JPH02204663A - Control method for multioctane value corresponding engine - Google Patents

Abstract

PURPOSE:To make fuel into combustion so efficiently all the time even if it is of different octane value by operating a changed state of heat generating rate, judging a combustion state, and also judging octane value of the service fuel on the basis of this judged result, then selecting an optimum driving parameter. CONSTITUTION:First of all, ignition timing and air-fuel ratio or the like in an idle running state after starting is set to an optimum driving state for judging the octane value of fuel by a driving condition setting means 1. Next, a combustion state judging means 2 operates a heat generating rate on the basis of each signal out of a cylinder internal pressure sensor and a crank angle sensor, judging a combustion state from the changed status, and the octane value of service fuel is judged by an octane value judging means 3 on the basis of this judged result. Then, a select means 4 selects an ignition timing map A or maps B, C to the judged octane value, and according to this selection, an engine is driven by a driving means 5. Thus, even if different octane value fuel is used, the engine is drivable so efficiently all the time.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application> The present invention relates to a method for controlling an engine compatible with multi-octane fuels, which operates with high efficiency even with fuels of different octane numbers.

<Conventional technology> In recent years, unleaded low-octane gasoline (octane number 91) has become available.
In addition to unleaded high octane gasoline (9 octane
8), engines that can operate on fuels of different octane ratings are attracting attention.

In this case, as the octane number of the fuel changes, the engine's optimal ignition timing also changes, which may cause knocking or the engine's maximum torque not be fully extracted, so it is necessary to change the ignition timing according to the octane number.

By the way, in order to most efficiently extract thermal energy as engine output, it is desirable to delay the maximum torque generated by combustion slightly from top dead center, but as is well known, the ignition timing to extract this maximum torque depends on the conditions under which knocking occurs. Since the engine is located close to the engine, the probability of knocking tends to increase as the maximum torque is extracted from the engine, so knocking control becomes necessary. .

In the conventional control method for engines compatible with multi-octane fuel, in-cylinder pressure sensors and acceleration sensors are attached to the engine's cylinder block, etc., to detect cylinder pressure vibrations and mechanical vibrations of the engine that occur due to knocking. By inputting this output into the ECU and calculating it, the ignition timing is delayed or advanced depending on the degree of knock in order to extract the maximum torque from the engine.

<Problems to be Solved by the Invention> In such a conventional control method for an engine compatible with multi-octane fuel, various sensors detect vibrations in the cylinder pressure due to knocking, and the ignition timing is determined to be appropriate for the octane rating of the fuel. Because the ignition timing was determined, the ignition timing could not be set unless the engine actually knocked, and each time the octane number of the fuel changed, knocking occurred and was detected to determine the ignition timing. This knocking occurs when the pressure rise caused by rapid combustion causes the gas in the combustion chamber to vibrate, producing a knocking sound, which causes an unpleasant crunching noise to the occupants. Furthermore, when knocking occurs, heat transfer improves due to combustion gas vibrations, so if this condition continues, there is a risk that the spark plug electrodes and piston will overheat and melt, causing damage to the engine.

Further, in this conventional knock control, when knocking is detected, the ignition timing is immediately retarded, and when the knocking-free state continues, the ignition timing is gradually advanced to control the ignition timing. As a result, time is lost until proper ignition timing is achieved.

The present invention solves these problems by determining the octane number of the fuel without causing knocking, and controlling the engine operation based on the result of the determination, thereby always achieving high efficiency even with different octane fuels. The purpose of this invention is to provide a control method for an engine that can operate on multi-octane fuel.

A method for controlling a multi-octane fuel compatible engine according to the present invention to achieve the above-mentioned object is a method for controlling a multi-octane fuel compatible engine that changes with combustion in a combustion chamber of a spark-ignition internal combustion engine under predetermined operating conditions. The combustion state is determined by detecting the combustion physical quantity, calculating the heat release rate or the state of change in the physical quantity correlated with the heat release rate from the change in the combustion physical quantity, and further using the engine based on the determination result. Determine the octane number of the fuel, select the optimal operating parameter for the determined octane number of the fuel from among a plurality of operating parameters according to the octane number of the fuel stored in advance, and based on the selected operating parameter. It is characterized by controlling the operation of the engine.

Operation: Under predetermined operating conditions, the combustion state of the engine is determined based on the heat release rate calculated from changes in combustion physical quantities or the state of changes in physical quantities that are correlated with the heat release rate, and the judgment results are displayed. Determine the octane number of the fuel used based on. Then, the optimum operating parameter for the determined octane fuel is selected from a plurality of pre-stored operating parameters, and the engine is operated with high efficiency without knocking based on this operating parameter.

Embodiments Hereinafter, embodiments of the present invention will be described in detail based on the drawings.

Fig. 1 is a block diagram of a control method for an engine compatible with multi-octane fuel according to an embodiment of the present invention, and Fig. 2 shows its combustion state determination means. Figure 3 (b) is a block diagram, Figure (e) is a flowchart, Figure 3 is a graph showing the relationship between heat release rate and crank angle for regular gasoline and premium gasoline, Figure 4 is a graph showing the relationship between the heat release rate and the crank angle of regular gasoline and premium gasoline. 3 is a flowchart showing the operation of a control method for a fuel compatible engine.

As shown in FIG. 1, the control method for an engine compatible with multi-octane fuel according to this embodiment includes an operating condition setting means 1, a combustion state determining means 2, an octane number determining means 3, and an ignition timing map selection means 4 having operating parameters. and engine operating means 5.

The operating condition setting means 1 is used to preset the ignition timing, air-fuel ratio, etc. in an idling state after the engine has been started to optimal values for determining the octane number of the fuel. In an engine with a displacement of 2000 cc, the ignition advance angle is set to 25 degrees at 1200 rpm and in a full load state.Therefore, based on this operating condition, the determination described below is made.

Next, the combustion state determining means 2 will be explained.

As shown in Fig. 2(a), compared to the heat release rate in the state without sufficient knocking shown by the broken line, the heat release rate in the state of not knocking but on the verge of knocking, shown by the single point tR line in the same figure, or The heat release rate during the knocking state, shown by the solid line in the same figure, varies greatly depending on how it falls. Therefore, if we use a certain standard to determine the rate at which the heat release rate changes in the falling region of the heat release rate from the maximum value to the completion of combustion, it is possible to It is possible to determine whether or not there is, and it is possible to determine the validity of operating condition settings such as ignition timing, air-fuel ratio settings, and boost pressure.

Therefore, in this embodiment, the falling region of the heat release rate, that is, the crank angle from the maximum value of the heat release rate to the completion of combustion is determined by the falling time 1θ in the detection region. . −〇. 1, and the detected value is compared with an absolute set value, which will be described later, to make a determination.

That is, this embodiment is implemented according to the apparatus and means shown in FIG. 2(b).

First, the crank angle θ is detected by the crank angle detection means 11, and the cylinder pressure P as a physical quantity of combustion is detected by the cylinder pressure detection means 12.

Next, the heat release rate calculating means 13 calculates the heat release rate using the following formula.

Heat generation amount: dQ=G-du+A-P-dV −
(1)-R Internal energy increment: d u=cv-dT=■=
1・dT −(2) PV=G −R−T where G is the amount of combustion gas, A is the heat equivalent of work, R is the gas constant, Cv is the constant volume specific heat, and k is the ratio of specific heats.

(11, (21, (from formula 33...(3) dQ = "A'RdT + A-P-dV k-1 (-P-dV-PdV for PdV + VdP+) Therefore, the heat generation rate (dQ/dθ) is It is as follows.

Here, combustion stroke (TDC ~ 50° after TDC) dV
Since d#'da at dP, the above equation can be approximated as follows.

±g−ΔV, and de = 1dθ In other words, the heat generation rate can be approximated by one break in the cylinder pressure.

In addition, since the heat release rate can be approximated by one break in the cylinder pressure, it can be said that this f11% heat release rate dQ dP has the same change situation at T and d6. I understand that. Therefore, this heat release rate dQ
It is also possible to replace da da with -dP-, and instead of measuring various values, measure the cylinder pressure P and crank angle θ, find the state of change, and use this instead of the heat release rate. good.

Note that when calculating the heat generation rate as described above, it is desirable to cut off high frequency vibration components due to knocking etc. with a filter. In other words, a high-frequency vibration component is always superimposed on the acupressure diagram, and by cutting this vibration component, the state of change in the heat release rate can be changed as shown in Figure 2 (a).
This is simplified as shown in . A Fourier series filter is effective as the above filter.

Subsequently, as shown in FIG. 2(b), the crank angle θ at which the heat generation rate reaches the maximum value and the crank angle θ at which combustion is completed are detected in advance by the fall time calculating means 14. The fall time 1θ, based on . . −〇. Calculate 1.

In this way, the fall time 1θ,. . −θ. 1 is calculated and the combustion state is determined.

Octane liI [i determining means 3 is the fall time 1θ1° calculated by the combustion state determining means 2 described above.

−θ. Octane number is determined based on 1. Premium gasoline and Reginilla gasoline, which have different octane numbers, have different heat release rates with respect to crank angle. As shown in Fig. 3, it is not so noticeable when the ignition timing is late, but the ignition timing is 25BTD as shown in Fig. 3 (Q), where the ignition timing is early.
In case C, under conditions where knock occurs, the slope of the fall is steeper when regular gasoline with a lower octane number is used than premium gasoline with a higher octane number. You can see that it is shorter.

Based on this, a plurality of types of fuels with different octane numbers are combusted in advance under the same operating conditions as described above, and the fall time 1θ of the heat release rate is determined by the combustion state determining means 2 about 40 times.

. −〇. 1, and based on these results, absolute set values of multiple types of octane ratings for fall times are set and stored in the ECU. Then, the determined fall time 1θ1° described above. −θ. 1 and a preset absolute setting value of the octane number to determine the octane number of the used fuel.

Note that the calculated fall time is 1θ1°. −〇. In addition to comparing with such an absolute set value, the octane number can be determined based on the ratio of the heat release rate to the maximum value or the crank angle θNl in the stable heat release rate rising region of the combustion state. Time 1θ1θ until a certain crank angle θN2
The determination may be made based on the ratio to N21. In addition, the reference time 1ON1 in the area where the maximum heat release rate and combustion state are stable.
-θH2' may be an average value obtained by processing a plurality of data.

The ignition timing map selection means 4 selects an ignition timing map having optimum operating parameters for the fuel used, based on the determination result of the octane number determination means 3. In this case, for example, a three-dimensional map of ignition timing with respect to engine speed and load (intake pressure, etc.) is set corresponding to each octane value, and is stored in the ECU. The ignition timing map selection means 4 selects from among these ignition timing maps that are equivalent to or close to the determined octane number. Also, at this time, the selection may be made by interpolating from two maps. In addition,
In addition to the above-mentioned items, the operating parameters of the ignition timing map include the air-fuel ratio, boost pressure, compression ratio, etc.

The engine operating means 5 operates the engine according to the selected ignition timing map.

The method of controlling the multi-octane fuel compatible engine described above will be explained based on the flowchart shown in FIG.

First, turn the ignition key to start the engine. At this time, if the idling operation of the engine is confirmed, the operating conditions for determining the octane number are set by the operating condition setting means 1 during the idling operation, and the operating conditions are supplied to the engine for a predetermined period of time. If not, no operating conditions are set, and the ignition timing map based on the previously determined octane number is selected.

With the operating conditions set and the engine operating according to the set values, the combustion state determining means 2 determines the fall time by calculating the state of change in the heat release rate from the change in the cylinder pressure.

The octane number of the used fuel is determined by the octane number determining means 3 in accordance with this determination result. When the octane number of the fuel is determined, the ignition timing map selection means 4 selects an appropriate map from among a plurality of ignition timing maps stored in advance in the ECU. Then, the engine is operated by the engine operating means 5 based on the operating parameters of the selected ignition timing map. After that, if the octane number checker does not receive an input signal by operating the manual switch, it will continue operation using the currently selected ignition timing map, but if it does, it will return to the stage before checking the engine's idling operation, and the above-mentioned effect will occur. will be repeated again.

Next, another embodiment of the combustion state determining means described above will be described.

FIG. 5 (bl) shows a second embodiment of the combustion state determining means.

This is done by cutting off the portion where there is relatively little change in the heat release rate between immediately after the maximum value and immediately before the completion of combustion. The detection area is set from θ9° to the crank angle θ1o which shows a heat release rate of 10% of the maximum value, and the fall time is 1θ. This is an example in which the measurement accuracy is improved by detecting -〇to'.

According to this, the fall time is 1θ. . −θ,. 1 calculation means 14A, the maximum value of the heat generation rate and the crank angle θ1° at that time. In addition to detecting the heat release rate, the heat release rate value of 90% and the heat release rate value of 10% of the maximum value of the heat release rate are calculated, and each crank angle θ, at that time. , θ1° is detected, and the crank angle θ1° indicates the maximum value of the heat generation rate. The subsequent fall time 1θ9° - θ1°1 is calculated. The other configurations and operations are the same as those in the above-mentioned *embodiment.

FIG. 6 (al and fbl show a third embodiment of the combustion state determining means).

From the same point of view as in the second embodiment, in order to more clearly show the tendency of the fall of the heat release rate, the time in the second half of the fall region, for example, 50% of the maximum value of the heat release rate is From the crank angle θ5° which indicates the heat release rate to the crank angle θ at which combustion is completed. Set up as the detection area, and its fall and time θ5゜-〇. This is an example in which 1 is detected.

According to this, the fall time is 1θ5°-θ. 1 calculation means 1
4B, the maximum value of the heat release rate and the crank angle θ at that time. . In addition to detecting , the value of the heat release rate of 50% of the maximum value of the heat release rate is calculated, and the crank angle θ at that time. and the crank angle θ at which combustion is completed. and the crank angle θ, which indicates the maximum value of the heat release rate. . The above fall time thereafter is 1θ5°-〇. Calculate 1. Other configurations and operations are similar to those of the previous embodiment.

FIGS. 7(a) and 7(bl) show a fourth embodiment of the combustion state determining means.

This is done by cutting off near the completion of combustion and setting the heat release rate at 50% of the maximum value, for example, in order to more clearly show the tendency of the decline in the heat release rate in the third embodiment. The crank angle θ exhibits a heat release rate of 10% of the maximum value of the heat release rate from the crank angle θ5° shown. In this example, the detection area is set as the detection area, and the fall time of 1θ6°−θ1°1 is detected.

According to this, the fall time is 1θ. −θ,. 1 calculation means 14C, the maximum value of the heat generation rate and the crank angle θ at that time. . In addition to detecting, the heat release rate value of 50% and the heat release rate value of 10% of the maximum value of the heat release rate are calculated, and the respective crank angles θ and θ at that time are detected. , the crank angle θ, which indicates the maximum value of the heat release rate. . The subsequent fall time Iθ5°−θ1°1 is calculated. Other configurations and operations are similar to those of the previous embodiment.

FIG. 8 (al, (b), (cl) indicates a fifth embodiment of the combustion state determining means.

This is done by detecting the maximum negative slope in the falling region of the heat release rate using the rate of change in the heat release rate (d"Q/dθ2), and comparing this detected value with the absolute set value as described above. In this example, the detected value can be determined based on the ratio of the heat release rate change rate to the maximum positive value.

Specifically, the heat release rate change rate calculating means 16 first calculates the heat release rate change rate (d'Q/dθ2) by approximating it by two breaks in the cylinder pressure (Fig. 8(b)). reference).

That is, from the above-mentioned equation (4), the rate of change in the heat release rate is as follows.

Here, in the combustion stroke (from top dead center to 50 degrees after top dead center), since it is a stop knee, the above equation can be approximated to dθ dθ as follows.

In other words, the rate of change in the heat generation rate can be changed by two levels of the cylinder pressure.

The apparatus and means for determining the cylinder pressure for two breaks are as shown in FIG.

That is, the cylinder pressure detection means 12 detects the cylinder pressure Pi sampled once using a sufficiently short sampling period, and the crank angle detection means 11 detects the crank angle θ. Next, the in-cylinder pressure calculation means 18
reads the cylinder pressure P1-1 at the previous sampling at the i time from the memory 17, calculates the rate of change per unit angle from both P1-1 and the cylinder pressure Pi at the 1st time, and calculates d.
Let P i /dθ. Then, the cylinder pressure Pi at one time
and its change $dPi/dθ are stored in the memory 17. After this, the in-cylinder pressure calculation means 19 reads the previous value dP, -, /dθ from the memory 17, and calculates dP, -,
The rate of change per unit angle is calculated from both /dθ and d P i /dθ at one time, and is set as d2Pi/dθ2.

d'Pi/dθ2 is stored in the memory 17.

It is convenient to approximate the rate of change in the heat release rate using the two-disconnection values of the cylinder pressure obtained in this way, but as mentioned above (5)
It may be determined strictly using a formula.

Then, the maximum value of the heat release rate and the crank angle θ at that time are detected, and the crank angle θ at which combustion is completed is determined. After detecting , the minimum value of the heat release rate change rate is detected within the falling region of the heat release rate. Other configurations and operations are similar to those of the previous embodiment.

In the above embodiment, it is preferable that the heat release rate change rate calculating means 16 calculates only the heat release rate change rate within the falling region of the heat release rate described above, since the calculation time can be shortened. In this case, it goes without saying that the minimum value of the heat release rate change rate cannot be compared with the maximum value of the heat release rate change rate that is outside the detection area.

FIG. 9 fa), fbl, and (C) show a sixth embodiment of the combustion state determining means.

This is a further development of the modified example of the fifth embodiment, and is an example in which the detection region of the heat release rate change rate is shortened to the latter half of the fall region of the heat release rate to increase the calculation speed. be.

According to this, in the heat release rate change rate calculation means 16A, the maximum value of the heat release rate and the crank angle θ1° at that time. In addition to detecting the heat release rate, a value of the heat release rate of 50% (or around this) of the maximum value of the heat release rate is calculated, and the crank angle θ1° indicating the maximum value of the heat release rate is calculated. Crank angle θ that indicates a heat release rate of 50% of the maximum heat release rate thereafter
The crank angle θ is 5°, indicating the completion of combustion.

and detect. Next, the rate of change in heat generation rate within the detection area in the latter half of the fall area of the heat generation rate is calculated and its minimum value is detected. Other configurations and operations are similar to those of the previous embodiment. In addition, until now, the time has been set to 10. -θ5; has been discussed, but the determination may also be made using absolute time (ms, ate,).

Further, in the above-described embodiment, the in-cylinder pressure was detected as a combustion physical quantity, and the state of change in the heat release rate was calculated from the change in the in-cylinder pressure to determine the combustion state of the engine, but the present invention is not limited to this. The physical quantity of combustion may be any amount of heat or a correlation with this amount of heat. Furthermore, as is clear from the other examples mentioned above, without strictly calculating the heat release rate, the in-cylinder pressure change rate and the fire caused when fuel burns are calculated as physical quantities that are correlated with the heat release rate. Alternatively, the intensity of the combustion light emitted from the combustion light or the intensity of a specific frequency band thereof may be determined.

<Effects of the Invention> As explained above, according to the control method for an engine compatible with multi-octane fuel of the present invention, the combustion The system detects the direct phenomenon of combustion, determines the combustion state, determines the octane number of the fuel used, and selects the optimal operating parameters based on this to operate the engine, so it is possible to control the engine accordingly. By quickly and accurately determining the octane number without causing knocking, the system can always operate with high efficiency even with fuels of different octane numbers.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a control method for an engine compatible with multi-octane fuel according to an embodiment of the present invention, and Fig. 2 shows its combustion state determination means. Figure 1b) is a block diagram, Figure (C) is a flowchart, Figure 3 is a graph showing the relationship between heat release rate and crank angle for regular gasoline and premium gasoline, and Figure 4 is for multi-octane fuel. 3 is a flowchart showing the operation of the engine control method. FIG. 5, FIG. 6, and FIG. 7 respectively show the second part of the combustion state determining means. Third. Regarding the fourth embodiment, each figure (a) is a graph showing the relationship between the crank angle and the heat release rate,
Each figure (b) is a block diagram. Furthermore, the eighth
Fig. 9 shows the fifth part of the combustion state determining means. Regarding the sixth embodiment, each figure (al is a graph showing the relationship between the crank angle and the heat generation rate, each figure (b) is a graph showing the relationship between the crank angle and the rate of change of the heat generation rate, Each figure (c) is a block diagram. Figure 10 (ta+) is a block diagram for obtaining the values of the cylinder pressure for two breakers, and Figure 10 (fb) is a flowchart showing the procedure. In the drawing, 1 is an operating condition setting means, 2 is a combustion state determining means, 3 is an octane number determining means, 4 is an ignition timing map selection means, and 5 is an engine operating means. Patent applicant Mitsubishi Motors Corporation Agent

Claims (2)

[Claims] (1) Detect the combustion physical quantity that changes with combustion in the combustion chamber of a spark-ignition internal combustion engine under predetermined operating conditions, calculate the state of change in the heat release rate from the change in the combustion physical quantity, and determine the combustion state of the engine. Further, the octane number of the used fuel is determined based on the determination result, and the optimal operating parameter for the determined octane number of the fuel is selected from among a plurality of operating parameters corresponding to the octane number of the fuel stored in advance. 1. A method of controlling an engine compatible with multi-octane fuel, the method comprising: selecting an operating parameter, and controlling the operation of the engine based on the selected operating parameter. (2) Detect the combustion physical quantity that changes with combustion in the combustion chamber of a spark-ignition internal combustion engine under predetermined operating conditions, and calculate the state of change in the physical quantity that correlates with the heat release rate from the change in the combustion physical quantity. The combustion state of the engine is determined based on the determination result, and the octane number of the used fuel is determined based on the determination result, and the determined octane number of the fuel is selected from among a plurality of operating parameters corresponding to the octane number of the fuel stored in advance. 1. A method for controlling an engine compatible with multi-octane fuel, the method comprising: selecting operating parameters most suitable for a multi-octane fuel; and controlling the operation of the engine based on the selected operating parameters.