JP2003214243A - Fuel property determination device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fuel property determination device which accurately determines the properties of fuel based on the speed of an engine. <P>SOLUTION: A fuel is determined as a heavy one when a determining threshold at an engine speed of NE comprises two values (NE1>NE2) and NE during the idle operation immediately after the start of the engine is NE2 or below, and when NE2<NE<NE1 and an engine speed variation ΔNE is equal to or learger than the threshold ΔNE1. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel property judging device for judging the property of fuel used in an internal combustion engine, and more particularly to a fuel property judging device for making a judgment based on the engine speed of the internal combustion engine.

[0002]

2. Description of the Related Art A fuel having a certain property is not always used for an internal combustion engine, but a fuel having a property that is harder to volatilize than an ordinary fuel is sometimes used.
The latter is called heavy fuel, while the former is called light fuel. In such a heavy fuel, if lean combustion is performed at a low temperature, the combustion is likely to be unstable, and therefore combustion control for performing stable combustion is required. On the other hand, with light fuel, stable combustion can be continued even under the same conditions, and if the combustion control equivalent to that with heavy fuel is performed, the emission may deteriorate. Therefore, it is necessary to determine the property of the fuel to be used and switch the combustion control according to the determined property of the fuel.

As a method for judging the property of the fuel to be used, as disclosed in Japanese Patent Laid-Open No. 4-194348, a method of making a judgment based on the fluctuation of the engine speed in a transient state, or Japanese Patent Laid-Open No. 9- As disclosed in Japanese Patent No. 324676, there is known a method of making a determination based on a difference in engine speed before and after a change in fuel injection timing.

[0004]

All of the conventional methods determine the fuel property based on the engine speed, but the fuel property determination must be performed promptly after the engine is started. Immediately after that, the engine speed greatly changes depending on the friction state of the engine. Further, fluctuations in engine speed also occur due to variations among cylinders. Therefore, it is difficult for the conventional method to eliminate these influences and perform accurate fuel property determination.

Therefore, it is an object of the present invention to provide a fuel property determination device capable of accurately determining the fuel property based on the engine speed.

[0006]

In order to solve the above problems, a fuel property determining apparatus according to the present invention is a fuel property determining apparatus for determining the property of fuel on the basis of an idle engine speed immediately after starting of an internal combustion engine. In, there are two judgment threshold values for the engine speed, the engine speed is lower than any of the thresholds, the engine speed is between both thresholds, and the engine speed fluctuation is larger than the predetermined threshold. In this case, it is characterized as a heavy fuel.

According to the present invention, the threshold value for determining the engine speed is set to two values, and when the engine speed is between the two thresholds, the heavy fuel is used when the engine speed fluctuation is larger than the predetermined threshold value. Combustion is stable with light fuel by judging that,
There is no erroneous determination when the friction is large and the rotation speed is low. Further, when the engine speed is lower than any of the determination threshold values, it is determined that the fuel is heavy fuel, so that the engine stop due to unstable combustion when heavy fuel is used can be prevented in advance. As a result, it is possible to accurately determine the fuel property regardless of the friction state of the engine and the variation between the cylinders.

Alternatively, in the fuel property determination device according to the present invention, when the engine speed correction control is performed, the engine speed is lower than a predetermined threshold value, or the speed fluctuation is larger than the predetermined threshold value. In addition, it is characterized in that the fuel is determined to be heavy fuel in any case where the correction control amount of the engine speed is larger than a predetermined threshold value.

When the engine speed is controlled by feedback or the like, control works to keep the engine speed constant even in the case of heavy fuel. Therefore, it may not be determined that only the engine speed is the threshold value. , Heavy fuel cannot be accurately determined. According to the present invention, it is possible to make an accurate determination even when correction control is being performed, by determining that the fuel is heavy fuel when the engine speed fluctuation is large despite the large correction amount.

It is preferable to prohibit the fuel property determination while the engine is operating after the determination is completed. Although the engine speed temporarily decreases abruptly at the time of starting the clutch meet of an MT vehicle, by prohibiting the determination after the determination is completed, this state will not be erroneously determined as heavy fuel and will be accurate. The fuel property can be determined.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In order to facilitate understanding of the description, the same reference numerals are given to the same constituent elements in each drawing as much as possible in the drawings, and redundant description will be omitted.

FIG. 1 is a schematic configuration diagram of an internal combustion engine control system including a first embodiment of a fuel property determination device according to the present invention. In this embodiment, the fuel property determination unit 10 that determines the fuel property is an engine ECU that controls the engine 2.
1, which is a part of the engine 1, is connected to the engine 2, and outputs a signal in accordance with a rotation speed sensor 3 for detecting the rotation speed thereof, a throttle opening sensor 4 for detecting the throttle opening, and a rotation position of a crankshaft (not shown). The output of the crank angle sensor 5 that outputs is input. Here, the fuel property determination unit 10
It may be a part of hardware of the engine ECU 1 or a part of a program executed by the engine ECU 1 configured by a microcomputer or the like.

Before explaining the operation of the present embodiment, the determination principle of the fuel property determination in the present embodiment will be briefly described.
FIG. 2 is a diagram showing changes in the engine speed at the time of starting and immediately after the start depending on the fuel property and the state of the engine 2.

When the fuel is a heavy fuel, the combustion becomes more unstable than when it is a light fuel. Therefore, if the other conditions in the engine 2 are the same, the engine speed NE is small and the fluctuation of the engine speed is small. ΔNE becomes large. However, when the rotational friction (friction) of the engine 2 is large, for example, when the running-in operation of a new car is insufficient, when using highly viscous oil, or when a long time has passed since oil change, when using the same fuel However, the rotational speed NE may decrease. Further, when there is an abnormality in the fuel supply system or the supply / exhaust system, the rotation speed fluctuation ΔNE can be large.

For example, when a low-friction and light fuel is used, the fluctuation of the engine speed becomes as shown by the line A in FIG. 4, the drop from the peak of the engine speed is small, and the engine speed is higher than that of NE1. It remains almost constant. At the high friction and heavy fuel use, which is the opposite of this, the engine speed at peak time is lower than that at the time of light fuel use due to low friction, as shown by the line B, and the rotation speed after peak. The number rapidly drops from this peak rotational speed, becomes lower than NE2 (<NE1), and the rotational speed fluctuation becomes large. Further, if the combustion becomes unstable, the operation cannot be continued as shown by the line B ′, and the engine may stop.

Further, even when the light fuel is used, in the case of high friction, the rotational speed at the peak is smaller than that in the case of low friction as shown by the line C, and the rotational speed after the depression is NE1. Will be lower. Further, when uneven supply due to an abnormality in the fuel supply system or pulsation due to an abnormality in the supply / exhaust system occurs, the rotation fluctuation becomes large as indicated by the line C ′. When heavy fuel is used and the friction is low, as shown by the line D, the rotation speed at the peak is higher than that of the high friction, and then the rotation speed drops rapidly, but is kept higher than NE2. However, the rotation speed fluctuation is large.

From the various rotational speed fluctuations shown in FIG. 2, the present inventors differ as the threshold value for the idle rotational speed determination.
If the values (NE1, NE2) are used and the idle speed is between two values, the engine friction state can be determined by referring to the drop in the speed after peak and the fluctuation in the speed. The present inventors have found that accurate fuel normality determination can be performed regardless of whether or not there is an abnormality in the fuel supply system or the supply / exhaust system.

Next, the operation of this embodiment will be specifically described with reference to FIGS. 3 is a flow chart for explaining the fuel property determination operation, FIG. 4 is a flow chart for the rotational speed variation calculation processing, and FIG. 5 is a timing chart showing an example of engine rotational speed variation based on this operation. This control is repeatedly executed in the fuel property determination unit 10 inside the engine ECU 1 from engine start to successful determination.

First, in step S2, the elapsed time t _start after the engine is started is compared with the threshold value t _th1 . t _start
If is less than or equal to t _th1 , it means that the engine has just started,
Since the engine 2 is not in a stable state after reaching the peak speed, the determination process is not performed and the process ends. t _start
If t _th1 is _exceeded , the process _proceeds to step S4,
It is determined whether or not feedback (F / B) control is being performed. When the F / B control based on the output of the rotation speed sensor 3 is being performed, the fuel property determination described below cannot be performed, so the process ends. If the F / B control is not being performed, the process proceeds to step S6.

In step S6, a heavy fuel judgment flag is set.
Determine the value of flagX. In this embodiment, when the value of flagX is 1, it is determined that the fuel is a heavy fuel.
A value of 0 indicates that the fuel is not determined to be heavy fuel. When it is already determined that the fuel is heavy fuel and flagX is set to 1, the subsequent processing is skipped and the processing ends. On the other hand, if flagX is set to 0, the process proceeds to step S8.

In step S8, it is determined whether or not the engine is in the idle operation state. Specifically, based on the output of the throttle opening sensor 4, when the throttle opening is in the fully closed state, it is determined as the idle operation state. When the engine is not idling, that is, when the accelerator pedal is operated or the throttle is opened by the operation of the auxiliary machine, normal determination cannot be performed, and the subsequent processing is skipped and the process ends.

If it is determined in step S8 that the engine is idling, the process proceeds to step S10 and the output value NE of the engine speed sensor 3 is fetched. Then, in step S12, this NE is compared with the threshold value NE2. When NE falls below NE2 as indicated by the line B in FIGS. 2 and 5, it is determined that heavy fuel is being used, and step S
The processing shifts to 20, the flagX is set to 1 and the determination processing is ended. When flagX is 1, the engine ECU 1 switches the combustion control of the engine 2 to the combustion stabilization control adapted to heavy fuel. As a result of stable combustion, the engine speed is maintained at NE1 or higher as shown by the line B ₂ in FIG. 5, engine stop does not occur, and emission deterioration is suppressed.

If NE is equal to or more than NE2 in step S12, the process proceeds to step S14, and this time NE is performed.
And the threshold value NE1 are compared. If NE is equal to or greater than NE1 as indicated by line A in FIGS. 2 and 5, step S
Then, the processing shifts to 22, the flagX is set to 0, and the processing is terminated. Thus, when flagX is 0, the engine EC
U1 continues the combustion control of the engine 2 as the control matched to the light fuel.

If NE is less than NE1 in step S14, that is, if the relationship of NE2≤NE <NE1 is established, the process proceeds to step S16 and the rotation speed fluctuation Δ
It is determined whether the NE calculation is successful. The ΔNE calculation process is performed in parallel with this control process, and the process shown in FIG. 4 is performed.

First, in step S30, the elapsed time t _start after the engine is started and the threshold value t _th2 (t _th1 <t _th2 ) are compared. If t _start is equal to or less than t _th2 , it is considered that the engine has not been started for a long time, and the rotation speed fluctuation is not calculated, and the calculation process is not performed. The process proceeds to step S40 to clear the ΔNE value and perform the process. To finish. If t _start exceeds t _th1 , the process proceeds to step S32, and it is determined whether or not the engine is idling. If the engine is not in the idle operation, it is determined that the rotation speed fluctuation is not calculated, and the calculation process is not performed. Then, the process proceeds to step S40, the value of ΔNE is cleared, and the process ends. When the engine is idling, the process proceeds to step S34, and the time interval for each constant rotation of the crankshaft, for example, the time T180 required for half rotation is fetched from the output of the crank angle sensor 5. In a succeeding step S36, it is determined whether or not the predetermined n values of T180 have been fetched. If the number of captured data is less than n, it is determined that sufficient data has not been obtained to collect fluctuations in the number of revolutions, and the process ends without performing the calculation process. On the other hand, if the number of captured images reaches n, step S38.
The flow shifts to and the fluctuation value ΔNE of the rotation speed is calculated based on the latest n data, and the process ends.

If the calculation of ΔNE is not successful,
Of step S16 in the flow shown in FIG.
After that, the subsequent processing is skipped and the process ends. Successful calculation
If yes, go from step S16 to step S18
And transition. In step S18, ΔNE thus obtained
And the threshold ΔNE1 are compared. Rotation at the time of ΔNE detection
If the number fluctuations are large and ΔNE ≧ ΔNE1, it means that
Then, the fluctuation of the rotational speed as shown by the line D in FIGS. 2 and 5 is shown.
If so, move to step S20 and set flagX to 1
Is set and the determination process ends. As mentioned earlier, fl
When agX is 1, the engine ECU 1
Switching combustion control to combustion stabilization control that matches heavy fuel
Get This stabilizes combustion, resulting in engine speed
Is line D in FIG. ₂Maintained above NE1 as indicated by
As a result, emission deterioration is suppressed.

On the other hand, when the rotational speed fluctuation at the time of detecting ΔNE is small and ΔNE <ΔNE1, that is, when the rotational speed fluctuation shown by the line C or C ′ in FIGS. 2 and 5 is exhibited. , The process proceeds to step S22, 0 is set in flagX, and the process is terminated. In this way, when flagX is 0, the engine ECU 1 continues the combustion control of the engine 2 as control matched to the light fuel.

By controlling in this manner, the fuel property can be determined with high accuracy at the initial stage of engine startup regardless of the friction state of the engine 2 and the states of the air supply / exhaust system and the fuel supply system. , It is possible to suppress unstable combustion due to misjudgment of heavy fuel as light fuel, and conversely, to suppress deterioration of emission due to misjudgment of light fuel as heavy fuel, and always perform optimal combustion control. It can be performed.

Next, another mode of the control processing of this embodiment will be described. FIG. 6 is a flowchart showing this control processing, and FIG. 7 is a timing chart showing an example of engine speed variation based on this control processing.

The operation from the first step S2 to S10 is basically the same as the control flow shown in FIG. However, in this control, fl referred to in step S6a
agX takes -1 when it is judged as a light fuel, 1 when it is judged as a heavy fuel, and 0 when it is not judged yet. Therefore, the case where flagX is not 0 in step S6a refers to the case where it is already determined that the fuel is a light fuel or a heavy fuel. In this case, the subsequent processing is skipped and the processing ends. As a result, for example, it is determined that the drop in the engine speed at the time of starting the clutch meat of the MT vehicle as shown by the line A ′ in FIGS. 2 and 7 is the drop in the engine speed due to combustion instability due to heavy fuel. Therefore, it is possible to reliably prevent erroneous determination.

After the NE is loaded in step S10,
The process proceeds to step S11, and it is determined whether or not ΔNE has been calculated. This ΔNE calculation can be performed by the processing shown in FIG. When ΔNE is not calculated, the subsequent processing is skipped and the process ends. When ΔNE is calculated, the process proceeds to step S13, and ΔNE thus obtained is compared with a threshold ΔNE2 (a value smaller than the threshold ΔNE1 described above is taken). When ΔNE is smaller than ΔNE2 (corresponding to the line A ′ or the line C in FIG. 7), it indicates that the combustion is stable. Therefore, the process proceeds to step S22a, and flag X indicates that the fuel is light fuel. The value -1 is set, and the process ends. ΔNE is ΔN
If it is equal to or more than E2, the process proceeds to step S12 and the rotation speed NE and the threshold value NE2 are compared. If NE is less than NE2, it is determined that heavy fuel is being used, the process proceeds to step S20, flagX is set to 1, and the determination process ends.

If NE is NE2 or more, step S1
Then, the flow shifts to 4, and this time NE is compared with the threshold value NE1.
If NE is equal to or greater than NE1, the process proceeds to step S18, and ΔNE is compared with the threshold ΔNE1. When ΔNE is ΔNE1 or more and the rotation speed fluctuation is large (corresponding to the line D in FIG. 7), it is determined that the fuel is heavy fuel and the step S20 is performed.
Then, the flag X is set to 1 and the determination process is terminated. When ΔNE is smaller than ΔNE1 and the rotation speed fluctuation is small, the fuel is determined to be light fuel, the process proceeds to step S22a, flagX is set to -1, and the process ends.

Even when such a determination process is performed, the fuel property can be determined with high accuracy at the initial stage of engine startup regardless of the friction state of the engine 2, the state of the supply / exhaust system and the fuel supply system. Therefore, it is possible to suppress unstable combustion due to erroneous determination of heavy fuel as light fuel, and conversely, to suppress emission deterioration due to erroneous determination of light fuel as heavy fuel. Combustion control can be performed. Further, after the determination, another factor such as M
Even when the engine speed decreases due to the start of the clutch meet in the T car, erroneous determination can be suppressed without requiring a special measuring device or determination program, and reliable determination can be performed.

In the first embodiment, the fuel property cannot be judged during the fast idle speed F / B control. The second embodiment described below is for performing fuel property determination during the fast idle speed F / B control.

FIG. 8 is a schematic configuration diagram of an internal combustion engine control system including the second embodiment. The difference between this embodiment and the first embodiment shown in FIG. 1 is that the ISC shown in FIG.
(Idle Speed Control) The output value of the ISC valve opening sensor 6 for detecting the opening of the valve 60 is input. The ISC valve 60 is provided in a branch pipe 71 that is a temporary branch of the intake pipe 7.
A throttle valve 40 is arranged in the main pipe 70 which is parallel to the main pipe 1. In the idle state, the throttle valve 40 is set to the fully closed state. At this time, by adjusting the opening degree of the ISC valve 60, the amount of air passing through the branch pipe 71 is adjusted to F / B.
By adjusting by control, the engine speed during idle operation is maintained at a predetermined speed.

Next, the operation of this embodiment will be described with reference to FIGS.
It will be specifically described with reference to. FIG. 10 is a flowchart for explaining the fuel property determination operation, and FIG. 11 is a timing chart showing an example of engine speed variation based on this operation. This control is repeatedly executed in the fuel property determination unit 10 inside the engine ECU 1 from engine start to successful determination, and the basic operation is the same as the determination operation shown in FIG. Therefore, different parts will be mainly described, and the same parts will be omitted.

The difference between the operation shown in FIG. 10 and the operation shown in FIG. 3 is that the determination operation during the F / B control in step S4 is omitted, and steps S14 and S18 are respectively replaced. The point is that steps S15 and S19 are provided.

In step S12, the engine speed NE is N.
If it is equal to or more than E2, the process proceeds to step S15 in this control operation. Here, the opening θ _ISC of the ISC valve 60 detected by the ISC valve opening sensor 6 is compared with the threshold θ _th . When θ _{I SC} is equal to or less than the threshold value θ _th , it is determined that the amount of idle speed correction is small, that is, the fuel is a light fuel whose combustion state is stable even without correction, and the process proceeds to step S22. Migrate and flagX
Is set to 0 and the processing is ended. In this way, when flagX is 0, the engine ECU 1 continues the combustion control of the engine 2 as control matched to the light fuel.

On the other hand, if θ _ISC is above the threshold θ _th , the routine proceeds to step S16, where the rotational speed fluctuation ΔNE
It is determined whether or not is calculated successfully. Since the ΔNE calculation process has been described above, its description is omitted.

If the calculation of ΔNE is not successful,
The subsequent processing is skipped and the process ends. If the calculation is successful, the process proceeds to step S19. Step S
At 19, the calculated ΔNE is compared with the threshold ΔNE1 ′.
The rotation speed fluctuation at the time of ΔNE detection is large, and ΔNE ≧ ΔN
If it becomes E1 ', the rotation speed fluctuation is large even after correction, and combustion is unstable, that is, it is determined that the fuel is heavy fuel, and the routine proceeds to step S20, where fl
The agX is set to 1 and the determination process ends. In this case, the engine ECU 1 switches the combustion control of the engine 2 to the combustion stabilization control adapted to the heavy fuel.

On the other hand, when the fluctuation in the number of revolutions at the time of detecting ΔNE is small and ΔNE <ΔNE1, it is determined that the combustion is stabilized by the correction, that is, the case of the light fuel, and step S22 is performed. Then, the flag X is set to 0, and the process ends. Thus flagX is 0
In the case of, the engine ECU 1 continues the combustion control of the engine 2 as the control matched with the light fuel.

According to the determination control of the present embodiment, the engine speed NE is lower than NE2 by the fast idle speed F / B control, and the line B2 in FIG.
Engine speed N as a result of F / B control
Although the decrease in E is suppressed, the fuel property can be accurately determined even when the control amount is large and the rotation speed fluctuation is large, as shown by the line D3 in FIG.

Further, even during the determination operation, the control for stabilizing the engine speed at the time of idling can be performed by the F / B control, so that the combustion can be further stabilized, the deterioration of the emission can be suppressed, and the driver can be suppressed. The ability can be improved.

Here, ISC is used as a method for correcting ISC.
Although the example of changing the opening degree of the valve has been described, the method of controlling the ignition timing, the throttle valve 40 by the electronic throttle valve
Even if the correction amount is large in any of the method of changing the opening degree itself, the method of increasing the fuel amount, and the method of combining these, the rotation speed fluctuation is large, that is, the combustion is unstable even by the correction. In this case, it may be determined as heavy fuel.

The control processes described above are merely examples, and various modifications can be made to achieve the same purpose. For example, different flags may be used for the light fuel and the heavy fuel, and the calculation flow of the rotation speed fluctuation may be incorporated in the control processing flow.

[0046]

As described above, according to the present invention, two determination threshold values for the engine speed during idling are provided, and when the engine speed during idling is lower than either threshold,
And the engine speed exists between both thresholds, and if the engine speed fluctuation is larger than a predetermined threshold, it is judged as heavy fuel, and the engine friction condition, fuel supply system, supply / exhaust system condition It is possible to accurately determine the fuel property regardless of the above.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an internal combustion engine control system including a first embodiment of a fuel property determination device according to the present invention.

FIG. 2 is a diagram illustrating the determination principle of the fuel property determination of the present invention.

FIG. 3 is a flowchart illustrating a determination operation of the fuel property determination device of FIG.

FIG. 4 is a flowchart of a rotational speed variation calculation process of the fuel property determination device of FIG.

FIG. 5 is a timing chart showing an example of engine speed variation based on the processing of FIG.

6 is a flowchart illustrating another determination operation of the fuel property determination device of FIG.

7 is a timing chart showing an example of engine speed variation based on the process of FIG.

FIG. 8 is a schematic configuration diagram of an internal combustion engine control system including a second embodiment of a fuel property determination device according to the present invention.

FIG. 9 is a diagram illustrating an arrangement state of ISC valves.

10 is a flowchart illustrating a determination operation of the fuel property determination device of FIG.

11 is a timing chart showing an example of engine speed variation based on the processing of FIG.

[Explanation of symbols]

1 ... Engine ECU, 2 ... Engine, 3 ... Rotation speed sensor, 4 ... Throttle opening sensor, 5 ... Crank angle sensor, 6 ... ISC valve opening sensor, 7 ... Intake pipe, 10 ...
Fuel property determination unit, 60 ... ISC valve, 70 ... Main pipe, 7
1 ... Branch pipe.

Claims (3)

[Claims] 1. A fuel property determination device for determining the property of fuel based on an idle engine speed immediately after starting of an internal combustion engine, wherein a fuel property determination device has two determination threshold values for the engine speed, and the engine speed is any threshold value. A fuel property determination device characterized by determining that the fuel is a heavy fuel when the engine speed is lower than the threshold value, when the engine speed is between both threshold values, and when the engine speed fluctuation is larger than a predetermined threshold value. 2. A fuel property determination device for determining a property of fuel based on an idle engine speed immediately after starting of an internal combustion engine, wherein the engine speed is set to a predetermined value when engine speed correction control is performed. Fuel characterized by being judged to be heavy fuel when it is either lower than a threshold value or when the rotational speed fluctuation is larger than a predetermined threshold value and the engine speed correction control amount is larger than a predetermined threshold value. Property determination device. 3. The fuel property determination device according to claim 1, wherein fuel property determination is prohibited during engine operation after completion of the determination.