JP4184105B2 - Method for determining the combustion state of an internal combustion engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a combustion state detection method for an internal combustion engine that detects vibrations that are difficult to detect as normal rotational fluctuations in the internal combustion engine.
[0002]
[Prior art]
Conventionally, in an internal combustion engine, that is, an engine mounted on a vehicle such as an automobile, detection of knocking or determination of a combustion state is performed by using an ionic current generated in the combustion chamber from the start of combustion to May be used for control. For example, it is known that the ignition timing is retarded when a peak value, which is one of the characteristics of the ion current, exceeds a reference characteristic in the operating state at that time (for example, Patent Document 1). In this Patent Document 1, when the peak value of the ion current exceeds the reference characteristic, an excessively good combustion state is detected, and in such a combustion state, combustion is slowed by retarding the ignition timing. In this way, the amount of NOx emission is reduced.
[0003]
In addition, there is known one that determines the generation timing of an ion current and controls the control value of the internal combustion engine near the stable operation limit of the internal combustion engine based on the determination result (for example, Patent Document 2). In this patent document 2, a state in which an ionic current is generated during the exhaust stroke is determined as a stable operation limit. When the stable operation limit is determined, for example, the air-fuel ratio is controlled to avoid misfire and The stable operation state is maintained within the operation limit.
[0004]
[Patent Document 1]
JP-A-7-293411 [Patent Document 2]
Japanese Patent Laid-Open No. 11-324881
[Problems to be solved by the invention]
By the way, it is known that the ignition timing is retarded in order to activate the catalyst early at the time of cold start, for example. This is because the exhaust temperature rises by retarding the ignition timing, and the catalyst is heated by the exhaust gas whose temperature has risen, thus promoting the activation of the catalyst. Usually, the retard amount is set in advance, and is set to an amount that does not cause a malfunction in the driving state, for example, rotation fluctuation.
[0006]
However, if the intake air amount is corrected to increase in order to maintain the idling speed in the operating state where the ignition timing is retarded in this way, detection is not possible with a normal detection method or detection device for detecting rotational fluctuations. Possible unsteady low frequency vibrations may occur. That is, in such an operating state, there is almost no combustion fluctuation that causes rotational fluctuation, but vibration that can be felt when it vibrates may occur. For this reason, it is difficult to increase the amount of retardation, and it is set to an amount until such a phenomenon occurs. However, the low-frequency vibration as described above sometimes occurs. For this reason, it is desired to detect the state where the ignition timing is retarded and the combustion becomes slow, and to set the optimum retard amount while avoiding the occurrence of low-frequency vibration.
[0007]
However, in the thing of patent document 1, since the combustion state is detected based on the peak value of ion current, when combustion becomes slow, such a combustion state may not be detected. That is, the peak of the ion current is not clear in the slow combustion state.
[0008]
Moreover, in the thing of patent document 2, it determines only by whether the generation | occurrence | production timing of an ionic current is an exhaust stroke, and it is unclear how close it is to the stable operation limit. Therefore, it is difficult to detect a slow combustion state within the stable operation limit.
[0009]
The object of the present invention is to eliminate such problems.
[0010]
[Means for Solving the Problems]
That is, the combustion state determination method for an internal combustion engine of the present invention is a combustion state determination method for an internal combustion engine that detects an ionic current generated in the combustion chamber of the internal combustion engine and determines a combustion state based on the characteristics of the detected ionic current. The first characteristic of the ion current detected in the first period including at least the first half of the combustion stroke, and the second characteristic relating to the exhaust stroke from the vicinity including the end point of the first period is detected. The slowness of combustion is detected using the second characteristic of the ionic current, and it is determined that the combustion state is lowered based on the slowness . The first characteristic and the second characteristic correspond to combustion. Thus, the slowness of combustion is defined by the ratio between the value taken by the first characteristic and the value taken by the second characteristic .
[0011]
The first period includes the starting point of the period, that is, the base point as the ignition timing, the point at which a predetermined time has elapsed from the ignition timing or the point at which the crank angle has been rotated, and the like, starting from such a base point, It is set so that at least the first half of the combustion stroke is included in the period. In addition, the second period is immediately before the end of the first period, the end time, or a time when a predetermined time different from the predetermined time has elapsed from the end time or when a predetermined crank angle is rotated different from the predetermined crank angle, etc. The start point of the period, that is, the base point is set in the vicinity including the end point, and is set to a length that ends during the exhaust stroke.
[0012]
According to such a configuration, for example, when the combustion becomes slow by retarding the ignition timing, the ion current that changes depending on the degree of the slowness is detected, and the first characteristic of the detected ion current in the first period is detected. Since the degree of slowness is detected based on the second characteristic in the second period, it becomes possible to accurately determine the slowed combustion state. Therefore, the ignition timing or the amount of fuel to be supplied is controlled based on the determined degree of slowness, in particular, to prevent unsteady low-frequency vibrations that may be mixed with steady vibrations during, for example, idle operation. Is possible.
[0013]
The time characteristic of the ion current is indicated by the time during which the state where the ion current is flowing, and indicates the time during which the ion current is present in the first period and the second period. . The waveform characteristic is a characteristic related to the waveform of the ion current, and includes the maximum value of the ion current value in the first period and the second period, an integrated value obtained by calculating to quantify the characteristics of the waveform, and the like.
[0014]
In order to improve the determination accuracy regardless of the operating state of the internal combustion engine, it is desirable to set the first period to be shorter as the load on the internal combustion engine increases.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0016]
The engine 100 shown schematically in FIG. 1 is a four-cylinder engine for an automobile. A throttle valve 2 that opens and closes in response to an accelerator pedal (not shown) is disposed in the intake system 1. Is provided with a surge tank 3. A fuel injection valve 5 is further provided in the vicinity of one end communicating with the surge tank 3, and the fuel injection valve 5 is controlled by the electronic control unit 6. A spark plug 18 is attached to the cylinder head 31 forming the combustion chamber 30 and generates sparks and serves as an ion current electrode. Further, an O ₂ sensor 21 for measuring the oxygen concentration in the exhaust gas is attached to the exhaust system 20 at a position upstream of the three-dimensional catalyst 22 disposed in a pipe line leading to a muffler (not shown). Yes.
[0017]
The electronic control device 6 is mainly configured by a microcomputer system including a central processing unit 7, a storage device 8, an input interface 9, an output interface 11, and an A / D converter 10. The input interface 9 includes an intake pressure signal a output from the intake pressure sensor 13 for detecting the pressure in the surge tank 3, that is, an intake pipe pressure, and an output from the cam position sensor 14 for detecting the rotation state of the engine 100. Cylinder discrimination signal G1, crank angle reference position signal G2, engine speed signal b, vehicle speed signal c output from the vehicle speed sensor 15 for detecting the vehicle speed, idle switch for detecting the open / closed state of the throttle valve 2 The IDL signal d output from 16, the water temperature signal e output from the water temperature sensor 17 for detecting the coolant temperature of the engine 100, the current signal h output from the O ₂ sensor 21, etc. are input. On the other hand, the output interface 11 outputs a fuel injection signal f to the fuel injection valve 5 and an ignition pulse g to the spark plug 18.
[0018]
A bias power source 24 for measuring ion current is connected to the spark plug 18 via a high voltage diode 23, and an ion current measuring circuit 25 is connected between the input interface 9 and the bias power source 24. ing. As the bias power source 24 and the ion current measuring circuit 25, various devices well known in the art can be applied.
[0019]
The electronic control device 6 has various information determined according to the operating state of the engine 100 using the intake pressure signal a output from the intake pressure sensor 13 and the rotation speed signal b output from the cam position sensor 14 as main information. The basic injection time (basic injection amount) is corrected by the correction coefficient to determine the fuel injection valve opening time, that is, the final injector energization time T, and the fuel injection valve 5 is controlled based on the determined energization time to correspond to the engine load. A program for injecting fuel into the intake system 1 is incorporated.
[0020]
In addition, while controlling the fuel injection of the engine 100 in this way, the electronic control device can detect the ionic current flowing in the combustion chamber at each ignition and determine the combustion state in the entire operation region of the engine 100. 6 is programmed.
[0021]
That is, the combustion state determination program starts from the first characteristic Cp of the ion current detected in the first period P including at least the first half of the combustion stroke and the exhaust stroke from the vicinity including the end point of the first period P. It is the structure which detects the slowness degree of combustion using the 2nd characteristic Cs of the ion current detected in this 2nd period S, and determines that the combustion state has fallen based on the said slowness degree. . In this embodiment, the combustion state determination program is executed in the idle operation state at the time of cold start. It is not executed in the operating state after warming up.
[0022]
In this embodiment, as shown in FIG. 2, the first period P is set to a period including the first half of the combustion stroke until the combustion is almost completed in the case of normal combustion from ignition. The end point of the first period P is set by the crank angle, for example, and is referred to as a combustion end predicted angle Ea. In this case, when the load of the engine 100 is increased, the combustion time in the normal operation state is shortened as the load is increased. Therefore, as shown in FIG. 3, the first period P is shortened as the load is increased. In addition, the combustion end prediction angle Ea is set by a map. The load of the engine 100 is detected based on the intake pipe pressure. Further, since the crank angle until the combustion is finished increases when the engine speed is high, the first period P is set by the map so as to increase as the engine speed increases. On the other hand, the second period S is set to a period related to the exhaust stroke after the combustion stroke of the cylinder in which the ionic current is detected, that is, a period related to the exhaust stroke from the end of the first period P. Therefore, since the first period P changes according to the load state of the engine 100 and the engine speed, the length of the second period S that starts from the predicted combustion end angle Ea also changes.
[0023]
In this embodiment, the first characteristic Cp and the second characteristic Cs are time characteristics of the ion current that flows corresponding to the combustion in order to detect the time during which the combustion continues. Therefore, the first characteristic Cp applies the duration of the ion current detected in the first period P, and the second characteristic Cs applies the duration of the ion current detected in the second period S, respectively.
[0024]
The outline of the combustion state determination program based on the ion current is as shown in FIG. In this embodiment, since the first period P is variable according to the operating state of the engine 100, the intake pipe pressure is detected and the engine speed is detected when the combustion state determination program is executed. The first period P corresponding to the operating state of the engine 100 at this time is determined by searching the map.
[0025]
In FIG. 4, in step S1, ignition is performed. Immediately after ignition, a voltage for detecting the ionic current is applied to the spark plug 18 by the bias power source 24, and the ionic current is detected by the ion current measuring circuit 25. When the combustion of the ionic current is normal, as shown in FIG. 2, the ionic current has a characteristic that the ionic current value becomes maximum within the first period P in which the combustion pressure becomes maximum and then gradually attenuates. On the other hand, as shown by the dotted line in the figure, when the combustion becomes slow, the maximum value of the ionic current value becomes lower than that in the normal combustion, and the time until the ionic current disappears becomes longer. It is what you have. And time progress in the 1st period P is measured by implementing ignition.
[0026]
In step S2, whether or not the first period P has ended is determined by whether or not the combustion end predicted angle Ea has been reached. That is, based on the engine speed signal b output from the cam position sensor 14, it is determined whether or not the crank angle has rotated, for example, 30 ° CA with the ignition time as a base point. In step S3, the duration of the ionic current detected in the first period P, that is, the first characteristic Cp is measured. Depending on the combustion state, the ion current disappears by the end of the first period P, and the first characteristic Cp becomes shorter than the time of the first period P. Conversely, when the first period P ends, the ion current is May continue.
[0027]
In step S4, it is determined whether or not the second period S has ended. In step S5, the duration of the ionic current detected in the second period S, that is, the second characteristic Cs is measured. In step S6, as shown in the following formula (1), the combustion parameter Pc is calculated by dividing the second characteristic Cs by the first characteristic Cp.
[0028]
Pc = Cs ÷ Cp (1)
The ion current detected by the ion current measuring circuit 25 is converted by the A / D converter 10 into digital data. The duration of the ionic current, that is, the first characteristic Cp and the second characteristic Cs are calculated by multiplying the A / D conversion period and the number of digital data until the current value becomes zero.
[0029]
A case where the engine 100 is started in such a configuration at the time of cold start will be described. At the time of cold start, the catalyst is not active because the engine 100 is cold. Therefore, since the emission decreases, the ignition timing is controlled so as to retard the ignition timing and raise the exhaust gas temperature. In this case, since the ignition timing is retarded, combustion may become slow. Then, if the combustion becomes too slow, rotational fluctuations occur. Therefore, it is necessary to determine the combustion state and control the ignition timing to be optimal, that is, not to cause rotational fluctuations and to increase the exhaust temperature.
[0030]
If ignition is performed at the retarded ignition timing (step S1), then step S2 is executed to determine whether or not the combustion end predicted angle Ea has been reached. If not, step S2 is repeatedly executed. Then, when the combustion end predicted angle Ea is reached, step S3 is executed, and the first characteristic Cp is measured. The first characteristic Cp is the time from when the ion current disappears before reaching the predicted combustion end angle Ea to the time when the ion current disappears, and when the ion current continues, the time from the ignition to the predicted combustion end angle Ea.
[0031]
After this, step S4 is executed, and if the second period S ends, step S5 is executed to measure the second characteristic Cs. In this case, the second characteristic Cs is the time from the predicted combustion end angle Ea to the point of disappearance when the ion current has disappeared by the end of the second period S, and the second characteristic Cs is the second when the ion current continues. This is the time until the end of the period S. When the first characteristic Cp and the second characteristic Cs are obtained as described above, step S6 is executed to calculate the combustion parameter Pc.
[0032]
The combustion parameter Pc increases as the ignition timing is retarded, as shown by curve A in FIG. That is, when the combustion is not slow and normal, the ionic current disappears in the first period P or disappears early in the second period S. Therefore, since the ratio of the second characteristic Cs to the first characteristic Cp is small, the combustion parameter Pc is small.
[0033]
On the other hand, in the cylinder where the combustion becomes slow and the ionic current is in the combustion stroke and continues to flow until the combustion stroke ends, the second characteristic Cs becomes large (long). Therefore, since the ratio of the second characteristic Cs to the first characteristic Cp is increased, the combustion parameter Pc is increased.
[0034]
Since the combustion parameter Pc exhibits such characteristics, the slowness of combustion can be detected based on the combustion parameter Pc. That is, when the combustion parameter Pc is a small value, the degree of slowness of combustion is small, and there is a margin for retarding the ignition timing. On the other hand, when the combustion parameter Pc is large, the degree of slowness of combustion is large and it can be determined that the combustion has slowed down and the ignition timing retardation has reached the limit or the limit It can be determined that it has exceeded.
[0035]
Therefore, it is possible to detect the degree of slowness of combustion from the combustion parameter Pc and control the ignition timing. For example, when the combustion parameter Pc increases as the ignition timing retards as shown in FIG. 5, paying attention to the portion where the combustion parameter Pc changes linearly, the linear change portion can be allowed. Set the target ignition timing, which is the ignition timing immediately before the slow combustion state, that is, the unsteady low-frequency vibration, and advance or retard the ignition timing so that the target ignition timing is reached. To control.
[0036]
By performing feedback control of the ignition timing corresponding to the linearly changing portion of the combustion parameter Pc in this way, it occurs in an unsteady state other than the steady vibration in the idling operation state, particularly in the idling operation at the cold start. In addition to preventing low-frequency vibrations that occur, and by retarding the ignition timing to the amount of retardation immediately before reaching such low-frequency vibrations, that is, the target ignition timing, the exhaust temperature is accurately raised and the catalyst Can be activated early. For this reason, the fall of the emission at the time of cold start can be prevented, and combustion can be stabilized. Note that the fuel injection amount may be controlled instead of the ignition timing. In this case, the fuel injection amount is increased when it is determined by the combustion parameter Pc that the combustion state is slow, in other words, the combustion state is decreasing.
[0037]
In this embodiment, since the combustion parameter Pc, which is a dimensionless value based on the ratio between the first characteristic Cp and the second characteristic Cs, is used, for example, the peak value (maximum value) of the detected ion current is used as it is. As in the case of use, it is possible to prevent the determination accuracy from being lowered due to the influence of the properties of the fuel, the temperature of the engine 100, and the like.
[0038]
Furthermore, since the first period P is shortened as the load on the engine 100 increases and the first period P is increased as the engine speed increases, the first period P is increased according to the operating condition of the engine. The period P can be adjusted. Therefore, high determination accuracy can be maintained even in an operation state in which the load of the engine 100 and the engine speed change with time, such as an idle operation state during cold start.
[0039]
The setting of the first period and the second period is not limited to the above embodiment, and the base point of the first period does not coincide with the ignition timing, and after a predetermined time has elapsed from the ignition timing or It may be set at a time after a predetermined crank angle rotation. In such a setting, the first period includes at least the first half of the combustion stroke. In addition, the second period is, for example, a point before the predetermined time that is different from the predetermined time at the end of the first period, a point before the predetermined crank angle rotation that is different from the predetermined crank angle, or an end point of the first period. It may be set after a predetermined time different from the predetermined time or after a predetermined crank angle rotation different from the predetermined crank angle.
[0040]
In addition, the first period P is set to a fixed length, and is set to a length at which the ionic current disappears within the first period P in the case of normal combustion. When the combustion is not slow, the above combustion is always performed. The parameter Pc may be 0. That is, when the first period P is set in this way, the first characteristic Cp takes some value unless misfiring. On the other hand, the second characteristic Cs takes a certain value when the combustion becomes slow and the ionic current continuously flows beyond the first period P. Therefore, with such a configuration, in the above formula (1), the second characteristic Cs becomes a certain value, and the combustion parameter Pc becomes larger than 0, whereby the slowness of combustion can be detected, and the slowness Based on the degree, it is possible to quickly determine that the combustion has decreased and slowed down. The characteristic of the combustion parameter Pc in this case is as shown by a curve B in FIG.
[0041]
Further, the combustion characteristic Pc may be obtained by dividing the second characteristic Cs by adding the first characteristic Cp and the second characteristic Cs. In addition, the maximum value of the ion current value in the first period P is divided by the maximum value obtained by subtracting the maximum value of the ion current value in the second period S from the maximum value of the ion current value in the first period P. The combustion parameter Pc may be used.
[0042]
Furthermore, the combustion parameter Pc may be defined by the degree of variation of the numerical value obtained from the ratio between the first characteristic Cp and the second characteristic Cs described above.
[0043]
In addition, the first characteristic Cp and the second characteristic Cs are the product of the maximum value of the ion current value in the first period P and the second period S, the duration of the ion current in each period and the maximum value of the ion current value. The integral value of the ion current waveform may be used. Even in the case of such first characteristic Cp and second characteristic Cs, the combustion parameter P is calculated by the above equation (1).
[0044]
Even in the combustion parameter Pc obtained by these calculation methods, since it is a non-dimensional value, the same effect as the above-described embodiment can be obtained.
[0045]
In addition, the specific configuration of each part is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.
[0046]
【The invention's effect】
Since the present invention has the configuration described above, for example, when the combustion becomes slow by retarding the ignition timing, an ion current that changes depending on the degree of the slowness is detected, and the first period of the detected ion current is detected. Since the degree of slowness is detected based on the first characteristic and the second characteristic in the second period, the slowed combustion state can be accurately determined. Therefore, the ignition timing or the amount of fuel to be supplied is controlled based on the detected degree of slowness, in particular, to prevent unsteady low-frequency vibrations that may be mixed, for example, in stationary vibrations during idle operation. Can do.
[Brief description of the drawings]
FIG. 1 is a schematic configuration explanatory diagram of an engine to which an embodiment of the present invention is applied.
FIG. 2 is an operation explanatory diagram according to the embodiment of the present invention.
FIG. 3 is a graph showing the relationship between the predicted combustion end angle and the engine speed in the embodiment of the present invention.
FIG. 4 is a flowchart showing a control procedure of the embodiment.
FIG. 5 is a graph showing the tendency of the combustion parameter with respect to the ignition timing in the embodiment of the present invention.
[Explanation of symbols]
6 ... Electronic control unit 7 ... Central processing unit 8 ... Storage device 9 ... Input interface 11 ... Output interface P ... First period S ... Second period Cp ... First characteristic Cs ... Second characteristic

Claims (2)

A method for determining a combustion state of an internal combustion engine that detects an ionic current generated in a combustion chamber of the internal combustion engine and determines a combustion state based on characteristics of the detected ionic current,
The first characteristic of the ion current detected in the first period including at least the first half of the combustion stroke, and the ion current detected in the second period related to the exhaust stroke from the vicinity including the end point of the first period. Detect the slowness of combustion using the second characteristic,
It is determined that the combustion state is lowered based on the degree of slowness ,
The first characteristic and the second characteristic are the time characteristic or waveform characteristic of the ion current that flows corresponding to combustion, and the degree of slowness of combustion is defined by the ratio between the value taken by the first characteristic and the value taken by the second characteristic A method for determining a combustion state of an internal combustion engine. 2. The combustion state determination method for an internal combustion engine according to claim 1 , wherein the first period is set to become shorter as the load on the internal combustion engine becomes higher .

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