GB2315160A - Energy regulator - Google Patents

Abstract

An energy regulator cyclically switches a load on and off for a power output less than a predetermined level and switches the load on continuously for a power output greater than the predetermined level. This enables the high power load to be switched at lower levels of cyclic power output (e.g. 30% or 50% of the maximum power output) and at higher power outputs, the load is not switched, thus minimising the effects of mains flicker. The load is, for example, a heating element in which the energy output is maintained by action of a bimetal strip 5, 13 which cyclically switches the heating element within the predetermined output power range. The power output of the energy regulator 1 is set by a rotary cam element 37 in which the surface 39 of the cam element 37 defines a discontinuity corresponding to the power output level at which the load is switched continuously on.

Description

ENERGY REGULATOR The present invention relates to an energy regulator for obtaining a variable power output. In particular it relates to an energy regulator of the kind which regulates a device by switching the device on and off to maintain a particular power output, the energy regulator providing a variable power output by varying the on/off time intenals.

More particularly, the present invention relates to an energy regulator of the kind which incorporates a bimetal element. The regulator utilises temperature-dependent deflection of a bimetal strip to fulfil a regulating function in a wide range of equipment, for example in domestic appliances such as cookers. The bimetal strip is heated by a heating element in intimate contact to actuate a switch mechanism by deflection of the bimetal strip to open and close electrical contacts for the supply of power to the load.

The setting at which the bimetal strip actuates the switch mechanism is determined by a rotate cam arrangement.

With the introduction of new European Legislation, only low level mains flicker is permitted when the devices are switched at high switching rates. The more frequent the switching. the lower the level of mains flicker permitted. Therefore, this has the effect of reducing the load current and hence the power level that can be switched at these frequencies.

The higher loads of particular interest are those having load currents in excess of 8 A or 10 A. for example a grill element of a domestic cooker. The high power requirement is in general applicable to the Full-On position where a fast response is required for the element to reach it desired temperature as quickly as possible. To control, the heater element. the energy regulator switches the element on for a predetermined time interval and off for a predetermined time interval which is dictated by the time required for the element to reach a particular level. Therefore. the variation of the output in such a regulator device is a function of time. consisting of an On time and Off time and is expressed as a percentage of the maximum power output.

Figure 1 shows an example of a typical output curve for a standard energy regulator.

The x-axis is the degrees of rotation of the control knob of the regulator and the y-axis is the percentage of power output. The following table is a set of data points taken from the plot of Figure 1 giving the on time and total time (on + off time) of the regulator: TABLE 1

Handle Rotation On Time Total Time Percentage Output (Degrees) (Seconds) (Seconds) (%) 75" 10.6 142.9 7.4 96" 9.7 86.9 11.2 117 9.7 86.9 15 138 10 64.5 17.8 159 11.1 45.4 24.4 1800 13.2 40.6 32.5 201 14.7 38 o8.7 222 17.1 37.3 45.8 260" 28.9 45.2 63.9 286 infinity infinity 100 It is understood that the figures provided in Table 1 are merely an example and the specific values may be varied to particular requirements while following the general curve of figure 1.

As can be seen from Fig. 1 and Table I above, the percentage output increases at a generall! even rate over the whole range of rotation of the knob of the regulator. The 286 position, in this particular example, being the Full-On position of the regulator in which the element is switched on all the time.

In the standard regulator, for a 50% power output, the on/off times are equal and the switching frequencies is approximately 5 operations per minute.

In practice the high power output/current load at the faster cycling settings may cause higher levels of mains flickers and, therefore. to provide lower levels, slower switching patterns have to be provided for these settings.

It is presently knoun that in order to regulate a high powered load, say 13.5 A, a second or third switch on the energy regulator can be utilised. An example of such a regulator is described in co-pending Patent Application No. EP 0682352 Al.

Such an energy regulator and load (elements) can be connected as shown, for example.

in Fig. 2a. The circuit comprises parallel loads A and B. Load A is connected to a first switch P 1 of the regulator and the additional load B is connected to a second (auxiliary) switch P2. In use, Pl switches the load A on/off to maintain a particular power output.

In the Full-on position (286" angular setting), both loads A and B remain on continuousl!- by activation of the auxiliary switch P2. The cyclic load A has a load of current of less than I OA. Therefore. in cycling load A only, high load currents are not switched to cause mains flicker.

A further circuit arrangement which enables cycling at less than 10 A is shown in Fig.

2b. In this circuit the loads A and B are connected in series. The regulator switches both elements connected in series over the cyclic range by activation of a first switch P 1.

The switched load current is then less than 10 A reducing the effects of mains flicker.

At the point of switching to the Full-on position the second switch P2 by-passes load A, this leaves the high powered load B in the circuit.

Another circuit for coping with switching load at less than 10 A is shown in Fig. 2c.

Two additional switches are used. known as an auxiliary front switch X fitted to the energy regulator. A dual load element A and B can be switched in a series/parallel configuration. This enables fast cycling and low power control to be performed at the low current series configuration and the higher output requirements obtained with the elements connected in parallel. Therefore, low current loads are switched in the cyclic range and for Full-on a high current load can be utilised.

The disadvantages of the above arrangements is that the elements have to be specially constructed as a dual element, thus increasing manufacturing costs. There would also be additional terminations and wiring together with possible redesign of the cooker to accommodate the modifications. Further. additional switching is required making the regulators more complex and more expensive to manufacture.

The regulator of the present invention seeks to overcome the above mentioned disadvantages.

Therefore the present invention provides an energy regulator connected to a load. the energy regulator cyclically switching the load on and off for a power output less than a predetermined level and switching the load on continuously for a power output greater than the predetermined level.

In the preferred embodiment, the energy regulator comprises a rotatory cam element for setting the power output by angular setting of the cam element. the periphery of the cam element comprising a cam surface having a discontinuity at which the load. for example, a heating element is switched on continuously for a power output greater than the predetermined level. The heating element is switched on and off by deflection of a bimetal strip which comprises a primary limb responsive to the heating element. and a compensator limb, the compensator limb terminating in a cam follower arranged thereupon the cam surface of the cam element. The cam element is attached to a user control knob to allow angular setting of the cam element.

The predetermined level may be 50% of the maximum pou-er output preferably, 30% of the maximum power output with a load current more than I OA.

Therefore, the regulator of the present invention avoids the faster cycling positions and limits the cyclic range to the low power outputs. This enables high power loads to be switched at lower levels of cyclic power output.

In the preferred embodiment, the cam profile of the energy regulator is arranged such that the power output increases to approximately 50%, preferably. 30% resulting in about one switching or less per minute and thereafter the energy regulator goes Full-on (100% output power) without any intermediate steps.

The cam profile is such that when turning from any dial setting to obtain greater than 30% output the index mechanism will over ride any intermediate setting, thus ensuring that only a Full-on position or an Off position is achievable. Electrical loads in excess of 10 A can thus be switched to comply with existing regulations. This therefore provides a device with operates within safe parameters and which does not involve complex design or additional components. Setting the level to 30% of the maximum is only an example.

The level can be set to any level provided the flicker rate requirements are met.

The invention will now. be explained in more detail by vay of the following description of a preferred embodiment and with reference to the accompanying drawings. in which: Figure 1 shows an output curve of a standard energy regulator: Figures 2a, 2b, 2c. show altemative known circuit arrangements for cyclically switching loads at less than 10A: Figure 3 shows an energy regulator according to the present invention; Figure 4 shows the profile of the cam surface of the cam element of the energy regulator according to the present invention; and Figure 5 shows an output curve of the energy regulator of the present invention.

The regulator comprises a primary bimetal leg 5 to which a ceramic substrate thick film heater 11 is secured by means of an eyelet 7 and a surrounding coil spring 9. A compensator strip 13 extends at approximately right angle to the primary strip 5 and is contiguous therewith. The primary strip and compensator strip are joined by a common base 15.

The base region 15 is secured to a pivot spring 17 in the form of a leaf spring, so that the primary bimetal strip 5 and the compensator bimetal strip 13 together with the substrate heater 11 pivot together as a rigid assembly.

The bimetal leg 5 bears on a deflectable snap action. spring member 27 by means of a calibration screw 33 so that the deflection of the bimetal leg 5 results in the electrical contacts 2.4 operating (make and break) as a function of the over centre action of the switch mechanism 6. Calibration is preset by adjustment of the calibration screw 33.

The regulator setting controlled by a user by means of a knob (not shown) mounted on a spindle 87 which is a cam element 37 is rotatably mounted. The outer circumference of the cam element presents a cam surface 39.

The compensator strip 13 is bent towards the cam element 37 and terminates in a cam follower 43 which bears against the cam surface 39. In accordance with the position of the knob. the position of the cam surface 39 contacted by the cam follower 43 alters the orientation of the compensator bimetal strip 13 relative to the pivot spring 17 and so.

also, the orientation of the primary bimetal strip 11 relative to the pivot spring. Thus. the position of the calibration screw 33 relative to the switch mechanism is also varied.

The calibration screw is used in initial set-up to calibrate the regulator as described above. It is set in the factory.

In use, the user turns the knob to orientated the compensator and primary bimetal strips 13, 5 by means of the cam action. This determines the power level to the substrate heater and to the corresponding load connected across the electric contacts 2,4. For a given set cant/spindle position the output power would by cyclic at contacts 2, 4.

The cam surface 39 is shaped to give the profile as shown in Fig. 4 to enable greater than 10A to be switched within the range of the mains flicker requirements. This gives the percentage power output as shown in Fig. 5 and in Table 2 below.

TABLE 2

Handle Rotation On Time Total Time Percentage Output (Degrees) (Seconds) (Seconds) (%) 75" 12.8 130.7 8.5 96" 12.2 107.3 11.4 117 12.4 98.6 126 138 12.1 8J.7 14.5 159 11.8 I 76.2 15.5 1800 11.7 67.9 17.2 201" 11.9 39.3 20.1 222 12.7 54.2 23.4 260 15.1 48.6 31.1 286 infinity infinity 100 The specific values provided in Table 2 are examples only. These may be varied to meet particular requirements while still being uithin the range of the mains flicker requirements.

By limiting the power output to less than 30% of the maximum power output over the angular setting range of the regulator (75 to 260 ). thus restricting the range to the area where cyclic rate is low, the maximum current that can be switched is more than 1 0A, providing acceptable levels of mains flicker. Thereafter. the element is switched continuously on at the full-on position (286 ).

With reference to Figure 4, the cam element profile is such that at A a low cyclic output is produced with an angular setting of typically 75" or 5 from the off position. A to C, angular range of approximately 75" to 260 , the cam profile provides a power output which has a linear rate of change within the range of approximately 6% to 30% power output. The high cyclic output position C. typically 260 or 290 angular setting from the off position, provides a level of output power which switches the load at approximately one switching operation per minute (See Figure 5 and Table 2). At D, the load is switched Full on (non cyclic), typicall! 285 or 3050 angular setting from the off position.

In the light of this disclosure, modification of the described embodiment, within the scope of the present invention as defined by the appended claims, will now become apparent to persons skilled in the art.

Claims (10)

CLAIMS:

1. An energy regulator connected to a load. the energy regulator c!clicall- switching the load on and off for a power output less than a predetermined level and switching the load on continuously for a power output greater than the predetermined level.

2. An energy regulator according to claim 1 comprising a rotatory cam element for setting the power output by angular setting of the cam element, the periphery of the cam element comprising a cam surface having a discontinuity at which the load is switched on continuously for a power output greater than the predetermined level.

3. An energy regulator according to claim 2, wherein the load is a heating element.

4. An energy regulator according to claim 3, wherein the regulator further comprises a bimetal strip comprising a primary limb responsive to the heating element, deflection of which cyclically switches the heating element on and off to maintain the heating element within a predetermined energy level.

5. An energy regulator according to claim 4. wherein the bimetal strip further comprises a compensator limb, the compensator limb terminating in a cam follower arranged thereupon the cam surface of the cam element.

6. An energy regulator according to claim 2, wherein the cam element is attached to a user control knob.

7. An energy regulator according to any one of the preceding claims, wherein the predetermined level is 50% of the maximum power output.

8. An energy regulator according to claim 7. wherein the predetermined level is 30% of the maximum power output.

9. An energy regulator according to claim 8 wherein the load current is more than 10 A.

10. An energy regulator substantially as hereinbefore described with reference to any one of Figures 3 to 5.