JPS6236551A - Oxygen concentration detector - Google Patents

Abstract

PURPOSE:To obtain the output proportional to the oxygen concentration in the lean and rich areas, by working oxygen ion conducting solid electrolytic members and two pairs of electrode members as two oxygen pump elements to always keep the oxygen density constant. CONSTITUTION:A spacer 3 is provided between oxygen ion conducting solid electrolytic members 1 and 2 and a clearance chamber 4 is formed as a gas retention chamber. An introduction hole 5 made up of an orifice 6 is placed between each one end of the members 1 and 2 to ease the inflow of an exhaust gas thereinto 4. Two pairs of electrode members 7a, 7b and 8a, 8b are fastened on the member 1 and the members 7a and 8a are placed in the clearance chamber 4. The member 1 and the electrode members 7a and 7b act as a drive oxygen pump element 9 while the member 1 and the electrode members 8a and 8b so as oxygen detection pump element 10. Current is supplied to the elements 9 and 10 from a current supply circuit 12.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oxygen degree detection device for detecting the oxygen concentration in gas such as engine exhaust gas.

In order to purify the exhaust gas of internal combustion engines and improve fuel efficiency, the oxygen concentration in the exhaust gas is detected, and the air-fuel ratio of the air-fuel mixture supplied to the engine is feedback-controlled to the target air-fuel ratio according to the detection results. There is an air-fuel ratio control device that does this.

Some oxygen concentration detection devices used in such air-fuel ratio control devices generate an output proportional to the oxygen concentration in the gas to be measured. For example, if a pair of electrode members is provided on an oxygen ion conductive solid electrolyte member, one electrode surface of the solid electrolyte member forms part of a gas retention chamber, and the gas retention chamber is connected to the gas to be measured through the introduction hole. A limiting current type oxygen concentration detection device in which communication is shifted is disclosed in Japanese Patent Laid-Open No. 72286/1986. In this oxygen concentration detection device, when the oxygen ion conductive solid electrolyte member and the pair of electrode members act as an oxygen pump element and a current is supplied between the electrodes so that the electrode on the gap chamber side becomes the negative electrode, the negative electrode surface On the side, oxygen gas in the gas R is ionized and moves within the solid electrolyte member toward the positive electrode surface, where it 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 being measured, so if the limiting current value is detected, the oxygen concentration in the gas being measured can be measured. be able to. However, when controlling the air-fuel ratio using such an oxygen & degree detection device, an output proportional to the oxygen concentration can only be obtained from the oxygen concentration in the exhaust gas within a range where the air-fuel ratio of the mixture is leaner than the stoichiometric air-fuel ratio. Therefore, it was impossible to control the air-fuel ratio by setting the target air-fuel ratio in the rich range. In addition, as an oxygen concentration detection device that can obtain an output proportional to the oxygen concentration in exhaust gas when the air-fuel ratio is in the lean and rich regions, two oxygen ion conductive solid electrolyte members are each provided with a pair of electrode members. One electrode surface of the solid electrolyte member forms a part of a gas retention chamber, and the gas retention chamber communicates with the gas to be measured through an introduction hole, and the other electrode surface of one solid electrolyte member is connected to an atmospheric chamber. A device designed to face each other is disclosed in Japanese Patent Laid-Open No. 59-192955. In this oxygen concentration detection device, one oxygen ion conductive solid electrolyte member and a pair of electrode members act as an oxygen concentration detection battery element, and the other oxygen ion conductive solid electrolyte material and a pair of electrode members act as an oxygen concentration detection battery element. It is adapted to act as a pump cord. When the voltage generated between the electrodes of the oxygen concentration detection battery element is equal to or higher than the reference voltage, a current is supplied so that oxygen ions move within the oxygen pump element toward the electrode on the gas retention chamber side, and the electrode of the oxygen concentration detection battery element By supplying current so that oxygen ions move within the oxygen pump element toward the electrode on the opposite side from the gas retention chamber side, the current is reduced at air-fuel ratios in the lean and rich regions. The value is proportional to the oxygen concentration. However, in such an oxygen concentration detection device, it is necessary to provide an atmospheric chamber to introduce the atmosphere, and there are also problems in that the configuration is considerably complicated and the cost is high.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an oxygen concentration detection device that has a simple configuration and can obtain an output proportional to the oxygen concentration with high accuracy even when the air-fuel ratio is in the lean or rich region. be.

The oxygen concentration detection device of the present invention includes an oxygen ion conductive solid electrolyte member and two pairs of N electrode members provided on the oxygen ion conductive solid electrolyte member, and the oxygen concentration detection device includes an oxygen ion conductive solid electrolyte member and two pairs of N electrode members provided on the oxygen ion conductive solid electrolyte member. A part of the oxygen ion conductive solid electrolyte member forms a gas retention chamber communicating with the gas introduction hole to be measured, and the oxygen ion conductive solid electrolyte member and the two pairs of electrode members act as two oxygen pump elements. It is characterized by .

Support-5-1 Embodiments of the present invention will be described below with reference to the drawings.

In the oxygen concentration detection device shown in FIG. 1, which is an embodiment of the present invention, a pair of flat oxygen ion conductive solid electrolyte members 1 and 2 are provided.

A spacer 3 is provided between the oxygen ion conductive solid electrolyte members 1 and 2 to keep them parallel to each other, and a gap chamber 4 is formed as a gas retention chamber by a member not shown. An introduction hole 5 is formed by an orifice 6 between one end of the oxygen ion conductive solid electrolyte members 1 and 2 for introducing exhaust gas of the gas to be measured into the gap chamber 4 . The introduction hole 5 is located in an exhaust pipe (not shown) of the internal combustion engine so that exhaust gas can easily flow into the gap chamber 4 . The oxygen ion conductive solid electrolyte member 1 includes two pairs of electrode members 7a.

7b, 8a, and 8b are fixed. Electrode members 7a, 8
a is located within the interstitial chamber 4. The oxygen ion conductive solid electrolyte member 1 and the electrode members 7a, 7b serve as the driving oxygen pump cord 9, and the oxygen ion conductive solid electrolyte member 1
The electrode members 8a and 8b act as an oxygen detection pump element 10. A heater element 1 is provided on the surface of the oxygen ion conductive solid electrolyte member 2 opposite to the gap chamber 4.
1 is provided.

Current is supplied to the drive oxygen pump element 9 and the oxygen detection pump element 10 from a current supply circuit 12 .

As shown in FIG. 2, the current supply circuit 12 includes an operational amplifier 13.
．． Resistors 14 to 18. It consists of a Zener diode 19 and an error amplifier 20. The output end of the operational amplifier 13 is connected to the electrode portion U7a via the resistor 14.

8 a and also connected to the inverting input terminal of the operational amplifier 13 . Further, the cathode of a Zener diode 19 is connected to this connection line, and the voltage VCC is supplied to the anode of the Zener diode 19 via a resistor 18. A resistor 15 is connected to the non-inverting input terminal of the operational amplifier 13.
A divided voltage VCC/2 of the voltage VCC by 16 is supplied. Voltage VCC is supplied to electrode member 8b via resistor 17.

One input terminal of the error amplifier 20 is connected to the electrode member 8b, and the other input terminal is connected to the resistor 18 and the Zener diode 19.
Connected to the connection line.

The output end of the error amplifier 20 is connected to the electrode member 7b.

In the oxygen concentration detection device according to the present invention having such a configuration, current is supplied to the heater element 11 from a heater current supply circuit (not shown), and the heater element 11 generates heat to exhaust the driving oxygen pump element 9 and the oxygen detection pump element 10. Heat to an appropriate temperature higher than gas.

A voltage VCC/2 is applied by an operational amplifier 13 to one electrode (N-pole member 7a, 8a) of the driving oxygen pump element 9 and the oxygen detection pump element 10.

The output voltage VOut of the operational amplifier 13 is the voltage V CC/
2 plus the terminal voltage of resistor 14, and resistor 1
4 represents a current to flowing between the electrodes of the driving oxygen pump element 9.
and the current ts flowing between the electrodes of the oxygen detection pump element 10. Therefore, if the resistance value of the resistor 14 is Rs, the output voltage Volt is VCC/2+(to+4s
) becomes Rs.

On the other hand, if the interelectrode voltage of the oxygen detection pump element 10 is vs, and the resistance value of the resistor 17 is Rr, then the oxygen detection pump element 1
The electric current His flowing between the electrodes at 0 is (VCC/2-Vs
) / Rr. Since the current ts flows from the other electrode (electrode member 8b) of the oxygen detection pump element 1o to one electrode, the oxygen in the interstitial chamber 4 is ionized and moves within the oxygen detection pump element 10, and from the other electrode. It is released as oxygen gas and the oxygen in the interstitial chamber 4 is pumped out. A voltage V+ (0-Vcc) proportional to the difference voltage between the interelectrode voltage Vs of the oxygen detection pump element 10 and the Zener voltage vz of the Zener diode 19 is output from the error amplifier 20, and VCC/2-V
+ is applied, and a current t flows between the electrodes of the drive M-pump element 9.
o flows. When the air-fuel ratio of the air-fuel mixture supplied to the engine is the stoichiometric air-fuel ratio, the same amount of oxygen pumped out by the oxygen detection pump element 10 is pumped into the gap chamber 4 from the outside by the driving oxygen pump element 9. At this time, a current to flows from one electrode to the other electrode (electrode member 7b) in the driving oxygen pump element 9, and a current tD and a current is
Since it is set so that the magnitude is the same and the direction is opposite, it becomes jo + cs - 0, and the voltage Vs is set to the predetermined reference voltage (
For example, it is controlled to 0.5V).

Next, when the air-fuel ratio is in the lean region, the amount of air flowing into the gap chamber 4 from the introduction hole 5 increases, so the oxygen detection pump element 10 operates to increase the amount of oxygen pumped out. As the current ts between the electrodes of the oxygen detection pump element 10 increases, the voltage Vs decreases, and the output voltage 1 of the error amplifier 20 reaches its upper limit. As the voltage (1) increases, the electrode voltage Vcc/2-V+ of the driving oxygen pump element 9 decreases, and the current io decreases, so the amount of oxygen pumped into the interstitial chamber 4 by the driving oxygen pump element 9 decreases. . Furthermore, when the air-fuel ratio becomes lean, the flow direction of the current to is reversed and flows from the other electrode to the one electrode of the driving oxygen pump element 9, and the driving oxygen pump element 9 pumps the air in the interstitial chamber 4 to the outside. put out. Therefore, the amount of oxygen pumped out by the oxygen detection pump element 10 does not increase and is kept constant, so that the internal resistance of the oxygen detection pump element 10 becomes constant. That is, since the current ts is maintained at the value when the air-fuel ratio is the stoichiometric air-fuel ratio, to+t
s>0, and to+ts is proportional to the oxygen concentration.

Next, when the air-fuel ratio is in the rich region, the amount of carbon monoxide flowing into the gap chamber 4 from the introduction hole 5 increases, so that the gap chamber 4
It reacts with oxygen in the interstitial chamber 4 to become carbon dioxide, consuming the oxygen in the interstitial chamber 4. In accordance with the amount of oxygen consumed, the current is between the electrodes of the oxygen detection pump element 10 decreases, the voltage Vs reaches an upper limit, and the output voltage 1 of the error amplifier 20 decreases. Due to the decrease in voltage V1, the electrode voltage V of the driving oxygen pump element 9
Since cc/2-V+ rises and the current tO increases, the amount of oxygen pumped into the interstitial chamber 4 by the driving oxygen pump element 9 increases compared to when the stoichiometric air-fuel ratio is present. Therefore, the amount of oxygen in the gap chamber 4 is equal to the stoichiometric air-fuel ratio, and the amount of oxygen pumped by the oxygen detection pump element 10 is controlled so as to be kept constant without decreasing.
The internal resistance of 0 becomes constant. That is, since the current ts is maintained at the value when the air-fuel ratio is the stoichiometric air-fuel ratio, to+ts
<O, and co+js is proportional to the oxygen concentration.

In the oxygen concentration detection device according to the present invention, MM
Feedback control is performed so that the driving oxygen pump element 9 pumps oxygen to or from the outside so that the amount of oxygen pumped by the detection pump element 10 is always constant, and the oxygen concentration in the interstitial chamber 4 is always kept constant. . Therefore,
Interelectrode voltage Vs and current is of oxygen detection pump element 10
is controlled to be constant, so in lean and rich regions, to+ts is proportional to m degrees of oxygen (14°7 is the stoichiometric air-fuel ratio) as shown in FIG. This oxygen concentration detection output can be obtained as a voltage from the output voltage yout of the operational amplifier 13 described above.

Note that since the oxygen ion conductive solid electrolyte member is generally isotropic, current may leak to some extent between the driving oxygen pump element 9 and the oxygen detection pump element 10. However, since each of these leakage currents is equal to the current toSis and has opposite signs, the oxygen S degree detection current t
There is no adverse effect on o+ts.

As described above, in the oxygen concentration detection device of the present invention, the oxygen ion conductive solid electrolyte member is provided with two pairs of electrode members, and the oxygen ion conductive solid electrolyte member including one of each of the two pairs of electrode members is provided with the oxygen ion conductive solid electrolyte member. A part of the solid electrolyte member forms a gas retention chamber that communicates with the gas introduction hole to be measured. The oxygen ion conductive solid electrolyte member and the two pairs of electrode members act as two oxygen pump elements, one oxygen pump element pumps oxygen from the outside or pumps it out, and the other oxygen pump element always pumps a constant amount of oxygen. The oxygen in the exhaust gas is controlled to be pumped out from the gas retention chamber to the outside by detecting the sum of the current values flowing between the electrodes of each oxygen pump element. Output proportional to concentration can be obtained with high precision. Further, the oxygen concentration detection device of the present invention has a simple configuration, so it is small in size and low in cost.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a circuit diagram showing a current supply circuit, and FIG. 3 is a diagram showing output characteristics of the device shown in FIG. 1. Explanation of symbols of main parts 1.2...Oxygen ion conductive solid electrolyte member 4
...I2!1 gap chamber 5...Introduction holes 7a, 7b, 8a, 8b--Electrode member 9...
... Drive oxygen pump element 10 ... Oxygen detection pump element 12 ... Current supply circuit Figure 1

Claims (1)

[Claims] The oxygen ion conductive solid electrolyte member includes an oxygen ion conductive solid electrolyte member and two pairs of electrode members provided on the oxygen ion conductive solid electrolyte member, and includes one of each of the two pairs of electrode members. Oxygen concentration detection characterized in that a gas retention chamber is formed, a part of which communicates with the gas introduction hole to be measured, and the oxygen ion conductive solid electrolyte member and two pairs of electrode members act as two oxygen pump elements. Device.