JP3582264B2 - Fuel injection control device and control method for direct injection spark ignition type internal combustion engine - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fuel injection control device and a control method for a direct injection spark ignition type internal combustion engine in which fuel is directly injected into a cylinder by a fuel injection valve and ignited by an ignition plug.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there has been known a direct injection type spark ignition type internal combustion engine in which an injection hole of an electromagnetic fuel injection valve is installed facing a cylinder and fuel is directly injected into the cylinder by the fuel injection valve ( For example, see JP-A-57-162915 and JP-A-8-35429. Many of such direct-injection spark ignition type internal combustion engines are provided with a concave portion on the piston crown surface in order to realize stratification of the air-fuel mixture.
[0003]
According to this direct injection type spark ignition type internal combustion engine, when the internal combustion engine is under a low load, the mixture is stratified by injecting fuel toward the concave portion formed on the piston crown surface mainly during the compression stroke. It can be formed by super-lean combustion. Therefore, the fuel consumption rate at low load can be reduced. In addition, when the engine is under a high load, there is an advantage that a homogeneous air-fuel mixture can be formed by injecting fuel mainly during the intake stroke, and a high torque can be secured.
[0004]
[Problems to be solved by the invention]
However, in the direct injection type spark ignition type internal combustion engine, when fuel injection is performed mainly during the intake stroke in order to generate a homogeneous mixture, the injected fuel droplets are formed on the piston crown surface. When the fuel enters the recess, the fuel stagnates in the piston recess and is not sufficiently diffused and mixed in the entire cylinder from the intake stroke to the compression stroke. There is a problem that shading occurs, combustion deteriorates, and torque decreases.
[0005]
In order to avoid this problem, it is necessary to experimentally determine the injection start timing at which good combustion can be obtained without fuel entering the piston concave portion, which imposes a heavy burden on time and cost. In particular, if the fuel injection timing in the fuel injection during the intake stroke is fixedly set, when the engine operating conditions change, the fuel may enter the piston recess, so that a large margin must be provided. Therefore, the start of fuel injection may be excessively delayed.
[0006]
[Means for Solving the Problems]
The present invention has been made in view of such a conventional problem, and has as its object to obtain an optimum fuel injection start timing according to an engine operating condition without using an experimental method. That is, the fuel injection control device for a direct injection spark ignition type internal combustion engine according to the present invention has, as shown in FIG. In a direct-injection spark ignition type internal combustion engine in which fuel is directly injected into a cylinder, means 1 for detecting an operating state of the engine, and a mounting position and a mounting angle of a fuel injection valve 4 when performing fuel injection during an intake stroke And the position of the outer edge facing the fuel injection valve in the recess of the piston crown surface from the crankpin radius, connecting rod length and the shape of the piston crown surface. 2 for setting the fuel injection start timing so that the fuel injection does not enter the inside of the piston crown recess from the outer edge of the piston crown recess, and the injection set by the fuel injection start timing setting means. And fuel injection control means 3 for controlling the fuel injection by the fuel injection valve 4 in accordance with the start timing, it is characterized in that it comprises a.
[0007]
That is, when the fuel is injected during the intake stroke, the fuel is injected from the fuel injection valve 4 toward the descending piston crown surface. It is uniquely determined from the mounting position and mounting angle of No. 4 and the speed of spraying, corresponding to the elapsed time after injection. Further, since the lowering position of the piston is uniquely determined according to the crank angle by the crankpin radius and the connecting rod length, the position of the outer edge of the piston crown concave portion to which the spray is directed is determined by the piston position and the piston position. It is determined according to the crank angle from the shape of the crown. When the tip of the fuel spray that proceeds along the mounting angle reaches the piston crown surface, at least the majority of the fuel is injected into the piston if the tip of the spray in the radial direction of the piston is already located outside the piston recess. Do not enter the recess. Therefore, the fuel injection start timing setting means 2 sequentially determines the fuel injection start timing at which the fuel spray does not enter the piston concave portion according to the engine operating state, based on the relationship between the tip position of the spray and the outer edge position of the piston crown concave portion. Set it.
[0008]
More specifically, according to the first aspect of the present invention, when the fuel is injected during the intake stroke in which the piston descends , the means for detecting the rotational speed of the engine, From the relationship between the position of the tip of the spray determined from the speed of the fuel injection valve and the position of the outer edge facing the fuel injection valve in the piston crown recess determined by the crank angle, the tip of the spray is more recessed than the outer edge of the piston crown recess. Means for setting the fuel injection start timing corresponding to the engine rotation speed so as not to enter the inside of the engine, and controlling the fuel injection by the fuel injection valve according to the injection start timing set by the fuel injection start timing setting means. Fuel injection control means.
[0009]
That is, among the above-mentioned parameters, the mounting position and the mounting angle of the fuel injection valve 4 and the spray speed, and the crank radius, the connecting rod length, and the shape of the piston crown are all known values by the internal combustion engine, and Since the relationship between the time and the crank angle is determined by the engine speed, a value corresponding to the engine speed can be immediately obtained from the optimum fuel injection start timing according to the engine speed.
[0010]
According to a second aspect of the present invention, there is provided a direct injection type spark ignition type internal combustion engine having a concave portion which becomes a part of a combustion chamber on a piston crown surface, and directly injecting fuel into a cylinder during an intake stroke in which a piston descends by a fuel injection valve. The present invention relates to a fuel injection control method for an engine,
Detects engine speed,
From the mounting position and mounting angle of the fuel injection valve and the spray speed, the position of the tip of the spray corresponding to the elapsed time after the start of the injection is obtained,
From the crankpin radius, the connecting rod length and the shape of the piston crown surface, the position corresponding to the crank angle of the outer edge portion facing the fuel injection valve in the piston crown recess,
The fuel injection start timing is set in accordance with the engine speed so that the tip of the spray does not enter the inside of the recess from the outer edge of the piston crown recess,
The fuel injection by the fuel injection valve is controlled according to the set injection start timing.
[0011]
【The invention's effect】
According to the fuel injection control device and method for a direct injection spark ignition type internal combustion engine according to the present invention, the relative position between the tip position of the spray as a function of time and the outer edge position of the piston crown concave portion as a function of the crank angle is determined. Based on the relationship, the fuel injection start timing is set so that the spray does not enter into the recess of the piston crown surface.Therefore, mainly at the time of a high engine load, etc., the deterioration of combustion and the torque caused by the concentration of the mixture in the combustion chamber are reduced. Can be prevented from decreasing. In particular, it is possible to set such an optimum fuel injection start timing without using an experimental method, and it is possible to always maintain the optimum fuel injection start timing irrespective of changes in engine operating conditions.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0013]
FIG. 2 shows a mechanical configuration of a direct injection type spark ignition type internal combustion engine to which the present invention is applied. This internal combustion engine mainly comprises a cylinder head 11 and a cylinder block 12, A plurality of cylinders 13 are formed in 12. A piston 14 is slidably fitted to the cylinder 13, and a lower portion of the cylinder head 11 that covers the cylinder 13 is formed with a concave portion that is a part of a combustion chamber. A port 15 and a pair of exhaust ports 16 are connected, and an intake valve 17 and an exhaust valve 18 open and close, respectively. An ignition plug 19 is arranged at the center of these four intake valves 17 and exhaust valves 18, that is, at the center position of the cylinder 13.
[0014]
An electromagnetic fuel injection valve 20 that opens and closes by an injection pulse signal is provided directly on the cylinder 13 on the outer peripheral portion on the intake valve 17 side at the upper end of the cylinder 13. The fuel injection valve 20 is for injecting fuel along the central axis of the fuel injection valve 20 from the injection hole at the tip, and is attached in a posture inclined obliquely downward as shown in the figure. . The mounting angle with respect to the horizontal plane of the cylinder is θinj.
[0015]
A recess 21 which is a part of the combustion chamber is formed in the crown surface of the piston 14. The concave portion 21 is partially formed in a range deviated to one of the crown surfaces of the piston 14, specifically, in a range deviated to the fuel injection valve 20 side, and includes the center of the piston 14 from the vicinity of the outer peripheral portion of the piston 14. Is formed. The outer edge 21 a of the recess 21 on the exhaust valve 18 side faces the injection hole of the fuel injection valve 20.
[0016]
The control device 22 for controlling the fuel injection valve 20 and the spark plug 19 is a so-called microcomputer system, which includes a CPU, a ROM, a RAM, an I / O, and the like. The control device 22 detects an engine operation state such as an air flow meter 23 for detecting an intake air amount of the internal combustion engine, a crank angle sensor 24 for detecting an engine crank angle position, and a throttle opening sensor 25 for detecting a throttle opening. The detection signal from the sensor which performs it is input. Then, as described later, the fuel injection start timing is set according to the detected engine operating state, and the fuel injection valve 20 is driven.
[0017]
Next, specific means for setting the fuel injection start timing so that the fuel spray does not enter the concave portion 21 of the crown surface of the piston 14 will be described. Basically, at low engine load, fuel is injected mainly into the recess 21 of the piston 14 during the compression stroke, and at high engine load, fuel is injected during the intake stroke to obtain a homogeneous mixture. It has become. When performing fuel injection during the intake stroke, the fuel spray injected from the fuel injection valve 20 follows the piston 14 descending according to the crank angle.
[0018]
As shown in FIG. 2, the position of the tip of the fuel spray F is set according to a coordinate axis in which the axis direction of the cylinder 13 is the Y axis and the direction orthogonal to the Y axis and the direction along the plane passing through the fuel injection valve 20 is the X axis. Xspray, Yspray), and assuming that the position of the outer edge 21a of the piston recess 21 facing the injection valve is (Xpis, Ypis), the condition that the tip of the fuel spray F does not enter the piston recess 21 is as follows: Yspray> Ypis In this case, Xspray> Xpis.
[0019]
That is, when the tip of the fuel spray F reaches the crown surface of the piston 14, if the X coordinate of the tip of the spray F is already located outside the outer edge 21 a of the piston recess 21, that is, on the exhaust valve 18 side, the fuel At least most do not enter the piston recess 21.
[0020]
Here, the coordinates Xspray, Yspray, Xpis, and Ypis can be calculated as follows.
[0021]
Assuming that the speed of the fuel spray is Vspray, the elapsed time from the start of fuel injection is Tspray, the coordinates of the mounting position of the fuel injection valve 20 is (Xinj, Yinj), and the mounting angle is θinj as described above, (Xspray, Yspray) are represented by the following equations, respectively.
[0022]
(Equation 1)
Xspray = Xinj tens Vspray · Tspray · sin (θinj)
[0023]
(Equation 2)
Yspray = Yinj tens Vspray · Tspray · cos (θinj)
The coordinates of the position of the outer edge 21a on the side of the biston recess 21 facing the fuel injection valve 20 are calculated using the shape of the piston 14, the crank radius R, the connecting rod length CONL, and the crank angle CA from the top dead center. It is shown by the following equations, respectively.
[0024]
(Equation 3)
Xpis (= const.)
[0025]
(Equation 4)
Ypis = Ypis1 + Ypis2 = (R + CONL-R · cos (CA) -sqrt (CONL 2 - (R · sin (CA)) 2)) + Ypis2
Here, Ypis1 is the distance from the upper end of the cylinder 3 to the upper surface of the piston 14, and Ypis2 is the distance from the upper surface of the piston 14 to the tip of the outer edge 21a. Note that sqrt is a square root.
[0026]
Assuming that the crank angle at which fuel injection starts is CAinj, there is a relationship between Tspray and CAinj as follows.
[0027]
(Equation 5)
Tspray = (60 / Ne) · 1000 · (1/360) · (CA-CAinj)
Here, Ne is the engine speed (rpm).
[0028]
From the above expression, when Yspray> Ypis, the range of the fuel injection start crank angle CAinj satisfying Xspray> Xpis can be obtained. Although this calculation can be performed sequentially by the control device 22, since the parameters other than the engine speed Ne are parameters that can be known in advance, the fuel injection start crank angle CAinj corresponding to each engine speed Ne is calculated in advance. Therefore, a method of storing the information in the control device 22 and referring to the stored information in accordance with the operating state of the engine is practical. The fuel spray speed Vspray is determined by the characteristics of the fuel injection valve 20 and the fuel pressure.
[0029]
Next, the operation of the present invention will be described with reference to FIGS. FIG. 3 illustrates a phenomenon that occurs in the method for setting the fuel injection start timing not according to the present invention. Most of the fuel injected from the fuel injection valve 20 in the early stage of the intake stroke enters the recess 21 in the crown surface of the piston 14 because the piston 14 is located near the top dead center. Thereafter, as the piston 14 descends, the fuel spray begins to diffuse throughout the cylinder 13. However, the fuel captured in the recess 21 of the piston 14 hardly spreads and mixes even during the intake stroke to the compression stroke. , Stays in the recess 21 until the compression top dead center. As a result, at the compression top dead center, the air-fuel mixture in the combustion chamber has a dark and light distribution in which the vicinity of the spark plug 19 is lean and the inside of the piston recess 21 is rich, which causes the combustion to deteriorate and the torque to decrease. May occur.
[0030]
On the other hand, according to the fuel injection start timing CAinj set by the present invention, as shown in FIG. 4, the fuel is injected so as to follow the descending piston 14, but the tip of the fuel spray is It does not reach the recess 21. Even if the spray tip catches up with the piston 14, the center of the spray collides with the crown surface on the exhaust valve 18 side with respect to the recess 21, and almost no fuel enters the recess 21. Therefore, the fuel spray is diffused and mixed throughout the cylinder 3. As a result, a homogeneous air-fuel mixture is formed at the compression top dead center, and good combustion is obtained. Therefore, a decrease in torque or the like does not occur.
[0031]
When a specific numerical value is put in the dimensions of each part shown in FIG. 2 and the above calculation is performed, Xinj = −40 (mm), Yinj = −8 (mm), Xpis = 7 (mm), Ypis2 = -6 (mm), Vspray = 20 (mm / ms), R = 43 (mm), CONL = 136 (mm), θinj = 33 (deg.), Ne = 1600 (rpm) The fuel injection start timing CAinj at which the fuel does not enter the concave portion 21 of the crown surface of the piston 14 is CAinj ≧ 80 deg. It becomes ATDC.
[0032]
FIG. 5 shows the result of measuring the change in the shaft torque using the fuel injection start timing (crank angle) as a parameter by an experiment using an actual machine having the above dimensions. The engine speed is 1600 rpm. In this case, as shown, the fuel injection start crank angle is approximately 80 deg. Before ATDC, a decrease in torque is observed. This is considered to be due to the non-uniformity of the mixture described above. In contrast, about 80 deg. After ATDC, torque reduction has not occurred, and good combustion is being performed.
[Brief description of the drawings]
FIG. 1 is a functional block diagram showing a configuration of the present invention.
FIG. 2 is a configuration explanatory diagram showing the configuration of an embodiment of the present invention.
FIG. 3 is an explanatory diagram showing a state of air-fuel mixture formation at a fuel injection start timing not according to the present invention.
FIG. 4 is an explanatory diagram showing a state of air-fuel mixture formation at a fuel injection start timing according to the present invention.
FIG. 5 is a characteristic diagram showing experimental results showing the effects of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Operating state detection means 2 ... Fuel injection start timing setting means 3 ... Fuel injection control means 4 ... Fuel injection valve

Claims (2)

In a direct-injection spark-ignition internal combustion engine having a concave portion that becomes a part of a combustion chamber in a piston crown surface, and injecting fuel directly into a cylinder by a fuel injection valve,
Means for detecting the rotational speed of the engine;
When performing fuel injection during the intake stroke in which the piston descends, the position of the tip of the spray determined from the mounting position and the mounting angle of the fuel injection valve and the speed of the spray, and the fuel injection valve in the piston crown recess determined by the crank angle Means for setting the fuel injection start timing in accordance with the engine speed so that the tip of the spray does not enter inside the recess from the outer edge of the piston crown recess from the relationship with the position of the facing outer edge,
Fuel injection control means for controlling fuel injection by the fuel injection valve according to the injection start timing set by the fuel injection start timing setting means,
A fuel injection control device for a direct injection spark ignition type internal combustion engine, comprising: Fuel injection control method for a direct-injection spark ignition type internal combustion engine having a concave portion that becomes a part of a combustion chamber on a piston crown surface and directly injecting fuel into a cylinder during an intake stroke in which a piston is lowered by a fuel injection valve At
Detects engine speed,
From the mounting position and mounting angle of the fuel injection valve and the spray speed, the position of the tip of the spray corresponding to the elapsed time after the start of the injection is obtained,
From the crank radius, the connecting rod length and the shape of the piston crown, the position corresponding to the crank angle of the outer edge facing the fuel injection valve in the piston crown recess,
The fuel injection start timing is set in accordance with the engine speed so that the tip of the spray does not enter the inside of the recess from the outer edge of the piston crown recess,
A fuel injection control method for a direct-injection spark ignition type internal combustion engine, comprising controlling fuel injection by the fuel injection valve according to the set injection start timing.

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