Measuring and testing – Gas analysis
Reexamination Certificate
1999-05-06
2001-11-06
Larkin, Daniel S. (Department: 2856)
Measuring and testing
Gas analysis
C073S023310, C073S031050
Reexamination Certificate
active
06311543
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a gas sensor, and more particularly, to a connection device for providing a heat-resistant joint between a ceramic element and lead strips.
2. Discussion of the Related Art
Oxygen sensor elements are known in the art to be made from ceramic elements. Commonly, ceramic elements are used in vehicles to determine the oxygen concentration of exhaust gases. Because the ceramic element is attached to an exhaust pipe, it will be exposed to high temperatures.
FIG. 10
shows a configuration of the type disclosed in Japanese Laid-Open Patent Publication No. 10-253579 and Published European Patent Application No. EP 836094 (the disclosures of which are hereby incorporated by reference) having improved heat stability in an oxygen sensor element with a ceramic element.
As shown in
FIG. 10
, a ceramic element
30
to be attached to an exhaust pipe (not shown) is electrically connected to lead strips
38
by fitting a metallic ring
31
thereto with an insulation sheet
39
being disposed between the metallic ring
31
and the lead strips
38
. Here, the metallic ring
31
is provided to have an appropriate interference amount and an appropriate minimum wall thickness.
Size reduction of the sensor is accompanied by reduction in the distance between an attachment portion of the sensor to an exhaust pipe and a connection portion between the ceramic element
30
and lead strip
38
. Consequently, the connection portion is exposed to even higher temperatures.
The ceramic element
30
has been found to be strong with respect to compressive stresses, but weak with respect to tensile stresses. When the electrodes of lead strip
38
and the ceramic element
30
are joined through interference fitting, compressive stresses act on the joint portion of the ceramic element
30
, which poses no problem. However, when the sensor is used at high temperatures, the joint portion undergoes thermal fatigue, thereby causing differences in thermal expansion among the elements of the sensor. The differences in thermal expansion result in the formation of cracks x, as shown in FIG.
10
. In the worst case, a malfunction of the ceramic element
30
will result. When the interference amount is decreased in order to avoid the crack problem, a retaining force for the electrodes of the lead strips
38
decreases, thereby failing to reliably join the electrodes and the ceramic element
30
.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to a connection device for a ceramic element that substantially obviates one or more of the problems encountered in the related art devices.
An object of the present invention is to provide a connection device for a ceramic element for strongly and reliably joining lead strips to a ceramic element in a configuration that prevents the formation of cracks in the ceramic element even in high temperature applications.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the connection device for a ceramic gas sensor element comprises a sensor assembly including a ceramic element having a thickness t, an electrical connection portion formed on a side of the ceramic element, and at least one electrical lead in contact with the electrical connection portion. The sensor assembly defines an outer dimension at a position corresponding to the electrical connection portion. A ring member for holding the at least one electrical lead in contact with the electrical connection portion is disposed around the sensor assembly with the ring member having an inner dimension at a position corresponding to the electrical connection portion that is smaller than the outer dimension of the sensor assembly. The ring member has an axial length L in contact with the sensor assembly, wherein the thickness t and the axial length L satisfy the relationship 0.23≦L/t≦13.
In another aspect, the connection device for a ceramic gas sensor element comprises an assembled body including a ceramic element having an electrical connection portion and lead strips in contact with the electrical connection portion and extending outward; and a ring member having an inner dimension smaller than an outer dimension of the assembled body, the ring member being interference-fitted onto the assembled body to thereby mechanically press the lead strips against the electrical connection portion of the ceramic element, wherein a thickness t of the ceramic element and an axial length L of a portion of the ring member in contact with the assembled body satisfy the relationship 0.23≦L/t≦13.
In a further aspect, the connection device for a ceramic gas sensor element comprises a ceramic element having a thickness t; an electrical connection portion formed on a side of the ceramic element; an electrical lead in contact with the electrical connection portion; an insulating layer disposed on the electrical lead; a ring member disposed around the ceramic element, the electrical connection portion, the electrical lead, and the insulating layer, the ring member for holding the electrical lead in contact with the electrical connection portion, wherein the ring member has an inner dimension that is smaller than an outer dimension defined by the ceramic element, the electrical connection portion, the electrical lead, and the insulating layer, and wherein the ring member has an axial length L in contact with the insulating layer such that the thickness t and the axial length L satisfy the relationship 0.23≦L/t≦13.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
REFERENCES:
patent: 4596132 (1986-06-01), Takami et al.
patent: 4983271 (1991-01-01), Kato
patent: 5329806 (1994-07-01), McClanahan et al.
patent: 196 38 208 (1998-04-01), None
patent: 0 624 790 (1994-11-01), None
patent: 0 836 094 A2 (1998-04-01), None
patent: 10-253579 (1998-09-01), None
patent: 10-253568 (1998-09-01), None
patent: WO 92/08127 (1992-05-01), None
Ito Masaya
Nishio Hisaharu
Yabuta Katsuhisa
Yoshikawa Takaya
Larkin Daniel S.
Morgan & Lewis & Bockius, LLP
NGK Spark Plug Co. Ltd.
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