JP6098536B2 - Control unit for direct injection engine - Google Patents

Description

  The technology disclosed herein relates to a control device for a direct injection engine.

  Patent Document 1 describes that in a compression self-ignition engine, a wall surface defining a combustion chamber is made of a heat insulating material to reduce cooling loss on the wall surface of the combustion chamber. Thermal efficiency is improved by reducing the cooling loss.

  Patent Document 2 describes an outer valve-opening injector that injects fuel into a combustion chamber of an engine. In the externally opened injector, the effective sectional area of the nozzle port through which fuel is injected changes by changing the lift amount of the valve body. Patent Document 3 describes a VCO (Valve Covered Orifice) nozzle type injector. The VCO nozzle type injector is configured so that the needle valve is directly seated on the seat portion where the nozzle opening is opened and the nozzle opening is closed, and according to the lift amount of the needle valve, The size of the cavitation region generated on the inner peripheral surface changes. As a result, in the VCO nozzle type injector, the effective sectional area of the nozzle port changes according to the lift amount of the needle valve, as in the case of the externally opened injector.

  In Patent Document 4, in an engine provided with an outer valve-opening injector that is arranged on the cylinder central axis and injects fuel in a cone shape, the fuel is injected into the cylinder at the later stage of the compression stroke, and combustion is performed. It describes that an air-fuel mixture layer and a surrounding gas layer (a gas layer containing fresh air) are formed in the room. In the engine described in Patent Document 4, cooling loss is reduced by causing the surrounding gas layer to function as a heat insulating layer during combustion of the air-fuel mixture forming the air-fuel mixture layer. Patent Document 4 also describes that the fuel concentration is made uniform in the fuel injection direction by changing the lift amount of the outer valve while the fuel is continuously being injected.

JP 2009-243355 A JP 2008-151043 A Japanese Patent No. 4194564 JP 2013-57266 A

  As described in Patent Document 4, in a configuration in which an air-fuel mixture layer is formed in the combustion chamber, the fuel concentration distribution in the air-fuel mixture layer is not always preferable, and the fuel concentration distribution is not preferred. It may be advantageous to make it homogeneous. For example, as the engine speed increases, the actual time for changing the crank angle is shortened, so the actual time that can be secured before ignition after fuel injection (hereinafter, this time may be referred to as the ignition delay time) is shortened. End up. This reduces the ignitability of compression self-ignition and lowers the combustion stability. In order to secure a sufficient ignition delay time, the fuel injection timing may be advanced to, for example, the first half of the intake stroke or the compression stroke. However, if the fuel injection timing is advanced, the compression stroke Since a gas having a high specific heat ratio including fuel is compressed, the compression end temperature is lowered, and in this case, the ignitability can be lowered. When the fuel concentration distribution is inhomogeneous, the relatively rich air-fuel mixture part increases the ignitability of compression self-ignition, so that the ignition delay time is shortened, and ignition and combustion occur at an appropriate timing even in the high rotation region. It becomes possible.

  In addition, in the air-fuel mixture layer, if the fuel concentration in the peripheral portion near the partition wall that partitions the combustion chamber is increased, the amount of heat generated in the peripheral portion increases, which may increase the cooling loss. Therefore, in order to reduce the cooling loss, it is necessary to make the fuel concentration non-homogeneous so that the fuel concentration in the central part is relatively high and the fuel concentration in the peripheral part is relatively low. preferable. However, when the engine load is increased and the fuel injection amount is increased, the fuel concentration becomes too high in the portion where the fuel concentration is relatively high, soot is generated, or unburned substances are generated. there is a possibility. Accordingly, in a high load region where the fuel injection amount increases, it is preferable to make the fuel concentration in the air-fuel mixture layer more uniform than inhomogeneous.

  The technology disclosed herein has been made in view of such a point, and an object thereof is to optimize the fuel concentration distribution in the gas mixture layer in accordance with the operating state of the engine.

  The technology disclosed herein is directed to a control device for a direct injection engine. This device includes a piston provided in a cylinder, an engine main body in which a combustion chamber is defined by the cylinder and the piston, an injector that injects fuel containing at least gasoline into the combustion chamber through an injection port, A control unit that controls the injection mode of the injector.

  The control unit causes the injector to perform multi-stage injection, and the control unit also determines the fuel concentration in the central portion of the combustion chamber and the fuel in the peripheral portion surrounding the central portion according to the operating state of the engine body. A homogeneous air-fuel mixture layer having substantially the same concentration or a non-homogeneous air-fuel mixture layer in which the fuel concentration in the central portion of the combustion chamber differs from the fuel concentration in the peripheral portion surrounding the central portion is formed. The injection mode of the injector is changed.

The multi-stage injection includes a first injection group in which a spray distance in the traveling direction of the fuel spray injected through the nozzle is short and spread in a radial direction perpendicular to the central axis of the injector, and the fuel spray It includes a second injection group that is a spray that has a long scattering distance in the traveling direction and is suppressed from spreading in the radial direction, and the control unit injects the first injection group in the multistage injection. By changing the ratio between the amount of fuel and the amount of fuel injected by the second injection group, the fuel gas mixture has a homogeneous fuel concentration with respect to the radial direction, or the fuel concentration does not increase with respect to the radial direction. A homogeneous mixture layer is formed.

The air-fuel mixture layer is a layer constituted and formed by a combustible air-fuel mixture in the combustion chamber. For example, the combustible air-fuel mixture may be defined as an air-fuel mixture having an equivalent ratio φ = 0.1 or more. Further, as the time elapses from the start of fuel injection, the fuel spray diffuses. Therefore, the size of the air-fuel mixture layer and the fuel concentration may be the size and concentration at the time of ignition. Therefore, the space region where the equivalence ratio φ = 0.1 or more in the combustion chamber at the time of ignition can be defined as the air-fuel mixture layer, and the fuel concentration in the air-fuel mixture layer at the time of ignition is specified. It is possible. Furthermore, the ignition can be determined when, for example, the combustion mass ratio of the fuel becomes 1% or more.

According to said structure, a control part forms a homogeneous mixed gas layer or a heterogeneous mixed gas layer in a combustion chamber according to the driving | running state of an engine main body. In the homogeneous mixture, the fuel concentration at the center in the combustion value is substantially equal to the fuel concentration in the periphery surrounding the center. The fuel concentration in the part is different. By changing the injection mode of the injector, a homogeneous mixture layer or a heterogeneous mixture layer is formed.

As a result, an air-fuel mixture layer that is optimal in terms of improving fuel efficiency and exhaust emission performance is formed in the combustion chamber in accordance with the operating state of the engine body.

Further, the fuel injected by the first injection group becomes spray that spreads in the radial direction orthogonal to the central axis of the injector, whereas the fuel injected by the second injection group is suppressed from spreading in the radial direction. When the amount of fuel injected by the first injection group is relatively large and the amount of fuel injected by the second injection group is relatively small, the fuel concentration outside in the radial direction is relatively high and A heterogeneous mixture layer is formed in which the fuel concentration in the radial direction is relatively low. Conversely, when the amount of fuel injected by the first injection group is relatively small and the amount of fuel injected by the second injection group is relatively large, the fuel concentration outside in the radial direction is relatively low and the radial direction An inhomogeneous mixture layer with a relatively high fuel concentration inside is formed. Further, when the amount of fuel injected by the first injection group and the amount of fuel injected by the second injection group are the same amount or substantially the same amount, the radially outer fuel concentration and the radially inner fuel concentration are the same. A homogeneous mixture layer is formed.

  Thus, by changing the ratio of the amount of fuel injected by the first injection group and the amount of fuel injected by the second injection group, an air-fuel mixture layer having a homogeneous fuel concentration with respect to the radial direction, the outer side in the radial direction is A heterogeneous mixture layer that is relatively rich or a heterogeneous mixture layer that is relatively rich in the radial direction can be formed.

  The injector has a nozzle body in which the nozzle hole is formed, and a valve body that opens and closes the nozzle hole, and is configured such that an effective sectional area of the nozzle hole increases as a lift amount of the valve body increases. The first injection group sets the effective cross-sectional area of the nozzle hole to a predetermined value and performs fuel injection a plurality of times at a predetermined injection interval. The second injection group sets the effective cross-sectional area of the nozzle hole to be higher than that of the first injection group. And / or multiple times of fuel injection with a fuel injection interval narrower than that of the first injection group.

  When fuel is injected into the combustion chamber through the nozzle, a negative pressure region is generated in the vicinity of the nozzle due to the Coanda effect. When the injection interval of the multistage injection is wide, the pressure in the negative pressure region can be recovered before the next fuel is injected, so the negative pressure region becomes smaller. When the negative pressure region is small, the fuel spray is not attracted to the negative pressure so much and is easily diffused. On the other hand, when the injection interval is narrow, fuel is injected one after another, so that the negative pressure in the negative pressure region is maintained and the negative pressure region becomes larger. When the negative pressure region is large, the fuel spray is attracted to the negative pressure and the spread is suppressed. That is, the wider the injection interval, the more easily the fuel spray diffuses in the combustion chamber, and the narrower the injection interval, the more spread of the fuel spray is suppressed.

  On the other hand, when the effective sectional area of the nozzle is large, the particle size of the fuel spray injected into the combustion chamber through the nozzle is large, and when the effective sectional area of the nozzle is small, the fuel spray injected into the combustion chamber through the nozzle is large. The particle size becomes smaller. As the particle size changes, the momentum of the fuel spray changes. That is, the larger the effective sectional area of the nozzle hole, the greater the momentum of the fuel spray, and the longer the spray distance of the fuel spray.

  In addition, the effective cross-sectional area of the nozzle hole affects the susceptibility of the fuel spray from the negative pressure region. That is, when the effective area of the nozzle hole is large, the particle size of the fuel spray is large, so that the fuel spray is not easily affected by the negative pressure region. The fuel spray having a large particle size is not attracted so much to the negative pressure region, and is less likely to be decelerated by the negative pressure region. On the other hand, when the effective sectional area of the nozzle is small, the particle size of the fuel spray is small, so that the fuel spray is easily affected by the negative pressure region. The fuel spray having a small particle size is easily attracted to the negative pressure region, and is easily decelerated by the negative pressure region.

  In comparison with the second injection group, the first injection group has a relatively large effective cross-sectional area and / or a relatively wide injection interval. Therefore, the first injection group forms a fuel spray that has a relatively long scattering distance in the traveling direction and spreads and spreads.

  On the other hand, the second injection group has a relatively small effective cross-sectional area of the nozzle and / or a relatively narrow injection interval, so the scattering distance in the traveling direction is relatively short and the spread is suppressed. Form a fuel spray.

  When the pressure in the cylinder is equal to or higher than a predetermined pressure, the control unit causes the injector to inject fuel so that the mixture layer and a gas layer around the mixture layer are formed in the combustion chamber. It may be formed.

  “When the pressure in the cylinder is equal to or higher than the predetermined pressure” means that the pressure in the cylinder increases with the progress of the compression stroke and becomes equal to or higher than the predetermined pressure. This includes the time when the pressure in the cylinder becomes equal to or higher than the predetermined pressure even during the intake stroke from the initial stage.

  By injecting combustion when the pressure in the cylinder is relatively high, scattering of fuel spray is limited. As a result, it is possible to form a gas layer around the air-fuel mixture layer while forming the air-fuel mixture layer with the air-fuel mixture having a predetermined equivalence ratio or more in the combustion chamber. The gas layer is a layer that does not substantially contain fuel, and includes fresh air and exhaust gas. It is permissible for the gas layer to contain some fuel.

  When the air-fuel mixture forming the air-fuel mixture burns, the surrounding gas layer functions as a heat insulating layer interposed between the air-fuel mixture layer and the wall surface defining the combustion chamber. This configuration greatly reduces the cooling loss.

  The engine body combusts the air-fuel mixture layer by compression self-ignition, and the control unit controls the homogeneous air-fuel mixture layer so that the ignition delay time of the air-fuel mixture changes according to the operating state of the engine main body. Alternatively, the heterogeneous mixture layer may be formed.

  By forming a heterogeneous mixture layer in the combustion chamber, the ignitability is enhanced at a location where the fuel concentration is relatively high in the mixture layer. That is, when the heterogeneous mixture layer is formed, the ignition delay time can be shortened compared to the case where the homogeneous mixture layer is formed. The ignition delay time is optimal according to the operating state of the engine body by switching between forming a homogeneous air-fuel mixture layer and forming a heterogeneous air-fuel mixture layer according to the operating state of the engine body. Turn into.

  The control unit may form a heterogeneous mixture layer in which the difference between the fuel concentration in the central portion and the fuel concentration in the peripheral portion in the mixture layer increases as the rotational speed of the engine body increases. Good.

  The higher the rotation speed of the engine body, the shorter the actual time from the start of fuel injection to the ignition, and a sufficient ignition delay time cannot be secured, leading to a decrease in ignitability and combustion stability. On the other hand, advancing the fuel injection timing causes a decrease in the compression end temperature, which is disadvantageous for the ignitability of compression self-ignition.

  On the other hand, as the difference between the fuel concentration in the central portion and the fuel concentration in the peripheral portion in the air-fuel mixture layer increases, the fuel concentration in a relatively rich portion increases, so the ignition delay time decreases.

  Therefore, the higher the engine speed, the shorter the actual delay time from the start of fuel injection to ignition by forming an inhomogeneous mixture layer with a large fuel concentration difference. Can be shortened, and the ignitability of compression self-ignition is improved, and as a result, the combustion stability is improved.

  The control unit may make the fuel concentration in the central portion of the air-fuel mixture layer richer than the fuel concentration in the peripheral portion when the engine body is in a high rotation state at a predetermined rotation speed or higher.

  By making the fuel concentration in the central portion richer than the fuel concentration in the peripheral portion, the fuel concentration in the peripheral portion becomes relatively lean. Thereby, when the air-fuel mixture constituting the air-fuel mixture layer burns, the amount of heat in the peripheral portion can be suppressed. Since the peripheral portion is closer to the wall surface defining the combustion chamber than the central portion, suppressing the amount of heat in the peripheral portion is advantageous in avoiding an increase in cooling loss. In addition, since the fuel concentration in the air-fuel mixture layer is inhomogeneous, the ignition delay time is shortened as described above. Therefore, it is possible to improve combustion stability when the operating state of the engine body is in the high rotation range.

  The control unit may make the fuel concentration in the peripheral portion of the air-fuel mixture layer richer than the fuel concentration in the central portion when the engine body is in a high rotation state at a predetermined rotation speed or higher.

  By making the fuel concentration in the peripheral part that constitutes the outer peripheral part of the air-fuel mixture layer relatively rich, the air-fuel mixture in the peripheral part starts compression self-ignition first and starts combustion, so the combustion concentration becomes inhomogeneous. Stirring of the mixed gas layer is promoted. This is advantageous for suppressing the generation of soot and unburned substances and shortening the combustion period.

  The control unit makes the fuel concentration in the central portion of the air-fuel mixture layer richer than the fuel concentration in the peripheral portion when the engine main body is at the first rotational speed or higher, and the engine main body is in the second state. When the rotational speed is equal to or higher than the rotational speed (where the first rotational speed is smaller than the second rotational speed), the fuel concentration in the peripheral portion of the air-fuel mixture layer may be made richer than the fuel concentration in the central portion. .

  By making the fuel concentration in the central part of the air-fuel mixture layer richer than the fuel concentration in the peripheral part when in the state of the first rotational speed or more, as described above, combustion stability is achieved in the region on the high speed side. Securement and reduction of cooling loss can be achieved.

  Making the fuel concentration in the peripheral part of the gas mixture layer richer than the fuel concentration in the central part when in the state of the second rotational speed or higher increases the relatively rich range. This is even more advantageous for improving and thus reducing the ignition delay time. Therefore, it is possible to secure combustion stability and improve exhaust emission performance as described above in the region on the higher rotation side.

  It should be noted that the first rotation speed and the second rotation speed may correspond to the boundary of each region when the engine operation region is divided into three regions of low rotation, middle rotation, and high rotation in the rotation speed direction. Good. In addition, the first rotational speed corresponds to a boundary when the engine operating region is divided into two regions of the low rotational speed and the high rotational speed in the rotational speed direction, and the second rotational speed is the high rotational speed region. You may define as rotation speed which divides the area | region of the high rotation side in the inside.

  The control unit forms an air-fuel mixture layer having a homogeneous fuel concentration in the direction of the central axis of the injector or an air-fuel mixture layer having an inhomogeneous fuel concentration in the direction of the central axis, depending on the operating state of the engine body. It is good also as.

  As described above, the fuel concentration distribution in the air-fuel mixture can be switched between homogeneous and non-uniform in the radial direction perpendicular to the central axis of the injector, as well as in the central axis direction. Is possible.

  Since the fuel spray injected from the injector nozzle gradually moves away from the nozzle, the fuel concentration at a location away from the nozzle increases. Therefore, in the direction of the central axis, the fuel concentration in the vicinity of the piston and the vicinity of the cylinder inner wall surface in the combustion chamber at the time of ignition can be high. When combustion is performed in this state, a large amount of heat is generated in the vicinity of the piston and the inner wall surface of the cylinder. As a result, the cooling loss through the piston or cylinder inner wall increases.

  On the other hand, an inhomogeneous mixture layer is formed in which the fuel concentration in the center of the combustion chamber is higher than the fuel concentration in the vicinity of the piston and in the vicinity of the cylinder inner wall surface relative to the central axis direction of the injector. Thus, it is possible to avoid the increase in the cooling loss described above.

  Further, when the load on the engine body increases and the fuel injection amount increases, if a heterogeneous mixture layer having a relatively high fuel concentration in the center of the combustion chamber is formed in the central axis direction of the injector, There is a risk that soot and unburned material may be generated in the part. In this case, it is preferable to form a homogeneous mixture layer in the direction of the central axis of the injector.

  As described above, by switching between the homogeneous mixture and the heterogeneity of the air-fuel mixture layer in the direction of the central axis of the injector in accordance with the operating state of the engine body, fuel efficiency and exhaust emission performance can be improved.

  As described above, according to the control device for a direct injection engine, the fuel concentration distribution and the exhaust emission performance can be improved by optimizing the fuel concentration distribution in the air-fuel mixture according to the operating state of the engine. Improvements can be made.

It is a schematic block diagram which shows a direct injection gasoline engine. It is sectional drawing which shows the internal structure of an injector. It is a figure which illustrates the driving | operation map of an engine. It is sectional drawing which shows notionally the shape of the air-fuel | gaseous mixture layer formed in a combustion chamber. It is a figure explaining the spread direction of the fuel spray injected from an injector. It is a figure which shows the injection interval of a fuel. It is a figure which shows the lift amount of an outside valve-opening type injector. (A) Conceptual diagram showing the spread of fuel spray when the fuel injection interval is long, (B) Conceptual diagram showing the spread of fuel spray when the fuel injection interval is short. (A) The conceptual diagram which shows the spread of fuel spray when the lift amount of an injector is small, (B) The conceptual diagram which shows the spread of fuel spray when the lift amount of an injector is large. It is a figure which shows the injection aspect in a low load and a low rotation area | region. It is a figure which shows the fuel concentration distribution of the combustion chamber in a low load and a low rotation area | region. It is a figure which shows the injection aspect in a low load and medium rotation area | region. It is a figure which shows the fuel concentration distribution of the combustion chamber in a low load and middle rotation area | region. It is a figure which shows the injection aspect in a low load and a high rotation area | region. It is a figure which shows the fuel concentration distribution of the combustion chamber in a low load and a high rotation area | region. It is a figure which shows the injection aspect in a medium load area | region. It is a figure which shows the fuel concentration distribution of the combustion chamber in a medium load area | region. It is sectional drawing which shows the internal structure of the injector which concerns on other embodiment.

  Hereinafter, exemplary embodiments will be described in detail with reference to the drawings.

  FIG. 1 schematically shows a direct injection engine 1 (hereinafter simply referred to as an engine 1). The engine 1 includes various actuators associated with the engine body, various sensors, and an engine controller 100 that controls the actuators based on signals from the sensors.

  The engine 1 is mounted on a vehicle such as an automobile, and its output shaft is connected to drive wheels via a transmission, although not shown. The vehicle is propelled by the output of the engine 1 being transmitted to the drive wheels. The engine body of the engine 1 includes a cylinder block 12 and a cylinder head 13 mounted thereon, and a plurality of cylinders 11 are formed in the cylinder block 12 (in FIG. 1). , Only one cylinder 11 is shown). Although not shown, a water jacket through which cooling water flows is formed inside the cylinder block 12 and the cylinder head 13.

  Here, the fuel of the engine 1 is gasoline in the present embodiment, but it may be gasoline containing bioethanol or the like, and may be any fuel as long as it is a liquid fuel containing at least gasoline.

  A piston 15 is slidably inserted into each cylinder 11. The piston 15 divides the combustion chamber 17 together with the cylinder 11 and the cylinder head 13. In the illustrated example, the combustion chamber 17 is a so-called pent roof type, and its ceiling surface (that is, the lower surface of the cylinder head 13) has a triangular roof shape composed of two inclined surfaces on the intake side and the exhaust side. The crown surface of the piston 15 has a convex shape corresponding to the ceiling surface, and a concave cavity (concave portion) 15a is formed at the center of the crown surface. The shape of the ceiling surface and the crown surface of the piston 15 may be any shape as long as a high geometric compression ratio described later is realized. For example, both the ceiling surface and the crown surface of the piston 15 (that is, the portion excluding the cavity 15a) may be configured by surfaces perpendicular to the central axis of the cylinder 11, and the ceiling surface is triangular as described above. While forming a roof shape, the crown surface of the piston 15 (that is, the portion excluding the cavity 15 a) may be configured by a surface perpendicular to the central axis of the cylinder 11.

  Although only one is shown in FIG. 1, two intake ports 18 are formed in the cylinder head 13 for each cylinder 11, each of which is a lower surface of the cylinder head 13 (that is, an inclined surface on the intake side on the ceiling surface of the combustion chamber 17). Opening to communicate with the combustion chamber 17. Similarly, two exhaust ports 19 are formed in the cylinder head 13 for each cylinder 11, and each opens to the lower surface of the cylinder head 13 (that is, the inclined surface on the exhaust side of the ceiling surface of the combustion chamber 17). 17 communicates. The intake port 18 is connected to an intake passage (not shown) through which fresh air introduced into the cylinder 11 flows. A throttle valve 20 for adjusting the intake flow rate is interposed in the intake passage, and the opening degree of the throttle valve 20 is adjusted in response to a control signal from the engine controller 100. On the other hand, the exhaust port 19 is connected to an exhaust passage (not shown) through which burned gas (that is, exhaust gas) from each cylinder 11 flows. Although not shown, an exhaust gas purification system having one or more catalytic converters is disposed in the exhaust passage. The catalytic converter includes a three-way catalyst.

  The cylinder head 13 is provided with an intake valve 21 and an exhaust valve 22 so that the intake port 18 and the exhaust port 19 can be shut off (closed) from the combustion chamber 17, respectively. The intake valve 21 is driven by an intake valve drive mechanism, and the exhaust valve 22 is driven by an exhaust valve drive mechanism. The intake valve 21 and the exhaust valve 22 reciprocate at a predetermined timing to open and close the intake port 18 and the exhaust port 19, respectively, and perform gas exchange in the cylinder 11. Although not shown, the intake valve drive mechanism and the exhaust valve drive mechanism each have an intake camshaft and an exhaust camshaft that are drivingly connected to the crankshaft. These camshafts are synchronized with the rotation of the crankshaft. Rotate. In addition, at least the intake valve drive mechanism includes a hydraulic, electric, or mechanical variable phase mechanism (VVT) 23 that can continuously change the phase of the intake camshaft within a predetermined angle range. It consists of In addition, you may make it provide the lift variable mechanism (CVVL (Continuous VariableValve Lift)) which can change a valve lift amount continuously with VVT23.

  A spark plug 31 is disposed on the cylinder head 13. The spark plug 31 is attached and fixed to the cylinder head 13 by a known structure such as a screw. In the illustrated example, the spark plug 31 is attached and fixed in a state inclined to the exhaust side with respect to the central axis of the cylinder 11, and the tip thereof faces the ceiling of the combustion chamber 17. The tip of the spark plug 31 is located in the vicinity of a nozzle port 41 of an injector 33 described later. The arrangement of the spark plug 31 is not limited to this. In the present embodiment, the ignition plug 31 is a plasma ignition type plug, and the ignition system 32 includes a plasma generation circuit. The spark plug 31 generates plasma by discharge by the ignition system 32 and injects the plasma into the cylinder from the tip of the spark plug 31 to ignite the fuel. The ignition system 32 receives a control signal from the engine controller 100 and energizes the ignition plug 31 to generate plasma at a desired ignition timing. The spark plug 31 is not limited to a plasma ignition type plug, but may be a spark ignition type plug that is commonly used.

  On the central axis of the cylinder 11 in the cylinder head 13, an injector 33 that directly injects fuel into the cylinder (that is, in the combustion chamber 17) is disposed. The injector 33 is fixedly attached to the cylinder head 13 with a known structure such as using a bracket. The tip of the injector 33 faces the center of the ceiling of the combustion chamber 17.

  As shown in FIG. 2, the injector 33 has an outer valve-opening type having a nozzle body 40 in which a nozzle port 41 for injecting fuel into the cylinder 11 is formed, and an outer valve 42 for opening and closing the nozzle port 41. It is an injector. The injector 33 injects fuel in a direction that is inclined with respect to a predetermined central axis S and spreads radially outward from the central axis S, and can adjust the effective sectional area of the nozzle port 41. It is configured. The nozzle port 41 is an example of a nozzle hole, and the outer opening valve 42 is an example of a valve body.

  The nozzle body 40 is a tubular member extending along the central axis S, and the fuel circulates therein. The opening edge of the nozzle port 41 is formed in a tapered shape whose diameter increases toward the tip side at the tip portion of the nozzle body 40. The proximal end of the nozzle body 40 is connected to a case 45 in which a piezo element 44 is disposed. The outer opening valve 42 includes a valve main body 42 a and a connecting portion 42 b that is connected from the valve main body 42 a through the nozzle main body 40 to the piezo element 44. The valve body 42 a is exposed to the outside from the nozzle body 40 at the tip of the nozzle body 40. When the portion of the valve body 42a on the side of the connecting portion 42b has substantially the same shape as the opening edge of the nozzle port 41, and the portion abuts (that is, sits) on the opening edge of the nozzle port 41, The nozzle port 41 is closed.

  The injector 33 is arranged such that the central axis S coincides with the central axis X of the cylinder 11 (that is, the cylinder central axis X) and the nozzle port 41 faces the ceiling portion of the combustion chamber 17.

  The piezo element 44 opens the nozzle port 41 by pressing the outer opening valve 42 in the direction of the central axis and lifting it from the opening edge of the nozzle port 41 of the nozzle body 40 by deformation due to application of voltage. At this time, the fuel is injected in a direction that is inclined with respect to the central axis S from the nozzle opening 41 and spreads in a radial direction centering on the central axis S. Specifically, the fuel is injected in a cone shape (specifically, a hollow cone shape) around the central axis S. The taper angle of the cone is 90 ° to 100 ° in the present embodiment (the taper angle of the inner hollow portion of the hollow cone is about 70 °). When the application of voltage to the piezo element 44 is stopped, the piezo element 44 returns to the original state, and the outer opening valve 42 closes the nozzle port 41 again. At this time, the compression coil spring 46 disposed around the connecting portion 42 b in the case 45 facilitates the return of the piezo element 44.

  As the voltage applied to the piezo element 44 increases, the lift amount (hereinafter simply referred to as lift amount) of the outer open valve 42 from the state in which the nozzle port 41 is closed increases (see also FIG. 7). The larger the lift amount, the larger the opening degree (that is, the effective sectional area) of the nozzle port 41 and the larger the particle size of the fuel spray injected from the nozzle port 41 into the cylinder. Conversely, the smaller the lift amount, the smaller the opening of the nozzle port 41 and the smaller the particle size of the fuel spray injected from the nozzle port 41 into the cylinder. The response of the piezo element 44 is fast, and, for example, about 20 multistage injections are possible in one cycle. However, the means for driving the outer valve 42 is not limited to the piezo element 44.

  The fuel supply system 34 includes an electric circuit for driving the outer opening valve 42 (piezo element 44) and a fuel supply system for supplying fuel to the injector 33. The engine controller 100 outputs an injection signal having a voltage corresponding to the lift amount to the electric circuit at a predetermined timing, thereby operating the piezo element 44 and the outer valve 42 via the electric circuit, A desired amount of fuel is injected into the cylinder. When the injection signal is not output (that is, when the voltage of the injection signal is 0), the nozzle opening 41 is closed by the outer opening valve. Thus, the operation of the piezo element 44 is controlled by the injection signal from the engine controller 100. Thus, the engine controller 100 controls the operation of the piezo element 44 to control the fuel injection from the nozzle port 41 of the injector 33 and the lift amount during the fuel injection.

  The fuel supply system is provided with a high-pressure fuel pump (not shown) and a common rail, and the high-pressure fuel pump pumps the fuel supplied from the fuel tank via the low-pressure fuel pump to the common rail. The pumped fuel is stored at a predetermined fuel pressure. The fuel stored in the common rail is injected from the nozzle port 41 by operating the injector 33 (that is, the outer opening valve 42 is lifted).

  The engine controller 100 is a controller based on a well-known microcomputer, and includes a central processing unit (CPU) that executes a program, a memory that is configured by, for example, RAM and ROM, and stores a program and data, And an input / output (I / O) bus for inputting and outputting signals. The engine controller 100 is an example of a control unit.

  The engine controller 100 includes at least a signal related to the intake air flow from the air flow sensor 71, a crank angle pulse signal from the crank angle sensor 72, an accelerator opening signal from the accelerator opening sensor 73 that detects the amount of depression of the accelerator pedal, And the vehicle speed signal from the vehicle speed sensor 74 is received, respectively. Based on these input signals, the engine controller 100 calculates control parameters of the engine 1, such as a desired throttle opening signal, fuel injection pulse, ignition signal, valve phase angle signal, and the like. Then, the engine controller 100 converts these signals into a throttle valve 20 (more precisely, a throttle actuator that moves the throttle valve 20), a fuel supply system 34 (more precisely, the above electric circuit), an ignition system 32, and Output to VVT23 or the like.

  Although not shown, the engine 1 is provided with an EGR passage that connects the intake passage and the exhaust passage, and includes an EGR system that recirculates part of the exhaust gas to the intake air. The engine controller 100 adjusts the exhaust gas recirculation amount through the EGR system according to the operating state of the engine 1.

  The geometric compression ratio ε of the engine 1 is 15 or more and 40 or less. In the present embodiment, the engine 1 is also an engine 1 having a relatively high expansion ratio as well as a high compression ratio because of the configuration where the compression ratio = expansion ratio. The thermal efficiency is improved by increasing the geometric compression ratio.

  As shown in FIG. 1, the combustion chamber 17 includes a wall surface of the cylinder 11, a crown surface of the piston 15, a lower surface (that is, a ceiling surface) of the cylinder head 13, and valve heads of the intake valve 21 and the exhaust valve 22. And a surface. And in this engine 1, in order to reduce a cooling loss, the heat insulation layer 61, 62, 63, 64, 65 is provided in each of these surfaces, and the combustion chamber 17 is thermally insulated. In addition, below, when these heat insulation layers 61-65 are named generically, a code | symbol "6" may be attached | subjected to a heat insulation layer. The heat insulation layer 6 may be provided on all of these section screens, or may be provided on a part of these section screens. Further, in the illustrated example, the heat insulating layer 61 on the cylinder wall surface is provided at a position above the piston ring 14 in a state where the piston 15 is located at the top dead center. 14 is configured not to slide. However, the heat insulating layer 61 on the cylinder wall surface is not limited to this configuration, and the heat insulating layer 61 may be provided over the entire stroke or a part of the stroke of the piston 15 by extending the heat insulating layer 61 downward. Further, a heat insulating layer may be provided on the port wall surface near the opening on the ceiling surface side of the combustion chamber 17 in the intake port 18 and the exhaust port 19, although it is not the wall surface that directly partitions the combustion chamber 17. In addition, the thickness of each heat insulation layer 61-65 illustrated in FIG. 1 does not show actual thickness, but is only an illustration, and does not show the magnitude relationship of the thickness of the heat insulation layer in each surface.

  The heat insulation structure of the combustion chamber 17 will be described in more detail. As described above, the heat insulating structure of the combustion chamber 17 is constituted by the heat insulating layers 61 to 65 provided on the respective screens that define the combustion chamber 17, and these heat insulating layers 61 to 65 are the combustion gas in the combustion chamber 17. Therefore, the heat conductivity is set to be lower than that of the metal base material constituting the combustion chamber 17. Here, for the heat insulating layer 61 provided on the wall surface of the cylinder 11, the cylinder block 12 is the base material, and for the heat insulating layer 62 provided on the crown surface of the piston 15, the piston 15 is the base material. For the heat insulating layer 63 provided on the ceiling surface, the cylinder head 13 is a base material, and for the heat insulating layers 64 and 65 provided on the valve head surfaces of the intake valve 21 and the exhaust valve 22, respectively, the intake valve 21 and the exhaust valve 22 are provided. Are the base materials. Accordingly, the base material is aluminum alloy or cast iron for the cylinder block 12, cylinder head 13 and piston 15, and heat-resistant steel or cast iron for the intake valve 21 and exhaust valve 22.

  In addition, the heat insulating layer 6 preferably has a volumetric specific heat smaller than that of the base material in order to reduce cooling loss. That is, the gas temperature in the combustion chamber 17 varies with the progress of the combustion cycle, but in a conventional engine that does not have the heat insulation structure of the combustion chamber 17, the cooling water flows in a water jacket formed in the cylinder head or cylinder block. Thus, the temperature of the surface defining the combustion chamber 17 is maintained substantially constant regardless of the progress of the combustion cycle.

  On the other hand, since the cooling loss is determined by cooling loss = heat transfer coefficient × heat transfer area × (gas temperature−temperature of the section screen), the cooling temperature increases as the temperature difference between the gas temperature and the wall surface temperature increases. The loss will increase. In order to suppress the cooling loss, it is desirable to reduce the difference between the gas temperature and the temperature of the section screen. However, when the temperature of the section screen of the combustion chamber 17 is maintained substantially constant by cooling water, It is unavoidable that the temperature difference increases with fluctuation. Therefore, it is preferable to reduce the heat capacity of the heat insulating layer 6 so that the temperature of the section screen of the combustion chamber 17 changes following the fluctuation of the gas temperature in the combustion chamber 17.

The heat insulating layer 6 may be formed, for example, by coating a ceramic material such as ZrO ₂ on the base material by plasma spraying. The ceramic material may contain a number of pores. If it does in this way, the thermal conductivity and volume specific heat of the heat insulation layer 6 can be made lower.

  Further, in the present embodiment, as shown in FIG. 1, a port liner 181 made of aluminum titanate having an extremely low thermal conductivity, excellent heat insulation, and excellent heat resistance is integrated with the cylinder head 13. A heat insulating layer is provided in the intake port 18 by casting. With this configuration, when fresh air passes through the intake port 18, it is possible to suppress or avoid an increase in temperature due to heat received from the cylinder head 13. As a result, the temperature of the fresh air introduced into the cylinder 11 (initial gas temperature) is lowered, so that the gas temperature at the time of combustion is lowered and the temperature difference between the gas temperature and the section screen of the combustion chamber 17 is reduced. Become advantageous. Lowering the gas temperature at the time of combustion can lower the heat transfer rate, which is advantageous for reducing the cooling loss. In addition, the structure of the heat insulation layer provided in the intake port 18 is not limited to the casting of the port liner 181.

In the engine 1, the geometric compression ratio ε is set to 15 ≦ ε ≦ 40 as described above. The theoretical thermal efficiency η _th in the Otto cycle, which is the theoretical cycle, is η _th = 1−1 / (ε ^κ−1 ), and the theoretical thermal efficiency η _th increases as the compression ratio ε increases. However, the illustrated thermal efficiency of the engine (more precisely, the engine having no combustion chamber insulation structure) peaks at a predetermined geometric compression ratio ε (for example, about 15), and the geometric compression ratio ε is more than that. However, the illustrated thermal efficiency does not increase, and conversely, the illustrated thermal efficiency decreases. This is because, when the geometric compression ratio is increased while the fuel amount and the intake air amount are kept constant, the higher the compression ratio, the higher the combustion pressure and the combustion temperature. As described above, the combustion pressure and the combustion temperature are increased because the cooling loss is increased.

  On the other hand, in this engine 1, the heat insulating structure of the combustion chamber 17 is combined as described above so that the illustrated thermal efficiency is increased at a high geometric compression ratio ε. That is, the heat loss of the combustion chamber 17 is reduced to reduce the cooling loss, thereby increasing the indicated thermal efficiency.

  On the other hand, merely reducing the cooling loss by insulating the combustion chamber 17 converts the reduced cooling loss into the exhaust loss and does not contribute much to the improvement in the illustrated thermal efficiency. In addition, the high expansion ratio accompanying the high compression ratio efficiently converts the combustion gas energy corresponding to the reduction in cooling loss into mechanical work. That is, it can be said that the engine 1 greatly improves the illustrated thermal efficiency by adopting a configuration that reduces both the cooling loss and the exhaust loss.

  In this engine 1, in addition to the heat insulation structure of the combustion chamber 17 and the intake port 18, a heat insulation layer is formed by a gas layer in the cylinder (inside the combustion chamber 17), thereby further reducing the cooling loss. Yes. This will be described in detail below.

  FIG. 3 illustrates an operation map when the engine 1 is warm. The engine 1 is basically configured to burn the air-fuel mixture in the combustion chamber 17 by compression self-ignition over the entire operation region. In the operation map shown in FIG. 3, a heat insulating layer made of a gas layer is formed in the combustion chamber 17 in a low load region lower than a predetermined load and a medium load region where the load is higher than the low load region. In other words, in an operating state where the engine load is relatively low and the fuel injection amount is relatively small, a heat insulation layer is formed in the combustion chamber 17 by a gas layer, thereby reducing cooling loss and improving thermal efficiency. Plan. Here, the low load region and the medium load region respectively correspond to the low region and the medium region when the engine load region is divided into three regions of low, medium, and high (for example, divided into three equal parts). May be defined. In particular, the middle load region may be a region of a predetermined load or less (for example, 70% load or less) with respect to the fully open load, for example.

  FIG. 4 conceptually shows the shape of the air-fuel mixture layer formed in the combustion chamber 17 in the low load and medium load regions. The formation of a heat insulating layer by a gas layer in the combustion chamber 17 means that an air-fuel mixture layer is formed at the center of the combustion chamber 17 and a gas layer containing fresh air is formed around it as shown in FIG. That is.

  The air-fuel mixture layer here is defined as a layer composed of a combustible air-fuel mixture (for example, an air-fuel mixture having an equivalent ratio φ = 0.1 or more). Further, as the time elapses from the start of fuel injection, the fuel spray diffuses, and the size of the air-fuel mixture layer is the size at the time of ignition. Furthermore, the ignition can be determined when, for example, the combustion mass ratio of the fuel becomes 1% or more.

  Further, the gas layer may be only fresh air, and may contain burned gas (that is, EGR gas) in addition to fresh air. As will be described later, it is allowed that a small amount of fuel is mixed in the gas layer as long as the gas layer serves as a heat insulating layer.

  By reducing the ratio (S / V ratio) between the surface area (S) and the volume (V) of the gas mixture layer, the heat transfer area with the surrounding gas layer is reduced during combustion, and the gas mixture layer and the cylinder 11 Due to the gas layer between the cylinder 11 and the wall surface, the flame of the gas mixture layer does not come into contact with the wall surface of the cylinder 11, and the gas layer itself becomes a heat insulating layer to suppress the release of heat from the wall surface of the cylinder 11. Will be able to. As a result, the cooling loss can be greatly reduced.

  The engine controller 100 includes a nozzle port 41 of the injector 33 in a period from the latter half of the compression stroke to the initial stage of the expansion stroke so that an air-fuel mixture layer is formed in the central portion of the combustion chamber 17 and a gas layer is formed around it. In order to inject fuel into the cylinder 11, the injection signal is output to the electric circuit of the fuel supply system. Here, the second half of the compression stroke is the second half when the compression stroke is divided into the first half and the second half. In addition, the initial stage of the expansion stroke is an initial stage when the expansion stroke is divided into three parts: an initial stage, a middle stage, and a final stage.

  In the low load region, since the fuel injection amount is relatively small, fuel is injected into the cylinder 11 from the injector 33 disposed on the central axis X of the cylinder 11 in the second half of the compression stroke to the initial stage of the expansion stroke. It is relatively easy to suppress the spread of the fuel spray by injecting and form the air-fuel mixture layer at the center in the combustion chamber 17 and the surrounding gas layer. However, since the fuel injection period becomes longer as the combustion injection amount increases, the fuel spray spreads particularly in the direction of the central axis X of the cylinder 11, and as a result, the air-fuel mixture layer forms, for example, the crown surface of the piston 15. Will come to touch. That is, the gas layer around the gas mixture layer is not reliably formed. As described above, the engine 1 has a high geometric compression ratio, and accordingly, the volume of the combustion chamber (that is, the space in the cylinder when the piston is located at the compression top dead center) is small. Therefore, in the engine 1, when the fuel spray spreads in the direction of the central axis X of the cylinder 11, the air-fuel mixture layer tends to touch the crown surface of the piston 15.

  Therefore, the engine 1 is formed in the combustion chamber 17 in order to reliably form the air-fuel mixture layer in the center of the combustion chamber 17 and the surrounding gas layer even in the middle load region where the fuel injection amount increases. Control the shape of the gas mixture. Specifically, as shown by the white arrow in FIG. 4, when the fuel injection amount increases, the fuel spray spreads outward in the radial direction intersecting the central axis X of the cylinder 11. As a result, the length of the air-fuel mixture layer in the direction of the central axis X is prevented from becoming longer, and the air-fuel mixture layer is prevented from touching the crown surface of the piston 15 while being spatially smaller than the direction of the central axis X. By expanding the air-fuel mixture layer in the radially outward direction with a sufficient margin, it is also avoided that the air-fuel mixture layer touches the inner wall of the cylinder 11. Controlling the shape of the air-fuel mixture layer formed in the combustion chamber 17 means that when the length in the central axis direction of the air-fuel mixture layer formed in the combustion chamber 17 is L and the radial width is W, By adjusting the ratio (L / W) between the length L and the width W, the fuel injection amount increased while the L / W ratio was set to a predetermined value or more in order to reduce the S / V ratio. Sometimes, the L / W ratio is reduced.

  In order to realize such control of the shape of the air-fuel mixture layer, in the engine 1, the fuel injection interval (see FIG. 6) by the injector 33 and the lift amount (see FIG. 7) are adjusted. Thereby, as shown in FIG. 5, the spread of the fuel spray in the traveling direction and the spread of the fuel spray in the radial direction are controlled independently. The interval between fuel injections is defined as the interval from the end of fuel injection to the start of the next fuel injection, as conceptually shown in FIG. As described above, this injector 33 has a high response and can perform about 20 multistage injections within 1 to 2 msec. Further, as conceptually shown in FIG. 7, the lift amount of the injector 33 is proportional to the fuel injection opening area. As described above, the larger the lift amount, the more the injection opening area (that is, the effective disconnection of the nozzle port 41). Area) increases, and the smaller the lift amount, the smaller the injection opening area.

  FIG. 8 shows a fuel spray when the fuel injection interval is lengthened (FIG. (A)) and when the injection interval is shortened (FIG. (B)) while the lift amount of the injector 33 is made constant. Conceptually shows the difference in the spread of The fuel spray injected in a hollow cone shape from the injector 33 flows in the combustion chamber 17 at a high speed. Therefore, a negative pressure region is generated along the central axis S of the injector 33 inside the hollow cone due to the Coanda effect. When the fuel injection interval is long, the pressure in the negative pressure region recovers between the fuel injection and the next fuel injection, so the negative pressure region becomes smaller. On the other hand, when the fuel injection interval is short, the fuel injection is repeated without a gap, so that the recovery of the pressure in the negative pressure region is suppressed. As a result, the negative pressure region becomes large as shown in FIG.

  The fuel spray is attracted to this negative pressure. Since the negative pressure region is formed on the center side in the radial direction around the central axis S, when the negative pressure region is relatively large, as shown in FIG. 8B, the fuel spray expands in the radial direction. Is suppressed. On the other hand, when the negative pressure region is relatively small, as shown in FIG. 8 (A), the fuel spray is not attracted so much, and thus tends to spread in the radial direction. That is, if the fuel injection interval of the injector 33 is shortened, the radial spread of the fuel spray can be suppressed. On the other hand, if the injection interval is increased, the radial spread of the fuel spray is promoted. Is possible.

  FIG. 9 shows a fuel spray when the lift amount of the injector 33 is reduced (FIG. (A)) and the lift amount is increased (FIG. (B)) while the fuel injection interval is made constant. Conceptually shows the difference in the spread of In this case, since the injection interval is the same, the negative pressure region in the combustion chamber 17 is the same, but the particle size of the fuel spray is different due to the difference in the lift amount. That is, when the lift amount of the injector 33 is reduced, the particle size of the fuel spray is also reduced, so that the momentum of the fuel spray is reduced. For this reason, the fuel spray is easily attracted to the center side in the radial direction by the negative pressure, and the outward spreading in the radial direction is suppressed as shown in FIG. On the other hand, when the lift amount of the injector 33 is increased, the particle size of the fuel spray increases, so the momentum of the fuel spray increases. For this reason, the fuel spray is less likely to be attracted to the negative pressure and easily spreads outward in the radial direction as shown in FIG. 9B. That is, if the lift amount of the injector 33 is increased, the spread of the fuel spray in the radial direction can be promoted. On the other hand, if the lift amount is decreased, the spread of the fuel spray in the radial direction can be suppressed. become.

  Further, since the fuel spray having a large particle size has a large momentum, the scattering distance in the traveling direction becomes long. Furthermore, the fuel spray having a large particle size is not easily decelerated due to the influence of the negative pressure region, and this also increases the scattering distance. On the other hand, since the fuel spray with a small particle size has a small momentum, the scattering distance in the traveling direction becomes short. Further, the fuel spray having a small particle size is easily decelerated under the influence of the negative pressure region, and this also shortens the scattering distance.

  As described above, by changing the injection interval and the lift amount of the injector 33, it is possible to independently control the spread of the fuel spray in the two directions of the radial direction and the traveling direction. Therefore, in this engine 1, the lift amount is relatively small and the injection interval is relatively small, and the first injection group including a plurality of fuel injections having a relatively large lift amount and a relatively large injection interval. The shape of the air-fuel mixture layer is controlled in combination with the second injection group including a plurality of fuel injections. In any of the injection groups, multi-stage injection that performs fuel injection a plurality of times is executed. Here, the multistage injection means continuous fuel injection in which the fuel injection interval (interval from the end of fuel injection to the start of the next fuel injection) is 0.5 ms or less.

  Specifically, the first injection group includes a predetermined number of fuel injections in which the lift amount of the injector 33 is larger than that of the second injection group and the fuel injection interval is larger than that of the second injection group. By increasing the injection interval, the negative pressure region becomes smaller. In addition, the momentum of the fuel spray is increased by increasing the lift amount to increase the particle size of the fuel spray. As a result, a fuel spray is formed in which the scattering distance in the traveling direction is relatively long and spread in the radial direction.

  The second injection group includes a predetermined number of fuel injections in which the lift amount of the injector 33 is smaller than that of the first injection group and the fuel injection interval is smaller than that of the first injection group. By reducing the injection interval, the negative pressure region is expanded. In addition, the momentum of the fuel spray is reduced by reducing the lift amount and the particle size of the fuel spray. As a result, a fuel spray is formed in which the scattering distance in the traveling direction is relatively short and the spread in the radial direction is suppressed.

  The engine controller 100 controls the air-fuel mixture layer to have a shape corresponding to the operating state of the engine 1 by changing the ratio of the first injection group and the second injection group according to the operating state of the engine 1. . As a basic principle, by increasing the proportion of the first injection group, an air-fuel mixture layer is formed that extends radially outward, while by increasing the proportion of the second injection group, the radially outer side An air-fuel mixture layer in which the spread to is suppressed is formed.

  Depending on the operating state of the engine 1, the first injection group is omitted and only the second injection group is executed, or only one fuel injection is included in the first injection group, and the second injection is performed thereafter. When the second injection group is omitted and only the first injection group is executed, or when the fuel injection included in the second injection group is only once and the first injection group is used. There is also. Further, the second injection group may be executed after the first injection group, or the first injection group may be executed after the second injection group.

  The engine controller 100 further controls the injection modes of the first injection group 8 and the second injection group 9 in accordance with the operating state of the engine 1 on the premise of the above-described multistage injection. FIG. 10 is a diagram showing an injection mode in a low load and low rotation range. FIG. 11 is a diagram showing a fuel concentration distribution in the combustion chamber in a low load and low rotation region. FIG. 12 is a diagram showing an injection mode in a low load and medium rotation range. FIG. 13 is a diagram showing a fuel concentration distribution in the combustion chamber in a low load and medium rotation region. FIG. 14 is a diagram showing an injection mode in a low load and high rotation region. FIG. 15 is a diagram showing a fuel concentration distribution in the combustion chamber in a low load and high rotation region. FIG. 16 is a diagram illustrating an injection mode in the medium load region. FIG. 17 is a diagram showing the fuel concentration distribution in the combustion chamber in the medium load region.

  Specifically, the engine controller 100 performs multi-stage injection including the first injection group 8 and the second injection group 9 between the latter half of the compression stroke and the early stage of the expansion stroke in the low rotation region in the low load region. Let me do it. As shown in FIG. 10, the first injection group 8 includes a first injection 81 having a predetermined lift amount and a second lift amount that is later than the first injection 81 and larger than the first injection 81. An injection 82 and a third injection 83 that is after the second injection 82 and has a smaller lift amount than the second injection 82 are included. Note that the lift amount of the third injection 83 is larger than the lift amount of the first injection 81. At this time, the lift amount of the fuel injection 90 included in the second injection group 9 is constant.

  Here, when the first injection 81 is performed, the fuel spray is more easily scattered in the combustion chamber 17 than when the second injection 82 is performed. That is, when fuel is injected into the combustion chamber 17, the atmospheric temperature in the combustion chamber 17 decreases and the air density increases. As the air density increases, the resistance increases and the fuel spray is less likely to scatter. When the first injection 81 is performed, the fuel injected into the combustion chamber 17 is absent or less than when the second injection 82 is performed, and the air density in the combustion chamber 17 is relatively low. Therefore, in the first injection 81, the particle size of the fuel spray is reduced by reducing the lift amount, and the momentum of the fuel spray is reduced. Thereby, the scattering distance of the fuel spray by the 1st injection 81 is suppressed, and this fuel spray tends to stay between the nozzle port 41 and the piston 15 in the central axis direction.

  On the other hand, when the second injection 82 is performed, the fuel spray is less likely to scatter in the combustion chamber 17 than when the first injection 81 is performed. In other words, the atmosphere temperature in the combustion chamber 17 is lowered by the first injection 81 and the air density is increased. Therefore, in the second injection 82, the lift amount is increased compared to the first injection 81, thereby increasing the particle size of the fuel spray and increasing the momentum of the fuel spray. Thereby, the scattering distance of the fuel spray by the second injection 82 is increased, and the fuel spray is prevented from staying in the vicinity of the nozzle port 41. As a result, the fuel spray tends to stay between the nozzle port 41 and the piston 15 in the central axis direction.

  Further, when the third injection 83 is performed, the fuel spray is more easily scattered in the combustion chamber 17 than when the second injection 82 is performed. Specifically, although the temperature in the combustion chamber 17 is decreasing, the fuel spray injected by the first injection 81 and the second injection 82 exists at the destination where the fuel is injected from the nozzle port 41. Fuel is less resistant and more likely to be scattered when injected during fuel spraying than when injected into air. Therefore, in the third injection 83, the lift amount is made smaller than that of the second injection 82, thereby reducing the particle size of the fuel spray and reducing the momentum of the fuel spray. Thereby, the scattering distance of the fuel spray by the third injection 83 is suppressed, and the fuel spray tends to stay between the nozzle port 41 and the piston 15 in the central axis direction.

  On the other hand, the fuel injection of the second injection group 9 has a relatively small momentum because the lift amount is relatively small and the particle size of the fuel injection is small. Therefore, the fuel spray of the second injection group 9 has a relatively short scattering distance and is easily decelerated under the influence of negative pressure. Therefore, the fuel spray by the second injection group 9 does not easily reach the piston 15 in the central axis direction, and tends to stay between the nozzle port 41 and the piston 15.

  Further, the total injection amount by the first injection group 8 and the total injection amount by the second injection group 9 are substantially the same amount. The second injection group 9 is completed before the compression top dead center.

  As a result of such fuel injection by the first injection group 8 and the second injection group 9, at the time of ignition (predetermined timing after compression top dead center), the fuel spray tends to concentrate near the center in the central axis direction. Become. Specifically, as shown in FIG. 11, the portion of the gas mixture layer where the fuel concentration is maximum is 25 in the space from the nozzle port 41 to the piston 15 with respect to the distance in the central axis direction from the nozzle port 41 toward the piston 15. % Area A1, 50% area A2, and 25% area A3 are included in 50% area A2. Note that the ignition of fuel can be determined, for example, when the combustion mass ratio of the fuel becomes 1% or more.

  On the other hand, the concentration distribution in the radial direction of the combustion chamber 17 at the time of ignition is substantially uniform as shown in FIG. This is because the injection amount of the first injection group 8 in which the fuel spray is formed with a relatively long scattering distance in the traveling direction and spread in the radial direction, and the scattering distance in the traveling direction is relatively short and the radial direction. This is because the injection amount of the second injection group 9 in which the fuel spray in which the spread is suppressed is the same amount. That is, as a result of the fuel spray reaching the radially outward direction by the first injection group 8 and the fuel spray reaching the radially inward direction by the second injection group 9, the fuel in the radial direction in the mixture layer Concentration is almost the same. Here, in the radial direction of the air-fuel mixture layer, when the range of 60% of the diameter of the air-fuel mixture layer is defined as the central portion and the surrounding portion is defined as the peripheral portion, the fuel in the central portion The difference between the concentration and the fuel concentration in the peripheral portion is equal to or less than a predetermined value is called homogeneous. As shown in FIG. 11, when the fuel concentration (that is, the equivalence ratio φ) is substantially constant from the central portion to the peripheral portion, the fuel concentration is homogeneous in the radial direction.

  When the fuel is combusted in this state, there is little fuel in the vicinity of the nozzle opening 41 and in the vicinity of the piston 15, so that the amount of heat generated by combustion in these places is reduced. On the other hand, in the intermediate portion between the nozzle port 41 and the piston 15, the fuel is relatively increased, and a large amount of heat is generated by combustion. As a result, heat dissipation through the wall surface (ceiling surface) of the cylinder 11 near the nozzle port 41 and the piston 15 is suppressed, and cooling loss is reduced.

  Moreover, since it is a low rotation area | region, the real time from the start of fuel injection to ignition can ensure comparatively long time. Therefore, it is not necessary to improve the ignitability, and as described later, making the fuel concentration in the radial direction inhomogeneous can cause inconveniences such as generation of soot. Thus, by making the fuel concentration uniform in the radial direction, a reduction in exhaust emission performance is avoided.

  In the middle rotation region of the low load region, the engine controller 100 includes the second injection in addition to the first injection group 8 including the first injection 81 and the second injection 82 as shown in FIG. The group 9 also includes a first injection 91 having a predetermined lift amount, a second injection 92 after the first injection 91 and having a lift amount larger than the first injection 91, and after the second injection 92. And the third injection 93 having a lift amount smaller than that of the second injection 92.

  At this time, the ratio of the second injection group 9 to the total fuel injection amount in one cycle increases as the rotational speed of the engine 1 increases. Therefore, the ratio of the second injection group 9 is greater than the ratio of the first injection group 8. In the example of FIG. 12, the number of fuel injections included in the first injection group 8 is decreased by one and the number of fuel injections included in the second injection group 9 is increased by two compared to the example of FIG. Yes. Specifically, in the first injection group 8, the third injection 83 is deleted, and only the first injection 81 and the second injection 82 are provided.

  Further, the injection timing of the multistage injection is advanced compared to the low rotation region. This is because, assuming that the fuel is ignited at a predetermined crank angle, the time from the start of fuel injection to the predetermined crank angle becomes shorter as the engine speed increases. That is, it is for securing sufficient time corresponding to the ignition delay between the start of fuel injection and the predetermined crank angle.

  The second injection group 9 will be described in detail. The second injection group 9 includes four first injections 91, three second injections 92, and four third injections 93.

  In the second injection group 9 as well, the lift amount of the fuel injection is adjusted in consideration of the ease of scattering of the fuel spray in the combustion chamber 17 as in the description of the first injection group 8 described above. That is, in the initial stage of the multi-stage injection, the air density in the combustion chamber 17 is low and the fuel spray is likely to be scattered. Therefore, by reducing the particle size of the fuel spray by the first injection 91, the fuel spray is easily decelerated, Fuel spray is retained between the nozzle port 41 and the piston 15 in the central axis direction. In the middle stage of the multi-stage injection, the air density in the combustion chamber 17 is high and the fuel spray is difficult to scatter. Therefore, by increasing the particle size of the fuel spray by the second injection 92, the fuel spray is difficult to decelerate. Is held between the nozzle port 41 and the piston 15 in the central axis direction. At the end of the multi-stage injection, the fuel spray is much in the combustion chamber 17 and the fuel spray is likely to be scattered. Therefore, by reducing the particle size of the fuel spray by the third injection 93, the fuel spray can be easily decelerated, and the fuel spray. Is held between the nozzle port 41 and the piston 15 in the central axis direction.

  Thus, in the middle rotation region of the low load region, not only the fuel spray by the first injection group 8 but also the fuel spray by the second injection group 9 is between the nozzle port 41 and the piston 15 in the central axis direction. The injector 33 is controlled to stay. Therefore, as shown in FIG. 13, the air-fuel mixture layer at the time of ignition is a 25% region A1, 50% in the space from the nozzle port 41 to the piston 15 with respect to the distance in the central axis direction from the nozzle port 41 toward the piston 15. The fuel concentration becomes maximum in 50% of the region A2 when the region A2 is divided into 25% of the region A3. At this time, by including the first injection 91, the second injection 92, and the third injection 93 also in the second injection group 9, the degree of concentration of the fuel spray in the region A2 of 50% compared to the region on the low rotation side. Is high.

  When the engine 1 has a high rotational speed, in order to ignite the fuel at a predetermined crank angle, it is necessary to ensure a sufficient time corresponding to the ignition delay between the start of fuel injection and the ignition. For this purpose, the fuel injection timing is advanced compared to when the rotational speed is low. However, when the fuel is injected into the combustion chamber 17, the specific heat ratio in the combustion chamber 17 is lowered. Therefore, as the fuel injection timing is advanced, the temperature of the compression end temperature is less likely to increase and ignition is difficult. On the other hand, as described above, by forming a portion where the fuel concentration is locally high, the ignitability can be improved, and the fuel can be ignited at a desired crank angle even when the rotational speed is high. It becomes possible.

  In addition, the ratio of the second injection group 9 to the total injection amount is higher than that in the low rotation side region. In the second injection group 9, the fuel spray has a small particle size and a large negative pressure region, so that the fuel spray is likely to gather near the radial center of the combustion chamber 17. Therefore, in the radial direction of the combustion chamber 17 at the time of ignition, the fuel concentration is maximum in the central portion in the radial direction, and the fuel concentration is lower in the peripheral portion than in the central portion. That is, by increasing the ratio of the second injection group 9, the fuel concentration distribution becomes non-homogeneous also in the radial direction of the combustion chamber 17, and a portion where the fuel concentration is locally high can be formed.

  Thus, in addition to providing the first injection 81 (91) and the second injection 82 (92) in the first injection group 8 or the second injection group, by increasing the ratio of the second injection group 9, the combustion chamber 17 By adjusting the fuel concentration distribution in both the central axis direction and the radial direction, that is, three-dimensionally, the fuel concentration in the combustion chamber 17 can be locally increased not only in the central axis direction but also in the radial direction. . As a result, a portion with a higher fuel concentration can be formed, and the ignitability can be further improved. This is advantageous in improving combustion stability in the middle rotation region.

  Further, since the ratio of the second injection group 9 increases as the rotational speed of the engine 1 increases, the local fuel concentration increases in the radial direction as the engine speed increases (that is, the fuel concentration at the center). Becomes higher). Increasing the fuel concentration difference in the air-fuel mixture layer is advantageous for further improving the ignitability on the high rotation side.

  When the fuel is combusted in this state, there is little fuel in the vicinity of the nozzle opening 41 and in the vicinity of the piston 15, so that the amount of heat generated by combustion in these places is small. As a result, heat dissipation through the wall surface (ceiling surface) of the cylinder 11 near the nozzle port 41 and the piston 15 is suppressed, and cooling loss is reduced.

  As shown in FIG. 14, the engine controller 100 includes the first injection 81, the second injection 82, and the third injection 83 in the low rotation speed in the high load region of the low load region. The second injection group 9 includes the first injection 91, the second injection 92, and the third injection 93 in the same manner as the region, and the same as in the intermediate rotation region. On the other hand, unlike the low rotation region and the medium rotation region, the ratio of the first injection group 8 with respect to the total fuel injection amount in one cycle increases as the rotation speed of the engine 1 increases. Therefore, the ratio of the first injection group 8 is greater than the ratio of the second injection group 9. In the example of FIG. 14, the number of injections included in the first injection group 8 is increased by one while the number of fuel injections included in the second injection group 9 is decreased by three compared to the example of FIG. Yes.

  Further, the injection timing of the multistage injection is advanced as compared with the middle rotation region. As described above, this is to ensure a sufficient time corresponding to the ignition delay between the start of fuel injection and the predetermined crank angle.

  About the 1st injection group 8, the 1st injection 81, the 2nd injection 82, and the 3rd injection 83 are included like the low load field. About the 2nd injection group 9, the 1st injection 91, the 2nd injection 92, and the 3rd injection 93 are included like the middle load field. As a result, as shown in FIG. 15, the air-fuel mixture layer at the time of ignition has a region A1 of 25% from the nozzle port 41 toward the piston 15 with respect to the distance from the nozzle port 41 to the piston 15 in the central axis direction. The fuel concentration becomes maximum in the 50% area A2 when the area is divided into 50% area A2 and 25% area A3.

  On the other hand, in the high rotation region, the injection amount of the first injection group 8 is made larger than the injection amount of the second injection group 9. As a result, the fuel spray that reaches radially outward increases and the fuel spray that reaches radially inward decreases. As a result, as shown in FIG. 15, in the radial direction, the fuel concentration is lowest in the central portion and the fuel concentration is highest in the peripheral portion. This is a characteristic opposite to that in the middle rotation region.

  Even in the high rotation region, as in the middle rotation region, it is effective to increase the ignitability by making the fuel concentration in the gas mixture layer inhomogeneous. At this time, by providing a portion having a locally high fuel concentration in the peripheral portion, a range in which the fuel concentration is high is wide compared to a case in which a portion having a locally high fuel concentration is provided in the central portion. This is advantageous in improving the ignitability. In addition, the surrounding portion is ignited first and combustion is started, but compared with the case where the central portion is ignited first and combustion is started, the stirring of the air-fuel mixture in the entire gas mixture layer is promoted. Will come to be. This is advantageous in improving the combustion state and suppressing the generation of soot and unburned substances. It is also advantageous for shortening the combustion period.

  Further, in the high speed region, the ratio of the first injection group 8 increases as the rotational speed of the engine 1 increases. Therefore, in the radial direction, the local fuel concentration increases as the speed increases (that is, The fuel concentration in the surrounding area will increase.) Enlarging the fuel concentration difference in the air-fuel mixture layer in this manner is advantageous for further improving the ignitability on the high rotation side.

  The point that the cooling loss is reduced due to the small amount of fuel in the vicinity of the nozzle opening 41 and the piston 15 is the same as described above.

  In the middle load region, the engine controller 100 controls the injector 33 so that the fuel injection interval of the first injection group 8 gradually increases and the lift amount gradually decreases. At this time, the lift amount of the fuel injection included in the second injection group 9 is constant. The second injection group 9 is completed before the compression top dead center.

  FIG. 16 illustrates a fuel injection mode in a medium load, for example, in a low rotation region. As shown in the figure, the first injection group 8 includes four fuel injections. The lift amount of the first fuel injection 81 is the largest. The second fuel injection 82 is performed at a relatively small first interval a1 from the first fuel injection 81. The lift amount of the second fuel injection 82 is smaller than that of the first fuel injection 81. The third fuel injection 83 is performed with a second interval a2 larger than the first interval a1 from the second fuel injection 82. The lift amount of the third fuel injection 83 is smaller than that of the second fuel injection 82. The fourth fuel injection 84 is performed with a third interval a3 larger than the second interval a2 from the third fuel injection 83. The lift amount of the fourth fuel injection 84 is smaller than that of the third fuel injection 83.

  Thus, in the first injection group 8, the later the injection timing, the longer the injection interval and the smaller the negative pressure region. Therefore, the fuel spray by the fuel injection at the beginning of the first injection group 8 has a relatively large negative pressure region, so that the fuel spray is directed radially outward with respect to the central axis S, that is, radially outward of the combustion chamber 17. Spreading is suppressed. On the other hand, the fuel spray by the fuel injection toward the end of the first injection group 8 spreads radially outward of the combustion chamber 17 because the negative pressure region is relatively small (that is, the progress of the fuel spray with respect to the central axis S). The angle of inclination of the direction increases).

  Here, the greater the outward spread of the fuel spray in the radial direction, the shorter the scattering distance in the central axis direction. That is, the fuel spray by the fuel injection at the beginning of the first injection group 8 has a small spread in the radial direction, so that the scattering distance in the central axis direction becomes long. On the other hand, since the fuel spray by the fuel injection toward the end of the first injection group 8 has a large spread in the radial direction, the scattering distance in the central axis direction becomes short. That is, the arrival positions of the fuel sprays can be made different from each other in the central axis direction. As a result, fuel can be dispersed and injected in the central axis direction, and fuel spray can be dispersed in the central axis direction.

  In addition, in the first injection group 8, the lift amount becomes smaller as the injection interval becomes longer. When the lift amount is small, the particle size of the fuel spray is small and the momentum is small, so that the scattering distance in the traveling direction of the fuel spray is short. That is, the longer the injection interval, that is, the greater the spread in the radial direction, the shorter the scattering distance in the traveling direction. For example, if the scattering distance in the traveling direction of each fuel spray in the first injection group 8 is constant, the fuel spray can be dispersed in the central axis direction by adjusting the spread of the fuel spray in the radial direction. However, the scattering distance in the radial direction of the fuel spray is not uniform in the central axis direction. That is, the greater the spread of the fuel spray in the radial direction, the longer the scattering distance in the radial direction of the fuel spray. On the other hand, by shortening the scattering distance in the traveling direction of the fuel spray having a large spread in the radial direction, the difference in the scattering distance in the radial direction of each fuel spray can be reduced. That is, the spread in the radial direction as the entire air-fuel mixture layer can be made as uniform as possible in the central axis direction.

  Further, when the scattering distance in the traveling direction of the fuel spray is shortened, the scattering distance in the central axis direction of the fuel spray is also shortened. The fuel spray having a large spread in the radial direction is a fuel spray that is desired to be disposed in the vicinity of the nozzle opening 41 by suppressing the scattering distance in the central axis direction. Therefore, reducing the particle size of the fuel spray, which has a large spread in the radial direction, and shortening the scattering distance in the traveling direction can not only equalize the scattering distance in the radial direction of the fuel spray, but also reduce the fuel spray. It is also effective from the viewpoint of disposing near the nozzle. That is, by adjusting the particle size of the fuel spray, the fuel spray can be easily arranged at a desired position in the central axis direction.

  On the other hand, the fuel injections 90, 90,... Of the second injection group 9 have a relatively short injection interval and a large negative pressure region. Further, the fuel injections 90, 90,... Of the second injection group 9 have a relatively small momentum because the lift amount is relatively small and the fuel spray particle size is small. For this reason, the fuel spray by the second injection group 9 has a relatively short scattering distance and is likely to gather at the center in the radial direction due to the influence of negative pressure. More specifically, the injection interval of the fuel injections 90, 90,... Is shorter than the first interval a1 between the first fuel injection 81 and the second fuel injection 82 of the first injection group 8. Therefore, the fuel spray by the second injection group 9 is scattered more radially inward than the fuel spray by the first injection group 8.

  Further, the total injection amount by the first injection group 8 and the total injection amount by the second injection group 9 are substantially the same amount.

  As a result of such fuel injection by the first injection group 8 and the second injection group 9, at the time of ignition (predetermined timing after compression top dead center), the fuel spray is distributed in the central axis direction, The fuel concentration distribution is substantially uniform in the central axis direction.

  Specifically, the fuel spray from the first fuel injection 81 (hereinafter referred to as “first fuel spray”) is scattered relatively freely, but the fuel spray from the second fuel injection 82 (hereinafter referred to as “fuel spray”). (Referred to as “second fuel spray”) is attracted to a large negative pressure region, and the spread in the radial direction is suppressed. Therefore, the fuel spray is scattered almost along the central axis S to the vicinity of the piston 15.

  In the third fuel injection 83, the negative pressure region is smaller than that in the second fuel injection 82. Therefore, although fuel spray by the third fuel injection 83 (hereinafter referred to as “third fuel spray”) is attracted to the negative pressure region, the inclination angle with respect to the central axis S is larger than that of the second fuel spray. And spread in the radial direction. Further, since the third fuel spray has a smaller particle size than the second fuel spray, the scattering distance in the traveling direction is short. Combined with the large spread in the radial direction and the short scattering distance in the traveling direction, the scattering distance in the central axis direction of the third fuel spray becomes shorter than that in the second fuel spray. That is, the third fuel spray is scattered only to a position closer to the nozzle opening 41 than the second fuel spray in the central axis direction. Further, since the third fuel spray has a short scattering distance in the traveling direction, the radial scattering distance is also short. Therefore, although the third fuel spray has a larger spread in the radial direction than the second fuel spray, the scattering distance in the radial direction is substantially the same as the second fuel spray.

  In the case of the fourth fuel injection 84, the negative pressure region is smaller than in the case of the third fuel injection 83. Therefore, although the fuel spray by the fourth fuel injection 84 (hereinafter referred to as “fourth fuel spray”) is attracted to the negative pressure region, the inclination angle with respect to the central axis S is larger than that of the third fuel spray. And spread in the radial direction. Further, since the fourth fuel spray has a smaller particle size than the third fuel spray, the scattering distance in the traveling direction is short. Combined with the large spread in the radial direction and the short scattering distance in the traveling direction, the scattering distance in the central axis direction of the fourth fuel spray becomes shorter than that in the third fuel spray. That is, the fourth fuel spray scatters only to a position closer to the nozzle opening 41 than the third fuel spray in the central axis direction. In addition, since the fourth fuel spray has a short scattering distance in the traveling direction, the radial scattering distance is also short. Therefore, although the fourth fuel spray has a larger spread in the radial direction than the third fuel spray, the scattering distance in the radial direction is substantially the same as the third fuel spray.

  As a result of such fuel injection by the first injection group 8, for example, at the time of ignition, the second fuel spray is located in the vicinity of the piston 15 in the central axis direction, and the third fuel spray is the piston 15 and the nozzle opening. The fuel spray for the fourth time is located in the vicinity of the nozzle port 41. Thus, the fuel spray by the first injection group 8 is dispersed in the central axis direction. Moreover, the scattering distance in the radial direction of any of the second to fourth fuel sprays is about the same.

  Thereafter, the fuel spray from the second injection group 9 is injected closer to the center in the radial direction than the fuel spray from the first injection group 8.

  As a result, at the time of ignition, the fuel spray is in a state of being approximately evenly distributed in the central axis direction. That is, as shown in FIG. 11, the fuel concentration distribution in the central axis direction is substantially uniform.

  Further, since the total injection amount by the first injection group 8 and the total injection amount by the second injection group 9 are substantially the same amount, the fuel by the second injection group 9 distributed in the radial center of the combustion chamber 17. The ratio of the spray and the fuel spray by the first injection group 8 distributed around the fuel spray by the second injection group 9 is approximately the same, and the fuel concentration distribution in the radial direction of the combustion chamber 17 is also shown in FIG. As shown, they are almost even.

  When the amount of fuel is large as in the middle load region, as described above, when the combustion concentration is locally increased, soot may be generated or unburned substances may be generated. On the other hand, when the fuel concentration distribution is homogenized in each of the axial direction and the radial direction as described above, the generation of soot and unburned material is suppressed, and the exhaust emission performance is improved. .

  As described above, the engine 1 includes the piston 15 provided in the cylinder 11, the engine body in which the combustion chamber 17 is partitioned by the cylinder 11 and the piston 15, and fuel including at least gasoline in the cylinder 11. And an engine controller 100 for controlling the injection mode of the injector 33. The engine controller 100 causes the injector 33 to perform multi-stage injection to control the engine. The vessel 100 also has a homogeneous air-fuel mixture layer in which the fuel concentration in the central portion in the combustion chamber 17 and the fuel concentration in the peripheral portion surrounding the central portion are substantially equal depending on the operating state of the engine 1. (About the radial direction of FIG. 10 and about the axial direction and radial direction of FIG. 16) or the center in the combustion chamber 17 So as to form a heterogeneous mixture layer (in the axial direction of FIG. 10, and in the axial direction and radial direction of FIG. 13) having a different fuel concentration in the peripheral portion surrounding the central portion. The injection mode of the injector 33 is changed.

  As a result, an air-fuel mixture layer that is optimal in terms of improving fuel consumption and exhaust emission performance corresponding to the operating state of the engine 1 is formed in the combustion chamber 17.

  The multi-stage injection includes a first injection group 8 that has a short scattering distance in the traveling direction of the fuel spray injected through the nozzle port 41 and spreads in a radial direction perpendicular to the central axis S of the injector 33, and The second spray group 9 is a spray that has a long scattering distance in the traveling direction of the fuel spray and the spread in the radial direction is suppressed. By changing the ratio of the amount of fuel injected by the first injection group 8 and the amount of fuel injected by the second injection group 9, a mixture layer having a homogeneous fuel concentration in the radial direction, or An air-fuel mixture layer in which the fuel concentration is heterogeneous with respect to the radial direction is formed.

  As shown in FIG. 14, when the amount of fuel injected by the first injection group 8 is relatively large and the amount of fuel injected by the second injection group 9 is relatively small, the fuel concentration outside in the radial direction is relatively high. And an inhomogeneous air-fuel mixture layer having a relatively low radial inner fuel concentration is formed (see FIG. 15). Conversely, when the amount of fuel injected by the first injection group 8 is relatively small and the amount of fuel injected by the second injection group 9 is relatively large as shown in FIG. A heterogeneous mixture layer is formed that is relatively low and has a relatively high radial inner fuel concentration (see FIG. 13). 10 and 16, when the amount of fuel injected by the first injection group 8 and the amount of fuel injected by the second injection group 9 are the same amount or substantially the same amount, the fuel concentration outside in the radial direction In addition, the fuel concentration on the inner side in the radial direction becomes substantially the same, and a homogeneous gas mixture layer is formed (see FIGS. 11 and 17).

  The injector 33 includes a nozzle body 40 in which the nozzle port 41 is formed, and an outer opening valve 42 that opens and closes the nozzle port 41. The larger the lift amount of the outer opening valve 42, the higher the amount of the nozzle port 41. The first injection group 8 is configured so that the effective sectional area of the nozzle port 41 is predetermined, the fuel injection is performed a plurality of times at a predetermined injection interval, and the second injection group is configured. 9 performs a plurality of fuel injections in which the effective sectional area of the nozzle port 41 is smaller than that of the first injection group 8 and / or the fuel injection interval is narrower than that of the first injection group 8.

  By using the outer valve opening type injector 33 whose effective sectional area is changed according to the lift amount, the first injection group 8 and the second injection group 9 having different fuel injection modes can be provided.

  The engine controller 100 causes the injector 33 to inject fuel into the combustion chamber 17 during the period from the latter half of the compression stroke to the initial stage of the expansion stroke, so that the gas mixture layer and the gas around the gas mixture layer are injected into the combustion chamber 17. Forming a layer.

  When the air-fuel mixture that forms the air-fuel mixture layer burns, the surrounding gas layer functions as a heat insulating layer interposed between the air-fuel mixture layer and the section screen that defines the combustion chamber 17 to reduce cooling loss. To be advantageous.

  The engine 1 burns the air-fuel mixture layer by compression self-ignition, and the engine controller 100 performs the homogeneous mixing so that the ignition delay time of the air-fuel mixture changes according to the operating state of the engine 1. A gas layer or the heterogeneous mixed gas layer is formed.

  By forming a heterogeneous mixture layer in the combustion chamber 17, the ignition delay is increased at a location where the fuel concentration is relatively high in the mixture layer, and therefore the ignition delay time can be shortened. The ignition delay time is optimized by switching between the formation of a homogeneous mixture layer and the formation of a heterogeneous mixture layer according to the operating state of the engine 1.

  The engine controller 100 forms a heterogeneous mixture layer in which the difference between the fuel concentration in the central portion and the fuel concentration in the peripheral portion in the mixture layer increases as the rotational speed of the engine 1 increases.

  The higher the number of revolutions of the engine 1, the shorter the actual time from the start of fuel injection to the ignition, and a sufficient ignition delay time cannot be secured, leading to a decrease in ignitability and a decrease in combustion stability. Thus, by increasing the difference between the fuel concentration in the central part and the fuel concentration in the peripheral part in the air-fuel mixture layer, the fuel concentration in a relatively rich part increases, so the ignition delay time is shortened.

  The engine controller 100 makes the fuel concentration in the central portion of the air-fuel mixture layer richer than the fuel concentration in the peripheral portion when the engine 1 is in a high rotation state of a predetermined number of revolutions or more (FIG. 13). reference). Thereby, it becomes possible to reduce a cooling loss, improving ignitability.

  The engine controller 100 makes the fuel concentration in the peripheral portion of the air-fuel mixture layer richer than the fuel concentration in the central portion when the engine 1 is in a high rotation state of a predetermined number of revolutions or more (FIG. 15). reference). Thereby, while improving ignitability, generation | occurrence | production of soot and generation | occurrence | production of an unburned substance are suppressed, and the improvement of exhaust emission performance is aimed at.

  When the engine 1 is in the middle rotation region, the engine controller 100 makes the fuel concentration in the central portion of the air-fuel mixture layer richer than the fuel concentration in the peripheral portion, so that the engine 1 enters the high rotation region. In some cases, the fuel concentration in the peripheral portion of the air-fuel mixture layer is made richer than the fuel concentration in the central portion. This makes it possible to improve fuel efficiency by reducing cooling loss and to improve exhaust emission performance.

  The engine controller 100 determines whether the fuel concentration is uniform in the direction of the central axis S of the injector 33 (see FIG. 17) or the concentration of fuel in the direction of the central axis S depending on the operating state of the engine 1. Forms a heterogeneous mixture layer (FIGS. 11, 13, and 15).

  By forming a mixer layer having a homogeneous fuel concentration or an inhomogeneous mixture layer in the axial direction in accordance with the operating state of the engine 1, fuel efficiency and exhaust emission performance can be improved.

<< Other Embodiments >>
As described above, the embodiment has been described as an example of the technique disclosed in the present application. However, the technology in the present disclosure is not limited to this, and can also be applied to an embodiment in which changes, replacements, additions, omissions, and the like are appropriately performed. Moreover, it is also possible to combine each component demonstrated by the said embodiment and it can also be set as new embodiment. In addition, among the components described in the accompanying drawings and detailed description, not only the components essential for solving the problem, but also the components not essential for solving the problem in order to exemplify the above technique. May also be included. Therefore, it should not be immediately recognized that these non-essential components are essential as those non-essential components are described in the accompanying drawings and detailed description.

  About the said embodiment, it is good also as the following structures.

  For example, the first injection group 8 is not limited to the injection mode shown in FIGS. The number of fuel injections in the first injection group 8 is not limited to 2 to 4 times. It may be 1 time or 5 times or more.

  The first injection group 8 includes a first injection 81 and a second injection 82, and in some cases, a third injection 83 or a fourth injection 84. The first injection group 8 includes these fuel injections. May not be included. For example, the lift amount of the fuel injection of the first injection group 8 may be constant.

  Further, the first injection group 8 has a larger lift amount and a larger injection interval than the second injection group 9, but only one of the lift amount and the fuel interval may be larger.

  Further, the second injection group 9 is not limited to the injection mode shown in FIGS. For example, the third injection 93 may be further included so that the second injection group 9 includes the first injection 91 and the second injection 92 even in the low load and low rotation region.

  Furthermore, in the multistage injection, the second injection group 9 is executed after the first injection group 8, but the first injection group 8 may be executed after the second injection group 9 by reversing this.

  Further, the fuel injection of the first injection group 8 may not be equally spaced. Further, the injection interval of the second injection group 9 may not be equal.

  Furthermore, in the said embodiment, although the 1st injection group 8 and the 2nd injection group 9 are included in the multistage injection, only one may be sufficient. That is, changing the ratio between the first injection group 8 and the second injection group 9 includes setting the ratio of one of the injection groups to zero and setting the ratio of the other injection group to one.

  Further, in the above example, the engine speed range is divided into low speed, medium speed, and high speed, and the injector mode is different in each. You may divide into two of low rotation and high rotation. In this case, in the low rotation region, the injection mode shown in FIG. 10 may be adopted to obtain the fuel concentration distribution in the air-fuel mixture layer as shown in FIG. On the other hand, in the high speed region, the injection mode shown in FIG. 12 may be adopted, and the fuel concentration distribution in the air-fuel mixture layer as shown in FIG. 13 may be obtained, or the injection mode shown in FIG. A fuel concentration distribution in the air-fuel mixture layer as shown in FIG. 15 may be obtained. Further, the engine speed range is divided into a low speed range and a high speed range. In the low speed range, the injection mode shown in FIG. 10 is adopted, and the fuel concentration in the air-fuel mixture layer as shown in FIG. While obtaining the distribution, in the high speed region, the injection mode shown in FIG. 12 is adopted so as to obtain the fuel concentration distribution in the air-fuel mixture layer as shown in FIG. May adopt the injection mode shown in FIG. 14 to obtain the fuel concentration distribution in the air-fuel mixture layer as shown in FIG.

  Moreover, the structure of an injector is not restricted to the said embodiment. As long as the effective cross-sectional area of the nozzle can be changed, any injector can be employed. For example, a VCO (Valve Covered Orifice) nozzle type injector 233 as shown in FIG. 18 may be used. FIG. 18 is a cross-sectional view showing the internal configuration of the injector 233.

  Specifically, the injector 233 includes a nozzle body 240 in which a nozzle port 241 that injects fuel into the cylinder 11 is formed, and a needle valve 242 that opens and closes the nozzle port 241. The nozzle body 240 is a tubular member extending along a predetermined central axis S, and the fuel circulates therein. The tip of the nozzle body 240 is formed in a conical shape. A mortar-shaped sheet portion 243 is formed on the inner peripheral surface of the tip portion of the nozzle body 240. A plurality of nozzle openings 241 are formed through the tip of the nozzle body 240. One end of the nozzle port 241 opens into the sheet portion 243. A plurality of nozzle ports 241 are arranged around the central axis S at equal intervals. The tip end portion of the needle valve 242 is formed in a conical shape and is seated on the seat portion 243 of the nozzle body 240. The nozzle port 241 is closed when the needle valve 242 is seated on the seat portion 243. The nozzle port 241 is an example of an injection port, and the needle valve 242 is an example of a valve body.

  The needle valve 242 is driven by a piezo element similarly to the injector 33. When the needle valve 242 is driven and lifted from the seat portion 243, a gap through which fuel can flow is formed between the seat portion 243 and the needle valve 242, and the fuel flowing through this gap passes through the nozzle port 241. Injected outside the nozzle body 240.

  At this time, cavitation occurs on the inner peripheral surface of the nozzle port 241 when fuel flows. The degree of cavitation (for example, the size of a region where cavitation occurs) varies according to the gap between the needle valve 242 and the seat portion 243, that is, the lift amount of the needle valve 242. Specifically, when the lift amount of the needle valve 242 is small and the gap between the needle valve 242 and the seat portion 243 is small, the region where cavitation occurs also becomes large. On the other hand, when the lift amount of the needle valve 242 is large and the gap between the needle valve 242 and the seat portion 243 is large, the region where cavitation occurs is also small. When the area where cavitation occurs is large, the effective sectional area of the nozzle port 241 is small. When the area where cavitation occurs is small, the effective cross-sectional area of the nozzle port 241 increases. That is, the smaller the lift amount of the needle valve 242, the smaller the effective sectional area of the nozzle port 241. The larger the lift amount of the needle valve 242, the larger the effective sectional area of the nozzle port 241.

  Furthermore, in the above embodiment, it is possible to change the shape of the air-fuel mixture layer in the combustion chamber 17 by changing the lift amount of the injector 33 and the fuel injection interval, but in addition to this, the fuel pressure To increase the range of change in the shape of the air-fuel mixture layer accompanying the change in the lift amount of the injector 33 and the fuel injection interval. That is, when the lift amount of the injector 33 is increased by increasing the fuel pressure, the kinetic energy of the fuel spray becomes larger, and when the fuel injection interval is reduced, the degree of negative pressure increases and the negative pressure region becomes larger. Expand more. As a result, the change width of the shape of the air-fuel mixture layer is further expanded.

  In the above example, the heat insulating structure of the combustion chamber 17 and the intake port 18 is adopted, and a heat insulating layer is formed by a gas layer in the cylinder (inside the combustion chamber 17). The invention can also be applied to an engine that does not employ the heat insulating structure of the combustion chamber 17 and the intake port 18.

  In addition, the fuel injection technique disclosed herein forms an air-fuel mixture layer and a surrounding gas layer in the combustion chamber 17, but is not limited thereto. Even when the gas layer does not exist and the air-fuel mixture layer contacts the wall surface of the combustion chamber 17, the fuel injection technique can be employed. For example, when the fuel injection amount increases with respect to the volume of the combustion chamber 17, the air-fuel mixture layer may come into contact with the wall surface of the combustion chamber 17. Even in such a case, the heat generation near the center of the combustion chamber 17 is increased, and the heat generation near the wall surface is suppressed, thereby suppressing the heat radiation from the wall surface of the combustion chamber 17 and cooling. Loss can be reduced.

  In the above example, the fuel injection timing is set to the period from the latter half of the compression stroke to the initial stage of the expansion stroke. This is to suppress the spread of fuel spray by injecting fuel into a high-pressure atmosphere in which the pressure in the cylinder 11 is equal to or higher than a predetermined pressure. For example, in an engine with a turbocharger, when the supercharging pressure is high, the pressure in the cylinder can be equal to or higher than a predetermined pressure even in the first half of the compression stroke or during the intake stroke. The fuel injection timing may be set according to the pressure state in the cylinder. In this case, the fuel injection timing may be set during the first half of the compression stroke or during the intake stroke.

1 Engine 11 Cylinder
15 Piston 17 Combustion chamber 33 Injector 40 Nozzle body 41 Nozzle port (jet port)
42 Outside valve (valve)
8 First injection group 9 Second injection group 100 Engine controller (control unit)
233 Injector 241 Nozzle port
242 Needle valve
S Center axis X Cylinder center axis

Claims (9)

An engine body having a piston provided in the cylinder, and a combustion chamber defined by the cylinder and the piston;
An injector for injecting fuel including at least gasoline into the combustion chamber through a nozzle;
A control unit for controlling the injection mode of the injector,
The control unit causes the injector to perform multi-stage injection,
The control unit may also be a homogeneous air-fuel mixture layer in which the fuel concentration in the central portion in the combustion chamber and the fuel concentration in the peripheral portion surrounding the central portion are substantially equal, depending on the operating state of the engine body, or Changing the injection mode of the injector so as to form a heterogeneous mixture layer in which the fuel concentration in the central portion of the combustion chamber differs from the fuel concentration in the peripheral portion surrounding the central portion ;
The multi-stage injection includes a first injection group in which a spray distance in the traveling direction of the fuel spray injected through the nozzle is short and spread in a radial direction perpendicular to the central axis of the injector, and the fuel spray Including a second injection group that has a long scattering distance in the traveling direction and is a spray in which spread in the radial direction is suppressed,
In the multi-stage injection, the control unit changes the ratio of the amount of fuel injected by the first injection group and the amount of fuel injected by the second injection group, so that the fuel concentration is changed with respect to the radial direction. A control device for a direct injection engine that forms a homogeneous air-fuel mixture layer or an air-fuel mixture layer whose fuel concentration is heterogeneous with respect to the radial direction . The direct injection engine control device according to claim 1 ,
The injector has a nozzle body in which the nozzle hole is formed and a valve body that opens and closes the nozzle hole, and is configured such that an effective sectional area of the nozzle hole increases as a lift amount of the valve body increases.
The first injection group has a predetermined effective cross-sectional area of the nozzle and performs fuel injection a plurality of times at a predetermined injection interval.
The second injection group is a direct injection that performs multiple fuel injections in which the effective sectional area of the nozzle is smaller than that of the first injection group and / or the fuel injection interval is narrower than that of the first injection group. Engine control device. In the control device for a direct injection engine according to claim 1 or 2 ,
When the pressure in the cylinder is equal to or higher than a predetermined pressure, the control unit causes the injector to inject fuel so that the mixture layer and a gas layer around the mixture layer are formed in the combustion chamber. Control device for forming direct injection engine. In the control apparatus of the direct-injection engine of any one of Claims 1-3 ,
The engine body combusts the air-fuel mixture layer by compression self-ignition,
The control unit controls the direct injection engine that forms a homogeneous mixture layer or a heterogeneous mixture layer so that the ignition delay time of the mixture changes according to the operating state of the engine body. . The control device for a direct injection engine according to claim 4 ,
The control unit is a direct injection engine that forms a heterogeneous mixture layer in which the difference between the fuel concentration in the central portion and the fuel concentration in the peripheral portion of the mixture layer increases as the rotational speed of the engine body increases. Control device. The direct-injection engine control device according to claim 5 ,
The control unit controls the direct injection engine that makes the fuel concentration in the central portion of the air-fuel mixture layer richer than the fuel concentration in the peripheral portion when the engine body is in a high rotation state at a predetermined rotation speed or higher. apparatus. The direct-injection engine control device according to claim 5 ,
The control unit controls the direct injection engine that makes the fuel concentration in the peripheral portion of the air-fuel mixture layer richer than the fuel concentration in the central portion when the engine body is in a high rotation state at a predetermined rotation speed or higher. apparatus. The direct-injection engine control device according to claim 5 ,
The control unit
When the engine body is in a state equal to or higher than the first rotational speed, the fuel concentration in the central portion of the air-fuel mixture layer is made richer than the fuel concentration in the peripheral portion,
When the engine body is in a state equal to or higher than the second rotational speed (provided that the first rotational speed is smaller than the second rotational speed), the fuel concentration in the peripheral portion of the mixture layer is richer than the fuel concentration in the central portion. Control device for direct injection engine. In the control device for a direct injection engine according to any one of claims 1 to 8 ,
The control unit forms an air-fuel mixture layer having a homogeneous fuel concentration in the direction of the central axis of the injector or an air-fuel mixture layer having an inhomogeneous fuel concentration in the direction of the central axis, depending on the operating state of the engine body. Control device for direct injection engine.

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