US2848580A - Electrical time delay switch - Google Patents

Description

a. w. DE LANCEY 2,48,58Q

ELECTRICAL TIME DELAY svmca Filed 001;. 6, 1.955

.NVENTOR PALPH MDEAANcEY BY w ATTORNEY United States Patent ELECTRICAL TIME DELAY SWITCH Ralph W. De Lancey, Des Plaines, 111., assigno r, by mesne assignments, to Controls Company of America, Schiller Park, 11]., a corporation of Delaware Original application August 10, 1954, Serial No. 448,96 6. Divided and this application October 6, 1955, Serial No. 538,882

Claims. (Cl. 200-122) This invention relates to electrical time delay devices and more specifically to a heat responsive electric switch automatically operable in response to the existence of certain conditions for a predetermined length of time and manually resettable after operation thereof. While this switch is useful for a variety of applications, it is particularly applicable to automatic heating equipment for cutting off such equipment upon failure of ignition. This application constitutes a division of my copending application for U. S. Patent Serial No. 448,966, filed August 10, 1954, entitled Electrical Control Devices.

Time delay switches have been developed for a variety of purposes utilizing mechanical, electrical and thermostatic elements for attaining the desired delay. For many applications the use of electrically heated bimetallic elements have been used to reduce the cost of the device but such switches have been found to be undependable and subject to relatively wide variations in operating characteristics. Other forms of delaying means have been found to be expensive and relatively large and cumbersome. Accordingly one object of the invention is the provision of an improved bimetallic switch operable in response to heat produced by an electric current and characterized by its simplicity, dependability and low cost.

Another object of the invention resides in the provision of an improved time delay switch movable from one position to another position in response to the heating of a bimetallic element and manually resettable to said one position and wherein the time delay produced by said bimetallic element is substantially unaffected by ambient temperatures so that it will respond uniformly throughout the life of the switch.

A further object of the invention is a new and improved temperature responsive time interval switch embodying a negative temperature coefficient resistor and automatically compensated to function uniformly irrespective of variations of ambient temperatures, operating voltages and the like. This switch provides an inexpensive, dependable and stable device particularly useful for controlling certain aspects of automatic heating equipment though certain features of construction are generally useful in other situations requiring precision timing of electrical equipment.

Another object of the invention is an improved lockout and reset switch for oil burner controls responsive to improper or unsafe burner operating conditions to prevent ignition or re-ignition of the burner until it has been properly reset and the equipment has been returned to a start position. This switch embodies, for instance, a resistor having a negative temperature coeflicient and functions accurately and positively, notwithstanding changes in the operating potentials or ambient temperature experienced in normal operation, to actuate said switch within closely prescribed limits. These characteristics not only enhance the safety factor of automatic heating equipment but are generally useful in any circuit v 2,848,580 Patented Aug. 19, 1958 requiring predetermined and dependable operation at all times and under widely varying operating conditions.

Still another object of the invention is an improved time delay switch for electrical control equipment.

The accompanying drawings show, for purpose of illustrating the present invention, an embodiment in which the invention may take form, it being understood that the drawings are illustrative of the invention rather than limiting the same.

In the drawings:

Figure l is a perspective view of an improved switch utilizing a bimetallic control element and a negative temperature coefficient resistor for timing;

Figure 2 is a cross sectional view taken along the line 2-2 of Figure 1;

Figure 3 is a cross sectional view taken along the line 33 of Figure 1;

Figure 4 is a cross sectional view taken along the line 4-4 of Figures 1 and 2 and showing the manual reset operation.

The time delay or reset switch in accordance with the invention generally comprises an electric switch having contacts held in either an open or closed position by cooperation with a composite bimetallic element. The composite element is heated by a negative temperature coefiicient resistor which decreases in resistance as his heated by the flow of current. This arrangement of elements has been found to produce a highly accurate and dependable timing device particularly for oil burning equipment to immobilize the entire heating plant upon failure of the burner to start properly and within a prescribed time.

In a typical application this reset switch forms part of the primary starting control or stack switch and functions to interrupt burner operation upon failure of the fuel to ignite within a predetermined period of time. This switch 52 is shown in Figs. 1 through 4, and comprises a base member in the form of an angle bracket, secured to a supporting plate 19, having an outwardly extending leg part 136 and a mounting leg part 137. The bracket part 136 supports the elements of the switch, including the bimetallic elements 138 and 139 and the contact members 73 and 74. The bimetallic elements which form a separate sub-assembly along with a negative temperature coefiicient resistor 71 are adjustably supported by one leg 142 of a U-shaped bracket 141. The opposing leg 143 of this bracket is secured to the supporting member or bracket 136 as by Welding or other suitable means. member 141 are adjustable relative one to the other by means of a screw 144 passing through an opening in leg 142 and threaded into the leg 143.

' The bimetallic member 138 is of composite construction and formed of two separate L-shaped pieces 145 and 146 welded or joined one to the other at 147 in the form of a U. In addition to the joinderof these bimetallic elements to form a unitary structure, they are reversely arranged to compensate for variations in ambient temperature. This is attained by joining the elements so that the layer 145b of element 145 abuts the corresponding layer 146a of element 146 at the joint 147 and the layer 145a abuts layer 14617. In this way, the elements 145 and 146 will deflect with ambient changes in temperature so that the free end of element 146 will remain substantially stationary. The end of element 145 is permanently coupled to leg 142 of bracket 141 by a pair of rivets 148 or other suitable means.

The end 146 of the element 138 carries the resistor 71 and bimetallic element 139. The resistor 71 which has a negative temperature coefiicient is held between a pair' of retaining members 149 and 150. They are formed of electrically conductive material and have circular cup-like The legs 142 and 143 of the U-shaped' portions 149' and 150' for retaining the disc-like resistor 71. The member 149 lies flat against and is electrically coupled to the end 146 of the bimetallic element 138. The other member 150 lies flat against one end of the bimetallic element 139 and the members are separated by an insulating spacer 151 of a thickness that will produce the desired pressure of the cup- like parts 148 and 150 against resistor 71. The entire assembly is held together by a pair of screws 152 insulated by substantially coextensive bushings 153 and threaded into a small metal plate 154. The plate 154 is also insulated from element 146 by an insulating spacer 155 and another insulating spacer 156 is positioned between the heads of screws 152 and element 139. In this way an electrical circuit is established from the bracket 137 to the V-shaped member 141, then through bimetallic members 145 and 146, bracket 149, resistor 71, bracket 150 and bimetallic element 139.

The contacts 73 and 74 and supporting structure 157 therefor shown in Figure 2 are also mounted on the leg 136 of mounting bracket 135 and are positioned for cooperation with the angled end 139 of the bimetallic element 139. The contact members or springs 73 and 74 are insulated from the bracket and from each other by insulated spacers 158, 159, 160 and 161, and the assembly is held together by a pair of screws 162 extending through insulating bushings 163 and threaded into a plate 164 underlying bracket 157. If desired, a plate 165 may be 7 interposed between the heads of screws 162 and the insulating spacer 161. i

In the normal position of the bimetallic elements 138 and 139, the end 139 of element 139 extends beneath the tensioned spring contact member 73 which bears against it to establish an electric circuit. In this position, the contact member 74 also contacts the member 73 so that a closed circuit is set up between contact member 74 and the mounting bracket 135.

The contact members 73 and 74 are arranged to be operated or reset by the button 50 carried by the plate 19 and pivoted about an axis 50'. This button functions as a bell crank and has on its inner end an upwardly extending pin 166 adapted to extend through an opening 167 in contact member 73 and bear against the contact member 74. The length of the pin 166 is suflicient to break the contact between members 73 and 74 before the shoulders 16S and 169 of the button 50 adjacent the pin 166 operate to lift the contact member 73.

In operation, the contacting members 73 and 74 are normally closed so that a circuit is established as described from bracket 135 to contact member 74. Assum- 'ing now that a voltage is applied between the bracket 135 and contact member 74 to cause current to flow through resistor 71, the resistor 71, which has a high resistance when cold, begins to heat slowly. The heat thus generated heats bimetallic elements 146 and 139 causing them to warp and initiate withdrawal of the end 139' of element 139 from beneath the contact 73. As the resistance of resistor 71 decreased, by reason of its negative coeflicient of resistance, heating will become more rapid and cause sufiicient warping of bimetallic elements 146 and 139 to finally withdraw the end 139' completely from beneath contact 73. Contacts 73 and 74 will open and interrupt the flow of current through resistor 71. With the circuit through resistor 71 now broken, the resistor will cool and the bimetallic elements 146 and 139 will return toward their normal positions. Contact member 73, however, prevents the return as the sloping edge 170 of member 139 now engages the edge of contact member 73 and is firmly held back. Before the switch will function again, the button 50 must be manually depressed and, upon so doing, both contacts 73 and 74 are raised in an open position by the pin 166 and shoulders 168 and 169 until the contact 73 is free of edge 170. The bimetallic members 138 and 139 then spring toward the contact member 73 so that the end 139 of element 139again 4 underlies the contact 73. Upon release of button 50, the contacts 73 and 74 will rest in a closed position on the bimetallic member 139. The position of the bimetallic member 139 relative to the contacts 73 and 74 is adjustable by screw 144 in the manner described, and this of course determines the time in which the switch will function in the manner described above.

This switch is particularly useful for turning ofi a piece of electrical equipment upon the expiration of a predetermined interval of time. In such a case it would be connected in series with the equipment. One specific application is in oil burner control equipment such as the primary or stack control previously discussed. The switch may be connected in series with the power circuit supplying the motor, ignition, valves, etc., or may be connected in series with a low voltage relay control. In either case it maintains a closed circuit for a predetermined time interval. If the burner starts properly, a switch in the control is closed in response to the heat generated and bypasses the timing or reset switch. However should the burner fail to ingnite, the reset switch will open and turn the oil burner off whereupon the switch must be manually reset to start the burner again.

If desired the switch in accordance with the invention may be provided with means for independently heating the resistor 71 and may include additional sets of contacts for controlling other circuits.

While only one embodiment of the invention has been shown and described, it is apparent that modifications, changes and alterations may be made without departing from the true scope and spirit thereof. a

What is claimed is:

1. A temperature responsive switch comprising a U- shaped ambient temperature compensated bimetallic member, adjustable means attached to one leg of said U-shaped member for supporting it, a second bimetallic member carried by and spaced from the other leg of said U-shaped member, a heater disposed between said bimetallic members, an angle end on said second member, a pair of switch members cooperating with and held in closed position by cooperation with said angle end, electrical connections between said U-shaped element, the heater, the second bimetallic element and said switch members whereby the passage of an electric current will heat the heater and cause said bimetallic element to move out of cooperation with said switch members to open them and break the electric current, and manual means for reclosing said switch members. I

2. A temperature responsive switch according to claim 1 wherein said heater has a negative temperature coeificient of resistance.

3. A temperature responsive switch comprising a pair of substantially spaced overlying bimetallic elements fastened together at one end, means for supporting one of said elements, a heater having a substantial negative temperature coefficient of resistance disposed between said elements, switch means cooperating with the other of said elements, said switch means being'actuated upon deflection of said element in response to heat generated by said heater and remaining in said actuated position, and manually operable means for resetting said switch means.

4. A temperature responsive switch according to claim 3 in which at least one of said bimetallic elements is arranged to compensate for ambient temperature changes.

5. A timing switch comprising a bimetallic element including a temperature compensated U-shaped element supported by one leg thereof and a second L-shaped element secured to and carried by the other leg of said U- sh aped element, switch means mechanically engaging said element and held in one position thereby, and an electric heater disposed between said other leg of said U-shaped element and said L-shaped element, said heater having a substantial negative temperature coeflicient of resistance and associated with said element whereby heating of said References Cited in the file of this patent UNITED STATES PATENTS Livingston June 5, 1923 Hall Mar. 18, 1924 Dubilier Feb. 21, 1933 Lawton Feb. 27, 1934 10 Brash May 29, 1934 Zierahn Mar. 8, 1938 6 Shaw Mar. 18, 1941 Riche Apr. 1, 1941 Hand July 8, 1941 WoodWorth Nov. 24, 1942 Crise Mar. 7, 1950 Judson Sept. 9, 1952 Zucke rman Nov. 10, 1953 Hotchkiss Aug. 7, 1956 FOREIGN PATENTS Sweden Mar. 17, 1938 Germany Mar. 27, 1933

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