Measuring and testing – Gas analysis – Gas of combustion
Reexamination Certificate
2000-12-15
2003-12-09
Williams, Hezron (Department: 2856)
Measuring and testing
Gas analysis
Gas of combustion
C073S031050, C073S023310, C422S094000, C204S424000
Reexamination Certificate
active
06658916
ABSTRACT:
TECHNICAL FIELD
The present disclosure relates generally to exhaust gas sensors capable of detecting and measuring exhaust gas compositions, and more particularly, relates to an improved compact design for exhaust gas sensors.
BACKGROUND
Automotive vehicles with an internal combustion engine have an exhaust system that includes a pathway for exhaust gas to move away from the engine. The temperature of the exhaust gases ranges from ambient temperature, when the engine has not been run recently, to higher than 1000° C. Frequently used in these exhaust systems is an Exhaust Gas Oxygen (EGO) sensor assembly, which allows for a determination of a rich or lean air/fuel ratio.
The sensing element of an EGO sensor consists of a dense oxygen-conducting zirconia (ZrO2) ceramic, most commonly cylindrically shaped having an opening at one end and having a rounded closure at the other end, with porous platinum electrodes, one on the outside and the other on the inside surfaces of the cylinder. The outside electrode is covered with a porous layer of spinel or magnesia alumina oxide, typically applied either by thermal spray deposit or a co-fired slurry dip coating. The materials are commercially available from many sources. This sensing element is mounted within a housing structure that seals the inside of the cylinder from the outside of the cylinder. When the EGO sensor is mounted onto the exhaust manifold of an engine, the outer electrode is exposed to the exhaust stream whereas the inner electrode is exposed to the ambient air as a reference oxygen atmosphere. When the air/fuel ratio is lean, the EGO sensor voltage output has a small value (e.g. 50 mV) because the oxygen partial pressure in the exhaust gas is not significantly different from the oxygen pressure in the air. When the air/fuel is rich, the EGO voltage output is large (e.g., 700-900 mV) because the thermodynamic equilibrium oxygen partial pressure of the exhaust gas is many orders of magnitude smaller than that of the air reference. Consequently, when the air/fuel ratio varies from the optimal stoichiometric ratio (e.g., 14.7:1), the EGO sensor output changes abruptly between a large and a small value. This sensor output signal is conveyed by means of an associated set of electrical output leads. This signal is then used by the engine control system to adjust the air/fuel ratio being supplied to the combustion chambers of the engine to a desired air/fuel ratio, generally very close to the stoichiometric air/fuel ratio.
Most current EGO sensors also include a heater that is inserted in the air reference. The heater assists the zirconia sensor, a heated exhaust gas oxygen (HEGO) sensor, in making more precise measurements over a wide range of exhaust gas temperatures, especially when the exhaust gas temperature is low. The addition of the heater also helps to decrease the light-off time of the sensor, that is the time that it takes for the sensor to reach the minimum temperature for proper operation.
EGO sensors are typically in direct contact with extremely hot exhaust gases and exhaust gas piping, and in some designs, with supplemental heat generated by a heater rod positioned within the lower region of the sensor itself. Consequently, these sensors are designed to protect heat sensitive components of the sensor from the extreme conditions of the operating environment. Typically, the sensor components having the lowest heat resistance are located in the upper region of the sensor. Such components include the grommet or cable seal, which generally comprises an elastomeric material such as Viton® rubber, and the cable insulation, which often comprises Teflon® (i.e., a fluorocarbon polymer) or similar material. The design parameters, e.g., the size and geometry, of typical EGO sensors are similarly limited by the various temperature constraints. For example, the sensor often has a sufficient height to remove the heat sensitive components in the upper region from the hot exhaust gas.
FIG. 1
shows a conventional heated exhaust sensor
10
having three wires extending therefrom, wherein two of the wires are for heating a sensing element
36
and the third wire is an engine management system (EMS) input generating its own low voltage signal. It will be understood that a single wire exhaust sensor is grounded to the exhaust manifold. Exhaust sensor
10
comprises a three-piece housing structure comprising an upper tubular shell
19
, a middle shell
26
and a lower tubular shell
31
. The metal housing has a longitudinal bore
36
with a sensing element
30
disposed therein. An electrically insulating ceramic material
24
is concentrically disposed around longitudinal bore
36
to support the sensing element
30
. Sensing element
30
is an exhaust sensing element of a known type with any conventional geometry, such as a generally flat elongated rectangular shape.
Lower tubular shell
31
has disposed therein a first section
30
a
of sensing element
30
. At section
30
a
thereof, sensing element
30
includes an exhaust constituent-responsive structure fabricated into sensing element
30
in a known manner, preferably along with a heater rod
29
of a known type. The lower tubular shell
31
includes perforations
33
formed therein through which exhaust gas enters and contacts the sensing element
30
. Exhaust gas temperatures contacting lower tubular shell may reach levels of about 1000° C. The middle shell
26
includes wrench flats
34
and a threaded portion
35
for threading into a manifold boss of an exhaust system (e.g., pipe of manifold). Upper tubular shell
19
extends from middle shell
26
to cable seal
13
. Upper tubular shell
19
houses a second section
30
b
of sensing element
30
, connector plug
32
, electrical wires
12
, and cable seal
13
. Upper tubular shell
19
is concentrically disposed around cable seal
13
, typically an elastomeric component, and is in direct contact therewith, securing it in place. Electrical wires
12
pass through cable seal
13
into connector plug
32
to form an electrical connection with sensing element
30
through electrical terminals
16
.
An outer shield
14
is concentrically disposed around upper tubular shell
19
to protect exhaust gas sensor
10
from the high temperature exhaust gas environment. Typically, outer shield
14
is concentrically disposed around upper tubular shell
19
from about the upper one-half to about the upper one-third of upper tubular shell
19
. An insulating material
15
, such as a breathable Teflon® (i.e., a fluorocarbon polymer) material, is disposed between outer shield
14
and upper tubular shell
19
at nearly all points. Outer shield
14
and upper tubular shell
19
are in direct physical contact at the lower end
37
of outer shield
14
.
In the typical manner of use, lower tubular shell
31
of the exhaust gas sensor
10
, is contacted with very hot exhaust gases generated by an engine. Contact with exhaust gases allows sensing element
30
to measure the component gases. During this process, substantial heat is undesirably conducted from lower tubular shell
31
to middle shell
26
, and further to upper tubular shell
19
. As upper tubular shell
19
is in direct contact with cable seal
16
, substantial heat is also conducted from upper tubular shell
19
to cable seal
16
and to electrical wires
12
disposed therein. Such conduction of extreme heat from lower tubular shell
31
to cable seal
16
and electrical wires
12
is highly undesirable due to the low heat resistance of cable seal
16
and wires
12
relative to other components of exhaust gas sensor
10
. As cable seal
16
and wires
12
are typically the first components of exhaust gas sensor
10
to deteriorate under high temperature operation, the reduction of heat conduction to them is advantageous. The reduction of heat conduction to the wires is typically gained by increasing the distance the wires are from the lower tubular shell
31
by increasing the length of an EGO sensor. An EGO sensor with a reduced size, however, would be advantageous for use in
Donelon Matthew J.
McCauley Kathryn
Cichosz Vincent A.
Delphi Technologies Inc.
Wiggins David J.
Williams Hezron
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