US3489976A - Self-protected time delay relay - Google Patents

Description

Jan. 13, 19-70 L. MARCQUX 3,489;76

SELF-PROTECTED TIME DELAY RELAY Filed Jan. 5, 1966 3 Sheets-Sheet l BIMfT/JL as w! B/ME' 7A1.

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Filed Jan. 5. 1966 L. MARCOUX 3,489,976

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United States Patent 3,489,976 SELF-PROTECTED TIME DELAY RELAY Leo Marcoux, Pawtucket, R.I., assignor to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware Filed Jan. 3, 1966, Ser. No. 518,296

Int. Cl. H01h 61/013, 61/02, 71/16 US. Cl. 337-102 v 6 Claims ABSTRACT OF THE DISCLOSURE A time-delay relay employing a thermally-responsive switch with heating means which initially generates a large quantity of heat to trip the relay after a predetermined period of time and then through self-regulation decreases the heat generation or power to a minimal level-just sufiicient to maintain a desired temperature to keep the contacts in the tripped condition. A first embodiment' shows a convention'tal hermetically-sealed thermally-responsive switch with a conventional first heater'in thermal relation therewith, the first heater is electrically connected in series with a second heater formed of material which has as a characteristic a resistivity temperature curve having a steep sloped positive temperature coefficient (PTC). The steep slope of the curve causes the decreases in power and prevents overheating with concomitant deleterious effects in the relay. A second embodiment employs a single heater which is composed of PTC material of the same type as described above in relation to the first embodiment. The heater self-heats until the heat dissipation balances the heat generation at a point on the steep slope of the PTC curve, as in the first embodiment with the same benefi- .cial effects.

This invention relates to electrical time delay relay switches and in particular to such switches which are especially suited for miniaturized, hermetically sealed constructions.

Among the several objects of this invention may be noted the provision of new and improved electrical relay switches which permit fast response, have meansprovided to prevent damage due to overheating and are adapted for miniaturization so as to be conveniently insertable into small spaces; the provision of such switches which are especially adapted for hermetically sealed constructions; the provision of such switches which are precise; the provision of such switches which are accurate, in compact and reliable in operation; the provision of such switches which provide for improved vibration and shock resistance and which are not position sensitive; and the provision of such switches which embody a minimum number of parts, are simple in construction and are economical to assemble and manufacture.

Other objects will be in part apparent and in part pointed out hereinafter.

The invention accordingly comprises the elements and combinations of elements, features of construction, and arrangements of parts which will be exemplified in the structures hereinafter described, and the scope of the application of which will be indicated in the following claims.

In the accompanying drawings, in which several of the various possible embodiments of the invention are illustrated:

FIGURE 1 is a vertical cross section taken through a first embodiment of my invention;

FIGURE 2 is a partial vertical cross section similar to FIG. 1 but showing the contacts in an open position;

FIGURE 3 is an electrical wiring diagram showing the circuit of the device illustrated in FIGS. 1 and 2;

FIGURE 4 is a chart showing heat and resistance curves of the illustrated device; and

FIGURE 5 is a vertical cross section taken through a second embodiment of my invention.

Similar reference characters indicate corresponding parts throughout the several views of the drawings. Dimensions of certain of the parts, as shown in the drawings, have been modified and/ or exaggerated for the purpose of clarity of illustration.

It is to be understood that the invention is not limited in its application to the details of construction and arrangement of parts illustrated in the accompanying drawings, since the invention is capable of other embodiments and of being practiced or carried out in various Ways. Also it is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.

The relays of the present invention are of the type which employ a thermally responsive switch for actuation upon a predetermined time delay. Difiiculties have been experienced in providing quick response in such relays due to the fact that in prior art relays in order to obtain quick response the heaters had to be of a relatively low resistance to generate the relatively large quantity of heat initially required, however such a heater deleteriously efiected the relay due to the excessive heat generated over long periods of time (after the contacts tripped).

In the present invention this difiiculty is obviated by providing heating means which initially generate a lar e quantity of heat to trip the relay and then through selfregulation decreases the heat generation to a minimal leveljust sufiicient to maintain a desired temperature to keep the contacts in the tripped position.

Referring to FIGS 1 and 2, there is shown a first embodiment of the invention generally referred to by numeral 8 and which is shown as a hermetically sealed time delay relay switch.

Relay switch 8 includes a conventional switch 10 which may take the form of a hermetically-sealed, thermallyresponsive, snap-acting electrical switch as shown and described in copending application Ser. No. 502,807 filed Oct. 6, 1965, to which reference may be had for a more detailed description. Switch 10 includes a cup-shaped housing or casing 12 formed of a readily weldable good electrically and thermally conductive material such as, for example, cold rolled steel. Housing 12 also includes a peripherally extending annular flange 40. Disposed in supportive and electrically conductive engagement with the bottom of housing 12, is a wave spring washer 14 formed of a spring material having good electrically and thermally conductive properties. A suitable example is beryllium copper. Washer 14 has a diameter which closely approximates that of the interior diameter of the cupshaped housing 12. The spring washer 14 is undulated in form, the peaks being indicated at 15 and the valleys at 17.

Supported on spring washer 14 is a snap-acting composite thermostatic bimetallic disc-type element 16 Of the type disclosed, for example, in US. Patent No. 1,448,- 240. Disc 15 is provided with a non-developable or deformed portion responsible for its snap action and has a diameter substantially equal to that of spring 14. As best seen in FIGURES 1 and 2, an electrical contact 18 is electrically connected and secured, as by welding, to the disc 16 at a central portion thereof for movement in response to snap movement of disc 16.

Switch includes a header having a flanged metallic ring 22 formed of a readily weldable and good heat and electrically conductive material such as, for example, low

carbon steel. Ring 22 includes an annularly extending flange 28 adjacent one end thereof as shown. An electrically conductive metallic tubular member 26, formed for example of a nickel-iron alloy, is embedded in and sealed to a glass filler or sealant 24 which is infused or sealed to ring 22 as shown.

The glass-to-metal hermetic seal for the header may be of a so-called matched seal construction or a compression seal. If a matched seal construction is employed, the material for ring 22 and tube 26 would be selected so as to have a coefficient of thermal expansion similar to that of the glass sealant. Examples of such materials are Kovar and Rodar.

Member 26 projects beyond the glass sealant 24 and ring 22, and is mounted in spaced, electrically insulated relation to ring 22.

Tube 26 telescopically receives an electrically conductive terminal member 30 formed of a good electrically conductive material such as, for example, a silver alloy. Member 30 is received with a tight sliding fit within tube 26 and provides an electrical contact 32 which is positioned for mating engagement with contact 18. Terminal member 30 is moved relative to tube 26 to adjust the relation between the bottom surface of contact 32 and an abutment surface 48 provided by ring 22 and also between contacts 18 and 32 to exert a predetermined force against the center of disc 16 (when the latter is in the FIG. 2 condition) to calibrate switch 10.

Switch 10 provides an electrically conductive current path leading from electrical conductor 29 to terminal 30, to contact 32, to contact 18, through thermostatic disc 16, to electrically conductive spring washer 14, to the electrically conductive housing 12 and ring 22 to electrical conductor 34.

Header ring 22 includes a skirt portion 46 which projects beyond the glass sealant 24 into the casing 12. The bottom edge of the skirt portion 46, provides an annularly extending stop or abutment 48 which overlies and is disposed adjacent the peripheral portion of disc 16 and is adapted for engagement therewith. Disc 16 also bears against stop 48 in snapping from the contacts-closed position shown in FIG. 1 to the contacts-open position shown in FIG. 2. Spring member 14 is at all times in annular engagement with and urges the peripheral portion of disc 16 for movement upwardly toward engagement with stop or abutment 48.

Conventional means for preventing undesirable contact actuation by creep action prior to the occurrence of snap action as employed in larger snap-acting thermally responsive devices are generally not practical or useful with miniaturized constructions of this type. Stop 48 is so spaced from the bottom of contact 32 so that disc 16 will not engage stop 48 in creeping from the contactsclosed toward the contacts-open position.

A conventional electrical wire heater 50 is positioned around casing 12 and is seated in annular channel 52 which is slidably received on casing 12. A second heater 54 is mounted in heat transfer relation to switch 10 as shown in FIGURE 1. Heater 54 takes the form of a pill of material which has as a characteristic a resistivity temperature curve having a steep-sloped positive temperature coeflicient (hereinafter referred to as PTC) The resistance of this material increases sharply above a threshold or anomaly temperature within a narrow temperature range. For example, as shown in curve 2, FIGURE 4, the resistance more than doubles within a temperature range of less than twenty degrees centigrade. Examples of such materials are certain doped barium titanates, e.g.

and carbon black loaded, cross-linked polyethylene. Heater 54 is attached to casing 12 in any conventional manner, e.g. by adhesive. An electrically insulating layer 56, e.g. resinous material, electrically separates heater 54 from the casing. Electrically conductive layers 58 and 59 are attached in a conventional manner (as by ultrasonic soldering in the case of a barium titanate heater or electrically insulating screws in the case of carbon-black loaded polyethylene) to spaced surfaces of the heater element as shown in FIG. 1. Conductor 60 electrically connects conductive layer 58 to heater 50 so that heaters 50 and 54 are connected in series relation to one another. Conductor 62 connects conductive layer 59 and conductor 64 connects heater 50 to a power source (not shown). Switch 10 and heaters 50, 54 are inserted in a cup-shaped casing 68 which may be hermetically sealed by header 70. Header 70 is constructed of eyelet member 72 formed with apertures 74 therein. Eyelet 72 has a flange 76 which mates with flange 78 of casing 68 and attached thereto as by welding. Conductors 29, 34, 62 and 64 are inserted through apertures 74 and glass material is then placed in eyelet 70 to form a hermetic seal for relay 8. Either a matched or compressive seal may be employed, as described in relation to switch 10 or alternatively, it may be desirable not to provide a hermetic seal. Conductors 29, 34, 62 and 64 serve to mount switch 10 within casing 68. It may be desirable to provide an electrically insulating lining in casing 68 to insure that no short circuiting could result from a displacement of switch 10 within casing 68.

The operation of the switch will now be described. The relay is activated by closing the switch S (see FIG. 3) which initiates the time delay interval and energizes the heaters 50 and 54. FIG. 4 shows heat and resistance versus temperature curves for a typical relay. When switch S is first closed the total heat generated by heaters 50 and 54, curve 1, is relatively high, approximately 18 watts as shown in FIG. 4. The resistance of the conventional heater 50 is essentially independent of temperature, however the resistance of heater 54, the FTC material, increases sharply above the anomaly temperature, see curve 2, which causes a decrease in the total heat generated at these temperatures, see curve 1. Curves 3 and 4 represent the heat generated by heaters 50 and 54 respectively.

The total heat generated may be calculated from the following:

P=E2/ avi- 54) where P is the heat generated, E is the applied voltage, R is the resistance of heater 50 and R is the resistance of heater 54.

Heat will be generated until it matches or balances heat dissipated and switch 8 then becomes stabilized at that temperature. This temperature will vary in accordance with ambient conditions in which switch 8 is located. Curves 5 and 6 represent the maximum and minimum heat dissipation. Therefore the points of intersection of 5 and 6 with curve 1 give the effective range of stabilization temperature.

The operating temperatures of switch 10 are selected so that switch 10 will trip on the initial temperaturerise and remain tripped as long as heaters 50, 54 are energized. It will be obvious that switch 10 can be of the type which will open or close on a rise in temperature depending upon the end use of the switch 10 circuit.

Thermostat (temperature) settings of switch 10 are chosen under the stabilization range so that the relay, once tripped, will remain tripped as long'as the heaters are energized regardless of ambient conditions. It will be noted that the heat generated after tripping is greatly reduced due to the sudden increase in resistance of heaters 54 beyond the anomaly point. This serves to conserve power as well as preventing continuous overheating which could be deleterious to the switch or environs. It will be seen that heaters 50, 54 will prevent relay 8 from cooling otf below the reset temperature of the thermostat. As long as heaters 50 and 54 are energized the relay will remain in the tripped position. The reset time of the thermostat is dependent upon ambient conditions.

The relay of the instant invention can be produced in a very small size, e.g. by A diameter. An extremely fast response is obtainable due to the use of PTC material with low initial resistance with concomitant high heat generation in combination with thermostat which has a very fast thermal response. Time delays of 2 to 10 seconds are obtainable with the relay. It will be seen that the heater and switch 10 circuits are independent resulting in more flexibility. Further, relay 8 is not sensitive to position orientation and is highly shock and vibration resistant since the only moving parts are in thermostat 10 which, as pointed out more fully in the copending application Ser. No. 502,807 now U.S. Patent No. 3,352,986 which issued Nov. 14, 1967, is particularly shock and vibration resistant.

Another embodiment is generally indicated in FIG. 5 as numeral 9. Relay 9 employs the same switch 10 as used in the FIGS. 1-3 embodiment. In this embodiment only one heater is used, viz. heater 80. Heater 80 is composed of PTC material of the same type as heater 54 previously described. Heater 80 is generally annular and provided with conductive layers 82, 84 electrically connected respectively to opposite faces thereof. Conductor 64 is electrically connected to layer 82 and conductor 62 is electrically connected to layer 84. The description of the remainder of switch 9 is the same as switch 8 and will not be repeated. It will be understood that upon a voltage applied across conductors 62 aand 64 a current will flow from conductor 64, to conductive layer 82, through PTC heater 80 to conductive layer 84 to conductor 62. Heater 80 will self-heat until the heat dissipated balances the heat generated at a temperature beyond the anomaly temperature of the PTC material, curve 2 of FIG. 4. As in the FIGS. 1-3 embodiment the heat generated will then be reduced to a low level just keeping the temperature on the steep portion of the resistance-temperature curves. The operating temperature of thermostat 10 is then chosen so that it will be beyond the anomaly temperature to take advantage of the lower heat geneartion realized at that portion of curve 2 but lower than the intersection of the maximum heat dissipation curve with the heat curve of heater 80 so that the switch 10 will remain tripped as long as heater 80 is energized.

Thus it will be seen that switch 9 is also shock resistant, position insensitive, relatively insensitive to changes in voltage, small, compact, economical to produce and provides means to prevent overheating over extended periods of time.

In view of the above, it will be seen that the several objects of the invention are achieved, and other advantageous results attained.

As many changes could be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense, and it is also intended that the appended claims shall cover all such equivalent variations as come within the true spirit and scope of the invention.

What is claimed is:

1. A time delay relay comprising:

a support,

a first circuit means on the support including a thermally responsive switch means, the switch means including contacts operatively associated with a thermostatic element, the contacts adapted to actuate into and out of engagement in response to the actuation of the thermostatic element at a first temperature,

a second circuit means on the support electrically isolated from the first circuit, the second circuit including a first electrical resistance heater formed of a steep-sloped PTC material positioned in heat transfer relation to the thermostatic element and having a first low resistance, high heat generating state at temperatures below a second temperature to cause actuation of the thermostatic element, the second temperature being lower than the first temperature, and a second high resistance, low heat generating state at temperatures above the second temperature to maintain the thermostatic element in the actuated condition, and

means to energize the second circuit to cause actuation of the contacts of the first circuit and thereafter maintain the contacts of the first circuit in the actuated condition as long as the second circuit is energized.

2. A relay device as defined in claim 1 in which the PTC material is selected from the group consisting of doped barium titanate and carbon black filled, cross-linked polyethylene.

3. A relay device as defined in claim 2 in which the doped barium titanate is Ba 977La 003TlO3- 4. A relay as defined in claim 1 further comprising:

a second heater positioned in heat transfer relation to the switch means and electrical connecting means connecting the first and second heaters in series relation to one another.

5. A relay as defined in claim 1 further comprising:

two conductive layers electrically connected to spaced portions of the first heater;

electrically insulating means separating the first heater from the switch means;

an open ended cup-shaped casing in which the switch means and heater is positioned; and

glass header means hermetically sealing the open end of the casing, the headers provided with apertures through which conductors leading to the heaters and the switch pass.

6. A hermetically sealed, vibration resistant electrical relay comprising:

(a) thermally responsive means having (i) a thermally conductive casing;

(ii) a fixed and a movable contact mounted in the casing and means to move the movable contact into and out of engagement with the fixed contact in response to predetermined temperature conditions; and

(iii) first and second electrical conductors attached to the respective contacts;

(b) a heater wire wrapped around the thermally responsive means to form an annular heater;

(c) a steep-sloped PTC element mounted in heat transfer relation to the thermally responsive means;

(d) electrical insulation interposed between the PTC element and the thermally responsive means;

(e) first and second electrically conductive layers attached to spaced portions of the PTC element;

(f) a third electrical conductor attached to one end of the heater wire, a fourth electrical conductor attached to the second electrically conductive layer and a fifth electrical conductor connecting the other end of the heater wire with the first electrically conductive layer;

(g) an open ended generally cup-shaped casing in which the thermally responsive means and the heaters are positioned; and

(h) a hermetic seal closing the open end of the casing formed of an eyelet with four apertures through i 7 which the first, second, third and fourth electrical conductors pass and glass material filling in the eyelet and electrically isolating the electrical conductors.

References Cited UNITED STATES PATENTS 1,701,757 2/1929 Lea 200-122 1,838,372 12/1931 De Castro 200-22 2,403,803 7/1946 Kearsley 200122 8 a I Hotchkiss 200122 Broadley et a1. 200122.03 Kohler 33828 Meijer 200-122 Marcox 219-505 US. Cl. X.R.

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