Electric heating – Heating devices – With heater-unit housing – casing – or support means
Reexamination Certificate
2001-05-11
2002-08-13
Walberg, Teresa (Department: 3742)
Electric heating
Heating devices
With heater-unit housing, casing, or support means
C219S532000, C219S541000, C219S402000, C392S487000, C373S114000, C373S119000, C432S209000
Reexamination Certificate
active
06433318
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed toward an electric heating apparatus and, more particularly, to an apparatus having a resistance wire with an in-line thermostatic electric current control element.
2. Related Art
Electric heater assemblies having a resistance wire with in-line thermostats are known in the art. A widely used example of such heater assemblies employs a thermostat with a pair of terminals, each having a right-angled bend, with the right-angled portion of each being secured by a pair of threaded nuts to the threaded distal end of a mounting screw. Typically, there is a lock washer on all contacting faces of the threaded nuts.
One example of this prior art arrangement is disclosed in U.S. Pat. No. 3,770,939 (the '939 patent”), and is shown in prior art
FIGS. 1A
,
1
B and
1
C of this disclosure. Referring to the prior art
FIG. 1A
, and the enlargement of its region
1
B shown by
FIG. 1B
, the prior art thermostat
10
has terminal flanges
14
and
16
extending therefrom, each having proximal and distal portions, labeled as
14
A and
14
B, and
16
A and
16
B, respectively. Distal portions
14
B and
16
B extend at right angles from their respective proximal portions
14
A and
16
A. Viewed from the
FIG. 1B
side projection AA, which is shown in
FIG. 1C
, the distal portion
16
B has a U-shaped cut-out portion
16
U, as does
14
B (not shown).
As shown in prior art
FIG. 1A
, a ladder frame
17
supports a resistive wire heating element
18
using a plurality of first tubular insulating bushings
20
. The bushings
20
are typically formed of ceramic. The frame
17
also supports a pair of second tubular insulating bushings
22
and
24
.
Referring to prior art
FIG. 1B
, a first thermostat wire connection screw
26
, having a head
26
A and a threaded distal end
26
B, extends through the first ceramic thermostat support bushing
22
. Likewise, a second thermostat wire connection screw
28
extends through the second ceramic thermostat support bushing
24
. A heater resistance wire end portion
30
is welded to the head
26
A of the first screw
26
. A first threaded nut
32
, with an associated lock washer
34
secures the first screw
26
to its ceramic bushing
22
. The second thermostat mounting screw
28
is secured to its corresponding bushing
24
by a second threaded nut
36
and associated lock washer
38
.
As shown in the prior art
FIG. 1B
, a fuse element
40
connects to the head
28
A of the second thermostat mounting screw by welding or by wrapping the connecting end
40
A of the fuse under the screw head
28
A, before tightening the second threaded nut
36
. If the connecting end is wrapped under the screw head, as in
FIG. 1B
, a flat washer
41
is preferable.
The thermostat
10
within prior art
FIGS. 1A-1B
is mounted as follows:
The first and second thermostat mounting screws
26
and
28
are secured to their respective bushings
22
and
24
by tightening the first and second threaded nuts
32
and
36
. After this assembly, a spacing A is between the inner faces of the first and second threaded nuts. Referring to
FIG. 1B
, the distance labeled A′ is from the distal portion
14
B of the first flange
14
of the thermostat
10
to the distal portion
16
B of the second flange
16
. The dimension A′ is slightly less than A. Referring to
FIG. 1C
, which depicts the U-shaped cutout
16
U of the second flange
16
, the cut-out is shaped and dimensioned to accommodate the threaded portion
28
B of the second screw
28
. Likewise, the cut-out (not shown) in the first flange
14
accommodates the threaded portion
26
B of the first screw
26
. Because of the dimensions A and A′, and the U-shaped cutouts in the thermostat flange distal portions
14
B and
16
B, the thermostat
10
can be placed into the position shown in
FIGS. 1A and 1B
. After such positioning the distal portion
14
B of the first flange
14
of thermostat
10
is secured by a third nut
42
, typically with a pair of lock washers (not shown), one on each side of the distal portion
14
B flange. In a mirror arrangement, the distal portion
16
B of the second flange
16
is secured by a fourth nut
44
, also typically with a pair of lock washers (not shown).
Although the above-described prior art structure mounts the thermostat
10
to the frame
17
in line with the heating element, there are shortcomings. One is the number of parts, namely six lock washers, one flat washer, four threaded nuts, and two screws. This quantity of parts creates and carries numerous costs, including vendor selection and monitoring costs, inventory costs, and quality control costs.
Another shortcoming is that the manual labor required to assemble its plurality of parts is time intensive. More specifically, the nuts
32
,
36
,
42
and
44
must be hand tightened by applying repeated short swing rotations with a small open-ended wrench.
Another shortcoming is that the heater resistance wire end portion
30
is welded to the head
26
A of the first screw
26
, and typically the welding is performed before the thermostat
10
is installed. Still further, the end of the fuse element
40
must be bent in two in two planes using an off-line subassembly operation such as, for example, hand-bending with a pair of needle-nose pliers, to properly wrap the end around the screw head
28
A. This bending operation adds manufacturing cost.
Referring to prior art
FIGS. 1A-1B
, still another shortcoming with such structure is that external connection terminals
46
are typically supported by third bushings
48
. The third bushings
48
are different from the second bushings
22
and
24
which support the first and second thermostat screws
26
and
28
. The result is a further increase in the parts count.
SUMMARY OF THE INVENTION
An object of the present invention is a heater apparatus having a frame supporting a resistance wire with an in-line thermostat having a reduced parts count as compared to the prior art.
Another object is a heater apparatus having a frame supporting a resistance wire with an in-line thermostat that is easier and quicker to assemble than the thermostat mounting apparatus of the prior art.
Still another object is a heater apparatus having a frame supporting a resistance wire with an in-line thermostat and an in-line fuse, with a mounting structure for the fuse having a reduced part count as compared to the prior art.
Another object is a heater apparatus having a frame supporting a resistance wire with an in-line thermostat and with external connection tabs mounted to the frame, where the thermostat and connection tab mounts employ identical components.
Yet another object of the present invention is a heater apparatus having a frame supporting a resistance wire with an in-line thermostat, employing a standard thermostat with flat terminals which have a threaded hole added for accepting a screw.
Still another object of the present invention is a heater apparatus having a frame supporting a resistance wire with an in-line thermostat, with a thermostat mounting structure that does not require welding attachments to the thermostat terminals.
A further objective of the present invention is a heater apparatus having a frame supporting a resistance wire with an in-line thermostat, employing uniform flat profile terminals for crimping to resistance wire ends and fuse wire ends, and for functioning as external electrical connection tabs and for single-screw attachment to the thermostat terminals.
Related to the above-identified objective, a still further objective is a structure for accommodating and mounting an in-line thermostat in a selectable rotational orientation. The selectable orientation provides improved access for servicing and replacing the thermostat in an installed heater assembly.
An example embodiment of the invention includes a metal frame supporting a plurality of first insulators supporting a heater element resistance wire. The frame further supports a pair of thermostat support insulators, or bush
Fuqua Shawntina T.
Walberg Teresa
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