JP2015113767A - Fuel injection control device for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel injection control device for an internal combustion engine which includes a fuel injection valve provided below an intake port for injecting fuel directly into a cylinder, for improving the homogeneity of air-fuel mixture in the cylinder even at a low engine speed.SOLUTION: The fuel injection control device for the internal combustion engine includes a control part for executing main injection control and sub injection control to execute partial lift injection continuously several times. The control part executes the main injection control in an intake stroke and also executes the sub injection control in a period right before an intake valve is closed in a compression stroke and when gas in the cylinder reversely flows into the intake port. During the sub injection control, it performs the partial lift injection more times in proportion as an engine speed is lower, and increases the rate of the total amount of fuel to be injected into the cylinder with the partial lift injection to the total amount of the fuel to be injected into the cylinder in one engine cycle.

Description

  The present invention relates to a fuel injection control device applied to an internal combustion engine including a fuel injection valve that directly injects fuel into a cylinder.

  Patent Document 1 discloses an in-cylinder injection spark ignition internal combustion engine. In this internal combustion engine, fuel injection by split injection is executed while the intake valve is open during the compression stroke. Thereby, the injected fuel flows out to the intake port together with the in-cylinder gas flowing backward to the intake port. The fuel that has flowed out to the intake port is vaporized in the intake port until the next engine cycle, and is introduced into the cylinder as a premixed fuel in the intake stroke of the next engine cycle. And since this homogeneous fuel mixture is formed in the cylinder by this premixed fuel, good combustion can be obtained.

JP 2009-293526 A

  However, each of the divided injections described in Patent Document 1 is a fuel injection by an operation of reducing the lift amount of the needle valve provided in the fuel injection valve after reaching the maximum lift amount (that is, full lift injection), and thus is injected. Fuel penetration is high. Therefore, there is a possibility that a part of the injected fuel still adheres to the inner wall surface of the cylinder or cannot be sufficiently mixed in the air flowing back to the intake port. As a result, there is a high possibility that the homogenization of the air-fuel mixture will be insufficient.

  On the other hand, the present inventor reduces the fuel penetration force by performing fuel injection (that is, partial lift injection) by driving the needle valve in a range smaller than the maximum lift amount. We are investigating how to improve the homogenization of the air-fuel mixture by thoroughly mixing the injected fuel into the air flowing back to the intake port. However, since the amount of fuel injection for such partial lift injection is small and the opening period of the intake valve during the compression stroke is limited, all fuel necessary for combustion is obtained by partial lift injection. It is difficult to cover.

  On the other hand, in the intake stroke, since air flows into the cylinder, the flow of air in the cylinder is relatively intense. Therefore, the fuel injected by the full lift injection can be appropriately dispersed in the cylinder by the flow of air. it can.

  Therefore, the inventor is considering performing full lift injection in the intake stroke and performing partial lift injection a plurality of times immediately before closing the intake valve in the compression stroke. As a result, the fuel is injected by partial lift injection in the previous compression stroke and flows back into the intake port to become a homogeneous mixture, and in the current intake stroke, it flows into the cylinder from the intake port and the full lift injection in the current intake stroke. From the air-fuel mixture formed by the fuel injected by the fuel, the knowledge that the combustion of the current cycle can be further stabilized while ensuring the amount of fuel necessary for the combustion of the current cycle.

  However, as the investigation proceeds, the lower the engine speed, the weaker the air flow in the cylinder. Therefore, the air-fuel mixture formed by the fuel injected by full lift injection does not have the desired characteristics (for example, homogeneity). Therefore, the knowledge that the number of partial lift injections and the ratio of the total amount of fuel injected by partial lift injection to the total amount of fuel used for combustion should be changed according to the engine speed.

  More specifically, the present invention relates to a fuel injection control device applied to an internal combustion engine provided with a fuel injection valve for directly injecting fuel into a cylinder below an intake port, the needle valve of the fuel injection valve Main injection control for executing injection in which the lift amount of the needle valve is changed in a range up to the maximum lift amount, and partial lift injection in which the lift amount of the needle valve is changed in a range up to a partial lift amount smaller than the maximum lift amount The present invention relates to a fuel injection control device including a control unit that executes sub-injection control that continuously executes a plurality of times. In the present invention, the control unit executes the main injection control in the intake stroke, and immediately before the intake valve in the compression stroke is closed, in a period in which the gas in the cylinder flows backward to the intake port. The sub-injection control is executed, and in the sub-injection control, the number of partial lift injections is increased as the engine speed is lower, and the partial lift with respect to the total amount of fuel injected into the cylinder in one engine cycle The ratio of the total amount of fuel injected into the cylinder by injection is increased.

  According to the present invention, as the engine speed is lower, the ratio of the total amount of partial lift injected fuel in the sub-injection control to the total amount of injected fuel in one engine cycle (hereinafter referred to as “partial lift injection ratio”) is increased. At this time, if the number of partial lift injections is the same, the injection amount per partial lift injection increases, and thus the penetration force increases, so that the fuel injected by the partial lift injection flows back to the intake port. It becomes difficult. However, according to the present invention, when the partial lift injection ratio is increased, the number of partial lift injections is also increased, so the increase in the injection amount per partial lift injection is reduced or made zero. be able to. Therefore, even if the partial lift injection ratio is increased, the fuel injected by the partial lift injection easily flows back to the intake port. For this reason, the lower the engine speed, the more fuel flows back to the intake port. In the intake stroke of the next engine cycle, more vaporized fuel is introduced into the cylinder. Therefore, the homogeneity of the air-fuel mixture in the cylinder can be improved even at the time of low engine rotation at which the air flow rate in the cylinder is low and the air-fuel mixture is difficult to homogenize.

FIG. 1 is a diagram showing an internal combustion engine to which a fuel injection control device according to an embodiment of the present invention is applied. FIG. 2 is a cross-sectional view of the fuel injection valve according to the first embodiment. FIG. 3A is a diagram showing the lift amount of the intake valve, the strength of the backflow of the in-cylinder airflow, and the relationship between the needle lift amount and the crank angle, and FIG. FIG. 4 is a diagram similar to A), showing a relationship when the engine speed is lower than the engine speed in FIG. 4A is a diagram showing a change in the needle lift amount of the full lift injection, and FIG. 4B is a diagram showing a change of the needle lift amount of the partial lift injection. FIG. 5 is a diagram showing the state of fuel spray injected by partial lift injection and the flow of in-cylinder gas flowing backward to the intake port. 6A is a diagram showing a map of partial lift injection ratios, and FIG. 6B is a diagram showing a map of the number of partial lift injections. FIG. 7A is a view of the shape of the fuel spray in the first embodiment viewed from above, and FIG. 7B is a view of the shape of the fuel spray in the first embodiment viewed from the side. . FIG. 8 is a diagram showing a map representing the execution region of the sub-injection control. FIG. 9 is a diagram showing an example of a fuel injection control flow of the first embodiment. FIG. 10 is a diagram illustrating an example of a fuel injection control flow of the second embodiment. FIG. 11 is a diagram showing an example of a fuel injection control flow of the third embodiment. FIG. 12 is a diagram showing an example of a fuel injection control flow of the fourth embodiment.

<First Embodiment>
Hereinafter, embodiments of the present invention will be described with reference to the drawings. A schematic sectional view of an internal combustion engine to which the fuel injection control device of the present invention is applied is shown in FIG. The internal combustion engine body 10 includes a cylinder head 11, a cylinder block 12, a fuel injection valve 13, an ignition device 14, an intake valve 15, an exhaust valve 16, a piston 17, a connecting rod 18, a crankshaft 19, and a crank position sensor 20. . The ignition device 14 includes an igniter, an ignition coil, and a spark plug.

  A combustion chamber (hereinafter also referred to as “in-cylinder”) 21 is defined by a cylinder head 11, a cylinder block 12, and a piston 17. A fuel injection valve 13, an ignition device 14, an intake valve 15, and an exhaust valve 16 are attached to the cylinder head 11. An intake port 22 and an exhaust port 23 are formed in the cylinder head 11. The intake port 22 communicates with the combustion chamber 21 at one end and communicates with an intake manifold (not shown) at the other end. The exhaust port 23 communicates with the combustion chamber 21 at one end and communicates with an exhaust manifold (not shown) at the other end.

  The fuel injection valve 13 is disposed in a portion of the engine body 10 below the intake port 22 above the fuel chamber 21 (for example, a portion of the cylinder head 11 or a portion of the cylinder block 12). The ignition device 14 is disposed in the cylinder head 11 so that the electrode 24 is positioned substantially at the upper center of the combustion chamber 21. The intake valve 15 is disposed in the cylinder head 11 so as to be able to reciprocate so as to open or shut off the communication portion between the combustion chamber 21 and the intake port 22. The exhaust valve 16 is disposed in the cylinder head 11 so as to be able to reciprocate so as to open or shut off the communication portion between the combustion chamber 21 and the exhaust port 23. The opening / closing timing of the intake valve 15 is variable and the opening / closing timing of the exhaust valve 16 is also variable by a known mechanism. The valve overlap amount is variable depending on the engine operating state. The intake valve 15 is normally opened during the exhaust stroke (from the expansion bottom dead center to the intake top dead center) and closed during the compression stroke (from the intake bottom dead center to the compression top dead center).

  The cylinder block 12 includes a piston 17, a connecting rod 18, a crankshaft 19, and a crank position sensor 20. The piston 17 is connected to the connecting rod 18 and is disposed so as to reciprocate within the cylinder block 12. The crankshaft 19 is connected to the connecting rod 18.

  The fuel injection valve 13, the ignition device 14, the crank position sensor 20, and the accelerator pedal depression amount sensor 26 are electrically connected to an electronic control unit (ECU) 90. The ECU 90 gives a control signal for controlling the operation of the fuel injection valve 13 and the ignition device 14 to the fuel injection valve 13 and the ignition device 14. The crank position sensor 20 detects the rotational position of the crankshaft 19. The ECU 90 calculates the engine speed based on information on the rotational position of the crankshaft 19 and the like. The accelerator pedal depression amount sensor 26 detects the depression amount of the accelerator pedal 25. The ECU 90 calculates the engine load based on information related to the depression amount of the accelerator pedal 25 and the like.

<Configuration of fuel injection valve>
FIG. 2 shows the configuration of the fuel injection valve 13. The fuel injection valve 13 includes a nozzle 30, a needle valve 31, a fuel injection hole (hereinafter “injection hole”) 32, a fuel passage 33, a solenoid 34, a spring 35, and a fuel intake port 36. The injection valve axis 37 is an axis extending in the longitudinal direction of the fuel injection valve 13. The fuel injection valve 13 is a so-called inner opening type fuel injection valve.

  The fuel injection valve 13 can selectively execute full lift injection or partial lift injection (details of these injections will be described later) by appropriately controlling the needle lift amount (that is, the lift amount of the needle valve 31). It is a fuel injection valve. The needle lift amount can be controlled by controlling the energization time to the fuel injection valve 13.

<Configuration of nozzle hole>
The nozzle hole 32 of the fuel injection valve 13 is a slit-shaped nozzle hole. That is, the shape of the cross section of the injection hole 32 when cut along a plane perpendicular to the injection axis of the injection hole 32 is a rectangle. The area of this cross section gradually increases in the direction from the inlet to the outlet of the nozzle hole 32. Therefore, the shape of the cross section of the injection hole 32 when it cuts by the plane along the longitudinal direction of a rectangular cross section is fan shape. The fuel injection valve 13 is located below the intake port 22 (the cylinder block 12 or the cylinder head) so that the plane along the longitudinal direction of the rectangular cross section of the injection hole 32 is perpendicular to the reciprocating direction of the piston 17. 11).

<Fuel injection control>
The fuel injection control of the first embodiment will be described with reference to FIG. In FIG. 3, the intake valve lift amount (that is, the lift amount of the intake valve 15), the backflow strength (that is, the strength of the in-cylinder gas that flows back from the cylinder to the intake port 22), the needle lift amount, The relationship with the crank angle is shown. In FIG. 3, the periods indicated by reference symbol #n and reference symbol # (n + 1) each indicate one engine cycle.

  In the first embodiment, in one engine cycle, main injection control (control indicated by reference sign FL in FIG. 3), sub-injection control (control indicated by reference sign PL in FIG. 3), Are executed sequentially. Hereinafter, the control that executes both the main injection control and the sub-injection control according to the first embodiment is also referred to as “premix control”.

<Main injection control>
The main injection control in the premix control is a control in which full lift injection is executed once, and is executed in a period from immediately after the intake valve 15 is opened to the intake bottom dead center (intake BDC) in the intake valve opening period Tiv. The As shown in FIG. 4A, full lift injection is fuel injection that raises the needle lift amount to the maximum lift amount (that is, maximum lift injection). FIG. 4A shows the transition of the needle lift amount of one full lift injection.

<Intake valve opening period>
The intake valve opening period Tiv is a period during which the intake valve 15 is open. In the first embodiment, as shown in FIG. 3, the intake valve 15 starts to open immediately after the intake top dead center (intake TDC), and is fully closed immediately after the intake bottom dead center. Accordingly, the intake valve lift amount is zero at the intake top dead center, is not zero at the intake bottom dead center, and is zero immediately after the intake bottom dead center. Although not shown, in the first embodiment, the exhaust valve 16 is fully closed before the intake valve 15 is opened. Therefore, there is no state in which the intake valve 15 and the exhaust valve 16 are open at the same time (so-called valve overlap).

<Sub-injection control>
The sub-injection control in the premix control is a control in which the partial lift injection is continuously executed a plurality of times. In the intake valve opening period Tiv, after the main injection control is executed, the backflow generation period (that is, the in-cylinder gas is taken in) (Period to flow back to port 22) Trf is executed. As shown in FIG. 4B, the partial lift injection is a fuel injection that raises the needle lift amount only to a lift amount smaller than the maximum lift amount (that is, partial lift injection). FIG. 4B shows the transition of the needle lift amount of three partial lift injections.

<Backflow generation period>
As described above, the reverse flow generation period Trf is a period in which the in-cylinder gas flows backward to the intake port 22, and more specifically, is a period from the intake bottom dead center until the intake valve 15 is fully closed. As described above, the intake valve 15 starts to open immediately after the intake top dead center and is fully closed immediately after the intake bottom dead center. That is, the backflow generation period Trf is a period during which the intake valve 15 is open in the compression stroke (from the intake bottom dead center to the compression top dead center). As shown in FIG. 5, the reverse flow is a flow of in-cylinder gas that flows out from the region in the cylinder below the intake valve 15 to the intake port 22.

<Total target injection amount>
In the first embodiment, the total amount of injected fuel in one engine cycle is necessary to achieve the target air-fuel ratio according to the intake air amount (that is, the amount of air sucked into the cylinder) during engine operation. The fuel is calculated as a total target injection amount (that is, the amount of fuel to be injected from the fuel injection valve in one engine cycle) Qt. That is, the total target injection amount means the total amount of fuel supplied to one cylinder per engine cycle.

<Partial lift injection ratio>
Furthermore, as a ratio of the total amount of injected fuel in the sub-injection control with respect to the total target injection amount, an appropriate ratio according to the engine operating state is obtained in advance by experiments or the like, and these obtained ratios are shown in FIG. As shown, the partial lift injection ratio is stored in the ECU 90 in the form of a function map of the engine speed NE and the engine load KL. In the map of FIG. 6A, the lower the engine speed NE, the larger the partial lift injection ratio, and the higher the engine load KL, the larger the partial lift injection ratio.

<Number of partial lift injections>
Furthermore, as the number of partial lift injections in one sub-injection control, an appropriate number corresponding to the engine operating state is obtained in advance by experiments or the like, and these obtained times are shown in FIG. 6 (B). As described above, the ECU 90 stores the partial lift injection frequency in the form of a function map of the engine speed NE and the engine load KL. In the map of FIG. 6B, the lower the engine speed NE, the greater the number of partial lift injections, and the higher the engine load KL, the greater the number of partial lift injections.

<Determination of injection amount>
In the first embodiment, during the engine operation, the fuel required to achieve the target air-fuel ratio is calculated as the total target injection amount Qt according to the intake air amount, and the engine speed NE and the engine load KL are calculated. The corresponding partial lift injection ratio Rp and the number N of partial lift injections are acquired from the maps of FIGS. 6 (A) and 6 (B), respectively. Then, by multiplying the total target injection amount Qt by the partial lift injection ratio Rp, the partial lift injection amount (that is, the total amount of injected fuel in the sub injection control) Qpt is obtained (Qpt = Qt * Rp). Next, by dividing the partial lift injection amount Qpt by the partial lift injection number N, a fuel injection amount Qp per partial lift injection is obtained (Qp = Qpt / N). Further, by subtracting the partial lift injection amount Qpt from the total target injection amount Qt, the full lift injection amount (that is, the total amount of injected fuel in the main injection control) is acquired (Qf = Qt−Qpt).

  In the main injection control, full lift injection is executed so that the fuel of the full lift injection amount Qf acquired in this way is injected from the fuel injection valve 13. On the other hand, in the sub-injection control, the partial lift injection is performed by the number N of partial lift injections so that the fuel of the partial lift injection amount Qp thus obtained is injected from the fuel injection valve 13 by one partial lift injection. Executed.

  As described above, in the first embodiment, the lower the engine speed, the larger the partial lift injection ratio and the higher the number of partial lift injections. Therefore, FIG. 3A showing the needle lift amount when the engine speed is relatively high and FIG. 3B showing the needle lift amount when the engine speed NE is relatively low. When the total target injection amount is the same, the total amount of fuel injected in the sub-injection control when the engine speed is relatively low is the sub-injection control when the engine speed is relatively high. The number of partial lift injections when the engine rotational speed is relatively low is larger than the total amount of injected fuel in the engine and when the engine rotational speed is relatively low. Of course, the full lift injection amount when the engine speed is relatively low is smaller than the full lift injection amount when the engine speed is relatively high.

<Effects of First Embodiment>
As the amount of fuel injected by one injection increases, mixing of the fuel and the air in the cylinder does not proceed easily. As indicated by reference numeral 51 in FIG. 7, the full lift injection is an injection that injects a relatively large amount of fuel at a time, and thus mixing of the fuel injected by the injection and the air in the cylinder proceeds. Hateful. However, according to the first embodiment, a part of the total target injection amount is injected by partial lift injection. Accordingly, the amount of fuel injected by full lift injection is reduced accordingly. For this reason, compared with the case where only the main injection control is executed without executing the sub-injection control, the mixing of the fuel injected by the full lift injection and the air in the cylinder is easy to proceed. For this reason, the homogeneity of the air-fuel mixture in the cylinder is improved.

  On the other hand, partial lift injection is an injection in which fuel is injected for a relatively short time, and the total amount of fuel injected by the injection is relatively small. Therefore, as indicated by reference numeral 50 in FIG. 7, the fuel spray by the injection receives the resistance of the in-cylinder gas and flies only relatively close to the fuel injection valve 13. That is, fuel spray by partial lift injection is distributed in a cylinder area below the intake valve 15 in the cylinder. In the first embodiment, the sub-injection control is executed during the backflow generation period. Therefore, the fuel injected by the partial lift injection flows back to the intake port 22 as shown in FIG. This fuel is sucked into the cylinder during the intake stroke in the next engine cycle. Since this fuel is sufficiently vaporized in the intake port until it is sucked into the cylinder, when this fuel is sucked into the cylinder during the intake stroke of the next engine cycle, A homogeneous mixture is formed. For this reason, the homogeneity of the air-fuel mixture in the cylinder is improved.

  Furthermore, when the engine speed is low, the airflow in the cylinder is weak and mixing of the fuel injected by the full lift injection and the air in the cylinder does not proceed easily. However, in the first embodiment, the amount of fuel injected by the sub-injection control is increased as the engine speed is lower. Therefore, the amount of fuel that is sucked into the cylinder after flowing back to the intake port 22 and sufficiently vaporizing increases. For this reason, even when the engine speed is low, the homogeneity of the air-fuel mixture in the cylinder is maintained. Moreover, since the amount of fuel injected by the sub-injection control is increased, the amount of fuel injected by the full lift injection is reduced. For this reason, the fuel injected by the full lift injection is easily mixed with air in the cylinder. From this, even when the engine speed is low, the homogeneity of the air-fuel mixture in the cylinder is maintained.

  Further, when the amount of fuel injected by the secondary injection control is increased, if the number of partial lift injections is the same, the injection amount per partial lift injection increases. In this case, even if the flight distance of the fuel spray by partial lift injection becomes long and the sub-injection control is executed during the backflow generation period, the fuel spray flies far beyond the intake valve 15 and enters the intake port 22. There is a possibility that it will not flow backward. However, in the first embodiment, when the engine speed is low and the amount of fuel injected by the secondary injection control is increased, the number of partial lift injections is also increased. Therefore, the fuel injected by the partial lift injection is maintained in a state where it easily flows back to the intake port. For this reason, even when the engine speed is low, the fuel injected by the partial lift injection flows back to the intake port and is sufficiently vaporized in the intake port by the intake stroke in the next engine cycle. In the intake stroke, the air is sucked into the cylinder, so that the homogeneity of the air-fuel mixture in the cylinder is maintained.

  Thus, according to the first embodiment, high homogeneity of the air-fuel mixture in the cylinder is ensured regardless of the engine speed.

<Mode of main injection control>
In the first embodiment, the main injection control is not limited to the control for executing the full lift injection once. The main injection control may be executed by executing the full lift injection a plurality of times or by executing the partial lift injection once. The lift injection may be executed a plurality of times.

<Execution conditions for sub-injection control>
When the engine speed NE is very high, one engine cycle is short in time, and therefore the backflow generation period is short. For this reason, even if the sub-injection control in the premix control is executed, there is a possibility that the predetermined number of partial lift injections cannot be completed during the backflow generation period. On the other hand, when the engine speed NE is very high, since the airflow in the cylinder is strong, mixing of the fuel and the air in the cylinder easily proceeds. Therefore, even if only full lift injection is performed, the homogeneity of the air-fuel mixture in the cylinder is sufficiently high. Therefore, as shown in FIG. 8, in the first embodiment, a threshold value Nth of the engine speed at which the homogeneity of the air-fuel mixture becomes sufficiently high even if only full lift injection is executed is determined, and the engine speed is When it is equal to or less than the threshold value Nth, premix control (that is, main injection control and sub-injection control) is executed, and when the engine speed is higher than the threshold value Nth, normal injection control that executes only one full lift injection is executed. You may be made to do.

<Lower limit of partial lift injection amount>
Note that if the injection amount per partial lift injection is too small, there is a possibility that the desired injection amount of fuel will not be stably injected by each partial lift injection. Therefore, in the first embodiment, the partial lift injection ratio and the number of partial lift injections are as follows. The injection amount per partial lift injection is an injection amount in which the fuel of the desired injection amount is stably injected by each partial lift injection. It is preferable that the setting is made as described above.

<Upper limit value of partial lift injection amount>
Furthermore, if the injection amount per partial lift injection is too large, the flight distance of the fuel injected by the partial lift injection is long, and there is a possibility that the fuel does not get on the in-cylinder gas flowing backward to the intake port. Therefore, in the first embodiment, the partial lift injection ratio and the number of partial lift injections are such that the amount of fuel injected per partial lift injection surely gets on the in-cylinder gas that flows back to the intake port. It is preferable to set it to be equal to or less than the injection amount.

<Control Flow of First Embodiment>
The fuel injection control flow of the first embodiment will be described. An example of this flow is shown in FIG. When the flow of FIG. 9 is started, first, in step 11, the total target injection amount Qt is calculated based on the intake air amount and the target air-fuel ratio.

  Next, at step 12, it is determined whether or not the engine speed NE is equal to or less than a threshold value Nth (NE ≦ Nth), that is, whether or not an execution condition for sub-injection control is satisfied. If NE.ltoreq.NEth, the execution condition of the sub-injection control is satisfied, so the routine proceeds to step 13, and the premix control (main injection control and sub-injection control) is executed by the steps after step 13. The On the other hand, if NE> Nth, the execution condition of the sub-injection control is not satisfied, so the routine proceeds to step 17 where the normal injection control for executing only one full lift injection is executed, and this routine is temporarily ended. To do. Note that in the normal injection control at this time, the fuel of the total target injection amount Qt is injected.

  In step 13, the partial lift injection ratio Rp corresponding to the engine speed NE and the engine load KL is acquired from the map of FIG. 6A, and the partial lift corresponding to the engine speed NE and the engine load KL. The number of injections N is acquired from the map of FIG. Next, in step 14, the full lift injection amount Qf and the injection amount Qp per partial lift injection are determined based on the total target injection amount Qt, the partial lift injection ratio Rp, and the number N of partial lift injections. Next, in step 15, the injection timings of full lift injection and partial lift injection are determined based on the valve opening timing and valve closing timing of the intake valve 15. Next, at step 16, main injection control and sub-injection control are sequentially executed, and this routine is temporarily ended. In the main injection control at this time, one full lift injection for injecting the fuel of the injection amount Qf is executed, and in the sub injection control, the partial lift injection for injecting the fuel of the injection amount Qp is performed for the number of injections N. Executed.

Second Embodiment
A second embodiment will be described. The second embodiment relates to fuel injection control when there is a valve overlap. If the above-described premix control is performed in a case where there is a valve overlap, there is a possibility that the fuel that has flowed into the cylinder from the intake port 22 during the intake stroke will flow out to the exhaust port 23 as it is. Therefore, in the second embodiment, when there is no valve overlap, premix control is permitted, and when there is valve overlap, premix control is prohibited and normal injection control that performs only one full lift injection is performed. Executed.

  In the case where there is a valve overlap, if the premix control is executed, the possibility that the fuel that has flowed into the cylinder from the intake port 22 during the intake stroke will flow out to the exhaust port 23 is determined by the amount of valve overlap. The larger the size, the higher. Therefore, in the second embodiment, when the valve overlap amount is equal to or less than the predetermined amount, the premix control is permitted, and when the valve overlap amount is larger than the predetermined amount, the premix control is prohibited and the normal injection control is performed. May be executed.

<Effects of Second Embodiment>
According to the second embodiment, in the case where there is a valve overlap, the outflow of fuel to the exhaust port is prevented, so that the emission is prevented from deteriorating.

<Control Flow of Second Embodiment>
The fuel injection control flow of the second embodiment will be described. An example of this flow is shown in FIG. Note that steps 21, 22, and 24-28 in FIG. 10 are the same as steps 11, 12, and 13-17 in FIG. 9, respectively, and thus description of these steps is omitted.

  In step 23 of FIG. 10, it is determined whether or not the valve overlap amount Tvo is 0 or less (Tvo ≦ 0). If Tvo ≦ 0, premix control is permitted. That is, the routine proceeds to step 24, and the premix control is executed after step 24. On the other hand, if Tvo> 0, the premix control is prohibited. That is, the routine proceeds to step 28, and the normal injection control that executes only one full lift injection is executed without executing the premix control.

<Third Embodiment>
The third embodiment relates to fuel injection control when fuel cut control (that is, control to stop fuel injection from the fuel injection valve 13) is started. When the fuel injection control shifts from the premix control to the fuel cut control, after the fuel cut control is started, in the first engine cycle, the fuel injection is stopped, but the intake port 22 in the previous engine cycle is stopped. The fuel that flows backward into the cylinder flows into the cylinder in this engine cycle. For this reason, emission worsens. Therefore, in the third embodiment, when execution of fuel cut control is requested, first, premix control is stopped, and normal injection control that executes only one full lift injection is executed, and the next engine is executed. In the cycle, fuel cut control is started. In the normal injection control, the fuel of the total target injection amount Qt is injected by one full lift injection.

<Effect of the third embodiment>
According to the third embodiment, the fuel cut control is started after the premix control is stopped. For this reason, since no fuel flows into the cylinder from the intake port after the start of the fuel cut control, the deterioration of the emission is prevented.

<Control Flow of Third Embodiment>
A fuel injection control flow of the third embodiment will be described. An example of this flow is shown in FIG. Note that steps 31, 33 to 39 in FIG. 11 are the same as steps 21, 22 to 28 in FIG. The flow described below relates to an internal combustion engine having a plurality of cylinders.

  In step 32 of FIG. 11, it is determined whether or not the fuel cut control request flag Fcs is reset (Fcs = 0), that is, whether or not execution of fuel cut control is requested. If Fcs = 0, execution of fuel cut control is not requested, so the routine proceeds to step 33, and after step 33, fuel injection control according to the first embodiment is executed.

  On the other hand, if Fcs = 1, execution of fuel cut control is requested, so the routine proceeds to step 40 where normal injection control is executed. Next, at step 41, it is determined whether or not the normal injection control at step 40 has been executed for all cylinders of the internal combustion engine. When it is determined that the normal injection control has been executed for all the cylinders, the routine proceeds to step 42, the fuel cut control is started, and this routine is once ended. Thereafter, as long as it is determined in step 32 that Fcs = 0, the fuel cut control is continued.

  On the other hand, if it is determined in step 41 that the normal injection control is not executed in all the cylinders, the routine returns to step 40, and the fuel cut is performed until it is determined in step 41 that the normal injection control is executed in all the cylinders. Control is not started and step 40 is repeatedly executed.

<Fourth embodiment>
The fourth embodiment relates to fuel injection control when fuel cut control is terminated. When the fuel injection control is shifted from the fuel cut control to the premix control, there is no fuel sucked into the cylinder from the intake port 22 in the first engine cycle after the start of the premix control. Accordingly, in this first engine cycle, the fuel in the cylinder is only the fuel injected by the main injection control in the premix control, so that the high homogeneity of the air-fuel mixture in the cylinder cannot be ensured, and furthermore, the cylinder The air / fuel ratio of the air / fuel mixture does not reach the desired air / fuel ratio. For this reason, the emission may be deteriorated. Therefore, in the fourth embodiment, when the end of the fuel cut control is requested, first, only the sub-injection control in the premix control is executed, and in the next engine cycle, the fuel cut control is ended and the pre-cut control is performed. Mixing control (that is, main injection control and sub-injection control) is started.

<Effects of Fourth Embodiment>
According to the fourth embodiment, after the sub-injection control in the premix control, the fuel cut control is terminated and the premix control is started. Accordingly, fuel flows into the intake port 22 in the engine cycle immediately before the start of the premix control. For this reason, when the premix control is started, fuel flows into the cylinder from the intake port 22, so that high homogeneity of the mixture in the cylinder is ensured, and further, the air-fuel ratio of the mixture in the cylinder is determined. It becomes the air fuel ratio of the period. For this reason, the deterioration of the emission is prevented.

<Control Flow of Fourth Embodiment>
A fuel injection control flow of the fourth embodiment will be described. An example of this flow is shown in FIG. Note that steps 51 and 53 to 57 in FIG. 12 are the same as steps 31 and 33 to 37 in FIG. 11, respectively, so description of these steps will be omitted. The flow described below relates to an internal combustion engine having a plurality of cylinders.

  In step 52 of FIG. 12, it is determined whether or not the fuel cut control end request flag Fce is set (Fce = 1), that is, whether or not the end of the fuel cut control is requested. If Fce = 0, the end of the fuel cut control is not requested, so the routine proceeds to step 64 and the fuel cut control is continued. On the other hand, if Fce = 1, since the end of the fuel cut control is requested, the routine proceeds to step 53.

  If it is determined in step 53 that NE ≦ Nth and then it is determined in step 54 that Tvo ≦ Tth, in steps 55 to 57, the full lift injection amount Qf and the partial lift injection per one time are determined. The injection amount Qp, the number N of partial lift injections, and the injection timing of full lift injection and partial lift injection are determined.

  Next, at step 58, only the sub-injection control in the premix control is executed. That is, the sub-injection control is executed in which partial lift injection for injecting fuel of the injection amount Qp is executed for the number of injections N. Next, at step 59, it is determined whether or not the sub-injection control at step 58 has been executed for all cylinders. If it is determined that the sub-injection control in step 58 has been executed for all the cylinders, the routine proceeds to step 60, where the fuel cut control is terminated, and then in step 61, the premix control is started, and this routine Is temporarily terminated.

  On the other hand, if it is determined in step 59 that the sub-injection control in step 58 has not been executed for all cylinders, the routine returns to step 58, and in step 59, it is determined that the sub-injection control in step 58 has been executed for all cylinders. Until this is done, the premix control is not started and step 58 is repeatedly executed.

  If it is determined in step 53 that NE> Nth, or if it is determined in step 54 that Tvo> Tth, the routine proceeds to step 62 and fuel cut control is immediately terminated. The normal injection control that executes only one full lift injection is executed, and this routine is temporarily ended.

DESCRIPTION OF SYMBOLS 13 ... Fuel injection valve, 14 ... Ignition device, 15 ... Intake valve, 16 ... Exhaust valve, 21 ... Combustion chamber (in-cylinder), 22 ... Intake port, 23 ... Exhaust port, 24 ... Spark plug electrode, 30 ... Nozzle , 31 ... Needle valve, 32 ... Fuel injection hole (injection hole), 90 ... Electronic control unit (ECU).

Claims (1)

A fuel injection control device applied to an internal combustion engine having a fuel injection valve for directly injecting fuel into a cylinder below an intake port, wherein a lift amount of a needle valve of the fuel injection valve is within a range up to a maximum lift amount. Main injection control for executing changed injection, and sub-injection control for continuously executing partial lift injection for changing the lift amount of the needle valve within a range up to a partial lift amount smaller than the maximum lift amount a plurality of times In a fuel injection control device comprising a control unit that executes
The control unit executes the main injection control in the intake stroke, and executes the sub-injection control in a period immediately before the intake valve in the compression stroke closes and the gas in the cylinder flows backward to the intake port. And
In the sub-injection control, the lower the engine speed is, the more the number of partial lift injections is increased, and the partial lift injection with respect to the total amount of fuel injected into the cylinder in one engine cycle is injected into the cylinder. Increase the proportion of the total amount of fuel,
A fuel injection control device configured as described above.

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