DE2343834A1 - Hot plate temperature limiter - has temperature sensitive element exposed to the heat of an electric hot-plate - Google Patents

Abstract

It interrupts or limits the current supply to the hot-plate at the set temperature by a contact. A safety contact is provided, operated by the same temperature sensitive element, which interrupts current supply at a temperature much higher than the set value. When this contact is operated once, it permanently disconnects the hot-plate owing to a locking device which keeps the contact open after its single operation. The safety contact operates a cut-off relay for the hot-plate. The temperature sensor is of a known type, consisting of an expansion rod in a sleeve. Sensors are made of materials with different coefficients of thermal expansion.

Description

PATEiNTANWÄl-ΓΕ

Dipl.-Ing. EGGS Dipl.-Chem. Dr. R U F F Dipl.-lng. J. B EIE R

7 STUTTGART 1 Neckarstrasse 5O Telephone C071O 22 7O 51

Jul 25, 1973 - JB / Va

Applicant: E.G.O. Electrical appliances Blanc and Fischer 7519 Oberderdingen / Württ.

A 14- 896

A 14 897

Temperature limiter

The invention relates to a temperature limiter with a temperature of an electric cooking appliance temperature-sensitive element that supplies power via at least one normally open contact at the set temperature to the electric cooker interrupts or limits.

Such temperature limiters are numerous on electric hotplates inserted in the event of incorrect operation or failure of a regulator or step switch, the electric hotplate switch off. They consist, for example, of an insulating housing in which a bimetal and a snap switch are arranged, which can turn off the power supply for the electric hotplate.

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Poateohöckkonto Stuttgart 42O3O Dresdner Bank Stuttgart Account β Oll 341

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These temperature limiters, which are very small and can therefore be easily accommodated at the points to be monitored, which are also under the name "Protector" in the trade, are primarily for normal electric hotplates with a cast iron body thought, with regard to the excess temperatures are not very sensitive. However, there are areas of application in which a temperature limit is very high must respond precisely and, on the other hand, absolute security must be created that the temperature limit not fail. This is the case, for example, with electric cooking appliances, which are normally used as the top plate Have a plate made of a glass ceramic that extends over several hotplates. On the one hand, this must be because of, de'r Compared to metal, lower heat transfer values of the glass ceramic, the working temperature of the heating elements under the glass ceramic plate are driven very high, and on the other hand it must be ensured that the glass ceramic plate is not overheated under any circumstances. Even though this glass ceramic has a high heat resistance and also heat shock resistance, but it can with local overheating, burst or suffer other permanent damage.

The object of the invention is to create a temperature limiter of the type mentioned in the introduction, in which a failure is largely excluded.

This object is achieved according to the invention in that one of the same temperature-sensitive element An actuatable safety contact is provided which, if the set temperature is significantly exceeded causes a shutdown.

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If there is a malfunction, for example by getting stuck of the Arbeitsleontakt, it is ensured that that if the set temperature is exceeded, the electric cooker is switched off. The Circuit can be chosen so that either only the individual hotplate or the entire electric cooker is switched off will. It has been shown, surprisingly, that this arrangement is more reliable than an arrangement in which two normal temperature limiters connected in series are. Part of the reason for this is that it should be almost impossible for both temperature limiters to use the to create the same thermal conditions on the electric cooker. It was also found that the_, great operational reliability of the limiter according to the invention is based on the fact that with a fixed temperature controller The contacts are practically the only parts that o Cause malfunction.

According to a particularly advantageous embodiment example the temperature limiter according to the invention constructed in such a way that the safety contact after being exceeded once the set temperature causes the electric cooker to switch off permanently. In this embodiment, which in turn either only the individual hotplate or the entire electric cooker is permanently switched off, it is ensured that the faulty temperature limiter will not continue to cook. Only after opening the Electric cooker .or. of the temperature limiter and replacement or repair, this is put back into operation.

According to a preferred embodiment, working and

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Safety contact can be actuated by a common snap spring. The two preloaded can also be used Spring parts to the contacts arranged at opposite ends of the common snap spring belong, on opposite sides and at different points of a common actuator be supported. Furthermore, the snap spring with its mounting and the contact spacings are preferably designed in such a way as to uaß after the switching process, only the normally open contact, but not the safety contact, returns to the initial position. With a particularly simple design of the temperature limiter, this measure ensures that You can no longer work with a faulty temperature limiter.

A design in which the safety contact is activated when the normally open contact is actuated is particularly advantageous or during the working movement of the temperature-sensitive element, it can be displaced slightly transversely to its lifting direction is. This measure ensures that the safety contact, which in most cases is in throughout the entire service life of the temperature controller should only respond once, if at all, even after years is still functional, as the lateral shift prevents it from sticking or welding.

Further advantages and features of the invention emerge from the subclaims and the description in connection with the drawings. Some embodiments of the invention and illustrated in the drawings explained in more detail below. Show it

1 shows a schematic section through a Temperature limiter according to the invention,

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2 and 3 a detail of a variant in two working positions,

4 and 5 details of further embodiments,

6 shows a sectional illustration of a further preferred embodiment,

7 to 9 show an enlarged detail from FIG. 6 in three different working positions and

Fig. 10 is an enlarged plan view of "*" a snap spring for a temperature limiter according to FIGS. 6 to 9

The temperature limiter 11 shown in Fig. 1 has a housing 12 and a temperature-sensitive attached thereto Element 13, aas as a thermal expansion element is trained. It consists, for example, of a tubular sleeve 14 made of stainless steel, which at its lower End, if necessary via an adjusting screw (not shown), is connected to a central rod 15. The rod 15 can be made of ceramic material, which is a very has a low coefficient of thermal expansion, while that of the sleeve 14 is larger. The temperature limiter is In the example shown, it is intended to monitor the temperature of a hotplate that is not below one shown glass ceramic plate is arranged. For this purpose, the temperature-sensitive element is between the, for example designed as a tubular heater heating element and the insulation pushed through. A temperature limiter can be installed per hotplate be provided.

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In the housing 12 of the temperature limiter 11 is a Rocker 16 in the form of a two-armed lever is arranged to be pivotable about an axis. One arm of the rocker 16 is with the rod 15 in connection, while the other arm has a stop 18 carries, which is designed in the form of an adjusting screw which is screwed into the rocker. On the same arm rests a pressure rod 19, the. durer an opening 20 protrudes in a carrier 21 made of insulating material around an axis. 22 pivotable on the housing 12 is mounted and carries a snap switch 23 in a recess on its side facing away from the rocker 16. This snap switch is designed in a manner known per se and has a snap spring 24, the bent open spring Spring part is supported on an abutment 25, which is designed in the manner of a leaf spring and with his part remote from the support is attached to the beam. The Lruckstab is based on this abutment 25 and it can thus be directed upwards in the drawing Press the snap switch to open it. Normally the working contacts 26, one of which is arranged on the end of the snap spring 23 is closed. The mating contact for this is attached to the carrier 21 and electrically connected to a terminal 27. At the end of the carrier remote from the axis 22, a safety contact 28 is arranged, which is connected to a mating contact cooperates, which is attached to the housing in an insulated manner and electrically connected to a terminal 29 connected is. The counter contact to the safety contact 28 can be adjusted via an adjusting screw 30.

The safety contact 28 is pressed onto its mating contact by a spring 31 which, in the example shown, acts on a sheet metal bracket 32 which is attached to the carrier 21.

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is brought. The support is counteracted by the spring 31 panned clockwise, d. H. an upward movement of the causing the switching off of the working contacts 26 The pressure rod 19 acts against the pressure of the spring $ 1.

From the schematic circuit diagram of FIG. 1 it can be seen that the contacts 26 and 28 are connected in series are, with the snap-on tube 24 taking over management tasks in the usual manner, and that the entire temperature limiter 11 electrically in series with the heating resistor 33 of a hotplate 34, indicated by dash-dotted lines, of the electric cooking appliance and is connected to an adjustable controller 35. Thus ~ flows through the temperature limiter 11 that supplied from the mains connection 36 of the hotplate 3 ^ Current. The controller 35 can be any controller, preferably however, an energy regulator which enables a stepless power supply to the heating resistor 33.

The temperature limiter 11 according to Fig. 1 works as follows: Normally · the contacts 26 and 28 are closed when switching on the heating resistor 33 by means of the controller 35, current flows through these contacts and heats the Cooking zone 34. The sleeve 14 expands more than the rod 15 with a smaller coefficient of thermal expansion, so that the rocker 16 is pivoted clockwise and over the pressure rod 19 on the abutment 25 for the snap spring 24 presses. When the snap point is reached, the snap spring 24 springs down and opens the Normally open contact 26. This switching state, through which the circuit leading to the heating resistor 33 is interrupted, occurs according to the setting of the temperature limiter when the temperatures at the hotplate 34 are still p; ut are below a value that is harmful to the glass ceramic plate. After one through the natural switching hysteresis

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the temperature limiter determined cooling of the temperature-sensitive Element 13 closes the working contact 26 again, and the hotplate 3 ^ is heated again.

The temperature limiter is not only used as a protective element, but also as a working element by using the energy regulator is regulated purely as a function of energy and this, for example, for quickly heating a cooking vessel can be put to full power. The temperature limiter 11 then ensures that there are still no excessive ones Temperatures occur.

It can therefore be seen that the working contact in the case of the indicated use responds relatively often. Nevertheless, it can happen, for example, that the working contact 26 does not open. This is indeed very rare with the relatively reliable operation of the snap-action switches and with most temperature limiters do not occur at all, but it can be caused by welding of the working contacts 26 or their electrical bridging occur in the event that the normally open contact is at the preset temperature does not open. In this case, the sleeve 14 expands further, as does the further pivoting of the rocker 16 clockwise the stop 18 comes to rest on the carrier 21. This was during the normal switching to the opening the working contacts 26 remained immobile, since the spring 31 is stronger than the counter pressure of the snap switch 23 on the push rod 19 during its normal switching.

By the stop 18, however, the carrier is pivoted clockwise and thereby opens the safety contact 28, so that despite the normally open contacts 26 the heating resistor 33 is turned off. By means of the screw 18, the temperature limiter 11 can be adjusted so that

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the opening of the safety contacts already shortly above the set target temperature for the opening of the working contacts 26 28 takes place, at least below the temperature harmful to the glass ceramic plate.

In the embodiment of FIG. 1, the closes Contact 28 again, if a cooling at ^ the hotplate 3 ^ or the temperature-sensitive element 13 has taken place. In certain embodiments, this would be a disadvantage. On the one hand, in the embodiment according to FIGS. 1 to 5, the safety contact 28 is designed as a "creeping" contact that tends to form arcing, and on the other hand the user would mostly not notice the malfunction of the normally open contact 26 at all, and when further In operation, only safety contact 28 would then have an effect. If this then fails, however, a Damage can occur to the glass ceramic plate, which then damages the entire electric cooker and makes it out of order would be set.

For this reason, in the embodiment in FIG. 2 with otherwise the same design (with the same parts bear the same reference numerals), a hasty device 38 is additionally provided, which has the shape of a pawl that of a spring 39 is loaded in the direction of the carrier 21.

While FIG. 2 shows the idle state or normal operation, FIG. 3 shows the state in which the safety contact was opened. It can be seen that by pivoting clockwise the locking device 38 is locked on the carrier and this now blocks against pivoting back counterclockwise, so that the safety contact 28 after a single opening remains open, even if the temperature on the hotplate

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has sunk again. This hotplate then fails and cannot be put back into operation, so the user is forced to check the temperature controller and have the error corrected.

In Fig. 4 a detail of an embodiment is shown, which can also correspond exactly to that of FIG. Here, however, the safety contact 28 and its mating contact are attached to the housing 12, and the carrier 21 acts on the safety contact 28 by contacting a stop 40, which acts as an extension of a resilient contact carrier can be designed for the safety contact 28.

In Fig. 5 a detail is shown in which in a modification 1, when the carrier 21 is pivoted clockwise, the normally open safety contact 28 ' is closed. In this case, the protective contact 28 'is in a special circuit, and its closing acts on a relay 41 pin, which over the main circuit the normally open contact 26, the heating resistor 33 and the controller normally holds closed and opens when the safety contact 28 'responds. This relay is preferred also designed so that it is self-retaining, α. H. does not close by itself after being addressed once.

In this context, it should be noted that the design with relays naturally also applies to the design of the temperature limiter according to Fig. 1 is conceivable, where aann the normally closed contact 28 forms a closed circuit at whose opening once the relay drops out. Here you just have to ensure that not when the network is switched off the same phenomenon occurs. In any case, this execution would be largely self-assured. Can also be used as a relay a thermal switch can be used.

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In the pig. 6 to 10 is a further, particularly preferred embodiment of the temperature limiter according to the invention shown. Here, too, the same parts have the same reference numerals as in FIG. 1. Here, too, there is a temperature-sensitive Element with a more expanding sleeve 14 use that with a-weaker expanding Inner rod 15 is connected via an adjusting screw 42. In contrast to FIG. 1, the rocker 16 is in the disconnection direction by a compression spring 43; H. clockwise, burdened, so that the opposite arm of the rocker 16 frictionally rests on the rod 15. The push rod 19 protrudes through an opening in an insulating material carrier 44 which is fixed to the housing and partially forms the housing, in its recess the contacts 26 and 28 are arranged with their switching mechanism. This switching mechanism consists of one on the insulating support 44 fixed angle lever 45, whose fixed arm is designed as a leaf spring and thus allows pivoting of the angle lever 45. On this arm the push rod 19 also acts and thus pivots the free arm 46 of the angle jack.

The actual switching mechanism can be seen particularly in FIGS. 7 to 9, the three working positions of the show the same part. The switching spring 47 of the switching mechanism, which can best be seen in FIG. 10, carries on their outer ends the working contact 26 and the safety contact 28. Two incisions are in the consisting of thin spring material switching spring, two outer continuous connecting parts 48 and two spring parts 49, 50 separated, of which the spring part 49 on the side of the safety contact 28 lies and actuates it, while the pedal part 50 is used to actuate the normally open contact 26 belongs and eats arranged on its side. The feather-

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parts are bent out in the usual way in an arc upwards and are supported with their facing one another also as cutting edges 51 designated ends in cutting edge bearings 52, the notches on two opposite Sides of the arm 46 are formed. The blade bearings for the spring parts 49 and 50 are on different ones Place the arm 46, with the cutting edge bearing for the spring part 50 for the normally open contact 26 being higher in the example shown here, d. H. more about equilibrium or Snap position facing, lies as the cutting edge bearing for the spring part 49 which actuates the safety contact 28.

The switching spring 47 with its contacts 26 and 28 is freely supported, d. H. it is in its position only by the abutment of its contacts 26, 28 on the corresponding mating contacts 53 »54- as well as by supporting their spring parts 49, 50 held in the cutter bearings 52. The mating contacts 531 54 are attached to contact carriers in the Isolierstoffträger 44 are set and to the connections

27 and 29 lead. It is in particular from FIGS. 7 to can still be seen that the contact spacing when the contact is open at the working contact 26 by a on the insulating material carrier 44 provided stop 55 is limited to a relatively low value, while it is the safety contact

28 can grow very large.

The temperature limiter 11 'according to FIGS. 6 to 10 works as follows:

With regard to the temperature-sensitive element 13 of the by the rocker 16 formed Actät'igungsgestänges as well as with respect There are no significant differences between the basic function and the embodiment according to FIG. When the sleeve expands 14 and pivoting the rocker 16 clockwise

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About the Lruckstab 19 of the angle lever 45 against the Pivoted clockwise, whereby the arm 46, v / ie from 8 can be seen, on the one hand upwards and on the other hand also, as indicated by the dashed lines is, is moved slightly laterally towards the safety contact 28. When the cutting edge bearing 52 for the spring part 50 comes over its snap point, the switching spring snaps 47 on the side of the normally open contact 26, and the normally open contact 26 lifts off from its mating contact 53 and rests against the stop 55. When it cools down, migrates the arm 46 of the bell crank 45 downwards, and the contact 26 closes again when the snap point for the spring part is exceeded. Bas is the normal operational sequence that expires each time the limit temperature is reached. Every time it gets like 'out!' 8 eu was aware of who Snap spring 47 in its longitudinal direction, d. h «, across the Contacts, moved back and forth, not only when switching, but also for each one below the switching point lying, caused by different temperatures on the element 13 movement. This prevents welding or gluing the safety contact 28 so that it is still ready for operation if it has been for years has remained without use.

In Fig. 9 the case is now shown in which the normally open contact 26 is not due to welding or gluing has opened, although the cutting edge bearing 52 for the spring part 50 long ago hiked over the Schnappunkt. In this case, by further expansion of the sleeve 14, the angle lever is pivoted further and the arm 46 is displaced so far up until the cutting edge bearing 52 for the spring part 49 comes over the snap point, so that then the safety contact 28 opens. As a result of his great

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is iiontaktah object does not come, the snap spring 47 thereby in a position from which eie even in the origin reduced _{distribution}} if a cooling of the! elements 15 enters "This phenomenon is characterized in that dii. "Spring parts 49, 50, which in the position according to Fig. '/ And now in the position according to .Fig. 8 exerted a spring effect on the l'ui] 46 downwards, which counteracted the force of the spring 43, this spring effect now not . more or in a greatly reduced extent, together with the ßeiuesiiun _t · have, the other resilient members in the switch, the contact gaps and the formation of knife-edge bearing is dimensioned to snap spring so that this latching occurs in the open position "of the Sicherheitekontaktes 28th -Auen here so arises the advantageous effect that the hotplate can only be put back into operation in addressing the safety contact if the Tempei'aturbegrenzer is repaired and the normally open contact 26 operates wieui v. The temperature limiter 11 ′ according to FIGS. 6 to 6 has the advantage that the temperature gap between the setpoint limiting temperature ¹ and the safety limit for the temperature established by the safety contact 28 is caused by the distance between the two cutter ^{bearings l} jd for the spring parts 49 , 50 is fixed and does not depend on adjustments. This distance can therefore be determined very precisely and does not tend to misalignment. The safety margin for the temperature is retained even if the target temperature is shifted. The entire temperature limiter needs one adjusting screw 42, which makes manufacturing and assembly much easier.

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Claims (1)

μι h-io / V / - Λ j - Expectations Temperature limiter with one of the temperature of a ϊ · Λ t: kt ju cooking appliance it beaui'sehlagt-en teuiperaturemprindliciieii element, α it interrupts or interrupts the power supply to the electric cooking appliance via at least one working contact at the first temperature. limited, aadui'ch marked, iiaii a by the same temperature-sensitive element (.15) actuatable LieherheitLlcontakt (28) is provided, iitii. ¹ if the set 'i'empei-atur tine is clearly exceeded, the supply will be switched off. 2. Temperature limiter according to claim 1, characterized gekeimaeichiiot that the Sicherheitükuntakt (28) after a single Uber g of the set temperature bev / irkt a permanent Abdes Elektrükochgeräteij. 'i'emperatux limiter according to Ansx ^ ruch 2, characterized in that that he has a caste facility (38) that: after opening the safety contact (28) t. Temperature limiter according to one of claims 1 or 2, characterized in that the safety contact (28 ') is a switch-off relay ('! I) for the hotplate or the electric cooker actuated. Tf miniature limiter according to one of claims 1 bib 4-, characterized by the fact that i'lenient (13) fine expansion member known per se with a Hiilce (14) and a rod (15) made of materials with different thermal expansion coefficients provided iot, 509815/0472 A 14 896/97 - 16 - 6. Temperature limiter according to claim 5> characterized in that the temperature sensitive element (1J) has a Actuating linkage, which consists of a two-armed rocker (16) and a push rod (19), on the actuating member (25, 45) acts for the contacts (26, 28). 7. Temperature limiter according to claim 6, characterized in that it has a snap switch (23) for the working . contact (26) has, on the snap spring (24) of the switch-off causing the switch-off pressure acts, and that eggs Snap switch (23) is arranged on a pivotable support (21) which is resilient against the switch-off pressure is loaded, and that a pivoting of the carrier (21) "'causes an actuation of the safety contact (28). 8. Temperature limiter according to claim 3 and 7j, characterized in that that the latching device (38) is a pawl which fixes the carrier (21) in the pivoted position. 9. Temperature limiter according to one of claims 5 to 8, characterized in that a stop (18) is provided on the actuating linkage (16) which allows pivoting of the carrier (21) causes 10, ¹ temperature limiter according to one of claims 1 to 6, characterized in that working and safety contacts (26, 28) are designed as snap contacts with different basic settings. 11. Temperature limiter according to claim 10, characterized in that that work and safety contacts (26, 28) can be actuated by a common snap spring (47). 509815/0472 12. Temperature limiter according to claim 11, characterized in that the two preloaded spring parts (49, 50), the belong to the contacts (26, 28) arranged at opposite ends of the common snap spring mutually opposite sides and supported at different points of a common actuating member (46) are. 13. Temperature limiter according to one of claims 11 or 12, characterized in that the snap spring (47) with its storage and the contact distances are designed and dimensioned such that after the respective switching process only the normally open contact (26), not o ^e ^ -o ^cn d-er safety contact (28), returns to the starting position. 14. Temperature limiter according to claim 13, characterized in that the contact distance of the Sicherheitskuntaktes (28) is greater than that of the work contact (26) 15. Temperature limiter according to one of claims 12 to 14, characterized in that the snap spring (47) only engages by means of the support of its spring parts (49, 50) the actuating member (46) and by means of its contact-bearing ends resting on the push-pull (55 »54) is held. 16. Temperature limiter according to one of claims 1 to 15, characterized in that the safety contact (28) upon actuation of the working contact (26) or upon the working movement of the temperature-sensitive element (13) is slightly displaceable transversely to its lifting direction. 509815/0472 Temperature limiter according to claim 16, characterized in that the actuating element consists of a lever (45) whose arm (4-6) carrying the support for the spring texles (49, i> 0) is essentially perpendicular to the snap spring (47 ) Performing Arbeitsmotion ^ "executes a movement component along the snap spring (4?). 509815/0472 Blank page