JP2011236808A - Injection control device of direct injection internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly set a frequency of divided injection when a temperature of an internal combustion engine is low, etc., in an injection control device of a direct injection internal combustion engine.SOLUTION: The injection control device 50 of the direct injection internal combustion engine includes: a dimensionless-distance calculation processing unit 52 for calculating a dimensionless distance where a distance from a fuel injection valve to a collision wall surface with which injected fuel collides is made to be dimensionless; a dimensionless-adhesion-length calculation processing unit 54 for calculating in advance a relation between the frequency and the dimensionless distance, in a dimensionless adhesion length where the sum of a length of fuel which is injected by the divided injection and adheres on the collision wall surface is made to be dimensionless; and a division frequency calculation processing unit 56 for calculating the frequency corresponding to the dimensionless distance of one fuel injection per cycle, on the basis of the relation between the frequency and the dimensionless distance when a target of a dimensionless adhesion length which is arbitrarily-set in advance is taken as the dimensionless adhesion length.

Description

  The present invention relates to an injection control device for a direct injection type internal combustion engine, and more particularly to an injection control device for a direct injection type internal combustion engine that can perform fuel injection per cycle divided into a plurality of divisions.

  An internal combustion engine injects fuel at a predetermined timing into a combustion chamber, which is a space between a cylindrical cylinder and the top of a piston that reciprocates within the cylinder, and burns the fuel to output power. Is an institution. As described above, fuel injection is performed at a predetermined timing in one cycle of the reciprocating motion of the piston. Therefore, it is fundamental that fuel injection is performed once per cycle. This is divided into a plurality of times per cycle to shorten the fuel injection time per time, and such a fuel injection method is called divided injection.

  For example, in Patent Document 1, as a control device for a fuel injection type internal combustion engine, the fuel supplied to the fuel injection means at the time of engine startup compared to during normal operation is improved in order to improve combustion at the time of cold start immediately after engine startup. It is disclosed to perform control to increase the pressure and divide the fuel injection for one cycle of the engine into a plurality of times. By doing so, it is stated that fuel can be miniaturized at the time of engine start and the amount of fuel adhering to the wall surface can be minimized.

Further, in Patent Document 2, as a combustion control device for a diesel engine, when the fuel is sprayed into the combustion chamber, the penetration force Sp in which the fuel spray travels through the air in the combustion chamber is described by the Guang'an equation. It is stated that it is expressed in distance. Here, Guang'an's formula is shown as Sp = Spb + 2.95 (ΔP × 10 ⁶ / ρf) ^0.25 × {Dn × (t−tb)} ^0.5 . ΔP is the differential pressure (MPa) between the atmospheric pressure and the injection pressure, ρf is the light oil density (kg / m ³ ), Dn is the nozzle diameter (mm), and t is the time after the start of injection.

  In order to prevent the penetrating force from becoming too large, the continuous valve opening time of the fuel injection valve is shortened or the fuel injection pressure is lowered. However, depending on the required torque of the engine, the former method may be used. In some cases, an amount of fuel commensurate with the amount of fuel cannot be injected within a single continuous valve opening time. In this case, it is stated that the fuel is divided into a plurality of times and injected. By doing so, even if the amount of fuel supplied in one combustion cycle of the cylinder is large, the continuous valve opening time for each divided time is shortened, and the penetration force of each fuel spray becomes small. Therefore, it is stated that fuel wall surface adhesion can be prevented.

JP 2006-336509 A JP 2003-286879 A

  As described above, for example, Guang'an's equation is used to suppress the fuel from adhering to the wall surface in the combustion chamber during fuel injection. By the way, when the wall surface of the combustion chamber is sufficiently warmed in the internal combustion engine, even if the fuel spray collides with the wall surface, the vaporization of the spray evaporates quickly. Adhesion to the wall is not a problem. The state in which the wall surface of the combustion chamber is sufficiently warm is sometimes called warm. On the other hand, when the wall surface of the combustion chamber is cold enough, the temperature of the wall surface is low, so the fuel spray does not vaporize and adheres in a liquid phase. Note that the temperature of the cooling water of the internal combustion engine can be used to determine whether it is warm or cold. Therefore, in the case of cold, since the wall surface temperature is low, the vaporization of vapor is slow, and further, the flame does not develop even when ignited in the combustion chamber, so that the fuel spray adheres to the wall surface. Thus, in the case of cold, a negative circulation is likely to occur between fuel adhesion and slow combustion. In order to avoid this, split injection is used. In this case, how to set the division number of the divided injection is not described in the prior art.

  An object of the present invention is to provide an injection control device for a direct injection internal combustion engine that can appropriately set the number of division injections when the cooling water temperature of the internal combustion engine is low.

  An injection control device for a direct injection internal combustion engine according to the present invention is based on the length of spray of fuel injection per cycle of the internal combustion engine from the fuel injection valve of the direct injection internal combustion engine into the cylinder. Dimensionless distance calculation means for calculating the dimensionless distance obtained by making the distance to the collision wall surface, which is the wall surface to which the injected fuel collides, and the total time of fuel injection performed in one cycle of the internal combustion engine are the same per cycle In the case of split injection in which the fuel injection is divided into a plurality of split times, the split is based on the length of fuel that is injected on the collision wall when the fuel is injected once per cycle. Non-dimensional adhesion length calculation means for calculating in advance the relationship between the number of divisions and the non-dimensional distance for the non-dimensional adhesion length obtained by making the total of the length of the fuel injected by the injection adhered on the collision wall surface non-dimensional; In advance Based on the relationship between the number of divisions at that time and the dimensionless distance, the number of divisions corresponding to the dimensionless distance for one fuel injection per cycle is calculated for the dimensionless adhesion length target set at will. , And a division number calculation means for making this the number of divisions of divided injection.

Further, in the injection control device for a direct injection internal combustion engine according to the present invention, the dimensionless distance calculating means has a spray length S = S = when the injection pressure is P and the injection period of fuel injection is τ. Based on Guang'an's equation expressed as αP ^0.25 τ ^0.5 , the length of spray when performing fuel injection once per cycle is S ₀ and the distance from the fuel injection valve to the collision wall is L _WALL. The distance x is calculated as x = L _WALL / S ₀ , and the dimensionless adhesion length calculation means sets the number of divisions as n and the dimensionless adhesion length y as y = (n ^0.5 −nx) (1−x). It is preferable to calculate as

Further, in the injection control device for a direct injection type internal combustion engine according to the present invention, the division number calculation means sets y = (n ^0.5 −nx) (1) with the dimensionless adhesion length y as the dimensionless adhesion length target y _T. From the relationship of -x), x _{i, yT} which is x when the number of divisions n = i is calculated, and fuel injection is performed once per cycle under predetermined operating conditions of the internal combustion engine. Means for calculating x _{0, yT} which is x _, and when x _{0, yT} is x _{2, yT} which is x when n = _{2, the} division number is set to n = 1 and x _{0 , yT} is less than x2 _{, yT} , and when x = 3, which is x when n = 3 _{, the} number of divisions is n = 2, and when _{x0, yT} is n = i X is less than x _{i, yT} , and x is greater than x _{(i + 1), yT} when n = (i + 1) times, and means for calculating the division number n as i times It is preferable to include.

In the injection control device for a direct injection type internal combustion engine according to the present invention, the division number calculation means sets the dimensionless adhesion length target y _T = 0, and y = (n ^0.5 −nx) (1−x) = 0. From the above relationship, x when the number of divisions n = 2, x2 _{, yT = 0} = 0.71, x3 when n = ₃ , _{yT = 0} = 0.58, n = 4 times a x when the x4, _yT = 0 = 0.50, a n = 5 times x when the calculated and x5, _yT = 0 = 0.45, of these with _x0, yT0 _{= 0} It is preferable to calculate the division number n by comparison.

  With the above configuration, the injection control device of the direct injection type internal combustion engine calculates a dimensionless distance based on the spray length with respect to the distance from the fuel injection valve to the collision wall surface, and the fuel injected by the divided injection is the collision wall surface. The dimensionless adhesion length based on the adhesion length at the time of one injection is obtained for the total of the adhesion length above, and the relationship between the number of divisions and the dimensionless distance is calculated in advance for the dimensionless adhesion length. Keep it. For a dimensionless adhesion length target that is arbitrarily set in advance, the number of divisions corresponding to the dimensionless distance for one fuel injection per cycle based on the relationship between the number of divisions at that time and the dimensionless distance. Is calculated as the number of division injections. In this way, for example, it is possible to determine the number of divisions for fuel deposition on the same collision wall surface as when the internal combustion engine is sufficiently warmed and performs fuel injection once per cycle. Therefore, for example, when the temperature of the internal combustion engine is low, if the divided injection is performed with the number of divisions obtained in this way, the internal combustion engine is sufficiently warmed and performs one fuel injection per cycle. The same fuel can be deposited on the impact wall. In this way, it is possible to appropriately set the division number of division injection.

Further, in the injection control device of the direct injection type internal combustion engine, when the injection pressure is P and the fuel injection period is τ, the Guang'an equation that the spray length S can be expressed as S = αP ^0.25 τ ^0.5 is used, When the calculation proceeds under the condition that the total time during the n divided injections is the same regardless of the number of divisions n, the dimensionless adhesion length y is expressed as y = (n ^0.5 −nx) (1−x). The Therefore, the division number n can be calculated using the dimensionless adhesion length.

Further, in the injection control device for a direct injection internal combustion engine, the relationship of y = (n ^0.5 −nx) (1−x) is used, y is a dimensionless adhesion length target y _T , and the number of divisions is n = i. X _{i, yT} , which is the time x, and x _{0, yT} , which is x when the fuel injection is performed once per cycle under the predetermined operating conditions of the internal combustion engine, are compared. When x _{0, yT} is equal to or greater than x _{2, yT} which is x when n = 2 times, the number of divisions is set to n = 1, and x _i is x when x is n = i times. _{, yT} , and when x = _{(i + 1), yT} which is x when n = (i + 1) times, the division number n is set to i times. In this way, for example, when the temperature of the internal combustion engine is low, it is possible to appropriately set the number of divided injections.

Further, in the injection control device of the direct injection type internal combustion engine, the dimensionless adhesion length target y _T = 0 and the number of divisions n = 2 times from the relationship y = (n ^0.5 −nx) (1−x) = 0. X2 when x, _{yT = 0} = 0.71, x3 when x = 3, _{yT = 0} = 0.58, x4 when n = 4, _{yT = 0} = 0.50, n = 5 times x when the x5, calculated as _yT-0 = 0.45, by comparison of these with x0, _yT-0, and calculates the division number n. In this way, for example, when the temperature of the internal combustion engine is low, it is possible to appropriately set the number of divided injections.

It is a figure which shows the injection control system of the direct injection type internal combustion engine containing the injection control apparatus of embodiment which concerns on this invention. In embodiment which concerns on this invention, it is a figure explaining the structure of the combustion chamber vicinity of a direct injection type internal combustion engine. In embodiment which concerns on this invention, it is a figure explaining the relationship between 1 time injection and n times of division | segmentation injection. In embodiment which concerns on this invention, it is a figure explaining the relationship between the injection period of fuel, and the length of spray. In embodiment which concerns on this invention, it is a figure explaining the relationship between a dimensionless distance and dimensionless adhesion length by making the frequency | count of a division into a parameter. FIG. 6 is a diagram for explaining how to set the number of divisions when a dimensionless distance is given with a dimensionless adhesion length target set to zero for a dimensionless adhesion length, using the enlarged view of FIG. 5. 6 is a flowchart illustrating a procedure for setting the number of divisions when the temperature of the internal combustion engine is low in the embodiment according to the present invention.

  Embodiments according to the present invention will be described below in detail with reference to the drawings. In the following, a diesel engine will be described as an internal combustion engine. However, any internal combustion engine capable of performing split injection may be used. For example, a gasoline engine may be used. Note that the internal combustion engine includes those with various specifications such as the number of cylinders and the arrangement form of the cylinders.

  In the following, a cylinder, a piston, an intake valve, an exhaust valve, and a fuel injection valve will be described as the configuration related to the combustion chamber. However, this is a description of the main elements, and of course as an internal combustion engine, Contains other elements. For example, a diesel engine includes a supercharger, EGR, a flow meter, and the like, and a gasoline engine includes an ignition plug, a throttle valve, an EGR, a flow meter, and the like, but these descriptions are merely omitted.

  In many cases, the fuel injection is performed a plurality of small injections such as pilot injection and after injection before and after one main injection. Hereinafter, the fuel injection will be described as related to the main injection, but the present invention can be applied when there is a possibility that the fuel spray adheres to the wall surface of the combustion chamber or the like by pilot injection, after injection, or the like.

  In the following, the fuel injection distance will be described as the distance from the injection port to the cavity called the cavity provided in the center of the upper surface of the piston. This is described as a representative example of the fuel collision wall surface. . The injection distance of the fuel injection is not limited to this, and can be a wide distance to the wall surface where the fuel spray collides.

  Below, the same code | symbol is attached | subjected to the same element in all the drawings, and the overlapping description is abbreviate | omitted. In the description in the text, the symbols described before are used as necessary.

  FIG. 1 is a diagram showing an injection control system 10 for a direct injection internal combustion engine. The injection control system 10 includes a direct injection type internal combustion engine main body 20 and an injection control device 50 that controls fuel injection. In particular, the injection control system 10 has a function of controlling the number of divided injections.

  The internal combustion engine body 20 is a 6-cylinder gasoline engine, and FIG. 1 shows a cross-sectional view of one of the cylinders.

  Here, a cylinder 22 having an opening at the top and a liner being press-fitted inside, a head portion 24 constituting a ceiling portion of the cylinder 22 and a piston 26 sliding inside the cylinder 22 are shown. ing. The movement of the piston 26 can be indicated by the crank angle θ, and the data is transmitted to the injection control device 50 via an appropriate signal line. The piston 26 has a cylindrical outer shape, and has a recess called a cavity 28 at the center of the upper surface thereof.

A space surrounded by the upper surface of the piston 26, the cylinder 22, and the head portion 24 is a combustion chamber 30. The head portion 24 is provided with an intake passage 32, an intake valve 34, an exhaust passage 36, an exhaust valve 38, a fuel injection valve 40, an injection port 42 thereof, and the like. The pressure in the intake passage 32 is detected by the pressure sensor as the air pressure P _A, the detection signal through an appropriate signal line is transmitted to the injection control unit 50. The temperature of the combustion chamber 30 can be indicated by the cooling water temperature T _W of the cylinder 22, and the data is transmitted to the injection control device 50 via an appropriate signal line.

  The fuel injection valve 40 is a valve that injects fuel into the combustion chamber 30 and is also called an injector. Specifically, it has a structure including a valve opening coil for opening and closing the injection port 42 with a needle valve. When the fuel is not injected, the needle valve closes the injection port 42, and when the fuel is injected, the needle valve moves to open the injection port 42.

  The actuator 44 is a drive device that drives the fuel injection valve 40. Specifically, the actuator 44 has a function of moving the needle valve with respect to the injection port 42 as described above. By controlling the operation timing of the actuator 44, the number of fuel injections performed in one cycle of the operation of the piston 26 can be changed. The operation of the actuator 44 is controlled by the injection control device 50.

  As such an actuator 44, it is desirable that a rising speed and a falling speed of movement of a needle valve called a needle are high. For example, a direct piezo injector that can move and drive a needle at high speed by an electrical signal using a piezoelectric element can be used. However, when high speed performance up to that point is not required, an electromagnetic drive injector using an exciting coil, a moving magnet, and a return spring can be used.

The high-pressure pump 46 is a fuel supply source having a function of compressing the fuel into high-pressure fuel and supplying the fuel to the fuel injection valve 40. A pressure accumulator is provided between the high-pressure pump 46 and the fuel injection valve 40, and the high-pressure fuel is temporarily accumulated here. The pressure in the accumulator portion is detected by the fuel pressure sensor as the original pressure P _I of the fuel, the detected signal through an appropriate signal line is transmitted to the injection control unit 50.

FIG. 2 is a diagram illustrating a structure in the vicinity of the combustion chamber 30 of the internal combustion engine body 20. Here, the relationship between the injection port 42 which is the opening at the tip of the fuel injection valve 40 and the distance L _WALL from the injection port 42 to the collision wall surface which is the wall surface where the injected fuel collides is shown. 2 shows a state in which the piston 26 is raised to near the top dead center, and the right drawing shows a state in which the piston 26 is lowered from the top dead center with respect to the left drawing.

The cone angle, which is the sandwiching angle of the spread of the spray injected from the injection port 42, is about 150 degrees to about 155 degrees, for example. Therefore, as shown in FIG. 2, the distance L _WALL varies depending on the position of the piston 26 of the internal combustion engine body 20. For example, in the figure on the left side of FIG. 2, the wall surface on which the injected fuel collides is at the outermost edge of the recess of the cavity 28 of the piston 26. In the diagram on the right side of FIG. 2, the wall surface with which the injected fuel collides becomes the inner wall of the cylinder 22.

As for the timing of fuel injection, as shown in the diagram on the left side of FIG. 2, the wall surface on which the injected fuel collides is generally placed inside the recess of the cavity 28 of the piston 26. In that case, as the maximum value of the distance L _WALL , the distance from the injection port 42 to the outermost edge of the cavity 28 of the piston 26 may be considered. Thus, in the case of the early injection in which fuel injection is performed earlier than the fuel injection timing in which the indentation region of the cavity 28 is used as a reference of the collision wall surface, and the post injection in which fuel injection is performed later, as shown in the right side of FIG. The collision wall surface becomes the liner of the inner wall of the cylinder 22.

As an example in which the collision wall surface becomes the inner wall of the cylinder 22, there is a premixed compression ignition technique in which a fuel having a low density is injected at an early stage to sufficiently diffuse to create an air-fuel mixture and then self-ignite. The early injection in the premixed compression ignition technique has an advantage that there is little NOx and soot because the combustion mixture is lean. On the other hand, since the fuel density is low in this early injection, the spray is often sprayed and the collision wall surface often becomes the liner of the inner wall of the cylinder 22. In this case, the distance L _WALL may be considered as shown on the right side of FIG.

Another example in which the collision wall surface is the inner wall of the cylinder 22 is post-injection in which the injection timing is considerably retarded from the top dead center. This is because injection for supplying THC and CO as reducing agents for the reduction of the NOx storage reduction catalyst, and for directly raising the exhaust gas temperature to regenerate the soot collected by the DPF. Injection, and THC and CO are supplied to increase the temperature of the gas in the oxidation catalyst. Since the injection timing is considerably retarded from the top dead center, the collision wall surface becomes a liner of the inner wall of the cylinder 22. Also in this case, the distance L _WALL may be considered as shown on the right side of FIG.

Since this L _WALL is the distance from the fuel injection valve 40 to the collision wall surface where the injected fuel collides, when examining whether or not the fuel injected from the fuel injection valve 40 adheres to the collision wall surface, etc. In addition, it is easiest to compare this L _WALL with the length of fuel spray. The relationship between L _WALL and the length of fuel spray will be described later.

  Returning to FIG. 1 again, the injection control device 50 is a control device having a function of controlling the operation of each element constituting the internal combustion engine body 20 as a whole in relation to the control of the operation of the fuel injection valve 40. Here, in particular, it has a function of controlling the number of divided injections. The injection control device 50 can be configured by a computer or the like suitable for mounting on a vehicle. The function of the injection control device 50 may be a part of the function of another on-vehicle control device. For example, the function of the injection control device 50 can be part of the function of the engine ECU (not shown).

  The injection control device 50 includes a dimensionless distance calculation processing unit 52, a dimensionless adhesion length calculation processing unit 54, and a division number calculation processing unit 56.

Here, the dimensionless distance calculation processing unit 52 uses the length of the spray of one fuel injection per cycle of the internal combustion engine as a reference, and the distance L from the fuel injection valve to the collision wall surface that is the wall surface on which the injected fuel collides. It is a means to calculate a dimensionless distance that is a dimensionless _WALL .

  Further, the dimensionless adhesion length calculation processing unit 54 performs the split injection in which the fuel injection per cycle is divided into a plurality of division times with the same overall fuel injection time performed in one cycle of the internal combustion engine. In addition, with reference to the length of the fuel injected when the fuel injection is performed once per cycle on the collision wall surface, the total length of the fuel injected by the divided injection attached on the collision wall surface is It is means for calculating in advance the relationship between the number of divisions and the dimensionless distance for the dimensionless dimensionless adhesion length.

  The division number calculation processing unit 56 sets a dimensionless adhesion length target arbitrarily set in advance as a dimensionless adhesion length, and once per cycle based on the relationship between the number of divisions and the dimensionless distance at that time. This is a division number calculation means for calculating the number of divisions corresponding to the dimensionless distance at the time of fuel injection and using this as the number of divisions of divided injection.

  Such a function can be realized by software. Specifically, it can be realized by executing a part corresponding to the fuel injection division number setting processing procedure of the engine control program. Some of these functions may be realized by hardware.

  Regarding the operation of the above configuration, the contents of each function of the injection control device 50 will be described in detail with reference to FIGS.

  FIG. 3 is a diagram for explaining the relationship between one-time injection and n-time divided injection. The horizontal axis is time, and the upper stage is one injection and the lower stage is n divided injections. Here, the one-time injection is when the number of fuel injections performed in one cycle of the internal combustion engine is one, and the n-time injection is performed by dividing the fuel injection per cycle of the internal combustion engine into n times. Is the case. The fuel injection here refers to main injection that is fuel injection that contributes to torque generation of the internal combustion engine. The optimization of the number of divisions described below can also be applied to pilot injection and after injection performed before and after the main injection, but the main injection will be described below unless otherwise specified.

ここで、ｃ_Vは、速度係数と呼ばれるもので、実験等で予め求めることができる。 In FIG. 3, the injection pressure at the time of one-time injection is shown as P ₀ (MPa), the fuel injection period as τ ₀ (s), and the fuel injection amount as Q ₀ (m ³ ). The injection pressure is shown as P (MPa), the fuel injection period as τ (s), and the fuel injection amount as Q (m ³ ). Here, when the fuel density is ρ (kg / m ³ ), the injection speed v _{0 at} the time of one injection can be obtained by the following equation (1).

Here, c _V is called a velocity coefficient, it can be obtained in advance by experiment or the like.

ここで、ｃ_Cは、収縮係数と呼ばれるもので、実験等で予め求めることができる。なお、ｎ回噴射のときの燃料の噴射期間τも、式（２）で、Ｐ₀をＰ、τ₀をτ、Ｑ₀をＱと置き換えることで、同様に求めることができる。ここで、係数Ｃは、次の式（３）で与えられる。

Using this equation (1), the fuel injection period τ _{0 at} the time of one injection can be obtained by the following equation (2), where d is the diameter of the injection port 42.

Here, c _C is called a shrinkage coefficient, and can be obtained in advance by experiments or the like. The fuel injection period τ at the time of n-time injection can be similarly obtained by replacing P ₀ with P, τ ₀ with τ, and Q ₀ with Q in equation (2). Here, the coefficient C is given by the following equation (3).

  As shown in FIG. 3, in the case of split injection, a period Δt during which fuel injection is not performed is provided between adjacent fuel injections. For this period Δt, rτ, which is a value obtained by multiplying τ by a preset coefficient r, where τ is each of the fuel injection periods of the divided injection, can be used. Here, the coefficient r can be set in the range of more than 0 and 1 or less.

  The fuel injection period τ of the divided injection is set so that the fuel injection per cycle is divided into a plurality of division times with the same time of fuel injection performed in one cycle of the internal combustion engine being the same. By doing in this way, as an internal combustion engine, the fuel consumption at the time of one injection and the fuel efficiency at the time of the divided injection of n times injection can be made the same. That is, the divided injection is executed under the condition that the fuel consumption is the same as that of the single injection.

For Figure 3, since the fuel injection period when the stroke injection is indicated by tau _0, so that the tau ₀ is equivalent to a total time of fuel injection be performed in one cycle of the internal combustion engine. Therefore, the relationship between τ ₀ and τ that satisfies the above condition is expressed by the following equation (4).

By applying the formula (2) to the formula (4), the following formula (5) is obtained.

By transforming this equation (5), the following equations (6) and (7) are obtained.

Then, the following equation (8) is obtained from the equations (6) and (7).

  When the formula (6) and the formula (8) are the same as the total time of fuel injection performed in one cycle of the internal combustion engine, the fuel injection per cycle is divided into n divided times. It is a basic formula showing the relationship between one-time injection and n-time injection.

Next, the relationship between the fuel injection period, the injection pressure, and the spray length will be described. Here, the spray length is the length of fuel spray when fuel is injected from the fuel injection valve 40 toward the combustion chamber 30. Regarding this relationship, Guang'an's formula described in Patent Document 2 is widely known. In general, Guang'an's formula assumes that the length of the fuel spray is S (m), the differential pressure between the atmospheric pressure and the injection pressure is ΔP (MPa), the fuel density is ρ _a (kg / m ³ ), The injection port diameter is d ₀ (mm), and the time after the start of injection is t (s), which is given by the following equation (9).

ここで、係数αは、次の式（１１）で示される。

Rewriting this, Guang's equation can be generally expressed by the following equation (10).

Here, the coefficient α is expressed by the following equation (11).

FIG. 4 is a diagram schematically showing Guang'an's equation, and the horizontal axis indicates the fuel injection period τ at the time of the n-time injection described in FIG. On the vertical axis, the fuel spray length is taken as the spray length S. In this example, the spray length S in the fuel injection period τ at the time of n injections is longer than L _WALL described in FIG. 2, and the difference is indicated by ΔS. Therefore, ΔS corresponds to the length that the injected fuel adheres on the collision wall surface. As described with reference to FIG. 2, the collision wall surface may be the upper surface of the piston 26 or the inner surface of the cylinder 22, so ΔS is the length of fuel attached to the upper surface of the piston 26 or the inner wall of the cylinder 22. 2 is the length of fuel attached, or the length of fuel attached to the upper surface of the piston 26 and the inner wall of the cylinder 22. As can be seen from FIG. 4, the longer the fuel injection period τ, the longer the fuel adheres.

The relationship between the spray length S at the time of n-time injection and the spray length S ₀ at the time of one-time injection is expressed by the following formula (12) using the formula (10).

Next, calculation of a change in ΔS when the injection is changed from n times to n times will be described. As the change of ΔS, the length that the injected fuel adheres on the collision wall surface when performing one fuel injection per cycle is Y ₀ = ΔS _0, and the fuel is injected by each fuel injection of the divided injection. The length of the fuel adhering on the collision wall surface can be evaluated as nΔS / ΔS ₀ where ΔS is set. Assuming that nΔS = Y, Y corresponds to the total length of the fuel injected by n fuel injections of the divided injections attached on the collision wall surface. Therefore, as a change of ΔS, a value represented by the following equation (13) can be used as a dimensionless adhesion length y obtained by making Y nondimensional with reference to Y ₀ = ΔS ₀ .

The denominator and numerator of equation (13) are divided by S ₀ to obtain the following equation (14).

When the formula (12) is applied to the formula (14), the following formula (15) is obtained.

式（１６）で示されるｘは、１回噴射のときにおける燃料噴射弁４０から燃焼室３０内への燃料噴射の噴霧の長さＳ₀を基準として、燃料噴射弁４０から噴射燃料が衝突する壁面である衝突壁面までの距離であるＬ_WALLを無次元化したものであるので、これを無次元距離と呼ぶことができる。図４の例のような場合、ｘは、０を超え、１未満である。なお、ｘ＝１のときは、Ｓ₀＝Ｌ_WALLで、噴射燃料が衝突壁面にぎりぎりで到達する場合で、燃料付着が生じない限界に相当する。 Here, x defined by the following equation (16) is used.

X expressed by the equation (16) collides with the injected fuel from the fuel injection valve 40 based on the spray length S ₀ of the fuel injection from the fuel injection valve 40 into the combustion chamber 30 at the time of one injection. Since L _WALL , which is the distance to the collision wall, which is a wall surface, is made dimensionless, this can be called a dimensionless distance. In the case of the example of FIG. 4, x is greater than 0 and less than 1. Note that when x = 1, S ₀ = L _WALL , which corresponds to the limit where fuel injection does not occur when the injected fuel reaches the collision wall surface.

When equation (15) is rewritten using equation (16), the following equation (17) is obtained. This expression (17) is a relational expression showing the relation between the number of divisions and the dimensionless distance with respect to the dimensionless adhesion length.

  FIG. 5 is a diagram showing a result of actually calculating the equation (17). Here, the number of divisions n is used as a parameter, the dimensionless distance x is taken on the horizontal axis, and the dimensionless adhesion length y is taken on the vertical axis.

  With reference to FIG. 5, on the same collision wall surface as when the fuel injection is performed once per cycle of the internal combustion engine under the reference operating condition with reference to the predetermined operating condition of the internal combustion engine. The number of divisions for fuel attachment can be determined. As an example of the predetermined operating conditions, a warm state in which the internal combustion engine is sufficiently warmed and fuel adhesion does not become a problem can be used. Of course, the operation state other than the warm state may be used as a reference. Hereinafter, the description will be continued assuming that the internal combustion engine is sufficiently warmed as a reference.

Here, the fuel deposition on the same collision wall surface as when the internal combustion engine is sufficiently warmed to perform fuel injection once per cycle means that the dimensionless deposition length y is the dimensionless deposition length target. Assuming that y _T = 0, the dimensionless distance x when the number of divisions n = i is obtained from the relationship between x and n in Expression (17) at that time. _Assuming that this value is x _{i, yT = 0} , this x _{i, yT = 0} indicates that the dimensionless distance x when the internal combustion engine is sufficiently warmed is x _{0, yT = 0} and x _{0, yT = 0} Must be smaller than. If x _i, if _{yT = 0} is greater than x _{0, yT = 0,} x _i, until _{yT = 0} is smaller than x _{0, yT = 0,} increases the number of divisions. In this way, an appropriate number of divisions can be set.

This will be described with reference to FIG. FIG. 6 is a partially enlarged view of FIG. 5, where y is in the range of 0 to 1. As described above, assuming that the dimensionless adhesion length target y _T = 0, the relationship between x and n at this time is x _{2, yT = 0} = 0.71 which is x when the number of divisions n = 2. _{X3, yT-0} = 0.58 when n = 3 times _{, x4} when y = 4 times _{, x4, yT = 0} = 0.50, n = 5 times _{x5, yT = 0} = 0.45 is calculated.

Here, assuming that the dimensionless distance x when the internal combustion engine is sufficiently warmed is x _{0, yT = 0} , x _{0, yT = 0} is x when n = 2 times, x _{2, yT = 0} When it is equal to or greater than 0.71, the number of divisions is set to n = 1. When x _{0, yT = 0} is less than x _{2, yT = 0} = 0.71, and x _{3, yT = 0} = 0.58 or more _, which is x when n = 3, the number of divisions is n = 2 times. When x _{0, yT = 0} is less than x _{3, yT = 0} = 0.58, and x _{4, yT = 0} = 0.50 _, which is x when n = 4, the number of divisions is n = 3 times. When x _{0, yT = 0} is less than x _{3, yT = 0} = 0.50, and x _{5, yT = 0} = 0.45 _, which is x when n = 5, the number of divisions is n = 4 times. Hereinafter, x _{0, yT = 0} is less than x _{i, yT = 0} when n = i times, and x _{(i + 1), yT =} x when n = (i + 1) times When the number is ₀ or more, the division number n is i.

  FIG. 7 is a flowchart that summarizes the contents described in FIG. 6 and explains the procedure for setting the number of divisions when the temperature of the internal combustion engine is low. Each procedure corresponds to each processing procedure of the engine control program.

When a portion corresponding to the fuel injection division number setting processing procedure of the engine control program rises, first, a dimensionless distance x = L _WALL / S ₀ when the internal combustion engine is sufficiently warmed is calculated (S10). This procedure is executed by the function of the dimensionless distance calculation processing unit 52 of the injection control device 50. The dimensionless distance when the internal combustion engine is sufficiently warmed is the dimensionless distance that is the reference condition when the divided injection is performed. How to set the dimensional distance has the meaning of S10.

Next, the calculated dimensionless distance x is compared with a previously calculated value (S12). The value calculated in advance is the relationship of y = y _T = (n ^0.5 −nx) (1−x) in Equation (17), where the dimensionless adhesion length y is the dimensionless adhesion length target y _T. Therefore, x _{i, yT = 0} is obtained by _obtaining x _{i, yT} which is x when the number of divisions n = i. The procedure for calculating in advance the relationship between the number of divisions and the dimensionless distance for the dimensionless adhesion length is executed by the function of the dimensionless adhesion length calculation processing unit 54 of the injection control device 50.

As described with reference to FIG. 6, when y _T = 0, x is x when the number of divisions n = _{2, yT = 0} = 0.71, and x is x when n = 3 _{3, yT = 0} = 0.58, x which is x when n = 4 times, _{4, yT = 0} = 0.50, x which is x when n = 5 times, _{5, yT = 0} = 0. 45 is calculated. It should be _noted that x _{i, yT} when y = y _T = 0 in equation (17) even when n is a large value, such as x _{5, yT = 0} = 0.41 which is x when n = 6 times. _{= 0} = n can be easily calculated from ^-0.5 .

In the comparison process of S12, as explained in FIG. 6, x _{0, yT = 0} which is x at the time of one fuel injection is x _{2, yT = 0} which is x when n = 2 times. In some cases, the number of divisions n is 1, and for n = 3 or more, x is less than x _{i, yT = 0} when n = i, and x when n = (i + 1) times. When x _{(i + 1), yT = 0} or more, the division number n is set to i times.

  Then, it is determined whether or not the calculated division number n is n = 1 (S14). If the result is affirmative, the division number n is determined as one. When the result is negative, it is determined whether or not the constraint condition is satisfied (S16).

  The constraint condition here is a condition for permitting divided injection. As one of the constraint conditions, P calculated by Expression (6) may not be too high as a constraint on the injection pressure P. For example, it is less than the hardware restriction of the high pressure pump 46 that determines the injection pressure, whether the combustion noise is not too high, or less than the restriction of the high pressure pump or the like. The other is that τ calculated by equation (7) is not too short as a constraint on the fuel injection period τ. This is, for example, whether the response speed of the actuator 44 is below a hardware constraint or the like.

  Further, in the actuator 44 of the fuel injection valve 40, it is necessary to consider a seat choke in which an orifice is substantially formed between the needle and the needle seat facing the needle. Since the sheet choke narrows the flow path through which the fuel passes, the pressure drops, the fuel becomes finer, the formation of the air-fuel mixture becomes slower, and the emission worsens. Since the sheet choke occurs twice as many times as the number of injections n, the larger the value of n, the more the sheet choke affects. In this way, the number of injections n is also limited. It should be noted that when the needle moves a very small amount at a high speed as in the case of using a direct piezo injector, the influence of the seat choke is reduced because this choke period is short.

  If the determination in S16 is negative, the number of divisions calculated in S12 is decreased by 1, and the determinations in S14 and S16 are repeated again. If the determination in S16 is affirmative, the number of times of split injection is set by the number of times n at that time (S20). The division number setting procedure so far is executed by the function of the division number calculation processing unit 56 of the injection control device 50. In this way, the number of divided injections performed when the internal combustion engine is not sufficiently warmed is appropriately set.

  The direct injection type internal combustion engine injection control device according to the present invention can be used for diesel engines, gasoline engines, and the like.

  DESCRIPTION OF SYMBOLS 10 Injection control system, 20 Internal combustion engine main body, 22 Cylinder, 24 Head part, 26 Piston, 28 Cavity, 30 Combustion chamber, 32 Intake path, 34 Intake valve, 36 Exhaust path, 38 Exhaust valve, 40 Fuel injection valve, 42 Injection Mouth, 44 Actuator, 46 High-pressure pump, 50 Injection control device, 52 Non-dimensional distance calculation processing unit, 54 Non-dimensional adhesion length calculation processing unit, 56 Division number calculation processing unit.

Claims (4)

From the fuel injection valve of the direct injection type internal combustion engine to the collision wall surface, which is the wall where the injected fuel collides, based on the spray length of one fuel injection per cycle of the internal combustion engine from the fuel injection valve into the cylinder A dimensionless distance calculating means for calculating a dimensionless distance obtained by making the distance dimensionless;
In the case of split injection in which fuel injection per cycle is divided into a plurality of split times with the same overall fuel injection time in one cycle of the internal combustion engine, the fuel injection is performed once per cycle. The number of divisions for the dimensionless deposition length, which is the dimensionless total of the length of the fuel injected by split injection on the collision wall surface, based on the length of the fuel injected on the collision wall surface. And a dimensionless adhesion length calculating means for calculating in advance the relationship between the dimensionless distance and
Calculates the number of divisions corresponding to the dimensionless distance for one fuel injection per cycle based on the relationship between the number of divisions and the dimensionless distance for a dimensionless adhesion length target set arbitrarily in advance. And a division number calculation means for making this the number of divisions of divided injection,
An injection control device for a direct injection internal combustion engine, comprising: The injection control device for a direct injection internal combustion engine according to claim 1,
The dimensionless distance calculation means
When the injection pressure is P and the fuel injection period is τ, the spray length S is one fuel injection per cycle based on the Guang'an equation that S = αP ^0.25 τ ^0.5 The length of the spray is S ₀ , the distance from the fuel injection valve to the collision wall is L _WALL , and the dimensionless distance x is calculated as x = L _WALL / S ₀ ,
The dimensionless adhesion length calculation means
An injection control device for a direct injection internal combustion engine, wherein the number of divisions is n and the dimensionless adhesion length y is calculated as y = (n ^0.5 −nx) (1−x). The injection control device for a direct injection internal combustion engine according to claim 2,
The division number calculation means
From the relationship y = (n ^0.5 −nx) (1−x), where the dimensionless adhesion length y is the dimensionless adhesion length target y _T , x _{i, yT} which is x when the number of divisions is n = i. Means for calculating
Means for calculating x _{0, yT} which is x when the fuel injection is performed once per cycle under predetermined operating conditions of the internal combustion engine;
When x _{0, yT} is equal to or more than x _{2, yT} which is x when n = 2, the number of divisions is n = 1, and x _{0, yT} is less than x _{2, yT} and n = 3 When x is _{x3, yT} or more, the number of divisions is n = 2 _{, and x0, yT} is less than _{xi, yT} which is x when n = i, and n = ( means for calculating the number n of divisions as i times when x _{(i + 1), yT,} which is x at _{i + 1)} times;
An injection control apparatus for a direct injection internal combustion engine, comprising: The direct injection type internal combustion engine injection control device according to claim 3,
The division number calculation means
Assuming that the dimensionless adhesion length target y _T = 0, from the relationship y = (n ^0.5 −nx) (1−x) = 0, x _{2, yT = 0} = x when the number of divisions n = 2. 0.71, x3 when n = 3, _{yT = 0} = 0.58, x4 when n = 4, _{yT = 0} = 0.50, n = 5 An injection control device for a direct injection internal combustion engine, wherein x is x5 and _{yT = 0} = 0.45, and the division number n is calculated by comparing these with x0 and _{yT0 = 0} .

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