JP5998752B2 - Spark ignition direct injection engine - Google Patents

Description

  The technology disclosed herein relates to a spark ignition direct injection engine.

  In Patent Document 1, when the engine is operating in a low-speed partial load region, a large amount of EGR gas (exhaust gas) is introduced into the cylinder to reduce pump loss and lower combustion temperature. Describes a spark ignition direct injection engine that reduces cooling loss and improves exhaust emission performance.

JP 11-294219 A

  As described above, introduction of a large amount of EGR gas into the cylinder is advantageous for reducing loss and improving exhaust emission performance, while lowering combustion stability.

  From the viewpoint of improving practical fuel efficiency, there is a strong demand to reduce the loss as much as possible in the partial load region in the low speed region, but this is also caused by a decrease in gas flow in the cylinder when the engine operating state is in the low speed region. As a result, the combustion stability tends to decrease. Therefore, the amount of EGR that can be introduced into the cylinder is limited (that is, the upper limit of the EGR rate is lowered).

  The technology disclosed herein has been made in view of the above points, and the object of the technology is to enable introduction of as much EGR gas as possible into a cylinder in a partial load region in a low speed region. The purpose is to reduce loss and improve exhaust emission performance.

  The technology disclosed herein relates to a spark ignition direct injection engine, and includes an engine body configured to have a cylinder, a fuel injection valve configured to inject fuel into the cylinder, and the fuel injection valve. A fuel pressure setting mechanism configured to set the pressure of the fuel to be injected, an ignition plug disposed facing the cylinder and configured to ignite an air-fuel mixture in the cylinder, and an exhaust The engine body is operated by controlling exhaust recirculation means configured to introduce gas into the cylinder, and at least the fuel injection valve, the fuel pressure setting mechanism, the spark plug, and the exhaust recirculation means. And a controller configured as described above.

The controller introduces the exhaust gas into the cylinder by the exhaust gas recirculation means when the operating state of the engine body is in a predetermined low load partial load region, and the fuel pressure setting mechanism The fuel injection valve is driven so that the pressure is set to a high fuel pressure of 30 MPa or more, the fuel injection is performed at least within the period from the late stage of the compression stroke to the early stage of the expansion stroke, and after the fuel injection is finished and the fuel injection The controller executes the retarded injection combustion such that the spark plug is driven within 3 milliseconds from the start of the ignition to spark-ignite the air-fuel mixture in the cylinder. The exhaust gas is introduced into the cylinder by the exhaust gas recirculation means when the engine is in a partial load region that is faster than the region, and from the latter half of the intake stroke to the middle of the compression stroke It drives the fuel injection valve to perform the fuel injection in the period of, and performs spark ignition to the mixture gas in the cylinder near the compression top dead center by driving the ignition plug.

  Here, the “predetermined low speed region” may be, for example, a region on the low speed side when the rotational speed region of the engine body is divided into a low speed and a high speed. It is good also as a low-speed area | region at the time of dividing into three high speeds, or a low-speed and medium-speed area | region.

  The “partial load area” may be an area excluding the fully open load and the fully open load area including the vicinity thereof, for example, and the load area of the engine main body is divided into three areas of low load, medium load and high load. In this case, it may be a low load to medium load region.

  Furthermore, “the latter stage of the compression stroke” may be the latter stage when the compression stroke is divided into three periods of the initial stage, the middle stage, and the latter stage. Similarly, the “first stage of the expansion stroke” is the initial stage, the middle stage, And it is good also as the initial stage when it divides into three periods of the latter term.

  According to the above configuration, when the operating state of the engine body is in the partial load region of the predetermined low speed region, the fuel is injected at a high fuel pressure of 30 MPa or more and at least within the period from the late stage of the compression stroke to the initial stage of the expansion stroke. . By injecting fuel into the cylinder at such a relatively late timing and at a high fuel pressure, the fuel is atomized and the turbulence of the gas in the cylinder near the compression top dead center becomes stronger, Disturbance energy increases. As a result, a combustible air-fuel mixture is quickly formed in the cylinder near the compression top dead center.

  If a combustible mixture is quickly formed in this way, the spark plug is driven within 3 milliseconds from the start of fuel injection, and spark ignition is performed on the combustible mixture. This makes it possible to start combustion in a state where the turbulent energy is strong before the turbulent energy in the cylinder is attenuated, so that the combustion stability is improved. This makes it possible to introduce a large amount of exhaust gas (that is, EGR gas) through the exhaust gas recirculation means in a low speed region where the gas flow in the cylinder is relatively weak. That is, the EGR rate in the cylinder is further increased, which is advantageous for reduction of pump loss in the partial load region, and is also advantageous for reduction of cooling loss and improvement of exhaust emission performance by lowering the combustion temperature.

  The spark ignition direct injection engine disclosed herein also includes an engine body configured to have a cylinder, a fuel injection valve configured to inject fuel into the cylinder, and the fuel injection valve injects the fuel injection valve. A fuel pressure setting mechanism configured to set the pressure of the fuel, a spark plug disposed to face the cylinder and configured to ignite an air-fuel mixture in the cylinder, and the exhaust gas to An exhaust gas recirculation unit configured to be introduced into the cylinder, and at least the fuel injection valve, the fuel pressure setting mechanism, the spark plug, and the exhaust gas recirculation unit are configured to operate the engine body. And a controller.

When the operating state of the engine body is in a partial load region in a predetermined low speed region, the controller increases the fuel pressure to a high fuel pressure of 30 MPa or more by the fuel pressure setting mechanism, and at least the expansion stroke from the latter stage of the compression stroke. The fuel injection valve is driven to perform fuel injection within a period up to the initial stage, and the excess air ratio λ of the air-fuel mixture is 1.1 or less, and EGR is the ratio of the exhaust gas to the gas in the cylinder The exhaust gas recirculation means introduces the exhaust gas into the cylinder so that the rate becomes equal to or higher than a predetermined rate, and after the fuel injection is finished, the spark plug is driven to ignite the air-fuel mixture in the cylinder. performed, perform the retarded injection combustion as the controller, when the operating state of the engine body is in the partial load region of the high-speed region than the low-speed region, the The exhaust gas is introduced into the cylinder by an air recirculation means, the fuel injection valve is driven so as to inject fuel within a period from the late stage of the intake stroke to the middle stage of the compression stroke, and near the compression top dead center The spark plug is driven to ignite the air-fuel mixture in the cylinder .

  According to this configuration, similarly to the above configuration, when the operating state of the engine body is in the partial load region of the predetermined low speed region, the fuel pressure is 30 MPa or more and at least within the period from the late stage of the compression stroke to the initial stage of the expansion stroke Inject fuel. As a result, a combustible mixture is rapidly formed. At this time, the fuel injection valve injects fuel into the cylinder so that the excess air ratio λ of the air-fuel mixture is 1.1 or less, that is, approximately the stoichiometric air-fuel ratio, and the EGR rate is greater than or equal to a predetermined value by the exhaust gas recirculation means. Then, exhaust gas (EGR gas) is introduced into the cylinder. The EGR rate may be set as high as possible under the condition that the excess air ratio λ of the air-fuel mixture is 1.1 or less.

  Then, after the fuel injection is finished, the spark plug is driven to ignite the air-fuel mixture in the cylinder. As described above, if a strong turbulent energy generated by fuel injection at a high fuel pressure is to be used, it is desirable to perform spark ignition immediately after the combustible air-fuel mixture is formed. Combustion stability is ensured while the rate is set high. As a result, the pump loss and the cooling loss can be reduced and the exhaust emission performance can be improved as in the above-described configuration.

  The controller performs the retarded injection combustion when the operating state of the engine main body is in a region excluding the fully open load region in the predetermined low speed region, and also supplies the cooled exhaust gas through the exhaust gas introduction means. It may be introduced into the cylinder.

  That is, it is preferable to stop the introduction of exhaust gas through the exhaust gas recirculation means when the operating state of the engine body is in the fully open load region. In this way, in the fully open load region, the fully open torque can be improved by introducing as much fresh air as possible into the cylinder.

  Further, the exhaust gas recirculation means described above may introduce either so-called external EGR gas or internal EGR gas into the cylinder, but when performing retarded injection combustion in a region excluding the fully open load region, cooling is performed. It is preferable to introduce the exhaust gas into the cylinder. As a result, the temperature in the cylinder is lowered to avoid abnormal combustion such as pre-ignition and knocking, and the torque can be improved and the fuel efficiency can be improved.

  The fuel injection valve may be configured as a multi-hole type.

  By using the multi-injection type fuel injection valve, it becomes possible to quickly form a homogeneous air-fuel mixture in the cylinder near the compression top dead center in combination with increasing the fuel pressure described above. . This is advantageous in further improving the combustion stability while introducing a large amount of EGR gas into the cylinder.

  The piston inserted in the cylinder so as to be capable of reciprocating movement has a concave cavity formed in the crown surface, and the controller performs fuel injection by the fuel injection valve when performing the retarded injection combustion. The start time may be set to a timing at which the fuel is injected into the cavity.

  By injecting the fuel into the narrow space in the cavity with a high fuel pressure, the gas flow in the cavity is strengthened. As a result, it is possible to further improve the combustion stability in an in-cylinder environment with a high EGR rate.

  The controller may set the maximum of the EGR rate to 40% or more when executing the retarded injection combustion.

  In other words, the execution of retarded injection combustion described above makes it possible to achieve a high EGR rate of 40% or more in the partial load region in the low speed region, effectively reducing pump loss and cooling loss, and improving exhaust emission performance. Is done.

  The fuel injection valve may be set such that a direction of fuel injection is deviated from the spark plug position.

  This configuration is advantageous for forming a homogeneous air-fuel mixture, and thus for improving combustion stability.

  As described above, this spark ignition direct injection engine has a high fuel pressure of 30 MPa or more, and injects fuel into the cylinder at a relatively late time from the late compression stroke to the early expansion stroke. Since the stability of combustion associated with spark ignition can be improved, it is possible to introduce as much EGR gas as possible into the cylinder when in the partial load region in the low speed region, and to reduce pump loss and cooling loss. Reduction and improvement of exhaust emission performance can be achieved.

It is the schematic which shows the structure of a spark ignition direct injection engine. It is a block diagram concerning control of a spark ignition direct injection engine. It is sectional drawing which expands and shows a combustion chamber. It is a figure which illustrates the operating area of an engine. (A) An example of fuel injection timing and ignition timing when performing high pressure retarded injection, and an example of the heat generation rate due to combustion associated therewith, (b) An example of fuel injection timing and ignition timing when performing intake stroke injection, It is an illustration of the heat release rate by the combustion accompanying it. It is a figure which compares the state of SI combustion by a high pressure retarded injection, and the state of conventional SI combustion.

  Hereinafter, an embodiment of a spark ignition direct injection engine will be described with reference to 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 includes a cylinder block 11 provided with a plurality of cylinders 18 (only one cylinder is shown in FIG. 1, but four cylinders are provided in series, for example), and the cylinder block 11 is arranged on the cylinder block 11. The cylinder head 12 is provided, and an oil pan 13 is provided below the cylinder block 11 and stores lubricating oil. 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 like a reentrant type in a diesel engine is formed on the top surface of the piston 14 as shown in an enlarged view in FIG. The cavity 141 is opposed to an 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 15 or more for the purpose of improving the theoretical thermal efficiency. In addition, what is necessary is just to set a geometric compression ratio suitably in the range of about 15-20. However, the geometric compression ratio of the engine 1 may be set to less than 15.

  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 detailed illustration of the configuration of the VVL 71 is omitted, two types of cams having different cam profiles, a first cam having one cam peak and a second cam having two cam peaks, and the 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. Further, the execution of the internal EGR is not realized only by opening the exhaust gas 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. The VVL 71 can also be omitted.

  As shown in FIG. 2, the exhaust side valve system having the VVL 71 has a variable phase mechanism (hereinafter referred to as VVT (hereinafter referred to as VVT)) that can change the rotational phase of the intake camshaft with respect to the crankshaft 15 as shown in FIG. 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. By the VVT 72 and the CVVL 73, the intake valve 21 can change its valve opening timing, valve closing timing, and lift amount.

  In addition, an injector 67 that directly injects fuel into the cylinder 18 is attached to the cylinder head 12 for each cylinder 18. As shown in an enlarged view in FIG. 3, the injector 67 is disposed so that its nozzle hole faces the inside of the combustion chamber 19 from the central portion of the ceiling surface of the combustion chamber 19. The injector 67 directly injects an amount of fuel into the combustion chamber 19 at an injection timing set according to the operating state of the engine 1 and according to the operating state of the engine 1. In this example, the injector 67 is a multi-hole injector having a plurality of nozzle holes, although detailed illustration is omitted. Thus, the injector 67 injects the fuel so that the fuel spray spreads radially downward from the center position of the combustion chamber 19. As indicated by the arrows in FIG. 3, the fuel spray injected radially from the central portion of the combustion chamber 19 at the timing when the piston 14 is located near the compression top dead center is a cavity formed on the top surface of the piston. It flows along the wall surface of 141. That is, the injector 67 is set such that the direction of fuel injection is deviated from the position of a spark plug 25 described later. Moreover, it can be paraphrased that the cavity 141 is formed so that the fuel spray injected at the timing when the piston 14 is positioned near the compression top dead center is contained therein. This combination of the multi-hole injector 67 and the cavity 141 is an advantageous configuration for shortening the mixture formation period and the combustion period after fuel injection. In addition, the injector 67 is not limited to a multi-hole injector, and may be an outside-opening type injector.

  A fuel tank (not shown) and the injector 67 are connected to each other by a fuel supply path. A fuel supply system 62 including a fuel pump 63 and a common rail 64 and capable of supplying fuel to the injector 67 at a relatively high fuel pressure is interposed on the fuel supply path. The fuel pump 63 pumps fuel from the fuel tank to the common rail 64, and the common rail 64 can store the pumped fuel at a relatively high fuel pressure. When the injector 67 is opened, the fuel stored in the common rail 64 is injected from the injection port of the injector 67. Here, although not shown, the fuel pump 63 is a plunger type pump and is driven by the engine 1. The fuel supply system 62 configured to include this engine-driven pump enables the fuel with a high fuel pressure of 30 MPa or more to be supplied to the injector 67. The fuel pressure may be set to about 120 MPa at the maximum. The pressure of the fuel supplied to the injector 67 is changed according to the operating state of the engine 1 as will be described later. The fuel supply system 62 is not limited to this configuration.

  As shown in FIG. 3, a spark plug 25 that ignites the air-fuel mixture in the combustion chamber 19 is attached to the cylinder head 12. In this example, 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. As shown in FIG. 3, the tip of the spark plug 25 is disposed facing the cavity 141 of the piston 14 located at the compression top dead center.

  As shown in FIG. 1, 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.

  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, a water-cooled intercooler / warmer 34 that cools or heats the air and a throttle valve 36 that adjusts the amount of intake air to each cylinder 18 are arranged. It is installed. An intercooler bypass passage 35 that bypasses the intercooler / warmer 34 is also connected to the intake passage 30. The intercooler bypass passage 35 is connected to an intercooler for adjusting the flow rate of air passing through the passage 35. A bypass valve 351 is provided. Adjusting the temperature of fresh air introduced into the cylinder 18 by adjusting the ratio between the passage flow rate of the intercooler bypass passage 35 and the passage flow rate of the intercooler / warmer 34 through the opening degree adjustment of the intercooler bypass valve 351. Is possible. The intercooler / warmer 34 can be omitted, and the intercooler bypass passage 35 can be omitted accordingly.

  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 direct catalyst 41 and an underfoot catalyst 42 are connected downstream of the exhaust manifold in the exhaust passage 40 as exhaust purification devices for purifying harmful components in the exhaust gas. 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.

  A portion between the surge tank 33 and the throttle valve 36 in the intake passage 30 and a portion upstream of the direct catalyst 41 in the exhaust passage 40 are used for returning a part of the exhaust gas to the intake passage 30. They are connected via a passage 50. 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 cooler bypass passage 53 can be omitted.

  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 / warmer 34, and the intercooler / warmer 34 downstream of the air cleaner 31. A second intake air temperature sensor SW3 for detecting the temperature of fresh air after passing through the EGR gas temperature sensor SW4, which 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 is attached to the intake port 16 and detects the temperature of the intake air just before flowing into the cylinder 18, and an in-cylinder pressure sensor SW6 that is attached to the cylinder head 12 and detects the pressure in the cylinder 18. The exhaust passage 40 is disposed in the vicinity of the connection portion of the EGR passage 50, and the exhaust temperature and the exhaust respectively. An exhaust temperature sensor SW7 and an exhaust pressure sensor SW8 for detecting force, and a linear O2 sensor SW9 for detecting the oxygen concentration in the exhaust gas, upstream of the direct catalyst 41, a direct catalyst 41 and an underfoot catalyst 42, The lambda O2 sensor SW10 that detects the oxygen concentration in the exhaust gas, the water temperature sensor SW11 that detects the temperature of the engine coolant, the crank angle sensor SW12 that detects the rotation angle of the crankshaft 15, and the accelerator pedal of the vehicle An accelerator opening sensor SW13 for detecting an accelerator opening degree corresponding to an operation amount (not shown), cam angle sensors SW14 and SW15 on the intake side and exhaust side, and a common rail 64 of the fuel supply system 62, and an injector 67 is a fuel pressure sensor SW16 for detecting the fuel pressure supplied to 67. .

  The PCM 10 performs various calculations based on these detection signals to determine the state of the engine 1 and the vehicle, and accordingly, the injector 67, the spark plug 25, the intake valve side VVT 72 and CVVL 73, and the exhaust valve side Control signals are output to the actuators of the VVL 71, the fuel supply system 62, and various valves (throttle valve 36, intercooler bypass valve 351, EGR valve 511, and EGR cooler bypass valve 531). Thus, the PCM 10 operates the engine 1.

  FIG. 4 shows an example of the operation region of the engine 1. The engine 1 is configured such that the air-fuel ratio of the air-fuel mixture becomes the stoichiometric air-fuel ratio (that is, the excess air ratio λ ≦ 1.1) in the entire operation region, whereby the three-way catalyst is used in the entire operation region. Is possible.

  On the other hand, the engine 1 has a low load when the partial load region (the region excluding the fully open load region of the engine 1 or the load region of the engine 1 is divided into three regions of low load, medium load and high load. In the region including medium load (region below the broken line in FIG. 4), in order to reduce pump loss and cooling loss, and to improve exhaust emission performance, a large amount of EGR gas, more precisely, theoretical As long as the air-fuel ratio λ ≦ 1.1, as much EGR gas as can be introduced into the cylinder 18 is introduced into the cylinder 18. On the other hand, when the load of the engine 1 is in the fully open load region (region above the broken line in FIG. 4), the introduction of EGR gas is stopped in order to introduce fresh air into the cylinder 18 as much as possible. This is effective for improving the full opening torque.

  Here, the EGR gas introduced into the cylinder 18 in the partial load region is basically exhaust gas recirculated to the intake side through the EGR passage 50, and in particular, EGR cooled by passing through the EGR cooler 52. Gas. As a result, it is advantageous for avoiding abnormal combustion such as pre-ignition and knocking by lowering the temperature in the cylinder 18, while reducing the cooling loss and suppressing the generation of RawNOx as the combustion temperature decreases. Figured. In the low-load side region, uncooled EGR gas, for example, external EGR gas that has passed through the EGR cooler bypass passage 53 or internal EGR gas generated by the operation of the VVL 71 on the exhaust side may be introduced into the cylinder 18. .

  Specifically, in the partial load region, while the throttle valve 36 is fully opened, the opening amount of the EGR valve 511 (and the EGR cooler bypass valve 531) is adjusted to adjust the amount of fresh air introduced into the cylinder 18 and the external EGR gas. Adjust the amount. Thus, introduction of a large amount of EGR gas into the cylinder 18 has advantages such as reduction of loss and improvement of exhaust emission performance, but the combustion stability is lowered and the combustion period greatly varies accordingly. There is also a risk of occurrence.

  Therefore, in this engine 1, in the partial load region where a large amount of EGR gas is introduced into the cylinder 18, the reciprocating speed of the piston is relatively low, so that the gas flow in the cylinder 18 becomes weak, In the low speed range where the combustion stability is particularly likely to deteriorate, specifically, in the operating range shown in FIG. With the pressure, as shown in FIG. 5A, fuel is injected into the cylinder 18 at a late timing near the compression top dead center, and spark ignition is performed. This improves the combustion stability in the partial load region in the low speed region where a large amount of EGR gas is introduced into the cylinder 18. This characteristic fuel injection mode is hereinafter referred to as “high pressure retarded injection” or simply “retarded injection”. In the illustrated example, the predetermined rotational speed N is set at a higher speed than an intermediate point in the engine rotational speed region. However, the present invention is not limited to this, and the region where high-pressure retarded injection is performed is, for example, the rotational speed of the engine 1. The region may be a region including a low speed region or a region including a low speed region and a medium speed region when the region is divided into three regions of low speed, medium speed, and high speed.

  Next, high pressure retarded injection will be described with reference to FIG. FIG. 6 shows the heat generation rate (upper diagram) and unsettled in the above-described spark ignition combustion (solid line) by high-pressure retarded injection and conventional SI combustion (broken line) in which fuel injection is performed during the intake stroke. It is a figure which compares the difference of a fuel-air mixture reaction progress (the following figure). The horizontal axis in FIG. 6 is the crank angle. As a precondition for this comparison, the operating state of the engine 1 is a low-speed partial load region, and the amount of fuel to be injected is the same in the case of SI combustion by high pressure retarded injection and conventional SI combustion.

  The purpose of high pressure retarded injection is to inject fuel at a high fuel pressure into the cylinder 18 to strengthen the gas flow in the cylinder 18, particularly in the cavity 141, thereby improving combustion stability. High pressure retarded injection also shortens the reaction time of the unburned mixture, thereby making it possible to avoid abnormal combustion.

  In conventional SI combustion, a predetermined amount of fuel is injected into the cylinder 18 during the intake stroke (see the broken line in the upper diagram of FIG. 6). In the cylinder 18, a relatively homogeneous air-fuel mixture is formed after the fuel injection until the piston 14 reaches the compression top dead center. In this example, ignition is executed at a predetermined timing indicated by a white circle after the compression top dead center, thereby starting combustion. After the start of combustion, as shown by the broken line in the upper diagram of FIG. 6, the combustion ends through a peak of the heat generation rate. The time from the start of fuel injection to the end of combustion corresponds to the reaction possible time of the unburned mixture (hereinafter sometimes simply referred to as reaction possible time). As shown by the broken line in the lower diagram of FIG. The reaction of the fuel mixture gradually proceeds. The dotted line in the figure shows the ignition threshold, which is the reactivity with which the unburned mixture reaches ignition, and the conventional SI combustion has a very low reaction time in combination with the low speed range. In the meantime, the reaction of the unburned mixture continues to progress during that time, so the reactivity of the unburned mixture exceeds the ignition threshold before and after ignition, and abnormal combustion such as premature ignition or knocking occurs. cause.

  As shown in FIG. 6, the reaction time of the unburned air-fuel mixture is a period during which the injector 67 injects fuel ((1) injection period), and the combustible air-fuel mixture around the spark plug 25 after the injection ends. Is the sum of the period until (2) mixture formation period and the period until combustion started by ignition ((3) combustion period), that is, (1) + (2) + (3). The high-pressure retarded injection shortens the injection period, the mixture formation period, and the combustion period, thereby shortening the reaction time.

  First, the high fuel pressure relatively increases the amount of fuel injected from the injector 67 per unit time. For this reason, when the fuel injection amount is constant, the relationship between the fuel pressure and the fuel injection period is generally such that the lower the fuel pressure, the longer the injection period, and the higher the fuel pressure, the shorter the injection period. Therefore, the high pressure retarded injection in which the fuel pressure is set to be significantly higher than the conventional one shortens the injection period.

  Further, the high fuel pressure is advantageous for atomization of the fuel spray injected into the cylinder 18 and makes the flight distance of the fuel spray longer. For this reason, the relationship between the fuel pressure and the fuel evaporation time is generally longer as the fuel pressure is lower, and the fuel evaporation time is longer as the fuel pressure is higher. Further, the time until the fuel spray reaches the fuel pressure and the spark plug 25 is generally longer as the fuel pressure is lower, and the time until the fuel spray is higher as the fuel pressure is higher. The air-fuel mixture formation period is a time obtained by adding the fuel evaporation time and the fuel spray arrival time around the spark plug 25. Therefore, the higher the fuel pressure, the shorter the air-fuel mixture formation period. Therefore, the high pressure retarded injection in which the fuel pressure is set to be significantly higher than the conventional case shortens the mixture formation period as a result of the fuel evaporation time and the fuel spray arrival time around the spark plug 25 being reduced. On the other hand, as shown by white circles in the figure, the conventional intake stroke injection at a low fuel pressure significantly increases the mixture formation period. In the SI mode, the combination of the multi-injector type injector 67 and the cavity 141 shortens the time until fuel spray reaches around the spark plug 25 after fuel injection. Effective for shortening.

  Thus, shortening the injection period and the mixture formation period makes it possible to set the fuel injection timing, more precisely, the injection start timing to a relatively late timing. Therefore, in the high pressure retarded injection, as shown in the upper diagram of FIG. 6, fuel injection is performed within the retard period from the latter stage of the compression stroke to the early stage of the expansion stroke. As the fuel is injected into the cylinder 18 at a high fuel pressure, the turbulence in the cylinder becomes stronger and the turbulence energy in the cylinder 18 increases. This high turbulence energy is a timing at which the fuel injection timing is relatively late. Therefore, it is advantageous for shortening the combustion period.

  That is, when the fuel injection is performed within the retard period, the relationship between the fuel pressure and the turbulent energy in the combustion period is generally lower as the fuel pressure is lower and the turbulent energy is lower as the fuel pressure is higher. Becomes higher. Here, even if fuel is injected into the cylinder 18 at a high fuel pressure, if the injection timing is in the intake stroke, the time until the ignition timing is long, or the cylinder 18 is in the compression stroke after the intake stroke. Due to the compression of the inside, the disturbance in the cylinder 18 is attenuated. As a result, when fuel is injected during the intake stroke, the turbulent energy during the combustion period becomes relatively low regardless of the fuel pressure level.

  In general, the relationship between the turbulent energy and the combustion period in the combustion period is such that the lower the turbulent energy, the longer the combustion period, and the higher the turbulent energy, the shorter the combustion period. Therefore, the relationship between the fuel pressure and the combustion period is such that the lower the fuel pressure, the longer the combustion period, and the higher the fuel pressure, the shorter the combustion period. That is, the high pressure retarded injection shortens the combustion period. In contrast, the conventional intake stroke injection at a low fuel pressure has a longer combustion period. The multi-injector type injector 67 is advantageous for improving the turbulent energy in the cylinder 18 and is effective for shortening the combustion period. In addition, the combination of the multi-injector type injector 67 and the cavity 141 provides fuel. Putting the spray in the cavity 141 is also effective for shortening the combustion period.

  As described above, the high pressure retarded injection shortens the injection period, the mixture formation period, and the combustion period, and as a result, as shown in FIG. 6, the fuel injection start timing SOI to the combustion end timing θend are not changed. It is possible to significantly shorten the reaction time of the fuel mixture as compared with the case of fuel injection during the conventional intake stroke. As a result of shortening this reaction possible time, as shown in the upper diagram of FIG. 6, in the conventional intake stroke injection at a low fuel pressure, as shown by a white circle, the reaction progress of the unburned mixture at the end of combustion is shown. However, when the ignition threshold is exceeded and abnormal combustion occurs, the high-pressure retarded injection suppresses the progress of the reaction of the unburned mixture at the end of combustion, as shown by the black circle, to prevent abnormal combustion. It can be avoided. It should be noted that the ignition timing is set to the same timing in the white circle and the black circle in the upper diagram of FIG.

  By setting the fuel pressure to, for example, 30 MPa or more, the combustion period can be effectively shortened. Moreover, the fuel pressure of 30 MPa or more can effectively shorten the injection period and the mixture formation period, respectively. The fuel pressure is preferably set as appropriate according to the properties of the fuel used, which contains at least gasoline. The upper limit may be 120 MPa as an example.

  Here, the high pressure retarded injection avoids the occurrence of abnormal combustion in the SI mode by devising the form of fuel injection into the cylinder 18. Unlike this, it is conventionally known that the ignition timing is retarded for the purpose of avoiding abnormal combustion. The retarding of the ignition timing suppresses the progress of the reaction by suppressing the increase in the temperature and pressure of the unburned mixture. However, retarding the ignition timing leads to a decrease in thermal efficiency and torque, whereas when performing high-pressure retarded injection, the ignition timing can be advanced by an amount that avoids abnormal combustion by devising the form of fuel injection. Since it is possible, thermal efficiency and torque are improved. That is, the high pressure retarded injection not only avoids abnormal combustion, but also makes it possible to advance the ignition timing by the amount that can be avoided, which is advantageous in improving fuel consumption.

  The high-pressure retarded injection effective for avoiding such abnormal combustion also increases the turbulent energy in the cylinder 18 at the ignition timing, as described above, so that even if a large amount of EGR gas is introduced into the cylinder 18, Improve stability.

  From the viewpoint of using the strong turbulence energy in the cylinder 18 by the high pressure retarded injection, it is preferable to perform the spark ignition promptly after the fuel injection is finished. Specifically, as shown in FIG. It is desirable to ignite the spark within 3 milliseconds from the beginning. By doing so, since spark ignition combustion is started before the strong turbulent energy in the cylinder 18 is attenuated, the combustion period is effectively shortened and the combustion stability is improved.

  Increasing the combustion stability in this way makes it possible to further increase the upper limit of the EGR rate. As a result, in the partial load region in the low speed region, the throttle valve 36 is fully opened and the opening degree of the EGR valve 511 is adjusted under the condition that the air-fuel ratio of the mixture is set to the stoichiometric air-fuel ratio (λ ≦ 1.1). As a result, the EGR rate can be increased to a predetermined value or more, so that the pump loss can be reduced. Further, by introducing the EGR gas cooled by the EGR cooler 52 into the cylinder 18, the temperature in the cylinder 18 is lowered, so that the cooling loss is reduced and the exhaust emission performance is improved.

  Here, by performing the high pressure retarded injection, in the partial load region in the low speed region, the EGR rate that is the ratio of the exhaust gas to the gas in the cylinder 18 can be set to 40% or more at the maximum. This makes it possible to effectively achieve the reduction of the pump loss and the cooling loss and the improvement of the exhaust emission performance described above.

  Further, in the fully open load region in the low speed region, by stopping the introduction of the EGR gas, it is possible to introduce fresh air into the cylinder 18 as much as possible, thereby improving the fully open torque.

  On the other hand, in the operation region of FIG. 4, the gas flow in the cylinder 18 is stronger in the region on the higher speed side than the low speed region where the high pressure retarded injection is performed, compared to the low speed region. Further, the squish flow in the cylinder 18 is also strengthened. Therefore, combustion stability is increased compared to the low speed range. Therefore, as shown in FIG. 4, in the region of the predetermined rotation speed N or more, as shown in FIG. 5B, fuel is injected into the cylinder 18 within the intake stroke period without performing retarded injection. The intake stroke period referred to here is not a period defined based on the piston position, but may be a period during which the intake valve 21 is open based on opening / closing of the intake valve 21. That is, the intake stroke period may deviate from the time when the piston reaches the intake bottom dead center depending on the closing timing of the intake valve 21 changed by the CVVL 73 or the VVT 72. In this region, it can be paraphrased that fuel is injected within the period from the intake stroke to the middle of the compression stroke. The fuel pressure at this time may be set relatively low. By doing so, the mechanical loss of the engine 1 is reduced.

  Performing the intake stroke injection without performing the high pressure retarded injection in the high speed region is advantageous for avoiding abnormal combustion. That is, in the high pressure retarded injection, since the fuel injection timing is set near the compression top dead center, in-cylinder gas not containing fuel, in other words, air having a high specific heat ratio is compressed in the compression stroke. As a result, in the high speed region, the compression end temperature in the cylinder 18 becomes high, and this high compression end temperature causes knocking.

  On the other hand, in the intake stroke injection, the specific heat ratio of the in-cylinder gas (that is, the air-fuel mixture containing fuel) during the compression stroke is lowered, thereby making it possible to keep the compression end temperature low. Since it becomes possible to suppress knocking by lowering the compression end temperature, it is possible to advance the ignition timing. Thus, in the high speed range, by performing the intake stroke injection, it is possible to improve the thermal efficiency while avoiding abnormal combustion.

  Even in the high speed region, in the partial load region below the broken line in the operation region shown in FIG. 4, a large amount of EGR gas is introduced into the cylinder 18 to reduce various losses and improve exhaust emission performance. As shown in the figure, in the fully open load region above the broken line, by stopping the introduction of EGR gas, fresh air can be introduced into the cylinder 18 as much as possible, which is advantageous in improving the fully open torque.

  Thus, in the partial load region in the low speed region, combustion stability is improved by performing high-pressure retarded injection, but performing high-pressure retarded injection is also possible by injecting fuel at a timing near the compression top dead center. This is equivalent to injecting fuel into the cavity 141 formed on the piston crown surface. Thus, by injecting fuel into the narrow space in the cavity 141 with high fuel pressure, the flow of gas in the cavity 141 is strengthened. As a result, combustion stability is further improved in a cylinder environment with a high EGR rate. It can be increased.

  In addition, since the injector 68 is a multi-hole type, it is possible to quickly form a homogeneous air-fuel mixture in the cavity 141, which is advantageous in further improving the combustion stability. Further, as illustrated in FIG. 3, the fuel injection direction of the injector 68 is set so as to deviate from the position of the spark plug 25, which is advantageous for the formation of a homogeneous air-fuel mixture, and hence the combustion stability is improved. To be advantageous.

  The technique disclosed here is not limited to application to the engine configuration described above. For example, fuel may be injected into the intake port 16 through a port injector provided separately in the intake port 16 instead of the injector 67 provided in the cylinder 18 during the intake stroke period.

  The engine 1 is not limited to an in-line 4-cylinder engine, and may be applied to an in-line 3-cylinder, in-line 2-cylinder, in-line 6-cylinder engine, or the like. Further, the present invention can be applied to various engines such as a V type 6 cylinder, a V type 8 cylinder, and a horizontally opposed 4 cylinder.

  The vehicle on which the engine 1 is mounted may be a hybrid vehicle.

  The operation region shown in FIG. 4 is an example, and various operation regions other than this can be provided.

  Further, the high-pressure retarded injection may be divided injection as necessary, and similarly, the intake stroke injection may also be divided injection as necessary. In these divided injections, fuel may be injected in each of the intake stroke and the compression stroke.

1 Engine (Engine body)
10 PCM (controller)
14 Piston 141 Cavity 18 Cylinder 25 Spark plug 50 EGR passage (exhaust gas recirculation means)
51 Main passage (exhaust gas recirculation means)
511 EGR valve (exhaust gas recirculation means)
53 EGR cooler bypass passage (exhaust gas recirculation means)
531 EGR cooler bypass valve (exhaust gas recirculation means)
62 Fuel supply system (fuel pressure setting mechanism)
67 Injector (fuel injection valve)
71 VVL (exhaust gas recirculation means)
72 VVT (exhaust gas recirculation means)
73 CVVL (exhaust gas recirculation means)

Claims (7)

An engine body configured to have cylinders;
A fuel injection valve configured to inject fuel into the cylinder;
A fuel pressure setting mechanism configured to set the pressure of the fuel injected by the fuel injection valve;
A spark plug disposed facing the cylinder and configured to ignite an air-fuel mixture in the cylinder;
Exhaust gas recirculation means configured to introduce exhaust gas into the cylinder;
A controller configured to operate the engine main body by controlling at least the fuel injection valve, the fuel pressure setting mechanism, the spark plug, and the exhaust gas recirculation means;
The controller, when the operating state of the engine body is in a partial load region of a predetermined low speed region,
Introducing the exhaust gas into the cylinder by the exhaust gas recirculation means;
The fuel pressure is set to a high fuel pressure of 30 MPa or more by the fuel pressure setting mechanism,
Driving the fuel injection valve to perform fuel injection at least within a period from the late stage of the compression stroke to the early stage of the expansion stroke; and
The retard injection combustion is performed such that the spark plug is driven to spark-ignite the air-fuel mixture in the cylinder after the fuel injection is finished and within 3 milliseconds from the start of the fuel injection .
The controller, when the operating state of the engine body is in a partial load region of a region faster than the low-speed region,
Introducing the exhaust gas into the cylinder by the exhaust gas recirculation means;
Driving the fuel injection valve to perform fuel injection within a period from the late stage of the intake stroke to the middle stage of the compression stroke; and
A spark ignition direct injection engine that drives the ignition plug near the compression top dead center to ignite the air-fuel mixture in the cylinder .
An engine body configured to have cylinders;
A fuel injection valve configured to inject fuel into the cylinder;
A fuel pressure setting mechanism configured to set the pressure of the fuel injected by the fuel injection valve;
A spark plug disposed facing the cylinder and configured to ignite an air-fuel mixture in the cylinder;
Exhaust gas recirculation means configured to introduce exhaust gas into the cylinder;
A controller configured to operate the engine main body by controlling at least the fuel injection valve, the fuel pressure setting mechanism, the spark plug, and the exhaust gas recirculation means;
The controller, when the operating state of the engine body is in a partial load region of a predetermined low speed region,
The fuel pressure is set to a high fuel pressure of 30 MPa or more by the fuel pressure setting mechanism,
Driving the fuel injection valve so as to perform fuel injection at least within a period from the late stage of the compression stroke to the early stage of the expansion stroke;
The exhaust gas is supplied to the cylinder by the exhaust gas recirculation means so that the excess air ratio λ of the air-fuel mixture is 1.1 or less and the EGR rate, which is the ratio of the exhaust gas to the gas in the cylinder, is a predetermined value or more. Introduced in and
After the fuel injection is finished, the spark plug is driven to perform spark injection on the air-fuel mixture in the cylinder, and the retard injection combustion is performed .
The controller, when the operating state of the engine body is in a partial load region of a region faster than the low-speed region,
Introducing the exhaust gas into the cylinder by the exhaust gas recirculation means;
Driving the fuel injection valve to perform fuel injection within a period from the late stage of the intake stroke to the middle stage of the compression stroke; and
A spark ignition direct injection engine that drives the ignition plug near the compression top dead center to ignite the air-fuel mixture in the cylinder . In the spark ignition direct injection engine according to claim 1 or 2,
The controller performs the retarded injection combustion when the operating state of the engine main body is in a region excluding the fully open load region in the predetermined low speed region, and also supplies the cooled exhaust gas through the exhaust gas introduction means. A spark ignition direct injection engine to be introduced into the cylinder. The spark ignition direct injection engine according to any one of claims 1 to 3,
The fuel injection valve is a spark ignition direct injection engine configured in a multi-hole type. The spark ignition direct injection engine according to any one of claims 1 to 4,
The piston inserted in the cylinder so as to be able to reciprocate is formed with a concave cavity on its crown surface,
The controller is a spark ignition direct injection engine that sets a start timing of fuel injection by the fuel injection valve to a timing at which the fuel is injected into the cavity when the retard injection combustion is executed. In the spark ignition direct injection engine according to any one of claims 1 to 5,
The controller is a spark ignition direct injection engine that sets the maximum of the EGR rate to 40% or more when the retard injection combustion is executed. In the spark ignition direct injection engine according to any one of claims 1 to 6,
The fuel injection valve is a spark ignition type direct injection engine in which the direction of fuel injection is set to be deviated from the position of the spark plug.

Images