CA1140973A - Cooking unit with energy saving switching devices - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

The disclosure teaches a cooking unit which includes at least one cascade cooking unit, the cascade cooking unit including a favored cooking plate having at least two electric heating elements and at least one additional cooking plate having at least one heating element. A thermal sensor is associated with the favored plate and is responsive to at least one of the heating elements of the favored cooking plate. A
thermostatic switch is responsive to the thermal sensor, the switch operating in a first mode to supply power solely to the elements of the favored plate and in response to a predetermined temperature sensed by the sensor operating in a second mode to supply power to only one of the elements of the favored plate and to supply power to at least one of the elements of the at least one additional plate through a series connection.

Description

114V~73 FIl~LD AND BACKGROUN~ OF THE INVENTION

Cooking units such as electric hobs, electric co~kers, portable eleetrie,cookers or the like are usually provided with from tw~ to four electric cooking plates eaeh of whieh has an output of from 1000 to 2000 W
so that food can be heated up relatively quiekly on these eooking plates, A four-plate unit can therefore have a max~mum output of 7 to 8 kW. This is often too mueh for a normal domestic mains supply, particularly if the mains voltage is only 120 volts. In addition, it is not possible to eonnect such a unit to a soeket which is ~used in the normal way. Cooking units have already been proposed whieh eontain a power eooking plate with a hlgh :Load and three cooking plates with a very low loa~
whieh are intended Ior eontinued eooking, With this arrange-ment, the house-wife has to heat up eaeh pan in sueeession on the one hi~h power plate, e.g. bring the contents thereof to the boil, then transfér the pans to the three plates of lower power for eontinued eooking, This makes the eooking more diffieult and demands partieular attention.

j SUMMARY OF THE INVENTION
The object ol the invention is to provide a cooking unit with at least two electrie~ooking plates, at least one of which is rhythmically regulated or controlled by a 1140~73 switching device which manages with a small connected load and contains cooker plates which can be used fully.
According to the invention there is provided a cooker unit comprising at least two electric cooking plates, means for supplying electrical power to the plates, and a switching device for regulating or con-trolling the supply of power to at least one of the plates rhythmically, the switching device of at least one favoured cooking plate being such that when at least one portion of its power is switched off, at least one subsequent cooking plate is supplied with power.
In accordance with a particular embodiment of the invention a cooking unit includes at least one cascade cooking unit, the cascade cooking unit including a favored cooking plate having at least two electric heating elements and at least one additional cooking plate having at least one heating element. A thermal sensor is associated with the favored plate and is responsive to at least one of the heating elements of the favored cooking plate. Thermostatic switching means are res-ponsive to the thermal sensor, the switching means oper-ating in a first mode to supply power solely to the elements of the favored plate and in response to a pre-determined temperature sensed by the sensor operating in a second mode to supply power to only one of the elements of the favored plate and to supply power to at least one of the elements of the at least one additional plate through a series connection.
A specific order of priority is thus deter-mined (which can however be changed or eliminated bymeans of changeover switches) so that the subsequent electric cooking plates are supplied with current when the first cooking plate switches off the power at least partially owing to its control or regulating procedure.

~.' Since the initial cooking process takes place quickly when using a cooking plate having a high connected load and the power needed for continued cooking often does not exceed 10 to 15% of the connected load, sufficiently long periods are available in which the subsequent cook-ing plates are switched on, In particular, when the intervals or switching periods are very short, the cooking procedures on the subsequent cooking plates are rarely disturbed and the consumer will hardly notice the inevitable disconnection pauses of the , - 2a -1~4~73 : ` .

subsequent cooking plates. This applies particularly when the cooking plates are arranged~patially in the cooking unit in their priority grading in such a way that the cooking plates which are used most on the basis of this arrangement are the first in the priority grading.
A rhythmic mode of operation of the switching devices is important in the favoured electriccooking plates, but a subsequent cooking plate could also have a different type of regulation, for example a filter pulse clrcuit.
10 The thermostat is preferably a so-called automati-c controller which operates with a hydraulic sensor box which is arranged in the central zone of the cooking plate and is pressed on to the bottom of the cooking pot.
In this arrangement, the electric cooking plate has two 15 heating reslstances and the controller has two associated contracts which switoh off at successive temperature values.
An additional cooking plate can be supplied completely or partially with current as soon as the first partial current is switched off.
In a particularly advantageous embodimcnt which not only keeps the connected load low but also saves energy, the switching device is a condition controller which responds to the steam produced in the cookin~ container.
When this condition controller, of the type described 25 in German Patent No. 1,029,502, is allocated to the favourod electric cooking plate, it is evell possiblc to ^ ll~V9~73 - prepare a meal con~sting Or several individual dishes on one eooking plate by stacking up,cooking containers, - ' the lower cont~n~s eæh heating the one above it, and using an additional subsèquent c,ooking plate, for example f~r frying purposes.
BRIEF DESC RIPTION OF THE DRAWINGS
Figures 1 to 3 are schematic circuit diagrams of ~th~ee cooking units;
Figure 4 shows a detail of a modified form of unit;
Figure' 5 shows the side view of a cooking unit; and Figure 6 shows the cireuit diagram of the cooking unit aecording to Figure 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
, The circuit illustrated in Figure 1 com~rises a cooking 15 unit 11 having four electric cooking plates 12, 13, 14 and 15, whieh ean be oonneeted to the domestie mains at a socket 17.
by means of a plug 16. The eooking unit ean be an electric eooker, an eleetrie~Db or a ~ortable eleetric cooker.
Eaeh eleetric cooking plate can be a eonventional cooking 20 plate made of oast material, each having two heating elements 18,19, which can be connected individually or together by two contaet arms 20,21 or switehing springs of'a switching device 22. The switching device 22 is a thormo-stat whieh ean be adjusted manually to the desired temperat,ure 25 by means of an adjusting head 23. Eaeh thermostat is provided with a sensor bo~ 2ll, whieh is spring-mounted in a conventional way (not shown) in the eentre ol' the eooking plate and can rest against the bottom of a cooking eontainer in order to detect its temperature. It is generally connected to the internally arranged heating element 19. The scnsor box 2~ is filled with an expansion fluid and connected via a capillary tube 25 with an expansion box 26 which 5 acts upon the contact arms 20,21 as a function of the - temperatur~ of the sensor box and the manual adjustment.
'The contact arms 20,21 are adjusted relative to each other in such a way that they switch in succession as the temperature rises, the contact arm 20 switching a , 10 few degrees before the contact arm 21. This substantially pre~ents the,desired temperature from being exceeded.
rrhe thermostat can be constructed in accordance with German Offenlegungsschrift No. 2,058,512 or German Patent No. 2,~ ,813. 'rhe contact arms 20,21 are also 15 electrically s,eparated on the input side and can havc two separate switching springs. 'rhe flxed contacts 27,28 of the switching device 22 leading to the hcating elements 18,19 are each provided with a fixed transYer contact 29,31 which c~operates with the corresponding 20 switching springs when the respective heating resista~e is switched oIf.
he he~tin~ resistances oI all cooking plates are connected via a return line 36 to one pole of the domestic mains and the contact arms 2~21 oY the switching device Yor the first cooking plate 12 to the other pole.

- _ 5 -114U9~3 - .
The transfer,contact 29 is connected to the contact..
. .arm 21 of the next switching device and the transfer ', contact 31 is connected to the.contact arm 20 of the . ,next switchin~ device, so that the transfer contact -, 5 of the internal heating resistance of each cooking plate is allocated to the external heating resistance . . . of another cooking plate. Owing to this-cross-over . circuit, the heating resistance which controls the .temperatuPe sensor 24 is charged at, any time.
10 , . Tlle cooking unit according to Figure 1 operates in the following manner. The connecting plug 16 is .connected to a soc~et whose fu-e corresponds to the ' maximum power of the highest rated cookin~ plate, for example 2000 W. Figure 1 shows a condition in which 15 the cooking plates 12,13 and 14 are switched on by activatin6 the adjusting button 23. With the,cooking plate 12, the initial cookin~ process ,in which both heating resistances .were switched on has already ended and the switchin~ device has received an ïndication from 20 the temperature,sensor 24 that thc adjusted temperature has been reached. An avera~e power of up to only about ,' 500 W is needed for continued cookin~, and this is supplied by switching the he~tin6 resistance 19 on and , off by means of contact arm 21 ,which in so daing switches

2~ ovcr between the contacts 28 and 51. With the cookin~

~'' ' ~ .

plate 12, both contacts 27 and 28 are disconnected so that both contact arms 20,21 are connected to the transfer contacts 29,31 which are connected to the contact arms 20,21 of the subsequent cookingplate 13.
The subsequent cooking plate 13 has also completed the initial cooking operation. Cooking plate 13 illustrates the condition in which the internal heating element 19 receives current (drawn in black), the heating up o~
which charges mainly the temperature sensor. The transfer contact 29 is open and the~eatin~ resistance 18 of the cooking plate 1ll does not receive any current although, like heating element 19, it is switched on by the switching device 22 an~ the cooking plate has not yet reached the sct temperaturc.
The condition illustrated does not last long because the cooklng plate 13 is switohed oii agnin by the contact 21 after a very ~hort period so that both heating resistanoes 18,19 of the cooking plate 1ll then receive current Since, in the case ol cooking plate 13, the heating ~esistance 18 is disconnected and the contact arm 20 is connected to thc transier contact 29, the contact arm 21 receives current Irom the cooking plate 1ll and its heating roYistanco 18. The initial cooking operation is delayed somewhat by cooIcing plate 1~l during the period when the cooking plate 13 receives its continucd cooking power. IIowevér, when cooking pla-tc 13 switches oIi ll~Og73 shortly aIterwards, cooking plate 1~-l receives full power.
When cooking plate 12 is-switched on, cooking plate 13 and the subsequent cooking plates act accordingly. rrhe cooking plates 12 to 15 are thereIore favoured over 5 each other in the sequence of their connection. Although three cooking plates operate, the maximum connected output is;not higher than for a single one. There is still sufficient switching time available for the last cooking plate owing to the small relative switching 10 r times The cooking unit 11l in Figure 2 also has four cooking plates, the cooking plates 12~ and 15t hawng a smaller diameter and a power of 1500 W, and the remaining cooklng plates 13l and ~ having a larger diameter and 15 a power of 1500 and 2000 W respectively. rrhe thermostats 22~ dlïfer lrom tho~e in Figure 1 only in that their structuré is that of a simple snap switch. rrho snap switch has a movable catch spring 37 and cons~sts of two contact halves 20t and 21~, made of resilient material, 20 from which are bent spring tongues which arc supportod in rigid supporting bearings 38,39 by means of which the current is supplied. rrhe spring halves are insorted into a central insulating block 55, upon which the expansion box 26 acts. rrhe contacts 27,28,29,31 cooperate 25 with contacts at the end OL~ the spring halves 20~,21~.
rrhiS double cat~h spring 37 is adjusted in such a way that the oontact half 21' switches off at a lower temperature 114~9'73 than the current half 20~.
Current is supplied from the domestic mains by a socket 16 via a manually activatable switch~6 which has two contact arms which switch on the cooking plates 5 in one position, switch on a socket 57 for additional appliances, for example a mixer, in a second position, and separate the cooking plates from the two poles of the domestic mains in a third position. In Figure 2, the thermostats 22~ of the two favoured cooking plates 10 121 and 14' preferably arranged in the front portion of the cooking unit 11' are connected to one pole of the mains while the cooking plates 13',15' with their heating resistances are connected to the transfer contacts 29,31 oI' their thermostats. As in Figure 1, the current 15 supply lines 38,39 to the contact arms 20',21', are eleotrloally connected together in the case of the Iavoured cooking plates 12t,1~l~, so that a normal double snap switch could be usod here without elcctric insulation between the two contact halves 20 t, 21' while although 20 t'he electric separation of the two contact arms'from each other is important in the subsequent cooking plates 13~',15~, the transfer contacts could be dispensed with.
It is assumed in the condition illustratcd in F~re 2 that all cooking plates are switched on. The 25 cooking plates 12',1~l~ have reached théir set temperature range. The continued cooking power 18' is just supplied to cooking plate 12~, while cooking platc '1ll' has switche~d off completely Accordingly, only one heating - _ g _ 9~3 element 18 is switched on in the cooking plate 13' eonnected downstream of cooking plate 12', while both ~eating elements are switched on at cooking plate 15 because it is still heating up.
Although the cooking ~unit 11' has two completely usable favoured cooking plates 12~,14l and the two subsequent pIates can be used almost always completely outside the heating up time of the favoured cooking plates, the eonneeted load is only 3500 W, say 16 Amperes at 220 V, providing that the heating resistances 18,19 are the same. The servieeability is there~ore ino~ased by dividing into two branches 12',131 and 14',151.
The switch 56 ensures bipolar disconneetion and ensures that the socket 57 is only used when the cooking plates ~re not switehed on. It eould also be connected to the free transfer eontaets of the eooking plates 13~, 15l, nnd thus be ineluded in th~ priority eireuit.
Figure 3 show~ a eooking unit with a manual switch 56, a soeket 57 as in Figure 2 and a cooking plate 12 as well as a thermostat 22 as in Figure 1. In this arrangement, a manual filter pulse switeh 58 is connected to the -first transfer contact 31 used and a filter pulse switeh 59 to the transfer eontaet 29, and these swigches eaeh control three heating elemen1;s ol cooking plates 13a~ via switching springs activated by cams. In this 114Q~73 embodiment, therefore, the cooking plate 13a is put into full operation once the heating resistance 19 o~ the cooking plate 12 has been switched of~ and the cooking plate 14a is put into operation completely once the heating resis-tance 18 has also been switched oIf.
The maximum connected power is 2500 W, although the combined wattage of the cooking plates is 4500 W.
Figure 4 shows a modified switching deyice 22"
whose cooking plate 12b has only one heating element 18 for the entire output. The expansion socket 26 acts on a bimetallic member 33 which is heated by a low power control heating resistance 3~l and is connected in parallel to~he heating resistance 18~. This heating resistance 18~ and the control heating resistance 34 ~e controlled by a gnap switch 35 which supplics the two heating résistances ln its "on~ positlon as illustrated, whereas, in the ~ofY" position, it is connected to the transfer oontact 29~ which i8 itself' connected to the I-ed line 30~ ~ the switching device of the next cooking plate which is completely switched on in this way.
The embodiment according to Figure ~ operates in the following manner. The thermostat oI this embodiment is rhythmic in operation and can be adjusted manually to a speciIic temperature value by the adjusting knob 23~. The bimetallic member 33 which is heated as the cooking plate is heated producès a rhythm, i.o. successive switching on and off of the single heating elements 18~, the relative switching on period changing in accordance wi-th the temperature adjustment (knob 23~) and the actual temperature on the cooking conainer. This relativ~ switching on period will diminish - - 114~}973 from about 100% during the lnitial cooking phase to about 10 to 20% during the continued cooking phase.
The-fuli power is available for the subsequent cooking plates in the pauses i.e. during the continued cooking phase between 80 and 90% of the time.
If the thermostat 24; 25, 26 illustrate~ in broken lines is omitted, a step-less rhythmic power control device is formed which supplies the subsequent cooking plate in its disconnected periods.
Figures 5 and 6 show a cooking unit lla which is designed as a portable unit and possess two cooking plates 12a and 13a. The cooking plate 12a is provided with a condition controller 40 which is connected to the cooking un~t lla via a flexible line 41 and is suitable for being placed on a lld 42 of a cooking pot 50 which has an opening 47 for the passage of steam, Three superi~posed cooking pots 50 which are designed so that they fit on to each other with the two lower cooking pots each heating the one above it, are placed on to the cooking plate 12a. Several different dishes can be cooked irI different cooking containers using a single cooking plate by means of this "tower" cooking.
The steam issuirlg out of the upper cGoking pot lid 42 shows that all cooking pots have reached the coGkir,g temperature. The steam acts on a barometric cell 43 which is filled with a liquid having a boiling point which is somewhat lower than the boiling point of water. The Issuing stea~ therefore 11~973 causes rapid evaporation in the cell 43 so that a switch - 44 in the condition controller 40 is activated via a membrane, this switch being designed as a snap switch and switching over between a contact 45 and a contact 46.
A change-over switch 48 is provided to allow the condition controller 40 and therefore the cooking plate 12a to be switched off completely. In the illustrated switch position of the change-over switch 48, the electric cooking plate 12a, which has only one heating resistance 18a, is switched on via the switch 44 and a control switch 49 as well as a temperature protection switch 52. The control switch 49 can be either a simple on/off switch, a 7-time switch oP even a stepless power control device. The temperature protection switch protects the cooking plate and cooking pots if the condition controller is accidentally not put on or if food has been put on without water.
The cooking plate 13a has a switching device 22 of the type shown in Figure 1. The common line 30 from the switching device 22 is connected to the transfer contact 46 of the condition controller 40 as well as to a contact of the change-over switch 48. Additional cooking plates, sockets or appliances can be connected in series with the cooking plate 13.
The cooking unit lla operates ln the following manner.

_ 13 -114~73 In order to prepare a complete meal with, for example, -four different dishes, three dishes to be cooked are poured into the three cooking pots 50 which are placed on top of each other and closed with the lid 42. The cooking plate 12a is switched on via the adjusting knob 5~ of the control switch 49 once the cooking pots 50 have been placed on the cooking plate 12a and the condition controller 40 has been placed on to the lid 42. The heating resistance 18' heats the three cooking po~s with its total output until the cooking temperature prevails in the uppermost cooking pot 50, steam issuing through the opening 47 heats the barometric cell 43 and switches the switch 44 from the contact 45 over to the contact 46. The cooking plate 12a is thus switched off and the cooking plate 13a, on which a further boiling or frying operating can be performed is supplied via the line 30. ~fter initial cooking, the continued cooking power is very low so that the cooking plate 13a is ready for use over 80%
of the time. The condition controller 40 functions in cooperation with the cooking plate 12a with a small time lag 50 that it switches off again seconds ater it has been switched on again. Such a short power surge is sufficient to allow steam to be evolved again.
It is therefore actually controlled to the "cook"

condition and not to the associated temperature which can only be detected imprecisely. The short interuptions of power are hardly noticeable in the cooking plate 13a.
This embodiment allows a meal with four or more different dishes to be cooked at the same time using one two-plate stove which has the connected load of only one cooking plate .
The change-over switch 48 ensures that the priority which the cooking plate 12a normally has over the cooking plate 13a is given to the latter and therefore that the cooking plate I2a is disconnected. It is also possible to change only the priority. Instead of using the condition controller 40 which is connected to the cooking unit lla via a flexible line 41, it is a].so possible to use a condition controller which transmits its on and off signals to the coGking unit without the use of wires (see German Auslegeschrift No. 2161371).
Numerous variations of the embodiments described and illustrated are possible within the scope of the invention. Although the cast cooking plates described are particularly advantageous in conjunction with the invention owing to their temperature-compensating properties, other cooking points can also be used, for example, each electric cooking plate can be formed by a heating unit beneath a glass ceramic plate, or the electric cooking - 114~973 plates can be formed by tubular heating bodies.
It is also possible to connect one or more independent cooking plates in parallel wlth the cooking plates which are connected in cascade.

Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:-

1. A cooking unit comprising:
at least one cascade cooking unit, said cascade cooking unit including a favored cooking plate having at least two electric heating elements;
at least one additional cooking plate having at least one heating element;
a thermal sensor associated with said favored plate and responsive to at least one of said heating elements of said favored cooking plate; and, thermostatic switching means responsive to said thermal sensor, said switching means operating in a first mode to supply power solely to said elements of said favored plate, and in response to a predetermined temper-ature sensed by said sensor operating in a second mode to supply power to only one of said elements of said favored plate and to supply power to at least one of said elements of said at least one additional plate through a series connection.

2. A cooking unit according to claim 1, wherein the thermostatic switching means operates in a third mode whereby power is supplied to said at least one additional plate and no power is supplied to said favored plate.

3. A cooking unit according to claim 1, wherein each of said at least one additional cooking units has a thermal sensor and a thermostatic switching means, each of said thermal switching means operating in said two modes.

4. A cooking unit according to claim 1, wherein the thermostatic switching means has at least one transfer con-tact for switching power between the favored cooking plate and said at least one cooking plate during the second mode.

5. A cooking unit according to claim 3, wherein each of the thermostatic switching means has at least two switch-ing contacts which switch at successive temperatures, each of the switching contacts switching one of the heating elements, at least that one of the switching contacts responding to the highest temperature having a transfer contact connected to a subsequent cooking plate.

6. A cooking unit according to claim 5, wherein all of the cooking plates have at least two heating ele-ments, each sensor being heated most directly by only one of the heating elements of its cooking plate defining a most effective heating element, the transfer contact con-necting the switching contact of the least effective heat-ing element of the favored cooking plate to the most effective heating elernent of the subsequent cooking plate.

7. A cooking unit according to claim 6, wherein each of the thermostatic switching means has a snap switch with a catch spring, said contacts cooperating with a catch spring contact at each end.

8. A cooking unit according to claim 1, wherein the thermostatic switching means has short switching periods.

9. A cooking unit according to claim 3, comprising a plurality of said cascade cooking units interconnected in series and/or parallel- inserted therefore.

10. A cooking unit according to claim 1, comprising a manually activatable switch, having a switching position in which all of the cooking plates are switched off and in which a connection to another electric cooking appliance is simultaneously provided.