JP3607393B2 - Air-fuel ratio control device and air-fuel ratio control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an air-fuel ratio control apparatus for an internal combustion engine, and more particularly to an air-fuel ratio control apparatus and an air-fuel ratio control method suitable for an in-cylinder injection engine or a lean combustion engine.
[0002]
[Prior art]
Among internal combustion engines, particularly for automobile engines with strict exhaust gas regulations, an oxygen sensor is provided in the exhaust passage to detect the oxygen contained in the exhaust near the sensor and estimate the air-fuel ratio of the air-fuel mixture supplied to the engine. Usually, feedback control is performed based on this estimated value, and the fuel supply amount is controlled so that the air-fuel ratio of the air-fuel mixture supplied to the engine converges to the target air-fuel ratio.
[0003]
[Problems to be solved by the invention]
In the above prior art, it cannot be said that sufficient consideration has been given to the stabilization of the air-fuel ratio when the engine is idling. In particular, the fuel is directly injected into the combustion chamber by the fuel injection valve attached to the cylinder of the engine. In the in-cylinder injection engine and the lean combustion engine, there has been a problem that stable air-fuel ratio control cannot be obtained during idling.
[0004]
This point will be described in more detail as follows.
First, in a fuel injection type engine, noise generated from a fuel supply system such as a fuel pump or a fuel pipe may affect the fuel injection amount, resulting in variations in the fuel injection amount.
Even in this case, in the conventional engine of the so-called intake pipe fuel injection system in which the fuel injection device is attached to the intake pipe side, it is inevitable that a wall flow that causes fuel to adhere to the inner wall of the intake pipe is inevitable. However, while there is a problem such as a delay in the air-fuel ratio control, noise is smoothed by this wall flow, and the fluctuation of the air-fuel ratio is not affected.
[0005]
Further, in the conventional air-fuel ratio control device in which the target air-fuel ratio is set in the vicinity of stoichiometric (stoichiometric air-fuel ratio), the fuel ratio is lower than that in the lean combustion type air-fuel ratio control device in which the target air-fuel ratio is set to lean (lean side). Similarly, since the influence of noise on the injection amount is small, such noise in the fuel supply system did not cause fluctuations in the air-fuel ratio.
[0006]
However, in the cylinder injection engine, since there is no wall flow as described above, the noise included in the fuel injection amount is not smoothed, directly causing the air-fuel ratio fluctuation of the engine and affecting the combustion state of the engine. A stable air-fuel ratio cannot be obtained at idling.
[0007]
Furthermore, in the case of a lean combustion engine in which the target air-fuel ratio is set to a lean region, the influence of noise on the fuel injection amount is greater than in the case where the stoichiometric air-fuel ratio is set to the target air-fuel ratio. It becomes stable.
[0008]
An object of the present invention is to provide an air-fuel ratio control device and an air-fuel ratio control method that are applied to an in-cylinder injection engine or a lean combustion engine so that air-fuel ratio control at idling can be obtained sufficiently stably. There is to do.
[0009]
[Means for Solving the Problems]
The above object is achieved by providing the following means a to d as shown in FIG.
a) An air-fuel ratio detecting means which is attached to the exhaust passage of the engine and estimates the air-fuel ratio of the air-fuel mixture supplied to the engine by detecting the oxygen concentration in the exhaust gas.
[0010]
b) An idling detection means for detecting when the engine is idling, and detecting a fuel injection amount signal at regular time intervals, for example, calculating the difference between the fuel injection amounts before and after the constant time interval, and the difference between the values is sufficiently small. A fuel injection amount signal stable detection means for determining that the injection amount signal is stable.
[0011]
c) Frequency and spectrum detection means for extracting a frequency component that seems to be noise generated from the fuel supply system from a signal obtained from the air-fuel ratio detection means when the engine is idling, and detecting the spectrum of the frequency component.
[0012]
d) Fuel injection amount correction means for correcting the fuel injection amount to the engine at idling based on the detected noise frequency component and spectrum.
[0013]
The air-fuel ratio detection means estimates the air-fuel ratio in the combustion chamber of the engine by detecting the oxygen concentration in the exhaust gas.
That is, if the air-fuel ratio of the air-fuel mixture supplied to the engine is the stoichiometric air-fuel ratio, oxygen and fuel react without excess or deficiency, so that the amount of oxygen contained in the exhaust gas after combustion becomes extremely small.
[0014]
When the air-fuel ratio of the air-fuel mixture supplied to the engine is higher than the stoichiometric air-fuel ratio, that is, when the air-fuel ratio is lean, the amount of oxygen contained in the air-fuel mixture is larger than the amount of oxygen required for the combustion reaction. Therefore, after combustion, the amount of oxygen contained in the exhaust is greater than that contained in the exhaust at the stoichiometric air-fuel ratio.
[0015]
Accordingly, the amount of oxygen contained in the exhaust gas is proportional to the air-fuel ratio of the air-fuel mixture in the combustion chamber, and the air-fuel ratio of the air-fuel mixture supplied to the engine is estimated by detecting the amount of oxygen contained in the exhaust gas. It becomes possible.
[0016]
Next, the potentiometer that detects the opening degree of the throttle valve attached to the intake pipe of the engine outputs a signal according to the opening degree of the valve. Therefore, the idling signal is output when the valve is fully closed. Can be determined.
[0017]
In addition, the pulse width of the fuel injection signal sent to the fuel injection device every predetermined time is stored, for example, the difference in the fuel injection amount before and after the predetermined time is calculated, and if the difference is small enough, the fuel injection is Since it can be determined that the signal has hardly changed, it is determined that the injection amount is stable.
[0018]
Next, the noise frequency component and its spectrum detection method will be described. The engine is determined to be idling by the idling detection means described above, and the injection amount signal is stabilized by the fuel injection amount stabilization timing determination means described above. The frequency component of the noise is detected by performing frequency analysis on the signal obtained from the air-fuel ratio sensor using, for example, FFT or the like during the period determined to be present.
Here, FFT is an abbreviation for Fast Fourier Transform, which is fast Fourier transform.
[0019]
This noise is generated from the fuel supply system and is caused by fuel pulsation in the fuel piping. For example, fuel pulsation according to the opening / closing cycle of the valve of the fuel pump, and fuel pulsation according to the injection cycle of the fuel injection valve Each has a unique frequency band such as pulsation.
[0020]
When the fluctuation of the pulse width is small enough that it can be said that the fuel injection pulse width is constant, the fluctuation of the inflow air amount is generally small enough, so the fluctuation of the air-fuel ratio of the engine should be sufficiently small, Even at this time, the amount of fuel injected from the fuel injection device varies due to the influence of noise generated by the above-described fuel supply system, causing a variation in the air-fuel ratio of the engine.
[0021]
Therefore, the frequency component of the noise can be extracted by performing frequency analysis on the signal obtained from the air-fuel ratio sensor.
In general, there are noises called white noise and colored noise, and it is considered that white noise and colored noise are mixed in the noise generated from the fuel injection system.
[0022]
White noise has a constant spectrum over the entire frequency range, but colored noise has a bias in the spectrum.
Therefore, when a frequency analysis is performed on a signal in which white noise and colored noise are mixed, a strong spectrum may be detected at a specific frequency.
According to the present invention, the object is achieved by extracting the components of the colored noise by frequency analysis of the air-fuel ratio signal according to this principle.
[0023]
Since the noise frequency component detecting means described above obtains the noise frequency and its spectrum, the detected noise is equal in frequency and spectrum, and an antiphase correction coefficient is added to the fuel injection width.
As a result, the signal finally sent to the fuel injection device changes at the same frequency and opposite phase as the noise, so that the influence of the noise can be canceled and the noise can be compensated. Become.
[0024]
In summary, in an embodiment of the present invention, when engine idling is detected, the injection amount before and after a certain time is compared, and the air-fuel ratio detection means obtains the amount of fuel before and after the injection amount is in a certain region. Frequency analysis of the obtained signal, and the spectrum of each frequency component is obtained. When a spectrum exceeding a certain fixed value is detected, the injection signal does not change during this period, so that this spectrum can be considered to be due to periodic noise generated by the fuel supply system.
[0025]
Therefore, as shown in FIG. 2, the air-fuel ratio can be stably controlled by correcting the fuel injection amount to the engine at idling according to the detected spectrum and its frequency.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an air-fuel ratio control apparatus according to the present invention will be described in detail with reference to an illustrated embodiment.
FIG. 3 shows an engine system to which one embodiment of the present invention is applied. As shown in the figure, air from the outside passes through the air cleaner 1 and is sucked into the engine 12 through the intake manifold 5.
[0027]
The cylinder of the engine 12 is provided with an injector (fuel injection valve) 6, and the fuel injected therefrom is mixed with the air sucked through the intake manifold 5 to form an air-fuel mixture inside the engine 12.
[0028]
This air-fuel mixture explodes due to a spark generated by the spark plug 7, and the energy generated at that time becomes a power source for the engine.
The exhaust gas after the explosion is sent to the catalyst 10 through the exhaust port 8, where the exhaust gas is purified and sent to the outside again.
[0029]
The amount of air sucked into the engine 12 is measured by the airflow sensor 2, and the flow rate signal is sent to the control unit 11 having a microcomputer inside and converted into the amount of air.
Further, a signal is output from the crank angle sensor 13 for each rotation angle of the crankshaft, supplied to the control unit 11, and converted into the rotation speed of the engine 12 with the crank angle per unit time.
In this way, the basic injection amount of fuel injected from the injector 6 is determined by the air amount calculated in the control unit 11 and the rotational speed.
[0030]
Further, the oxygen concentration contained in the exhaust gas is detected by the air-fuel ratio sensor 9, and this signal is supplied to the control unit 11, where the air-fuel ratio of the air-fuel mixture in the engine is calculated. That is, the relationship between the oxygen concentration contained in the exhaust gas and the air-fuel ratio is as shown in FIG. 5, and therefore the air-fuel ratio can be obtained by the air-fuel ratio sensor 9 that detects the oxygen concentration.
The air-fuel ratio sensor 9 is not limited to the oxygen sensor that detects the oxygen concentration described above, but may be a CO sensor that detects the concentration of carbon monoxide.
[0031]
The control unit 11 sequentially corrects the basic injection amount so that the air-fuel ratio of the engine air-fuel mixture becomes the target air-fuel ratio according to the calculated air-fuel ratio.
The throttle valve 3 for adjusting the amount of air flowing into the engine 12 is provided with a potentiometer 14 as an opening sensor, from which a signal is output according to the opening of the valve.
The signal value obtained from the potentiometer 14 is used for determination at the time of idling and acceleration of the engine 12, and the fuel injection amount and the ignition advance are corrected accordingly.
[0032]
Instead of the potentiometer 14, a switch that turns on and off at an idle position according to the operation of the accelerator pedal may be used.
[0033]
Here, reference numeral 4 denotes an idling bypass air passage, which bypasses the throttle valve 3 and allows intake air to pass therethrough, thereby controlling the idling rotational speed.
[0034]
Next, the air-fuel ratio control method according to this embodiment will be described with reference to the flowchart of FIG.
(STEP1)
First, in step 1, it is determined whether the idle SW is on (YES) or off (NO). The idle SW is a value that is turned on and off in the control unit 11 based on a signal value output from the potentiometer 14 attached to the throttle valve 3 in FIG.
[0035]
That is, when the control unit 11 detects the signal value of the potentiometer 14 output when the throttle valve 3 is in the fully closed state, the throttle valve 3 is determined to be in the fully closed state, and the idle SW is turned on. This control is not performed while the fuel ratio control is started and the idle SW is off.
[0036]
(STEP2)
In the embodiment of the present invention, noise in the fuel injection system is detected by frequency analysis of the air-fuel ratio signal detected by the air-fuel ratio sensor 9, and the air-fuel ratio is stabilized by correcting the fuel injection amount. In step 2, the timer t used for sampling the air-fuel ratio sensor signal is reset.
At the same time, the fuel injection amount at this time is defined as TIO.
[0037]
As will be described below, the timer t samples the signal from the air-fuel ratio sensor during a period when the preset sampling execution time TS is below.
[0038]
(STEP3)
Here, the stable timing of the fuel injection amount is determined.
Therefore, the difference between the fuel injection amount TI calculated by the control unit 11 and the fuel injection amount TIO set in step 2 every time the cylinder is exploded, that is, every time the reference signal obtained from the crank angle sensor 13 is generated. Calculate
If the absolute value of the difference is smaller than the predetermined threshold value δ, the process proceeds to step 4, and if it is larger, the process returns to step 1 again.
[0039]
That is, here, it is a part for determining whether or not the change width of the injection signal calculated by the control unit 11 is within a range that does not affect the fluctuation of the air-fuel ratio in the engine. Therefore, the threshold value δ satisfies this condition. It is necessary to set an appropriate value, and here, the threshold value δ is 0.1 ms.
The threshold value δ may be determined empirically according to each engine.
[0040]
(STEP4)
When it is determined in step 3 that there is almost no change in the fuel injection amount calculated by the unit, the process proceeds to step 4 to compare the values of the sampling execution time TS and the value of the timer t.
If the timer t is equal to or less than the sampling execution time TS, the process proceeds to step 5, and if the timer t is greater than the sampling execution time TS, the process proceeds to step P6. That is, the air-fuel ratio signal is sampled during t <TS, and after TS has elapsed, the process proceeds to frequency analysis.
[0041]
Note that the value of the sampling execution time TS is related to the detectable frequency. That is, the minimum frequency Fmin that can be detected is Fmin = 1 / TS.
It becomes.
Here, 2 seconds is sufficient as the sampling execution time TS, and the minimum frequency Fmin that can be detected at this time is 0.5 Hz.
[0042]
(STEP5)
Here, the signal from the air-fuel ratio sensor 9 is sampled. Specifically, the signal from the air-fuel ratio sensor 9 is stored in the RAM in the control unit 11.
[0043]
Even if the fuel supply amount is the same, the engine air-fuel ratio fluctuates substantially periodically due to the noise of the fuel injection system as shown in FIG.
Therefore, in this step 5, sampling is performed in order to detect the fluctuation of the air-fuel ratio.
[0044]
Here, the above processing from Step 1 to Step 5 is summarized as follows.
That is, this process is executed when the engine is idling, and the air-fuel ratio signal is sampled during the sampling execution time TS. While sampling is being performed, it is determined whether or not the injection signal calculated by the control unit 11 has changed, and if a large change is detected, the sampling process is immediately stopped.
[0045]
The processing from step 2 to step 5 is configured to be performed at the timing of each explosion of each cylinder, and the value sampled in step 5 is also set as one explosion. For example, the process is performed every time a reference signal synchronized with the rotation of the engine is input from the crank angle sensor 13 to the unit.
Further, during this sampling, the number of the cylinder in which the thinnest air-fuel ratio, that is, the maximum air-fuel ratio is detected is stored in the memory in the control unit 11.
[0046]
Next, after the sampling of the air-fuel ratio signal during the sampling execution time TS is completed, the process proceeds to step 6 where the frequency analysis of the air-fuel ratio signal is performed, and the frequency component of noise is extracted in step 7, based on this. The correction coefficient is calculated in step 8, which will be described in detail below.
[0047]
(STEP6)
The frequency analysis of the air-fuel ratio signal sampled in step 5 is performed. As this frequency analysis method, FFT is used.
If the engine 12 is a four-cylinder engine and idling at a rotational speed of 800 rpm, the number of data of the air-fuel ratio signal sampled in 2 seconds is 53.
[0048]
FIG. 7 shows an example of the air-fuel ratio spectrum obtained by this frequency analysis. Since the sampling interval at this time is equal to the reference signal interval, it is 37.5 ms, and therefore the detectable frequency is 0.5 Hz. To 164 Hz, and the step is about 3.2 Hz.
[0049]
(STEP7)
In step 7, it is checked whether or not there is a spectrum value of each frequency obtained in step 6 that exceeds a predetermined threshold value (a constant value).
This threshold value is set to an extent that affects the fluctuation of the air-fuel ratio of the engine, and specifically, it should be determined empirically according to the specifications of each engine.
[0050]
If a spectrum exceeding a certain value is detected, it is determined that this is due to periodic noise, and that the noise is sufficient to cause fluctuations in the air-fuel ratio in the engine 12. At this time, the process proceeds to Step 8.
On the other hand, when a spectrum exceeding the threshold value (a constant value) is not detected, it is determined that noise that causes fluctuations in the air-fuel ratio of the engine is not mixed in the injection signal, and the processing after step 8 is not performed again. Return to step 1.
[0051]
(STEP8)
In step 8, a correction coefficient f for correcting the influence of the noise detected in step 7 is calculated. This correction coefficient f is added to the fuel injection amount and works to cancel the influence of noise.
That is, the periodic noise detected in step 7 has the same change as the air-fuel ratio shown in the upper diagram of FIG.
Therefore, as shown in the middle diagram of FIG. 8, if a value that changes at the same frequency and opposite phase as the noise change is calculated and used as the correction coefficient f, the correction coefficient f is used to obtain the lower level of FIG. As shown in the figure, the influence of noise can be canceled out.
[0052]
The noise frequency at this time has already been calculated in step 8, and in order to change the correction coefficient f in the opposite phase to the noise, the cylinder having the maximum air-fuel ratio detected in step 5 is referred to. This is possible.
That is, the initial value of the correction coefficient f is set to the maximum value in the variation range, and the amplitude of the correction coefficient f is obtained from the spectrum calculated in step 6.
And the correction | amendment by this is made to start from the fuel injection of the cylinder which showed the above-mentioned maximum air fuel ratio.
[0053]
(STEP9)
In step 9, the correction coefficient f calculated in step 8 is added to the fuel injection amount TI, and this is newly set as the fuel injection amount TI2.
As shown in the upper diagram of FIG. 8, the air-fuel ratio due to the fuel injection amount TI changes due to noise, but the fuel injection amount TI2 to which the correction coefficient f is added is shown in the middle diagram of FIG. As shown in FIG. 8, since it changes at the same frequency as the noise detected in step 7 and in the opposite phase, the air-fuel ratio by the fuel injection amount TI2 is changed so as to cancel the influence of noise, and is shown in the lower diagram of FIG. Thus, a stable air-fuel ratio without fluctuation is obtained.
When the fuel injection signal TI2 including the first noise correction coefficient f is thus calculated, the process returns to step 1 and calculation of the next new correction coefficient f is started.
[0054]
In this embodiment, if the previous correction coefficient f is sufficiently effective, in Step 7, noise that causes fluctuations in the air-fuel ratio in the engine is not detected.
[0055]
Therefore, in this case, the correction coefficient f is not updated and the process returns to Step 1 again. As a result, while the engine is idling, the air-fuel ratio in the engine is constantly sampled and the frequency analysis is performed. The correction coefficient f is updated only when noise that causes a change in the fuel ratio is detected.
[0056]
Therefore, according to this embodiment, noise due to the fuel supply system can be accurately detected, and as a result, fluctuations in the air-fuel ratio can be sufficiently suppressed. Even when applied to an engine, the air-fuel ratio during idling can be sufficiently stabilized, and exhaust gas purification and fuel efficiency improvement can be reliably obtained.
[0057]
【The invention's effect】
According to the present invention, it is possible to appropriately control the air-fuel ratio at the time of idling by using a signal from an air-fuel ratio detection means such as an air-fuel ratio sensor, so that an in-cylinder injection type engine and a lean combustion type engine can be used. By applying this, it is possible to sufficiently stabilize the air-fuel ratio during idle operation, and it is possible to reliably purify exhaust gas and improve fuel efficiency.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a basic configuration of an air-fuel ratio control apparatus according to the present invention.
FIG. 2 is a functional block diagram of an air-fuel ratio control apparatus according to the present invention.
FIG. 3 is a configuration diagram showing an example of an engine system to which an embodiment of an air-fuel ratio control apparatus according to the present invention is applied.
FIG. 4 is a flowchart showing the operation of one embodiment of the present invention.
FIG. 5 is a characteristic diagram showing the relationship between the air-fuel ratio of the air-fuel mixture in the engine and the concentration of oxygen contained in the exhaust gas.
FIG. 6 is a timing chart showing an example of air-fuel ratio fluctuations due to periodic noise appearing in the fuel supply system.
FIG. 7 is an explanatory diagram of a spectrum detected from a change in air-fuel ratio.
FIG. 8 is an explanatory diagram of a noise correction operation according to an embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Air cleaner 2 Air flow sensor 3 Throttle valve 4 Bypass air passage 5 for idling Intake manifold 6 Injector (fuel injection device)
7 Spark plug 8 Exhaust manifold 9 Air-fuel ratio sensor 10 Catalyst 11 Control unit 12 Engine 13 Crank angle sensor 14 Potentiometer for detecting throttle valve opening

Claims (12)

An air-fuel ratio detecting means for detecting an air-fuel ratio from an exhaust component of a direct injection engine or a lean combustion engine is provided, and the amount of fuel to be supplied to the engine is controlled by feedback control based on a detection result by the air-fuel ratio detecting means. In the air-fuel ratio control device,
Providing a spectrum detection means for extracting a periodic component of noise generated by the fuel supply system from the air-fuel ratio signal detected by the air-fuel ratio detection means;
An air-fuel ratio control apparatus configured to correct a fuel supply amount based on a detection result by the spectrum detection means. In claim 1,
An air-fuel ratio control apparatus characterized in that the air-fuel ratio detection means comprises an oxygen sensor. In claim 1,
An air-fuel ratio control apparatus, wherein the air-fuel ratio detection means is constituted by a CO sensor. In claim 1 ,
The periodic component of noise generated by the fuel supply system is a periodic component including any one of an opening / closing cycle of a fuel pump valve, a fuel pulsation cycle in a fuel pipe, and an injection cycle of a fuel injection valve. Control device . An air-fuel ratio detecting means for detecting an air-fuel ratio from an exhaust component of a direct injection engine or a lean combustion engine is provided, and the amount of fuel to be supplied to the engine is controlled by feedback control based on a detection result by the air-fuel ratio detecting means. In the air-fuel ratio control method ,
The frequency of the change in the air-fuel ratio detected by the air-fuel ratio detection means is analyzed to calculate the spectrum of noise generated by the fuel supply system,
Calculating a correction value based on a frequency component exceeding a certain value in the spectrum;
An air-fuel ratio control method characterized in that the fuel supply amount is controlled in accordance with the correction value . In claim 5 ,
The difference between the latest fuel supply amount and the fuel supply amount before a certain time is taken, and the value of this difference is within a certain value, so that the stable timing of the fuel supply amount is judged. Air-fuel ratio control method. In claim 5 ,
An air-fuel ratio control method, wherein the frequency analysis is analysis by FFT. In claim 5 ,
An air-fuel ratio control method, wherein a frequency band of a spectrum detected by the frequency analysis is set according to an opening / closing cycle of a valve of a fuel pump. In claim 5 ,
An air-fuel ratio control method, wherein a frequency band of a spectrum detected by the frequency analysis is set according to a frequency band unique to a fuel pipe. In claim 5 ,
An air-fuel ratio control method, wherein a frequency band of a spectrum detected by the frequency analysis is set according to an injection cycle of a fuel injection valve. In claim 5 ,
5. The method for controlling an air-fuel ratio of a direct injection engine according to claim 4, wherein the cycle for detecting the air-fuel ratio is time-synchronized. In claim 5 ,
An air-fuel ratio control method, wherein the air-fuel ratio detection cycle is set in accordance with an engine rotation cycle.

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