JP5907012B2 - Spark ignition direct injection engine - Google Patents

Description

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

  For example, as shown in Patent Document 1, a combustion mode in which an air-fuel mixture in a cylinder is ignited by compression is known as a technique for achieving both improvement in exhaust emission performance and improvement in thermal efficiency. In this compression ignition combustion, it is necessary to raise the temperature in the cylinder to some extent in order to improve ignitability and stability.

  However, in an engine that performs fuel cut when decelerating, the temperature in the cylinder decreases during the fuel cut, and when restarting fuel supply, the temperature in the cylinder decreases to such an extent that it is difficult to perform compression ignition. May end up.

  Therefore, in the engine according to Patent Document 1, at the time of return from the fuel cut, the spark ignition combustion is executed to increase the temperature in the cylinder, and then the combustion shifts to the compression ignition combustion.

JP 2004-316544 A

  However, the situation where the temperature in the cylinder at the time of return from the fuel cut is low is not preferable for spark ignition combustion, and there is room for improvement. If spark ignition combustion cannot be performed properly, the in-cylinder temperature cannot be raised sufficiently, and the subsequent compression ignition combustion may not be stabilized.

  The technology disclosed herein has been made in view of such a point, and an object thereof is to improve the ignitability of spark ignition combustion when returning from a fuel cut.

The technology disclosed herein is provided with an engine body having a cylinder, a fuel injection valve configured to inject fuel into the cylinder, and facing the cylinder. Controlling the spark plug configured to ignite, the exhaust gas recirculation mechanism configured to introduce exhaust gas into the cylinder, and at least the fuel injection valve, the spark plug, and the exhaust gas recirculation mechanism; A spark ignition direct injection engine comprising a controller configured to operate an engine body, an exhaust valve that opens and closes an exhaust port that opens to the cylinder, and a valve mechanism that drives the exhaust valve. The controller performs compression ignition combustion for burning the air-fuel mixture in the cylinder by self-ignition at least when the operating state of the engine body is in a predetermined low load region. When the engine body is decelerated while driving and the accelerator is off, fuel injection from the fuel injection valve is stopped and fuel cut is performed. When the engine speed decreases to a predetermined value, the fuel The fuel injection of the injection valve is configured to resume, and during the fuel cut, the exhaust gas recirculation mechanism is operated to introduce exhaust gas into the cylinder and to restart the fuel injection of the fuel injection valve. Sometimes, the ignition plug is operated while the exhaust gas recirculation mechanism is operated, and the engine body is operated by spark ignition combustion, and then the operation of the engine body is performed by the compression ignition combustion and is operated during the fuel cut. The exhaust gas recirculation mechanism is the exhaust valve and the valve mechanism, and the exhaust valve is opened twice in each of the exhaust stroke and the intake stroke. And it performs come. Here, the “low load region” may be a low load when the operation region is divided into three regions of low load, medium load, and high load.

  According to this configuration, the fuel cut is executed when the engine body is decelerated while the accelerator is off, and the fuel injection is resumed when the engine speed is reduced to a predetermined value. And when restarting fuel injection, after driving | operating by spark ignition combustion, it transfers to the driving | operation by compression ignition combustion.

  In addition, exhaust gas is introduced into the cylinder during fuel cut. Thereby, the temperature drop in the cylinder due to the fuel cut, particularly the temperature drop in the cylinder immediately after the fuel cut can be suppressed. After that, if the fuel cut and the introduction of exhaust gas are continued, the burned gas will not be newly generated, so the ratio of burned gas contained in the mixture in the cylinder will gradually decrease, and the ratio of fresh air Is getting higher. As a result, when the fuel injection is restarted and the spark ignition combustion is executed, the ratio of fresh air in the cylinder is high.

  In this way, it is possible to improve the ignitability of the spark ignition combustion by suppressing the temperature drop in the cylinder immediately after the fuel cut and securing a certain amount of fresh air when the fuel injection is resumed.

  When the ignitability of the spark ignition combustion is improved, the spark ignition combustion can be appropriately executed. Since the exhaust gas recirculation mechanism is also operated when performing spark ignition combustion, burned gas by spark ignition combustion is introduced into the cylinder as EGR gas, and the temperature in the cylinder can be sufficiently increased. As a result, the compression ignition combustion that is performed following the spark ignition combustion can be performed stably.

By adopting the double opening of the exhaust, the heat of the burned gas can be effectively used for maintaining the temperature of the cylinder. In other words, exhaust gas recirculation methods include intake double opening and external EGR. However, since the exhaust port is hotter than the intake port and the external EGR passage, it is possible to reduce the heat that escapes to the outside when the burned gas is once exhausted from the cylinder.

In addition, it is advantageous to open the exhaust twice from the viewpoint of the charging efficiency of the intake air after resuming the fuel injection. That is, for example, when the double opening of the intake air is adopted, the intake port and its surroundings are heated by the burned gas. As a result, intake charging efficiency deteriorates. On the other hand, if the exhaust is opened twice, the intake port is not heated by the burned gas, so that deterioration of the charging efficiency can be avoided.

Further, a plurality of the exhaust gas recirculation mechanisms are provided, and the plurality of exhaust gas recirculation mechanisms are different from each other in a method of introducing exhaust gas into the cylinder, and the controller is configured so that an operating state of the engine body is the predetermined When at least one of the exhaust gas recirculation mechanisms is operated, exhaust gas is introduced into the cylinder by operating the exhaust gas recirculation mechanism, and the exhaust gas recirculation mechanism operated during the fuel cut is It may be the same as the exhaust gas recirculation mechanism operated in the low load region.

According to this configuration, when performing the fuel cut, the exhaust gas is introduced into the cylinder by the exhaust gas recirculation mechanism in the same manner as the predetermined low load region in which the compression ignition combustion is performed. When the fuel cut is performed, the engine load decreases, and the operating state of the engine tends to shift to the predetermined low load region. That is, when the fuel injection is resumed after the fuel cut, the operating state of the engine is often in the predetermined low load region. Therefore, by making the exhaust gas recirculation mechanism operated during the fuel cut the same as the exhaust gas recirculation mechanism operated in the predetermined low load region, the exhaust gas is introduced when shifting from the fuel cut to the fuel injection restart Therefore, the exhaust gas can be introduced smoothly during the transition.

  According to the spark ignition direct injection engine, by introducing exhaust gas into the cylinder during the fuel cut, the temperature drop in the cylinder due to the fuel cut is reduced as much as possible while the fuel injection is resumed in the cylinder. Since a certain amount of fresh air can be secured, the ignitability of spark ignition combustion at the time of resuming fuel injection can be improved.

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 the fuel injection timing when the intake stroke injection is performed in the CI mode, an example of the heat generation rate of the CI combustion associated therewith, (b) an example of the fuel injection timing when the high pressure retarded injection is performed in the CI mode, , An example of the heat generation rate of CI combustion associated therewith, (c) an example of the fuel injection timing and ignition timing when performing high pressure retarded injection in the SI mode, and an example of the heat generation rate of SI combustion associated therewith, (d) SI 4 is an example of fuel injection timing and ignition timing when split injection of intake stroke injection and high pressure retarded injection is performed in the mode, and the heat generation rate of SI combustion associated therewith. It is a figure which compares the state of SI combustion by a high pressure retarded injection, and the state of conventional SI combustion. It is a flowchart which shows the fuel cut process at the time of deceleration. It is a figure which shows the state of each element of the engine before fuel cut, (A) is a fuel injection timing, a pressure change in a cylinder, and a spark ignition timing when performing spark ignition, (B) The lift amount of the intake valve (broken line) and the lift amount of the exhaust valve (solid line), (C) shows the opening of the throttle valve, and (D) shows the components in the cylinder. It is a figure which shows the state of each element of the engine under fuel cut, (A) is a fuel injection timing, a pressure change in a cylinder, and a spark ignition timing when performing spark ignition, (B) The lift amount of the intake valve (broken line) and the lift amount of the exhaust valve (solid line), (C) shows the opening of the throttle valve, and (D) shows the components in the cylinder. It is a figure which shows the state of each element of the engine at the time of fuel-injection restart, (A) is a fuel-injection timing, the pressure change in a cylinder, and a spark-ignition timing in the case of performing spark ignition, (B) is a figure. The lift amount of the intake valve (broken line) and the lift amount of the exhaust valve (solid line), (C) shows the opening of the throttle valve, and (D) shows the components in the cylinder. It is a figure which shows the state of each element of the engine after CI mode transition, (A) is a fuel injection timing, a pressure change in a cylinder, and a spark ignition timing when performing spark ignition, (B) is a figure. The lift amount of the intake valve (broken line) and the lift amount of the exhaust valve (solid line), (C) shows the opening of the throttle valve, and (D) shows the components in the cylinder. It is a figure which shows the state of each element before the fuel cut of the engine which concerns on a reference form , (A) is a fuel-injection timing, a pressure change in a cylinder, and, when performing spark ignition, spark-ignition timing, (B) is the lift amount (broken line) of the intake valve and the lift amount (solid line) of the exhaust valve, (C) is the opening of the throttle valve, (D) is the component in the cylinder, (E) Indicates the opening of the EGR valve, and (F) indicates the opening of the EGR cooler bypass valve. It is a figure which shows the state of each element in the fuel cut of the engine which concerns on a reference form , (A) is a fuel-injection timing, the pressure change in a cylinder, and a spark ignition timing, when performing spark ignition, (B) is the lift amount (broken line) of the intake valve and the lift amount (solid line) of the exhaust valve, (C) is the opening of the throttle valve, (D) is the component in the cylinder, (E) Indicates the opening of the EGR valve, and (F) indicates the opening of the EGR cooler bypass valve. It is a figure which shows the state of each element at the time of the fuel injection restart of the engine which concerns on a reference form , (A) is a fuel ignition timing, a pressure change in a cylinder, and a spark ignition timing when performing spark ignition. , (B) are the lift amount of the intake valve (broken line) and the lift amount of the exhaust valve (solid line), (C) is the opening of the throttle valve, (D) is the component in the cylinder, (E ) Shows the opening of the EGR valve, and (F) shows the opening of the EGR cooler bypass valve. It is a figure which shows the state of each element after the CI mode transfer of the engine which concerns on a reference form , (A) is a fuel-injection timing, the pressure change in a cylinder, and a spark ignition timing, when performing spark ignition. , (B) are the lift amount of the intake valve (broken line) and the lift amount of the exhaust valve (solid line), (C) is the opening of the throttle valve, (D) is the component in the cylinder, (E ) Shows the opening of the EGR valve, and (F) shows the opening of the EGR cooler bypass valve.

  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.

Embodiment 1
1 and 2 show a schematic configuration of an engine (engine body) 1 according to the first embodiment. 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 and stabilizing the compression ignition combustion described later. In addition, what is necessary is just to set a geometric compression ratio suitably in the range of about 15-20.

  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 the operating state of one of the second cams to the exhaust valve 22. 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. That is, the exhaust valve 22 and the VVL 71 constitute one exhaust recirculation mechanism, for example, a first exhaust recirculation mechanism. Moreover, VVL71 comprises a valve operating mechanism.

  In the following explanation, operating the VVL 71 in the normal mode and not opening the exhaust twice is referred to as “turning off the VVL 71”, and operating the VVL 71 in the special mode and opening the exhaust twice. , “Turn on VVL 71”. 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.

  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. Thereby, the injector 67 injects the fuel so that the fuel spray spreads radially from the center position of the combustion chamber 19. The injector 67 constitutes a fuel injection valve.

  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. 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. 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 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 return a part of exhaust gas (EGR gas) to the intake passage 30. Is connected through an EGR 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 passage 50, the main passage 51, the EGR valve 511, the EGR cooler 52, the EGR cooler bypass passage 53, and the EGR cooler bypass valve 531 constitute one exhaust recirculation mechanism, for example, a second exhaust recirculation mechanism.

  The engine 1 includes a deceleration regeneration system 80. The deceleration regeneration system 80 includes a generator (alternator) 81 that is driven by the engine 1 to generate electric power, and a battery 82 to which the generator 81 is connected. The generator 81 is rotationally driven through a belt by the crankshaft of the engine 1 while the engine 1 is in operation. However, the generator 81 is configured to be able to switch between a power generation state in which power is generated by being driven by the engine 1 and a non-power generation state in which power is not generated even when driven by the engine 1. The power generated by the generator 81 is stored in the battery 82 or supplied to a vehicle electrical load (not shown). In place of the battery 82, a power storage device such as a capacitor may be used.

  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. Exhaust temperature sensor SW7 and exhaust pressure sensor SW8 for detecting a force, and is disposed on the upstream side of the direct catalyst 41, the linear O ₂ sensor SW9, direct catalyst 41 and underfoot catalyst 42 for detecting the oxygen concentration in the exhaust gas The lambda O ₂ 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 vehicle An accelerator opening sensor SW13 for detecting an accelerator opening corresponding to an operation amount of an accelerator pedal (not shown), intake-side and exhaust-side cam angle sensors SW14, SW15, and a common rail 64 of the fuel supply system 62 are attached. The fuel pressure sensor SW16 detects the fuel pressure supplied to the injector 67. The

  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, the generator 81, 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. This engine 1 is a compression ignition combustion in which combustion is performed by compression self-ignition without ignition by the spark plug 25 in a low load region where the engine load is relatively low for the purpose of improving fuel consumption and exhaust emission performance. I do. However, as the load on the engine 1 increases, in the compression ignition combustion, the combustion becomes too steep and causes problems such as combustion noise. Therefore, in the engine 1, in a high load region where the engine load is relatively high, the compression ignition combustion is stopped, and the engine 1 is switched to the spark ignition combustion using the spark plug 25. As described above, the engine 1 has a CI (Compression Ignition) mode in which compression ignition combustion is performed and an SI (Spark Ignition) mode in which spark ignition combustion is performed in accordance with the operation state of the engine 1, in particular, the load of the engine 1. It is configured to switch. However, the boundary line for mode switching is not limited to the illustrated example.

  The CI mode is further divided into three areas according to the engine load. Specifically, in the region (1) where the load is the lowest in the CI mode, in order to improve the ignitability and stability of the compression ignition combustion, the EGR gas having a relatively high temperature (hereinafter also referred to as hot EGR gas) is used as the cylinder. 18 is introduced. This is because the VVL 71 is turned on and the exhaust valve 22 is opened twice during the intake stroke. The introduction of hot EGR gas is advantageous in increasing the compression end temperature in the cylinder 18 and improving the ignitability and stability of the compression ignition combustion in the light load region (1). In the region (1), as shown in FIG. 5 (a), the injector 67 injects fuel into the cylinder 18 at least during the period from the intake stroke to the middle of the compression stroke, thereby producing a homogeneous lean air-fuel mixture. Form. The excess air ratio λ of the air-fuel mixture may be set to, for example, 2.4 or more. By doing so, it is possible to suppress the generation of RawNOx and improve the exhaust emission performance. Then, as shown in FIG. 5A, the lean air-fuel mixture undergoes compression self-ignition near the compression top dead center.

  Although details will be described later, in a region with a high load in region (1), specifically, a region including the boundary between region (1) and region (2), at least within a period from the intake stroke to the middle of the compression stroke Although the fuel is injected into the cylinder 18, the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio (λ≈1). By setting the stoichiometric air-fuel ratio, a three-way catalyst can be used, control at the time of switching between the SI mode and the CI mode is simplified, and the CI mode can be expanded to the high load side. Also contribute.

  In the CI mode, in the region (2) where the load is higher than that in the region (1), as in the high load side of the region (1), at least in the period from the intake stroke to the middle of the compression stroke, fuel is injected into the cylinder 18. The fuel is injected (see FIG. 5A) to form a homogeneous air / fuel ratio (λ≈1).

  In the region (2), the temperature in the cylinder 18 naturally increases as the engine load increases, so the hot EGR gas amount is reduced to avoid pre-ignition. This is due to the adjustment of the amount of internal EGR gas introduced into the cylinder 18.

  In the region (2), EGR gas having a relatively low temperature (hereinafter also referred to as “cooled EGR gas”) is introduced into the cylinder 18. Thus, by introducing the hot hot EGR gas and the cold cooled EGR gas into the cylinder 18 at an appropriate ratio, the compression end temperature in the cylinder 18 is made appropriate, and the rapid ignition while ensuring the ignitability of the compression ignition. Avoid combustion and stabilize compression ignition combustion. The EGR rate as a ratio of the EGR gas introduced into the cylinder 18 including the hot EGR gas and the cooled EGR gas is as high as possible under the condition that the excess air ratio of the mixture is set to λ≈1. Set to EGR rate. Therefore, in the region (2), the fuel injection amount increases as the engine load increases, so the EGR rate gradually decreases.

  In the region (3) where the load is highest in the CI mode, including the boundary line between the CI mode and the SI mode, the compression end temperature in the cylinder 18 is further increased. Therefore, as in the region (1) and the region (2) In addition, if fuel is injected into the cylinder 18 during the period from the intake stroke to the middle of the compression stroke, abnormal combustion such as pre-ignition occurs. On the other hand, if a large amount of cooled EGR gas having a low temperature is introduced to lower the compression end temperature in the cylinder, the ignitability of the compression ignition is deteriorated. That is, since compression ignition combustion cannot be stably performed only by temperature control in the cylinder 18, in this region (3), in addition to temperature control in the cylinder 18, it is prematurely devised by devising a fuel injection mode. Stabilize compression ignition combustion while avoiding abnormal combustion such as ignition. Specifically, this fuel injection mode has a fuel pressure significantly higher than that in the conventional case, and as shown in FIG. 5 (b), at least a period from the latter stage of the compression stroke to the initial stage of the expansion stroke (hereinafter referred to as this The fuel is injected into the cylinder 18 within a period (referred to as a retard period). This characteristic fuel injection mode is hereinafter referred to as “high pressure retarded injection” or simply “retarded injection”. Such high-pressure retarded injection stabilizes compression ignition combustion while avoiding abnormal combustion in the region (3). Details of the high-pressure retarded injection will be described later.

  In the region (3), similarly to the region (2), high-temperature hot EGR gas and low-temperature cooled EGR gas are introduced into the cylinder 18 at an appropriate ratio. As a result, the compression end temperature in the cylinder 18 is appropriately set to stabilize the compression ignition combustion.

  In contrast to the CI mode divided into three regions according to the engine load, the SI mode is divided into two regions, region (4) and region (5), according to the engine speed. ing. The region (4) corresponds to a low speed region when the operation region of the engine 1 is divided into a low speed and a high speed in the illustrated example, and the region (5) corresponds to a high speed region. The boundary between the region (4) and the region (5) is also inclined in the rotational speed direction with respect to the load level in the operation region shown in FIG. 4, but the boundary between the region (4) and the region (5) Is not limited to the illustrated example.

  In each of the region (4) and the region (5), the air-fuel mixture is set to the stoichiometric air-fuel ratio (λ≈1) as in the regions (2) and (3). Therefore, the air-fuel ratio of the air-fuel mixture is made constant at the theoretical air-fuel ratio (λ≈1) across the boundary between the CI mode and the SI mode. This allows the use of a three-way catalyst. In the region (4) and the region (5), the throttle valve 36 is basically fully opened, while the opening amount of the EGR valve 511 is adjusted and the amount of fresh air and the amount of external EGR gas introduced into the cylinder 18 are adjusted. Adjust. Adjusting the gas ratio introduced into the cylinder 18 in this way reduces pump loss and introduces a large amount of EGR gas into the cylinder 18, thereby suppressing the combustion temperature of spark ignition combustion and reducing cooling loss. Figured. In the region (4) and the region (5), the external EGR gas cooled mainly through the EGR cooler 52 is introduced into the cylinder 18. This is advantageous for avoiding abnormal combustion and also has an advantage of suppressing generation of Raw NOx. The opening degree of the EGR valve 511 and the opening degree of the EGR cooler bypass valve 531 decrease as the engine load increases. At this time, the opening degree of the EGR valve 511 is relatively larger than the opening degree of the EGR cooler bypass valve 531, that is, the cooled EGR gas is larger than the hot EGR gas. As the engine load increases, the EGR cooler bypass valve 531 is fully closed before the EGR valve 511. In the fully open load range, the external EGR is set to zero by closing the EGR valve 511.

  As described above, the geometric compression ratio of the engine 1 is set to 15 or more (for example, 18). Since the high compression ratio increases the compression end temperature and the compression end pressure, it is advantageous for stabilizing the compression ignition combustion in the CI mode, particularly in a low load region (for example, the region (1)). On the other hand, the high compression ratio engine 1 has a problem that abnormal combustion such as pre-ignition and knocking is likely to occur in the SI mode which is a high load region.

  Therefore, in the engine 1, in the region (4) and the region (5) of the SI mode, abnormal combustion is avoided by performing the above-described high-pressure retarded injection. More specifically, in the region (4), fuel is injected into the cylinder 18 with a high fuel pressure of 30 MPa or more and within the retard period from the late compression stroke to the early expansion stroke, as shown in FIG. 5 (c). Only high-pressure retarded injection is performed. On the other hand, in the region (5), as shown in FIG. 5 (d), a part of the fuel to be injected is injected into the cylinder 18 within the intake stroke period in which the intake valve 21 is open. The remaining fuel is injected into the cylinder 18 within the retard period. That is, in the region (5), fuel split injection is performed. Here, the intake stroke period during which the intake valve 21 is open is not a period defined based on the piston position, but a period defined based on opening / closing of the intake valve, and the intake stroke referred to here is VVT72. Depending on the closing timing of the intake valve 21 that is changed by the CVVL 73, the piston may deviate from the time when the piston reaches the intake bottom dead center.

  Next, the high pressure retarded injection in the SI mode will be described with reference to FIG. FIG. 6 shows the heat generation rate (upper diagram) and the progress of the unburned mixture reaction in the SI combustion (solid line) by the high pressure retarded injection described above and the conventional SI combustion (broken line) in which fuel injection is performed during the intake stroke. It is a figure which compares the difference in a degree (lower 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 both a high-load low-speed region (that is, region (4)), and the amount of fuel to be injected is the case of SI combustion by high-pressure retarded injection and conventional SI combustion. They are the same as each other.

  First, in the conventional SI combustion, a predetermined amount of fuel is injected into the cylinder 18 during the intake stroke (broken line in the upper diagram). 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.

  On the other hand, the high pressure retarded injection aims to shorten the reaction possible time, thereby avoiding abnormal combustion. That is, as shown in FIG. 6, the possible reaction time is a period during which the injector 67 injects fuel ((1) injection period), and after the injection is completed, a combustible mixture is formed around the spark plug 25. (2) The mixture formation period) and the period until the combustion started by ignition is completed ((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. This will be described in order.

  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.

  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.

  As described above, the high pressure retarded injection in the SI mode can shorten the injection period, the mixture formation period, and the combustion period, but the high pressure retarded injection performed in the CI mode region (3) It is possible to shorten the injection period and the mixture formation period. In other words, the turbulence in the cylinder 18 is increased by injecting the fuel into the cylinder 18 at a high fuel pressure, so that the mixing performance of the atomized fuel is increased and the fuel is injected at a late timing near the compression top dead center. However, a relatively homogeneous air-fuel mixture can be quickly formed.

  In the high pressure retarded injection in the CI mode, fuel is injected at a late timing near the compression top dead center in a relatively high load region, for example, while preventing premature ignition during the compression stroke period, as described above. Since a substantially homogeneous air-fuel mixture is quickly formed, it is possible to reliably perform compression ignition after the compression top dead center. Thus, in the expansion stroke period in which the pressure in the cylinder 18 gradually decreases due to motoring, the compression ignition combustion is performed, so that the combustion becomes slow, and the pressure increase in the cylinder 18 due to the compression ignition combustion (dP / It is avoided that dt) becomes steep. Thus, as a result of eliminating the NVH restriction, the CI mode region is expanded to the high load side.

  Returning to the description of the SI mode, as described above, the high pressure retarded injection in the SI mode shortens the reaction time of the unburned mixture by performing the fuel injection within the retard period. In the low speed range where the engine 1 has a relatively low rotational speed, the actual time for the crank angle change is long, which is effective. On the other hand, in the high speed range where the engine 1 has a relatively high rotational speed, the actual Not very effective due to short time. On the contrary, in the retard 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. Therefore, when only the retard injection is performed in the region (5), it may occur that the ignition timing must be retarded to avoid knocking.

  Therefore, as shown in FIG. 4, in the region (5) where the rotational speed is relatively high in the SI mode, as shown in FIG. 5 (d), a part of the fuel to be injected is cylinder 18 within the intake stroke period. And the remaining fuel is injected into the cylinder 18 within the retard period. In the intake stroke injection, it is possible to lower the specific heat ratio of the in-cylinder gas (that is, the air-fuel mixture containing fuel) during the compression stroke, thereby keeping the compression end temperature low. Thus, since the compression end temperature is lowered, knocking can be suppressed, so that the ignition timing can be advanced.

  Further, by performing the high pressure retarded injection, as described above, the turbulence becomes strong in the cylinder 18 (combustion chamber 19) near the compression top dead center, and the combustion period is shortened. This is also advantageous in suppressing knocking, and the ignition timing can be further advanced. Thus, in the region (5), by performing split injection of intake stroke injection and high pressure retarded injection, it is possible to improve thermal efficiency while avoiding abnormal combustion.

  In order to shorten the combustion period in the region (5), a multi-point ignition configuration may be adopted instead of performing high pressure retarded injection. That is, a plurality of ignition plugs are arranged facing the combustion chamber, and in the region (5), the intake stroke injection is executed and each of the plurality of ignition plugs is driven to perform multipoint ignition. By doing so, since the flame spreads from each of the plurality of fire types in the combustion chamber 19, the flame spreads quickly and the combustion period is shortened. As a result, the combustion period is shortened similarly to the case where high pressure retarded injection is employed, which is advantageous for improving the thermal efficiency.

  As described above, the engine 1 is operated according to each operation region.

<Fuel cut during deceleration>
Further, the engine 1 is controlled so as to perform a so-called fuel cut that stops the fuel supply from the injector 67 during deceleration. This fuel cut during deceleration can improve fuel efficiency. The fuel cut during deceleration of the engine 1 by the PCM 10 will be described in detail below with reference to FIGS. FIG. 7 is a flowchart showing processing of fuel cut during deceleration (hereinafter also simply referred to as “fuel cut”). FIGS. 8-11 is a figure which shows the state of each element of the engine 1 in fuel cut control. 8A to 11A show the fuel injection timing, the pressure change in the cylinder 18, and the spark ignition timing when spark ignition is performed, and FIG. 8B shows the intake valve. 21 shows the lift amount of 21 (broken line) and the lift amount of the exhaust valve 22 (solid line), (C) shows the opening of the throttle valve 36, and (D) shows the components in the cylinder 18. Is shown.

  In the following description, a case where fuel cut is performed from the state (4) where the engine 1 is operating in the SI mode will be described. Specifically, the engine 1 is operating as shown in FIG. That is, as shown in FIG. 8B, the exhaust valve 22 is opened in the exhaust stroke, and the intake valve 21 is opened in the intake stroke. Then, as shown in FIG. 8A, high-pressure retarded injection is performed at the latter stage of the compression stroke and before the compression top dead center, and ignited after the compression top dead center. At this time, the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio (λ≈1), and the amount of fresh air and the amount of EGR gas are adjusted so that the amount of fresh air is commensurate with the fuel injection amount. In this example, the throttle valve 36 is fully open as shown in FIG. On the other hand, the EGR valve 511 and the EGR cooler bypass valve 531 are fully closed. Therefore, the state in the cylinder 18 before and after combustion is almost fresh before combustion, fuel is injected there, and most of it is burned gas after combustion.

  First, in step S1, the PCM 10 determines whether or not a fuel cut execution condition is satisfied. Here, the execution condition is that the engine speed is not less than a predetermined value (for example, 1500 rpm) and the accelerator opening is zero (that is, the accelerator is off). That is, when the accelerator opening becomes zero, it is possible to determine the deceleration state of the engine 1 due to the accelerator off, but when the engine speed is too low, the fuel cut is not executed. This execution condition is an example, and the present invention is not limited to this. When the execution condition is satisfied, the PCM 10 proceeds to step S2, while when the execution condition is not satisfied, the PCM 10 repeats step S1.

  In step S2, the PCM 10 performs a fuel cut. That is, the PCM 10 stops the fuel injection of the injector 67. At this time, the fuel injection of the injectors 67 of all cylinders is stopped simultaneously. Thereafter, the PCM 10 proceeds to step S3.

  At the time of deceleration, the PCM 10 sets the generator 81 in a power generation state, converts the kinetic energy of the vehicle into electric energy, and collects it as electric power. At this time, the PCM 10 fully opens the throttle valve 36 as shown in FIG. By carrying out like this, pump loss can be reduced and the kinetic energy of the engine 1 can be efficiently converted into electric energy.

  Subsequently, in step S <b> 3, the PCM 10 introduces EGR gas into the cylinder 18. Specifically, the PCM 10 turns on the VVL 71 and opens the exhaust valve 22 twice during the intake stroke as shown in FIG. 9B. As a result, hot EGR gas is introduced into the cylinder 18 and temperature drop in the cylinder 18 is suppressed. In particular, as described above, when the throttle valve 36 is fully opened to reduce pump loss, the amount of fresh air introduced into the cylinder 18 tends to increase, but by introducing hot EGR gas, The amount of fresh air introduced into the cylinder 18 can be suppressed, and the temperature drop in the cylinder 18 immediately after the fuel cut can be suppressed.

  Subsequently, in step S4, the PCM 10 determines whether or not a resumption condition for fuel injection is satisfied. Here, the resumption condition is that the engine 1 is in a predetermined operation state. Specifically, the engine speed is lower than a predetermined value (for example, 800 rpm) lower than the engine speed of the execution condition. is there. This predetermined value is slightly higher than the idle speed. The operation state that satisfies this restart condition is included in the region (1). Note that this restart condition is an example, and the present invention is not limited to this.

  Normally, when a fuel cut is executed, the engine load decreases rapidly, and the operating state of the engine 1 falls within the region (1). Then, the engine speed gradually decreases. As a result, the engine 1 eventually enters the predetermined operating state (the engine speed is equal to or less than a predetermined value). When the restart condition is satisfied, the PCM 10 proceeds to step S5. When the restart condition is not satisfied, the PCM 10 repeats step S4.

  In step S5, the PCM 10 restarts fuel injection and combustion. Specifically, as shown in FIG. 10A, the PCM 10 resumes combustion in the SI mode. At this time, high-pressure retarded injection is executed.

  Further, as shown in FIG. 10B, the PCM 10 controls the CVVL 73 so that the lift amount is low according to the torque. At this time, the PCM 10 continues to introduce the EGR gas by opening the exhaust twice. The excess air ratio of the air-fuel mixture is λ≈1. The throttle valve 36 is fully opened as shown in FIG. In the present embodiment, the SI mode is only one cycle, and then the PCM 10 proceeds to step S6.

  When the fuel injection is resumed, the temperature drop of the cylinder 18 is suppressed by the introduction of the hot EGR gas, and the ratio of fresh air in the cylinder 18 is increased by the continued introduction of the EGR gas as shown in FIG. Since it increases, the ignitability in SI mode can be improved. That is, since the combustion is not performed during the fuel cut, even if the EGR gas is recirculated into the cylinder 18, the ratio of the burned gas contained therein gradually decreases. That is, as time passes, the ratio of burned gas in the cylinder 18 decreases and the ratio of fresh air increases. In particular, when the lockup mechanism of the automatic transmission is operating, even if fuel cut is performed, the engine speed does not decrease rapidly but gradually decreases. Therefore, it takes a long time from the start of the fuel cut until the resumption condition is satisfied, and most of the EGR gas can be fresh.

  If the fuel cut is continued to some extent in this way, the cylinder 18 is in a state where a certain amount of fresh air is secured. As the amount of fresh air in the cylinder 18 increases, flame propagation improves, and the ignitability in the SI mode improves.

  However, since the ratio of fresh air in the cylinder 18 increases when fuel injection is resumed, if fuel injection is performed during the period from the intake stroke to the middle of the compression stroke, abnormal combustion such as pre-ignition may occur. is there. Therefore, high-pressure retarded injection is executed. Thereby, abnormal combustion can be avoided.

  At this time, the introduction of the hot EGR gas being performed in step S3 is continued even in the SI mode. That is, the burnt gas after the spark ignition combustion in the SI mode returns to the cylinder 18 as hot EGR gas. As a result, after spark ignition combustion, the temperature in the cylinder 18 becomes high. Here, in order to increase the amount of hot EGR gas introduced more than fresh air, the second valve opening timing of the exhaust valve 22 is made earlier than the valve opening timing of the intake valve 21. As a result, it is possible to create a state in which only the exhaust valve 22 is opened at the beginning of the intake stroke, so that hot EGR gas can be preferentially sucked into the cylinder 18.

  Thereafter, in step S6, the PCM 10 shifts to the CI mode. At this time, as shown in FIG. 11D, the burned gas after the spark ignition combustion in the previous step S5 is recirculated into the cylinder 18 in the cylinder 18. Therefore, the inside of the cylinder 18 is at a high temperature, and compression ignition combustion can be executed. As shown in FIG. 11B, the intake valve 21 is controlled to have a low lift amount corresponding to the torque, and the throttle valve 36 is fully opened as shown in FIG. 11C. Yes. Further, as shown in FIG. 11B, the exhaust gas is continuously opened twice, and the hot EGR gas is introduced into the cylinder 18, so that the working gas fuel ratio G / F becomes lean. The excess air ratio λ of the air-fuel mixture is set to 2.4 or more, for example.

  However, since the inside of the cylinder 18 is at a high temperature, high pressure retarded injection is executed as shown in FIG. 11A in order to avoid abnormal combustion such as premature ignition. Thereby, stabilization of compression ignition combustion is achieved, avoiding abnormal combustion.

  Thus, the fuel cut control is completed, and thereafter, the engine 1 is operated in the operation mode corresponding to the operation region described above.

  Therefore, the engine 1 according to the first embodiment is disposed so as to face the engine body having the cylinder 18, the injector 67 configured to inject fuel into the cylinder 18, and the cylinder 18. An ignition plug 25 configured to ignite the air-fuel mixture therein, an exhaust gas recirculation mechanism (exhaust valve 22 and VVL 71) configured to introduce EGR gas into the cylinder 18, at least the injector 67, A PCM 10 configured to operate the engine main body by controlling the spark plug 25 and the exhaust gas recirculation mechanism, and the PCM 10 is at least when the operating state of the engine main body is in a predetermined low load region. Then, the engine body is operated by performing compression ignition combustion in which the air-fuel mixture in the cylinder 18 is combusted by self-ignition. When the engine body is decelerated in the off state, fuel injection from the injector 67 is stopped and fuel cut is executed. When the engine speed decreases to a predetermined value, the fuel injection of the injector 67 is performed. When the fuel cut is performed, the exhaust gas recirculation mechanism is operated to introduce EGR gas into the cylinder 18 and the fuel injection of the injector 67 is resumed. The ignition plug 25 is operated while operating the engine and the engine body is operated by spark ignition combustion, and then the operation of the engine body is performed by the compression ignition combustion.

  According to this configuration, EGR gas is introduced into the cylinder 18 during fuel cut. While combustion is not performed during the fuel cut, the temperature in the cylinder 18 tends to decrease. However, by introducing EGR gas, the temperature decrease in the cylinder 18 immediately after the fuel cut can be suppressed.

  Further, if the fuel cut and the introduction of the EGR gas are continued, no burned gas is generated during the fuel cut, so the ratio of burned gas contained in the air-fuel mixture in the cylinder 18 gradually decreases, The rate will increase. As a result, when the fuel injection is restarted and spark ignition combustion is executed, a certain amount of fresh air can be secured. Thereby, the ignitability of spark ignition combustion can be improved. In addition, as described above, the temperature drop in the cylinder 18 is suppressed as much as possible by introducing the EGR gas, which contributes to the improvement of the ignition performance of the spark ignition combustion.

  If the ignitability of the spark ignition combustion can be improved, the temperature in the cylinder 18 can be sufficiently increased by the spark ignition combustion, and the subsequent compression ignition combustion can be stably executed.

  Further, a plurality of exhaust gas recirculation mechanisms are provided, and the plurality of exhaust gas recirculation mechanisms are different from each other in a method of introducing exhaust gas into the cylinder 18, and the PCM 10 is configured such that the operating state of the engine body is the predetermined value. The EGR gas is introduced into the cylinder 18 by operating at least one of the exhaust gas recirculation mechanisms when in the low load region, and the exhaust gas recirculation mechanism operated during the fuel cut is The exhaust gas recirculation mechanism is operated in the low load region.

  For example, in the above-described embodiment, the exhaust gas recirculation mechanism includes the exhaust gas valve 22 and the VVL 71, the first exhaust gas recirculation mechanism that performs internal EGR, the EGR passage 50, the main passage 51, the EGR valve 511, the EGR cooler 52, and the EGR cooler. There is a second exhaust gas recirculation mechanism that includes the bypass passage 53 and the EGR cooler bypass valve 531 and performs external EGR. The exhaust gas recirculation mechanism during fuel cut is the same as the exhaust gas recirculation mechanism that operates in the predetermined low load region. That is, it is common to the first exhaust gas recirculation mechanism that performs the internal EGR. By doing so, the EGR method is not changed when shifting from fuel cut to resuming combustion injection, so that EGR gas can be introduced smoothly and torque shocks and the like can be suppressed.

  The exhaust gas recirculation mechanism is not limited to that described above. For example, an exhaust gas recirculation mechanism that performs external EGR may not include an EGR cooler bypass passage. The exhaust gas recirculation mechanism that performs internal EGR includes an intake valve and a valve operating mechanism for the intake valve, and opens the intake valve twice in each of the exhaust stroke and the intake stroke. It may have an intake valve, an exhaust valve, and a valve mechanism that drives the intake valve and the exhaust valve, respectively, and provides a negative overlap period in which both the intake valve and the exhaust valve are closed in the exhaust stroke or the intake stroke. It may be a thing.

  The engine 1 further includes an exhaust valve 22 that opens and closes an exhaust port 17 that opens to the cylinder 18, and a VVL 71 that drives the exhaust valve 22, and the operating state of the engine body is the predetermined low load region. The exhaust gas recirculation mechanism that is activated when the exhaust valve 22 is in the exhaust valve 22 and the VVL 71 are configured to open the exhaust valve 22 twice in each of the exhaust stroke and the intake stroke. Yes.

  That is, in this engine 1, the operating state of the engine 1 when the fuel injection resumption condition is satisfied is included in the region (1), and the exhaust gas recirculation mechanism operated in the region (1) is the exhaust valve 22 and the VVL 71. is there. Further, the exhaust gas recirculation mechanism when executing the fuel cut is also the exhaust valve 22 and the VVL 71, which are the same as those in the region (1). By adopting the double opening of the exhaust gas in this way, the heat of the burned gas can be effectively utilized for maintaining the temperature of the cylinder 18. That is, in the case of the external EGR, the burned gas flows through the EGR passage 50 and the intake port 16, and the burned gas is recirculated to the intake port 16 in the case where the intake air is opened twice. On the other hand, when the exhaust is opened twice, the burned gas is once discharged to the exhaust port 17. Since the exhaust port 17 has a higher temperature than the EGR passage 50 and the intake port 16, it is possible to reduce heat that escapes from the burned gas to the outside. Furthermore, if the fuel cut continues, the ratio of burned gas in the EGR gas decreases, the temperature of the EGR gas decreases, and the temperature of the EGR gas may become lower than the exhaust port 17 or the like. Here, since the temperature of the exhaust port 17 is the highest in the intake port 16, the exhaust port 17 and the EGR passage 50, a part of the air-fuel mixture is discharged from the cylinder 18 by adopting the double opening of the exhaust, While returning to the cylinder 18 as EGR gas, more heat is absorbed and returned to the cylinder 18.

  Further, it is advantageous to open the exhaust twice from the viewpoint of the charging efficiency of the intake air after resuming the fuel injection. In other words, if the intake double opening is adopted, the intake port 16 and its surroundings are heated by the burned gas. As a result, intake charging efficiency deteriorates. On the other hand, if the exhaust is opened twice, the intake port 16 is not heated by the burned gas, so that deterioration of the charging efficiency can be avoided.

《 Reference form 》
Subsequently, a reference form will be described.

The reference form is different from the first embodiment in the EGR system during fuel cut. The configuration of the engine 1 and the flow of fuel cut are the same as in the first embodiment. Hereinafter, the fuel cut during deceleration of the engine 1 according to the reference embodiment will be described with reference to FIGS. 12-15 is a figure which shows the state of each element of the engine which concerns on a reference form . 12A to 15A are the fuel injection timing and the pressure change in the cylinder, and the spark ignition timing when spark ignition is performed, and FIG. 12B is the lift amount of the intake valve (broken line). And (C) is the throttle valve opening, (D) is the component in the cylinder, (E) is the EGR valve opening, and (F) is the exhaust valve lift amount (solid line). The opening degree of the EGR cooler bypass valve is shown.

  In the following description, a case where fuel cut is performed from the state (4) where the engine 1 is operating in the SI mode will be described.

  In this description, the engine 1 is operating in a relatively low load region (4) before the execution condition is satisfied. That is, as shown in FIGS. 12E and 12F, each of the EGR valve 511 and the EGR cooler bypass valve 531 is opened at a predetermined opening. Therefore, as shown in FIG. 12D, EGR gas is introduced into the cylinder 18 by external EGR.

  Then, after the execution condition is satisfied and the fuel cut is executed, EGR gas is introduced into the cylinder 18 by the external EGR. This process corresponds to step S3 in FIG. Specifically, as shown in FIGS. 13E and 13F, the PCM 10 fully closes the EGR valve 511 and fully opens the EGR cooler bypass valve 531. As a result, as shown in FIG. 13D, hot EGR gas is introduced into the cylinder 18 and temperature drop in the cylinder 18 is suppressed. At this time, the exhaust double opening as in the first embodiment is not executed (see FIG. 13B).

  The EGR valve 511 and the EGR cooler bypass valve 531 are not limited to the above state. For example, the EGR valve 511 may be opened. When the EGR valve 511 is opened, cooled EGR gas is introduced into the cylinder 18. Since the cooled EGR gas is hotter than fresh air, the temperature in the cylinder 18 is reduced compared to a configuration in which EGR gas is not introduced into the cylinder 18, that is, in a configuration in which only fresh air is introduced into the cylinder 18. Can be suppressed.

  Thereafter, when the restart condition is satisfied (step S4), fuel supply and combustion are restarted (step S5). Specifically, as shown in FIG. 14A, the PCM 10 resumes combustion in the SI mode. At this time, the PCM 10 continues to introduce the EGR gas by the external EGR as shown in FIGS.

  Then, after executing the SI mode for only one cycle, the mode shifts to the CI mode (step S6). At this time, as shown in FIGS. 15E and 15F, the PCM 10 continues to introduce the EGR gas by the external EGR.

Therefore, the engine 1 of the reference embodiment is disposed so as to face the cylinder 18, the engine body having the cylinder 18, the injector 67 configured to inject fuel into the cylinder 18, and the cylinder 18. An ignition plug 25 configured to ignite the air-fuel mixture, and an exhaust gas recirculation mechanism configured to introduce EGR gas into the cylinder 18 (EGR passage 50, EGR valve 511, and EGR cooler bypass valve 531); A PCM 10 configured to operate the engine body by controlling at least the injector 67, the spark plug 25, and the exhaust gas recirculation mechanism, and the PCM 10 has at least a predetermined operating state of the engine body. When in the low load region, compression ignition combustion is performed to burn the air-fuel mixture in the cylinder 18 by self-ignition. The engine body is operated, and when the engine body decelerates with the accelerator off, the fuel injection from the injector 67 is stopped and fuel cut is executed, and the engine speed decreases to a predetermined value. The fuel injection of the injector 67 is sometimes resumed, and during the fuel cut, the exhaust gas recirculation mechanism is operated to introduce EGR gas into the cylinder 18 and the fuel injection of the injector 67 When the engine is restarted, the ignition plug 25 is operated while operating the exhaust gas recirculation mechanism, the engine body is operated by spark ignition combustion, and then the operation of the engine body is performed by compression ignition combustion.

  According to this configuration, as in the first embodiment, the ignitability of spark ignition combustion can be improved, and the subsequent compression ignition combustion can be stably executed.

  Further, a plurality of exhaust gas recirculation mechanisms are provided, and the plurality of exhaust gas recirculation mechanisms are different from each other in a method of introducing exhaust gas into the cylinder, and the PCM 10 has the exhaust gas recirculation mechanism immediately before the fuel cut. When at least one is operated, the exhaust gas recirculation mechanism that is operated during the fuel cut and when the fuel injection is restarted is made the same as the exhaust gas recirculation mechanism that was operated immediately before the fuel cut.

For example, in the above-described embodiment, the exhaust gas recirculation mechanism includes the exhaust gas valve 22 and the VVL 71, the first exhaust gas recirculation mechanism that performs internal EGR, the EGR passage 50, the main passage 51, the EGR valve 511, the EGR cooler 52, and the EGR cooler. There is a second exhaust gas recirculation mechanism that includes the bypass passage 53 and the EGR cooler bypass valve 531 and performs external EGR. The exhaust gas recirculation mechanism during the fuel cut is the same as the exhaust gas recirculation mechanism that was operating immediately before the fuel cut. That is, when the second exhaust gas recirculation mechanism is operated immediately before the fuel cut, the second exhaust gas recirculation mechanism is also operated during the fuel cut and when the fuel injection is resumed. By doing so, the EGR system is not changed when shifting to the fuel cut from immediately before the fuel cut, so that the EGR gas can be smoothly introduced and torque shock or the like can be suppressed. When the first exhaust gas recirculation mechanism is operated immediately before the fuel cut, the first exhaust gas recirculation mechanism is also operated during the fuel cut and when the fuel injection is resumed.
<< Other Embodiments >>
In the first and second embodiments, the fuel injection of the injectors 67 of all the cylinders is stopped at the same time when the fuel is cut, but the present invention is not limited to this. For example, first, the fuel injection of the injectors 67 of the half cylinders may be stopped, and then the fuel injection of the injectors 67 of the remaining cylinders may be stopped stepwise. Thereby, the torque shock of the engine 1 at the time of fuel cut etc. can be relieved.

  In the above description, the case where the fuel cut is executed from the state in which the engine 1 is operating in the region (4) has been described. However, the present invention is not limited to this. For example, the fuel cut may be executed from the state where the engine 1 is operating in the region (3).

  In the first and second embodiments, when the fuel injection is resumed, the SI mode is performed only for one cycle and the mode is shifted to the CI mode. However, the present invention is not limited to this. That is, the SI mode may be shifted to the CI mode after several cycles of the SI mode. For example, the temperature in the cylinder 18 may be monitored, and the mode may be shifted to the CI mode when the temperature in the cylinder 18 exceeds a predetermined value due to combustion in the SI mode.

  In the first embodiment, the EGR gas is introduced by opening the exhaust twice in the operation state that satisfies the restart condition, but the present invention is not limited to this. In an operating state that satisfies the restart condition, EGR gas may be introduced by double opening of intake air or external EGR. In that case, the introduction of the EGR gas during the fuel cut is also made to coincide with the EGR system in the operation state that satisfies the restart condition.

In the reference embodiment , the case where the introduction of the EGR gas by the external EGR is executed immediately before the fuel cut is described, but the present invention is not limited to this. Immediately before the fuel cut, internal EGR such as opening twice of exhaust gas or opening air twice may be executed. In that case, the introduction of EGR gas during the fuel cut is also made to coincide with the EGR system just before the fuel cut.

  Alternatively, the EGR method during the fuel cut may be different from the EGR method in the operation state that satisfies the restart condition and the EGR method immediately before the fuel cut.

  In the first and second embodiments, the EGR gas is introduced after the fuel cut, but the present invention is not limited to this. For example, the fuel cut may be performed after the introduction of EGR gas, or the fuel cut and the introduction of EGR gas may be performed simultaneously.

  As for the other steps, the order may be changed in a timely manner or may be processed in parallel as long as the above-described effects are achieved.

  In addition, fuel may be injected into the intake port 16 through a port injector separately provided 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.

  Further, in the above description, the air-fuel ratio of the air-fuel mixture is set to the stoichiometric air-fuel ratio (λ≈1) in the predetermined operation region, but the air-fuel ratio of the air-fuel mixture may be set to lean. However, setting the air-fuel ratio to the stoichiometric air-fuel ratio has the advantage that a three-way catalyst can be used.

  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.

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

  As described above, the technology disclosed herein is useful for a spark ignition direct injection engine.

1 Engine (Engine body)
10 PCM (controller)
17 exhaust port 18 cylinder 22 exhaust valve (exhaust gas recirculation mechanism)
25 Spark plug 50 EGR passage (exhaust gas recirculation mechanism)
51 Main passage (exhaust gas recirculation mechanism)
511 EGR valve (exhaust gas recirculation mechanism)
52 EGR cooler (exhaust gas recirculation mechanism)
53 EGR cooler bypass passage (exhaust gas recirculation mechanism)
531 EGR cooler bypass valve (exhaust gas recirculation mechanism)
67 Injector (fuel injection valve)
71 VVL (exhaust gas recirculation mechanism)

Claims (2)

An engine body having a cylinder;
A fuel injection valve configured to inject fuel into the cylinder;
A spark plug disposed facing the cylinder and configured to ignite an air-fuel mixture in the cylinder;
An exhaust gas recirculation mechanism configured to introduce exhaust gas into the cylinder;
A controller configured to operate the engine body by controlling at least the fuel injection valve, the spark plug, and the exhaust gas recirculation mechanism ;
An exhaust valve that opens and closes an exhaust port that opens to the cylinder;
A valve mechanism for driving the exhaust valve ,
The controller is
When at least the operating state of the engine body is in a predetermined low load region, the engine body is operated by performing compression ignition combustion for burning the air-fuel mixture in the cylinder by self-ignition,
During deceleration of the engine body with the accelerator off, fuel injection from the fuel injection valve is stopped and fuel cut is performed. When the engine speed decreases to a predetermined value, the fuel injection valve Configured to resume fuel injection,
During the fuel cut, exhaust gas is introduced into the cylinder by operating the exhaust gas recirculation mechanism,
When resuming the fuel injection of the fuel injection valve, after operating the spark plug while operating the exhaust gas recirculation mechanism and operating the engine body by spark ignition combustion, the engine body is operated by the compression ignition combustion. Migrate ,
The exhaust gas recirculation mechanism operated during the fuel cut is the exhaust valve and the valve mechanism, and is a spark ignition type direct opening mechanism that opens the exhaust valve twice in each of the exhaust stroke and the intake stroke. Jet engine. In the spark ignition direct injection engine according to claim 1,
A plurality of the exhaust gas recirculation mechanisms are provided,
The plurality of exhaust gas recirculation mechanisms are different from each other in the method of introducing exhaust gas into the cylinder,
The controller is
When the operating state of the engine body is in the predetermined low load region, exhaust gas is introduced into the cylinder by operating at least one of the exhaust gas recirculation mechanism,
A spark ignition direct injection engine in which the exhaust gas recirculation mechanism operated during the fuel cut is made the same as the exhaust gas recirculation mechanism operated in the predetermined low load region.

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