JPH022536B2 - - Google Patents

Description

[Detailed description of the invention]

2. Description of the Related Art Oxygen sensors that use a solid electrolyte material as an oxygen detection element are widely used as oxygen sensors for detecting the oxygen concentration in exhaust gas in various types of combustion equipment, including internal combustion engines. In this type of oxygen sensor, an internal electrode extending upward from the closed end of a bottomed cylindrical oxygen detection element made of zirconia or the like and a corresponding external electrode are made to have air permeability by, for example, platinum baking. The inner electrode is formed in a layered manner, and the former internal electrode is drawn outward by an output wire having a coiled lead wire having an air flow path in the center so as to allow the outside air to flow to the closed end. The latter external electrode was designed to be electrically connected to a metal shell having a protective tube with a small hole for bringing external exhaust gas into contact with it, but there were various difficulties in sealing the metal shell and the oxygen detection element. Ta. In other words, in such a conventional oxygen sensor, the metal shell and the oxygen detection element are sealed together by seating a large-diameter flange provided on the body of the oxygen detection element on a step surface provided on the inner diameter surface of the metal shell. A seal for an internal combustion engine ignition plug with high lubricity and excellent sealing properties is placed in the annular gap formed between the small diameter portion above the flange of the oxygen detection element and the stepped surface of the shaft hole of the metal shell. Talc powder or carbon powder, which is widely used as an adhesive, is filled and compressed, and above it is a metal sleeve that surrounds and insulatingly protects the connection between the internal electrode layer and the output wire. The upper end surface of the metal shell was pressed inward. When an oxygen sensor is installed in a high-temperature exhaust gas pipe, especially an exhaust pipe as an exhaust gas detection device for an internal combustion engine, the temperature rise at the sealed part is several hundred degrees, which is much higher than in the case of a spark plug for an internal combustion engine. In severe cases, temperatures can reach as much as 650℃. On the other hand, it has been found that carbon has poor oxidation resistance and begins to oxidize at around 400℃, decreasing its volume and losing its sealing effect, which may eventually lead to loosening of the sealed part. The decrease in volume caused by oxidation was previously reported by the applicant in Japanese Patent Application No. 159029/1983
57-82762), a metal ring having a coefficient of thermal expansion lower than that of the metal shell is inserted between the sealed part made of fine graphite powder and the metal sleeve, and This is improved by crimping the upper edge of the metal shell, which is provided with an annular groove that is locally heated by electricity near the outer periphery of the metal ring, and applying a strong compressive force to the sealed portion. However, there were still concerns about durability due to oxidation of the graphite powder. On the other hand, when talc is used, gas is generated which is thought to be caused by crystallized water released from the filled talc, and this gas enters the metal sleeve along the outer circumferential surface of the oxygen detection element and is used for the output extraction. It has been discovered that the air flowing through the central opening of the coiled lead wire of the electric wire contaminates the atmosphere inside the oxygen detection element, reducing the output. The present invention considers that the graphite powder described above is inherently disadvantageous as a sealant for this type of oxygen sensor, which reaches temperatures of several hundred degrees Celsius, and as a result of further investigation into fine powder of talc as an alternative, we found that the The occurrence of this problem can be eliminated by pre-calcining at 550℃ or higher, and as the calcination temperature increases, the slipperiness decreases and the packing density decreases, but in the case of oxygen sensors. This method was developed based on the fact that the pressure of the gas it receives is very low, only about 1Kg/ ^cm2 , and does not require a large packing density for the sealant. By using fine powder of calcined talc, we succeeded in obtaining an oxygen sensor with the necessary sealing effect (airtightness) and satisfactory durability. The drawing shows an embodiment of the oxygen sensor according to the present invention, in which 1 is made of an oxygen ion conductive solid electrolyte such as stabilized zirconia, and has a bottomed cylindrical shape with a bottomed hole 11 and a large diameter flange 12 on the body. The oxygen detection element shown in FIG. The external electrode 2b, which reaches the collar 12 through the above, is formed of a porous thin film made of a refractory metal such as platinum. 3 is inserted into an exhaust pipe (not shown), and is provided with a plurality of small holes 31a, 31a, . A step seat 32 has a protection tube 31 protruding downward, seats the collar 12 of the oxygen detection element, and electrically connects the external electrode 2b.
A metal shell 4 is filled into an annular gap formed between a large-diameter shaft hole 33 above a stepped seat 32 of the metal shell and a small-diameter head 14 above a collar 12 of the oxygen detection element. , indicates a compressed sealant, and in the present invention, fine powder of talc calcined at 550-1000°C is used. Reference numeral 5 denotes a large-diameter collar 51 disposed above the sealant 4 and fitted to the inner wall surface of the large-diameter shaft hole 33 of the metal shell and the outer diameter surface of the small-diameter head 14 of the oxygen detection element. The metal sleeve 6 is fitted onto the metal sleeve 51 and crimped by the upper end surface of the metal shell 3, and the metal sleeve 5 is used to prevent loosening of the sealant 4. Metal cannula 5 with a metal ring to prevent
However, as shown in the figure, a thin groove 34 is provided on the outer circumferential surface of the metal shell 3 corresponding to the metal ring 6, and when the upper end surface of the metal shell 3 is swaged, it can be made at the same time. When the thin-walled groove is softened and deformed by applying electricity to further enhance the sealing effect, a small-diameter portion 61 corresponding to the amount of deformation in the inner diameter direction of the deformed thin-walled groove 34 is provided. Note that 7 is a metal ring that seals the sealant 4 downward, and 8 and 9 are packings made of Valka sheet and metal plate that also increase the elasticity of the sealant 4 and seal it upward. can also be omitted. Next, 100 is press-fitted into a screw 11a formed at the open end of the bottomed hole 11 of the oxygen detection element to be mechanically held, and is electrically connected to the internal electrode layer 2a extending to the screw 11a. An output conductor is shown having a coiled terminal 101 connected to the output conductor, and its front end is covered with a metal mesh 113 and an elastic insulating material 112 such as silicone rubber, and the output conductor is wound so as to communicate with the outside air at its central opening 111a. It is connected to the coiled lead wire 111 at the center of the output wire 110. Reference numeral 120 denotes an insulating tube made of synthetic resin or ceramic, which is provided on the inner diameter surface of the metal sleeve 5 to ensure insulation of the output wire 100, and is seated at the upper end of the bottomed hole 11 of the oxygen detection element. The upper end of the metal sleeve 5 is fixed by crimping or the like via a rigid spring 140 held by a fixed support piece 130. Further, 150 indicates a metal cap that holds the output wire 110 coaxially with the metal sleeve 5 through a soft insulating tube 160 made of silicone rubber or the like, and is crimped or otherwise tightened at the upper end of the metal sleeve 5. The metal tube 5 is fixed by a hole 111a, which is also bored in the side wall of the metal sleeve 5 below, and is connected to the opening 111a at the center of the coiled lead wire 111 of the output take-out electric wire. An annular gap G surrounding the air hole 52 passing through the air hole 52 is provided. Note that the extension of the metal cap forming the annular gap G may be contaminated with oil or dust.
However, in some cases, the metal cap 150 may be omitted and the metal sleeve 5 may be extended upward to directly connect the soft insulating tube 16.
0 can be sealed and the air hole 52 can be omitted. Moreover, when the air hole 52 is provided, a solid wire 110 for output extraction may be used. Note that a soft insulating tube 1 is connected to the output conductor 100.
The electrical connection mechanism of the output take-out electric wire 110 and the mechanical assembly mechanism of the output take-out electric wire 110 to the metal sleeve 5 are shown as typical configurations. Another configuration can be adopted as long as the internal electrode layer that communicates with the shaft hole and is provided in the shaft hole of the oxygen detection element can be reliably connected to the output wire. Example Oxygen detection element 1 made of stabilized zirconia in the shape of a cylinder with a bottom, in which a flange 12 with an outer diameter of 15 mm and a width of 4 mm is formed on the body, and a small diameter head 14 with an outer diameter of 10 mm is provided above the flange. is stored in the large diameter shaft hole 33 of the metal shell 3 that loosely fits with the outer diameter surface of the collar 12 of the oxygen detection element,
Directly supported on the stepped seat 32, and the large diameter shaft hole 33
550°C, 800°C,
Filled with fine powder of talc and graphite (100 mesh passes) calcined at 1000℃ and 1100℃ for 2 hours each, pressurized at 2500Kg, and compressed the filled powder to a depth of 9mm from the upper end surface of the metal shell (see above). Tsuba 12
A metal ring 6 with a height of 6 mm and an inner and outer diameter approximately equal to the annular gap is placed on top of the filling powder, and the metal ring 6 of the metal shell 3 is A thin groove 34 having a width of 2.5 mm and a thickness of 0.8 mm between the outer diameter surface and the inner diameter surface corresponding to No. 6 is energized, and heated to approximately 800°C. The following table shows the results of measuring the durability at high temperatures of samples obtained by crimping the end faces with 4000 kg. Durability at high temperatures was determined by applying an air pressure of 4 kg/cm ² and measuring the time until air leaked from the seal.

[Table] As shown in the previous table, when conventional fine graphite powder is used as a sealant for an oxygen sensor, after 300 hours when heated at 550℃, and after 100 hours at 650℃. However, the present invention, which uses fine talc powder calcined within the range of 550 to 1000°C, showed much higher durability, but up to 1100°C, which is outside the range. No effect was observed when the calcination temperature was increased. This is thought to be due to the characteristic of talcum, which is that the release of crystallized water rapidly increases from around 1000℃, resulting in a significant decrease in density. As shown in the previous table, fine talc powder exhibits higher durability at lower calcination temperatures;
When calcined in Therefore, it is disadvantageous to raise the calcination temperature more than necessary, and from this point of view, the calcination temperature is actually 800
Appropriate temperature is around ℃.

[Brief explanation of drawings]

The drawing is a quarter-half vertical sectional view showing an embodiment of the oxygen sensor of the present invention. 1...Oxygen detection element, 12...Large diameter tsuba, 13
a... Closed end, 14... Head with small diameter, 2a... Internal electrode layer, 2b... External electrode layer, 3... Metal shell, 31... Protection tube, 31a, 31a... Opening, 32 ... Step seat, 33 ... Shaft hole, 4 ... Sealing agent, 110 ... Output extraction wire.

Claims (1)

[Claims] 1. The body of a bottomed cylindrical oxygen detection element, which has an internal electrode that extends upward from the inner surface of the closed end and is connected to the output extraction wire and is in contact with the outside air, and a corresponding external electrode that extends upward from the outer surface. A large-diameter flange provided on the metal shell is seated in a stepped seat in the shaft hole of the metal shell to electrically connect the external electrode to the metal shell, and a small-diameter head above the flange of the oxygen detection element. and the shaft hole of the metal shell surrounding the main metal fitting, and the annular gap formed therebetween is filled with a sealing agent made of talc powder calcined at 550 to 1000°C to seal them together. oxygen sensor.