JPH10176594A - Combustion fluctuation detecting method for internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the erroneous detection of the combustion fluctuation from stoichiometric control to lean burn control by measuring the period when an ionic current is generated in a combustion chamber, calculating an interim fluctuation coefficient based on the measured period, setting a ratio corresponding to the air-fuel ratio, and calculating the fluctuation coefficient. SOLUTION: An electronic control device 6 corrects the basic injection time with various correction coefficients obtained from the output signals of an intake pressure sensor 13 and a cam position sensor 14 to obtain the effective injection time, controls the opening time of a fuel injection valve 5, and feeds an ionic current in a combustion chamber 10 at each ignition when a combustion fluctuation is detected. The electronic control device 6 calculates the fluctuation coefficient of combustion based on the generating period of the ionic current, and it compares the target fluctuation coefficient with the calculated fluctuation coefficient to detect a combustion fluctuation. The electronic control device 6 measures the period when the ionic current is generated, calculates the interim fluctuation coefficient based on the measured period, sets a ratio corresponding to the air-fuel ratio at the time when the interim fluctuation coefficient is calculated, and calculates the fluctuation coefficient based on this ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting combustion fluctuations in an internal combustion engine for an internal combustion engine, which mainly detects fluctuations in combustion due to lean combustion or the like in an internal combustion engine for an automobile based on the time during which an ionic current is generated. is there.

[0002]

2. Description of the Related Art In recent years, in order to improve fuel efficiency, it is necessary to perform operation control by so-called lean burn control (hereinafter abbreviated as "lean burn control") in which an internal combustion engine, that is, an engine is operated at a leaner air-fuel ratio than a stoichiometric air-fuel ratio. Sex is growing. In response to such needs, this type of engine generates an ionic current in a combustion chamber immediately after combustion, as described in, for example, Japanese Patent Application Laid-Open No. 6-34491.
Measure the time during which the ion current flows, that is, the duration,
It is known that the combustion time is measured based on the measured time, and the limit of the lean burn control is detected based on the combustion time. The combustion time is measured by setting a comparison level corresponding to stoichiometric control for controlling the air-fuel ratio near the stoichiometric air-fuel ratio, and measuring the time during which an ion current exceeding the comparison level exists. Then, the fluctuation state of the measured combustion time, that is, the fluctuation rate is calculated, and the air-fuel ratio in the lean burn control is feedback-controlled based on the fluctuation rate.

[0003]

The amount of ion current generated is affected by the load and the air-fuel ratio. For example, there is a difference between a low air-fuel ratio and a high air-fuel ratio. As shown by the solid line in FIG. 8, when the air-fuel ratio is near the stoichiometric air-fuel ratio, the stoichiometric ion current Is is large and is generated at a value that can be easily compared with the comparison level LCs. On the other hand, as shown by the dotted line in the figure, at the time of the lean burn control with a high air-fuel ratio, only the lean ion current In having a magnitude almost equal to the comparison level LCs is generated.

For this reason, when trying to measure the combustion time from the lean ion current In, the lean ion current In
Since the comparison level LCs is larger than the current value, accurate measurement becomes impossible. In order to solve such a problem, the comparison level is set at the same level as the case of the lean burn control, as shown by the dashed line in FIG.
When Cn is set, the fluctuation rate of combustion may change because an unnecessary level of ion current is also measured during stoichiometric control. In other words, a portion including a component such as noise, which has a low current value and is not measured at the comparison level LCs at the time of stoichiometry, is measured at the comparison level LCn at the time of lean burn, and thus includes an error. Then, the fluctuation rate rises due to this error, and when the air-fuel ratio is controlled based on the difference from the target fluctuation rate, the difference is large. For example, the air-fuel ratio is controlled to the rich side to further increase the combustion fluctuation. Sometimes.

[0005] An object of the present invention is to solve such a problem.

[0006]

In order to achieve the above object, the present invention takes the following measures. That is, the method for detecting combustion fluctuation of the internal combustion engine according to the present invention calculates the fluctuation rate of the time length of the period during which the ionic current is generated, and calculates the fluctuation rate based on the ratio set according to the air-fuel ratio. Finally, the rate of change is calculated. According to such a configuration, a fluctuation rate corresponding to the air-fuel ratio can be obtained, so that it is possible to prevent erroneous detection of combustion fluctuation from stoichiometric control to lean burn control.

[0007]

According to the present invention, an ion current is caused to flow in a combustion chamber of an internal combustion engine for each ignition, and a fluctuation rate of combustion is calculated based on a time during which the ion current is generated, and is set as a target. A combustion fluctuation detection method for an internal combustion engine that detects a fluctuation in combustion based on a result of comparing a fluctuation rate and a calculated fluctuation rate, and measures a time period during which an ion current is generated,
The provisional change rate is calculated based on the measured time, a ratio is set according to the air-fuel ratio at the time of calculating the provisional change rate, and the change rate is calculated based on the set ratio of the provisional change rate. This is a method for detecting combustion fluctuation of an internal combustion engine.

[0008]

An embodiment of the present invention will be described below with reference to the drawings. An engine 100 schematically shown in FIG. 1 is 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), and a surge tank 3 on the downstream side thereof. Is provided.
A fuel injection valve 5 is further provided near one end communicating with the surge tank 3, and the electronic control unit 6 controls the opening of the fuel injection valve 5 based on a basic injection amount TP described later. ing. A spark plug 18 is attached to a position corresponding to the ceiling of the combustion chamber 10. 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-way catalyst 22 provided in a pipe leading to a muffler (not shown). I have.

The electronic control unit 6 includes a central processing unit 7
, A storage device 8, an input interface 9, and an output interface 11. The microcomputer system mainly includes a microcomputer system having an input interface 9 for detecting a pressure in the surge tank 3. An intake pressure signal a output from the intake pressure sensor 13;
A cylinder discrimination signal G1, a crank angle reference position signal G2, an engine speed signal b output from a cam position sensor 14 for detecting a rotation state of the engine 100, and a vehicle speed output from a vehicle speed sensor 15 for detecting a vehicle speed. signal c, a water temperature signal e from LL signal d, the water temperature sensor 17 for detecting a cooling water temperature of the engine from an idle switch 16 for detecting the open or closed state of the throttle valve 2, the current from the O ₂ sensor 21 as described above The signal h and the like 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.

The spark plug 18 is connected via a high voltage diode 23 to a bias power supply 24 for measuring an ion current and a circuit 25 for measuring an ion current. Various circuits known in the art can be used as the ion current measurement circuit 25 itself including the bias power supply 24. The bias power supply 24 applies a high voltage to the spark plug 18 via the high-voltage diode 23 so that an ion current after ignition flows into the combustion chamber 10. Further, the ion current measuring circuit 25 is electrically connected to the input interface 9 of the electronic control unit 6, measures the ion current generated by applying a high voltage in an analog manner, and outputs an analog signal corresponding to the generated ion current. Is input to the electronic control unit 6.

The electronic control unit 6 includes an intake pressure signal a output from the intake pressure sensor 13 and a cam position sensor 14.
And the rotation speed signal b output from the main engine as main information, and corrects the basic injection time TP with various correction coefficients determined according to the engine state to obtain an effective injection time TAU, based on the effective injection time TAU. A fuel injection valve opening time, that is, an injector final energization time T is determined, and the fuel injection valve 5 is controlled based on the determined energization time so that fuel corresponding to the engine load is injected from the fuel injection valve 5 to the intake system 1. Program is built-in.

In this program, the engine 10
An ionic current is caused to flow through the combustion chamber 10 for each ignition, and a fluctuation rate of combustion is calculated based on a time during which the ionic current is generated, and a target fluctuation rate is compared with the calculated fluctuation rate. Detects fluctuations in combustion based on the results, measures the time during which ion current is generated, calculates the provisional fluctuation rate based on the measured time, and calculates the air-fuel ratio at the time when the provisional fluctuation rate is calculated. Is set, and the variation rate is calculated based on the provisional variation rate.

In this embodiment, the air-fuel ratio is determined by multiplying the effective injection time TAU at the stoichiometric air-fuel ratio, that is, the fuel injection amount by a predetermined coefficient. That is, in the lean burn control, the fuel injection amount is controlled so that the air-fuel ratio becomes lean in a state where no combustion fluctuation occurs. Air-fuel ratio in the lean burn control, since the O ₂ can not be detected in the sensor 21, which detects the air-fuel ratio by monitoring the coefficient multiplied to the effective injection time TAU. Note that O ₂
Instead of the sensor 21, the air-fuel ratio may be detected by an air-fuel ratio sensor capable of detecting from the air-fuel ratio in the stoichiometric control to the air-fuel ratio in the lean burn control.

The outline of the combustion fluctuation rate calculation program in the combustion fluctuation detecting method is as shown in FIG. When a bias voltage is applied to the spark plug 18 from the bias power supply 24 immediately after ignition, the ion current for measuring the combustion time TCBTIM
After flowing rapidly, the pressure decreases before TDC and then increases again, and flows into the combustion chamber 10 so that the current value becomes a peak value near the crank angle where the combustion pressure becomes maximum. The ionic current exhibiting such a behavior is measured for the time during which the ionic current flows for each ignition in a predetermined cylinder.

[0015] Combustion time TCMBTIM by ion current
For example, as shown in FIG. 3, when the detected ion current waveform flows to a high level when a current value equal to or higher than a comparison level Lc set in accordance with the ion current at the time of the lean burn control flows, When the waveform is less than Lc, the waveform is shaped so as to be at a low level, and one measurement is finished at each falling edge of the obtained waveform shaping signal. If the number of measurements exceeds a predetermined number, or the next ignition timing , The combustion time TCMBT
It is measured as IM. That is, the combustion time T
The CMBTIM is performed every time the waveform shaping signal falls, and when the above condition is satisfied, the measurement is terminated assuming that the ion current has finally disappeared.

More specifically, as shown in FIG. 4, first, it is determined whether or not it is the falling (OFF) timing of the waveform shaping signal (step S1). It is determined whether the number of drops exceeds a predetermined number n, for example, three times from the ignition (step S2). If the count exceeds the predetermined number n counted from the ignition timing, the time from ignition measured up to that time is set as the measured combustion time TCMBTIM (step S5). On the other hand, if the number is equal to or smaller than the predetermined number n, the combustion time TCMBTIM measured so far is updated (step S3). After updating the combustion time TCMBTIM, it is determined whether or not the next ignition is performed (step S).
4) If this is not the next ignition, this measurement routine is terminated. In this way, when the number of falling times exceeds the predetermined number n counted from the ignition timing, and when the next ignition timing is reached, the measurement of the combustion time TCMBTIM is terminated.

In the above measurement routine, instead of the step of determining the next ignition, as shown in FIG. 5A, it is determined whether or not the calculation end timing TCALEND is reached (step S4a). It may be. In this case, if the calculation end timing TCALEND, the combustion time TCMBTIM is determined, and if not, the routine ends. Calculation end timing TCA
As shown in FIG. 5B, LEND is set corresponding to a position where the crank angle after the top dead center becomes smaller as the engine speed NE becomes higher.

The combustion time TCMB thus measured
The provisional fluctuation rate Ht of the TIM is calculated by the following calculation formula, and then calculated based on a combustion fluctuation rate correction coefficient Kf which is a ratio set according to the air-fuel ratio at that time, to determine a final value. . As shown in FIG. 6, the combustion fluctuation rate correction coefficient Kf is such that the air-fuel ratio is a low value at the stoichiometric air-fuel ratio,
The air-fuel ratio is set to increase as the air-fuel ratio increases, and to become a constant value at a predetermined air-fuel ratio, for example, 18 or more.

The provisional fluctuation rate Ht is calculated by, for example, the following equation. That is, the provisional fluctuation rate Ht is calculated from the combustion time TCMBTIM _n measured this time and, for example, seven combustion times TCMBTIM measured before the combustion time TCMBTIM _n.
Of the moving average TCMBTIM _av of
Deviation ΔTC between the absolute value of the difference between CMBTIM _av and the current combustion time TCMBTIM _n and the moving average TCMBTIM _av
The MBTIM is calculated, and is calculated from the deviation ΔTCMBTIM and the moving average TCMBTIM _av . TCMBTIM _av = (TCMBTIM _n + TCMBTIM _n-1 + …… + TCMBTIM
_n−7 ) / 8 ΔTCMBTIM = (| TCMBTIM _av −TCMBTIM _n |) / 8 Ht = ΔTCMBTIM / TCMBTIM _av where TCMBTIM _n is the value of the current ion current generation time and TCMBTIM is the value measured one time before. _n-1 and the value measured eight times before is TCMBTIM _n-7 .

The provisional fluctuation rate Ht obtained as described above
Since the ion current comparison level Lc is adjusted to the ion current value at the time of the lean burn control, it includes a slight fluctuation of the ion current and a measurement error in the stoichiometric operation state. The value increases or decreases even though it is not. Therefore,
The provisional fluctuation rate Ht is corrected based on the combustion fluctuation rate correction coefficient Kf as described below.

Referring to FIG. 2, in step S11, an air-fuel ratio is calculated. The air-fuel ratio is calculated by multiplying the effective injection time TAU during stoichiometric control by a lean coefficient set from a lean feedback correction coefficient, a lean learning correction coefficient, and the like. Therefore, the air-fuel ratio may be detected by checking the above-described correction coefficient. Step S
In step 12, the combustion variation rate correction coefficient Kf is calculated based on the calculated air-fuel ratio.
Ask for. The combustion fluctuation rate correction coefficient Kf is set in correspondence with the air-fuel ratio using a map. .0. In step S13, a combustion variation rate H is calculated by multiplying the calculated provisional combustion rate Ht by a combustion variation rate correction coefficient Kf.

In such a configuration, the combustion time TCM
The comparison level Lc set for measuring BTIM is:
Since it is set in accordance with the lean burn control, in the case of the stoichiometric control, a low level ion current is determined, so that the combustion time becomes longer or conversely becomes shorter,
As shown by the dotted line in FIG. 7, the calculated provisional fluctuation rate Ht increases. However, by executing steps S11 to S13, the combustion fluctuation rate correction coefficient Kf becomes 0 in a state where the control is performed at substantially the stoichiometric air-fuel ratio, so that the calculated fluctuation rate H becomes 0, and the comparison level Lc becomes stoichiometric. It is possible to obtain a variation rate H equivalent to the case where it is set in accordance with the control. On the other hand, in the case of the lean burn control, since the combustion fluctuation rate correction coefficient Kf is set to 1.0, the provisional fluctuation rate Ht becomes the final fluctuation rate H as it is, and the set comparison level Lc is sufficiently reflected. Will be done.

As described above, since an appropriate combustion fluctuation rate H can be obtained in both the stoichiometric control and the lean burn control, the deviation from the target fluctuation rate can be accurately detected. Therefore, when performing lean burn control,
The control limit can be detected with high accuracy, and as a result, combustion fluctuation can be reduced. Note that the present invention is not limited to the embodiments described above.

In addition, the configuration of each section is not limited to the illustrated example, and various modifications can be made without departing from the spirit of the present invention.

[0025]

According to the present invention, as described in detail above, the ratio is set according to the air-fuel ratio to calculate the fluctuation rate.
Even in an operating state in which the measured combustion time fluctuates more than the actual one, the fluctuation rate can be accurately obtained, so that the limit in the case of performing the lean burn control can be accurately detected. Therefore, the feedback control of the air-fuel ratio can be easily performed in the lean burn control.

[Brief description of the drawings]

FIG. 1 is a schematic configuration explanatory view showing one embodiment of the present invention.

FIG. 2 is a flowchart showing a control procedure of the embodiment.

FIG. 3 is a waveform chart for explaining a method of measuring a combustion time according to the embodiment.

FIG. 4 is a flowchart showing a control procedure for measuring a combustion time according to the embodiment.

FIG. 5 is a flowchart illustrating another control procedure for measuring the combustion time according to the embodiment, and a graph illustrating a setting state of a calculation end timing.

FIG. 6 is a graph schematically showing the contents of a map of a combustion fluctuation rate correction coefficient of the embodiment.

FIG. 7 is an operation explanatory view of the embodiment.

FIG. 8 is a graph showing a relationship between a comparison level and an ion current in a conventional method for measuring combustion time.

[Explanation of symbols]

 Reference Signs List 6 ... Electronic control device 7 ... Central processing unit 8 ... Storage device 9 ... Input interface 10 ... Combustion chamber 11 ... Output interface 24 ... Bias power supply 25 ... Ion current measurement circuit

Claims (1)

[Claims] An ion current flows through a combustion chamber of an internal combustion engine at each ignition, and a fluctuation rate of combustion is calculated based on a time during which the ion current is generated. A method of detecting combustion fluctuations in an internal combustion engine that detects fluctuations in combustion based on the results of comparison with the above, measuring the time during which ion current is generated, and calculating a provisional fluctuation rate based on the measured time. And setting a ratio corresponding to the air-fuel ratio at the time of calculating the provisional change rate, and calculating the change rate based on the set ratio of the provisional change rate.