JP6521006B2 - Supercharged engine - Google Patents

Description

  The technology disclosed herein relates to a supercharged engine.

  Patent Document 1 describes an engine that burns an air-fuel mixture in a combustion chamber by compression ignition in a predetermined region of low load and low rotation. This engine has a negative overlap period in which both the intake valve and the exhaust valve are closed by setting the closing timing of the exhaust valve before top dead center and the opening timing of the intake valve after top dead center in the predetermined region. Is provided. As a result, the high temperature EGR gas is introduced into the combustion chamber, the temperature in the combustion chamber becomes high, and the air-fuel mixture is compression-ignited.

  Patent Document 2 describes an engine in which a mechanical supercharger and an intercooler are provided in an intake passage, and the supercharged intake air is cooled and supplied to the engine. This engine deenergizes the mechanical supercharger by turning off the electromagnetic clutch in a predetermined operating condition, and closes the control valve of the air bypass passage bypassing the mechanical supercharger and the inter , Pre-rotation mechanical supercharger by pressure difference. This prevents the occurrence of torque shock when the electromagnetic clutch is turned on.

JP, 2009-197740, A Patent No. 3564989

  In order to realize stable combustion, the temperature in the combustion chamber at the time of combustion must be adjusted to an appropriate range. For example, when the outside air temperature is high, the compression end temperature, which is the temperature in the combustion chamber when the compression top dead center is reached, may become too high, causing problems such as occurrence of premature ignition or combustion noise exceeding the allowable value. There is.

  The technique disclosed herein has been made in view of the above point, and its object is to adjust the temperature of the combustion chamber at the time of combustion to an appropriate temperature in a supercharged engine.

  The supercharger-equipped engine disclosed herein includes an intake passage connected to a combustion chamber of the engine, a supercharger disposed in the intake passage, and a switching unit that switches between driving and non-driving of the supercharger. An intercooler disposed downstream of the turbocharger in the intake passage, a bypass passage connecting an upstream of the turbocharger in the intake passage and a downstream of the intercooler, and the bypass passage disposed in the bypass passage. And a control unit connected to the switching unit and the flow control valve and outputting a control signal to the switching unit and the flow control valve.

  And the forced rotation control for driving the supercharger in a state in which the flow control valve is opened such that the gas flowing through the intake passage circulates through the bypass passage in a non-supercharged state, Pre-rotation control that controls the supercharger to close the flow control valve in a non-driven state so that the supercharger operates with a pressure difference between the upstream and the downstream in a supercharged state; Switch according to the temperature of the

  Here, the “engine” may be a four-stroke engine which is operated by the combustion chamber repeating an intake stroke, a compression stroke, an expansion stroke and an exhaust stroke. The "supercharger" is, for example, a mechanical supercharger driven by an engine. It may be a motorized turbocharger driven by electrical energy.

  As the engine load increases, the amount of fuel increases, so it is necessary to increase the amount of intake according to the amount required. Also, even when the engine speed is high, it is necessary to increase the intake amount in accordance with the required amount. In such a case, a supercharger is attached to this engine in order to secure a necessary intake amount.

  When the engine operates in a region requiring supercharging, the control unit switches the switching unit to drive the supercharger, and adjusts the opening degree of the flow control valve disposed in the bypass passage on the closing side. As a result, the intake air (mainly fresh air but may include EGR gas) is introduced into the combustion chamber in a state pressurized above the pressure in natural intake.

  When the intake air is pressurized, its temperature rises. Since the intercooler is disposed downstream of the supercharger in the intake passage, the temperature of the pressurized intake air is adjusted to an appropriate temperature by cooling with the intercooler.

  On the other hand, when operating in an area where the engine does not require supercharging, such as in a low load low rotation area, the control unit switches the switching unit to non-drive to stop the operation of the supercharger and is disposed in the bypass passage. Adjust the opening of the flow control valve on the open side (usually fully open). As a result, the intake air flowing through the intake passage bypasses the turbocharger and is smoothly introduced into the combustion chamber through the bypass passage with little resistance. The engine operates in a non-supercharged state (natural intake state).

  When the engine is operating in a non-supercharged state, the temperature of the intake air depends on the outside air temperature (the temperature of the outside air) because the intake air is introduced directly into the combustion chamber. Therefore, if the outside air temperature becomes excessively high, the temperature of the combustion chamber may deviate from the appropriate range, and appropriate combustion may not be realized.

  On the other hand, in this engine, forced rotation control and pre-rotation control are switched according to the temperature of the engine.

  In the forced rotation control, the control unit drives the turbocharger with the flow control valve opened so that the gas flowing through the intake passage circulates through the bypass passage in a non-supercharged state. That is, the forced rotation control drives the supercharger in a non-supercharged state (natural intake state), and repeatedly circulates the intake through the bypass passage while utilizing the intercooler to introduce the intake into the combustion chamber. Cooling.

  Since the intake air can be repeatedly cooled by the circulation of the intake air through the intercooler, the intake air temperature can be properly maintained even if the outside air temperature becomes excessively high. By adjusting the opening degree of the flow control valve, the amount of intake air introduced into the combustion chamber can be adjusted with high accuracy as compared with the case of performing natural intake. As a result, even if the outside air temperature becomes excessively high, the temperature of the combustion chamber can be maintained in an appropriate range, and stable combustion can be realized.

  In forced rotation control, a supercharger is driven. Therefore, the fuel consumption performance of the engine is reduced because the driving resistance is large as compared with the non-driving case. On the other hand, pre-rotation control can cool the intake air without driving the supercharger.

  Specifically, in the prerotation control, the turbocharger is controlled to close the flow control valve in a non-driven state. As a result, a pressure difference occurs between the upstream side and the downstream side of the supercharger, so that the supercharger operates, ie, pre-rotates, under the action of the pressure difference. The pre-rotation of the supercharger causes part of the intake air to flow downstream through the supercharger, and after being cooled by the intercooler, is introduced into the combustion chamber. Thus, the pre-rotation control also makes it possible to cool the intake air by utilizing the intercooler.

  Since the prerotation control has a smaller driving resistance than the forced rotation control, it is possible to suppress the deterioration of the fuel efficiency performance of the engine. On the other hand, in terms of cooling capacity, forced rotation control that can cool the intake air multiple times with the intercooler is superior to pre-rotation control. Therefore, to cool intake air, forced rotation control is more suitable than pre-rotation control.

  However, in a normal engine, the intake passage and the bypass passage are incorporated into the engine in a unitized state, together with a supercharger and an intercooler. Specifically, the unitized devices, the intake passage, and the bypass passage are integrated with the engine so as to be in close contact with the cylinder head, which is the main body of the engine, and the outer surface of the cylinder block.

  Therefore, the intake air receives heat generated by the engine while passing through the intake passage and the bypass passage. When the temperature of the engine rises, in the case of forced rotation control in which the intake air is repeatedly circulated via the intake passage and the bypass passage, the amount of heat received by the intake air from the engine significantly increases. As a result, in the forced rotation control, even if the cooling capacity is excellent, the substantial cooling capacity may be reduced due to the increase in heat received from the engine. The amount of heat received from the engine may exceed the cooling capacity by forced rotation control, which may cause an adverse effect.

  On the other hand, in prerotation control, the intake air cooled by the intercooler is directly introduced into the combustion chamber. Therefore, even if the temperature of the engine rises, its effect is small compared to forced rotation control, and high cooling performance can be exhibited.

  As described above, in this engine, the forced rotation control and the pre-rotation control are switched according to the temperature of the engine, so that the cooling of the intake air can be efficiently performed by selecting the appropriate control. As a result, the combustion chamber at the time of combustion can be adjusted to an appropriate temperature while suppressing the influence of the temperature of the engine.

  Specifically, the prerotation control may be performed when the temperature of the engine is equal to or higher than a predetermined reference temperature, and the forced rotation control may be performed when the temperature of the engine is less than the reference temperature.

  According to this configuration, the temperature of the engine, which is the reference at which the intake air can be properly cooled by the forced rotation control, is preset as the predetermined reference temperature. The prerotation control is performed when the reference temperature is higher and the forced rotation control is performed when the temperature is lower than the reference temperature. Therefore, proper control selection becomes more reliable, and intake cooling can be performed stably and efficiently. .

  A main cooling unit for cooling the engine and a sub cooling unit for cooling the intercooler may be further provided, and the main cooling unit and the sub cooling unit may be provided independently of each other.

  According to this configuration, the sub-cooling unit for cooling the intercooler is configured separately from the main cooling unit for cooling the engine, so that the intercooler can be cooled separately from the engine. Therefore, even when the temperature of the engine becomes high and the cooling performance of the main cooling section is lowered, the intercooler can be cooled without being affected by it, so the cooling of the intake air by the forced rotation control and the prerotation control is stable It can do.

  The switching between the forced rotation control and the pre-rotation control may be performed in a predetermined region where the air-fuel mixture in the combustion chamber is burned by compression self-ignition.

  In order to stably realize combustion by compression self-ignition, it is necessary to adjust the temperature in the combustion chamber to an appropriate range. For example, if the compression end temperature becomes too high, the combustion by the compression self-ignition becomes steep, and the combustion noise exceeds the allowable value.

  In this configuration, switching between forced rotation control and pre-rotation control is performed in a predetermined region where such combustion by self-ignition ignition is performed. By switching between forced rotation control and pre-rotation control, it is possible to adjust the temperature of the combustion chamber at the time of combustion to an appropriate temperature while suppressing the influence of the temperature of the engine, so that combustion by appropriate compression self-ignition is stabilized. Can be realized.

  In that case, the control unit is further provided with a temperature sensor that detects an outside air temperature and outputs a detection signal to the control unit, and the control unit is configured to detect the outside temperature when the temperature of the engine is less than the reference temperature in the predetermined area. The preliminary rotation control may be performed when the air temperature is equal to or higher than a predetermined first temperature, and the forced rotation control may be performed when the outside air temperature exceeds a predetermined second temperature higher than the first temperature.

  In forced rotation control, a supercharger is driven. Therefore, the fuel consumption performance of the engine is reduced because the driving resistance is large as compared with the non-driving case. Therefore, in this configuration, prior to the forced rotation control, pre-rotation control capable of cooling the intake air without driving the supercharger is performed.

  Since the prerotation control has a smaller driving resistance than the forced rotation control, it is possible to suppress the deterioration of the fuel efficiency performance of the engine. On the other hand, in terms of cooling capacity, forced rotation control that can cool the intake air multiple times with the intercooler is superior to pre-rotation control. Therefore, in this configuration, the forced rotation control is performed when the outside air temperature exceeds the predetermined second temperature higher than the first temperature. As a result, it is possible to efficiently cool the intake air while suppressing the decrease in the fuel efficiency performance.

  The engine may have a geometric compression ratio of 13 or more and 30 or less.

  If the geometric compression ratio of the engine is relatively high, which is advantageous for stabilization of combustion by compression self-ignition, it may lead to pre-ignition. If the engine has a geometric compression ratio of 13 or more and 30 or less, combustion by compression self-ignition can be stabilized while avoiding pre-ignition. Also, if the geometric compression ratio is excessively high, cooling loss and mechanical loss will increase, but even if the geometric compression ratio is high, such defects can be suppressed if not excessive. Fuel efficiency of the engine is improved.

  The fuel supplied to the combustion chamber may include at least gasoline.

  Fuel containing gasoline may cause pre-ignition in a high temperature combustion chamber, but by maintaining the intake temperature properly, pre-ignition can be avoided even when using fuel containing gasoline. The combustion by the compression self-ignition can be stabilized.

  According to the disclosed technology, an increase in the intake air temperature can be avoided, so the combustion chamber can be adjusted to an appropriate temperature.

FIG. 1 is a diagram illustrating the configuration of an engine. The intake side is on the left side in the drawing, and the exhaust side is on the right side in the drawing. FIG. 2 is a view illustrating the configuration of the combustion chamber, and the upper view is a plan view equivalent view of the combustion chamber, and the lower portion is a cross-sectional view taken along II-II. FIG. 3 is a plan view illustrating the configuration of the combustion chamber and the intake system. The intake side is on the right side of the drawing, and the exhaust side is on the left of the drawing. FIG. 4 is a block diagram illustrating the configuration of a control device of an engine. FIG. 5 is a diagram illustrating the configuration of a cooling device of an engine. FIG. 6 is a diagram illustrating an operating region of an engine and a driving / non-driving region of a turbocharger. FIG. 7 is a diagram illustrating the fuel injection timing and the ignition timing in each operation region and the combustion waveform. FIG. 8 is a flow diagram illustrating the flow of switching the operation of the engine between the supercharged state and the non-supercharged state. FIG. 9 is a schematic view showing a supercharging system at the time of supercharging operation. FIG. 10 is a schematic view showing a supercharging system during non-supercharging operation. FIG. 11 is a schematic view showing a supercharging system at the time of prerotation control. FIG. 12 is a diagram showing the relationship between the flow rate of gas flowing through the intercooler and the temperature in the surge tank during prerotation control. FIG. 13 is a schematic view showing a supercharging system at the time of forced rotation control. FIG. 14 is a flow chart showing an example of a flow of cooling control of intake air at the time of non-supercharging operation. FIG. 15 is a flow chart showing an example of a flow of intake air cooling control based on an application example of an engine.

  Hereinafter, embodiments of the disclosed technology will be described in detail based on the drawings. However, the following description is merely illustrative in nature, and does not limit the present invention, its application, or its application.

<SPCCI combustion>
The present inventors have considered a combustion form that combines SI (Spark Ignition) combustion and CI (Compression Ignition) combustion. SI combustion is combustion with flame propagation initiated by forcibly igniting the mixture in the combustion chamber. CI combustion is combustion initiated by compression self-ignition of the mixture in the combustion chamber. The combustion mode that combines SI combustion and CI combustion is that the mixture gas in the combustion chamber is forcibly ignited to start combustion by flame propagation, and the pressure rise by SI heat generation and flame propagation. The unburned mixture in the combustion chamber is combusted by compression ignition. This combustion mode is hereinafter referred to as SPCCI (SPark Controlled Compression Ignition) combustion.

  In the combustion by compression ignition, when the temperature in the combustion chamber before the start of compression varies, the timing of compression ignition changes significantly. In SPCCI combustion, by adjusting the heating value of SI combustion, it is possible to absorb temperature variations in the combustion chamber before the start of compression. The timing of compression ignition can be controlled by adjusting the start timing of SI combustion by adjusting the ignition timing, for example, according to the temperature in the combustion chamber before the start of compression. SPCCI combustion can control CI combustion by SI combustion.

  Since SI combustion due to flame propagation has a slower pressure rise than CI combustion, SPCCI combustion can suppress the generation of combustion noise. Further, since the CI combustion shortens the combustion period more than the SI combustion, the SPCCI combustion is advantageous for the improvement of the fuel consumption.

<Specific example of engine>
FIG. 1 shows the overall configuration of a supercharged engine (engine 1) to which the combustion technology by SPCCI combustion is applied.

  The engine 1 is a four-stroke engine operated by the combustion chamber 17 repeating an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. The engine 1 is mounted on a four-wheeled vehicle. By driving the engine 1, the car travels. The fuel of the engine 1 is gasoline in this configuration example. The fuel may be gasoline including bioethanol and the like. The fuel of the engine 1 may be any fuel as long as it is a liquid fuel containing at least gasoline.

  The engine 1 includes a cylinder block 12 and a cylinder head 13 mounted thereon. The cylinder block 12 and the cylinder head 13 constitute an engine body 100. A plurality of cylinders 11 are formed in the cylinder block 12. 1 and 2 show only one cylinder 11. The engine 1 is a multi-cylinder engine.

  A piston 3 is slidably inserted in each cylinder 11. The piston 3 is connected to the crankshaft 15 via a connecting rod 14. The piston 3 defines the combustion chamber 17 together with the cylinder 11 and the cylinder head 13. The “combustion chamber” is not limited to the meaning of the space when the piston 3 reaches the compression top dead center. The term "combustion chamber" may be used in a broad sense. That is, the “combustion chamber” may mean a space formed by the piston 3, the cylinder 11 and the cylinder head 13 regardless of the position of the piston 3.

  The lower surface of the cylinder head 13, that is, the ceiling surface of the combustion chamber 17, is constituted by an inclined surface 1311 and an inclined surface 1312 as shown in the lower part of FIG. The inclined surface 1311 has an upward slope toward the injection axis X2 of the injector 6 described later from the intake side. The inclined surface 1312 has an upward slope from the exhaust side toward the injection axis X2. The ceiling surface of the combustion chamber 17 has a so-called pent roof shape.

  The upper surface of the piston 3 is raised toward the ceiling surface of the combustion chamber 17. A cavity 31 is formed on the upper surface of the piston 3. The cavity 31 is recessed from the upper surface of the piston 3. The cavity 31 faces the injector 6 described later.

  The center of the cavity 31 is offset to the exhaust side with respect to the central axis X1 of the cylinder 11. The center of the cavity 31 coincides with the injection axis X 2 of the injector 6. The cavity 31 has a convex portion 311. The convex portion 311 is provided on the injection axis X2 of the injector 6. The convex portion 311 is substantially conical. The convex portion 311 extends upward from the bottom of the cavity 31 toward the ceiling surface of the combustion chamber 17.

  The cavity 31 also has a recess 312 provided around the protrusion 311. The recessed portion 312 is provided so as to surround the entire circumference of the convex portion 311. The cavity 31 has a symmetrical shape with respect to the injection axis X2.

  The circumferential side surface of the recessed portion 312 is inclined from the bottom surface of the cavity 31 toward the opening of the cavity 31 with respect to the injection axis X2. The inner diameter of the cavity 31 gradually increases from the bottom of the cavity 31 toward the opening of the cavity 31.

  The shape of the combustion chamber 17 is not limited to the shape illustrated in FIG. For example, the shape of the cavity 31, the shape of the upper surface of the piston 3, and the shape of the ceiling surface of the combustion chamber 17 can be changed as appropriate. For example, the cavity 31 may be symmetrical with respect to the central axis X1 of the cylinder 11. The inclined surface 1311 and the inclined surface 1312 may be shaped symmetrically with respect to the central axis X1 of the cylinder 11. In the cavity 31, a shallow bottom portion shallower than the recessed portion 312 may be provided at a position facing the spark plug 25 described later.

  The geometric compression ratio of the engine 1 is set to 13 or more and 30 or less (preferably 20 or less). The engine 1 performs SPCCI combustion in which SI combustion and CI combustion are combined in a part of the operating region. SPCCI combustion performs CI combustion using heat generation and pressure increase due to SI combustion. In the engine 1, it is not necessary to increase the temperature of the combustion chamber 17 (that is, the compression end temperature) when the piston 3 reaches compression top dead center for self-ignition of air-fuel mixture. That is, although the engine 1 performs CI combustion, its geometric compression ratio is set relatively low. Lowering the geometric compression ratio is advantageous for reducing cooling loss and reducing mechanical loss. The geometric compression ratio of the engine 1 may be 14 to 17 in the regular specification (the fuel octane number is about 91), and may be 15 to 18 in the high fuel specification (the fuel octane number is about 96).

  An intake port 18 is formed in the cylinder head 13 for each cylinder 11. The intake port 18 has two intake ports, a first intake port 181 and a second intake port 182, as shown in FIG. The first intake port 181 and the second intake port 182 are aligned in the axial direction of the crankshaft 15, that is, in the front-rear direction of the engine 1. The intake port 18 is in communication with the combustion chamber 17. The intake port 18 is a so-called tumble port, which is not shown in detail. That is, the intake port 18 is shaped such that a tumble flow is formed in the combustion chamber 17.

  An intake valve 21 is disposed at the intake port 18. The intake valve 21 opens and closes between the combustion chamber 17 and the intake port 18. The intake valve 21 is opened and closed at a predetermined timing by a valve operating mechanism. The valve operating mechanism may be a variable valve operating mechanism that varies valve timing and / or valve lift. In this configuration example, as shown in FIG. 4, the variable valve mechanism has an intake electric motor S-VT (Sequential-Valve Timing) 23. The intake electric motor S-VT 23 is configured to continuously change the rotational phase of the intake camshaft within a predetermined angular range. As a result, the opening timing and closing timing of the intake valve 21 change continuously. The valve operating mechanism of the intake valve 21 may have a hydraulic S-VT instead of the electric S-VT.

  Further, an exhaust port 19 is formed in the cylinder head 13 for each cylinder 11. The exhaust port 19 also has two exhaust ports, a first exhaust port 191 and a second exhaust port 192, as shown in FIG. The first exhaust port 191 and the second exhaust port 192 are aligned in the front-rear direction of the engine 1. The exhaust port 19 communicates with the combustion chamber 17. An exhaust valve 22 is disposed at the exhaust port 19. The exhaust valve 22 opens and closes between the combustion chamber 17 and the exhaust port 19. The exhaust valve 22 is opened and closed at a predetermined timing by a valve operating mechanism. The valve operating mechanism may be a variable valve operating mechanism that varies valve timing and / or valve lift. In this configuration example, as shown in FIG. 4, the variable valve mechanism has an exhaust electric motor S-VT 24. The exhaust motor S-VT 24 is configured to continuously change the rotational phase of the exhaust camshaft within a predetermined angular range. Thereby, the opening timing and closing timing of the exhaust valve 22 continuously change. The valve operating mechanism of the exhaust valve 22 may have a hydraulic S-VT instead of the electric S-VT.

  The engine 1 adjusts the length of the overlap period related to the opening timing of the intake valve 21 and the closing timing of the exhaust valve 22 by the intake electric motor S-VT 23 and the exhaust electric motor S-VT 24. As a result, hot burnt gas is trapped in the combustion chamber 17. That is, internal EGR (Exhaust Gas Recirculation) gas is introduced into the combustion chamber 17. In addition, the residual gas in the combustion chamber 17 is scavenged by adjusting the length of the overlap period.

  An injector 6 is attached to the cylinder head 13 for each cylinder 11. The injector 6 is configured to inject fuel directly into the combustion chamber 17. The injector 6 is disposed facing the inside of the combustion chamber 17 in the valley portion of the pent roof where the inclined surface 1311 on the intake side and the inclined surface 1312 on the exhaust side intersect. As shown in FIG. 2, the injection axis of the injector 6 is disposed parallel to the central axis X1 of the cylinder 11. The injection axis X2 of the injector 6 is offset from the central axis X1. The injection axis of the injector 6 and the position of the convex portion 311 of the cavity 31 coincide with each other. The injector 6 is opposed to the cavity 31. The injection axis of the injector 6 may coincide with the central axis X1 of the cylinder 11. Also in this case, it is desirable that the injection axis of the injector 6 and the position of the convex portion 311 of the cavity 31 be coincident with each other.

  The injector 6 is constituted by a multi-hole type fuel injection valve having a plurality of injection holes, although the detailed illustration is omitted. The injector 6 injects fuel so that the fuel spray spreads radially from the center of the combustion chamber 17 and spreads obliquely downward from the ceiling of the combustion chamber 17 as shown by a two-dot chain line in FIG. In the present configuration example, the injector 6 has ten injection holes, and the injection holes are disposed equiangularly in the circumferential direction. The axis of the injection hole is circumferentially offset with respect to the spark plug 25 described later, as shown in the upper view of FIG. That is, the spark plug 25 is sandwiched between the axes of two adjacent injection holes. This prevents the fuel spray injected from the injector 6 from directly hitting the spark plug 25 and wetting the electrode.

  A fuel supply system 61 is connected to the injector 6. The fuel supply system 61 includes a fuel tank 63 configured to store fuel, and a fuel supply passage 62 connecting the fuel tank 63 and the injector 6 to each other. A fuel pump 65 and a common rail 64 are interposed in the fuel supply passage 62. The fuel pump 65 pumps fuel to the common rail 64. The fuel pump 65 is a plunger type pump driven by the crankshaft 15 in this configuration example. The common rail 64 is configured to store the fuel pumped by the fuel pump 65 at a high fuel pressure. When the injector 6 is opened, the fuel stored in the common rail 64 is injected from the injection hole of the injector 6 into the combustion chamber 17. The fuel supply system 61 is configured to be able to supply fuel with a high pressure of 30 MPa or more to the injector 6. The maximum fuel pressure of the fuel supply system 61 may be, for example, about 120 MPa. The pressure of the fuel supplied to the injector 6 may be changed according to the operating state of the engine 1. The configuration of the fuel supply system 61 is not limited to the above configuration.

  A spark plug 25 is attached to the cylinder head 13 for each cylinder 11. The spark plug 25 forcibly ignites the mixture in the combustion chamber 17. In this configuration example, as shown also in FIG. 2, the spark plug 25 is disposed on the intake side across the central axis X1 of the cylinder 11. The spark plug 25 is adjacent to the injector 6. The spark plug 25 is located between the two intake ports 18. The spark plug 25 is attached to the cylinder head 13 in such a way as to approach the center of the combustion chamber 17 from the upper side to the lower side. The electrode of the spark plug 25 faces the combustion chamber 17 and is located near the ceiling surface of the combustion chamber 17.

  An intake passage 40 is connected to one side of the engine 1. The intake passage 40 communicates with the intake port 18 of each cylinder 11. The intake passage 40 is a passage through which intake air introduced into the combustion chamber 17 (mainly new air, but may include EGR gas, also referred to simply as “gas”) flows. An air cleaner 41 for filtering fresh air is disposed at the upstream end of the intake passage 40. In the vicinity of the downstream end of the intake passage 40, a surge tank 42 is disposed. The intake passage 40 downstream of the surge tank 42 constitutes an independent passage branched for each cylinder 11. The downstream end of the independent passage is connected to the intake port 18 of each cylinder 11.

  A throttle valve 43 is disposed between the air cleaner 41 and the surge tank 42 in the intake passage 40. The throttle valve 43 is configured to adjust the introduction amount of fresh air into the combustion chamber 17 by adjusting the opening degree of the valve.

  A supercharger 44 is disposed downstream of the throttle valve 43 in the intake passage 40. The supercharger 44 is configured to supercharge the gas introduced into the combustion chamber 17. In this configuration example, the turbocharger 44 is a mechanical turbocharger driven by the engine 1. The mechanical supercharger 44 may be, for example, of the roots type. The configuration of the mechanical turbocharger 44 may be any configuration. The mechanical supercharger 44 may be of the Richolem type, vane type or centrifugal type.

  An electromagnetic clutch 45 (switching unit) is interposed between the turbocharger 44 and the engine 1. The electromagnetic clutch 45 transmits driving power from the engine 1 to the turbocharger 44 and blocks transmission of driving power between the turbocharger 44 and the engine 1. As will be described later, the supercharger 44 is switched between on (drive) and off (non-drive) as the ECU 10 switches between disconnection and connection of the electromagnetic clutch 45.

  In the engine 1, the supercharger 44 supercharges the gas introduced into the combustion chamber 17, that is, the intake air is introduced into the combustion chamber 17 at a pressure higher than that of natural intake (supercharged state); However, it is configured so as not to supercharge the gas introduced into the combustion chamber 17, that is, to switch between introducing the intake air into the combustion chamber 17 by natural intake (non-supercharged state).

  The supercharger 44 can, for example, increase the pressure of intake to a compression ratio of 1.5 to 2.5. The supercharger 44 has a discharge power higher than the intake performance of the engine 1. By increasing the supercharging pressure, a sufficiently large amount of intake air can be sent to the downstream side of the supercharger 44 of the intake passage 40 than the amount of intake air that can be introduced into the combustion chamber 17.

  An intercooler 46 is disposed downstream of the turbocharger 44 in the intake passage 40. The intercooler 46 is configured to cool the gas compressed at the turbocharger 44. The intercooler 46 may be configured to be, for example, water-cooled (or oil-cooled).

  A bypass passage 47 is connected to the intake passage 40. The bypass passage 47 connects the upstream portion of the turbocharger 44 and the downstream portion of the intercooler 46 with each other in the intake passage 40 so as to bypass the turbocharger 44 and the intercooler 46. An air bypass valve 48 (ABV, flow control valve) is disposed in the bypass passage 47. The air bypass valve 48 regulates the flow rate of gas flowing through the bypass passage 47. In this configuration example, a supercharging system 49 is configured by the supercharger 44, the bypass passage 47, the intercooler 46, and the air bypass valve 48.

  The intake passage 40 including a supercharging system 49 enclosed by a two-dot chain line K in FIG. 1 is unitized and assembled around the engine body 100. Specifically, the unitized air cleaner 41, the intake passage 40, the supercharger 44, the intercooler 46, the bypass passage 47, etc. are integrally assembled to the engine body 100 in a state where they are close to the outer surface of the engine body 100. It is done.

  The engine 1 has a swirl generating portion that generates a swirl flow in the combustion chamber 17. The swirl generating portion is a swirl control valve 56 attached to the intake passage 40. The swirl control valve 56 is disposed in the secondary passage 402 among the primary passage 401 connected to the first intake port 181 and the secondary passage 402 connected to the second intake port 182. The swirl control valve 56 is an opening adjustment valve capable of reducing the cross section of the secondary passage. When the degree of opening of the swirl control valve 56 is small, of the first intake port 181 and the second intake port 182 aligned in the front-rear direction of the engine 1, the intake flow rate flowing into the combustion chamber 17 from the first intake port 181 is relative. And the flow rate of intake air flowing from the second intake port 182 into the combustion chamber 17 is relatively reduced, so the swirl flow in the combustion chamber 17 becomes strong. When the degree of opening of the swirl control valve 56 is large, the intake flow rate flowing into the combustion chamber 17 from each of the first intake port 181 and the second intake port 182 becomes substantially even, so the swirl flow in the combustion chamber 17 is weak. Become. When the swirl control valve 56 is fully opened, no swirl flow occurs. The swirl flow circulates in the counterclockwise direction in FIG. 3 as indicated by the arrow (see also the white arrow in FIG. 2).

  An exhaust passage 50 is connected to the other side of the engine 1. The exhaust passage 50 is in communication with the exhaust port 19 of each cylinder 11. The exhaust passage 50 is a passage through which the exhaust gas discharged from the combustion chamber 17 flows. The upstream portion of the exhaust passage 50 constitutes an independent passage which branches for each cylinder 11, although detailed illustration is omitted. The upstream end of the independent passage is connected to the exhaust port 19 of each cylinder 11.

  The exhaust passage 50 is provided with an exhaust gas purification system having a plurality of catalytic converters. The upstream catalytic converter, which is not shown, is disposed in the engine room. The upstream catalytic converter includes a three-way catalyst 511 and a GPF (Gasoline Particulate Filter) 512. The downstream catalytic converter is disposed outside the engine room. The downstream catalytic converter has a three-way catalyst 513. The exhaust gas purification system is not limited to the configuration of the illustrated example.

  An EGR passage 52 constituting an external EGR system is connected between the intake passage 40 and the exhaust passage 50. The EGR passage 52 is a passage for recirculating a part of the burned gas to the intake passage 40. The upstream end of the EGR passage 52 is connected between the upstream catalytic converter and the downstream catalytic converter in the exhaust passage 50. The downstream end of the EGR passage 52 is connected to the upstream of the turbocharger 44 in the intake passage 40.

  A water-cooled EGR cooler 53 is disposed in the EGR passage 52. The EGR cooler 53 is configured to cool the burned gas. An EGR valve 54 is also disposed in the EGR passage 52. The EGR valve 54 is configured to adjust the flow rate of the burnt gas flowing through the EGR passage 52. By adjusting the opening degree of the EGR valve 54, it is possible to adjust the reflux amount of the cooled burned gas, that is, the external EGR gas.

  In this configuration example, the EGR system 55 includes an external EGR system configured to include the EGR passage 52 and the EGR valve 54, and an interior configured to include the intake electric motor S-VT 23 and the exhaust motor S-VT 24 described above. And an EGR system.

  As shown in FIG. 5, the cooling device 71 of the engine 1 includes a main circuit 71A (main cooling unit) and a sub circuit 71B (sub cooling unit). The main circuit 71A and the sub circuit 71B are independent of each other. That is, the refrigerant (cooling water) does not move back and forth between the main circuit 71A and the sub circuit 71B.

  The main circuit 71A has a main radiator 72 that cools the refrigerant using traveling wind, and a variable displacement water pump 74 that supplies the engine body 100 with the refrigerant cooled by the main radiator 72. The water pump 74 is driven by the engine 1. The refrigerant supplied to the engine main body 100 cools each part of the engine main body 10 and then is discharged from the engine main body 100 and returns to the main radiator 72.

  Similar to the main radiator 72, the sub circuit 71B includes a sub radiator 75 for cooling the refrigerant using traveling air, and an electric water pump 76 for supplying the refrigerant cooled by the sub radiator 75 to the intercooler 46. ing. The refrigerant supplied to the intercooler 46 cools the gas passing through the intercooler 46, and then is discharged from the intercooler 46 and returns to the sub radiator 75.

  The refrigerant flowing through the main circuit 71A passes through the inside of the engine body 100. The refrigerant flowing through the sub circuit 71B does not pass through the inside of the engine body 100. Therefore, the refrigerant flowing through the sub circuit 71B is less affected by the temperature of the engine body 100 than the refrigerant flowing through the main circuit 71A. Therefore, the subcircuit 71 can effectively cool the intercooler 46 in a state independent of the engine body 100.

  The engine 1 includes an ECU (Engine Control Unit) 10. The ECU 10 is a well-known microcomputer-based controller, and as shown in FIG. 4, a central processing unit (CPU) 101 that executes a program and, for example, a random access memory (RAM) or a ROM. A memory 102 configured by (Read Only Memory) to store programs and data, and an input / output bus 103 for inputting / outputting an electric signal are provided. The ECU 10 is an example of a control unit.

  As shown in FIGS. 1 and 4, various sensors SW <b> 1 to SW <b> 17 are connected to the ECU 10. The sensors SW1 to SW17 output detection signals to the ECU 10. The sensors include the following sensors.

  That is, an air flow sensor SW1 disposed downstream of the air cleaner 41 in the intake passage 40 and detecting the flow rate of fresh air flowing through the intake passage 40; a first intake temperature sensor SW2 detecting the temperature of the fresh air; The first pressure sensor SW3 disposed downstream of the connection position of the EGR passage 52 at 40 and upstream of the turbocharger 44 and detecting the pressure of the gas flowing into the turbocharger 44; A second intake air temperature sensor SW4 disposed downstream of the engine 44 and upstream of the connection position of the bypass passage 47 and detecting the temperature of the gas flowing out of the turbocharger 44, attached to the surge tank 42, and A second pressure sensor SW5 for detecting the pressure of gas downstream of the feeder 44, attached to the cylinder head 13 corresponding to each cylinder 11, and A finger pressure sensor SW6 for detecting the pressure in the burning chamber 17, an exhaust temperature sensor SW7 disposed in the exhaust passage 50 and detecting the temperature of the exhaust gas discharged from the combustion chamber 17, upstream of the catalytic converter upstream in the exhaust passage 50 A linear O2 sensor SW8 disposed in the exhaust gas for detecting the oxygen concentration in the exhaust gas, a lambda O2 sensor SW9 disposed downstream of the three-way catalyst 511 in the upstream catalytic converter and detecting the oxygen concentration in the exhaust gas Water temperature sensor SW10 attached to 1 and detecting the temperature of the cooling water, crank angle sensor SW11 attached to the engine 1 and detecting the rotation angle of the crankshaft 15, attached to the accelerator pedal mechanism and operating the accelerator pedal Accelerator opening sensor SW1 that detects the accelerator opening corresponding to the amount , An intake cam angle sensor SW13 attached to the engine 1 for detecting the rotation angle of the intake camshaft, an exhaust cam angle sensor SW14 attached to the engine 1 for detecting the rotation angle of the exhaust camshaft, disposed in the EGR passage 52 And an EGR differential pressure sensor SW15 that detects a differential pressure upstream and downstream of the EGR valve 54, and a fuel pressure sensor SW16 that is attached to the common rail 64 of the fuel supply system 61 and that detects the pressure of the fuel supplied to the injector 6. It is. The third intake temperature sensor SW17 is disposed near the downstream side of the surge tank 42 and detects the temperature of the gas flowing out of the surge tank 42 and introduced into the combustion chamber 17.

  The ECU 10 determines the operating state of the engine 1 based on these detection signals and calculates the control amount of each device. The ECU 100 controls the control signal related to the calculated control amount as the injector 6, spark plug 25, intake motor S-VT 23, exhaust motor S-VT 24, fuel supply system 61, throttle valve 43, EGR valve 54, supercharger 44. The electromagnetic clutch 45, the air bypass valve 48, and the swirl control valve 56 are output.

  For example, the ECU 10 adjusts the opening pressure of the air bypass valve 48 based on the front-rear differential pressure of the turbocharger 44 obtained from the detection signals of the first pressure sensor SW3 and the second pressure sensor SW5, to thereby obtain the supercharging pressure. adjust. In addition, the ECU 10 adjusts the opening degree of the EGR valve 54 based on the differential pressure across the EGR valve 54 obtained from the detection signal of the EGR differential pressure sensor SW15, whereby the amount of external EGR gas introduced into the combustion chamber 17 Adjust the

(Operating area of engine)
FIG. 6 illustrates the operating range map 501, 502 of the engine 1. The operating area map 501, 502 of the engine 1 is determined by the load and the rotational speed, and is divided into five areas for high and low of the load and high and low of the rotational speed. Specifically, the five regions include idle operation and include a low load region (1) -1 (corresponding to the "low load side region") that extends to low and medium rotation regions, and a load more than the low load region. Medium load area (1) -2 (corresponds to "high load side area") which spreads to high and low rotation and medium rotation areas, and in a region where the load is higher than middle load region (1) -2, and full open load Medium rotation area (2) of high load area including low speed area (3) whose rotation speed is lower than middle rotation area (2) in high load area, and low load area (1) -1, medium load area (1) -2, a high load medium rotation area (2), and a high speed low rotation area (4) having a rotational speed higher than that of the high load low rotation area (3).

  Here, when the low rotation region, the middle rotation region, and the high rotation region are all divided into three regions of the low rotation region, the middle rotation region, and the high rotation region in the rotational speed direction, respectively. The low rotation region, the middle rotation region, and the high rotation region may be used. In the example of FIG. 6, the number of rotations less than N1 is low, the number of rotations N2 or more is high, and the number of rotations N1 or more and N2 is medium. The rotational speed N1 may be, for example, about 1200 rpm, and the rotational speed N2 may be, for example, about 4000 rpm.

  In FIG. 6, the operation area maps 501 and 502 of the engine 1 are drawn in two parts for ease of understanding. A map 501 shows the state of air-fuel mixture and the form of combustion in each region. The map 502 shows a supercharging region where the supercharger 44 is driven and a non-supercharging region where the supercharger 44 is not driven. The two-dot chain line in FIG. 6 indicates the load-load line (Road-Load Line) of the engine 1.

  The engine 1 performs SPCCI combustion in a low load range (1) -1, a medium load range (1) -2, and a high load medium rotation range (2) mainly for the purpose of improving the fuel efficiency and the exhaust gas performance. I do. The engine 1 also performs SI combustion in other areas, specifically, in a high load low rotation area (3) and a high rotation area (4). Hereinafter, the operation of the engine 1 in each region will be described with reference to the fuel injection timing and the ignition timing shown in FIG.

(Low load area (1) -1)
When the engine 1 is operating in the low load range (1) -1, the engine 1 performs SPCCI combustion in which SI combustion and CI combustion are combined.

  The reference numeral 601 in FIG. 7 indicates the fuel injection timing (reference numerals 6011, 6012) and the ignition timing (reference numeral 6013) when the engine 1 is operating in the operation state 601 shown in FIG. 6 in the low load region (1) -1. An example of each of the combustion waveforms (that is, waveforms showing changes in heat release rate with respect to crank angle, reference numeral 6014) is shown.

  In the SPCCI combustion, the ignition plug 25 forcibly ignites the mixture in the combustion chamber 17 so that the mixture causes SI combustion by flame propagation, and the heat of SI combustion generates heat in the combustion chamber 17. As the temperature rises and the pressure in the combustion chamber 17 rises due to flame propagation, the unburned air-fuel mixture performs CI combustion by self-ignition.

  By adjusting the amount of heat generation of SI combustion, it is possible to absorb temperature variations in the combustion chamber 17 before the start of compression. Even if the temperature in the combustion chamber 17 before the start of compression varies, for example, if the start timing of SI combustion is adjusted by adjusting the ignition timing, it is possible to control the timing of the self-ignition.

  When performing the SPCCI combustion, the spark plug 25 ignites the air-fuel mixture at a predetermined timing near the compression top dead center, whereby combustion by flame propagation starts. Heat generation during SI combustion is milder than heat generation during CI combustion. Therefore, the waveform of the heat release rate has a relatively small rising slope. Although not shown, pressure fluctuation (dp / dθ) in the combustion chamber 17 also becomes gentler during SI combustion than during CI combustion.

  As the temperature and pressure in the combustion chamber 17 increase due to SI combustion, the unburned mixture self-ignites. In the example of FIG. 7, the slope of the heat release rate waveform changes from small to large at the timing of self-ignition. That is, the waveform of the heat release rate has an inflection point at the timing when the CI combustion starts.

  After the start of CI combustion, SI combustion and CI combustion are performed in parallel. The rate of heat release is relatively large because CI combustion generates heat more than SI combustion. However, since the CI combustion is performed after the compression top dead center, the piston 3 is lowered by motoring. It is avoided that the slope of the heat release rate waveform becomes too large due to the CI combustion. Dp / dθ at the time of CI combustion also becomes relatively mild.

  Although dp / dθ can be used as an index representing combustion noise, as described above, SPCCI combustion can reduce dp / dθ, thereby making it possible to avoid combustion noise becoming too large. . Combustion noise can be reduced to an acceptable level or less.

  By the completion of the CI combustion, the SPCCI combustion is ended. CI combustion has a shorter combustion period than SI combustion. SPCCI combustion has an earlier combustion finish timing than SI combustion. In other words, SPCCI combustion can bring the combustion end timing during the expansion stroke closer to the compression top dead center. SPCCI combustion is more advantageous for improving the fuel consumption performance of the engine 1 than SI combustion.

  In order to improve the fuel consumption performance of the engine 1, the EGR system 55 introduces EGR gas into the combustion chamber 17 when the engine 1 is operating in the low load range (1) -1.

  In addition, when the engine 1 is operating in the low load range (1) -1, a strong swirl flow is formed in the combustion chamber 17. The swirl flow is strong at the outer peripheral portion of the combustion chamber 17 and weak at the central portion. The swirl control valve (SCV) 56 is a predetermined opening on the fully closed or closed side. As described above, since the intake port 18 is a tumble port, an oblique swirl flow having a tumble component and a swirl component is formed in the combustion chamber 17.

  When the engine 1 operates in the low load range (1) -1, the swirl ratio is 2 or more, preferably 4 or more. Here, when the swirl ratio is defined, the “swirl ratio” is a value obtained by dividing the value obtained by measuring and integrating the intake flow lateral angular velocity for each valve lift by the engine angular velocity.

  The swirl ratio can be adjusted by the opening degree of the swirl control valve 56. For example, in the engine 1, when the swirl control valve 56 is fully open, the swirl ratio is about 6. For example, in order to set the swirl ratio to 4 or more and 6 or less, the opening degree of the swirl control valve 56 may be adjusted in a range where the opening ratio is 0 to 15%.

  When the engine 1 operates in the low load range (1) -1, the air-fuel ratio (A / F) of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio in the entire combustion chamber 17. That is, the excess air ratio λ of the air-fuel mixture exceeds 1 in the entire combustion chamber 17. More specifically, the A / F of the mixture in the entire combustion chamber 17 is 30 or more. The excess air ratio immediately before the mixture starts combustion is 2 or more. By doing this, the generation of RawNOx can be suppressed, and the exhaust gas performance can be improved.

  When the engine 1 operates in the low load range (1) -1, the mixture is stratified between the central portion and the outer peripheral portion in the combustion chamber 17. The fuel concentration of the air-fuel mixture in the central portion is higher than the fuel concentration in the outer peripheral portion. Specifically, the A / F of the air-fuel mixture in the central portion is 20 or more and 35 or less, and the A / F of the air-fuel mixture in the outer peripheral portion is 35 or more and 50 or less. The value of the air-fuel ratio is the value of the air-fuel ratio at the time of ignition which corresponds to the time immediately before the mixture starts combustion, and the same applies to the following description.

  When the engine 1 operates in the low load range (1) -1, the injector 6 basically injects fuel into the combustion chamber 17 during the intake stroke and during the compression stroke (reference numeral 6011, 6012). The fuel injected during the intake stroke diffuses throughout the combustion chamber 17 until the ignition timing. The fuel injected during the intake stroke forms a mixture of the central portion and the outer peripheral portion. The fuel injected during the compression stroke is transported to the vicinity of the spark plug 25 in the central portion of the combustion chamber 17 by the swirl flow, because the time to the ignition timing is short. The fuel injected during the compression stroke forms an air-fuel mixture in the center along with part of the fuel injected during the intake stroke. The mixture is stratified in the central portion and the outer peripheral portion of the combustion chamber 17.

  After the end of the fuel injection, the spark plug 25 ignites the mixture in the central portion of the combustion chamber 17 at a predetermined timing before compression top dead center (reference numeral 6013). Since the air-fuel mixture in the central portion has a relatively high fuel concentration, the ignitability is improved and SI combustion by flame propagation is stabilized. By stabilizing SI combustion, CI combustion starts at an appropriate timing. In SPCCI combustion, the controllability of CI combustion is improved. As a result, when the engine 1 operates in the low load range (1) -1, both suppression of the generation of combustion noise and improvement of the fuel efficiency performance by shortening the combustion period are compatible.

  In the low load range (1) -1, the engine 1 leans the air-fuel mixture to the stoichiometric air fuel ratio to perform SPCCI combustion, so the low load range (1) -1 can be called "SPCCI lean range" .

(Medium load area (1) -2)
Even when the engine 1 is operating in the medium load range (1) -2, the engine 1 performs SPCCI combustion as in the low load range (1) -1.

  The reference numeral 602 in FIG. 7 indicates the fuel injection timing (reference numerals 6021 and 6022) and the ignition timing (reference numeral 6023) when the engine 1 is operating in the operation state 602 shown in FIG. And combustion waveforms (reference numeral 6024).

  The EGR system 55 introduces EGR gas into the combustion chamber 17 when the operating state of the engine 1 is in the medium load range (1) -2.

  Further, when the engine 1 is operated in the medium load range (1) -2, the swirl ratio is 2 or more, preferably 4 or more in the combustion chamber 17 as in the low load range (1) -1. Strong swirl flow is formed. The swirl control valve (SCV) 56 is a predetermined opening on the fully closed or closed side. Since the turbulent energy in the combustion chamber 17 is increased by intensifying the swirl flow, the SI combustion flame propagates rapidly when the engine 1 is operated in the medium load range (1) -2, and the SI combustion is performed. Is stabilized. The stability of the SI combustion improves the controllability of the CI combustion. By optimizing the timing of the CI combustion in the SPCCI combustion, it is possible to suppress the generation of combustion noise and to improve the fuel consumption performance. In addition, variation in torque between cycles can be suppressed.

  When the engine 1 operates in the medium load range (1) -2, the air-fuel ratio (A / F) of the air-fuel mixture is the stoichiometric air-fuel ratio (A / F = 14.7) in the entire combustion chamber 17. The excess air ratio immediately before the mixture starts combustion is 1 or less. As the three-way catalyst purifies the exhaust gas discharged from the combustion chamber 17, the exhaust gas performance of the engine 1 is improved. The A / F of the mixture may be made to fall within the purification window of the three-way catalyst. Therefore, the excess air ratio λ of the mixture may be 1.0 ± 0.2.

  When the engine 1 is operating in the operating state 602, fuel injection (code 6021) in the intake stroke and fuel injection (code 6022) in the compression stroke are performed. By performing the injection 6021 during the intake stroke, the fuel can be distributed substantially uniformly in the combustion chamber 17. By performing the injection 6022 during the compression stroke, when the load is high in the middle load range (1) -2, the temperature in the combustion chamber 17 is lowered by the latent heat of vaporization of the fuel to prevent abnormal combustion such as knocking . The ratio of the injection amount of the injection 6021 to the injection amount of the injection 6022 may be, for example, 95: 5. In the low load operating condition in the medium load range (1) -2, the injection 6022 may be omitted.

  The fuel-air mixture burns by flame propagation by the spark plug 25 igniting the air-fuel mixture at a predetermined timing before compression top dead center (reference numeral 6023). After the start of combustion by flame propagation, the unburned mixture is self-ignited to burn CI. The fuel injected by the injection 6022 mainly undergoes SI combustion. The fuel injected by the injection 6021 mainly burns CI.

  In the medium load range (1) -2, the engine 1 performs SPCCI combustion with the air-fuel mixture at the theoretical air fuel ratio, so the medium load range (1) -2 can be referred to as "SPCCI λ = 1 range".

(High load medium rotation range (2))
Even when the engine 1 is operating in the high load medium rotation area (2), the engine 1 performs SPCCI combustion as in the low load area (1) -1 and the medium load area (1) -2.

Reference numeral 603 in FIG. 7 indicates the fuel injection timing (reference numerals 6031 and 6032) and ignition when the engine 1 is operated in the low-load operation state 603 shown in FIG. 6 in the high load medium rotation region (2). An example of each of the timing (reference numeral 6033) and the combustion waveform (reference numeral 6034) is shown.
The reference numeral 604 in FIG. 7 indicates the fuel injection timing (reference numeral 6041) and the ignition timing (when the engine 1 is operating in the high-load operation state 604 shown in FIG. An example of each of a code | symbol 6042) and a combustion waveform (code | symbol 6043) is shown.

  The EGR system 55 introduces EGR gas into the combustion chamber 17 when the operating state of the engine 1 is in the high load medium rotation region (2). The engine 1 reduces the amount of EGR gas as the load increases. At full open load, the EGR gas should be zero.

  In addition, even when the engine 1 is operated in the high load medium rotation area (2), the swirl ratio is 2 or more, preferably 4 or more in the combustion chamber 17 as in the low load area (1) -1. Strong swirl flow is formed. The swirl control valve (SCV) 56 is a predetermined opening on the fully closed or closed side.

  When the engine 1 is operated in the high load medium rotation region (2), the air fuel ratio (A / F) of the mixture is richer than the stoichiometric air fuel ratio or the stoichiometric air fuel ratio in the entire combustion chamber 17 (that is, The excess air ratio λ of the mixture is λ ≦ 1).

  When the engine 1 operates in the low rotation speed operating state 603, the injector 6 injects fuel in the intake stroke (reference numeral 6031) and injects fuel at the end of the compression stroke (reference numeral 6032). The ratio of the injection amount of the injection 6031 to the injection amount of the injection 6032 may be, for example, 95: 5.

  The spark plug 25 ignites the mixture in the central portion of the combustion chamber 17 near the compression top dead center (reference numeral 6033). The spark plug 25 ignites, for example, after compression top dead center. Since the spark plug 25 is disposed at the central portion of the combustion chamber 17, the mixture at the central portion starts SI combustion by flame propagation by the ignition of the spark plug 25. The flames of the SI combustion propagate along the strong swirl flow in the combustion chamber 17 in the circumferential direction. At a predetermined position in the circumferential direction on the outer peripheral portion of the combustion chamber 17, the unburned mixture is compression-ignited and CI combustion starts (see a combustion waveform 6034).

  When the engine 1 operates in the high revolution side operating state 604, the injector 6 starts fuel injection in the intake stroke (reference numeral 6041).

  The injection 6041 starting in the intake stroke may start fuel injection in the first half of the intake stroke. The end of injection 6041 may be in the compression stroke beyond the intake stroke. By setting the injection start of the injection 6041 to the first half of the intake stroke, an air-fuel mixture for CI combustion is formed in the outer peripheral portion of the combustion chamber 17 and an air-fuel mixture for SI combustion in the central portion of the combustion chamber 17 be able to. Since the number of revolutions is high and abnormal combustion is unlikely to occur, the post-stage injection can be omitted.

  The spark plug 25 ignites the mixture in the central portion of the combustion chamber 17 near the compression top dead center (reference numeral 6042). The spark plug 25 ignites, for example, after compression top dead center. Thereby, SPCCI combustion is performed (see combustion waveform 6043).

  Since the engine 1 performs SPCCI combustion by enriching the air-fuel mixture to the theoretical air fuel ratio or the theoretical air fuel ratio in the high load middle rotation region (2), the high load middle rotation region (2) is “SPCCI λ ≦ 1 region” It can be called.

(High load low rotation area (3))
When the rotational speed of the engine 1 is low, the time required for the crank angle to change by 1 ° becomes long. If fuel is injected into the combustion chamber 17 in the first half of the intake stroke or compression stroke, for example, in the high load low rotation region (3), as in the high load medium rotation region (2), the fuel reaction progresses too much. May cause an early ignition. When the engine 1 is operating in the high load low rotation range (3), it becomes difficult to perform the above-described SPCCI combustion.

  Therefore, when the engine 1 is operating in the high load low rotation range (3), the engine 1 performs SI combustion, not SPCCI combustion.

  The reference numeral 605 in FIG. 7 indicates the fuel injection timing (reference numerals 6051 and 6052) and the ignition timing (reference numeral 6053) when the engine 1 is operating in the operation state 605 shown in FIG. And combustion waveforms (symbol 6054) are shown.

  The EGR system 55 introduces EGR gas into the combustion chamber 17 when the operating condition of the engine 1 is in the high load low rotation region (3). The engine 1 reduces the amount of EGR gas as the load increases. At full open load, the EGR gas should be zero.

  When the engine 1 is operating in the high load low rotation range (3), the air-fuel ratio (A / F) of the air-fuel mixture is the stoichiometric air-fuel ratio (A / F = 14.7) in the entire combustion chamber 17 is there. The A / F of the mixture may be made to fall within the purification window of the three-way catalyst. Therefore, the excess air ratio λ of the mixture may be 1.0 ± 0.2. By setting the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio, the fuel efficiency performance is improved in the high load low rotation region (3). When the engine 1 operates in the high load low rotation range (3), the fuel concentration of the entire mixture in the combustion chamber 17 is 1 or less at the excess air ratio λ and in the high load middle rotation range (2) The excess air ratio λ may be greater than the excess air ratio λ, preferably in the high load medium rotation region (2).

  When the engine 1 operates in the high load low rotation range (3), the injector 6 is in the intake stroke and in a period from the end of the compression stroke to the beginning of the expansion stroke (hereinafter, this period is referred to as a retard period) At each timing, fuel is injected into the combustion chamber 17 (reference numerals 6051 and 6052). The final stage of the compression process may be the final stage when the compression process is divided into three equal parts: initial, middle, and final. Further, the initial stage of the expansion stroke may be an initial stage when the expansion stroke is divided into three equal parts: initial, middle and final.

  By injecting the fuel twice, it is possible to reduce the amount of fuel injected in the retard period. By injecting the fuel during the intake stroke (reference numeral 6051), the formation time of the air-fuel mixture can be sufficiently secured. In addition, by injecting fuel during the retard period (reference numeral 6052), the flow in the combustion chamber 17 can be enhanced immediately before ignition, which is advantageous for stabilization of SI combustion. This form of fuel injection is particularly effective when the geometric compression ratio of the engine 1 is low.

  After injecting the fuel, the spark plug 25 ignites the air-fuel mixture at a timing near the compression top dead center (reference numeral 6053). The spark plug 25 may perform ignition, for example, after compression top dead center. The mixture performs SI combustion in the expansion stroke. Since SI combustion starts in the expansion stroke, CI combustion does not start (see combustion waveform 6054).

  In the high load and low rotation region (3), the engine 1 injects fuel during the retard period from the end of the compression stroke to the beginning of the expansion stroke to perform SI combustion. Therefore, the high load and low rotation region (3) It can be called "SI area".

(High rotation area (4))
When the rotational speed of the engine 1 is high, the time required for the crank angle to change by 1 ° becomes short. Therefore, for example, in the high rotation region in the high load region, as described above, performing the split injection during the compression stroke makes it difficult to perform stratification of the mixture in the combustion chamber 17. When the rotation speed of the engine 1 becomes high, it becomes difficult to perform the above-described SPCCI combustion.

  Therefore, when the engine 1 is operating in the high rotation range (4), the engine 1 performs not the SPCCI combustion but the SI combustion. The high rotation region (4) extends over the entire load direction from low load to high load.

  Reference numeral 606 in FIG. 7 indicates the fuel injection timing (reference numeral 6061) and the ignition timing (reference numeral 6062) when the engine 1 is operating in the operation state 606 shown in FIG. 6 in the high rotation range (4). An example of each of the combustion waveforms (symbol 6063) is shown.

  The EGR system 55 introduces EGR gas into the combustion chamber 17 when the operating state of the engine 1 is in the high rotation region (4). The engine 1 reduces the amount of EGR gas as the load increases. At full open load, the EGR gas should be zero.

  When the engine 1 is operated in the high rotation range (4), the swirl control valve (SCV) 56 is fully opened. No swirl flow is generated in the combustion chamber 17, and only the tumble flow is generated. By making the swirl control valve 56 fully open, it is possible to increase the filling efficiency in the high rotation area (4) and to reduce the pump loss.

  When the engine 1 operates in the high rotation range (4), the air-fuel ratio (A / F) of the air-fuel mixture is basically the stoichiometric air-fuel ratio (A / F = 14.7) in the entire combustion chamber 17 It is. The excess air ratio λ of the mixture may be 1.0 ± 0.2. The excess air ratio λ of the air-fuel mixture may be less than 1 in the high load region including the full open load in the high rotation region (4).

  When the engine 1 operates in the high rotation range (4), the injector 6 starts fuel injection in the intake stroke. The injector 6 injects the fuel at one time. In the operating state 605, the load on the engine 1 is high, so the amount of fuel injection is large. The fuel injection period changes according to the fuel injection amount. By starting fuel injection during the intake stroke, it is possible to form a homogeneous or substantially homogeneous mixture in the combustion chamber 17. In addition, when the rotation speed of the engine 1 is high, the vaporization time of the fuel can be secured as long as possible, so it is possible to reduce the unburned loss and suppress the generation of soot.

  The ignition plug 25 ignites the air-fuel mixture at an appropriate timing before compression top dead center after the end of fuel injection (reference numeral 6062).

  In the high rotation region (4), the engine 1 starts fuel injection in the intake stroke to perform SI combustion, so the high rotation region (4) can be called an “intake-SI region”.

(Operating a turbocharger)
As shown in the lower diagram 502 of FIG. 6, a part of the low load range (1) -1 and a part of the medium load range (1) -2 on the low load and low rotation side in the entire operating range of the engine 1 In part 1, the supercharger 44 is turned off, that is, not driven, and the operation of the engine 1 is not charged (this non-supercharged area corresponds to the "predetermined area").

  Specifically, in the low rotation region in the low load region (1) -1, the supercharger 44 is turned off. In the high rotation side region in the low load region (1) -1, the supercharger 44 is turned on in order to secure the necessary intake charge corresponding to the increase in the rotational speed of the engine 1 Increase the boost pressure. Further, the supercharger 44 is turned off in the low load low rotation side region in the medium load region (1) -2, and the fuel injection amount in the high load side region in the medium load region (1) -2. The supercharger 44 is turned on in order to secure the necessary intake charge amount corresponding to the increase of the engine speed, and it is necessary to cope with the increase in the rotational speed of the engine 1 in the high rotation side region. The turbocharger 44 is turned on to ensure the intake charge.

  In each of the high load and medium speed range (2), the high load and low speed range (3), and the high speed range (4), the supercharger 44 is turned on over the entire area (S / C ON Reference), the operation of the engine 1 is supercharged.

  FIG. 8 shows a flow in which the ECU 10 switches the operation of the engine 1 between the supercharged state and the non-supercharged state. The ECU 10 reads the signals of the sensors SW1 to SW17 (step S1). The ECU 10 determines the operating range of the engine 1 and determines whether there is a supercharging request (step S2). As a result, when the ECU 10 determines that supercharging is required (YES in step S2), the electromagnetic clutch 45 is connected, and the air bypass valve 48 (ABV) is adjusted on the closing side to adjust the opening degree. , Supercharging operation is performed (step S3).

  FIG. 9 shows a supercharging system 49 at the time of supercharging operation. The air bypass valve 48 (ABV) is held almost closed. When the electromagnetic clutch 45 is connected and the supercharger 44 is driven, the gas on the upstream side of the supercharger 44 is drawn into the supercharger 44 and is pressurized downstream of the supercharger 44. It is discharged to the side. The pressurization raises the temperature of the gas, but after being cooled by the intercooler 46 and adjusted to an appropriate temperature, it flows into the surge tank 42.

  In order to adjust the supercharging pressure of the gas introduced into the combustion chamber 17, the opening degree of the air bypass valve 48 is adjusted. As a result, part of the gas flowing into the surge tank 42 flows back to the upstream of the turbocharger 44 through the bypass passage 47. In the supercharging state, the downstream side of the supercharger 44 in the intake passage 40 is held at a higher pressure than the upstream side of the supercharger 44 (statically or dynamically, the first pressure sensor SW3 The pressure detected by the second pressure sensor SW5 is higher than the pressure detected by

  If the ECU 10 determines that there is no supercharging request (NO in step S2), the connection of the electromagnetic clutch 45 is shut off, and the air bypass valve 48 (ABV) is adjusted to the same level as full opening full opening. Thus, the non-supercharging operation (natural intake) is performed (step S4).

  FIG. 10 shows a supercharging system 49 at the time of non-supercharging operation. The air bypass valve 48 is adjusted to an opening degree at a level equivalent to full opening or full opening. The supercharger 44 does not operate (rotate) because the connection of the electromagnetic clutch 45 is cut off. Gas flowing upstream of the turbocharger 44 in the intake passage 40 bypasses the turbocharger 44 and the intercooler 46 and flows into the surge tank 42 through the bypass passage 47. Since the bypass passage 47 is in communication with both the upstream and downstream sides of the turbocharger 44 in the intake passage 40, the gas passes through the bypass passage 47 without resistance. In the non-supercharged state, both the upstream side and the downstream side of the turbocharger 44 in the intake passage 40 are statically held at the same pressure (the pressure detected by the first pressure sensor SW3, and the second pressure sensor Almost the same as the pressure detected by SW5).

(The influence of outside temperature during non-supercharged operation)
During the supercharging operation, the intercooler 46 regulates the temperature of the gas introduced into the combustion chamber 17. However, during the non-supercharging operation, the gas is directly introduced into the combustion chamber, so the temperature of the gas Depends on the temperature of Therefore, if the outside air temperature becomes excessively high, the temperature of the combustion chamber may deviate from the appropriate range, and appropriate combustion may not be realized.

  In particular, in this engine 1, SPCCI combustion is performed in a predetermined range of low load range (1) -1 and medium load range (1) -2 in which non-supercharging operation is performed, so the temperature of the combustion chamber is appropriate. Should be kept in range. Specifically, if the compression end temperature is too high, control of the CI combustion by SI combustion becomes unstable, such as the timing of starting the CI combustion becoming earlier, which may lead to problems such as premature ignition.

  Therefore, the engine 1 is configured to be able to execute prerotation control and forced rotation control so that the influence of the outside air temperature can be suppressed and the temperature of the combustion chamber can be maintained in an appropriate range even in such a predetermined region. ing.

  Specifically, when the temperature of the combustion chamber can be maintained in an appropriate range by natural intake, the non-supercharging operation is performed as it is. On the other hand, when the outside air temperature becomes high and the temperature (intake air temperature) of the intake air introduced into the combustion chamber 17 becomes high depending on natural intake and the temperature of the combustion chamber can not be maintained in an appropriate range (the outside air temperature is predetermined Pre-rotation control or forced rotation control is executed, and cooling of the intake air is performed so that the temperature of the combustion chamber can be maintained in an appropriate range.

(Pre-rotation control)
FIG. 11 shows the supercharging system 49 at the time of prerotation control. At the time of execution of prerotation control, the ECU 10 maintains the air bypass valve 48 in a non-supercharged state so that the supercharger 44 is not driven so that the supercharger 44 is operated by the pressure difference between the upstream and downstream thereof. Control to close.

  By controlling the air bypass valve 48 from the substantially full open state to the closing side, the flow passage cross-sectional area of the bypass passage 47 is reduced, and the flow passage resistance of the bypass passage 47 is increased. As a result, a pressure difference occurs between the upstream and the downstream of the turbocharger 44, and the turbocharger 44 rotates, more specifically, the rotor of the turbocharger 44 rotates (pre-rotation) based on the pressure difference. Once the supercharger 44 starts pre-rotation, since the inertial force acts, the super-charger 44 can be pre-rotated stably even with a relatively weak differential pressure thereafter.

  The pre-rotation of the supercharger 44 causes a portion of the gas flowing on the upstream side of the supercharger 44 in the intake passage 40 to be drawn into the supercharger 44 as indicated by a broken line in FIG. The gas drawn into the turbocharger 44 passes through the intercooler 46 and flows into the surge tank 42. The gas is cooled by passing through the intercooler 46. On the other hand, the gas passing through the bypass passage 47 is not cooled. The gas introduced into the combustion chamber 17 is cooled according to the flow rate of the gas passing through the intercooler 46.

  FIG. 12 shows the relationship between the ratio of the flow rate of gas passing through the intercooler 46 to the flow rate of gas passing through the bypass passage 47 (hereinafter simply referred to as “flow rate ratio”) and the gas temperature in the surge tank 42. An area S1 shown in the figure is an area of the gas temperature (hereinafter referred to as "in-surge tank temperature") in the surge tank 42 capable of maintaining the temperature of the combustion chamber in an appropriate range.

  In the same figure, as indicated by a solid line including a plurality of triangular marks, the temperature in the surge tank is reduced as the flow rate ratio increases. The temperature in the surge tank is substantially equal to the temperature of the gas introduced into the combustion chamber 17. That is, if the temperature in the surge tank is adjusted through the flow rate ratio, the temperature of the gas introduced into the combustion chamber 17 can be kept within a predetermined appropriate range.

  In order to adjust the flow rate ratio to bring the temperature in the surge tank into an appropriate range, the air bypass valve 48 is adjusted to the closing side when the outside air temperature is high than when it is low. In this configuration example, the ECU 10 controls the air bypass valve 48 so as to gradually close from the fully open state to the fully closed state as the outside air temperature rises, based on the control map.

  Specifically, the ECU 10 acquires the outside air temperature based on the first intake air temperature sensor SW2, and acquires the temperature in the surge tank based on the third intake air temperature sensor SW17. The temperature in the surge tank may be indirectly determined based on the load, engine rotation speed, and various parameters indicating the operating state of the engine 1 and the outside air temperature.

  The ECU 10 stores in advance a control map that relates the temperature in the surge tank and the throttle amount. The ECU 10 determines and adjusts the opening degree of the air bypass valve 48 corresponding to the temperature in the surge tank so that the temperature in the surge tank falls within the appropriate range S1 based on the control map.

  As the air bypass valve 48 is adjusted to the closing side, the flow passage resistance of the bypass passage 47 increases. As a result, the differential pressure between the upstream side and the downstream side of the turbocharger 44 increases, pre-rotation of the turbocharger 44 is promoted, the amount of gas passing through the intercooler 46 increases, and the flow rate ratio also increases. Do. By doing so, the temperature in the surge tank is adjusted to fall within the appropriate range S1. When the pre-rotation control is performed, the pressure detected by the first pressure sensor SW3 and the pressure (dynamic pressure) detected by the second pressure sensor SW5 change according to the opening degree of the air bypass valve 48. However, the pressure difference tends to be larger than that in the normal non-supercharged operation (natural intake) and smaller than that in the supercharged operation.

  In addition, at the time of execution of prerotation control, the opening degree of the throttle valve 43 is adjusted to an opening degree equivalent to full opening or full opening. That is, when the opening degree of the throttle valve 43 is narrowed, there is a possibility that the pump loss may increase when the supercharger 44 is pre-rotated. By maximizing the opening degree of the throttle valve 43, an increase in pump loss can be avoided. The same applies to the execution of the forced rotation control. When the forced rotation control is performed, the opening degree of the throttle valve 43 is adjusted to the full opening or the opening equivalent to the full opening.

(Forced rotation control)
When the outside air temperature is further increased, as indicated by a virtual line in FIG. 12, the temperature in the surge tank may increase, and it may be difficult to keep the temperature in the surge tank within the appropriate range S1 in the cooling by prerotation control. . In such a case, the engine 1 is configured to perform forced rotation control.

  Specifically, when the outside air temperature is equal to or higher than the first temperature TS1 at which the temperature of the combustion chamber can not be maintained in an appropriate range by natural intake, prerotation control is performed, and the temperature of the combustion chamber is also properly adjusted by prerotation control. If the predetermined second temperature TS2 which can not be maintained in the predetermined range is exceeded, forced rotation control is performed (second temperature TS2> first temperature TS1).

  FIG. 13 shows the supercharging system 49 at the time of forced rotation control. At the time of forced rotation control, the supercharger 44 is forcibly driven in a non-supercharged state in which the air bypass valve 48 is opened so that the gas flowing through the intake passage 40 circulates through the bypass passage 47.

  Specifically, the air bypass valve 48 is adjusted to an opening degree at the same level as full opening or full opening. In that state, the supercharger 44 is driven with the electromagnetic clutch 45 connected. As a result, the gas flowing upstream of the turbocharger 44 in the intake passage 40 is drawn into the turbocharger 44. The gas drawn into the turbocharger 44 is cooled through the intercooler 46 and then flows into the surge tank 42.

  Since the bypass passage 47 is in communication with both the upstream side and the downstream side of the turbocharger 44 in the intake passage 40 (statically, the same pressure state), the part other than the part introduced into the combustion chamber 17 The gas flows backward in the bypass passage 47 without resistance and returns to the upstream side of the turbocharger 44 in the intake passage 40. The gas returned to the upstream side of the turbocharger 44 in the intake passage 40 is drawn into the turbocharger 44 again.

  That is, in the supercharging system 49, the gas flowing through the intake passage 40 is circulated repeatedly through the supercharger 44, the intercooler 46, the surge tank 42, and the bypass passage 47. Since the gas passes through the intercooler 46 repeatedly in the circulating process, the gas introduced into the combustion chamber 17 can be effectively cooled. In the case of pre-rotation control, forced rotation control is superior to pre-rotation control in terms of cooling performance because it passes through the intercooler 46 once.

  Therefore, even if it is difficult to properly maintain the intake air temperature in the preliminary rotation control due to the outside air temperature becoming excessively high, the intake air temperature can be properly maintained by performing the forced rotation control. According to the forced rotation control, it is possible to adjust the amount of intake air introduced into the combustion chamber 17 with high accuracy by adjusting the opening degree of the air bypass valve 48 as compared to the case where natural intake is performed. As a result, even when the outside air temperature becomes excessively high, the temperature of the combustion chamber 17 can be maintained in an appropriate range, and stable SPCCI combustion can be realized.

  When forced rotation control is performed, the pressure detected by the first pressure sensor SW3 and the pressure detected by the second pressure sensor SW5 are statically the same pressure, but the driving state of the turbocharger 44 is dynamically It changes according to. However, the pressure difference tends to be larger than that in the normal non-supercharged operation (natural intake) and smaller than that in the supercharged operation.

  The prerotation control and the forced rotation control are performed in predetermined regions across the low load region (1) -1 and the middle load region (1) -2, and the first temperature TS1 and 2) The temperature TS2 is lower in the area (high load side area) located in the medium load area (1) -2 than in the low load area (1) -1 area (low load side area) It has become.

  That is, in the low load side region, the mixture before the start of combustion is in a lean state where the fuel concentration is thin. On the other hand, in the high load side region, the mixture before the start of combustion is in a rich rich state of the fuel concentration. Therefore, since the combustion temperature is higher in the high load side area than in the low load side area, the compression end temperature tends to be higher than in the low load side area. Therefore, when the outside air temperature is high, the temperature of the combustion chamber 17 is more likely to deviate from the appropriate range than the low load side area in the high load side area.

  Therefore, the temperature of the combustion chamber 17 can be reduced by setting the first temperature TS1 and the second temperature TS2 serving as the reference for performing the prerotation control and the forced rotation control to a low value on the high load side compared to the low load side. Deviation from the appropriate range can be avoided more reliably.

  In particular, in the high load side region, it is preferable to perform forced rotation control more positively than pre-rotation control. The low load region and the high load region are both regions of non-supercharging operation, and the amount of intake air introduced into the combustion chamber 17 is relatively small. On the other hand, in the high load side area, since the load is larger than the low load area, the output power is larger than the low load side area. Therefore, as the output power is large, in the high load side area, the influence of the driving load which is increased by driving the supercharger 44 becomes smaller than that in the low load area. Since the drive power of the supercharger 44 can be increased and the circulation amount of intake air can be further increased in the high load side area as the influence of the drive load becomes smaller, execution of forced rotation control causes the intake of the intercooler 46 to be performed. Cooling can be promoted. The intake air temperature can be more stably and properly maintained.

(Effect of engine temperature)
As described above, the intake passage 40 including the supercharging system 49 is incorporated in the engine body 100 so as to be in close contact with the outer surface of the engine body 100 which is heated by combustion in a unitized state.

  Therefore, the gas passing through the intake passage 40 and the bypass passage 47 receives heat generated by the engine body 100 while passing through them. When the temperature of the engine body 100 rises, in the case of forced rotation control in which the gas is repeatedly circulated via the intake passage 40 and the bypass passage 47, the amount of heat received by the gas from the engine significantly increases. As a result, in the forced rotation control, even if the cooling capacity is excellent, an increase in the amount of heat received from the engine body 100 may reduce the substantial cooling capacity. The amount of heat received from the engine may exceed the cooling capacity by forced rotation control, which may cause an adverse effect.

  In contrast, in the prerotation control, the gas cooled by the intercooler 46 is directly introduced into the combustion chamber 17. Therefore, even if the temperature of the engine main body 100 becomes high, its influence is small compared to the forced rotation control, and high cooling performance can be exhibited.

  Therefore, in the engine 1, pre-rotation control and forced rotation control are configured to be switched according to the temperature of the engine body 100.

  Specifically, prerotation control is performed when the temperature of the engine body 100 is equal to or higher than a predetermined reference temperature Te, and forced rotation control is performed when the temperature of the engine body 100 is lower than the reference temperature Te. The reference temperature Te is, for example, a temperature of 90 ° C. or more, and is set in advance in the ECU 10. When the reference temperature Te becomes higher than that, even if forced rotation control is performed, appropriate cooling can not be performed, and the temperature is such that the cooling capacity becomes equal to or less than the pre-rotation control. The ECU 10 obtains the temperature of the engine body 100 from the temperature of the cooling water flowing through the main circuit 71A, which is detected by, for example, the water temperature sensor SW10.

  As described above, according to the temperature of the engine main body 100, in the engine 1, the control can be switched to the control that can appropriately exhibit the cooling capacity, so the intake can be cooled efficiently. As a result, it is possible to adjust the temperature of the combustion chamber 17 at the time of combustion to an appropriate temperature while suppressing the influence of the temperature of the engine body 100.

(Intake cooling control during non-supercharged operation)
FIG. 14 shows an example of the flow of cooling control of intake air during non-supercharging operation. While the non-supercharging operation is being performed, the ECU 10 acquires the outside air temperature based on the detection signal input from the first intake air temperature sensor SW2, and determines whether the outside air temperature is equal to or higher than the first temperature TS1. It is continuously determined (step S11).

  Thus, when the ECU 10 determines that the outside air temperature is not higher than the first temperature TS1 (NO in step S11), the ECU 10 continues and carries out the normal non-supercharging operation (step S12).

  In contrast, when it is determined that the outside air temperature is equal to or higher than the first temperature TS1 (YES in step S11), the ECU 10 executes prerotation control (step S13). Specifically, the electromagnetic clutch 45 is shut off, and the air bypass valve 48 is controlled to close in a non-driven state where mechanical power does not act on the turbocharger 44.

  The ECU 10 also continuously determines whether the outside air temperature is equal to or higher than the second temperature TS2 (step S14). When the ECU 10 determines that the outside air temperature is not the second temperature TS2 or more (NO in step S14), the ECU 10 continues the preliminary rotation control. If the ECU 10 determines that the outside air temperature is not higher than the first temperature TS1 while continuing the preliminary rotation control (NO in step S11), the ECU 10 returns to the normal non-supercharging operation (step S12).

  On the other hand, when the outside air temperature further rises and the ECU 10 determines that the outside air temperature is equal to or higher than the second temperature TS2 (YES in step S14), cooling of the intake air by forced rotation control is performed.

  At this time, the ECU 10 indirectly acquires the temperature of the engine body 100 based on the detection signal input from the water temperature sensor SW 10, and continuously determines whether the temperature of the engine body 100 is equal to or higher than the reference temperature Te. It is determined (step S15).

  Then, when the ECU 10 determines that the temperature of the engine body 100 is equal to or higher than the reference temperature Te (YES in step S15), the proper rotation control can not be performed in the forced rotation control, and the pre-rotation control has more cooling performance. Continue pre-rotation control because it is excellent. If it is prerotation control, since driving resistance is smaller than forced rotation control, it is advantageous also in terms of fuel consumption performance.

  On the other hand, when the ECU 10 determines that the temperature of the engine body 100 is not higher than the reference temperature Te (NO in step S15), forced rotation control is executed (step S16). In the case of forced rotation control, since the intake air can be effectively cooled, the intake air temperature can be returned to an appropriate state in a short time, and the temperature in the combustion chamber at the time of combustion can be appropriately adjusted.

  Then, when the ECU 10 determines that the outside air temperature is not higher than the first temperature TS1 (NO in step S11), the ECU 10 returns to the normal non-supercharging operation (step S12).

<Application Example of Engine 1>
The switching between the prerotation control and the forced rotation control may be performed according to the driver's request for acceleration.

  Specifically, in the predetermined region described above, when the outside temperature is equal to or higher than the first temperature TS1, the preliminary rotation control is performed first, and the forced rotation control is performed when the driver's acceleration request operation is performed. Configure as.

  When forced rotation control is performed, the turbocharger 44 is switched from non-drive to drive. When an impact occurs at the time of the switching, and the impact is transmitted to the driver, the driver may feel discomfort when the driver does not perform the operation. On the other hand, in this configuration, when the outside temperature is equal to or higher than the first temperature TS1 in the predetermined region, prerotation control that cools the intake air in the non-driving state of the turbocharger 44 is performed, and the driver's acceleration request operation is Forced rotation control is performed when it is performed.

  In the case of the prerotation control, the supercharger 44 can be maintained in the non-driven state, so that the intake air can be cooled without making the driver feel discomfort. Then, when the driver performs an acceleration request operation such as stepping on the accelerator, the forced rotation control is executed. If the acceleration request operation is performed, even if an impact is generated by switching the turbocharger 44, the driver recognizes that the impact is due to the operation, so that the driver can be prevented from feeling discomfort.

  FIG. 15 shows an example of the flow of intake air cooling control based on this application example. The basic flow is the same as the flow of FIG. 14, so the same reference numerals are used for the same components, and the description thereof is omitted.

  The ECU 10 continuously determines whether or not the driver has made an acceleration request, for example, from a detection signal input from the accelerator opening sensor SW12 while the prerotation control is being performed (step S20). .

  Then, when there is no acceleration request from the driver (NO in step S20), the ECU 10 continues and executes the prerotation control.

  On the other hand, when the driver requests acceleration (YES in step S20), cooling of intake air is performed by forced rotation control, and forced rotation control is performed unless the temperature of engine body 100 is equal to or higher than reference temperature Te. (Step S16).

  Even if the supercharger 44 is switched from non-drive to drive by the execution of forced rotation control and an impact occurs, the driver recognizes that it is an impact due to the acceleration request operation performed by the driver. You can avoid feeling. And, in the case of the forced rotation control, since the intake air can be effectively cooled, the intake air temperature can be returned to an appropriate state in a short time, and the temperature of the combustion chamber at the time of combustion can be appropriately adjusted.

1 engine 3 piston 6 injector (fuel injection part)
10 ECU (control unit)
17 combustion chamber 25 spark plug (ignition unit)
40 intake passage 44 supercharger 45 electromagnetic clutch (switching unit)
46 Intercooler 47 Bypass passage 48 Air bypass valve (flow control valve)

Claims (6)

An intake passage connected to the combustion chamber of the engine;
A supercharger disposed in the intake passage;
A switching unit that switches between driving and non-driving of the turbocharger;
An intercooler disposed downstream of the supercharger in the intake passage;
A bypass passage connecting the upstream of the turbocharger in the intake passage and the downstream of the intercooler;
A flow control valve disposed in the bypass passage;
A control unit connected to the switching unit and the flow control valve and outputting a control signal to the switching unit and the flow control valve;
Equipped with
Forced rotation control for driving the supercharger in a state in which the flow control valve is opened so that the gas flowing in the intake passage circulates through the bypass passage in a non-supercharged state; Pre-rotation control to control the supercharger to close the flow control valve in the non-driven state so that the supercharger is operated by the pressure difference between the upstream and the downstream in the state of Is configured to switch according to
An engine with a supercharger , wherein the prerotation control is performed when the temperature of the engine is equal to or higher than a predetermined reference temperature, and the forced rotation control is performed when the temperature of the engine is lower than the reference temperature . In the supercharged engine according to claim 1,
A main cooling unit for cooling the engine;
And a sub-cooling unit configured to cool the intercooler.
An engine with a supercharger, wherein the main cooling unit and the sub cooling unit are provided independently of each other. In the supercharged engine according to claim 1 or 2,
An engine with a supercharger, wherein switching between the forced rotation control and the pre-rotation control is performed in a predetermined region where air-fuel mixture in the combustion chamber burns by compression self-ignition. In the supercharged engine according to claim 3,
It further comprises a temperature sensor that detects an outside air temperature and outputs a detection signal to the control unit,
The control unit performs the pre-rotation control when the temperature of the engine is lower than the reference temperature and the outside air temperature is equal to or more than a predetermined first temperature in the predetermined area, and the outside air temperature is lower than the outside air temperature. An engine with a supercharger, which performs the forced rotation control when exceeding a predetermined second temperature higher than the first temperature. In the supercharged engine according to any one of claims 1 to 4,
The engine is a supercharged engine having a geometric compression ratio of 13 or more and 30 or less. The supercharged engine according to any one of claims 1 to 5, wherein
The fuel supplied to the combustion chamber is at least a turbocharged engine including gasoline.

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