US 3626348 A
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7 United States Patent  Inventor Ralph W. Alten Detroit, Mich. [21 Appl. No. 812,642  Filed Apr. 2, 1969  Patented Dec. 7, 1971  Assignee Essex International lnc.
Fort Wayne, Ind.
 CURRENT-REGULATING APPARATUS 17 Claims, 3 Drawing Figs.
 11.8. C1 338/20, 338/31,338/10l  lnt.Cl l-l01c 7/10  Field of Search 338/31, 101,115,113, 20; 323/68  References Cited UNITED STATES PATENTS 1,873,499 8/1932 Steinmayer 338/31 X 2,403,534 7/1946 Kehse 3,205,709 9/1965 Gearingetal.
Primary Examiner-Rodney D. Bennett, Jr. Assistant Examiner-Richard E. Berger Att0rneyLearman and McCulloch PAT-ENTED 0E1: Yum 1625348 4 l2 I0 I20 '8 2o 24 22 '5 E E I6 I 24b E) FIGI.
INVENTOR RALPH W. ALTEN CURRENT-REGULATING APPARATUS This invention relates to apparatus for regulating the current in a current-conductive circuit and more particularly to a current regulator construction employing a variable resistance the resistance of which is adjusted by springlike bimetallic element forming a part of the current-conductive circuit.
Devices for interrupting or regulating current have been employed in the past and in general have operated to break the continuity of the circuit in the event of electrical malfunction or overload. This is particularly undesirable if the device to which the current normally is supplied is one to which at least some current must be supplied at all times if the device is to function as intended.
Current regulators of the type disclosed herein may be utilized in either AC or DC circuits, and conveniently may be employed in the automotive field to control the current to window lift motors, seat adjustment motors, and the like. Apparatus constructed according to the invention is particularly adapted for use in a vehicle lamp circuit inasmuch as an overload current supplied to the lamps can be limited to a safe value for a sufficient length of time to enable a vehicle operating at night to reach a repair station.
A current regulator according to the invention comprises a compressible and expansible stack or column of individual resistance elements, such as carbon discs, and a bimetallic element bearing forcibly against the column. The force with which the bimetallic element bears against the stacked discs determines the state of compression of the stack and the effective electrical resistance thereof. The current to be regulated passes through the carbon discs and through the bimetallic element, thereby heating the latter. The bimetallic element deflects in response to changes in its temperature so as to increase or decrease the resistance of the stacked resistance elements and decrease or increase, respectively, the current without interrupting the circuit.
The principal objectives and advantages of the invention will be pointed out specifically or will become apparent from the following description when it is considered in conjunction with the appended claims and the accompanying drawings, in which:
FIG. 1 is an exploded view of the parts comprising a current regulator constructed according to the invention, the casing being shown in section;
FIG. 2 is an exploded perspective view illustrating the relative positions of the parts of the current regulator, the casing being omitted; and
FIG. 3 is a longitudinal sectional view of the apparatus with the parts shown in assembled relation.
Apparatus constructed according to the invention comprises a casing formed of any suitable insulating material such as plastic or fiber and having a bore 12 therein internally threaded at one end as at 12a. The casing 10 is open at one end and at the other end has an end wall 10a on which may be mounted a terminal connector 14 by means of a rivet 15 passing through a suitable aperture formed in the flange 14a of the connector 14 and through an aperture 16 formed in end wall 10a. A metal disc 18 is mounted on the inside of the wall 100 and has an aperture 18a therein adapted to receive the rivet 15. The end of the rivet 15 is peened over to form a head 15a for maintaining assembled the flange 14a, the wall 10a and the disc 18.
The apparatus includes a plurality of conductive resistance members 20 arranged in a column or stack. The members 20 preferably are carbon discs. The extreme left-hand carbon disc has an opening 20a to receive the rivet head 15a. The other discs need not be apertured.
Threaded into the open end of the casing 10 is an externally threaded cap member 22 formed of insulating material. Connected to the cap 22 by means of a rivet 15b is one end of a bimetal member or spring 24, the opposite end of which is free. The member 24 is fabricated from two back-to-back metal strips 24a and 24b bonded together and having different coefficients of thermal expansion, whereby the member 24 will deflect in a manner well known in the art in response to a change in its temperature. The bimetallic member 24 normally is generally U-shaped with the higher expansive strip 24a being on the outside of the U.
The member 24 serves as a compression spring which exerts a force against one end of the column of carbon discs 20 tending to compress the stack of discs between the member 24 and the housing wall 10a. A conductive, metal disc 21 may be provided between the column of carbon discs and the free end of the bimetal member 24 to provide suitable electrical contact and protect the end disc from damage by contact with the free end of the bimetal member 24. The rivet 15b passes through apertures formed in a terminal connector 25 and in the cap 22.
Although practically all conventional bimetallic members are suitable for use in the construction disclosed herein, bimetallic material of the type sold under the trademark Saflex by Wilco Manufacturing Company and described in its I969 Bulletin is preferred. Such material is preferred because, at temperatures below a predetermined or threshold temperature, an increase in temperature of the bimetallic member will cause the latter to deflect in one direction, and at temperatures above the predetermined temperature, an increasing temperature will cause the bimetallic member flex in the opposite direction. For example, at temperatures below a threshold temperature of approximately 250 F., an increase in temperature will cause the free end of the bimetallic member 24 to advance toward the carbon pile and apply more force thereon, thereby reducing its effective resistance and permitting more current to flow therethrough. At temperatures above about 250 F., however, the free end of the bimetallic member 24 will more in the opposite direction so as to reduce the force on the carbon, thereby increasing the resistance of the column of carbon and reducing the current flow. The temperature of the bimetallic member, of course, is proportional to the current flowing therethrough.
In operation, the current regulator is connected by means of the terminals 14 and 25 in the circuit in which the current is to be limited. Current thus may pass through the connector 14, the rivet 15, the metal disc 18, the carbon discs 20, the metal disc 21, the bimetal member 24, the rivet 15b, and finally the terminal 25. The member 24 may be preloaded to varying degrees by means of the closure 12. if the flow of current through the bimetallic element 24 is insufficient to heat the member 24 above its threshold temperature, the member 24 will tend to flex in such manner as to cause its free end to move toward the stack of carbon discs, thereby compressing the stack and decreasing the resistance to current flow. When there is sufficient current to heat the member 24 above its threshold temperature, as will be the case when an overload current flows, the member 24 will flex in such manner as to cause its free end to move in the opposite direction or away from the column of carbon discs. This will decrease the force exerted on the stack of discs and permit the column of discs to expand, thereby increasing the effective electrical resistance in the circuit to limit the flow of overload current. When the overload current has diminished, the member 24 will cool and flex in such direction as to increase the force exerted on the stack of carbon discs, whereby the cycle may be repeated.
If the member 24 is formed of Saflex or equivalent material and is at any given time at its threshold temperature, a change in its temperature either above or below the threshold temperature will cause it to flex in such direction as to reduce the force applied on the carbon pile, thus increasing the resistance of the latter. If the member 24 is formed of conventional bimetal material, however, any increase in its temperature will result in a lessening of the force applied on the carbon discs.
The disclosed embodiment is representative of the presently preferred form of the invention but is intended to be illustrative rather that definitive thereof.
l. Current-regulating apparatus for regulating the current in a circuit, said apparatus comprising expansible and compressible resistance means forming part of said circuit, the resistance of said resistance means being variable according to its state of compression, and a generally U-shaped, bimetallic, thermally sensitive, force-applying spring means forming part of said circuit and having opposite ends one of which acts on said resistance means to apply a compressive force thereto, the force exerted on said resistance means by said force-applying means being variable according to the temperature thereof.
2. Current-regulating apparatus for regulating the current in a circuit, said apparatus comprising a casing; a stack of electrically conductive, individual resistor elements in said casing; and electrically conductive, spring means reacting between said casing and said stack and exerting a force on the latter tending to compress said stack, said spring means being operative to flex in response to a change in its temperature either above or below a predetermined temperature and decrease the force exerted on said stack.
3. The apparatus set forth in claim 2 wherein said spring means comprises a generally U-shaped electrically conductive, bimetallic compression spring.
4. Current-regulating apparatus for regulating the current in a circuit, said apparatus comprising expansible and compressible resistance means forming part of said circuit, the resistance of said resistance means being variable according to its state of compression; and means for varying, without interrupting, the current in said circuit and including thermally sensitive, force-applying spring means forming part of said circuit and acting on said resistance means to apply a compressive force thereto, the force exerted on said resistance means by said force applying means being variable according to the temperature thereof.
5. Current regulating apparatus for regulating current in a circuit, said apparatus comprising a casing; a stack of electrically conductive, individual resistor elements in said casing; and means responsive to a variation in the current flow in the circuit for varying, without interrupting, the current in said circuit and including a generally U-shaped, electrically conductive, bimetallic spring reacting between said casing and said stack and exerting a force on the latter tending to compress said stack, said bimetallic spring being operable to flex in response to a change in it temperature and thereby vary the force exerted on said stack.
6. The apparatus set forth in claim 5 wherein said bimetallic compression spring comprises back-to-back metal strips each having a different coefficient of thermal expansion, one side of one of said strips being in bearing relation with both said casing and said stack of elements.
7. Current regulating apparatus for regulating current in a circuit, said apparatus comprising electrically conductive, compressible and expansible resistance means having an effective resistance which varies according to its state of compression; and electrically conductive, thermally responsive spring means exerting force on said resistance means for varying, without interrupting, the current flow in said circuit, said force applying means being electrically connected with said resistance means so that a current in said circuit may flow through said resistance means and said force-applying means, said force-applying means being responsive to variations in said current to change the force exerted on said resistance means and vary the efiective resistance thereof.
8. Apparatus as set forth in claim 4 wherein said resistance means and said force-applying means are in series.
9. Apparatus as set forth in claim 4 wherein the temperature of said force-applying means is dependent on the flow of current through said resistance means.
10. Apparatus as set forth in claim 4 wherein the force exerted by said force-applying means on said resistance means decreases in response to an increase in the temperature of said force-applying means.
l1. Apparatus as set forth in claim 4 wherein the force exerted by said force-applying means on said resistance means increases in response to a decrease in the temperature of said force-applying means. I
12. Apparatus as set forth in claim 1 including a casing having an open end and closure means removably mounted on said casing to close the open end thereof, said bimetallic member being mounted within said housing and having its other end bearing on said closure means.
13. Apparatus as set forth in claim 5 wherein flexing of said bimetallic compression spring in a manner to decrease the force exerted on said stack is dependent on an increase in temperature of said spring.
14. Apparatus as set forth in claim 5 wherein flexing of said bimetallic compression spring in a manner to increase the force exerted on said stack is dependent on a reduction in temperature of said spring. 1
15. Apparatus as set forth in claim 7 wherein said force-applying means comprises a bimetallic conductor.
16. Apparatus as set forth in claim 15 wherein said bimetallic conductor is substantially U-shaped.
17. Apparatus as set forth in claim 16 wherein said bimetallic conductor is composed of back-to-back metal strips having different coefficients of thermal expansion, the higher expansion strip constituting the outer part of the U.