US 3848213 A
A time delay relay is disclosed in which bimetal snap disc actuators are heated by a PTC heater to cause the operation of an associated switch after a predetermined time delay interval. The bimetal snap discs are supported in metal retaining cups positioned on opposite sides of the heater. The retaining cups function to support the snap discs, position the heater, provide an electrical connection for the heater, and to provide a heat conducting flow path between the heater and each associated disc. In one embodiment, a single snap disc assembly is positioned on each side of the heater. In another embodiment, the assemblies provide two separate bimetal snap discs on each side of the heater.
Description (OCR text may contain errors)
United States Patent Schmitt [4 1 Nov. 12, 1974 TIME DELAY RELAY  Inventor: Donald J. Schmitt, Mansfield, Ohio  Assignee: Therm-O-Disc Incorporated,
Mansfield, Ohio  Filed: Oct. 15, 1973  Appl. No.: 406,539
 U.S. Cl. 337/107, 337/354  Int. Cl. H0lh 71/22  Field of Search 337/59, 75, 102, 107, 354, 337/355  References Cited UNITED STATES PATENTS 3,489,976 l/197O Marcoux 337/102 3,500,275 3/1970 Oravec.. 337/75 3,582,853 6/1971 Morris 337/354 X 3,713,062 l/1973 Butler ct al. 337/107 Primary Examiner J. D. Miller Assistant ExaminerFred E. Bell Attorney, Agent, or Firm-McNenny, Farrington, Pearne & Gordon [5 7] ABSTRACT A time delay relay is disclosed in which bimetal snap disc actuators are heated by a PTC heater to cause the operation of an associated switch after a predetermined time delay interval. The bimetal snap discs are supported in metal retaining cups positioned on opposite sides of the heater. The retaining cups function to support the snap discs, position the heater, provide an electrical connection for the heater, and to provide a heat conducting flow path between the heater and each associated disc. In one embodiment, a single snap disc assembly is positioned on each side of the heater. In another embodiment, the assemblies provide two separate bimetal snap discs on each side of the heater.
13 Claims, 3 Drawing Figures TIME DELAY RELAY BACKGROUND OF THE INVENTION This invention relates generally to relay devices and more particularly to a novel and improved time delay relay employing a plurality of bimetal snap disc actuators, in combination with a single PTC heater.
PRIOR ART It is known to combine a PTC heater and a bimetal snap disc operated switch to provide a time delay relay or sequencer. The US. Letters Pat. No. 3,489,976 discloses such a device. It is also known to provide a multiple disc device as illustrated in the US. Letters Pat. No. 3,500,275 with a PTC heater to provide a time delay relay in which a first switch operates after a first time interval, and a second switch operates after a second and longer time delay interval. In such latter device, a single heater element provides two different time delay intervals. In both such known devices, the PTC heater works only from one side.
SUMMARY OF THE INVENTION In accordance with the present invention, a time delay relay is provided in which one or more bimetal snap discs are positioned on each side of a PTC heater, so that the heater functions from both sides to operate snap discs selected to provide the desired time delay intervals. In the illustrated preferred embodiments, metallic disc retainers function to position the associated disc, to provide a good heat conducting path between the heater and the associated disc, and also to provide the electrical connections for the heater. In one illustrated embodiment, a single disc is mounted on each side of a PTC heater. The two discs are each selected to provide a predetermined time delay. Usually the time delay interval of one disc exceeds the time delay interval of the other disc.
In a second illustrated embodiment, two bimetal snap discs are located on each side of the PTC heater. In this embodiment, there are four separate snap discs which are all operated by the single heater. The various snap discs are selected to produce the desired delay interval with each disc operating with a different delay than the other discs. Consequently, four separate and distinct time delay intervals are obtained with the second embodiment of this invention.
BRIEF DESCRIPTION OF THE DRAWINGS 'FIG. 1 is a side elevation in longitudinal section illustrating a first embodiment of this invention in which a single bimetal snap disc is mounted on each side of a PTC heater;
FIG. 2 is a fragmentary perspective view of one of the disc retaining cups illustrated in FIG. 1; and
FIG. 3 is a side elevation in longitudinal section of a second embodiment of this invention in which two bimetal snap discs are mounted on each side of the single PTC heater.
DETAILED DESCRIPTION OF THE DRAWINGS Referring to FIG. 1, the first illustrated embodiment of this invention includes a pair of identical switch bodies and 11 each of which supports a switch 12 and 13, respectively. Each of the switches 12 and 13 includes a fixed contact support 14 secured to the associated body by a rivet l6 and providing a fixed contact 17. A resilient movable contact support 18 is provided with a movable contact 19 at its outer end which is movable into and out of engagement with the associated fixed contact. The movable contact arm is secured to the associated body by a rivet 21 and is electrically connected to a terminal member 22.
Identical disc cups 23 and 24 are mounted on the bodies 10 and 11, respectively. A bimetal snap disc 26 is supported in the disc cup 23, and a second bimetal snap disc 27 is supported in the disc cup 24. Each of the discs is formed with a shallow dished shape and operates to snap back and forth between two positions of stability upon reaching predetermined calibration temperatures. The switch 12 is operated by the disc 26 through a bumper 28. Similarly, the switch 13 is operated by the disc 27 by a bumper 29. The two bumpers are sized with clearance so that each switch opens and closes after its disc is in snap movement.
Mounted between the adjacent ends of the two disc cups 23 and 24 is a PTC heater 31 which exhibits a relatively low resistance below a predetermined temperature and a sharply increasing resistance above such predetermined temperature. Such positive temperature coefficient (PTC) heaters are known to persons skilled in the art and may be, for example, of the type described in the US. Letters Pat. Nos. 3,434,089 or 3,489,976. In the illustrated embodiment, the PTC heater is generally cylindrical in shape and has one face 32 engaging the end wall of the cup 23 and its opposite face 33 in engagement with the end wall of the cup 24.
Preferably, the interfaces between the ends of the PTC heater and the end walls of the two cups 23 and 24 are provided with an electrically and thermally conductive cement 35, such as a conductive epoxy cement to insure that a good electrical connection is provided at each interface and also to insure that a good thermal connection is provided. The cup 23 is provided with a tenninal extension 34, and the cup 24 is provided with a terminal extension 36. The two terminals 34 and 36 are connected to the source of electrical power for operating the PTC heater 3].
With this arrangement, it is not necessary to provide separate connecting means to the PTC heater, and each of the cups functions in three separate manners. Each cup serves to position the associated disc, to conduct heat from the PTC heater to the associated disc, and to provide the electrical connection for the PTC heater.
In some instances, it may be desirable to provide one or both of the cups 23 and 24 with a spring structure to compensate for variations in tolerance of the various parts of the assembly and to insure a good intimate contact exists between each cup and the adjacent face of the heater. One structure for providing this spring action is illustrated in FIG. 2, wherin the cup 24 is formed with a spring section 41 in its end wall. The spring section is produced by forming two parallel cuts 42 permitting the spring section to be deformed beyond 45 through which the terminals 14 and 22 project.
Each of the end caps also provides a side wall 47 shaped to closely fit and support the associated body and 11. The side walls 47 are formed with an axially extending recess 48 to receive one of the two terminals 34 or 36 as the associated body is moved axially to the assembled position. Mating projections 49 formed on the other end cap projects along the recesses to completely close the assembled device. Excepting along the recesses and projections, the two end caps abut at the interface 51. With this structure, two end caps, like the two bodies, can be identical to minimize tooling costs and inventory requirements. In fact, all of the elements in the assembled device, excepting the heater and the two discs, are identical.
The heater, because of its PTC characteristics, initially draws arelatively heavy current, and therefore, heats rapidly to the temperature at which the resistance increases. The current then decreases as the resistance increases with the result that the heater tends to stabilize at a given temperature determined by the resistance curve of the heater. Such heaters tend to be relatively insensitive to voltage fluctuation. In order for the discs to operate, it is necessary that the stabilization temperature of the heater be above the calibration temperature of the discs.
In practice, the selection of the discs is dictated by the characteristics of the PTC heater, the rate of heat transfer from the heater to the discs, and the time delay interval desired. If, in a particular assembly, a disc with a given calibration temperature provides a time delay which is too short, a disc is selected with a higher calibration temperature to increase the time delay. Conversely, if a given disc provides a time delay which is too long, a disc with a lower calibration temperature should be selected to reduce the time delay.
Normally, the two switches are required to operate at different time delay intervals. Since in the illustrated embodiment the rate of heat flow from the two sides of the heater is substantially the same, the two discs are selected to have two different calibration temperatures.
When the heater is de-energized after the operation of both switches, the switches sequence back to their normally closed position after a period of time determined by the operating temperatures of the disc and the rate of cooling of the entire device. In a given assembly, the time delay of a particular disc on heating is determined by its upper calibration temperature, and the time delay on cooling is determined by its lower calibration temperature.
' In the second illustrated embodiment of the present invention illustrated in FIG. 3, similar switch assemblies are again provided on each side of a PTC heater 61. In this embodiment, a switch body 62 is again mounted in an endcap 63, and a switch body 64 is mounted in an end cap 66. The two switch bodies and the two end caps are identical. Further, each of the two assemblies in this embodiment is provided with two discs and two switches.
In FIG. 3, the two switch assemblies are illustrated in positions in which the left-hand assembly is rotated 90 with respect to the right-hand assembly. Therefore, in FIG. 3, the innermost switch is fully illustrated on the right-hand side, and the outermost switch is fully illustrated on the lefthand side. For purposes of explanation, similar reference numerals will be used to designate similar elements on the two assemblies. A reference numeral without a prime is intended to indicate an element on the right assembly, and the same reference numeral with a prime added, designates the corresponding element on the left assembly. During the initial discussion, reference will be made only to the right assembly with the understanding that the structure on the left assembly is identical.
A disc retainer cup 67 is mounted on the body 62, but in this embodiment, the retainer cup is provided with two shoulders to support two separate bimetal snap discs 68 and 69. The innermost disc 68 operates a movable contact support arm 71 through a centrally located bumper 72. The bumper 72 extends through an opening 73 in the disc 69 and an opening 74 in the movable contact support arm 76. A tubular bumper 77 engages the disc 69 and functions to operate the movable contact support arm 76.
Each of the innermost switches includes a fixed contact 81 on a terminal member 82 which is secured in position by a rivet 83. Mounted on the free end of the movable contact arm 76 is a contact 84. The opposite end of the movable contact arm 76 is electrically connected to a terminal 86 and is mounted by a rivet 87.
Referring now to the left-hand side of the figure, each of the outermost switches includes a movable contact support arm 71 which carries a movable contact 91 at its free end. The contact support arm 71' is electrically connected to a terminal 92' and is mounted by a rivet 93. The fixed contact 94 of the switch is mounted on a terminal 96 secured in position by a rivet97'.
Here again, the disc caps 67 and 67 of each assembly function to provide the electrical connections for the PTC heater 61, to support the associated discs, and also to provide heat conduction from'the adjacent interface of the PTC heater to the associated discs. In this embodiment, however, four separate and distinct time delay intervals are provided 'for the operation of the four separate switches. The snap disc 68, for example, can be selected with a calibration temperature to operate its associated switch after a first predetermined time interval while the snap disc 68' is selected with a different calibration temperature so that it operates its associated switch after a predetermined time interval different than the first predetermined time interval. Similarly, the snap discs 69 and 69' are selected with still other different calibration temperatures so that their associated switches operate with third and fourth time delay intervals. In this embodiment, it is, therefore, possible to use a single PTC heater to operate four separate and distinct switches with four separate and distinct time delay intervals.
In accordance with one aspect of the present invention, a PTC heater is combined with the two switch assemblies so that each switch assembly receives heat from one face of the heater. In its broader aspects, this invention also contemplates the use of other types of heaters which do not necessarily provide a PTC characteristic.
It should be recognized that with the present invention, multiple time delays can be obtained in a simple and reliable manner, and that the cost of manufacture is minimized while good reliability and long-life characteristics are achieved.
Although preferred embodiments of this invention are illustrated, it should be understood that various modifications and rearrangements of parts may be resorted to without departing from the scope of the invention disclosed and claimed herein.
What is claimed is:
1. A relay comprising A. an electric heater,
B. a first assembly positioned on one side of said heater,
C. a second assembly positioned on the opposite side of said heater,
D. each assembly including,
a. a disc retainer, b. a bimetal snap disc supported by said retainer,
c. and a switch operated by said snap disc,
E. each retainer being formed of a material having good electrical conducting properties and good heat conducting properties,
F. said retainers engaging opposite sides of said heater and providing the electric connection for energizing said heater,
G. said retainers also providing the principal heat flow path between said heater and the associated disc.
2. A relay as set forth in claim 1 wherein said heater is a PTC heater operable when energized to attain a temperature higher than the operating temperatures of said discs.
3. A relay as set forth in claim 2 wherein a heat and electrically conductive cement is provided between each retainer in said heater.
4. A relay as set forth in claim 3 wherein spring means are provided to insure good contact between said retainers and said heater.
5. A relay as set forth in claim 2 wherein spring means are provided to insure good contact between said retainers and said heater.
6. A relay as set forth in claim 2 wherein at least one assembly includes two snap discs supported in its retainer, and two switches one of which is operated by each snap disc.
7. A relay as set forth in claim 2 wherein both assemblies are provided with two snap discs and two switches one of which is operated by each associated snap disc.
8. A relay as set forth in claim 7 wherein each disc 9. A relay as set forth in claim 2 wherein each disc is calibrated to provide a time delay different than the 5 time delays of the other discs.
10. A time delay relay comprising A. a PTC heater having opposite substantially parallel faces,
B. first and second similar assemblies positioned on opposite sides of said heater with one assembly p0- sitioned adjacent to each of said faces C. each assembly including a. a retainer,
b. a temperature responsive element in thermal contact with said retainer and,
c. a switch operated by said temperature responsive element, and
D. a housing enclosing said heater and said assemblies,
E. each retainer being formed of the material providing good electrical conductive qualities and good thermal conductive qualities,
F. each retainer engaging one of said parallel faces and,
a. providing a connection therewith for energizing said heater, and
b. a conductive heat flow path between said heater and associated temperature responsive element,
wherein each assembly includes two temperature responsive elements and two separate switches with one of said temperature responsive elements operating each of said switches.
12. A time delay relay as set forth in claim 10 wherein said temperature responsive elements are bimetal snap discs.
13. A time delay relay as set forth in claim 10 wherein said housing is formed of two similar parts, and said assemblies are similar.