JP4010149B2 - Fuel property determination device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel property determination device that determines the property of fuel used in an internal combustion engine, and more particularly to a fuel property determination device that makes a determination based on the engine speed of the internal combustion engine.
[0002]
[Prior art]
A fuel having a certain property is not necessarily used for an internal combustion engine, and a fuel having a property of being less volatile than a normal fuel may be used. The latter is called heavy fuel, while the former is called light fuel. In such heavy fuels, when lean combustion is performed at low temperature, combustion tends to become unstable, and thus combustion control is necessary to perform stable combustion. On the other hand, light fuel can continue stable combustion even under the same conditions, and rather, emission control may deteriorate if combustion control equivalent to that of heavy fuel is performed. Therefore, it is necessary to switch the combustion control according to the determined fuel property by determining the property of the fuel to be used.
[0003]
As a method for determining the properties of the fuel to be used, as disclosed in Japanese Patent Application Laid-Open No. 4-194348, a method for determining based on fluctuations in engine speed in a transient state, or Japanese Patent Application Laid-Open No. 9-324676. As disclosed in Japanese Patent Application Laid-Open No. H11-209, 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]
[Problems to be solved by the invention]
All of the conventional methods determine the fuel properties based on the engine speed, but the fuel properties need to be determined promptly after the engine is started. It varies greatly depending on the friction state. Further, fluctuations in engine speed are also caused by variations between cylinders. Therefore, with the conventional method, it is difficult to accurately determine the fuel properties by eliminating these effects.
[0005]
Accordingly, an object of the present invention is to provide a fuel property determination device capable of performing accurate fuel property determination based on the engine speed.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, a fuel property determination device according to the present invention is a fuel property determination device that determines the property of a fuel based on an idle engine speed immediately after the start of the internal combustion engine. It is determined that the fuel is heavy when there are binary values and the engine speed is lower than any of the threshold values, and when the engine speed is between both threshold values and the engine speed fluctuation is greater than a predetermined threshold value. It is characterized by.
[0007]
According to the present invention, when the engine speed determination threshold value is set to two values and the engine speed is between the two threshold values, the heavy fuel is determined when the engine speed fluctuation is larger than the predetermined threshold value. Thus, although the combustion is stable with the light fuel, there is no erroneous determination when the friction is large and the rotational 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. As a result, accurate fuel property determination can be performed regardless of the friction state of the engine and the variation between cylinders.
[0010]
It is preferable to prohibit fuel property determination during engine operation after completion of determination. When starting an MT car at the time of clutch meet, the engine speed temporarily decreases temporarily. By prohibiting the determination after the determination is once completed, this state is not erroneously determined as heavy fuel and accurate. Fuel property can be judged.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings. In order to facilitate the understanding of the description, the same reference numerals are given to the same components in the drawings as much as possible, and duplicate descriptions are omitted.
[0012]
FIG. 1 is a schematic configuration diagram of an internal combustion engine control system including a first embodiment of a fuel property determination apparatus according to the present invention. In this embodiment, the fuel property determination unit 10 that determines the fuel property is a part of the engine ECU 1 that controls the engine 2. The fuel property determination unit 10 is connected to the engine 2 and detects the rotation speed and the throttle sensor 3. The outputs of a throttle opening sensor 4 that detects the opening and a crank angle sensor 5 that outputs a signal according to the rotational position of a crankshaft (not shown) are input. Here, the fuel property determination unit 10 may be a part of the hardware of the engine ECU 1 or may be a part of a program executed by the engine ECU 1 configured by a microcomputer or the like.
[0013]
Before describing 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 graph showing fluctuations in the engine speed at the start and immediately after the start depending on the fuel properties and the state of the engine 2.
[0014]
If the fuel is heavy fuel, combustion becomes unstable compared to the case of light fuel. Therefore, if the other conditions in the engine 2 are the same, the engine speed NE is small and the engine speed fluctuation ΔNE is large. Become. However, when the rotational friction (friction) of the engine 2 is large, for example, when the running-in operation of a new car or the like is insufficient, when using highly viscous oil, when a long time has passed since oil change, etc., when using the same fuel However, the rotational speed NE can be reduced. Further, when there is an abnormality in the fuel supply system or the supply / exhaust system, the rotational speed fluctuation ΔNE can be large.
[0015]
For example, when light fuel is used with low friction, the fluctuation of the engine speed becomes as shown by line A in FIG. 4, and the drop from the peak of the engine speed is small, and it remains almost constant at an engine speed higher than NE1. Maintained. When heavy fuel is used with high friction, which is the opposite of the above, the engine speed is lower than that when using light fuel with low friction as shown by line B. The number drops rapidly from this peak rotational speed, becomes lower than NE2 (<NE1), and the rotational speed fluctuation increases. Further, when combustion becomes unstable, the operation cannot be continued as indicated by the line B ′, and the engine may stop.
[0016]
Even when light fuel is used, when the friction is high, as shown by the line C, the rotational speed at the peak time is smaller than that when the friction is low, and the rotational speed after falling is lower than NE1. . Further, when supply unevenness due to abnormality in the fuel supply system or pulsation due to abnormality in the supply / exhaust system occurs, the rotational fluctuation increases as shown by the line C ′. When using heavy fuel and low friction, as indicated by line D, the peak speed is higher than that of high friction, and then the speed decreases rapidly but remains higher than NE2. However, the rotational speed fluctuation is large.
[0017]
From the various rotational speed fluctuations shown in FIG. 2, the present inventors use different binary values (NE1, NE2) as the threshold values for determining the idle rotational speed, and when the idle rotational speed exists between the two values. If the judgment is made by referring to the drop in the engine speed after the peak time and the engine speed fluctuation, it is possible to make an accurate fuel normal judgment regardless of the engine's friction status, fuel supply system, and supply / exhaust system abnormality. And found the present invention.
[0018]
Next, the operation of the present embodiment will be specifically described with reference to FIGS. FIG. 3 is a flowchart for explaining the fuel property determination operation, FIG. 4 is a flowchart of the rotation speed fluctuation calculation process, and FIG. 5 is a timing chart showing an example of the engine speed fluctuation based on this operation. This control is repeatedly executed in the fuel property determination unit 10 in the engine ECU 1 from the engine start to the determination success.
[0019]
First, in step S2, an elapsed time t _start after the engine is started and a threshold value t _th1 are compared. When t _start is equal to or less than t _th1, it is immediately after the engine is started, and it is determined that the engine 2 is not in a stable state after reaching the peak, so that the determination process is not performed and the process is terminated. If t _start exceeds t _th1 , the process _proceeds to step S4 to determine whether feedback (F / B) control is being performed. When the F / B control based on the output of the rotational speed sensor 3 is being performed, the fuel property determination described below cannot be performed, and thus the process is terminated. If the F / B control is not being performed, the process proceeds to step S6.
[0020]
In step S6, the value of the heavy fuel determination flag flagX is determined. In this embodiment, when the value of flagX is 1, it indicates that the fuel is already determined as heavy fuel, and when the value of flagX is 0, it indicates the case where the fuel is not determined as heavy fuel. If it is already determined that the fuel is heavy and 1 is set in flagX, the subsequent process is skipped and the process is terminated. On the other hand, if 0 is set in flagX, the process proceeds to step S8.
[0021]
In step S8, it is determined whether or not the engine is idling. Specifically, based on the output of the throttle opening sensor 4, the case where the throttle opening is in the fully closed state is determined as the idle operation state. When the idling operation is not being performed, that is, when the accelerator pedal operation is performed or the throttle is opened by the operation of the auxiliary device, normal determination cannot be performed, so that the subsequent processing is skipped and the processing ends.
[0022]
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 captured. In step S12, this NE is compared with the threshold value NE2. As shown by line B in FIG. 2 and FIG. 5, when NE falls below NE2, it is determined that heavy fuel is being used, and the process proceeds to step S20 to determine by setting flagX to 1 The process ends. When flagX is 1, the engine ECU 1 switches the combustion control of the engine 2 to the combustion stability control that matches the heavy fuel. The results thereby combustion is stabilized, the engine speed is maintained at NE1 above as indicated by line B ₂ in FIG. 5, not the engine stop or the like occurs, deterioration of emissions is suppressed.
[0023]
If NE is greater than or equal to NE2 in step S12, the process proceeds to step S14, where NE is compared with threshold NE1. If NE is equal to or greater than NE1 as indicated by line A in FIGS. 2 and 5, the process proceeds to step S22, 0 is set in flagX, and the process ends. In this way, when flagX is 0, the engine ECU 1 continues the combustion control of the engine 2 as a control that matches the light fuel.
[0024]
If NE is less than NE1 in step S14, that is, if the relationship NE2 ≦ NE <NE1 is established, the process proceeds to step S16 to determine whether the calculation of the rotational speed fluctuation ΔNE is successful. . The ΔNE calculation process is performed in parallel with the present control process, and a process as shown in FIG. 4 is performed.
[0025]
First, in step S30, an elapsed time t _start after engine start is compared with a threshold value t _th2 (t _th1 <t _th2 ). If t _start is equal to or less than t _th2 , the calculation process is not performed assuming that the engine speed has not started and the engine speed fluctuation is not calculated, and the process proceeds to step S40 to clear the value of ΔNE. Exit. If t _start exceeds t _th1 , the process proceeds to step S32 to determine whether or not the idling operation is being performed. If the idling operation is not being performed, the calculation process is not performed on the assumption that the rotational speed fluctuation is not calculated, 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 every fixed rotation of the crankshaft, for example, the time T180 required for half rotation is taken from the output of the crank angle sensor 5. In the next step S36, it is determined whether or not predetermined n values of T180 have been fetched. If less than n are captured, it is determined that sufficient data is not obtained to collect the rotational speed fluctuation, and the process is terminated without performing the calculation process. On the other hand, if n has been acquired, the process proceeds to step S38, where the fluctuation value ΔNE of the rotational speed is calculated based on the latest n pieces of data, and the process ends.
[0026]
If the calculation of ΔNE is not successful, after step S16 in the flow shown in FIG. 3, the subsequent process is skipped and the process ends. If the calculation is successful, the process proceeds from step S16 to step S18. In step S18, ΔNE thus obtained is compared with threshold value ΔNE1. When the rotational speed fluctuation at the time of detecting ΔNE is large and ΔNE ≧ ΔNE1, that is, when the rotational speed fluctuation as shown by the line D in FIGS. 2 and 5 is shown, the process proceeds to step S20. Set flagX to 1 to finish the determination process. As described above, when flagX is 1, the engine ECU 1 switches the combustion control of the engine 2 to the combustion stability control that matches the heavy fuel. The results thereby combustion is stabilized, the engine rotational speed is maintained as the NE1 above indicated by line D ₂ in FIG. 5, the deterioration of emissions is suppressed.
[0027]
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 as shown by the line C or C ′ in FIGS. 2 and 5 is shown, The process proceeds to step S22, in which 0 is set in flagX, and the process ends. In this way, when flagX is 0, the engine ECU 1 continues the combustion control of the engine 2 as a control that matches the light fuel.
[0028]
By controlling in this way, the fuel property can be determined with high accuracy at the initial stage of the engine start regardless of the friction state of the engine 2, the state of the supply / exhaust system or the fuel supply system. It is possible to suppress the occurrence of unstable combustion due to misjudgment of fuel as light fuel, and conversely to suppress emission deterioration due to misjudgment of light fuel as heavy fuel, and always perform optimum combustion control. Can do.
[0029]
Next, another form of the control process of this embodiment will be described. FIG. 6 is a flowchart showing this control process, and FIG. 7 is a timing chart showing an example of engine speed fluctuation based on this control process.
[0030]
The operation from the first step S2 to S10 is basically the same as the control flow shown in FIG. However, in this control, flagX referred to in step S6a is -1 when it is determined as light fuel, 1 when it is determined as heavy fuel, and 0 when it is not determined. Therefore, the case where flagX is not 0 in step S6a refers to the case where it is already determined that the fuel is light or heavy, and in this case, the subsequent processing is skipped and the processing is terminated. Thus, for example, a decrease in engine speed at the start of a clutch meet of an MT vehicle as indicated by a line A ′ in FIGS. 2 and 7 is determined as a decrease in the engine speed due to heavy fuel instability. And erroneous determination can be reliably prevented.
[0031]
After NE is captured in step S10, the process proceeds to step S11, and it is determined whether ΔNE has been calculated. This ΔNE calculation can be performed by the processing shown in FIG. If ΔNE has not been 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 value ΔNE2 (takes a value smaller than the above-described threshold value ΔNE1). If ΔNE is smaller than ΔNE2 (corresponding to line A ′ or line C in FIG. 7), it indicates that combustion is stable, so that the process proceeds to step S22a and flagX is light fuel. -1 shown is set and the process is terminated. If ΔNE is greater than or equal to ΔNE2, the process proceeds to step S12, and the rotational speed NE is compared with the threshold value NE2. When NE falls below NE2, it is determined that heavy fuel is used, the process proceeds to step S20, 1 is set in flagX, and the determination process ends.
[0032]
If NE is greater than or equal to NE2, the process proceeds to step S14, where NE is compared with threshold NE1. If NE is greater than or equal to NE1, the process proceeds to step S18, where ΔNE is compared with threshold value ΔNE1. If ΔNE is equal to or greater than ΔNE1 and the rotational speed fluctuation is large (corresponding to line D in FIG. 7), it is determined that the fuel is heavy, and the process proceeds to step S20. To do. When ΔNE is smaller than ΔNE1 and the rotational speed fluctuation is small, it is determined that the fuel is light, the process proceeds to step S22a, −1 is set in flagX, and the process is terminated.
[0033]
Even when such a determination process is performed, the fuel property can be determined with high accuracy at the initial stage of the engine start regardless of the friction state of the engine 2, the supply / exhaust system and the fuel supply system. It is possible to suppress the occurrence of unstable combustion due to misjudgment of heavy fuel as light fuel, and conversely the emission deterioration due to misjudgment of light fuel as heavy fuel. It can be carried out. Furthermore, even if another factor after the determination, for example, a decrease in the engine speed due to the start of clutch meet in the MT car, erroneous determination can be suppressed without requiring a special measuring device or determination program, and a reliable determination can be made. Yes.
[0034]
In the first embodiment, fuel property determination cannot be performed during the first idle speed F / B control. In the second embodiment described below, fuel property determination is performed during the first idle speed F / B control.
[0035]
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 output value of the ISC valve opening sensor 6 that detects the opening of the ISC (idle speed control) valve 60 shown in FIG. It is a point. The ISC valve 60 is provided in a branch pipe 71 that temporarily branches the intake pipe 7, and a throttle valve 40 is disposed in a main pipe 70 that is parallel to the branch pipe 71. In the idle state, the throttle valve 40 is set to a fully closed state. At this time, by adjusting the opening of the ISC valve 60 and adjusting the amount of air passing through the branch pipe 71 by F / B control, the engine speed during idling is maintained at a predetermined speed. is there.
[0036]
Next, the operation of the present embodiment will be specifically described with reference to FIGS. 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 fluctuation based on this operation. This control is repeatedly executed in the fuel property determination unit 10 in the engine ECU 1 from the engine start to the determination success, 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.
[0037]
The difference between the operation shown in FIG. 10 and the operation shown in FIG. 3 is that the determination operation during F / B control in step S4 is omitted, and steps S15 and S18 are replaced with steps S15 and S18, respectively. S19 is provided.
[0038]
If the engine speed NE is greater than or equal to NE2 in step S12, 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 . If θ _ISC is equal to or less than the threshold θ _th , it is determined that the idle speed correction amount is small, that is, it is a light fuel with a stable combustion state without correction, and the routine proceeds to step S22. Then, 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 a control that matches the light fuel.
[0039]
On the other hand, if θ _ISC exceeds the threshold θ _th , the process proceeds to step S16 to determine whether or not the calculation of the rotational speed variation ΔNE is successful. Since the ΔNE calculation process has been described above, a description thereof will be omitted.
[0040]
If the calculation of ΔNE is not successful, the subsequent process is skipped and the process ends. If the calculation is successful, the process proceeds to step S19. In step S19, the obtained ΔNE is compared with the threshold value ΔNE1 ′. If the rotational speed fluctuation at the time of detecting ΔNE is large and ΔNE ≧ ΔNE1 ′, the rotational speed fluctuation is large even if correction is performed, and the combustion is unstable, that is, the fuel is heavy. Determination is made, the process proceeds to step S20, 1 is set in flagX, and the determination process ends. In this case, the engine ECU 1 switches the combustion control of the engine 2 to the combustion stability control that matches the heavy fuel.
[0041]
On the other hand, if the rotational speed fluctuation 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 light fuel, and the process proceeds to step S22. Then, 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 a control that matches the light fuel.
[0042]
According to the determination control of the present embodiment, the engine rotation speed NE is also decreased by the first idle rotation speed F / B control, and the engine rotation speed NE is shown by the line B2 in FIG. Although the decrease in the number NE is suppressed, the fuel property can be accurately determined even in the case shown by the line D3 in FIG.
[0043]
And even during the determination operation, the engine speed during idling can be controlled by F / B control, so that combustion can be made more stable, emission deterioration can be suppressed, and drivability can be improved. Can be improved.
[0044]
Here, an example of changing the opening of the ISC valve as an ISC correction method has been described. However, a method of controlling the ignition timing, a method of changing the opening of the throttle valve 40 using an electronic throttle valve, and a method of increasing the fuel In addition, in any of the methods combining these methods, the heavy fuel may be determined when the fluctuation in the rotational speed is large even when the correction amount is large, that is, the combustion is unstable even by the correction.
[0045]
Each control process described above is merely an example, and various modifications can be made to achieve the same kind of purpose. For example, different flags may be used for light fuel and heavy fuel, and a calculation flow for rotation speed fluctuation may be incorporated in the control processing flow.
[0046]
【The invention's effect】
As described above, according to the present invention, the determination threshold for the engine speed at idling is set to two values, and the engine speed at idling is lower than any threshold, and the engine speed is between both thresholds. By determining that the fuel is heavy when the engine speed fluctuation is greater than a predetermined threshold, it is possible to accurately determine the fuel properties regardless of the engine friction state, fuel supply system, and supply / exhaust state It can be performed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an internal combustion engine control system including a first embodiment of a fuel property determination apparatus according to the present invention.
FIG. 2 is a diagram for explaining the determination principle of fuel property determination according to the present invention.
FIG. 3 is a flowchart illustrating a determination operation of the fuel property determination apparatus of FIG. 1;
4 is a flowchart of a rotation speed variation calculation process of the fuel property determination device of FIG. 1;
FIG. 5 is a timing chart showing an example of engine speed fluctuation based on the processing of FIG. 3;
6 is a flowchart illustrating another determination operation of the fuel property determination apparatus of FIG.
7 is a timing chart showing an example of engine speed fluctuation based on the processing of FIG. 6;
FIG. 8 is a schematic configuration diagram of an internal combustion engine control system including a second embodiment of the fuel property determination device according to the present invention.
FIG. 9 is a diagram illustrating an arrangement state of an ISC valve.
FIG. 10 is a flowchart illustrating a determination operation of the fuel property determination apparatus of FIG.
11 is a timing chart showing an example of engine speed fluctuation based on the processing of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Engine ECU, 2 ... Engine, 3 ... Speed sensor, 4 ... Throttle opening sensor, 5 ... Crank angle sensor, 6 ... ISC valve opening sensor, 7 ... Intake pipe, 10 ... Fuel property determination part, 60 ... ISC valve, 70 ... main pipe, 71 ... branch pipe.

Claims (2)

In the fuel property determination device for determining the property of the fuel based on the idle engine speed immediately after the start of the internal combustion engine,
When there are two threshold values for determining the engine speed, the engine speed is lower than either threshold, and when the engine speed is between both threshold values and the engine speed fluctuation is greater than the predetermined threshold A fuel property judging device for judging heavy fuel. 2. The fuel property determination apparatus according to claim 1 , wherein the fuel property determination is prohibited during engine operation after completion of the determination.

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