during the first half of the compression stroke.

After the test discharge, in the latter half of the compression stroke, auxiliary ignition is performed by the spark plug 25 before the mixture is ignited. As described above, the first ignition period is set to be longer than the second ignition period. Therefore, the auxiliary ignition control unit 84 makes the ignition period of the auxiliary ignition longer when the state of the engine 1 is in the first region R1 than when it is in the second region R2.

Then, 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 to ignite the mixture in the cylinder 11. At this time, the auxiliary ignition distributes plasma and warms the less turbulent parts of the cylinder 11, 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. 17 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 SWO7. The required torque calculated in step S2 corresponds to the load to be determined when calculating the ignition period of the auxiliary ignition.

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

Next, in step S4, the ECU 10 sets the main ignition timing. This main ignition timing is the ignition timing for actually igniting the air-fuel mixture.

Next, in step S5, the ECU 10 sets the timing of the inspection discharge. The ECU 10 sets the timing of the inspection discharge to a time after the intake valve 21 is closed and at a time when the mixture in the cylinder 11 is not ignited.

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 time of the discharge path that occurred in the ignition plug 25 during the inspection discharge. Although not shown in the flowchart, before executing the inspection discharge, the main injection is performed at the injection time set in step S3.

Next, in step S7, the ECU 10 estimates the flow velocity of the intake air 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 less than the first predetermined value Vp1. If the estimated flow speed is less than the first predetermined value Vp1 (YES), the ECU 10 proceeds to step S8. On the other hand, if the estimated flow speed is higher than the first predetermined value Vp1 (NO), the ECU 10 proceeds to step S12.

In step S9, the ECU 10 determines whether the state of the engine 1 belongs to the first region R1, i.e., whether it belongs to the region below the first comparison value B1, based on the engine load calculated in step S2 and the estimated flow speed calculated in step S7. The ECU 10 makes the determination by reading the map shown in FIG. 13. 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 ignition period of the auxiliary ignition to the first ignition period. After step S10, the process proceeds to step S19.

In step S11, the ECU 10 sets the ignition period of the auxiliary ignition to the second ignition period. After step S11, the process proceeds to step S19.

On the other hand, 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 predetermined value Vp2. If the estimated flow speed is higher than the second predetermined 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 predetermined value Vp2 (NO), the ECU 10 proceeds to step S13.

In step S13, the ECU 10 determines that auxiliary ignition is not performed. After step S13, the ECU 10 returns.

In step S14, the ECU 10 determines whether the state of the engine 1 belongs to the third region R3 based on the engine load calculated in step S2 and the estimated flow speed calculated in step S7. The ECU 10 reads the map shown in FIG. 13 to make the determination. If the state of the engine 1 belongs to the third region R3 (YES), the ECU 10 proceeds to step S15. On the other hand, if the state of the engine belongs to the fourth region R4 or the fifth region R5 (NO), the ECU 10 proceeds to step S16.

In step S15, the ECU 10 sets the ignition period of the auxiliary ignition to the third ignition period. After step S15, the ECU 10 proceeds to step S19.

On the other hand, in step S16, the ECU 10 determines whether the state of the engine 1 belongs to the fourth region R4. If the result is YES, meaning that the state of the engine 1 belongs to the fourth region R4, the ECU 10 proceeds to step S17. On the other hand, if the result is NO, meaning that the state of the engine 1 belongs to the fifth region R5, the ECU 10 proceeds to step S18.

In step S17, the ECU 10 sets the ignition period of the auxiliary ignition to the fourth ignition period. After step S17, the ECU 10 proceeds to step S19.

In step S18, the ECU 10 sets the ignition period of the auxiliary ignition to the fifth ignition period. After step S18, the ECU 10 proceeds to step S19.

As shown in FIG. 17, in step S19, which follows steps S10, S11, S15, S17, and S18, the ECU 10 sets the ignition timing of the auxiliary ignition. The ECU 10 sets the ignition timing of the auxiliary ignition to a timing that is more advanced than the main ignition timing set in step S4. When the estimated flow speed calculated in step S7 is equal to or less than a first predetermined value Vp1, the ECU 10 sets the ignition timing of the auxiliary ignition to a timing in the latter half of the compression stroke, whereas when the estimated flow speed calculated in step S7 is higher than a second predetermined value Vp2, the ECU 10 sets the ignition timing of the auxiliary ignition to a timing in the first or second half of the compression stroke. The ECU 10 returns after step S19.

After the flow chart, the ECU 10 executes auxiliary ignition and main ignition. This allows the plasma to be distributed to areas with low turbulence depending on the state of the vertical vortex in the cylinder 11, stabilizing the combustion speed in the cylinder 11.

(summary)
Therefore, this embodiment includes an operating state detector (sensors SW1 to SW9) that detects the operating state of the engine 1, an ignition device 7, an injector 6, and an ECU 10 that is electrically connected to the operating state detector. The ECU 10 has a main fuel injection unit 81 that sets a main fuel injection amount and a main fuel injection timing, which is the injection timing, 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 the amount of main fuel set at the main fuel injection timing; a main ignition control unit 82 that executes main ignition for igniting the air-fuel mixture in the cylinder 11 to combust the mixture after the main fuel injection timing; a flow velocity estimation unit 83 that controls the ignition device 7 to apply a voltage between the electrodes of the ignition plug 25 and execute a discharge for detecting a parameter related to a current value of a discharge path generated between the electrodes, during a period when the mixture is not ignited, and estimates the level of the flow velocity of the intake air in the cylinder 11 from the parameter in the discharge; and an auxiliary ignition control unit 84 that controls the ignition device 7 to execute auxiliary ignition for providing auxiliary ignition energy to the air-fuel mixture, on the retard side of the main fuel injection timing and at the main ignition timing, when the estimated flow velocity estimated by the flow velocity estimation unit 83 is less than a predetermined value. When the estimated flow velocity is set in a region lower than the first predetermined value Vp1 and is equal to or lower than a first comparison value B1 that varies depending on the engine load, the auxiliary ignition control unit 84 controls the ignition device 7 to increase the ignition energy provided by the auxiliary ignition, compared to when the estimated flow velocity is higher than the first comparison value B1. This adjusts the amount of auxiliary ignition energy according to the engine load, and adjusts the amount of plasma generated. The plasma generated by the auxiliary ignition increases the temperature of the mixture in the region where flame propagation is difficult. As a result, the combustion speed can be stabilized.

In particular, in this embodiment, the lower the engine load, the closer the first comparison value B1 is to the first predetermined value Vp1. When the estimated flow rate is less than the first predetermined value Vp1, the flow of the mixture in the latter half of the compression stroke is a one-way flow from the exhaust side to the intake side. In addition, when the engine load is low, the intake amount and the injection amount of the main fuel injection are small. For this reason, it is very difficult for the flame to propagate on the exhaust valve 22 side, which is located on the opposite side to the flow of the mixture. By making the first comparison value B1 closer to the first predetermined value Vp1 as the engine load is lower, the amount of auxiliary ignition energy can be increased when the engine load is low. This makes it possible to further stabilize the combustion speed.

In addition, in this embodiment, when the engine load is constant and the estimated flow speed is equal to or lower than the first comparison value B1, the auxiliary ignition control unit 84 increases the amount of auxiliary ignition energy as the estimated flow speed decreases. In other words, the lower the estimated flow speed, the earlier the forward unidirectional flow from the exhaust valve 22 side to the intake valve 21 side occurs. Therefore, the lower the estimated flow speed, the more the amount of auxiliary ignition energy is increased, raising the temperature of the mixture over a wide range on the exhaust valve 22 side. This promotes flame propagation, making it possible to stabilize the combustion speed.

Other Embodiments
The technology disclosed herein is not limited to the above-described embodiment, and may be substituted without departing from the spirit and scope of the claims.

For example, in the above embodiment, the parameters are detected after the intake valve 21 of the engine 1 is closed to estimate the center of the vertical vortex. However, the present invention is not limited to this, and the center of the transverse vortex may also be estimated by detecting parameters during the intake stroke. After the center of the transverse vortex is estimated, the ignition timing of the auxiliary ignition can be set according to the central positions of the transverse and vertical vortices.

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.

The above-described embodiments are merely examples and should not be interpreted as limiting the scope of the present disclosure. The scope of the present disclosure is defined by the claims, and all modifications and variations that fall within the scope of equivalence of the claims are within the scope of the present disclosure.

The technology disclosed herein is useful as an engine system having an engine with a cylinder having a pent roof type ceiling, an ignition device including a spark plug located in the center of the cylinder, and a fuel injection valve located in the center of the cylinder.

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 82 Main ignition control unit 83 Flow velocity estimation unit 84 Auxiliary ignition control unit B1 First comparison value (comparison value)
SW7 Accelerator opening sensor (driving state detector)
Vp1 First Predetermined Value

Claims (5)

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 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 main ignition control unit that controls the ignition device to execute main ignition for igniting the air-fuel mixture in the cylinder to combust the air-fuel mixture after the main fuel injection timing;
a flow velocity estimation unit that controls the ignition device to apply a voltage between electrodes of the spark plug and detect 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 a flow velocity of the intake air based on the parameter;
an auxiliary ignition control unit that controls the ignition device to execute auxiliary ignition for providing auxiliary ignition energy to the air-fuel mixture at a timing that is retarded from the main fuel injection timing and advanced from the main ignition timing when the estimated flow velocity estimated by the flow velocity estimating unit is less than a predetermined value;
having
the auxiliary ignition control unit controls the ignition device to increase the ignition energy provided by the auxiliary ignition when the estimated flow velocity is set in a region lower than the predetermined value and is equal to or lower than a comparison value set corresponding to the engine load, compared to when the estimated flow velocity is higher than the comparison value. 2. The engine system according to claim 1,
An engine system, characterized in that the comparison value has a value closer to the predetermined value as the engine load is lower. 3. The engine system according to claim 1,
The engine system according to claim 1, wherein the flow velocity estimation unit controls the ignition device so as to detect the parameter after an intake valve of the engine is closed. In the engine system according to any one of claims 1 to 3,
The engine system according to claim 1, wherein the flow velocity estimation unit controls the ignition device so as to detect the parameter during a compression stroke. In the engine system according to any one of claims 1 to 4,
an auxiliary ignition control unit that, when the engine load is constant and the estimated flow speed is equal to or lower than the comparison value, increases the ignition energy provided by the auxiliary ignition as the estimated flow speed becomes lower.

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