JP2019039363A - Compression self-ignition engine with supercharger - Google Patents

Abstract

To appropriately control a temperature in a combustion chamber during combustion.SOLUTION: A compression self-ignition engine with a supercharger includes a selection unit 45 for selecting a supercharger 44 arranged in an intake passage 40 to be driven or not to be driven, an intercooler 46 arranged downstream of the supercharger 44, and a flow control valve 48 arranged in a bypass passage 47 connecting the upstream of the supercharger 44 and the downstream of the intercooler 46. In a predetermined region where air-fuel mixture is combusted by compression self-ignition in the state that the supercharger 44 is not driven, a control unit 10 performs forcible rotation control to drive the supercharger 44 in the non-supercharged state of opening the flow control valve 48 so that, when an outside air temperature is equal to or higher than a predetermined first temperature TS1, gas circulates through the bypass passage 47.SELECTED DRAWING: Figure 13

Description

  The technology disclosed herein relates to a compression self-ignition engine with a supercharger.

  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 the intake valve and the exhaust valve are both closed by setting the exhaust valve closing timing before top dead center and the intake valve opening timing after top dead center in the predetermined region. Is provided. Thereby, since high temperature EGR gas is introduced into the combustion chamber, the temperature in the combustion chamber becomes high, and the air-fuel mixture is compressed and 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. In a predetermined operating state, the engine deactivates the mechanical supercharger by turning off the electromagnetic clutch, and closes the control valve in the air bypass passage that bypasses the mechanical supercharger and the inter. The mechanical supercharger is pre-rotated by the pressure difference. This prevents the occurrence of torque shock when the electromagnetic clutch is turned on.

JP 2009-197740 A Japanese Patent No. 3564989

  In order to achieve stable combustion by compression self-ignition, the temperature in the combustion chamber 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, becomes too high, the combustion due to compression self-ignition becomes steep, and the combustion noise exceeds the allowable value. .

  The technology disclosed herein has been made in view of such a point, and an object thereof is to appropriately adjust the temperature in the combustion chamber at the time of combustion in a compression self-ignition engine with a supercharger. .

  A compression self-ignition engine with a supercharger disclosed herein includes an intake passage connected to a combustion chamber of the engine, a supercharger disposed in the intake passage, and driving and non-driving of the supercharger. A switching unit for switching between, an intercooler disposed downstream of the supercharger in the intake passage, a bypass passage connecting the upstream of the supercharger and the downstream of the intercooler in the intake passage, and the bypass passage A flow control valve disposed in the control section, the switching section, and a control section connected to the flow control valve and outputting a control signal to the switching section and the flow control valve; And a temperature sensor that outputs a detection signal to the control unit.

  In a predetermined region where the air-fuel mixture in the combustion chamber burns by compression self-ignition in a non-supercharged state, when the outside air temperature is equal to or higher than a predetermined first temperature, gas flowing through the intake passage passes through the bypass passage. In order to circulate, the control unit performs forced rotation control for driving the supercharger with the flow rate control valve opened.

  Here, the “engine” may be a four-stroke engine that operates when the combustion chamber repeats 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 an electric supercharger driven by electric energy.

  As the engine load increases, the amount of fuel increases, so it is necessary to increase the intake amount in accordance with the required amount. Similarly, when the engine speed increases, it is necessary to increase the intake amount in accordance with the required amount. In such a case, in order to secure a necessary intake air amount, this engine is provided with a supercharger.

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

  When the intake air is pressurized, the 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 the engine is operated in a region where supercharging is unnecessary, such as a low-load low-speed region, the control unit switches the switching unit to non-drive to stop the operation of the supercharger and is disposed in the bypass passage. The opening of the flow control valve is adjusted on the open side (normally fully open). Thus, the intake air flowing through the intake passage bypasses the supercharger and is smoothly introduced into the combustion chamber through the bypass passage with almost no resistance. The engine is operated in a non-supercharged state (natural intake state).

  In this engine, combustion by compression self-ignition is performed in a predetermined region where operation is performed in such a non-supercharged state. As described above, combustion by compression self-ignition requires adjusting the temperature in the combustion chamber to an appropriate range in order to realize appropriate combustion.

  However, when the engine is operating in this region, the intake air is directly introduced into the combustion chamber, so the temperature of the intake air depends on the outside air temperature (the temperature of the outside air). Therefore, if the outside air temperature becomes excessively high, the temperature of the combustion chamber may deviate from an appropriate range, and appropriate combustion may not be realized.

  On the other hand, in this engine, when the outside air temperature is equal to or higher than a predetermined first temperature that can deviate from the appropriate temperature range of such a combustion chamber, the control unit is configured to circulate the gas flowing through the intake passage through the bypass passage. However, the supercharger is driven in a non-supercharged state with the flow control valve opened (forced rotation control). That is, while maintaining the non-supercharged state, the supercharger is driven and the intake air introduced into the combustion chamber is cooled using the intercooler while the intake air is repeatedly circulated through the bypass passage.

  Since the intake air can be repeatedly cooled by the circulation of the intake air through the intercooler, the intake air temperature can be appropriately maintained even when the outside air temperature becomes excessively high. Compared to natural intake, the amount of intake air introduced into the combustion chamber can be adjusted with higher accuracy by adjusting the opening of the flow control valve. As a result, even when the outside air temperature becomes excessively high, the temperature of the combustion chamber can be maintained in an appropriate range, and combustion by stable compression self-ignition can be realized.

  In the predetermined region, when the outside air temperature is equal to or higher than the first temperature, the control unit is configured so that the supercharger is operated by a pressure difference between the upstream side and the downstream side in a non-supercharged state. Performing pre-rotation control for controlling the flow rate control valve to be closed while maintaining the non-driving state, and performing the forced rotation control when the outside air temperature exceeds a predetermined second temperature higher than the first temperature, It is good.

  In the forced rotation control, the supercharger is driven. Therefore, compared with the non-driving case, the driving resistance is large, so the fuel efficiency performance of the engine is lowered. Therefore, in this configuration, prior to the forced rotation control, pre-rotation control that can cool the intake air without driving the supercharger is performed.

  In the pre-rotation control, the flow control valve is controlled to be closed while the supercharger is not driven. As a result, a pressure difference is generated between the upstream side and the downstream side of the supercharger, and the supercharger is operated, that is, pre-rotated by the action of the differential pressure. By pre-rotating the supercharger, a part of the intake air flows into the downstream side through the supercharger, is cooled by the intercooler, and is then introduced into the combustion chamber. As described above, the pre-rotation control can also cool the intake air by utilizing the intercooler.

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

  In the predetermined region, when the outside air temperature is equal to or higher than the first temperature, the control unit is configured so that the supercharger is operated by a pressure difference between the upstream side and the downstream side in a non-supercharged state. Pre-rotation control for controlling the flow rate control valve to be closed while maintaining the non-driving state may be performed, and the forced rotation control may be performed when an acceleration request operation is performed by the driver.

  When forced rotation control is performed, the supercharger is switched from non-drive to drive. When an impact is generated at the time of switching and the impact is transmitted to the driver, the driver may feel uncomfortable when the driver is not performing an operation. On the other hand, in this configuration, when the outside air temperature is equal to or higher than the first temperature in the predetermined region, the pre-rotation control that can cool the intake air while the supercharger is not driven is performed, and the driver's acceleration request operation is performed. Forced rotation control is performed.

  With pre-rotation control, the supercharger can be maintained in a non-driven state, so that the intake air can be cooled without making the driver feel uncomfortable. When the driver performs an acceleration request operation such as depressing the accelerator, the driver recognizes the shock due to the operation even if an impact due to the switching of the supercharger 44 is applied. You can avoid memorizing.

  The predetermined region includes a low load side region where the excess air ratio immediately before starting combustion of the air-fuel mixture is 2 or more, and a high load side where the air excess rate immediately before combustion of the air fuel mixture is started is 1 or less. The control unit may perform the forced rotation control when the outside air temperature is equal to or higher than the first temperature in at least the high load side region.

  That is, in the low load side region, the amount of fuel introduced into the combustion chamber is adjusted to be smaller than the intake air amount, and the air-fuel mixture immediately before starting combustion in the combustion chamber is in a lean state with a low fuel concentration. On the other hand, in the high load side region, the air-fuel mixture immediately before the start of combustion in the combustion chamber is made equal to or lower than the stoichiometric air-fuel ratio, and the fuel concentration is higher and relatively rich than the low load side region. The

  Therefore, since the combustion temperature in the high load side region is higher than that in the low load side region, the temperature immediately before the combustion of the air-fuel mixture starts tends to be higher than in the low load side region. Therefore, when the outside air temperature is high, the high load side region is more likely to deviate from the appropriate range of the combustion chamber temperature than the low load side region, so it is desirable that the intake air can be cooled more stably and strongly.

  On the other hand, according to this configuration, when the outside air temperature is equal to or higher than the first temperature at least in the high load side region, the forced rotation control with excellent cooling capacity is performed, so that the intake air can be stably and strongly cooled.

  Both the low load region and the high load side region are regions where the engine does not require supercharging, and the amount of intake air introduced into the combustion chamber is relatively small. On the other hand, since the load is higher in the high load side region than in the low load region, the output power is larger than that in the low load side region. Therefore, as the output power is large, the influence of the driving load that is increased by driving the supercharger is smaller in the high load side region than in the low load region. Since the influence of the driving load is reduced, in the high load side area, the driving force of the turbocharger can be increased to further increase the amount of intake air circulation. Can promote. The intake air temperature can be maintained more stably and appropriately.

  In this case, the forced rotation control is performed in both the high load side region and the low load side region, and the first temperature is lower in the high load side region than in the low load side region. It may be.

  As described above, in the high load side region, when the outside air temperature is high, the temperature of the combustion chamber is likely to deviate from an appropriate range than in the low load side region. Therefore, by setting the first temperature as a reference for performing the forced rotation control to a value lower than that in the low load side region, it is possible to more reliably avoid the temperature of the combustion chamber from deviating from an appropriate range.

  A main cooling unit that cools the engine and a sub-cooling unit that cools 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 that cools the intercooler is configured separately from the main cooling unit that cools the engine, and the intercooler can be cooled separately from the engine. Therefore, even if the engine temperature becomes high and the cooling performance of the main cooling section decreases, the intercooler can cool without being affected by this, so the intake air cooling by forced rotation control and pre-rotation control is stable. Yes.

  The engine may have a geometric compression ratio of 13 to 30.

  A relatively high geometric compression ratio of the engine is advantageous for stabilizing combustion by compression self-ignition, but may also cause premature 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 premature ignition. Further, if the geometric compression ratio is excessively increased, cooling loss and mechanical loss increase. However, even if the geometric compression ratio is increased, such a problem can be suppressed if it is not excessive. The fuel efficiency of the engine is improved.

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

  Fuel containing gasoline may cause premature ignition in a high-temperature combustion chamber, but avoiding premature ignition even when using fuel containing gasoline by maintaining the intake air temperature appropriately Combustion due to compression self-ignition can be stabilized.

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

FIG. 1 is a diagram illustrating a configuration of an engine. The intake side is the left side of the page, and the exhaust side is the right side of the page. FIG. 2 is a diagram illustrating the configuration of the combustion chamber, in which the upper diagram is a plan view equivalent view of the combustion chamber, and the lower portion is a II-II sectional view. FIG. 3 is a plan view illustrating the configuration of the combustion chamber and the intake system. The intake side is the right side of the page, and the exhaust side is the left side of the page. FIG. 4 is a block diagram illustrating the configuration of the engine control apparatus. FIG. 5 is a diagram illustrating a configuration of an engine cooling device. FIG. 6 is a diagram illustrating an engine operation region and a supercharger drive / non-drive region. FIG. 7 is a diagram illustrating fuel injection timing and ignition timing, and combustion waveforms in each operation region. FIG. 8 is a flowchart illustrating a flow of switching the engine operation between a supercharged state and a non-supercharged state. FIG. 9 is a schematic diagram showing a supercharging system during supercharging operation. FIG. 10 is a schematic diagram showing a supercharging system during non-supercharging operation. FIG. 11 is a schematic diagram showing a supercharging system during pre-rotation control. FIG. 12 is a diagram showing the relationship between the flow rate ratio of the gas flowing through the intercooler and the temperature in the surge tank during the pre-rotation control. FIG. 13 is a schematic diagram showing a supercharging system during forced rotation control. FIG. 14 is a flowchart showing an example of the flow of intake air cooling control during non-supercharging operation. FIG. 15 is a flowchart showing an example of the flow of intake air cooling control based on an application example of the 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 use.

<SPCCI combustion>
The inventors of the present application have considered a combustion mode combining SI (Spark Ignition) combustion and CI (Compression Ignition) combustion. SI combustion is combustion with flame propagation that starts by forcibly igniting the air-fuel mixture in the combustion chamber. CI combustion is combustion that starts when the air-fuel mixture in the combustion chamber undergoes compression self-ignition. Combustion mode combining SI combustion and CI combustion means that when combustion is forcibly ignited in the air-fuel mixture in the combustion chamber and combustion by flame propagation is started, the heat generated by SI combustion and the pressure increase due to flame propagation The unburned air-fuel mixture in the combustion chamber is burned by compression ignition. Hereinafter, this combustion mode is 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 greatly. In SPCCI combustion, by adjusting the calorific value of SI combustion, it is possible to absorb temperature variations in the combustion chamber before compression starts. If the start timing of SI combustion is adjusted by adjusting the ignition timing, for example, according to the temperature in the combustion chamber before the start of compression, the timing of compression ignition can be controlled. SPCCI combustion can control CI combustion by SI combustion.

  In SI combustion by flame propagation, since the pressure rise is more gradual than CI combustion, SPCCI combustion can suppress the generation of combustion noise. Further, since CI combustion has a shorter combustion period than SI combustion, SPCCI combustion is advantageous in improving fuel efficiency.

<Specific examples of engine>
FIG. 1 shows the overall configuration of an engine with a supercharger (engine 1) to which the combustion technology by SPCCI combustion is applied.

  The engine 1 is a four-stroke engine that operates when the combustion chamber 17 repeats an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke. The engine 1 is mounted on a four-wheeled vehicle. The vehicle travels when the engine 1 is driven. The fuel of the engine 1 is gasoline in this configuration example. The fuel may be gasoline containing bioethanol or 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 placed on the cylinder block 12. The cylinder block 12 and the cylinder head 13 constitute an engine body 100. A plurality of cylinders 11 are formed inside the cylinder block 12. 1 and 2, only one cylinder 11 is shown. 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 a 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 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 composed of an inclined surface 1311 and an inclined surface 1312 as shown in the lower diagram of FIG. 2. The inclined surface 1311 has an upward slope from the intake side toward an injection axis X2 of an injector 6 described later. 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 an injector 6 described later.

  The center of the cavity 31 is shifted to the exhaust side with respect to the center axis X <b> 1 of the cylinder 11. The center of the cavity 31 coincides with the injection axis X2 of the injector 6. The cavity 31 has a convex portion 311. The convex portion 311 is provided on the injection axis X <b> 2 of the injector 6. The convex part 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 concave portion 312 provided around the convex portion 311. The recessed portion 312 is provided so as to surround the entire circumference of the protruding portion 311. The cavity 31 has a symmetrical shape with respect to the injection axis X2.

  The peripheral side surface of the recessed portion 312 is inclined with respect to the injection axis X2 from the bottom surface of the cavity 31 toward the opening of the cavity 31. 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, the shape of the ceiling surface of the combustion chamber 17, and the like can be changed as appropriate. For example, the cavity 31 may be symmetric with respect to the central axis X1 of the cylinder 11. The inclined surface 1311 and the inclined surface 1312 may be symmetric with respect to the central axis X <b> 1 of the cylinder 11. Further, in the cavity 31, a shallow bottom portion that is shallower than the recessed portion 312 may be provided at a location facing a 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 combining SI combustion and CI combustion in a part of the operation region. SPCCI combustion performs CI combustion using heat generation and pressure increase due to SI combustion. The engine 1 does not need to increase the temperature of the combustion chamber 17 (that is, the compression end temperature) when the piston 3 reaches the compression top dead center due to the self-ignition of the air-fuel mixture. That is, the engine 1 performs CI combustion, but its geometric compression ratio is set to be relatively low. Lowering the geometric compression ratio is advantageous in reducing cooling loss and 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-octane specification (the fuel octane number is about 96).

  An intake port 18 is formed in the cylinder head 13 for each cylinder 11. As shown in FIG. 3, the intake port 18 has two intake ports, a first intake port 181 and a second intake port 182. The first intake port 181 and the second intake port 182 are aligned in the axial direction of the crankshaft 15, that is, the front-rear direction of the engine 1. The intake port 18 communicates with the combustion chamber 17. Although not shown in detail, the intake port 18 is a so-called tumble port. That is, the intake port 18 has such a shape that a tumble flow is formed in the combustion chamber 17.

  An intake valve 21 is disposed in 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. This valve mechanism may be a variable valve mechanism that makes the valve timing and / or valve lift variable. In this configuration example, as shown in FIG. 4, the variable valve mechanism has an intake electric S-VT (Sequential-Valve Timing) 23. The intake motor S-VT 23 is configured to continuously change the rotation phase of the intake camshaft within a predetermined angle range. Thereby, the valve opening timing and the valve closing timing of the intake valve 21 are continuously changed. The valve mechanism of the intake valve 21 may have a hydraulic S-VT instead of the electric S-VT.

  The cylinder head 13 is also provided with an exhaust port 19 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 arranged 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 in 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 mechanism. This valve mechanism may be a variable valve mechanism that makes the valve timing and / or valve lift variable. In this configuration example, as shown in FIG. 4, the variable valve mechanism has an exhaust electric S-VT 24. The exhaust electric S-VT 24 is configured to continuously change the rotation phase of the exhaust camshaft within a predetermined angle range. Thereby, the valve opening timing and the valve closing timing of the exhaust valve 22 continuously change. Note that 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 S-VT 23 and the exhaust electric S-VT 24. As a result, hot burned gas is confined in the combustion chamber 17. That is, an internal EGR (Exhaust Gas Recirculation) gas is introduced into the combustion chamber 17. Further, 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 combustion chamber 17 in a valley portion of the pent roof where the intake-side inclined surface 1311 and the exhaust-side inclined surface 1312 intersect. As shown in FIG. 2, the injector 6 has an injection axis disposed in parallel to the central axis X <b> 1 of the cylinder 11. The injection axis X2 of the injector 6 is shifted from the central axis X1. The injection axis of the injector 6 coincides with the position of the convex portion 311 of the cavity 31. The injector 6 faces the cavity 31. The injection axis of the injector 6 may coincide with the central axis X1 of the cylinder 11. Even 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 coincide with each other.

  Although not shown in detail, the injector 6 is constituted by a multi-injection type fuel injection valve having a plurality of injection holes. As shown by a two-dot chain line in FIG. 2, the injector 6 injects the 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. In the present configuration example, the injector 6 has ten nozzle holes, and the nozzle holes are arranged at an equal angle in the circumferential direction. As shown in the upper diagram of FIG. 2, the axis of the nozzle hole is displaced in the circumferential direction with respect to a spark plug 25 described later. That is, the spark plug 25 is sandwiched between the shafts of two adjacent nozzle holes. Thereby, it is avoided that the spray of the fuel injected from the injector 6 directly hits the spark plug 25 and wets 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 path 62 that connects 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 path 62. The fuel pump 65 pumps fuel to the common rail 64. In this configuration example, the fuel pump 65 is a plunger-type pump driven by the crankshaft 15. The common rail 64 is configured to store the fuel pumped from 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 into the combustion chamber 17 from the injection hole of the injector 6. The fuel supply system 61 is configured to be able to supply high pressure fuel of 30 MPa or more to the injector 6. The maximum fuel pressure of the fuel supply system 61 may be about 120 MPa, for example. 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 air-fuel mixture in the combustion chamber 17. In this configuration example, the spark plug 25 is disposed on the intake side across the central axis X1 of the cylinder 11 as shown in FIG. 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 so as to be inclined from the top to the bottom toward the center of the combustion chamber 17. 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 fresh air but may also contain EGR gas, also simply referred to as “gas”). An air cleaner 41 that filters fresh air is disposed at the upstream end of the intake passage 40. A surge tank 42 is disposed near the downstream end of the intake passage 40. The intake passage 40 downstream of the surge tank 42 constitutes an independent passage that branches 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 amount of fresh air introduced into the combustion chamber 17 by adjusting the opening of the valve.

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

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

  In the engine 1, the supercharger 44 supercharges gas introduced into the combustion chamber 17, that is, introduces intake air into the combustion chamber 17 at a pressure higher than that of natural intake (supercharged state), and the supercharger 44. However, the gas introduced into the combustion chamber 17 is not supercharged, that is, the intake air is introduced into the combustion chamber 17 by natural intake (non-supercharging state).

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

  An intercooler 46 is disposed downstream of the supercharger 44 in the intake passage 40. The intercooler 46 is configured to cool the gas compressed in the supercharger 44. The intercooler 46 may be configured to be, for example, a water cooling type (or oil cooling type).

  A bypass passage 47 is connected to the intake passage 40. The bypass passage 47 connects the upstream portion of the supercharger 44 and the downstream portion of the intercooler 46 in the intake passage 40 so as to bypass the supercharger 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 adjusts the flow rate of the 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.

  In FIG. 1, an intake passage 40 including a supercharging system 49 surrounded by a two-dot chain line K 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, and the like are assembled to the engine body 100 in a state of being close to the outer surface of the engine body 100. It has been.

  The engine 1 has a swirl generator that generates a swirl flow in the combustion chamber 17. The swirl generator 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 that can narrow the cross section of the secondary passage. When the opening of the swirl control valve 56 is small, the intake air flow rate flowing into the combustion chamber 17 from the first intake port 181 among the first intake port 181 and the second intake port 182 aligned in the front-rear direction of the engine 1 is relatively. And the intake flow rate flowing into the combustion chamber 17 from the second intake port 182 relatively decreases, so that the swirl flow in the combustion chamber 17 becomes stronger. When the 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 uniform, so the swirl flow in the combustion chamber 17 is weak. Become. When the swirl control valve 56 is fully opened, no swirl flow is generated. The swirl flow circulates counterclockwise in FIG. 3 as indicated by the arrows (see also the white arrows in FIG. 2).

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

  An exhaust gas purification system having a plurality of catalytic converters is disposed in the exhaust passage 50. Although not shown, the upstream catalytic converter 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 shown in the figure.

  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 returning a part of 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 side of the supercharger 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 burnt gas flowing through the EGR passage 52. By adjusting the opening degree of the EGR valve 54, the recirculation amount of the cooled burned gas, that is, the external EGR gas can be adjusted.

  In this configuration example, the EGR system 55 includes an external EGR system configured to include an EGR passage 52 and an EGR valve 54, and an internal configuration configured to include the above-described intake electric S-VT 23 and exhaust electric S-VT 24. 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 go back and forth between the main circuit 71A and the sub circuit 71B.

  The main circuit 71 </ b> A includes a main radiator 72 that cools the refrigerant using traveling wind, and a variable capacity water pump 74 that supplies the refrigerant cooled by the main radiator 72 to the engine body 100. 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, is then discharged from the engine main body 100, and returns to the main radiator 72.

  Similarly to the main radiator 72, the sub circuit 71B includes a sub radiator 75 that cools the refrigerant using traveling air, and an electric water pump 76 that supplies 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, is then 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 engine body 100. Therefore, the refrigerant flowing through sub circuit 71B is less susceptible to the temperature of engine body 100 than the refrigerant flowing through main circuit 71A. Therefore, the sub circuit 71 can effectively cool the intercooler 46 in a state independent of the engine main body 100.

  The engine 1 includes an ECU (Engine Control Unit) 10. The ECU 10 is a controller based on a well-known microcomputer, and as shown in FIG. 4, a central processing unit (CPU) 101 for executing a program and, for example, a RAM (Random Access Memory) or ROM A memory 102 configured by (Read Only Memory) and storing programs and data, and an input / output bus 103 for inputting and outputting electrical signals 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. Sensors SW1-SW17 output a detection signal to ECU10. The sensors include the following sensors.

  That is, the air flow sensor SW1 that is disposed downstream of the air cleaner 41 in the intake passage 40 and detects the flow rate of fresh air flowing through the intake passage 40, the first intake temperature sensor SW2 that detects the temperature of fresh air, and the intake passage 40, the first pressure sensor SW3 that is disposed downstream of the connection position of the EGR passage 52 and upstream of the supercharger 44 and detects the pressure of the gas flowing into the supercharger 44, and supercharging in the intake passage 40 The second intake air temperature sensor SW4, which is disposed downstream of the machine 44 and upstream of the connection position of the bypass passage 47 and detects the temperature of the gas flowing out from the supercharger 44, is attached to the surge tank 42, and A second pressure sensor SW5 for detecting the pressure of the gas downstream of the feeder 44, attached to the cylinder head 13 corresponding to each cylinder 11, and each A finger pressure sensor SW6 that detects the pressure in the firing chamber 17, an exhaust temperature sensor SW7 that is disposed in the exhaust passage 50 and detects the temperature of the exhaust gas discharged from the combustion chamber 17, and is upstream of the upstream catalytic converter in the exhaust passage 50. And a linear O2 sensor SW8 that detects the oxygen concentration in the exhaust gas, a lambda O2 sensor SW9 that is arranged downstream of the three-way catalyst 511 in the upstream catalytic converter and detects the oxygen concentration in the exhaust gas, the engine 1 is a water temperature sensor SW10 that detects the temperature of cooling water, a crank angle sensor SW11 that is attached to the engine 1 and detects the rotation angle of the crankshaft 15, and is attached to an accelerator pedal mechanism and operates the accelerator pedal. Accelerator opening sensor SW1 for detecting the accelerator opening corresponding to the amount An intake cam angle sensor SW13 that is attached to the engine 1 and detects the rotation angle of the intake camshaft, an exhaust cam angle sensor SW14 that is attached to the engine 1 and detects the rotation angle of the exhaust camshaft, and is disposed in the EGR passage 52 The EGR differential pressure sensor SW15 that detects the differential pressure upstream and downstream of the EGR valve 54, and the 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. Further, the third intake air 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 sends control signals relating to the calculated control amount to the injector 6, spark plug 25, intake electric S-VT 23, exhaust electric S-VT 24, fuel supply system 61, throttle valve 43, EGR valve 54, supercharger 44. Output to the electromagnetic clutch 45, the air bypass valve 48, and the swirl control valve 56.

  For example, the ECU 10 adjusts the boost pressure by adjusting the opening of the air bypass valve 48 based on the differential pressure across the turbocharger 44 obtained from the detection signals of the first pressure sensor SW3 and the second pressure sensor SW5. adjust. Further, 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 is adjusted. Adjust.

(Engine operating range)
FIG. 6 illustrates operation region maps 501 and 502 of the engine 1. The operation region maps 501 and 502 of the engine 1 are determined by the load and the rotational speed, and are divided into five regions with respect to the load level and the rotational speed level. Specifically, the five regions include an idle operation and a low load region (1) -1 (corresponding to a “low load side region”) that extends to a region of low rotation and medium rotation, and the load is higher than that of the low load region. Medium load region (1) -2 (corresponding to “high load side region”) that is high and spreads in the region of low rotation and medium rotation, a region where the load is higher than the medium load region (1) -2, and full open load A medium rotation region (2) including a high load region, a low rotation region (3) having a lower rotational speed than the medium rotation region (2) in the high load region, and a low load region (1) -1 and a medium load region (1) -2, high-load mid-rotation region (2), and high-load region (4) having a higher rotational speed than the high-load low-rotation region (3).

  Here, the low rotation region, the medium rotation region, and the high rotation region are each when the entire operation region of the engine 1 is divided into approximately three equal parts of the low rotation region, the medium rotation region, and the high rotation region in the rotation speed direction. The low rotation region, the middle rotation region, and the high rotation region may be used. In the example of FIG. 6, the rotation speed less than N1 is low rotation, the rotation speed N2 or more is high rotation, and the rotation speed N1 or more and less than N2 is medium rotation. For example, the rotational speed N1 may be about 1200 rpm, and the rotational speed N2 may be about 4000 rpm, for example.

  In FIG. 6, for easy understanding, the operation region maps 501 and 502 of the engine 1 are divided into two parts. A map 501 shows the state of the air-fuel mixture and the combustion mode in each region. A map 502 shows a supercharging region where the supercharger 44 is driven and a non-supercharging region where the supercharger 44 is not driven. Note that a two-dot chain line in FIG. 6 indicates a road-load line of the engine 1.

  The engine 1 performs SPCCI combustion in a low load region (1) -1, a medium load region (1) -2, and a high load medium rotation region (2) mainly for the purpose of improving fuel consumption and exhaust gas performance. I do. The engine 1 also performs SI combustion in other regions, specifically, the high load low rotation region (3) and the high rotation region (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 region (1) -1, the engine 1 performs SPCCI combustion combining SI combustion and CI combustion.

  Reference numeral 601 in FIG. 7 indicates fuel injection timing (reference numerals 6011 and 6012) and ignition timing (reference numeral 6013) when the engine 1 is operating in the operating state 601 shown in FIG. 6 in the low load region (1) -1. ), And a combustion waveform (that is, a waveform indicating a change in the heat generation rate with respect to the crank angle, reference numeral 6014).

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

  By adjusting the calorific value of the SI combustion, the temperature variation in the combustion chamber 17 before the start of compression can be absorbed. Even if the temperature in the combustion chamber 17 before the start of compression varies, the self-ignition timing can be controlled by adjusting the SI combustion start timing by adjusting the ignition timing, for example.

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

  When the temperature and pressure in the combustion chamber 17 are increased by SI combustion, the unburned mixture is self-ignited. In the example of FIG. 7, the slope of the heat generation rate waveform changes from small to large at the timing of self-ignition. That is, the heat generation rate waveform has an inflection point at the timing when CI combustion starts.

  After the start of CI combustion, SI combustion and CI combustion are performed in parallel. Since CI combustion generates more heat than SI combustion, the heat generation rate is relatively large. However, since CI combustion is performed after compression top dead center, the piston 3 is lowered by motoring. It is avoided that the inclination of the waveform of the heat generation rate due to CI combustion becomes too large. Dp / dθ during CI combustion also becomes relatively gentle.

  dp / dθ can be used as an index representing combustion noise. However, since SPCCI combustion can reduce dp / dθ as described above, it is possible to avoid excessive combustion noise. . Combustion noise can be suppressed below an acceptable level.

  When CI combustion ends, SPCCI combustion ends. CI combustion has a shorter combustion period than SI combustion. In SPCCI combustion, the combustion end timing is earlier than SI combustion. In other words, SPCCI combustion can bring the combustion end time during the expansion stroke closer to the compression top dead center. The SPCCI combustion is more advantageous for improving the fuel efficiency of the engine 1 than the SI combustion.

  In order to improve the fuel efficiency 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 region (1) -1.

  When the engine 1 is operating in the low load region (1) -1, a strong swirl flow is formed in the combustion chamber 17. The swirl flow is strong at the outer periphery of the combustion chamber 17 and weak at the center. The swirl control valve (SCV) 56 has 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 is operated in the low load region (1) -1, the swirl ratio is 2 or more, preferably 4 or more. Here, 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 this engine 1, when the swirl control valve 56 is fully opened, 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 region (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. In other words, 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 air-fuel mixture is 30 or more in the entire combustion chamber 17. The excess air ratio immediately before the air-fuel mixture starts to burn is 2 or more. By carrying out like this, generation | occurrence | production of RawNOx can be suppressed and exhaust gas performance can be improved.

  When the engine 1 operates in the low load region (1) -1, the air-fuel 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 at the center is higher than the fuel concentration at the outer periphery. Specifically, the A / F of the air-fuel mixture in the central part is 20 or more and 35 or less, and the A / F of the air-fuel mixture in the outer peripheral part is 35 or more and 50 or less. Note that the value of the air-fuel ratio is the value of the air-fuel ratio at the time of ignition corresponding to immediately before the air-fuel mixture starts to burn, and the same applies in the following description.

  When the engine 1 operates in the low load region (1) -1, the injector 6 basically injects fuel into the combustion chamber 17 during the intake stroke and during the compression stroke (reference number). 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 an air-fuel mixture at the center and the outer periphery. The fuel injected during the compression stroke is transported to the vicinity of the spark plug 25 at the center of the combustion chamber 17 by the swirl flow without much diffusion because the time until the ignition timing is short. The fuel injected during the compression stroke forms a central air-fuel mixture together with a part of the fuel injected during the intake stroke. The air-fuel mixture is stratified in the central portion and the outer peripheral portion of the combustion chamber 17.

  After completion of fuel injection, the spark plug 25 ignites the air-fuel mixture at the center 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 the SI combustion, the CI combustion starts at an appropriate timing. In SPCCI combustion, controllability of CI combustion is improved. As a result, when the engine 1 is operated in the low load region (1) -1, both the suppression of the generation of combustion noise and the improvement of the fuel consumption performance due to the shortening of the combustion period are compatible.

  In the low load region (1) -1, the engine 1 leans the air-fuel mixture from the stoichiometric air-fuel ratio and performs SPCCI combustion. Therefore, the low load region (1) -1 can be referred to as a "SPCCI lean region". .

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

  Reference numeral 602 in FIG. 7 indicates fuel injection timing (reference numerals 6021 and 6022) and ignition timing (reference numeral 6023) when the engine 1 is operating in the operation state 602 shown in FIG. 6 in the middle load region (1) -2. ) And a combustion waveform (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 region (1) -2.

  Also, when the engine 1 is operated in the medium load region (1) -2, the swirl ratio is 2 or more, preferably 4 or more, in the combustion chamber 17 as in the low load region (1) -1. A strong swirl flow is formed. The swirl control valve (SCV) 56 has a predetermined opening on the fully closed or closed side. By strengthening the swirl flow, the turbulent energy in the combustion chamber 17 increases, so that when the engine 1 is operated in the medium load region (1) -2, the flame of SI combustion propagates quickly and SI combustion occurs. Is stabilized. The controllability of CI combustion is enhanced by the stabilization of SI combustion. By optimizing the timing of CI combustion in SPCCI combustion, it is possible to suppress the generation of combustion noise and improve fuel efficiency. Further, torque variation between cycles can be suppressed.

  When the engine 1 operates in the medium load region (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 air-fuel mixture starts to burn 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 air-fuel mixture may be set within the purification window of the three-way catalyst. Therefore, the excess air ratio λ of the air-fuel mixture may be set to 1.0 ± 0.2.

  When the engine 1 is operating in the operating state 602, fuel injection during the intake stroke (reference numeral 6021) and fuel injection during the compression stroke (reference numeral 6022) 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 region (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 and the injection amount of the injection 6022 may be 95: 5 as an example. The injection 6022 may be omitted in the low load operation state in the middle load region (1) -2.

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

  In the medium load region (1) -2, the engine 1 performs SPCCI combustion with the air-fuel mixture as the stoichiometric air-fuel ratio, and therefore the medium load region (1) -2 can be referred to as “SPCCIλ = 1 region”.

(High load medium rotation range (2))
Even when the engine 1 is operating in the high load mid-rotation region (2), the engine 1 performs SPCCI combustion in the same manner as the low load region (1) -1 and the medium load region (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 operating in the low-rotation side operation state 603 shown in FIG. An example of each of the time (reference numeral 6033) and the combustion waveform (reference numeral 6034) is shown.
Reference numeral 604 in FIG. 7 denotes a fuel injection timing (reference numeral 6041) and an ignition timing (when the engine 1 is operating in the high-rotation-side operation state 604 shown in FIG. Reference numeral 6042) and an example of the combustion waveform (reference numeral 6043) are 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 mid-rotation region (2). The engine 1 reduces the amount of EGR gas as the load increases. At full open load, the EGR gas may be zero.

  Also, when the engine 1 is operated in the high load mid-rotation region (2), the swirl ratio is 2 or more, preferably 4 or more, in the combustion chamber 17 as in the low load region (1) -1. A strong swirl flow is formed. The swirl control valve (SCV) 56 has a predetermined opening on the fully closed or closed side.

  When the engine 1 operates in the high load mid-rotation region (2), the air-fuel ratio (A / F) of the air-fuel 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-side operation 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). For example, the ratio between the injection amount of the injection 6031 and the injection amount of the injection 6032 may be 95: 5.

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

  When the engine 1 is operated in the operation state 604 on the high rotation side, the injector 6 starts fuel injection in the intake stroke (reference numeral 6041).

  The injection 6041 that starts in the intake stroke may start fuel injection in the first half of the intake stroke. The end of the injection 6041 may be during the compression stroke beyond the intake stroke. By starting the injection of the injection 6041 in 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 is formed in the central portion of the combustion chamber 17. be able to. Since the rotational speed is high and abnormal combustion is unlikely to occur, the latter-stage injection can be omitted.

  The spark plug 25 ignites the air-fuel mixture at the center of the combustion chamber 17 in the vicinity of the compression top dead center (reference numeral 6042). The spark plug 25 performs ignition after the compression top dead center, for example. Thereby, SPCCI combustion is performed (see combustion waveform 6043).

  In the high load mid-rotation region (2), the engine 1 performs SPCCI combustion with the air-fuel mixture richer than the stoichiometric air-fuel ratio or the stoichiometric air-fuel ratio. Can be called.

(High load, low rotation range (3))
When the rotational speed of the engine 1 is low, the time required for the crank angle to change by 1 ° becomes long. In the high load low rotation region (3), as in the high load medium rotation region (2), for example, if fuel is injected into the combustion chamber 17 in the first half of the intake stroke or compression stroke, the reaction of the fuel proceeds excessively. May cause premature ignition. When the engine 1 is operating in the high-load low-rotation region (3), it is difficult to perform the aforementioned SPCCI combustion.

  Therefore, when the engine 1 is operating in the high load low rotation region (3), the engine 1 performs SI combustion instead of SPCCI combustion.

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

  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 low rotation region (3). The engine 1 reduces the amount of EGR gas as the load increases. At full open load, the EGR gas may be zero.

  When the engine 1 is operating in the high-load low-rotation region (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 air-fuel mixture may be set within the purification window of the three-way catalyst. Therefore, the excess air ratio λ of the air-fuel mixture may be set to 1.0 ± 0.2. By setting the air-fuel ratio of the air-fuel mixture to the stoichiometric air-fuel ratio, the fuel consumption performance is improved in the high load low rotation region (3). When the engine 1 is operated in the high load low rotation region (3), the fuel concentration of the entire air-fuel mixture in the combustion chamber 17 is 1 or less in the excess air ratio λ and the high load medium rotation region (2). The excess air ratio λ may be greater than or equal to the excess air ratio λ, preferably greater than the excess air ratio λ in the high load mid-rotation region (2).

  When the engine 1 is operated in the high-load low-rotation region (3), the injector 6 includes 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 end of the compression stroke may be the end when the compression stroke is divided into three equal parts, the initial period, the middle period, and the final period. Further, the initial stage of the expansion stroke may be an initial stage when the expansion stroke is divided into three equal parts in the initial stage, the middle period, and the final stage.

  By injecting fuel in two steps, the amount of fuel injected within the retard period can be reduced. By injecting fuel during the intake stroke (reference numeral 6051), it is possible to secure a sufficient time for forming the air-fuel mixture. Further, by injecting fuel during the retard period (reference numeral 6052), the flow in the combustion chamber 17 can be increased immediately before ignition, which is advantageous for stabilizing SI combustion. This form of fuel injection is particularly effective when the geometric compression ratio of the engine 1 is low.

  The spark plug 25 ignites the air-fuel mixture at a timing near the compression top dead center after fuel injection (reference numeral 6053). The spark plug 25 may ignite after compression top dead center, for example. The air-fuel mixture undergoes 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 low rotation region (3), the engine 1 performs SI combustion by injecting fuel during the retard period from the end of the compression stroke to the early stage of the expansion stroke. It can be called “SI region”.

(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 ° is shortened. Therefore, for example, in the high rotation region in the high load region, as described above, it is difficult to stratify the air-fuel mixture in the combustion chamber 17 by performing the divided injection during the compression stroke. When the rotational speed of the engine 1 becomes high, it becomes difficult to perform the aforementioned SPCCI combustion.

  Therefore, when the engine 1 is operating in the high speed region (4), the engine 1 performs SI combustion instead of SPCCI combustion. The high rotation region (4) extends over the entire load direction from a low load to a high load.

  Reference numeral 606 in FIG. 7 denotes a fuel injection timing (reference numeral 6061) and an ignition timing (reference numeral 6062) when the engine 1 is operating in the operating state 606 shown in FIG. An example of each combustion waveform (reference numeral 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 may be zero.

  When the engine 1 is operated in the high speed region (4), the swirl control valve (SCV) 56 is fully opened. A swirl flow is not generated in the combustion chamber 17 and only a tumble flow is generated. By fully opening the swirl control valve 56, the charging efficiency can be increased in the high rotation region (4), and the pump loss can be reduced.

  When the engine 1 operates in the high speed region (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 air-fuel mixture may be 1.0 ± 0.2. Note that the excess air ratio λ of the air-fuel mixture may be less than 1 in the high load region including the fully open load in the high rotation region (4).

  When the engine 1 operates in the high speed region (4), the injector 6 starts fuel injection during the intake stroke. The injector 6 injects fuel in a lump. Note that the operating state 605 has a large amount of fuel injection because the load of the engine 1 is high. The fuel injection period changes according to the fuel injection amount. By starting fuel injection during the intake stroke, a homogeneous or substantially homogeneous mixture can be formed in the combustion chamber 17. Further, when the engine 1 has a high rotation speed, the fuel vaporization time can be ensured as long as possible, so that unburned loss can be reduced and soot generation can be suppressed.

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

  In the high speed region (4), the engine 1 starts fuel injection in the intake stroke and performs SI combustion, so the high speed region (4) can be referred to as an “intake-SI region”.

(Supercharger operation)
As shown in the lower diagram 502 in FIG. 6, a part of the low load region (1) -1 on the low load / low rotation side in the entire operation region of the engine 1 and one part of the medium load region (1) -2. In the section, the supercharger 44 is turned off, that is, in a non-driving state, and the operation of the engine 1 is in a non-supercharging state (this non-supercharging region corresponds to a “predetermined region”).

  Specifically, the supercharger 44 is turned off in the low rotation side region in the low load region (1) -1. In the region on the high rotation side in the low load region (1) -1, the supercharger 44 is turned on in order to ensure a necessary intake charge amount 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 turbocharger 44 is turned on in order to ensure the necessary intake charge amount corresponding to the increase in the engine speed, and is necessary in response to the increase in the rotational speed of the engine 1 in the high speed region. In order to ensure the intake charge amount, the supercharger 44 is turned on.

  In each of the high load medium rotation region (2), the high load low rotation region (3), and the high rotation region (4), the supercharger 44 is turned on over the entire region (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 a supercharged state and a non-supercharged state. ECU10 reads the signal of each sensor SW1-SW17 (step S1). The ECU 10 determines the operating region of the engine 1 and determines whether there is a supercharging request (step S2). As a result, when the ECU 10 determines that there is a supercharging request (YES in step S2), the electromagnetic clutch 45 is connected, and the air bypass valve 48 (ABV) is closed and the opening degree is adjusted. Then, the supercharging operation is executed (step S3).

  FIG. 9 shows a supercharging system 49 during supercharging operation. The air bypass valve 48 (ABV) is held in a substantially closed state. 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 downstream of the supercharger 44 in a pressurized state. Discharged to the side. Although the temperature of the gas rises due to pressurization, the gas is cooled by the intercooler 46 and adjusted to an appropriate temperature, and then 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. Thereby, a part of the gas flowing into the surge tank 42 flows backward through the bypass passage 47 and upstream of the supercharger 44. In the supercharged 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 (both statically and 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 electromagnetic clutch 45 is disconnected and the opening degree of the air bypass valve 48 (ABV) is adjusted to the same level as when the valve is fully opened and fully opened. Thus, the non-supercharging operation (natural intake) is executed (step S4).

  FIG. 10 shows a supercharging system 49 during non-supercharging operation. The air bypass valve 48 is adjusted to a fully open position or an opening level equivalent to the fully open position. The supercharger 44 does not operate (rotate) because the electromagnetic clutch 45 is disconnected. The gas flowing upstream of the supercharger 44 in the intake passage 40 bypasses the supercharger 44 and the intercooler 46 and flows into the surge tank 42 through the bypass passage 47. Since the bypass passage 47 communicates with both the upstream side and the downstream side of the supercharger 44 in the intake passage 40, the gas passes through the bypass passage 47 without receiving resistance. In the non-supercharging state, both the upstream side and the downstream side of the supercharger 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). The pressure detected by SW5 is almost the same).

(Influence of outside temperature during non-supercharging operation)
During the supercharging operation, the temperature of the gas introduced into the combustion chamber 17 is adjusted by the intercooler 46. However, during the non-supercharging operation, the gas is directly introduced into the combustion chamber. Temperature). Therefore, if the outside air temperature becomes excessively high, the temperature of the combustion chamber may deviate from an appropriate range, and appropriate combustion may not be realized.

  In particular, in this engine 1, SPCCI combustion is performed in a predetermined region of the low load region (1) -1 and the medium load region (1) -2 in which the non-supercharging operation is performed. Need to keep in range. Specifically, if the compression end temperature becomes too high, the control of CI combustion by SI combustion becomes unstable, such as the timing at which CI combustion starts, and there is a risk of causing problems such as premature ignition.

  Therefore, the engine 1 is configured such that the pre-rotation control and the forced rotation control can be executed 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, the temperature of the intake air introduced into the combustion chamber 17 (intake air temperature) increases depending on natural intake air, and the temperature of the combustion chamber cannot be maintained in an appropriate range (the outside air temperature is predetermined). When the temperature is equal to or higher than the first temperature TS1, the pre-rotation control or the forced rotation control is executed, and the intake air is cooled so that the temperature of the combustion chamber can be maintained in an appropriate range.

(Pre-rotation control)
FIG. 11 shows a supercharging system 49 during pre-rotation control. When executing the pre-rotation control, the ECU 10 controls the air bypass valve 48 in a state in which the supercharger 44 is not driven so that the supercharger 44 is operated by a pressure difference between the upstream side and the downstream side in the non-supercharged state. Control to close.

  By controlling the air bypass valve 48 from the substantially fully opened state to the closed 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 is generated between the upstream side and the downstream side of the supercharger 44, and the supercharger 44 is rotated based on the differential pressure. Specifically, the rotor of the supercharger 44 is rotated (pre-rotation). Once the supercharger 44 begins to pre-rotate, an inertial force acts, and thereafter, the supercharger 44 can be stably pre-rotated even with a relatively low differential pressure.

  As the supercharger 44 pre-rotates, a part of the gas flowing upstream of the supercharger 44 in the intake passage 40 is drawn into the supercharger 44 as indicated by a broken line in FIG. The gas drawn into the supercharger 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 the gas passing through the intercooler 46 to the flow rate of the gas passing through the bypass passage 47 (hereinafter simply referred to as “flow rate ratio”) and the gas temperature in the surge tank 42. A region S1 shown in the figure is a region of the gas temperature in the surge tank 42 (hereinafter referred to as “surge tank internal temperature”) in which the temperature of the combustion chamber can be maintained in an appropriate range.

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

  In order to adjust the flow rate ratio and keep the temperature in the surge tank within an appropriate range, the air bypass valve 48 is adjusted to the closed 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 that it gradually closes from the fully open state toward the fully closed state as the outside air temperature increases 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 surge tank internal temperature may be indirectly determined based on various parameters indicating the operating state of the engine 1, such as the load and the engine speed, and the outside air temperature.

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

  The flow resistance of the bypass passage 47 increases as the air bypass valve 48 is adjusted to the closed side. Thereby, the differential pressure between the upstream side and the downstream side of the supercharger 44 is increased, the pre-rotation of the supercharger 44 is promoted, the amount of gas passing through the intercooler 46 is increased, and the flow rate ratio is also increased. To 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 executed, 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 is larger than that in the normal non-supercharging operation (natural intake) state, and the pressure difference tends to be smaller than that in the supercharging operation state.

  Note that when the pre-rotation control is executed, the opening degree of the throttle valve 43 is adjusted to be fully open or equivalent to the fully open position. That is, when the opening degree of the throttle valve 43 is reduced, there is a possibility that the pump loss increases 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 forced rotation control. When the forced rotation control is executed, the opening degree of the throttle valve 43 is adjusted to be fully open or an opening degree equivalent to full opening.

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

  Specifically, the pre-rotation control is performed when the outside air temperature is equal to or higher than the first temperature TS1 at which the temperature of the combustion chamber cannot be maintained in an appropriate range by natural intake, and the temperature of the combustion chamber is also adjusted by the pre-rotation control. When the temperature exceeds a predetermined second temperature TS2 that cannot be maintained within a certain range, forced rotation control is performed (second temperature TS2> first temperature TS1).

  FIG. 13 shows a supercharging system 49 during 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 a fully open position or an opening level equivalent to the fully open position. In this state, the supercharger 44 is driven with the electromagnetic clutch 45 connected thereto. Thereby, the gas flowing upstream of the supercharger 44 in the intake passage 40 is drawn into the supercharger 44. The gas drawn into the supercharger 44 is cooled through the intercooler 46 and then flows into the surge tank 42.

  Since the bypass passage 47 communicates with both the upstream side and the downstream side of the supercharger 44 in the intake passage 40 (statically in the same pressure state), other than the amount introduced into the combustion chamber 17. The gas flows back through the bypass passage 47 without receiving resistance, and returns to the upstream side of the supercharger 44 in the intake passage 40. The gas that has returned to the upstream side of the supercharger 44 in the intake passage 40 is drawn into the supercharger 44 again.

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

  Therefore, even when the outside air temperature becomes excessively high and it becomes difficult to properly maintain the intake air temperature by the pre-rotation control, the intake air temperature can be appropriately maintained by performing the forced rotation control. According to the forced rotation control, the amount of intake air introduced into the combustion chamber 17 can be adjusted with higher accuracy by adjusting the opening of the air bypass valve 48 than when performing natural intake. 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.

  During the execution of forced rotation control, 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 dynamically, the driving state of the supercharger 44, etc. It changes according to. However, the pressure difference is larger than that in the normal non-supercharging operation (natural intake) state, and the pressure difference tends to be smaller than that in the supercharging operation state.

  These pre-rotation control and forced rotation control are performed in a predetermined region extending from the low load region (1) -1 to the medium load region (1) -2. 2 The temperature TS2 is lower in the region (high load side region) located in the middle load region (1) -2 than in the region located in the low load region (1) -1 (low load side region). It has become.

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

  Therefore, by setting the first temperature TS1 and the second temperature TS2, which are the reference for performing the pre-rotation control and the forced rotation control, to lower values in the high load side region than in the low load side region, the temperature of the combustion chamber 17 can be increased. Deviating from the proper range can be avoided more reliably.

  In particular, in the high load side region, it is preferable to perform forced rotation control more actively than pre-rotation control. Both the low load region and the high load region are non-supercharging operation regions, and the amount of intake air introduced into the combustion chamber 17 is relatively small. On the other hand, since the load is higher in the high load side region than in the low load region, the output power is larger than that in the low load side region. Therefore, as the output power is large, the influence of the driving load that is increased by driving the supercharger 44 is smaller in the high load side region than in the low load region. Since the influence of the driving load is reduced, in the high load side region, the driving force of the supercharger 44 can be increased and the amount of intake air circulated can be increased. Therefore, by executing the forced rotation control, the intake air intake by the intercooler 46 is increased. Cooling can be promoted. The intake air temperature can be maintained more stably and appropriately.

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

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

  On the other hand, in the pre-rotation 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 increases, the influence is less than that of forced rotation control, and high cooling performance can be exhibited.

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

  Specifically, pre-rotation 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 higher, and is set in the ECU 10 in advance. If the reference temperature Te is higher than that, proper cooling cannot be performed even if the forced rotation control is performed, and the cooling capacity is equal to or lower than the pre-rotation control. The ECU 10 acquires the temperature of the engine main body 100 from the temperature of the cooling water flowing through the main circuit 71A, for example, detected by the water temperature sensor SW10.

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

(Intake air cooling control during non-supercharging operation)
FIG. 14 shows an example of the flow of intake air cooling control during non-supercharging operation. While the non-supercharging operation is being executed, 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. The determination is made continuously (step S11).

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

  On the other hand, when the ECU 10 determines that the outside air temperature is equal to or higher than the first temperature TS1 (YES in step S11), the ECU 10 executes pre-rotation control (step S13). Specifically, the electromagnetic clutch 45 is disconnected, and the air bypass valve 48 is controlled to be closed in a state in which the turbocharger 44 is not driven so that mechanical power does not act on the turbocharger 44.

  Further, the ECU 10 continuously determines whether or not the outside air temperature is equal to or higher than the second temperature TS2 (step S14). If the ECU 10 determines that the outside air temperature is not equal to or higher than the second temperature TS2 (NO in step S14), the ECU 10 continues to perform the pre-rotation control. When the pre-rotation control is continued, if the ECU 10 determines that the outside air temperature is not equal to or higher than the first temperature TS1 (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 becomes higher and the ECU 10 determines that the outside air temperature is equal to or higher than the second temperature TS2 (YES in step S14), the cooling of the intake air by the forced rotation control is executed.

  At this time, the ECU 10 indirectly acquires the temperature of the engine main body 100 based on the detection signal input from the water temperature sensor SW10, and continuously determines whether the temperature of the engine main body 100 is equal to or higher than the reference temperature Te. Judgment is made (step S15).

  If 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 forced rotation control cannot perform proper cooling, and the pre-rotation control has a cooling performance. Since it is excellent, the pre-rotation control is continued. In the pre-rotation control, the driving resistance is smaller than the forced rotation control, which is advantageous 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 equal to or higher than the reference temperature Te (NO in step S15), forced rotation control is executed (step S16). With forced rotation control, the intake air can be effectively cooled, so that the intake air temperature can be restored to an appropriate state in a short time, and the temperature in the combustion chamber during combustion can be adjusted appropriately.

  If the ECU 10 determines that the outside air temperature is not equal to or 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>
Switching between the pre-rotation control and the forced rotation control may be performed according to the driver's acceleration request operation.

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

  When forced rotation control is performed, the supercharger 44 is switched from non-drive to drive. When an impact is generated at the time of switching and the impact is transmitted to the driver, the driver may feel uncomfortable when the driver is not performing an operation. On the other hand, in this configuration, when the outside air temperature is equal to or higher than the first temperature TS1 in the predetermined region, the pre-rotation control that can cool the intake air while the supercharger 44 is not driven is performed, and the driver's acceleration request operation is performed. If so, forced rotation control is performed.

  With the pre-rotation control, the supercharger 44 can be maintained in a non-driven state, so that the intake air can be cooled without making the driver feel uncomfortable. And when a driver | operator performs acceleration request operation, such as stepping on an accelerator, forced rotation control is performed. If the acceleration requesting operation is performed, the driver recognizes the impact due to the operation even when an impact due to the switching of the supercharger 44 is applied, so that the driver can avoid feeling uncomfortable.

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

  While the pre-rotation control is being performed, the ECU 10 continuously determines whether or not there has been an acceleration request from the driver based on, for example, a detection signal input from the accelerator opening sensor SW12 (step S20). .

  And when there is no acceleration request | requirement from a driver | operator (it is NO at step S20), ECU10 continues and implements pre-rotation control.

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

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

1 Engine 3 Piston 6 Injector (fuel injection part)
10 ECU (control unit)
17 Combustion chamber 25 Spark plug (ignition part)
40 Intake passage 44 Supercharger 45 Electromagnetic clutch (switching part)
46 Intercooler 47 Bypass passage 48 Air bypass valve (flow control valve)

Claims (8)

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 supercharger;
An intercooler disposed downstream of the supercharger in the intake passage;
A bypass passage connecting the upstream of the supercharger and the downstream of the intercooler in the intake passage;
A flow control valve disposed in the bypass passage;
A controller that is connected to the switching unit and the flow rate control valve and outputs a control signal to the switching unit and the flow rate control valve;
A temperature sensor that detects the outside air temperature and outputs a detection signal to the control unit;
With
In a predetermined region where the air-fuel mixture in the combustion chamber burns by compression self-ignition in a non-supercharged state, the gas flowing through the intake passage circulates through the bypass passage when the outside air temperature is equal to or higher than a predetermined first temperature. The compression self-ignition engine with a supercharger, wherein the control unit performs forced rotation control for driving the supercharger with the flow rate control valve opened. The compression self-ignition engine with a supercharger according to claim 1,
In the predetermined region, when the outside air temperature is equal to or higher than the first temperature, the control unit is configured so that the supercharger is operated by a pressure difference between the upstream side and the downstream side in a non-supercharged state. Performing pre-rotation control for controlling the flow rate control valve to be closed while maintaining the non-driving state, and performing the forced rotation control when the outside air temperature exceeds a predetermined second temperature higher than the first temperature, A compression self-ignition engine with a turbocharger. In the compression self-ignition type engine with a supercharger according to claim 1 or 2,
In the predetermined region, when the outside air temperature is equal to or higher than the first temperature, the control unit is configured so that the supercharger is operated by a pressure difference between the upstream side and the downstream side in a non-supercharged state. A pre-rotation control for controlling the flow rate control valve to be closed while maintaining the non-driving state of the engine, and performing a forced rotation control when a driver's acceleration request operation is performed. Ignition engine. In the compression self-ignition type engine with a supercharger according to claim 1 or 2,
The predetermined region includes a low load side region where the excess air ratio immediately before starting combustion of the air-fuel mixture is 2 or more, and a high load side where the air excess rate immediately before combustion of the air fuel mixture is started is 1 or less. An area, and
A compression self-ignition engine with a supercharger in which the controller performs the forced rotation control when the outside air temperature is equal to or higher than the first temperature at least in the high load side region. The compression self-ignition engine with a supercharger according to claim 4,
The forced rotation control is performed in both the high load side region and the low load side region,
The compression self-ignition engine with a supercharger, wherein the first temperature is lower in the high load side region than in the low load side region. In the compression self-ignition type engine with a supercharger according to any one of claims 1 to 4,
A main cooling section for cooling the engine;
A sub-cooling unit that cools the intercooler,
A compression self-ignition engine with a supercharger, wherein the main cooling part and the sub cooling part are provided independently of each other. The compression self-ignition engine with a supercharger according to any one of claims 1 to 5,
The engine is a compression self-ignition engine with a supercharger having a geometric compression ratio of 13 to 30. In the compression self-ignition type engine with a supercharger according to any one of claims 1 to 6,
The fuel supplied to the combustion chamber is a compression self-ignition engine with a supercharger including at least gasoline.

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