JP4749171B2 - Air-fuel ratio determination method for internal combustion engine based on ion current - Google Patents

Description

  The present invention relates to an air-fuel ratio determination method for an internal combustion engine configured to be able to determine an air-fuel ratio related to combustion of the internal combustion engine from an ionic current generated in the combustion chamber.

Conventionally, an internal combustion engine, that is, an engine mounted on a vehicle such as an automobile, tends to be operated in a lean state (a mixture is thin) with a high air-fuel ratio in order to improve fuel efficiency and purify exhaust gas. An engine that is operated with such an air-fuel ratio lean is known in which the combustion state is determined using an ionic current in order to make the air-fuel ratio as lean as possible. For example, in Patent Document 1, the duration of the ion current is measured while the ion current generated in the combustion chamber of the engine after ignition exceeds a predetermined value, and the parameter indicating the variation in the measured duration is a determination value. In this case, the lean limit corresponding to the limit air-fuel ratio at which torque fluctuation occurs is detected.
Japanese Patent No. 3150429

  It is known that when the stoichiometric air-fuel ratio is in a good combustion state, the ionic current increases rapidly after ignition, reaches a maximum near the top dead center where the combustion pressure becomes maximum, and then decays rapidly and disappears. It has been. When the engine is operated with the actual air-fuel ratio leaner than the stoichiometric air-fuel ratio, the ionic current is generated for a longer time than in the above-mentioned good combustion state, and the maximum timing shifts to the bottom dead center side. In addition, the maximum current value is smaller than that in a good combustion state. If the air-fuel ratio is controlled so that the actual air-fuel ratio becomes leaner, the timing at which the ion current becomes maximum is biased to the timing corresponding to the later stage of combustion, and that timing varies with each ignition. Become.

  As described above, the behavior of the ionic current changes corresponding to the air-fuel ratio. However, in Patent Document 1 described above, the duration of the ionic current is measured, Since the lean limit is detected based on the measured duration, it may not be detected depending on the state of generation of the ionic current. That is, as described above, when the air-fuel ratio becomes leaner, the time when the ionic current becomes maximum is biased to the time corresponding to the later stage of combustion, but even in this case, the air-fuel ratio is lean. Similar or longer durations are measured. Therefore, it is impossible to detect a state in which the air-fuel ratio shifts to leaner.

  Therefore, the present invention aims to eliminate such problems.

That is, the air-fuel ratio determination method for an internal combustion engine based on an ionic current according to the present invention generates a peak determination period and an ionic current including a timing when the characteristic value of the ionic current generated in the combustion chamber at each ignition is maximum in the internal combustion engine. and a and are generation period is measured, a air-fuel ratio determining method for an internal combustion engine based on an ion current determines the air-fuel ratio by using the the measured peak determination period generation period, the variation of the measured generation period combustion air in the late actual air-fuel ratio is greater than the criterion is determined to have become leaner than the stoichiometric air-fuel ratio, the variation of the measured peak judgment period is burning for determining the air-fuel ratio in the initial state ion determines that the actual air-fuel ratio is greater than the criterion is even leaner than the air-fuel ratio determined by the occurrence period measured for determining the state Characterized in that based on the flow.

  According to such a configuration, when the air-fuel ratio is lean based on the ion current that changes in response to the change in the air-fuel ratio when the engine is operating, the air-fuel ratio is determined according to the degree of leanness. It becomes possible to do. In other words, as the air-fuel ratio becomes lean, the timing at which the characteristic value of the ionic current exhibits the maximum shifts, but the air-fuel ratio is determined based on the degree of variation in the peak determination period. It becomes possible to determine the case of leaner than that.

  According to such a configuration, the first determination value and the second determination value are set in different setting states, and the degree of the air-fuel ratio is determined according to the degree of variation of the period measured based on each determination value. To do. In this way, since the degree of lean can be determined by setting two determination values for determining the ion current generation state, it is possible to simplify the configuration of the circuit and control program for the determination. Become.

  The characteristic value of the ion current in the present invention refers to the current value and voltage value of the ion current.

  The present invention has a configuration as described above, and measures the generation period in which the ionic current is generated and the peak determination period including the time when the characteristic value exhibits the maximum, and is based on the degree of variation. The degree of the fuel ratio can be determined.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

An engine 100 schematically shown in FIG. 1 is a spark-ignition four-cycle 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 an intake system 1 thereof. A surge tank 3 is provided on the downstream side. 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. The cylinder head 31 forming the combustion chamber 30 is provided with an intake valve 32 and an exhaust valve 33, and with a spark plug 18 that generates sparks and serves as an electrode for detecting the ionic current I. Further, in the exhaust system 20, an O ₂ sensor 21 for measuring the oxygen concentration in the exhaust gas is located upstream of the three-way catalyst 22 which is a catalyst device arranged in a pipe line leading to a muffler (not shown). Is attached. In FIG. 1, the configuration of one cylinder of engine 100 is shown as a representative.

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 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 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, from the output interface 11, a fuel injection signal f is output to the fuel injection valve 5, and an ignition pulse g is output to the spark plug 18.

  A bias power source 24 for measuring the ion current I is connected to the spark plug 18, and an ion current measuring circuit 25 is connected between the input interface 9 and the bias power source 24. The spark plug 18, the bias power supply 24 and the ion current measurement circuit 25 constitute an ion current detection system 40. The bias power source 24 applies a measurement voltage (bias voltage) for measuring the ion current to the spark plug 18 when the ignition pulse g disappears. The ion current I flowing between the inner wall of the combustion chamber 30 and the center electrode of the spark plug 18 and between the electrodes of the spark plug 18 by applying the measurement voltage is measured by the ion current measuring circuit 25. . As the bias power source 24 and the ion current measuring circuit 25, various devices well known in the art can be applied.

  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 energization time of the injector, and the fuel injection valve 5 is controlled by the determined energization time in accordance with the engine load. A program for injecting fuel into the intake system 1 is incorporated. In addition, while controlling the fuel injection of the engine 100 in this way, a period in which the ion current I generated in the combustion chamber 30 is detected at each ignition and the detected ion current I is equal to or more than two determination values having different values. The electronic control unit 6 is programmed so as to determine the actual degree of air-fuel ratio based on the fluctuation rate indicating the variation calculated from a plurality of measured periods.

  In such a configuration, the air-fuel ratio determination program is executed by the following procedure. 2 and 3 illustrate the air-fuel ratio determination procedure. In the air-fuel ratio determination program, a first determination value H1 and a second determination value H2 for measuring the generation period in which the detected ion current I is generated are set. The first determination value H1 is set to a value that can detect that the ion current I is generated, and the generation period P1 during which the ion current I is generated is measured by the first determination value H1. is there. The second determination value H2 is set to a value at which it can be detected that the combustion is good, and the peak determination including a time when the current value that is the characteristic value of the ion current I exhibits the maximum by the second determination value H2. The period P2 is measured. FIG. 4 shows the relationship between the first determination value H1 and the second determination value H2 together with the current waveform of the ion current I.

  The ionic current I shown in the figure is detected when the combustion state is good. After flowing rapidly after ignition, it decreases again before the top dead center TDC, and then increases again with the passage of time. The current value becomes the maximum near the crank angle at which becomes the maximum, and then gradually decreases and usually disappears near the end of the expansion stroke.

  In the ion current I showing such a current waveform, the generation period P is obtained by measuring a period during which the current value of the ion current I exceeds the first determination value H1. In this case, the generation period P1 of the ion current I is measured by either the actual time from the start of measurement to the end of measurement or the crank angle. The measurement period during which the generation period P1 of the ion current I is measured is set, for example, from ignition to the end of the expansion stroke. During the measurement period, the period during which the ion current I exceeds the first determination value H1 is measured. Thus, the generation period P1 of the ion current I is set. The first determination value H1 is preferably as low as possible, but is set to be higher than the noise level when the ion current I is detected so that the ion current I is not erroneously detected.

  The ionic current I shows various behaviors depending on the combustion state. For example, in the case of combustion in the vicinity of the theoretical air-fuel ratio, the ionic current I shows the behavior described above, but the amount of fuel in the air-fuel mixture is small relative to the air. When the air-fuel ratio becomes lean, the maximum current value decreases, and therefore the peak determination period P2 becomes shorter and the generation period P1 of the ionic current I tends to become shorter according to the amount of fuel. In addition, when the air-fuel ratio becomes leaner, the time when the current value of the ion current I becomes maximum tends to shift to the second half of combustion.

This air-fuel ratio determination program is executed by measuring the generation period P1 and the peak determination period P2 of the ion current I from a specific cylinder, and is executed for each cylinder and the four cylinders are combined. Any of those that are executed.

  First, in step S1, the generation period P1 of the ion current I for each ignition is measured. The generation time P1 of the ion current I is measured by the time or the crank angle during which the ion current I exceeds the first determination value H1. The measured generation period P1 of the ionic current I is temporarily stored in the storage device 8. The generation period P1 of the stored ionic current I is a predetermined number (plural) in order to calculate the average value (moving average).

  In step S2, the fluctuation rate of the occurrence period P1 (hereinafter referred to as the occurrence period fluctuation rate) is calculated. The occurrence period variation rate is an average value of deviations obtained by calculating an average value based on the occurrence period P1 measured this time and a predetermined number of occurrence periods P1 stored, and subtracting each occurrence period P1 from the average value. The average is calculated by dividing by the average value of the occurrence period P1. The occurrence period variation rate is determined based on a determination criterion that is set so that an occupant can experience the operating state of the engine 100 that changes due to the variation in the air-fuel ratio. is there. The determination criteria are specifically determined by the mounted state of the engine 100 and the specifications of the entire vehicle. For example, 40% for idling operation, and for driving in steady driving For example, 20% is set according to the operating state of the engine 100.

  In step S3, the peak determination period P2 of the detected ion current I is measured based on the second determination value H2. That is, the time when the current value of the ionic current I exceeds the second determination value H2 from the lower side to the upper side (time when the current value exceeds the second determination value H2 from the upper side to the lower side) ) Until the peak determination period P2. The measurement of the peak determination period P2 substantially corresponds to detection of the time when the current value of the ionic current I exceeds the second determination value H2 and the time when it falls below the second determination value H2. The measured peak determination period P2 is temporarily stored in the storage device 8 in the same manner as the occurrence period P1, and a predetermined number (plurality) is calculated in the storage device 8 to calculate the average value (moving average). It is remembered.

  In step S4, the fluctuation rate of the peak determination period P2 (hereinafter referred to as the peak determination fluctuation rate) is calculated. The calculation method of the peak determination variation rate is the same as that of the occurrence period variation rate. This peak determination variation rate is a value indicating how much the time at which the current value of the ion current I becomes maximum is varied, and is used to determine the state of the air-fuel ratio in the later stage of combustion. The determination is based on a determination criterion set so that it can be determined that the state is not good. This determination criterion is specifically determined by the mounting state of the engine 100 and the specifications of the entire vehicle, but is set to, for example, about 50% regardless of the operating state of the engine 100, for example.

  Next, in step S11, a correction coefficient for controlling the operating state is calculated from the calculated peak determination variation rate. The correction coefficient is set so as to increase as the peak determination variation rate increases. For example, the correction coefficient is set on the map in a tendency as shown in FIG.

  In step S12, the generation period variation rate and the combustion state determination value are compared. As shown in FIG. 6, this combustion state determination value is set based on the generation period variation rate due to the generation period P1 measured in the combustion at almost the stoichiometric air-fuel ratio. It is set so that it can be determined when the vehicle has become lean. When it is determined that the generation period variation rate exceeds the combustion state determination value, it is determined that the actual air-fuel ratio is biased toward the lean side from the stoichiometric air-fuel ratio. As shown in the figure, when the air-fuel ratio is rich, the peak determination fluctuation rate tends to increase (become) in the same manner as the occurrence period fluctuation rate, but the whole is empty. There is a tendency for the air-fuel ratio to rise later as the air-fuel ratio becomes leaner, that is, as the air-fuel ratio becomes leaner, after the fluctuation of the generation period fluctuation rate becomes larger.

  Then, after determining that the actual air-fuel ratio is biased toward the lean side, in step S13, the fuel injection amount is corrected using the correction coefficient obtained in step S11, and in other words, the fuel injection amount is empty. Performs feedback control of the fuel ratio.

  In such a configuration, when the engine 100 is operated, Steps S1 to S4 are executed every time ignition is performed, the generation period variation rate reflecting the variation of the air-fuel ratio corresponding to the early stage of combustion, and the air-fuel ratio corresponding to the later stage of combustion. It is possible to determine how lean the air-fuel ratio is by calculating the peak determination variation rate that reflects the variation of the above. If the generation period variation rate exceeds the combustion state determination value (step S12), air-fuel ratio feedback control is performed using the correction coefficient (step S11) calculated based on the peak determination variation rate, and the generation period variation rate is determined. The determined actual air-fuel ratio is set to the rich side from the lean state.

  Therefore, in the operating state in which the air-fuel ratio is changing to the lean side, the air-fuel ratio is changed to the stoichiometric air-fuel ratio before the air-fuel ratio based on the peak determination variation rate further changes to the lean side and the combustion state becomes unfavorable. The combustion state can be stabilized.

  In addition, the first determination value H1 for measuring the generation period variation rate to determine the degree of variation in the generation period in the early stage of combustion and the peak determination to determine the degree of variation in the period in which the ion current I is maximized in the later stage of combustion. Since only two determination values, the second determination value H2 for measuring the variation rate, are set, the circuit configuration and the control program can be simplified.

  In the above-described embodiment, the air-fuel ratio lean is determined based on the occurrence period variation rate, and the air-fuel ratio feedback control is not performed based on the occurrence period variation rate, and the correction is set based on the peak determination variation rate. Although the air-fuel ratio feedback control was performed by the coefficient to prevent the air-fuel ratio from becoming leaner, a correction coefficient was set based on the generation period variation rate, and the generation period variation rate exceeded the combustion state determination value. In this case, the air-fuel ratio feedback control is performed with the correction coefficient, and the air-fuel ratio is further leaned, that is, the air-fuel ratio is controlled to the optimum state without performing the air-fuel ratio determination based on the peak determination fluctuation rate. May be.

  Next, a second embodiment will be described.

  In the second embodiment, both the above-described generation period variation rate and peak determination variation rate are compared with a common reference value, and based on the result, the control correction amount is adjusted to perform air-fuel ratio feedback control. It is comprised as follows.

  Specifically, the air-fuel ratio determination program in the second embodiment is executed by the procedure shown in FIG. Note that the second embodiment also has the routine from step S1 to step S4 described above. That is, the air-fuel ratio determination program in the second embodiment is configured by Steps S1 to S4 and Steps S21 to S24 described below.

  First, in step S21, it is determined whether or not the peak determination variation rate exceeds a reference value. In step S22, it is determined whether the occurrence period variation rate exceeds the reference value. The reference value may be equivalent to the combustion state determination value described above. And it is used in common for the peak determination variation rate and the occurrence period variation rate.

  In step S23, the fuel injection amount is corrected by the first control correction amount, and air-fuel ratio feedback control is performed. In step S24, the fuel injection amount is corrected by the second control correction amount set smaller than the first control correction amount, and air-fuel ratio feedback control is performed.

  In such a configuration, the ionic current I generated at each ignition varies depending on the air-fuel ratio, and the variation occurs in the ionic current I generation state in the early stage of combustion and the ionic current generated in the later stage of combustion. What is different from the state of occurrence of I is used. In other words, as the air-fuel ratio becomes leaner, the generation period becomes longer or shorter depending on the degree of lean, and the generation period variation rate indicating the generation state of the ionic current I in the initial stage of combustion, that is, the degree of variation in the generation period, is obtained. It rises rapidly.

  When engine 100 is operated, steps S1 to S4 are executed to calculate each of the occurrence period variation rate and the peak determination variation rate. When the engine 100 is operated with the actual air-fuel ratio leaner than the stoichiometric air-fuel ratio, the generation period fluctuation rate becomes higher when the air-fuel ratio becomes lean, and when the air-fuel ratio becomes more lean, the peak determination fluctuation rate Becomes higher.

  In this air-fuel ratio determination program, it is first determined whether or not the peak determination variation rate exceeds the reference value (step S21), so that the air-fuel ratio can be quickly dealt with when the air-fuel ratio is becoming leaner. ing. That is, if the peak determination variation rate exceeds the reference value and the engine 100 is in an unfavorable operation state, for example, if the engine operation state is unstable due to a relatively large rotation variation, the first control correction amount in step S23. Thus, the air-fuel ratio feedback control is performed, so that the air-fuel ratio can be quickly corrected in the direction of the theoretical air-fuel ratio.

  When it is determined that the peak determination variation rate is equal to or less than the reference value, it is determined whether or not the occurrence period variation rate exceeds the reference value (step S22). When it is felt that the operating state is different from the normal state, the air-fuel ratio feedback control is performed with the second control correction amount, so that excessive control such that the air-fuel ratio becomes too rich can be suppressed.

  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.

BRIEF DESCRIPTION OF THE DRAWINGS Structure explanatory drawing which shows schematic structure of the engine of embodiment of this invention. The flowchart which shows the control procedure of the embodiment. The flowchart which shows the control procedure of the embodiment. The graph which shows the relationship between the 1st determination value of the same embodiment, and a 2nd determination value with an ion current waveform. The graph which shows the relationship between the peak determination fluctuation rate and correction coefficient of the embodiment. The graph which shows the relationship between the generation | occurrence | production period variation rate and peak determination variation rate of the embodiment, and an air fuel ratio. The flowchart which shows the control procedure of 2nd embodiment of this invention.

Explanation of symbols

6 ... Electronic control unit 7 ... Central processing unit 8 ... Storage unit 9 ... Input interface 11 ... Output interface I ... Ion current P1 ... Generation period P2 ... Peak judgment period H1 ... First judgment value H2 ... Second judgment value

Claims (1)

In an internal combustion engine, the generation period during which the ionic current is generated is measured by the time during which the ionic current exceeds the first determination value or the crank angle, and the second determination is greater than the first determination value. The peak judgment period includes the time when the characteristic value of the ion current generated in the combustion chamber at each ignition exhibits the maximum from the time when the value exceeds the lower side to the upper side to the time when the second judgment value is exceeded from the upper side to the lower side. An air-fuel ratio determination method for an internal combustion engine based on an ionic current that measures and measures an air-fuel ratio using a measured generation period and a peak determination period,
The average value is calculated from the occurrence period measured this time and the specified number of occurrence periods stored, and the average value of the deviation obtained by subtracting each occurrence period from the average value is divided by the average value of the occurrence period. to, determines that the actual air-fuel ratio when the determination criterion is greater than for determining the state of the air-fuel ratio generation period fluctuation rate in the initial combustion of the measured generation period is in the leaner than the stoichiometric air-fuel ratio,
The average value is calculated from the peak determination period measured this time and the predetermined number of stored peak determination periods, and the average of the deviations obtained by subtracting each peak occurrence period from the average value is calculated using the average value of the peak determination period. dividing by calculating the air-fuel ratio of peak judgment rate of change in the measured peak determination period is determined by the generation period of the actual air-fuel ratio when the determination criterion is greater than that measured for determining the state of the air-fuel ratio in the late combustion An air-fuel ratio determination method for an internal combustion engine based on an ionic current that is further determined to be lean.

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