Gas sensor element

1. A gas sensor element comprising:

a main body including a solid electrolyte body having oxygen ion conductivity, a measurement gas-side electrode provided on one surface of the solid electrolyte body and a reference gas-side electrode provided on the other surface of the solid electrolyte body;

a trap layer formed of a porous material and covering an outer peripheral surface of the main body, the trap layer allowing a measurement gas to permeate therethrough while trapping poisoning substances contained in the measurement gas; and

a protective layer covering an outer peripheral surface of the trap layer and having a water-impermeable property and a porosity of 5% or less, wherein

in the protective layer, there is formed at least one measurement gas introduction port for introducing the measurement gas to the measurement gas-side electrode via the trap layer.

2. The gas sensor element as set forth in claim 1 , wherein:

the solid electrolyte body is plate-shaped,

the main body further includes a gas introduction passage, through which the measurement gas is introduced to the measurement gas-side electrode, and a porous diffusion-resistant layer arranged in the gas introduction passage,

the gas introduction passage has a main body-side introduction port that opens on the outer peripheral surface of the main body, and

the at least one measurement gas introduction port of the protective layer is formed to penetrate the protective layer and located to have the trap layer interposed between the at least one measurement gas introduction port and the main body-side introduction port.

3. The gas sensor element as set forth in claim 2 , wherein a total cross-sectional area of the at least one measurement gas introduction port of the protective layer is greater than a total cross-sectional area of the main body-side introduction port.

4. The gas sensor element as set forth in claim 1 , wherein the at least one measurement gas introduction port is formed within the range of a width of 0.5 mm-2.0 mm.

5. The gas sensor element as set forth in claim 1 , wherein the trap layer is two-layer structured to include a first trap layer and a second trap layer,

the second trap layer is formed of ceramic particles to cover the outer peripheral surface of the main body and the first trap layer is formed of ceramic particles to cover an outer peripheral surface of the second trap layer,

a particle diameter of the ceramic particles forming the first trap layer is greater than a particle diameter of the ceramic particles forming the second trap layer, and

the second trap layer is formed so that its thickness is partially increased at four corners of the outer peripheral surface of the main body.

6. A gas sensor element comprising:

a main body including a cup-shaped solid electrolyte body having oxygen ion conductivity, a measurement gas-side electrode provided on an outer peripheral surface of the solid electrolyte body and a reference gas-side electrode provided on an inner peripheral surface of the solid electrolyte body;

a trap layer formed of a porous material and covering an outer peripheral surface of the main body, the trap layer allowing a measurement gas to permeate therethrough while trapping poisoning substances contained in the measurement gas; and

a protective layer covering an outer peripheral surface of the trap layer and having a water-impermeable property and a porosity of 5% or less, wherein

in the protective layer, there is provided at least one measurement gas introduction port for introducing the measurement gas to the measurement gas-side electrode via the trap layer, and

the at least one measurement gas introduction port is formed to penetrate the protective layer and located to have the trap layer interposed between the at least one measurement gas introduction port and the measurement gas-side electrode.