JP3559890B2 - How to select fuel injectors - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for selecting a fuel injection valve for a direct injection spark ignition type internal combustion engine.
[0002]
[Prior art]
In recent years, a direct injection spark ignition type internal combustion engine has attracted attention. In this engine, switching control of a combustion method is performed according to engine operating conditions, that is, by injecting fuel in an intake stroke, homogeneous combustion in a combustion chamber is performed. Switching control between homogeneous combustion performed by forming a combustible air-fuel mixture and stratified combustion performed by injecting fuel in a compression stroke to make the combustible air-fuel mixture unevenly distributed in a specific range (around a spark plug) in a combustion chamber. It is common.
[0003]
In such a direct-injection spark ignition type internal combustion engine, injection is performed at a high fuel pressure in order to enable injection during the compression stroke and to improve the atomization level from the viewpoint of combustion stability.
Therefore, when the load is low, it is necessary to perform injection with a very short pulse width. Further, since lean combustion is performed by stratified combustion, highly accurate and stable injection in a low pulse width region is required.
[0004]
However, in the current fuel injection valve, there is a limit in securing the linearity of the injection flow rate characteristic in a low pulse width region, which is a factor limiting lean combustion.
Therefore, in the non-linear region where the linearity of the fuel injection valve is not maintained, the pulse width correction is performed so as to obtain the ideal linear injection flow rate by using the characteristic that the fuel injection valve can perform the injection with good reproducibility. Amendment) (see Japanese Utility Model Laid-Open No. 59-49739).
[0005]
[Problems to be solved by the invention]
However, the linearity correction alone only approximates the ideal straight line, and the flow rate variation in the low pulse width region still exists and is large.
As a method of coping with the flow rate variation, it is effective to set a learning correction value by learning control, that is, learning based on an air-fuel ratio feedback correction value during air-fuel ratio feedback control, and to perform correction based on the learning correction value. However, since the low pulse width region is a stratified combustion region and performs lean combustion, it is difficult to perform air-fuel ratio feedback control, and therefore cannot directly learn. For this reason, it corresponds by performing estimation learning based on the learning correction value in the homogeneous combustion region on the high pulse width side.
[0006]
However, since the flow rate variation tends to increase as the pulse width decreases, even if the learning correction value in the homogeneous combustion region on the high pulse width side where learning progresses is reflected in the stratified combustion region on the low pulse width, on the contrary, In some cases, controllability deteriorated.
For example, when the injection flow rate is larger than the target value in the homogeneous combustion region on the high pulse width side, but the injection flow rate is smaller than the target value in the stratified combustion region on the low pulse width side, the fuel injection amount is determined by learning in the homogeneous combustion region. When the learning correction value is set so as to perform the decrease correction, when the correction is performed in the stratified combustion region using the learning correction value, even though the injection flow rate is smaller than the target value in the stratified combustion region, By performing the further decrease correction, the injection flow rate becomes smaller than the target value.
[0007]
In view of such circumstances, the present invention provides a method for selecting a fuel injection valve for a direct injection spark ignition type internal combustion engine so that a learning result in a homogeneous combustion region can be correctly reflected in control in a stratified combustion region. The purpose is to provide.
[0008]
[Means for Solving the Problems]
Therefore, the method for selecting a fuel injection valve according to the present invention measures the injection flow rate of the fuel injection valve at a first predetermined pulse width in the homogeneous combustion region on the high load side that performs the air-fuel ratio feedback control, The injection flow rate of the fuel injection valve is measured at the second predetermined pulse width in the stratified combustion region on the low load side where the air-fuel ratio feedback control is not performed. Then, regarding the injection flow rate at the first predetermined pulse width and the injection flow rate at the second predetermined pulse width, (1) the injection flow rate at the first predetermined pulse width is close to the upper limit value (the predetermined value larger than the median value). -The upper limit value) , the injection flow rate at the second predetermined pulse width is close to the upper limit value ( the range from the predetermined value larger than the median value to the upper limit value) , and (2) the injection flow rate at the first predetermined pulse width is In the vicinity of the median (the predetermined range before and after the median) , the injection flow rate at the second predetermined pulse width is near the median (the predetermined range before and after the median) , and (3) the injection at the first predetermined pulse width. The flow rate is near the lower limit value (a range of a predetermined value smaller than the lower limit value to the median value) , and the injection flow rate at the second predetermined pulse width is near the lower limit value (a range of the predetermined value smaller than the lower limit value to the median value) . The fuel injection valve that corresponds to the target is selected and mounted on a direct-injection spark ignition internal combustion engine. To (claim 1).
[0009]
Here, the first and second predetermined pulse widths obtain predetermined required injection flow rates in the homogeneous combustion region and the stratified combustion region based on the basic pulse width-injection flow characteristic of the fuel injection valve. Is set as a pulse width necessary for the operation (claim 2).
[0010]
【The invention's effect】
According to the first aspect of the present invention, the engine having the same tendency as the injection flow rate in the homogeneous combustion region and the injection amount characteristic in the stratified combustion region is selected and mounted on the engine. The result can be correctly reflected in the stratified combustion region.
According to the second aspect of the present invention, since the measurement is performed using the pulse width after the linearity correction, it is possible to perform the selection without being affected by the non-linearity.
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
The method of selecting a fuel injection valve according to the present invention is shown as a flowchart in FIG. 1. Prior to the description, a method of calculating a fuel injection pulse width of a fuel injection valve in a direct injection spark ignition type internal combustion engine, and a linearity The correction and the like will be described.
[0012]
During homogeneous combustion, the target air-fuel ratio is set to stoichiometric, a basic fuel injection pulse width for homogeneous combustion corresponding to the target air-fuel ratio is calculated, and an air-fuel ratio feedback correction value (correction coefficient) is set by air-fuel ratio feedback control. Further, a learning correction value (correction coefficient) is set based on the air-fuel ratio feedback correction value by learning control, and the fuel injection pulse width TI is calculated by multiplying the learning correction value (correction coefficient).
[0013]
At the time of stratified combustion, the target air-fuel ratio is set to lean, the basic fuel injection pulse width for stratified combustion corresponding to the target air-fuel ratio is calculated, and the learning correction estimated and learned based on the learning correction value at the time of homogeneous combustion is calculated. The fuel injection pulse width TI is calculated by multiplying the value (correction coefficient).
The linearity correction is performed on the fuel injection pulse width TI calculated as described above as follows.
[0014]
FIG. 2 shows a basic pulse width-injection flow rate characteristic of the fuel injection valve, and shows that linearity is lost in a low pulse width region.
Therefore, if the required injection flow rate on the ideal straight line with the pulse width TI calculated as described above is QF, the actual injection flow rate will be QI if the pulse width TI remains unchanged, and the required injection flow rate QF will be insufficient. I do. In order to obtain the required injection flow rate QF, the pulse width needs to be TF.
[0015]
Therefore, for the calculated pulse width TI, the pulse width TF for obtaining the required injection flow rate on the ideal straight line is determined by experiments or the like, and stored as a table (TI → TF conversion table), and this table is referred to. Then, the calculated pulse width TI is converted into a pulse width TF for obtaining the required injection flow rate, and output, thereby correcting the linearity.
[0016]
In practice, the final pulse width is set by adding an invalid injection pulse width TS for the valve opening operation to the converted pulse width TF.
When driving the fuel injector with this final pulse width, as shown in FIG. 3, a high current (peak current of 6 to 10 A) is applied to open the fuel injector, and thereafter, In order to keep the valve open, control is performed to switch to a small current (hold current of 2 to 4 A). With such control, the linearity correction can be achieved by stabilizing the valve opening characteristics.
[0017]
FIGS. 4A and 4B show variations in the pulse width-injection flow rate characteristics, wherein FIG. 4A shows the results before the linearity correction and FIG. 4B shows the results after the linearity correction.
Before the linearity correction (A), in the low pulse width region, not only the variation is large but also the deviation from the ideal straight line is large. After the linearity correction (B), the deviation from the ideal straight line is small, but the deviation is small. Shows that it is still large.
[0018]
Therefore, it is necessary to perform estimation learning based on the learning result in the homogeneous combustion region and perform learning correction in the stratified combustion region, and to make the learning result in the homogeneous combustion region correctly reflected in the stratified combustion region. It is necessary to select the fuel injection valve before mounting the fuel injection valve.
For this selection, as shown in FIG. 4B, a first predetermined pulse width, that is, a homogeneous combustion pulse width control point is set in a homogeneous combustion region on the high load side where the air-fuel ratio feedback control is performed (for example, , About 0.8 ms). Further, a second predetermined pulse width, that is, a stratified combustion pulse width control point is set in the stratified combustion region on the low load side where the air-fuel ratio feedback control is not performed (for example, about 0.6 ms).
[0019]
FIG. 5 shows the range of variation of the injection flow rate error (%) after linearity correction with respect to the pulse width.
Here, in the case of the fuel injection valve having the characteristic shown as NG in the figure, that is, although the injection flow rate is smaller than the target value in the homogeneous combustion region on the high pulse width side, the injection flow rate is smaller than the target value in the stratified combustion region on the low pulse width side. If it is larger, a learning correction value is set so as to increase the fuel injection amount by learning in the homogeneous combustion region, and if the correction is performed in the stratified combustion region using the learned correction value, the stratified combustion region In spite of the fact that the injection flow rate is larger than the target value, the fuel injection valve having such a characteristic needs to be eliminated because the injection flow rate becomes further larger than the target value by further increasing the correction.
[0020]
On the other hand, in the case of the fuel injection valve having the characteristic shown as OK in the drawing, that is, the injection flow rate is smaller than the target value in the homogeneous combustion region on the high pulse width side, and the injection flow rate is also lower in the stratified combustion region on the low pulse width side. If the value is smaller than the value, a learning correction value is set so as to increase the fuel injection amount by learning in the homogeneous combustion region, and when the correction is performed in the stratified combustion region using the learning correction value, the stratified combustion Since the increase correction is performed in the region, the injection flow rate can be made closer to the target value, and a fuel injection valve having such characteristics can be employed.
[0021]
Therefore, the fuel injection valve corresponding to any of the following (1) to (3) may be selected and mounted on the engine.
(1) The injection flow rate at the homogeneous combustion pulse width control point is near the upper limit, and the injection flow rate at the stratified combustion pulse width control point is near the upper limit value. (2) The injection flow rate at the homogeneous combustion pulse width control point is at the center. In the vicinity of the value, the injection flow rate at the stratified combustion pulse width control point is near the median value. (3) The injection flow rate at the homogeneous combustion pulse width control point is near the lower limit, and the injection flow rate at the stratified combustion pulse width control point is Those near the lower limit.
[0022]
More specifically, the fuel injection valve corresponding to any of the following (1) to (3), which enters the hatched area shown as OK in FIG. 6, may be selected and mounted on the engine.
(1) The injection flow rate error at the homogeneous combustion pulse width control point is in the range of + 0.5% to + 4.5%, and the injection flow rate error at the stratified combustion pulse width control point is in the range of + 4% to + 12%. (2) Injection flow rate error at the homogeneous combustion pulse width control point is in the range of -2% to + 2%, and injection flow error at the stratified combustion pulse width control point is in the range of -4% to + 4%. (3) The injection flow rate error at the homogeneous combustion pulse width control point is in the range of -4.5% to -0.5%, and the injection flow rate error at the stratified combustion pulse width control point is in the range of -12% to -4%. Range of things.
[0023]
Lastly, a method for selecting a fuel injection valve according to the present invention will be described with reference to the flowchart of FIG.
In step 1 (referred to as S1 in the figure, the same applies hereinafter), the injection flow rate after the linearity correction is measured at the homogeneous combustion pulse width control point, and the injection flow rate error is determined.
In step 2, the injection flow rate after linearity correction is measured at the stratified combustion pulse width control point, and an injection flow rate error is determined.
[0024]
In step 3, the injection flow rate (homogeneous flow rate) at the homogeneous combustion pulse width control point is near the upper limit value, specifically, whether the injection flow rate error is in the range of + 0.5% to + 4.5%. Is determined.
In the case of YES, the process proceeds to step 4 to determine whether the injection flow rate (stratified flow rate) at the stratified combustion pulse width control point is near the upper limit value, specifically, whether the injection flow rate error is in the range of + 4% to + 12%. Determine whether or not. As a result, in the case of YES, "OK" is determined in step 5.
[0025]
In step 6, it is determined whether the injection flow rate (homogeneous flow rate) at the homogeneous combustion pulse width control point is near the median value, specifically, whether the injection flow rate error is in the range of −2% to + 2%. .
In the case of YES, the process proceeds to step 7, where the injection flow rate (stratification flow rate) at the stratified combustion pulse width control point is near the median value, specifically, the injection flow rate error is in the range of -4% to + 4%. It is determined whether or not. As a result, in the case of YES, "OK" is set in step 8.
[0026]
In step 9, whether the injection flow rate (homogeneous flow rate) at the homogeneous combustion pulse width control point is near the lower limit value, specifically, whether the injection flow rate error is in the range of -4.5% to -0.5% It is determined whether or not.
In the case of YES, the process proceeds to step 10 and determines whether or not the injection flow rate (stratified flow rate) at the stratified combustion pulse width control point is near the lower limit value, specifically, when the injection flow rate error is -12% to -4%. It is determined whether it is within the range. As a result, in the case of YES, "OK" is determined in step 11.
[0027]
If the value does not fall in any of the ranges, "NG" is set in step 12.
Based on this result, if "OK", it can be mounted on the engine, and if "NG", it is discarded.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a method of selecting a fuel injection valve according to the present invention. FIG. 2 is an explanatory diagram of linearity correction. FIG. 3 is an explanatory diagram of fuel injector drive current. FIG. 4 is a pulse width before and after linearity correction. FIG. 5 is a diagram showing a variation in injection flow rate characteristic. FIG. 5 is a diagram showing a variation in injection flow rate error after linearity correction. FIG. 6 is a diagram showing a range of OK.

Claims (2)

Measuring the injection flow rate of the fuel injection valve at a first predetermined pulse width in the homogeneous combustion region on the high load side that performs the air-fuel ratio feedback control;
With the second predetermined pulse width in the stratified combustion region on the low load side where the air-fuel ratio feedback control is not performed, the injection flow rate of the fuel injection valve is measured,
Regarding the injection flow rate at the first predetermined pulse width and the injection flow rate at the second predetermined pulse width,
(1) a range of a predetermined value to an upper limit in which the injection flow rate at the first predetermined pulse width is larger than the central value to a predetermined value to an upper limit value ;
(2) a predetermined range in which the injection flow rate at the first predetermined pulse width is around a median value, and an injection flow rate at a second predetermined pulse width is around a median value ;
(3) a range in which the injection flow rate at the first predetermined pulse width is smaller than the lower limit value to the median value , and a range of the injection flow rate at the second predetermined pulse width is smaller than the lower limit value to the median value ;
A fuel injection valve corresponding to any of the above, and mounting the fuel injection valve on a direct injection spark ignition type internal combustion engine. The first and second predetermined pulse widths are necessary to obtain predetermined required injection flow rates in the homogeneous combustion region and the stratified combustion region based on the basic pulse width-injection flow characteristics of the fuel injector. 2. The method for selecting a fuel injection valve according to claim 1, wherein the pulse width is set as an appropriate pulse width.

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