JP5834650B2 - Spark ignition direct injection engine - Google Patents

Description

  The present invention belongs to a technical field related to a spark ignition direct injection engine provided with an outer valve-open injector.

  For example, in Patent Document 1, in order to increase the theoretical thermal efficiency of a spark-ignition gasoline engine, a cavity recessed in the lower surface of the cylinder head and a protrusion projecting from the piston crown surface divide the combustion chamber into the central combustion chamber and the main combustion chamber. The combustion chamber as a whole is set to a compression ratio as high as about 16, and the air-fuel mixture is relatively rich in the central combustion chamber, and the air-fuel mixture is relatively lean in the main combustion chamber. Thus, an engine having a lean air-fuel mixture is described for the entire combustion chamber.

  Further, for example, Patent Document 2 discloses a technique in which a surface that forms a combustion chamber of an engine is formed of a heat insulating material including a large number of bubbles from the viewpoint of reducing cooling loss and improving thermal efficiency. . The compression ratio of the engine of this Patent Document 2 is 16.

Japanese Patent Laid-Open No. 9-217627 JP 2009-243355 A

  By the way, in the Otto cycle, which is the theoretical cycle of a spark ignition engine, the theoretical thermal efficiency increases as the compression ratio of the engine increases and as the specific heat ratio of the gas increases. For this reason, the combination of a high compression ratio and lean air-fuel mixture as described in Patent Document 1 is advantageous to some extent for improving thermal efficiency (illustration thermal efficiency). However, in this case, the illustrated thermal efficiency is maximized at a compression ratio of about 15, and even if the compression ratio is increased further, the illustrated thermal efficiency does not increase (inversely, the higher the compression ratio is, the lower the illustrated thermal efficiency is). . This is because, since the air-fuel mixture is lean, a relatively large amount of air is introduced into the cylinder. On the other hand, a large amount of air in the cylinder is greatly compressed as the compression ratio increases, and the combustion pressure and temperature are reduced. This is because it becomes significantly higher. That is, the amount of heat released through the cylinder wall and the like is increased by a high combustion pressure and combustion temperature, and the cooling loss is greatly increased. As a result, the illustrated thermal efficiency is lowered.

  In this regard, as described in Patent Document 2, if the cylinder wall surface is made of a heat insulating material to insulate the combustion chamber, the cooling loss can be reduced.

  However, as in Patent Document 2, there is a limit to the reduction of the cooling loss due to the heat insulation of the combustion chamber using the heat insulating material, and when trying to increase the geometric compression ratio to about 30 for example, the cooling loss It is difficult to drastically reduce the cost, and even if a significant reduction in cooling loss can be realized, the cost is greatly increased.

  Therefore, a gas layer containing fresh air (which may contain fresh air and burned gas) is formed at the outer peripheral portion in the cylinder of the engine, and an air-fuel mixture layer is formed at the central portion. If the gas is burned, the gas layer between the gas mixture layer and the cylinder wall surface prevents the flame of the gas mixture layer from coming into contact with the cylinder wall surface, and the gas layer serves as a heat insulating layer. The release of heat from can be suppressed. The gas layer and the gas mixture layer have such a size (length) that the fuel is injected into the cylinder by the injector during the compression stroke, and the penetration of the fuel spray does not reach the outer periphery of the cylinder. If it suppresses to, it can be formed.

  As the injector, an outer valve-opening type injector that has a basically small penetration and can freely change the penetration is preferable. In this outer valve type injector, the penetration of fuel spray injected from the nozzle port into the cylinder increases as the lift amount of the outer valve that opens and closes the nozzle port from the closed state increases. .

  Here, when the operating state of the engine (in particular, the cylinder pressure at the time of fuel injection) changes, the fuel spray penetration may change, and the fuel spray may reach a size that reaches the outer periphery of the cylinder. For this reason, it is necessary to adjust the fuel spray penetration to a predetermined size (length) so that the fuel spray does not reach the outer periphery of the cylinder according to the operating state of the engine. Change of the fuel pressure by adjusting the fuel pressure supplied to the injector from the fuel pump (high pressure fuel pump) driven by the camshaft of the engine or by changing the lift amount of the injector open valve. It is conceivable to do so.

  However, when the fuel pressure is changed by the pressure regulating valve, when the engine load is in the low load region, the ratio of the mechanical resistance by the fuel pump to the engine load increases, and the fuel consumption may deteriorate. On the other hand, when the lift amount is changed, when the engine load is in the high load region, the lift amount is basically large, the injection amount is large, and the particle size of the fuel spray is large. In some cases, soot is not burned and carbon is generated or carbonized, resulting in a worse emission.

  The present invention has been made in view of such a point, and an object of the present invention is to operate the engine in order to form a gas layer in the outer peripheral portion of the cylinder and an air-fuel mixture layer in the central portion. Accordingly, when adjusting the penetration of the fuel spray injected into the cylinder by the outer valve-opening injector to a predetermined magnitude, it is intended to suppress deterioration of fuel consumption and emission as much as possible.

In order to achieve the above object, according to the present invention, an open valve that opens and closes a nozzle port for injecting fuel into a cylinder, and the nozzle port is opened by lifting the open valve from a state in which the nozzle port is closed. The valve opening drive means for injecting fuel into the cylinder from the nozzle port, and the larger the lift amount of the outer valve from the closed state of the nozzle port, the larger the lift amount from the nozzle port to the cylinder. A fuel pump that is driven through a rotating member of the engine and supplies fuel to the spark ignition direct injection engine having an injector configured to increase the penetration of fuel spray injected into the inside And controlling the operation of the fuel pressure adjusting means for adjusting the fuel pressure supplied from the fuel pump to the injector, the valve opening drive means and the fuel pressure adjusting means, In the compression stroke, fuel is injected into the cylinder from the nozzle port so that a gas layer containing fresh air is formed at the outer periphery of the cylinder and an air-fuel mixture layer is formed at the center, and the injected fuel spray Injection control means for adjusting the penetration of the fuel to a predetermined magnitude, and the injection control means sets the fuel pressure to a constant value when the engine load is in a low load region where the engine load is equal to or less than a predetermined value. At the same time, the fuel spray penetration is adjusted to the predetermined magnitude by changing the lift amount by the outer valve drive means according to the operating state of the engine, while the engine load is more than the predetermined value. in case also in higher high load region, as well as setting the lift amount to a constant value, depending on operating conditions of the engine, by the fuel pressure adjusting means By changing the charge pressure, and the penetration of the fuel spray a configuration that is configured to adjust to the predetermined size.

  With the above configuration, the gas layer located around the gas mixture layer prevents the flame of the gas mixture layer from coming into contact with the cylinder wall surface, and the gas layer serves as a heat insulating layer to release heat from the cylinder wall surface. Can be suppressed. Thereby, even if a geometric compression ratio becomes high, a cooling loss can be reduced significantly.

  When the engine load is in the low load region, the lift amount is basically small, the injection amount is small, and the particle size of the fuel spray is small, whereby the entire injected fuel burns normally. As a result, by changing the lift amount of the outer valve according to the operating state of the engine, the penetration of the fuel spray does not reach a predetermined size (the fuel spray does not reach the outer periphery (gas layer) in the cylinder). By adjusting the size, the emission does not deteriorate as in the case where the lift amount is large. In addition, when the engine load is in the low load region, the fuel pressure is set to a constant value so that the ratio of the mechanical resistance of the fuel pump to the engine load becomes as small as possible to suppress the deterioration of fuel consumption. Can do.

  On the other hand, when the engine load is in the high load region, even if the fuel pressure is changed, the ratio of the mechanical resistance by the fuel pump to the engine load is basically small, the sensitivity of the mechanical resistance is small, and the fuel efficiency is reduced. There is almost no influence. As a result, fuel consumption can be prevented from deteriorating by adjusting the fuel spray penetration to the predetermined magnitude by changing the fuel pressure according to the operating state of the engine. Further, when the engine load is in a high load region, the deterioration of the emission can be suppressed by setting the lift amount of the outer valve to a constant value so that the entire injected fuel burns normally. .

  In the spark ignition direct injection engine, the geometric compression ratio of the engine is 18 or more and 40 or less, and the injection control means is configured to inject fuel into the cylinder from the nozzle opening in the latter half of the compression stroke. It is preferable.

  That is, when the geometric compression ratio is 18 or more and 40 or less, there is a limit to the reduction of cooling loss due to the heat insulation of the combustion chamber, but in the present invention, heat insulation by the gas layer in the cylinder (combustion chamber). By forming the layer, the cooling loss can be greatly reduced. Further, the fuel injection in the latter half of the compression stroke shortens the time until ignition, and the injected fuel is less likely to mix with the gas layer on the outer peripheral portion, so that the gas layer can be secured during combustion.

  Alternatively, when the geometric compression ratio of the engine is 18 or more and 40 or less, and the injection control means is such that when the engine load is in the high load region, the start of fuel combustion is after compression top dead center. The fuel may be injected from the nozzle opening into the cylinder near the compression top dead center.

  As a result, the crank angle point (usually 4 ° to 15 ° CA after compression top dead center) when the pressure increase rate, which is the pressure change in the cylinder with respect to the crank angle change during motoring of the engine, becomes a negative maximum value. In the vicinity thereof, the fuel can be combusted. As a result, even if the engine load is high, the vibration noise (so-called NVH) level can be reduced.

  In the spark ignition direct injection engine, when the engine load is in the low load region, the excess air ratio λ in the entire cylinder is 2 or more, or the weight ratio G / F of gas to fuel in the cylinder is 30 or more. It is preferably set.

  As a result, in the low load region, RawNOx can be reduced while achieving thermal insulation by the heat insulation layer and improving the illustrated thermal efficiency.

As described above, according to the spark ignition direct injection engine of the present invention, when the engine load is in the low load region where the engine load is equal to or less than the predetermined value, the fuel pressure is set to a constant value and the engine operating state is set. Accordingly, the fuel spray penetration is adjusted to a predetermined size by changing the lift amount of the outer valve by the outer valve drive means, while the engine load is in a high load region higher than the predetermined value. In the above, the lift amount is set to a constant value, and the fuel pressure penetration is adjusted to the predetermined magnitude by changing the fuel pressure by the fuel pressure adjusting means according to the operating state of the engine. By adjusting the fuel spray penetration according to the operating state of the engine while suppressing deterioration of fuel consumption and emission Rukoto becomes possible.

1 is a schematic view showing a spark ignition direct injection engine according to an embodiment of the present invention. It is sectional drawing which shows the internal structure of an injector. It is a figure which shows an example of the control map which switches lift amount control and fuel pressure control. It is a graph which shows the relationship between a lift amount and penetration. It is a graph which shows the relationship between a fuel pressure and penetration.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 schematically shows a spark ignition direct injection engine 1 (hereinafter simply referred to as an engine 1) according to an embodiment of the present invention. In the present embodiment, the engine 1 includes various actuators attached to 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 (cylinders) are formed inside the cylinder block 12 (in FIG. 1). Only one 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.

  A piston 15 is slidably inserted into each cylinder 11, and the piston 15 defines a combustion chamber 17 together with the cylinder 11 and the cylinder head 13. In this embodiment, the combustion chamber 17 is a so-called pent roof type, and the ceiling surface (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 15a is formed at the center of the crown surface. The shape of the ceiling surface and the crown surface of the piston 1 may be any shape as long as a high geometric compression ratio described later is possible. For example, the ceiling surface and the crown surface of the piston 1 ( Both of the portions excluding the cavity 15a may be configured by a surface perpendicular to the central axis of the cylinder 11, and the ceiling surface forms a triangular roof as described above, while the crown surface (cavity) of the piston 1 The portion excluding 15a) may be constituted by a plane 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, and each is open to an inclined surface on the intake side on the lower surface of the cylinder head 13 (the ceiling surface of the combustion chamber 17). By doing so, it communicates with the combustion chamber 17. Similarly, two exhaust ports 19 are formed in the cylinder head 13 for each cylinder 11, and each of the exhaust ports 19 opens to an inclined surface on the exhaust side of the lower surface of the cylinder head 13 (the ceiling surface of the combustion chamber 17). Communicate. 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 (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 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. Further, at least the intake valve drive mechanism includes a hydraulic or mechanical phase variable mechanism (Variable Valve Timing: VVT) 23 that can continuously change the phase of the intake camshaft within a predetermined angle range. ing. In addition, you may make it provide the lift variable mechanism (CVVL (Continuous Variable ValveLift)) which can change a valve lift amount continuously with VVT23.

  A spark plug 31 is disposed on the cylinder head 13. The ignition plug 31 is attached and fixed to the cylinder head 13 by a known structure such as a screw. In the present embodiment, 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 (electrode) 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. The spark plug 31 generates a spark by the ignition system 32. The ignition system 32 receives a control signal from the engine controller 100 and energizes the spark plug 31 to generate a spark at a desired ignition timing. As an example, the ignition system 32 may include a plasma generation circuit, and the ignition plug may be a plasma ignition type plug. The use of a plasma ignition type plug with high ignition energy is advantageous in improving the ignition stability.

  An injector 33 that directly injects fuel into the cylinder (inside the combustion chamber 17) is disposed on the central axis of the cylinder 11 in the cylinder head 13. 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 is an outer valve-opening type injector having an outer valve 42 that opens and closes a nozzle port 41 that injects fuel into the cylinder. The nozzle port 41 is formed in a tapered shape whose diameter increases toward the distal end side at the distal end portion of the fuel pipe 43 extending along the central axis of the cylinder 11. The end of the fuel pipe 43 on the base end side is connected to a case 45 in which a piezo element 44 serving as an external valve opening drive means 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 fuel pipe 43 to the piezo element 44. A portion of the valve body 42a on the side of the connecting portion 42b has substantially the same shape as the nozzle port 41, and when the portion is in contact (sitting) with the nozzle port 41, the nozzle port 41 is closed. . At this time, the tip side portion of the valve main body 42 a is in a state of protruding to the outside of the fuel pipe 43.

  The piezo element 44 lifts the outer open valve 42 from the state in which the nozzle opening 41 is closed by pressing the outer open valve 42 toward the combustion chamber 17 in the central axis direction of the cylinder 11 by deformation due to application of voltage. Then, the nozzle port 41 is opened. At this time, fuel is injected from the nozzle port 41 into the cylinder in a cone shape (specifically, a hollow cone shape) centered on the central axis of the cylinder 11. The taper angle of the cone is 90 ° to 100 ° in this embodiment (the taper angle of the inner hollow portion 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. The larger the lift amount, the larger the opening of the nozzle port 41, the greater the penetration of fuel spray injected from the nozzle port 41 into the cylinder, and the longer the amount of fuel injected per unit time. The particle size of the fuel spray increases and increases.

  The fuel supply system 34 includes an electric circuit 35 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 35 at a predetermined timing, thereby operating the piezo element 44 and the outer valve 42 via the electric circuit 35. Thus, a desired amount of fuel is injected into the cylinder. When the injection signal is not output (when the voltage of the injection signal is 0), the nozzle port 41 is closed by the outer opening valve 42. 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 and the lift amount during the fuel injection.

  The fuel supply system is provided with a high-pressure fuel pump 37 and a common rail (not shown). The high-pressure fuel pump 37 pumps fuel supplied from a fuel tank via a low-pressure fuel pump (not shown) to the common rail. The common rail stores the pumped fuel at a predetermined fuel pressure. The fuel stored in the common rail is injected from the nozzle port 41 by the operation of the injector 33 (the open valve 42 is lifted). The high-pressure fuel pump 37 is a plunger-type pump, and is driven by an engine rotation member (for example, a camshaft) to supply fuel to the injector 33 via the common rail.

  A predetermined fuel pressure stored in the common rail (that is, a fuel pressure supplied from the high-pressure fuel pump 37 to the injector 33) can be adjusted by a pressure regulating valve 36 provided in the high-pressure fuel pump 37. The pressure regulating valve 36 is constituted by an electromagnetic valve, and the operation is controlled by the engine controller 100. That is, when the engine controller 100 outputs a valve control signal, the pressure regulating valve 36 has an opening corresponding to the voltage of the valve control signal via an electric circuit (not shown) different from the electric circuit 35. Operates on. The fuel pressure is determined according to the opening of the pressure regulating valve 36. Therefore, the pressure regulating valve 36 constitutes a fuel pressure adjusting means for adjusting the fuel pressure supplied from the high pressure fuel pump 37 to the injector 33.

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

  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 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, a fuel injection pulse, an ignition signal, a valve phase angle signal, and the like. Then, the engine controller 100 outputs these signals to the throttle valve 20 (throttle actuator that moves the throttle valve 20), the fuel supply system 34 (the electric circuit 35 and the pressure regulating valve 36), the ignition system 32, the VVT 23, and the like.

  The geometric compression ratio ε of the engine 1 is 18 or more and 40 or less. The geometric compression ratio ε is particularly preferably 25 or more and 35 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 the compression ratio = expansion ratio. In addition, you may employ | adopt the structure (for example, Atkinson cycle and a mirror cycle) used as compression ratio <= expansion 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 (ceiling surface) of the cylinder head 13, and a valve head surface of each of the intake valve 21 and the exhaust valve 22. , Are partitioned. And in order to reduce a cooling loss, the combustion chamber 17 is thermally insulated by providing the heat insulation layers 61, 62, 63, 64, and 65 on each of these surfaces. 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 present embodiment, in addition to the heat insulation structure of the combustion chamber 17 and the intake port 18 described above, a heat insulation layer is formed by a gas layer in the cylinder (inside the combustion chamber 17), thereby greatly reducing the cooling loss. ing.

  Specifically, the engine controller 100 performs compression so that a gas layer containing fresh air is formed at the outer peripheral portion of the cylinder (in the combustion chamber 17) of the engine 1 and an air-fuel mixture layer is formed at the center. In the stroke, in order to inject fuel into the cylinder from the nozzle port 41 of the injector 11, an injection signal is output to the electric circuit 35 of the fuel supply system 34 and a valve control signal is output to the pressure regulating valve 36. That is, fuel is injected into the cylinder by the injector 33 in the compression stroke, and the penetration of the fuel spray is suppressed to such a size (length) that the fuel spray does not reach the outer periphery (gas layer) in the cylinder. Thus, stratification is realized in which an air-fuel mixture layer is formed at the center of the cylinder and a gas layer containing fresh air is formed around the air-fuel mixture layer. This gas layer may be only fresh air, and may contain burned gas (EGR gas) in addition to fresh air. It should be noted that there is no problem even if a small amount of fuel is mixed in the gas layer, and the fuel layer may be leaner than the gas mixture layer so that the gas layer can serve as a heat insulating layer.

  The fuel injection timing by the injector 33 is preferably in the latter part of the compression stroke (particularly, the latter half when the compression stroke is divided into about three equal parts from the previous period, the middle period, and the latter period). This shortens the time until ignition, makes it difficult for the fuel in the air-fuel mixture to mix with the gas layer on the outer periphery thereof, and ensures the gas layer during combustion.

  In particular, when the engine load is in a high load region higher than a predetermined value, fuel is injected into the cylinder from the nozzle port 41 near the compression top dead center so that the start of fuel combustion is after the compression top dead center. It is preferable to do so. As a result, the crank angle point (usually 4 ° to 15 ° CA after compression top dead center) at which the pressure increase rate, which is the pressure change in the cylinder with respect to the crank angle change during motoring of the engine 1, becomes a negative maximum value or more. In the vicinity thereof, the fuel can be burned, and as a result, the vibration noise (NVH) level can be reduced even when the engine load is high.

  When ignition is performed by the spark plug 31 in a state where the gas layer and the air-fuel mixture layer are formed as described above, the gas mixture between the air-fuel mixture layer and the wall surface of the cylinder 11 causes the flame of the air-fuel mixture layer to be in the cylinder 11. The gas layer becomes a heat insulating layer without coming into contact with the wall surface of the cylinder 11, and the release of heat from the wall surface of the cylinder 11 can be suppressed. As a result, the cooling loss can be greatly reduced.

  It should be noted that if the cooling loss is simply reduced, the reduced cooling loss is converted into exhaust loss and does not contribute much to the improvement in the illustrated thermal efficiency. The energy of the combustion gas corresponding to the reduced cooling loss is efficiently converted into mechanical work. That is, it can be said that the illustrated thermal efficiency is greatly improved in the engine 1 by adopting a configuration that reduces both the cooling loss and the exhaust loss.

  Here, when the engine operating state (in particular, the cylinder pressure during fuel injection) changes, the fuel spray penetration changes, and the fuel spray may reach a size that reaches the outer periphery of the cylinder. For this reason, it is necessary to adjust the fuel spray penetration to a predetermined size (length) so that the fuel spray does not reach the outer periphery of the cylinder in accordance with the operating state of the engine.

  The adjustment of the penetration is performed by the engine controller 100 by controlling the operation of the injector 33 (outer opening valve 42) and the pressure regulating valve 36, and by the lift amount of the outer opening valve 42 and the fuel pressure by the pressure regulating valve 36. Thus, the engine controller 100 constitutes the injection control means of the present invention.

  As shown in FIG. 3, when the engine load is in a low load region (lift amount control region in FIG. 3) where the engine load is equal to or less than a predetermined value, the engine controller 100 corresponds to the piezo element according to the operating state of the engine 1. The fuel spray penetration is adjusted to the predetermined size by changing the lift amount of the outer opening valve 42 by 44 (lift amount control is performed), while the engine load is higher than the predetermined value. When in the fuel pressure control region of FIG. 3, the fuel spray penetration is controlled by changing the fuel pressure by the pressure regulating valve 36 (performing fuel pressure control) according to the operating state of the engine 1. Adjust to size. In FIG. 3, the predetermined value for separating the two regions increases as the engine speed increases, but is not limited to this. For example, the predetermined value is a constant value regardless of the engine speed. There may be.

  When the engine load is in the low load region, the fuel pressure is set to a constant value so that the ratio of the mechanical resistance by the high-pressure fuel pump 37 to the engine load is as small as possible. When the engine load is in the high load region, the lift amount of the outer opening valve 42 is set to a constant value so that the entire injected fuel burns normally.

  That is, when the engine load is in the low load region, the lift amount is basically small, the injection amount is small, and the particle size of the fuel spray is small, whereby the entire injected fuel burns normally. As a result, by changing the lift amount of the outer valve according to the operating state of the engine 1, the fuel spray penetration is adjusted to the predetermined size, so that the emission is as if the lift amount is large. There will be no deterioration. Here, when the engine load is in the low load region and the adjustment of the penetration is made by changing the fuel pressure, the ratio of the mechanical resistance by the high-pressure fuel pump 37 to the engine load increases and the fuel consumption deteriorates. Occurs. However, in this embodiment, the fuel pressure is set to a constant value such that the ratio of the mechanical resistance by the high-pressure fuel pump 37 to the engine load is as small as possible, so that deterioration of fuel consumption can be suppressed.

  On the other hand, when the engine load is in the high load region, even if the fuel pressure is changed, the ratio of the mechanical resistance by the high-pressure fuel pump 37 to the engine load is basically small, and the sensitivity of the mechanical resistance is small. There is almost no impact on fuel consumption. As a result, by changing the fuel pressure according to the operating state of the engine 1 and adjusting the fuel spray penetration to the predetermined magnitude, deterioration of fuel consumption can be suppressed. Here, when the engine load is in the above-described high load region, if an attempt is made to adjust the penetration by changing the lift amount of the outer valve, the lift amount is basically large, the injection amount is large, and the particle size of the fuel spray is large. Since it becomes large, a part of the injected fuel does not burn, but soot is generated or carbonized, and the emission may be deteriorated. However, in the present embodiment, the lift amount of the outer opening valve 42 is set to a constant value so that the entire injected fuel burns normally, so that deterioration of emissions can be suppressed.

  In the low load region (lift amount control region), the excess air ratio λ in the entire cylinder (in the combustion chamber 17) is 2 or more, or the weight ratio G / of the gas (fresh air, EGR gas) in the cylinder to the fuel. F is set to 30 or more. Thereby, in the low load region, RawNOx can be reduced while achieving thermal insulation by the heat insulation layer and improving the illustrated thermal efficiency. From the viewpoint of reducing RawNOx, the excess air ratio λ ≧ 2.5 is more preferable. In addition, since the illustrated thermal efficiency reaches a peak when the excess air ratio λ = 8, the range of the excess air ratio λ is preferably 2 ≦ λ ≦ 8 (more preferably 2.5 ≦ λ ≦ 8). Note that the lean air-fuel mixture sets the throttle valve 20 on the open side, which can contribute to the improvement of the indicated thermal efficiency by reducing the gas exchange loss (pumping loss).

  On the other hand, in the high load region (fuel pressure control region), the air excess ratio λ = 1 in the entire cylinder is set with priority on torque (in the air-fuel mixture layer, the air excess ratio λ <1). In this embodiment, the region where the excess air ratio λ is λ ≧ 2 and the region where λ = 1 coincide with the lift amount control region and the fuel pressure control region, respectively, but λ ≧ 2 or more. The predetermined value that separates the region that becomes and the region that satisfies λ = 1 may be different from the predetermined value that separates the lift amount control region and the fuel pressure control region.

  FIG. 4 shows fuel spraying according to the lift amount of the outer valve 42 when the cylinder pressure is 9 MPa (corresponding to the pressure at the compression top dead center when the geometric compression ratio ε is 30). The change of penetration (the reach of fuel spray from the nozzle port 41) is shown. The fuel pressure is set to a constant value of 10 MPa. As the cylinder pressure decreases, the penetration increases at any lift. The fuel spray penetration is determined in advance according to the lift amount at the in-cylinder pressure, and the penetration is L (fuel spray is at the outer periphery of the cylinder in the cylinder pressure estimated from the engine operating state in the low load region). Change the lift amount so that it does not exceed (the size to reach).

  FIG. 5 shows changes in the fuel spray penetration according to the fuel pressure when the cylinder pressure is 9 MPa. The lift amount is set to a constant value. As in FIG. 4, as the cylinder pressure decreases, the penetration increases at any fuel pressure. The fuel spray penetration corresponding to the fuel pressure at the cylinder pressure is obtained in advance, and the fuel pressure is changed so that the penetration does not exceed L at the cylinder pressure estimated from the engine operating state in the high load region. To do.

  Therefore, in the present embodiment, when the engine load is in a low load region where the engine load is equal to or less than a predetermined value, the lift amount of the outer valve 42 is changed by the piezo element 44 according to the operating state of the engine 1. While adjusting the fuel spray penetration to a predetermined magnitude, the fuel pressure is changed by the pressure regulating valve 36 in accordance with the operating state of the engine 1 when the engine load is in a high load region higher than the predetermined value. As a result, the fuel spray penetration is adjusted to the above predetermined size, so that the fuel spray penetration can be adjusted according to the operating state of the engine while suppressing deterioration of fuel consumption and emission. become.

  The present invention is not limited to the embodiment described above, and can be substituted without departing from the spirit of the claims.

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

  In the above-described embodiment, the injector 33 is a piezo-type outer valve-opening injector that drives the outer valve 42 by the piezo element 44. However, the outer valve that injects fuel from the nozzle port 41 into the cylinder. The driving means is not limited to the piezo element 44.

  The above-described embodiments are merely examples, and the scope of the present invention should not be interpreted in a limited manner. The scope of the present invention is defined by the scope of the claims, and all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  INDUSTRIAL APPLICABILITY The present invention is useful for a spark ignition direct injection engine having an outer valve-opening injector, and particularly useful for reducing a cooling loss while increasing a geometric compression ratio.

1 Spark ignition direct injection engine 11 Cylinder
33 Injector 36 Pressure regulating valve (fuel pressure adjusting means)
37 High-pressure fuel pump 41 Nozzle port 42 Open valve 44 Piezo element (external valve drive means)
100 Engine controller (injection control means)

Claims (4)

An external opening valve that opens and closes a nozzle port that injects fuel into the cylinder, and the external opening valve is lifted from a state in which the nozzle port is closed to open the nozzle port, thereby injecting fuel from the nozzle port into the cylinder. The outer valve opening drive means, and the greater the lift amount of the outer valve from the state in which the nozzle port is closed, the greater the penetration of fuel spray injected from the nozzle port into the cylinder. A spark ignition direct injection engine having a configured injector,
A fuel pump that is driven through the rotating member of the engine and supplies fuel to the injector;
Fuel pressure adjusting means for adjusting the fuel pressure supplied from the fuel pump to the injector;
By controlling the operation of the outer valve drive means and the fuel pressure adjusting means, a gas layer containing fresh air is formed at the outer peripheral portion in the cylinder of the engine, and an air-fuel mixture layer is formed at the center. Injection control means for injecting fuel into the cylinder from the nozzle opening in the compression stroke and adjusting the penetration of the injected fuel spray to a predetermined magnitude;
When the engine load is in a low load region where the engine load is a predetermined value or less, the injection control means sets the fuel pressure to a constant value, and according to the operating state of the engine, the outer valve opening drive means By changing the lift amount, the fuel spray penetration is adjusted to the predetermined magnitude, while the lift amount is set to a constant value when the engine load is in a high load region higher than the predetermined value. and sets, in accordance with the operating condition of the engine by changing the fuel pressure by the fuel pressure adjusting means, characterized in that the penetration of the fuel spray is configured to adjust to the predetermined size Spark ignition direct injection engine. The spark ignition direct injection engine according to claim 1,
The geometric compression ratio of the engine is 18 or more and 40 or less,
The spark ignition type direct injection engine, wherein the injection control means is configured to inject fuel into the cylinder from the nozzle opening in the latter half of the compression stroke. The spark ignition direct injection engine according to claim 1,
The geometric compression ratio of the engine is 18 or more and 40 or less,
The injection control means injects fuel into the cylinder from the nozzle opening in the vicinity of the compression top dead center so that the start of fuel combustion is after the compression top dead center when the engine load is in the high load region. A spark ignition direct injection engine characterized by being configured as described above. In the spark ignition direct injection engine according to any one of claims 1 to 3,
When the engine load is in the low load region, the excess air ratio λ in the entire cylinder is set to 2 or more, or the weight ratio G / F of gas to fuel in the cylinder is set to 30 or more. Ignition direct injection engine.

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