JP6687449B2 - Control device and control method for direct injection engine - Google Patents

Description

  The present invention relates to a technique for increasing the exhaust temperature and promoting the activity of an exhaust purification catalyst in a direct injection spark ignition engine (hereinafter referred to as “direct injection engine”) in which fuel is directly injected into a cylinder.

  When the engine is started from the cold state, the exhaust purification catalyst in the exhaust passage is activated early so that the ignition timing is retarded to raise the exhaust temperature and the heat of the exhaust heats the exhaust purification catalyst. Is being done. Then, when retarding the ignition timing, the fuel to be supplied to the engine per one combustion cycle is injected into the intake stroke and the compression stroke separately, and the fuel injected during the intake stroke is injected into the air in the cylinder. It is known that the fuel injected during the compression stroke is unevenly distributed around the spark plug while the fuel is injected into the entire cylinder (hereinafter referred to as “in-cylinder flow”) and diffused throughout the cylinder. As a result, the fuel around the spark plug becomes a spark, and it becomes possible to realize stable combustion even at a late ignition timing.

  Here, in the fuel injection during the compression stroke, if the in-cylinder flow remains and its strength is excessively maintained, the spray of injected fuel is carried along with the in-cylinder flow and ignites the fuel. It becomes difficult to keep it well around the plug. Therefore, combustion is not stable and there is a risk of misfire.

  Patent Document 1 discloses that a means for enhancing the flow of air in the cylinder is provided in order to enable stratified combustion at the time of starting the engine, and this means compensates for the insufficient strength of the flow in the cylinder at the time of start. . The enhanced in-cylinder flow prevents advance of the fuel injected during the compression stroke, and the fuel spray is diverted upward from the vicinity of the crown surface of the piston so that it is unevenly distributed around the spark plug.

JP, 2004-218646, A (paragraph 0009).

  The technique of Patent Document 1 promotes stratification of fuel by positively strengthening the flow even under conditions where the air flow in the cylinder is weak (specifically, when the engine is started), and the ignition is first performed after the start. It is possible to carry out stratified combustion from the cylinder that reaches the temperature. In Patent Document 1, the control of the exhaust gas temperature for activating the exhaust gas purification catalyst is performed by refueling after ignition (paragraph 0007).

  INDUSTRIAL APPLICABILITY The present invention facilitates the uneven distribution of the fuel around the spark plug by weakening the flow of air in the cylinder, and thus stabilizes the exhaust temperature to increase when starting the engine from a cold state. The purpose is to achieve combustion.

  The present invention, in one form, provides a method for controlling a direct injection engine.

A method according to an aspect of the present invention is a direct injection engine that includes a spark plug and a fuel injection valve that is capable of directly injecting fuel into a cylinder, and sets a fuel injection start timing of the fuel injection valve during normal operation. By setting it during the intake stroke, the injected fuel is carried in the air flow in the cylinder and diffused in the cylinder, and when the catalyst is warmed up, the fuel injection of the fuel injection valve is divided into intake stroke injection and compression stroke injection. At the same time , the intake stroke injection start timing is set earlier than the injection start timing at which the pre-calculated exhaust particulate number becomes the allowable upper limit value and the pre-calculated combustion instability becomes at the allowable upper limit value. Set to the period .

  According to the present invention, it is possible to weaken the flow of air in the cylinder by utilizing the kinetic energy of the fuel spray and form a flow state suitable for uneven distribution of the fuel around the spark plug.

FIG. 1 is an overall configuration diagram of an engine according to an embodiment of the present invention. FIG. 2 is an explanatory diagram showing an effect (decrease in tumble flow strength) due to collision with fuel spray. FIG. 3 is an explanatory diagram showing changes in the number of exhaust particulates and the combustion instability depending on the injection timing of the intake stroke injection. FIG. 4 is an explanatory diagram showing the relationship between the fuel spray and the air in the cylinder in the flow direction according to the piston position. FIG. 5: is explanatory drawing which shows the center line of a spray beam of a fuel injection valve. FIG. 6 is a flowchart showing a basic flow of catalyst warm-up control according to the embodiment of the present invention. FIG. 7 is an explanatory diagram showing the relationship between the fuel injection pressure (fuel pressure), the number of injection splits, and the number of exhaust particulates. FIG. 8 is an explanatory diagram showing changes in the number of exhaust particulates and the combustion instability with respect to changes in the injection condition of the intake stroke injection. FIG. 9 is an explanatory diagram showing the relationship among the injection period, the particulate requirement injection limit and the stability requirement injection limit under various injection conditions of the intake stroke injection.

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

(Overall structure of engine)
FIG. 1 is an overall configuration diagram of a direct injection engine (a spark ignition direct injection engine, hereinafter referred to as “engine”) 1 according to an embodiment of the present invention.

  The main body of the engine 1 is formed by the cylinder block 1A and the cylinder head 1B, and a cylinder or a cylinder is formed as a space surrounded by the cylinder block 1A and the cylinder head 1B. Although FIG. 1 shows only one cylinder, the engine 1 may be a multi-cylinder type direct injection engine having a plurality of cylinders.

  A piston 2 is inserted in the cylinder block 1A so as to be vertically reciprocally movable along a cylinder center axis Ax, and the piston 2 is connected to a crankshaft (not shown) via a connecting rod 3. The reciprocating motion of the piston 2 is transmitted to the crankshaft through the connecting rod 3 and converted into the rotary motion of the crankshaft. Here, the cavity 21a is formed in the crown surface 21 of the piston 2, and while suppressing the smooth flow of the air sucked into the cylinder through the intake port 4a from being blocked by the piston crown surface 21, The fuel injected by the fuel injection valve 6 is guided by the wall surface of the cavity 21a and directed toward the spark plug 7.

  The cylinder head 1B has a lower surface that defines a pent roof type combustion chamber Ch. A combustion chamber Ch is formed as a space surrounded by the lower surface of the cylinder head 1B and the piston crown surface 21. In the cylinder head 1B, a pair of intake passages 4 is formed on one side of the cylinder center axis Ax and a pair of exhaust passages 5 is formed on the other side as passages that connect the combustion chamber Ch and the outside of the engine. An intake valve 8 is arranged at a port portion (intake port) 4a of the intake passage 4, and an exhaust valve 9 is arranged at a port portion (exhaust port) 5a of the exhaust passage 5. Air taken into the intake passage 4 from the outside of the engine is sucked into the cylinder during the opening period of the intake valve 8, and exhaust gas after combustion is discharged into the exhaust passage 5 during the opening period of the exhaust valve 9.

  A spark plug 7 is further installed in the cylinder head 1B along the cylinder center axis Ax between the intake port 4a and the exhaust port 5a, and a pair of intake ports 4a and 4a are provided on one side of the cylinder center axis Ax. The fuel injection valve 6 is set between them. The fuel injection valve 6 is configured and arranged so that fuel can be directly injected into the cylinder. In the present embodiment, the fuel injection valve 6 is a multi-hole type fuel injection valve, and the fuel is injected in a direction diagonally intersecting the cylinder center axis Ax, in other words, a spray beam described later. It is arranged on the intake port 4a side of the cylinder center axis Ax so that the center of gravity line Af and the cylinder center line Ax intersect at an acute angle.

  In the present embodiment, the tumble control valve 10 is installed in the intake passage 4, and the opening area of the intake passage 4 is substantially narrowed by the tumble control valve 10 so that the air flow in the cylinder is strengthened. In the present embodiment, as the flow of air, the air sucked into the cylinder through the intake port 4a is on the opposite side of the cylinder center axis Ax from the intake port 4a, in other words, on the exhaust port 5a side in the cylinder space. Is formed in the direction from the lower surface of the cylinder head 1B toward the piston crown surface 21, and the tumble control valve 10 enhances the tumble flow. The in-cylinder flow enhancement can be achieved not only by installing the tumble control valve 10 but also by changing the shape of the intake passage 4. For example, by making the intake passage 4 more upright, air is introduced into the cylinder at a gentler angle with respect to the cylinder center axis Ax.

  A catalyst (not shown) for purifying exhaust gas is interposed in the exhaust passage 5. In the present embodiment, the exhaust gas purification device is a three-way catalyst, and the exhaust gas after combustion discharged to the exhaust passage 5 is converted into nitrogen oxides (NOx), carbon monoxide (CO) and hydrocarbons by the exhaust gas purification catalyst. After the harmful components such as (HC) are purified, they are released into the atmosphere.

(Outline of engine control)
The operation of the engine 1 is controlled by the electronic control unit 101. The electronic control unit 101 constitutes an “engine control unit”. The electronic control unit 101 receives the detection signals of the accelerator sensor 201, the rotation speed sensor 202, and the cooling water temperature sensor 203, as well as the detection signals of an air flow meter, an air-fuel ratio sensor, and the like (not shown). The accelerator sensor 201 detects the amount of operation of the accelerator pedal by the driver. The operation amount of the accelerator pedal serves as an index of the load required for the engine 1. The rotation speed sensor 202 detects the rotation speed of the engine 1. A crank angle sensor can be used as the rotation speed sensor 202, and a unit crank angle signal or a reference crank angle signal output by the crank angle sensor can be converted into a rotation speed per unit time (engine speed). Then, the rotation speed is detected. The cooling water temperature sensor 203 detects the temperature of the engine cooling water. The temperature of the engine lubricating oil may be used instead of the temperature of the engine cooling water. The air flow meter is installed in the introduction portion of the intake passage 4 to detect the flow rate of the air sucked into the engine 1 (intake air amount), and the air-fuel ratio sensor is installed in the exhaust passage 5 to detect the air-fuel ratio of the exhaust gas. To do. The electronic control unit 101 has a storage unit that holds map data in which various operation control parameters such as the fuel injection amount are assigned according to the operating conditions such as the load of the engine 1, the rotation speed, and the cooling water temperature. Then, during actual operation of the engine 1, the fuel injection amount, the fuel injection timing, the ignition timing, etc. are set by referring to the map data of the storage unit based on the operating state of the engine 1.

(Details of catalyst warm-up control)
In the present embodiment, when the engine 1 is started from the cold state, the exhaust purification catalyst is activated early, so the ignition timing by the spark plug 7 is significantly retarded compared to the normal time to raise the exhaust temperature and The control for raising the temperature of the exhaust purification catalyst by the heat contained in the catalyst (hereinafter referred to as "catalyst warm-up control") is executed. Specifically, during normal time, the ignition timing is set to MBT (optimal ignition timing at which the engine torque is maximized) or in the vicinity thereof, while during catalyst warm-up, the ignition timing is delayed relative to the normal ignition timing. And set during the expansion stroke (for example, in the first half of the expansion stroke, more specifically, in the range of 10 to 30 deg after the compression top dead center at the crank angle). Along with the ignition timing retard correction, the fuel to be supplied to the engine 1 per combustion cycle is injected separately into the intake stroke and the compression stroke, and the fuel injected during the intake stroke is injected into the entire cylinder. The fuel injected during the compression stroke is unevenly distributed around the spark plug 7. In the present embodiment, the fuel injection is performed once in each of the intake stroke and the exhaust stroke, the fuel injection timing during the intake stroke is the first half of the intake stroke, and the fuel injection timing during the compression stroke is the second half of the compression stroke. The timing is set so that the spray of the injected fuel has enough time to reach the vicinity of the spark plug 7 by the ignition timing.

  In the catalyst warm-up control, the fuel injection amount per combustion cycle is divided into an intake stroke and a compression stroke, the fuel injected during the compression stroke is unevenly distributed around the spark plug 7, and the ignition timing is retarded. It depends on the combustion mode (hereinafter referred to as "stratified retard combustion"). The air-fuel ratio of the exhaust gas discharged by the stratified retard combustion is a stoichiometric air-fuel ratio or an air-fuel ratio leaner than this. In the present embodiment, since the air-fuel ratio of exhaust gas is set to the stoichiometric air-fuel ratio, the amount of fuel that can be completely combusted with the intake air amount per combustion cycle is calculated, and a part of this fuel amount (for example, 20 to 20) is calculated. 90%) is the fuel injection amount during the intake stroke, and the rest is the fuel injection amount during the compression stroke.

  Then, the fuel injected by the fuel injection during the intake stroke (hereinafter referred to as "intake stroke injection") is diffused throughout the cylinder to form a homogeneous mixture leaner than the stoichiometric air-fuel ratio in the cylinder. On the other hand, the fuel injected by the fuel injection during the compression stroke (hereinafter referred to as "compression stroke injection") collides with the wall surface of the cavity 21a and is wound up toward the ignition plug 7, and is unevenly distributed around the ignition plug 7, A stratified air-fuel mixture richer than the air-fuel ratio is formed. By operating the spark plug 7 in this state and performing spark ignition, combustion that is resistant to misfire and strong against disturbance is realized.

  In the present embodiment, each of the intake stroke injection and the compression stroke injection is executed by one injection operation. However, the intake stroke injection is divided, and the fuel to be injected during the intake stroke is divided into two or more injection operations. You may inject it. Furthermore, it is possible to divide the fuel injection amount of the compression stroke injection into two or more injection operations for injection.

(Setting of fuel injection timing)
Setting of fuel injection timing in stratified retard combustion will be described with reference to FIGS.

  In the present embodiment, “fuel injection timing” or “injection timing” refers to the start timing of the injection operation by the fuel injection valve 6 unless otherwise specified.

  FIG. 2 shows changes in the strength of the tumble flow formed in the cylinder from the intake stroke to the compression stroke. In the figure, the chain double-dashed line shows the change when the engine 1 is operated without executing the intake stroke injection for the cylinder, and the solid line shows the change when the intake stroke injection is executed according to the present embodiment.

  In the intake stroke, when the intake valve 8 is driven to open and the intake port 4a is opened, air is sucked into the cylinder and swirls in the longitudinal direction about an axis perpendicular to the cylinder central axis Ax. (Tumble flow) is formed. The tumble flow increases the strength by the air swirling in the cylinder increasing the flow velocity as the piston 2 descends. However, as the piston 2 further descends and the in-cylinder volume increases, the flow velocity of the air swirling in the cylinder decreases, so that the strength of the tumble flow is 1 at the flow velocity turning point (crank angle Cr1). After reaching the peak P1 (hereinafter referred to as “first peak”) for the first time, it starts to decrease thereafter. When the piston 2 moves up in the compression stroke, the in-cylinder volume decreases and the strength of the tumble flow starts to increase, and the crank angle Cr2 reaches a second peak (hereinafter referred to as "second peak") P2. Then, as the piston 2 approaches the top dead center (compression top dead center), the tumble flow gradually collapses, thereby gradually lowering the strength. In this way, the tumble flow forms an intensity peak once in the intake stroke and once in the compression stroke. Here, when the intensity at the second peak P2 is high, the tumble flow maintains a high intensity at the injection timing IT2 of the compression stroke injection, the spray of the injected fuel is flown along with the tumble flow, and the spark plug 7 It becomes difficult to favorably localize the surrounding area.

  In the present embodiment, the injection timing IT1 of the intake stroke injection is set to a relatively early timing during the intake stroke, so that the fuel spray is caused to collide with the tumble flow rather than being spread on the tumble flow. As a result, the kinetic energy of the spray is used to reduce the strength of the tumble flow.

  FIG. 2 also shows fuel injection timings IT1 and IT2 in the present embodiment. In the present embodiment, the spray of the fuel injected during the intake stroke collides with the tumble flow before reaching the first peak P1 to reduce the strength at the first peak P1 of the tumble flow, and as a result, the compression stroke. The strength of the tumble flow remaining in the cylinder at the injection timing IT2 of the injection is reduced.

  FIG. 3 shows changes in the exhaust particulate number PN (solid line A) and the combustion instability CS (solid line B) according to the injection timing IT1 of the intake stroke injection.

  The exhaust particulate number PN is an index indicating what proportion of the fuel injected by the fuel injection valve 6 adheres to the piston crown surface 21. The fuel attached to the piston crown surface 21 does not burn during the cycle and is carried over to the next and subsequent cycles, so that the liquefied fuel accumulates on the piston crown surface 21. When the exhaust purification catalyst activates in this state and the catalyst warm-up control ends and the control shifts to normal control, the accumulated fuel burns due to the flame that has propagated to the vicinity of the crown surface, and the number of particles in the exhaust (the number of exhaust particles) Will increase. The exhaust particulate number PN changes according to the position of the piston 2 at the fuel injection timing IT1, is highest when the fuel injection timing IT1 is set near the top dead center, and is delayed from the timing near the top dead center. Will decrease. After reaching the minimum value, it tends to gradually increase. In other words, when the fuel injection timing IT1 approaches the top dead center from the timing near the bottom dead center, the exhaust particulate number PN changes from a declining trend to a gradual increasing trend, and then with the approach to the top dead center. It has a tendency to increase rapidly. From this point of view, in the present embodiment, the allowable upper limit value PNlim of the exhaust particulate number PN is set, and the injection timing IT1 of the intake stroke injection is limited to the time when the exhaust particulate number PN becomes the allowable upper limit value PNlim or less. Specifically, the timing at which the rate of change ΔPN of the number PN of exhaust particulates per unit crank angle exceeds a predetermined value is set as the particulate required injection limit ITs and is made to correspond to the operating conditions such as the rotation speed of the engine 1 and the cooling water temperature. The fuel injection timing IT1 is limited in advance to the crank angle range Rpn after the required particulate injection limit ITs from the viewpoint of the exhaust particulate number PN.

  On the other hand, the combustion instability CS is an index showing the stability of the stratified retard combustion, and in the process of delaying the injection timing IT1 of the intake stroke injection from the timing near the top dead center, the instability of the combustion is determined. The degree of increase (in other words, how much the stability of the stratified retard combustion is impaired by the retard of the fuel injection timing IT1) is shown.

  FIG. 4 shows the relationship between the fuel spray and the air in the cylinder in the flow direction according to the piston position.

  In the figure, the symbol At represents the central axis of the tumble flow, and Af represents the center line of the spray beam of the fuel injected by the fuel injection valve 6. Further, the symbol Sa indicates the center line of the mainstream of the tumble flow.

  FIG. 5 shows a spray beam center of gravity line Af defined for the multi-hole fuel injection valve 6. In the present embodiment, the fuel injection valve 6 having six injection holes is adopted, and the spray beam center of gravity line Af is defined as a straight line connecting the tip of the fuel injection valve 6 and the spray beam center CB. Here, the spray beam center CB means that the spray beams B1 to B6 are formed by the fuel injected from the respective injection holes (FIG. 5 shows only the four spray beams B1 to B4 for the sake of convenience). The center of a circle connecting the tips of the spray beams B1 to B6 at the time when a certain time has elapsed.

  Returning to FIG. 4, FIG. 4A shows a relatively early time point after top dead center, and FIG. 4B shows a later time point than that shown in FIG. Therefore, at the time point shown in FIG. 4B, the piston 2 is below the time point shown in FIG.

  In the intake stroke, the air taken into the cylinder swirls in the vertical direction around an axis At that is perpendicular to the cylinder center axis Ax, and forms a tumble flow. The central axis At at which the tumble flow swirls is called the "vortex center of the tumble flow". As a guide, the vortex center At of the tumble flow is the cylinder center axis Ax distant from the piston crown surface 21 by a distance L / 2 = (Hch + S) / 2 when the combustion chamber height is Hch and the stroke amount is S. When it is necessary to define the vortex center At in the upper position, this geometrical position may be adopted. Here, focusing on the relationship between the fuel spray and the flow direction of the air, at a relatively early time point shown in FIG. 4A, the vortex center At of the tumble flow is the spray beam center of gravity line Af or its extension line and the cylinder. It exists above the intersection with the central axis Ax. On the other hand, at the time shown in FIG. 4B, the vortex center At of the tumble flow is moving downward with the movement of the piston 2 as compared with the position shown in FIG. It exists below the intersection of the line Af or its extension and the cylinder center axis Ax.

  In the relationship shown in FIG. 4A, the fuel spray and the air flow are opposed to each other, and at the collision position of the fuel and the kinetic energy of the spray, the tumble flow is weakened and the strength of the tumble flow is reduced. To do. On the other hand, in the relationship shown in FIG. 4B, at the collision position between the fuel spray and the air, the tumble flow is strengthened by the combination of the spray advancing direction vector and the air swirling direction vector. This results in increased strength. Since the strength of the tumble flow increases, a strong tumble flow remains in the cylinder at the injection timing IT2 of the compression stroke injection, and the spray of the injected fuel is flown along with the tumble flow and the spark plug 7 It cannot be unevenly distributed in the surrounding area, and the stability of combustion is impaired.

  In the present embodiment, the injection timing IT1 of the intake stroke injection is limited from the viewpoint of the combustion instability CS in addition to the exhaust particulate number PN.

  Referring also to FIG. 3, the combustion instability CS changes depending on the position of the vortex center At of the tumble flow, and when the injection timing IT1 of the intake stroke injection is set to an early timing after top dead center. The vortex center At of the tumble flow is located above the center line Af of the spray beam, and the tumble flow is weakened by the collision of the fuel spray with the air, so that the tumble flow is suppressed to a low level (in other words, the combustion is stabilized). On the other hand, when the piston 2 descends and the vortex center At of the tumble flow approaches the intersection of the spray beam center of gravity line Af (or its extension) and the cylinder center axis Ax, the effect of killing by the kinetic energy of the spray is exerted. It gradually diminishes and the combustion instability CS increases. Then, when the vortex center At of the tumble flow passes over this intersection and moves below the spray beam center of gravity line Af, the spray flow is reversed due to the combination of the spray advancing direction vector and the air swirling direction vector. As a result of intensifying the tumble flow, the combustion instability CS rapidly increases. From this point of view, in the present embodiment, the allowable upper limit value CSlim of the combustion instability CS is set and the injection timing IT1 of the intake stroke injection is allowed by the combustion instability CS in the same manner as the restriction on the exhaust particulate number PN. It is limited to the time when the upper limit value CSlim or less. Specifically, a timing at which the rate of change ΔCS of the combustion instability CS per unit crank angle exceeds a predetermined value is set as the stability request injection limit ITe, and from the viewpoint of the combustion instability CS, the fuel injection timing IT1 is set. The crank angle range Rcs before the stability request injection limit ITe is limited.

  Then, in the present embodiment, the injection timing IT1 of the intake stroke injection is set to the crank angle range in which the above two regions Rpn and Rcs overlap, specifically, the range from the fine particle required injection limit ITs to the stability required injection limit ITe. Set in R.

(Explanation by flow chart)
FIG. 6 is a flowchart showing the basic flow of catalyst warm-up control according to this embodiment.

  In the present embodiment, the combustion mode when operating the engine 1 is switched between stratified retard combustion and homogeneous combustion.

  In S101, various operating states such as the load and rotation speed of the engine 1 are read. The operating state of the engine 1 is calculated based on the detection signals of the accelerator sensor 201, the rotation speed sensor 202, the cooling water temperature sensor 203, and the like, by an operating state calculation routine that is separately executed.

  In S102, the operating mode of the engine 1 is determined based on the detected operating state. If the engine 1 is in the catalyst warm-up mode, the process proceeds to S103, and if it is in the normal mode, the process proceeds to S104. The electronic control unit 101 selects the catalyst warm-up mode when starting the engine 1 from the cold state, and selects the normal mode after the exhaust purification catalyst is activated and the catalyst warm-up is completed. Whether or not the engine 1 is in the cold state can be determined based on the cooling water temperature or the like when the engine 1 is started.

  In S103, the combustion mode is set to stratified retard combustion. Then, the catalyst warm-up control is executed by the processing of S105 to 109.

  In S104, the combustion mode is set to homogeneous combustion. In the homogeneous combustion, the fuel injection amount per one combustion cycle is calculated based on the load and the rotation speed of the engine 1, and the fuel injection timing is set during the intake stroke. Then, the injected fuel is placed on the tumble flow and diffused throughout the cylinder to form a homogeneous mixture, and the homogeneous mixture is ignited at or near the MBT. The fuel injection timing in the homogeneous combustion is later than the injection timing IT1 of the intake stroke injection in the stratified retard combustion with respect to the crank angle, and the ignition timing is earlier than the ignition timing in the stratified retard combustion.

  In S105, as the basic setting for stratified retard combustion, in addition to the fuel pressure PF, the injection division number n of the intake stroke injection, the injection timing IT1, the injection timing IT2 of the compression stroke injection, the ignition timing Ig, etc. are read. In the basic setting, the number of injection divisions n of the intake stroke injection is 1, and the injection timing IT1 is an injection period Δt corresponding to the fuel injection amount rather than the end timing of the injection operation determined based on the stability required injection limit ITe. It is set in the previous period.

Here, the electronic control unit 101 calculates the basic fuel supply amount Qfbase based on the load and the rotation speed of the engine 1 and corrects it according to the cooling water temperature and the like, so that one combustion cycle is performed. The fuel injection amount Qinj is calculated. Then, 20 to 90% (= Qinj × 0.2 to Qinj × 0.9) of the calculated fuel injection amount Qinj is set as the injection amount Q1 of the intake stroke injection, and the rest is set as the injection amount Q2 of the compression stroke injection. The electronic control unit 101 further converts the injection amount Q1 of the intake stroke injection into the following equation to convert it into the injection period Δt, and calculates the injection timing IT1 of the intake stroke injection.
Qinj = ρ × A × Cd × √ {(Pinj-Pf) / ρ} × Δt (1)

  In the above equation (1), the fuel density is ρ, the injection nozzle total area is A, the nozzle flow rate coefficient is Cd, the fuel injection pressure or fuel pressure is Pf, and the cylinder pressure is Pa.

  In S106, it is determined whether or not the injection timing (operation start timing) IT1 of the intake stroke injection is after the particulate matter required injection limit ITs. If it is after the required particle injection limit ITs, it is assumed that the exhaust particle number PN is suppressed to the allowable upper limit value PNlim or less, and the routine proceeds to S108. If not after ITs, the routine proceeds to S107.

  In S107, the operation start timing of the intake stroke injection is corrected to a timing after the particulate matter required injection limit ITs.

  In S108, it is determined whether or not the operation end timing of the intake stroke injection is before the stability required injection limit ITe. If it is before the stability required injection limit ITe, the control of this routine is ended and before ITe. If not, the process proceeds to S109. That is, in S106 and 108, it is determined whether or not the injection period Δt of the intake stroke injection is within the range R from the required particle injection limit ITs to the required stability injection limit ITe.

  Here, in the present embodiment, the injection timing IT1 of the intake stroke injection is used as the start timing of the injection operation, and when the injection timing IT1 is set, the operation end timing defined as the timing before the stability required injection limit ITe is used as a reference. . Therefore, in S108, a positive determination is always made, and the control of this routine ends. However, the injection timing IT1 can also be set as a timing after the particulate matter required injection limit ITs. In this case, a positive determination is always made in S106, and the process proceeds to S108. However, depending on the injection period Δt, the determination result in S108 may be negative and the process may proceed to S109.

  In S109, the operation end timing of the intake stroke injection is corrected to a time before the stability required injection limit ITe.

(Fuel injection timing correction)
The correction of the injection timing IT1 of the intake stroke injection will be described with reference to FIGS. 7 and 8.

  FIG. 7 shows the relationship between the fuel pressure PF, the injection division number n of the intake stroke injection, and the exhaust particulate number PN.

  The number of exhaust particulates PN decreases as the number of injection divisions n increases and the injection amount per injection operation decreases, and when the number of injection divisions n is constant, it tends to decrease with an increase in the fuel pressure PF. Have. This is because the kinetic energy of the spray formed by one injection operation decreases as the injection amount per injection operation decreases, and the injection rate increases as the fuel pressure PF increases. It is considered that this is because atomization of the injected fuel is promoted.

  FIG. 8 shows changes in the exhaust particulate number PN and the combustion instability CS with changes in the injection conditions of the intake stroke injection (the number of injection divisions n, the fuel pressure PF).

  As described above, the exhaust particulate number PN has a large number of injection divisions n (in other words, a small injection amount per injection operation) and a high fuel pressure PF under a constant injection timing IT1. It tends to decrease with time (FIG. 7). Therefore, the curve showing the change in the number of exhaust particulates PN shifts toward the advance side so as to shift from the chain double-dashed line A ′ to the solid line A as the injection division number n increases and the fuel pressure PF increases. On the other hand, the curve showing the change in the combustion instability CS also changes slightly with the increase in the number of injection splits n and the increase in the fuel pressure PF, and the retard angle side shifts from the one-dot chain line B ′ to the solid line B. Transition to. This is because the kinetic energy of the spray formed by one injection operation is reduced, the action of the tumble flow enhancement by the combination with the advancing direction vector of the spray is reduced, and the atomization of the injected fuel is promoted. It is thought that this is because the effect of strengthening the tumble flow is similarly diminished. In this way, by increasing the number of injection divisions n or increasing the fuel pressure PF, the particle demand injection limit ITs changes from the time ITs1 before the change to the time ITs2 after the change, and the stability request injection limit ITe becomes The time ITe1 before the change is changed to the time ITe2 after the change. Therefore, by changing the injection condition, the range R in which the intake stroke injection is allowed can be expanded from the range R1 before the change to the range R2 after the change.

  Returning to FIG. 6, in the present embodiment, when the injection timing IT1 of the intake stroke injection is not after the fine particle required injection limit ITs in S106, the process proceeds to S107 and the injection division number n is increased (for example, from once to twice). Increase) and decrease the injection amount per injection operation. As a result, the range R in which the intake stroke injection is allowed is expanded, and the injection timing IT1 (or the start timing of the first injection operation in the case of dividing the injection into two times) is corrected after the particulate matter request injection limit ITs (ITs2).

  The above is the contents of the catalyst warm-up control, and the effects obtained by this embodiment will be summarized below.

(Explanation of effects)
First, in the present embodiment, in the direct injection engine 1 including the spark plug 7 and the fuel injection valve 6 that is provided so that the fuel can be directly injected into the cylinder, the catalyst is warmed up and supplied per combustion cycle. The fuel to be injected is injected separately into the intake stroke and the compression stroke, and the injection timing IT1 of the fuel injection (intake stroke injection) during the intake stroke is performed by spraying the fuel in which the air flow (tumble flow) in the cylinder is injected. It was time to be weakened by the collision with. As a result, the angular momentum of the tumble flow is reduced by using the kinetic energy of the spray, and the strength of the tumble flow that remains in the cylinder during fuel injection during the compression stroke (compression stroke injection) decreases, so that the injection is performed. It becomes easy to make the fuel spray properly unevenly distributed around the ignition plug 7. Therefore, when starting the engine 1 from the cold state, it is possible to realize stable combustion for raising the exhaust temperature and activate the exhaust purification catalyst early.

  Furthermore, by lowering the tumble flow intensity due to collision with the spray at a relatively early point in the intake stroke, it is possible to collide with the spray while the tumble flow is underdeveloped, and to effectively weaken the tumble flow.

  Then, the air sucked into the cylinder through the intake port 4a forms a flow that passes through the in-cylinder space on the exhaust port 5a side with respect to the cylinder center axis Ax in the direction from the lower surface of the cylinder head 1B toward the piston crown surface 21. In the direct injection engine 1 in which the fuel injection valve 6 is arranged on the intake port 4a side with respect to the cylinder center axis Ax, the injection timing IT1 of the intake stroke injection is set to the in-cylinder space where the flow of the spray is the exhaust port 5a side. Is set to a time that is opposed to the flow (tumble flow) of the air that has passed in the direction toward the piston crown surface 21, thereby providing a specific method for weakening the tumble flow due to collision with the spray.

  Secondly, in the present embodiment, the fuel adhesion rate, which is the adhesion rate of the fuel injected by the fuel injection valve 6 to the piston crown surface 21, is estimated from the injection timing IT1 of the intake stroke injection to increase the fuel adhesion rate. , It was decided to reduce the injection amount per one injection operation of the intake stroke injection. Specifically, when the injection timing IT1 of the intake stroke injection is before the particulate matter required injection limit ITs, the injection amount per one injection operation is reduced. As a result, the kinetic energy of the spray can be reduced, and an increase in the amount of discharged particles caused by the injected fuel adhering to the piston crown surface 21 can be suppressed.

  Here, in changing the fuel injection amount, the range R in which the intake stroke injection is allowed can be expanded by increasing the injection division number n of the intake stroke injection and decreasing the injection amount per injection operation. Therefore, it is possible to realize stable combustion while maintaining the total injection amount of the intake stroke injection as much as possible.

  Thirdly, in the present embodiment, the combustion mode during catalyst warm-up is injected by dividing the fuel injection amount per combustion cycle into the intake stroke and the compression stroke, and the ignition timing Ig by the spark plug 7 is set to the normal timing. It was decided to be due to the stratified retarded combustion that retards the ignition timing in. As a result, the fuel injected by the compression stroke injection is appropriately unevenly distributed around the spark plug 7, stable combustion resistant to disturbance is realized, and the exhaust purification catalyst can be activated early.

  Here, in the compression stroke injection, the injected fuel is unevenly distributed in the vicinity of the spark plug 7 and is used as the ignition point for combustion, but as a result of the correction of the injection timing IT1, the total injection quantity of the intake stroke injection is insufficient. If this occurs, the shortage may be transferred to the compression stroke injection and supplied. In this way, by injecting the fuel injection amount per one combustion cycle separately in the intake stroke and the compression stroke, it contributes to stable combustion and prevents the fuel injection amount in the entire cycle from becoming insufficient. You can

(Description of other embodiments)
In the above description, in the correction of the injection timing IT1 of the intake stroke injection (S107 in FIG. 6), the injection amount per injection operation is decreased, and specifically, the injection division number n of the intake stroke injection is increased. And

  The correction of the injection timing IT1 is not limited to the change of the injection division number n.

  FIG. 9 shows the relationship among the injection period Δt, the required particulate injection limit ITs, and the stability required injection limit ITe under various injection conditions of the intake stroke injection.

  FIG. 9A shows that the fuel injection amount (in other words, the fuel injection amount per one combustion cycle) Qinj according to the operating state of the engine 1 is large, and the injection timing (operation start timing) IT1a read as the basic setting. Is before the particulate matter required injection limit ITsa. In this case, the rate of adhesion of the injected fuel to the piston crown surface 21 is high, and the amount of exhaust particulates exceeding the allowable upper limit value PMlim is discharged.

  Here, in the example described above, by increasing the number of times of injection division n, the injection amount per injection operation is decreased and the kinetic energy of the spray is decreased (FIG. 9C). As a result, the fine particle request injection limit ITsc moves to the advance side more than in the case of the basic setting (ITsa), and the range R (ITsc to ITe) in which the intake stroke injection is allowed is expanded. The fuel that is insufficient due to the increase in the injection split number n can be transferred to the compression stroke injection and supplied.

  On the other hand, in another embodiment, the injection division number n is not increased and remains at 1 to reduce the total injection amount of the intake stroke injection, thereby shortening the injection period Δtb (FIG. 9B). . As a result, the injection amount per injection operation is substantially reduced as in the case where the number of injection divisions n is increased, the kinetic energy of the spray is reduced, and the injected fuel is less likely to adhere to the piston crown surface 21. be able to.

  Furthermore, in another embodiment, the fuel injection pressure (fuel pressure) PF is increased without changing the injection amount per injection operation (FIG. 9D). Thereby, the injection rate is increased, and the injection period Δtd of the intake stroke injection is shortened as compared with the case of the basic setting (Δta). Then, the atomization of the injected fuel is promoted by the increase of the fuel pressure PF, and the adhesion of the fuel to the piston crown surface 21 is suppressed, so that the effect of moving the required particle injection limit ITsd to the advance side can be obtained. , The injection allowable range R (ITsd to ITe) is expanded. Further, when the fuel pressure PF is increased, not only the adhesion of the fuel to the crown surface is suppressed but also the injection amount can be increased by increasing the injection rate, so that the injection period is shortened (see FIG. 9). Compared with the case where the injection amount itself is reduced as in (b)), the homogeneity of the air-fuel mixture can be enhanced while contributing to the suppression of exhaust particulate emission and the realization of stable combustion.

  Some of the concepts that can be derived from the above description are listed below.

  The air taken into the cylinder through the intake port forms a flow that passes through the space inside the cylinder on the side opposite to the intake port with respect to the center axis of the cylinder in the direction from the lower surface of the cylinder head to the crown surface of the piston, In a direct-injection engine in which a fuel injection valve is arranged on the intake port side with respect to the shaft, at a predetermined time during the intake stroke for injecting fuel, the flow of spray is in the cylinder space on the side opposite to the intake port in the piston crown surface. It is a control method of the engine, which is a time when it faces the flow of the air passing in the direction toward.

  An engine that includes an ignition plug and a fuel injection valve that is capable of directly injecting fuel into a cylinder, and that executes fuel injection stroke injection in which the fuel injection valve injects fuel at a predetermined time during the intake stroke when the catalyst warms up. And a first predetermined range in which the adherence rate of the injected fuel to the piston crown surface is suppressed to a predetermined value or less with respect to the injection timing of the intake stroke injection, and the air flow in the cylinder is A method of controlling an engine, wherein a second predetermined range that is weakened by a collision of injected fuel with a spray is set, and an injection timing of intake stroke injection is limited to an overlapping range of the first and second predetermined ranges. . Along with this, when the injection timing of the intake stroke injection is out of the overlapping range, the injection amount per injection operation in the intake stroke injection is decreased or the fuel injection pressure is increased. Is.

  Although the embodiment of the present invention has been described above, the present invention is not limited to this, and various changes and modifications can be made within the scope of the matters described in the claims. There is no end.

DESCRIPTION OF SYMBOLS 1 ... Direct injection engine 1A ... Cylinder block 1B ... Cylinder head 2 ... Piston 21 ... Piston crown 21a ... Cavity 3 ... Connecting rod 4 ... Intake passage 4a ... Intake port 5 ... Exhaust passage 5a ... Exhaust port 6 ... Fuel injection valve 7 ... spark plug 8 ... intake valve 9 ... exhaust valve 10 ... tumble control valve 101 ... electronic control unit (engine controller)
201 ... Accelerator sensor 202 ... Rotation speed sensor 203 ... Cooling water temperature sensor Af ... Spray beam center of gravity line At ... Tumble flow vortex center Ax ... Cylinder center axis Ch ... Combustion chamber Sa ... Main tumble flow center line B1 to B4 ... Spray beam CB ... center of spray beam

Claims (8)

Spark plug,
In a method for controlling a direct injection engine, which comprises a fuel injection valve provided so that fuel can be directly injected into a cylinder,
During normal operation, by setting the fuel injection start timing of the fuel injection valve during the intake stroke, the injected fuel is carried on the flow of air in the cylinder and diffused into the cylinder,
When the catalyst is warmed up, the fuel injection of the fuel injection valve is divided into intake stroke injection and compression stroke injection, and the start timing of the intake stroke injection is an injection start in which the number of exhaust particulates calculated in advance becomes an allowable upper limit value. Set later than the timing and before the injection start timing when the combustion instability calculated in advance becomes the allowable upper limit value ,
Control method for direct injection engine. The direct injection according to claim 1 , wherein the injection start timing at which the number of exhaust particulates reaches an allowable upper limit is set to an injection start timing at which the increase curve of the number of exhaust particulates with respect to the injection start timing exceeds a predetermined increase rate. Engine control method. Said combustion instability allowable upper limit to become injection start timing, the growth curve of the combustion instability for the injection start timing is set to injection start timing exceeding a predetermined increase rate, according to claim 1 or claim Direct injection engine control method described in 2 . To increase the fuel deposition rate is attachment ratio against the piston crown surface of the fuel injected by the intake stroke injection, decreasing the injection amount per injection operation in the intake stroke injection, of claims 1 to 3 The method for controlling a direct injection engine according to any one of claims. The control method for a direct injection engine according to claim 4 , wherein the injection amount per one injection operation is reduced by increasing the number of injection divisions of the intake stroke injection. 4. The injection pressure of fuel in the intake stroke injection is increased with respect to the increase of the fuel adhesion rate, which is the adhesion rate of the fuel injected by the intake stroke injection to the piston crown surface, according to any one of claims 1 to 3. A method for controlling a direct injection engine according to item. 7. The direct injection engine control according to claim 1 , wherein when the catalyst is warmed up, the ignition timing by the spark plug is set to be retarded compared to a normal time after the catalyst is warmed up. Method. Spark plug,
A fuel injection valve provided so that fuel can be directly injected into the cylinder;
An exhaust purification catalyst installed in the exhaust passage,
An engine control unit for controlling the operation of the fuel injection valve;
In a control device for a direct injection engine configured to include
The engine control unit is
During normal operation, by setting the fuel injection start timing of the fuel injection valve during the intake stroke, the injected fuel is carried on the flow of air in the cylinder and diffused into the cylinder,
During catalyst warm-up in which the exhaust purification catalyst is activated from a low temperature state, the fuel injection of the fuel injection valve is divided into intake stroke injection and compression stroke injection, and the start timing of the intake stroke injection is calculated in advance by the exhaust gas calculated in advance. The number of particles is later than the injection start timing when the allowable upper limit value is set, and the combustion instability calculated in advance is set to a period before the injection start timing when the allowable upper limit value is set,
Control device for direct injection engine.

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