JP7637334B2 - Engine System - Google Patents

Description

The present invention relates to an engine system that performs control to activate a catalyst installed in the exhaust passage of the engine.

Conventionally, when a catalyst installed in the exhaust passage of an engine is in an inactive state, such as when the engine is started, specifically when the temperature of the catalyst is below the activation temperature, a control (catalyst activation control) is performed to quickly heat the catalyst to activate it in order to ensure the catalyst's exhaust gas purification performance. A known example of such catalyst activation control is a control that delays the ignition timing until after the top dead center of compression in order to cause high-temperature exhaust gas to flow into the catalyst when the engine is cold, thereby heating the catalyst.

This type of technology is disclosed, for example, in Patent Document 1. Patent Document 1 discloses a technology for controlling catalyst activation to ignite after top dead center of compression when the engine is cold, in which fuel is injected three times (split injection) during the intake stroke, the first half of the compression stroke, and the second half of the compression stroke, and in the first half of the compression stroke, fuel is injected toward the center of the vortex of the tumble flow generated in the combustion chamber. In this way, even if the ignition timing is delayed until after top dead center of compression to activate the catalyst early, it is possible to prevent fuel adhesion to the piston and deterioration of emissions performance, while forming a rich region around the spark plug to improve combustion stability.

JP 2016-223411 A

In the technology disclosed in the above-mentioned Patent Document 1, fuel is injected toward the vortex center of the tumble flow, and the penetrating force of the fuel in the injection direction is reduced by the tumble flow perpendicular to the injection direction, thereby preventing the fuel from penetrating the tumble flow and adhering to the piston. However, with this technology, there were cases where it was not possible to sufficiently prevent fuel from adhering to the piston. The reasons for this are as follows.

The tumble flow generated inside the cylinder is a vertical vortex, and as it flows up and down inside the cylinder, it tends to come into contact with the piston crown. Therefore, with the technology disclosed in the above-mentioned Patent Document 1, even if the injected fuel does not penetrate the tumble flow and adhere to the piston, the fuel may ride the tumble flow downward and come into contact with and adhere to the piston. This can result in a deterioration of emissions performance.

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 effectively suppress fuel adhesion to the piston by utilizing the swirl flow inside the cylinder by appropriately splitting the fuel injection when controlling to activate the catalyst.

In order to achieve the above object, the present invention provides an engine system including an engine having a cylinder forming a combustion chamber, a piston reciprocating in the cylinder, a fuel injection valve arranged at an angle with respect to the axial direction of the piston and directly injecting fuel into the cylinder, and an ignition plug arranged to ignite a mixture of fuel and intake air in the cylinder, a swirl flow generating mechanism that generates a swirl flow in the cylinder of the engine, a catalyst arranged in an exhaust passage of the engine and purifying exhaust gas, and a controller configured to control the fuel injection valve and the ignition plug, and configured to control the ignition plug so that it ignites after top dead center of compression when the catalyst is in an inactive state. and a controller configured to perform, when the catalyst is in an inactive state, a first injection of fuel injecting during the intake stroke of the engine, a second injection of fuel injecting after the first injection, and a third injection of fuel injecting during the compression stroke of the engine after the second injection, and to control the fuel injection valve so that the fuel injection amount of the first injection is greater than the fuel injection amounts of the second and third injections and the fuel injection amount of the third injection is greater than the fuel injection amount of the second injection, and the controller is configured to control the fuel injection valve so that the first injection is performed in the first half of the intake stroke, the second injection is performed in the second half of the intake stroke, and the third injection is performed in the first half of the compression stroke .

In the present invention configured in this manner, when the catalyst is in an inactive state and a swirl flow (lateral vortex) is generated in the combustion chamber due to the introduction of intake air into the combustion chamber, the controller controls the spark plug to ignite after top dead center of compression, and controls the fuel injection valve (injector) to perform split injection consisting of first to third injections. Specifically, the controller controls the fuel injection valve to perform a first injection in which the maximum amount of fuel is injected during the intake stroke, a second injection in which an amount of fuel less than the first injection is injected after the first injection, and a third injection in which an amount of fuel greater than the second injection is injected during the compression stroke after the second injection.

At the timing of the first injection (i.e., the intake stroke), the swirl flow is strong, so the fuel injection amount of this first injection is set to the maximum amount, thereby increasing the penetration force of the fuel spray of the first injection (hereinafter referred to as "spray penetration force"). This allows the fuel spray of the first injection to penetrate the swirl flow and reach the vicinity of the vortex center, and then to remain near the vortex center. In other words, the fuel spray of the first injection can be accurately retained near the spark plug. Next, at the timing of the second injection after the first injection, the swirl flow is weak, so by making the fuel injection amount of the second injection smaller than that of the first injection to reduce the spray penetration force, the fuel spray of the second injection can be accurately retained near the spark plug. Next, at the timing of the third injection after the second injection, the swirl flow is weak as in the second injection, but a secondary flow (hereinafter referred to as "secondary flow") that occurs in conjunction with the swirl flow and moves from the periphery of the combustion chamber toward the center can be used. Therefore, at the timing of the third injection, this secondary flow can be used together with the swirl flow, so even if the fuel injection amount of the third injection is greater than that of the second injection, the fuel spray from the third injection can be accurately retained near the spark plug.

As described above, according to the present invention, by appropriately setting the fuel injection amount of each of the first to third injections (split injections), the swirl flow (including the secondary flow caused by the swirl flow) in the combustion chamber can be used to accurately retain the fuel spray from each injection near the spark plug. This makes it possible to effectively suppress fuel adhesion to the piston and prevent deterioration of emissions performance even if the ignition timing is delayed until after the compression top dead center in order to activate the catalyst early. In addition, a fuel-rich region is formed near the spark plug, so combustion stability can be ensured.
Furthermore, according to the present invention, since the swirl flow is strong in the first half of the intake stroke and weak in the second half of the intake stroke, by setting the fuel injection amounts of the first and second injections as described above in accordance with the strength of this swirl flow, the fuel sprays from the first and second injections can be more reliably retained in the vicinity of the spark plug.

In the present invention, the engine system is preferably applied to a vehicle having an automatic transmission, and the controller is configured to control the fuel injection valve so as to change the timing of the first to third injections and the fuel injection amount of each of the first to third injections depending on whether the automatic transmission is in a driving range or a non-driving range.
According to the present invention configured in this manner, the fuel injection timing and fuel injection amount for each of the first to third injections are changed according to the range of the automatic transmission, so that catalyst activity control suitable for each of the driving range and non-driving range can be performed.

In the present invention, preferably, the controller is configured to control the engine so as to further change the engine speed and the ignition timing of the spark plugs depending on whether the automatic transmission is in a driving range or a non-driving range.
According to the present invention thus configured, the engine speed and ignition timing are further changed in accordance with the range of the automatic transmission, so that catalyst activity control can be performed more appropriately for each of the driving range and the non-driving range.

In the present invention, the engine system is preferably applied to a vehicle having a manual transmission, and the controller is configured to control the fuel injection valve to perform the first to third injections when the catalyst is in an inactive state, when the gear position of the manual transmission is set to neutral gear, or when the clutch of the manual transmission is disengaged.
According to the present invention thus configured, the first to third injections according to the present invention can be performed accurately in a situation where catalyst activation control can be implemented in a vehicle having a manual transmission.

In the present invention, preferably, the crown surface of the piston is formed substantially flat without any cavity being formed therein.
According to the present invention configured in this manner, it is possible to more effectively suppress fuel adhesion to the piston (fuel adhesion to the cavity, etc.) during catalyst activation control.

In the present invention, the spark plug is preferably provided in the center of the ceiling of the combustion chamber.
Preferably, the swirl flow generating mechanism is a swirl control valve provided in an intake passage of the engine.

According to the engine system of the present invention, when controlling to activate the catalyst, split fuel injection can be performed appropriately, making use of the swirl flow inside the cylinder to effectively suppress fuel adhesion to the piston.

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. 5 is a time chart showing a typical example of split injection according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of a basic concept for retaining fuel spray around an ignition plug. 5A to 5C are explanatory diagrams of the flow of fuel sprays to be formed in a combustion chamber by first to third injections in the embodiment of the present invention. This is an explanatory diagram of Einstein's teacup problem. 4 is a flowchart showing an overall control according to an embodiment of the present invention. 4 is a flowchart showing catalyst activity control according to an embodiment of the present invention. 5 is a flowchart showing another example of catalyst activity control according to an 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 (hereinafter referred to as "SCV") 43 that opens and closes the flow path of the intake port 18. Note that FIG. 1 shows only one intake port 18 with an SCV 43, and does not show the other intake port 18 without an 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 (lateral vortex/transverse vortex) in the combustion chamber 16. This SCV 43 corresponds to an example of a "swirl flow generating mechanism" in the present invention. Note that the "swirl flow generating mechanism" is not limited to using the SCV 43, and in another example, the intake port may be formed in such a manner that a swirl flow is generated in the combustion chamber 16, in which case the intake port corresponds to the "swirl flow generating mechanism."

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, a crank angle sensor S2, a water temperature sensor S3, a vehicle speed sensor S4, and an ignition switch S5. The accelerator opening sensor S1 detects the accelerator opening corresponding to the amount of operation of the accelerator pedal. The crank angle sensor S2 detects the rotation angle of the crankshaft 12 (corresponding to the engine speed). The water temperature sensor S3 detects the temperature (water temperature) of the cooling water that cools the engine 1. The vehicle speed sensor S4 detects the vehicle speed. The ignition switch S5 is a switch that is operated by the driver to start the vehicle. Signals (detection signals and operation signals) output from these sensors and switches S1 to S5 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 signals input from the above sensors and switches S1 to S5. The control logic is stored in memory 80b. The control logic includes calculating the target amount and/or the control amount using a map stored in 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. In this embodiment, when the catalyst 45 is in an inactive state at the start of the engine 1, the PCM 80 performs a control (catalyst activation control) to delay the ignition timing of the spark plug 32 until after the top dead center of compression in order to cause the catalyst 45 to be quickly heated and activated by flowing high-temperature exhaust gas into the catalyst 45. Specifically, the PCM 80 performs this catalyst activation control when the conditions for executing the catalyst activation control are met, that is, immediately after the start of the engine 1 or when the vehicle is stopped, the water temperature is within a predetermined range (for example, −10 to 45° C.), and the predicted temperature of the catalyst 45 (hereinafter referred to as the “predicted catalyst temperature”) is less than a predetermined temperature (for example, less than 300° C.). In addition, the PCM 80 sets the SCV 43 to be fully closed so that a swirl flow is generated in the combustion chamber 16 during such catalyst activation control.

As described in the above Patent Document 1, delaying the ignition timing until after the top dead center of the compression stroke tends to reduce ignition stability and combustion stability. To address this issue, there is a method of forming a fuel-rich region around the spark plug 32 by injecting fuel multiple times (i.e., split injection) over the intake stroke and compression stroke. However, when such split injection is performed, some of the fuel adheres to the piston 14, which can increase smoke and HC (unburned gas), and can worsen emissions performance. Therefore, in this embodiment, when catalyst activation control is performed, split injection is performed so that the fuel injected from the injector 28 is retained near the spark plug 32 in order to prevent the fuel from adhering to the piston 14.

The basic concept of split injection according to this embodiment will be described with reference to FIG. 4. FIG. 4 is a time chart showing a typical example of split injection according to this embodiment. As shown in FIG. 4, in this embodiment, when performing catalyst activation control in which ignition is performed after the compression top dead center in order to activate the catalyst 45 early, the PCM 80 controls the injector 28 to perform a first injection in which fuel is injected during the intake stroke, a second injection in which fuel is injected after the first injection, and a third injection in which fuel is injected during the compression stroke after the second injection. In the example shown in FIG. 4, the first injection is performed in the first half of the intake stroke, the second injection is performed in the second half of the intake stroke, and the third injection is performed in the first half of the compression stroke (note that the first and second half of each stroke correspond to the front and rear parts when the period of each stroke is divided in half). In this embodiment, the PCM 80 controls the injector 28 so that the fuel injection amount Q1 of the first injection is greater than the fuel injection amounts Q2 and Q3 of the second and third injections, and the fuel injection amount Q3 of the third injection is greater than the fuel injection amount Q2 of the second injection.

Next, the reason for performing split injection as shown in FIG. 4 will be explained with reference to FIG. 5 to FIG. 7. First, with reference to FIG. 5, the basic idea for retaining the fuel injected from the injector 28 near the spark plug 32 (i.e., forming a fuel-rich region around the spark plug 32) in order to suppress fuel adhesion to the piston 14 while ensuring combustion stability during catalyst activation control will be explained.

Figure 5(A) is a schematic diagram of the state of the combustion chamber 16 when fuel is injected from the injector 28, as viewed from the side (perpendicular to the axial direction of the piston 14), and Figure 5(B) is a schematic diagram of the state of the combustion chamber 16 as viewed from above (the direction indicated by the arrow A01 in Figure 5(A)). In Figures 5(A) and (B), the arrow A02 indicates the swirl flow generated in the combustion chamber 16 by the SCV 43, and the symbol F01 indicates the fuel spray injected from the injector 28. This swirl flow is a transverse vortex (a horizontal vortex) with its vortex center approximately at the center of the combustion chamber 16.

In order to retain the fuel injected from the injector 28 near the spark plug 32, it is considered that the fuel spray F01 from the injector 28 should be caused to flow as shown by the arrow A03 in Fig. 5(B). In other words, it is considered that the fuel spray F01 should first overcome the swirl flow, penetrate the swirl flow, and reach the vicinity of the spark plug 32 (effectively the vortex center of the swirl flow), and then the fuel spray F01 that has reached the vicinity of the spark plug 32 should be defeated by the swirl flow, and ride on the swirl flow near the spark plug 32 while rotating and flowing. To achieve this type of flow of the fuel spray F01, the penetration force (spray penetration force) of the fuel spray F01 when injected from the injector 28 should be set so that it is greater than the force caused by the swirling flow (hereinafter referred to as the "swirling flow force") so that the fuel spray F01 accurately reaches the vicinity of the ignition plug 32, and the spray penetration force from the injector 28 should be set so that the spray penetration force when the fuel spray F01 reaches the vicinity of the ignition plug 32 is smaller than the swirling flow force.

The magnitude of this spray penetration basically depends on the amount of fuel injected from the injector 28 (assuming constant fuel pressure). In other words, when the amount of fuel injected is large, the spray penetration is large, and when the amount of fuel injected is small, the spray penetration is small. Therefore, in this embodiment, the spray penetration is controlled by adjusting the amount of fuel injected. Specifically, the spray penetration of each split injection is controlled by adjusting the amount of fuel injected for each split injection.

The magnitude of the swirling force of the swirl flow generated in the combustion chamber 16 changes depending on the stage of the intake stroke or compression stroke of the engine 1. Specifically, the swirling force of the swirl flow is greatest in the first half of the intake stroke, and gradually decreases in the latter half of the intake stroke and the compression stroke. The flow pattern of the fuel spray generated in the combustion chamber 16 changes depending on the relationship between the swirling force of the swirl flow and the spray penetration force. Therefore, in this embodiment, the fuel injection amounts Q1 to Q3 of the first to third injections are set to adjust the spray penetration force of each of the first to third injections according to the magnitude of the swirling force of the swirl flow generated at the timing of the first to third injections so that each of the first to third injected fuels is appropriately retained around the ignition plug 32 as described above (specifically, Q1>Q3>Q2).

Next, referring to FIG. 6, the flow of the fuel spray to be formed in the combustion chamber 16 by each of the first to third injections in this embodiment will be described. Similar to FIG. 5(B), FIGS. 6(A) to (C) show schematic views of the combustion chamber 16 seen from above, with the arrow A10 indicating the swirl flow generated in the combustion chamber 16 by the SCV 43, and the symbols F11, F12, and F13 indicating the first to third injected fuel sprays, respectively. Specifically, FIG. 6(A) shows the flow of the fuel spray F11 by the first injection, FIG. 6(B) shows the flow of the fuel spray F12 by the second injection in addition to the fuel spray F11 by the first injection, and FIG. 6(C) shows the flow of the fuel spray F13 by the third injection in addition to the fuel sprays F11 and F12 by the first and second injections.

First, since the swirl flow is strong at the timing of the first injection, in this embodiment, the fuel injection amount Q1 of the first injection is increased so that the fuel spray F11 from the first injection penetrates the swirl flow and then remains near the spark plug 32 (see arrow A11 in FIG. 6A) in order to increase the spray penetration of the first injection. In other words, since the swirl flow is strong at the timing of the first injection, even if the spray penetration of the first injection is increased to a certain extent, the fuel spray F11 does not penetrate the entire swirl flow, so the fuel injection amount Q1 of the first injection can be increased. In addition, when the first injection is performed, in order to prevent misfire (semi-misfire) during subsequent flame propagation, the fuel injection amount Q1 is increased from the viewpoint of disposing part of the fuel spray F11 near the periphery of the combustion chamber 16 (see arrow A12), so as to increase the spray penetration of the first injection. For this reason, in this embodiment, the fuel injection amount Q1 of the first injection is the largest among the fuel injection amounts Q1 to Q3 of the first to third injections.

Next, since the swirl flow is weakened at the timing of the second injection after the first injection, in this embodiment, the fuel injection amount Q2 of the second injection is reduced (Q2<Q1) so that the spray penetration of the second injection is smaller than that of the first injection, and the fuel spray F12 from the second injection is accurately retained near the spark plug 32 (see arrow A13 in Figure 6(B)).

Next, at the timing of the third injection after the second injection, the swirl flow is weak as in the second injection, but a secondary flow (described in detail later) that occurs in association with this swirl flow and flows from the periphery to the center of the combustion chamber 16 can be utilized. Therefore, by utilizing this secondary flow together with the swirl flow at the timing of the third injection, the fuel spray F13 from the third injection can be accurately retained near the spark plug 32 even if the spray penetration force of the third injection is made greater than that of the second injection (see arrow A14 in FIG. 6C). Therefore, in this embodiment, the fuel injection amount Q3 of the third injection is made greater than the fuel injection amount Q2 of the second injection (Q3>Q2).

Next, referring to FIG. 7, the secondary flow used when performing the above-mentioned third injection will be specifically described. FIG. 7 is a diagram for explaining Einstein's teacup problem. Specifically, FIG. 7(A) to (C) show the state inside a cup when a specific fluid is flowed so as to rotate horizontally inside the cup. FIG. 7(A) is a schematic diagram showing the flow velocity distribution inside the cup. As shown in FIG. 7(A), the flow velocity of the fluid is low near the bottom of the cup due to friction between the fluid and the bottom. Next, FIG. 7(B) is a schematic diagram showing the forces acting on the fluid near the bottom of the cup. As shown in FIG. 7(B), it can be seen that near the bottom of the cup, the centrifugal force directed outward from the center of the cup and the pressure gradient force directed inward toward the center of the cup are not balanced, that is, the centrifugal force is smaller than the pressure gradient force. This is because the flow velocity is low near the bottom of the cup, and therefore the centrifugal force is small.

Next, Figure 7 (C) is a schematic diagram showing the flow velocity distribution on the cross section of the cup. As shown in Figure 7 (C), it can be seen that a secondary flow is occurring as indicated by arrow A3. Specifically, this secondary flow corresponds to a radial flow in which the fluid flows toward the center of the cup near the bottom of the cup, the fluid flows upward at the center of the cup, and the fluid flows from the center toward the periphery as it moves away from the bottom of the cup. This type of secondary flow occurs because the centrifugal force and the pressure gradient force are not balanced near the bottom of the cup.

Here, at the timing of the third injection as described above (for example, in the first half of the compression stroke), the piston crown surface 14a that hits the bottom surface of the combustion chamber 16 is in a position close to the fuel spray F13 from the injector 28 (in other words, the fuel spray F13 is located near the bottom surface of the combustion chamber 16). As described in FIG. 7, a secondary flow is generated near the bottom surface of the combustion chamber 16, which flows from the periphery of the combustion chamber 16 to the center and then upward at the center due to the swirl flow that flows so as to rotate horizontally within the combustion chamber 16. Therefore, at the timing of the third injection, such a secondary flow acts on the fuel spray F13 by the third injection. Therefore, even if the spray penetration force of the fuel spray F13 by the third injection is increased to a certain extent (i.e., even if the fuel injection amount Q3 of the third injection is increased to a certain extent), the fuel spray F13 can be accurately retained near the ignition plug 32.

[Processing flow]
Next, a specific control flow according to this embodiment will be described with reference to Figures 8 and 9. Figure 8 is a flowchart showing the overall control according to this embodiment, and Figure 9 is a flowchart showing the catalyst activation control performed in this overall control. These controls are repeatedly executed at a predetermined cycle by the PCM 80. Note that, in a situation where the overall control of Figure 8 is executed, it is assumed that the SCV 43 is set to be fully closed so that a swirl flow is generated in the combustion chamber 16.

When the overall control of FIG. 8 is started, in step S11, the PCM 80 acquires various information. Specifically, the PCM 80 acquires at least signals from the accelerator opening sensor S1, crank angle sensor S2, water temperature sensor S3, vehicle speed sensor S4, and ignition switch S5 as described above. After this, in steps S12 to S15, the PCM 80 determines the conditions for executing catalyst activation control.

First, in step S12, the PCM 80 determines whether the vehicle has not just been started. If the PCM 80 has not received a signal from the ignition switch S5, it determines that the vehicle has not just been started (step S12: Yes) and proceeds to step S13. On the other hand, if the PCM 80 has received a signal from the ignition switch S5, it determines that the vehicle has not just been started (step S12: No) and proceeds to step S14.

Next, in step S13, the PCM 80 determines whether the vehicle is stopped. If the vehicle speed detected by the vehicle speed sensor S4 is approximately 0 km/h, the PCM 80 determines that the vehicle is stopped (step S13: Yes) and proceeds to step S14. In contrast, if the vehicle speed detected by the vehicle speed sensor S4 is not approximately 0 km/h, the PCM 80 determines that the vehicle is not stopped (step S13: No) and ends the overall control.

Next, in step S14, the PCM 80 determines whether the water temperature detected by the water temperature sensor S3 is within a predetermined range (e.g., -10 to 45°C). As a result, if the water temperature is within the predetermined range (step S14: Yes), the PCM 80 proceeds to step S15, and if the water temperature is not within the predetermined range (step S14: No), the PCM 80 ends the overall control.

Next, in step S15, the PCM 80 determines whether the predicted catalyst temperature is less than a predetermined temperature (e.g., less than 300°C). In one example, the PCM 80 calculates the exhaust gas heat quantity based on the operating conditions of the engine 1, such as the exhaust gas temperature and exhaust gas amount, and calculates the predicted catalyst temperature from this exhaust gas heat quantity. In another example, the PCM 80 may calculate the predicted catalyst temperature based on the exhaust gas temperature detected by a temperature sensor provided on the exhaust passage 44 near the catalyst 45. If the result of the determination in step S15 is that the predicted catalyst temperature is less than the predetermined temperature (step S15: Yes), the PCM 80 proceeds to step S16, and if the predicted catalyst temperature is equal to or greater than the predetermined temperature (step S15: No), the PCM 80 ends the overall control.

The state in which the process proceeds to step S16 is one in which the catalyst 45 is in an inactive state and catalyst activation control for activating the catalyst 45 can be executed. Therefore, in step S16, the PCM 80 executes catalyst activation control. Basically, in this catalyst activation control, the PCM 80 controls the injector 28 to perform split injections (first to third injections) and controls the ignition plug 32 to ignite after the top dead center of compression. Specifically, the PCM 80 controls the injector 28 to perform a first injection in which the maximum amount of fuel Q1 is injected during the intake stroke, a second injection in which fuel Q2 (<Q1) is injected after the first injection, and a third injection in which fuel Q3 (>Q2) is injected after the second injection and during the compression stroke. This catalyst activation control will be described in detail later with reference to FIG. 9.

Next, the PCM80 proceeds to step S17 and determines whether the predicted catalyst temperature has reached or exceeded a predetermined temperature (e.g., 300°C or higher). As a result, if the predicted catalyst temperature is below the predetermined temperature (step S17: No), the PCM80 returns to step S16. In this case, the catalyst activation control is continued until the predicted catalyst temperature reaches or exceeds the predetermined temperature. On the other hand, if the predicted catalyst temperature is above the predetermined temperature (step S17: Yes), the PCM80 proceeds to step S18.

Next, in step S18, the PCM 80 ends the catalyst activation control and executes normal control (normal operation control) for the engine 1. In this normal operation control, the PCM 80 controls the injector 28 to inject fuel only once (lump injection) during the intake stroke, and controls the ignition plug 32 to ignite at a timing during the compression stroke (e.g., 5 degrees after compression TDC) that is more advanced than during the catalyst activation control. The PCM 80 also controls the engine 1 so that the engine speed becomes the idle speed (e.g., 1200 rpm). After this, the PCM 80 ends the overall control.

Next, referring to FIG. 9, the catalyst activation control according to this embodiment will be specifically described. This catalyst activation control is performed in step S16 in FIG. 8. First, in step S21, the PCM 80 acquires the range currently set in the automatic transmission (AT) mounted on the vehicle. For example, the PCM 80 acquires the range detected by a range sensor.

Next, in step S22, the PCM 80 determines whether the range acquired in step S21 is a driving range. Specifically, if the acquired range is D range (drive range), R range (reverse range), or M range (manual range), the PCM 80 determines that the range of the automatic transmission is a driving range (step S22: Yes) and proceeds to step S23. In contrast, if the acquired range is N range (neutral range) or P range (parking range), the PCM 80 determines that the range of the automatic transmission is a non-driving range (step S22: No) and proceeds to step S24.

In step S23, the PCM 80 executes catalyst activation control using a setting for a predetermined driving range. Specifically, the PCM 80 first executes catalyst activation control by applying a relatively low engine speed (e.g., 800 rpm). This is to suppress sudden acceleration (jumping out) when the driver releases his/her foot from the brake pedal. The PCM 80 also sets a set of fuel injection timing and fuel injection amount to be applied to each of the first to third injections when performing catalyst activation control in the driving range. For example, the PCM 80 sets the fuel injection timing (crank angle) of each of the first to third injections to 240 degrees, 215 degrees, and 110 degrees (the intake TDC is 360 degrees and the compression BDC is 180 degrees), and sets the fuel injection amounts Q1, Q2, and Q3 of each of the first to third injections to 50%, 15%, and 35% (the total injection amount is 100%). In addition, the PCM 80 sets the ignition timing to a relatively early time after the compression top dead center (for example, 20 degrees after the compression TDC). This is because, since the engine load is relatively high in the driving range, sufficient exhaust gas heat is generated without much retarding the ignition timing, whereas, since a relatively low engine speed is applied in the driving range as described above, the swirl flow in the combustion chamber 16 becomes weak, and therefore the ignition timing cannot be retarded too much to ensure combustion stability.

On the other hand, in step S24, the PCM 80 executes catalyst activation control using a setting for the non-driving range that has been determined in advance. Specifically, the PCM 80 first executes catalyst activation control by applying a relatively high engine speed (e.g., 1500 rpm). This is because the non-driving range does not experience sudden starts (jumping out) like the driving range described above. The PCM 80 also sets a set of fuel injection timing and fuel injection amount to be applied to each of the first to third injections when performing catalyst activation control in the non-driving range. For example, the PCM 80 sets the fuel injection timing (crank angle) of each of the first to third injections to 250 degrees, 170 degrees, and 100 degrees, and sets the fuel injection amounts Q1, Q2, and Q3 of each of the first to third injections to 40%, 25%, and 35% (total injection amount is 100%). The PCM 80 also sets the ignition timing to a relatively late timing after the compression top dead center (e.g., 25 degrees after the compression TDC). This is because, as described above, a relatively high engine speed is applied in the non-driving range, which creates a strong swirl flow in the combustion chamber 16, ensuring combustion stability even if the ignition timing is retarded. However, since the engine load is relatively low in the non-driving range, sufficient exhaust gas heat is not generated unless the ignition timing is retarded to a certain extent.

Note that while FIG. 9 shows catalyst activation control performed in a vehicle equipped with an automatic transmission (AT), catalyst activation control as shown in FIG. 10 is performed in a vehicle equipped with a manual transmission (MT). FIG. 10 is a flowchart showing another example of catalyst activation control according to this embodiment. This catalyst activation control is also performed in step S16 of FIG. 8.

First, in step S31, the PCM 80 acquires the gear position and clutch state (clutch disengagement or engagement state) of the manual transmission (MT) installed in the vehicle. For example, the PCM 80 acquires this gear position and clutch state information from a specified sensor.

Next, in step S32, the PCM 80 determines whether the gear of the manual transmission is in neutral gear based on the gear position acquired in step S31. As a result, if the gear of the manual transmission is in neutral gear (step S32: Yes), the PCM 80 proceeds to step S34, and if the gear of the manual transmission is not in neutral gear (step S32: No), the PCM 80 proceeds to step S33.

Next, in step S33, the PCM 80 determines whether the clutch of the manual transmission is disengaged based on the clutch state acquired in step S31. As a result, if the clutch is disengaged (step S33: Yes), the PCM 80 proceeds to step S34, and if the clutch is engaged (step S33: No), the PCM 80 ends catalyst activation control. In the latter case, the vehicle is not stopped, and catalyst activation control is not possible to be executed.

When the process proceeds to step S34, the manual transmission is in neutral or the clutch is disengaged, meaning that catalyst activation control can be performed. Therefore, in step S34, the PCM 80 performs catalyst activation control. In this case, the PCM 80 performs catalyst activation control using a predefined setting for the non-driving range, similar to step S24 in FIG. 9. Therefore, a detailed description of this will be omitted here.

[Action and Effect]
Next, the operation and effect of the engine system 100 according to this embodiment will be described. According to this embodiment, when the catalyst 45 is in an inactive state and a swirl flow is generated in the combustion chamber 16 by the SCV 43, the PCM 80 controls the injector 28 to perform split injections consisting of first to third injections, and controls the ignition plug 32 to ignite after the top dead center of compression. Specifically, the PCM 80 controls the injector 28 to perform a first injection in which the maximum amount of fuel Q1 is injected during the intake stroke, a second injection in which fuel Q2 (<Q1) is injected after the first injection, and a third injection in which fuel Q3 (>Q2) is injected during the compression stroke after the second injection.

At the timing of the first injection, the swirl flow is strong, so the fuel injection amount Q1 of the first injection is maximized to increase the spray penetration. As a result, the fuel spray from the first injection penetrates the swirl flow and reaches the vicinity of the vortex center, so that it can be retained near the vortex center, that is, it can be retained accurately near the spark plug 32. Next, at the timing of the second injection, the swirl flow is weak, so the fuel injection amount Q2 of the second injection is made smaller than that of the first injection to reduce the spray penetration, so that the fuel spray from the second injection can be retained accurately near the spark plug 32. Next, at the timing of the third injection, the swirl flow is weak, but a secondary flow that is generated in conjunction with the swirl flow and moves from the periphery of the combustion chamber 16 to the center is generated. Therefore, at the timing of the third injection, this secondary flow can be used together with the swirl flow, so that the fuel spray from the third injection can be retained accurately near the spark plug 32 even if the fuel injection amount Q3 of the third injection is made larger than that of the second injection.

As described above, according to this embodiment, by appropriately setting the fuel injection amount for each of the first to third injections (split injections), the swirl flow (lateral vortex) in the combustion chamber 16 can be used to accurately retain the fuel spray from each injection near the spark plug 32. As a result, even if the ignition timing is delayed until after the compression top dead center in order to activate the catalyst 45 early, it is possible to effectively suppress fuel adhesion to the piston 14 and prevent deterioration of emissions performance. In addition, a rich region is formed near the spark plug 32, which can also improve combustion stability.

In addition, according to this embodiment, the PCM 80 controls the injector 28 to perform the first injection in the first half of the intake stroke and the second injection in the second half of the intake stroke. Since the swirl flow is strong in the first half of the intake stroke and weak in the second half of the intake stroke, the fuel injection amounts Q1 and Q2 of the first and second injections are set as described above according to the strength of the swirl flow (Q1>Q2), so that the fuel spray from the first and second injections can be accurately retained near the spark plug 32.

Furthermore, according to this embodiment, when the engine system 100 is applied to a vehicle having an automatic transmission, the PCM 80 changes the fuel injection timing and fuel injection amount of each of the first to third injections depending on whether the automatic transmission is in the driving range or the non-driving range, so that control suitable for each of the driving range and the non-driving range can be performed. In addition, according to this embodiment, the PCM 80 further changes the engine speed and ignition timing depending on whether the automatic transmission is in the driving range or the non-driving range, so that control suitable for each of the driving range and the non-driving range can be performed.

In addition, according to this embodiment, when the engine system 100 is applied to a vehicle having a manual transmission, the PCM 80 performs the first to third injections described above only when the manual transmission is in neutral gear or the clutch of the manual transmission is disengaged. This allows the first to third injections according to this embodiment to be performed accurately in a situation where catalyst activation control can be performed in a vehicle having a manual transmission.

In addition, according to this embodiment, the piston crown surface 14a does not have a cavity and is formed almost flat, so that adhesion of fuel to the piston 14 (such as adhesion of fuel to the cavity) during catalyst activation control can be effectively suppressed.

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

Claims (7)

1. An engine system comprising:
an engine including: a cylinder forming a combustion chamber; a piston reciprocating in the cylinder; a fuel injection valve arranged at an angle with respect to an axial direction of the piston and 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 flow generating mechanism for generating a swirl flow in the cylinder of the engine;
a catalyst provided in an exhaust passage of the engine for purifying exhaust gas;
a controller configured to control the fuel injector and the spark plug, the controller configured to control the spark plug to ignite after top dead center of compression of the engine when the catalyst is in an inactive state;
having
When the catalyst is in the deactivated state, the controller
performing a first injection of injecting fuel during an intake stroke of the engine, a second injection of injecting fuel after the first injection, and a third injection of injecting fuel after the second injection during a compression stroke of the engine;
a fuel injection amount of the first injection is greater than the fuel injection amounts of the second and third injections, and a fuel injection amount of the third injection is greater than a fuel injection amount of the second injection,
configured to control the fuel injector;
the controller is configured to control the fuel injection valve so that the first injection is performed in a first half of an intake stroke, the second injection is performed in a second half of an intake stroke, and the third injection is performed in a first half of a compression stroke . The engine system is applied to a vehicle having an automatic transmission,
2. The engine system according to claim 1, wherein the controller is configured to control the fuel injection valve so as to change the timing of the first to third injections and the fuel injection amount of each of the first to third injections depending on whether the automatic transmission is in a driving range or a non-driving range. 3. The engine system according to claim 2, wherein the controller is configured to control the engine so as to further change an engine speed and an ignition timing of the spark plug when the automatic transmission is in the drive range and when the automatic transmission is in the non-drive range . The engine system is applied to a vehicle having a manual transmission,
2. The engine system according to claim 1, wherein the controller is configured to control the fuel injection valve to perform the first, second and third injections when the catalyst is in the deactivated state, when a gear position of the manual transmission is set to a neutral gear, or when a clutch of the manual transmission is disengaged. 5. The engine system according to claim 1 , wherein a crown surface of the piston is substantially flat without a cavity being formed therein. 6. The engine system according to claim 1 , wherein the ignition plug is provided in a central portion of a ceiling of the combustion chamber. 7. The engine system according to claim 1 , wherein the swirl flow generating mechanism is a swirl control valve provided in an intake passage of the engine.

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