US3845440A

US3845440A - Time delay relay

Info

Publication number: US3845440A
Application number: US00421552A
Authority: US
Inventors: E Hunter
Original assignee: Texas Instruments Inc
Current assignee: Texas Instruments Inc
Priority date: 1973-12-04
Filing date: 1973-12-04
Publication date: 1974-10-29
Anticipated expiration: 1991-10-29

Abstract

A time delay relay comprising a set of electrical contacts movable between circuit-making and circuit-breaking positions and thermally responsive means for actuating the contacts to move them from one to the other position at a predetermined temperature. The relay includes thermal storage means in heat exchange relationship with the thermally responsive actuating means. The thermal storage means comprises a body of material which will change from a first to a second physical state at a temperature intermediate that of the ambient of the relay and the predetermined temperature. Heatable means is positioned in heat exchange relationship with the thermal storage means so as to effect a transfer of heat therebetween and cause the body of material to change states so that the transfer of heat between the heatable means and the thermally responsive means is delayed and the period of time required for the thermally responsive means to reach the predetermined temperature is extended.

Description

United States Patent [191 [11] 3,845,440

Hunter Oct. 29, 1974 i 1 TIME DELAY RELAY [75] Inventor: Eugene A. Hunter, Plano, Tex. ABSTRACT ['73] Assignee; Texas Instruments Incorporated A time delay relay comprising a set Of electrical Dallas, Tex. contacts movable between circuit-making and circuitbreaking positions and thermally responsive means for [22] Wed: 1973 actuating the contacts to move them from one to the 2 APPL 421,552 other position at a predetermined temperature. The relay includes thermal storage means in heat exchange relationship with the thermally responsive actuating [52] US. Cl 337/341, 337/3, 337/298, means The thermal Storage means comprises a body 1337/1101 of material which will change from a first to a second Ft. Cl. p y l state at a temperature intermediate h of [58] held of Search 337/401 30 the ambient of the relay and the predetermined tem- 337/336' 60/528 529 perature. Heatable means is positioned in heat exchange relationship with the thermal storage means so [56] References cued as to effect a transfer of heat therebetween and cause UNITED STATES PATENTS the body of material to change states so that the trans- 3,575,645 4/1971 Doversberger et al. 337/3 fer of heat between the heatable means and the ther- 3,624,578 11/197! Stocker et a1 337/299 mally responsive means is delayed and the period of Primary Examiner-Har0ld Broome Attorney, Agent, or FirmJohn A. Haug; James P. McAndrews; Edward J. Connors, Jr.

time required for the thermally responsive means to reach the predetermined temperature is extended.

10 Claims, 2 Drawing Figures TIME DELAY RELAY BACKGROUND OF THE INVENTION This invention relates to time delay relays and more particularly to thermal time delay relays.

As the use of such relays in many types of control systems has increased, there has been a growing need for thermal time delay relays which would provide longer time delays. In order to increase the delay periods of these relays the thermal mass thereof has been increased and/or the operating temperature has been elevated. However, it is impractical to increase the size and operating temperatures sufficiently to achieve extended time delays of, for example, several hours, particularly where the available mounting space and application requirements limit such increases in size and operating temperature.

SUMMARY OF THE INVENTION Among the several objects of this invention may be noted the provision of time delay relays which have extended periods of delay and yet are compact in size and do not require excessive operating temperatures and the provision of such thermal time delay relays which are economical in construction and reliable in operation. Other objects and features will be in part apparent and in part pointed out hereinafter.

Briefly, a time delay relay of this invention comprises a set of electrical contacts movable between circuitmaking and circuit-breaking positions and thermally responsive means for actuating said contacts to move them from one position to the other at a predetermined temperature. Thermal storage means are positioned in heat exchange relationship with the actuating means. The storage means is constituted by a body of material which will change from a first to a second physical state at a temperature intermediate that of the ambient of the relay and the predetermined temperature. A heatable means, such as an electrical resistance heater, is positioned in heat exchange relationship with the thermal storage means so as to effect a transfer of heat therebetween and cause the body of material to change states so that the transfer of heat between the heatable means and the thermally responsive means is delayed and the period of time required for the thermally responsive means to reach the predetermined temperature is extended.

BRIEF DESCRIPTION OF DRAWINGS DESCRIPTION OF A PREFERRED EMBODIMENT Referring now to the drawings, a thermal time delay relay of this invention is indicated generally at reference numeral 1. This relay comprises a thermostatic switch 3 including a thermally responsive actuator 5, a thermal storage device 7' and a heater 9 stacked within a compartment 1:1 of an insulated housing 13. These components are held in respective contact with each other within the insulated compartment by an insulating cover 15 that has depending retainer lugs 15a to maintain the switch and storage device in coaxial alignment, and a spring terminal finger 17 that biases the entire stacked assembly against the inner surface of the cover.

Switch 3 has a switch arm 19, one end of which is welded to the inner end of a terminal lug 21. The free end of switch arm 19 has a pair of opposed contacts 23 movable between two fixed or

stationary contacts

25,27 constituted by the inner ends of

terminal lugs

29,31. These three lugs are secured in an inverted cupshaped case 33 of insulating material.

The intermediate portion of switch arm 19 is dimpled to provide a boss 35 aligned with one end of a transfer pin 37 axially slidable in a bore 39 of a generally cylindrical pin guide 41. The other end of pin 37 rests on the central portion of thermal actuator 5 constituted by a snap-acting composite bimetallic disc, such as disclosed in US. Pat. No. 1,448,240. Because of the nondevelopable or dished shape of the thermally responsive disc 5, it will snap from one curavture position to an opposite curvature position upon the temperature increasing to a predetermined level and will abruptly reverse its curvature when cooled below that level.

The undersurface of guide 41 is recessed to accommodate the flexing movement of disc 5 which peripherally rests on an annular ledge formed by a cup-shaped closure 43, the upper end of which is swaged over and grips the lower edge of housing 33 to secure together the housing and pin guide. Closure 43 is formed of a thermally conductive material, such as aluminum or copper, to provide excellent heat transfer with and heat exchange between thermal storage device 7.

Thermal storage device 7 comprises a capsule or cartridge of a thermally and electrically conductive material, such as aluminum or copper, partially filled with a body of material 45 which will change from one physical state to another at a temperature between ambient and the temperature at which the disc will snap to actuate the contacts. The body of material 45 contained in capsule 7 may be either a solid or a liquid at ambient temperatures of the relay. If a solid material is used, its fusion temperature is somewhat below that at which the disc snaps. If material 45 is a liquid at ambient temperatures, it will vaporize or boil at a temperature somewhat less than the actuation temperature of the switch. Exemplary of thermal storage materials that are solid at ambient temperatures but change to a liquid state or fuse at temperatures within typical operating ranges of thermal relays are many different waxes and paraffms, Roses and Woods metals and sulfur. These materials have melting pointsthat range between about and 250F. Glycerol which melts at about 68F. but solidifies at lower temperatures is another useful thermal storage material. These materials have heats of fusion ranging from about 12-100 Btu/lb. Typical thermal storage materials that are liquid at ambient relay temperatures but boil at temperatures below maximum useful operating temperatures of thermal relays are methanol, ethanol and water with boiling points between about l50F. and 212F. and heats of vaporization between about 365-950 Btu/lb.

Heater 9 is a pill or disc of an electrical resistance material, preferably one formed from a steepsloped positive temperature coefficient (PTC) material such as certain doped barium titanates. It is secured to the undersurface of thermal capsule 7 and supplied with electrical power by means of terminal finger 17 ofa terminal'lug 47 which extends outwardly through cover and another terminal lug 49 the inner end of which has a similar spring finger 51 contacting the electrically and thermally conductive capsule 7.

Operation of relay 1 is as follows: Assuming that at ambient relay temperatures the switch contacts and disc 5 are in the solid line positions and electrical power is supplied toheater 9 via terminal fingers 17 and 51, the heater will generate heat with its resistance increasing with temperature until it reaches stabilization current and temperature conditions at a level that exceeds that at which disc 5 will snap into its broken line position and move contact arm 19 into its broken line position. However, as the thermal storage material is heated to the temperature at which it will change state, heat will continue to be absorbed by the heat storage device and contained thermal storage material without any substantial change in the temperature thereof until a sufficient quantity of heat is absorbed to effect a change of state of the material. This heat of fusion or vaporization may be many times the normal heat capacity of the material and thus the heat content of the material 45 is greatly increased as it undergoes a change in state without any substantial change in temperature. Therefore the thermal storage device or thermal capacitor 7 delays the transfer of heat between the heater 9 and the thermal actuator disc 5 until sufficient heat is absorbed by material 45 and thereafter it will increase in temperature with further heat input until the operating temperature of disc 5 is reached.

As switch 3 may be connected into any conventional control circuit as a normally open or normally closed switch, the abrupt lifting of pin 37 as disc 5 snaps will open or close the circuit as desired. After this time delay in actuation of relay 1, the switch contacts thereof will remain in the broken line positions as long as electrical power continues to be supplied via terminal lugs 47.49 and disc 5 will be maintained at a temperature determined by the stabilization current and temperature of the PTC heater 9.

A similar time delay is achieved as material 45 is permitted to cool to an ambient temperature or one below that at which material 45 changes state to its original state and disc 5 abruptly returns to its solid line position and pin 37 moves down permitting the switch arm 19 to return to its solid line position. Thus relay 1 is effective as an extended time delay relay when permitted to cool from its operating temperature as well as being heated thereto. in both instances the heat absorbed or given off as material 5 changes from one to the other of its physical states delays the change in temperature ofdisc 5 and the actuation of the set of switch contacts.

A typical application for thermal relays of this invention is as a defrost initiation thermostat in a refrigerator-freezenln such an application the ambient of the relay would be about 35-55F. or perhaps lower, but in any event well below the temperature at which the thermal storage material will change from a solid to a liquid, or a liquid to a gas. The heater 9 stabilizes at a temperature of over l00F., for example, and the thermal actuator is maintained in its hot" curvature position at this temperature. The time delay utilized would be that required to permit the temperature of the disc and thermal storage device to drop to a temperature of about 50F. or less whereupon the disc will abruptly change its curvature from its hot to its cold position. FIG. 2 illustrates the extended time delay obtained with a relay 1 using a thermal storage device with 97.1 g. of wax (obtainable under the trade designation DW37 from Dura Commodities Corporation of Harrison, NY.) with a melting point of about F, a specific heat of 0.465 Cal/g. 25C. and a heat of fusion of 55.3 Cal./g. The solid line curve of FIG. 2 illustrates the relation of temperature to time of relay 1 after the power to the heater 9 is cut off and the relay cools in an environment of about 52F, the refrigerator ambient, as illustrated by the dashed line curve. As indicated, the relay temperature decreases in about 15 minutes from about F. to about 80F. at which temperature the relay substantially remains for about 3 /2 hours during the transition or change of state of the wax from a liquid to a solid, after which the relay temperature will drop to the refrigerator ambient of about 52F. in about 45 minutes. Thus the delay between the time of deenergization of heater 9 and the snapping of the disc as it actuates from its hot" to its cool" curvature is greatly extended by the heat given off, in this instance, during the change of state of the wax.

It will be understood that the extent of the delay is conveniently controlled by the type and amount of thermal storage material used, the shape and type of capsule or container utilized for device 7, the type of heater used, the amount of insulation employed and the operating temperatures and differential of the thermal actuator used. Thus one skilled in the art can conveniently provide relays with any preselected delay and operating range in accordance with the present invention.

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

As various 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.

What is claimed is:

l. A time delay relay comprising:

a set of electrical contacts movable between circuitmaking and circuit-breaking positions;

thermally responsive means for actuating said contacts to move them from one to the other position at a predetermined temperature;

thermal storage means in heat exchange relationship with the thermally responsive actuating means, said storage means comprising a body of material which will change from a first to a second physical state at a temperature intermediate that of the ambient of the relay and the predetermined temperature; and

heatable means in heat exchange relationship with said thermal storage means adapted to effect a transfer of heat therebetween and cause said material to change states whereby the transfer of heat between said heatable means and the thermally responsive means is delayed and the period of time required for the thermally responsive means to reach the predetermined temperature is extended.

5. A relay asset forth in claim 1 wherein the storage means material is a liquid at ambient temperatures and a gas at the predetermined temperature.

6. A relay as set forth in claim 4 wherein the storage means material is a wax.

7. A relay as set forth in claim 4 wherein the material is glycerol.

8. A relay as set forth in claim 3 wherein the thermally responsive means is a dish-shaped bimetallic disc which abruptly changes its curvature as its temperature exceeds the predetermined temperature and will abruptly revert to its original curvature after the temperature thereof falls below the predetermined temperature. 1 9. A relay as set forth in claim 8 wherein the storage means material is one that is a solid at ambient temperatures and a liquid at the predetermined temperature.

10. A relay as set forth in claim 9 wherein the relay contacts, thermally responsive means and heater are all enclosed in a housing of thermal insulation material.

Claims

1. A time delay relay comprising: a set of electrical contacts movable between circuitmaking and circuit-breaking positions; thermally responsive means for actuating said contacts to move them from one to the other position at a predetermined temperature; thermal storage means in heat exchange relationship with the thermally responsive actuating means, said storage means comprising a body of material which will change from a first to a second physical state at a temperature intermediate that of the ambient of the relay and the predetermined temperature; and heatable means in heat exchange relationship with said thermal storage means adapted to effect a transfer of heat therebetween and cause said material to change states whereby the transfer of heat between said heatable means and the thermally responsive means is delayed and the period of time required for the thermally responsive means to reach the predetermined temperature is extended.

2. A relay as set forth in claim 1 wherein the heatable means is a heater for supplying heat to the thermal storage means.

3. A relay as set forth in claim 2 wherein the heater is a body of electrical resistance material having a positive temperature coefficient.

4. A relay as set forth in claim 1 wherein the storage means material is one that is a solid at ambient temperatures and a liquid at the predetermined temperature.

5. A relay as set forth in claim 1 wherein the storage means material is a liquid at ambient temperatures and a gas at the predetermined temperature.

6. A relay as set forth in claim 4 wherein the storage means material is a wax.

7. A relay as set forth in claim 4 wherein the material is glycerol.

8. A relay as set forth in claim 3 wherein the thermally responsive means is a dish-shaped bimetallic disc which Abruptly changes its curvature as its temperature exceeds the predetermined temperature and will abruptly revert to its original curvature after the temperature thereof falls below the predetermined temperature.

9. A relay as set forth in claim 8 wherein the storage means material is one that is a solid at ambient temperatures and a liquid at the predetermined temperature.