JP3873955B2 - Fuel property determination device for internal combustion engine - Google Patents

Description

  The present invention relates to an apparatus for determining the properties (heavy and light) of fuel used in an internal combustion engine.

In Patent Document 1, a rotational speed deviation is detected every predetermined cycle (for example, engine 1/2 rotation) after a predetermined cranking time (for example, cranking rotational speed 300 rpm), and the integrated value of the deviation is a predetermined value. It is described that, when the above is reached, the property (heavy or light) of the fuel used is determined based on whether or not the number of elapsed cycles up to that time is equal to or greater than a predetermined value.
JP-A-9-151777

However, as in Patent Document 1, if the fuel property is determined after a while after the first explosion, not only the feedback is delayed in time but also the determination accuracy may be lowered.
An object of the present invention is to make it possible to quickly and accurately determine the fuel properties at the time of starting.

In an internal combustion engine having a fuel injection valve for each cylinder in the intake passage, the present invention is such that the injected fuel adheres to the intake port as a wall flow within the first round from the start of fuel injection, and for heavy fuel with a low vaporization rate. Since a lot of fuel remains as a wall flow in the intake port, we paid attention to the difference in the amount of fuel flowing into the cylinder due to the difference in fuel properties, and a large difference in the rotational speed change (rise).
Therefore, the heavy / lightness of the fuel used is determined based on the degree of change in the rotational speed from the expansion stroke of the first fuel injection cylinder at the start to the expansion stroke of the last fuel injection cylinder in the first round. However, when starting in a high temperature state (during hot restart), it becomes difficult to make a difference, so heavy / light quality determination based on the degree of change in rotational speed is prohibited.

  According to the present invention, it is possible to accurately determine the heavy / lightness of the used fuel in a very short time until the fuel injection is completed at the time of starting, and it is possible to prevent erroneous determination by prohibiting the heavy / lightness determination at the time of hot restart.

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram of an internal combustion engine (hereinafter referred to as an engine) showing an embodiment of the present invention.
The combustion chamber 3 defined by the piston 2 of each cylinder of the engine 1 is provided with an intake valve 5 and an exhaust valve 6 so as to surround the spark plug 4. 7 is an intake passage and 8 is an exhaust passage.
A throttle valve 9 is provided in the intake passage 7 upstream of the intake manifold. The intake passage 7 is also provided with an electromagnetic fuel injection valve 10 for each cylinder at each branch portion (position facing the intake port on the cylinder head side) of the intake manifold. Fuel is injected.

  Here, the operation of the fuel injection valve 10 is controlled by an engine control unit (hereinafter referred to as ECU) 11, which outputs a crank angle signal in synchronism with a cam angle sensor 12 for cylinder discrimination and engine rotation. Thus, the crank angle sensor 13 capable of detecting the engine rotational speed Ne together with the crank angle position, the air flow meter 14 for detecting the intake air amount Qa upstream of the throttle valve 9 in the intake passage 7, and the water temperature sensor 15 for detecting the engine cooling water temperature Tw. The signal is input from the above.

  Regarding the control of the fuel injection of the fuel injection valve 10 by the ECU 11, the basic fuel injection amount Tp = K · Qa / Ne (K is a constant) is calculated based on the intake air amount Qa and the engine speed Ne, After correction, a final fuel injection amount Ti = Tp · COEF (COFF is various correction coefficients) is determined, and a drive pulse signal having a pulse width corresponding to Ti is set at a predetermined timing synchronized with engine rotation. Output to the fuel injection valve 10 to cause fuel injection.

Here, the various correction coefficients COEF include an increase correction coefficient (hereinafter referred to as an increase correction coefficient after start) KAS for increasing the fuel at the start and after the start, as shown in the following equation.
COEF = 1 + KAS + ...
Further, the post-startup increase correction coefficient KAS is calculated by the following equation.
KAS = MTKAS × TMKAS
MTKAS is a table value (water temperature increase rate) corresponding to the engine coolant temperature Tw, and is large when the water temperature is low, and decreases as the water temperature increases. Different tables are used for heavy fuel and light fuel. FIG. 2 is a schematic diagram of a water temperature increase rate (MTKAS) table. There is a large difference in the fuel vaporization rate between the heavy fuel and the light fuel at a low water temperature Tw, but the difference is reduced at a high water temperature Tw. Therefore, the increase rate MTKAS is set according to the water temperature Tw for each fuel as shown in the figure.

TMKAS is a table value (time correction coefficient) corresponding to the elapsed time after startup, and becomes smaller with the passage of time after startup.
The present invention provides a fuel property determination device for correcting the fuel injection amount based on the fuel property, such as switching the water temperature increase rate (MTKAS) table for setting the post-startup increase correction coefficient KAS as described above. To do.

The fuel property determination device according to the present invention is realized by executing a predetermined program in the ECU 12, and will be described below according to a flowchart.
FIG. 3 is a flowchart of a fuel property determination routine. Note that this embodiment is a four-cylinder engine.
In S1, it is determined whether or not the engine is started at a high temperature (hot restart). Specifically, the coolant temperature Tw immediately before the start is detected, and it is determined whether or not it is a hot restart depending on whether or not this is a predetermined value Twh or more. As long as it represents the engine temperature, fuel temperature, oil temperature, or the like may be used instead of the cooling water temperature Tw. Alternatively, the engine stop time before the start (the time from the previous engine stop to the current start) may be measured, and whether or not the hot restart is performed may be determined based on whether or not the engine stop time is equal to or less than a predetermined value.

In the case of a hot restart, heavy / light quality determination based on the degree of change in the rotation speed is prohibited, and the processing is terminated assuming that heavy / light quality determination is impossible.
If it is not during hot restart, the process proceeds to S2.
In S2, the initial injection cylinder is determined. That is, for fuel injection control by cylinder, cylinder discrimination is performed to determine which stroke each cylinder is in, and fuel injection to each cylinder is performed according to the cylinder discrimination result. Cylinders (cylinders that perform the fuel injection first and reach the expansion stroke first) are determined. Normally, fuel injection is performed in the exhaust stroke of each cylinder. However, for faster start-up, fuel injection is performed in the intake stroke for the first injection cylinder. Fuel injection into the injection cylinder is performed simultaneously.

When the initial injection cylinder (cylinder that first performs fuel injection and reaches the expansion stroke first) is determined, Nc indicating the number of cylinders from the first fuel injection cylinder is set to 1, and the process proceeds to S3.
In S3, the angular velocity ω1 (deg / s) at the time of compression top dead center (TDC) is detected for the first injection cylinder (Nc = 1). That is, the angular velocity ω is detected at the time of compression TDC, and this is set as the angular velocity ω1 at the time of compression TDC.

In S4, the maximum angular velocity ω2 (deg / s) in the expansion stroke is detected for the first injection cylinder (Nc = 1).
Specifically, the calculation is performed by a subroutine shown in FIG. The subroutine of FIG. 4 is executed after the angular velocity ω1 at the time of compression top dead center (TDC) is detected. After initializing ωmax in S31 (ωmax = 0), in S32, for example, at a sampling interval of every 10 ° crank angle. The angular velocity ω is detected. Then, ω detected in S33 is compared with ωmax, and when ω> ωmax, ωmax is updated with ωmax = ω in S34. In S35, it is determined whether or not the vicinity of the bottom dead center (BDC) at which the expansion stroke ends is reached. If not, the process returns to S32 and sampling is continued. When it reaches the vicinity of BDC, the process proceeds to S36, and the current ωmax is set to the expansion stroke maximum angular velocity ω2.

In addition to detecting the maximum angular velocity in the expansion stroke, as a value near the maximum angular velocity in the expansion stroke, the angular velocity near the middle position of the expansion stroke is detected, or the angular velocity near the bottom dead center (BDC) of the expansion stroke is determined. You may make it detect.
In S5, angular acceleration Δω = ω2−ω1 is calculated from the compression TDC angular velocity ω1 and the expansion stroke maximum angular velocity ω2. More accurately, the angular acceleration Δω = (ω2−ω1) / dt may be calculated. dt is the time from the detection of ω1 to the detection of ω2.

In S6, the first explosion determination is performed. The initial explosion determination is made based on a comparison between the angular acceleration Δω that is the degree of change in the rotational speed of each cylinder and a predetermined threshold value ΔωS, and when Δω ≧ ΔωS, the initial explosion is determined.
When the initial explosion determination is not made (when Δω <ΔωS), the process proceeds to S7.
In S7, it is determined whether or not Nc = 4 (the fourth injection cylinder from the first injection cylinder, that is, the last injection cylinder in the case of four cylinders). If NO, the number of cylinders Nc is increased by 1 in S8. By executing S3 to S5, the angular acceleration Δω is calculated from the compression TDC angular velocity ω1 and the expansion stroke maximum angular velocity ω2 for the next cylinder, and the initial explosion determination is performed again in S6.

Even if the initial explosion determination is repeated from Nc = 1 to Nc = 4, it is not determined as the initial explosion. If the determination at S7 is Nc = 4, that is, even if the first round is completed, the initial explosion determination is not made. If not, it is determined that heavy / lightness determination is impossible, and the process ends. At this time, the reason why the first explosion is not reached within the first round is that the fuel vaporization rate is low, and it may be determined that the fuel is heavy.
If the initial explosion determination is made within the first round in S6, the process proceeds to S9.

In S9, the angular acceleration Δω, which is the degree of change in rotational speed for each cylinder, calculated in S5 (or S14 described later) is compared with a predetermined threshold value ΔωL (> ΔωS), and Δω ≧ ΔωL. It is determined whether or not.
If Δω <ΔωL, the process proceeds to S10.
In S10, it is determined whether or not Nc = 4 (the fourth injection cylinder from the first injection cylinder, that is, the last injection cylinder in the case of four cylinders). If NO, the cylinder number Nc is increased by 1 in S11. As in S3 to S5, by executing S12 to S14, the angular acceleration Δω is calculated from the angular velocity ω1 at the time of compression TDC and the maximum angular velocity ω2 at the expansion stroke for the next cylinder, and Δω ≧ ΔωL again in S9. Determine whether or not.

As a result, if Δω ≧ ΔωL is satisfied in the first round in the determination in S9, the process proceeds to S15 at that time, and it is determined that the light is light, and the process is terminated.
In contrast, if Δc <ΔωL for any cylinder in the determination in S9 and Nc = 4 in the determination in S10, that is, if Δω ≧ ΔωL is not satisfied within the first round, S10 The process proceeds from step S16 to step S16, and the process is terminated.

FIG. 5A shows the change in the angular velocity ω (deg / s) with the horizontal axis representing the crank angle from the start of the second expansion stroke to the end of the sixth expansion stroke in terms of the number of expansion strokes after cylinder discrimination. An example is shown.
FIG. 5 (b) shows the number of expansion strokes after cylinder discrimination as the horizontal axis corresponding to the horizontal axis of FIG. 5 (a), and for each cylinder calculated from the change in angular velocity ω of FIG. 5 (a) ( The angular acceleration Δω (deg / s2) for each expansion stroke) is shown.

In FIGS. 5A and 5B, the solid line represents the case of heavy fuel, and the dotted line represents the case of light fuel.
In this example, the cylinder with the number of expansion strokes of 3 is the initial injection cylinder. In any case, angular acceleration Δω = (ω2−) calculated from the compression TDC angular velocity ω1 and the expansion stroke maximum angular velocity (angular velocity at the intermediate position of the expansion stroke) ω2 in the first injection cylinder (expansion stroke number 3). The first explosion is determined based on the determination based on ω1) / dt. In the case of light fuel, at the same time as the initial explosion determination, Δω ≧ ΔωL, and it is determined that the fuel is light. In the case of heavy fuel, Δω ≧ ΔωL is not satisfied within the first round (3 to 6 in the number of expansion strokes), and it is determined that the fuel is heavy.

FIG. 6 is a flowchart of a fuel injection amount control heavy / light setting routine for performing heavy setting or light setting for fuel injection amount control using the fuel property determination according to the present invention, which is executed simultaneously with the engine key switch being turned on. The
In S101, heavy setting is performed as an initial setting. As a result, the heavy fuel table of the light fuel table and the heavy fuel table shown in FIG. 2 is used. This is because if heavy fuel is used and the lightness is set, startability deteriorates.

In S102, it is determined whether or not the heavy / lightness determination (fuel property determination routine in FIG. 3) is completed, and the process proceeds to S103 after waiting for the determination.
In S103, the process branches based on the result of the heavy / lightness determination. If it is determined to be heavy, it is not necessary to change the initial setting, and the process ends. If it is determined to be light, change to the light setting. As a result, the light fuel table of the light fuel table and the heavy fuel table in FIG. 2 is used, and fuel efficiency can be improved. If it is heavy or light indefinite (YES in S1 in FIG. 3 or YES in S7 and processing is terminated), the initial setting (heavy setting) is focused on starting performance and stability after starting. The processing is terminated as it is.

Accordingly, when heavy / lightness determination is prohibited during hot restart, the initial setting (heavy setting) remains unchanged.
According to the present embodiment, in an engine having a fuel injection valve for each cylinder in the intake passage, the intake port is not wet and the injected fuel flows through the wall flow within the first round from the first fuel injection cylinder at the start. In view of the fact that a heavy fuel with a low vaporization rate remains as a wall flow in the intake port, a difference in the amount of fuel flowing into the cylinder appears, and a large difference appears in the rotational speed change degree (the degree of increase) Based on the degree of change in the rotational speed from the expansion stroke of the first fuel injection cylinder to the expansion stroke of the last fuel injection cylinder in the first round, the fuel injection is completed during the start-up by determining the heavy and light fuel used. It is possible to accurately determine the heavy and lightness of the fuel used in a very short time.

On the other hand, at the time of hot restart, the difference in the rotational speed change due to the difference in the fuel properties becomes difficult to occur, so that the misjudgment can be prevented by prohibiting the heavy / light judgment. In addition, it can be easily determined whether it is at the time of hot restart by determining based on the cooling water temperature or the like or based on the engine stop time before starting.
Further, according to the present embodiment, the degree of change in the rotational speed is the angular velocity ω1 at the start of the expansion stroke (in the vicinity of the compression top dead center) and the maximum angular velocity in the expansion stroke (or a value in the vicinity thereof) for at least one cylinder. ) By calculating based on the difference (ω2−ω1) from ω2, it is possible to accurately grasp the degree of change in rotational speed. The detection can be facilitated by detecting the angular velocity near the intermediate position of the expansion stroke or the angular velocity near the bottom dead center of the expansion stroke as the value near the maximum angular velocity in the expansion stroke. In particular, if an angular velocity near the middle position of the expansion stroke is used, detection is easy because the absolute difference is large. If the angular velocity near the bottom dead center of the expansion stroke is used, the work amount of the expansion stroke can be detected stably.

In addition, according to the present embodiment, the determination can be easily made by determining the lightness and lightness by comparing with a predetermined threshold value (ΔωL) of the degree of change in rotational speed.
Further, according to the present embodiment, the rotational speed change degree is calculated for each cylinder, and can be determined with higher accuracy by repeatedly comparing the rotational speed change degree obtained for each cylinder with a threshold value.

Further, according to the present embodiment, when the degree of change in the rotational speed of any cylinder in the first round exceeds the threshold value, it can be determined more quickly by determining that it is light.
Further, according to the present embodiment, when the degree of change in the rotational speed of all the cylinders in the first round does not exceed the threshold value, it can be determined with high accuracy by determining that it is heavy.
In addition, according to the present embodiment, when the initial explosion determination is performed and the initial explosion determination is not made within the first round, the erroneous determination can be prevented by prohibiting the heavy / light determination based on the rotational speed change degree. it can.

Further, according to the present embodiment, the initial explosion determination is performed based on a comparison between the rotation speed change degree for each cylinder and the second threshold value (ΔωS) of the predetermined rotation speed change degree. The first explosion determination can be executed using the same parameters as the heavy / light determination.
In the embodiment described above, the rotational speed change degree is compared with a predetermined threshold value (ΔωL) to determine whether it is heavy or light. Depending on the level, the degree of heavy / lightness may be determined (calculated).

Engine system diagram showing an embodiment of the present invention Schematic diagram of water temperature increase rate table Flow chart of fuel property determination routine Flow chart of expansion stroke maximum angular velocity detection subroutine The figure which shows the change of angular velocity and angular acceleration with respect to the number of expansion strokes after cylinder discrimination Flow chart of heavy / lightness setting routine for fuel injection amount control

Explanation of symbols

1 engine
7 Intake passage
10 Fuel injection valve
11 ECU
12 Cam angle sensor
13 Crank angle sensor
15 Water temperature sensor

Claims (12)

In an internal combustion engine having a fuel injection valve for each cylinder in the intake passage,
While determining the heavy and light of the fuel used based on the degree of change in rotational speed from the expansion stroke of the first fuel injection cylinder at the start to the expansion stroke of the last fuel injection cylinder of the first round,
A fuel property determination device for an internal combustion engine, which prohibits heavy / lightness determination based on the degree of change in rotational speed when starting in a high temperature state.   The rotational speed change degree is calculated based on a difference between an angular velocity at the start of the expansion stroke and a maximum angular velocity in the expansion stroke or a value in the vicinity thereof for at least one cylinder. A fuel property determination device for an internal combustion engine.   3. The fuel property determination apparatus for an internal combustion engine according to claim 2, wherein an angular velocity in the vicinity of an intermediate position in the expansion stroke is detected as a value in the vicinity of the maximum angular velocity in the expansion stroke.   3. The fuel property determination apparatus for an internal combustion engine according to claim 2, wherein an angular velocity in the vicinity of the bottom dead center of the expansion stroke is detected as a value in the vicinity of the maximum angular velocity in the expansion stroke.   The fuel property determination device for an internal combustion engine according to any one of claims 1 to 4, wherein heavy or light is determined by comparison with a predetermined threshold value of a rotational speed change degree.   6. The fuel property determination apparatus for an internal combustion engine according to claim 5, wherein the rotation speed change degree is calculated for each cylinder, and the comparison between the rotation speed change degree obtained for each cylinder and a threshold value is repeated.   7. The fuel property determining apparatus for an internal combustion engine according to claim 6, wherein when the degree of change in rotational speed of any cylinder in the first round exceeds a threshold value, the fuel property is determined to be light.   8. The fuel property determining apparatus for an internal combustion engine according to claim 6, wherein when the degree of change in rotational speed of all the cylinders in the first round does not exceed a threshold value, the fuel property is determined to be heavy.   The first and second explosion determination is performed, and if the first explosion determination is not made within the first round, the heavy and light determination based on the rotation speed change degree is prohibited. An internal combustion engine fuel property determination device.   10. The fuel for an internal combustion engine according to claim 9, wherein the initial explosion determination is made based on a comparison between a rotational speed change degree for each cylinder and a second threshold value of a predetermined rotational speed change degree. Property determination device.   The internal combustion engine fuel property determination apparatus according to any one of claims 1 to 10, wherein the start-up in a high-temperature state is detected when the coolant temperature at the start-up is equal to or higher than a predetermined value. .   11. The fuel property of the internal combustion engine according to claim 1, wherein when the engine is started in a high temperature state, the engine stop time before the engine start is detected to be a predetermined value or less. Judgment device.

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