US3119912A

US3119912A - Thermal current switch

Info

Publication number: US3119912A
Application number: US67742A
Authority: US
Inventors: Fehrenbach Alfred; Fraatz Heinrich
Original assignee: Licentia Patent Verwaltungs GmbH
Current assignee: Licentia Patent Verwaltungs GmbH
Priority date: 1959-11-09
Filing date: 1960-11-07
Publication date: 1964-01-28
Anticipated expiration: 1981-01-28
Also published as: DE1095378B; NL257709A

Description

1964 v A. FEHRENBACH ETAL 3, ,9

THERMAL CURRENT SWITCH Filed Nov. '7. 1960 Fig! 2 7 I 8a 5 a 9 /3 6- I l 8 W (mam WM Jn venfars Jay: W

Patented Jan. 28, 1954 3,119,912 THERMAL CURRENT SWITCH Alfred Fehrenhach, Alexander Diirries, and Heinrich Fraatz, Hameln, Germany, assignors to Licentia Patent-Verwaltungs-Gnu.b..H., Frankfurt am Main, Germany Filed Nov. '7, 1960, Ser. No. 67,742 Claims priority, application Germany Nov. 9, 1959 3 Claims. (Cl. 200-416) The present invention relates to a thermal current switch for use as an overload protective device in relatively low power equipment, such as household appliances, oflice machines, small power tools, automotive equipment, and the like.

Equipment of the above type must be provided with suitable protective means which will prevent damage in case of an overload. These means may be in the form of a thermal current switch which must often be accommodated in very small spaces, and which must be such that it can be mass-produced at low cost so as not unduly to aiiect the manufacturing costs of the apparatus with which the switch is to be used. Thus, there is a definite need for a compact and inexpensive switch which is able to open an electric circuit in response to temperature rises resulting from excess current, and which switch meets the usual requirements insofar as insulation and reliability are concerned.

l-leretofore known switches have proven to be too complicated and too expensive, nor have existing switches been able to meet the rigid space limitations which are imposed by the design of modern compact and light weight electrical appliances. The reason for this is that known switches incorporate a large number of parts, including a plurality of individual springs which serve different functions. For instance, in one known type of switch, one spring is provided for producing the requisite contact pressure between the fixed and movable contacts, another spring is provided for moving the contacts apart upon overload, and yet another spring is provided resetting the switch.

it is, therefore, an object of the present invention to provide a thermal current switch which overcomes the above disadvantages.

It is another object of the present invention to provide a thermal current switch which is exceedingly simple in that it incorporates very few parts, each readily susceptible to mass-production techniques.

The objects of the present invention also include the provision of a switch which will open under overload condition even though it is attempted to hold the position manually in closed position.

With the above objects in view, the present invention resides mainly in a thermal current switch which incorporates but a single spring which is relied on to produce the requisite contact pressure between the fixed and movable contacts, to separate the contacts upon overload condition, and to produce the resetting force for closing the switch.

More particularly, the present invention resides in a thermal current switch which comprises a fixed contact, a bimetallic element, an actuator such as a push button carrying a movable contact bridge for connecting the fixed contact and the bimetallic element, and a single spring coacting with the contact bridge for producing contact pressure between the contact bridge and the fixed contact when the switch is closed, for moving the contact bridge out of engagement with the fixed contact upon the occurrence of an overload which produces a deflection of the bimetallic element, and for producing the resetting force for closing the switch.

Additional objects and advantages of the present invention will become apparent upon consideration of the following description when taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is an elevational view showing the position of the operative components of a switch according to the present invention when the switch is closed.

FIGURE 2 is a sectional view taken substantially along line 22 of FIGURE 1.

FIGURE 3 is a view similar to FIGURE 1, showing the position of the operative components during an intermediate stage as they move, upon the occurrence of an overload, from closed to open position.

FIGURE 4 is a view similar to FIGURE 1, showing the position of the operative components in the open positron.

FIGURE 5 is a View similar to FIGURE 1, showing the position of the operative components in case the push button is held down at the moment of overload.

Referring now to the drawing and to FIGURES l and 2 thereof in particular, there is shown a thermal current switch in its normal closed position. The switch comprises a housing 1, showing in outline form in FIGURE 1 with FEGURE 2 showing this housing as being composed of similar halves. The housing contains a push button 2 which is mounted for reciprocatory movement relative to the housing 1 between the operative or depressed position shown in FIGURE 1 and the inoperative or released position shown in FIGURES 3 and 4. The push button 2 carries at its lower end a pivot pin 3 whose extreme ends are slidably received within grooves 5 formed in the housmg.

The pivot pin 3 serves to connect the push button 2 to a contact bridge 4 which is in the form of an elongated conductive element having at approximately its middle two upwardly bent ears in through which the pivot pin 3 passes, so that the contact bridge 4 is pivotable with respect to the push button 2; and forms a two-armed lever having arms of approximately equal lengths.

The upper surface of the left arm of the contact bridge 4, as viewed in FIGURE 1, carries a movable contact 6 which cooperates with a fixed contact '7 carried by a terminal strip 14 mounted in the housing 1, whereas the upper surface portion at the end of the right arm is engaged by a detent carried at the free end of a bimetallic strip 8 whose lower end is connected to the housing 1 as well as to a terminal strip 15.

The upper end of a coil spring 9 surrounds a projection ll located on the underside of the contact bridge 4 at a point intermediate the pivotal connection between the bridge and the push button, i.e., the middle of the contact bridge, and the surface portion engaged by the detent 8a. The lower end of the spring 9 is received in a well or recess lltl formed in the housing 1. This spring, which, as shown, is loosely inserted into the switch, is the only spring element that is needed. as will be explained below.

The switch further comprises two abutments l2 and 13, the purpose of which will be explained below. Also, the housing l is formed with openings 16 and 17 through which may pass mounting elements, so that the switch may readily be mounted on the appliance with which it is used by threading it onto suitable mounting rods.

The operation of the switch will now be explained with reference to FIGURES l, 3, 4 and 5.

FIGURE 1 shows the switch in closed position, the contacts 6 and '7 being held in engagement with each other with the necessary contact pressure and the right end of the contact bridge being pressed against the detent 8a of the bimetal strip 8 by the action of the spring 9 which, in this position, is in compressed state. Thus, an electric current may flow from the terminal strip 14-, through the contacts 7, 6, the contact bridge 4, the detent 8a, the bimetal strip 8, and the terminal strip 15. The bimetallic strip d, of course, is shown in the position which it occupies when the current flowing through the switch is not greater than the maximum permissible current.

Should now the current through the switch exceed the permissible maximum, the temperature of the bimetallic strip 3 will increase to a point where the strip will deflect such as to move the detent 3a out of engagement with the contact bridge 4. As a result, the spring 9 will pivot the right arm of the contact bridge 4- upwardly, thereby urging the push button upwardly towards its inoperative position. During the first stage of the switch opening movement, shown in FIGURE 3, the contacts 6, 7 will remain in engagement with each other, i.e., the contact bridge 4 pivots at first about the point of engagement between the two contacts 6 and 7. This engagement will not be broken until the left arm of the contact bridge 4 strikes the abutment 12. The kinetic energy of the contact bridge, at the instant it reaches against the abutment 12, will cause the bridge to be subjected to an abrupt striking effect which increases the speed with which the contacts 6 and 7 are separated, i.e., the contacts will be opened in a sudden or jerky manner. This means that the contacts 6 and 7 will be separated from each other more quickly than if the abutment 12 were not provided.

After striking the abutment 12, the contact bridge 4 continues its movement until it engages the lower abutment 13, as shown in FIGURE 4. This is the position of the component parts after the switch-opening movement has been completed.

After the bimetallic strip 8 has cooled, the switch may be closed by depressing the push button 2. This will move the pivot pin 2% downwardly, so that the contact bridge 4 will at first remain in engagement with and pivot about the abutment 1.3 inasmuch as the spring 9 tends to rotate the contact bridge 4 in counterclockwise direction. The depressing of the push button will compress the spring 9 until the right arm engages the detent Sn, and the contacts 6 and 7 may then be brought into engagement with each other by releasing the push button 2; this will cause the contact bridge 4 to pivot about the detent 8a, under the influence or" the spring 9, in clockwise direction. The switch is thus reset into closed position and is ready to function again in case of overload.

it will be seen from the above that the single spring 9 serves a three-fold function, namely, the spring (1) pro- 'duces the contact pressure between the movable contact *6 of the contact bridge 4 and the fixed contact 7 when the switch is in closed position, (2) moves the contact bridge 4 out of engagement with the fixed contact 7 upon the occurrence of an overload which produces a deflection of the bimetallic strip 8, and (3) produces the resetting force for closing the switch. Inherent in (2) is, of course, that the spring 9 also acts to move the push button 2 from its operative position to its inoperative position.

FIGURE shows that if it were attempted to hold :the switch closed manually at the instant an overload current flows through the switch, the switch would still open. This is so because upon deflection of the bimetallic strip 8, the right arm of the contact bridge 4 will be moved upwardly under the influence of the spring 9, thereby separating the contacts 6 and 7. Of course, the contact bridge would then not first pivot about the point of engagement between the contacts 6 and 7, but would immediately pivot about the pivot pin 3. The contact bridge 4 would ultimately assume the position illustrated in FIGURE 5 wherein the right arm is shown as engaging the abutment 13. Upon release .of the push button 2, the operative components of the switch would assume the position shown in FIGURE 4.

FIGURE 5 also shows that if it is attempted to reclose the switch before the bimetallic strip 8 has cooled sufficiently to allow the detent 8a to engage the right arm of the contact bridge 4, the contact bridge 4 would simply pivot about abutment 113, i.e., if the push button is depressed while the parts are as shown in FIGURE 4, they will simply assume the position shown in FIGURE 5 and no resetting of the switch is possible. Of course, once the bimetallic strip 8 has cooled sulficiently to return to the condition shown in FIGURE 1, the above-described resetting operation could be carried out.

It will be understood that the above description of the present invention is susceptible to various modifications, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

We claim:

1. A thermal current switch comprising, in combination: a housing; a fixed contact carried by said housing; a bimetallic strip having one end thereof connected to said housing, said bimetallic strip having at its other end a detent; a push button mounted in said housing for reciprocatory movement relative thereto and carrying a pivot pin having ends slidably received in grooves of said housing; a contact bridge pivotally connected to said pivot pin, said pivot pin being connected to said contact bridge at a point intermediate its ends so that said contact bridge forms a two-armed lever, said contact bridge carrying on one arm thereof a movable contact cooperating with said fixed contact, the other arm of said contact bridge being engageable by said detent of said bimetallic strip; and a single spring coacting with said contact bridge for producing contact pressure between said fixed and movable contacts when said switch is in closed position, for moving said contacts out of engagement with each other upon the occurrence of an overload which produces a deflection of said bimetallic strip resulting in a disengagement of said detent from said other arm of said contact bridge, and for producing the resetting force for closing the switch, said spring being loosely inserted in said housing, one end of said spring being received within a recess in said housing and the other end of said spring being operatively connected to said other arm of said contact bridge to act on a point thereof which is between the point at which said pivot pin is connected to said contact bridge and the point at which said detent of said bimetallic strip engages said other arm of said contact bridge.

2. A thermal current switch as defined in claim 1 wherein the operative connection between said contact bridge and said spring is established by a projection carried by said contact bridge, said projection being in engagement with said other end of said spring.

3. A thermal current switch as defined in claim 1, further comprising an abutment for increasing the speed with which said contacts are separated under the influence of said single spring, said abutment being located to be engaged by said one arm of said contact bridge when the latter is moved under the influence of said spring, thereby allowing pivoting of said contact bridge, still under the influence of said spring, about said abutment to separate said movable contact from said fixed contact.

References Cited in the file of this patent UNITED STATES PATENTS 2,335,082 Platz Nov. 23, 1943 2,409,917 Von Hoorn Oct. 22, 1946 2,418,537 Wood Apr. 8, 1947 2,492,382 lngwersen Dec. 27, 1949 2,741,681 Allard Apr. 10, 1956 2,952,757 Ellenberger Sept. 13, 1960