DE2750955A1 - THERMAL SWITCH - Google Patents

Description

09 6 5

LIMITORAG, Hergiswil

Thermal switch

The present invention relates to a thermal switch with a bimetal temperature sensor and a connecting element, which transfers the bend of this temperature sensor to a flat spring which has two stable positions, on which a first contact head is attached, which is pressed against a second contact head in a stable position of the spring will.

Thermal switches are used in particular as safety switches that supply power to motors and transformers or interrupt electrical household appliances if the temperature of the machine or device is above a permissible Value increases. There are several tasks to be solved in the construction of such switches. The switch is supposed to power the circuit with a preset and reproducible as precisely as possible Interrupt the temperature, and when the

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With the switch, the contact heads should be separated from one another so quickly and far enough that practically no burn-off occurs on the contact surfaces. In particular, the Thermal switches intended for use in household appliances have the smallest possible dimensions and if possible can be manufactured inexpensively. Because of their many possible uses, several thermal switches constructed according to different principles are already known.

For example, US Pat. No. 2,777,032 (Burch) describes a thermal switch with a directly heated switching element that triggers the interruption of a circuit. at In this switch, said switching element is designed as an E-shaped flat spring made from a bimetal. the Both free ends of the outer legs of this spring are pressed together during assembly of the switch in the spring plane and in this state on a mounting plate or attached to the switch housing. By compressing the two outer legs of the spring, the middle leg of the spring is deflected out of the spring plane and then points to each Side of this level a stable position. In addition, the spring is built into the switch in such a way that when it is heated The bending force generated in the bimetal is opposite to the spring force and even when a temperature that can be set by the design and assembly of the spring is exceeded exceeds. On the free end of the middle leg of the

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A first contact head is arranged on a flat spring, which is in the first stable position at normal ambient temperature is applied to a second stationary contact head and closes the circuit. As soon as the current flowing through the spring and the current heat generated by this exceeds a predetermined value, also exceeds the bending force of the bimetal the spring force, and the middle leg of the spring jumps from its first to the second stable position, the Contact heads are separated from each other.

In this switch, the force with which the first contact head is pressed against the second contact head corresponds to the Difference between the practically constant spring force and the temperature-dependent bending force of the bimetal. When warming of the switch, the contact pressure decreases, and when the switching temperature is exceeded, the two Contact heads separated from each other relatively slowly. It goes without saying that small arcs occur in this mode of operation and a relatively strong burn-off of the contact surfaces cannot be avoided. If you want to avoid that through Exceeding the switching temperature opened switches when cooling down and falling below the switching temperature closes again automatically, the spring force and the bending force of the switch line must be checked very carefully, Processing and assembly can be adjusted, which makes the cheap production of this thermal switch practical impossible.

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In CH-PS 537,088 (speaker ft Schuh) there is another Thermal switch described. This switch also uses an E-shaped flat spring, which works in the same way is biased as described above and has two stable positions. In contrast to the embodiment already described, however, the spring is not made of a bimetal produced, and the movable contact head is not arranged on one leg, but on the web connecting the three legs of the spring. To trigger this switch a bimetal is used, which is heated directly or indirectly by the current of the circuit to be monitored and its bending by means of a plunger on the free end of the middle leg of the spring is transmitted to deflect it. As soon as the middle leg is above a certain Point is deflected out, the spring jumps to, the arranged on the spring bar contact head from another stationary contact head is released.

With this thermal switch, too, the middle leg of the flat spring, which causes the spring to jump around and thus the Loosening of one contact head from the other causes it to be shifted slowly and continuously into its switching position as the temperature rises. As a result, the desired switchover point widens to a switchover range is, and also with this switch, the contact pressure with increasing temperature and especially in reverse

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switching range reduced. The practical disadvantages of a such an arrangement have already been described above.

Furthermore, two thermal switches are known from DT-PS 2 ' 121'802 (Thermik-Gerätebau) and DT-AS 21 4 3 652 (Micro-Therm), which have a spring with only one stable position. A contact head is attached to this spring, or the spring presses against a contact bridge provided for connecting two contact heads. Furthermore, a dome-shaped bimetallic snap disk is provided in each of these switches, which rests directly or indirectly on the spring and jumps around at a predetermined temperature, thereby deforming the spring and opening the switch.

Both switches have at least two important disadvantages. When the switch is opened, the switching path is the movable one The contact head or the contact bridge is at best as long as the working stroke of the dome-shaped bimetallic snap disk, which limits the current carrying capacity of the switch. When the bimetal snap disk cools and springs back the switches are necessarily closed again under the action of the spring, which is only in a stable position, which can result in continued switching on and off of the switch, a condition common to a safety switch is usually not allowed.

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The present invention is therefore based on the object of creating a thermal switch which has a precisely adjustable, reproducible switch temperature, the contact surfaces of which are pressed against one another with practically constant pressure until the switching temperature is reached and when it is opened are suddenly released from each other, the switching distance is large enough to average currents in common To interrupt voltages with certainty, and which does not switch itself on again after cooling down.

According to the invention, this object is achieved with a thermal switch solved, in which the temperature sensor is designed as a bimetallic snap disk, the connecting element snapping over the snap disk only transfers to the spring when the distance between the bimetallic snap disk and the spring is increased when snapping over, the first contact head is arranged in the region of a free end of the spring and the distance between this contact head and the bending area of the spring is greater than the distance between the point of application of the connecting element and this bending area.

In a preferred embodiment of the new switch a restoring device is provided for transmitting an external force to the spring so that it comes out of the the jumping over of the bimetallic snap disk causes the second stable position to spring back into the first stable position.

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With the new thermal switch, the choice of material and the dimensions and shape of the bimetallic snap disk the switching temperature can be set very precisely, and this is also the case with a very long operating time and high switching frequency practically unchanged. Because with the new switch the force causing the spring to jump over does not occur continuously, but abruptly when the switching temperature is reached, is the contact pressure constant until the contact is opened and also in the immediate vicinity of the switching temperature. And because the working stroke of the bimetal snap disk is only used to deflect the spring is used from its first stable position and the spring is then used under its own power in the second stable position jumps, a switching distance that is significantly larger than the working stroke of the bimetallic snap disk can be achieved will. The ratio of the switching distance to the working stroke is further improved by the greater distance according to the invention between the contact head and the bending area of the spring

compared to the distance between the point of application of the connecting element and the bending area. Because of the movement transmission from the bimetallic snap disk, which is only effective in one direction The spring also ensures that the switch does not turn itself off again after it has been switched off can turn on. Finally, because of the good working stroke ratio of the bimetallic snap disk, the switch can to the switching path of the movable contact from individual

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parts are manufactured, their Masshaitigkelt in the area of the usual tolerances, and even when installing the switch, no additional adjustment or balancing operations are required in order to achieve the desired switching accuracy and safety. It is therefore possible to manufacture the new switch economically and in large numbers.

A preferred embodiment of the invention is described below with the aid of the figures. Show it:

1 shows the plan view of an E-shaped spring installed in a cylindrical housing with a contact head fastened to its middle limb,

Fig. 2 shows the section through a built-in thermal switch in a cylindrical housing with closed contact, and

3 shows the same section as FIG. 2 through a thermal switch with open contact.

In Fig. 1, the plan view of an E-shaped spring 10 is shown. The free ends of the two outer legs 11, 12 these springs are fastened to a base plate 15 with the aid of bolts 13 and 14, respectively. The free ends of the Legs pressed against each other in the spring plane so that

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the spring is always tensioned, which has the consequence that the middle leg 17 is bent out of the spring plane. Approximately in the middle of this middle leg, a bore 16 is provided through which the upper cylinder 32 is a yet to be described connecting member 29 is performed. A contact head 18 is located at the free end of the middle leg attached. The bending zone of the middle leg is located in the area of the connecting web 19 of the three spring legs.

Fig. 2 shows the section through a preferred embodiment of the new thermal switch. The switch has a cup-shaped Housing 21, which is made of a thermally highly conductive material. The one adjacent to the bottom 22 The lower part of the housing wall has a smaller inner diameter than the upper wall part. On the one forming the transition Paragraph 2 3, the base plate 15 is placed and with the help of a bead crimped into the upper housing part 24 pressed against the heel. The bead is not only used to attach the base plate, but also enables an improved Heat conduction from the housing wall to the base plate. The base plate has a central bore 25 through which the connecting member 29 is guided. The lower housing part and the base plate define a space 26 in which a Dome-shaped bimetallic snap disk 27 is arranged. In the middle of the snap disk there is a hole 30.

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brought through which the lower cylinder 28 of the connecting member 29 is guided. The diameter of this lower cylinder is at its free end z. B. thickened by upsetting, so that a bead 31 is formed which prevents the snap disk from being lifted off the connecting member. The link also has an upper cylinder 32 which is guided through the bore 16 in the middle leg of the flat spring and its free end also to a bead 33 is widened, which prevents lifting of the spring from the link. The distance between the facing surfaces of the upper and lower bead practically corresponds the distance between the center of the middle leg of the spring and the snap disk when the latter faces the base plate with its convex surface, as shown in FIG is shown. The movable contact head 18 rests on a stationary contact head 35. This second contact head 35 is attached to an electrical lead which, in the example shown, is designed as a tube 36 into which a lead wire (not shown) can be soldered. The pipe 36 is cast with an insulating potting compound 37 in a cylinder 38 which is pressed into the upper part of the housing. In the middle part of the inner case is still a slidable ring 40 is arranged, the lower edge 41 of which is to be placed on the outer edges of the bolt 13, 14 attached ends of the two outer legs of the spring is provided. The top of the ring

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40 has three extensions offset by 120, of which only the extensions 42, 43 can be seen in FIG. These extensions engage through segment-like formations in the cylinder 38 and are for sliding the ring in axial direction provided, as will be described.

The operation of the new thermal switch is described below with the aid of FIG. This is shown in FIG. 3 the lower part of the thermal switch shown in Fig. 2 again and in the same section as in Fig. 2, but with the open Contacts shown. As long as the ambient temperature and in particular the temperature in the room 26 below a predetermined one Switching temperature, the bimetal snap disk 27 has the shape shown in FIG. 2, and the contact head 18 is pressed onto the contact head 35 by the middle leg 17 of the spring 10. Then there is an electrically conductive connection from the metallic housing 21 via the base plate 15, the two bolts 13, 14, the E-shaped flat spring 10, the movable contact head 18, the stationary contact head 35 to the tubular line 36. As soon as the ambient temperature If a value has risen which also causes the temperature in space 26 to rise above the switching temperature, the dome-shaped jumps Bimetallic snap disk so that it assumes the position shown in FIG. 3, in which the concave surface the snap disk of the base plate 15 faces. When changing

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jump of the snap disk, the outer edge of the disk rests against the base plate, and the center of the disk becomes lifted off the base plate. The connecting member 29 is suddenly pulled downwards by the stroke of the dome-shaped snap-action disk. This displacement of the connecting link is transmitted to the middle leg of the flat spring, which is thereby removed from its first leg shown in FIG stable position on the (in the figures) upper side of the spring plane is pulled down over the switching point and as a result of the spring tension jumps into its second stable position on the lower side of the spring plane. The movable contact head 18 suddenly separated from the stationary contact head 35, and the electrically conductive one described above The connection between the housing 21 and the tubular line 36 is interrupted. It goes without saying that in the described arrangement, the switching path of the contact head 18 is much greater than the working stroke of the connecting link caused by the bimetallic snap disk jumping over 29, because the distance of the contact head 18 from the bending zone of the middle spring leg is about twice as large as the distance of the area of application of the connecting link from the bending zone, because the working stroke only removes the spring leg must deflect the position shown in Fig. 2 to just above the switching point and because the spring leg does not have the shape of a straight lever due to the spring tension, but in each of its two stable positions one die

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Has deflection enlarging bend.

The two cylinders 28, 32 at the ends of the connecting member 29 are together somewhat longer than the working stroke of the bimetallic snap disk. Therefore, when the snap disk cools down, it falls below the switching temperature and the disk snaps back in the position shown in Fig. 2, the connecting member moved by the working stroke of the snap disk, but the middle one The leg of the E-shaped spring remains in its second stable position shown in FIG. 3. The switch is about it necessarily open when the switching temperature is exceeded, but not closed again when the temperature falls below this level.

The slidable ring 40 is provided for closing the switch. As already described above, has this ring has three extensions 42, 43 protruding from the housing. When these extensions are pushed into the switch are, the ring is pushed down and presses in the area of the two bolts 13, 14 on the outer edges of the Flat spring. This displacement of the spring caused by this relative to its fastening points causes the spring to spring into position their first stable position, with the middle leg pressing the contact head 16 against the contact head 35 again.

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The thermal switch described can be produced with different dimensions and for different switching capacities. A preferred embodiment is intended for installation in household appliances and in particular in electric water pots. This embodiment has an outside diameter of only 6.3 mm and safely switches off a current of 5 amperes at an operating voltage of 220 volts AC. The switching temperature is about 120 ^° C. The set spring tension causes a contact pressure of at least 0.4 N, and the mutual arrangement of the individual components is selected in such a way that a displacement of about 0.15 mm transmitted from the connecting member to the middle leg of the spring sufficient to open the switch, the switching distance of the movable contact head being about 1.0 mm. The working stroke of the bimetallic snap disk is about 0.25 mm, which is almost twice as large as is necessary for the deflection and jumping of the spring. This measure not only results in a high level of switching reliability, but also enables the switch to be manufactured economically.

It goes without saying that the described structure of the new Thermos holder can be changed when the switch for special uses are provided. Example catfish can the switch is inserted into an electrically insulating sleeve 50 (indicated by a dashed line in FIG. 2)

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ben, which are advantageously made of Nomex Aramyd paper consists. So that the electrical transition resistance between the stationary contact head 35 and the supply line The tube 36 used is as small as possible, the contact head can with the aid of a tool inserted into the tube riveted to the pipe. To fasten the tube 36 in the cylinder 38, instead of the casting compound described, it is advantageous a tempered glass seal can be used. It is also possible to approach the cylindrical casing 38 dispense and connect the potting compound or the hard glass seal directly to the ring 40. In this embodiment is when switching back the spring from the second corresponding to the open contact to the closed one Contact corresponding first position with the ring 40 also the stationary contact head 35 shifted, and after jumping over of the spring, the stationary contact head and the ring are affected by the spring force transmitted via the movable contact head pushed back into their original position. Although the ring 40 to reset the switch in the simplest If the shape is moved manually, mechanical elements such as pistons, cylinders, and diaphragms can also be used for this purpose or levers are brought into action. Finally, every person skilled in the art is familiar with the fact that the temperature at which the Bimetallic snap disk swings around due to the selection of the bimetal, its dimensions and the shape of the disk in one wide range is adjustable.

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Claims (7)

PATENT CLAIMS Iy thermal switch with a bimetal temperature sensor and a Connecting element that bends this temperature sensor transfers to a flat spring having two stable positions, on which a first Kohtafctkopf is attached, which in one stable position of the spring on a second contact head is pressed, characterized in that the bimetal temperature sensor is designed as a bimetal snap disk (27) is, the connecting element (29) only transmits the snap of the snap disk to the spring (10), if the distance between the bimetallic snap disk and the spring is increased when snapping over, the first contact head (18) is arranged in the area of a free end (17) of the spring and the distance between this contact head and the bending area (19) of the spring is greater than the distance between the point of application (16) of the connecting element and this bending area. 2. Thermal switch according to claim 1, characterized by a reset device (40) for transmitting an outer Force on the spring (10) so that it comes from the second caused by the bimetallic snap disk (27) jumping over stable position (Fig. 3) springs back into the first stable position (Fig. 2). 3. Thermal switch according to claim 1, characterized in that the spring (10) is designed as an E-shaped flat spring, with three legs (11, 12, 17), of which the two outer legs (11, 12) are pressed against each other to generate the spring tension on a carrier plate (15) are attached, while the inner leg (17) deflects transversely to the plane determined by the flat spring. 809821/0806 1 7 b UJ bb bar is and because of the spring tension both on the one and on the other side of this level a stable position has (Fig. 2 and Fig. 3). 4. Thermal switch according to claim 3, characterized in that the carrier plate (15) has a bore (25) for performing the Has connecting element (29) and on one surface of this plate the two outer legs (11, 12) of the E-shaped flat spring (10) are attached and the bimetallic snap disk (27) is arranged on the other surface of the plate is and the rod-shaped connecting element through a hole (16 or 30) in the middle leg (17) of the flat spring and is guided in the middle of the bimetallic snap disk and thickening at its outer ends Has beads (33 or 31) that the distance between the bimetallic snap disk and the corresponding area of the limit the middle leg of the flat spring. 5. Thermal switch according to claims 2 and 4, characterized in that that the carrier plate (15) with the flat spring (10), the bimetallic snap disk (27) and the connecting element (29) is installed in a cup-shaped housing (21) and, with the bottom (22) of the housing, delimits a chamber (26) in which the bimetallic snap disk is arranged and a closure piece (36, 37, 38) is introduced, to which the second contact head (35) is attached. 6. Thermal switch according to claims 2 and 5, characterized in that that on the edge (38) of the closure piece (36, 37, 38) several extending in the longitudinal direction of the housing (21) Recesses are arranged through the outwardly protruding and intended to attack the external force extensions (42, 43) of the resetting device (40) are performed. 809821/0806 27509bb 7. Thermal switch according to claim 6, characterized in that the closure piece (36, 37, 38) and the resetting device (40) are designed as a unitary assembly which to reset the E-shaped flat spring (10) in the first stable position (Fig. 2) in the housing (21) is. S / now 1.11.77 809821/0806