U.S. patent application number 09/276334 was filed with the patent office on 2001-12-06 for exhaust constituent sensor and method of packaging the same.
Invention is credited to HORTON, JOHN A., NELSON, CHARLES SCOTT, VARGO, JAMES P..
Application Number | 20010047938 09/276334 |
Document ID | / |
Family ID | 23056228 |
Filed Date | 2001-12-06 |
United States Patent
Application |
20010047938 |
Kind Code |
A1 |
NELSON, CHARLES SCOTT ; et
al. |
December 6, 2001 |
EXHAUST CONSTITUENT SENSOR AND METHOD OF PACKAGING THE SAME
Abstract
In an exemplary embodiment, the present invention provides an
exhaust constituent sensor comprising a planar sensing element
securely held in place within a tubular shield by disposing a high
temperature mat support between the tubular inner shield and the
planar sensing element. The high temperature mat support comprises
suitable mat material, e.g., ceramic fibers or metal mesh, and
preferably, comprises silica fibers, alumina fibers, alumina fibers
with vermiculite, or any other suitable mat material providing the
desired support, strength, and thermal and electrical insulating
properties described herein. It is within the scope of the
invention that the high temperature mat support may be in the form
of a fibrous material or a more rigid preform structure, wherein in
both instances, the high temperature mat support is adapted to be
disposed concentrically around the planar sensing element for
secure packaging thereof.
Inventors: |
NELSON, CHARLES SCOTT;
(CLIO, MI) ; VARGO, JAMES P.; (SWARTZ CREEK,
MI) ; HORTON, JOHN A.; (CLIO, MI) |
Correspondence
Address: |
VINCENT A CICHOSE
GENERAL MOTHRS CORPORATION
LEGAL STAFF
P O BOX 33114
DETROIT
MI
48232
|
Family ID: |
23056228 |
Appl. No.: |
09/276334 |
Filed: |
March 25, 1999 |
Current U.S.
Class: |
204/426 ;
204/428 |
Current CPC
Class: |
G01N 27/4071
20130101 |
Class at
Publication: |
204/426 ;
204/428 |
International
Class: |
G01N 027/407 |
Claims
What is claimed is:
1. An exhaust constituent sensor, comprising: an elongated planar
sensing element having a first end for connecting with at least one
electrical terminal, a second and opposite end for contacting
exhaust gas, and a central portion extending therebetween; a
tubular shield within which at least a portion of said planar
sensing element extends; a high temperature mat support disposed
between said tubular shield and said planar sensing element and
about said central portion of said elongated planar sensing
element; and a shell for mounting said tubular shield to a conduit
through which said exhaust gas flows.
2. The exhaust constituent sensor as set forth in claim 1 wherein
said high temperature mat support is concentrically disposed around
at least said central portion of said planar sensing element.
3. The exhaust constituent sensor as set forth in claim 1 wherein
said high temperature mat support extends between and contacts both
said planar sensing element and an inner surface of said tubular
shield.
4. The exhaust constituent sensor as set forth in claim 1 wherein
said high temperature mat support comprises: a ceramic fibrous
mat.
5. The exhaust constituent sensor as set forth in claim 4 wherein
said ceramic fibrous mat comprises: alumina fibers, silica fibers,
or a mixture thereof.
6. The exhaust constituent sensor as set forth in claim 5 wherein
said ceramic fibrous mat includes vermiculite.
7. The exhaust constituent sensor as set forth in claim 1 wherein
said high temperature mat support is in the form of a rigid
preform, said preform structure having an outer surface for
contacting and seating against an inner surface of said tubular
shield, and wherein said preform structure includes a central
opening through which said planar sensing element passes.
8. The exhaust constituent sensor as set forth in claim 7 wherein
an inner thermal insulating support member is disposed between said
preform structure and said planar sensing element, said inner
support member being formed of steatite, alumina, or a ceramic
material.
9. The exhaust constituent sensor as set forth in claim 8 wherein
said inner thermal support member comprises: a pair of
semi-circular ceramic support members, each member having a planar
inner surface and an arcuate outer surface, said planar inner
surface contacting a planar surface of said planar sensing element
and said arcuate outer surface for contacting said preform
structure.
10. The exhaust constituent sensor as set forth in claim 1 further
including: an inner thermal insulating material disposed between
said high temperature mat support and said planar sensing element,
wherein said inner thermal insulating material contacts at least a
portion of said planar sensing element.
11. The exhaust constituent sensor as set forth in claim 10 wherein
said inner thermal insulating material comprises a pair of a
semicircular support members disposed on first and second planar
surfaces of said planar sensing element.
12. The exhaust constituent sensor as set forth in claim 10 wherein
said inner thermal insulating material is formed of steatite,
alumina, or a ceramic material.
13. The exhaust sensor as set forth in claim 1 wherein said high
temperature mat support is strengthened by adding a binder or by
further compressing said high temperature mat support.
14. The exhaust constituent sensor as set forth in claim 1 wherein
said high temperature mat support comprises a flexible fibrous
blanket material.
15. A method for producing an exhaust constituent sensor,
comprising: providing an elongated planar sensing element having a
first end for connection with at least one electrical terminal, an
opposite second end for contacting exhaust gas, and a central
portion extending therebetween; disposing a high temperature mat
support about at least said central portion of said planar sensing
element, said high temperature mat support securely holding said
planar sensing element within said sensor; and disposing said high
temperature mat support and said planar sensing element within a
tubular shield within which at least said central portion of said
planar sensing element extends.
16. The method as set forth in claim 15 further including: wrapping
said high temperature mat support around at least said central
portion of said planar sensing element, wherein said high
temperature mat support comprises a fibrous which contacts at least
said central portion of said planar sensing element.
17. The method as set forth in claim 15 wherein said high
temperature mat support is in the form of a rigid preform
structure, wherein said preform structure includes an opening
through which said planar sensing element passes, said preform
structure having an outer surface for contacting and seating
against an inner surface of said tubular shield when said preform
structure is disposed within said tubular shield.
18. The method as set forth in claim 17 further including:
disposing first and second semi-circular thermal insulating members
between said preform structure and said planar sensing element,
said first and second semi-circular thermal insulating members each
including a planar inner surface for seating against said planar
sensing element and an outer arcuate surface for seating against an
inner arcuate surface of said preform structure.
19. The method as set forth in claim 16 further including:
disposing an inner thermal insulating material between said planar
sensing element and said high temperature mat support.
20. The method as set forth in claim 19 wherein said inner thermal
insulating material comprises first and second semi-circular
thermal insulating members, said first semi-circular thermal
insulating member contacting a first planar surface of said planar
sensing element and said second semi-circular thermal insulating
member contacting an opposing second planar surface of said planar
sensing element.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to planar sensors.
More particularly, the present invention relates to a method of
supporting and holding a planar sensing element of an exhaust
constituent sensor in a robust simple package.
BACKGROUND OF THE INVENTION
[0002] Exhaust constituent sensors have been used for many years in
automotive vehicles to sense the presence of constituents in
exhaust gasses (e.g., oxygen, hydrocarbons, nitrous oxides) and to
sense, for example, when an exhaust gas content switches from rich
to lean or lean to rich. One known type of exhaust constituent
sensor includes a flat plate exhaust sensor formed of various
layers of ceramic and electrolyte materials laminated and sintered
together with electrical connections placed between the layers in a
known manner.
[0003] Because automotive exhaust constituent sensors are mounted
to members of the vehicle exhaust flow system, the sensors must be
durable, able to withstand vibration and jarring such as would
occur during installation and normal vehicle operation and able to
withstand shock from the occasional stone or other small road
debris that may happen to be thrown at the sensor, for example, by
the vehicle's tires.
[0004] Typically, great care is required when packaging and holding
the flat plate sensing element within the outer housing (body) of
the exhaust constituent sensor. The flat plate sensing element can
be both difficult and expensive to package within the body of the
exhaust constituent sensor since it generally has one dimension
that is very thin and is usually made of a brittle material. For
example, one method of protecting the planar sensing element is to
encase and hold the planar sensing element in proper position
within a glass tube which is itself bonded to a metal shield of the
exhaust constituent sensor. This process is time consuming and is
therefore expensive in terms of manufacturing costs. Consequently,
great care and time consuming effort must be taken to prevent the
planar sensing element from being damaged by exhaust, heat, impact,
vibration, the environment, etc.
SUMMARY OF THE INVENTION
[0005] The present invention comprises exhaust constituent sensors
and a method of manufacturing same, and more particularly relates
to a method of supporting and holding a planar sensing element in a
robust simple package. One embodiment comprises an exhaust
constituent sensor, comprising a planar sensing element securely
held in place within a tubular shield by disposing a high
temperature mat support between the tubular shield and the planar
sensing element. It being understood that the high temperature mat
support of the present invention comprises mat materials which are
designed to withstand the heat generated in a spark ignition
environment.
[0006] The high temperature mat support positions and secures the
planar sensing element within the tubular shield and also
advantageously provides an exhaust gas barrier in the sensor so
that exhaust gas is blocked from a central portion and an upper
portion of the planar sensing element. The high temperature mat
support further provides an instrument to dissipate heat from the
inside of the sensor. The dissipation of heat from the planar
sensing element reduces the possibility that excessive heat
contacts the electrical connection of the planar sensing element
during operation.
[0007] Advantageously, this invention provides an exhaust
constituent sensor having improved holding of the planar sensing
element within a sensor housing which provides improved resistance
to failures caused by exposures to exhaust, heat, impact,
vibration, and other environmental hazards which adversely effect
the performance of the exhaust constituent sensor. Furthermore, the
sensor of the present invention greatly simplifies the overall
process of packaging a planar sensing element within an exhaust
constituent sensor and as a result reduces the associated costs of
the process.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The present invention will now be described by way of
example with reference to the following Figures, which are meant to
be exemplary, not limiting, and in which:
[0009] FIG. 1 is a cross-sectional side view of one embodiment of
an exhaust constituent sensor embodying the present invention;
and
[0010] FIG. 2 is a cross-sectional side view of a second embodiment
of the exhaust constituent sensor of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0011] Referring now to FIG. 1, the example exhaust constituent
sensor 10 shown includes a housing structure generally formed of an
upper shield 20, a lower shield 30, an inner shield 40 and a shell
50. A terminal connector 60 and a portion of a planar sensing
element 80 are disposed within upper shield 20. Planar sensing
element 80 is an exhaust constituent sensing element of a known
type with any conventional geometry, such as a generally flat
elongated rectangular shape. At a first end 82 thereof, planar
sensing element 80 includes an exhaust constituent-responsive
structure fabricated into planar sensing element 80 in a known
manner, preferably along with a heater (not shown) of a known type.
At an opposite end 84 of planar sensing element 80, lower ends 104
and 106 of terminals 100 and 102, respectively, contact external
pads (not shown) on end 84 to provide electrical connection between
terminals 100 and 102 and planar sensing element 80. Ends 104 and
106 of terminals 100 and 102, respectively, are maintained against
end 84 of planar sensing element 80 by a compressive force applied
by disposing end 84 of planar sensing element 80 between lower ends
104 and 106. Preferably, terminals 100 and 102 comprise spring
terminals, the use of which is know in the art and the compressive
force generated by disposing end 84 between spring terminals 100
and 102 securely maintains end 84 in electrical contact
therewith.
[0012] The inner shield 40 has a partially closed first end 42 and
an open second end 44 opposite first end 42. A centrally located
annular opening 46 is provided at first end 42 and is sized to
receive end 84 of planar sensing element 80. Disposed within inner
shield 40 are a central portion 83 of planar sensing element 80, a
pair of inner thermal insulating members 120, and a high
temperature mat support 90. In accordance with the present
invention, the pair of inner thermal insulating members 120 are
provided for securely positioning and protecting planar sensing
element 80 within exhaust constituent sensor 10, wherein first end
82 and second end 84 of planar sensing element 80 extend beyond the
pair of inner thermal insulating members 120 when the pair of inner
thermal insulating members 120 are disposed onto a first surface 86
and an opposing second surface 88 of the planar sensing element 80.
In an exemplary embodiment, the pair of inner thermal insulating
members 120 are semi-circular in shape and provide structural
rigidity and protection to exhaust constituent sensor 10, and more
specifically to planar sensing element 80 which is disposed
therebetween. Example material for the pair of inner thermal
insulating members 120 is steatite, rigid alumina, ceramic, or
other suitable high temperature material providing the desired
support, strength and thermal and electrical insulating properties
described hereinbelow. As used herein, the term "high temperature
material" refers to materials which are designed for use in a spark
ignition engine environment, where temperatures range from about
300.degree. C. to about 1000.degree. C.
[0013] Disposed between the pair of inner thermal insulating
members 120 and inner shield 40 is high temperature mat support 90
for further insulation and packaging of planar sensing element 80,
wherein high temperature mat support 90 comprises a mat material
designed for use in a spark ignition engine environment. More
specifically, high temperature mat support 90 is formed of a mat
material designed to withstand continuous exposure to temperatures
on the order of about 300.degree. C. to about 1000.degree. C.
(temperature range observed in spark ignition engine environment).
High temperature mat support 90 extends from first end 42 to second
end 44 of inner shield 40 so that high temperature mat support 90
is in contact with and abuts against an inner surface 41 of inner
shield 40. High temperature mat support 90 provides the desired
structural support to exhaust constituent sensor 10 by
concentrically surrounding planar sensing element 80 and the pair
of inner thermal insulating members 120 to thereby securely hold
planar sensing element 80 in place. Furthermore, high temperature
mat support 90 also acts as a thermal and gas barrier to inhibit
access of excessive heat and exhaust gasses, respectively.
[0014] High temperature mat support 90 comprises mat materials
designed to withstand the high temperatures observed in a spark
ignition engine environment and in an exemplary embodiment, high
temperature mat support 90 comprises a ceramic fibrous material or
a metal mesh material. When a ceramic fibrous material is used, the
orientation and size of the ceramic fibers are not critical to the
practice of the present invention; however, the fibers are
preferably orientated in a random fashion instead of a more ordered
orientation of the fibers. In one preferred embodiment, high
temperature mat support 90 comprises a mat material formed of
ceramic fibers, including but not limited to silica fibers, alumina
fibers, or mixtures thereof. Furthermore, vermiculite may be
incorporated into the ceramic fibrous material as a component. As
is known, vermiculite is a form of the mineral mica, and materials
having vermiculite incorporated therein will slightly expand in
volume when the materials are subjected to increases in
temperature. More preferably, high temperature mat support 90
comprises a fibrous material formed of random alumina fibers and
vermiculite. By incorporating vermiculite into the alumina fibrous
material, high temperature mat support 90 will slightly expand when
subjected to the high temperature environment of the exhaust
system, resulting in high temperature mat support 90 expanding
against inner surface 41 to provide a more effective support and
gas barrier.
[0015] Exhaust gas is blocked from central portion 83 of planar
sensing element 80 by the pair of inner thermal insulating members
120 and high temperature mat support 90 which prevent exhaust
gasses from migrating within sensor 10 toward the electrical
connection. Heat is dissipated from the pair of inner thermal
insulating members 120 and planar sensing element 80 when the
exhaust constituent sensor 10 is subjected to high temperatures due
to the heat being drawn away therefrom by high temperature
protective mat support 90 which conducts the heat therefrom to
prevent excessive heat from contacting the electrical connection of
planar sensing element 80.
[0016] In one form, high temperature mat support 90 comprises a
flexible mat material, similar to a flexible fibrous blanket
material which is easily disposed around the pair of inner thermal
insulating members 120 and planar sensing element 80 by
concentrically wrapping high temperature mat support 90 around at
least a portion of the same so that the overall diameter of the
inner components (planar sensing element 80, pair of inner thermal
insulating members 120 and high temperature mat support 90) closely
approximates the inner diameter of inner shield 40. Accordingly,
when planar sensing element 80, the pair of inner thermal
insulating members 120 and high temperature mat support 90 are
disposed within inner shield 40, the components of sensor 10 are
effectively and easily packaged within inner shield 40 resulting in
planar sensing element 80 being securely held in place.
[0017] In the example shown in FIG. 1, a lower end 22 of the upper
shield 20 extends to an upper portion 43 of high temperature mat
support 90 and engages closed first end 42 of the inner shield 40
by a secure friction fit or other securing means known in the art,
e.g., compressive forces exerted during assembly. In an exemplary
embodiment, a first subassembly 150 comprises upper shield 20, a
cable seal 140, and terminal connector 60, whereby upper shield 20
holds cable seal 140 and terminal connector 60 securely in place
between upper shield 20. First subassembly 150 is securely coupled
to a second subassembly 160 by inserting end 84 of planar sensing
element 80 into an opening 61 located between terminals 100 and 102
until a first end 62 of terminal connector 60 seats against first
closed end 42 of inner shield 40. Second subassembly 160 comprises
inner shield 40 which is concentrically disposed around high
temperature mat support 90, the pair of inner thermal insulating
members 120 and planar sensing element 80. Alternatively, sensor 10
may be assembled without the use of subassemblies, whereby all
individual components are properly positioned and secured during
the assembly process.
[0018] Shell 50 includes a body portion 52 and a threaded portion
54 at a second end 55. Body portion 52 is shaped to accommodate a
wrench or other tool for tightening threaded portion 54 into a
mount welded to an exhaust pipe or other component of an exhaust
flow system enabling a sensor chamber 31 located within lower
shield 30 to be located within a flow of exhaust gasses to be
measured. A first end 53 of shell 50 is disposed proximate lower
end 22 of the upper shield 20 when shell 50 is securely disposed
around inner shield 40 by means known in the art; and preferably,
shell 50 is coupled to inner shield 40 by being crimped thereto
during the assembly process, as described in more detail
hereinafter. Accordingly, shell 50 holds inner shield 40 in
compressive force engagement. Formed at second end 55 of shell 50
is a shoulder 56 for contacting open second end 44 of inner shield
40, whereby inner shield 40 and an end 121 of pair of inner thermal
insulating members 120 rests against shoulder 56 when shell 50 is
secured to inner shield 40 during assembly.
[0019] Formed at second end 55 of shell 50 is an annular recess 57
for receiving a flared open end 32 of the lower shield 30. Flared
open end 32 of lower shield 30 receives end 82 of planar sensing
element 80, whereby end 82 is disposed within sensing chamber 31 to
permit contact with and sensing of exhaust gas. Lower shield 30 has
a closed end 34 opposite flared open end 32 of inner shield 30,
wherein flared open end 32 is secured to second end 55 of shell 50
by disposing flared open end 32 into annular recess 57 and securing
flared open end 32 therein by welding it in place or holding it in
place by a secure friction fit.
[0020] Lower shield 30 defines sensing chamber 31 and disposed
within lower shield 30 is an internal shield 35 which has an open
end 36 for receiving planar sensing element 80 and a closed end 37
adjacent and parallel to closed end 34 of lower shield 30. Lower
shield 30 and internal shield 35 form a plurality of vents 38 for
allowing passage of exhaust gas in and out of sensing chamber 31 so
that the gasses may be sensed by receptive first end 82 of planar
sensing element 80. A plurality of openings 47 permits exhaust gas
to flow into exhaust constituent sensor 10, and more specifically,
exhaust gas flows through openings 47 and vents 38 into sensing
chamber 31.
[0021] The use of terminal connector 60 is known in the art and a
suitable terminal connector 60 is also known in the art as an edge
card connector or a clam shell connector. Terminal connector 60
typically includes a plurality of electrical terminals with each
having a corresponding electrical wire connected thereto. For the
purpose of illustration only, sensors 10 and 10' of FIGS. 1 and 2
are shown having a pair of electrical terminals 100 and 102, which
are adapted to be connected to electrical wires 130 and 132 in a
known manner. Electrical wires 130 and 132 pass through cable seal
140 which generally comprises a thermoplastic or a thermoset
material suitable for use in a high temperature environment, e.g.,
spark ignition engine. Cable seal 140 is maintained in place by
upper shield 20 which has an upper end 23 forming a seat around a
shoulder 142 of cable seal 140, wherein upper shield 20 is crimped
in place around cable seal 140 to further secure the same. A
central portion 24 of upper shield 20 is disposed around terminal
connector 60 and a lower end 22 of upper shield 20 forms a
cylindrical opening tightly fit around closed first end 42 of inner
shield 40 when sensor 10 is assembled. Lower end 22 preferably is
held in place by either a tight friction fit or a weld. Preferably,
lower end 22 of upper shield 20 has an increased diameter than
upper end 23 of upper shield 20 so that it may receive closed first
end 42 of inner shield 40, whereby upper shield 20 is preferably
secured in a leak-proof manner to closed first end 42 of inner
shield 40. Lower end 22 may be secured to closed first end 42 by
crimping lower end 22 thereto, as is known in the art, and a
crimped portion 28 of lower end 22 will result from such crimping
action, as is shown in FIG. 1. It being understood, that when upper
shield 20 is crimped to inner shield 40, crimped portion 28 will
annularly extend around an outer surface 45 of upper shield 20 and
for purposes of illustration only the cross-sectional views of
FIGS. 1 and 2 show an uncrimped portion opposite crimped portion
28.
[0022] For the structures shown in FIGS. 1 and 2, example material
for the shields 20, 30, 40, and 35 and for the shell 50 is high
chrome or high nickel stainless steel, all steels chosen for high
temperature endurance, high-strength and corrosion resistance.
Terminal connector 60 may be formed of a thermoplastic or thermoset
material (e.g., plastic) or ceramic durable in the high temperature
environments to which exhaust constituent sensor 10 is exposed.
[0023] It is within the scope of this invention that high
temperature mat support 90 may be made into a more rigid preform
with the pair of inner thermal insulating members 120 either being
already molded into high temperature mat support 90 or as separate
articles. The use of a single or two piece, more rigid preform
advantageously eliminates the process of concentrically disposing
high temperature mat support 90 around at least a portion of the
pair of inner thermal insulating members 120. A preform of the mat
material provides a more rigid article and in the case of high
temperature mat support 90, the preform provides a structural
member which is easily disposed within inner shield 40 to securely
hold planar sensing element 80 in place. The manufacture of the
preform formed of the mat material may be according to known
methods in the relevant arts.
[0024] Now turning to FIG. 2, a second exemplary embodiment of the
present invention is generally designated as 10'. High temperature
mat support 90 extends from closed first end 42 to open second end
44 and extends between planar sensing element 80 and inner surface
41 of inner shield 40. Thus, the use of the pair of inner thermal
insulating members 120 is eliminated in this embodiment by
strengthening high temperature mat support 90 so that it provides
the desired support, strength, and thermal and electrical
insulating properties required for sensor 10' to effectively
operate in the exhaust system. High temperature mat support 90 may
be strengthened by known methods, including but not limited to
increasing the binder content of high temperature mat support 90,
adding additional binders, or by further compressing high
temperature mat support 90.
[0025] As shown in FIG. 2, the preform of high temperature mat
support 90 includes a central opening for receiving planar sensing
element 80 when high temperature mat support 90 is concentrically
disposed around at least a portion of planar sensing element 80. It
is also within the scope of the invention that high temperature mat
support 90 may be used in sensor 10' of FIG. 2 in the non preform
state, wherein high temperature mat support 90 is concentrically
wrapped around at least a portion of planar sensing element 80
prior to disposing both within inner shield 40.
[0026] Sensors 10 and 10' may be constructed according to methods
known in the art, including but not limited to using crimping means
to securely couple the outer components thereof. When crimping
means are used, upper shield 20 is securely coupled to first end 42
of inner shield 40 so that end 84 of planar sensing element 80 is
received within upper shield 20 and more particularly between
terminals 100 and 102 to provide electrical connection between
terminals 100 and 102 and planar sensing element 80. Lower shield
30 is securely coupled to shell 50 by engaging flared open end 32
of lower shield 30 with annular recess 57. Shell 50 is itself
securely coupled to inner shield 40 by crimping shell 50 thereto,
whereby first end 82 of planar sensing element 80 is disposed
within sensing chamber 31 to permit contact with and sensing of
exhaust gas.
[0027] Thus in accordance with the present invention, planar
sensing element 80 is securely held in place within the exhaust
constituent sensor of the present invention by disposing a
protective high temperature mat support 90 in either a preform or
fibrous blanket type state around at least a portion of planar
sensing element 80. High temperature protective mat support 90 is
intended to concentrically surround at least a portion of planar
sensing element 80 to protect planar sensing element 80 and hold
the same in place within sensor 10 or 10'. The packaging methods of
the present invention offer several advantages over conventional
methods of packaging planar sensing element 80 within an exhaust
constituent sensor. First, sensors 10 and 10' of the present
invention are of a much more simpler design which reduces the
manufacturing process by eliminating time consuming steps. As a
result, the present invention offers a more cost effective
packaging process, while maintaining the desired and necessary
structural, thermal, and electrical characteristics described
hereinbefore. Furthermore, because the pair of inner thermal
insulating members 120 and high temperature mat support 90 act as a
thermal and gas barrier, the overall length of sensors 10 and 10'
may be reduced.
[0028] Typically, the length of conventional exhaust constituent
sensors fall within a limited range because the length had to be
such that excessive heat radiating outward from the exhaust system
was prevented from contacting the electrical connection at one end
of the sensor. Because the sensor of the present invention offers
improved thermal dissipation of excessive heat, the length of the
sensor may be reduced. This of importance for a number of reasons,
including that it represents a reduction in costs and it permits
the sensor to be mounted in locations which were otherwise not
accessible because of the length of the sensor. Alternatively, the
length of sensor 10 or 10' may be maintained at a conventional
length; however, because of the improvements of the present
invention noted herein, sensor 10 or 10' may be used in an
environment having higher temperatures. This provides greater
versatility in positioning and mounting sensor 10 or 10' within the
exhaust system.
[0029] While preferred embodiments have been shown and described,
various modifications and substitutions may be made thereto without
departing from the spirit and scope of the invention. Accordingly,
it is to be understood that the present invention has been
described by way of illustrations and not limitation.
* * * * *