JPH055722A - Method for detecting air/fuel ratio - Google Patents

Abstract

PURPOSE:To enable a detection accuracy and a responsiveness to be improved simultaneously in a method for detecting an air/fuel ratio using an air/fuel ratio sensor which is equipped with an oxygen pump element and an oxygen light an darkness battery element. CONSTITUTION:An air/fuel ratio sensor which is provided with an oxygen pump element which supplies oxygen to a measurement gas chamber and unloads oxygen from it and an oxygen light and darkness battery element which generates a voltage corresponding to oxygen concentration of the measurement gas chamber is used and a rectangular current with two types of alternate currents, namely a current of 200muA in positive direction for unloading oxygen from the measurement gas chamber and a current which has a larger absolute value than it which is 300muA in negative direction for supplying oxygen to the measurement gas chamber, is supplied to the above oxygen pump element. A duty ratio of the rectangular current is adjusted so that a generation voltage of an oxygen light and darkness battery element reaches a specified value and the air/fuel ratio is detected based on the duty ratio after adjustment. A veneration voltage of the oxygen light and darkness battery becomes a waveform which is symmetrical left and right and response can be improved by increasing frequency of the rectangular current.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio detecting method for detecting the air-fuel ratio in various combustion equipment such as an internal combustion engine by using an oxygen sensor which generates a signal corresponding to the oxygen concentration in exhaust gas.

[0002]

2. Description of the Related Art Conventionally, as a method of detecting an air-fuel ratio of an internal combustion engine, etc., an oxygen pump element for supplying / discharging an amount of oxygen corresponding to the amount of electricity supplied to the measuring gas chamber, A method using an air-fuel ratio sensor including an oxygen concentration battery element that generates a voltage corresponding to a ratio with a reference oxygen concentration (for example, oxygen concentration in the atmosphere) is known. In this method, the current supplied to the oxygen pump element is adjusted so that the generated voltage of the oxygen concentration cell element becomes a predetermined value, and the air-fuel ratio is detected based on the adjusted current value.

For example, an oxygen concentration battery element using a solid electrolyte mainly composed of zirconia installed in an exhaust pipe of a gasoline engine is one that generates a voltage of a predetermined value when the engine is driven at a stoichiometric air-fuel ratio. is there. In an air-fuel ratio sensor equipped with this type of oxygen concentration battery element, the current supplied to the oxygen pump element is adjusted so that the generated voltage of the oxygen concentration battery element reaches its predetermined value. Whether the air-fuel ratio is rich or lean, depending on whether it is the negative direction for supplying oxygen to the negative direction or the positive direction for discharging oxygen from the measurement gas chamber, is rich or lean depending on the magnitude of the energizing current. You can know the degree.

[0004]

However, when the air-fuel ratio is detected based on the current value of the current flowing through the oxygen pump element in this way, the value obtained as the current value is subjected to complicated conversion to obtain the air-fuel ratio. It is necessary to calculate, the structure of the device becomes complicated, and there is a limit to improvement of detection accuracy.

Therefore, the current supplied to the oxygen pump element is set to a rectangular current in which two kinds of preset current values in the negative direction and the positive direction alternate, so that the generated voltage of the oxygen concentration battery element becomes a predetermined value. Another possible method is to adjust the duty ratio of the rectangular current and detect the air-fuel ratio based on the duty ratio. In this case, the process of calculating the air-fuel ratio from the duty ratio of the rectangular current can be performed by software using a one-chip microcomputer, and the configuration of the detection device can be simplified and the detection accuracy can be improved.

In FIG. 4, an air-fuel ratio sensor is installed in the exhaust pipe of a gasoline engine driven at the stoichiometric air-fuel ratio,
Current values of 0 μA and −200 μA are
The waveform of the rectangular current and the generated voltage of the oxygen concentration battery element when a rectangular current alternating with a duty ratio of 0.5 is applied to the oxygen pump element are shown. In the figure, the current value of the rectangular current is drawn as + in the positive direction.
Further, the oxygen concentration cell element generates a voltage of 450 mV with respect to the oxygen concentration in the exhaust pipe when the gasoline engine is driven at the stoichiometric air-fuel ratio.

As shown in the figure, when the rectangular current becomes -200 μA and oxygen is supplied to the measurement gas chamber, the oxygen concentration in the measurement gas chamber rises and the difference from the reference oxygen concentration decreases, so that the oxygen concentration cell element is reduced. Generated voltage decreases. Then, when the rectangular current becomes +200 μA and oxygen is discharged from the measurement gas chamber, the oxygen concentration in the measurement gas chamber decreases and the difference from the reference oxygen concentration increases, so that the generated voltage of the oxygen concentration battery element increases. Then, the rectangular current again becomes −200 μA, and the behavior that the generated voltage of the oxygen concentration battery element decreases is periodically repeated, and the generated voltage of the oxygen concentration battery element generates an electromotive force in the vicinity of the stoichiometric air-fuel ratio, It comes to vibrate in the width of mV.

In this case, however, the change in the generated voltage of the oxygen concentration battery element becomes steeper when it rises than when it falls, for the reasons described below. That is, hydrocarbons,
An unburned gas such as hydrogen or CO has a small molecular weight and easily enters the measurement gas chamber through the gas diffusion limiting section. Therefore, the oxygen supplied to the measurement gas chamber by the negative current is partially consumed by the oxidation reaction with these unburned gases, so that the drop in the voltage generated by the oxygen concentration cell is slowed down.

On the other hand, when the air-fuel ratio is detected on the basis of the duty ratio, the detection result can be obtained only for each cycle of the rectangular current. Therefore, it is necessary to increase the frequency in order to improve the detection response. However, when the voltage waveform of the oxygen concentration battery element is asymmetric as described above, the generated voltage of the oxygen concentration battery element sometimes deviates greatly in the direction of higher voltage when the frequency is increased above a predetermined value.

FIG. 5 exemplifies the waveform of the rectangular current and the generated voltage of the oxygen concentration cell device, which were measured under the same conditions as in FIG. 4 except that the frequency of the rectangular current was 40 Hz. In this case, the generated voltage of the oxygen concentration battery element is 600 m
It vibrates in the vicinity of V in small steps. If the frequency of the rectangular current is too high, the amount of oxygen exhausted from the measurement gas chamber cannot be supplied by the negative direction current due to the positive direction current, and the oxygen concentration in the measurement gas chamber is lower than the oxygen concentration in the exhaust pipe. It is considered that the air-fuel ratio of the gasoline engine is rich as a result of detection. Therefore, it is difficult to improve the detection responsiveness by the method of detecting the air-fuel ratio based on the duty ratio of the current supplied to the oxygen pump element.

Therefore, the present invention has been made for the purpose of improving both detection accuracy and responsiveness in a method of detecting an air-fuel ratio using an air-fuel ratio sensor equipped with an oxygen pump element and an oxygen concentration cell element.

[0012]

SUMMARY OF THE INVENTION The present invention, which has been made to achieve the above object, comprises a measuring gas chamber communicating with a measuring gas atmosphere through a gas diffusion limiting section, and oxygen in an amount corresponding to the amount of electricity supplied. An air-fuel ratio sensor including an oxygen pump element for supplying and exhausting to and from the measurement gas chamber, and an oxygen concentration cell element for generating a voltage corresponding to the ratio of the oxygen concentration in the measurement gas chamber to a reference oxygen concentration. In an air-fuel ratio detecting method for detecting an air-fuel ratio using, a current value in the positive direction for discharging oxygen from the measurement gas chamber, and a negative value having an absolute value larger than the current value and supplying oxygen to the measurement gas chamber. Current value in the direction, a rectangular current in which two kinds of current values alternate is supplied to the oxygen pump element, and the duty ratio of the rectangular current is adjusted so that the generated voltage of the oxygen concentration battery element becomes a predetermined value. , After adjusting the rectangular current Air-fuel ratio detection method characterized by detecting the air-fuel ratio based on Yuti ratio, a is the gist.

[0013]

In the air-fuel ratio detecting method of the present invention thus constructed, the duty ratio of the rectangular current supplied to the oxygen pump element is adjusted so that the generated voltage of the oxygen concentration battery element becomes a predetermined value, and the duty ratio is adjusted. The air-fuel ratio is detected based on Since the process of calculating the air-fuel ratio from the duty ratio of the rectangular current can be performed by software using a one-chip microcomputer, the configuration of the detection device can be simplified and the detection accuracy can be improved.

Since the negative current value forming the rectangular current is larger in absolute value than the positive current value,
The rate of change of the generated voltage of the oxygen concentration battery element when the voltage rises and when it decreases can be made substantially the same. Therefore, it is possible to prevent the generated voltage of the oxygen concentration battery element from increasing when the frequency of the rectangular current is increased.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an air-fuel ratio detection device of an embodiment to which the present invention is applied. First, the air-fuel ratio sensor 1 includes an oxygen pump element 3 having porous electrodes 3b and 3c formed on both sides of a solid electrolyte substrate 3a and an oxygen concentration cell element having porous electrodes 5b and 5c formed on both sides of the solid electrolyte substrate 5a. 5
And a spacer 9 which is laminated between these two elements 3 and 5 to form the measurement gas chamber 7. The air-fuel ratio sensor 1 is attached to the exhaust system of an internal combustion engine (not shown).

Here, the solid electrolyte substrates 3a and 5a are formed of a yttria-zirconia solid solution, and the porous electrode 3
b, 3c, 5b and 5c are yttria as a co-base
It is formed from a zirconia solid solution and the balance platinum. still,
As a material for the solid electrolyte substrates 3a and 5a, in addition to yttria-zirconia solid solution, calcia-zirconia solid solution is known. A metal oxide solid solution or the like can be used.

Further, a shield 11 made of a solid electrolyte is attached so as to cover the porous electrode 5c outside the oxygen concentration battery element 5. On the other hand, as the material of the spacer 9, alumina, spinel, forsterite, steatite,
Zirconia or the like is used. The porous electrodes 3c and 5b are exposed inside the measurement gas chamber 7, and the tip of the spacer 9 is a gas diffusion for communicating the measurement gas chamber 7 with the measurement gas atmosphere in the exhaust pipe. A hole 13 is provided. The gas diffusion holes 13 are filled with a porous filler material 15 made of alumina, whereby
A gas diffusion limiting portion 17 is formed to rate-control the inflow of the measurement gas into the measurement gas chamber 7.

Next, the porous electrode 3b of the oxygen pump element 3 is
Between 3c, a DC power supply 21 is connected via a contact R1 of the relay 19, and a DC power supply 23 is connected in parallel with it via a contact R2 of the relay 19. The contact R1 is a so-called b contact that is normally closed and that opens when the solenoid coil L of the relay 19 is excited, while the contact R2 is one.
Is a so-called a contact which is normally open and is closed when the solenoid coil L is excited. A signal from an electronic control circuit ECU having a drive circuit and the like is input to the solenoid coil L, which drives the relay 19.

The DC power supply 23 supplies a current of 200 μA from the porous electrode 3b to the porous electrode 3c, and the DC power supply 21 supplies a current of 300 μA from the porous electrode 3c to the porous electrode 3b. It is a thing. On the other hand, between the porous electrodes 5b and 5c, a direct current power supply 25 for constantly supplying a current of 27.5 μA from the porous electrode 5c to the porous electrode 5b is connected, and further generated between the porous electrodes 5b and 5c. The voltage to be applied is input to the electronic control circuit ECU.

Next, the operation of the air-fuel ratio detecting device thus constructed will be described. First, the DC power supply 25 is the porous electrode 5c.
When a current of 27.5 μA is constantly supplied from the electrode to the porous electrode 5b, the oxygen gas in the measurement gas chamber 7 is ionized on the surface of the porous electrode 5b and then moves to the surface of the porous electrode 5c through the solid electrolyte substrate 5a. Then, it becomes oxygen gas again. Since the porous electrode 5c is covered with the shield 11 and has a predetermined leakage resistance, the surface of the porous electrode 5c is maintained at a reference oxygen concentration, for example, at an oxygen concentration equal to or higher than the atmospheric concentration. The method of obtaining a reference oxygen concentration by supplying a constant current to the oxygen concentration battery element is detailed in JP-A-61-296262 and will not be described in detail here.

Next, the electronic control circuit ECU applies a rectangular pulse current to the solenoid coil L at the set frequency. When a pulsed current is applied to the solenoid coil L, the contact R2 is closed and the DC power source 23 causes the porous electrode 3
A current of 200 μA is supplied from b to the porous electrode 3c. Then, the oxygen gas in the measurement gas chamber 7 is ionized on the surface of the porous electrode 3c, then moves to the surface of the porous electrode 3b through the solid electrolyte substrate 3a, and is again discharged as oxygen gas into the measurement gas atmosphere.

On the other hand, when the pulsed current that has been applied to the solenoid coil L falls, the contact R1 is closed and the DC power source 21 supplies a current of 300 μA from the porous electrode 3c to the porous electrode 3b. Then, the oxygen gas in the measurement gas atmosphere is ionized on the surface of the porous electrode 3b and then supplied into the measurement gas chamber 7 through the solid electrolyte substrate 3a. That is, the oxygen pump element 3 is 200 μA in the positive direction.
And rectangular current of 300 μA in the negative direction, a rectangular current alternating with a rectangular pulse applied to the solenoid coil L is applied.

When the oxygen gas is supplied and exhausted in this way and the oxygen concentration in the measurement gas chamber 7 changes, the oxygen concentration on the surface of the porous electrode 5b also changes accordingly. On the other hand, the oxygen concentration battery element 5 generates a voltage corresponding to the oxygen concentration ratio between the surface of the porous electrode 5b and the surface of the porous electrode 5c, which changes the potential difference between the electrodes 5b and 5c. Electronic control circuit ECU
The voltage generated between the porous electrodes 5b and 5c is input, and the duty ratio of the pulsed current supplied to the solenoid coil L is adjusted so that this voltage has a predetermined value. Further, the electronic control circuit ECU detects the air-fuel ratio of the internal combustion engine based on the adjusted duty ratio of the pulsed current, and outputs the detection result to an air-fuel ratio control system (not shown).

In FIG. 2, an air-fuel ratio sensor 1 is installed in an exhaust pipe of a gasoline engine driven at a stoichiometric air-fuel ratio, and a rectangular current supplied to an oxygen pump element 3 is supplied at a frequency of 1 Hz.
The waveform of the rectangular current supplied to the oxygen pump element 3 and the generated voltage of the oxygen concentration battery element 5 are shown when the duty ratio is 0.5. In the drawing, the current value of the rectangular wave current is drawn as + in the positive direction. Further, the oxygen concentration battery element 5 generates a voltage of 450 mV with respect to the oxygen concentration in the exhaust pipe when the gasoline engine is driven at the stoichiometric air-fuel ratio.

As shown in the figure, when the rectangular current becomes -300 μA and oxygen is supplied to the measurement gas chamber 7,
Since the oxygen concentration in the inside increases and the difference in oxygen concentration between the surface of the porous electrode 5b and the surface of the porous electrode 5c decreases, the generated voltage of the oxygen concentration battery element 5 decreases. Subsequently, when the rectangular current becomes +200 μA and oxygen is discharged from the measurement gas chamber 7, the oxygen concentration in the measurement gas chamber 7 decreases, and the difference in oxygen concentration between the surface of the porous electrode 5b and the surface of the porous electrode 5c is reduced. Due to the expansion, the generated voltage of the oxygen concentration battery element 5 rises.
Then, the behavior that the rectangular current again becomes −300 μA and the generated voltage of the oxygen concentration battery element 5 decreases is periodically repeated, and the generated voltage of the oxygen concentration battery element 5 is 450 m.
It comes to vibrate around V.

This is because the duty ratio of the rectangular current is 0.5.
This is because the average value of the oxygen concentration in the measurement gas chamber 7 becomes equal to the oxygen concentration in the exhaust pipe. Further, in the present embodiment, the absolute value of the positive direction current is set to 1.5 times the absolute value of the negative direction current, so that the generated voltage of the oxygen concentration battery element 5 changes at the time of increasing and decreasing. Are almost the same and exhibit a substantially symmetrical curve.

Therefore, even if the frequency of the rectangular current is increased,
If the duty ratio is 0.5, the average value of the oxygen concentration in the measurement gas chamber 7 and the oxygen concentration in the exhaust pipe can be matched. FIG. 3 shows the waveform of the rectangular current and the generated voltage of the oxygen concentration battery element 5, which were measured under the same conditions as in FIG. 2 except that the frequency of the rectangular current was 40 Hz. In this case, the change in the generated voltage of the oxygen concentration battery element 5 is small, but it still oscillates around 450 mV. That is, it can be seen that the average value of the oxygen concentration in the measurement gas chamber 7 and the oxygen concentration in the exhaust pipe match.

As described above, in this embodiment, even if the frequency of the rectangular current supplied to the oxygen pump element 3 is increased, the duty ratio of the rectangular current is 0.5 for the gasoline engine driven at the stoichiometric air-fuel ratio. The generated voltage of the oxygen concentration battery element 5 can be made to correspond to 450 mV.

Therefore, for example, when the duty ratio of the rectangular current supplied to the oxygen pump element 3 must be smaller than 0.5 in order to set the generated voltage of the oxygen concentration battery element 5 to 450 mV, that is, the measurement gas chamber 7 When the negative current for supplying oxygen to the engine must be supplied longer than the positive current, the air-fuel ratio of the gasoline engine is rich, and conversely, the generated voltage of the oxygen concentration battery element 5 is 450 m.
When the duty ratio of the rectangular current supplied to the oxygen pump element 3 must be greater than 0.5 in order to obtain V, that is, the positive current for discharging oxygen from the measurement gas chamber 7 is longer than the negative current. When it is necessary to energize, it can be determined that the air-fuel ratio of the gasoline engine is lean. Further, such detection of the air-fuel ratio can be similarly performed even if the frequency of the rectangular current is high.

Furthermore, the process of calculating the air-fuel ratio from the duty ratio of the rectangular current can be performed by software using a one-chip microcomputer, and the structure of the detection device can be simplified and the detection accuracy can be improved. .. As described above, in the air-fuel ratio detecting device of the present embodiment, the air-fuel ratio of the internal combustion engine is detected based on the duty ratio of the rectangular current flowing through the oxygen pump element 3, thereby simplifying the structure of the detecting device and detecting accuracy. Can be improved, and the responsiveness can be improved by further increasing the frequency of the rectangular current.

In this embodiment, the rectangular current flowing through the oxygen pump element 3 is composed of two kinds of current values of +200 μA and -300 μA. This current value is used for the characteristics of the air-fuel ratio sensor and for the detection. It can be set to an appropriate value according to the air-fuel ratio to be set.

[0032]

As described above in detail, in the air-fuel ratio detecting method of the present invention, the air-fuel ratio is detected based on the duty ratio of the rectangular current supplied to the oxygen pump element. In addition, the detection accuracy can be improved.

Further, since the generated voltage of the oxygen concentration cell element does not increase even if the frequency of the rectangular current supplied to the oxygen pump element is increased, the frequency of the rectangular wave can be increased to improve the detection response. ..

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram illustrating an air-fuel ratio detection device according to an embodiment.

FIG. 2 is an explanatory diagram showing a waveform of a low-frequency rectangular current supplied to the oxygen pump element of the embodiment and a generated voltage of the oxygen concentration battery element.

FIG. 3 is an explanatory diagram showing the waveform of a high-frequency rectangular current supplied to the oxygen pump element of the example and the generated voltage of the oxygen concentration battery element.

FIG. 4 is an explanatory diagram showing a waveform of a low-frequency rectangular current supplied to an oxygen pump element of a conventional example and a generated voltage of an oxygen concentration battery element.

FIG. 5 is an explanatory diagram showing a waveform of a high-frequency rectangular current supplied to an oxygen pump element of a conventional example and a generated voltage of an oxygen concentration battery element.

[Explanation of symbols]

1 ... Air-fuel ratio sensor 3 ... Oxygen pump element 5 ...
Oxygen concentration battery element 7 ... Measuring gas chamber 17 ... Gas diffusion limiting section 19
… Relays 21,23,25… DC power supply

Claims (1)

Claim: What is claimed is: 1. A measuring gas chamber communicating with a measuring gas atmosphere through a gas diffusion limiting section, and oxygen for supplying and discharging to the measuring gas chamber an amount of oxygen corresponding to the amount of electricity supplied. A pump element,
In an air-fuel ratio detecting method for detecting an air-fuel ratio using an air-fuel ratio sensor, which comprises an oxygen concentration cell element that generates a voltage corresponding to the ratio of the oxygen concentration of the measurement gas chamber and a reference oxygen concentration, Two kinds of alternating current values, a positive current value for discharging oxygen from the measurement gas chamber and a negative current value having an absolute value larger than the current value and supplying oxygen to the measurement gas chamber, are alternating. A rectangular current is applied to the oxygen pump element, the duty ratio of the rectangular current is adjusted so that the generated voltage of the oxygen concentration battery element reaches a predetermined value, and the duty is adjusted based on the adjusted duty ratio of the rectangular current. An air-fuel ratio detection method characterized by detecting a fuel ratio.