JP6555539B2 - Control device for compression self-ignition engine - Google Patents

Description

  The present invention relates to a control device for a compression self-ignition engine having an engine configured to self-ignite an air-fuel mixture in a combustion chamber.

  A technique related to the present invention is disclosed in Patent Document 1, for example. In Patent Document 1, in a compression self-ignition engine that applies auxiliary energy to an air-fuel mixture in a combustion chamber to promote self-ignition, a target in-cylinder temperature at top dead center is set, and the target in-cylinder temperature is A technique for controlling the in-cylinder temperature with an intake air heating device provided in an intake passage so as to be realized is disclosed.

JP 2001-73775 A

  By the way, the present inventors have considered a combustion mode combining SI (Spark Ignition) combustion and CI (Compression Ignition) combustion. In other words, the SI combustion (corresponding to the first combustion) is performed by forcibly igniting the air-fuel mixture in the combustion chamber, and the unburned air-fuel mixture in the combustion chamber is self-ignited by the heat generated by the SI combustion. (Corresponding to the second combustion). Since SI combustion has a relatively small pressure fluctuation, it is possible to suppress the generation of combustion noise. Also, by performing CI combustion, the combustion period is shortened and combustion efficiency is improved compared to combustion by flame propagation. Therefore, the combustion mode combining SI combustion and CI combustion can improve fuel efficiency while suppressing the generation of combustion noise. This combustion mode is hereinafter referred to as “SI-CI combustion” because SI combustion controls CI combustion.

  Furthermore, the inventors of the present invention regarding SI-CI combustion, the ratio of the amount of heat generated by SI combustion to the total amount of heat generated in SI combustion and CI combustion or the amount of heat generated in CI combustion in one combustion cycle of the engine. By defining the “SI rate” as an index related to the engine and changing this SI rate according to the operating state of the engine, it is possible to suppress the generation of combustion noise and improve fuel efficiency over a wide operating range. The point which can be compatible with this was discovered.

  Here, in order to suppress combustion noise, it is desirable to appropriately control the SI rate. However, if the SI rate is determined only from the viewpoint of suppressing combustion noise, it becomes difficult to control the self-ignition timing in CI combustion. If the self-ignition timing of CI combustion deviates from a desired timing, it leads to deterioration of fuel consumption and combustion stability.

  The present invention has been made to solve the above-described problems of the prior art, and appropriately controls both the SI rate and the self-ignition timing in a control device for a compression self-ignition engine that performs SI-CI combustion. The purpose is to do.

To achieve the above object, the present invention provides a combustion chamber for combusting a mixture of fuel and air, an injector for injecting fuel to supply fuel into the combustion chamber, and an ignition for igniting the mixture in the combustion chamber. And an engine configured to self-ignite an air-fuel mixture in the combustion chamber, and adjusting the introduction of fresh air and burned gas into the combustion chamber of the engine, A state quantity setting device configured to set the engine to a desired state, and a controller configured to operate the engine by at least controlling the injector and spark plug of the engine and the state quantity setting device. A control device for an ignition type engine, wherein in the engine, an air-fuel mixture is combusted by flame propagation by ignition of a spark plug. The second combustion in which the air-fuel mixture burns by self-ignition due to this flame propagation is performed, and the controller generates the first and second combustion during one combustion cycle of the engine based on the operating state of the engine. First control means for controlling the SI rate as an index related to the ratio of the amount of heat generated by the first combustion to the total amount of heat to be generated or the amount of heat generated in the second combustion, and the self-ignition timing that is the time when self-ignition occurs And a second control means for controlling the combustion state of both the first and second combustion in accordance with the operating state of the engine during one combustion cycle of the engine by both the first and second control means. change, after it has finished ejecting the total fuel to be injected from the injector during one combustion cycle of the engine in order to achieve the first combustion and second combustion, the point to perform ignition Controlling the plug, characterized in that.

  According to the present invention configured as described above, the controller includes both the first combustion by flame propagation and the first control means for controlling the SI rate and the second control means for controlling the self-ignition timing of the second combustion. Both combustion states of the second combustion due to self-ignition are changed according to the operating state of the engine. Thereby, the combustion waveform which combined the 1st and 2nd combustion can be made into a desired combustion waveform. Specifically, a desired SI rate and self-ignition timing can be appropriately realized. As a result, it becomes possible to achieve improvements in fuel consumption, combustion stability and combustion noise suppression.

In the present invention, preferably, the first control means of the controller performs control to increase the SI rate as the engine load as the engine operating state increases.
In the present invention configured as described above, when the engine load is low, the first control unit can shorten the combustion period by reducing the SI rate, thereby improving the fuel consumption. On the other hand, the first control means can suppress the generation of combustion noise due to the second combustion by increasing the SI rate when the engine load is high.

In the present invention, preferably, the second control means of the controller performs control to set the self-ignition timing to the retard side as the engine load as the engine operating state increases.
In the present invention configured as described above, since the combustion noise is not a serious problem when the engine load is low, the second control means sets the self-ignition timing to a relatively advanced angle side, so that self-ignition is achieved. Stability can be ensured. On the other hand, when the engine load is high, the second control means can set the self-ignition timing to the retard side, thereby extending the period during which the second combustion is performed as much as possible and ensuring fuel consumption.

In the present invention, preferably, the second control means of the controller sets the self-ignition timing to the retard side within a range not exceeding the predetermined retard limit.
According to the present invention configured as described above, since the retard of the self-ignition timing is limited by the retard limit, the self-ignition stability of the second combustion can be ensured.

In the present invention, preferably, the first and second control means of the controller maintain the combustion center of gravity position in the combined combustion of the first and second combustion substantially constant irrespective of the engine load as the engine operating state. In order to control the SI rate and the self-ignition timing.
According to the present invention configured as described above, the position of the center of gravity of combustion in the combined combustion of the first and second combustion is maintained substantially constant, so that the required torque from the driver can be appropriately ensured. For example, if the center of gravity of combustion is maintained near the compression top dead center (the crank angle near the compression top dead center and after the compression top dead center), the fuel efficiency can be effectively improved.

In the present invention, preferably, the first control means of the controller controls the ignition timing by the spark plug to adjust the SI rate.
According to the present invention configured as described above, the SI rate can be appropriately controlled by adjusting the ignition timing by the spark plug that starts the first combustion. In a typical example, the SI rate can be increased by advancing the ignition timing, and the SI rate can be decreased by retarding the ignition timing.

In the present invention, preferably, the first control means of the controller adjusts the SI rate by controlling the state quantity setting device so as to adjust the ratio of fresh air and burned gas introduced into the combustion chamber.
According to the present invention configured as described above, the SI ratio is appropriately adjusted by controlling the in-cylinder state (for example, in-cylinder temperature) by adjusting the ratio of fresh air and burned gas introduced into the combustion chamber. Can be controlled. For example, the SI ratio can be appropriately controlled by delaying the start of the first combustion by adjusting the ratio between the fresh air and the burned gas to increase the in-cylinder temperature before the start of combustion.

In the present invention, it is preferable that the controller injects fuel before and after the ignition timing by the spark plug so as to form a substantially homogeneous mixture in the combustion chamber, and the latter-stage injection. The first control means controls the fuel injection amount from the injector in the subsequent stage injection to perform the first stage injection for injecting the fuel at a timing before and at a timing away from the ignition timing. Adjust.
In the present invention configured as described above, basically, when performing split injection including pre-injection and post-injection, the fuel injected by the post-injection undergoes the first combustion, and the fuel injected by the pre-injection is the main fuel. In addition, since the second combustion is performed, the SI rate can be appropriately controlled by adjusting the fuel injection amount from the injector in the latter-stage injection.

In this invention, Preferably, the 2nd control means of a controller controls the ignition timing by a spark plug, and adjusts self-ignition timing.
According to the present invention configured as described above, the subsequent self-ignition timing of the second combustion can be appropriately controlled by adjusting the start timing of the first combustion according to the ignition timing by the spark plug.

In the present invention, preferably, the controller sets a target SI rate and a target self-ignition timing according to the operating state of the engine, and both the target SI rate and the target self-ignition timing are set by both the first and second control means. Control is performed to adjust the SI rate and the self-ignition timing so that is realized.
According to the present invention configured as described above, desired combustion in which the first and second combustion are combined by adjusting the SI rate and the self-ignition timing so that the target SI rate and the target self-ignition timing are realized. A waveform can be appropriately realized.

In the present invention, preferably, the controller obtains the state in the combustion chamber before the start of the first combustion to be set according to the target SI rate and the target self-ignition timing, and introduces the state into the combustion chamber to realize this state. The state quantity setting device is controlled to adjust the ratio between the fresh air and the burned gas, and the actual combustion chamber state before the start of the first combustion is acquired, and based on this state, the target self-ignition timing is obtained. The ignition timing by the spark plug is controlled so that is realized.
According to the present invention configured as described above, the control for adjusting the in-cylinder state is performed before the start of combustion, the actual in-cylinder temperature before the start of combustion is obtained, and the ignition timing is based on the in-cylinder temperature. By controlling this, it is possible to reliably realize the target SI rate and the target self-ignition timing.

In another aspect, in order to achieve the above object, the present invention provides a combustion chamber for burning a mixture of fuel and air, an injector for injecting fuel to supply fuel into the combustion chamber, and mixing in the combustion chamber. An engine having at least a spark plug for igniting the engine, the engine configured to self-ignite the air-fuel mixture in the combustion chamber, and adjusting the introduction of fresh air and burned gas into the combustion chamber of the engine A state quantity setting device configured to set the combustion chamber to a desired state, and a controller configured to operate the engine by at least controlling the injector and spark plug of the engine and the state quantity setting device. In the engine, the air-fuel mixture is combusted by flame propagation due to ignition of the spark plug. And the second combustion in which the air-fuel mixture burns by self-ignition due to this flame propagation is performed, and the controller performs the first and second in one combustion cycle of the engine based on the engine load. Control for adjusting the SI rate as an index related to the ratio of the amount of heat generated by the first combustion to the total amount of heat generated in the combustion or the amount of heat generated in the second combustion, and the self-ignition timing when self-ignition occurs In one combustion cycle of the engine, the ignition timing by the spark plug, the fuel injection amount and / or fuel injection timing by the injector, and the fresh air introduced into the combustion chamber by the state quantity setting device By adjusting at least one of the ratio with the fuel gas and controlling both the SI rate and the self-ignition timing, the first and second fuels Modify both combustion state of the operating condition of the engine, after it has finished inject the total fuel to be injected from the injector during one combustion cycle of the engine in order to achieve the first combustion and second combustion, ignition The spark plug is controlled to perform the following.
According to the present invention configured as described above, a combustion waveform obtained by combining the first and second combustions can be set to a desired combustion waveform, that is, a desired SI rate and self-ignition timing can be appropriately realized. . Therefore, it becomes possible to achieve improvements in fuel consumption, ensuring combustion stability, suppressing combustion noise, and the like.

In the present invention, preferably, the controller performs control to increase the SI rate and control to set the self-ignition timing to the retard side as the engine load increases.
According to the present invention configured as described above, the combustion waveform corresponding to the engine load can be appropriately realized by controlling the SI rate and the self-ignition timing according to the engine load.

In the present invention, preferably, the controller controls the ratio of fresh air and burnt gas introduced into the combustion chamber by the state quantity setting device to adjust the SI rate, and controls the ignition timing by the spark plug to control itself. Adjust the ignition timing.
According to the present invention configured as described above, the SI ratio is appropriately adjusted by controlling the in-cylinder state (for example, in-cylinder temperature) by adjusting the ratio of fresh air and burned gas introduced into the combustion chamber. In addition, by adjusting the start timing of the first combustion according to the ignition timing by the spark plug, the subsequent self-ignition timing of the second combustion can be appropriately controlled.

In the present invention, it is preferable that the state quantity setting device is a variable valve mechanism configured to vary the valve timing of an intake valve and / or an exhaust valve provided in the engine, and the controller is already installed from the exhaust port of the engine. The ratio of fresh air to be introduced into the combustion chamber and the internal EGR gas by controlling the variable valve mechanism so as to adjust the valve timing of the intake valve and / or the exhaust valve in order to return the combustion gas as internal EGR gas to the combustion chamber. Adjust.
According to the present invention configured as described above, it is possible to appropriately control the in-cylinder state (for example, the in-cylinder temperature) before combustion by adjusting the ratio between the fresh air introduced into the combustion chamber and the internal EGR gas. it can.
In yet another aspect, the present invention provides a combustion chamber for burning a mixture of fuel and air, an injector for injecting fuel to supply fuel into the combustion chamber, an ignition plug for igniting the mixture in the combustion chamber, The engine is configured to self-ignite the air-fuel mixture in the combustion chamber, and by adjusting the introduction of fresh air and burned gas into the combustion chamber of the engine, the combustion chamber has a desired interior. A compression self-ignition engine having a state quantity setting device configured to set a state, a controller configured to operate the engine by at least controlling an injector and spark plug of the engine and the state quantity setting device In the engine, in the engine, the first combustion in which the air-fuel mixture is combusted by flame propagation by ignition of the spark plug, and this fire A second combustion in which the air-fuel mixture burns by self-ignition due to the propagation is performed, and the controller calculates the total amount of heat generated in the first and second combustions during one combustion cycle of the engine based on the operating state of the engine. Alternatively, the first control means for controlling the SI rate as an index related to the ratio of the amount of heat generated by the first combustion to the amount of heat generated in the second combustion, and the self-ignition timing, which is the time when self-ignition occurs, are controlled. A second control means, and both the first and second control means change the combustion state of both the first and second combustion in accordance with the operating state of the engine during one combustion cycle of the engine, The first control means of the controller performs control to increase the SI rate as the engine load as the engine operating state increases.
In yet another aspect, the present invention provides a combustion chamber for burning a mixture of fuel and air, an injector for injecting fuel to supply fuel into the combustion chamber, an ignition plug for igniting the mixture in the combustion chamber, The engine is configured to self-ignite the air-fuel mixture in the combustion chamber, and by adjusting the introduction of fresh air and burned gas into the combustion chamber of the engine, the combustion chamber has a desired interior. A compression self-ignition engine having a state quantity setting device configured to set a state, a controller configured to operate the engine by at least controlling an injector and spark plug of the engine and the state quantity setting device In the engine, in the engine, the first combustion in which the air-fuel mixture is combusted by flame propagation by ignition of the spark plug, and this fire A second combustion in which the air-fuel mixture burns by self-ignition due to the propagation is performed, and the controller calculates the total amount of heat generated in the first and second combustions during one combustion cycle of the engine based on the operating state of the engine. Alternatively, the first control means for controlling the SI rate as an index related to the ratio of the amount of heat generated by the first combustion to the amount of heat generated in the second combustion, and the self-ignition timing, which is the time when self-ignition occurs, are controlled. A second control means, and both the first and second control means change the combustion state of both the first and second combustion in accordance with the operating state of the engine during one combustion cycle of the engine, The first and second control means of the controller substantially sets the position of the center of gravity of combustion in the combined combustion of the first and second combustion, regardless of the engine load as the engine operating state. So as to maintain a constant, to control the SI ratio and ignition timing, characterized in that.
In yet another aspect, the present invention provides a combustion chamber for burning a mixture of fuel and air, an injector for injecting fuel to supply fuel into the combustion chamber, an ignition plug for igniting the mixture in the combustion chamber, The engine is configured to self-ignite the air-fuel mixture in the combustion chamber, and by adjusting the introduction of fresh air and burned gas into the combustion chamber of the engine, the combustion chamber has a desired interior. A compression self-ignition engine having a state quantity setting device configured to set a state, a controller configured to operate the engine by at least controlling an injector and spark plug of the engine and the state quantity setting device In the engine, in the engine, the first combustion in which the air-fuel mixture is combusted by flame propagation by ignition of the spark plug, and this fire A second combustion in which the air-fuel mixture burns by self-ignition due to the propagation is performed, and the controller calculates the total amount of heat generated in the first and second combustions during one combustion cycle of the engine based on the operating state of the engine. Alternatively, the first control means for controlling the SI rate as an index related to the ratio of the amount of heat generated by the first combustion to the amount of heat generated in the second combustion, and the self-ignition timing, which is the time when self-ignition occurs, are controlled. A second control means, and both the first and second control means change the combustion state of both the first and second combustion in accordance with the operating state of the engine during one combustion cycle of the engine, The controller is configured to inject the fuel before the ignition timing by the spark plug and at a timing close to the ignition timing so as to form a substantially homogeneous mixture in the combustion chamber. The first control means controls the amount of fuel injected from the injector in the second-stage injection, and controls the injector to execute the first-stage injection before the second-stage injection and at a timing away from the ignition timing. , Adjusting the SI rate.

  ADVANTAGE OF THE INVENTION According to this invention, in the control apparatus of the compression self-ignition engine which performs SI-CI combustion, both SI rate and self-ignition timing can be controlled appropriately.

1 is a schematic configuration diagram of a compression self-ignition engine according to an embodiment of the present invention. It is sectional drawing of the combustion chamber of the compression self-ignition engine by embodiment of this invention. It is a block diagram which shows the electric constitution of the control apparatus of the compression self-ignition engine by embodiment of this invention. It is explanatory drawing about the driving | running | working area | region of the engine by embodiment of this invention. It is explanatory drawing about the definition of the SI rate in SI-CI combustion by embodiment of this invention. In the embodiment of the present invention, the change in SI ratio, the change in state quantity in the combustion chamber, the change in overlap period of the intake valve and the exhaust valve, and the change in fuel injection timing and ignition timing with respect to the engine load It is explanatory drawing of. It is explanatory drawing about the relationship between the engine load in embodiment of this invention, SI rate, and self-ignition timing. In embodiment of this invention, it is explanatory drawing about the method of controlling SI rate according to the cylinder temperature before a combustion start. In embodiment of this invention, it is explanatory drawing about the method of controlling SI rate so that desired self-ignition timing may be implement | achieved according to the in-cylinder temperature before a combustion start. It is a flowchart which shows the basic control of SI-CI combustion by embodiment of this invention. It is explanatory drawing about the estimation method of the in-cylinder temperature before combustion by embodiment of this invention. It is a block diagram which shows the 1st control model by embodiment of this invention. It is a block diagram which shows the 2nd control model by embodiment of this invention. It is a block diagram which shows the 3rd control model by embodiment of this invention. It is a time chart at the time of performing SI-CI combustion control by the embodiment of the present invention.

  Hereinafter, a control device for a compression self-ignition engine according to an embodiment of the present invention will be described with reference to the accompanying drawings.

<Device configuration>
First, with reference to FIG. 1 thru | or FIG. 3, the structure of the control apparatus of the compression self-ignition engine by this embodiment is demonstrated. FIG. 1 is a diagram illustrating the configuration of a compression self-ignition engine according to this embodiment. FIG. 2 is a cross-sectional view illustrating the configuration of the combustion chamber according to the present embodiment. In FIG. 1, the intake side is the left side of the drawing, and the exhaust side is the right side of the drawing. The intake side in FIG. 2 is the right side of the drawing, and the exhaust side is the left side of the drawing. FIG. 3 is a block diagram illustrating the configuration of the control device for the compression self-ignition engine according to the present embodiment.

  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.

  Specifically, the engine 1 includes a cylinder block 12 and a cylinder head 13 placed thereon. 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 formed 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 upper surface of the piston 3 is a flat surface. 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 has a shallow dish shape. The cavity 31 faces an injector 6 described later when the piston 3 is positioned near the compression top dead center.

  The cavity 31 has a convex portion 311. The convex portion 311 is provided substantially at the center of the cylinder 11. The convex part 311 is substantially conical. The convex portion 311 extends upward from the bottom of the cavity 31 along the central axis X of the cylinder 11. The upper end of the convex portion 311 is almost the same height as the upper surface of the cavity 31. The cavity 31 also has a concave portion 312 provided around the convex portion 311.

As shown in FIG. 2, 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. The inclined surface 1311 has an upward slope from the intake side toward the axis X. The inclined surface 1312 has an upward slope from the exhaust side toward the axis X. The ceiling surface of the combustion chamber 17 has a so-called pent roof shape.
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.

  The geometric compression ratio of the engine 1 is set high for the purpose of improving the theoretical thermal efficiency and stabilizing the CI (Compression Ignition) combustion described later. Specifically, the geometric compression ratio of the engine 1 is 17 or more. The geometric compression ratio may be 18, for example. What is necessary is just to set a geometric compression ratio suitably in the range of 17-20.

  Two intake ports 18 are formed in the cylinder head 13 for each cylinder 11. The intake port 18 communicates with 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 an intake valve mechanism. In this configuration example, the intake valve mechanism has an intake electric VVT (Variable Valve Timing) 23 which is a variable valve mechanism as shown in FIG. The intake electric VVT 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 intake valve mechanism may have a hydraulic VVT instead of the electric VVT.

  The cylinder head 13 is also formed with two exhaust ports 19 for each cylinder 11. 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 an exhaust valve mechanism. In this configuration example, the exhaust valve mechanism has an exhaust electric VVT 24 that is a variable valve mechanism as shown in FIG. The exhaust electric VVT 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. The exhaust valve mechanism may have a hydraulic VVT instead of the electric VVT.

  Although details will be described later, the engine 1 adjusts the length of the overlap period related to the opening of the intake valve 21 and the opening of the exhaust valve 22 by the intake electric VVT 23 and the exhaust electric VVT 24. As a result, residual gas in the combustion chamber 17 is scavenged, hot burned gas is confined in the combustion chamber 17 (that is, internal exhaust gas recirculation (EGR) gas is introduced into the combustion chamber 17). Or). In this configuration example, the intake electric VVT 23 and the exhaust electric VVT 24 constitute an internal EGR system as one of the state quantity setting devices. Note that the internal EGR system is not necessarily configured by VVT.

  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 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 is arranged such that its injection axis is along the central axis X of the cylinder 11. The injection axis of the injector 6 and the position of the convex portion 311 of the cavity 31 substantially coincide. The injector 6 faces the cavity 31. The injection axis of the injector 6 may not coincide with the center axis X 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. The injector 6 injects fuel so that the fuel spray spreads radially from the center of the combustion chamber 17 as indicated by arrows in FIG.

As will be described later, the injector 6 may inject fuel at the timing when the piston 3 is positioned near the compression top dead center. In that case, when the injector 6 injects the fuel, the fuel spray flows downward along the convex portion 311 of the cavity 31 while mixing with fresh air, and along the bottom surface and the peripheral side surface of the concave portion 312, the combustion chamber. From the center of 17, it spreads radially outward in the radial direction. Thereafter, the air-fuel mixture reaches the opening of the cavity 31 and flows from the radially outer side toward the center of the combustion chamber 17 along the inclined surface 1311 on the intake side and the inclined surface 1312 on the exhaust side.
The injector 6 is not limited to a multi-hole injector. The injector 6 may employ an external valve opening type injector.

  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 port 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 center axis X of the cylinder 11. 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. As shown in FIG. 2, 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 gas introduced into the combustion chamber 17 flows. 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. Although the detailed illustration is omitted, the intake passage 40 downstream of the surge tank 42 constitutes an independent passage branched for each cylinder 11. The downstream end of the independent passage is connected to the intake port 18 of each cylinder 11.

  A throttle valve 43 is disposed between the air cleaner 41 and the surge tank 42 in the intake passage 40. The throttle valve 43 is configured to adjust the amount of fresh air introduced into the combustion chamber 17 by adjusting the opening of the valve. The throttle valve 43 constitutes one of state quantity setting devices.

  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 or a centrifugal type.

  An electromagnetic clutch 45 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 on and off. That is, in the engine 1, the supercharger 44 can switch between supercharging the gas introduced into the combustion chamber 17 and the supercharger 44 not supercharging the gas introduced into the combustion chamber 17. It is configured to be able to.

  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.

  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 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.

When the supercharger 44 is turned off (that is, when the electromagnetic clutch 45 is disconnected), the air bypass valve 48 is fully opened. As a result, the gas flowing through the intake passage 40 bypasses the supercharger 44 and is introduced into the combustion chamber 17 of the engine 1. The engine 1 is operated in a non-supercharged state, that is, in a natural intake state.
When the supercharger 44 is turned on (that is, when the electromagnetic clutch 45 is connected), part of the gas that has passed through the supercharger 44 flows backward through the bypass passage 47 upstream of the supercharger. . Since the reverse flow rate can be adjusted by adjusting the opening degree of the air bypass valve 48, the supercharging pressure of the gas introduced into the combustion chamber 17 can be adjusted. In this configuration example, the supercharger 44, the bypass passage 47, and the air bypass valve 48 constitute a supercharging system 49. The air bypass valve 48 constitutes one of state quantity setting devices.

  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 one or more catalytic converters 51 is disposed in the exhaust passage 50. The catalytic converter 51 includes a three-way catalyst. Note that the exhaust gas purification system is not limited to the one including only the three-way catalyst.

  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 downstream of the catalytic converter 51 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 that includes an EGR passage 52 and an EGR valve 54, and an internal EGR system that includes the above-described intake electric VVT 23 and exhaust electric VVT 24. It is configured. The EGR valve 54 also constitutes one of the state quantity setting devices.

  The control device for the compression self-ignition engine includes an ECU (Engine Control Unit) 10 for operating the engine 1. The ECU 10 is a controller based on a well-known microcomputer, and includes a central processing unit (CPU) that executes a program and, for example, a RAM (Random Access Memory) and a ROM (Read Only Memory). A memory for storing programs and data, and an input / output bus for inputting and outputting electrical signals. The ECU 10 is an example of a controller.

  As shown in FIGS. 1 and 3, various sensors SW <b> 1 to SW <b> 16 are connected to the ECU 10. Sensors SW1-SW16 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-cylinder 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 a catalytic converter 51 in the exhaust passage 50. A linear O ₂ sensor SW8 that is disposed upstream of the exhaust gas and detects the oxygen concentration in the exhaust gas, and a lambda O ₂ sensor SW9 that is disposed downstream of the catalytic converter 51 in the exhaust passage 50 and detects the oxygen concentration in the exhaust gas. A water temperature sensor SW10 that is attached to the engine 1 and detects the temperature of the cooling water, a crank angle sensor SW11 that is attached to the engine 1 and detects the rotation angle of the crankshaft 15, an accelerator pedal mechanism, and an accelerator pedal Accelerator opening sensor SW12 for detecting the accelerator opening corresponding to the operation 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 an EGR passage 52 are arranged. In addition, an EGR differential pressure sensor SW15 that detects a differential pressure upstream and downstream of the EGR valve 54, and a fuel pressure sensor SW16 that is attached to the common rail 64 of the fuel supply system 61 and detects the pressure of the fuel supplied to the injector 6 is there.

  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 a control signal related to the calculated control amount to the electromagnetic clutch 45 of the injector 6, spark plug 25, intake electric VVT 23, exhaust electric VVT 24, fuel supply system 61, throttle valve 43, EGR valve 54, and supercharger 44. And output to the air bypass valve 48. 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. Details of control of the engine 1 by the ECU 10 will be described later.

<Engine operating range>
FIG. 4 illustrates an operation region of the engine 1. The operating region of the engine 1 is roughly divided into three regions with respect to the load level. Specifically, the three regions include a low load region (A) including idle operation, a high load region (C) including a fully open load, and a low load region (A) and a high load region (C). It is a medium load region (B). The engine 1 performs combustion by compression self-ignition in an intermediate load region with the main purpose of improving fuel consumption and exhaust gas performance. Hereinafter, combustion modes in each of the low load region, the medium load region, and the high load region will be described in order.

(Low load area)
When the operating state of the engine 1 is in the low load region, the fuel injection amount is small. Therefore, the amount of heat generated when the air-fuel mixture burns in the combustion chamber 17 is small, and the temperature (in-cylinder temperature) of the combustion chamber 17 is lowered. Further, since the temperature of the exhaust gas is lowered, even if the internal EGR gas is introduced into the combustion chamber 17 as will be described later, the in-cylinder temperature does not rise to such an extent that self-ignition can be stably performed. The combustion mode when the operating state of the engine 1 is in the low load region is SI (Spark Ignition) combustion in which the air-fuel mixture is combusted by flame propagation when the spark plug 25 ignites the air-fuel mixture in the combustion chamber 17. is there. Hereinafter, the combustion mode in the low load region may be referred to as low load SI combustion.

  When the operating state of the engine 1 is in the low load region, the air-fuel ratio (A / F) of the air-fuel mixture is the stoichiometric air-fuel ratio (A / F = 14.7). 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.

  In order to improve the fuel consumption performance of the engine 1, the EGR system 55 introduces EGR gas into the combustion chamber 17 when the operating state of the engine 1 is in a low load region. The G / F of the air-fuel mixture, that is, the mass ratio of the total gas and fuel in the combustion chamber 17 is set to 18.5 or more and 30 or less. The mixture is EGR lean. The dilution ratio of the mixture is high. If the G / F of the air-fuel mixture is set to 25, for example, SI combustion can be performed stably in the low load operation region without causing the air-fuel mixture to self-ignite. In the low load region, the G / F of the air-fuel mixture is kept constant regardless of the load level of the engine 1. By doing so, SI combustion is stabilized throughout the low load region. Further, the fuel efficiency of the engine 1 is improved and the exhaust gas performance is improved.

When the operating state of the engine 1 is in the low load region, since the amount of fuel is small, in order to set the λ of the air-fuel mixture to 1.0 ± 0.2 and G / F to 18.5 or more and 30 or less, combustion The filling amount of the gas introduced into the chamber 17 must be less than 100%. Specifically, the engine 1 executes throttling for adjusting the opening degree of the throttle valve 43 and / or a mirror cycle for delaying the closing timing of the intake valve 21 after the intake bottom dead center.
In the low-load low-rotation region in the low-load region, the combustion temperature of the air-fuel mixture and the exhaust gas temperature may be increased by further reducing the gas filling amount. This is advantageous in maintaining the catalytic converter 51 in an active state.

(Medium load area)
When the operating state of the engine 1 is in the medium load region, the fuel injection amount increases. Since the in-cylinder temperature increases, self-ignition can be performed stably. In order to improve fuel consumption and exhaust gas performance, the engine 1 performs CI combustion in the medium load region.

  In the combustion by self-ignition, when the temperature in the combustion chamber 17 before the start of compression varies, the timing of self-ignition greatly changes. Therefore, the engine 1 performs SI-CI combustion combining SI combustion and CI combustion in the medium load region. In the SI-CI combustion, when the spark plug 25 forcibly ignites the air-fuel mixture in the combustion chamber 17, the air-fuel mixture is burned by flame propagation, and the heat generated in the SI combustion causes the air-fuel mixture in the combustion chamber 17 to burn. As the temperature increases, the unburned mixture burns 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.

  In SI-CI combustion, in order to accurately control the timing of self-ignition, the timing of self-ignition must change in response to changing the ignition timing. It is preferable that the sensitivity at which the self-ignition timing changes is high with respect to the change in the ignition timing.

  According to the study by the present inventors, if the λ of the air-fuel mixture is 1.0 ± 0.2 and the G / F of the air-fuel mixture is 18.5 or more and 30 or less, self- It turns out that the timing of ignition changes. Therefore, when the operating state of the engine 1 is in the medium load region, the engine 1 is in a state in the combustion chamber 17 where the λ of the mixture is 1.0 ± 0.2 and the G / F of the mixture is Set to 18.5 or more and 30 or less.

  By accurately controlling the timing of self-ignition, an increase in combustion noise can be avoided when the operating state of the engine 1 is in the middle load region. Further, by performing the CI combustion with the dilution ratio of the air-fuel mixture as high as possible, the fuel efficiency performance of the engine 1 can be enhanced. Furthermore, by setting λ of the air-fuel mixture to 1.0 ± 0.2, it becomes possible to purify the exhaust gas by the three-way catalyst, so that the exhaust gas performance of the engine 1 becomes good.

As described above, in the low load region, the G / F of the mixture is set to 18.5 or more and 30 or less (for example, 25), and λ of the mixture is set to 1.0 ± 0.2. The state quantity in the combustion chamber 17 does not fluctuate greatly between when the operating state of the engine 1 is in the low load region and when it is in the medium load region. Therefore, the robustness of the control of the engine 1 against the change in the load of the engine 1 is enhanced.
When the operating state of the engine 1 is in the medium load region, the amount of fuel increases, unlike in the low load region, so there is no need to adjust the filling amount of the gas introduced into the combustion chamber 17. The opening degree of the throttle valve 43 is fully open.

  When the load on the engine 1 is increased and the fuel amount is further increased, it is natural to set the λ of the mixture to 1.0 ± 0.2 and the G / F of the mixture to 18.5 or more and 30 or less. In the intake state, the amount of gas introduced into the combustion chamber 17 is insufficient. Therefore, the supercharger 44 supercharges the gas introduced into the combustion chamber 17 in a region where the load is higher than the predetermined load in the medium load region. The medium load region (B) is a region that is higher than the predetermined load, and is a first medium load region (B1) that performs supercharging, and a region that is below the predetermined load and that does not perform supercharging. It is divided into a medium load region (B2). The predetermined load is, for example, a ½ load. The second medium load region is a region having a lower load than the first medium load region. Hereinafter, the combustion mode in the first medium load region may be referred to as supercharged SI-CI combustion, and the combustion mode in the second medium load region may be referred to as non-supercharged SI-CI combustion.

  In the second medium load region where supercharging is not performed, as the amount of fuel increases, fresh air introduced into the combustion chamber 17 increases while EGR gas decreases. The G / F of the air-fuel mixture decreases as the load on the engine 1 increases. Since the opening of the throttle valve 43 is fully opened, the engine 1 adjusts the amount of fresh air introduced into the combustion chamber 17 by adjusting the amount of EGR gas introduced into the combustion chamber 17. . In the second medium load region, the state quantity in the combustion chamber 17 is, for example, λ of the air-fuel mixture becomes substantially constant at 1.0, while the G / F of the air-fuel mixture is changed in the range of 25 to 28.

  In contrast, in the first medium load region where supercharging is performed, the engine 1 increases both fresh air and EGR gas introduced into the combustion chamber 17 as the amount of fuel increases. The G / F of the air-fuel mixture is constant even when the load on the engine 1 increases. In the first medium load region, the state quantity in the combustion chamber 17 is, for example, λ of the air-fuel mixture becomes substantially constant at 1.0, and G / F of the air-fuel mixture is constant at 25.

(High load area)
When the operating state of the engine 1 is in the high load region, the fuel injection amount is large. Therefore, even if SI-CI combustion is performed, it becomes difficult to suppress combustion noise. In addition, since the in-cylinder temperature becomes high, abnormal combustion such as pre-ignition and knocking is likely to occur even if CI combustion is performed. Therefore, the combustion mode when the operating state of the engine 1 is in the high load region is SI combustion. Hereinafter, the combustion mode in the high load region may be referred to as high load SI combustion.

  When the operating state of the engine 1 is in the high load region, λ of the air-fuel mixture is 1.0 ± 0.2. Further, the G / F of the air-fuel mixture is set to 18.5 or more and 30 or less. In the high load region, the opening degree of the throttle valve 43 is fully open, and the supercharger 44 performs supercharging.

  In the high load region, the engine 1 reduces the amount of EGR gas as the load increases. The G / F of the air-fuel mixture decreases as the load on the engine 1 increases. Since the amount of fresh air introduced into the combustion chamber 17 is increased by the amount of EGR gas reduced, the amount of fuel can be increased. This is advantageous in increasing the maximum output of the engine 1. The G / F of the air-fuel mixture is changed, for example, in the range of 17 to 25 in the high load region.

  The state quantity in the combustion chamber 17 does not fluctuate greatly between when the operating state of the engine 1 is in the high load region and when it is in the medium load region. The robustness of the control of the engine 1 against the change of the load of the engine 1 is increased.

As described above, the engine 1 performs SI combustion in a high load region, but there is a problem that abnormal combustion such as pre-ignition and knocking is likely to occur due to a high geometric compression ratio and the like. .
Therefore, the engine 1 is configured to avoid abnormal combustion by devising the form of fuel injection in the high load region. Specifically, the ECU 10 injects fuel into the combustion chamber 17 at a high fuel pressure of 30 MPa or more and at a timing within a period from the latter stage of the compression stroke to the early stage of the expansion stroke (hereinafter, this period is referred to as a retard period). Thus, a control signal is output to the fuel supply system 61 and the injector 6. The ECU 10 also outputs a control signal to the spark plug 25 so that the air-fuel mixture is ignited at a timing near the compression top dead center after fuel injection. In the following description, injecting fuel into the combustion chamber 17 at a high fuel pressure and at a timing within the retard period is referred to as high-pressure retarded injection.

  High pressure retarded injection avoids abnormal combustion by shortening the time during which the air-fuel mixture reacts. That is, the reaction time of the air-fuel mixture includes (1) a period during which the injector 6 injects fuel (that is, an injection period), and (2) after the fuel injection is completed, This is a time obtained by adding the period until formation (that is, the mixture formation period) and (3) the period until SI combustion started by ignition ends ((3) combustion period).

  When fuel is injected into the combustion chamber 17 at a high fuel pressure, the injection period and the mixture formation period become shorter. When the injection period and the air-fuel mixture formation period are shortened, the timing for starting fuel injection can be made closer to the ignition timing. In the high pressure retarded injection, since the fuel is injected into the combustion chamber 17 at a high pressure, the fuel is injected at the timing within the retard period from the latter stage of the compression stroke to the early stage of the expansion stroke.

  When fuel is injected into the combustion chamber 17 at a high fuel pressure, the turbulent energy in the combustion chamber 17 increases. When the fuel injection timing is brought close to the compression top dead center, SI combustion can be started with high turbulent energy in the combustion chamber 17. As a result, the combustion period is shortened.

  The high pressure retarded injection can shorten the injection period, the mixture formation period, and the combustion period. Compared with the case where fuel is injected into the combustion chamber 17 during the intake stroke, the high-pressure retarded injection can greatly shorten the time for the air-fuel mixture to react. In the high pressure retarded injection, the time for which the air-fuel mixture reacts is shortened, so that abnormal combustion can be avoided.

  In the technical field of engine control, in order to avoid abnormal combustion, the ignition timing is conventionally retarded. However, if the ignition timing is delayed, the fuel consumption performance decreases. The high pressure retarded injection need not retard the ignition timing. By using high-pressure retarded injection, fuel efficiency is improved.

  If the fuel pressure is, for example, 30 MPa or more, the injection period, the mixture formation period, and the combustion period can be effectively shortened. The fuel pressure is preferably set as appropriate according to the properties of the fuel. As an example, the upper limit value of the fuel pressure may be 120 MPa.

  Here, when the rotational speed of the engine 1 is low, the time required for the crank angle to change by the same angle is long. Therefore, shortening the reaction time of the air-fuel mixture by high-pressure retarded injection is to avoid abnormal combustion. Is particularly effective. On the other hand, when the rotational speed of the engine 1 is increased, the time when the crank angle changes by the same angle is shortened. For this reason, shortening the reaction time of the air-fuel mixture is not so effective in avoiding abnormal combustion.

  The high-pressure retarded injection also injects fuel into the combustion chamber 17 only after the compression top dead center is reached. Therefore, in the compression stroke, in the combustion chamber 17, a gas that does not contain fuel, in other words, a specific heat ratio. High gas is compressed. If high pressure retarded injection is performed when the number of revolutions of the engine 1 is high, the in-cylinder temperature at the compression top dead center, that is, the compression end temperature becomes high. An increase in the compression end temperature may cause abnormal combustion such as knocking.

  Therefore, in the engine 1, the high load region (C) is divided into the first high load region (C1) on the low rotation side and the second high load region (C2) having a higher rotational speed than the first high load region (C1). ). The first high load region may include a low rotation region and a medium rotation region when the high load region is divided into three regions of low rotation, medium rotation, and high rotation. The second high load region may include a high rotation region obtained by dividing the inside of the high load region into three regions of low rotation, medium rotation, and high rotation.

In the first high load region, the injector 6 receives the control signal from the ECU 10 and performs the above-described high-pressure retarded injection. In the second high load region, the injector 6 receives a control signal from the ECU 10 and injects fuel at a predetermined timing during the intake stroke. The fuel injection performed during the intake stroke does not require high fuel pressure. The ECU 10 outputs a control signal to the fuel supply system 61 so that the fuel pressure is lower than the fuel pressure of the high pressure retarded injection (for example, the fuel pressure is less than 40 MPa). By reducing the fuel pressure, the mechanical resistance loss of the engine 1 is reduced, which is advantageous for improving fuel consumption.
By injecting fuel into the combustion chamber 17 during the intake stroke, the specific heat ratio of the gas in the combustion chamber 17 is lowered, so that the compression end temperature is lowered. Since the compression end temperature becomes low, the engine 1 can avoid abnormal combustion. Since it is not necessary to retard the ignition timing in order to avoid abnormal combustion, in the second high load region, the spark plug 25 is mixed at the timing near the compression top dead center, as in the first high load region. I ignite my mind.

  In the first high load region, the air-fuel mixture does not reach self-ignition due to the high pressure retarded injection, and therefore the engine 1 can perform stable SI combustion. In the second high load region, the air-fuel mixture does not reach self-ignition due to fuel injection during the intake stroke, and therefore the engine 1 can perform stable SI combustion.

<SI-CI combustion>
Next, the above-described SI-CI combustion will be described in more detail with reference to FIGS. FIGS. 5A to 5C show waveforms illustrating the change in the heat generation rate with respect to the crank angle in SI-CI combustion. When the ignition plug 25 ignites the air-fuel mixture in the vicinity of the compression top dead center, more precisely at a predetermined timing before the compression top dead center, combustion by flame propagation starts. Heat generation during SI combustion is milder than heat generation during CI combustion. Therefore, the waveform of the heat generation rate has a relatively small slope. Although not shown, the pressure fluctuation (dp / dθ) in the combustion chamber 17 during SI combustion is also gentler than that during CI combustion.

  When the in-cylinder temperature and the in-cylinder pressure are increased by SI combustion, the unburned mixture is self-ignited. In the example of FIG. 5A, the inclination of the waveform of the heat generation rate changes from small to large almost at the compression top dead center. 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. As described above, since SI-CI combustion can reduce dp / dθ, it is possible to avoid excessive combustion noise. become. Combustion noise can be suppressed below an acceptable level.

When CI combustion ends, SI-CI combustion ends. CI combustion has a shorter combustion period than SI combustion. In SI-CI combustion, the combustion end time is earlier than SI combustion. In other words, the SI-CI combustion can bring the combustion end time during the expansion stroke closer to the compression top dead center. SI-CI combustion is more advantageous for improving the fuel efficiency of the engine 1 than SI combustion.
Therefore, SI-CI combustion can achieve both prevention of combustion noise and improvement in fuel efficiency.

  Here, the SI rate is defined as a parameter indicating the characteristic of SI-CI combustion. The SI rate is defined as the ratio of the amount of heat generated by SI combustion to the total amount of heat generated by SI-CI combustion. That is, in FIG. 5A, the SI rate is SI rate = (SI combustion area) / (SI-CI combustion area). The SI rate is a ratio between SI combustion and CI combustion in SI-CI combustion combining SI combustion and CI combustion. When the SI rate is high, the SI combustion rate is high, and when the SI rate is low, the CI combustion rate is high.

  The SI rate is not limited to the above-described definition. Various definitions can be considered for the SI rate. For example, the SI rate may be the ratio of the amount of heat generated by SI combustion to the amount of heat generated by CI combustion. That is, in FIG. 5A, SI rate = (SI combustion area) / (CI combustion area) may be used.

In SI-CI combustion, the waveform of the heat generation rate has an inflection point at the timing when CI combustion starts. Therefore, as shown in FIG. 5B, the inflection point in the waveform of the heat release rate may be used as a boundary, and the range on the advance side of the boundary may be SI combustion and the range on the retard side may be CI combustion. In this case, as shown by hatching in FIG. 5B, the SI rate is calculated based on the area Q _{SI in} the range on the advance side from the boundary and the area Q _{CI in} the range on the retard side from the SI rate = Q _SI / (Q _SI + Q _CI ) may be set, or SI rate = Q _SI / Q _CI may be set. In addition, the SI rate may be defined on the basis of a part of the area rather than the entire area on the advance side from the boundary and a part of the area on the retard side from the boundary.

In addition, the SI rate is not defined based on the heat generation, but the SI rate = Δθ _SI / (Δθ from the crank angle Δθ _SI in the advance side range and the crank angle Δθ _{CI in} the retard side range from the boundary. _SI + Δθ _CI ), or SI rate = Δθ _SI / Δθ _CI .

Further, the SI rate = ΔP _SI / (ΔP _SI + ΔP _CI ) may be calculated from the peak ΔP _SI of the heat generation rate in the range on the advance side of the boundary and the peak ΔP _CI of the heat generation rate in the range on the retard side. , SI rate = ΔP _SI / ΔP _CI .

In addition, the SI rate = φ _SI / (φ _SI + φ _CI ) may be calculated based on the inclination φ _SI of the heat generation rate in the advance angle range from the boundary and the heat generation rate inclination φ _CI in the retard angle range. The SI rate may be φ _SI / φ _CI .

  Also, here, based on the heat generation rate waveform, the area (that is, the amount of heat generation), the length of the horizontal axis (that is, the size of the crank angle), the length of the vertical axis (that is, the heat generation amount) The SI rate is defined from the magnitude of the generation rate) or the slope (that is, the rate of change of the heat generation rate). Although illustration is omitted, based on the waveform of the in-cylinder pressure (P), the SI rate may be similarly defined from the area, the length of the horizontal axis, the length of the vertical axis, or the slope.

In SI-CI combustion, the inflection point of the combustion waveform related to the heat generation rate or pressure does not always appear clearly. The following definition may be used as the definition of the SI rate that is not based on the inflection point. That is, as shown in FIG. 5C, in the combustion waveform, the range on the advance side from the compression top dead center (TDC) is SI combustion, and the range on the retard side from the compression top dead center is CI combustion. Also good. Then, as described above, the area (Q _SI , Q _CI ), the horizontal axis length (Δθ _SI , Δθ _CI ), the vertical axis length (ΔP _SI , ΔP _CI ), or the slope (φ _SI , Φ _CI ), the SI rate may be defined.

Further, the SI rate may be defined not based on the combustion waveform actually performed in the combustion chamber 17 but based on the fuel amount. As will be described later, in the middle load region where SI-CI combustion is performed, split injection including front-stage injection and rear-stage injection is performed. The fuel injected into the combustion chamber 17 by the post-injection is not diffused in the combustion chamber 17 and is positioned in the vicinity of the spark plug 25 because the time from injection to ignition is short. Therefore, the fuel injected into the combustion chamber 17 by the post-stage injection mainly burns by SI combustion. On the other hand, the fuel injected into the combustion chamber 17 by the pre-stage injection mainly burns by CI combustion. Therefore, the SI rate can be defined based on the fuel amount (m ₁ ) injected by the front injection and the fuel amount (m ₂ ) injected by the rear injection. That is, the SI rate = m ₂ / (m ₁ + m ₂ ) may be set, or the SI rate = m ₂ / m ₁ may be set.

<Basic engine operation control>
As described above, the engine 1 switches between SI combustion and SI-CI combustion according to the operating state. The engine 1 also changes the SI rate according to the operating state of the engine 1. Since the operating range in which combustion is performed by self-ignition is expanded, the engine 1 is compatible with both suppressing the generation of combustion noise and improving fuel consumption.

  FIG. 6 shows the change in the SI ratio, the change in the state quantity in the combustion chamber 17 with respect to the load of the engine 1, the change in the valve opening period of the intake valve and the valve opening period of the exhaust valve, and the fuel injection timing. And changes in ignition timing are illustrated. Hereinafter, the basic operation control of the engine 1 according to the present embodiment will be described on the assumption that the load of the engine 1 gradually increases at a predetermined rotational speed.

(Low load area (low load SI combustion))
In the low load region (A), the engine 1 performs low load SI combustion. When the operating state of the engine 1 is in the low load region, the SI rate is constant at 100%.

  In the low load region, as described above, the G / F of the air-fuel mixture is kept constant between 18.5 and 30. The engine 1 introduces fresh air and burned gas in an amount corresponding to the amount of fuel into the combustion chamber 17. As described above, the amount of fresh air introduced is adjusted by throttling and / or mirror cycles. Since the dilution rate is high, the in-cylinder temperature is increased in order to stabilize SI combustion. The engine 1 introduces internal EGR gas into the combustion chamber 17 in a low load region.

  The internal EGR gas is introduced into the combustion chamber 17 by providing a negative overlap period in which both the intake valve 21 and the exhaust valve 22 are closed across the exhaust top dead center (that is, the burned gas is introduced into the combustion chamber). 17). The internal EGR gas amount is adjusted by adjusting the opening timing of the intake valve 21 by the intake electric VVT 23 and adjusting the opening timing of the exhaust valve 22 by the exhaust electric VVT 24. This is done by appropriately setting the length.

  In the low load region, the filling amount introduced into the combustion chamber 17 is adjusted to less than 100%. As the amount of fuel increases, the amount of fresh air introduced into the combustion chamber 17 and the amount of internal EGR gas gradually increase. The EGR rate in the low load region (that is, the mass ratio of EGR gas to the total gas in the combustion chamber 17) is, for example, 50%.

  The injector 6 injects fuel into the combustion chamber 17 during the intake stroke. In the combustion chamber 17, a homogeneous air-fuel mixture is formed in which the excess air ratio λ is 1.0 ± 0.2 and G / F is 18.5-30. When the spark plug 25 ignites the air-fuel mixture at a predetermined timing before the compression top dead center, the air-fuel mixture burns by flame propagation without reaching self-ignition.

(Second medium load region (non-supercharged SI-CI combustion))
When the load of the engine 1 becomes high and the operation state enters the second middle load region (B2), the engine 1 switches from the low load SI combustion to the non-supercharged SI-CI combustion. The SI rate is less than 100%. As the load on the engine 1 increases, the amount of fuel increases. When the load is low in the second medium load region, the rate of CI combustion is increased as the fuel amount increases. The SI rate gradually decreases as the load on the engine 1 increases. In the example of FIG. 6, the SI rate decreases to a predetermined value (minimum value) of 50% or less.
Since the amount of fuel increases, the combustion temperature becomes higher in the second medium load region. If the in-cylinder temperature becomes too high, heat generation at the start of CI combustion becomes intense. If it becomes so, combustion noise will increase.

  Therefore, in the second medium load region, the ratio of the internal EGR gas and the external EGR gas to the change in the load of the engine 1 in order to adjust the temperature before the compression start in the combustion chamber 17. To change. That is, as the load on the engine 1 increases, the hot internal EGR gas is gradually reduced and the cooled external EGR gas is gradually increased. The negative overlap period is changed from the maximum to zero as the load increases in the second medium load region. The internal EGR gas becomes zero when the load becomes highest in the second medium load region.

  The opening degree of the EGR valve 54 is changed in the second medium load region so that the external EGR gas increases as the load increases. The amount of the external EGR gas introduced into the combustion chamber 17 is adjusted, for example, between 0 to 30% when expressed in terms of the EGR rate. In the second medium load region, the EGR gas is replaced from the internal EGR gas to the external EGR gas as the load on the engine 1 increases.

  Note that the amount of EGR gas introduced into the combustion chamber 17 is continuous between the low load region and the second medium load region. In the low load region in the second medium load region, a large amount of internal EGR gas is introduced into the combustion chamber 17 as in the low load region. Since the in-cylinder temperature becomes high, the air-fuel mixture reliably ignites when the load on the engine 1 is low. The external EGR gas is introduced into the combustion chamber 17 in the high load region in the second medium load region. Since the in-cylinder temperature is lowered, combustion noise associated with CI combustion can be suppressed when the load on the engine 1 is high.

  In the second medium load region, the filling amount introduced into the combustion chamber 17 is made 100%. The opening degree of the throttle valve 43 is fully open. By adjusting the amount of EGR gas that is a combination of the internal EGR gas and the external EGR gas, the amount of fresh air introduced into the combustion chamber 17 is adjusted to an amount corresponding to the fuel amount.

  In the non-supercharged SI-CI combustion, the timing of self-ignition is advanced as the CI combustion ratio increases. If the timing of self-ignition becomes earlier than the compression top dead center, heat generation when CI combustion starts becomes intense. If it becomes so, combustion noise will increase. Therefore, when the load on the engine 1 reaches the predetermined load L1, the engine 1 gradually increases the SI rate as the load on the engine 1 increases.

  That is, the engine 1 increases the rate of SI combustion as the fuel amount increases. Specifically, in non-supercharged SI-CI combustion, the ignition timing is gradually advanced as the fuel amount increases. As described above, the in-cylinder temperature is adjusted by reducing the introduction amount of the internal EGR gas and increasing the introduction amount of the external EGR gas. Therefore, even if the fuel amount increases, the in-cylinder temperature due to SI combustion. It is possible to suppress the rise. The rate of change in the heat generation rate of SI combustion should be almost unchanged even when the load increases. If the ignition timing is advanced, the amount of heat generated by SI combustion increases as the SI combustion starts earlier.

  As a result of suppressing the temperature rise in the combustion chamber 17 due to SI combustion, the unburned air-fuel mixture self-ignites at a timing after the compression top dead center. The heat generation by the CI combustion is almost the same even if the load of the engine 1 is high because the heat generation amount of the SI combustion is increased. Therefore, it is possible to avoid an increase in combustion noise by setting the SI rate gradually higher in accordance with the load on the engine 1 becoming higher. Note that the combustion center of gravity of non-supercharged SI-CI combustion is retarded as the load increases.

  In the second medium load region, the injector 6 injects fuel into the combustion chamber 17 in two steps of the front injection and the rear injection during the compression stroke. The front-stage injection injects fuel at a timing away from the ignition timing, and the rear-stage injection injects fuel at a timing close to the ignition timing. In the combustion chamber 17, a substantially homogeneous air-fuel mixture with an excess air ratio λ of 1.0 ± 0.2 and a G / F of 18.5-30 is formed. Since the air-fuel mixture is substantially homogeneous, it is possible to improve fuel efficiency by reducing unburned loss and to improve exhaust gas performance by avoiding the generation of smoke.

  When the spark plug 25 ignites the air-fuel mixture at a predetermined timing before the compression top dead center, the air-fuel mixture burns by flame propagation. Thereafter, the unburned mixture self-ignites and performs CI combustion. The fuel injected by the latter-stage injection mainly undergoes SI combustion. The fuel injected by the pre-stage injection mainly undergoes CI combustion. Since the pre-injection is performed during the compression stroke, it is possible to prevent the fuel injected by the pre-injection from inducing abnormal combustion such as premature ignition. Moreover, the fuel injected by the latter stage injection can be stably burned by flame propagation.

(First medium load region (supercharged SI-CI combustion))
When the load on the engine 1 further increases and the operating state of the engine 1 enters the first medium load region (B1), the supercharger 44 supercharges fresh air and external EGR gas. Both the amount of fresh air introduced into the combustion chamber 17 and the amount of external EGR gas increase as the load on the engine 1 increases. The amount of external EGR gas introduced into the combustion chamber 17 is, for example, 30% in terms of the EGR rate. The EGR rate is constant regardless of the load level of the engine 1. Accordingly, the G / F of the air-fuel mixture is also constant regardless of the load of the engine 1. Note that the amount of EGR gas introduced into the combustion chamber 17 is continuous between the second medium load region and the first medium load region.

  The SI rate is a predetermined value less than 100%, and is constant with respect to the load of the engine 1. When comparing the SI rate in the second medium load region, particularly the SI rate that is higher than the predetermined load L1 and gradually increases as the load of the engine 1 increases, the SI rate in the first medium load region is The SI rate in the first medium load region with a high load of 1 is higher than the SI rate in the second medium load region. The SI rate is continuous at the boundary between the first medium load region and the second medium load region.

  Also in the supercharged SI-CI combustion, the ignition timing is gradually advanced as the fuel amount increases. As described above, since the amount of fresh air and EGR gas introduced into the combustion chamber 17 is increased by supercharging, the heat capacity is large. Even if the amount of fuel increases, it is possible to suppress an increase in in-cylinder temperature due to SI combustion. The waveform of the heat generation rate of supercharged SI-CI combustion increases in a similar manner as the load increases.

  That is, the rate of change in the heat generation rate of SI combustion hardly changes, and the amount of heat generation in SI combustion increases. The unburned mixture self-ignites at approximately the same timing after compression top dead center. The amount of heat generated by CI combustion increases as the load on the engine 1 increases. As a result, in the first medium load region, both the heat generation amount of SI combustion and the heat generation amount of CI combustion increase, so the SI rate becomes constant with respect to the load of the engine 1. When the peak of heat generation of CI combustion increases, the combustion noise increases. However, since the load of the engine 1 is relatively high in the first medium load region, a certain level of combustion noise can be tolerated. Note that the combustion center of gravity of supercharged SI-CI combustion is retarded as the load increases.

  In the first intermediate load region, an overlap period is provided in which both the intake valve 21 and the exhaust valve 22 are opened across the exhaust top dead center. The burned gas remaining in the combustion chamber 17 is scavenged by the supercharging pressure. Thereby, since the in-cylinder temperature is lowered, it is possible to prevent abnormal combustion from occurring when the load on the engine 1 is relatively high. In addition, by reducing the in-cylinder temperature, the self-ignition timing can be set to an appropriate timing in a region where the load of the engine 1 is relatively high, and the SI rate can be maintained at a predetermined SI rate. . Further, the amount of fresh air in the combustion chamber 17 can be increased by scavenging the burned gas.

  In the first medium load region, the injector 6 injects fuel into the combustion chamber 17 in two steps of the pre-stage injection and the post-stage injection during the compression stroke, as in the second medium load region. The front-stage injection injects fuel at a timing away from the ignition timing, and the rear-stage injection injects fuel at a timing close to the ignition timing. In the combustion chamber 17, a substantially homogeneous air-fuel mixture with an excess air ratio λ of 1.0 ± 0.2 and a G / F of 18.5-30 is formed. Since the air-fuel mixture is substantially homogeneous, it is possible to improve fuel efficiency by reducing unburned loss and to improve exhaust gas performance by avoiding the generation of smoke.

  When the spark plug 25 ignites the air-fuel mixture at a predetermined timing before the compression top dead center, the air-fuel mixture burns by flame propagation. Thereafter, the unburned mixture self-ignites and performs CI combustion. The fuel injected by the latter-stage injection mainly undergoes SI combustion. The fuel injected by the pre-stage injection mainly undergoes CI combustion. Since the pre-injection is performed during the compression stroke, it is possible to prevent the fuel injected by the pre-injection from inducing abnormal combustion such as premature ignition. Moreover, the fuel injected by the latter stage injection can be stably burned by flame propagation.

(High load range (high load SI combustion))
When the load on the engine 1 further increases and the operating state of the engine 1 enters the high load region (C), the engine 1 performs high load SI combustion. Therefore, the SI rate is 100% in the high load region.

  The throttle valve 43 is fully open. The supercharger 44 supercharges fresh air and external EGR gas even in a high load region. The EGR valve 54 adjusts the opening to gradually reduce the amount of external EGR gas introduced as the load on the engine 1 increases. By doing so, the fresh air introduced into the combustion chamber 17 increases as the load on the engine 1 increases. As the amount of fresh air increases, the amount of fuel can be increased, which is advantageous in increasing the maximum output of the engine 1. Note that the amount of EGR gas introduced into the combustion chamber 17 is continuous between the first medium load region and the high load region.

  Also in the high load region, similarly to the first medium load region, an overlap period is provided in which both the intake valve 21 and the exhaust valve 22 are opened with the exhaust top dead center interposed therebetween. The burned gas remaining in the combustion chamber 17 is scavenged by the supercharging pressure. Thereby, generation | occurrence | production of abnormal combustion is suppressed. In addition, the amount of fresh air in the combustion chamber 17 can be increased.

  In the region on the low rotation side of the high load region (that is, the first high load region (C1)), the injector 6 injects fuel into the combustion chamber 17 within the retard period as described above. In the region on the high rotation side of the high load region (that is, the second high load region (C2)), the injector 6 injects fuel into the combustion chamber 17 during the intake stroke. In any case, in the combustion chamber 17, a substantially homogeneous mixture having an excess air ratio λ of 1.0 ± 0.2 and a G / F of 18.5 to 30 is formed. When the spark plug 25 ignites the air-fuel mixture at a predetermined timing before the compression top dead center, the air-fuel mixture burns by flame propagation. In the high load region, the air-fuel mixture undergoes SI combustion without reaching self-ignition by high-pressure retarded injection or fuel injection during the intake stroke.

<Relationship between engine load, SI rate and self-ignition timing>
Next, control of the SI rate and self-ignition timing according to the present embodiment will be described. In the present embodiment, the ECU 10 functions as means (first and second control means) for controlling each of the SI rate and the self-ignition timing, and by these means, during one combustion cycle of the engine 1, SI combustion and Both combustion states of the CI combustion are changed according to the operating state of the engine 1. By doing so, a desired SI-CI combustion waveform is realized. Specifically, a desired SI rate and self-ignition timing are realized.

  With reference to FIG. 7, in this embodiment, the control of the SI rate and the self-ignition timing executed by the ECU 10 according to the engine load will be specifically described. FIG. 7 is a diagram for explaining the relationship between the engine load, the SI rate, and the self-ignition timing in the present embodiment.

  In FIG. 7, the abscissa indicates the crank angle, and the ordinate indicates the heat generation rate (dQ / dθ), and a plurality of combustion waveforms of SI-CI combustion applied in accordance with the engine load (in other words, heat generation). Shape). Such a combustion waveform shown in FIG. 7 is typically applied in the above-described second medium load region B2 where supercharging is not performed, more specifically, in a region exceeding the predetermined load L1 in the second medium load region B2. (See FIG. 6). Note that, since the amount of generated heat Q increases as the engine load increases, the area of “dQ / dθ” increases. In FIG. 7, from the viewpoint of focusing on the shape of the combustion waveform, the value of “dQ / dθ” Shows a combustion waveform in which is normalized to have approximately the same area.

  First, as shown in the graph G11, when the engine load is relatively low, the combustion noise is not a problem. Therefore, the ECU 10 has a crank angle near the compression top dead center (TDC) that can realize stable self-ignition. (Relatively advanced crank angle) is applied to the self-ignition timing of CI combustion. In addition, since the fuel consumption is better when the combustion period is shorter, the ECU 10 decreases the SI rate in SI-CI combustion, that is, increases the ratio of CI combustion in SI-CI combustion. Next, as shown in the graph G12, as the engine load increases, the ECU 10 increases the SI rate (arrows A11 and A12) and suppresses the period during which CI combustion is performed in order to suppress the generation of combustion noise. The self-ignition timing of CI combustion is retarded so as to extend as much as possible (arrow A13).

Next, as shown in the graph G13, the ECU 10 increases the SI rate as the engine load increases and retards the self-ignition timing (arrows A14, A15, A16). When reaches a predetermined retardation limit θ _lim , the self-ignition timing is fixed to this retardation limit θ _lim so that the self-ignition timing is not retarded from the retardation limit θ _lim . This retard angle limit θ _lim is determined based on the limit ignition timing at which the CI combustion self-ignition stability is ensured, and by limiting the retard angle of the self-ignition timing by such retard angle limit θ _lim . , CI combustion self-ignition stability is ensured. The retardation limit θ _lim is not limited to being set to a fixed value, and may be changed according to various states of the engine 1 (for example, the in-cylinder temperature).

  Next, as the engine load further increases, the ECU 10 determines the crank angle at which the heat generation rate (dQ / dθ) in SI combustion becomes almost maximum as shown in the graph G14 (the broken line graph G15 indicating only SI combustion also). In addition, the self-ignition stability of CI combustion is ensured by applying the self-ignition timing. Specifically, the ECU 10 applies the crank angle corresponding to the heat generation peak (50% combustion position) of SI combustion to the self-ignition timing. Then, when the engine load further increases, the ECU 10 shifts from the second middle load region B2 to the first middle load region B1, thereby suppressing combustion noise by executing supercharging by the supercharger 44. Like that. The combustion waveform applied in this case is almost the same as that of the graph G14.

  Further, in the present embodiment, as shown in FIG. 7, the ECU 10 makes the combustion gravity center position in the SI-CI combustion almost constant regardless of the engine load so as to reliably satisfy the target engine torque according to the driver request. Thus, the SI rate and the self-ignition timing are set. In particular, since the fuel efficiency improves when the combustion center of gravity in SI-CI combustion is in the vicinity of 2 to 6 degrees (ATDC 2 to 6 degrees) after compression top dead center, the ECU 10 determines the combustion center of gravity in such SI-CI combustion. The SI rate and self-ignition timing are set in consideration of the engine load so that the position is maintained. At this time, the ECU 10 further adjusts the in-cylinder temperature before the start of combustion. Typically, the ECU 10 performs control to increase the in-cylinder temperature before the start of combustion as the engine load decreases (in other words, performs control to decrease the in-cylinder temperature before the start of combustion as the engine load increases). For example, the ECU 10 performs control to increase the internal EGR rate so as to increase the in-cylinder temperature before the start of combustion. Thereby, the start of SI combustion can be delayed, that is, the start of SI combustion can be prevented from being accelerated.

In a state where the in-cylinder temperature before the start of combustion is relatively low, the ignition timing for SI combustion may be advanced so that the SI rate increases as the engine load increases. In this case, from the viewpoint of ensuring flame propagation and cooling loss suppression (that is, to prevent SI combustion from starting too early), set the ignition timing to the advance side within a range that does not exceed the predetermined advance limit. It is good to do.
However, in a state where the in-cylinder temperature before the start of combustion is relatively high, it is preferable to increase the SI rate by decreasing the in-cylinder temperature as much as the engine load increases. This is because if the in-cylinder temperature before the start of combustion is high, the in-cylinder temperature quickly reaches the ignition temperature after SI combustion, so that CI combustion may occur earlier than the desired self-ignition timing.

<Relationship between in-cylinder temperature and SI rate>
Next, control of the SI rate and the in-cylinder temperature according to the present embodiment will be described. In the present embodiment, the ECU 10 functions as means (first and second control means) for controlling each of the SI rate and the in-cylinder temperature, and by these means, during one combustion cycle of the engine 1, SI combustion and Both combustion states of the CI combustion are changed according to the operating state of the engine 1. By doing so, a desired SI-CI combustion waveform is realized. Specifically, a desired SI rate and self-ignition timing are realized.

  With reference to FIG.8 and FIG.9, in this embodiment, control of the SI rate which ECU10 performs according to the in-cylinder temperature (temperature in the combustion chamber 17) before a combustion start is demonstrated concretely.

  FIG. 8 is an explanatory diagram of a method for controlling the SI rate according to the in-cylinder temperature before the start of combustion in the present embodiment. FIG. 8 shows the crank angle on the horizontal axis and the in-cylinder temperature on the vertical axis. The graph G21 shows only the operation of the piston 3 when the in-cylinder temperature before the start of combustion is relatively low (corresponding to motoring). The graph G23 shows the change in the in-cylinder temperature only due to the operation of the piston 3 when the in-cylinder temperature before the start of combustion is relatively high. Further, the graph G22 shows the change in the in-cylinder temperature when the SI combustion is performed so that the self-ignition is generated at the compression top dead center (TDC) when the in-cylinder temperature before the start of the combustion is relatively low. Graph G24 shows the change in the in-cylinder temperature when the SI combustion is performed so that self-ignition occurs almost at the compression top dead center when the in-cylinder temperature before the start of combustion is relatively high.

From the graphs G21 to G24, when the in-cylinder temperature before the start of combustion is relatively low, a temperature rise amount (generated heat amount) as indicated by arrow A21 is required, and when the in-cylinder temperature before the start of combustion is relatively high A temperature increase amount (generated heat amount) due to SI combustion as indicated by an arrow A22 is required. From this, it is understood that when the in-cylinder temperature before the start of combustion is low, a large amount of temperature rise (generated heat amount) due to SI combustion is required.
Therefore, in the present embodiment, the ECU 10 increases the SI rate when the in-cylinder temperature before the start of combustion is low than when the in-cylinder temperature before the start of combustion is high. Thus, by performing control according to the in-cylinder temperature before the start of combustion, the target SI rate can be realized, and the target self-ignition timing can be realized as a result.

  Next, FIG. 9 is an explanatory diagram of a method for controlling the SI rate so as to realize a desired self-ignition timing in accordance with the in-cylinder temperature before the start of combustion in the present embodiment. In FIG. 9, the horizontal axis indicates the crank angle, and the vertical axis indicates the heat generation rate (dQ / dθ). Graph G31 shows a combustion waveform (in other words, heat generation shape) applied when the in-cylinder temperature before the start of combustion is relatively low, and graph G32 shows when the in-cylinder temperature before the start of combustion is relatively high. The combustion waveform to be applied (in other words, the heat generation shape) is shown.

In the present embodiment, the ECU 10 controls the SI rate so as to realize a desired self-ignition timing of CI combustion (that is, target self-ignition timing) regardless of the in-cylinder temperature before the start of combustion. Specifically, as described above, the ECU 10 increases the SI rate as the in-cylinder temperature before the start of combustion decreases (in other words, the SI rate decreases as the in-cylinder temperature before the start of combustion increases). In this case, the ECU 10 increases the SI rate as the in-cylinder temperature before the start of combustion decreases at the same engine load. For example, the ECU 10 controls the area of “dQ / dθ” up to the self-ignition timing θ _CL as the SI rate, that is, the amount of heat generated by SI combustion so that the target self-ignition timing is realized. Further, the ECU 10 increases the SI rate by, for example, advancing the ignition timing by the spark plug 25 to accelerate the start of SI combustion.

<SI-CI combustion control>
Next, in the present embodiment, in order to achieve desired SI-CI combustion (specifically, desired SI rate, self-ignition timing, etc.) that can achieve improvements in fuel efficiency, ensuring combustion stability, suppressing combustion noise, and the like. Next, the details of the SI-CI combustion control performed by the ECU 10 will be described.

(Basic control configuration)
First, an outline of SI-CI combustion control according to the present embodiment will be described. In the present embodiment, first, the ECU 10 sets a target SI rate and a target self-ignition timing according to the operating state of the engine 1, and SI-CI to be set according to the target SI rate and the target self-ignition timing. The in-cylinder temperature before the start of combustion, specifically, the in-cylinder temperature at the time of closing the intake valve 21 (hereinafter referred to as “IVC” as appropriate) is obtained, and the EGR rate is set so as to realize this in-cylinder temperature. Control etc. In this way, control for realizing a desired self-ignition timing, in other words, control for setting a desired in-cylinder state before the start of SI-CI combustion is performed in advance.

  Next, the ECU 10 obtains the in-cylinder temperature at the IVC time point from the sensor detection value after the control as described above, and controls the ignition timing based on this in-cylinder temperature so that the target self-ignition timing is realized. In this way, the target self-ignition timing is appropriately realized by performing control with quicker response than the above-described control such as the EGR rate, that is, ignition control immediately before SI-CI combustion.

  Next, after the SI-CI combustion is actually performed by the control as described above, the ECU 10 determines the IVC time point before the SI-CI combustion based on the in-cylinder pressure detected by the finger pressure sensor SW6 during the SI-CI combustion. Find the in-cylinder temperature at. Then, the ECU 10 is calculated based on the obtained in-cylinder temperature in order to realize two in-cylinder temperatures calculated when the next SI-CI combustion is performed, specifically, the target self-ignition timing. The in-cylinder temperature and the in-cylinder temperature calculated from the sensor detection value thereafter are corrected. By doing so, the calculation (estimation) accuracy of the in-cylinder temperature is improved, and the SI rate and the self-ignition timing can be accurately controlled.

  Next, the basic configuration of SI-CI combustion control according to the present embodiment will be specifically described with reference to FIGS. 10 and 11. FIG. 10 is a flowchart showing basic control of SI-CI combustion according to the present embodiment, and FIG. 11 is an explanatory diagram of a method for estimating the in-cylinder temperature before combustion according to the present embodiment. Note that the flow shown in FIG. 10 is repeated by the ECU 10 when the engine 1 is in an operating state where SI-CI combustion is performed, typically when the engine load is in the medium load region (B1 or B2). Executed.

  When the flow of FIG. 10 is started, first, in step S11, the ECU 10 reads the detection signals of the sensors SW1 to SW16, determines the operating state of the engine 1, and determines the target SI rate and the target self-ignition timing. Set. Specifically, the ECU 10 obtains a target engine torque corresponding to the accelerator opening detected by the accelerator opening sensor SW12, and sets a target SI rate and a target self-ignition timing suitable for realizing the target engine torque. To do.

  Next, in step S12, the ECU 10 uses the predetermined combustion model and in-cylinder state estimation model to determine the in-cylinder temperature at the IVC time point that should be set to achieve the target self-ignition timing. A method of obtaining the in-cylinder temperature at the time of IVC will be specifically described with reference to FIG. In step S12, the ECU 10 obtains a target air amount corresponding to the operating state of the engine 1 in addition to the in-cylinder temperature at the time of IVC.

  FIG. 11 shows the crank angle on the horizontal axis and the in-cylinder temperature on the vertical axis, the graph G41 shows the change in the in-cylinder temperature due to SI-CI combustion, and the graph G42 shows only the operation of the piston 3 ( It shows the change in the in-cylinder temperature due to the motoring).

First, the ECU 10 obtains the in-cylinder temperature at the self-ignition portion (unburned portion) at the compression top dead center (TDC) from the target self-ignition timing (θ _CL ) set as described above (point P11) (point). P12). Next, the ECU 10 subtracts the temperature increase of the self-ignition portion due to SI combustion corresponding to the target SI rate as shown by the arrow A3 from the obtained in-cylinder temperature, so that the compression top dead center at the time of motoring is reduced. The in-cylinder temperature is obtained (point P13).

  Next, the ECU 10 obtains the in-cylinder temperature at the intake bottom dead center (BDC) by subtracting the temperature rise due to the compression of the air-fuel mixture during the polytropic process of the engine 1 from the obtained in-cylinder temperature (point P14). ). Next, the ECU 10 obtains the in-cylinder temperature at the time of IVC by converting the obtained in-cylinder temperature in the polytropic process (point P15). In FIG. 11, a point P16 indicates the crank angle and the in-cylinder temperature when SI combustion is started by ignition of the spark plug 25.

  Returning to FIG. 10, in step S13, the ECU 10 uses the predetermined in-cylinder state estimation model in consideration of the current intake air amount to realize the in-cylinder temperature at the IVC time obtained in step S12. The degree of EGR gas to be introduced into the gas (that is, the EGR rate) is obtained. Typically, the ECU 10 obtains an internal EGR rate necessary for realizing the in-cylinder temperature at the time of IVC.

  Next, in step S14, the ECU 10 controls various actuators using a predetermined in-cylinder state control model in order to realize the EGR rate obtained in step S13. Typically, the ECU 10 simply introduces the intake electric VVT 23 and the exhaust electric VVT 24 (hereinafter referred to as “the combination of these” in order to introduce the internal EGR gas corresponding to the internal EGR rate for realizing the in-cylinder temperature at the time of IVC. The phase angle of the intake / exhaust VVT 23, 24 ”may be controlled. Further, the ECU 10 opens the throttle valve 43, the air bypass valve 48, the electromagnetic clutch 45 shut-off / connection, and the EGR valve 54 open so as to realize the target air amount obtained in step S12. Control the degree. Such a control of the ECU 10 changes the state in the combustion chamber 17 to a desired state.

  Next, in step S15, the ECU 10 reads the detection signals of the sensors SW1 to SW16 and obtains the in-cylinder temperature at the actual IVC time using a predetermined in-cylinder state estimation model. Specifically, the ECU 10 detects the intake air amount detected by the air flow sensor SW1, the intake air temperature detected by the first intake air temperature sensor SW2 and the second intake air temperature sensor SW4, the intake cam angle sensor SW13 and the exhaust cam angle. The intake camshaft and exhaust camshaft rotation angles detected by the sensor SW14 are acquired, and the in-cylinder temperature at the time of IVC is obtained based on these. In this case, ECU10 calculates | requires the flow volume and temperature of intake gas (fresh air) and EGR gas, and calculates | requires the in-cylinder temperature at the time of IVC based on an in-cylinder state estimation model.

  In step S15, the ECU 10 obtains the intake charge amount and the oxygen concentration in the cylinder as the state quantity in the cylinder in addition to the in-cylinder temperature, and the air-fuel ratio of the exhaust gas after combustion is the stoichiometric air-fuel ratio (that is, The fuel injection amount from the injector 6 is determined so that λ = 1). In this case, the ECU 10 determines the fuel injection amounts of the front-stage injection and the rear-stage injection when performing split injection including the front-stage injection and the rear-stage injection. Basically, the fuel injected by the post-stage injection undergoes SI combustion, and the fuel injected by the pre-stage injection mainly undergoes CI combustion. Therefore, from the viewpoint of controlling the SI rate, the fuel injection amount of the post-stage injection with respect to the pre-stage injection It is preferable to adjust the ratio (when the air-fuel ratio is made lean, the fuel injection amount of the post-injection may be adjusted independently). Then, the ECU 10 controls the injector 6 to inject the fuel injection amount determined in this way. Further, the ECU 10 controls the injector 6 so that fuel is injected at an injection timing based on a preset map.

  Next, in step S16, the ECU 10 obtains the self-ignition timing in CI combustion from the in-cylinder temperature at the IVC time obtained in step S15, using a predetermined in-cylinder state estimation model. Specifically, the ECU 10 obtains each state quantity in the order of point P15 → point P14 → point P13 → point P12 → point P11 in detail in the reverse order of the procedure described with reference to FIG. Then, the self-ignition time in CI combustion is obtained.

  Next, at step S17, the ECU 10 performs ignition by the spark plug 25 so that the target self-ignition timing set at step S11 is realized as much as possible using a predetermined combustion model based on the self-ignition timing obtained at step S16. Decide when. That is, the ECU 10 determines the ignition timing by the spark plug 25 for starting SI combustion so that the CI combustion starts as close to the target self-ignition timing as possible. The ECU 10 controls the spark plug 25 so that ignition is performed at the ignition timing thus determined.

  After such step S17, SI-CI combustion including SI combustion and CI combustion is performed in the engine 1. And the process of step S18 is performed after completion | finish of SI-CI combustion. In step S18, the ECU 10 uses the predetermined combustion model and the in-cylinder state estimation model on the basis of the in-cylinder pressure detected by the finger pressure sensor SW6 during the SI-CI combustion, and performs the SI-CI combustion. The in-cylinder temperature at the previous IVC time is obtained. That is, the ECU 10 retrospectively obtains the in-cylinder temperature at the IVC time before the start of the previous SI-CI combustion. The method for obtaining the in-cylinder temperature at the time of IVC will be specifically described with reference to FIG. 11 again.

As shown in FIG. 11, first, the ECU 10 obtains the self-ignition timing (θ _CL ) from the in-cylinder pressure detected by the finger pressure sensor SW6 (point P11). For example, the ECU 10 determines the crank angle corresponding to the inflection point in the detected in-cylinder pressure waveform (corresponding to the heat generation rate waveform) as the self-ignition timing. Then, the ECU 10 obtains the in-cylinder temperature at the self-ignition portion (unburned portion) at the compression top dead center (TDC) from the self-ignition timing (θ _CL ) (P12).

  Next, the ECU 10 determines the in-cylinder temperature at the compression top dead center during motoring by subtracting the temperature increase of the self-ignition part due to SI combustion as indicated by the arrow A3 from the determined in-cylinder temperature ( Point P13). Next, the ECU 10 obtains the in-cylinder temperature at the intake bottom dead center (BDC) by subtracting the temperature rise due to the compression of the air-fuel mixture during the polytropic process of the engine 1 from the obtained in-cylinder temperature (point P14). ). Next, the ECU 10 obtains the in-cylinder temperature at the time of IVC by converting the obtained in-cylinder temperature in the polytropic process (point P15).

  Returning to FIG. 10, in step S19, the ECU 10 corrects the in-cylinder temperature calculated in the current SI-CI combustion based on the in-cylinder temperature at the IVC time in the previous SI-CI combustion obtained in step S18. To do. Specifically, the ECU 10 corrects the in-cylinder temperature estimation error based on the in-cylinder state estimation model executed in step S12 and step S15 for the current SI-CI combustion. That is, the ECU 10 determines the in-cylinder temperature at the IVC time calculated to realize the target self-ignition timing (step S12), and the in-cylinder temperature at the IVC time calculated from the sensor detection value thereafter (step S15). ) Is corrected based on the in-cylinder temperature obtained in step S18. In this case, the ECU 10 does not correct the in-cylinder temperature calculated in steps S12 and S15 so as to match the in-cylinder temperature in step S18, but becomes clear after actual SI-CI combustion by SI-CI combustion control. In step S19, correction is performed in order to correct the estimation error caused by the in-cylinder state estimation model corresponding to the control error.

(Control block)
Next, the detailed contents of the SI-CI combustion control according to the present embodiment will be described with reference to FIGS. FIG. 12 is a block diagram showing a first control model for controlling the in-cylinder state in advance so as to realize the target self-ignition timing in the present embodiment. FIG. 13 is a block diagram showing a second control model for performing quick control of responsiveness so as to realize the target self-ignition timing based on the sensor detection value after the control in the first control model in the present embodiment. . FIG. 14 shows a cylinder estimated in the present embodiment based on the in-cylinder pressure detected during SI-CI combustion, and estimated by the first and second control models in the subsequent SI-CI combustion. It is a block diagram which shows the 3rd control model for correct | amending internal temperature. The ECU 10 is configured to execute control in the first to third control models.

  In the first control model shown in FIG. 12, first, the ECU 10 refers to a map set in advance and obtains a target engine torque corresponding to the accelerator opening detected by the accelerator opening sensor SW12. A target combustion pressure corresponding to the target engine torque is obtained. Next, the ECU 10 obtains a target combustion pressure to be finally applied and a target combustion mode based on the current operating state of the engine 1. Basically, one of a combustion mode in which only SI combustion is performed and a combustion mode in which SI-CI combustion including SI combustion and CI combustion is performed is applied to the target combustion mode.

  Next, the ECU 10 obtains a target air amount, a target self-ignition timing, and a target SI rate as the target combustion state based on the final target combustion pressure and the target combustion mode. Next, the ECU 10 obtains the in-cylinder temperature at the target self-ignition timing by subtracting the temperature increase of the self-ignition part due to SI combustion corresponding to the target SI rate using a predetermined combustion model (in-cylinder at TDC). The temperature may be obtained), and the in-cylinder temperature at the time of IVC is obtained from this in-cylinder temperature using a predetermined in-cylinder state estimation model. Since the method of obtaining the in-cylinder temperature at the time of IVC is as described in FIGS. 10 and 11, the description thereof is omitted here. Further, the ECU 10 determines the in-cylinder temperature at the time of IVC in this way, based on the in-cylinder temperature in the previous SI-CI combustion estimated in the third control model (see FIG. 14). The estimation error of the in-cylinder temperature due to the state estimation model is corrected.

  Next, the ECU 10 refers to a preset map or the like, and based on the target air amount and the in-cylinder temperature at the time of IVC, the target EGR rate indicating the degree of EGR gas to be introduced into the combustion chamber 17, particularly A target internal EGR rate is obtained. Then, the ECU 10 obtains a target valve closing timing (target IVC) of the target intake valve 21 and a target valve closing timing (target EVC) of the target exhaust valve 22 for realizing the target internal EGR rate. Next, the ECU 10 determines a target phase angle (target intake / exhaust VVT) of each of the intake / exhaust VVTs 23 and 24 corresponding to the target IVC and the target EVC using a predetermined in-cylinder state control model, and sets the target phase angle to the target phase angle. The intake and exhaust VVTs 23 and 24 are controlled so as to be set.

  Almost in parallel with the control of the intake and exhaust VVTs 23 and 24, the ECU 10 uses a predetermined in-cylinder state control model to achieve the target air amount described above, and uses the predetermined throttle position and target external EGR. A rate, a target air bypass opening, and a target clutch opening (corresponding to disconnection / connection of the electromagnetic clutch 45) are determined. Then, the ECU 10 controls the throttle valve 43 according to the target throttle opening, controls the EGR valve 54 according to the target external EGR rate, controls the air bypass valve 48 according to the target air bypass opening, and opens the target clutch. The electromagnetic clutch 45 is controlled according to the degree. Thereafter, SI-CI combustion is performed in the engine 1.

  Next, in the second control model shown in FIG. 13, first, the ECU 10 detects the intake air amount detected by the airflow sensor SW1 and the intake air temperature detected by the first intake air temperature sensor SW2 and the second intake air temperature sensor SW4. Further, the rotation angles of the intake camshaft and the exhaust camshaft detected by the intake cam angle sensor SW13 and the exhaust cam angle sensor SW14 are acquired. Next, the ECU 10 obtains the actual intake gas (fresh air) state quantity, typically temperature and pressure, based on the intake air quantity and the outside air EGR rate corresponding to these sensor detection values. In addition, the ECU 10 determines the actual internal EGR based on the phase angles of the intake and exhaust VVTs 23 and 24 corresponding to the rotation angles of the intake camshaft and the exhaust camshaft (basically, the phase angle is on the advance side). The state quantity of gas, typically temperature and pressure, is determined.

  Next, the ECU 10 obtains the in-cylinder temperature at the actual IVC time point from the above-described intake gas state quantity and internal EGR gas state quantity using a predetermined in-cylinder state estimation model. In this case, the ECU 10 corrects the estimation error due to the in-cylinder state estimation model based on the in-cylinder temperature in the previous SI-CI combustion estimated in the third control model (see FIG. 14), and at the time of IVC. Obtain the in-cylinder temperature. In addition to the in-cylinder temperature, the ECU 10 obtains an intake charge amount, an in-cylinder oxygen concentration, and the like as state quantities in the cylinder.

  Next, the ECU 10 controls the injector 6 so that the air-fuel ratio of the exhaust gas after combustion becomes the stoichiometric air-fuel ratio (that is, λ = 1) based on the intake charge amount as the state quantity in the cylinder and the oxygen concentration in the cylinder. The fuel injection amount from is determined. In this case, the ECU 10 determines the fuel injection amounts of the front-stage injection and the rear-stage injection when performing split injection including the front-stage injection and the rear-stage injection. Then, the ECU 10 controls the injector 6 to inject the fuel injection amount determined in this way. Further, the ECU 10 controls the injector 6 so that fuel is injected at an injection timing based on a preset map.

  Further, the ECU 10 obtains the self-ignition timing by obtaining the in-cylinder temperature at which self-ignition occurs from the obtained in-cylinder temperature at substantially the same time as the control of the injector 6. Since the method for obtaining the self-ignition timing is as described in FIGS. 10 and 11, the description thereof is omitted here. Next, the ECU 10 determines a target ignition timing by the spark plug 25 so as to realize the initially set target self-ignition timing based on the determined self-ignition timing using a predetermined combustion model. Then, the ECU 10 controls the spark plug 25 so that ignition is performed at the target ignition timing thus determined. Thereafter, SI-CI combustion is performed in the engine 1.

  Note that the second control model is not limited to being performed after the first control model, and the second control model may be performed substantially in parallel with the first control model. Similarly, in the flow of FIG. 10, the processes in steps S15 to S17 corresponding to the second control model may be performed substantially in parallel with the processes in steps S11 to S14 corresponding to the first control model. Good. In one example, before reaching the crank angle corresponding to IVC, the ECU 10 obtains the in-cylinder temperature at the time of IVC and repeatedly controls the internal EGR rate and the like using the first control model. In the middle, the process for obtaining the ignition timing for realizing the target self-ignition timing by obtaining the in-cylinder temperature at the time of IVC based on the sensor detection value by the second control model is repeatedly performed. In this example, the ECU 10 interrupts execution of the first control model after reaching the crank angle corresponding to IVC, and the ignition timing obtained from the in-cylinder temperature corresponding to the sensor detection value when reaching the IVC. Ignition control is performed using.

  Next, in the third control model shown in FIG. 14, first, the ECU 10 detects the cylinder detected by the finger pressure sensor SW <b> 6 during the SI-CI combustion after the SI-CI combustion in the engine 1. Get internal pressure. Next, the ECU 10 obtains the combustion state of SI-CI combustion using a predetermined fuel detection model. For example, the ECU 10 determines an inflection point or the like in the acquired in-cylinder pressure waveform (corresponding to the heat generation rate waveform) as the combustion state.

  Next, the ECU 10 obtains the in-cylinder temperature at the self-ignition timing from the combustion state of SI-CI combustion using a predetermined in-cylinder state estimation model, and obtains the in-cylinder temperature at the time of IVC from this in-cylinder temperature. Since the method of obtaining the in-cylinder temperature at the time of IVC is as described in FIGS. 10 and 11, the description thereof is omitted here. Next, the ECU 10 corrects the in-cylinder temperature calculated in the current SI-CI combustion based on the obtained in-cylinder temperature at the IVC time point. That is, the ECU 10 corrects the estimation error of the in-cylinder temperature by the in-cylinder state estimation model executed in the current SI-CI combustion. Specifically, the ECU 10 determines the in-cylinder temperature at the IVC time point (see FIG. 12) calculated to realize the target self-ignition timing in the first control model, and the sensor detection value in the second control model. The calculated in-cylinder temperature at the time of IVC (see FIG. 13) is corrected. Basically, the in-cylinder temperature obtained from the third control model is set as an actual value (reference value), and the in-cylinder temperature obtained from the first and second control models with respect to the in-cylinder temperature as the actual value. Is treated as including an error, and the above correction is performed.

(Time chart)
Next, with reference to FIG. 15, the time chart at the time of performing SI-CI combustion control by this embodiment is demonstrated.

  FIG. 15 shows, in order from the top, the heat generation rate (dQ / dθ), the closing timing of the intake valve 21 (actual IVC and target IVC), and the in-cylinder temperature at the IVC time point estimated in the second control model (hereinafter referred to as “in-cylinder temperature”). Is called “temperature estimated value based on intake / exhaust model” as appropriate), the in-cylinder temperature at the time of IVC estimated in the third control model (hereinafter referred to as “temperature estimated value based on combustion model”), and combustion model The correction amount of the error of the temperature estimated value by the intake / exhaust model with respect to the temperature estimated value, the estimated temperature after correction, the ignition timing, the self-ignition timing, and the SI rate are shown. FIG. 15 shows the crank angle on the horizontal axis, and shows changes in parameters with respect to the crank angle. FIG. 15 shows only the closing timing (IVC) of the intake valve 21, but the closing timing (EVC) of the exhaust valve 22 also changes in the same way as IVC.

FIG. 15 shows an example in which the error (true value) of the temperature estimated value by the intake / exhaust model with respect to the temperature estimated value by the combustion model changes by about 50 [K] due to disturbance immediately after the start of the nth cycle. First, the ECU 10 estimates the in-cylinder temperature at the IVC time point using the second control model, and obtains 400 [K] as the estimated temperature value based on the intake / exhaust model (arrow A41). Then, SI-CI combustion is performed in the engine 1, and after this combustion, the ECU 10 performs self-ignition timing θ _CL in the SI-CI combustion based on the in-cylinder pressure detected by the finger pressure sensor SW6 according to the third control model. The in-cylinder temperature at the IVC time is estimated from the in-cylinder temperature at (IV A), and 450 [K] is obtained as the estimated temperature value by the combustion model. In this case, the error of the temperature estimated value by the intake / exhaust model with respect to the temperature estimated value by the combustion model is Δ50 [K] (arrow A43). Therefore, the ECU 10 sets the correction amount of the error of the temperature estimated value by the intake / exhaust model to 50 [K] with respect to the temperature estimated value by the combustion model (arrow A44), and the estimated temperature by the intake / exhaust model is 450 [K] from this correction amount. (Arrows A45 and A46). This estimated temperature is deviated from the target temperature 480 [K]. Therefore, in the nth cycle, since the temperature estimation error correction by the intake / exhaust model has shifted, the self-ignition timing deviates from the target self-ignition timing, and the SI rate also deviates from the target SI rate.

  Next, the ECU 10 corrects the target IVC of the intake valve 21 by the first control model so that the estimated temperature after correction becomes 480 [K] (arrow A47). As a result, the temperature estimation error (change) in the nth cycle is reflected. Next, the ECU 10 estimates the in-cylinder temperature at the IVC time point using the second control model, obtains 420 [K] as an estimated temperature value based on the intake / exhaust model (arrow A48), and the 420 [K] is described above. Correction is made to 470 [K] by the correction amount 50 [K] (arrows A49 and A50). Further, the ECU 10 corrects the ignition timing based on the corrected estimated temperature 470 [K] (arrow A51). As a result, the ignition timing reflecting both the intake state in the current (n + 1) th cycle and the combustion result in the previous nth cycle is applied.

Next, SI-CI combustion is performed in the engine 1, and after this combustion, the ECU 10 performs self-ignition timing θ in the SI-CI combustion based on the in-cylinder pressure detected by the finger pressure sensor SW6 according to the third control model. _The in-cylinder temperature at the time of IVC is estimated from the in-cylinder temperature at _CL , and 470 [K] is obtained as the estimated temperature value by the combustion model. In this case, since the deviation of the estimation of the intake / exhaust model does not change greatly, the error of the temperature estimated value remains Δ50 [K] (arrow A52). For this reason, the temperature was correctly estimated in this n + 1 cycle (arrow A53). Therefore, in the current n + 1 cycle, the self-ignition timing almost coincides with the target self-ignition timing. On the other hand, in the current n + 1 cycle, the actual IVC of the intake valve 21 is still deviated from the target IVC, so that the SI rate remains slightly deviated from the target SI rate. Thereafter, in the n + 2 cycle, the temperature estimation error by the intake / exhaust model is correctly corrected, and the estimated temperature after correction becomes the target temperature 480 [K], so the actual IVC of the intake valve 21 reaches the target IVC, The SI rate almost coincides with the target SI rate.

  Note that the deviation in the correction of the temperature estimation error due to the intake / exhaust model as described above is caused by a delay in the operation of a device that adjusts the in-cylinder state (intake / exhaust VVT23, 24 that adjusts the internal EGR, etc.) This can be caused by not operating properly.

<Effect>
Next, main effects of the control device for the compression self-ignition engine according to the above-described embodiment will be described.

  According to this embodiment, based on the operating state of the engine 1 (engine load or the like), the control for adjusting the SI rate and the control for adjusting the self-ignition timing and / or the in-cylinder temperature are performed, and SI combustion and CI combustion are performed. The combustion state in the SI-CI combustion including is controlled. Thereby, desired SI-CI combustion can be realized appropriately. Specifically, each of the SI rate and self-ignition timing in SI-CI combustion can be appropriately set to the target value. As a result, it becomes possible to achieve improvements in fuel consumption, combustion stability and combustion noise suppression.

  Further, according to the present embodiment, control (such as control of internal EGR gas) is performed to adjust the in-cylinder temperature before the start of SI-CI combustion, and after this control, the actual in-cylinder temperature before the start of combustion is obtained. The SI rate is adjusted by controlling the ignition timing based on the in-cylinder temperature. As a result, the SI rate can be appropriately controlled in consideration of control deviations of various state quantity setting devices.

  Further, according to the present embodiment, various control values for adjusting the SI rate in the current combustion cycle are corrected based on the in-cylinder temperature acquired in the previous combustion cycle, so the target SI rate in SI-CI combustion Can be effectively realized, and can be reliably ignited at the target self-ignition time. Specifically, it is possible to appropriately realize a desired combustion state for both a transient combustion state and a steady combustion state in SI-CI combustion.

<Modification>
Below, the modification of above-described embodiment is demonstrated.

  In the above-described embodiment, the in-cylinder temperature at the closing timing (IVC time) of the intake valve 21 is used, but instead of this, various cylinder temperatures are used by using the in-cylinder temperature at the intake bottom dead center (BDC time). Control may be performed.

  In the above-described embodiment, the in-cylinder temperature is obtained from the intake air amount detected by the airflow sensor SW1 in the second control model. However, in another example, the in-cylinder pressure is detected from the in-cylinder pressure detected by the finger pressure sensor SW6. The internal temperature may be obtained. In the third control model, the in-cylinder temperature is obtained from the in-cylinder pressure detected by the finger pressure sensor SW6. In another example, the in-cylinder temperature is obtained from the intake air amount detected by the airflow sensor SW1. May be.

1 engine 10 ECU (controller)
17 Combustion chamber 23 Intake motor VVT (state quantity setting device, variable valve mechanism)
24 Exhaust electric VVT (state quantity setting device, variable valve mechanism)
25 Spark plug 49 Supercharging system (state quantity setting device)
44 Turbocharger 43 Throttle valve (state quantity setting device)
48 Air bypass valve (state quantity setting device)
54 EGR valve (state quantity setting device)
55 EGR system (state quantity setting device)
6 Injector

Claims (18)

An engine comprising at least a combustion chamber for burning a mixture of fuel and air, an injector for injecting fuel to supply fuel into the combustion chamber, and an ignition plug for igniting the mixture in the combustion chamber. The engine configured to self-ignite the air-fuel mixture in the combustion chamber;
A state quantity setting device configured to set the combustion chamber to a desired state by adjusting the introduction of fresh air and burned gas into the combustion chamber of the engine;
A controller configured to operate the engine by at least controlling the injector and spark plug of the engine and the state quantity setting device;
A control device for a compression self-ignition engine having
In the engine, a first combustion in which the air-fuel mixture is combusted by flame propagation by ignition of the spark plug and a second combustion in which the air-fuel mixture is combusted by self-ignition due to the flame propagation are performed,
The controller performs the first combustion on the total amount of heat generated in the first and second combustion or the amount of heat generated in the second combustion in one combustion cycle of the engine based on the operating state of the engine. First control means for controlling the SI rate as an index related to the ratio of the amount of heat generated, and second control means for controlling the self-ignition timing, which is the time when the self-ignition occurs,
By both the first and second control means, during one combustion cycle of the engine, and changed in accordance with the combustion state of both said first and second combustion to the operating state of the engine,
Controlling the spark plug to ignite after completing the injection of all the fuel to be injected from the injector during one combustion cycle of the engine to realize the first combustion and the second combustion;
A control device for a compression self-ignition engine characterized by that. The first control means of the controller performs control to increase the SI rate as the engine load as the operating state of the engine increases.
The control device for a compression self-ignition engine according to claim 1. The second control means of the controller performs control to set the self-ignition timing to the retard side as the engine load as the operating state of the engine increases.
The control device for a compression self-ignition engine according to claim 1 or 2. The second control means of the controller sets the self-ignition timing to the retard side within a range not exceeding a predetermined retard limit.
A control device for a compression self-ignition engine according to claim 3. The first and second control means of the controller maintain the position of the center of gravity of combustion in the combined combustion of the first and second combustion substantially constant regardless of the engine load as the operating state of the engine. Controlling the SI rate and the self-ignition timing;
The control device for a compression self-ignition engine according to any one of claims 1 to 4. The first control means of the controller controls the ignition timing by the spark plug to adjust the SI rate;
The control device for a compression self-ignition engine according to any one of claims 1 to 5. The first control means of the controller adjusts the SI rate by controlling the state quantity setting device so as to adjust the ratio of fresh air and burned gas introduced into the combustion chamber.
The control device for a compression self-ignition engine according to any one of claims 1 to 6. The controller includes a post-injection in which fuel is injected before and after the ignition timing by the spark plug so as to form a substantially homogeneous mixture in the combustion chamber, and before the post-injection. And controlling the injector to perform pre-stage injection that injects fuel at a timing away from the ignition timing,
The first control means adjusts the SI rate by controlling a fuel injection amount from the injector in the post-stage injection.
The control device for a compression self-ignition engine according to any one of claims 1 to 7. The second control means of the controller controls the ignition timing by the spark plug to adjust the self-ignition timing;
The control device for a compression self-ignition engine according to any one of claims 1 to 8. The controller sets a target SI rate and a target self-ignition timing according to the operating state of the engine, and these target SI rate and target self-ignition timing are realized by both the first and second control means. So as to control the SI rate and the self-ignition timing,
The control device for a compression self-ignition engine according to any one of claims 1 to 9. The controller is
The state in the combustion chamber before the start of the first combustion to be set according to the target SI rate and the target self-ignition timing is obtained, and fresh air and burned gas introduced into the combustion chamber to realize this state Controlling the state quantity setting device to adjust the ratio with gas,
Acquiring an actual state in the combustion chamber before the start of the first combustion, and controlling an ignition timing by the spark plug so as to realize the target self-ignition timing based on the state;
The control device for a compression self-ignition engine according to claim 10. An engine comprising at least a combustion chamber for burning a mixture of fuel and air, an injector for injecting fuel to supply fuel into the combustion chamber, and an ignition plug for igniting the mixture in the combustion chamber. The engine configured to self-ignite the air-fuel mixture in the combustion chamber;
A state quantity setting device configured to set the combustion chamber to a desired state by adjusting the introduction of fresh air and burned gas into the combustion chamber of the engine;
A controller configured to operate the engine by at least controlling the injector and spark plug of the engine and the state quantity setting device;
A control device for a compression self-ignition engine having
In the engine, a first combustion in which the air-fuel mixture is combusted by flame propagation by ignition of the spark plug and a second combustion in which the air-fuel mixture is combusted by self-ignition due to the flame propagation are performed,
The controller is
Based on the engine load, in one combustion cycle of the engine, related to the total amount of heat generated in the first and second combustion or the ratio of the amount of heat generated by the first combustion to the amount of heat generated in the second combustion Performing control to adjust the SI rate as an index to perform and control to adjust the self-ignition timing, which is the time when the self-ignition occurs,
In one combustion cycle of the engine, ignition timing by the spark plug, fuel injection amount and / or fuel injection timing by the injector, fresh air and burned gas introduced into the combustion chamber by the state quantity setting device, And adjusting both the SI rate and the self-ignition timing to change the combustion state of both the first and second combustion to the operating state of the engine. depending change it,
Controlling the spark plug to ignite after completing the injection of all the fuel to be injected from the injector during one combustion cycle of the engine to realize the first combustion and the second combustion;
A control device for a compression self-ignition engine characterized by that. The controller performs control to increase the SI rate and control to set the self-ignition timing to the retard side as the engine load increases.
The control device for a compression self-ignition engine according to claim 12. The controller adjusts the SI rate by controlling a ratio of fresh air and burned gas introduced into the combustion chamber by the state quantity setting device, and controls ignition timing by the spark plug to control the self-ignition. Adjust the time,
The control device for a compression self-ignition engine according to claim 12 or 13. The state quantity setting device is a variable valve mechanism configured to vary the valve timing of an intake valve and / or an exhaust valve provided in the engine,
The controller controls the variable valve mechanism to adjust the valve timing of the intake valve and / or the exhaust valve so as to return burned gas from the exhaust port of the engine as internal EGR gas to the combustion chamber. Adjusting the ratio of fresh air and internal EGR gas introduced into the combustion chamber;
The control device for a compression self-ignition engine according to any one of claims 1 to 14. An engine comprising at least a combustion chamber for burning a mixture of fuel and air, an injector for injecting fuel to supply fuel into the combustion chamber, and an ignition plug for igniting the mixture in the combustion chamber. The engine configured to self-ignite the air-fuel mixture in the combustion chamber;
A state quantity setting device configured to set the combustion chamber to a desired state by adjusting the introduction of fresh air and burned gas into the combustion chamber of the engine;
A controller configured to operate the engine by at least controlling the injector and spark plug of the engine and the state quantity setting device;
A control device for a compression self-ignition engine having
In the engine, a first combustion in which the air-fuel mixture is combusted by flame propagation by ignition of the spark plug and a second combustion in which the air-fuel mixture is combusted by self-ignition due to the flame propagation are performed,
The controller performs the first combustion on the total amount of heat generated in the first and second combustion or the amount of heat generated in the second combustion in one combustion cycle of the engine based on the operating state of the engine. First control means for controlling the SI rate as an index related to the ratio of the amount of heat generated, and second control means for controlling the self-ignition timing, which is the time when the self-ignition occurs,
Both the first and second control means change the combustion state of both the first and second combustions in accordance with the operating state of the engine during one combustion cycle of the engine,
The first control means of the controller performs control to increase the SI rate as the engine load as the operating state of the engine increases.
A control device for a compression self-ignition engine characterized by that. An engine comprising at least a combustion chamber for burning a mixture of fuel and air, an injector for injecting fuel to supply fuel into the combustion chamber, and an ignition plug for igniting the mixture in the combustion chamber. The engine configured to self-ignite the air-fuel mixture in the combustion chamber;
A state quantity setting device configured to set the combustion chamber to a desired state by adjusting the introduction of fresh air and burned gas into the combustion chamber of the engine;
A controller configured to operate the engine by at least controlling the injector and spark plug of the engine and the state quantity setting device;
A control device for a compression self-ignition engine having
In the engine, a first combustion in which the air-fuel mixture is combusted by flame propagation by ignition of the spark plug and a second combustion in which the air-fuel mixture is combusted by self-ignition due to the flame propagation are performed,
The controller performs the first combustion on the total amount of heat generated in the first and second combustion or the amount of heat generated in the second combustion in one combustion cycle of the engine based on the operating state of the engine. First control means for controlling the SI rate as an index related to the ratio of the amount of heat generated, and second control means for controlling the self-ignition timing, which is the time when the self-ignition occurs,
Both the first and second control means change the combustion state of both the first and second combustions in accordance with the operating state of the engine during one combustion cycle of the engine,
The first and second control means of the controller maintain the position of the center of gravity of combustion in the combined combustion of the first and second combustion substantially constant regardless of the engine load as the operating state of the engine. Controlling the SI rate and the self-ignition timing;
A control device for a compression self-ignition engine characterized by that. An engine comprising at least a combustion chamber for burning a mixture of fuel and air, an injector for injecting fuel to supply fuel into the combustion chamber, and an ignition plug for igniting the mixture in the combustion chamber. The engine configured to self-ignite the air-fuel mixture in the combustion chamber;
A state quantity setting device configured to set the combustion chamber to a desired state by adjusting the introduction of fresh air and burned gas into the combustion chamber of the engine;
A controller configured to operate the engine by at least controlling the injector and spark plug of the engine and the state quantity setting device;
A control device for a compression self-ignition engine having
In the engine, a first combustion in which the air-fuel mixture is combusted by flame propagation by ignition of the spark plug and a second combustion in which the air-fuel mixture is combusted by self-ignition due to the flame propagation are performed,
The controller performs the first combustion on the total amount of heat generated in the first and second combustion or the amount of heat generated in the second combustion in one combustion cycle of the engine based on the operating state of the engine. First control means for controlling the SI rate as an index related to the ratio of the amount of heat generated, and second control means for controlling the self-ignition timing, which is the time when the self-ignition occurs,
Both the first and second control means change the combustion state of both the first and second combustions in accordance with the operating state of the engine during one combustion cycle of the engine,
The controller includes a post-injection in which fuel is injected before and after the ignition timing by the spark plug so as to form a substantially homogeneous mixture in the combustion chamber, and before the post-injection. And controlling the injector to perform pre-stage injection that injects fuel at a timing away from the ignition timing,
The first control means adjusts the SI rate by controlling a fuel injection amount from the injector in the post-stage injection.
A control device for a compression self-ignition engine characterized by that.

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