U.S. patent application number 10/411240 was filed with the patent office on 2003-10-30 for method of adjusting output of gas sensor.
This patent application is currently assigned to DENSO CORPORATION. Invention is credited to Moriguchi, Keigo, Nakae, Makoto.
Application Number | 20030201193 10/411240 |
Document ID | / |
Family ID | 26546397 |
Filed Date | 2003-10-30 |
United States Patent
Application |
20030201193 |
Kind Code |
A1 |
Moriguchi, Keigo ; et
al. |
October 30, 2003 |
Method of adjusting output of gas sensor
Abstract
A method of adjusting an output of a gas sensor element is
provided. The gas sensor element includes a lamination of a solid
electrolyte body, a target gas-exposed electrode, a reference
gas-exposed electrode, and a diffused resistance layer in which a
target gas to be measured diffuses. The target gas-exposed
electrode is disposed on a first surface of the solid electrolyte
body exposed to the target gas. The reference gas-exposed electrode
is disposed on a second surface of the solid electrolyte body
exposed to a reference gas. The diffused resistance layer is
disposed on the first surface of the solid electrolyte body. The
target gas-exposed electrode and the reference gas-exposed
electrode produce a sensor output. The adjustment of the sensor
output is achieved by decreasing a diffusion length of the target
gas in the diffused resistance layer as a function of a quantity of
the sensor output to be adjusted by, for example, removing a
portion of the diffused resistance layer.
Inventors: |
Moriguchi, Keigo;
(Takahama-shi, JP) ; Nakae, Makoto; (Toyoake-shi,
JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
1100 N GLEBE ROAD
8TH FLOOR
ARLINGTON
VA
22201-4714
US
|
Assignee: |
DENSO CORPORATION
|
Family ID: |
26546397 |
Appl. No.: |
10/411240 |
Filed: |
April 11, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10411240 |
Apr 11, 2003 |
|
|
|
09663345 |
Sep 15, 2000 |
|
|
|
6569303 |
|
|
|
|
Current U.S.
Class: |
205/775 ;
205/783 |
Current CPC
Class: |
G01N 27/407
20130101 |
Class at
Publication: |
205/775 ;
205/783 |
International
Class: |
G01N 027/26 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 17, 1999 |
JP |
11-264192 |
Aug 1, 2000 |
JP |
2000-233596 |
Claims
What is claimed is:
1. A gas sensor output adjusting method comprising: preparing a gas
sensor element including a lamination of a solid electrolyte body,
a target gas-exposed electrode, a reference gas-exposed electrode,
and a diffused resistance layer in which a target gas to be
measured diffuses, the target gas-exposed electrode being disposed
on a first surface of the solid electrolyte body exposed to the
target gas, the reference gas-exposed electrode being disposed on a
second surface of the solid electrolyte body exposed to a reference
gas, the diffused resistance layer being disposed on the first
surface of the solid electrolyte body, the target gas-exposed
electrode and the reference gas-exposed electrode producing a
sensor output; and decreasing a diffusion length of the target gas
in the diffused resistance layer as a function of a quantity of the
sensor output to be adjusted.
2. A gas sensor output adjusting method as set forth in claim 1,
wherein the decreasing the diffusion length is achieved by removing
a portion of the diffused resistance layer.
3. A gas sensor output adjusting method as set forth in claim 1,
wherein said diffused resistance layer includes a porous layer and
a dense layer and wherein the decreasing the diffusion length is
achieved by removing a portion of the porous layer.
4. A gas sensor output adjusting method as set forth in claim 1,
wherein said diffused resistance layer includes a porous layer and
wherein the decreasing the diffusion length is achieved by removing
a portion of the porous layer.
5. A gas sensor output adjusting method as set forth in claim 1,
wherein said diffused resistance layer includes a porous layer and
a dense layer and wherein the decreasing the diffusion length is
achieved by removing a portion of the dense layer.
6. A gas sensor output adjusting method comprising: preparing a gas
sensor element including a lamination of a solid electrolyte body,
a target gas-exposed electrode, a reference gas-exposed electrode,
and a diffused resistance layer in which a target gas to be
measured diffuses, the target gas-exposed electrode being disposed
on a first surface of the solid electrolyte body exposed to the
target gas, the reference gas-exposed electrode being disposed on a
second surface of the solid electrolyte body exposed to a reference
gas, the diffused resistance layer being disposed on the first
surface of the solid electrolyte body, the target gas-exposed
electrode and the reference gas-exposed electrode producing a
sensor output; and decreasing a gas-diffusing sectional area of the
diffused resistance layer within which the target gas diffuses as a
function of a quantity of the sensor output to be adjusted.
7. A gas sensor output adjusting method as set forth in claim 6,
wherein said diffused resistance layer includes a porous layer and
a dense layer and wherein the decreasing the gas-diffusing
sectional area of the diffused resistance layer is achieved by
partially sealing a surface of the porous layer exposed to the
target gas.
8. A gas sensor output adjusting method as set forth in claim 6,
wherein said diffused resistance layer includes a porous layer and
a dense layer and wherein the decreasing the gas-diffusing
sectional area of the diffused resistance layer is achieved by
forming a plurality of output-adjusting holes in the dense layer
which lead to the porous layer and sealing a given number of the
output-adjusting holes as a function of the quantity of the sensor
output to be adjusted.
9. A gas sensor output adjusting method comprising: preparing a gas
sensor element including a lamination of a solid electrolyte body,
a target gas-exposed electrode, a reference gas-exposed electrode,
and a diffused resistance layer in which a target gas to be
measured diffuses, the target gas-exposed electrode being disposed
on a first surface of the solid electrolyte body exposed to the
target gas, the reference gas-exposed electrode being disposed on a
second surface of the solid electrolyte body exposed to a reference
gas, the diffused resistance layer having an outer surface exposed
to the target gas, an inner surface opposite the outer surface,
disposed on the first surface of the solid electrolyte body, and
side surfaces formed between the outer and inner surfaces, defining
portions of side surfaces of the lamination, the target gas-exposed
electrode and the reference gas-exposed electrode producing a
sensor output; and decreasing a diffusion length of the target gas
in the diffused resistance layer as a function of a quantity of the
sensor output to be adjusted by removing a portion of the diffused
resistance layer obliquely to at least one of the side surfaces of
the lamination.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field of the Invention
[0002] The present invention relates generally to a method of
adjusting an output of a gas sensor element which may be employed
in air-fuel ratio control for an internal combustion engine of
automotive vehicles.
[0003] 2. Background Art
[0004] A typical gas sensor element employed in the air-fuel ratio
control for automotive vehicles includes a solid electrolyte body
made of an oxygen ion conductive material, a gas measuring and a
reference gas-exposed electrode, and a diffused resistance layer.
The diffused resistance layer is disposed on a surface of the
target gas-exposed electrode exposed to a target gas to be
measured. The target gas, thus, reaches the target gas-exposed
electrode through the diffused resistance layer.
[0005] When the voltage is applied to the target gas-exposed
electrode and the reference gas-exposed electrode, the current
flowing through these electrodes is determined as a function of the
number of oxygen molecules passing through the diffused resistance
layer. The current flowing through the electrodes, thus, shows
characteristics that it is saturated at a given value as long as
the concentration of oxygen in a target gas is constant.
[0006] FIG. 16 represents the relation between the voltage applied
to the target gas-exposed electrode and the reference gas-exposed
electrode and the current output picked up from the electrodes for
difference concentrations a to d of oxygen (a>b>c>d). The
drawing shows that application of a suitable voltage, for example,
voltage V to the target gas-exposed electrode and the reference
gas-exposed electrode causes the current to flow through the
electrodes as a function of the concentration of oxygen. For
instance, when the concentration of oxygen is a, the current Ia
flows through the electrodes. This is the principle of measurement
of the concentration of oxygen in the above gas sensor element.
[0007] However, when the above type of gas sensor elements are
mass-produced, they may have a unit-to-unit variation in the above
described characteristics. If there is no unit-to-unit variation,
the application of voltage to the target gas-exposed electrode and
the reference gas-exposed electrode of each gas sensor element
exposed to a target gas whose concentration of oxygen is a will
cause the current Ia to be, as shown in FIG. 16, produced by the
electrodes. If, however, there is the unit-to-unit variation, the
currents produced by the gas sensor elements show the distribution,
as shown in FIG. 17. Some of the gas sensor elements producing the
currents outside the range .DELTA.Ia will produce great measurement
errors that arc objectionable in practical use.
[0008] In order to eliminate the unit-to-unit variation of the gas
sensor elements caused by production errors, Japanese Utility Model
Second Publication No. 7-27391 teaches use of a correction circuit
which corrects the output current of each gas sensor element. This
method, however, results in complexity of the whole circuit
structure of gas sensors and an increase in manufacturing cost.
SUMMARY OF THE INVENTION
[0009] It is therefore a principal object of the present invention
to avoid the disadvantages of the prior art.
[0010] It is another object of the present invention to provide a
simple and low-cost adjusting method of adjusting an output of a
gas sensor.
[0011] According to one aspect of the invention, there is provided
a gas sensor output adjusting method of adjusting a sensor output
of a gas sensor element. The gas sensor element includes a
lamination of a solid electrolyte body, a target gas-exposed
electrode, a reference gas-exposed electrode, and a diffused
resistance layer in which a target gas to be measured diffuses. The
target gas-exposed electrode is disposed on a first surface of the
solid electrolyte body exposed to the target gas. The reference
gas-exposed electrode is disposed on a second surface of the solid
electrolyte body exposed to a reference gas. The diffused
resistance layer is disposed on the first surface of the solid
electrolyte body. The target gas-exposed electrode and the
reference gas-exposed electrode produce the sensor output. The
adjustment of the sensor output is achieved by decreasing a
diffusion length of the target gas in the diffused resistance layer
as a function of a quantity of the sensor output to be
adjusted.
[0012] In the preferred mode of the invention, the decreasing the
diffusion length is achieved by removing a portion of the diffused
resistance layer.
[0013] The diffused resistance layer includes a porous layer and a
dense layer. The decreasing the diffusion length may be achieved by
removing a portion of the porous layer.
[0014] The diffused resistance layer may include only the porous
layer.
[0015] The decreasing the diffusion length may alternatively be
achieved by removing a portion of the dense layer so as to broaden
an area of the porous layer exposed to the target gas.
[0016] According to the second aspect of the invention, there is
provided a gas sensor output adjusting method of adjusting a sensor
output of a gas sensor element. The gas sensor element includes a
lamination of a solid electrolyte body, a target gas-exposed
electrode, a reference gas-exposed electrode, and a diffused
resistance layer in which a target gas to be measured diffuses. The
target gas-exposed electrode is disposed on a first surface of the
solid electrolyte body exposed to the target gas. The reference
gas-exposed electrode is disposed on a second surface of the solid
electrolyte body exposed to a reference gas. The diffused
resistance layer is disposed on the first surface of the solid
electrolyte body. The target gas-exposed electrode and the
reference gas-exposed electrode produce the sensor output. The
adjustment of the sensor output is achieved by decreasing a
gas-diffusing sectional area of the diffused resistance layer
within which the target gas diffuses as a function of a quantity of
the sensor output to be adjusted.
[0017] In the preferred mode of the invention, the diffused
resistance layer includes a porous layer and a dense layer. The
decreasing the gas-diffusing sectional area of the diffused
resistance layer is achieved by partially sealing a surface of the
porous layer exposed to the target gas.
[0018] The decreasing the gas-diffusing sectional area of the
diffused resistance layer may alternatively be achieved by forming
a plurality of output-adjusting holes in the dense layer which lead
to the porous layer and sealing a given number of the
output-adjusting holes as a function of the quantity of the sensor
output to be adjusted.
[0019] According to the third aspect of the invention, there is
provided a gas sensor output adjusting method of adjusting a sensor
output of a gas sensor element. The gas sensor element includes a
lamination of a solid electrolyte body, a target gas-exposed
electrode, a reference gas-exposed electrode, and a diffused
resistance layer in which a target gas to be measured diffuses. The
target gas-exposed electrode is disposed on a first surface of the
solid electrolyte body exposed to the target gas. The reference
gas-exposed electrode is disposed on a second surface of the solid
electrolyte body exposed to a reference gas. The diffused
resistance layer having an outer surface exposed to the target gas,
an inner surface opposite the outer surface, disposed on the first
surface of the solid electrolyte body, and side surfaces formed
between the outer and inner surfaces, defining portions of side
surfaces of the lamination. The target gas-exposed electrode and
the reference gas-exposed electrode produce the sensor output. The
adjustment of the sensor output is achieved by decreasing a
diffusion length of the target gas in the diffused resistance layer
as a function of a quantity of the sensor output to be adjusted by
removing a portion of the diffused resistance layer obliquely to at
least one of the side surfaces of the lamination.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The present invention will be understood more fully from the
detailed description given hereinbelow and from the accompanying
drawings of the preferred embodiments of the invention, which,
however, should not be taken to limit the invention to the specific
embodiments but are for the purpose of explanation and
understanding only.
[0021] In the drawings:
[0022] FIG. 1(a) is a partially plan view which shows a gas sensor
element whose output is adjusted by a method according to the
present invention;
[0023] FIG. 1(b) is a vertical sectional view of FIG. 1(a);
[0024] FIG. 2 is a partially vertical sectional view of a gas
sensor element;
[0025] FIG. 3 is an exploded view which shows a gas sensor
element;
[0026] FIG. 4 is a graph which shows the relation of a removed
thickness of a gas sensor element and a corresponding output
current;
[0027] FIG. 5 is a graph which shows a variation in output current
of mass-produced gas sensor elements;
[0028] FIG. 6 is a perspective view which shows a gas sensor
element whose output is adjusted by a method according to the
second embodiment of the invention;
[0029] FIG. 7 is a vertical sectional view of FIG. 6;
[0030] FIG. 8 is a graph which shows the relation of a removed
thickness of a gas sensor element and a corresponding output
current in the second embodiment;
[0031] FIG. 9 is a vertical sectional view which shows a gas sensor
element whose output is adjusted by a modification of the second
embodiment;
[0032] FIG. 10 is a vertical sectional view which shows a gas
sensor element whose output is adjusted by a method according to
the third embodiment of the invention;
[0033] FIG. 11 is a vertical sectional view which shows a gas
sensor element whose output is adjusted by a method according to
the fourth embodiment of the invention;
[0034] FIG. 12(a) is a partially plan view which shows a gas sensor
element whose output is adjusted by a method according to the fifth
embodiment of the invention;
[0035] FIG. 12(b) is a vertical sectional view of FIG. 12(a);
[0036] FIG. 13(a) is a partially plan view which shows a gas sensor
element whose output is adjusted by a method according to a
modification of the fifth embodiment of the invention;
[0037] FIG. 13(b) is a vertical sectional view of FIG. 13(a);
[0038] FIG. 14(a) is a partially plan view which shows a sensor
element according to the sixth embodiment of the invention;
[0039] FIG. 14(b) is a vertical sectional view of FIG. 14(a);
[0040] FIG. 15(a) is a partially plan view which shows a sensor
element according to the seventh embodiment of the invention;
[0041] FIG. 15(b) is a vertical sectional view of FIG. 15(a);
[0042] FIG. 16 is a graph which shows the relation between the
voltage applied to a target gas-exposed electrode and a reference
gas-exposed electrode of a conventional gas sensor element and the
current output picked up from the electrodes for difference
concentrations a to d of oxygen (a>b>c>c); and
[0043] FIG. 17 is a graph which shows a variation in output current
of mass-produced conventional gas sensor elements.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] Referring now to the drawings, wherein like numbers refer to
like parts in several views, particularly to FIGS. 1(a) and 1(b),
there is shown a gas sensor whose output is controlled by an output
adjusting method according to the present invention.
[0045] The gas sensor may be used with an automotive control system
designed to control the quantity of fuel injected into an internal
combustion engine as a function of the concentration of gas such as
oxygen or nitrogen oxide contained in exhaust gasses measured by
the gas sensor under feedback control to bring the air-fuel ratio
into agreement with a target one. The gas sensor may also be
designed to measure the concentration of CO or HC.
[0046] The gas sensor includes a gas sensor element 1 which, as
shown in FIGS. 1(a) and 1(b), consists of a solid electrolyte body
12, a reference gas-exposed electrode 122, a target gas-exposed
electrode 121, and a diffused resistance layer 11. The target
gas-exposed electrode 121 and the reference gas-exposed electrode
122 are formed on opposed surfaces of the solid electrolyte body
12. The diffused resistance layer 11 is disposed on the surface of
the solid electrolyte body 12 so that it is exposed to the gas to
be measured which will also be referred to as a target gas below.
The diffused resistance layer 11 may alternatively be so disposed
as to cover only the target gas-exposed electrode 121.
[0047] The adjustment of an output of the gas sensor element 1 is
achieved by decreasing the diffusion length of the target gas in
the diffused resistance layer 11, i.e., removing a desired
thickness .DELTA.t from each side surface 101 of the gas sensor
element 1 perpendicular thereto.
[0048] The gas sensor element 1 is, as can be seen from FIG. 1(b),
a flat element formed by a lamination of a heater substrate 14 made
of, for example, a ceramic material, an insulating spacer 13, the
solid electrolyte body 12, and the diffused resistance layer 11.
The heater substrate 14 has disposed thereon heater element 140
producing the heat when energized electrically. The insulating
spacer 13 has formed therein a reference gas chamber 130 exposed to
the atmosphere to introduce thereinto the air as a reference gas.
The solid electrolyte body 13 is made of an oxygen ion conductive
material such as a ceramic material and has, as described above,
the electrodes 121 and 122 formed on the opposed surfaces thereof.
The diffused resistance layer 11 is formed on the solid electrolyte
body 12 so as to cover the whole of the electrode 121 and made of,
for example, a ceramic material.
[0049] The diffused resistance layer 11 is installed on
a-gas-exposed portion of the gas sensor element 1 exposed to the
target gas to be measured in concentration and consists of a
lamination of a dense layer 111 and a porous layer 112. The dense
layer 111 is designed not to permit the target gas to pass through
it, while the porous layer 112 permits the target gas to pass
through it.
[0050] The heater substrate 14 has disposed thereon, as shown in
FIG. 3, the heater element 140, the heater lead 141, and the heater
terminals 145 and 146. The heater substrate 14 has also formed on
the reverse surface thereof outer terminals (not shown) which
electrically connect the heater terminals 145 and 146 to a power
supply (not shown), respectively.
[0051] The solid electrolyte body 12 has disposed thereon leads
123, 124, an inner terminal 126, outer terminals 125 and 128, and a
through hole 127. The lead 123 connects the target gas electrode
121 and the outer terminal 125. The lead 124 connects the reference
gas-exposed electrode 122 and the inner terminal 126. The inner
terminal 126 electrically connects with the outer terminal 128
through the hole 127. The outer terminals 125 and 128 connect with
an external voltage source (not shown). The application of voltage
to the outer terminals 125 and 128 will cause the gas sensor
element 1 to produce an output current as a function of the
concentration of gas.
[0052] The path of the target gas diffusing in the gas sensor
element 1 is shown in FIG. 2.
[0053] The target gas enters the porous layer 112 from the side
surface 101 of the gas sensor element 1, moves, as indicated by an
arrow, in the porous layer 112, and reaches the target gas-exposed
electrode 121. Specifically, the arrow in FIG. 2 indicates the
diffusion path. The distance between the side surface 101 and the
surface of the target gas-exposed electrode 121 corresponds to the
diffusion length.
[0054] The decreasing the diffusion length will cause the output of
the gas sensor element 1 to be increased.
[0055] The adjustment of the output of the gas sensor element 1 is,
as described above, by removing the desired thickness .DELTA.t from
each of the side walls 101 of the gas sensor element 1, i.e., sides
of the heater substrate 14, the spacer 13, the solid electrolyte
body 12, and the diffused resistance layer 11 from a direction
perpendicular to the side walls 101. This removal is achieved by
machining, as shown in FIGS. 1(a) and 1(b), only side portions of
the gas sensor element 1 having disposed therein the diffused
resistance layer 11 using a grinding stone made of diamond powder.
In order to avoid breakage of the gas sensor element 1 during the
grinding or use, a front portion of the gas sensor element 1 in
which the diffused resistance layer 11 is disposed near the
boundary 190 between the front portion and a rear portion of the
gas sensor element 1 which has no diffused resistance layer is
tapered. The removal of the side portions of the gas sensor element
1 may alternatively be accomplished using a laser or chemical
etching techniques.
[0056] If a desired degree to which the output of the gas sensor
element 1 is to be adjusted is not great, only one of the side
surfaces 101 of the gas sensor element 1 may be removed.
[0057] The production method of the gas sensor element 1 will be
described below.
[0058] First, a heater substrate sheet, a spacer preform, a solid
electrolyte body sheet, a porous layer sheet, and a shielding layer
sheet are made using ceramic material and binder.
[0059] On the heater substrate sheet, the heater element 140, the
heater leads 141, the terminals 145 and 146, and the outer
terminals (not shown) which are to be connected to the power supply
are, as shown in FIG. 3, printed. On the solid electrolyte body
sheet, the electrodes 121 and 122, the leads 123 and 124, and the
terminals 125, 126, and 128 are printed. Subsequently, the heater
substrate sheet, the spacer preform, the solid electrolyte body
sheet, the porous layer sheet, and the shielding layer sheet are
pressed to form a lamination.
[0060] The thus formed lamination is baked within a furnace heated
according to a given temperature profile to make the gas sensor
element 1.
[0061] Finally, an output of the gas sensor element 1 is adjusted
in the following manner.
[0062] The gas sensor element 1 is first connected to a check
circuit. The voltage is applied to the target gas-exposed electrode
121 and the reference gas-exposed electrode 122 while exposing them
to a gas having a selected oxygen concentration. An output current
of the gas sensor element 1 is measured and compared with a map
listing the relation between a ground amount (i.e., a removed
thickness) and a current change to determine the thickness of each
side of the gas sensor element 1 to be removed, for example, in
unit of millimeter.
[0063] Finally, each side of the gas sensor element 1 is machined
using a grinding stone made of diamond powder to remove the
determined thickness therefrom so as to bring the output of the gas
sensor element 1 into agreement with a target value.
[0064] A method of making the above map will be discussed
below.
[0065] First, a test piece of the gas sensor element 1 is prepared.
A change in output current is measured while grinding each of the
side walls 101 of the test piece.
[0066] The output current is the current measured when a given
voltage is applied to the electrodes 121 and 122. The output of the
gas sensor element 1 measured when no voltage is applied is defined
as a reference output. The removed thickness .DELTA.t of each side
surface 101 and a corresponding change in output current are
plotted to make the map, as shown in FIG. 4.
[0067] The operation of the gas sensor element 1 will be discussed
below.
[0068] The application of a given voltage to the target gas-exposed
electrode 121 and the reference gas-exposed electrode 122 causes
the current to flow through the electrodes 121 and 122. The current
is determined as a function of the number of oxygen molecules
passing through the diffused resistance layer 11.
[0069] The diffusion length of the target gas in the diffused
resistance layer 11, as shown in FIG. 2, corresponds to the length
of a path extending from each side surface 101 to the target
gas-exposed electrode 121. The decreasing the diffusion length is,
therefore, achieved by only removing the thickness .DELTA.t from
each side surface 101, thereby resulting in an increase in output
current flowing through the electrodes 121 and 122.
[0070] In a case where the voltage V is applied to a plurality of
mass-produced sensor elements 1 when the concentration of oxygen
contained in the target gas is a, and the distribution of output
currents, as represented by G in FIG. 5, is derived which spreads
across Ia over an allowable measurement range .DELTA.Ia, side
surfaces of some of the sensor elements 1 which produce current
outputs within a range, as indicated by hatched lines, are ground
by the thickness .DELTA.t to decrease the diffusion length. This
causes the distribution of current outputs thereof to be changed so
as to spread, as represented by G', across Ia', thus resulting in a
variation in current outputs of the sensor elements 1 falling
within the allowable measurement range .DELTA.Ia. Specifically,
this adjustment absorbs a unit-to-unit variation of the
mass-produced sensor elements 1, thereby enabling production of the
sensor elements 1 having desired output characteristics at low
costs.
[0071] The output adjusting method according to the second
embodiment will be described below with reference to FIGS. 6 to
9.
[0072] In this embodiment, the decreasing the diffusion length of
the diffused resistance layer 11 for adjusting the output of the
gas sensor element 1 is, as shown in FIGS. 6 and 7, accomplished by
chamfering the corner C of each of the side surfaces 101 of the
diffused resistance layer 11 so that each of the chamfered side
surfaces 101 may make angle .theta. with those before being
chamfered (i.e., the side surfaces 101 of the insulating spacer
13). A maximum thickness of a removed portion of each side surface
101 is .DELTA.t. If it is not required to adjust the output of the
gas sensor element 1 greatly, only one of the side surfaces 101 of
the gas sensor element 1 may be removed.
[0073] FIG. 8 represents the relation between the removed thickness
.DELTA.t of each side surface 101 and a corresponding change in
output current of the gas sensor element 1 measured in a similar
manner to that as discussed in FIG. 4. It is found that the
thickness .DELTA.t may be selected from a range of 0 to 0.6 mm and
that the output current of the gas sensor element 1 is changed as
much as 40% by removing the side surfaces 101 by 0.6 mm.
Specifically, the chamfering of the side surfaces 101 of the
diffused resistance layer 11 enables the adjustment of the output
of the gas sensor element 1 in a wide range and also results in a
great decrease in volume of the diffused resistance layer 11 to
shorten the diffusion length of the target gas in the diffused
resistance layer 11 more greatly, thereby enabling production of
the high-response gas sensor element 1.
[0074] The decreasing the diffusion length of the diffused
resistance layer 11 may alternatively be, as shown in FIG. 9,
accomplished by grinding the side surfaces 101 of only the diffused
resistance layer 11 perpendicular thereto by the thickness
.DELTA.t. If it is not required to adjust the output of the gas
sensor element 1 greatly, only one of the side surfaces 101 of the
gas sensor element 1 may be removed.
[0075] The output adjusting method according to the third
embodiment will be described below with reference to FIG. 10. In
this embodiment, the decreasing the diffusion length of the
diffused resistance layer 11 is accomplished by grinding the side
surfaces 101 of only the porous layer 112 perpendicular thereto by
the thickness .DELTA.t. If it is not required to adjust the output
of the gas sensor element 1 greatly, only one of the side surfaces
101 of the gas sensor element 1 may be removed.
[0076] The output adjusting method according to the fourth
embodiment will be described below with reference to FIG. 11.
[0077] The diffused resistance layer 11 of the sensor element in
this embodiment consists only of the porous layer 112. The target
gas, therefore, diffuses from the upper surface 119 of the porous
layer 112 to the target gas-exposed electrode 121. Accordingly, the
decreasing the diffusion length of the diffused resistance layer 11
for adjusting the output of the gas sensor element 11 is achieved
by grinding the porous layer 112 in a thickness-wise direction
thereof, that is, in parallel to the upper surface 119.
[0078] The output adjusting method according to the fifth
embodiment will be described below with reference to FIGS. 12(a) to
13(b).
[0079] The decreasing the diffusion length is achieved by removing
the part of the dense layer 111 of the diffused resistance layer
11.
[0080] Specifically, the rectangular window 161 is, as clearly
shown in FIGS. 12(a) and 12(b), formed in the dense layer 111 which
reaches the porous layer 112. The window 161 works to introduce the
target gas, as indicated by an arrow in FIG. 12(b), to the porous
layer 112, thereby decreasing the diffusion length by a distance
.DELTA.m between the side surface 101 of the gas sensor element 1
and the window 161.
[0081] The cut-away portion 162, as shown in FIGS. 13(a) and 13(b),
may alternatively be formed in the dense layer 111 which reaches
the porous layer 112. The cut-away portion 162 introduces the
target gas, as indicated by an arrow in FIG. 13(b), to the porous
layer 112, thereby decreasing the diffusion length by a distance
.DELTA.n between the side surface 101 of the gas sensor element 1
and the cut-away portion 162.
[0082] The output adjusting method according to the sixth
embodiment will be described below with reference to FIGS. 14(a)
and 14(b).
[0083] The decreasing the diffusion length in this embodiment is
achieved by decreasing a side area of the diffused resistance layer
11 at which the target gas enters.
[0084] Specifically, the shielding member 171 is installed on one
of the side surfaces 101 to decrease the side area of the diffused
resistance layer 11 (i.e., the porous layer 112), thereby
decreasing a sectional area of the diffused resistance layer 11
within which the target gas diffuses, resulting in a decrease in
volume of the target gas entering the diffused resistance layer 11
to decrease the output current of the gas sensor element 1.
[0085] The length .DELTA.l of the shielding portion 171 is
determined as a function of a desired quantity of output current of
the gas sensor element 1 to be adjusted. The shielding portion 171
is made of a crystal glass which prohibits the penetration of the
target gas and which has preferably a coefficient of thermal
expansion close to that of the porous layer 112 in order to avoid
generation of thermal stress.
[0086] The shielding member 171 may be installed on each of the
side surfaces 101.
[0087] The output adjusting method according to the seventh
embodiment will be described below with reference to FIGS. 15(a)
and 15(b).
[0088] The decreasing the diffusion length in this embodiment is,
like the sixth embodiment, achieved by decreasing a sectional area
of the diffused resistance layer 11.
[0089] Specifically, an array of output adjusting holes 175 are
formed in the dense layer 111 which lead to the porous layer 112. A
desired number of the output adjusting holes 175 are sealed with a
crystal glass which prohibits the penetration of the target
gas.
[0090] If all the output adjusting holes 175 are not sealed, the
gas-diffused sectional area of the gas sensor element 1 within
which the target gas diffuses corresponds to the sum of an area of
the porous layer 112 facing the target gas and a total sectional
area of the output adjusting holes 175. Therefore, if one of the
output adjusting holes 175 is closed, the gas-diffused sectional
area of the gas sensor element 1 is decreased by the sectional area
of the one output adjusting hole 175. The number of the output
adjusting holes 175 to be closed is determined as a function of the
quantity of output current to be adjusted.
[0091] While the present invention has been disclosed in terms of
the preferred embodiments in order to facilitate better
understanding thereof, it should be appreciated that the invention
can be embodied in various ways without departing from the
principle of the invention. Therefore, the invention should be
understood to include all possible embodiments and modifications to
the shown embodiments which can be embodied without departing from
the principle of the invention as set forth in the appended
claims.
* * * * *