Gas sensor

Details Gas sensor Gas sensor

1999-08-19

2001-10-02

Tung, T. (Department: 1743)

Chemistry: electrical and wave energy

Apparatus

Electrolytic

C204S424000, C204S428000

Reexamination Certificate

active

06296748

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a gas sensor, such as an oxygen sensor, HC sensor, NOx sensor, etc., which measures a gas introduced into the sensor and detects a component of the gas.
2. Description of the Related Art
Conventional gas sensors have a metal casing, inside which resides a detection element formed in a bar-like or cylindrical shape and having, at a tip, a detecting section to detect a component gas. For a gas sensor using air as a reference gas, e.g. an oxygen sensor, it is necessary to provide a portion for introducing air into the casing and accommodating a detection element or providing a filter support cylinder coupled to a rear end of the casing. This type of air introducing element can be formed, for example, by opening a gas passage hole in a rear end side wall of the casing or filter support cylinder and covering it with a water repellent filter. Meanwhile, an air introducing element may be provided by a lead wire insertion hole formed in a rubber grommet sealing lead wire extension port. This method introduces air into a casing through a gap formed between a coat material covering a lead-wire outer surface and a lead wire insertion hole.
In some conventional structures as described above, a ceramic separator formed with a lead wire insertion hole is provided in a casing (or filter support cylinder) in order to prevent a short circuit between lead wires extending from a detection element and heater. This ceramic separator is formed in a cylindrical shape matched to the casing, and is usually arranged at a rear end inside of the casing (or filter support cylinder) in order to be positioned on a side to extend a lead wire therefrom. On the other hand, an air introducing element as above is formed at the casing (or filter support cylinder) rear end, and a gap is provided between an outer peripheral surface and an inner peripheral surface of the casing (or filter support cylinder), in many cases, to provide a passage for the introduced air. However, recently there has been a movement toward reducing the size of the sensor, and, thus, there is an effort to reduce the diameter of the casing (or filter support cylinder) as small as possible. Thus, due to this effort to reduce sensor size, it is becoming difficult to provide a sufficient gap between the ceramic separator and the casing (or filter support cylinder). Although it is theoretically possible to reduce the diameter of the ceramic separator, there is a limitation on the ability to reduce the diameter of the ceramic separator size reduction on the assumption of securing and still maintain the basic function of the ceramic separator and prevent against shorting between the lead wires.
It is therefore an object of the invention to provide a gas sensor which can efficiently flow air through the casing while having a sufficient on-axis sectional area for a ceramic separator that allows lead wires to pass through.
SUMMARY OF THE INVENTION
In order to solve the problems described above, the invention provides a first structure of a gas sensor that includes a detection element formed in an axial form, a cylindrical casing for accommodating the detection element, and a ceramic separator in a columnar form placed in an axial direction of the casing and having a plurality of lead wire insertion holes formed penetrating therethrough in the axial direction to pass through each lead wire from the detection element, wherein the ceramic separator depicts inscribed and circumscribed circles about a geometric center of gravity of an external shape line on an arbitrary section plane (hereinafter referred to as a contour forming on-axis section plane) perpendicular to the axis and on which an external shape of the ceramic separator can be represented in a continuous single contour, wherein, if depicting a virtual reference circle positioned intermediate between the inscribed circle and the circumscribed circle, the contour forming on-axis section plane having an external shape line that in one par is positioned on an inner side of the reference circle and in other part on an outer side of the reference circle.
The structure described above essentially provides a ceramic separator having an outer shape line on a contour forming on-axis section plane that at least partly departs from a circular shape.
FIG. 8
shows an example of a case where, for example, the main body portion has an outer shape line SH rendered in a squared form on the contour forming on-axis section plane. With respect to an outer shape SH, inscribed and circumscribed circles IC and OC are depicted about a geometric center of gravity, and a reference circle SC is depicted between these circles. It can be understood that the outer shape line SH is at some points within the reference circle SC and at other points outside the reference circle SC. This would be true for a shape that departs from a circular shape (polygonal, elliptical, etc.) and is not limited to only a squared shape like outer shapeline SH.
That is, in a conventional gas sensor structure, the ceramic separator, without exception, is circular in shape on a contour forming an on-axis section plane. As described earlier, there has been difficulty in expanding the gap defined with a casing or filter support cylinder inner surface. According to the invention, however, the external shape line of the ceramic separator on a contour forming an on-axis sectional plane is constructed as to depart from the traditional circular shape. This makes it possible to locally expand the gap between the outer peripheral surface of the ceramic separator and the casing or filter support cylinder inner surface. Due to this, passage of external air into the casing occurs efficiently while providing the ceramic separator with a sufficient on-axis sectional area for inserting through lead wires.
Incidentally, where the ceramic separator has, for example, a main body portion in a columnar shape and a flanged separator side support portion formed projected on an outer peripheral surface of the main body, the external shape line on the contour forming on-axis section plane may be at least one of an external shape line of the main body portion and an external shape line of the separator side support portion.
The invention also provides another gas sensor structure that includes a detection element formed in an axial form, a cylindrical casing for accommodating the detection element, a filter support cylinder provided generally coaxial to the casing over an rear end portion of the casing, a ceramic separator in an columnar form placed in an axial direction of the filter support cylinder and having a plurality of lead wire insertion holes formed penetrating therethrough in the axial direction to pass through each lead wire from the detection element, a flanged separator-side support portion formed in an outer peripheral surface of the ceramic separator, a filter arranged on a rear side of the separator-side support portion and on an rear end side of the filter support cylinder, which blocks a liquid from passing through but allows a gas to pass therethrough, and a gas communication portion formed in the separator-side support portion in the axial direction.
Incidentally, in the description of the invention above, the axial side toward the tip of the detection element is the “front side (tip side)”, while the side opposite to this is a “rear side (rear end side)”.
In this manner, a flanged separator side support portion is formed on an outer peripheral surface of the ceramic separator. A filter is arranged on a rear side of this separator side support portion and on a rear end side of the filter support cylinder, which blocks a liquid from passing through, but allows a gas to pass. A gas communication portion is axially formed in the separator side support portion. This allows the air introduced through the filter to be smoothly and speedily introduced to an inside of the casing through the gas communication portion axially formed in the separator side support portion. Moreover,

Affiliated with

Also associated with

Rating

Gas sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Gas sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gas sensor will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2570287