Engine System

Abstract

To appropriately perform split injection of fuel to utilize a swirl flow in a cylinder and effectively suppress adhesion of fuel to a piston when performing control for bringing a catalyst in an active state.SOLUTION: In an engine system 100, a PCM 80 controls a spark plug 32 so as to ignite after a compression top dead center in a state where a swirl flow is generated in a combustion chamber 16 by an SCV 43 when a catalyst 45 is in an inactive state, and controls an injector 28 so as to perform split injection consisting of first to third injections. Specifically, the PCM 80 controls the injector 28 so as to perform the first injection for injecting the maximum amount of fuel during an intake stroke, a second injection for injecting fuel less than that of the first injection after the first injection, and a third injection for injecting fuel more than that of the second injection after the second injection in a compression stroke.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to an engine system that performs control to activate a catalyst provided in an exhaust passage of the engine. [Background technology]

[0002] Conventionally, when a catalyst provided in an exhaust passage of an engine is in an inactive state, such as when the temperature of the catalyst is below its activation temperature, control is performed to quickly raise the temperature of the catalyst to an active state in order to ensure the exhaust gas purification performance of the catalyst (catalyst activation control). A known example of such catalyst activation control is a control that delays the ignition timing until after the compression top dead center in order to raise the temperature of the catalyst by flowing high-temperature exhaust gas into the catalyst when the engine is cold.

[0003] 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 the 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 the top dead center of compression to activate the catalyst early, it is possible to prevent the fuel from adhering to the piston and to prevent the deterioration of emission performance, while forming a rich region around the spark plug to improve combustion stability. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-223411 A Summary of the Invention [Problem to be solved by the invention]

[0005] 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 the adhesion of fuel to the piston could not be sufficiently prevented. The reasons for this are as follows.

[0006] The tumble flow generated in the cylinder is a vertical vortex, and as it flows vertically in the cylinder, it tends to come into contact with the piston crown. Therefore, in 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 on the tumble flow and flow downward, resulting in contact and adhesion to the piston. As a result, there is a possibility that the emission performance may deteriorate.

[0007] 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 performing split fuel injection when controlling to activate the catalyst. [Means for solving the problem]

[0008] In order to achieve the above object, the present invention provides an engine system including 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 for purifying exhaust gas, and a controller configured to control the fuel injection valve and the ignition plug, the controller being configured to purify the exhaust gas when the catalyst is in an inactive state, and a 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, wherein the controller is configured to perform a first injection of fuel injecting fuel during an intake stroke of the engine, a second injection of fuel injecting fuel after the first injection, and a third injection of fuel injecting fuel after the second injection and during a compression stroke of the engine when the catalyst is in an inactive state, and to control the fuel injector so that a fuel injection amount of the first injection is greater than a fuel injection amount 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, The controller is configured to control the fuel injector to perform the first injection in the first half of the intake stroke, the second injection in the second half of the intake stroke, and the third injection in the first half of the compression stroke. It is characterized by:

[0009] In the present invention thus configured, 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 the top dead center of compression and controls the fuel injection valve (injector) to perform divided injections 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 smaller than the first injection is injected after the first injection, and a third injection in which an amount of fuel larger than the second injection is injected during the compression stroke after the second injection.

[0010] 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 ignition plug. Next, at the timing of the second injection after the first injection, the swirl flow is weak, so the fuel injection amount of the second injection is made smaller than that of the first injection to reduce the spray penetration force, so that the fuel spray of the second injection can be accurately retained near the ignition 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 utilized. Therefore, at the timing when the third injection is performed, this secondary flow can be utilized together with the swirl flow, so that even if the fuel injection amount of the third injection is made greater than that of the second injection, the fuel spray from the third injection can be accurately retained near the spark plug.

[0011] 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 such swirl flow, the fuel sprays from the first and second injections can be more reliably retained near the spark plug.

[0013] 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, making it possible to perform catalyst activity control appropriate for each of the driving range and non-driving range.

[0014] 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.

[0015] 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 configured as described above, 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.

[0016] 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 thus configured, it is possible to more effectively suppress fuel adhesion to the piston (fuel adhesion to the cavity, etc.) during catalyst activation control.

[0017] 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. Effect of the Invention

[0018] According to the engine system of the present invention, when control is performed to activate the catalyst, by appropriately splitting the fuel injection, the swirl flow within the cylinder can be utilized to effectively suppress fuel adhesion to the piston. [Brief description of the drawings]

[0019] [Figure 1] 1 is a schematic configuration diagram of an engine system according to an embodiment of the present invention. [Diagram 2] FIG. 1 is a perspective view of an engine according to an embodiment of the present invention. [Diagram 3] 1 is a block diagram showing an electrical configuration of an engine system according to an embodiment of the present invention. FIG. [Figure 4] 5 is a time chart showing a typical example of split injection according to an embodiment of the present invention. [Diagram 5] FIG. 2 is an explanatory diagram of a basic concept for retaining fuel spray around an ignition plug. [Figure 6] FIG. 3 is an explanatory diagram of the flow of fuel sprays to be formed in a combustion chamber by each of first to third injections in an embodiment of the present invention. [Figure 7] This is an explanatory diagram of Einstein's teacup problem. [Figure 8] 4 is a flowchart showing an overall control according to an embodiment of the present invention. [Figure 9] 4 is a flowchart showing catalyst activity control according to an embodiment of the present invention. [Figure 10] 5 is a flowchart showing another example of catalyst activity control according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an engine system according to an embodiment of the present invention will be described with reference to the accompanying drawings.

[0021] [Engine system configuration] FIG. 1 is a schematic diagram of an engine system according to this 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.

[0022] Intake air is supplied to the engine 1 through an intake passage 40. A throttle valve 41 capable of adjusting the amount of intake air supplied to the engine 1, a surge tank 42 for temporarily storing the intake air to be supplied to the engine 1, and the like are provided on the intake passage 40. A portion of the intake passage 40 constitutes an intake port 18 connected to the engine 1.

[0023] In the engine 1, two independent intake ports 18 and two independent exhaust ports 20 are connected to each cylinder 2, and an intake valve 22 and an exhaust valve 24 that open and close the opening on the combustion chamber 16 side are disposed in the intake port 18 and the exhaust port 20, respectively. Here, as the intake valve 22 opens and the piston 14 descends, the intake air that flows from the intake port 18 into the combustion chamber 16 generates a tumble flow (vertical vortex / vertical vortex).

[0024] Further, 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 passage of the intake port 18. Note that Fig. 1 shows only one of the intake ports 18 provided with the SCV 43, and does not show the other intake port 18 not provided with the SCV 43.

[0025] 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. The 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, an intake port may be formed in such a form that a swirl flow is generated in the combustion chamber 16, in which case the intake port corresponds to the "swirl flow generating mechanism."

[0026] The lower surface of the cylinder head 6 of the engine 1 forms a ceiling 26 of the combustion chamber 16. This ceiling 26 is a so-called pent roof type having 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 provided at an angle with respect to the axial direction of the piston 14 (i.e., the moving direction of the piston 14). More specifically, the injector 28 is disposed such that its nozzle faces the inside of the combustion chamber 16 obliquely downward from between the two intake ports 18 on the periphery of the ceiling 26 of the combustion chamber 16.

[0027] Furthermore, a spark plug 32 that forcibly ignites the air-fuel mixture in the combustion chamber 16 is attached to the cylinder head 6 of the engine 1 for each cylinder 2. The spark plug 32 is disposed 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 the 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 the exhaust valve 24, or a variable valve phase mechanism that can change the rotational phase of the camshaft relative to the crankshaft 12.

[0028] 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. An EGR passage 46 for recirculating the exhaust gas to the intake passage 40 is connected to the downstream side of the catalyst 45 in the exhaust passage 44. An EGR cooler 47 for cooling the exhaust gas (hereinafter referred to as "EGR gas") to be recirculated, 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.

[0029] Next, Fig. 2 is a perspective view showing detailed structures 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 a plurality of nozzle holes 30. The injector 28 is provided 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.

[0030] Moreover, the piston crown surface 14a forming the top of the piston 14 is formed in a convex shape so as to rise 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 moving direction of the piston 14). No so-called cavity is formed in the piston crown surface 14a.

[0031] The piston crown surface 14a also includes 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. The injector-side slope 14c and the anti-injector-side slope 14d are formed so as to fit along the ceiling 26 of the combustion chamber 16 (see FIG. 1).

[0032] Furthermore, horizontal surfaces 14e are formed at the injector side end and the opposite side end of the piston crown surface 14a. Furthermore, an exhaust valve recess 14f is formed on the opposite side inclined surface 14d of the piston crown surface 14a so as to prevent contact between the piston 14 and the exhaust valve 24. Note that contact between the piston 14 and the intake valve 22 is prevented by the injector side inclined surface 14c and the like.

[0033] 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 that is composed of circuits and is based on a well-known microcomputer. The PCM 80 includes one or more microprocessors 80a as a central processing unit (CPU) that executes programs, a memory 80b that is composed of, for example, a random access memory (RAM) or a read only memory (ROM) and stores programs and data, and an input / output bus that inputs and outputs electrical signals.

[0034] A variety of 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 an accelerator opening corresponding to an amount of operation of an accelerator pedal. The crank angle sensor S2 detects a rotation angle of the crankshaft 12 (corresponding to an engine speed). The water temperature sensor S3 detects a temperature (water temperature) of the cooling water that cools the engine 1. The vehicle speed sensor S4 detects the speed of the vehicle. The ignition switch S5 is a switch 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.

[0035] 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 the memory 80b. The control logic includes calculating a target amount and / or a control amount using a map stored in the memory 80b. The PCM 80 outputs a control signal related to the calculated control amount mainly to the injector 28, the spark plug 32, the SCV 43, and the EGR valve 48.

[0036] [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, such as when the engine 1 is started, the PCM 80 performs control (catalyst activation control) to delay the ignition timing of the spark plug 32 until after the top dead center of compression so that the catalyst 45 is 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 engine 1 is started 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 “predicted catalyst temperature” as appropriate) 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.

[0037] Here, as described in the above Patent Document 1, when the ignition timing is delayed until after the compression top dead center, ignition stability and combustion stability tend to decrease. To address this, 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, part of the fuel adheres to the piston 14, which may increase smoke and HC (unburned gas), thereby deteriorating the emission performance. Therefore, in this embodiment, when catalyst activity 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 suppress the adhesion of the fuel to the piston 14.

[0038] 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 half and the second half of each stroke correspond to the front and rear parts when the period of each stroke is divided in half). Furthermore, 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, Q3 of the second and third injections, and so that the fuel injection amount Q3 of the third injection is greater than the fuel injection amount Q2 of the second injection.

[0039] Next, the reason for performing the split injection as shown in Fig. 4 will be described 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., for 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 described.

[0040] 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 (in a direction perpendicular to the axial direction of the piston 14), and FIG. 5(B) is a schematic diagram of the state of the combustion chamber 16 as viewed from above (in the direction indicated by the arrow A01 in FIG. 5(A)). In FIGS. 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 the vortex center at approximately the center of the combustion chamber 16.

[0041] In order to cause the fuel injected from the injector 28 to remain 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). That is, 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, having reached the vicinity of the spark plug 32, the fuel spray F01 should be defeated by the swirl flow, and ride on the swirl flow near the spark plug 32 while rotating and flowing. In order to realize such a 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 swirl flow (hereinafter referred to as the "swirling flow force") so that the fuel spray F01 accurately reaches the vicinity of the spark plug 32, and so that the spray penetration force from the injector 28 is smaller than the swirling flow force when the fuel spray F01 reaches the vicinity of the spark plug 32.

[0042] Such spray penetration basically has a magnitude corresponding to the amount of fuel injected from the injector 28 (assuming constant fuel pressure). That is, when the amount of fuel injected is large, the spray penetration becomes large, and when the amount of fuel injected is small, the spray penetration becomes small. Therefore, in this embodiment, the spray penetration is controlled by adjusting the amount of fuel injected. Specifically, the spray penetration by each split injection is controlled by adjusting the fuel injection amount of each split injection.

[0043] Moreover, 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 the largest 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, in order to appropriately retain each of the first to third injected fuels around the ignition plug 32 as described above, 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 depending on the magnitude of the swirling force of the swirl flow generated at the timing of the first to third injections (specifically, Q1>Q3>Q2).

[0044] Next, referring to Fig. 6, the flow of fuel sprays to be formed in the combustion chamber 16 by each of the first to third injections in this embodiment will be described. Figs. 6(A) to (C) are schematic views of the combustion chamber 16 as seen from above, similar to Fig. 5(B), where the arrow A10 indicates the swirl flow generated in the combustion chamber 16 by the SCV 43, and the symbols F11, F12, and F13 indicate 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.

[0045] First, at the timing of the first injection, since the swirl flow is strong, in this embodiment, the fuel spray F11 from the first injection stays near the ignition plug 32 after penetrating this swirl flow (see arrow A11 in Fig. 6(A)). To increase the spray penetration force of the first injection, the fuel injection amount Q1 of the first injection is increased. In other words, since the swirl flow is strong at the timing of the first injection, even if the spray penetration force of the first injection is increased to a certain extent, the fuel spray F11 will not penetrate the entire swirl flow. Therefore, the fuel injection amount Q1 of the first injection can be increased. Also, when performing the first injection, from the perspective of preventing misfire (partial misfire) during flame propagation after this, and arranging a part of the fuel spray F11 near the periphery of the combustion chamber 16 (see arrow A12), the fuel injection amount Q1 is increased to increase the spray penetration force of the first injection. For these reasons, in this embodiment, among the fuel injection amounts Q1 to Q3 of the first to third injections, the fuel injection amount Q1 of the first injection is the largest.

[0046] Next, at the timing of the second injection after the first injection, since the swirl flow has weakened, in this embodiment, the fuel injection amount Q2 of the second injection is decreased (Q2 < Q1) so that the spray penetration force 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 ignition plug 32 (see arrow A13 in Fig. 6(B)).

[0047] Next, at the timing of the third injection after the second injection, the swirl flow is as weak as when the second injection was performed, but a secondary flow (details will be described later) from the periphery to the center of the combustion chamber 16 that occurs along with this swirl flow can be utilized. Therefore, at the timing of the third injection, by utilizing such a secondary flow together with the swirl flow, even if the spray penetration force of the third injection is made larger than that of the second injection, the fuel spray F13 from the third injection can be accurately retained near the ignition plug 32 (see arrow A14 in Fig. 6(C)). Therefore, in this embodiment, the fuel injection amount Q3 of the third injection is made larger than the fuel injection amount Q2 of the second injection (Q3 > Q2).

[0048] 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)-(C) show the state inside a cup when a predetermined fluid is flowed so as to rotate in a horizontal direction 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 force 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.

[0049] Next, Fig. 7(C) is a schematic diagram showing the flow velocity distribution on the cross section of the cup. As shown in Fig. 7(C), it can be seen that a secondary flow is generated as indicated by the 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, flows upward at the center of the cup, and flows from the center toward the periphery when it moves away from the bottom of the cup. This type of secondary flow is generated because the centrifugal force and the pressure gradient force are not balanced near the bottom of the cup.

[0050] Here, at the timing of performing 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 toward the center and flows upward at the center due to a swirl flow that flows so as to rotate laterally within the combustion chamber 16. Therefore, at the timing of performing the third injection, such a secondary flow acts on the fuel spray F13 by the third injection. Therefore, even if the spray penetration of the fuel spray F13 by the third injection is increased to some extent (that is, even if the fuel injection amount Q3 of the third injection is increased to some extent), the fuel spray F13 can be accurately retained near the ignition plug 32.

[0051] [Processing flow] Next, a specific control flow according to this embodiment will be described with reference to Fig. 8 and Fig. 9. Fig. 8 is a flowchart showing the overall control according to this embodiment, and Fig. 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. In addition, in a situation where the overall control of Fig. 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.

[0052] 8 is started, the PCM 80 acquires various information in step S11. Specifically, the PCM 80 acquires at least signals from the accelerator opening sensor S1, the crank angle sensor S2, the water temperature sensor S3, the vehicle speed sensor S4, and the ignition switch S5. After that, in steps S12 to S15, the PCM 80 determines the execution conditions for catalyst activation control.

[0053] First, in step S12, the PCM 80 determines whether or not the vehicle has 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 just been started (step S12: No) and proceeds to step S14.

[0054] 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. On the other hand, 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.

[0055] Next, in step S14, the PCM 80 determines whether the water temperature detected by the water temperature sensor S3 is within a predetermined range (for example, −10 to 45° C.). 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.

[0056] 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 the exhaust gas amount, and calculates the predicted catalyst temperature from the 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 higher than the predetermined temperature (step S15: No), the PCM 80 ends the overall control.

[0057] The situation of proceeding to step S16 is that the catalyst 45 is in an inactive state and the situation where the catalyst activity control for activating the catalyst 45 can be executed. Therefore, in step S16, the PCM 80 executes the catalyst activity control. Basically, in this catalyst activity control, the PCM 80 controls the injector 28 to perform split injection (first to third injections) and controls the spark plug 32 to ignite after top dead center of compression. Specifically, the PCM 80 performs a first injection for injecting the maximum amount Q1 of fuel during the intake stroke, a second injection for injecting fuel Q2 (<Q1) after this first injection, and a third injection for injecting fuel Q3 (>Q2) after this second injection and during the compression stroke, and controls the injector 28 to perform these injections. Note that this catalyst activity control will be described in detail with reference to FIG. 9 later.

[0058] Next, the PCM 80 proceeds to step S17 and determines whether the predicted catalyst temperature has reached a predetermined temperature or higher (for example, 300°C or higher). As a result, when the predicted catalyst temperature is less than the predetermined temperature (step S17: No), the PCM 80 returns to step S16. In this case, the catalyst activity control is continuously executed until the predicted catalyst temperature reaches the predetermined temperature or higher. On the other hand, when the predicted catalyst temperature is the predetermined temperature or higher (step S17: Yes), the PCM 80 proceeds to step S18.

[0059] Next, in step S18, the PCM 80 ends the catalyst activity 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 (batch injection) during the intake stroke and controls the spark plug 32 to ignite at a timing during the compression stroke that is advanced compared to the catalyst activity control (for example, 5 degrees after compression TDC). Also, the PCM 80 controls the engine 1 so that the engine speed becomes the idle speed (for example, 1200 rpm). After this, the PCM 80 ends the overall control.

[0060] Next, the catalyst activation control according to this embodiment will be specifically described with reference to Fig. 9. This catalyst activation control is performed in step S16 of 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.

[0061] Next, in step S22, the PCM 80 judges 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 judges that the range of the automatic transmission is a driving range (step S22: Yes) and proceeds to step S23. On the other hand, if the acquired range is N range (neutral range) or P range (parking range), the PCM 80 judges that the range of the automatic transmission is a non-driving range (step S22: No) and proceeds to step S24.

[0062] In step S23, the PCM 80 executes the catalyst activation control using a setting for a driving range determined in advance. Specifically, the PCM 80 first executes the catalyst activation control by applying a relatively low engine speed (e.g., 800 rpm). This is to suppress sudden start (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 the 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%). Also, the PCM 80 sets the ignition timing to a relatively early timing 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, a sufficient amount of exhaust gas heat is generated without retarding the ignition timing much, whereas, since the engine speed is relatively low in the driving range as described above, the swirl flow in the combustion chamber 16 becomes weak, and therefore, in order to ensure combustion stability, the ignition timing cannot be retarded much.

[0063] On the other hand, in step S24, the PCM 80 executes the catalyst activation control using a setting for the non-driving range that is determined in advance. Specifically, the PCM 80 first executes the catalyst activation control by applying a relatively high engine speed (for example, 1500 rpm). This is because the sudden start (jumping out) that occurs in the non-driving range does not occur in the non-driving range. 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 the 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 (for example, 25 degrees after the compression TDC). This is because, in the non-driving range, a relatively high engine speed is applied as described above, which causes a strong swirl flow in the combustion chamber 16, ensuring combustion stability even if the ignition timing is retarded. On the other hand, in the non-driving range, the engine load is relatively low, so unless the ignition timing is retarded to some extent, sufficient exhaust gas heat is not generated.

[0064] In addition, while Fig. 9 shows the catalyst activation control performed in a vehicle equipped with an automatic transmission (AT), in a vehicle equipped with a manual transmission (MT), the catalyst activation control as shown in Fig. 10 is performed. Fig. 10 is a flowchart showing another example of the catalyst activation control according to this embodiment. This catalyst activation control is also performed in step S16 of Fig. 8.

[0065] First, in step S31, the PCM 80 acquires the gear position and clutch state (clutch disengagement or engagement state) of the manual transmission (MT) mounted on the vehicle. For example, the PCM 80 acquires the gear position and clutch state information from a predetermined sensor.

[0066] 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.

[0067] 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 the catalyst activation control. This is because in the latter case, the vehicle is not stopped and the catalyst activation control cannot be executed.

[0068] When the process proceeds to step S34, the manual transmission is in neutral or the clutch is disengaged, so that catalyst activation control can be executed. Therefore, in step S34, the PCM 80 executes catalyst activation control. In this case, the PCM 80 executes catalyst activation control using a preset setting for a non-driving range, similar to step S24 in FIG. 9. Therefore, a detailed description thereof will be omitted here.

[0069] [Action and Effects] Next, the operation and effects of the engine system 100 according to the present embodiment will be described. According to the present embodiment, when the catalyst 45 is in an inactive state, the PCM 80 controls the injector 28 to perform split injection consisting of the first to third injections in a state where a swirl flow is generated in the combustion chamber 16 by the SCV 43, and controls the ignition plug 32 to ignite after top dead center of compression. Specifically, the PCM 80 performs a first injection that injects the maximum amount Q1 of fuel during the intake stroke, a second injection that injects fuel Q2 (<Q1) after the first injection, and a third injection that injects fuel Q3 (>Q2) after the second injection and during the compression stroke, and controls the injector 28 to perform these injections.

[0070] Since the swirl flow is strong at the timing of the first injection, the spray penetration force is increased by maximizing the fuel injection amount Q1 of the first injection. As a result, the fuel spray by the first injection can be made to reach near the center of the vortex by penetrating the swirl flow, and thus can be retained near the center of the vortex, that is, accurately retained near the ignition plug 32. Next, since the swirl flow is weak at the timing of the second injection, the fuel injection amount Q2 of the second injection is made smaller than that of the first injection to reduce the spray penetration force, so that the fuel spray by the second injection can be accurately retained near the ignition plug 32. Next, at the timing of the third injection, although the swirl flow is weak, a secondary flow from the periphery to the center of the combustion chamber 16, which is generated accompanying this swirl flow, is occurring. Therefore, at the timing of the third injection, since this secondary flow can be used together with the swirl flow, even if the fuel injection amount Q3 of the third injection is made larger than that of the second injection, the fuel spray by the third injection can be accurately retained near the ignition plug 32.

[0071] As described above, according to this embodiment, by appropriately setting the fuel injection amount of 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 the deterioration of emission performance. In addition, a rich region is formed near the spark plug 32, which can also improve combustion stability.

[0072] 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 in accordance with the strength of the swirl flow (Q1>Q2), so that the fuel sprays from the first and second injections can be accurately retained near the spark plug 32.

[0073] 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.

[0074] 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 only when the manual transmission is in neutral or the clutch of the manual transmission is disengaged. This allows the first to third injections according to this embodiment to be performed appropriately in a situation where catalyst activation control can be executed in a vehicle having a manual transmission.

[0075] Furthermore, according to this embodiment, the piston crown surface 14a is formed substantially flat without any cavity formed therein, 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. [Explanation of symbols]

[0076] 1 Engine 2-cylinder 14 Piston 14a Piston crown surface 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

1. 1. An engine system comprising: an engine including: a cylinder that defines a combustion chamber; a piston that reciprocates in the cylinder; a fuel injection valve that is inclined with respect to an axial direction of the piston and 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 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; 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, 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.

2. 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. 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.

4. 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. 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. 6. The engine system according to claim 1, wherein the spark plug is provided in a central portion of a ceiling of the combustion chamber.

7. 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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