JP2005337166A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suitably perform combustion when a combustion mode is changed to homogeneous combustion at lean air fuel ratio from stratified combustion at lean air fuel ratio and is changed to stratified combustion at lean air fuel ratio from homogeneous combustion at lean air fuel ratio. <P>SOLUTION: When the combustion mode need to be changed to homogeneous lean combustion from stratified lean combustion, a command to change a condition of the intake air flow changing means under a first condition to a second condition is issued to perform homogeneous stoichiometric combustion forming roughly homogeneous air fuel mixture in whole inside of a cylinder and burning the same under stoichiometric condition, or homogeneous rich combustion forming roughly homogeneous air fuel mixture in whole inside of the cylinder and burning the same at rich air fuel ratio for a predetermined period of time. When combustion mode need to be changed to stratified lean combustion from homogeneous lean combustion, a command to change the condition of the intake air flow changing means from the second condition to the first condition, and homogeneous stoichiometric combustion or homogeneous rich combustion is performed for the predetermined period of time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fuel injection device for an internal combustion engine.

  Combustion mode (so-called stratified combustion) in which air-fuel mixture is formed in a stratified form only around the spark plug (so-called stratified combustion) and combustion mode (so-called homogeneous) in which air-fuel mixture is uniformly formed throughout the cylinder and burned Patent Document 1 discloses an internal combustion engine that can selectively execute (combustion). In addition, the internal combustion engine includes a first fuel injection valve that directly injects fuel into the cylinder and a second fuel injection valve that injects fuel into the intake passage, and the first fuel is used when performing stratified combustion. The fuel is injected from the injection valve, and when performing homogeneous combustion, the fuel is injected from the second fuel injection valve.

  By the way, in stratified combustion, fuel is collected around the spark plug and burned, so even if the amount of fuel injected from the fuel injection valve (hereinafter simply referred to as “fuel injection amount”) is relatively small, Can be burned well. That is, if an air-fuel mixture is formed in the entire cylinder when the fuel injection amount is small, the air-fuel ratio of the air-fuel mixture becomes much leaner than the stoichiometric air-fuel ratio, making combustion difficult. However, even if the fuel injection amount is small, if the air-fuel mixture is formed in a stratified manner only around the spark plug, even if the air-fuel ratio is extremely lean when viewed from the average air-fuel ratio in the entire cylinder, The air-fuel ratio is not so lean when viewed from the air-fuel ratio of only the air-fuel mixture. For this reason, if stratified combustion is used, even if the average air-fuel ratio of the air-fuel mixture as viewed in the entire cylinder is extremely lean, combustion can be performed satisfactorily. Therefore, stratified combustion is generally used in an engine operation region where the fuel injection amount is small (that is, an engine operation region where the required load is small).

  On the other hand, if the amount of fuel injection is large and stratified combustion is performed and an air-fuel mixture is formed only around the spark plug, too much fuel is concentrated around the spark plug, and combustion is not performed well. End up. Therefore, generally, homogeneous combustion is used in an engine operation region where the fuel injection amount is large (that is, an engine operation region where the required load is large).

  By the way, in an internal combustion engine that can selectively execute stratified combustion and homogeneous combustion, a valve that shuts off or opens one of the two intake ports leading to each cylinder (so-called swirl control valve). There is something with. This valve (hereinafter referred to as “SC valve”) closes one intake port by closing the valve so that air flows into the cylinder only from the remaining one intake port. The swirl flow (so-called swirl) is formed. According to this swirl, fuel is well mixed with air in the cylinder, so in general, when performing homogeneous combustion, the SC valve is closed to form a swirl in the cylinder, and stratified combustion When performing the operation, the SC valve is opened so as not to form a swirl in the cylinder.

JP 7-103049 A JP 2000-364409 A

  Thus, in an internal combustion engine equipped with an SC valve, in order to perform stratified combustion and homogeneous combustion satisfactorily, when performing stratified combustion, the SC valve is in a fully opened state, and when performing homogeneous combustion. It is important that the SC valve is completely closed. However, it takes a certain amount of time for the SC valve to actually open after the command to open the SC valve is issued, and after the command to close the SC valve is generated, It takes a certain amount of time for the valve to actually close. That is, generally, there is a response delay in the SC valve.

  Therefore, for example, when the combustion mode is changed from stratified combustion to homogeneous combustion, combustion is not performed well until the SC valve is switched from the opened state to the closed state. Of course, even when the combustion mode is changed from homogeneous combustion to stratified combustion, combustion is not performed well until the SC valve is switched from the closed state to the opened state.

  In general, this is an internal combustion engine capable of selectively executing stratified combustion and homogeneous combustion, comprising an intake flow changing means for changing the flow of air flowing into the cylinder, and the intake flow changing means The same applies to an internal combustion engine that changes the state according to whether stratified combustion or homogeneous combustion is performed. In addition, this is particularly true for an internal combustion engine capable of selectively executing stratified combustion at a lean air-fuel ratio and homogeneous combustion at a lean air-fuel ratio as viewed in the entire cylinder, and the flow of air flowing into the cylinder. The same applies to an internal combustion engine that includes an intake flow changing means for changing and changes the state of the intake flow changing means depending on whether stratified combustion or homogeneous combustion is performed. .

  Accordingly, an object of the present invention is to change the combustion mode from stratified combustion at a lean air-fuel ratio to homogeneous combustion at a lean air-fuel ratio and from homogeneous combustion at a lean air-fuel ratio to a lean air-fuel ratio in such an internal combustion engine. When changing to stratified combustion, it is to make the combustion good.

  In order to solve the above problems, in the first invention, a fuel injection valve that injects fuel into the intake passage, a fuel injection valve that injects fuel into the cylinder, and an intake air that changes the flow of air flowing into the cylinder An intake flow change means having at least a response delay, and the air-fuel mixture is formed only around the spark plug as a whole with the intake flow change means in the first state. Stratified lean combustion in which combustion is performed at a lean air-fuel ratio, and homogeneous lean combustion in which a substantially homogeneous air-fuel mixture is formed in the entire cylinder and combustion is performed at a lean air-fuel ratio as a whole after the state of the intake flow changing means is set to the second state In an internal combustion engine capable of selectively executing the command, the command for switching the state of the intake flow changing means in the first state to the second state when the combustion mode should be changed from stratified lean combustion to homogeneous lean combustion When you issue Furthermore, for a predetermined period, a homogeneous stoichiometric combustion in which a substantially homogeneous air-fuel mixture is formed in the entire cylinder and burned by stoichiometry, or a substantially homogeneous air-fuel mixture is formed in the entire cylinder and burned at a rich air-fuel ratio. When the homogeneous rich combustion is performed and the combustion mode is to be changed from the homogeneous lean combustion to the stratified lean combustion, a command for switching the state of the intake flow changing means in the second state to the first state is issued, Homogeneous stoichiometric combustion or homogeneous rich combustion is performed for a predetermined period.

In the second invention, in the first invention, the predetermined period is a period corresponding to a response delay of the intake flow changing means.
In a third invention, in the first invention, further comprising an evaporated fuel passage for releasing evaporated fuel into the intake passage, wherein the predetermined period corresponds to a response delay of the intake flow changing means, or This is a period until the evaporated fuel in the intake passage becomes smaller than a predetermined amount.
According to a fourth aspect, in the third aspect, a period during which the amount of evaporated fuel in the intake passage is less than a predetermined amount of time until the amount of evaporated fuel in the intake passage becomes substantially zero. It is.

In the fifth aspect, when it is determined in the fourth aspect that the combustion mode should be changed between stratified lean combustion and homogeneous lean combustion, the evaporated fuel is discharged from the evaporated fuel passage to the intake passage. To stop.
According to a sixth aspect, in the first aspect, the apparatus further includes a throttle valve disposed in the intake passage, and when the combustion mode is stratified lean combustion, the opening degree of the throttle valve is controlled corresponding to the stratified lean combustion. When the combustion mode is homogeneous lean combustion, the opening of the throttle valve is controlled corresponding to the homogeneous lean combustion, and the predetermined period when the combustion mode should be changed from stratified lean combustion to homogeneous lean combustion Then, the throttle valve opening is controlled corresponding to the homogeneous lean combustion, and the throttle corresponding to the stratified lean combustion is applied during the predetermined period when the combustion mode should be changed from the homogeneous lean combustion to the stratified lean combustion. The opening of the valve is controlled.

  In the seventh invention, in the fourth invention, when the combustion mode is in the stratified lean combustion mode, the fuel ignition timing by the spark plug is controlled corresponding to the stratified lean combustion mode, and the combustion mode is in the homogeneous lean combustion mode. Sometimes the fuel ignition timing by the spark plug is controlled corresponding to the homogeneous lean combustion mode, and during the predetermined period, the fuel ignition timing by the spark plug is controlled corresponding to the predetermined period, The fuel ignition timing in a predetermined period is later than the fuel ignition timing when the combustion mode is in the stratified lean combustion mode and later than the fuel ignition timing when the combustion mode is in the homogeneous lean combustion mode.

  According to the present invention, when the combustion mode is changed from stratified combustion to homogeneous combustion, until the state of the intake flow changing means is changed from the first state to the second state, and the combustion When the mode is changed from homogeneous combustion to stratified combustion until the state of the intake flow changing means is changed from the second state to the first state (hereinafter referred to as “change of the state of the intake flow changing means”). Homogeneous transition stoichiometric combustion or homogeneous rich combustion is performed. Here, since the homogeneous stoichiometric combustion and the homogeneous rich combustion are comparatively stable combustion, even if the combustion in the transition period of the change of the state of the intake flow changing means is difficult to stabilize, According to the invention, combustion can be performed stably.

  Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a body of an internal combustion engine, 2 is a cylinder block, 3 is a piston, 4 is a cylinder head, 5 is a combustion chamber (hereinafter also referred to as “cylinder”), 6 is an intake valve, 7 is an intake port, An exhaust valve, 9 is an exhaust port, and 10 is a spark plug. A cavity 12 is provided on the wall surface of the piston 3 on the combustion chamber 5 side.

  The cylinder head 4 is provided with a fuel injection valve (hereinafter referred to as “in-cylinder fuel injection valve”) 11 capable of directly injecting fuel into the cylinder 5. The cylinder head 4 is also provided with a fuel injection valve (hereinafter referred to as “port fuel injection valve”) 11 a that can inject fuel into the intake port 7.

  A surge tank 14 is connected to the intake port 7 via an intake branch pipe 13. The surge tank 14 is connected to an air flow meter 16 through an intake pipe 15. A throttle valve 18 is disposed in the intake pipe 15. A step motor 19 is connected to the throttle valve 18.

  Moreover, in FIG. 1, 20 is a fuel tank. The fuel in the fuel tank 20 is supplied to the fuel injection valves 11 and 11a by a fuel pump (not shown). The fuel tank 20 is connected to a canister 22 via a first vapor passage 21. An activated carbon 23 is disposed in the canister 22. The activated carbon 23 adsorbs evaporated fuel (hereinafter referred to as “vapor”) generated in the fuel tank 20. Further, the canister 22 is connected to the surge tank 14 via the second vapor passage 24. A valve (hereinafter referred to as a “purge control valve”) 25 that closes or opens the second vapor passage 24 is disposed in the second vapor passage 24. When the purge control valve 25 is closed, the second vapor passage 24 is shut off, and when the purge control valve 25 is opened, the second vapor passage 24 is opened.

  When the purge control valve 25 is opened while negative pressure is generated in the surge tank 14, the vapor adsorbed by the activated carbon 23 (and the vapor in the fuel tank 20) passes through the second vapor passage 24. The vapor is introduced into the surge tank 14 and finally supplied to each cylinder 5. Of course, if the purge control valve 25 is closed, the amount of vapor introduced into the surge tank 14 via the second vapor passage 24 becomes zero.

  An exhaust pipe 28 is connected to the exhaust port 9. Further, a passage (hereinafter referred to as “EGR passage”) 26 for introducing the exhaust gas in the exhaust pipe 28 into the surge tank 14 extends from the exhaust pipe 28 to the surge tank 14. A valve (hereinafter referred to as “EGR control valve”) 27 for controlling the amount of exhaust gas introduced into the surge tank 14 is disposed in the EGR passage 26. The opening degree of the EGR control valve 27 is controlled so that a desired amount of exhaust gas is supplied into each cylinder according to the operating state of the internal combustion engine.

  As shown in FIG. 2, a pair of intake ports 7 and a pair of exhaust ports 9 are connected to each cylinder 5. The port fuel injection valve 11a is disposed in the cylinder head 4 so as to inject fuel into one intake port (hereinafter referred to as “first intake port”) 7a. The other intake port (hereinafter referred to as “second intake port”) 7b has a valve (a so-called swirl control valve that shuts off or opens the second intake port 7b, hereinafter referred to as “SC”). 30) (referred to as “valve”). A step motor 31 is connected to the SC valve 30, and the SC valve 30 is driven by the step motor 31.

  When the SC valve 30 is closed, the second intake port 7b is blocked by the SC valve 30. At this time, since air is sucked into the cylinder 5 only through the first intake port 7a, a swirling flow of air (so-called swirl) is generated in the cylinder 5. On the other hand, when the SC valve 30 is opened, the second intake port 7b is opened. At this time, since air is sucked through the first intake port 7a and the second intake port 7b, a swirling flow of air is not generated in the cylinder 5.

  Next, the combustion mode in this embodiment will be described. In the present embodiment, basically, stratified lean combustion and homogeneous lean combustion are selectively executed according to the engine operating state (specifically, the engine speed and the required load). That is, in this embodiment, as shown in FIG. 3, stratified lean combustion is performed in a region I where the engine speed N is relatively small and the required load L is relatively small. Here, stratified lean combustion means that fuel in an amount such that the air-fuel ratio becomes lean when viewed in the cylinder 5 as a whole is injected from the in-cylinder fuel injection valve 11 at the end of the compression stroke, and thus around the spark plug 10. Only a stratified mixture is formed, and this mixture is ignited by a spark plug 10 to cause combustion. Note that when performing stratified lean combustion, the SC valve 30 is opened.

  On the other hand, in the present embodiment, as shown in FIG. 3, homogeneous lean combustion is performed in the region II other than the region I. Here, the homogeneous lean combustion means that the amount of fuel whose air-fuel ratio is leaner than the stoichiometric air-fuel ratio when viewed in the cylinder 5 as a whole is injected from the port fuel injection valve 11a during the intake stroke. The air-fuel mixture is uniformly formed in the entire interior 5 and the air-fuel mixture is ignited by the spark plug 10 for combustion. When performing homogeneous lean combustion, the SC valve 30 is closed, and a swirling flow of air is generated in the cylinder 5.

  In addition, the air-fuel ratio when viewed in the entire cylinder 5 when stratified lean combustion is being performed is generally higher than the air-fuel ratio when viewed in the entire cylinder 5 when homogeneous lean combustion is being performed. It is lean.

  In the region II, when the engine speed N is relatively large or when the required load L is relatively large, homogeneous stoichiometric combustion or homogeneous rich combustion may be performed. Here, the homogeneous stoichiometric combustion means that the entire fuel in the cylinder 5 is injected by injecting fuel from the port fuel injection valve 11a during the intake stroke so that the air-fuel ratio becomes the stoichiometric air-fuel ratio when viewed in the entire cylinder 5. The air-fuel mixture is homogeneously formed, and the air-fuel mixture is ignited by the spark plug 10 for combustion. In addition, homogeneous rich combustion refers to injection of fuel from the port fuel injection valve 11a during the intake stroke with an amount of fuel whose air-fuel ratio is richer than the stoichiometric air-fuel ratio when viewed in the cylinder 5 as a whole. An air-fuel mixture is uniformly formed in the entire interior, and this air-fuel mixture is ignited by a spark plug 10 to cause combustion.

  FIG. 4 shows a map used to determine the amount of fuel injected from each fuel injection valve 11, 11a. In the present embodiment, the fuel injection amount Q is determined as a function of the engine speed N and the required load L. In the map shown in FIG. 4, the fuel injection amount Q increases as the engine speed N increases, and the fuel injection amount Q tends to increase as the required load L increases. Therefore, the fuel injection amount Q tends to be larger when the homogeneous lean combustion is performed than when the stratified lean combustion is performed.

  FIG. 5 shows a map used for determining the fuel ignition timing by the spark plug 10. In the present embodiment, the fuel injection amount Q is determined as a function of the engine speed N and the required load L. According to the map shown in FIG. 5, the fuel ignition timing T generally tends to be earlier when homogeneous lean combustion is performed than when stratified lean combustion is performed. Further, according to the map shown in FIG. 5, the fuel ignition timing is determined so that the internal combustion engine outputs the highest torque with the highest efficiency.

  FIG. 6 shows a map used to determine the opening of the throttle valve 18 (hereinafter referred to as “throttle opening”). In the present embodiment, the throttle opening Dth is determined by a function of the engine speed N and the required load L. According to the map shown in FIG. 6, the throttle opening Dth generally tends to increase as the engine speed N increases and as the required load L increases.

  FIG. 7 shows a map used to determine the opening degree of the EGR control valve 27 (hereinafter referred to as “EGR opening degree”). In the present embodiment, the EGR opening degree Degr is determined as a function of the engine speed N and the required load L. According to the map shown in FIG. 7, the EGR opening degree Degr generally tends to be smaller as the engine speed N is larger and smaller as the required load L is larger.

  The purge control valve 25 is closed while the operation of the internal combustion engine is stopped and while stratified lean combustion is being performed, and is opened while homogeneous lean combustion is being performed. It is done. Accordingly, when homogeneous lean combustion is being performed, the port is set so that the air-fuel ratio in the cylinder 5 becomes the target air-fuel ratio in accordance with the amount of vapor introduced into the surge tank 14 via the second vapor passage 24. The fuel injection amount from the fuel injection valve 11a is adjusted.

  Incidentally, as described above, in the present embodiment, basically, the fuel injection amount Q is calculated from the map shown in FIG. 4 based on the engine speed N and the required load L, and FIG. The fuel ignition timing T is determined from the map shown, and stratified lean combustion or homogeneous lean combustion is performed. However, in the present embodiment, when the combustion mode is changed from stratified lean combustion to homogeneous lean combustion, or when the combustion mode is changed from homogeneous lean combustion to stratified lean combustion, control different from the control described above is performed. Next, this control will be described.

  First, control when the combustion mode is changed from stratified lean combustion to homogeneous lean combustion will be described with reference to FIG. 8, (A) shows the combustion mode, (B) shows a command for the SC valve 30 (in the figure, "ON" shows a command for opening the SC valve 30, and "OFF" shows SC). (C) shows the actual state of the SC valve 30 (in the figure, “open” indicates that the SC valve 30 is fully open, and “closed”). "" Indicates that the SC valve 30 is in the fully closed state), and (D) indicates the state of the purge control valve 25 (in the figure, "open" indicates that the purge control valve 25 is in the open state). "Closed" indicates that the purge control valve 25 is in a closed state), (E) indicates the opening of the throttle valve 18, and (F) indicates the fuel ignition timing (" "Advanced" indicates that the fuel ignition timing is early, and "slow" indicates the fuel ignition timing Shows slower) shows a (G) is the time.

  In the example shown in FIG. 8, time t0 is the time when it is determined that the combustion mode should be changed from stratified lean combustion to homogeneous lean combustion. When it is determined that the combustion mode should be changed from stratified lean combustion to homogeneous lean combustion at time t0, as shown in FIG. A command is issued to enter the fully closed state. Then, as shown in FIG. 8C, the SC valve 30 in the fully opened state gradually shifts to the fully closed state, and becomes fully closed at time t1. Hereinafter, a period from time t0 to time t1 is referred to as a “combustion mode switching transient period”.

  Now, when the fuel injection amount Q is determined from the map shown in FIG. 4, an amount of fuel that makes the air-fuel ratio lean in the entire cylinder 5 lean is injected from the port fuel injection valve 11a. Become. However, according to the present embodiment, in the combustion mode switching transition period t0 to t1, an amount of fuel in which the air-fuel ratio seen in the entire cylinder 5 becomes the stoichiometric air-fuel ratio or rich is injected from the port fuel injection valve 11a. At this time, the SC valve 30 may be in the process of shifting from the fully open state to the fully closed state (that is, a swirl may be being formed in the cylinder 5), so that homogeneous stoichiometric combustion or homogeneous rich Combustion takes place. According to this, combustion can be stably and satisfactorily performed even in a period in which combustion becomes unstable at a lean air-fuel ratio, which is a combustion mode switching transient period.

  In the example shown in FIG. 8, the combustion mode is finally changed from stratified lean combustion to homogeneous lean combustion (that is, the purge control valve 25 in the closed state should be opened). In this embodiment, as shown in FIG. 8D, the purge control valve 25 is opened when the combustion mode switching transition period is reached.

  Further, in the present embodiment, in the combustion mode switching transition period, as shown in FIG. 8 (E), the throttle opening Dth is set to the same throttle opening as in the case of performing homogeneous lean combustion (that is, The throttle opening is determined based on the map shown in FIG. 6 even during the combustion mode switching transition period. In the illustrated example, the throttle opening during the combustion mode switching transition period is made smaller than the throttle opening when stratified lean combustion is performed. According to this, when the combustion mode switching transient period has elapsed, the throttle opening Dth is the throttle opening for performing homogeneous lean combustion, so immediately after the combustion mode switching transient period has elapsed, The combustion mode can be shifted to homogeneous lean combustion.

  Further, in the present embodiment, during the combustion mode switching transition period, homogeneous stoichiometric combustion or homogeneous rich combustion is performed. Therefore, assuming that the fuel ignition timing is determined from the map shown in FIG. As a result, the output torque of the internal combustion engine suddenly increases and a so-called torque shock occurs. Therefore, in the present embodiment, even if homogeneous stoichiometric combustion or homogeneous rich combustion is performed during the combustion mode switching transition period, the output torque of the internal combustion engine does not increase rapidly, or the output torque of the internal combustion engine increases. The fuel ignition timing T is set to be slower than the case where stratified lean combustion is performed and later than the case where homogeneous lean combustion is performed so that the fuel ignition timing T is suppressed to a predetermined value or less (that is, the fuel ignition timing T). The ignition timing is set later than the timing determined from the map shown in FIG. 5 during the combustion mode switching transition period).

  Here, the extent to which the fuel ignition timing is delayed in the combustion mode switching transition period is determined as follows. That is, the fuel ignition timing is delayed in order to suppress torque shock, and the output torque of the internal combustion engine changes according to the amount of air sucked into each cylinder 5 and the fuel injection amount. Therefore, in the present embodiment, when the combustion mode switching transition period starts, the amount of change in the target throttle opening and the amount of change in the target fuel injection amount are calculated. Then, based on these amounts of change, the amount of change in the output torque of the internal combustion engine when the fuel ignition timing is the fuel ignition timing when performing stratified lean combustion or homogeneous lean combustion is calculated. Then, the extent to which the fuel ignition timing is delayed is determined so that the amount of change in the output torque becomes zero (or substantially zero). In general, the extent to which the fuel ignition timing is delayed tends to increase as the amount of change in output torque increases.

  Since the throttle valve 18 also has a response delay, even when the target throttle opening is changed when the combustion mode switching transition period is entered, the amount of air sucked into each cylinder 5 is at a stroke. It does not change and changes gradually (there is a so-called first order lag). Therefore, when the combustion mode switching transition period is entered, the degree of delay of the combustion ignition timing may be determined in consideration of the primary delay of the change in the amount of air taken into each cylinder 5.

  Further, in the example described with reference to FIG. 8, the throttle opening during the combustion mode switching transient period is the throttle opening when performing homogeneous lean combustion, which is that the combustion mode switching transient period has elapsed. This is because the throttle opening at the time is the throttle opening for homogeneous lean combustion, but it is more important to suppress the occurrence of torque shock during the transition period of combustion mode switching. If this is the case, the throttle opening during the combustion mode switching transition period should be made smaller than the throttle opening for homogeneous lean combustion, or smaller than the throttle opening for stratified lean combustion. Also good.

  Next, control when the combustion mode is changed from homogeneous lean combustion to stratified lean combustion will be described with reference to FIG. 9A to 9G are the same as FIGS. 8A to 8G. In the example shown in FIG. 9, time t2 is the time when it is determined that the combustion mode should be changed from homogeneous lean combustion to stratified lean combustion. When it is determined at time t2 that the combustion mode should be changed from homogeneous lean combustion to stratified lean combustion, as shown in FIG. A command is issued to fully open. Then, as shown in FIG. 9C, the SC valve 30 in the fully closed state gradually shifts to the fully opened state, and becomes fully opened at time t3. In this example, the period from time t2 to time t3 is the “combustion mode switching transient period”.

  Now, when the fuel injection amount Q is determined from the map shown in FIG. 4, an amount of fuel that makes the air-fuel ratio lean in the entire cylinder 5 lean is injected from the in-cylinder injection valve. . However, according to the present embodiment, in the combustion mode switching period t2 to t3, an amount of fuel in which the air-fuel ratio seen in the entire cylinder 5 becomes the stoichiometric air-fuel ratio or rich is injected from the port fuel injection valve 11a. At this time, the SC valve 30 may be in the middle of the transition from the fully closed state to the fully open state (that is, a swirl may still be formed in the cylinder 5), and the homogeneous stoichiometric combustion or homogeneous Rich combustion is performed. According to this, combustion can be stably and satisfactorily performed even in a period in which combustion becomes unstable at a lean air-fuel ratio, which is a combustion mode switching transient period.

  Further, in the example shown in FIG. 9, the combustion mode is finally changed from homogeneous lean combustion to stratified lean combustion (that is, the purge control valve 25 in the valve open state should be closed). In this embodiment, as shown in FIG. 9D, the purge control valve 25 is closed when the combustion mode switching transition period is reached.

  Further, in the present embodiment, in the combustion mode switching transition period, as shown in FIG. 9E, the throttle opening Dth is set to the same throttle opening as when stratified lean combustion is performed (that is, The throttle opening is determined based on the map shown in FIG. 6 even during the combustion mode switching transition period. In the illustrated example, the throttle opening during the combustion mode switching transition period is larger than the throttle opening when performing homogeneous lean combustion. According to this, when the combustion mode switching transient period has elapsed, since the throttle opening Dth is the throttle opening when performing stratified lean combustion, immediately after the combustion mode switching transient period has elapsed, The combustion mode can be shifted to stratified lean combustion.

  Furthermore, in the present embodiment, during the combustion mode switching transition period, homogeneous stoichiometric combustion or homogeneous rich combustion is performed. Therefore, assuming that the fuel ignition timing is determined from the map shown in FIG. 5, at time t2. Torque shock will occur. Therefore, in the present embodiment, even when homogeneous stoichiometric combustion or homogeneous rich combustion is performed during the combustion mode switching transition period, the output torque of the internal combustion engine does not increase rapidly, or the output torque of the internal combustion engine is determined in advance. The fuel ignition timing T is set to be slower than the case where the homogeneous lean combustion is performed and later than the case where the stratified lean combustion is performed (that is, the fuel ignition timing so that the fuel ignition timing T is suppressed below the predetermined value). Is made later than the timing determined from the map shown in FIG. 5 during the combustion mode switching transition period).

  In the example described with reference to FIG. 9, the throttle opening during the combustion mode switching transient period is the throttle opening when stratified lean combustion is performed, and this is because the combustion mode switching transient period has elapsed. This is because the throttle opening at the time is the throttle opening for stratified lean combustion, but it is more important to suppress the occurrence of torque shock during the transition period of combustion mode. If this is the case, the throttle opening during the transition period of the combustion mode is made smaller than the throttle opening when performing stratified lean combustion, or smaller than the throttle opening when performing homogeneous lean combustion. Also good.

  In the above example, when the combustion mode is changed from homogeneous lean combustion to stratified lean combustion, the purge control valve 25 is closed when the combustion mode switching transient period is reached. Even after the transition period elapses, vapor may remain in the intake passage from the surge tank 14 to the cylinder 5. In this case, the combustion becomes unstable when the combustion mode switching transient period elapses and the combustion mode is changed to stratified lean combustion.

  Therefore, in the above-described example, when the combustion mode should be changed from homogeneous lean combustion to stratified lean combustion, the period until the SC valve 30 changes from the fully closed state to the fully open state is referred to as the “combustion mode switching transient period”. Instead of this, the period until the SC valve 30 changes from the fully closed state to the fully open state and the vapor in the intake passage from the surge tank 14 to the cylinder 5 after the purge control valve 25 is closed is zero (or The longer period of the period until it becomes substantially zero) may be the “combustion mode switching transient period”. According to this, when the combustion mode is changed from homogeneous lean combustion to stratified lean combustion, combustion can be stabilized more reliably.

  10 to 13 show an example of a flowchart for executing the control according to the present embodiment. First, FIG. 10 shows an example of a flowchart for controlling the combustion mode. In the flowchart of FIG. 10, first, in step 10, it is determined whether or not a change in the combustion mode is requested (that is, the combustion mode should be changed). Here, if it is not determined that the change of the combustion mode is requested, the routine ends. However, if it is determined that the change of the combustion mode is requested, the routine proceeds to step 11.

  In step 11, it is determined whether or not the current combustion mode is stratified lean combustion. Here, when it is determined that the current combustion mode is stratified lean combustion (in this case, the combustion mode should be changed from stratified lean combustion to homogeneous lean combustion), the routine proceeds to step 12. On the other hand, when it is determined that the current combustion mode is not stratified lean combustion, that is, when the current combustion mode is determined to be homogeneous lean combustion (in this case, the combustion mode is changed from homogeneous lean combustion to stratified lean combustion). If it is time to change to lean combustion), the routine proceeds to step 17.

  In step 12, a request (command) for fully closing the SC valve 30 (denoted as “SCV” in the figure) is issued, and then in step 13, the purge control valve 25 (in the figure, “PCV”) is issued. A request (command) to open the valve is issued, and then in step 14, homogeneous stoichiometric combustion or homogeneous rich combustion is performed. That is, according to step 14, the throttle opening is set to the throttle opening when homogeneous lean combustion is performed, and the amount of fuel at which the air-fuel ratio viewed in the entire cylinder 5 becomes the stoichiometric air-fuel ratio or rich is the port fuel injection valve. The fuel is ignited by the spark plug 10 at the fuel ignition timing that is injected from 11a and determined as described above.

  Next, at step 15, it is determined whether or not the period T (this is the period after the change of the combustion mode is requested at step 10) is longer than the combustion mode switching transient period Tth (T> Tth). Is done. When it is determined that T ≦ Tth, the routine returns to step 14 and step 14 is repeated until it is determined in step 15 that T> Tth. On the other hand, if it is determined in step 15 that T> Tth, the routine proceeds to step 16 where homogeneous lean combustion is performed. That is, according to step 16, the throttle opening is set to the throttle opening when homogeneous lean combustion is performed, and an amount of fuel that makes the air-fuel ratio lean in the entire cylinder 5 lean is injected from the port fuel injection valve 11a. The fuel is ignited by the spark plug 10 at the fuel ignition timing when performing homogeneous lean combustion.

  On the other hand, in step 17, a request (command) for making the SC valve 30 fully open is issued. Next, in step 18, a request (command) for making the purge control valve 25 closed, is issued, and then step 19 In the above, homogeneous stoichiometric combustion or homogeneous lean combustion is performed. That is, according to step 19, the throttle opening is set to the throttle opening when stratified lean combustion is performed, and the amount of fuel at which the air-fuel ratio viewed in the entire cylinder 5 becomes the stoichiometric air-fuel ratio or rich is the port fuel injection valve. The fuel is ignited by the spark plug 10 at the fuel ignition timing that is injected from 11a and determined as described above.

  Next, at step 20, it is determined whether or not the period T (this is also the period that has elapsed since the change of the combustion mode was requested at step 10) is longer than the combustion mode switching transient period Tth (T> Tth). Is done. If it is determined that T ≦ Tth, the routine returns to step 19 and repeats step 19 until it is determined in step 20 that T> Tth. On the other hand, if it is determined in step 20 that T> Tth, the routine proceeds to step 21 where stratified lean combustion is performed. That is, according to step 21, the throttle opening is set to the throttle opening when stratified lean combustion is performed, and an amount of fuel in which the air-fuel ratio viewed in the entire cylinder 5 becomes lean is injected from the in-cylinder fuel injection valve 11. The fuel is ignited by the spark plug 10 at the fuel ignition timing when stratified lean combustion is performed.

  FIG. 11 is a diagram showing an example of a flowchart for calculating the combustion mode switching transient period T used in steps 15 and 20 of FIG. In the flowchart of FIG. 11, first, at step 30, it is determined whether or not a change of the combustion mode is requested (that is, the combustion mode should be changed). Here, if it is not determined that the change of the combustion mode is requested, the routine ends. However, if it is determined that the change of the combustion mode is requested, the routine proceeds to step 31.

  In step 31, it is determined whether or not the current combustion mode is stratified lean combustion. Here, when it is determined that the current combustion mode is stratified lean combustion (that is, when the combustion mode should be changed from stratified lean combustion to homogeneous lean combustion), in step 32, in step 15 of FIG. The period Td (this is the time taken for the SC valve 30 to change from the fully closed state to the fully open state, or the time taken for the SC mode 30 to change from the fully open state to the fully closed state) during the combustion mode switching transition period T used This is the so-called response delay time of the SC valve 30). In this case, in step 15 of FIG. 10, Td is used as the combustion mode switching transient period T.

  On the other hand, when it is determined in step 31 that the current combustion mode is not stratified lean combustion (that is, when the combustion mode should be changed from homogeneous lean combustion to stratified lean combustion), in step 33, the period Td However, the vapor in the intake passage from the surge tank 14 to the cylinder 5 is zero (or substantially zero) after the period Tp (the change of the combustion mode is requested and the purge control valve 25 is closed). It is determined whether it is longer (Td> Tp).

  When it is determined in step 33 that Td> Tp, in step 34, Td is input during the combustion mode switching transient period T used in step 20 of FIG. In this case, in step 20 of FIG. 10, Td is used as the combustion mode switching transient period T. On the other hand, when it is determined in step 33 that Td ≦ Tp, Tp is input in step 35 to the combustion mode switching transient period T used in step 20 of FIG. In this case, in step 20 of FIG. 10, Tp is used as the combustion mode switching transient period T.

  FIG. 12 is a diagram illustrating an example of a flowchart for calculating the target throttle opening during the combustion mode switching transition period. In the flowchart of FIG. 12, first, at step 40, it is determined whether or not a change of the combustion mode is requested (that is, the combustion mode should be changed). Here, if it is not determined that the change of the combustion mode is requested, the routine ends. However, if it is determined that the change of the combustion mode is requested, the routine proceeds to step 41.

  In step 41, it is determined whether or not the current combustion mode is stratified lean combustion. Here, when it is determined that the current combustion mode is stratified lean combustion (that is, when the combustion mode should be changed from stratified lean combustion to homogeneous lean combustion), in step 42, the target throttle opening TDth is set. The throttle opening Dthh when performing homogeneous lean combustion is input. In this case, the throttle opening during the combustion mode switching transition period is the throttle opening at the time of performing homogeneous lean combustion.

  On the other hand, when it is determined in step 41 that the current combustion mode is not stratified lean combustion (that is, when the combustion mode should be changed from homogeneous lean combustion to stratified lean combustion), in step 43, the target throttle opening is performed. At the degree TDth, the throttle opening degree Dths when performing stratified lean combustion is input. In this case, the throttle opening during the combustion mode switching transition period is the throttle opening when stratified lean combustion is performed.

  FIG. 13 is a diagram illustrating an example of a flowchart for calculating the degree of delaying the fuel ignition timing (so-called retardation amount) in the combustion mode switching transition period. In the flowchart of FIG. 13, first, in step 50, it is determined whether or not a change in the combustion mode is requested (that is, the combustion mode should be changed). Here, if it is not determined that the change of the combustion mode is requested, the routine ends. However, if it is determined that the change of the combustion mode is requested, the routine proceeds to step 51.

  In step 51, the amount of change ΔGa in the amount of air taken into each cylinder 5 is calculated based on the amount of change in the throttle opening when entering the combustion mode switching transition period. Next, in step 52, a change amount ΔQ of the fuel injection amount when entering the combustion mode switching transition period is calculated. Then, based on these changes ΔGa and ΔQ, the retard amount ΔT of the fuel ignition timing is calculated.

  In the above-described embodiment, the present invention is applied to an internal combustion engine provided with an SC valve driven by a step motor. For example, an SC valve driven by a DC motor or a diaphragm type operated by negative pressure is used. The present invention can also be applied to an internal combustion engine equipped with an SC valve. In the above-described embodiment, the present invention is applied to an internal combustion engine including an SC valve for forming a swirl in the cylinder 5. For example, the flow of air flowing into the cylinder 5 is changed. The present invention can also be applied to an internal combustion engine provided with a means having a response delay.

  Further, the period until the SC valve is fully opened to the fully closed state, or the period until the SC valve is fully closed to the fully opened state is a substantially constant period determined for each SC valve. In the embodiment described above, the combustion mode switching transition period may be a predetermined period obtained in advance.

1 is an overall view of an internal combustion engine to which the present invention is applied. It is a figure which shows the intake port and exhaust port which lead to one cylinder. It is a figure for demonstrating a combustion mode, in the figure, N is an engine speed, L is a required load, I is the area | region where stratified lean combustion is performed, II is an area | region where homogeneous lean combustion is performed. It is a figure which shows the map used in order to determine a fuel injection amount, in which N is an engine speed, L is a request | requirement load, and Q is a fuel injection amount. It is a figure which shows the map used in order to determine fuel ignition timing, in the figure, N is an engine speed, L is a request | requirement load, T is a fuel ignition timing. It is a figure which shows the map used in order to determine throttle opening, in the figure, N is an engine speed, L is a required load, Dth is a throttle opening. It is a figure which shows the map used in order to determine an EGR opening degree, in which N is an engine speed, L is a required load, and Degr is an EGR opening degree. It is a figure which shows the time chart for demonstrating control when changing a combustion mode from stratified lean combustion to homogeneous lean combustion. It is a figure which shows the time chart for demonstrating control when changing a combustion mode from homogeneous lean combustion to stratified lean combustion. It is a figure which shows an example of the flowchart which controls a combustion mode. It is a figure which shows an example of the flowchart which calculates a combustion mode switching transition period. It is a figure which shows an example of the flowchart which calculates the target throttle opening in a combustion mode switching transition period. It is a figure which shows an example of the flowchart which calculates the amount of retardation of fuel ignition timing in a combustion mode switching transition period.

Explanation of symbols

1 ... Internal combustion engine body 5 ... Combustion chamber (cylinder)
DESCRIPTION OF SYMBOLS 10 ... Spark plug 11 ... In-cylinder fuel injection valve 11a ... Port fuel injection valve 18 ... Throttle valve 20 ... Fuel tank 22 ... Canister

Claims (7)

  A fuel injection valve for injecting fuel into the intake passage, a fuel injection valve for injecting fuel into the cylinder, and an intake flow changing means for changing the flow of air flowing into the cylinder, and at least a response delay in the intake flow change Stratified lean combustion in which an air-fuel mixture is formed almost only around the spark plug and burned at a lean air-fuel ratio as a whole after the intake flow changing means is in the first state, and the intake flow change Combustion in an internal combustion engine capable of selectively executing homogeneous lean combustion in which a substantially homogeneous air-fuel mixture is formed in the entire cylinder and burned at a lean air-fuel ratio as a whole after the state of the means is set to the second state When the mode should be changed from stratified lean combustion to homogeneous lean combustion, a command to switch the state of the intake flow changing means in the first state to the second state is issued, and the entire in-cylinder is set for a predetermined period. Almost homogeneous Homogeneous stoichiometric combustion in which aeration is formed and combustion is performed with stoichiometry, or homogeneous rich combustion in which a substantially homogeneous mixture is formed throughout the cylinder and combustion is performed at a rich air-fuel ratio, while the combustion mode is homogeneous lean combustion When changing from stratified lean combustion to the stratified lean combustion, a command to switch the state of the intake flow changing means in the second state to the first state is issued, and homogeneous stoichiometric combustion or homogeneous rich combustion is performed for a predetermined period of time. A fuel injection device for an internal combustion engine.   2. The fuel injection device for an internal combustion engine according to claim 1, wherein the predetermined period is a period corresponding to a response delay of the intake flow changing means.   An evaporative fuel passage for releasing the evaporative fuel into the intake passage, and a time period in which the predetermined period corresponds to a response delay of the intake flow changing means, or a predetermined amount of evaporative fuel in the intake passage 2. The fuel injection device for an internal combustion engine according to claim 1, wherein the fuel injection device is a period until it becomes less.   4. The period when the amount of evaporated fuel in the intake passage is smaller than a predetermined amount is a period until the amount of evaporated fuel in the intake passage becomes substantially zero. Fuel injection device for internal combustion engine.   5. The method according to claim 4, wherein when it is determined that the combustion mode should be changed between stratified lean combustion and homogeneous lean combustion, the discharge of the evaporated fuel from the evaporated fuel passage to the intake passage is stopped. A fuel injection device for an internal combustion engine as described.   A throttle valve disposed in the intake passage, and when the combustion mode is stratified lean combustion, the opening degree of the throttle valve is controlled corresponding to the stratified lean combustion, and when the combustion mode is homogeneous lean combustion The throttle valve opening is controlled in response to homogeneous lean combustion, and the throttle valve is in response to homogeneous lean combustion during the predetermined period when the combustion mode should be changed from stratified lean combustion to homogeneous lean combustion. The opening degree of the throttle valve is controlled corresponding to the stratified lean combustion in the predetermined period when the opening degree is controlled and the combustion mode should be changed from the homogeneous lean combustion to the stratified lean combustion. The fuel injection device for an internal combustion engine according to claim 1.   When the combustion mode is the stratified lean combustion mode, the fuel ignition timing by the spark plug is controlled corresponding to the stratified lean combustion mode, and when the combustion mode is the homogeneous lean combustion mode, the spark plug corresponding to the homogeneous lean combustion mode. In the predetermined period, the fuel ignition timing by the spark plug is controlled in correspondence with the predetermined period, and the fuel ignition timing in the predetermined period is the combustion mode. 5. The fuel injection device for an internal combustion engine according to claim 4, wherein the fuel injection timing is later than a fuel ignition timing when the combustion mode is in the stratified lean combustion mode and is later than a fuel ignition timing when the combustion mode is in the homogeneous lean combustion mode.

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