DE2459649A1 - Boiling plate with three heating resistors - is controlled by seven position switch and temperature limiter on boiling plate - Google Patents

Abstract

The limiter switch is used to turn off a part of the heating apparatus and the limiter has at its fixed limiting temperature a narrow temperature differential between switching on and off, and is thermally tightly coupled with the boiling plate (11) heater temperature; the power of the disconnected heaters (N2, N3) is more than half of total power (N1, N2, N3). The result is that rapid heating takes place up to the chosen temperature, at which point most of the heating is discontinued and the heater (N1) provides sufficient heat to maintain a steady temperature. A hand knob is provided for switching the apparatus on and off.

Description

Electric hotplate with one consisting of three heating resistors Heating The invention relates to an electric hotplate having one of three Heating resistors existing heating, which can be switched by a 7-step switch and one attached to the perforated plate to the temperature of the hotplate appealing temperature limiter that switches off part of the heating.

The power of the electric hotplate is controlled by a 7-step switch is still the most commonly used hotplate. The switch is relative easy to manufacture and the circuit has one zero position and six power levels also for them Housewife very obvious. As the performance of the 7-stroke platters so high that an accidental idling at a high power setting would lead to excessive temperatures, a circuit breaker has been developed (German patent specification 1 123 059), which switches off part of the power when its Response temperature is exceeded. This circuit breaker works with one of a bimetal operated snap switch and is in the unheated central zone an electric hotplate arranged. There it is at the temperature of the hotplate influenced and still at an acceptable temperature level. The circuit breaker was set up in such a way that it switched off at 3200C, but it only switches afterwards The temperature falls to approx. 220 ° C again. The shutdown temperature had to be like this low because the hotplate has exceeded its temperature, i.e. after Shutdown got up to 500 ° C. The idle temperature was well above 3200C. The circuit breaker was connected in such a way that it switched off a heating resistor could, namely one that, depending on the specific heating surface load, between 30 and 50% of the total output. For example, in the case of an electric hotplate with a diameter of 180 mm and a total power of 2000 watts, the power of the by the circuit breaker to be switched off heating resistor 850 watts. The remaining The remaining power of 1150 watts was on the one hand low enough to damage the hotplate to prevent if this ran empty at full power setting, provided that you are at the Turning on flammable parts kept sufficiently far from the hotplate, and on the other hand was high enough to work with the remaining balance to be able to. It has been shown that the circuit breaker in all cooking and Roasting processes that take place at a higher temperature, for example when roasting or deep-frying, after a certain time switched off the partial power passed through it, However, this did not turn on again.

This is not very annoying with normal roasting processes, as the Power consumption is relatively low. The record then got sufficient performance about the heating to make the high temperature quickly and then automatically switched back to a lower output. With the one mentioned For example, this means that the electric hotplate when frying in the stationary state does not consume more than 1150 watts of power.

However, some operations cannot be carried out with this, for example deep-frying relatively large quantities, where large quantities are usually stored in a large container Fat must be brought to a high temperature and this temperature after Immersing the food to be fried with a relatively large effort must be kept. The remaining power after the circuit breaker responded but do not increase, otherwise the hotplate will accidentally idle the temperature would have been too high.

The object of the invention is therefore to provide an electric hotplate of the initially mentioned mentioned type so that it benefits relatively even in the stationary state is able to deliver close to their total performance without the Protection against accidental idling suffers.

This object is achieved according to the invention in that the temperature limiter a small switching temperature difference in the range of its fixed limit temperature between switching on and off, thermally closely related to the temperature of the heating the electric hotplate is coupled and that the power of the switched-off part the heating is more than half of the total output of the electric hotplate.

Through these measures, an electric hotplate is created that a power output close to the total installed power of the electric hotplate allows, even in the steady state at a relatively high temperature. That is amazing in that one can say yes the remaining service after shutdown by the protective device to less than half of the total output belittles. As a result and through the provision of a thermally closely coupled and Sensitively reacting temperature limiter, which thus becomes a rule or control element however, it is possible to use the temperature limiter even when working with relative high temperature in the steady state wSAer to switch on. Despite this possibility, not only for the full line area of the electric hotplate Heating up, but also to use it in a stationary state, is the protective effect of the The temperature limiter is not deteriorated, on the contrary, it is even improved been. In a preferred embodiment of the invention has an electric hotplate a diameter of 180 mm and a total installed power of 2000 watts has a residual power of 650 watts, while the other two heating resistors of 400 and 950 watts through the temperature limiter or control element can be switched off. This will the idle power so low that the installation of the hotplate with 7-stroke control is now also possible in very flat hobs that are built into kitchen furniture and therefore relatively close to possibly flammable and temperature-sensitive Objects.

As already mentioned, the power of the switched off is preferably Part of the heating at around two thirds of the total output. The after shutdown remaining power should preferably be more than 25%. The shutdown too large a part of the total output would result in an unusable output gradation for the 7-stroke switch. For the shutdown of the entire power would be In addition to the feed lines that are usual here, two additional feed lines to the electric hotplate necessary.

The temperature limiter preferably provides two heating resistors switched off. The temperature limiter in the common supply line can also be used for this two heating resistors are so that no additional leads or more Contact tracks on the temperature limiter are necessary.

The heating resistor with the greatest power is preferred and the one with the lowest power is switched off by the temperature limiter. It this ensures that a sufficiently large part of the overall performance is switched off and yet the power grading can take place very evenly.

It should also be noted that within the limits for the remaining power between 25 and 50 and preferably between 30 and 40 ffi of the total output the exact limitation of the remaining power depending on the heating surface load can be chosen. Requires a hotplate with a very high heating surface load a lower residual power than a plate with a lower heating surface load.

The limiting temperature is also preferably selected to be higher than it was the case with the known temperature limiters. It should take care of it care must be taken to ensure that the residual power that cannot be switched off by the temperature limiter Do not heat the electric hotplate above the limit temperature when idling be able to. This was the case with the previous electric hotplates with a circuit breaker not guaranteed because on the one hand the limiting temperature is set very low and on the other hand the remaining power was very high.

The temperature limiter used in the invention can be of the type as proposed in German patent application P 24 22 625.3. Its arrangement, as described in the German patent application, is also particularly advantageous P 24 22 624.2 was proposed.

Further advantages and features of the invention emerge from the subclaims and the description in connection with the drawings. An embodiment the invention is illustrated in the drawing and will be explained in more detail below. 1 shows a schematic representation of an electric hotplate with a Temperature limiter and an associated 7-step switch, Fig. 2 one from below Seen view of an electric hotplate with a temperature limiter, Fig. 3 a Section along the line III-III in FIG. 2, FIG. 4 shows a detail of a variant in one Sectional representation in which the cutting line lies transversely to that of FIG. 3 and FIG. 5 shows a longitudinal section through a temperature limiter.

The electric hotplate shown in Fig. 1 has three as possible Heating resistors N1, N2 and N3 evenly distributed over the heating ring surface. the preferred power distribution to the individual resistors is as follows (examples for some common hotplate sizes): Plate diameter (mm) 145 180 220 Total output (W) 1500 2000 2600 Nl (W) 400 650 750 N2 (W) 350 400 550 N3 (W) 750 950 1300 In the common feed line 8 to the resistors N2 and N3, a temperature limiter 20 with a switch 21 is switched on. Furthermore the circuit of the three resistors N1, N2 and N3 is exactly the same as for the corresponding ones Resistances of common 7-stroke plates. The single lead 7 of the resistor N1, the common lead 8 of the resistors N2 and N3, the common lead 9 of the resistors N1 and N2 and the individual supply line 10 of the resistor N3 lead to terminals 1, 2, 3, 4 of a 7-cycle switch 5, der'mit its connections P1 and P2 is connected to a normal household electricity network. In most cases still existing signal contacts are not shown here.

The 7-stroke switch 5 is of the usual design and has a zero position, in which all resistors are disconnected from the mains and six power levels, which are adjustable on the knob 6. In the highest power level (switch position 3) all three resistors are connected in parallel by connecting the mains Pl and P2 are connected to output connections 1, 2 and 3, 4. At the next low switch position 2.5, P1 is connected to 2 and P2 to 3 and 4, so that the resistors N2 and N3 are connected in parallel, i.e. with their respective rated power switched on are. In switch position 2, P1 is connected to 2 and P2 to 4, so that only the Resistor N3 is effective with its rated power. In switch position 1.5 is the Mains connection Pl connected to the output terminal 2 and P2 with 3, so that only the Heating resistor N2 is switched on. The two lowest levels result from the series connection of the resistors by changing the switch position 1 the resistors -N2 and N3 are connected in series (P1 to 4 and P2 to 3) and With switch position 0.5, all three heating resistors are connected in series are (P2 at 1 and Pl at 4).

Due to the above-mentioned conditions it can be seen that the Temperature limiter 20 switches off an output between 2/3 and 3/4 of the total output, namely, for example, with the 1500 watt plate mentioned above, 1100 watts (remaining power 400 W), with the 2000 W plate 1350 W (remaining power 650 W) and with the 2600 W plate 1850 W (remaining power 750 W). This order of magnitude between 1/4 and 1/3 residual power is particularly preferred.

The temperature limiter 20 is thermally close to the heating of the Coupled hotplate, as will be explained in more detail below. It has a shutdown temperature between 400 and 4500C, preferably 4200 and is due to its in the following still described construction, after it has been switched off at the limit temperature switch on again when the temperature drops by 10 or 200C.

The temperature limiter is theoretically in the switch positions effective above 1.5, but is normally only effective in the upper switch positions speak to. In contrast to the circuit breakers commonly used up to now, it switches even in the steady state the power previously switched off closes again when the temperature has dropped a little. This is done on the one hand the relatively high power switched off, on the other hand due to the low switching temperature difference in connection with the close thermal coupling. Above all, these remain Switching processes also in a timely manner, i.e. during a normal cooking process there are numerous switch-on and switch-off periods. This was the case with the previous circuit breakers unfavorable, since the switching periods there were so long that a reasonable one Working with it was not possible.

With the electric hotplate according to the invention, it is therefore possible also inpatient services in the order of 2/3 to 3/4 of the total output to use.

In the example of the 2000 W plate described above, when working with a medium of high temperature with a relatively high decrease in power (for example a large cooking vessel filled with fat in which French fries are made should) the following conditions prevail: After heating up with 2000 W switches the temperature limiter 20 from the resistors N2 and N3 with a total of 1350 W, so that a remaining power of 650 W remains. The shutdown takes place at the limit temperature of 420 ° C. By switching off the relatively large proportion of the power from the heating resistors N2 and N3 the temperature of the heater drops relatively quickly and it takes place A relatively short time again switching on the temperature limiter 20, so that then the full 2000 W is available again. It is assumed that the switch-off time of the temperature limiter 20 is half of the switched-on time (relative Duty cycle 2/3).

The resistances N2 and N3 would then be average still 900 W (Z / 3 of 1350) emit, so that a total output of 1550 W is available would stand. Compared to the comparable hotplate described above, in which the highest continuous power output is 1150 W, this is an essential one Advantage. Nevertheless, the hotplate according to the invention would only have an idle power of 650 W, i.e. only less than 1/3 of the total power and only less more than Have 1/2 of the remaining power of 1150 W in the plate according to the prior art.

In the following, an electric hotplate will be described with reference to FIGS and a temperature limiter described for carrying out the subject matter of Invention can be used: In Fig. 2, the electric hotplate is shown from below, which, as can also be seen from FIG. 3, consists of a hotplate body 12 made of cast material consists, which has a heating ring area 13 on the underside. There lie in Grooves 14 heating resistors 15 in the form of coils, which are inserted into the individual resistors Nl, N2 and N3 are split. They are embedded in an insulating compound 16 that the spirally extending grooves fills. The heating ring area is through to the outside an annular rib 17 and delimited on the inside by an annular rib 18. Within the Annular rib 18 is an unheated central zone 19, in the middle of which a central eye 23 is cast, which is used to attach the hotplate or covers. In this respect, it is a conventional electric hotplate.

In the area of the unheated central zone 19 is the switch 21 receiving Housing 22 of the temperature limiter 20 is arranged. The housing is made of insulating material, for example steatite, and has a substantially flat rectangular shape with corners 24 chamfered towards the annular rib 18, as can be seen from FIG the height dimensions of the housing 22 is very small and also the radial Dimensions are so small that the housing 22 between the central eye 23 in the Center of the unheated central zone and the ring rib can be conveniently placed. The beveled corners 24, which adapt to the shape, also contribute to this allow the central zone.

Somewhat off-center protrudes from the outward-facing, the sloping one Corners 24 bearing side of the housing a temperature sensing element 25 from an expansion sleeve 26 made of material with a relatively high coefficient of thermal expansion and a transfer rod 27 made of low thermal material material disposed therein Expansion coefficients, for example a ceramic rod, is there (Fig. 5).

Fig. 2 shows that the rod-shaped temperature sensing element 25 of the unheated Central zone from essentially radial (slightly offset to the side compared to a radius) protrudes over the heating ring area 13. It runs through a recess 28 the annular rib 18 therethrough. The flat design of the housing allows the Temperature sensing element 25 immediately adjacent to the underside (in the drawings the top) of the insulating compound surrounding the heating conductor runs, advantageously even in a certain thermal contact, which, however, is due to the expansion movements the expansion sleeve 26 should not be very strong. On the outside is for it to ensure that between the temperature sensing element with its the expansion sleeve urd adjusting screw 29 connecting the transmission rod and the outer annular rib 17 there is still enough space for the rod to expand.

From the back of the housing 22, the temperature sensing element 25 connections 30, which are connected via lines 31, lead away. The lines 31 lead through an insulating bushing 32 from the unheated central zone. This is, as can be seen from Fig. 2, with a in the inner annular rib 18 inserted flat, can-shaped cap 33 closed, together with a conventional lower plate cover, not shown a screw screwed into the central eye 23 is fastened. The cap 33 is used to protect the part of the temperature limiter containing the switch from dust and other disruptive environmental influences. The lines 31 can conveniently be on both Sides are guided past the central eye 23, since the connections 30 are in the vicinity of the two narrow sides of the housing 22 lie.

In Fig. 4 an embodiment is shown in which in the rest the same design of the unheated central zone and the temperature limiter 20 of the Heating ring area of the electric hotplate 11 is covered by a metal sheet 34, which the has annular shape of the heating ring area 13, but is slightly larger, so that it can be pressed between the annular ribs 17 and 18 and there itself holds.

This sheet lies just above the underside of the insulating compound 16 and closes this completely tightly against external influences (e.g. dust generation). Simultaneously creates this in thermal contact with the insulating compound or the protruding, the ribs separating the grooves 14 form an ideal heat transfer surface for close thermal coupling of the temperature sensing element 25 to the temperature of the Heating ring area. The temperature sensing element 25 then also sells just below (in the drawing above) this sheet 34. In the illustrated Ausführungsbeiqiel three quarters of it is enclosed by a cover 35 which has the cross-sectional shape of a large omega and is bent from sheet metal. The cover 35 is corresponding the longitudinal extent of the temperature sensing organ 25 elongated and lies with their Flanges 36 on the sheet 34 and can there for example be fixed by spot welding. It is also possible for the cover 35 to be advantageous to connect directly to the cap 33, so that the entire temperature limiter is enclosed and thermally coupled even more closely to the electric hotplate. Nevertheless is only the temperature sensing element of the high temperature of the heating ring area exposed and can react very quickly to changes in the heating conductor temperature, while the housing 22 with the temperature-sensitive switch in the area of the unheated Central zone, i.e. a colder area. It can be seen that both the cover 35 and the sheet 34 both to protect the electric hotplate and the temperature limiter serves to protect against contamination or other environmental influences, as well as for close thermal coupling of the temperature sensing element with as little as possible thermal inertia to the temperature of the heating conductor.

Details of the temperature limiter can be seen in FIG. The temperature sensing element 25 already described protrudes through an opening in the housing 22 through. The expansion sleeve 26 has a flange 37 on which a disc 70 is attached to enlarge the flange.

The housing is made of one piece of ceramic insulating material, e.g. steatite, manufactured and has a recess 40, which on one side, i.e. transversely to the expansion element, is open and after the switch has been installed by an insulating cover 71 (Fig. 3) is closed. The flange 37 with washer 70 is from the side in a Inserted slot 38 of the housing in the area of the opening 78 for the temperature sensing element and thus defines this.

In the recess 40, the switch 21 is in the form of a snap switch arranged. The snap switch 21 has a Schnappf eder 41 with a spring tongue 42 which is bent out of this and which is attached to a support bearing 43 supports.

The actuation point 44 on which the transmission rod 27 engages, is relatively view at the support bearing 43, so that because of the low lever arm The switch switches with the greatest sensitivity, i.e. its switching difference between Switching off and switching on again is a distance at actuation point 44 of approx. 1/100 mm.

The snap spring 41 carries at its free end a contact 45 which with one inserted into a slot in the housing from the side and thereby mating contact part 46 fastened and integral with connection 30 cooperates, An abutment 7, also fixed by inserting and bent from sheet metal ensures a support for the snap spring in the open position of the contacts and is arranged so that the snap spring is only necessary to open the contacts the necessary distance. This also improves the sensitivity of the switch. The other connection 30 is designed as a one leading out of the recess 40 Slit 72 inserted curved support 73 in the form of a sheet metal strip, its end lying in the recess 40 by lateral insertion into a Slot 74 is set. The base part 75 of the snap switch is on the sheet metal strip 73 21 attached, which is at one end of the support bearing 43 and at the other end there attached snap edder carries. The carrier 73 is supported in the area of the actuation point 44 on the housing.

The case is essentially rectangular with those already mentioned beveled corners 24.

It becomes a very simply structured and very sensitive temperature limiter created that gets by with the smallest dimensions. The temperature limiter shown in FIG can, for example, with an effective length of the expansion sleeve of only about 45 mm with a temperature difference of 360 degrees compared to room temperature Provide an expansion path of approx. 35/100 mm. With a switching path of 1/100 mm between When switching on and off, the hysteresis of the temperature limiter is around 10 grd. This is extremely little compared to about 80 - 100 degrees with which one has to reckon with bimetal switches. Nevertheless, no leverage is necessary, rather, the transmission rod can directly access the actuation point 44 of the snap spring 41 act. It should also be mentioned that the expansion sleeve 26 is preferably For manufacturing reasons, a circular cross-section kat, but also, in particular to adapt to the surface of the heating ring area, a different cross-section, for example flattened on one side or square.

By in the transverse direction to the temperature sensing element and thus to the main force curve Undivided design of the housing ensures that none in the direction of force Electricities occur that could lead to inexact switching.

This is also ensured by the fact that the switch and the temperature switching element normally held by the snap spring 41 in a frictional connection.

It can be seen that the expansion sleeve 26 is a heat transfer member 76 is attached in the form of a sheet metal disc. On the one hand, this makes for a large Heat transfer surface for radiation and convection transfer and can through Contact with parts of the hotplate or the plate 34 also heats up by conduction transfer the expansion sleeve. Also folding the pane into one to the Hotplate parallel plane can be advantageous.

It is also preferred to measure the heat transfer resistance of the temperature sensing element, if necessary. including the heat transfer members, by appropriate surface treatment to reduce. A coating with a highly heat-resistant, rough paint coating 77, which is the relatively smooth and bare surface of the mostly Stainless steel expansion sleeve is essential in its heat transfer properties improved.

Claims (22)

Expectations 1. Electric hotplate with one consisting of three heating resistors Heating, which can be switched by a 7-step switch, and one on the hotplate attached temperature limiter that responds to the temperature of the hotplate, which switches off part of the heating, that is, e t that the temperature limiter (20) is in the range of its fixed limiting temperature has a low switching temperature difference between switching on and off, thermal is closely coupled to the temperature of the heating of the electric hotplate (11) and that the power of the switched-off part of the heating (N2, N3) is more than half the total power (N1, N2, N3) of the electric hotplate (11). 2. Electric hotplate according to claim 1, characterized in that the remaining power after the shutdown by the temperature limiter (20) (N1) is more than 25% of the total output (N1, N2, N3). 3. Electric hotplate according to claim 1 or 2, characterized in that that the temperature limiter (20) can not be switched off residual power (N1) between 25 and 35% of the total output (N1, N2, N3). 4. Electric hotplate according to one of the preceding claims, characterized characterized that the power of the switched off part of the heating (N2, N3) approx. 2/3 of the total output (N1, N2, N3) is. 5. Electric hotplate according to one of the preceding claims, characterized characterized in that the temperature limiter (20) switches off two heating resistors (N2, N3). 6. Electric hotplate according to claim 5, characterized in that the temperature limiter (20) in the common supply line (8) to two heating resistors (N2, N3) is switched on. 7. Electric hotplate according to claim 5 or 6, characterized in that that the heating resistor (N3) with the greatest power and the heating resistor (N2) with the lowest power can be switched off by the temperature limiter (20). 8. Electric hotplate according to one of the preceding claims, characterized characterized in that those heating resistors (N2, N3) can be switched off by the 7-step switch (5) in the second highest power level (switching level 2.5) in Parallel connection are switched on. 9. Electric hotplate according to one of the preceding claims, characterized marked that the largest heating resistance (N3) approx. 50%, the second largest heating resistance (N1) approx. 30% and the smallest heating resistor (N2) approx. 20% of the total output. 10. Electric hotplate according to one of the preceding claims, characterized characterized in that the residual power not to be switched off by the temperature limiter (20) (N1) Do not heat the electric hotplate above the limit temperature when idling be able to. 11. Electric hotplate according to one of the preceding claims, characterized characterized in that the residual power not to be switched off by the temperature limiter (20) (Nl) the electric hotplate (11) does not exceed the restart temperature when idling the temperature limiter (20) is able to heat up. 12. Electric hotplate according to one of the preceding claims, characterized characterized in that the limit temperature is between 400 and 4500C. 13. Electric hotplate according to one of the preceding claims, characterized characterized in that the temperature limiter (20) has a switching temperature difference below 20 ° C. 14. Electric hotplate according to claim 13, characterized in that the temperature limiter (20) has a switching temperature difference of approx. 10 ° C. 15. Electric hotplate according to one of the preceding claims, characterized characterized in that the temperature sensing element (25) of the temperature limiter (20) the heating conductor (15) lies just below the electrical insulation (16). 16. Electric hotplate according to claim 15, characterized in that the temperature sensing element (25) an expansion sleeve (26) with a larger thermal Has expansion coefficient that the expansion movement over one in it arranged transfer rod (27) with a lower coefficient of thermal expansion transmits to the temperature limiter (20); 17. Electric hotplate according to claim 16, characterized in that the temperature sensing element (25) is direct acts without translation on the snap spring (41) of a snap switch (21). 18. Electric hotplate according to one of the preceding claims, characterized characterized- that the temperature sensing element (25) of the temperature limiter (20) with a part of low thermal inertia is in thermal contact, which is immediately adjacent the heating conductor (15) is arranged on the electrical insulation (16). 19. Electric hotplate according to claim 18, characterized in that the part a'den Heizringbereich (13) of the electric hotplate (11) covering, tight on the heating ring area (13) running along sheet (34). 20. Electric hotplate according to one of the preceding claims, characterized characterized in that the temperature sensing element (25) of the temperature limiter (20) at least is partially surrounded by a cover (35) which is connected to the electric hotplate (11) is in thermal contact. 21. Electric hotplate according to one of claims 15 to 20, characterized characterized in that the temperature sensing element (25) across the heating ring area (13) the electric hotplate (11) protrudes and that the snap switch (21) receiving Housing (22) of the temperature limiter (20) in the unheated central zone (19) of the Electric hotplate (11) lies. 22. Electric hotplate according to one of claims 15 to 21, characterized characterized in that the temperature sensor (25) has a surface structure (77) has a low heat transfer resistance and / or a high degree of absorption. L e r s e i t e