Abstrict
A self-regulating electric heater includes a plurality of ceramic
PTC resistors having flat contact surfaces on their opposite sides
disposed between a pair of flat electrode plates with the contact
surfaces in electrical and thermal contact with the plates. A support
frame of electrically insulative material is formed with receiving
portions respectively for the PTC resistors and the electrode plates
to positions and hold the resistors and plates in assembled relationship
for insertion as a single assembly into a closed-end cavity in a
metallic radiator with the electrode plates in good heat transfer
contact with the inner wall surface of the cavity. The frame is
provided with spring seats receiving springs which coact with the
radiator to bias the support frame into the cavity to insure stable
intimate thermal contact between the electrode plates and inner
cavity wall. The PTC resistors may be provided with chamfered edges
along the peripheries of the flat contact surfaces thereof. The
electrode plates may be provided with a beveled corner adjacent
to the closed end of the cavity to avoid stress between the plates
and cavity wall when the support frame is inserted into the cavity.
Claims
What is claimed is:
1. A self-regulating electric heater comprising:
a radiator formed of a dimensionally stable material, said radiator
having a cavity;
a pair of electrode plates;
at least one PTC resistor arranged in electric and heat transfer
contact with said electrode plates; and
a support frame of electrically insulative material, said frame
being formed with receiving portions respectively for said at least
one PTC resistor and the electrode plates for holding the same in
said electric and thermal contact, said frame being received in
said cavity with both of said electrode plates in heat transfer
contact with an inner wall of the cavity:
spring means, having two ends, one end of which is connected to
said radiator; and
spring seat means on said support frame for receiving the other
end of said spring means, said spring means urging the support frame
into the cavity in the direction of biasing the electrode plates
into intimate heat transfer contact with the inner wall of the cavity.
2. The self-regulating electric heater as set forth in claim 1,
wherein said support frame is provided with a separate receiving
portion for each one of said at least one PTC resistor electrically
connected between said electrode plates.
3. The self-regulating electric heater as set forth in claim 1,
wherein said support frame is in the form of a plate member having
a shape corresponding to the shape of the cavity of the radiator,
said plate member is formed in opposite surfaces with recesses defining
said receiving portions for the electrode plates and is formed therein
with a penetrating hole defining the receiving portion for each
of said at least one PTC resistor, each PTC resistor being received
in a hole and having substantially flat contacting surfaces on the
respective opposite sides thereof, said penetrating hole having
both its ends open into said recesses respectively and having a
depth smaller than the thickness of the PTC resistor such that the
electrode plates in said recesses are in electric and heat transfer
contact with substantially the entire flate surfaces of the PTC
resistor in said hole, respectively.
4. The self-regulating electric heater as set forth in claim 1,
wherein each of said electrode plates is formed with a terminal
portion which extends outwardly of the cavity for supplying electric
power to said at least one PTC resistor.
5. The self-regulating electric heater as forth in claim 1, wherein
said at least one PTC resistor has substantially flat contact surfaces
on the opposites sides thereof and is made and said at least one
PTC resistor has chamfered edges respectively along the peripheries
of said flat contact surfaces.
6. A self-regulating electric heater comprising:
a radiator formed of a dimensionally stable material, said radiator
having a cavity;
a pair of electrode plates;
at least one PTC resistor arranged in electirc and heat transfer
contact with said electrode plates; and
a support frame of electrically insulative material, said frame
being formed with receiving portions respectively for said at least
one PTC resistor and the electrode plates for holding the same in
said electric and thermal contact, said frame being received in
said cavity with both of said electrode plates in heat transfer
contact with an inner wall of the cavity, wherein said support frame
is in the form of a plate member having a shape corresponding to
the shape of the cavity of the radiator, said plate member is formed
in opposite surfaces with recesses defining said receiving portions
for the electrode plates and is formed therein with a penetrating
hole defining the receiving portion for each of said at least one
PTC resistor, each PTC resistor being received in a hole and having
substantially flat contacting surfaces on the respective opposite
sides thereof, said penetrating hole having both its ends open into
said recesses respectively and having a depth smaller than the thickness
of the PTC resistor such that the electrode plates in said recesses
are in electric and heat transfer contact with substantially the
entire flat surfaces of the PTC resistor in said hole, respectively,
wherein said cavity has a closed end and said at least one PTC resistor
is made of ceramic material and wherein each of the electrode plates
has beveled corner edges adjacent to said closed end of said cavity
of the radiator for avoiding excess stress from being between the
electrode plates and the wall of the cavity when th support frame
is assembled into the cavity.
7. The self-regulating electric heater as set forth in claim 6,
wherein said at least one PTC resistor is made of cermic material
and said at least one PTC resistor has chamfered edges respectively
along the peripheries of said flat contact surfaces on the opposite
sides thereof.
Description BACKGROUND OF THE DISCLOSURE
1. Fields of the Invention
The present invention relates to a self-regulating electric heater
employing a resistor of positive temperature coefficient of resistivity
(hereinafter referred to as PTC resistor) as a heating element,
and more particularly to a self-regulating electric heater such
as may be adapted to an oral inhalation device for producing steam
which is to be inhaled in spray form together with suitable medicines
carried on the steam.
2. Description of the Prior Art
Such PTC resistor has been found to be advantageous when used as
heaters because of its self-regulating characteristic. However,
the size of the PTC resistor is practically limited to be comparatively
small so that the amount of heat dissipated therefrom is limited
to a lower level. Therefore, there have been proposed for the purpose
of increasing heat transfer efficiency many schemes to reduce as
much as possible heat loss in transferring the heat derived from
the PTC resistor to a casing to which it is attached together with
electrodes supplying electricity to the PTC resistor and from which
the heat is dissipated for heating purpose. Among the above schemes
is to have the electrodes in pressing contact with the casing to
provide a close and stable heat transfer relation therebetween as
disposing the PTC resistor between the electrodes. Exemplary of
the above is shown in U.S. Pat. No. 4,147,927 for a self-regulating
heating element in which two electrically and thermally conductive
flat strips or electrodes parallel to and spaced from each other
are positioned in a longitudinally arranged tubular body with one
or more PTC resistors between and in electrical and heat-exchange
contact with the parallel flat strips. The flat strips are inserted
in the tubular body to be in resilient contact with the inner surface
of the body while the PTC resistors are fixed between the strips
by respective layers of solder. However, such soldering connection
between the PTC resistors and the strips should require a maximum
contacting area therebetween for maintaining the heat transfer efficiency,
which can be only achieved with a careful and skillful soldering
technique, therefore rendering the assembly of the heater cumbersome.
Also from the point of view that the solder is likely to melt at
the operating temperature of the heater so as to render the PTC
resistors no longer fixed on the strips, the PTC resistors are susceptible
to possible mechanical shocks acted upon the heater such that they
might be moved out of optimum electrical and heat transfer relation
from the strips, rendering the heater ineffective. But without such
soldering connection, the assembly of the members into the body
would be much complicated since the strips and the PTC resistors,
which are the separate members, must be inserted in the body at
a time in such a way as to be correctly positioned with respect
to each other and to the body. Accordingly, for satisfying easier
assembling as well as stable and effective thermal contact between
the PTC resistors and the electrodes, it is required to support
the PTC resistor in correct position relative to the electrodes
without using the solder and the like prior to assembling these
members into the body or casing. However, there is no provision
in the prior art for the above construction.
SUMMARY OF THE INVENTION
The above disadvantages have been obviated by the present invention
which introduces a unique support frame for mounting thereon at
least one PTC resistor and electrode plates supplying electric power
thereto respectively at fixed positions relative to each other.
The support frame carrying the above members is received in a cavity
of a radiator so that the electrode plates are in heat transfer
contact with the inner surface of the radiator defining the cavity.
On the side of the support frame, the PTC resistor and the electrode
plates are disposed in respective receiving portions so that the
PTC resistor is kept in electrical and heat transfer relation to
the electrode plates. Accordingly, the PTC resistor and the electrode
plates are cooperative with the support frame to provide a single
structure which can be easily inserted in the cavity of the radiator
as maintaining the PTC resistor in proper position relative to the
electrode plates during the assembly. The PTC resistor thus kept
in fixed position relative to the electrode plates on the support
frame will not become out of the initial proper contacting relation
with the electrode plates when subjected to possible shocks applied
to the heater after the assembly.
It is therefore a primary object of the present invention to provide
a self-regulating electric heater capable of being easily assembled
yet assuring stable and shock-free contact relationship of the PTC
resistor with the electrodes thereof.
In a preferred embodiment, said support frame is formed with spring
seats each for receiving the one end of a spring which has the other
end connected to the radiator. The spring serves to urge the support
frame into the cavity in the direction of biasing the electrode
plates into close heat transfer contact with the inner surface of
the radiator. With the result of this, the support frame carrying
the PTC resistor and the electrode plates is held firmly in the
cavity to make the electrode plates kept in close contact with the
inner surface of the cavity, eliminating the shaking of the electrode
plates in the cavity which would otherwise impair the efficiency
to a certain extent in transmitting the heat from the electrode
plates to the radiator.
It is accordingly another object of the present invention to provide
a self-regulating electric heater which keeps maximum heat transfer
relation between the electrode plates and the radiator over a longer
time period of use and in which the spring employed for this purpose
can be readily seated on the support frame to facilitate the assembly
of the heater.
Said support frame consists of a plate member to be inserted in
the correspondingly shaped cavity of the radiator and is formed
in opposite surfaces thereof with recesses respectively for receiving
the electrode plates and also formed therein with at least one penetrating
hole for receiving the PTC resistor in the form of a flat mass having
substantially flat contacting surfaces spaced from one another on
the opposite sides thereof. Said hole for the PTC resistor is shaped
to be open at its both ends into the respective recesses and to
have a depth smaller than the thickness of the PTC resistor such
that the electrode plates in said recesses can be in electric and
heat transfer contact with substantially the entire flat surfaces
of the PTC resistor in said hole, respectively, whereby the PTC
resistor can be held by the support frame in such a manner as to
be kept in maximum heat transfer relation with the respective electrode
plates.
It is a further object of the present invention to provide a self-regulating
electric heater which assures maximum heat transfer relation between
the PTC resistor and the electrode plates and therefore between
the PTC resistor and the radiator.
In addition, each of said electrode plates is formed with a terminal
portion which extends outwardly of the cavity for supplying electric
power to the PTC resistor. This facilitates the electrical connection
of the heater with a power source, which is a still further object
of the present invention.
In the present invention, there are disclosed still other useful
features including schemes for protecting the PTC resistor, which
is in most cases is fragile, from being damaged due to forces possibly
acting between the radiator and the support frame at the time of
inserting the support frame in the cavity of the radiator.
These and other advantages become more apparent from the following
detailed description of the embodiment when taken in conjunction
with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front view, partly in section and partly in elevation,
showing a self-regulating electric heater according to a preferred
embodiment of the present invention;
FIG. 2 is a side view, partly in section and partly in elevation,
of the above heater;
FIG. 3 is an exploded view in perspective representation of the
above heater;
FIG. 4 is a bottom view of the above heater;
FIG. 5 is a front view of a support frame with electrode plates
mounted thereon employed in the above heater;
FIG. 6 is a sectional view taken along line 6--6 of FIG. 5;
FIG. 7 is a sectional view taken along line 7--7 of FIG. 5;
FIG. 8 is a front view of a support frame with electrode plates
mounted thereon in accordance with a modification of the above embodiment;
and
FIG. 9 is a sectional view taken along line 9--9 of FIG. 8.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
Referring now to FIGS. 1 to 3, there is illustrated a self-regulating
electric heater in accordance with a preferred embodiment of the
present invention. The heater comprises a radiator 1 formed with
a pair of parallel cavities 2 each for receiving a support frame
10 of insulative material which carries thereon two pieces of PTC
resistors 20 and a pair of electrode plates 30 in such a manner
that each PTC resistor 20 is in electrical and heat transfer contact
with the electrode plates 30. The radiator 1 is made of a high thermal
conductive material such as zinc and aluminium and is shaped by
the known die-casing method to have said cavities 2 each in the
form of a laterally elongated and deep configuration with a generally
inverted V-shaped cross section closed at the upper end and opened
at the lower end, each cavity 2 defining on the upper surface of
the radiator 1 correspondingly shaped rib 3 and being narrower toward
the rounded top than at the lower end defining a rectangular opening
through which the said support frame 10 is inserted. Formed in the
peripheral portion of the radiator 1 are holes 4 through which fasteners
such as screws are inserted for fixing the radiator to a device
utilizing the heater. An extension plate or lug 5 with holes 6 is
also provided for fixing the radiator 1.
Said support frame 10 is made of electrically insulative and heat-resistant
material, for example, polyphenylene sulfide in the form of a plate
member with a wedge-shaped cross section at the longitudinal ends.
Rectangular recesses 11 respectively for receiving therein said
electrode plates 30 are formed in the opposite sides of the support
frame 10 in such a way that each recess 11 leaves therearound a
peripheral rim 12 which is only interrupted at 13 intermediate the
length of the lower edge of support frame 10 and which has at its
side portions inclined surfaces conforming with the inner wall of
said cavity 2. Also formed in the support frame 10 are spaced holes
14 each of which is opened into the recesses 11 on both sides of
the support frame 10 for receiving one PTC resistor 20. Said PTC
resistor 20 is in the form of a rounded disk-like mass made of a
ceramic material to have on the opposite sides thereof contacting
surfaces which are substantially flat and spaced from each other.
Each of said holes 14 is designed to have a depth less than the
thickness of the PTC resistor 20 to a slight extent, so that the
PTC resistor 20, when received in the hole 14, has its contacting
surfaces projecting slightly into the recesses 11, whereby substantially
the entire contacting surfaces of the PTC resistors 20 are in electrical
and heat transfer contact with the electrode plates 30 received
in the adjacent recesses 11, as shown in FIG. 6.
Each of said electrode plates 30 is made of a high thermal conductivity
material, for example, copper to be in the form of a rectangular
plate with a wedge-shaped cross section defined by a vertical surface
on one side and an inclined surface with respect thereto on the
other side thereof and is so dimensioned that, when fitted in each
one of said recesses 11 with the vertical surface being in electrical
and thermal contact with the contacting surfaces of the PTC resistors
20, said inclined surface projects slightly on the general outer
surface of the support frame 10, as shown in FIGS. 6 and 7, while
its periphery being within the confines of said rim 12, as shown
in FIG. 5. Extending integrally from the lower edge of each electrode
plate 30 is a terminal lug 32 which projects through the interruption
13 of said rim 12 into one of tubular sockets 15 of the support
frame 10 in which it is connected to one end of a lead 33 for receiving
electric current from a suitable power source. Said tubular sockets
15 extends integrally from the intermediate portion of the bottom
of the support frame 10 to be arranged side by side at such portions
that they project outwardly of the cavity 2 or downwardly below
the bottom surface of the radiator 1 when the support frame 10 is
received in the cavity 2. Also integral with the support frame 10
are a pair of bosses 16 which project downwardly on both sides of
said sockets 15, each serving as a spring seat on which is fitted
the one end of a coil spring 17 of heat-resistant stainless steel
used to fasten the support frame 10 to the radiator 1.
The support frame 10 after receiving the PTC resistors 20 and the
electrode plates 30 in respective positions is wrapped by an insulative
and heat-resistant adhesive film 18 of polyimide-amide in such a
manner that the surfaces of the electrode plates 30 are fully and
tightly covered thereby, said film 18 is further wrapped by another
insulative sheet 19 of high thermal conductive material such as
a silicon rubber having alumina particles dispersed therein to thereby
constitute a heater block which can be inserted as a single structure
into the cavity 2. With this arrangement, double-insulation can
be effected between the electrode plates 30 on the support frame
10 and the wall of the cavity 2 of the radiator 1. In the figures,
although the two support frames 10 are wrapped by the common film
18 and the common sheet 19, they may be wrapped separately by the
film 18 and the sheet 19.
Said radiator 1 is provided on its bottom with integral studs 7
with screw holes 8 which are located between the bottom openings
of the cavities 2 and spaced longitudinally of the radiator 1 and
which receive respectively screws 24 fixing brackets 25 onto the
bottom of the radiator 1. It is these brackets 25 against which
the opposite ends of said springs 17 bear respectively so that said
heater blocks are fixedly held within the respective cavities 2.
A pair of said springs 17 urge each heater block into the corresponding
cavity 2 in such a way that the electrode plates 30 on both sides
of the block are pressed through said insulative film 18 and sheet
19 against the inner wall of the cavity 2, as shown in FIG. 1. This
makes the electrode plates 30 to be in close heat transfer relation
to the radiator 1 while the radiator 1 is kept insulated for efficiently
dissipating the heat derived from the PTC resistors 20 to radiator
1 through the electrode plates 30 in a safe manner. It is noted
at this time that the biasing force of the springs 17 also acts
to press the electrode plates 30 against the PTC resistors 20 as
a result of the wedge bonding of the electrode plates 30 to the
inner wall of the cavity 2 for ensuring close electric and thermal
relation therebetween which is free from possible shocks applied
to the heater. Thus, the electrode plates 30 are kept over the operating
life of the heater to be in optimum electrical and heat transfer
relation to the PTC resistors 20 as well as to be in optimum heat
transfer relation to the radiator 1, enabling the heater to operate
at its maximum efficiency during the use thereof.
In the present embodiment, each electrode plate 30 is provided
respectively at its upper corner portions with bevelled edges 34,
as shown in FIGS. 3 and 5, to eliminate the possibility of creating
a pressure point between the electrode plate 30 and the inner surface
of the cavity 2. Said corner portions 9 of the cavity 2 are not
biased when the heater block is biasingly received in the cavity
2 and would otherwise certainly exert forces on an electrode plate
30 without said bevelled edges 34 or without the upper corner portions
of the electrode plate 30 being cut away. Such forces, if present,
would in turn adversely damage the PTC resistors that are held in
close contact with the electrode plate 30 and are fragile due to
their ceramic construction. Accordingly, said bevelled edges 34
are found to be advantageous for avoiding the application of such
forces to the electrode plates 30 and to the PTC resistors 20, thus
protecting the PTC resistors 20 from being damaged.
FIGS. 8 and 9 show a modification of the above embodiment in which
chamfered edges 22 are formed along the peripheries of the contacting
surfaces engaged by electrodes 30A on both sides of each PTC resistor
20A or along the portions that are most sensible for the above-mentioned
forces. Thus, this modification provides an alternative measure
of protecting the PTC resistor 20A by forming the chamfered edges
22 thereon instead of forming said bevelled edges 32 on the electrode
plate 30 as seen in the above embodiment. |