JP5803326B2 - Lean burn engine with turbocharger - Google Patents

Description

  The technology disclosed herein relates to a lean burn engine with a supercharger.

  For example, Patent Document 1 describes a technique related to control of a turbocharged engine, and this technique uses external EGR control when the operating state of the engine is in an operating range from low speed and low load to medium speed and medium load. Scavenging control is performed when the operating state is in the operating range from low speed and high load to medium speed and high load, and scavenging control and external EGR control are performed when in the operating range of high speed and high load. Yes. As a result, in the high-speed and high-load operation region, after reducing the high temperature residual gas in the cylinder, the cooled external EGR gas is introduced into the cylinder to improve torque and improve fuel efficiency while suppressing abnormal combustion. Is planned. As described above, in the turbocharged engine of Patent Document 1, by introducing the cooled external EGR gas into the cylinder, knocking in a high-speed and high-load region is avoided, thereby improving torque. Yes.

JP 2010-24974 A

  By the way, for example, a lean burn engine in which the air fuel ratio A / F is set to 30 or more is effective for achieving both suppression of RawNOx generation and low fuel consumption. In a lean burn engine that is operated with an ultra lean air-fuel mixture, for example, a turbocharger that is driven by exhaust energy is combined to ensure a desired torque.

  However, the inventors of the present application try to maintain a super lean air-fuel mixture particularly in a high load region because the compressor efficiency of the turbocharger decreases in the high speed region in such a lean burn engine with a turbocharger. As a result, the pumping loss of the engine increased, and it became difficult to secure high torque, and the fuel consumption was greatly deteriorated.

  The technology disclosed herein has been made in view of such a point, and the object is to maintain a super lean air-fuel mixture by improving the compressor efficiency of the turbocharger in a high speed region. An object of the present invention is to realize a lean burn engine with a supercharger that suppresses the generation of RawNOx, reduces the pumping loss of the engine, secures a desired high torque, and improves fuel efficiency.

  The inventors of the present application maintain an ultra-lean air-fuel mixture in the above-described high-speed and high-load region, thereby increasing the pumping loss of the engine, making it difficult to secure a desired high torque and deteriorating fuel consumption. The mechanism of was analyzed as follows.

  That is, in a high speed region where the engine speed is relatively high, a high torque corresponding to the high load region is generated, so that the fuel injection amount increases. Therefore, for example, if an ultra-lean air-fuel mixture with an A / F of 30 or more is to be maintained, the flow rate of compressed air supplied from the compressor to the cylinder must be greatly increased. Reduces compressor efficiency.

  On the other hand, a reduction in the compressor efficiency of the turbocharger increases the compressor power, and hence the necessary turbine power. To increase turbine power, the gas temperature at the turbine inlet or the pressure must be increased. As mentioned above, if the engine is operated with a super lean mixture with an A / F of 30 or more, The exhaust gas temperature becomes relatively low. Therefore, in order to increase turbine power, the engine exhaust pressure must be increased. However, increasing the exhaust pressure increases the pumping loss of the engine, making it difficult to secure high torque and further reducing fuel consumption. End up.

  Therefore, the inventors of the present application focused on changing the operating conditions of the turbocharger compressor in order to increase the compressor efficiency in a high speed and high load region. That is, the external EGR control is executed so that the flow rate of the compressor slides to the low flow rate side. As a result, the compressor efficiency is improved, and in the high speed and high load range, the maintenance of ultra lean air-fuel mixture and the reduction of pumping loss are both achieved, thereby ensuring high torque and improving fuel efficiency.

  Specifically, a lean burn engine with a supercharger disclosed herein includes an engine body configured to have an operation region that is operated with an air-fuel mixture leaner than a stoichiometric air-fuel ratio, and an intake side of the engine body. A turbocharger including a compressor disposed on the exhaust side and a turbine disposed on an exhaust side and configured to supercharge a gas introduced into a cylinder of the engine body; and a burned gas in the cylinder EGR means configured to introduce the engine and a controller configured to control operation of the engine.

When the engine body is at least after being warmed up, the controller is configured to provide the turbocharger when the engine body rotation speed exceeds a predetermined rotation speed and the engine load is in a low load region lower than the predetermined load. The working gas fuel ratio G / F is set to 30 or more, or the air fuel ratio A / F is set to 30 or more by supercharging with a machine, and the engine speed exceeds the predetermined speed, and the engine When the load is in a high load region equal to or higher than the predetermined load, the burned gas is recirculated to the intake side through a high-pressure EGR passage that connects the upstream side of the turbine on the exhaust side and the downstream side of the compressor on the intake side. by performing supercharging by the turbocharger sets the G / F to 30 or more, the and the rotational speed of the engine body than the predetermined rotational speed, the When the engine load is at a predetermined high-load region, while introducing burned gas into the cylinder by the EGR means, the air fuel ratio A / F to stoichiometric air-fuel ratio.

  Here, the EGR means may be configured to include a high-pressure EGR system that recirculates the burnt gas to the intake side through an EGR passage that connects the upstream side of the turbine on the exhaust side and the downstream side of the compressor on the intake side. In addition to this high-pressure EGR system, the EGR means also has a low-pressure EGR system that recirculates burnt gas to the intake side through an EGR passage that connects the downstream of the turbine on the exhaust side and the upstream of the compressor on the intake side, and / or An internal EGR system that introduces burned gas into the cylinder by controlling the operation of the intake and exhaust valves may be further included.

  According to this configuration, when the engine operating state is in the high speed region and the engine load is in the low load region lower than the predetermined load, the working gas fuel ratio G / F is 30 or more, or the air fuel ratio A / F is set to 30 or more. That is, G / F ≧ 30 may be set when the burned gas is introduced into the cylinder by the EGR means, and A / F ≧ 30 may be set when the burned gas is not introduced into the cylinder. Here, the EGR means may be any of a high pressure EGR system, a low pressure EGR system, and an internal EGR system. By thus operating the engine body with an ultra-lean air-fuel mixture, raw NOx generation suppression and low fuel consumption are compatible in the low load region.

  On the other hand, when the engine operating region is in the high speed region and the engine load is in a high load region equal to or higher than a predetermined load, the EGR passage that connects the upstream of the turbine on the exhaust side and the downstream of the compressor on the intake side to each other The burnt gas is recirculated to the intake side through. That is, in the high load region, the external EGR gas is introduced into the cylinder by the high pressure EGR system. As a result, the external EGR gas is recirculated downstream of the compressor and introduced into the cylinder. Therefore, when the total amount of gas introduced into the cylinder is assumed to be the same, the flow rate through the compressor is The amount of EGR gas that is refluxed is lower than when EGR gas is not refluxed. This improves the compressor efficiency by changing the operating condition of the compressor to the low flow rate side in the high speed region, and lowers the turbine power required for realizing G / F ≧ 30. In other words, the engine exhaust pressure can be lowered. In other words, in a high-speed and high-load region, an ultra-lean gas mixture with a G / F of 30 or more is maintained and the production of RawNOx is suppressed, and the pumping loss of the engine is reduced. It is also advantageous for improvement.

  Therefore, when the engine body is operating at high speed and in a high load range, it is possible to simultaneously achieve the desired high torque and improve fuel efficiency by maintaining a super lean air-fuel mixture and reducing the pumping loss of the engine. To do.

  The controller may set the G / F to 30 or more while recirculating burnt gas to the intake side through the EGR passage even when the engine load is a fully open load.

  As described above, by improving the compressor efficiency, it is possible to set G / F to 30 or more while ensuring a desired high torque even at a fully open load.

  The controller may execute compression ignition combustion at least in the low load region. The compression ignition combustion makes it possible to improve both exhaust emission and thermal efficiency.

  As described above, the lean burn engine with a supercharger takes in burnt gas through an EGR passage that connects the upstream side of the turbine on the exhaust side and the downstream side of the compressor on the intake side in a high speed and high load region. Since the compressor operating conditions have been changed by recirculating to the side, and the compressor efficiency has been improved, it is possible to achieve the desired balance by maintaining a super lean air-fuel mixture (G / F ≧ 30) and reducing the pumping loss of the engine. It is possible to simultaneously ensure high torque and improve fuel efficiency.

It is the schematic which shows the structure of a lean burn engine with a supercharger. It is a block diagram concerning control of a lean burn engine with a supercharger. It is a figure which illustrates the operating area of an engine. It is a figure which shows an example of a compressor map. It is a figure which shows an example of the relationship between an engine speed and compressor efficiency. It is a figure which shows an example of the relationship between an engine speed and a compressor mass flow. It is a figure which shows an example of the relationship between an engine speed and a total gas mass flow. It is a figure which shows an example of the relationship between an engine speed and a pumping loss.

  Hereinafter, an embodiment of a lean burn engine with a supercharger will be described based on the drawings. The following description of preferred embodiments is exemplary. 1 and 2 show a schematic configuration of an engine (engine body) 1. The engine 1 is a spark ignition gasoline engine that is mounted on a vehicle and supplied with fuel containing at least gasoline. The engine 1 is provided with a cylinder block 11 provided with a plurality of cylinders 18 (only one shown), a cylinder head 12 provided on the cylinder block 11, and a cylinder block 11 below the cylinder block 11. And an oil pan 13 in which oil is stored. A piston 14 connected to the crankshaft 15 via a connecting rod 142 is fitted in each cylinder 18 so as to be able to reciprocate. A cavity 141 having a reentrant shape is formed on the top surface of the piston 14. The cavity 141 faces a direct injection injector 67 described later when the piston 14 is positioned near the compression top dead center. The cylinder head 12, the cylinder 18, and the piston 14 having the cavity 141 define a combustion chamber 19. The shape of the combustion chamber 19 is not limited to the illustrated shape. For example, the shape of the cavity 141, the top surface shape of the piston 14, the shape of the ceiling portion of the combustion chamber 19, and the like can be changed as appropriate.

  The engine 1 is set to a relatively high geometric compression ratio of 14 or more for the purpose of improving the theoretical thermal efficiency, stabilizing the compression ignition combustion described later, and the like. In addition, what is necessary is just to set a geometric compression ratio suitably in the range of about 14-20. However, the geometric compression ratio of the engine 1 is not limited to this range.

  The cylinder head 12 is provided with an intake port 16 and an exhaust port 17 for each cylinder 18. The intake port 16 and the exhaust port 17 have an intake valve 21 and an exhaust for opening and closing the opening on the combustion chamber 19 side. Each valve 22 is disposed.

  Among the valve systems that drive the intake valve 21 and the exhaust valve 22, respectively, on the exhaust side, the operation mode of the exhaust valve 22 is switched between a normal mode and a special mode, for example, a hydraulically operated variable mechanism (see FIG. 2). Hereinafter, a VVL (Variable Valve Lift) 71 is provided. Although the VVL 71 is not shown in detail in its configuration, two types of cams having different cam profiles, a first cam having one cam crest and a second cam having two cam crests, and its first And a lost motion mechanism that selectively transmits an operating state of one of the second cams to the exhaust valve. When the operating state of the first cam is transmitted to the exhaust valve 22, the exhaust valve 22 operates in the normal mode in which the valve is opened only once during the exhaust stroke, whereas the operating state of the second cam is the exhaust valve. When transmitting to the engine 22, the exhaust valve 22 operates in a special mode in which the exhaust valve is opened during the exhaust stroke and is also opened during the intake stroke so that the exhaust is opened twice. The normal mode and the special mode of the VVL 71 are switched according to the operating state of the engine. Specifically, the special mode is used in the control related to the internal EGR. In order to enable switching between the normal mode and the special mode, an electromagnetically driven valve system that drives the exhaust valve 22 by an electromagnetic actuator may be employed. Also, the execution of internal EGR is not realized only by opening the exhaust twice. For example, the internal EGR control may be performed by opening the intake valve 21 twice or by opening the intake valve twice, or by providing a negative overlap period in which both the intake valve 21 and the exhaust valve 22 are closed in the exhaust stroke or the intake stroke. Internal EGR control that causes the fuel gas to remain in the cylinder 18 may be performed.

  As shown in FIG. 2, the exhaust side valve system having the VVL 71 is arranged on the intake side as shown in FIG. 2. 72) and a lift variable mechanism (hereinafter referred to as CVVL (Continuously Variable Valve Lift)) 73 capable of continuously changing the lift amount of the intake valve 21. . The VVT 72 may employ a hydraulic, electromagnetic, or mechanical structure as appropriate, and illustration of the detailed structure is omitted. The CVVL 73 can also adopt various known structures as appropriate, and the detailed structure is not shown. With the VVT 72 and the CVVL 73, the intake valve 21 can change its valve opening timing, valve closing timing, and lift amount.

  Further, for each cylinder 18, a direct injection injector 67 that directly injects fuel into the cylinder 18 and a port injector 68 that injects fuel into the intake port 16 are attached to the cylinder head 12.

  The direct injection injector 67 is disposed so that its injection port faces the inside of the combustion chamber 19 from the central portion of the ceiling surface of the combustion chamber 19. The direct injection injector 67 directly injects an amount of fuel into the combustion chamber 19 at an injection timing according to the operating state of the engine 1 and according to the operating state of the engine 1. In this example, the direct injection injector 67 is a multi-injector type injector having a plurality of injection holes, although detailed illustration is omitted. Thereby, the direct injection injector 67 injects the fuel so that the fuel spray spreads radially. At the timing when the piston 14 is positioned near the compression top dead center, the fuel spray injected radially from the central portion of the combustion chamber 19 flows along the wall surface of the cavity 141 formed on the top surface of the piston. As a result, it reaches around the spark plug 25 described later. It can be paraphrased that the cavity 141 is formed so that the fuel spray injected at the timing when the piston 14 is located near the compression top dead center is contained therein. The combination of the multi-hole injector 67 and the cavity 141 is advantageous in that it shortens the time until the fuel spray reaches around the spark plug 25 after fuel injection and shortens the combustion period. is there. In addition, the direct injection injector 67 is not limited to a multi-injection type injector, and an external valve-opening type injector may be adopted as the direct injection injector.

  As shown in FIG. 1, the port injector 68 is arranged facing an independent passage communicating with the intake port 16 to the intake port 16 and injects fuel into the intake port 16. One port injector 68 may be provided for each cylinder 18, and if two intake ports 16 are provided for one cylinder 18, the port injector 68 is provided for each of the two intake ports 16. Also good. The format of the port injector 68 is not limited to a specific format, and various types of injectors can be appropriately employed.

  The fuel tank (not shown) and the direct injection injector 67 are connected to each other by a high-pressure fuel supply path. A high-pressure fuel supply system 62 that includes a high-pressure fuel pump 63 and a common rail 64 and supplies fuel to the direct injection injector 67 at a relatively high fuel pressure is interposed on the high-pressure fuel supply path. The high-pressure fuel pump 63 pumps fuel from the fuel tank to the common rail 64, and the common rail 64 stores the pumped fuel at a high fuel pressure. When the direct injection injector 67 is opened, the fuel stored in the common rail 64 is injected from the injection port of the direct injection injector 67. Here, although not shown, the high-pressure fuel pump 63 is a plunger type pump, and is driven by the engine 1 by being connected to a timing belt between a crankshaft and a camshaft, for example. The high-pressure fuel supply system 62 configured to include this engine-driven pump makes it possible to supply fuel with a high fuel pressure of 40 MPa or more to the direct injection injector 67. The pressure of the fuel supplied to the direct injection injector 67 is changed according to the operating state of the engine 1. The high-pressure fuel supply system 62 is not limited to this.

  Similarly, the fuel tank (not shown) and the port injector 68 are connected to each other by a low-pressure fuel supply path. On this low pressure fuel supply path, a low pressure fuel supply system 66 for supplying fuel with a relatively low fuel pressure to the port injector 68 is interposed. Although not shown in detail, the low-pressure fuel supply system 66 includes an electric or engine-driven low-pressure fuel pump and a regulator, and is configured to supply a predetermined pressure of fuel to each port injector 68. . Since the port injector 68 injects fuel into the intake port, the pressure of the fuel supplied by the low pressure fuel supply system 66 is set lower than the pressure of the fuel supplied by the high pressure fuel supply system 62. In this example, two types of injectors, a direct injection injector 67 and a port injector 68, are provided. However, the port injector 68 can be omitted.

  A spark plug 25 that ignites the air-fuel mixture in the combustion chamber 19 is also attached to the cylinder head 12. The spark plug 25 is disposed through the cylinder head 12 so as to extend obliquely downward from the exhaust side of the engine 1. The tip of the spark plug 25 is disposed facing the combustion chamber 19 in the vicinity of the tip of the direct injection injector 67 disposed at the center of the combustion chamber 19.

  An intake passage 30 is connected to one side of the engine 1 so as to communicate with the intake port 16 of each cylinder 18. On the other hand, an exhaust passage 40 for discharging burned gas (exhaust gas) from the combustion chamber 19 of each cylinder 18 is connected to the other side of the engine 1. The intake passage 30 and the exhaust passage 40 are provided with a turbocharger 61 that supercharges intake air, as will be described in detail later.

  An air cleaner 31 that filters intake air is disposed at the upstream end of the intake passage 30. A surge tank 33 is disposed near the downstream end of the intake passage 30. The intake passage 30 downstream of the surge tank 33 is an independent passage branched for each cylinder 18, and the downstream end of each independent passage is connected to the intake port 16 of each cylinder 18.

  Between the air cleaner 31 and the surge tank 33 in the intake passage 30, the compressor 611 of the turbocharger 61, the intercooler 34 that cools the air compressed by the compressor 611, and the amount of intake air to each cylinder 18 A throttle valve 36 for adjustment is provided.

  The upstream portion of the exhaust passage 40 is constituted by an exhaust manifold having an independent passage branched for each cylinder 18 and connected to the outer end of the exhaust port 17 and a collecting portion where the independent passages gather. . A turbine 612 of the turbocharger 61 is arranged on the downstream side of the exhaust manifold in the exhaust passage 40, and the exhaust gas purification device for purifying harmful components in the exhaust gas is directly installed downstream of the turbine 612. A catalyst 41 and an underfoot catalyst 42 are connected to each other. Each of the direct catalyst 41 and the underfoot catalyst 42 includes a cylindrical case and, for example, a three-way catalyst disposed in a flow path in the case. As will be described later, in this engine system, the generation of RawNOx is suppressed by setting the working gas fuel ratio G / F ≧ 30 or the air fuel ratio A / F ≧ 30 in at least a part of the operation region. Yes. As a result, this engine system is configured as a system that does not require a NOx purification catalyst.

  A portion between the surge tank 33 and the throttle valve 36 in the intake passage 30 and a portion upstream of the turbine 612 in the exhaust passage 40 are an EGR passage 50 for returning a part of the exhaust gas to the intake passage 30. Connected through. The EGR passage 50 includes a main passage 51 in which an EGR cooler 52 for cooling the exhaust gas with engine coolant is disposed, and an EGR cooler bypass passage 53 for bypassing the EGR cooler 52. ing. The main passage 51 is provided with an EGR valve 511 for adjusting the amount of exhaust gas recirculated to the intake passage 30, and the EGR cooler bypass passage 53 has a flow rate of exhaust gas flowing through the EGR cooler bypass passage 53. An EGR cooler bypass valve 531 for adjustment is provided. The EGR system including the EGR passage 50 that communicates the downstream side of the intake passage 30 with respect to the compressor 611 and the upstream side of the exhaust passage 40 with respect to the turbine 612 may be referred to as a high-pressure EGR system hereinafter.

  The engine 1 also includes a low pressure EGR system separately from the high pressure EGR system. The low pressure EGR system is an L / P (Low Pressure) EGR that connects a portion downstream of the underfoot catalyst 42 in the exhaust passage 40 and a portion upstream of the compressor 611 of the turbocharger 61 in the intake passage 30. A passage 54 and an L / P EGR valve 541 that is interposed on the L / P EGR passage 54 and adjusts the recirculation amount of the exhaust gas to the intake passage 30 are configured.

  The turbocharger 61 includes a compressor 611 disposed in the intake passage 30 and a turbine 612 disposed in the exhaust passage 40. The compressor 611 is disposed between the air cleaner 31 and the intercooler 34 in the intake passage 30. On the other hand, the turbine 612 is disposed between the exhaust manifold and the direct catalyst 41 in the exhaust passage 40. The turbine 612 is rotated by the exhaust gas flow, and the compressor 611 connected to the turbine 612 is operated by the rotation of the turbine 612.

  An exhaust bypass passage 43 that bypasses the turbine 612 is connected to the exhaust passage 40. The exhaust bypass passage 43 is provided with a waste gate valve 431 for adjusting the amount of exhaust flowing into the exhaust bypass passage 43.

  The engine 1 configured as described above is controlled by a powertrain control module (hereinafter referred to as PCM) 10. The PCM 10 includes a microprocessor having a CPU, a memory, a counter timer group, an interface, and a path connecting these units. This PCM 10 constitutes a controller.

As shown in FIGS. 1 and 2, detection signals from various sensors SW <b> 1 to SW <b> 16 are input to the PCM 10. The various sensors include the following sensors. That is, the air flow sensor SW1 that detects the flow rate of fresh air, the intake air temperature sensor SW2 that detects the temperature of fresh air, the downstream side of the intercooler 34, and the air cooler 31 after passing through the intercooler 34 The EGR gas temperature sensor SW4, which detects the temperature of the external EGR gas, is disposed in the vicinity of the connection portion of the EGR passage 50 with the intake passage 30 and detects the temperature of the external EGR gas. An intake port temperature sensor SW5 that detects the temperature of the intake air just before flowing into the cylinder 18 and an in-cylinder pressure sensor SW6 that is mounted on the cylinder head 12 and detects the pressure in the cylinder 18, and EGR in the exhaust passage 40. Exhaust temperature that is disposed near the connection portion of the passage 50 and detects the exhaust temperature and the exhaust pressure, respectively. Capacitors SW7 and exhaust pressure sensor SW8, disposed between the linear O ₂ sensor SW9, direct catalyst 41 and underfoot catalyst 42 and is disposed on the upstream side, for detecting the oxygen concentration in the exhaust gas of the direct catalyst 41 In addition, a lambda O ₂ sensor SW10 that detects the oxygen concentration in the exhaust, a water temperature sensor SW11 that detects the temperature of the engine coolant, a crank angle sensor SW12 that detects the rotation angle of the crankshaft 15, and an accelerator pedal (not shown) Accelerator opening sensor SW13 for detecting the accelerator opening corresponding to the manipulated variable, cam angle sensors SW14 and SW15 on the intake and exhaust sides, and common rail 64 of high-pressure fuel supply system 62, and direct injection injector 67 This is a fuel pressure sensor SW16 for detecting the fuel pressure supplied to the fuel.

  The PCM 10 performs various calculations based on these detection signals to determine the state of the engine 1 and the vehicle, and in response to this, the direct injection injector 67, the port injector 68, the spark plug 25, the VVT 72 on the intake valve side, To CVVL 73, exhaust valve side VVL 71, high pressure fuel supply system 62, and actuators of various valves (throttle valve 36, EGR valve 511, EGR cooler bypass valve 531, L / P EGR valve 541, waste gate valve 431) Output a control signal. Thus, the PCM 10 operates the engine 1.

  FIG. 3 shows an example of the operation region of the engine 1. This operation region indicates the operation region after the engine is warmed up. This engine 1 is a part of the first and second operation regions in order to achieve both suppression of raw NOx generation and low fuel consumption. In the region, the lean burn engine has a working gas fuel ratio G / F set to 30 or higher, or an air fuel ratio A / F set to 30 or higher. On the other hand, as will be described in detail later, in the third region of low speed and high load, the air fuel ratio is set to the stoichiometric air fuel ratio.

  Further, for the purpose of improving fuel efficiency and exhaust emission, the engine 1 does not perform ignition by the spark plug 25 in a part of the operating region, specifically, the first region after the engine 1 is warmed up. In addition, it is configured to perform compression ignition combustion in which combustion is performed by compression self-ignition. However, in the compression ignition combustion, when the load of the engine 1 is high, the combustion becomes too steep and causes problems such as combustion noise. Therefore, in the engine 1, spark ignition combustion using the spark plug 25 is performed in the second and third regions where the engine load is relatively high. In the second region, compression ignition combustion may be performed in a region lower than the predetermined load. In the following, a mode in which compression ignition combustion is performed may be referred to as a CI (Compression Ignition) mode, and a mode in which spark ignition combustion is performed may be referred to as an SI (Spark Ignition) mode.

  As shown in FIG. 3, the first region is a region where the engine load is relatively low. To be exact, on the low speed side where the engine speed is equal to or less than the predetermined speed N1 (however, the speed N1 corresponds to approximately the middle of the engine speed range), the first region is the high load side This is an area from low load to approximately medium load, excluding the area corresponding to 3 areas. However, in the medium speed region, a high load region is also included in the first region. On the other hand, on the high speed side where the engine speed is higher than the predetermined engine speed N1, the first area is an area excluding the second area where the area increases as the engine speed increases, and in the medium speed area, the load is low. To the high load, and in the high speed range, it corresponds to the low load. The first area is set to the CI mode as described above. In the CI mode, the direct injection injector 67 or the port injector 68 basically injects fuel at a relatively early timing, for example, during an intake stroke or a compression stroke, thereby forming a relatively homogeneous lean mixture. The mixture is subjected to compression self-ignition near the compression top dead center. In the first region, SI combustion may be performed in the high load region.

  In the first region that is in the CI mode, in a region where the load is relatively low, internal EGR control is used together from the viewpoint of stabilizing the compression ignition combustion by increasing the in-cylinder temperature. In other words, the exhaust valve 22 is opened twice during the intake stroke under the control of the VVL 71, whereby the internal EGR gas is introduced into the cylinder 18. On the other hand, in the relatively high load region in the first region, as the engine load increases, the in-cylinder temperature increases and the compression ignition combustion becomes steep, so the internal EGR control is stopped and the high pressure EGR system is stopped. Alternatively, the control is switched to the external EGR control in which the relatively low temperature EGR gas is introduced into the cylinder 18 by the low pressure EGR system. In some areas, for example, in the middle load area, the internal EGR control and the external EGR control may be used in combination. In some areas, both the internal EGR control and the external EGR control may be stopped.

  Thus, in the first region, the supercharging of the intake air by the turbocharger 61 and the internal EGR control and / or the external EGR control are performed to introduce the burned gas into the cylinder 18. Is set to 30 or more. Further, when both the internal EGR control and the external EGR control are stopped, A / F is set to 30 or more. Such an ultra-lean air-fuel mixture is effective in suppressing the production of RawNOx and is also advantageous in improving fuel consumption.

  As shown in FIG. 3, the second region is a region where the load is higher than that of the first region on the high speed side where the engine speed is higher than N1, and as described above, the second region has a higher engine speed. The higher the value, the larger the load direction. The second region includes a fully open region on the high speed side. In the second region, since the fuel injection amount increases because the load is relatively high, in order to achieve G / F ≧ 30 or A / F ≧ 30, the total gas amount introduced into the cylinder must be increased. Don't be.

  Here, FIG. 4 is an example of a compressor map showing the efficiency of the compressor with the vertical axis representing the compression ratio and the horizontal axis representing the flow rate, and FIG. 5 illustrates the relationship between the engine speed and the compressor efficiency of the turbocharger 61. 6 is a diagram showing an example of the relationship between the engine speed and the mass flow rate passing through the compressor. FIG. 7 is a diagram showing the engine speed and the total number of cylinders introduced into the cylinder. It is a figure which shows an example of the relationship with a gas mass flow rate. In these drawings, the solid line indicates the supercharging limit when the external EGR control by the high pressure EGR system is stopped and A / F = 30, and the broken line indicates the G / F by executing the external EGR control by the high pressure EGR system. The supercharging limit is shown when = 30.

  First, according to FIG. 5, when the engine speed is relatively high, the compressor efficiency is lower when the external EGR control is stopped than when the external EGR control is executed. This is because in order to achieve A / F ≧ 30 when the external EGR control is stopped, the flow rate passing through the compressor 611 must be increased. As shown in FIG. This is because the turbocharger 61 will be operated. In FIG. 4, “3000”, “4000”, and “5000” indicate the engine speed, and particularly in the vicinity of 4000 to 5000 rpm, the compressor efficiency is deteriorated. In order to improve the compressor efficiency, it is conceivable to reduce the passage flow rate of the compressor 611 as indicated by a white arrow in FIG.

  In this regard, executing the external EGR control by the high-pressure EGR system stops the EGR control, particularly on the high speed side, as the burned gas is introduced downstream of the compressor 611 as shown in FIG. This makes it possible to reduce the flow rate of the compressor 611 as compared to when it is present. Thus, by executing the external EGR control by the high pressure EGR system and changing the operating condition of the compressor 611, the compressor efficiency when the engine speed is relatively high as shown in FIGS. It becomes possible to improve. As shown in FIG. 7, the total gas mass flow rate introduced into the cylinder is substantially the same when the external EGR control by the high pressure EGR system is executed and when the external EGR control is stopped. In any case, G / F ≧ 30 or A / F ≧ 30 is achieved.

  As shown in FIG. 5, when the engine speed is relatively low, the compressor efficiency is higher when the external EGR control is stopped than when the external EGR control is executed.

  Thus, increasing the compressor efficiency in the second region, which is a high speed and high load region, is advantageous in reducing the required turbine power. This makes it possible to reduce the inlet pressure of the turbine 612, in other words, the exhaust pressure of the engine 1, and reduce the pumping loss. FIG. 8 shows an example of the relationship between the engine speed and the pumping loss of the engine 1. In FIG. 8, the solid line indicates that the external EGR control by the high pressure EGR system is stopped and A / F = 30. The pumping loss at the supercharging limit point is shown, and the broken line shows the pumping loss at the supercharging limit point when G / F = 30 by executing external EGR control by the high pressure EGR system. According to this, when the engine speed is relatively high, when the external EGR control is executed, the pumping loss is reduced compared to when the external EGR control is stopped.

  Therefore, in the second region, which is a high-speed and high-load region, the compressor efficiency is increased by executing external EGR control by the high-pressure EGR system, maintaining a super lean mixture with G / F ≧ 30 and reducing the pumping loss of the engine. Both. This is advantageous in ensuring high torque and improving fuel efficiency as described above, as well as in suppressing generation of RawNOx even in the second region where the load is relatively high.

  Further, in the second region where the engine load is relatively high, the compression ignition combustion becomes steep combustion. Therefore, in the second region, at least the region on the high load side is set to the SI mode, unlike the first region. In the SI mode, basically, for example, during the intake stroke or compression stroke, the direct injection injector 67 injects fuel into the cylinder 18 to form a homogeneous or stratified mixture, and in the vicinity of the compression top dead center. The mixture is ignited by performing ignition. Note that the low load side region in the second region may be in SI mode or CI mode.

  As shown in FIG. 3, the third region is a region having a higher load than the first region on the low speed side where the engine speed is N1 or less. Since the third region is on the low speed side, the exhaust energy is low in the first place, and in the third region including the fully open region, a turbo that satisfies G / F ≧ 30 and A / F ≧ 30 while ensuring a desired high torque. The supercharging capability of the supercharger 61 cannot be obtained. Therefore, in the third region, the air fuel ratio is set to the theoretical air fuel ratio (λ = 1). In the third region, the SI mode may be set due to the restriction of combustion noise, but the third region may be set in the CI mode.

  In the third region, an external EGR gas is introduced by a high pressure EGR system or a low pressure EGR system in order to reduce pumping loss and excessive engine torque. The execution of the external EGR control is also advantageous for avoiding knocking in the third region of low speed and high load where knocking is relatively likely to occur.

  Thus, in this lean burn engine, in the high speed region where the engine speed is higher than N1, in the second region on the high load side, the burned gas is transferred into the cylinder 18 by executing the external EGR control by the high pressure EGR system. In order to increase the compressor efficiency of the turbocharger 61, it is possible to set G / F to 30 or more in the second region including the fully open load. That is, both the raw NOx generation suppression and the desired high torque can be ensured. Further, since the pumping loss of the engine 1 is reduced by increasing the compressor efficiency, it is advantageous for improving the fuel consumption.

  In addition, for example, in addition to the turbocharger 61, an auxiliary supercharger such as an electric boost is provided, and in the third region where the turbocharger 61 is limited to the theoretical air-fuel ratio by the supercharge limit, the G An ultra lean operation with / F ≧ 30 or A / F ≧ 30 may be performed. Instead of providing an auxiliary supercharger such as an electric boost, an electric turbocharger in which an electric motor is attached to the shaft of the turbocharger 61 may be adopted.

1 Engine (Engine body)
10 PCM (controller)
18 cylinder 50 EGR passage 531 EGR valve (EGR means)
61 Turbocharger 611 Turbine 612 Compressor

Claims (3)

An engine body configured to have an operation region that is operated with an air-fuel mixture leaner than a stoichiometric air-fuel ratio;
A turbocharger including a compressor disposed on an intake side of the engine body and a turbine disposed on an exhaust side, and configured to supercharge a gas introduced into a cylinder of the engine body;
EGR means configured to introduce burned gas into the cylinder;
A controller configured to control operation of the engine body ,
The controller is when the engine body is at least after warming up,
When the rotational speed of the engine body exceeds a predetermined rotational speed and the engine load is in a low load region lower than the predetermined load, supercharging by the turbocharger is performed and the working gas fuel ratio G / F is 30 or more. Or, the air fuel ratio A / F is set to 30 or more,
When the rotational speed of the engine body exceeds the predetermined rotational speed and the engine load is in a high load region equal to or higher than the predetermined load, the upstream side of the turbine on the exhaust side and the downstream side of the compressor on the intake side While recirculating burnt gas to the intake side through high-pressure EGR passages connected to each other, supercharging by the turbocharger is performed and the G / F is set to 30 or more ,
When the rotational speed of the engine body is equal to or lower than the predetermined rotational speed and the engine load is in a predetermined high load region, the burned gas is introduced into the cylinder by the EGR means, and the air fuel ratio A / A lean burn engine with a supercharger that makes F the theoretical air-fuel ratio . The lean burn engine with a supercharger according to claim 1,
The controller is a lean burn engine with a supercharger that sets the G / F to 30 or more while recirculating burnt gas to the intake side through the EGR passage even when the engine load is a full load. In the lean burn engine with a supercharger according to claim 1 or 2,
The controller is a lean burn engine with a supercharger that performs compression ignition combustion at least in the low load region.