US3248502A - Thermally responsive circuit breaker for electric cigar lighter - Google Patents

Description

pril 26. 1966 A. T. LYBROOK 3,248,502

THERMALLY RESPONSIVE CIRCUIT BREAKER FOR ELECTRIC CIGAR LIGHTER Filed Oct. 18, 1963 FIG. 2

IN VENTOR. Arm/d I Lybrook United States Patent Q 3,248,502 THERMALLY RESPONSIVE CIRCUIT BREAKER FOR ELECTRIC CIGAR LIGHTER Arnold T. Lybrook, Lancaster, Ohio, assignor to Essex Wire Corporation, Fort Wayne, Ind., a corporation of Michigan Filed Oct. 18, 1963, Ser. No. 317,247 3 Claims. (Cl. 200-122) This invention relates to a cigar lighter and, more particularly to an electrical circuit breaker for a cigar lighter, such circuit breaker being responsive to temperature.

The temperature responsive circuit breaker of this invention is particularly adapted for use with an electric cigar lighter of the type commonly used in motor vehicles. It has been a common practice to protect such cigar lighters from overheating by use of thermally responsive circuit breakers connected in series with the electrical heating elements of such devices. Whenever the heating elements of the cigar lighters became overheated, the circuit breakers opened the circuits to the heating elements. Some of the prior circuit breakers of this character were of the destructible fuse type or of the manually resettable latch type. The replacement or resetting of such circuit breakers was in most instances a diflicult' or inconvenient operation for the ordinary vehicle user. Other types of thermally responsive circuit breakers which automatically reclosed upon the cooling of the cigar lighter heating elements were not entirely satisfactory as they would repeatedly reenergize the heating elements with possible resultant damage to the cigar lighters. The prior circuit breakers for cigar lighters also had other disadvantages such as being large, complex or expensive.

It is, therefore, an object of this invention to provide an improved thermally responsive circuit breaker for cigar lighters and the like which will substantially reduce the current flow to an overheated heating element, thereafter maintain the current flow at such reduced value until the cause of over-heating has been obviated, and then automatically reestablish the normal energizing circuit for the ci-garlighter.

Another object of this invention is to provide acircuit breaker of the foregoing character which has a small, simple construction of few parts and which may be economically manufactured and calibrated.

A further object of this invention is to provide a thermally responsive circuit breaker which includes improved means -for supporting a heating resistor adjacent a bimetal thermally responsive contact member.

These and other objects are attained in accordance with this invention by providing a circuit breaker having a heat conducting first terminal adapted to be mounted in heat and electrical conducting relation with the energizing terminal of -a cigar lighter socket having contact means for energizing the heating element of a cigar lighter igniting plug. A bimetal element is secured in heat and electrical conducting relation with the first terminal and is movable in response to heat received therefrom to disengage a pair of normally closed contacts shunting a heater resistor. This heater resistor is can ried by support members in heat transmitting relation with respect to the bimetal element so as to keep the bimetal element in a contact disengaged position in response to current flow through the resistor after dis engagement of the contacts. The bimetal element together with a spring clamp support member are secured by the first terminal to a disc closing one end of a tubular housing. The other end of the housing is closed by another disc to which a support member carrying one of the contacts is secured by asecond terminal adapted to be connected to a source of power. The spring clamp support member is formed with a resilient arm having an aperture receiving one terminal end of the resistor with a snug fit and biasing the other terminal end of the resistor into electrical engagement with the support member.

Other objects and features of the invention will be apparent from the following description and the accompanying drawing, in which: 7

FIGURE 1 is a side elevation view of a thermallyresponsive circuit breaker embodying the invention;

FIGURE 2 is a sectional view taken along the line 2'2 of FIGURE 1, showing the contact member in closed-circuit position;

FIGURE 3 is an axial sectional view of a cigar lighter assembly shown with the circuit breaker attached thereto, the contact member of the circuit breaker being shown in open-circuit position; and

FIGURES 4 and 5 are perspective views of parts of the circuit breaker.

Referring to the drawing, there is shown a thermallyresponsive circuit breaker comprising two generally circular end plates or discs 11 and 12, preferably stamped from sheet insulating material, and a tubular sheet metal housing 13. The opposite edges of the side walls of the housing 13 are provided with projecting lugs 14 engaging grooves 15 in the end plates 11 and 12 and crimped over the end plates 11 and 12 for holding the two end plates tightly to the housing 13. The various parts of the circuit breaker 10 are secured to the end plates 11 and 12 in two main subassemblies 16 and 17, more particularly shown in FIGURES 4 and 5, respectively. A current-limiting heater resistor 18 is carried by the subassernblies 16 and 17 in a manner to be described later.

The subassembly 16 includes the end plate 11 to which a spring clamp 19 and a thermally responsive bimetal element 20 are secured by a terminal bushing 21. The spring clamp 19 is formed from a strip of suitable resilient material, such as brass, and comprises an arm 22 extending at an angle of substantially 60 with another arm 23. Each arm is provided with an aperture, the arm 22 having a heater-engaging aperture 24 and the arm 23 having an aperture 25 through which the terminal bushing 21 passes. The bimetal element 20 is formed from thermostatic bimetal material of the type comprising welded-together layers of metals having dissimilar temperature coefiicients. The bimetal element 20 is generally L-shaped and includes a thermally responsive arm portion 26 and an enlarged base portion 27. An electrical contact 28 comprising a section of contact metal in strip form is welded to the arm portion 2 6 near an end portion 29 that is formed at a angle with the arm portion 26. The base portion 2 7 is pro- I vided with a central aperture 30 through which passes the terminal bushing 21. Two lugs 31 projecting from the base portion 27 have their ends bent to extend into the slots 32 of the end plate 11 to prevent the bimetal element 20 from rotating relative to the end plate 11. The base portion 27 of element 20 is also provided with two extensions 33 between which is received a complemental lug 34 extending from the arm 23 of the spring clamp -.19 to prevent the latter from turning relative to the bimetal element 20. The terminal bushing 21 which is formed of a metal having high heat con ductivity such as brass is preferably tubular and internally threaded as indicated at 35. The terminal bushing 21 passes through a suitable central opening in the end plate 11, the aperture 30 in the bimetal element 20 and the aperture 25 in the spring clamp 19. The spring clamp or supporting member 19 and the bimetal elem9 ment are secured to the end plate 11 by turning the inner end 36 of the terminal bushing 21 over upon the arm 23 of the spring clamp with a retaining flange 37 of the terminal bushing 21 engaging the outer side of the end plate 11.

The subassembly 17 includes a supporting member 41 preferably made from sheet metal, which is secured to the end plate 12 by a terminal stud 41. The supporting member 41) is generally U-shaped and has two substantially parallel legs 42 and 43 connected at one end. At its free end, the leg 42 is formed with a U-shaped slot 44 through which passes the terminal stud 41. Two tabs 4-5 extending from the side edges of the leg 42 have their ends bent to extend into the slots 4-6 of the end plate 12 to prevent the supporting member from turning relative to the end plate 12. The free end of the leg 43 has a transversely bent extension or contact portion 47 to which is welded an electrical contact 48 comprising a section of contact metal in strip form. The contact 48 is preferably positioned at a right angle with respect to its cooperating contact 28. The leg 43 is provided with an elongated opening 49 generally centrally thereof and extending to the contact portion 47. The terminal stud 41 which is formed of electrically conductive metal, such as brass, has a head 50 engaging the leg 42 of the supporting member 41) and a threaded shank 51 passing through the slot 44 in the leg 42 and through a suitable central opening in the end plate 12. The projecting end of the shank 51 receives a washer 52 and a nut 53 which is tightened to secure the supporting member 4t) to the end plate 12.

The heater 18 preferably is in the form of a well-known type of electrical resistor comprising a rigid rod-like core 60 with conductive terminals 61 and 62 secured to the ends thereof. The core 611 may be formed of braided glass fiber strands having a conductive material associated therewith to provide the desired resistance value. The core 60 has a substantial degree of rigidity resulting from a dielectric coating applied thereto. The terminals 61 and 62 are preferably identical and each comprises a cylindrical metal band or cup secured, as by crimping, in good electrical and tight mechanical connection with the core 60.

The terminals 61 and 62, respectively, of the resistor heater 18 are located in the aperture 24 of the spring clamp 19 and the opening 49 of the supporting member 40. The spacing of the inner end 36 of the terminal bushing 21 from the head 50 of the terminal stud 41 in the assembled circuit breaker 1t) obviously is somewhat greater than the length of. the resistor heater 1%. To hold the heater 18 in place, the aperture 24 is contoured to closely fit the terminal 61. That is, the diameter of the aperture 24 is but slightly larger than that of the terminal 61 so as to enable ready insertion of the terminal into the aperture yet to cause the terminal to fit snugly in the aperture. By reason of this snug fit, the heater 18 is supported in the arm 22 of the spring clamp 19 with its principal axis generally perpendicular to the plane of the arm 22. The opening 49 of the supporting member 40 has rounded ends similarly contoured to closely fit the terminal 62 but has a length somewhat greater than its width to facilitate insertion of the terminal 62 into the opening 49. It will be apparent that should the heater terminals 61 and 62 be of other shapes, the aperture 24 and the opening 49 would conform thereto.

Subsequent to the completion of the housing 13 and the subassemblies 16 and 17, the arm 22 of the spring clamp 19 is flexed manually to a position generally parallel withthe arm 23; and the terminal 61 of the heater resistor 18 is then inserted into the aperture 24. With the arm 22 held in this generally parallel position, the subassemblies 16 and 17 are fitted to the ends of the housing 13 in proper relation. As these parts are fitted together, the terminal 62 of the heater 18 is inserted into the opening 49 of the leg 43, after which the arm 23 is released. The lugs 14 of the housing 13 are then crirnped over the end plates 11 and 12 to complete the assembly of the circuit breaker 10. Inasmuch as the flexed arm 23 attempts to resume its initial position, it urges the heater 18 to the position shown in FIGURES 2 and 3 with the heater terminal 62 in tight engagement with the end edge of the opening 49 of the supporting member 41 adjacent the contact portion 47. At the same time, the resiliency of the spring clamp 19 also tends to turn the arm 22 with respect to the heater terminal 61. As such turning movement is limited by the sung fit of the terminal 61 in the aperture 24, the arm 22 at the edges of the aperture 24 will thereafter bear firmly on the terminal 61 and hold the heater 18 thereon. Thus, the heater terminals 61 and 62, respectively, have firm pressure contact and good electrical connection with the spring clamp 19 and the supporting member 40.

The circuit breaker 10 preferably is calibrated prior to its assembly by the accurate forming of the various parts. As the functioning of thermostatic bimetal material follows definite physical laws, the calibration of the circuit breaker 10 is effected by forming the end portion 29 of the bimetal element 20 in a predetermined relation with respect to the mounting base portion 27 at a normal ambient temperature. Because the constructions of the circuit breaker parts provide for their assembly in an accurately aligned relationship, the circuit breaker 11 is operative at a desired temperature determined by the form and material of the bimetal element 20.

Referring now to FIGURE 3, the circuit breaker 10 is shown attached to a plug-type automatic cigar lighter of conventional structure such as is commonly used in motor vehicles. The cigar lighter includes a socket 71 which may be mounted in the dashboard 72 of the motor vehicle and is thus in electrical connection with the grounded battery terminal of the motor vehicle. A terminal stud 73 of brass or other heat-conductive metal is supported by the insulator 741 in the base of the socket '71. Bimetal latch contacts 75 are supported on the insulator 74 in electrical connection with the terminal stud 73.

An igniting plug or unit 76 is removably received in the socket 71. Attached to the inner end of the igniting plug 76 is a heating'element assembly comprising a shallow metal cup 77 containing a spiral wound heating coil or element 78 of fiat metal ribbon. The inner end of the heating element '78 is electrically connected to the main body of the igniting plug 76 so as to be in electrical connection with the socket 71. The outer end of the heating element 78 is attached to the cup 77 which is insulated from the main body of the igniting plug 76. The cup 77 is adapted for cooperation with the bimetal latch contacts 75 to selectively establish an igniting or heating circuit under the control of the user of the cigar lighter 70. The bimetal latch contacts 75 function in a well-known manner to hold the igniting plug 76 in the heating position shown in FIGURE 3 until the heat from the heating element 78 causes outward movement of the bimetal latch contacts 75. Thereupon, the released igniter plug 76 moves to a normal position (not'shown) within the socket 71 from which the igniter plug 76 may be withdrawn for use.

The terminal bushing 21 of the circuit breaker 10 is threaded upon the terminal stud '73 of the cigar lighter socket 71 to mount the circuit breaker 10 upon the socket. It will be evident that the terminal bushing 21 is in both heat-conductive and electrically-conductive relation with the terminal stud 73. A connection may be made from the undergrounded terminal of the vehicle battery to the terminal stud 41 of the circuit breaker 10.

In the normal, non-heated condition of the circuit breaker 10, as shown in FIGURE 2, the contacts 28 and 48 are engaged to provide a current path from the terminal stud 41 to the bimetal latch contacts 78 through the supporting member 40, contacts 28 and 48, bimetal element 20, spring clamp 19, terminal bushing 21 and terminal stud 73. Upon the igniting plug "76 being pushed into the socket 71 to establish a heating circuit through the cup 77 and the bimetal latch contacts 75, the resultant passage of current flow through the heating element 78 raises its temperature until the cup 77 is released by the bimetal latch contacts 75. Some heat from the energized heating element 78 will be transferred to the base portion 27 of the bimetal element through the terminal bushing 21 and the terminal stud 73.

During normal operation of the cigar lighter 70, the bimetal element 20 will not be heated sufficiently to cause separation of the contact 28 from the contact 48. However, if for some reason, the heating element 78 is energized for a longer period of time or is overheated because of a short-circuit in the heating element 78, the excessive heating of the heating element 78 causes the bimetal element 20 to be heated sufficiently to move the contact 28 out of engagement with the contact 48. Upon separation of the contacts 28 and48, the heater 18 will be connected in series circuit with the heating element 78. It will be noted that in the unheated condition of the circuit breaker the heater 18 is effectively shortcircuited or shunted by the bimetal element 20 through the contacts 28 and 48.

The heater 18 is selected to have a resistance value greater than that of the heating element 78 so as to substantially reduce the current flow to the cigar lighter 70 when the contacts 28 and 48-separate. At the same time, the resistance value of the heater 18 must be moderately low to cause the current passing through it to generate enough heat to keep the bimetal element 20 in open circuit position once the contacts 28 and 48 have been separated and as long as current continues to flow through the circuit breaker 10. The particular resistance value of the heater 18 depends upon the current rating of the heating element 78 but preferably is on the order of twice the resistance value of the heating element 78.

In the event of a short circuit occurring in the cigar lighter socket 71, it will be evident that the passage of the consequent high current through the bimetal element 20 will result in the heating of the bimetal element 20 by virtue of its resistance. Under such a condition, the contacts 28 and 48 will be separated in the same manner as occurs when the heating element 78 becomes overheated to cause the current How to the socket 71 to pass through the current-limiting resistor heater 18. The heat generated by the current flow through the heater 18 holds the bimetal element in open circuit position and prevents reclosure of the contacts 28 and 48 while the excessive current condition exists.

It will be evident that when the abnormal condition which causes operation of the circuit breaker 10 has been corrected, the circuit through the heater 18 is interrupted. The bimetal element 20 will then cool and return to its normal position with the contact 28 and 48 engaged.

While the invention has been illustrated and described in its preferred embodiment and has included certain details, it should be understood that the invention is not to be limited to these precise details since the same may be carried out in other ways falling within the scope of the invention as claimed.

What is claimed is: 1

1. An improved circuit breaker for a cigar lighter having a socket in which a removable igniting plug having a heating element is adapted to be received and manually moved into position to be heated and a heat conducting terminal having contact means thereon engaging said igniting plug when said igniting plug is in position to energize said heating element, an improved circuit breaker comprising: a tubular housing; a disc of insulating material secured in each end of said housing; a first heat conducting terminal member extending through and secured to a first one of said discs and adapted to be mounted in heat and electrical conducting relation with the cigar lighter heat conducting terminal; a second terminal member extending through and secured to the second of said discs, and adapted for connection to a source of electrical power; a support member within said housing secured to said second disc in electrical connection with said second terminal member by an inner portion thereof; a first electrical contact fixed on said first support member in electrical connection therewith; a thermally-responsive bimetal element within said housing secured to said first disc at one end in heat and electrical conducting relation with said first terminal member by an inner portion thereof, said bimetal element having a second electrical contact fixed on its other end in electrical connection therewith and normally engaging said first contact, said bimetal element being movable in response to heat received from said first terminal member upon a predetermined heating of said cigar lighter heating element to disengage said second contact from said first contact; a U-shaped spring clamp member within said housing having a first arm secured to said first disc.

in electrical connection with said bimetal element by said inner portion of said second terminal member, said spring clamp member having a resilient, free second arm provided with an aperture; and a current-limiting heater resistor within said housing comprising a rigid, rod-like core having first and second terminals secured to its respective ends, said first resistor terminal extending through said aperture in said second arm of said spring clamp member and fitting snugly in said aperture, said resistor having said second resistor terminal biased into electrical engagement with said support member by said spring clamp member whereby said resistor is shunted by said bimetal element when said first and second contacts are in engagement, said resistor being supported in heat transmitting relation with respect to said bimetal element by said spring clamp member and said support member, the resistance value of said resistor being sufiicient to cause the current passing therethrough to generate enough heat to keep said bimetal element in a disengaged contact position after disengagement of said contacts.

2. An improved circuit breaker according to claim 1, wherein said support member is provided with a slot for receiving said second resistor terminal.

3. An improved circuit breaker according to claim 1, wherein said bimetal element has a small resistance value relative to that of said resistor but of a sufficient value to cause said bimetal member to disengage said second contact from said first contact in response to self-heating caused by an abnormally high current flow therethrough greater than a predetermined value.

References Cited by the Examiner UNITED STATES PATENTS 1,701,757 2/1929 Lea 200122 2,403,803 7/ 1946 Kearsley 200-122 2,704,318 3/1955 Jorgensen et al. 200116 X 2,914,637 11/1959 Wuerth 200122 BERNARD A. GILHEANY, Primary Examiner. L. A. WRIGHT, Assistant Examiner.

Claims (1)

1. AN IMPROVED CIRCUIT BREAKER FOR A CIGAR LIGHTER HAVING A SOCKET IN WHICH A REMOVABLE IGNITING PLUG HAVING A HEATING ELEMENT IS ADAPTED TO BE RECEIVED AND MANUALLY MOVED INTO POSITION TO BE HEATED AND A HEAT CONDUCTING TERMINAL HAVING CONTACT MEANS THEREON ENGAGING SAID IGNITING PLUG WHEN SAID IGNITING PLUG IS IN POSITION TO ENERGIZE SAID HEATING ELEMENT, AN IMPROVED CIRCUIT BREAKER COMPRISING: A TUBULAR HOUSING; A DISC OF INSULATING MATERIAL SECURED IN EACH END OF SAID HOUSING; A FIRST HEAT CONDUCTING TERMINAL MEMBER EXTENDING THROUGH AND SECURED TO A FIRST ONE OF SAID DISCS AND ADAPTED TO BE MOUNTED IN HEAT AND ELELCTRICAL CONDUCTING RELATION WITH THE CIGAR LIGHTER HEAT CONDUCTING TERMINAL; A SECOND TERMINAL MEMBER EXTENDING THROUGH AND SECURED TO THE SECOND OF SAID DISCS, AND ADAPTED FOR CONNECTION TO A SOURCE OR ELECTRICAL POWER; A SUPPORT MEMBER WITHIN SAID HOUSING SECURED TO SAID SECOND DISC IN ELECTRICAL CONNECTION WITH SAID SECOND TERMINAL MEMBER BY AN INNER PORTION THEREOF; A FIRST ELECTRICAL CONTACT FIXED ON SAID FIRST SUPPORT MEMBER IN ELECTRICAL CONNECTION THEREWITH; A THERMALLY-RESPONSIVE BIMETAL ELEMENT WITHIN SAID HOUSING SECURED TO SAID FIRST DISC AT ONE END IN HEAT AND ELECTRICAL CONDUCTING RELATION WITH SAID FIRST TERMINAL MEMBER BY AN INNER PORTION THEREOF, SAID BIMETAL ELEMENT HAVING A SECOND ELECTRICAL CONTACT FIXED ON ITS OTHER END IN ELECTRICAL CONNECTION THEREWITH AND NORMALLY ENGAGING SAID FIRST CONTACT, SAID BIMETAL ELEMENT BEING MOVABLE IN RESPONSE TO HEAT RECEIVED FROM SAID FIRST TERMINAL MEMBER UPON A PREDETERMINED HEATING OF SAID CIGAR LIGHTER HEATING ELEMENT TO DISENGAGE SAID SECOND CONTACT FROM SAID FIRST CONTACT; A U-SHAPED SPRING CLAMP MEMBER WITHIN SAID HOUSING HAVING A FIRST ARM SECURED TO SAID FIRST DISC

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