JP2015148178A - Control device for compression self-ignition engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve a fuel consumption of a compression self-ignition engine in particular in a relatively high load area.SOLUTION: A control device (PCM100) causes an engine to perform a compression self-ignition combustion with an excess air factor λ being 2.5 or more when an operation state of an engine main body (engine 10) is kept in a lean area (normal operation areas A1, A2) lower than a prescribed changing-over load corresponding to a medium load, and in turn when the operation state of the engine main body (engine 10) is kept in an area λ=1 (retarded operation areas B1, B2) more than a changing-over load, it causes an engine to perform a compression self-ignition combustion with the excess air factor λ being 1. The control device also sets opening of a throttle valve 33 to a full admission in a full-load area and at the same time does not provide any reflux flow of exhaust gas under a prescribed low load area in the lean area, and in turn in the area of λ=1, adjusts a reflux volume of cooled exhaust gas to cause the excess air ratio λ to be set to 1.

Description

  The technology disclosed herein relates to a control device for a compression self-ignition engine.

  Patent Document 1 describes a high compression ratio engine in which the geometric compression ratio ε is set to 18 ≦ ε ≦ 40. This engine is designed to improve exhaust emission performance and improve thermal efficiency by performing compression self-ignition combustion with a lean excess air ratio λ of 2.5 or more in the low-load and medium-load operation regions. .

JP 2013-53607 A

  According to the study by the inventors of the present application, when the excess air ratio λ of the air-fuel mixture is set to 2.5 or more, although it is possible to suppress the generation of RawNOx by reducing the combustion temperature, it increases the engine load. Accordingly, when the fuel injection amount increases, it becomes difficult to maintain the excess air ratio λ at 2.5 or more. Therefore, as described in Patent Document 1, the excess air ratio λ is set to 1 in the region on the high load side in order to suppress the emission of NOx using a three-way catalyst. However, in the region on the high load side where the excess air ratio λ is 1, there is a demand for improving the fuel efficiency while maintaining the exhaust emission performance as in the region on the low load side.

  The technology disclosed herein has been made in view of such a point, and an object of the technology is to improve fuel consumption particularly in a high-load region in a compression self-ignition engine.

  The technology disclosed herein relates to a control device for a compression self-ignition engine, and the control device includes an engine body having a cylinder having a geometric compression ratio set to 20 or more, A cold EGR means configured to recirculate after cooling a part of the exhaust gas, and a controller configured to operate the engine body by subjecting the air-fuel mixture in the cylinder to compression self-ignition combustion; .

  The controller sets the excess air ratio λ of the air-fuel mixture in the cylinder to 2.5 or more when the operating state of the engine body is in a lean region lower than a predetermined switching load corresponding to a medium load. When the operation state of the engine body is in the λ = 1 region that is equal to or higher than the switching load, the excess air ratio λ is set to 1, and the controller performs self-combustion combustion. In the full load range of the engine main body operating range, the throttle valve opening provided on the intake passage communicating with the cylinder is set to fully open, and in a predetermined low load side region in the lean region, the exhaust gas On the other hand, in the λ = 1 region, the excess air ratio λ is set to 1 by refluxing the exhaust gas cooled through the cold EGR means.

  By setting the geometric compression ratio to a high compression ratio of 20 or more, it is advantageous for improving thermal efficiency, and the temperature and pressure (compression end temperature and pressure) in the cylinder at the compression top dead center are increased. . This improves the stability of the compression self-ignition combustion by improving the ignitability by compression self-ignition when the load on the engine body is relatively low. The upper limit of the geometric compression ratio may be 40, for example.

  In the above configuration, when the engine is in a lean region lower than a predetermined switching load corresponding to a medium load, the compressed air is burned by increasing the excess air ratio λ of the air-fuel mixture in the cylinder to 2.5 or more. By setting the excess air ratio λ to 2.5 or more, the combustion temperature is reduced, and the generation of RawNOx can be suppressed. The upper limit of the excess air ratio λ may be 8, for example. This is because when the excess air ratio λ exceeds 8, the illustrated thermal efficiency decreases.

  In the lean region, the opening degree of the throttle valve provided on the intake passage is set to fully open. This reduces pump loss. Therefore, in the lean region, the exhaust emission performance is improved and the fuel efficiency is improved by the compression self-ignition combustion with the high compression ratio and the excess air ratio λ of 2.5 or more. In addition, in a predetermined low load side region in the lean region, it is possible to ensure the stability of compression self-ignition combustion when the load on the engine body is low by not performing exhaust gas recirculation.

  In a region where the load is higher than the lean region, it becomes difficult to increase the excess air ratio λ to 2.5 or more as the load of the engine body increases (that is, a large amount of fuel increases as the fuel injection amount increases). Because air must be introduced into the cylinder), compression ignition combustion is performed with an excess air ratio λ of 1.

  In order to set the excess air ratio λ to 1, it is necessary to adjust the amount of fresh air introduced into the cylinder according to the amount of fuel, but the amount of fresh air introduced is adjusted by narrowing the throttle valve opening. As a result, the pump loss increases and the fuel consumption deteriorates. In the above-described configuration, even in the λ = 1 region, the opening of the throttle valve is maintained fully open as in the lean region. By doing so, an increase in pump loss is avoided, and deterioration in fuel consumption is avoided. Here, “setting the opening of the throttle valve to fully open” includes substantially opening the opening of the throttle valve in addition to fully opening the opening of the throttle valve. That is, to throttle the throttle valve so as to obtain an intake negative pressure that allows the exhaust gas to recirculate through the cold EGR means corresponds to substantially opening the throttle valve.

  Thus, in the above configuration, in the λ = 1 region, the amount of exhaust gas introduced into the cylinder through the cold EGR means is adjusted while the throttle valve opening is set to be fully open. That is, when the recirculation amount of the exhaust gas is increased, the fresh air introduced into the cylinder decreases, and when the recirculation amount of the exhaust gas is decreased, the fresh air amount introduced into the cylinder increases. Thus, through adjustment of the exhaust gas recirculation amount, the amount of fresh air introduced into the cylinder, more precisely, the amount of oxygen in the cylinder is adjusted, and the excess air ratio λ is set to 1. As a result, even in the λ = 1 region, which is a relatively high load side region, the pump loss is reduced, which is advantageous for improving fuel efficiency, and the three-way catalyst is used by setting the excess air ratio λ to 1. This makes it possible to improve the exhaust emission performance. Further, introducing the cooled exhaust gas into the cylinder by the cold EGR means is advantageous for reducing the combustion temperature and suppressing RawNOx when the high compression ratio engine is operated on the high load side.

  The control device for the compression self-ignition engine further includes a fuel injection valve that injects fuel into the cylinder, and the controller injects the entire amount of fuel injection before the compression top dead center in the lean region. In the λ = 1 region, before the compression top dead center, by injecting an amount of fuel that causes an oxidation reaction without reaching a thermal flame reaction, the temperature in the cylinder after the compression top dead center is reached. Pre-stage injection that provides a temperature maintenance period in which fluctuations fall within a predetermined temperature range, and fuel is injected after the pre-stage injection, and compression self-ignition is performed after the compression top dead center and within the temperature maintenance period. The fuel injection valve executes the main injection to be combusted, and the controller also changes the EGR rate in accordance with the load of the engine body in the λ = 1 region, and in the lean region. , Adjacent to the λ = 1 region In the high load side region of the constant, so as to approach the EGR rate is set in the switching load of the lambda = 1 area, to increase the EGR rate according to the load increases the engine body may be.

  Here, the EGR rate can be defined by the volume ratio of the exhaust gas to the total gas in the cylinder (exhaust gas amount / total gas amount in the cylinder).

  According to the above-described configuration, in the lean region, the fuel injection valve executes the entire amount of fuel injection before the compression top dead center. The fuel injection may be performed at the end when the compression stroke is divided into an initial period, a middle period, and an end period. Further, the fuel injected during the compression stroke may be injected in a lump or may be divided and injected. The lean air-fuel mixture formed in the cylinder by the fuel injection before the compression top dead center is compressed and ignited near the compression top dead center and burns.

  On the other hand, in the λ = 1 region, the load on the engine body is relatively high and the air-fuel ratio is also relatively rich. Therefore, as in the lean region, compression self-ignition combustion was performed near the compression top dead center. Then, the rate of pressure increase during combustion tends to be high. In particular, since the geometric compression ratio of the engine body is set to 20 or higher, the combustion noise level tends to increase as the pressure increase rate increases.

  Therefore, in the λ = 1 region, the pressure increase rate during combustion is lowered by delaying the timing of compression self-ignition to an appropriate timing after compression top dead center. Specifically, when the combustion period of compression self-ignition combustion becomes the maximum negative value of the pressure increase rate during motoring (that is, when combustion is not accompanied when the crankshaft of the engine is rotated by a motor) Or until the combustion center of the compression autoignition combustion overlaps with a period during which the negative compression increase rate is large (that is, 10 to 20 ° CA after the compression top dead center). .

  However, since the in-cylinder temperature gradually decreases as the expansion stroke proceeds, there is a risk of misfire even if the compression self-ignition combustion is delayed. In this regard, in the above-described configuration, the pre-stage injection is performed before the compression top dead center. The fuel injected into the cylinder by this pre-stage injection is a relatively small amount and undergoes an oxidation reaction without reaching a hot flame reaction. In the present specification, the fact that the fuel undergoes an oxidation reaction without reaching a hot flame reaction may be referred to as a “partial oxidation reaction”. Thereby, the temperature in the cylinder at the compression top dead center is adjusted. That is, the compression end temperature increases as the injection amount of the upstream injection increases. As a result of the increase in the compression end temperature, it is possible to provide a period during which the temperature in the cylinder falls within a predetermined temperature range after the compression top dead center.

  Thus, the fuel injected by the main injection after the pre-stage injection is subjected to compression self-ignition combustion within the temperature maintenance period. As a result, the retarded compression self-ignition combustion can be stably performed, and in the λ = 1 region, the combustion noise can be reduced while performing the compression self-ignition combustion.

  Here, the pre-stage injection not only suppresses a decrease in the temperature in the cylinder during the expansion stroke period, but also prevents the temperature in the cylinder from becoming too high. If the in-cylinder temperature becomes too high, there is a risk that soot will be generated by locally igniting the fuel before it is properly mixed when the main injection is performed. That is, the occurrence of soot can be reduced by keeping the variation in the in-cylinder temperature within a predetermined temperature range.

  In the λ = 1 region, the cooled exhaust gas corresponding to the load on the engine body is recirculated into the cylinder through the cold EGR means. This contributes to the temperature adjustment in the cylinder and is advantageous for stabilizing the retarded compression self-ignition combustion, and the slowdown of the compression self-ignition combustion reduces the combustion noise level within the range where the combustion noise level is not increased. It makes it possible to advance the timing as much as possible. This is advantageous in improving fuel consumption because the combustion period of compression self-ignition combustion is advanced as much as possible.

  Here, when the lean region and the λ = 1 region are compared, the excess air ratio λ is set to 1 in the λ = 1 region and the period of the compression self-ignition combustion is delayed, so that the thermal efficiency is higher than that of the lean region. Can decline. In the above-described configuration, in the high load side region adjacent to the λ = 1 region in the lean region, the cooled exhaust gas is recirculated, so that the temperature state in the cylinder can be lowered accordingly. This is advantageous in extending the lean region to the high load side as much as possible, and in turn is advantageous in improving fuel consumption.

  Further, in the high load side region in the lean region, as the engine load increases, the EGR rate is increased so that the EGR rate is the same at the switching load that is the boundary between the lean region and the λ = 1 region. Yes. This is because the EGR rate is continuous even when the engine load continuously changes and shifts from the lean region to the λ = 1 region, or when the λ = 1 region shifts to the lean region. Will change. This is effective for smooth transition between regions to avoid the occurrence of torque shock or the like and the deterioration of exhaust emission performance.

  The controller decreases the EGR rate as the load of the engine body increases in the λ = 1 region, and the controller also performs the pre-injection in a predetermined high load side region in the λ = 1 region. Between the main injection and the main injection, an amount of fuel that undergoes an oxidation reaction without causing a hot flame reaction is injected, and a second pre-injection that adjusts the length of the temperature maintenance period is performed, and the main injection This timing may be retarded with respect to the timing of main injection in a region where the load is lower than the predetermined high load side region.

  In the λ = 1 region, by reducing the EGR rate as the load on the engine body increases, the amount of fresh air introduced into the cylinder increases as the load on the engine body increases. Therefore, the amount of fresh air necessary for setting the excess air ratio λ to 1 is secured against the amount of fuel that increases as the load on the engine body increases.

  On the other hand, as the engine load increases, the recirculation amount of the cooled exhaust gas decreases and the fuel amount increases. Therefore, in a predetermined high load side region within the λ = 1 region, combustion noise is reduced. In order to reduce this, it is necessary to retard the period of the compression self-ignition combustion more than the low load side region in the λ = 1 region.

  In the above configuration, in the predetermined high load side region in the λ = 1 region, the second upstream injection is performed between the upstream injection and the main injection. The fuel injected by the second pre-stage injection undergoes an oxidation reaction without reaching a flame reaction, generates a small amount of heat, and suppresses a decrease in the in-cylinder temperature accompanying the progress of the expansion stroke, while the in-cylinder temperature is reduced. Prevent it from becoming too high. When the fuel undergoes a hot flame reaction, a large amount of heat is generated, and the in-cylinder temperature may become too high. On the other hand, if the fuel undergoes an oxidation reaction without reaching a hot flame reaction, only a small amount of heat is generated, and an excessive rise in the in-cylinder temperature can be suppressed (that is, a partial oxidation reaction).

  By performing the second pre-injection in this way, it is possible to further increase the period during which the temperature variation in the cylinder after the compression top dead center falls within a predetermined temperature range (that is, the temperature maintenance period). As a result, even if the period of compression self-ignition combustion is further retarded, stabilization is achieved, and an increase in combustion noise is avoided in a predetermined high load side region in the λ = 1 region. In order to further retard the period of compression self-ignition combustion, the timing of main injection in a predetermined high load side region is retarded with respect to the timing of main injection in a region with a lower load than this high load side region. .

  Further, in the λ = 1 region including the high load side region, as described above, the cooled exhaust gas is recirculated into the cylinder, so that the combustion is slowed down, which is advantageous in reducing the combustion noise. Therefore, the high load side area that requires the second pre-injection can be reduced to the high load side by the amount of recirculation of the cooled exhaust gas (the area can be reduced). In the high load side region, by performing the second pre-stage injection, the main injection time is delayed, so the fuel consumption can be reduced. However, reducing the high load side region reduces the region disadvantageous for fuel consumption. Therefore, it becomes advantageous for improvement of fuel consumption.

  In the load region between the predetermined high load side region and the predetermined low load side region in the lean region, the controller sets an EGR rate to an intermediate value of an EGR rate that changes in the λ = 1 region. It may be set as follows.

  In the λ = 1 region, as described above, in order to set the excess air ratio λ to 1, the recirculation amount of the exhaust gas is adjusted in accordance with the load of the engine body. That is, the EGR rate changes according to the load on the engine body. On the other hand, the responsiveness of changing the EGR rate through the cold EGR means is low. Therefore, immediately after the operating state of the engine changes and shifts from the lean region to the λ = 1 region, there is a possibility of deviating from the EGR rate commensurate with the load of the engine body. When the deviation of the EGR rate is large, the exhaust emission performance is deteriorated and the time required until the deviation of the EGR rate is eliminated becomes long.

  In this regard, in the above configuration, the predetermined high load side region in the lean region (as described above, the region set to the EGR rate that approaches the EGR rate set in the switching load) and the predetermined low load In the load region with the side region (as described above, the region where exhaust gas recirculation is not performed from the viewpoint of combustion stability (the EGR rate is zero)), the intermediate value of the EGR rate that changes in the λ = 1 region is Set the EGR rate. By doing so, even if a shift in the EGR rate occurs when shifting from the lean region to the λ = 1 region, the maximum shift amount is regulated to a predetermined value or less. That is, the shift in the EGR rate can be made as small as possible, and the time required for the shift in the EGR rate to disappear after the shift to the λ = 1 region is shortened, so that the deterioration of the exhaust emission performance is suppressed. The

  As described above, according to the control device for the compression self-ignition engine, in the λ = 1 region on the high load side, the air is obtained by recirculating the cooled exhaust gas while maintaining the opening degree of the throttle valve fully open. By performing compression self-ignition combustion with an excess ratio λ of 1, it is possible to reduce pump loss and improve fuel efficiency, and it is possible to improve exhaust emission performance using a three-way catalyst. .

It is the schematic which shows the structure of a compression self-ignition engine. It is a block diagram which shows the structure which concerns on control of a compression self-ignition engine. 3 is a map related to engine operation control. The figure which shows the change of the fuel injection timing and the injection period with respect to the engine load, the figure which illustrates the temperature change in the cylinder (upper figure), and the figure which shows the change of the EGR rate with respect to the engine load (right figure) is there. It is a flowchart which concerns on engine control.

  Hereinafter, an embodiment of a control device for a compression self-ignition engine will be described with reference to the drawings. The following description is exemplary.

(Overall configuration of engine system)
1 and 2 show a configuration of an engine system 1 according to the embodiment. The engine system 1 is a system mounted on a vehicle. The engine system 1 includes an engine main body (hereinafter simply referred to as “engine”) 10, various actuators associated with the engine 10, various sensors, and a PCM (Powertrain Control Module) that controls the actuators based on signals from the sensors. , Controller) 100.

  Although not shown, the output shaft of the engine 10 is connected to drive wheels via a transmission. The vehicle is propelled by the output of the engine 10 being transmitted to the drive wheels. The engine 10 includes a cylinder block 12 and a cylinder head 13 mounted thereon, and a plurality of cylinders 11 are formed inside the cylinder block 12 (only one is shown in FIG. 1). . 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 in each cylinder 11, and the piston 15 divides a combustion chamber together with the cylinder 11 and the cylinder head 13. In this embodiment, the combustion chamber 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 15 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 15 ( Both of the portions excluding the cavity 15a may be formed of 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 15 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 opens to the lower surface of the cylinder head 13 (the inclined surface on the intake side on the ceiling surface of the combustion chamber). This communicates with the combustion chamber. Similarly, two exhaust ports 19 are formed in the cylinder head 13 for each cylinder 11, and each communicates with the combustion chamber by opening on the lower surface of the cylinder head 13 (the inclined surface on the exhaust side of the ceiling surface of the combustion chamber). ing.

  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, 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 exchange gas 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 this example, the intake valve driving mechanism and the exhaust valve driving mechanism are a hydraulic or electric variable phase mechanism (Variable Valve Timing: VVT) capable of continuously changing the phase of the intake camshaft within a predetermined angle range. 23 at least (see FIG. 2). In addition, you may make it provide the lift variable mechanism which can change valve lift amount with VVT23. The lift variable mechanism may be a CVVL (Continuous Variable Valve Lift) capable of continuously changing the lift amount.

  The intake port 18 of each cylinder 11 communicates with the intake passage 30 via an intake manifold not explicitly shown in FIG. Similarly, the exhaust port 19 of each cylinder 11 communicates with the exhaust passage 40 via an exhaust manifold that is not clearly shown.

  In the intake passage 30, an air cleaner 31, a compressor 81 of the turbocharger 8, an intercooler 32 that cools the air compressed by the compressor 81, and a throttle valve that adjusts the amount of intake air to each cylinder 11. 33 are arranged in order from upstream to downstream.

  The exhaust passage 40 includes a turbine 82 of the turbocharger 8 and a direct catalyst 41 and an underfoot catalyst 42 as an exhaust purification device that purifies harmful components in the exhaust gas from the upstream side to the downstream side. Are arranged in order. Each of the direct catalyst 41 and the underfoot catalyst 42 includes a cylindrical case and a three-way catalyst disposed in a flow path in the case.

  The downstream portion of the compressor 81 in the intake passage 30 (more precisely, the downstream portion of the throttle valve 33) and the upstream portion of the turbine 82 in the exhaust passage 40 return a part of the exhaust gas to the intake passage 30. Are connected by a high pressure EGR passage 510. The high-pressure EGR passage 510 is provided with a high-pressure EGR valve 511 for adjusting the recirculation amount of the exhaust gas to the intake passage 30 and a water-cooled EGR cooler 512 for cooling the exhaust gas. A high pressure EGR system 51 is configured including the high pressure EGR passage 510, the high pressure EGR valve 511, and the EGR cooler 512.

  Further, the upstream portion of the compressor 81 in the intake passage 30 and the downstream portion of the turbine 82 in the exhaust passage 40 (more precisely, between the direct catalyst 41 and an exhaust shutter valve 43 described later) The gas is connected by a low pressure EGR passage 520 for returning a part of the gas to the intake passage 30. The low-pressure EGR passage 520 is provided with a low-pressure EGR valve 521 for adjusting the amount of exhaust gas recirculated to the intake passage 30 and an air-cooled EGR cooler 522 for cooling the exhaust gas.

  The exhaust shutter valve 43 is disposed downstream of the connection portion of the low pressure EGR passage 520 in the exhaust passage 40. The exhaust shutter valve 43 is a flow rate adjustment valve whose opening degree can be adjusted. By setting the exhaust shutter valve 43 to the closed side, the flow rate passing therethrough is reduced, and the exhaust passage 40 of the low-pressure EGR passage 520 is reduced. The side pressure can be relatively increased with respect to the pressure on the intake passage 30 side. A low pressure EGR system 52 is configured including the low pressure EGR passage 520, the low pressure EGR valve 521, the EGR cooler 522, and the exhaust shutter valve 43.

  The turbocharger 8 includes a compressor 81 disposed in the intake passage 30 and a turbine 82 disposed in the exhaust passage 40, and the compressor 81 and the turbine 82 are connected to each other. The turbine 82 is rotated by the exhaust gas flow, thereby operating the compressor 81. In this example, the turbocharger is a VGT (Variable Geometry Turbo) having a variable nozzle 83. However, the configuration of the turbocharger is not limited to VGT.

  In the engine 10, an injector 34 that directly injects fuel into the cylinder (combustion chamber) is disposed on the central axis of the cylinder 11 in the cylinder head 13. The injector 34 is attached and fixed to the cylinder head 13 with a known structure such as using a bracket. The tip of the injector 34 faces the center of the ceiling of the combustion chamber.

  In this example, the injector 34 is an externally opened injector. That is, although detailed illustration of the configuration is omitted, the nozzle opening is opened by opening and closing the nozzle opening for injecting fuel into the cylinder 11, and the opening valve lifts to the cylinder 11 side. To do. At this time, fuel is injected from the nozzle opening into the cylinder 11 in a cone shape (specifically, a hollow cone shape) centered on the central axis of the cylinder 11. The greater the lift amount of the outer valve, the greater the opening of the nozzle opening, the greater the penetration of fuel spray injected into the cylinder 11 from the nozzle opening, and the fuel injected per unit time. The amount increases and the particle size of the fuel spray increases. However, the injector 34 is not limited to the external valve opening type, and may be a multi-hole injector.

  The fuel supply system 35 includes an electric circuit for driving the outer valve and a fuel supply system for supplying fuel to the injector 34. The PCM 100 outputs an injection signal having a voltage corresponding to the lift amount to the electric circuit at a predetermined timing, thereby operating an outer valve through the electric circuit to supply a desired amount of fuel to the cylinder 11. Inject into. When the injection signal is not output (when the voltage of the injection signal is 0), the nozzle port is closed by the outer valve. In this way, the PCM 100 controls the operation of the outer valve to control the fuel injection from the nozzle opening of the injector 34 and the lift amount at the time of the fuel injection.

  The fuel supply system is provided with a high-pressure fuel pump (not shown) and a common rail. The high-pressure fuel pump pumps 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. When the injector 34 is operated, the fuel stored in the common rail is injected from the nozzle port.

  Here, the fuel of the engine 10 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.

  An ozone generator 36 is disposed in the combustion chamber of the engine 10. The ozone generator 36 is fixed to the cylinder head 13 by a known structure such as a screw. The tip of the ozone generator 36 faces the ceiling of the combustion chamber. The tip of the ozone generator 36 is located in the vicinity of the nozzle opening of the injector 34. The ozone generator 36 has two electrodes that are insulated from each other and arranged to face each other. The ozone generator 36 is driven by an ozone generation system 37. The ozone generation system 37 has an ozone generation circuit. The ozone generation system 37 receives a control signal from the PCM 100 and outputs a high-frequency high-frequency voltage to the ozone generator 36. The ozone generator 36 generates ozone between two electrodes when a high frequency voltage is applied. By changing the magnitude or frequency of the high-frequency voltage applied to the ozone generator 36, the ozone concentration can be adjusted. The arrangement and configuration of the ozone generator 36 are not limited to this.

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

  Connected to the PCM 100 are a vehicle speed sensor 71 that detects the vehicle speed, an accelerator opening sensor 72 that detects the accelerator opening, and an engine rotation speed sensor 73 that detects the rotation speed of the engine 10.

  An air flow sensor 74 that detects the flow rate (and temperature) of fresh air flowing through the intake passage 30 is disposed on the intake passage 30, and the air flow sensor 74 outputs the detected flow rate and outside air temperature to the PCM 100.

  The surge tank 38 is provided with an intake pressure sensor (supercharging pressure sensor) 75 for detecting the pressure of air supplied to the combustion chamber, and the exhaust passage 40 is provided with an exhaust pressure for detecting the pressure upstream of the turbine. A sensor 76 is provided. Each sensor 75 and 76 is connected to the PCM 100 and outputs the detected value to the PCM 100.

  Then, the PCM 100 determines the operating state of the engine 10 based on the signals from the above-described sensors and the like, and sets the control parameter of the engine 10 corresponding thereto. The PCM 100 outputs signals corresponding to the control parameters to the throttle valve 33, the fuel supply system 35, the VVT 23, the exhaust shutter valve 43, the high pressure EGR valve 511, the low pressure EGR valve 521, the ozone generation system 37, and the like. .

(Engine structure)
Next, the configuration of the engine body will be described in more detail. The geometric compression ratio ε of the engine 10 is 20 or more and 40 or less. The geometric compression ratio ε is particularly preferably 25 or more and 35 or less. Since the engine 10 has a configuration in which the compression ratio = expansion ratio, the engine 10 has a relatively high expansion ratio as well as a high compression ratio. In addition, you may employ | adopt the structure (for example, Atkinson cycle and a mirror cycle) used as compression ratio <= expansion ratio. When the intake valve is closed late, the effective compression ratio of the engine 10 is set to 12 or more. Preferably, the effective compression ratio of the engine 10 is set to 18 or more.

  The combustion chamber is defined by the wall surface of the cylinder 11, the crown surface of the piston 15, the lower surface (ceiling surface) of the cylinder head 13, and the valve head surfaces of the intake valve 21 and the exhaust valve 22. And in order to reduce a cooling loss, the combustion chamber is heat-insulated by providing a heat insulation layer in each of these surfaces. A heat insulation layer may be provided in all of these section screens, and may be provided in a part of these section screens. Further, a heat insulating layer may be provided on the port wall surface in the vicinity of the opening on the ceiling surface side of the combustion chamber in the intake port 18 and the exhaust port 19, although it is not a wall surface that directly partitions the combustion chamber.

  The heat insulation structure of the combustion chamber will be described in more detail. As described above, the heat insulating structure of the combustion chamber is configured by the heat insulating layers provided on the respective screens that divide the combustion chamber. These heat insulating layers release the heat of the combustion gas in the combustion chamber through the screen. In order to suppress this, the thermal conductivity is set lower than that of the metal base material constituting the combustion chamber. Here, for the heat insulating layer provided on the wall surface of the cylinder 11, the cylinder block 12 is the base material, and for the heat insulating layer provided on the crown surface of the piston 15, the piston 15 is the base material, and the ceiling surface of the cylinder head 13. The cylinder head 13 is a base material for the heat insulating layer provided on the intake valve 21 and the exhaust valve 22 is the base material for the heat insulating layers provided on the valve head surfaces of the intake valve 21 and the exhaust valve 22, respectively. . 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 insulation layer preferably has a volumetric specific heat smaller than that of the base material in order to reduce cooling loss. In other words, the gas temperature in the combustion chamber fluctuates depending on the progress of the combustion cycle, but in a conventional engine that does not have a heat insulation structure of the combustion chamber, the cooling water flows through the water jacket formed in the cylinder head or cylinder block. The temperature of the surface defining the combustion chamber 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 cooling loss, it is desirable to reduce the difference between the gas temperature and the temperature of the section screen. However, if the temperature of the section screen of the combustion chamber is maintained approximately constant by cooling water, the fluctuation of the gas temperature Along with this, it is inevitable that the temperature difference increases. Therefore, it is preferable to reduce the heat capacity of the heat insulating layer so that the temperature of the section screen of the combustion chamber changes following the fluctuation of the gas temperature in the combustion chamber.

The heat insulation layer 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 heat conductivity and volume specific heat of a heat insulation layer 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 fresh air introduced into the cylinder 11 (initial gas temperature) is lowered, so that the gas temperature during combustion is lowered, which is advantageous in reducing the temperature difference between the gas temperature and the combustion chamber section screen. become. 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 and the intake port 18, a heat insulation layer is formed by a gas layer in the cylinder (combustion chamber), so that the cooling loss is greatly reduced.

  Specifically, in the PCM 100, the injector 34 after the compression stroke is formed so that a gas layer containing fresh air is formed in the outer peripheral portion of the cylinder (combustion chamber) of the engine 10 and an air-fuel mixture layer is formed in the central portion. An injection signal is output to the electric circuit of the fuel supply system 35 in order to inject fuel into the cylinder from the nozzle opening of the nozzle. That is, fuel is injected into the cylinder by the injector 34 after the compression stroke, and the penetration of the fuel spray is suppressed to a size (length) that prevents the fuel spray from reaching the outer periphery of the cylinder. Stratification is realized in which an air-fuel mixture layer is formed at the center of the gas and a gas layer containing fresh air is formed around it. 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.

  If the fuel self-ignites with the gas layer and the mixture layer formed as described above, the gas layer between the mixture layer and the wall surface of the cylinder 11 causes the flame of the mixture layer to become the wall surface of the cylinder 11. The gas layer serves as a heat insulating layer without being in contact with the gas, 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 reducing the cooling loss only converts the reduced cooling loss into an 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 10 by adopting a configuration that reduces both the cooling loss and the exhaust loss.
(Engine fuel injection control)
The engine 10 self-ignites and burns the fuel injected into the cylinder by the injector 34 in the entire operation region. More specifically, the engine 10 is a low load / medium load operating region in which the engine load is lower than a predetermined load (that is, a switching load) indicated by a solid line in FIG. The operation region A has a higher load side operation region than the normal operation region A, and includes a retard operation region B that performs retarded self-ignition combustion. The retard operation region B can be rephrased as an operation region that is greater than or equal to the switching load. As will be described later, the normal operation region A is divided into a region A1 and a region A2 for the load level, and the retard operation region B is divided into a region B1 and a region B2 for the load level.

  FIG. 4 illustrates the fuel injection timing and the combustion period in the normal operation region A and the retard operation region B. FIG. 4 also illustrates changes in the EGR rate in the normal operation region A and the retard operation region B (right diagram). FIG. 4 further illustrates a temperature change in the cylinder 11 at a predetermined load in the retard operation region B (upper diagram).

  As shown in FIG. 4, in the normal operation region A, fuel injection (that is, main injection) is performed a plurality of times (that is, four times in the example) before the compression top dead center, and fuel is injected near the compression top dead center. Self-igniting and burning. The PCM 100 adjusts the fuel amount, the fuel injection timing, and the fuel injection mode according to the engine speed, the engine load, and the effective compression ratio. The fuel injection may be performed in the range of ATDC-15 ° to -5 ° CA. In this way, it is possible to start main combustion near the compression top dead center while avoiding the generation of soot.

  In the normal operation region A, the excess air ratio λ in the entire cylinder (combustion chamber) is set to 2.5 or more (or the weight ratio G / F of gas to fuel in the cylinder is 35 or more). Thereby, RawNOx can be reduced while achieving thermal insulation by the heat insulation layer and improving the illustrated thermal efficiency. Since the illustrated thermal efficiency peaks when the excess air ratio λ = 8, the range of excess air ratio λ is preferably 2.5 ≦ λ ≦ 8. The normal operation region A can be called a lean region because the excess air ratio λ is 2.5 or more.

  In the normal operation region A, the opening degree of the throttle valve 33 is set to fully open. This contributes to the improvement of the indicated thermal efficiency by reducing the pump loss.

  As described above, in the normal operation region A, the excess air ratio λ is set to 2.5 or more. However, when the load on the engine 10 increases and the amount of fuel increases, the excess air ratio λ may be set to 2.5 or more. Can be difficult. Therefore, in this engine 10, the excess air ratio λ is set to 1 in the retard operation region B where the load of the engine 10 is relatively high. In the retard operation region B, it becomes possible to maintain good exhaust emission performance using a three-way catalyst. The retard operation region B can be called the λ = 1 region because the excess air ratio λ is 1.

  The retard operation region B is divided into a low load side region B1 and a high load side region B2 with respect to the load level of the engine 10. Among these, in the low load side region B1, the pre-injection before the compression top dead center and the main injection after the compression top dead center are executed after the pre-stage injection.

  As illustrated in FIG. 4, the pre-stage injection is performed at a time of, for example, about 20 ° CA before compression top dead center. This is the time when the region deviated from the wrinkle generation region shown in FIG. The amount of fuel injected into the cylinder 11 by the pre-injection is a relatively small amount that causes an oxidation reaction without reaching a hot flame reaction. The fuel injected by this pre-stage injection undergoes an oxidation reaction without reaching a thermal flame reaction (that is, by a partial oxidation reaction), thereby adjusting the temperature in the cylinder 11 at the compression top dead center. The compression end temperature increases as the injection amount of the upstream injection increases. Therefore, an amount of fuel such that the compression end temperature becomes a desired temperature is injected into the cylinder 11 by the pre-injection.

  As the expansion stroke progresses after the compression top dead center, the temperature in the cylinder 11 gradually decreases during motoring. However, by appropriately increasing the compression end temperature by the pre-stage injection, the temperature after the compression top dead center is reached. It is possible to suppress the in-cylinder temperature from falling below a predetermined level. That is, the pre-stage injection is for maintaining the in-cylinder temperature after the compression top dead center while preventing the in-cylinder temperature from becoming too high. By this pre-stage injection, the air-fuel mixture after compression top dead center expands, that is, substantially isothermally expands in a state in which the temperature change is suppressed within a predetermined temperature range. In this specification, this substantially isothermal expansion is simply referred to as “isothermal expansion”.

  The main injection is an injection for generating main combustion that generates engine torque (combustion that generates the largest amount of heat in one cycle). The total injection amounts of the upstream injection and the main injection are set so that the excess air ratio λ of the entire cylinder is 1. The main injection is performed at a predetermined time after the compression top dead center. This is a time when the fuel is out of the soot generation region and corresponds to a time when the fuel can be subjected to compression self-ignition in a period in which the temperature in the cylinder after the compression top dead center falls within a predetermined temperature range. Here, ignition means a point in time when the combustion mass ratio of the fuel becomes 10% or more. The main injection is executed after the compression top dead center and during the expansion stroke (more specifically, the initial stage when the expansion stroke is divided into three equal parts in the initial, middle and final stages). Since the main injection causes main combustion that generates torque, it is necessary to inject fuel corresponding to the required torque. For example, in the main injection, it is preferable to inject 3/4 or more of the total injection amount including the injection amount by the pre-stage injection and the injection amount by the main injection.

  Thus, in the low load side region B1 in the retard operation region B, the compression self-ignition combustion period is delayed from the combustion period in the normal operation region A as shown in FIG. The combustion period of compression auto-ignition combustion overlaps with the time point at which the pressure increase rate during motoring becomes a negative maximum value, or the period during which the combustion center of compression auto-ignition combustion has a large negative compression increase rate (that is, The angle is delayed until it overlaps with 10-20 ° CA after compression top dead center. Hereinafter, the self-ignition combustion that retards the ignition timing may be referred to as “retard self-ignition combustion”. This retarded self-ignition combustion avoids an increase in combustion noise.

  When the main combustion is retarded in this way, there is a limit to the period during which the retard can be performed. That is, as the expansion stroke progresses, the in-cylinder temperature decreases with an increase in the in-cylinder volume. If the main combustion is retarded too much, a misfire occurs. The lowering speed of the in-cylinder temperature in the expansion stroke is faster as the compression ratio is higher. Therefore, the higher the compression ratio, the shorter the retardable period. However, the period during which the main combustion can be retarded can be extended by maintaining the in-cylinder temperature after compression top dead center by the pre-stage injection.

  However, when increasing the in-cylinder temperature after compression top dead center, if the in-cylinder temperature is too high, the fuel injected by the main injection will ignite locally before mixing with the air in the cylinder, There is a risk of causing wrinkles. However, according to the pre-stage injection, the fluctuation of the in-cylinder temperature after the compression top dead center is suppressed within a predetermined temperature range, so that an excessive increase in the in-cylinder temperature is also suppressed. As a result, it is possible to suppress the occurrence of soot by locally igniting the fuel from the main injection.

  Therefore, the upper limit of the “predetermined temperature range” is a temperature lower than the temperature at which the fuel from the main injection ignites before being mixed with the air in the cylinder. The lower limit value of the predetermined temperature range is a temperature higher than the temperature at which the in-cylinder temperature at the compression top dead center is reduced by performing motoring. That is, the in-cylinder temperature from the compression top dead center to the occurrence of main combustion by the pre-injection is lower than the temperature at which the fuel from the main injection ignites before being mixed with the air in the cylinder, and at the compression top dead center. The in-cylinder temperature is maintained at a temperature higher than the temperature reduced by performing motoring. For example, the “predetermined temperature range” is 100 degrees. More specifically, the in-cylinder temperature from the compression top dead center until the main combustion occurs is maintained at 1000 to 1100K.

  In contrast to the low load side region B1 in which the retarded self-ignition combustion is performed by performing the pre-stage injection and the main injection, the pre-stage injection before the compression top dead center is performed in the high load side region B2 in the retard operation region B. And the second pre-stage injection between the main injection after the compression top dead center and the retarded self-ignition combustion. In the high load region B2, it is necessary to further retard the compression self-ignition combustion period than the low load region B1 in order to avoid combustion noise. However, if there is a large delay from the compression top dead center, even if an attempt is made to maintain the temperature in the cylinder by the pre-stage combustion described above, the temperature may not be maintained and may be reduced, resulting in a misfire. In other words, the second pre-injection generates heat for maintaining the in-cylinder temperature from the compression top dead center until the main injection fuel self-ignites substantially at the in-cylinder temperature at the compression top dead center. And thereby adjusting the temperature maintenance period.

  The second pre-stage injection also injects fuel by an amount that provides an air-fuel ratio that causes partial oxidation reaction of the injected fuel, and the in-cylinder temperature after compression top dead center is maintained for a predetermined period. It is for maintaining the temperature at which self-ignition is possible. In the second pre-stage injection, although the fuel undergoes an oxidation reaction but does not reach a hot flame reaction, only a quantity of heat that suppresses a decrease in in-cylinder temperature after compression top dead center is generated. The second pre-stage injection is for maintaining the in-cylinder temperature after the compression top dead center while preventing the in-cylinder temperature from becoming too high. By this second pre-stage injection, the temperature maintenance period after the compression top dead center becomes longer in the region B2 on the high load side than in the region B1 on the low load side.

  Thus, in the high load side region B2, the injection timing of the main injection is retarded from the injection timing in the low load side region B1. However, the timing of the main injection is the timing at which the fuel is ignited while the variation in the in-cylinder temperature is within the predetermined temperature range in the expansion stroke, and the combustion period of the main combustion is in the cylinder during motoring. This is the same timing as when the pressure increase rate reaches the maximum negative value. By relatively retarding the timing of main injection, the compression self-ignition timing is delayed, and as a result, the period of compression self-ignition combustion is retarded relative to the low load side region B1. Thus, it is possible to avoid combustion noise even in the high load region B2.

  The injection amount of the second upstream injection increases as the load on the engine 10 increases. As the load increases, the timing of the main injection needs to be delayed in order to delay the combustion period. Therefore, by increasing the injection amount of the second pre-stage injection, the period for maintaining the predetermined temperature after the compression top dead center is increased. Lengthen. Thereby, although the injection start timing of the second front stage injection hardly changes with the load of the engine 10, the injection end timing becomes later as the load of the engine 10 becomes higher.

  The injection start timing of the main injection is gradually retarded as the load on the engine 10 increases. This corresponds to delaying the period of compression self-ignition combustion and delaying the injection end timing of the second pre-stage injection. The main injection that contributes to the engine torque increases as the load on the engine 10 increases.

  On the other hand, the pre-stage injection is substantially constant with respect to the load of the engine 10 over the entire retard operation region B, both in the injection amount and the injection timing.

  Even in the high load side region B2, the total injection amounts of the pre-stage injection, the second pre-stage injection, and the main injection are set so that the excess air ratio λ of the entire cylinder becomes 1. The injection amount by the front injection is about 5% of the total injection amount, and the injection amount by the second front injection is about 15% of the total injection amount. The injection amount of the main injection is about 80% of the total injection amount.

  The upper diagram shown in FIG. 4 shows an example of a temperature change in the cylinder 11 in the high-load region B2 in which the front injection, the second front injection, and the main injection are performed (see the solid line). As described above, the fuel injected into the cylinder 11 by the pre-injection adjusts the compression end temperature, and the fuel injected into the cylinder 11 by the second fuel injection after the compression top dead center is caused by the partial oxidation reaction. The period during which the temperature in the cylinder 11 after the compression top dead center is maintained within a predetermined range is extended. The broken line indicates the temperature change in the cylinder 11 after compression top dead center during motoring. Thus, the fuel injected into the cylinder by the main injection is compressed and ignited at a predetermined time and burned.

  In addition, in the combustion transition region adjacent to the switching load between the normal operation region A and the retard operation region B and surrounded by the one-dot chain line in FIG. 4, a plurality of times before the compression top dead center in the normal operation region A described above. Fuel injection and pre-injection and main injection in the low load side region B1 in the retard operation region B are performed.

  In the retard operation region B, as described above, at least the pre-injection and the main injection are performed to retard the period of compression ignition combustion, but if necessary, after the main injection, the ozone generator Ozone may be added into the cylinder 11 by 36 (see FIG. 4). That is, the PCM 100 causes the ozone generator 36 to generate ozone after causing the injector 34 to perform the pre-injection and the main injection. The fuel injected into the cylinder 11 by the main injection is given energy by ozone and is easily self-ignited and combusted. That is, ozone assists the self-ignition combustion of fuel.

  According to the pre-stage injection (and the second pre-stage injection), it is possible to suppress the decrease in the in-cylinder temperature after the compression top dead center, and therefore it is possible to extend the period during which the self-ignition combustion can be retarded. However, there is a limit even if the period of retarding can be extended. On the other hand, by adding ozone, the fuel can be self-ignited even if the ignition timing is retarded to a point where ignition is difficult or impossible without addition of ozone. The addition of ozone makes it possible to extend the retarding period when retarding autoignition combustion.

  Ozone addition may be performed constantly. By adding ozone, it is possible to reduce the injection amounts of the first-stage injection and the second-stage injection. The ozone addition may be executed only when the in-cylinder temperature after compression top dead center is lower than a predetermined temperature. This predetermined temperature is a temperature at which self-ignition combustion of the fuel can be performed without adding ozone. That is, as described above, this is a temperature corresponding to the lower limit value when the in-cylinder temperature fluctuation from the compression top dead center until the fuel is ignited by the main injection is maintained within a predetermined temperature range by the pre-stage injection. That is, ozone may be added in a situation where it is difficult to perform self-ignition combustion of fuel by main injection only by maintaining the in-cylinder temperature after compression top dead center by pre-stage injection.

  Ozone addition may be performed only in the high load side region B2 in the retard operation region B, or may be performed over the entire retard operation region B.

  Further, the concentration of ozone generated by the ozone generator 36 may be increased, for example, as the load on the engine 10 is higher. The higher the concentration of ozone, the stronger the assist of self-ignition combustion, and the self-ignition becomes possible or the ignition timing is advanced even if the temperature in the cylinder is low. On the other hand, increasing the ozone concentration is disadvantageous for fuel consumption deterioration and engine 10 corrosion. Therefore, the concentration of ozone may be increased as the load on the engine 10 is higher so that the minimum amount of ozone is added.

  The ozone addition time may be delayed as the load on the engine 10 increases. As shown in the right diagram of FIG. 4, the ignition timing of the main combustion is delayed as the ozone addition timing is delayed. Therefore, the ozone addition timing may be delayed so as to correspond to the retard amount of the compression self-ignition combustion period. By doing so, it is possible to set the compression self-ignition combustion period to an appropriate time corresponding to the load of the engine 10.

(Engine EGR control)
Next, EGR control (intake charge amount control) of the engine 10 will be described. First, the normal operation region A is divided into a low load side region A1 and a high load side region A2 with respect to the engine load level. In the low load side region A1 (that is, corresponding to a predetermined low load side region in the lean region), since the load of the engine 10 is low, the high pressure EGR system 51 and the low pressure EGR system 52 are used to ensure combustion stability. The exhaust gas does not recirculate through the air. On the other hand, in the high load side region A2, the exhaust gas is recirculated through the high pressure EGR system 51 and the low pressure EGR system 52. The ratio of the exhaust gas recirculation amount by the high pressure EGR system 51 and the exhaust gas recirculation amount by the low pressure EGR system 52 is appropriately set according to the operating state of the engine 10. As described above, since the high pressure EGR system 51 and the low pressure EGR system 52 include the EGR coolers 512 and 522, the exhaust gas recirculated through any of the systems 51 and 52 becomes the cooled exhaust gas.

  As shown by the solid line in the right diagram of FIG. 4, the EGR rate in the region A2 on the high load side is constant at a predetermined value up to a predetermined load, while between the predetermined load and the switching load, the engine 10 As the load increases, the EGR rate is set to gradually increase. Thus, the switching load coincides with the EGR rate set in the retard operation region B as will be described later. However, more precisely, the EGR rate in the high load side region A2 matches the EGR rate set in the retard operation region B at a load lower than the switching load.

  In the retard operation region B, the EGR rate is set to continuously change so as to correspond to the engine load so that the excess air ratio λ becomes 1. Even in the normal operation region A, the EGR rate is continuously changed in the region adjacent to the retard operation region B. Thus, when the load of the engine 10 continuously increases and decreases and shifts from the normal operation region A to the retard operation region B, or when shifts from the retard operation region B to the normal operation region A, EGR The rate can be changed continuously. Since the responsiveness of the high pressure EGR system 51 and the low pressure EGR system 52 is low, continuously changing the EGR rate improves the followability to changes in the engine load, thereby reducing exhaust emission performance, generating torque shocks, etc. It becomes effective in avoiding.

  Further, in the region up to the predetermined load in the high load side region A2, the EGR rate is made constant at a predetermined value as described above. This EGR rate corresponds to an intermediate value of the EGR rate that changes in the retard operation region B. By doing this, as will be described in detail later, when the operating state of the engine 10 changes and shifts from the normal operation region A to the retard operation region B, it is possible to reduce the deviation of the EGR rate. Here, the intermediate value may be a value between the maximum value and the minimum value of the EGR rate set in the retard operation region B, and may be a median value between the maximum value and the minimum value. It does not have to be. The intermediate value can be set to an appropriate value.

  In the high load side region A2 of the normal operation region A, as indicated by a two-dot chain line in FIG. 5, the EGR rate may be gradually decreased as the load on the engine 10 decreases.

  As described above, the opening degree of the throttle valve 33 is set to be fully open over the entire normal operation region A. This reduces pump loss. Here, making the opening degree of the throttle valve 33 fully open includes making the opening degree substantially fully open. This allows the throttle valve 33 to be slightly throttled so that the intake negative pressure is generated so that the exhaust gas can be recirculated through the high-pressure EGR passage 510.

  In the retard operation region B, the excess air ratio λ is set to 1, but at that time, the recirculation amount of the exhaust gas is adjusted according to the load of the engine 10 while the opening degree of the throttle valve 33 is fully opened. 11 adjusts the amount of fresh air introduced into the air 11 (more precisely, the amount of oxygen), and sets the excess air ratio λ to 1. That is, as the load on the engine 10 increases, the amount of fuel increases and the amount of air commensurate with it increases, so the EGR rate gradually decreases as the load on the engine 10 increases as shown in the right diagram of FIG. The EGR rate becomes 0 at full open load. Thereby, in the retard operation area | region B, it becomes advantageous to the improvement of illustrated thermal efficiency by reducing pump loss.

  Here, in the engine system 1, EGR coolers 512 and 522 are interposed in each of the high pressure EGR passage 510 and the low pressure EGR passage 520 to cool the exhaust gas and return it to the cylinder 11. For this reason, it is avoided that the temperature state in the cylinder 11 becomes too high. In the retard operation region B, this slows down the compression self-ignition combustion by the main injection, which is advantageous for reducing combustion noise. As a result, in each of the low load side region B1 and the high load side region B2 in the retard operation region B, the period of the compression self-ignition combustion can be advanced as much as possible. That is, in the region B, it is advantageous for improving fuel consumption. Further, advancing the compression self-ignition combustion period as much as possible makes it possible to reduce the fuel amount of the second pre-stage injection in the high-load region B2. This also makes it possible to advance the timing of the main injection, which is advantageous for improving fuel efficiency, and can increase the injection amount of the main injection. This is advantageous for torque generation. In other words, reducing the amount of fuel in the second pre-injection can be paraphrased as reducing the area in which the second pre-injection is necessary. When comparing the low load side region B1 and the high load side region B2, the low load side region B1 in which the period of self-ignition combustion is advanced is more advantageous for fuel consumption. The reduction in the area B2 is advantageous in improving fuel consumption.

  On the other hand, in the normal operation region A, in the high load side region adjacent to the retard operation region B, the exhaust gas is recirculated from the viewpoint of smoothing the transition between the normal operation region A and the retard operation region B. However, also in this region, by recirculating the cooled exhaust gas, the self-ignition combustion becomes slow, which is advantageous in reducing combustion noise. As a result, it is advantageous to expand the normal operation region A in which combustion noise can be avoided to the high load side.

  Further, in the medium load region in the normal operation region A, the EGR rate is set to an intermediate value of the EGR rate that can change in the retard operation region B. Suddenly, as shown by the dashed arrow in the right diagram of FIG. 4, the deviation from the EGR rate corresponding to the required load that can occur immediately after the transition from the normal operation region A to the retard operation region B is reduced. It becomes possible. In FIG. 4, the deviation of the EGR rate corresponds to the deviation between the tip of the dashed arrow and the alternate long and short dash line. Responsiveness of the high pressure EGR system 51 and the low pressure EGR system 52 is low with respect to a change in the load of the engine 10. Although the deviation of the EGR rate in the retard operation region B causes the deviation of the excess air ratio λ and reduces the exhaust emission performance, by reducing the deviation, the deterioration of the exhaust emission performance becomes as small as possible, It is possible to shorten the time until the deviation of the EGR rate is eliminated as much as possible.

  Next, the above-described engine control executed by the PCM 100 will be described with reference to the flowchart shown in FIG. In step S1 after the start, the signals of the accelerator opening sensor 72, the engine speed sensor 73, the airflow sensor 74, and the vehicle speed sensor 71 are read. In the subsequent step 2, the PCM 100 reads the intake valve based on the read signals. 21 and the phase angle of the exhaust valve 22 are set.

  In step S3, the PCM 100 determines the operating region of the engine 10 based on the read accelerator opening and the engine speed, and determines the fuel injection amount and the fuel injection timing based on the operating region and each signal value. Each is determined (step S4).

  In step S5, the PCM 100 determines the amount of ozone generated and the timing thereof based on the operating range of the engine 10 and each signal value. In the subsequent step S6, the PCM 100 determines the load on the engine 10. A target EGR rate is set based on the target.

  Thus, according to the valve phase angle, fuel injection amount and fuel injection timing, ozone generation amount and generation timing, and target EGR rate set in steps S2, S4 to S6, the throttle valve 33, injector 34, VVT 23, exhaust gas The engine 10 is operated by controlling the shutter valve 43, the high pressure EGR valve 511, the low pressure EGR valve 521 and the ozone generator 36.

  In the above-described configuration, the heat insulating structure of the combustion chamber and the intake port 18 is adopted, and the heat insulating layer by the gas layer is formed in the cylinder (combustion chamber). The present technology can also be applied to an engine that does not employ a gas layer or an engine that does not form a heat insulating layer by a gas layer.

  In the above configuration, the present technology has been described by taking an engine with a turbocharger as an example. However, the present technology can also be applied to a naturally aspirated engine that does not include a turbocharger. In the naturally aspirated engine, the low pressure EGR system 52 is omitted.

  Further, the temperature range in which the variation in the in-cylinder temperature after the compression top dead center is accommodated is not limited to 100 degrees. Any other value such as 90 degrees or 110 degrees may be used as long as it is a temperature range that prevents abnormal combustion of the fuel and enables retarded self-ignition combustion.

  Similarly, the in-cylinder temperature while the variation in the in-cylinder temperature is within a predetermined temperature range is not limited to 1000 to 1100K. Other values such as 950 to 1100K, 1000 to 1150K, and 1100 to 1200K may be used as long as the temperature is such that the abnormal combustion of the fuel is prevented and the retarded self-ignition combustion is possible.

1 Engine system 10 Engine (engine body)
11 cylinder 100 PCM (controller)
30 Intake passage 33 Throttle valve 34 Injector (fuel injection valve)
51 High pressure EGR system (Cold EGR means)
52 Low pressure EGR system (Cold EGR means)

Claims (4)

An engine body configured with a cylinder having a geometric compression ratio set to 20 or more;
Cold EGR means configured to recirculate after cooling a part of the exhaust gas in the cylinder;
A controller configured to operate the engine body by compressing self-ignition combustion of the air-fuel mixture in the cylinder, and
When the operating state of the engine body is in a lean region lower than a predetermined switching load corresponding to a medium load, the controller compresses the excess air ratio λ of the air-fuel mixture in the cylinder to 2.5 or more. On the other hand, when the operation state of the engine body is in the λ = 1 region equal to or higher than the switching load, the excess air ratio λ is set to 1, and the self-ignition combustion is performed.
The controller also sets the opening of the throttle valve provided on the intake passage communicating with the cylinder to be fully open in the full load range of the operation range of the engine body,
In a predetermined low load side region in the lean region, the exhaust gas is not recirculated,
In the λ = 1 region, the control device for a compression self-ignition engine that sets the excess air ratio λ to 1 by recirculating the exhaust gas cooled through the cold EGR means. The control device for a compression self-ignition engine according to claim 1,
A fuel injection valve for injecting fuel into the cylinder;
The controller is
In the lean region, before the compression top dead center, the fuel injection valve performs the entire amount of fuel injection,
In the λ = 1 region, before the compression top dead center, by injecting an amount of fuel that causes an oxidation reaction without reaching a thermal flame reaction, the temperature variation in the cylinder after the compression top dead center is changed to a predetermined value. Pre-stage injection that provides a temperature maintenance period that falls within the temperature range; and main injection that injects fuel after the pre-stage injection and that is after compression top dead center and that performs compression self-ignition combustion within the temperature maintenance period. The fuel injection valve is executed,
The controller also changes an EGR rate in accordance with a load level of the engine body in the λ = 1 region, and a predetermined high load side region adjacent to the λ = 1 region in the lean region. Then, the control device for a compression self-ignition engine that increases the EGR rate as the load of the engine body increases so as to approach the EGR rate set in the switching load in the λ = 1 region. The control device for a compression self-ignition engine according to claim 2,
In the λ = 1 region, the controller decreases the EGR rate as the load on the engine body increases.
The controller also injects an amount of fuel that undergoes an oxidation reaction between the preceding injection and the main injection without causing a thermal flame reaction in a predetermined high load side region in the λ = 1 region. The second pre-stage injection for adjusting the length of the temperature maintenance period is performed, and the timing of the main injection is retarded with respect to the timing of the main injection in a region where the load is lower than the predetermined high load side region Control device for compression self-ignition engine. In the control device of the compression self-ignition engine according to claim 2 or 3,
In the load region between the predetermined high load side region and the predetermined low load side region in the lean region, the controller sets an EGR rate to an intermediate value of an EGR rate that changes in the λ = 1 region. A control device for a compression self-ignition engine set to be

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