JP2005256777A - Cylinder direct injection type engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable injected fuel to be contained in a cavity even when fuel is injected at an early stage, resulting in enlargement of an operation region where stratified charge combustion can be effected, in a cylinder direct injection type engine to produce stratified charge air-fuel mixture by injecting fuel directly in a cavity. <P>SOLUTION: The cylinder direct injection engine is provided with a crank shaft 42; a piston 3 slidably contained in a cylinder 22 and having a cavity 31 formed in a crown surface; a fuel injection valve 14 to inject fuel toward the cavity; and double link type piston crank mechanisms (40, 41, and 44) coupled to the piston 3, the crank shaft 42, and an engine element 2 and altering the piston motion of the piston. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an in-cylinder direct injection engine that directly injects fuel into a cylinder.

Japanese Patent Laid-Open No. 2003-83119 (Patent Document 1) directly injects fuel from a fuel injection valve into a cylinder, forms a stratified mixture in the cylinder, and burns at an air-fuel ratio that is significantly leaner than the stoichiometric air-fuel ratio An in-cylinder direct injection engine is disclosed. In this engine, the fuel is injected toward the cavity formed in the piston crown surface at a time earlier than the compression top dead center of the piston, the fuel and air are mixed in the cavity, and the homogeneous air-fuel mixture in the cavity. Is formed.
JP 2003-83119 A

  In order to homogenize the air-fuel mixture in the cavity, it is necessary to inject fuel at an earlier time and to ensure time for fuel and air to mix.

  However, since the fuel spray injected from the fuel injection valve diffuses away from the injection port, if the fuel injection timing is advanced, the fuel injected from the fuel injection valve does not fit in the cavity after a certain period. It will stick out. If the fuel protrudes from the cavity, the fuel adheres to the inner wall of the cylinder, etc., so that the amount of unburned HC increases, and the cooling loss of the engine increases, resulting in deterioration of fuel consumption. In the above prior art, the fuel and air mixing time is ensured by advancing the fuel injection timing. However, considering that the injected fuel is surely contained in the cavity, there is a limit to the advancement of the fuel injection timing. is there.

  During high-speed operation where the actual cycle time is shortened or during high-load operation where the amount of fuel injected increases, it is necessary to secure the time for fuel and air to be mixed by advancing the fuel injection timing. Since there is a limit to the early timing of fuel injection, it has been difficult to expand the stratified combustion operation region to the high rotation side and the high load side.

  The present invention has been made in view of such a technical problem, and in a direct injection type in-cylinder engine that forms a stratified mixture by injecting fuel into a cavity, the fuel is injected even if it is injected early. An object is to expand the operating range in which stratified combustion can be performed by allowing the fuel to be contained in the cavity.

  In an in-cylinder direct injection engine, a crankshaft, a piston slidably accommodated in the cylinder and having a cavity formed in a crown surface, a fuel injection valve for injecting fuel toward the cavity, a piston and a crank A multi-link piston crank mechanism connected to the shaft and the engine body for changing the piston motion of the piston;

  If the piston motion is changed by using the multi-link type piston crank mechanism, the acceleration of the piston near the top dead center can be reduced and the rising speed of the piston until it approaches the top dead center can be increased. As a result, even if the fuel injection timing is advanced, the fuel spray can be contained in the cavity, and the mixing time of fuel and air (real time) can be ensured. Can be expanded to the load side.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  1 and 2 show the configuration of a spark ignition gasoline engine according to the present invention. FIG. 1 shows the engine viewed from the axial direction of the crankshaft, and FIG. 2 shows the engine viewed from the intake side. It is.

  A combustion chamber 4 is defined between the cylinder head 1, the cylinder block 2 and the piston 3, and an intake port 5 and an exhaust port 6 formed in the cylinder head 1 communicate with the combustion chamber 4. The intake port 5 and the exhaust port 6 are opened and closed at predetermined timings by an intake valve 10 and an exhaust valve 11 driven by an intake cam 8 and an exhaust cam 9, respectively.

  An ignition plug 13 is provided in the approximate center of the upper portion of the combustion chamber 4 so as to project the gap into the combustion chamber 4, and a fuel injection valve 14 is provided near the ignition plug 13 with its nozzle hole. It is provided so as to protrude into the combustion chamber 4. A plurality of nozzle holes of the fuel injection valve 14 are formed at the tip, and fuel can be injected into the combustion chamber 4 at a predetermined spray angle θ as shown in FIG.

  The cylinder block 2 is formed with a cylinder 22 that slidably accommodates the piston 3, and a cooling water passage 24 is formed around the cylinder 22. Further, a cylindrical cavity 31 is recessed in the approximate center of the crown surface 3 a of the piston 3.

  The piston 3 is connected to the crankshaft 42 via a connecting rod 40 (first link) and a lower link 41 (second link). A control link 44 (third link) is connected to the lower link 41, and the other end of the control link 44 is connected to an engine body, for example, a lower portion of the cylinder block 2 via an eccentric portion 46 of the control shaft 45. It is connected. In this embodiment, the control link 44 is connected to the lower link 41, but the control link 44 may be connected to the connecting rod 40 instead of the lower link 41. In this manner, the piston 3 is connected to the crankshaft 42 through the “double link” including the connecting rod 40, the lower link 41, and the control link 44, and the mechanism for driving the piston 3 is referred to as a “double link type piston crank mechanism”. Called.

  The multi-link type piston crank mechanism will be further described. FIG. 4 is a view of FIG. 1 as viewed from the direction of the arrow X. The control shaft 45 is pivotally supported on the lower part of the cylinder block 2 via bearing covers 50 and 51. The eccentric portion 45 formed in the middle of the control shaft 45 is disposed between the bearing covers 50 and 51, and the control link 44 is connected to the outer periphery of the eccentric portion 45. A worm wheel 53 is provided at one end of the control shaft 45, and a motor 54 is connected to the worm wheel 53 via a worm gear 55. The motor 54 is driven in response to a signal from the engine controller 20. When the motor 54 is driven to rotate, the worm gear 55 and the worm wheel 53 rotate, whereby the control shaft 45 rotates and the rotation angle of the eccentric portion 46 changes. .

  When the rotation angle of the eccentric portion 46 is changed, the rotation center of the control link 44 with respect to the engine body moves, so that the piston motion (the piston top dead center position, acceleration near the top dead center) when the crankshaft 42 rotates is changed. Change. For example, if the rotation angle of the eccentric portion 46 is adjusted to an appropriate angle, only the acceleration of the piston 3 near the top dead center can be reduced without changing the top dead center position of the piston 3 almost. If the acceleration of the piston 3 near the top dead center is reduced, the speed of the piston 3 when it rises to near the top dead center increases, so that the piston 3 approaches the top dead center at an earlier time and the piston 3 Stays longer near the dead center. Alternatively, although not used in this embodiment, it is possible to raise the top dead center position of the piston 3 to increase the compression ratio of the engine and reduce the acceleration of the piston 3 near the top dead center. It is also possible to lower the top dead center position 3 to reduce the compression ratio and to reduce the acceleration near the top dead center.

  FIG. 5 shows a history of piston motion when the acceleration of the piston 3 near the top dead center is reduced without changing the top dead center position of the piston 3. For comparison, FIG. 5 shows a history of piston motion of the engine (hereinafter referred to as a multi-link type engine) including the multi-link type piston crank mechanism shown in FIGS. Piston motion of an engine equipped with a conventional single link type piston crank mechanism (configuration in which the piston and crankshaft are directly connected by a connecting rod) with the same height from the shaft center to the cylinder upper surface (hereinafter referred to as a single link type engine) Show.

  As shown in this figure, in the multi-link engine, the acceleration near the top dead center is smaller than the acceleration near the bottom dead center, and the piston motion history becomes a sine curve near the top dead center. That is, without substantially changing the top dead center position of the piston 3, only the acceleration of the piston 3 near the top dead center can be made smaller than the acceleration of the piston 3 near the single link type engine or near the bottom dead center. . The fact that the acceleration of the piston 3 near the top dead center becomes small means that the piston 3 approaches the top dead center position at an earlier time, and the displacement amount of the piston 3 near the top dead center becomes small. Means staying longer near top dead center.

  6 (a) to 6 (c) and FIGS. 7 (a) to 7 (c) show the state of fuel spray in the combustion chamber in time series when fuel is injected toward the cavity at a certain crank angle. Is. FIG. 6 shows a case of a single link type engine, and FIG. 7 shows a case of a multi-link type engine in which the piston acceleration near the top dead center is made smaller than that of the single link type engine without changing the top dead center position of the piston. Fuel is injected at the same crank angle in both FIGS. 6 and 7, but the piston motion is different between the multi-link engine and the single-link engine, so the piston position is different even at the same crank angle and injected into the combustion chamber. The movement of fuel spray is different between the two.

  In the single link type engine, as shown in FIGS. 6A to 6C, the piston acceleration near the top dead center is large because the piston acceleration near the top dead center is large. At the timing of fuel injection, the piston is still in a low position. Therefore, the fuel spray injected from the fuel injection valve does not fit in the cavity and protrudes outside the cavity. The fuel spray that protrudes from the cavity is reflected on the outside of the piston crown and flows toward the cylinder side wall, so it adheres to the cylinder side wall, increasing the amount of unburned HC and increasing the engine cooling loss. It becomes a cause to deteriorate the fuel consumption.

  On the other hand, in the multi-link engine, as shown in FIGS. 7A to 7C, even if fuel is injected at the same timing as the single-link engine, the piston 3 is closer to the top dead center. Therefore, almost all of the injected fuel spray is contained in the cavity, and further, a circulating flow that is guided to the bottom and side surfaces of the cavity and swirls vertically toward the vicinity of the spark plug provided in the center of the combustion chamber. Thus, it is possible to enclose the surrounding air and form a homogeneous air-fuel mixture with little concentration unevenness in the cavity and above (in the vicinity of the spark plug). In other words, in a multi-link engine, fuel spray can be stored in the cavity even when fuel is injected earlier than in a single-link engine, and the mixing time (real time) of fuel and air is sufficiently long. can do.

  Referring back to FIG. 1, the engine configuration according to the present invention will be further described. The engine controller 20 includes a rotation speed sensor (crank angle sensor) 25 for detecting the rotation speed of the engine as a signal indicating the engine operating state, an accelerator. Signals from an accelerator operation amount sensor 26 that detects the pedal operation amount, a throttle opening sensor 27 that detects the throttle valve opening, and the like are input.

  The engine controller 20 calculates a target engine torque based on the input signal, the amount of fuel injected from the fuel injection valve 14 so as to realize the target engine torque, the timing of fuel injection, and the ignition by the spark plug 13. Controls timing and throttle valve opening.

  Further, the engine controller 20 refers to a combustion mode map as shown in FIG. 9 according to the operating point of the engine, switches the combustion mode of the engine, and in the low / medium rotation and low / medium load region, the top dead center of the compression stroke. A stratified combustion mode in which fuel is injected into the cavity before this to form a homogeneous mixture in and above the cavity 31, and the combustion chamber 4 as a whole is burned at an air / fuel ratio that is significantly leaner than the stoichiometric air / fuel ratio. And In a high rotation region where the actual cycle time is shortened or in a high load region where the amount of fuel to be injected increases and the fuel injection time is increased, fuel is injected into the cylinder 22 during the intake stroke, and the fuel and air mixing time is increased. Is set to a homogeneous combustion mode in which combustion is performed after a homogeneous air-fuel mixture having a stoichiometric air-fuel ratio is formed in the entire combustion chamber 4. Further, in the engine according to the present invention, by utilizing the characteristics of the multi-link type piston crank mechanism, the acceleration near the top dead center of the piston 3 is switched according to the combustion mode of the engine, and the region where the stratified combustion operation can be performed is provided. Expands to higher speeds and higher loads than single link engines.

  FIG. 8 is a flowchart showing the contents of the combustion mode switching control performed by the engine controller 20 and is executed every predetermined time, for example, every 10 msec.

  According to this, first, in step S1, the engine speed and the engine load are read. The detection value of the rotation speed sensor 25 is read as the engine rotation speed, and the target engine torque calculated in the engine controller 20 is read as the engine load. Here, the target engine torque is used as a value indicating the engine load. Instead, the accelerator operation amount, the fuel injection amount (the valve opening time of the fuel injection valve 14, the energization of the fuel injection valve 14) is used. Time, target fuel injection amount calculated by the engine controller, etc.) may be used.

  Next, in step S2, the engine combustion mode is determined with reference to the combustion mode map shown in FIG. 9 based on the engine speed and load read in step S1. When it is determined that the operating point of the engine is in the region A (first operating region) which is the low / medium speed rotation and low / medium load region, the process proceeds to step S3 and the region A is moved to the high rotation side and the high load side. If it is determined that the vehicle is in the region B (second operation region) set so as to surround the outside of the region A, the process proceeds to step S5.

  In step S3, where the engine operating point is in the region A, the engine combustion mode is switched to the stratified combustion mode. In the stratified combustion mode, fuel is injected into the cavity 31 before the compression top dead center, and a homogeneous air-fuel mixture is formed in and above the cavity 31 (near the spark plug 13). Switch to the stratified combustion mode where ignition and combustion are performed by spark ignition.

  Furthermore, in this stratified combustion mode, it is necessary to sufficiently mix fuel and air in the cavity 31 to form a homogeneous mixture in and above the cavity 31, so in step S4, the motor 54 is driven. The rotational angle of the eccentric portion 46 of the control shaft 45 is changed, and the acceleration of the piston 3 near the top dead center is decreased while the top dead center position of the piston 3 remains unchanged. As a result, the rising speed until the piston 3 approaches the top dead center increases, and the piston 3 approaches the top dead center position at an earlier time (with an earlier crank angle), so that the fuel is faster than the single link engine. Even if the fuel is injected at the time, the injected fuel can be accommodated in the cavity 31, and the mixing time can be increased, so that the injected fuel and air can be sufficiently mixed.

  On the other hand, in step S5, which has been performed assuming that the operating point of the engine is in the region B which is the high rotation / high load region, the engine combustion mode is switched to the homogeneous combustion mode. In the homogeneous combustion mode, fuel is injected into the cylinder 22 during the intake stroke of the engine, the fuel and air are sufficiently mixed to form a homogeneous mixture in the entire combustion chamber 4, and spark ignition from the spark plug 13 is performed. Ignite and burn. Further, in step S6, the motor 54 is driven to rotate the eccentric portion 46, and the acceleration of the piston near the top dead center is decreased while the top dead center position of the piston remains unchanged. Thereby, the piston 3 can be quickly retracted from the vicinity of the top dead center, and the engine cooling loss due to the piston 3 remaining in the vicinity of the top dead center position for a long time can be suppressed.

  As described above, in the engine according to the present invention, the piston motion of the piston 3 is changed using the multi-link piston crank mechanism in the stratified combustion mode to reduce the acceleration of the piston 3 near the top dead center. 9 (region A in FIG. 9) can be expanded to a higher load side and a higher rotation side than the single link type engine as indicated by an arrow Y in FIG. This is because even if fuel is injected earlier, the fuel spray can be stored in the cavity 31, and the piston 3 stays in the vicinity of the top dead center for a long time, so that the fuel and air are sufficiently mixed. It is because it can do.

  Furthermore, since a high-temperature and high-pressure field is continuously formed in the vicinity of the top dead center, fuel atomization and evaporation are promoted, and stable combustion can be realized. Also, if the stratified combustion region is expanded to the high load side, the amount of injected fuel increases, so in a single link engine, mixing of fuel and air does not proceed sufficiently, and overmixing with an equivalence ratio of 2 or more The increase in black smoke, which is supposed to be generated from the air mass, becomes a problem, but in the multi-link engine according to the present invention, since the mixture is sufficiently homogenized, the generation of black smoke can be sufficiently suppressed. .

  Further, since the fuel injection valve 14 is provided at the center of the upper portion of the combustion chamber 4 and the cavity 31 is recessed at the center of the crown surface of the piston 3, the combustion is performed at the center of the combustion chamber away from the side surface of the combustion chamber. Can be reduced, and fuel consumption can be improved.

  Subsequently, a second embodiment of the present invention will be described.

  The configuration of the engine according to the second embodiment is the same as that of the first embodiment shown in FIGS. 1 to 4, but the engine combustion mode is different. In the second embodiment, compression self-ignition operation without using a spark plug is performed in a low / medium speed rotation and low / medium load region (first operation region), and ignition is performed in a high speed or high load region (second operation region). Perform spark ignition operation using a plug.

  FIG. 10 is a flowchart showing the contents of the combustion mode switching control performed by the engine controller 20, and is executed every predetermined time, for example, every 10 msec.

  This will be described. First, in step S11, the engine speed and the engine load are read. The detection value of the rotation speed sensor 25 is read as the engine rotation speed, and the target engine torque calculated inside the engine is read as the engine load. Here, the target engine torque is used as a value indicating the engine load. Instead, the accelerator operation amount, the fuel injection amount (the valve opening time of the fuel injection valve 14, the energization time to the fuel injection valve 14, A target fuel injection amount or the like calculated by the engine controller may be used.

  In step S12, based on the engine speed and load read in step S11, the engine combustion mode is determined with reference to the combustion mode map shown in FIG. When it is determined that the engine operating point is in the region C that is the low and medium speed rotation and low load region, the process proceeds to step S13, and when it is determined that the engine operating point is in the region D that is the low and medium speed rotation and medium load region. Proceeding to step S15, when it is determined that the vehicle is in the region E that is the high rotation or high load region outside the region D, the process proceeds to step S17.

  In step S13, which has proceeded assuming that the engine operating point is in region C, the engine combustion mode is set to the stratified compression self-ignition mode. In the stratified compression self-ignition mode, fuel is injected before the compression top dead center to form a homogeneous mixture in the cavity 31 and above (in the vicinity of the spark plug 13). Drive to ignite. Furthermore, in order to form a homogeneous air-fuel mixture in and above the cavity 31, the injection timing at which the injected fuel can be accommodated in the cavity 31 is advanced, and the mixing time of the fuel and air in the cavity 31 is increased. Since it is better to make it longer, and in order to auto-ignite the air-fuel mixture at a high temperature and high pressure in the combustion chamber, it is better that the compression ratio of the engine is high. The acceleration before and after the top dead center is reduced and the top dead center position of the piston 3 is raised to increase the compression ratio of the engine. Specifically, the motor 54 is driven to rotate the eccentric portion 46 of the control shaft 45 by a predetermined amount, and the rotation angle is changed.

  Since the cavity 31 is recessed substantially at the center of the piston crown surface 3 a and is disposed at the approximate center of the combustion chamber 4, the combustion flame is far from the wall surface of the combustion chamber 4 during operation in this stratified compression self-ignition mode. Thus, the cooling loss of the engine is reduced, and in combination with the high compression ratio of the engine, combustion with good fuel consumption can be realized. Further, by using a multi-link type piston crank mechanism, fuel spray can be stored in the cavity 31 even if the fuel injection timing is advanced, and the mixing time of the fuel and air in the cavity 31 is reduced. Since the length is increased, the operating range in which the stratified compression self-ignition operation can be performed can be expanded to the high load side and the high rotation side as compared with the single link type engine.

  On the other hand, in step S15 which has proceeded as being in the region D, the combustion mode of the engine is set to the homogeneous compression self-ignition mode. In region D, the engine load is higher than in region C, so the amount of fuel injected from the fuel injection valve 14 increases, and when the mixture is stratified as in region C, the fuel in the cavity 31 becomes thicker. In addition, even if the acceleration of the piston 3 near the top dead center is lowered using the multi-link type piston crank mechanism, it is difficult to ensure a sufficient mixing time of fuel and air.

  Therefore, in this region D, the stratification of the air-fuel mixture is stopped, a substantially homogeneous air-fuel mixture is formed in the entire combustion chamber 4 and the compression self-ignition operation without using the spark plug 13 is performed. As a method of forming a substantially homogeneous air-fuel mixture in the entire combustion chamber 4, the fuel is injected a plurality of times such that the first injection is injected outside the cavity 31 and the second injection is injected into the cavity 31. The fuel and air in the combustion chamber 4 are injected at an early timing such that the fuel spray does not directly enter the cavity 31. Any method such as a method of sufficiently mixing may be adopted.

  Further, in order to make the air-fuel mixture in the combustion chamber 4 homogeneous, it is preferable to reduce the acceleration of the piston 3 near the top dead center to ensure a sufficient mixing time, and to perform the compression self-ignition operation. Since the combustion chamber should be at a high temperature and high pressure, the acceleration of the piston 3 near the top dead center is reduced and the top dead center position of the piston 3 is raised using a multi-link piston crank mechanism. Increase the compression ratio of the engine.

  In this homogeneous combustion self-ignition mode, a substantially homogeneous air-fuel mixture is formed in the entire combustion chamber 4 to cause compression self-ignition. Therefore, there is a problem of pre-ignition and knocking caused by the presence of a locally rich air-fuel mixture. Can be avoided. In addition, by using a multi-link type piston crank mechanism to increase the compression ratio of the engine, it is possible to increase the combustion stability during compression self-ignition combustion and to expand the operating range in which compression self-ignition operation is possible. .

  When the operating point of the engine is in the region E, the process proceeds to step S17, and the engine combustion mode is switched to the spark ignition mode. In the spark ignition mode, fuel is injected into the cylinder 22 during the intake stroke of the engine, and the fuel and air are sufficiently mixed and then ignited using the spark plug 13. This is because the amount of fuel injected is increased in the high load region, and the actual cycle time is shortened in the high rotation region, so that a sufficient mixture time of fuel and air cannot be secured, thereby forming a homogeneous mixture. This is because it is difficult to prematurely ignite and knock.

  Further, in step S18, the acceleration of the piston 3 near the top dead center is increased using the multi-link piston crank mechanism, and the piston 3 is quickly retracted from the vicinity of the top dead center to reduce the engine cooling loss. Further, the top dead center position of the piston 3 is lowered to lower the compression ratio of the engine, thereby suppressing the occurrence of pre-ignition and knocking in a high load and high rotation region, thereby realizing a high output operation.

  As described above, in this embodiment, the compression self-ignition operation is performed in the low / medium speed rotation and low load region. At this time, the acceleration of the piston 3 near the top dead center is reduced by using the multi-link type piston crank mechanism. In addition, since the top dead center position of the piston 3 is raised to increase the compression ratio, the compression ignition operation can be stably performed, and the operation range in which the compression self-ignition operation can be performed is high, The fuel consumption can be improved by expanding to the load side.

  Further, in a high rotation or high load region, the piston acceleration mechanism near the top dead center is increased by using a multi-link piston crank mechanism, and the top dead center position of the piston 3 is lowered to lower the compression ratio. Therefore, pre-ignition and knocking in a high rotation and high load region can be effectively suppressed.

  Subsequently, a third embodiment of the present invention will be described.

  12 and 13 show the configuration of a diesel engine according to the present invention. FIG. 12 shows the engine viewed from the axial direction of the crankshaft, and FIG. 2 shows the engine viewed from the intake side. The basic configuration is almost the same as that of the spark ignition type gasoline engine shown in FIGS. 1 to 4, but since it is a diesel engine, no spark plug is provided and there is no throttle valve. A throttle opening sensor for detecting the opening is not provided.

  The same reference numerals are assigned to the same components as those in the first embodiment, and the description thereof will be omitted. The description will focus on the different components. In the third embodiment, pre-ignition and knocking are prevented from vibrations generated during combustion. An abnormal combustion detection sensor 28 for detecting the occurrence is provided in the cylinder block 2 of the engine. The detection result of the abnormal combustion detection sensor 28 is input to the engine controller 20. Here, the occurrence of pre-ignition and knocking is detected from vibrations generated during combustion, but other methods such as detecting pre-ignition and knocking by detecting the combustion pressure of the engine are used. May be detected.

  In the third embodiment, the fuel and air are mixed in advance by injecting fuel into the cavity 31 at a time earlier than the compression top dead center according to the operating point of the engine. A premixed combustion mode in which the air-fuel mixture is compressed and ignited after forming the air, and like conventional diesel engines, only air is pre-compressed to high temperature and high pressure, and fuel is injected into the air at high temperature and high pressure Switch the diffusion combustion mode.

  FIG. 14 is a flowchart showing the contents of the combustion mode switching control performed by the engine controller 20 and is executed every predetermined time, for example, every 10 msec.

  This will be described. First, in step S21, the engine speed and the engine load are read. A value detected by the rotation speed sensor 25 is read as the engine rotation speed, and a target engine torque calculated inside the engine is read as the engine load. Here, the target engine torque is used as a value indicating the engine load, but instead of this, the accelerator operation amount, the fuel injection amount (the valve opening time of the fuel injection valve 14, the energization time to the fuel injection valve 14, the engine controller) The target fuel injection amount or the like calculated by (1) may be used.

  In step S22, based on the engine speed and load read in step S21, the combustion mode of the engine is determined with reference to the combustion mode map shown in FIG. When it is determined that the operating point of the engine is in the region F that is the low / medium speed rotation and low / medium load region, the process proceeds to step S23 and is determined to be in the region G that is the high rotation or high load region outside the region G. If so, the process proceeds to step S27.

  In step S23, which has been performed assuming that the engine operating point is in the region F, the engine combustion mode is switched to the premix combustion mode. In the premix combustion mode, fuel is injected into the cavity 31 before the compression top dead center. The fuel and air are mixed in advance to form a homogeneous mixture in the cavity 31, and the mixture is compressed and ignited. Furthermore, in the premixed combustion mode, it is necessary to inject fuel at an early stage to ensure sufficient time for mixing the fuel and air, so the piston motion is changed using a multi-link piston crank mechanism, The acceleration of the piston 3 in the vicinity of the top dead center is decreased, and the rising speed of the piston 3 until it approaches the vicinity of the top dead center is increased.

  Further, in step 25, it is determined whether or not premature ignition is detected by the abnormal combustion detection sensor 28. If pre-ignition is detected and the deterioration of the isovolume is observed, the process proceeds to step S26, where the piston motion is further changed using the multi-link piston crank mechanism, and the top dead center position of the piston 3 is changed. Lower the compression ratio of the engine to suppress pre-ignition.

  On the other hand, in step S27, where the operating point of the engine is in the region G, the engine combustion mode is switched to the diffusion combustion mode. In the diffusion combustion mode, only air is compressed in the compression stroke, and combustion is performed by injecting fuel into the air at a high temperature and high pressure. Further, in step S28, the acceleration of the piston 3 near the top dead center is increased using the multi-link type piston crank mechanism so that the piston 3 can be quickly retracted from the vicinity of the top dead center. The amount of heat escaping through the piston 3 is reduced, and the operation with less cooling loss is performed.

  Thus, in the third embodiment, premixed combustion can be realized in the low and medium rotation and low and medium load regions, and NOx and black smoke in the exhaust can be reduced simultaneously. In particular, by combining a multi-link type piston crank mechanism to reduce the piston acceleration near the top dead center, the fuel spray is contained in the cavity even when the fuel is injected earlier, and the fuel and air are contained in the cavity 31. Can be sufficiently mixed, so that the operating range in which the premixed combustion operation can be performed can be expanded to the high rotation side and the high load side as compared with the conventional diesel engine. At this time, it is also monitored whether or not pre-ignition of fuel is occurring in the engine. When pre-ignition of fuel is occurring, the top dead center of the ston 3 using a multi-link piston crank mechanism is performed. Since the point position is lowered and the compression ratio of the engine is lowered, pre-ignition of fuel can be suppressed.

  Furthermore, in the third embodiment, the combustion is switched to diffusion combustion in the high rotation or high load region, but the piston acceleration near the top dead center is also increased using the multi-link piston crank mechanism, so that the engine cooling loss is reduced. As a result, fuel consumption can be improved compared to conventional diesel engines.

  INDUSTRIAL APPLICABILITY The present invention can be applied to an engine that forms a stratified mixture in a combustion chamber, and is useful for expanding the operating range in which stratified combustion operation can be performed and improving the fuel consumption of the engine.

It is the figure which looked at the spark ignition type gasoline engine (double link type engine) provided with the multiple link type piston crank mechanism from the axial direction of the crankshaft. It is the figure seen from the intake side similarly. It is the figure which showed the mode of the fuel spray injected from a fuel injection valve. It is a figure for demonstrating the eccentric part of a multilink type piston crank mechanism. It is a figure for demonstrating the piston motion of a multilink type engine. It is the figure which showed the state of the fuel spray in a combustion chamber at the time of a time series in the case of injecting fuel with a certain crank angle in a single link type engine. FIG. 7 is a diagram showing, in chronological order, the state of fuel spray in the combustion chamber when fuel is injected at the same timing (crank angle) as in FIG. 6 in a multi-link engine. It is the flowchart which showed the combustion mode switching control which an engine controller performs. It is a combustion mode map of an engine. 6 is a flowchart showing another example of combustion mode switching control performed by the engine controller (second embodiment). It is another example of the combustion mode map of an engine. It is the figure which looked at the diesel engine provided with the multiple link type piston crank mechanism from the axial direction of the crankshaft (3rd Embodiment). It is the figure seen from the intake side similarly. It is the flowchart which showed the combustion mode switching control which an engine controller performs in 3rd Embodiment. It is a combustion mode map of an engine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Crankshaft 2 Cylinder block 3 Piston 3a Piston crown 4 Combustion chamber 13 Spark plug 14 Fuel injection valve 20 Engine controller 22 Cylinder 25 Rotational speed sensor 26 Accelerator operation amount sensor 27 Throttle opening sensor 28 Abnormal combustion detection sensor 31 Cavity 40 Connecting rod (First link)
41 Lower link (second link)
42 Crankshaft 44 Control link (third link)
45 Control shaft 46 Eccentric part 53 Worm wheel 54 Motor 55 Worm gear

Claims (15)

A crankshaft,
A piston slidably received in the cylinder and having a cavity formed in the crown surface;
A fuel injection valve for injecting fuel toward the cavity;
A multi-link piston crank mechanism connected to the piston, the crankshaft, and the engine body to change the piston motion of the piston;
An in-cylinder direct injection engine characterized by comprising: The fuel injection valve is provided at the center of the upper combustion chamber of the engine,
The cavity is a cavity recessed in the center of the crown surface of the piston.
The in-cylinder direct injection engine according to claim 1.   3. The cylinder according to claim 1, further comprising means for changing piston motion of the piston using the multi-link type piston crank mechanism to reduce acceleration of the piston near top dead center. Direct injection engine.   The piston motion of the piston is changed using the multi-link type piston crank mechanism, and the acceleration of the piston near the top dead center is the same as the stroke amount and the height from the crankshaft center to the cylinder upper surface is the same. 3. The direct injection type in-cylinder engine according to claim 1 or 2, further comprising means for reducing the size of the engine.   And a means for changing the piston motion of the piston using the multi-link type piston crank mechanism so as to make the acceleration of the piston near the top dead center smaller than the acceleration of the piston near the bottom dead center. An in-cylinder direct injection engine according to claim 1 or 2. A first mode in which fuel is injected from the fuel injection valve at a timing such that the fuel spray is contained in the cavity; and a second mode in which fuel is injected from the fuel injection valve at a timing at which the fuel spray protrudes outside the cavity. Means for switching between the modes,
The piston motion of the piston is changed using the multi-link type piston crank mechanism, and the acceleration of the piston near the top dead center in the first mode is changed to the piston near the top dead center in the second mode. Means for making the acceleration smaller than
An in-cylinder direct injection engine according to any one of claims 1 to 5, characterized by comprising: With spark plug,
In the first mode, fuel is injected from the fuel injection valve toward the cavity before the compression top dead center to form a richer air-fuel mixture in the cavity than outside the cavity, and from the spark plug It is a stratified combustion mode that ignites the mixture by spark ignition of
The second mode is a homogeneous combustion mode in which a homogeneous mixture is formed in the entire combustion chamber by injecting fuel in the intake stroke, and the mixture is ignited by spark ignition from the ignition plug.
The in-cylinder direct injection engine according to claim 6. With spark plug,
In the first mode, fuel is injected from the fuel injection valve toward the cavity before compression top dead center to form a richer air-fuel mixture in the cavity than outside the cavity, and by compression self-ignition It is a stratified compression self-ignition mode that burns the air-fuel mixture,
The second mode is a homogeneous combustion mode in which fuel is injected in the intake stroke to form a homogeneous mixture in the entire combustion chamber, and the mixture is ignited by spark ignition from the spark plug.
The in-cylinder direct injection engine according to claim 6. In the first mode, fuel is injected from the fuel injection valve toward the cavity before the compression top dead center, and fuel and air are premixed in the cavity, and the air-fuel mixture is combusted by compression self-ignition. Premixed combustion mode,
The second mode is a diffusion combustion mode in which only air is compressed to a high temperature and high pressure, and combustion is performed by injecting fuel into the air that has reached this high temperature and pressure.
The in-cylinder direct injection engine according to claim 6.   When the engine operating point is in the first operating region, the engine is operated in the first mode, and the engine operating point is on the higher rotation side than the first operating region. The in-cylinder direct injection engine according to any one of claims 6 to 9, wherein the engine is operated in a second mode.   When the engine operating point is in the first operating region, the engine is operated in the first mode, and the engine operating point is on a higher load side than the first operating region. The in-cylinder direct injection engine according to any one of claims 6 to 9, wherein when the engine is in a region, the engine is operated in the second mode.   The in-cylinder according to claim 8, wherein, in the stratified compression self-ignition mode, the piston motion of the piston is changed using the multi-link piston crank mechanism to raise the top dead center position of the piston. Direct injection engine. Means for detecting abnormal combustion of the engine,
When abnormal combustion of the engine is detected during operation in the premixed combustion mode, the piston motion of the piston is changed using the multi-link piston crank mechanism to lower the top dead center position of the piston. The in-cylinder direct injection engine according to claim 9. The multi-link piston crank mechanism is composed of first, second and third links,
The first link connects the piston and the second link;
The second link connects the crankshaft of the engine and the first link;
The third link connects the first or second link and the engine body;
The in-cylinder direct injection engine according to any one of claims 1 to 13, wherein   The in-cylinder direct injection according to claim 14, wherein the multi-link type piston crank mechanism changes a piston motion of the piston by moving a rotation center of the third link with respect to the engine body. Expression engine.

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