JP2014051937A - Spark ignition type engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress occurrence of preignition in changing a shift of a manual transmission in starting.SOLUTION: An engine 1 includes: a manual transmission 91; an injector 67; and a PCM (powertrain control module) 10. The PCM 10 retards fuel injection time by the injector 67 in comparison with that before changing a state of the manual transmission 91, when the manual transmission 91 is changed from a neutral state, and a rotational frequency of an engine body is lowered in starting.

Description

  The technology disclosed herein relates to a spark ignition engine.

  Patent Document 1 discloses an engine that suppresses pre-ignition that causes self-ignition earlier than desired timing. Specifically, in an engine that executes internal EGR by providing a negative overlap period in which both the intake valve and the exhaust valve are closed before and after the intake top dead center, The period from the intake top dead center to the intake valve open timing is shorter than the period from the exhaust valve close timing to the intake top dead center. In this way, a part of the gas remaining in the cylinder is blown back into the intake port when the intake valve is opened, and the residual gas is again sucked into the cylinder together with fresh air. Since a part of the residual gas is blown back into the intake port, the residual gas is cooled, so that the temperature in the cylinder can be lowered and the occurrence of pre-ignition is suppressed.

JP 2009-197740 A

  The engine according to Patent Document 1 has a problem of premature ignition that occurs due to an increase in fuel injection amount and an increase in temperature in the cylinder in a high rotation / high load region. However, the cause of premature ignition is not limited to this, and premature ignition can occur in various situations.

  The present inventor has found that pre-ignition can occur when the manual transmission is shifted up, particularly when starting.

  The technology disclosed herein has been made in view of such a point, and an object thereof is to suppress premature ignition when a shift of a manual transmission is changed when starting.

  The technology disclosed herein includes an engine body having a cylinder and a geometric compression ratio set to 15 or more, a manual transmission connected to the engine body, and fuel injection into the cylinder. A spark ignition engine comprising: a fuel injection valve configured to operate at least the fuel injection valve; and a controller configured to operate the engine main body by controlling the fuel injection valve. Sometimes, when the manual transmission is changed from the neutral state and the rotational speed of the engine body decreases, the fuel injection timing by the fuel injection valve is retarded from that before the change of the state of the manual transmission.

  In an engine equipped with a manual transmission, when the manual transmission is shifted from the neutral state to the first speed, the second speed, or the like at the time of starting, the engine speed decreases when the clutch that is once disconnected is reengaged. When the engine speed decreases, the time during which the unburned air-fuel mixture in the cylinder is exposed to high temperatures becomes longer. As a result, the possibility of premature ignition is increased.

  Therefore, according to the above configuration, when the manual transmission is changed from the neutral state at the time of starting and the rotation speed of the engine body decreases, the fuel injection timing by the fuel injection valve is changed. Make the angle slower than before. By doing so, the time during which the unburned mixture in the cylinder is exposed to a high temperature can be shortened, and as a result, the occurrence of premature ignition can be suppressed.

  Further, the technology disclosed herein has an engine body having a cylinder and a geometric compression ratio set to 15 or more, a manual transmission connected to the engine body, and fuel injection into the cylinder. A spark ignition engine comprising: a fuel injection valve configured to operate; and a controller configured to operate the engine body by controlling at least the fuel injection valve, wherein the controller includes: The fuel injection valve is configured to cause the fuel injection valve to perform split injection including at least the front-stage injection and the rear-stage injection after the front-stage injection between the intake stroke and the compression stroke. When the rotational speed of the engine main body is reduced due to the change from the neutral state, the ratio of the injection amount of the rear stage injection to the total injection amount by the fuel injection valve is set before the state change of the manual transmission It shall also be increased.

  According to the above configuration, when the manual transmission is changed from the neutral state at the time of starting and the rotational speed of the engine main body is reduced, the ratio of the injection amount of the latter stage injection in the divided injection is increased. By doing so, it is possible to reduce the fuel that is exposed to a high temperature in the cylinder, and to suppress the occurrence of pre-ignition.

  The spark ignition engine further includes a fuel pressure setting mechanism configured to set a pressure of fuel injected by the fuel injection valve, and the controller changes the manual transmission from a neutral state when starting. Then, the fuel pressure of the fuel injection when the rotational speed of the engine main body is decreased may be made higher than before the state change of the manual transmission by controlling the fuel pressure setting mechanism.

  According to the above configuration, when the manual transmission is changed from the neutral state at the time of starting and the rotational speed of the engine body decreases, the fuel injection timing is retarded, or the injection of the latter stage injection among the divided injections When increasing the proportion of the amount, the fuel pressure is increased. Therefore, even when the fuel injection timing is retarded or the ratio of the injection amount of the subsequent injection in the divided injection is increased, the required amount of fuel can be injected by the desired ignition timing.

  Further, when the fuel pressure is increased, the injection period and the mixture formation period can be shortened. Therefore, compared with the case where only the injection timing is retarded with the same fuel pressure, the time during which the unburned mixture is exposed to a high temperature can be shortened.

  In addition, when the fuel pressure is raised, the mixing property of the atomized fuel is increased, and a substantially homogeneous air-fuel mixture can be quickly formed. Therefore, even if the injection timing is retarded, the ignitability can be improved.

  Further, the controller may increase the fuel pressure by controlling the fuel pressure setting mechanism when the manual transmission is changed from the neutral state at the time of starting.

  According to the above configuration, when the manual transmission is changed from the neutral state at the time of starting, the fuel pressure is increased regardless of whether or not the rotational speed of the engine body has decreased. By so doing, when the engine speed subsequently decreases, high pressure fuel can be supplied immediately.

  30 MPa or more may be sufficient as the pressure of the fuel raised rather than before the state change of the said manual transmission.

  The spark ignition engine further includes an exhaust gas recirculation mechanism configured to introduce exhaust gas into the cylinder, and the controller causes the exhaust gas recirculation mechanism to introduce the exhaust gas into the cylinder during idling. In addition, the engine body may be operated by performing compression ignition combustion in which the air-fuel mixture in the cylinder is combusted by self-ignition.

  According to the above configuration, during idling, the exhaust gas is introduced into the cylinder and compression ignition combustion is performed. That is, in the state before the manual transmission is changed from the neutral state at the time of starting, the unburned mixture is easily ignited in the cylinder. If the time during which the fuel mixture is exposed to high temperatures becomes longer, pre-ignition tends to occur. That is, in the engine having such a configuration, it is particularly effective to retard the fuel injection timing as described above, or to increase the ratio of the injection amount of the rear stage injection in the divided injection.

  Further, the controller may perform control to retard the fuel injection timing or increase the ratio of the injection amount of the post-stage injection when the temperature in the cylinder is equal to or higher than a predetermined temperature. Good.

  That is, when the temperature in the cylinder is low, the possibility of premature ignition is low. Therefore, only when the temperature in the cylinder is high, control for retarding the fuel injection timing or control for increasing the ratio of the injection amount of the post-stage injection is performed. Thus, when the possibility of premature ignition is low, the period during which the fuel is mixed with fresh air by the intake air flow can be lengthened, and a homogeneous air-fuel mixture can be formed.

  According to the spark ignition engine, pre-ignition can be prevented from occurring when the shift of the manual transmission is changed when starting.

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 figure which shows the state of the clutch in the retard control at the time of start, a shift, and an engine speed. It is a flowchart which shows the process of retard control at the time of start.

  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 is arranged on the intake side as shown in FIG. 2. 72) and a lift variable mechanism (hereinafter referred to as CVVL (Continuously Variable Valve Lift)) 73 capable of continuously changing the lift amount of the intake valve 21. . The VVT 72 may employ a hydraulic, electromagnetic, or mechanical structure as appropriate, and illustration of the detailed structure is omitted. The CVVL 73 can also adopt various known structures as appropriate, and the detailed structure is not shown. 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. These EGR passage 50, main passage 51, EGR valve 511, EGR cooler 52, EGR cooler bypass passage 53, and EGR cooler bypass valve 531 constitute one exhaust recirculation mechanism, for example, a second exhaust recirculation mechanism.

  A manual transmission 91 is connected to the crankshaft 15 of the engine 1 via a clutch 92. The gear of the manual transmission 91 is changed according to the driver's operation of the shift lever 93.

  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> 18 are input to the PCM 10. The various sensors include the following sensors. That is, on the downstream side of the air cleaner 31, the air flow sensor SW 1 that detects the flow rate of fresh air, the intake air temperature sensor SW 2 that detects the temperature of fresh air, and the downstream side of the intercooler / warmer 34, and the intercooler / warmer 34. 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 has an exhaust temperature and exhaust gas 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 and SW15, a common rail 64 of the fuel supply system 62, and an injector A fuel pressure sensor SW16 for detecting the fuel pressure supplied to the engine 67 and detecting the vehicle speed. A vehicle speed sensor SW17 to be output and a position sensor SW18 to detect the position of the shift lever 93.

  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 longer as the fuel pressure is lower, and the injection period is shorter as the fuel pressure is higher. 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.

  The relationship between the turbulent energy and the combustion period in the combustion period is generally 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-hole injector 67 is advantageous for improving the turbulence energy in the cylinder 18 and is effective for shortening the combustion period. 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 control at start-up>
Further, the engine 1 performs a retard control at the time of start to retard the fuel injection timing when there is a shift change at the time of start (including reverse). Hereinafter, the starting retard control of the engine 1 will be described in detail with reference to FIGS. FIG. 7 is a diagram showing the state of the clutch, shift, and engine speed in the retard control at start. FIG. 8 is a flowchart showing a start retard control process.

  This starting retard control is performed when the operating state of the engine 1 is in the idling region. The idling region is the region (0) in FIG. 4 and is included in the region (1). That is, in the idling region, the engine 1 performs internal EGR by opening the exhaust twice, and injects fuel at least within the period from the intake stroke to the middle of the compression stroke, and performs compression ignition combustion.

  At the time of starting, first, the clutch pedal is operated by the driver, and the clutch 92 is disengaged (see FIG. 7A). Thereafter, the shift lever 93 is operated by the driver, and the gear in the manual transmission 91 is changed from a neutral gear to a gear position suitable for starting from 1st speed, 2nd speed, or R (reverse). Thereafter, the clutch pedal is operated by the driver, and the clutch 92 is gradually engaged. At this time, the engine speed temporarily decreases as the clutch 92 is engaged. When the engine speed decreases, the fuel injection amount increases and the engine speed returns to the original state (see the arrow in FIG. 4).

  Thus, when the gear of the manual transmission 91 is changed from neutral at the start (strictly speaking, when the clutch 92 is subsequently engaged), the engine speed is temporarily reduced. As a result, the time required for one cycle in the engine 1 becomes longer. As a result, the time during which the fuel in the cylinder 18 is exposed to a high temperature becomes longer, and the possibility of premature ignition increases. In particular, in the idling region, hot EGR gas is introduced into the cylinder 18 by opening the exhaust twice, and the air-fuel mixture is self-ignited. In such an environment, if the time during which the fuel is exposed to a high temperature is prolonged, the air-fuel mixture may self-ignite before the desired ignition timing.

  Therefore, retard injection is performed when there is a high possibility that pre-ignition can occur at the start.

  Specifically, the PCM 10 reads various signals in step S1. Specifically, the PCM 10 reads output signals from at least the water temperature sensor SW11, the crank angle sensor SW12, the fuel pressure sensor SW16, the vehicle speed sensor SW17, and the position sensor SW18.

  In step S2, the PCM 10 determines whether or not the temperature in the cylinder 18 is high. Specifically, the PCM 10 determines whether or not the temperature of the engine cooling water is equal to or higher than a predetermined water temperature. The predetermined water temperature may be set to a temperature at which abnormal combustion such as pre-ignition can occur when fuel is injected into the cylinder during the intake stroke period. That is, the temperature in the cylinder 18 is indirectly determined from the temperature of the engine coolant. The PCM 10 proceeds to step S3 when the temperature of the engine cooling water is equal to or higher than the predetermined water temperature, and proceeds to return when the temperature of the engine cooling water is lower than the predetermined water temperature. In other words, when the engine coolant temperature is lower than the predetermined water temperature, the possibility of premature ignition is low, so high pressure retarded injection is not performed, and normal fuel injection in the idling region (at least from the intake stroke to the middle of the compression stroke) Fuel injection at a low fuel pressure during the period of

  Next, in step S3, the PCM 10 determines whether or not the vehicle is stopped. Specifically, the PCM 10 determines whether or not the vehicle speed is equal to or lower than a predetermined vehicle speed. The predetermined vehicle speed may be set to a vehicle speed at which it can be determined that the vehicle is stopped, for example, 5 km / h. The PCM 10 proceeds to step S4 when the vehicle speed is equal to or lower than the predetermined vehicle speed, and proceeds to return when the vehicle speed is faster than the predetermined vehicle speed.

  In step S4, the PCM 10 determines whether or not the manual transmission 91 has been shifted from the neutral state. Specifically, the PCM 10 detects whether or not the shift lever 93 has been changed from neutral to another speed such as 1st speed, 2nd speed, or R based on the output signal from the position sensor SW18. The PCM 10 proceeds to step S5 when the shift lever 93 is changed from neutral, and proceeds to return when the shift lever 93 is not changed from neutral.

  In step S5, the PCM 10 controls the fuel supply system 62 to increase the fuel pressure. Specifically, the PCM 10 increases the fuel pressure to 30 MPa or more.

  Subsequently, in step S6, the PCM 10 determines whether or not the engine speed has decreased. Specifically, the PCM 10 determines whether or not the engine speed has become a predetermined speed or less. The predetermined rotational speed may be set to a rotational speed at which abnormal combustion such as pre-ignition can occur when fuel is injected into the cylinder during the intake stroke period. The PCM 10 proceeds to step S7 when the engine speed is equal to or lower than the predetermined speed, but repeats step S6 when the engine speed is higher than the predetermined speed.

  In step S6, it is determined whether or not the engine speed has decreased from before the shift change, or whether or not the engine speed has decreased by a predetermined value or more from before the shift change. Good.

  In step S7, the PCM 10 retards the fuel injection timing. Specifically, the PCM 10 performs fuel injection into the cylinder 18 at a predetermined timing at least within a period from the late stage of the compression stroke to the early stage of the expansion stroke. At this time, the fuel pressure is set to 30 MPa or more in the previous step S5.

  That is, when the temperature in the cylinder 18 is high, and the manual transmission 91 is shifted from neutral to another gear position when starting, and the engine speed decreases, the fuel injection timing is retarded. Thereby, since the time which an air-fuel mixture is exposed to high temperature can be shortened, it can suppress that abnormal combustion, such as premature ignition, arises.

  On the other hand, when the temperature in the cylinder 18 is low, when the vehicle is not stopped, or when the manual transmission 91 is not shifted from neutral, fuel injection is executed with the normal setting of the idling region.

  Therefore, the engine 1 of the first embodiment has the cylinder 18, the engine main body in which the geometric compression ratio is set to 15 or more, the manual transmission 91 connected to the engine main body, and the cylinder 18. An injector 67 configured to inject fuel; and a PCM 10 configured to operate the engine main body by controlling at least the injector 67. The PCM 10 is configured so that the manual transmission 91 is When the rotational speed of the engine main body is reduced from the neutral state, the fuel injection timing by the injector 67 is retarded from before the state change of the manual transmission 91.

  According to the above configuration, when the manual transmission 91 is changed from the neutral state at the time of starting and the engine body speed is reduced, the fuel injection timing is retarded, so that the unburned mixture is exposed to a high temperature. The time it takes is shortened. As a result, the occurrence of abnormal combustion such as premature ignition can be suppressed.

  The engine 1 further includes a fuel supply system 62 configured to set the pressure of the fuel injected by the injector 67, and the PCM 10 includes the manual transmission 91 changed from a neutral state at the start and the The fuel pressure of the fuel injection when the rotational speed of the engine body is reduced is controlled to be higher than that before the state change of the manual transmission 91 by controlling the fuel supply system 62. That is, the fuel pressure when retarding the fuel injection timing is made higher than that before the manual transmission 91 is changed. Specifically, the fuel pressure is set to 30 MPa or more.

  If the combustion injection timing is retarded, the time from the start of injection to the desired ignition timing is shortened. Depending on the pressure of the fuel, the required fuel may not be completely injected by the desired ignition timing. Therefore, by increasing the fuel pressure, the amount of fuel injected per unit time increases, so that the required fuel can be injected completely by the desired ignition timing.

  Further, when the fuel pressure is increased, the injection period and the mixture formation period can be shortened. Therefore, compared with the case where only the injection timing is retarded with the same fuel pressure, the time during which the unburned mixture is exposed to a high temperature can be shortened.

  In addition, when the fuel pressure is raised, the mixing property of the atomized fuel is increased, and a substantially homogeneous air-fuel mixture can be quickly formed. Therefore, even if the injection timing is retarded, the compression ignition can be reliably performed.

  The PCM 10 controls the fuel supply system 62 to increase the fuel pressure when the manual transmission 91 is changed from the neutral state at the time of start.

  In the fuel supply system 62, the fuel pressure is increased by the fuel pump 63. Therefore, it takes some time to increase the fuel pressure. Therefore, in preparation for when the engine speed decreases, the fuel pressure is increased in advance when the shift of the manual transmission 91 is changed. By doing so, high pressure fuel can be injected immediately when the engine speed subsequently decreases.

  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 is operated by the exhaust valve 22 and the VVL 71 during idling. The exhaust gas is introduced into the cylinder 18 and 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.

  The engine 1 is in an idling state before starting, and at the time of idling, EGR is performed and compression ignition combustion is performed. That is, before starting, the inside of the cylinder 18 is heated to an environment in which the air-fuel mixture self-ignites. Therefore, in such a state, if the engine speed decreases and the time during which the unburned mixture is exposed to a high temperature becomes longer, abnormal combustion such as pre-ignition tends to occur. That is, in such an engine 1, it is particularly effective to perform the aforementioned retard injection.

  Further, the PCM 10 performs control to retard the fuel injection timing when the temperature in the cylinder 18 is equal to or higher than a predetermined temperature.

  That is, if the temperature in the cylinder 18 is low, there is a low possibility that abnormal combustion such as pre-ignition occurs even if the engine speed decreases. Therefore, when the temperature in the cylinder 18 is low, the fuel injection timing is not unnecessarily retarded. Accordingly, a homogeneous air-fuel mixture can be formed by combining the intake air flow and the lengthening of the air-fuel mixture formation period.

  In addition, when retarding the fuel injection timing, the PCM 10 uniformly delays the fuel injection timing until a predetermined timing within a period from the latter stage of the compression stroke to the early stage of the expansion stroke, but is not limited thereto. For example, the PCM 10 may adjust the amount by which the fuel injection timing is retarded according to the temperature in the cylinder 18 (for example, the temperature of engine cooling water). Specifically, the amount by which the fuel injection timing is retarded may be increased as the temperature in the cylinder 18 is higher. That is, as the temperature in the cylinder 18 increases, the possibility of abnormal combustion such as pre-ignition increases, and accordingly, the amount by which the fuel injection timing is retarded is increased. By doing so, it is possible to achieve a balance between avoiding abnormal combustion and forming a homogeneous air-fuel mixture.

  At that time, the fuel pressure may also be adjusted according to the temperature in the cylinder 18 (for example, the temperature of the engine coolant). Specifically, the fuel pressure may be increased as the temperature in the cylinder 18 increases. According to the above configuration, as the temperature in the cylinder 18 increases, the fuel injection timing is retarded, so the period from the fuel injection start timing to the desired ignition timing is shortened. For this reason, there is a possibility that necessary fuel may not be injected by the desired ignition timing. Therefore, the fuel pressure is set to such a pressure that the necessary fuel can be injected during the period from the retarded fuel injection timing to the desired ignition timing.

<< Embodiment 2 >>
Next, Embodiment 2 will be described.

  The engine 1 according to the second embodiment performs split fuel injection.

  Specifically, the PCM 10 controls the injector 67 at least in the idling region (0), once during the intake stroke to the middle of the compression stroke, once during the latter half of the compression stroke and the beginning of the expansion stroke, a total of 2 Fuel injections are performed. Hereinafter, the previous fuel injection is referred to as the front injection, and the subsequent fuel injection is referred to as the rear injection.

  Normally, the PCM 10 increases the injection amount of the pre-stage injection more than the injection amount of the post-stage injection, and controls the injector 67 so that more fuel is injected before the end of the compression stroke. For example, the ratio of the injection amount of the front injection and the injection amount of the rear injection is set to 9: 1.

  On the other hand, when the temperature in the cylinder 18 is high, the manual transmission 91 is shifted from neutral to another gear position at the time of starting, and the engine speed decreases, the ratio of the injection amount of the subsequent injection to the total injection amount Is higher than before the shift change. For example, the ratio of the injection amount of the front injection and the injection amount of the rear injection is set to 1: 9. Thereby, there can exist an effect similar to the above-mentioned retard injection. That is, by increasing the ratio of the post-injection injection amount, the fuel that is exposed to high temperatures can be reduced, and the occurrence of abnormal combustion such as premature ignition can be suppressed.

  Further, when increasing the ratio of the injection amount of the post-stage injection, the fuel pressure is increased. Specifically, the fuel pressure is set to 30 MPa.

  When the ratio of the injection amount of the post-injection is increased, depending on the fuel pressure, the required fuel may not be completely injected by the desired ignition timing. Therefore, by increasing the fuel pressure, the amount of fuel injected per unit time increases, so that the required fuel can be injected completely by the desired ignition timing.

  Further, when the fuel pressure is increased, the injection period and the mixture formation period can be shortened. Therefore, the time during which the unburned mixture is exposed to a high temperature can be shortened as compared with a case where only the ratio of the injection amount of the subsequent injection is increased at the same fuel pressure.

  In addition, when the fuel pressure is raised, the mixing property of the atomized fuel is increased, and a substantially homogeneous air-fuel mixture can be quickly formed. Therefore, even if the ratio of the injection amount of the post-stage injection is increased, the compression ignition can be surely performed.

  Similarly to the first embodiment, the PCM 10 increases the fuel pressure in advance when the shift of the manual transmission 91 is changed. Further, the PCM 10 performs control to increase the ratio of the post-injection injection amount when the temperature in the cylinder 18 is equal to or higher than a predetermined temperature.

  Therefore, the engine 1 of the second embodiment includes the cylinder 18 and has an engine main body whose geometric compression ratio is set to 15 or more, a manual transmission 91 connected to the engine main body, and the cylinder 18. An injector 67 configured to inject fuel; and a PCM 10 configured to operate the engine body by controlling at least the injector 67, wherein the PCM 10 is between an intake stroke and a compression stroke. The injector 67 is configured to cause the injector 67 to perform split injection including at least the front-stage injection and the rear-stage injection after the front-stage injection, and the engine main body is changed when the manual transmission 91 is changed from the neutral state when starting. The ratio of the injection amount of the latter stage injection to the total injection amount by the injector 67 To be higher than before the state change of 該手 dynamic transmission 91.

  According to the above configuration, when the manual transmission 91 is changed from the neutral state at the time of start-up and the rotational speed of the engine main body decreases, the ratio of the injection amount of the post-injection increases, so that it is exposed to a high temperature for a long time. Fuel is reduced. As a result, the occurrence of abnormal combustion such as premature ignition can be suppressed.

  In addition, the ratio of the injection quantity of the above-mentioned front | former stage injection and the injection quantity of a back | latter stage injection is an example, Comprising: Other ratios may be sufficient.

  Further, as long as the pre-injection is first and the post-injection is later, the respective injection timings may be set at any timing. For example, both the pre-stage injection and the post-stage injection may be set between the late stage of the compression stroke and the early stage of the expansion stroke.

Furthermore, the ratio of the post-injection injection amount to the total injection amount may be adjusted according to the temperature in the cylinder 18. Specifically, the ratio of the injection amount of the post-stage injection to the total injection amount may be increased as the temperature in the cylinder 18 becomes higher. Furthermore, if the injection amount of the post-injection is too large, it may occur that the necessary fuel cannot be injected by the desired ignition timing if the fuel pressure remains low. Therefore, the fuel pressure may be increased in accordance with an increase in the ratio of the post injection amount to the total injection amount.
<< Other Embodiments >>
In the above-described embodiment, the compression ignition combustion is performed in the idling region (0) while performing the internal EGR by opening the exhaust twice, but this is not restrictive. That is, EGR may or may not be performed in the idling region (0). Even if EGR is performed, it does not have to be due to the double opening of the exhaust. Also, the combustion mode is not limited to compression ignition combustion.

  In the first embodiment, the fuel injection timing is retarded to a predetermined timing within the period from the late stage of the compression stroke to the early stage of the expansion stroke when there is a shift change at the start and the engine speed decreases. It is not limited to. That is, as long as the fuel injection timing is retarded from before the shift change, the fuel injection timing is not limited to the above timing.

  In the above embodiment, the fuel pressure is increased when the fuel injection timing is retarded, or when the ratio of the injection amount of the post-injection is increased, but this is not a limitation. That is, without changing the fuel pressure, the fuel injection timing may be retarded or the ratio of the injection amount of the subsequent injection may be increased.

  Each step in the flowchart 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)
62 Fuel supply system (fuel pressure setting mechanism)
67 Injector (fuel injection valve)
71 VVL (exhaust gas recirculation mechanism)
91 Manual transmission

Claims (8)

An engine body having cylinders and a geometric compression ratio set to 15 or higher;
A manual transmission connected to the engine body;
A fuel injection valve configured to inject fuel into the cylinder;
A controller configured to operate the engine body by controlling at least the fuel injection valve;
When the manual transmission is changed from the neutral state at the time of starting and the rotational speed of the engine body is reduced at the time of starting, the controller retards the fuel injection timing by the fuel injection valve from before the state change of the manual transmission. A spark ignition engine. An engine body having cylinders and a geometric compression ratio set to 15 or higher;
A manual transmission connected to the engine body;
A fuel injection valve configured to inject fuel into the cylinder;
A controller configured to operate the engine body by controlling at least the fuel injection valve;
The controller is
Between the intake stroke and the compression stroke, the fuel injection valve is configured to cause the fuel injection valve to perform split injection including at least the front injection and the rear injection after the front injection,
When the manual transmission is changed from the neutral state at the time of start-up, and the rotational speed of the engine body decreases, the ratio of the injection amount of the rear stage injection to the total injection amount by the fuel injection valve is set before the state change of the manual transmission. Spark ignited engine to make it higher. The spark ignition engine according to claim 1 or 2,
A fuel pressure setting mechanism configured to set a pressure of fuel injected by the fuel injection valve;
The controller controls the fuel pressure setting mechanism by controlling the fuel pressure setting mechanism when the manual transmission is changed from the neutral state at the time of start and the engine body speed decreases, and the fuel pressure setting mechanism controls the manual transmission. A spark ignition engine that is higher than before the change of state. The spark ignition engine according to claim 3,
The controller is a spark ignition type engine that controls the fuel pressure setting mechanism to increase the fuel pressure when the manual transmission is changed from the neutral state at the time of starting. The spark ignition engine according to claim 3,
A spark ignition engine in which the pressure of the fuel that is increased more than before the state change of the manual transmission is 30 MPa or more. The spark ignition engine according to claim 1 or 2,
An exhaust gas recirculation mechanism configured to introduce exhaust gas into the cylinder;
When idling, the controller introduces the exhaust gas into the cylinder by the exhaust gas recirculation mechanism and performs compression ignition combustion in which the air-fuel mixture in the cylinder is combusted by self-ignition so as to operate the engine body. A spark ignition engine that is configured to. The spark ignition engine according to claim 1,
The controller is a spark ignition engine that performs control to retard the fuel injection timing when the temperature in the cylinder is equal to or higher than a predetermined temperature. The spark ignition engine according to claim 2,
The controller is a spark ignition engine that performs control to increase a ratio of an injection amount of the post-stage injection when a temperature in the cylinder is equal to or higher than a predetermined temperature.

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