JPH0672863B2 - Oxygen concentration detector - Google Patents

Description

TECHNICAL FIELD The present invention relates to an oxygen concentration detection device for detecting the oxygen concentration in exhaust gas of an internal combustion engine.

Background Art An air-fuel ratio that detects the oxygen concentration in the exhaust gas to purify the exhaust gas of an internal combustion engine, improves fuel efficiency, etc., and feedback controls the air-fuel ratio of the air-fuel mixture supplied to the engine to the target air-fuel ratio according to the oxygen concentration detection result There is a fuel ratio control device.

As an oxygen concentration detection device used in such an air-fuel ratio control device, there is one that generates an output proportional to the oxygen concentration in the exhaust gas. For example, electrode pairs are provided on both main surfaces of a flat plate-shaped oxygen ion conductive solid electrolyte member, one electrode surface of the solid electrolyte member forms a part of a gas retention chamber, and the gas retention chamber is covered with exhaust gas or the like. A limiting current type oxygen concentration sensor that communicates with a measuring gas through an introduction hole is disclosed in Japanese Patent Laid-Open No. 52-
It is disclosed in Japanese Patent No. 72286. In this oxygen concentration sensor, when the oxygen ion conductive solid electrolyte member and the electrode pair act as an oxygen pump element to supply a current between the electrodes so that the gas retention chamber side electrode becomes the negative electrode, the negative electrode surface side Oxygen gas in the gas in the gas retention chamber is ionized, moves inside the solid electrolyte member toward the positive electrode surface, and is released as oxygen gas from the positive electrode surface. The limiting current value that can flow between the electrodes at this time is almost constant regardless of the applied voltage and is proportional to the oxygen concentration in the gas to be measured. Therefore, if the limiting current value is detected, the oxygen concentration in the gas to be measured is measured. be able to. However, when controlling the air-fuel ratio using such an oxygen concentration detection device, an output proportional to the oxygen concentration can be obtained from the oxygen concentration in the exhaust gas only when the air-fuel ratio of the air-fuel mixture is leaner than the stoichiometric air-fuel ratio. Therefore, the air-fuel ratio control in which the target air-fuel ratio is set in the rich region was impossible. As an oxygen concentration detection device that can obtain an output proportional to the oxygen concentration in the exhaust gas in the lean and rich regions of the air-fuel ratio, two flat plate-shaped oxygen ion conductive solid electrolyte members are provided with electrode pairs on each of which two solids are provided. One of the electrode surfaces of the electrolyte member forms a part of the gas retention chamber, and the gas retention chamber communicates with the gas to be measured through the introduction hole, and the other electrode surface of the one solid electrolyte member faces the atmosphere chamber. Such an arrangement is disclosed in JP-A-59-192955. In this oxygen concentration detecting device, one oxygen ion conductive solid electrolyte member and the electrode pair act as an oxygen concentration ratio detecting battery element, and the other oxygen ion conductive solid electrolyte material and the electrode pair act as an oxygen pump element. It is like this. When the voltage generated between the electrodes of the oxygen concentration ratio detection battery element is equal to or higher than the reference voltage, a current is supplied so that oxygen ions move in the oxygen pump element toward the gas retention material side electrode, and the oxygen concentration ratio detection battery element When the generated voltage between the electrodes is less than the reference voltage, by supplying current so that oxygen ions move in the oxygen pump element toward the electrode on the side opposite to the gas retention chamber side, the air-fuel ratio in the lean and rich regions is increased. The current value is proportional to the oxygen concentration.

In such an oxygen concentration detection device, when an excessive current is supplied to the oxygen pump element, a blackening phenomenon occurs that deprives the solid electrolyte member of oxygen. For example, when ZrO ₂ (zirconium dioxide) is used as the solid electrolyte member, excess oxygen is supplied to the oxygen pump element to remove oxygen O ₂ from ZrO ₂ to deposit zirconium Zr. This blackening phenomenon rapidly advances the deterioration of the oxygen pump element and deteriorates the performance of the oxygen concentration detecting device.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an oxygen concentration detection device capable of reliably preventing the occurrence of the blackening phenomenon.

The oxygen concentration detecting device of the present invention is characterized by having a limiting means for limiting the voltage applied between the electrodes of the oxygen pump element to a predetermined voltage or less.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an oxygen concentration detection device of an oxygen concentration proportional output type which is an embodiment of the present invention. In this oxygen concentration detection device, a substantially rectangular parallelepiped oxygen ion conductive solid electrolyte member 1 is provided. A gas retention chamber 2 is formed in the oxygen ion conductive solid electrolyte member 1. The gas retention chamber 2 communicates with an introduction hole 4 for introducing the exhaust gas of the gas to be measured from the outside of the solid electrolyte 1. The introduction hole 4 has exhaust gas inside the gas retention chamber 2 inside an exhaust pipe (not shown) of an internal combustion engine. It is located so that it can easily flow into. Further, the oxygen ion conductive solid electrolyte member 1 is formed with an atmosphere reference chamber 5 for introducing the atmosphere so as to separate the wall from the gas retention chamber 2. Electrode pairs 7a, 7b, 6a, 6b are formed on the wall between the gas retention chamber 2 and the atmospheric reference chamber 5 and on the wall opposite to the atmospheric reference chamber 5, respectively. The solid electrolytic chamber member 1 and the electrode pair 6a, 6b act as the oxygen pump element 8, and the solid electrolyte member 1 and the electrode pair 7
The a and 7b act as the battery element 9. A heater element 10 is provided on the outer wall surface of the atmospheric reference chamber 5. Heater element
10 is adapted to generate heat by being supplied with electric current at the same time when an ignition switch (not shown) is turned on.

ZrO ₂ (zirconium dioxide) is used as the oxygen ion conductive solid electrolyte member 1, and Pt (platinum) is used as the electrodes 6a to 7b.

As shown in FIG. 2, the electrode 6b of the oxygen pump element 8 and the electrode 7b of the battery element 9 are grounded. Electrode of battery element 9
A differential amplifier circuit 16 is connected to 7a, and the differential amplifier circuit 16 outputs a voltage corresponding to the difference voltage between the voltage generated between the electrodes 7a and 7b of the battery element 9 and the output voltage of the reference voltage source 17. Reference voltage source
The output voltage of 17 is a voltage corresponding to the theoretical air-fuel ratio (for example, 0.
4V). The limiting circuit 18 is connected to the output terminal of the differential amplifier circuit 16. The limiting circuit 18 is an operational amplifier 19 and a resistor 2.
The operational amplifier 19 includes an inverting amplifier circuit, and a feedback resistor 21 is connected between the input and output ends of the operational amplifier 19, and Zener diodes 22 and 23 are connected in series. Zener diodes 22 and 23 form a series circuit in which their anodes are connected to each other. Zener diodes 22 and 23 have the same characteristics. The output terminal of the limiting circuit 18 is connected to the electrode 6a of the oxygen pump element 8 via the current detection resistor 24. The voltage across the current detection resistor 24 is output as the oxygen concentration detection value.

In such a configuration, the differential amplifier circuit 16 and the first limiting circuit
When the power supply voltage is applied to 18 and the supply of pump current to the oxygen pump element 8 is started, if the air-fuel ratio of the air-fuel mixture supplied to the engine at that time is in the lean region, the battery element 9
Since the voltage generated between the electrodes 7a and 7b of the differential voltage becomes lower than the output voltage of the reference voltage source 17, the output level of the differential amplifier circuit 16 becomes a negative level, and this negative level signal is supplied to the first limiting circuit 18. . The first limiter circuit 18 inverts and amplifies the negative level signal output from the differential amplifier circuit 16 to generate a resistance as a positive level signal.
24 and the oxygen pump element 8 are connected in series. Since a pump current flows from the electrode 6a to the electrode 6b in the oxygen pump element 8, oxygen in the gas retention chamber 2 is ionized at the electrode 6b and moves in the oxygen pump element 8 to be released as oxygen gas from the electrode 6a. Then, oxygen in the gas retention chamber 2 is pumped out.

By pumping out oxygen in the gas retention chamber 2, an oxygen concentration difference occurs between the exhaust gas in the gas retention chamber 2 and the atmosphere in the atmosphere reference chamber 5. A voltage Vs corresponding to this oxygen concentration difference is generated between the electrodes 7a and 7b of the battery element 9, and this voltage Vs is supplied to the non-inverting input terminal of the differential amplifier circuit 16. Since the output voltage of the differential amplifier circuit 16 is a voltage proportional to the difference voltage between the voltage Vs and the output voltage of the reference voltage source 17, the pump current value is proportional to the oxygen concentration in the exhaust gas, and the pump current value is the resistance 24 It is output as the voltage across both ends.

When the air-fuel ratio is in the rich region, the voltage Vs exceeds the output voltage of the reference voltage source 17. Therefore, the output level of the differential amplifier circuit 16 is inverted from the negative level to the positive level. This positive level is further inverted and amplified by the first limiting circuit 18 and supplied to the series circuit of the resistor 24 and the oxygen pump element 8, so that the pump current flowing between the electrodes 6a and 6b of the oxygen pump element 8 is reduced,
The current direction is reversed. That is, since the pump current flows from the electrode 6b in the direction of the electrode 6a, external oxygen is ionized at the electrode 6a and moves in the oxygen pump element 8 to be released from the electrode 6b as oxygen gas into the gas retention chamber 2 to generate oxygen. Are pumped into the gas retention chamber 2. Therefore, oxygen is pumped in and out by supplying the pump current so that the oxygen concentration in the gas retention chamber 2 is always constant, so that the pump current value I _P and the output voltage of the differential amplifier circuit 16 are lean. And is proportional to the oxygen concentration in the exhaust gas in the rich region.

Next, when the difference between the voltage generated between the electrodes 7a and 7b of the battery element 9 and the output voltage of the reference voltage source 17 becomes large, the differential amplifier circuit
16 output voltage becomes large. When the output voltage of the differential amplifier circuit 16 is V _A , the resistance value of the resistor 20 is R ₂₀ , and the resistance value of the resistor 21 is R ₂₁ , the output voltage V _B of the first limiting circuit 18 is normally − (R ₂₁ / R
₂₀ ) It becomes V _A. -(R ₂₁ / R ₂₀ ) V _A is Zener diode 2
When the Zener voltage Vz of 2, 23 is exceeded, the Zener diode 23 acts when the output voltage of the differential amplifier circuit 16 is a negative level, and the Zener diode 22 acts when the output voltage of the differential amplifier circuit 16 is a positive level. As a result, the output voltage V _B of the first limiting circuit 18 becomes substantially equal to the Zener voltage Vz. Therefore resistance
The magnitude of the voltage supplied to the series circuit of 24 and the oxygen pump element 8 becomes the Zener voltage Vz or less,
It is possible to limit the pump current flowing between the electrodes 6a, 6b of the.

FIG. 3 shows another embodiment of the present invention. In this oxygen concentration detecting device, the limiting circuit 2 including a series circuit of Zener diodes 25 and 26 is provided on the electrode 6a of the oxygen pump element 8.
7 is connected. The anodes of the zener diodes 25 and 26 are connected to each other, the cathode of the zener diode 25 is connected to the electrode 6a, and the zener diode 26 is grounded. The Zener diodes 25 and 26 have the same characteristics. Therefore, the voltage applied between the electrodes 6a and 6b of the oxygen pump element 8 is equal to or lower than the Zener voltage of the Zener diodes 25 and 26. The other structure is the same as that of the apparatus shown in FIG.

The limiting circuit 18 of the device shown in FIG. 2 and the limiting circuit 27 of the device shown in FIG. 3 may be provided in the same device and may be used together. It is possible to more reliably limit the voltage applied to the voltage to the predetermined voltage or less.

Further, in the embodiment of the present invention, the Zener diode is used in the limiting circuit, but the present invention is not limited to this, and if the voltage applied between the electrodes of the oxygen pump element can be limited to a predetermined voltage or less by another element, the Zener diode is used. It is not necessary to use a diode.

Effects of the Invention As described above, the oxygen concentration detecting device of the present invention is provided with the limiting means for limiting the voltage applied between the electrodes of the oxygen pump element to a predetermined voltage or less. Therefore, by setting the limiting voltage of the voltage applied between the electrodes of the oxygen pump element so that the pump current does not flow excessively when the internal resistance between the electrodes of the oxygen pump element is minimum, the occurrence of the blackening phenomenon is ensured. It can be avoided, and rapid deterioration of the device can be prevented.

[Brief description of drawings]

1 is a diagram showing a detection part of an oxygen concentration detection device according to the present invention, FIG. 2 is a circuit diagram showing an electric circuit part of the device of FIG. 1,
FIG. 3 is a circuit diagram showing another embodiment of the present invention. Explanation of symbols of main parts 1 …… Oxygen ion conductive solid electrolyte member 2 …… Gas retention chamber 4 …… Introduction hole 8 …… Oxygen pump element 9 …… Battery element 17 …… Reference voltage source 18,27 …… Limit circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiyuki Mieno 1-4-1, Chuo, Wako-shi, Saitama Honda R & D Co., Ltd. (56) Reference JP-A-59-208451 (JP, A) JP Sho 61-213664 (JP, A)

Claims (1)

[Claims] 1. A base having an oxygen ion conductive solid electrolyte wall portion and forming a gas retention chamber communicating with the outside through a gas diffusion control means, and a base material sandwiched between the inner and outer wall surfaces of the solid electrolyte wall portion. And a voltage applying means for applying a voltage corresponding to a difference voltage between a reference voltage and a voltage between one electrode pair of the two electrode pairs to each other. And an oxygen concentration detecting device for outputting a current flowing between the other electrode pair as an oxygen concentration detection value, wherein the voltage applied between the other electrode pair by the voltage applying means is equal to or lower than a predetermined voltage. An oxygen concentration detecting device having a limiting means for limiting.