John
Crawshaw, Jones
Colin
Edward
John
Crawshaw, Jones
Colin
Edward
| 1. | An electrical apparatus comprising thermostatically controlled electrical heating means, said thermostatic control supplying power to said heating means cyclically in response to a sensed temperature, and means for opening switch means in the power supply to the heating means after a certain number of cycles of operation of said heating means, wherein said switch opening means comprises a bimetallic or other operating member responsive to the power supply to said heating means and which moves in response to the current flowing to the heating means, a linearly displaceable actuating member for operating said switch means and a rack provided along said member, said operating member being provided or cooperating with pawl means for engaging said rack, whereby successive movements of said operating member are transmitted to and cause linear displacement of said actuating member to open said switch means after a certain cumulative displacement thereof. |
| 2. | Apparatus as claimed in claim 1 wherein said pawl means is formed as a resilient member which is mounted on a movable end of the operating member and which has a tongue resiliently engaging the rack. |
| 3. | Apparatus as claimed in claim 1 or 2 further comprising a locking pawl in the form of a resilient member having a tongue engaging the rack. |
| 4. | Apparatus as claimed in any preceding claim comprising a bimetallic operating member and in which the pawl engages the rack at different positions in response to a change in ambient temperature and the bimetallic member and pawl are so arranged that substantially the same displacement of the rack for each bimetal deflection is achieved regardless of the position of engagement in normal operation. |
| 5. | Apparatus as claimed in any preceding claim wherein said actuating member is moved by a bimetallic operating member as the latter cools, whereby power is not being supplied to the heating means at the time the switch means are opened. |
| 6. | Apparatus as claimed in any preceding claim comprising means for resetting the position of said actuating member, said reset means acting to disengage said pawl means from said rack so as to allow said actuating member to return towards its original position. |
| 7. | Apparatus as claimed in claim 6 wherein said reset means is manually operable. |
| 8. | Apparatus as claimed in claims 6 or 7 wherein said reset means is responsive to the movement of the apparatus and comprises an inertial device. |
| 9. | Apparatus as claimed in claims 7 or 8 in which the switch means opens by snap action and is bistable whereby it remains open until it is manually reset regardless of whether the reset means for the actuating member is operated. |
| 10. | Apparatus as claimed in claims 8 or 9 wherein said inertial device comprises an eccentrically mounted weight which cooperates with said pawl means to disengage said means from the rack. |
| 11. | Apparatus as claimed in claims 8 or 9 wherein said inertial device comprises a freely movable weight which cooperates with a reset member which acts to disengage said pawl means from said rack. |
| 12. | Apparatus as claimed in any of claims 6 to 11 wherein said actuating member returns towards its original position under gravity. |
| 13. | Apparatus as claimed in any preceding claim comprising means for varying the number of cycles of the power supply required to open the switch means in response to the orientation of the apparatus. |
| 14. | Apparatus as claimed in claim 14 wherein said means comprises an extension member which is mounted on the actuating member such that it moves with the actuating member in the direction of opening of the switch contacts and can move between a first position, when the apparatus is in a first orientation, in which it extends the effective length of a relevant portion of the actuating member, and a second position, when the apparatus is in a second orientation, in which it does not. |
| 15. | Apparatus as claimed in claim 14 wherein said extension member is pivotally mounted on said actuating member. |
| 16. | A switch unit adapted to be placed in the power supply to a thermostatically controlled electrically heated appliance comprising a switch means having a set of switch contacts, and means for opening said contacts comprising a bimetallic or other operating member arranged to be responsive to said power supply so as to move in response to the current flowing to the heating means, a linearly displaceable actuating member for operating said switch means and provided with a rack extending therealong, said operating member being provided or cooperating with pawl means for engaging said rack, whereby successive movements of said operating member are transmitted to and cause displacement of said actuating member to open said switch means after a certain cumulative displacement thereof. |
| 17. | An electrical apparatus comprising thermostatically controlled electrical heating means, said thermostatic control supplying power to said heating means cyclically in response to a sensed temperature, and means for opening switch means in the power supply to the heating means after a predetermined number of cycles of operation of said heating means, said switch opening means comprising a bimetallic or other operating member arranged to be responsive to the power supply to said heating means and which moves in response to the current flowing to the heating means, a displaceable actuating member for operating said switch means and provided with a rack, said operating member being provided or cooperating with pawl means for engaging said rack, whereby successive movements of said operating member are transmitted to and cause displacement of said actuating member to open said switch means after a predetermined cumulative displacement thereof, and means for resetting the actuating member comprising means for disengaging the pawl means from the rack in response to movement of the apparatus. |
| 18. | Apparatus as claimed in claim 17 wherein said resetting means includes an inertial device. |
| 19. | An electric iron, provided with a pawl and rack mechanism operable in response to thermostatically controlled cyclical heating of the iron such that the rack cooperates with switch contacts to disable the iron after a certain predetermined effective cumulative movement of the rack, comprising means for disengaging the pawl from the rack and for resetting the rack in response to movement of the iron, and for varying said predetermined effective cumulative movement of the rack depending on whether the iron rests on its sole plate or heel. |
The present invention relates to electrical apparatus of the kind having thermostatically controlled electrical heating means, and also to switches for use in such apparatus.
Some household electrical appliances of the kind referred to have the feature that after a given period of time, the power supply to the heating means is interrupted. Normally an electronic clock circuit is provided within the appliance and, once the given period of time, as counted by the clock circuit, has elapsed, the power supply is cut off. An appliance of this type is a domestic iron where, after say a period of ten minutes non-use in a defined position, as sensed for example by a mercury switch, the power to the heating element is cut off. Such timed automatic switch-off controls are relatively expensive and not very reliable in use.
In appliances with thermostatically controlled heating means, once the appliance has reached working temperature, the heating means will cycle on and off indefinitely under the control of the thermostat. In a domestic iron, a typical cycle time is of the order of one minute, within which minute power would be supplied to the heating means- for say 7 seconds and disconnected for the remaining 53 seconds. Under equilibrium conditions, the cycle time does not vary substantially from cycle to cycle.
It has been proposed in DE-A-3703884 to use the cycling of the thermostatically controlled heating means of an appliance as a convenient clock for controlling the interruption of power to the appliance after a predetermined number of cycles of the thermostatic control corresponding to a desired elapsed period of
time.
The system disclosed in DE-A-3703884 is an electronic system wherein the number of operations of the thermostatic control is counted electronically, and when a desired count is reached, a switch is opened to interrupt the power supply. However, electronic controls may be expensive and also not ideal for use in conditions of high temperature and particular high humidity as may be experienced in appliances such as irons and steam irons, for example.
The present invention seeks to provide a control which overcomes the above problems.
From a first aspect therefore the invention provides an electrical apparatus comprising thermostatically controlled electrical heating means, said thermostatic control supplying power to said heating means cyclically in response to a sensed temperature, and means for opening switch means in the power supply to the heating means after a certain number of cycles of operation of said heating means, wherein said switch opening means comprises a bimetallic or other operating member responsive to the power supply to said heating means and which moves in response to the current flowing to the heating means, a linearly displaceable actuating member for operating said switch means and a rack provided along said member, said operating member being provided or cooperating with pawl means for engaging said rack, whereby successive movements of said operating member are transmitted to and cause linear displacement of said actuating member to open said switch means after a certain cumulative displacement thereof.
A bimetallic operating member will heat up and deform while power is supplied to the heating means and will return towards its original configuration as it cools, when the thermostatic control has cut the power supply to the heating means. Successive movements of
the bimetallic member in one direction will be converted into a cumulative linear displacement of the actuating member by the rack and pawl mechanism. Other forms of operating member for the pawl means are possible. Such an arrangement avoids the disadvantages of the electronically controlled prior art system discussed above. Moreover the linear rack and pawl mechanism provides certain significant advantages.
For example, it will be appreciated that the ambient temperature which is experienced by the control in an appliance such as an iron will vary considerably in use from say 20°C or lower before the device is switched on, up to perhaps 150°C when the device is being used. Thus the position at which the pawl engages the rack, before it deflects due to the heating effect of the current flowing through it, may vary substantially. Furthermore when the device is first switched on, a particularly large deflection of the bimetal will occur. A linear rack is a particularly advantageous mechanism by which these variations may be accommodated while allowing for a consistent movement of the rack in response to the cyclical deflection of the bimetallic member during normal operation. Furthermore, a linear rack will allow a compact construction to be employed in most circumstances. The use of a linearly moveable rack also enables the preferred control conveniently to include means for resetting the actuating member in response to movement of the apparatus and for varying the predetermined number of cycles in response to a selected orientation of the apparatus, as discussed in more detail above.
Preferably the bimetallic member is a generally U shaped leaf member with the respective ends of the limbs fixed in a support and connected to the power supply so that power flows through the member in use. As the bimetallic member heats up and cools down, the cross- member between the limbs will move back and forth by a
predetermined amount in a plane generally perpendicular to the member.
Conveniently the pawl means is formed as a resilient member mounted on a movable end of the bimetallic member and having a tongue engaging the rack. A locking pawl, also conveniently in the form of a resilient member having a tongue engaging the rack, may be provided to prevent the actuating member moving back towards its original position when the movable pawl and rack are not operatively engaged.
Various arrangements of the bimetallic member can be envisaged in accordance with the invention. In one embodiment, it may be generally at right angles to the rack, and thus deflect in a direction generally parallel to the rack. A pawl member may then be mounted on the bimetallic member to extend generally vertically to engage the rack at a position above the bimetallic member. In another embodiment, however, the bimetallic member extends at an angle to the rack, and a pawl member mounted on a lower end of the bimetallic member extend upwardly at an angle to the rack. The assembly of the bimetallic and pawl members is, therefore, in this case generally V shaped. This has been found to be a very satisfactory arrangement in that by virtue of the geometry, the component of the force exerted by the pawl member on the rack in a direction normal to the direction of movement of the rack as the bimetallic member deflects is minimised.
It will be appreciated that the movement of the bimetallic member either as it heats up or cools down may be used to displace the actuating member. It is however preferred that it is the movement produced as the bimetallic member cools which is used, since during such movement the heating means will not be energised. Thus, when the cumulative displacement of the actuating member required to open the switch contacts has been attained, no power will be flowing through the contacts
at that time, which means that there is no possibility of arcing at the contacts. This will give a much improved contact life, and will reduce any problems on calibration of the device which would be caused through contact wear.
In preferred embodiments of the invention, means are provided whereby the actuating member may be reset either before or after the required number of cycles required to discontinue the power supply to the heating means has been reached. The resetting means may be either manual or automatic. A manual reset might be contemplated in an appliance such as a coffee maker where one might wish to extend the period of time the heating means was allowed to operate. A simple button connected to a suitable operating means could therefore be provided which would be pressed by the user as required. An automatic reset might be considered in an appliance such as a domestic iron where operation of the power cut off would not be required during normal use of the iron but would be when the iron is left at rest. A suitable automatic reset mechanism for such appliances where in normal use the appliance is constantly moving, but when not in use is at rest, could therefore be responsive to movement of the device, and most simply may comprise an inertial device.
The reset mechanism may comprise a reset member, which when acted upon by a manually depressed button, an inertial weight or other member disengages the movable pawl and any locking pawl from the rack, which will allow the actuating member to return towards its original position.
Since the movement of the actuating member is linear, this will allow it to move under its own weight if in an appropriate orientation. However if necessary, or appropriate, spring means may be provided to effect or assist in the movement.
In those embodiments which employ an inertial reset
mechanism, the mechanism may for example include an eccentrically pivoted weight having a tongue which disengages the pawls. An alternative arrangement could include a free-rolling member which engages a pivotally mounted member which disengages the pawl.
The reset feature as described above may be of application in controls which do not employ linear racks. For example one could envisage an arrangement using a spring-loaded ratchet wheel as the actuating member, wherein a pawl is disengaged manually or automatically from the wheel which then returns to its original position under the force of the spring. From a second aspect, therefore the invention provides an electrical apparatus comprising thermostatically controlled electrical heating means, said thermostatic control supplying power to said heating means cyclically in response to a sensed temperature, and means for opening switch means in the power supply to the heating means after a predetermined number of cycles of operation of said heating means, said switch opening means comprising a bimetallic or other operating member arranged to be responsive to the power supply to said heating means and which moves in response to the current flowing to the heating means, a displaceable actuating member for operating said switch means and provided with a rack, said operating member being provided or cooperating with pawl means for engaging said rack, whereby successive movements of said operating member are transmitted to and cause displacement of said actuating member to open said switch means after a predetermined cumulative displacement thereof, and means for resetting the actuating member comprising means for disengaging the pawl means from the rack in response to movement of the apparatus. The actuating member may open the switch contacts directly or indirectly. In a particularly simple arrangement, the actuating member may therefore bear
directly on a resilient member carrying a movable contact. However, various alternative forms of switch can be envisaged. For example a movable contact could be mounted on a snap-action actuator which may be either mono-stable so that it will return to a closed position automatically once the actuating member is reset or bi¬ stable so that it will assume a stable "off" configuration after operation and must be positively reset, after reset of the actuating member itself. Where a bi-stable actuator is used, means may also be provided to move the actuator to the 'off position independently of the actuating member. Conveniently the switch reset mechanism may co-operate with the mechanism for resetting the actuating member such that movement to reset the switch automatically resets the actuating member.
Means may be provided in preferred embodiments whereby the number of cycles of power supply required to open the switch contacts may be varied. Such variation could be achieved manually by, for example, varying the original position of the actuating member, by a suitable mechanism. The variations could also be achieved automatically in dependence on the orientation of the apparatus. In domestic irons for example, it is desirable, if the iron is rested on its sole plate, that the heating means is switched off relatively quickly since damage would otherwise occur to the underlying surface, for example, a garment. If however it is rested on its heel, a slower switch off is desirable. Preferably the automatic variation is achieved by means of an extension member which is mounted for movement with the actuating member such that in a first orientation of the apparatus, it assumes a first position in which it effectively extends a relevant portion of the actuating member in the direction of the switch opening movement, but in a second orientation of the appliance it assumes a second position in which it
does not, whereby the displacement of the actuating member required to open the switch means is greater when the appliance is in the second orientation. By "a relevant portion" is, of course, meant a portion of the actuating member which normally co-operates with the switch means to open them.
This is a particularly simple arrangement which is facilitated considerably by the use of the linearly movable actuating member, since in a given operating position of the apparatus as a whole the orientation of the actuating means does not vary as it is moved under the action of the bimetallic member. Thus the orientation of the extension member relative to the relevant portion of the actuating member will also remain unchanged in a given orientation, and whether it acts to extend the actuating member or not will be determined solely by the operative position of the apparatus as a whole. The extension member is preferably pivotally mounted on the actuating member such that it moves with the actuating member in the direction of opening of the switch contacts but is able to pivot into and out of the first and second positions in dependence upon the orientation of the apparatus. The extension member may be suitably counter weighted to facilitate the movement from one position to the other under gravity.
While the above discussion has been in terms of an electrical apparatus or appliance embodying means for detecting and summing the number of on/off cycles of power supply to the heating means of the appliance and for opening switch means in the power supply when a given sum has been reached, it will be appreciated that these means may be provided in a self contained switch unit which is adapted to be inserted in the power supply to the heating means.
Accordingly, viewed from a third aspect the invention provides a switch unit adapted to be placed in
the power supply to a thermostatically controlled electrically heated appliance comprising a switch means having a set of switch contacts, and means for opening said contacts comprising a bimetallic or other operating member arranged to be responsive to said power supply so as to move in response to the current flowing to the heating means, a linearly displaceable actuating member for operating said switch means and provided with a rack extending therealong, said operating member being provided or cooperating with pawl means for engaging said rack, whereby successive movements of said operating member are transmitted to and cause displacement of said actuating member to open said switch means after a certain cumulative displacement thereof.
Viewed from a still further aspect the invention provides an electric iron, provided with a pawl and rack mechanism operable in response to thermostatically controlled cyclical heating of the iron such that the rack cooperates with switch contacts to disable the iron after a certain predetermined effective cumulative movement of the rack, comprising means for disengaging the pawl from the rack and for resetting the rack in response to movement of the iron, and for varying said effective predetermined cumulative movement of the rack depending on whether the iron rests on its sole plate or heel. Such an arrangement may involve the use of a ratchet wheel instead of the preferred linearly movable rack discussed above. Three preferred embodiments of the invention will be described by way of example only, with reference to the accompanying schematic drawings in which:
Fig. 1 is a cross-sectional view of a first switch unit embodying the invention taken along the line A-A of Fig. 3;
Fig. 2 is a schematic-part section taken along the line B-B of Fig. 1;
Fig. 3 is a schematic-part section taken along the line C-C of Fig. 2;
Fig. 4 is an enlarged scrap view of the area arrowed X in Fig. 1; Fig. 5 is a side view of a second switch unit embodying the invention, looking in the direction of arrow D of Fig. 6, with the wall of the housing omitted for clarity;
Fig. 6 is a schematic section along the line E-E of Fig. 5;
Fig. 7 is a section along line F-F of Fig. 5 with certain components omitted for clarity, showing the switch in one mode of operation;
Fig. 8 is a schematic section along the same line showing the switch in a second mode of operation;
Fig. 9 is a cutaway schematic perspective view of a further embodiment; and
Fig. 10 is a side view of the embodiment of Fig. 9.
Figures 1 to 4 show a switch unit suitable for installation in a coffee maker or other thermostatically controlled electrical appliance or apparatus for which a manual reset is suitable. The thermostatic control will open and close separate switch contacts in dependence upon the temperature of the appliance to supply power to the heating means in a cyclical manner. The switch unit comprises a moulded housing 1 constructed from two cooperating portions 2, 3 which are fastened together by screws 4. Terminals 5,6 project from the housing and, in use, are connected into the power supply circuit to the heating means of the appliance.
Terminal 5 is connected to a resilient member 7 which carries at one end a contact 8. Terminal 6 is connected to the end of a first limb 9 of a generally U shaped bimetallic leaf member 10. The end of the second limb 11 of the bimetallic leaf member 10 is connected to a link 12 which carries at its other end a contact 13. The ends of the limbs 9,11 of the bimetallic leaf member
are fixed between supports 14,15 provided in the housing 1.
The bimetallic leaf member 10 is provided at its free end 16 with a pawl member 17 which engages with a rack 18 formed down one side of an actuating member 19 which is slidably mounted in grooves 23,24 in the housing portion 2,3. The actuating member 19 is movable from the position shown in Fig. 1 to an upper position wherein its upper surface engages and moves upwardly a projecting portion 34 of the contact carrying member 7 to break the contacts 8,13.
The pawl member 17 comprises a resilient leaf 20 which is retained at one end on the bimetallic leaf member 10 by lugs 21 and which has at its other end a tongue 22 which engages with the teeth of the rack 18. The pawl 17 and rack 18 are constructed such that the tongue 22 will operatively engage the teeth of the rack 18 and thus move the actuating member 19 only when moving in an upward direction. A locking pawl 25 is provided to hold the actuating member 19 in position while the pawl member 17 is disengaged from the rack 18 in its downward movement, and thus allows the successive movements of the bimetallic leaf member 10 to be accumulated in the movement of the actuating member 19. The locking pawl 25 is similar in construction to the pawl member 17, comprising a resilient leaf 26 mounted at one end 27 in the housing 1, and having an upwardly pointing tongue 28 at its other end. The tongue 28 becomes disengaged from the rack 18 as the latter is moved upwardly by the pawl member 17.
The actuating member 19 is formed with a slot 29 along its longitudinal axis through which extends a reset member 30. The reset member comprises a button 31 extending from the housing 1 for actuation by a user of the appliance, a collar 32 to limit its backward and forward movement, a shoulder 33 which engages with the
resilient leaf 26 of the locking pawl 25, and a projection 34 extending through an elongate aperture extending along the resilient leaf 26 and engaging the resilient leaf 20 of the pawl member 17. The resilience of these respective leaves 20,26 provides a restoring force for the reset member 30.
The operation of the switch will now be described. It will be seen that when the switch unit is connected into the power supply for the heating means of the appliance, a circuit will be completed through the terminal 5, resilient member 7, contact 8, contact 13, link 12, bimetallic leaf member 10 and terminal 6.
Thus when the thermostatic switch contacts of the appliance are closed, and the contacts 8,13 are closed, a current will flow through the bimetallic leaf member 10. The magnitude of current flowing will, of course, depend on the rating of the heating means, but for say a 2KW heating element the current would be approximately 8 Amps. This current will produce a considerable heating effect in the bimetallic leaf member 10 with the result that its free end 16 will deflect. In the embodiment shown, the member 10 is chosen such that it will deflect downwardly under heating. When the thermostatic switch contacts are broken, the current through the bimetallic leaf member 10 ceases and the member therefore cools and returns to its original position. Since in a typical thermostat cycle, the thermostat contacts are made for a relatively short period, say 15% of the cycle time, there is ample time for the leaf member 10 to cool and return to its original position. Furthermore, since the cycle time and the portion of that time in which the thermostatic switch contacts are closed remain substantially constant, a predetermined, consistent deflection of the free end 16 of the bimetallic leaf member 10 will be achieved.
By virtue of the geometry of the pawl member 17 and rack 18 as discussed earlier, as the bimetallic leaf
member 10 is heated by the current flowing through it and deflects in a downward direction, the tongue 22 will move over the teeth of the rack 18, and will not operatively engage therewith until the thermostatic contacts of the appliance open and the bimetallic leaf member 10 begins to cool and deflect upwardly.
Thus the motion of the bimetallic leaf member 10 is transmitted to the actuating member 19 only during the return movement of the former, that is while it is cooling and while the thermostatic switch contacts of the appliance are open. As such no current will be flowing through the contacts 8,13 while the actuating member 19 is being moved upwardly which means that after successive operations of the thermostat when the actuating member has travelled sufficiently to open the contacts 8,13 no current will be flowing at the time when they are opened which, as discussed above, offers signi .cant advantages.
At the end of each thermostatic cycle, the actuating member 19 is held in position by the locking pawl 25 which means that the upward movement of the bimetallic leaf member 10 during the next cycle will be added to those of the previous cycles, whereby the actuating member is progressively raised along the grooves towards the contact carrying member 7. Since the movement of the bimetallic leaf member 10 is substantially consistent from cycle to cycle, the time until the contacts 8,13 are broken will be determined by the cycle time of the thermostat, the deflection of the bimetallic leaf member 10 during each cycle, and the distance travelled by the actuating member. These may be chosen to suit the particular appliance in question. In a coffee maker for example, the desired time may be in the region of one hour, the thermostat cycle time around 2 minutes the deflection of the bimetallic per cycle around 0.6 mm and the total movement of the actuating member 19 around 18 mm. Once the actuating
member 19 breaks the contacts 8,13 no power can be supplied to the heating means until the switch unit has been reset. This is done by depressing the button 31 of the reset member which causes the shoulder 33 and projection 34 to act upon the resilient leaves 20,26 of the pawl 17 and locking panel 25 to disengage them from the rack 18 and allow the actuating member 19 to return to its original position under gravity. The reset member 30 is returned to its original position under the resilience of the leaves 20,26 upon release. Of course the appliance may be reset at any time during operation by depressing the button 31.
Turning now to Figs. 5 to 8 there is shown a second switch unit 50 which is suitable for use in a domestic iron.
The switch unit 50 comprises a housing 51, and terminals 52,53 for connection into the power supply circuit to the heating means of the appliance. Terminal 52 is connected to a resilient leaf member 54 which is supported at one end in the housing and carries a contact 55 on its other end. A portion 56 of the leaf member 54 extends beyond the contact for a purpose to be described later. Terminal 53 is connected to one end of a first limb 57 of a generally U shaped bimetallic leaf member 58. The end of the second limb 59 of the bimetallic leaf member 58 is connected to one end of a link 60 which carries at its other end a contact 61. The ends of the limbs 57,59 of the bimetallic leaf member are fixedly supported in the housing 51. As in the earlier embodiment, the bimetallic leaf member 58 is provided at its free end 62 with a resilient pawl member 63. The pawl member 63 is attached to an upturned end of the bimetallic leaf member at one end by for example spot welding and has a tongue 64 at its other end for engaging a rack 65 formed down one side of an actuating member 66. Further, a resilient locking pawl member 67, which is fixed in the
housing at one end, has a tongue 68 which engages the rack 65 below the tongue f.4.
The actuating member 66 is slidably mounted in grooves 69,70 provided in the housing, and is raised by the movement of the bimetallic leaf member 58 in the same manner as in the earlier embodiment. In this embodiment, however, an extension member 71 is pivotally mounted on the actuating member 66. The extension member has an upper portion 78 and a lower counterweight portion 79, which overlies the actuating member 66, with resilient legs 72,73 projecting from the upper portion 78 and having spigots 74,75 at their lower ends which pivotally engage in complementary sockets formed in the actuating member 66. The actuating member 66 is recessed to accommodate the legs 72,73 in their upright position.
The extension member 71 is pivotable between the two positions shown in Fig. 7. In the position illustrated in solid lines, the switch unit is upright and the upper portion 78 of the extension member 71 overlies the contact breaking surface 85 of the actuating member 66. The dotted line represents the position of the extension member 71 when the switch unit is turned on its side, with the resilient legs 72,73 lower most. In this position, to which the extension member 71 has pivoted by virtue of the mass of its upper portion 78, the upper portion 78 no longer overlies the contact breaking surface 85 of the actuating member 66. It will be apparent therefore that when the switch unit is in its upright position (in particular when the iron is resting on its sole plate) the contacts 55,61 will be broken by the upper surface 86 of the extension member 71, and that the actuating member needs only to move a distance "a" to break the contacts. However, in its side on position (when the iron is resting on its heel) the contacts 55,61 will be broken by the upper surface 85 of the actuating member 66 which must
therefore travel a greater distance, "b" to break the contacts. This condition is shown in Figure 7B. The counterweight 79 acts to return the extension member 71 to its upright position when the switch unit is returned to its upright position.
As in the earlier embodiment, the time taken to open the switch contacts 55,61 will depend on the thermostat cycle time, the amount of movement of the bimetallic leaf member 58 in each cycle and the distance to be moved by the actuating member. In an iron a desirable switch off time in the sole plate down and heel down positions are 2 minutes and 10 minutes respectively, and the typical cycle time is one minute. Accordingly the characteristic of the bimetallic leaf member 58, the pawl member 63 and -the rack 68, should be such as to allow the distance 'a' to be covered in two thermostat cycles and distance 'b' in ten cycles.
The switch unit 50 of this embodiment is also provided with reset means, but which is automatic and responsive to movement of the switch rather than manually operated. As mentioned earlier, this is a very desirable feature in appliances such as irons, where the power should not be cut off during use, but only during periods of rest. The reset means comprises an inertial mass 80 which is eccentrically pivotally mounted in pivot blocks 81,82 in the housing 5. The mass 80 is provided with a bent finger 83 which engages behind the resilient locking pawl 67. As the switch unit 50 moves in a direction having a component perpendicular to the pivotal axis of the mass 80, the mass 80 will pivot around this axis and cause the finger 83 firstly to push against the locking pawl 67 and disengage it from the rack 65. Moreover, the locking pawl member 67 is formed so as to lie in close proximity to the resilient pawl member 63 in this region, continued movement of the finger 83 will cause the locking pawl member 67 to press against the pawl member 63 and disengage it from the
rack 68 to allow the actuating member 66 to fall back to its original position under gravity. Thus as the switch unit is being moved, the actuating member 66 is constantly being reset and the switch unit will not operate until it has been left at rest for the desired period of time. To reset the switch unit after switch off, it need only be shaken in the appropriate direction.
Figs. 9 and 10 show a third switch unit 100 embodying the invention which is also intended for use in a domestic iron. The switch is shown in the orientation it will assume when the iron is resting sole plate down.
The unit 100 comprises a housing 101 and terminals 102,103 for connection into the power supply circuit to the iron heating means. Terminal 102 which is formed from strip material carries a fixed contact 104 on its other end. The other terminal 103 supports (by spot or laser welding) the end of one limb 105 of a U shaped bimetallic leaf member 106. The other limb 107 of the bimetallic leaf member 106 is spot or laser welded to a support plate 108 which also supports the crimped end 109 of a snap action actuator 110. The actuator 110 is of a type well known in the art, having a centrally released tongue 111 which mounts a movable contact 112. The actuator is a bi-stable device, as will be described later. Thus in the condition shown in the Figures, a circuit is formed between the terminals 102,103 through the bimetallic member 106, the actuator 110 and the contacts 104,112. Thus when power is supplied to the heating element of the iron, the bimetallic member will heat up under the effect of the current and its free end 113 move to the right in the sense of Fig. 10. When the current stops, it will cool and the free end 113 move back towards the left.
The free end 113 of the bimetallic member 106 mounts, again by spot welding, one end of a movable
resilient pawl 114, which has a tongue 115 which engages in a rack 116 formed down one face of an actuating member 117. A resilient fixed locking pawl 118 has a tongue 119 which also engages in the rack 116. In the condition shown, the locking pawl 118 engages the rack 116 above the movable pawl 114. However, it will be appreciated that depending on the ambient temperature, the reference position of engagement of the movable pawl 114 with the rack will vary, moving either up or down from the position shown. The linear rack 116 accommodates such ambient movement easily, while still giving a constant movement under the operational deflection of the bimetallic member 106. Furthermore, the angled arrangement of the bimetallic member 106 and movable pawl 114 minimises the horizontal forces exerted by the pawl 114 on the rack 116, so facilitating, for example, resetting of the device as hereinafter described.
The actuating member 117 is moved in a linear manner in the housing by the pawl 114 in response to the successive movements of the bimetallic member 106. As in the earlier embodiments, movement of the actuating member 117 occurs only during the cooling movement of the bimetallic member 106 and slippage of the member 117 is prevented by the locking pawl 118.
As in the embodiment of Figs. 4 to 8, the actuating member 117 pivotally supports an extension member in the form of a rocker arm 120. The rocker arm 120 is movable between the position shown in Fig. 10 in which its upper portion 124 lies between a forwardly projecting portion 121 of the actuating member 117 and the free end 122 of the actuator blade 110, and a position in which it pivots out from between these members, as will happen when the switch is turned through approximately 90° anti-clockwise. The rocker arm has a counterweight portion 123 to cause the arm to assume the position shown in Fig. 10 when the switch is upright. Thus, when
for example an iron containing the switch is in a sole plate down position, the upper portion 124 of the rocker arm 120 will after a relatively small movement of the actuating member 110 co-operate with the free end 122 of the actuator 110, so lifting it to cause the movable contact 112 to move away from the fixed contact 104 with a snap action. However, in the heel down position, i.e. rotated 90° anti-clockwise, the rocker arm 120 pivots out of the way and the projection 121 of the actuating member 117 will co-operate with the actuator 110 after a greater movement of the actuating member.
The present embodiment also employs an inertial automatic reset mechanism. A free-rolling cylindrical weight 130 co-operates with a cam surface 131 of a generally U shaped pivot arm 132. The movable pawl 114 is provided with a laterally extending cranked arm 133 which extends across the front edge of the pivot arm 132. The fixed pawl 118 is provided with a laterally extending arm 134 which extends across the edge in the opposite direction. During normal operation of the iron, the cylindrical weight repeatedly causes the pivot arm 132 to pivot clockwise in the sense of Fig. 10, whereupon the edge of the pivot arm 132 engages the laterally extending arms 133 and 134 of the pawls and pulls the pawls out of engagement with the rack 116 which then falls back to its original position under gravity. Thus the device is constantly being reset.
As was stated earlier, the actuator blade 110 is a bi-stable blade, i.e. it has two stable positions on either side of an unstable position. As the free end
122 is raised by the rocker arm 120 or actuating member 117, the geometry of the blade 110 changes and the tongue ill moves, with a snap action, from a first stable position in which the contacts 112 and 104 are closed to a second stable position in which they are open. Even if the actuating member 117 is then reset, the blade will remain in this stable configuration, and
the device will still be disabled. This provides an additional level of safety in the event that the device should be jolted to reset the actuating member.
A blade reset member 135 is pivotally mounted about an axis 136, and movable by means of a rod 137 which extends from the housing through a slot 138. To reset the blade, the rod 137 is moved to the right in the sense of Fig. 9, so that the outer portion 139 of the reset member 135 will engage the underside of the tongue 110 and push the tongue upwardly whereupon the tongue will snap back to a contacts closed position. At the same time the rod 137 also engages the lower end 140 of the pivot arm 132 so as to cause that arm to pivot and disengage the pawls 114,118 from rack 116 to reset the actuating member 117, so as not to prevent the resetting of the blade.
It will also be seen that when the contacts are closed if the rod 137 is moved to the left, the portion 141 of the reset member will engage the free end 122 of the actuator and, upon sufficient movement, cause the contacts 104,112 to snap open. Thus the reset member effectively acts as an on-off switch.
Of course for a simpler construction a mono-stable blade (i.e. one whose only stable configuration is in the contacts closed condition) could be used and the reset member 135 dispensed with. In that case, as in the earlier embodiment, after the switch contacts have opened, they may be reset merely by shaking the device to cause the weight 130 to pivot arm 132 to disengage the pawls 114,118 from the rack 116.
Thus while embodying the same basic principles as the first embodiment, the second and third embodiments include additional features which make them applicable to appliances where an automatic reset facility is required and where differing cut-out times are required in different orientations. It will be appreciated that these features may be used separately in appliances if
only one is required. Furthermore while the embodiments described show switch units adapted to be inserted into the power supply to an appliance heating means, the invention is not limited to self contained switch units. The bimetallic member could be replaced by another form of operating member e.g. a solenoid device or other electro-magnetic or electro-thermal device cooperating with a pawl engagable with the rack. It is also envisaged that if an appliance may be used in countries with differing mains voltages, in order to keep the heating effect in the bimetal constant, selectively operable shunts could be placed in the supply circuit such that there will be constant current flowing through the bimetal .