JP7564997B2 - Engine System - Google Patents

Description

The present invention relates to an engine system having a swirl control valve that generates a swirl flow inside a cylinder.

A technology has been known in the past in which a swirl control valve (hereinafter referred to as "SCV") is provided in one of the two intake ports that supply intake air to each cylinder, and the SCV is set to a closed opening (for example, fully closed) to generate a swirl flow in the cylinder. For example, Patent Document 1 discloses a technology in which the opening of such an SCV is switched depending on the operating state of the engine. Specifically, in this technology, the SCV is closed in the low load range of the engine, and is opened in the high load range of the engine. In particular, in the low load range, fuel is injected during the compression stroke when a swirl flow is generated, thereby achieving stratified combustion operation of the engine, and in the high load range, fuel is injected during the intake stroke when a tumble flow is generated, thereby achieving homogeneous combustion operation of the engine.

JP 2002-130025 A

However, while the SCV opening is being changed to the open side in response to a change in the engine's operating state, the amount of exhaust gas that is blown back from the exhaust passage to the intake passage during the overlap period of the intake valve and exhaust valve becomes greater than before the change in opening (i.e., when the SCV opening is set to the closed side). In other words, the amount of burnt gas remaining in the cylinder that flows back into the intake passage increases. As a result, the amount of burnt gas (i.e., so-called internal EGR gas) introduced into the cylinder increases, reducing combustion stability.

The present invention has been made to solve the problems of the conventional technology described above, and aims to provide an engine system that can improve the deterioration of combustion stability caused by an increase in internal EGR gas when the opening of the swirl control valve changes to the open side.

To achieve the above object, the present invention provides an engine system comprising: an engine having a cylinder forming a combustion chamber, a piston reciprocating in the cylinder, a fuel injection valve for directly injecting fuel into the cylinder, and an ignition plug for igniting a mixture of fuel and intake air in the cylinder; a swirl control valve provided in an intake passage supplying intake air to the cylinder of the engine and configured to generate a swirl flow in the cylinder when set to a closed opening; and a controller configured to control the fuel injection valve and the swirl control valve, the controller being configured to control the opening of the swirl control valve in accordance with the operating state of the engine, the controller being configured to control the fuel injection valve so that the fuel injection timing by the fuel injection valve is retarded from the fuel injection timing applied before the opening is changed while the opening of the swirl control valve is changed to the open side in accordance with the operating state of the engine.

In the present invention configured in this manner, while the controller is changing the opening of the swirl control valve (SCV) to the open side in response to a change in the operating state of the engine, the controller retards the fuel injection timing of the fuel injection valve from the fuel injection timing applied before the change in the opening. When the fuel injection timing is retarded in this manner, the formation of a swirl flow in the combustion chamber is almost complete. Therefore, the fuel injected at this time is less likely to be swirled by the swirl flow, and is more likely to penetrate the swirl flow, reach the center of the combustion chamber, and remain in this center. As a result, a fuel-rich region is formed around the spark plug, and combustion stability can be ensured. Therefore, according to the present invention, when the opening of the SCV is changed to the open side, the decrease in combustion stability due to an increase in internal EGR gas can be improved.

In the present invention, the controller is preferably configured to control the fuel injection valve so that, when the change in the opening of the swirl control valve to the open side is completed, the fuel injection timing by the fuel injection valve is advanced from the fuel injection timing applied during the change in the opening.
According to the present invention configured in this manner, when the change in the SCV opening is completed, the controller returns the fuel injection timing that was temporarily retarded during this change to the normal fuel injection timing that is not retarded. This limits the change in the fuel injection timing to the period during which the SCV opening is changing, and returns the fuel injection timing to its original state after the change in the SCV opening is completed, thereby ensuring the stability of control over the fuel injection timing.

In the present invention, the controller is preferably configured to control the fuel injection valve so that the amount by which the fuel injection timing is retarded increases as the amount of change in the opening degree of the swirl control valve toward the opening side increases.
The greater the change in the SCV opening, the stronger the gas flow, and the longer it takes for the swirl flow to stabilize. Therefore, the greater the change in the SCV opening, the greater the retard amount of the fuel injection timing, so that fuel injection is put on hold until the swirl flow stabilizes. This allows the injected fuel to be accurately placed in the center of the combustion chamber without being affected by the swirl flow, even when the change in the SCV opening is large.

In the present invention, preferably, the fuel injection valve is provided inclined with respect to the axial direction of the piston.
Preferably, the piston crown surface is substantially flat without any cavity formed therein, and the spark plug is provided in the center of the roof of the combustion chamber.

The engine system of the present invention can improve the deterioration of combustion stability caused by an increase in internal EGR gas when the opening of the swirl control valve changes to the open side.

1 is a schematic configuration diagram of an engine system according to an embodiment of the present invention. FIG. 1 is a perspective view of an engine according to an embodiment of the present invention. 1 is a block diagram showing an electrical configuration of an engine system according to an embodiment of the present invention. FIG. 3 illustrates operating regions for an engine according to an embodiment of the present invention. FIG. 10 is an explanatory diagram of a decrease in combustion stability due to an increase in internal EGR gas that occurs when the SCV is switched from fully closed to fully open. FIG. 11 is an explanatory diagram of the effect of retarding the fuel injection timing when the SCV is switched from fully closed to fully open in the embodiment of the present invention. 4 is a time chart showing an example of control according to the embodiment of the present invention. 4 is a flowchart showing a control according to the embodiment of the present invention. FIG. 11 is an explanatory diagram of the retard amount of the fuel injection timing applied in accordance with the amount of change in the SCV opening in the modified embodiment of the present invention.

An engine system according to an embodiment of the present invention will now be described with reference to the accompanying drawings.

[Engine system configuration]
FIG. 1 is a schematic diagram of an engine system according to the present embodiment. As shown in FIG. 1, the engine system 100 has an engine 1 mounted on a vehicle. The engine 1 is a gasoline engine to which fuel containing at least gasoline is supplied. Specifically, the engine 1 has a cylinder block 4 in which cylinders 2 are provided (note that only one cylinder 2 is illustrated in FIG. 1, but for example, four cylinders 2 are provided in series), a cylinder head 6 disposed on the cylinder block 4, and an oil pan 8 disposed below the cylinder block 4 and storing lubricating oil. A piston 14 connected to a crankshaft 12 via a connecting rod 10 is inserted in each cylinder 2 so as to be able to reciprocate. The cylinder head 6, the cylinder 2, and the piston 14 define a combustion chamber 16 of the engine 1.

Intake air is supplied to the engine 1 through an intake passage 40. A throttle valve 41 that can adjust the amount of intake air supplied to the engine 1, and a surge tank 42 that temporarily stores the intake air to be supplied to the engine 1 are provided on the intake passage 40. A portion of the intake passage 40 forms an intake port 18 connected to the engine 1.

The engine 1 has two independent intake ports 18 and two exhaust ports 20 connected to each cylinder 2, and these intake ports 18 and exhaust ports 20 are provided with intake valves 22 and exhaust valves 24 that open and close the openings on the combustion chamber 16 side. When the intake valves 22 open and the piston 14 descends, the intake air that flows from the intake ports 18 into the combustion chamber 16 generates a tumble flow (vertical vortex/vertical vortex).

In addition, in each cylinder 2, one of the two intake ports 18 is provided with a swirl control valve (SCV) 43 that opens and closes the flow path of the intake port 18. Note that FIG. 1 illustrates only one of the intake ports 18 with the SCV 43 provided, and does not illustrate the other intake port 18 without the SCV 43. When the SCV 43 is closed, intake air flows into the combustion chamber 16 from only one of the two intake ports 18, generating a swirl flow (a lateral vortex/transverse vortex) in the combustion chamber 16.

The lower surface of the cylinder head 6 of the engine 1 forms the ceiling 26 of the combustion chamber 16. This ceiling 26 is a so-called pent roof type, with two opposing inclined surfaces extending from the center to the lower end of the cylinder head 6. In addition, an injector (fuel injection valve) 28 that directly injects fuel into the cylinder 2 (direct injection) is attached to the cylinder head 6 for each cylinder 2. The injector 28 is installed at an angle to the axial direction of the piston 14 (i.e., the direction of movement of the piston 14). More specifically, the injector 28 is disposed so that its nozzle faces the inside of the combustion chamber 16 diagonally downward from between the two intake ports 18 on the periphery of the ceiling 26 of the combustion chamber 16.

Furthermore, the cylinder head 6 of the engine 1 is fitted with a spark plug 32 for each cylinder 2, which forcibly ignites the air-fuel mixture in the combustion chamber 16. The spark plug 32 is arranged penetrating the cylinder head 6 so as to extend downward from the center of the ceiling 26 of the combustion chamber 16. The cylinder head 6 is also provided with a valve drive mechanism 36 that drives the intake valve 22 and exhaust valve 24 of each cylinder 2. The valve drive mechanism 36 is, for example, a variable valve lift mechanism that can change the lift amount of the intake valve 22 and exhaust valve 24, or a variable valve phase mechanism that can change the rotational phase of the camshaft relative to the crankshaft 12.

As described above, the intake passage 40 is connected to one side of the engine 1, while the exhaust passage 44, which discharges burnt gas (exhaust gas) from the combustion chamber 16 of each cylinder 2, is connected to the other side of the engine 1. A catalyst 45 (more specifically, a catalytic converter) for purifying the exhaust gas is provided on the exhaust passage 44. In addition, an EGR passage 46 for recirculating the exhaust gas to the intake passage 40 is connected downstream of the catalyst 45 in the exhaust passage 44. An EGR cooler 47 for cooling the exhaust gas to be recirculated (hereinafter referred to as "EGR gas") and an EGR valve 48 for adjusting the amount of EGR gas to be recirculated to the intake passage 40 are provided on the EGR passage 46.

Next, FIG. 2 is a perspective view showing the detailed structure of the piston 14, injector 28, and spark plug 32 of the engine 1 according to this embodiment. As shown in FIG. 2, the injector 28 is a multi-hole injector having multiple nozzle holes 30. The injector 28 is installed so that the axial direction of the injector 28 is inclined downward at a predetermined angle from the horizontal direction. As a result, the fuel spray injected from each nozzle hole 30 of the injector 28 spreads radially from the peripheral portion of the ceiling 26 of the combustion chamber 16 diagonally downward.

The piston crown surface 14a that forms the top of the piston 14 is formed in a convex shape that rises toward the center. Specifically, in the center of the piston crown surface 14a, a flat surface 14b is formed over a relatively wide area along a horizontal plane perpendicular to the axial direction of the piston 14 (in other words, the direction of movement of the piston 14). No so-called cavity is formed in the piston crown surface 14a.

The piston crown surface 14a also has an injector-side slope 14c that extends obliquely upward from the end of the piston crown surface 14a on the injector 28 side toward the center, and an anti-injector-side slope 14d that extends obliquely upward from the end of the piston crown surface 14a on the side away from the injector 28 (hereinafter referred to as the "anti-injector side" as necessary) toward the center. These injector-side slope 14c and anti-injector-side slope 14d are formed to fit along the ceiling 26 of the combustion chamber 16 (see FIG. 1).

A horizontal surface 14e is formed on the injector side end and the opposite end of the piston crown surface 14a. Furthermore, an exhaust valve recess 14f is formed on the opposite injector side slope 14d of the piston crown surface 14a, which is recessed to prevent contact between the piston 14 and the exhaust valve 24. Contact between the piston 14 and the intake valve 22 is prevented by the injector side slope 14c, etc.

Next, FIG. 3 is a block diagram showing the electrical configuration of the engine system 100 according to this embodiment. The PCM (Powertrain Control Module) 80 is a controller based on a well-known microcomputer and is configured with circuits. The PCM 80 includes one or more microprocessors 80a as a central processing unit (CPU) that executes programs, a memory 80b configured, for example, of a RAM (Random Access Memory) or a ROM (Read Only Memory) that stores programs and data, and an input/output bus for inputting and outputting electrical signals.

Various sensors are connected to the PCM 80. Specifically, the PCM 80 is mainly connected to an accelerator opening sensor S1 and a crank angle sensor S2. The accelerator opening sensor S1 detects the accelerator opening corresponding to the amount of accelerator pedal operation, and the crank angle sensor S2 detects the rotation angle of the crankshaft 12 (corresponding to the engine speed). The detection signals output from these sensors S1 and S2 are input to the PCM 80.

The PCM 80 calculates the control amount of each device according to a predetermined control logic based on the detection signals input from the above-mentioned sensors S1 and S2. The control logic is stored in the memory 80b. The control logic includes calculating the target amount and/or the control amount using a map stored in the memory 80b. The PCM 80 outputs control signals related to the calculated control amounts mainly to the injector 28, the spark plug 32, the SCV 43, and the EGR valve 48.

[Control content]
Next, the contents of the control performed by the PCM 80 in this embodiment will be described. Basically, the PCM 80 switches the SCV 43 between open and closed states in response to changes in the operating state of the engine 1, that is, switches the SCV 43 from fully closed to fully open, or switches the SCV 43 from fully open to fully closed. In this way, it switches whether or not to introduce the swirl flow by the SCV 43 into the combustion chamber 16 in response to the operating state of the engine 1. In this embodiment, the PCM 80 performs control to improve a decrease in combustion stability caused by an increase in internal EGR gas, which may occur particularly when the SCV 43 is switched from fully closed to fully open.

First, referring to FIG. 4, the operating range of engine 1 where SCV 43 is set to fully closed or fully open will be described. FIG. 4 shows the operating range of engine 1 defined by the engine speed shown on the horizontal axis and the engine load shown on the vertical axis. In operating range R1 where the engine speed is less than the speed threshold N1 (e.g., 2500 rpm) and the engine load is less than the load threshold L1, SCV 43 is set to fully closed, that is, engine 1 is operated using the swirl flow generated by SCV 43. In addition, in this operating range R1, when such a swirl flow is generated, fuel is injected from injector 28 only once (lump injection) during the intake stroke of engine 1, thereby realizing homogeneous combustion in engine 1.

On the other hand, in the operating region R2 where the engine speed is equal to or greater than the speed threshold N1 or the engine load is equal to or greater than the load threshold L1, the SCV 43 is set to full open, i.e., the engine 1 is operated without using a swirl flow. In addition, in the operating region R2 where the engine speed is less than the speed threshold N1, stratified combustion is achieved in the engine 1 by injecting fuel multiple times (split injection) from the injector 28 during the intake stroke and compression stroke of the engine 1. In contrast, in the operating region R2 where the engine speed is equal to or greater than the speed threshold N1, homogeneous combustion is achieved in the engine 1 by injecting fuel only once (lump injection) from the injector 28 during the intake stroke of the engine 1.

Note that FIG. 4 shows an example in which the rotation speed threshold N1 and the load threshold L1 are constant values, but in other examples, the rotation speed threshold N1 may be made smaller as the engine load increases, or the load threshold L1 may be made smaller as the engine rotation speed increases.

Next, referring to Figure 5, we will specifically explain the decrease in combustion stability due to an increase in internal EGR gas that can occur when the SCV 43 is switched from fully closed to fully open. Figures 5(A) to (D) each show a schematic diagram of the state inside cylinder 2 (inside combustion chamber 16) during the intake stroke, with dashed arrows indicating the flow of exhaust gas and solid arrows indicating the flow of fresh air. Specifically, Figures 5(A) to (C) are schematic diagrams showing the state inside cylinder 2 as viewed from the side, and Figure 5(D) is a schematic diagram showing the state inside cylinder 2 shown in Figure 5(C) as viewed from above.

First, when the operating state of the engine 1 changes, specifically when the engine speed becomes equal to or exceeds the speed threshold N1 or when the engine load becomes equal to or exceeds the load threshold L1, that is, when the region to which the engine speed and engine load belong changes from the operating region R1 to the operating region R2, the SCV 43 is switched from fully closed to fully open. When the SCV 43 is switched from fully closed to fully open in this manner, a state in which only one intake port 18 is connected to each cylinder 2 transitions to a state in which two intake ports 18 are connected to each cylinder 2. Therefore, while the SCV 43 is switched from fully closed to fully open, the amount of exhaust gas blown back from the exhaust system to the intake system during the overlap period of the intake valve 22 and the exhaust valve 24, that is, the amount of exhaust gas flowing back to the intake passage 40 side through the exhaust valve 24 and the intake valve 22 in sequence, becomes greater than before the switching (when the SCV 43 is fully closed), as shown in FIG. 5 (A). As a result, as shown in Figures 5(B) and (C), the amount of exhaust gas (internal EGR gas) introduced into the combustion chamber 16 together with the fresh air increases during the intake stroke of the engine 1.

In this situation, as shown in FIG. 5(C), fuel F1 is injected from the injector 28. Specifically, fuel F1 is injected at the fuel injection timing during the intake stroke (hereinafter referred to as the "basic injection timing") that is normally applied depending on the operating state of the engine 1. The basic injection timing is a relatively early timing during the intake stroke. If the crank angles of the intake TDC and compression BDC are 360 degrees and 180 degrees, respectively (hereinafter the same), the crank angle corresponding to this basic injection timing is, for example, 280 to 300 degrees. When fuel is injected at such a basic injection timing, almost all of the fuel F1 tends to be disposed near the periphery of the combustion chamber 16, as shown in FIG. 5(D). This is for the following reasons.

First, at a relatively early time such as the basic injection timing in the intake stroke, the swirl flow has not yet been completely formed in the combustion chamber 16, that is, the swirl flow is in the process of being formed. During the process of forming such a swirl flow, flows in various directions exist in the combustion chamber 16, so the fuel F1 injected at this time flows in various directions. After this, while the swirl flow is being formed, almost all of the fuel F1 is carried by this swirl flow and flows laterally. As a result, when the formation of the swirl flow is completed, almost all of the fuel F1 is located near the periphery of the combustion chamber 16. As a result, the fuel around the spark plug 32 located in the center of the combustion chamber 16 becomes lean, and the combustion stability decreases.

In this embodiment, in order to improve such a decrease in combustion stability, the PCM 80 controls the injector 28 to temporarily retard the fuel injection timing from the basic injection timing while the SCV 43 is being switched from fully closed to fully open. For example, in this embodiment, the PCM 80 adopts the timing after the formation of the swirl flow in the combustion chamber 16 is almost complete as the fuel injection timing to be applied while the SCV 43 is being switched from fully closed to fully open, that is, the fuel injection timing retarded from the basic injection timing, rather than the timing during the formation of the swirl flow in the combustion chamber 16 as in the basic injection timing.

The effect of applying such a retarded fuel injection timing will be specifically explained with reference to Figure 6. Figures 6(A) and (B) also each show a schematic diagram of the state inside cylinder 2 (inside combustion chamber 16) during the intake stroke, with dashed arrows indicating the flow of exhaust gas and solid arrows indicating the flow of fresh air. Specifically, Figure 6(A) is a schematic diagram of the state inside cylinder 2 as seen from the side, and Figure 6(B) is a schematic diagram of the state inside cylinder 2 shown in Figure 6(A) as seen from above.

As shown in FIG. 6(A), in this embodiment, the PCM 80 injects fuel F21 from the injector 28 at an injection timing (e.g., 250 degrees in crank angle) that is retarded from the basic injection timing while the SCV 43 is being switched from fully closed to fully open. As shown in FIG. 6(B), some of the fuel F21 injected in this manner is disposed near the periphery of the combustion chamber 16, while the remaining fuel F22 is disposed in the center of the combustion chamber 16 (i.e., near the spark plug 32). This is for the following reasons.

First, in the relatively late fuel injection timing, which is retarded from the basic injection timing, used in this embodiment, the formation of the swirl flow in the combustion chamber 16 is almost complete. Therefore, in the fuel F21 injected at this time, unlike the fuel F1 injected at the basic injection timing, almost all of the fuel is once flowed in various directions and then carried along by the swirl flow that is being formed. Therefore, the fuel F21 injected as in this embodiment is less likely to be carried away by the swirl flow, and is more likely to penetrate the swirl flow and reach the center of the combustion chamber 16 (the vortex center of the swirl flow) and remain in this center. As a result, according to this embodiment, a fuel-rich region is formed around the spark plug 32, thereby improving the deterioration of combustion stability caused by the increase in internal EGR gas described above.

Next, referring to Figures 7 and 8, the control performed when the SCV 43 is switched from fully closed to fully open in this embodiment will be specifically described. First, Figure 7 is a time chart showing an example of the control according to this embodiment. From the top, Figure 7 shows the time changes of the accelerator opening, engine speed, engine load, SCV opening, and fuel injection timing.

At time t1, engine speed and engine load increase as the throttle opening increases. During this time, the PCM 80 gradually retards the fuel injection timing. This is because the fuel injection timing is advanced to ensure sufficient mixture mixing time in the low load region where flow is weak, in order to accurately achieve homogeneous combustion.

Then, at time t2, the region to which the engine speed and engine load belong changes from operating region R1 to operating region R2 (see FIG. 4). Therefore, at time t2, the PCM 80 starts to switch the opening of the SCV 43 from fully closed to fully open. During the period from time t2 to time t3 during which the opening of the SCV 43 is being switched from fully closed to fully open, the PCM 80 temporarily retards the fuel injection timing of the injector 28 from the basic injection timing (see the white arrow).

Then, at time t3 when the switching of the SCV 43 is completed, the PCM 80 advances the fuel injection timing of the injector 28 from the fuel injection timing that was applied during the switching of the SCV 43. In other words, the PCM 80 returns the fuel injection timing that was temporarily retarded to a non-retarded fuel injection timing. This ensures the stability of the control regarding the fuel injection timing.

Next, FIG. 8 is a flowchart showing the control according to this embodiment. This control is repeatedly executed at a predetermined cycle by the PCM 80. First, in step S11, the PCM 80 acquires various information. Specifically, the PCM 80 acquires at least the detection signals of the accelerator opening sensor S1 and the crank angle sensor S2 as described above.

Next, in step S12, the PCM 80 determines the current operating state of the engine 1, specifically the current engine speed and engine load, based on the information acquired in step S11. In this case, the PCM 80 determines the engine speed based on the crank angle (rotation angle of the crankshaft 12) corresponding to the detection signal of the crank angle sensor S2. In addition, the PCM 80 determines the target torque of the vehicle based on the accelerator opening corresponding to the detection signal of the accelerator opening sensor S1, and then determines the engine load corresponding to this target torque.

Next, in step S13, the PCM 80 determines whether to switch the SCV 43 from fully closed to fully open based on the operating state of the engine 1 identified in step S12. In this case, the PCM 80 performs the SCV 43 switching determination by determining whether the region to which the engine speed and engine load belong has changed from operating region R1 to operating region R2 (see FIG. 4). As a result, if it is not determined that the SCV 43 should be switched from fully closed to fully open (step S13: No), the PCM 80 exits the flow shown in FIG. 8.

On the other hand, if it is determined that the SCV 43 should be switched from fully closed to fully open (step S13: Yes), the PCM 80 proceeds to steps S14 and S15. In this case, the PCM 80 controls the SCV 43 to switch the opening of the SCV 43 from fully closed to fully open (step S14), and controls the injector 28 to temporarily retard the fuel injection timing from the basic injection timing (step S15). For example, the PCM 80 sets the fuel injection timing by applying a predetermined retard amount (typically a fixed value) to the basic injection timing. In one example, this retard amount is set based on the timing in the intake stroke at which the formation of a swirl flow is completed in the combustion chamber 16.

Next, in step S16, the PCM 80 determines whether the switching of the SCV 43 from fully closed to fully open has been completed. In one example, the PCM 80 determines the switching of the SCV 43 by comparing the elapsed time from the start of the switching of the opening of the SCV 43 with a predetermined time (corresponding to the time required for the switching of the SCV 43, which is determined in advance). In another example, the PCM 80 determines the switching of the SCV 43 based on a detection signal from a sensor that detects the opening of the SCV 43. If it is determined that the switching of the SCV 43 has not been completed as a result of such a determination (step S16: No), the PCM 80 performs the determination of step S16 again. In other words, the PCM 80 repeats the determination of step S16 until the switching of the SCV 43 is completed.

On the other hand, if it is determined that the switching of the SCV 43 has been completed (step S16: Yes), the PCM 80 proceeds to step S17. In step S17, the PCM 80 advances the fuel injection timing of the injector 28 from the fuel injection timing that was applied during the switching of the SCV 43. In other words, the PCM 80 returns the fuel injection timing that was temporarily retarded to the fuel injection timing that is not retarded (specifically, the fuel injection timing that is normally applied depending on the operating state of the engine 1). Then, the PCM 80 exits the flow shown in FIG. 8.

[Action and Effect]
Next, the operation and effect of the engine system 100 according to the present embodiment will be described. According to this embodiment, the PCM 80 controls the injector 28 so as to retard the fuel injection timing from the basic injection timing while the SCV 43 is switched from fully closed to fully open. At the time retarded from the basic injection timing in this manner, the formation of a swirl flow in the combustion chamber 16 is almost completed. Therefore, the fuel injected at this time is not easily swirled by the swirl flow, and penetrates the swirl flow to reach the center of the combustion chamber 16 and is likely to remain in this center (see FIG. 6B). As a result, a fuel-rich region is formed around the spark plug 32, and combustion stability can be ensured. Therefore, according to this embodiment, when the SCV 43 is switched from fully closed to fully open, the deterioration of combustion stability due to the increase in internal EGR gas can be improved.

Furthermore, according to this embodiment, when the switching of the SCV 43 from fully closed to fully open is completed, the PCM 80 advances the fuel injection timing of the injector 28 from the fuel injection timing applied during the switching of the SCV 43. In other words, the fuel injection timing that was temporarily retarded is returned to the normal fuel injection timing that is not retarded. This limits the change in the fuel injection timing to the period during which the opening of the SCV 43 is being switched, and returns the fuel injection timing to its original state after the switching of the opening of the SCV 43 is completed, thereby ensuring the stability of control over the fuel injection timing.

In addition, according to this embodiment, when the engine 1 is operated without using the swirl flow generated by the SCV 43 (particularly in the region where the engine speed is less than the speed threshold N1 in the operating region R2 in FIG. 4), the PCM 80 injects fuel (split injection) during the intake stroke and compression stroke of the engine 1, thereby effectively achieving stratified charge combustion in the engine 1.

[Modification]
In the above embodiment, an example is shown in which the SCV 43 is fixed to either the fully closed or fully open state (obviously, an intermediate opening between the fully closed and fully open states is passed through during the change in the opening degree, but the fixed setting is either the fully closed or fully open state), but in another example, the SCV 43 may be fixedly set to various intermediate opening degrees between the fully closed and fully open states. In this other example, the PCM 80 sets the opening degree of the SCV 43 to an intermediate opening degree according to the operating state of the engine 1. In this case, while changing the opening degree of the SCV 43 to the open side according to the change in the operating state of the engine 1, the PCM 80 retards the fuel injection timing of the injector 28 from the fuel injection timing applied before the change in the opening degree.

In the other example described above, the PCM 80 sets the retard amount of the fuel injection timing according to the amount of change in the opening of the SCV 43 (SCV opening change amount). With reference to FIG. 9, a method of setting the retard amount according to the amount of change in the SCV opening will be described. In FIG. 9, the horizontal axis shows the amount of change in the SCV opening, and the vertical axis shows the amount of retard of the fuel injection timing. As shown in FIG. 9, the greater the amount of change in the SCV opening, the greater the retard amount of the fuel injection timing is set by the PCM 80. Note that the maximum value of the amount of change in the SCV opening is the amount of change in the opening when the SCV 43 is switched from fully closed to fully open, and when this maximum value of the amount of change in the SCV opening is applied, the amount of retard of the fuel injection timing is also maximum.

Here, the greater the change in SCV opening, the stronger the gas flow, and so it takes time for the swirl flow to stabilize. Therefore, the greater the change in SCV opening, the greater the retard amount of the fuel injection timing the PCM 80 will be, so that fuel injection will wait until the swirl flow stabilizes. This makes it possible to accurately position the injected fuel in the center of the combustion chamber 16 (i.e., around the spark plug 32) without being affected by the swirl flow, even when the change in SCV opening is large.

Reference Signs List 1 engine 2 cylinder 14 piston 16 combustion chamber 18 intake port 28 injector (fuel injection valve)
32 Spark plug 40 Intake passage 43 Swirl control valve (SCV)
44 Exhaust passage 45 Catalyst 46 EGR passage 48 EGR valve 80 PCM (controller)
100 Engine System

Claims (5)

1. An engine system comprising:
an engine including a cylinder forming a combustion chamber, a piston reciprocating in the cylinder, a fuel injection valve that directly injects fuel into the cylinder, and an ignition plug that ignites a mixture of fuel and intake air in the cylinder;
a swirl control valve provided in an intake passage that supplies intake air to the cylinder of the engine and configured to generate a swirl flow in the cylinder when the swirl control valve is set to a closed side opening degree;
a controller configured to control the fuel injection valve and the swirl control valve, the controller being configured to control an opening degree of the swirl control valve in response to an operating state of the engine;
having
the controller is configured to control the fuel injection valve so as to retard the fuel injection timing by the fuel injection valve from the fuel injection timing applied before the change in the opening degree, while changing the opening degree of the swirl control valve to the open side in accordance with the operating state of the engine. The engine system according to claim 1, wherein the controller is configured to control the fuel injection valve so that, when the change in the opening of the swirl control valve to the open side is completed, the fuel injection timing of the fuel injection valve is advanced from the fuel injection timing applied during the change in the opening. The engine system according to claim 1 or 2, wherein the controller is configured to control the fuel injection valve so that the greater the change in the opening of the swirl control valve, the greater the amount of retardation of the fuel injection timing. 4. The engine system according to claim 1 , wherein the fuel injection valve is provided at an angle with respect to an axial direction of the piston. The crown surface of the piston is formed substantially flat without any cavity formed therein,
The spark plug is provided in the center of the ceiling of the combustion chamber.
An engine system according to any one of claims 1 to 4 .

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