JPH0626387A - Air/fuel ratio control device for spark-ignition type internal combustion engine - Google Patents

Abstract

PURPOSE:To eliminate affection by variation in load to make a stable air/fuel ratio control by providing a rotational speed detecting means and a comparison means to compare a particular frequency component taken out from a faulty component detecting means and output a control signal. CONSTITUTION:A voltage signal corresponding to the number of rotations is detected by a speed detecting means A. From it, a particular frequency component which becomes especially large when an engine burns unstably is taken out by a faulty component detecting means B. A comparator means C compares the magnitude of the taken-out particular frequency component with a reference value, and outputs a control signal to reduce a difference between them. An air/fuel ratio adjusting means D operates according to the control signal. Also a load detecting means E to detect a load on the engine to correct the operating condition of the air/fuel ratio adjusting means D according to the detected load. Thus the device can cope with a fault resulting in variation in rotational speed which differs from that in normal condition, and the engine can be operated while an air/fuel ratio is controlled properly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of an air-fuel ratio control device in a spark ignition type internal combustion engine.

[0002]

2. Description of the Related Art In air-fuel ratio control for purifying exhaust gas of an internal combustion engine, it is well known that the air-fuel ratio is open-controlled according to input conditions such as intake negative pressure and intake temperature. However, the control of such a system cannot cope with a change in engine performance due to deterioration of used parts, for example. Figure 2
As shown in the figure, the NOx amount discharged from the engine has a characteristic that it decreases as the air-fuel ratio λ becomes thinner, but this characteristic moves to the right of the figure as shown by the broken line when the temperature becomes high, Alternatively, if the gap of the spark plug becomes large and it becomes difficult to ignite, it will move to the left as shown by the chain line, and will greatly fluctuate from the solid line standard state according to various conditions. The area to the right of the X mark is the misfire area.

In conventional control, proper control is performed by detecting the conditions that affect the characteristics and performing map switching and correction as described above. For example, deterioration of the ignition system and Abnormality of the air-fuel ratio control device cannot be dealt with at all because there is no suitable detection means. Therefore, if the control map deviates from the actual state and the target performance cannot be obtained, or if misfire is likely to occur and the engine is stopped in an extreme case, it is possible to appropriately respond to various environmental changes. could not. As a general closed control, there is a feedback system using a three-way catalyst, but this requires an expensive three-way catalyst.

[0004]

SUMMARY OF THE INVENTION The present invention focuses on such a point, and it is an object of the present invention to appropriately control the air-fuel ratio even when the engine is deteriorated, especially when the combustion state is abnormal, and to carry out stable exhaust gas purification. It was made as.

[0005]

In order to achieve the above object, in the present invention, a rotation speed detecting means for constantly detecting the engine rotation speed and converting it into a voltage signal corresponding to the rotation speed, and the obtained voltage. An abnormal component detection means for extracting a specific frequency component that becomes particularly large during unstable combustion of the engine from the signal, and a control signal for reducing the difference between the extracted specific frequency component and a reference value. It is provided with a comparing means for outputting and an air-fuel ratio adjusting means which operates according to a control signal. Further, load detecting means for detecting the load of the engine is provided, and the operating state of the air-fuel ratio adjusting means is corrected according to the detected load. FIG. 1 is a diagram showing the configuration of the present invention, in which A is rotational speed detecting means, B is abnormal component detecting means, C is comparing means, D is air-fuel ratio adjusting means, and E is load detecting means.

[0006]

Since the engine is accelerated in each combustion stroke of each cylinder and minutely and periodically fluctuates, the voltage signal corresponding to the rotational speed contains most frequency components according to the fluctuation period. That is, this voltage signal reflects the result of combustion.For example, when a cylinder misfires, acceleration is not performed, so the voltage signal decreases at the time corresponding to the combustion stroke of that cylinder, and Component with twice the period of time, that is, half the frequency component of normal time
(0.5th order component) occurs. This 1/2 frequency component is an abnormal component that is rarely included in normal conditions, and by detecting an increase in this component, it is possible to ensure not only complete misfire but also temporary misfire and partial combustion. To be detected.

FIG. 3 is a graph showing the relationship between NOx and Pmi fluctuation rate (indicated average effective pressure fluctuation rate). It is known that the Pmi fluctuation rate increases when the combustion state of the engine becomes unstable due to misfire or partial combustion, but the Pmi fluctuation rate maintains the relationship as shown in the figure regardless of the load, and the present invention According to the research conducted by the researcher, there is a close relationship with the amount of the abnormal component contained in the voltage signal corresponding to the rotation speed, and it is found that the abnormal component and the value of the Pmi fluctuation rate match very well as shown in FIG. Was issued. Therefore, if the operating state of the air-fuel ratio adjusting means is controlled according to the magnitude of the specific frequency component extracted from the abnormal component detecting means, the air-fuel ratio control can be performed even in an abnormal situation where a rotation speed variation different from that in the normal state occurs. It becomes possible to carry out properly.

[0008]

EXAMPLE An example of the illustrated gas engine will be described below. Since the present invention detects the state of the engine due to combustion abnormality such as misfire, in this embodiment, misfire determination is performed together with the air-fuel ratio control. In FIG. 5, 1 is a gas engine, 2 is a rotation speed sensor, 3 is an F / V converter, 4 is a bandpass filter, 5 is a control unit, 6 is an air-fuel ratio control valve,
7 is a main jet, 8 is gas, and the air-fuel ratio control valve 6
Are provided so as to bypass the main jet 7. 11 is a mixer, 12 is an intake pipe, 13 is a throttle valve, 14 is air, and gas 8 is the mixer 11 and air 1
4, and is supplied to the engine 1 through the intake pipe 12 and the throttle valve 13. 15 is an intake pipe 12 for load detection
A pressure sensor, 16 is provided in the.

The main part of the control unit 5 is a CPU 5a and a memory 5
The memory 5b stores data such as maps and reference values. An electromagnetic pickup is used for the rotation speed sensor 2, the output of which is sent to an F / V converter 3 where it is converted into a voltage signal V ₀ , and further the voltage of a specific frequency component that has passed through a bandpass filter 4. The signal V ₁ is input to the control unit 5. The output signal L of the pressure sensor 15 and the ignition signal of the ignition pulsar 16 are also input to the control unit 5, and the control unit 5 controls the control signal S ₁ based on these signals.
Is output to activate the air-fuel ratio control valve 6, or an alarm signal S ₂ is output to notify a predetermined device or department of abnormality such as misfire.

In the above configuration, the F / V converter 3
Outputs a voltage signal V ₀ as shown in FIG. That is, in the normal state, the voltage signal V ₀ periodically fluctuates as indicated by the solid line, and if the engine 1 has, for example, four cylinders, the fluctuation cycle T corresponds to exactly one revolution. ing. When a cylinder here is misfiring, the voltage signal V ₀ drops as shown by the broken line because there is no acceleration due to combustion of that cylinder, and the fluctuation cycle of this portion is 2T, which is half the frequency at normal times. The 0.5th order component that it has will be generated.

FIG. 7 exemplifies the distribution of frequency components included in the voltage signal V _0. F ₁ is a frequency component corresponding to the period T, F ₂ is a frequency component having a frequency twice that of the component F _1. , F ₃ are 1/2 times the component F ₁ , that is, the components of the 0.5th frequency. The component F ₁ is generated by combustion, and the component F ₂ is generated by inertia. Usually, the component F ₁ is the largest as shown by the solid line, and the component F ₃ is hardly generated, but when a misfire occurs. , The component F ₃ becomes abnormally large as indicated by the broken line. The band-pass filter 4 is a filter that passes the 0.5th-order frequency component F ₃ described above, and the control unit 5 uses the voltage signal V ₁ having the frequency component of F ₃ as a reference value for air-fuel ratio control or for misfire determination. It is configured to output the control signal S ₁ or the alarm signal S ₂ in comparison with the reference value of. As the bandpass filter 4, it is desirable that the passband can be arbitrarily changed according to the engine speed and the number of cylinders.

Here, assuming that the regulation value of NOx is A and the stable operation limit value of the Pmi fluctuation rate is B in FIG. 3, the Pmi fluctuation rate may be controlled within the range of C in the figure. Then, as shown in FIG. 4, the abnormal component, that is, the above-mentioned 0.5th-order component F ₃ and Pmi
Since there is a fixed relationship with the value of the fluctuation rate, the component F ₃
By controlling the air-fuel ratio control valve 6 so as to enter the range D corresponding to the range C, the air-fuel ratio can be properly controlled even when an abnormality occurs in the combustion state.

The flowchart of FIG. 9 shows the procedure of the air-fuel ratio control described above. First, in step S1, the voltage signal V ₁ having the frequency component of F ₃ is sequentially input at a predetermined sampling interval, and the number of times of input reaches a predetermined number. Then, the process proceeds to step S2 to calculate the average value Vm ₁ of the voltage signal V ₁ . Next, in step S3, the average value Vm ₁ is set to the preset reference value Vt.
If Vm ₁ > Vt, the process proceeds to step S4, the opening of the air-fuel ratio control valve 6 is calculated from the map of the memory 5b, and the air-fuel ratio control valve 6 is driven to the dark side. If Vm ₁ > Vt, the process proceeds to step S5. Thus, the air-fuel ratio control valve 6 is driven to the lean side. The above is the basic procedure, and the correction steps will be described below.

Since the voltage signal V ₁ having the frequency component of F ₃ changes depending on the load, it is desirable to correct the actual control according to the load. That is, as the load increases, the force pushing the piston in the combustion stroke and the deceleration in the compression stroke both increase, and the amplitude of the rotational fluctuation increases accordingly, and the voltage signal V ₁ passing through the bandpass filter 4 also increases. . Since the signal V ₁ and the load change while maintaining a constant relationship as shown by the solid line in FIG. 8, the load is detected by the pressure sensor 15 and the signal V ₁ is changed as shown by the broken line in FIG. 8 according to the result. Correct it.

The variable resistor 20 in FIG. 5 is a correction resistor for this purpose. For example, the controller 5 adjusts the resistance value of the variable resistor 20 so that the characteristic shown by the broken line in FIG. It can be carried out. Step S11 in FIG. 9 is for correction by such means, and the corrected voltage signal V ₁ is input to the control unit 5. This correction does not depend on the variable resistor 20 as described above. For example, the map to be used is switched according to the load,
Alternatively, the data read from the map can be corrected by a means such as a correction. Figure 9
Steps S12 and S13 of FIG. 9 show the case where the correction is performed by such a method.

Although not described in detail because it is not the object of the invention, in this embodiment, misfire determination is also performed by comparing the average value Vm ₁ with a reference value for misfire determination in a step corresponding to step S3. The alarm signal S ₂ is output when the average value Vm ₁ exceeds the reference value.

[0017]

As is apparent from the above description, the present invention extracts a specific frequency component which becomes particularly large during unstable combustion of the engine from the voltage signal corresponding to the engine speed,
This is used to control the air-fuel ratio.
Therefore, it is possible to cope with an abnormality that causes a rotation speed variation different from that in a normal state, which has been difficult to deal with conventionally, and it is possible to operate the engine while appropriately controlling the air-fuel ratio. Further, in the case of correcting the operating state of the air-fuel ratio adjusting means according to the load, it is possible to eliminate the influence of load fluctuations and perform more stable air-fuel ratio control.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of the present invention.

FIG. 2 is a diagram showing a relationship between an air-fuel ratio and NOx.

FIG. 3 is a diagram showing a relationship between NOx and Pmi fluctuation rate.

FIG. 4 is a diagram showing a relationship between a Pmi fluctuation rate and an abnormal component.

FIG. 5 is a schematic configuration diagram of an embodiment of the present invention.

FIG. 6 is a waveform diagram of a voltage signal corresponding to the rotation speed.

FIG. 7 is a distribution diagram of frequency components of a voltage signal corresponding to the rotation speed.

FIG. 8 is a diagram showing a relationship between a load and a voltage signal.

FIG. 9 is a flowchart showing a control procedure of the embodiment.

[Explanation of Codes] 1 engine 2 rotation speed sensor 3 F / V converter 4 bandpass filter 5 control unit 5a CPU 5b memory 6 air-fuel ratio control valve 15 pressure sensor 20 variable resistor V ₀ voltage signal corresponding to rotation speed V ₁ Voltage signal of specific frequency component Vt Reference value S ₁ Control signal

Claims (2)

[Claims] 1. A rotation speed detecting means for constantly detecting the engine rotation speed and converting it into a voltage signal corresponding to the rotation speed, and taking out a specific frequency component which becomes particularly large during unstable combustion of the engine from the obtained voltage signal. Abnormal component detecting means, comparing means for outputting a control signal for comparing the magnitude of the extracted specific frequency component with a reference value to reduce the difference between the two, and air-fuel ratio adjusting means that operates according to the control signal. An air-fuel ratio control device for a spark ignition type internal combustion engine, comprising: 2. An air-fuel ratio of a spark ignition type internal combustion engine according to claim 1, wherein load detecting means for detecting the load of the engine is provided, and the operating state of the air-fuel ratio adjusting means is corrected according to the detected load. Control device.