Gas sensor

Details Gas sensor Gas sensor

1998-12-23

2002-07-16

Williams, Hezron (Department: 2856)

Measuring and testing

Gas analysis

C204S424000

Reexamination Certificate

active

06418777

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas sensor for detecting a component of a gas to be measured (hereinafter referred to as a measurement gas), such as an oxygen sensor, an HC sensor, an NO
x
sensor, or a like sensor.
2. Description of the Related Art
Conventionally, there has been known a gas sensor composed of an outer cylinder, a metallic shell disposed inside the outer cylinder, and a sensor element disposed inside the metallic shell for detecting a component of a measurement gas. In a gas sensor having such a structure, a gap between the outer surface of the sensor element and the inner surface of the metallic shell or that between the outer surface of the sensor element and the inner surface of an insulator disposed between the metallic shell and the sensor element is generally filled with a sealing material layer, as of glass.
For example, an oxygen sensor for automobile use is often mounted in an exhaust manifold or an exhaust pipe located near a suspension system and tires. In this case, a stone flipped from a tire may hit the sensor so that a mechanical shock acts on the sensor, or the sensor may be subjected to a strong thermal shock caused by splashing of water during exposure to high temperature. Further, the sensor element of the sensor has a coefficient of thermal expansion smaller than that of the sealing material layer. Therefore, in a glass sealing step, the sensor element receives a radial compressive force due to a thermal history (heating/cooling), so that stress concentration occurs in a boundary region between a portion of the sensor element covered with the sealing material layer and an uncovered portion. If a mechanical shock caused by a flipped stone or the like or a thermal shock caused by splashing of water acts on the sensor in such a state, a resultant stress acts at a boundary region (hereinafter referred to as “sealing boundary portion”) between the portion of the sensor element covered with the sealing material layer and the uncovered portion, so that the sensor element is easily broken.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a gas sensor in which stress caused by application of a mechanical or thermal shock on the sensor does not concentrate at the sealing boundary portion and which therefore has excellent durability.
To achieve the above object, a gas sensor of the present invention comprises an outer cylinder, a metallic shell, a sensor element, a sealing material layer, and a cushion layer. The metallic shell is joined to the outer cylinder. The sensor element is disposed inside the metallic shell and is adapted to detect a component of a measurement gas. The sealing material layer is mainly made of glass and is disposed between the outer surface of the sensor element and the inner surface of the metallic shell or between the outer surface of the sensor element and the inner surface of an insulator disposed between the metallic shell and the sensor element. The cushion layer is made of a porous inorganic substance and is disposed on at least one side of the sealing material layer with respect to the axial direction of the sensor element.
The above-described structure of the gas sensor of the present invention prevents local application of a strong bending stress onto the sealing boundary portion, which would otherwise occur when mechanical or thermal shock acts on the sensor element.


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Translation of portions of Japanese Utility Model No. 6-23964.

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