JP2004232568A - Method of determining combustion state of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of detecting a combustion state of an internal combustion engine to detect a vibration difficult to be detected as a normal rotating fluctuation in an internal combustion engine. <P>SOLUTION: In this method of detecting a combustion state of an internal combustion engine for detecting ion current generated in a combustion chamber of an internal combustion engine and determining a combustion state based on a characteristic of the detected ion current, a degree of slow combustion is detected using a first characteristic of ion current detected during a first period including at least a combustion process and a second characteristic of icon current detected during a second period from the proximity including the end timing of the first period and proximity of an exhaust process, to determine deterioration of the combustion state based on the degree of the slow combustion. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for detecting a combustion state of an internal combustion engine, which detects vibration that is difficult to detect as normal rotation fluctuation in the internal combustion engine.
[0002]
[Prior art]
Conventionally, in an internal combustion engine mounted on a vehicle such as an automobile, an engine uses an ionic current generated in a combustion chamber from the start of combustion to detect occurrence of knocking, determine a combustion state, and perform other operations. Sometimes used for control. For example, there has been known an apparatus that retards the ignition timing when a peak value, which is one of the characteristics of the ion current, exceeds a reference characteristic in an operating state at that time (for example, Patent Document 1). In Patent Document 1, the excessively good combustion state is detected when the peak value of the ion current exceeds the reference characteristic, and in such a combustion state, the combustion is slowed by retarding the ignition timing. Is controlled so as to reduce the NOx emission amount.
[0003]
There is also known an apparatus 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 Patent Document 2, a state in which an ion current is generated during an exhaust stroke is determined to be a stable operation limit. When the stable operation limit is determined, for example, the air-fuel ratio is controlled to avoid misfiring, This maintains a stable operation state within the operation limit.
[0004]
[Patent Document 1]
JP-A-7-293411 [Patent Document 2]
JP-A-11-324881
[Problems to be solved by the invention]
Incidentally, it is known that the ignition timing is retarded in order to activate the catalyst early, for example, during a cold start. This is because the exhaust gas temperature is increased by retarding the ignition timing, and the catalyst is heated by the exhaust gas having the increased temperature, so that the activation of the catalyst is promoted. Normally, the retard amount is set in advance, and is set to an amount that does not cause a problem in the operation state, for example, rotation fluctuation.
[0006]
However, if the intake air amount is increased and corrected in order to maintain the idling speed in such an operating state in which the ignition timing is retarded, the normal detection method or detection device for detecting the rotation fluctuation cannot detect the rotation fluctuation. Possible unsteady low frequency oscillations may occur. In other words, in such an operating state, combustion fluctuation such as rotation fluctuation hardly occurs, but vibration that can be sensed as being vibrated may occur. For this reason, it is difficult to increase the amount of retardation, and the retardation amount is set to such an amount as to cause such a phenomenon. However, the above-described low-frequency vibration sometimes occurs. Therefore, it is desired that the ignition timing is retarded to detect a state in which combustion becomes slow, and that an optimal retard amount is set by avoiding the occurrence of low-frequency vibration.
[0007]
However, in the case of Patent Document 1, since the combustion state is detected based on the peak value of the ion current, when the combustion becomes slow, such a combustion state may not be detected in some cases. That is, in a slow combustion state, the peak of the ionic current is not clear.
[0008]
Further, in the case of Patent Document 2, the determination is made only based on whether or not the generation timing of the ion current is the exhaust stroke, and it is unknown how close the operation limit is to the stable operation limit. Therefore, it is difficult to detect a slow combustion state within the stable operation limit.
[0009]
An object of the present invention is to solve such a problem.
[0010]
[Means for Solving the Problems]
That is, the method for determining a combustion state of 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 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 ionic current detected in the first period including at least the first half of the combustion stroke, and the first characteristic detected in the second period of the exhaust stroke from the vicinity including the end point of the first period. The degree of slowness of combustion is detected using the second characteristic of the ionic current, and it is determined that the combustion state is reduced based on the degree of slowness of combustion.
[0011]
The first period, the starting point of the period, i.e., the starting point as the ignition timing, the time when a predetermined time has elapsed from the ignition timing or the time when the crank angle is rotated by a predetermined crank angle, and the like, starting from such a starting point, At least the first half of the combustion stroke is set to be included in the period. In addition, the second period is immediately before the end time of the first period, the end time, or the time when a predetermined time different from the predetermined time elapses from the end time or when a predetermined crank angle different from the predetermined crank angle is rotated. , A start point of the period, that is, a base point, is set near the end point, and the length is set to a length that ends during the exhaust stroke.
[0012]
According to such a configuration, for example, when combustion is slowed by retarding the ignition timing, an ion current that changes according to the degree of the slowdown 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 slow combustion state. Therefore, the ignition timing or the amount of fuel to be supplied is controlled based on the determined degree of slowness, and in particular, to prevent unsteady low-frequency vibration that may be mixed with steady vibration during idle operation, for example. Becomes possible.
[0013]
In order to improve the determination accuracy, the first characteristic and the second characteristic are time characteristics or waveform characteristics of the ion current, and the degree of slowness of combustion is defined by a ratio between the first characteristic and the second characteristic. Are preferred. The time characteristic of the ionic current is indicated by the time during which the state in which the ionic current is flowing continues, and indicates the time during which the ionic current is present in the first period and the second period. . The waveform characteristics are characteristics relating to the waveform of the ionic current, and include a maximum value of the ionic current value in the first period and the second period, an integrated value obtained by calculating a characteristic of the waveform into a numerical value, and the like.
[0014]
Also, 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 in order to improve the determination accuracy.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0016]
The engine 100 schematically shown in FIG. 1 is of a four-cylinder type for an automobile, and its intake system 1 is provided with a throttle valve 2 that opens and closes in response to an accelerator pedal (not shown). Is provided with a surge tank 3. A fuel injection valve 5 is further provided near one end communicating with the surge tank 3, and the fuel injection valve 5 is controlled by an electronic control unit 6. A spark plug 18 that generates sparks and serves as an electrode for ion current is attached to a cylinder head 31 that forms the combustion chamber 30. 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 a three-dimensional catalyst 22 provided in a pipe leading to a muffler (not shown). I have.
[0017]
The electronic control unit 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. An input interface 9 has an intake pressure signal a output from an intake pressure sensor 13 for detecting the pressure in the surge tank 3, that is, an intake pipe pressure, and an output from a cam position sensor 14 for detecting a rotation state of the engine 100. The cylinder discrimination signal G1, the crank angle reference position signal G2, the engine speed signal b, the vehicle speed signal c output from the vehicle speed sensor 15 for detecting the vehicle speed, and the idle switch for detecting the open / close state of the throttle valve 2. An IDL signal d output from the engine 16, a water temperature signal e output from the water temperature sensor 17 for detecting the cooling water temperature of the engine 100, a current signal h output from the O ₂ sensor 21, and the like 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 supply 24 for measuring an ion current is connected to the spark plug 18 via a high-voltage diode 23, and an ion current measurement circuit 25 is connected between the input interface 9 and the bias power supply 24. ing. As the bias power supply 24 and the ion current measurement circuit 25, various types well known in the art can be applied.
[0019]
The electronic control unit 6 uses 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, and various types of information determined according to the operating state of the engine 100. 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 energization time T of the injector. The fuel injection valve 5 is controlled based on the determined energization time, and is controlled according to the engine load. A program for injecting the fuel into the intake system 1 is stored.
[0020]
In addition, while controlling the fuel injection of the engine 100 in this way, the electronic control unit is configured to detect the ionic current flowing in the combustion chamber for each ignition and to determine the combustion state in the entire operating range of the engine 100. 6 is programmed.
[0021]
That is, the combustion state determination program executes the first characteristic Cp of the ionic current detected in the first period P including at least the first half of the combustion stroke, and the vicinity including the end point of the first period P to the exhaust stroke. The degree of slowness of combustion is detected using the second characteristic Cs of the ionic current detected in the second period S, and it is determined that the combustion state is reduced based on the degree of slowness. . In this embodiment, the combustion state determination program is executed in an idle operation state at the time of a cold start. It is not executed in the operating state after warm-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 from combustion to normal completion of combustion in the case of normal combustion. The end point of the first period P is set by, for example, a crank angle, and is referred to as a predicted combustion end angle Ea. In this case, when the load on the engine 100 increases, the combustion time in the normal operating state decreases as the load increases. Therefore, as shown in FIG. 3, the first period P decreases as the load increases. Then, 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. If the engine speed is high, the crank angle until the end of combustion increases, so the first period P is set by the above map so as to become longer as the engine speed increases. On the other hand, the second period S is set to a period during which the combustion stroke of the cylinder in which the ionic current is detected is substantially completed and the exhaust stroke is performed, that is, the period from the end of the first period P to the exhaust stroke. Therefore, since the first period P changes according to the load state of the engine 100 and the engine speed, the length also changes in the second period S started from the combustion end predicted angle Ea.
[0023]
In this embodiment, the first characteristic Cp and the second characteristic Cs are time characteristics of the ion current flowing in response to the combustion in order to detect the time during which the combustion is continued. 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.
[0024]
An outline of the combustion state determination program based on the ion current is as shown in FIG. In this embodiment, the first period P has a variable length according to the operating state of the engine 100. Therefore, when the combustion state determination program is executed, the intake pipe pressure is detected and the engine speed is detected. The first period P according to the operating state of the engine 100 at this time is determined by searching a map.
[0025]
In FIG. 4, in step S1, ignition is performed. Immediately after the ignition, a voltage for detecting an ionic current is applied to the spark plug 18 by the bias power supply 24, and the ionic current is detected by the ionic current measuring circuit 25. When the combustion is normal, as shown in FIG. 2, the ion current has a characteristic that the ion current value becomes maximum in the first period P when the combustion pressure becomes maximum, and thereafter gradually decreases. On the other hand, as shown by the dotted line in the figure, when the combustion becomes slow, the maximum value of the ion current value becomes lower than that in the normal combustion, and the time until the ion current disappears becomes longer. Have Then, by performing the ignition, the lapse of time in the first period P is measured.
[0026]
In step S2, it is determined whether or not the first period P has ended based on whether or not the combustion end prediction angle Ea has been reached. That is, it is determined whether or not the crank angle has been rotated by, for example, 30 ° CA based on the ignition timing based on the engine speed signal b output from the cam position sensor 14. In step S3, the continuation time of the ion current detected in the first period P, that is, the first characteristic Cp is measured. Depending on the combustion state, the ionic current disappears before the end of the first period P, and the first characteristic Cp becomes shorter than the time of the first period P. May be continuing.
[0027]
In step S4, it is determined whether the second period S has ended. In step S5, the continuation time of the ion current detected in the second period S, that is, the second characteristic Cs is measured. In step S6, as shown in the following equation (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 measurement circuit 25 is converted by the A / D converter 10 into digital data. Then, the duration of the ion current, that is, the first characteristic Cp and the second characteristic Cs are calculated by multiplying the A / D conversion cycle by the number of digital data until the current value becomes zero.
[0029]
In such a configuration, a case where the engine 100 is started during a cold start will be described. During a 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 increase the exhaust gas temperature. In this case, since the ignition timing is retarded, combustion may be slow. Then, if the combustion becomes too slow, the rotation fluctuates. Therefore, it is necessary to determine the combustion state and control the ignition timing to an optimum one, that is, control so that the rotation fluctuates and the exhaust gas temperature becomes high.
[0030]
When the ignition is performed with the retarded ignition timing (step S1), step S2 is thereafter executed to determine whether or not the combustion end predicted angle Ea has been reached, and 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. If the ionic current has disappeared before reaching the combustion end predicted angle Ea, the first characteristic Cp is a time until the extinction point, and if the ion current has continued, it is a time from ignition to the combustion end predicted angle Ea.
[0031]
Thereafter, step S4 is executed, and when 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 combustion end predicted angle Ea to the time of its disappearance when the ion current has disappeared by the end of the second period S. 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 indicated by the curve A in FIG. That is, when the combustion is not slow, the ion current disappears in the first period P, or disappears earlier 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, if the combustion becomes slow and the ion current continues to flow in the cylinder in the combustion stroke 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 increases, the combustion parameter Pc increases.
[0034]
Since the combustion parameter Pc exhibits such characteristics, the degree of 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. Conversely, when the combustion parameter Pc is large, the degree of slowness of combustion is large, and it can be determined that combustion is slowing down, and the retardation of the ignition timing has reached or reached the limit. It can be determined that it has exceeded.
[0035]
Therefore, it becomes possible to detect the degree of slowness of combustion by the combustion parameter Pc and control the ignition timing. For example, when the combustion parameter Pc increases as shown in FIG. 5 according to the retardation of the ignition timing, a portion where the combustion parameter Pc changes linearly can be allowed in the linear change portion. Set a target ignition timing that is the ignition timing immediately before the occurrence of a slow combustion state, that is, an unsteady low-frequency vibration, and advance or retard the ignition timing so that the target ignition timing is reached. To control.
[0036]
In this way, by performing the feedback control of the ignition timing corresponding to the linearly changing portion of the combustion parameter Pc, especially in the idling operation at the time of the cold start, an unsteady vibration other than the steady vibration in the idling operation state is generated. In addition to preventing low-frequency vibrations, the amount of retardation immediately before such low-frequency vibrations, that is, the ignition timing is retarded to the target ignition timing, so that the exhaust gas temperature can be raised accurately and the catalyst Can be activated early. For this reason, it is possible to prevent the emission from decreasing during the cold start and to stabilize the combustion. 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 that the combustion state is deteriorating according to the combustion parameter Pc.
[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. 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 as in the case of using the fuel cell.
[0038]
Furthermore, the first period P is shortened as the load on the engine 100 increases, and the first period P is lengthened as the engine speed increases. 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 over time, such as an idle operation state at the time of a cold start.
[0039]
Note that 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 point after a predetermined crank angle rotation. In such a case, the first period includes at least the first half of the combustion stroke. In the second period, the base point is, for example, a time before a predetermined time different from the predetermined time at the end of the first period, a time before a predetermined crank angle rotation different from the predetermined crank angle, or a time at the end of the first period. May be set after a predetermined time different from the predetermined time or after a rotation of a predetermined crank angle different from the predetermined crank angle.
[0040]
Further, the first period P is set to a fixed length, and in a case of normal combustion, it is always set to a length in which the ionic current disappears within the first period P. If the combustion is not slow, the above combustion is always performed. The parameter Pc may be set to 0. That is, when the first period P is set in this manner, the first characteristic Cp takes a certain value unless a misfire occurs. On the other hand, the second characteristic Cs takes a certain value when the combustion becomes slow and the ion current continuously flows beyond the first period P. Therefore, with such a configuration, in the above equation (1), the second characteristic Cs takes a certain value, and the combustion parameter Pc becomes larger than 0, so that the degree of slowness of combustion can be detected, and the slowness of combustion can be detected. It is possible to quickly determine that the combustion has slowed down due to the degree based on the degree. 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. It may be the combustion parameter Pc.
[0042]
Furthermore, the combustion parameter Pc may be defined by the degree of variation in 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 maximum value of the ion current value in the first period P and the second period S, and the product of the ion current duration and the maximum value of the ion current value in each period. , The integral value of the ion current waveform. Even in the case of such a first characteristic Cp and a second characteristic Cs, the combustion parameter P is calculated by the above equation (1).
[0044]
Even the combustion parameter Pc obtained by these calculation methods is a dimensionless value, so that the same operational effects as those of the above-described embodiment can be obtained.
[0045]
In addition, the specific configuration of each unit 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 combustion is slowed by retarding the ignition timing, an ion current that changes according to 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 slow 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 vibration that may be mixed with steady vibration during idling operation, for example. Can be.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an engine to which an embodiment of the present invention is applied.
FIG. 2 is an operation explanatory view in the embodiment of the present invention.
FIG. 3 is a graph showing a relationship between a predicted combustion end angle and an engine speed in the embodiment of the present invention.
FIG. 4 is a flowchart showing a control procedure according to the embodiment.
FIG. 5 is a graph showing a tendency of a combustion parameter with respect to an 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 (3)

A method for determining a combustion state of an internal combustion engine that detects an ion current generated in a combustion chamber of the internal combustion engine and determines a combustion state based on characteristics of the detected ion current,
The first characteristic of the ionic current detected in the first period including at least the first half of the combustion stroke, and the ionic current detected in the second period related to the exhaust stroke from the vicinity including the end point of the first period. Detecting the degree of slowness of combustion using the second characteristic,
A method for determining a combustion state of an internal combustion engine, comprising: determining that a combustion state has decreased based on the degree of slowness. 2. The method according to claim 1, wherein the first characteristic and the second characteristic are a time characteristic or a waveform characteristic of the ion current, and the degree of slowness of combustion is defined by a ratio of the first characteristic and the second characteristic. A method for determining the combustion state of an internal combustion engine. 3. The method according to claim 1, wherein the first period is set to be shorter as the load on the internal combustion engine increases.

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