GB2319115A

GB2319115A - Energy regulator

Info

Publication number: GB2319115A
Application number: GB9623192A
Authority: GB
Inventors: John Edwin Tooke
Original assignee: Diamond H Controls Ltd
Current assignee: Diamond H Controls Ltd
Priority date: 1996-11-07
Filing date: 1996-11-07
Publication date: 1998-05-13
Anticipated expiration: 2016-11-07
Also published as: GB2319115B; GB9623192D0

Abstract

An energy regulator comprises a bimetal element 2, an electrical heater member 1 and a resilient coupling member 4 for coupling the heater member and the bimetal element whereby relative movement takes place between the bimetal element and the heater member at the coupling member upon heating and cooling of the bimetal element. The bimetal element bends abruptly away or curves away from the heater member at its zone of contact with the electrical heater member to leave only a point or minimal area of direct contact or a spacer element 6 is provided between the electrical heater member and the bimetal element to prevent direct contact therebetween so as to delay the heating of the bimetal element by the heater member and slow the cycling rate of the regulator.

Description

IMPROVEMENTS IN OR RELATING TO THERMAL CONTROL MEANS Field Of The Invention The present invention relates to electrical energy regulator devices employing a bimetal element and an associated electrical heater for cycling the supply of current to one or more electrical appliances/loads.

Background To The Invention Energy regulators are employed widely for control of both domestic and industrial electrical appliances and are most commonly used for controlling supply of electrical energy to heating appliances/loads such as domestic cookers/hobs and water heaters.

Although energy regulators have in the past been constructed using electrical resistive heating coil wound around a bimetal element the much superior preferred modern configuration uses an electrical resistive film mounted on a substrate as the heating element in intimate contact with the bimetal element.

Examples of such relevant prior art designs include those discussed in the present applicant's UK patent number GB 1 201 537. Further detailed disclosure of prior art energy regulators of the aforementioned type is also given in European patent application number EP 0 682 352.

As highlighted by European patent 0 682 352, the primary objective of developments in energy regulator design in recent years is improving efficiency by enhancing the rate of cycling of the regulator.

In an electromechanical energy regulator the power to the load is switched ON and OFF cyclically in such a way that the ratio of the ON time to the TOTAL cycle time (ON time plus OFF time) gives the percentage of full power which will be delivered to the load.

Generally the cyclical operation of the conventional energy regulator (Figure 1 prior art) is achieved by a heater 1, in the form of a thick film substrate, and bimetal 2 operating onto a snap switch 3 via a calibration screw. In operation the heater heats up the bimetal which deflects until the deflection is sufficient to operate the snap switch. This switch action switches OFF the load and the power to the heater. Since the bimetal is no longer being heated it relaxes reducing the deflection. As the deflection relaxes through the differential of the snap switch (the differential is the difference in mechanical movement of the snap switch between its switch OFF position and its switch ON position) the switch action will switch ON the load and the power to the heater. The cycle will repeat.

The ON time of the energy regulator is controlled by a combination of the heating effect of the heater, the differential of the switch and relative physical positions of the switch and bimetal. The power level is adjusted mechanically (generally by a rotating shaft and cam arrangement) which adjusts the relative physical positions of the bimetal to switch mechanism.

The OFF time of the energy regulator is controlled by a combination of the differential of the switch, relative physical positions of the switch and bimetal and the cooling rate of the heater and bimetal.

Cycle times for this type of energy regulator vary naturally as the power setting is adjusted and generally the fastest cycle occurs around the 50% power setting.

In existing designs the fastest cycle time can result in electromagnetic interference (mains flicker) with other electrical appliances when driving high current loads. The switching frequency for a standard/typical energy regulator set to the fastest cycling position (50to) is approximately 5 operations per minute (24 seconds/cy). In practice this would limit the load current switched by the contacts to approximately 10A for a resistive load and less for a more complex load waveform (Tungsten Halogen). To enable higher power loads to be switched, more than 10A, and still comply with the E.M.C directive (mains flicker) would necessitate a slower switching pattern. The cycle time/switching frequency can to some extent be adjusted by adjusting the contact gap of the switch, although too much adjustment can result in unreliable operation of the switch.

It is a major objective of the present invention to provide an energy regulator that overcomes the significant problem of existing energy regulator design without significantly compromising performance and without risk of arcing or otherwise undermining the reliability of the device.

Summary Of The Invention An energy regulator which cycles the supply of current to an electrical appliance, the regulator comprising a bimetal element and an electrical heater member and a resilient coupling member for coupling the heater member and the bimetal element whereby relative movement takes place between the bimetal element and the heater member at the coupling member upon heating and cooling of the bimetal element, characterised in that the bimetal element is formed at its zone of contact with the electrical heater member with a curved forms that bows away from the heater member leaving a minimal area of direct contact or in that a spacer element is provided between the electrical heater member and the bimetal element to prevent direct contact therebetween and to give a delay in heating of the bimetal by the heater to slow the cycling rate of the regulator.

Preferably the spacer element comprises a substantially incompressible insert of known thickness to provide a predictable extent of slowing of the cycling rate of the regulator.

The insert can be any suitable thickness but less than 0.5 millimetres. Suitably the insert is of substantially uniform cross-sectional thickness and is advantageously formed of a heat insulating material such as mica.

Alternatively, however, the insert may be formed of a heat conductive material such as, for example, brass.

Whether the insert is relatively more or less heat conducting will affect the required thickness of insert.

The present invention enables the cycle time of the energy regulator to be lengthened adequately by reduction of heat transfer from the heater to the bimetal, increasing the cycle ON time and hence the OFF time in a reliable way such that the power dissipated in the heater remains substantially the same and the general operation of the energy regulator is not deleteriously affected.

It has been found that slowing up cycle time to between 30 and 70 seconds at the fastest cycling position (50%) enables compliance with the E.M.C (mains flicker) requirements for load currents in excess of 10A The actual switching time (cycle time) for a particular load current and hence acceptable mains flicker is dependent of many external factors, in particular element/load design, appliance design, heating and cooling rates, environmental conditions. These variations can be accommodated and are achievable through using the proposed spacer between the heater and bimetal, without significantly affecting performance.

Brief Description Of The Drawings Figure 1 is a diagrammatic view of a prior art configuration of energy regulator.

A preferred embodiment of the present invention will now be more particularly described, by way of example, with reference to Figures 2, 3 and 4 of the accompanying drawings, wherein: Figure 2 is a diagrammatic side elevation view similar to that of Figure 1 but illustrating the preferred embodiment of the present invention; and Figures 3 and 4 are graphical illustrations of the effect of spacer thickness (yaxis) on the length of cycle time of the energy regulator (x-axis).

Description Of The Preferred Embodiment Referring firstly to Figure 1 which illustrates the prior art arrangement of thermal actuating energy regulator, the regulator comprises a bimetal element 2 in intimate contact with an electrical heater member 1. The heater member 2 is secured to the bimetal element 2 by a coupling member comprising a rivet 4 that has a compression spring 40 held captive on its shank to resiliently bias the bimetal element 1 against the heater member 2. The rivet 4 and spring 40 together hold the bimetal 2 and heater member 1 in intimate contact over the length L. Over this length, the heat from the heater member 1 will be transmitted substantially by conduction to the bimetal 2. When the bimetal 2 bends under the influence of the heater member 1 a calibration screw 5 mounted in the free end of the bimetal 2 will bear onto a snap switch 3 causing the switch to flex and snap open to break the contact and cut off supply of electrical energy to the appliance supplied by the energy regulator.

Referring now to Figure 2, the intimate contact of the bimetal element 2 and heater member 1 is prevented by a washer/spacer 6 which is suitably formed of mica or another thermally insulating material, but which may also be a thermally conductive material, provided that it is of adequate thickness. The spacer 6 is suitably shaped as a centrally apertured flat circular disc that is slidably mounted onto the shaft of the rivet 4.

Due to the air gap created by the spacer 6, transfer of heat from the heater member 1 to the bimetal element 2 will be mainly by radiation and not conduction. The transfer of heat is considerably slower than by conduction and consequently the time taken to open the snap switch 3 is substantially greater.

The heater member 1 attains a higher temperature compared to the conventional arrangement, and then cools at a similar rate to the conventional arrangement.

Thus the ON time and the OFF time are extended by a controlled amount.

Consequently the cycle time is increased without jeopardising the performance/reliability of the control.

The material (heat conducting or insulating) and area of the spacer 6 can be adjusted to tailor the characteristics of the energy regulator to the particular application. Slower cycle times give wide variations of temperature on appliance elements, however these variations can better be tolerated by some appliances such as grill elements (which also generally are high current loads).

In general the faster the cycle time of an energy regulator the better the performance, since faster cycle times give a more even heating effect, especially useful on hob elements. The applicant has found, however, that for the majority of appliances cycle times of the order of 45 - 65 seconds in length, at the fastest cycling position (50%) which are virtually double those of common conventional energy regulators, have no significant deleterious effect on performance whilst avoiding or mitigating the risk of electromagnetic incompatibility at higher load current switching.

From trials carried out using spacers made in the first instance of mica (see Figure 3) it has been found that a reliable directly proportional linear relationship exists between thickness of spacer 6 (logged as air gap in millimetres between heater member 1 and bimetal 2) and the total cycle time of the energy regulator (logged as the fastest cycle position duration in seconds).

The directly linearly proportional relationship between thickness/air gap and total cycle time is lost when the thickness reaches a level of greater than 0.4 millimetres, with the graph reaching an asymptote at approximately 0.5 millimetre thickness.

When the same trial was carried out using a brass spacer 6 (see Figure 4) the performance characteristics were similar but with a less marked increase in cycle time for corresponding increase in thickness of spacer 6. Notably again the directly proportional linear relationship between thickness of spacer 6 and cycle length ceased at above 0.4 millimetres thickness, reaching an asymptote shortly above that level of thickness.

To provide an adjustable control of the delaying of the cycling, the thickness of the spacer 6 at least across that part of it which separates the bimetal element 2 from the heater member 1, in use, may be made adjustably variable. For example, the spacer 6 may be formed with an ellipsoidal cam profile and be rotatable to thereby vary the separation of bimetal 2 and heater member 1, in use. Alternatively the spacer 6 may have a stepped or sloping (ie wedge shaped) elongate form and be longitudinally slidable between the bimetal 2 and heater member 1 so that the further the spacer 6 is inserted therebetween the greater the spacing thereof.

It will be appreciated that the present invention provides a simple but effective method for accurately controlling the extension of the cycle time of the energy regulator to enable the energy regulator to perform effectively and mitigate or eradicate the electromagnetic interference with other appliances, when switching high load currents.

Claims

1. An energy regulator which cycles the supply of current to an electrical appliance, the regulator comprising a bimetal element and an electrical heater member and a resilient coupling member for coupling the heater member and the bimetal element whereby relative movement takes place between the bimetal element and the heater member at the coupling member upon heating and cooling of the bimetal element, characterised in that the bimetal element is formed at its zone of contact with the electrical heater member with a curved form that bends abruptly away or curves away from the heater member leaving only a point or minimal area of direct contact or in that a spacer element is provided between the electrical heater member and the bimetal element to prevent direct contact therebetween and to give a delay in heating of the bimetal by the heater to slow the cycling rate of the regulator.

2. An energy regulator as claimed in Claim 1, wherein the spacer element is a substantially incompressible insert of known thickness to provide a predictable extent of slowing of the cycling rate of the regulator.

3. An energy regulator as claimed in Claim 1 or 2, wherein the insert is less than 0.5 millimetres in thickness.

4. An energy regulator as claimed in Claim 1, 2 or 3, wherein the insert is of a heat insulating material such as mica.

5. An energy regulator as claimed in any preceding Claim, wherein the cycle time is between 30 and 70 seconds per cycle when the regulator is set to its fastest cycling setting.

6. An energy regulator as claimed in any preceding Claim, wherein the thickness of the spacer element that spaces the bimetal element and heater member apart in use is adjustable in situ to adjustably vary the extent of slowing of the cycling rate of the regulator.

7. An energy regulator as claimed in any preceding Claim, wherein the spacer element is formed of, on or mounted to the coupling member and may for example comprise a shoulder on the coupling member.

8. An energy regulator substantially as hereinbefore described with reference to any suitable combination of the accompanying drawings.

9. An energy regulator as claimed in any preceding Claim wherein the bimetal is domed or otherwise raised to a point at its zone of contact with the heater member.