JPH0868776A - Oxygen sensor with seal of fluoroelastomer - Google Patents

Abstract

PURPOSE: To increase resistance to high-temperature circumstances by sealing an electric conductor means from a sensitive element with fluoroelastomer. CONSTITUTION: A sensitive element 5 (platina covered zirconia, e.g.) is located in a housing 4 to generate electric signal in response to oxygen concentration in exhaust gas. A wiring 3 (an electric conductor means) is extended into a mainbody member to receive aen electric signal from the sensitive element 5. The wiring 3 is extended to the outside of the mainbody member to send the signal to an oxygen control means. The wiring 3 is passed through an elastomer seal 8 to the outside of the sensor 1. The seal 8 is formed of high- temperature resistant cured elastic copolymer (fluoroelastomer). Cured elastic coplymer fluoride has high resistance to high-temperature decomposition under the existance of exhaust gas from an engine. In is used as sealing material to increase the protection of inside electric components and ensure accurate operation of the sensitive element 5.

Description

Detailed Description of the Invention

The present invention relates to an oxygen sensor having sealing means which is particularly resistant to motor vehicle engine exhaust gases and engine compartment vapors at high temperatures.

Oxygen sensors are exposed to high temperatures in the presence of combustion gases. Such sensors are typically located in an environment exposed to contact with fuels and oils, which are liquids or vapors on the outside, from which fuels and oils are exposed to internal sensing elements and associated circuitry. It must be isolated to prevent performance degradation. For example, exposure of the sensing element to pollutants in the air can affect sensor performance. Therefore, sealing means that are resistant to high temperature environments are needed for efficient operation and extended service life.

A recent trend in automotive engine compartment designs has created the need to place oxygen sensors in locations that are exposed to temperatures as high as 300 ° C. Such conditions cause rapid deterioration of the elastic seal used to isolate and protect the internal mechanisms of the oxygen sensor.
Therefore, there is a need in the art for oxygen sensors that incorporate sealing means based on elastomeric materials having greater high temperature resistance.

The present invention is an oxygen sensor for use at temperatures in excess of 200 ° C., said sensor providing an electrical signal in response to the oxygen content sensed by said sensor in engine exhaust gas. In response to a signal, oxygen is supplied to the means for controlling the supply of oxygen to the engine, the sensor comprises a body member, the body member being i) an opening for admitting engine exhaust gas; A sensing element that is exposed to the gas entering the body member through the opening and that produces an electrical signal in response to the oxygen content of the gas, iii) receives the electrical signal and derives the signal from the body member. An electrical conductor means for transmitting to the control means, and iv) a seal function between the conductor means and the body member. And a means for preventing gases other than the engine exhaust from coming into contact with the sensing element, the sealing means comprising perfluoroolefin and at least one other perfluorocomonomer. To an oxygen sensor characterized by comprising a cured elastic copolymer of

Although the present invention is not limited to a particular design of oxygen sensor, the particular design of the sensor shown in the drawings is described below for purposes of illustrating the application of elastomeric copolymers.

As shown in the drawings, the oxygen sensor comprises a body member, which comprises a plurality of interconnected housings 4, 7, 9, and 10. The sensing element 5, eg platinum coated zirconia, is located within the body member, primarily within the housing 4 of the body member. The housing 4 has openings, as shown in the drawing, which allow the engine exhaust gases to enter the sensor and in particular come into contact therewith, thereby exposing the sensing element to these gases. The sensing element 5 produces an electrical signal in response to the oxygen concentration in the exhaust gas. The housing 9 is mainly a reinforcing member for the main body member. Other surrounding housings 7, 4
And 10 are directly or indirectly mounted to the housing 9, which has a threaded section used to install the device in the engine exhaust system.
Electrical conductor means, shown in the drawing to include wires 3, extend into the body member and are in electrical communication with the sensing element to receive electrical signals from the sensing means. Wiring 3 also extends outside the body member to signal this signal to oxygen control means (not shown) which is common in the art. The electrical conductor means is also 1
Components of electrically insulating housings of the series 2, 6 and 1
1. Pass through the components of the housing, for example of ceramic material, and these components of the housing are enclosed within a protective body member. The wire 3 exits the sensor 1 through an elastomeric seal 8. In the illustrated embodiment, the seal 8 indirectly forms a seal between the wiring 3 and the body member via the insulating housing component 11. Alternatively, the seal 8 can be directly interposed between the wiring of the electrical conductor means and the metal housing components. The seal is generally cylindrical, has holes corresponding to the number, size and location of circuit traces, and directly or indirectly seals the space between the traces and the body member.

The main function of the seal 8 is to isolate the interior of the sensor from atmospheric gases, in particular oxygen, so that the sensing element is exposed to exhaust gas only. In the process of providing this isolation protection, the seals are also harmful pollutants,
For example, it prevents particles or oil from the engine from entering the sensor. Another function of the seal is to place the wires securely within the body member and prevent the wires from fraying against the insulating housing. The seal also serves to prevent exhaust gases from escaping through the oxygen sensor into the atmosphere.

An oxygen sensor is installed in the exhaust system and is used to monitor the oxygen content of the exhaust gas. The difference in oxygen concentration between the exhaust gas and the atmosphere causes the sensing element 5 to generate an electrical signal proportional to the difference in concentration. The voltage so generated is low when the engine is running "lean" (high air / fuel ratio), but the engine is "rich".
High when rotating at (low air / fuel ratio). The signal is transmitted through line 3 to the engine oxygen control means, which responds to the transmitted signal to appropriately alter the supply of air / fuel mixture to the engine. Since this device is located in the hot exhaust gas, the temperature in the sealing area is generally above 200 ° C, and 315
It may be as high as ℃.

A feature of the present invention is the advantageous construction of the seal between the electrical wiring 3 and the body member (insulating housing), usually in the form of a bush or grommet. The seal is composed of a cured high temperature resistant elastomeric copolymer (fluoroelastomer) which is described in more detail below.
The cured fluorinated elastic copolymer is highly resistant to the decomposing effects of high temperatures in the presence of engine exhaust gases and simulated engine compartment fluids and vapors, and its use as a sealing material. Enhances the protection of the use of internal electrical components and ensures the correct operation of the sensing element. Such oxygen sensors have two
Suitable for use in environments exposed to temperatures above 00 ° C.

Fluoroelastomer sealing elements, eg
Thus, there are few suitable materials available to make the seal 8.
Both are copolymerized monomers of two major perfluoromonomers.
Choose from a cured elastic copolymer composed of
To be done. In addition, the copolymer may be less
Copolymerization of at least one fluorinated cure site monomer
Units may be included. First major comonoma
Is a perfluoroolefin, such as tetrafluoro
It is polyethylene. Other major perfluorocomonomer
Is perfluoro (alkyl vinyl) ether CF₂= C
FO (R_f‘O） _n(R_f"O)_mR_fAnd where R_f’
And R_f"Is a different straight chain having 2 to 6 carbon atoms
A branched or branched perfluoroalkylene group
Where m and n are independently 0-10, and R_fIs
A perfluoroalkyl group having 1 to 6 carbon atoms
is there. The preferred class of perfluoro (vinyl ether)
The formula is CF₂= CFO (CF₂CFXO)_nR_fThe compound of
Include, where X is F or CF₃And n is 0 to 5
And R_fIs a par with 1 to 6 carbon atoms
It is a fluoroalkyl group. Most preferred perfluoro
(Vinyl ether) has n = 0 or 1 and R
_fContains 1 to 3 carbon atoms. Such an overshoot
An example of a fluorinated ether is perfluoro (methyl vinyl) ether.
Ether and perfluoro (propyl vinyl) ether
Includes. Other monomers have the formula CF₂= CF [O (CF₂)_mCF₂CFZO]_nR_f (I) (wherein R_fIs a perfluor having 1 to 6 carbon atoms
Is an alkyl group, m is 0 or 1, and n is 0 to
5 and Z is F or CF₃Is. ) And the formula CF₂= CFO [(CF₂CFCF₃O)_n(CF₂CF₂ CF₂O)_m(CF₂)_pCF₃ (II) (wherein m and n are 0 to 10 and p is 0 to
It is 3. ) Compounds.

Minor amounts of copolymerized fluorinated cure site monomer units can also optionally be present in the polymer in addition to the perfluorocomonomer. Generally, these cure site monomers are present in amounts up to about 3 mol%. They can be free of hydrogen atoms or can contain hydrogen hydrogen atoms. Monomers suitable cure site, brominated fluoroolefins, for example, bromotrifluoroethylene and 4-bromo-3,3,4,4-tetrafluoro butene; brominated fluoroethers, for example, CF ₂ = CF-
OR _f CF ₂ Br, where R _f is a perfluoroalkylene group containing 1 to 9 carbon atoms, and vinylidene fluoride. Monomers preferred cure site is a fluorinated vinyl ether containing perfluorophenyl (C ₆ F ₅₎ or cyano substituents, for example, the formula _{CF 2 = CF-O (CF} 2) n -C 6 F 5 (III) ( wherein, n is _{1~8.) CF 2 = CF-} O (CF 2) 3 -O-C 6 F 5 (IV) CF 2 = CF- [OCF 2 -CF 3 CF] n -O- C ₆ F ₅ (V) (wherein, n is _{1~2.) CF 2 = CF-} O (CF 2) in _n -CN (VI) (wherein, n is 2 to 12, preferably 2 to . a _{4) CF 2 = CF-O} -CF 2 - [CFCF 3 -O-CF 2] n -CFCF 3 -CN (VII) ( wherein, n 0-4, are preferably 0 to 2 .) and _{CF 2 = CF- [OCF 2 -CF} 3 CF] x -O- (CF 2) n -CN (VIII) ( wherein, x is 1-2, and n is 1 Encompasses represented by those with a 4.).

The fluorinated polymer can also contain end groups derived from initiators and chain transfer agents. Depending on the initiator and chain transfer agent used, such end groups are reactive and can participate in the curing reaction. Suitable initiators include compounds that are the source of end groups of halogens, such as hydroiodic acid, hydrobromic acid, and metals belonging to Group IA, IB, IIA, IIB, such as Li. , Na, K, Rb, Cs, Be, M
g, Ca, Sr, Ba, Cu, Ag, Zn, Cd, and transition metals such as Fe, Co, Ni, Ru, R
h, Pd, Pt, or metals belonging to Group III and Group IVB, such as Al, Ga, Sn, and Pb
Iodide and bromide. Suitable chain transfer agents are methylene iodide, isopropanol, monoiodoperfluoroalkanes such as monoiodoperfluoromethane and methaneiodoperfluoropropane; perfluoroalkyl bromide, 4-bromo-perfluorobutene-1, 1, , 4-diiodoperfluorohexane, 1,
Includes 4-diiodoperfluorohexane, and 1,4-diiodoperfluorooctane.

Particularly preferred for fabrication of the sealing element are tetrafluoroethylene, perfluoro (methylvinyl) ether, and perfluoro (8-cyano-5-methyl-3,6-dioxa-1-octene). It is a copolymer.

The fluoroelastomer composition used to make the seal elements used in the present invention is prepared by compounding an uncured fluoroelastomer and a curing agent at a temperature below the cure temperature of the polymer. The compounded composition is then molded (pressed) into a seal, for example a gammet, press cured and then usually post cured. The compositions of the present invention may be cured by commonly used crosslinking systems in combination with the particular copolymerized cure site monomers present, as known to those skilled in the art.
For example, when a cure site containing a pentafluorophenyl group is present, it is based on an aliphatic diamine or, preferably, the dipotassium salt of bisphenol AF, KOC.
₆ H ₄ -C (CF ₃₎ may be used curative systems based on ₂ -C ₆ H ₄ OK. When a curing moiety containing a cyano substituent is present, a curing agent system based on organotin compounds is usually selected. Suitable organotin compounds are
Includes allyl-, propargyl-, triphenyl- and allenyl tin hardeners. Tetraphenyltin is the preferred curing agent for use in combination with the cyano-substituted cure site.

Polymers containing cure site monomers, as well as polymers without copolymerized cure site monomers, can be cured by the free radical method using a peroxide curing agent. For example, dialkyl peroxides that decompose at temperatures above 50 ° C. are particularly preferred when the composition is to be processed at elevated temperatures prior to curing. Ditertiary butyl peroxide having a third carbon atom attached to peroxy oxygen is often particularly useful. Examples of the most useful peroxides of this type are 2,5-dimethyl-2,5-di (t-butylperoxy) hexyne-3 and 2,5-dimethyl-2,
5-di (t-butylperoxy) hexane. Other peroxides include dicumyl peroxide, dibenzoyl peroxide, t-butyl perbenzoate, and di [1,3-dimethyl-2- (t-butylperoxy) butyl] carbonate. Organic peroxide is
Generally, an amount of peroxide of about 1 to 3 parts per 100 parts of fluoropolymer is present. Also, a wide variety of peroxide coagents can be used, of which trimetalyl isocyanurate, triallyl isocyanurate, and trimethylolpropane trimethacrylate are preferred. The peroxide synergist is generally present in an amount of about 1 to 3 parts per 100 parts fluoropolymer.

Additionally, the dual curing system can be used with perfluoroelastomers containing nitrile groups. Dual curing systems include tin catalysts that can crosslink perfluoroelastomers through nitrile groups, such as triphenyltin hydroxide; peroxides that can crosslink perfluoroelastomers, such as 2,5-
It consists of bis (t-butyl peroxide) -2,5-dimethylhexane; and a synergist of dienes and trienes, such as triallyl isocyanurate. The amount of curing agent used will necessarily depend on the degree of crosslinking desired in the final product, as well as the type and concentration of reactive moieties in the perfluoroelastomer. Generally, about 1-10 phr of curing agent can be used, and 2-5 phr should be satisfactory for most purposes. Other additives that are typically used with perfluoroelastomers, such as carbon black, fillers, stabilizers, plasticizers, lubricants, or processing aids, as long as they have adequate stability under the intended conditions of use. Can be incorporated into the composition of the present invention. In particular, low temperature performance can be enhanced by the addition of perfluoropolyether, while at the same time maintaining better high temperature performance. Perfluoropolyethers that can be used in the compositions of the present invention are those in which the oxygen atoms are separated by saturated fluorocarbon groups in the polymer backbone of the molecule. More than one type of fluorocarbon group can be present in the molecule.

It is particularly desirable to use large particle size carbon black to enhance the high temperature performance of the fluoroelastomer composition. About 20-70 phr
(Parts by weight per 100 parts by weight of rubber), preferably 25
It has been discovered that fluoroelastomers containing ~ 45 parts by weight provide a useful combination of thermal stability and processability. The preferred carbon black is ASTM
At least 100 nm as determined by D3849;
It has an average particle size of 500 nm.

[0018]

EXAMPLES VF ₂ -HFP copolymer 100 phr (fluorine content 66%) Magnesium oxide 3 carbon black 30 calcium carbonate 6 curing agent I 1.8 curing agent II 4 using a composition of pressure 177 ° C. × 10 Bushings were prepared under curing conditions of minutes and oven heating 232 ° C x 24 hours. When this bush was subjected to an aging test in which it was exposed to circulating air at 275 ° C. for 70 hours in an oven, a weight loss of 4% was observed (known example).

On the other hand, a composition of 55.8TFE-42PMVE-2.2CNVE 100phr copolymer (fluorine content 73%) crown ether 0.3 carbon black 12 tetraphenyltin 3 was used, pressurization 204 ° C. × 15 minutes and oven heating. The bush was manufactured under curing conditions of 305 ° C. × 26 hours (in a nitrogen atmosphere). When this bush was subjected to the same aging test as described above, the weight loss thereof was only 1% (Example of the present invention).

[Note] VF ₂ : vinylidene fluoride HFP: hexafluoropropylene TFE: tetrafluoroethylene PMVE: perfluoromethyl vinyl ether CNVE: CF ₂ ═CF—O—CF ₂ (CF ₃ ) CF—O—
(CF _{2) 2} -CN (monomer x is n 1 is 2 in Formula VIII) crown ether: 18-crown-6 crown _{ether, (C 2 H 4) 6} O 6 curing agent I: DuPont Made by "Viton Curati
ve No.20 "(benzyl mixture of triphenyl phosphonium chloride 33 wt% and VF ₂ -HFP copolymer 67 wt%) curing agent II: DuPont Co." Viton Cur
According to ative No.30 "(a mixture of bisphenol AF50 wt% and VF ₂ -HFP copolymer 50 wt%) present invention, as it is clear from the test results of the above Examples, for use in temperatures above 200 ° C. The oxygen sensor of the present invention, in which the conductor means is separated from the body member by a seal composed of the aforementioned cured fluoroelastomer composition, is highly resistant to operating temperatures above 200 ° C. And provides an increased service life over prior art oxygen sensors.The oxygen sensor of the present invention is used in locations where it is exposed to temperatures as high as 300 ° C in automotive engines. Fit to do.

The main features and aspects of the present invention are as follows.

An oxygen sensor for use at temperatures in excess of 1.200 ° C., wherein the sensor responds to the oxygen content sensed by the sensor in engine exhaust gas with an electrical signal responsive to the electrical signal. In response to the means for controlling the supply of oxygen to the engine, the sensor comprises a body member, the body member being i) an opening for entering engine exhaust gas; ii) housed in the body member; A sensing element that is exposed to the gas entering the body member through an opening and produces an electrical signal in response to the oxygen content of the gas, iii) receives the electrical signal and derives from the body member to control the signal Electrical conductor means for transmitting to the means, and iv) forming a sealing relationship between the conductor means and the body member. And in an oxygen sensor having means for preventing gases other than the engine exhaust from coming into contact with the sensing element, the sealing means is a cure of perfluoroolefin and at least one other perfluorocomonomer. Oxygen sensor, characterized in that it comprises an elastic copolymer.

2. The oxygen sensor of claim 1 wherein the sealing means comprises a cured elastomeric copolymer of perfluoroolefin, at least one other perfluorocomonomer and a fluorinated cure site monomer.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of one embodiment of the oxygen sensor of the present invention.

[Explanation of symbols]

 1 Oxygen Sensor 2, 6, 11 Housing Components 3 Wiring 4, 7, 9, and 10 Interconnected Housing 5 Sensing Element 8 Fluoroelastomer Seal

Claims (1)

[Claims] 1. An oxygen sensor for use at temperatures above 200.degree. C., the sensor providing an electrical signal in response to the oxygen content sensed by the sensor in engine exhaust gas. In response to the means for controlling the supply of oxygen to the engine,
The sensor comprises a body member, and the body member is
i) an opening for admitting engine exhaust gas, ii) a sensing element housed within the body member, exposed to the gas entering the body member through the opening, and generating an electrical signal in response to the oxygen content of the gas, iii. ) An electrical conductor means for receiving said electrical signal and for delivering said signal to said control means by being derived from said body member, and iv) forming a sealing relationship between said conductor means and said body member, said engine In an oxygen sensor having means for preventing gases other than exhaust gases from coming into contact with the sensing element, the sealing means comprises a cured elastomeric copolymer of perfluoroolefin and at least one other perfluorocomonomer. Oxygen sensor characterized by becoming.