Oxygen sensor with heater

Claim 2

An oxygen sensor comprising: a tubular solid electrolyte body having an elongate bore which is closed at one end of said tubular solid electrolyte body and open at the other end, and further having reference and measuring electrodes on inner and outer surfaces thereof, respectively; a housing supporting said tubular solid electrolyte body such that said outer surface thereof is exposed at said one end to exhaust gas, said housing maintaining said elongate bore in gas-tight condition with respect to said exhaust gas; and a bar-shaped heater inserted in said elongate bore in said tubular solid electrolyte body, and comprising a heating resistor having a positive temperature coefficient, a ceramic body carrying said heating resistor so as to embed the heating resistor, and a pair of lead wires for connecting said heating resistor to an electric power source, said ceramic body having on its outer peripheral surface a pair of terminal pads connected to said heating resistor, an end portion of each of said lead wires being brazed to corresponding one of said terminal pads with a mass of brazing material containing silver, an exposed surface of said mass of brazing material being coated with a metallic layer made of metal which is different from silver or its alloy.

Claim 3

An oxygen sensor as recited in claim 1, wherein said metallic layer is a metal plating.

Claim 4

An oxygen sensor as recited in claim 2, wherein said metal plating is an electroless plating.

Claim 5

An oxygen sensor as recited in claim 3, wherein said electroless plating comprises nickel.

Claim 6

An oxygen sensor as recited in claim 2, wherein said metal plating comprises nickel.

Claim 7

An oxygen sensor as recited in claim 1, wherein said positive temperature coefficient is not less than 0.3%/°C.

Claim 8

An oxygen sensor as recited in claim 1, wherein said metallic layer has a thickness of not less than one micron.

Claim 9

An oxygen sensor comprising: a tubular solid electrolyte body having an elongate bore which is closed at one end of said tubular solid electrolyte body and open at the other end, and further having reference and measuring electrodes on inner and outer surfaces thereof, respectively; a housing supporting said tubular solid electrolyte body such that said outer surface thereof is exposed at said one end to exhaust gas, said housing maintaining said elongate bore in gas-tight condition with respect to said exhaust gas; and a bar-shaped heater inserted in said elongate bore in said tubular solid electrolyte body, and comprising a heating resistor having a positive temperature coefficient, a ceramic body carrying said heating resistor so as to embed the heating resistor, and a pair of lead wires for connecting said heating resistor to an electric power source, said ceramic body having on its outer peripheral surface a pair of terminal pads connected to said heating resistor, an end portion of each of said lead wires being brazed to corresponding one of said terminal pads with a mass of brazing material containing silver, an exposed surface of said mass of brazing material being coated with a metallic layer made of metal which is different from silver or its alloy, said metallic layer being coated with a heat-resistant layer.

Claim 10

An oxygen sensor comprising: a tubular solid electrolyte body having an elongate bore which is closed at one end of said tubular solid electrolyte body and open at the other end, and further having reference and measuring electrodes on inner and outer surfaces thereof, respectively; a housing supporting said tubular solid electrolyte body such that said outer surface thereof is exposed at said one end to exhaust gas, said housing maintaining said elongate bore in gas-tight condition with respect to said exhaust gas; and a bar-shaped heater inserted in said elongate bore in said tubular solid electrolyte body, and comprising a heating resistor having a positive temperature coefficient, a ceramic body carrying said heating resistor so as to embed the heating resistor, and a pair of lead wires for connecting said heating resistor to an electric power source, said ceramic body having on its outer peripheral surface a pair of terminal pads connected to said heating resistor, an end portion of each of said lead wires being brazed to corresponding one of said terminal pads with a mass of brazing material containing silver, an exposed surface of said mass of brazing material being coated with a metallic layer made of metal which is different from silver or its alloy, said metallic layer being coated with a heat-resistant layer.

Claim 11

An oxygen sensor as recited in claim 8, wherein said heat-resistant layer is made of an inorganic material.

Claim 12

An oxygen sensor as recited in claim 8, wherein said metallic layer is a metal plating.

Claim 13

An oxygen sensor as recited in claim 10, wherein said metal plating is an electroless plating.

Claim 14

An oxygen sensor as recited in claim 11, wherein said electroless plating comprises nickel.

Claim 15

An oxygen sensor as recited in claim 10, wherein said metal plating comprises nickel.

Claim 16

An oxygen sensor as recited in claim 8, wherein said positive temperature coefficient is not less than 0.3%/°C.

Claim 17

An oxygen sensor as recited in claim 8, wherein said metallic layer has a thickness of not less than one micron.