Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H37/00—Thermally-actuated switches
  • H01H37/02—Details
  • H01H37/32—Thermally-sensitive members
  • H01H37/52—Thermally-sensitive members actuated due to deflection of bimetallic element
  • H01H37/54—Thermally-sensitive members actuated due to deflection of bimetallic element wherein the bimetallic element is inherently snap acting
  • H01H37/5409—Bistable switches; Resetting means
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H3/00—Mechanisms for operating contacts
  • H01H3/32—Driving mechanisms, i.e. for transmitting driving force to the contacts
  • H01H3/48—Driving mechanisms, i.e. for transmitting driving force to the contacts using lost-motion device
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H37/00—Thermally-actuated switches
  • H01H37/02—Details
  • H01H37/60—Means for producing snap action

Definitions

• This invention concerns improvements relating to thermal controls and has particular, though not exclusive, application to thermal controls utilized in electrically heated water boiling vessels such as domestic kettles and jug kettles for example where the generation of steam when water boils in the vessel is sensed by a bimetallic actuator which changes state and causes an overcentre trip lever to operate thereby opening a set of switch contacts and disrupting the electrical supply to the heating element of the vessel.
• thermal controls are well known and are commonly referred to as "steam controls”.
• the Z5 steam control comprises a
• bimetallic actuator in the form of a circular disc-shaped blade having a generally U-shaped cut-out which releases a tongue from the blade, the blade being dished so as to be movable between oppositely curved configurations with a snap action.
• bimetallic actuators are well known and when mounted into a control by the periphery of the disc-shaped blade
• the bimetallic blade is thus mounted to a cover moulding of the control and the free end of the tongue co-operates with an overcentre mechanism via a push rod.
• the overcentre mechanism comprises a trip lever and a spring which are mounted in series with each other between spaced-apart abutments in a body part of the control, the overcentre arrangement being movable with a snap action between stable positions on either side of an unstable central position.
• the spring has integral contact-carrying extensions which move with the spring as the overcentre mech.anism moves between its two stable positions and either make contact with or break contact from fixed switch contacts provided in the control, but in other arrangements the trip lever has a switch-operating part
• overcentre mechanism is moved into and through its central unstable position and snaps to its other stable position.
• the spring extensions follow the movement of the overcentre mechanism and the contacts on the ends of the spring extensions move apart from the fixed contacts in the control, thereby disrupting the supply of current through the control to the vessel heating element.
• the trip lever has to be operated manually so as to restore the overcentre mechanism to its original state, this movement also serving to depress the push-rod and push the tongue of the bimetal towards the position it occupied in the original cold condition of the bimetal and thus seek to reset the bimetal.
• the bimetal will seek to oppose this resetting action if its temperature has not cooled.
• bimetal approaches its snap point, and this can raise the snap temperature of the bimetal towards a level where operation of the control may not be guaranteed, particularly if the vessel is operated at an elevated location where the boiling point of water is less than 100°C.
• responsive control comprising a snap-acting bimetallic actuator arranged to
• the overcentre mech.anism is movable between first and second, cold and hot positions in response to operation of said bimetallic actuator and, for resetting the bimetallic actuator to its cold condition, the overcentre mechanism is manually movable beyond its cold position, in a direction from its hot to its cold position, against spring bias.
• a push rod for example is selected so that the bimetal operating temperature is not subject to being affected by loading of the bimetal by the push rod and its associated overcentre mechanism until the bimetal has moved to and through its unstable centre position, the consequent shortness in the push rod length, considered from the viewpoint of resetting the bimetal, being accommodated by providing additional resetting movement, against spring bias, in the overcentre
• the trip lever of the overcentre mechanism thus has two free rest positions corresponding to the two stable positions of the overcentre
• a vessel provided with such a control will have an ON/OFF knob attached to the trip lever for manual operation by the user and in operating the knob to reset the vessel after it has boiled and automatically switched off, the user will be required to push the knob from its OFF position to an ON position as is conventional, but there will be a slight resistance to the final movement of the knob and upon release of the manual operating force, the knob will resile slightly; the user will hardly notice the difference.
• the resilient stop can be provided in any convenient manner and in the following several exemplary arrangements will be described, namely one in which the stop is defined by an abutment in the switch body which co-operates with the spring component of the overcentre mechanism, another in which a separate spring associated with the trip lever performs a similar function and another in which the stop is defined by a resilient tongue released from a body moulding of the control much in the same fashion as a tongue is released from the bimetal.
• the intermediate member is provided between the C-spring and the trip lever and is arranged to be pivotally movable, the intermediate member having a part which functions
• Figures 1 and 2 are side elevation views, partly in phantom, of a first embodiment of steam control according to the present invention, Figure 1 showing the embodiment in its contacts-closed rest position and Figure 2 showing that the trip lever of the embodiment can be pushed forward so as to effect additional bimetal resetting movement of the push-rod;
• Figures 3, 4 and 5 are sectional side elevation views of a second embodiment similar to the first, Figure 3 showing the ON (cold) condition of the embodiment, Figure 4 showing the OFF (hot) condition and Figure 5 showing the forced reset condition;
• Figures 6 to 9 show a third embodiment, Figure 6 showing the embodiment in its contacts-closed rest position, Figure 7 being similar to Figure 6 but showing that the trip lever can be pushed forward so as to effect additional bimetal resetting movement of the push-rod, Figure 8 being a perspective view of a moulded plastics body part of the embodiment showing
• Figures 10 to 21 show a fourth embodiment, Figures 10 to 13 being,
• Figure 11 showing the upper side of the embodiment, a perspective view ( Figure 12) showing the under side of the embodiment and an enlarged view ( Figure 13) of the portion designated C in Figure 12, all with the embodiment in its ON (contacts closed) condition, Figures 14 to 17 being similar views all with the embodiment in its forced reset condition, and Figures 18 to 21 being similar views all with the embodiment in its OFF (contacts open) condition.
• the switch shown therein comprises a moulded plastics body part 1 which supports an overcentre mechanism constituted by a spring 2 and a trip lever 3 mechanically in series with each other between spaced-apart abutments 4 and 5.
• the spring 2 is E-shaped, as
• a push-rod 11 locates in a bore formed in the body part 1 of the switch and co-operates with a snap-acting bimetallic switch actuator (not shown) to determine the condition of the overcentre mechanism.
• a snap-acting bimetallic actuator is a bimetal, commonly of dished configuration, which is movable between stable positions on opposite sides of an intermediate unstable position.
• the push-rod 11 is movable in its locating bore in dependence upon the condition of the bimetal, the push-rod bearing upon an imdersurface of the trip lever 3 as shown so as to cause the trip lever to pivot in a clockwise direction about the abutment 5 when the push-rod 11 is pushed upwards (as viewed in the drawings) by the bimetallic switch actuator changing shape, with a snap action and at a substantially predetermined temperature, from its cold condition to its hot condition when steam impinges upon it in use.
• the clockwise pivotal movement of the trip lever 3 causes the overcentre mechanism to move with snap action to and through its central unstable position and into its contacts-open condition, such movement causing the elongate side elements 7
• the trip lever 3 is provided with an operating
• the knob 12 To reset the switch, the knob 12 is moved in the direction of the arrow shown in Figure 2, this causing the overcentre mechanism to return to its original contacts-closed condition.
• the resetting, anticlockwise movement of the trip lever 3 depresses the push-rod 11 and this movement is employed to reset the bimetal.
• the push-rod 11 is of a length much shorter than in conventional arrangements and just less than the distance between the location
• this abutment 13 is spaced from the body moulding 1 when the overcentre mechanism is in its free, cold (low temperature) condition.
• the C-spring element 6 is arranged to abut a surface 14 of the body moulding 1 when the overcentre mechanism is in its free cold condition, as shown in Figure 1, and this provides a return force tending to restore the trip lever to its free cold condition when, in order to reset the switch, the trip lever is pivoted anticlockwise so as to cause the abutment 13 to contact the body moulding 1 as shown in Figure 2.
• FIGS. 3 to 5 show a second embodiment of the invention which is similar in many respects to the first embodiment.
• the same reference
• first embodiment is served by the bottoming of the C-spring 6 on the surface
• the left-hand tip of the spring 20 locates on a ledge 21 on the underside of the trip lever 3, to give a positive, known, position which acts as a rotation stop when the trip lever is moved to its "on" position.
• the form of the spring is such that, as it is located, it always applies a force to the ledge which is high enough to give a positive feel to the trip lever as it is
• Figures 3, 4 and 5 show the three possible positions of the trip lever.
• the trip lever In the "on” position shown in Figure 3, with the trip lever resting on a backstop 22 which acts through the spring 20 the push rod 11 has the correct geometry to work with the bimetal 16 when it operates.
• the forced reset position shown in Figure 5 the trip lever is rotated anticlockwise, against the force of the spring 20 resting on the backstop 22. The spring 20 therefore is lifted off its ledge 21, and the push rod 11 is pushed towards the bimetal 16 to ensure it resets.
• the force on the trip lever is removed, it returns to the "on” position.
• the trip lever 3 In the "off position shown in Figure 4, the trip lever 3 is rotated clockwise, the spring 20 remains seated on its ledge 21, and the contacts are opened. By selecting the force between the spring 20 and its support ledge 21 it is possible to provide a positive "on" position, which can be moved to the
• FIGS. 6 and 7 show the switch body moulding 1 together with the overcentre arrangement consisting of spring 2 and trip lever 3 and the push-rod 11 assembled into an outer body moulding 15 which, as described in GB-A-2 331 848 aforementioned, provides a mounting for a snap-acting bimetallic switch actuator 16 in the form of a dished circular bimetal blade having released therefrom a tongue 17 the free end of which serves to operate the push-rod 11 as the bimetal switches between its oppositely curved configurations.
• the trip lever 3 is formed with an abutment 13, but in the present embodiment the abutment 13 co-operates with a plastics material spring member 18 which is released from the bottom surface of the inner body moulding 1 of the device and is limited in the extent of its available movement by the underlying part of outer body moulding 15 as shown in Figure 7.
• FIGs 8 and 9 are perspective views, from above and below respectively, of the inner body moulding 1 of the switch of Figures 6 and 7
• Figure 6 shows the overcentre mechanism in its free rest condition
• Figure 7 shows the trip lever 12 pivoted anticlockwise so as to depress the spring member 18 into contact with the underlying surface of outer body moulding 15 thus limiting the extent of anticlockwise movement of the trip lever.
• Figures 10 to 21 show a fourth embodiment and again, wherever possible, the same reference numerals as were used in the drawings showing the previous embodiments are used in Figures 10 to 21 to designate the same or similar parts.
• the principal feature distinguishing the fourth embodiment from the previous embodiments is its use of an intermediate member 30 which is located between the C-spring 6 and the trip lever 3, the intermediate member being formed with a V-notch 31 on one side for engagement with the respective end of C-spring 6 and with a N-projection 32 on its other side which is received in a V-notch 33 of the trip lever 3, the N-notch 33 and the V-projection 32 being sized to permit the intermediate member 30 a limited degree of pivotal movement relative to the trip lever 3.
• the intermediate member 30 which is located between the C-spring 6 and the trip lever 3
• the intermediate member being formed with a V-notch 31 on one side for engagement with the respective end of C-spring 6 and with a N-projection 32 on its other side which is received in a V-notch 33 of the trip lever 3, the N
• member 30 furthermore has first and second depending nose portions 34 and 35 which, in central cross-section as shown in Figures 10, 14 and 18 give the
• intermediate member 30 an inverted, generally U-shaped appearance, one of
• the action of the C-spring 6 tends to rotate the auxiliary moulding 30 in an anticlockwise direction, because of the relative positions of the three fulcrum points (a,b,c). This tends to lift the operating nose 34 of the auxiliary moulding away from the bimetal 16, giving the correct push rod gap for the break action of the bimetal.
• the backstop nose 35 of the auxiliary moulding 30 acts as a resilient stop for the rotation of the trip lever 3, and the shape of the two mouldings 36,3 ensures that their relative rotation is limited to give the correct overall geometry, by means of the stop shown at 37.
• FIGs 14 to 17 show the "Forced reset” state, when the trip lever 3 is rotated anticlockwise beyond its normal “on” position, in order to ensure that
• Figures 18 to 21 show the "OFF" state, with the trip lever 3 rotated clockwise and with the force of the C-spring 6 transmitted through the auxiliary moulding 30 which has no other function in this position.
• a control which has a push-rod formed integrally with a trip lever in a bimetal operated overcentre arrangement is the boil control part of a Strix U-Series control substantially as described in WO-A-9534187 with reference to Figures 15, 16A and 16B thereof.
• the trip lever in this control is a moulded plastics member which is pivotally mounted with respect to a moulded plastics chassis and pivotal movement of the trip lever in a direction to cause the push-rod to reset the bimetal is limited by engagement of the trip lever with the chassis.
• the trip lever movement would be irrespective of the see-saw abutment(s), but in resetting operating the arrangement would be such that the see-saw abutment(s) came into play, causing the trip lever to rock forwardly (from right to left as viewed in the figures) about the abutment(s) with its right-hand end displacing slightly from the abutment 5 against the action of the C-spring element 6.
• the push rod will load the bimetal insignificantly in the cold condition of the control if the control is used in a disposition as shown in the drawings. It would be a simple matter to arrange that this was not the case, as in the embodiment of Figures 10 to 21, for example by having the head of the push rod engaged loosely in an accommodating formation in the trip lever or having a weak spring acting on the push rod so that the push rod was held up away from the bimetal in the

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• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Cookers (AREA)
• Thermally Actuated Switches (AREA)

Applications Claiming Priority (3)

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• 1999
  • 1999-02-25 GB GBGB9904391.1A patent/GB9904391D0/en not_active Ceased
• 2000
  • 2000-02-25 GB GB0004564A patent/GB2347271B/en not_active Expired - Fee Related
  • 2000-02-25 EP EP00906497A patent/EP1163690A1/de not_active Withdrawn
  • 2000-02-25 WO PCT/GB2000/000694 patent/WO2000051151A1/en not_active Application Discontinuation
  • 2000-02-25 AU AU28155/00A patent/AU2815500A/en not_active Abandoned
  • 2000-02-25 CN CN 00803337 patent/CN1339168A/zh active Pending

Non-Patent Citations (1)

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