JP4092489B2 - Fuel injection control device for in-cylinder direct injection spark ignition engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a fuel injection control device for an in-cylinder direct injection spark ignition engine.
[0002]
[Prior art]
In an in-cylinder direct injection spark ignition engine including a piston, a fuel injection valve that directly injects fuel into a combustion chamber, and an ignition plug, a substantially cylindrical peripheral wall surface on the piston crown surface, A cavity having a bottom wall surface that is smoothly connected and a substantially conical bulge portion that is smoothly connected to the bottom wall surface is formed, and a spark plug is disposed in the vicinity of the bulge portion. There has been proposed one in which fuel is injected in a substantially hollow conical shape from the upper part of the combustion chamber and fuel injection from a fuel injection valve is performed in a compression stroke (see Patent Document 1).
[0003]
[Patent Document 1]
JP 2001-271688 A
[0004]
[Problems to be solved by the invention]
By the way, in a direct-injection spark ignition engine, in order to ignite and burn the air-fuel mixture steadily, a mixture of an appropriate size and an appropriate air-fuel ratio is selected according to the engine operating conditions (rotation speed and load). It is important to form an air mass above the cavity. At that time, it is desirable that the air-fuel ratio distribution in the air-fuel mixture is uniform from the viewpoint of exhaust reduction. For example, if the air-fuel ratio distribution in the air-fuel mixture is biased and there is a rich portion, unburned HC and CO increase, or the combustion temperature rises locally, causing NOx generation. When the portion is present, the flame extinguishes and unburned HC and CO increase.
[0005]
For this reason, in the above-mentioned conventional device, in the process in which the fuel adhering to the cavity peripheral wall is vaporized by injecting the fuel spray into the substantially hollow cone shape at the end of the compression stroke and causing the fuel spray to collide with the cavity peripheral wall. An air-fuel mixture is formed above the cavity while concentrating on the cavity protrusion.
[0006]
However, since the time from the compression stroke injection to the ignition is originally short, when the engine temperature is lower than the predetermined value, the vaporization of the adhered fuel is not sufficiently accelerated by the ignition, and when the fuel pressure is lower than the predetermined value. Since the speed in the injection direction becomes small and vaporization of the attached fuel is not sufficiently promoted until ignition, it is considered that a doughnut-shaped air-fuel mixture is only formed above the cavity. In this donut-shaped air-fuel mixture, there is little or no fuel in the portion corresponding to the donut hole, so this donut hole portion unfortunately reaches the spark plug located just above the cavity ridge. When this occurs, ignition of the air-fuel mixture fails or misfires, making it difficult to stably perform stratified combustion.
[0007]
Therefore, an object of the present invention is to realize stable stratified combustion even when the engine temperature is lower than a predetermined value or when the fuel pressure is lower than a predetermined value.
[0008]
[Means for Solving the Problems]
The present invention provides an in-cylinder direct injection spark ignition engine including a piston, a fuel injection valve that directly injects fuel into a combustion chamber, and an ignition plug, and a substantially cylindrical peripheral wall surface on a crown surface of the piston. A cavity having a bottom wall surface that is smoothly connected to the peripheral wall surface is formed, the spark plug is disposed in the vicinity of a position directly above the center of the bottom wall surface, and is formed in a substantially hollow conical shape from the upper part of the combustion chamber from the fuel injection valve. In addition to injecting fuel, the fuel injection from the fuel injection valve is divided into two parts, ie, near the intake top dead center and the compression stroke.
[0009]
【The invention's effect】
According to the present invention, by the first fuel injection near the intake top dead center, the spray of fuel injected in the shape of a substantially hollow cone adheres to the vicinity of the center in the cavity. Since there is sufficient time for vaporization, the vaporization is promoted and a first air-fuel mixture is formed near the center of the cavity. After that, the second air-fuel mixture formed by the second fuel injection in the compression stroke becomes donut-like, and there is little or no fuel in the portion of the donut hole. Since the first air-fuel mixture formed by the first fuel injection in the vicinity of the intake top dead center functions to fill, a uniform air-fuel mixture can be formed above the cavity as a whole. This enables stable stratified combustion.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0011]
FIG. 1 is a schematic configuration diagram of an engine according to the first embodiment. In FIG. 1, the cylinder head 2 is formed with a pent roof-like combustion chamber 3 having a substantially evenly inclined roof on the left and right sides in the figure, and an intake port 4 for introducing intake air to the left and right roof portions is also combusted. Exhaust ports 5 for exhausting subsequent gas are respectively opened. A cylinder 7 is formed in the cylinder block 6 in the vertical direction in the figure, and a piston 8 slides in the vertical direction in the cylinder 7. The intake valve 15 and the exhaust valve 16 open and close the ports 4 and 5 in accordance with the movement of the piston 8. That is, each cam (not shown) that pushes down the valves 15 and 16 against a spring is fixed to a cam shaft driven by the engine.
[0012]
In this embodiment, in order to realize stable stratified combustion even when the fuel pressure is lower than a predetermined value, the arrangement of the fuel injection valve 11 and the spark plug 12 and the shape of the cavity 9 formed on the piston crown surface are devised. ing. That is, a fuel injection valve 11 whose vertical direction is the injection center direction is provided at a substantially central position of the ceiling of the combustion chamber 3, and a spark plug 12 is provided on the right side thereof. The fuel injection valve 11 injects fuel in a substantially hollow conical shape, and the vertical component of the spray penetration force is made larger than the horizontal component.
[0013]
A truncated cone-shaped cavity 9 is formed at a substantially central portion of the piston crown surface. The cavity 9 has a peripheral wall surface 9a having a truncated conical side surface and a bottom wall surface 9b smoothly connected to the peripheral wall surface 9a.
[0014]
The fuel injection valve 11 injects fuel from the upper part of the combustion chamber 3 in a substantially hollow conical shape. In the engine controller 25, when the fuel pressure Pf is lower than a predetermined value LPf, the fuel injection valve 11 Stratified combustion is realized by performing fuel-injection divided injection in two times, near the intake top dead center and the compression stroke. When the fuel pressure Pf is equal to or higher than the predetermined value LPf, stratified combustion is realized by performing compression stroke injection as in the conventional apparatus.
[0015]
A method for realizing stratified combustion when the fuel pressure Pf is lower than the predetermined value LPf will be described with reference to FIG. 6. In FIG. 6, time passes from the upper side to the lower side, The second stage (b) at the time of fuel injection near the dead center (at the time of the first fuel injection) shows the state at the time of fuel injection at the compression stroke (at the time of the second fuel injection), and the third stage. The eyes and the fourth stage (c) and (d) show the subsequent state in the compression stroke as a model.
[0016]
When the fuel pressure Pf is lower than the predetermined value LPf, a predetermined amount of fuel is injected in the vicinity of the intake top dead center (initial stage of the intake stroke) (see FIG. 6A). Since the fuel pressure is low, at the piston position near the intake top dead center, the injected substantially hollow conical fuel spray adheres to the bottom wall surface 9b near the center of the cavity in a substantially liquid state. The adhering fuel is vaporized between the intake stroke and ignition to form a first air-fuel mixture near the center of the cavity 9 (see FIG. 6B).
[0017]
In the compression stroke after the first fuel injection, the remaining fuel is injected (see FIG. 6B). The second fuel injection timing is set within a range in which the injected substantially hollow conical fuel spray reaches the radially outer periphery of the cavity bottom wall surface 9b. The fuel injected for the second time is longer than the first fuel injection in the vicinity of the intake top dead center from the time of injection until it reaches the cavity bottom wall surface 9b. While evaporating, the fuel grows from the cavity central axis toward the cavity circumferential wall surface to form a donut-shaped second air-fuel mixture mass (see FIG. 6C).
[0018]
In this case, the fuel corresponding to the donut hole in the donut-shaped air-fuel mixture is in a state where there is no or little fuel, because the fuel pressure Pf is lower than the predetermined value LPf, and thus the diffusion of the air-fuel mixture becomes insufficient. This is because the air-fuel mixture does not diffuse into the donut hole.
[0019]
However, the portion of the donut hole in the donut-shaped second gas mixture formed by the second compression stroke injection is the first gas mixture already formed in the center of the cavity by the first fuel injection. Therefore, when ignition is performed, one homogeneous air-fuel mixture as a whole is formed above the cavity 9 (see FIG. 6D).
[0020]
In other words, when the fuel pressure Pf is lower than the predetermined value LPf and the fuel injection is performed only once in the compression stroke as in the conventional device, a donut-shaped air-fuel mixture can only be formed in this embodiment. However, when this donut hole portion reaches the vicinity of the spark plug 12, the doughnut-shaped mixture cannot be ignited or misfires, the combustion stability is lowered, and it is difficult to realize stable stratified combustion. However, according to the present embodiment, the first air-fuel mixture is formed in the vicinity of the cavity center axis in advance by performing the first fuel injection near the intake top dead center prior to the compression stroke injection. The doughnut-shaped portion of the doughnut-shaped second air-fuel mixture formed during the compression stroke injection is filled with the first air-fuel mixture to form one homogeneous air-fuel mass as a whole. This It is possible to achieve the boss was stratified charge combustion.
[0021]
Returning to FIG. 1, a predetermined fuel pressure is required to inject fuel directly into the combustion chamber 3 by the fuel injection valve 11. Therefore, a high pressure fuel pump (not shown) is driven by an intake valve camshaft (not shown), and fuel boosted by the high pressure fuel pump is guided to the fuel injection valve 11 through the high pressure fuel pipe. . A fuel pressure sensor 31 is provided in the high pressure fuel pipe, and a signal from the fuel pressure sensor 31 is sent to the engine controller 25. Since the required fuel pressure changes according to the operating state, the engine controller 25 controls the operation of the high-pressure fuel pump so that the actual fuel pressure matches the required fuel pressure.
[0022]
The engine controller 25 also receives signals from the air flow meter 32, the crank angle sensor 33, and the water temperature sensor 34, and performs fuel injection through the fuel injection valve 11 so that stratified combustion is realized regardless of the fuel pressure level. Further, the ignition timing is controlled via the spark plug 12.
[0023]
A signal from the accelerator sensor 35 is also input, and the engine controller 25 controls the electronically controlled throttle valve opening so as to obtain an optimum torque according to the accelerator opening and the engine speed.
[0024]
The fuel injection control based on the fuel pressure executed by the engine controller 25 will be described in detail with reference to the flowchart shown in FIG.
[0025]
In step 1 (hereinafter referred to as “S1”), the intake air amount QM detected by the air flow meter 32, the engine speed NE detected by the crank angle sensor 33, and the fuel pressure detected by the fuel pressure sensor 31 Pf, the coolant temperature Tw detected by the water temperature sensor 34, and the accelerator opening APO detected by the accelerator sensor 35 are read. In S2, the target torque TTC is obtained from the accelerator opening APO. The target torque TTC can be obtained, for example, by previously storing table data assigned with the accelerator opening APO as a parameter in a memory in the engine controller 25 and referring to this table data from the accelerator opening APO.
[0026]
In S3, the target equivalence ratio TFBYA is obtained from the engine speed NE and the target torque TTC. The target equivalent ratio TFBYA is obtained by storing map data in which the rotational speed NE and the target torque TTC are assigned as parameters, for example, in a memory in the engine controller 25 and referring to the map data according to these values. Can do.
[0027]
In S4, a basic fuel injection amount Qf0 is calculated. The basic fuel injection amount Qf0 is a fuel injection amount for performing stratified combustion at the stoichiometric air fuel ratio (target amount ratio TFBYA = 1), and is calculated from the intake air amount QM and the engine rotational speed NE by the following equation.
[0028]
Qf0 = K × QM / NE (1)
Where K is a constant,
In S5, the fuel pressure Pf is compared with a predetermined value LPf. Here, the predetermined value LPf has a high injection direction speed of the injected fuel spray, and in a single injection of only the compression stroke, there is no lean air-fuel mixture over the central axis of the cavity 9 and a homogeneous air-fuel mixture is formed. The lower limit of the possible fuel pressure. The value of LPf is confirmed in advance by experiments.
[0029]
When the fuel pressure Pf is equal to or higher than the predetermined value LPf, the operation proceeds to the operation of performing one injection in the compression stroke of S6 to S8. That is, in S6, the fuel injection amount Qfa at the time of compression high / low injection is set by the following equation.
[0030]
Qfa = Qf0 × TFBYA × (1 + Ktp) (2)
Where Ktp: correction coefficient,
Expression (2) is an expression for correcting the basic fuel injection amount Qf0 with the target equivalent ratio TFBYA and the correction coefficient Ktp.
[0031]
Here, the correction coefficient Ktp is a correction coefficient corresponding to the degree of vaporization of the injected fuel. Since the degree of vaporization of the injected fuel depends on the coolant temperature Tw and the fuel pressure Pf, table data assigned as parameters is stored in a memory in the engine controller 25, and the map is obtained from the coolant temperature Tw and the fuel pressure Pf. It can be obtained by referring to the data. For example, in the map data, as shown in FIG. 3, the fuel injection amount Qfa at the time of compression injection is set to increase as the coolant temperature Tw becomes lower and the fuel pressure Pf becomes lower.
[0032]
In S7, the fuel injection timing ITa at the time of the compression stroke injection is set according to the engine speed NE and the target torque TTC. The fuel injection timing ITa is obtained by storing map data in which the engine rotational speed NE and the target torque TTC are assigned as parameters in a memory in the engine controller 25 and referring to the map data from these values. Can do.
[0033]
In S8, stratified combustion is realized by executing a single compression stroke injection using the fuel injection amount Qfa thus determined and the fuel injection timing ITa.
[0034]
On the other hand, when the fuel pressure Pf is smaller than the predetermined value LPf in S5, the operation proceeds to the operation of performing split injection twice in the vicinity of the intake top dead center (initial stage of the intake stroke) and the compression stroke in S9 to S15. That is, in S9, the target equivalent ratio TFBYA1 for the first fuel injection near the intake top dead center is set, and in S10, the target equivalent ratio TFBYA2 for the second fuel injection in the compression stroke is set.
[0035]
Here, between these two target equivalent ratios TFBYA1 and TFBYA2 and the total target equivalent ratio TFBYA obtained in S3,
TFBYA = TFBYA1 + TFBYA2 (3)
There is a relationship. Further, since the target equivalent ratio TFBYA1 for the first fuel injection is a value that decreases as the fuel pressure Pf increases, the target equivalent ratio TFBYA2 for the second fuel injection is calculated from the total target equivalent ratio TFBYA determined in S3. This is a value obtained by subtracting the target equivalent ratio TFBYA1 for the first fuel injection (see FIG. 4). At the time of application, characteristics of the TFBYA1 and TFBYA2 with respect to the fuel pressure Pf and the target equivalent ratio TFBYA are obtained in advance through experiments or the like and stored in the memory in the engine controller 25 as map data, and the fuel pressure Pf and the target equivalent ratio TFBYA. Can be obtained by referring to each map data.
[0036]
In S11 and S12, the first fuel injection amount Qfb1 and the second fuel injection amount Qfb2 are calculated by the following equations.
[0037]
Qfb1 = Qf0 × TFBYA1 × (1 + Ktp1) (4)
Qfb2 = Qf0 × TFBYA2 × (1 + Ktp2) (5)
However, Ktp1, Ktp2: correction coefficient,
The correction coefficients Ktp1 and Ktp2 in the equations (4) and (5) are both correction coefficients according to the vaporization degree of the adhered fuel, and the fuel vaporization degree depends on the cooling water temperature Tw and the fuel pressure Pf. The correction coefficient table is created using the fuel pressure Pf as a parameter. For example, as shown in FIG. 5, the fuel injection amounts Qfb1 and Qfb2 are increased as the cooling water temperature Tw becomes lower and the fuel pressure Pf becomes lower.
[0038]
If the first fuel injection is performed in the vicinity of the intake top dead center in the split injection, the time for the fuel to evaporate is sufficient before ignition, and the vaporization of the attached fuel is promoted. Under the same conditions, the compression stroke is injected once. The degree of vaporization of the fuel is higher than when performing it. Accordingly, the corrected fuel value for the fuel that is not vaporized may be smaller than in the case of the single compression stroke injection, and Ktp1 is between the two correction coefficients Ktp1, Ktp2 used for the split injection and the correction coefficient Ktp used for the single compression stroke injection. The relationship <Ktp2 = Ktp is established. For this reason, when performing the divided injection, the total fuel injection amount is smaller than when the single injection of the compression stroke is performed under the same conditions.
[0039]
In S13, the second fuel injection timing ITb2 in the split injection is set according to the engine speed NE and the target torque TTC.
[0040]
In this case, since there is fuel adhering to the first fuel injection that forms the first air-fuel mixture in the vicinity of the center of the cavity 9, the second fuel injection timing Is set within a range in which the fuel spray by the second fuel injection reaches the outer periphery in the radial direction of the bottom wall surface 9b of the cavity.
[0041]
Since the second fuel injection in the split injection is a compression stroke injection, the second fuel injection timing ITb2 in the split injection can be simply determined by referring to the same map as the fuel injection timing ITa set in S7. The characteristics of ITb2 with respect to the engine speed NE and the target torque TTC are obtained in advance through experiments or the like, and stored in the memory in the engine controller 25 as map data, and the engine speed NE and the target torque TTC are stored. The map data can be obtained by referring to the map data.
[0042]
On the other hand, the first fuel injection timing ITb1 in the divided injection is set in the vicinity of the intake top dead center, which is the timing at which the fuel adheres to the center of the cavity. The value of ITb1 is set after actually confirming whether or not fuel adheres to the central portion of the cavity.
[0043]
In S14 and S15, the first fuel injection amount Qfb1, the first fuel injection timing ITb1, the second fuel injection amount Qfb2, and the second fuel injection timing ITb2 set in this way are used, and in the vicinity of the intake top dead center. Stratified combustion is realized by executing the first fuel injection in the split injection and the second fuel injection in the split injection in the compression stroke.
[0044]
Here, the operation of this embodiment will be described with reference to FIG. 6 again.
[0045]
According to the present embodiment (the invention described in claim 1), when the fuel pressure Pf is lower than the predetermined value LPf, the first fuel injection near the intake top dead center is injected in a substantially hollow cone shape. The fuel spray adheres to the vicinity of the center in the cavity 9, and the adhering fuel has sufficient time for the fuel to vaporize before ignition, so that the vaporization is promoted. (See FIGS. 6B and 6C). After that, the second air-fuel mixture formed by the second fuel injection in the compression stroke becomes a donut shape because the air-fuel mixture does not diffuse sufficiently because the fuel pressure is low. Although not present or few, the portion of the donut hole is filled with the first air-fuel mixture formed by the first fuel injection in the vicinity of the intake top dead center. It becomes possible to form one homogeneous air-fuel mixture as a whole in the sky (see FIGS. 6C and 6D), and stable stratified combustion can be performed.
[0046]
This embodiment (claims) 8 According to the invention), since split injection is performed when the fuel pressure Pf is lower than the predetermined value LPf (see S5 and S9 to S15 in FIG. 2), in the fuel injection only in the compression stroke, the injection direction speed of the injected fuel is However, it is possible to form a homogeneous air-fuel mixture above the cavity 9 even at a low fuel pressure where a doughnut-like air-fuel mixture is only formed at a low speed and therefore it is difficult to realize stable stratified combustion. For example, when the fuel pump fails and does not increase to the set fuel pressure, when the fuel pressure does not rise when the set fuel pressure enters the high operating range from the low operating range, it is stable even at the start. Stratified combustion can be performed.
[0047]
When the fuel pressure Pf is lower than the predetermined value LPf, the injection direction speed of the injected fuel increases as the fuel pressure Pf increases, and the vaporization degree of the fuel adhering to the bottom wall surface 9b increases. Therefore, even when the fuel pressure Pf is high. If the fuel injection amount Qfb1 near the intake top dead center is the same as when the fuel pressure Pf is low, fuel will be injected unnecessarily, which may increase the discharge amount of unburned HC. (Claims 9 The fuel injection amount Qfb1 in the vicinity of the intake top dead center is decreased by the correction coefficient Ktp1 as the fuel pressure Pf increases (see the lower part of FIG. 5), so the fuel for realizing stratified combustion is reduced. The fuel injection can be minimized to prevent unnecessary fuel injection, and the discharge of unburned HC can be minimized.
[0048]
Next, FIG. 7 is a schematic configuration diagram of the engine of the second embodiment of the present invention, which replaces FIG. 1 of the first embodiment. The difference from the first embodiment lies in the configuration of the cavity 9 as shown in FIG. That is, the diameter of the substantially cylindrical portion (upper cavity) surrounded by the upper peripheral wall surface 9d is made larger than the diameter of the substantially cylindrical portion (lower cavity) surrounded by the lower peripheral wall surface 9c. A ring-shaped upper bottom wall surface 9f is formed that is positioned substantially parallel to the lower bottom wall surface 9e. Of course, the lower peripheral wall surface 9c and the lower bottom wall surface 9e are smoothly connected to the upper peripheral wall surface 9d and the upper bottom wall surface 9f.
[0049]
Further, in the engine controller 25, when the combustion chamber temperature Tcc is lower than the predetermined value LTcc, the fuel injection from the fuel injection valve 11 is divided into two parts, the vicinity of the intake top dead center and the compression stroke. Realize stratified combustion. When the combustion chamber temperature Tcc is equal to or higher than the predetermined value LTcc, stratified combustion is realized by performing compression stroke injection in the same manner as in the conventional apparatus.
[0050]
Also in this embodiment, a method for realizing stratified combustion when the combustion chamber temperature Tcc is lower than the predetermined value LTcc will be described with reference to FIG. (A) is when fuel is injected near the top dead center of intake (first fuel injection), and (b) is the second stage when fuel is injected during the compression stroke (second fuel injection). In the third and fourth stages (c) and (d), the subsequent state in the compression stroke is shown as a model.
[0051]
When the combustion chamber temperature Tcc is lower than the predetermined value LTcc, a predetermined amount of fuel is supplied in the vicinity of the top dead center of the intake air (in the initial stage of the intake stroke) so that the injected substantially hollow conical fuel spray is directed to the lower bottom wall surface 9e. It injects (refer to Drawing 13 (a)). Since the temperature in the combustion chamber is low, at the piston position near the intake top dead center, the fuel injected by the first fuel injection adheres to the lower bottom wall surface 9e in a substantially liquid state. The adhering fuel is vaporized between the intake stroke and the ignition, and a first air-fuel mixture is formed in the vicinity of the center portion of the cavity 9 (see FIG. 13B).
[0052]
The remaining fuel is injected in the compression stroke so that the injected substantially conical fuel spray is directed toward the ring-shaped upper bottom wall surface 9f (see FIG. 13B). That is, the second fuel injection timing is set to a fuel injection timing that can be reliably received by the upper bottom wall surface 9f even if the injection angle is the same as the first fuel injection angle. The fuel injected for the second time has a certain amount of time from injection to the upper bottom wall surface 9f, so that the fuel adhering to the upper bottom wall surface 9f is somewhat vaporized. A flow that grows in the direction of the wall surface is generated, and a donut-shaped second air-fuel mixture is formed as in FIG. 4C (see FIG. 13C).
[0053]
Then, during the remaining compression stroke, the donut hole portion of the donut-shaped second air-fuel mixture formed by the second fuel injection is formed at the center of the cavity by the first fuel injection. Since the first air-fuel mixture is filled, one homogeneous air-fuel mass is formed as a whole above the cavity during ignition, and stable stratified combustion can be realized (FIG. 13 (d)). )reference).
[0054]
That is, in the case where the combustion chamber temperature Tcc is lower than the predetermined value LTcc, when fuel injection is performed only once in the compression stroke, only a donut-shaped air-fuel mixture is formed, making it difficult to realize stable stratified combustion. However, according to the second embodiment, prior to the compression stroke injection, the first fuel near the intake top dead center so that the injected substantially hollow conical fuel spray is directed to the lower bottom wall surface 9e. By performing injection, a first air-fuel mixture is formed in the vicinity of the cavity central axis, and the injected substantially hollow conical fuel spray is now directed to the upper bottom wall surface 9f in the second compression stroke. By performing fuel injection, a doughnut-shaped second air-fuel mixture is formed, and in this case, the portion of the donut hole of the second air-fuel mixture is filled with the first air-fuel mixture, and as a whole, one homogeneous mass is formed. A mixed air mass is formed, and this It is possible to achieve a more stable stratified combustion.
[0055]
The fuel injection control based on the combustion chamber temperature performed by the engine controller 25 will be described with reference to the flowchart of FIG. The same step numbers are assigned to the same parts as those in FIG.
[0056]
The difference from FIG. 2 will be mainly described. This is the operation of S21 to S26. First, in S21, the combustion chamber temperature Tcc is estimated. The combustion chamber temperature Tcc shows a tendency as shown in FIG. 9 according to the engine speed NE and the target torque TTC. Therefore, these tendencies are obtained in advance through experiments or the like and stored in the memory in the engine controller 25 as map data. It can be estimated by referring to the map data from the engine speed NE and the target torque TTC.
[0057]
In S22, the combustion chamber temperature Tcc is compared with a predetermined value LTcc. The relationship between the temperature Tcc in the combustion chamber and the vaporization rate of the fuel in the combustion chamber has a relationship as shown in FIG. 10, for example, and the predetermined value LTcc is uniform in the upper center of the cavity 9 by one injection only in the compression stroke. This is the lower limit value of the combustion chamber temperature corresponding to the fuel vaporization rate capable of forming an air-fuel mixture (there is no lean air-fuel mixture). The actual value of LTcc is confirmed in advance by experiments. If the combustion chamber temperature Tcc is equal to or higher than the predetermined value LTcc, vaporization of the injected fuel is promoted even in a single injection of only the compression stroke, and a homogeneous air-fuel mixture is formed in the center of the sky above the cavity 9, and combustion is performed against this. If the room temperature Tcc is less than the predetermined value LTcc, it means that the fuel vaporization is insufficient with a single injection of only the compression stroke, and a homogeneous air-fuel mixture cannot be formed in the center of the sky above the cavity 9. For this reason, when the combustion chamber temperature Tcc is equal to or higher than the predetermined value LTcc, the operation proceeds to the operation of performing the single injection in the compression stroke of S6 to S8.
[0058]
On the other hand, if the combustion chamber temperature Tcc is smaller than the predetermined value LTcc in S22, the operation proceeds to the operation of performing the divided injection in the vicinity of the intake top dead center (initial stage of the intake stroke) and the compression stroke after S9.
[0059]
In S9 and S10, as in the first embodiment, target equivalent ratios TFBYA1 and TFBYA2 for the first and second fuel injections are set.
[0060]
In S23 and S24, the respective fuel injection amounts Qfb1 and Qfb2 in the divided injection are calculated by the above equations (4) and (5). However, as the correction coefficients Ktp1 and Ktp2 for adjusting the degree of vaporization of the fuel used here (also for the correction coefficient Ktp used in FIG. 8 S6), for example, the characteristics as shown in FIG. 11 are given. That is, the combustion chamber temperature Tcc is obtained as a parameter instead of the cooling water temperature Tw (see the upper part of FIG. 11). Thus, the correction coefficients Ktp1 and Ktp2 are obtained according to the combustion chamber temperature Tcc, which has a strong correlation with the fuel vaporization degree in the combustion chamber, and the basic fuel injection amount Qf0 is corrected according to the fuel vaporization degree by using the correction coefficients Ktp1 and Ktp2. As a result, the calculation accuracy of the fuel injection amounts Qfb1 and Qfb2 in the divided injection can be further improved.
[0061]
In S25, the first fuel injection timing ITb1 in the divided injection is set. Unlike the first embodiment, the first fuel injection timing ITb1 is calculated as a function of the combustion chamber temperature Tcc. For example, as shown in FIG. 12, the initial value of ITb1 is the intake top dead center, and the retarded angle increases as the combustion chamber temperature Tcc increases within the range in which the injected substantially hollow conical fuel spray is directed to the lower bottom wall surface 9e. It is a characteristic to do. In practice, ITb1 can be obtained by storing the data in the engine controller 25 as table data using the combustion chamber temperature Tcc as a parameter and referring to the table data from the combustion chamber temperature Tcc.
[0062]
In S26, the second fuel injection timing ITb2 in the split injection is set in the same manner as in the first embodiment in accordance with the engine speed NE and the target torque TTC. However, unlike the first embodiment, the second fuel injection timing ITb2 is set within a range in which the injected substantially conical fuel spray is directed toward the upper bottom wall surface 9f.
[0063]
In S14 and S15, the first fuel injection amount Qfb1, the first fuel injection timing ITb1, the second fuel injection amount Qfb2, and the second fuel injection timing ITb2 set in this way are used, and in the vicinity of the intake top dead center. Stratified combustion is realized by executing the first fuel injection in the split injection and the second fuel injection in the split injection in the compression stroke.
[0064]
Second Embodiment (Claims) 2 According to the invention), when the combustion chamber temperature Tcc is lower than the predetermined value LTcc, the fuel spray injected in a substantially hollow conical shape is directed toward the lower bottom wall surface 9e in the vicinity of the intake top dead center. Since the fuel injection is performed, since the first air-fuel mixture formed by the fuel adhering to the lower bottom wall surface 9e stays in the lower cavity, it is possible to prevent the diffusion outward in the radial direction. Stratified combustion can be performed stably.
[0065]
Second Embodiment (Claims) 3 According to the invention described in FIG. 8, when the combustion chamber temperature Tcc (engine temperature) is lower than the predetermined value LTcc, split injection is performed (FIG. 8, S22, S9, S10, S23, S24, S25, S26, S14, S15). ) In the fuel injection only in the compression stroke, vaporization of the injected fuel is not promoted and a doughnut-shaped air-fuel mixture is formed, so that even in the low temperature at which stable stratified combustion is difficult to realize, It becomes possible to form one homogeneous air-fuel mixture in the sky, and stratified combustion can be stably performed even when the combustion chamber temperature Tcc becomes low during the operation after the engine warm-up is completed.
[0066]
When the combustion chamber temperature Tcc is lower than the predetermined value LTcc, the higher the combustion chamber temperature Tcc, the shorter the time until the fuel attached to the upper bottom wall surface 9f evaporates and the diffusion of the vaporized fuel proceeds. Even when the combustion chamber temperature Tcc is high, at the same fuel injection timing ITb1 in the vicinity of the intake top dead center as when the combustion chamber temperature Tcc is low, it becomes impossible to keep the air-fuel mixture as an appropriate air mass. Embodiment (Claims) 4 The fuel injection timing ITb1 in the vicinity of the intake top dead center is delayed as the combustion chamber temperature Tcc increases (see FIG. 12), so that the fuel is injected in the vicinity of the intake top dead center. According to the time until the fuel is vaporized, it is possible to keep the air-fuel mixture in the sky above the cavity 9, and stable stratified combustion can be obtained even when the combustion chamber temperature Tcc is high.
[0067]
When the combustion chamber temperature Tcc is lower than the predetermined value LTcc, the higher the combustion chamber temperature Tcc, the higher the degree of vaporization of the fuel adhering to the lower bottom wall surface 9e. Therefore, even when the combustion chamber temperature Tcc is high, the combustion chamber temperature Tcc If the fuel injection amount Qfb1 is the same as when the fuel is low, fuel will be injected unnecessarily, which may increase the amount of unburned HC, but the second embodiment (claims) 5 According to the invention, the fuel injection amount Qfb1 in the vicinity of the intake top dead center is decreased by the correction coefficient Ktp1 as the combustion chamber temperature Tcc increases (see the upper part of FIG. 11), so the fuel for realizing stratified combustion As a result, it is possible to prevent unnecessary fuel injection and minimize the discharge of unburned HC.
[0068]
Among engine temperatures, the temperature in the combustion chamber has a strong correlation with the degree of fuel vaporization in the combustion chamber, and the second embodiment (claims) 6 According to the invention described in (1), the combustion chamber temperature Tcc is estimated, and when the temperature Tcc is lower than the predetermined value LTcc, the divided injection is performed. Therefore, the determination accuracy of whether or not the divided injection is performed is improved.
[0069]
When the combustion chamber temperature Tcc is lower than the predetermined value LTcc, the higher the combustion chamber temperature Tcc, the shorter the time until the fuel adhering to the lower bottom wall surface 9e evaporates and the diffusion of the vaporized fuel proceeds. If the fuel injection timing ITb1 in the vicinity of the top dead center is retarded too much, the fuel spray injected in a substantially hollow conical shape cannot be directed to the lower bottom wall surface 9e, and the first mixing is performed at the center of the cavity 9. The air mass cannot be formed in the second embodiment (claims). 7 According to the invention), the delay of the fuel injection timing ITb1 in the vicinity of the intake top dead center is performed within a range in which the spray of fuel injected in a substantially hollow conical shape is directed to the lower bottom wall surface 9e. (See FIG. 12), the first air-fuel mixture formed from the fuel adhering to the lower bottom wall surface 9e can always be retained in the lower cavity 9 to prevent the diffusion outward in the radial direction, and the combustion chamber temperature Tcc can be reduced. Stable stratified combustion can be obtained even at high temperatures.
[0070]
Next, the flowchart of FIG. 14 is for performing fuel injection control at the start based on the temperature in the combustion chamber of the third embodiment. In addition, the same step number is attached | subjected to the part same as FIG. 8 of 2nd Embodiment.
[0071]
In S31, the ignition key switch is switched from the off position to the on position. When the ignition key switch is turned to the starter activation position, the starter is activated and the engine starts cranking. In S32, cylinder discrimination is performed using a signal from the crank angle sensor 33 input by the rotation of the engine. In S33, the intake air amount QM, the engine speed NE, the fuel pressure Pf, the cooling water temperature Tw, the starting water temperature Tws, Read the cycle number Ncyl of each cylinder from the explosion. The cycle number Ncyl of each cylinder from the first explosion can be determined from the number of injections of the fuel injection valve 11, the number of ignitions of the spark plug 12, and the like.
[0072]
In S34, the target torque TTC is calculated according to the coolant temperature Tw and the engine speed NE, and in S3, the target equivalent ratio TFBYA is obtained from the target torque TTC and the engine speed NE.
[0073]
In S35, a basic fuel injection amount Qf0 is calculated. The basic fuel injection amount Qf0 may be basically calculated by the same method as in FIG. 2S4. However, the intake air amount QM cannot be detected due to the inrush current of the air flow meter 32 for several cycles after the start. Only during several cycles, the basic fuel injection amount Qf0 cannot be calculated by the same method as in FIG. 2S4. For this reason, the characteristics of the basic fuel injection amount Qf0 with respect to the coolant temperature Tw and the engine speed NE are obtained in advance through experiments or the like and stored in the memory in the engine controller 25 as map data. It is obtained by referring to the map data from Tw and engine speed NE.
[0074]
In S36, the combustion chamber temperature Tcc is estimated. The combustion chamber temperature Tcc shows a tendency as shown in FIG. 15 according to the starting water temperature Tws and the number of cycles Ncyl of each cylinder from the first explosion. It is stored in the internal memory and estimated by referring to the map data from the starting water temperature Tws and the cycle number Ncyl of each cylinder from the first explosion.
[0075]
In S37 and S38, the combustion chamber temperature Tcc and the predetermined value LTcc are compared, and the fuel pressure Pf and the predetermined value LPf are compared. The predetermined value LTcc is the same as the predetermined value LTcc used in FIG. 8S22, and the predetermined value LPf is the same as the predetermined value LPf used in FIG. 2S5. S9, S10, S23, S24, S25, S26, S14 when the combustion chamber temperature Tcc is lower than the predetermined value LTcc and when the fuel pressure Pf is lower than the predetermined value LPf even if the combustion chamber temperature Tcc is equal to or higher than the predetermined value LTcc. , S15, that is, split injection in the vicinity of the intake top dead center (the initial stage of the intake stroke) and the compression stroke is performed to realize stratified combustion.
[0076]
When the combustion chamber temperature Tcc is equal to or higher than the predetermined value LTcc and the fuel pressure Pf is equal to or higher than the predetermined value LPf, the fuel injection control at the time of start shown in FIG. 14 is terminated, and thereafter, after the start shown in FIGS. Transition to fuel injection control.
[0077]
Even when the temperature Tcc of the combustion chamber is lower than the predetermined value LTcc at the time of cold start, when fuel injection is performed only once in the compression stroke, only a donut-like air-fuel mixture is formed, and stable stratified combustion is realized. Although difficult, according to the third embodiment, prior to the compression stroke injection, 1 near the intake top dead center is set so that the injected substantially hollow conical fuel spray is directed to the lower bottom wall surface 9e. By performing the second fuel injection, a first air-fuel mixture is formed in the vicinity of the center axis of the cavity 9, and the injected substantially hollow conical fuel spray is now directed toward the upper bottom wall surface 9f. A second doughnut-shaped air-fuel mixture is formed by performing the second fuel injection at this time. In this case, the donut-shaped portion of the donut-shaped second air-fuel mixture is filled with the first air-fuel mixture 1 over the cavity 9 as a whole Of and of forming a homogeneous mixture mass, thereby also realizing a stable stratified combustion in the case of low combustion chamber temperature Tcc in until completion of the warm-up from the time of cold start.
[0078]
In the second and third embodiments, the combustion chamber temperature Tcc is estimated, the temperature Tcc is determined by (1) whether or not to perform split injection, and (2) the setting of fuel injection amounts Qfb1 and Qfb2 in split injection, {Circle around (3)} The case of using the first fuel injection timing ITb1 in split injection has been described. However, since the piston crown surface temperature can be estimated by the same method as the combustion chamber temperature, the temperature of the combustion chamber is changed. The piston crown surface temperature can be used. Also, it is conceivable that the piston crown surface temperature changes depending on the vaporization degree of the adhered fuel, and the combustion chamber temperature changes depending on the vaporization degree of the fuel injected from the fuel injection valve. By estimating, the fuel injection control according to the present invention can be performed with higher accuracy.
[0079]
Although the third embodiment has been described as applied to the engine having the configuration shown in FIG. 7, the third embodiment can also be applied to the engine having the configuration shown in FIG. 1.
[0080]
The present invention is not only applicable to the engine having the configuration shown in FIGS. 1 and 7, but can also be applied to the engine having the configuration described in JP-A-11-82028. A similar effect can be obtained.
[0082]
The function of the injection execution means described in claim 1 is performed by S9 to S15 in FIG. 2 and by S9, S10, S23, S24, S25, S26, S14, and S15 in FIGS.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an engine according to a first embodiment of the present invention.
FIG. 2 is a flowchart for explaining fuel injection control based on fuel pressure in the first embodiment.
FIG. 3 is a characteristic diagram of a correction coefficient corresponding to the degree of fuel vaporization during a single compression stroke injection.
FIG. 4 is a characteristic diagram showing the relationship between two target equivalent ratios and total target equivalent ratios in split injection.
FIG. 5 is a characteristic diagram of a correction coefficient corresponding to the degree of fuel vaporization during split injection.
FIG. 6 is a model diagram showing the behavior of fuel and air-fuel mixture formation in the combustion chamber of the first embodiment.
FIG. 7 is a schematic configuration diagram of an engine according to a second embodiment.
FIG. 8 is a flowchart for explaining fuel injection control based on the temperature in the combustion chamber of the second embodiment.
FIG. 9 is a characteristic diagram of combustion chamber temperature.
FIG. 10 is a characteristic diagram showing the relationship between fuel vaporization rate and combustion chamber temperature.
FIG. 11 is a characteristic diagram of a correction coefficient corresponding to the degree of fuel vaporization during split injection according to the second embodiment.
FIG. 12 is a characteristic diagram of the first fuel injection timing in split injection.
FIG. 13 is a model diagram showing the behavior of fuel and air-fuel mixture formation in the combustion chamber of the second embodiment.
FIG. 14 is a flowchart for explaining fuel injection control at the start based on the temperature in the combustion chamber of the third embodiment.
FIG. 15 is a characteristic diagram of the temperature in the combustion chamber immediately after starting.
[Explanation of symbols]
3 Combustion chamber
8 Piston
9 cavity
9a wall surface
9b Bottom wall
9c Lower peripheral wall
9d Upper peripheral wall
9e Lower bottom wall
9f Upper bottom wall
11 Fuel injection valve
12 Spark plug
25 Engine controller

Claims (10)

In a cylinder direct injection spark ignition engine comprising a piston, a fuel injection valve that is provided at a substantially central position of the fuel chamber ceiling with the injection center direction being vertically downward, and injects fuel directly into the combustion chamber, and an ignition plug,
Forming a cavity having a substantially cylindrical peripheral wall surface and a bottom wall surface smoothly connected to the peripheral wall surface on the crown surface of the piston;
The spark plug is disposed in the vicinity of the center wall of the bottom wall,
The fuel is injected from the fuel injection valve in a substantially hollow conical shape from the upper part of the combustion chamber, and the fuel injection from the fuel injection valve is divided into two parts, that is, the vicinity of the intake top dead center and the compression stroke. Equipped with an injection execution means ,
The fuel injection in the vicinity of the intake top dead center is set so that the spray of the fuel injected in the substantially hollow conical shape is directed to the substantially central position of the bottom wall surface, and the fuel injected in the substantially hollow conical shape Fuel injection in the compression stroke is performed so that the spray is directed around the radially outer side of the bottom wall surface;
A first air-fuel mixture is formed in the vicinity of the center of the cavity by fuel injection near the intake top dead center, and a second air-fuel mixture is formed into a donut shape by fuel injection in the subsequent compression stroke. An in-cylinder direct injection characterized by forming a uniform air-fuel mixture over the cavity as a whole by filling and filling the hole portion of the donut with the first air-fuel mixture Fuel ignition control system for a spark ignition engine. The cavity is
A substantially cylindrical lower peripheral wall surface;
A lower bottom wall surface smoothly connected to the lower peripheral wall surface;
A substantially cylindrical upper peripheral wall surface above the lower peripheral wall surface and having a larger diameter than the lower peripheral wall surface;
A ring-shaped upper bottom wall surface smoothly connected to the upper peripheral wall surface;
Have
The fuel spray in the vicinity of the intake top dead center is set so that the fuel spray injected in the substantially hollow cone shape is directed to the lower bottom wall surface, and the fuel spray injected in the substantially hollow cone shape is in the upper direction. The fuel injection control device for a direct injection spark ignition engine according to claim 1 , wherein fuel injection is performed in the compression stroke so as to be directed toward a bottom wall surface . An in-cylinder direct injection spark ignition engine according to claim 1 or 2 , further comprising engine temperature detecting means for detecting engine temperature, wherein the split injection is performed when the engine temperature is lower than a predetermined value . Fuel injection control device. The fuel injection control device for a direct injection spark ignition engine according to claim 3 , wherein the fuel injection timing near the intake top dead center is retarded as the engine temperature increases . The fuel injection control device for a direct injection spark ignition engine according to claim 3 , wherein the fuel injection amount in the vicinity of the intake top dead center is decreased as the engine temperature becomes higher. 4. The fuel injection control device for a direct injection spark ignition engine according to claim 3 , wherein the engine temperature detecting means is means for estimating a temperature of the piston crown surface or a temperature in the combustion chamber . Engine temperature detecting means for detecting engine temperature is provided, and when the engine temperature is lower than a predetermined value, the split injection is performed , and the fuel injection timing near the intake top dead center is retarded as the engine temperature increases. The in- cylinder direct injection type according to claim 2 , wherein the retard is made within a range in which the spray of fuel injected in the substantially hollow conical shape is directed to the lower bottom wall surface. A fuel injection control device for a spark ignition engine. 3. The direct injection spark ignition engine according to claim 1 , further comprising a fuel pressure detecting unit configured to detect a fuel pressure, wherein the split injection is performed when the fuel pressure is lower than a predetermined value . Fuel injection control device. 9. The fuel injection control device for a direct injection spark ignition engine according to claim 8 , wherein the fuel injection amount near the intake top dead center is decreased as the fuel pressure increases . A combustion chamber provided with a piston formed with a cavity having a substantially cylindrical peripheral wall surface and a bottom wall surface smoothly connected to the peripheral wall surface, and an injection center direction vertically downward at a substantially central position of the fuel chamber ceiling A fuel injection valve that injects fuel in a substantially conical shape from the top of the cylinder toward the cavity, a spark plug that is disposed near the center of the bottom wall surface, and an injection execution that controls injection from the fuel injection valve In-cylinder direct injection spark ignition engine comprising means,
The injection execution means performs the first injection when the piston is in the vicinity of the intake top dead center, and performs the second injection when the piston is in the compression stroke and is at a lower position than when the first injection is performed. To perform split injection,
A first air-fuel mixture is formed in the vicinity of the center of the cavity by fuel injection near the intake top dead center, and a second air-fuel mixture is formed into a donut shape by fuel injection in the subsequent compression stroke. formed, this donut hole portion said first mixture mass as a whole in the cylinder you and forming one homogenous mixture mass in high over the cavity direct injection spark ignition by filling the Engine fuel injection control device.

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