JP5907013B2 - 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. Moreover, the engine which concerns on patent document 1 is comprised so that a fuel cut may be performed at the time of deceleration.

JP 2004-316544 A

  By the way, during the fuel cut as described above, since combustion is not performed in the cylinder, the oxygen concentration in the cylinder increases. That is, when the fuel injection after the fuel cut is resumed, the oxygen concentration in the cylinder is increased as compared with that before the fuel cut.

  Here, when performing compression ignition combustion at the time of resumption of fuel injection, if the oxygen concentration is too high, the pressure increase rate (dP / dt) in the cylinder becomes steep. As a result, there is a risk of causing large combustion noise.

  The technology disclosed herein has been made in view of such a point, and an object thereof is to reduce combustion noise at the time of resuming combustion after fuel cut.

The technology disclosed herein is configured to set an engine body having a cylinder, a fuel injection valve configured to inject fuel into the cylinder, and a pressure of the fuel injected by the fuel injection valve. A spark ignition type direct injection engine comprising: a fuel pressure setting mechanism that is configured; and a controller configured to operate the engine body by controlling at least the fuel injection valve and the fuel pressure setting mechanism, The controller is in a compression ignition mode in which the engine body is operated by performing compression ignition combustion in which the air-fuel mixture in the cylinder is combusted by self-ignition when at least the operation state of the engine body is in a predetermined low load region, When the engine body is decelerated when the accelerator is off, the fuel injection from the fuel injection valve is stopped and fuel cut is performed. The fuel injection of the fuel injection valve is resumed when the engine speed decreases to a predetermined value, and the fuel injection is resumed in a situation where the operating state of the engine body is in the predetermined low load region In the transient mode, the fuel pressure is controlled by the fuel pressure setting mechanism so that the fuel pressure is set to a high fuel pressure of 30 MPa or more and 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. The engine body is operated, and thereafter, the fuel injection timing is advanced within the period from the intake stroke to the middle of the compression stroke to shift to the compression ignition mode.

  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. The “late compression stroke” may be the late phase when the compression stroke is divided into three periods, an initial phase, a middle phase, and a late phase. Similarly, the “expansion stroke initial phase” refers to the expansion stroke as the initial phase, the middle phase, and It is good also as the initial stage when it divides into three periods of the latter term.

  According to the above-described configuration, the fuel cut is executed at the time of deceleration when the accelerator is off. When the fuel cut is executed, combustion is not performed, so the oxygen concentration in the cylinder gradually increases. If the compression ignition combustion is performed while the oxygen concentration in the cylinder is high when the combustion injection is resumed, the premature ignition combustion during the compression stroke period may occur and the pressure rise may be steep.

  Therefore, when the fuel injection is resumed in a situation where the operation state of the engine body is normally in a predetermined low load region where compression ignition combustion is performed, the fuel pressure is set to a high fuel pressure of 30 MPa or more, and the fuel is expanded from the latter stage of the compression stroke A transient mode is executed in which fuel is injected into the cylinder within the period up to the beginning of the stroke. This characteristic fuel injection mode is hereinafter referred to as “high pressure retarded injection” or simply “retarded injection”.

  In this way, since fuel is injected into the cylinder at least at a later time from the latter stage of the compression stroke to the early stage of the expansion stroke, the compression ignition is generally after the compression top dead center and premature ignition is avoided. Thereby, combustion noise is suppressed.

  Further, relatively increasing the fuel pressure increases the amount of fuel injected per unit time. When compared with the same fuel injection amount, a high fuel pressure shortens the period during which fuel is injected into the cylinder, that is, the injection period. This is advantageous for relatively shortening the time from the start of fuel injection to compression ignition. That is, since the time during which the fuel is exposed to the air-fuel mixture having a high oxygen concentration is shortened, it is possible to avoid pre-ignition in this respect.

  In addition, high fuel pressure is advantageous for atomization of the fuel spray injected into the cylinder, and turbulence in the cylinder near the compression top dead center increases as fuel is injected into the cylinder with high fuel pressure. The turbulent energy in the cylinder increases. These factors increase the mixing performance of the fuel in the cylinder near the compression top dead center so that a relatively homogeneous combustible mixture can be formed in a short time.

  Thus, a relatively homogeneous air-fuel mixture formed by fuel injection at a high fuel pressure is reliably compressed and ignited after compression top dead center, and stably combusted during the expansion stroke period. That is, since a relatively homogeneous combustible mixture is rapidly formed after the start of fuel injection, the combustible mixture is reliably compressed and ignited at an appropriate time after the compression top dead center. Further, in the expansion stroke, the cylinder pressure gradually decreases due to motoring, so that the increase in pressure in the cylinder due to combustion is avoided, and the combustion becomes relatively slow and stable. This also suppresses combustion noise. The fuel injection may be divided and performed. In the case of divided injection, at least one of the divided fuel injections is relatively slow from the late stage of the compression stroke to the early stage of the expansion stroke. Just go to the time.

  Thus, after performing the transient mode, the oxygen concentration in the cylinder decreases, and abnormal combustion is less likely to occur. Therefore, after the excessive mode, the fuel injection timing is advanced to shift to the compression ignition mode.

  The controller enters the transient mode when the fuel injection is restarted when the operating state of the engine body is in the predetermined low load region and the temperature in the cylinder is equal to or higher than the predetermined temperature. Also good.

  That is, the higher the temperature in the cylinder, the more likely abnormal combustion such as pre-ignition occurs. Therefore, high pressure retarded injection is executed when the temperature in the cylinder is equal to or higher than a predetermined temperature. Conversely, when there is a low possibility of abnormal combustion such as premature ignition, it is not necessary to execute high pressure retarded injection, so fuel injection is performed at normal fuel pressure and fuel injection timing. This makes it possible to ensure a long mixture formation period, which is advantageous for the formation of a homogeneous mixture, and improves ignitability and combustion stability in the compression ignition mode.

  Further, in the transient mode, the controller may adjust the fuel injection timing according to the temperature in the cylinder to perform compression ignition combustion.

  That is, if the fuel injection timing is set too late, there is a risk of misfire. Therefore, the fuel injection timing is adjusted according to the temperature in the cylinder. Specifically, the fuel injection timing is advanced as the temperature in the cylinder is lower. By doing so, compression ignition combustion can be performed without misfire.

  Further, the spark ignition direct injection engine further includes an ignition plug disposed so as to face the cylinder and configured to ignite an air-fuel mixture in the cylinder, and the controller includes the transient mode. In this case, the spark plug may be operated after compression top dead center.

  That is, in the transient mode, ignition may be performed by operating the spark plug auxiliary after the compression top dead center. Thereby, misfire can be avoided reliably.

  Further, the controller has a high fuel pressure mode in which the fuel pressure is set to a high fuel pressure of 30 MPa or more by the fuel pressure setting mechanism to operate the engine body, and when the fuel cut is performed from the high fuel pressure mode, The fuel pressure setting mechanism may be controlled so that the fuel pressure in the high fuel pressure mode is maintained until the compression ignition mode is entered.

  According to the above configuration, the controller sets the fuel pressure to a high fuel pressure of 30 MPa or more depending on the operating state of the engine body. When the fuel cut is executed from such an operating state, the combustion injection at a high fuel pressure is executed when the combustion injection is restarted. Therefore, the fuel pressure is maintained at a high pressure without lowering. By so doing, when restarting fuel injection, high pressure fuel can be injected early.

  The spark ignition direct injection engine further includes an exhaust gas recirculation mechanism configured to introduce exhaust gas into the cylinder, and the controller includes the exhaust gas recirculation means during the fuel cut by the exhaust gas recirculation means. You may make it introduce | transduce the said exhaust gas.

  According to the above configuration, the exhaust gas is introduced into the cylinder during the fuel cut. As a result, an increase in oxygen concentration in the cylinder during fuel cut can be suppressed.

  According to the spark ignition direct injection engine, combustion noise can be reduced by performing high pressure retarded injection when resuming fuel injection after fuel cut.

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. Is a diagram showing a state of each element of the fuel cut previous engine, (A), the pressure change in the fuel injection timing and the cylinder, as well as sparks ignition timing, (B), the lift of the intake valve ( (Broken line) and the lift amount (solid line) of the exhaust valve, (C) shows the opening of the throttle valve, and (D) shows the components in the cylinder. Is a diagram showing a state of each element of the engine during the fuel cut, (A), the pressure change in the cylinder, (B), the lift of the lift amount (dashed line) and an exhaust valve of an intake valve (solid line ), (C) shows the opening of the throttle valve, and (D) shows the components in the cylinder. Is a diagram showing a state of each element of the engine at the time of resuming the fuel injection, (A), the pressure changes in the fuel injection timing and the cylinder, (B), the lift of the intake valve (broken line) and an exhaust valve (C) shows the opening of the throttle valve, and (D) shows the components in the cylinder. Is a diagram showing a state of each element of the engine after the CI mode transition, (A), the pressure changes in the fuel injection timing and the cylinder, (B), the lift of the intake valve (broken line) and an exhaust valve (C) shows the opening of the throttle valve, and (D) shows the components in the cylinder.

  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 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. This fuel supply system 62 constitutes a fuel pressure setting mechanism.

  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. The direct catalyst 41 and the underfoot catalyst 42 constitute a catalyst.

  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 (compression ignition mode) for performing compression ignition combustion and an SI (Spark for performing spark ignition combustion) in accordance with the operating state of the engine 1, in particular, the load of the engine 1. (Ignition) mode. 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). 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.

  Thus, in the regions (3) to (5), high-pressure retarded injection is executed, and this operating state is also referred to as a high fuel pressure mode.

  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 determines whether or not the fuel pressure is high. Specifically, the PCM 10 determines whether or not the fuel pressure is 30 MPa or more. Note that 30 MPa is an example, and other values may be used. When the fuel pressure is 30 MPa or more, the process proceeds to step S3, and when the fuel pressure is less than 30 MPa, the process proceeds to step S4. As described above, when the operating state of the engine 1 immediately before the fuel cut is in the regions (3) to (5), the fuel pressure mode is the high fuel pressure mode of 30 MPa or more. That is, in such a case, the PCM 10 proceeds to step S3. On the other hand, when the operating state of the engine 1 immediately before the fuel cut is in the above (1) and (2), the process proceeds to step S4 without passing through step S3.

  In step S3, the PCM 10 controls the fuel supply system 62 so as to maintain the fuel pressure at a high pressure at least until a transition mode to be described later ends. That is, the fuel supply system 62 normally operates the pressure reducing valve to lower the fuel pressure when it is not necessary to increase the fuel pressure. However, when the fuel cut is executed, fuel injection at a high fuel pressure may be executed when the fuel injection is resumed later, so that the increased fuel pressure is not lowered. Thereafter, the PCM 10 proceeds to step S4.

  In step S4, 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 S5.

  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> 5, 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 an increase in oxygen concentration 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 an increase in the oxygen concentration in the cylinder 18 can be suppressed.

  Subsequently, in step S6, the PCM 10 determines whether or not a fuel injection resumption condition 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. When the restart condition is satisfied, the PCM 10 proceeds to step S7. When the restart condition is not satisfied, the PCM 10 repeats step S6.

In step S <b> 7, the PCM 10 determines whether or not the operating state of the engine 1 is within the regions (1) to ( 2 ). That is, the PCM 10 determines whether or not the operating state of the engine 1 when the restart condition is satisfied is the compression ignition mode. PCM10, when the operating state of the engine 1 is contained in the area (1) to (2) in the the process proceeds to step S8, not the operating condition of the engine 1 is contained in the area (1) - (2) If not, the process proceeds to step S11.

  In the compression ignition mode, since the air-fuel mixture is ignited in the vicinity of the compression top dead center in the cylinder 18, premature ignition is likely to occur if the oxygen concentration becomes high in this state. That is, step S7 determines whether or not the pre-ignition is likely to occur when the oxygen concentration increases.

  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). Therefore, normally, when the restart condition is satisfied, the operating state of the engine 1 is in the region (1). Therefore, when step S6 is satisfied, step S7 is also satisfied.

  In step S8, the PCM 10 determines whether or not the temperature in the cylinder 18 is equal to or higher than a predetermined temperature. Specifically, the PCM 10 determines whether or not the engine coolant temperature is equal to or higher than a predetermined water temperature based on the detection result from the water temperature sensor SW11. That is, the temperature in the cylinder 18 is indirectly determined from the temperature of the engine coolant. If the engine cooling water temperature is equal to or higher than the predetermined water temperature, the process proceeds to step S9. If the engine cooling water temperature is lower than the predetermined water temperature, the process proceeds to step S10.

  In step S9, the PCM 10 is in a transient mode. The transient mode is performed only for one cycle. In this transient mode, the PCM 10 performs compression ignition combustion by performing high pressure retarded injection, as shown in FIG. Specifically, fuel having a pressure of 30 MPa or more is injected into the cylinder 18 at a predetermined timing at least within a period from the latter stage of the compression stroke to the early stage of the expansion stroke.

  Since the fuel cut is executed until the transition mode is entered, even if the internal EGR is executed as described above, the ratio of burnt gas contained in the EGR gas is low and the ratio of fresh air is high. ing. That is, the oxygen concentration in the cylinder 18 is high.

  Therefore, by delaying the fuel injection timing by high-pressure retarded injection, abnormal combustion such as pre-ignition can be avoided even in a situation where the oxygen concentration is high and the combustion noise is suppressed. Can do.

  Note that the PCM 10 may adjust at least one of the fuel injection timing and the pressure in accordance with the temperature in the cylinder 18 (specifically, the coolant temperature of the engine cooling water). For example, the higher the temperature in the cylinder 18, the higher the possibility of abnormal combustion such as pre-ignition, so the fuel injection timing is delayed and the fuel pressure is increased accordingly. Conversely, when the temperature in the cylinder 18 is low, the fuel injection timing is advanced and the fuel pressure is reduced. Here, only one of the fuel injection timing and the fuel pressure may be adjusted.

  At this time, the PCM 10 continues to open the exhaust twice as shown in FIG. Further, the air fuel ratio A / F of the air-fuel mixture is set to the stoichiometric air fuel ratio.

  In the transient mode, although compression ignition combustion is performed, auxiliary spark ignition may be performed after the compression top dead center. Specifically, the PCM 10 operates the spark plug 25 after the compression top dead center in the transient mode. As a result, misfire can be prevented even when the fuel injection timing is delayed.

  Thereafter, in step S10, the PCM 10 shifts to the CI mode. At this time, the PCM 10 continues to open the exhaust twice. Therefore, the EGR gas is recirculated into the cylinder 18 as shown in FIG. When the transition mode of step S9 is passed, since the burned gas is exhausted to the exhaust port 17 by the compression ignition combustion in the transient mode, most of the EGR gas is also burned gas. Therefore, the oxygen concentration in the cylinder 18 is reduced, and the possibility of abnormal combustion such as premature ignition is low. Therefore, the fuel injection timing is set between the intake stroke and the middle of the compression stroke, and the fuel pressure is set to a low pressure of less than 30 MPa. Thereby, a strong intake air flow and a long air-fuel mixture formation period combine to form a homogeneous air-fuel mixture, and the homogeneous air-fuel mixture is compressed and ignited in the vicinity of compression top dead center.

  Further, as described above, the burned gas generated by the transient mode is at a relatively low temperature, so that the temperature state in the cylinder 18 becomes low. This also avoids premature ignition. On the other hand, the burned gas is hotter than fresh air. Therefore, the cylinder 18 can be maintained at an appropriate temperature at which compression ignition combustion can be performed.

  On the other hand, when it is determined in step S8 that the engine coolant temperature is lower than the predetermined water temperature, the process proceeds to step S10 without passing through step S9. When the temperature of the engine coolant is low, that is, when the temperature in the cylinder 18 is low, the possibility of abnormal combustion such as premature ignition is low even if fuel injection is performed during the intake stroke period.

Further, when it is determined in step S7 that the operating state of the engine 1 is not within the regions (1) to ( 2 ), in step S11, the operation mode according to the region including the operating state of the engine 1 is set. Restart fuel injection. For example, if the region including the operating state of the engine 1 is a region in which high pressure retarded injection is performed, fuel injection is resumed using the high pressure retarded injection, and the region including the operating state of the engine 1 indicates the combustion injection timing. In a region where normal fuel injection that is not retarded is performed, fuel injection is resumed using normal fuel injection.

Therefore, the engine 1 according to the first embodiment sets the engine body having the cylinder 18, the injector 67 configured to inject fuel into the cylinder 18, and the pressure of the fuel injected by the injector 67. And a PCM 10 configured to operate the engine body by controlling at least the injector 67 and the fuel supply system 62. The PCM 10 includes at least the engine body. When the operating state is in a predetermined low load region (1) to ( 2 ), the compression ignition mode in which the air-fuel mixture in the cylinder 18 is combusted by self-ignition to perform the compression ignition combustion to operate the engine main body is set. When the engine body is decelerated when the engine is off, the injector 67 The fuel injection of the injector 67 is resumed when the fuel injection is stopped and the fuel cut is executed, and the rotation speed of the engine main body is reduced to a predetermined value. When the fuel injection is resumed in a state where the fuel is in the predetermined low load region (1) to ( 2 ), the fuel supply system 62 sets the fuel pressure to a high fuel pressure of 30 MPa or more and at least from the later stage of the compression stroke. The engine body is operated in a transient mode in which the injector 67 is controlled so as to perform fuel injection within a period up to the beginning of the expansion stroke, and then the fuel injection timing is advanced to shift to the compression ignition mode.

  According to the above configuration, since the high pressure retarded injection is executed when returning from the fuel cut, an increase in combustion noise can be suppressed even when the oxygen concentration in the cylinder 18 is high. After the combustion in the transient mode, the oxygen concentration in the cylinder 18 that has risen due to the fuel cut decreases, so that abnormal combustion such as premature ignition is caused even when the mode is switched to the compression ignition mode. Compression ignition combustion can be performed.

The PCM 10 is in the transient mode when the operating state of the engine body is in the predetermined low load region (1) to ( 2 ) and the temperature in the cylinder 18 is equal to or higher than the predetermined temperature. It is time to resume fuel injection.

That is, when the fuel injection is restarted in a situation where the operating state of the engine body is in the predetermined low load region (1) to ( 2 ), the high pressure retarded injection is not always performed, and the temperature in the cylinder 18 High pressure retarded injection is performed when the condition that the temperature exceeds a predetermined temperature is satisfied. When the temperature in the cylinder 18 is low, even if the oxygen concentration in the cylinder 18 is high, the possibility of abnormal combustion such as pre-ignition is low, so high-pressure retarded injection is not performed. In such a case, fuel injection is performed during the normal intake stroke period. Thus, a homogeneous air-fuel mixture can be formed by combining a strong intake air flow and a long air-fuel mixture formation period.

  Further, in the transient mode, the PCM 10 adjusts the fuel injection timing according to the temperature in the cylinder 18 to perform compression ignition combustion.

  That is, the possibility of occurrence of abnormal combustion such as premature ignition changes according to the temperature in the cylinder 18. Although retarding the fuel injection timing is effective in avoiding abnormal combustion, it may cause misfire. Therefore, the combustion injection timing is retarded as the temperature in the cylinder 18 is higher, and the fuel injection timing is advanced as the temperature in the cylinder 18 is lower. Thus, when the possibility of abnormal combustion is high, the fuel injection timing can be retarded to avoid abnormal combustion, while when the possibility of abnormal combustion is low, the fuel injection timing is unnecessarily retarded. Without misfire, misfire can be avoided. In addition, by advancing the fuel injection timing, a homogeneous air-fuel mixture can be formed by combining the intake air flow and the longer period of the air-fuel mixture formation period.

  The engine 1 further includes a spark plug 25 disposed so as to face the cylinder 18 and configured to ignite the air-fuel mixture in the cylinder 18, and the PCM 10 is in the transient mode. The spark plug 25 is operated after the compression top dead center.

  As described above, if the fuel injection timing is retarded, misfire may occur. Therefore, by operating the ignition plug 25 after the compression top dead center, it is possible to ignite auxiliaryly and avoid misfire.

  Further, the PCM 10 has a high fuel pressure mode in which the fuel body is operated at a high fuel pressure of 30 MPa or more by the fuel supply system 62, and the fuel cut is performed from the high fuel pressure mode. Until shifting to the compression ignition mode, the fuel supply system 62 is controlled so as to maintain the fuel pressure in the high fuel pressure mode.

  In other words, when fuel cut is performed from the high fuel pressure mode, combustion injection is performed at a high fuel pressure when the transition mode is entered when the combustion injection is resumed later. Like to maintain. Since a certain amount of time is required to raise the fuel pressure, fuel injection with a high fuel pressure can be performed early by maintaining a high fuel pressure.

  The engine 1 further includes an exhaust valve 22 and a VVL 71 as an exhaust gas recirculation mechanism configured to introduce exhaust gas into the cylinder 18, and the PCM 10 includes the exhaust valve 22 and the exhaust valve 22 during the fuel cut. The exhaust gas is introduced into the cylinder 18 by the VVL 71.

By introducing the exhaust gas into the cylinder 18 in this way, it is possible to suppress an increase in the oxygen concentration in the cylinder 18 during fuel cut.
<< Other Embodiments >>
In the above-described embodiment, the fuel injection of the injectors 67 of all 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 above embodiment, compression ignition combustion is performed when fuel injection is resumed, but the present invention is not limited to this. For example, spark ignition combustion may be performed when fuel injection is resumed. In other words, even when compression ignition combustion is performed when fuel injection is resumed or when spark ignition combustion is performed, abnormal combustion may occur if the oxygen concentration in the cylinder 18 is high. Therefore, it is preferable to perform high pressure retarded injection at the time of return after fuel cut, whether it is compression ignition combustion or spark ignition combustion.

  Moreover, although the said transient mode is performed only for 1 cycle, it is not restricted to this. For example, the transient mode may be performed for two cycles or more.

  In the above embodiment, the internal EGR is performed by opening the exhaust twice during the fuel cut. However, the present invention is not limited to this. For example, internal EGR by opening the intake air twice may be performed, or external EGR using the EGR passage 50 or the like may be performed. In other words, the EGR method is not limited to opening the exhaust twice. Furthermore, the structure which does not perform EGR during a fuel cut may be sufficient. However, EGR is preferably performed from the viewpoint of suppressing an increase in oxygen concentration in the cylinder 18 during fuel cut.

  In the above embodiment, 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.

  Moreover, in the said embodiment, although the temperature in the cylinder 18 is indirectly detected using the water temperature of engine cooling water, it is not restricted to this. Any configuration can be adopted as long as the temperature in the cylinder 18 can be detected.

  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)
18 cylinder 22 exhaust valve (exhaust gas recirculation mechanism)
25 Spark plug 62 Fuel supply system (fuel pressure setting mechanism)
67 Injector (fuel injection valve)
71 VVL (exhaust gas recirculation mechanism)
80 Deceleration regeneration system

Claims (6)

An engine body having a cylinder;
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 controller configured to operate the engine body by controlling at least the fuel injection valve and the fuel pressure setting mechanism;
The controller is
When at least the operating state of the engine body is in a predetermined low load region, a compression ignition mode in which the engine body is operated by performing compression ignition combustion that burns 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,
When the fuel injection is resumed in a state where the operating state of the engine body is in the predetermined low load region, the fuel pressure is set to a high fuel pressure of 30 MPa or more by the fuel pressure setting mechanism, and at least from the later stage of the compression stroke The engine body is operated in a transient mode in which the fuel injection valve is controlled to perform fuel injection within a period up to the initial period, and then the fuel injection timing is advanced within a period from the intake stroke to the middle of the compression stroke. A spark ignition direct injection engine that shifts to the compression ignition mode.
In the spark ignition direct injection engine according to claim 1,
The controller enters the transient mode when the fuel injection is restarted when the operating state of the engine body is in the predetermined low load region and the temperature in the cylinder is equal to or higher than the predetermined temperature. Ignition direct injection engine. In the spark ignition direct injection engine according to claim 1,
In the transient mode, the controller is a spark ignition type direct injection engine that adjusts the fuel injection timing according to the temperature in the cylinder to perform compression ignition combustion. The spark ignition direct injection engine according to claim 2,
Further comprising an ignition plug disposed facing the cylinder and configured to ignite the air-fuel mixture in the cylinder;
The controller is a spark ignition direct injection engine that operates the spark plug after compression top dead center in the transient mode. In the spark ignition direct injection engine according to claim 1,
The controller is
A high fuel pressure mode for operating the engine body with a high fuel pressure of 30 MPa or more by the fuel pressure setting mechanism;
A spark ignition direct injection engine that controls the fuel pressure setting mechanism so as to maintain the fuel pressure in the high fuel pressure mode until the shift to the compression ignition mode is performed when the fuel cut is performed from the high fuel pressure mode. In the spark ignition direct injection engine according to claim 1,
An exhaust gas recirculation mechanism configured to introduce exhaust gas into the cylinder;
The controller is a spark ignition direct injection engine in which the exhaust gas is introduced into the cylinder by the exhaust gas recirculation means during the fuel cut.

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