Abstrict
An electrode structure includes: a metallic electrode; a case for
accommodating and holding the electrode, and one end of a lead wire
connecting to the electrode; and an insulating member interposed
between the electrode and the case in order to ensure insulation
between the electrode and the case, in which structure a waterproof
member is interposed between the case and the lead wire in order
to prevent the incoming of water from between the case and the lead
wire, and an electric heater havinging the above electrode structure.
An electrode structure of an electric heater, includes: a first
electrode; a second electrode of a cylinder shape, having a base
portion connected with the first electrode and a top end portion
connected with a lead wire; an insulating member having a thermal
resistance, pierced by the second electrode; an elastic insulator
having a thermal resistance, covering at least a portion of the
second electrode; a case for accommodating and holding the second
electrode, having a predetermined length L; and a rubber sealing
member attached to the top end of the case. The electrode structure
is preferably used by connecting to a conductive substance accommodated
in a metallic housing, to apply electricity to the conductive substance.
The conductive substance is preferably a metallic honeycomb structure.
The given length L mentioned above is preferably L.gtoreq.40 mm.
Claims
What is claimed is:
1. An electrode assembly comprising:
(a) an electrode structure comprising:
a metallic electrode;
a case for accommodating and holding the electrode and one end
of a lead wire connecting to the electrode, the case having (1)
an upper portion with a diameter smaller than the diameter of the
remainder of the case and (2) a length sufficient to house a waterproof
member completely therein;
an insulating member interposed between the electrode and the case
in order to ensure insulation between the electrode and the case,
and
a waterproof member interposed between the case and the lead wire
at the upper portion of the case apart from the insulating member
in order to prevent the passage of water through the gap between
the case and the lead wire and
(b) a conductive substance connected to the electrode structure
and accommodated in a metallic housing, in order to apply electricity
to the conductive substance.
2. An electrode assembly according to claim 1, wherein the conductive
substance is a metallic honeycomb structure.
3. An electrode assembly according to claim 1, wherein the waterproof
member is a heat-resistant and insulating organic compound or a
glass.
4. An electrode assembly according to claim 3, wherein the organic
compound is a fluorine-containing organic compound.
5. An electrode structure according to claim 1, wherein at least
one crimped portion is formed at the tapered upper end portion of
the case.
6. An electrode assembly according to claim 1, wherein a gap between
the case and the waterproof member and a gap between the waterproof
member and the lead wire are sealed with an adhesive.
7. An electrode assembly according to claim 1, wherein the insulating
member is constituted by a first insulator, a second insulator and
an inorganic powder filled between the first and second insulators.
8. An electrode assembly according to claim 7, wherein the first
insulator and the second insulator are each made of a ceramic.
9. An electrode structure according to claim 7, wherein the inorganic
powder is filled by pressurization.
10. An electrode assembly according to claim 1, wherein the insulating
member is constituted by a first insulator, a second insulator and
a cement sealing material filled between the first and second insulators.
11. An electrode assembly according to claim 1, wherein a gap between
the electrode and the insulating member and a gap between the insulating
member and the case are each sealed with a metal sealing material.
12. An electrode assembly according to claim 11, which further
comprises, between the electrode and the case, a spring member for
absorbing the difference in thermal expansion between the electrode,
the case and the insulating member and a pressing member for transmitting
a load to the spring member.
13. An electrode assembly according to claim 12, wherein the pressing
member is a nut fitted to the electrode.
14. An electrode assembly according to claim 12, wherein the pressing
member is fixed to the electrode by welding.
15. An electrode assembly according to claim 12, wherein the pressing
member is fixed to the electrode by crimping.
16. An electrode assembly according to claim 1, wherein the insulating
member is an insulating coating material coated on at least one
of the electrode and the case.
17. An electrode assembly according to claim 16, wherein the gap
between the electrode and the case is sealed with an inorganic powder.
18. An electrode assembly according to claim 16, wherein the insulating
coating material is an alumina and is plasma-sprayed.
19. An electrode assembly according to claim 16, wherein the insulating
coating material is a ceramic.
20. An electrode assembly according to claim 1, wherein the insulating
member is an insulating coating material coated on the electrode
and the gap between the case and the insulating coating material
is sealed with a metal sealing material.
21. An electrode assembly according to claim 1, wherein the insulating
member is an insulating coating material coated on the case and
a gap between the electrode and the insulating coating material
is sealed with a metal sealing material.
22. An electrode assembly according to claim 1, wherein the lead
wire is covered with a covering material which functions also as
a waterproof member.
23. An electrode structure according to claim 1 wherein said electrode
assembly is housed within an electric heater.
24. An electrode assembly according to the claim 1, wherein the
metallic electrode has an uncoated surface throughout.
25. An electrode assembly according to claim 1, wherein the case
is formed of a single component.
26. An electrode assembly according to claim 1, wherein the case
is comprised of at least two separate components, and the components
partially fit within each other.
27. An electrode assembly according to claim 26, wherein the insulating
member is interposed between the electrode and the first case.
28. An electrode assembly according to claim 1, wherein said waterproof
member has no groove.
29. An electrode assembly according to claim 1, wherein said upper
portion of the case has an extremity that is outwardly beveled or
straight.
30. An electrode structure of an electric heater, comprising:
a first electrode;
a second electrode of a cylinder shape, having a base portion connected
with the first electrode and a top end portion connected with a
lead wire;
an insulating member having a thermal resistance, pierced by the
second electrode;
an elastic insulator having a thermal resistance, covering at least
a portion of the second electrode;
a case for accommodating and holding the second electrode, having
a predetermined length L; and
a rubber sealing member attached to the top end of the case.
31. An electrode structure of an electric heater according to claim
30, wherein said predetermined length L is 40 mm or more.
32. An electrode structure of an electric heater according to claim
30, wherein the second electrode is fixed to the case by means of
said elastic insulator or said insulating member and is thread-mounted
on the first electrode.
33. An electrode structure of an electric heater according to claim
32, wherein said ceramic powder is filled up in a gap between said
insulating member and the second electrode, and said glass insulator
is positioned between said case and the second electrode.
34. An electrode structure of an electric heater according to claim
30, wherein the top end portion of the second electrode is formed
to have a shape of a hexagon, a rectangle, or having a hole that
is hexagonal.
35. An electrode structure of an electric heater according to claim
30, wherein the base portion of the second electrode is connected
with the first electrode by welding.
Description BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an electrode structure and an
electric heater comprising the electrode structure. More particularly,
the present invention relates to an electrode structure provided
in an exhaust gas system of an internal combustion engine and connected
to, for example, a conductive substance accommodated in a metallic
housing in order to apply electricity to the conductive substance
to heat it and thereby purify the exhaust gas generated during the
cold periods (e.g. cold start) of engine, as well as to an electric
heater comprising the electrode structure.
(2) Description of the Prior Art
A technique is known in which, in a catalytic converter used for
purification of the exhaust gas generated in automobiles, etc.,
an electric heater is provided to raise the temperature of the converter
catalyst to its working temperature as quickly as possible.
In this technique, as shown in FIG. 20, an electric heater 101
and an auxiliary catalyst 102 are provided upstream of a main catalyst
100, that is, between an engine and the main catalyst 100 in an
exhaust pipe 150, to purify harmful substances present in the exhaust
gas generated during cold engine periods. In this system for exhaust
gas purification, when the main catalyst 100 is not activated (for
example, during cold engine periods such as cold start and the like),
the electric heater 101 is put in an ON operation for a given length
of time (e.g. 40 seconds) to raise the temperatures of the electric
heater 101 and the auxiliary catalyst 102 to respective given temperatures
(e.g. 400-500.degree. C.) or above to activate the electric heater
101 and the auxiliary catalyst 102 in a short time and allow the
electric heater 101 and the auxiliary heater 102 to conduct gas
purification during cold engine periods. After the engine has been
warmed up, purification of harmful substances present in the exhaust
gas is conducted by the electric heater 101, the auxiliary heater
102 and the main catalyst 100.
The above electric heater generally comprises: a metallic honeycomb
structure; a metallic housing (e.g. a can) for accommodating and
holding the honeycomb structure; and an electrode for applying electricity
to the honeycomb structure which is a conductive substance.
As electrode structures of electric heaters, there have conventionally
been known those shown in FIGS. 21(A)-21(C).
In FIG. 21(A), a positive screw portion 103 is provided by carving.
An electrode pole 105 Is fixed by an electrode 104. A first and
a second insulating members 106 and 107, respectively, are engaged
with the electrode pole 105 around the electrode pole 105. In a
gap between the first insulating member 106 and the second insulating
member 107 is placed a ceramic powder 108 such as cement. The ceramic
powder 108 is packed in a space formed by the first and the second
insulating members 106 and 107 and a fixing ring 109. On the electrode
pole 105, a nut 111 is thread-mounted via a washer 110. Thus, the
first and the second insulating members 106 and 107, and the like
are fixed to the electrode pole 105.
In the conventional embodiment shown in FIG. 21(A), an electrical
insulation against a metallic housing (case) 160, which works as
an exhaust pipe, is ensured by the first and the second insulating
members 106 and 107. An exhaust gas is sealed by the ceramic powder
108. The electrode 104 inside the metal housing 160 is connected
with a part of honeycomb structure 133 by means of a metallic connecting
member 135.
FIG. 21(B) shows another electrode structure called a plasma coating
type. An insulating member 112 such as ceramic is coated on a predetermined
portion of a pole by a discharge of plasma so as to obtain an electrode
pole 113. The electrode pole 113 is inserted in and engaged with
a ring 115 fixed to a metallic housing 114.
In this plasma coating type of electrode structure, the aforementioned
coated portion having the insulating member 112 is forcibly inserted
in and engaged with the ring 115, by which an electrical insulation
against a metallic housing and a sealing against an exhaust gas
are ensured.
FIG. 21(C) shows still another electrode structure called a metal
seal type. The top end portion of an electrode pole 117 is provided
with a positive screw portion 116 by curving. The electrode pole
119 is fixed to an electrode 117. A first insulating member 120
and a second insulating member 122 are engaged with the electrode
pole 117 therearound. The first insulating member 120 is provided
with a first ring 118 and a second ring 127 on both the upper and
the lower surfaces of a protrusion. That is, an electrode structure
of a metal seal type is provided with the first insulating member
120 and the second insulating member 122 are fixed in predetermined
places by a net 123 and inserted in and engaged with a metallic
housing 126.
The metal seal type of electrode structure is electrically insulated
against a metal housing 126 by the first and the second insulating
members 120 and 122 and sealed against exhaust gas by the first
and the second metallic ring 118 and 127.
In the electric heater comprising such an electrode structure,
there is preferred, for conveniences such as easy fitting to an
exhaust pipe of an automobile, etc., an electrode structure which
is connected to a lead wire connecting to an external electric source
and in which one end of the lead wire is contained for reliable
electrical connection between the electrode and the lead wire. This
electrode structure, however, has problems in that, when an automobile
is driven in rainy weather, etc. on rain puddles of roads or during
flooding, water adheres onto the electrode of the electric heater
101, which may cause electrical short-circuiting and consequent
misoperation of heater (see FIG. 22).
SUMMARY OF THE INVENTION
In view of the above situation, the present invention has been
made to provide an electrode structure for electric heater, which
can prevent the adhesion of water to the electrode of the heater
even when an automobile provided with such an electric heater is
driven through rain puddles or during flooding, as well as an electric
heater comprising such an electrode structure.
According to the present invention, there is provided an electrode
structure comprising: a metallic electrode; a case for accommodating
and holding the electrode, and one end of a lead wire connecting
to the electrodes and an insulating member interposed between the
electrode and the mass in order to ensure insulation between the
electrode and the case, in which structure a waterproof member is
interposed between the case and the lead wire in order to prevent
the incoming of water from between the case and the lead wire, and
an electric heater comprising the above electrode structure.
According to the present invention, there is further provided an
electrode structure of an electric heater, comprising: a first electrode;
a second electrode of a cylinder shape, having a base portion connected
with the first electrode and a top end portion connected with a
lead wire; an insulating member having a thermal resistance, pierced
by the second electrode; an elastic insulator having a thermal resistance,
covering at least a portion of the second electrode; a case for
accommodating and holding the second electrode, having a predetermined
length L; and a rubber sealing member attached to the top end of
the case.
The electrode structure of the present invention is preferably
used by connecting to a conductive substance accommodated in a metallic
housing, to apply electricity to the conductive substance. The conductive
substance is preferably a metallic honeycomb structure.
The given length L mentioned above is preferably L.gtoreq.40 mm.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view showing an embodiment of the electrode
structure of the present invention.
FIG. 2 is a partial sectional view showing an embodiment of another
waterproof structure between electrode case and lead wire, used
in the electrode structure of the present invention.
FIG. 3 is a partial sectional view showing another embodiment of
the electrode structure of the present invention.
FIG. 4 is a partial sectional view showing still another embodiment
of the electrode structure of the present invention.
FIG. 5 is a partial sectional view showing still another embodiment
of the electrode structure of the present invention.
FIG. 6 is a partial sectional view showing still another embodiment
of the electrode structure of the present invention.
FIG. 7 is a partial sectional view showing an embodiment of the
fixation between pressing member and electrode, used in the electrode
structure of the present invention.
FIG. 8 is a partial sectional view showing still another embodiment
of the electrode structure of the present invention.
FIG. 9 is a partial sectional view showing still another embodiment
of the electrode structure of the present invention.
FIG. 10 is a sectional view showing still another embodiment of
the electrode structure of the present invention.
FIG. 11 is a perspective view showing the detail of the upper portion
of a ceramic sleeve used in the electrode structure of the present
invention.
FIG. 12 is a plan view of the electrode structure shown in FIG.
10.
FIG. 13 is a characteristic view showing the relation between distance
from electrode and temperature, in a conventional electric heater.
FIG. 14 is a sectional view showing still another embodiment of
the electrode structure of the present invention.
FIG. 15 is a perspective view of the front end of the second electrode
used in the electrode structure shown in FIG. 14.
FIG. 16 is another perspective view of the front end of the second
electrode used in the electrode structure shown in FIG. 14.
FIG. 17 is a sectional view showing still another embodiment of
the electrode structure of the present invention.
FIG. 18 is a plan view of a two-electrode electric heater using
the electrode structure of the present invention.
FIG. 19 is a plan view of a one-electrode electric heater using
the electrode structure of the present invention.
FIG. 20 is a view showing the structure of the key portion of the
exhaust system of internal combustion engine in an automobile.
FIGS. 21(A), 21(B), and 21(C) are sectional views showing embodiments
of conventional electrode structures.
FIG. 22 is a view showing the arrangement of the exhaust system
of internal combustion engine in an automobile.
FIG. 23 is a partial view showing an embodiment of the connection
between electrode and lead wire, used in the electrode structure
of the present invention.
FIG. 24 is a partial view showing another embodiment of the connection
between electrode and lead wire, used in the electrode structure
of the present invention.
FIG. 25 is a partial view showing still another embodiment of the
connection between electrode and lead wire, used in the electrode
structure of the present invention.
FIG. 26 is a partial view showing still another embodiment of the
connection between electrode and lead wire, used in the electrode
structure of the present invention.
FIG. 27 is a partial view showing still another embodiment of the
connection between electrode and lead wire, used in the electrode
structure of the present invention.
FIG. 28 is a partial view showing still another embodiment of the
connection between electrode and lead wire, used in the electrode
structure of the present invention.
FIG. 29 is a partial view showing still another embodiment of the
connection between electrode and lead wire, used in the electrode
structure of the present invention.
FIG. 30 is a plan view showing an embodiment of the pressing member
used in the electrode structure of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The electrode structure according to the present invention ie hereinafter
described specifically. Description is made first on the members
constituting the electrode structure.
The waterproof member used in the electrode structure of the present
invention, is preferably a heat-resistant insulating organic compound
or a glass. Specific examples of the insulating organic compound
are preferably fluorine-containing organic compounds such as polytetrafluoroethylene
(trade name: Teflon), fluororubber and the like, with Teflon being
particularly preferred for its low weight decrease at high temperatures.
Teflon may contain a glass for higher heat resistance. The heat
resistance of the waterproof member is preferably at least 100.degree.
C., more preferably at least 150.degree. C.
In the present electrode structure, the case is preferably crimped
from outside at the portion where the waterproof member is interposed
between the case and the lead wire, to ensure waterproofness inside
the electrode. The waterproofness inside the electrode can also
be ensured by, in place of employing the crimping, sealing the gap
between the case and the waterproof member and/or the gap between
the waterproof member and the lead wire with an adhesive. Herein,
the waterproofness inside the electrode is preferably set at 1 cc/min
or lees in terms of the amount of water incoming at 0.5 atm. Preferably,
the adhesive has a large expansion coefficient so as to be able
to follow the repetition of high temperature and low temperature
as encountered in the exhaust system of automobile and also has
water repellency for possible contact with water. A preferable adhesive
is, therefore, an organic adhesive and specific examples thereof
are a polyimide, etc.
The circumference of the lead wire is ordinarily covered with a
covering material. The covering material preferably has a heat resistance
of at least 100.degree. C. Specific examples of the covered lead
wire are a lead wire comprising a core and TEFLON (polytetrafluoroethylene)
covering the circumference of the core, and a lead wire comprising
a core, a polyimide tape covering the circumference of the core
and a knitted and braided glass fiber covering the polyimide tape.
The diameter of the core of the lead wire is preferably 1.0-5.0
mm. The core is preferably one obtained by intertwisting thin wires
each having a diameter of 0.5 mm or less.
The electrode is preferably a metal rod. The electrode is fixed
to the case connecting to a metallic housing, via an insulating
member. One end of the electrode located inside the housing is connected,
directly or via a metallic connecting member, to part of a conductive
substance accommodated in the metallic housing by welding or the
like.
Meanwhile, the other end of the electrode is connected to the lead
wire. The connection between the electrode and the lead wire is
conducted by various methods such as direct welding, via connecting
member and the like.
The insulating member is preferably constituted by a first insulator,
a second insulator and an inorganic powder filled between the first
insulator and the second insulator, because this constitution has
excellent gas sealability and, even when the solid matters incoming
from outside the exhaust pipe collide with the electrode structure,
hardly reduces the gas sealability and insulating property. The
inorganic powder is filled preferably by pressurization. The specific
material for the inorganic powder is preferably talc, kaolin or
the like. Each of the first and second insulators preferably has
such a structure as to be able to hold the inorganic powder between
the electrode and the case. The first and second insulators can
be made of a ceramic material having a desired strength, for example,
an alumina material or a porcelain material. Preferably, the inorganic
powder is filled between the first and second insulators, for example,
by applying a load of at least 200 kg. Allowing the second insulator
to have different levels at the side being in direct contact with
the inorganic powder is preferable because the filled inorganic
powder does not get loose even when a heat cycle and/or a vibration
is applied thereto.
The gap between the insulating member and the electrode and the
gap between the insulating member and the case may be sealed with
a metal sealing material; and simultaneously therewith, a spring
member for absorbing the difference in thermal expansion between
the electrode, the case and the insulating material and a pressing
member for transmitting a load to the spring member may be provided
between the electrode and the case. By constituting the present
electrode structure as mentioned above, gas sealability can be maintained
by the metal sealing material and the difference in thermal expansion
between the electrode, the case and the insulating member can be
absorbed by the spring member. The fixation of the pressing member
to the electrode may be conducted by fitting a pressing member formed
in a nut shape, to the electrode, or by caulking or welding part
of the pressing member to the electrode.
The gap between the electrode and the case may be insulated by
coating an insulating coating material on at least one of the electrode
and the case, or on both of them. Pressure penetration of the electrode
coated with the insulating coating material, into the case is preferable
from the standpoint of gas sealability. The insulating coating material
is preferably alumina, a ceramic or the like. It is preferable to
use alumina by plasma spraying.
When the electrode is coated with the insulating coating material,
it is preferable for the gas sealability of the electrode to seal
the gap between the case and the insulating coating material with
a metal sealing material; when the case is coated with the insulating
coating material, it is preferable for the same reason to seal the
gap between the electrode and the insulating sting material with
the same metal sealing material.
Sealing the gap between the electrode and the case with an inorganic
powder is preferable for the gas sealability and impact resistance
of the electrode. The inorganic powder is filled preferably by pressurization,
as mentioned above.
The gas sealability of the electrode can also be obtained by sealing
the gap between the insulator, the case and the electrode with a
cement sealing material.
The conductive substance is typically a metallic honeycomb structure.
When the conductive substance is a metallic honeycomb structure,
the electrode structure of the present invention is an electrode
structure for an electric heater provided in, for example, a catalytic
converter for purification of automobile exhaust gas. Various conductive
substances other than metallic honeycomb structure can also be used.
The present invention is hereinafter described in more detail referring
to the embodiments shown in the drawings. However, the present invention
is in no way restricted to these embodiments .
FIG. 1 is a view showing an embodiment of the electrode structure
according to the present invention. In FIG. 1, 2 is a metallic housing;
4 is a case for holding an electrode; 6 is an electrode consisting
of a metal rod; 16 is a metallic connecting member; 18a is a first
insulator; 18b is a second insulator; 18d is an inorganic powder:
20 is a lead wire; 22 is a waterproof member; and 24 is a caulking
ring.
In the electrode structure shown in FIG. 1, the electrode 6 is
inserted into a hole formed in the metallic housing 2 and is fixed
to the case 4 connected to the metallic housing 2, via an insulating
member 18 constituted by the first insulator 18a, the second insulator
18b and the inorganic powder 18d filled between the first insulator
18a and the second insulator 18b. In the embodiment of FIG. 1, the
case 4 has a double structure in which a second case 4b is partially
inserted into a first case 4a and in which the second case 4b is
caulked at the circumference of the upper end via the caulking ring
24.
By using the caulking ring 24, the inorganic powder 18d can be
filled by pressurization without applying an excessive stress to
the second insulator 18b. It is preferable that the caulking ring
24 is made of a material having a thermal expansion coefficient
larger than that of the second insulator 4b, because, when the electrode
structure is heated, the caulking ring 24 can absorb the difference
in thermal expansion between the second insulator 4b and the insulating
member 18 and can ensure good sealability. It is also preferable
that the first case 4a and the second case 4b are fixed by welding
or the like over the entire circumference in order to prevent the
incoming of water from the gap between the two insulators. The fixation
is conducted preferably by laser welding over the entire circumference.
The waterproof member 22 is interposed between the case 4 and the
lead wire 20, and the case 4 is caulked from outside at the portion
where the waterproof member 22 is interposed between the case 4
and the lead wire 20. This can eliminate the gap between the case
4 and the waterproof member 22 and the gap between the waterproof
member 22 and the lead wire 20, and ensures the prevention of water
incoming from the gap between the case 4 and the lead wire 20. Between
the upper end of the electrode 6 and the lower end of the lead wire
20 is provided a connecting member 30 for electrical connection
between the electrode 6 and the lead wire 20. One end of the electrode
6 located inside the metallic housing 2 is connected to part of
a conductive substance (not shown in FIG. 1) via the metallic connecting
member 16.
The electrode structure of FIG. 1 is superior in assembling efficiency,
productivity and gas sealability. The structure hardly reduces the
gas sealability and insulating property even in collision with solid
matters incoming from outside the exhaust pipe, and is strong and
highly safe.
In the electrode structure of FIG. 1, when different levels 32
are formed at the lower side of the second insulator 18b, there
occurs no loosening of the filling state of the inorganic powder
18d filled between the first insulator 18a and the second insulator
18b, even when the structure undergoes a heat cycle and/or a vibration.
FIG. 2 is another embodiment of the waterproof structure between
the case and the lead wire. In this embodiment, a lead wire 20 is
covered with a first waterproof member 40 at the circumference;
the lower portion of the first waterproof member 40 is clamped with
a first case 44; round the upper portion of the first waterproof
member 40 is wound a waterproof tube 42 such as TEFLON (polytetrafluoroethylene)
tube or the like; the waterproof tube 42 is clamped with a second
case 46; and the second case 46 is caulked from outside at the portions
X and Y.
In this waterproof structure, in the portion X, since the waterproof
tube 42 is clamped between the first case 44 and the second case
46, difference in thermal expansion hardly occurs and waterproofness
is secured. Further, in the Y portion, since both the first waterproof
member 40 and the waterproof tube 42 are caulked together, no water
incoming occurs and very high waterproofness can be secured.
In an embodiment of FIG. 3, a one-piece case 4 is used in place
of the case 4 of double structure shown in FIG. 1; an insulating
member is interposed between the case 4 and an electrode 6; and
a waterproof member 22 is interposed between the case 4 and a lead
wire 20. The case 4 is caulked, via a caulking member 48, at the
portion close to the upper and of a second insulator 18b.
FIG. 4 is still another embodiment of the waterproof structure
between the case and the lead wire. In this embodiment, the covering
material 50 for a lead wire 20 functions also as a waterproof member,
and the covering material 50 is directly caulked from the circumference
of a case 4. It is necessary or preferable that the covering material
50 for the lead wire 20 has the above-mentioned properties of a
waterproof member. In this embodiment, therefore, the number of
parts can be reduced and improved assembling efficiency can be obtained.
FIG. 5 is an embodiment of the electrode structure according to
the present invention, wherein the gap between the electrode and
the insulating member (provided between the case and the electrode)
and the gap between the insulating member and the case are each
sealed with a metal sealing material.
In the electrode structure shown in FIG. 5, a first insulator 18a,
a second insulator 18b and a third insulator 18c are provided between
a first case 44 or a second case 46 and a lead wire 20 or an electrode
6; the gap between the third insulator 18c and the second case 46
and the gap between the third insulator 18c and the electrode 6
are each sealed with a metal sealing material 56; a coned disc spring
58 is supported by pressing members 60 as shown in FIG. 30, at the
top and the bottom; the upper pressing member 60 is supported by
a flange 62 formed at the lower end of a connecting member 30.
The waterproof structure in the electrode structure of FIG. 5 is
the same as shown in FIG. 1. The flange 62 provided at the lower
end of the connecting member 30 transmits, together with the pressing
member 60, a load applied to the electrode owing to the difference
in thermal expansion, to the coned disc spring 58 efficiently.
FIG. 6 is another embodiment of the electrode structure according
to the present invention, wherein the gap between the electrode
and the insulating member (provided between the case and the electrode)
and the gap between the insulating member and the case are each
sealed with a metal sealing material.
In the electrode structure shown in FIG. 6, the gap between an
electrode 6 and a case 4 is insulated by a first insulator 18a and
a second insulator 18b; the gap between the second insulator 18b
and the electrode 6 and the gap between the second insulator 18b
and the case 4 are each sealed with a metal sealing material 56.
The main differences of this electrode structure from the electrode
structure of FIG. 5 are that the case 4 is formed in one piece,
the electrode 6 has a portion 64 for supporting the first insulator
18a, and pressing members 60 are pressed onto a coned disc spring
58 by caulking the shoulder portion 66 of the case 4.
The fixation of pressing member 60 to electrode 6 may be conducted
also by, as shown in FIG. 7, forming a pressing member-holding portion
64 at a desired position of an electrode 6 and fitting, to the portion,
the inside of a pressing member 60 of partially-cut-ring shape (see
FIG. 30).
FIG. 8 is an embodiment of the electrode structure of the present
invention, wherein the electrode and the case are insulated by coating
the electrode with an insulating coating material by plasma spraying.
In this embodiment an electrode coated with an insulating coating
material 18f is inserted into a second case 46 under pressure. In
this electrode structure, the waterproof structure is the same as
shown in FIG. 1.
FIG. 9 is an embodiment of the present electrode structure, wherein
the gap between a first insulator 18a, a second insulator 18b and
a second case 46 is sealed with a cement sealing material 18e. By
having such a constitution, the electrode structure can have gas
sealability. In this electrode structure, the waterproof structure
is the same as shown in FIG. 1.
FIG. 10 is a cross-sectional view showing still another embodiment
of an electrode structure of an electric heater of the present invention.
In the figure, a first electrode 72 of an electric heater 71 on
which a catalyst is loaded faces a case (metallic housing) 73. The
case is provided with a negative screw by carving. A first peripheral
cylinder 74 having a hexagonal portion and a positive screw portion
is threadably attached to the aforementioned negative screw by means
of a washer 75a. The first peripheral cylinder 74 is unitarily joined
to a second peripheral cylinder 75 having a cross-section of ring.
The second peripheral cylinder 75 is unitarily joined to the third
peripheral cylinder 76. Thus, a case for accommodating and holding
an electrode is composed of the first peripheral cylinder 74, the
second peripheral cylinder 75, and the third peripheral cylinder
76. The length L from the bottom and of the first peripheral cylinder
74 to the top end of the third peripheral cylinder 76 is 40 mm or
more. Incidentally, the first electrode 72 is connected to a honeycomb
structure 77 of an electric heater 71 by means of a connecting member
145.
78 denotes a second electrode of a pole shape made of a metal such
as iron. The second electrode has a discoid protrusion 81 in the
upper-middle portion. A positive screw is formed in the base portion
79 by carving, thereby the second electrode is threadably attached
to the first electrode 72 having a negative screw. Further, the
second electrode 78 pierces an almost cylindrical, ceramic sleeve
(insulating member) 80 made of alumina or the like. The top end
of the ceramic sleeve 80 abuts on the protrusion 81.
To be specific, the ceramic sleeve 80 has a portion 80a having
steps in predetermined portions of the inner surface of the ceramic
sleeve 80. The inner surface around the top end is formed about
perpendicularly and the open end is slightly tapered. That is, in
the open end of the inner surface 86 of the ceramic sleeve 80, as
shown in FIG. 11, four tapered depressions 85 are formed. The depressions
85 are filled with a compressed ceramic powder 87. The second electrode
78 and the second peripheral cylinder 75 rotate unitarily.
Between the lower portion of the ceramic sleeve 80 and the first
peripheral cylinder 74 is positioned a first metallic sleeve 82.
Specifically, a protrusion 80b formed on the ceramic sleeve 80 is
locked by a notch formed on the first metallic sleeve 82. On the
top of the first metallic sleeve 82 is positioned a second metallic
sleeve 84 via a ceramic powder 83 such as talc, alumina, and magnesia.
The second metallic sleeve 84 abuts on the first peripheral cylinder
74. The top of the first peripheral cylinder 74 is caulked so that
the ceramic powder 83 between the first metallic sleeve 82 and the
second metallic sleeve 84 is compressed. The compressed ceramic
powder 83 ensures an electrical insulation against the outside.
In the gap over the protrusion 81 of the second electrode 78 between
the second electrode 78 and the second peripheral cylinder 75 is
filled up a glass insulator 82, which is a type of an elastic insulator
having thermally resistant properties, so as to ensure an electrical
insulation against the second peripheral cylinder 75.
A lead wire 89 is fixed to the top of the second electrode 78.
A covered portion 90 of the lead wire 89 is protruded. To the top
end of the third peripheral cylinder 76 is attached a rubber sealing
member 91 having a thermal resistance.
In the electrode structure of the embodiment, as shown in FIG.
12, B portion is crimped so as to unify the third peripheral cylinder
76 and the covered portion 90, C portion is caulked so as to unify
the second and the third peripheral cylinders 75 and 76, the glass
insulator 88, and the second electrode 78, and D portion is crimped
so as to unify the first and the second peripheral cylinder 74 and
75, the second metallic sleeve 84, and the second electrode 78.
The first peripheral cylinder 74 is rotated by turning a hexagonal
portion with a tool or the like so as to be threadably attached
to a case 73, thereby the second electrode 78 is threadably attached
to the first electrode 72. Thus, the second electrode 78 can be
easily incorporated into an electric heater 71. that is, the ceramic
powder 87 is pressed and covers the second electrode 78 by threaded
engagement of the first, the second, and the third peripheral cylinders
74, 75 and 76 with the case 73, and as a result, the second electrode
78 unitarily rotate with the first, the second, and the third peripheral
cylinders 74, 75, and 76, and threadably attached to the first electrode
72.
Since, the predetermined length L from the bottom end of the first
peripheral cylinder 74 to the top end of the third peripheral cylinder
76 (case for accommodating and holding an electrode) is specified
to 40 mm or more, a rubber sealing member 91 can be mounted on the
top of the third peripheral cylinder 76. That is, upon combustion
in an internal combustion engine or the like, a temperature of the
case 73 generally rises up to around 900.degree. C.-100.degree.
C., while a heat-resisting temperature of a rubber sealing member
is about 250.degree. C. even if the rubber is a fluoro rubber having
a thermal resistance, such as polytetrafluoroethylene (PTFB), etc.
Therefore, it is difficult to mount the rubber sealing member on
the portion near the case 73. Sealing around the electrode with
a rubber sealing member is required to make an electrode structure
of an electric heater waterproof. However, even a rubber sealing
member having a thermal resistance has a heat-resisting temperature
of at most around 250.degree. C., and therefore, a rubber sealing
member cannot be incorporated into an electrode structure and there
has been no measure for a waterproof device. Therefore, water penetrated
into the periphery of an electrode of an electric heater when an
automobile ran through a puddle or upon a flood, thereby causing
misoperation of heater.
An electric heater was measured for temperatures near a case. The
present inventors have found, from the results of the experiment,
that temperature is 200.degree. C. or lower in the place having
distance of 40 mm or more from a periphery of the case as shown
in FIG. 13. Accordingly, in the present embodiment, the predetermined
length L was specified to 40 nm or more so that the temperature
of a rubber sealing member 91 does not reach its heat-resisting
temperature. That is, the second electrode 78 is provided so as
to protrude from the first electrode 72, the second electrode pierces
the ceramic sleeve 80, sealing against exhaust gas and electrical
insulating are achieved by ceramic powders 83 and 87 and a glass
insulator 88, and protection from water was achieved by mounting
a rubber sealing material 91 on the top end of the third peripheral
cylinder 76, the rubber sealing material having a distance of 40
mm or more from the first electrode 72. Since the first, the second,
and the third peripheral cylinders 74, 75, and 76 are unified with
the second electrode 78 or the like, by threadably attaching the
first peripheral cylinder 74 to the case 73 by rotating the hexagonal
portion, the second electrode is simultaneously connected with the
first electrode 72 and can be easily incorporated into the electrode
structure.
FIG. 14 shows still another embodiment of an electrode structure
of the present invention. A depression is formed between a ceramic
sleeve 92 and a first peripheral cylinder 74. A ceramic powder 93
is filled in the depression. On the ceramic powder 93 is placed
a metallic sleeve 94, which abuts on the first peripheral cylinder
74. Like the aforementioned embodiment shown in FIG. 10, a metallic
sleeve 94 and the first peripheral cylinder 74 are caulked, thereby
compressing a ceramic powder 93 and ensuring an electrical insulation
or the like. The top portion of a second electrode 95 is formed
to have a shape of hexagon as shown in FIG. 15 or a rectangle as
shown in FIG. 16, or a shape having a hexagonal hole (not shown).
The second electrode 95 is connected with a first electrode 72 by
a predetermined tool. The upper portion of the ceramic sleeve 92
is tapered off to the top. A glass insulator 96 is filled up in
a space formed by the tapered portion of the ceramic sleeve 92,
a second peripheral cylinder 75, and the second electrode 95, thereby
the electrode structure is electrically insulated and sealed against
exhaust gas.
In the aforementioned embodiment shown in FIG. 14, the second electrode
95 is fixed to the first electrode 72 by a threaded engagement.
However, as an embodiment shown in FIG. 17, a second electrode 97
may be connected to a first electrode 98 by welding (solder 99).
Incidentally, the present invention can be applied to both an electric
heater having two electrodes and an electric heater having one electrodes.
The former is shown in FIG. 18, and the latter is shown in FIG.
19 in which only an end of the electrode is attached to the heater.
In the present electrode structure, the electrode and the lead
wire are connected by various methods. Embodiments of such connecting
methods are shown in FIGS. 23-29.
In FIG. 23, an electrode 6 and a lead wire 20 are connected via
a connecting member 30. The connecting member 30 is fixed to the
lead wire 20 by the nail portion 68 of the connecting member 30
formed at the one end. The supporting portion 70 of the connecting
member 30 formed at the other end is curved outwardly and is projection-welded
to the electrode 6 via the curvature.
In FIG. 24, a connecting member 30 is fixed to a lead wire 20 by
the nail portion 68 of the connecting member 30 formed at the one
end and is fixed to an electrode 6 by caulking, from outside, the
electrode-holding portion 70 of the connecting member 30 formed
at the other end. The gap between the electrode 6 and the connecting
member 30 may be spot-welded.
In FIG. 25, a connecting member 30 is fixed to a lead wire 20 by
the nail portion 68 of the connecting member 30 formed at the one
and, and is fixed to an electrode 6 by engaging the female screw
portion of the connecting member 30 formed at the other end, with
the male screw portion formed on the upper portion of the electrode
6.
In FIG. 26, a lead wire 20 is welded directly to an electrode 6.
In FIG. 27, one end of an electrode 6 is formed in a cylindrical
shape; into the cylindrical portion is inserted one end of a lead
wire 20; the cylindrical portion is caulked from outside; thereby,
the lead wire 20 is fixed to the electrode 6.
FIG. 28 is an embodiment in which an electrode 6 and a lead wire
20 are connected at right angles. A nut-shaped connecting member
30 is connected to one end of a lead wire 20, and the connecting
member 30 is fixed to one end of an electrode 6 by the use of a
bolt 52.
FIG. 29 is also an embodiment in which an electrode 6 and a lead
wire 20 are connected at right angles, as in FIG. 28. At one end
of a lead wire 20 is formed an electrode-holding portion 70 having
a hole 54 capable of accommodating one end of an electrode 6, and
the hole 54 and one end of the electrode 6 are engaged and connected
with each other.
[Evaluation]
The following water absorption test was conducted for the electrode
structure of FIG. 1 (an embodiment of the present electrode structure)
and a conventional electrode structure shown in FIG. 21(a).
A water absorption test was conducted by allowing an electrode
structure to stand in a state of 100% humidity and measuring the
change with time, of insulation resistance between the electrode
and the case. As a result, the present electrode structure maintained
a high insulation resistance of 1 M.OMEGA. or more even after having
been allowed to stand for 200 minutes; in contrast, in the conventional
electrode structure, the insulation resistance decreased to less
than 1 M.OMEGA. after having been allowed to stand for 30 minutes.
As stated above, the electrode structure of the present invention,
into which one end of a lead wire connecting thereto is inserted,
is superior in assembling efficiency, electrical insulation, exhaust
gas sealability and waterproofness. Therefore, when an automobile
having an electric heater using such an electric structure is driven
on puddles of roads or during flooding, there is no water adhesion
onto the electrode and misoperation of the heater can be prevented. |