JP2826595B2 - Combustion determination method for spark ignition internal combustion engine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combustion determination method capable of detecting a direct phenomenon of combustion in a spark ignition internal combustion engine to quickly and accurately determine the quality of a combustion state.

<Prior Art> In a normal combustion in a spark ignition internal combustion engine, a part of an air-fuel mixture is ignited by a spark given from a spark plug, and the flame propagates in the air-fuel mixture. Because part or all of the air-fuel mixture in the part is heated by compression, it occurs by self-ignition and burning at a time without waiting for propagation of the flame. Knocking is one of the most harmful phenomena for spark-ignited internal combustion engines, because the sudden rise in pressure in the combustion chamber and the propagation of pressure waves due to this rapid combustion cause mechanical vibrations of each part of the engine and overheating of spark plugs and pistons. It can be said that it is one.

However, since the ignition timing at which the maximum torque is extracted from this spark ignition internal combustion engine (hereinafter simply referred to as the engine) is close to the condition where knocking occurs as is well known, if the maximum torque is to be extracted from the engine, The knocking tends to be more likely to occur.

Therefore, conventionally, an in-cylinder pressure sensor or an acceleration sensor is attached to the engine body to detect the vibration of the in-cylinder pressure caused by knocking or the acceleration generated in the engine body, thereby detecting whether the operating condition is good or not and the validity of the ignition timing. Or the like, or the ignition timing during operation is corrected to reduce the occurrence of knocking while extracting the maximum torque from the engine.

<Problems to be Solved by the Invention> However, in the conventional method of detecting the vibration of the in-cylinder pressure caused by the occurrence of knocking and the acceleration generated in the engine body by the in-cylinder pressure sensor or the acceleration sensor, the engine is actually knocked. Therefore, it is basically impossible to detect a state immediately before knocking to prevent knocking or determine a margin for knocking. In addition, there has been a problem that the in-cylinder pressure sensor is susceptible to erroneous detection in response to mechanical vibration.

<Means for Solving the Problems> The present inventors have researched a method that can reliably prevent knocking while extracting the maximum torque from a spark ignition internal combustion engine, and have conducted various experiments. An unusual phenomenon was discovered. That is, in the vicinity of the knocking occurrence condition, the combustion speed is increased even though knocking does not occur, and the change in the heat generation rate is indicated by the one-dot chain line in FIG. It becomes sharp near the condition.
The cause is considered as follows.

First, the chemical reaction of normal combustion is performed through a first stage peroxide reaction, a second stage cool flame reaction (or formaldehyde reaction), and a third stage hot flame reaction. It is the third stage that causes an explosive reaction during this stage.
1, The second stage is when the hydrocarbons in the fuel contain formaldehyde or O
H, is a precursor reaction be decomposed into free radicals of the high energy, such as HO _2.

Here, in the vicinity of the knocking occurrence condition, the first and second stage precursor reactions are proceeding in the unburned region in the combustion chamber where the pressure and temperature are on the verge of self-ignition, and there are many free radicals of high energy, It is considered that the state is more chemically activated than usual. For this reason, when the flame surface reaches there, it is considered that the third-stage flame reaction immediately occurs without delay required for the precursor reaction, and the flame speed and, consequently, the heat generation rate increase.

Then, when G is the amount of combustion gas, A is the heat equivalent of work, P is the pressure in the combustion chamber, and dV is the amount of change in the volume of the combustion substance, the heat generation amount dQ is dQ = G · du + A · P · dV (1) Becomes In the equation (1), du is the internal energy increment, and Cv
Is constant heat, dT is temperature change, R is gas constant, and k is specific heat ratio. It is. Substituting equation (2) and equation of state of gas PV = GRT into equation (1) Becomes When θ is the crank angle phase, the heat release rate Is from equation (3) Becomes Here, in the combustion stroke, which is a crank angle phase from compression top dead center (θ = 0 °) to 50 ° (θ = 50 °) after compression top dead center, Therefore, equation (4) is Can be approximated. That is, in the combustion stroke between the crank angle phases, it is understood that the heat release rate can be approximated by the first derivative of the pressure in the combustion chamber.

Therefore, the present invention has been completed based on the above-mentioned findings, and its purpose is to detect a state immediately before knocking to prevent knocking beforehand, and to quickly and effectively determine a combustion state in a bench test or the like. It is an object of the present invention to provide a method for determining combustion.

In order to achieve the above object, a method for determining combustion of a spark ignition internal combustion engine according to the present invention detects the in-cylinder pressure of a spark ignition internal combustion engine, and calculates the in-cylinder pressure change rate from the in-cylinder pressure.
A good or bad combustion state is determined according to a change state of the in-cylinder pressure change rate in a fall region of the in-cylinder pressure change rate.

<Operation> When abnormal combustion such as knocking is likely to occur, a large change is seen in the falling direction of the heat generation rate as compared with the normal combustion.

This is because, for example, in a state where knocking is likely to occur, the heat generation rate in the latter half of combustion increases due to the precursor reaction, and as a result, the remaining unburned portion at the end of combustion decreases and the combustion period becomes shorter.

Therefore, if the state of the falling region of the in-cylinder pressure change rate, which is proportional to the above-mentioned heat generation rate, is detected and determined based on the slope amount of the falling time, the combustion state can be determined.

<Embodiment> An embodiment of a combustion determination method for a spark ignition internal combustion engine according to the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a first embodiment of the present invention. That is, FIG. 1A shows the relationship between the heat release rate (dQ / dθ) of the spark ignition internal combustion engine and the crank angle θ. As shown by a broken line in FIG.
Compared to the heat generation rate in the state where knocking is not sufficiently performed, the heat generated in the state immediately before knocking that is not knocked as shown by the dashed line in FIG. The occurrence rate greatly changes in the falling direction. Therefore, if the rate of change of the heat release rate in the fall region of the heat release rate from the maximum value of the heat release rate to the completion of combustion is determined according to a certain criterion, for example, in the state immediately before knocking without knocking It is possible to determine whether or not there is, and it is possible to determine the appropriateness of setting of operating conditions such as ignition timing, air-fuel ratio setting, and supercharging pressure.

Therefore, in the present embodiment, the fall 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 detected as the fall time | θ ₁₀₀ −θ ₀ |
The determination is made by comparing this detected value with, for example, an absolute set value (this differs depending on the type of the internal combustion engine).

That is, the present embodiment is carried out according to the apparatus and means shown in FIG. 1 (b) and the flowchart shown in FIG. 1 (c).

First, the crank angle θ is detected by the crank angle detecting means 1, and the in-cylinder pressure P is detected by the in-cylinder pressure detecting means 2.

Next, the heat release rate calculation means 3 calculates the heat release rate using the above-described equation (4).

When calculating the heat release rate, it is desirable that high frequency vibration components due to knocking or the like be cut by a filter. In other words, the high-frequency vibration component is always superimposed on the acupressure diagram, and by cutting this vibration component,
The change state of the heat release rate is simplified as shown in FIG. As the above filter, a Fourier series filter is used when real-time performance is required for on-board knocking control, etc., and when real-time performance is not important for bench test measurement equipment, a direct FFT method is used. The filter used or the filter using the spline function method is effective.

Subsequently, as shown in FIGS. 1 (b) and 1 (c), the fall time calculating means 4 detects the crank angle θ ₁₀₀ at which the heat release rate has the maximum value and the crank angle θ _{0 at} which the combustion is completed, which is detected in advance. And the fall time | θ ₁₀₀ −θ ₀ |

At this time, when the method of the present invention is performed in a bench test measuring instrument or the like, it is desirable to cut a large peak generated by knocking. This means that if a peak is simply taken from the change in the heat release rate when knocking occurs, the peak due to knocking often becomes the maximum value, and the maximum value to be detected by the method of the present invention is the peak during normal combustion. It depends. As the above cutting method,
The waveform pattern of the heat generation rate during normal combustion is memorized, and the part that deviates greatly from this is cut. The peak due to knocking always occurs after the peak that occurs during normal combustion, so during one cycle of combustion It is effective to disregard the peak that occurs later among the two peaks that occur. However, even if the peak due to knocking is erroneously determined to be the maximum value of the heat release rate, the result of determination based on the fall time, the amount of inclination, and the like is a determination of a situation in which knocking is likely to occur. May be.

The fall time | θ ₁₀₀ −θ ₀ thus calculated
| Is compared with, for example, an absolute set value to determine whether or not abnormal combustion occurs. The determination signal is sent to various combustion control means in the case of on-board knocking control, and in the case of a bench test measuring instrument. Output to display means and recording means, respectively. For example, in the case of on-board knocking control, when the calculated fall time | θ ₁₀₀ −θ ₀ | is larger than the absolute set value and knocking is not likely to occur, the ignition timing is gradually advanced to increase the maximum torque. On the other hand, when the knocking occurs or the knocking is likely to occur because the knocking is smaller than the absolute set value, a knocking avoidance signal is sent to various combustion control means. When an electronic ignition timing control device is used as the various combustion control means, knocking is avoided by retarding the ignition timing based on the signal. Also, EGR
When the electronic control EGR valve of the device is used, the average valve opening time (duty ratio) is increased to increase the amount of EGR,
Further, when a wastegate valve of the supercharger is used, it may be opened to release the supercharging pressure.

As a method of determining the combustion state based on the calculated fall time | θ ₁₀₀ −θ ₀ |, in addition to the comparison with the above-described absolute set value, the ratio of the heat release rate to the maximum value and the stability of the combustion state are Crank angle θ _{N1 in} the rising region of the determined heat release rate
Crank angle theta time to _N2 in the | θ _N1 -θ _N2 | may determine a ratio to. The reference time | θ _N1 −θ _N2 | in the region where the maximum value of the heat release rate and the combustion state are stable is
The average value obtained by processing a plurality of data may be used. Further, the determination level of the above ratio varies depending on the operating conditions.
A mapped value may be used.

Next, FIGS. 2A and 2B show a second embodiment of the present invention.

This is done by cutting off a portion where the change in heat release rate is relatively small immediately after the maximum value of the heat release rate and immediately before the completion of combustion, and for example, a crank angle showing a heat release rate of 90% of the maximum value of the heat release rate. Crank angle θ indicating a heat release rate of 10% of the maximum value from θ ₉₀
Set up to ₁₀ as the detection area and its fall time | θ ₉₀
This is an example in which −θ ₁₀ | is detected to improve the measurement accuracy.

According to this, the fall time | θ ₉₀ −θ ₁₀ |
, The maximum value of the heat release rate and the crank angle θ at that time
_In addition to detecting ₁₀₀ , the maximum heat release rate of 90
% Of the heat release rate and the value of the heat release rate of 10%, and the respective crank angles θ ₉₀ , θ ₁₀ at that time are detected, and the crank angle θ _{100 or more} indicating the maximum value of the heat release rate is detected. The fall time | θ ₉₀ −θ ₁₀ | is calculated. Other configurations and operations are the same as those of the first embodiment.

FIGS. 3A and 3B show a third embodiment of the present invention.

This is because, from the same point of view as in the second embodiment, in order to make the tendency of the heat release rate fall more remarkably, the heat in the latter half of the fall region, for example, 50% of the maximum value of the heat release rate, is set. The range from the crank angle θ ₅₀ indicating the occurrence rate to the crank angle θ ₀ at which combustion is completed is set as a detection region, and the fall time | θ ₅₀ −θ ₀ |
This is an example in which is detected.

According to this, the fall time | θ ₅₀ −θ ₀ | in the calculation means 4B, the maximum value of the heat release rate and the crank angle θ ₁₀₀ at that time are calculated.
In addition to calculating the heat release rate 50% of the maximum value of the heat release rate and calculating the crank angle θ at that time.
_{Then, the} fall time | θ ₅₀ −θ ₀ | after the crank angle θ ₁₀₀ indicating the maximum value of the heat release rate is calculated by detecting ₅₀ and the crank angle θ _{0 at the} completion of combustion. Other configurations and actions are the first
This is the same as the embodiment.

FIGS. 4A and 4B show a fourth embodiment of the present invention.

This is because, in order to make the tendency of the heat release rate falling in the third embodiment more prominent, the vicinity of the completion of combustion is cut off, and for example, the heat release rate of 50% of the maximum value of the heat release rate is reduced. The range from the crank angle θ ₅₀ shown to the crank angle θ ₁₀ showing the heat release rate of 10% of the maximum value of the heat release rate is set as the detection area, and the fall time | θ ₅₀ −θ ₁₀ | is detected. It is an example.

According to this, the fall time | θ ₅₀ −θ ₁₀ |
, The maximum value of the heat release rate and the crank angle θ at that time
_In addition to detecting ₁₀₀ , the maximum heat release rate of 50
% Of the heat release rate and the value of the heat release rate of 10% are detected, and the crank angles θ ₅₀ and θ ₁₀ at that time are detected, and the crank angle θ _{100 or more} indicating the maximum value of the heat release rate is detected. The fall time | θ ₅₀ −θ ₁₀ | is calculated. Other configurations and operations are the same as those of the first embodiment.

In each of the above embodiments, the time required for the transition from the first value of the heat release rate set in advance to the second value smaller than the first value in the fall region of the heat release rate depends on the time. As described above, the in-cylinder pressure change rate proportional to the heat release rate is calculated to determine the fall of the in-cylinder pressure change rate. The good or bad of the combustion state may be determined according to the time required for the transition from the first value of the in-cylinder pressure change rate set in advance to the second value smaller than the first value in the region. According to this, control such as speed-up of calculation can be simplified, which is suitable for on-board knocking control or the like that requires real-time performance.
Moreover, so far the time | θ _a -θ _b | have been discussed as the period of the absolute time (ms, etc) may be determined using a. In either case, it is desirable that the determination value be changed for each condition such as the number of rotations.

FIGS. 5A, 5B and 5C show a fifth embodiment of the present invention.

This is because the maximum negative slope in the falling region of the heat release rate is detected by the change rate of the heat release rate (d ² Q / dθ ² ), and this detected value is compared with the absolute set value as described above. This is an example in which the determination is made by performing the above operation. In the present embodiment, the determination of the detection value can also be made based on the ratio of the rate of change of heat release rate to the positive maximum value.

Specifically, the heat release rate change rate calculating means 6 first obtains the change rate (d ² Q / dθ ² ) of the heat release rate by approximating it by the second derivative of the in-cylinder pressure (see FIG. 5 (b)). ).

That is, the change rate of the heat generation rate is as follows from the above-described equation (4).

Here, in the combustion stroke (top dead center to 50 ゜ after top dead center) Therefore, the above equation can be approximated as follows.

That is, the rate of change of the heat release rate can be approximated by the second derivative of the in-cylinder pressure.

The apparatus and means for obtaining the second derivative of the in-cylinder pressure are as shown in FIG.

That is, the in-cylinder pressure Pi sampled at i times by the in-cylinder pressure detecting means 2 is detected using a sufficiently short sampling cycle, and the crank angle θ is detected by the crank angle detecting means 1.
Is detected. Next, the in-cylinder pressure first-order differential calculating means 8 reads from the memory 7 the in-cylinder pressure P at the time of the previous sampling at the time of i times.
_i-1 is read out, and the rate of change per unit angle is calculated from both Pi _-1 and the in-cylinder pressure Pi at the time of i times to obtain dPi / dθ. Then, the in-cylinder pressure Pi and its change rate dPi / dθ at the time of i times are stored in the memory 7. Thereafter, the in-cylinder pressure second-order differential calculating means 9 reads the previous dP _i-1 / dθ from the memory 7 and obtains dP _i-1 / dθ.
Then, the rate of change per unit angle is calculated from both dPi / dθ at the time i and dPi / dθ to obtain d ² Pi / dθ ² . d ² Pi / dθ ² is stored in the memory 7.

It is convenient to approximate the rate of change of the heat release rate with the second-order differential value of the in-cylinder pressure obtained in this way, but it may be strictly obtained by the above-mentioned equation (6).

Then, the maximum value of the heat release rate and the crank angle θ at that time
_After detecting ₁₀₀ and the crank angle θ _{0 at} which combustion is completed, the minimum value of the rate of change of the heat generation rate is detected within the fall range of the heat generation rate. Other configurations and operations are the same as those of the first embodiment.

In the above embodiment, it is preferable that the heat release rate change rate calculating means 6 calculate only the heat release rate change rate in the fall region of the heat release rate because the calculation time can be reduced. In this case, it is needless to say 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 out of the detection area.

FIGS. 6 (a), (b) and (c) show a sixth embodiment of the present invention.

This is an example in which the modification of the fifth embodiment is further developed, and the calculation speed is increased by shortening the detection area of the heat release rate change rate to the latter half of the fall area of the heat release rate.

According to this, in the heat release rate change rate calculating means 6A,
In addition to detecting the maximum value of the heat release rate and the crank angle θ ₁₀₀ at that time, a value of the heat release rate of 50% (or near) of the maximum value of the heat release rate is calculated, and the heat release rate is calculated. Are detected, the crank angle θ ₅₀ indicating the heat generation rate of 50% of the maximum value of the heat generation rate after the crank angle θ ₁₀₀ indicating the maximum value and the crank angle θ ₀ indicating the completion of combustion. Next, the rate of change of the heat release rate in the latter half of the fall area of the heat release rate is calculated to detect the minimum value. Other configurations and operations are the same as those of the first embodiment.

Also in this embodiment, the change rate of the heat generation rate (the amount of falling slope) is strictly obtained by the above-described equation (6) in accordance with the control purpose and the capability of the heat generation rate change rate calculating means 6A. Alternatively, as is apparent from the above-described equation (7), the rate of change of the heat release rate may be replaced by the second-order differential value of the in-cylinder pressure (in other words, the slope of the falling rate of the in-cylinder pressure change rate). Needless to say good things.

<Effects of the Invention> As described above, according to the combustion determination method for a spark ignition internal combustion engine of the present invention, the fall time, the slope amount, and the like in the fall region of the in-cylinder pressure change rate proportional to the heat release rate Since the combustion state is determined by detecting the direct phenomenon of combustion, there is no work to replace the combustion of the engine with air column vibration or the intrusion of mechanical noise as seen in the conventional example, and it is quick and accurate. The combustion state can be determined. Especially,
ADVANTAGE OF THE INVENTION According to this invention, it can be determined whether it is in the combustion state just before the knocking which is not knocking, and the occurrence of knocking can be prevented beforehand by combination with the knocking avoiding means.

[Brief description of the drawings]

FIG. 1 relates to a first embodiment of a method for judging combustion of a spark ignition internal combustion engine according to the present invention. FIG. 1 (a) is a graph showing a relationship between a crank angle and a heat generation rate, and FIG. 1 (b) is a block diagram. Figure,
FIG. 3C is a flowchart. FIG. 2, FIG. 3,
FIG. 4 relates to the second, third, and fourth embodiments of the present invention. FIG. 4 (a) is a graph showing the relationship between the crank angle and the heat release rate, and FIG. 4 (b) is a block diagram. FIG. 5 and 6 relate to the fifth and sixth embodiments of the present invention. FIG. 5 (a) is a graph showing the relationship between the crank angle and the heat release rate, and FIG. Is a graph showing the relationship between the crank angle and the rate of change of the heat release rate, and each figure (c) is a block diagram. FIG. 7A is a block diagram for obtaining the second order differential value of the in-cylinder pressure, and FIG. 7B is a flowchart showing the procedure. In the figure, reference numeral 1 denotes crank angle detecting means, 2 denotes in-cylinder pressure detecting means, 3 denotes heat generation rate calculating means, 4, 4A, 4B, and 4C denote fall time calculating means, 5 denotes discriminating means, and 6, 6A denotes Heat generation rate change rate calculation means, 7 is a memory, 8 is in-cylinder pressure first-order differentiation calculation means, and 9 is in-cylinder pressure second-order differentiation calculation means.

Continuation of the front page (72) Inventor Hiromitsu Ando 5-33-8 Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Corporation (72) Inventor Daisuke Mibayashi 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi (72) Inventor Masato Yoshida 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi Motors Corporation (72) Inventor Kazuhiro Shiraishi 5-33-8 Shiba, Minato-ku, Tokyo Mitsubishi (56) References JP-A-54-112 (JP, A) JP-A-55-148937 (JP, A) JP-A-59-136543 (JP, A) JP-A-59-136544 (JP, A) JP-A-61-250366 (JP, A) JP-A-62-248824 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F02D 45/00

Claims (3)

(57) [Claims] An in-cylinder pressure of a spark ignition internal combustion engine is detected, and a rate of change of the in-cylinder pressure is calculated from the in-cylinder pressure. A method for determining combustion in a spark ignition internal combustion engine, the method comprising determining whether a combustion state is good or bad. 2. An in-cylinder pressure of a spark ignition internal combustion engine is detected, and a rate of change of the in-cylinder pressure is calculated from the in-cylinder pressure. A combustion determination method for a spark ignition internal combustion engine, wherein a determination is made as to whether a combustion state is good or bad according to a time required for a transition from a value of 1 to a second value smaller than the first value. 3. The in-cylinder pressure of the spark ignition internal combustion engine is detected, the rate of change of the in-cylinder pressure is calculated from the in-cylinder pressure, and the quality of the combustion state is determined according to the slope of the fall of the in-cylinder pressure change rate. A combustion determination method for a spark ignition internal combustion engine, characterized in that: