JP3615574B2 - Oxygen sensor with fluoroelastomer seal - Google Patents

Description

[0001]
The present invention relates to an oxygen sensor having sealing means that is particularly resistant to automotive engine exhaust and engine compartment vapor at elevated temperatures.
[0002]
The oxygen sensor is exposed to high temperatures in the presence of combustion gases. Such sensors are typically located in an environment that is exposed to contact with fuels and oils that are externally liquid or vapor, and from these fuels and oils internal sensing elements and associated circuitry. It must be isolated to prevent performance degradation. For example, exposure of the sensing element to airborne contaminants can affect sensor performance. Thus, a sealing means that is resistant to high temperature environments is necessary for efficient operation and extended service life.
[0003]
Recent automotive engine compartment design trends have created the need to place oxygen sensors in locations exposed to temperatures as high as 300 ° C. Such conditions cause a rapid deterioration of the elastic seal used to isolate and protect the internal mechanism of the oxygen sensor. For this reason, there is a need in the art for oxygen sensors that incorporate sealing means based on elastomeric materials having greater high temperature resistance.
[0004]
The present invention is an oxygen sensor for use at temperatures above 200 ° C., wherein the sensor is responsive to the oxygen content sensed by the sensor in engine exhaust gas and responsive to the electrical signal. The oxygen sensor is supplied to means for controlling the supply of oxygen to the engine, and the sensor is composed of a main body member, the main body member being i) an opening for introducing engine exhaust gas, ii) being accommodated in the main body member, and the opening A sensing element that is exposed to the gas entering the body member through and generates an electrical signal in response to the oxygen content of the gas, iii) receiving the electrical signal and deriving from the body member to transmit the signal to the control means Electric conductor means for transmitting to the iv, and iv) forming a sealing relationship between the conductor means and the body member In the oxygen sensor having means for preventing gases other than the engine exhaust gas from coming into contact with the sensing element, the sealing means is a cured elasticity of perfluoroolefin and at least one other perfluorocomonomer. The present invention relates to an oxygen sensor comprising a copolymer.
[0005]
Although the present invention is not limited to a specific design of oxygen sensor, for the purpose of illustrating the application of an elastic copolymer, the specific design of the sensor shown in the drawings is described below.
[0006]
As shown in the drawings, the oxygen sensor comprises a body member, which is composed of a plurality of interconnected housings 4, 7, 9, and 10. The sensing element 5, for example platinum-coated zirconia, is located in the body member, primarily in the housing 4 of the body member. The housing 4 has openings as shown in the drawing, allowing engine exhaust gases to enter the sensors and, in particular, to contact them thereby exposing the sensing elements to these gases. The sensing element 5 generates 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. The other surrounding housings 7, 4 and 10 are attached directly or indirectly to the housing 9, which has a threaded section that is used to install the device in the engine exhaust system. The electrical conductor means, shown in the drawing as including wiring 3, extends into the body member and is in electrical communication with the sensing element to receive electrical signals from the sensing means. The wiring 3 also extends outside the body member and sends this signal to oxygen control means (not shown) that are common in the field. The electrical conductor means also passes through a series of electrically insulating housing components 2, 6, and 11, for example, ceramic material housing components, and these housing components are within the body member for protection. Is surrounded by Wire 3 exits 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 an insulating housing component 11. Alternatively, the seal 8 can be interposed directly between the electrical conductor means wiring and the metal housing components. The seal is generally cylindrical, has holes corresponding to the number, size and position of circuit wiring and seals the space between the wiring and the body member directly or indirectly as the case may be.
[0007]
The main function of the seal 8 is to isolate the interior of the sensor from atmospheric gases, particularly oxygen, so that the sensing element is exposed only to the exhaust gas. In the process of providing this isolation protection, the seal also prevents harmful contaminants such as particles or oil from the engine from entering the sensor. Another function of the seal is to place the wiring securely within the body member and to prevent the wiring from being worn against the insulating housing. The seal also serves to prevent exhaust gases from escaping into the atmosphere through the oxygen sensor.
[0008]
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 concentration difference. The voltage so generated is low when the engine is running at “lean” (high air / fuel ratio), but the engine is “rich” (low air / fuel ratio). High when rotating at. A signal is transmitted through line 3 to the engine oxygen control means, which appropriately changes the supply of the air / fuel mixture to the engine in response to the transmitted signal. Since the device is located in hot exhaust gas, the temperature in the sealed area is typically above 200 ° C and can be as high as 315 ° C.
[0009]
A feature of the present invention is the advantageous configuration of the seal, usually in the form of a bush or grommet, between the electrical wiring 3 and the body member (insulating housing). This seal is comprised of a cured high temperature resistant elastic copolymer (fluoroelastomer), described in more detail below. The cured fluorinated elastomeric copolymer is highly resistant to high temperature decomposing action in the presence of engine exhaust 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 are suitable for use in environments where they are exposed to temperatures in excess of 200 ° C.
[0010]
Suitable materials that can be used to fabricate fluoroelastomer sealing elements, such as seal 8, are selected from cured elastic copolymers composed of copolymerized units of at least two major perfluoromonomers. In addition, the copolymer may optionally further contain copolymerized units of at least one fluorinated cure site monomer. The first major comonomer is a perfluoroolefin, such as tetrafluoroethylene. Other major perfluoro comonomers'_{'is (O} m _{R f,} wherein _{R f (O n R f)} and _{R f} "perfluoro (alkyl vinyl) ether _CF 2 = CFO _{R f)'} is 2 Different linear or branched perfluoroalkylene groups having 6 carbon atoms, m and n are independently 0-10, and R _f is a perfluoroalkyl group having 1-6 carbon atoms. A fluoroalkyl group; A preferred class of perfluoro (vinyl ether) encompasses compounds of the formula _{CF 2 = CFO (CF 2 CFXO} ) n R f, where X is F or CF _3, n is 0-5, and _{R f} Is a perfluoroalkyl group having 1 to 6 carbon atoms. The most preferred perfluoro (vinyl ether) is where n is 0 or 1 and R _f contains 1 to 3 carbon atoms. Examples of such perfluorinated ethers include perfluoro (methyl vinyl) ether and perfluoro (propyl vinyl) ether. Other monomers have the formula CF ₂ = CF [O (CF ₂ ) _m CF ₂ CFZO] _n R _f (I)
Wherein R _f is a perfluoroalkyl group having 1 to 6 carbon atoms, m is 0 or 1, n is 0 to 5 and Z is F or CF ₃ .
And the formula CF ₂ ═CFO [(CF ₂ CFCF ₃ O) _n (CF ₂ CF ₂
CF ₂ O) _m (CF ₂ ) _p CF ₃ (II)
Wherein m and n are 0-10 and p is 0-3.
These compounds are included.
[0011]
A small amount of copolymerized fluorinated cure site monomer units can also be present in the polymer, if desired, in addition to the perfluorocomonomer. Generally, these cure site monomers are present in an amount up to about 3 mole percent. They can be free of hydrogen atoms or can contain hydrogen hydrogen atoms. Suitable cure site monomers include brominated fluoroolefins such as bromotrifluoroethylene and 4-bromo-3,3,4,4-tetrafluorobutene; brominated fluoroethers such as CF ₂ ═CF—OR _f CF ₂ Br, (wherein _{R f} is a perfluoroalkylene group containing 1-9 carbon atoms), and including vinylidene fluoride. Preferred cure site monomers are perfluorophenyl (C ₆ F ₅ ) or fluorinated vinyl ethers containing a cyano substituent, for example the formula CF ₂ ═CF—O (CF ₂ ) _n —C ₆ F ₅ (III)
(In the formula, n is 1 to 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)
(In the formula, n is 1 to 2.)
_{CF 2 = CF-O (CF} 2) n -CN (VI)
(In the formula, n is 2 to 12, preferably 2 to 4.)
_{CF 2 = CF-O-CF} 2 - [CFCF 3 -O-CF 2] n -CFCF 3 -CN (VII)
(In the formula, n is 0 to 4, 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 1-4)
The thing represented by is included.
[0012]
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 halogen end group sources such as hydroiodic acid, hydrobromic acid, and metals belonging to Group IA, Group IB, Group IIA, Group IIB, such as Li , Na, K, Rb, Cs, Be, Mg, Ca, Sr, Ba, Cu, Ag, Zn, Cd, and transition metals such as Fe, Co, Ni, Ru, Rh, Pd, Pt, or second Includes metals belonging to Group III and Group IVB, such as iodides and bromides of Al, Ga, Sn, and Pb. Suitable chain transfer agents are methylene iodide, isopropanol, monoiodoperfluoroalkanes such as monoiodoperfluoromethane and methaneiodoperfluoropropane; perfluoroalkyl bromide, 4-bromo-perfluorobutene-1, 1 , 4-diiodoperfluorohexane, 1,4-diiodoperfluorohexane, and 1,4-diiodoperfluorooctane.
[0013]
Particularly preferred for the fabrication of the sealing element is a copolymer of tetrafluoroethylene, perfluoro (methyl vinyl) ether, and perfluoro (8-cyano-5-methyl-3,6-dioxa-1-octene). .
[0014]
The fluoroelastomer composition used in the fabrication of the sealing element used in the present invention is made 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, such as a gammet, press cured, and then usually post cured. The compositions of the present invention can be cured by commonly used crosslinking systems in combination with the monomers of the particular copolymerized cure site present, as is known to those skilled in the art. For example, when a cure moiety containing a pentafluorophenyl group is present, it is based on an aliphatic diamine or preferably on the dipotassium salt of bisphenol AF KOC ₆ H ₄ -C (CF ₃ ) ₂ -C ₆ H ₄ OK Based curing agent systems can be used. When a cure site containing a cyano substituent is present, a curing agent system based on an organotin compound is usually selected. Suitable organotin compounds include allyl-, propargyl-, triphenyl- and allenyl tin curing agents. Tetraphenyltin is a preferred curing agent for use in combination with a cyano substituted cure moiety.
[0015]
Polymers containing monomers with cure moieties, as well as polymers without copolymerized cure moiety 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 bonded to peroxy oxygen is particularly beneficial in many cases. 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. The organic peroxide is generally present in an amount of about 1-3 parts peroxide per 100 parts fluoropolymer. A wide variety of peroxide coagents can also be used, among which trimethallyl isocyanurate, triallyl isocyanurate, and trimethylolpropane trimethacrylate are preferred. The peroxide synergist is generally present in an amount of about 1-3 parts per 100 parts of the fluoropolymer.
[0016]
In addition, a dual curing system can be used with perfluoroelastomers containing nitrile groups. Double curing systems are tin catalysts that can crosslink perfluoroelastomers through nitrile groups, such as triphenyltin hydroxide; peroxides that can crosslink perfluoroelastomers, such as 2,5-bis (t-butyl peroxide) -2,5-dimethylhexane; and diene and triene synergists 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. In general, about 1 to 10 phr of curing agent can be used, and 2 to 5 phr is satisfactory for most purposes. Other additives 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 use conditions Can be incorporated into the composition of the present invention. In particular, the low temperature performance can be enhanced by the addition of perfluoropolyether, while at the same time better high temperature performance can be maintained. Perfluoropolyethers that can be used in the compositions of the present invention are those in which 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.
[0017]
In order to enhance the high temperature performance of the fluoroelastomer composition, it is particularly desirable to use large particle size carbon black. It has been discovered that fluoroelastomers containing about 20-70 phr (parts by weight per 100 parts rubber), preferably 25-45 parts by weight, provide a useful combination of thermal stability and processability. Preferred carbon blacks have an average particle size of at least 100 nm to 500 nm as determined by ASTM D3849.
[0018]
【Example】
VF ₂ -HFP copolymer 100phr
(Fluorine content 66%)
Magnesium oxide 3
Carbon black 30
Calcium carbonate 6
Curing agent I 1.8
Curing agent II 4
The bushing was manufactured under the curing conditions of pressure 177 ° C. × 10 minutes and oven heating 232 ° C. × 24 hours. When this bushing was subjected to an aging test in an oven exposed to circulating air at 275 ° C. for 70 hours, a weight loss of 4% was observed (known example).
[0019]
on the other hand,
55.8TFE-42PMVE-2.2CNVE 100phr
Copolymer (fluorine content 73%)
Crown ether 0.3
Carbon black 12
Tetraphenyltin 3
Using this composition, a bush was produced under curing conditions of pressurization 204 ° C. × 15 minutes and oven heating 305 ° C. × 26 hours (in a nitrogen atmosphere). When this bush was subjected to the same aging test as described above, the weight loss was only 1% (Example of the present invention).
[0020]
[註]
VF _2: vinylidene fluoride HFP: hexafluoropropylene TFE: tetrafluoroethylene PMVE: perfluoro methyl vinyl ether _{CNVE: CF 2 = CF-O} -CF 2 (CF 3) CF-O- (CF 2) 2 -CN
(Monomer where x is 1 and n is 2 in Formula VIII)
Crown ether: 18-crown-6-crown ether,
(C ₂ H ₄ ) ₆ O ₆
Curing agent I: “Viton Curative No. 20” (mixture of 33% by weight of benzyltriphenylphosphonium chloride and 67% by weight of VF ₂ -HFP copolymer) manufactured by Deyupon
Curing agent II: “Viton Curative No. 30” (mixture of 50% by weight of bisphenol AF and 50% by weight of VF ₂ -HFP copolymer) manufactured by Deyupon
According to the present invention, as is apparent from the test results of the above examples, an oxygen sensor that can be used at temperatures exceeding 200 ° C. is provided. The oxygen sensor of the present invention, in which the conductor means is isolated from the body member with a seal made of the aforementioned cured fluoroelastomer composition, is highly resistant at operating temperatures in excess of 200 ° C. and exceeds the prior art oxygen sensors. Provide increased service life. Such an oxygen sensor of the present invention is suitable for use in a position exposed to a temperature as high as about 300 ° C. of an automobile engine.
[0021]
The main features and aspects of the present invention are as follows.
[0022]
1. An oxygen sensor for use at temperatures in excess of 200 ° C., wherein the sensor is responsive to an oxygen content sensed by the sensor in engine exhaust gas and responsive to the electrical signal. The oxygen sensor is supplied to a means for controlling the supply of the engine, and the sensor comprises a main body member, the main body member being i) an opening for introducing engine exhaust gas, ii) being accommodated in the main body member, and passing through the opening. A sensing element that is exposed to the gas entering the body member and generates an electrical signal in response to the oxygen content of the gas; iii) receives the electrical signal and is derived from the body member to transmit the signal to the control means And iv) forming a sealing relationship between the conductor means and the body member, The oxygen sensor having means for preventing gas other than engine exhaust gas from coming into contact with the sensing element, wherein the sealing means is a cured elastic copolymer of perfluoroolefin and at least one other perfluorocomonomer An oxygen sensor comprising:
[0023]
2. The oxygen sensor of claim 1 wherein the sealing means comprises a cured elastic copolymer of perfluoroolefin, at least one other perfluorocomonomer, and a monomer at the fluorinated cure site.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view of one embodiment of an oxygen sensor of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Oxygen sensor 2, 6, 11 Housing component 3 Wiring 4, 7, 9, and 10 Interconnecting housing 5 Sensing element 8 Fluoroelastomer seal

Claims (1)

An oxygen sensor for use at temperatures in excess of 200 ° C., wherein the sensor is responsive to the oxygen content sensed by the sensor in engine exhaust gas in response to the electrical signal and the engine in response to the electrical signal. The sensor comprises a main body member, the main body member being i) an opening for introducing engine exhaust gas, ii) being accommodated in the main body member, and passing through the opening. A sensing element that is exposed to the gas entering and generates an electrical signal in response to the oxygen content of the gas, iii) an electrical that receives the electrical signal and is derived from the body member to transmit the signal to the control means A conductor means; and iv) forming a sealing relationship between the conductor means and the body member, In the oxygen sensor gas other than emission exhaust gases has a means for preventing the coming into contact with the sensing element, said sealing means tetrafluoroethylene, perfluoro (methyl vinyl) ether and perfluoro (8-cyano - An oxygen sensor comprising a cured elastic copolymer of 5-methyl-3,6-dioxa-1-octene) .

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