JPS62249046A - Oxygen sensor for internal combustion engine - Google Patents

Abstract

PURPOSE:To eliminate oscillation and overshoot by gradually changing an impressed voltage in the stage of changing over the direction of the impression. CONSTITUTION:An oxygen concn. detecting part 6 is formed by juxtaposing measuring electrodes 3, 4 on a substrate 2 and printing an oxide semiconductor 5 thereon. An oxygen pump part 10 is formed by providing pump electrodes 8, 9 to both faces of a solid electrolyte 7. The oxygen pump part 10 is laminated via a spacer 11 onto the oxygen concn. detecting part 6 and an introducing hole 13 to introduce an exhaust gas is formed to a spacing part 12 formed therebetween. The change of the resistance value of the oxide semiconductor 5 between the measuring electrodes 3 and 4 is taken out as the partial voltage e1 of a resistor R1 and is compared with a reference voltage e2 in an operational amplifier Op. The output voltage e3 of the operational amplifier Op inverts to positive and negative according to the result of the comparison between the voltage e1 and e2. An input resistor R3 is interposed to the input side of the amplifier Op and a negative feedback resistor R4 is interposed thereto so that the impressed voltage is gradually changed in the stage of changing over the impression direction of the impressed voltage.

Description

Detailed Description of the Invention <Industrial Application Field> The present invention is installed in the exhaust system of an internal combustion engine to measure the oxygen concentration in the exhaust gas, which is closely related to the air-fuel ratio of the mixture supplied to the engine. The present invention relates to an oxygen sensor used for detecting and providing a feedback signal in air-fuel ratio feedback control, and particularly relates to improvements in the control circuit portion thereof.

(Prior art) Conventionally, this type of oxygen sensor has been able to detect a wide range of oxygen concentrations from a high oxygen concentration region (air-fuel ratio lean region) to a low oxygen concentration region (air-fuel ratio lynch region), according to SAE Paper 8.
50378 or Japanese Patent Application No. 60-167440.

This will be explained with reference to FIG. A pair of measurement electrodes 3 and 4 made of platinum are arranged side by side on a substrate 2 made of alumina or the like in which a heating heater l is embedded, and on these measurement electrodes 3 and 4 there is a material such as titania whose resistance value changes depending on the oxygen concentration. The oxygen concentration sensing portion 6 is formed by printing the oxide semiconductor 5 . Further, a pair of pump electrodes 8 and 9 made of platinum are provided on both sides of an oxygen ion conductive solid electrolyte 7 made of zirconia or the like to form an oxygen pump section 10. Then, the oxygen pump section 10 is stacked above the oxygen concentration detection section 6 via a frame-shaped spacer 11 made of alumina, for example, so that a sealed gap is created between the oxygen concentration detection section 6 and the oxygen pump section 10. An introduction hole 13 for introducing engine exhaust gas into the gap 12 is formed in the solid electrolyte 7 of the oxygen pump section IO.

According to this configuration, since the resistance value of the oxide semiconductor 5 changes according to the change in the amount of oxygen in the gap 12, the atmosphere in the gap 12 is detected based on this resistance value change,
According to this detection result, the amount of current flowing through the oxygen pump section IO is controlled so as to keep the atmosphere in the gap 12 constant (for example, at a stoichiometric air-fuel ratio), and the oxygen concentration in the exhaust gas can be detected from the amount of current at that time.

For example, when detecting the air-fuel ratio in a lean region where the oxygen concentration in the exhaust gas is high, a voltage is applied using the outer pump electrode 8 as the anode and the gap side pump electrode 9 as the cathode. Then, oxygen (0 oxygen ions) proportional to the current flows into the gap 1.
2 It is pumped from the inside to the outside. Then, when the applied voltage exceeds a predetermined value, the flowing current reaches a limit value, and by measuring this limit current value, the oxygen concentration in the exhaust gas, in other words, the air-fuel ratio can be detected. Conversely, the pump electrode 8 is a cathode,
By using the pump electrode 9 as an anode to pump oxygen into the gap 12, detection can be performed in a rich region where the oxygen concentration in the exhaust gas is low.

Therefore, the change in the resistance value of the oxide semiconductor 5 between the measurement electrodes 3 and 4 is extracted as a divided voltage e1 with respect to the resistor R, and compared with a reference voltage e2 in the operational amplifier OF. This operational amplifier O7 has an output voltage e as shown in FIG. 6 with respect to the input divided voltage 81.

The output voltage e is reversed between positive and negative depending on the comparison result between eI and e2. Then, this output voltage e3 is applied between the pump electrodes 8.9, and the current I flowing between the pump electrodes 8.9 is applied to the voltage V from both ends of the current detection resistor Rt.
, , V2 to detect the oxygen concentration.

In this way, such an oxygen sensor can perform detection over a wide range of oxygen concentrations, and is also called a wide range air-fuel ratio sensor.

<Problems to be Solved by the Invention> However, in such a conventional oxygen sensor, since there is a distance between the oxygen concentration detection part and the oxygen pump part, an oscillation phenomenon as shown in FIG. Even when the oxygen sensor is placed in a constant atmosphere, due to the time delay between the detection part and the pump part, the pump part may excessively pump in and out oxygen, causing the current to become unstable, or as shown in Figure 8. There is an overshoot phenomenon as shown in Figure 2, that is, when the atmosphere changes and the current 2 changes, I changes significantly and then stabilizes, making it impossible to accurately detect the air-fuel ratio. Ta.

In view of these conventional problems, it is an object of the present invention to alleviate oscillation and overshoot phenomena to enable more accurate air-fuel ratio detection.

(Means for solving the problem) Therefore, the present invention compares a divided voltage based on the resistance value of the oxide semiconductor between the measurement electrodes with a reference voltage, and applies the voltage between the pump electrodes according to the comparison result. Means for gradually changing the applied voltage when switching the direction of application of the voltage between the pump electrodes when detecting the oxygen concentration based on the current flowing between the pump electrodes by changing the direction of the voltage application It is designed to provide a.

<Function> In the above configuration, since the applied voltage is gradually changed when switching the direction of application of the applied voltage, oscillation and overshading phenomenon can be eliminated.

<Example> The present invention will be explained in detail below.

FIG. 1 shows a first embodiment, which differs from the conventional example in that the input side of the operational amplifier OF is used as a means for gradually changing the applied voltage when switching the direction of applying the voltage between the pump electrodes 8 and 9. An input resistor R1 is interposed between the output side and the input side, and a negative feedback resistor R4 is interposed between the output side and the input side. still,
R4>R3.

In this way, by providing a gain to the operational amplifier OF and amplifying the difference, the characteristics of the output voltage e3 of the operational amplifier Op become as shown in FIG. 2, and have a predetermined slope. This slope can be set by selecting R3° and R4. Thereby, oscillation and overshoot phenomena can be alleviated.

FIG. 3 shows a second embodiment, which differs from the conventional example in that the output side of the operational amplifier O1 is used as a means for gradually changing the applied voltage when switching the direction of application of the voltage between the pump electrodes 8 and 9. A delay circuit consisting of a resistor Rs and a capacitor C is provided.

In this way, the output voltage e of the operational amplifier O2.

When the voltage is reversed, the applied voltage e4 is gradually raised as shown in FIG. 4 to prevent oscillation and overshoot phenomena.

<Effects of the Invention> As explained above, according to the present invention, the above-mentioned oscillation and overshoot phenomenon can be eliminated, and the effect that accurate air-fuel ratio detection can be obtained can be obtained.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an oxygen sensor showing a first embodiment of the present invention, FIG. 2 is a characteristic diagram of the output voltage of an operational amplifier in the first embodiment, and FIG. 3 is a diagram showing a second embodiment of the present invention. A configuration diagram of an oxygen sensor showing an example, FIG. 4 is a characteristic diagram of output voltage in the second embodiment of the same as above, FIG. 5 is a configuration diagram of an oxygen sensor showing a conventional example, and FIG. A characteristic diagram of the output voltage, FIG. 7 is a diagram showing an oscillation phenomenon, and FIG. 8 is a diagram showing an overshoot phenomenon.

Claims (1)

[Claims] A pair of measurement electrodes are arranged side by side on a substrate, and an oxide semiconductor whose resistance value changes depending on the oxygen concentration is laminated on these measurement electrodes to form an oxygen concentration detection section. An oxygen pump section is provided with a pair of pump electrodes on both sides of an oxygen ion conductive solid electrolyte having an introduction hole for engine exhaust gas through a frame-shaped spacer, and the oxidation between the measurement electrodes is Comparing a divided voltage based on the resistance value of the physical semiconductor with a reference voltage, switching the direction of applying the voltage between the pump electrodes according to the comparison result, and detecting the oxygen concentration based on the current flowing between the pump electrodes. An oxygen sensor for an internal combustion engine, characterized in that the oxygen sensor for an internal combustion engine is provided with means for gradually changing the applied voltage when switching the direction of application of the voltage between the pump electrodes.