US2727131A - Current sensitive switches and electric irons embodying such switches - Google Patents

Description

Dec. 13, 1955 w. M. RUSSELL 2,727,131

CURRENT SENSITIVE SWITCHES AND ELECTRIC IRONS EMBODYING SUCH SWITCHES Filod Jan. 27, 1953 3 Sheets-Sheet l l5 2/ n 2o '1 1 I I 3/ 30 l L? O 26 27 l 35 225 N ,6 29 22a 2" 24 28 w 25 I 22 23 36 O Q 37 FIE-Solo lnvemor y Attorney W. M. RUSSELL CURRENT SENSITIVE SWITCHES AND ELECTRIC IRONS EMBODYING SUCH SWITCHES Dec. 13, 1955 3 Sheets-Sheet 2 Filed Jan. 27, 1953 FUE QO lnvenfor WWHM I Rose 8 w @604, Hwy Afl'rney /7 49 ZZSZW Dec. 13, 19.55 -w. M. RUSSELL 2,727,131

CURRENT SENSITIVE SWITCHES AND ELECTRIC IRONS EMBODYING SUCH SWITCHES Filed Jan. 27, 1955 I5 Sheets-Sheet 5 Inventor B W 6 ygwy' Afforney United States Patent pun CURRENT SENSITIVE SWITCHES AND ELECTRIC IRONS EMBQDYING SUCH SWITCHES William Morris Russell, Bromley, England, assignor to Morphy-Richards Limited, St. Mary Cray, England, a British company Application January 27, 15 53, Serial No. 333,469

11 Claims. (Cl. 21925) This invention relates to an electric switch for controlling an ancillary circuit in accordance with the value of the current flowing in a main circuit.

Broadly, the invention lies in the provision of a switch for the purpose stated, which comprises two members both responsive to the current flowing in a main circuit, but having relatively slow and fast speeds of response. The slow response member acts to cause eventually the operation of switching means in the ancillary circuit unless the value of the current in the main circuit bears a predetermined relationship to a critical value, in which case the fast response member acts to inhibit the operation of said switching means. The arrangement can be such that a normally open ancillary circuit is completed by said switching means, the switching means operating only when the current in the main circuit is less than a critical value.

A switch in accordance with the invention has particular application in an electric smoothing iron of the type for use on electricity supplies of diiferent voltages. This type of iron has two heater elements; a main heater element which is energised whatever the supply voltage may be, and an ancillary heater element which is energised only when the supply is of a voltage below a critical value. Although there are a few exceptions, in general public supply voltages lie either in the range 100 to 120 volts or in the range 200 to 250 volts. Thus, the critical value can be taken as some value intermediate 120 and 209 volts and the heater elements can be chosen so that the two elements on the lower range of voltages give substantially the same sole-plate temperature as the single main element on the higher range. If the iron is fitted with a thermostat this relationship will, of course, apply for each setting of the thermostat.

Thus, the invention also comprises an electric smoothing iron of the type specified, which iron is provided with a switch as broadly defined above, to effect automatically the inclusion of the ancillary heater element in the iron circuit it, but only if, the voltage of the supply to which the iron is connected is below a critical value.

In accordance with the invention there can be provided an electric smoothing iron having a normally closed main circuit which includes a main heater element, a normally open ancillary circuit in shunt to the main circuit and including an ancillary heater element, and a switch responsive to the flow or" current in the main circuit and adapted to close the ancillary circuit if, but only if, that current is below a given critical value.

In order that the invention may be more fully and clearly understood, there will now be described with reference to the accompanying drawings, an electric switch constructed in accordance with the invention for use in effecting the automatic switching of the ancillary heater element in an electric iron of the type specified.

In the drawings:

Figure 1 is a plan view of the sole plate of an electric smoothing iron fitted with a main and ancillary heater element, a thermostat and a switch in accordance with 2,727,131 Patented Dec. 13, 1955 the present invention, and the parts of said switch being shown in a somewhat simplified manner;

Figure 2 is a plan View of the switch of Figure 1, on an enlarged scale, and shown in greater detail;

Figure 3 is an end view of the switch from above in Figure 2;

Figure 4 is a side view of the switch from the right in Figure 2;

Figure 5 is a side view of the switch from the left in Figure 2; and

Figure 6 is a sectional side view of the switch taken on the line VIVI of Figure 2.

There is shown in Figure l, a sole plate 10 of a smoothing iron having a main and ancillary heater element for the purpose previously mentioned. The two heater elements are held against the sole plate 14) by means of two clamping members 11 (the elements being hidden thereby in the view of Figure 1); the manner of thus securing the heater elements forms no part of the present invention, and is fully described in the complete specification of my copending application S. N. 314,442 now Patent No. 2,701,293. Mounted on the sole plate ltl are a thermostat 12 and a switch 13 constructed in accordance with the invention. The thermostat includes a temperature responsive device such as a bimetal strip which operates contacts to open and close the iron circuit in such a way as tends to maintain the sole plate temperature at the thermostat setting. The construction of such thermo stats is well known and will not be described herein beyond the statement that the two terminals of the thermostat are provided by a screw 14 and metal strip 15.

Before describing in detail the construction of the switch 13, the electrical arrangements of the switch and the iron in which it is incorporated will be explained with reference to Figure 1.

The switch components are mounted on a base 16 of insulating material and include three metal plates 17, 18 and 19 which as well as providing the main mechanical support for the moving parts of the switch function as electrical connectors. A lever 20 is pivotally supported on the base 16 and is electrically connected to plate 17. To the short arm of this lever, one end of a hot wire 21 is attached; the other end of the hot wire is supported by but insulated from plate 17 and is electrically connected to one lead 22a of a heater coil 22. The heater coil is wound on and serves to heat a bimetal strip 23 and its other lead 22b is connected to plate 18. The left end (in Figure 1) of the bimetal is fixed, and a contact or operating lever 24 is held against the other end by a spring strip 25 secured to plate 17. Contact 26 carried by lever 24 is connected electrically to plate 17 via lever 24 and spring strip 25. Contact 26 cooperates with a fixed contact 27 which is in electrical communication with plate 19; this pair of contacts efiect the completion of the ancillary circuit when required. Strip 25 carries a contact 28 which co-operates with a fixed contact 29 on plate 18. Plate 18 also carries contact 30 co-operating with contact 31 on the longer arm of the lever 20.

Two terminals 32 and 33 insulatingly mounted on sole plate 10 are adapted to be connected to an electricity supply in any suitable manner. When the iron is initially connected to the supply, the iron circuit is as follows: from terminal 33 through wire 34 to terminal 14 of thermostat 12, terminal 15 of the thermostat to plate 17 of switch 13, lever 20, hot wire 21, bimetal heater coil 22, plate 18, conducting strip 35 which is connected to one end of the main heater element. The other end of this element is connected by conducting strip 36 to terminal 32 thereby completing the circuit so that the main heater element is energised. One end of the ancillary heater element is also connected to strip 36, the other end however is connected by strip 37 to plate 19 and hence initially the ancillary element is not in circuit.

The mechanical arrangements (to be described later) of switch 13 and the relative speeds of response of hot wire 21 and bimetal strip 22 to the heating effect of the current are such that contacts 26 and 27 will close if, but only if, the current is below a critical value. This critical value corresponds to a critical voltage value below which it is necessary that the ancillary heater element is energised. Closure of contacts 26 and 27 effect the connection of the ancillary element in the iron circuit by completing a circuit from plate 17 through the ancillary element to connect it in parallel with the main element. This circuit is as follows: plate 17, spring strip 25, contact lever 24, contact 26, contact 27,'plate 19, strip 37, the ancillary heater element and strip 36.

If the supply voltage is greater than the aforesaid critical'value then contacts 26 and 27 do not close and the ancillary heater element remains out of circuit. When the switch 13 has operated, whether to connect the ancillary element or not, contacts 28 and 29 close thereby connecting plate 17 to plate 18 via strips 25 and said contacts. This connection short circuits the hot wire 21 and bimetal heater 22 which remain short-circuited as long as the iron is hot.

The construction and mechanical operation of the switch 13 will now be described in greater detail with reference to Figures 2 to 6. The three metal plates 17, 18 and 19 are fastened to the insulating base 16 by means of eyelets such as 38. A U-bracket 39 has a longer limb which is located in a recess in the base 16 and is secured between the base and plate 17. A pin 40 is supported between the limbs of bracket 39; the lever 20 is pivotally secured on this pin by bending two marginal portions of the lever around the pin, the central portion thus left forming the shorter armof the lever. Electrical connection of the lever 20 to plate 17 is ensured by a flexible, conductive strip 41 spot welded to lever 20 and to a flange 17bo n plate 17. i

The hot wire 21 consists of a nickel-chrome tape, one endof which is secured to the shorter arm of lever 20; the tape then passes through a longitudinal slot in the other arm of the lever. The means forsecuring the other end of the tape are adjustable to enable the initial position of the lever 20 to be varied and comprises a flanged plate 42. This plate has a L-shaped flange 42a (see Figure 4) by means of which itis supported some distance above plate 17 ona pivot pin 43. Another flange 42b. held against an adjustable stop 44. by means of a spring 45. To a third flange 420 of plate 42, an angle bracket 46 is fastened by means of an eyelet 47; bracket 46 and eyelet 47 are electrically insulated from plate 42- hy means of two insulating washers 48. The end of the hotwire 2 1 is threaded through the eyelet 47 and through holes in bracket 46 to which it, is then spot welded; Also spot welded to the bracket is one lead 22a of the bimetal heater coil 22. This lead passes through an insulating sleeve 49., the coil proper being wound about the bimetal strip 23 from which it is insulated by two thin mica strips 50. The other lead 22b of the coil 22 is accommodated in'a groove in the underside of the base 16 and passes through a hole in the base to be spot welded to the plate 18. i

' The bimetal strip 23 is secured at one end to a flange 175 on plate 17. It is required that contact or operating lever 24 should be able to pivot about a first fulcrum provided by the end of the longer arm of lever'20 or about a second fixed fulcrum provided by the flange 170. The lever 24 is therefore not secured to any other part of the switch 13 but is held in the required position by means of the spring strip 25 which is secured at one end to the flange 17c. The other end of the spring 25"is hooked around the free end of the bimetal strip "23 so as to hold it against the curved end of'the contact lever 24; The other end of the contact lever is bent so as to engage the flange 17c, whilst intermediate its ends the lever has a stop 24a bent-out of the lever. This stop passes through a slot in strip 25 and is adapted to engage the end of lever 20.

As previously explained, when the iron is connected to a supply, current will flow through hot wire 21 and bimetal heater 22. Thus, the temperature of the hot wire will increase and consequently its length will increase thereby permitting lever 20 to be turned in an anti-clockwise direction by spring 51. It will be noted that the movement of hot wire 21 is magnified by the arrangement of lever 20. At the same time, the temperature of bimetal strip 23 increases, this strip being arranged so that its free end moves in a direction towards the top of Figure 2 with increase in temperature. The curved end of contact lever 24 moves with the bimetal and initially the contact lever pivots about flange 17c.

it is arranged that if the supply voltage is above the critical voltage previously referred to, the speed of response of the hot wire relative to the bimetal strip is such that the end of lever '20 has moved clear of "stop 240 before it can be engaged thereby. Lever 24 will therefore continue to pivot about flange 17c so that contacts 26 and 27 are not closed and the ancillary heater element remains out of circuit. In due course the movement of lever 24 will bring contact 28 into engagement with fixed contact 29 thereby short-circuiting the hot wire and bimetal heater as explained above.

If the voltage supplied to the iron is below the critical value, i. e. it is such that both heater elements must be energised to give the required temperature, then the relative movements of levers 20 and 24 produced are such that stop 24a engages the end of lever 20. Thereafter, lever 24 pivots about the end of lever 20 in an anti-clockwise direction so that contact 26 moves towards contact 27. Eventually contacts 26 and 27 will close thereby completing the ancillary heater element circuit as is required. As before, the bimetal will continue to move until the contacts 28 and 29 close. It should be noted that contact 27 is carried by a flexible strip 52 secured to a flange 19a on plate 19. In this way, contact 27 is permitted to move with contact 26 after they'have closed and before contacts 28 and 29 close.

Contact 29 is in the form of a screw in a flange 18a on plate 18, to which flange it is locked by means of a nut 53. This arrangement permits the position of contact 29 tobe pre-set' so that contacts 28 and 29 close at the optimum time. Flange also carries contact 30 which co-operates with contact 31. This pair of contacts are in parallel with contacts 28 and 29 and act as a safety means to prevent damage to the switch 13 should the voltage be so great as to cause lever 20 to move sharply over, contacts 30 and 31 then closing in advance of contacts 28 and 29 and serving the same purpose.

In order to prevent repeated operations of the, switch after it has once operated to effect control of the aricillary heater circuit, it is arranged that as long as the iron remains at the temperatures normally used, the heat from the sole plate is suflicient to maintain the bimetal strip in a position in which the short-circuiting contacts 2 8 and 29 are closed.

While the switch construction described above is at. present the preferred embodiment of the invention, modified constructions for use in a smoothing iron or for other uses can be adopted without departing from the scope of: the invention. For example, a bimetal strip can be employed for both the slow and the fast current responsive members. The slow response bimetal is heated by conduction from a member on which a heater coil is wound while the fast response bimetal is selfheated, that is it is heated by flow of current through the strip itself, which is longitudinally slotted to provide a narrow current path of 'zig-zag'form.

1 claim:

1. An electric switch for controlling an ancillary circuit in accordance with the value of the current flowing in a main circuit, said switch comprising a base, switch contacts for inclusion in the ancillary circuit, operating means for said switch contacts and first and second current responsive members mounted on said base which move in response to thecurrent flowing in the main circuit, said second member having a faster speed of response than said first member, said first and second current responsive members being constructed and arranged so that the movement of one of said members causes actuation of said operating means when the current in the main circuit diifers in one sense from a predetermined critical value and the movement of the other of said members prevents such actuation when said current difiers in the opposite sense from said critical value.

2. An electric switch for controlling an ancillary circuit in accordance with the value of the current flowing in a main circuit, said switch comprising a base, normally open contacts for inclusion in the ancillary circuit, contact operating means adapted to close said contacts when actuated, and first and second current responsive members mounted on said base which move in response to the current flowing in the main circuit, said second member having a greater rate of displacement than said first member, said first and second current responsive members being constructed and arranged so that when the current in the main circuit is less than a predetermined critical value the displacement of said first member actuates said contact operating means and when the current in the main circuit is greater than said predetermined critical value, the displacement of said second member modifies the displacement of said first member and thereby prevents it from actuating said contact operating means.

3. An electric switch for controlling an ancillary circuit in accordance with the value of the current flowing in a main circuit, said switch comprising a base, circuit switching means for inclusion in the ancillary circuit, operating means adapted to operate said circuit switching means when actuated, and first and second temperature sensitive members mounted on said base, each of which moves in response to heat produced by the current flowing in the main circuit to produce a displace ment of the member at a rate dependent on the value of said current, the displacement of said second temperature sensitive member occurring for any value of current at a greater rate than that of said first member, the first and second temperature sensitive members being constructed and arranged so that when said current differs in one sense from a predetermined critical value, the displacement of said first member is such as to cause actuation of said operating means and when said current differs in the opposite sense from said critical value, the displacement of said second member prevents displacement of said first member from causing actuation of said operating means.

4. An electric switch for controlling an ancillary circuit in accordance with the value of the current flowing in a main circuit, said switch comprising a base, normally open contacts for inclusion in the ancillary circuit, con tact operating means adapted to close said contacts when actuated, and first and second temperature sensitive members mounted on said base each of which is so positioned with respect to said main circuit as to be heated when current flows therethrough and adapted to be displaced in response to heat produced by said current, the rate of displacement ofsaid second member being greater for a given value of said current than that of said first member, said first and second temperature sensitive members being constructed and arranged so that when said current is less than a predetermined critical value the displacement of said first member is such as to produce actuation of said contact operating means and when said 6 current is greater than said critical value, the displacement of said second member is such that the displacement of said first member is modified thereby to prevent its actuation of said contact operating means.

5. An electric switch for controlling an ancillary circuit in accordance with the value of the current flowing in a main circuit, said switch comprising normally open contacts for inclusion in the ancillary circuit, an electric heating coil in the main circuit, a bimetal strip in heat exchange relationship with said heating coil, a hot wire in the main circuit, the length of which hot wire increases when its temperature is raised by current flowing therethrough, and contact-operating means for operating said contacts, said contact-operating means being under the joint control of said bimetal strip and said hot wire, the arrangement being such that when the current in the main circuit is less than a predetermined critical value said contacts are closed and when said current is greater than said critical value said contacts remain open.

6. An electric switch for controlling an ancillary circuit in accordance with the value of the current flowing in a main circuit, said switch comprising normally open contacts for inclusion in the ancillary circuit, an electric heating coil in the main circuit, a bimetal strip in heat exchange relationship with said heating coil, a hot wire also in the main circuit the length of which hot wire increases when its temperature is raised by current flowing therethrough, a swingable lever which controls the position of one of said contacts and is coupled to said bimetal strip, a first fulcrum normally adjacent said lever, the exact position of which fulcrum is controlled by said hot wire, and a second fixed fulcrum adjacent said lever, whereby bending of said bimetal strip due to an increase in the temperature thereof causes said lever to pivot about said first fulcrum to close said contacts when said current is less than a predetermined critical value but to pivot about said second fulcrum without closing said contacts when said current is greater than said predetermined critical value, said first fulcrum being withdrawn from its position adjacent said lever as the result of the increase in length of said hot wire in response to said greater current.

7. An electric switch as claimed in claim 6 in which said heating coil and said hot wire are connected in series and comprising further normally open contacts connected in parallel with said series-connected heating coil and hot wire, said lever being arranged so as to eventually close said further contacts after pivoting about said first or second fulcrum.

8. An electric switch for controlling an ancillary circuit in accordance with the value of the current flowing in a main circuit, said switch comprising a base, first normally open contacts for inclusion in the ancillary circuit, a bimetal strip having one end attached to said base an electric heating coil adapted to heat said bimetal strip, a hot wire the length of which increases substantially when current flows therethrough, said heating coil and said hot wire being connected in series for inclusion in the main circuit, a first lever pivotally mounted on said base and having a short arm and a long arm with a first fulcrum in the free end thereof said hot wire having one end attached to said base and the other end to said short arm of said first lever, a spring attached between said long arm of said first lever and said base and arranged to maintain said hot wire under tension, a second fulcrum fixed to said base, a second lever mounted so as to be capable of pivoting about said first or second fulcrum, means coupling said second lever to said bimetal strip whereby bending of said bimetal strip due to the heating thereof effects pivotal movement of said second lever, second normally open contacts connected in parallel with said seriesconnected heating coil and hot wire, the arrangement being such that when the current in the main circuit is less than a predetermined critical value said second lever is pivoted about said first fulcrum to close said first con- 7 tactsand .thereafiter closes said second contacts and when ai u rents r ate tha ai c tical val v ai se ver is p vptd a sut a d se n t lc um nd clos s on y said second contacts.

9. An electric switch as claimed in claim 8 comprising third normally open contacts connected in parallel with sai d second contacts and adapted to be closed by said first lever if the movement thereof is excessive.

it). An electric smoothing iron for use on electricity supplies of different voltages comprising a main heater element. for connection to the supply whatever its voltage and an ancillary heater element for connection to. the supply only when the voltage thereof is less than a predetermined critical value and a switch for automatically efiecting. such connection of the ancillary element, said switch. comprising a base, normally open contacts conlfiQted in series with the ancillary heater element and adaptedv to be connected. in series with the supply the supply, contact-operatingmeans onsaid base adapted to close said. contacts when actuated, and first and second temperature-sensitive members onsaid. base each of which is displaced in response to heat produced by the current flowing in the main heater element, the rate of displacement of said second member being greater for a given value of said current than. that of said first member, said first and second temperature sensitive members being constructed and arranged so that when said current is less than a. predetermined. critical value, which corresponds to said critical voltage value, the displacement of: said first member is such as to produce actuation of said contact. operating means and when said current is greater than said critical value, the displacement of said second member is such as to prevent the displacement of idv first m m r n m a ins a tuat on of sai sonta operating means.

11. An electric smoothing iron for. use on electricity upn o diff re t v t c m r s n a a n hea er element adapted to be connected to-the supply whatever its voltage and: an ancillary heater elementv connected. in parallel with said. main heater element only when the supply is of a voltage less than a predetermined. critical value, and a switch comprising a base, normally open contacts in series with the ancillary element, a bime al strip carried on said base. heated by thecurrent flowing in the main element, afirst member actuated by the movement of said bimetal strip when it is; heated. to cause closure. of said contacts unless the supply voltage is greater: than said critical value, a hot wire also heated by the current flowing in the mainelement, and a second member. ac: tuated by movement of thehot wire when it. is heated, the displacement of said secondtrnember when the supply voltage is greater than: said critical value being. such as to modify the displacement of said first member. so as.

to prevent its closing said 'contacts.

References Cited in the tile of this patent UNITED STATESv BATENTS 921,625 Phelps May 11, 1909 1,044,269 ShaIer Nov. 12', 1912 1,434,633 Rohne- Nov. 7, 1922 2,137,073 Bletz Nov. 15, 1938- 2,218,778 Weimer' Oct. 22-, 1940 2,345,413 Morton Mar. 28; 1944

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