JPS5963555A - Oxygen sensor - Google Patents

Abstract

PURPOSE:To provide a higher degree of freedom in a control range with respect to the feedback control of an air to fuel ratio and simplification of the construction wherein an oxygen sensor exhibiting two kinds of characteristics is mounted in a detection part by forming said sensor into one unit. CONSTITUTION:Electrodes 7a, 7b, 7c, 7d are provided in both side parts of the parts which constitute a closed chamber A of a ceramic sintered body 6 and face to each other. The electrodes 7a, 7b, 7c, 7d consisting of, for example, platinum plated externally with gold are used in order to decrease their catalytic effect. Electrode protective layers 8a, 8b, 8c, 8d consisting of porous ceramics cover the top surfaces of the respective electrodes. Diffusion pores 5a, 5b are provided to the electrode protective layers, the respective electrodes and the ceramic sintered body. A voltage is impressed through a resistance at both terminals of the electrodes 7c, 7d, and the current to be conducted is so controlled that the electromotive force induced in the electrodes 7a, 7d is maintained constant by regulating the voltage. The platinum Pt electrodes 9a, 9b provided on both surfaces in the part of the open chamber B in the body 6 constitute a sensor for detecting a theoretical air to fuel ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oxygen sensor that is used, for example, to field-pack control the air-fuel ratio of an air-fuel mixture in an internal combustion engine and detects the oxygen concentration in exhaust gas.

Oxygen sensors installed in the exhaust gas of internal combustion engines and used for feedback control of the air-fuel ratio of the air-fuel mixture generally exhibit an output characteristic in which the output voltage changes in a switching manner around the stoichiometric air-fuel ratio. The air-fuel ratio is controlled by the output so that it becomes the stoichiometric air-fuel ratio. Therefore, this oxygen sensor generates a relatively stable output in response to the oxygen concentration in the exhaust gas, but since it can only detect the stoichiometric air-fuel ratio, it cannot be controlled to the stoichiometric air-fuel ratio in the air-fuel ratio control. There are limits to what you can do.

Therefore, in order to improve this problem, an oxygen pump-type oxygen sensor has been proposed that can proportionally (in an analog manner) detect the lean side air-fuel ratio where the oxygen concentration increases. The structure of this sensor is as shown in No. 11d, with an annular spacer (
3) to constitute a hollow part, and each of the above-mentioned disks (1)
Platinum (Pt) electrodes (4a) on each side of (2)
C4b) (4c) (4d) are deposited, and each electrode and disk (1) (2) has a pore (5a) in the center.
), (5b) are provided.

Now, the DC voltage CVP) across the electrodes (4c) (4d)
When is applied through the resistor (RL), oxygen gas is released from the inside (hollow part) to the outside (to be measured gas side) through the zirconia disk (2) as a solid electrolyte oxygen pump. When oxygen gas is released from the hollow part, the electrode (4a) (
At the same time, an electromotive force is generated at both ends of 4b) due to the difference in oxygen concentration, and at the same time, the gas to be measured diffuses through the pores <5a) (5b). At this time, each electrode (4
c) If the current (IP) flowing between (4d) is controlled,
At constant temperature, the current IP exhibits a value proportional to the oxygen concentration as shown in FIG. 2, so it can be used as an oxygen sensor. By the way, this type of sensor exhibits linear characteristics with respect to the oxygen concentration in N2 gas or CO2 gas, as shown in Figure 2. There is a problem that the characteristics are unstable with respect to the oxygen concentration, and in particular, the characteristics near the stoichiometric air-fuel ratio and the low oxygen concentration exhibit unstable characteristics such as a significant decrease in output with respect to the oxygen temperature.

Therefore, in feedback air-fuel ratio control of an internal combustion engine, if the above two types of oxygen sensors are selected and combined as appropriate depending on the engine operating mode and the air-fuel ratio is feedback-controlled, a wide range of air-fuel ratios can be achieved, including the stoichiometric air-fuel ratio or lean air-fuel ratio. It is possible to perform feedback control.

This invention has been made in view of the above-mentioned points, and by configuring the oxygen sensor exhibiting the above-mentioned two trap characteristics as one unit (one structural unit ratio), it is possible to carve into the air-fuel ratio refeedback control and increase the control range. It is an object of the present invention to provide an oxygen sensor that can increase the degree of freedom and also simplify the mounting structure for the detection section. Embodiments of the present invention shown in the figures will be described below. In Figure 3 (6
) is a ceramic sintered body having the properties of a solid electrolyte made of zirconium oxide stabilized with 1034% Y2O8.
β). Electrodes (7a) (7b) (7c) (
7d) is provided. 1118ii (7a) (
7b) (7c) (7d) For example, platinum plated with gold on the upper surface is used in order to reduce the catalytic action.

(8a) (8b) (8c) (8d) is an electrode protective layer made of porous ceramic and covers the upper surface of each of the electrodes. These electrode protective layers, each electrode, and the ceramic sintered body are provided with diffusion pores (5a) (5b), and although not shown, electrodes (7c) (7
A voltage is applied to both ends of electrode (7a) (7d) through a resistor, and the current caused by this voltage is controlled so that the electromotive force induced in the electrodes (7a) (7d) is constant. (9a) and (9h) are platinum (pt) electrodes provided on both sides of the open chamber (B) portion of the ceramic sintered body (6), and constitute a stoichiometric air-fuel ratio detection sensor. An electrode protective layer (8e) made of porous ceramic is provided on the upper surface of the outer electrode (9a). OI is a temperature sensor held on the outer surface of the ceramic sintered body (6), and its upper surface is covered with a protective layer (8f) made of porous ceramic. (11) is an exhaust pipe to which the sensor configured as described above is attached and through which engine exhaust gas flows.

To explain the manufacturing process of such a sensor in more detail, first, a thin plate with a thickness of, for example, 0.5 nm is constructed from a ZrO Two pieces are cut out, and the central part of the part that should constitute the closed chamber (A) in the figure is etched by ultrasonic machining, for example, with a 0.
After drilling a hole of 0.7 m in length, platinum was deposited on both sides of the two thin plates centering around the hole, and then gold plating was performed to form an electrode. Similarly, platinum electrodes are provided on both sides of the part of the thin plate that should constitute the open chamber (B), and a temperature sensor is provided on the side of the thin plate that should constitute the open chamber (B) that is in contact with the exhaust gas. After mounting, the top surface of each of these electrodes and the temperature sensor is covered with a protective layer.

Further, for example, from the plate-shaped sintered body having a thickness IIl]I11, the outer shape forms the rectangular shape, and each of the chambers (A) (
B) is constructed by cutting out a spacer having holes and notches of predetermined dimensions, and N on both sides of this spacer.
After coating aO-5iO2-A620J with a glass frit having a softening point of 1000°C, the two thin plates with the electrodes and temperature sensor were placed on both sides of this spacer and heated to 1160°C in a furnace. and connect them to form an integrated sensor.

Next, the function of the oxygen sensor configured in this manner will be explained.

In the closed chamber (A) of Fig. 3, although not shown, when a voltage is applied to both ends of one electrode (7c) (7d) through a resistor, as in Fig. 1, the ceramic solid electrolyte acts as an oxygen pump and gases oxygen. is released from the inside (closed chamber A) to the outside (exhaust gas side). Then, the inside (occlusion chamber A) and the outside (
(7a)
The ceramic solid electrolyte between (7b) acts as an oxygen concentration battery, and an electromotive force is generated due to the difference in oxygen concentration.At the same time, the inside (closed chamber (A))
The gas to be measured is diffused. At this time, if a voltage is applied to both ends of the electrodes (7c) and (7d) through a resistor so as to keep the electromotive force constant at 15 mV, at constant temperature (7 = 800°C), the normal current (IP) and the exhaust gas due to the applied voltage. The oxygen concentration in the gas exhibits a proportional value as shown in FIG. 4(A). Figure 4 (B) shows the platinum electrode (7aC (7b) (7c) (
7d) has a value measured with a non-gold-plated material that has a catalytic action, and the output characteristics are those of the electrode (7a) (7b) (7
c) It is more stable if the catalytic action of (7d) is suppressed. In the open chamber CB), an operational output as a ceramic solid electrolyte oxygen concentration cell type stoichiometric air-fuel ratio detection sensor is generated between the platinum electrodes (9a) and (9b) due to catalytic activity. As for the output characteristics, as shown in FIG. 5, the output changes stepwise at the stoichiometric air-fuel ratio.

Exhaust gas temperature is measured using temperature sensor αQ.

Protective layer (8a) (8b) '(8c) (8d) (
8e) (8f) is made of porous ceramic and serves to protect each electrode and sensor. The exhaust gas to be measured is introduced through the exhaust pipe 0υ.

As explained above, according to the present invention, since two types of oxygen sensors are integrated, it is possible to put into practical use a small and inexpensive sensor that exhibits two types of output characteristics with respect to the oxygen concentration in the exhaust gas of an internal combustion engine. Furthermore, the structure for mounting on the detection section can be simplified, and furthermore, the degree of freedom in controlling the air-fuel ratio of the internal combustion engine can be increased.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional oxygen sensor, and Figure 2 is a cross-sectional view of a conventional oxygen sensor.
Figure 8 is a cross-sectional view showing an oxygen sensor according to an embodiment of the present invention, and Figure 4 is a characteristic diagram of the sensor measuring oxygen concentration in exhaust gas. FIG. 5 is a characteristic diagram of the stoichiometric air-fuel ratio sensor. (1), (2)... Zirconia disc, (3)...
・・・・・・Annular spacer for hollow formation, (4a) (4b
) (4c) (4d) --- Platinum electrode, (5aX5b)
...... Diffusion pores, (6) ... Ceramic sintered body made of zirconia, (7a) (7b) (7c
) (7d) -=・”'Gold-plated platinum electrode, (8a) (8
b) (8c) (8d) (8e) (8f)
・ Electrode protective layer, (9a) (9b)...Platinum electrode, 0Q... Temperature sensor, 0υ...
...Exhaust pipe, (A) ......Occluded chamber, C
B)......Open room agent Shin Kuzuno - Figure 1/? P Fig. 2 02 (%) Fig. 3 Fig. 4 Fig. 5 Room fuel ratio 'I) 3''I'llength' 1.Indication of 1.
21st name oxygen sensor 3 of No. 00 No. 28 invention, extractor representative stand piece 111 Part (1) Specification 711 is corrected as per the following. 1. Indication of the incident Patent Application No. 167200/1983 8.
Relationship between the person making the amendment and the case f! Ode Applicant Office 1-5-15 Tsuchiyama, Himeji City, Hyogo Prefecture Name General Automobile Safety Pollution Technology Research Association Representative Saka 1) Kuni
Kotobuki 4, Agent address: 2-2-3-6 Marunouchi, Chiyoda-ku, Tokyo, Detailed description of the patented invention in the specification subject to amendment 1 Brief description of drawings column 6, Contents of the amendment

Claims (1)

[Claims] A first electrode pair forming a closed chamber having diffusion pores and a concave release chamber opening to the atmosphere in a base body having properties of a solid electrolyte, and functioning as an oxygen pump by sandwiching the base portion constituting the closed chamber. and a second electrode pair that induces a voltage, and an eighth electrode pair is provided sandwiching the base portion constituting the open chamber; An oxygen sensor having an integrated configuration of an oxygen pump type sensor constituted by a second pair of electrodes and a stoichiometric air-fuel ratio sensor constituted by a third pair of electrodes provided on the base portion.