Now, a gas sensor of an embodiment according to the present invention and a related method of manufacturing the gas sensor are described below in detail with reference to the accompanying drawings. However, the present invention is construed not to be limited to such an embodiment described below and technical concepts of the present invention may be implemented in combination with other known technologies or the other technology having functions equivalent to such known technologies.
In the following description, it is construed that a portion of the gas sensor adapted to be inserted to an exhaust pipe of an internal combustion engine of a motor vehicle is referred to as a “leading end portion” and an opposite side of the gas sensor exposed to an atmosphere is referred to as a “base end” or a “base end portion”.
Also, it will be appreciated that the gas sensor of the present embodiment according to the present invention may have a wide variety of applications to an oxygen sensor, an A/F sensor, a NOx sensor, etc.
A gas sensor of an embodiment according to the present invention is described below in detail with reference to
As shown in
As shown in
Further, as shown in
The housing 4 is internally formed with a first large diameter inner wall 4d and a second small diameter inner wall 4e, with a holder rest shoulder 4f being formed between the first and second inner walls 4d, 4e.
The insulating element holder 3 includes a large diameter cylindrical body 3b and a small diameter cylindrical body 3c, with an engaging shoulder 3ba being formed between the cylindrical bodies 3b, 3c.
The insulating element holder 3 is accommodated in the housing 4 such that the large diameter cylindrical body 3a is accommodated in the large diameter inner wall 4d of the housing 4 and the small diameter cylindrical body 3b is accommodated in the small diameter inner wall 4e of the housing 4 with a packing element 5 being interposed between the engaging shoulder 3ba of the insulating element holder 3 and the holder rest shoulder 4f of the housing 4 to provide a sealing effect.
The packing element 5 separates a measuring gas side ambience 100 and an atmospheric side ambience 150 from each other in the gas sensor 1 in a hermetically sealing effect.
The gas sensor 1 of the present embodiment comprises, in addition to the gas sensing element 2, the insulating element holder 3 and the housing 4, an atmospheric side insulator 8, a measuring gas side cover 11 fixedly mounted on an end face of the lower cylindrical body 4c of the housing 4, and an atmospheric side cover 12 fixedly mounted on the upper cylindrical body 4b of the housing 4 by welding The atmospheric side ambience 100 is defined in the atmospheric side cover 12 and the measuring gas side ambience 150 is defined in the measuring gas side cover 11.
The atmospheric side insulator 8 has an axially extending cavity 8a that accommodates therein spring terminals 10, 10 held in electrical contact with electrode terminals (not shown) of the gas sensing element 2. The spring terminals 10, 10 are electrically connected to lead wire portions 13, 13.
The atmospheric side cover 12 has an upwardly extending base end section 12a formed in a smaller diameter than that of the other part and having a plurality of ventilation openings 12b formed at circumferentially spaced positions. The base end section 12a of the atmospheric side cover 12 carries thereon a filter cover 14 formed with a plurality of ventilation openings 14a at circumferentially spaced positions in radial alignment with the ventilation openings 12b formed on the base end section 12a of the atmospheric side cover 12 to introduce atmospheric air into the atmospheric side ambience 100.
A ventilation filer 16 is interposed between the base end section 12a of the atmospheric side cover 12 and the filter cover 14 in a position to provide a waterproof function between the ventilation openings 14a of the filter cover 14 and the ventilation openings 12b of the base end section 12a of the atmospheric side cover 12 while admitting atmospheric air to an inside of the atmospheric side cover 12.
As shown in
The measuring gas side cover 11 takes a double-layer structure that includes an inner protecting cover 11a, formed with a plurality of openings 11aa, and an outer protecting cover 11b having a plurality of openings 11ba. Thus, the openings 11aa, 11ba play roles as gas flow ports through which measuring gases are introduced to an inside of the measuring gas side cover 11 in contact with a detecting section 2a of the gas sensing element 2.
As best shown in
Further, the small diameter cylindrical body 3c of the insulating element holder 3 has a leading end face 3d at which a cushioning filler 30 is provided. The cushioning filler 30 is partially filled in a leading end portion of the element inserting bore 3a of the insulating element holder 3 to resiliently support the gas sensing element 2 in fixed place.
The cushioning filler 30 is formed in the leading end portion of the element inserting bore 3a of the insulating element holder 3 by carrying out filling step and firing step in manners described below.
That is, in filling step, ceramic slurry is prepared by mixing at least ceramic powder and binder. Then, ceramic slurry is filled into a ring-like space 32 between the gas sensing element 2 and the element inserting bore 3a in an area close proximity to the end face 3d of the small diameter portion 3c of the insulating element holder 3 as shown in
In next firing step, ceramic slurry is fired together with the insulating element holder 3 and the gas sensing element 2, thereby forming the cushioning filler 30 in a ring shape contour in cross section as shown in
With the gas sensor 1 shown in
In preparing ceramic slurry used for filling step, ceramic slurry contains 47 to 53 wt % of ceramic powder for a gross weight of ceramic slurry. In addition, the binder content lies in a value ranging from 5 to 10 wt % for a weight of ceramic solids.
Further, examples of ceramic powder include, for instance, alumina powder, zirconia powder or the like.
Furthermore, examples of binder include alumina sol, aluminum nitrate or the like.
Moreover, the filling step is carried out so as to allow the cushioning filler 30 to be filled in the ring-like space 32 between the gas sensing element 2 and the element inserting bore 3a such that at least four corners of the gas sensing element 2 is sealed and fixed in place on a plane perpendicular to an axis of the gas sensing element 2.
While the gas sensor 1 of the present embodiment is shown in
Now, a method of manufacturing the gas sensor 1 is described below in detail.
In fabricating the gas sensing element 2, a plurality of given green sheets are laminated and pressed against each other, thereby obtaining an unburned laminate body. Thereafter, the unburned laminate body is burned forming of the gas sensing element 2.
Further, the insulating element holder 3 can be fabricated by firing a ceramic body made of, for instance, alumina or the like.
Thereafter, the gas sensing element 2 is inserted through the element inserting bore 3a of the insulating element holder 3. Then, airtight sealant 6 is poured to the cavity 3e of the insulating element holder 3 from a base end portion 3f of the insulating element holder 3 to fill a clearance in the form of the ring-like space 32 between the insulating element holder 3 and the gas sensing element 2. This enables the gas sensing element 2 to be strongly fixed to the insulating element holder 3 at the base end portion 3f of the insulating element holder 3.
Examples of airtight sealant 6 include suitable materials such as, for instance, crystallized glass, inorganic filling materials or the like.
In forming the cushioning filler 30, filling step is conducted to fill ceramic slurry to the ring-like space 32 between the insulating element holder 3 and the gas sensing element 2, after which firing step is carried out in the manner set forth above.
During filling step, as shown in
In carrying out filling step set forth above, for instance, ceramic powder, binder, water and additive are mixed to each other thereby preparing ceramic slurry as set forth above.
Further, ceramic powder has an average particle diameter in a range from 10 to 30 μm.
Next, firing step is conducted to fire ceramic slurry together with the insulating element holder 3 and the gas sensing element 2 at a given temperature for a given time interval, thereby obtaining the cushioning filler 30. When this takes place, both the gas sensing element 2 and the insulating element holder 3 are heated together with ceramic slurry. This allows binder and water or the like to vaporize, thereby causing ceramic powder components to be solidified and hardened thereby forming the cushioning filler 30.
Thus, with the airtight sealant 6, filled in the cavity 3e of the insulating element holder 3 in the base end portion 3f thereof, and the cushioning filler 30 located in the distal end portion of the insulating element holder 3 on the end face 3d thereof, the gas sensing element 2 can be fixedly retained at two axially spaced positions.
Subsequently, the packing element 5 is inserted to the small diameter cylindrical section 3c of the insulating element holder 3. Then, the insulating element holder 3 and the packing element 3, rigidly carrying thereon the gas sensing element 2 unitized to the insulating element holder 3 by means of the airtight sealant 6 and the cushioning filler 30, are inserted to the housing 4 until the packing element 5 is sandwiched between the annular shoulder 3ba of the large diameter cylindrical section 3b and the annular rest portion 4f of the housing 4. Under such a situation, the large diameter cylindrical section 3b is accommodated in the large diameter inner wall 4d of the housing and the small diameter cylindrical section 3c is accommodated in the small diameter inner wall 4e.
With such a structure set forth above, the gas sensor 1 of the present embodiment has various advantageous effects listed below.
Ceramic slurry contains 47 to 53 wt % of ceramic solids for a gross weight of ceramic slurry and 5 to 10 wt % of binder for a gross weight of the ceramic solids. Thus, the cushioning filler 30 can have adequate strength.
After ceramic slurry filled to the space 32 between the element inserting bore 3a of the insulating element holder 3 and the gas sensing element 2 in the area near the face end 3d of the insulating element holder 3, the insulating element holder 3, the gas sensing element 2 and ceramic slurry are subjected to firing step. Thus, upon completions of filling step and firing step of ceramic slurry, the cushioning filler 30 composed of ceramic slurry and having adequate strength can be formed in the area between the gas sensing element 2 and the insulating element holder 3. Therefore, the presence of the cushioning filler 30 with adequate strength can suppress the gas sensing element 2 from vibrating due to vibration of the internal combustion engine during operation thereof.
That is, with the manufacturing method set forth above, it becomes possible to easily manufacture a gas sensor that can prevent a gas sensing element from damage.
Further, ceramic powder used in filling step has an average particle diameter ranging from 10 to 30 μm. This allows filling step to be effectively carried out such that the cushioning filler 30 is filled between the gas sensing element 2 and the insulating element holder 3 so as to have adequate strength.
As shown in
With the manufacturing method of the gas sensor, as set forth above, it becomes possible to manufacture a gas sensor that has remarkable vibration-proof to provide elongated operating life.
Test pieces were prepared using ceramic slurries composed of binders in various contents and ceramic powders with various particle diameters as ceramic solids. Impact tests were conducted on the resulting test pieces with test results indicated in a graph of
In conducting impact tests, base end portions of the test pieces were restricted in fixed place and the test pieces were applied with impacts in various magnitudes along a direction perpendicular to an axis of the gas sensing element 2.
Also, component elements of each test piece bear the same reference numerals as those used in
In this Example 1, gas sensors were fabricated as test pieces using ceramic slurries containing 45 wt % of ceramic solids in a fixed value with binder contents and average particle diameters of ceramic powders altered in various values as described below. That is, the binder contents were altered in various values ranging from 5 to 15 wt %. In addition, the average particle diameters of ceramic powder were altered in various values ranging from 0 to 50 μm. Moreover, ten pieces of samples were prepared for each test piece.
Then, impacts were applied to the ten pieces of the samples and calculations were executed to check an average value of impact accelerations acting on the ten pieces of samples whose gas sensing elements 2 were damaged.
In making judgments on whether or not damages occurred on the gas sensing elements 2, a voltage was applied to each heater incorporated in each sample to cause electric current flow therethrough and judgment was made by checking whether or not the heater of the gas sensing element 2 was conducting.
Measured results are indicated on the graph shown in
From the above, it is important from a viewpoint of ensuring strength of the cushioning fillers 30 that the binder content lies in a value ranging from 5 to 10 wt % for the weight of ceramic solids and an average particle diameter of ceramic powder lies in a value from 10 to 30 μm.
In this Example 2, tests were conducted on test pieces to check the relationship between a ceramic solid content (wt %) in ceramic slurry and impact acceleration applied to the gas sensing elements 2 for damages caused to occur therein with test results indicated in a graph of
Also, component elements of each test piece bear the same reference numerals as those used in
In this Example 2, gas sensors were fabricated having cushioning fillers 30 containing ceramic solids in various values. Also, ten pieces of samples were prepared for each test piece.
Thereafter, the samples are applied with impacts in the same ways as those of Example 1 mentioned above.
Then, impacts were applied to the ten pieces of the samples and calculations were executed to check an average value of impact accelerations acting on the ten pieces of samples whose gas sensing elements 2 were damaged.
In addition, ceramic slurry was selected to have 7.5 wt % of binder content to a weight of ceramic solids and ceramic powder having an average particle diameter of 20 μm.
Example 2 has the other conditions similar to those of Example 1.
Measured results are indicated on the graph shown in
From the above, it is turned out to be important from a viewpoint of ensuring strength of the cushioning fillers 30 that the content of ceramic solids contained in ceramic slurry lies in a value from 47 to 53 wt %.
While the specific embodiments of the present invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure. Accordingly, the particular arrangements disclosed are meant to be illustrative only and not limited to the scope of the present invention, which is to be given the full breadth of the following claims and all equivalents thereof.
Number | Date | Country | Kind |
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2006-116995 | Apr 2006 | JP | national |