GB1563026A

GB1563026A - Controllers for controlling the supply of electrical power to a load

Info

Publication number: GB1563026A
Application number: GB23585/77A
Authority: GB
Original assignee: EGO Regeltechnik GmbH
Current assignee: EGO Regeltechnik GmbH
Priority date: 1976-06-09
Filing date: 1977-06-03
Publication date: 1980-03-19
Also published as: ES459593A1; DE2625716C3; AU511604B2; FR2354656B1; SE7706664L; PL120656B1; YU142977A; FI62426B; JPS57145289A; DK249677A; JPS6367318B2; AT376520B; CA1088601A; JPS52153147A; PL198728A1; AU2570877A; ZA773233B; JPS5745010B2; CH616012A5; SE413168B

Abstract

The power control device (11) cyclically supplies electric power in individual power pulses to a load or, respectively, an electric hot plate. It is manually adjustable by rotating a control cam member (19). The control cam member acts via a bimetallic compensation strip (26) on the rotatably supported carrier (29) of a snap switch (27), the operating point of which is acted on by a leg of a L-shaped bimetallic member (36) heated by a voltage winding. The snap switch is rotatably supported and the bimetallic compensation strip is mounted at one end and essentially parallel to the snap switch so that a bimetallic compensation strip/snap switch unit is formed which can be jointly routed about an axis (28). The bimetallic compensation strip is virtually unaffected by the temperature of the bimetallic operating strip (36) which results in reliable compensation of the ambient temperature. The heated bimetallic member (36) and the snap switch and a switch operated by a switching cam (20) for carrying out a two-pole disconnection are arranged in one plane around the adjusting shaft and provide for a flat construction of the device. <IMAGE>

Description

(54) IMPROVEMENTS IN CONTROLLERS FOR CONTROLLING THE SUPPLY OF ELECTRICAL POWER TO A LOAD (71) We, E.G.O. REGELTECHNIK GMBH. a German Company. of 7519 Oberderdingen, Federal Republic of Germany, do hereby declare the invention for which we pray that a patent may be granted to us.

and the method by which it is to be performed, to be particularly described in and by the following statement: The invention relates to a power controller for the controllable supply of electrical power to a load, having a bimetal member, which is heated in dependence upon the connected power and which acts upon a snap switch spring.

A power controller is described in the publication "Conti-Elektro-Berichte" (Conti-Electro-Reports), October/December 1959, Pages 285 to 290. The power controller illustrated in Figure 3 on page 285 of this publication has a working bimetal strip to which a compensating bimetal strip is connected at right angles. In the region of the internal corner between these two interconnected bimetal strips, the latter are pivotably mounted on a pin disposed in the switch socket. The compensating bimetal strip acts upon an encapsulated switch.

Adjustment is effected bv means of a control cam which acts upon the free end of the working bimetal strip by way of a roller.

a separately mounted lever and an adjusting screw. A mechanical switch with two contact springs is disposed opposite the bimetal strip.

For structural reasons the bimetal strip of such a controller can only have a length which is not much longer than half the switch dimensions. Consequently its thickness dimension and its working travel are then also smaller. In addition. the heat of the bimetal strip is transferred to the directly attached compensating bimetal strip so that this compensating bimetal strip operates constantly in a range of relatively high temperature and its actual object, the taking into account the influence of ambient temperature, can only be partially achieved.

Adjusting the working region by pivoting the working bimetal strip with the aid of a lever mechanism is a complicated task and leads to the reproducibility of the individual part loads being inaccurate. In particular, this reproducibility is poor in the critical upper and lower power ranges. a part load of, for example, 5%, which is necessary to be able to heat up an electric hotplate, cannot be positively controlled with such a controller.

Power controllers with a pivotable snap switch have been described, for example, in German Patent Specification No. 16 40 084.

The bimetal strip therein is directly connected to the snap spring and the control is effected by way of a cam disc and a lever having a stop whose distance relative to the working bimetal strip is adjusted during the adjusting process. This system permits the use of only relatively thin and labile bimetal strips and presents problems with the addition of a compensation device, not envisaged in this publication.

An object of the invention is to provide a power controller which is easy to manufacture on a small scale and enables the power settings to be reproduced very well despite relatively low requirements being set on the precision of the construction. In particular, the compensation for the ambient temperature is to be reliably achieved.

According to the present invention, a power controller for the controllable supply of electrical power to a load, comprises a housing. electrical switch means for switching power to the load, a pivotably mounted bimetal member, means for heating the latter when power is supplied to the load via said switch means. said switch means comprising a snap-acting switch spring carrying a movable electrical contact cooperable with a fixed electrical contact, the bimetal member having a limb which extends at an angle to the remainder of the bimetal member and which acts upon the snap spring. a pivotally mounted ambient temperature compensating bimetal strip which is secured to the snap spring and which extends substantially parallel to the snap spring at one side thereof.

and a control cam which acts upon a free end of the compensating bimetal strip.

A compensating bimetal/snap spring unit is therefore formed which is jointly pivotable. The compensating bimetal strip is only influenced to a very small extent by the temperature of the working bimetal member and can therefore achieve its task of compensation. Moreover, it is also heatshielded by the snap spring lying parallel thereto. It may be short and relatively strong. However. the working bimetal member alwavs remains in its position and only one of its ends moves towards the snap spring in accordance with the extent of its heating.

For this purpose. the bimetal member is preferably L-shaped, the longer bimetal bi limb being provided with a heating device and being possibly supported on the housing by way of an adjusting screw under spring force.

According to a further feature of the invention, provision is made for a diode to be provided in a controller to be operated with alternating current. the diode being connected in circuit with the heating means for the bimetal member by a switch. actuable by the adjusting shaft. only in the upper power range and being disconnected in the lower power range.

A relatively large-dimensioned bimetal heating means, which is consequently less influenced by the wire gauge. may therefore be provided. In the lower power range this heating means is fully effective so that the bimetal member quickly heats up. resulting in the overall power being quickly disconnected. The resultant short relative connection period also keeps the heating of the switch within limits since the bimetal heating means is only switched on during the connection of the load. However. in the upper power range which may begin. for example. at 20etc relative connection period.

the diode is connected in series with the bimetal heating means. The heating means of the bimetal thereby only ever receives a half-wave of the alternating current and thus only half the power. Consequently the development of heat is less and the higher outputs are easier to control. In this region.

the development of heat would be particuarly unwelcome because there is a long connection period here also for the bimetal heating means. In addition. the temperatures at the bimetal are kept low and the entire switch heating remains low so that the ambient temperature can also be compensated for advantageously It is particularly preferable for the diode at the rear side of the housing of the power controller remote from the operated side to be disposed directly on the switch which bridges it. Such an embodiment keeps the expense for the arrangement and switching in circuit of the diode very low and the diode is disposed in the cool external region of the switch. The switch connecting the diode may be a simple switch which does not need any snap mechanism.

The invention will be further described, by way of example. with reference to the accompanying drawings. in which: Figure 1 is a plan view of one embodiment of a power controller according to the invention. seen from the operated side, with a closure cover removed: Figure 2 is a section along the line II-II in Figure 1: Figure 3 is a rear view of the power controller of Figure 2. seen from the left; and Figure 4 is a schematic circuit diagram of the power controller shown in Figures 1 to 3.

One embodiment of power controller 11 is shown in Figures 1 to 3. It has a rear housing part 12 (or housing part remote from the operated side) made of plastics material and in the form of a rectangular or preferably square block with an internal cavity 25. This cavity is sealed by a plateshaped cover 13 which faces towards the operated side and has centering dowels 17 which engage in centering recesses 16 on the housing part 12. A screw-threaded bush 14 is secured to the cover 13 and an adjusting shaft 15, which carries an adjusting knob 60 indicated in Figure 4, protrudes through the threaded bush. The adjusting shaft 15 protrudes into a central hole 23 in a control body 18 which is made of insulating material and carries on its outer periphery a control cam 19 and a switching cam 20. At its end remote from the operated side. the control body 18 has a bearing pin 21 which protrudes through an aperture 24 in the rear housing part 12 and comprises a further switching cam 22 on the rear side of the housing part 12.

A compensating bimetal strip 26 cooperates with the control cam 19. this compensating bimetal strip being in the form of a transmission lever which has a front curved end by which the bimetal strip 26 is pressed against the control cam 19 under the force of a spring 34. The compensating bimetal strip 26 is relatively thick and rigid and is pivotably mounted. by its end opposite the front curved end by which it abuts the control cam 19. by means of a pivot 28. At this end. the compensating bimetal strip is attached to a switch carrier 29 of a snap switch 27, so that the compensating bimetal strip is parallel to the switch carrier 29 and is slightly spaced therefrom.

The snap switch carrier compensating bimetal unit 26/29 is therefore pivotable as a whole about the pivot 28.

Disposed on the switch carrier 29 is a snap spring 30 which is supported in the conventional manner on a support bearing and which has a bowed resilient tongue under buckling stress. The snap spring carries at its free end its movable contact 31, which co-operates with a fixed counter-contact 32, and is fixed at its opposite end by an adjusting screw 33, which has an annular groove into which a fork-like end of the snap spring is inserted. A terminal end of an electrical supply line 35 is welded to one fork end whereby the snap spring is electrically connected to a terminal 68 for a load 70, such as a cooker hotplate element.

The snap switch 27 is actuated by a bimetal member 36 which is L-shaped. This L is completely made of bimetallic strip and a pivot 37 is mounted in the internal angle of the L, this pivot. like the pivot 28, being advantageously journalled in recesses which are located respectivelv in the housing part 12 and the cover 13 and in which the pivot ends are received when these two housing parts are assembled together.

The long, heated limb 38 of the bimetal member 36 carries a heating winding or coil 39 which is supplied with current by way of two supply leads. An adjusting screw 40 which is pressed by a spring 41 against an inner intermediate wall 42 of the housing part 12 is screwed into the free end of the heated limb 38.

At the end of the short limb 43 of the bimetal member 36 there is a cranked portion 44 which presses against the actuating point of the snap spring 30.

The heated limb 38 of the bimetal member 36 is located in a chamber 71 which is partially sealed off by the intermediate wall 42 and is ventilated bv ventilation slots 45.

It can be seen that the snap switch carrier/compensation bimetal unit 26/29. on the one hand. and the long limb 38 of the bimetal member 36. on the other hand. are disposed at an angle to one another and enclose the control body 18 therebetween.

In the corner of the housing cavity 25 opposite this angle, a mechanical switch is disposed which has a switch slide 5() actuated by the switching cam 20. This switch slide 50 is made of plastics material and has the form of a rectangular rod. one of whose ends is rounded off to co-operate with the switching cam 20 and a compression spring 54 acts upon its other end. The switch slide 50 extends substantially diagonally so that it can have the greatest possible length with the smallest space required.

The switch slide has projections 51 which form abutments for contact arms 52, 53 which are pushed onto the switch slide and protrude beyond it on both sides. The switch slide 50 preferably comprises an insulating member so as to be able to push up the contact arms and secure them by snapping open. Each contact arm carries a contact on each of its two ends.

The switch slide 50 is guided by guides 55 which have the form of metal plates which protrude from the base of the housing part 12 and are directed at right angles to the switch slide. Four guides 55 are provided, each two of which lie opposite one another.

They guide the switch slide and partially overlap it. some of these guides 55 carry fixed contacts 56 and the guides 55 protrude through the base of the housing part 12 to form connection lugs of the plug-in lug type on the rear side.

The rear side of the power controller 11 can be seen in Figure 3. This shows that the switching cam 22 co-operates with a switch 61, which is of very small and easy construction. in the form of a contact spring which is designed to short-circuit a diode 62. In this case. the diode is soldered by its connections 63. 64 directly onto the associated connecting plug or the contact spring, and the contact spring is embraced by the connection 63 and can short-circuit the diode 62 by touching its connection 64.

The power controller operates as follows: In Figure 1, the disconnected state is shown wherein the switching cam 20 has pressed the switch slide 50 back against the force of the compression spring 54 and has thus removed the contact arm 52 for the signal pilot light contact and the contact arm 53 for the disconnection of the second pole from the appropriate fixed contacts. When the control body 18 or the adjusting shaft is in this position, the compensating bimetal strip 26 is located in a recess in the control cam 19 so that the control body is positively held in this "off" position.

When the energy regulator" is connected (by turning the control body 18 in a clockwise direction). the control cam 20 first of all releases the control slide 50 which, under the force of the spring 54. applies its contact arms 52, 53 which are at least partially resilient against the guides 55 such that they are bridged. On the one hand, therefore. the signal contact line 66, 67 is closed and. on the other hand, one pole of the load 70. for example the heating element of an electric hotplate, is closed.

Because of the action of the spring 34. the compensating bimetalisnap switch unit 26/29 pivots into a position which corresponds to the respective position of the control cam 19. The contacts 31 and 32 are closed, so that the bimetallic member 36 is heated by its heating winding 39. The switch 61 is closed in the lower power range, for example when the adjusting shaft is in a position corresponding to power values between 5 and 20% of the total power. With a low set power, therefore, the diode 62 is bridged so that the full heating power of the heating winding 39 is effective.

Consequently, the limb 38 of the bimetallic member 36 deflects relatively quickly and presses upon the snap switch in the disconnecting direction by way of the short limb 43 and the cranked portion 44, so that this snap switch is opened again after a relatively short time.

After the bimetal member has cooled down. the snap switch 27 re-closes and the working process starts again. In the upper operating range, on the one hand. the compensating bimetal/snap switch unit 26/29 is swivelled further in an anti-clockwise direction and, on the other hand, the diode is effective because of the opening of the switch 61.

The heating winding 39 is therefore only operated with a respective half-wave of the alternating current, i.e. with half the heating power. The bimetal member therefore needs substantially longer to be deflected to such an extent that it can open the snap switch and thus disconnect the power supply to the load 70. At the very high temperatures of the bimetal member, the cooling down process is also effected more quickly so that a longer relative connection period is ensured.

The power controller as described and illustrated has numerous advantages: Despite its clear and reliable construction, it can be produced at relatively low building cost and operates with relatively large paths and forces for the switching process. In particular. the high forces are essential.

They are obtained because of the rather large dimensions of the bimetal member.

Because of the favourable structure. the working bimetal members may be rather long and the compensation bimetal strip may be rather short and strong. The entire system is positively moved by the springs 3jar.

41 into a specific position so that there is only one point at which play may occur, namely the point of contact between the snap spring 30 and the bowed portion 44 of the working bimetal member 36.

There is a further advantage in constructing the bimetal member 36 as an L-shaped member made from bimetal strip. Normally it is very difficult to compensate such a controller bv a compensating bimetal strip because the two bimetal strips operate within different temperature ranges. The deflection path of a bimetal strip per unit of temperature does, however, decrease with rising temperature so that the compensation can only ever be accurate for one working range. The bimetal member described here, however, has, so to speak, a double heating device. The short limb 43 runs parallel to the snap spring 30 at a relatively small distance therefrom. This spring is supplied with current by way of the supply line 35 and is relatively thin. It is therefore heated when current flows through it, even though to a certain extent. This heat additionally heats the short limb 43, but noticeably only at higher power stages because in other cases the snap spring hardly gets above ambient temperature. However, the negative effect of the deflection path, which is regressive with the temperature, is thereby compensated for or counteracts this negative phenomenon.

The compensating bimetal strip is, however, shielded from the temperature as much as possible. It is perpendicular to the long limb 38 of the working bimetal member 36 and has no heat conductive connection therewith. It is also largely shielded relative to the hot chamber by the intermediate wall 42. It is protected by the switch carrier 29 from the temperature produced by the snap spring. This arrangement therefore ensures that the compensating bimetal strip can actually fulfil the purpose for which it is intended. namely to effect a compensation for the variable ambient temperature, and must not operate in a temperature which is substantially high relative to the surroundines.

The working bimetal member and the compensating bimetal/snap spring unit 26/29 take up two sides of the switch housing so that one corner remains entirely free for the switch 50 to 56. The arrangement of this very small-built switch in the same radial plane as the other parts of the power controller enables this controller to be produced with a very small structural dimension. The depth in the direction of the adjusting shaft may, for example. be less than 25 mm so that it is also possible to install it with a vertical shaft in very flat cooking troughs.

The behaviour of the power controller is very positively influenced by the diode 62.

The middle power range is rarely a problem for such controller. The real problem lies in the upper power range and in particular, however, in the lower power range. In the case of today's hotplates with relatively high power. however, the lower power range is in fact critical when it is also desirable to heat up the hotplate. Outputs of up to 51e of the total power and below (100 W with a 2000 W hotplate) must be positively controlled.

However, this requires very high outputs on the bimetal member because this has to react very quickly. These high outputs would, however, not only heat the controller very intensely in the higher power range and use energy, but also raise the temperatures at the bimetal member inadmissibly.

This problem can be easily solved by the advantageous no-loss regulating down of the bimetal heating power, consequently without any lost heat, by means of the diode.

The high power, for which the bimetal heating winding is designed, is no disadvantage because this is only ever used in the lower power range and the relative connection periods there are of course only very short. The heating of the controller by the heating winding 39 is therefore very low.

Conversely, the power in the high power range is limited by the diode so that the heating of the switch also remains within limits during the relatively long connection periods there. Another advantage is that the heating winding 39 may be simply constructed. If it was desirable to make the power less, then problems would arise because the resistance wires for the low outputs would become very thin with mains voltage and especially in the case of higher mains voltages, thereby also causing the operational reliability to suffer.

Attention is drawn to co-pending Application No. 7596/79 (Serial No 1563027) in which is claimed a power controller for the controllable supply of electrical a.c. power to a load comprising a housing. power switch means for switching power to the load, a bimetal member for operating said power switch means, heating means for heating said bimetal member when power is supplied to said load via said power switch means, a diode and control means having a control cam which acts at least indirectlv on said bimetal member and having auxiiiary switch means for connecting said diode in circuit with said heating means only in an upper power range. wherebv said heating means only receives half wave power in said upper range but receives full wave power in a lower power range.

WHAT WE CLAIM IS: 1. A power controller for the controllable supply of electrical power to a load.

comprising a housing. electrical switch means for switching power to the load. a pivotably mounted bimetal member, means for heating said bimetal member when power supplied to the load via said switch means. said switch means comprising snapacting, switch spring carrying a movable electrical contact cooperable with a fixed electrical contact, the bimetal member having a limb which extends at an angle to the remainxder of the bimetal member and which acts upon the snap spring. a pivotally mounted ambient temperature compensating bimetal strip which is secured to the snap spring and which extends substantially parallel to the snap spring at one side thereof, and a control cam which acts upon a free end of the compensating bimetal strip.

2. A controller as claimed in claim 1, in which the bimetal member is L-shaped and its longer bimetallic limb is provided with the heating means.

3. A controller as claimed in claim 2 in which said longer limb is supported against the housing by way of an adjusting screw and under spring force.

4. A controller as claimed in claim 2 or 3 in which the shorter limb extends parallel to the snap spring, the snap spring being arranged to conduct the current supply to the movable contact.

5. A controller as claimed in claim 2. 3 or 4 in which the longer bimetallic limb is located in a chamber which is at least partially heat protected with respect to the compensating bimetal strip and the snap switch spring.

6. A controller as claimed in claim 5 in which said chamber is provided with heat shield means.

7. A controller as claimed in claim 5 or 6 in which said chamber is provided with ventilating means.

8. A controller as claimed in any preceding claim, in which the heating means for the bimetal member is so connected that, in use, it will be in parallel with the load.

9. A controller as claimed in any preceding claim, in which the snap spring is adjustable by means of a screw which is remote from the contact of the snap spring and which has a notch in which the snap spring is guided to support the latter.

10. A controller as claimed in any preceding claim, in which the snap spring and the bimetal member are mounted in the housing by means of pivot pins whose ends are received in holes in two housing parts which are assembled together to form the housing.

11. A controller as claimed in claim 10 in which one of the housing parts has a cavity which accommodates the principal components of the controller and the other housing part is a cover which closes off the cavity.

12. A controller as claimed in any preceding claim, in which a mechanical mains switch for disconnection of the load from the mains and/or the operation of signal means is arranged in the housing at right angles to an adjusting shaft of the control cam and substantially in the same plane as the snap switch spring and the bimetal member.

13. A controller as claimed in claim 12 in which the mains switch has a switch slide which is actuable by a switching cam connected to the control cam and which has transversely extending contact arms.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. would, however, not only heat the controller very intensely in the higher power range and use energy, but also raise the temperatures at the bimetal member inadmissibly. This problem can be easily solved by the advantageous no-loss regulating down of the bimetal heating power, consequently without any lost heat, by means of the diode. The high power, for which the bimetal heating winding is designed, is no disadvantage because this is only ever used in the lower power range and the relative connection periods there are of course only very short. The heating of the controller by the heating winding 39 is therefore very low. Conversely, the power in the high power range is limited by the diode so that the heating of the switch also remains within limits during the relatively long connection periods there. Another advantage is that the heating winding 39 may be simply constructed. If it was desirable to make the power less, then problems would arise because the resistance wires for the low outputs would become very thin with mains voltage and especially in the case of higher mains voltages, thereby also causing the operational reliability to suffer. Attention is drawn to co-pending Application No. 7596/79 (Serial No 1563027) in which is claimed a power controller for the controllable supply of electrical a.c. power to a load comprising a housing. power switch means for switching power to the load, a bimetal member for operating said power switch means, heating means for heating said bimetal member when power is supplied to said load via said power switch means, a diode and control means having a control cam which acts at least indirectlv on said bimetal member and having auxiiiary switch means for connecting said diode in circuit with said heating means only in an upper power range. wherebv said heating means only receives half wave power in said upper range but receives full wave power in a lower power range. WHAT WE CLAIM IS:

1. A power controller for the controllable supply of electrical power to a load.

14. A controller as claimed in claim 13,

in which the housing is substantially rectangular or square and the switch slide lies diagonally in a corner of the housing.

15. A controller as claimed in claim 13 or 14 in which the switch slide is made of insulating material and is guided between at least four metallic guides which are at right angles to the switch slide and which lie opposite each other in pairs, and in which the metallic guides carry or form fixed contacts with which the contact arms cooperate, and the metallic guides protrude through the housing to form connecting tabs.

16. A controller as claimed in any preceding claim, in which the control cam has a control body with a moulded-on bearing pin which is guided in an opening in the side of the housing remote from the operating side and in which an adjusting shaft of the control cam protrudes into a central blind hole in the control cam body and is journalled in the operating side of the housing.

17. A controller as claimed in any preceding claim, which is adapted to operate with alternating current and which further comprises a diode and auxiliary switch contacts actuable by a further cam for connecting said diode in circuit with the heating means for the bimetal member only in the upper power range and not in the lower power range. the further cam being connected to the control cam.

18. A controller as claimed in claim 17 in which the diode is in series with the heating means and the auxiliarv switch contacts are arranged to shunt the diode in the lower power range.

19. A controller as claimed in claim 17 or 18, in which the diode is arranged on the rear side of the housing remote from its operating side and is disposed directly on the auxiliary switch contacts.

20. A controller as claimed in claim 19 when appendant to claim 16. in which the bearing pin of the control body carries the further cam for the auxiliarv switch.

21. A power controller for the controllable supply of electrical power to a load.

constructed and adapted to operate substantiallv as herein described with reference to and as illustrated in the accompanying drawings.